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An exogenous contrast agent, in medical imaging for example, is a liquid injected into the patient intravenously that enhances visibility of a pathology, such as a tumor.An exogenous factor is any material that is present and active in an individual organism or living cell but that originated outside that organism, as opposed to an endogenous factor.
The X-factor in astrophysics, often labeled X CO, is an empirically determined proportionality constant which converts carbon monoxide (CO) emission line brightness to molecular hydrogen (H 2) mass. The term X-factor was coined in a 1983 paper titled "Gamma-rays from atomic and molecular gas in the first galactic quadrant" and published in The ...
Scientific laws or laws of science are statements, based on repeated experiments or observations, that describe or predict a range of natural phenomena. [1] The term law has diverse usage in many cases (approximate, accurate, broad, or narrow) across all fields of natural science ( physics , chemistry , astronomy , geoscience , biology ).
The most common forms are the following: = = / = / = (+) /, where x 0 expresses the initial quantity x(0). Parameters (negative in the case of exponential decay): The growth constant k is the frequency (number of times per unit time) of growing by a factor e ; in finance it is also called the logarithmic return, continuously compounded return ...
In mathematics, a function is a rule for taking an input (in the simplest case, a number or set of numbers) [5] and providing an output (which may also be a number). [5] A symbol that stands for an arbitrary input is called an independent variable, while a symbol that stands for an arbitrary output is called a dependent variable. [6]
A variable in an experiment which is held constant in order to assess the relationship between multiple variables [a], is a control variable. [2] [3] A control variable is an element that is not changed throughout an experiment because its unchanging state allows better understanding of the relationship between the other variables being tested.
An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs when a particular factor is manipulated.
Partial mean life associated with individual processes is by definition the multiplicative inverse of corresponding partial decay constant: = /. A combined τ c {\displaystyle \tau _{c}} can be given in terms of λ {\displaystyle \lambda } s: