Polymer-Supported Vinyl Sulfone as an Efficient Reagent for the Synthesis of 3-Monosubstituted Isoxazoles

Polystyrene-supported vinyl sulfone reagent has been developed and used for solid-phase organic synthesis of 3-monosubstituted isoxazoles by 1,3-dipolar cycloaddition reaction with nitrile oxides and subsequent cleavage from the polymer support through an elimination reaction in the presence of potassium tert-butoxide. The advantages of this method include straightforward operation, good yield, and high purity of the crude products.     

Amphiphilicity and self-assembly of multi-walled carbon nanotubes grafted with polystyrene in different molecular weight

Polystyrene (PS) with molecular weight of 2.58?×?10⁴ was grafted to multi-walled carbon nanotubes (MWCNTs) via covalent bonds. The modified tubes can self-assemble as regular bundles in tetrahydrofuran (THF) and benzene while unmodified ones cannot but agglomerate seriously and irregularly in the same solvents. In order to find out the role that polymer plays in self-assembly, a series of PS in different molecular weights were synthesized and grafted on the surface of MWCNTs. THF and benzene are two selective solvents because they are well compatible with PS but bad with tubes. Consequently, grafted MWCNTs show amphiphilicity in them. Solvent-philic/solvent-phobic interaction controls the self-assembly driving force. Small PS offers MWCNTs worse compatibility and poorer amphiphilicity than big PS. With amphiphilicity faded, grafted tubes lose self-assembly ability gradually. Meanwhile, degenerated compatibility cripples tubes’ mobility. Therefore, both number and size of self-assemblies (SAs) decline when molecular weight of grafted PS diminishes. SAs lose their regularity and structural integrativity at the same time. Turbiscan stability index was introduced to quantify the compatibility between dispersate and solvents. Besides, a solvent-philic/solvent-phobic balance system was proposed to calculate compatibility and amphiphilicity of all the modified tubes. This model establishes a connection between compatibility, amphiphilicity, and self-assembly behaviors of modified MWCNTs.     

Synchronization of Chaotic Optical Systems by Remote Feedback Controlling

A dynamical variable feedback scheme is proposed to synchronize chaotic motion of two identical and nearly identical laser systems with an injected signal. The feedback synchronization method works well while the conventional variable-replacement synchronization methods are not realizable. Various practical situations for synchronizing two chaotic laser systems located distance away from each other are taken into account. The application of this synchronization approach to wide range of practical systems is emphasized.     

基于密度泛函理论下O和Na掺杂单层h-BN的电子结构性质和光学效应的分析

基于密度泛函理论的第一性原理方法研究了O、Na单掺杂及O和Na共掺杂单层h-BN的形成能、电子结构和光学性质.结果表明:单掺杂体系中,O掺杂N位置、Na掺杂B位置时,掺杂形成能最低;共掺杂体系中,O和Na邻位掺杂,掺杂形成能最低.与单层h-BN相比,引入杂质原子后的体系禁带宽度均减小,其中O掺杂为n型掺杂,Na掺杂为p型掺杂,而O和Na共掺h-BN体系为直接带隙材料,有利于提高载流子的迁移率.在光学性质方面,Na掺杂h-BN体系与O和Na共掺h-BN的静介电常数均增大,在低能区介电虚部和光吸收峰均发生红移,其中Na掺杂体系红移最为显著,极化能力最强.因此Na单掺和O和Na共掺有望增强单层h-BN的光催化能力,可扩展其在催化材料、光电器件等领域的应用.     

FeOx上AsH3吸附净化的密度泛函研究

基于密度泛函理论研究了AsH₃和O₂分子在α-Fe₂O₃(001)表面和FeO(100)表面的吸附及共吸附性质.结果表明：AsH₃和O₂分子在α-Fe₂O₃(001)表面最稳定的吸附构型都是Hollow吸附位点. AsH₃分子在FeO(100)表面最稳定的吸附位点为Top O吸附位点. O₂分子在FeO(100)表面最稳定的吸附位点为Hollow吸附位点. O₂分子在α-Fe₂O₃(001)和FeO(100)表面吸附后均被活化从而促进AsH₃分子的催化氧化. AsH₃分子在α-Fe₂O₃(001)表面最小的吸附能为-0.7991 eV,在FeO(100)表面最小的吸附能为-0.9117 eV.吸附值数据表明AsH     

Photon statistical properties of the cavity field in the two-atom Jaynes-Cummings model

The model that two two-level atoms interact with a singel-mode cavity is studied. The exact solution of the time evolution operator for the two-atom Jaynes-Cummings model is presented by the bare-states approach. Furthermore, we investigate the dynamical     

船舶水下辐射噪声信号理论模型及仿真

分析典型船舶水下辐射噪声实验数据,获取船舶水下辐射噪声功率谱特征,阐明了准周期随机声脉冲序列信号模型作为船舶水下辐射噪声模型的合理性和普适性,在此基础上,引入爆炸衰减型余弦脉冲信号作为该模型的基本组成单元,给予理论分析,据以数值构建船舶辐射噪声,并与海上试验获取的商船辐射噪声数据进行对比,结果明显一致,证明了该方法的有效性和实用性.     

Atomic Coherent Trapping and Properties of Trapped Atom

Based on the theory of velocity-selective coherent population trapping, we investigate an atom-laser system where a pair of counterpropagating laser fields interact with a three-level atom. The influence of the parametric condition on the properties of the system such as velocity at which the atom is selected to be trapped, time needed for finishing the coherent trapping process, and possible electromagnetically induced transparency of an altrocold atomic medium,etc., is studied.     

Growth and Characteristics of Epitaxial AlxGa1-xN by MOCVD1

AlxGa1-xN epilayers with a wide Al composition range （0.2 ≤ x ≤0.68） were grown on AlN/sapphire templates by low-pressure metalorganic chemical vapour deposition （LP-MOCVD）. X-ray diffraction results reveal that both the （0002） and （1015） full widths at half-maximum （FWHM） of the AlxGa1-xN epilayer decrease with increasing Al composition due to the smaller lattice mismatch to the AlN template. However, the surface morphology becomes rougher with increasing Al composition due to the weak migration ability of Al atoms. Low temperature photolumineseence （PL） spectra show pronounced near band edge （NBE） emission and the NBE FWHM becomes broader with increasing Al composition mainly caused by alloy disorder. Meanwhile, possible causes of the low energy peaks in the PL spectra are discussed.     

Growth and Characteristics of Epitaxial AlxGa1-xN by MOCVD

Al_xGa_1-xN epilayers with a wide Al composition range (0.2≤x≤ 0.68) were grown on AlN/sapphire templates by low-pressure metalorganic chemical vapour deposition (LP-MOCVD). X-ray diffraction results reveal that both the (0002) and (10^-15) full widths at half-maximum (FWHM) of the Al_xGa_1-xN epilayer decrease with increasing Al composition due to the smaller lattice mismatch to the AlN template. However, the surface morphology becomes rougher with increasing Al composition due to the weak migration ability of Al atoms. Low temperature photoluminescence (PL) spectra show pronounced near band edge (NBE) emission and the NBE FWHM becomes broader with increasing Al composition mainly caused by alloy disorder. Meanwhile, possible causes of the low energy peaks in the PL spectra are discussed.