Pd-C高温共晶点复现装置研制

主要针对Pd-C高温共晶点复现装置的组成进行介绍,其中包括复现用高温均热炉炉体、温度控制系统、真空泵、充气保护装置、水冷系统、复现用的石墨坩埚、二等B型标准热电偶和Pt-Pd热电偶等。针对石墨坩埚的灌注和共晶点复现过程进行了描述,根据复现的试验数据进行了相应的分析。     

Similarity solutions for slender dry patches with thermocapillarity

The lubrication approximation is used to investigate slender dry patches in an infinitely wide film of viscous fluid flowing steadily on an inclined plane that is either heated or cooled relative to the surrounding atmosphere. Four non-isothermal situations in which thermocapillary effects play a significant role are considered.Similarity solutions describing a thermocapillary-driven flow with a dry patch that is widening or narrowing due to either gravitational or surface-tension effects on a non-uniformly heated or cooled substrate are obtained, and examples of these solutions, when the substrate temperature gradient depends on the longitudinal coordinate according to a general power law, are presented. When gravitational effects are strong, the solution contains a free parameter, and for each value of this parameter there is a unique solution representing both a narrowing pendent dry patch and a widening sessile dry patch, whose transverse profile has a monotonically increasing shape. When surface-tension effects are strong, the solution also contains a free parameter, and for each value of this parameter there is both a unique solution representing a narrowing dry patch, whose transverse profile has a monotonically increasing shape, and a one-parameter family of solutions representing a widening dry patch, whose transverse profile has a capillary ridge near the contact line and decays in an oscillatory manner far from it.Similarity solutions are also obtained for both a gravity-driven and a constant-surface-shear-stress-driven flow with a dry patch that is widening or narrowing due to thermocapillarity on a uniformly heated or cooled substrate. The solutions in both cases contain a free parameter, and for each value of this parameter there is a unique solution representing both a narrowing dry patch on a heated substrate and a widening dry patch on a cooled substrate, whose transverse profile has a monotonically increasing shape.     

The surface tension of HFC refrigerants and mixtures

The surface tension of the refrigerants R32, R125, R134a, R143a and R152a, as well as the binary refrigerant mixtures R32-R125, R32-R134a, R125-R134a, R125-R143a, R125- R152a, R143a-R134a and R134a-R152a, and the commercially available ternary mixtures R404A and R407C was measured across the temperature range from −50 to 60°C using a measuring unit based on the capillary rise method. Different formulations for calculation of the surface tension of the binary and ternary mixtures on the basis of the surface tension of the pure refrigerants were tested. With an approach based on mass proportions in the mixture, a good correspondence between the measured and calculated values was achieved.     

Three-dimensional stress and deformation fields around flat and slant cracks under remote Mode I loading conditions

This paper investigates the phenomenon of slant fracture observed in stable tearing tests of many ductile materials, where an initially flat crack, loaded under remote Mode I conditions, tends to grow into a slant crack and stay in the slant configuration until final fracture. In an effort to identify potential reasons why cracks prefer to grow in a slant manner, three-dimensional finite element analyses of crack-front stress and deformation fields in Arcan-type specimens containing a flat or slant crack are performed under elastic–plastic and remote Mode-I loading conditions. In particular, the crack-tip opening displacement (COD) at a position behind the crack tip, the mean stress, the effective stress, and a constraint factor (defined as the ratio of the mean stress and effective stress) are studied and compared for the two types of cracks. Analysis results reveal several stress/deformation field variations around flat and slant cracks under identical remote loading conditions. First, close to the crack front, the COD of a slant crack is greater than that of a flat crack. Second, at the specimen’s mid-plane, a flat crack leads to a higher constraint value ahead of the crack than a slant crack. Third, the effective stress ahead of a slant crack is greater than that ahead of a flat crack, especially close to the crack front. The above results seem to suggest that slant fracture may be preferred because a slant crack enhances the driving force in the form of a higher near-tip COD value and because a shearing type of failure is promoted in the case of a slant crack compared to a tensile type of failure in the case of a flat crack.     

Multi-product continuous plant scheduling: combination of decomposition,genetic algorithm,and constructive heuristic

We propose a polylithic method for medium-term scheduling of a large-scale industrial plant operating in a continuous mode. The method combines a decomposition approach, a genetic algorithm (GA) and a constructive MILP-based heuristic. In the decomposition, decisions are made at two levels, using the rolling horizon approach. At the upper level, a reduced set of products and the time period is chosen to be considered in the lower level. At the lower level, a short-term scheduling MILP-model with event-based representation is used. A heuristic solution to the lower level problem is found using a constructive Moving Window heuristic guided by a genetic algorithm. The GA is applied for finding efficient utilisation of critical units in the lower level problem. For solving the one unit scheduling problem, a parallel dynamic programming algorithm is proposed. Implementation of the dynamic programming algorithm for a graphics processing unit (GPU) is incorporated in the GA for improving its performance. The experimental study of the proposed method on a real case of a large-scale plant shows a significant improvement of the solution quality and the solving time comparing to the pure decomposition algorithm proposed in the earlier study, and confirmed suitability of the proposed approach for the real-life production scheduling. In particular, the reduction of the number of changeovers and their duration in the obtained solution as well as the CPU time of solving the problem was about 60% using the new approach.     

摩擦调节剂抑制钢轨波磨的机理研究

基于轮轨之间的摩擦耦合自激振动引起钢轨波磨的观点,论文建立了车辆稳态通过小半径曲线时由轮对－钢轨－轨枕组成的轮轨系统有限元弹性振动摩擦自激振动有限元模型,用ABAQUS软件对该模型的运动稳定性进行了分析,重点研究了轮轨摩擦系数和蠕滑力-蠕滑率曲线负斜率对轮轨系统摩擦自激振动的影响。计算结果显示,轮轨摩擦系数对轮轨摩擦自激振动有重要影响,当控制摩擦系数 时可以消除钢轨磨耗型波磨,蠕滑力-蠕滑率曲线负斜率对钢轨波磨有显著影响。     

单源随机向量及其在随机分析中的应用

受正交展开思想的启发,定义了单源随机向量,证明了该文提出的单源随机向量的独立性,并就单源随机向量在随机分析中的应用进行了阐述,算例计算表明了这种单源分析方法的有效性。用单源随机向量表达复杂的随机系统,仅需1个基本随机变量,这对大幅减少随机分析的难度和计算量有重要意义,对基于相关理论的随机分析,如随机结构、随机场、随机过程以及复合随机问题,该方法都有应用价值。随机系统用单源随机向量模拟以后,相应的分析方法还有待进一步深入研究。     

Rapid inversion of eddy current data for conductivity and thickness of metal coatings

A feature-based method that determines the thickness and electrical conductivity of a coating on a metal plate from the change in the frequency-dependent impedance of an eddy-current probe coil is presented. Recently a least-squares solution of this problem was presented, which, however, requires approximately 20 CPU minutes on a DEC 5000 work station for the analysis of each set of measurements. We show that a feature-based approach can reduce the time to a few seconds on the same processor. We start by showing that a three-parameter scaling of the resistive component of the impedance change vs. frequency leads to a simple and nearly universal curve. Consequently these parameters provide a simple and compact way of expressing the data. Next, we show that the three scaling parameters can be used to construct a look-up table that determines the conductivity and thickness of the coating. Finally, we test the method using experimental data.     

A new reliability measure based on specified minimum distances before the locations of random variables in a finite interval

A new reliability measure is proposed and equations are derived which determine the probability of existence of a specified set of minimum gaps between random variables following a homogeneous Poisson process in a finite interval. Using the derived equations, a method is proposed for specifying the upper bound of the random variables' number density which guarantees that the probability of clustering of two or more random variables in a finite interval remains below a maximum acceptable level. It is demonstrated that even for moderate number densities the probability of clustering is substantial and should not be neglected in reliability calculations.In the important special case where the random variables are failure times, models have been proposed for determining the upper bound of the hazard rate which guarantees a set of minimum failure-free operating intervals before the random failures, with a specified probability. A model has also been proposed for determining the upper bound of the hazard rate which guarantees a minimum availability target. Using the models proposed, a new strategy, models and reliability tools have been developed for setting quantitative reliability requirements which consist of determining the intersection of the hazard rate envelopes (hazard rate upper bounds) which deliver a minimum failure-free operating period before random failures, a risk of premature failure below a maximum acceptable level and a minimum required availability. It is demonstrated that setting reliability requirements solely based on an availability target does not necessarily mean a low risk of premature failure. Even at a high availability level, the probability of premature failure can be substantial. For industries characterised by a high cost of failure, the reliability requirements should involve a hazard rate envelope limiting the risk of failure below a maximum acceptable level.     

Development of Catalytic Converters Using Detonation Spraying

One of the trends in hydrogen power engineering is the development of devices for the preparation of synthesis gas by the catalytic reforming of a hydrocarbon feedstock. Studies show the advantages of catalytic converters based on a modular catalyst support with a honeycomb-type structure produced from a metal foil, both sides of which are coated with highly porous oxide ceramics. The drawback of this design is a poor ability of the coating to withstand high-temperature operating conditions. The coating may detach from the substrate because of the difference in thermal expansion coefficients between the metal foil and the ceramic coating. Besides, a corrosion of metal foil takes place. The result of the present study is the development and application of a two-step coating method, which allows significantly increasing the service life of the catalyst supports. At the first step, a low-porosity ceramic layer is deposited on a metal foil by detonation spraying. At the second step, a high-porosity layer of a ceramic catalyst is deposited from suspension. In this work, the peculiarities of the detonation spraying of the ceramic coating on a metal foil and the design of the obtained catalytic converter have been addressed.     

Statistical Analysis of Macromolecular Chains in the Space Filled by Nanoparticles

The paper presents a combination of worm-like chain numerical models and one with a finite set of nano-particles. The primary objective of the models was to analyze the distribution of space in a system filled by particles. Information on the distribution of space was compared to properties of chains inside the set of particles. The set of nanoparticles was constructed with a tool generating a finite set of particles that is randomly distributed in a given space. The particles have a prescribed volume fraction and uniform size. First, the proportions of chains and particles were compared. The length of chain was expressed in terms of end-to-end length. It was then compared to the size of gaps between two particles. The volume of chain was compared to the volume of space delimited by the particles. Next, a set of 10,000 random chains was generated and these were introduced into the particle set. The contact of a chain with the surface of a particle resulted in the special structural elements of the chain: a chain connecting two different particles, a loop which begins and ends at the same particle, a part of a chain which is completely adhered to the particle surface, a chain attached to a particle with one free end, as well as completely free chains. The chains were classified under three classes: chains which were not in contact with particles, chains which were in contact with one particle, and chains which were in contact with two or more particles. A statistical representation of each class is presented. The contact between chain and particle can influence macroscopic properties such as those that are elastic.     

Coarse-Grained Finite-Temperature Theory for the Bose Condensate in Optical Lattices

In this paper, we derive a coarse-grained finite-temperature theory for a Bose condensate in a one-dimensional optical lattice, in addition to a confining harmonic trap potential. We start with a two-particle irreducible (2PI) effective action on the Schwinger-Keldysh closed-time contour path. In principle, this action involves all information of equilibrium and non-equilibrium properties of the condensate and noncondensate atoms. In constructing a theory for the condensate and noncondensate in a periodic lattice potential, a difficulty arises from the rapid spatial variation due to a lattice potential, compared to the length scale of the harmonic potential. We employ a coarse-graining procedure to eliminate this rapid variation. By introducing a variational ansatz for the condensate order parameter in an effective action, we derive a coarse-grained effective action, which describes the dynamics on the length scale much longer than a lattice constant. Using the variational principle, coarse-grained equations of motion for condensate variables are obtained. These equations include a dissipative term due to collisions between condensate and noncondensate atoms, as well as noncondensate mean-field. As a result of a coarse-graining procedure, the effects of a lattice potential are incorporated into equations of motion for the condensate by an effective mass, a renormalized coupling constant, and an umklapp scattering process. To illustrate the usefulness of our formalism, we discuss a Landau instability of the condensate moving in optical lattices by using the coarse-grained generalized Gross-Pitaevskii hydrodynamics. We find that the collisional damping rate due to collisions between the condensate and noncondensate atoms changes its sign when the condensate velocity exceeds a renormalized sound velocity, leading to a Landau instability consistent with the Landau criterion. Our results in this work give an insight into the microscopic origin of the Landau instability.      

Efficient evaluation of three-phase coexistence lines

The Gibbs-Duhem integration method is a means for evaluating phase diagrams by molecular simulation. Starting from a state of known phase coexistence, one applies the Clapeyron equation to trace out subsequent points on the saturation line. Each simulation yields a coexistence state, and particle exchanges are not invoked to insure equality of fugacities. We describe and demonstrate here the extension of this method to three-phase coexistence, namely, among a solid, a liquid, and a gas. In one application, we compute the saturation pressure and temperature as a function of composition (more accurately, as a function of fugacity fraction) for six Lennard-Jones two-component mixtures. In a second study, we traverse a mutation pathway; that is, we evaluate three-phase equilibriaas a function of the intermolecular potential. In particular, we define a path that transforms the Lennard-Jones model into a square well, and thus in our calculations we quantify the effect of the shape of the repulsive and attractive portions of the potential on the triple point. In the end we have what is, to our knowledge, the First estimate of a state of solid-fluid coexistence for a square well model. In both applications we assume that the fee crystal structure represents the thermodynamically stable solid phase.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

多分辨率社团结构挖掘在故障定位中的应用

由于战场环境下对武器系统自我修复与重构功能的需求,以及分布式系统结构的特殊性,使得分布式武器装备具有众多的功能节点以及复杂的交联关系,对其进行快速故障定位已成为武器系统维修保障的重要研究内容。文中运用复杂网络理论对分布式系统建模,结合复杂网络社团性这一特点,提出了多分辨率模型映射的新观点,并以自律分散自动测试系统作为分析载体,运用多分辨率社团挖掘的方法,进行多分辨率故障回溯推理,为实现新型分布式武器系统的故障定位提供了新思路。     

Real-time calibration of open-loop piezoelectric actuators for interferometric applications

In the present paper a piezoelectric actuator realized for interferometric applications is described, together with a numerical model to simulate its electro-mechanical behavior. The actuator is an open-loop device made up of three piezoelectric ceramics glued into a stainless steel case and connected directly to the parallel port of a personal computer by control electronics developed on purpose. It consists of a 16 bit digital-to-analog converter whose voltage is fixed by the parallel port, a charge amplifier which provides the voltage to the piezoelectric ceramics and a current divider for the control of the voltage on each channel. The layout based on three active elements has allowed to obtain a device which is able to perform a straight expansion with a negligible tilting, a desirable feature for an actuator used for interferometric applications. The hysteretic behavior, a typical characteristic of this kind of actuator, was simulated by a numerical model, based on the Prandtl–Ishlinskii hysteresis operator, which shows a high capability to predict the input–output response at any level of the input signal, and it is efficient enough for use in real-time applications.     

衍射法X射线激光分束光栅平行度测量系统(英文)

介绍了软X射线光栅分束镜Mach-Zehnder干涉等离子体诊断系统调整用双频光栅线条平行度的衍射法测量系统.该系统主要由激光器,准直镜,待测光栅,精密转台(含角度测量仪),直线工作台,光栅调节架和探测器组成.分析了系统中各种误差对测量精度的影响其中包括距离测量误差、波长误差、光栅准直误差即光栅刻线与入射光和反射光组成的平面不垂直、光栅转动过程的误差、光栅表面面型误差、探测器误差,经计算得到系统的绝对误差为minute.计算表明,该系统的测量精度满足软X射线Mach-Zehnder干涉系统对双频调整光栅的性能要求.     

An intermittent control model of flexible human gait using a stable manifold of saddle-type unstable limit cycle dynamics

Stability of human gait is the ability to maintain upright posture during walking against external perturbations. It is a complex process determined by a number of cross-related factors, including gait trajectory, joint impedance and neural control strategies. Here, we consider a control strategy that can achieve stable steady-state periodic gait while maintaining joint flexibility with the lowest possible joint impedance. To this end, we carried out a simulation study of a heel-toe footed biped model with hip, knee and ankle joints and a heavy head-arms-trunk element, working in the sagittal plane. For simplicity, the model assumes a periodic desired joint angle trajectory and joint torques generated by a set of feed-forward and proportional-derivative feedback controllers, whereby the joint impedance is parametrized by the feedback gains. We could show that a desired steady-state gait accompanied by the desired joint angle trajectory can be established as a stable limit cycle (LC) for the feedback controller with an appropriate set of large feedback gains. Moreover, as the feedback gains are decreased for lowering the joint stiffness, stability of the LC is lost only in a few dimensions, while leaving the remaining large number of dimensions quite stable: this means that the LC becomes saddle-type, with a low-dimensional unstable manifold and a high-dimensional stable manifold. Remarkably, the unstable manifold remains of low dimensionality even when the feedback gains are decreased far below the instability point. We then developed an intermittent neural feedback controller that is activated only for short periods of time at an optimal phase of each gait stride. We characterized the robustness of this design by showing that it can better stabilize the unstable LC with small feedback gains, leading to a flexible gait, and in particular we demonstrated that such an intermittent controller performs better if it drives the state point to the stable manifold, rather than directly to the LC. The proposed intermittent control strategy might have a high affinity for the inverted pendulum analogy of biped gait, providing a dynamic view of how the step-to-step transition from one pendular stance to the next can be achieved stably in a robust manner by a well-timed neural intervention that exploits the stable modes embedded in the unstable dynamics.     

Neural networks for contract bridge bidding

The objective of this study is to explore the possibility of capturing the reasoning process used in bidding a hand in a bridge game by an artificial neural network. We show that a multilayer feedforward neural network can be trained to learn to make an opening bid with a new hand. The game of bridge, like many other games used in artificial intelligence, can easily be represented in a machine. But, unlike most games used in artificial intelligence, bridge uses subtle reasoning over and above the agreed conventional system, to make a bid from the pattern of a given hand. Although it is difficult for a player to spell out the precise reasoning process he uses, we find that a neural network can indeed capture it. We demonstrate the results for the case of one-level opening bids, and discuss the need for a hierarchical architecture to deal with bids at all levels.     

Performances d'une machine tritherme à éjecteur utilisant des mélanges de fluides frigorigènesPerformance analysis of a jet cooling system using refrigerant mixtures

The optimisation of a jet cooling system using refrigerant mixtures as substitutes of pure refrigerants has been investigated. A steady-state simulation program, for given temperatures of the sources, integrating simple models of each component has been developed. A Peng-Robinson equation of state assuming equality of the fugacities of the two phases was used to model the thermodynamic properties of the vapour and liquid-vapour equilibrium. The refrigerants investigated in this study are: the pure refrigerants R142b, R152a, RC318, R124, R134a, R22 and the binary refrigerants R22/RC318, R22/R142b, R22/R124, R22/R152a, R22/R134a, R134a/R142b, R152a/R142b and R134a/R152a. Results show that the use of a binary mixture does not always increase the performance of system. Generally, when the mixture is strongly zeotropic (e.g.: R22/RC318), the cooling efficiency of the system decreases. However, when the mixture is mildly zeotropic (e.g. R134a/R142b) or almost azeotropic (e.g. R134a/R152a), efficiency and energetic efficiency increase.     

On accuracy improvement of microscopic stress/stress sensitivity analysis with the mesh superposition method for heterogeneous materials considering geometrical variation of inclusions

In this paper, a new method is proposed for improving accuracy of microscopic stress analysis/stress sensitivity analysis of heterogeneous materials considering a geometrical variation of inclusions using the mesh superposition method-based approach. In particular, the analysis, which considers a location variation of inclusions in heterogeneous materials with location change of a local mesh, is a target problem. This problem must be accurately solved for, eg, reliability evaluation with the multiscale stochastic stress analysis considering a microscopic geometrical variation of composites. The influence of a geometrical random variation of inclusions on the stress field is not negligible; further, a finite element mesh must be substantially updated for the evaluation of stress field for a significant realization. Therefore, the mesh superposition method based approach is adopted. In this paper, a problem point in the stress/stress sensitivity analysis considering the geometrical variation of inclusions when using the mesh superposition method is discussed, and improved approaches based on an improved formulation and a relocalization analysis are proposed. The proposed approaches are applied to a stress/stress sensitivity analysis of a heterogeneous material associated with a microstructure of composites. With the numerical results, effectiveness of the proposed approach is discussed.