Structure Factor and Distribution Function of Degenerate Bose Gases Without Anomalous Averages

The structure factor and single-particle distribution function of degenerate Bose gas are calculated within the canonical ensemble without using anomalous averages. The hypothesis about the C-number behavior of the particle density operator with zero momentum (in the Bose condensate) is accepted. The poles of the “density-density” Green function and the single-particle Green’s function are identical and correspond to the well known spectrum of phonon-roton excitations.     

Peculiarities in the formation of gold nanoparticles by ion implantation in stabilized zirconia

The investigation of bulk single crystals and sputter-deposited films of yttria-stabilized zirconia (YSZ) upon irradiation by gold (Au) ions with an average energy of 160 keV followed by postimplantation annealing revealed peculiarities in the formation of nanocrystalline metal (nc-M) particles in this matrix. In the case of irradiation to small doses (∼5 × 10¹⁵ cm⁻²), the optical absorption spectra of samples showed evidence of the formation of nanoclusters of matrix cations (nc-Zr). In these samples, postimplantation annealing at temperatures ∼700°C and above leads to the formation of nc-Au particles. Local elemental analysis of individual nc-M particles in the YSZ matrix irradiated to a dose of 4 × 10¹⁶ cm⁻² and annealed at 800°C showed the presence of metal nanoparticles with complex compositions including both implanted Au and matrix Zr atoms.     

Diurnal dynamics of soil brightness temperatures observed at frequencies of 1.4 and 6.9 GHz in the processes of freezing and thawing

The results of experimental investigation and simulation of the diurnal dynamics of soil brightness temperatures at frequencies of 1.4 and 6.9 GHz at a nadir angle of 45° in cyclic processes of freezing and thawing are presented. By the remote radiometric method, the thickness of the freezing layer have been determined, and the effects of nonnisothermal moisture transfer in the surface soil layers have been discovered. It is found that the thickness of the transition layer, which is located between the frozen layer and the underlying soil, increases as the depth of freezing increases. It is shown that the hydrophysical characteristics of soils can be studied by the remote radiometric method.     

Analysis of variations of the dynamic characteristics of acoustic-emission sources under static loading of metal specimens

Changes in the energy of acoustic-emission (AE) signals and their cross-correlation coefficient for sources of different types have been experimentally studied for statically loaded specimens. The results allow separation of AE signals appearing during irreversible changes in the region of stress concentrators and signals of other types.     

Annealing-induced evolution of the structural and morphological properties of a multilayer nanoperiodic SiO x /ZrO2 system containing Si nanoclusters

The structural and morphological properties of nanoperiodic structures produced by the alternate vacuum evaporation of SiO and ZrO₂ followed by annealing at temperatures of 500–1100°C are studied by the transmission electron microscopy of a transverse cross section. Upon annealing at temperatures below 700°C, the layers are amorphous. Upon annealing at 900°C and 1000°C, nanocrystals separated by twinned boundaries or amorphous regions are formed in the ZrO₂ layers. The formation of Si nanocrystals in the SiO _x layers occurs upon annealing at 1000°C and 1100°C. At 1100°C, because of the reaction between SiO _x and ZrO₂, spherical Si _x Zr _y O _z -type nanocrystals are formed in place of the ZrO₂ layers; the nanocrystal diameters exceed the initial layer thickness. The annealing-induced structural evolution is consistent with the previously considered behavior of the optical and luminescence properties of the system.     

Loss of carbon during plasma-spraying of clad carbide powders

Composition of particles upon atomization of unclad and clad powders is studied. It is estabished that the losses of carbon upon atomization of unclad particles are different for different carbides and increase in the sequence Cr₃C₂-TiC-WC. Upon atomization of clad powders, we observed the highest carbon losses for the particles of tungsten carbide, somewhat smaller losses for titanium carbide, and almost negligible losses for chromium carbide.Translated from Poroshkovaya Metallurgiya, No. 10, pp. 75–78, October, 1992.