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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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Higgs mechanism Phys.
Theoretical description how the fundamental particles obtain their masses. It is named after Peter Higgs of Edinburgh University, Scotland. It forms part of the Standard Model that the vacuum is not empty but filled with a condensate of Higgs particles. All other particles (leptons, quarks etc.) continuously 'collide' with Higgs particles as they travel through the vacuum. Consequently, the mass of a particle is the resistance experienced by the particle as it interacts with the Higgs particles. The stronger the interaction the heavier the particle becomes.

high-speed steel Eng.
A steel that will remain hard even at dull red hot temperature and capable of cutting other metals at a high rate. It is an iron alloy with 12-22% tungsten and may contain small amount of molybdenum, vanadium and cobalt. It is mainly used for cutting tools.

histochemistry Chem.
The scientific study of chemical distribution of tissues by means of their chemical reaction. Often involves the use of light microscopy or electron microscopy, chromatography and autoradiography.

histology Biol.
The study of tissues, especially tissue architecture, at the level of cells and extracellular matrices. The study usually involves the use of light microscopy or electron microscopy and stain dyes to highlight the biological structures.

HIV Biol., Med.
Stands for the Human Immunodeficiency Virus. A retrovirus that specifically target CD4+ white blood cells (cells that fight disease) in human. The HIV inserts its own genetic materials into the cell's DNA to produce more virus particles. This causes the CD4+ cells to die and the body's ability to fight diseases decreases as the number of CD4+ cells drops. A critical stage is reached where the patient is said to develop AIDS - Acquired Immune Deficiency Syndrome. AIDS usually occurs when the CD4+ cell count is reduced to 200 per cubic mm of blood. Normal healthy adult has between 600-1200 count. As at the year 2003, there are about 40 million people world wide are living with AIDS.

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