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Index (H)

HA - HC

HD - HF

HG - HJ

HK - HN

HO - HR

HS - HV

HW - HZ

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


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H5N1 Biol., Med.
An influenza virus that infect birds (avian influenza) that could mutate to infect human as well. As of January 2006, more than 140 cases of human infection due to H5N1 have been confirmed in thirteen countries across mainly Asia and some part of Europe.

The name H5N1 refers to the subtypes of surface antigens present in thre virus: hemaglutinin type 5 and neuraminidase type 1 and belong to genotype Z. H5N1 infection of human has similar symptom to those of common flu such as fever, sore throat and muscles and cough. However, the mortality rate is much higher, at 52% Therefore, the H5N1 is considered to be the potential flu pandemic threat to human population. The 1918 Spanish flu pandemic that killed some 100 million humans is thought to be of avian origin that cross infect human.

hadron Phys.
An elementary particle that interacts strongly with other particles. Hadrons include both mesons and baryons. In Greek hadron means strong.

half-life Chem.
The time taken to change one half of a reactant to product. The term is usually applied to radioactive decay which is the amount of time it takes for half an initial amount of a radioisotope to undergo sponrtaneously radio active decay (disintegration) to form another isotope. For example, uranium-238 has a half-life of 4.5 x 109 years to form thorium-234 with an emission of alpha particle.

half-thickness Phys.
Also called half-value layer (HVL), it is the thickness of a specified material that reduces the intensity of a beam of radiation to half of its original value. The value is therefore dependant on the type of radiation and its energy.

halite Min.
A mineral form of sodium chloride, also commonly known as rock salt. It has a characteristic cubic appearance, colorless or cloudy white and sometimes may appear gray, pink or brown due to the presence of contaminants. Halite is often found associate with gypsum and anhydrite. It is commonly found to evaporative brine lakes and extinct salt lakes and seas all over the world but notably Salt Lake City, Utah, Germany and France.

halogens Chem.
A group of elements that occupy Group 7 in the Periodic Table of the Elements. The elements consist of fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). The name 'halogen' derives from Greek, meaning 'slat-producer'. So called due to halogens react with metals to form salts. For instance, chlorine reacts with sodium to give sodium chloride (NaCl) or table salt.

hard water Chem.
Waters contain calcium or magnesium salts that reduce their ability to form lather with soap. This is due to the formation of insoluble calcium or magnesium salts of fatty acids from soap and is the reason for the formation of 'bathtub crud'.

Hartree-Fock theory Phys.
Abbreviated as HF theory, it is a fundamental assumption in practical molecular orbital calculations that assumes every electron in a molecular system 'sense' all others an average field and that the electron correlation is neglected. The fundamental approximation is important in solving Schrodinger wave equation for many-electron systems.

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