| ATEM | analytic transmission electron microscopy |
|---|---|
| BEI | back-scattered electron imaging; biological exposure indexes; butanol-extractable iodine |
| BeV, Bev | billion electron volts |
| CEM | computerized electroencephalographic map; conventional transmission electron microscope |
| CIDEP | chemically induced dynamic electron polarization |
| positive image | <microscopy> A developed image in which dark areas correspond to dark areas of the original subject. (05 Aug 1998) |
|---|---|
| positive lens | <physics> Any lens with a positive focal length. Such lenses are thicker in the centre than around the circumference. There are three types of positive lenses, double convex or biconvex, planoconvex, converging concavoconvex or converging meniscus. (05 Aug 1998) |
| positive meniscus | A convexoconcave lens in which the power of the convexity exceeds that of the concavity. Synonym: positive meniscus. (05 Mar 2000) |
| positive-negative pressure breathing | Inflation of the lungs with positive pressure and deflation with negative pressure by an automatic ventilator. (05 Mar 2000) |
| positive ocular | <microscopy> A Ramsden ocular or any modification of it. The diaphragm is below the field lens. (05 Aug 1998) |
| positive phase | The period following the negative phase, during which the opsonic index rises. (05 Mar 2000) |
| positive-pressure respiration | A method of mechanical ventilation in which pressure is maintained to increase the volume of gas remaining in the lungs at the end of expiration, thus reducing the shunting of blood through the lungs and improving gas exchange. (12 Dec 1998) |
| positive-pressure respiration, intrinsic | Non-therapeutic positive end-expiratory pressure occurring frequently in patients with severe airway obstruction. It can appear with or without the administration of external positive end-expiratory pressure (positive-pressure respiration). It presents an important load on the inspiratory muscles which are operating at a mechanical disadvantage due to hyperinflation. Auto-peep may cause profound hypotension that should be treated by intravascular volume expansion, increasing the time for expiration, and/or changing from assist mode to intermittent mandatory ventilation mode. (12 Dec 1998) |
| positive rays | Those originating in a gas discharge tube and moving in a direction opposite to that of cathode ray's; made up of positively charged ions. Synonym: positive rays. (05 Mar 2000) |
| positive scotoma | A scotoma that is perceived as a black spot within the field of vision. (05 Mar 2000) |
| positive stain | <technique> Direct binding of a dye with a tissue component to produce contrast; in electron microscopy, heavy metals like uranyl and lead salts are used to bind to selective cell constituents to produce increased density to the electron beam, i.e., contrast. (05 Mar 2000) |
| positive strand RNA viruses | Class IV and VI viruses that have a single stranded RNA genome that can act as mRNA plus strand) and in which the virus RNA is itself infectious. Includes Picornaviridae, Togaviridae and Retroviridae. (18 Nov 1997) |
| positive supporting reactions | Consisting of those reflex muscular contractions whereby the body is supported against gravity; seen in an exaggerated form in the decerebrate animal, negative supporting reaction's, consisting of inhibition of the extensor muscles and unfixing of the joints which thus enable the limb to be flexed and moved into a new position. Synonym: supporting reflexes. (05 Mar 2000) |
| positive taxis | The attraction of protoplasm toward a stimulus. (05 Mar 2000) |
| positive thermotaxis | Attraction of a plant or animal to heat. (05 Mar 2000) |