Results 1 - 10 of 36
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[en] The characteristic feature of the S- centres is the p-hole, which corresponds to the lack of one electron to the Ar configuration. Because of this simple structure these centres can be regarded as model systems for the study of defect electrons and for their theoretical treatment. The validity of calculations from first principles made for one-electron systems can be tested for defect-electron systems too. The distribution of the unpaired electron over several shells of neighbour ions was determined by ENDOR measurements in KCl. Experimental data are presented and compared with theoretical calculations
[en] The objective of this project was the study of the effects of gravity and curvature on the velocity profiles and pressure gradient for three different fluids flowing through a bend. The bend was of 90 having square cross-section (1 cm/sup */ 1cm). The flow at inlet was assumed uniform. The three fluids under analysis were Sodium, Lithium and Water. For this purpose Navier Stoke's equations that model the flow were discretized using power law scheme. A computer code SIMPMHD as transformed to solve the problem. Flow was considered laminar and results that is velocity and pressure gradient profiles obtained were compared with the theoretical. The results obtained differ from the theoretical results due to turbulence, which was not considered in the present study. The pressure drop calculated through the bend was compared with the pressure drop through same length of horizontal pipe. For laminar case the results were found satisfactory. (author)
[en] Calculations of a stable configuration and the electron structure of A-center in Si passivated by one or two hydrogen atoms are carried out using the semi-empirical method of modified disregard by two-atomic overlap and the non-empirical method of χλ-discrete variations. It is found that, differing from vacancy complexes, H implantation to A-center doesn't lead to defect state removal from a forbidden zone
[en] We present the metallicity distribution of red giant branch (RGB) stars in M31's stellar halo, derived from photometric metallicity estimates for over 1500 spectroscopically confirmed RGB halo stars. The stellar sample comes from 38 halo fields observed with the Keck/DEIMOS spectrograph, ranging from 9 to 175 kpc in projected distance from M31's center, and includes 52 confirmed M31 halo stars beyond 100 kpc. While a wide range of metallicities is seen throughout the halo, the metal-rich peak of the metallicity distribution function becomes significantly less prominent with increasing radius. The metallicity profile of M31's stellar halo shows a continuous gradient from 9 to ∼100 kpc, with a magnitude of ∼ – 0.01 dex kpc–1. The stellar velocity distributions in each field are used to identify stars that are likely associated with tidal debris features. The removal of tidal debris features does not significantly alter the metallicity gradient in M31's halo: a gradient is maintained in fields spanning 10-90 kpc. We analyze the halo metallicity profile, as well as the relative metallicities of stars associated with tidal debris features and the underlying halo population, in the context of current simulations of stellar halo formation. We argue that the large-scale gradient in M31's halo implies M31 accreted at least one relatively massive progenitor in the past, while the field to field variation seen in the metallicity profile indicates that multiple smaller progenitors are likely to have contributed substantially to M31's outer halo.
[en] Possible reasons of the photocurrent decrease under illumination are discussed by comparison of all experimental data obtained in the previous studies of the photosensitivity degradation in CdS:Cu single crystals. By further studies a photosensitivity decrease is found to be due to vanishing of the shallow donors which compensate the r-centres. A degradation mechanism consisting in transformation of the shallow donors into rapid recombination s-centres, due to their association, is suggested. On heating in darkness these s-centres dissociate to recover both, the initial density of the shallow donors and the high photosensitivity. (author)
[en] The effect of low energy N+ ion irradiation on InP samples has been studied using depth resolved Doppler S-parameter measurements. InP samples have been irradiated with 85 keV N+ ions to a dose of 1 x 1013 to 1 x 1016 cm-2. Defect sensitive lineshape S-parameter and the complimentary W-parameter have been deduced at various depths. From the variation of S and from the slope of S-W correlation plots, it is concluded that monovacancies are present up to a dose of 1 x 1015 cm-2, while divacancies are present in 1 x 1016 cm-2 dose sample. (author)
[en] Relaxation of photoconductivity of ZnSr crystal in case of a photoconductivity burst when exposing a sample to light with quantum energy E=1.305 eV after preliminary excitation by light with quantum energy 2.61 eV. The phenomenon of nonequilibrium photoconductivity considered permitted to suggest a new method for determination of the energy position of local levels in the forbidden band of semiconductors. Investigations carried out permitted to detect in ZnSe acceptors, lying in the forbidden band, as well as deep centers. It is supposed that the effect of spectral memory of photoconductivity of high-ohmic crystals (ZnSe, ZnS, CdS) relates to the existence of defects with metastable states in them
[en] We report on the presence of large amounts of million-degree gas in the Milky Way’s interstellar and circum-galactic medium. This gas (1) permeates both the Galactic plane and the halo, (2) extends to distances larger than 60–200 kpc from the center, and (3) its mass is sufficient to close the Galaxy’s baryon census. Moreover, we show that a vast, ∼6 kpc radius, spherically symmetric central region of the Milky Way above and below the 0.16 kpc thick plane has either been emptied of hot gas or the density of this gas within the cavity has a peculiar profile, increasing from the center up to a radius of ∼6 kpc, and then decreasing with a typical halo density profile. This, and several other converging pieces of evidence, suggest that the current surface of the cavity, at 6 kpc from the Galaxy’s center, traces the distant echo of a period of strong nuclear activity of our supermassive black hole, occurring about 6 Myr ago.