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排序方式: 共有67条查询结果,搜索用时 15 毫秒
31.
Wangwei Lu Kai Jiang Zhuangzhuang Chu Minglong Yuan Zhenya Tang Yu‐Yue Qin 《Packaging Technology and Science》2021,34(1):3-10
In this study, polylactic acid (PLA) films with different nano‐ZnO concentration (0, 1, 3, 5, 7, 9, and 15%wt) were obtained by casting method. Overall migration values and specific migration values were studied in different food simulants (10% [v/v] ethanol and isooctane). The results demonstrated that overall migration of the composite films and specific migration of Zn2+ was higher in 10% (v/v) ethanol solution than in isooctane solution. The release of Zn2+ was affected by the percentage of nano‐ZnO in the composite films and food simulants. The migration of Zn in this study was mainly caused by polymer softening and degradation leading to the dissolution of Zn. Scanning electron microscope analysis indicated that with the migration of Zn2+, the structure of the composite films changed greatly. Differential scanning calorimeter analysis indicated that the thermal stability was decreased and the glass transition temperature and crystallization temperature were reduced. 相似文献
32.
垂直并流向上气固两相流中流动结构的分析及曳力系数的计算 总被引:2,自引:0,他引:2
This study investigates the heterogeneous structure and its influence on drag coefficient for concurrent up gas-solid flow.The energy-minimization multi-scale (EMMS) model is modified to simulate the variation of structure parameters with solids concentration,showing the tendency for particles to aggregated to form clusters and for fluid to pass around clusters.The global drag coefficient is resolved into that for the dense phase,for the dilutephase and for the so-called inter-phase,all of which can be obtained from their respective phase-specific structure parameters.The computational results show that the drag coefficients of the different phases are quite different,and the global drag coefficient calculated from the EMMS approach is much lower than that from the correlation of Wen and Yu.The simulation results demonstrate that the EMMS approach can well describe the heterogeneous flow structure,and is very promising for incorporation into the two-fluid model or the discrete particle model as the closure law for drag coefficient. 相似文献
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以天津地铁某区间工程为依托,采取现场监测和数值模拟相结合的方式,利用FLAC3D软件模拟盾构开挖动态过程,研究隧道开挖对地层变形的扰动规律,发现考虑注浆孔分布的非均匀注浆形式模拟最接近实际情况,通过数值模拟有效地模拟了现场实测结果,进而将结果推广,得到各种注浆参数对注浆效果的影响。数值模拟结果表明:一定范围内注浆压力越大土体沉降越小,当注浆压力大于一定值时(本例为0.2MPa,各地区情况不同),对地表沉降的影响不再明显;注浆不及时的地表沉降明显大于注浆及时的情况,同步注浆可以很大程度上减少土体的沉降值;在一定范围内增大注浆量可以有效地减少地面沉降,即地面沉降随盾尾空隙填充率的增加而减少。 相似文献
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目的:探究白藜芦醇(resveratrol,RSV)对D-半乳糖(D-galactose,D-gal)致衰老小鼠脑神经细胞的保护机制。方法:采用腹腔注射D-gal建立小鼠亚急性衰老模型;检测其体质量、脑器官指数、记忆能力变化;用流式细胞仪检测脑神经细胞的凋亡率、活性氧(reactive oxygen species,ROS)水平、线粒体膜电位(mitochondrial membrane potential,MMP)变化;测定线粒体Caspase-9和Caspase-3的活力;采用Western blotting法检测线粒体细胞色素c(cytochrome c,Cyt c)、胞浆Cyt c的表达差异。结果:实验周期内各组间小鼠体质量均无显著变化(P>0.05);而与对照组相比,D-gal组小鼠脑器官指数显著减小(P<0.05),穿越隐藏平台次数减少,脑神经细胞凋亡率极显著升高(P<0.01),表明D-gal对小鼠脑神经细胞造成明显损伤。与D-gal组相比,RSV处理组小鼠脑器官指数均上升,其中D-gal+RSV(25)组效果最明显(P<0.05);穿越隐藏平台次数均有增加,但无显著性差异(P>0.05);神经细胞凋亡率均极显著降低(P<0.01),表明RSV对D-gal致衰老小鼠脑神经细胞具有保护作用。与Control组相比,D-gal组小鼠脑神经细胞ROS水平极显著升高(P<0.01),MMP极显著降低(P<0.01),Caspase-9和Caspase-3活力极显著上升(P<0.01),线粒体Cyt c表达下降、胞浆Cyt c表达增加,表明D-gal对小鼠线粒体功能造成损伤;而与D-gal组相比,RSV处理组小鼠脑神经细胞ROS水平均极显著下降(P<0.01),MMP均极显著升高(P<0.01),Caspase-9和Caspase-3活力均极显著降低(P<0.01),线粒体Cyt c表达显著上升(P<0.05),胞浆Cyt c表达显著降低(P<0.05)。结论:RSV能通过线粒体通路对D-gal致衰老小鼠脑神经细胞产生保护作用。 相似文献
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桔梗中桔梗总皂苷和桔梗皂苷D的超声波提取工艺 总被引:1,自引:0,他引:1
分别以水和甲醇为提取溶剂,研究超声波法提取桔梗中桔梗总皂苷和桔梗皂苷D的工艺条件。采用正交试验法,考察提取次数(A)、料液比(B)、提取时间(C)、超声功率(D)对桔梗总皂苷和桔梗皂苷D提取率的影响。以水为提取溶剂时,超声提取桔梗总皂苷的影响顺序:提取次数>超声功率>料液比>提取时间,最优组合A3B3C3D2;提取桔梗皂苷D的影响顺序:超声功率>料液比>提取次数>提取时间,最优组合A2B3C1D1。以甲醇为提取溶剂时,超声提取桔梗总皂苷的影响顺序:提取次数>超声功率>提取时间>料液比,最优组合A3B2C1D3;提取桔梗皂苷D的影响顺序:提取时间>提取次数>料液比>超声功率,最优组合A2B1C2D3。 相似文献
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为了提高量子点敏化太阳能电池中量子点的光电化学稳定性,本文以巯基丙酸为稳定剂,水相合成 CdXZn1-XTe量子点,再包覆CdS制备核壳量子点 CdXZn1-XTe/CdS。我们采用X射线衍射与X射线光电子能谱研究了样品的晶体结构和化学成分,并对样品的光学吸收、稳态荧光与荧光衰减行为进行了研究,结果表明三元量子点 CdXZn1-XTe的能级结构同时具有尺寸可调性和组分可调性,易于与CdS形成核壳Ⅱ型结构量子点,从而有效地提高了量子点的荧光寿命。 CdXZn1-XTe量子点与 CdXZn1-XTe/CdS量子点的荧光衰减曲线为多指数衰减形式,平均激子寿命分别为24.07 ns,39.80 ns。 相似文献
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Jing Zhou Bin Song Huijun Qin Wangwei Lu Gaoling Zhao Zhongping Huang Gaorong Han 《Journal of the American Ceramic Society》2020,103(2):1010-1017
Tm3+ doped zinc silicate glass-ceramics composed of SiO2-Al2O3-ZnO-K2O-Tm2O3 embedded with ZnO nanocrystals were successfully fabricated by melt-quenching method with subsequent heat treatment. Tm3+ ions and ZnO nanocrystals were introduced as blue and yellow luminescence centers, respectively. The effects of heat treatment, excitation wavelength and Tm3+ doping concentration on the photoluminescence behaviors of these glass-ceramics were studied. Short-time (5 minutes) heat treatment was considered as the optimal heat treatment time, which facilitates simultaneously emitting narrow blue peak located at 453 nm and a broad yellow band centered at 580 nm. Blue and yellow emissions could be attributed to the 1D2 → 3F4 transition of Tm3+ and Zni/Oi-related defect emission of ZnO nanocrystals, respectively. The combination of these two emissions allows the realization of white light emitting in the glass-ceramic samples. Furthermore, tunable luminescent color and chromaticity coordinates, including yellow, white and blue, can be realized by varying the pumping wavelengths as well as the content of Tm3+ dopant in the glass matrix. Nearly perfect white light emission with Commission Internationale de l'Eclairage coordinate (x = 0.33, y = 0.32) was achieved for the 0.05 mol% Tm3+ doped glass-ceramic embedding ZnO nanocrystals by heat treatment at 750°C for 5 minutes under the excitation of 360 nm. These luminescent glass-ceramics doped with Tm3+ ion and ZnO nanocrystals could be a promising candidate for white light emitting devices under near-ultraviolet excitation. 相似文献