| field survey | The planned collection of data among noninstitutionalised persons in the general population. (05 Mar 2000) |
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| horizontal survey | <epidemiology> A study of a community, perhaps stratified by age, sex, ethnicity etc., but at one point in time or over a short time interval. Although a snapshot, horizontal surveys of prevalence and intensity within different age classes of a community can nevertheless provide valuable information on the rate at which hosts acquire infection through time, provided that the host and parasite populations have remained approximately stable for a period of time (i.e. Stable endemicity). Same as cross-sectional study , converse of longitudinal study. (05 Dec 1998) |
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| skeletal survey | A radiographic examination of all or selected parts of the skeleton, as for occult fractures, metastases, etc. (05 Mar 2000) |
| survey | 1. To inspect, or take a view of; to view with attention, as from a high place; to overlook; as, to stand on a hill, and survey the surrounding country. "Round he surveys and well might, where he stood, So high above." (Milton) 2. To view with a scrutinizing eye; to examine. "With such altered looks, . . . All pale and speechless, he surveyed me round." (Dryden) 3. To examine with reference to condition, situation, value, etc.; to examine and ascertain the state of; as, to survey a building in order to determine its value and exposure to loss by fire. 4. To determine the form, extent, position, etc, of, as a tract of land, a coast, harbor, or the like, by means of linear and angular measurments, and the application of the principles of geometry and trigonometry; as, to survey land or a coast. 5. To examine and ascertain, as the boundaries and royalties of a manor, the tenure of the tenants, and the rent and value of the same. Origin: OF. Surveoir, surveer; sur, sor, over, E. Sur + veoir, veeir, to see, F. Voir, L. Videre. See Sur-, and Vision, and cf. Supervise. Source: Websters Dictionary (01 Mar 1998) |
| survey line | A line scribed on an abutment tooth of a dental cast by means of a dental surveyor indicating the height of contour of the tooth according to a specific path of insertion, a line which serves as a guide in the proper location of various parts of a clasp assembly for a removable partial denture. Synonym: clasp guideline, Cummer's guideline. (05 Mar 2000) |
| auditory field | The space included within the limits of hearing of a definite sound, as of a tuning fork. (05 Mar 2000) |
| bright field illumination | <microscopy> The method of lighting the specimen with a solid cone of rays. Transmitted bright field illumination is performed by a substage condenser. Reflected bright field illumination is performed by a vertical illuminator. Compare: dark field illumination (05 Aug 1998) |
| bright field imaging | <microscopy> An imaging mode in a transmission electron microscopy that uses only unscattered Electrons to form the image. Contrast in such an image is due entirely to mass-thickness variations in amorphous samples, and may include diffraction contrast in crystalline samples. (05 Aug 1998) |
| bright field microscopy | <technique> Optical microscopy, in which absorption to a great extent and diffraction to a minor extent give rise to the image, as opposed to phase contrast or interference methods of microscopy. (18 Nov 1997) |
| Broca's field | The posterior part of the inferior frontal gyrus of the left or dominant hemisphere, corresponding approximately to Brodmann's area 44; Broca identified this region as an essential component of the motor mechanisms governing articulated speech. Synonym: Broca's area, Broca's field, motor speech centre. (05 Mar 2000) |
| cardioid dark field condenser | <microscopy> A condenser designed with two reflecting surfaces, the first, a spherical surface which reflects the rays to a second, cardioid (heart-shaped) surface. The virtue in such an arrangement is that, if the cardioid surface is of true figure, the lens is both achromatic and aplanatic. It has a limiting numerical aperture of about 1.0. Thus objectives of a greater numerical aperture cannot be used successfully with it. A true cardioid figure is the trace of a point on the circumference of a circle rolling around an equal, fixed circle. (05 Aug 1998) |
| magnetic field | The sphere of influence of a magnet. (05 Mar 2000) |
| magnetic field gradient | In magnetic resonance imaging, a magnetic field that varies with location, superimposed on the uniform field of the magnet, to alter the resonant frequency of nuclei and allow recovery of their spatial position. Synonym: field gradient. (05 Mar 2000) |
| paraboloid dark field condenser | <microscopy> A lens of parabolic shape. The vertex end is ground back so that its focus can be brought into coincidence with the specimen on the slide. A central stop is provided to block the central rays. It is used chiefly for medium- power work. (05 Aug 1998) |
| receptive field | That part of the retina whose photoreceptors (rods and cones) pertain to a single optic nerve fibre. The response of a neuron to stimulation of its receptive field depends on the type of neuron and the part of the field that is illuminated; an "on-centre" neuron is stimulated by light falling at the centre of its receptive field and inhibited by light falling at the periphery; an "off-centre" neuron reacts in exactly the opposite fashion; that is, it is inhibited by light falling at the centre of its receptive field. In either case, the net response depends on a complex switching action in the retina. When an entire receptive field is equally illuminated, the response of receptors at the centre of the field predominates. (05 Mar 2000) |
| visual field | The area simultaneously visible to one eye without movement; often measured by means of a bowl perimeter located 330 mm from the eye. (05 Mar 2000) |