High-field magnetization process of granular Co–Cu alloys prepared by melt spinning

High solid-solubility Co₁₅Cu₈₅ alloys have been prepared by melt spinning and submitted to isothermal and anisothermal annealing to obtain granular alloys. The X-ray diffraction (XRD) patterns were measured to investigate the decomposition of supersaturated solid solution induced by annealing. The atomic diffusion and structural evolution during the heat treatment were investigated. In view of the problems limiting their application, the high-field magnetization curves were measured. By a fit to the high-field magnetization curves, the granular alloys are found hard to be magnetically saturated at the early stage of nucleation and growth. The magnetization behavior was correlated to the annealed-induced structural evolution and also to the magnetoresistance effect.     

Measurement of the top quark pair production cross section in pp collisions at s=7TeV in dilepton final states with ATLAS

A measurement of the production cross section of top quark pairs ($t\overline{t}$) in proton–proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of $35{\mathrm{pb}}^{?1}$, a $t\overline{t}$ production cross section ${\sigma }_{t\overline{t}}=177\pm 20(\text{stat.})\pm 14(\text{syst.})\pm 7(\text{lum.})\text{pb}$ is measured for an assumed top quark mass of $m_t=172.5\text{GeV}$. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions.     

系列双核Ln(III)配合物的晶体结构和磁性

合成了分子式为[Ln~2(phen)~2L],phen=C~1~2H~8N~2[ALn=Nd,L=(CH~3COO)~4(ONO~2)~2,BLn=Sm,L=(C~6H~5COO)~6,CLn=Eu,L=(C~6H~5COO)~6]3种同双核配合物。用X射线四圆衍射仪测定了3种化合物的结构。在化合物A分子中,2个Nd(III)原子由4个CH~3COO^-基团桥联,以phen和ONO~2^-为端基,构成了一个具有C~2对称性的双核分子。配合物B和C具有完全相同的结构,它们是以4个苯甲酸根为桥,2个phen和2个C~6H~5COO^-为端基的中心对称双核分子,其中6个苯甲酸根的成键状态可分为3种状况。在3种化合物中,每个Ln均为9配位,呈不规则多面体。Ln-Ln距离,A为0.397nm,B和C均为0.405nm。测定了各配合物的变温磁化率,通过对磁性质研究,发现化合物A在低温下具有反铁磁物质行为,并由理论拟合,求得了磁参数g,J值。     

KCuZrSe~3的中温固相合成及晶体结构

用反应性熔盐法在中温(500℃)下合成KCuZrSe~3。该晶体属正交晶系,空间群为Cmcm,Z=4。晶胞参数,a=0.3883(7)nm,b=1.4447(2)nm,c=1.0186(3)nm。V=0.5715(2)nm^3,Dc=5006mg.nm^-^3,Mr=430.74,F(000)=760,μ=25.217mm^-^1,λ(MoKα)=0.07107nm。R[R^2>2σ(F^2)]=0.0471。KCuZrSe~3具有层状结构。[CuZrSe~3]^-为带负电的层,按ABAB方式规程。K^+位于相邻两层之间。Zr^4^+与Se^2^-成八面体配位,Cu^+与Se^2^-为四面体配位,K^+与Se^2^-为四方反棱柱配位。配位多面体都有一定的变形。反应性熔盐法中温合成的这一晶体为热力学稳定相。     

铅硫二元团簇Pb~nS~n~-~1^+ (n=2～4)的从头算研究

用密度泛函方法,对铅硫团簇Pb~nS~n~-~1^+(n=2～4)的各种可能的异构体进行计算。结果表明异构体Pb~S^+(C~2~v)、Pb~3S~2^+(C~2~v)和Pb~4S~3^+(C~3~v)最为稳定,是该类团簇系列中最稳定的存在形式。同时,该类团簇的最低空轨道(LUMO)能量较低,容易得到电子,表明其相应的中性团簇也能稳定存在。     

芳基脲类衍生物的合成、活性和量子化学计算

芳基脲类化合物是抑制细胞分裂生长的一种抑制剂。本研究报导合成的六个芳基脲类化合物,并利用油菜试法测定了它们抑制油菜胚根生长的生物活性;采用MOPAC程序中的PM3方法进行了量化计算,计算结果较好地解释了新合成化合物结构与生物活性的相关性。     

不同阴/阳离子表面活性剂复配体系的缔合结构研究

测定了十二烷基磺酸钠(AS)/十六烷基三甲基溴化铵(CTAB)/正丁醇(n-C4H9OH)/正庚烷(n-C7H16)/水(H2O),十二烷基硫酸钠(SDS)/十六烷基三甲基溴化铵(CTAB)/正丁醇(n-C4H9OH)/正庚烷(n-C7H16)/水(H2O)体系的微乳液正四面体相图,并用电导法划分了AS/CTAB/n-C4H9OH/n-C7H16/H2O体系微乳液的结构(W/O,B.C.和O/W);同时研究AS/CTAB/n-C4H9OH/n-C7H16/H2O/盐类(NaCl,CaCl2或AlCl3)体系和SDS/CTAB/n-C4H9OH/n-C7H16/H2O/盐类(NaCl,CaCl2或AlCl3)体系形成中相微乳的盐宽,从中得出上述两体系中相微乳的盐宽随盐类阳离子价态的增大而的规律。     

导电高聚物修饰纳米尺度TiO~2多孔膜电极的光电化学研究

用光电化学方法研究了用导电高聚物修饰的纳米晶TiO~2多孔膜电极在不含氧化还原对和含不同氧化还原对体系电解质溶液中的光电转换过程。TiO~2/导电高聚物多孔膜电极为双层n型半导体结构,内层TiO~2多孔膜的禁带宽度为3.26eV,外层聚吡咯(PPy)膜的禁带宽度为2.23eV,而聚苯胺(PAn)膜的禁带宽度为2.88eV。用导电高聚物修饰半导体电极能使其在可见光区的光吸收增加,光电流增强,且起始波长红移至>600nm,使宽禁带半导体电极的光电转换效率得到明显改善。     

用介观动力学模拟Pluronic L64/水/p-Xylene体系的相分离

用介观动力学在介观层次上对不同组分的PluronicL64/水/p-xylene三元体系的相分离进行了研究,得到了和实验相吻合的结果。计算表明对于纯p-xylene溶剂和有含少量水的p-xylene溶剂,体系没有发生相分离,随着水的含量增加,体系发生了明显的相分离,产生了不同形态的胶团。本研究还通过对比不同溶剂组分下的体系介观形貌,讨论了水在体系相分离中的作用。同时通过分析模拟了1000步后体系中水的分布,证实在胶团核中存在自由水(freewater)的猜想。     

Assessment of HgCdTe photodiodes and quantum well infrared photoconductors for long wavelength focal plane arrays

Recent trends in infrared detectors are towards large, electronically addressed two-dimensional arrays. In the long wavelength infrared (LWIR) spectral range HgCdTe focal plane arrays (FPAs) occupy a dominant position. However, the slow progress in the development of large LWIR photovoltaic HgCdTe infrared imaging arrays and the rapid achievements of novel semiconductor heterostructure systems have made it necessary to foresee the future development of different material technologies in fabrication large FPAs. Among the competing technologies in LWIR are the quantum well infrared photoconductors (QWIPs) based on lattice matched GaAs/AlGaAs and strained layer InGaAs/AlGaAs material systems. This paper compares the technical merits of two IR detector arrays technologies; photovoltaic HgCdTe and QWIPs. It is clearly shown that LWIR QWIP cannot compete with HgCdTe photodiode as the single device especially at higher temperature operation (>70 K) due to fundamental limitations associated with intersubband transitions. However, the advantage of HgCdTe is less distinct in temperature range below 50 K due to problems involved in HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunnelling, surface and interface instabilities). Even though the QWIP is a photoconductor, several of its properties such as high impedance, fast response time, long integration time, and low power consumption, well satisfy the requirements of fabrication of large FPAs. Due to the high material quality at low temperature, QWIP has potential advantages over HgCdTe for very LWIR (VLWIR) FPA applications in terms of the array size, uniformity, yield and cost of the systems.