Angstrom, definition

Angles, diffraction, table, for various common jmonochromators, 318-327 Angstrom (A), definition, 307 Angstroms, conversion from kX units to, 7, 307... 

Angstrom unit (A), definition, 307 Antimony, determination by x-ray emission spectrography, 328 in silicate, determination by absorption-edge method, 140 in solution, determination by absorption-edge method, 140 Aperture, relative, of x-ray optical system, 113... 

The numerical values of most physical quantities are expressed in terms of units. The distance between two points, for example, can be specified by the number of meters (or feet, Angstroms, etc.). Similarly, time cap be expressed in seconds, days or, say, years. However, the number of days per year varies from one year to another. The quantities, distance (length) and time, as well as mass, are usually chosen to be primary quantities. In terms of them Newton s second law for the force on an object, can be written as force = mass, distance/(time)2. The definition of the primary quantities allows dimensional expressions to be written, such as [force] — MLT-2 in the present example. Note, however, that in everyday life one speaks of the weight of an object (or a person). Of course the weight is not the mass, but rather the force acting on the object by the acceleration due to gravity [acceleration] = LT 2. 

Angstrom units, definition, 128 Anthracene, carcinogenic activity, 45 Anthracenedihydrodiols, synthesis, 45 Arylnitrones, reaction mechanism, 363f... 

It has been observed by some experimenters, but not by the others, that the experimental lattice constant a in crystals of ordinary size was different from that, a + A a, found in extremely small crystals. A recent example72 refers to vacuum-deposited copper grains whose diameter D (they were, of course, not spherical) varied from 24 to 240 angstroms. The lattice constants calculated from the (111) reflexions increased from 3.577 to 3.6143 angstroms when the grain volume decreased, but the particle size had no definite effect on the reflexions from the 220 plane. 

Fig. 17.4. Definition of position relative to dipole, and potential change (V) versus lateral distance from X (Angstrom), where d = XO and qL = 2 Debye.

Another extremely important parameter of any surface technique is the depth of penetration (d ), which is a characteristic distance from the surface that the measurement will probe. Table V gives approximate depths of penetration for the methods discussed in this section for measurement of TPE surfaces. Since Table V shows that the depth of penetration varies widely, the change in composition can be monitored from the surface almost continuously to thousands of angstroms. Alternatively, some methods discussed in this section measure the morphology near the surface. Studies of TPE surfaces are less numerous than investigations of bulk properties, which in general speaks to the relative lack of importance of the surface properties of TPEs for most applications. However, exceptions to the latter generalization definitely exist, for example in the medical device area. 

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