| plasma focus | <radiobiology> The Plasma Focus is another device which depends on the pinch effect. Possible applications include both fusion and plasma propulsion, as well as other plasma research. In essence the plasma focus is generated by discharge of a current across the ends of two coaxial insulated conducting pipes. The Plasma Focus caused a huge stir when they generated copious neutrons, until it was discovered that the source of the neutrons was knockoffs from deuterium due to pinch accelerated electrons or ions. Plasma focus is sort of a point version of the Zpinch. (09 Oct 1997) |
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| condenser, variable-focus | <microscopy> Essentially an Abbe condenser in which the upper lens element is fixed and the lower movable. The lower lens may be used to focus the illumination between the elements so that it emerges from the stationary lens as a large diameter parallel bundle. The field of low-power objectives may thus be filled without removing the top element. at the opposite extreme it can be adjusted to have a numerical aperture as high as 1.3. See: illumination, critical. (05 Aug 1998) |
| principal focus | The real or virtual meeting point of rays passing into a lens parallel to its axis. (05 Mar 2000) |
| spleen focus-forming viruses | Murine leukaemia viruses that are replication-defective and rapidly transforming. The envelope gene plays an essential role in initiating erythroleukaemia, manifested by splenic foci, splenomegaly, and polycythemia. Spleen focus-forming viruses are generated by recombination with other viral types including friend p (polycythemia), friend a (anaemia), rauscher, and cas (from wild mice at lake casita, california). (12 Dec 1998) |
| natural focus of infection | An ecosystem in which an infectious agent normally persists in nature; e.g., yellow fever virus in a jungle monkey-Haemagogus mosquito ecosystem. (05 Mar 2000) |
| depth of focus | <microscopy> The depth or thickness of the image space that is simultaneously in acceptable focus. The range of distances between a lens and image plane (target in the video pickup device) for which the image formed by the lens at a given setting is clearly focused. With a high-numerical aperture microscope objective, the depth of field is very shallow, but the depth of focus can be quite deep and reach several millimetres. (05 Aug 1998) |
| focus | Group of (frequently neoplastic) cells, identifiable by distinctive morphology or histology. (18 Nov 1997) |
| focus-forming assay | <investigation> A lab technique used to find out if a particular piece of DNA contains oncogenes (genes which are associated with cancer). This is done by putting the DNA into animal cells which normally show contact inhibition, or which stop growing when they come into physical contact with other cells or reach a certain density in the culture. If the cells lose contact inhibition and form areas of densely-packed cells (called foci) after receiving the DNA, it means that the DNA did contain oncogenes. (05 Jan 1997) |
| focus-forming unit | A measurement of the concentration of live virus in a given amount of fluid. This is measured by spreading a known amount of the fluid over a layer of cultured cells which are infected by the virus, then counting the number of areas in the culture which look infected. (09 Oct 1997) |
| focus groups | A method of data collection and a qualitative research tool in which a small group of individuals are brought together and allowed to interact in a discussion of their opinions about topics, issues, or questions. (12 Dec 1998) |
| focus, principal | <physics> The point at which a lens focuses an axial object point. Synonymous with focal point. (05 Aug 1998) |
| Friend spleen focus forming virus | <virology> Defective virus found in certain strains of Friend virus, detected by its ability to form foci in spleens of mice and believed to be responsible in those strains for the production of a leukaemia associated with polycythaemia rather than anaemia. (18 Nov 1997) |
| analgesia, patient-controlled | Relief of pain, without loss of consciousness, through an analgesic agent administered by the patient. It has been used successfully to control postoperative pain, during labour, after burns, and in terminal care. The choice of agent, dose, and lockout interval greatly influence effectiveness. The potential for overdose can be minimised by combining small bolus doses with a mandatory interval between successive doses (lockout interval). (12 Dec 1998) |
| patient | 1. A person who is receiving medical treatment, especially in a hospital. 2. A person who is registered with a doctor, dentist, etc and is treated by him when necessary. (18 Nov 1997) |
| patient admission | The process of accepting patients. The concept includes patients accepted for medical and nursing care in a hospital or other health care institution. (12 Dec 1998) |