| PSD | particle size distribution; peptone, starch, and dextrose; periodic synchronous discharge; phase-sen... |
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| PTC | papillary thyroid carcinoma; percutaneous transhepatic cholangiography; phase transfer catalyst; phe... |
| ROPE | respiratory-ordered phase encoding |
| RP | radial pulse; radiopharmaceutical; rapid processing [of film]; Raynaud phenomenon; reactive protein;... |
| RP-HPLC | reverse phase-high performance liquid chromatography |
| vertical growth phase | Spread of melanoma cells from the epidermis into the dermis and later the subcutis, from which site metastasis may take place. (05 Mar 2000) |
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| Gibb's phase rule | An expression of the relationships existing between systems in equilibrium: P + V = C + 2, where P is the number of phases, V the variance or degrees of freedom, and C the number of components; it also follows that the variance is, V = C + 2 -P. For H2O at its triple point, V = 1 + 2 -3 = 0, i.e., both temperature and pressure are fixed. Synonym: Gibb's phase rule. (05 Mar 2000) |
| reduction phase | The stage of nuclear changes in the sexual cells during which reduction of the chromosomes takes place; it embraces the cell generations of the spermatocytes and oocytes. Synonym: reduction phase. (05 Mar 2000) |
| resting phase | More appropriately called interphase. The interval in the cell cycle between two cell divisions when the individual chromosomes cannot be distinguished, interphase was once thought to be the resting phase but it is far from a time of rest for the cell. It is the time when DNA is replicated in the cell nucleus. (12 Dec 1998) |
| vulnerable phase | A period in the cardiac cycle during which an ectopic impulse may lead to repetitive activity such as flutter or fibrillation of the affected chamber. (05 Mar 2000) |
| meiotic phase | The stage of nuclear changes in the sexual cells during which reduction of the chromosomes takes place; it embraces the cell generations of the spermatocytes and oocytes. Synonym: reduction phase. (05 Mar 2000) |
| reversed phase chromatography | A form of partitionary chromatography in which the stationary phase is more polar than the mobile phase. (05 Mar 2000) |
| growth phase | <microbiology> The characteristic periods in the growth of a bacterial culture, as indicated by the shape of a graph of viable cell number versus time. (09 Oct 1997) |
| phallic phase | In psychoanalytic personality theory, the stage in psychosexual development, occurring when a child is between 2 and 6 years of age, during which interest, curiosity, and pleasurable experiences are centreed around the penis in boys and the clitoris in girls. See: genital phase. (05 Mar 2000) |
| phase | Any one of the varying aspects or stages through which a disease or process may pass. Origin: Gr. Phasis = an appearance (18 Nov 1997) |
| phase-amplitude contrast | <microscopy> The separation and recombination of direct vs. Diffracted rays in a light microscope adjusted to Kohler illumination. at the lower focal plane of the condenser there is an annular diaphragm with an opaque central stop. Through this diaphragm rays are focused as a hollow cone onto the specimen. In the back focal plane of the objective there is a conjugate annular diaphragm (phase plate). If here the undiffracted rays are retarded (by a transparent film of proper thickness on the annulus of the phase plate), bright contrast results. If, instead, the phase-delay film is on the central spot, dark contrast results. With either a bright or a dark-contrast phase plate, the annulus is usually coated with a partially absorbing (very thin) film of silver (Zernike method) or carbon soot (Wilska method) to reduce the higher amplitude (intensity) of the undiffracted rays. (05 Aug 1998) |
| phase angle | <microscopy> The angular equivalent of the time displacement between corresponding points on two sine waves of the same frequency. (05 Aug 1998) |
| phase contrast | <microscopy> An optical method devised by F. Zernike for converting the focused image of a phase object (one with differences in refractive index or optical path but not in absorbance), which ordinarily is not visible in focus, into an image with good contrast. (05 Aug 1998) |
| phase-contrast microscope | <instrument> A specially constructed microscope that has a special condenser and objective containing a phase-shifting ring whereby small differences in index of refraction are made visible as intensity or contrast differences in the image; particularly useful for examining structural details in transparent specimens such as living or unstained cells and tissues. (05 Mar 2000) |
| phase contrast microscopy | <investigation> A simple nonquantitative form of interference micoscopy of great utility in visualising live cells. Small differences in optical path length due to differences in refractive index and thickness of structures are visualised as differences in light intensity. (18 Nov 1997) |