| hard sore | The primary skin lesion of syphilis which begins at the site of infection after an interval of 10-30 days as a papule or red ulcerated skin lesion. (27 Sep 1997) |
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| hard tarter | <dentistry> A calcium salt concretion which forms on your teeth. Calculus deposits form on the teeth in areas which you do not floss or brush. If these concretions are left to build up on the tooth enamel, they will irritate the gum tissue, push it away from the tooth and promote progressive bone loss. Eventually the teeth can loosen and fall out. These deposits can be removed by a dentist or a dental hygienist on an annual to biannual basis. (27 Sep 1997) |
| hard tissue | Tissue that has become mineralised, tissue having a firm intercellular substance, e.g., cartilage and bone. (05 Mar 2000) |
| hard tubercle | A tubercle lacking necrosis. (05 Mar 2000) |
| hard ulcer | <dermatology> The primary skin lesion of syphilis which begins at the site of infection after an interval of 10-30 days as a papule or red ulcerated skin lesion. (27 Sep 1997) |
| hard water | <chemistry> Hard water is water which contains minerals like calcium carbonate, magnesium carbonate, bicarbonates, sulphates, or chlorides, because it has been exposed to rocks or rocky soils. Hard water can corrode, discolour, or deposit its minerals, in and around materials such as water pipes. (09 Oct 1997) |
| anode rays | Those originating in a gas discharge tube and moving in a direction opposite to that of cathode ray's; made up of positively charged ions. Synonym: positive rays. (05 Mar 2000) |
| Becquerel rays | An obsolete term for radiations given off by uranium and other radioactive substances; these include alpha, beta, and gamma ray's. (05 Mar 2000) |
| gamma rays | Very powerful and penetrating, high-energy electromagnetic radiation of shorter wavelength than that of X-rays. They are emitted by a decaying nucleus, usually between 0.01 and 10 mev. They are also called nuclear X-rays. (12 Dec 1998) |
| parallel rays | Ray's parallel to the axis of an optical system. (05 Mar 2000) |
| marginal rays | In geometric optics, those ray's originating from the periphery. (05 Mar 2000) |
| paraxial rays | In geometric optics, those ray's focused at the principal point. (05 Mar 2000) |
| cathode rays | A stream of electrons emitted from the negative electrode (cathode) in a Crookes tube; their bombardment of the anode or the glass wall of the tube gives rise to X-ray's. (05 Mar 2000) |
| glass rays | Those formed by cathode ray's striking the wall of an X-ray tube. (05 Mar 2000) |
| cephalometric X-rays | <dentistry> An X-ray of the head that shows whether your teeth are aligned properly, and whether they are growing properly. (08 Jan 1998) |