| parametric instability | <physics> Instability which occurs in a system whose equilibrium is weakly modulated in time or space. The modulation produces a coupling of the linear eigenmodes of the system and can lead to destabilisation. (09 Oct 1997) |
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| vertical instability | <radiobiology> A type of magnetohydrodynamic (n=0) instability where the plasma drifts vertically upward. Nearly all tokamaks are vertically unstable (all highly shaped ones are). Controlling this instability is possible in many cases, and is an important facet of machine design. Vertical instabilities give rise to halo effects. (09 Oct 1997) |
| rhinitis, vasomotor | A form of rhinitis brought about by changes in vascular tone and permeability. The aetiology is obscure. (12 Dec 1998) |
| chromosomal instability syndromes | A group of mendelian conditions associated with chromosomal instability and breakage in vitro, they often manifest an increased tendency to certain types of malignancies. See: Bloom's syndrome, fragile X syndrome, xeroderma pigmentosum. (05 Mar 2000) |
| heat instability test | A test for the presence of unstable haemoglobins; fresh red blood cells lysed in distilled water develop a precipitate within one hour at 50캜 if unstable haemoglobin is present. (05 Mar 2000) |
| disruptive instability | <radiobiology> Instability which causes a disruption. See: disruption. (09 Oct 1997) |
| instability | The quality or state of being unstable. (18 Nov 1997) |
| interchange instability | <radiobiology> In the simplest form, if you place a high-density fluid on top of a low density fluid, gravity will pull the high density fluid downwards so that the low-density fluid ends up on top. The two fluids therefore interchange places. More generally, an interchange instability occurs when two types of fluid are situated with an external force such that the potential energy is not a minimum, the two fluids will then interchange locations to bring the potential energy to a minimum. In plasmas with magnetic fields, the plasma may interchange position with the magnetic field. A prime example is the flute instability in mirror machines. (See magnetohydrodynamic, instability, flute, mirror.) (09 Oct 1997) |
| trapped-particle instability | <radiobiology> Slowly-growing class of instabilities driven by particles which cannot circulate freely in a toroidal system. See: banana orbit. (09 Oct 1997) |
| two-stream instability | <radiobiology> Instability which can develop when a stream of particles of one type has a velocity distribution with its peak well separated from that of another type of particle through which it is flowing. A stream of energetic electrons passing through a cold plasma can, for example: excite ion waves which will grow rapidly in magnitude at the expense of the kinetic energy of the electrons. (09 Oct 1997) |
| joint instability | Lack of stability of a joint or joint prosthesis. Factors involved are intra-articular disease and integrity of extra-articular structures such as joint capsule, ligaments, and muscles. (12 Dec 1998) |
| universal instability | <radiobiology> Low-frequency instability resulting from the presence of density gradients perpendicular to the magnetic field lines. An instability of this type is generally localised and usually has a small rate of growth. (09 Oct 1997) |
| flute instability | <radiobiology> Term used to describe an interchange instability in which the perturbation is uniform parallel to the magnetic field. In cylindrical geometry, the structure resembles a fluted column (as in classical architecture). Occurs in some mirror machines. (09 Oct 1997) |
| anaemia of chronic disease | <disease> A form of anaemia which develops as the result of a long-term infection or illness. Chronic diseases can interfere with red blood cell production in addition to shortening red blood cell life span in the body. Symptoms are largely due to the underlying disease. Haemoglobin and haematocrit are generally low. Iron studies may be low to normal. Red blood cell indices may usually normal. (27 Sep 1997) |
| benign familial chronic pemphigus | Recurrent eruption of vesicles and bullae that become scaling and crusted lesions with vesicular borders, predominantly of the neck, groin, and axillary regions; autosomal dominant inheritance, presenting in late adolescence or early adult life. Synonym: Hailey-Hailey disease. (05 Mar 2000) |