A moving-coil designed micro-mechanics tester with application on MEMS

A moving-coil designed micro-mechanics tester, named as MicroUTM (universal testing machine), is in-house developed in this paper for micro-mechanics tests. The main component is a moving coil suspended in a uniform magnetic field through a set of springs. When a current passes through the coil, the electromagnetic force is proportional to the magnitude of the current, so the load can easily be measured by the current. The displacement is measured using a capacitive sensor. The load is calibrated using a Sartorius BP211D analytical balance, with a resolution/range of 0.01 mg/80 g or 0.1 mg/210 g. The displacement is calibrated using a HEIDENHAIN CT-6002 length gauge with an accuracy of +/- 0.1 mu m. The calibration results show that the load range is +/- 1 N and the displacement range is +/- 300 mu m. The noise levels of the load and displacement are 50 mu N and 150 nm, respectively. The nonlinearity of the load is only 0.2%. Several in-plane load tests of the MEMS micro-cantilever are performed using this tester. Experimental results, with excellent repeatability, demonstrate the reliability of the load measurement as well as the flexible function of this tester.

Potential energy model for turbulent entrainment across density interface in a linearly stratified fluid

A potential energy model is developed for turbulent entrainment in the absence of mean shear in a linearly stratified fluid. The relation between the entrainment distance D and the time t and the relation between dimensionless entrainment rate E and the local Richardson number are obtained. An experiment is made for examination. The experimental results are in good agreement with the model, in which the dimensionless entrainment distance D is given by DBAR = A(i)(SBAR)-1/4(fBAR)1/2(tBAR)1/8, where A(i) is the proportional coefficient, S is the dimensionless stroke, fBAR is the dimensionless frequency of the grid oscillation, tBAR the dimensionless time.

Stress-distribution around a rigid line in dissimilar media

The elastic plane problem of a rigid line inclusion between two dissimilar media was considered. By solving the Riemann-Hilbert problem, the closed-form solution was obtained and the stress distribution around the rigid line was investigated. It was found that the modulus of the singular behavior of the stress remains proportional to the inverse square root of the distance from the rigid line end, but the stresses possess a pronounced oscillatory character as in the case of an interfacial crack tip.

一种基于比例反馈控制原理的动载荷时域反演方法

通过借鉴系统控制论中的比例反馈控制原理，提出了一种新的结构动载荷时域反演方法。该方法在原开环系统的输出与结构模型之间连接一个虚拟的比例反馈增益，使得原来的开环系统成为一个虚拟的闭环反馈控制系统，系统控制信号为实测的结构加速度响应。反馈控制器将系统输出与控制信号之间的差值进行放大后作为反馈不断输入到结构模型中，直到差值趋于稳定，此时该差值与反馈增益的乘积经过高通滤波后即得到所反演的动态载荷。该方法将载荷反演问题的求解转化为正问题中的结构瞬态响应求解，采用一般的数值解法如New-mark法即可实现，因此计算比较简便迅速。该方法仅需要测量结构的加速度响应即可进行反演，便于实际应用，而且并不十分依赖于真实的初始条件，由于不存在误差累积的现象，反演结果具有较好的稳定性。最后，通过海洋平台结构冰载荷反演的模型实验和数值仿真证明了该方法的有效性。

A Breakdown Criterion of Free Molecular Flows and an Optimum Analysis of EBPVD

Two important issues in electron beam physical vapor deposition (EBPVD) are addressed. The first issue is a validity condition of the classical cosine law widely used in the engineering context. This requires a breakdown criterion of the free molecular assumption on which the cosine law is established. Using the analytical solution of free molecular effusion flow, the number of collisions (N-c) for a particle moving from an evaporative source to a substrate is estimated that is proven inversely proportional to the local Knudsen number at the evaporation surface. N-c = 1 is adopted as a breakdown criterion of the free molecular assumption, and it is verified by experimental data and DSMC results. The second issue is how to realize the uniform distributions of thickness and component over a large-area thin film. Our analysis shows that at relatively low evaporation rates the goal is easy achieved through arranging the evaporative source positions properly and rotating the substrate.

Study of the damage-induced anisotropy of quasi-brittle materials using the component assembling model

Damage-induced anisotropy of quasi-brittle materials is investigated using component assembling model in this study. Damage-induced anisotropy is one significant character of quasi-brittle materials coupled with nonlinearity and strain softening. Formulation of such complicated phenomena is a difficult problem till now. The present model is based on the component assembling concept, where constitutive equations of materials are formed by means of assembling two kinds of components' response functions. These two kinds of components, orientational and volumetric ones, are abstracted based on pair-functional potentials and the Cauchy - Born rule. Moreover, macroscopic damage of quasi-brittle materials can be reflected by stiffness changing of orientational components, which represent grouped atomic bonds along discrete directions. Simultaneously, anisotropic characters are captured by the naturally directional property of the orientational component. Initial damage surface in the axial-shear stress space is calculated and analyzed. Furthermore, the anisotropic quasi-brittle damage behaviors of concrete under uniaxial, proportional, and nonproportional combined loading are analyzed to elucidate the utility and limitations of the present damage model. The numerical results show good agreement with the experimental data and predicted results of the classical anisotropic damage models.

Membrane Deformability and Membrane Tension of Single Isolated Mitochondria

Mitochondria dynamics is crucial to many biological processes such as mitochondria fusion and fission, which is highly correlated to the mechanics of single mitochondria. However, the mechanobiological coupling of mitochondria has been poorly understood. Here membrane deformability and membrane tension of individual mitochondria isolated from MtDsRed labeled human embryonic T-Rex-293 kidney cells were measured using a micropipette aspiration assay. The results demonstrated that membrane deformation of isolated mitochondria exhibited an elastic transition phase followed by an equilibrium phase, and mitochondrial membrane tension was proportional to the area compressibility. It was also indicated that mitochondrial membrane deformability was significantly affected by physical chemical factors such as osmotic pressure or pH value, and was further correlated to mitochondrial functionality in different respiratory states and Ca2+ regulation. These findings provide a new insight into understanding the mechanical regulation of mitochondrial physiology.

Three-photon-excited upconversion luminescence of YVO4 single crystal by infrared femtosecond laser irradiation

We report on the upconversion luminescence of a pure YVO4 single crystal excited by an infrared femtosecond laser. The luminescent spectra show that the upconversion luminescence comes from the transitions from the lowest excited states T-3(1), T-3(2) to the ground state (1)A(1) of the VO43-. The dependence of the fluorescence intensity on the pump power density of laser indicates that the conversion of infrared irradiation to visible emission is dominated by three-photon excitation process. We suggest that the simultaneous absorption of three infrared photons promotes the VO43- to excited states, which quickly cascade down to lowest excited states, and radiatively relax to ground states, resulting in the broad characteristic fluorescence of VO43-. (c) 2005 Optical Society of America.

Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy (E) over bar on cluster size (n) over bar in a large range of (n) over bar approximate to 3 x 10(3) similar to 3 x 10(6) has been measured. The experimental results indicate that when the cluster size (n) over bar <= 3 x 10(5), the average ion energy (E) over bar proportional to (n) over bar (0.5), Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.

Characterization of a multi-keV x-ray source produced by nanosecond laser irradiation of a solid target: The influence of laser focus spot and target thickness

The influence of focus spot and target thickness on multi-keV x-ray sources generated by 2 ns duration laser heated solid targets are investigated on the Shenguang II laser facility. In the case of thick-foil targets, the experimental data and theoretical analysis show that the emission volume of the x-ray sources is sensitive to the laser focus spot and proportional to the 3 power of the focus spot size. The steady x-ray flux is proportional to the 5/3 power of the focus spot size of the given laser beam in our experimental condition. In the case of thin-foil targets, experimental data show that there is an optimal foil thickness corresponding to the given laser parameters. With the given laser beam, the optimal thin-foil thickness is proportional to the -2/3 power of the focus spot size, and the optimal x-ray energy of thin foil is independent of focus spot size. (C) 2008 American Institute of Physics.

Ion acceleration with mixed solid targets interacting with circularly polarized lasers

The interaction of a circularly polarized laser pulse with a mixed solid target containing two species of ions is studied by particle in cell simulations and analytical model. After the interaction tends to be stable, it is demonstrated that the acceleration is more efficient for the heavier ions than that in plasmas containing a single kind of heavy ion and the acceleration efficiency is higher when its proportion is lower. To obtain monoenergetic heavy-ion beams, a sandwich target with a thin mixed ion layer between two light ion layers and a microstructured target are proposed. The influences of parameters of the laser pulse and target on ion acceleration are discussed in detail. It is found that, when the target is thick enough, a cold target is more appropriate for heavy-ion acceleration than a warm target, and the velocity of the reflected heavy ions is proportional to the laser amplitude.

Study on the interaction of intense femtosecond laser pulses with nanometre-sized hydrogen clusters

The interaction of intense femtosecond laser pulses with hydrogen clusters has been experimentally studied. The hydrogen clusters were produced from expansion of high-pressure hydrogen gas (backed up to 8x10(6)Pa) into vacuum through a conical nozzle cryogenically cooled by liquid nitrogen. The average size of hydrogen clusters was estimated by Rayleigh scattering measurement and the maximum proton energy of up to 4.2keV has been obtained from the Coulomb explosion of hydrogen clusters under 2 x 10(16)W/cm(2) laser irradiation. Dependence of the maximum proton energy on cluster size and laser intensity was investigated, indicating the correlation between the laser intensity and the cluster size. The maximum proton energy is found to be directly proportional to the laser intensity, which is consistent with the theoretical prediction.

The accuracy of Kirchhoff's approximation in describing the far field speckles produced by random self-affine fractal surfaces

Based on the rigorous formulation of integral equations for the propagations of light waves at the medium interface, we carry out the numerical solutions of the random light field scattered from self-affine fractal surface samples. The light intensities produced by the same surface samples are also calculated in Kirchhoff's approximation, and their comparisons with the corresponding rigorous results show directly the degree of the accuracy of the approximation. It is indicated that Kirchhoff's approximation is of good accuracy for random surfaces with small roughness value w and large roughness exponent alpha. For random surfaces with larger w and smaller alpha, the approximation results in considerable errors, and detailed calculations show that the inaccuracy comes from the simplification that the transmitted light field is proportional to the incident field and from the neglect of light field derivative at the interface.

Scheme for unconventional geometric quantum computation in cavity QED

In this paper, we present a scheme for implementing the unconventional geometric two-qubit phase gate with nonzero dynamical phase based on two-channel Raman interaction of two atoms in a cavity. We show that the dynamical phase and the total phase for a cyclic evolution are proportional to the geometric phase in the same cyclic evolution; hence they possess the same geometric features as does the geometric phase. In our scheme, the atomic excited state is adiabatically eliminated, and the operation of the proposed logic gate involves only the metastable states of the atoms; thus the effect of the atomic spontaneous emission can be neglected. The influence of the cavity decay on our scheme is examined. It is found that the relations regarding the dynamical phase, the total phase, and the geometric phase in the ideal situation are still valid in the case of weak cavity decay. Feasibility and the effect of the phase fluctuations of the driving laser fields are also discussed.

光谱相位相干技术测量飞秒脉冲的倍频误差

从理论上推导了第Ⅱ类相位匹配下宽带飞秒脉冲的二次谐波光场,分析输入飞秒脉冲的非共线相位匹配方式、脉冲带宽引起相位失配与群速失配对测量的影响。结果表明,为了消除飞秒脉冲的带宽影响,需要对测量记录的光强乘以一个调制因子;测量相位误差与非共线相位匹配的夹角和晶体长度成正比;相位失配与群速失配产生相位测量误差,且第Ⅱ类相位匹配方式下脉冲附加相位值较大;强度和相位误差需要在脉冲重建结果中补偿。