Contributions of the interior and surface states of charge carriers to the emission spectra of CdS quantum dots in borosilicate glasses

The photoluminescence spectra of CdS quantum dots grown in a borosilicate glass by sol-gel technology are recorded and analyzed. It is shown that the photoluminescence spectra of the samples are related to annihilation of free (interior) excitons in the ground state and excited state. Emission associated with the surface states of the quantum dots is detected in the region around 2.7 eV for the first time. The emission is due to recombination of electrons localized at the surface with heavy holes in the free states of the quantum dots. Resonance excitation of the structures makes it possible to reveal the specific features of the localized surface states responsible for the photoluminescence band. The properties of the band are, to a large extent, similar to the properties of the emission bands of both three-dimensional media (amorphous semiconductors and substitution alloys) and two-dimensional systems (quantum wells and superlattices).     

An efficient electron-beam-pumped semiconductor laser for the green spectral range based on II–VI multilayer nanostructures

Emission characteristics of an electron-beam-pumped Cd(Zn)Se/ZnMgSSe semiconductor laser are studied. The laser’s active region consists of a set of ten equidistant ZnSe quantum wells containing fractional-monolayer CdSe quantum-dot inserts and a waveguide formed by a short-period superlattice with the net thickness of ～0.65 μm. Lasing occurs at room temperature at a wavelength of 542 nm. Pulsed power as high as 12 W per cavity face and an unprecedentedly high efficiency of ～8.5% are attained for the electron-beam energy of 23 keV.     

Physicochemical principles of preparation of emulsion fuels

The basic physicochemical principles of preparation of emulsion fuel compositions based on heavy and extra-heavy crude cuts were analyzed with consideration of the nature and content of the phases constituting the emulsion, type of chemical additives — emulsifiers and stabilizers, and type of equipment for production of emulsion fuels. __________ Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 5, pp. 51–56, September–October, 2007.     

Radioecological state of the territory and water area in Guba Andreev

The radioecological conditions which developed on the territory over the long operating time of the object of the naval fleet in Guba Andreev are described. The results of an analysis of the sources of the real and potential danger and measures to prevent dangerous effects for the environment and the workers at the time remediation work is performed are discussed. __________ Translated from Atomnaya énergiya, Vol. 101, No. 1, pp. 49–55, July, 2006.     

Identification of the temperature field and stresses in a thermosensitive cylinder according to the surface strains

We identify the time dependence of temperature of a surface of a long hollow thermosensitive cylinder and its thermal and thermal stressed states according to the known temperature and strains on the other surface. The posed problem is reduced to the inverse problem of thermoelasticity. By using the solution of the direct problem of thermoelasticity, we perform the numerical verification of the proposed procedure of solution of the inverse problem. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 55–61, November–December, 2007.     

Hydrogen degradation of steels in gas mains after long periods of operation

We study the degradation of the mechanical and corrosion properties of 17G1S steel in gas mains as a result of operation for 28–40 yr. We reveal the simultaneous decrease in its strength and hardness, on the one hand, and impact toughness and crack resistance, on the other hand. The indicated parameters prove to be most sensitive to the in-service degradation of the metal. The degradation of steel leads to the increase in the strain-hardening coefficient and the appearance of the yield plateau in the tensile stress-strain diagram and causes the appearance of sensitivity to hydrogen embrittlement increasing in the process of operation. We analyze the role of absorbed hydrogen affecting the mechanism of strain aging and responsible for the appearance of defects. It is shown that the polarization resistance can be used not only for monitoring of the corrosion state of gas pipelines but also for the prediction of changes in their mechanical properties in the process of operation. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 97–104, September–October, 2007.     

Fabrication of Strain-Relaxed Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript>/Si(001) Buffer Layers of Low Surface Roughness

The results are presented of the fabrication of strain-relaxed graded Si_{1 − x} Ge_x/Si(001) buffer layers with a maximum Ge fraction of about 0.25 that have a low density of threading dislocations (<10⁶ cm⁻²) and low surface roughness. The buffer layers are grown by atmospheric-pressure hydride CVD. It is found that chemical mechanical polishing can reduce their surface roughness to a level comparable with that of the original Si(001) substrates. It is shown that the polished buffer layers can serve as substrates for MBE-grown SiGe/Si heterostructures.__________Translated from Mikroelektronika, Vol. 34, No. 4, 2005, pp. 243–250.Original Russian Text Copyright © 2005 by Vostokov, Drozdov, Krasil’nik, Kuznetsov, Novikov, Perevoshchikov, Shaleev.     

Kinetics of small fatigue cracks in steel during cyclic loading

The kinetics of development of fatigue microcracks in a high-strength 08Kh14AN4MD steel is studied when a cantilever specimen with several notches is subjected to rotational bending tests. The specific feature of the tests consists in the fact that, when the specimen is loaded at a constant load, different stress amplitudes are realized in different notches. As a result, after the sample has failed across the section with the maximum stress, a longitudinal polished section of the specimen contains fatigue cracks having nucleated in the mouths of the other notches at lower stress amplitudes. A relation between inflection points in the fatigue curve and the conditions of local and developed yield in a notch has been established. Fatigue fracture mechanisms at a superhigh number of loading cycles are studied, and their relation to the structure near a crack is found. A rapid method for estimating the fatigue limit at a superhigh number of loading cycles is proposed.     

A note on the variance of rank-based selection strategies for genetic algorithms and genetic programming

This paper evaluates different forms of rank-based selection that are used with genetic algorithms and genetic programming. Many types of rank based selection have exactly the same expected value in terms of the sampling rate allocated to each member of the population. However, the variance associated with that sampling rate can vary depending on how selection is implemented. We examine two forms of tournament selection and compare these to linear rank-based selection using an explicit formula. Because selective pressure has a direct impact on population diversity, we also examine the interaction between selective pressure and different mutation strategies.     

Three-dimensional structure of the cloud of a carbon pellet evaporated in plasma of Wendelstein 7-AS stellarator

Experiments performed on a Wendelstein 7-AS stellarator revealed asymmetry of the cloud of an ablating carbon pellet. The cloud is elongated in the direction of large radius toward stronger fields, that is, opposite to the direction expected due to the toroidal drift. In order to study the effect in more detail, the three-dimensional structure of the cloud was analyzed by computer tomography. The results confirmed asymmetry of the cloud. This asymmetry is related to a drift flow existing in the plasma and directed along large radius toward stronger fields. The drift velocity is numerically estimated at ～300 m/s.