| thermal sense | The ability to distinguish differences of temperature. Synonym: temperature sense, thermal sense, thermic sense, thermesthesia. Origin: thermo-+ G. Aisthesis, sensation (05 Mar 2000) |
|---|---|
| thermal sensors | Sensors that detect tiny changes in heat or temperature. (14 Nov 1997) |
| thermal spectrum | The part of the invisible spectrum of wave length just longer than that of visible red light. Synonym: thermal spectrum. (05 Mar 2000) |
| thermal velocity | <radiobiology> Average speed (magnitude of velocity) of a particle at a given temperature (in a Maxwellian velocity distribution). (09 Oct 1997) |
| activation | <radiobiology> Activation occurs when a particle interacts with an atomic nucleus, shifting the nucleus into an unstable state, and causing it to become radioactive. In fusion research, where deuterium-tritium is a common fuel mixture, the neutron released when (D + T) combine to form (4He + n) can activate the reactor structure. In this case the 4He is inert, the neutron sticks to another nucleus, and the neutron + nucleus reaction creates an actvation product. Sometimes called radioactivation. See: activation product, activation analysis. (09 Oct 1997) |
| activation analysis | <radiobiology> Method for identifying and measuring chemical elements in a sample of material. Sample is first made radioactive by bombardment with neutrons, charged particles, or gamma rays. Newly formed radioactive atoms in the sample then give off characteristic radiations (such as gamma rays) that tell what kinds of atoms are present, and how many. (09 Oct 1997) |
| activation energy | <chemistry> The amount of energy (expressed in joules) that is needed to convert all the molecules in one mole of a reacting substance from a ground state to the transition state. (06 May 1997) |
| activation product | <radiobiology> The unstable nucleus formed when activation occurs. (See activation above.) (09 Oct 1997) |
| amino acid activation | The first step of protein synthesis, whereby an amino acid reacts with adenosine triphosphate in the presence of aminoacyl RNA synthetase to produce an amino acid adenylate, which provides the energy necessary for the attachment of the amino acid to a specific transfer RNA molecule. (12 Dec 1998) |
| macrophage activation | The process of altering the morphology and functional activity of macrophages so that they become avidly phagocytic. It is initiated by lymphokines, such as the macrophage activation factor (maf) and the macrophage migration-inhibitory factor (mmif), immune complexes, c3b, and various peptides, polysaccharides, and immunologic adjuvants. (12 Dec 1998) |
| gene activation | The process of activation of a gene so that it is expressed at a particular time. This process is crucial in growth and development. (05 Mar 2000) |
| Gibbs energy of activation | The Gibbs energy that must be added to that already possessed by a molecule or molecules in order to initiate a reaction. (05 Mar 2000) |
| virus activation | The mechanism by which latent viruses, such as genetically transmitted tumour viruses or prophages of lysogenic bacteria, are induced to replicate and are released as infectious viruses. It may be effected by various endogenous and exogenous stimuli, including B-cell lipopolysaccharides, glucocorticoid hormones, halogenated pyrimidines, ionizing radiation, ultraviolet light, and superinfecting viruses. (12 Dec 1998) |
| cis activation | <molecular biology> Activation of a gene by an activator located on the same chromosome i.e. Not by a diffusible product. (18 Nov 1997) |
| complement activation | The sequential activation of serum components c1 through c9, initiated by an erythrocyte-antibody complex or by microbial polysaccharides and properdin, and producing an inflammatory response. (12 Dec 1998) |