Magnetic flux-line lattices and vortices in the copper oxide superconductors

A variety of recent experiments on both the static and the dynamic properties of vortices and flux-line lattices in the mixed state of the copper oxide superconductors are discussed. The experiments are of two basic types: (i) experiments that image the magnetic flux patterns either with magnetic decoration or neutrons and give information about static structures, and (ii) experiments that explore the dynamics of vortices either through the resistivity or other electrodynamic responses of the material. Results of these experiments argue in favor of the existence of a true phase transition in the high-field vortex state from a low-temperature superconducting vortex glass phase into a disordered high-temperature vortex fluid phase. The vortex glass phase transition model does a good job of explaining high-precision measurements of the dynamics at the transition. At low fields and temperatures, very long range hexatic order in the flux-line lattice is observed.     

Surface pinning as a determinant of the bulk flux-line lattice structure in copper oxide superconductors

Direct knowledge of crystal defects and their perturbation of magnetic flux lines is essential to understanding pinning and to devising approaches that enhance critical currents in superconductors with high critical temperatures (T(c)). Atomic force microscopy was used to simultaneously characterize crystal defects and the magnetic flux-line lattice in single crystals of Bi(2)Sr(2)CaCu(2)O(8). Images show that surface defects, which are present on all real samples, pin the flux-line lattice. Above a critical height, the pinning interaction is sufficiently strong to form grain boundaries in the bulk flux-line lattice. These results elucidate the structure of the defects that pin flux lines and demonstrate that surface pinning, through the formation of grain boundaries, can determine the bulk flux-line lattice structure in high-T(c) materials. The implications of these results to the bulk flux-line lattice structure observed in previous experiments and to enhancing critical currents are discussed.     

Coupling of nitrous oxide and methane by global atmospheric chemistry

Nitrous oxide (N(2)O) and methane (CH(4)) are chemically reactive greenhouse gases with well-documented atmospheric concentration increases that are attributable to anthropogenic activities. We quantified the link between N(2)O and CH(4) emissions through the coupled chemistries of the stratosphere and troposphere. Specifically, we simulated the coupled perturbations of increased N(2)O abundance, leading to stratospheric ozone (O(3)) depletion, altered solar ultraviolet radiation, altered stratosphere-to-troposphere O(3) flux, increased tropospheric hydroxyl radical concentration, and finally lower concentrations of CH(4). The ratio of CH(4) per N(2)O change, -36% by mole fraction, offsets a fraction of the greenhouse effect attributable to N(2)O emissions. These CH(4) decreases are tied to the 108-year chemical mode of N(2)O, which is nine times longer than the residence time of direct CH(4) emissions.     

不同化学方法修饰后酵母菌吸附铜离子研究

采用酸化并在不同温度下烘干、丙酮处理、氢氧化钠处理、酯化及掩蔽氨基等化学方法对酵母菌进行修饰处理,分别研究其对铜离子的生物吸附情况。实验结果表明,高温下烘干会破坏酵母菌的结构,使得其对Cu2+的吸附量下降。酵母菌经丙酮和氢氧化钠处理后吸附量增加,而经酯化及掩蔽氨基处理后可使吸附量降低。     

Metal oxide chemistry in solution: the early transition metal polyoxoanions

Many of the early transition elements form large polynuclear metal-oxygen anions containing up to 200 atoms or more. Although these polyoxoanions have been investigated for more than a century, detailed studies of structure and reactivity were not possible until the development of modern x-ray crystallographic and nuclear magnetic resonance spectroscopic techniques. Systematic studies of small polyoxoanions in inert, aprotic solvents have clarified many of the principles governing their structure and reactivity, and also have made possible the preparation of entirely new types of covalent derivatives such as CH(2)Mo(4)O(15)H(3-), C(5)H(5)TiMo(5)O(18)(3-), and (OC)(3)Mn(Nb(2)W(4)O(19))(3-). Since most early transition metal polyoxoanions have structures based on close-packed oxygen arrays containing interstitial metal centers, their chemistry offers a rare opportunity to study chemical transformations in detail on well-defined metal oxide surfaces.     

纳米氧化铜表面超疏水膜的制备

通过控制氧化法在铜基底表面制得了氧化铜纳米花瓣膜,然后分别用十二烷基硬脂酸、硬脂酸、十二烷基硫醇和线性低密度聚乙烯对其表面进行修饰.结果表明:试验得到了超疏水复合膜,表面接触角均超过150°,滚动角小于5°.其中,十二烷基硫醇修饰时,可在短时间内(1h)得到疏水性较高的纳米复合膜,表面的接触角达到165°.通过晶型分析讨论纳米氧化铜的形成机理,并用X-射线粉末衍射(XRD)、接触角测量、表面反射红外光谱(IR)及扫描电子显微镜(SEM)对复合膜进行了表征分析,结果表明,试验成功制备了具有不同形貌的超疏水性纳米结构复合膜.     

Ferroelectricity at the nanoscale: local polarization in oxide thin films and heterostructures

Ferroelectric oxide materials have offered a tantalizing potential for applications since the discovery of ferroelectric perovskites more than 50 years ago. Their switchable electric polarization is ideal for use in devices for memory storage and integrated microelectronics, but progress has long been hampered by difficulties in materials processing. Recent breakthroughs in the synthesis of complex oxides have brought the field to an entirely new level, in which complex artificial oxide structures can be realized with an atomic-level precision comparable to that well known for semiconductor heterostructures. Not only can the necessary high-quality ferroelectric films now be grown for new device capabilities, but ferroelectrics can be combined with other functional oxides, such as high-temperature superconductors and magnetic oxides, to create multifunctional materials and devices. Moreover, the shrinking of the relevant lengths to the nanoscale produces new physical phenomena. Real-space characterization and manipulation of the structure and properties at atomic scales involves new kinds of local probes and a key role for first-principles theory.     

外源NO对铜、镉胁迫下狭叶香蒲生理反应的影响

为研究外源一氧化氮(NO)对狭叶香蒲耐Cu、Cd胁迫的影响,进而揭示其缓解Cu、Cd胁迫的生理机制,以狭叶香蒲幼苗为试材,在Cu或Cd的胁迫下,分别添加0μmol/L、50μmol/L、75μmol/L和100μmol/L SNP(硝普钠,为NO供体),检测叶片和根系中抗氧化酶活性以及丙二醛(MDA)、抗坏血酸、蛋白质和叶绿素含量。结果表明:在25 mg/L Cu2+或1.5 mg/L Cd2+处理下施加不同浓度的SNP引起反应的生理指标有所不同,总体表现为叶片和根中超氧化物歧化酶(SOD)、过氧化物酶(POD)活性和蛋白质、抗坏血酸含量升高,MDA含量下降,叶绿素含量不受影响。说明外源NO能在一定程度上缓解Cu及Cd胁迫对狭叶香蒲幼苗造成的伤害。     

纳米氧化铜对砷胁迫下水稻种子发芽及幼苗生长的影响

为了研究纳米氧化铜（nCuO）对砷（As）胁迫下水稻种子发芽以及幼苗生长的影响,在培养皿中进行12 d的种子发芽试验。结果表明：2 mg·L^-1砷处理下,添加低浓度纳米氧化铜（0.5和1 mg·L^-1）可以缓解水稻幼苗的砷毒害,添加高浓度的纳米氧化铜（10、20和50 mg·L^-1）会抑制水稻种子的发芽率和根长,降低干重。与单独砷处理相比,添加纳米氧化铜可以提高水稻叶片SOD活性(0.5、1和20 mg·L^-1)及CAT活性（1、10、20和50 mg·L^-1）。水稻地上部和根部砷含量随着纳米氧化铜的加入而降低。由此可见,不同浓度的纳米氧化铜对砷胁迫下种子发芽和幼苗生长的影响不同。     

无机及分析化学课程体系的教学改革与实践

“无机及分析化学”是农林院校大学生必修的重要基础课,也是培养高素质、创新型农业人才的基石课程。针对国家专业结构调整,亟需创新型农业人才及高校逐年扩招这一新形势,无机及分析化学课程围绕高素质、创新人才的培养,重点在师资队伍的建设、新教学体系的构建、实践创新教学等方面进行了系统深入的改革尝试,取得了良好效果。主要研究内容与成果：1．针对专业合并的新形势,构建了新的教学体系。2．建立一支结构合理的师资队伍。3．针对创新人才培养的需要,在考试方法改革方面进行了尝试。4．针对现代教育需要,实现多手段立体化教学。5．开发试题库及试卷评估体糸,实现全方位优化整合。     

Structural basis of biological N2O generation by bacterial nitric oxide reductase

Nitric oxide reductase (NOR) is an iron-containing enzyme that catalyzes the reduction of nitric oxide (NO) to generate a major greenhouse gas, nitrous oxide (N(2)O). Here, we report the crystal structure of NOR from Pseudomonas aeruginosa at 2.7 angstrom resolution. The structure reveals details of the catalytic binuclear center. The non-heme iron (Fe(B)) is coordinated by three His and one Glu ligands, but a His-Tyr covalent linkage common in cytochrome oxidases (COX) is absent. This structural characteristic is crucial for NOR reaction. Although the overall structure of NOR is closely related to COX, neither the D- nor K-proton pathway, which connect the COX active center to the intracellular space, was observed. Protons required for the NOR reaction are probably provided from the extracellular side.     

Astronomers paint the big picture and fill in the blanks

Pittsburgh-Most everything in astronomy is big. But the truly outsized features of the universe-vast filaments of galaxies and its great dark voids-were highlighted when 772 researchers gathered here on 11-15 June for the 186th meeting of the American Astronomical Society. Talks included a new explanation for the large-scale "tapestry" of the universe and a new glimpse of what may fill its voids.     

The ground state of the pseudogap in cuprate superconductors

We present studies of the electronic structure of La(2-x)BaxCuO4, a system where the superconductivity is strongly suppressed as static spin and charge orders or "stripes" develop near the doping level of x = (1/8). Using angle-resolved photoemission and scanning tunneling microscopy, we detect an energy gap at the Fermi surface with magnitude consistent with d-wave symmetry and with linear density of states, vanishing only at four nodal points, even when superconductivity disappears at x = (1/8). Thus, the nonsuperconducting, striped state at x = (1/8) is consistent with a phase-incoherent d-wave superconductor whose Cooper pairs form spin-charge-ordered structures instead of becoming superconducting.     

Ecological chemistry and the palatability spectrum

A new bioassay for comparing the palatability to avian predators of monarch butterflies reared on various asclepiadaceous food plants containing cardiac glycosides indicates a palatability spectrum. The monarchs reared on one plant species are six times as emetic as those fed another, while those raised on an asclepiad which lacks cardiac glycosides are not emetic at all.     

Photoemission studies of high-tc superconductors: the superconducting gap

Over the last several years there have been great improvements in the energy resolution and detection efficiency of angle-resolved photoemission spectroscopy. These improvements have made it possible to discover a number of fascinating features in the electronic structure of the high transition temperature (T(c)) superconductors: apparently bandlike Fermi surfaces, flat-band saddle points, and nested Fermi surface sections. Recent work suggests that these features, previously thought explainable only by one-electron band theory, may be better understood with a many-body approach. Furthermore, other properties of the high-T(c) superconductors, which are difficult to understand with band theory, are well described using a many-body picture. Angle-resolved photoemission spectroscopy has also been used to investigate the nature of the superconducting pairing state, revealing an anisotropic gap consistent with a d-wave order parameter and fueling the current debate over s-wave versus d-wave superconductivity.