Sound radiation from perforated plates

A practical engineering noise control measure that can often be used for plate-like structures is to construct them from perforates. This can dramatically reduce the sound radiation from such structures. Here, a prediction model is developed to quantify this effect. It is an extension of Laulagnet's model for the radiation from an unbaffled plate, which expresses the surface pressure difference as well as the plate velocity as a sum over plate modes. The perforation is included in terms of a continuously distributed surface impedance, which for moderately sized holes is predominantly inertial. Results show that the radiation efficiency reduces, not only as the perforation ratio increases but also as the hole size reduces for a given perforation ratio. Experimental validation is given which shows a good agreement with the predictions. An approximate formula is also proposed for the effect of perforation which corresponds well with the analytical calculations up to half the critical frequency and could be used for an engineering application to predict the noise reduction due to perforation. A model for the case of a perforated plate embedded in an equally perforated baffle is also discussed for comparison.     

A Multiphase Godunov Method for Compressible Multifluid and Multiphase Flows

We propose a new model and a solution method for two-phase compressible flows. The model involves six equations obtained from conservation principles applied to each phase, completed by a seventh equation for the evolution of the volume fraction. This equation is necessary to close the overall system. The model is valid for fluid mixtures, as well as for pure fluids. The system of partial differential equations is hyperbolic. Hyperbolicity is obtained because each phase is considered to be compressible. Two difficulties arise for the solution: one of the equations is written in non-conservative form; non-conservative terms exist in the momentum and energy equations. We propose robust and accurate discretisation of these terms. The method solves the same system at each mesh point with the same algorithm. It allows the simulation of interface problems between pure fluids as well as multiphase mixtures. Several test cases where fluids have compressible behavior are shown as well as some other test problems where one of the phases is incompressible. The method provides reliable results, is able to compute strong shock waves, and deals with complex equations of state.     

共振波长对导模共振生物传感器灵敏度的影响

导模共振生物传感器由于具有微型化、免标签、高通量和实时检测等优势被广泛研究。利用严格耦合波理论分析了该生物传感器对样品折射率和厚度的灵敏度随共振波长的变化规律。当样品厚度和共振波长一定时,其折射率灵敏度恒定;随着共振波长的增大,折射率灵敏度显著提高。当样品折射率和共振波长一定时,厚度灵敏度随着厚度的增加而降低,最后趋近于0;当共振波长增加时,厚度灵敏度明显提高,厚度测量范围增大。结果表明:选取较长的共振波长有利于样品的检测和分析。     

Polarized electron scattering on spin zero and polarized spin-1/2 targets: Deep inelastic scattering,elastic electron-muon scattering,and elastic electron-nucleon scattering

A covariant formulation is developed and used to derive cross sections for the analysis of experiments in which polarized electrons (muons) are scattered from spin-zero and from polarized spin-1/2 targets. The analysis is based upon the single virtual photon representation of the electromagnetic interaction, initially, neither high-energy nor low-energy approximations are made so that one may derive results in which the orientation of the polarization vectors of the interacting particles changes as a result of the scattering. The general formulation is valid for all polarization configurations for the electron and nucleon in deep inelastic scattering, and for all polarization configurations for the initial and final state particles in elastic scattering. From the general covariant results, specific cross sections are derived for deep inelastic scattering as well as elastic scattering of electrons on muons, nucleons, and spin zero targets. In the latter case, the actual polarization vector for the scattered electron is determined. In the other cases discussed, this vector may be obtained from the cross sections. In addition, a method is presented for defining covariant cross sections, and this method is used to obtain results in the center-of-mass system as well as the laboratory system. Furthermore, explicit cross sections for virtual photon absorption are derived. Finally, in the appendices, an alternative method for the evaluation of traces is given as well as a discussion of the relativistic limit.     

A solution of a non-homogeneous orthotropic cylindrical shell for axisymmetric plane strain dynamic thermoelastic problems

A solution of a non-homogeneous orthotropic elastic cylindrical shell for axisymmetric plane strain dynamic thermoelastic problems is developed. Firstly, a new dependent variable is introduced to rewrite the governing equation, the boundary conditions as well as the initial conditions. Secondly, a special function is introduced to transform the inhomogeneous boundary conditions to the homogeneous ones. Then by virtue of the orthogonal expansion technique, the equation with respect to the time variable is derived, of which the solution can be obtained. The displacement solution is finally presented, which can degenerate in a rather straightforward way to the solution for a homogeneous orthotropic cylindrical shell and isotropic solid cylinder as well as that for a non-homogeneous isotropic cylindrical shell. Using the present method, integral transform can be avoided. It is fit for a cylindrical shell with arbitrary thickness subjected to arbitrary thermal loads. It is also very convenient to deal with dynamic thermoelastic problems for different boundary conditions. Besides, the numerical calculation involved is very easy to be performed. Several examples are presented.     

极性超晶格中电子—声子的相互作用

本文在Wendler、潘金声研究双层极性晶体时得出的声子振动极化场所满足的微分、积分方程及归一化条件的基础上,讨论周期性排列的层状极性晶体中声子振动极化场所满足的微分、积分方程,得到了SO声子的色散关系,SO声子和LO声子极化强度矢量.用声子产生、湮灭算符表出了声子振动能量及电子—声子的相互作用哈密顿量.     

高斯分布及截断和抽样

 详细推论了高斯分布的轴对称电子束的截断方法和确定截断因子的表达式。结果表明在截断因子为0.9时,电子束发射度等于均方根发射度的二倍, 而当电子束发射度等于均方根发射度时, 截断因子仅为0.59。给出了四维坐标变量的几率密度函数公式, 并简述了相应的抽样方法。     

980 nm 垂直腔面发射激光器低欧姆接触电阻制备

研究了980 nm的垂直腔面发射激光器(VCSEL)欧姆接触技术.降低VCSEL的欧姆接触电阻,可有效地提高VCSEL的输出功率和延长其可靠性.P面采用高掺杂的P-GaAs/Ti/Pt/Au系统,N面采用N-GaAs/Ge/Au/Ni/Au系统,通过优化合金温度,得到了最佳优化合金温度为440 ℃,最低欧姆接触电阻值为0.04 Ω,同时对比了440 ℃和450 ℃器件的输出功率和转换效率之间的对比关系.测试结果表明,440 ℃器件的欧姆接触电阻0.04 Ω,峰值波长980.1 nm,光谱的半高宽0.8 nm,平行发散角θ_‖ 15.2°,垂直发散角θ_⊥ 13.5°,输出功率1.4 W,转换效率最大值为14.4%,而450℃的器件欧姆接触电阻为0.049 Ω,输出功率为1.3 W,转换效率为12.8%.通过优化合金温度能有效地降低980 nm的VCSEL欧姆接触电阻.     

Study of acoustic bubble cluster dynamics using a lattice Boltzmann model

The search for the development of a reliable mathematical model for understanding bubble dynamics behavior is an ongoing endeavor.A long list of complex phenomena underlies the physics of this problem.In the past decades,the lattice Boltzmann method has emerged as a promising tool to address such complexities.In this regard,we have applied a 121-velocity multiphase lattice Boltzmann model to an asymmetric cluster of bubbles in an acoustic field.A problem as a benchmark is studied to check the consistency and applicability of the model.The problem of interest is to study the deformation and coalescence phenomena in bubble cluster dynamics,as well as the screening effect on an acoustic multibubble medium.It has been observed that the LB model is able to simulate the combination of the three aforementioned phenomena for a bubble cluster as a whole and for every individual bubble in the cluster.     

A fully analytic treatment of resonant inductive coupling in the far field

For the application of resonant inductive coupling for wireless power transfer, fabrication of flat spiral coils using ribbon wire allows for analytic expressions of the capacitance and inductance of the coils and therefore the resonant frequency. The expressions can also be used in an approximate way for the analysis of coils constructed from cylindrical wire. Ribbon wire constructed from both standard metals as well as high temperature superconducting material is commercially available, so using these derived expressions as a basis, a fully analytic treatment is presented that allows for design trades to be made for hybrid designs incorporating either technology. The model is then extended to analyze the performance of the technology as applied to inductively coupled communications, which has been demonstrated as having an advantage in circumstances where radiated signals would suffer unacceptable levels of attenuation.     

Sharpness Matching between Digital Image Display Devices

A method is presented for matching apparent sharpness between digital image display devices with different characteristics. The sharpness is most precisely described by the point spread function (PSF) as opposed to dot density such as DPI (dot per inch). The difference between devices is expressed as difference between transfer functions obtained from the PSFs. In the presented method, spatial frequency filtering for one digital image is carried out where the ratio of the transfer functions or its modified version is used as filter. The modification is introduced as a clipping operation to reduce excessive enhancement when the ratio of the transfer functions has a high pass characteristic with large gain. Through computer simulation including a subjective evaluation experiment and numerical evaluation, the effectiveness of filtering operation for sharpness matching is demonstrated.     

多个硅通孔引起的热应力对迁移率和阻止区的影响

本文主要讨论了多个硅通孔引起的热应力对迁移率和阻止区的影响, 得到了器件沟道沿[100]方向时, 硅通孔之间的角度和间距对电子迁移率和阻止区的影响. 设定两种阻止区区域, 即迁移率变化分别为5%和10%的区域, 且主要考虑相邻TSV之间的区域. 仿真结果表明: 当硅通孔和X轴所成角度为π/4时, 电子迁移率变化和阻止区区域最小, 但是可布置器件区域不规则, 不易于布局. 随着间距的增加, 电子迁移率变化和阻止区区域逐渐增大, 趋向于单个TSV的情况; 当角度为0 时, 电子迁移率变化和阻止区区域变大, 可布置器件区域为硅通孔围成的中心小区域上, 形状比较规则, 便于布局. 而且随着间距的增加, 电子迁移率变化和阻止区区域越来越小, 趋向于单个硅通孔的情况.     

Diagrammatic analysis of correlations in polymer fluids: Cluster diagrams via Edwards’ field theory

Edwards’ functional integral approach to the statistical mechanics of polymer liquids is amenable to a diagrammatic analysis in which free energies and correlation functions are expanded as infinite sums of Feynman diagrams. This analysis is shown to lead naturally to a perturbative cluster expansion that is closely related to the Mayer cluster expansion developed for molecular liquids by Chandler and co-workers. Expansion of the functional integral representation of the grand-canonical partition function yields a perturbation theory in which all quantities of interest are expressed as functionals of a monomer-monomer pair potential, as functionals of intramolecular correlation functions of non-interacting molecules, and as functions of molecular activities. In different variants of the theory, the pair potential may be either a bare or a screened potential. A series of topological reductions yields a renormalized diagrammatic expansion in which collective correlation functions are instead expressed diagrammatically as functionals of the true single-molecule correlation functions in the interacting fluid, and as functions of molecular number density. Similar renormalized expansions are also obtained for a collective Ornstein-Zernicke direct correlation function, and for intramolecular correlation functions. A concise discussion is given of the corresponding Mayer cluster expansion, and of the relationship between the Mayer and perturbative cluster expansions for liquids of flexible molecules. The application of the perturbative cluster expansion to coarse-grained models of dense multi-component polymer liquids is discussed, and a justification is given for the use of a loop expansion. As an example, the formalism is used to derive a new expression for the wave-number dependent direct correlation function and recover known expressions for the intramolecular two-point correlation function to first-order in a renormalized loop expansion for coarse-grained models of binary homopolymer blends and diblock copolymer melts.     

On the Generation of Extremely Short Light Pulses in Effectively One-Dimensional Schemes

Using the method of the Green’s function for a wave equation, it is shown that, in a one-dimensional geometry, the field emitted by a resonant medium that is composed by a system of coupled or free charges is proportional not to the acceleration of charges, as is usually assumed, but, rather, to their velocity that they acquire as a result of the action of a light pulse on initially stationary charges. This feature opens up new opportunities for the generation of ultrashort pulses of one-cycle and subcycle durations, as well as for the diagnostics of media and materials using such ultrashort pulses.     

The Electronic and Magnetic Properties of FCC Iron Clusters in FCC 4D Metals

The electronic and magnetic structures of small FCC iron clusters in FCC Rh, Pd and Ag were calculated using the discrete variational method as a function of cluster size and lattice relaxation. It was found that unrelaxed iron clusters, remain ferromagnetic as the cluster sizes increase, while for relaxed clusters antiferromagnetism develops as the size increases depending on the host metal. For iron in Rh the magnetic structure changes from ferromagnetic to antiferromagnetic for clusters as small as 13 Fe atoms, whereas for Fe in Ag antiferromagnetism is exhibited for clusters of 24 Fe atoms. On the hand, for Fe in Pd the transition from ferromagnetism to antiferromagnetism occurs for clusters as large as 42 Fe atoms. The difference in the magnetic trends of these Fe clusters is related to the electronic properties of the underlying metallic matrix. The local d densities of states, the magnetic moments and hyperfine parameters are calculated in the ferromagnetic and the antiferromagnetic regions. In addition, the average local moment in iron-palladium alloys is calculated and compared to experimental results.     

Design of a silicon-based plasmonic optical sensor for magnetic field monitoring in the infrared

Surface plasmon resonance (SPR) sensor chip is proposed for magnetic field monitoring in the infrared wavelength region. The structure is based on silicon substrate and gold as SPR-active metal used with an appropriate magnetic fluid film. The angular interrogation method has been used to study the sensor’s performance in terms of large shift and small width of the SPR curve for a wide range of magnetic field between 30 and 220 Oe. The effect of field incidence angle is also studied on the proposed sensor’s performance, and it is observed that the field should be incident as parallel to the magnetic fluid surface as possible. Any possibility of oxidation problem to the proposed SPR sensor is addressed by using a stable buffer layer. All the performance parameters were found to be significantly large for the above field incidence condition. The proposed sensor is able to achieve a resolution of the order as high as 0.18 Oe for magnetic field detection.     

Steady state self-focusing, self-modulation of laser beam in an inhomogeneous plasma

Laboratory as well as PIC simulation experiments reveal strong flow of energetic electrons co-moving with laser beam in laser plasma interaction. Equation governing the evolution of complex envelope in slowly varying envelope approximation is nonlinear parabolic equation. Variational approach is used to solve this problem and a Lagrangian for the problem is set up. Assuming a trial Gaussian profile, authors solve the reduced Lagrangian problem for beam width and curvature. Two scale lengths for inhomogenity along the direction of propagation, one for nonlinearity and other for diffraction management are introduced. Self-focusing, self-modulation as well as self-trapping of the laser-electron-beam plasma system is studied under variety of parameters.     

Functional integral equation for the complete effective action in quantum field theory

Based on a methodological analysis of the effective action approach, certain conceptual foundations of quantum field theory are reconsidered to establish a quest for an equation for the effective action. Relying on the functional integral formulation of Lagrangian quantum field theory, we propose a functional integral equation for the complete effective action which can be understood as a certain fixed-point condition. This is motivated by a critical attitude toward the distinction, artificial from an experimental point of view, between classical and effective action. While for free field theories nothing new is accomplished, for interacting theories the concept differs from the established paradigm. The analysis of this new concept concentrates on gauge field theories, treating QED as the prototype model. An approximative approach to the functional integral equation for the complete effective action of QED is exploited to obtain certain nonperturbative information about the quadratic kernels of the action. As a particular application the approximate calculation of the QED coupling constant α is explicitly studied. It is understood as one of the characteristics of a fixed point given as a solution of the functional integral equation proposed. Finally, within the present approach the vacuum energy problem is considered, as are possible implications for the concept of induced gravity.     

XRF induced by PIXE: Comparison with radioisotope XRF

XRF induced by PIXE (XRF-PIXE) using silver as a primary target was compared with a standard radioisotope XRF system using Cd-109 as a primary exciting source, for the analysis of single-element thin standards. The sensitivity of the two methods were determined for elements from Cl to Mo. XRF is found to be more sensitive for elements from Cl to Mn, whereas XRF-PIXE is found to be more suitable for elements from Fe to Mo. Both techniques can be considered as complementary to each other.