2(1/4)Cr-1 Mo钢的短裂纹疲劳断裂特征

本文用弹塑性断裂力学分别研究了在空气和氢中 ,压力容器器壁的承载材料 2 ( 1 / 4 )Cr— 1 Mo钢的短裂纹低频疲劳特性 ,结果表明 :都可用 da/ d N =C(ΔJ) n 的关系式计算上述两环境中的短裂纹扩展速率 .裂纹呈穿晶扩展 .氢明显增加了 2 ( 1 / 4 ) Cr— 1 Mo钢的断裂敏感性     

一种高精度多通道数据采集存储电路的设计

为满足多路多种类信号高精度采样的需求,设计了一种基于FPGA的高精度多通道数据采集存储电路.设计采用新型的高精度Δ-∑模数转换器(Δ-ΣADC)对模拟信号进行采样转换,并给出了电路的硬件设计和控制逻辑设计.具体介绍了抗混叠滤波电路的设计,并详细分析了影响Δ-ΣADC采集精度的因素;设计采用FPGA作为主控芯片,实现对整体电路的逻辑控制.测试结果表明,设计实现了对16路模拟信号的高精度采集存储,满足实际需求.     

大型精轧支撑辊疲劳断裂失效分析

某单位1580生产线精轧支撑辊在轧制过程中突然发生断裂,为查明失效原因,利用光学显微镜、拉伸、冲击试验机以及扫描电镜对轧辊材料显微组织、力学性能、断口形貌、起裂源位置进行了综合分析。结果表明,精轧支撑辊芯部材料为球墨铸铁,其组织主要由珠光体、棒状渗碳体、球状石墨及聚集在石墨周围的牛眼状铁素体构成。组织洁净度较差,夹杂物主要为球状Al₂O₃-MgO-SiO₂、Al₂O₃-MgO、Al₂O₃氧化物,尺寸集中在10～15 μm。支撑辊断口呈现典型旋转弯曲疲劳断口特征,裂纹源区位于轧辊内部且为多源起裂,断口内部呈现典型“鱼眼”特征,“鱼眼”区中最大夹杂物直径3 mm,为球状Al₂O₃-MgO-SiO₂。裂纹源最大拉应力30 MPa。裂纹在夹杂物周围萌生时其裂纹尖端最大应力强度因子为1.385 MPa·m^1/2,大于内部起裂裂纹扩展门槛值,因此裂纹在夹杂物与基体界面处形核。裂纹扩展至“鱼眼”区之外时,裂纹在应力作用下快速扩展并汇聚形成一条长裂纹,最终导致轧辊发生瞬断。     

降解植物甾醇产雄甾1,4-二烯-3,17-二酮工程菌株的构建及转化培养基优化

雄甾-1,4-二烯-3,17-二酮(ADD)作为甾体激素药物不可替代的中间体,是多种激素类药物的原材料。在分枝杆菌(Mycobacterium sp.ZFZ)体内过表达3-甾酮-Δ¹脱氢酶(KstD),获得一株ADD生产菌,随后研究了不同培养基组成对该菌株生产ADD的影响。在单因素的基础上,以ADD产量为衡量指标,采用响应面法优化了转化培养基的组成,并建立各影响因素变化的二次回归方程。结果表明,最适宜的转化培养条件为玉米浆23 g/L、葡萄糖9 g/L、硝酸钠2.8 g/L、磷酸氢二钾2 g/L。此条件下底物甾醇浓度为10 g/L时,ADD的产量可达(4.12±0.18) g/L,ADD产量比出发菌株提高了近18倍。     

The Delta 5,7-Sterols and Astaxanthin in the Marine Microheterotroph Schizochytrium sp. S31

The thraustochytrids, the heterotrophic marine microorganisms, have received increasing attention because of their capacity for the production of high-value products such as docosahexaenoic acid (DHA), carotenoids, and sterols. In this study, three potential Δ^5,7-sterols, showing similar UV absorption spectra to that of ergosterol, in the thraustochytrid Schizochytrium sp. S31, were estimated by the ultraperformance liquid chromatography (UPLC) − APCI−MS/MS method. The proposed structures of three Δ^5,7-sterols were ergosta-5,7,24(28)-trien-3β-ol, ergosta-5,7-dien-3β-ol, and 24-ethylcholesta-5,7,22-trien-3β-ol. The contents of astaxanthin, ergosterol, and the other three Δ^5,7-sterols in Schizochytrium sp. S31 during the cultivation performed in three separate batches were analyzed by a fast UPLC–PDA method. The results demonstrated that astaxanthin, ergosterol, and ergosta-5,7-dien-3β-ol were the predominant carotenoid and Δ^5,7-sterols, respectively, and their contents kept increasing during the growth and reached a maximum after 23 days of cultivation. The estimated maximum contents of astaxanthin and four Δ^5,7-sterols, including ergosterol, ergosta-5,7-dien-3β-ol, ergosta-5,7,24(28)-trien-3β-ol, and 24-ethylcholesta-5,7,22-trien-3β-ol were 2.31, 4.02, 3.43, 0.30, and 0.97 mg g⁻¹ dry biomass, respectively. These findings are different to other strains reported in the composition and accumulation of Δ^5,7-sterols and carotenoids. The present study suggests that Schizochytrium sp. S31 might be a promising marine microorganism for the productions of high-value natural pigment astaxanthin, the provitamin D₂ ergosterol, and the provitamin D₄ ergosta-5,7-dien-3β-ol, and taken as a model organism to study the sterologenesis of the microorganisms because of its complexity of sterol compositions.     

抑制PCB电磁辐射干扰的设计

针对现在PCB的多层化、器件的集成化、高速化,ΔI噪声成为共模辐射的主要来源。本文提出了如何采用阻尼电阻抑制PCB差模辐射;合理利用去耦电容器,应用多个电容并联的方式,并充分考虑PCB的层间电容,实现PCB共模辐射的抑制。     

Application of support vector regression analysis to estimate total organic carbon content of Cambay shale in Cambay basin,India – a case study

The objective of the present study is to estimate total organic carbon (TOC) content over the entire thickness of Cambay Shale, in the boreholes of Jambusar–Broach block of Cambay Basin, India. To achieve this objective, support vector regression (SVR), a supervised data mining technique, has been utilized using five basic wireline logs as input variables. Suitable SVR model has been developed by selecting epsilon-SVR algorithm and varying three different kernel functions and parameters like gamma and cost on a sample dataset. The best result is obtained when the radial-basis kernel function with gamma = 1 and cost = 1, are used. Finally, the performance of developed SVR model is compared with the ΔlogR method. The TOC computed by SVR method is found to be more precise than the ΔlogR method, as it has better agreement with the core-TOC. Thus, in the present study area, the SVR method is found to be a powerful tool for estimating TOC of Cambay Shale in a continuous and rapid manner.     

Performance of cable-stayed bridge pylons subjected to blast loading

Since the terrorist attacks of 2001, concern about potential car bomb attacks on buildings and infrastructure such as bridges and tunnels has increased tremendously. Design for better performance of these structures subjected to blast load is important to prevent progressive collapse of the structure and catastrophic loss of lives. The objective of this research was to study the performance of hollow steel box and concrete-filled composite pylons of a cable-stayed bridge subjected to blast loads. Car bomb detonation on the deck is assumed to be the most likely scenario to occur. A coupled numerical approach with combined Lagrangian and Eulerian models was used to consider the interaction of the deck and pylon with the air that transfers the explosion effect to the bridge. The non-linear explicit finite element analysis program, MD Nastran SOL700 was used to simulate the spatial and time variation of the blast load as well as blast shock wave-bridge interaction response. The blast resistance of two different types of pylons was investigated in a comparative study. The study established damage patterns of the pylon and showed superior performance of the concrete-filled composite pylon over the hollow steel box pylon. For the hollow steel box pylon, the P-Δ effect on the instability of the pylon subjected to blast load was significant.     

Short communication: effect of production variables on the cis-9, trans-11 conjugated linoleic acid content of cows' milk

Although there have been numerous studies investigating effects of nutrition and individual variation on the concentration of cis-9, trans-11 conjugated linoleic acid (rumenic acid; RA) in milk, there is limited information on relationships among RA content of milk and production variables. The objective of the current analysis was to examine the effects of production variables on RA content and desaturase index of milk fat. A total of 430 samples were collected from cows fed a commercial total mixed ration in winter and grazing in summer. Across a >6-fold range in production variables, RA content of milk ranged from 1 to 32 mg/g of fatty acids and desaturase index ranged from 0.03 to 0.15. Days in milk, milk yield, milk fat content, and milk fat yield had minimal or no effect on RA content of milk fat or desaturase index (R² values all <0.08). Thus, whereas nutrition and individual variation are major factors affecting RA content and desaturase index of milk fat, these values are minimally affected by days in milk, milk yield, milk fat content, and milk fat yield. Differences in these parameters do not need to be considered, therefore, when designing management strategies to increase RA content of milk fat.