In chemistry, a steady state is a situation in which all state variables are constant in spite of ongoing processes that strive to change them. For an entire system to be at steady state, i.e. for all state variables of a system to be constant, there must be a flow through the system (compare mass balance). A simple example of such a system is the case of a bathtub with the tap running but with the drain unplugged: after a certain time, the water flows in and out at the same rate, so the water level (the state variable Volume) stabilizes and the system is in a steady state.
The steady state concept is different from chemical equilibrium. Although both may create a situation where a concentration does not change, in a system at chemical equilibrium, the net reaction rate is zero (products transform into reactants at the same rate as reactants transform into products), while no such limitation exists in the steady state concept. Indeed, there does not have to be a reaction at all for a steady state to develop.
In systems theory, a system in a steady state has numerous properties that are unchanging in time. This means that for those properties p of the system, the partial derivative with respect to time is zero:
The concept of steady state has relevance in many fields, in particular thermodynamics, economics, and engineering. Steady state is a more general situation than
dynamic equilibrium. If a system is in steady state, then the recently observed behavior of the system will continue into the future. In stochastic systems, the probabilities that various states will be repeated will remain constant.
In many systems, steady state is not achieved until some time after the system is started or initiated. This initial situation is often identified as a transient state, start-up or warm-up period.
While a dynamic equilibrium occurs when two or more reversible processes occur at the same rate, and such a system can be said to be in steady state, a system that is in steady state may not necessarily be in a state of dynamic equilibrium, because some of the processes involved are not reversible.
In electronics, steady state is an equilibrium condition of a circuit or network that occurs as the effects of transients are no longer important.
Steady state determination is an important topic, because many design specifications of electronic systems are given in terms of the steady-state characteristics. Periodic steady-state solution is also a prerequisite for small signal dynamic modeling. Steady-state analysis is therefore an indispensable component of the design process.
Calculation methods
Steady state calculation methods can be sorted into time-domain algorithms (time domain sensitivities, shooting) and frequency-domain algorithms (harmonic balance) methods, are the best choice for most microwave circuits excited with sinusoidal signals (e.g. mixers, power amplifiers).
Time domain methods
Time domain methods can be further divided into one step methods (time domain sensitivities) and iterative methods (shooting methods). One step methods require derivatives to compute the steady state; whenever those are not readily available at hand, iterative methods come into focus.
Calculations indicate that the time required for the chemistry of the upper atmosphere to reach a steady-state after the injection of Freon-type materials would be several decades.
The space resolved steady-state and time resolved PL studies along with the scanning electron microscope images reveal that the laser affected and unaffected regions comprise distinguishable carrier recombination mechanisms.
... but about coordination between two states that develops at a steady pace that can evolve or relatively slow down under the influence of the chemistry of personal relations between heads of state.
But Lovelock may be most widely known for his Gaia theory – that Earth functioned, as he put it, as a "living organism" that is able to "regulate its temperature and chemistry at a comfortable steady state.".
