MgB2 superconducting thin films with a transition temperature of 39 kelvin

We fabricated high-quality c axis-oriented epitaxial MgB2 thin films using a pulsed laser deposition technique. The thin films grown on (1 i 0 2) Al2O3 substrates have a transition temperature of 39 kelvin. The critical current density in zero field is approximately 6 x 10(6) amperes per cubic centimeter at 5 kelvin and approximately 3 x 10(5) amperes per cubic centimeter at 35 kelvin, which suggests that this compound has potential for electronic device applications, such as microwave devices and superconducting quantum interference devices. For the films deposited on Al2O3, x-ray diffraction patterns indicate a highly c axis-oriented crystal structure perpendicular to the substrate surface.     

Atomic Control of the SrTiO3 Crystal Surface

The atomically smooth SrTiO(3) (100) with steps one unit cell in height was obtained by treating the crystal surface with a pH-controlled NH(4)F-HF solution. The homoepitaxy of SrTiO(3) film on the crystal surface proceeds in a perfect layer-by-layer mode as verified by reflection high-energy electron diffraction and atomic force microscopy. Ion scattering spectroscopy revealed that the TiO(2) atomic plane terminated the as-treated clean surface and that the terminating atomic layer could be tuned to the SrO atomic plane by homooepitaxial growth. This technology provides a well-defined substrate surface for atomically regulated epitaxial growth of such perovskite oxide films as YBa(2)Cu(3)O(7-delta).     

4-羟基-3-甲氧基苯乙腈的合成方法改进研究

[目的]改进4-羟基-3-甲氧基苯乙腈的合成工艺。[方法]以香兰素为原料,采用KF/Al2O3为脱水剂,经过多步反应合成了4-羟基-3-甲氧基苯乙腈。[结果]反应的优化条件为:3-甲氧基-4-乙酰氧基苯乙醛和盐酸羟胺的摩尔比为1.0∶1.2;反应温度为100℃;反应时间为7.5 h;KF和Al2O3的质量比为1.0∶1.5。用元素分析,红外光谱和1H NMR确定了目标化合物的结构。[结论]该路线是一种简单、经济的方法。     

Stabilization of atomic hydrogen in both solution and crystal at room temperature

Atomic hydrogen has been stably encapsulated in both solution and crystal at room temperature. Upon gamma-ray irradiation of [(CH(3))(3)Si](8)Si(8)O(20), which is the trimethylsilylated derivative of the silicate anion with a double four-ring (D4R) cage, electron spin resonance (ESR) spectra revealed that a single hydrogen atom is encapsulated in the center of the D4R cage and is stable for periods of many months. Attack by chemically reactive species such as oxygen was prevented by the D4R cage, but the ESR signal of the hydrogen atom was sensitive to the magnetic interaction caused by the presence of the O(2) molecule near the cage.     

竹炭生物模板辅助合成纳米Co_3O_4及其电化学电容性能

选用廉价、多孔、可再生的竹炭作为模板,结合溶胶-凝胶法成功地制备了纳米Co3O4。借助X-射线衍射(XRD)测试以及透射电镜(TEM)测试对所制备的纳米材料的晶型和形貌大小进行了表征。测试结果表明产物为球形立方相Co3O4,其平均直径为35nm左右。进一步通过循环伏安和恒流充放电测试研究了所得纳米Co3O4样品的电容器性能。测试结果表明,所得Co3O4电极在6mol/L KOH溶液中,-0.1~0.5V(vs Ag/AgCl)电位范围内,具有较好的循环稳定性,单电极的放电比容量达到了250F/g。     

Magnetic resonance properties of some lunar material

Paramagnetic resonance spectra of Apollo 11 fines and rocks were measured at 9 and 35 gigahertz and at 4 degrees , 80 degrees , and 300 degrees K. At both frequencies the material has an intense absorption at g = 2, with a line width of approximately 950 gauss. Fe ions with strong exchange interactions produce this resonance. A comparison of the resonance absorption due to Fe(3+) showed that the energy of the crystal field interaction was approximately 0.1 per centimeter. Mn(2+) was identified in several samples, and an absorption at g = 1.89 was tentatively attributed to Ti(3+). The nuclear magnetic resonance spectra of (27)Al had a distribution of asymmetry parameters eta ranging from 0.25 to 0.75 and had nuclear quadrupole coupling constants e(2)qQ/h of approximately 3 megahertz.     

Fe3 O4／TiO2复合物的制备

[目的]以钛铁矿为原料,制备包覆性Fe_3O_4/TiO_2磁性光催化剂。[方法]研究不同温度、反应时间、钛铁矿颗粒大小、是否冷凝回流等条件下钛铁矿的溶解情况以及TiO_2、Fe_3O_4/TiO_2的产率和催化效果,并采用X射线粉末衍射仪(XRD)、红外光谱(FT-IR)、扫描电镜(SEM)、透射电镜(TEM)等对催化剂产物进行表征,且验证催化剂的磁性能。[结果]该方法可以制备出磁性良好、包覆效果好、较纯净的Fe_3O_4/TiO_2包覆性光催化材料。[结论]制备出的Fe_3O_4/TiO_2复合物保持了Fe_3O_4的磁性,是一种性能优良的包覆性光催化材料。     

超声化学共沉淀法制备SO4^2-/ZrO2/Al2O3固体酸及其催化作用

采用超声化学共沉淀法制备SO4^2-/ZrO2/Al2O3固体超强酸催化剂,采用FT-IR、TG-DTG对催化剂进行了表征,并对催化剂的酸性强度及催化乙二胺合成哌嗪的性能进行了研究．结果表明,该催化剂具有桥式双配位结构,该结构在温度超过700℃时被破坏;随浸渍溶液浓度增大,催化剂的酸性强度和含硫量均先增大后减小;随陈化时间增加,催化剂的酸性强度增大,但陈化时间超过9h后,催化剂的酸性强度没有明显变化;焙烧温度不超过550℃时,催化剂的酸性强度随焙烧温度升高而增强,但温度超过550℃后,催化剂的酸性强度随焙烧温度升高反而降低;随催化剂中Al摩尔分数的增大,催化剂的酸性强度先增大后减小．引入Al对于提高乙二胺的转化率、改善哌嗪的收率和选择性具有一定的作用,并且哌嗪的收率和选择性随Al含量的增大而增大．     

Rhodizite: structure and composition

The mineral rhodizite could not be assigned a chemical formula on the basis of chemical analyses. The solution of the crystal structure reported here reveals that CsB(12)Be(4)Al(4)O(28) is the ideal formula. The oxygen atoms occupy all but four sites per cell of cubic close packing whose period is (1/2)a. The boron, beryllium, and aluminum atoms occupy interstices of this array, the first two in tetrahedral coordination, the last in octahedral coordination. Together these atoms form a continuous network whose composition is B(12)Be(4)Al(4)O(28), which should be neutral. The alkali atom is enclosed in a cage in this network and presumably is not behaving as an ion.     

TiO2/MIL-53(Al)和TiO2/Al2O3催化剂的制备及其光催化性能研究

采用溶剂热法合成了MIL-53(Al),以此为载体负载TiO_2制备得到TiO_2/MIL-53(Al)光催化剂用于污水中次甲基蓝的催化降解研究,并与传统载体材料Al_2O_3负载的TiO_2催化剂的光催化效果进行比较。样品通过热重-差热扫描量热(TG-DSC)、红外光谱(FTIR)、扫描电镜(SEM)、X射线衍射(XRD)、N_2物理吸附-脱附等方法进行表征。采用光度吸收法分析污水中次甲基蓝的降解率,结果显示,TiO_2/MIL-53(Al)光催化剂对次甲基蓝的光催化降解率达到98.6%,而TiO_2/Al_2O_3光催化剂对次甲基蓝的降解率只有70.3%,TiO_2/MIL-53(Al)光催化剂对污水中次甲基蓝的降解去除能力明显优于TiO_2/Al_2O_3光催化剂对次甲基蓝的降解去除能力。     

Structure of the hydrated alpha-Al(2)O(3) (0001) surface

The physical and chemical properties of the hydrated alpha-Al(2)O(3) (0001) surface are important for understanding the reactivity of natural and synthetic aluminum-containing oxides. The structure of this surface was determined in the presence of water vapor at 300 kelvin by crystal truncation rod diffraction at a third-generation synchrotron x-ray source. The fully hydrated surface is oxygen terminated, with a 53% contracted double Al layer directly below. The structure is an intermediate between alpha-Al(2)O(3) and gamma-Al(OH)(3), a fully hydroxylated form of alumina. A semiordered oxygen layer about 2.3 angstroms above the terminal oxygen layer is interpreted as adsorbed water. The clean alpha-Al(2)O(3) (0001) surface, in contrast, is Al terminated and significantly relaxed relative to the bulk structure. These differences explain the different reactivities of the clean and hydroxylated surfaces.     

Anticorrelated seismic velocity anomalies from post-perovskite in the lowermost mantle

Earth's lowermost mantle has thermal, chemical, and mineralogical complexities that require precise seismological characterization. Stacking, migration, and modeling of over 10,000 P and S waves that traverse the deep mantle under the Cocos plate resolve structures above the core-mantle boundary. A small -0.07 +/- 0.15% decrease of P wave velocity (Vp) is accompanied by a 1.5 +/- 0.5% increase in S wave velocity (V(s)) near a depth of 2570 km. Bulk-sound velocity [Vb = (Vp2 - 4/3Vs2)1/2] decreases by -1.0 +/- 0.5% at this depth. Transition of the primary lower-mantle mineral, (Mg(1-x-y) Fe(x)Al(y))(Si,Al)O3 perovskite, to denser post-perovskite is expected to have a negligible effect on the bulk modulus while increasing the shear modulus by approximately 6%, resulting in local anticorrelation of Vb and Vs anomalies; this behavior explains the data well.     

Kornerupine: its crystal structure

Three-dimensional analysis of the crystal structure of kornerupine reveals the crystallochemical formula Mg(VI)(2)Mg(VI)AlVI(6)[Si(2)O(7)] [(Al,Si)(2) SiO(10)]O(4)(OH), with four formula units in the structure cell of a = 16.100 (2) A, b = 13.767(2) A, c = 6.735(2) A; space group, Cmcm. The unusual crystal structure includes walls of Al-O edge and corner-sharing octahedra, and chains of alternating Mg-O and Al-O octahedra fused to the walls by further edge-sharing to form dense slabs. These slabs are held together by [Si(2)O(7)] corner-sharing tetrahedral pairs and [(Al,Si)(2)SiO(10)] corner-sharing tetrahedral triplets.     

An Inorganic Double Helix: Hydrothermal Synthesis, Structure, and Magnetism of Chiral [(CH3)2NH2]K4[V10O10(H2O)2(OH)4(PO4)7]{middle dot}4H2O

Very complicated inorganic solids can be self-assembled from structurally simple precursors as illustrated by the hydrothermal synthesis of the vanadium phosphate, [(CH(3))(2)NH(2)]K(4)[V(10)O(10)(H(2)O)(2)(OH)(4)(PO(4))(7)].4H(2)O, 1, which contains chiral double helices formed from interpenetrating spirals of vanadium oxo pentamers bonded together by P(5+). These double helices are in turn intertwined with each other in a manner that generates unusual tunnels and cavities that are filled with (CH(3))(2)NH(2)(+) and K(+) cations, respectively. The unit cell contents of dark blue phosphate 1, which crystallizes in the enantiomorphic space group P4(3) with lattice constants a = 12.130 and c = 30.555 angstroms, are chiral; only one enantiomorph is present in a given crystal. Magnetization measurements show that 1 is paramagnetic with ten unpaired electrons per formula unit at higher temperatures and that antiferromagnetic interactions develop at lower temperatures.     

Low-field magnetic separation of monodisperse Fe3O4 nanocrystals

Magnetic separations at very low magnetic field gradients (<100 tesla per meter) can now be applied to diverse problems, such as point-of-use water purification and the simultaneous separation of complex mixtures. High-surface area and monodisperse magnetite (Fe3O4) nanocrystals (NCs) were shown to respond to low fields in a size-dependent fashion. The particles apparently do not act independently in the separation but rather reversibly aggregate through the resulting high-field gradients present at their surfaces. Using the high specific surface area of Fe3O4 NCs that were 12 nanometers in diameter, we reduced the mass of waste associated with arsenic removal from water by orders of magnitude. Additionally, the size dependence of magnetic separation permitted mixtures of 4- and 12-nanometer-sized Fe3O4 NCs to be separated by the application of different magnetic fields.     

外源一氧化氮对铝胁迫下烟草叶片光能利用和光保护系统及活性氧代谢的影响

以云烟100(耐铝)和云烟105(铝敏感)为材料,采用水培法研究外源一氧化氮(NO)对铝胁迫下烟草植株生长、叶片活性氧含量、光合特性、叶绿素荧光参数、光呼吸和抗氧化酶活性的影响。结果表明,铝胁迫显著降低了烟草叶片叶绿素含量、净光合速率(Pn)、最大光化学效率(Fv/Fm)、PSII光合电子传递量子效率(FPSII)和光化学猝灭系数(q P),提高了反应中心PSII过剩激发能,从而导致叶片超氧阴离子(O_2·)和过氧化氢(H_2O_2)含量升高,植株生物量下降。外源NO可显著提高铝胁迫下烟草叶片叶绿素含量、Pn、Fv/Fm、FPSII、q P和植株生物量,降低反应中心PSII过剩激发能和叶片O_2·、H_2O_2含量,且云烟105变化幅度高于云烟100。此外,外源NO还显著提高了铝胁迫下烟草叶片非光化学猝灭系数、光呼吸速率、超氧化物歧化酶和抗坏血酸过氧化物酶活性,说明NO可通过提高烟草叶片光化学反应能力、热耗散、光呼吸以及抗氧化酶活性来降低反应中心PSII过剩激发能,防止或清除叶绿体内产生的活性氧,缓解铝对烟草的毒害,这种缓解效应在敏感基因型云烟105中表现更明显。     

Plasma observations near saturn: initial results from voyager 2

Results of measurements of plasma electrons and poitive ions made during the Voyager 2 encounter with Saturn have been combined with measurements from Voyager 1 and Pioneer 11 to define more clearly the configuration of plasma in the Saturnian magnetosphere. The general morphology is well represented by four regions: (i) the shocked solar wind plasma in the magnetosheath, observed between about 30 and 22 Saturn radii (RS) near the noon meridian; (ii) a variable density region between approximately 17 RS and the magnetopause; (iii) an extended thick plasma sheet between approximately 17 and approximately 7 RS symmetrical with respect to Saturn's equatorial plane and rotation axis; and (iv) an inner plasma torus that probably originates from local sources and extends inward from L approximately 7 to less than L approximately 2.7 (L is the magnetic shell parameter). In general, the heavy ions, probably O(+), are more closely confined to the equatorial plane than H(+), so that the ratio of heavy to light ions varies along the trajectory according to the distance of the spacecraft from the equatorial plane. The general configuration of the plasma sheet at Saturn found by Voyager 1 is confirmed, with some notable differences and additions. The "extended plasma sheet," observed between L approximately 7 and L approximately 15 by Voyager 1 is considerably thicker as observed by Voyager 2. Inward of L approximately 4, the plasma sheet collapses to a thin region about the equatorial plane. At the ring plane crossing, L approximately 2.7, the observations are consistent with a density of O(+) of approximately 100 per cubic centimeter, with a temperature of approximately 10 electron volts. The location of the bow shock and magnetopause crossings were consistent with those previously observed. The entire magnetosphere was larger during the outbound passage of Voyager 2 than had been previously observed; however, a magnetosphere of this size or larger is expected approximately 3 percent of the time.     

外源一氧化氮对铝胁迫下烟草叶片呼吸作用和活性氧代谢的影响

为探明外源一氧化氮(NO)提高烟草耐铝性的生理机制,采用水培法研究了NO供体硝普钠(SNP)对铝胁迫下2个不同耐铝性烟草品种云烟100(耐铝)和云烟105(敏感)植株生长、叶片活性氧(ROS)含量、呼吸作用和线粒体抗氧化酶活性的影响。结果表明,铝胁迫显著降低了烟草叶片总呼吸速率、细胞色素呼吸速率、交替呼吸速率、细胞色素氧化酶(COX)活性和丙酮酸含量,导致叶片O—·2产生速率升高和H2O2大量积累,植株生物量显著下降,且云烟105变幅高于云烟100;外源NO处理显著缓解铝对烟草植株生长的抑制,提高叶片总呼吸速率、细胞色素呼吸速率、交替呼吸速率、COX活性和丙酮酸含量,降低叶片O—·2产生速率和H2O2含量,且对云烟105的缓解效果显著高于云烟100。此外,外源NO处理进一步提高铝胁迫下烟草叶片线粒体超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性,且云烟105增幅显著大于云烟100。综上所述,外源NO处理可通过提高烟草叶片呼吸作用和线粒体抗氧化酶活性来清除线粒体内ROS含量,从而缓解铝对烟草的毒害作用,且对敏感基因型的缓解效应较耐铝基因型更为明显。     

钙质结核的微形态及矿物学特征

土壤中的钙质结核可分为软结核、硬结核和钙质硬盘３种形态，其化学组成以ＣａＣＯ３为主，矿质全量组成的各氧化物平均含量水平的顺序为：ＣａＯ〉ＳｉＯ２〉Ａｌ２Ｏ３〉Ｆｅ２Ｏ３〉ＭｇＯ〉Ｋ２Ｏ〉Ｎａ２Ｏ〉ＴｉＯ２〉ＭｎＯ〉Ｐ２Ｏ５。但在某些软结核中，ＳｉＯ２含量仍大于ＣａＯ含量。微形态分析结果表明，软结核为碳酸盐颗粒的胶结体，常嵌埋较多的土壤基质、石英、长石等粗颗粒；硬结核多为碳酸盐和方解石的胶结体，许多     

Multiferroic BaTiO3-CoFe2O4 Nanostructures

We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO3 (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The films are epitaxial in-plane as well as out-of-plane with self-assembled hexagonal arrays of CoFe2O4 nanopillars embedded in a BaTiO3 matrix. The CoFe2O4 nanopillars have uniform size and average spacing of 20 to 30 nanometers. Temperature-dependent magnetic measurements illustrate the coupling between the two order parameters, which is manifested as a change in magnetization at the ferroelectric Curie temperature. Thermodynamic analyses show that the magnetoelectric coupling in such a nanostructure can be understood on the basis of the strong elastic interactions between the two phases.