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## #226 2018-09-22 03:00:33

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

207) Camel

Camels are mammals with long legs, a big-lipped snout and a humped back. There are two types of camels: dromedary camels, which have one hump, and Bactrian camels, which have two humps. Camels' humps consist of stored fat, which they can metabolize when food and water is scarce.

In addition to their humps, camels have other ways to adapt to their environment. They have a third, clear eyelid that protects their eyes from blowing sand. Two rows of long lashes also protect their eyes. Sand up the nose can be a problem, but not for camels. They can shut their nostrils during sand storms.

Humans have used camels as a means of transport for thousands of years. They can carry about 375 to 600 lbs. (170 to 270 kilograms) on their backs, according to National Geographic. This earned these beasts of burden a nickname, "ships of the desert." Domestic camels are often the main source of meat, milk and even leather or wool products.

Size

Most camels tower above humans. A Bactrian camel, according to the San Diego Zoo, grows to a shoulder height of 6 feet (1.8 meters) and a body length of 10 feet (3 m). They normally weigh 1,320 to 2,200 lbs. (600 to 1,000 kg) when they are fully grown.

Dromedary camels get up to about 6.5 feet (2 m) tall at the shoulder and weigh 880 to 1,325 lbs. (400 to 600 kg).

Diet

Camels aren't picky about what they eat. Their thick lips allow them to eat things that most other animals couldn't, such as thorny plants. Camels are herbivores, though, so you won't find them eating meat.

Filling up on water, when it's available, is very important for camels. They can drink 30 gallons (113 liters) of water in just 13 minutes. Their bodies rehydrate faster than any other mammal.

When there is little food and water, the camel's hump fat releases water; 9.3 grams of fat releases 1.13 grams of water, according to research by the University of Singapore. Camels can survive up to six months without food or water.

Habitat

The two types of camel are found in different parts of the world. The dromedary camel, also called an Arabian camel, can be found in North Africa and the Middle East. The Bactrian camel lives in Central Asia. No matter the type, camels are usually found in the desert, prairie or steppe. Though many people think that camels only live in hot climates, they do well in temperature ranges from 20 degrees F (minus 29 degrees C) to 120 degrees F (49 degrees C).

Habits

Camels like to stay together in groups called herds. The herds are led by a dominant male, while many of the other males form their own herd called a bachelor herd. Camels are very social and like to greet each other by blowing in each other's faces.

Offspring

After a gestation of 12 to 14 months, a mother camel will find a private spot to have her young. Female camels usually only have one baby, but sometimes camels have twins.

Baby camels are called calves. The newborn calf is able to walk within 30 minutes, though the two won't rejoin the herd until around two weeks later. Camels become fully mature when they are 7 years old. Camels live around 17 years.

Classification/Taxonomy

Dromedary camels (Camelus dromedarius) and the domestic Bactrian camel (Camelus bactrianus) were named in 1758 by Swedish zoologist Carl Linnaeus, who only knew of the domestic variety. Wild Bactrian camels (Camelus ferus) were discovered in 1878 by Nikolai Prejevalsky, a Russian geographer who explored Mongolia and Tibet.

For many years, the wild Bactrian was thought to be a subspecies of the domestic Bactrian. However, in recent years, DNA analysis confirmed that C. ferus was a separate species, according to the San Diego Zoo. The main difference between the two species is that the wild Bactrian has three more chromosome pairs than the domestic Bactrian.

Here is the classification of camels, according to Integrated Taxonomic Information System:

Kingdom: Animalia
Subkingdom: Bilateria
Infrakingdom: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclass: Tetrapoda
Class: Mammalia
Subclass: Theria
Infraclass: Eutheria
Order: Artiodactyla
Family: Camelidae
Genus: Camelus

Species:

Camelus bactrianus (Bactrian camel)
Camelus dromedarius (one-humped camel)

Subspecies:

Camelus bactrianus bactrianus
Camelus bactrianus ferus (wild Bactrian camel)

The wild Bactrian camel is considered critically endangered by the International Union for Conservation of Nature and has a population that is decreasing. In fact, wild camels are one of the most endangered large mammals. According to the Wild Camel Protection Foundation, there are fewer than 1,000 wild camels alive.

Other facts

Camels can run at 25 mph (40 kph) for long periods. If their owner is in a hurry, they can kick their speed up to 40 mph (67 kph).

The camel's hump is like a storage container. When camels use their stored fat, their hump will diminish. When they eat and drink again the hump will refill with fat.

Camels have oval-shaped red blood cells that help continue blood flow during times when water is scarce.

Camels are known for spitting on people. In fact, the animals are throwing up the contents of their stomach along with spit. This is a defense tactic when the animals feel threatened.

The large beasts make a variety of moans, groans and deep, throaty bellows. One of the camel's noises was even used to voice the character Chewbacca in the Star Wars movies.

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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## #227 2018-09-23 00:00:03

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

208) Cotopaxi

Cotopaxi, volcanic peak, in the Cordillera Central of the Andes, central Ecuador. Rising to 19,393 feet (5,911 metres), it is among the world’s highest volcanoes. Cotopaxi has an almost perfectly symmetrical cone, interrupted only by one minor cone—the Cabeza del Inca (“Inca’s Head”). The mountain has a long record of violent eruption. The largest historical eruptions took place in 1744, 1768, 1877, and 1904. The eruption of 1877 was known for its lahars (volcanic mudflows) that traveled more than 60 miles (100 km) to meet the Pacific Ocean to the west and the Amazon River basin to the east. After the most-recent significant eruption, which occurred in 1904, minor eruptions took place in 1940 and 2015.

The terrain around the mountain’s base has many times been devastated by earthquakes or been buried in pumice and ash blown out of the crater. The mountain itself is built up of alternating flows of dark-coloured trachytic lava and falls of lighter-coloured ash. The crater at the top is 2,300 feet (700 metres) in diameter from north to south and 1,650 feet (500 metres) from east to west. Its depth is 1,200 feet (366 metres). The base of the volcano stands on open mountain grassland, but the whole upper part of the mountain is covered with permanent snow.

The first European to attempt an ascent of Cotopaxi was Alexander von Humboldt in 1802. He failed to reach the top and pronounced the mountain unclimbable. Other failures in 1831 and 1858 seemed to confirm this verdict. But in 1872 the German scientist and traveler Wilhelm Reiss succeeded in reaching the top on November 28, and in May of the following year A. Stübel was also successful. Cotopaxi and its surrounding grasslands are protected in Cotopaxi National Park, a major tourist attraction.

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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## #228 2018-09-24 00:05:48

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

209) Victoria Falls

The Victoria Falls, one of the world's "natural wonders," are situated on the Zambezi River, on the border between Zambia and Zimbabwe. Vastly larger than North America's Niagara Falls, the Victoria Falls are rivaled only by South America's Iguazu Falls in volume. While Iguazu is divided into over 270 relatively "small" falls and cataracts, Victoria Falls is 1.06 miles wide, making it the largest curtain of water in the world. It drops between 295 feet and 355 feet into the Zambezi Gorge and an average of 1.804 million cubic feet of water plummeting over the edge every minute.

First seen by a European, Scottish missionary-explorer David Livingstone, in 1885, they are also a UNESCO World Heritage Site. The falls are considered a remarkable spectacle because of the peculiar, narrow, slot-like chasm into which the water falls, so one can view the falls face-on. The falls are part of two national parks, Mosi-oa-Tunya National Park in Zambia and Victoria Falls National Park in Zimbabwe. The Falls are one of Southern Africa's major tourist attractions.

History

The earliest known inhabitants of the area around Victoria Falls were Khoisan hunter-gatherers (bushmen). They were followed by Tokaleya people, who called the falls Shongwe. Later, the Ndebele named them aManza Thunqayo, and the Makololo called them Mosi-oa-Tunya, meaning "The smoke that thunders."

The first European to see the falls was David Livingstone on November 17, 1855, during his 1852-1856 journey from the upper Zambezi to the mouth of the river. Livingstone reached the Falls from upriver and rowed across to a small island that now bears the name Livingstone Island. Livingstone had previously been impressed by the Ngonye Falls further upstream, but found the new falls much more impressive, and named them after Queen Victoria. He wrote of the falls "No one can imagine the beauty of the view from anything witnessed in England. It had never been seen before by European eyes; but scenes so lovely must have been gazed upon by angels in their flight."

In 1860, Livingstone returned to the area and made a detailed study of the falls with the explorer John Kirk. Other early European visitors included Portuguese explorer Serpa Pinto; Czech explorer Emil Holub, who made the first detailed plan of the falls and its surroundings in 1875 (published in 1880); and British artist Thomas Baines, who executed some of the earliest paintings of the falls. Until the area was opened up by the building of the railway in 1905, however, the falls were seldom visited by other Europeans.

The falls

The falls lie about midway down the course of the Zambezi. For a considerable distance above the falls, the Zambezi flows over a level sheet of basalt, in a valley bounded by low and distant sandstone hills. The river's course is dotted with numerous, tree-clad islands, which increase in number as the river approaches the falls.

The falls are formed as the Zambezi plummets into a narrow chasm about 400 feet wide, carved by its waters along a fracture zone in the earth's crust. Numerous islets at the crest of the falls divide the water to form a series of falls.

The falls are extremely broad at about 1.06 miles across, and the height of the cascade varies from 263 feet at the right bank to 354 feet in the center. This makes Victoria roughly twice the height of Niagara Falls, and well over twice the width of the horseshoe falls (Niagara's main portion). The falling water generates spray and mist that rises typically to a height of over 1312 feet (and sometimes even twice as high), and is visible from up to over 30 miles away. At full moon, a "moonbow" can be seen in the spray instead of the daylight rainbow.

During the wet season, the falls have over 19-million cubic feet of water falling over its crestline each minute, and spray from this rises several hundreds of feet into the air because of the incredible force of the falling water. The 1958 flood of the Zambezi saw the falls reach record volumes of over 27-million cubic feet per minute. This compares to the Niagara Falls which has about six million cubic feet of water passing its crestline per minute in peak flow. This compares also to the Iguazu Falls of South America in terms of of size with peak volume.

The fall is broken into four parts by islands on the lip of the precipice. Close to the right bank is a sloping cataract 35 miles wide called the Leaping Water. Then beyond the 984-foot-wide Boaruka Island is the main fall, about 1509 feet across. Livingstone Island divides the main fall from another broad channel about 1739 feet wide, while on the left bank of the river is the Eastern Cataract.

Below the falls

The only outlet to the chasm into which the river falls is a narrow channel, cut in the barrier wall at a point about two thirds of the distance along from the western end. This channel is about 100 feet wide, and the whole volume of the river pours through it for 394 feet before emerging into a zigzagging series of gorges about 50 miles long which conduct the river past the basalt plateau.

At the end of its first gorge, the river has hollowed out a deep pool called the Boiling Pot. About 492 feet across, its surface is smooth at low water, but at high water is marked by slow, enormous swirls and heavy boilings. As the river exits the Boiling Pot, the channel turns sharply westward and enters the next of the zigzagging gorges. The walls of the gorges are over 394 feet high.

In the wet season (typically October through April), the river discharges as much as 320,000 cubic feet of water per second. At this time, the water rolls over the main falls in an unbroken expanse. The dry season may see the falls diminish to just a few narrow cascades, with the spray and mist almost absent and the flow reduced to as little as 12,500 cubic feet per second. At this time it is possible to look into the normally obscured depths of the gorge. The level of the river in the gorge varies by up to 66 feet between maximum flow in April and the end of the dry season in October.

Just below the Boiling Pot, and almost at right angles to the falls, the gorge is spanned by a bridge, one of only five over the Zambezi river, which was completed in April 1905 and was initially intended as a link in Cecil Rhodes' Cape-Cairo railway plan. The bridge is 820 feet long, with a main arch spanning 492 feet, and the top of the bridge is 410 feet above the low-water level of the river. The bridge carries a road and railway linking the towns of Victoria Falls and Livingstone and the road and rail networks of Zambia and Zimbabwe.

Tourism

Before the railway link to Bulawayo was completed in 1905, the falls were not often visited. They were an increasingly popular attraction during British colonial rule of the area and the tourist town of Victoria Falls grew up on the Zimbabwe side. From the late 1960s onwards visitor numbers dropped due to Zimbabwe's "2nd Chimurenga" also known as the Rhodesian Bush War, which sometimes resulted in military incursions into Zambia. The hostilities caused the latter to impose travel restrictions, such as border closures and other security measures, including the stationing of soldiers to restrict access to the gorges and some parts of the falls.

Zimbabwean independence in 1980 brought comparative peace, and the 1980s saw a renewed surge in tourism, and the development of the region as a center for extreme sports played a large role in this. By the end of the 1990s, almost 300,000 people were visiting the falls annually, and this was expected to rise to over a million in the next decade.

The numbers of people visiting the Zimbabwe side of the falls has historically been much higher than the number visiting the Zambia side, due to the greater development of the visitor facilities there. However, the number of tourists visiting Zimbabwe began to decline in the early 2000s as civil unrest brewed surrounding the continuing rule of Robert Mugabe. In 2006, hotel occupancy on the Zimbabwean side hovered at around 30 percent, while the Zambian side was at near-capacity, with rates reaching US \$630 per night. The rapid development has prompted the United Nations to consider revoking the Falls' status as a World Heritage Site. The two countries permit tourists to make day trips from one side to the other without the necessity of obtaining a visa in advance, but visas issued at the border are expensive.

National parks

The falls are part of two, small, national parks, Mosi-oa-Tunya National Park in Zambia and Victoria Falls National Park in Zimbabwe, which contain abundant wildlife including sizable populations of elephants, buffalo, and giraffes. The river at this point also contains a large population of hippos.

Mosi-oa-Tunya national park provides a habitat for two white rhinos. The rhinos are the only white rhinos in Zambia, but are not indigenous, having been imported from South Africa. Within the park is a small cemetery at the site of the original British settlement in the area, Old Drift.

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.

Online

## #229 2018-09-24 18:45:37

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

210) Rubik's Cube

Background

Rubik's cube is a toy puzzle designed by Erno Rubik during the mid-1970s. It is a cube-shaped device made up of smaller cube pieces with six faces having differing colors. The primary method of manufacture involves injection molding of the various component pieces, then subsequent assembly, labeling, and packaging. The cube was extremely popular during the 1980s, and at its peak between 1980 and 1983, 200 million cubes were sold world wide. Today sales continue to be over 500,000 cubes sold world wide each year.

The Rubik's cube appears to be made up of 26 smaller cubes. In its solved state, it has six faces, each made up of nine small square faces of the same color. While it appears that all of the small faces can be moved, only the corners and edges can actually move. The center cubes are each fixed and only rotate in place. When the cube is taken apart it can be seen that the center cubes are each connected by axles to an inner core. The corners and edges are not fixed to anything. This allows them to move around the center cubes. The cube maintains its shape because the corners and edges hold each other in place and are retained by the center cubes. Each piece has an internal tab that is retained by the center cubes and trapped by the surrounding pieces. These tabs are shaped to fit along a curved track that is created by the backs of the other pieces. The central cubes are fixed with a spring and rivet and retain all the surrounding pieces. The spring exerts just the right pressure to hold all the pieces in place while giving enough flexibility for a smooth and forgiving function.

History

Puzzle makers have been creating problems for people to solve for centuries. Some of the earliest puzzles date back to the time of the ancient Greeks and Romans. The Chinese have a ring puzzle that is thought to have been developed during the second century a.d. This was first described by Italian mathematician Girolamo Carolano (Cardan) in 1550. When the printing press was invented, complete books of mathematical and mechanical problems designed specifically for recreation were circulated.

From these early riddles and word problems, toy puzzles were naturally developed. In 1857, the Irish mathematician Sir William Hamilton invented the Icosian puzzle. Sometime around 1870, the famous 15 Puzzle was introduced, reportedly by Sam Lloyd. This puzzle involved numerical tiles that had to be placed in order and became extremely popular in the early twentieth century. In 1883, French mathematician Edouard Lucas created the Tower of Hanoi puzzle. This puzzle was made up of three pegs and a number of discs with different sizes. The goal was to place the discs on the pegs in the correct order.

There are various puzzles that involve colored square tiles and colored cubes. Some early precursors to the Rubik's cube include devices such as the Katzenjammer and the Mayblox puzzle. The Mayblox puzzle was created by British mathematician Percy MacMahon in the early 1920s. In the 1960s, Parker Bothers introduced another cube puzzle type toy called Instant Insanity. This toy achieved a moderate level of popularity in the United States. The early 1970s brought with it a device called the Pyraminx, which was invented by Uwe Meffert. This toy was a pyramid that had movable pieces that were to be lined up according to color.

Erno Rubik, an architect and professor at the University of Budapest developed the first working prototype of the Rubik's cube in 1974. He received a Hungarian patent in 1975. Apparently, it was also independently designed by Terutoshi Ishige, an engineer from Japan, who received a Japanese patent in 1976. Professor Rubik created the cube as a teaching aid for his students to help them recognize three-dimensional spatial relationships. When he showed the working prototype to his students, it was an immediate hit.

Over the next few years, Rubik worked with a manufacturer to allow production of the cube on a mass scale. After three years of development, the first cubes were available on toy store shelves in Budapest. While the cube remained popular in Hungry, the political atmosphere of the time made it difficult for it to be introduced in the United States. The two men who were most responsible for making the cube an international success were Dr. Laczi Tibor and Tom Kremer of Seven Towns Ltd., London. Seven Towns licensed the Rubik Cube invention from Professor Rubik for worldwide distribution. Dr. Tibor worked within Hungry to convince bureaucrats to allow the technology out of the country. Kremer found a United States toy maker, the Ideal Toy company, who was willing to help market the product. The product was an immediate hit, and during the 1980s, over 200 million cubes were sold. Around 1983, the frenzied popularity of the cube began to wane and sales slowed drastically. It remained in small scale production until Seven Towns took over the marketing, and licensed the Rubik Cube to the Oddzon Company for the United States market in 1995. Since that time sales have steadily increased to over 500,000 units a year.

Design

The most important part in the manufacture of a Rubik's cube is designing the mold for the various pieces. A mold is a cavity carved into steel that has the inverse shape of the part that it will produce. When liquid plastic is put into the mold, it takes on the mold's shape when it cools. The creation of the mold is extremely precise. The cavity is highly polished to remove any flaws on the surface. Any flaw would be reproduced on each of the millions of pieces that the mold will produce. In the manufacture of the cube parts, a two piece mold is typically employed. During production, the two mold pieces are brought together to form the plastic part and then opened to release it. The tool includes ejector pins that release the molded parts from the tools as it opens. All the parts are molded with auto gating tools that automatically remove the parts from the sprue as it is ejected. The molds are also produced with a slight taper, called release angle, which aids in removal. Finally, when molds are designed, they are slightly bigger than the pieces that they ultimately will produce. This is because as the plastics cool, they shrink. Different plastics will have a different shrink rate, and each tool must be specifically designed for the material that will be used.

The commercial cube is composed of six fixed cubes, eight movable cubes on the corners and 12 movable cubes on the edges. Each cube is one of six colors. The Rubik's cube has red, yellow, blue, green, white, and orange colors. In its solved state, each color is on only one face. When the cube is rotated, the edges and corners move and the cube becomes scrambled. The challenge of the puzzle is to restore each cube to its original position. The cube is extremely challenging because there are slightly more than 43 quintillion (4.3 × {10}^{19}) possible arrangements, and only one solution.

The standard Rubik's cube has sides of about 2.2 in (5.7 cm) per square. Various other sizes have also been produced such as a 1.5 in (3.8 cm) mini cube, a 0.8 in (2 cm) key chain micro cube, and a 3.5 in (9 cm) giant cube. While the standard cube is a 3 × 3 × 3 segmentation other types have also been introduced. Some of the more interesting ones include the 2 × 2 × 2 cube, the 4 × 4 × 4 cube (called Rubik's Revenge) and the 5 × 5 × 5 cube. The shape has also been varied and puzzles in the form of a tetrahedral, a pyramid, and an octahedral are among types that were produced. The Rubik's cube also led to the development of game derivatives like the Rubik's cube puzzle and the Rub it cube eraser.

Raw Materials

The individual pieces that make up the Rubik's cube are typically produced from plastic. Plastics are high molecular weight materials that can be produced through various chemical reactions called polymerization. Most of the plastics used in a Rubik's cube are thermoplastics. These compounds are rigid, durable, and can be permanently molded into various shapes. The plastics used in the Rubik's cube are acrylonitrile butadiene styrene (ABS) and nylon. Other plastics that might be used include polypropylene (PP), high impact polystyrene (HIPS), and high density polyethylene (HDPE).

For decorative purposes, a colorant is typically added to the plastic. The pieces of a Rubik's cube are typically black. During production, colored stickers are put on the outside of the cube to denote the color of a side. The plastics that are used during production are supplied to the manufacturer in a pellet form complete with the filler and colorants. These pellets can then be loaded into the molding machines directly.

The Manufacturing

Process

The manufacture of the first Rubik's cube prototypes was by hand. During the late 1970s, methods for mass production were developed and continue to be used today. Typically, production is a step by step process that involves injection molding of the pieces, fitting the pieces together, decorating the Rubik's cube, and putting the finished product in packaging.

Molding

(1) When production is initiated, the plastic pellets are transformed into Rubik's cube parts through injection molding. In this process, the pellets are put into the hopper of an injection molding machine. They are melted when they are passed through a hydraulically controlled screw. As the screw turns, the melted plastic is shuttled through a nozzle and physically forced, or injected, into the mold. Just prior to the arrival of the molten plastic, the two halves of the mold are brought together to create a cavity that has the identical shape of the Rubik's cube part. This could be an edge, a corner, or the center piece. Inside the mold, the plastic is held under pressure for a specific amount of time and then allowed to cool. While cooling, the plastic hardens inside the mold. After enough time passes, the mold halves are opened and the cube pieces are ejected. The mold then closes again and the process begins again. Each time the machine moulds a set of parts is one cycle of the machine. The Rubik's cube cycle time is around 20 seconds.

(2) After the cube parts are ejected from the mold, they are dropped into container bins and hand inspected to ensure that no significantly damaged parts are used. The waste sprue material is set aside to be reused or scrapped. Waste material can be ground up and melted again to make new parts, however reground material can degrade and cause poor quality parts. Rubik's cubes are always made from virgin material and never use reground waste plastic.

Parts assembly

(3) The Rubik's cube parts are taken to an assembly line. In this phase of production, the individual cube pieces are put together. Starting with the nylon core, each ABS center cube is riveted to the core with a spring spacer. The rivet is carefully controlled with a depth stop to ensure the spring is compressed just the right amount. Each center cube has a plastic cover that is glued on to hide the rivet. One of the six center cubes is left until the last part of the assembly. The ABS edges and corner pieces are individually stacked around the core. The cube is built from the bottom up and the last piece to be assembled is the final center cube which is again riveted into the core with a spring spacer and the final cap is glued on.

Labeling

(4) Next, the Rubik's cube faces need to be labeled. The labels are made from sheet polypropylene material that is printed with the colors. The printed sheet PP is then laminated with a clear PP protective covering. The material is then die cut with the labels wound onto rolls. The labels are made with all nine squares of each face exactly aligned. This way the labels can be perfectly aligned when they are applied to the cube.

Packaging

(5) After all the labeling is completed, the cubes are put in their final packaging. This can be a small box that has an instruction booklet included or a plastic blister pack with a cardboard backing. The package serves the dual purpose of protecting the Rubik's cube from damage caused by shipping and advertising the product. The Rubik's cube packages are put into cases and moved to a pallet. The pallets are then loaded on trucks and the products are shipped all over the world.

Quality Control

To ensure that each toy will be a high quality product, quality control inspectors check the product at each phase of production. The incoming plastic pellets are chemically tested to determine whether they meet certain chemical specifications. These include checks on appearance, color, melting point, toxicity, and molecular weight.

The quality of the individual parts are also inspected just after exiting the mold. Since thousands of parts are made daily, a complete inspection would be difficult. Consequently, line inspectors may randomly check the plastic parts at fixed time intervals and check to ensure they meet size, shape, and consistency specifications. This sampling method provides a good indication of the quality of the overall Rubik's cube production run. Things that are looked for include deformed parts, improperly fitted parts and inappropriate labeling. While visual inspection is the primary test method employed, more rigorous measurements may also be performed. Measuring equipment is used to check the length, width, and thickness of each part. Typically, devices such as a vernier caliper, a micrometer, or a microscope are used. Just prior to putting a cube in the packaging it may be twisted to ensure that it holds together and is in proper working order. This can be done by hand or by a turning machine. If a toy is found to be defective it is placed aside to be reworked later.

The Future

While the extreme popularity of the Rubik's cube subsided around 1984. it has recently made a significant come back. This has been a result of impressive marketing efforts by Seven Towns. In the future, this marketing effort should continue to increase sales of the Rubik's cube. In addition to the cube, other derivative puzzles have been introduced including the Rubik's snake, Rubik's triamid, and the Rubik's magic folding puzzle. It is expected that new variants will also be introduced in the near future.

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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## #230 2018-09-25 00:12:53

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

211) Mutilated Chessboard Problem

A regular chessboard is an 8×8 grid (having 64 squares). If you are given 32 dominos where each domino can cover two squares on the chessboard, you can cover all the squares of the chessboard.

Someone mutilated the chessboard and removed the upper left and lower right corners. The mutilated board has 62 squares.  You are given 31 dominos. Can you tile the mutilated chessboard with the 31 dominos?

Let students try to find a way to tile the mutilated board. After a while some of them will claim that it can’t be done. The algorithms we have sketched so far describe how something can be done. If the board can indeed not be tiled, how do we proceed?

One could write a program that systematically generates all possible ways to tile the mutilated board. The number of ways the mutilated chess board can be tiled is finite, but it is a large number.  If the program fails to find a possible tiling, we can conclude none exists.

However, we can show that no tiling exists by a direct proof. This means that a program checking all possible tilings would not find one.

Here is the argument:

A tile placed on the chessboard will always cover one white square and one black square. Therefore, a collection of tiles placed on the board will cover equal numbers squares of each color. The mutilated board has two white squares removed and it thus has 30 white squares and 32 black squares.  If every tile covers one black and one white square and we have more white squares, we can conclude that the mutilated board cannot be tiled.  If the two black corners are removed instead, then 32 white squares and 30 black squares remain, so it is again impossible.

We can tile a mutilated board only if one white and one black corner are removed (but the problem said corners on opposite sides of a diagonal were removed).

The mutilated chessboard problem is a tiling puzzle proposed by philosopher Max Black in his book Critical Thinking (1946). It was later discussed bySolomon W. Golomb (1954), Gamow & Stern (1958) and by Martin Gardner in his Scientific American column "Mathematical Games". The problem is as follows:

Suppose a standard 8×8 chessboard has two diagonally opposite corners removed, leaving 62 squares. Is it possible to place 31 dominoes of size 2×1 so as to cover all of these squares?

Most considerations of this problem in literature provide solutions "in the conceptual sense" without proofs. John McCarthy proposed it as a hard problem for automated proof systems. In fact, its solution using the resolution system of inference is exponentially hard.

Solution

The puzzle is impossible to complete. A domino placed on the chessboard will always cover one white square and one black square. Therefore, a collection of dominoes placed on the board will cover an equal numbers of squares of each color. If the two white corners are removed from the board then 30 white squares and 32 black squares remain to be covered by dominoes, so this is impossible. If the two black corners are removed instead, then 32 white squares and 30 black squares remain, so it is again impossible.

Gomory's theorem

The same impossibility proof shows that no domino tiling exists whenever any two white squares are removed from the chessboard. However, if two squares of opposite colors are removed, then it is always possible to tile the remaining board with dominoes; this result is called Gomory's theorem, and is named after mathematician Ralph E. Gomory, whose proof was published in 1973. Gomory's theorem can be proven using a Hamiltonian cycle of the grid graph formed by the chessboard squares; the removal of two oppositely colored squares splits this cycle into two paths with an even number of squares each, both of which are easy to partition into dominoes.

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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## #231 2018-09-25 16:10:15

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

212) Watermelon

Watermelon, (Citrullus lanatus), succulent fruit and vinelike plant of the gourd family (Cucurbitaceae), native to tropical Africa and cultivated around the world. The fruit contains vitamin A and some vitamin C and is usually eaten raw. The rind is sometimes preserved as a pickle.

The history of watermelons is a long one. There is a Sanskrit word for watermelon, and fruits are depicted in early Egyptian art, indicating an antiquity in agriculture of more than 4,000 years. Domestication and selective breeding have resulted in intensely sweet large fruits with tender flesh and fewer seeds. Some modern “seedless” cultivars have almost no viable seeds.

The watermelon plant is an annual that grows well in hot climates. Its vines grow on the ground and have branched tendrils, deeply cut leaves, and flowers borne singly in the axil of a leaf (e.g., where the leaf joins the stem). Each light yellow flower is either male or female, producing only pollen or fruit, respectively.

The fruit is a type of berry known botanically as a pepo. The sweet juicy flesh may be reddish, white, or yellow; flesh colour, shape of the fruit, and thickness of the rind depend on the variety. Watermelon weight varies from 1 to 2 kg (2.5 to 5 pounds) to 20 kg (44 pounds) or more. The number of fruits per vine varies from 2 to 15.

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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## #232 2018-09-26 00:15:37

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

213) Wheat

Wheat, any of several species of cereal grasses of the genus Triticum (family Poaceae) and their edible grains. Wheat is one of the oldest and most important of the cereal crops. Of the thousands of varieties known, the most important are common wheat (Triticum aestivum), used to make bread; durum wheat (T. durum), used in making pasta (alimentary pastes) such as spaghetti and macaroni; and club wheat (T. compactum), a softer type, used for cake, crackers, cookies, pastries, and flours. Additionally, some wheat is used by industry for the production of starch, paste, malt, dextrose, gluten, alcohol, and other products
.
The wheat plant has long slender leaves and stems that are hollow in most varieties. The inflorescences are composed of varying numbers of minute flowers, ranging from 20 to 100. The flowers are borne in groups of two to six in structures known as spikelets, which later serve to house the subsequent two or three grains produced by the flowers. Though grown under a wide range of climates and soils, wheat is best adapted to temperate regions with rainfall between 30 and 90 cm (12 and 36 inches). Winter and spring wheat are the two major types of the crop, with the severity of the winter determining whether a winter or spring type is cultivated. Winter wheat is always sown in the fall; spring wheat is generally sown in the spring but can be sown in the fall where winters are mild.

The nutritional composition of the wheat grain varies somewhat with differences in climate and soil. On an average, the kernel contains 12 percent water, 70 percent carbohydrates, 12 percent protein, 2 percent fat, 1.8 percent minerals, and 2.2 percent crude fibres. Thiamin, riboflavin, niacin, and small amounts of vitamin A are present, but the milling processes removes most of those nutrients with the bran and germ.

Most wheat used for food requires processing. The grain is cleaned and then conditioned by the addition of water so that the kernel breaks up properly. In milling, the grain is cracked and then passed through a series of rollers. As the smaller particles are sifted out, the coarser particles pass to other rollers for further reduction. About 72 percent of the milled grain is recovered as white flour. Flour made from the whole kernel is called graham flour and becomes rancid with prolonged storage because of the germ-oil content retained. White flour, which does not contain the germ, preserves longer. Inferior and surplus wheats and various milling by-products are used for livestock feeds.

The greatest portion of the wheat flour produced is used for breadmaking. Wheats grown in dry climates are generally hard types, having protein content of 11–15 percent and strong gluten (elastic protein). The hard type produces flour best suited for breadmaking. The wheats of humid areas are softer, with protein content of about 8–10 percent and weak gluten. The softer type of wheat produces flour suitable for cakes, crackers, cookies, and pastries and household flours. Durum wheat semolina(from the endosperm) is used for making pastas, or alimentary pastes.

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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## #233 2018-09-27 00:15:37

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

214) Galvanizing

Galvanizing, protection of iron or steel against exposure to the atmosphere and consequent rusting by application of a zinc coating. Properly applied, galvanizing may protect from atmospheric corrosion for 15 to 30 years or more. As discontinuities or porosity develop in the coating, galvanic or electrolytic action ensues; the iron or steel, however, is protected by sacrificial corrosion, a phenomenon in which, as long as the zinc and the iron are in contact, atmospheric oxidation spares the iron and affects the zinc.

Zinc may be applied by two general methods: hot dipping and electrolytic deposition.

In hot-dip processes, cleaned iron or steel, usually in sheet form, is passed through a flux such as a zinc–ammonium chloride and guided through a bath of molten zinc. In wire galvanizing, the wire is drawn through successive pickling, annealing, and washing operations. It is dried before passing into the galvanizing pan and is drawn out through wipers of charcoal, coke, sand, or asbestos.

In one hot-dip process, intermetallic compounds of iron and zinc are formed on the surface of the steel or iron being treated by heating it in the presence of finely divided zinc below the melting point of the zinc. In another, molten zinc is applied in a fine spray to the surface of the cleaned iron or steel; the zinc adheres tightly to the surface.

In electrolytic deposition, or electroplating, a pure coating of completely controlled thickness of zinc may be applied without heat. More care is required, and for articles that must be made watertight, the electrolytic processes do not have the soldering effect of the hot processes. The zinc coating, however, has greater adherence than that formed in the hot-dip process.

Sherardizing, means of forming a uniform, corrosion-resistant coating of zinc on the surface of iron or steel objects. The process, practiced since about 1900, is named for its English inventor Sherard O. Cowper-Coles. The object is heated in a sealed container with finely divided zinc to a temperature below the point at which zinc melts. The two metals amalgamate, forming alloys of zinc and iron and an external layer of pure zinc in an adherent coating that resists corrosion and also makes an excellent base for paint.

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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## #234 2018-09-28 00:49:09

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

215) Neuron

Neurons are the basic working unit of the nervous system , sending, receiving, and storing signals through a unique blend of electricity and chemistry. The human brain has more than 100 billion neurons.

Neurons that receive information and transmit it to the spinal cord or brain are classified as afferent or sensory; those that carry information from the brain or spinal cord to the muscles or glands are classified as efferent or motor. The third type of neuron connects the vast network of neurons and may be referred to as interneuron, association neuron, internuncial neuron, connector neuron, and adjustor neuron.

Although neurons come in many sizes and shapes, they all have certain features in common. Each neuron has a cell body where the components necessary to keep the neuron alive are centered. Additionally, each neuron has two types of fiber. The axon is a large tentacle and is often quite long. (For example, the axons connecting the toes with the spinal cord are more than a meter in length.) The function of the axon is to conduct nerve impulses to other neurons or to muscles and glands. The signals transmitted by the axon are received by other neurons through the second type of fiber, the dendrites. The dendrites are usually relatively short and have many branches to receive stimulation from other neurons. In many cases, the axon (but not the cell body or the dendrites) has a white, fatty covering called the myelin sheath. This covering is believed to increase the speed with which nerve impulses are sent down the axon.

An unstimulated neuron has a negative electrical charge. The introduction of a stimulus makes the charge a little less negative until a critical point—the threshold—is reached. Then the membrane surrounding the neuron changes, opening channels briefly to allowing positively charged sodium ions to enter the cell. Thus, the inside of the neuron becomes positive in charge for a millisecond (thousandth of a second) or so. This brief change in electrical charge is the nerve impulse, or spike, after which the neuron is restored to its original resting charge.

This weak electrical impulse travels down the axon to the synapse . The synapse or synaptic gap forms the connection between neurons, and is actually a place where the neurons almost touch , but are separated by a gap no wider than a few billionths of an inch. At the synapses, information is passed from one neuron to another by chemicals known as neurotransmitters. The neurotransmitter then combines with specialized receptor molecules of the receiving cell.

Neurotransmitters either excite the receiving cell (that is, increase its tendency to fire nerve impulses) or inhibit it (decrease its tendency to fire impulses), and often both actions are required to accomplish the desired response. For example, the neurons controlling the muscles that pull your arm down (the triceps) must be inhibited when you are trying to reach up to your nose (biceps excited); if they are not, you will have difficulty bending your arm.

Physiological psychologists are interested in the involvement of the nervous system in behavior and experience. The chemistry and operation of the nervous system is a key component in the complex human puzzle. A number of chemical substances act as neurotransmitters at synapses in the nervous system and at the junction between nerves and muscles. These include acetylcholine, dopamine, epinephrine (adrenalin), and neuropeptides (enkephalins, endorphins, etc.). A decrease in acetylocholine has been noted in Alzheimer's disease which causes deterioration of the thought processes; shortage of dopamine has been linked to Parkinson's disease , whereas elevated dopamine has been observed in schizophrenics.

Drugs that affect behavior and experience—the psychoactive drugs —generally work on the nervous system by influencing the flow of information across synapses. For instance, they may interfere with one or several of the stages in synaptic transmission, or they may have actions like the natural neurotransmitters and excite or inhibit receiving cells. This is also true of the drugs which are used in the treatment of certain psychological disorders.

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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## #235 2018-09-29 00:22:29

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

216) Silicon Dioxide

Silicon dioxide, also known as silica, is the most abundant mineral in the Earth's crust, and it is found on every continent in forms ranging from fine powders to giant rock crystals. In addition to having a natural beauty in its raw mineral form, the substance has useful properties with important applications in everyday life.

Features

A crystalline solid at normal temperatures, pure silicon dioxide is white in color and has a density of 2.2 grams per cubic centimeter. It is composed of one atom of silicon and two atoms of oxygen; the atoms are bound together tightly making it resistant to many harsh chemicals. In nature, it takes the form of sand or quartz crystals, and is relatively hard compared to most minerals. Silicon dioxide is highly resistant to heat, with a melting point of 1,650 degrees Celsius (3,000 degrees Fahrenheit).

Types

Although sand and quartz crystals may appear different, they are both made primarily of silicon dioxide. The chemical makeup of these types is exactly the same, and the properties are generally the same, but they were formed under different conditions. Sand particles are very small, but tough and hard. Some quartz crystals have a milky-white appearance. So-called milky quartz is quite abundant, so it is common to find large rocks of this type of quartz. Mineral impurities can turn quartz purple, light pink, or other colors, resulting in precious or semi-precious stones such as amethyst, citrine, rose quartz, and smoky quartz.

Function

Silicon dioxide is used in a number of different ways. One of the most common uses is to make glass, which is superheated and pressurized silicon dioxide. It is also manufactured for use in toothpaste. Because of its hardness, it helps to scrub away plaque on teeth. It is also a major ingredient in cement and used as a pesticide. Silica gel is a food additive and desiccant that helps absorb water.

Warning

While silicon dioxide is for the most part harmless, it poses health risks when inhaled. In powder form, small particles of the mineral can lodge in the esophagus and the lungs. It does not dissolve in the body over time, so it builds up, irritating sensitive tissues. One such condition is called silicosis, which causes shortness of breath, fever, and coughing and causes the skin to turn blue. Other conditions include bronchitis and, rarely, cancer.

Geography

Silicon dioxide is found just about everywhere in the world, as it is the most common mineral in the crust. On the surface of the earth, it is prevalent in rocky or mountainous regions. It is also present in the form of sand in the deserts and coasts of the world.

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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## #236 2018-09-30 00:20:56

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

217) Rice

Rice, cereal grain (Oryza sativa) of the grass family (Graminae), probably native to the deltas of the great Asian rivers—the Ganges, the Chang (Yangtze), and the Tigris and Euphrates. The plant is an annual, from 2 to 6 ft (61–183 cm) tall, with a round, jointed stem; long, pointed leaves; and edible seeds borne in a dense head on separate stalks. Wild rice is obtained from a different grass plant.

Cultivation and Harvesting

Methods of growing differ greatly in different localities, but in most Asian countries the traditional hand methods of cultivating and harvesting rice are still practiced. The fields are prepared by plowing (typically with simple plows drawn by water buffalo, but also with motorized tillers), fertilizing (usually with dung or sewage), and smoothing (by dragging a log over them). The seedlings are started in seedling beds and, after 30 to 50 days, are transplanted by hand to the fields, which have been flooded by rain or river water. During the growing season, irrigation is maintained by dike-controlled canals or by hand watering. The fields are allowed to drain before cutting.

Rice when it is still covered by the brown hull is known as paddy; rice fields are also called paddy fields or rice paddies. Before marketing, the rice is threshed to loosen the hulls—mainly by flailing, treading, or working in a mortar—and winnowed free of chaff by tossing it in the air above a sheet or mat.

In the United States and in many parts of Europe, rice cultivation has undergone the same mechanization at all stages of cultivation and harvesting as have other grain crops. Rice was introduced to the American colonies in the mid-17th cent. and soon became an important crop. Although U.S. production is less than that of wheat and corn, rice is grown in excess of domestic consumption and has been exported, mainly to Europe and South America. Chief growing areas of the United States are in California, Mississippi, Texas, Arkansas, and Louisiana. The world's leading rice-producing countries are China, India, Indonesia, Bangladesh, and Thailand. Total annual world production is more than half a billion metric tons.

Importance of Rice as a Food

It has been estimated that half the world's population subsists wholly or partially on rice. Ninety percent of the world crop is grown and consumed in Asia. American consumption, although increasing, is still only about 25 lb (11 kg) per person annually, as compared with 200 to 400 lb (90–181 kg) per person in parts of Asia. Rice is the only major cereal crop that is primarily consumed by humans directly as harvested, and only wheat and corn are produced in comparable quantity. Plant breeders at the International Rice Research Institute in the Philippines, attempting to keep pace with demand from a burgeoning world population, have repeatedly developed improved varieties of "miracle rice" that allow farmers to increase crop yields substantially. Other varieties with specialized characteristics, such as one that tolerates prolonged flooding, also have been developed. Studies have shown that rice yields are adversely affected by warmer nighttime temperatures, leading to concerns about the effects that global warming may have on rice crops.

Brown rice has a greater food value than white, since the outer brown coatings contain the proteins and minerals; the white endosperm is chiefly carbohydrate. As a food rice is low in fat and (compared with other cereal grains) in protein. The miracle rices have grains richer in protein than the old varieties. In the East, rice is eaten with foods and sauces made from the soybean, which supply lacking elements and prevent deficiency diseases. Elsewhere, especially in the United States, rice processing techniques have produced breakfast and snack foods for retail markets. Deficient in gluten, rice cannot be used to make bread unless its flour is mixed with flour made from other grains.

Other Uses

For feeding domestic animals, the bran, meal, and chopped straw are useful, especially when mixed with the polishings or given with skim milk. The polishings are also an important source of furfural and other chemurgic products. The straw, which is soft and fine, is plaited in East Asia for hats and shoes, and the hulls supply mattress filling and packing material. Laundry starch is manufactured from the broken grain, which is also used by distillers. A distilled liquor called arrack is sometimes prepared from a rice infusion, and in Japan the beverage sake is brewed from rice. Rice paper is made from a plant of the ginseng family.

History of Rice Cultivation

Rice has been cultivated in China since ancient times and was introduced to India before the time of the Greeks. Chinese records of rice cultivation go back 4,000 years. In classical Chinese the words for agriculture and for rice culture are synonymous, indicating that rice was already the staple crop at the time the language was taking form. In several Asian languages the words for rice and food are identical. Many ceremonies have arisen in connection with planting and harvesting rice, and the grain and the plant are traditional motifs in Oriental art. Thousands of rice strains are now known, both cultivated and escaped, and the original form is unknown.

Rice cultivation has been carried into all regions having the necessary warmth and abundant moisture favorable to its growth, mainly subtropical rather than hot or cold. The crop was common in West Africa by the end of the 17th cent. It is thought that slaves from that area who were transported to the Carolinas in the mid-18th cent. introduced the complex agricultural technology, thus playing a key part in the establishment of American rice cultivation. Their labor then insured a flourishing rice industry. Modern culture makes use of irrigation, and a few varieties of rice may be grown with only a moderate supply of water.

Classification

Rice is classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.

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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## #237 2018-10-01 01:08:56

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

218) Argon

Argon (Ar), chemical element, inert gas of Group 18 (noble gases) of the periodic table, terrestrially the most abundant and industrially the most frequently used of the noble gases. Colourless, odourless, and tasteless, argon gas was isolated (1894) from air by the British scientists Lord Rayleighand Sir William Ramsay. Henry Cavendish, while investigating atmospheric nitrogen (“phlogisticated air”), had concluded in 1785 that not more than 1/120 part of the nitrogen might be some inert constituent. His work was forgotten until Lord Rayleigh, more than a century later, found that nitrogen prepared by removing oxygen from air is always about 0.5 percent more dense than nitrogen derived from chemical sources such as ammonia. The heavier gas remaining after both oxygen and nitrogen had been removed from air was the first of the noble gases to be discovered on Earth and was named after the Greek word argos, “lazy,” because of its chemical inertness. (Heliumhad been spectroscopically detected in the Sun in 1868.)

In cosmic abundance, argon ranks approximately 12th among the chemical elements. Argon constitutes 1.288 percent of the atmosphere by weight and 0.934 percent by volume and is found occluded in rocks. Although the stable isotopes argon-36 and argon-38 make up all but a trace of this element in the universe, the third stable isotope, argon-40, makes up 99.60 percent of the argon found on Earth. (Argon-36 and argon-38 make up 0.34 and 0.06 percent of Earth’s argon, respectively.) A major portion of terrestrial argon has been produced, since the Earth’s formation, in potassium-containing minerals by decay of the rare, naturally radioactive isotope potassium-40. The gas slowly leaks into the atmosphere from the rocks in which it is still being formed. The production of argon-40 from potassium-40 decay is utilized as a means of determining Earth’s age (potassium-argon dating).

Argon is isolated on a large scale by the fractional distillation of liquid air. It is used in gas-filled electric light bulbs, radio tubes, and Geiger counters. It also is widely utilized as an inert atmosphere for arc-welding metals, such as aluminum and stainless steel; for the production and fabrication of metals, such as titanium, zirconium, and uranium; and for growing crystals of semiconductors, such as silicon and germanium.

Argon gas condenses to a colourless liquid at −185.8° C (−302.4° F) and to a crystalline solid at −189.4° C (−308.9° F). The gas cannot be liquefied by pressure above a temperature of −122.3° C (−188.1° F), and at this point a pressure of at least 48 atmospheres is required to make it liquefy. At 12° C (53.6° F), 3.94 volumes of argon gas dissolve in 100 volumes of water. An electric discharge through argon at low pressure appears pale red and at high pressure, steely blue.

The outermost (valence) shell of argon has eight electrons, making it exceedingly stable and, thus, chemically inert. Argon atoms do not combine with one another; nor have they been observed to combine chemically with atoms of any other element. Argon atoms have been trapped mechanically in cagelike cavities among molecules of other substances, as in crystals of ice or the organic compound hydroquinone (called argon clathrates).

atomic number : 18
atomic weight : 39.948
melting point : −189.2° C (−308.6° F)
boiling point : −185.7° C (−302.3° F)
density (1 atm, 0° C)    : 1.784 g/litre
oxidation state : 0

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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## #238 2018-10-03 00:06:26

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

219) Caterpillar Inc.

Caterpillar Inc., formerly (1925–86) Caterpillar Tractor Company, major American manufacturer of earth-moving, construction, agricultural, and materials-handling equipment. Its headquarters are in Peoria, Illinois.

The Caterpillar Tractor Company had its origins in two California-based agricultural-equipment companies headed respectively by Charles Holt and Daniel Best in the late 19th century. By the 1890s both firms were making steam-driven wheeled tractors and harvesters to replace horse-drawn harvesting machines on large farms. Benjamin Holt, one of several brothers in the Holt Manufacturing Company, invented the familiar “caterpillar” tractor in about 1906. The tractor ran on continuous metal-belted tracks instead of wheels, and the tracks kept the heavy vehicle from sinking in mud or dirt. The new machines were immediately successful as all-terrain haulers and graders, and the Holts opened a new manufacturing plant in Peoria, Illinois, the site of the firm’s future headquarters. During World War I British and American forces successfully used such treads on their armoured tanks, and the Holt firm prospered further by making thousands of (gasoline-powered) tractors that hauled supplies and ammunition for the Allies.

In 1925 the Holt Manufacturing Company merged with another tractor manufacturer, the C.L. Best Tractor Company, which had been founded by a son of Daniel Best. The new company was incorporated as the Caterpillar Tractor Company, and its headquarters moved to Peoria.

The company stayed afloat during the Great Depression partly by selling tractors and combines to the Soviet Union to facilitate that country’s first Five-Year Plan (1929–33). In 1931 Caterpillar perfected a tractor driven by a diesel engine rather than a gasoline one, and diesel engines soon became standard for all types of heavy-duty vehicles. During World War II, Caterpillar made the diesel engines that powered the Sherman (M4) tank. The firm’s tractor and truck sales skyrocketed after the war, when these machines were needed for reconstruction projects and the building of roads and dams in countries around the world. The name Caterpillar became practically synonymous with bulldozers during this period. The company experienced a series of labour conflicts with its unionized American workforce beginning in 1961, but its growth has continued. The firm adopted its current name in 1986.

Caterpillar Inc. now makes tractors, trucks, loaders, excavators, graders, scrapers, and other heavy machines used in agriculture, construction, mining, logging, and industrial warehousing. The company also makes diesel and gasoline engines for use in trucks, locomotives, ships and boats, and electricity-generating systems. More than one-half of the company’s sales are to customers outside of the United States.

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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## #239 2018-10-03 16:40:47

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

220) Pea

Pea, (Pisum sativum), also called garden pea, herbaceous annual plant in the family Fabaceae, grown virtually worldwide for its edible seeds. Peas can be bought fresh, canned, or frozen, and dried peas are commonly used in soups. Some varieties, including sugar peas and snow peas, produce pods that are edible and are eaten raw or cooked like green beans; they are popular in East Asian cuisines. The plants are fairly easy to grow, and the seeds are a good source of protein and dietary fibre.

While the origins of domesticated peas have not been definitely determined, the pea is one of the oldest cultivated crops. The wild plant is native to the Mediterranean region, and ancient remains dating to the late Neolithic Period have been found in the Middle East. European colonization introduced the crop to the New World and other regions throughout the globe. In the mid-1800s, peas in a monastery garden in Austria were famously used by the monk Gregor Mendel in his pioneering studies of the nature of heredity.

The pea plant is a hardy leafy annual with hollow trailing or climbing stems that reach up to 1.8 metres (6 feet) in length. The stems feature terminal tendrils that facilitate climbing and bear compound leaves with three pairs of leaflets. The reddish purple, pink, or white flowers, growing two to three per stalk, are butterfly-shaped. The fruit is a pod that grows to 10 cm (4 inches) long, splitting in half when ripe. Inside the pod, 5 to 10 seeds are attached by short stalks. The seeds are green, yellow, white, or variegated.

In the home garden, peas should be planted in fertile well-drained soil in an unshaded spot. The cool part of the growing season favours growth and development, and peas are sometimes grown in the winter and early spring in warmer climates. The most common diseases that affect peas are root rot, powdery mildew, and several viral diseases. Widely grown varieties include dwarf, half-dwarf, trailing, smooth-seeded, and wrinkled-seeded. Canning and freezing processes vary according to variety, plant size, shape and size of the pods, and period of maturation.

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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## #240 2018-10-05 00:27:51

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

221) Anesthesia

Anesthesia is the term given to the loss of feeling or sensation. In medical terms, it is the method of decreasing sensitivity to pain in a patient so that a medical procedure may be performed. Anesthesia may be accomplished without the loss of consciousness, or with partial or total loss of consciousness.

There are two kinds of anesthesia: general anesthesia, which affects the entire body and causes a loss of consciousness, and local anesthesia, in which only the area being operated on is affected. With local anesthesia, the patient may be conscious during the course of the operation or given a sedative, a drug that induces drowsiness or sleep.

Anesthesiology is the branch of medicine dealing with anesthesia and anesthetics. Anesthetics can be administered by doctors (called anesthesiologists) or by specially trained nurses (called CRNAs, certified registered nurse anesthetists) working under a doctor's guidance. The development of modern anesthesia has made possible complex operations such as open heart surgery.

History of anesthesia

Methods for lessening the sensation of pain during surgery date back to ancient times. Before the discovery of substances that produced general anesthesia, patients needing surgery for illness or injury had to rely on alcohol, opium (a natural narcotic derived from the opium poppy), or fumes from an anesthetic-soaked cloth to deaden the pain of the surgeon's knife. Often a group of men held the patient down during an operation in case the opium or alcohol wore off. Under these conditions, many patients died of shock from the pain of the operation itself.

Nitrous oxide, ether, and chloroform. The gases nitrous oxide, ether, and chloroform were first used as anesthetics in the nineteenth century, ushering in the modern era of anesthesia. Nitrous oxide, or laughing gas, was discovered as an anesthetic by English chemist Humphry Davy (1791–1867) in 1799. Davy's finding was ignored until the next century, when Connecticut dentist Horace Wells (1815–1848) began to experiment using nitrous oxide as an anesthetic during tooth surgery. In 1845, he attempted to demonstrate its pain-blocking qualities to a public audience but was unsuccessful when he began to pull a tooth before the patient was fully anesthetized. The patient cried out in pain and, as a result, another 20 years passed before nitrous oxide was accepted for use as an anesthetic.

The first use of ether as an anesthetic during an operation was claimed by surgeon Crawford W. Long (1815–1878) of Georgia in 1842. The operation, however, was unrecorded, so official credit went instead to Massachusetts dentist William Morton (1819–1868) for his 1846 public demonstration of an operation using ether performed in a Boston hospital. While Morton administered the gas to the patient through an inhaling device, John C. Warren (1778–1856) removed a neck tumor without the patient feeling any pain. Following this landmark use of ether as an anesthetic, general anesthesia began to be practiced all over the United States and Europe.
Chloroform was introduced as a surgical anesthetic by Scottish obstetrician James Young Simpson (1811–1870) in 1847. After first experimenting with ether, Simpson searched for an anesthetic that would make childbirth less painful for women. Although it eased the pain of labor, chloroform had higher risks than those associated with ether. Neither ether nor chloroform are used in surgery today.

Emergence of anesthesiology

Anesthesiology was slow to develop as a medical specialty. By the end of the nineteenth century, ether—which was considered safer than chloroform—was administered by persons with little medical experience. Nurses were eventually assigned to this task, becoming the first anesthetists at the turn of the century.
As surgical techniques progressed in the twentieth century, there was a corresponding demand for specialists in the area of anesthesia. To meet this need, the American Society of Anesthetists was formed in 1931, followed by the American Board of Anesthesiology in 1937, which certified anesthetists as specialists. In the next 50 years, over 13,000 physicians and nurses were certified as specialists in the field of anesthesiology.

Types of anesthesia

Modern anesthesia uses both chemical agents and nondrug methods as preparation for medical procedures. Chemical agents are drugs that can be administered by mouth, by injection into muscle or under the skin with a needle, intravenously (by needle into a vein), or with a gas mask for inhalation. They also come in forms such as creams, gels, or liquids that can be applied or sprayed directly onto the area being treated. Nondrug methods include acupuncture (the insertion of fine needles into the body to relieve pain) and the Lamaze method of natural childbirth, which involves breathing, focusing, and relaxation techniques to limit pain during labor and delivery.

General anesthesia. General anesthesia consists of placing the patient in an initial state of unconsciousness, keeping the patient unconscious while surgery is being performed, and bringing the patient back to consciousness after the surgery is over.

A drug commonly used to bring about unconsciousness is thiopentone sodium, a drug that acts within 30 seconds after being injected intravenously. The unconscious state is then maintained with other drugs. Inhaled anesthetics (gases or liquids that change readily into gases) are also used to bring about and maintain unconsciousness. These include nitrous oxide, halothane, enflurane, and isoflurane. A combination of barbiturates, nitrous oxide, narcotics (drugs that cause sleep and relieve pain), and muscle relaxants is often used throughout the course of an operation. This is usually safer than giving a very large dose of a single drug that can have serious side effects.

During surgery, the anesthesiologist or anesthetist keeps a constant watch on the patient's blood pressure, breathing, and heartbeat, and adjusts the levels of anesthetics being administered as necessary.

Local anesthesia. Local anesthesia is accomplished using drugs that temporarily block the sensation of pain in a certain area of the body while the patient remains awake. These drugs act by preventing nerve cells from sending pain messages to the brain. Some local anesthetics are benzocaine, lidocaine, and procaine (Novocain). They are used in dental and surgical procedures, medical examinations, and for relieving minor symptoms such as itching or the pain of toothaches or hemorrhoids. Spinal anesthesia, sometimes called a saddleblock, is achieved by injecting anesthetics with a fine needle into the spine, which numbs the abdomen, lower back and legs. It is sometimes used in such procedures as childbirth and hip and knee surgery.

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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## #241 2018-10-07 00:39:52

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

222) Chameleon

Chameleon, (family Chamaeleonidae), any of a group of primarily arboreal (tree-dwelling) Old World lizards best known for their ability to change body colour. Other characteristics of chameleons include zygodactylous feet (with toes fused into opposed bundles of two and three), acrodont dentition (with the teeth attached to the edge of the jaw), eyes that move independently, atrophied venom glands that produce harmless trace amounts of venom, and a long, slender projectile tongue. The name has also been applied to the false chameleon, or anole, a New World lizard of the genus Anolis (family Iguanidae).

Four genera of true chameleons have been described: Bradypodion, Brookesia, Chamaeleo, and Rhampholeon. Two additional genera (Calumma and Furcifer) are recognized by some researchers. More than 150 species are currently known, and additional ones remain to be named. About half of the species occur only in Madagascar, whereas others occur mostly in sub-Saharan Africa. Two species occur in Asia; one is native to southern India and Sri Lanka (Chamaeleo zeylanicus), and the other (the European chameleon, C. chamaeleon) is found from the Middle East to southern Spain. The most familiar chameleons belong to the genus Chamaeleo, and these have prehensile tails that wrap in a coil-like fashion around limbs to maintain balance. In contrast, most species of pigmy chameleons in the genera Brookesia (Madagascar) and Rhampholeon (Africa) have short stubby tails that are not prehensile; however, pigmy chameleons in Bradypodion have longer tails that are prehensile.

The longest chameleon in the world is Parson’s chameleon (Calumma parsonii), which may grow up to 69.5 cm (about 27 inches) long. On the other hand, the world’s shortest chameleon, Brookesia micra, has a maximum length of 29 mm (about 1 inch). Most chameleons, however, are 17–25 cm (7–10 inches) long. The body is laterally compressed, the tail is sometimes curled, and the bulged eyes move independently of one another. Also, some chameleons possess helmet-shaped heads.

Some species have conspicuous head ornamentation that may include as many as three long horns projecting forward. Such features are either exclusive to or better developed in males, and at least some of these features are related to territorial defense. A defending male responds to an invader by expanding the body, puffing out the throat, and elevating or waving special head flaps. If this display fails to intimidate the intruder, the defender charges and snaps his jaws. The differences in appearance between the genders result from a process known as male/female selection, in which individual males with extreme ornamentation have a higher breeding success; they pass on the genes that form the basis for these features at a faster rate than those individuals lacking ornamentation.

Each species is capable of undergoing a particular range of colour change. The mechanism involves the dispersal or concentration of pigment granules (melanophore cells) in the cells that contain them. These cells are under the control of the autonomic nervous system. Colour change is determined by such environmental factors as light and temperature as well as by emotions—such as fright and those associated with victory or defeat in battle with another chameleon. Many chameleons can assume a green, yellow, cream, or dark brown coloration. Frequently, this occurs with lighter or darker spots on the background colour of the body. Some of the most striking colours appear in males during mating. Some achieve colour patterns that are so vivid and complex that it is hard to imagine that they serve any natural purpose. It is a popular misconception that the chameleon changes its colour to match that of the background.

The chameleon’s specialized vision and a specialized tongue-projection system permit the capture of insects and even birds from a distance. The chameleon’s eyes are very good at detecting and regulating light. The lens of a chameleon’s eye is capable of focusing extremely rapidly, and it can enlarge visual images much like a telephoto lens. Although many other lizards also use the tongue to capture prey, most can expel it only a short distance. In contrast, chameleons can launch their tongues at great speed to a distance of more than twice their body length, and they can strike and capture their prey with great accuracy. The hydrostatic force resulting from rapid contraction of a ringed accelerator muscle is used to project the tongue toward the chameleon’s prey; a sticky tongue tip adheres to the victim’s body; and strong retractor muscles pull the tongue and prey back into the mouth.

Most species are egg layers. Typically, females descend from their shrub or tree to bury between 2 and 40 eggs in the soil or rotting logs, and incubation lasts about three months. Some species, such as the large Jackson’s chameleon (C. jacksonii), bear their young live; however, they do this without a placenta between the mother and the developing young. All nutrients necessary for development are contained within the egg itself, which simply develops within the female’s oviduct minus a shell.

In addition, the Madagascan chameleon, F. labordi, has been widely acknowledged as the vertebrate with the shortest life span. The eggs of F. labordi hatch in November, and the young chameleons grow extremely fast; they mature to adulthood just two months later. After an intense competition for mates, eggs are laid in February, and the entire adult population perishes.

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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## #242 2018-10-09 00:32:36

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

223) Polyethylene terephthalate

Polyethylene terephthalate (PET or PETE), a strong, stiff synthetic fibre and resin, and a member of the polyester family of polymers. PET is spun into fibres for permanent-press fabrics, blow-molded into disposable beverage bottles, and extruded into photographic film and magnetic recording tape.

PET is produced by the polymerization of ethylene glycol and terephthalic acid. Ethylene glycol is a colourless liquid obtained from ethylene, and terephthalic acid is a crystalline solid obtained from xylene. When heated together under the influence of chemical catalysts, ethylene glycol and terephthalic acid produce PET in the form of a molten, viscous mass that can be spun directly to fibres or solidified for later processing as a plastic. In chemical terms, ethylene glycol is a diol, an alcohol with a molecular structure that contains two hydroxyl (OH) groups, and terephthalic acid is a dicarboxylic aromatic acid, an acid with a molecular structure that contains a large, six-sided carbon(or aromatic) ring and two carboxyl (CO2H) groups. Under the influence of heat and catalysts, the hydroxyl and carboxyl groups react to form ester (CO-O) groups, which serve as the chemical links joining multiple PET units together into long-chain polymers. Water is also produced as a by-product.

The presence of a large aromatic ring in the PET repeating units gives the polymer notable stiffness and strength, especially when the polymer chains are aligned with one another in an orderly arrangement by drawing (stretching). In this semicrystalline form, PET is made into a high-strength textile fibre marketed under such trademarked names as Dacron, by the American DuPont Company, and Terylene, by the British Imperial Chemical Industries PLC. The stiffness of PET fibres makes them highly resistant to deformation, so they impart excellent resistance to wrinkling in fabrics. They are often used in durable-press blends with other fibres such as rayon, wool, and cotton, reinforcing the inherent properties of those fibres while contributing to the ability of the fabric to recover from wrinkling.

PET is also made into fibre filling for insulated clothing and for furniture and pillows. When made in very fine filaments, it is used in artificial silk, and in large-diameter filaments it is used in carpets. Among the industrial applications of PET are automobile tire yarns, conveyor belts and drive belts, reinforcement for fire and garden hoses, seat belts (an application in which it has largely replaced nylon), nonwoven fabrics for stabilizing drainage ditches, culverts, and railroad beds, and nonwovens for use as diaper topsheets and disposable medical garments. PET is the most important of the man-made fibres in weight produced and in value.

At a slightly higher molecular weight, PET is made into a high-strength plastic that can be shaped by all the common methods employed with other thermoplastics. Magnetic recording tape and photographic film are produced by extrusion of PET film (often sold under the trademarks Mylar and Melinex). Molten PET can be blow-molded into transparent containers of high strength and rigidity that are also virtually impermeable to gas and liquid. In this form, PET has become widely used in carbonated-beverage bottles and in jars for food processed at low temperatures. The low softening temperature of PET—approximately 70 °C (160 °F) prevents it from being used as a container for hot-filled foods.

PET is the most widely recycled plastic. PET bottles and containers are commonly melted down and spun into fibres for fibrefill or carpets. When collected in a suitably pure state, PET can be recycled into its original uses, and methods have been devised for breaking the polymer down into its chemical precursors for resynthesizing into PET. The recycling code number for PET is #1.

PET was first prepared in England of the Calico Printers Association during a study of phthalic acid begun in 1940. Because of wartime restrictions, patent specifications for the new material were not immediately published. Production by Imperial Chemical of its Terylene-brand PET fibre did not begin until 1954. Meanwhile, by 1945 DuPont had independently developed a practical preparation process from terephthalic acid, and in 1953 the company began to produce Dacron fibre. PET soon became the most widely produced syntheticfibre in the world. In the 1970s, improved stretch-molding procedures were devised that allowed PET to be made into durable crystal-clear beverage bottles—an application that soon became second in importance only to fibre production.

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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## #243 2018-10-11 00:29:11

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

224) Lake Titicaca

Lake Titicaca, Spanish Lago Titicaca, the world’s highest lake navigable to large vessels, lying at 12,500 feet (3,810 metres) above sea level in the Andes Mountains of South America, astride the border between Peru to the west and Bolivia to the east. Titicaca is the second largest lake of South America (after Maracaibo). It covers some 3,200 square miles (8,300 square km) and extends in a northwest-to-southeast direction for a distance of 120 miles (190 km). It is 50 miles (80 km) across at its widest point. A narrow strait, Tiquina, separates the lake into two bodies of water. The smaller, in the southeast, is called Lake Huiñaymarca in Bolivia and Lake Pequeño in Peru; the larger, in the northwest, is called Lake Chucuito in Bolivia and Lake Grande in Peru.

The meaning of the name Titicaca is uncertain, but it has been variously translated as Rock of the Puma or Crag of Lead. Titicaca lies between Andean ranges in a vast basin (about 22,400 square miles [58,000 square km] in area) that comprises most of the Altiplano (High Plateau) of the central Andes. In the snow-covered Cordillera Real on the northeastern (Bolivian) shore of the lake, some of the highest peaks in the Andes rise to heights of more than 21,000 feet (6,400 metres).

The lake averages between 460 and 600 feet (140 and 180 metres) in depth, but the bottom tilts sharply toward the Bolivian shore, reaching its greatest recorded depth of 920 feet (280 metres) off Isla Soto in the lake’s northeast corner.

More than 25 rivers empty their waters into Titicaca; the largest, the Ramis, draining about two-fifths of the entire Titicaca Basin, enters the northwestern corner of the lake. One small river, the Desaguadero, drains the lake at its southern end. This single outlet empties only 5 percent of the lake’s excess water; the rest is lost by evaporation under the fierce sun and strong winds of the dry Altiplano.

Titicaca’s level fluctuates seasonally and over a cycle of years. During the rainy season (summer, from December to March) the level of the lake rises, normally to recede during the dry winter months. It was formerly believed that Titicaca was slowly drying up, but modern studies have seemed to refute this, indicating a more or less regular cycle of rise and fall.

Titicaca’s waters are limpid and only slightly brackish, with salinity ranging from 5.2 to 5.5 parts per 1,000. Surface temperatures average 56 °F (14 °C); from a thermocline at 66 feet (20 m) temperatures drop to 52 °F (11 °C) at the bottom. Analyses show measurable quantities of sodium chloride, sodium sulfate, calcium sulfate, and magnesium sulfate in the water.

Lake Titicaca’s fish life consists principally of two species of killifish (Orestias)—a small fish, usually striped or barred with black—and a catfish (Trichomycterus). In 1939, and subsequently, trout were introduced into Titicaca. A large frog (Telmatobius), which may reach a length of nearly a foot, inhabits the shallower regions of the lake.

Forty-one islands, some of them densely populated, rise from Titicaca’s waters. The largest, Titicaca Island (Spanish: Isla de Titicaca, also called Isla del Sol), lies just off the tip of the Copacabana Peninsula in Bolivia.

Ruins on the lake’s bottom (where the remains of a temple were discovered in 2000), on its shore, and on the islands attest to the previous existence of one of the oldest civilizations known in the Americas. The chief site is at Tiwanaku, Bolivia, at the southern end of the lake. On Titicaca Island ruins of a temple mark the spot where, according to the tradition of the Incas (a Quechuan people of Peru who established an empire about 1100 CE), the legendary founders of the Inca dynasty, Manco Capac and Mama Ocllo, were sent down to Earth by the Sun.

The Aymara people living in the Titicaca Basin still practice their ancient methods of agriculture on stepped terraces that predate Inca times. They grow barley, quinoa (a type of pigweed that produces a small grain), and the potato, which originated on the Altiplano. The highest cultivated plot in the world was found near Titicaca—a field of barley growing at a height of 15,420 feet (4,700 metres) above sea level. At this elevation the grain never ripens, but the stalks furnish forage for llamas and alpacas, the American relatives of the camel that serve the Indians as beasts of burden and provide meat and wool. The lake plain is covered with vast numbers of pre-Columbian raised platform fields and ditches, now abandoned, which were constructed to improve drainage and enhance the region’s agricultural potential. This ancient system of reclamation has been revived in some areas in both Peru and Bolivia.

The remnants of an ancient people, the Uru, still live on floating mats of dried totora (a reedlike papyrus that grows in dense brakes in the marshy shallows). From the totora, the Uru and other lake dwellers make their famed balsas—boats fashioned of bundles of dried reeds lashed together that resemble the crescent-shaped papyrus craft pictured on ancient Egyptian monuments.

In 1862 the first steamer to ply the lake was prefabricated in England and carried in pieces on muleback up to the lake. Today vessels make regular crossings from Puno, on the Peruvian shore, to the small Bolivian port of Guaqui. A narrow-gauge railway connects Guaqui with La Paz, capital of Bolivia. One of the world’s highest railways runs from Puno down to Arequipa and the Pacific, completing for land-bound Bolivia, an important link with the sea, and also to Cuzco.

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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## #244 2018-10-13 00:30:56

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

225) Christ the Redeemer

Christ the Redeemer, Portuguese Cristo Redentor, colossal statue of Jesus Christ at the summit of Mount Corcovado, Rio de Janeiro, southeastern Brazil. It was completed in 1931 and stands 98 feet (30 metres) tall, its horizontally outstretched arms spanning 92 feet (28 metres). The statue, made of reinforced concrete clad in a mosaic of thousands of triangular soapstone tiles, sits on a square stone pedestal base about 26 feet (8 metres) high, which itself is situated on a deck atop the mountain’s summit. The statue is the largest Art Deco-style sculpture in the world and is one of Rio de Janeiro’s most recognizable landmarks.

In the 1850s the Vincentian priest Pedro Maria Boss suggested placing a Christian monument on Mount Corcovado to honour Isabel, princess regent of Brazil and the daughter of Emperor Pedro II, although the project was never approved. In 1921 the Roman Catholic archdiocese of Rio de Janeiro proposed that a statue of Christ be built on the 2,310-foot (704-metre) summit, which, because of its commanding height, would make it visible from anywhere in Rio. Citizens petitioned Pres. Epitácio Pessoa to allow the construction of the statue on Mount Corcovado.

Permission was granted, and the foundation stone of the base was ceremonially laid on April 4, 1922—to commemorate the centennial on that day of Brazil’s independence from Portugal—although the monument’s final design had not yet been chosen. That same year a competition was held to find a designer, and the Brazilian engineer Heitor da Silva Costa was chosen on the basis of his sketches of a figure of Christ holding a cross in his right hand and the world in his left. In collaboration with Brazilian artist Carlos Oswald, Silva Costa later amended the plan; Oswald has been credited with the idea for the figure’s standing pose with arms spread wide. The French sculptor Paul Landowski, who collaborated with Silva Costa on the final design, has been credited as the primary designer of the figure’s head and hands. Funds were raised privately, principally by the church. Under Silva Costa’s supervision, construction began in 1926 and continued for five years. During that time materials and workers were transported to the summit via railway.

After its completion, the statue was dedicated on October 12, 1931. Over the years it has undergone periodic repairs and renovations, including a thorough cleaning in 1980, in preparation for the visit of Pope John Paul II to Brazil that year, and a major project in 2010, when the surface was repaired and refurbished. Escalators and panoramic elevators were added beginning in 2002; previously, in order to reach the statue itself, tourists climbed more than 200 steps as the last stage of the trip. In 2006, to mark the statue’s 75th anniversary, a chapel at its base was consecrated to Our Lady of Aparecida, the patron saint of Brazil.

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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## #245 2018-10-15 00:28:14

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

226) Caribbean

The Caribbean islands lie on the northern and eastern sides of the Caribbean Sea, stretching in an elongated S shape from the Bahamas and Cuba in the north and west to Trinidad in the south. The islands are divided into two main groups: the large islands of the Greater Antilles and the smaller islands of the Lesser Antilles. Strong historical connections with the islands mean that the mainland territories of Guyana and Belize are frequently categorized as part of the Caribbean.

The First Inhabitants

The Caribbean islands were probably first settled from the South American mainland. When Europeans arrived in the region there were three main groups of people living there. The Ciboney people were found in parts of Hispaniola and Cuba. The Arawak people occupied most of the Greater Antilles, while the Caribs lived throughout the Lesser Antilles. The Caribs were the latest to arrive in the region, migrating northward. As a result of this movement, the peoples of the Caribbean were experiencing change before the arrival of Europeans. However, the arrival of people from the Old World set in motion transformations on a previously unimaginable scale.

The Arrival Of Europeans

In 1492 the three ships of Christopher Columbus's Spanish expedition made landfall in the Bahamas, before heading south to Cuba and Hispaniola. Columbus famously thought that he had reached the East Indies and clung to this belief until his death in 1506. On his second voyage to the New World, Columbus brought seventeen ships, over a thousand soldiers, and European plants, horses, and livestock. This expedition explored and named many of the Caribbean islands, landing on Dominica, Guadeloupe, Montserrat, Antigua, Puerto Rico, and Jamaica.

The first Spanish settlements were in the Greater Antilles, the largest being on Hispaniola. The principal aim of Spanish colonization was to find and extract silver and gold, and Spanish settlers established mines as well as breeding horses and livestock. By the early sixteenth century, large deposits of gold and silver had been discovered in the mainland areas of Mexico and Peru. Thereafter, Spanish Caribbean settlements operated as staging posts and recruitment areas for expeditions to these regions.

The Spanish sought to convert the original inhabitants of the region to Christianity, but these efforts met with little success, and relations between the two groups were generally violent and exploitative. The Spaniards conquered the islands by force and gave no quarter when faced with resistance. They coerced native people into working in the mines, and disturbed local patterns of food production, causing many to starve. Furthermore, natives of the islands lacked immunities to European diseases. It is unclear exactly what proportion of them died as a result of illnesses imported from the Old World, but the arrival of Europeans in the region was certainly a social and demographic disaster, and native people were either destroyed or integrated into the Spanish society. The vast majority were wiped out within a few generations, certainly on the larger islands.

The End Of Spanish Hegemony

Prior to the end of the sixteenth century, Spain was the only colonial power in the Caribbean. However, Spain's power and influence was declining in Europe and it was increasingly difficult to exclude the English, Dutch, and French from the Caribbean. Initially, the only challenge to Spanish hegemony came from the increasingly common raids on ships and ports by pirates, such as John Hawkins and Francis Drake, who came in search of Spanish gold and silver. Buccaneers (raiders operating from bases in the Caribbean) continued to harass and plunder ships and ports in the region until the eighteenth century.

By the seventeenth century the period of Spanish hegemony was over, and the English, French, and Dutch began to trade and form colonies in the Caribbean. European powers fought to expand their empires and gain dominance of the sea, and because the financial value of Caribbean products and trade was high, competition between the main powers was particularly fierce in the region. The Caribbean became a focal point in the increasingly globalized conflicts between Britain and France during the eighteenth century. At times of war, sea battles were fought and islands were captured and recaptured. Between 1762 and 1814 control of the island of St. Lucia alternated between Britain and France seven times.

Sugar And Slavery

The expansion of sugar production and slavery helped to ensure that Caribbean colonies were economically and strategically vital to European governments. During the seventeenth century, having experimented with other crops, notably tobacco, northern European settlers began planting sugar, which grew well in tropical conditions and fetched a high price in Europe. Until the mid-eighteenth century, the wealthiest English plantation colony was Barbados, which was then superseded by the larger island of Jamaica, conquered from the Spanish in 1655. The most lucrative sugar colony in the Caribbean was French Saint-Domingue, in the western third of Hispaniola.

Effective sugar production required large holdings of land. This resulted in the creation of plantations that often covered thousands of acres. The cultivation and processing of this crop was also extremely labor-intensive, and, having experimented with indigenous slaves and indentured European labor, Caribbean planters turned to African slaves to meet their labor needs. Slaves imported from the west coast of Africa proved hardier than the indigenous islanders and a more reliable source of labor than European workers. Existing slaving networks in Africa ensured that there was a steady supply of slaves to meet European demand, and because they were treated as items of personal property, enslaved people could be easily bought and sold. The transatlantic slave trade therefore solved the planters' labor problems and permanently altered all aspects of life in the Caribbean colonies. Over five million Africans arrived in the Caribbean, having endured the horrors of the Middle Passage across the Atlantic.

Sugar plantations and the institution of slavery expanded together and had reached the height of their growth and profitability by the end of the eighteenth century. The precise demographic structure of slave societies differed from place to place, but everywhere in the Caribbean they were characterized by large black majorities, as slaves came to heavily outnumber the white inhabitants of the islands. For example, in 1800 there were about twenty slaves to every white person on the island of Jamaica. Across the region, a class of free colored people also emerged, occupying a social and legal position in between the islands' enslaved majorities and privileged white minorities.

Several factors discouraged whites from permanently settling in the region. A plethora of highly contagious diseases and the threat of slave uprisings rendered life in the Caribbean uncomfortable and dangerous. Many larger proprietors lived in Europe as absentees, and those whites who remained in the region did not consider the islands to be a permanent home and maintained a close affinity with the colonial metropole. Caribbean slaveholders also relied upon European military support to control their slaves. Such ties of dependency helped to ensure that Caribbean colonists did not follow their mainland Spanish and North American counterparts in demanding independence from European colonial systems.

In all colonies, slaves were worked hard and faced harsh treatment. In spite of this, enslaved people across the region created viable cultures that allowed them to resist the effects of slavery. Afro-Caribbean cultures emerged that reconfigured African beliefs, practices, and traditions in a New World setting. These cultures often merged with European traditions, especially because many slaves were converted to Christianity and most were forced to learn the language of their masters.

Resistance to slavery was a constant feature of life in the colonies. This ranged from day-to-day forms of resistance, such as working slowly, all the way to large-scale rebellions. Many slaves attempted to run away, and on larger islands, such as Jamaica and Hispaniola, some formed semiautonomous "Maroon" communities. While slave rebellions were common in the Caribbean, most ended in failure. In Saint-Domingue, however, unrest caused by the French Revolution resulted in a successful slave uprising—led by Toussaint L'Ouverture, a former slave—which culminated in the creation of the independent state of Haiti in 1804.

The Ending Of Caribbean Slavery

In 1807 the British abolished the transatlantic slave trade after a popular campaign led mainly by wealthy evangelicals. This came at a time when slave-produced sugar was still profitable. In the British Caribbean, an economic slump followed the ending of the trade, partly as a result of the demographic impact of abolition. In the British Caribbean, slaves eventually gained emancipation in 1838 as the result of continued pressure in Britain and ongoing slave resistance in the Caribbean. In the remaining French territories of Martinique and Guadeloupe, slavery ended in 1848, while slaves in the Dutch Caribbean were freed in 1863.

The abolition of slavery did not end the tensions that characterized societies long based on racialized social and economic divisions. Emancipated slaves sought independence from the sugar estates. Former slaveholders used a range of tactics to try to retain the freed people's labor, limit their access to land, and prevent their involvement in political life, causing tensions that resulted in protests and riots in British Caribbean territories throughout the postemancipation period. Some planters, especially those in Trinidad and Guyana, responded to their labor problems by importing South and East Asian indentured workers. Many of these laborers settled permanently, contributing to the social and cultural composition of those colonies.

Even as the sugar industry in the British and French Caribbean declined during the nineteenth century, Cuban production rose rapidly. Abundant fertile land, the removal of Spanish trade restrictions, and technological advances meant that the island experienced an economic boom that lasted until the late nineteenth century. Black slaves were used on Cuban plantations along with free workers from Europe, Asia, and Mexico, making the social structure and labor relations in the colony distinct from those in the British and French islands. Slavery survived in Cuba until the 1880s, when the institution was gradually phased out before a complete abolition in 1886.

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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## #246 2018-10-15 13:52:13

Monox D. I-Fly
Member
From: Indonesia
Registered: 2015-12-02
Posts: 2,000

### Re: Miscellany

ganesh wrote:

221) Anesthesia

Methods for lessening the sensation of pain during surgery date back to ancient times. Before the discovery of substances that produced general anesthesia, patients needing surgery for illness or injury had to rely on alcohol, opium (a natural narcotic derived from the opium poppy), or fumes from an anesthetic-soaked cloth to deaden the pain of the surgeon's knife. Often a group of men held the patient down during an operation in case the opium or alcohol wore off. Under these conditions, many patients died of shock from the pain of the operation itself.

I am grateful that I am living in the current era. Some days ago, October 6th, I underwent a cataract surgery and probably would have died if that was the method they used.

Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away.
May his adventurous soul rest in peace at heaven.

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## #247 2018-10-15 14:48:31

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

221) Anesthesia

Methods for lessening the sensation of pain during surgery date back to ancient times. Before the discovery of substances that produced general anesthesia, patients needing surgery for illness or injury had to rely on alcohol, opium (a natural narcotic derived from the opium poppy), or fumes from an anesthetic-soaked cloth to deaden the pain of the surgeon's knife. Often a group of men held the patient down during an operation in case the opium or alcohol wore off. Under these conditions, many patients died of shock from the pain of the operation itself.

I am grateful that I am living in the current era. Some days ago, October 6th, I underwent a cataract surgery and probably would have died if that was the method they used.

Miracles owing to Giant strides in the twenty-first century Medical Science, Monox D. I-Fly! Happy to learn the surgery went well! Good wishes!

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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## #248 2018-10-16 00:11:26

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

227) Distillation

Distillation, process used to separate the substances composing a mixture. It involves a change of state, as of liquid to gas, and subsequent condensation. The process was probably first used in the production of intoxicating beverages. Today, refined methods of distillation are used in many industries, including the alcohol and petroleum industries.

The Basic Distillation Process

A simple distillation apparatus consists essentially of three parts: a flask equipped with a thermometer and with an outlet tube from which the vapor is emitted; a condenser that consists of two tubes of different diameters placed one within the other and so arranged that the smaller (in which the vapor is condensed) is held in a stream of coolant in the larger; and a vessel in which the condensed vapor is collected. The mixture of substances is placed in the flask and heated. Ideally, the substance with the lowest boiling point vaporizes first, the temperature remaining constant until that substance has completely distilled. The vapor is led into the condenser where, on being cooled, it reverts to the liquid (condenses) and runs off into a receiving vessel. The product so obtained is known as the distillate. Those substances having a higher boiling point remain in the flask and constitute the residue.

Since a perfect separation is never effected, the distillate is often redistilled to increase its purity (hence the expression "double distilled" or "triple distilled"). Many alcoholic beverages are distilled, e.g., brandy, gin, whiskey, and various liqueurs. The apparatus used, called the still, is the same in principle as other distillation apparatus.

The Fractional Distillation Process

When the substance with the lowest boiling point has been removed, the temperature can be raised and the distillation process repeated with the substance having the next lowest boiling point. The process of obtaining portions (or fractions) in this way is one type of fractional distillation. A more efficient method of fractional distillation involves placing a vertical tube called a fractionating column between the flask and the condenser. The column is filled with many objects on which the vapor can repeatedly condense and reevaporate as it moves toward the top, effectively distilling the vapor many times. The less volatile substances in the vapor tend to run back down the column after they condense, concentrating themselves near the bottom. The more volatile ones tend to reevaporate and keep moving upward, concentrating themselves near the top. Because of this the column can be tapped at various levels to draw off different fractions. Fractional distillation is commonly used in refining petroleum, some of the fractions thus obtained being gasoline, benzene, kerosene, fuel oils, lubricating oils, and paraffin.

The Destructive Distillation Process

Another form of distillation involves heating out of free contact with air such substances as wood, coal, and oil shale and collecting separately the portions driven off; this is known as destructive distillation. Wood, for example, when treated in this way yields acetic acid, methyl or wood alcohol, charcoal, and a number of hydrocarbons. Coal yields coal gas, coal tar, ammonia, and coke. Ammonia is also obtained by the destructive distillation of oil shale.

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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## #249 2018-10-16 21:22:45

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

228) Compact Fluorescent Light Bulbs

Introduction

A compact fluorescent light bulb is a device that creates light using about one fourth as much power as a conventional, incandescent light bulb for a given amount of light. Large amounts of electricity are used to power light bulbs in industrial countries. Because most electricity worldwide is generated by burning coal, which releases the greenhouse gas carbon dioxide (CO2), replacing incandescent bulbs with compact fluorescent light bulbs (CFLs) can reduce the amount of greenhouse gases emitted, especially in warmer climates, and have an impact on the amount of global climate change. CFLs contain small amounts of the toxic metal mercury and are more expensive than incandescent light bulbs. They last longer than incandescents and, averaged over the lifetime of the device, cost less to run.

Historical Background and Scientific Foundations

Conventional light bulbs operate on the principle of heating a small wire or filament until it glows brightly. Most of the energy consumed by an incandescent bulb is turned into heat, not light. Fluorescent light bulbs operate on the principle that certain gas mixtures, such as mercury vapor mixed with xenon or argon, emit ultra-violet radiation (a form of light invisible to the human eye) when excited by an electric current. A coating on the inside of a glass tube filled with such a gas can absorb the ultraviolet radiation and re-radiate it as visible light.

Incandescent bulbs convert about 90% of the electricity they consume into heat, whereas fluorescent light bulbs convert only about 30% into heat. The result is that a fluorescent bulb uses much less electricity to provide a given amount of light. Heat from light bulbs is often undesirable. In air-conditioned buildings, for example, electricity must be purchased to remove the heat produced by interior lighting, so owners pay twice, once to make the unwanted heat and once to remove it.

Scientists first noticed the production of electromagnetic radiation by electrified gases in the late nineteenth century. The invention of the commercial fluorescent light bulb is credited to German inventor Edmund Germer (1901–1987), who in 1926 patented a fluorescent bulb that used an inner bulb coating to convert ultraviolet light to relatively pleasing white light.

Fluorescent lights have traditionally been designed as long tubes, either straight or looping, because lower electric currents (which are easier to produce and safer for the consumer) are needed to produce a given amount of light from a longer tube. Small or “compact” fluorescent light bulbs that could be screwed into a conventional light socket would require either complex, maze-like glassware to pack long gas paths into small volumes or high currents that would waste power.

In the 1970s, a number of inventors sought solutions to these design barriers. Several designs that worked in the laboratory were produced, but no commercially viable design was put forward until the idea of bending a tube into a double-spiral shape was invented by Edward Hammer at the General Electric Corporation in 1976. Although it was more difficult and expensive to make such tubes than to make conventional bulbs, gradual improvements in technique made it possible for spiral-bulb compact fluorescents to be marketed starting in 1995.

Impacts and Issues

CFLs cost much more per unit than incandescent light bulbs, but last longer: about 7,500 hours versus only 1,000 for an incandescent bulb. Because they use less power, burden air conditioning less, and last longer, they end up costing less despite their higher up-front cost. A savings of \$30 or more per bulb is cited by the U.S. Environmental Protection Agency (EPA) when CFLs are used instead of traditional incandescent bulbs. Because most electricity is generated by burning coal and CFLs save electricity, CFLs tend to cause less carbon dioxide to be emitted, which helps mitigate global climate change.

Globally, electric lighting causes carbon dioxide emissions equivalent to 70% of those from passenger vehicles. Thus, if every American home replaced just one incandescent bulb with a CFL, the carbon dioxide savings would be roughly equivalent to taking 800,000 cars off the road. Because of the cost and other advantages, some governments have considered, or have taken, action to speed the replacement of incandescent with fluorescent bulbs. In 2007, Australia became the first nation to announce that it would phase out incandescent bulbs entirely by 2012. Also in 2007, California was considering legislation that would ban the sale of incandescent light bulbs between 25 watts and 150 watts.

WORDS TO KNOW

GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.

ULTRAVIOLET: Light that vibrates or oscillates at a frequency of between 7.5 x {10}^{14} and 3 x {10}^{16} Hz (oscillations per second), more rapid than the highest-frequency color visible to the human eye, which is violet (hence the term “ultraviolet,” literally above-violet). Ultraviolet light is absorbed by ozone (O3) in Earth's stratosphere. This absorption serves both to shield the surface from this biologically harmful form of radiation and to heat the stratosphere, with important consequences for the global climate system.

WATT: Unit of power or rate of expenditure of energy. One watt equals 1 joule of energy per second. A 100-watt light bulb dissipates 100 joules of energy every second, i.e., uses 100 watts of power. Earth receives power from the sun at a rate of approximately 1.75 x {10}^{17} watts.

American consumers have been slow to adopt CFLs: only 2% to 5% of the 2 billion light bulbs sold in the United States each year are CFLs. Critics have pointed out that CFLs, like all fluorescent bulbs, contain the highly toxic metal mercury—about 5 milligrams (mg) per bulb. About 600 million fluorescent bulbs containing a total of 13,600 kg (30,000 lb) of mercury are thrown into U.S. landfills every year. However, because coal-burning also releases mercury and because CFLs prevent the burning of so much coal, an incandescent bulb causes the release, on average, of about 3.7 times more mercury per hour of lighting provided than does a CFL.

A more efficient, less toxic, and longer-lasting lighting technology—light-emitting diodes (LEDs)—is currently under development. LEDs remain relatively expensive, however, and are unlikely to displace CFLs in most applications in the near future.

Because of their mercury content, broken CFLs should not be touched with bare hands. They should also be recycled as toxic waste, not dumped in ordinary trash. Such dumping is illegal in California and several other U.S. states.

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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## #250 2018-10-17 00:13:30

ganesh
Registered: 2005-06-28
Posts: 38,058

### Re: Miscellany

229) Rotterdam

Rotterdam, major European port and second largest city of the Netherlands. It lies about 19 miles (30 km) from the North Sea, to which it is linked by a canal called the New Waterway. The city lies along both banks of the New Meuse (Nieuwe Maas) River, which is a northern distributary of the Rhine River.

The name Rotterdam was first mentioned in 1283, when a small tract of reclaimed land was created by draining the mouth of the Rotte River (another distributary in the Rhine River delta). Rotterdam developed as a fishing village and was chartered in 1328. In 1340 the town received permission to dig a canal to the Schie (another tributary of the New Meuse River), and it became the major port of the province. In the 17th century, when the discovery of the sea route to the Indies gave an enormous impetus to Dutch commerce and shipping, Rotterdam expanded its harbours and accommodations along the Meuse. Before the end of the century it was, after Amsterdam, the second merchant city of the country.

Rotterdam adjusted to the changed circumstances after the French occupation, which, from 1795 until the fall of Napoleon in 1815, halted most trade. Transit trade grew more important, and between 1866 and 1872 the New Waterway was dug from Rotterdam to the North Sea to accommodate larger oceangoing steamships. In 1877 the city was connected with the southern Netherlands by a railroadcrossing the Meuse River. The simultaneous construction of a traffic bridge across the Meuse opened that river’s south bank, where large harbour facilities, extending westward, sprang up between 1892 and 1898. Between 1906 and 1930 Rotterdam’s Waal Harbour was built; it became the largest dredged harbour in the world.

During World War II Rotterdam’s city centre and more than one-third of the port’s facilities were destroyed by the Germans. The city hall (1918), the main post office (1923), and the stock exchangewere among the few public buildings that escaped destruction. The 15th-century Grote Kerk (Great Church), or St. Laurenskerk (St. Lawrence’s Church), was burned in 1940 but was later restored.

Rotterdam literally rose from its ashes after its devastation by bombing during World War II. A totally new inner city was laid out, with a spacious and functional architecture oriented toward the river and a series of experiments at complete city planning that have attracted both professional and touristic admiration. The Lijnbaan Shopping Centre became the prototype for similar centres in Europe and America that allowed only pedestrian traffic.

Rotterdam’s economy is still almost completely based on shipping. The port lies at the heart of the densely populated and industrialized triangle of London, Paris, and the German Ruhr district and at the mouths of two important rivers (the Rhine and the Meuse), yet it is also open to the North Sea, the world’s most heavily navigated sea. The amount of sea-transported goods that pass through Rotterdam’s harbour and that of its outport, Europoort, is the largest in the world in terms of capacity, with much of its cargoes consisting of crude oil or petroleum products. Rotterdam is also one of the largest grain and general-cargo harbours on the continent. It is a major transhipment port for inland Europe, with tens of thousands of Rhine River barges using its facilities.

Since the late 1940s Rotterdam’s oil-processing, or petrochemical, industry has grown in importance. The city has several large oil refineries. Pipelines from Rotterdam transport seaborne crude oil, refinery products, ethylene and natural gas, and naphtha to Amsterdam, the province of Limburg, the southern island district of Zeeland, the Belgian city of Antwerp, and to Germany. Rotterdam was served by Zestienhoven Airport to the northwest of the city, (now Rotterdam The Hague Airport.)

Cultural institutions in Rotterdam include De Doelen concert hall (1966), noted for its acoustic perfection. The Boymans-van Beuningen Museum has a remarkable collection of paintings by Dutch and Flemish masters. Other museums in the city include the Museum of Ethnology, the Prince Henry Maritime Museum, and the Historical Museum. The city is also the home of the Erasmus University of Rotterdam (1973). The Royal Rotterdam Zoological Garden Foundation is a well-known zoo.

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.

Online