| late reaction | A local or generalised response that begins 24 to 48 hours after exposure to an antigen. See: cell-mediated reaction. Synonym: contact hypersensitivity, delayed hypersensitivity, late reaction, tuberculin-type hypersensitivity. (05 Mar 2000) |
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| late replicating chromosome | A chromosome (often anomalous) that is shown, e.g., by incorporation of a labelled nucleotide, to undergo delayed duplication preliminary to mitosis; formerly used as a means of distinguishing members of a group of chromosome's. (05 Mar 2000) |
| late rickets | <pathology> A condition marked by softening of the bones (due to impaired mineralisation, with excess accumulation of osteoid), with pain, tenderness, muscular weakness, anorexia and loss of weight, resulting from deficiency of vitamin D and calcium. Origin: Gr. Malakia = softness (18 Nov 1997) |
| late seizure | A seizure that occurs greater than one week after a craniocerebral trauma or CNS insult. (05 Mar 2000) |
| late seral species | Shade tolerant species, primarily vine maple shrubs and western red cedar and western hemlock trees. These species follow the mid seral species in natural succession. (05 Dec 1998) |
| late seral treatment | A treatment in which late seral species will be established after thinning. (05 Dec 1998) |
| late-successional forest | Forest seral stages which include mature and old- growth age classes. (05 Dec 1998) |
| late-successional reserve | An area of forest where the management objective is to protect and enhance conditions of late successional and old-growth forest ecosystems. (05 Dec 1998) |
| late syphilis | Involvement of the cardiovascular or central nervous system, or the development of a gumma in any organ, due to infection with Treponema pallidum; usually several years to 2-3 decades after the initial infection. Synonym: tertiary syphilis. (05 Mar 2000) |
| late systole | The interval in the cardiac rhythm immediately preceding diastole. Synonym: late systole. (05 Mar 2000) |
| 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) |