On one- and two-parameter analyses of short fatigue crack growth

Recent data on short fatigue crack growth in two cast and hot isostatically pressed (hipped) aluminum alloys obtained by Shyam, Allison and Jones have been analyzed in terms of a previously proposed one-parameter short crack model which includes consideration of elastic–plastic effects, the Kitagawa effect and the development of crack closure in the wake of a newly formed crack. The material constants obtained in a prior investigation of short crack growth behavior in a cast aluminum alloy tested under fully reversed loading were used as a basis for the present analysis. The predicted rates of fatigue crack propagation are in accord with the experimental results. In the discussion, aspects of the two-parameter approach presented by Shyam et al. are compared with those of the one-parameter method of analysis used herein.     

Objects after Image

For 12 years, the Koshirakura Landscape Workshop has been an annual summer event. Located in a beautiful and remote region of Japan, it encourages a small group of architecture students to respond to the setting by creating projects that read, represent and spatially reconfigure the landscape into new constructions. Shin Egashira reveals how, over time, these constructions in turn act as a continuous form of documentation and reflection. Copyright © 2008 John Wiley & Sons, Ltd.     

冻干技术生产活性龙芽葱木的研究

对龙芽葱木采用真空冷冻干燥生产技术处理,通过温度、厚度实验使干燥时间与生产能力达到最好效果。外形美观,复水快、复水率高。     

Isolation and Characterization of Saponin-Producing Fungal Endophytes from Aralia elata in Northeast China

The purpose of this study was to investigate the diversity of endophytic fungi of Aralia elata distributed in Northeast China as well as their capacity to produce saponins. Ninety-six strains of endophytic fungi were isolated, and polymerase chain reaction (PCR) and sequencing were employed to identify the isolates. The saponin concentrations of the culture filtrates of representative strains were measured. The agar diffusion method was used to test antimicrobial activity, while high-performance liquid chromatography (HPLC) was employed to identify the saponins produced by representative strains. Alternaria, Botryosphaeria, Camarosporium, Cryptosporiopsis, Diaporthe, Dictyochaeta, Penicillium, Fusarium, Nectria, Peniophora, Schizophyllum, Cladosporium and Trichoderma species were isolated in this study. Overall, 25% of the isolates belonged to Diaporthe (Diaporthe eres), and 12.5% belonged to Alternaria. The highest concentration of saponins was produced by G22 (2.049 mg/mL). According to the results of the phylogenetic analysis, G22 belonged to the genus Penicillium. The culture filtrate of G22 exhibited antibacterial activity against Staphylococcus aureus, and ginsenosides Re and Rb2 were detected in G22 culture filtrates by HPLC.     

飞天蜈蚣七皂苷提取动力学研究

采用球形模型,以Fick第二定律为基础,建立飞天蜈蚣七皂苷的提取动力学模型.对飞天蜈蚣七皂苷进行乙醇回流提取,在不同的液料比(体积质量比)、提取温度及提取时间等条件下,对提取液中皂苷的质量浓度进行检测.再根据该球形模型方程分别推算出了提取速率常数、活化能、相对萃余率、有效扩散系数等动力学函数值.根据该模型方程推算出的提...     

Studies on cytotoxic triterpene saponins from the leaves of Aralia elata

Aralia elata has long been used as a tonic, anticancer and antidiabetic agent in China and Japan, and is widely consumed as food. Phytochemical investigation of the leaves of A. elata has led to the isolation of four new compounds, 3-O-[β-d-glucopyranosyl(1 → 3)-β-d-glucopyranosyl] echinocystic acid 28-O-β-d-glucopyranosyl ester (congmuyenoside I, 1), 3-O-[β-d-glucopyranosyl(1 → 2)-β-d-glucopyranosyl] hederagenin 28-O-β-d-glucopyranosyl ester (congmuyenoside II, 2), 3-O-{[β-d-glucopyranosyl(1 → 2)]-[β-d-glucopyranosyl(1 → 3)-β-d-glucopyranosyl(1 → 3)]-β-d-glucopyranosyl} echinocystic acid 28-O-β-d-glucopyranosyl ester (congmuyenoside III, 3) and 3-O-β-d-glucopyranosyl caulophyllogenin 28-O-β-d-glucopyranosyl ester (congmuyenoside IV, 4), and eight known triterpene saponins (5–12). The structural determination was accomplished with spectroscopic analysis, in particularly ¹³C NMR, 2D NMR and HR-ESI-MS techniques. In addition, compounds 5–10 were found for the first time in the genus Aralia. Compounds 1–12 were tested for their inhibition of the growth of HL60, A549 and DU145 cancer cells. In addition, compound 8 showed significant cytotoxic activities against HL60, A549 and DU145 cancer cells with IC₅₀ values of 15.62, 11.25 and 7.59 μM, respectively.     

辽东楤木叶片皂苷超声提取工艺优化研究

以辽东楤木叶片为试材,采用超声波提取法,以乙醇为提取溶剂提取并测定楤木皂苷含量。在单因素实验的基础上进行正交实验,研究叶片中楤木皂苷的最佳提取工艺。结果表明,叶片楤木皂苷的最佳提取工艺为乙醇浓度70%、溶剂倍量40、提取温度70℃、提取时间75min。采用最佳的超声提取工艺测定叶片中楤木皂苷含量为92.77mg/g。经优化的超声提取工艺操作简单、提取时间短、提取效率高且结果稳定。     

盐析辅助酶提取龙牙楤木皂苷及其抗氧化活性研究

以龙牙楤木为试验原料,采用盐析辅助酶法提取龙牙楤木皂苷,在单因素试验的基础上,采用响应面优化提取工艺并对比研究盐析辅助酶法、溶剂提取法制备的龙牙楤木皂苷抗氧化活性的区别。结果表明盐析辅助酶法最佳工艺为:酶解pH 5.405、酶解温度61.3℃、磷酸氢二钠添加量7.74%、酶解时间90 min、纤维素酶添加量1.5%,在此条件下龙牙楤木皂苷得率3.97%,该方法与溶剂提取法相比,可显著提高皂苷得率。抗氧化活性试验表明,盐析辅助酶法和溶剂提取法制备的龙牙楤木皂苷对DPPH自由基的IC50值依次为0.342 mg/mL、0.365 mg/mL,对超氧阴离子自由基的IC50值依次为1.220 mg/mL、1.432 mg/mL,总还原能力由强到弱为:Vc盐析辅助酶法溶剂提取法。本试验研究为龙牙楤木皂苷高效提取以及初步明确其抗氧化功能提供科学数据参考。     

回流提取长白楤木嫩芽皂苷、黄酮工艺研究

根据中心组合(Box-Behnken)试验设计原理采用响应面分析法,在单因素试验基础上,分别对回流法提取长白楤木中的皂苷与黄酮的工艺参数进行优化。结果表明：回流法提取长白楤木中皂苷的最优工艺参数组合为乙醇体积分数80%、料液比1:65.3(g/mL)、时间2h、温度94.1℃,预测皂苷最大提取量为74.65mg/g,实际测得皂苷最大提取量为70.25mg/g;回流法提取长白楤木中黄酮的最优工艺参数组合为乙醇体积分数60%、料液比1:60(g/mL)、时间4h、温度100℃,预测最大提取量为20.56mg/g,实际测得最大提取量为19.86mg/g。     

Effect of microstructural modification on damage tolerance of 34CrMo4 shaft steel

Overall damage tolerances of the heat‐treated 34CrMo4 steels having ferritic‐pearlitic, bainitic, and tempered‐martensitic microstructures were evaluated based on their threshold stress intensity factor prior to small crack propagation, fatigue strength, and fracture toughness under static loading. Kitagawa‐Takahashi diagrams were constructed to determine the limiting size of small crack propagation. The micromechanical effects of carbide morphology and phase distribution on quasi‐static and dynamic mechanical properties were also elaborated. Fractographic investigations were carried out on the notched fatigue test specimens to distinguish deterioration and deformation mechanism of the microstructure under reversed cyclic loads. Finally, improvements in the damage tolerance were discussed to present the advantages and disadvantages of each heat treatment procedure to minimize in‐service fatigue failures.