油底壳冲压过程的有限元数值模拟

采用有限元软件MARC，基于更新拉格朗日的弹塑性本构方程建立了一个有限元模型来模拟油底壳的成形过程。模拟得出了油底壳变形过程中板材的应力、应变、摩擦和厚度分布，揭示了成形过程中金属的塑性变形规律，并预测了可能发生失效的区域，为成形工艺设计提供了有效的分析工具。     

Realisation of linear time-varying systems

In this paper, the realisation problem of linear multi-input multi-output, time-varying systems is studied. The approach, based on the theory of non-commutative polynomial rings, yields explicit and simple formulas for computation of the state coordinates as well as for state equations in observable canonical form. The formulas are based on (left) Euclidean polynomial division.     

Electrochemical copper (II) sensor based on chitosan covered gold nanoparticles

This study outlines a new sensing platform based on glassy carbon electrodes modified by gold nanoparticles (AuNPs) for the determination of heavy metal. A glassy carbon electrode was modified by chitosan stabilized AuNPs. AuNPs were prepared by reducing gold salt with a polysaccharide chitosan. Here, chitosan acted as a reducing/stabilizing agent. The AuNPs were characterized with UV–Visible absorption spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. Chitosan covered AuNPs were immobilized on the glassy carbon electrode for the determination of Cu (II) in aqueous solutions. The electrochemical determination of Cu (II) ions was performed using the differential pulse voltammetry technique. Some parameters for Cu (II) determination, such as pH, preconcentration time and electrolysis potential of Cu (II), were optimized. The detection limit was calculated as 5 × 10^?9 mol L^?1 by means of the 3:1 current-to-noise ratio. The interference of Cr(III), Fe(II), Ni(II), Pb(II), Mg(II), Zn(II), Ba(II) ions was investigated and showed a negligible effect on the electrode response. Recovery studies were carried out using tap water.     

Estimation of the efficiency of asymmetrical digital subscriber line (ADSL) technology

In the present study, the data transmission rate available by means of the ADSL technology is estimated. Theoretical and practical estimates are obtained for a three kilometer telephone cable and for the one that occurs most commonly in practice. Computations are performed of the theoretically available rate and of the rate of the data transmission along independent quadrature amplitude modulation (QAM) channels with a preset total error probability and under the use of an error-correcting code. The theoretical data is compared to the values obtained by the experiment.     

Thermal conductivity of bulk ZnO after different thermal treatments

Thermal conductivities (κ) of melt-grown bulk ZnO samples thermally treated under different conditions were measured using scanning thermal microscopy. Samples annealed in air at 1050°C for 3 h and treated with N-plasma at 750°C for 1 min. exhibited κ=1.35±0.08 W/cm-K and κ=1.47±0.08 W/cm-K, respectively. These are the highest values reported for ZnO. Atomic force microscopy (AFM) and conductive-AFM measurements revealed that surface carrier concentration as well as surface morphology affected the thermal conductivity.     

电阻焊变压器的直流磁化及危害浅析

本文介绍了阻焊变压器产生直流磁化的原因、危害和预防措施。对于现行使用的电阻焊机老式控制箱和正确设计选择新型控制箱具有积极作用。     

The investigation of the tensile behaviors of single L‐joint type bonded with adhesive and rivet

In this study, tensile behaviour of single “L” type joints was investigated experimentally and numerically. Aluminium pieces with 2 mm, 3 mm and 4 mm thicknesses were used as joint materials. Overlap lengths were chosen as 10 mm, 15 mm and 20 mm. Joints were executed with two different rivets as steel and aluminium and 3 M 2216 epoxy based adhesive. Experiments were carried out by means of Shimadzu universal testing machine with 5 kN load cell. While the numerical study was carried out, using ANSYS Workbench, finite element analysis program, models were formed with the same properties as experimental works. Results showed that the samples with 20 mm overlap length had the highest strength of all models. Models with steel rivet had higher strength than models with aluminium rivets for all overlap lengths.     

Solving PDEs with the aid of two-dimensional Haar wavelets

Two-dimensional Haar wavelets are applied for solution of the partial differential equations (PDEs). The proposed method is mathematically simple and fast. To demonstrate the efficiency of the method, two test problems (solution of the diffusion and Poisson equations) are discussed. Computer simulation showed that the method guarantees the necessary exactness already for a small number of grid points.     

Composition of negative air ions as a function of ion age and selected trace gases: Mass- and mobility distribution

In order to explore an additional window to look into the mechanisms behind atmospheric ion and particle formation, an advanced method, which combines the study of ageing of air ions by both mobility and mass spectrometry is developed and examined. The technique behind this method can produce new air ions and trace their evolution within the age interval from a few tenths of a second up to about 20 s. We measure the mobility spectra from 2.37 down to 0.0013 cm² V^?1 s^?1 and the mass spectra of these ions up to m/z 2000. The results demonstrate the ability of the method to trace the temporal evolution of the ions. The composition of negative air ions at an age of about 1 s is clearly different from that at about 20 s, contrarily to certain former results according to which the small ion evolution should mainly terminate within about a second. We investigate how variations in humidity and the elevated concentrations of iodine and diethylamine (DEA) modify the composition of the negative air ions. The concentrations of DEA and iodine are above their common values in the air, but also in these cases the observed trends should be applicable to the atmosphere. All the vapours investigated in this study modify the ion composition in quite a specific way. Most prominent transformations are induced by iodine, which transforms the mass spectrum of cluster ions into few dominant peaks at m/z 381 and 635. In mobility spectrum, it generates a large number of new heavy ions with the sizes of 4?40 nm, the heavy ions in turn decrease the concentration of cluster ions due to ion–aerosol attachment. The peaks at m/z 381 and 635 can be assigned to ions I^?(I₂) and I^?(I₂)₂, respectively. At an enhanced concentration of diethylamine vapour (DEA), the new ions NO₃^?(HNO₃)(DEA) seem very plausible to explain the appearance of the peak at m/z 198 in the mass-spectrum. DEA evokes a multimodal mobility spectrum with modes at about 1.75, 10 and 20 nm. Both the DEA and iodine generate the changes in the size distribution of aerosol particles, which can be associated with a new particle formation. The experiments with enhanced water vapour concentrations revealed a new peak at m/z 250, which could be assigned to HCO₃^?(HNO₃)₃ ions.     

汽车制造业对敏捷系统的需求将越来越迫切

从产量角度看,敏捷制造系统的产量始于传统柔性制造系统的结束点(年产量大于5万件),并有很大一部分和传统自动线(年产量大于2万件)重合.如果使用CNC加工中心加工轻合金零件,对于敏捷制造系统而言,其投资平衡点大约为年产30万件(铸铁件约为年产20万件).这仅是从产量上进行分析,还未考虑敏捷系统对于不同品种工件的柔性乃至多品种共线生产的优点.