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Index (R)

RA - RC

RD - RF

RG - RJ

RK - RN

RO - RR

RS - RV

RW - RZ

Moment of truth
The fastest man-made object that ever leave the Earth is the Pinoeer 10 spacecraft, launched in 1972, and attained a speed of more than 32000 mph.


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RF value Chem.
In chromatography, it is the ratio of the distance traveled by the solvent front divided by the distance traveled by a given component. The value is the characteristics of the component at a known temperature and can be used for identification of the component.

rabies Med.
A viral infection that affects the nervous system. Rabies virus belongs to the order Mononegavirales. It is usually transmitted to humans from saliva of an infected animal bites. The virus-induced aggressive biting behavior in the host animal maximize chances of viral infection of a new host. Infected dogs are the commonest source but in developed countries most cases of rabies are due to bites from infected bats. Nevertheless, the reservoirs for the disease can also include raccoons, foxes etc.

Symptoms usually occur 2-8 weeks after infection and this includes fever, headache, numbness and tingling around the wound. Later stage symptoms include spasms, hallucinations, paralysis and coma. If untreated, the infection is almost always fatal.

radian Math.
Abbreviated as rad, it is the SI unit of planar angle quantity, defined as the angle stretch out at the center of a circle by an arc (a) equal in length to the radius (r) and is equivalent to about 57°.2958. This means that 2p rad = 360°.

radian

1 rad = 57°.2958 when r = a.

radioisotope Chem.
An isotope that is capable to undergo radioactive decay. Also known as radioactive isotope.

random error Math.
A non-reproducible error originating from uncontrolled factors in an experiment. This error affects the accuracy of a result, but does not have any consistent effect across the entire sample. Random error is sometimes referred as noise.

random mutagenesis Biochem.
Technique to alter amino sequences in a protein by generating thousands of mutants, using various methods such as chemical mutation, ultra-violet light etc. Sometimes also known as directed evolution.

Raoult's law Chem.
A partial pressure law for solvent which states that p = p0X, where p is the vapor pressure of the solvent (which contains a solute), X is the mole fraction of the solvent and p0 is the vapor pressure of the pure solvent (contain no solute). A solution that totally obey Raoult's law is call an ideal solution. The law usually holds for dilute solutions and deviation from the law for mixture of liquids cause the formation of azeotropes. The law was discovered by the French chemist François Raoult (1830-1901).

rarefaction Phys., Chem.
A decrease in the pressure of a fluid or gas and therefore of its density.

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