Simultaneous measurements of thermal conductivity and thermal diffusivity of Se90?xTe5Sn5Inx (x?=?0, 3, 6, and 9) multi-component chalcogenide glasses

Measurements of thermal conductivity and thermal diffusivity of twin pellets of Se_90−x Te₅Sn₅In _x (x = 0, 3, 6, and 9) chalcogenide glasses were carried out at room temperature using transient plane source technique. The measured values of thermal conductivity and thermal diffusivity were used to determine the specific heat per unit volume of these glasses in the composition range of investigation. Results indicated that both values of thermal conductivity and thermal diffusivity were increased with addition of indium concentration at the cost of selenium, whereas the specific heat per unit volume was slightly decreases with increase of indium content. This compositional dependence behavior of the thermal conductivity and diffusivity can be explained in terms of the iono-covalent type of bonds, which In (indium) makes with Se as it is incorporated in the Se–Te–Sn glass.     

如何解决矢量控制技术的使用难题

引言在过去几十年中,感应马达正在逐渐被采用磁场定向控制(FOC)技术的马达所替代,在未来几年里全球将会因这种马达的广泛采用而节约大量能源。通过采用FOC技术,设备厂商可以缩小系统规范要求的马达尺寸。磁场定向控制FOC技术对运算量的要求远大于传统的标量技术(scalar techniq     

Transient thermoelastic problem of a nonhomogeneous rectangular plate

This article deals with the determination of temperature distribution, displacement, and thermal stresses in a rectangular plate with inhomogeneous material properties. All the material properties except Poisson’s ratio and density are assumed to be given by a simple power law in y coordinate. The system of fundamental equations formulated has been solved by integral transform method. The effects of thermal and mechanical inhomogeneity on temperature and thermal stress distributions are examined. Numerical calculations are performed by taking into account the variation in inhomogeneous property of shear modulus of elasticity and depicted graphically.     

Substrate quality impact on the carrier concentration of undoped annealed HgCdTe LPE layers

The impact of Te precipitates and impurities, in CdZnTe or CdTe substrates, on grown liquid phase epitaxy (LPE) HgCdTe layer hole concentrations was studied. The carrier concentrations in capped annealed LPE HgCdTe layers grown on CdZnTe substrates with large densities of Te precipitates are frequently significantly higher than those expected for HgCdTe annealed under Hg-deficient conditions. The carrier concentration in the LPE layer, due to the diffusion of copper ions from contaminated CdTe substrates into the layer, is strongly affected by the polarity of the (111)-oriented substrates. Layers grown on the (111)A face showed very high concentrations of Cu, whereas in those grown on the (111)B face normal carrier concentrations were achieved. These phenomena are discussed on the basis of defects formed either in the epilayer or in the layer-substrate interface.     

Backscattering-induced crosstalk in WDM optical wireless communication

The crosstalk effect of aerosol backscatter on the performance of a wavelength-division-multiplexed (WDM) optical wireless communication (OWC) system is investigated, analyzed, and quantified. An OWC link could be a segment within a metropolitan area network (MAN) or a ground-station-to-space link of a satellite communication system. In these cases, a WDM transmitter and receiver are housed in one transceiver unit with parallel, or near-parallel, optic axes. The crosstalk at the receiver is caused by light from the transmitted signal of the same transceiver, which has been backscattered by molecules and aerosols in the atmosphere. This is exacerbated in the presence of fog and haze, in which case both the desired signal from another transceiver is attenuated by scattering and the backscatter-induced crosstalk increases. A bit-error-rate (BER) model is derived that takes into consideration the dominant noise sources, including backscatter-induced crosstalk and signal mixing with amplified stimulated emission (ASE) from an optical preamplifier at the receiver. The numerical calculations in this paper indicate that, in moderate fog, the BER may increase by an order of magnitude or more due to backscatter, depending upon the atmospheric extinction coefficient.     

Continuum damage modeling of dynamic crack velocity,branching, and energy dissipation in brittle materials

This study is aimed at evaluating continuum scale predictions of dynamic crack propagation and branching in brittle materials using local damage modeling. Classical experimental results on crack branching in PMMA and the corresponding nonlocal modeling results by Wolff et al. (Int J Numer Meth Eng 101(12):933, 2015) are used as a benchmark. An isotropic damage model based on a frame-invariant effective strain is adapted. Mesh objectivity is achieved by calibrating the damage model for a suitable element size and subsequently retaining that mesh size in all subsequent analyses. Crack propagation and branching are predicted by simulating accurately the test conditions. It is found that a local, rate-independent damage model considerably overpredicts the dynamic crack velocity and the extent of crack branching. Subsequently, the effect of various strain rate-dependent phenomena, viz. material viscoelasticity, rate-dependent strength, fracture energy, and failure strain is evaluated. Incorporating the material strain rate effects is found to improve the predictions and match the test data. In this regard, radially scaling the damage law is found to work the best. Despite an overprediction of micro-branching, the macro-crack branching is found to occur in agreement with the Yoffe instability criterion. Overall, various experimentally observed aspects of dynamic cracks are reproduced, including acceleration of cracks to a steady state velocity, increased micro-branching and macro-branching with increased strain rates, and crack velocity dependence of energy dissipation and fracture surface area.

     

On thermoelastic problem of a thermosensitive functionally graded rectangular plate with instantaneous point heat source

The present article attempts to investigate transient thermoelastic problem of a functionally graded thin rectangular plate with thermosensitive and spatial variable dependent material properties. All the material properties are assumed to be isotropic. Kirchhoff’s variable transformation is used to deal with the nonlinearity of the three dimensional heat conduction equation and that equation is solved by the integral transform method considering an instantaneous point heat source. The thermoelastic behavior of the rectangular plate is studied together with the thermal deflection and thermally induced resultant moments. Numerical computations are carried out for ceramic-metal-based functionally graded material, in which alumina is selected as ceramic and nickel as metal. The results are illustrated graphically.     

Approximation Algorithms for Minimizing Average Distortion

This paper considers embeddings f of arbitrary finite metrics into the line metric ℜ so that none of the distances is shrunk by the embedding f; the quantity of interest is the factor by which the average distance in the metric is stretched. We call this quantity the average distortion of the non-contracting map f. We prove that finding the best embedding of even a tree metric into a line metric to minimize the average distortion is NP-hard, and hence focus on approximating the average distortion of the best possible embedding for the given input metric. We give a constant-factor approximation for the problem of embedding general metrics into the line metric. For the case of n-point tree metrics, we provide a quasi-polynomial time approximation scheme which outputs an embedding with distortion at most (1 + ε) times the optimum in time n^{O(log n/ε^2)}. Finally, when the average distortion is measured only over the endpoints of the edges of an input tree metric, we show how to exploit the structure of tree metrics to give an exact solution in polynomial time.