| vacuum | Origin: L, fr. Vacuus empty. See Vacuous. 1. <physics> A space entirely devoid of matter (called also, by way of distinction, absolute vacuum); hence, in a more general sense, a space, as the interior of a closed vessel, which has been exhausted to a high or the highest degree by an air pump or other artificial means; as, water boils at a reduced temperature in a vacuum. 2. The condition of rarefaction, or reduction of pressure below that of the atmosphere, in a vessel, as the condenser of a steam engine, which is nearly exhausted of air or steam, etc.; as, a vacuum of 26 inches of mercury, or 13 pounds per square inch. Vacuum brake, a kind of continuous brake operated by exhausting the air from some appliance under each car, and so causing the pressure of the atmosphere to apply the brakes. <medicine> Vacuum pan, a glass tube provided with platinum electrodes and exhausted, for the passage of the electrical discharge; a Geissler tube. Vacuum valve, a safety valve opening inward to admit air to a vessel in which the pressure is less than that of the atmosphere, in order to prevent collapse. Torricellian vacuum. See Torricellian. Source: Websters Dictionary (01 Mar 1998) |
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| vacuum casting | The casting of a metal in the presence of a vacuum. (05 Mar 2000) |
| vacuum curettage | Aspiration of the contents of the uterus with a vacuum curette. (12 Dec 1998) |
| vacuum desiccator | A desiccator that can be evacuated. (05 Mar 2000) |
| vacuum disk phenomenon | The appearance of a radiolucent stripe in an intervertebral disk, a manifestation of disk degeneration; a misnomer since there is gas present. (05 Mar 2000) |
| vacuum extraction, obstetrical | Removal of the foetus from the uterus or vagina at or near the end of pregnancy with a metal traction cup that is attached to the foetus' head. Negative pressure is applied and traction is made on a chain passed through the suction tube. (12 Dec 1998) |
| vacuum extractor | Device for producing traction upon the head of a foetus by means of a soft cup held by a vacuum. (05 Mar 2000) |
| vacuum flask | <apparatus> A glass vessel, often silvered, with two walls, the space between which is evacuated; used for maintaining materials at constant temperature or, more usually, at low temperature. Synonym: vacuum flask. (05 Mar 2000) |
| vacuum headache | Headache due to closure of the frontal sinus. (05 Mar 2000) |
| vacuum pan | A device for growing crystals from solutions by gradually lowering the pressure within the sealed container holding the liquid. (09 Oct 1997) |
| vacuum tube | A glass tube from which the air has been removed, containing two or more electrodes, between which passes an electrical current or spark; used in the production of X-rays, or to control circuits. Previously in wide use, the vacuum tube has been supplanted by transistors in electronic circuits. (05 Mar 2000) |
| absolute unit | A unit whose value is constant regardless of place or time and not derived from dependent on gravitation. (05 Mar 2000) |
| alexin unit | The smallest amount (highest dilution) of complement that will cause haemolysis of a unit of red blood cells in the presence of a haemolysin unit. Synonym: alexin unit. (05 Mar 2000) |
| Allen-Doisy unit | The quantity of oestrogen capable of producing in a spayed mouse a characteristic change in the vaginal epithelium, namely, disappearance of leukocytes and appearance of cornified cells, as determined by a vaginal smear; equal approximately to one-half of an estrone unit. Synonym: mouse unit. (05 Mar 2000) |
| amboceptor unit | haemolysin unit |