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#1576 2022-11-25 13:55:03

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1549) Volcano

Summary

A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

On Earth, volcanoes are most often found where tectonic plates are diverging or converging, and most are found underwater. For example, a mid-ocean ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from the core–mantle boundary, 3,000 kilometers (1,900 mi) deep in the Earth. This results in hotspot volcanism, of which the Hawaiian hotspot is an example. Volcanoes are usually not created where two tectonic plates slide past one another.

Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool the Earth's troposphere. Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines.

Details

A volcano is a vent in the crust of Earth or another planet or satellite, from which issue eruptions of molten rock, hot rock fragments, and hot gases. A volcanic eruption is an awesome display of Earth’s power. Yet, while eruptions are spectacular to watch, they can cause disastrous loss of life and property, especially in densely populated regions of the world. Sometimes beginning with an accumulation of gas-rich magma (molten underground rock) in reservoirs near Earth’s surface, they can be preceded by emissions of steam and gas from small vents in the ground. Swarms of small earthquakes, which may be caused by a rising plug of dense, viscous magma oscillating against a sheath of more-permeable magma, may also signal volcanic eruptions, especially explosive ones. In some cases, magma rises in conduits to the surface as a thin and fluid lava, either flowing out continuously or shooting straight up in glowing fountains or curtains. In other cases, entrapped gases tear the magma into shreds and hurl viscous clots of lava into the air. In more violent eruptions, the magma conduit is cored out by an explosive blast, and solid fragments are ejected in a great cloud of ash-laden gas that rises tens of thousands of metres into the air. One feared phenomenon accompanying some explosive eruptions is the nuée ardente, or pyroclastic flow, a fluidized mixture of hot gas and incandescent particles that sweeps down a volcano’s flanks, incinerating everything in its path. Great destruction also can result when ash collects on a high snowfield or glacier, melting large quantities of ice into a flood that can rush down a volcano’s slopes as an unstoppable mudflow.

Strictly speaking, the term volcano means the vent from which magma and other substances erupt to the surface, but it can also refer to the landform created by the accumulation of solidified lava and volcanic debris near the vent. One can say, for example, that large lava flows erupt from Mauna Loa volcano in Hawaii, referring here to the vent; but one can also say that Mauna Loa is a gently sloping volcano of great size, the reference in this case being to the landform. Volcanic landforms have evolved over time as a result of repeated volcanic activity. Mauna Loa typifies a shield volcano, which is a huge, gently sloping landform built up of many eruptions of fluid lava. Mount Fuji in Japan is an entirely different formation. With its striking steep slopes built up of layers of ash and lava, Mount Fuji is a classic stratovolcano. Iceland provides fine examples of volcanic plateaus, while the seafloor around Iceland provides excellent examples of submarine volcanic structures.

Volcanoes figure prominently in the mythology of many peoples who have learned to live with eruptions, but science was late in recognizing the important role of volcanism in the evolution of Earth. As late as 1768, the first edition of the Encyclopædia Britannica gave voice to a common misconception by defining volcanoes as “burning mountains, which probably are made up of sulphur and some other matter proper to ferment with it, and take fire.” Today geologists agree that volcanism is a profound process resulting from the thermal evolution of planetary bodies. Heat does not easily escape from large bodies such as Earth by the processes of conduction or radiation. Instead, heat is transferred from Earth’s interior largely by convection—that is, the partial melting of Earth’s crust and mantle and the buoyant rise of magma to the surface. Volcanoes are the surface sign of this thermal process. Their roots reach deep inside Earth, and their fruits are hurled high into the atmosphere.

Volcanoes are closely associated with plate tectonic activity. Most volcanoes, such as those of Japan and Iceland, occur on the margins of the enormous solid rocky plates that make up Earth’s surface. Other volcanoes, such as those of the Hawaiian Islands, occur in the middle of a plate, providing important evidence as to the direction and rate of plate motion.

The study of volcanoes and their products is known as volcanology, but these phenomena are not the realm of any single scientific discipline. Rather, they are studied by many scientists from several specialties: geophysicists and geochemists, who probe the deep roots of volcanoes and monitor signs of future eruptions; geologists, who decipher prehistoric volcanic activity and infer the likely nature of future eruptions; biologists, who learn how plants and animals colonize recently erupted volcanic rocks; and meteorologists, who determine the effects of volcanic dust and gases on the atmosphere, weather, and climate.

Clearly the destructive potential of volcanoes is tremendous. But the risk to people living nearby can be reduced significantly by assessing volcanic hazards, monitoring volcanic activity and forecasting eruptions, and instituting procedures for evacuating populations. In addition, volcanism affects humankind in beneficial ways. Volcanism provides beautiful scenery, fertile soils, valuable mineral deposits, and geothermal energy. Over geologic time, volcanoes recycle Earth’s hydrosphere and atmosphere.

Additional Information

Volcanoes are Earth's geologic architects. They've created more than 80 percent of our planet's surface, laying the foundation that has allowed life to thrive. Their explosive force crafts mountains as well as craters. Lava rivers spread into bleak landscapes. But as time ticks by, the elements break down these volcanic rocks, liberating nutrients from their stony prisons and creating remarkably fertile soils that have allowed civilizations to flourish.

There are volcanoes on every continent, even Antarctica. Some 1,500 volcanoes are still considered potentially active around the world today; 161 of those—over 10 percent—sit within the boundaries of the United States.

But each volcano is different. Some burst to life in explosive eruptions, like the 1991 eruption of Mount Pinatubo, and others burp rivers of lava in what's known as an effusive eruption, like the 2018 activity of Hawaii's Kilauea volcano. These differences are all thanks to the chemistry driving the molten activity. Effusive eruptions are more common when the magma is less viscous, or runny, which allows gas to escape and the magma to flow down the volcano's slopes. Explosive eruptions, however, happen when viscous molten rock traps the gasses, building pressure until it violently breaks free.

How do volcanoes form?

The majority of volcanoes in the world form along the boundaries of Earth's tectonic plates—massive expanses of our planet's lithosphere that continually shift, bumping into one another. When tectonic plates collide, one often plunges deep below the other in what's known as a subduction zone.

As the descending landmass sinks deep into the Earth, temperatures and pressures climb, releasing water from the rocks. The water slightly reduces the melting point of the overlying rock, forming magma that can work its way to the surface—the spark of life to reawaken a slumbering volcano.

Not all volcanoes are related to subduction, however. Another way volcanoes can form is what's known as hotspot volcanism. In this situation, a zone of magmatic activity—or a hotspot—in the middle of a tectonic plate can push up through the crust to form a volcano. Although the hotspot itself is thought to be largely stationary, the tectonic plates continue their slow march, building a line of volcanoes or islands on the surface. This mechanism is thought to be behind the Hawaii volcanic chain.

Where are all these volcanoes?

Some 75 percent of the world's active volcanoes are positioned around the ring of fire, a 25,000-mile long, horseshoe-shaped zone that stretches from the southern tip of South America across the West Coast of North America, through the Bering Sea to Japan, and on to New Zealand.

This region is where the edges of the Pacific and Nazca plates butt up against an array of other tectonic plates. Importantly, however, the volcanoes of the ring aren't geologically connected. In other words, a volcanic eruption in Indonesia is not related to one in Alaska, and it could not stir the infamous Yellowstone supervolcano.

What are some of the dangers from a volcano?

Volcanic eruptions pose many dangers aside from lava flows. It's important to heed local authorities' advice during active eruptions and evacuate regions when necessary.

One particular danger is pyroclastic flows, avalanches of hot rocks, ash, and toxic gas that race down slopes at speeds as high as 450 miles an hour. Such an event was responsible for wiping out the people of Pompeii and Herculaneum after Mount Vesuvius erupted in A.D. 79.

Similarly, volcanic mudflows called lahars can be very destructive. These fast-flowing waves of mud and debris can race down a volcano's flanks, burying entire towns.

Ash is another volcanic danger. Unlike the soft, fluffy bits of charred wood left after a campfire, volcanic ash is made of sharp fragments of rocks and volcanic glass each less than two millimeters across. The ash forms as the gasses within rising magma expand, shattering the cooling rocks as they burst from the volcano's mouth. It's not only dangerous to inhale, it's heavy and builds up quickly. Volcanic ash can collapse weak structures, cause power outages, and is a challenge to shovel away post-eruption.

Can we predict volcanic eruptions?

Volcanoes give some warning of pending eruption, making it vital for scientists to closely monitor any volcanoes near large population centers. Warning signs include small earthquakes, swelling or bulging of the volcano's sides, and increased emission of gasses from its vents. None of those signs necessarily mean an eruption is imminent, but they can help scientists evaluate the state of the volcano when magma is building.

However, it's impossible to say exactly when, or even if, any given volcano will erupt. Volcanoes don't run on a timetable like a train. This means it's impossible for one to be “overdue” for eruption—no matter what news headlines say.

What is the largest eruption in history?

The deadliest eruption in recorded history was the 1815 explosion of Mount Tabora in Indonesia. The blast was one of the most powerful ever documented and created a caldera—essentially a crater—4 miles across and more than 3,600 feet deep. A superheated plume of hot ash and gas shot 28 miles into the sky, producing numerous pyroclastic flows when it collapsed.

The eruption and its immediate dangers killed around 10,000 people. But that wasn't its only impact. The volcanic ash and gas injected into the atmosphere obscured the sun and increased the reflectivity of Earth, cooling its surface and causing what's known as the year without a summer. Starvation and disease during this time killed some 82,000 more people, and the gloomy conditions are often credited as the inspiration for gothic horror tales, such as Mary Shelley's Frankenstein.

Although there have been several big eruptions in recorded history, volcanic eruptions today are no more frequent than there were a decade or even a century ago. At least a dozen volcanoes erupt on any given day. As monitoring capacity for—and interest in—volcanic eruptions increases, coverage of the activity more frequently appears in the news and on social media. As Erik Klemetti, associate professor of geosciences at Denison University, writes in The Washington Post: “The world is not more volcanically active, we’re just more volcanically aware.”

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1577 2022-11-26 13:54:20

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1550) Tianjin Grand Bridge

Summary

Tianjin Grand Bridge (Langfang–Qingxian viaduct) is a railway viaduct bridge that runs between Langfang and Qingxian, part of the Beijing–Shanghai High-Speed Railway. It is one of the longest bridges in the world with a total length of about 113.7 kilometers (70.6 mi). It was completed in 2010 and opened in 2011. At the time Guinness World Records recorded it as the second longest bridge in the world.

The design of the elevated track was chosen on the one hand to avoid numerous individual structures for crossing roads and railways, and on the other to shorten the construction period. In addition, the railway line requires less land area in this design: a railway embankment requires 28.4 hectares per routed kilometer, the bridge but only 10.9 ha, less than half the area.

The bridge consists of 32 m long box girders weighing 860 tons each. These girders were created in two workplaces along the bridge, brought to the installation site on the bridge section already installed, and then placed on the piers by a special crane.

Details

The Tianjin Grand Bridge extends 113.7 km (70.6 miles) between Langfang and Qingxian and serves as a railway viaduct for the Beijing-Shanghai High-Speed Railway. The bridge opened in 2011 and is the third longest bridge in the world.

Just a few kilometers from Tianjin’s skyscrapers, European-style buildings and the upscale residential area of Wudadao (the city’s Five Great Boulevards), a viaduct soars over the city for 113 kilometres (70 miles).

This city of 15 million inhabitants is known for the vitality of its port – in fact Tianjin means “heavenly river ford” in Chinese — and is internationally famous for hosting the summer session of the World Forum in Davos. It’s also home to an incredible infrastructure. The Tianjin Grand Bridge is one of the longest bridges in the world, and along its massive span races the high-speed railway line between Beijing and Shanghai, one of the busiest and most profitable sustainable mobility routes in the country.

The construction of the Tianjin Grand Bridge

Building the Tianjin Grand Bridge was a very complex project. Much of the viaduct runs through the densely populated urban area surrounding the metropolis. The idea of running the high-speed train along an elevated viaduct was a smart solution: every kilometre of railway built on the ground would have required 28.4 hectares (70 acres) of earthworks, and therefore would have had a devastating environmental impact on the urban area. Opting for an elevated solution, on the other hand, made it possible to reduce the infrastructure’s physical impact in urban areas as much as possible, without forcing the project designers to change the train’s route.

Of course, building the viaducts of such a long bridge within an urban area required special precautions, such as breaking up the ashlars. So the viaduct was designed in 32 sections, each weighing 860 tons. They were each installed in different ways and at different times.

Despite these difficulties, construction was carried out in record time. Work on the project began in 2006 and was completed in 2010, with the inauguration on June 30, 2011. At the time of completion, the bridge was listed in Guinness World Records as the second longest bridge in the world.

Crossing the Tianjin Grand Bridge by train

Sitting at the window of one of the high-speed trains that dart from Beijing to Shanghai is like taking a trip through the thousand faces of China. Travelling across the 113 kilometres of the Tianjin viaduct means moving through a landscape that changes constantly, from the most densely populated areas to the expanses of water in the Pearl River Delta and then to the underground.

The route also includes the entrance to a tunnel over 6 km (3.7 miles) long that connects two artificial islands. In order to achieve all this, the government made the huge investment of around $20 billion, made possible by China’s development policies. When the Tianjin Bridge was built, China put the construction of high-speed rail lines as a top priority.

The high-speed rail programme started in 2003 with the project of a 404 km (251 mile) line between Qinhuangdao and Shenyang. From then until 2013, two years after the completion of the viaduct, the active lines in the country covered 10,000 kilometres (6,213 miles). Railway viaducts were some of the most complex works in this gargantuan effort. In addition to the Tianjin Grand Bridge, the 164-km (101-mile) long Danyang-Kunshan Grand Bridge and the 48 km (30 mile) long Beijing Grand Bridge were built in those years. In order to understand the importance of these viaducts in the design phase, consider that 69% of the track built for the Shi-Zheng line runs on viaducts.

The Tianjin Grand Bridge and the Chinese high-speed network

The bullet train race from Beijing to Shanghai knows no obstacles.  This is why the solution chosen for the route from Langfang to Qingxian was a viaduct designed to support high-speed travel, which has become China’s preferred transport model. According to official reports from the China Railway Corporation (the public company that manages the construction of the network), the country has 30,000 kilometers (18,641 miles) of high-speed lines and aims to reach 38,000 kilometers (23,612 miles) by 2025. The race to build more track continues, and people continue to flock to these bullet trains to move between the country’s megacities. In 2017, the sixth anniversary of the opening of the line between Shanghai and Chengdu, the Chinese authorities report that 630 million people took the train that year alone.

Numbers that are repeated virtually unchanged for all the major routes that connect the country’s east with the west, and the south with the north — enormous distances that are shortened thanks to high-speed trains, supersonic arrows that soon promise to reach speeds of 600 kilometers per hour (372 mph).

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1578 2022-11-27 02:02:11

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1551) Magic Square

Summary

In recreational mathematics, a square array of numbers, usually positive integers, is called a magic square if the sums of the numbers in each row, each column, and both main diagonals are the same. The order of the magic square is the number of integers along one side (n), and the constant sum is called the magic constant. If the array includes just the positive integers  1,2,...,n^{2}, the magic square is said to be normal. Some authors take magic square to mean normal magic square.

Magic squares that include repeated entries do not fall under this definition and are referred to as trivial. Some well-known examples, including the Sagrada Família magic square and the Parker square are trivial in this sense. When all the rows and columns but not both diagonals sum to the magic constant we have semimagic squares (sometimes called orthomagic squares).

The mathematical study of magic squares typically deals with their construction, classification, and enumeration. Although completely general methods for producing all the magic squares of all orders do not exist, historically three general techniques have been discovered: by bordering method, by making composite magic squares, and by adding two preliminary squares. There are also more specific strategies like the continuous enumeration method that reproduces specific patterns. Magic squares are generally classified according to their order n as: odd if n is odd, evenly even (also referred to as "doubly even") if n is a multiple of 4, oddly even (also known as "singly even") if n is any other even number. This classification is based on different techniques required to construct odd, evenly even, and oddly even squares. Beside this, depending on further properties, magic squares are also classified as associative magic squares, pandiagonal magic squares, most-perfect magic squares, and so on. More challengingly, attempts have also been made to classify all the magic squares of a given order as transformations of a smaller set of squares. Except for n ≤ 5, the enumeration of higher order magic squares is still an open challenge. The enumeration of most-perfect magic squares of any order was only accomplished in the late 20th century.

Magic squares have a long history, dating back to at least 190 BCE in China. At various times they have acquired occult or mythical significance, and have appeared as symbols in works of art. In modern times they have been generalized a number of ways, including using extra or different constraints, multiplying instead of adding cells, using alternate shapes or more than two dimensions, and replacing numbers with shapes and addition with geometric operations.

Details

Magic square is a square matrix often divided into cells, filled with numbers or letters in particular arrangements that were once thought to have special, magical properties. Originally used as religious symbols, they later became protective charms or tools for divination; and finally, when the original meanings were lost, people considered them mere curiosities or puzzles—except for some Western mathematicians who continue to study them as problems in number theory.

The most familiar lettered square in the Western world is the well-known SATOR square, composed of the words SATOR, AREPO, TENET, OPERA, and ROTAS. Arranged both vertically and horizontally, the meaningless phrase reads through the centre TENET, thus forming the two arms of a hidden cross. Examples of this square from the 1st century AD were found in the ruins of Pompeii, and it was still employed during the 19th century in Europe and the United States for fancied protection against fire, sickness, and other disasters.

Otherwise, numbered squares have always been far more significant, particularly in China (where they may have originated), the Arab world, and India.

In the arithmetical magic squares, the numbers are generally placed in separate cells and arranged so that each column, every row, and the two main diagonals can produce the same sum, called the constant. A standard magic square of any given number contains the sequence of natural numbers from 1 to the square of that number. Thus, the magic square of 3 contains the numbers 1 to 9. If these nine numbers are simply listed in three rows or three columns, they form the natural square of 3. A natural square has no “magical” properties, but one is often made as a first step in constructing a proper magic square. When these nine numbers in the 3 × 3 frame are rearranged so that they can produce a constant sum of 15, they constitute the magic square of 3.

Magic Square Puzzles

Magic squares are one of the simplest forms of logic puzzles, and a great introduction to problem solving techniques beyond traditional arithmetic algorithms. Each square is divided into cells, and the rules require that the sum of any row, column or diagonal in the square be the same. Given a magic square with empty cells, your job is to solve the puzzle by supplying the missing numbers. This page has 3x3, 4x4 and 5x5 magic square worksheets that will get you ready for other challenges like the printable sudoku puzzles and more!

3x3 Magic Square Puzzles

The 3x3 magic squares on these puzzle worksheets are the least complex form of magic squares you can solve. There are normal versions (with numbers 1-9) and non-normal versions that produce a different 'magic number' when solved. Give them a try before moving on to the 4x4 magic squares!

4x4 Magic Square Puzzles

These harder 4x4 magic squares are step up from the 3x3 puzzles, but still fairly easy to solve if you have been practicing your addition worksheets. The normal squares with values 1-16 are easy to solve, but the non-normal squares may need your calculator!

5x5 Magic Square Puzzles

Normal 5x5 magic squares have numbers from 1-25 and can be a real brain twister. The non-normal versions of the 5x5 puzzles are great exercises for kids (or adults!) who have solid problem solving skills.

6x6 Magic Square Puzzles

Thse worksheets start with normal 6x6 magic squares having numbers from 1-36, but the non-normal versions of the 6x6 puzzles are tremdously difficult to solve and will likely require your calculator and some time.

Try These Printable Magic Square Puzzle Worksheets!

Magic square puzzles are one of the earliest types of number puzzles, dating from the 6th or 7th century BCE. We find early records of magic square puzzles coming from China and Arabia.

Other puzzle types, including sudoku, require similar skills to solve, making magic square puzzles a good introduction to the broader class of missing number logic puzzles.

A magic square has the property that the sum of the numbers in every row is the same value, and also the sum of the numbers in every column is that same value, and also the sum of the two diagonals is that same value. When solving a magic square puzzle, some of the cells will be blank and your challenge is to figure out what numbers go into those cells to make all of the row, column and diagonal sums equal.

Normal Magic Squares versus Non-Normal Magic Squares

A magic square is considered 'normal' if the square contains numbers that are the smallest possible values. For example, a 3x3 magic square has nine cells and a normal 3x3 magic square will only contain the numbers 1-9 in it. Similarly, a 4x4 magic square with 16 cells contains only the values 1 through 16, and a 5x5 magic square only contians the values 1 through 25.

A non-normal square does not use minimal numbers in its cells, so the sums of the rows, columns and diagonals may be larger.

What is the Order for a Magic Square?

The Order for a magic square dimension of the horizontal and vertical axis of the square. Because it's square, these values for a given puzzle are the same. For example, for a 3x3 magic square we say it is an 'order 3' magic square. A 4x4 magic square is order 4, a 5x5 is order 5 and so on.

What is the Magic Constant for a Magic Square?

The Magic Constant is the value that you get for each row, column or diagonal sum in a magic square. For a normal magic square, a curious property is the magic constant for a normal magic square of a given order is always the same.

The magic constant for a order-3 normal magic square (a 3x3 magic square) will always be 15. Similarly, order 4 normal magic squares will always have a magic constant of 34, order 5 normal magic squares will have a constant of 65 and order 6 normal magic squares will have a magic constant of 111. These constants will come in handy when solving the normal magic square puzzles here!

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1579 2022-11-28 00:03:45

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1552) Dam

Summary

A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect or store water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions. The earliest known dam is the Jawa Dam in Jordan, dating to 3,000 BC.

The word dam can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old cities, such as Amsterdam and Rotterdam.

Modern era

The era of large dams was initiated with the construction of the Aswan Low Dam in Egypt in 1902, a gravity masonry buttress dam on the Nile River. Following their 1882 invasion and occupation of Egypt, the British began construction in 1898. The project was designed by Sir William Willcocks and involved several eminent engineers of the time, including Sir Benjamin Baker and Sir John Aird, whose firm, John Aird & Co., was the main contractor. Capital and financing were furnished by Ernest Cassel. When initially constructed between 1899 and 1902, nothing of its scale had ever before been attempted;[36] on completion, it was the largest masonry dam in the world.

The Hoover Dam is a massive concrete arch-gravity dam, constructed in the Black Canyon of the Colorado River, on the border between the US states of Arizona and Nevada between 1931 and 1936 during the Great Depression. In 1928, Congress authorized the project to build a dam that would control floods, provide irrigation water and produce hydroelectric power. The winning bid to build the dam was submitted by a consortium called Six Companies, Inc. Such a large concrete structure had never been built before, and some of the techniques were unproven. The torrid summer weather and the lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned over the dam to the federal government on 1 March 1936, more than two years ahead of schedule.

By 1997, there were an estimated 800,000 dams worldwide, some 40,000 of them over 15 m (49 ft) high. In 2014, scholars from the University of Oxford published a study of the cost of large dams – based on the largest existing dataset – documenting significant cost overruns for a majority of dams and questioning whether benefits typically offset costs for such dams.

Details

A dam is a structure built across a stream, a river, or an estuary to retain water. Dams are built to provide water for human consumption, for irrigating arid and semiarid lands, or for use in industrial processes. They are used to increase the amount of water available for generating hydroelectric power, to reduce peak discharge of floodwater created by large storms or heavy snowmelt, or to increase the depth of water in a river in order to improve navigation and allow barges and ships to travel more easily. Dams can also provide a lake for recreational activities such as swimming, boating, and fishing. Many dams are built for more than one purpose; for example, water in a single reservoir can be used for fishing, to generate hydroelectric power, and to support an irrigation system. Water-control structures of this type are often designated multipurpose dams.

Auxiliary works that can help a dam function properly include spillways, movable gates, and valves that control the release of surplus water downstream from the dam. Dams can also include intake structures that deliver water to a power station or to canals, tunnels, or pipelines designed to convey the water stored by the dam to far-distant places. Other auxiliary works are systems for evacuating or flushing out silt that accumulates in the reservoir, locks for permitting the passage of ships through or around the dam site, and fish ladders (graduated steps) and other devices to assist fish seeking to swim past or around a dam.

A dam can be a central structure in a multipurpose scheme designed to conserve water resources on a regional basis. Multipurpose dams can hold special importance in developing countries, where a single dam may bring significant benefits related to hydroelectric power production, agricultural development, and industrial growth. However, dams have become a focus of environmental concern because of their impact on migrating fish and riparian ecosystems. In addition, large reservoirs can inundate vast tracts of land that are home to many people, and this has fostered opposition to dam projects by groups who question whether the benefits of proposed projects are worth the costs.

In terms of engineering, dams fall into several distinct classes defined by structural type and by building material. The decision as to which type of dam to build largely depends on the foundation conditions in the valley, the construction materials available, the accessibility of the site to transportation networks, and the experiences of the engineers, financiers, and promoters responsible for the project. In modern dam engineering, the choice of materials is usually between concrete, earthfill, and rockfill. Although in the past a number of dams were built of jointed masonry, this practice is now largely obsolete and has been supplanted by concrete. Concrete is used to build massive gravity dams, thin arch dams, and buttress dams. The development of roller-compacted concrete allowed high-quality concrete to be placed with the type of equipment originally developed to move, distribute, and consolidate earthfill. Earthfill and rockfill dams are usually grouped together as embankment dams because they constitute huge mounds of earth and rock that are assembled into imposing man-made embankments.

Additional Information

A dam is a structure built across a river or stream to hold back water. People have used different materials to build dams over the centuries. Ancient dam builders used natural materials such as rocks or clay. Modern-day dam builders often use concrete.

Manmade dams create artificial lakes called reservoirs. Reservoirs can be used to store water for farming, industry, and household use. They also can be used for fishing, boating, and other leisure activities. People have used dams for many centuries to help prevent flooding.

The ancient Mesopotamians may have been some of the first humans to build dams. The oldest known dam is the Jawa Dam, located in present-day Jordan. It was built in the fourth century B.C.E. Dams provided farmers with a steady source of water to irrigate crops. This allowed ancient Mesopotamians to feed a growing population.

The Romans were master-dam builders too. They used dams to divert water for drinking, bathing, and irrigation. One of the oldest dams still in use is the Cornalvo Dam in Spain. The ancient Romans built it in the first or second century C.E.

The force of flowing water creates mechanical power. People have harnessed this power for centuries with the use of dams. Small dams powered paddle wheels in pre-industrial Europe and America. These were used to help saw logs or grind corn and other grains.

During the Industrial Revolution, engineers began to build bigger dams. These industrial-sized dams could hold back more water to power the big machinery of factories and mines. They also could turn giant turbines to generate electricity.

The early 1900s ushered in an era of “big dam” building in America as demands for electricity increased. During the Great Depression, President Franklin D. Roosevelt put Americans back to work building massive dam projects. The most famous of these is the Hoover Dam.

The Hoover Dam sits on the border between Nevada and Arizona. It was completed in 1936. The Hoover Dam is regarded as an engineering marvel. It was the tallest dam ever built at the time—222 meters (727 feet). The dam helped to control the flow of water on the Colorado River by creating Lake Mead, one of the largest reservoirs in the United States. Lake Mead provides drinking water for the city of Las Vegas.

Dams have long been viewed as a symbol of human ingenuity. However, ecologists who study rivers and lakes have uncovered some environmental downsides to dam construction. Dams change the way rivers function, and in some cases, this can harm local fish populations.

Flooding landscapes to create reservoirs can have consequences for biodiversity as well. Brazilian biologist Raffaello Di Ponzio studies the impact of big dam projects on the plants and animals of the Amazon Rainforest. More than 200 hydroelectric dams have been proposed in Brazil. While these dams could help satisfy growing South American energy demands, they would also flood more than 10 million hectares (25 million acres) of the Amazon Rainforest.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1580 2022-11-28 21:28:46

ganesh
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Posts: 40,614

Re: Miscellany

1553) Ointment

Summary

Ointments are viscous, unctuous, semisolid preparations containing either dissolved or suspended functional ingredients. The ointment base needs to be heated to above its melting temperature prior to the addition of the other ingredients. Low-shear or mixing speeds are typically used when the ointment base or finished formulation is cold/thick. Mixing speeds and shear can be increased when the ointment base is liquid, to uniformly disperse the functional ingredients. Mixers used for ointments typically employ dual-motion counter-rotating blades with side scrapers, to keep the material in constant movement and provide efficient heat transfer from the walls of the mixing vessel. External powder eductors can be used to incorporate solid ingredients.

The use of excessive shear when the ointment base (or finished formulation) is cold/thick will cause loss of structure and viscosity. This loss of structure will be seen as oil “bleed” or syneresis as the lighter fractions of the base separate from the bulk formulation on standing.

Typical ointment bases comprise petrolatum and mineral oil, or petrolatum and waxy/fatty alcohol combinations, the ratio and grades of these components being selected to give the desired finished product viscosity/spreadability. Proprietary ointment bases are also available.

Details

An ointment is a homogeneous, viscous, semi-solid preparation, most commonly a greasy, thick oil (oil 80% - water 20%) with a high viscosity, that is intended for external application to the skin or mucous membranes. Ointments have a water number that defines the maximum amount of water that they can contain. They are used as emollients or for the application of active ingredients to the skin for protective, therapeutic, or prophylactic purposes and where a degree of occlusion is desired.

Ointments are used topically on a variety of body surfaces. These include the skin and the mucous membranes of the eye (an eye ointment), chest, nose etc. An ointment may or may not be medicated.

Ointments are usually very moisturizing, and good for dry skin. They have a low risk of sensitization due to having few ingredients beyond the base oil or fat, and low irritation risk. There is typically little variability between brands of drugs. They are often disliked by patients due to greasiness.

The vehicle of an ointment is known as the ointment base. The choice of a base depends upon the clinical indication for the ointment. The different types of ointment bases are:

* Absorption bases, e.g., beeswax and wool fat
* Emulsifying bases, e.g., cetrimide and emulsifying wax
* Hydrocarbon bases, e.g., ceresine, microcrystalline wax, hard paraffin, and soft paraffin
* Vegetable oil bases, e.g., almond oil, coconut oil, olive oil, peanut oil, and sesame oil
* Water-soluble bases, e.g., macrogols 200, 300, 400

The medicaments are dispersed in the base and are divided after penetrating the living cells of the skin.

The water number of an ointment is the maximum quantity of water that 100g of a base can contain at 20 °C.

Ointments are formulated using hydrophobic, hydrophilic, or water-emulsifying bases to provide preparations that are immiscible, miscible, or emulsifiable with skin secretions. They can also be derived from hydrocarbon (fatty), absorption, water-removable, or water-soluble bases.

Evaluation of ointments:

* Drug content
* Release of medicament from base
* Medicament penetration
* Consistency of the preparation
* Absorption of medicament into blood stream
* Irritant effect

Properties which affect choice of an ointment base are:[citation needed]

* Stability
* Penetrability
* Solvent property
* Irritant effects
* Ease of application and removal

Methods of preparation of ointments:

* Fusion: In this method the ingredients are melted together in descending order of their melting points and stirred to ensure homogeneity.
* Trituration: In this finely subdivided insoluble medicaments are evenly distributed by grinding with a small amount of the base followed by dilution with gradually increasing amounts of the base.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1581 2022-11-29 15:03:59

ganesh
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Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1554) Chimney

Summary

A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the stack, or chimney effect. The space inside a chimney is called the flue. Chimneys are adjacent to large industrial refineries, fossil fuel combustion facilities or part of buildings, steam locomotives and ships.

In the United States, the term smokestack industry refers to the environmental impacts of burning fossil fuels by industrial society, including the electric industry during its earliest history. The term smokestack (colloquially, stack) is also used when referring to locomotive chimneys or ship chimneys, and the term funnel can also be used.

The height of a chimney influences its ability to transfer flue gases to the external environment via stack effect. Additionally, the dispersion of pollutants at higher altitudes can reduce their impact on the immediate surroundings. The dispersion of pollutants over a greater area can reduce their concentrations and facilitate compliance with regulatory limits.

Details

Chimney is a structure designed to carry off smoke from a fireplace or furnace. A chimney also induces and maintains a draft that provides air to the fire.

In western Europe before the 12th century, heating fires were almost invariably placed in the middle of a room, and chimneys were therefore rare. Most of the characteristic forms of modern chimneys originated in northern Europe, when masonry techniques were developed that allowed the construction of a hearth along a wall with a fireproof backstop and flue. Some medieval chimney stacks were tubular, and some had ingenious conical caps with hooded side vents to shield against rain. During the 15th and 16th centuries, tall chimneys elaborately decorated with carvings, niches, and inlays formed an important part of the architectural ensemble. As housing grew more commodious and many rooms in a single dwelling were equipped with fireplaces, flues were grouped to carry smoke to a central chimney of masonry. In English housing of this time, each flue emerging at the roof line was treated as a separate columnar structure with base, cap, and polygonal shaft, generally of elaborately shaped bricks. Chimneys of the 17th and 18th centuries tended to be rectangular and to have projecting top courses that formed protective caps. In North America a massive chimney of this type became the central feature of the colonial New England farmhouse. As coal was introduced for domestic heating, chimney construction became the subject of serious study, and in the late 18th century Sir Benjamin Thompson established the definitive forms and proper relationships of the chimney’s essential parts.

An ordinary domestic chimney consists of three parts: the throat, the smoke chamber, and the flue. The throat is the opening immediately above the fire; it usually narrows to a few inches in width just below the damper, a door that can be closed when the furnace or fireplace is not in use. Above the damper is the smoke chamber. At the bottom of the smoke chamber is a smoke shelf formed by setting back the masonry at the top of the throat to the line of the back wall of the flue; its function is to deflect downdrafts that might otherwise blow smoke out into the room. The smoke chamber narrows uniformly toward the top; it slows down drafts and acts as a reservoir for smoke trapped in the chimney by gusts across the chimney top. The flue, the main length of the chimney, is usually of masonry, often brick, and metal-lined. Vertical flues perform best, though a bend is sometimes included to reduce rain splash; bends are also necessary when several flues are united in a common outlet.

Industrial chimneys are usually free-standing single flues with cylindrical cores of firebrick and outer jackets of steel, brick, or reinforced concrete, often with an insulating air space between to allow for differential expansion. Because the taller the chimney, the better the draft, some industrial chimneys are more than 300 feet (91.5 m) in height.

How a chimneys work

Chimneys operate on the principle that hot air increase above cold air. The movement of hot gases orient from the fire creates a pressure difference between the inside of the flue and the room. It is called a “draught” and it forces air into the fireplace, These air feeds the flames as it rushes past the fire. The hotter the hearth , the faster the air increase and the better the chimney works. The motion of air through the chimney is helped by the fact that air in the house is warmer than the air outside.
If the chimney is not working perfectly then sufficient draught will not be generated inside the flue and subsequently not enough air will be sucked into the fire for it to burn perfectly.

Though a chimney appears to drag, & smoke appears to naturally rise, it is more accurate to think of the weight of thick outside air pushing down to force air into the building then push the warmer , lighter, waste gases out up the stack, somewhat like an bubble rises in water.

This tiny difference in pressure between inside & outside the flue is what makes a chimney function. Predicting the standard of flue draught for a chimney is extremely difficult and requires experience and a degree of technical knowledge.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1582 2022-11-30 13:34:03

ganesh
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Posts: 40,614

Re: Miscellany

1555) Canoe

Summary

A canoe is a lightweight narrow water vessel, typically pointed at both ends and open on top, propelled by one or more seated or kneeling paddlers facing the direction of travel and using a single-bladed paddle.

In British English, the term canoe can also refer to a kayak, while canoes are called Canadian or open canoes to distinguish them from kayaks.

Canoes were developed by cultures all over the world, including some designed for use with sails or outriggers. Until the mid-19th century, the canoe was an important means of transport for exploration and trade, and in some places is still used as such, sometimes with the addition of an outboard motor. Where the canoe played a key role in history, such as the Northern United States, Canada, and New Zealand, it remains an important theme in popular culture.

Canoes are now widely used for competition and pleasure, such as racing, whitewater, touring and camping, freestyle and general recreation. Canoeing has been part of the Olympics since 1936. The intended use of the canoe dictates its hull shape, length, and construction material. Historically, canoes were dugouts or made of bark on a wood frame, but construction materials evolved to canvas on a wood frame, then to aluminum. Most modern canoes are made of molded plastic or composites such as fiberglass or those incorporating kevlar, or graphite.

Details

A canoe is a lightweight boat pointed at both ends and propelled by one or more paddles (not oars). Paddlers face the bow.

There are two main forms of the canoe. The modern recreational or sport Canadian canoe is open from end to end; it is propelled with a paddle having a single blade. The kayak has a covered deck with a well, or math, into which the paddler snugly fits; it is propelled with a double-bladed paddle. Other boats sometimes called canoes include the dugout (a shaped and hollowed-out log), or pirogue.

Columbus recorded the word canoa as that used by West Indians to describe their pirogue-like boats. The earliest canoes had light frames of wood or, for the Eskimo kayak, whalebone covered by tightly stretched bark of trees (usually birch, occasionally elm) or animal skins (the kayak). Others were made from pieces of bark sewed together with roots and caulked with resin; sheathing and ribs were pressed into the sheet of bark, which was hung from a gunwale temporarily supported by stakes. The birchbark canoe was first used by the Algonquin Indians in what is now the northeastern part of the United States and adjacent Canada, and its use passed westward. Such canoes were used for carrying goods, hunters, fishermen, and warriors. The craft varied in length from about 4.5 metres (15 feet)—6 metres (20 feet) being most common—to about 30 metres (100 feet) in length for some war canoes; sometimes as many as 20 paddlers were employed. The dugout was used by Indians in what is now the southeastern United States and along the Pacific coast as far north as modern Canada, as well as by peoples in Africa, New Zealand, and elsewhere in the Pacific. For use in the open sea, canoes were fitted with outriggers, or pairs of canoes were linked by spars (see catamaran). The early French missionaries and explorers in northern North America used birchbark canoes, as did the voyageurs and others later engaged in the fur trade, which required relatively large canoes.

Modern sport and recreation canoes are of varying size but are usually about 4.5–6 metres (15–20 feet) in length and about 85 cm (33 inches) in breadth. Depth is about 30 to 36 cm (12 to 14 inches), with the ends rising slightly higher. Canoes are made of wood, canvas over wood frames, aluminum, molded plastic, fibreglass, or synthetic fibre composites. The optimum material for canoe construction varies by the intended usage of the craft. Fibre composite canoes constructed of materials such as Kevlar offer excellent durability with minimal weight, making them well suited for canoe camping that requires numerous portages. Aluminum and molded plastic canoes are highly impact resistant and are used primarily on rivers where possible collisions with rocks and other submerged objects might damage a fibreglass canoe. Some canoes are designed or adapted to be propelled by a sail, and some aluminum and molded plastic canoes are made with square sterns to accommodate outboard motors. The introduction of the faltboat (German: Faltboot, “folding boat”) early in the 20th century greatly extended the use of the kayak for canoeists who did not live near water but who could easily transport the folded craft to water.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1583 2022-12-01 13:57:26

ganesh
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Posts: 40,614

Re: Miscellany

1556) Shipyard

Summary

A shipyard (also called a dockyard or boatyard) is a place where ships are built and repaired. These can be yachts, military vessels, cruise liners or other cargo or passenger ships. Dockyards are sometimes more associated with maintenance and basing activities than shipyards, which are sometimes associated more with initial construction. The terms are routinely used interchangeably, in part because the evolution of dockyards and shipyards has often caused them to change or merge roles.

Countries with large shipbuilding industries include Australia, Brazil, China, Croatia, Denmark, Finland, France, Germany, India, Ireland, Italy, Japan, the Netherlands, Norway, the Philippines, Poland, Romania, Russia, Singapore, South Korea, Sweden, Taiwan, Turkey, the United Arab Emirates, Ukraine, the United Kingdom, the United States and Vietnam. The shipbuilding industry is more fragmented in Europe than in Asia where countries tend to have fewer, larger companies. Many naval vessels are built or maintained in shipyards owned or operated by the national government or navy.

Shipyards are constructed near the sea or tidal rivers to allow easy access for their ships. The United Kingdom, for example, has shipyards on many of its rivers.

The site of a large shipyard will contain many specialised cranes, dry docks, slipways, dust-free warehouses, painting facilities and extremely large areas for fabrication of the ships. After a ship's useful life is over, it makes its final voyage to a shipbreaking yard, often on a beach in South Asia. Historically shipbreaking was carried on in drydock in developed countries, but high wages and environmental regulations have resulted in movement of the industry to developing regions.

Details

A shipyard is a shore establishment for building and repairing ships. The shipbuilding facilities of the ancient and medieval worlds reached a culmination in the math of Venice, a shipyard in which a high degree of organization produced an assembly-line technique, with a ship’s fittings added to the completed hull as it was floated past successive docks. In 18th-century British shipyards, the hull was towed to a floating stage called a sheer hulk, where it received its masts and rigging. Modern ships also are launched incomplete.

Typically, a shipyard has a limited number of building berths, sloping down toward the waterway, with large adjacent working areas. Plates and sections are delivered to a point distant from the berth and converge toward the berth as they are assembled into components and subassemblies, which are ultimately welded together. Very large ships are often built in deep drydocks because of the greater convenience in lowering large components. When the hull is complete, water is admitted and the ship floated to the fitting-out basin.

History

The world's earliest known dockyards were built in the Harappan port city of Lothal circa 2400 BC in Gujarat, India. Lothal's dockyards connected to an ancient course of the Sabarmati river on the trade route between Harappan cities in Sindh and the peninsula of Saurashtra when the present-day surrounding Kutch desert formed a part of the Arabian Sea.

Lothal engineers accorded high priority to the creation of a dockyard and a warehouse to serve the purposes of naval trade. The dock was built on the eastern flank of the town, and is regarded by archaeologists as an engineering feat of the highest order. It was located away from the main current of the river to avoid silting, but provided access to ships at high tide as well.

The name of the ancient Greek city on the Gulf of Corinth, Naupactus, means "shipyard" (combination of the Greek words "ship, boat"; and "builder, fixer"). Naupactus' reputation in this field extends to the time of legend, in which it is depicted as the place where the Heraclidae built a fleet to invade the Peloponnesus.

In the Spanish city of Barcelona, the Drassanes shipyards were active from at least the mid-13th century until the 18th century, although at times they served as a barracks for troops as well as an math. During their time of operation the Drassanes were continuously changed, rebuilt and modified, but two original towers and part of the original eight construction-naves remain today. The site is currently a maritime museum.

From the 14th century, several hundred years before the Industrial Revolution, ships were the first items to be manufactured in a factory - in the Venice math of the Venetian Republic in present-day Italy. The math apparently mass-produced nearly one ship every day using pre-manufactured parts and assembly lines. At its height in the 16th century the enterprise employed 16,000 people.

Spain built component ships of the Great Armada of 1588 at ports such as Algeciras or Málaga.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1584 2022-12-02 14:13:19

ganesh
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Posts: 40,614

Re: Miscellany

1557) Bone

Summary

A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have complex internal and external structures.[2] They are lightweight yet strong and hard and serve multiple functions.

Bone tissue (osseous tissue), which is also called bone in the uncountable sense of that word, is hard tissue, a type of specialized connective tissue. It has a honeycomb-like matrix internally, which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells. Osteoblasts and osteocytes are involved in the formation and mineralization of bone; osteoclasts are involved in the resorption of bone tissue. Modified (flattened) osteoblasts become the lining cells that form a protective layer on the bone surface. The mineralized matrix of bone tissue has an organic component of mainly collagen called ossein and an inorganic component of bone mineral made up of various salts. Bone tissue is mineralized tissue of two types, cortical bone and cancellous bone. Other types of tissue found in bones include bone marrow, endosteum, periosteum, nerves, blood vessels and cartilage.

In the human body at birth, there are approximately 300 bones present; many of these fuse together during development, leaving a total of 206 separate bones in the adult, not counting numerous small sesamoid bones. The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear.

The Greek word for bone is "osteon", hence the many terms that use it as a prefix—such as osteopathy. In anatomical terminology, including the Terminologia Anatomica international standard, the word for a bone is os (for example, os breve, os longum, os sesamoideum).

Details

Bone is a rigid body tissue consisting of cells embedded in an abundant hard intercellular material. The two principal components of this material, collagen and calcium phosphate, distinguish bone from such other hard tissues as chitin, enamel, and shell. Bone tissue makes up the individual bones of the human skeletal system and the skeletons of other vertebrates.

The functions of bone include (1) structural support for the mechanical action of soft tissues, such as the contraction of muscles and the expansion of lungs, (2) protection of soft organs and tissues, as by the skull, (3) provision of a protective site for specialized tissues such as the blood-forming system (bone marrow), and (4) a mineral reservoir, whereby the endocrine system regulates the level of calcium and phosphate in the circulating body fluids.

Evolutionary origin and significance

Bone is found only in vertebrates, and, among modern vertebrates, it is found only in bony fish and higher classes. Although ancestors of the cyclostomes and elasmobranchs had armoured headcases, which served largely a protective function and appear to have been true bone, modern cyclostomes have only an endoskeleton, or inner skeleton, of noncalcified cartilage and elasmobranchs a skeleton of calcified cartilage. Although a rigid endoskeleton performs obvious body supportive functions for land-living vertebrates, it is doubtful that bone offered any such mechanical advantage to the teleost (bony fish) in which it first appeared, for in a supporting aquatic environment great structural rigidity is not essential for maintaining body configuration. The sharks and rays are superb examples of mechanical engineering efficiency, and their perseverance from the Devonian Period attests to the suitability of their nonbony endoskeleton.

In modern vertebrates, true bone is found only in animals capable of controlling the osmotic and ionic composition of their internal fluid environment. Marine invertebrates exhibit interstitial fluid compositions essentially the same as that of the surrounding seawater. Early signs of regulability are seen in cyclostomes and elasmobranchs, but only at or above the level of true bone fishes does the composition of the internal body fluids become constant. The mechanisms involved in this regulation are numerous and complex and include both the kidney and the gills. Fresh and marine waters provide abundant calcium but only traces of phosphate; because relatively high levels of phosphate are characteristic of the body fluids of higher vertebrates, it seems likely that a large, readily available internal phosphate reservoir would confer significant independence of external environment on bony vertebrates. With the emergence of terrestrial forms, the availability of calcium regulation became equally significant. Along with the kidney and the various component glands of the endocrine system, bone has contributed to development of internal fluid homeostasis—the maintenance of a constant chemical composition. This was a necessary step for the emergence of terrestrial vertebrates. Furthermore, out of the buoyancy of water, structural rigidity of bone afforded mechanical advantages that are the most obvious features of the modern vertebrate skeleton.

Chemical composition and physical properties

Depending upon species, age, and type of bone, bone cells represent up to 15 percent of the volume of bone; in mature bone in most higher animals, they usually represent only up to 5 percent. The nonliving intercellular material of bone consists of an organic component called collagen (a fibrous protein arranged in long strands or bundles similar in structure and organization to the collagen of ligaments, tendons, and skin), with small amounts of proteinpolysaccharides, glycoaminoglycans (formerly known as mucopolysaccharides) chemically bound to protein and dispersed within and around the collagen fibre bundles, and an inorganic mineral component in the form of rod-shaped crystals. These crystals are arranged parallel with the long axes of collagen bundles and many actually lie in voids within the bundles themselves. Organic material constitutes 50 percent of the volume and 30 percent of the dry weight of the intercellular composite, with minerals making up the remainder. The major minerals of the intercellular composite are calcium and phosphate. When first deposited, mineral is crystallographically amorphous, but with maturation it becomes typical of the apatite minerals, the major component being hydroxyapatite. Carbonate is also present—in amounts varying from 4 percent of bone ash in fish and 8 percent in most mammals to more than 13 percent in the turtle—and occurs in two distinct phases, calcium carbonate and a carbonate apatite. Except for that associated with its cellular elements, there is little free water in adult mammalian bone (approximately 8 percent of total volume). As a result, diffusion from surfaces into the interior of the intercellular substance occurs at the slow rates more typical of diffusion from surfaces of solids than within liquids.

The mineral crystals are responsible for hardness, rigidity, and the great compressive strength of bone, but they share with other crystalline materials a great weakness in tension, arising from the tendency for stress to concentrate about defects and for these defects to propagate. On the other hand, the collagen fibrils of bone possess high elasticity, little compressive strength, and considerable intrinsic tensile strength. The tensile strength of bone depends, however, not on collagen alone but on the intimate association of mineral with collagen, which confers on bone many of the general properties exhibited by two-phase materials such as fibre glass and bamboo. In such materials the dispersion of a rigid but brittle material in a matrix of quite different elasticity prevents the propagation of stress failure through the brittle material and therefore allows a closer approach to the theoretical limiting strength of single crystals.

The fine structure of bone has thus far frustrated attempts to determine the true strength of the mineral-matrix composite at the “unit” structural level. Compact (cortical) bone specimens have been found to have tensile strength in the range of 700–1,400 kg per square cm (10,000–20,000 pounds per square inch) and compressive strengths in the range of 1,400–2,100 kg per square cm (20,000–30,000 pounds per square inch). These values are of the same general order as for aluminum or mild steel, but bone has an advantage over such materials in that it is considerably lighter. The great strength of bone exists principally along its long axis and is roughly parallel both to the collagen fibre axis and to the long axis of the mineral crystals.

Although apparently stiff, bones exhibit a considerable degree of elasticity, which is important to the skeleton’s ability to withstand impact. Estimates of modulus of elasticity of bone samples are of the order of 420 to 700 kg per square cm (6,000 to 10,000 pounds per square inch), a value much less than steel, for example, indicating the much greater elasticity of bone. Perfect elasticity exists with loads up to 30 to 40 percent of breaking strength; above this, “creep,” or gradual deformation, occurs, presumably along natural defects within the bony structure. The modulus of elasticity in bone is strikingly dependent upon the rate at which loads are applied, bones being stiffer during rapid deformation than during slow; this behaviour suggests an element of viscous flow during deformation.

As might be anticipated from consideration of the two-phase composition of bone, variation in the mineral-collagen ratio leads to changes in physical properties: less mineral tends ultimately to greater flexibility and more mineral to increased brittleness. Optimal ratios, as reflected in maximal tensile strength, are observed at an ash content of approximately 66 percent, a value that is characteristic of the weight-bearing bones of mammals.

Bone morphology

Grossly, bone tissue is organized into a variety of shapes and configurations adapted to the function of each bone: broad, flat plates, such as the scapula, serve as anchors for large muscle masses, while hollow, thick-walled tubes, such as the femur, the radius, and the ulna, support weight or serve as a lever arm. These different types of bone are distinguished more by their external shape than by their basic structure.

All bones have an exterior layer called cortex that is smooth, compact, continuous, and of varying thickness. In its interior, bony tissue is arranged in a network of intersecting plates and spicules called trabeculae, which vary in amount in different bones and enclose spaces filled with blood vessels and marrow. This honeycombed bone is termed cancellous or trabecular. In mature bone, trabeculae are arranged in an orderly pattern that provides continuous units of bony tissue aligned parallel with the lines of major compressive or tensile force. Trabeculae thus provide a complex series of cross-braced interior struts arranged so as to provide maximal rigidity with minimal material.

Bones such as vertebrae, subject to primarily compressive or tensile forces, usually have thin cortices and provide necessary structural rigidity through trabeculae, whereas bones such as the femur, subject to prominent bending, shear, or torsional forces, usually have thick cortices, a tubular configuration, and a continuous cavity running through their centres (medullary cavity).

Long bones, distinctive of the body’s extremities, exhibit a number of common gross structural features. The central region of the bone (diaphysis) is the most clearly tubular. At one or commonly both ends, the diaphysis flares outward and assumes a predominantly cancellous internal structure. This region (metaphysis) functions to transfer loads from weight-bearing joint surfaces to the diaphysis. Finally, at the end of a long bone is a region known as an epiphysis, which exhibits a cancellous internal structure and comprises the bony substructure of the joint surface. Prior to full skeletal maturity the epiphysis is separated from the metaphysis by a cartilaginous plate called the growth plate or physis; in bones with complex articulations (such as the humerus at its lower end) or bones with multiple protuberances (such as the femur at its upper end) there may be several separate epiphyses, each with its growth plate.

Additional Information:

Bones: All you need to know

Bones are more than just the scaffolding that holds the body together. Bones come in all shapes and sizes and have many roles. In this article, we explain their function, what they consist of, and the types of cells they involve.

Bones are living, active tissues that the body is constantly remodeling.

Their functions include supporting body structure, protecting vital organs, and allowing the body to move. Also, they provide an environment for bone marrow, where the body creates blood cells, and they act as a storage area for minerals, particularly calcium.

The skeleton accounts for around 15%Trusted Source of body weight. At birth, humans have around 270Trusted Source soft bones. As they grow, some fuse.

By adulthood, people have between 206 and 213 bones. The reason for the difference is that some people have more or fewer bones in their ribs, vertebrae, fingers, and toes.

The largest bone in the human body is the thighbone, or femur, and the smallest is the stapes in the middle ear, at around 3 millimetersTrusted Source long.

Bones consist mostly of the protein collagen, which forms a soft framework. The mineral calcium phosphate hardens this framework, giving it strength. The bones contain 99% of the body’s calcium.

Bones have an internal structure similar to a honeycomb, which makes them rigid yet relatively light.

The structure of bones

Bones are composed of two types.

Compact (cortical) bone is a hard outer layer that is dense, strong, and durable. It makes up around 80% of adult bone mass and forms the outer layer of bone.

Cancellous (trabecular or spongy) bone makes up the remaining 20% of bone and consists of a network of trabeculae, or rod-like, structures. It is lighter, less dense, and more flexible than compact bone.

Bones also contain:

* osteoblasts and osteocytes, responsible for creating bone
*vosteoclasts, or bone-resorbing cells
* osteoid, a mix of collagen and other proteins
* inorganic mineral salts within the matrix
*bnerves and blood vessels
* bone marrow
* cartilage
* membranes, including the endosteum and periosteum

Bone cells

Bones are not static tissue but need constant maintenance and remodeling. There are threeTrusted Source main cell types involved in this process.

Osteoblasts are responsible for generating and repairing bone. They produce a protein mixture that doctors call osteoid, which is mineralized and becomes bone.

Osteocytes are inactive osteoblasts that are mineralized and remain within the bone they have created. They communicate with other bone cells and help support metabolic functions within the bone.

Osteoclasts are large cells with more than one nucleus. They useTrusted Source acids resulting from certain reactions to break down used bone. This process is called resorption. Osteoclasts help remodel injured bones and create pathways for nerves and blood vessels to travel through.

Bone marrow

Bone marrow is present in almost all bones where cancellous, or spongy, bone is present.

Bone marrow produces blood cells, including:

* red blood cells, which deliver oxygen to cells
* white blood cells, essential for the body’s immune system
* platelets, which the body uses for clotting

The marrow produces around 2 million red blood cells every second. It also produces lymphocytes, or the white blood cells involved in the immune response.

Extracellular matrix

Bones are essentially living cells embedded in a mineral-based organic matrix. This extracellular matrix consists of organic components (mostly type 1 collagen) and inorganic components, including hydroxyapatite and other salts, such as calcium and phosphate.

Collagen gives bone its tensile strength, namely resistance to pulling apart. Hydroxyapatite gives the bones compressive strength, or resistance to compression.

What do bones do?

Bones serve various functions that affect the whole body. StudiesTrusted Source show that, in addition to structure and movement, bones support energy metabolism, the production of blood cells, the immune system, and brain function.

Mechanics

Bones provide a frame to support the body. Muscles, tendons, and ligaments attach to bones. Without anchoring to bones, muscles could not move the body.

Protection

Some bones protect the body’s internal organs. For instance, the skull protects the brain, and the ribs protect the heart and lungs.

Synthesis

Cancellous bone is a vital reservoir for developing red blood cells, platelets, and white blood cells. Also, the body destroys defective and old red blood cells in bone marrow.

Metabolism

The metabolic functions of bone include:

* Storage: Bones act as a reserve for minerals, particularly calcium and phosphorous. Bone marrow adipose tissue can also store fatty acids.
* Endocrine function: Bones produce the precursors to various hormones, including those involved in growth, insulin production, and brain development. They release hormones that act on the kidneys and influence blood sugar regulation and fat deposition.
* Calcium balance: Bones can raise or reduce calcium in the blood by forming bone, or breaking it down in a process called resorption.
* pH balance: Some research has suggested bones can release or absorb alkaline salts, helping blood to stay at the right pH level, but scientists need more studies to confirm this.
* Detoxification: Bones can absorbTrusted Source heavy metals such as lead, mercury, and math from the blood.

Types of bone

There are five types of bones in the human body:

* Long bones: These are mostly compacted bones with little marrow and include most of the bones in the limbs. They tend to support weight and help movement.
* Short bones: These have a squat, cubed shape and include bones of the wrist and ankle.
* Flat bones: These have a flat, broad surface. They consist of two outer layers of compact bone and an inner layer of spongy bone. The bones of the skull, breastbone, ribs, and shoulder blades are flat bones. They tend to have a protective role.
* Sesamoid bones: These are embeddedTrusted Source in muscles and tendons near the surfaces of joints. They include the patella or kneecap. They protect tendons from wear and stress.
* Irregular bones: These bones do not fit into the first four categories and have an unusual shape. They include the bones of the spine and pelvis. They often protect organs or tissues.

The bones of the skeleton belong to two groups: The appendicular and axial skeletons.

The appendicular skeleton comprises 126 bones, including those of the limbs, shoulders, and pelvic girdle. It provides structure and support to other parts of the body.

The axial skeleton has less range of motion than the appendicular skeleton. It comprises the bones of the skull, vertebral column, and thoracic cage.

Bone remodeling

The body is always remodeling bone. This allows the body to fix damaged bone, reshape the skeleton during growth, and regulate calcium levels.

Remodeling is a two-part process. During formation, the body lays down new bone tissue. In resorption, osteoclasts break down and remove bone.

If one part of the skeleton comes under increased stress over time — for instance, during exercise — the sections of bone under most pressure will become thicker in response.

Osteocytes, osteoclasts, and osteoblasts play key roles, but other elements also contribute. These include parathyroid hormone, vitamin D, estrogen, and testosterone.

What is osteoporosis?

Osteoporosis is a bone disease that involves a reductionTrusted Source in bone mineral density. This increases the risk of fractures.

It most commonly occurs in females after menopause. However, it can affect males too, and it can start before menopause.

Osteoporosis occurs either when removal or resorption of bone happens too quickly, new bone forms too slowly, or for both reasons.

Risk factors include:

* low calcium levels
* vitamin D deficiency
* smoking tobacco
* using corticosteroids
* a high alcohol intake

Screening can help prevent or slow the progression of osteoporosis. Tests can show that osteopenia, the early stage of osteoporosis, is present. At this point, a doctor may recommend dietary measures or supplements.

As bone deterioration worsens, medications are available to slow its progression.

What other bone diseases are there?

Recent research : Currently, researchers are looking into ways to regenerate bone. This could help people with osteoarthritis, osteoporosis, and other conditions. It could also help mend broken bones.

Bone regeneration is a complex process. Scientists are currently looking at various aspects, including ways to:

* speed up mineral production for the generation of new bone
* use natural or synthetic grafts to enhance bone healing
* scaffold new bone and allow growth to occur
* use artificial biomaterials to achieve bone regeneration
* stimulate nerve pathways to encourage authentic bone production
* regenerate bones with surfaces that allow for nutrient absorption
* use stem cells to encourageTrusted Source bone to regenerate

Frequently asked questions

Here are some answers to questions people often ask about bones:

Why are bones important for overall health?

Bones support the body’s structure and protect vital organs, but they also play a key role in blood cell production, the immune system, the storage of calcium, the release of essential hormones, and many other functions.

What things are important for bone health?

Following a varied diet with plenty of calcium, getting enough vitamin D, and exercising are important for bone health. Avoiding smoking and limiting alcohol intake can also help prevent osteoporosis.

How do you know if your bones are unhealthy?

Various health problems can affect the bones. Signs of osteoporosis include a loss of height, an increasingly stooped posture, and fractures that happen often or easily. A screening test can show if a person has reduced bone density.

Bone pain can be a sign of bone damage, infection, or bone cancer. Bones can become soft if there is a vitamin D deficiency. This can lead to bent shins in children, known as rickets. In adults, doctors call this osteomalacia.

A nontraumatic bone fracture in adults over 50 years old may also be an early sign of undiagnosed cancer, such as metastatic breast or lung cancer or multiple myeloma.

In short

Bones play an essential role in the structure and function of the human body.

As well as enabling movement, they maintain appropriate levels of many compounds. They regulate hormonal pathways, contribute to metabolism, support the immune system, and more.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1585 2022-12-03 14:12:16

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1558) Dentist

Summary

What Is a Dentist?

Dentists are trained professionals who help care for the teeth and mouth. Regularly seeing a dentist can help you to maintain a good level of dental health, which may have a direct impact on your overall well-being.

What Does a Dentist Do?

A dentist has many responsibilities, and one of the most important is promoting good dental hygiene. This helps to prevent complications in your mouth or other parts of the body.

A dentist also diagnoses and treats problems of the gums, teeth, and mouth. Dentists use modern technology and equipment like X-ray machines, lasers, drills, brushes, scalpels, and other medical tools when performing dental procedures. They also wear protective equipment like gloves, masks, and safety glasses to prevent the spread of germs or bacteria.

Some common dentistry tasks include:

* Teaching people about dental hygiene
* Filling cavities
* Removing buildup or decay from teeth
* Repairing or removing damaged teeth
* Reviewing X-rays and diagnostics
* Giving anesthesia
* Putting in fillings or sealants
* Checking the growth of teeth and jawbones.

Dentistry requires a team approach, and the dentist is the leader. Working with the dentist are dental assistants, hygienists, and lab technicians. Together, the team ensures that people get quality dental care.

Details

A dentist, also known as a dental surgeon, is a health care professional who specializes in dentistry (the diagnosis, prevention, management, and treatment of diseases and conditions of the oral cavity and other aspects of the craniofacial complex including the temporomandibular joint). The dentist's supporting team aids in providing oral health services. The dental team includes dental assistants, dental hygienists, dental technicians, and sometimes dental therapists.

History:

Middle Ages

In China as well as France, the first people to perform dentistry were barbers. They have been categorized into 2 distinct groups: guild of barbers and lay barbers. The first group, the Guild of Barbers, was created to distinguish more educated and qualified dental surgeons from lay barbers. Guild barbers were trained to do complex surgeries. The second group, the lay barbers, were qualified to perform regular hygienic services such as shaving and tooth extraction as well as basic surgery. However, in 1400, France made decrees prohibiting lay barbers from practicing all types of surgery. In Germany as well as France from 1530 to 1575 publications completely devoted to dentistry were being published. Ambroise Paré, often known as the Father of Surgery, published his own work about the proper maintenance and treatment of teeth. Ambroise Paré was a French barber surgeon who performed dental care for multiple French monarchs. He is often credited with having raised the status of barber surgeons.

Modern dentistry

Pierre Fauchard of France is often referred to as the "father of modern dentistry" for being the first to publish a scientific textbook (1728) on the techniques and practices of dentistry. Over time, trained dentists immigrated from Europe to the Americas to practice dentistry, and by 1760, America had its own native born practicing dentists. Newspapers were used at the time to advertise and promote dental services. In America from 1768 to 1770 the first application of dentistry to verify forensic cases was being pioneered; this was called forensic dentistry. With the rise of dentists, there was also the rise of new methods to improve the quality of dentistry. These new methods included the spinning wheel to rotate a drill and chairs made specifically for dental patients.

In the 1840s the world's first dental school and national dental organization were established. Along with the first dental school came the establishment of the Doctor of Dental Surgery degree, often referred to as a DDS degree. In response to the rise in new dentists as well as dentistry techniques, the first dental practice act was established to regulate dentistry. In the United States, the First Dental Practice Act required dentists to pass each specific state medical board exam in order to practice dentistry in that particular state. However, because the dental act was rarely enforced, some dentists did not obey the act. From 1846 to 1855 new dental techniques were being invented such as the use of ester anesthesia for surgery, and the cohesive gold foil method which enabled gold to be applied to a cavity. The American Dental Association was established in 1859 after a meeting with 26 dentists. Around 1867, the first university-associated dental school was established, Harvard Dental School. Lucy Hobbs Taylor was the first woman to earn a dental degree.

In the 1880s, tube toothpaste was created which replaced the original forms of powder or liquid toothpaste. New dental boards, such as the National Association of Dental Examiners, were created to establish standards and uniformity among dentists. In 1887 the first dental laboratory was established; dental laboratories are used to create dentures and crowns that are specific to each patient. In 1895 the dental X-ray was discovered by a German physicist, Wilhelm Röntgen.

In the 20th century, new dental techniques and technology were invented such as the porcelain crowns (1903), Novocain (a local anesthetic) 1905, precision cast fillings (1907), nylon toothbrushes (1938), water fluoridation (1945), fluoride toothpaste (1950), air driven dental tools (1957), lasers (1960), electric toothbrushes (1960), and home tooth bleaching kits (1989) were invented. Inventions such as the air driven dental tools ushered in a new high-speed dentistry.

Responsibilities

By nature of their general training, a licensed dentist can carry out most dental treatments such as restorative (dental restorations, crowns, bridges), orthodontics (braces), prosthodontic (dentures, crown/bridge), endodontic (root canal) therapy, periodontal (gum) therapy, and oral surgery (extraction of teeth), as well as performing examinations, taking radiographs (x-rays) and diagnosis. Additionally, dentists can further engage in oral surgery procedures such as dental implant placement. Dentists can also prescribe medications such as antibiotics, fluorides, pain killers, local anesthetics, sedatives/hypnotics and any other medications that serve in the treatment of the various conditions that arise in the head and neck.

All DDS and DMD degree holders are legally qualified to perform a number of more complex procedures such as gingival grafts, bone grafting, sinus lifts, and implants, as well as a range of more invasive oral and maxillofacial surgery procedures, though many choose to pursue residencies or other post-doctoral education to augment their abilities. A few select procedures, such as the administration of General anesthesia, legally require postdoctoral training in the US. While many oral diseases are unique and self-limiting, poor conditions in the oral cavity can lead to poor general health and vice versa; notably, there is a significant link between periodontal and cardiovascular disease. Conditions in the oral cavity may also be indicative of other systemic diseases such as osteoporosis, diabetes, AIDS, and various blood diseases, including malignancies and lymphoma.

Several studies have suggested that dentists and dental students are at high risk of burnout. During burnout, dentists experience exhaustion, alienate from work and perform less efficiently. A systemic study identified risk factors associated with this condition such as practitioner's young age, personality type, gender, the status of education, high job strain and/or working hours, and the burden of clinical degrees requisites. The authors of this study concluded that intervention programs at an early stage during the undergraduate level may provide practitioners with a good strategy to prepare for / cope with this condition.

Regulations

Depending on the country, all dentists are required to register with their national or local health board, regulators, and professional indemnity insurance, in order to practice dentistry. In the UK, dentists are required to register with the General Dental Council. In Australia, it is the Dental Board of Australia, while in the United States, dentists are registered according to the individual state board. The main role of a dental regulator is to protect the public by ensuring only qualified dental practitioners are registered, handle any complaints or misconduct, and develop national guidelines and standards for dental practitioners to follow.

Specialty (dentistry)

For many countries, after satisfactory completion of post-graduate training, dental specialists are required to join a specialist board or list, in order to use the title 'specialist'.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1586 2022-12-04 14:10:08

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1559) Psychiatry

Summary

Psychiatry is the medical specialty devoted to the diagnosis, prevention, and treatment of mental disorders. These include various maladaptations related to mood, behaviour, cognition, and perceptions.

Initial psychiatric assessment of a person typically begins with a case history and mental status examination. Physical examinations and psychological tests may be conducted. On occasion, neuroimaging or other neurophysiological techniques are used. Mental disorders are often diagnosed in accordance with clinical concepts listed in diagnostic manuals such as the International Classification of Diseases (ICD), edited and used by the World Health Organization (WHO) and the widely used Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association (APA). The fifth edition of the DSM (DSM-5) was published in May 2013 which re-organized the larger categories of various diseases and expanded upon the previous edition to include information/insights that are consistent with current research.

Combined treatment with psychiatric medication and psychotherapy has become the most common mode of psychiatric treatment in current practice, but contemporary practice also includes a wide variety of other modalities, e.g., assertive community treatment, community reinforcement, and supported employment. Treatment may be delivered on an inpatient or outpatient basis, depending on the severity of functional impairment or on other aspects of the disorder in question. An inpatient may be treated in a psychiatric hospital. Research within psychiatry as a whole is conducted on an interdisciplinary basis with other professionals, such as epidemiologists, nurses, social workers, occupational therapists, or clinical psychologists.

Details

Psychiatry is the science and practice of diagnosing, treating, and preventing mental disorders.

The term psychiatry is derived from the Greek words psyche, meaning “mind” or “soul,” and iatreia, meaning “healing.” Until the 18th century, mental illness was most often seen as demonic possession, but it gradually came to be considered as a sickness requiring treatment. Many judge that modern psychiatry was born with the efforts of French physician Philippe Pinel in the late 1700s. His contemporary in the United States, statesman and physician Benjamin Rush, introduced a comparable approach. Perhaps the most significant contributions to the field occurred in the late 19th century, when German psychiatrist Emil Kraepelin emphasized a systematic approach to psychiatric diagnosis and classification and Austrian psychoanalyst Sigmund Freud, who was familiar with neuropathology, developed psychoanalysis as a treatment and research approach.

In countries such as the United States and the United Kingdom, psychiatrists have both a bachelor’s degree and a medical degree and at least four years of specialty training in psychiatry. In the United States and Canada, specialty training occurs during a period of residency, which typically begins with work in a hospital setting in which the resident learns to provide supervised care to acutely ill individuals. Following this period of hospital training, which lasts at least one year, residents are required to complete an additional three or more years of training that includes designated clinical and didactic experiences. These experiences must take place in structured educational programs that expose the resident to the biological, psychological, and sociocultural determinants of the major psychiatric disorders. Graduates of residency programs in the United States and Canada or of equivalent programs in other countries are designated as having achieved the knowledge, skills, and attitudes of the profession. These individuals have the ability to address the complicated ethical questions that often arise in the care of patients whose capacity for participation in their own treatment may be compromised. In many countries, before psychiatrists can begin practicing, they must take and pass both written and oral examinations. In the United States, successful completion of these exams enables psychiatrists to become board certified, meaning they have met the national benchmark criteria of competency required for the practice of psychiatry.

Certified psychiatrists should be able to employ treatments, such as drug therapy, electroconvulsive therapy, and biofeedback, to address biological dimensions of mental and emotional disorders. In addition, they should be prepared to apply different forms of psychotherapy, such as cognitive behavioral or interpersonal psychotherapies, to the psychological elements of mental and emotional dysfunction. Certified psychiatrists must be able to combine different treatments based on their understanding of the complexities of mind-brain interactions; this often involves an understanding of environmental factors and of how these factors apply to individuals with severe and persistent mental illness. Most mental and emotional disorders require a pluralistic treatment approach because they affect so many facets of the human experience. As a result, psychiatrists frequently work as part of a multidisciplinary treatment team with psychologists, social work professionals, occupational therapists, and psychiatric nurses.

In addition to overall competency to deal with psychiatric disorders, some psychiatrists pursue subspecialty training and associated certification. Examples of subspecialties include addiction psychiatry, forensic psychiatry, geriatric psychiatry, and psychosomatic psychiatry. Subspecialty education typically involves an additional one to two years of training. Other forms of subspecialty education, which are not recognized by board certification in the United States, include fellowships in emergency psychiatry and in neuropsychiatry, which focuses on the treatment of psychiatric symptoms in individuals with neurological disorders, such as traumatic brain injury and stroke.

There has been rapid growth in the science of psychiatry because of the development of technology that allows measurement and observation of brain function. Neuroimaging techniques, such as magnetic resonance imaging (MRI), positron emission tomography (PET), and single photon emission computed tomography (SPECT), have begun to answer basic questions about both psychopathologic disorders and normal development and function. These technologies can be used to integrate the different dimensions of the biopsychosocial model—biology, psychology, and sociology—that have been characterized independently.

shutterstock_795967777.jpg.webp


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1587 2022-12-05 00:09:59

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1560) Spirit level

Summary

A Spirit Level is a tool used to indicate how parallel (level) or perpendicular (plumb) a surface is relative to the earth. A spirit level gets its name from the mineral spirit solution inside the levels.A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or videographic work.

Details

A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or videographic work.

Construction

Early tubular spirit levels had very slightly curved glass vials with constant inner diameter at each viewing point. These vials are incompletely filled with a liquid, usually a colored spirit or alcohol, leaving a bubble in the tube. They have a slight upward curve, so that the bubble naturally rests in the center, the highest point. At slight inclinations the bubble travels away from the marked center position. Where a spirit level must also be usable upside-down or on its side, the curved constant-diameter tube is replaced by an uncurved barrel-shaped tube with a slightly larger diameter in its middle.

Alcohols such as ethanol are often used rather than water. Alcohols have low viscosity and surface tension, which allows the bubble to travel the tube quickly and settle accurately with minimal interference from the glass surface. Alcohols also have a much wider liquid temperature range, and will not break the vial as water could due to ice expansion. A colorant such as fluorescein, typically yellow or green, may be added to increase the visibility of the bubble.

A variant of the linear spirit level is the bull's eye level: a circular, flat-bottomed device with the liquid under a slightly convex glass face with a circle at the center. It serves to level a surface across a plane, while the tubular level only does so in the direction of the tube.

Calibration

To check the accuracy of a carpenter's type level, a perfectly horizontal surface is not needed. The level is placed on a flat and roughly level surface and the reading on the bubble tube is noted. This reading indicates to what extent the surface is parallel to the horizontal plane, according to the level, which at this stage is of unknown accuracy. The spirit level is then rotated through 180 degrees in the horizontal plane, and another reading is noted. If the level is accurate, it will indicate the same orientation with respect to the horizontal plane. A difference implies that the level is inaccurate.

Adjustment of the spirit level is performed by successively rotating the level and moving the bubble tube within its housing to take up roughly half of the discrepancy, until the magnitude of the reading remains constant when the level is flipped.

A similar procedure is applied to more sophisticated instruments such as a surveyor's optical level or a theodolite and is a matter of course each time the instrument is set up. In this latter case, the plane of rotation of the instrument is levelled, along with the spirit level. This is done in two horizontal perpendicular directions.

Sensitivity

Sensitivity is an important specification for a spirit level, as the device's accuracy depends on its sensitivity. The sensitivity of a level is given as the change of angle or gradient required to move the bubble by unit distance. If the bubble housing has graduated divisions, then the sensitivity is the angle or gradient change that moves the bubble by one of these divisions. 2 mm (0.079 in) is the usual spacing for graduations; on a surveyor's level, the bubble will move 2 mm (0.079 in) when the vial is tilted about 0.005 degree. For a precision machinist level with 2 mm (0.079 in) divisions, when the vial is tilted one division, the level will change 0.0005 in (0.013 mm) one foot from the pivot point, referred to by machinists as 5 tenths per foot. This terminology is unique to machinists and indicates a length of 5 tenths of 1 thousandth of an inch.

There are different types of spirit levels for different uses:

* Surveyor's leveling instrument
* Carpenter's level (either wood, aluminium or composite materials)
* Mason's level
* Torpedo level
* Post level
* Line level
* Engineer's precision level
* Electronic level
* Inclinometer
* Slip or Skid Indicator
* Bull's eye level

A spirit level is usually found on the head of combination squares.

Carpenter's bulls-eye level

'Tilting level', dumpy level or 'automatic level' are terms used to refer to types of 'leveling instruments' as used in surveying to measure height differences over larger distances. A surveyor's leveling instrument has a spirit level mounted on a telescope (perhaps 30 power) with cross-hairs, itself mounted on a tripod. The observer reads height values off two graduated vertical rods, one 'behind' and one 'in front', to obtain the height difference between the ground points on which the rods are resting. Starting from a point with a known elevation and going cross country (successive points being perhaps 100 meters (328 ft) apart) height differences can be measured cumulatively over long distances and elevations can be calculated. Precise levelling is supposed to give the difference in elevation between two points one kilometer (0.62 miles) apart correct to within a few millimeters.

Carpenter's level

A traditional carpenter's spirit level looks like a short plank of wood and often has a wide body to ensure stability, and that the surface is being measured correctly. In the middle of the spirit level is a small window where the bubble and the tube is mounted. Two notches (or rings) designate where the bubble should be if the surface is level. Often an indicator for a 45 degree inclination is included.

Line level

A line level is a level designed to hang on a builder's string line. The body of the level incorporates small hooks to allow it to attach and hang from the string line. The body is lightweight, so as not to weigh down the string line, it is also small in size as the string line in effect becomes the body; when the level is hung in the center of the string, each 'leg' of the string line extends the level's plane.

Engineer's precision levels

An engineer's precision level permits leveling items to greater accuracy than a plain spirit level. They are used to level the foundations, or beds of machines to ensure the machine can output workpieces to the accuracy pre-built in the machine.

History

The history of the spirit level was discussed in brief in an 1887 article appearing in Scientific American. Melchisédech Thévenot, a French scientist, invented the instrument some time before February 2, 1661. This date can be established from Thevenot's correspondence with scientist Christiaan Huygens. Within a year of this date the inventor circulated details of his invention to others, including Robert Hooke in London and Vincenzo Viviani in Florence. It is occasionally argued that these "bubble levels" did not come into widespread use until the beginning of the 18th century, the earliest surviving examples being from that time, but Adrien Auzout had recommended that the Académie Royale des Sciences take "levels of the Thevenot type" on its expedition to Madagascar in 1666. It is very likely that these levels were in use in France and elsewhere long before the turn of the century.

The Fell All-Way precision level, one of the first successful American made bull's eye levels for machine tool use, was invented by William B. Fell of Rockford, Illinois in 1939. The device was unique in that it could be placed on a machine bed and show tilt on the x-y axes simultaneously, eliminating the need to rotate the level 90 degrees. The level was so accurate it was restricted from export during World War II. The device set a new standard of .0005 inches per foot resolution (five ten thousands per foot or five arc seconds tilt). Production of the level stopped around 1970, and was restarted in the 1980s by Thomas Butler Technology, also of Rockford, Illinois, but finally ended in the mid-1990s. However, there are still hundreds of the devices in existence.

Alternatives

Alternatives include:

* Reed level
* Laser line level
* Water level

Today level tools are available in most smartphones by using the device's accelerometer. These mobile apps come with various features and easy designs. Also new web standards allow websites to get orientation of devices.

Digital spirit levels are increasingly common in replacing conventional spirit levels, particularly in civil engineering applications such as traditional building construction and steel structure erection, for on-site angle alignment and leveling tasks. The industry practitioners often refer to those levelling tools as a "construction level", "heavy duty level", "inclinometer", or "protractor". These modern electronic levels are capable of displaying precise numeric angles within 360° with 0.1° to 0.05° accuracy, can be read from a distance with clarity, and are affordably priced due to mass adoption. They provide features that traditional levels are unable to match. Typically, these features enable steel beam frames under construction to be precisely aligned and levelled to the required orientation, which is vital to ensure the stability, strength and rigidity of steel structures on sites. Digital levels, embedded with angular MEMS technology effectively improve productivity and quality of many modern civil structures. Some recent models feature waterproof IP65 and impact resistance features for harsh working environments.

Spirit-Level.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1588 2022-12-06 00:03:25

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1561) Helium Dating

Summary

Helium dating is a method of age determination that depends on the production of helium during the decay of the radioactive isotopes uranium-235, uranium-238, and thorium-232. Because of this decay, the helium content of any mineral or rock capable of retaining helium will increase during the lifetime of that mineral or rock, and the ratio of helium to its radioactive progenitors then becomes a measure of geologic time. If the parent isotopes are measured, the helium dating method is referred to as uranium–thorium–helium dating; if only the alpha-particle emission and helium content are measured, the method is called the alpha-helium radioactive clock. Alpha particles are the nuclei of helium atoms emitted from the nucleus of the radioactive progenitor.

Before the use of mass spectrometry in isotopic geochronology, helium dating provided most of the dates used in the early geologic time scales. Helium ages, however, tend to be too low because the gas escapes from the rock. A thermal event that will leave most radioactive clocks relatively unaffected may have a drastic effect on the helium radioactive clock. In the future, helium dating may be found very useful for dating rocks of the late Cenozoic and Pleistocene, because rocks and minerals of this age have not been subject to the complex history of older rocks and minerals; thus, all the helium is more likely to have been retained. Fossils, as well as minerals and rocks, may be dated by helium dating. The relatively large amount of helium produced in rocks may make it possible to extend helium dating to rocks and minerals as young as a few tens of thousands of years old.

Details

Helium dating may refer to the traditional uranium–thorium dating (abbreviated U–Th/He dating) or to a variety of He diffusion methods that utilize the mobility of He atoms to determine the thermal history of a rock. Helium diffusion experiments are often used to help interpret information retrieved from U–Th/He thermochronometric experiments. Kinematic parameters derived from He diffusion is done through estimating He diffusion over a range of temperatures. The use of density functional theory helps in estimating energy barriers for He to overcome as it diffuses across various crystallographic directions. Discrepancies, however, between observed and predicted He diffusion rates is still a problem and likely stem from unresolved problems in crystal defects and radiation damage in natural grains as opposed to theoretical grains. Depending on the mineral analyzed there are different assumptions to be made on He mobility. For example, He diffusion in minerals such as zircon, rutile, and monazite have been shown to be strongly anisotropic.

A relatively new dating method, tritium–helium dating has been developed for determining rates of oxygen utilization in the ocean.

4He/3He Thermochronometry

Traditional U–Th/He thermochronometry determines the temperature Tc that the analyzed sample had at a time in the past corresponding to the age given by its content of parent and daughter nuclides. More information, however, can be concluded about a mineral's thermal history if an analysis of the He distribution in-situ is performed. Similar to the argon–argon dating (which uses 40Ar and 39Ar isotopes) where 39Ar is a second non-radiogenically produced isotope derived from 39K, each step-heating release of 39Ar can be directly associated with a date. With Helium-3 (3He) production the 4He/3He evolution is interpreted to provide an intragranular Helium-4 (4He) distribution. This method is superior in two ways: diffusion kinetics for 4He can be precisely determined and the 4He distribution provides a continuous path in a time-temperature history s opposed to a single point in a bulk-grain date.

More specifically, the 4He distribution in a grain is a function of the time-integrated internal production from parent nuclides, minus diffusion loss and alpha ejection. This is done in conjunction with the assumption that the model is a spherical grain and calculations correlate with a radial position within that sphere. These calculations also assume that diffusion is isotropic.

Use to support creationism

In 1997, the Institute of Creation Research began a research project, named "RATE" (Radioisotopes and the Age of The Earth), which aimed at determining the validity of scientifically-accepted radiometric dating. One paper published from this research project describes the perceived issues of uniformitarian (U–Th)/He dating. In this paper the commonly-accepted ingrowth-diffusion equation (as first published in 1998) is erroneously rewritten to confirm creationist belief that the Earth formed roughly 6000 years ago. The assumptions made in the creationist arguments also neglect the sensitivity that He diffusion methods have in regard to temperature fluctuations over time – especially since the granodiorite analyzed in the study has very complex geologic and thermal history.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1589 2022-12-07 00:34:48

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1562) Sea of Tranquility

Summary

Mare Tranquillitatis (Latin tranquillitātis, the Sea of Tranquillity or Sea of Tranquility) is a lunar mare that sits within the Tranquillitatis basin on the Moon. It is the first location on another world to be visited by humans.

The mare material within the basin consists of basalt formed in the intermediate to young age group of the Upper Imbrian epoch. The surrounding mountains are thought to be of the Lower Imbrian epoch, but the actual basin is probably Pre-Nectarian. The basin has irregular margins and lacks a defined multiple-ringed structure. The irregular topography in and near this basin results from the intersection of the Tranquillitatis, Nectaris, Crisium, Fecunditatis, and Serenitatis basins with two throughgoing rings of the Procellarum basin. Palus Somni, on the northeastern rim of the mare, is filled with the basalt that spilled over from Tranquillitatis.

This mare has a slight bluish tint relative to the rest of the Moon and stands out quite well when color is processed and extracted from multiple photographs. The color is likely due to higher metal content in the basaltic soil or rocks.

Unlike many other maria, there is no mass concentration (mascon), or gravitational high, in the center of Mare Tranquillitatis. Mascons were identified in the center of other maria (such as Serenitatis or Imbrium) from Doppler tracking of the five Lunar Orbiter spacecraft in 1968. The gravity field was mapped at higher resolution with later orbiters such as Lunar Prospector and GRAIL, which unveiled an irregular pattern.

Details

The Sea of Tranquility has long captivated astronomers. Once thought to be an ocean on the Moon, its relatively smooth fields of basaltic lavas and equatorial position made it an ideal location for the first manned lunar landing. On July 20, 1969 Neil Armstrong and Buzz Aldrin left the first human footprints on the Moon near the southwestern shores of Mare Tranquillitatis.

Mare Tranquillitatis (approximately 873 km in diameter) lies in the Tranquillitatis basin (centered on 0.68 N, 23.43 E; extending, roughly, from 20.4 N-4.4 S, 15.0-45.9 E). This basin is thought to have been formed as a result of a very large impact in the Moon's early history, likely more than 3.9 billion years ago. The crater was then flooded with mare basalts, making it appear dark when viewed from Earth, and making it smooth and relatively flat, as seen in LOLA data. There is only a little over a 500 m elevation difference between the highest and lowest points within the mare, excluding overprinted craters. The mare has an irregular margin because several basins, including Serenitatis and Nectaris, intersect in this region. See if you can find other features surrounding Mare Tranquillitatis on a map of the Moon.

For other information and exploration news, check out one of Science@NASA's Apollo Chronicles featuring Neil Armstrong and Buzz Aldrin's experience in the Sea of Tranquility, the featured LROC images of a wrinkle ridge in the Mare Tranquillitatis Constellation Region of Interest, and the Apollo landing sites.

The Sea of Tranquility is the landing site of Apollo 11, the mission that gave mankind its first ever walk on the Moon.

Walk? Yes, that’s right. The Sea of Tranquility is not actually a sea, so Neil Armstrong didn’t have to walk on water. In fact, there isn’t a single sea on the lunar surface. The Sea of Tranquility is actually a lunar mare. Now, although the plural of ‘mare’, ‘maria’, is a Latin word that means ‘seas’, these maria don’t have water in them.

Lunar maria were named as such because early astronomers mistook these areas as seas. You see, when you look at the Moon, particularly its near side (well, we don’t actually get to see the far side), i.e., the side which practically constantly stares at us at night, you’ll notice certain features that are darker than others.

Compare the Moon to a grey-scale model of the Earth, and you’ll easily mistake those dark patches for seas. By the way, in case you’ve been reading article titles (not the entire article) on this site lately, you might recall us mentioning water on the Moon. There’s water alright … underneath the surface, so even assuming that they’re plentiful, they don’t qualify as seas.

Let’s go back to our main topic. Called Mare Tranquillitatis in Latin, the Sea of Tranquility is found in the Tranquillitatis basin of the Moon and is composed of basalt. Maria are seen from Earth as relatively dark because the lighter colored areas are much elevated than them and hence are better illuminated by light coming from the Sun.

Whenever color is processed and extracted from multiple photographs, the Sea of Tranquility gives off a slightly bluish shade. This is believed to be caused by the relatively higher metal content in the area.

The actual landing site of Apollo 11’s lunar module is now named Statio Tranquillitatis or Tranquility Base. To the north of that specific area you’ll find three small craters aptly named Aldrin, Collins, and Armstrong, the privileged crew of Apollo 11.

The lunar module of Apollo 11 was not the only spacecraft to have landed on the Sea of Tranquility. There was also the Ranger 8 spacecraft … although “crash landed” is a more appropriate term. It wasn’t a failed mission though, since it was really meant to impact the lunar surface after taking pictures throughout its flight before striking the Moon.

apollo-11.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1590 2022-12-08 00:13:20

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1563) Sedative

Summary

A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS (Central Nervous System) depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but the majority of them affect the neurotransmitter gamma-aminobutyric acid (GABA). In spite of the fact that each sedative acts in its own way, most produce relaxing effects by increasing GABA activity.

This group is related to hypnotics. The term sedative describes drugs that serve to calm or relieve anxiety, whereas the term hypnotic describes drugs whose main purpose is to initiate, sustain, or lengthen sleep. Because these two functions frequently overlap, and because drugs in this class generally produce dose-dependent effects (ranging from anxiolysis to loss of consciousness) they are often referred to collectively as sedative-hypnotic drugs.

Sedatives can be used to produce an overly-calming effect (alcohol being the most common sedating drug). In the event of an overdose or if combined with another sedative, many of these drugs can cause deep unconsciousness and even death.

Details

Sedatives are a type of prescription medication that slows down your brain activity. They’re typically used to make you feel more relaxed.

Doctors commonly prescribe sedatives to treat conditions like anxiety and sleep disorders. They also use them as general anesthetics.

Sedatives are controlled substances. This means their production and sales are regulated. In the United States, the Drug Enforcement Administration (DEA) regulates controlled substances. Selling or using them outside these regulations is a federal crime.

Part of the reason sedatives are so heavily regulated is that they can be highly addictive. They can cause people to become dependent on them beyond their control.

It’s important to be careful when using these medications to avoid dependency and addiction. Don’t take them unless your doctor has prescribed them to you. Take them only as prescribed.

Let’s go into more detail about how they work, what precautions to take if you use them, and some less potentially harmful alternatives you may want to try instead.

How do they work?

Sedatives work by modifying certain nerve communications in your central nervous system (CNS) to your brain. In this case, they relax your body by slowing down brain activity.

Specifically, sedatives make the neurotransmitter called gamma-aminobutyric acid (GABATrusted Source) work overtime. GABA is responsible for slowing down your brain. By upping its level of activity in the CNS, sedatives allow GABA to produce a much stronger effect on your brain activity.

Types of sedatives

Here’s a a quick breakdown of the common types of sedatives. They’re all controlled substances.

Benzodiazepines

Examples of drugs

* alprazolam (Xanax)
* lorazepam (Ativan)
* diazepam (Valium)

What they treat

* anxiety
* panic disorders
* sleep disorders

Barbiturates

Examples of drugs

* pentobarbital sodium (Nembutal)
* phenobarbital (Luminal)

What they treat

* used for anesthesia

Hypnotics (non-benzodiazepines)

Examples of drugs

zolpidem (Ambien)

What they treat

* sleep disorders

Opioids/narcotics

Examples of drugs

* hydrocodone/acetaminophen (Vicodin)
* oxycodone (OxyContin)
* oxycodone/acetaminophen (Percocet)

What they treat

* pain

Side effects

Sedatives can have both short- and long-term side effects.

Some of the immediate side effects you might notice include:

* sleepiness
* dizziness
* blurred vision
* not being able to see depth or distance as well as usual (impaired perception)
* slower reaction time to things around you (impaired reflexes)
* slower breathing
* not feeling as much pain as usual (sometimes not even sharp or intense pain)
* having trouble focusing or thinking (impaired cognition)
* speaking more slowly or slurring your words

Long-term sedative use can lead to the following side effects:

* frequently forgetting or losing your memory (amnesia)
* symptoms of depression, such as fatigue, feelings of hopelessness, or suicidal thoughts
* mental health conditions, such as anxiety
* liver dysfunction or liver failure from tissue damage or overdose
* developing a dependency on sedatives that can lead to irreversible effects or withdrawal symptoms, especially if you stop using them abruptly

Dependency and addiction

Dependency develops when your body becomes physically dependent on the sedative and can’t function normally without it.

Signs of dependency

You may be experiencing dependency if you find yourself taking them regularly and feel you can’t stop taking them. This may be especially evident if you’re going beyond your prescribed dose or a safe amount.

Dependence also becomes evident when you need a higher dose to achieve the same effect. This means your body has become used to the drug and needs more to achieve the desired effect.

Withdrawal symptoms

Dependency tends to become most obvious if you experience withdrawal symptoms. This happens when your body responds to the absence of the sedatives with uncomfortable or painful physical and mental symptoms.

Common withdrawal symptoms include:

*increased anxiety
* irritability
* inability to sleep

In some cases, you can become sick or experience seizures if you’re body is used to high amounts of the sedative and go “cold turkey” without easing yourself off the drug.

Dependence develops depending on your body’s tolerance to the drug. It can happen over a few months or as quickly as a few weeks or less.

Older adults may be more susceptible to certain sedatives, such as benzodiazepines, than younger people.

Recognizing dependence and withdrawal symptoms

Dependence can be hard to recognize. The clearest symptom is that you can’t stop thinking about taking the drug.

This may be clearer when you compulsively think about the medication when having any symptom related to the condition you’re using it to treat and think that using it is the only way you’ll be able to cope with it.

In these cases, your behavior and mood can change instantly (often negatively) when you realize you can’t have it right away.

Some of these symptoms, especially mood changes, can happen immediately.

Other symptoms point to withdrawal. These symptoms may appear several days or weeks after stopping use. Withdrawal symptoms can include:

* nausea
* vomiting
* losing consciousness

Opioid caution

Opioids are especially prone to becoming addictive and producing harmful symptoms that can lead to overdose. These symptoms include:

* slowed or absent breathing
* slowed heart rate
* extreme fatigue
* small pupils

Opioid overdose has a high risk of death.

Always talk to your doctor before taking any opioid to avoid possible harmful or deadly symptoms of opioid addiction and overdose.

Other cautions

Even if you’re taking small doses of sedatives as prescribed by your doctor, you can still take extra care to make sure you stay safe:

* Avoid alcohol. Alcohol also works like a sedative, so drinking and taking a sedative at the same time can compound the effectsTrusted Source and lead to dangerous, life-threatening symptoms, such as loss of consciousness or stopping breathing.
* Don’t mix sedatives together or with other medications that have similar effects. Mixing sedatives together or taking them with other medications that cause drowsiness, such as antihistamines, can lead to harmful side effects, even overdose.
* Don’t take sedatives while pregnant without consulting a doctor. Sedatives in high doses can harm a fetusTrusted Source unless taken in a controlled medical environment.
* Don’t smoke marijuana. Using marijuana may actually reduce the effects of sedatives, particularly ones used for anesthesia. A 2019 study found that marijuana users needed a higher dose of sedatives to get the same effects as a regular dose for someone who doesn’t use marijuana.

Alternatives to sedatives

If you’re concerned about developing a dependency on sedative medications, talk to your doctor about alternatives.

Antidepressants, like SSRIs, can help treat anxiety or panic disorders. Stress-reduction techniques can also help, such as:

* exercise
* meditation
* aromatherapy with essential oils (especially lavender)

Practicing good sleep hygiene is another tool to help manage sleep disorders. Go to sleep and wake up at the same time (even on your days off) and don’t use electronics close to bedtime. Here are 15 other tips to sleep well at night.

If lifestyle changes don’t help you sleep, talk to your doctor about taking supplements, such as melatoninTrusted Source or valerian rootTrusted Source.

When to see a doctor

Talk to your doctor if you feel like you can’t stop yourself from using sedatives.

Addiction is a brain disorder. Don’t feel like there’s something wrong with you or a loved one with an addiction or that you’re failing yourself or others.

Your doctor may also be able to recommend an addiction counselor, therapist, or a treatment center that can address both the medical and psychiatric effects of addiction.

If you have concerns about any sedatives that your doctor prescribes, ask your doctor or pharmacist these questions:

* Is it addictive?
* How much is too much of a dose?
* Are there any harmful side effects?

Having an open, honest conversation with an expert can help you feel more comfortable using them.

The bottom line

Sedatives are powerful. They lower brain activity and relax your mind.

They can be effective treatments for conditions that make you feel overly wired, fearful, antsy, or tired, such as anxiety or sleep disorders. But they can also become addictive, especially if they’re misused.

Talk to your doctor before you start taking sedatives and be sure to follow their directions.

Help is available in many forms if you’re concerned about an addiction to sedatives. Don’t hesitate to reach out.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1591 2022-12-08 20:56:37

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1564) Vitamin B Complex

Summary

B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. Though these vitamins share similar names (B1, B2, B3, etc.), they are chemically distinct compounds that often coexist in the same foods. In general, dietary supplements containing all eight are referred to as a vitamin B complex. Individual B vitamin supplements are referred to by the specific number or name of each vitamin, such as B1 for thiamine, B2 for riboflavin, and B3 for niacin. Some are more commonly recognized by name than by number, for example pantothenic acid, biotin, and folate.

Each B vitamin is either a cofactor (generally a coenzyme) for key metabolic processes or is a precursor needed to make one and is thus an essential nutrient.

What is vitamin B complex?

Vitamin B complex is composed of eight B vitamins:

* B1 (thiamine)
* B2 (riboflavin)
* B3 (niacin)
* B5 (pantothenic acid)
* B6 (pyridoxine)
* B7 (biotin)
* B9 (folic acid)
* B12 (cobalamin)

Each of these essential vitamins contributes to your overall bodily function. Read on to learn more about how these nutrients benefit you, how much you need, whether you should take supplements, and more.

What are the health benefits of B Complex vitamins?

B vitamins play a vital role in maintaining good health and well-being. As the building blocks of a healthy body, B vitamins have a direct impact on your energy levels, brain function, and cell metabolism.

Vitamin B complex may help prevent infections and help support or promote:

* cell health
* growth of red blood cells
* energy levels
* eyesight
* brain function
* digestion
* appetite
* proper nerve function
* hormones and cholesterol production
* cardiovascular health
* muscle tone

For those who pregnant

B vitamins are especially important for those who are pregnant or breastfeeding. These vitamins aid in fetal brain development, and they reduce the risk of birth defects.

For people who are expecting, B vitamins may help manage energy levels, ease nausea, and lower the risk of developing preeclampsia.

For boosting testosterone

B vitamins are sometimes included in “testosterone-boosting” supplements and are thought to increase testosterone levels in men, which naturally decrease with age. However, human studies confirming these claims are lacking.

In spite of the lack of evidence for any testosterone-boosting effects, because B vitamins are helpful in hormone regulation, it’s possible that B vitamins may help regulate male hormones as well as female hormones.

How much vitamin B complex do you need?

The recommended daily amount of each B vitamin varies.

According to the National Institutes of Health (NIH)Trusted Source, the recommended daily intake for women is:

* B1: 1.1 milligrams (mg)
* B2: 1.1 mg
* B3: 14 mg NE
* B5: 5 mg
* B6: 1.3 mg
* Biotin: 30 micrograms (mcg)
* Folic acid: 400 mcg DFE
* B12: 2.4 mcg

For men, the NIH recommends the following daily intake:

* B1: 1.2 mg
* B2: 1.3 mg
* B3: 16 mg NE
* B5: 5 mg
* B6: 1.3 mg
* Biotin: 30 mcg
* Folic acid: 400 mcg DFE
* B12: 2.4 mcg

Older adults and those who are pregnant may require higher amounts of B vitamins. Your doctor can provide dosage information tailored to your individual needs.

Certain underlying health conditions can prevent your body from properly absorbing vitamin B. You should also talk with your doctor about your vitamin B intake if you have:

* celiac disease
* HIV
* Crohn’s disease
* alcohol use disorder
* kidney conditions
* rheumatoid arthritis
* ulcerative colitis
* inflammatory bowel disease

What foods is it found in?

Lots of foods contain B vitamins, making it easy to get enough from your diet. It’s best to get your B vitamins from a wide variety of food sources. This helps ensure you’re getting enough of each type.

You can find vitamin B in:

* milk
* cheese
* eggs
* liver and kidney
* meat, such as chicken and red meat
* fish, such as tuna, mackerel, and salmon
* shellfish, such as oysters and clams
* dark green vegetables, such as spinach and kale
* vegetables, such as beets, avocados, and potatoes
* whole grains and cereals
* beans, such as kidney beans, black beans, and chickpeas
* nuts and seeds
* fruits, such as citrus, banana, and watermelon
* soy products, such as soy milk and tempeh
* blackstrap molasses
* wheat germ
* yeast and nutritional yeast

How can you tell if you’re deficient?

Most people get enough B vitamins by eating a balanced diet. However, it’s still possible to be deficient, especially if you’ve been taking certain medications for a while, such as proton pump inhibitors, or if you follow a very strict vegan or vegetarian diet.

The following symptoms may signal you’re not getting enough B vitamins:

* skin rashes
* cracks around the mouth
* scaly skin on the lips
* swollen tongue
* fatigue
* weakness
* anemia
* confusion
* irritability or depression
* nausea
* abdominal cramps
* diarrhea
* constipation
* numbness or tingling in the feet and hands

If you’re experiencing any of these symptoms and aren’t sure why, make an appointment to talk with your doctor.

Although it’s possible that you’re experiencing a vitamin B deficiency, these symptoms also overlap with many other underlying conditions. Your doctor can make a diagnosis and advise you on next steps.

Can being deficient increase your risk of certain conditions?

If you’re deficient in B vitamins you may experience a range of symptoms, depending on which B vitamins you’re lacking.

If left untreated, a deficiency could increase your risk for:

* anemia
* digestive issues
* skin conditions
* infections
* peripheral neuropathy

Vitamin B12 deficiency, in particular, may increase your risk of neuropsychiatric disorders. Researchers are also investigating its role in hyperhomocysteinemia and atherosclerosis.

Babies born to individuals who were deficient in folic acid during pregnancy may be more likely to have certain birth defects.

Are supplements necessary?

Most people get enough B vitamins through their diet. Whole foods are also the best way for your body to absorb these vitamins.

It’s not necessary to take a supplement unless your doctor has confirmed that you’re deficient in a specific B vitamin. If they note a deficiency, they’ll most likely tell you whether you should take a specific B supplement or add a vitamin B complex supplement to your routine.

You may be more likely to need supplementation if you:

* are age 50 or older
* are pregnant
* have certain chronic health conditions
* take certain long-term medications
* eat a strictly meat-free diet

One thing to keep in mind: Supplements aren’t regulated by the Food and Drug Administration (FDA), so you should only buy from a trusted, reputable brand. This helps ensure you’re taking a high quality product without any questionable additives.

If your doctor has noted a deficiency, they may be able to recommend a specific brand of supplements.

You should always read all labels carefully and follow any directions given by the manufacturer. If you have questions about the dosage, talk with your doctor.

What happens if you get too much vitamin B complex?

You’re unlikely to get too much vitamin B complex from your diet. That’s because B complex vitamins are water soluble. That means they aren’t stored in your body but are excreted in your urine daily.

You’re also unlikely to get too much vitamin B if you’re taking any supplementation as directed.

That said, as with most supplements, it’s possible to consume too much at once — especially if you’re taking a supplement without receiving a deficiency diagnosis from your doctor.

When consumed in excess, a few different B vitamins can have specific side effects. For instance:

* Vitamin B6. Too much B6 may lead to peripheral neuropathy, which is a loss of feeling in the arms and legs.
* Folate or folic acid. Too much of this vitamin can cover up the symptoms of a vitamin B12 deficiency, which can eventually lead to nervous system damage.
* Niacin. Too much niacin may cause skin flushes. Long-term excessive use may lead to liver damage.

While there isn’t enough research to say exactly what will happen if you consume too much B complex, more is not necessarily better, especially over the long term.

Talk with a doctor about supplements

It’s always a good idea to talk with your doctor before you add any supplements to your routine.

You can discuss your desired health goal and why you think supplementation is necessary. Your doctor can help you determine if this is the best treatment option and advise you on any next steps.

Some supplements can interact with certain underlying conditions and medications, so it’s important to keep your doctor informed.

You should also see your doctor if you think you may be deficient in B vitamins. They can help determine what’s causing your symptoms and, if needed, recommend ways to increase your B vitamin intake.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1592 2022-12-09 17:36:49

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1565) Computer Virus

Summary

A computer virus is a a portion of a computer program code that has been designed to furtively copy itself into other such codes or computer files. It is usually created by a prankster or vandal to effect a nonutilitarian result or to destroy data and program code or, in the case of ransomware, to extort payment.

A virus consists of a set of instructions that attaches itself to other computer programs, usually in the computer’s operating system, and becomes part of them. In most cases, the corrupted programs continue to perform their intended functions but surreptitiously execute the virus’s instructions as well. A virus is usually designed to execute when it is loaded into a computer’s memory. Upon execution, the virus instructs its host program to copy the viral code into, or “infect,” any number of other programs and files stored in the computer. The infection can then transfer itself to files and code on other computers through memory-storage devices, computer networks, or online systems. The replicating viruses can multiply until they destroy data or render other program codes meaningless. A virus may simply cause a harmless joke or cryptic message to appear on a computer user’s monitor when the computer is turned on. A more damaging virus can wreak havoc on an extremely large computer system within a matter of minutes or hours, causing it to crash and thereby destroy valuable data, or can disable a computer system until a ransom is paid.

Details

A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code. If this replication succeeds, the affected areas are then said to be "infected" with a computer virus, a metaphor derived from biological viruses.

Computer viruses generally require a host program. The virus writes its own code into the host program. When the program runs, the written virus program is executed first, causing infection and damage. A computer worm does not need a host program, as it is an independent program or code chunk. Therefore, it is not restricted by the host program, but can run independently and actively carry out attacks.

Virus writers use social engineering deceptions and exploit detailed knowledge of security vulnerabilities to initially infect systems and to spread the virus. Viruses use complex anti-detection/stealth strategies to evade antivirus software. Motives for creating viruses can include seeking profit (e.g., with ransomware), desire to send a political message, personal amusement, to demonstrate that a vulnerability exists in software, for sabotage and denial of service, or simply because they wish to explore cybersecurity issues, artificial life and evolutionary algorithms.

Computer viruses cause billions of dollars' worth of economic damage each year.

In response, an industry of antivirus software has cropped up, selling or freely distributing virus protection to users of various operating systems.

Design:

Parts

A computer virus generally contains three parts: the infection mechanism, which finds and infects new files, the trigger, which determines when to activate the payload, and the payload, which is the malicious code to execute.

Infection mechanism

Also called the infection vector, this is how the virus spreads. Some viruses have a search routine, which locate and infect files on disk.[35] Other viruses infect files as they are run, such as the Jerusalem DOS virus.

Trigger

Also known as a logic bomb, this is the part of the virus that determines the condition for which the payload is activated. This condition may be a particular date, time, presence of another program, size on disk exceeding a threshold, or opening a specific file.

Payload

The payload is the body of the virus that executes the malicious activity. Examples of malicious activities include damaging files, theft of confidential information or spying on the infected system. Payload activity is sometimes noticeable as it can cause the system to slow down or "freeze". Sometimes payloads are non-destructive and their main purpose is to spread a message to as many people as possible. This is called a virus hoax.

Phases

Virus phases is the life cycle of the computer virus, described by using an analogy to biology. This life cycle can be divided into four phases:

i) Dormant phase

The virus program is idle during this stage. The virus program has managed to access the target user's computer or software, but during this stage, the virus does not take any action. The virus will eventually be activated by the "trigger" which states which event will execute the virus. Not all viruses have this stage.

ii) Propagation phase

The virus starts propagating, which is multiplying and replicating itself. The virus places a copy of itself into other programs or into certain system areas on the disk. The copy may not be identical to the propagating version; viruses often "morph" or change to evade detection by IT professionals and anti-virus software. Each infected program will now contain a clone of the virus, which will itself enter a propagation phase.

iii) Triggering phase

A dormant virus moves into this phase when it is activated, and will now perform the function for which it was intended. The triggering phase can be caused by a variety of system events, including a count of the number of times that this copy of the virus has made copies of itself. The trigger may occur when an employee is terminated from their employment or after a set period of time has elapsed, in order to reduce suspicion.

iv) Execution phase

This is the actual work of the virus, where the "payload" will be released. It can be destructive such as deleting files on disk, crashing the system, or corrupting files or relatively harmless such as popping up humorous or political messages on screen.

Targets and replication

Computer viruses infect a variety of different subsystems on their host computers and software. One manner of classifying viruses is to analyze whether they reside in binary executables (such as .EXE or .COM files), data files (such as Microsoft Word documents or PDF files), or in the boot sector of the host's hard drive (or some combination of all of these).

A memory-resident virus (or simply "resident virus") installs itself as part of the operating system when executed, after which it remains in RAM from the time the computer is booted up to when it is shut down. Resident viruses overwrite interrupt handling code or other functions, and when the operating system attempts to access the target file or disk sector, the virus code intercepts the request and redirects the control flow to the replication module, infecting the target. In contrast, a non-memory-resident virus (or "non-resident virus"), when executed, scans the disk for targets, infects them, and then exits (i.e. it does not remain in memory after it is done executing).

Many common applications, such as Microsoft Outlook and Microsoft Word, allow macro programs to be embedded in documents or emails, so that the programs may be run automatically when the document is opened. A macro virus (or "document virus") is a virus that is written in a macro language and embedded into these documents so that when users open the file, the virus code is executed, and can infect the user's computer. This is one of the reasons that it is dangerous to open unexpected or suspicious attachments in e-mails. While not opening attachments in e-mails from unknown persons or organizations can help to reduce the likelihood of contracting a virus, in some cases, the virus is designed so that the e-mail appears to be from a reputable organization (e.g., a major bank or credit card company).

Boot sector viruses specifically target the boot sector and/or the Master Boot Record (MBR) of the host's hard disk drive, solid-state drive, or removable storage media (flash drives, floppy disks, etc.).

The most common way of transmission of computer viruses in boot sector is physical media. When reading the VBR of the drive, the infected floppy disk or USB flash drive connected to the computer will transfer data, and then modify or replace the existing boot code. The next time a user tries to start the desktop, the virus will immediately load and run as part of the master boot record.

Email viruses are viruses that intentionally, rather than accidentally, uses the email system to spread. While virus infected files may be accidentally sent as email attachments, email viruses are aware of email system functions. They generally target a specific type of email system (Microsoft Outlook is the most commonly used), harvest email addresses from various sources, and may append copies of themselves to all email sent, or may generate email messages containing copies of themselves as attachments.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1593 2022-12-10 14:34:45

ganesh
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Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1566) Bottle

Summary

A bottle is a narrow-necked, rigid or semirigid container that is primarily used to hold liquids and semiliquids. It usually has a close-fitting stopper or cap to protect the contents from spills, evaporation, or contact with foreign substances.

Although early bottles were made from such materials as gourds and animal skins, glass eventually became the major material employed. Before 1500 BC the Egyptians produced glass bottles by covering silica paste cores with molten glass and digging out the core after the bottle hardened. By 200 BC glassblowing was practiced in China, Persia (modern Iran), and Egypt. Except for making the finest and most costly decorative bottles, hand methods were eventually replaced by processes employing metal molds, and automatic equipment for the continuous manufacture of bottles was introduced commercially in 1903.

Glass bottles afford highly effective protection of their contents and are attractive because of their transparency and high gloss and the variety of shapes attainable. Fragility is a major disadvantage, and only coloured glass protects those products sensitive to the action of light. Returnable glass bottles, which can be reused a number of times, are the least expensive to manufacture on a per use basis; although repeated handling costs may dissipate any saving. Lightweight, nonreturnable types achieved popularity in the 1960s, but by the 1970s returnable bottles were being promoted as one means of combating the ecological problem of disposal of solid wastes.

Details

A bottle is a narrow-necked container made of an impermeable material (such as glass, plastic or aluminium) in various shapes and sizes that stores and transports liquids. Its mouth, at the bottling line, can be sealed with an internal stopper, an external bottle cap, a closure, or induction sealing.

Types:

Glass

A glass bottle is a bottle made from glass. Glass bottles can vary in size considerably, but are most commonly found in sizes ranging between about 200 millilitres and 1.5 litres. Common uses for glass bottles include food condiments, soda, liquor, cosmetics, pickling and preservatives; they are occasionally also notably used for the informal distribution of notes. These types of bottles are utilitarian and serve a purpose in commercial industries.

The glass bottle represented an important development in the history of wine, because, when combined with a high-quality stopper such as a cork, it allowed long-term aging of wine. Glass has all the qualities required for long-term storage. It eventually gave rise to "château bottling", the practice where an estate's wine is put in a bottle at the source, rather than by a merchant. Prior to this, wine used to be sold by the barrel (and before that, the amphora) and put into bottles only at the merchant's shop, if at all. This left large and often abused opportunities for fraud and adulteration, as consumers had to trust the merchant as to the contents. It is thought that most wine consumed outside of wine-producing regions had been tampered with in some way. Also, not all merchants were careful to avoid oxidation or contamination while bottling, leading to large bottle variation. Particularly in the case of port, certain conscientious merchants' bottling of old ports fetch higher prices even today. To avoid these problems, most fine wine is bottled at the place of production (including all port, since 1974).

There are many sizes and shapes of bottles used for wine. Some of the known shapes:

* "Bordeaux": This bottle is roughly straight sided with a curved "shoulder" that is useful for catching sediment and is also the easiest to stack. Traditionally used in Bordeaux but now worldwide, this is probably the most common type.
* "Burgundy": Traditionally used in Burgundy, this has sides that taper down about 2/3 of the height to a short cylindrical section, and does not have a shoulder.
* "Champagne": Traditionally used for Champagne, it is similar to a Burgundy bottle, but with a wider base and heavier construction to withstand the pressure from the carbonation of the sparkling wine.

Codd-neck bottle

In 1872, British soft drink makers Hiram Codd of Camberwell, London, designed and patented a bottle designed specifically for carbonated drinks. The Codd-neck bottle was designed and manufactured to enclose a marble and a rubber washer/gasket in the neck. The bottles were filled upside down, and pressure of the gas in the bottle forced the marble against the washer, sealing in the carbonation. The bottle was pinched into a special shape, as can be seen in the photo to the left, to provide a chamber into which the marble was pushed to open the bottle. This prevented the marble from blocking the neck as the drink was poured.

Soon after its introduction, the bottle became extremely popular with the soft drink and brewing industries, mainly in Europe, Asia and Australasia, though some alcohol drinkers disdained the use of the bottle. One etymology of the term codswallop originates from beer sold in Codd bottles, though this is generally dismissed as a folk etymology.

The bottles were regularly produced for many decades, but gradually declined in usage. Since children smashed the bottles to retrieve the marbles, they are relatively scarce and have become collector items; particularly in the UK. A cobalt-coloured Codd bottle today fetches hundreds of British pounds at auction. The Codd-neck design is still used for the Japanese soft drink Ramune and in the Indian drink called Banta.

Plastic

The plastic is strain oriented in the stretch blow molding manufacturing process. Plastic bottles are typically used to store liquids such as water, soft drinks, motor oil, cooking oil, medicine, shampoo, milk, and ink. The size ranges from very small sample bottles to very large carboys. The main advantages of plastic bottles over glass are their superior resistance to breakage, in both production and transportation, as well as their light weight and low cost of production. Disadvantages include widespread plastic pollution.

Aluminium

An aluminium bottle is a bottle made of aluminium (or aluminum, outside of British English). In some countries, it is also called a "bottlecan". It usually holds beer, soft drinks or wine.

Hot water

A hot water bottle is a bottle filled with hot water used to provide warmth. It can be made from various materials, most commonly rubber, but has historically been made from harder materials such as metal, glass, earthenware, or wood.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1594 2022-12-11 14:23:09

ganesh
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Posts: 40,614

Re: Miscellany

1567) Halite

Summary

Halite is a naturally occurring sodium chloride (NaCl), common or rock salt. Halite occurs on all continents in beds that range from a few metres to more than 300 m (1,000 feet) in thickness. Termed evaporite deposits because they formed by the evaporation of saline water in partially enclosed basins, they characteristically are associated with beds of limestone, dolomite, and shale. Halite also occurs as a sublimation product in volcanic regions, an efflorescence in arid regions, and an evaporation product near salt springs. Deformation of halite beds sometimes results in the extrusion of plugs of salt through overlying sediment, as in salt domes and diapirs. Halite is found in large deposits in southeastern Russia; Dax, Fr.; Punjab, India; Ontario, Canada; and New York, Texas, and Louisiana, U.S.

Details

Halite, commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride (NaCl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on inclusion of other materials, impurities, and structural or isotopic abnormalities in the crystals. It commonly occurs with other evaporite deposit minerals such as several of the sulfates, halides, and borates.

Occurrence

Halite dominantly occurs within sedimentary rocks where it has formed from the evaporation of seawater or salty lake water. Vast beds of sedimentary evaporite minerals, including halite, can result from the drying up of enclosed lakes and restricted seas. Such salt beds may be hundreds of meters thick and underlie broad areas. Halite occurs at the surface today in playas in regions where evaporation exceeds precipitation such as in the salt flats of Badwater Basin in Death Valley National Park.

In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and under much of the Michigan Basin. Other deposits are in Ohio, Kansas, New Mexico, Nova Scotia and Saskatchewan. The Khewra salt mine is a massive deposit of halite near Islamabad, Pakistan.

Salt domes are vertical diapirs or pipe-like masses of salt that have been essentially "squeezed up" from underlying salt beds by mobilization due to the weight of the overlying rock. Salt domes contain anhydrite, gypsum, and native sulfur, in addition to halite and sylvite. They are common along the Gulf coasts of Texas and Louisiana and are often associated with petroleum deposits. Germany, Spain, the Netherlands, Denmark, Romania and Iran also have salt domes. Salt glaciers exist in arid Iran where the salt has broken through the surface at high elevation and flows downhill. In these cases, halite is said to be behaving like a rheid.

Unusual, purple, fibrous vein-filling halite is found in France and a few other localities. Halite crystals termed hopper crystals appear to be "skeletons" of the typical cubes, with the edges present and stairstep depressions on, or rather in, each crystal face. In a rapidly crystallizing environment, the edges of the cubes simply grow faster than the centers. Halite crystals form very quickly in some rapidly evaporating lakes resulting in modern artifacts with a coating or encrustation of halite crystals. Halite flowers are rare stalactites of curling fibers of halite that are found in certain arid caves of Australia's Nullarbor Plain. Halite stalactites and encrustations are also reported in the Quincy native copper mine of Hancock, Michigan.

Mining

The world's largest underground salt mine is the Sifto Salt Mine. It produces over 7 million tons of rock salt per year using the room and pillar mining method. It is located half a kilometre under Lake Huron in Ontario, Canada.[16] In the United Kingdom there are three mines; the largest of these is at Winsford in Cheshire, producing, on average, one million tonnes of salt per year.

Uses

Salt is used extensively in cooking as a flavor enhancer, and to cure a wide variety of foods such as bacon and fish. It is frequently used in food preservation methods across various cultures. Larger pieces can be ground in a salt mill or dusted over food from a shaker as finishing salt.

Halite is also often used both residentially and municipally for managing ice. Because brine (a solution of water and salt) has a lower freezing point than pure water, putting salt or saltwater on ice that is below 0 °C (32 °F) will cause it to melt—this effect is called freezing-point depression. It is common for homeowners in cold climates to spread salt on their sidewalks and driveways after a snow storm to melt the ice. It is not necessary to use so much salt that the ice is completely melted; rather, a small amount of salt will weaken the ice so that it can be easily removed by other means. Also, many cities will spread a mixture of sand and salt on roads during and after a snowstorm to improve traction. Using salt brine is more effective than spreading dry salt because moisture is necessary for the freezing-point depression to work and wet salt sticks to the roads better. Otherwise the salt can be wiped away by traffic.

In addition to de-icing, rock salt is occasionally used in agriculture. An example of this would be inducing salt stress to suppress the growth of annual meadow grass in turf production. Other examples involve exposing weeds to salt water to dehydrate and kill them preventing them from affecting other plants. Salt is also used as a household cleaning product. Its coarse nature allows for its use in various cleaning scenarios including grease/oil removal, stain removal, dries out and hardens sticky spills for an easier clean.

Some cultures, especially in Africa and Brazil, prefer a wide variety of different rock salts for different dishes. Pure salt is avoided as particular colors of salt indicates the presence of different impurities. Many recipes call for particular kinds of rock salt, and imported pure salt often has impurities added to adapt to local tastes. Historically, salt was used as a form of currency in barter systems and was exclusively controlled by authorities and their appointees. In some ancient civilizations the practice of salting the earth was done to make conquered land of an enemy infertile and inhospitable as an act of domination or spite. One biblical reference to this practice is in Judges 9:45: "he killed the people in it, pulled the wall down and sowed the site with salt."

Polyhalite, a mineral fertiliser, is not an NaCl-polymer, but hydrated K2Ca2Mg-sulfate.

Shotgun shells containing rock salt (instead of metal pellets) are a less lethal deterrent.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1595 2022-12-12 01:48:46

ganesh
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Posts: 40,614

Re: Miscellany

1568) Petromax

Petromax is a brand name for a type of pressurised paraffin lamp (US: kerosene lamp) that uses a mantle. They are as synonymous with the paraffin lamp in Continental Europe as Tilley lamps are in Britain and Coleman lanterns are in the United States.

History

The Petromax lamp was created in 1910 in Germany by Max Graetz (1851–1937), who also named the brand, on the basis of a spirit lamp that was already well-known.

Graetz was president of the firm Ehrich & Graetz in Berlin, which developed the lamp, and also the primary designer.

He had wanted to create a lighting system fueled by paraffin, which was then a new product. Graetz invented a process to make a gas out of paraffin; which has a very high caloric value and could make a very hot blue flame.

Graetz then designed a pressure lamp, working with vaporized paraffin. To start this process, the lamp was preheated with methylated spirit (denatured alcohol), in later models with an integrated blow torch called "Rapidstarter" running from the paraffin tank directly. In a closed tank, paraffin was pressurised with a hand pump. The heat produced by the mantle was then used to vaporize the paraffin, which is mixed with air and blown in to mantle to burn. Around the year 1916, the lantern and its name started to spread around the world. The name Petromax derives from "Petroleum" and "Max Graetz".

The design was such a success that it still is being used to this day. The name Petromax has become synonymous with paraffin pressure lamps in many countries. The design of the lamps was later used to create a cooker based on the same principles.

In many countries "Petromax" is a registered Trademark, e.g. for the US by Britelyt Inc. or for Germany and some other European countries by Pelam International Ltd.

The Petromax design has been often copied, today such as by Tower in China, Lea Hin in Indonesia or Prabhat in India.

Kerosene Pressure Lantern Principles of Operation

Auer von Welsbach invented the principle of the gas flame heated incandescent mantle light in 1885. In the blue flame of a Bunsen burner he heated a woven fabric which glowed six times more brightly than the flame itself. The fabric was hung above the burner, the sole source of heat, in a shape which inspired the name of "mantle" (i.e., a cloak). The mantle was composed of a loosely woven cotton mesh, soaked in a liquid solution of thorium and cerium nitrate. Upon igniting a mantle for the first time, the cotton burnt away, leaving a rigid, brittle "skeleton" of thorium and cerium oxides. These oxides emitted brilliant light when heated to very high temperatures -- the principle of incandescence. This newfound principle was revolutionary, especially in the application of street lighting, and quickly became widespread throughout the industrialized world.

Before long, the idea of using liquid fuels for this type of lighting was explored. By the end of the 19th century, the first alcohol and kerosene fueled incandescent lamps had been developed. These liquid fuel lamps used pressure to force the fuel towards the burner, and the heat of the burner's flame to vaporize the liquid fuel. They are thus often termed "pressure lamps / lanterns". One of the first and most successful kerosene fueled pressure lanterns was invented in 1910 by Max Graetz – the world famous Petromax. The Petromax lantern, and its smaller cousin the Geniol lantern, remain popular to this day, both in the private sector and for professional applications.

Principle of PetromaxThe Petromax lantern acts as a small "gasworks". The fuel tank is pressurized to approximately 2 atmospheres (2 bar, or 30 psi) with air introduced by a built-in hand pump. This pressure is then used to force the liquid kerosene up into the vaporizer (or "generator", as it is sometimes called). Initially, the vaporizer must be pre-heated to gasify the liquid kerosene within it, prior to igniting the lantern's mantle. This preheating may be accomplished by burning alcohol poured in to a preheating cup located at the base of the vaporizer. Alternately, a built-in kerosene-fueled blowtorch, the "Rapid" preheater located on the side of most Petromax lanterns, may be used to heat the vaporizer. Once in operation, the heat from the lantern's blue flame (encased within the mantle) is used to gasify the liquid kerosene rising through the vaporizer. The liquid kerosene boils away into vapor at approximately 250° C (480° F), about halfway up the height of the vaporizer -- see illustration. The gaseous kerosene continues its journey through the vaporizer's circular loop, increasing in temperature, until it exits the small orifice in the vaporizer's nipple at nearly the speed of sound (1000 ft./sec.). Upon exiting the nipple, the gaseous fuel begins to expand and combine with air in small square chamber at the side of the lantern's inner casing. The expansion of the gas and turbulent mixing with the air are responsible for the hissing noise of the Petromax lantern while in operation. The gaseous kerosene and air are swept into the mixing tube where the two are thoroughly combined in the turbulent flow. This ensures complete combustion of the mixture upon exiting the ceramic nozzle, resulting in a hot, clean blue flame.

These principles of operation are generally applicable to any incandescent pressure lantern or lamp (e.g. – Coleman, Tilley, etc.), although fuel types, vaporization temperatures, and operating pressures / procedures may vary.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1596 2022-12-13 00:08:15

ganesh
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Posts: 40,614

Re: Miscellany

1569) Ultimate tensile strength

Summary

Ultimate tensile strength (UTS), often shortened to tensile strength (TS), is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the material breaks soon after the yield point have been reached.

What Is Tensile Strength?

Imagine a strip of paper being pulled at its two ends with your fingers. You are applying a tensile force on the strip. When this tensile force crosses a certain threshold, the paper tears. The tensile stress at which this takes place is the tensile strength of that material, in this case paper.

When excessive tension is applied, both ductile, as well as brittle materials will approach a point of failure. Initially there will be a uniform deformation observed. All throughout the body of the material, its length will increase while its width reduces at the same rate.

Ultimate tensile strength is the amount of stress that pushes materials from the state of uniform plastic deformation to local concentrated deformation. The necking phenomenon begins at this point.

Necking process

Ultimate tensile strength is an intensive property. In other words, it does not depend on the size of the sample. The same material with varying cross-sectional area will have the same value of tensile strength.

As this type of fracture in a system can cause failure and possibly endanger life, it is imperative that this parameter is considered while selecting appropriate materials for an application.

There are 4 major regions that a stress-strain curve can be divided into:

* Proportional limit
* Yield limit
* Strain hardening
* Necking

Proportional Limit

In the proportional limit, the specimen material acts like a spring and any strain caused is completely reversible. On the stress-strain curve, this area is called the Hooke’s region. The reason lies with the applicability of Hooke’s Law for forces that fall into the area.

Yield Limit

As soon as the specimen passes the proportional limit, it enters the yield limit region. At this point, permanent deformation sets in. From this point on, it doesn’t matter if you release the tensile force or apply a force in the opposite direction, the specimen will not return to its original dimensions.

Strain Hardening Region

On further increasing the tensile stress, the specimen enters the strain hardening region. This is a very unique section because you are changing the crystal structure of the material. The material is under enough stress that its very microstructure is modified.

As the name suggests, the material becomes harder and tougher. This hardening can be very useful and so it is not necessarily a bad thing (cold hardening, cold forming processes actually use this region to impart strength to the workpiece).

Necking Region

Right before entering the necking phase, the material is the strongest it will ever be. We have strain hardened it to its maximum limit. When we enter the necking phase, the material starts to get weaker. It is characterized by a local reduction in cross-section.

Beyond this point, the material is only moving towards failure. It can handle less stress with increasing strain.

We can sort of go back to the original equation that says stress is equal to force per unit area and infer that the smaller the area, the higher the stress. The material moves beyond this point until rupturing.

Ultimate Tensile Strength on the Curve

The point that separates the strain hardening region and the necking region is the ultimate strength for that material. At this point, the maximum amount of strain hardening has taken place. The material is handling the highest amount of load it can handle safely.

Ultimate strength is, therefore, a crucial point to be considered on the stress-strain curve. It shows the maximum amount of stress a material can bear before failure.

Details

Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials the ultimate tensile strength is close to the yield point, whereas in ductile materials the ultimate tensile strength can be higher.

The ultimate tensile strength is usually found by performing a tensile test and recording the engineering stress versus strain. The highest point of the stress–strain curve is the ultimate tensile strength and has units of stress. The equivalent point for the case of compression, instead of tension, is called the compressive strength.

Tensile strengths are rarely of any consequence in the design of ductile members, but they are important with brittle members. They are tabulated for common materials such as alloys, composite materials, ceramics, plastics, and wood.

Definition

The ultimate tensile strength of a material is an intensive property; therefore its value does not depend on the size of the test specimen. However, depending on the material, it may be dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material.

Some materials break very sharply, without plastic deformation, in what is called a brittle failure. Others, which are more ductile, including most metals, experience some plastic deformation and possibly necking before fracture.

Tensile strength is defined as a stress, which is measured as force per unit area. For some non-homogeneous materials (or for assembled components) it can be reported just as a force or as a force per unit width. In the International System of Units (SI), the unit is the pascal (Pa) (or a multiple thereof, often megapascals (MPa), using the SI prefix mega); or, equivalently to pascals, newtons per square metre (N/m^2). A United States customary unit is pounds per square inch (lb/{in}^2 or psi). Kilopounds per square inch (ksi, or sometimes kpsi) is equal to 1000 psi, and is commonly used in the United States, when measuring tensile strengths.

Testing

Typically, the testing involves taking a small sample with a fixed cross-sectional area, and then pulling it with a tensometer at a constant strain (change in gauge length divided by initial gauge length) rate until the sample breaks.

When testing some metals, indentation hardness correlates linearly with tensile strength. This important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers. This practical correlation helps quality assurance in metalworking industries to extend well beyond the laboratory and universal testing machines.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1597 2022-12-13 21:45:27

ganesh
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Posts: 40,614

Re: Miscellany

1560) Bus

Summary

A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for charter purposes, or through private ownership. Although the average bus carries between 30 and 100 passengers, some buses have a capacity of up to 300 passengers. The most common type is the single-deck rigid bus, with double-decker and articulated buses carrying larger loads, and midibuses and minibuses carrying smaller loads. Coaches are used for longer-distance services. Many types of buses, such as city transit buses and inter-city coaches, charge a fare. Other types, such as elementary or secondary school buses or shuttle buses within a post-secondary education campus, are free. In many jurisdictions, bus drivers require a special large vehicle licence above and beyond a regular driving licence.

Buses may be used for scheduled bus transport, scheduled coach transport, school transport, private hire, or tourism; promotional buses may be used for political campaigns and others are privately operated for a wide range of purposes, including rock and pop band tour vehicles.

Horse-drawn buses were used from the 1820s, followed by steam buses in the 1830s, and electric trolleybuses in 1882. The first internal combustion engine buses, or motor buses, were used in 1895. Recently, interest has been growing in hybrid electric buses, fuel cell buses, and electric buses, as well as buses powered by compressed natural gas or biodiesel. As of the 2010s, bus manufacturing is increasingly globalised, with the same designs appearing around the world.

Details

A bus is any of a class of large, self-propelled, wheeled vehicles that are designed to carry passengers, generally on a fixed route. They were developed at the beginning of the 20th century to compete with streetcars by providing greater route flexibility. The bus was a natural outgrowth of the horse-driven coach. Today buses are defined as vehicles that accommodate more than 10 passengers.

Development

In 1830 Sir Goldworthy Gurney of Great Britain designed a large stagecoach driven by a steam engine that may have been the first motor-driven bus. In 1895 an eight-passenger omnibus, driven by a four-horsepower single-cylinder engine, was built in Germany. Early buses in the United States were operated by sightseeing companies in New York City. One type of these open vehicles built by Mack Trucks, Inc., in 1900 had a nominal seating capacity of 20 with a four-cylinder gasoline engine developing 40 horsepower at street speeds of up to 32 km (20 miles) per hour.

Until the 1920s the technical history of the bus was that of the motor truck, because the early bus consisted of a bus body mounted on a truck chassis. The majority of present-day school buses are made in this way. In 1921 the first vehicle with a chassis specifically designed for bus service was made in the United States by Fageol Safety Coach Company of Oakland, Calif. The widened and lengthened frame was 30 cm (12 inches) lower than a truck frame. In 1926 Fageol developed the first integral-frame bus, with twin engines mounted amidships under the floor. The integral frame utilized the roof, floor, and sides of the bus as structural members.

Other early bus manufacturers were Mack and Yellow Truck & Coach in the United States, both of which built gasoline-electric models. In these buses a gasoline engine drove a direct-current generator, and the output of the generator provided electrical power for the driving motors on the rear wheels. In 1928 transcontinental bus service was initiated in the United States. In 1931 the first rear engine in an integral-frame bus was introduced. Two-stroke-cycle diesel engines were first used in buses in 1938 and are still found in most city and intercity models.

Air suspensions were introduced in 1953 and continue to be employed on integral-frame bus models. They consist of multiple heavy rubber bellows, or air springs, mounted at each axle. The air springs are supplied with air from a reservoir in which the pressure is maintained at about 690 kilopascals (100 pounds per square inch). An advantage gained from this type of suspension is that, as the load increases or decreases, the level and height of the vehicle remain constant. This is accomplished by valves that increase pressure in the air spring. The increased unit pressure multiplied by a nearly constant area gives a greater load capacity.

Unlike the leaf spring but like the coil spring, the air spring is capable of withstanding only vertical forces. Consequently, braking and cornering forces must be absorbed by radius rods. These are sets of links or arms with one end attached to the axle housing and the other end jointed to attach to the body.

Modern buses

There are four main types of buses: city or transit, suburban, intercity or tour, and school. The city bus operates within the city limits and is characterized by low maximum speed, low-ride platform, provision for standing and wheelchair passengers, two entrances on the curb side, low-back seats, and no luggage space. The suburban bus is designed for short intercity runs and has high-back seats, luggage compartments and racks, and a single, front entrance.

The intercity type has a high-ride platform to provide maximum luggage space under the passengers, high-back seats, overhead luggage racks, television monitors, individual reading light and ventilation controls, and a restroom. A typical intercity coach weighs about 12,000 kg (26,000 pounds), has a capacity of up to 47 passengers, a two-stroke-cycle V-8 diesel engine with up to 450 horsepower, an electronically controlled automatic transmission, and air brakes. School buses generally consist of a 50-passenger bus body, with special signal lamp and safety provisions, mounted on a long-wheelbase truck chassis. As fuel costs increased during the 1990s and 2000s, bus ridership increased in many urban regions around the world.

Articulated buses were first used in Europe in the 1950s. In this arrangement a trailer body is connected to the rear of a conventional front-engine bus by means of a hitch, a flexible diaphragm, and a continuous floor panel with arcuate mating surfaces during turn maneuvers. This arrangement permits up to a 75 percent increase in seating capacity and a 20 percent improvement in fuel efficiency per seat-kilometre. The turning radius is the same as that of a conventional bus. Manufacture of this design was begun in the United States in the 1980s by several European firms. Double decking, increased seating comfort, and larger glass areas have been trends in tour buses, principally in Europe and Asia.

A typical cross-country bus has been estimated to remove 17 cars from the highway and to achieve 69 passenger-km per litre (162 passenger-miles per gallon). Experimental hybrid-electric bus designs are being built, based on automobile practice. Intermodal transit systems with coordinated bus, train, and private car continue to be studied because of their efficiency and pollution reduction potential.

New exhaust emission standards for buses went into effect in the United States in 2006 and 2007, requiring that smog-related emissions be reduced by 95 percent and soot by 90 percent relative to 2000 levels. The reductions have required a switch to reformulated diesel fuels with sulfur content capped at 15 parts per million.

BL04_Tata_bus.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1598 2022-12-14 04:07:08

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1561) Spray painting

Spray painting is a painting technique in which a device sprays coating material (paint, ink, varnish, etc.) through the air onto a surface. The most common types employ compressed gas—usually air—to atomize and direct the paint particles.

Spray guns evolved from airbrushes, and the two are usually distinguished by their size and the size of the spray pattern they produce. Airbrushes are hand-held and used instead of a brush for detailed work such as photo retouching, painting nails, or fine art. Air gun spraying uses generally larger equipment. It is typically used for covering large surfaces with an even coating of liquid. Spray guns can be either automated or hand-held and have interchangeable heads to allow for different spray patterns.

Single color aerosol paint cans are portable and easy to store.

History

Spraying paint with compressed air can be traced back to its use on the Southern Pacific Railway in the early 1880s In 1887 Joseph Binks, the maintenance supervisor at Chicago's Marshall Field's Wholesale Store developed a hand-pumped cold-water paint spraying machine to apply whitewash to the subbasement walls of the store. Francis Davis Millet, the decorations director for the World's Columbian Exposition in Chicago in 1893, used Binks and his spray painting system to apply whitewash consisting of a mix of oil and white lead to the buildings at the Exposition, taking considerably less time than traditional brush painting and turning it into what has been called the White City. In 1949, Edward Seymour developed a type of spray painting, aerosol paint, that could be delivered via a compressed aerosol in a can.

Types:

Air gun spraying

This process occurs when the paint is applied to an object through the use of an air-pressurized spray gun. The air gun has a nozzle, paint basin, and air compressor. When the trigger is pressed the paint mixes with the compressed air stream and is released in a fine spray.

Types of nozzles and sprays

Due to a wide range of nozzle shapes and sizes, the consistency of the paint can be varied. The shape of the workpiece and the desired paint consistency and pattern are important factors when choosing a nozzle. The three most common nozzles are the full cone, hollow cone, and flat stream. There are two types of air-gun spraying processes. In a manual operation method the air-gun sprayer is held by a skilled operator, about 6 to 10 inches (15–25 cm) from the object, and moved back and forth over the surface, each stroke overlapping the previous to ensure a continuous coat. In an automatic process the gun head is attached to a mounting block and delivers the stream of paint from that position. The object being painted is usually placed on rollers or a turntable to ensure overall equal coverage of all sides.

High volume low pressure

High volume low pressure (HVLP) is similar to a conventional spray gun using a compressor to supply the air, but the spray gun itself requires a lower pressure (LP). A higher volume (HV) of air is used to aerosolize and propel the paint at lower air pressure. The result is a higher proportion of paint reaching the target surface with reduced overspray, materials consumption, and air pollution.

A regulator is often required so that the air pressure from a conventional compressor can be lowered for the HVLP spray gun. Alternatively, a turbine unit (commonly containing a vacuum cleaner type motor, reverse mounted) can be used to propel the air without the need for an airline running to the compressor.

A rule of thumb puts two-thirds of the coating on the substrate and one third in the air. True HVLP guns use 8–20 cfm (13.6–34 m^3/h), and an industrial compressor with a minimum of 5 horsepower (3.7 kW) output is required. HVLP spray systems are used in the automotive, decorative, marine, architectural coating, furniture finishing, scenic painting, and cosmetic industries.

Low volume low pressure

Like HVLP, low volume low pressure (LVLP) spray guns also operate at a lower pressure (LP), but they use a low volume (LV) of air when compared to conventional and HVLP equipment. This is a further effort at increasing the transfer efficiency (amount of coating that ends up on the target surface) of spray guns while decreasing the amount of compressed air consumption.

Electrostatic spray painting

The electrostatic painting was first patented in the U.S. by Harold Ransburg in the late 1940s. Harold Ransburg founded Ransburg Electrostatic Equipment and discovered that electrostatic spray painting was an immediate success as manufacturers quickly perceived the substantial materials savings that could be achieved. In electrostatic spray painting or powder coating, the atomized particles are made to be electrically charged, thereby repelling each other and spreading themselves evenly as they exit the spray nozzle. The object being painted is charged oppositely or grounded. The paint is then attracted to the object giving a more even coat than wet spray painting, and also greatly increasing the percentage of paint that sticks to the object. This method also means that paint covers hard to reach areas. The whole may then be baked to properly attach the paint: the powder turns into a type of plastic. Car body panels and bike frames are two examples where electrostatic spray painting is often used.

There are three main technologies for charging the fluid (liquid or powders):

* Direct charging: An electrode is immersed in the paint supply reservoir or the paint supply conduit.
* Tribo charging: This uses the friction of the fluid which is forced through the barrel of the paint gun. It rubs against the side of the barrel and builds up an electrostatic charge.
* Post-atomization charging: The atomized fluid comes into contact with an electrostatic field downstream of the outlet nozzle. The electrostatic field may be created by electrostatic induction or corona, or by one or more electrodes (electrode ring, mesh, or grid).

Rotational bell


With this method the paint is flung into the air by a spinning metal disc ("bell"). The metal disc also imparts an electrical charge to the coating particle.

Electric fan

There is a variety of hand-held paint sprayers that either combine the paint with air or convert the paint to tiny droplets and accelerate these out of a nozzle.

Hot spray

By heating the full-bodied paint to 60-80 °C, it is possible to apply a thicker coat. Originally the paint was recirculated, but as this caused bodying up, the system was changed to direct heating on line. Hot spraying was also used with Airless and Electrostatic Airless to decrease bounce-back. Two-pack materials usually had premix before tip systems using dual pumps.

Air assisted airless spray guns

These use air pressure and fluid pressure 300 to 3,000 pounds per square inch (2,100–20,700 kPa) to achieve atomization of the coating. This equipment provides high transfer and increased application speed and is most often used with flat-line applications in factory finish shops.

The fluid pressure is provided by an airless pump, which allows much heavier materials to be sprayed than is possible with an air spray gun. Compressed air is introduced into the spray via an air nozzle (sometimes called air cap) similar to a standard conventional spray gun. The addition of compressed air improves the fineness of atomization. Additionally, unlike a pure airless spray gun, an AA gun has some control over fan spray to round spray. Some electric airless sprayers (Wagner and Graco) are fitted with a compressor to allow the use of an air-assisted airless gun in situations where portability is important.

Airless spray guns

These operate connected to a high-pressure pump commonly found using 300 to 7,500 pounds per square inch (2,100–51,700 kPa) pressure to atomize the coating, using different tip sizes to achieve the desired atomization and spray pattern size. This type of system is used by contract painters to paint heavy duty industrial, chemical, and marine coatings and linings.

Advantages of airless spray are:

* The coating penetrates better into pits and crevices.
* A uniform thick coating is produced, reducing the number of coats required.
* A very "wet" coating is applied, ensuring good adhesion and flow-out.

Most coatings can be sprayed with very little thinner added, thereby reducing drying time and decreasing the release of solvent into the environment.

Care must be used when operating, as airless spray guns can cause serious injury,[9] such as injection injuries, due to the paint ejecting from the nozzle at high pressure.

Airless pumps can be powered by different types of motor: electric, compressed air (pneumatic), or hydraulic. Most have a paint pump (also called a lower) that is a double-acting piston, in which the piston pumps the paint in both the down and the upstroke. Some airless pumps have a diaphragm instead of a piston, but both types have inlet and outlet valves.

Most electric-powered airless pumps have an electric motor connected through a gear train to the paint piston pump. The pressure is achieved by stopping and starting the motor via a pressure sensor (also called a transducer); in more advanced units, this is done by digital control in which the speed of the motor varies with the demand and the difference from the pressure set-point, resulting in very good pressure control. Some direct drive piston pumps are driven by a gasoline engine with pressure control via an electric clutch. In electric diaphragm pumps, the motor drives a hydraulic piston pump that transmits the oil displaced by the piston, to move the diaphragm.

Hydraulic and air-powered airless pumps have linear motors that require a hydraulic pump or an air compressor, which can be electric or gasoline-powered, although an air compressor is usually diesel-powered for mobile use or electric for fixed installations. Some airless units have the hydraulic pump and its motor, built onto the same chassis as the paint pump.

Hydraulic or air-powered airless provide a more uniform pressure control since the paint piston moves at a constant speed except when it changes direction. In most direct drive piston pumps, the piston is crankshaft driven in which the piston will be constantly changing speed. The linear motors of hydraulic or compressed air drive pumps are more efficient in converting engine power to material power than crankshaft-driven units. All types of paint can be painted using an airless method.

Automated linear spray systems

Manufacturers who mass-produce wood products use automated spray systems, allowing them to paint materials at a very high rate with a minimum of personnel. Automated spray systems usually incorporate a paint-saving system that recovers paint not applied to the products. Commonly, linear spray systems are for products which are lying flat on a conveyor belt and then fed into a linear spray system, where automated spray guns are stationed above. When the material is directly below the guns, the guns begin to paint the material. Materials consist of lineal parts usually less than 12 inches (30 cm) wide, such as window frames, wood molding, baseboard, casing, trim stock, and any other material that is simple in design. These machines are commonly used to apply the stain, sealer, and lacquer. They can apply water- or solvent-based coatings. In recent years ultraviolet-cured coatings have become commonplace in profile finishing, and there are machines particularly suited to this type of coating.

Automated flatline spray systems

Mass-produced material is loaded on a conveyor belt where it is fed into one of these flatline machines. Flatline machines are designed to specifically paint material that is less than 4 inches (10 cm) thick and complex in shape, for example, a kitchen cabinet door or drawer front. Spray guns are aligned above the material and the guns are in motion to hit all the grooves of the material. The guns can be moved in a cycle, circle, or can be moved back and forth to apply the paint evenly across the material. Flatline systems are typically large and can paint doors, kitchen cabinets, and other plastic or wooden products.

Spray booth

A spray booth is a pressure-controlled closed environment, originally used to paint vehicles in a body shop. To ensure the ideal working conditions (temperature, airflow, and humidity), these environments are equipped with ventilation, consisting of mechanical fans driven by electric motors, and optionally burners to heat the air to speed paint drying. Toxic solvents and paint particles are exhausted outside, possibly after filtering and treatment to reduce air pollution. Prevention of fires and dust explosions is also a high priority. To assist in the removal of the over sprayed paint from the air and to provide efficient operation of the down-draft, water-washed paint spray booths utilize paint detackifying chemical agents.

Artists may also make use of spray booth facilities to enable them to use spray paints (including automotive finishes) efficiently and safely. They may rent space and time in auto body shops or set up their facilities in association with schools or artist cooperatives.

Safety

Spray painting poses health hazards that affect the respiratory, nervous, and circulatory systems. Similarly, using solvents to clean one's hands of paint marks and residue may cause skin irritation or even more serious issues since many are carcinogenic or neurotoxic. There are risks involved in working with substances such as paint and thinner, which contain compounds that are potentially harmful to health, or even fatal.

Appropriate training for personnel who are responsible for conducting the painting procedures is important, which may be from a professional training provider or the product supplier. There are also hazards related to the disposal of wastes and materials that are contaminated with potentially harmful chemicals. Decontamination procedures and Material Safety Data Sheets for various products are important. Safety is improved through:

* Personal protective equipment (PPE) use: PPE must be used when handling spray paint materials, particularly PPE that offers protection to the skin. Some of the essential personal protective equipment are overalls with a hood, protective goggles for the eyes, half-mask respirators, and single-use nitrile gloves. One of the most essential types of PPE is respiratory protective equipment (RPE). Nevertheless, basic RPE does not offer ample protection from the negative effects of isocyanates in human tissue. Paint products containing isocyanates must be handled while donning an air-fed RPE that has a 20 or higher APF (assigned protection factor). Air-fed respiratory protective equipment needs extra attention since they provide breathable air to the user. When in use, measures must be implemented to prevent contamination of the air supply since there is a risk of harmful substances entering the intake valve if it is not positioned outside of the spray area.

* Health monitoring: To avoid the development of illnesses associated with exposure to isocyanates, health authorities recommend that people who use spray paint products that contain the substance provide a urine sample after a work shift at least once a year, with high frequencies in first few months on the job. A urine sample with ascertain levels of exposure, not the presence of disease associated with harmful chemicals.

* Proper storage: Since paints and thinners are fire hazards, extra care must be taken not only while they are in use. Fire safety should also be considered when storing paint supplies.In the United States, the Occupational Safety and Health Administration (OSHA) provides guidelines for the proper storage of flammable materials.[12] Many products used in spray paint are flammable such that fire risk is likely within a distance of 15 cm from the nozzle. As such, ignition sources must be placed at a safe distance. Also, there is a risk of dust explosions when finely-divided paint particles become airborne.

* Proper recordkeeping: One of the basic tenets of risk control is the maintenance of updated health records of personnel handling spray paint products. Confidential data on biological monitoring results must be appropriately kept. Records of the schedule and result of testing procedures should also be kept. Some of the most important tests to be conducted regularly are air quality testing, testing of pressure systems and electrical systems, and testing of compressor reservoir air filters.

Defects

* Orange peel, an undesirable rippled texture
* Fisheye, blemishes caused by contamination such as oil or water

Other applications

One application of spray painting is graffiti. The introduction of inexpensive and portable aerosol paint has been a boon to this art form, which has spread all over the world. Spray painting has also been used in fine art. Jules Olitski, Dan Christensen, Peter Reginato, Sir Anthony Caro, and Jean-Michel Basquiat have used airbrushes, for both painting and sculpture.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1599 2022-12-15 01:52:51

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1562) Mansion

A mansion is a large dwelling house. The word itself derives through Old French from the Latin word mansio "dwelling", an abstract noun derived from the verb manere "to dwell". The English word manse originally defined a property large enough for the parish priest to maintain himself, but a mansion is no longer self-sustaining in this way (compare a Roman or medieval villa). Manor comes from the same root—territorial holdings granted to a lord who would "remain" there.

Following the fall of Rome, the practice of building unfortified villas ceased. Today, the oldest inhabited mansions around the world usually began their existence as fortified houses in the Middle Ages. As social conditions slowly changed and stabilised fortifications were able to be reduced, and over the centuries gave way to comfort. It became fashionable and possible for homes to be beautiful rather than grim and forbidding allowing for the development of the modern mansion.

In British English, a mansion block refers to a block of flats or apartments designed for the appearance of grandeur. In many parts of Asia, including Hong Kong and Japan, the word mansion also refers to a block of apartments. In modern Japan, a "manshon", stemming from the English word "mansion", is used to refer to a multi-unit apartment complex or condominium.

15th-18th-century development

In Europe, from the 15th century onwards, a combination of politics and advances in weaponry negated the need for the aristocracy to live in fortified castles. As a result, many were transformed into mansions without defences or demolished and rebuilt in a more modern, undefended style. Due to intermarriage and primogeniture inheritance amongst the aristocracy, it became common for one noble to often own several country houses. These would be visited rotationally throughout the year as their owner pursued the social and sporting circuit from country home to country home. Many owners of a country house would also own a town mansion in their country's capital city. These town mansions were referred to as 'houses' in London, 'hôtels particuliers' in Paris, and 'palaces' in most European cities elsewhere. It might be noted that sometimes the house of a clergyman was called a "mansion house" (e.g., by the Revd James Blair, Commissary in Virginia for the Bishop of London, 1689–1745, a term related to the word "manse" commonly used in the Church of Scotland and in Non-Conformist churches. H.G. Herklots, The Church of England and the American Episcopal Church).

As the 16th century progressed and the Renaissance style slowly spread across Europe, the last vestiges of castle architecture and life changed; the central points of these great houses became redundant as owners wished to live separately from their servants, and no longer ate with them in a Great hall. All evidence and odours of cooking and staff were banished from the principal parts of the house into distant wings, while the owners began to live in airy rooms, above the ground floor, with privacy from their servants, who were now confined, unless required, to their specifically delegated areas—often the ground and uppermost attic floors. This was a period of great social change, as the educated prided themselves on enlightenment.

The uses of these edifices paralleled that of the Roman villas. It was vital for powerful people and families to keep in social contact with each other as they were the primary moulders of society. The rounds of visits and entertainments were an essential part of the societal process, as painted in the novels of Jane Austen. State business was often discussed and determined in informal settings. Times of revolution reversed this value. During July/August 1789, a significant number of French country mansions (chateaux) were destroyed by the rural population as part of the Great Fear—a symbolic rejection of the feudal rights and restraints in effect under the Ancien Régime.

Until World War I it was not unusual for a moderately sized mansion in England such as Cliveden to have an indoor staff of 20 and an outside staff of the same size,[citation needed] and in ducal mansions such as Chatsworth House the numbers could be far higher. In the great houses of Italy, the number of retainers was often even greater than in England; whole families plus extended relations would often inhabit warrens of rooms in basements and attics. Most European mansions were also the hub of vast estates.

19th-century development

The 19th century saw the continuation of the building of mansions in the United States and Europe. Built by self-made men, these were often smaller than those built by the old European aristocracy. These new builders of mansions did not confine themselves to just the then-fashionable Gothic tastes in architecture, but also experimented with 19th-century versions of older Renaissance and Tudoresque styles; The Breakers in Rhode Island is a fine example of American Renaissance revivalism.

During the 19th century, like the major thoroughfares of all important cities, Fifth Avenue in New York City, was lined with mansions. Many of these were designed by the leading architects of the day, often in European Gothic Revival style, and were built by families who were making their fortunes, and thus achieving their social aspirations. However, nearly all of these have now been demolished, thus depriving New York of a boulevard to rival, in the architectural sense, those in Paris, London or Rome—where the many large mansions and palazzi built or remodeled during this era still survive. Mansions built in the countryside were not spared either. One of the most spectacular estates of the U.S., Whitemarsh Hall, was demolished in 1980, along with its extensive gardens, to make way for suburban developments.

Grand Federal style mansions designed by Samuel McIntire inhabit an area that, in 2012, is the largest collection of 17th- and 18th-century structures in the United States of America. This district in Salem, Massachusetts, is called the McIntire Historic District with the center being Chestnut Street. McIntire's training came from his father and from books. He and his brothers, Joseph and Angler, began their careers as housewrights and carpenters while in their teens but, early on, Samuel's work caught the eye of Salem's pre-eminent merchant, Elias Hasket Derby. Over the next quarter century, McIntire built or remodelled a number of homes for Derby and members of his extended family. McIntire also worked occasionally on Derby's vessels, and wasn't averse to fixing a wagon or building a birdhouse if his patron so desired. Hamilton Hall is a National Historic Landmark at 9 Chestnut Street in Salem, Massachusetts. Hamilton Hall was built in 1805 by Samuel McIntire and added to the National Register of Historic Places in 1970. "King" Derby's stamp of approval opened many other doors for McIntire, who went on to design and build mansions for John Gardner, Jerethmiel Peirce, Simon Forrester, and other wealthy Salem shipowners. He also built, on elegant Chestnut Street, a function hall (named for Alexander Hamilton) and church for the town's merchant class. McIntire also designed the former Salem Court House and Registry of Deeds.

After 1793, Samuel McIntire worked exclusively in the architectural style developed by Robert Adam in Great Britain and brought to America by the great Boston architect, Charles Bulfinch. The delicate Adam style, which emphasized decorative elements and ornamentation, was tailor-made for McIntire, whose unerring sense of design and proportion was exceeded only by his skill as a woodcarver. Carved swags, rosettes, garlands, and his signature sheaths of wheat dominate wood surfaces in McIntire homes built between 1793 and his death in 1811.

Even in Europe, some 19th-century mansions were often built as replicas of older houses, the Château de Ferrières in France was inspired by Mentmore Towers, which in turn is a copy of Wollaton Hall. Other mansions were built in the new and innovative styles of the new era such as the arts and crafts style: The Breakers is a pastiche of an Italian Renaissance palazzo; Waddesdon Manor in Buckinghamshire is a faithful mixture of various French châteaux. One of the most enduring and most frequently copied styles for a mansion is the Palladian – particularly so in the 18th century. However, the Gothic style was probably the most popular choice of design in the 19th century. The most bizarre example of this was probably Fonthill Abbey which actually set out to imitate the mansions which had truly evolved from medieval Gothic abbeys following the Dissolution of the Monasteries in the 16th century.

Mansions built during and after the 19th century were seldom supported by the large estates of their predecessors. These new mansions were often built as the week-end retreats of businessmen who commuted to their offices by the new railways, which enabled them to leave the city more easily.

Latin America

The Quinta Gameros is a Porfirian-era mansion located in Chihuahua, Mexico. The building, designed in a French style, is testimony to an era when France asserted greater soft power in the region than either Spain or Portugal.

In Latin America, the grand rural estate, the Hacienda, Estancia, in Portuguese speaking Brazil Fazenda or Estância, with the mansion as its stately center, is a characteristic feature.

Mansions tended to follow European architectural styles. Whereas until the second half of the 19th century, Portugal and Spain as the colonial (or former colonial) powers were the eminent models for architecture and upper-class lifestyle, towards the end of the 19th century they were sometimes replaced by then more dominant powers like France or England.

In comparably developed, densely populated countries like Mexico, feudal estates and their mansions were as grand and stately as in the Mediterranean old world, whereas where estates were founded in the sparsely populated remote areas like the Pampa of Argentina or Uruguay, where iron pillars, doors, windows, and furniture had to be brought from Europe by ship and afterwards ox cart, buildings were smaller, but normally still aspiring to evoke a stately impression, often featuring, like their earlier Italian counterparts, a morador.

In Venezuela, the traditional Spanish mansions with a garden in the center of the property are usually referred as "Quinta".

Size

Some realtors in the US term mansions as houses that have a minimum of 8,000-square-foot (740 m^2) of floor space. Others claim a viable minimum could instead be 5,000-square-foot (460 m^2) of floor space, especially in a city environment.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#1600 2022-12-16 00:11:50

ganesh
Administrator
Registered: 2005-06-28
Posts: 40,614

Re: Miscellany

1563) Sail

Summary

A sail is a tensile structure—made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may be made from a combination of woven materials—including canvas or polyester cloth, laminated membranes or bonded filaments—usually in a three- or four-sided shape.

A sail provides propulsive force via a combination of lift and drag, depending on its angle of attack—its angle with respect to the apparent wind. Apparent wind is the air velocity experienced on the moving craft and is the combined effect of the true wind velocity with the velocity of the sailing craft. Angle of attack is often constrained by the sailing craft's orientation to the wind or point of sail. On points of sail where it is possible to align the leading edge of the sail with the apparent wind, the sail may act as an airfoil, generating propulsive force as air passes along its surface—just as an airplane wing generates lift—which predominates over aerodynamic drag retarding forward motion. The more that the angle of attack diverges from the apparent wind as a sailing craft turns downwind, the more drag increases and lift decreases as propulsive forces, until a sail going downwind is predominated by drag forces. Sails are unable to generate propulsive force if they are aligned too closely to the wind.

Sails may be attached to a mast, boom or other spar or may be attached to a wire that is suspended by a mast. They are typically raised by a line, called a halyard, and their angle with respect to the wind is usually controlled by a line, called a sheet. In use, they may be designed to be curved in both directions along their surface, often as a result of their curved edges. Battens may be used to extend the trailing edge of a sail beyond the line of its attachment points.

Other non-rotating airfoils that power sailing craft include wingsails, which are rigid wing-like structures, and kites that power kite-rigged vessels, but do not employ a mast to support the airfoil and are beyond the scope of this article.

Details

Sail is an extent of fabric (such as canvas) by means of which wind is used to propel a ship through water.

The first sails were most likely animal skins that were used to harness wind power for rafts or boats consisting of a single log. The next probable step was the use of woven reed mats stretched between poles. Depictions of cloth sails appear in predynastic (c. 3300 BC) Egyptian art, and ships from other early Mediterranean civilizations were equipped with sails.

Sailcloth was woven from flax fibre during the period when England, France, and Spain were striving for supremacy of the seas. Fibre flax is still used for sails, although cotton has replaced it for better quality canvas. Cotton sails became popular in Europe after the U.S. racing yacht America, using cotton sails, decisively defeated a fleet of British yachts in 1851. Cotton sailcloth has the advantage over flax, hemp, ramie, jute, and combinations of these materials as a fabric in that it can be woven more closely and therefore will not stretch out of shape as easily or lose as much wind through the pores of the material. Sails made of cotton, however, are very stiff, which makes them difficult to handle.

The chief modern users of quality sailcloth are yachtsmen, who generally prefer the polyester fibre Dacron (or Terylene, its British equivalent). These synthetic fabrics were first introduced in 1950, and they proved much superior to any type of cotton or other synthetic materials. Sails made of Dacron maintain just the correct amount of stretch and so require no “breaking in” period. The greater strength of the fabric permits the use of lighter-weight sails, which maintain their original shape for years. Because this fabric is heat-treated by pressing it between hot rollers of metal, its fibres are flattened and interlocked, giving it a smooth, almost frictionless surface and very little porosity. The stitches, however, do not mesh with the fabric but protrude above the surface of the sail, causing the sail twine to become abraded more rapidly than with other sailcloth.

The basic steps in manufacturing a sail may be outlined as follows: (1) The sailmaker studies the sail plan or measures the vessel’s rig. (2) The stretch and the amount of draft (i.e., the curvature of the surface) are calculated. (3) The actual plan of the sail is chalked out to full scale on the floor of the sail loft. (4) The cloths are laid down over this plan, and their actual length and shape are marked on each individual cloth. (5) The cloths are numbered and then cut to the dimensions outlined by the markings. (6) The cloths are sewn together. A special sail twine is used as thread, and after the needle is threaded the twine is waxed so it will hold the right-hand twist then given to it. This twist helps the thread to mesh with the fabric. (7) After all the cloths are sewn together, patches are attached to the corners, and tabling (hems on the edges) is sewn on the luff (forward edge) and the foot—the places where the greatest strain develops. (8) The finishing touches are applied. The luff rope is sewn inside the leading edge of the sail to prevent the sail from being stretched out of shape. Strong ropes (boltropes) are sewn to the luff and foot, and various fittings, such as metal slides, grommets, reef points, cringles, etc., are attached to the sail.

The two major categories of sails are square sails and fore-and-aft sails (which are usually triangular). The first type is generally set in a position across the longitudinal axis of the ship; the second type of sail is set along this axis. Square sails drive the craft forward by the pressure of the wind on the afterside of the sail only; with fore-and-aft sails, both sides may be used for forward propulsion.

Sails are divided further into groups of primary and secondary sails. Primary sails are those that supply the chief propelling force in ordinary weather; secondary sails are those that aid the primary sails either by helping to balance the ship or by providing additional driving power. There are six classes of primary sales: square sails, gaff sails, jib-headed sails (Bermuda or Marconi), spritsails, lugsails, and lateen sails. Secondary sails are variations of these basic types. In addition, sails are often grouped according to their function, usually as cruising sails for ordinary weather, summer sails for tropical weather, storm sails for extremely heavy weather, and racing sails.

The name of a sail is frequently derived from the name of the piece of rigging on which it is set or from its location with reference to a nearby piece of gear. The nearest mast is often the primary reference point; therefore, the names of the masts and their location are important. Starting at the bow in a two-masted vessel, the masts are termed the foremast and the mainmast; when the aftermast is considerably smaller they are named the mainmast and the mizzenmast. In all three-masted vessels the names of the masts are foremast, mainmast and mizzenmast.

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