高温度梯度定向凝固温度场的实验测定及微机数据处理

本文简介了自制高性能,高温度梯度定向凝固实验装置和技术。给出一种实验测定高温度梯度定向凝固,液、固相区温度场的新方法,并研制了实验数据转换和处理的计算程序。本方法不仅提高了温场的测量精度,而且还大大提高了实验数据的处理速度。通过误差分析,论证了本方法可显著地提高界面液相温度梯度的测量精度。     

Nanoscale gradient copolymer films via single-step deposition from the vapor phase

Organic gradient materials are an inherent part of many functional structures in the natural world. Synthetic organic materials, like polymers, are thus the perfect choice to artificially recreate these structures for functional purposes. This work reports on new high-quality gradient copolymer films via large-area deposition from the vapor phase and circumvents thus problems related to current wet chemistry approaches. It enables furthermore for the first time the transfer of this gradient approach to the nanoscale, introducing a new class of organic gradient nanomaterials. This facilitates completely new organic gradient functionality on the nanoscale, not achievable with materials currently in use. Fully functional gradient films of 21 nm have been synthesized, which open up new pathways for many application fields. Their versatility is demonstrated by some application examples ranging from every day life (adhesion of PTFE in frypans) to advanced subwavelength devices on large-area substrates as well as complex geometries.     

一种特殊烧结技术对梯度结构硬质合金性能影响的研究

研究了分段烧结制备梯度结构硬质合金技术以及粘结剂含量对梯度硬质合金的力学性能、梯度结构的影响.测试了梯度硬质合金刀片的切削性能.结果表明,分段烧结技术能成功地制备梯度结构硬质合金,且随着钴含量增多,合金梯度层厚度增厚,梯度结构更明显;合金的强度与磁饱和提高.切削试验表明:具有梯度结构涂层硬质合金刀片的切削性能比无梯度结构涂层硬质合金刀片的切削性能更为优良.达到同一磨损高度VB=0.15mm时,前者的切削寿命较后者提高了近一倍.     

High-Precision Automatic Control of the Gradient of the Index of Refraction of Glass Plates

A method and optical interference circuit intended for exact gradient measurements of the parameters of glass elements are described, and an estimation of the absolute measurement error of the gradient of the index of refraction of thin glass plates is conducted.     

Effect of the growth conditions on the spatial features of Re nanowires produced by directional solidification

The effects of the solidification parameters, such as growth rate and temperature gradient, on the distance and diameter of Re nanowires have been examined. Both the spacing and diameter increase with decreasing growth rate and temperature gradient, respectively. The ratio of fiber spacing to diameter is 9.1. In addition, it was demonstrated that the temperature gradient influences interface undercooling in the same way as the growth rate and may be used as an additional parameter to control fiber spacing and diameter.     

磁性流体在均匀梯度磁场中的摩擦学性能测试研究

基于均匀梯度磁场能较准确反映出磁场影响磁性流体摩擦性能的认识,制造了一对产生均匀梯度磁场的线圈安置于改造后的UMT3摩擦试验机中。选用聚α-烯烃合成油基磁性流体为润滑油,测试不同均匀梯度磁场大小、不同载荷和不同往复频率下的磁性流体摩擦学性能。结果显示：载荷、往复运动频率一定时,磁性流体的摩擦系数随均匀梯度磁场的增大而减小;载荷、均匀梯度磁场一定时,磁性流体的摩擦系数随随往复运动频率的增大而减小;磁性流体在均匀梯度磁场中比无磁场中具有更高的承载能力和更长的耐磨寿命。     

凸组合投影算法中的组合因子对算法效率的影响

在求解生产生活中各类实际问题的优化模型的算法研究中,投影梯度算法在解决凸约束最优化问题上一直被学者所重视．本文考虑凸组合投影算法求解凸约束最优化问题,在此凸组合投影算法中,由投影梯度法得到的点与上一步迭代点的凸组合得到新的迭代点．此算法不仅利用投影算法得到的点的信息而且也利用了前一步点的信息．进一步,通过数值实验分析凸组合算法的效率及凸组合因子对算法的影响．数值试验结果表明,这种凸组合算法总体比原来投影梯度法更稳定,而且这种凸组合算法在适当的凸组合因子下较投影梯度法收敛更快．     

梯度微结构对金属玻璃拉伸增韧的影响

本文通过数值模拟分析了梯度微结构对Ti₄₆Zr₂₀V₁₂Cu₅Be₁₇金属玻璃（Metallic Glass,MG）拉伸性能的影响。将自由体积理论以UMAT子程序形式导入ABAQUS中,模拟分析MG基体中剪切带的演化。在此模型中,颗粒和初始自由体积被以各种梯度方程的形式分布于MG基体中,对材料模型施加单轴拉伸荷载。结果表明：含有颗粒按凹槽状梯度分布的MG基复合材料拉伸塑性最好,并且变形呈现颈缩现象;对于初始自由体积呈凸形分布的MG塑性被很好改善;当改变自由体积梯度分布程度时,梯度越小,塑性提高越明显;而就颗粒来说,两侧密集区层数越多,变形中越不容易出现穿透试样的主剪切带。     

In situ pulsed-field gradient NMR determination of the size of oil bodies in vegetable seeds. Analysis of the effect of the gradient pulse length

We report a pulsed-field gradient NMR study of the size of the oil bodies in lettuce seeds. The pulsed-field gradient spin-echo method (PFGSE) was applied to measure the self-diffusion coefficient of triacylglycerol molecules (TAG) inside the oil bodies. The confined nature of TAG diffusion is used to determine the size dispersion of the oil bodies. At long diffusion time, we measure a spin-echo attenuation that is related to the form factor of the confining volumes in the reciprocal q space, where q is proportional to the product of the gradient intensity and the length of the pulse gradient. Specific care was taken in analyzing the influence of the gradient pulse length delta on the shape of the PFGSE decay in order to construct the function corresponding to the short gradient pulse approximation (SGP). The SGP model gives an analytical framework for the PFGSE signal that enables the size distribution of the oil bodies to be determined. The SGP function was unambiguously obtained by varying the gradient pulse length delta in order to linearly extrapolate at delta = 0 the SGP limit. In this work, we also consider the Gaussian phase distribution (GPD) assumption that is often used to analyze confined diffusion experiments. Although the GPD assumption is known to be inaccurate in predicting the fine structure of the PFGSE function in q space, we point out that in the present case it can be used to take into account the finite value of delta. A log-normal distribution of the radius values was assumed in simulating the PFGNMR experiments since this type of distribution is observed in vegetable seeds by transmission electronic microscopy. From a practical and experimental standpoint, the NMR measurements reported here require no specific treatment of the seeds and the size of oil bodies is determined "in situ" on seeds poured into the NMR tube.     

In situ analysis of three-dimensional electrolyte convection evolving during the electrodeposition of copper in magnetic gradient fields

A novel three-dimensional particle tracking velocimetry technique was used to examine the flow during electrodeposition of Cu. For the first time electrode-normal, circumferential, and radial velocities were spatially resolved during deposition in superimposed low and high magnetic gradient fields. In this way the complex interaction of magnetic field gradient force and Lorentz force induced convective effects could be measured and analyzed. Magnetic field gradient force induced electrolyte flow was detected only in high gradient magnetic fields, and it was found to be directed toward regions of gradient maxima. Since this electrode-normal flow causes enhanced transport of Cu(2+) ions from the bulk electrolyte to those regions of the working electrode where maxima of magnetic gradients are present, a structured deposit is formed during diffusion-limited electrodeposition. Lorentz force driven convection was observed during deposition in the low and the high magnetic gradient experiments. The overall fluid motion and the convection near the working electrode were determined experimentally and discussed with regard to the acting magnetic forces and numerical simulations.     

Effect of a composition gradient on the magnetoelastic sensitivity of Ni-Fe films

Measurements of the magnetoelastic sensitivity of electrodeposited 1 μ cylindrical Ni-Fe films indicate that the magnetostriction of these films becomes more positive upon annealing. A composition gradient has been observed through the thickness of these films. In addition, electron diffraction results indicate that the composition gradient is substantially reduced during an anneal at 250 °C. To understand the change in magnetoelastic sensitivity the effect of the composition gradient has been considered. The change in the magnetoelastic sensitivity due to the elimination of the composition gradient is shown to be in agreement with observed changes.     

Reconstruction and assessment of the least-squares and slope discrepancy components of the phase

The concept of slope discrepancy developed in the mid-1980's to assess measurement noise in a wave-front sensor system is shown to have additional contributions that are due to fitting error and branch points. This understanding is facilitated by the development of a new formulation that employs Fourier techniques to decompose the measured gradient field (i.e., wave-front sensor measurements) into two components, one that is expressed as the gradient of a scalar potential and the other that is expressed as the curl of a vector potential. A key feature of the theory presented here is the fact that both components of the phase (one corresponding to each component of the gradient field) are easily reconstructable from the measured gradients. In addition, the scalar and vector potentials are both easily expressible in terms of the measured gradient field. The work concludes with a wave optics simulation example that illustrates the ease with which both components of the phase can be obtained. The results obtained illustrate that branch point effects are not significant until the Rytov number is greater than 0.2. In addition, the branch point contribution to the phase not only is reconstructed from the gradient data but is used to illustrate the significant performance improvement that results when this contribution is included in the correction applied by an adaptive optics system.     

On the accuracy of quantitative measurements of the local surface potential

The region of the main potential drop in a sharp p ⁺−n ⁺ junction in GaAs has been studied using the conventional and gradient scanning Kelvin probe force microscopy (KPFM) techniques. It is shown that the gradient method offers advantages for quantitative measurements. An algorithm for the program implementing the gradient KPFM method on standard commercial atomic-force microscopes is proposed. It is established that the layer of adsorbed water contributes to the measured width of the main potential drop region.     

Magnetic resonance imaging gradient coil design by combiningoptimization techniques with the finite element method

In this paper, the optimization techniques of complex method, steepest descent, and conjugate gradient are investigated in terms of their convergence behaviors. The conjugate gradient method is then combined with finite element analysis techniques to develop a magnetic resonance imaging (MRI) G_z gradient coil design strategy which maximizes the field linearity within a specified region of interest. It is found that conjugate gradient optimization in conjunction with the finite element method is a powerful and flexible coil design approach with the potential to incorporate complex coil geometries, inhomogeneous media, and transient current excitation     

飞机发动机用梯度封严涂层的研究

为了进一步提高封严涂层与基体材料之间的附着性能,对梯度封严涂层与1Cr18Ni9Ti不锈钢之间的附着性能进行了探讨。采用拉开法测试梯度封严涂层与1Cr18Ni9Ti不锈钢之间的附着强度,并用冷热循环法测试梯度封严涂层的耐冷热循环性能,与普通封严涂层的附着强度及耐冷热循环性能进行比较,结果发现：梯度封严涂层的附着强度比普通封严涂层的附着强度有提高,而且梯度封严涂层的耐冷热循环性能明显优于普通封严涂层。     

Gradient crystal plasticity as part of the computational modelling of polycrystals

This paper describes how gradient hardening can, in a thermodynamically consistent fashion, be included into a crystal plasticity model. By assuming that the inelastic part of the free energy includes contributions from the gradient of hardening along each slip direction, a hardening stress due to the second derivative of the hardening along each slip direction can be derived. For a finite element model of the grain structure a coupled problem with displacements and gradient hardening variables as degrees of freedom is thereby obtained. This problem is solved using a dual mixed approach. In particular, an algorithm suitable for parallelization is presented, where each grain is treated as a subproblem. The numerical results show that the macroscopic strength increases with decreasing grain size as a result of gradient hardening. Finally, the results of different prolongation assumptions, i.e. how to impose the macroscopic deformation gradient on a representative volume element, are compared. Copyright © 2007 John Wiley & Sons, Ltd.     

The kinetics of the crystallization in bismuth-containing heterosystems Al-In-Sb-Bi and Ga-As-P-Bi

The kinetics of the crystallization of multicomponent bismuth-containing heterosystems Al-In-Sb-Bi and Ga-As-P-Bi in the field of a temperature gradient is investigated. The possible mechanism of the crystallization of bismuth-containing multicomponent solid solutions A^III B^V in the field of a temperature gradient is established. It is shown that temperature dependence of the speed of zone movement at the gradient crystallization in the given systems exhibits a hysteresis.     

Investigation of the effect of stress gradient along the thickness of a plane specimen on cyclic durability

A procedure is developed for fatigue testing of plane specimens with off-center, zero cycle, tensile loading. In order to study the effect of stress gradient on durability, the procedure facilitates the stress gradient to be varied along the thickness of a specimen with the maximum stress being fixed on one of the specimen's surfaces. The dependence of durability on stress gradient is obtained for a standard-size aluminum alloy specimen.Translated from Problemy Prochnosti, No. 2, pp. 91–94, February, 1992.     

粘结相梯度结构硬质合金的研究现状

概述了国内外梯度结构硬质合金的发展,介绍了采用正碳烧结工艺制备WC-Co梯度结构硬质合金的工艺和梯度形成机理,并列举了粘结相梯度结构硬质合金的实际应用,展望了该合金的应用开发前景.     

A gradient‐only line search method for the conjugate gradient method applied to constrained optimization problems with severe noise in the objective function

A new implementation of the conjugate gradient method is presented that economically overcomes the problem of severe numerical noise superimposed on an otherwise smooth underlying objective function of a constrained optimization problem. This is done by the use of a novel gradient‐only line search technique, which requires only two gradient vector evaluations per search direction and no explicit function evaluations. The use of this line search technique is not restricted to the conjugate gradient method but may be applied to any line search descent method. This method, in which the gradients may be computed by central finite differences with relatively large perturbations, allows for the effective smoothing out of any numerical noise present in the objective function. This new implementation of the conjugate gradient method, referred to as the ETOPC algorithm, is tested using a large number of well‐known test problems. For initial tests with no noise introduced in the objective functions, and with high accuracy requirements set, it is found that the proposed new conjugate gradient implementation is as robust and reliable as traditional first‐order penalty function methods. With the introduction of severe relative random noise in the objective function, the results are surprisingly good, with accuracies obtained that are more than sufficient compared to that required for engineering design optimization problems with similar noise. Copyright © 2004 John Wiley & Sons, Ltd.