Correlation between the photoluminescence and different types of Si nano-clusters in amorphous silicon

This paper presents the results of PL spectrum study for Si nano-clusters in amorphous silicon matrix. The hydrogenated amorphous Si layers were prepared by the hot-wire CVD method on glass substrates. The layers were deposited at different wafer temperatures 280, 360, 420 and 460 °C and at one filament temperature of 1650 °C. The joint analysis of PL and X-ray diffraction spectra in dependence on the technological conditions and on different sizes of Si nano-clusters has been done. The mechanisms of PL are discussed as well.     

Emission and strain in InGaAs/GaAs quantum wells with InAs quantum dots obtained at different temperatures

The photoluminescence (PL), its temperature dependence and X ray diffraction (XRD) have been studied in the symmetric In_0.15Ga_0.85As/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs), obtained with the variation of QD growth temperatures (470–535 °C). The increase of QD growth temperatures is accompanied by the enlargement of QD lateral sizes (from 12 up to 28 nm) and by the shift non monotonously of PL peak positions. The fitting procedure has been applied for the analysis of the temperature dependence of PL peaks. The obtained fitting parameters testify that in studied QD structures the process of In/Ga interdiffusion between QDs and capping/buffer layers takes place partially. However this process cannot explain the difference in PL peak positions.     

Designing,calculation, and optimization of polymeric honeycomb pipes

The problem of optimization of the honeycomb wall structure of pipes subjected to static loads is investigated. As the basic engineering design parameter of the pipes, their ring rigidity is assumed. The corresponding optimization problem is formulated. Starting from the necessary ring rigidity of cylindrical pipes made of polymeric materials with honeycomb walls, their geometrical, physicomechanical, and technological parameters are determined. Based on the calculations, the optimum geometry (wall thickness, diameter, and the number of layers) of the pipes is found. Numerical results are presented and analyzed. Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 6, pp. 853–860, November–December, 2008.     

Reasons of emission inhomogeneity in InAs quantum dot structures

The photoluminescence (PL) inhomogeneity has been studied in InAs quantum dots (QDs) embedded in the symmetric In_0.15Ga_0.85As/GaAs quantum wells (QWs) with QDs grown at different temperatures. It was shown that three reasons are responsible for the emission inhomogeneity in studied QD structures: (i) the high concentration of nonradiative recombination centers in the capping In_0.15Ga_0.85As layer at low QD growth temperatures, (ii) the QD density and size distributions for the structure with QD grown at 510 ^°C, (iii) the high concentration of nonradiative recombination centers in the GaAs barrier at higher QD growth temperatures.     

Influence of disorder on superconductivity in non-magnetic rare-earth nickel borocarbides

The effect of substitutional disorder on the superconducting properties of YNi₂B₂C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. For the two series of (Y, Lu)Ni₂B₂C and Y(Ni, Pt)₂B₂C compounds, the upper critical field H _c2(T) and the specific heat c _p(T, H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as T _c, the upper critical field H _c2(0) at T=0 and a characteristic positive curvature of H _c2(T) observed for these compounds near T _c. The H _c2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni, Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(Ni_1−x , Pt _x )₂B₂C samples for x=0.1.     

Stress-strain state and stability of polymeric tubes with a honeycomb wall

A problem of determination of the stress-strain state, stability and optimization of the honeycomb structure of a polymeric tube wall under the action of a static force load is considered. As is customary in engineering practice, the ring rigidity of the tube is taken as its main design quantity. The corresponding problem of optimization is formulated. From the condition of provision of the required value of the ring rigidity of a honeycomb polymeric cylindrical shell, we determine the geometric, physicomechanical, and technological parameters. On the basis of the performed calculations, a justification of an optimal geometry (the thickness of the wall, the diameter of a winding tubule, and the number of layers of the tube structure) is presented. Numerical results and their analysis are presented.     

Analysis of contact stresses in structural joints of composite shell with steel banding

Based on the generalized Timoshenko-type shell theory, a numerical-analytical procedure for determining contact stresses from the interaction between a cylindrical composite shell and rigid bandings is proposed. Specific cases of loading and contact interaction (ideal contact through an adhesive interlayer) are considered. The contact problems are reduced to the solution of a Fredholm integral equation of the second-kind. A calculation analysis is performed. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 1, pp. 109–120, January–February, 2000.     

Contact interaction of cylindrical shells of different lengths

We solve a problem of determination of the contact rigidity of a structural joint of a steel thin-walled pipe under the action of internal pressure with a shroud made of a composite material using a special technology. A mathematical model of the contact interaction of the pipe and shroud modeled by cylindrical shells of different length was constructed using the classical Kirchhoff–Love theory of shells. We obtain an analytic solution of the contact problem under conditions of ideal contact of the elements of the structural joint by the conjugation method. A numerical analysis of the influence of geometric and physicomechanical characteristics of the shroud on the contact pressure and rigidity of the shrouded pipe is presented.     

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

Non-resonant microwave absorption (NRMA) studies of superconducting MgB₂ and a sample containing ∼10% by weight of MgO in MgB₂ are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB₂ sample. A linear temperature dependence of the lower critical field H _c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB₂ + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB₂ sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below T _c while in the MgB₂ + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.     

Wear resistance of bodies protected by a thin composite coating

The mechanical contact interaction of bodies with a thin composite coating is investigated with account of wear. The thermal effects are not considered. The coating is modeled by a thin plate. Between the body and the coating is an interlayer, which is modeled by a Winkler body with one modulus of subgrade reaction. Under the action of a rigid stamp on the coating, the process of abrasive wear proceeds. The contact interaction of the coating with the base is described by using the model of an intermediate layer. To determine the stress-strain state of the coating, equations of the generalized theory of plates including the shear strains and the compression of normal are utilized. For the contact wear problem formulated, the basic integral equation with a Fredholm-type kernel is derived, and its solution algorithm is proposed. Numerical results are presented. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 319–330, May–June, 2006.