An optical gas sensor based on ellipsometric readout

A gas sensor system based on ellipsometric readout is presented. It includes a gas chamber and a compact ellipsometer operated in off- mode. Small, low-cost optical components are used to demonstrate that this advanced methodology can be implemented in simplified instrumentation. The off- ellipsometric sensing principle and transducer mechanisms of the sensing layers, as well as the instrumentation, are described. The application of the sensor system is exampled with experimental results on low-concentration alcoholic gases (methanol, ethanol, and 2-propanol) using porous silicon as a sensing layer. Optimization of the optics of the sensor system, improvement of sensitivity or alteration of selectivity by modification of sensing layers, and multisensing by using several ellipsometric units in parallel are discussed.     

Active aberration correction for the writing of three-dimensional optical memory devices

We describe an active optical system that both measures and corrects the aberrations introduced when writing three-dimensional bit-oriented optical memory by a two-photon absorption process. The system uses a ferroelectric liquid-crystal spatial light modulator (FLCSLM) configured as an arbitrary wave-front generator that is reconfigurable at speeds as great as 2.5 kHz. A method of aberration measurement by the FLCSLM wave-front generator is described. The same device is also used to correct the induced aberrations by preshaping the wave fronts with the conjugate phase aberration as well as to scan the focal spot in three dimensions. Experimental results show the correction of both on- and off-axis aberrations, allowing the writing of data at depths as great as 1 mm inside a LiNbO3 crystal.     

Molecular anions of uranium fluorides and oxides: First principle based relativistic calculations

Structures and energetics of the molecular anions UF ₆ ^? , UF_5/?, UF_4/?, UO_3/t-, and UO_2/t- were calculated using the density functional theory within the framework of the precision two-component relativistic pseudopotential model. Differences in the structures of the ions and the corresponding neutral molecules were analyzed, and the adiabatic electron affinities of these molecules were estimated.     

Optical image hiding with silhouette removal based on the optical interference principle

The earlier proposed interference-based encryption method with two phase-only masks (POMs), which actually is a special case of our method, is quite simple and does not need iterative encoding. However, it has been found recently that the encryption method has security problems and cannot be directly applied to image encryption due to the inherent silhouette problem. Several methods based on chaotic encryption algorithms have been proposed to remove the problem by postprocessing of the POMs, which increased the computation time or led to digital inverse computation in decryption. Here we propose a new method for image encryption based on optical interference and analytical algorithm that can be directly used for image encryption. The information of the target image is hidden into three POMs, and the silhouette problem that exists in the method with two POMs can be resolved during the generation procedure of POMs based on the interference principle. Simulation results are presented to verify the validity of the proposed approach.     

Spectral multi-demultiplexer based on a three-dimensional holographic wedge-shaped optical element

An analysis is made of the possibility of developing a new holographic multi-demultiplexer using the principle of a series device constructed as a single three-dimensional optical wedge-shaped element. Pis’ma Zh. Tekh. Fiz. 24, 79–86 (September 26, 1998)     

Closed-form inversion of the reflection ellipsometric function of a film-substrate system: absorbing-substrate optical constant

A closed-form inversion expression for obtaining the optical constant (complex refractive index) of the substrate of an absorbing-film-absorbing-substrate system from one reflection ellipsometry measurement is derived. If, in addition, the film thickness is to be determined, a second measurement at another angle of incidence may or may not be used. The derived formula does not introduce errors itself, and tolerates errors in input variables very well. Random and systematic errors in the measured ellipsometric parameters do not affect the value obtained for the optical constant of the substrate: it is always the true value to two decimal places. Two examples in ellipsometry and in the design of reflection-type optical devices, one each, are presented and discussed. In addition, experimental results for a commercially available wafer are also presented. Two other closed-form inversion expressions for obtaining the optical constant of the substrate from two and three measurements are also presented and briefly discussed.     

基于主成分分析的温度对Flash存储器电参数一致性分析

针对温度对闪存(Flash)存储器电参数的一致性影响特性尚不清晰、一致性分析评价方法不明确等问题,提出采用主成分分析法对Flash存储器中的不同电参数进行一致性分析。实验结果表明:温度会对Flash存储器的电参数漂移产生影响,随着温度的升高或降低,Flash存储器电参数的主成分均值与方差具有相反的变化趋势。基于主成分分析法为Flash存储器的电参数一致性评价提供一种手段,温度对其电参数一致性的影响特性对保障产品的质量及改进设计具有指导意义。     

A damage model based on Kelvin eigentensors and Curie principle

A general anisotropic damage model is developed that accounts for the thermodynamics of irreversible processes in the framework of generalized standard materials and Kelvin tensor decomposition. Damage is described by fourth-rank tensors, one per eigenspace of the initial stiffness tensor. Their number thus ranges from two for an initially isotropic material to six for an initially triclinic material. The yield criteria are expressed in terms of a limiting energy for each eigenspace. The second-rank eigentensors (at most six) of the fourth-rank damage tensors define the direction of influence of the damage, while the associated eigenvalues characterize its intensity. These eigentensors evolve during loading, inducing an evolution of the symmetry group of the elastic tensor subject to the constraints of the Curie principle.     

一种基于生物免疫原理的入侵检测新模型

入侵检测系统可以从生物免疫系统的很多特点中得到启发，文中利用生物免疫原理设计了一个新的入侵检测框架模型，该框架在传统信息传输网基础上构建了免疫淋巴网，用来监控和管理传统传输网的行为。模型中还应用了阴性选择、克隆选择等免疫算法，使得该模型对于入侵检测问题有较好的敌我识别功能。     

On crushing response of the three-dimensional closed-cell foam based on Voronoi model

The crushing response of the three dimensional closed-cell foams is investigated using mesoscale numerical models based on Voronoi tessellation. The crushing stress at the impact and stationary sides of the Voronoi structures are obtained. The effects of the impact velocity, the cell shape irregularity degree, the relative density, inertia of cell walls and the dependence of the base material on the crushing stress are discussed. Meanwhile, the contention of the rate dependency of cellular materials are expounded by the comparison of numerical results of the Voronoi model and solid continuum model as well as the shock wave theory, in which the densification strain and plateau stress are calculated using the energy absorption efficiency approach.     

Fast auto-focus scheme based on optical defocus fitting model

An optical defocus fitting model-based (ODFM) auto-focus scheme is proposed. Considering the basic optical defocus principle, the optical defocus fitting model is derived to approximate the potential-focus position. By this accurate modelling, the proposed auto-focus scheme can make the stepping motor approach the focal plane more accurately and rapidly. Two fitting positions are first determined for an arbitrary initial stepping motor position. Three images (initial image and two fitting images) at these positions are then collected to estimate the potential-focus position based on the proposed ODFM method. Around the estimated potential-focus position, two reference images are recorded. The auto-focus procedure is then completed by processing these two reference images and the potential-focus image to confirm the in-focus position using a contrast based method. Experimental results prove that the proposed scheme can complete auto-focus within only 5 to 7 steps with good performance even under low-light condition.     

Development of a three-dimensional finite-element model for high-temperature superconductors based on the H-formulation

Finite-element models are a powerful and widely used tool for evaluating the ac losses of HTS tapes and wires as well as of assemblies such as cables and coils. The H-formulation, which uses the magnetic field components as state variables, has proved to be an efficient implementation to solve 2-D problems, involving infinitely long or axially-symmetric geometries; an excellent agreement with experimental data has been found in many cases. However, the simulation of certain applications requires a full 3-D model. In this paper we report on the development of a 3-D model based on the H-formulation. We describe the implementation of Maxwell equations, the imposition of current constraints and we discuss the issues related to meshing 3-D volumes. The model is validated by comparing the results with those obtained with 2-D models in cases that can be investigated in 2-D; then, it is used to simulate cases that can be handled only in 3-D.     

基于手眼模型的三维激光雷达外参数标定

无人车三维激光雷达与GPS/INS组合导航系统融合使用,需要对两者之间的相对位姿进行标定。针对车辆运动过程点云畸变的现象,提出了一种单帧点云中激光扫描点坐标修正方法。针对标定问题,建立了标定模型,提出了一种基于ICP算法和手眼标定模型及最小二乘法进行外参数标定的方法。通过蒙特卡罗仿真实验,对该方法的有效性和精度进行了仿真和验证。在实验室JJUV-6无人车平台上进行标定试验,得到两者之间的三维位姿关系。对比标定前后三维点云重建效果,点云重叠度接近于配准效果。基于应用的目的,基本满足二维地图构建和三维环境重建的需求。     

基于塑性理论的形状记忆合金本构模型、试验和数值模拟

通过拉伸试验,研究了超弹性形状记忆合金（SMA）丝在不同应变幅值反复加卸载条件下的滞回变形行为。在测得试验数据的基础上,针对目前广泛使用的SMA Graesser＆Cozzarelli模型仅描述了小应变情况下SMA特性,而在大应变下SMA马氏体的硬化特性不能得到描述的问题,提出了修正的SMA本构模型,并把模型拟合结果和实验数据进行了比较分析。结果表明,模型数值拟合结果和试验数据吻合很好,可以很好地描述SMA在不同应变幅值下的应力-应变关系;且模型形式简单,概念明确,参数容易得到,具有一定的工程应用价值。     

Simulation for intergranular stress corrosion cracking based on a three-dimensional polycrystalline model

In stress corrosion cracking of stainless steel, two different schemes of analysis of crack growth should be employed for the crack initiation phase and crack growth phase. However, this distinction is not clear-cut in the crack initiation phase, since the vicinity of the pre-existing crack is a preferential area of crack initiation due to concentration of stress. Therefore, initiation of crack tends to occur at the tip of a pre-existing crack and it can be regarded as crack growth. In this study, the contribution of this type of apparent crack growth, referred to as initiation dominant growth (IDG), to crack growth was evaluated by a Monte Carlo simulation. A three-dimensional polycrystalline body was generated by Voronoi tessellation. The cracks were assumed to grow along grain boundaries. The effect of stress-concentration around pre-existing cracks was taken into account by applying the finite element method. Initiation and propagation of the cracks were modeled based on concepts of damage mechanics. The simulation could reproduce the changes in number of cracks and the sum of crack length obtained experimentally as well as preferential crack initiation at the stress-concentration zones and suppression of crack initiation in stress-shielding zones. It was shown that the contribution of IDG to crack growth was large for small cracks, and that damage by crack initiation accounted for more than 50% of total damage even when the length of a crack was 0.6 mm at the surface.     

A new sliding scale principle and the spectroscopic ADC based on this principle

A new sliding scale averaging scheme is proposed. For a N-bit ADC the number of bits M for a sliding scale may be increased up to N−2. At the same time the full number of channels can be used, which is impossible for the conventional sliding scale method. Experiments have been carried out to verify the principle.     

Unidimensional model of polarisation changes in piezoelectric ceramics based on the principle of maximum entropy production

This paper presents a one-dimensional model for piezoelectric ceramics developed using the principle of maximum entropy production. Changes in polarisation are assumed to occur only as a consequence of domain wall movement. Such movement, it is assumed, can occur as a consequence of applied load or applied electric field. Simulations of experiments conducted by Fang and Li (J Mater Sci, 34:4001–4010, 1999) are presented and show good agreement with the experimental results. This suggests that abrupt domain switching (known to occur in piezoelectric ceramics at very high applied stresses and fields) may have less influence on the dissipative behaviour of piezoelectric sensors and actuators than previously thought.     

超弹性形状记忆合金的神经网络连续本构模型

对超弹性形状记忆合金(SMA)丝在不同应变幅值和荷载速率下进行加卸载单轴拉伸试验,分析其滞回特性随环境因素的变化规律。将径向基函数神经网络(RBFNN)和Graesser模型结合起来,Graesser模型参数取自试验曲线,能由数学式确定的模型参数和应变幅值、荷载速率一起作为网络的输入信息,不能由数学式确定的模型参数作为输出神经元。数值计算表明,RBFNN可以精确地预测Graesser模型参数,且计算的SMA应力-应变曲线与Graesser模型结果吻合很好。