Acoustic carpet invisibility cloak with two open windows using multilayered homogeneous isotropic material

We present a method for designing an open acoustic cloak that can conceal a perturbation on flat ground and simultaneously meet the requirement of communication and matter interchange between the inside and the outside of the cloak. This cloak can be constructed with a multilayered structure and each layer is an isotropic and homogeneous medium. The design scheme consists of two steps: firstly, we apply a conformal coordinate transformation to obtain a quasi-perfect cloak with heterogeneous isotropic material; then, according to the profile of the material distribution, we degenerate this cloak into a multilayered-homogeneous isotropic cloak, which has two open windows with negligible disturbance on its invisibility performance. This may greatly facilitate the fabrication and enhance the applicability of such a carpet-type cloak.     

延性金属层裂强度对温度、晶粒尺寸和加载应变率的依赖特性及其物理建模

层裂强度表征了材料内部最大动态抗拉能力,并与材料本身的力学性质以及损伤早期演化相关.建立层裂强度计算的解析表达式,深入认识层裂强度所包含的微细观物理涵义,有利于更好地优化延性金属材料的层裂强度.目前大量的实验表明:延性金属材料的层裂强度对加载拉伸应变率、温度效应以及材料初始微细观结构具有很强的依赖关系.本文基于对孔洞成核与增长的损伤早期演化特性的分析,以及对温度效应和晶粒尺寸与材料本身力学性质之间关系的分析,给出了简单、实用的层裂强度的解析物理模型,物理模型的计算结果与典型延性金属高纯铝、铜和钽的层裂强度实验结果基本符合,从而验证了我们给出的层裂强度模型具有较好的适用性和预测性.     

Finite temperature effect on mechanical properties of graphene sheets with various grain boundaries

The mechanical properties of graphene sheets with various grain boundaries are studied by molecular dynamics method at finite temperatures.The finite temperature reduces the ultimate strengths of the graphenes with different types of grain boundaries.More interestingly,at high temperatures,the ultimate strengths of the graphene with the zigzagorientation grain boundaries at low tilt angles exhibit different behaviors from those at lower temperatures,which is determined by inner initial stress in grain boundaries.The results indicate that the finite temperature,especially the high one,has a significant effect on the ultimate strength of graphene with grain boundaries,which gives a more in-depth understanding of their mechanical properties and could be useful for potential graphene applications.     

Transient lightning responses of grounding systems buried in horizontal multilayered earth with a hybrid method

Combined with the Fast Fourier Transform (FFT), a mathematical hybrid method for accurately computing the lightning response from grounding systems buried in multilayered earth model has been developed in this paper. In the method, electrical circuit consists of “T” typical of basic elements. To accelerate calculations of the method, quasi-static complex image method and closed form of Green's function and analytical formula for mutual induction and impedance coefficients were introduced into this method. With the inverse FFT, the method can be used for studying performances of transient lightning response from the grounding systems.     

An experimental investigation of dynamic crack propagation in a brittle material reinforced with a ductile layer

The fracture behavior of a dynamically loaded edge crack in a brittle-ductile layered material, as a function of applied loading rate, was experimentally investigated. Layered specimens were prepared by sandwiching a thin layer of ductile aluminum between two thick layers of brittle Homalite-100. The layers were bonded using Loctite Depend 330 adhesive, and a naturally sharp edge crack was introduced in one of the Homalite-100 layers. These single-edge notched specimens were loaded in dynamic three-point bending using a modified Hopkinson bar. The fracture process was imaged in real time using dynamic photoelasticity in conjunction with digital high-speed photography, and the applied load and load-point displacement histories were determined from the strain signals recorded at two locations on the Hopkinson bar. The results of this study indicated two distinct mechanisms of dynamic failure, depending on the applied loading rate. At lower loading rates, the starter crack arrested on reaching the aluminum layer and then caused delamination along the aluminum–Homalite interface. On the contrary, as the loading rate was increased, interfacial delamination was followed by crack re-initiation in the Homalite layer opposite to the initial starter crack. It was determined that the times required for crack initiation, delamination and crack re-initiation decreased as the loading rate was increased. However, it was also observed that the applied load values associated with each event increased with increasing loading rate. These observations indicate that both the dynamic failure process and plausibly the failure mode transition are affected by the rate-dependent properties of Homalite, aluminum and the interfacial bond. Finally, based on the measured peak loads and the observed failure mechanisms it was concluded that the incorporation of a thin ductile reinforcement layer can increase both the overall fracture toughness and strength of a nominally brittle material.     

考虑非均匀温度分布效应的缓冲器插入最优尺寸研究

基于非均匀温度分布效应对互连延时的影响, 提出了一种求解互连非均匀温度分布情况下的缓冲器最优尺寸的模型. 给出了非均匀温度分布情况下的RC互连延时解析表达式, 通过引入温度效应消除因子, 得出了最优插入缓冲器尺寸以使互连总延时最优. 针对90 nm和65 nm工艺节点, 对所提模型进行了仿真验证, 结果显示, 相较于以往同类模型, 本文所提模型由于考虑了互连非均匀温度分布效应, 更加准确有效, 且在保证互连延时最优的情况下有效地提高了芯片面积的利用.     

Instability of Fabry-Perot interferometer with a multilayered paramagnetic filling

The results of the analysis of the stability of stationary solutions of wave equations discribing a behavior of the nonlinear Fabry-Perot interferometer with a saturated paramagnetic filling are presented in this paper. The cases when paramagnetic medium is characterized by a homogeneously and nonhomogeneously broadened line of the magnetic resonance have been considered. Areas of unstable behavior of these characteristics of the resonance structure have been found.     

考虑温度分布效应的非对称RLC树时钟偏差研究

提出了一种RLC互连树零时钟偏差构建方法.给出了RLC互连温度非均匀分布及其延时的解析公式,并推导计算了最优的零时钟偏差点,所提模型同时考虑了互连温度非均匀分布、电感效应及不对称互连结构对零时钟偏差点的影响.针对65 nm工艺节点对所提模型进行了仿真验证,结果显示,相较于同类模型,最大误差不超过1%. 关键词： RLC')" href="#">RLC 温度分布 不对称互连结构 零时钟偏差点     

Study of the effects of grain size on the mechanical properties of nanocrystalline copper using molecular dynamics simulation with initial realistic samples

Abstract

Molecular dynamics simulations have been performed to study the mechanical properties of a columnar nanocrystalline copper with a mean grain size between 9.0 and 24 nm. A melting–cooling method has been used to generate the initial samples: this method produces realistic samples that contain defects inside the grains such as dislocations and vacancies. The results of uniaxial tensile tests applied to these samples reveal the presence of a critical mean grain size between 16 and 20 nm, for which there is an inversion of the conventional Hall–Petch relation. The principal mechanisms of deformation present in the samples correspond to a combination of dislocations and grain boundary sliding. In addition, this analysis shows the presence of sliding planes generated by the motion of perfect edge dislocations that are absorbed by grain boundaries. It is the initial defects present inside the grains that lead to this mechanism of deformation. An analysis of the atomic configurations further shows that nucleation and propagation of cracks are localised on the grain boundaries especially on the triple grains junctions.     

弓张式超磁致伸缩材料换能器的设计与分析

为了提高超磁致伸缩换能器的作动行程,以获得足够大的发音强度,并使之满足发音装置体积小、装配零件少的要求,结合超磁致伸缩材料（GMM）的优良特性,提出一种基于三角放大原理的弓张式GMM换能器。该换能器以GMM棒作为驱动元件,通过固定弓张结构的一端,将双向输出转变为单向输出,同时利用柔性铰链结构,进一步增大换能器的位移输出。通过分析换能器的工作原理,计算得到其理论放大倍数为2.73,与所建立的有限元仿真模型计算得到的放大倍数2.8相近。制作了试验样机并搭建了相应的试验系统,得到在1 kHz范围内换能器最大输出位移为15.5 m,与仿真结果14.058 m相近。提出的弓张结构实现了换能器的位移放大,相应的分析方法也较好地反映了换能器的输出特性。     

Hydrostatic pressure and temperature effects on the binding energy and optical absorption of a multilayered quantum dot with a parabolic confinement

The influence of hydrostatic pressure, temperature, and impurity on the electronic and optical properties of spherical core/shell/well/shell(CSWS) nanostructure with parabolic confinement potential is investigated theoretically. The energy levels and wave functions of the structure are calculated by using shooting method within the effective-mass approximation.The numerical results show that the ground state donor binding energy as a function layer thickness very sensitively depends on the magnitude of pressure and temperature. Also, we investigate the probability distributions to understand clearly electronic properties. The obtained results show that the existence of the pressure and temperature has great influence on the electronic and optical properties.     

Effect of sintering temperature on mechanical behaviour and bioactivity of sol-gel synthesized bioglass-ceramics using rice husk ash as a silica source

Bioglass-ceramics with SiO₂-Na₂O-CaO composition was prepared by sol-gel method using rice husk ash as a silica source. Material was sintered at different temperatures ranging from 900 to 1050 °C for 2 h. Phase-formation behaviour, densification characteristics, and mechanical strength of glass-ceramics were investigated. The material sintered at 1000 °C showed a good mechanical strength. Mechanical properties were correlated with microstructural features. Both in vitro bioactivity and biodegradability of sintered material were investigated by incubating in simulated body fluid and Tris buffer solution, respectively. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to investigate the surface deposition during body fluid incubation. Both bioactivity and degradability decreased with increase in sintering temperature.     

高分子颗粒孔隙结构材料的吸声特性研究

在噪声控制与治理工程中，许多场合了消除由物体表面产生的反射声波，往往需要在物体表面敷设具有吸声性能的材料或结构，以吸收入射声波的声能，本文对一种新型的以高分子材料为基底的颗粒型微孔结构进行了吸声特性研究，首先对颗粒微孔结构的吸声机理进行分析，认为由于受材料自身化学性质与结构特征所决定，这种颗粒微孔结构除了具一般多孔吸声材料的空气粘滞阻力作用吸声外，还存在颗粒材料的内部的弹性弛豫效应吸声，因而吸怕系     

Strain measurement of SU-8 photoresist by a digital image correlation method with a hybrid genetic algorithm

Digital image correlation (DIC) is a whole-field and non-contact strain measuring method. It could provide deformation information of a specimen by processing two digital images that are captured before and after the deformation. To search the deformed images, a hybrid genetic algorithm, in which a simulated annealing mutation process and adaptive mechanisms are added to the real-parameter genetic algorithm, is proposed in this work. To increase the accuracy and reliability of this method, some key parameters of this method are suggested. Then, this method is used to measure the strain during the micro tensile testing of SU-8 photoresist. In addition to the conventional single region, a double region is proposed to calculate the strain by DIC. The results indicate that while the strains obtained by single region are reasonable, those obtained by double region are accurate. Also the mechanical properties of SU-8 could be accurately obtained.     

The dissipative modulated structures in a distribution of interacting vacancies in the elastically anisotropic body-centred cubic crystals under an isothermal irradiation

ABSTRACT

Dissipative mechanism of formation of a modulated structure of vacancies in a body-centred cubic (b.c.c.) crystal is considered as its intrinsic property under an isothermal irradiation irrespectively of elastic-anisotropy factor sign. Conditions of self-organisation of a precursor of formation of a ‘superlattice’ of nanovoids, namely, the modulated structure in a spatial distribution of the diffusing vacancies generated by irradiation, because of the instability of their homogeneous distribution as a result of interaction between them in a b.c.c. host crystal under irradiation, are analysed. As shown for the first time, the ‘cohesive’ and ‘elastic’ couplings between interacting (and diffusing) vacancies have a crucial role in a pattern-selection process accordingly with different (positive or negative) elastic-anisotropy factors.     

Experimental studies of influence of the turbulent flow structure on temperature distribution in a compact heat exchanger

Results of experimental investigation of temperature distribution over the surface of a complex heat exchanger (the Frenkel packing type) are presented. Measurements were carried out in the air flow between two sheets with triangular corrugations directed at 90° to each other. Measurements were carried out by the microthermocouples glued on the heated outer surface. The effect of Reynolds numbers, a gap between corrugated sheets, and substitution of one corrugated sheet by the smooth one on temperature distribution over the heat exchanger surface in the turbulent air flow is analysed. According to the performed experiments, there is a significant effect of a gap and applied perturbations on the type of temperature distribution over the perimeter of a heated cell.     

Thermally assisted switching in FePt single-domain particles with a Gaussian distribution of temperature

Magnetic nanoscale systems,including nanodots,nanofibers,nanowires and nanoparticles,are currently attracting great interest due to their interesting physical and promising applications in various fields,such as magnetic recording,sensors,target drugs and catalysts,as well as others.To achieve ultrahigh recording density,the method of heat assisted magnetic recording(HAMR) has been introduced.In this work,with the help of a Monte Carlo method,the mechanisms of thermally assisted magnetization switching in F...     

Temperature dependence of switching field distribution in a NiFe wire with a pad

The distribution of switching fields (H_sw) in a NiFe wire was investigated as a function of temperature between 5 and 300 K. The sample structure under investigation is Ta/NiFe/Cu/NiFe wire (150 nm width) connecting to a square pad (large area) at an end. Magnetization reversal phenomena are very sensitively detected using the giant magnetoresistance effect. With repeating magnetoresistance measurements, we obtained a histogram of H_sw with three narrow peaks at each temperature. The origin of three peaks can be attributed to the existence of three different kinds of magnetic domain structures at the pad area, which was confirmed by magnetic force microscopy observation.     

Energy transmission through a double-wall structure with an acoustic enclosure: Rotational effect of mechanical links

This paper investigates the rotational effect of mechanical links on energy transmission of a double-wall structure with an enclosure. A criterion is proposed to identify energy transmission mechanisms and predict the dominant transmitting path. Studies in different frequency ranges show a more significant energy transmission due to the rotational effect of the link at higher frequencies compared with lower ones. Comparison between the translational effect and the rotational effect on energy transmission shows that although both effects are important for the transmission mechanism analysis, the rotational effect on energy transmission is more remarkable at high frequencies for a soft translational link; whereas is insensitive for a stiff one.     

Determination of temperature distribution and control parameter in a two-dimensional parabolic inverse problem with overspecified data

In this paper, we present a new algorithm to solve a two-dimensional parabolic inverse problem with a source parameter, which appears in many physical phenomena. A linearized compact difference scheme for this problem is constructed using the finite difference method. The discretization accuracy is second-order in time and fourth-order in space. We obtain the unique solvability and present an alternating direction implicit algorithm to solve this difference scheme. The results of numerical experiments are presented to demonstrate the accuracy of this algorithm.