Question: How does a biological system react after detecting a perturbation?
About the article "Biology", section "Homeostasis".

Candidate passages:
Perturbation or perturb may refer to:  Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly  Perturbation (geology), changes in the nature of alluvial deposits over time  Perturbation (astronomy), alterations to an object's orbit—e.g., caused by gravitational interactions with other bodies  Perturbation theory (quantum mechanics), a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one  Perturbation (biology), an alteration of the function of a biological system, induced by external or internal mechanisms  Perturbation (transport), operation of a transport system outside of timetable such that delays in arrival and departure from defined locations are present.
Perturbation function, mathematical function which relates the primal and dual problems.  
"Resilience" is the tendency of a system to return to a previous state after a perturbation.
"Elasticity" and "amplitude" are measures of resilience.
Elasticity is the speed with which a system returns.
Amplitude is a measure of how far a system can be moved from the previous state and still return.
Ecology borrows the idea of neighborhood stability and a domain of attraction from dynamical systems theory. 
In mathematics and physics, a non-perturbative function or process is one that cannot be accurately described by perturbation theory.
An example is the functionformula_1.
The Taylor series at x = 0 for this function is exactly zero to all orders in perturbation theory, but the function is non-zero if "x" ≠ 0.
The implication of this for physics is that there are some phenomena which are impossible to understand by perturbation theory, regardless of how many orders of perturbation theory we use.
Instantons are an example.
Therefore, in theoretical physics, a non-perturbative solution or theory is one that does not require perturbation theory to explicate, or does not simply describe the dynamics of perturbations around some fixed background.
For this reason, non-perturbative solutions and theories yield insights into areas and subjects perturbative methods cannot reveal. 
Time-independent perturbation theory is one of two categories of perturbation theory, the other being time-dependent perturbation (see next section).
In time-independent perturbation theory the perturbation Hamiltonian is static (i.e., possesses no time dependence).
Time-independent perturbation theory was presented by Erwin Schrödinger in a 1926 paper, shortly after he produced his theories in wave mechanics.
In this paper Schrödinger referred to earlier work of Lord Rayleigh, who investigated harmonic vibrations of a string perturbed by small inhomogeneities.
This is why this perturbation theory is often referred to as Rayleigh–Schrödinger perturbation theory. 
The aim of a Strategic Early Warning System (SEWS) is to assist organizations in dealing with discontinuities or strategic surprises.
By detecting weak signals (Igor Ansoff, 1975), which can be perceived as important discontinuities in an organizational environment, SEWS allows organizations to react strategically ahead of time.