Universal probes of two-dimensional topological insulators: dislocation and π flux

We show that the π flux and the dislocation represent topological observables that probe two-dimensional topological order through binding of the zero-energy modes. We analytically demonstrate that π flux hosts a Kramers pair of zero modes in the topological Γ (Berry phase Skyrmion at the zero momentum) and M (Berry phase Skyrmion at a finite momentum) phases of the M-B model introduced for the HgTe quantum spin Hall insulator. Furthermore, we analytically show that the dislocation acts as a π flux, but only so in the M phase. Our numerical analysis confirms this through a Kramers pair of zero modes bound to a dislocation appearing in the M phase only, and further demonstrates the robustness of the modes to disorder and the Rashba coupling. Finally, we conjecture that by studying the zero modes bound to dislocations all translationally distinguishable two-dimensional topological band insulators can be classified.     

Epitaxy of Ⅲ-nitrides on two-dimensional materials and its applications

Ⅲ-nitride semiconductor materials have excellent optoelectronic properties, mechanical properties, and chemical stability, which have important applications in the field of optoelectronics and microelectronics. Two-dimensional(2D)materials have been widely focused in recent years due to their peculiar properties. With the property of weak bonding between layers of 2D materials, the growth of Ⅲ-nitrides on 2D materials has been proposed to solve the mismatch problem caused by heterogeneous epitax...     

Reduction of interference fringes in absorption imaging of cold atom cloud using eigenface method

Eigenface method used in face recognition is introduced to reduce the pattern of interference fringes appearing in the absorption image of cold rubidium atom cloud trapped by an atom chip. The standard method for processing the absorption image is proposed, and the origin of the interference fringes is analyzed. Compared with the standard processing method which uses only one reference image, we take advantage of fifty reference images and reconstruct a new reference image which is more similar to the absorption image than all of the fifty original reference images. Then obvious reduction of interference fringes can be obtained.     

Plastic analysis of the crack problem in two-dimensional decagonal Al-Ni-Co quasicrystalline materials of point group 10,■

The fundamental plastic nature of the quasicrystalline materials remains an open problem due to its essential complicacy.By developing the proposed generalized cohesive force model,the plastic deformation of crack in point group 10,10 decagonal quasicrystals is analysed strictly and systematically.The crack tip opening displacement(CTOD) and the size of the plastic zone around the crack tip are determined exactly.The quantity of the crack tip opening displacement can be used as a parameter of nonlinear fracture mechanics of quasicrystalline material.In addition,the present work may provide a way for the plastic analysis of quasicrystals.     

Radiofrequency forward Mössbauer scattering method in study of magnetic materials

Mössbauer spectra in forward scattering scheme were measured for iron borate (FeBO ₃) exposed to radiofrequency (rf) field below the Neel temperature. The spectra have satellites spaced by doubled rf field frequency. The semiclassical model of Mössbauer transmission through a thick magnetic sample under rf reversals of a hyperfine field is proposed. This model reproduces all features of the measured spectra. Experiments and model calculations indicate additional possibilities of this measurement scheme for study the soft magnetic materials.     

Element-free Galerkin （EFG） method for a kind of two-dimensional linear hyperbolic equation

The present paper deals with the numerical solution of a two-dimensional linear hyperbolic equation by using the element-free Galerkin (EFG) method which is based on the moving least-square approximation for the test and trial functions. A variational method is used to obtain the discrete equations, and the essential boundary conditions are enforced by the penalty method. Compared with numerical methods based on mesh, the EFG method for hyperbolic problems needs only the scattered nodes instead of meshing the domain of the problem. It neither requires any element connectivity nor suffers much degradation in accuracy when nodal arrangements are very irregular. The effectiveness of the EFG method for two-dimensional hyperbolic problems is investigated by two numerical examples in this paper.     

The complex variable meshless local Petrov—Galerkin method of solving two-dimensional potential problems

Based on the complex variable moving least-square(CVMLS) approximation and a local symmetric weak form,the complex variable meshless local Petrov-Galerkin(CVMLPG) method of solving two-dimensional potential problems is presented in this paper.In the present formulation,the trial function of a two-dimensional problem is formed with a one-dimensional basis function.The number of unknown coefficients in the trial function of the CVMLS approximation is less than that in the trial function of the moving least-square(MLS) approximation.The essential boundary conditions are imposed by the penalty method.The main advantage of this approach over the conventional meshless local Petrov-Galerkin(MLPG) method is its computational efficiency.Several numerical examples are presented to illustrate the implementation and performance of the present CVMLPG method.     

Investigation on method for measuring dynamic shear modulus of underwater acoustic structure materials

1IfltroductionSince6o's,withthedevelopmentoflargemolecularmaterialsandcompositematerials,structurematerialsinunderwateracousticapplicationshavemadeagreatchanges.Forex-ample,thepropertiesofsonardomesthatmadefromreinforcedpolymersinsteadofstainlesssteelhavebeenimprovedobviously.Inordertodesignrationally,itisnecessaryforengineerstofindouttheiracousticpropertiescompletely.Accordingtotheelastictheories,twokindsofwave:longitudinalwaveandshearwavewillbeexcitedontheboundaryoftwomediumswhilethesoundsar…     

Analysis of the nonlinear absorption mechanisms in ablation of transparent materials by high-intensity and ultrashort laser pulses

The mechanisms of nonlinear absorption in transparent materials under irradiation with ultrashort laser pulses are considered theoretically. Nitride semiconductor, sapphire and others transparent dielectrics were investigated. The ablation threshold for these materials is within multi-TW/cm² range. The model was used based on the tunneling absorption under the irradiation by high-intensity ultrashort pulses in terms of the theory of ionization of solid in a field of strong electromagnetic wave. The effect of the energy gap of material on the threshold of laser ablation was adequately explained.     

A robust method for inverse halftoning via two-dimensional nonlinear pyramid

Based on the principle of spatial pyramid for signal,a multi-scale transform of two-dimensional (2D) in- terpolating pyramid is constructed by the nonlinear median operator.The transform properties of error diffuse halftoning noise on multiple scales are investigated and analyzed through experiments.According to these properties,a robust inverse halftoning method is proposed.The halftoning image is firstly pre- processed by a Gaussian low-pass filter,and decomposed by the one-scale transform.Then a Wiener filter is employed to the detailed coefficients.Finally an inverse image is reconstructed.Experimental results show that the proposed transform has the advantage of separating the halftoning noise and image detail over linear multi-resolution transform.The presented inverse halftoning method performs some excellent abilities on sharp edge,high peak signal-to-noise ratio (PSNR),and small memory requirement.     

Nonlinear generation and propagation of sum frequency and difference frequency acoustic wares within a two-dimensional rectangular duct

1IntroductionNonlilleargenerationandpropagationofacousticwavswithinatwo-dimensionalrectan-gularducthavedrawnmoreandmoreattention,andhavebeendiscussedilltensivelyinthepastdecades.Yetmuchattentionwasdrawntothecaseinwhichacousticwaveswithintheductwereexcitedbyanexcitationsourcewithasinglefrequency[1-4].Inpracticalissues,however,theexcitationsourcemayincludetwoormorefrequencies,andaseriesofacousticpropagatingmodeswithdifferentfrequencieswillbegenerated.Duetothenonlinearityoffiuidmediumwithintheduc…     

The first detection of photomodulation by both DC and in-phase AC susceptibility for organic/inorganic hybrid materials containing cyano-bridged Gd–Cr complex and azobenzene

New organic/inorganic hybrid material containing a ferrimagnetic cyano-bridged binuclear complex, [Gd(DMF)₄(H₂O)₃Cr(CN)₆]·H₂O (DMF=N,N′-dimethylformamide), and photochromic azobenzene in poly(methylmethacrylate) (PMMA) cast films has been prepared. We characterized magnetic properties of bulk [Gd(DMF)₄(H₂O)₃Cr(CN)₆]·H₂O and confirmed that it was not changed by light illumination at all. For the first time, we could detect reversible changes of both DC and in-phase AC susceptibility for the hybrid materials accompanying with cis–trans photoisomerization of azobenzene after UV and visible light illumination for 3 min at 3 K. We also discuss the kind of detectable magnetic changes (e.g. DC, in-phase AC, and both DC and in-phase AC) and the nature of some photo-magnetic functional hybrid materials (cis–trans photoisomerization and increase/decrease of magnetization) known to estimate their mechanism and interactions.     

The method eliminating nearfield effect for measurement sound absorption coefficient

The numerical simulation is used in this work to study the nearfieldradiation pressure of a piston projector,the smooth effect on the pressure fieldby using a“big”receiver and the influence of the nearfield and in the transitionregion on measurement of sound absorption coefficient.The result indicatesthat the big error would appear when using usual absorption coefficientmeasurement method.According to the reason causing the error,the methodeliminating nearfield effect (MENE) is proposed and some digital results aregiven for a/λ=3,9 and b=0,0.5a,a(a and b are the transducer and re-ceiver radii respectively).The calculation results show that the method not onlywidens measurement range in nearfield,but also gives accurate results.     

Fission barrier of actinide nuclei with double-Λ particles within the Skyrme–Hartree–Fock method

Fission barrier of actinide nuclei including two Λ hyperons is studied in the framework of the Skyrme–Hartree–Fock approach at zero temperature. We adopt the zero-range Skyrme-type interaction between Λ–N and Λ–Λ. Fission barrier is investigated using several parameter sets for ΛΛ interactions. We obtain the result that the barrier height becomes higher as the number of Λ particle increases and the barrier width has a dependence on the ΛΛ interaction. A relation between Λ binding energy and density distribution of Λ particle inside a core nucleus is also discussed. We found that the both Λ particles are attracted into heavier fission fragment.     

Photoinduced absorption within the valence Γ and the conduction L-subband manifolds in undoped GaSb/AlSb superlattices

We report the observation of L-valley conduction intersubband absorption together with Γ- valence intersubband in optically excited undopeal, indirect binary-binary short period GaSb/AlSb superlattices. The transitions were identified by comparing their position and polarization with calculations which take into account both valence and conduction subbands. The dependence of the intersubband absorption on the temperature, excitation intensity and modulation frequency, indicates that the photoexcited carriers are trapped with an activation energy of ≃50 meV and are long lived (≃5μ sec).     

Reduction of two-dimensional G-invariant σ-models

The Euclidean two-dimensional SO(n)-invariant -model is reduced to the system of equations for the Toda lattice. The similar reduction is studied for the SU(n)-invariant -model.     

Effects of solvent composition on the electrochemical performance of Li2FeSiO4/C cathode materials synthesized via tartaric-acid-assisted sol–gel method

Li₂FeSiO₄/C composites were synthesized via a tartaric-acid-assisted sol–gel method with ethanol and ethylene glycol (EG) as mixed solvents. Effects of solvent composition on the physical properties and electrochemical performances of Li₂FeSiO₄/C were studied. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performances of Li₂FeSiO₄/C were evaluated by galvanostatic charge–discharge and electrochemical impedance spectra (EIS) measurements. The results show that the addition of EG to ethanol solvent during preparation has a positive effect on the electrochemical performance of Li₂FeSiO₄/C. The sample synthesized using EG–ethanol with the volume ratio of 2:7 has the best electrochemical performance. It delivers an initial discharge capacity of 105 mAh g^?1 at C/16. AC impendence investigation shows that Li₂FeSiO₄/C synthesized using the optimal EG/ethanol volume ratio has lower resistance of electrode/electrolyte interface and higher lithium-ion diffusion coefficient than that synthesized using ethanol as solvent.