Theoretical study of surface plasmons coupling in transition metallic alloy 2D binary grating

The excitation of a surface plasmon polariton (SPP) wave on a metal–air interface by a 2D diffraction grating is numerically investigated. The grating consists of homogeneous alloys of two metals of a formula A_xB_1−x, or three metals of a formula A_xB_yC_z, where A, B and C could be silver (Ag), copper (Cu), gold (Au) or aluminum (Al).It is observed that all the alloys of two metals present a very small change of surface plasmon resonance (SPR) irrespective of composition x. Moreover, the addition of 25% of Al to two metals alloy is insufficient to change the SPR curves. The influence of the different grating parameters is discussed in details using rigorous coupled-wave analysis (RCWA) method. Furthermore, the SPR is highly dependent on grating periods (d_x and d_y) and the height of the grating h. The results reveal that d_x= d_y= 700 nm, h=40 nm and duty cycle w=0.5 are the optimal parameters for exciting SPP.     

Fluorescence methods to study lipid-protein association: The interaction of protein kinase C with lipid-loaded mixed micelles

The interaction of protein kinase C with lipids was studied in a mixed micellar system. Two fluorescence spectroscopic methods are presented with a different but complementary information content. Diffusion monitored by fluorescence correlation spectroscopy provides information on the interaction of the protein with the whole lipid aggregate. Resonance energy transfer from tryptophans to pyrene-labeled lipids monitored by time-correlated single-photon counting supplies information on the interaction of the protein with specific lipid cofactors within the micelle. The results can be extended to postulate new mechanisms for the activation of protein kinase C by the signal transduction cascades in the cell. Both fluorescence spectroscopic methods can be easily applied to other protein systems which interact with lipids.     

Theoretical study on interaction of cytochrome f and plastocyanin complex by a simple coarse-grained model with molecular crowding effect

ABSTRACT

We present a simple coarse-grained model with the molecular crowding effect in solvent to investigate the structure and dynamics of protein complexes including association and/or dissociation processes and investigate some physical properties such as the structure and the reaction rate from the viewpoint of the hydrophobic intermolecular interactions of protein complex. In the present coarse-grained model, a function depending upon the density of hydrophobic amino acid residues in a binding area of the complex is introduced, and the function involves the molecular crowding effect for the intermolecular interactions of hydrophobic amino acid residues between proteins. We propose a hydrophobic intermolecular potential energy between proteins by using the density-dependent function. The present coarse-grained model is applied to the complex of cytochrome f and plastocyanin by using the Langevin dynamics simulation to investigate some physical properties such as the complex structure, the electron transfer reaction rate constant from plastocyanin to cytochrome f and so on. We find that for proceeding the electron transfer reaction, the distance between metals in their active sites is necessary within about 18 Å. We discuss some typical complex structures formed in the present simulation in relation to the molecular crowding effect on hydrophobic interactions.     

Theoretical study on the molecular tautomerism of the 3-hydroxy-pyridin-4-one system

3-hydroxy-pyridin-4-one is a parent molecule for the family of hydroxypyridinones that are known in coordination chemistry as efficient metal ions chelators. In this work, relative stabilities of some possible tautomers were investigated using several quantum chemical methods: CBS (complete basis set methods), Gn, DFT (density functional theory), Hartree–Fock and MP2. Performed calculations show that the system under consideration exists as a mixture of two tautomers with comparable energies. Among them, the hydroxypyridinone structure of the studied molecular system seems to be a bit more stable than the o-dihydroxypyridine one, by a few kJ/mol only. Aromaticity and intra-molecular hydrogen bonding are the main effects influencing the stability of the studied tautomeric structures. Consequently, aromatic effects were calculated using several indices of aromaticity: HOMA (harmonic oscillator model of aromaticity), NICS (nucleus independent chemical shift), H, PDI (para delocalisation index), MCI (multi-centre index) and ASE (aromatic stabilisation energy). The strength of possible intra-molecular hydrogen bonds (H-bonds) was determined by means of the AIM (atoms-in-molecules) method and by calculating enthalpies for theoretical reactions that do or do not involve H-bonds. The AIM method was employed to understand how variations in atomic energies influence the stability of different tautomeric structures.     

Computational study on the half-metallicity in transition metal–oxide-incorporated 2D g-C3N4 nanosheets

In this study, based on the first-principles calculations, we systematically investigated the electronic and magnetic properties of the transition metal–oxide-incorporated 2D g-C₃N₄ nanosheet (labeled C₃N₄– TM–O, TM= Sc–Mn). The results suggest that the TM–O binds to g-C₃N₄ nanosheets strongly for all systems. We found that the 2D C₃N₄–TM–O framework is ferromagnetic for TM= Sc, Ti, V, Cr, while it is antiferromagnetic for TM= Mn. All the ferromagnetic systems exhibit the half-metallic property. Furthermore, Monte Carlo simulations based on the Heisenberg model suggest that the Curie temperatures (T_c) of the C₃N₄–TM–O (TM= Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K, and 190 K, respectively. Based on Bader charge analysis, we found that the origin of the half-metallicity at Fermi energy can be partially attributed to the transfer of electrons from TM atoms to the g-C₃N₄ nanosheet. In addition, we found that not only electrons but also holes can induce half-metallicity for 2D g-C₃N₄ nanosheets, which may help to understand the origin of half-metallicity for graphitic carbon nitride.     

Theoretical study of the structured blue emission of PbWO 4

The experimentally observed structure in the blue emission of PbWO 4 crystals is analyzed theoretically. The full interaction Hamiltonian, including ligand field, Jahn-Teller, pseudo Jahn-Teller, and spin-orbit interactions is considered. The emission-band shape is numerically calculated using Monte-Carlo integration using both semiclassical and quantum-mechanical approaches. Theoretical results are qualitatively compared to experimentally observed spectra.     

基于四节点RSSI的三维空间定位算法

针对提高室内三维空间的定位精度和速度的问题,从减少节点数量、建立特定坐标系的角度提出了一种基于四节点和特定坐标系的三维空间定位算法。该算法引入位置相对固定的四个节点,提高解算速度;充分考虑有效反射区对衰减指数影响,根据伯鲁斯特角将天线辐射场区分为叠加加强区和叠加减弱区,建立三维坐标系进行定位,结合信号强度指示(Received Signal Strength Indicator, RSSI)衰减模型,在叠加减弱区定位,把三维空间问题转化到二维空间,降低定位算法的复杂度。文中分别阐述方法的原理与验证,结果表明,四节点定位算法的解算速度比降低复杂度(Complexity-Reduced Trilateration Approach , COLA)定位算法有较大提高,该算法平均定位误差小于2米。     

DSC study of superionic phase transition in (NH4)4H2(SeO4)3 single crystals

DSC and complex impedance studies of the protonic conductor (NH₄)₄H₂(SeO₄)₃, which undergoes a superionic phase transition of first order at T_s = 378 K show that the activation energy of ionic conductivity d(lg σ)/dt and the ordering enthalpy ΔC_p of the crystal are proportional: d(lg σ)/dT = XΔC_p/RT_s + const, as found for MAg₄I₅ crystals undergoing a second-order superionic phase transition. Thus the short-range order environment of the species involved in fast-ion transport plays the main role in the superionic phase transition. This is also supported by the value of the entropy change at T_s, ΔS = 43 J/mole·K. A new metastable phase was found to be induced on heating the (NH₄)₄H₂(SeO₄)₃ crystal above T_s.     

D+CD4→CD3+D2反应的量子含时动力学研究

运用半刚体振动转子靶(semirigid vibrating rotor target)模型,利用含时波包法(TDWP method),对反应D+CD4→CD3+D2进行了量子含时动力学研究与计算.反应几率随平动能的变化图象,呈现出显著的量子共振特性.并通过对v=0时,j=0,1,2的反应几率以及j=0时,v=0,1的反应几率的计算,对该反应的空间效应进行了研究与分析.     

Mo掺杂4H-SiC的磁性和光学性能的第一性原理研究

基于第一性原理密度泛函理论（DFT）的广义梯度近似（GGA）的平面波赝势法（PBE）,计算了4H-SiC的本征体系、过渡金属元素Mo单掺杂4H-SiC体系的电子结构、磁性和光学特性。结果表明：Mo掺杂将导致4H-SiC由本征非磁性变为p型磁性半导体材料,其带隙值由2.88 eV 变为0.55 eV。当Mo掺杂浓度为1.359×1021 cm-3时,磁矩为0.98 ,这表明掺Mo后的4H-SiC材料可以作为自旋电子元器件的备选材料。此外,Mo掺杂4H-SiC体系在（100）和（001）方向的静态介电常数分别为3.780和3.969。介质函数虚部不为0的起始点发生红移,表明掺杂使电子更容易跃迁。     

Substituent effects on the reduction of 2–alkylcyclohexanones by LiAlH4: an investigation of conformational equilibria and transition states

Transition state (TS) structures for the reduction of 2‐Me and 2‐i‐Pr‐cyclohexanone by LiAlH₄ were optimized by density functional theory (B3LYP/6‐31G(d,p)). Four TS structures corresponding to axial and equatorial attacks by LiAlH₄ were located for each ketone conformer. Electronic potential maps were used to investigate the substituent electronic effect on the TS stabilization. The uneven carbonyl orbital distribution in the LUMO (π*) was also analyzed. Reduction stereoselectivity was shown to depend on both the ketone conformational ratio and on the reaction TS. Copyright © 2010 John Wiley & Sons, Ltd.     

一簇金刚石晶格上S~4模型的相变

采用重整化群和累积展开的方法,研究了一簇金刚石晶格上S~4模型的相变,求得了系统的临界点.结果表明:当分支数m=2和m 12时,该系统只存在一个Gauss不动点K~*=b_2/2, u_2~*=0;当分支数3≤m≤12时,该系统不仅有Gauss不动点,还存在一个Wilson-Fisher不动点,并且后一个不动点对系统的临界特性产生决定性的影响.     

Theoretical study on the band structure and optical properties of 4H-SiC

We have studied the band structure and optical properties of 4H-SiC by using a full potential linearized augmented plane waves (FPLAPW) method. The density of states (DOS) and band structure are presented. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With band gap correction, the real part of the dielectric function has been derived from the imaginary part by the Kramers－Kronig (KK) dispersion relationship. The values of reflectivity for normal incidence as a function of photon energy have also been calculated. We found the theoretical results are in good agreement with the experimental data.     

Theoretical study on the improvement of the doping efficiency of Al in 4H-SiC by co-doping group-IVB elements

The p-type doping efficiency of 4H silicon carbide (4H-SiC) is rather low due to the large ionization energies of p-type dopants. Such an issue impedes the exploration of the full advantage of 4H-SiC for semiconductor devices. In this study, we show that co-doping group-IVB elements effectively decreases the ionization energy of the most widely used p-type dopant, i.e., aluminum (Al), through the defect-level repulsion between the energy levels of group-IVB elements and that of Al in 4H-SiC. Among group-IVB elements Ti has the most prominent effectiveness. Ti decreases the ionization energy of Al by nearly 50%, leading to a value as low as ~0.13 eV. As a result, the ionization rate of Al with Ti co-doping is up to ~5 times larger than that without co-doping at room temperature when the doping concentration is up to 10¹⁸ cm^-3. This work may encourage the experimental co-doping of group-IVB elements such as Ti and Al to significantly improve the p-type doping efficiency of 4H-SiC.     

The study of transition on NiFe2O4 nanoparticles prepared by co-precipitation/calcination

In this study, the NiFe₂O₄ nanoparticles have been prepared by co-precipitation and calcination process. Using a vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometer of X-ray (EDX), and X-ray photoelectron spectroscopy (XPS), the samples obtained by co-precipitation and then by further calcination have been analyzed. The experimental results show that the precursor synthesized by co-precipitation is the composite of both amorphous FeOOH and Ni(OH)₂, but has no amorphous NiFe₂O₄. The results of both EDX and XPS revealed that the FeOOH species is wrapped up by Ni(OH)₂ species. In the calcination process, the amorphous composite is dehydrated and transformed gradually into crystalline NiFe₂O₄ nanoparticles, with the metal ions diffusing. The reaction is different from the one used to prepare other ferrite (e.g., CoFe₂O₄, MnFe₂O₄, Fe₃O₄, etc.) nanoparticles directly by co-precipitation. With increasing calcination temperature, the NiFe₂O₄ grains grow and the magnetization is enhanced.     

高离化态类Ne离子的与X射线激光有关的3p-3s跃迁的理论研究

利用多组态Dirac-Fock(MCDF)理论方法,系统研究了与X射线激光有关的类Ne等电子系列离子(Z=50～57)的2s22p6、2s22p53e和2s2p63e(e=s、p、d)激发态的能级以及跃迁几率、波长和振子强度.详细讨论了关联效应对与X射线激光有关的能级寿命以及跃迁几率的影响,给出并分析了与x射线激光有关的3p-3s跃迁的波长,几率和振子强度的变化规律,部分计算结果与已有的理论和实验结果作了比较.     

4-氨基-3,5-二硝基吡唑二聚体分子间相互作用的理论研究

在密度泛函（DFT）B3LYP/6-311++G**水平下,求得4-氨基-3,5-二硝基吡唑（LLM-116）二聚体势能面上的4种全优化几何构型。经基组叠加误差（BSSE）和零点能（ZPE）校正, 求得分子间最大相互作用能为 –29.56 kJ×mol-1。研究表明,其相互作用是放热过程,并随着温度的升高,相互作用减弱;自然键轨道（NBO）分析揭示了相互作用的本质;对优化构型进行振动分析,得其红外光谱,并基于统计热力学求得200.0-800.0 K 温度范围从单分子形成二聚体的热力学性质变化。     

钪原子的自电离里德伯能级3d4s(~1D_2)nf~2D_(3/2),3d4s(~1D_2)nf~2F_(5/2)和3d4s(~1D_2)np~2D_(3/2)的理论研究

在多通道量子亏损理论框架下,利用相对论多通道理论,分别在冻结实近似和考虑偶极极化下计算钪原子的Jπ=(3/2)-,(5/2)-的三个收敛于[Ar]3d4s(1D2)的自电离里德伯系列的能级.对3d4s(1D2)np2D3/2和3d4s(1D2)nf2F5/2这两个系列,计算结果表明,考虑偶极极化效应后,理论计算和实验测量的量子数亏损之差普遍小于0.01.而对3d4s(1D2)nf2D3/2系列,考虑偶极极化效应后的结果和仅考虑冻结实的结果比较接近,理论计算和实验测量的量子数亏损之差普遍在0.04左右.     

F3+和Ne4+离子的光电离截面的理论计算

利用R矩阵方法计算了F³⁺和Ne⁴⁺离子的基态2s²2p²(³P)和激发态2s²2p² (¹D,¹S),2s2p³ (⁵S^o)的分波光电离截面、总光电离截面,分析辨认出了这些离子在自光电离过 关键词： 3+离子和Ne⁴⁺离子')" href="#">F³⁺离子和Ne⁴⁺离子 光电离 自电离共振 R矩阵')" href="#">R矩阵     

Verwey相变处Fe3O4的结构、磁性和电输运特性

作为典型的金属–绝缘体转变,Fe3O4的Verwey相变蕴涵的丰富物理现象与微观机制,因而受到了人们的广泛关注.在Verwey相变处,Fe3O4的晶体结构、电子结构以及磁各向异性等均发生转变,但其磁基态并未发生改变.与其他强关联体系相比,Fe3O4的Verwey相变不需要考虑磁交换耦合作用的变化,有利于揭示强关联体系中金属–绝缘体转变的物理本质.本文从晶体结构、电荷有序、电输运特性、磁性和铁电特性等方面简要地介绍了Fe3O4的Verwey相变的研究历史和现状.