instability

Dictionary: in·sta·bil·i·ty (ĭn'stə-bĭl'ĭ-tē) pronunciation

n., pl., -ties.

Lack of physical stability; unsteadiness.
The quality or condition of being erratic or undependable: emotional instability; political instability.

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Thesaurus: instability

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noun

The quality or condition of being physically unsteady: precariousness, ricketiness, shakiness, unstableness, unsteadiness, wobbliness. See flexible/rigid.
The quality or condition of being erratic and undependable: insecureness, insecurity, precariousness, shakiness, unstableness, unsteadiness, unsureness. See change/persist, strong/weak.

Antonyms: instability

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Definition: imbalance, inconstancy
Antonyms: balance, constancy, soundness, stability, steadfastness

Geography Dictionary: instability

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The condition of a parcel of air which has positive buoyancy, and thus a tendency to rise through the atmosphere. It is the temperature of the parcel relative to the ambient air which is critical, since this affects densities. A parcel remains unstable if it cools more slowly than the surrounding, stationary air. Absolute instability occurs when an air parcel, displaced vertically, is hastened in the direction of the displacement, and such a move will be checked when the temperature of the parcel is at one with its surroundings. The potential instability of a parcel of air can be calculated using a tephigram.

Conditional instability occurs when a parcel of air would become unstable if lifted by some other force. This can take place when a lower, stable parcel of air is overlain by an unstable layer. If any agency, such as a mountain, or the moistening of the lower-level air, can ‘nudge’ it upwards, it will become unstable. Convective instability is a tendency of an air parcel towards instability when it has been lifted bodily until completely saturated. This will often occur when it responds to the inevitable stirrings in the atmosphere.

The atmosphere is said to be unstable if the environmental lapse rate is greater than both the dry and saturated adiabatic lapse rates; that is, when the fall of temperature with height of the environmental air is more rapid than that experienced by a rising air parcel, so that the air parcel continues to be less dense than the ambient air.

Architecture: instability

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In a structure, the sudden loss of stiffness that limits its load-carrying capability, and in some cases results in the structure’s failure.

Sports Science and Medicine: instability

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Lack of stability in a joint, often through lax ligaments associated with hyperflexibility. Joint instability predisposes an athlete to injuries such as recurrent dislocations.

Wikipedia: Instability

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For inherently unstable aircraft, see Relaxed stability.

A ball on the top of a hill is an unstable situation.

Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. Not all systems that are not stable are unstable; systems can also be marginally stable or exhibit limit cycle behavior.

In control theory, a system is unstable if any of the roots of its characteristic equation has real part greater than zero. This is equivalent to any of the eigenvalues of the state matrix having real part greater than zero.

In structural engineering, a structure can become unstable when excessive load is applied. Beyond a certain threshold, structural deflections magnify stresses, which in turn increases deflections. This can take the form of buckling or crippling. The general field of study is called structural stability.

1 Fluid instabilities
2 Plasma instabilities
- 2.1 List of plasma instabilities
3 Instabilities of stellar systems
4 See also
5 Notes
6 External links

Fluid instabilities

Hydrodynamics simulation of the Rayleigh–Taylor instability ^[1]

Unstable flow structure generated from the collision of two impinging jets.

Fluid instabilities occur in liquids, gases and plasmas, and are often characterized by the shape that form; they are studied in fluid dynamics and magnetohydrodynamics. Fluid instabilities include:

Ballooning mode instability (some analogy to the Rayleigh–Taylor instability); found in the magnetosphere
Atmospheric instability
- Hydrodynamic instability or dynamic instability (atmospheric dynamics)
  - Inertial instability; baroclinic instability; symmetric instability, conditional symmetric or convective symmetric instability; barotropic instability; Helmholtz or shearing instability; rotational instability
- Hydrostatic instability or static instability/vertical instability (parcel instability), thermodynamic instability (atmospheric thermodynamics)
  - Conditional or static instability, buoyant instability, latent instability, nonlocal static instability, conditional-symmetric instability; convective, potential, or thermal instability, convective instability of the first and second kind; absolute or mechanical instability
Bénard instability
Drift mirror instability
Kelvin–Helmholtz instability (similar, but different from the diocotron instability in plasmas)
Rayleigh–Taylor instability
Plateau-Rayleigh instability (similar to the Rayleigh–Taylor instability)
Richtmyer-Meshkov instability (similar to the Rayleigh–Taylor instability)

Plasma instabilities

Plasma instabilities can be divided into two general groups (1) hydrodynamic instabilities (2) kinetic instabilities. Plasma instabilities are also categorised into different modes:

Mode (azimuthal wave number)	Note	Description	Radial modes	Description
m=0		Sausage instability: displays harmonic variations of beam radius with distance along the beam axis	n=0	Axial hollowing
			n=1	Standard sausaging
			n=2	Axial bunching
m=1		Sinuous, kink or hose instability: represents transverse displacements of the beam cross-section without change in the form or in a beam characteristics other than the position of its center of mass
m=2	Filamentation modes: growth leads towards the breakup of the beam into separate filaments.	Gives an elliptic cross-section
m=3		Gives a pyriform (pear-shaped) cross-section

Source: Andre Gsponer, "Physics of high-intensity high-energy particle beam propagation in open air and outer-space plasmas" (2004)

List of plasma instabilities

Bennett pinch instability (also called the z-pinch instability )
Beam acoustic instability
Bump-in-tail instability
Buneman instability,^[2] (same as Farley-Buneman instability?)
Cherenkov instability,^[3]
Chute instability
Coalescence instability,^[4]
Collapse instability
Counter-streaming instability
Cyclotron instabilities, including:

Alfven cyclotron instability
Electron cyclotron instability
Electrostatic ion cyclotron Instability
Ion cyclotron instability
Magnetoacoustic cyclotron instability
Proton cyclotron instability
Nonresonant Beam-Type cyclotron instability
Relativistic ion cyclotron instability
Whistler cyclotron instability

Diocotron instability,^[5] (similar to the Kelvin-Helmholtz fluid instability).
Disruptive instability (in tokamaks)
Double emission instability
Drift wave instability
Edge-localized modes [2]
Electrothermal instability
Farley-Buneman instability
Fan instability
Filamentation instability
Firehose instability (also called Hose instability)

Flute instability
Free electron maser instability
Gyrotron instability
Helical instability (helix instability)
Helical kink instability
Hose instability (also called Firehose instability)
Interchange instability
Ion beam instability
Kink instability
Lower hybrid (drift) instability (in the Critical ionization velocity mechanism)
Magnetic drift instability
Modulation instability
Non-Abelian instability (see also Chromo-Weibel instability)
Chromo–Weibel instability
Non-linear coalescence instability
Oscillating two stream instability, see two stream instability
Pair instability
Parker instability (magnetic buoyancy instability)
Peratt instability (stacked toroids)
Pinch instability
Sausage instability
Slow Drift Instability
Tearing mode instability
Two stream instability
Weak beam instability
Weibel instability
z-pinch instability, also called Bennett pinch instability

Instabilities of stellar systems

Galaxies and star clusters can be unstable, if small perturbations in the gravitational potential cause changes in the density that reinforce the original perturbation. Such instabilities usually require that the motions of stars be highly correlated, so that the perturbation is not "smeared out" by random motions. After the instability has run its course, the system is typically "hotter" (the motions are more random) or rounder than before. Instabilities in stellar systems include:

Bar instability of rapidly-rotating disks
Jeans instability
Firehose instability
Gravothermal instability
Radial-orbit instability
Various instabilities in cold rotating disks

Notes

^ Shengtai Li, Hui Li "Parallel AMR Code for Compressible MHD or HD Equations" (Los Alamos National Laboratory) [1]
^ Buneman, O., "Instability, Turbulence, and Conductivity in Current-Carrying Plasma" (1958) Physical Review Letters, vol. 1, Issue 1, pp. 8-9
^ Kho, T. H.; Lin, A. T., "Cyclotron-Cherenkov and Cherenkov instabilities" (1990) IEEE Transactions on Plasma Science (ISSN 0093-3813), vol. 18, June 1990, p. 513-517
^ Finn, J. M.; Kaw, P. K., "Coalescence instability of magnetic islands" (1977) Physics of Fluids, vol. 20, Jan. 1977, p. 72-78. (More citations)
^ Uhm, H. S.; Siambis, J. G., "Diocotron instability of a relativistic hollow electron beam" (1979) Physics of Fluids, vol. 22, Dec. 1979, p. 2377-2381.

External links

eFluids Fluid Flow Image Gallery

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Translations: Instability

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Dansk (Danish)
n. - usikkerhed, ustadighed, instabilitet

Nederlands (Dutch)
onevenwichtigheid, labiliteit, onvastheid

Français (French)
n. - instabilité, (Mécan) déséquilibrage, (Météo) instabilité, manque de solidité, mobilité, instabilité (de caractère)

Deutsch (German)
n. - Instabilität, Labilität

Ελληνική (Greek)
n. - αστάθεια, ρευστότητα

Italiano (Italian)
instabilità

Português (Portuguese)
n. - instabilidade (f)

Русский (Russian)
неустойчивость

Español (Spanish)
n. - inestabilidad, desequilibrio

Svenska (Swedish)
n. - instabilitet, obeständighet

中文（简体）(Chinese (Simplified))
不安定, 基础薄弱, 不稳定

中文（繁體）(Chinese (Traditional))
n. - 不安定, 基礎薄弱, 不穩定

한국어 (Korean)
n. - 불안정, 변하기 쉬움

日本語 (Japanese)
n. - 不安定, 不安定状態

العربيه (Arabic)
‏(الاسم) عدم استقرار‏

עברית (Hebrew)
n. - ‮חוסר יציבות, חוסר שיווי-משקל, אי-סדירות‬

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