Analysis of electromagnetic scattering from dielectric objects above a lossy half-space by multiresolution preconditioned multilevel fast multipole algorithm

In this study, a synthesis of the multilevel fast multipole algorithm (MLFMA) and the multiresolution (MR) preconditioning technique is presented for the analysis of scattering from homogeneous dielectric targets above a lossy half-space. The Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) integral equation and the MLFMA are used for efficient analysis of scattering problems in half-space. The MR preconditioning technique is used to speed up the convergence rate of the iterative solver. The numerical results are presented to demonstrate that the proposed method is efficient for the scattering from homogeneous dielectric objects above a lossy half-space.     

Study on the effect of corrosion on the tensile behavior of an AZ91 alloy

The effect of corrosion on the tensile behavior of an as‐cast AZ91 alloy was investigated via systematical experiments. The corrosion residual strength of the AZ91 magnesium alloy is approximately negative linear dependent on the extreme depth of corrosion pit, which was quantitatively obtained by the corrosion morphology analysis and the statistic analysis. Experimental results reveal that the corrosion residual strength of the AZ91 magnesium alloy dropped quickly in the first 40 h due to the initiation and development of the corrosion pit and subsequently decreased slowly as a result of the development of the corrosion pit encountered the β phase. The β phase at the grain boundary of the primary α phase acts as an effective barrier to prevent the development of the corrosion pit into the alloy matrix and thus remarkably prevents the drop of the corrosion residual strength. In general, the variation of the corrosion residual strength exhibits an exponential decay regulation within the testing time. Consequently, the empirical prediction of the corrosion residual strength was given with regard to the variation of the corrosion residual strength varied with the immersion time.     

Analysis for the wear resistance anisotropy of diamond cutting tools in theory and experiment

In this work, the dynamic micro-mechanical strengths of diamond crystal are deduced in theory, including the tensile, shearing and compressive strengths. The calculated results reveal that the dynamic micro-mechanical strengths have great anisotropy, but the tensile strengths are less than the shearing and compressive ones in any orientation of any plane. Subsequently, a novel evaluation factor is proposed, which integrates from the theoretical tensile strength in the orientation of flank face paralleling to the cutting direction and the theoretical tensile strength in the orientation of rake face paralleling to the chip flowing direction. And then as expected, the anisotropy of the resistance to wear of diamond cutting tools can be predicted exactly through comparing the evaluation factor. Theoretical analyses indicate the larger the evaluation factor, the greater the wear resistance of diamond cutting tool is. Finally, the cutting experiments are carried out on the (1 1 1) silicon wafers, and the sampled data are well consistent with the theoretical predictions, which validates that the proposed evaluation factor is suited for predicting the anisotropy of the resistance to wear of diamond cutting tools.     

Performance of a direct ethylene glycol fuel cell with an anion-exchange membrane

This paper reports on the development and performance test of an alkaline direct ethylene glycol fuel cell. The fuel cell consists of an anion-exchange membrane with non-platinum electrocatalysts at both the anode and cathode. It is demonstrated that this type of fuel cell with relatively cheap membranes and catalysts can result in a maximum power density of 67 mW cm⁻² at 60 °C, which represents the highest performance that has so far been reported in the open literature. The high performance is mainly attributed to the increased kinetics of both the ethylene glycol oxidation reaction and oxygen reduction reaction rendered by the alkaline medium with the anion-exchange membrane.     

A Study on the Selectivity of Methanol Aromatization

Abstract

The present study describes the performance of the HZSM-5 zeolite catalyst modified by Cu, Zn, Ga, La, P, Ag, and other ions for the conversion of methanol to aromatics in a fixed-bed reactor, and the influences of the system pressure and temperature on methanol aromatization are in discussion. The results show that the optimum single ion for the modification of catalyst was Zn or Cu. The optimum combined ions were Zn and Ga. The yield of aromatics could reach up to 66.6% on the catalyst modified with Ga2% and Zn10%.     

Thermal Stability in Nanocrystalline Fe-30?Wt?Pct Ni Alloy Induced by Surface Mechanical Attrition Treatment

By means of surface mechanical attrition treatment (SMAT), a nanocrystalline surface layer is produced in Fe-30 wt pct Ni alloy, accompanying the formation of the strain-induced martensite. The thermal stability of nanocrystalline martensite and parent phase austenite in Fe-30 wt pct Ni alloy is studied by X-ray diffraction (XRD) and transmission electron microscope (TEM). The grain growth kinetics parameters, time exponent, n, and activation energy, Q, for both martensite and austenite, are determined, respectively. The TEM observations indicate that abnormal grain growth occurs during annealing at high temperatures.     

Investigation on heat and mass transfer in 3D woven fibrous material

A 3D mathematical model is developed to describe coupled heat and mass transfer in woven fibrous materials with consideration of its geometrical characters. The liquid water diffusion tensor is derived by matrix transformation. The finite volume method is used to discrete the governing equations, and the obtained linear discrete equations are solved by iteratively utilizing the TDMA (Tri-Diagonal Matrix Algorithm). A high order and absolutely stable difference scheme for water vapor diffusing in fiber is developed. The processes of liquid water transfer in the yarns, water vapor in both inter-yarn and intra-yarn, and their interaction with heat transfer are illustrated by a series of 3D or 4D diagrams. The effects of porosity of the yarn ε and the fabric count on heat and mass transfer are also discussed. The predictions of temperature changes on the fabric surface are compared with experimental measurements, good agreement is observed between the two.     

Research on intercrystalline corrosion,exfoliation corrosion,and stress corrosion cracking of Al–Zn–Mg–Sc–Zr alloy

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.     

Image matching using enclosed region detector

Affine-invariant region detection is the basic technique for visual matching and has been widely applied in many areas. In this paper, we propose a simple yet effective method to detect the affine-invariant regions from gray image, which is called enclosed region. The enclosed region is detected based on the observation that one physical object is enclosed by the same region before and after affine transformation. The proposed method is a three-step method. Firstly, we segment the initial regions by using thresholds on the image. Secondly, external enclosing region (EER) and internal enclosed region (IER) are defined for each initial region, and we select the enclosed regions from the initial regions through applying histogram constraints on EER and IER. Thirdly, the largely overlapping regions are removed. Experiments on typical images exhibit the robustness of the proposed enclosed region detector. Extensively quantitative evaluation and comparison demonstrate that the proposed method outperforms state-of-the-art methods.     

Thermal Effects and Small Signal Modulation of 1.3-μm InAs/GaAs Self-Assembled Quantum-Dot Lasers

We investigate the influence of thermal effects on the high-speed performance of 1.3-μm InAs/GaAs quantum-dot lasers in a wide temperature range (5–50°C). Ridge waveguide devices with 1.1 mm cavity length exhibit small signal modulation bandwidths of 7.51 GHz at 5°C and 3.98 GHz at 50°C. Temperature-dependent K-factor, differential gain, and gain compression factor are studied. While the intrinsic damping-limited modulation bandwidth is as high as 23 GHz, the actual modulation bandwidth is limited by carrier thermalization under continuous wave operation. Saturation of the resonance frequency was found to be the result of thermal reduction in the differential gain, which may originate from carrier thermalization.