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Moment of truth
The Sun, with a diameter of 1,392,000 km, is made of 94% hydrogen atoms.

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Deacon's process Chem.
An industrial process for producing chlorine by oxidizing hydrogen chloride in air at 400-450C using a copper chloride or copper sulfate catalyst. It was patented in 1870 by Henry Deacon (1822-1876)

debye Chem.
A unit of dipole moment of a molecule in the cgs system. Usually abbreviated as D and 1 D = 10-18 statcoulomb centimeter. In other words, it is the dipole moment produced by two charges of opposite sign, each with an electrical charge of 1 statcoulomb and placed 10-18 cm apart. In the International Standard (SI) unit, a debye has a unit of 3.33564 x 10-30 coulomb meter. It is a vector quantity and direction is pointed towards the negatively charged species. The unit is named after Josephus Wilhelmus Debye, a Dutch-American physicist (1884-1996).

decrepitation Chem.
A crackling noise produced when certain crystals are heated. For example, lead(II) nitrate which split and crackle before the crystals decompose. The crackling may also be due to changes in structure resulting from loss of water of crystallization.

deep vein thrombosis (DVT) Med.
A blood clot that develops in a deep vein, usually in a lower leg surrounded by the muscles and cause calf swelling and pain, especially when standing or walking. Since the blood clot occurs inside a blood vessel, this can be dangerous especially the clots are big which can partially or totally block the blood flow in the vein. It is possible for a piece of blood clot to break off and travels in the bloodstream and to become lodged in the lungs and block blood flow. This may then cause chest pain and shortness of breath.

deliquescence Chem.
The absorption of moisture from the atmosphere by a hygroscopic solid substance to such an extent that a concentrated solution of the solid eventually forms. An example of such substance is calcium chloride solid, which is a good dehydrating agent, forming a colorless concentrated liquid when water is absorbed.

denaturation Biol.
Destruction of the native three-dimensional structure of a biological molecule (such as protein enzyme) by heat, extremes of pH, heavy metal ions, detergents etc.

density bottle Phys.
A thin glass bottle, with its volume accurately calibrated, used for the determination of the density of a liquid by weighing. It is also used to determine the density of small soil particles or granular materials. It is also known as pycnometer.

density of state Phys.
A function that describes the number of quantum state per unit energy interval at energy E. It describes the number of allowed translational energy level per unit interval at energy E of a system. The higher the energy, the density of state increases. This means that there are more energy levels per unit energy interval, until continuum approximation is reached where the energy levels become indistinguishable.

dermatology Med.
Study of medical science relates to the skin and its diseases.

deuterium Chem.
An isotope of the element hydrogen. It has a symbol D or 1H2 woth mass number 2, which contains one proton and one neutron at the atomic nucleus. Deuterium consists of 0.015% in natural hydrogen. The oxide form, D2O, is called heavy water and is used to moderate fission reactions in nuclear reactors.

deuterium oxide Chem.
See heavy water.

device driver Comp.
Commonly known as driver. It is a group of computer program files that enable a hardware device to work properly and communicate with the computer's operating system. Each hardware of different brand and model may need a different set of device driver, which if it is not installed, the hardware may not be able to operate when connected to a computer. The driver is installed once when a new hardware is connected to the computer. However, newer version of driver may be available which need to install from time to time, usually to improve the hardware stability and performance.

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