氮化硼包裹的立方氧化锆纳米颗粒

氧化锆基陶瓷材料具有高硬度、高强度、耐磨损、耐高温及电绝缘等优良性能 ,在结构和功能材料上有广泛的应用。纯二氧化锆主要有单斜相、四方相和立方相三种晶型。常压下 ,温度低于 12 0 5℃时为单斜相 ,12 0 5℃到 2 377℃之间为四方相 ,2 377℃到熔点 2 710℃之间为立方相。要获得室温下稳定的立方相二氧化锆 ,需要掺杂其他阳离子。石墨或六方氮化硼 (ｈ ＢＮ)包裹的纳米颗粒近期受到广泛关注[1～ 4] ,相对惰性的外包裹层可以保护内部的纳米颗粒不受外部环境的影响 ,如氧化、腐蚀等。本文用高分辨电子显微镜研究气 固多相反应合成的六方…     

Inhibition of various steps in the replication cycle of vesicular stomatitis virus contributes to its photoinactivation by AlPcS4 or Pc4 and red light

Vesicular stomatitis virus (VSV) was used as a model virus to study the processes involved in photoinactivation by aluminum phthalocyanine tetrasulfonate (AlPcS4) or silicon phthalocyanine HOSiPcOSi(CH3)2(CH2)3N(CH3)2 (Pc4) and red light. Previously a very rapid decrease in the intracellular viral RNA synthesis after photodynamic treatment was observed. This decrease was correlated to different steps in the replication cycle. Binding of VSV to host cells and internalization were only slightly impaired and could be visualized by electron microscopy. The capability of the virus to fuse with membranes in an acidic endosomal environment was studied using both pyrene-labeled liposomes and a hemolysis assay as a model. These tests indicate a rapid decrease of fusion capacity after AlPcS4 treatment, which correlated with the decrease in RNA synthesis. For Pc4 treatment no such correlation was found. The fusion process is the first step in the replication cycle, affected by AlPcS4 treatment, but also in vitro RNA polymerase activity was previously shown to be inhibited. Inactivation of VSV by Pc4 treatment is apparently caused by damage to a variety of viral components. Photodynamic treatment of virus suspensions with both sensitizers causes formation of 8-oxo-7,8-dihydroguanosine in viral RNA as measured by HPLC with electrochemical detection. This damage might be partly responsible for inhibition of the in vitro viral RNA polymerase activity by photodynamic treatment.     

The effects of preservation methods, dyes and acidification on the isotopic values (δ15N and δ13C) of two zooplankton species from the KwaZulu-Natal Bight, South Africa

Stable isotope measurements are an important tool for ecosystem trophic linkage studies. Ideally, fresh samples should be used for isotopic analysis, but in many cases organisms must be preserved and analysed later. In some cases dyes must be used to help distinguish organisms from detritus. Since preservatives and dyes are carbon-based, their addition could influence isotopic readings. This study aims to improve understanding of the effects of sample storage method, dye addition and acidification on the δ(15)N and δ(13)C values of zooplankton (Euphasia frigida and Undinula vulgaris). Zooplankton was collected and preserved by freezing, or by the addition of 5% formalin, 70% ethanol, or 5% formalin with added Phloxine B or Rose Bengal, and stored for 1 month before processing. Samples in 5% formalin and 70% ethanol were also kept and processed after 3 and 9 months to study changes over time. Formalin caused the largest enrichment for δ(13)C and a slight enrichment for δ(15)N, while ethanol produced a slight depletion for δ(13)C, and different effects on δ(15)N depending on the species. In formalin, dyes depleted the δ(13)C values, but had variable effects on δ(15)N, relative to formalin alone. Acidification had no significant effect on δ(15)N or δ(13)C for either species. Long-term storage showed that the effects of the preservatives were species-dependent. Although the effects on δ(15)N varied, a relative enrichment in (13)C of samples occurred with time. This can have important consequences for the understanding of the organic flow within a food web and for trophic studies. .     

大学物理教育改革势在必行

1996年7月31日到8月3日，来自28个国家的约280名物理学家参加了在马里兰大学举办的“国际大学物理教育会议”(ICUPE)，这个会议围绕以下三个主题：     

计算材料学为电子显微学创造新的机遇

计算材料学为电子显微学创造新的机遇叶恒强王雨晨（中国科学院金属研究所，固体原子像开放研究实验室，沈阳１１００１５）近年来，由于计算机及计算技术的飞速发展，计算实验科学正悄然与许多领域交叉，并兴起为新的分支。如象物理科学中除理论物理、实验物理外，正在发...     

A highly accurate plucking mechanism for acoustical measurements of stringed instruments

This paper introduces a fully automated plucking apparatus for stringed instruments. The basic idea of the proposed mechanism is to make use of the constant tensile strength of bare wires. It defines the plucking intensity of a clasped string by pulling the wire until it breaks. The main components of the apparatus are bare wires for the string plucking, solenoids for the transmission of traction, bipolar transistors for the electric circuit switching, and a signal generator for the trigger settings. The mean average of the correlation coefficients between several individual excitations is well above 99%.     

Understanding diffusion in nanoporous materials

Can we predict diffusion behavior of molecules in confinement by looking at the match between the molecule and the structure of the confinement? This question has proven difficult to answer for many decades. As a case study, we use methane and a simple model of ellipsoids to arrive at a molecular picture that allows us to make a classification of pore topologies and to explain their diffusion behavior as a function of loading. Our model is surprisingly simple: regarding a structure as consisting of interconnected ellipsoids is enough to understand the full loading dependence.     

Fragment growing induces conformational changes in acetylcholine-binding protein: a structural and thermodynamic analysis

Optimization of fragment hits toward high-affinity lead compounds is a crucial aspect of fragment-based drug discovery (FBDD). In the current study, we have successfully optimized a fragment by growing into a ligand-inducible subpocket of the binding site of acetylcholine-binding protein (AChBP). This protein is a soluble homologue of the ligand binding domain (LBD) of Cys-loop receptors. The fragment optimization was monitored with X-ray structures of ligand complexes and systematic thermodynamic analyses using surface plasmon resonance (SPR) biosensor analysis and isothermal titration calorimetry (ITC). Using site-directed mutagenesis and AChBP from different species, we find that specific changes in thermodynamic binding profiles, are indicative of interactions with the ligand-inducible subpocket of AChBP. This study illustrates that thermodynamic analysis provides valuable information on ligand binding modes and is complementary to affinity data when guiding rational structure- and fragment-based discovery approaches.