| point-spread function | <microscopy> The mathematical representation of the image of a point source. For a diffraction-limited optical system operating in the absence of aberrations, the point-spread function is the Airy disk. See: three-dimensional diffraction pattern. (05 Aug 1998) |
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| point system test types | A near-vision test chart in which the various test types are multiples of a point (1/72 inch), lower-case letters being one-half the designated point size; reading 4-point at 16 inches is normal, and is designated N-4. (05 Mar 2000) |
| point tenderness | <clinical sign> A finding on physical examination that can indicate a localised inflammatory process due to injury or disease. Point tenderness will be discovered over fracture sites (in bone injury). (27 Sep 1997) |
| critical point | A point at which two phases become identical; thus, at a given critical temperature and critical pressure, the liquid and gaseous state of a particular substance can no longer be differentiated. (05 Mar 2000) |
| critical point drying | <procedure> A method for preparing specimens for the scanning electron microscope that avoids the problems of shrinkage caused by normal drying procedures. Water in the specimen is replaced by an intermediate fluid, for example liquid carbon dioxide, avoiding setting up a liquid/gas interface and then the second fluid is allowed to vaporise by raising the temperature above the critical point, the temperature at which the liquid state no longer occurs. (18 Nov 1997) |
| posterior focal point | The point of a compound optical system where parallel rays entering the system are focused. (05 Mar 2000) |
| power point | In dentistry, the vertical dimension at which the greatest masticatory force may be registered. (05 Mar 2000) |
| preauricular point | A point of the posterior root of the zygomatic arch lying immediately in front of the upper end of the tragus. (05 Mar 2000) |
| Halle's point | <anatomy> A point at the intersection of a horizontal line touching the anterior superior spine of the ilium and a perpendicular line drawn from the spine of the pubis; here the ureter can be most readily palpated. (05 Mar 2000) |
| pressure point | A cutaneous locus having pressure-sensitive elements which when compressed, pressure is appreciated. (05 Mar 2000) |
| primary point of ossification | This is the first site where bone begins to form in the shaft of a long bone or in the body of an irregular bone. Synonym: punctum ossificationis primarium, primary point of ossification. (05 Mar 2000) |
| principal point | <microscopy> Mutually conjugate points lying on the lens axis and producing a magnification of one. Object and image distance as well as focal length are calculated (measured) from these points. (05 Aug 1998) |
| heat-rigor point | <cell biology> The degree of elevated temperature at which coagulation of protoplasm occurs with death of the cell. (05 Mar 2000) |
| x-point | <radiobiology> Place where the poloidal magnetic field vanishes in such a way that two flux surfaces appear to cross, for example where the main plasma joins the divertor or between magnetic islands. Location where magnetic reconnection takes place. See: magnetic reconnection, divertors, O-point. (09 Oct 1997) |
| secondary point of ossification | This is the centre of bone formation appearing later than the punctum ossificationis primarium, usually in epiphysis. Synonym: punctum ossificationis secundarium, secondary point of ossification. (05 Mar 2000) |