Changes of thermal properties and microstructure of nano‐ZnO/polylactic acid composite films during Zn migration

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.     

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

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.     

MATLAB GUI在铁磁谐振仿真中的应用

在10kV低压配电网中,由电磁式电压互感器铁芯饱和引起的铁磁谐振现象会严重影响电力系统的安全稳定运行.以某10 kV中性点不接地配网系统为研究对象,采用Matlab/Simulink建立铁磁谐振仿真模型,以单相短路接地故障消失作为谐振触发条件,研究系统对地电容对于谐振类型的影响.为优化Simulink仿真过程中修改元件...     

沉淀硬化不锈钢机械能助渗铝工艺研究

通过机械能助渗铝工艺,实现了对沉淀硬化不锈钢的低温渗铝.在500℃渗铝 10h,得到厚约11μm的均一渗铝层.通过力学性能检测及显微硬度分析对渗铝层进行研究,发现可以在保证基体材料的力学性能基本无损耗的情况下,渗层硬度是基体材料的2倍以上.     

盾构施工中注浆因素对地表沉降的影响研究

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。     

白藜芦醇对衰老小鼠脑神经细胞的保护机制

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。     

桔梗中桔梗总皂苷和桔梗皂苷D的超声波提取工艺

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。     

核壳Ⅱ型量子点 CdXZn1-XTe/CdS的水相制备与光学性能研究

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。     

黑灵芝多糖对糖尿病大鼠血糖血脂调节及肠道菌群的影响

2型糖尿病是一种以高血糖和胰岛素抵抗为特征的代谢性疾病,它的发生、发展与肠道菌群密切相关.本实验旨在研究黑灵芝多糖对2型糖尿病大鼠的保护作用,探讨其对肠道菌群结构和代谢产物的影响.方法:选取Wistar大鼠,给予高糖高脂饲料喂养8周,采用链脲佐菌素(streptozotocin,STZ)尾静脉注射法建立大鼠糖尿病模型....     

Color-tunable and white emission of Tm3+ doped transparent zinc silicate glass-ceramics embedding ZnO nanocrystals

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 Zn_i/O_i-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.