铝型材推弯工艺

通过铝型材圆环的推弯实验,研究了推弯工艺原理、变形过程,结合有限元模拟得到了和实验结果相吻合的型材厚度分布、成形零件卸载回弹后的曲率半径及型材截面畸变.结果表明:推弯零件曲率及截面畸变一致性高,成形模具结构简单且便于调整,数值模拟可以用于推弯工艺的优化分析.     

Evaluating the design of flexible manufacturing systems

Evaluating the design of flexible manufacturing systems is complex. Developing a measure of performance useful for evaluating alternate designs continues to be interesting. Here, total productivity of the system is proposed as an appropriate measure. Specification of parameters based upon strategic considerations for this measure are discussed. Finally, the usefulness of the measure is demonstrated through an example.     

Signal processing using cellular neural networks

The cellular neural network (CNN) architecture combines the best features from traditional fully-connected analog neural networks and digital cellular automata. The network can rapidly process continuous-valued (gray-scale) input signals (such as images) and perform many computation functions which traditionally were implemented in digital form. Here, we briefly introduce the the theory of CNN circuits, provide some examples of CNN applications to image processing, and discuss work toward a CNN implementation in custom CMOS VLSI. The role of analog computer-aided design (CAD) will be briefly presented as it relates to analog neural network implementation.This work is supported in part by the Office of Naval Research under Contract N00014-89-J1402, and the National Science Foundation under grant MIP-8912639.     

Energy efficiency, carbon emissions and economic development in Venezuela

Venezuela's vast natural resource base has largely shaped the nation's economic and energy-use patterns. Major opportunities exist for improving the efficiency of energy use in Venezuela and, consequently, restraining the growth of energy-related carbon emissions. This paper presents a detailed report of one potential development path for Venezuela and estimates the ensuing levels of energy demand and CO₂ emissions associated with pursuing this path through the year 2025. The results indicate that by adopting a development strategy that incorporates structural changes in the economy, fuel-switching measures and improved end-use efficiencies, Venezuela can introduce energy efficiency and carbon restraints as part of its economic development process.     

The relationship among oxygen content, defect distribution and superconductivity in BiSrCaCuO systems

The effect of oxygen content on superconductivity of the 2212 and 2223 phase has been studied. By comparing the excess oxygen, the modulation vector, the XRD patterns, and the electric resistivity of 2212 and 2223 phase samples obtained with different post-annealing conditions, i.e., annealing at 600°C or quenching from 860°C, it was found that the super-conductivity is markedly influenced by both the defect distribution in non-Bi layers and the interstitial oxygens incorporated in the Bi-O layers. A tentative explanation for this is given.     

Improved Prediction of Ozone Levels in Urban and Rural Atmospheres

Based on data obtained in terms of the first International cooperative program on the effects of acidic precipitations on materials (ICP Materials) of the United Nations European Commission on Economics (UN ECE), the relations between the ozone O₃ and nitrogen dioxide NO₂ concentrations in combination with the sunshine effect (taken into account either as the solar radiation (Rad) or the sunshine duration (Sun)) are considered. Analysis based on monthly and annual averages led to a new equation recommended for predicting ozone levels over rural, urban, and industrial areas of Europe as a function of NO₂ concentration and Sun parameter. Using Rad instead of Sun provides similar results, but, for practical usage, the equation involving a more easily available parameter Sun was recommended. The new equation corrects and improves the earlier proposed one, in which the concentration of ozone was given as a function of NO₂ concentration solely, and is included in the UN ECE Manual on mapping critical loads / levels and geographical areas where they are exceeded.     

Thermomechanical stress fields in high-temperature fibrous composites. I: Unidirectional laminates

This two-part paper presents a closed-form procedure for evaluation of estimates of local thermomechanical stress fields in two-phase fibrous composites and laminates. The first part is concerned with a unidirectional elastic laminate subjected to uniform mechanical loads and to uniform changes in temperature. Both phases are assumed to be elastic, with temperature-dependent moduli and expansion coefficients; the solution reflects the influence of thermomechanical interactions. Exact solutions are not possible for any real system, because the local geometry is not known in detail. Instead, estimates of the fields are found from a modified Mori-Tanaka approximation. Examples are presented for two SiC/Ti---Al---Nb composites. Local stresses of interest are found after cooling from fabrication to room temperature. The presence of local yielding, and the influence of coupling terms on the local stress magnitudes are examined. Extension of the results to laminated plates is presented in Part II (Dvorak, G.J., Chen, T. & Teply, J., Composites Science and Technology, 43 (1992) 359–368, this issue).     

Observation of atomic steps on CaCO3 crystal surface

By using scanning polarization force microscopy,the deliquescence process and the atomic steps on the cleavage surface of CaCO3 in air were studied in situ.Under an exposure to medium umidity(-57%),the sloiw step movement has been observed.     

Synthesis, characteristics and oxygen-sensitive properties of SrMgxTi 1 − xO3 nanocrystals

SrMg_xTi_{1 - x}O₃ nanocrystals (x = 0.1–0.6) were synthesized by the stearic acid gel method. Powder samples were characterized by X-ray diffraction and X-ray photoelectron (XP) spectroscopy. The results showed that the lattice parameter a and the O 1s XP spectrum changed not only with the Mg content x but also with the grain size d of the samples. The conductivity of a thick film specimen fabricated on an aluminium oxide wafer was investigated in a nitrogen—oxygen atmosphere.