On the Einstein Relation in Ternary Semiconductors in the Presence of Crossed Electric and Magnetic Fields

We investigate theoretically the Einstein relation for the diffusivity-mobility ratio of the electrons in ternary semiconductors at low temperatures in the presence of crossed electric and quantizing magnetic fields on the basis of threeband Kane model. It is found, taking n-Hg_1-xCd_xTe as an example, that DMR shows an oscillatory magnetic field dependence. Besides, the DMR increase both with increasing electron concentration and decreasing alloy composition respectively.     

A Note on the Proof of Magnetic Flux Quantization from ODLRO

It is noticed that the excellent proof of the connection of magnetic flux quantization and off-diagonal long range order (ODLRO) presented recently by Nieh, Su and Zhao suffers from an imperfection, namely, the f-factors in the case of finite translation do not satisfy f(a)f(b)=f(a+b), which was employed in the proof. A corrected proof is proposed to remedy this point.     

A Gauge Theoretical View of the Charge Concept in Einstein Gravity

We will discuss some analogies between internal gauge theories and gravity in order to better understand the charge concept in gravity. A dimensional analysis of gauge theories in general and a strict definition of elementary, monopole, and topological charges are applied to electromagnetism and to teleparallelism, a gauge theoretical formulation of Einstein gravity. As a result we inevitably find that the gravitational coupling constant has dimension /l ², the mass parameter of a particle dimension /l, and the Schwarzschild mass parameter dimension l (where l means length). These dimensions confirm the meaning of mass as elementary and as monopole charge of the translation group, respectively. In detail, we find that the Schwarzschild mass parameter is a quasi–electric monopole charge of the time translation whereas the NUT parameter is a quasi–magnetic monopole charge of the time translation as well as a topological charge. The Kerr parameter and the electric and magnetic charges are interpreted similarly. We conclude that each elementary charge of a Casimir operator of the gauge group is the source of a (quasi-electric) monopole charge of the respective Killing vector.     

Effects of Screening and Finite Phonon Energy on the Transport in Quantized Layers in Compound Semiconductors

Analytical expressions for the momentum relaxation times of the conduction electrons in a non-degenerate two dimensional electron gas in the surface of a compound semiconductor have been obtained for interactions with the piezoelectric and deformation potential acoustic phonons taking due account of the screening of the perturbing potential under the the condition of low lattice temperature when the phonon energy cannot be neglected in comparison to the average thermal energy of the electrons and for that matter the equipartition approximation for the phonon distribution is hardly valid. The relaxation times calculated for inversion layers in GaAs and ZnO are found to depend upon the carrier energy, the lattice temperature and the impurity concentration in rather complex manners which are significantly different from what follows from the traditional approach of either neglecting the phonon energy or disregarding the process of screening. It is seen how the finite value of the phonon energy and the screening of the perturbing potential change the mobility characteristics significantly at the low lattice temperatures. The temperature dependence of the zero field mobility that one obtains using the relaxation times calculated here is quite different from the traditional laws.     

Magnetic field enhancement of heat transport in the 2D Heisenberg antiferromagnet K2V3O8

The thermal conductivity and heat capacity of single crystals of the spin 1/2 quasi-2D Heisenberg antiferromagnet K(2)V(3)O(8) have been measured from 1.9 to 300 K in magnetic fields from 0 to 8 T. The zero field thermal conductivity data are consistent with resonant scattering of phonons by magnons near the zone boundary. Application of a magnetic field greater than 1 T, however, produces a new magnetic ground state with substantial heat transport by long wavelength magnons.     

核磁共振二维谱反演技术综述

二维谱的出现是核磁共振（NMR）检测技术的一次飞跃,从二维谱中可以快速、精确地对不同组分进行区分,因而在测录井和常规实验中被广泛采用. 为了给相关研究提供借鉴和参考,推动二维反演技术的发展,该文对近年来国内外在核磁共振二维谱反演技术领域的研究进展进行了综述. 从实验采集数据中反演出二维谱的过程,比一维反演需要解决更多、更复杂的问题. 通过研究罚函数正则化和子空间正则化两大类方法,分析了不同二维反演算法的优点和不足. 根据对近年来国内外相关文献的深入分析可知,虽说目前已有的二维反演算法都存在一定的局限性,但其仍然具有很大的发展空间.     

A model for the metal-to-insulator transition in V2O3

The metal-to-insulator transition in V₂O₃ is described by a model that is based on the electronic band structure of this material. The vanadium 3d-t _2g band decomposes in the trigonal symmetry into two bands, a _1g and e _π. The a _1g band consists of orbitals connecting pairs of c-axis neighbouring atoms, while the e _π band consists of orbitals in the plane perpendicular to the c-axis. The change in distance between c-axis neighbours changes the nature of the a _1g band from molecular (delocalized) to atomic (localized). The localization of the a _1g electrons causes through the atomic exchange interaction also the localization of the e _π electrons, and this localization creates a gap in the e _π band which causes the material to become insulating. This model is treated in the Hartree-Fock approximation (the ‘Excitonic’ model) at zero and finite temperatures, and various aspects of the transition, such as changes in the c/a ratio, the creation of magnetic moments, changes in covalency, the effect of pressure and the order of the transition, are investigated.     

Identification and Analysis of Magnetic Structures on HL-2A

1 Introduction Tearing modes in tokamak plasmas have been studied for many years In HL-2A tokamak, MHD instabilities are investigated by means of the Mirnov probes. The mode number can be determined by the methods of phase comparison analysis or correlation analysis from the experimental data of Mirnov probes, but the analysis of complicated mode structures is difficult. An identification and analysis method of magnetic islands is presented basing on simulation of the perturbation current and magnetic field in plasmas.     

Magnetic susceptibility and electron spin resonance of the semiconducting mixed crystal V2MoO8 (V2O5 · MoO3)

The transition metal lattice sites of V₂MoO₈ are occupied by vanadium- and molybdenum ions in a disordered way. Our measurements of the magnetic susceptibility and the electric conductivity show that V₂MoO₈ is paramagnetic and semiconducting. The ESR investigations prove the existence of localizedd electrons (Anderson localization). A hopping process of thesed electrons in vanadium 3d orbitals leads to an ESR line narrowing. Above 50 K a line broadening occurs which is interpreted as a shortening of the effective lifetime of the localizedd electrons.     

Magnetic moment of the 3+, one millisecond isomer in self-conjugate46V

Theg-factor of the one millisecond isomer (first excited state at 801 keV) in self-conjugate⁴⁶V was measured by the perturbed angular distribution method. The isomeric state was populated by the heavy ion reaction³²S(¹⁶O,pn)⁴⁶V and recoil implanted into a liquid metal. The result,g=+0.546(10) extends the known isoscalar moments to heavier nuclei and is in close agreement with all previously measured isoscalar moments in thef _7/2 shell. Theγ-ray angular distribution confirms the spin 3 assignment of the isomeric state.     

Specific Features of Nonlinear Spin Wave Localization in a Layered Ferromagnet under the Action of the Magnetic Anisotropy of Layers

Physics of the Solid State - A trilayer structure model has been investigated, in which uniaxial ferromagnetic layers and thin-film interfaces between them are characterized by the magnetic...     

Theoretical study of the magnetoresistance under electric field in III–V diluted magnetic semiconductor

In this paper we study the magnetoresistance and the coupling energy in heterostructures formed by two magnetic layers Ga_1−xMn_xAs separated by a nonmagnetic spacer GaAs under an electric field and develop a mean-field theory of carrier in diluted magnetic semiconductor. Our main result indicates that magnetoresistance can be dramatically suppressed by an external electric field.     

Theoretical Analysis of the Gain in FEL with Helical and Tapered Axial Magnetic Fields

Efficiency enhancement in the free-electron laser is described with a taPered axial guide field. A 3-dimensional analytical decription of this process in the strong-pump regime is given by means of the energy theory based on the dynamic equations. With its clear physical meaning and simple calculation, this theoretical analysis method can also be appropriate to other kinds of FELs.     

Theoretical investigation on the reaction kinetics of NO2 with CH3OH and HCHO under combustion conditions

Methanol (CH₃OH) and formaldehyde (HCHO) reacting with nitrogen dioxide (NO₂) contribute to the largest uncertainty for the CH₃OH/NO_x low temperature combustion mechanism. CH₃OH and NO₂ only undergo H-abstraction reactions, while HCHO + NO₂ involves multiple reaction channels, among which H-abstraction dominates. In the present work, a high level quantum chemical method, CCSD(T)/aug-cc-pVQZ//M06–2X-D3/6-311++G(d,p), was employed to investigate the reaction pathways. The reaction kinetics were explored by RRKM/master equation simulations with multidimensional small-curvature tunneling (SCT) corrections and hindered rotor approximations. The H-abstraction reactions with barriers higher than 20 kcal/mol indicate a nonnegligible quantum tunneling effect even under combustion conditions. Our computations predict the tunneling factors to be 3–4 for the studied reactions at 500 K. A significant tunneling effect is also expected for H-abstraction of large alcohols and aldehydes by NO₂. The computed total rate coefficients show good agreement with previous experimental measurements over narrow ranges of temperature and pressure, ensuring the accuracy of the reported branching ratios covering a wide T, P range for the two reactions. The results of CH₃OH + NO₂ reveal the dominant role of HONO_cis + CH₂OH. It's also uncovered the dominance of HONO_cis + CHO pathway in HCHO + NO₂ under the studied conditions. The detailed reaction kinetics information reported in this work is useful for building rate rules for the mechanisms of other nitrogen-containing alcohol-based fuels.     

Theoretical studies of the optical and EPR spectra for V in Y2O3 crystal

In this paper, we give an alternative suggestion that both the observed optical and electron paramagnetic resonance (EPR) spectra of Yttrium oxide (Y₂O₃):V³⁺ are attributed to V³⁺ ions at the S₆ site of Y₂O₃. This suggestion is different from the opinion in the previous paper that the optical and EPR spectra are attributed to V³⁺ ions at the C₂ and S₆ sites, respectively. From the suggestion, the optical band positions and spin-Hamiltonian parameters are calculated by diagonalizing the complete energy matrix for 3d² ions in trigonal symmetry. The results are in good agreement with the experimental values, suggesting that both the observed optical and EPR spectra in Y₂O₃:V³⁺ may be due to V³⁺ at S₆ site of Y₂O₃ crystal.     

Fe2O3上AsH3催化氧化反应机理的理论研究

本文采用密度泛函理论方法研究了Fe₂O₃上AsH₃的催化氧化反应机理.该反应以Fe₂O₃中的两个Fe原子为不同的活性中心进行研究,每个活性中心均设计了3个步骤. AsH₃分子依次与3个O₂分子在催化剂上相互作用分别形成中间体H₃AsO₂、H₃AsO₄及最终产物H₃AsO₆.研究发现,当氧化反应发生在1号铁原子(Fe1)附近,其速度控制步骤活化自由能垒为49.99 kcal/mol;当氧化反应发生在2号铁原子(Fe2)附近,其活化自由能垒为21.20 kcal/mol,与直接氧化(50.14 kcal/mol)相比大大降低.可见AsH₃在Fe₂O₃上的催化氧化反应更易发生在Fe2附近.     

电荷调控下Ti3C2O2和V2CO2吸附CH4的第一性原理计算

本文采用第一性原理计算首先研究了Ti3C2O2和V2CO2与CH4气体分子之间的相互作用,发现Ti3C2O2和V2CO2对CH4的吸附较弱属于物理吸附,不适宜用作探测CH4。在此基础上研究了电荷调控下CH4气体分子与Ti3C2O2和V2CO2之间的相互作用。结果表明：随着体系电荷态的增加,Ti3C2O2和V2CO2对CH4气体分子的吸附作用逐渐增加变为化学吸附。当体系电荷态大于或等于-2时,CH4气体分子在Ti3C2O2和V2CO2表面可以被有效捕获。撤去电荷后,Ti3C2O2、V2CO2与CH4气体分子之间的吸附恢复至物理吸附,CH4气体分子易脱附。因此,通过调控Ti3C2O2和V2CO2的电荷态,可以简单地实现CH4的捕获与释放。Ti3C2O2和V2CO2有望成为CH4探测或捕获材料。     

A density-wave-like transition in the polycrystalline V3Sb2 sample with bilayer kagome lattice

Recently,transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum phenomena.Here we report on the synthesis,structure,and physical properties of a bilayer kagome lattice compound V₃Sb₂.The polycrystalline V₃Sb₂ samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850℃.Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at Tdw≈160 K with a large thermal hysteresis,even though some sample-dependent behaviors were observed presumably due to the different preparation conditions.Upon cooling through Tdw,no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction measurements.This transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa,around which no sign of superconductivity was observed down to 1.5 K.Specific-heat measurements revealed a relatively large Sommerfeld coefficientγ=18.5 mJ·mol^-1·K^-2,confirming the metallic ground state with moderate electronic correlations.Density functional theory calculations indicate that V₃Sb₂ shows a non-trivial topological crystalline property.Thus,our study makes V₃Sb₂ a new candidate of metallic kagome compound to study the interplay between density-wave-order,nontrivial band topology,and possible superconductivity.     

Effect of the metal-insulator transition on vanadium K-photoabsortion spectrum in V2O3

The effect of the metal-insulator phase transition on the X-ray K-absorption spectrum of V in V₂O₃ was measured by synchrotron radiation. A different behavior of the transition to 3d vs 4p states in the two phases was observed. These results have been correlated with the change in the screening of the 1s hole due to the variation of the dielectric constant ?(q, ω) in the two phases.