氯化 Ti3AlC2 陶瓷制备碳化物衍生碳的结构表征

以三元碳化物陶瓷Ti_3AlC_2为原料,在500°C~1000°C温度范围内氯化制备具有纳米孔结构的碳化物衍生碳(Ti_3AlC_2-CDC)。高温氯化制备得到的Ti_3AlC_2-CDC由无定形碳和石墨组成。氯化温度越高,石墨化程度越明显,石墨有序度越高。Ti_3AlC_2-CDC的结构与前驱体Ti_3AlC_2的层状结构保持一致。但随着温度升高,Ti_3AlC_2-CDC会逐渐裂解为单片层或多片层。采用N2吸附技术研究了700°C、800°C和1000°C下制备的Ti_3AlC_2-CDC的孔隙结构特征,通过分析试样的吸附等温线特征和孔径分布探讨了温度对CDC孔结构的影响。     

梯度纤维多孔材料的吸声特性及结构优化

利用金属纤维为原料,制成内部具有梯度孔结构的金属纤维多孔吸声材料。梯度孔结构可分为孔隙度梯度和丝径梯度,分别研究了这2种梯度结构的吸声特性。结果表明,厚度在6~30 mm范围内时,孔隙度梯度结构按照孔隙度从大到小的顺序排列有利于提高全频的吸声性能;厚度为3 mm时,孔隙度梯度结构的排列顺序对吸声性能的影响规律恰好相反;丝径梯度结构的吸声特点是当厚度为3 mm时,细丝径纤维多孔材料在前,全频吸声性能较好;当厚度≥15mm时,粗丝径纤维多孔材料在前,全频吸声性能好;厚度在3~15 mm之间,2种排列方式的丝径梯度结构的吸声-频率曲线存在一个交点,随着厚度的增加,该交点逐渐向低频方向移动。     

Slow interfacial charge recombination in solid-state dye-sensitized solar cell using Al2O3-coated nanoporous TiO2 films

Al₂O₃-coated TiO₂ porous films were used to fabricate solid-state dye-sensitized solar cells using CuI as hole conductor. Investigation with transient photovoltage measurements showed that the Al₂O₃ interlayer slowed down the interfacial recombination of electrons in TiO₂ with holes in CuI by forming a potential barrier at the TiO₂/CuI interface. As a consequence, the cell made from Al₂O₃-coated TiO₂ film showed superior cell performance than the cell made from TiO₂ film only, especially under relative high intensity of simulated sunlight.     

Negligible particle-specific antibacterial activity of silver nanoparticles

For nearly a decade, researchers have debated the mechanisms by which AgNPs exert toxicity to bacteria and other organisms. The most elusive question has been whether the AgNPs exert direct "particle-specific" effects beyond the known antimicrobial activity of released silver ions (Ag(+)). Here, we infer that Ag(+) is the definitive molecular toxicant. We rule out direct particle-specific biological effects by showing the lack of toxicity of AgNPs when synthesized and tested under strictly anaerobic conditions that preclude Ag(0) oxidation and Ag(+) release. Furthermore, we demonstrate that the toxicity of various AgNPs (PEG- or PVP- coated, of three different sizes each) accurately follows the dose-response pattern of E. coli exposed to Ag(+) (added as AgNO(3)). Surprisingly, E. coli survival was stimulated by relatively low (sublethal) concentration of all tested AgNPs and AgNO(3) (at 3-8 μg/L Ag(+), or 12-31% of the minimum lethal concentration (MLC)), suggesting a hormetic response that would be counterproductive to antimicrobial applications. Overall, this work suggests that AgNP morphological properties known to affect antimicrobial activity are indirect effectors that primarily influence Ag(+) release. Accordingly, antibacterial activity could be controlled (and environmental impacts could be mitigated) by modulating Ag(+) release, possibly through manipulation of oxygen availability, particle size, shape, and/or type of coating.     

Assembly, characterization and swelling kinetics of Ag nanoparticles in PDMAA-g-PVA hydrogel networks

A series of poly(N,N-dimethylacrylamide)-g-poly(vinyl alcohol) (PDMAA-g-PVA) graft hydrogel networks were designed and prepared via a free radical polymerization route initiated by a PVA-(NH₄)₂Ce(NO₃)₆ redox reaction. Silver nanoparticles with high stability and good distribution behavior have been self-assembled by using these hydrogel networks as a nanoreactor and in situ reducing system. Meanwhile the PDMAA or PVA chains can efficiently act as stabilizing agents for the Ag nanoparticles in that Ag⁺ would form complex via oxygen atom and nitrogen atom, and form weak coordination bonds, thus astricting Ag⁺. The structure of the PDMAA-g-PVA/Ag was characterized by a Fourier transform infrared spectroscope (FTIR). The morphologies of pure PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones were observed by a scanning electron microscopy (SEM) and transmission electron microscope (TEM). TEM micrographs revealed the presence of nearly spherical and well-separated Ag nanoparticles with diameters ranging from 10 to 20 nm, depending on their reduction routes. XRD results showed all relevant Bragg's reflection for crystal structure of Ag nanoparticles. UV–vis studies apparently showed the characteristic surface plasmon band at 410–440 nm for the existence of Ag nanoparticles within the hydrogel matrix. The swelling kinetics demonstrated that the transport mechanism belongs to non-Fickian mode for the PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones. With increasing the DMAA proportion, the r₀ and S_∞ are enhanced for each system. The assembly of Ag nanoparticles and the swelling behavior may be controlled and modulated by means of the compositional ratios of PVA to DMAA and reduction systems.     

A Weak Signal Extraction Method for Human Blood Glucose Noninvasive Measurement using Near Infrared Spectroscopy

Background interference from optical absorption of matrix components, low spectral selectivity and low spectral sensitivity are the main interference factors for human blood glucose noninvasive measurement using near infrared (NIR) spectroscopy. In order to extract the weak glucose concentration information, a modified uninformative variable elimination (mUVE) method combined with successive projections algorithm (SPA) named as mUVE-SPA, is proposed. mUVE is used to eliminate matrix background and high-frequency noise by wavelet multi-resolution technology. SPA is followed to select variables with minimum colinearity by projection algorithm in a vector space. The proposed method was applied in two NIR spectra data sets (plasma samples experiment in vitro and human blood glucose noninvasive measurement experiment in vivo) respectively. The performance and adaptability of the proposed strategy were discussed. The results indicate that the proposed hybrid method can give an alternative path to extract weak glucose information and yield more parsimonious models with higher precision.     

可信云服务

云服务是一类依托于云计算平台的新兴网络服务,其外包服务模式以及云平台自身的安全风险引起了用户的信任问题.云服务可信与否成为用户业务向云迁移的最大顾虑.如何构建安全可信的云服务,成为近年来研究领域的热点之一.该文在分析云计算安全威胁的基础上,提出了可信云服务的定义,并从用户信任预期、安全威胁来源和技术针对的安全目标等角度对可信云服务研究技术的类型进行了划分;然后,系统地梳理了数据存储外包、计算外包、虚拟机外包等典型云服务的安全可信研究工作;最后,探讨了可信云服务的未来研究趋势.     

Phase evolution of SiOC-based ceramic nanocomposites derived from a polymethylsiloxane modified by Hf- and Ti-alkoxides

SiOC/HfO₂-based ceramic nanocomposites with in situ formed HfO₂ nanoparticles were prepared via a single-source precursor (SSP) approach starting from a polymethylsilsesquioxane (PMS) modified by Hf- and Ti-alkoxides. By varying the alkyl-group of the employed Hf-alkoxides, SiOC/HfO₂-based ceramic nanocomposites with different HfO₂ polymorphs formed via thermal decomposition of the SSP under the same heat-treatment conditions. Using PMS chemically modified by Hf(OⁿBu)₄, tetragonal HfO₂ phase was formed after the synthesis at 1100°C in Ar, whereas both, tetragonal and monoclinic HfO₂ nanocrystals, were analyzed when replacing Hf(OⁿBu)₄ by Hf(OⁱPr)₄. After oxidation of the synthesized nanocomposites in air at 1500°C, a facile formation of oxidation-resistant HfSiO₄ (hafnon) phase occurred by the reaction of HfO₂ nanocrystals with silica present in the SiOC nanocomposite matrix derived from Hf(OⁱPr)₄-modified SSPs. Moreover the amount of hafnon is dramatically increased by the additional modification of the polysiloxane with Ti-alkoxides. In contrast, ceramic nanocomposites derived from Hf(OⁿBu)₄-modified SSPs, almost no HfSiO₄ is detected after oxidation at 1500°C even though in the case of Ti-alkoxide-modified single-source precursor.     

沙葱提取物抑制小鼠高脂血症作用的研究

目的 探究沙葱(Allium Mongolicum Regel)乙醇提取物抑制实验小鼠高脂血症形成的作用。方法 采用高脂饲料诱导小鼠建立高脂血症模型。用昆明种雌性小鼠随机分为对照组、高脂饲料空白模型组和沙葱剂量组,沙葱剂量组是在高脂饲料中每克分别添加0.025 mL/g、0.075 mL/g和0.15 mL/g的沙葱提取物(相当于0.25 g、0.75 g和1.5 g新鲜沙葱),分别为沙葱低剂量组、中剂量组和高剂量组。实验持续6周,每周称量小鼠体重,每2周采血一次,检测血脂相关指标,计算对照组、高脂饲料空白模型组和沙葱各剂量组的动脉粥样硬化指数(AI)和血脂综合指数(LCI)。结果 用高脂饲料成功建立高脂血动物模型;从第二周开始,相对于空白组小鼠,沙葱中、高剂量组小鼠总胆固醇(TC)、甘油三酯(TG)、低密度脂蛋白胆固醇(LDL-C)、AI、LCI值均有不同程度的降低。在第六周时,与空白组相比,高剂量组小鼠TC、TG、LDL-C、AI、LCI分别下降了 36.25%、58.79%、37.78%、54.98%、78.61%。结论 沙葱提取物可有效抑制高脂饲料小鼠血浆TC、TG、LDL-C,和AI、LCI的升高,可抑制实验小鼠高脂症的形成,其降血脂作用表现出一定的量效关系和时效关系,有可能预防并减少动脉粥样硬化的发生。     

CdS/ZnO核壳结构纳米微粒的合成及其发射光谱研究

采用单分子前驱体热分解的方法合成了单分散CdS纳米晶,以CdS纳米晶作为核,在CTAB辅助下,对其表面进行修饰,荧光光谱表明CdS/ZnO核壳结构被成功合成。考查了温度对包覆的影响,结果表明,随着温度的升高晶体结晶越好,包覆越来越完全,ZnO包覆在CdS纳米晶的表面而掩盖了CdS纳米晶的缺陷,使得缺陷发光减弱而带隙发光增强。