| G1 | presynthetic gap [phase of cells prior to DNA synthesis] |
|---|---|
| G2 | postsynthetic gap [phase of cells following DNA synthesis] |
| HFO-A | high-frequency oscillatory [ventilation]-active [expiratory phase] |
| IPD | idiopathic Parkinson disease; idiopathic protracted diarrhea; immediate pigment darkening; increase ... |
| IPG | impedance plethysmography; inspiration-phase gas |
| 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) |
| phase, crystal | <microscopy> A specific crystal structure, usually given a name. (05 Aug 1998) |
| phase encoding | In magnetic resonance imaging, the technique of inducing a gradient in the magnetic field in the Y-axis to induce phase differences with location. Synonym: gradient encoding. (05 Mar 2000) |
| phase I block | Inhibition of nerve impulse transmission across the myoneural junction associated with depolarisation of the motor endplate, as in the muscle paralysis produced by succinylcholine. (05 Mar 2000) |
| phase II block | Inhibition of nerve impulse transmission across the myoneural junction unaccompanied by depolarisation of the motor endplate, as in the muscle paralysis produced by tubocurarine. (05 Mar 2000) |
| phase image | A magnetic resonance image showing only phase shift information, to detect motion. (05 Mar 2000) |
| phase plate | <microscopy> The plate used near the back focal plane of a microscope objective lens (in conjunction with an annulus at the front focal plane of the condenser lens) to achieve phase contrast. The phase plate selectively shifts the phase of the waves diffracted by the specimen by a quarter wave and reduces the amplitude of the undeviated, direct beam. (05 Aug 1998) |
| phase, resting | 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) |
| 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) |
| phase separation | <chemistry> The separation of fluid phases that contain different concentrations of common components. Occurs with partially miscible solvents used in many biochemical separation methods. Also temperature dependent phase separation occurs with some detergent solutions. With reference to membranes means the segregation of lipid components into domains that have different chemical composition. (31 Dec 1997) |
| phase shift | <microscopy> A change in the phase relationship between two alternating quantities of the same frequency. (05 Aug 1998) |