How can ice float on water..?

Ice floats on water because a piece of ice is lighter than the same amount of water.  The ice is not very much lighter than the water, so it floats low in the water.

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When water freezes to ice, the water molecules line up in rows.  But as they do so, the molecules move apart slightly.  The ice increases in size as it forms and this gives ice a lower density than water, making it float in water.

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The force between the molecules is very strong, and nothing can resist the expansion that occurs as the ice forms.  This is why water pipes sometimes burst in winter.  The ice expands and cracks the pipe.  Then when the weather gets warmer, the ice melts and water pours from the cracked pipe.  It is unusual for liquid to expand on freezing, but it is a good thing that water does so.  The layer of ice that may form over lakes and the sea in winter prevents the water beneath from freezing.

What is deep freezing...?

Deep Freezing is a method of preserving food by lowering its temperature to 18 degree centigrade or below.  It stops almost all spoilage processes, although there may be some residual enzyme activity in uncooked vegetables, which is why these are blanched (dipped in hot water to destroy the enzymes) before freezing.  Micro-organisms cannot grow or divide while frozen, but most remain alive and can resume activity once defrosted.  Commercial techniques freeze foods rapidly in order to prevent the growth of large ice crystals which would damage the food tissue on thawing.

When were the Present Continents Formed...?

At the very time when oil was beginning to form, an enormous shift took place in the Earth's crust, which slowly resulted in the formation of the present continents.

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Numerous studies, even in recent years, confirm the theory that the great continental mass pushed out of the sea in the earlier periods and then split apart into several pieces which drifted about the Earth for hundreds of millions of years.  Finally, between the middle of Cretaceous and early Tertiary Periods (100 million to 50 million years ago) these pieces split up again to form land masses recognisable in form to the continents of today.  These sections are still drifting apart.
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This interesting suggestion, first put forward by the German meteorologist, Alfred Wegener (1880-1930), is known as the theory of 'continental drift'.  Wegener, who was also a daring explorer and experience geologist, published his ideas in a book printed in 1912.  It naturally created a great stir in scientific circles, which soon split into two groups, one of his supporters and one of his opponents.  They are both eager to prove or disprove his theory.
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In a few words, wegener's idea was as follows: in dim, distant times the continental masses were joined together in a single block (or shield), which Wegener called Pangaea.  The rest of the Earth was covered by a primeval mass of water, the Pantalaxia.
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During the Eocene Period, about 50 million years ago, a slow but steady movement then began.  The Pangaea cracked and, pulled apart by the rotating movement of the Earth, the bits began to drift away from each other as if they were floating on a heavier, more elastic base.
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According to Wegener, it was because of this shifting that the folds occurred in the Earth's crust which lifted up the loftiest mountain chains still existing in the world today.
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HIV - 'RESERVOIR' FOUND IN BRAIN...ANI

Aussie scientists have discovered that the brain also acts as a key "reservoir" for HIV, a finding that may be a serious threat to the search for a way to eradicate the virus from the body.  While scientists are using antiretroviral drugs to get rid of HIV altogether, they are finding it difficult to perfect techniques to kill off infected cells in the known reservoirs for HIV in the body.

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Melbourne-based Dr. Melissa Churchill said that HIV was known to hide out in the thymus and lymph tissues, the gut, spleen, testes, bone marrow, but they have recently found that it also resides in astrocyte cells in the brain.

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"The astrocytes are basically the support cells - they mop up toxins released from other cells and maintain a really nice environment for the neurons to function," quoted Churchill as saying of the vital role played by these cells for congnition.

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"Previously, People weren't sure if we have to actually consider it as a genuine viral reservoir, but it is," she added.

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Churchill and an international team of researchers used latest in high-powered microscopes to examine brain tissue from HIV-Positive people to gauge the presence of the virus in these astrocyte cells.

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She said that it was believed that the virus had about a "One per cent" presence, but the research showed it was up to 19 percent and "very significant".

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In her opinion, the discovery poses several new challenges for scientists now progressing the work of finding ways to eradicate HIV from the body.

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"One of the issues of the brain as a reservoir is that it's quite inaccessible to the immune system and to anti-retrovirals," Churchill said.....Deccan Chronicle Article by ANI

Cool The Planet PLANT A TREE.. M. Sonalee

Planting trees has often been the first line of defence against global warming.  Trees, after all, cool the atmosphere by drinking in the carbon dioxide from the air.  Scientists say that trees absorb and store the key greenhouse gases emitted by cars and power plants.  All plants absorb carbon dioxide but trees process significantly more than smaller plants do, due to their large size and extensive and root structures.

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Says environmentalist Subhas Datta, "In essence, trees are like the kings of the plant world.  They have much more "woody biomass" to store carbon dioxide than smaller plants."  Subsequently, they are considered nature's most efficient carbon sinks.

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According to Datta, certain trees are better absorbents of carbon dioxide than others.  "There 'carbon traps' usually grow quickly and live long," says Datta.  Unfortunately, both qualities cannot be found together in foliage.  Normally younger trees grow faster but their older partners are better absorbents.

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It has been found that trees that grow slower can store much more carbon over their significantly longer lives.  A study shows that tropical, evergreen forests are better at tackling global warming.  According to a study by Dr Govindasamy Bala of Lawrence Livermore National Laboratory, evergreens like confers and red cedar, "cut down on emissions and help keep the planet cool."  Dr Bala also observes that the further a person moves away from the equator these gains are eroded.  According to researchers, planting trees in mid and high latitude locations do not have similar effects.  In fact, on the contrary they could increase temperatures by 2100.

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Therefore, you need to plant the right tree at the right location to avail of the benefits of carbon sequestration.  If one takes the US into consideration, each specific region will have a tree that is the best absorbent in that region.  For instance, in Hawaii, it is the eucalyptus; loblolly pine acts best as an absorbent in the Southeast while poplars are best in the Great Lakes.

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Stan Wullschleger, who is a researcher at Tennessee's Oak Ridge National Laboratory specialising in the physiological response of plants to global climate change, observes that there are dozens of tree species that could be planted depending on location, soil and climate.

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It is prudent to remember that ultimately a tree of any shape, size or genetic origin can help absorb carbon dioxide.  "The least expensive option is to plant a tree in your garden (if you have one) as it will help offset the production of carbon dioxide," suggests Datta.

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Trees that are low maintenance are the best absorbents.  This has been pointed out by Dave Nowak, a researcher at the US Forest Service's Northern Research Station in Syracuse, New York.  While studying the use of trees for carbon sequestration in 2002, he discovered that trees like the common horse-chestnut, black walnut, London plane, American Sweetgum, Douglas fir, ponderosa pine, red pine, white pine, hispaniolan pine, scarlet oak, red oak, Virginia live oak and bald cypress are very good at absorbing and storing carbon dioxide.  In his research paper, Nowak advises urban land developers to avoid trees that require a lot of maintenance, as the burning of fossil fuels to power equipment like trucks and chainsaws will only erase the carbon absorption gains otherwise made.

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So, if you want to tackle global warming, all that you need to do is to plant a neem tree in your garden or anywhere in the vicinity! Simple, isn't is?

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How Thermos Keeps Coffee Hot Or Lemonade Cool...

According to Prevost's Theory of Exchange, the colder of two bodies always absorbs heat waves until both bodies are the same temperature.  By this theory, it would be natural for scalding coffee or ice-cold lemonade in a Thermos to lose heat or gain it respectively.  But a Thermos is designed to cut down the exchange of heat between the inside and the outside of the bottle by hampering the three ways in which heat can travel :

Conduction, Convection, and Radiation.

  A standard Thermos, made of metal or plastic, has an inner container consisting of a double glass bottle.  A near vacuum exists between the two layers of glass, and the lips of the bottles are sealed by melting the edges together.  Glass is used because it is a poor conductor of heat, which means that in glass heat does not pass rapidly from molecule to molecule as it does in a better heat conductor such as copper.  The stopper and pads that hold the bottle in place in the outer container are generally made of cork, also a very poor conductor of heat.  The near vacuum between the two layers of glass limits the possibility of heat escaping from or penetrating the Thermos by convection - the transmission of heat by means of the movement of heated matter from one place to another in a liquid or gas.  Since, however, heat can travel through a vacuum by radiation, the facing surfaces of glass are coated with a silvery solution of aluminium which reflects heat waves and does not absorb them.

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Sir James Dewar invented the thermos or "Vacuum bottle" in 1885 to keep heat from the liquid gas with which he was experimenting.  The happy by-product of his ingenuity has made our life pleasurable when we are on a picnic or long distance travel.

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What is a Pacemaker?

An artificial pacemaker is used when a person's own heart pacemaker is not working properly. It is an electronic device for stimulating the heart.

Heart muscles contract regularly. However, their natural rate (about 40 beats per minute) is too slow. To increase the rate to around 70 beats, the heart has its own pacemaker. This is a small mass, or node, of nerve tissues in the right auricle.

Certain heart diseases cause this pacemaker to fail. However, the heart can be kept going with a battery powered electronic pacemaker. Some artificial pacemakers are implanted in the chest. Others are small enough to be passed along a vein to the heart. The simplest pacemakers keep the heart going at a steady 70 beats per minute. But sometimes it is possible to get the person's own nervous system to control the pacemaker. In this case the heart can still beat faster or slower according to the body's needs.

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Remote Sensing..

Q: What is Remote Sensing?

A: Remote Sensing is the technique of collecting information by observing the surface of the Earth and other planetary bodies through sensors on aircraft and space satellites. The basic tool used here is photography-infrared and false colour photography in particular. Modern remote sensing satellites are equipped with special cameras which take photographs of any particular region of the Earth's surface in several colours simultaneously. These separate images can be electronically proceessed to produce multicolour images and maps outlining areas of specific interest such as diseased or pest-infected crops, forest areas and vegetation, rich fishing areas in seas, even underground water and mineral reserves. Remote Sensing is an indispensable tool for better monitoring and management of natural resources.

The Acid Rain__

What is acid rain?

Acid rain is the name given to rain, snow or sleet contaminated with acid substances so that its acidity is greater than the limit expected by normal concentrations of carbon dioxide dissolving in the rain to give carbonic acid. The increased acidity is caused by larger concentrations of a number of contaminants, principally the strong acids, nitric and sulphuric, which arise from industrial effluents containing oxides of nitrogen and sulphur.

It can mark fruit and leaves, and adversely affect soil but its main effect is on acquatic ecosystems especially in regions which cannot naturally buffer acidic inputs such as those with thin soils and granite rocks. Disappearance of fish from many scandinavian lakes is largely a result of pollution by acid rain.

Feel of Metal

Why does metal feel cold?

When you touch something made of metal, it feels cold. The reason for this is that some heat flows from your fingers into the surface of the metal. Because the skin on your fingers loses heat, it gets cold and the metal feels cold.

Metal objects feel cold in a cool climate because metal is a good conductor of heat. This means that heat flows through metal easily. Heat, therefore, leaves the skin of your fingers and flows into the metal. It does this because your fingers are warmed than the metal. The heat moves on through the metal, so that the surface of the metal does not get as warm as the skin on your fingers. Heat continues to flow from your fingers into the metal, and it feels cold.

Wood or cloth are poor conductors of heat. The surface of an object made of wood or cloth quickly warms up as you touch it, and it does not feel cold.

Appearance of Swimmiting Pool

Why does a swimming pool appear less deep than it really is?

This is due to the phenomenon of refraction of light. The rays of light coming from the bottom of the pool (or from the coil lying at the bottom of the can) travel from water to air. As the rays pass from denser (water) to rarer (air) medium they bend away from the normal. When the rays are produced back they form an image of the coil (bottom of the poor) are a point which is a little above the real position. Hence the coil appears to be slightly raised and the pool appears to be less deep than it really is.

Why is it harmful to see solar eclipse with naked eye?

Why is it harmful to see solar eclipse with naked eye?

Doctors always warn people, especially children, against watching the solar eclipse, either directly or through smoking glasses or even in shallow water as in a utensil. The harmful rays in the sunlight (infrared rays) are at the maximum during the eclipse, which might burn the most sensitive part of retina, forea and macula, leading to irreversible loss of eyesight.

The surface of the sun is about four times as hot as a furnace. The lens or cornea in our eyes acts like a burning-glass. If one looks straight at the Sun, the lens will be destroyed for life. Even if we look at the Sun through smoked glass, the Sun may look dim, but the dangerous heat rays can still pass through. Whenever there is an eclipse of the Sun, some people are blinded because they take foolish risks of this sort.

What is synthetic rubber ?

What is synthetic rubber ?

Synthetic rubber is made of certain kinds of hydrocrabons. Of these, butadine is the most important. These hydrocarbons are obtained from coal, crude petroleum and alcohol. By the end of the Second World War, the combined production of synthetic rubber by USA and Germany alone was almost equal to that of natural rubber. Synthetic rubber is more oil-resistant than natural rubber. In the international market, natural rubber is facing severe competition from synthetic rubber.

Why do bees buzz?

Why do bees buzz?

The buzzing, sound is only caused by rapid fluttering of the bees'wings. The wings of the bees work like that of an electric fan. In hot weather, bees even carry water drops and spray droplets on their hives with their wings to cool it.

Why do leaves fall in autumn?

Why do leaves fall in autumn?

The green colour in the leaves is due to a pigment, chlorophyll, in the plant. In autumn, the leaves stop making this pigment, thus the leaves turn yellow. Every leaf has a large vein underneath which carries water for nourishing it. This soon becomes dry in a yellow leaf so that water no longer flows through it. Thus the leaf dies and its grip on the branches loosens. When a strong wind blows, it breaks the leaf's grip and thus the leaves fall off in autumn.

Why a pin-prick hurts?

Why a pin-prick hurts?

Human body is covered with skin. This skin is made up of several layers. Beneath the outermost layer are found millions of very small points. These are connected to a number of little threads called nerves. When the skin is pressed upon or touched, the nerves communicate the sensation to the brain. Thus the skin with the little nerves provides us with one of the five senses - "touch". If a pin goes into the outer layer and touches one of these little points, the touch becomes "pain"

Blood Clot?

How does the blood clot?

Clotting is a natural phenomenon tht checks excessive loss of blood in case of injury. Clotting takes place whenever the tissue is injured. There are three types of cells in our blood - red blood cells, white blood cells and platelets. It is these platelets that help in forming clots to stop bleeding. The platelets gather at the site of the injured cell and prevent the red blood vessels from flowing out. They form a plug across the opening and release chemicals that convert liquid blood protein fibrinogen into insoluble fibrin. Fibrin forms a mesh of thread like fibres that trap platelets and other blood cells, thereby forming a clot.

Difference between ballistic missile and cruise missle?

What is the difference between ballistic missile and cruise missile?

A ballistic missile is a missile that follows a prescribed course that cannot be significantly altered after the missile has burned its fuel (i.e., its course is governed by the law of ballistics). In order to cover large distances, ballistic missiles are usually launched very high into the air or in space.

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A cruise missile is a guided missile which uses a lifting wing and most often a jet propulsion system to allow sustained flight. Cruise missiles are, in essence, unmanned aircraft. They are generally, designed to carry a large conventional or nuclear warhead many hundreds of miles with excellent accuracy. Modern cruise missiles normally travel at subsonic speed, are self-navigating and fly low in order to avoid radar detection.

What is Superfluidity?

What is Superfluidity?

Superfluidity is a phase of matter characterised by the complete absence of viscosity. Thus, superfluids placed in a close loop can flow endlessly without friction. Superfluidity was discovered by Pyotr Leonidvich Kapitsa, John F. Allen and Don Misener in 1937. The study of superfluidity is called quantum hydrodynamics.

Night Blindness/Colour Blindness.....

What is the difference between night blindness and colour blindness?

Night blindness refers to the inability of the eye to adapt to reduced illumination, therefore, leading to a complaint of not being able to see in the dark. Individuals complaint of not being able to see in the dark. Individuals suffering from night blindness not only see poorly at night, but also require some time fore their eyes to adjust from brightly lit areas to dim ones.

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Colour blindness, on the other hand, refers to the difficulty in seeing differences between some of the colours that other people can easily distinguish. It is most often genetic in nature, but might also occur because of the eye, nerve, or brain damage or due to exposure to certain chemicals.