二次电子发射和负离子存在时的鞘层结构特性

 建立了包括电子、离子、器壁发射二次电子以及负离子多种成分的等离子体无碰撞鞘层的基本模型,讨论了二次电子发射和负离子对1维稳态等离子体鞘层结构的影响,并且分析了多种成分等离子体鞘层内的二次电子和负离子的相互作用。结果表明：二次电子发射系数的增加和负离子含量的增加,都将导致鞘层的厚度有所减小;二次电子发射系数超过临界发射系数之后,鞘层不再是离子鞘。随着器壁材料二次电子发射系数的增加,鞘层中的负离子密度分布也逐渐增加;负离子的增加,导致二次电子临界发射系数有所增加。另外,在等离子体鞘层中二次电子发射和负离子的存在,也影响着鞘层中电子的放电特性与器壁材料的腐蚀。     

基于Sigmoid函数局部视觉适应模型的真实影像再现

为解决图像采集与显示设备之间的动态范围差异,色调映射技术试图建立一种由高到低的动态范围映射关系,可用于一般图像的真实影像再现.在不同亮度适应水平下,人眼能产生不同的响应特性及对比度敏感性,从而同时响应不同明暗的光强.由此建立了一种局部视觉适应的再现算法,采用具有参数控制的Sigmoid函数来模拟视觉适应的S形非线性特点,得到不同局部亮度适应水平下的压缩曲线,因此能较好地协调图像整体对比度、亮度调整与局部增强之间的关系,在增强图像较暗区域的同时,极大程度地保持亮区细节.经主观评价与特征统计参数相结合的方法验证,该算法能有效地实现动态范围压缩,保持图像细节而避免伪像,具有一定的色彩恒定性,且复杂度低,具有很好的实用性.     

First principles study of microscopic structures and layer-anion interactions in layered double hydroxides intercalated various univalent anions

Density functional theory has been used to investigate microscopic structures and electronic properties of LDHs containing F⁻, Cl⁻, Br⁻, I⁻, OH⁻, , , . Both electrovalent bonds and covalent bonds were found in the layer. For halogen anions, the strength of interaction was accorded with electronegative intensity. And the LUMOs dispersed throughout the interlayer region. While for complicated anions, the strength was accorded with the discrepancy of electronegative intensity between center atom and bonding atoms, the LUMOs almost localized in interlayer anions. p Orbital of metal cations and s orbital of anions provided major contributions to electrovalent parts of system, while s orbital of metal cations and p orbital of anions provided major contributions to covalent parts. This has the further significance in Forcefield design for LDHs simulation. Multiple hydrogen bonds were existed in LDHs-X system. The more the number of multiple hydrogen bonds formed, the weaker the strength of single multi-hydrogen bonds was. Multiple hydrogen bonds will bring stronger interaction between interlayer guest anion and host LDHs-layer than single hydrogen bond.     

海藻酸钠的疏水改性及释药性能研究

为了提高对疏水性药物的负载量和缓释作用,将海藻酸钠氧化后与十二胺反应使其进行疏水改性.对改性后聚合物结构进行了表征.研究了聚合物在水溶液及盐溶液中的粘度变化;将聚合物分散于NaCl/CaCl2的混合溶液中制备成凝胶微球,对药物布洛芬进行了包埋释放实验.结果表明,疏水改性后的海藻酸钠粘度增加,其凝胶微球对布洛芬负载量提高,具有较好的缓释作用.     

单分散磁性纳米粒子靶向药物载体

本文综述了单分散磁性氧化铁纳米粒子的主要制备方法、表面修饰以及在生物医学靶向药物方面的应用研究进展。金属有机前驱体高温热分解法、溶剂热合成法和LSS（liquid-solid-solution）法是目前制备高质量单分散磁性纳米粒子比较有效的手段。通过表面修饰制备出的具有良好水溶性、生物相容性和活性功能基团的磁靶向药物载体将可能实现定位蓄积、高效载药、控制释药和可生物降解等靶向治疗癌症的目的。开发出具有荧光检测、主动靶向识别、高效载药、智能控药释放、无毒副作用和生物相容性于一体的多功能靶向药物载体将是其发展趋势。     

Antioxidant enzymes expression and activity in liver of stressed wistar rat

Altered activities of antioxidant defence system enzymes and the levels of free radicals scavengers have been found to correlate with various physiological or pathological conditions, including stress. The aim of this study was to determine the effects of chronic 21 day isolation stress on antioxidant enzymes (AOEs) expression and activity in Wistar rat liver tissue. The serum corticosterone (CORT) and glucose (GLU) levels were also measured, as one of the most important indicators of stress. Our data revealed that in chronic stress conditions, when both CORT and GLU were low, the AOEs expression was markedly induced. This increase in MnSOD, CuZnSOD, and catalase exhibited similar trend implying efficient detoxification of and H₂O₂. However, this trend was not followed by the respective enzyme activity. While the total SOD activity was induced by the stress, catalase activity remained unaltered. This discrepancy led us to a conclusion that chronic isolation stress may cause oxidant-antioxidant imbalance in rat liver tissue, favoring H₂O₂ accumulation. The article is published in the original.     

A General Approach to the Synthesis of Gold–Metal Sulfide Core–Shell and Heterostructures

Cores and effect : Water‐dispersible core–shell structures and heterostructures incorporating gold nanocrystals of different shapes (polyhedra, cubes, and rods) and a variety of transition metal sulfide semiconductors (ZnS, CdS, NiS, Ag₂S, and CuS) are synthesized using cetyltrimethylammonium bromide‐encapsulated gold nanocrystals and metal thiobenzoates as starting materials.

     

Densification of silica glass at ambient pressure

We show that densification of silica glass at ambient pressure as observed in irradiation experiments can be attributed to defect generation and subsequent structure relaxation. In our molecular dynamics simulations, defects are created by randomly removing atoms, by displacing atoms from their nominal positions in an otherwise intact glass, and by assigning certain atom excess kinetic energy (simulated ion implantation). The former forms vacancies; displacing atoms and ion implantation produce both vacancies and "interstitials." Appreciable densification is induced by these defects after equilibration of the defective glasses. The structural and vibrational properties of the densified glasses are characterized, displaying resembling features regardless of the means of densification. These results indicate that relaxation of high free-energy defects into metastable amorphous structures enriched in atomic coordination serves as a common mechanism for densification of silica glass at ambient pressure.     

Raman spectroscopic investigation of carbon nanowalls

Two-dimensional carbon nanowalls (CNWs) were prepared by microwave plasma-enhanced chemical-vapor deposition and scanning electron microscopy was used to observe their morphologies. The Raman observations of different sample orientations and polarizations show that CNWs are well crystallized. Micro-Raman scattering measurements were also carried out with different excitation laser lines (325, 488, 514, 532, and 633 nm). The D band shows a very strong shift of 46.19 cm(-1)eV with excitation laser energy and this has been explained by the double resonance effect. The decreasing intensity ratios IDIG and ID'/IG with increasing laser excitation energy were detected and discussed.