2.25Cr-1Mo与2.25Cr-1Mo-0.25V钢冷却转变对比分析

采用相变仪、光学显微镜及扫描电镜研究了2.25Cr-1Mo和2.25Cr-1Mo-0.25V钢冷却转变过程,并分析了钒对其冷却转变的影响。结果表明,与2.25Cr-1Mo钢的CCT曲线相比,2.25Cr-1Mo-0.25V钢铁素体转变区及贝氏体转变区均向右移,并且在现有试验条件下已无法观察到珠光体转变区;钒添加到2.25Cr-1Mo钢中,能够提高钢的淬透性,2.25Cr-1Mo-0.25V钢在48 000 ℃/h冷速下能生成部分马氏体;钒能够细化钢板显微组织,与2.25Cr-1Mo钢相比,2.25Cr-1Mo-0.25V钢在800 ℃/h冷速下组织更为细小。     

蒸汽动力系统可调节性分析

工厂中经常出现的变动情况决定蒸汽动力系统须具有一定的可调节性。本文以总复合曲线为工具,分析比较了采用背压式汽轮机组和采用抽汽凝汽式汽轮机组的蒸汽动力系统,并用一例子说明如何借助总复合曲线设计可调节性好的蒸汽动力系统。     

热阻和回热损失对埃里克森循环性能的影响

建立受热阻和回热损失影响的埃里克森循环模型,以输出功率为目标函数,导出循环的基本优化关系式,由此获得循环的特性曲线,并对特殊的工况点作了详细的讨论,从而得到一些新的结论。     

Effects of diffusion on the kinetic study of the system BADGE n = 0/m‐xylylenediamine

The curing reactions of an epoxy system composed of a diglycidyl ether of bisphenol A (BADGE n=0) and m‐xylylenediamine (m‐XDA) were studied. Two models, the first based solely on chemical kinetics and the second accounting for diffusion, were used and compared to the experimental data. The epoxy resin was used as received in a first series of experiments. In a second series of experiments, the resin was purified in vacuo (180°C and 1 mmHg). The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre‐ and postvitrification stages. The investigation was made in the temperature range 50–110°C, which is considered optimum for the isothermal curing of the epoxy system studied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2997–3005, 1999     

双排桩丁坝在涌潮作用下的内力测试和分析

基于现场测试的成果,利用常数法、m法和编制的有限元程序对实际工况进行计算比较,研究分析了双排桩丁坝在涌潮作用下的受力机理.由于前排桩和后排桩的受荷模式不同、刚度不同,从而桩头弯矩不同.测试结果和理论分析表明,双排桩丁坝的桩体约束条件介于桩头自由和桩头固接之间,常数法和m法的计算都基于桩头完全固接的假设,其计算结果与实际情况相差较大,而有限元法计算假设较少,计算结果与实测值吻合较好.     

In Situ Observation of P91 High-Alloy Steel Solidification Characteristics at Different Cooling Rates

To clarify the effect of different radial cooling intensities on the formation of central cracks in large round bloom continuous casting, it is necessary to study the solidification characteristics and dynamics of P91 high-alloy steel at different cooling rates (CRs) to improve the central defects. In this article, the solidification characteristics of P91 high-alloy steel at different CRs are studied by using the Thermo-Calc software, high-temperature laser confocal microscopy, scanning electron microscopy, and optical microscopy. Meanwhile, the growth kinetics of δ-Fe and γ-Fe phases under different CRs are determined. The results show that the solidification path of P91 high-alloy steel is L(L + δ-Fe) → (L + γ-Fe + δ-Fe) → (δ-Fe + γ-Fe). The δ-Fe and γ-Fe phase precipitation process is divided into two stages. Stage I is the nucleation and rapid growth phase, in which a high undercooling is required. Stage II is the slow growth stage, where the undercooling decreases and remains constant. The initial growth linear velocities of the δ-Fe phase are 0.51, 2.72, and 2.09 μm s⁻¹ at CRs of 10, 50, and 100 °C min⁻¹, respectively, while those of the γ-Fe phase are 0.10, 1.42, and 1.41 μm s⁻¹.     

Flexural design curves of steel plate I-girders at elevated temperatures: I-girders with yield or local buckling failure mode

The present study was undertaken to characterize the structural behavior and ultimate flexural strength of steel plate I-girders under pure flexural moment at elevated temperatures. A novel design procedure along with flexural design curves was proposed to predict the flexural behavior of the I-girders and estimate corresponding ultimate flexural strengths. The main strategy of the procedure is to find an ambient-temperature equivalent of the I-girder by quantifying and formulating the effects of elevated temperatures. The proposed procedure comprises overall and partial phases. The former phase deals with the determination of equivalent laterally unbraced length, and the latter phase addresses the equivalent web and compression flange slenderness parameters. The calibration factor was defined to adapt the design curves to the effects of high compression flange slenderness parameters and residual stress at elevated temperatures. To generate comparative results, a numerical study was conducted by analyzing 216 finite element (FE) models. Fifty-four out of 216 FE models with different cross-sectional elements were dedicated to the I-girders fail by yield or local buckling failure mode, the results of which are reported in the present paper. Data fitting analysis was carried out to capture the variation of calibration factor with respect to compression flange slenderness parameters. By calibrating the proposed design procedure, the results were converged and, therefore, good conformity was reached between the numerical and parametric results.     

高密度接种胶球藻C-169处理脱色酵母发酵废水条件优化

本文探究了胶球藻C-169的营养方式,并在未灭菌的脱色酵母废水中高密度接种胶球藻C-169,系统比较了接种密度、废水浓度对胶球藻C-169的生长及其处理酵母废水效果的影响。结果表明,胶球藻C-169可以利用葡萄糖和蔗糖进行异养和混养生长。混养条件是胶球藻C-169快速扩种的最佳条件。在混养条件下,胶球藻生长速度最快,最适葡萄糖浓度为20 g/L。通过单因素实验研究培养条件(接种密度、废水起始浓度)对胶球藻C-169的生长和废水处理效果的影响,建立的最佳培养条件为:起始接种密度不低于1 g/L,脱色废水稀释倍数为2倍。在此条件下,胶球藻C-169的生物量产率为0.23 g/(L·d),脱色废水COD(化学需氧量)、总氮、总磷的去除率分别为49.54%、70.39%和98.09%。此研究表明胶球藻C-169在藻菌共生条件下对酵母废水的净化具有很大潜力。     

Some Geometric Invariants of Pseudo-Spherical Evolutes in the Hyperbolic 3-Space

In this paper, we study the pseudo-spherical evolutes of curves in three dimensional hyperbolic space. We use techniques from singularity theory to investigate the singularities of pseudo-spherical evolutes and establish some relationships between singularities of these curves and geometric invariants of curves under the action of the Lorentz group. Besides, we defray with illustration some computational examples in support our main results.     

A User Authentication Protocol Combined with the Trust Model,Biometrics and ECC for Wireless Sensor Networks

In this article, a new user authentication protocol using trust model, elliptic curve cryptography and biometrics for WSNs is submitted. The result of the trust model analysis indicates that the model can improve the model’s ability of withstanding attacks from the malicious nodes. The results of safety analysis and performance analysis for our proposed user authentication protocol demonstrate that this protocol can be flexible to all sorts of common known attacks and performs similarly or better compared with some active user authentication protocols. It is suitable for WSNs which have a prominent request for the security and the performance.