zeroorder

Zero-order is a term used across disciplines to denote a process, rate, or quantity that remains constant with respect to a variable or that represents a baseline level. It is used to describe phenomena where the controlling factor is absent, saturated, or intentionally set to a fixed value.

In chemistry and pharmacology, zero-order kinetics refers to a reaction or elimination process whose rate is independent of the reactant’s concentration. The rate is constant (for example, a fixed amount per unit time) until the limiting reagent is exhausted or the catalytic system becomes saturated. This behavior contrasts with first-order or Michaelis-Menten kinetics, where the rate depends on concentration. In pharmacology, zero-order kinetics can occur when drug-metabolizing enzymes or transport mechanisms are saturated, leading to drug clearance that proceeds at a roughly constant rate regardless of concentration.

In signal processing and control theory, a zero-order hold is a method of converting a discrete-time signal to a continuous-time signal by maintaining each sampled value constant over the sampling interval. It is used in digital-to-analog conversion and in implementing discrete-time controllers. The zero-order hold shapes the system’s frequency response and can introduce phase lag and ripple, affecting the accuracy of the reconstructed signal.

In mathematics, the zero-th derivative (the zero-order term) of a function is the function itself. The concept provides a baseline from which higher-order derivatives describe rates of change. In broader usage, zero-order can describe a constant term or a reference condition against which variable behavior is measured.