Showing papers on "Dispersion relation published in 2011"

Phonons in single-layer and few-layer MoS 2 and WS 2

Abstract: We report ab initio calculations of the phonon dispersion relations of the single-layer and bulk dichalcogenides MoS2 and WS2. We explore in detail the behavior of the Raman-active modes A1g and E 1 2g as a function of the number of layers. In agreement with recent Raman spectroscopy measurements [C. Lee et al., ACS Nano 4, 2695 (2010)], we find that the A1g mode increases in frequency with an increasing number of layers while the E 1g mode decreases. We explain this decrease by an enhancement of the dielectric screening of the long-range Coulomb interaction between the effective charges with a growing number of layers. This decrease in the long-range part overcompensates for the increase of the short-range interaction due to the weak interlayer interaction.

Pion-pion scattering amplitude. IV. Improved analysis with once subtracted Roy-like equations up to 1100 MeV

Abstract: We improve our description of π π scattering data by imposing additional requirements on our previous fits, in the form of once-subtracted Roy-like equations, while extending our analysis up to 1100 MeV. We provide simple and ready to use parametrizations of the amplitude. In addition, we present a detailed description and derivation of these once-subtracted dispersion relations that, in the 450 to 1100 MeV region, provide an additional constraint which is much stronger than our previous requirements of forward dispersion relations and standard Roy equations. The ensuing constrained amplitudes describe the existing data with rather small uncertainties in the whole region from threshold up to 1100 MeV, while satisfying very stringent dispersive constraints. For the S0 wave, this requires an improved matching of the low and high energy parametrizations. Also for this wave we have considered the latest low energy K_(l4) decay results, including their isospin violation correction, and we have removed some controversial data points. These changes on the data translate into better determinations of threshold and subthreshold parameters which remove almost alldisagreement with previous chiral perturbation theory and Roy equation calculations below 800 MeV. Finally, our results favor the dip structure of the S0 inelasticity around the controversial 1000 MeV region.

PT-symmetry in honeycomb photonic lattices

Abstract: We apply gain and loss to honeycomb photonic lattices and show that the dispersion relation is identical to tachyons---particles with imaginary mass that travel faster than the speed of light. This is accompanied by -symmetry breaking in this structure. We further show that the -symmetry can be restored by deforming the lattice.

Gravity or turbulence? Velocity dispersion–size relation

Abstract: We discuss the nature of the velocity dispersion versus size relation for molecular clouds. In particular, we add to previous observational results showing that the velocity dispersions in molecular clouds and cores are not purely functions of the spatial scale but involve surface gas densities as well. We emphasize that hydrodynamic turbulence is required to produce the first condensations in the progenitor medium. However, as the cloud is forming, it also becomes bound, and gravitational accelerations dominate the motions. Energy conservation in this case implies |Eg |∼ Ek, in agreement with observational data, and providing an interpretation for two recent observational results: the scatter in the δv–R plane, and the dependence of the velocity dispersion on the surface density δv 2 /R ∝ � . We argue that the observational data are consistent with molecular clouds in a state of hierarchical and chaotic gravitational collapse, i.e. developing local centres of collapse throughout the whole cloud while the cloud itself is collapsing, and making equilibrium unnecessary at all stages prior to the formation of actual stars. Finally, we discuss how this mechanism need not be in conflict with the observed star formation rate.

A global model of Love and Rayleigh surface wave dispersion and anisotropy, 25–250 s

Abstract: SUMMARY A large number of fundamental-mode Love and Rayleigh wave dispersion curves were determined from seismograms for 3330 earthquakes recorded on 258 globally distributed seismographic stations. The dispersion curves were sampled at periods between 25 and 250 s to determine propagation-phase anomalies with respect to a reference earth model. The data set of phase anomalies was first used to construct global isotropic phase-velocity maps at specific frequencies using spherical-spline basis functions with a nominal uniform resolution of 650 km. Azimuthal anisotropy was then included in the parametrization, and its importance for explaining the data explored. Only the addition of 2ζ azimuthal variations for Rayleigh waves was found to be resolved by the data. In the final stage of the analysis, the entire phase-anomaly data set was inverted to determine a global dispersion model for Love and Rayleigh waves parametrized horizontally using a spherical-spline basis, and with a set of B-splines to describe the slowness variations with respect to frequency. The new dispersion model, GDM52, can be used to calculate internally consistent global maps of phase and group velocity, as well as local and path-specific dispersion curves, between 25 and 250 s.

Precise determination of the f(0)(600) and f(0)(980) pole parameters from a dispersive data analysis

Abstract: We use our latest dispersive analysis of π π scattering data and the very recent K_(l4) experimental results to obtain the mass, width, and couplings of the two lightest scalar-isoscalar resonances. These parameters are defined from their associated poles in the complex plane. The analytic continuation to the complex plane is made in a model-independent way by means of once-and twice-subtracted dispersion relations for the partial waves, without any other theoretical assumption. We find the f(0)(600) pole at [457_(-13)^(+14)] – i[279_(-7)^(+11)+ MeV and that of the f(0)(980) at (996 ± 7) – i[25_(-6)^(+10)] MeV, whereas their respective couplings to two pions are 3.59_(-0.13)^(+0.11) and 2.3 ± 0.2 GeV.

DIRECT IMAGING OF QUASI-PERIODIC FAST PROPAGATING WAVES OF ∼2000 km s–1 IN THE LOW SOLAR CORONA BY THE SOLAR DYNAMICS OBSERVATORY ATMOSPHERIC IMAGING ASSEMBLY

Abstract: Quasi-periodic, propagating fast mode magnetosonic waves in the corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new SDO AIA instrument. In the 2010 August 1 C3.2 flare/CME event, we find arc-shaped wave trains of 1–5% intensity variations (lifetime ∼200 s) that emanate near the flare kernel and propagate outward up to ∼400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 ± 130kms −1 . Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k–! diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin. This k–! ridge shows a broad frequency distribution with indicative power at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s) temporally coincides with quasi-periodic pulsations of the flare, suggesting a common origin. The instantaneous wave energy flux of (0.1–2.6)× 10 7 ergs cm −2 s −1 estimated at the coronal base is comparable to the steady-state heating requirement of active region loops. Subject headings: Sun: activity—Sun: corona—Sun: coronal mass ejections—Sun: flares—Sun: oscillations—waves

Homogenization of periodic elastic composites and locally resonant sonic materials

Abstract: A method for homogenization of an elastic composite with periodic microstructure is presented, focusing on the Floquet-type elastic waves. The resulting homogenized frequency-dependent elasticity and mass density then automatically satisfy the overall conservation laws and by necessity produce the exact dispersion relations. It is also shown that the dispersion relations and the associated field quantities can be accurately calculated using a mixed variational approach, based on the microstructure of the associated unit cell. The method is used to calculate the dynamic effective parameters for a layered composite by using both the exact solution and the results of the mixed variational formulation. The exact and approximate results are shown to be in close agreement, which makes it possible to use the approximate method for the proposed type of homogenization in cases where an exact solution does not exist. The homogenized frequency-dependent effective parameters give rise to the concept of dynamic Ashby charts that can be used to illustrate the effect of the microstructural architecture on the dynamic properties of a composite. In particular, the charts vividly display how this effective stiffness and density vary with frequency and may attain negative values within certain frequency ranges which can be changed as desired using the microarchitecture while keeping the volume fraction of the unit cell's constituents constant.

Magnetohydrodynamic waves in solar partially ionized plasmas: two-fluid approach

Abstract: Context. Partially ionized plasma is usually described by a single-fluid approach, where the ion-neutral collision effects are expressed by Cowling conductivity in the induction equation. However, the single-fluid approach is not valid for time-scales less than ion-neutral collision time. For these time-scales the two-fluid description is the better approximation. Aims. We aim to derive the dynamics of magnetohydrodynamic (MHD) waves in two-fluid partially ionized plasmas and to compare the results with those obtained under single-fluid description. Methods. Two-fluid equations are used, where ion-electron plasma and neutral particles are considered as separate fluids. Dispersion relations of linear waves are derived for the simplest case of homogeneous medium. Frequencies and damping rates of waves are obtained for different parameters of background plasma. Results. We found that two- and single-fluid descriptions give similar results for low-frequency waves. However, the dynamics of MHD waves in the two-fluid approach is significantly changed when the wave frequency becomes comparable with or higher than the ion-neutral collision frequency. Alfven and fast magneto-acoustic waves attain their maximum damping rate at particular frequencies (for example, the peak frequency equals 2.5 times the ion-neutral collision frequency for 50% of neutral hydrogen) in the wave spectrum. The damping rates are reduced for the higher frequency waves. The new mode of slow magneto-acoustic wave appears for higher frequency branch, which is connected to neutral hydrogen fluid. Conclusions. The single-fluid approach perfectly deals with slow processes in partially ionized plasmas, but fails for time-scales shorter than ion-neutral collision time. Therefore, the two-fluid approximation should be used for the description of relatively fast processes. Some results of the single-fluid description should be revised in future such as the damping of high-frequency Alfven waves in the solar chromosphere due to ion-neutral collisions.

Direct Imaging by SDO AIA of Quasi-periodic Fast Propagating Waves of ~2000 km/s in the Low Solar Corona

Abstract: Quasi-periodic, propagating fast mode magnetosonic waves in the corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new SDO AIA instrument. In the 2010 August 1 C3.2 flare/CME event, we find arc-shaped wave trains of 1-5% intensity variations (lifetime ~200 s) that emanate near the flare kernel and propagate outward up to ~400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 +/- 130 km/s. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-$\omega$ diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin. This k-$\omega$ ridge shows a broad frequency distribution with indicative power at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s) temporally coincides with quasi-periodic pulsations of the flare, suggesting a common origin. The instantaneous wave energy flux of $(0.1-2.6) \times 10^7 ergs/cm^2/s$ estimated at the coronal base is comparable to the steady-state heating requirement of active region loops.

Local resonances-induced low-frequency band gaps in two-dimensional phononic crystal slabs with periodic stepped resonators

Abstract: In this paper, the numerical investigation of Lamb wave propagation in two-dimensional phononic crystals composed of an array of stepped resonators on a thin slab is presented. The dispersion relations, power transmission spectra and spectra of resonances are studied using a finite-element method. Because of the simultaneous mechanisms of the local resonances and Bragg scattering, the structures exhibit low-frequency forbidden bands and Bragg band gaps, which can be effectively shifted by changing the resonator geometries as well as the lattice symmetries of the resonator array. As a result, a low-frequency gap within the audible regime can be demonstrated. Furthermore, for a finite phononic crystal slab, the calculated transmission and resonance spectra show an evident resonance nature which can be directly related to the formation of the low-frequency gaps. Based on the spectra of elastic waves through the single-layer stepped resonators, the resonances of the stepped resonators are found to either induce high reflection or intensify the transmission. The effects of different excitation conditions for generating specific slab modes with different polarization states on the acoustic energy transmission and attenuation are also studied. The results show that the polarization states of the incident slab modes influence the spectra of resonances, power transmission and attenuation.

Loss-compensated and active hyperbolic metamaterials

Abstract: We have studied the dispersion relations of multilayers of silver and a dye-doped dielectric using four methods: standard effective-medium theory (EMT), nonlocal-effect-corrected EMT, nonlinear equations based on the eigenmode method, and a spatial harmonic analysis method. We compare the validity of these methods and show that metallic losses can be greatly compensated by saturated gain. Two realizable applications are also proposed. Loss-compensated metal-dielectric multilayers that have hyperbolic dispersion relationships are beneficial for numerous applications such as subwavelength imaging and quantum optics.

Material loss influence on the complex band structure and group velocity in phononic crystals

Abstract: The influence of material loss on the complex band structure of two-dimensional phononic crystals is investigated. A viscoelasticity model is added to the extended plane-wave expansion (EPWE) method, with viscosity proportional to the frequency. It is found that losses have a stronger influence on the real than on the imaginary part of Bloch waves, in contrast with propagation in homogeneous media. Flat bands, i.e., bands initially showing low group velocity without losses, acquire an enhanced damping as compared to bands with larger group velocities. Losses are also found to limit the appearance of large group slownesses, or conversely small group velocities.

Dispersion Characteristics of a Metamaterial-Based Parallel-Plate Ridge Gap Waveguide Realized by Bed of Nails

Abstract: The newly introduced parallel-plate ridge gap waveguide consists of a metal ridge in a metamaterial surface, covered by a metallic plate at a small height above it. The gap waveguide is simple to manufacture, especially at millimeter and sub-millimeter wave frequencies. The metamaterial surface is designed to provide a frequency band where normal global parallel-plate modes are in cutoff, thereby allowing a confined gap wave to propagate along the ridge. This paper presents an approximate analytical solution for this confined quasi-TEM dominant mode of the ridge gap waveguide, when the metamaterial surface is an artificial magnetic conductor in the form of a bed of nails. The modal solution is found by dividing the field problem in three regions, the central region above the ridge and the two surrounding side regions above the nails. The fields within the side regions are expressed in terms of two evanescent TE and TM modes obtained by treating the bed of nails as an isotropic impedance surface, and the field in the central ridge region is expanded as a fundamental TEM parallel-plate mode with unknown longitudinal propagation constant. The field solutions are linked together by equalizing longitudinal propagation constants and imposing point-continuity of fields across the region interfaces, resulting in a transcendental dispersion equation. This is solved and presented in a dispersion diagram, showing good agreement with a numerical solution using a general electromagnetic solver. Both the lower and upper cutoff frequencies of the normal global parallel-plate modes are predicted, as well as the quasi-TEM nature of the gap mode between these frequencies, and the evanescent fields in the two side regions decay very rapidly away from the ridge.

Dispersion relation analysis of solar wind turbulence

Abstract: Frequency versus wave number diagram of turbulent magnetic fluctuations in the solar wind was determined for the first time in the wide range over three decades using four Cluster spacecraft. Almost all of the identified waves propagate quasi‐perpendicular to the mean magnetic field at various phase speeds, accompanied by a transition from the dominance of outward propagation from the Sun at longer wavelengths into mixture of counter‐propagation at shorter wavelengths. Frequency‐wave number diagram exhibits largely scattered populations with only weak agreement with magnetosonic and whistler waves. Clear identification of a specific normal mode is difficult, suggesting that nonlinear energy cascade is operating even on small‐scale fluctuations.

The controlling effect of ion temperature on EMIC wave excitation and scattering

Abstract: [1] The dispersion relation of parallel propagating EMIC waves is investigated in a magnetized homogeneous plasma consisting of hot H+ and He+ ions We demonstrate that the hot plasma effects associated with He+ and H+ significantly modify the cold plasma dispersion relation, especially near ΩHe+ For plasmas with a sufficiently small fraction of warm He+ and a sufficiently dense, hot and anisotropic H+ population, the cold plasma stop band above ΩHe+ may vanish, and waves near ΩHe+ may be unstable The maximum wavenumber for unstable L-mode waves due to the hot plasma modification is used to identify the plasma conditions required for EMIC wave scattering of MeV electrons We conclude that relatively extreme conditions (ωpe/|Ωe| > ∼25, and H+ anisotropy >1) are required for resonance with electrons near 1 MeV, which limits such scattering only to the region just inside the plasmasphere or storm time plumes

Band diagram of spin waves in a two-dimensional magnonic crystal.

Abstract: The dispersion curves of collective spin-wave excitations in a magnonic crystal consisting of a square array of interacting saturated nanodisks have been measured by Brillouin light scattering along the four principal directions of the first Brillouin zone. The experimental data are successfully compared to calculations of the band diagram and of the Brillouin light scattering cross section, performed through the dynamical matrix method extended to include the dipolar interaction between the disks. We found that the fourfold symmetry of the geometrical lattice is reduced by the application of the external field and therefore equivalent directions of the first Brillouin zone are characterized by different dispersion relations of collective spin waves. The dispersion relations are explained through the introduction of a bidimensional effective wave vector that characterizes each mode in this magnonic metamaterial.

Excitation of magnetosonic waves in the terrestrial magnetosphere: Particle-in-cell simulations

Abstract: [1] Two-dimensional electromagnetic particle-in-cell simulations are performed to study the temporal development of an ion Bernstein instability driven by a proton velocity distribution with positive slope in the perpendicular velocity distribution fp(v⊥), where ⊥ denotes directions perpendicular to the background magnetic field B0. A subtracted Maxwellian distribution is first used to construct the positive slope in fp(v⊥), and linear kinetic dispersion analysis is performed. The results of a simulation using such an initial proton distribution agree well with the linear kinetic analysis. The simulation results demonstrate that the ion Bernstein instability grows at propagation angles nearly perpendicular to B0 and at frequencies close to the harmonics of the proton cyclotron frequency. The distribution in the simulation is further generalized to contain a proton shell with a finite thermal spread and a relatively cold ion background. The simulation results show that the presence of the cold background protons and the increase of the shell velocity shift the excited waves close to the cold plasma dispersion relation for magnetosonic waves, i.e., ωr = kvA, where ωr is the wave frequency, k is the wave number, and vA is the Alfven velocity. The general features of the simulated field fluctuations resemble observations of fast magnetosonic waves near the geomagnetic equator in the terrestrial magnetosphere. A test particle computation of energetic electrons interacting with the simulated electromagnetic fluctuations suggests that this growing mode may play an important role in the acceleration of radiation belt relativistic electrons.

Evidence for acoustic-like plasmons on epitaxial graphene on Pt(111)

Abstract: The dispersion and the damping of the sheet plasmon in a graphene monolayer grown on Pt(111) have been studied by using angle-resolved electron energy loss spectroscopy. We found that the dispersion relation of the plasmon mode confined in the graphene sheet is linear, as a consequence of the screening by the metal substrate. Present results demonstrate that the presence of an underlying metal substrate could have striking consequences on the plasmon propagation even in the case of a system which exhibits a weak graphene-substrate interaction. Moreover, we found that Landau damping essentially occurs via interband excitations starting above the Fermi wave vector. On the contrary, intraband transitions do not have a significant influence on the collective mode.

Scalar Wave Equation Modeling with Time-Space Domain Dispersion-Relation-Based Staggered-Grid Finite-Difference Schemes

Abstract: The staggered-grid finite-difference (SFD) method is widely used in numerical modeling of wave equations. Conventional SFD stencils for spatial derivatives are usually designed in the space domain. However, when they are used to solve wave equations, it becomes difficult to satisfy the dispersion relations exactly. Liu and Sen (2009c) proposed a new SFD scheme for one-dimensional (1D) scalar wave equation based on the time–space domain dispersion relation and plane wave theory, which is made to satisfy the exact dispersion relation. This new SFD scheme has greater accuracy and better stability than a conventional scheme under the same discretizations. In this paper, we develop this new SFD scheme further for numerical solution of 2D and 3D scalar wave equations. We demonstrate that the modeling accuracy is second order when the conventional 2 M -th-order space-domain SFD and the second order time-domain finite-difference stencils are directly used to solve the scalar wave equation. However, under the same discretization, our 1D scheme can reach 2 M -th-order accuracy and is always stable; 2D and 3D schemes can reach 2 M -th-order accuracy along 8 and 48 directions, respectively, and have better stability. The advantages of the new schemes are also demonstrated with dispersion analysis, stability analysis, and numerical modeling.

Few-photon transport in low-dimensional systems

Abstract: We analyze the role of quantum interference effects induced by an embedded two-level system on the photon transport properties in waveguiding structures that exhibit cutoffs (band edges) in their dispersion relation. In particular, we demonstrate that these systems invariably exhibit single-particle photon-atom bound states and strong effective nonlinear responses on the few-photon level. Based on this, we find that the properties of these photon-atom bound states may be tuned via the underlying dispersion relation and that their occupation can be controlled via multiparticle scattering processes. This opens an interesting route for controlling photon transport properties in a number of solid-state-based quantum optical systems and the realization of corresponding functional elements and devices.

Electron-acoustic solitary waves in the presence of a suprathermal electron component

Abstract: The nonlinear dynamics of electron-acoustic localized structures in a collisionless and unmagnetized plasma consisting of “cool” inertial electrons, “hot” electrons having a kappa distribution, and stationary ions is studied. The inertialess hot electron distribution thus has a long-tailed suprathermal (non-Maxwellian) form. A dispersion relation is derived for linear electron-acoustic waves. They show a strong dependence of the charge screening mechanism on excess suprathermality (through κ). A nonlinear pseudopotential technique is employed to investigate the occurrence of stationary-profile solitary waves, focusing on how their characteristics depend on the spectral index κ, and the hot-to-cool electron temperature and density ratios. Only negative polarity solitary waves are found to exist, in a parameter region which becomes narrower as deviation from the Maxwellian (suprathermality) increases, while the soliton amplitude at fixed soliton speed increases. However, for a constant value of the true Mach number, the amplitude decreases for decreasing κ.

Edge plasmons in graphene nanostructures

Abstract: Plasmon modes in graphene are influenced by the unusual dispersion relation of the material. For bulk plasmons this results in a n(1/4) dependence of the plasma frequency on the charge density, as opposed to the n(1/2) dependence in two-dimensional electron gas (2DEG); yet, bulk plasmon dispersion in graphene follows a similar q(1/2) behavior as for other two-dimensional materials. In this work we consider finite graphene nanostructures, semi-infinite sheets, and circular disks and study edge plasmons that are confined to the boundaries of the structures. We find that, for abrupt edges, graphene edge plasmons behave analogously to those in 2DEGs, but, for gradual edge profiles, important distinctions arise. In particular, we show that for a linear edge profile, graphene supports fewer edge modes than a 2DEG at a given q, and the edge monopole plasmon dispersion in graphene follows a q(1/4) law in contrast to the q(0) behavior seen in 2DEGs. RAMOWITZ M, 1964

Dispersion-relation phase spectroscopy of intracellular transport.

Abstract: We used quantitative phase imaging to measure the dispersion relation, i.e. decay rate vs. spatial mode, associated with mass transport in live cells. This approach applies equally well to both discrete and continuous mass distributions without the need for particle tracking. From the quadratic experimental curve specific to diffusion, we extracted the diffusion coefficient as the only fitting parameter. The linear portion of the dispersion relation reveals the deterministic component of the intracellular transport. Our data show a universal behavior where the intracellular transport is diffusive at small scales and deterministic at large scales. Measurements by our method and particle tracking show that, on average, the mass transport in the nucleus is slower than in the cytoplasm.

Warm plasma effects on electromagnetic ion cyclotron wave MeV electron interactions in the magnetosphere

Abstract: [1] The full kinetic linear dispersion relation in a warm plasma with He+ and O+ ions is used to estimate the minimum resonant electron energies required for resonant scattering of relativistic electrons by electromagnetic ion cyclotron waves. We find two significant differences from the cold-plasma approximation: (1) waves can be excited inside the stop bands and at ion gyrofrequencies for relatively small wave numbers k Ωp/vA experience strong cyclotron damping. We show that, in general, minimum resonant energy of electrons Emin depends only on the wave number k, magnetic field strength B, and plasma mass density ρ and depends on the wave frequency ω only implicitly, via the dispersion relation. Formulae for Emin as function of ω based on cold-plasma approximation predict the lowest energy loss where ω → since in this approximation k → ∞ at these frequencies. We show this inference is incorrect and that kinetic effects mean that the ion gyrofrequencies are no longer necessarily preferential for low energy loss. The lowest values of Emin are obtained where the dispersion supports the largest wave numbers k and in the regions of the largest mass densities ρ and the lowest magnetic fields B. For realistic magnetospheric conditions Emin ∼ 2 MeV and can only drop to ∼500 keV inside dense plasmaspheric plumes, with plasma density of the order of 500 cm−3, or during plasmaspheric expansions to high L shells (L ∼ 7).

Electron-acoustic solitary waves in the presence of a suprathermal electron component

Abstract: The nonlinear dynamics of electron-acoustic localized structures in a collisionless and unmagnetized plasma consisting of "cool" inertial electrons, "hot" electrons having a kappa distribution, and stationary ions is studied. The inertialess hot electron distribution thus has a long-tailed suprathermal (non-Maxwellian) form. A dispersion relation is derived for linear electron-acoustic waves. They show a strong dependence of the charge screening mechanism on excess suprathermality (through \kappa). A nonlinear pseudopotential technique is employed to investigate the occurrence of stationary-profile solitary waves, focusing on how their characteristics depend on the spectral index \kappa, and the hot-to-cool electron temperature and density ratios. Only negative polarity solitary waves are found to exist, in a parameter region which becomes narrower as deviation from the Maxwellian (suprathermality) increases, while the soliton amplitude at fixed soliton speed increases. However, for a constant value of the true Mach number, the amplitude decreases for decreasing \kappa.

Slow wave phenomena in photonic crystals

Abstract: Slow light in photonic crystals and other periodic structures is associated with stationary points of the photonic dispersion relation, where the group velocity of light vanishes. It is shown that in certain cases, the vanishing group velocity is accompanied by the so-called frozen mode regime, when the incident light can be completely converted into the slow mode with huge diverging amplitude. The frozen mode regime is a qualitatively new wave phenomenon – it does not reduce to any known electromagnetic resonance. Formally, the frozen mode regime is not a resonance, in a sense that it is not particularly sensitive to the size and shape of the photonic crystal. The frozen mode regime is more robust and powerful, compared to any known slow-wave resonance. It has much higher tolerance to absorption and structural imperfections.

Geometry of physical dispersion relations

Abstract: To serve as a dispersion relation, a cotangent bundle function must satisfy three simple algebraic properties These conditions are derived from the inescapable physical requirements that local matter field dynamics must be predictive and allow for an observer-independent notion of positive energy Possible modifications of the standard relativistic dispersion relation are thereby severely restricted For instance, the dispersion relations associated with popular deformations of Maxwell theory by Gambini-Pullin or Myers-Pospelov are not admissible Dispersion relations passing the simple algebraic checks derived here correspond to physically admissible Finslerian refinements of Lorentzian geometry

Love Wave at a Layer Medium Bounded by Irregular Boundary Surfaces

Abstract: The problem of the propagation of a Love wave in a corrugated isotropic layer over a homogeneous isotropic half-space has been investigated. The dispersion relation of Love wave propagation in a co...