| XD | x-ray diffraction |
|---|---|
| XRD | x-ray diffraction |
| 'Greek letter alpha' | angular acceleration; first [carbon atom next to the carbon atom bearing the active group in organic... |
| AO | abdominal aorta; achievement orientation; acid output; acridine orange; ankle orthosis; anodal openi... |
| DOA | date of admission; dead on arrival; Department of Agriculture; depth of anesthesia; differential opt... |
| optical axis | <physics> The line passing through both the centres of curvature of the optical surfaces of a lens, the optical centreline for all the centres of a lens system. (09 Oct 1997) |
|---|---|
| optical density | 1. <chemistry, investigation> Absorbance is defined as a logarithmic function of the percent transmission of a wavelength of light through a liquid. 2. <microbiology> This can be used as a measure of the amount of light absorbed by a suspension of bacterial cells or a solution of an organic molecule, it is measured by a colourimeter or spectrophotometer. Absorbance values are used to plot the growth of bacteria in suspension cultures and to gauge the purity and concentration of molecules (such as proteins) in solution. See: absorption. (15 Jan 1998) |
| optical flat | <microscopy> Usually, a glass or quartz plate or disk, the thickness of which should be at least 1/10 of its diameter. It is ground until any remaining unevenness can be measured only by interferometric methods. Their maximum departure from flatness usually is less than 1/10 of the sodium doublet (589.3 nm). (05 Aug 1998) |
| optical illusions | An illusion of vision usually affecting spatial relations. (12 Dec 1998) |
| optical image | An image formed by the refraction or reflection of light. (05 Mar 2000) |
| optical index | <microscopy> A constant applied to objectives for purposes of comparison. It takes into account the focal length or magnifying power of the lens and also the numerical aperture. It was offered by Nelson and by Coles, but little use has been made of the optical index figure, probably because the equations of the two men differed and the resulting figures have been at variance. (05 Aug 1998) |
| optical iridectomy | Iridectomy performed for the purpose of improving vision by making an artificial pupil. Peripheral iridectomy, in narrow-angle glaucoma, the surgical removal of a minute portion of the iris at its root; in intracapsular extraction of cataract, removal of one or more minute sections near the peripheral border, leaving the pupillary margin intact. Synonym: buttonhole iridectomy, stenopeic iridectomy. Sector iridectomy, an iridectomy in which a portion of the pupillary margin is excised. (05 Mar 2000) |
| optical isomerism | Stereoisomerism involving the arrangement of substituents about an asymmetric atom or atoms (usually carbon) so that there is a difference in the behaviour of the various isomers with regard to the extent of their rotation of the plane of polarised light. Compare: stereoisomerism. (05 Mar 2000) |
| optical isomers | Isomers differing only in the spatial arrangement of groups around a central atom. Optical isomers rotate the plane of polarized light in different directions. For all biological molecules in which the possibility of optical isomerism exists, only one of the isomers is functional. (18 Nov 1997) |
| optical keratoplasty | Transplantation of transparent corneal tissue to replace a leukoma or scar that impairs vision. (05 Mar 2000) |
| optical microscope | <instrument, microscopy> A very ambiguous term since all microscopes involve optics, better to specify light, acoustic, X-ray or electron microscope, etc. (05 Aug 1998) |
| optical noise | <microscopy> Image defects that become especially conspicuous when the image is enhanced. In video microscopy, includes hot spots, mottle, uneven illumination, etc. (05 Aug 1998) |
| optical pachymeter | A lens and/or mirror used to measure corneal thickness. (05 Mar 2000) |
| optical righting reflexes | Visual stimuli that enable an animal to maintain the correct position of the head in space, by bringing about movements of the muscles of the neck and limbs. (05 Mar 2000) |
| optical rotatory dispersion | The method of measuring the dispersion of an optically active molecule to determine the relative magnitude of right- or left-handed components and sometimes structural features of the molecule. (12 Dec 1998) |