Showing papers on "Dispersion relation published in 2001"

Plasma oscillations in Hall thrusters

Abstract: The nature of oscillations in the 1 kHz–60 MHz frequency range that have been observed during operation of Hall thrusters is quantitatively discussed. Contours of various plasma parameters measured inside the accelerating channel of a typical Hall thruster are used to evaluate the various stability criteria and dispersion relations of oscillations that are suspected to occur. A band by band up-to-date overview of the oscillations is carried out with a description of their observed behavior and a discussion of their nature and dependencies through comparison of the calculated contours to reported observations. The discussion encompasses the excitation of low frequency azimuthal drift waves that can form a rotating spoke, axially propagating “transit-time” oscillations, azimuthal drift waves, ionization instability-type waves, and wave emission peculiar to weakly ionized inhomogeneous plasmas in crossed electric and magnetic fields.

Spin waves and electronic interactions in La2CuO4

Abstract: The magnetic excitations of the square-lattice spin-1/2 antiferromagnet and high- T(c) parent compound La2CuO4 are determined using high-resolution inelastic neutron scattering. Sharp spin waves with absolute intensities in agreement with theory including quantum corrections are found throughout the Brillouin zone. The observed dispersion relation shows evidence for substantial interactions beyond the nearest-neighbor Heisenberg term which can be understood in terms of a cyclic or ring exchange due to the strong hybridization path around the Cu4O4 square plaquettes.

Monte Carlo Study of Phonon Transport in Solid Thin Films Including Dispersion and Polarization

Abstract: The Boltzmann Transport Equation (BTE) for phonons best describes the heat flow in solid nonmetallic thin films. The BTE, in its most general form, however, is difficult to solve analytically or even numerically using deterministic approaches. Past research has enabled its solution by neglecting important effects such as dispersion and interactions between the longitudinal and transverse polarizations of phonon propagation. In this article, a comprehensive Monte Carlo solution technique of the BTE is presented. The method accounts for dual polarizations of phonon propagation, and non-linear dispersion relationships. Scattering by various mechanisms is treated individually. Transition between the two polarization branches, and creation and destruction of phonons due to scattering is taken into account. The code has been verified and evaluated by close examination of its ability or failure to capture various regimes of phonon transport ranging from diffusive to the ballistic limit. Validation results show close agreement with experimental data for silicon thin films with and without doping. Simulation results show that above 100 K, transverse acoustic phonons are the primary carriers of energy in silicon.

Quantum phases in an optical lattice

Abstract: We present the zero-temperature phase diagram of bosonic atoms in an optical lattice, using two different mean-field approaches. The phase diagram consists of various insulating phases and a superfluid phase. We explore the nature of the insulating phase by calculating both the quasiparticle and quasihole dispersion relation. We also determine the parameters of our single band Bose-Hubbard model in terms of the microscopic parameters of the atoms in the optical lattice.

Nonreciprocal magnetic photonic crystals

Abstract: We study band dispersion relations omega(k-->) of a photonic crystal with at least one of the constitutive components being a magnetically ordered material. It is shown that by proper spatial arrangement of magnetic and dielectric components one can construct a magnetic photonic crystal with strong spectral asymmetry (nonreciprocity) omega(k-->) not equal omega(-k-->). The spectral asymmetry, in turn, results in a number of interesting phenomena, in particular, one-way transparency when the magnetic photonic crystal, being perfectly transparent for a Bloch wave of frequency omega, "freezes" the radiation of the same frequency omega propagating in the opposite direction. The frozen radiation corresponds to a Bloch wave with zero group velocity partial differential omega(k)/ partial differential k=0 and, in addition, with partial differential(2)omega(k)/ partial differential k(2)=0.

Silicon‐Based Photonic Crystals

Abstract: In semiconductors electrons propagate in a periodic poten-tial, which originates from the atomic lattice. This modifiesthe dispersion relation of free electrons and a band structurewith a bandgap occurs in the case of semiconductors. Theincorporation of electrically active defects allows the manipu-lation of the electronic properties, which gave birth to a largevariety of electronic devices. There are distinct electrical andelectro-optical properties of the different semiconductormaterials, the dominant and most studied semiconductorbeing silicon.For more than ten years, the optical analogues to electronicsemiconductors, the so-called photonic crystals, have been thesubject of intense international research efforts. Photoniccrystals are materials with a periodically varying index ofrefraction. This allows the control of the propagation of elec-tromagnetic waves, similar to electrons in a semiconductorcrystal. By analogy with semiconductors, the periodicity of theunderlying lattice structure is of the same order of magnitudeas the wavelength of the electromagnetic radiation.Despite the far-reaching analogies between electronicwaves in semiconductors and electromagnetic waves in pho-tonic crystals, there are pronounced differences between thetwo as is noticeable from the corresponding equations of mo-tion. Electrons are described by a scalar wavefield. In con-trast, the electromagnetic field is vectorial by nature. Further-more, the time-independent Schrodinger equation allowssolutions with negative energy eigenvalues, whereas the corre-sponding wave equation in electrodynamics contains only thesquare of the eigenfrequencies, hence negative eigenvaluesare excluded from the outset. It may be inferred from the fewphotonic crystals that appear in nature, in contrast to ubiqui-tous semiconductor materials, that these differences have adisadvantageous effect on the likelihood of the formation ofphotonic bandgaps. From the multitude of the optical phe-nomena only, for example, the colorful speckles of opals, somecrystallites on the wings of butterflies and the spine of the sea-mouse

The robustness of inflation to changes in super-planck-scale physics

Abstract: We calculate the spectrum of density fluctuations in models of inflation based on a weakly self-coupled scalar matter field minimally coupled to gravity, and specifically investigate the dependence of the predictions on modifications of the physics on length scales smaller than the Planck length. These modifications are encoded in terms of modified dispersion relations. Whereas for some classes of dispersion relations the predictions are unchanged compared to the usual ones which are based on a linear dispersion relation, for other classes important differences are obtained, involving tilted spectra, spectra with exponential factors and with oscillations. This is the case when the dispersion relation becomes complex. We conclude that the predictions of inflationary cosmology in these models are not robust against changes in the super-Planck-scale physics.

Dispersion relation and optical transmittance of a hexagonal photonic crystal slab

Abstract: The dispersion relation and the optical transmittance of a two-dimensional photonic crystal composed of the hexagonal array of cylindrical air holes fabricated in a dielectric slab were analyzed by group theory and the numerical calculation based on the finite-difference time-domain method. The decay rate of the leaky modes that exist above the light line (the dispersion relation in air) in the band diagram was also evaluated, from which the absence of the coupling between certain internal eigenmodes and the external radiation field was shown. This phenomenon was related to symmetry mismatching by the group-theoretical argument. It was also shown that a certain leaky band has a quality factor as large as 3000 over its entire spectral range. These features as well as the opaque frequency regions due to symmetry mismatching were clearly demonstrated by the calculated optical transmission spectra.

Stopping Light via Hot Atoms

Abstract: We prove that it is possible to freeze a light pulse (i.e., to bring it to a full stop) or even to make its group velocity negative in a coherently driven Doppler broadened atomic medium via electromagnetically induced transparency (EIT). This remarkable phenomenon of the ultraslow EIT polariton is based on the spatial dispersion of the refraction index n(omega,k), i.e., its wave number dependence, which is due to atomic motion and provides a negative contribution to the group velocity. This is related to, but qualitatively different from, the recently observed light slowing caused by large temporal (frequency) dispersion.

Surface polaritons of a left-handed material slab

Abstract: The dispersion relations of the surface polaritons of a slab made of a material which has dispersive permittivity and permeability, and is left-handed over a frequency band in the microwave range of several GHz, are investigated. Four branches of p polarized surface polaritons and two branches of s polarized ones are found to exist. The possibility of experimentally observing the surface polaritons by the attenuated total reflection method is demonstrated.

The near-surface current velocity determined from image sequences of the sea surface

Abstract: A method to measure the ocean's near-surface current velocity vector based on the analysis of remote sea-surface image sequences was developed. The spatial and temporal records were transformed to the wavenumber-frequency domain, resulting in a three-dimensional (3-D) image power spectrum. In the spectrum, the signal energy of the waves is localized on a shell defined by the dispersion relation of surface waves. The sum of the sensor's velocity and the near-surface current profile deforms the dispersion shell due to the Doppler-frequency shift. An iterative least-squares fitting technique and an error-estimation model was implemented. To improve the method's accuracy, spectral wave energy found in higher harmonics of the dispersion shell and aliasing effects are taken into account. The most important nonlinear mechanism leading to higher harmonics is explained as resulting from wave shadowing due to the low grazing angles typical for ground- or ship-based radars. The improved method is examined analytically and is tested with Monte Carlo simulations. The variation of the shape of the measured or simulated 3-D image spectra, especially the peak wavenumber, the directional spread, and the main travel direction, controls the behavior and accuracy of the technique. A comparison of velocities acquired by nautical radar and independent Doppler log current measurements is presented. The technique's accuracy, its limits, and its adaptability are discussed. Additional improvements are proposed.

Low energy analysis of πN→πN

Abstract: We derive a representation for the pion nucleon scattering amplitude that is valid to the fourth order of the chiral expansion. To obtain the correct analytic structure of the singularities in the low energy region, we have performed the calculation in a relativistic framework (infrared regularization). The result can be written in terms of functions of a single variable. We study the corresponding dispersion relations and discuss the problems encountered in the straightforward nonrelativistic expansion of the infrared singularities. As an application, we evaluate the corrections to the Goldberger-Treiman relation and to the low energy theorem that relates the value of the amplitude at the Cheng-Dashen point to the σ-term. While chiral symmetry does govern the behaviour of the amplitude in the vicinity of this point, the representation for the scattering amplitude is not accurate enough to use it for an extrapolation of the experimental data to the subthreshold region. We propose to perform this extrapolation on the basis of a set of integral equations that interrelate the lowest partial waves and are analogous to the Roy equations for ππ scattering.

Longitudinal and Transverse Waves in Yukawa Crystals

Abstract: A unified theoretical treatment is given of longitudinal (or compressional) and transverse modes in Yukawa crystals, including the effects of damping. Dispersion relations are obtained for hexagonal lattices in two dimensions and bcc and fcc lattices in three dimensions. Theoretical predictions are compared with two recent experiments.

Guided waves energy velocity in absorbing and non-absorbing plates

Abstract: This paper presents a study of the velocity of the propagation of energy in guided waves in plates. The motivation of the work comes from the practical observation that the conventional approach to predicting the velocities of pulses or wave packets, that is, the simple group velocity calculation, breaks down when the guided waves are attenuative. The conventional approach is therefore not valid for guided waves in absorbing materials or for leaky waves. The paper presents a theoretical derivation of an expression to predict the energy velocity of guided waves in an isotropic plate, based on the integration of the Poynting energy vectors. When applied to modes with no attenuation, it is shown analytically from this expression that the energy velocity is always identical to the group velocity. On the other hand, when applied to attenuative modes, numerical integration of the expression to yield the true energy velocity shows that this can differ quite significantly from the group velocity. Experimental validation of the expression is achieved by measuring the velocity of wave packets in an absorbing plate, under such conditions when the energy velocity differs substantially from the group velocity. Excellent agreement is found between the predictions and the measurements. The paper also shows the Poynting vectors in the various model studies, and some interesting phenomena relating to their directions.

Nonlinear self-sustained structures and fronts in spatially developing wake flows

Abstract: A family of slowly spatially developing wakes with variable pressure gradient is numerically demonstrated to sustain a synchronized finite-amplitude vortex street tuned at a well-defined frequency. This oscillating state is shown to be described by a steep global mode exhibiting a sharp Dee–Langer-type front at the streamwise station of marginal absolute instability. The front acts as a wavemaker which sends out nonlinear travelling waves in the downstream direction, the global frequency being imposed by the real absolute frequency prevailing at the front station. The nonlinear travelling waves are determined to be governed by the local nonlinear dispersion relation resulting from a temporal evolution problem on a local wake profile considered as parallel. Although the vortex street is fully nonlinear, its frequency is dictated by a purely linear marginal absolute instability criterion applied to the local linear dispersion relation.

An Ultrasimple Spectral Parameterization for Nonorographic Gravity Waves

Abstract: This paper describes a new computationally efficient, ultrasimple nonorographic spectral gravity wave parameterization model. Its predictions compare favorably, though not perfectly, with a model of gravity wave propagation and breaking that computes the evolution with altitude of a full, frequency- and wavenumber-dependent gravity wave spectrum. The ultrasimple model depends on making the midfrequency (hydrostatic, nonrotating) approximation to the dispersion relation, as in Hines’ parameterization. This allows the full frequency–wavenumber spectrum of pseudomomentum flux to be integrated with respect to frequency, and thus reduced to a spectrum that depends on vertical wavenumber m and azimuthal direction ϕ only. The ultrasimple model treats the m dependence as consisting of up to three analytically integrable segments, or “parts.” This allows the total pseudomomentum flux to be evaluated by using analytical expressions for the areas under the parts rather than by performing numerical quadratur...

Low energy analysis of pi N --> pi N

Abstract: We derive a representation for the pion nucleon scattering amplitude that is valid to the fourth order of the chiral expansion. To obtain the correct analytic structure of the singularities in the low energy region, we have performed the calculation in a relativistic framework (infrared regularization). The result can be written in terms of functions of a single variable. We study the corresponding dispersion relations and discuss the problems encountered in the straightforward nonrelativistic expansion of the infrared singularities. As an application, we evaluate the corrections to the Goldberger-Treiman relation and to the low energy theorem that relates the value of the amplitude at the Cheng-Dashen point to the \sigma-term. While chiral symmetry does govern the behaviour of the amplitude in the vicinity of this point, the representation for the scattering amplitude is not accurate enough to use it for an extrapolation of the experimental data to the subthreshold region. We propose to perform this extrapolation on the basis of a set of integral equations that interrelate the lowest partial waves and are analogous to the Roy equations for \pi\pi scattering.

High-Frequency Low-Loss Ultrasonic Modes in Imbedded Bars

Abstract: The dispersion relationships of a system comprising a circular bar imbedded in a solid medium having a lower acoustic impedance than the bar have been predicted. A generic study of such systems has been undertaken, motivated by a particular interest in the case of a circular steel bar imbedded in cement grout which has application to the inspection of tendons in post-tensioned concrete bridges; measurements to confirm the predictions have been carried out for this case. The attenuation dispersion curves show a series of attenuation minima at roughly equal frequency spacing. The attenuation minima occur at the same frequencies as energy velocity maxima and they correspond to points at which the particle displacements and energy of the particular mode are concentrated towards the center of the bar so leakage of energy into the imbedding medium is minimized. The attenuation at the minima decreases with increasing frequency as the energy becomes more concentrated at the middle of the bar, until the material attenuation in the bar becomes a significant factor and the attenuation at the minima rises again. For the particular case of a steel bar in cement grout, the minimum attenuation is reached at a frequency-radius product of about 23 MHz-mm. The frequency-radius product at which the minimum attenuation is reached and the value of the minimum attenuation both increase as the acoustic impedance of the imbedding medium increases.

Elastic waves in anisotropic laminates

Abstract: FUNDAMENTS OF WAVES IN ELASTIC SOLIDS Introduction Formulation of Longitudinal Wave in a Bar Free Wave Motion in Infinite Bars Free Wave Motion in a Finite Bar Forces Wave Motion in an Infinite Bar Forced Wave Motion in a Finite Bar Transient Waves in an Infinite Bar Remarks WAVES IN PLATES OF FUNCTIONALLY GRADED MATERIAL Introduction Element of Linear Property Variation Boundary and Continuity Conditions Transient Response Evaluation of Confluent Hypergeometric Function Examples Remarks FREE WAVE MOTION IN ANISOTROPIC LAMINATES Introduction Basic Equations Derivation of Dispersion Equation Strain Energy Distribution Examples Remarks FORCED WAVE MOTION IN COMPOSITE LAMINATES Introduction Basic Equations Boundary and Interface Conditions Displacement in the Wavenumber Domain A Technique for the Inverse Fourier Integration Response in Time Domain Poles and Complex Paths Examples Remarks CHARACTERISTICS OF WAVES IN COMPOSITE LAMINATES Introduction Dispersion Equation Group Velocities Phase Velocity Surface Phase Slowness Surface Phase Wave Surface Group Velocity Surface Group Slowness Surface Group Wave Surface Examples Remarks FREE WAVE MOTION IN ANISOTROPIC LAMINATED BARS: FINITE STRIP ELEMENT METHOD Introduction System Equation Examples Remarks FREE WAVE MOTION IN COMPOSITE LAMINATED BARS: SEMI-EXACT METHOD Introduction System Equation Examples of Harmonic Waves in Bars Edge Waves in Semi-Infinite Laminates Remarks TRANSIENT WAVES IN COMPOSITE LAMINATES Introduction HNM Formulation Equation in Wavenumber Domain Displacement in Wavenumber Domain Response in Space-Time Domain Response to Line Time-Step Load Response to Point Time-Step Load Techniques for Inverse Fourier Integral Response to Transient Load of Arbitrary Time Function Remarks WAVES IN FUNCTIONALLY GRADED PLATES Introduction Dynamic System Equation Dispersion Relation Group Velocity Response Analysis Two-Dimensional Problem Computational Procedure Dispersion Curves Transient Response to Line Time-Step Loads Remarks WAVES IN ANISOTROPIC FUNCTIONALLY GRADED PIEZOELECTRIC PLATES Introduction Basic Equations Approximated Governing Equations Equations in Transform Domain Characteristics of Waves in FBPM Plates Transient Response Analysis Interdigital Electrodes Excitation Displacement and Electrostatics Potential Response Computation Procedure Dispersion Curves Excitation of Time-Step Shear Force in y Direction Excitation of a Line Electrode Excitation of Interdigital Electrodes Remarks STRIP ELEMENT METHOD FOR STRESS WAVES IN ANISOTROPIC SOLIDS Introduction System Equation SEM for Static Problems (Flamant's Problem) SEM for Dynamic Problems Remarks WAVE SCATTERING BY CRACKS IN COMPOSITE LAMINATES Introduction Governing Differential Equations Particular Solution Application of the SEM to Cracked Laminates Solution in the Time Domain Examples of Scattered Wave Fields Characterization of Horizontal Cracks Characterization of Vertical Surface-Breaking Cracks Characterization of Middle Interior Vertical Cracks Characterization of Arbitrary Interior Vertical Cracks Remarks WAVES SCATTERING BY FLAWS IN COMPOSITE LAMINATES Introduction Applications of the SEM to Plates Containing Flaws Examples for Wave Scattering in Laminates SH Waves in Sandwich Plates Strip Element Equation for SH Waves Particular Solution Complementary Solution General Solution SH Waves Scattered by Flaws Remarks BENDING WAVES IN ANISOTROPIC LAMINATED PLATES Introduction Governing Equation Strip element Equation Assembly of Element Equations Static Problems for Orthotropic Laminated Plates Wave Motion in Anisotropic Laminated Plates CHARACTERISTICS OF WAVES IN COMPOSITE CYLINDERS Introduction Basic Equations Dispersion Relations Examples Remarks WAVE SCATTERING BY CRACKS IN COMPOSITE CYLINDERS Introduction Basic Equations Axisymmetric Strip Element Examples Remarks INVERSE IDENTIFICATION OF IMPACT LOADS USING ELASTIC WAVES Introduction Two-dimensional Line Load Two-dimensional Extended Load Three-dimensional Concentrated Load Examples Remarks INVERSE DETERMINATION OF MATERIAL CONSTANTS OF COMPOSITE LAMINATES Introduction Inverse Operation Uniform-Micro Genetic Algorithms Examples Remarks

Energetics of long internal gravity waves in large lakes

Abstract: An analytical model is used to determine dispersion relations and the ratio of potential to kinetic energy in linear basin-scale internal waves in lakes affected by the earth's rotation. It is shown that the wave frequency and energy partitioning in elliptic lakes are dependent only on the direction of propagation relative to the earth's rotation, the aspect ratio, the horizontal mode (azimuthal and radial), and the Burger number (Si 5 ci/Lf, where ci is the non- rotating phase speed, L is a length scale that characterizes the lake dimension, and f is the Coriolis parameter). For the cyclonic (rotating in the same direction as the earth's rotation), lowest radial mode (a Kelvin wave for small Si and a Poincarewave for largeSi), the total potential to kinetic energy ratio was always greater than unity for all azimuthal modes. For all other radial modes (Poincarewaves for allSi), both cyclonic and anticyclonic, the ratio is substantially less than unity, especially as the Burger number decreases. The results demonstrate that basin-scale Poincarewaves follow the same rotation-gravity balance as unbounded plane progressive Poincarewaves, in which rotation plays an increasingly important role as the Burger number decreases. The solutions are applied to field experiments conducted in Lake Kinneret (Israel) to determine the dissipation timescale of the basin-scale internal waves. It is further shown that features of the spatial structure of isopycnal displacement and velocity scales may be inferred from a single station that measures potential energy fluctuations. The response of a stratified lake to wind forcing is a topic that has received much attention. Some fraction of the en- ergy input by the wind goes into generating internal waves, with basin-scale waves containing the most energy and re- sponsible for transporting mass and momentum over large scales (Imberger 1998). The total energy in the internal wave field is of particular interest, especially when determining the efficiency of energy transfer from the wind to internal waves or when trying to determine the decay timescale of the internal wave field. In nonrotating systems, internal wave energy is partitioned equally between kinetic and potential forms (Gill 1982). We refer to partitioning as the average potential energy in the wave over one period, divided by the average kinetic energy over one period. The introduction of rotation (Gill 1982) alters the equi-partitioning of energy. For linear progressive waves in a laterally unbounded, rotating system, the ratio of potential to kinetic energy is 22 PE v 2 f 5

Water depth and surface current retrievals from airborne optical measurements of surface gravity wave dispersion

Abstract: Visible images of nearshore ocean waves obtained from an aircraft have been utilized to estimate the surface currents and water depth below the waves. A digital framing camera was mounted in a motion-stabilized turret and used to obtain temporal sequences of high-quality optical images of shoaling ocean waves. Data on the position and attitude of the camera/turret were used to map the image data to a rectilinear coordinate system at the level of the surface, effectively separating the spatial and temporal modulations due to the waves. The resulting three-dimensional (3-D) space-time data sets were Fourier transformed to obtain frequency-wave number spectra of these modulations. These spectra contain information on the propagation characteristics of the waves, such as their wavelengths and frequencies, and their directions and speeds of propagation. The water depth and current vector have been estimated by choosing these parameters so that a “best” fit is obtained between the theoretical dispersion relation for linear gravity waves and these 3-D wave spectra. Image data sets were acquired during the Shoaling Waves Experiment (SHOWEX) along the quasi-linear coastline in the vicinity of the Army Corps of Engineers' Field Research Facility (FRF) near Duck on the North Carolina Outer Banks. Summary wave parameters and bathymetry and current retrievals are typically within 10% of contemporaneous in situ measurements, though outliers occur.

Electromagnetic energy transport along arrays of closely spaced metal rods as an analogue to plasmonic devices

Abstract: The transport of electromagnetic energy along structures consisting of arrays of closely spaced metal rods (spacing = 0.2 cm) was investigated in the microwave regime at 8.0 GHz (lambda= 3.7 cm). The dispersion relation shows that information transport occurs at a group velocity of 0.6c. The electromagnetic energy is highly confined to the arrays (90% within a distance of 0.05lambda from the array). The propagation loss in a straight array is 3 dB/8 cm. Routing of energy around 90° corners is possible with a power loss of 3–4 dB. Analogies to plasmon wires consisting of arrays of nm-size metal clusters are discussed.

Micro-mechanical modelling of granular material. Part 1: Derivation of a second-gradient micro-polar constitutive theory

Abstract: This contribution is one in a series of two papers. In the current paper a constitutive law is developed that includes the micro-structural effects by particle displacement as well as particle rotation. Both degrees of freedom can be related to corresponding macroscopic kinematic continuum variables, where the resulting gradients of displacement are selected up to the fourth-order and the gradients of rotation up to the third order. The elastic micro-structural properties for an individual particle are used to derive the macro-level behavior for a fabric of equal-sized spherical particles, leading to a second-gradient micro-polar formulation. In this model, all coefficients are expressed in terms of particle stiffness and particle structure. It is shown that the second-gradient micro-polar model can be reduced to simpler forms, such as the classic linear elastic model, the second-gradient model and the Cosserat model. In the accompanying paper these reduced forms are treated in more detail by analyzing the corresponding dispersion relations for plane body wave propagation.

Off-branch polaritons and multiple scattering in semiconductor microcavities

Abstract: Angle-resolved measurements show unexpected emission resonances of the polaritons in a semiconductor microcavity. These resonances appear when more than one in-plane polariton mode is macroscopically occupied. The new resonances observed in angle-resolved luminescence do not lie on the expected polariton branches and possess different dispersion relations with negative effective mass. The experimental results can be well explained using an interacting polariton model that treats multiple scattering. The k dispersion of the luminescence resonances is reproduced using the Bogolubov approximation that deals with the macroscopic coherence of the signal, pump, and idler modes. This model also explains many puzzling features such as the stimulation of resonant Rayleigh scattering in the backward direction. In addition, the use of nonresonant control beams for coherent control of the polaritons is shown both experimentally and theoretically. The rich complexity of new phenomena in optically excited semiconductor microcavities can be attributed to the distinctive anti-Hermitian or anomalous coupling between polaritons.

Imaging of friedel oscillation patterns of two-dimensionally accumulated electrons at epitaxially grown InAs(111)A surfaces

Abstract: The local density of states (LDOS) at the epitaxially grown InAs surface on a GaAs(111) A substrate were characterized using low-temperature scanning tunneling microscopy. Using dI/dV signal mapping, LDOS standing waves were clearly imaged at point defects and within nanostructures. Measurement of the wavelength as a function of bias voltage showed a nonparabolic dispersion relation for the conduction band. The observed wave features originate from the Friedel oscillations of the two-dimensional electron gas in the semiconductor surface accumulation layer.

Galaxy groups at intermediate redshift

Abstract: Galaxy groups likely to be virialized are identified within the CNOC2 intermediate-redshift galaxy survey. The resulting groups have a median velocity dispersion, σ1 200 km s-1. The virial mass-to-light ratios, using k-corrected and evolution-compensated luminosities, have medians in the range of 150-250 h M☉/L☉, depending on group definition details. The number-velocity dispersion relation at σ1 200 km s-1 is in agreement with the low-mass extrapolation of the cluster-normalized Press-Schechter model. Lower velocity dispersion groups are deficient relative to the Press-Schechter model. The two-point group-group autocorrelation function has r0 = 6.8 ± 0.3 h-1 Mpc, which is much larger than the correlations of individual galaxies, but about as expected from biased clustering. The mean number density of galaxies around group centers falls nearly as a power law with r-2.5 and has no well-defined core. The projected velocity dispersion of galaxies around group centers is either flat or slowly rising outward. The combination of a steeper than isothermal density profile and the outward rising velocity dispersion implies that the mass-to-light ratio of groups rises with radius if the velocity ellipsoid is isotropic but could be nearly constant if the galaxy orbits are nearly circular. Such strong tangential anisotropy is not supported by other evidence. Although the implication of a rising M/L must be viewed with caution, it could naturally arise through dynamical friction acting on the galaxies in a background of classical collisionless dark matter.

Photonic bands of metallic systems. I. Principle of calculation and accuracy

Abstract: The dispersion relation, the field distribution, and the lifetime of the radiational eigenmodes in two-dimensional photonic crystals composed of metallic cylinders were calculated for the E polarization by means of the numerical simulation of the dipole radiation based on the finite-difference time-domain (FDTD) method. The convergence and the central processing unit time were compared with the plane-wave expansion method. The opaque frequency ranges in the transmission spectra calculated by the method of Pendry and MacKinnon corresponded quite well to the band gaps and the antisymmetric modes found in the photonic band diagram. The dispersion relation and the symmetry of the eigenmodes obtained by the numerical calculation were consistent with the prediction of the group theory and the analytical expression by the long-wavelength approximation.

Collective Dynamics in Fully Hydrated Phospholipid Bilayers Studied by Inelastic X-Ray Scattering

Abstract: The short wavelength density fluctuation of DLPC (dilaurylphosphatidylcholine) bilayers close to full hydration has been studied by the inelastic x-ray scattering technique below and above the main transition temperature. The analysis based on a generalized three effective eigenmode theory allows us to construct the dispersion relation of the high frequency sound mode for the first time. The marked softening of the excitation near k = 14 nm(-1), corresponding to the lipid chain-chain correlation peak in the structure factor, in the L(alpha) phase implies prevalent occurrences of short-wavelength in-plane motions of lipid chains that might be of importance for transportation of small molecules across membranes.