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Moment of truth
The Voyager I spacecraft is the most distant man-made object in the universe. It was launched in 1977 and as in 2002, it was more than 8 billions miles from the Earth.

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soda ash Chem.
Common name for anhydrous sodium carbonate, Na2CO3.

sodalite Min.
sodalite mineral A rather scarce mineral use mainly as ornaments. Usually appear blue-grey with white streaks (picture right). Small crystals are translucent, whereas large specimens are opaque. Sodalite is a sodium-containing mineral (Na4Al3(SiO4)3Cl) of which it is named after. It has a hardness of 6 and is usually associated with mineral calcite, nepheline and cancrinite and also in cavities in ejected volcanic rocks.

Abbreviation for Small Outline Double Inline Memory Module. It is a small modular circuit board with memory chips mounted on it. IT is similar to DIMM except that SO-DIMM is used in computer laptops or notebooks. Available in several versions such as 200-pin (connectors), 144-pin and 72-pin.

soft water Chem.
Water that easily forms a lather with soap. It does not contain soluble ions such as calcium or magnesium ions that can prevent the formation of lather. See also hard water.

solar flare Astron.
A sudden eruption, releasing intensive energy on the surface of the Sun. It occurs when the magnetic energy builds up in photosphere and chromosphere is suddenly released, emitting charged particles (protons, electrons) and radiations of all wavelengths: from long radio waves to short gamma rays. The amount of energy releases could be in the range of 1021 - 1025 J.

solar wind Astron.
A flow of hot charged particles (plasma) leaving the Sun at a speed of 300-800 km per second. It consists mainly of protons and electrons. It distorts the Earth's magnetic field and causes acceleration in the tails of comets.

solid oxide fuel cell (SOFC) Chem.
A fuel cell that has an output from 1 kW to 2 MW. The difference between the conventional 'clean' hydrogen fuel cell and that of SOFC is that the latter is fed with hydrocarbon fuel such as methane, propane and butane and operating at a high temperature of 700C to 1200C. A SOFC is made of four layers (single cell), three of which are ceramics. These single cell, each is only a few millimeters thick, can then stacked together in hundreds to give the final product of SOFC.

The cathode is made of electrically conductive ceramics which is exposed to air so that the electrons reduce the oxygen molecules to ions. These ions then diffuse through an electrolyte to oxidize the fuel at the anode side, releasing the electron that travel through the external circuitry to the cathode side.

soliton Phys.
A stable, localized vibrational waves that propagate through a medium without spreading. The phenomenon was first observed in uranium crystals by Michael Manley of the Los Alamos Laboratory and others from the US and Germany. The group found that when the crystal was heated to 450 K, localised vibrations, with wavelength as small as the spacing between two atoms, were formed. Understanding how solitons behave in crystalline materials may have implication in new forms of mechanical deformations and bond breaking process.

solvolysis Chem.
A reaction between a compound and its solvent. One common example of solvolysis is the hydrolysis, where the solvent is the water.

specific gravity Phys.
See relative density

specific heat capacity Chem., Phys.
Energy require to raise the temperature of a substance of unit mass by 1 K. The SI unit is J kg-1 K-1. In chemistry, it is usually described in J g-1 K-1. See also heat capacity.

spectral class Astron.
Star classification scheme which based on the stellar spectral lines. It indicates the color and the temperature of a star. In fact, the color of a star is related to the temperature through the phenomenon blackbody radiation, which desribes a material glows when heated to a high enough temperature. Table below shows spectral classification of stars based on the temperature.

Spectral class




40 000



27 000



10 000














Each main spectral class (represented by the alphabets O, B, A, F, G, K and M) can be subdivided into ten smaller gradations which are indicated as numbers, in the order of decreasing temperature, from 0 to 9. For example K0 is the hottest in the spectral class K and K5 is slightly cooler, at a temperature around 4000C. The Sun (yellowish) is classified as a G2 star, corresponds to a temperature of about 5500C. A star with temperature up to 50 000C is classified as the W star, but such a star is very rare.

spin Hall effect Phys.
A magnetization effect that causes electrons of different spins (up and down) to build up on opposite sides of a sample in the presence of an electric field. The effect was predicted by D. I. Dyakonov and V. I. Perel, two Russian physicists in 1971. They predicted that current-carrying electrons with opposite spins are to move towards opposites of a semiconductor wire even without a magnetic field or magnetic materials. The effect was first discovered in November 2004 by a group of scientists led by D. Auschalom at the University of California. It has potential applications in fabrication of future electronic devices including quantum computing and telecommunication.

spirits of salt Chem.
Common name for hydrogen chloride, so-called because of its derivation from the addition of sulfuric acid to sodium chloride (common salt).

sputter Phys.
Emission of neutral or charged atoms as a result of bombardment of a surface by high-energy projectiles. The latter can be either a single atom or a cluster of atoms.

spyware Comp.
A program, like adware, but with malicious intent that, once installed on a computer, steals personal and confidential information such as bank and credit card details. Methods of stealing can vary, such as using a key logger program that tracks what is being typed on the keyboard.

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