| double refraction | <microscopy> The refraction of light in two slightly different directions to form two rays or vector components. Each ray is polarized, and their vibration directions are perpendicular to each other. Furthermore, each ray has a different velocity, and therefore a different refractive index. See: birefringence. (05 Aug 1998) |
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| double salt | A salt in which two different positive ions are bonded to the same negative ion, or vice versa; e.g., NaKSO4. (05 Mar 2000) |
| double stain | <technique> A mixture of two dyes, each of which stains different portions of a tissue or cell. (05 Mar 2000) |
| double tachycardia | The simultaneous tachycardia of two ectopic pacemakers, e.g., atrial and junctional tachycardia. (05 Mar 2000) |
| double tertian | Denoting malarial infections with two different sets of organisms producing daily paroxysms. See: quotidian malaria. (05 Mar 2000) |
| double tertian malaria | See: quotidian malaria. (05 Mar 2000) |
| double thymidine block | <cell culture, procedure> A lab technique used to synchronise the cell cycles of all the cells in a culture. This is done by adding excessive amounts of thymidine (a deoxynucleoside) to the culture so that DNA replication is blocked. Eventually, all of the cells will reach the same point in the cell cycle and stop. (09 Oct 1997) |
| double track sign | In paediatric radiology, a less common sign of congenital pyloric stenosis, when barium is caught between mucosal folds in the hypertrophied pylorus. (05 Mar 2000) |
| double vision | <ophthalmology, symptom> The perception of two images of a single object. Synonym: ambiopia, double vision, binocular polyopia. (18 Nov 1997) |
| double-blind | <statistics> A kind of clinical study in which neither the participants nor the person administering treatment know which treatment any particular subject is receiving. Usually the comparison is between an experimental drug and a placebo or standard comparison treatment. This method is believed to achieve the most accuracy because neither the doctor nor the patient can affect the observed results with their psychological bias. (10 Oct 1997) |
| double-blind experiment | <statistics> An experiment conducted with neither experimenter nor subjects knowing which experiment is the control; prevents bias in recording results. See: double-masked experiment. (05 Mar 2000) |
| double-blind method | <statistics> A method of studying a drug or procedure in which both the subjects and investigators are kept unaware of who is actually getting which specific treatment. (12 Dec 1998) |
| double-blind study | A study in which neither the experimenter nor any other assessor of the results, including patients, know which group is subject to which procedure, thus helping assure that the biases or expectations of either will not influence the results. (05 Mar 2000) |
| double-channel catheter | A catheter with two lumens, allowing irrigation and aspiration. Synonym: two-way catheter. (05 Mar 2000) |
| double-ender | A locomotive with pilot at each end. Source: Websters Dictionary (01 Mar 1998) |