Solvothermal synthesis of nanocrystalline zinc oxide doped with Mn2+, Ni2+, Co2+ and Cr3+ ions

ZnO nanopowders doped with Mn²⁺, Ni²⁺, Co²⁺ and Cr³⁺ ions have been synthesised for the first time using a solvothermal reaction with microwave heating. The nanopowders were produced from a solution of zinc acetate and manganese (II), chromium (III), nickel (II) and cobalt (II) acetates, using ethylene glycol as a solvent. The content of Ni²⁺, Co²⁺ and Cr³⁺ ions in the solution and in the solid phase were close to each other up to 5 mol%. The doping level of Mn²⁺ ions in the solid is about 50% of that in the solution. No phases or compounds other than ZnO were detected by X-ray diffraction with Mn²⁺, Co²⁺ and Ni²⁺ doping. With Cr³⁺ ions a small amount of chromium oxide was found. None of the powders displayed any luminescence after doping. The Mn²⁺-doped powder displayed a paramagnetic behaviour. ESR and magnetisation investigations have revealed that no clustering of Mn²⁺ ions occurred up to a doping level of 3.9 mol%. The average grain size of powders doped with Ni²⁺, Cr³⁺, Co²⁺ and Mn²⁺ for a 10 mol% ion content in the solution was about 20 nm and the grain size dispersion 30%. With increasing dopant content the grain size decreased. It appears that the solvothermal process employed allows relatively high doping levels of the transition metal ions to be achieved without any dopant clustering or oxide precipitation.     

Hans Bethe, My Teacher

I sketch my experiences with Hans Bethe (1906–2005) as a teacher at Cornell University, beginning with my doctoral studies in 1961 and continuing with my work with him on a quantum-mechanics textbook. Hans Bethe, My Teacher: Based on my talk at the Bethe Memorial,Aspen Center for Physics,Aspen,CO, in August 2006. Roman Jackiw: Roman Jackiw is Jerrold Zacharias Professor of Physics at the Massachusetts Institute of Technology.     

基于神经网络的多联变频空调电子膨胀阀控制系统研究

空调制冷系统具有滞后大、非线性等特点,采用普通控制方式时效果不尽人意。采用BP-PID控制器对系统电子膨胀阀开度进行控制,并设计了BP-PID控制器。实践结果表明,该控制方法简单有效,很好地满足了用户的实际需要。     

Entanglement dynamics and Bell violation of three-qubit states coupled to an XY spin chain with Dzyaloshinski–Moriya interaction

We investigate the entanglement dynamics and Bell violation of three-qubit quantum states under an environment consisting of an XY spin chain with Dzyaloshinski–Moriya (DM) interaction. From the results, we find that the entanglement dynamics depends not only on the DM interaction, the magnetic field, and the anisotropy parameter but also on the number of the freedom degrees of the environment. The decoherence-free subspaces of our model have been identified and the Bell violation of quantum states is also discussed.     

基于光外差技术的超宽带频率响应测量系统

介绍了一种利用光外差技术测量光电探测器超宽带频率响应的测试方法。将一个可调谐外腔激光器和一个固定波长的分布反馈激光器（DFB-LD’s）产生的激光输入到光电探测器进行混频。通过对可调激光器腔长的控制,可以在光电探测器产生从DC到上百GHz的拍频信号,在无需额外校准光源的情况下就可以进行光电探测器超宽带频率响应特性的测试,这是该方法最突出的优点。实验证明该方法比较准确、简便、易于操作。在实验中,对两个不同的InGaAs p-i—n探测器进行测量,得到器件的3dB带宽分别为14．4GHz和40GHz。该测量方法对同类实验的研究和应用都具有实用意义。     

Melaminium maleate monohydrate

In the title compound, 2,4,6‐tri­amino‐1,3,5‐triazin‐1‐ium maleate monohydrate, C₃H₇N₆⁺·C₄H₃O₄⁻·H₂O, containing singly protonated melaminium residues, maleate(1−) anions and water mol­ecules, the components are linked by hydrogen bonds into a three‐dimensional framework structure. The melaminium residues are connected by two pairs of N—H⋯N hydrogen bonds into chains in the form of stacks, with a distance of 3.26 (1) Å between the triazine rings, clearly indicating π–π interactions. The maleate anion contains an intramolecular O—H⋯O hydrogen bond and the anions interact with the water mol­ecules via O—H⋯O hydrogen bonds, forming zigzag chains, also in the form of stacks, in which the almost‐planar maleate anions are separated by 3.26 (1) Å. The experimental geometries of the ions are compared with molecular‐orbital calculations of their gas‐phase geometries.     

Fluoride anion sensing using colorimetric reagents containing binaphthyl moiety and urea binding site

Four 1,1′-binaphthalene based bis-urea derivatives bearing aryl groups at end-on nitrogen atoms IIIa–d were synthesized as potential sensor molecules. These receptors show characteristic UV-VIS spectral changes on complexation with anions and they exhibit selective recognition of F⁻ over other halide anions. Interaction of a fluoride anion with urea NH groups was confirmed by ¹H NMR data. The presence of an electron-withdrawing nitro group in N′-aryls (receptors IIIa and IIIb) appeared to be necessary for naked-eye colorimetric detection. These receptors show dramatic color change from light-yellow to orange (IIIa) or to orange-red (IIIb) in the presence of guest fluoride anions already at concentrations of 10⁻⁵ mol dm⁻³ of the receptor and host.     

Synthesis and Characterization of New M‐Triazole Complexes (M = Co,Cu, Zn)

Three new complexes with the ligand 3,5‐diamino‐1,2,4‐triazole (Hdatrz), [Co₃(μ₂‐Hdatrz)₆(H₂O)₆]·(NO₃)₈·4H₂O ( 1 ), [Cu₃(μ₂‐Hdatrz)₄(μ₂‐Cl)₂(H₂O)₂Cl₂]·Cl₂·4H₂O·2C₂H₅OH ( 2 ) and {[Zn₂(μ₂‐SO₄) (μ₃‐datrz)₂]·2H₂O}_n ( 3 ) have been synthesized and structurally characterized. Complex 1 has a linear trinuclear mixed‐valence cobalt structure with six neutral triazole ligands in the N(1), N(2)‐bridging mode. The central cobalt atom, Co(1), is coordinated to six nitrogen atoms (octahedral) whereas the terminal cobalt atom, Co(2), is coordinated to an N₃O₃ moiety (octahedral). In complex 1 , the uudd cyclic water clusters, nitrate anions and the trimeric cations are linked to a supramolecular structure. Complex 2 features a linear trinuclear copper(II) core, with four N(1), N(2)‐bridging triazole ligands and two chlorido bridges. The central copper atom is coordinated to an N₄Cl₂ moiety (octahedral) whereas the terminal copper is coordinated to an N₂Cl₂O moiety (square‐pyramidal). In complex 2 , tetrahedral hydrogen bonding interactions play an important role to form a supramolecular network. Complex 3 exhibits a polymeric structure, with N(1), N(2), N(4)‐bridging triazolate ligands and sulfate bridges, in which zinc is coordinated to an N₃O moiety (tetrahedral). In complex 3 , water molecules and sulfate anions construct the sulfate‐water supramolecular chain with hydrogen bonding interactions. In addition, the complexes were investigated by elemental analyses, IR spectroscopic, and thermogravimetric measurements.     

Synthesis of hexahydrocarbazoles by cyclisation of 3-(but-3-enyl) indole derivatives

A new cyclisation of 3-(but-3-enyl) indole derivatives that produces policyclic compounds with a hexahydrocarbazole structure is described. In this reaction three stereogenic centres are generated in one step, and this process can be considered as evidence of the biogenetic relationship between anominine and tubingensin A.     

Crystal structure prediction of flexible molecules using parallel genetic algorithms with a standard force field

This article describes the application of our distributed computing framework for crystal structure prediction (CSP) the modified genetic algorithms for crystal and cluster prediction (MGAC), to predict the crystal structure of flexible molecules using the general Amber force field (GAFF) and the CHARMM program. The MGAC distributed computing framework includes a series of tightly integrated computer programs for generating the molecule's force field, sampling crystal structures using a distributed parallel genetic algorithm and local energy minimization of the structures followed by the classifying, sorting, and archiving of the most relevant structures. Our results indicate that the method can consistently find the experimentally known crystal structures of flexible molecules, but the number of missing structures and poor ranking observed in some crystals show the need for further improvement of the potential. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009