At room temperature, it is a nearly colorless, flavorless, and odorless liquid. Many substances dissolve in water and it is commonly seen as "the universal solvent"; because of this, water in nature and in use is rarely clean, and may have some properties different than those in the laboratory. But there are many compounds that are essentially, if not completely, insoluble in water. Water is the only common, pure substance found naturally in all three states of matter—for other substances, see Chemical properties.
Pure water is tasteless. It is the other chemicals in the water which may give water a flavour.
Generally, the volume of a liquid increases when heated, however the volume of water "decreases" when heated within the temperature range of 0°C to 4°C. Its volume increases only when heated above 4°C. Such behavior is one of a number of water's anomalous properties.
This property of volume decrease allows fish and other aquatic animals to survive in a body of water when ice has frozen on the surface. In cold climates, when the temperature of a body of water reaches at 4°C, the layers of water near the top in contact with cold air continue to lose heat energy and their temperature falls below 4°C. On cooling below 4°C, these layers rise rather than sink, as water has maximum density at 4°C. Thus the layer of water with a temperature of 4°C remains at the bottom, while layers of water 3°C, 2°C, 1°C and 0°C are formed above. Because ice is poor conductor of heat, it does not allow heat energy transfer from the liquid water beneath the layers of ice, which prevents the liquid water from freezing. Hence, aquatic creatures survive in such places.
Lymphatic system
In mammals, the lymphatic system is a network of thin vessels that branch, like blood vessels, into tissues throughout the body. It is part of the immune system. It is a one-way system which carries cells and fluid back to the blood system.
Lymphatic vessels carry lymph, a colorless, watery fluid and white blood cells. It comes from interstitial fluid in the tissues which is squeezed out of the blood vessels. The lymphatic system transports infection-fighting cells called lymphocytes, and is involved in the removal of foreign matter and cell debris by phagocytes. A second function is to transport fats from the small intestine to the blood.
Lymphatic fluid gathers from the tissues and enters the valved lymphatic ducts. It is the valves which make sure the lymph flows the right way. On its way back to the blood system, the lymph passes through glands called lymph nodes, in places like the back of the neck, the armpits and the groin. Lymph nodes swell in the region of an infected body part. This acts to keep the infection from spreading. It prevents or reduces the pathogens getting into the general blood circulation and reaching other parts of the body.
Lymph ends up back in the blood system. In mammals under normal conditions most of the lymph is returned to the blood stream through lymph-vein communications at the base of the neck. Some vertebrates have more complex lymphatic systems. Amphibians for example have multiple "lymph hearts" to control the flow of lymph.
Chastity
Chastity is the sexual behavior of a man or woman which is right and proper according to the moral rules of a culture or religion. It has recently begun to mean sexual abstinence (not having sex at all), especially before marriage. However, it can also be used for all kinds of people (even married people) with more meaning than simply not having sex. The word chastity came from the Latin word "castitatem", meaning "purity".
Metallic bond
A metallic bond is the sharing of many detached electrons between many positive ions, where the electrons act as a "glue" giving the substance a definite structure. It is unlike covalent or ionic bonding.
Metals have low ionization energy. Therefore, the valence electrons can be delocalized throughout the metals. Delocalized electrons are not associated with a particular nucleus of metal, instead, they are free to move throughout the whole crystalline structure forming a "sea" of electrons.
The electrons and the positive ions in the metal have a strong attractive force between them. Therefore, metals often have high melting or boiling points. The principle is similar to that of ionic bonds.
Metallic bonds causes many of the traits of metals, such as strength, malleability, ductility, luster, conduction of heat and electricity.
Because the electrons move freely, the metal has some electrical conductivity. It allows the energy to pass quickly through the electrons, generating an electric current. Metals conduct heat for the same reason: the free electrons can transfer the energy at a faster rate than other substances with electrons that are fixed into position. There also are few non-metals that conduct electricity: graphite (because, like metals, it has free electrons), and ionic compounds that are molten or dissolved in water, which have free moving ions.
Metal bonds have at least one valence electron which they do not share with neighboring atoms, and they do not lose electrons to form ions. Instead, the outer energy levels (atomic orbitals) of the metal atoms overlap. They are similar to covalent bonds. Not all metals exhibit metallic bonding. For example, mercury ions () form covalent metal-metal bonds.
An alloy is a solution of metals. Most alloys are shiny like pure metals are.
Heat conduction
Heat conduction (or thermal conduction) is the movement of heat from one object to another one that has different temperature when they are touching each other. For example, we can warm our hands by touching hot-water bottles. When the cold hands touch the hot-water bottle, heat flows from the hotter object (hot-water bottle) to the colder one (hand). People make things with different thermal conductivity, for example cookware to heat things or insulated containers to keep hot things hot or cold things cold.
Other ways to transfer heat are by thermal radiation and/or convection. Usually more than one of these processes happen at the same time.
In the atomic theory solids, liquids and gases are made of tiny particles called "atoms". The temperature of the material measures how fast the atoms are moving and the heat measures the total amount of energy due to the vibration of the atoms.
Conduction can happen when one part of a material is heated. The atoms in this part vibrate faster and are more likely to hit their neighbors. The collisions cause those atoms also to move faster, passing the heat energy to them. In this way the energy travels through the solid. (Rather like the way energy passes along a set of tumbling dominos).
The atomic picture also helps explain why conduction is more important in solids: in solids the atoms are close together and unable to move around. In liquids and gases the particles can move past each other, so the collisions are less common.
The law of heat conduction, also known as Fourier's law, means that the rate, in time, of heat transfer through a material is proportional to the negative gradient in the temperature and to the area at right angles, to that gradient, through which the heat is flowing:
where:
Thermal conductivity usually varies with temperature, but the variation can be small, over a significant range of temperatures, for some common materials.
Judith Weir
Judith Weir (born 11 May 1954) is a British composer. She is well known for her theatre works, choral music, orchestral music and chamber music.
Weir was born in Cambridge, England to Scottish parents. While she was still at school she trained with the composer John Tavener. She played the oboe in the National Youth Orchestra of Great Britain. She then studied at the University of Cambridge where her teacher was Robin Holloway.