Energies and widths of triply excited states of lithiumlike oxygen and neon

Seven low-lying triply exited states of lithium-like oxygen and neon are calculated with the multichannel saddle-point and saddle-point complex-rotation methods. The term energies are given for these excited states, along with level shifts and partial Auger widths from dominant decay channels. The mass polarization effect and relativistic corrections are included. The radiative transition rates are also calculated. These results are compared with other theoretical data in the literature. Received: 25 May 1998 / Revised: 28 July 1998 / Accepted: 25 August 1998     

On features of the magnetic structure of spherical iron nanoparticles

The results of research into the behavior of the magnetic structure inherent to spherical ferromagnetic nanoparticles with radii of 5–30 nm are presented. The behavioral features are investigated in an external magnetic field by means of computer modeling. The hysteresis loops and formation of the vortex structure of magnetization are analyzed using particles with different sizes. The size effect of changes in the magnetization symmetry, which is analogous to phase transitions of the second kind, is established. The magnetic moments of spherical iron nanoparticles with radii of 5–30 nm are calculated. Calculations are performed by means of the Nmag micromagnetic simulation package.     

带宽对平顶高斯宽带激光传输特性的影响

研究了横向分布为平顶高斯模式的宽带激光在自由空间的传输特性,分析了频带宽度对其强度分布的影响。首先推导了平顶高斯模式宽带激光的每一频率分量在自由空间的传输公式,然后将频率域的传输公式通过傅里叶变换得到时间域的传输公式。基于推导的公式通过数值算例给出了不同频带宽度激光光束的强度分布结果,详细分析了空间模式的变化和时空耦合现象。研究结果表明:随着传输距离增大,平顶高斯空间模式趋于高斯分布。同时随着带宽增大,平顶高斯模式宽带激光表现出更强的时空耦合现象,并导致其空间横向分布发生明显变化。变化的主要特征为波前的强度分布随带宽增大而变窄,波后的强度分布则随带宽增大而远离轴中心向外扩展。     

传输同步辐射X射线的锥形单毛细管的物理特性

根据北京同步辐射装置生物大分子实验站(2W1A)的条件和应用,从理论上研究了锥形单毛细管传输同步辐射X射线的物理特性.计算了锥管传输效率随锥管长度、X射线能量的变化规律;计算了锥管出口处的光强分布,强度增益随工作距离的变化规律.结果表明:与传输发散X射线相比,锥形单毛细管传输平行X射线的物理特性有明显的不同.     

Theoretical investigations of magnetic properties of ferromagnetic single-walled nanotubes

The magnetic behaviors of ferromagnetic single-walled nanotubes are systematically investigated by use of the many-body Green's function method of quantum statistical theory. The spontaneous magnetization, absolute value of ferromagnetic energy, area of hysteresis loop and coercivity increase with diameter of the tubes and spin quantum number, and decrease with temperature. Curie temperature increases with diameter and spin quantum number. As the diameter of the tube tends to infinity, all the numerical results approach to those of a two-dimensional monolayer. The dependences of initial susceptibility on temperature and diameter below and above Curie point are contrary. The calculated results are compared with experimental results where possible, and are qualitatively in agreement with the latter. The Curie temperature is determined by the tube diameter and independent of rolling helicities.     

Measurement of mean flows of Faraday waves

We measure the velocities of the mean flows that are driven by curved rolls in a pattern formation system. Curved rolls in Faraday waves are generated in experimental cells consisting of channels with varying widths. The mean flow magnitudes are found to scale linearly with roll curvatures and squares of wave amplitudes, agreeing with the prediction from the analysis of phase dynamics expansion. The effects of the mean flows on reducing roll curvatures are also seen.     

Analysis of continuous generation of electron beams in medium-pressure gases

Stationary and stable open discharges are obtained in air, helium, and helium with an admixture of a few percent of air. The structure of the generator of an electron beam with a wide set of cathode and insulator materials is described. The experiments are performed under an air pressure of hundreds of pascals and under a helium pressure of thousands of pascals. The current-voltage characteristics of the discharge are measured and the results on the maximal current density attained are compared with the available data.     

Estimation of physical parameters of magnetic nanoparticles

The results of estimation of the magnetic moment and sizes of magnetic nanoparticles in a magnetic fluid obtained using the technique based on measuring the field dependence of the acoustomagnetic effect are considered in the paper. The samples with different magnetic phase concentrations are analyzed. The obtained results compared with the data of magnetogranularmetric analyses are studied.     

Inclusion of spatial effects in the description of the resolution of neutron powder diffractometers

The methods previously developed for analytically describing the resolution of neutron powder diffractometers with the inclusion of spatial effects have been applied to analysis of a particular instrument. The results are compared with the data obtained using the Monte Carlo simulation and with the experimental results. The results obtained using two calculation methods are shown to be close to each other, and the effective parameters of the facility are determined.     

Photophysical Properties and Probability of Hydrogenation of C60

The photophysical properties of fullerene C₆₀ are studied by quantum chemistry. The calculated values are in good agreement with experiment. The probabilities of formation of hydrofullerenes with a varying number of attached hydrogen atoms are analyzed using the method of molecular electrostatic potential.     

Phase diagrams of laser-processed nanoparticles of brass

Nanoparticles of brass are prepared by ablation of a brass target in ethanol using radiation of a copper-vapor laser at various laser fluences. The nanoparticles are characterized by TEM and optical spectroscopy. The multipulse laser irradiation leads to formation both the nanoparticles in liquid and well-ordered micro-structures on a surface of a target. It is revealed that both the morphology and absorption spectra of brass nanoparticles depend on presence of the micro-structures. Nanoparticles with the various phase diagrams are formed from a flat brass surface and from the same surface with micro-structures. The results are compared with a model of phase diagrams, in which size and composition effects are taken into account.     

Influence of ion implantation on the thermal diffusivity of semiconductors

The influence of ion implantation on the thermal diffusivities of semiconductors are studied using the mirage effect. The dependences of the thermal diffusivities on the implantation doses are obtained. For silicon wafers implanted by boron, phosphorus and arsenic ions, with constant implantation energy, the thermal diffusivities decrease with increasing dose, when the doses are less than some critical values. The theoretical calculation results by using a one-dimensional multilayer model are in good agreement with the experimental ones. On the other hand, for gallium-arsenide wafers implanted with silicon ions, it is found experimentally that the thermal diffusivity increases with the implantation dose.     

Peninsula of neutron stability of nuclei in the neighborhood of neutron magic number N = 126

The properties of the ground state of even-even nuclei with extreme neutron excess that are remote from the known neutron drip line (NDL) are calculated. The calculations are based on the Hartree-Fock method with Skyrme forces SkM*, SkI2, Sly4, Ska) with allowance for axial deformation and the BCS pairing approximation. It is shown that the isotone chain at the neutron number N = 126 beyond the NDL forms a peninsula of nuclei that are stable with respect to the emission of one neutron (PNS). The neutron and proton density distributions of the PNS nuclei have spherical symmetry. A mechanism for restoring the stability of nuclei beyond the NDL is discussed. The obtained results are compared with those from Hartree-Fock-Bogoliubov calculations for long isotope chains of Zr and Pd up to the NDL.     

熔锥平面型三光纤耦合特性分析

以线性耦合波方程为基础，分析了具有不同耦合强度的平面型三光纤耦合系统的模场特性和功率耦合特性，并与常规的平面型三光纤耦合系统的耦合特性作了比较，给出的耦合器谱响应实验结果与理论结果较为一致。     

Zitterbewegung of wave packets and conductance of a quasi-one-dimensional channel in the presence of spin-orbit coupling

The electron energy spectrum and wave functions for a quasi-one-dimensional channel with Rashba spin-orbit coupling are calculated. The dynamics of wave packets in thin wires based on GaAs/In_0.23Ga_0.77As and AlGaAs/GaAs heterostructures with Rashba spin-orbit coupling are studied. Spin polarizations are found. The effect of splitting of wave packets with respect to their centers of mass and Zitterbewegung of their centers are discovered. The characteristics of wave-packet oscillations and spin density for free electrons and under confinement conditions are compared. A method for controlling the conductance of the quasi-one-dimensional channel using a controlling electrode is proposed.     

Calculation of multiloop amplitudes in the theory of closed oriented superstrings

Multiloop superstring amplitudes are obtained upon integrating local amplitudes with respect to modular parameters of the Schottky supergroup and with respect to vertex coordinates in the nonsplit (1|1) complex supermanifold. Ambiguities in this integration are removed by the condition requiring that the local symmetries of the amplitudes under discussion be conserved. Local superstring amplitudes are calculated by summing local fermion-string amplitudes. The resulting superstring amplitudes are free from divergencies. The vacuum amplitude is zero, in just the same way as the one-, two-, and three-point massless-boson amplitudes are. The amplitudes in question vanish after integration of corresponding local amplitudes with respect to interaction-vertex coordinates and with respect to the limiting points of the Schottky supergroup, with the exception of those (3|2) points that are fixed by SL(2) symmetry.     

Comparison of different types of secondary mirrors for solar application

Two-stage solar concentrators make solar beams downwards providing flexible choices for energy utilization. Five types of secondary mirrors (a flat mirror, an ellipsoidal mirror, a hyperboloidal mirror with upper/lower sheet and a paraboloidal mirror) are compared. Effects of geometry parameters and concentrator precisions on the optical performance are analyzed using Advanced System Analysis Program. The results indicate that concentrators with a flat mirror or hyperboloidal mirror with lower sheet are more sensitive to rim angle or relative location. The secondary mirror is better a convex surface especially when rim angle is more than 90°. A flat mirror or hyperboloidal mirror with lower sheet performs better with higher redirect focal points. A hyperboloidal mirror with upper sheet is the best however numerical aperture changing. The intercept factors decreased with the increase of random errors or optical errors. Both the fabrication and assemblage requirements for a concentrator with a hyperboloidal mirror with lower sheet are the strictest. Experiments are carried out based on a hyperboloidal mirror with upper sheet. The experiments results are in accordance with the ray-tracing results. Therefore, further studies on optimization of the two-stage concentrators using the ray-tracing model can be conducted.     

On the role of vacancies in pore formation in the course of anodizing of silicon carbide

Experimental data on the preparation of stoichiometric nanoporous silicon carbide are analyzed. Theoretical calculations are performed under the assumption that nanopores are formed through the vacancy diffusion mechanism. The results obtained confirm the hypothesis that the formation of pores with a steadystate radius of several tens of nanometers in silicon carbide can be associated with the diffusion and clustering of vacancies. The experimental data indicating that the proposed mechanism of formation of nanoporous silicon carbide correlates with the existing model of formation of porous silicon carbide with a fiber structure are discussed. This correlation can be revealed by assuming that nanopores are formed at the first stage with subsequent transformation of the nanoporous structure into a fiber structure due to the dissolution of the material in an electrolyte.     

阴阳极等离子体运动对强箍缩离子束二极管束流特性的影响

 主要研究了阴阳极等离子体运动对“闪光二号”加速器强箍缩离子束二极管束流特性的影响。给出了考虑阴阳极产生的等离子体运动对二极管间隙影响的Child-langmuir流、弱聚焦流、强聚焦流和饱和顺位流4个阶段的离子流和二极管总束流修正公式，利用这些修正公式计算的二极管总束流和离子束流强度与实测结果符合很好，在此基础上分析了提高离子束流强度和效率的方法，通过调整加速器参数，实验得到了峰值能量约500 keV，峰值电流约160 kA的高功率离子束。     

光纤光栅振动传感匹配检测方法的研究

介绍了用匹配光纤布拉格光栅（FBG）对振动传感进行直接的光强调制，从而完成传感及解调过程的方法，首先从理论上推导了光纤光栅的反射，透射谱的表达式，对光纤光栅的传感机制给出了定性的解释，并建立了数学模型进行模拟，进而报道了利用匹配光纤光栅进行单点解调，将振动传感信号变为解调光栅的输出光强信号，从而进行检测的方法，实验结果与理论吻合得很好，证明该方法是可行的。