| collision tumour | Two originally separate tumour's, especially a carcinoma and a sarcoma, that appear to have developed by chance in close proximity, so that an area of mingling exists. See: carcinosarcoma. (05 Mar 2000) |
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| collision | <physics> Refers to the close approach of two or more particles, photons, atoms, nuclei, etc, during which such quantities as energy, momentum, and charge may be altered. More-or-less synonymous with scattering, except in scattering one generally thinks of one of the particles as being at rest, and the other colliding particles scatter from their initial direction of motion due to the collision. (09 Oct 1997) |
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| collision cross-section | <radiobiology> Effective surface area of a particle when it collides with another, describes probability of collisions between the two particles. (09 Oct 1997) |
| collision frequency | <chemistry> The rate at which chemical species collide, used in theories of chemical kinetics. Also, the frequency with which gaseous molecules collide. (09 Oct 1997) |
| collision theory | <chemistry> A mathematical description of the number of collisions between molecules in a sample of matter per unit time, useful for predicting rates of reaction. (09 Oct 1997) |
| collision time | <radiobiology> Typical time which passes between two consecutive collision events for a given particle. Inverse of the collision frequency, equal to the mean free path divided by the particle's velocity. In plasmas, the (Coulomb) collision time decreases with increasing density, and increases with increasing temperature. (09 Oct 1997) |
| coulomb collision | <physics> An interparticle collision where the Coulomb's force (electrical attraction and repulsion) is the governing force. Coulomb collisions have a number of interesting properties, but these are better described in textbooks. The interaction of the charged particles with each other's electric fields results in deflections of the particles away from their initial paths. See: Coulomb's Law, electrostatic force. (21 Jun 2000) |
| effective collision radius | <radiobiology> Effective size of a particle equal to the square root of (cross-section/pi). Determines the effective range of interaction of the particle. (09 Oct 1997) |
| acinar cell tumour | A solid and cystic tumour of the pancreas, occurring in young women; tumour cells contain zymogen granules. (05 Mar 2000) |
| acute splenic tumour | Acute splenitis, enlargement, and softening of the spleen, usually due to bacteraemia or severe bacterial toxaemia. (05 Mar 2000) |
| adenoid tumour | Adenoma, or neoplasm with glandlike spaces. (05 Mar 2000) |
| adenomatoid odontogenic tumour | A benign epithelial odontogenic tumour appearing radiographically as a well-circumscribed radiolucent-radiopaque lesion usually surrounding the crown of an impacted tooth in an adolescent or young adult; characterised histologically by columnar cells organised in a duct-like configuration interspersed with spindle-shaped cells and amyloid-like deposition that gradually undergoes dystrophic calcification. Synonym: adenoameloblastoma, ameloblastic adenomatoid tumour. (05 Mar 2000) |
| adenomatoid tumour | A small, circumscribed, benign tumour of the genital tract, composed of small glandlike spaces lined by flattened or cuboidal mesothelium-like cells. (12 Dec 1998) |
| adipose tumour | <oncology, tumour> Clumps of fat cells. Literally, fat cancer. These are benign tumours that can form in the breast. (16 Dec 1997) |
| adrenal gland tumour | <oncology> A benign tumour or adenoma, that usually results in the excess production of adrenal gland hormones. (27 Sep 1997) |
| adrenal rest tumour | A rare, usually benign, ovarian tumour thought to be derived from embryonic rest cells of the adrenals. This tumour causes various degrees of masculinization. (12 Dec 1998) |