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排序方式: 共有580条查询结果,搜索用时 31 毫秒
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Natsumi Fukushi Miku Yoshizawa Shota Onosato Motohiro Hanada Wataru Takarada 《Journal of Macromolecular Science: Physics》2018,57(2):110-128
Multiple melting behavior of high-speed melt-spun polylactide (PLA) fibers was investigated by temperature modulated differential scanning calorimetry (TMDSC) in the heating process with various modulation periods in the calorimeter. In the case of the as-spun PLA fibers taken-up at 1 km/min, a melting endothermic peak and a recrystallization exothermic peak appeared at the same peak temperature of 151°C in the reversing and non-reversing heat flows (RHF and NRHF), respectively, whereas at 168°C, an endothermic peak was observed in both the RHF and NRHF. On the other hand, the as-spun PLA fibers taken-up at a high-speed of 6 km/min showed the melting in both the RHF and NRHF, but the recrystallization behavior was not obvious in the NRHF at the shorter modulation period conditions. The obtained data were analyzed based on the kinetic modeling of melting proposed by Toda et al. The real and imaginary parts of the complex apparent heat capacity in the melting region showed a strong modulation period dependence for both the low- and high-speed spun fibers. The endothermic heat flow of melting was separated by extrapolating the frequency to zero. For the PLA fibers spun at 1 km/min, a set of melting and recrystallization peaks in the RHF and NRHF appeared even for the melting at 168°C. In other words, the simultaneous occurrence of melting and recrystallization was confirmed through this extrapolation. For the 6 km/min PLA fibers, the presence of an exothermic heat of recrystallization was clearly confirmed at a peak temperature of 164°C. 相似文献
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列车荷载作用下轨道和地基的动响应分析 总被引:15,自引:0,他引:15
分析了列车运动荷载引起的应力波在轨道结构和周围地基中的传播,用动力子结构方法求解了铁路轨道和多层地基的相互作用问题,特别是在模型中考虑了轨枕离散支撑的作用.研究的对象结构包括列车运动荷载和受轨枕支撑的钢轨,以及下面的无限分层黏弹性地基.通过傅里叶变换求解微分形式的支配方程,得到了在频域和波数领域中的钢轨以及周围地基的振动准解析解,而响应时程则通过傅里叶逆变换得到.利用结果可以评估高速铁路列车运行时产生的轨道与周围地基的振动强度;同时提出了一种直观的方法来确定轨道与地基中产生共振时列车运行的临界速度. 相似文献
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高速铣削难加工材料时硬质合金刀具前刀面磨损机理及切削性能研究 总被引:17,自引:4,他引:13
采用涂层硬质合金刀具和细晶粒硬质合金刀具对超高强度合金钢(硬度>50HRC、抗拉强度σb>1.4 GPa)和马氏体不锈钢(硬度>30HRC)等难加工材料进行了干式高速端面铣削试验;选择刀具寿命作为刀具切削性能的评价指标,利用X射线能谱仪和扫描电子显微镜分析了硬质合金刀具前刀面的磨损形态、磨损机理以及刀具的切削性能.结果表明:在难加工材料的高速铣削过程中,涂层硬质合金刀具主要失效形式为前刀面磨损,细晶粒硬质合金刀具主要失效形式为前刀面月牙洼磨损与剥落;2种刀具的主要磨损机理均为扩散磨损和氧化磨损.对细晶粒硬质合金刀具而言,在考虑刀具材料与工件材料适配性的基础上,必须利用合理的刃口强化处理来降低磨损初期的刃口微崩刃倾向. 相似文献
578.
Yuan-Hang Chang Lian Yu Han Yang Jian Xu Yu-Jie Fu 《Journal of separation science》2023,46(22):2300370
This research investigated the effectiveness of an integrated method for the extraction and separation of naphthoquinones and diarylheptanes from exocarp of Juglands mandshurica Maxim. (namely, green walnut husks). The target compounds were obtained by ultra-turrax homogenization (UTH) coupled with ultrasound-assisted extraction (UAE) technology followed by high-speed countercurrent chromatography (HSCCC). The UTH-UAE extraction method achieved higher efficiency with 2.49- and 2.36-fold to those by UAE, and 1.39- and 1.34-fold to those by UTH in a short time. HSCCC was adopted for further separation and purification; six target compounds, namely, regiolone (RE), juglone (JU), myricatomento-genin (MG), galleon (GA), 2-oxatrycyclo[13.2.2.13,7]eicosa-3,5,7(20),15,17,18-hexaen-10-16-diol (OE), and juglanin A (JA), were separated with more than 95.37% purities and more than 84.71% final recovery rates, respectively. In this study, the integrated strategy of extraction and separation could get high purity compounds quickly, which would provide time and solvent saved method for the natural products separation from plants. 相似文献
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Xuan Sun Li Xu Huijiao Yan Peng Li Hidayat Hussain Jiguo Liu Jinjie Zhang Daijie Wang 《Journal of separation science》2023,46(19):2300238
Gynostemma pentaphyllum (Thunb.) Makino represents the popular health food and supplemental product with broad pharmacological activities. The highly polar glycosides, including flavonoids and saponins, are major effective active components that contain diverse sugar positions and quantities, which result in diverse chemical polarities, making it challenging to separate and isolate these components. The present work described the rapid and efficient linear gradient counter-current chromatography to preparatively separate glycosides from aboveground parts of G. pentaphyllum. Besides, the ethyl acetate and n-butanol binary mobile phases were achieved through adjusting associated proportions. Six glycosides, including quercetin-3-O-neohesperidoside ( 1 ), kaempferol-3-O-robinobioside ( 2 ), kaempferol-3-O-neohesperidoside ( 3 ), gypenoside LVI ( 4 ), ginsenoside Rb3 ( 5 ), and gypenoside XLVI ( 6 ), were isolated at the purities greater than 98%. Moreover, electrospray ionization mass spectrometry and nuclear magnetic resonance tandem mass spectrometry were conducted for structural identification. According to our findings, the established linear gradient counter-current chromatography was an efficient approach to separate the highly polar glycosides from aboveground parts of G. pentaphyllum. Our proposed strategy can be used to separate active compounds from other complex natural products. 相似文献