CTS-26型超声探伤仪典型故障的分析与排除

在简要介绍CTS-26型超声探伤仪工作原理及组成的基础上。对其几种典型故障作了具体的分析和处理。     

Rejection of narrowband interference in DS spread spectrum systemsemploying minimum redundant nonlinear filters

A new nonlinear filter structure, the minimum redundant nonlinear filter (MRNF), for combating narrowband interference in direct sequence spread spectrum systems is proposed. Analytical expressions for the signal-to-noise ratio improvement factors are derived under the condition of single tone interference. The results show that the MRNF provides significantly better performance than the minimum redundant transversal filter     

High-speed Modulation of InGaAs: Sb-GaAs-GaAsP quantum-well vertical-cavity surface-emitting lasers with 1.27-/spl mu/m emission wavelength

1.27-/spl mu/m InGaAs: Sb-GaAs-GaAsP vertical-cavity surface-emitting lasers (VCSELs) were grown by metal-organic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% as the temperature raised from room temperature to 70/spl deg/C. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is measured to be 10.7 GHz with modulation current efficiency factor (MCEF) of /spl sim/5.25 GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C.     

应用ATV71变频器有效解决给粉机变频器低电压跳闸问题

本文分析了给粉机变频器低电压跳闸的原因和解决办法，为解决给粉机变频器低电压跳闸，消除设备隐患提供了经验。     

A recurrent neural network for solving a class of general variational inequalities.

This paper presents a recurrent neural-network model for solving a special class of general variational inequalities (GVIs), which includes classical VIs as special cases. It is proved that the proposed neural network (NN) for solving this class of GVIs can be globally convergent, globally asymptotically stable, and globally exponentially stable under different conditions. The proposed NN can be viewed as a modified version of the general projection NN existing in the literature. Several numerical examples are provided to demonstrate the effectiveness and performance of the proposed NN.     

Modeling of Bolt Joint Behavior of Cast Aluminum Alloy (A380-T5) by Coupling Creep and Plasticity in Finite Element Analysis

Aluminum casting alloys exhibit creep behavior when the materials are exposed to high temperature and load. In this article, the stress- and temperature-dependent creep behavior of a die casting A380-T5 aluminum alloy was simulated using a classical constitutive model. The bolt-load retention behavior of the material was analyzed in a head bolt joint in an aluminum engine under thermal cycle condition using the finite element method. In this simulation, transient thermal analysis was performed first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. This temperature was then input as the thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load retention. The finite element analysis (FEA) model for the bolt-load retention simulation includes not only the plasticity in all metal components but also the creep properties of head bolt threads in the cast aluminum engine block. The FEA model was validated by good correlation between the predicted head bolt-load loss and the experimental measurement during engine thermal cycling. The simulation results also indicated that creep in the head bolt threads of cast aluminum engine block was mainly responsible for the load loss in the head bolt joint. This article is based on a presentation given in the symposium entitled “Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties” which occurred March 12–16, 2006 during the TMS Annual Meeting in San Antonio, Texas under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee.     

太阳能真空管的发展方向

现在市场上的太阳能真空管如图1所示。Ⅰ型,就是现在普通的全玻璃真空管。其特点为:玻璃管吸收到的太阳热直接传给水,传热热阻很小。但是真空管内有水而带来的缺点:易冻坏,结水污,热效率低。为了使真空管内无水而发展的其他形式,如Ⅱ、Ⅲ、Ⅳ型。Ⅱ型,就是在普通的全玻璃真空管(Ⅰ型)内放置金属热管。其特点为:真空管内无水,玻璃管吸收到的太阳热通过超导的金属热管传给水。但是,由于玻璃管与金属热管之间的传热热阻太大,使玻璃管上的吸热涂层老是处于高温工况下,同时抵消了由于真空管内无水而带来的热效率的提高。Ⅲ型,就是金属吸热体的真…     

Prediction of Fatigue Performance in Aluminum Shape Castings Containing Defects

Fatigue properties of cast aluminum components are controlled by maximum defect size in the material. The larger the maximum defect size, the lower the fatigue strength and life. In the presence of casting defects, crack initiation can be ignored and fatigue life is mainly spent in crack propagation. Therefore, fatigue life of aluminum castings can be predicted by long or short crack growth models. The main problem is defining a starting defect size from readily available data, such as twodimensional (2-D) pore size measurements on metallographic sections. In this article, an extremevalue statistics (EVS) method was used to estimate the maximum defect size in 319 castings from conventional metallographic data. The maximum defect size predicted by EVS agrees quite well with the initiation defect sizes measured from fracture surfaces, and the predicted fatigue life is in reasonable agreement with the experimental data.     

高碳铬铁电炉高基质干式打结料的研究

通过对组成打结料成分特性的研究，提出以优质原料生产的MgO-CaO-Fe2O3系合成砂为骨料，用MgO〉97％，粒度〈0．088mm烧结镁砂做细粉，适当添加超微粉等工艺措施，制成适当高碳铬铁电炉炉底用的高基质打结料，通过调控基质成分，实现材料相和固相的复合烧结。     

Optimal Conditions for Preparing Ultra-Fine CeO2 Powders in A Submerged Circulative Impinging Stream Reactor

Cerium carbonate powders were produced in a submerged circulation impinging stream reactor (SCISR) from Ce(NO3)3·6H2O. NH4HCO3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide (CeO2) powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce(NO3)3 and NH4HCO3 solutions were 0.25 and 0.3 mol·L-1, respectively. The concentration of PEG4000 added in these two solutions was 4 g·L-1. The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r·min-1, 80 ℃, 20 min, 5～6, 5 min and 1 h, respectively. The final product, CeO2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 ℃. The finally produced CeO2 powders were torispherical particles with a narrow size distribution of 0.8～2.5 μm. The crystal structure of CeO2 powders belonged to cubic crystal system and its space point group was O5H-FM3M. Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor (STR).