Ne原子与H2分子碰撞的同位素替代效应研究

使用密耦近似（Close-Coupling）方法、采用Tang-Toennies势模型计算了惰性气体原子Ne与H₂分子及同位素D₂分子在碰撞能量为83.8 meV时的微分散射截面及分波截面, 并与实验值和文献值进行比较.计算得到的微分散射截面值与实验值符合得较好,分波截面值与文献值也相符合.使用同样的方法和模型,文中对Ne-H₂(D₂,T₂)三个体系的微分截面和分波截面进行了系统计算和比较分析,得出对称同位素替代碰撞体系的散射截面规律. 关键词： 2(D₂')" href="#">Ne-H₂(D₂ 2)碰撞')" href="#">T₂)碰撞 Tang-Toennies势模型 密耦方法 同位素替代     

Ne原子与H2分子碰撞的同位素替代效应研究

使用密耦近似（Close-Coupling）方法、采用Tang-Toennies势模型计算了惰性气体原子Ne与H₂分子及同位素D₂分子在碰撞能量为83.8 meV时的微分散射截面及分波截面, 并与实验值和文献值进行比较.计算得到的微分散射截面值与实验值符合得较好,分波截面值与文献值也相符合.使用同样的方法和模型,文中对Ne-H₂(D₂,T₂)三个体系的微分截面和分波截面进行了系统计算和比较分析,得出对称同位素替代碰撞体系的散射截面规律.     

Temperature-electric field hysteresis loop of multicaloric effects in PbZr0.8Ti0.2O3 thin films

The Multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin films is investigated with the application of sine wave electric field, dc electric field and stress using a phase field method combined with the thermodynamic analysis. The simulation results show that the adiabatic temperature change-electric field curve presents a shape of butterfly in the presence of the sine wave electric field. In order to detect the effect of the sine wave electric field, the multicaloric effect and the domain structures under the direct electric field and the sine wave electric field are compared. It is found that the domain switching behaviors are quite different under the different applied electric fields. And the negative multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin film is attribute to the domain switching under the external field.     

Theoretical and experimental study of the electronic structure of tin dioxide

The electronic structure of tin dioxide has been theoretically studied within the linearized augmented plane wave method using the Wien2k program package. The total and local partial electron densities of states have been calculated. The X-ray emission K-spectrum of oxygen has been calculated. The X-ray absorption spectra of the tin M _4,5-edge and oxygen K-edge have been calculated by simulating the supercell and core hole. The calculated results have been compared with the experimental data obtained using synchrotron radiation.     

Investigation of total and partial magnetic moments of Mn2NiAl with pressure at a several temperatures

ABSTRACT

The first principles calculations of structural and magnetic properties of the Heusler material Mn₂NiAl, have been studied using a full potential linearized augmented plane wave (FP-LAPW) within the density-functional theory (DFT). The phase stability of the cubic austenitic (L2₁₎ structure for Mn₂NiAl in both Cu₂MnAl (Fm3?m space group) and Hg₂CuTi (F43?m space group) type of structures with ferromagnetic and antiferromagnetic states, has been treated by applying the generalized gradient approximation proposed by Wu and Cohen (WC-GGA) alongside with the martensitic structure of Mn₂NiAl. The analysis of phase stability, cohesive energy and the calculated formation enthalpy of Mn₂NiAl reveal that the ferromagnetic MnMnNiAl is the most stable type of structure. Moreover, the calculated lattice parameters are found to be in good agreement with theoretical data. The variation of total magnetic moments M_T(μ_B), M_Mn (μ_B), M_Ni (μ_B) and M_Al (μ_B) in Mn₂NiAl with pressure at varying temperature (0, 273 and 344?K), have been calculated.     

The structure and ferroelastic phase transition of BiVO4

The structure of BiVO₄ has been determined by the Rietveld method at 300, 573 and 898 K and confirms the space group of the ferroelastic phase as 12/a and that of the paraelastic phase as 14₁/a. The displacement vectors of the atoms involved in the switching of ferroelastic states are calculated and indicate that the Bi displacements are the controlling factors in the process. An analysis is given of the eigenvectors of the B_g mode responsible for the transition.     

β-Si3N4电子结构和光学性质的第一性原理研究

采用基于密度泛函的平面波赝势方法(PWP)和广义梯度近似(GGA)，计算了β相氮化硅(β-Si₃N₄)的电子结构和光学性质，得到的晶格常数、能带结构等均与实验结果较好符合.进一步还研究了β-Si₃N₄的光吸收系数以及禁带宽度随外压力的变化规律，为β-Si₃N₄材料在高压条件下的应用提供了理论参考. 关键词： β相氮化硅 电子结构 能带结构 光学性质     

On switching behavior of ferrite substrate with magnetostatic and spin wave exchange term

Due to the generation of magnetostatic and spin waves, switching phenomena of ferrite substrate with a normal magnetic biasing field is presented. Generally below the X-band of microwave range, the Pozar’s quasi TEM waves (extraordinary waves) were studied, but for the study of X-band there should be an inclusion of spin wave exchange term (ωr) in the magnetostatic wave analysis which depends upon the static internal field (Hex). This term is included in analysis because the wavelength of microwave approach is the inter-atomic distance of ferrite material. In this work we synthesize LiTi ferrite through Solid State Reaction Technique (SSRT) and obtained electric and magnetic properties for the analysis. Absorbing and transmission power coefficients have been calculated to obtain the power loss and transmitted power through the substrate, respectively. The absorbing power coefficient verifies the switching behavior of substrate for certain range of applied external magnetic field (H _o) which depends on the resonance line width parameter (ΔH) of ferrite material.     

Influence of fatigue processes on the switching currents in lead titanate and lead zirconate-titanate films

The processes of polarization fatigue in PbTiO₃ and Pb(Zr_0.5Ti_0.5)O₃ films on silicon substrates have been studied by the method of switching in rectangular pulsed fields. Dependences of the switchable polarization, the maximum switching current i _max, and the switching time ??s on the number of switching cycles have been obtained from the data on the switching currents. It has been shown that the mobility of domain walls is retained in the fatigue processes and the observed fatigue is connected with switching off a fraction of the switchable volume due to pinning of reverse domain nuclei by charged defects.     

Acoustic properties of biaxial crystal of double lead molybdate Pb2MoO5

The acoustic properties of crystalline double lead molybdate, which are promising for acoustooptics, have been investigated. All elasticity coefficients of Pb₂MoO₅ crystal, the phase velocities of acoustic waves, and the angles between the vectors of phase and group velocities of this material have been determined. The acoustic parameters of the crystal have been calculated based on experimental data from the Schaefer-Bergmann diagrams. The phase velocity of acoustic waves along some directions has also been determined by the standard (in acoustics) echo-pulse method.     

Relaxation contribution to shear moduli of the low-temperature phase of solid C60

The relaxation contribution of the molecular reorientation in an elastic field of an acoustic wave to the effective shear moduli is calculated in the framework of the phenomenological two-level model of orientational states in the low-temperature phase of solid C₆₀. The polarity of the rotation axis of C₆₀ molecules and the possible existence of orientational domains in the structure of the low-temperature phase are taken into consideration. The estimates obtained are compared with the available experimental data.     

An experimental and theoretical study of shock-wave propagation through reactive gases under conditions causing a transformation of the flow structure

Experimental observations of the transformation of the structure of shock waves entering the discharge gap of either a transverse or decaying glow discharge are presented. It is found that the total impulse of the shock wave pressure remains constant. A variation in the speed of sound, that is, the shock wave velocity, at which total dispersion of the wave occurs is found to be nonmonotonous across the discharge gap. The times over which the wave structure keeps changing after switching off the discharge have been more accurately determined. On the basis of the obtained experimental data and earlier results, a conclusion on the mechanism of this effect has been drawn. This mechanism is related to the dispersion of disturbances making up the wave structure in a relaxing medium (such as the glow discharge plasma). On the basis of a theory of this kind of dispersion, using the experimental data, and comparing energetic and temporal characteristics of the internal states of the plasma under study and the mode of sound disturbances (which according to the experiment, are responsible for the effect), we have succeeded in determining the O₂(a ¹Δ_g) state whose relaxation brings about this effect.     

Nuclear magnetic resonance study of potassium dihydrophosphate

A powder sample of potassium dihydrophosphate KH₂PO₄ has been studied by the ³¹P NMR method in a wide temperature range covering the ferroelectric phase transition. Changes in the position and shape of the resonance line at the transition to the ferroelectric phase have been revealed. The parameters of the chemical shift tensor of ³¹P (isotropic shift, anisotropy, and asymmetry) in the ferroelectric phase have been calculated from the experimental data. A sharp increase in the anisotropy of the tensor at the phase transition has been demonstrated. Dielectric measurements have also been carried out to verify the transition temperature.     

A “4π-type” study of the reaction p(d,pp)n at Ed = 26.5 MeV

Experimental data on the three-nucleon reaction p(d, pp)n at E_d = 26.5 MeV obtained with the multidetector system BOL, covering most of the phase space, are presented. The data are compared with Faddeev calculations using a local S-wave potential for the nucleon-nucleon interaction. The calculated cross sections, which are in general not sensitive to the precise choice of the nucleon-nucleon potential, agree well with the data over the major part of phase space. We have, though, discovered a region in phase space with a strong discrepancy. In the same region, around a neutron c.m. angle of 140°, the calculations are sensitive to the N-N potential. Theoretical and experimental angular distributions in the p-n recoil c.m. subsystem for proton- neutron energies below 0.5 MeV agree in absolute magnitude, both being isotropic. For larger relative energies, a discrepancy develops, part of which might be related to missing higher par- tial wave components in the N-N interaction, rather than to Coulomb or S-wave scattering effects. The total breakup cross section has been deduced from the data as 169 ± 36 mb.     

Calculation of molecular one-electron properties using coupled Hartree-Fock methods

Various second-order properties for H₂O have been computed using a near Hartree-Fock gaussian wave function and a coupled Hartree-Fock scheme. Satisfactory agreement with experimental data is obtained for vibrational frequencies and for magnetic properties. The calculated electric polarizability only accounts for 64 per cent of the experimental value.     

液晶N相→SA相相变点附近的反常声衰减

本文考虑在N→S_A相变中,当T→T_c⁺(相交点)时,声在液晶中传播引起的压力效应。使用模-模耦合方法计算了声的衰减和色散,得到在高频区间,声的衰减有反常发散行为,在低频极限声衰减的临界指数为2.5.当T→T_c⁺时,本文的理论曲线大体上与实验结果相一致。     

The Mathematical Modelling of the Switching Arc

For developing and optimizing of high-voltage SF₆-puffer breaker a mathematical model of the switching arc is an important tool for the manufacturer. A physico-mathematical model was build up to simulate the behaviour of the switching arc near current zero. To proof the model the influence of steepness of current and voltage, of the gas pressure and the position of the upstream electrode on the breaking capacity have been calculated. First work has been done to use the model to simulate the dielectric behaviour too. To minimize computer time and to get more informations on the integral model the characteristic functions have been calculated with the pm-model. The result shows the influence of the steepness of the current before current zero.     

钠玻璃与钛玻璃在静水压下的弹性性能

用超声脉冲重叠法测量了钠玻璃(float glass)和钛玻璃(SiO₂+8.4wt%TiO₂)从大气压到2GPa静水压条件下的纵波声速和横波声速.发现两种玻璃有不同的变化规律.钛玻璃的纵波声速和横波声速,与钠玻璃的横波声速都随压力的增加而减小;而钠玻璃的纵波声速随压力的增加先增大,后减小.这一现象不同于别的氧化硅玻璃.对实验结果进行了讨论,并计算了弹性模量在压力下的变化和Murnaghan状态方程参数. 关键词： 高压 超声 玻璃     

Dynamics of Electronic States and Magnetoabsorption in 3D Topological Insulators in a Quantizing Magnetic Field

Quantum states have been calculated analytically; the dynamics of a wave packet in a magnetic field has been investigated, and the optical absorption coefficient has been calculated for surface states in 3D topological insulators of the Bi₂Te₃ family. We have detected a qualitative effect of the hexagonal warping of the spectrum on the structure of wavefunctions at the Landau levels, its manifestation in the features of the wave packet dynamics in a quantizing magnetic field, as well as in the frequency dependence of the optical absorption coefficient, in which new peaks that are absent in the isotropic model of the spectrum appear depending on the polarization of the incident wave. The effects considered here can be manifested in the optical and transport experiments with topological insulators, which makes it possible to determine the parameters of their band structure.     

Superconductivity at dielectric pairing of spatially separated quasiparticles

A new mechanism of the superconductivity based upon the pairing of the spatially separated electrons and holes due to their Coulomb attraction is presented. In the systems considered the phase of the order parameter is not fixed and therefore the charges superfluid flow connected with non-dissipative electrical currents is possible. The critical temperature T_c may be high (? 100°K). The critical current has been found. The diamagnetic response and the coefficient of the electromagnetic wave absorption in the systems have been calculated. The possible experiments are discussed.