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Moment of truth
The word 'nanotechnology' is first coined by University of Tokyo researcher Norio Taniguchi back in 1974.

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heat capacity Chem., Phys.
The amount of energy require to raise a unit temperature to an object, and has a unit of JK-1 (joule per kelvin). In practice, a specific heat capacity is measured which is the energy required to raise a unit of temperature to a sample of unit mass and has a unit of J K-1 kg-1. In chemistry, the molar heat capacity is usually used which has a unit of J K-1 mol-1. For a gas, the heat capacity can be either described at constant pressure, or constant volume. In the former case, more energy is required in order for the gas to expand and do works. Whereas, the latter is essentially an increase to the internal energy of the gas.

heat shock proteins Biochem.
A group of proteins that are induced when a cell undergoes various types of environmental stress like heat, cold and oxygen deprivation. They are present in all cells in all life forms. It is also known as stress proteins and abbreviated as HSPs. However, HSPs can also present in cells under normal physiological conditions, acting as protein chaperones.

heavy hydrogen Chem.
An isotope of hydrogen with one neutron. Also called deuterium.

heavy spar Min.
A mineral form of barium sulfate, BaSO4. Also called baryte (means heavy in Greek) or barite. It occurs naturally as tabular crystals (orthorhombic) , in granular or in massive form, usually colorless or white, but can be stained with yellow, red, blue or green colorations. It is widely distributed and often associated with quartz, fluorite, lead and zinc minerals. Barite (chief ore) is the main source of barium and is also used in oil drilling to help control pressure, as a pigment and filler.

heavy water Chem.
Common name for deuterium oxide. It is a water that consists of heavier isotope of hydrogen, deuterium. It is a colorless liquid with its physical properties slightly different to that of normal water, and has a symbol D2O (mp=3.8C, bp=101.4C). It occurs about 0.003% by weight in natural water, which can be separated by fractional distillation or by electrolysis. It is used in moderating neutron flux in nuclear industry and as labelling in the studies of chemical reaction mechanisms.

heliopause Astron.
The transition region of boundary of heliosphere or the outer edge of heliosheath. It defines the end of the solar influence and the beginning of the interstellar spaces where interstellar winds dominate.

heliosheath Astron.
Outer edge of heliosphere where the solar wind's density and speed decrease dramatically. The region is still dominated by the Sun's magnetic field and particles but is rapidly diminishes. The size of heliosheath is thought to be tens of AU thick.

heliosphere Astron.
Region of space centered around the Sun over which the solar wind and solar magnetic field extend. The exact size of heliosphere is not known, but is thought to extend more than 50 AU. The shape of heliosphere is thought to be semi-circular or tear-drop shape, with the tear front facing the direction of the Sun's motion.

helium burning Astron.
A thermonuclear process that occurs in the core of giant stars that is thought to occur once the supply of hydrogen is exhausted. The process is thought to initiate at around 108 K in the core and the following reaction results:

helium burning

The net effect is the use of 3 helium to produce one carbon nucleus. The '*' refers to carbon in excited states.

hematite Min.
A mineral form of iron(III) oxide (Fe2O3). It is the chief ore of iron. Usually red in color but can sometimes be found as greyish black crystals. Frequently, the red coloring in rocks is due to the presence of hematite, especially in sedimentary areas. It is used in polishing and as a pigment in paints. The word hematite is derived from the Greek haima, meaning blood.

Henry's law Chem.
A pressure-solubility law which states that the mass of gas dissolved by a given volume of solvent at a certain temperature is directly proportional to the pressure of the gas. However, the law applies only if the dissolving process is a physical process, that is, the gas does not react chemically with the solvent.

hertz Metro.
The SI unit of frequency equal to one cycle per second. Symbol Hz. It is named after Heinrich Hertz (1857-1894), a German physicist.

Heusler alloys Eng.
Ferromagnatic alloys of manganese, copper, aluminium, nickel and sometimes other metals, which find important uses as permanent magnets. Named after Fritz Heusler, a German mining engineer and chemist in 19th century. The original alloy also contained tin, Cu2MnSn. Other examples are Cu2MnAl, Pd2MnAl, etc.

hexose Chem.
A monosaccharide (such as glucose) that has six carbon atoms in molecules. See carbohydrates.

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