The possibility of increasingTc in oxide high-Tc superconductor films: Interaction with elastic fields of defects

The influence onT _c of dilatation centers (DC) as elastic defects near the surface or in thin films of oxide high-T_c superconductors is considered. The distribution function ofT _c in this case was obtained. This is the Lorentzian with center shifted to largerT _c values. The half width of theT _c distribution n (n is the concentration of DC) is larger than its center shift and corresponds to the increase ofT _c fluctuations near the surface. As a result, a continuum percolation behavior with increasing critical temperature percolation levelT ^(c) near the surface appears. The inequalityn>T ^(c)>T _c ^initial is fulfilled. ForT>T ^(c) the quasi-2D Josephson media takes place where a finite superconductive domain withT _c ^local >T ^(c) exists. The influence of DC considerably increases for strong DC such as off-center impurity ions.     

基于弹性形变摩擦力的光学天线伺服系统建模

提出了一种弹性形变摩擦力模型,用于描述光学天线伺服系统的非线性效应。弹性形变摩擦力模型将摩擦力表示为相对运动物体表面接触形变产生的弹性力,与Stribeck模型相比,弹性形变在相对运动过程中连续变化,消除了零速度摩擦力不连续性,与LuGre模型相比,参数较少且无需求解微分方程,降低了模型辨识难度。以伺服系统模型输出速度与实测输出速度的误差平方和为评价函数,采用遗传算法辨识基于三种摩擦力模型的伺服系统参数。实验结果表明:在相同的遗传进化迭代次数下,弹性形变摩擦力模型精度比Stribeck模型提高2.3倍,比LuGre模型提高4.6倍。验证了弹性形变摩擦力模型用于伺服系统非线性建模的可行性。     

稀疏约束的时空正则相关滤波无人机视觉跟踪

目的 基于相关滤波的跟踪算法在无人机(unmanned aerial vehicle,UAV)视觉跟踪领域表现出卓越的性能。现有的相关滤波类跟踪算法从样本区域的所有特征中学习滤波器,然而某些来自遮挡或形变的特征可能会污染滤波器,降低模型判别能力。针对此问题,提出一种稀疏约束的时空正则相关滤波跟踪算法。方法 在相关滤波目标函数上施加空间弹性网络约束以自适应地抑制跟踪过程中的干扰特征,同时集成空间—时间正则相关滤波算法(spatial-temporal regularized correlation filter,STRCF)中的时间正则项以增强滤波器抑制畸变的能力。采用交替方向乘子法(alternating direction method of multipliers,ADMM)将带有约束项的目标函数转化为两个具有闭式解的子问题迭代求局部最优解。此外,提出一种相关滤波框架通用的加速策略,根据当前帧的目标位移量,对检测定位阶段的特征矩阵进行等距离的循环移位,将其作为在线学习阶段的特征矩阵,每帧可节省一次训练样本的特征提取操作,提高跟踪速度。结果 在3个UAV数据集上与14种主流跟踪算法进...     

圆柱壳弹性波超材料分级排列的带隙拓宽方法研究

圆柱壳弹性波超材料的弯曲波带隙拓宽问题限制其满足实际工程中的宽频隔振要求,针对该问题,本文首先研究了基于局域共振机理的圆柱壳弹性波超材料弯曲波带隙特点,研究局域谐振器质量和弹簧劲度系数的关系,然后将周期分级排列的组合方式应用于圆柱壳类弹性波超材料的带隙拓宽中,并利用有限元法进行能带结构和振动传输特性计算.研究结果显示：该方法可实现弯曲波带隙的拓宽;利用组合法构建的轴向周期分级排列圆柱壳弹性波超材料可实现705-1226Hz频率范围内弯曲波的高效衰减,带隙拓宽至分别为单一谐振器的2.55倍,这表明该方法在宽频减振方面具有明显优势,应用前景广阔.     

不同形变配准对头颈部CT图像的剂量评估研究

形变图像配准(deformable image registration, DIR)是自适应放射治疗(adaptive radiotherapy, ART)中轮廓推衍和剂量累积的关键过 程。 本研究比较3种不同形变配准算法在自适应放疗过程中轮廓推衍和剂量累积的变化。选择头 颈部癌症患者的放疗影像数据图像进行这项研究,刚性配准后采用B样条弹性配准和LCC- Demons配准算法,其中B样条弹性算法研究了两种优化指标:归一化互相关、归一化互相 关结合弯曲能量惩罚(bending energy penalty, BEP) 正则化。剂量评估采用剂量参数D₉₅、Dmin、D_mean、Dmax和均 匀性指数(homogeneity index, HI)来评价累积剂量与初始剂量的差异。几何评估使用Dice 相似性系数(Dice similarity coefficient, DSC)和 Hausdorff距离(Hausdorff distance, HD)来评价体积之间的重叠度。经过实验,几何评估所得的PTV(planning target volume)靶区、左腮腺、 右腮腺Dice系数在B样条弹性配准的两种优化算法和LCC-Demons算法中分别为:0. 82、 0.83、0.86,其中在LCC-Demons算法下得到的Dice系数达到了最大值0.91, 所得的Hausdorff距离均在1—3 mm之间,DSC重叠度结果与表明偏差 距离均在临床可接受的 范围内。对于剂量评估,相应的HI值分别为:1.089、1.082、1.081,LCC-Demons同样达到 了最小值1.081,本实验中LCC-Demons在轮廓推衍和剂量映射中均取 得了较好的效果,同 时也为临床环境下对配准质量的评估提供了一定的借鉴。     

Diamond semiconductor and elastic strain engineering

Diamond,as an ultra-wide bandgap semiconductor,has become a promising candidate for next-generation microelec-tronics and optoelectronics due to its numerous advantages over conventional semiconductors,including ultrahigh carrier mo-bility and thermal conductivity,low thermal expansion coefficient,and ultra-high breakdown voltage,etc.Despite these ex-traordinary properties,diamond also faces various challenges before being practically used in the semiconductor industry.This review begins with a brief summary of previous efforts to model and construct diamond-based high-voltage switching diodes,high-power/high-frequency field-effect transistors,MEMS/NEMS,and devices operating at high temperatures.Following that,we will discuss recent developments to address scalable diamond device applications,emphasizing the synthesis of large-area,high-quality CVD diamond films and difficulties in diamond doping.Lastly,we show potential solutions to modulate diamond’s electronic properties by the“elastic strain engineering”strategy,which sheds light on the future development of diamond-based electronics,photonics and quantum systems.     

An exact Peano Series solution for bending analysis of imperfect layered functionally graded neutral magneto-electro-elastic plates resting on elastic foundations

In this article, a three-dimensional solution is presented for the bending analysis of functionally graded and layered neutral magneto-electro-elastic plates resting on two-parameter elastic foundations, considering imperfect interfacial bonding. The equations of motion, Gauss's equations for electrostatics and magnetostatics, and boundary and interface conditions are satisfied exactly regardless of the number of layers. No assumptions on deformations, stresses, and magnetic and electric fields along the thickness direction are introduced. The interfacial imperfection is modeled using a generalized spring layer. The state-space method is employed for solving the governing partial differential equations. Effects of a two-parameter elastic foundation, gradient index, bonding imperfection, and applied mechanical and electrical loads on the response of the functionally graded magneto-electro-elastic plate are discussed. The obtained exact solution can serve as a benchmark for assessing the accuracy of layered functionally graded magneto-electro-elastic plate theories.     

Bending-stretching analysis of thick functionally graded micro-plates using higher-order shear and normal deformable plate theory

In the present article, higher-order shear and normal deformable plate theory together with modified couple stress theory are developed to study the bending analysis of thick functionally graded rectangular micro-plates. One material length scale parameter is used for capturing the size effects. Utilizing the variational approach and also a principle of virtual displacement, a new form of equilibrium equations and the corresponding boundary conditions are derived. It is assumed that material properties vary through the thickness according to the power law function. Finally, an analytical solution for the bending problem of a simply supported FG rectangular micro-plate is presented.     

A sweeping window method for detection of flaws using an explicit dynamic XFEM and absorbing boundary layers

We present a sweeping window method in elastodynamics for detection of multiple flaws embedded in a large structure. The key idea is to measure the elastic wave propagation generated by a dynamic load within a smaller substructural detecting window domain, given a sufficient number of sensors. Hence, rather than solving the full structure, one solves a set of smaller dynamic problems quickly and efficiently. To this end, an explicit dynamic extended FEM with circular/elliptical void enrichments is implemented to model the propagation of elastic waves in the detecting window domain. To avoid wave reflections, we consider the window as an unbounded domain with the option of full‐infinite/semi‐infinite/quarter‐infinite domains and employ a simple multi‐dimensional absorbing boundary layer technique. A spatially varying Rayleigh damping is proposed to eliminate spurious wave reflections at the artificial model boundaries. In the process of flaw detection, two phases are proposed: (i) pre‐analysis—identification of rough damage regions through a data‐driven approach, and (ii) post‐analysis‐–identification of the true flaw parameters by a two‐stage optimization technique. The ‘pre‐analysis’ phase considers the information contained in the ‘pseudo’ healthy structure and the scattered wave signals, providing an admissible initial guess for the optimization process. Then a two‐stage optimization approach (the simplex method and a damped Gauss–Newton algorithm) is carried out in the ‘post‐analysis’ phase for convergence to the true flaw parameters. A weighted sum of the least squares, of the residuals between the measured and simulated waves, is used to construct the objective function for optimization. Several benchmark examples are numerically illustrated to test the performance of the proposed sweeping methodology for detection of multiple flaws in an unbounded elastic domain. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanical properties of concrete containing phase-change material

This study aimed to investigate the mechanical properties of concrete containing solid–liquid phase-change material (PCM) and focused on two key factors. First, a systematic study on the mechanical performance of PCM-modified concretes was conducted, including compressive, elastic modulus, and shrinkage tests. Second, because PCM provides high latent heat during the solid–liquid phase change, the effects of the solid phase and liquid phase on the mechanical properties of concrete were also explored. Results of this study showed that the solid–liquid phase of PCM affected the mechanical properties of concrete. For example, the compressive strength of 10% PCM concrete in solid phase (23 °C) and liquid phase (40 °C) at 28 days was 29.30 and 19.57 MPa, respectively. In addition, with increasing PCM content, the mechanical properties were degraded. For example, 10, 20, and 30% of PCM content lowered the compressive strength by 35.4, 58.4, and 74.3%, respectively. Therefore, concrete with PCM may not be suitable for structural elements. However, PCM is an important solution for optimizing energy consumption in modern buildings. It can absorb or emit large amounts of heat to store or release thermal energy. These properties can be used to control building temperatures resulting in energy saving and carbon reduction.