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#701 2020-06-16 00:54:27

ganesh
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Registered: 2005-06-28
Posts: 31,452

Re: Miscellany

581) Lizard

Lizards are reptiles. There are over 4,675 species of lizard, according to the San Diego Zoo. Others sources say there are about 6,000 species. Included in this large number are lizards with four legs, some with two legs and some with no legs at all; lizards with frills, horns or wings; and lizards in nearly every color imaginable.

Size

Lizards generally have small heads, long bodies and long tails. With so many species of lizard, it's understandable that they come in a wide variety of sizes. The largest lizard is the Komodo dragon. It grows up to 10 feet (3 meters) long and weighs up to 176 lbs. (80 kilograms). The smallest lizard is the tiny dwarf gecko, which grows to 0.6 inches (1.6 centimeters) long and weighs .0042 ounces (120 milligrams).

Habitat

Lizards are found all over the world in almost every type of terrain. Some live in trees; others prefer to live in vegetation on the ground, while others live in deserts among rocks. For example, the Texas horned lizard is found in the warm areas with little plant cover in southern North America. The northern fence lizard, on the other hand, likes to live in cool pine forests in northern North America.

Habits

Most lizards are active during the day. Lizards are cold-blooded animals, which means they rely on their environment to help warm their bodies. They use the heat of the sun to raise their body temperatures and are active when their bodies are warm. The sun also helps lizards produce vitamin D. Their days are spent sun-bathing on rocks, hunting for food or waiting for food to come their way.

Some lizards are territorial, while others can easily live with dozens of other lizards of many different species. Other than mating times, most lizards are not social, though. There are some exceptions. For example, the desert night lizard lives in family groups, according to research by the University of California.

A lizard's scaly skin does not grow as the animal ages. Most lizards shed their skin, or molt, in large flakes. Lizards also have the ability to break off part of their tails when a predator grabs it.

Diet

Many lizards are carnivores, which means they eat meat. A typical diet for a lizard includes ants, spiders, termites, cicadas, small mammals and even other lizards. Caiman lizards eat animals with shells, such as snails.

Other lizards are omnivores, which means they eat vegetation and meat. One example of an omnivore lizard is Clark's spiny lizard. These lizards like fruits, leaves and vegetables.

Some lizards are herbivores and only eat plants. The marine iguana, which lives in the Galapagos Islands, eats algae from the sea. Iguanas and spiny-tailed agamids also eat plants.

Offspring

Many lizards lay eggs while others bear live young. For example, frilled lizards lay eight to 23 eggs, according to National Geographic, while some skinks have live young. The gestation for a lizard egg can last up to 12 months.

Most baby lizards are self-sufficient from birth and are able to walk, run and feed on their own. The young reach maturity at 18 months to 7 years, depending on the species. Some lizards can live up to 50 years.

Classification/taxonomy

Here is the classification of lizards according to Integrated Taxonomic Information System (ITIS):

Kingdom: Animalia
Subkingdom: Bilateria
Infrakingdom: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclass: Tetrapoda
Class: Reptilia
Order: Squamata
Suborders: Amphisbaenia, Autarchoglossa, Gekkota, Iguanias, Serpentes

The suborder Dibamidae, with the genera Anelytropsis and Dibamus, may also be included, though ITIS says these categories have "uncertain position."

Conservation status

Lizards vary in their conservation status, much like their traits vary. Many, according to the International Union for Conservation of Nature's Red List of Threatened Species, are endangered or critically endangered, meaning they may be close to extinction. Some lizards that are critically endangered include Campbell's alligator lizard, St. Croix Ameiva, Frost's arboreal alligator lizard, Be’er Sheva fringe-fingered lizardand the Doumergue's fringe-fingered lizard.

Other facts

Frill neck lizards have a large, round collar of skin that pops up when they are trying to intimidate attackers.

The green basilisk lizard can run on water at about 5 feet (1.5 m) per second for 15 feet (4.5 m), or more according to National Geographic. Their special feet give them more surface area to hold them up and as they run, they create air bubbles that keep them afloat.

Chameleons' tongues are longer than their bodies, and their eyes can look in two different directions at once.

You can shine a light in a banded gecko's ear and the light will come out the other side, according to the American Museum of Natural History.

Two species — the Mexican beaded lizard of western Mexico and the Gila monster of the southwestern United States and northwestern Mexico, are venomous, according to Encyclopedia Britannica.

q-how-to-get-rid-of-lizards-gardening-gardening-pests.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#702 2020-06-17 00:38:16

ganesh
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Re: Miscellany

582) Earthworm

Earthworm, also called angleworm, any one of more than 1,800 species of terrestrial worms of the class Oligochaeta (phylum Annelida)—in particular, members of the genus Lumbricus. Seventeen native species and 13 introduced species (from Europe) occur in the eastern United States, L. terrestris being the most common. Earthworms occur in virtually all soils of the world in which the moisture and organic content are sufficient to sustain them. One of the most detailed studies of earthworm activities was conducted by English naturalist Charles Darwin.

Members of one Australian species can grow as long as 3.3 metres (about 11 feet). L. terrestris grows to about 25 centimetres (10 inches). This species is reddish brown, but some earthworms (e.g., Allolobophora chlorotica, native to Great Britain) are green. The reddish tinge of L. terrestris results from the presence of the pigment hemoglobin in its blood.

The earthworm body is divided into ringlike segments (as many as 150 in L. terrestris). Some internal organs, including the excretory organs, are duplicated in each segment. Between segments 32 and 37 is the math, a slightly bulged, discoloured organ that produces a cocoon for enclosing the earthworm’s eggs. The body is tapered at both ends, with the tail end the blunter of the two. Earthworms cannot see or hear, but they are sensitive to both light and vibrations.

Their food consists of decaying plants and other organisms; as they eat, however, earthworms also ingest large amounts of soil, sand, and tiny pebbles. It has been estimated that an earthworm ingests and discards its own weight in food and soil every day.

Earthworms are hermaphroditic; i.e., functional reproductive organs of both, male and female,  occur in the same individual. The eggs of one individual, however, are fertilized by the male gamete of another individual. During mating two earthworms are bound together by a sticky mucus while each transfers sperm to the other. The worms separate and form cocoons; the cocoon moves forward, picking up eggs at the 14th segment; at the 9th and 10th segments it picks up the male gamete deposited by the other earthworm. The cocoon slides over the head, and fertilization takes place. Within 24 hours after the worms mate, the cocoon is deposited in the soil.

Miniature earthworms usually emerge from the cocoon after two to four weeks. They become mating mature in 60 to 90 days and attain full growth in about one year.

Earthworms usually remain near the soil surface, but they are known to tunnel as deep as 2 m during periods of dryness or in winter. One Asian species is known to climb trees to escape drowning after heavy rainfall.

Earthworms provide food for a large variety of birds and other animals. Indirectly they provide food for humans by assisting plant growth. Earthworms aerate the soil, promote drainage, and draw organic material into their burrow. This last service accelerates the decomposition of organic matter and produces more nutritive materials for growing plants. Earthworms also serve as fish bait; hence, the name angleworm.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#703 2020-06-18 01:10:13

ganesh
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Posts: 31,452

Re: Miscellany

583) Internal-combustion engine

Internal-combustion engine, any of a group of devices in which the reactants of combustion (oxidizer and fuel) and the products of combustion serve as the working fluids of the engine. Such an engine gains its energy from heat released during the combustion of the nonreacted working fluids, the oxidizer-fuel mixture. This process occurs within the engine and is part of the thermodynamic cycle of the device. Useful work generated by an internal-combustion (IC) engine results from the hot gaseous products of combustion acting on moving surfaces of the engine, such as the face of a piston, a turbine blade, or a nozzle.

Internal-combustion engines are the most broadly applied and widely used power-generating devices currently in existence. Examples include gasoline engines, diesel engines, gas-turbine engines, and rocket-propulsion systems.

Internal-combustion engines are divided into two groups: continuous-combustion engines and intermittent-combustion engines. The continuous-combustion engine is characterized by a steady flow of fuel and oxidizer into the engine. A stable flame is maintained within the engine (e.g., jet engine). The intermittent-combustion engine is characterized by periodic ignition of air and fuel and is commonly referred to as a reciprocating engine. Discrete volumes of air and fuel are processed in a cyclic manner. Gasoline piston engines and diesel engines are examples of this second group.

Internal-combustion engines can be delineated in terms of a series of thermodynamic events. In the continuous-combustion engine, the thermodynamic events occur simultaneously as the oxidizer and fuel and the products of combustion flow steadily through the engine. In the intermittent-combustion engine, by contrast, the events occur in succession and are repeated for each full cycle.

With the exception of rockets (both solid rocket motors and liquid-propellant rocket engines), internal-combustion engines ingest air, then either compress the air and introduce fuel into the air or introduce fuel and compress the air-fuel mixture. Then, common to all internal-combustion engines, the air-fuel mixture is burned, work is extracted from the expansion of the hot gaseous products of combustion, and ultimately the products of combustion are released through the exhaust system. Their operation can be contrasted with that of external-combustion engines (e.g., steam engines), in which the working fluid does not chemically react and energy gain is achieved solely through heat transfer to the working fluid by way of a heat exchanger.

The most common internal-combustion engine is the four-stroke, gasoline-powered, homogeneous-charge, spark-ignition engine. This is because of its outstanding performance as a prime mover in the ground transportation industry. Spark-ignition engines also are used in the aeronautics industry; however, aircraft gas turbines have become the prime movers in this sector because of the emphasis of the aeronautics industry on range, speed, and passenger comfort. The domain of internal-combustion engines also includes such exotic devices as supersonic combustion ramjet engines (scramjets), such as those proposed for hypersonic aircraft, and sophisticated rocket engines and motors, such as those used on U.S. space shuttles and other space vehicles.

IC-Engine.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#704 2020-06-19 01:16:41

ganesh
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Re: Miscellany

584) Cardiopulmonary resuscitation

Cardiopulmonary resuscitation (CPR): First aid

Cardiopulmonary resuscitation (CPR) is a lifesaving technique useful in many emergencies, including a heart attack or near drowning, in which someone's breathing or heartbeat has stopped. The American Heart Association recommends that everyone — untrained bystanders and medical personnel alike — begin CPR with chest compressions.

It's far better to do something than to do nothing at all if you're fearful that your knowledge or abilities aren't 100 percent complete. Remember, the difference between your doing something and doing nothing could be someone's life.

Here's advice from the American Heart Association:

•    Untrained. If you're not trained in CPR, then provide hands-only CPR. That means uninterrupted chest compressions of 100 to 120 a minute until paramedics arrive (described in more detail below). You don't need to try rescue breathing.
•    Trained and ready to go. If you're well-trained and confident in your ability, check to see if there is a pulse and breathing. If there is no breathing or a pulse within 10 seconds, begin chest compressions. Start CPR with 30 chest compressions before giving two rescue breaths.
•    Trained but rusty. If you've previously received CPR training but you're not confident in your abilities, then just do chest compressions at a rate of 100 to 120 a minute. (Details described below.)

The above advice applies to adults, children and infants needing CPR, but not newborns (infants up to 4 weeks old).

CPR can keep oxygenated blood flowing to the brain and other vital organs until more definitive medical treatment can restore a normal heart rhythm.

When the heart stops, the lack of oxygenated blood can cause brain damage in only a few minutes. A person may die within eight to 10 minutes.

To learn CPR properly, take an accredited first-aid training course, including CPR and how to use an automated external defibrillator (AED). If you are untrained and have immediate access to a phone, call  or your local emergency number before beginning CPR. The dispatcher can instruct you in the proper procedures until help arrives.

Before you begin

Before starting CPR, check:

•    Is the environment safe for the person?
•    Is the person conscious or unconscious?
•    If the person appears unconscious, tap or shake his or her shoulder and ask loudly, "Are you OK?"
•    If the person doesn't respond and two people are available, have one person call 911 or the local emergency number and get the AED, if one is available, and have the other person begin CPR.
•    If you are alone and have immediate access to a telephone, call 911 or your local emergency number before beginning CPR. Get the AED, if one is available.
•    As soon as an AED is available, deliver one shock if instructed by the device, then begin CPR.

Remember to spell C-A-B

The American Heart Association uses the letters C-A-B — compressions, airway, breathing — to help people remember the order to perform the steps of CPR.

Compressions: Restore blood circulation

1.    Put the person on his or her back on a firm surface.
2.    Kneel next to the person's neck and shoulders.
3.    Place the heel of one hand over the center of the person's chest, between the nipples. Place your other hand on top of the first hand. Keep your elbows straight and position your shoulders directly above your hands.
4.    Use your upper body weight (not just your arms) as you push straight down on (compress) the chest at least 2 inches (approximately 5 centimeters) but not greater than 2.4 inches (approximately 6 centimeters). Push hard at a rate of 100 to 120 compressions a minute.
5.    If you haven't been trained in CPR, continue chest compressions until there are signs of movement or until emergency medical personnel take over. If you have been trained in CPR, go on to opening the airway and rescue breathing.

Airway: Open the airway

•    If you're trained in CPR and you've performed 30 chest compressions, open the person's airway using the head-tilt, chin-lift maneuver. Put your palm on the person's forehead and gently tilt the head back. Then with the other hand, gently lift the chin forward to open the airway.

Breathing: Breathe for the person

Rescue breathing can be mouth-to-mouth breathing or mouth-to-nose breathing if the mouth is seriously injured or can't be opened.

1.    With the airway open (using the head-tilt, chin-lift maneuver), pinch the nostrils shut for mouth-to-mouth breathing and cover the person's mouth with yours, making a seal.
2.    Prepare to give two rescue breaths. Give the first rescue breath — lasting one second — and watch to see if the chest rises. If it does rise, give the second breath. If the chest doesn't rise, repeat the head-tilt, chin-lift maneuver and then give the second breath. Thirty chest compressions followed by two rescue breaths is considered one cycle. Be careful not to provide too many breaths or to breathe with too much force.
3.    Resume chest compressions to restore circulation.
4.    As soon as an automated external defibrillator (AED) is available, apply it and follow the prompts. Administer one shock, then resume CPR — starting with chest compressions — for two more minutes before administering a second shock. If you're not trained to use an AED, a 911 or other emergency medical operator may be able to guide you in its use. If an AED isn't available, go to step 5 below.
5.    Continue CPR until there are signs of movement or emergency medical personnel take over.

To perform CPR on a child

The procedure for giving CPR to a child age 1 through puberty is essentially the same as that for an adult. The American Heart Association also recommends the following to perform CPR on a child:

Compressions: Restore blood circulation

If you are alone and didn't see the child collapse, perform five cycles of compressions and breaths on the child — this should take about two minutes — before calling or your local emergency number and getting the AED, if one is available.

If you're alone and you did see the child collapse, call  or your local emergency number and get the AED, if one is available, before beginning CPR. If another person is available, have that person call for help and get the AED while you begin CPR.
1.    Put the child on his or her back on a firm surface.
2.    Kneel next to the child's neck and shoulders.
3.    Use two hands, or only one hand if the child is very small, to perform chest compressions. Press straight down on (compress) the chest about 2 inches (approximately 5 centimeters). If the child is an adolescent, push straight down on the chest at least 2 inches (approximately 5 centimeters) but not greater than 2.4 inches (approximately 6 centimeters). Push hard at a rate of 100 to 120 compressions a minute.
4.    If you haven't been trained in CPR, continue chest compressions until there are signs of movement or until emergency medical personnel take over. If you have been trained in CPR, go on to opening the airway and rescue breathing.

Airway: Open the airway
•    If you're trained in CPR and you've performed 30 chest compressions, open the child's airway using the head-tilt, chin-lift maneuver. Put your palm on the child's forehead and gently tilt the head back. Then with the other hand, gently lift the chin forward to open the airway.

Breathing: Breathe for the child

Use the same compression-breath rate that is used for adults: 30 compressions followed by two breaths. This is one cycle.
1.    With the airway open (using the head-tilt, chin-lift maneuver), pinch the nostrils shut for mouth-to-mouth breathing and cover the child's mouth with yours, making a seal.
2.    Prepare to give two rescue breaths. Give the first rescue breath — lasting one second — and watch to see if the chest rises. If it does rise, give the second breath. If the chest doesn't rise, repeat the head-tilt, chin-lift maneuver and then give the second breath. Be careful not to provide too many breaths or to breathe with too much force.
3.    After the two breaths, immediately begin the next cycle of compressions and breaths. If there are two people performing CPR, conduct 15 compressions followed by two breaths.
4.    As soon as an AED is available, apply it and follow the prompts. Use pediatric pads if available, for children up to age 8. If pediatric pads aren't available, use adult pads. Administer one shock, then resume CPR — starting with chest compressions — for two more minutes before administering a second shock. If you're not trained to use an AED, a 911 or other emergency medical operator may be able to guide you in its use.

Continue until the child moves or help arrives.

To perform CPR on a baby 4 weeks old and older

Most cardiac arrests in babies occur from lack of oxygen, such as from drowning or choking. If you know the baby has an airway obstruction, perform first aid for choking. If you don't know why the baby isn't breathing, perform CPR.

To begin, examine the situation. Stroke the baby and watch for a response, such as movement, but don't shake the baby.

If there's no response, follow the C-A-B procedures below for a baby under age 1 (except newborns, which includes babies up to 4 weeks old) and time the call for help as follows:
•    If you're the only rescuer and you didn't see the baby collapse, do CPR for two minutes — about five cycles — before calling 911 or your local emergency number and getting the AED. If you did see the baby collapse, call or your local emergency number and get the AED, if one is available, before beginning CPR.
•    If another person is available, have that person call for help immediately and get the AED while you attend to the baby.

Compressions: Restore blood circulation

1.    Place the baby on his or her back on a firm, flat surface, such as a table. The floor or ground also will do.
2.    Imagine a horizontal line drawn between the baby's nipples. Place two fingers of one hand just below this line, in the center of the chest.
3.    Gently compress the chest about 1.5 inches (about 4 centimeters).
4.    Count aloud as you pump in a fairly rapid rhythm. You should pump at a rate of 100 to 120 compressions a minute.

Airway: Open the airway
•    After 30 compressions, gently tip the head back by lifting the chin with one hand and pushing down on the forehead with the other hand.

Breathing: Breathe for the baby

1.    Cover the baby's mouth and nose with your mouth.
2.    Prepare to give two rescue breaths. Use the strength of your cheeks to deliver gentle puffs of air (instead of deep breaths from your lungs) to slowly breathe into the baby's mouth one time, taking one second for the breath. Watch to see if the baby's chest rises. If it does, give a second rescue breath. If the chest does not rise, repeat the head-tilt, chin-lift maneuver and then give the second breath.
3.    If the baby's chest still doesn't rise, continue chest compressions.
4.    Give two breaths after every 30 chest compressions. If two people are conducting CPR, give two breaths after every 15 chest compressions.
5.    Perform CPR for about two minutes before calling for help unless someone else can make the call while you attend to the infant.
6.    Continue CPR until you see signs of life or until medical personnel arrive.

cardiopulmonary-head-tilting.jpg.png


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#705 2020-06-20 01:09:00

ganesh
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Re: Miscellany

585) Alfalfa

Alfalfa, (Medicago sativa), also called lucerne or purple medic, perennial, cloverlike, leguminous plant of the pea family (Fabaceae), widely grown primarily for hay, pasturage, and silage. Alfalfa is known for its tolerance of drought, heat, and cold and for the remarkable productivity and quality of its herbage. The plant is also valued in soil improvement and is grown as a cover crop and as a green manure.

The plant, which grows 30–90 cm (1–3 feet) tall, arises from a much-branched crown that is partially embedded in the surface layer of soil. As the plant develops, numerous stems bearing trifoliolate leaves (compound leaves with three leaflets) arise from the crown buds. Racemes of small flowers arise from the upper axillary buds of the stems. In sunny regions with moderate heat, dry weather, and pollinating insects, these flowers can abundantly produce corkscrew-coiled legumes containing two to eight or more seeds. Similar to many other members of Fabaceae, alfalfa plants house symbiotic soil bacteria (rhizobia) in their root nodules to “fix” nitrogen from the air into the soil, thus making it accessible to other plants. When grown as a cover crop or as part of a crop rotation, alfalfa improves the soil nutrient levels and lessens the need for synthetic fertilizers.

The primary root of alfalfa can attain great depths, an adaptation for drought tolerance. In porous subsoils, taproots as long as 15 metres (50 feet) have been recorded in plants over 20 years of age. The roots of seedlings also grow rapidly, reaching soil depths of 90 cm (3 feet) after two months and 180 cm (6 feet) after five months. Newly established fields of alfalfa often survive severe summer drought and heat when other leguminous plants with shallower and more-branching roots succumb. These long taproots also improve soil quality by decreasing soil compaction.

Alfalfa has a remarkable capacity to rapidly regenerate new stems and leaves following cutting. As many as 13 crops of hay can be harvested in a single growing season because of this abundant regrowth. The frequency of harvest and the total seasonal yields depend largely on the length of the growing season, the adaptability of the soil, the abundance of sunshine, and especially the amount and distribution of rainfall or irrigation during the growing season. Green leafy alfalfa hay is very nutritious and palatable to livestock, containing about 16 percent proteins and 8 percent mineral constituents. It is also rich in vitamins A, E, D, and K.

Like all crops, alfalfa is beset by the hazards of climate, diseases, and insects. Among the more serious of these are winterkill, bacterial wilt disease, alfalfa weevil, lugus bugs, grasshoppers, spotted aphids, and leafhoppers. In humid areas and in irrigated areas, alfalfa stands of three or more years of age have often become badly thinned by infestations of the soil-borne bacterial wilt organism Phytomonas insidiosum.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#706 2020-06-21 00:50:31

ganesh
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Re: Miscellany

586) Colosseum

Colosseum, also called Flavian Amphitheatre, giant amphitheatre built in Rome under the Flavian emperors. Construction of the Colosseum was begun sometime between 70 and 72 CE during the reign of Vespasian. It is located just east of the Palatine Hill, on the grounds of what was Nero’s Golden House. The artificial lake that was the centrepiece of that palace complex was drained, and the Colosseum was sited there, a decision that was as much symbolic as it was practical. Vespasian, whose path to the throne had relatively humble beginnings, chose to replace the tyrannical emperor’s private lake with a public amphitheatre that could host tens of thousands of Romans.

The structure was officially dedicated in 80 CE by Titus in a ceremony that included 100 days of games. Later, in 82 CE, Domitian completed the work by adding the uppermost story. Unlike earlier amphitheatres, which were nearly all dug into convenient hillsides for extra support, the Colosseum is a freestanding structure of stone and concrete, using a complex system of barrel vaults and groin vaults and measuring 620 by 513 feet (189 by 156 metres) overall. Three of the arena’s stories are encircled by arcades framed on the exterior by engaged columns in the Doric, Ionic, and Corinthian orders; the structure’s rising arrangement of columns became the basis of the Renaissance codification known as the assemblage of orders. The main structural framework and facade are travertine, the secondary walls are volcanic tufa, and the inner bowl and the arcade vaults are concrete.

The amphitheatre seated some 50,000 spectators, who were shielded from the sun by a massive retractable velarium (awning). Supporting masts extended from corbels built into the Colosseum’s top, or attic, story, and hundreds of Roman sailors were required to manipulate the rigging that extended and retracted the velarium. The Colosseum was the scene of thousands of hand-to-hand combats between gladiators, of contests between men and animals, and of many larger combats, including mock naval engagements. However, it is uncertain whether the arena was the site of the martyrdom of early Christians.

The Colosseum was damaged by lightning and earthquakes in medieval times and, even more severely, by vandalism. All the marble seats and decorative materials disappeared, as the site was treated as little more than a quarry for more than 1,000 years. Preservation of the Colosseum began in earnest in the 19th century, with notable efforts led by Pius VIII, and a restoration project was undertaken in the 1990s. It has long been one of Rome’s major tourist attractions, receiving close to seven million visitors annually. Changing exhibitions relating to the culture of ancient Rome are regularly mounted.

colosseum.png


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#707 2020-06-22 01:03:00

ganesh
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Re: Miscellany

587) Chrysanthemum

Chrysanthemum, (genus Chrysanthemum), genus of about 40 species of flowering plants in the aster family (Asteraceae), native primarily to subtropical and temperate areas of the Old World. Chrysanthemums are especially common in East Asia, where they are often depicted in art. Cultivated species, often called mums, are grown as fall-blooming ornamentals and are important in the floral industry. Florists’ chrysanthemum (Chrysanthemum ×morifolium) has more than 100 cultivars, including button, pompon, daisy, and spider forms.

Most plants of the genus are perennial herbs or subshrubs. Many have simple aromatic leaves that alternate along the stem. Some have both disk and ray flowers in the heads, but others lack ray or disk flowers. Cultivated species and hybrids usually have large flower heads; those of wild species are much smaller.

The taxonomy of the genus is contentious and has undergone a number of revisions. Species formerly included in the genus Chrysanthemum include corn marigold (Glebionis segetum); costmary (Tanacetum balsamita); feverfew (T. parthenium); tansy (T. vulgare); Marguerite, or Paris daisy (Argyranthemum frutescens); and Shasta daisy (hybrid forms of Leucanthemum maximum).

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#708 2020-06-23 02:44:11

ganesh
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Re: Miscellany

588) Shamrock

Shamrock, any of several similar-appearing trifoliate plants—i.e., plants each of whose leaves is divided into three leaflets. Plants called shamrock include the wood sorrel (Oxalis acetosella) of the family Oxalidaceae, or any of various plants of the pea family (Fabaceae), including white clover (Trifolium repens), suckling clover (T. dubium), and black medic (Medicago lupulina). According to Irish legend, St. Patrick, patron saint of Ireland, first chose the shamrock as a symbol of the Trinity of the Christian church because of its three leaflets bound by a common stalk. Wood sorrel is shipped from Ireland to other countries in great quantity for St. Patrick’s Day.

The shamrock pea (Parochetus communis), a creeping legume with bicoloured blue and pink flowers, is grown in pots and in hanging baskets.

xshamrock.jpg.pagespeed.ic.ZzZ7dctZ3X.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#709 2020-06-24 00:59:56

ganesh
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Re: Miscellany

589) Daffodil

Daffodil, (Narcissus pseudonarcissus), also called common daffodil or trumpet narcissus, bulb-forming plant in the amaryllis family (Amaryllidaceae), widely cultivated for its trumpetlike flowers. Daffodils are native to northern Europe and are grown in temperate climates around the world. The daffodil’s popularity has resulted in the production of many varieties; in addition to the classic yellow form, the trumpet and petals may themselves be of contrasting yellow, white, pink, or orange.

The daffodil is a perennial and grows to about 41 cm (16 inches) in height. Each plant features five or six linear leaves that grow from the bulb and are about 30 cm (12 inches) long. The stem bears one large yellow blossom with a corolla deeply cleft into six lobes and a central bell-shaped crown, or corona, that is frilled at its edges. This trumpet shape contains the stamens and is the flower’s most conspicuous feature.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#710 2020-06-25 00:56:35

ganesh
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Re: Miscellany

590) Thunder

Thunder, sound caused by a lightning discharge. Lightning heats the air in its path and causes a large over-pressure of the air within its channel. The channel expands supersonically into the surrounding air as a shock wave and creates an acoustic signal that is heard as thunder. The loudest thunder heard after a flash to the ground is actually produced by the return stroke that follows the path forged by the initial stroke, or stepped leader. The return stroke is louder because it contains a larger and faster-rising electric current than either the leader or a discharge within a cloud. Because the path of a lightning channel is usually branched, tortuous, and very long, sound waves from more distant portions arrive later than those from nearer portions, accounting for the duration of thunder and for the characteristic claps and rumbles. The distance to a flash can be estimated by measuring the time delay between the flash of light and the thunder—the formula being about three seconds for each kilometre (or five seconds for each mile). Thunder is seldom heard at distances greater than about 20 km (12 miles).

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#711 2020-06-26 01:10:37

ganesh
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Re: Miscellany

591) Beach

Beach, sediments that accumulate along the sea or lake shores, the configuration and contours of which depend on the action of coastal processes, the kinds of sediment involved, and the rate of delivery of this sediment. There are three different kinds of beaches. The first occurs as a sediment strip bordering a rocky or cliffy coast; the second is the outer margin of a plain of marine or fluvial accumulation (free beaches); and the third, of fairly peculiar character, consists of the narrow sediment barriers stretching for dozens or even hundreds of kilometres parallel to the general direction of the coast. These barriers separate lagoons from the open sea and generally are dissected by some tidal inlets. Certain sediment forelands, such as spits, points, and tombolos (which connect an island with a mainland), also occasionally are called beaches.

The upper limit of the active beach is the swash line reached by highest sea level during big storms. The lower beach margin is beneath the water surface and can be determined only if there is a definite border present between the sediment layer and the naked surface of the rocky bench. If the sediment cover extends into deep water, the lowest beach margin may be defined as the line where the strongest waves no longer sort and move the sand. It occurs approximately at a depth equal to one-third the wavelength or 10 times the wave height.

The profile of an active beach varies greatly. Its form and dimensions depend on a number of factors, such as wave parameters, tide height, and sediment composition and distribution. The following, however, constitute some of the profile elements that commonly occur. At the upper part, above high sea level, a beach terrace is located, and there may be a series of beach ridges or berms created by the waves of a previous major storm. This terrace surface is inclined seaward. The next element is a steeper, frontal beach slope or face, and beneath it a low-tide terrace may be developed. If the tides are high enough (more than 2 m [6.6 feet]), the frontal slope may be more than 1 km (0.6 mile) in width in regions with abundant sand and a shallow bottom. In some areas the low-tide terrace terminates with another inclined shoreface, if the nearshore sea zone is rather deep. Finally, one or several parallel, submarine, long-shore bars with intervening troughs may exist along sandy shores; if present, these bars constitute the last profile element.

Some minor relief forms are usually present on the surface of sand beaches. These include oscillation ripples, swash or rill furrows, and the well-known beach cusps (concave seaward) at the beach margin.

Given the established system of strong waves normal to the shoreline, submarine bars are sometimes dismembered and are converted into large crescent elements convex seaward. These relief forms reflect the existence of large water eddies with vertical axes, which form as a result of the ebb and flow of the water. Often the water outflow proceeds in the form of linear rip currents. These may be so strong that they cause erosion of deep channels in the submarine slopes.

In many countries the wind strongly affects the dynamics of the beach. The beach is exposed to the sea wind, and sand is usually blown off to the rear parts of the beach, where it forms small hummocks. As these join together, foredunes are being built, and, if the beach is well-supplied with sand in the right area, several rows of dunes will be formed. When the sand is abundant, dunes will shift to adjacent low-lying plains and may bury fertile soils, woods, and buildings.

If sand is no longer delivered to the region of developed dunes, gaps will form in the ridges parallel to the shore. In such zones, parabolic dunes with their summits coastward are created. After long stabilization, the summits of the parabolas may be broken through by the wind, thus gradually forming a series of ridges parallel to the prevailing winds.

Beach sands in temperate latitudes consist mainly of quartz, some feldspars, and a small percentage of heavy minerals. In the tropics, however, calcareous beaches composed of skeletal remnants of marine organisms and precipitated particles, such as oolites, are widespread.

Sometimes the basement layers of the beach are cemented by calcium carbonate, precipitated from the groundwater. This will commonly result if fresh water penetrates a beach from swamps behind it. If the beach undergoes erosion and thus retreats, the cemented strata become exposed; termed beach rock, they are widespread in the tropics and along the shores of the Mediterranean, Black, and Caspian seas.

The practical significance of beaches is not limited to their function as protectors of the coast or as recreation sites. The sorting mechanism of the offshore waves and currents determines the accumulation of heavy-mineral (specific weight more than 2.7) concentrates. On any sand beach there are thin layers of dark sand that can be seen. Some heavy minerals contain valuable metals, such as titanium, zirconium, germanium, tin, uranium, and gold. In many places the concentrations are so great that they are of industrial significance; placer deposits are worked in India, Brazil, Japan, Australia, Russia, and Alaska. Heavy-mineral concentrates also are extracted from the submarine slopes by means of dredging ships.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#712 2020-06-27 01:12:41

ganesh
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Re: Miscellany

592) Mineral water

Mineral water, water that contains a large quantity of dissolved minerals or gases. Mineral water from natural springs commonly has a high content of calcium carbonate, magnesium sulfate, potassium, and sodium sulfate. It may also be impregnated with such gases as carbon dioxide or hydrogen sulfide. Mineral water is produced artificially by adding salts to distilled water or aerating it with carbon dioxide. The mineral content of both natural and artificial mineral water varies greatly, and in some cases it may be less than that of ordinary tap water.

Since ancient times people have bathed in water from mineral springs, especially hot springs, because of its supposed therapeutic value for rheumatism, arthritis, skin diseases, and various other ailments. Many such springs have become sites for health spas and resorts, some of the most famous of which are Bath, Somerset, England; Baden-Baden and Wiesbaden, Germany; and Saratoga Springs, New York. The use of mineral water as a beverage has increased greatly since the mid-1970s. Large quantities of bottled water from mineral springs in France, Italy, and other European countries are exported each year.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#713 2020-06-28 00:57:43

ganesh
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Re: Miscellany

593) Kookaburra

Kookaburra, also called laughing kookaburra or laughing jackass, (species Dacelo novaeguineae), eastern Australian bird of the kingfisher family (Alcedinidae), whose call sounds like fiendish laughter. This gray-brown, woodland-dwelling bird reaches a length of 43 cm (17 inches), with an 8- to 10-cm (3.2- to 4-inch) beak. In its native habitat it eats invertebrates and small vertebrates, including venomous snakes. In western Australia and New Zealand, where it has been introduced, the kookaburra has been known to attack chickens and ducklings. Defending their territory year-round, a monogamous pair of these birds lays two clutches of two to four white eggs in its nest in a tree hole. The young often remain with the parents and help raise the next year’s brood.

Also sometimes called the “bushman’s clock,” the kookaburra is heard very early in the morning and just after sunset. The related blue-winged kookaburra (D. leachii), which does not “laugh,” is found across northern Australia.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#714 2020-06-29 01:17:34

ganesh
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Re: Miscellany

594) Gene

Gene, unit of hereditary information that occupies a fixed position (locus) on a chromosome. Genes achieve their effects by directing the synthesis of proteins.

In eukaryotes (such as animals, plants, and fungi), genes are contained within the cell nucleus. The mitochondria (in animals) and the chloroplasts (in plants) also contain small subsets of genes distinct from the genes found in the nucleus. In prokaryotes (organisms lacking a distinct nucleus, such as bacteria), genes are contained in a single chromosome that is free-floating in the cell cytoplasm. Many bacteria also contain plasmids—extrachromosomal genetic elements with a small number of genes.

The number of genes in an organism’s genome (the entire set of chromosomes) varies significantly between species. For example, whereas the human genome contains an estimated 20,000 to 25,000 genes, the genome of the bacterium Escherichia coli O157:H7 houses precisely 5,416 genes. Arabidopsis thaliana—the first plant for which a complete genomic sequence was recovered—has roughly 25,500 genes; its genome is one of the smallest known to plants. Among extant independently replicating organisms, the bacterium Mycoplasma genitalium has the fewest number of genes, just 517.

A brief treatment of genes follows.

Chemical Structure Of Genes

Genes are composed of deoxyribonucleic acid (DNA), except in some viruses, which have genes consisting of a closely related compound called ribonucleic acid (RNA). A DNA molecule is composed of two chains of nucleotides that wind about each other to resemble a twisted ladder. The sides of the ladder are made up of sugars and phosphates, and the rungs are formed by bonded pairs of nitrogenous bases. These bases are adenine (A), guanine (G), cytosine (C), and thymine (T). An A on one chain bonds to a T on the other (thus forming an A–T ladder rung); similarly, a C on one chain bonds to a G on the other. If the bonds between the bases are broken, the two chains unwind, and free nucleotides within the cell attach themselves to the exposed bases of the now-separated chains. The free nucleotides line up along each chain according to the base-pairing rule—A bonds to T, C bonds to G. This process results in the creation of two identical DNA molecules from one original and is the method by which hereditary information is passed from one generation of cells to the next.

Gene Transcription And Translation

The sequence of bases along a strand of DNA determines the genetic code. When the product of a particular gene is needed, the portion of the DNA molecule that contains that gene will split. Through the process of transcription, a strand of RNA with bases complementary to those of the gene is created from the free nucleotides in the cell. (RNA has the base uracil, U, instead of thymine, so A and U form base pairs during RNA synthesis.) This single chain of RNA, called messenger RNA (mRNA), then passes to the organelles called ribosomes, where the process of translation, or protein synthesis, takes place. During translation, a second type of RNA, transfer RNA (tRNA), matches up the nucleotides on mRNA with specific amino acids. Each set of three nucleotides codes for one amino acid. The series of amino acids built according to the sequence of nucleotides forms a polypeptide chain; all proteins are made from one or more linked polypeptide chains.

Experiments conducted in the 1940s indicated one gene being responsible for the assembly of one enzyme, or one polypeptide chain. This is known as the one gene–one enzyme hypothesis. However, since this discovery, it has been realized that not all genes encode an enzyme and that some enzymes are made up of several short polypeptides encoded by two or more genes.

Gene Regulation

Experiments have shown that many of the genes within the cells of organisms are inactive much or even all of the time. Thus, at any time, in both eukaryotes and prokaryotes, it seems that a gene can be switched on or off. The regulation of genes between eukaryotes and prokaryotes differs in important ways.

The process by which genes are activated and deactivated in bacteria is well characterized. Bacteria have three types of genes: structural, operator, and regulator. Structural genes code for the synthesis of specific polypeptides. Operator genes contain the code necessary to begin the process of transcribing the DNA message of one or more structural genes into mRNA. Thus, structural genes are linked to an operator gene in a functional unit called an operon. Ultimately, the activity of the operon is controlled by a regulator gene, which produces a small protein molecule called a repressor. The repressor binds to the operator gene and prevents it from initiating the synthesis of the protein called for by the operon. The presence or absence of certain repressor molecules determines whether the operon is off or on. As mentioned, this model applies to bacteria.

The genes of eukaryotes, which do not have operons, are regulated independently. The series of events associated with gene expression in higher organisms involves multiple levels of regulation and is often influenced by the presence or absence of molecules called transcription factors. These factors influence the fundamental level of gene control, which is the rate of transcription, and may function as activators or enhancers. Specific transcription factors regulate the production of RNA from genes at certain times and in certain types of cells. Transcription factors often bind to the promoter, or regulatory region, found in the genes of higher organisms. Following transcription, introns (noncoding nucleotide sequences) are excised from the primary transcript through processes known as editing and splicing. The result of these processes is a functional strand of mRNA. For most genes this is a routine step in the production of mRNA, but in some genes there are multiple ways to splice the primary transcript, resulting in different mRNAs, which in turn result in different proteins. Some genes also are controlled at the translational and posttranslational levels.

Gene Mutations

Mutations occur when the number or order of bases in a gene is disrupted. Nucleotides can be deleted, doubled, rearranged, or replaced, each alteration having a particular effect. Mutation generally has little or no effect, but, when it does alter an organism, the change may be lethal or cause disease. A beneficial mutation will rise in frequency within a population until it becomes the norm.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#715 2020-06-30 00:51:51

ganesh
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Re: Miscellany

595) Duck

Duck, any of various species of relatively small, short-necked, large-billed waterfowl. In true ducks—i.e., those classified in the subfamily Anatinae in the waterfowl family Anatidae—the legs are placed rearward, as in swans, rather than forward, as in geese. The result is a distinctive waddling gait. Most true ducks, including a few inaccurately called geese (e.g., sheldgeese) by reason of size and build, also differ from swans and true geese in the following characteristics: males (drakes) and females (hens or ducks) exhibit some degree of differentiation in plumage and in call, males molt twice annually, females lay large clutches of smooth-shelled rather than rough-shelled eggs, and both males and females have overlapping scales on the skin of the leg. The wild mallard (Anas platyrhynchos) is believed to be the ancestor of all domestic ducks, and it has undergone numerous crossbreedings and mutations since it was first domesticated in China between 2,000 and 3,000 years ago.

All true ducks, except those in the shelduck group (the tribe Tadornini) and sea ducks (the tribes Mergini and Somateriini), mature in the first year and pair only for the season—unlike the late-maturing, life-mating true geese and swans. Ducks are generally divided into three major groups, dabbling (shallow-water), diving, and perching ducks, based on their characteristic behaviours. The mallard, a typical dabbling duck (any of about 38 species of Anas and about 5 species in other genera), is one of the most popular game birds.

Pintails, teals, shovelers, and wigeons are also dabbling ducks classified in Anas, in addition to the gadwall (A. strepera) and the black ducks (A. sparsa, A. rubripes, and A. superciliosa). Perching ducks such as the muscovy (Cairina moschata), the wood duck (Aix sponsa), and the mandarin duck (Aix galericulata) have long claws and are the most arboreal of ducks, often roosting in trees. The diving ducks (or sea ducks) include the greatest number of marine species, such as eiders (which are variously classified as members of the tribe Mergini or placed in a separate tribe Somateriini) and scoters (Melanitta), but they also include primarily freshwater species such as mergansers (Mergus and Lophodytes), the ring-necked duck (Aythya collaris), and the pochards (Aythya and Netta), including the scaups (A. marila, A. affinis, and A. novaeseelandiae) and the canvasback (A. valisineria). The redhead (A. americana), the goldeneye (Bucephala clangula and B. islandica), and the bufflehead (B. albeola) are diving ducks that live in fresh and salt water, depending on the season. Members of the stifftail group, typified by the blue-billed ruddy duck (Oxyura jamaicensis), are highly aquatic diving ducks characterized by legs set far toward the rear of the body. The whistling ducks (Dendrocygna), also called tree ducks, are not true ducks but are more closely related to geese and swans. Ducks that are not included in those larger groups are the freckled duck (Stictonetta naevosa) and the torrent duck (Merganetta armata), as well as the shelducks (Tadorna) and the steamer ducks (Tachyeres). All ducks, geese, and swans belong to the family Anatidae.

Duck raising is practiced on a limited scale in most countries, usually as a small-farm enterprise, although large flocks are bred in some areas of England, the Netherlands, and the United States. The American Poultry Association lists 17 domesticated breeds, divided into four classes: heavy, medium, lightweight, and bantam. The White Pekin, originally from China, is the most widely raised duck in the United States, because it is meaty, fast growing, and prodigious in egg production. Duck feathers are also of some value, though they have been largely replaced by synthetics. Eiderdown, the down feathers of the common eider (Somateria mollissima), are still of wide commercial value for use in luxury quilts and pillows.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#716 2020-06-30 13:00:09

Agnishom
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Re: Miscellany

ganesh wrote:

581) Lizard

Lizards are reptiles. There are over 4,675 species of lizard, according to the San Diego Zoo. Others sources say there are about 6,000 species. Included in this large number are lizards with four legs, some with two legs and some with no legs at all; lizards with frills, horns or wings; and lizards in nearly every color imaginable.

Size

Lizards generally have small heads, long bodies and long tails. With so many species of lizard, it's understandable that they come in a wide variety of sizes. The largest lizard is the Komodo dragon. It grows up to 10 feet (3 meters) long and weighs up to 176 lbs. (80 kilograms). The smallest lizard is the tiny dwarf gecko, which grows to 0.6 inches (1.6 centimeters) long and weighs .0042 ounces (120 milligrams).

Habitat

Lizards are found all over the world in almost every type of terrain. Some live in trees; others prefer to live in vegetation on the ground, while others live in deserts among rocks. For example, the Texas horned lizard is found in the warm areas with little plant cover in southern North America. The northern fence lizard, on the other hand, likes to live in cool pine forests in northern North America.

Habits

Most lizards are active during the day. Lizards are cold-blooded animals, which means they rely on their environment to help warm their bodies. They use the heat of the sun to raise their body temperatures and are active when their bodies are warm. The sun also helps lizards produce vitamin D. Their days are spent sun-bathing on rocks, hunting for food or waiting for food to come their way.

Some lizards are territorial, while others can easily live with dozens of other lizards of many different species. Other than mating times, most lizards are not social, though. There are some exceptions. For example, the desert night lizard lives in family groups, according to research by the University of California.

A lizard's scaly skin does not grow as the animal ages. Most lizards shed their skin, or molt, in large flakes. Lizards also have the ability to break off part of their tails when a predator grabs it.

Diet

Many lizards are carnivores, which means they eat meat. A typical diet for a lizard includes ants, spiders, termites, cicadas, small mammals and even other lizards. Caiman lizards eat animals with shells, such as snails.

Other lizards are omnivores, which means they eat vegetation and meat. One example of an omnivore lizard is Clark's spiny lizard. These lizards like fruits, leaves and vegetables.

Some lizards are herbivores and only eat plants. The marine iguana, which lives in the Galapagos Islands, eats algae from the sea. Iguanas and spiny-tailed agamids also eat plants.

Offspring

Many lizards lay eggs while others bear live young. For example, frilled lizards lay eight to 23 eggs, according to National Geographic, while some skinks have live young. The gestation for a lizard egg can last up to 12 months.

Most baby lizards are self-sufficient from birth and are able to walk, run and feed on their own. The young reach maturity at 18 months to 7 years, depending on the species. Some lizards can live up to 50 years.

Classification/taxonomy

Here is the classification of lizards according to Integrated Taxonomic Information System (ITIS):

Kingdom: Animalia
Subkingdom: Bilateria
Infrakingdom: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclass: Tetrapoda
Class: Reptilia
Order: Squamata
Suborders: Amphisbaenia, Autarchoglossa, Gekkota, Iguanias, Serpentes

The suborder Dibamidae, with the genera Anelytropsis and Dibamus, may also be included, though ITIS says these categories have "uncertain position."

Conservation status

Lizards vary in their conservation status, much like their traits vary. Many, according to the International Union for Conservation of Nature's Red List of Threatened Species, are endangered or critically endangered, meaning they may be close to extinction. Some lizards that are critically endangered include Campbell's alligator lizard, St. Croix Ameiva, Frost's arboreal alligator lizard, Be’er Sheva fringe-fingered lizardand the Doumergue's fringe-fingered lizard.

Other facts

Frill neck lizards have a large, round collar of skin that pops up when they are trying to intimidate attackers.

The green basilisk lizard can run on water at about 5 feet (1.5 m) per second for 15 feet (4.5 m), or more according to National Geographic. Their special feet give them more surface area to hold them up and as they run, they create air bubbles that keep them afloat.

Chameleons' tongues are longer than their bodies, and their eyes can look in two different directions at once.

You can shine a light in a banded gecko's ear and the light will come out the other side, according to the American Museum of Natural History.

Two species — the Mexican beaded lizard of western Mexico and the Gila monster of the southwestern United States and northwestern Mexico, are venomous, according to Encyclopedia Britannica.

https://cdn-fastly.hometalk.com/media/2016/09/11/3543516/q-how-to-get-rid-of-lizards-gardening-gardening-pests.jpg

What do you think of Reptoid Humanoids?


'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.

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#717 2020-06-30 13:24:53

ganesh
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Re: Miscellany

Agnishom wrote:
ganesh wrote:

581) Lizard

What do you think of Reptoid Humanoids?

Reptilian humanoids, or anthropomorphic reptiles, have appeared in folklore, fiction, and conspiracy theories.

In mythology

Many cultures have legends of creatures which are part human and part reptile. One of the first historical depictions of a reptilian humanoid was the Ancient Egyptian deity Sobek, who had the head of a crocodile. He was depicted with similar traits, such as being aggressive and animalistic.

In South Asian and Southeast Asian mythology, the Nāga are semi-divine creatures which are half-human and half-serpent.

In folklore

Sightings of humanoid reptile cryptids are common in the Southern United States, where swamps are common. In the late 1980s, there were hundreds of supposed sightings of a "Lizard Man" in Bishopville, South Carolina.

In fiction

Anthropomorphic reptilian races or beings commonly appear in fantasy and science fiction. They can be based on various reptiles, like crocodiles, alligators, snakes, dinosaurs, and the fictional dragons. They are often depicted as powerful warriors, though their relative intelligence to humans varies - as with other anthropomorphic races, a greater resemblance to humans often denotes more "civilized" behavior.

PS: Anthropomorphism is the attribution of human traits, emotions, or intentions to non-human entities. It is considered to be an innate tendency of human psychology.

Personification is the related attribution of human form and characteristics to abstract concepts such as nations, emotions, and natural forces, such as seasons and weather.

Both have ancient roots as storytelling and artistic devices, and most cultures have traditional fables with anthropomorphized animals as characters. People have also routinely attributed human emotions and behavioral traits to wild as well as domesticated animals.

Reptilians (also called Reptoids,Reptiloids, or Draconians) are purported Reptilian Humanoids that play a prominent role in science fiction, as well as modern ufology and conspiracy theories.


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#718 2020-07-01 01:24:58

ganesh
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Re: Miscellany

596) Nile River

The Nile: Longest River in the World

The Nile River, considered the longest river in the world, is approximately 4,258 miles (6,853 kilometers) long, but its exact length is a matter of debate. Flowing northward through the tropical climate of eastern Africa and into the Mediterranean Sea, the river passes through 11 countries: Tanzania, Uganda, Rwanda, Burundi, the Democratic Republic of the Congo, Kenya, Ethiopia, Eritrea, South Sudan, Sudan and Egypt.

The Nile has two major tributaries: the longer White Nile, considered the prime stream and headwaters; and the Blue Nile, which carries about two-thirds of the river's water volume and most of the silt.

The White Nile begins at Lake Victoria, Africa's largest lake, which touches the countries of Uganda, Kenya and Tanzania. But Lake Victoria isn't necessarily the most distant and "true" source of the Nile River because the lake itself has many feeder rivers coming in from the surrounding mountains. In 2006, a British explorer named Neil McGrigor said he'd traveled to the Nile's most distant source at the beginning of the Kagera River, Lake Victoria's longest feeder river.

Still, experts do not agree which tributary of the Kagera is the longest — and therefore the most distant — source of the Nile. Ultimately, it would be either the Ruvyironza in Burundi or the Nyabarongo from the Nyungwe Forest in Rwanda.

Much less disputable is the Blue Nile's source at Lake Tana in Ethiopia. The Blue Nile meets up with the White Nile near Sudan's capital city, Khartoum. From there, the river flows north through the desert in Egypt, and finally, by way of a large delta, the Nile flows into the Mediterranean Sea.

The Nile Delta

he Nile waters flow at an average volume of 300 million cubic meters (79.2 billion gallons) per day, according to Travelling Along Rivers, a Dutch bilingual travel magazine. It takes approximately three months for the waters near the town of Jinja, Uganda (the point where the Nile leaves Lake Victoria), to reach the Mediterranean Sea.

The Nile Delta is approximately 100 miles (161 km) long from north to south, and it spreads out along about 150 miles (241 km) of Egyptian coastline, from Alexandria in the west to Port Said in the east. It is one of the world's largest river deltas with about 40 million inhabitants — approximately half of Egypt's population. Just before reaching the Mediterranean Sea, the river splits into two main branches, the Rosetta Branch (to the west) and the Damietta (to the east).

Ancient mythology of the Nile

Perhaps no river on Earth has captured the human imagination quite like the Nile River. From stories of Pharaohs and man-eating crocodiles to the discovery of the Rosetta stone, it was here, along the river's fertile banks, that one of the world's most remarkable civilizations — Ancient Egypt — was born around 3000 B.C. The Nile was not only the source of life for the ancient Egyptians, but is still so today for the millions of people living along its banks.

Known as both the "Father of Life" and the "Mother of All Men," the Nile was the center of life in Ancient Egypt. In the ancient Egyptian language, the Nile was called Ḥ'pī or Iteru, meaning "river." The Ancient Egyptians also called the river Ar or Aur, which means "black," in reference to the black silt left behind after the yearly flooding.
The Nile River was central to the Ancient Egyptians rise to wealth and power. Since rainfall is almost non-existent in Egypt, the Nile River and its yearly floodwaters offered the people a fertile oasis for rich agriculture.

The Nile is associated with many gods and goddesses, all of whom the Egyptians believed were deeply intertwined with the blessings and curses of the land, weather, culture and abundance of the people. They believed the gods were intimately involved with the people and could help them in all facets of their lives.

In some myths, the Nile was considered a manifestation of the god Hapi who blessed the land with abundance, according to the Ancient History Encyclopedia. Isis, the goddess of the Nile and the "Giver of Life," was believed to have taught the people how to farm and work the land.

The water god Khnum, who ruled over all forms of water, even the lakes and rivers in the underworld, was believed to be in charge of the amount of silt that flooded the river banks every year. In later dynasties, Khnum branched out to become the god of rebirth and creation as well.

Flooding

Each year, heavy summer rains upstream and melting snow in the Ethiopian Mountains would fill the Blue Nile well over its capacity and send a torrent of water downstream. The extra water would then spill over the banks onto the dry desert land of Egypt. Once the floods subsided, thick black silt, or mud, would be left behind on the ground. The silt created rich, fertile soil for planting crops — vital in this land of so little rain. Approximately 96 percent of the sediment carried by the Nile River originates in Ethiopia, according to the New World Encyclopedia. The silt area was known as the Black Land, while the desert lands further out were known as the Red Land.

Each year, the Ancient Egyptian people eagerly awaited and thanked the gods for the life-giving floods. If the floods were too small, there would be difficult times ahead with little food. If the floods were too large, it could cause flooding harm in the surrounding villages.

The Egyptian calendar was divided into three stages based on the yearly flood cycle: Akhet, the first season of the year, which covered the flooding period between June and September; Peret, the growing and sowing time from October to mid-February; and Shemu, the time of harvesting between mid-February and the end of May.

In 1970, the Aswan High Dam was built in Egypt to help regulate the Nile's flooding. Although the floods were desperately needed in older times, they are less necessary and even a nuisance to modern civilization with its irrigation systems. Even though the floods no longer occur along the Nile, the memory of this fertile blessing is still celebrated in Egypt today, mainly as an entertainment for tourists. The annual celebration, known as Wafaa El-Nil, begins on August 15th and lasts for two weeks.

Sharing the Nile

Because 11 countries must share one precious resource, there are bound to be disputes. The Nile Basin Initiative (NBI), an intergovernmental partnership among all the Basin States, was formed in 1999. It offers a forum for discussion and coordination among the countries to help manage and share the river's resources.

Joseph Awange is an associate professor in the department of spatial sciences at Curtin University in Australia. Using satellites, he has been monitoring the volume of water in the Nile River and reporting the findings to the Basin countries so they can effectively plan for sustainable use of the river's resources.

Of course, getting all the countries to agree on what they believe is fair and equal use of the Nile's resources is no easy task. "Lower countries (Egypt and Sudan) rely on some old treaty that they signed with Britain decades ago to impose unrealistic water use conditions to the upper countries," said Awange. "For this reason, some countries, e.g., Ethiopia, have decided to disregard the treaty and are busy constructing large hydropower dams within the Blue Nile."

Awange is referring to the Grand Ethiopian Renaissance Dam (GERD), currently under construction on the Blue Nile. It is located just over 300 miles northwest of Ethiopia's capital, Addis Ababa. When complete, the GERD will be the largest hydroelectric dam in Africa and one of the largest in the world. Controversy has surrounded the project since its beginning in 2011 as downstream nations rely heavily on the Nile's waters for their drinking water, agriculture and industrial needs.

Wildlife

The Nile River and its banks are abundant with many varieties of animal life. These include the rhinoceros, African tigerfish (the "piranha of Africa"), Nile monitors, enormous Vundu catfish, hippopotamuses, wildebeests, baboons, frogs, mongooses, turtles, tortoises and over 300 species of birds. Hundreds of thousands of water birds spend their winters in the Nile Delta. This includes the world's largest concentrations of little gulls and whiskered terns.

Possibly the most well-known animal — and most feared — is the Nile crocodile. This fearsome predator has a reputation as a man eater and rightly so. Nile crocodiles can reach lengths of 18 to 20 feet, and unlike their American cousins, can be quite aggressive toward people. Estimates say that about 200 people a year are killed by these reptiles, according to National Geographic.

Nile.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#719 2020-07-02 00:47:35

ganesh
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Posts: 31,452

Re: Miscellany

597) Nichrome

Nichrome, also known as nickel chrome, is an alloy produced by mixing nickel, chromium and, occasionally, iron. Best known for its heat resistance, as well as its resistance to both corrosion and oxidation, the alloy is incredibly useful for a number of applications. From industrial manufacturing to hobby work, nichrome in the form of wire is present in a range of commercial products, crafts and tools. It also finds applications in specialized settings.

Nichrome wire is an alloy made from nickel and chromium. It resists heat and oxidation and serves as a heating element in products such as toasters and hair dryers. Hobbyists use nichrome wire in ceramic sculpture and glassmaking. The wire can also be found in laboratories, construction and specialized electronics.

Nichrome Properties

Though there are various recipes for nichrome that are dependent on its intended use, the most common form of the alloy is produced from a ratio of 60 percent nickel and 40 percent chromium. Regardless of ratio, all nichrome alloys share properties that make the alloy noteworthy. Nichrome is resistant to heat and corrosion in water, and when heated, it forms a thin layer of chromium oxide that makes it practically immune to oxidation. Most notably, nichrome is highly resistive, causing it to heat up even when exposed to a small electrical current. These traits give nichrome wire a wide variety of uses across industries.

Heating Elements

Because nichrome wire is so resistant to electricity, it is incredibly useful as a heating element in commercial products and home tools. Toasters and hair dryers use coils of nichrome wire to create large amounts of heat, as do toaster ovens and storage heaters. Industrial furnaces also use nichrome wire to function. A length of nichrome wire can also be used to create a hot wire cutter, which can be used either at home or in an industrial setting to cut and shape certain foams and plastics.

Hobby Help

Because nichrome wire is an effective heating element, it is frequently used in hobbies and art forms. For example, ceramic sculptors and glassmakers both use nichrome – both as a support in their more complex works and as part of their firing kilns. Because nichrome can withstand high temperatures, using nichrome wire as a skeleton allows artists to keep their projects together during the firing process without fear of breakage.

Specialty Applications

Nichrome's characteristics also make it useful in specialty products and projects. Nichrome wire works exceptionally well as a remote igniter and is regularly used in fireworks. It can be used in laboratories to detect the presence of trace metals in flames, and customized electronic cigarettes and other vaporizers often use nichrome wire in their construction.

Nichrome Wire

Nichrome wire is made of a non-magnetic alloy composed primarily of nickel, chromium, and iron. Nichrome is characterized by its high resistivity and good oxidation resistance. Nichrome wire also has good ductility after use and excellent weldability.

The number that comes after the Nichrome wire type indicates the percentage of nickel in the alloy. For example, "Nichrome 60" has approximately 60% Nickel in its composition.

Applications for Nichrome wire include heating elements of hair dryers, heat sealers, and ceramic support in kilns.

Types of Nichrome Wire

Nichrome 20

This alloy has moderate resistance to oxidation.
Applications: Refractory anchor bolts, element fastener, and terminals attached to nickel-chromium heating elements.

Nichrome 30

This alloy is also used for heating cables and rope heaters in defrosting and de-icing elements, resistors, floor heaters, electric blankets and pads, baseboard heaters, and car seats.

Applications: Heavy duty rheostats, open coil heaters in HVAC systems, night-storage heaters, solid hot plates, convection heaters, and fan heaters.

Nichrome 40

Applications: Night-storage heaters, convection heaters, heavy duty rheostats, fan heaters, heating cables and rope heaters in defrosting and de-icing elements, electric blankets and pads, car seats, baseboard heaters and floor heaters, and resistors.

Specifications

Nichrome 60

Melting Temperature: 1350°C (2462°F)
Maximum Operating Temperature: 1150°C (2100°F)
Density: 0.2979 lbs/cubic in.
Specific heat capacity @ 68°F: 0.11 Btu/lb°F
Thermal Expansion: 14 x 10 to the -6 per °C

Nichrome 80

Melting Temperature: 1400°C (2552°F)
Maximum Operating Temperature: 1180°C (2150°F)
Density: 0.304 lbs/cubic in.
Specific heat capacity @ 68°F: 0.11 Btu/lb°F
Thermal Expansion: 14 x 10 to the -6 per °C

Nichrome 60

Nichrome 60 wire is generally used to manufacture electrical resistance for insulated and open appliances. It is widely used in the application of industrial furnaces and even provides the means to melt metals. At high temperatures, Nichrome 60 wire will resist embrittlement, meaning that it will last you longer than less resolute variations. It has good plasticity when cold, making it easy to weld, manipulate and shape to serve your specific needs.

Nichrome 60 is less resistant to rust and oxidation as Kanthal, but it has a higher high wet corrosion resistance and is made of a non-magnetic alloy. This means that in acidic environments or areas where a wire is likely to come in contact with a liquid or electrolyte medium, Nichrome 60 wire will resist degradation at a higher level and continue to function for a longer period of time.

nichrome-wire-18-gauge-250x250.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#720 2020-07-03 00:55:00

ganesh
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Posts: 31,452

Re: Miscellany

598) Rat

Rat, (genus Rattus), the term generally and indiscriminately applied to numerous members of several rodent families having bodies longer than about 12 cm, or 5 inches. (Smaller thin-tailed rodents are just as often indiscriminately referred to as mice.) In scientific usage, rat applies to any of 56 thin-tailed, medium-sized rodent species in the genus Rattus native to continental Asia and the adjacent islands of Southeast Asia eastward to the Australia-New Guinea region. A few species have spread far beyond their native range in close association with people. The brown rat, Rattus norvegicus (also called the Norway rat), and the house rat, R. rattus (also called the black rat, ship rat, or roof rat), live virtually everywhere that human populations have settled; the house rat is predominant in warmer climates, and the brown rat dominates in temperate regions, especially urban areas. Most likely originating in Asia, the brown rat reached Europe in the mid-1500s and North America around 1750. The house rat most likely originated in India.

Brown and house rats exploit human food resources, eating and contaminating stored grains and killing poultry. They have been responsible for the depletion or extinction of native species of small mammals, birds, and reptiles, especially on oceanic islands. Both the brown and house rat have been implicated in the spread of 40 diseases among humans, including bubonic plague, food poisoning, schistosomiasis, murine typhus, tularemia, and leptospirosis. On the other hand, the brown rat has been used in laboratories worldwide for medical, genetic, and basic biological research aimed at maintaining and improving human health. Rats are also kept as pets.

General Features

Rats are generally slender with a pointed head, large eyes, and prominent, thinly furred ears. They have moderately long legs and long, sharp claws. The bald soles of their narrow hind feet possess fleshy pads of variable size, depending on species. The brown rat has a larger body than the house rat, and its tail is shorter relative to the body. The brown rat also has thicker fur and 12 pairs of mammae instead of 10. Tail length among rats ranges from shorter than body length to appreciably longer. The tail appears smooth and bald but is actually covered with very short, fine hairs. In a very few species, these hairs become longer toward the tip, which gives the tail a slightly tufted appearance. As with any large group of rodents, body size varies within the genus. Most species are about the size of Hoffman’s rat (R. hoffmanni), native to the Indonesian island of Sulawesi and weighing 95 to 240 grams (3.4 to 8.5 ounces), with a body length of 17 to 21 cm (6.7 to 8.3 inches) and a tail about as long. One of the smaller species is Osgood’s rat (R. osgoodi) of southern Vietnam, with a body 12 to 17 cm long and a somewhat shorter tail. At the larger extreme is the Sulawesian white-tailed rat (R. xanthurus), measuring 19 to 27 cm long with a tail of 26 to 34 cm.

Like Hoffman’s rat, most species have a moderately short, soft, and dense coat. In some species the coat may be thicker and longer, somewhat woolly, or long and coarse; in others, such as the Sulawesian white-tailed rat and the Sikkim rat (R. remotus) of India, long and slender guard hairs resembling whiskers extend 4 to 6 cm beyond the coat on the back and rump. Very few Rattus species have spiny fur. Hoffman’s rat also exhibits the basic colour pattern seen in the genus—upperparts of brownish yellow peppered with black to dark brown and speckled with buff and underparts from silvery gray to dark gray, sometimes suffused with buff tones. Tail, ears, and feet are dark brown. As with fur texture, colour is variable. The Sikkim rat has brownish upperparts and a pure white underside; the Himalayan field rat (R. nitidus) has a brown back, gray underparts, and feet of pearly white. Others have very dark fur, such as the Mentawai rat (R. lugens) native to islands off the west coast of Sumatra. It has brownish black upperparts and a grayish black belly. Although the tail is uniformly gray to dark brown in most rats (sometimes nearly black), a few species show one of two bicoloured patterns: brown on the tail’s entire upper surface with a paler tone or pure white on the undersurface, as in the Himalayan field rat (R. nitidus) and the Turkestan rat (R. turkestanicus), or brown all around the basal third to half of the tail with the rest uniformly white, as in Hoogerwerf’s rat (R. hoogerwerfi) and the white-tailed rat of Sulawesi.

Natural History

In their natural habitats rats are primarily nocturnal—the brown rat is a prominent exception, being active day and night in both urban and rural environments. All rats are terrestrial, and many are also arboreal. The Sulawesian white-tailed rat is an excellent climber and exhibits the classic combination of arboreal traits within Rattus: a very long tail relative to body length, extremely long guard hairs over the back and rump, and wide hind feet with prominent, fleshy footpads. This rodent dens among the roots of large trees (generally strangler figs) and forages high in the crowns of understory and canopy trees. By contrast, those species having a tail considerably shorter than body length, short guard hairs over the back and rump, and inconspicuous pads on the soles of their hind feet tend to be primarily ground-dwelling. Most rats can swim; species with thick and somewhat woolly fur generally swim well, and some are adept swimmers that forage in aquatic environments. The brown rat, for example, has a terrestrial rat’s characteristic morphology and is a comparatively poor climber, but it has dense fur and readily enters lakes and streams and sewers to hunt for fish, invertebrates, or other food. The house rat, on the other hand, is extremely agile above the ground, being able to climb and run along narrow branches and wires.

Rats are thought to eat everything, a conception that comes from familiarity with the highly adaptable brown rat and house rat, but diet actually differs according to species and habitat. Where it lives with humans, the house rat does consume nearly anything digestible, especially stored grains. The brown rat is basically omnivorous but prefers a carnivorous diet, aggressively pursuing a wide variety of prey including shrimp, snails, mussels, insects, bird eggs and young, amphibians, eels, fish, pheasant, pigeons, poultry, rabbits, and carrion. Many rainforest species, including the Sulawesian white-tailed rat and Hoffman’s rat, eat only fruit and the seeds within, but some, such as the Philippine forest rat (R. everetti), also eat insects and worms. Other tropical species, such as the rice-field rat (R. argentiventer) and Malayan field rat (R. tiomanicus), primarily consume the insects, snails, slugs, and other invertebrates found in habitats of forest patches, secondary growth, scrubby and fallow fields, palm plantations, and rice fields.

Some rats excavate burrows or build their nests beneath boulders, rotting tree trunks, or other kinds of shelter on the forest floor; they may also shelter in deep rock crevices or caves and in dwellings from small village huts to large city buildings. Rat reproduction has been most intensively studied in the brown rat. This prolific rodent reaches sexual maturity at three months and may produce up to 12 litters of 2 to 22 young (8 or 9 is usual) per year, with peaks in the spring and autumn and a gestation period of 21 to 26 days. Breeding occurs throughout the year in many tropical species but in others may be restricted to wet seasons or summer months. Litter sizes in tropical forest species tend to be much smaller (one to six), and seasonal breeders, particularly in Australian habitats, produce significantly fewer annual litters.

Classification And Paleontology

Members of the genus Rattus are native to temperate and tropical continental Asia, the Australia–New Guinea region, and islands between those landmasses. Five clusters of species within the genus are recognized by some authorities.

The norvegicus group, consisting only of the brown rat, may have originated in northern or northeastern China.

Most of the 20 species in the rattus group are indigenous to subtropical and tropical Asia from peninsular India to southeastern China, Southeast Asia, Taiwan, some islands in the Philippines, and Sulawesi. They live in lowland and montane rainforests, scrublands, agricultural and fallow fields, and human structures. In addition to the house rat, the distributions of four other species (R. argentiventer, R. nitidus, R. exulans, and R. tanezumi) extend outside continental Southeast Asia, from the Sunda Shelf to New Guinea and beyond to some Pacific islands, and most likely represent introductions facilitated by human activities.

The 19 species in the “Australia–New Guinea” group are native to Australia, New Guinea and adjacent islands, and the Moluccan and Lesser Sunda Islands between Australia–New Guinea and continental Southeast Asia. They occupy habitats including sandy flats, open grasslands, and grassy areas within forest, heaths, savannas, and tropical rainforests.

The xanthurus group comprises five species indigenous to Sulawesi and nearby Peleng Island, where they inhabit tropical rainforest formations at all elevations.

There are 11 species whose relationships are unresolved. These have endemic ranges from peninsular India through Southeast Asia to the Philippines. Most now live, or once lived, in tropical rainforests; two species are extinct.

Rattus species belong to the subfamily Murinae (Old World rats and mice) of the “true” mouse and rat family, Muridae, within the order Rodentia. Among their closest living relatives are the bandicoot rats (genera Bandicota and Nesokia). Information about the evolutionary history of the genus is scanty; fossils from the Pleistocene Epoch (2,600,000 to 11,700 years ago) in Asia, Java, and Australia represent the oldest extinct species of Rattus.

A-brown-rat-walking-over-a-mossy-rock.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#721 2020-07-04 00:59:51

ganesh
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Posts: 31,452

Re: Miscellany

599) Gazelle

Gazelle, any of several fleet, medium-sized antelopes with slender, evenly developed limbs, level backs, and long necks. Most gazelles are tan-coloured, with white underparts and rump patch, a dark side stripe, and contrasting facial markings. They inhabit the arid lands of Asia from China to the Arabian Peninsula, North Africa from the Saharan deserts to the sub-Saharan Sahel, and northeast Africa from the Horn of Africa to Tanzania. Most gazelles are placed in the genus Gazella, family Bovidae (order Artiodactyla).

Gazelles have adapted to inhabit waterless steppe, subdesert, and even desert. They can extract water from the plants they browse without having to drink. They have narrow jaws and incisor rows for highly selective feeding on the most nutritious growth. Their urine is concentrated, and, before excretion, moisture is extracted from their fecal pellets. Their coats are light-coloured and reflective. They can tolerate an increase in their core temperature by as much as 5 °C (9 °F). Gazelles seek shade and avoid activity in the hottest weather by feeding at night and early morning when plants contain the most moisture. If all else fails, they can cool down by rapid nasal panting.

The genus Gazella was traditionally considered to contain 14 species. However, specialists in the taxonomy of the gazelle tribe (Antilopini), using genetic techniques for studying phylogenetic relationships, now believe that gazelles stem from not one but several different ancestors. Accordingly, six species, all African, have been removed from Gazella by some authorities and placed in two different genera. The three largest species—the dama gazelle, Grant’s gazelle, and Soemmering’s gazelle—are placed in the genus Nanger (formerly considered a subgenus), and three of the smaller species—Thomson’s gazelle, the red-fronted gazelle, and the Mongalla gazelle—have become the genus Eudorcas. The Gazella genus as traditionally defined includes eight species that occur only in Africa, five that occur only in Asia, and one species that occurs both in Africa and Asia. In the revised classification, Gazella contains ten species—three exclusively African, five exclusively Asian, and one shared by both continents.

Asian Gazelles

The Arabian Peninsula is the centre of diversity of the revised genus Gazella, with six species: the mountain gazelle (G. gazella), the goitred, or sand, gazelle (G. subgutturosa), the Arabian gazelle (G. arabica; now extinct), the Saudi gazelle (G. saudiya; now extinct in the wild), the Queen of Sheba’s gazelle (G. bilkis; now extinct), and the dorcas gazelle (G. dorcas). The dorcas gazelle also ranges into North Africa. The range of the goitred gazelle extends across the Asian deserts to China, though its population is greatly reduced in numbers. A sixth Asian gazelle, the Indian gazelle or chinkara (G. bennetti), survives in the deserts of India and Pakistan.

Tribe Antilopini includes several Asian species of the genus Procapra that are also called gazelles: the Tibetan gazelle (P. picticaudata), Przewalski’s gazelle (P. przewalskii), and the Mongolian gazelle (P. gutturosa). The last, with a population estimated at well over one million, may be the most numerous of all hoofed mammals.

African Gazelles

Of the three exclusively African Gazella species, two range north of the Sahara (along with the dorcas gazelle). The Atlas gazelle, also called Cuvier’s, or the edmi, gazelle (G. cuvieri), is found in the Atlas Mountains. The rhim, or slender-horned, gazelle (G. leptoceros) is the most desert-adapted African gazelle and lives in the Sahara’s great sand deserts (ergs) from Algeria to Egypt. The third indigenous species, Speke’s gazelle (G. spekei), inhabits the coastal plain of Somalia.

The dorcas gazelle, though still the most abundant and widespread of the Saharan antelopes, has been eliminated from most of its North African range. However, sizable populations survive in the Sahel from Mauritania to the Nile and in the lowlands of countries bordering the Red Sea.

Thomson’s gazelle (Eudorcas thomsonii) is still common in East Africa and abundant in the Serengeti ecosystem of Tanzania. An isolated species, the Mongalla gazelle (E. albonotata), occurs in eastern South Sudan and southwestern Ethiopia. The red-fronted gazelle (E. rufifrons) is a Sahel version of Thomson’s gazelle but is distinguished by a more rufous colour and a reddish border between the narrow black flank stripe and white underparts.

The dama gazelle (Nanger dama) is the largest gazelle, weighing up to 75 kg (165 pounds) and standing up to 120 cm (47 inches) at the shoulder. Formerly common in the grasslands and subdesert of the Sahel from Mauritania to Sudan, it now exists only in endangered remnant populations. This gazelle is unusual both for its form and for geographic variations in its colour pattern, which range from predominately rufous with extensive white underparts, rump, legs, and head in the west (N. dama mhorr) to nearly white in the east (N. dama ruficollis).

Grant’s gazelle (N. granti) has the largest horns (up to 80 cm [31 inches]) and is still widespread both in and outside protected areas through most of its range from South Sudan to central Tanzania. Soemmering’s gazelle (N. soemmeringii) inhabits the arid savanna country of northeast Africa, where it is the ecological equivalent of Grant’s gazelle. Clark’s gazelle (Ammordorcas clarkei) of northeast Africa is also known as the dibatag.

Ecology And Behaviour

Like most antelopes of arid regions, gazelles are nomadic, migratory, or both. All gazelles are gregarious; females and young band together, as do bachelor males. During migration, the males and females  associate in mixed herds, but they are segregated by territorial males whenever breeding opportunities arise. Gazelles are unusually endowed with glands; these are located between the hooves, in the groin (inguinal glands), on the front of the forelegs, and ahead of the eyes (preorbital glands). In males of some species (Thomson’s, red-fronted, Speke’s, and goitred) the preorbitals produce a sticky black secretion that is daubed on twigs and grass stems to demarcate territories. However, the main way of posting territories, in all members of the gazelle tribe, is with urine and feces, which males deposit on dung middens in a linked, highly ritualized performance.

Because antelopes living in open plains can be run down by motorized vehicles, all gazelles (with few exceptions) have been decimated over most of their range by relentless hunting. Habitat degradation and competition with livestock have also harmed gazelle populations.

thomsons-gazelle-2-340x200.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#722 2020-07-05 01:06:41

ganesh
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Re: Miscellany

600) Salt

Salt (NaCl), sodium chloride, mineral substance of great importance to human and animal health, as well as to industry. The mineral form halite, or rock salt, is sometimes called common salt to distinguish it from a class of chemical compounds called salts.

Salt is essential to the health of both people and animals. Table salt, used universally as a seasoning, is fine-grained and of high purity. To ensure that this hygroscopic (i.e., water-attracting) substance will remain free-flowing when exposed to the atmosphere, small quantities of sodium aluminosilicate, tricalcium phosphate, or magnesium silicate are added. Iodized salt—that is, salt to which small quantities of potassium iodide have been added—is widely used in areas where iodine is lacking from the diet, a deficiency that can cause swelling of the thyroid gland, commonly called goitre. Livestock also require salt; it is often made available in solid blocks.

The meat-packing, sausage-making, fish-curing, and food-processing industries use salt as a preservative or seasoning or both. It is employed for curing and preserving hides and as a brine for refrigeration.

In the chemical industry, salt is required in the manufacture of sodium bicarbonate (baking soda), sodium hydroxide (caustic soda), hydrochloric acid, chlorine, and many other chemicals. Salt is also employed in soap, glaze, and porcelain enamel manufacture and enters into metallurgical processes as a flux (a substance promoting fusing of metals).

When applied to snow or ice, salt lowers the melting point of the mixture. Thus, large amounts are used in northern climates to help rid thoroughfares of accumulated snow and ice. Salt is used in water-softening equipment that removes calcium and magnesium compounds from water.

History Of Use

In some parts of the Western Hemisphere and in India, the use of salt was introduced by Europeans, but in parts of central Africa it is still a luxury available only to the rich. Where people live mainly on milk and raw or roasted meat (so that its natural salts are not lost), sodium chloride supplements are unnecessary; nomads with their flocks of sheep or herds of cattle, for example, never eat salt with their food. On the other hand, people who live mostly on cereal, vegetable, or boiled meat diets require supplements of salt.

The habitual use of salt is intimately connected with the advance from nomadic to agricultural life, a step in civilization that profoundly influenced the rituals and cults of almost all ancient nations. The gods were worshipped as the givers of the kindly fruits of the earth, and salt was usually included in sacrificial offerings consisting wholly or partly of cereal elements. Such offerings were prevalent among the Greeks and Romans and among a number of the Semitic peoples.

Covenants were ordinarily made over a sacrificial meal, in which salt was a necessary element. The preservative qualities of salt made it a peculiarly fitting symbol of an enduring compact, sealing it with an obligation to fidelity. The word salt thus acquired connotations of high esteem and honour in ancient and modern languages. Examples include the Arab avowal “There is salt between us,” the Hebrew expression “to eat the salt of the palace,” and the modern Persian phrase namak ḥarām, “untrue to salt” (i.e., disloyal or ungrateful). In English the term “salt of the earth” describes a person held in high esteem.

Salt contributes greatly to our knowledge of the ancient highways of commerce. One of the oldest roads in Italy is the Via Salaria (Salt Route) over which Roman salt from Ostia was carried into other parts of Italy. Herodotus tells of a caravan route that united the salt oases of the Libyan Desert. The ancient trade between the Aegean and the Black Sea coast of southern Russia was largely dependent on the salt pans (ponds for evaporating seawater to obtain salt) at the mouth of the Dnieper River and on the salt fish brought from this district.

Cakes of salt have been used as money in Ethiopia and elsewhere in Africa and in Tibet. In the Roman army an allowance of salt was made to officers and men; in imperial times, this salarium (from which the English word salary is derived) was converted into an allowance of money for salt.

China, the United States, India, Germany, Canada, and Australia are the world’s largest salt producers in the early 21st century.

Occurrence

Seawater

Though the material that gives seawater its salty flavour is composed of many substances, sodium chloride, or common salt, is by far the predominant compound. On the assumption that 1 gallon (about 4 litres) of seawater contains 0.231 pound (about 105 grams) of salt and that rock salt on the average is 2.17 times as dense as water, it has been estimated that if the oceans of the world were completely dried up, they would yield at least 4.5 million cubic miles of rock salt, or about 14.5 times the bulk of the entire continent of Europe above the high-water mark.

Seawater contains on the average about 3 percent salt, although the actual concentration varies from about 1 percent (in the polar seas) to 5 percent. Enclosed waters such as the Mediterranean and Red seas contain a higher proportion of salt than does the open ocean at the same latitude. Irrespective of the source of the seawater, salt obtained by the evaporation of seawater has the following composition: sodium chloride 77.76 percent, magnesium chloride 10.88 percent, magnesium sulfate 4.74 percent, calcium sulfate 3.60 percent, potassium chloride 2.46 percent, magnesium bromide 0.22 percent, and calcium carbonate 0.34 percent.

Natural brines

Brine is water containing a high concentration of salt. Natural brines of commercial importance are found in the Dead Sea as well as in Austria, France, Germany, India, the United States, and the United Kingdom. Salt in brines is nearly always accompanied by chlorides and sulfates of potassium, calcium, and magnesium; carbonates and the element bromine often are present as well.

The Dead Sea, which covers an area of 1,020 square km (394 square miles), contains approximately 12,650,000,000 tons of salt. The Jordan River, which contains only 35 parts of salt per 100,000 parts of water, adds 850,000 tons of salt to this total each year.

The concentration of salts in the Dead Sea varies from 270 to 300 parts per thousand to a depth of 40 metres (130 feet); it increases gradually from 40 to 100 metres (130 to 330) feet and remains a fairly constant 332 parts per thousand below 100 metres. Dead Sea water is relatively free from sulfates and has a high proportion of potassium and bromine. Because atmospheric conditions favour evaporation by sunlight (solar evaporation) for about eight months of the year, the production of salt, potassium, and bromine is feasible in the Dead Sea area. The process used for recovery of salt and potash is similar to that described below under Salt manufacture. The Indian brines at Khārāghoda resemble seawater in the character of their dissolved salts but are much more concentrated and in some cases virtually saturated; that is, they have dissolved all the salt they can.

Certain natural brines occurring in the United Kingdom and the United States are of special interest because they contain salts, such as the chlorides of barium and strontium, that are not usually found in brines. Special processing methods are required to produce salt from such brines. In Britain these unusual brines are found at great depths during test drillings for petroleum, while in the United States such brines occur in deep wells in several places.

Rock salt

Rock salt is crystalline sodium chloride, called halite by mineralogists. It occurs widely in the form of rock masses and beds and is abundant in rocks from all geologic periods. Because of its great solubility in water, it occurs under extremely thick cover in humid regions but lies close to the surface in arid regions.

All major rock salt deposits originated from the evaporation of seawater at some time during the geologic past. Approximately 78 percent of the mineral matter in normal seawater is sodium chloride. Upon evaporation of about nine-tenths of the volume of seawater, rock salt is precipitated. Calcium sulfate (gypsum and anhydrite) and potassium and magnesium salts also are precipitated. Deposits are found in beds from a few feet to many hundreds of feet thick. The ages of these beds range through much of geologic time. Because evaporation of a large quantity of seawater leaves only a small amount of salt, it is theorized that many extremely thick rock salt beds were deposited in partly enclosed arms of the seas in which evaporation was greater than the inflow of salt water. A barrier on the seafloor at the entrance to the basin prevented the outflow of the concentrated saline water.

Such bedded salt deposits occur in the Punjab Salt Range in Pakistan and in Iran; however, these deposits have been little exploited. Similar deposits in the United States and Canada are worked extensively for both industrial and domestic use. Other important salt deposits, usually classified by the age of the surrounding rock, are found in Germany, Nova Scotia, the sub-Carpathian region extending from Poland through Hungary and Romania, and the province of Sichuan in China, where salt wells have been in existence for more than 2,000 years.

Another economically important type of rock salt deposit is the salt domes, which were formed when earth pressure forced up plugs of rock salt measuring approximately a mile across. The domes appear to result from pressure, which pushes the salt up through the rocks from depths as great as 50,000 feet (15,000 metres). Many domes occur at shallow depths and are extensively mined. Domes in the sub-Carpathian region of Europe have been worked since ancient times. The North German Plain has many extensively mined domes, which are thought to have originated below 6,000 feet; domes also are abundant along the U.S. Gulf Coast. Rock salt may be obtained from domes by the usual mining methods or by drilling wells into the salt strata and pumping water down to dissolve the salt; the brine is then returned to the surface, where it is processed like natural brine.

Salt Manufacture

At one time almost all the salt used in commerce was produced from the evaporation of seawater, and sea salt still is a staple commodity in many maritime countries, especially where the climate is dry and the summer is long. Commercial salt is manufactured from rock salt, as well as from seawater and other natural and artificial brines. Most of the artificial brines are obtained by pumping water into underground salt beds. A considerable amount of brine itself is used directly in industrial countries.

Manufacture from rock salt

The beds of rock salt are mined or quarried by the usual excavation methods, depending on the depths and thicknesses of the deposits and on local conditions. The mined rock salt sometimes is dissolved and the salt manufactured by treatment of the brine, as described below. The method affords opportunities for purification of the salt. When the rock salt is of a high degree of purity, as in Poland and the United States, the salt may be ground, screened, and marketed without further processing. The salt is mined in large lumps that are first crushed, then more finely ground and screened by size into various grades; the salt is then bulk-loaded into trucks, hoppers, or barges or loaded into bags for further handling. Bulk handling has been greatly facilitated by the use of anticaking agents which allow the salt to be stored uncovered and outdoors without becoming a hard mass again.

Manufacture from seawater and brines

Only a certain quantity of salt will dissolve in water at any given temperature. Once the solution contains as much salt as it can hold, it is said to be saturated; any further additions of salt will not dissolve.

Evaporation is the reverse of this process. When an aqueous solution of several salts (seawater, for example) is evaporated, each of the salts precipitates as it reaches its point of saturation in the solution. Thus, the different salts in seawater will precipitate at different times, forming layers on the bottom of the evaporating pond. For seawater and many brines, the order of deposition is calcium carbonate, calcium sulfate, sodium chloride, magnesium sulfate, potassium magnesium chloride, and magnesium chloride.

Solar evaporation

In maritime countries where there is a negative evaporation rate—i.e., the amount of water evaporating exceeds the amount of rainfall by at least 75 cm (about 30 inches)—salt is produced by solar evaporation from seawater. The processes used are similar in general principle from country to country, but details of equipment vary from sophisticated in the United States to quite primitive in developing nations.

A preliminary concentration is usually accomplished by allowing the seawater to flow through a series of gates constructed of wood or a combination of wood and concrete into a series of shallow ponds separated by dikes. In these ponds the solution is concentrated to a specific gravity of about 1.22; this means that a given volume of brine is 1.22 times as dense as a given volume of pure water. At this stage, suspended impurities such as sand, clay, and the less soluble salts such as calcium carbonate, or chalk, and calcium sulfate are removed. Solar evaporation of the Dead Sea water is hastened by adding dye to the water. The dye permits more heat to be absorbed from sunlight in thinner layers of brine so that shallow ponds may be used and the penetration of brine into the ground is reduced.

Once it has been concentrated, the brine is run through a series of crystallizing pans, usually four in number, where the salt is deposited as evaporation proceeds. In the first crystallizing pan, the brine is concentrated to a specific gravity of 1.23 and remains partly contaminated with calcium sulfate. The specific gravity of the solution in the pan increases slowly during crystallization of the salt, reaching 1.24 in the second pan. In the third pan the specific gravity of the solution reaches 1.25, and the salt deposited there contains small amounts of magnesium sulfate as an impurity. The final solution, termed bitterns, has a specific gravity of 1.25–1.26 and is used in some countries (United States and Israel) in the manufacture of potash, bromine, epsom salts (magnesium sulfate), and magnesium chloride.

In developing countries the salt in each crystallizing pan is raked into rows, where it is allowed to drain for several days. After that it is collected into heaps, drained again, lifted from the pans, and finally dried. In industrial countries the salt is harvested mechanically and washed with saturated brine. It is then dewatered, washed with fresh water, and stored for further processing or direct sale.

Use of artificial heat

In areas where bedded deposits can be solution-mined, evaporated salt is recovered from these solutions with artificial heat. Some evaporated salt also is made from natural brine or solar salt. Formerly, brine was concentrated in open pans over fire. More recently, steam-jacketed vessels have been used. The largest amount of salt produced in the colder climates is rock salt. The largest amount of evaporated salt is produced by multiple-effect vacuum evaporators, and an important quantity is made in so-called open crystallizers or grainers that produce a type of crystal preferred for use in some of the food industries. The brine, natural or artificial, is first pumped into settling tanks, where calcium and magnesium compounds may be removed by chemical treatment. In grainer operations the settled and filtered brine is delivered to the grainer, a long open trough heated with steam coils. The brine is fed into the grainer at approximately the same rate at which evaporation is taking place and at a temperature only slightly below that of the brine in the grainer. The residue of brine, or bitterns, may be removed continuously, once a day, or less often. Evaporation occurs at the surface of the liquid, and the crystals originate there. They remain at the surface, held up by the surface tension of the brine. The crystal grows at the top edges, becoming a small inverted hollow pyramid, or hopper. Eventually the hopper sinks and ceases to grow. When the crystals are recovered, the salt is largely in the form of flakes, hence the name flake salt.

When multiple-effect evaporators are used, the vacuum in each vessel is adjusted so that the vapour from the first vessel is hot enough to boil the brine in the second, the vapour from the second supplying the heat to operate the third vessel or effect. The brine is usually sent through the stages or effects in succession, although in the case of salt manufacture fresh brine may be fed to each stage if desired. With open pans, 4,500 to 5,400 kg (10,000 to 12,000 pounds) of steam are required to produce 900 kg (1 ton) of salt. With triple-effect evaporation, 630 kg (1,400 pounds) of steam produce 1 ton of salt.

The Alberger process is partially a vacuum-pan and partially a grainer operation in which cubic crystals are formed in the solution fed to the grainer pans by a partial vacuum-pan evaporation. These seed crystals in the grainer produce a salt that is a mixture of the grainer-type flake and the flake grown on seed crystals. About 1,360 kg (3,000 pounds) of steam are required to produce one ton of salt. Salt from the Alberger process is centrifuged (spun) from the brine and then dried. Table salt may have small amounts of aluminum calcium silicate, calcium silicate, magnesium silicate, tricalcium silicate, magnesium carbonate, or tricalcium phosphate added to keep it free-flowing. Iodized salt has potassium iodide added. In some countries yellow prussiate of soda, to prevent caking, is added in minute amounts as regulated by the government.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#723 2020-07-06 00:14:24

ganesh
Administrator
Registered: 2005-06-28
Posts: 31,452

Re: Miscellany

601) Convalescent plasma therapy

Overview

Convalescent plasma therapy is an experimental treatment that some doctors are using for people with severe coronavirus disease 2019 (COVID-19).
No drug has been proved to be safe and effective for treating COVID-19. The U.S. Food and Drug Administration (FDA) hasn't approved any drugs specifically to treat people with COVID-19.

But, people who've recovered from COVID-19 have antibodies — proteins the body uses to fight off infections — to the disease in their blood. The blood from people who've recovered is called convalescent plasma. Plasma is the liquid portion of the blood.

Researchers hope that convalescent plasma can be given to people with severe COVID-19 to boost their ability to fight the virus. It also might help keep people who are moderately ill from becoming more ill and experiencing COVID-19 complications.

If you've had COVID-19 and recovered from it, consider donating blood through the American Red Cross or your local donation center. Either can provide information about the donation process.

Why it's done

Convalescent plasma therapy may be helpful for people with COVID-19 who aren't helped by other treatments. Some people with COVID-19 become very sick and don't respond to other treatments or drugs. These people often develop acute respiratory distress syndrome (ARDS) — a severe lung condition. They often require mechanical assistance, such as a ventilator, to breathe. These people also are in danger of developing organ failure.

It could also help other people who may have a higher risk of serious illness, such as people with chronic medical conditions, for example, heart disease or diabetes, or those who have weakened immune systems. Convalescent plasma could help these people from getting sicker if they get COVID-19.

Convalescent plasma might also be considered for family members or health care workers who have been exposed to someone with COVID-19 to potentially prevent them from getting COVID-19.

Doctors may choose to enroll the person with COVID-19 in an expanded access program and order convalescent plasma for him or her. This type of program provides access to investigational new drugs outside of clinical trials. This type of program is sometimes necessary when a disease is very severe or life-threatening, and there is no available treatment.

Risks

Blood and plasma have been used to treat many other conditions, and they're usually very safe. The risk of contracting COVID-19 infection from receiving convalescent plasma therapy hasn't been tested yet. But researchers believe that the risk is very low because the plasma donor has fully recovered from the infection.

Convalescent plasma therapy carries the risk of:
•    Allergic reactions
•    Lung damage and difficulty breathing
•    Transmission of infections, including HIV and hepatitis B and C

The risk of these infections is very low, because donated blood must meet certain requirements outlined by the FDA. Before donated blood can be used, it must be tested for safety. It then goes through a process to separate out blood cells so that all that's left is plasma with antibodies.

Although many people experience no symptoms, others have mild to severe medical complications that lead to death in some people.

What you can expect

Your doctor may consider you a candidate for convalescent plasma therapy if you're seriously ill with COVID-19 in the hospital. Your doctor will decide if it will be beneficial for you and may enroll you in the treatment program. If you or a family member has questions about convalescent plasma therapy, ask your doctor.
Your doctor will order convalescent plasma that is compatible with your blood type from your hospital's local blood supplier.

Before the procedure

Before convalescent plasma therapy, your health care team prepares you for the procedure. A health care team member inserts a sterile single-use needle connected to a tube (intravenous, or IV, line) into a vein in one of your arms.

During the procedure

When the plasma arrives, the sterile plasma bag is attached to the tube and the plasma drips out of the bag and into the tube. It takes about one to two hours to complete the procedure.

After the procedure

Because this investigational therapy hasn't yet been tested, you'll be closely monitored after the convalescent plasma procedure.

Your doctor will record your response and reaction to the treatment. He or she may record how long you needed to stay in the hospital or if you needed help with breathing or other therapies following the convalescent plasma procedure.

Results

It's not yet known if convalescent plasma therapy will be an effective treatment for COVID-19. You might not experience any benefit.

However, this treatment might improve your ability to recover from the disease.

The collective results from people receiving convalescent plasma therapy can provide information about the effectiveness of the therapy and whether it can become an approved therapy to treat COVID-19. In preliminary treatment, many people have benefited from convalescent plasma therapy. Researchers continue to evaluate the results from people who received the therapy.

By studying results of this therapy for COVID-19, doctors are getting closer to finding a treatment. In addition, learning more about the use of convalescent plasma therapy now will help health care workers be better prepared to provide optimal patient care.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#724 2020-07-07 01:12:19

ganesh
Administrator
Registered: 2005-06-28
Posts: 31,452

Re: Miscellany

602) Scaffold

Scaffold, in building construction, temporary platform used to elevate and support workers and materials during the construction, repair, or cleaning of a structure or machine; it consists of one or more planks of convenient size and length, with various methods of support, depending on the form and use.

In timber scaffolding, support for the planks is provided by a timber frame fabricated and erected at the site. The frame may consist of vertical posts, horizontal longitudinal members, called ledgers, transverse members supported by the ledgers, and longitudinal and transverse cross-bracing. The planks rest on the transverse members.

Trestle supports are used for work on a large area if little or no adjustment of height is required (e.g., for plastering the ceiling of a room). The trestles may be of special design or simply wooden sawhorses of the type used by carpenters. Specially designed trestles may be adjusted to provide for working heights of from 7 to 18 feet (2 to 5 m).

Tubular scaffolding of steel or aluminum has largely replaced timber scaffolding on most construction projects. Tubular scaffolding can easily be erected in any shape, length, or height. Sections may be mounted on casters to provide a highly mobile staging. The scaffolding may be enclosed with canvas or plastic sheeting for protection against the weather.

Tubular hoisting towers may be quickly assembled from steel tubes or pipes about 3 inches (8 cm) in diameter with standard connections.

A suspended scaffold consists of two horizontal putlogs, short timbers that support the flooring of the scaffold, each attached to a drum mechanism. Cables extend from each drum to an outrigger beam attached overhead to the structure frame. Ratchet devices on the drums provide for raising or lowering the putlogs between which spanning planks form the working surface. Power scaffolding may be raised or lowered by means of an electric motor operated by the worker on the scaffold.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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#725 2020-07-08 00:38:21

ganesh
Administrator
Registered: 2005-06-28
Posts: 31,452

Re: Miscellany

603) Masonry

Masonry, the art and craft of building and fabricating in stone, clay, brick, or concrete block. Construction of poured concrete, reinforced or unreinforced, is often also considered masonry.

The art of masonry originated when early man sought to supplement his valuable but rare natural caves with artificial caves made from piles of stone. Circular stone huts, partially dug into the ground, dating from prehistoric times have been found in the Aran Islands, Ireland. By the 4th millennium BCE, Egypt had developed an elaborate stone masonry technique, culminating in the most extravagant of all ancient structures, the pyramids.

The choice of masonry materials has always been influenced by the prevailing geological formations and conditions in a given area. Egyptian temples, for example, were constructed of limestone, sandstone, alabaster, granite, basalt, and porphyry quarried from the hills along the Nile River. Another ancient centre of civilization, the area of western Asia between the Tigris and Euphrates, lacked stone outcroppings but was rich in clay deposits. As a result, the masonry structures of the Assyrian and Persian empires were constructed of sun-dried bricks faced with kiln-burned, sometimes glazed, units.

Stone and clay continued to be the primary masonry materials through the Middle Ages and later. A significant development in masonry construction in ancient times was the invention of concrete by the Romans. Although well-cut blocks of stone masonry could be erected without benefit of mortar, the Romans recognized the value of cement, which they made from pozzolanic tuff, a volcanic ash. Mixed with water, lime, and stone fragments, the cement was expanded into concrete. Walls of this concrete, faced with various stone or fired-clay materials, were more economical and faster to erect than walls made of stone blocks.

Because it provided more freedom in shaping structures, concrete helped the Romans develop the arch into one of the great basic construction forms. Prior to the arch, all builders in stone had been handicapped by the stone’s fundamental lack of tensile strength—that is, its tendency to break under its own weight when supported on widely separated piers or walls. The Egyptians had roofed temples with stone slabs but had been forced to place the supporting columns close together. The Greeks had used wooden roof beams covered with thin stone; such beams were subject to weather and fire. The Roman arch avoided tension entirely, keeping all the masonry in compression, from the keystone to the piers. Stone in compression has great strength, and the Romans built huge arched bridges and aqueducts in large numbers. Extending their arch into a tunnel, they invented the barrel vault, with which they successfully roofed such buildings as the Temple of Venus in Rome. Several arches intersecting at a common keystone could be used to form a dome, such as that of the Pantheon in Rome. Two intersecting barrel vaults gave rise to the groin vault, which was used in some of the great Roman public baths.

The Roman arch underwent a significant modification in the Middle Ages in the evolution of the pointed arch, which provided a strong skeleton resting on well-spaced piers. The massive, rigid masonry structures of the Romans gave way to soaring vaults supported by external flying buttresses (external bracing). The use of smaller-sized stones and thick mortar joints created an elastic, slender structure that stressed the masonry to its fullest. The bearing of unit upon unit required the use of mortar to distribute the contact stresses.

With the advent of Gothic forms, masonry construction in a historic sense had solved the problem of spanning space entirely by material in compression, the only design formula suitable to stone. With the advent of the truss in the 16th century, the rise of scientific structural analysis in the 17th century, and the development of high-tensile resistant materials (steel and reinforced concrete) in the 19th century, the importance of masonry as a practical material for spanning space declined. It owes its revival largely to the invention of portland cement, the principal ingredient of concrete, which in the 20th century returned unit masonry to its essentially pre-Roman role of forming vertical wall enclosures, partitions, and facings.

Masonry construction begins with extractive materials, such as clay, sand, gravel, and stone, usually mined from surface pits or quarries. The most widely used rocks are granite (igneous), limestone and sandstone (sedimentary), and marble (metamorphic). In addition to rocks, clays of varying types are manufactured into bricks and tiles. Concrete blocks are fabricated from cement, sand, aggregate, and water.

For the shaping and dressing of stone a great variety of tools can be used. These range from such hand-held tools as hammers, mallets, chisels, and gouges to machines including frame and circular saws, molding and surfacing machines, and lathes. There are also various appliances for handling stone at the building site, ranging from different forms of light hand tackle to machine-driven cranes.

Many architects value masonry for its colour, scale, texture, pattern, and look of permanence. In addition to its aesthetic appeal, masonry has a number of other desirable properties, such as its value in controlling sound, resisting fire, and insulating against daily fluctuations in temperature.

Beginning with 20th-century housing, masonry was frequently used over wood-stud construction. Cavity walls, highly resistant to moisture, were often built of two vertical layers of masonry separated by a layer of insulating material. Some foundations were built of concrete blocks, and many building codes required the use of masonry in fire walls.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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

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