| ultracentrifugation | <procedure> Centrifugation at very high g forces: used to separate molecules for example mitochondrial from nuclear DNA on a caesium chloride gradient. (18 Nov 1997) |
|---|---|
| ultracentrifuge | A high-speed centrifuge (up to 100,000 rpm) by means of which large molecules, e.g., of protein or nucleic acids, are caused to sediment at practicable rates; used for determinations of molecular weights, separation of large molecules, criteria of homogeneity of large molecules, conformational studies, etc. (05 Mar 2000) |
| ultracytostome | Former name for micropore. Origin: ultra-+ G. Kytos, cell, + stoma, mouth (05 Mar 2000) |
| ultradian | Relating to biologic variations or rhythms occurring in cycles more frequent than every 24 hours. Compare: circadian, infradian. Origin: ultra-+ L. Dies, day (05 Mar 2000) |
| ultradian rhythm | See: ultradian. (05 Mar 2000) |
| ultradolichocephalic | Denoting a very long skull, one with a cephalic index of less than 65. (05 Mar 2000) |
| ultrafilter | A semipermeable membrane (collodion, fish bladder, or filter paper impregnated with gels) used as a filter to separate colloids and large molecules from water and small molecules, which pass through. (05 Mar 2000) |
| ultrafiltration | <procedure> Filtration under pressure. In the kidney, an ultrafiltrate is formed from plasma because the blood is at higher pressure than the lumen of the glomerulus. Also used experimentally to fractionate and concentrate solutions in the laboratory using selectively permeable artificial membranes. (18 Nov 1997) |
| ultrafiltration coefficient | The filtration coefficient of a semipermeable membrane. (05 Mar 2000) |
| ultrafiltration fermenter | An apparatus for continuous fermentation that is run inconjunctionwith a continuous microfiltration system to constantly remove thelow-molecular-weight product of the fermentation. (09 Oct 1997) |
| ultralente insulin | A form of zinc precipitated insulin in suspension in which the particle size is large, and thus release into the bloodstream after subcutaneous injection is slow; it can be mixed with other insulins having different particle sizes to achieve different durations of activity. Can be derived from porcine, bovine, or genetically engineered human type. (05 Mar 2000) |
| ultraligation | Ligation of a blood vessel beyond the point where a branch is given off. (05 Mar 2000) |
| ultramarine | <chemistry> A blue pigment formerly obtained by powdering lapis lazuli, but now produced in large quantities by fusing together silica, alumina, soda, and sulphur, thus forming a glass, coloured blue by the sodium polysulphides made in the fusion. Also used adjectively. Green ultramarine, a green pigment obtained as a first product in the manufacture of ultramarine, into which it is changed by subsequent treatment. Ultramarine ash or ashes, a pigment which is the residuum of lapis lazuli after the ultramarine has been extracted. It was used by the old masters as a middle or neutral tint for flesh, skies, and draperies, being of a purer and tenderer gray that produced by the mixture of more positive colours. Fairholt. Origin: Cf. Sp. Ultramarino. So called because the lapis lazuli was originally brought from beyond the sea, from Asia. Source: Websters Dictionary (01 Mar 1998) |
| ultramicroscope | <instrument, microscopy> A term applied to particles less than 0.1 ~m in diameter, hence too small to be truly resolved by the light micro- scope. Under the ultramicroscope they look like stars in the sky. Their differences in size are merely indicated by differences in brightness. (05 Aug 1998) |
| ultramicroscopic | <optics> Particles which, although visible in the ultramicroscope, are too small to be resolved by visible light. This places their size between 0.2 Lm and 0.005 Lm. (05 Aug 1998) |