Characterization of pulsed laser generated plasma through its perturbation in an electric field

The perturbation produced by pulsed laser generated discharge in an electric field is studied as a tool for breakdown characterization. A focused high-power pulsed laser induces a discharge in air or in a solid target, that is placed between the plates of a planar charged capacitor. The induced discharge generates a temporal redistribution of the electrical charges on the plates that can be easily measured by a resistor connected to the ground plate. This signal depends on the energy used to generate the breakdown, the capacitor applied voltage, and the distance between the plates. In this work, we show that this signal can be readily used to optimize the relevant parameters involved in laser-induced breakdown spectroscopy in gases and in solid targets.     

Realization of Quantum Maxwell's Demon with Solid-State Spins

We report experimental realization of a quantum version of Maxwell's demon using solid state spins where the information acquiring and feedback operations by the demon are achieved through conditional quantum gates.A unique feature of this implementation is that the demon can start in a quantum superposition state or in an entangled state with an ancilla observer. Through quantum state tomography, we measure the entropy in the system, demon, and the ancilla, showing the influence of coherence and entanglement on the result. A quantum implementation of Maxwell's demon adds more controllability to this paradoxical thermal machine and may find applications in quantum thermodynamics involving microscopic systems.     

Generalization of thermodynamic potentials including information

In this work we analyze the connection between information theory and thermodynamics. Three different potentials are presented, all related to the Kullback–Leibler divergence. These potentials represent three different conditions of energy and information exchange between a reservoir and a subsystem. The first potential describes a situation where the two systems are exchanging energy without any external control. The second potential considers the situation where the reservoir can get information through the state of another secondary system about the internal state of the subsystem. This information can then be used by a Maxwell demon to increase the free energy of the subsystem. In this second scenario it is assumed that the energy cost of the information probe and the Maxwell demon are at the expense of the reservoir. Finally, a third case is considered where the information obtained through the secondary system is used not only to manipulate an internal Maxwell demon, but to perform directly work over the subsystem. This last case involves a direct modification of the Hamiltonian of the subsystem.     

Influence of stiffeners on plate vibration and radiated noise excited by turbulent boundary layers

The influence of stiffeners on plate vibration and noise radiation induced by turbulent boundary layers is investigated by wind tunnel measurements. Plates with and without stiffeners are tested under the flow speed of 60 m/s, 71 m/s and 86 m/s, respectively. The stiffeners are set either perpendicular or parallel to the direction of the free stream. Measured vibration and noise levels are compared with theoretical calculations, where wall pressure cross-spectra are described by the Corcos model. For the plates tested, it is evident that stiffeners perpendicular to the direction of the free stream could increase noise radiation, but have almost no influence on vibration level of plates.     

Capacitor-based detection of nuclear magnetization: nuclear quadrupole resonance of surfaces

We demonstrate excitation and detection of nuclear magnetization in a nuclear quadrupole resonance (NQR) experiment with a parallel plate capacitor, where the sample is located between the two capacitor plates and not in a coil as usually. While the sensitivity of this capacitor-based detection is found lower compared to an optimal coil-based detection of the same amount of sample, it becomes comparable in the case of very thin samples and even advantageous in the proximity of conducting bodies. This capacitor-based setup may find its application in acquisition of NQR signals from the surface layers on conducting bodies or in a portable tightly integrated nuclear magnetic resonance sensor.     

Ramo-Shockley relation for a series <Emphasis Type="Italic">RCL</Emphasis> circuit

The current induced by the passage of an external point charge through a plane vacuum capacitor in an RCL circuit free of current (voltage) sources is calculated. The case is also analyzed when an internal point charge is emitted by one of the capacitor plates, moves to the other plate, and is absorbed by it. A technique is proposed to measure the internal charge and its velocity component perpendicular to the capacitor plates in a passive RCL circuit.     

从电容器内抽出铜板时外力、电荷及场强分布的讨论

对电容器充电后，在切断电源或保持与电源连接的两种不同条件下，从电容器内抽出铜板过程中，作的外力和极板上电荷的分布及极板间的电场分布进行了分析讨论。     

On the limitation imposed by gravity on measurements of the critical viscosity of a pure fluid

Measurements of the viscosity of a fluid by means of a parallel plate torsional oscillator are conventionally limited to a plate separation that is much larger than the viscous penetration depth of the fluid contained between the plates. Here we demonstrate that, in principle, useful measurements can be carried out in the opposite regime where the thickness is smaller than the penetration depth. An alternative method, described in the last part of this paper, for alleviating the restriction imposed by the density stratification that results from the earth's gravity, is to use electrostriction, rather than the inertial force, to drive the fluid between the plates.     

Nonlocal continuum-based modeling of a nanoplate subjected to a moving nanoparticle. Part II: Parametric studies

The possible usage of nanoplates in transporting of nanovehicles encouraged the author to propose some nonlocal plate models in the companion paper where the nanovehicle (i.e., moving nanoparticle) was modeled by a moving point load by considering its friction with the upper surface of the nanoplate. In this paper, a comprehensive parametric study is carried out to study the effects of length to thickness ratio of the nanoplate, small-scale parameter, and velocity (or angular velocity) of the moving nanoparticle on dynamic response of nonlocal Kirchhoff, Mindlin, and higher-order plates subjected to a moving nanoparticle. Herein, dynamic response of the nanoplate covers both time histories and dynamic amplitude factors of the in- and out-of-plane displacements. The capabilities of various nonlocal plate models in predicting the displacement field caused by friction and mass weight of the moving nanoparticle are then explored through various numerical analyses for two cases: (i) the moving nanoparticle moves along a diagonal of the nanoplate; (ii) the moving nanoparticle orbits on an ellipse path whose center is coincident with the nanoplate's center. The obtained results indicate that due to the incorporation of small-scale effect into shear strain energy of the nanoplate, an appropriate nonlocal plate model should be used. The results show that the choice of the nanoplate model to use relies on the small-scale parameter, geometrical properties of the nanoplate, and velocity of the moving nanoparticle.     

不同铺设角度下层合板结构参数对声功率影响*

本文研究了不同纤维铺设角度的层合板结构参数对声功率的影响,从而为层合板的低噪声设计提供理论依据。通过分层有限元理论获得层合板结构动力学响应,基于声辐射模态概念分析不同铺设角度下层合板不同铺设方式、宽厚比和弹性模量比对其声功率影响。结果表明,层合板的铺设角度和宽厚比对复合材料层合板结构的声辐射功率影响较大。首先相同铺设角度的层合板,改变弹性模量比,声功率变化不明显;其次改变不同的铺设角度,宽厚比较小的层合板声功率下降的空间更大,更易于声功率的降低。层合板作为结构件时,从降低声功率角度而言总体上对称铺设结构比单向铺设层合板结构有优势,并且相同铺设角度下,反对称铺设层合板可获得更小的辐射声功率。     

马赫-曾德尔型相移矢量剪切干涉仪

为了实现对激光波面的等光程测试,设计了一个新颖的相移矢量剪切干涉仪。该干涉仪以马赫曾德尔结构为基础,为等光程干涉仪。通过在相干的两路光束中分别插入楔角方向正交放置的楔板实现矢量剪切;其中一块楔板分成两块(平板部分和楔板部分),楔板部分沿平板部分的表面移动,通过改变光程差来实现相移,2π相移所需的移动距离为几毫米的量级,该相移方法在相移精度控制上比较简单。文中还对楔板引入的横向剪切误差和相移误差进行了分析,最后给出了实验所得的一组相移干涉图。     

Experimental simulation and theoretical analysis of the thermal deformation of dielectric plates under submicrosecond radiation heating

The flexural deformation of dielectric plates subjected to submicrosecond thermal stresses generated by volume and surface sources is studied. The action of such stresses is simulated by laser irradiation of colored glass plates with different optical absorption factors. Such an approach to simulating the thermomechanical action of radiation on dielectric materials allows researchers to visualize the qualitative and quantitative thermoelastic response of the plates to the action of pulsed sources of thermal stresses with different spatial parameters. For volume sources of thermal stresses, it is shown that the thermal deformation of a dielectric plate can be viewed as a set of quasi-harmonic extension-compression wave processes combined with the quasi-static bend of the plate. Under the action of surface sources of submicrosecond thermal stresses, the deformation mechanism is a superposition of the thermal deformation of a thin surface layer and a pulse wave process resulting in the bend of the plate when the pulses reverberate between the surfaces of the plate. Approximate analytical models of thermal deformation due to pulsed thermal disturbances are suggested that make it possible to predict the extent of bend versus the absorbed energy dose under the action of both volume and surface sources of thermal stresses.     

微型激光光学引擎中光学噪音的抑制

分析了微型激光投影引擎的两种主要光学噪音|干涉网格和激光散斑产生的基理|提出采用振动的随机位相板同时实现干涉网格和激光散斑抑制的方法并进行了理论分析|自行设计了微型激光投影引擎,利用微型电控马达带动随机位相板振动,用CCD相机在不同的F#及曝光时间下对投影图像进行了采集,并对图像的散斑对比度行了测试.结果表明,通过静止的随机位相板可以很好地抑制干涉网格噪音|通过使随机位相板以大于视觉暂留效应形成的融合频率进行振动,可以同时抑制干涉网格和激光散斑,使得散斑对比度小于5%,达到投影观察的要求.     

Noise promotes species diversity in nature

Species diversity in nature is accomplished by coexistence. In a spatial environment, inferior but rapidly moving species can coexist with superior but relatively stationary species. Recent work showed that chaotic dynamics can provide the spatiotemporal variation in the fitness required for coexistence, via the dynamical mechanism of synchronization and intermittency. Utilizing a realistic model that consists of two interacting species in a two-patch environment, we discovered a stochastic-resonance phenomenon where noise can significantly enhance the coexistence and thereby promote species diversity.     

The electrostatic capacitance of an inclined plate capacitor

Considering the dimension and relative position of the two plates, the capacitance of an inclined plate capacitor is precisely calculated. Conformal mappings are employed and elliptic functions are used for achieving the general result. Taking the fringing effect into account, the inner capacitance and outer capacitance of the inclined angle are added to obtain a reliable result. The expression for computing the fringing capacitance of a parallel-plate capacitor and the capacitance of a parallel-strip transmission line in a plane are presented as special cases.     

周期多孔板的面内振动衰减域及其优化

针对Bragg散射型周期多孔板难以实现较低起始频率并维持较宽衰减域的问题,优化设计了一种含菱形孔的周期多孔板。采用有限元法结合周期边界条件,并运用COMSOL对周期多孔板的面内弹性波频散关系进行计算,通过ANSYS模拟有限尺寸周期多孔板的频率响应,将周期多孔板悬吊进行了正弦波激励的振动试验。研究结果表明,含菱形孔的周期多孔板相比于含圆形和六边形孔的周期多孔板具有更宽的衰减域;材料属性对衰减域影响较大,丁晴橡胶和硅橡胶易于获得低频衰减域;孔隙率的增大有利于获得低频宽带的衰减域;增大菱形孔水平夹角能获得较宽的衰减域。对衰减域的形成机理分析发现,含菱形孔的周期多孔板同时具有Bragg散射型和局域共振型声子晶体的特性,表明两种衰减域机理具有内在的联系。优化设计的周期多孔板存在一条5281.76 Hz至8824.30 Hz的完全衰减域,经过至少2个周期,振动即得到较明显衰减。数值和试验得到的衰减区具有较高的一致性。该研究为减振降噪板的开发提供了新的思路,且由于制作过程便捷,在改善建筑声环境中具有潜在的应用前景。      

Dynamic responses of Reissner–Mindlin plates with free edges resting on tensionless elastic foundations

Dynamic response analysis is presented for a Reissner–Mindlin plate with four free edges resting on a tensionless elastic foundation of the Winkler-type and Pasternak-type. The mechanical loads consist of transverse partially distributed impulsive loads and in-plane static edge loads while the temperature field is assumed to exhibit a linear variation through the thickness of the plate. The material properties are assumed to be independent of temperature. The two cases of initially compressed plates and of initially heated plates are considered. The formulations are based on Reissner–Mindlin first-order shear deformation plate theory and include the plate–foundation interaction and thermal effects. A set of admissible functions is developed for the dynamic response analysis of moderately thick plates with four free edges. The Galerkin method, the Gauss–Legendre quadrature procedure and the Runge–Kutta technique are employed in conjunction with this set of admissible functions to determine the deflection-time and bending moment–time curves, as well as shape mode curves. An iterative scheme is developed to obtain numerical results without using any assumption on the shape of the contact region. The numerical illustrations concern moderately thick plates with four free edges resting on tensionless elastic foundations of the Winkler-type and Pasternak-type, from which results for conventional elastic foundations are obtained as comparators. The results confirm that the plate will have stronger dynamic behavior than its counterpart when it is supported by a tensionless elastic foundation.     

An alternative to modal analysis for material stiffness and damping identification from vibrating plates

This paper presents an alternative to modal analysis to extract stiffness and damping parameters from thin vibrating plates. Full-field slope measurements are performed through a deflectometry technique on a plate vibrating at a given frequency. Images are recorded in phase and at π/2 lag from the excitation. From this information, deflection fields are computed by integration and curvature fields are obtained by differentiation. This information is then input into the principle of virtual work to extract both stiffness and damping parameters. This procedure, known as the Virtual Fields Method, is detailed in the paper and the notion of special optimized virtual fields is extended to the present problem. Validation on simulated data is performed before moving to experimental data. One of the main advantages of this technique is that it is completely insensitive to the damping coming from the boundary conditions. This is illustrated experimentally on two tests where a viscoelastic layer and rubber washers are added in the experimental set up.     

用脉冲激光全息术测量喷雾场中粒子的分布和运动速度

本文叙述了用脉冲激光全息术测量喷雾场中粒子的分布和运动速度的原理，阐明了同轴全息和离轴全息在测量雾场的应用范围，重点讨论了离轴全息。测量光学系统是４Ｆ系统，它可以测量粒子浓度大的雾场中大于５μｍ的粒子分布和运动速度。在平行光场区段，可进行不同装置、不同景深的喷雾研究，使每个粒子具有相同的放大倍数，它给再现、数据处理、粒子大小的标定都有很大的好处。文中还分析了在底片上形成干涉的各种情况；粒子直径ｄ，远场数Ｎ和从底片到粒子的距离Ｚ的关系。给出脉冲间隔为５μｓ；１０μｓ粗度为±０．１μｓ时不同直径粒子的分布和运动速度在电视屏幕上显示出来的照片。在上述实验结果的基础上讨论了粒子的识别，噪音的消除等问题。