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A quantity x depends exponentially on time t if = / where the constant a is the initial value of x, () =, the constant b is a positive growth factor, and τ is the time constant—the time required for x to increase by one factor of b: (+) = (+) / = / / = ().
RGR is a concept relevant in cases where the increase in a state variable over time is proportional to the value of that state variable at the beginning of a time period. In terms of differential equations , if S {\displaystyle S} is the current size, and d S d t {\displaystyle {\frac {dS}{dt}}} its growth rate, then relative growth rate is
This means that the time constant is the time elapsed after 63% of V max has been reached Setting for t = for the fall sets V(t) equal to 0.37V max, meaning that the time constant is the time elapsed after it has fallen to 37% of V max. The larger a time constant is, the slower the rise or fall of the potential of a neuron.
This time can be calculated by dividing the natural logarithm of 2 by the exponent of growth, or approximated by dividing 70 by the percentage growth rate [1] (more roughly but roundly, dividing 72; see the rule of 72 for details and derivations of this formula). The doubling time is a characteristic unit (a natural unit of scale) for the ...
Symbolically, this process can be expressed by the following differential equation, where N is the quantity and λ is a positive rate called the exponential decay constant, disintegration constant, [1] rate constant, [2] or transformation constant: [3]
In mathematics, a rate is the quotient of two quantities, often represented as a fraction. [1] If the divisor (or fraction denominator) in the rate is equal to one expressed as a single unit, and if it is assumed that this quantity can be changed systematically (i.e., is an independent variable), then the dividend (the fraction numerator) of the rate expresses the corresponding rate of change ...
The RC time constant, denoted τ (lowercase tau), the time constant (in seconds) of a resistor–capacitor circuit (RC circuit), is equal to the product of the circuit resistance (in ohms) and the circuit capacitance (in farads):
Half-life is constant over the lifetime of an exponentially decaying quantity, and it is a characteristic unit for the exponential decay equation. The accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed.