| microscope, field emission | <microscopy> An image-forming device in which a strong electrostatic field causes cold emission of electrons from a sharply rounded point or from a specimen that has been placed on that point. The electrons are accelerated to a phosphorescent screen, or photographic film, giving a visible picture of the variation of emission over the specimen surface. (05 Aug 1998) |
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| microscopic field | The area within which objects are visible with microscope oculars and objectives of various magnifying powers. (05 Mar 2000) |
| washed field technique | The cutting of cavity preparations in teeth utilizing a constant irrigant which is immediately removed from the mouth by means of a vacuum device. (05 Mar 2000) |
| Cohnheim's field | A polygonal mosaic-like figure formed by a group of myofibrils, as seen in the cross-section of a skeletal muscle fibre examined under the microscope; a shrinkage artifact of fixation. Synonym: Cohnheim's field. (05 Mar 2000) |
| Wernicke's field | The region of the cerebral cortex thought to be essential for understanding and formulating coherent, propositional speech; it encompasses a large region of the parietal and temporal lobes near the lateral sulcus of the left cerebral hemisphere; corresponding approximately to Brodmann's areas 40, 39, and 22. Synonym: sensory speech centre, Wernicke's area, Wernicke's field, Wernicke's region, Wernicke's zone. (05 Mar 2000) |
| wide field ocular | An ocular that gives a larger than usual field of view and a high eyepoint. (05 Mar 2000) |
| condenser, dark field | <microscopy> A condenser forming a hollow cone of light with its apex (or focal point) in the plane of the specimen. When used with an objective having a numerical aperture lower than the minimum numerical aperture of the hollow cone, only light deviated by the specimen enters the objective. Objects are seen as bright images against a dark background. The ordinary bright field condenser of low power, used with a central stop, makes a good dark field condenser. They all form a dark field while illuminating the specimen with a hollow cone of light. The lower limiting aperture of the condenser must be greater than the numerical aperture of the objective with which it is to be used. Thus, no direct light enters the objective, the specimen is seen by reflected or scattered light on a dark background. See: condensers See: special dark field condensers: paraboloid, cardioid and Cassegrainian. (05 Aug 1998) |
| constant field equation | An equation derived to predict membrane potentials in terms of the membrane's permeability to ions and their concentrations on either side. Synonym: constant field equation, Goldman-Hodgkin-Katz equation, GHK equation. (05 Mar 2000) |
| poloidal field | <physics> In toroidal devices, the magnetic field that encircles the plasma axis. (i.e., loops around the torus the short way.) (09 Oct 1997) |
| poloidal field coil | <radiobiology> In toroidal devices (e.g., tokamaks), the sets of windings which are (typically) aligned along the plasma axis and produce poloidal fields. These include ohmic heating, shaping, vertical, equilibrium, and divertor windings. (09 Oct 1997) |
| curvature of field | <microscopy> A property of lens that causes the image of a plane to be focused into a curved surface instead of a plane. The image plane formed by a single lens is naturally curved. While one part of the field will be in good focus, the rest will need refocusing to be sharp. While the eye may partially correct for this, a camera lens will not, and the final image as photographed will not be in perfect focus over the entire image plane. (05 Aug 1998) |
| prerubral field | See: fields of Forel. (05 Mar 2000) |
| pulsed-field gel electrophoresis | Gel electrophoresis in which, after electrophoretic migration has begun, the current is briefly stopped and reapplied in a different orientation; allows for the purification of long DNA molecules. Synonym: pulsed-field gel electrophoresis. (05 Mar 2000) |
| pulse field electrophoresis | <investigation> A method used for high resolution electrophoretic separation of very large (megabase) fragments of DNA. Electric fields 100 |
| pulse-field gel electrophoresis | Gel electrophoresis in which, after electrophoretic migration has begun, the current is briefly stopped and reapplied in a different orientation; allows for the purification of long DNA molecules. Synonym: pulsed-field gel electrophoresis. (05 Mar 2000) |