instability

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instability

1. tendency to variable or unpredictable behaviour
2. Physics a fast growing disturbance or wave in a plasma

instability

[‚in·stə′bil·əd·ē]
(control systems)
A condition of a control system in which excessive positive feedback causes persistent, unwanted oscillations in the output of the system.
(physics)
A property of the steady state of a system such that certain disturbances or perturbations introduced into the steady state will increase in magnitude, the maximum perturbation amplitude always remaining larger than the initial amplitude.

instability

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

instability

instabilityclick for a larger image
i. A state of the atmosphere in which a parcel of air will continue to rise, if for any reason, it is pushed up. Any instability in the atmosphere means turbulent conditions exist. The environmental lapse rate (ELR) in this case will be higher than both dry and saturated adiabatic lapse rates. Dry adiabatic lapse rate (DALR) is the rate of decrease of temperature with height of a parcel of dry air lifted adiabatically. Its value is 3°/1000 ft. Saturated adiabatic lapse rate (SALR) is the lapse rate of a parcel of saturated air and its value is 1.5°/1000 ft.
ii. A tendency of a body to continue moving away from its original state when disturbed by an external force and to continue after that force has been withdrawn.
iii. The failure of structures, such as the buckling of plates and panels under compression, and the failure of struts under end loads.
References in periodicals archive ?
Bloem, "Postural instability in Parkinson's disease," Clinical Neurology and Neurosurgery, vol.
TeleWii opens new opportunities for treating postural instability, giving individuals access of care from their home [10] especially for those residing in rural areas.
A slowly progressive neurodegenerative disorder, PD is characterized by symptoms of bradykinesia, tremor, rigidity, and postural instability. As the disease progresses, individuals experience additional symptoms such as freezing gait, difficulty swallowing, drooling, and voice softening.
The comparable postural instability at height in the RE and VE reflects a similarly reduced potential for visual stabilization, which is best revealed under unstable support conditions.
Prediction of osteoporotic fractures by postural instability and bone density.
Cardinal Manifestations Tremor Rigidity Bradykinesia Postural instability Secondary Manifestations Incoordination Micrographia Blurred vision Impaired upward gaze Blepharospasm Glabellar reflex Dysarthria Dysphagia reflex Sialorrhea Masked facies Hand and foot deformities Dystonia Edema Scoliosis Kyphosis Pain and sensory symptoms Seborrhea Constipation Urinary urgency, hesitancy, and frequency Loss of libido Impotence Freezing Dementia Depression From Stern MB, Hurtig HI, eds.
report on a retrospective review of pre- and postoperative data in 130 patients, suggesting that postural instability and worse pre-DBS motor score are the strongest predictors of poorer functional and QOL outcomes, while age at surgery and duration of the disease did not seem to influence the outcome.
Postural instability in diabetic neuropathic patients at risk of foot ulceration.
He displayed significant postural instability, he began experiencing "on-off" phenomena, and his dyskinesias became worse than they had ever been.
(For an alternative to the motion cue conflict approach, see the Appendix: Postural Instability Theory.)
Movement disorders common to HD and PD include akinesia, hypokinesia, dyskinesia and postural instability. Secondary musculoskeletal and cardiovascular changes may also occur as a result of inactivity or disuse.