Peritectic phase growth in directionally solidified Cu-70% Sn alloy

The growth mechanism of the peritectic η phase involving the peritectic reaction and peritectic transformation in Cu-70%Sn alloy was investigated under directional solidification. The results show that a major growth mechanism in thickening of the peritectic η-layer is not the peritectic reaction but the peritectic transformation. The transformation temperature and isothermal time play crucial roles in determining the volume fraction and the thickness of the peritectic η phase. With the increase of the temperature and isothermal time, the volume fraction of the peritectic η phase increases. The regressed data show that the relationship between the thickness of η phase (Δx) and the transformation temperature (T) meets the following equation In Δx=6.5−1673 1 / T. Additionally, there exists a relationship between the thickness of the η phase (Δx) and the isothermal time (t) at the 9 mm solidification distance below the peritectic reaction interface, Δx=0.72t ^1/2, which is consistent with the theoretical model. Supported by the National Science Foundation of China (Grant No. 50395102)     

Analysis and optimization of trimorph ring transducers

The Kirchoff-Love plate theory and electroelasticity theory are combined to simulate the dynamic behaviors of the trimorph ring transducers under different boundary conditions. The transducer consists of an isotropic elastic ring laminated between two identical piezoelectric rings. Their electric current response, resonant frequencies, antiresonant frequencies and electromechanical coupling coefficients (EMCCs) are theoretically formulated and studied by numerical simulation. Also, the resonant frequencies and their corresponding mode shape are simulated by the finite element modelling to verify the theoretical results. Finally, to obtain the maximum energy conversion efficiency, the dynamic EMCC is optimized by varying the proportion of piezoelectric and elastic parts. It is shown that the dynamic EMCC depends on geometric thickness and radii ratios. Optimum settings for a particular transducer to reach the maximum dynamic EMCC are found for different boundary conditions. The trimorph ring transducer for the fixed inner and free outer surfaces boundary condition has slightly lower resonant and anti-resonant frequencies, and larger EMCCs than that for the free inner and fixed outer surfaces boundary condition does.     

Gauged harmonic maps,Born‐Infeld electromagnetism,and magnetic vortices

We study maps from a 2‐surface into the standard 2‐sphere coupled with Born‐Infeld geometric electromagnetism through an Abelian gauge field. Such a formalism extends the classical harmonic map model, known as the σ‐model, governing the spin vector orientation in a ferromagnet allows us to obtain the coexistence of vortices and antivortices characterized by opposite, self‐excited, magnetic flux lines. We show that the Born‐Infeld free parameter may be used to achieve arbitrarily high local concentration of magnetic flux lines that the total minimum energy is an additive function of these quantized flux lines realized as the numbers of vortices antivortices. In the case where the underlying surface, or the domain, is compact, we obtain a necessary sufficient condition for the existence of a unique solution representing a prescribed distribution of vortices antivortices. In the case where the domain is the full plane, we prove the existence of a unique solution representing an arbitrary distribution of vortices and antivortices. Furthermore, we also consider the Einstein gravitation induced by these vortices, known as cosmic strings, establish the existence of a solution representing a prescribed distribution of cosmic strings cosmic antistrings under a necessary sufficient condition that makes the underlying surface a complete surface with respect to the induced gravitational metric. © 2003 Wiley Periodicals, Inc.     

High performance 1689-nm quantum well diode lasers

1689-nm diode lasers used in medical apparatus have been fabricated and characterized. The lasers had pnpn InP current confinement structure, and the active region consisted of 5 pairs of InGaAs quantum wells and InGaAsP barriers.     

PURE STATE APPROACH TO $C(X)×_\alpha Z_n$

ＰＵＲＥ ＳＴＡＴＥ ＡＰＰＲＯＡＣＨ ＴＯ Ｃ（ｘ）_αＺ_nＬＩＢＩＮＧＲＥＮ；ＬＩＮＱＩＮＧ（ＩｎｓｔｉｔｕｔｅｏｆＭａｔｈｅｍａｔｉｃｓ，ＡｃａｄｅｍｉａＳｉｎｉｃａ，Ｂｅｉｊｉｎｇ１０００８０，Ｃｈｉｎａ．Ｐｒｏｊｅｃｔｓｕｐｐｏｒｔｅｄｂｙｔｈ?..     

An electrooptic intensity modulator with improved linearity

A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths.<>     

一个非协调膜元的高精度分析

本文讨论一个四自由度三角形非协调膜元的整体超收敛性，外推和亏量校正。     

New theorems for bianisotropic media

The general volume equivalence theorem for bianisotropic scatterers is presented, where the equivalent electric and magnetic currents are determined by a pair of coupled vector integral equations. Moreover, using the general volume equivalence theorem and conventional image principle, image theory is developed for a bianisotropic body over an infinite perfect electric or magnetic conducting ground plane.     

Theoretical study on gain and tuning characteristics of infrared-microwave pumped NH3 FIR laser

Based on the semi-classical density matrix equation theory, the gain and tuning characteristics of infrared-microwave pumped NH₃ FIR laser were studied. It was shown that quasi-continuously tuning could be obtained by the tuning of microwave frequency and the efficiency of the laser could be enhanced by electric dipole transition enhancement effect, but compromise should be made between FIR laser output and frequency tuning range.     

波束扫描合成孔径雷达成像处理

本文主要研究了滤束扫描合成孔径雷达的杨像处理方法，分析了ＳＣＡＮＳＡＲ的工作原理、信号格式、信号结构和信号参数限制，成像处理算法包括块数据成像算法和块图像拼接算法两部分，频谱分析法和时域频域混合相关法被用于数据成像，块图像的拼接是利用时间有系剪裁块图像再顺次拼接，计算机仿真验证了本文提出的ＳＣＡＮＳＡＲ信号格式和成像算法的可行性。