| first-order kinetics | A term describing the reaction rate of a chemical reaction in which the rate is proportional to the concentration (in moles) of only one of the reactants. Such a reaction might have an equation like rate = k[A], where k is the reaction rate constant and [A] is the concentration of a reactant A. (09 Oct 1997) |
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| first-order reaction | A reaction the rate of which is proportional to the concentration of the single substance undergoing change; radioactive decay is a first-order process, defined by the equation -(dN/dt)=kN, where N is the number of atoms subject to decay (reaction), t is time, and k is the first-order decay (reaction) constant, i.e., the fraction of all atoms decaying per unit of time. See: decay constant, order. (05 Mar 2000) |
| first parallel pelvic plane | The upper opening of the true pelvis, bounded anteriorly by the pubic symphysis and the pubic crest on either side, laterally by the iliopectineal lines, and posteriorly by the promontory of the sacrum. Synonym: apertura pelvis superior, aditus pelvis, first parallel pelvic plane, pelvic brim, pelvic inlet, pelvic plane of inlet, plane of inlet. (05 Mar 2000) |
| first rank symptoms | Those symptom's that, when present, indicate that the diagnosis of schizophrenia is likely, provided that organic or toxic aetiology is ruled out: delusion of control, thought broadcasting, thought withdrawal, thought insertion, hearing one's thoughts spoken aloud, auditory hallucinations that comment on one's behaviour, and auditory hallucinations in which two voices carry on a conversation. Synonym: first rank symptoms, schneiderian first rank symptoms. (05 Mar 2000) |
| first-set rejection | Allograft transplantation between two organisms not previously sensitised to the graft tissue. Necrosis of the graft usually occurs within 10 days of transplantation. (05 Mar 2000) |
| first stage of labour | The part of labour when the cervix dilates fully (to 10 centimeters). The first stage of labour is also called the stage of dilatation. (12 Dec 1998) |
| first temporal convolution | A longitudinal gyrus on the lateral surface of the temporal lobe between the lateral (sylvian) fissure and the superior temporal sulcus. Synonym: gyrus temporalis superior, first temporal convolution, superior temporal convolution. (05 Mar 2000) |
| first visceral cleft | <anatomy> The cleft between the hyoid and mandibular arches of the embryo; the external auditory meatus is developed from its dorsal portion. Synonym: first visceral cleft. (05 Mar 2000) |
| acute lower GI haemorrhage | <gastroenterology> Typical presentation: Sudden onset of brisk rectal bleeding without blood in gastric aspirate Diagnostic considerations: diverticulosis, angiodysplasia, ischemic colitis, inflammatory bowel disease (rarely), polyps are usually present, carcinoma causing a chronic bleed, haemorrhoids. (12 Dec 1998) |
| anterior surface of lower limb | The anterior surface of the inferior limb. Synonym: facies anterior membri inferioris. (05 Mar 2000) |
| arterial arch of lower eyelid | Formed by the medial palpebral artery which communicates with a branch of the lacrimal artery along the tarsal margin. Synonym: arcus palpebralis inferior. (05 Mar 2000) |
| bones of lower limb | These include the inferior limb girdle (hip bone) and the skeleton of the free inferior limb (femur, tibia, fibula, patella, tarsus, metatarsus, and bones of the toes). Synonym: ossa membri inferioris, bones of inferior limb. (05 Mar 2000) |
| regions of lower limb | The topographic divisions of the lower limb: gluteal, thigh (or femoral), knee, leg (or crural), ankle, and foot. Synonym: regiones membri inferioris, regions of inferior limb. (05 Mar 2000) |
| mean lower low water | <marine biology> The average height of the lower low waters over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value. (09 Oct 1997) |
| cesarian section, lower segment | A Cesarian section in which the surgical incision (cut) is made in the lower segment of the uterus. (12 Dec 1998) |