Energy balance calculations have been made of a cylindrical high-pressure LTE discharge which contains small quantities of metal halides with a large excess of mercury. It is assumed that the partial pressures of emitting atoms remain at a constant value throughout the arc, and that the emission coefficient for atoms and ions can be calculated using the Corliss and Bozman (1962) transition probabilities. The model has been used to compare the effects of adding different elements (scandium and iron) and mixtures of elements on the temperature profile, and other properties of metal halide lamps. The self-absorbed radiation of the mercury atoms must be included in order to obtain realistic temperature profiles. It is assumed that for all lines emitted by the added elements, the arc is optically thin.
A survey of the region of sky between declinations _4° and -64° has been completed at a frequency of 29·9 MHz at the Fleurs Radio Observatory of the School of Electrical Engineering, University of Sydney. Aperture synthesis has been used to form a beam of 0°.8 diameter. The flux densities of 175 sources have been measured and referred to absolute measurements of certain strong sources. Most of the source fluxes are consistent with an extrapolation of the power law spectra determined from high frequency measurements but a few show significant deviations. Absorption by the interstellar medium of sources at low galactic latitudes has only been observed for I b I < 3° and appears to be negligible at higher latitudes.
Operating wall temperature and electrode separation are important factors in the design of efficient high-pressure sodium lamps. The authors have measured and calculated how the arc efficacy varies with wall temperature and input power per unit length. In their experiments they controlled the wall temperature by passing gases with different thermal conductivities over the arc tube. Their experiments showed that the arc efficacy increases at rates of 3.75+or-0.15% per 100K rise in wall temperature and 3.5+or-0.3% per 1 Wmm-1 increase in electrical power input. The corresponding calculated average rates are 2.1% per 100K and 1.7% per 1 Wmm-1. The satisfactory agreement of their experiments with their calculations resolves a discrepancy between their computer model predictions and those of Waymouth and Wyner (1981). Their two-zone model predicted that the efficacy decreases as the electrical power input increases. Although they have found that the proportion of the total radiation emitted in the D-lines decreases as the power input increases, this is more than compensated by an increase in the total radiated power at the expense of thermal conduction.
The net emission coefficient of a self-absorbed spectral line can be described by a semi-empirical formula which contains terms representing the generation and absorption of radiation. Four empirical constants are determined by applying least-squares fitting to the results of an exact radiation flux density calculation in a cylindrical arc tube. Calculations on the D-lines under conditions which are typical of high-pressure sodium lamps are described. In this case, the empirical formula predicts radiation flux densities which agree to better than 10% with the exact calculation even when the arc tube bore and arc temperature are changed by 15% from their original values. This method allows economical and accurate calculation of energy balances in arcs containing several self-absorbed spectral lines.
The parameters describing the linear effect of an electric field on the X-band electron paramagnetic resonance frequency of the impurity Cr3+, charge compensated by Li+, in zinc tungstate have been measured. This allows an explanation of the anomalous behaviour of the resonance linewidth when the magnetic field is rotated in the magnetic zx plane. The linewidth in specimens of high Cr3+ concentration is almost entirely due to the internal electric fields arising from the charged impurities Cr3+ and Li+ acting via the linear electric field effect. The resulting linewidth arises from the equal and opposite shifts in the resonance frequency for the two non-equivalent sites for Cr3+ in the zinc tungstate lattice. The root-mean-square internal field has been measured and agreement found with the value calculated by assuming the Li+ and Cr3+ ions to be randomly distributed throughout the lattice. A specimen of lower Cr3+ concentration has been investigated, and an explanation of the complete behaviour of the linewidth in terms of a simple model is presented.
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