VIBRATION ANALYSIS OF A BEAM WITH EMBEDDED SHAPE MEMORY ALLOY WIRES

In this study, analytical relations for evaluating the exact solution of natural fre- quency and mode shape of beams with embedded shape memory alloy （SMA） wires are presented. Beams are modeled according to Euler-Bernoulli, Timoshenko and third order beam （Reddy） the- ories. A relation is obtained for determining the effect of axial load generated by the recovery action of pre-strained SMA wires. By defining some dimensionless quantities~ the effect of different me- chanical properties on the frequencies and mode shapes of the system are carefully examined. The effect of axial load generated by SMA wires with buckling load and frequency jump is accurately studied.     

约束梁柱构件抗火性能研究进展

约束构件抗火性能和抗火设计是近年国内外相关学者关注的热点之一.笔者简要介绍了约束构件(包括约束梁、约束柱)抗火性能所取得的成果,总结了约束构件在火灾下的工作行为、抗火性能研究以及抗火设计方法的进展,指出了约束构件抗火研究目前存在的主要问题,并对下一步工作进行了展望.     

Designing shielded radio-frequency phased-array coils for magnetic resonance imaging

In this paper, an approach to the design of shielded radio-frequency (RF) phased-array coils for magnetic resonance imaging (MRI) is proposed. The target field method is used to find current densities distributed on primary and shield coils. The stream function technique is used to discretize current densities and to obtain the winding patterns of the coils. The corresponding highly ill-conditioned integral equation is solved by the Tikhonov regularization with a penalty function related to the minimum curvature. To balance the simplicity and smoothness with the homogeneity of the magnetic field of the coil’s winding pattern, the selection of a penalty factor is discussed in detail.     

Impacts of higher-order dispersions and saturable nonlinearities on modulation instability in negative-refractive metamaterials

On the basis of the standard linear stability analysis and Drude electromagnetic model,the impacts of higher-order dispersions and three kinds of typical saturable nonlinearities on modulation instability(MI) have been analyzed and calculated for negative-refractive metamaterials(MMs).Our results show that the MI gain spectra consist of only one spectral region instead of one or two regions in ordinary materials,which may be close to or far from the zero point.Particularly,the spectrum far from the zero point has a high cut-off frequency but a narrow spectral width,which is obviously beneficial to the generation of high-repetition-rate pulse trains.Moreover,MI characteristics here will vary with the normalized angular frequency which can be modified by adjusting the structures of negative-refractive MMs,signifying the controllability of bistable solitons and MI based applications.The effects of saturable nonlinearities are similar to those in ordinary materials.     

箱式约束变分不等式的一类新光滑gap函数

针对箱式约束变分不等式问题,利用一类积分型全局最优性条件,提出了一个新光滑gap函数．该光滑gap函数形式简单且具有较好的性质．利用该gap函数,箱式约束变分不等式可转化为等价光滑优化问题进行求解．进一步地,讨论了可保证等价光滑优化问题的任意聚点为箱式约束变分不等式问题解的条件．以一个简单的摩擦接触问题为例阐释了该方法的应用．最后,利用标准的变分不等式考题验证了方法的有效性．     

压缩感知在合成发射孔径医学超声成像中的应用

为了解决合成发射孔径技术在医学超声成像实现中面临的数据量大及接收通道多的问题,提出一种超声成像系统频率域稀疏性模型的压缩感知成像算法。首先对超声系统频率域稀疏性模型进行了验证;然后根据稀疏性模型利用压缩感知理论对回波信号进行压缩采样,并使用最优化方法完成回波信号重建;最终通过合成发射孔径技术完成超声成像。针对医学成像中常用的点目标及模拟胎儿目标进行成像仿真实验,对重建图像在均方误差、分辨率及成像质量等方面与常规成像结果对比分析。实验结果表明在保证成像质量的同时,仅使用30%原始数据量及50%总接收通道数目可完成成像;频率域稀疏性模型的压缩感知成像算法可以大幅度减少合成发射孔径成像所需数据量及接收通道数,极大地降低了系统复杂度。      

PPLN晶体差频测量飞秒激光脉冲的载波包络相移

在飞秒激光频率梳系统中，通常采用自参考技术测量飞秒激光脉冲的载波包络相移，但该技术需要采用光子晶体光纤进行光谱扩展从而增加了系统的不稳定性，这种技术已经制约了高稳定度的飞秒激光频率梳的发展.采用PPLN晶体差频法测量了宽谱钛宝石振荡器输出的7fs激光脉冲的载波包络频移，得到了大于30dB的拍频信号，为研制无光纤的新一代高稳定度光学频率梳奠定了基础.     

破片撞击装药点火实验和数值模拟

实验中采用升 降法得到了破片撞击装药点火的临界速度范围,数值模拟中采用节点约束 分离方法、热弹塑性材料本构方程和化学动力学方程描述了炸药的破坏行为和点火反应。实验结果与数值模拟结果吻合较好。研究结果表明,采用节点约束 分离方法、热弹塑性材料本构方程和化学动力学方程可以有效地描述装药在破片撞击作用下的破坏行为和点火反应。     

Solvent Effect on Characteristic Vibration of IR Spectrum of 4,4'-Dibromodiphenyl Ether

The optimal geometry, IR spectrum and vibration assignment of 4,4＇-dibromodiphenyl ether（BDE-15） in gas phase were calculated via the density functional theory（DFT） at the level of B3LYP/6-3 l＋G（d）. Based on the vi- bration assignment, the calculation of vibration frequencies and intensities of 5 main vibration types of BDE-15 in 25 kinds of solvents was carried out by means of a self-consistent reaction field（SCRF） theoretical model at the level of B3LYP/6-31＋G（d） to analyze the solvent effect on the vibration of IR spectrum of BDE-15. To study the solvent ef- fect further, C--O asymmetric stretching vibration fluctuating, which is relatively acute in both vibration frequency and intensity, was selected as the characteristic vibration to establish different linear solvation energy relation（LSER） models for solvent categoring. Solvent parameters（a, /3, ~r＊）, acceptable number（AN） and quantitative structure- activity relationship（QSAR） models were established via chemical quantum parameters of solvent moleculer, which were first been introduced to investigate different solvent-solute interaction mechanisms in alcoholic and non-alcoholic solvents on molecular level. At last, a single solvent molecule was embedded in the framework of po- larizable continuum model（PCM） to validate the effect of hydrogen bonding on solvent-solute interaction in alcohol solvents. The obtained results show that 5 main vibration types of BDE-15 in different solvents have small variation range in frequency and intensity and all the vibration frequencies in solvents are lower than those in gas phase, de- creasing along with the increasing of the dielectric Constant（e） of solvents exponentially. In contrast, all the vibration intensities in solvents are greater than those in gas phase and present positive exponential trend. Twenty-five solvents were divided into two categories（non-alcoholic solvents and alcoholic solvents） by LSER. The CmO asymmetric stretching vibration was mainly reg     

Non-smooth bifurcations in a double-scroll circuit with periodic excitation

The fast-slow effect can be observed in a typical non-smooth electric circuit with order gap between the natural frequency and the excitation frequency. Numerical simulations are employed to show complicated behaviours, especially different types of busting phenomena. The bifurcation mechanism for the bursting solutions is analysed by assuming the forms of the solutions and introducing the generalized Jacobian matrix at the non-smooth boundaries, which can also be used to account for the evolution of the complicated structures of the phase portraits with the variation of the parameter. Period-adding bifurcation has been explored through the computation of the eigenvalues related to the solutions. At the non-smooth boundaries the so-called `single crossing bifurcation' can occur, corresponding to the case where the eigenvalues jump only once across the imaginary axis, which leads the periodic burster to have a quasi-periodic oscillation.