盖下坝水电站施工期温度应力及损伤仿真分析

结合盖下坝水电站工程实际情况,采用ANSYS软件及其二次开发技术,对该混凝土拱坝施工期的温度场和应力场进行全过程的三维仿真计算,得出施工期最高温度和最大温度应力.同时,利用损伤有限元程序对该大坝进行了损伤仿真计算,得出施工期重要时刻的损伤场.仿真结果表明,在合理的温控措施下,大坝施工期温度应力远小于设计容许值,损伤值也较小,施工期不会出现宏观裂缝.     

多变量自回归模型在三江平原井灌水稻需水量预测中的应用

应用多变量自回归模型ARV(n), 利用三江平原腹地-富锦市1985～1999年气象资料, 按水稻生育期划分6个生育阶段, 建立了井灌水稻生育期内需水量预测模型. 经模型拟合与预测, 效果良好, 可以为该地区开展节水灌溉、灌溉用水管理、合理开发利用地下水资源, 缓解地下水危机提供参考依据.     

A switching power amplifier with feedback for improving total harmonic distortion

A high efficiency and low distortion and switching power amplifier is proposed. We use feedback to reduce the total harmonic distortion (THD) and the DC output bias current. The experimental results show that the proposed circuit has 0.24% total harmonic distortion and 91% power efficiency while the DC output bias current is 12 μA at 1.5 V supply voltage.     

Magnetic contributions to the thermodynamic functions of pure Ni,Co, and Fe

An empirical mathematical equation is proposed for the magnetic contribution to the specific heat of pure metals. The corresponding functions for enthalpy, entropy, and Gibbs energy are of simple form. Two parameters used for each element are the critical temperature,T _c, and the total magnetic entropy. The parameters have been determined from a careful separation of magnetic and nonmagnetic contributions to the specific heat. Debye temperatures for Ni, Co, and Fe have been determined considering data to much higher temperatures than other studies. The magnetic specific heats extracted from experimental data agree very well with the proposed equation over the entire temperature range and for all three elements. Comparisons with different mathematical functions found in the literature give agreement only for the case of iron. The total magnetic entropy given by a classical relation is found to be high, and a quantitative correction is given. Various magnetic standard states are discussed. The lattice stabilities of bcc- and fcc-iron are calculated assuming that the difference of the nonmagnetic specific heats is linear from 500 K to 1810 K. A simple equation is obtained in which the anomalous temperature dependence is explained by the independently determined magnetic contribution. The calculated values agree very well with Orr and Chipman’s assessment. The stability of bcc iron at low temperatures is quantitatively rationalized.     

The extraction of platinum from Pt(II) chloride solution by a quaternary ammonium compound

The fundamental aspects of the extraction and stripping of platinum (II) from its chloride solution by Aliquat 336 diluted with toluene have been studied. The extraction and stripping was at 99.5 and 97.6% equilibrium within 30 s and 20 min respectively. The percentage extraction increased slightly with decreasing hydrochloric acid concentration. In 0.1 mol dm^?3 hydrochloric acid, 1.0 volume percent Aliquat 336 in toluene could load 9.8 mmol dm^?3 of platinum (II). The percentage stripping of platinum (II) from Pt(II)-load organic solvent increased with increasing sodium bisulphite concentration. The enthalpy changes of extraction and of stripping were 12.8 and 114.9 kJ mol^?1 respectively. Both of the reactions were endothermic.     

Soft-output equalization and TCM for wireless personalcommunication systems

This paper investigates the use of a maximum a posteriori probability (MAP) algorithm to realize soft-output equalization in a concatenated equalization and trellis-coded modulation (TCM) decoding-based wireless communication system. Specifically, we first begin with a general MAP algorithm and then focus on studying Bahl's (1974) MAP and Lee's (1974) MAP algorithms. We then propose a modified version of Lee's MAP algorithm which is much simpler than the original, in terms of complexity, and is more practical. In particular, a very simple channel estimation method which employs orthogonal training sequences is proposed. In order to improve the system performance, equal-gain combining and selection diversity are also considered. Finally, we compare the performance of the MAP algorithm-based equalization with our previously proposed equalization scheme, which combines decision feedback equalization and TCM     

Identification of heat load loops and downstream paths in heat exchanger networks

To achieve the optimal trade-off between economies and operability, simplifications of heat exchanger networks (HENs) are required. To do so, identifications of heat load loops and downstream paths are necessary. This paper proposes new methods for identifications of independent and dependent loops as well as downstream paths in HENs, respectively. Stream table and node adjacency matrix are defined in this paper to represent the structures of HENs. Based on graph theory, identification of loops in HENs is decomposed into three procedures: (a) finding a maximal tree, (b) identifying a maximal set of independent loops and (c) searching all loops. Locating the downstream paths in HENs is accomplished by finding directed trees which are generated by modifying the procedure for finding a maximal tree. A complex network with a splitting stream is used for detailed illustrations of the procedures.     

Factors associated with the therapeutic efficacy of retinoic acids on malignant lymphomas

We recently reported the successful use of retinoic acids in the treatment of refractory lymphoma. The biologic determinants predicting response of lymphomas to retinoic acid remain unknown. This study was conducted to explore this question using in vitro models. Sensitivity of representative lymphoma cells to 13-cis-retinoic acid was determined. Sensitive and resistant cell lines were then compared for their baseline and/or retinoic-acid-regulated expression of total cellular retinoic acid binding protein, retinoic acid receptor (RAR)-alpha, RAR-beta, RAR-gamma mRNA, retinoid X receptor (RXR)-alpha, RXR-beta, RXR-gamma mRNA, transforming growth factor (TGF)-beta 1 and TGF-beta 1 receptors, and Fas (Apo-I) mRNA. The results showed that four of five T, two of three Hodgkin's, and none of six B cell lymphoma cell lines were sensitive (IC30 < 1.5 mmol/L) to 13-cis-retinoic acid. Further analyses revealed several of the above-mentioned parameters may be relevant to retinoic acid sensitivity. Baseline expression of TGF-beta 1 receptors was present in all of the five sensitive cell lines examined, but in only one of the four resistant cell lines. The correlation of Fas expression and retinoic acid sensitivity was good for B cell lines, but not apparent for T cell or Hodgkin's cell lines. On exposure to retinoic acid, an immediate and prolonged upregulation of RAR-alpha mRNA expression, lasting for more than 12 hours, occurred in all sensitive cell lines, but only minimal or transient induction was seen in resistant cells. Together, these data suggested that; 1) retinoic acid has a preferential effect on T cell and Hodgkin's lymphoma cell lines; 2) autoregulation of RAR-alpha by retinoic acids, and the presence of TGF-beta 1 receptors may be relevant to the response of lymphomas to treatment with retinoic acids.     

The effect of education on mortality among older Taiwanese and its pathways

The present research examines the impact of education on the mortality of older Taiwanese during a 4-year interval from April 1989 to April 1993. Data used for this study come from the Taiwan Survey of Health & Living Status of the Elderly (1989). The research decomposes the effect of education into the direct effect and the indirect effects by means of health status, health behaviors, and social relationships. We have shown that, of the total effect of educational attainment on the mortality of older Taiwanese, about 83% represents indirect influences by means of the 3 mediating factors, particularly health status. On the other hand, the magnitude of the direct effect, which might reflect influences of additional intervening variables on old-age mortality, is low and not statistically significant. The results demonstrate that the apparent strong effect of education on mortality among older Taiwanese can be accounted for parsimoniously through 3 major pathways.