Spatial filtering velocimetry of objective speckles for measuring out-of-plane motion

This paper analyzes the dynamics of objective laser speckles as the distance between the object and the observation plane continuously changes. With the purpose of applying optical spatial filtering velocimetry to the speckle dynamics, in order to measure out-of-plane motion in real time, a rotational symmetric spatial filter is designed. The spatial filter converts the speckle dynamics into a photocurrent with a quasi-sinusoidal response to the out-of-plane motion. The spatial filter is here emulated with a CCD camera, and is tested on speckles arising from a real application. The analysis discusses the selectivity of the spatial filter, the nonlinear response between speckle motion and observation distance, and the influence of the distance-dependent speckle size. Experiments with the emulated filters illustrate performance and potential applications of the technology.     

Time-shift estimation and focusing through distributed aberrationusing multirow arrays

The effects of element height on time-shift estimation and transmit focus compensation are demonstrated experimentally. Multirow ultrasonic transducer arrays were emulated by combining adjacent elements of a 3.0-MHz, 0.6-mm pitch, two-dimensional array to define larger virtual elements. Pulse-echo data were acquired through tissue-mimicking distributed aberrators, and time-shift maps estimated from those data were used for transmit focus compensation. Compensated beams formed by arrays with fine row pitches were similar, but focus restoration was significantly less effective for "1.75-D" arrays with a coarse row pitch. For example, when focus compensation was derived from strongly aberrated random scattering data [70-ns nominal rms arrival time fluctuation with 7 mm FWHM (full-width at half-maximum) correlation length], the mean -20 dB lateral beamwidths were 5.2 mm for f/2.0 arrays with 0.6- and 1.8-mm row pitches and 9.5 mm for an f /2.0 array with 5.4-mm pitch. Time-shift maps estimated from random scattering data acquired with 5.4-mm pitch arrays included large discontinuities caused by low correlation of signals received on vertically and diagonally adjacent emulated elements. The results indicate that multirow arrays designed for use with aberration correction should have element dimensions much less than 75% of the correlation length of the aberration and perhaps as small as 25 to 30% of the correlation length     

Assessment of the final metrological characteristics of a MOEMS-based NDIR spectrometer through system modeling and data processing

A model of a miniaturized non-dispersive infrared (NDIR) gas analysis system, aiming to predict the final system specifications, is presented. It comprises the different elements of the NDIR detector, including a surface micromachined Fabry-Perot tunable filter. These models have been used to estimate the response of the NDIR system to different gas mixtures. Multivariate regression methods like partial least squares allow recovering the true sample composition from the IR absorption spectra measured with the NDIR system, despite the limited selectivity of the filter. Combining model and data processing permits to predict the effect on the final system specification of design parameters. Here, we compare the effect of the technology used for the filter on the system errors.     

On criteria for accepting a response surface model

One of the key problems in response surface analysis is the judgement whether a response surface model is a sufficiently accurate representation of the true response function based on a finite set of experiments. The use of response surface techniques in the context of structural reliability led to the definition of a special lack of fit measure and the formulation of a criterion for accepting response surface models using this measure. The purpose of this paper is to derive and justify two alternative criteria based on this lack of fit measure. Some examples are given to demonstrate the validity of the derived criteria.     

Time reversal for crack identification

A general computational methodology is proposed for identifying cracks in structures. It is based on a time reversal (TR) technique and on the notion of refocusing. In the proposed procedure, a known source generates waves in the structure, and the time-varying response of the structure is measured only at certain points and times. In an industrial application this step is performed experimentally, but in the present study it is emulated numerically. Relying on a computational model of the structure and on the measured signals, a TR solution is obtained for each assumed set of crack parameters. This amounts to evolving the solution backward in time, till the initiation time of the original source. The crack identification is based on seeking, among all crack candidates, the crack which yields the best wave refocusing at the true source location. To test the proposed methodology, a simple rectangular membrane model governed by the 2D time-dependent scalar wave equation is employed. Finite element discretization of the structure and an explicit time-stepping scheme are used. The performance of the method is tested under various conditions and with various amounts of partial information. Its sensitivity to noise and to perturbations in the material properties is also investigated.     

双向梯度复合材料板瞬态热应力分析

该文通过编写一种8节点高阶双向梯度单元建立了结构的连续梯度有限元模型,采用细观力学方法结合混合律准则描述了双向梯度单元变化的热物理属性。分别采用有限单元-有限差分法和有限单元法分析了在循环热载荷作用下双向梯度板Al 1100/Ti-6Al-4V/ZrO2的瞬态热传导和热弹性问题,给出了温度场和瞬态热应力场的时间响应历程和空间分布形式。最后讨论了相关参数的影响规律,得到了一些重要的结论:冷却阶段更加容易萌生表面裂纹;沿x方向组分的分布形式影响了瞬态热应力的大小,但对其时间响应和分布形式影响很小;沿y方向组分的分布形式影响了瞬态热应力的时间响应和分布形式,但对其大小影响很小。     

Adaptive response surface method based on a double weighted regression technique

In structural reliability analysis where the structural response is computed from the finite element method, the response surface method is frequently used. Typically, the response surface is built from polynomials whereof unknown coefficients are estimated from an implicit limit state function numerically defined at fitting points. The locations of these points must be selected in a judicious way to reduce the computational time without deteriorating the quality of the polynomial approximation. To contribute to the development of this method, we propose some improvements. The response surface is successively formed in a cumulative manner. An adaptive construction of the numerical design is proposed. The response surface is fitted by the weighted regression technique, which allows the fitting points to be weighted according to (i) their distance from the true failure surface and (ii) their distance from the estimated design point. This method aims to minimize computational time while producing satisfactory results. The efficiency and the accuracy of the proposed method can be evaluated from examples taken from the literature.     

The diffraction response interpolation method

Computer modeling of the output voltage in a pulse-echo system is computationally very demanding, particularly when considering reflector surfaces of arbitrary geometry. A new, efficient computational tool, the diffraction response interpolation method (DRIM), for modeling of reflectors in a fluid medium, is presented. The DRIM is based on the velocity potential impulse response method, adapted to pulse-echo applications by the use of acoustical reciprocity. Specifically, the DRIM operates by dividing the reflector surface into planar elements, finding the diffraction response at the corners of the elements, calculating the response integrated over the surface element by time-domain convolutions with analytically determined filters, and summing the responses from the individual surface elements. As the method is based on linearity, effects such as shadowing, higher-order diffraction, nonlinear propagation, cannot be directly incorporated in the modeling. The DRIM has been compared to other modeling tools when possible. Excellent agreement between the results obtained with the DRIM and the alternative techniques have been found, and the DRIM offers reductions in computation time in the range from 30 to 400 times. Experimental results obtained using a planar circular transducer together with cylindrical reflectors were compared to DRIM results and fairly good agreement was observed.     

Robust Optimization of Experimentally Derived Objective Functions

In the design or improvement of systems and processes, the objective function is often a performance response surface estimated from experiments. A standard approach is to identify the levels of the design variables that optimize the estimated model. However, if the estimated model varies from the true model due to random error in the experiment, the resulting solution may be quite far from optimal. We consider all points in the confidence intervals associated with the estimated model and construct a minimax deviation model to find a robust solution that is resistant to the error in the estimated empirical model. We prove a reduction theorem to reduce the optimization model to a tractable, finite, mathematical program. The proposed approach is applied to solve for a robust order policy in an inventory problem and is compared with the canonical approach using a Monte Carlo simulation.     

An improved approximation for the spatial impulse response of a rectangular transducer

One common approximation for a field point located in the far field of the transducer is to trapezoidally-shaped function to approximate the true spatial impulse response. A quadrilaterally shaped function is proposed here. The quadrilaterally shaped function also includes the trapezoidally shaped function as a special case. This paper shows that the quadrilateral approximation applied in the specifically defined field location is superior to the trapezoidal approximation for the true spatial impulse response function when the transducer elements have the aspect ratio of approximately 10, typical of those found in 1.5 D arrays.     

On the numerical integration of interface elements

Eigenmode analyses of the element stiffness matrices have been used to assess the impact of the applied integration scheme on the stress predictions of two- and three-dimensional plane interface elements. It is demonstrated that large stress gradients over the element and coupling of the individual node-sets of the interface element may result in an oscillatory type of response. For line elements and linear plane interface elements the performance can be improved by using either a nodal lumping scheme or Newton-Cotes or Lobatto integration schemes instead of the more traditional Gauss scheme. For quadratic interface elements the same holds true except for a nodal lumping scheme.     

Generalized pointwise bias error bounds for response surface approximations

This paper proposes a generalized pointwise bias error bounds estimation method for polynomial‐based response surface approximations when bias errors are substantial. A relaxation parameter is introduced to account for inconsistencies between the data and the assumed true model. The method is demonstrated with a polynomial example where the model is a quadratic polynomial while the true function is assumed to be cubic polynomial. The effect of relaxation parameter is studied. It is demonstrated that when bias errors dominate, the bias error bounds characterize the actual error field better than the standard error. The bias error bound estimates also help to identify regions in the design space where the accuracy of the response surface approximations is inadequate. It is demonstrated that this information can be utilized for adaptive sampling in order to improve accuracy in such regions. Copyright © 2005 John Wiley & Sons, Ltd.     

On-chip surface-based detection with nanohole arrays

A microfluidic device with integrated surface plasmon resonance (SPR) chemical and biological sensors based on arrays of nanoholes in gold films is demonstrated. Widespread use of SPR for surface analysis in laboratories has not translated to microfluidic analytical chip platforms, in part due to challenges associated with scaling down the optics and the surface area required for common reflection mode operation. The resonant enhancement of light transmission through subwavelength apertures in a metallic film suggests the use of nanohole arrays as miniaturized SPR-based sensing elements. The device presented here takes advantage of the unique properties of nanohole arrays: surface-based sensitivity; transmission mode operation; a relatively small footprint; and repeatability. Proof-of-concept measurements performed on-chip indicated a response to small changes in refractive index at the array surfaces. A sensitivity of 333 nm per refractive index unit was demonstrated with the integrated device. The device was also applied to detect spatial microfluidic concentration gradients and to monitor a biochemical affinity process involving the biotin-streptavidin system. Results indicate the efficacy of nanohole arrays as surface plasmon-based sensing elements in a microfluidic platform, adding unique surface-sensitive diagnostic capabilities to the existing suite of microfluidic-based analytical tools.     

Solarization: Reversal Effects Arising from Variation of Developed-Grain Size with Exposure

With heavy exposures, effects akin to solarization and re-reversal may be encountered because of variations in developed grain size and shape. At ordinary maximum density, developed grains are of irregular spiky shape: with increase of exposure they develop in a more compact manner, so that the shapes of developed grains are very similar to those of undeveloped grains. With still heavier exposures, the shape of the developed grain is again irregular.

It is shown that these effects are due to variations in the number of developable surface latent image specks. Development is "compact" when initiated by a large number of latent image specks scattered over the surface of a grain, while irregular development results from initiation by one, or a few, specks. Thus the fall of density with increasing exposure beyond that required for maximum density is due to increase in the number of surface specks, while the rise at heavier exposures is due to reduction in speck number owing to the onset of true solarization. In conformity with this interpretation the effects are more pronounced with short than with long exposure times.

The relationship between the above effects and true solarization and re-reversal is illustrated for the emulsion which prompted this study, and is also discussed briefly in general terms.     

Magnetic-type resonance in nonmagnetic line wire excited by surface plasmons in microwave range

A magnetic resonance microwave response has been detected and identified in a structure of parallel nonmagnetic wires or a single line wire perpendicular to the electric field of a plane electromagnetic wave in the case where the wires are arranged near an array (grating) of resonant surface-plasmon-generating elements and oriented along the direction of wave propagation. A giant resonance is observed for a definite (resonance) length of the wire(s) in a certain frequency range corresponding to the existence of surface plasmons (below the resonance frequency of the plasmon-generating array). It is suggested that the magnetic response of the wire(s) is due to the excitation of resonance currents by the magnetic field of surface plasmons. Using the observed phenomena, it is possible to obtain new magnetic metamaterials (in particular, those possessing simultaneously negative effective dielectric permittivity and magnetic permeability) tunable in a broad frequency range.     

Fortran 90模拟C++函数重载

函数重载是C++语言多态性的重要体现,也是面向对象程序设计的常用方法,Fortran 90不支持面向对象程序设计,但已经具有一些现代语言特征,为模拟面向对象程序设计提供可能,在分析C++函数重载机制的基础上,通过对Fortran 90相关语言元素、工具的探索,提出利用Fortran 90新增加的接口块这一利器模拟C++函数重载的方法,实例运行结果表明,该方法现实可行,从而扩展Fortran 90的应用范围,并为模拟面向对象程序设计提供思路。     

考虑两类装配式节点非线性行为的框架结构响应分析

装配式混凝土框架结构在中国应用广泛,目前主要按“等同现浇”原则进行设计和结构计算。然而,由节点非线性行为不同引起的结构响应差异不可忽视。该文考虑到两类典型的装配式节点非线性行为与现浇节点的区别,研究了这些区别对框架结构地震响应产生的影响。对于效仿连接节点,由其构造形式分析了节点的受力机制,并据此解释了其与现浇节点在试验现象上的差异,提出了两类节点无量纲化的滞回模型,并通过已有试验结果验证了所提模型的合理性。对于非效仿连接节点,从设计角度出发,系统研究了后张无粘结混合装配预应力混凝土节点的力学行为。研究内容采用动力时程分析方法,从结构位移响应、梁柱延性需求、残余变形等方面揭示了装配式框架与现浇框架的差异。该文的研究结果对装配式框架结构在高地震烈度区的应用具有实用的参考价值。     

变频空调压缩机频率控制算法的设计与研究

应用常见的几种模糊控制算法对变频压缩机进行控制研究，并使用理想房间温度模型进行仿真。在此基础上，提出了一种带自调整函数的模糊控制算法，仿真和对比实验结果证明，系统响应快、超调小，进一步改善了变频空调的控制品质。     

用聚乙烯片连续测量太阳紫外辐射的研究

本文对用聚乙烯作为潜在的廉价的光接收体以测量抵达地面的太阳紫外辐射进行了研究。发现含特定添加剂的厚度0.2mm的聚乙烯片可用来连续累积测定波长范围300～400hm的太阳与天空紫外光的辐照量,按照光电法仪器的订定,投射到聚乙烯片曝露表面的太阳与天空紫外光的辐照量是归属为由聚乙烯的光降解导致生成的末端乙烯基的909cm~(-1)红外吸收峰的吸光度增量的幂函数。同时聚乙烯的光降解亦与其他气候因素有关,但它们的影响可以通过由曝露期间的平均气温建立的经验式予以修正,用本法在广州进行的全年连续监测结果表明,它的测量值与以光电转换为工作原理的仪器之测量值比较,偏差小于10％。