| mean sea level | <marine biology> A tidal datum: the arithmetic mean of hourly water elevations observed over a specific 19-year cycle. Points on land can be referenced to a mean sea level, in which case the datum assumes zero elevation. (09 Oct 1997) |
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| gray level also gray value | <microscopy> The brightness of pixels in a digitised video image, commonly expressed in integers ranging from 0 (black) to 255 (white) for an 8-bit digital signal. (05 Aug 1998) |
| gray level histogram | <microscopy> In digital image processing, a histogram that depicts the number of pixels at each gray value. The histogram can be used to measure the areas that have given ranges of gray values or to adjust image contrast by histogram stretching or equalisation. See: Image histogram. (05 Aug 1998) |
| cohb level | A blood test which is performed on an arterial specimen and is a measurement of the amount of carbon monoxide which is present and bound to haemoglobin. This is an important test to diagnosis carbon monoxide toxicity (smoke inhalation). Normal carboxyhaemoglobin may be from 3% to as high as 12% in heavy smokers. Symptoms of carbon monoxide poisoning begin at about 20% carboxyhaemoglobin. (27 Sep 1997) |
| white level | <microscopy> Also reference white level. The IEEE scale, or voltage level, of the video picture signal that corresponds to a specified maximum limit for white peaks. (05 Aug 1998) |
| window level | The CT number setting in Hounsfield units of the midpoint of the window width, which is the gray scale of the image; a typical window level for imaging the lungs if -500; for the abdomen, 0. (05 Mar 2000) |
| hearing level | The measure of the status of hearing as read directly on the hearing loss scale of an audiometer; described in decibels as a deviation from a standard value for zero on the audiometer. (05 Mar 2000) |
| serum iron level | A test that measures the amount of iron (Fe ++) in the blood. The test is performed when iron deficiency is suspected. Normal serum iron is 60 to 170 mcg/dl. Increased levels may be seen in the following: haemochromatosis, haemolysis, haemolytic anaemia, hepatitis, liver necrosis, haemosiderosis, iron poisoning and lead toxicity. Lower than normal levels are seen in chronic GI blood loss, iron deficiency anaemia, insufficient dietary iron, malabsorption, chronic heavy menstrual bleeding, nephrosis and late pregnancy. (27 Sep 1997) |
| sound pressure level | A measure of sound energy relative to 0.0002 dynes/cm2, expressed in decibels. (05 Mar 2000) |
| substrate-level phosphorylation | Synthesis of high-energy phosphate bonds through reaction of inorganic phosphate with an activated (usually) organic substrate. (09 Oct 1997) |
| no-observed-adverse-effect level | The highest dosage administered that does not produce toxic effects. The noael will depend on how closely dosages are spaced (lowest-observed-adverse-effect level and no-observed-effect level) and the number of animals examined. The ultimate objective is usually to determine not the "safe" dosage in laboratory animals but the "safe" dosage for humans. Therefore, the extrapolation most often required of toxicologists is from high-dosage studies in laboratory animals to low doses in humans. (casarett and doull's toxicology: the basic science of poisons, 4th ed) (12 Dec 1998) |
| organic level | The amount of organic matter prescribed to be left after logging. (05 Dec 1998) |
| trophic level | <biology> Stage in a food chain or web leading from primary producers (lowest trophic level) through herbivores to primary and secondary carnivores (consumers- highest level). (09 Oct 1997) |
| lactate level | A test that measures the amount of lactic acid in the blood. Lactic acid is an intermediate product of carbohydrate metabolism and is derived mainly from muscle cells and red blood cells. Exercise will normally raise lactic acid levels. Conditions of oxygen deprivation (for example shock, heart failure, lung disease) will trigger anaerobic metabolism within muscle tissue resulting in lactic acid build up in the tissues. Normal lactic acid levels are 4.5 to 19.8 mg/dl. (27 Sep 1997) |
| lactic acid level | <investigation> A test that measures the amount of lactic acid in the blood. (25 Jun 1999) |