Power absorption coefficient, temperature

The dielectric loss spectrum at 293 K consists of the main microwave peak at 10 Hz (3.3 cm ) with a barely resolved shoulder at v ca 1.5x10 Hz corresponding to the maximum of the power absorption coefficient at v ca SO cm in the far infrared spectrum. If the measurement temperature is towered, the microwave loss peak, ascribed by the authors to p relaxation process, moves out ccmsidetably to lower frequendes and becomes resolved from the far infrared peak which is shifted with decreasing temperature in the opposite direction. 

It would appear that measurement of the integrated absorption coefficient should furnish an ideal method of quantitative analysis. In practice, however, the absolute measurement of the absorption coefficients of atomic spectral lines is extremely difficult. The natural line width of an atomic spectral line is about 10 5 nm, but owing to the influence of Doppler and pressure effects, the line is broadened to about 0.002 nm at flame temperatures of2000-3000 K. To measure the absorption coefficient of a line thus broadened would require a spectrometer with a resolving power of 500000. This difficulty was overcome by Walsh,41 who used a source of sharp emission lines with a much smaller half width than the absorption line, and the radiation frequency of which is centred on the absorption frequency. In this way, the absorption coefficient at the centre of the line, Kmax, may be measured. If the profile of the absorption line is assumed to be due only to Doppler broadening, then there is a relationship between Kmax and N0. Thus the only requirement of the spectrometer is that it shall be capable of isolating the required resonance line from all other lines emitted by the source. 

The rapid increase in the thermal conductivity of liquid selenium with temperature can be attributed to the photon component of the thermal conductivity. For liquids with a small absorption coefficient, this radiation term should rise as a third power of the absolute temperature. From the results of the thermal conductivity data we can, therefore, get information about two optical parameters, i.e., the optical absorption coefficient, a, and the refractive index, n, in the form a/n. ... 

As in all light water-moderated and low-enrichment reactors, the fuel Doppler reactivity coefficient is negative and prompt in its effect, opposing reactor power transients. When reactor power increases, UO2 temperature increases with minimum time delay, resulting in higher neutron absorption by resonance capture in the U-238. 

The curves of Fig. 120 show the variation of the absorption coefficient at 2400 A with time for polycaproamide fiber, oxidized in air at various temperatures. For small oxygen pressures, the dependence of the rate of the oxidation of polycaprolactam on the oxygen pressure to the power 0.75 is expressed by a straight line (Fig. 121). This permits us to derive an empirical equation for the dependence of the rate of absorption of oxygen on the pressure [30] ... 

The absorptive nature of the process was shown by the proportionality of the temperature jumps at 0.694 and 1.06 ym, calculated from the conductance increase after relaxation of the excess H and OH ions, to the energy inputs calculated from the small signal absorption coefficients of H O. Scattering phenomena were not expected at the power densities used in these experiments, and would have exhibited identical non-linear behaviour in H O... 

This derivation highlights several key features of solid-state laser refrigeration. First, Eq. (12) shows that the pump absorption coefficient diminishes exponentially as the temperature is lowered, which is a result of the thermal depletion of the initial state II). This reduces the net power density that can be extracted from the solid (Eq. 11) and ultimately sets a lower limit for the temperature that can be reached by laser cooling. Finding materials with a small ground-state crystal-field sphtting 5Eg) is advantageous in this respect. 

With t in °F, n was found to have the value 0.0115. As an alternate correlation, Vivian and Whitney noted that the absorption coefficient is approximately proportional to the sixth power of the absolute temperature over the relatively narrow range studied (35° to 90°P). 

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