Scientific dictionary main page

Scientific dictionary

science park

Table of Elements

Chemical information

Science dictionary

scientific data

site map

Gift Shop

Index (B)









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

A   B   C   D   E   F   G   H   I   J   K   L   M  
N   O   P   Q   R   S   T   U   V   W   X   Y   Z  

back (BD-BF) BG - BJ next page (BK- BN)

Big Bang nucleosynthesis Phys.
Also abbreviated as BBN, it is the process of producing light nuclei when the universe is first few minutes old after the Big Bang. The process is thought to begin when the universe has cooled sufficiently for protons and neutrons to form from the primordial plasma, from which deuterium nuclei were formed. The deuterium then underwent further nuclear reactions to form helium-4 nuclei along with helium-3 and lithium-7. The theory was first proposed by George Gamow and Ralph Alpher in the 1940s in an attempt to explain the origin of all the chemical elements.

It is thought that the amount of these nuclei produced depended on the temperature and densities of the universe when it was just a few minutes old. Therefore, by measuring their abundances, the BBN models can provide an estimate of the mean baryon density of the universe, which is a fundamental parameter in cosmology. However, it is found that the total mass density of the universe is about six times that of baryon density derived from the BBN models. This evidently points to the existence of mysterious, non-baryonic dark matter.

binding energy Phys.
It is the least energy needed in order to completely disassemble a nucleus into the constituent protons and neutrons. It is also equal to the energy that would be released if the nucleus were to be created from its disassembled constituents. In fact the mass of a nucleus is less than the sum of the masses of its constituents. The difference in mass, m, can be obtained using the Einstein's equation of E = mc2 where E is the nuclear binding energy and c is the speed of light.

biodegradation Biol.
The destruction or break-down of substances by bacteria.

biotite Min.
A common rock-forming silicate mineral. It is usually black, dark brown in color, but sometimes appear small sparkle yellow due to weathering. It has a sheet-like crystal structure and belong to mica group of minerals, with a layered structure of iron magnesium aluminium silicate sheets sandwiched between a layer of potassium ions.

bittern salt Chem.
The solution of salts remaining when sodium chloride is crystallized from sea water. The concentrated solution contains very soluble salts such as sodium sulfate and magnesium chloride. The term 'bittern' is derived from the word bitter.

biuret test Biochem.
A biochemical test for the presence of proteins in solution. The test is carried out by adding sodium hydroxide to the test solution and then drops of copper(II) sulfate solution (1%) are added slowly. The reagent turns violet when proteins are present, due to the formation of copper ion complex with peptide bonds. The solution appears pinkish violet if short-chain polypeptides are present. The test was named after the substance biuret, H2NCONHCONH2, which is formed when urea is heated.

Bjerrum length Chem.
The distance at which the electrostatic (Coulombic) interaction between two elementary charges is comparable in magnitude to the thermal energy scale kT where k is the Boltzmann constant and T is the temperature of the system in kelvin. It gives a measure of the screening effect between two charges in a certain media. Bjerrum length is defined as

Bjerrum length

where e is the elementary charge, e0 and e are the permitivity values of vacuum and the media respectively. For water, e = 80 and lB = 7 nm.

back (BD-BF) BG - BJ next page (BK- BN)

A   B   C   D   E   F   G   H   I   J   K   L   M  
N   O   P   Q   R   S   T   U   V   W   X   Y   Z  

| Copyright | Privacy | Disclaimer | Contact |

2004-2010, all rights reserved.