Structural Analysis of silica aerogels for the interlayer dielectric in semiconductor devices

As semiconductor devices have become miniaturized and highly integrated, interconnection problems such as RC delays, power dissipation, and crosstalk appear. To alleviate these problems, materials with a low dielectric constant should be used for the interlayer dielectric in nanoscale semiconductor devices. Silica aerogel as a porous structure composed of silica and air can be used as the interlayer dielectric material to achieve a very low dielectric constant. However, the problem of its low stiffness needs to be resolved for the endurance required in planarization. The purpose of this study is to discover the geometric effect of the electrical and mechanical properties of silica aerogel. The effects of porosity, the distribution of pores, the number of pores on the dielectric constant, and elastic modulus were analyzed using FEM. The results suggest that the porosity of silica aerogel is the main parameter that determines the dielectric constant and it should be at least 0.76 to have a very low dielectric constant of 1.5. Additionally, while maintaining the porosity of 0.76, the silica aerogel needs to be designed in an ordered open pores structure (OOPS) containing 64 or more pores positioned in a simple cubic lattice point to endure in planarization, which requires an elastic modulus of 8 GPa to prevent delamination.     

改进的CAGAN在虚拟试衣中的应用

针对CAGAN（Conditional Analogy GAN）换衣后效果模糊，在目标衣服与原始衣服长短不一致时效果一般，相对目标衣服保留过少的细节等问题做了相关研究并对CAGAN进行了改进，提出了新的虚拟试衣方式。经过改进的CAGAN生成一个粗糙的结果，由该结果得到目标衣服穿在模特身上改变形状后的mask，接下来利用mask对目标衣服进行变形，综合变形的衣服和第一步的结果便得到最终的试衣图像。实验结果表明，该方法解决了前面存在的问题，而且取得了非常好的效果。     

Elastic Properties and Stacking Fault Energies of Borides,Carbides and Nitrides from First-Principles Calculations

Owing to the excellent elastic properties and chemical stability, binary metal or light element borides, carbides and nitrides have been extensively applied as hard and low-compressible materials. Researchers are searching for harder materials all the time. Recently, the successful fabrication of nano-twinned cubic BN(Tian et al. Nature 493:385–388, 2013) and diamond(Huang et al. Nature 510:250–253, 2014) exhibiting superior properties than their twin-free counterparts allows an efficient way to be harder. From this point of view, the borides, carbides and nitrides may be stronger by introducing twins, whose formation tendency can be measured using stacking fault energies(SFEs). The lower the SFEs, the easier the formation of twins. In the present study, by means of first-principles calculations, we first calculated the fundamental elastic constants of forty-two borides, seventeen carbides and thirty-one nitrides, and their moduli, elastic anisotropy factors and bonding characters were accordingly derived. Then, the SFEs of the {111} 112 glide system of twenty-seven compounds with the space group F43 m or Fm3m were calculated. Based on the obtained elastic properties and SFEs, we find that(1) light element compounds usually exhibit superior elastic properties over the metal borides, carbides or nitrides;(2) the 5 d transitionmetal compounds(ReB_2, WB, OsC, RuC, WC, OsN_2, TaN and WN) possess comparable bulk modulus( B) with that of cBN( B = 363 GPa);(3) twins may form in ZrB, HfN, PtN, VN and ZrN, since their SFEs are lower or slightly higher than that of diamond(SFE = 277 mJ/m~2). Our work can be used as a valuable database to compare these compounds.     

Microstructure and interface-adhesion of thermally sprayed continuous gradient elastic modulus FeCrAl-ceramic coatings

The bond strength between thermally sprayed metal bond-coats and ceramic top-coats is a key factor in determining their service life. However, most studies focus on interface modifications. In this research, based on FeCrAl bond-coats prepared by arc spraying, top-coats (Al₂O₃-40 wt% TiO₂) were prepared by plasma spraying, and heat treatment was carried out in a hypoxic atmosphere. Continuous gradient elastic modulus FeCrAl-ceramic coatings were successfully prepared, and the microstructural and mechanical properties from the substrate to the top-coats were systematically investigated. The Al₂O₃ content gradually decreased from the top-coats to the substrate, forming continuous gradient elastic modulus FeCrAl-ceramic coatings. The oxide formed during the heat treatment filled the defects in the bond-coats and greatly improved the mechanical properties of the coating. The bonding strength of the continuous gradient elastic modulus coating was 21.7% greater than that of the as-received coating.     

Wave scattering through an orthotropic thermoelastic slab sandwiched between two isotropic elastic half-spaces

Abstract

Present study deals with the scattering of a plane wave through an orthotropic thermoelastic slab sandwiched between two elastic half-spaces. Unlike the classical theory of thermoelasticity, we have employed non-classical thermoelastic theories (LS-theory and GL-theory) to analyze the scattering of plane waves. The amplitude ratios for different waves have been computed numerically for the considered generalized theories of thermoelasticity. The effect of the slab thickness on the amplitude ratios has been shown graphically. Moreover, the amplitude ratios of different waves (i.e., reflected, transmitted, forward and backward waves) are compared for different values of slab thickness under both the LS-theory and GL-theory.     

绿色合成型混凝土的弹性恢复机制研究

研究了绿色合成型混凝土的弹性恢复性能,结果表明,在满足安全储备的情况下,可充分利用混凝土材料。     

First-principles density functional calculations of physical properties of orthorhombic Au2Al crystal

The study attempts to perform a systematical investigation of the thermodynamic, mechanical and electronic properties of orthorhombic Au₂Al crystal by using first-principles calculations incorporated with a quasi-harmonic Debye model. In addition, their temperature, hydrostatic pressure and direction dependences are also addressed. The investigation begins with evaluation of the equilibrated lattice constants and elastic constants of Au₂Al single crystal. Next, the mechanical features of the single crystal, such as ductile-brittle characteristic and elastic anisotropy, are assessed based on the Cauchy pressures, shear anisotropy factors and directional Young's modulus. Alternatively, the pressure-dependence of polycrystalline mechanical properties of Au₂Al, including bulk, shear and Young's moduli, and ductility, brittleness and microhardness characteristics are also estimated. Furthermore, the study also characterizes the temperature-dependence of thermodynamic properties of Au₂Al single crystal, namely, Debye temperature and heat capacity. At last, electronic characteristic analysis is carried out to predict the electronic band structures and density of states profiles of the crystal.The calculation results indicate that Au₂Al crystal is an elastically anisotropic material at zero pressure and a highly ductile material with low stiffness. In addition, the Young's moduli of the crystal would be markedly enhanced with the increase of the hydrostatic pressure. It is also found that the heat capacity of Au₂Al at low temperature strictly sticks to the Debye T³ law.     

改进HSR-FCN的服装图像识别分类算法研究

目前网络上的服装图像数量增长迅猛，对于大量服装图像实现智能分类的需求日益增加。将基于区域的全卷积网络（Region-Based Fully Convolutional Networks，R-FCN）引入到服装图像识别中，针对服装图像分类中网络训练时间长、形变服装图像识别率低的问题，提出一种新颖的改进框架HSR-FCN。新框架将R-FCN中的区域建议网络和HyperNet网络相融合，改变图片特征学习方式，使得HSR-FCN可以在更短的训练时间内达到更高的准确率。在模型中引入了空间转换网络，对输入服装图像和特征图进行了空间变换及对齐，加强了对多角度服装和形变服装的特征学习。实验结果表明，改进后的HSR-FCN模型有效地加强了对形变服装图像的学习，且在训练时间更短的情况下，比原来的网络模型R-FCN平均准确率提高了大约3个百分点，达到96.69%。     

WSNs中规避攻击者的源位置隐私保护路由协议

为了保证无线传感器网络（Wireless Sensor Networks，WSNs）中的源节点位置隐私安全，同时实现安全性能和网络能耗的均衡，提出了WSNs中规避攻击者的源节点位置隐私路由协议，该协议假设节点具有检测攻击者的能力，通过发出危险警告消息使路由路径上的节点采取路由改变策略，使攻击者无法回溯到源节点，延长了源节点保持位置隐私的安全时间。理论分析和仿真实验表明，该协议在消耗较少的通信开销的情况下保证了源节点位置的高度隐私。     

Lithium metal hydrides (Li2CaH4 and Li2SrH4) for hydrogen storage; mechanical,electronic and optical properties

Hydrogen storage is a critical step for commercialisation of hydrogen consumed energy production. Among other storage methods, solid state storage of hydrogen attracts much attention and requires extensive research. This study rationally and systematically designs novel solid state hydrides; Li₂CaH₄ (GHD is obtained as −6.95 wt %) and Li₂SrH₄ (GHD is obtained as −3.83 wt %) using computational method. As a first step, we suggest and predict crystal structures of solid state Li₂CaH₄ and Li₂SrH₄ hydrides and look for synthesizability. Then, the mechanical stabilities of hydrides are identified using elastic constants. Both hydrides fulfil the well-known Born stability criteria, indicating that both Li₂CaH₄ and Li₂SrH₄ are mechanically stable materials. Several critical parameters, bulk modulus, shear modulus, Cauchy pressures, anisotropy factors of hydrides and bonding characteristics are obtained and evaluated. Furthermore, electronic and optical band structures of hydrides are computed. Both Li₂CaH₄ and Li₂SrH₄ have indirect bands gaps as 0.96 eV (Г-U) and 1.10 eV (Г-R). Thus, both materials are electronically semiconducting. Also, Bader charge analysis of hydrides have been carried out. Charge density distribution suggests an ionic-like (or polarized covalent) bonding interaction between the atoms.