| equatorial | <astronomy> An instrument consisting of a telescope so mounted as to have two axes of motion at right angles to each other, one of them parallel to the axis of the earth, and each carrying a graduated circle, the one for measuring declination, and the other right ascension, or the hour angle, so that the telescope may be directed, even in the daytime, to any star or other object whose right ascension and declination are known. The motion in right ascension is sometimes communicated by clockwork, so as to keep the object constantly in the field of the telescope. Called also an equatorial telescope. The term equatorial, or equatorial instrument, is sometimes applied to any astronomical instrument which has its principal axis of rotation parallel to the axis of the earth. Source: Websters Dictionary (01 Mar 1998) |
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| equatorial cleavage | Cleavage in which the plane of cytoplasmic division is at right angles to the axis of the ovum. (05 Mar 2000) |
| equatorial division | Nuclear division in which each chromosome divides equally. (05 Mar 2000) |
| equatorial guinea | A republic in central africa, north of gabon and bounded on the west by the atlantic ocean. Its capital is malabo. Equatorial guinea was discovered by the portuguese in 1491 and ceded to spain in 1778. The country gained independence in 1968. Equatorial refers to its location near the equator in the broad region long known as guinea . (12 Dec 1998) |
| equatorial plane | In metaphase of mitosis, the plane that touches all of the centromeres and their spindle attachments. (05 Mar 2000) |
| equatorial plate | <cell biology> Region of the mitotic spindle where chromosomes are aligned at metaphase: as its name suggests, it lies midway between the poles of the spindle. (06 Mar 1998) |
| equatorial staphyloma | A staphyloma occurring in the area of exit of the vortex veins. Synonym: scleral staphyloma. (05 Mar 2000) |
| acromioclavicular disk | The articular disk of fibrocartilage usually found between the acromial end of the clavicle and the medial border of the acromion. Synonym: discus articularis acromioclavicularis, acromioclavicular disk, Weitbrecht's cartilage. (05 Mar 2000) |
| Airy disk | <microscopy> The image of a bright point object as focused by a lens system. With monochromatic light, it consists of a central point of maximum intensity surrounded by alternate circles of light and darkness caused by the reinforcement and interference of diffracted rays. The light areas are called maxima and the dark areas minima. The distribution of light from the centre to the outer areas of the figure was investigated mathematically by Sir George Airy. The diffraction disk forms a basis for determining the resolving power of an ideal lens system. The diameter of the disk depends largely on the aperture of the lens. The diffraction of light causing the Airy disk is a factor limiting the resolution of a well corrected optical system. The bright disk of light (surrounded by alternating dark and bright diffraction rings)that is formed by a perfect diffraction-limited lens, focusing an image of an infinitely small source of light. For a minute absorbing spot, the diffraction pattern is a dark Airy disk surrounded by brighter and darker diffraction rings. Since the Airy disk is the smallest unit that makes up the image of a luminous or absorbing object (formed by a properly corrected microscope lens in focus), the radius of the disk determines the limit of resolution of the microscope. (05 Aug 1998) |
| articular disk | A plate or ring of fibrocartilage attached to the joint capsule and separating the articular surfaces of the bones for a varying distance, sometimes completely; it serves to adapt two articular surfaces that are not entirely congruent. Synonym: discus articularis, articular disk, fibrocartilago interarticularis, fibroplate, interarticular fibrocartilage, intra-articular cartilage. (05 Mar 2000) |
| blastodermic disk | The aggregation of blastomeres of a telolecithal ovum after cleavage has occurred. (05 Mar 2000) |
| blood disk | <haematology> A discoid cell (3m diameter) found in large numbers in blood, important for blood coagulation and for haemostasis by repairing breaches (small breaks) in the walls of blood vessels. Platelet _ granules contain lysosomal enzymes, dense granules contain ADP (a potent platelet aggregating factor) and serotonin (a vasoactive amine). They also release platelet-derived growth factor which presumably contributes to later repair processes by stimulating fibroblast proliferation. Synonym: thrombocytes. (09 Oct 1997) |
| bulging disk | A condition that results in the abnormal protrusion (bulging), herniation or prolapse of a vertebral disc from its normal position in the vertebral column. The displaced disc may exert force on a nearby nerve root causing the typical neurologic symptoms of radiating pain (to an extremity), numbness, tingling and weakness. Recurrent episodes of severe back pain are common. Treatment includes non-steroidal anti-inflammatories, corticosteroids and rest. More advanced cases may require surgical intervention (for example laminectomy, micro-disc surgery). (27 Sep 1997) |
| Burlew disk | An abrasive-impregnated rubber wheel used in dentistry for polishing. Synonym: Burlew wheel. (05 Mar 2000) |
| vacuum disk phenomenon | The appearance of a radiolucent stripe in an intervertebral disk, a manifestation of disk degeneration; a misnomer since there is gas present. (05 Mar 2000) |