occlusal position
| half-life | 1. <pharmacology> The period over which the concentration of a specified chemical or drug takes to fall to half its original concentration in the specified fluid or blood. 2. <radiobiology> The time required to reduce the amount of a radionuclide to one-half the amount originally present. Physical or radioactive half-life refers to reduction of activity by radioactive decay, biological half-life refers to biological elimination from the body and effective half-life refers to the combined action of radioactive decay and biological elimination. (16 Dec 1997) |
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| half-moon | 1. The moon at the quarters, when half its disk appears illuminated. 2. The shape of a half-moon; a crescent. "See how in warlike muster they appear, In rhombs, and wedges, and half-moons, and wings." (Milton) 3. An outwork composed of two faces, forming a salient angle whose gorge resembles a half-moon; now called a ravelin. 4. <zoology> A marine, sparoid, food fish of California (Caesiosoma Californiense). The body is ovate, blackish above, blue or gray below. Synonym: medialuna. Source: Websters Dictionary (01 Mar 1998) |
| half-ray | <geometry> A straight line considered as drawn from a center to an indefinite distance in one direction, the complete ray being the whole line drawn to an indefinite distance in both directions. Source: Websters Dictionary (01 Mar 1998) |
| half-reactions | <chemistry> The two parts of an oxidation-reduction reaction, one representing oxidation, the other reduction. (09 Jan 1998) |
| half register | <molecular biology> A misalignment between two identical sets of repeating units of nucleotides within two copies of the same chromosome (one set of repeating units per copy of the chromosome), where repeating unit A from one set is inappropriately aligned with repeating unit B on the other set, so that ABABAB on one set would be aligned with BABABA on the other set instead of the correct ABABAB with ABABAB. (13 Nov 1997) |
| half-tetrad analysis | <genetics> The analysis of tetrad chromosomes (a pair of homologous chromosomes, thus four total chromosomes) after recombination when only half of the tetrad (two of the four chromosomes) can be analysed. (13 Nov 1997) |
| half-time | The time, in a first-order chemical (or enzymic) reaction, for half of the substance (substrate) to be converted or to disappear. Compare: half-life. (05 Mar 2000) |
| half-value layer | <radiobiology> The thickness of a specified material (usually a specific absorber), which attenuates a beam of radiation so that the exposure rate or absorbed dose rate at a specified point is reduced by half. (20 Sep 2002) |
| drug half-life | The amount of time it takes for one-half of an administered drug to be lost through biological processes (metabolism and elimination). (27 Sep 1997) |
| effective half-life | <radiobiology> Time required for a radioactive substance contained in a biological system (such as a person or an animal) to reduce its radioactivity by half, as a combination result of radioactive decay and biological elimination from the system. (09 Oct 1997) |
| elimination half-life | <pharmacology> The time it takes for the body to eliminate or breakdown half of a dose of a pharmacologic agent. (09 Oct 1997) |
| acorn-shell | <zoology> One of the sessile cirripeds; a barnacle of the genus Balanus. Source: Websters Dictionary (01 Mar 1998) |
| argus shell | <zoology> A species of shell (Cypraea argus), beautifully variegated with spots resembling those in a peacock's tail. Source: Websters Dictionary (01 Mar 1998) |
| ark shell | <zoology> A marine bivalve shell belonging to the genus Arca and its allies. Source: Websters Dictionary (01 Mar 1998) |
| boat shell | <zoology> A marine gastropod of the genus Crepidula. The species are numerous. It is so named from its form and interior deck. A marine univalve shell of the genus Cymba. Source: Websters Dictionary (01 Mar 1998) |