Variation of the electronic properties of zigzag boron nitride nanotubes by Al-doping: a DFT study

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes.     

含磁控和荷控两种忆阻器的混沌电路设计与仿真

利用惠普实验室荷控和磁控两种忆阻器模型设计了一个五阶混沌电路. 数值仿真结果表明该电路在参数变化情况下能产生Hopf分岔和反倍周期分岔两种分岔行为,并能产生双涡卷、单涡卷、周期态等不同相轨道. 为了验证电路的混沌行为,利用基本元器件设计了惠普实验室荷控和磁控忆阻器模拟器,并将其应用到对所设计电路中进行Pspice仿真,电路仿真结果验证了理论分析的正确性. 关键词： 混沌电路 HP忆阻器 模拟器 Pspice仿真     

基于格子Boltzmann方法的液滴沿固壁铺展动态过程模拟

矿井喷雾降尘是利用水雾使粉尘润湿沉降的过程,考虑到固体与液体间分子作用力,本文采用格子Boltzmann方法对液滴沿固壁铺展的动力学行为进行了数值模拟,结果发现铺展直径及动态接触角随时间呈指数规律,确定了液滴表面张力与铺展最大直径间的关系,固壁润湿性对铺展最大速度值影响较大,这些与物理试验及文献结果符合良好. 进一步考察了疏水性强的固壁,发现当液滴表面张力足够小时,铺展接触角可以在90°以下,与理论公式符合. 研究发现铺展过程中伴随着振荡,且铺展到最大时液膜有回缩趋势. 关键词： 液滴 格子Boltzmann方法 铺展 数值模拟     

周期性纳米洞内边缘氧饱和石墨烯纳米带的电子特性

利用基于密度泛函理论的第一性原理方法,研究了内边缘氧饱和的周期性凿洞石墨烯纳米带（G NR）的电子特性. 研究结果表明：对于凿洞锯齿形石墨烯纳米带（ZGNRs）,在非磁性态时不仅始终为金属,且金属性明显增强;反铁磁态（AFM）时为半导体的ZGNR,凿洞后可能成为金属;但铁磁态（FM）为金属的ZGNR,凿洞后一般变为半导体或半金属. 而对于凿洞的扶手椅形石墨烯（AGNRs）,其带隙会明显增加. 深入分析发现：这是由于氧原子对石墨烯纳米带边的电子特性有重要的影响,以及颈次级纳米带（NSNR）及边缘次级纳米带（ESNR）的不同宽度及边缘形状（锯齿或扶手椅形）能呈现出不同的量子限域效应. 这些研究对于发展纳米电子器件有重要的意义. 关键词： 石墨烯纳米带 纳米洞 内边缘氧饱和 电子特性     

Hybrid Particle–Continuum Simulations of Polymer Brushes in Shear Flow

A hybrid particle–continuum method is used to study the shear flow confined between two opposing walls, one of which is coated with polymer chains. Molecular dynamics (MD) is used in the particle region near the brush and Navier–Stokes (NS) equations are applied in the remaining region where the continuum assumption holds. The information exchange from the continuum region to the particle region is implemented using the constrained particle dynamics. Both Couette shear flow and oscillatory flow are considered in the present work. The effect of the shear flow on the conformational characteristics of polymer brushes is analyzed. In the overlap region, the velocities obtained from MD simulations are smoothly connected with those from NS equations. Our investigations demonstrate that the hybrid particle–continuum model is valid in exploring the shear behavior of polymer brushes.     

Prediction of Structure and Energy of Trans-1,4-Polybutadiene Glassy Surface by Atomistic Simulations of Free-Standing Ultrathin Films

Atomistic modeling of amorphous trans-1,4-polybutadiene (TPBD), using molecular mechanics and molecular dynamics (MD) simulations, is performed to generate three-dimensionally periodic bulk and two-dimensionally periodic thin film condensed phases. The condensed structures are constructed using multiple polymer chains. Structural and energetic relaxations and sampling of properties are performed using MD in the canonical ensemble (NVT) by a procedure that relieves local high-energy spots and brings the system to realistic thermodynamic states. The calculated surface energy for TPBD, 30.72 erg/cm², is in excellent agreement with the reported experimental value of 31 erg/cm². The structure of the surface layers is probed in terms of the atomic mass density variations, bond-bond orientation function profiles, and the distribution of the dihedral angles about the rotatable backbone bonds. The thickness of the surface layer over which the density varies smoothly but rapidly is found to be approximately 15 Å. The level of agreement of the calculated surface energy with the experimental value is superior in comparison to previous investigations in the literature using the atomistic approach for flexible polymers.     

The Electronic Absorption Spectra of Binuclear Complexes,[Cu(o-phen) (sal)No3 and [Cu2 (sacch)4(im)4] Crystal

The electronic absorption spectra of crystals of the title componds were recorded and the experimental results were explained quantitatively with the ligand field theory and the radial wave function of bound Cu(II) cation. With these spactra, the range of magnetic interactions between two Cu(II) ions of the title compounds are discussed.     

Spectra Studies of Complexes Between Palladium (II), Nickel (II) and Amino Acids

The complexes of Ni (His) 2·H2O, Ni (Gly) 2·2H2O, Pd (His)Cl2·H2O and Pd(Gly) 2·2H2O were synthesized. And the IR, electronic absorption and photoacoustic spectra of these complexes were measured in solid state. The nature of the metal-carboxylate coordinate bond were deduced from the variation in the carboxyl stretching frequencies. And the d-d transition absorptions of these complexes were interpreted quantitatively with the 3d scaling radial theory. Therefore, the structural characterizations were also discussed with their spectral behaviors.     

Performance characteristics of single photon pulse ranging system using Monte Carlo simulation

Single photon pulse ranging system with extremely high sensitivity has been widely used in distance measurement and 3D imaging. To analyze the factors that affect the measurement precision and accuracy will help to improve system performance. According to system structure and principle, we mainly discussed the following factors: laser intensity, pulse width, detection efficiency and time jitter. A simulation model based on Monte Carlo stochastic method was constructed in this paper, and we get the specific influence of factors on measurement precision and accuracy by simulation. Finally, we set up laboratory experiment system and took effective experiments on ranging precision and accuracy.     

Research on the passive nuclear level gauge

ABSTRACT

Using the ‘quadruple combination detection’ automatic calibration method to solve the traditional passive nuclear ash hopper material level meter calibration problem. The method adopts the ‘contour multistage measurement’ mode, fitted the ratio of absorbed dose rate detected by adjacent cascade probe with corresponding actual material level after measurement, then use the fitting parameters to calibrate automatically which do not need ash hopper stop working, And this can effectively save the calibration time and cost. The method can effectively eliminate the material level measuring error brought by the changes of radioactive activity in the coal ash, which improve the measuring precision and material level positioning accuracy. There are many factors affecting the radioactive activity of coal ash which vary in Different feeding period, or after refueling. And this may cause measurement error and misinformation. Using quadruple combination detection and contour multistage measurement mode, when the radioactive activity in the coal ash changes, the passive nuclear meter level gauge can be revised according to the calibration curve or calibrated automatically. Which eliminated the effects brought by the changing of coal ash radioactive activity, saved onerous repeatedly calibration procedure, also improve the accuracy of the calibration, avoid misjudgment, and can improve the accuracy of measurement.