Wikipedia
D-value may refer to:
- D-value (microbiology) - the decimal reduction time, the time required at a certain temperature to kill 90% of the organisms being studied
- D-value (meteorology) in meteorology refers to the deviation of actual altitude along a constant pressure surface from the standard atmosphere altitude of that surface.
- D-value (transport) - a rating in kN that is typically attributed to mechanical couplings
- Cohen's d in statistics - The expected difference between the means between an experimental group and a control group, divided by the expected standard deviation. It is used in estimations of necessary sample sizes of experiments.
- d', a sensitivity index.
In microbiology, D-value refers to decimal reduction time (or decimal reduction dose) and is the time (or dose) required at a given condition (e.g. temperature), or set of conditions, to kill 90% (or 1 log) of the exposed microorganisms. The term originated from assessing microbial thermal resistance and thermal death time analysis; however, it has analogous uses in other microbial resistance and death rate applications, such as (but not limited to) those of ethylene oxide and radiation processing.
Thus after a colony is reduced by 1 D, only 10% of the original organisms remain, i.e., the population number has been reduced by one decimal place in the counting scheme. Generally, each lot of a sterilization-resistant organism is given a unique D-value. When referring to D-values, for the purpose of thermal analysis, it is proper to give the temperature as a subscript of the "D". For example, given a hypothetical organism which is reduced by 90% after exposure to temperatures of 150° C for 20 minutes, the D-value would be written as D = 20 minutes. If generally describing D-value for any temperature, a common abbreviation is D (where T is temperature) until a value for T is relevant to express, specifically. Another more general abbreviated expression of D-value is D (as to denote 10% reduction).
D-value determination is often carried out to measure a disinfectant's efficiency to reduce the number of microbes present in a given environment.
In transport, D-value is a rating in kN that is typically attributed to mechanical couplings, and reflects dynamic loading limits between a towing vehicle and a trailer. The corresponding formula for a truck and trailer combination, used to determine the required D-value of a coupling, is:
T = Weight of towing vehicle including the vertical load on the fifth wheel
R = Total weight of the loaded semi-trailer
U = Vertical load on the fifth wheel
g = Acceleration due to gravity (assumed to be 9.81 m/s 2 )
D (kN) = g x ((0.6 x T x R)/(T + R - U))