Band structures of elastic waves in two-dimensional eight-fold solid–solid quasi-periodic phononic crystals

Combined with the supercell method,band structures of the anti-plane and in-plane modes of two-dimensional(2D)eight-fold solid–solid quasi-periodic phononic crystals(QPNCs) are calculated by using the finite element method.The influences of the supercell on the band structure and the wave localization phenomenon are discussed based on the modal distributions.The reason for the appearance of unphysical bands is analyzed.The influence of the incidence angle on the transmission spectrum is also discussed.     

The measurement of bending wave intensity in a two-dimensional structure

I.IntroductionOfallstructuralwaves,bendingwaveismostimportant.Itiseasilyexcitedandresultsinairbornenoiseradiation'Inpractice,itisnecessarytodeterminetheenergydistributionandpowertransmissionincoupledstructl1res.Bendingwaveenergycanbecalculatedfrombendingwaveaccelerationwhilebendingwavepowertransmissionischaracterizedbybendingwaveintensitywhichisavectorgivillgthemagnitudeanddirection.TheengineeringaPplicationofthevectorpropertyofbendingwaveilltensityisnumerous[1~3]buttheinvestigationinitispre…     

Phonon considerations in the reduction of thermal conductivity in phononic crystals

Periodic porous structures offer unique material solutions to thermoelectric applications. With recent interest in phonon band gap engineering, these periodic structures can result in reduction of the phonon thermal conductivity due to coherent destruction of phonon modes characteristic in phononic crystals. In this paper, we numerically study phonon transport in periodic porous silicon phononic crystal structures. We develop a model for the thermal conductivity of phononic crystal that accounts for both coherent and incoherent phonon effects, and show that the phonon thermal conductivity is reduced to less than 4% of the bulk value for Si at room temperature. This has substantial impact on thermoelectric applications, where the efficiency of thermoelectric materials is inversely proportional to the thermal conductivity.     

Correlation of the properties of ionic conductivity–structure for the RbGaO2 solid electrolyte

Physics of the Solid State - The crystal structure of rubidium gallate RbGaO2 in the temperature range of 300–853 K has been investigated using high-temperature neutron diffraction. The...     

Observations of band structure and reduced group velocity in epitaxial GaN–sapphire 2D photonic crystals

We report experimental results for the band structure of 2-dimensional triangular photonic crystals of air holes in an epitaxial group III–nitride waveguide film. Surface coupling techniques enable the observation of sharp resonance dips in the transmission spectra due to a resonance phenomenon between the incident light and Bloch modes of the photonic crystal. The position of the dips has been measured as a function of angle of incidence and the photonic band structure has been successfully constructed by the measurement. Corresponding Bloch-mode group velocities have also been obtained. Received: 28 May 2001 / Published online: 23 October 2001     

d-wave pairing of spin-polaron quasiparticles in the spin–fermion model of the electronic structure of the CuO2 plane

Bulletin of the Russian Academy of Sciences: Physics - It is shown that the strong coupling between spin moments of copper ions and oxygen holes resulting from the hybridization processes in the...     

Decay π → + ν in the field of a plane electromagnetic wave with allowance for the polarizability of the pion

The process + in the field of a plane electromagnetic wave is investigated with allowance for the complex structure of the pion. Exact values are obtained for the probability of pion decay in circularly and elliptically polarized fields. Pion structure effects become observable for 5, where .Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 65–68, December, 1991.     

Time-frequency analysis of the dispersive Rayleigh wave in stratified media

The dispersive characteristic of the Rayleigh wave propagating in a stratified media was analyzed by a time-frequency analysis method, the Reassignment of Smooth Pseudo-Wigner Ville Distribution (RSPWVD). Theoretical simulations and experiments were implemented for a homogeneous half-space and a two-layered half-space. It is indicated that the group velocity dispersion curves in different frequency ranges obtained by experimental result are all corresponding to the dominant modes in their surface displacement amplitudes. Such a mode identification of the multi-mode Rayleigh waves is required in inversing the medium parameters.     

New bulk and surface phonon–plasmon modes in Raman spectra of porous n-InP

We report the Raman study of porous doped InP. The additional Raman bands were found in comparison with unporous doped InP. The effective medium theory is used to show that these bands may be assigned to a new coupled LO-phonon–plasmon mode and a contribution from surface polaritons.     

Efficient β-formulation for the FEM analysis of leaky modes in general anisotropic channel waveguides

An efficient method to model guided and leaky modes of anisotropic dielectric waveguides with arbitratry dielectric tensor ¯¯ is presented. This method takes advantage of a particular -formulation approach of the finite element method (FEM), leading to an optimized use of the computational resources.     

Ginzburg–Landau description of laminar-turbulent oblique band formation in transitional plane Couette flow

Plane Couette flow, the flow between two parallel planes moving in opposite directions, is an example of wall-bounded flow experiencing a transition to turbulence with an ordered coexistence of turbulent and laminar domains in some range of Reynolds numbers [R _g, R _t] . When the aspect-ratio is sufficiently large, this coexistence occurs in the form of alternately turbulent and laminar oblique bands. As R goes up trough the upper threshold R _t, the bands disappear progressively to leave room to a uniform regime of featureless turbulence. This continuous transition is studied here by means of under-resolved numerical simulations understood as a modelling approach adapted to the long time, large aspect-ratio limit. The state of the system is quantitatively characterised using standard observables (turbulent fraction and turbulence intensity inside the bands). A pair of complex order parameters is defined for the pattern which is further analysed within a standard Ginzburg–Landau formalism. Coefficients of the model turn out to be comparable to those experimentally determined for cylindrical Couette flow.     

Thermal expansion anisotropy of β-TlInS2 crystals in the course of phase transitions

Basing on the thermal expansion studies performed for β-TlInS₂ crystals in the course of their phase transitions, we have found that the crystals aged for one year are composed from at least two polytypes, which undergo phase transitions at different temperatures. The detailed analysis of anisotropy of the thermal expansion demonstrates that all of the diagonal components of the thermal expansion tensor associated with the eigensystem have almost the same modules but differ by their signs. This leads to appearance of an elliptical conical surface of zero thermal expansion. The orientation of this surface does not depend on the temperature in the temperature interval under study. We have also found that the thermal expansion coefficients along the crystallographic a and b axes are close to zero.     

Enhanced absorption process in the thin active region of GaAs based p–i–n structure

The optical absorption is the most important macroscopic process to characterize the microscopic optical transition in the semiconductor materials. Recently, great enhancement has been observed in the absorption of the active region within a p–n junction. In this paper, Ga As based p–i–n samples with the active region varied from 100 nm to 3 μm were fabricated and it was observed that the external quantum efficiencies are higher than the typical results, indicating a new mechanism beyond the established theories. We proposed a theoretical model about the abnormal optical absorption process in the active region within a strong electric field, which might provide new theories for the design of the solar cells,photodetectors, and other photoelectric devices.     

Fluid–triangular solid phase transitions in a system of two-dimensional nematic quadrupoles

Density functional theory of freezing is used to study the phase transitions in a system of spherical colloidal particles dispersed in nematic host confined to two dimensions. We have considered both the one-component and two-component systems of the colloidal dispersions. Particles are assumed to interact via director distortion-mediated purely repulsive potential which scales as the fifth power of the inverse interparticle separation. The pair correlation functions needed as input information in the density functional theory are calculated by solving Roger–Young integral equation theory. In one-component system, a triangular crystalline phase is found to be stable. On the other hand, considering the freezing of the fluid phase of the binary mixture into a substitutionally disordered triangular solid, the temperature–composition phase diagram is found to have spindle shape for the ratio of quadrupole moment of the particles of the components being 0.9 and 0.8. The phase diagram changes to an azeotrope at a ratio 0.7. The results are verifiable in real-space experiments on nematic quadrupoles confined to a two-dimensional plane.     

Dispersion law and lifetime of holes with negative effective masses in Γ1v band of crystals having the diamond structure

It is shown that in the bottom valence band _1v of crystals, having the diamond structure, holes are described by a standard dispersion law with a negative effective mass. Interaction of these holes with phonons is considered. The lifetime of holes due to this interaction is estimated. In Ge, at 20°K, it can reach 10^–9 sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 10–13, February, 1984.     

Separation of different wave components in the Bethe–Salpeter wave function

The scalar products of polarization tensor and unit vectors are presented explicitly in spherical coordinate system expanded in terms of spherical harmonic functions. By applying the obtained formulae, different wave components in the Salpeter wave function can be shown explicitly, and the results are consistent with the results obtained by L–S coupling analysis. The cancelation formula is given, by which the terms with pure L = J + 1 wave components in the Salpeter wave function for the bound state with h_P=(-1)^J\eta_{\rm P}=(-1)^J can be obtained by separating the L = J − 1 wave components from mixing terms. This separation provides the basis for studying higher-order contributions from the coupling of L = J − 1 and J + 1 wave states, and for solving the Salpeter equation exactly without approximation.     

Bifurcation analysis and the travelling wave solutions of the Klein–Gordon–Zakharov equations

In this paper, we investigate the bifurcations and dynamic behaviour of travelling wave solutions of the Klein–Gordon–Zakharov equations given in Shang et al, Comput. Math. Appl. 56, 1441 (2008). Under different parameter conditions, we obtain some exact explicit parametric representations of travelling wave solutions by using the bifurcation method (Feng et al, Appl. Math. Comput. 189, 271 (2007); Li et al, Appl. Math. Comput. 175, 61 (2006)).     

Rotational band contour analysis in the 2760 Å system of p-chlorofluorobenzene

The origin band of the 2760 å system of p-chlorofluorobenzene has been shown to be a type B band of a prolate asymmetric top. The electronic assignment of the system is therefore ¹ B ₂-¹ A ₁.

The excited state rotational constants are:

compared with the estimated ground state constants:

The rotational origin of the band is at 36275·1 ± 0·2 cm^-1.