- 行业: Printing & publishing
- Number of terms: 178089
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- Company Profile:
McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
An instrument used for making measurements of light, or electromagnetic radiation, in the visible range. In general, photometers may be divided into two classifications: laboratory photometers, which are usually fixed in position and yield results of high accuracy; and portable photometers, which are used in the field or outside the laboratory and yield results of lower accuracy. Each class may be subdivided into visual (subjective) photometers and photoelectric (objective or physical) photometers. These in turn may be grouped according to function, such as photometers to measure luminous intensity (candelas or candlepower), luminous flux, illumination (illuminance), luminance (photometric brightness), light distribution, light reflectance and transmittance, color, spectral distribution, and visibility. Since visual photometric methods have largely been supplanted commercially by physical methods, they receive only casual attention here, but because of their simplicity, visual methods are still used in educational laboratories to demonstrate photometric principles.
Industry:Science
An instrument used in astronomical research to study naturally occurring radio emission from stars, galaxies, quasars, pulsars, interstellar clouds, and other astronomical bodies between wavelengths of about 1 mm (300 GHz) and 10 m (30 MHz). At the short wavelength end, the performance is limited by the opacity of the terrestrial atmosphere, and at the long wavelength end by the opacity of the ionosphere.
Industry:Science
An instrument used to collect, measure, or analyze electromagnetic radiation from distant objects. A telescope overcomes the limitations of the eye by increasing the ability to see faint objects and discern fine details. In addition, when used in conjunction with modern detectors, a telescope can “see” light that is otherwise invisible. The wavelength of the light of interest can have a profound effect on the design of a telescope.
Industry:Science
An instrument used to indicate whether load currents and voltages are in time-phase with one another.
Industry:Science
An instrument used to obtain an enlarged image of a small object. In general, a compound microscope consists of a light source, a condenser, an objective, and an ocular or eyepiece, which can be replaced by a recording device such as a photoelectric tube or a photographic plate. The optical microscope is limited by the wavelengths of the light used and by the materials available for manufacturing the lenses.
Industry:Science
An instrument used to obtain an enlarged image of a small object. The image may be seen, photographed, or sensed by photocells or other receivers, depending upon the nature of the image and the use to be made of the information of the image. Microscopes are classified as simple or compound according to the kind of radiation used to form the image, and the use for which they are designed.
Industry:Science
An instrument which directly or indirectly controls one or more sources of heating and cooling to maintain a desired temperature. To perform this function a thermostat must have a sensing element and a transducer. The sensing element measures changes in the temperature and produces a desired effect on the transducer. The transducer converts the effect produced by the sensing element into a suitable control of the device or devices which affect the temperature. The most commonly used principles for sensing changes in temperature are (1) unequal rate of expansion of two dissimilar metals bonded together (bimetals), (2) unequal expansion of two dissimilar metals (rod and tube), (3) liquid expansion (sealed diaphragm and remote bulb or sealed bellows with or without a remote bulb), (4) saturation pressure of a liquid-vapor system (bellows), and (5) temperature-sensitive resistance element.
Industry:Science
An instrument with two legs used for measuring linear dimensions. Calipers may be fixed, adjustable, or movable. Fixed calipers are used in routine inspection of standard products; adjustable calipers are used similarly but can be reset to slightly different dimensions if necessary. Movable calipers can be set to match the distance being measured. The legs may pivot about a rivet or screw in a firm-joint pair of calipers; they may pivot about a pin, being held against the pin by a spring and set in position by a knurled nut on a threaded rod; or the legs may slide either directly (caliper rule) or along a screw (micrometer caliper) relative to each other.
Industry:Science
An instrumental analytical technique used in qualitative or quantitative chemical analysis. It is conducted by monitoring and measuring the spectrum of light emitted by the material being analyzed.
Industry:Science
An instrumental technique that measures the elemental and molecular composition of solid materials. Secondary ion mass spectrometry also provides methods of visualizing the two- and three-dimensional composition of solids at lateral resolutions approaching several hundred nanometers and depth resolutions of 1–10 nm. This technique employs an energetic ion beam to remove or sputter the atomic and molecular constituents from a surface in a very controlled manner. The sputtered products include atoms, molecules, and molecular fragments that are characteristic of the surface composition within each volume element sputtered by the ion beam. A small fraction of the sputtered atoms and molecules are ionized as either positive or negative ions, and a measurement by secondary ion mass spectrometry determines the mass and intensity of these secondary ions by using various mass analysis or mass spectrometry techniques. In this technique, the sputtering ions are referred to as the primary ions or the primary ion beam, while the ions produced in sputtering the solid are the secondary ions. Most elements in the periodic table produce secondary ions, and secondary ion mass spectrometry can quantitatively detect elemental concentrations in the part per million to part per billion range by using appropriate standards and specialized analytical conditions. Molecular detection limits by secondary ion mass spectrometry range between 0.1% and part-per-million concentration levels.
Industry:Science
