Showing papers on "Wave propagation published in 2005"

Seismic signatures and analysis of reflection data in anisotropic media

Abstract: 1. Elements of basic theory of anisotropic wave propagation. 2. Influence of anisotropy on point-source radiation and AVO analysis. 3. Normal-moveout velocity in layered anisotropic media. 4. Nonhyperbolic reflection moveout. 5. Reflection moveout of mode-converted waves. 6. P-wave time-domain signatures in transversely isotropic media. 7. Velocity analysis and parameter estimation for VTI media. 8. P-wave imaging for VTI media.

Wave propagation in carbon nanotubes via nonlocal continuum mechanics

Abstract: Wave propagation in carbon nanotubes (CNTs) is studied with two nonlocal continuum mechanics models: elastic Euler-Bernoulli and Timoshenko beam models [Philos. Mag. 41, 744 (1921)]. The small-scale effect on CNTs wave propagation dispersion relation is explicitly revealed for different CNTs wave numbers and diameters by theoretical analyses and numerical simulations. The asymptotic phase velocities and frequency are also derived from nonlocal continuum mechanics. The scale coefficient in nonlocal continuum mechanics is roughly estimated for CNTs from the obtained asymptotic frequency. In addition, the applicability and comparison of the two nonlocal elastic beam models to CNTs wave propagation are explored through numerical simulations. The research findings are proved effective in predicting small-scale effect on CNTs wave propagation with a qualitative validation study based on the published experimental reports in this field.

Flexural wave propagation in single-walled carbon nanotubes

Abstract: The paper presents the study on the flexural wave propagation in a single-walled carbon nanotube through the use of the continuum mechanics and the molecular dynamics simulation based on the Terroff-Brenner potential. The study focuses on the wave dispersion caused not only by the rotary inertia and the shear deformation in the model of a traditional Timoshenko beam, but also by the nonlocal elasticity characterizing the microstructure of carbon nanotube in a wide frequency range up to THz. For this purpose, the paper starts with the dynamic equation of a generalized Timoshenko beam made of the nonlocal elastic material, and then gives the dispersion relations of the flexural wave in the nonlocal elastic Timoshenko beam, the traditional Timoshenko beam and the Euler beam, respectively. Afterwards, it presents the molecular dynamics simulations for the flexural wave propagation in an armchair (5,5) and an armchair (10,10) single-walled carbon nanotubes for a wide range of wave numbers. The simulation results show that the Euler beam holds for describing the dispersion of flexural waves in the two single-walled carbon nanotubes only when the wave number is small. The Timoshenko beam provides a better prediction for the dispersion of flexural waves in the two single-walled carbon nanotubes when the wave number becomes a little bit large. Only the nonlocal elastic Timoshenko beam is able to predict the decrease of phase velocity when the wave number is so large that the microstructure of carbon nanotubes has a significant influence on the flexural wave dispersion.

Calculation of pitch angle and energy diffusion coefficients with the PADIE code

Abstract: [1] We present a new computer code (PADIE) that calculates fully relativistic quasi-linear pitch angle and energy diffusion coefficients for resonant wave-particle interactions in a magnetized plasma. Unlike previous codes, the full electromagnetic dispersion relation is used so that interactions involving any linear electromagnetic wave mode in a predominantly cold plasma can be addressed for any ratio of the plasma-frequency to the cyclotron frequency ωpe/∣Ωe∣. The code can be applied to problems in astrophysical, magnetospheric, and laboratory plasmas. The code is applied here to the Earth's radiation belts to calculate electron diffusion by whistler mode chorus, electromagnetic ion cyclotron (EMIC), and Z mode waves. The high-density approximation is remarkably good for electron diffusion by whistler mode chorus for energies E ≥ 100 keV, even for ωpe/∣Ωe∣ ≈ 2 but underestimates diffusion by orders of magnitude at low energies (∼10 keV). When a realistic angular spread of propagating waves is introduced for EMIC waves, electron diffusion at ∼0.5 MeV is only slightly reduced compared with the assumption of field-aligned propagation, but at ∼5 MeV, electron diffusion at pitch angles near 90° is reduced by a factor of 5 and increased by several orders of magnitude at pitch angles 30°–80°. Scattering by EMIC waves should contribute to flattening of the distribution function. The first results for electron diffusion by Z mode waves are presented. They show that unlike the whistler and EMIC waves, energy diffusion exceeds pitch angle diffusion over a broad range of pitch angles less than 45°. The results suggest that Z mode waves could provide a significant contribution to electron acceleration in the radiation belts during storm times.

Finite element prediction of wave motion in structural waveguides.

Abstract: A method is presented by which the wavenumbers for a one-dimensional waveguide can be predicted from a finite element (FE) model. The method involves postprocessing a conventional, but low order, FE model, the mass and stiffness matrices of which are typically found using a conventional FE package. This is in contrast to the most popular previous waveguide/FE approach, sometimes termed the spectral finite element approach, which requires new spectral element matrices to be developed. In the approach described here, a section of the waveguide is modeled using conventional FE software and the dynamic stiffness matrix formed. A periodicity condition is applied, the wavenumbers following from the eigensolution of the resulting transfer matrix. The method is described, estimation of wavenumbers, energy, and group velocity discussed, and numerical examples presented. These concern wave propagation in a beam and a simply supported plate strip, for which analytical solutions exist, and the more complex case of a viscoelastic laminate, which involves postprocessing an ANSYS FE model. The method is seen to yield accurate results for the wavenumbers and group velocities of both propagating and evanescent waves.

A variational formulation of kinematic waves: basic theory and complex boundary conditions

Abstract: This paper proves that the solution of every well-posed kinematic wave (KW) traffic problem with a concave flow-density relation is a set of least-cost (shortest) paths in space-time with a special metric. The equi-cost contours are the vehicle trajectories. If the flow-density relation is strictly concave the set of shortest paths is unique and matches the set of waves. Shocks, if they arise, are curves in the solution region where the shortest paths end. The new formulation extends the range of applications of kinematic wave theory and simplifies it considerably. For example, moving restrictions such as slow buses, which cannot be treated easily with existing methods, can be modeled as shortcuts in space-time. These shortcuts affect the nature of the solution but not the complexity of the solution process. Hybrid models of traffic flow where discrete vehicles (e.g., trucks) interact with a continuum KW stream can now be easily implemented.

Canalization of subwavelength images by electromagnetic crystals

Abstract: An original regime of operation for flat superlenses formed by electromagnetic crystals is proposed. This regime does not involve negative refraction and amplification of evanescent waves in contrast to the perfect lenses formed by left-handed media. The sub-wavelength spatial spectrum of a source is canalized by the eigenmodes of the crystal having the same longitudinal components of wave vector and group velocities directed across the slab. The regime is implemented at low frequencies with respect to the crystal period by using capacitively loaded wire media. The resolution of λ/6 is demonstrated. The thickness of the lens is not related with the distance to the source and the lens can be made thick enough.

THz Sommerfeld wave propagation on a single metal wire

Abstract: We report an experimental and theoretical study of THz Sommerfeld wave propagation on a single copper wire. THz pulses are optoelectronically generated and launched onto 0.52-mm-diam copper wire, and the guided THz pulses are detected at the end of the wire by a standard photoconductive antenna. Very low attenuation and group velocity dispersion are observed, and the measured radial field amplitude of the Sommerfeld wave is inversely proportional to the radial distance. These results are consistent with theoretical predictions. Experimental results from curved wires show the weakly guiding property of the THz Sommerfeld wave, which will limit its applications.

Strongly nonlinear waves in a chain of Teflon beads.

Abstract: One-dimensional “sonic vacuum” type phononic crystals were assembled from a chain of polytetrafluoroethylene (PTFE,Teflon) spheres with different diameters in a Teflon holder. It was demonstrated that this polymer-based sonic vacuum, with exceptionally low elastic modulus of particles, supports propagation of strongly nonlinear solitary waves with a very low speed. These solitary waves can be described using the classical nonlinear Hertz law despite the viscoelastic nature of the polymer and high strain rate deformation of the contact area. The experimentally measured speeds of solitary waves at high amplitudes are close to the theoretically estimated values with a Young’s modulus of 1.46 GPa obtained from shock wave experiments. This is significantly higher than the Young’s modulus of PTFE from ultrasonic measurements. Trains of strongly nonlinear solitary waves excited by an impact were investigated experimentally and were found to be in reasonable agreement with numerical calculations based on Hertz interaction law though exhibiting a significant dissipation.

Impact of inherent periodic structure on effective medium description of left-handed and related metamaterials

Abstract: We study the frequency dependence of the effective electromagnetic parameters of left-handed and related metamaterials of the split ring resonator and wire type. We show that the reduced translational symmetry speriodic structured inherent to these metamaterials influences their effective electromagnetic response. To anticipate this periodicity, we formulate a periodic effective medium model which enables us to distinguish the resonant behavior of electromagnetic parameters from effects of the periodicity of the structure. We use this model for the analysis of numerical data for the transmission and reflection of periodic arrays of split ring resonators, thin metallic wires, cut wires, as well as the left-handed structures. The present method enables us to identify the origin of the previously observed resonance-antiresonance coupling as well as the occurrence of negative imaginary parts in the effective permittivities and permeabilities of those materials. Our analysis shows that the periodicity of the structure can be neglected only for the wavelength of the electromagnetic wave larger than 30 space periods of the investigated structure.

Discrete surface solitons.

Abstract: It is theoretically shown that discrete nonlinear surface waves are possible in waveguide lattices. These self-trapped states are located at the edge of the array and can exist only above a certain power threshold. The excitation characteristics and stability properties of these surface waves are systematically investigated.

Introduction to nearshore hydrodynamics

Abstract: Hydrodynamical Background Theory of Linear Waves Energy Balance for Non-Breaking and Breaking Waves Wave Breaking Wave Models Based on Linear Wave Theory Nonlinear Waves: Analysis of Parameters Stokes Wave Theory, Stream Function Theory Long Wave Theory, Boussinesq Waves Wave Boundary Layers The Equations for Nearshore Circulation Cross-Shore Currents, Undertow Quasi-3D Nearshore Circulation Models Other Nearshore Phenomena.

How Hertzian Solitary Waves Interact with Boundaries in a 1D Granular Medium

Abstract: We perform measurements, numerical simulations, and quantitative comparisons with available theory on solitary wave propagation in a linear chain of beads without static preconstraint. By designing a nonintrusive force sensor to measure the impulse as it propagates along the chain, we study the solitary wave reflection at a wall. We show that the main features of solitary wave reflection depend on wall mechanical properties. Since previous studies on solitary waves have been performed at walls without these considerations, our experiment provides a more reliable tool to characterize solitary wave propagation. We find, for the first time, precise quantitative agreements.

A pole-zero matching method for EBG surfaces composed of a dipole FSS printed on a grounded dielectric slab

Abstract: A method is presented, for the efficient derivation of the dispersion equation associated with electromagnetic bandgap (EBG) structures composed by lossless frequency selective surfaces (FSS) printed on stratified dielectric media The method, valid for the range of frequency where a single propagating Floquet mode occurs, is based on Foster's reactance theorem applied to an equivalent transmission line network This theorem implies that the admittance functions of frequency which represent the FSS satisfy the pole-zero analytical properties of the driving point LC admittance functions By these basic properties and by the full-wave identification of the FSS resonances, an analytical form of the dispersion equation is obtained This equation is next solved for both surface wave and leaky wave modes by a conventional numerical technique The results are successfully compared with those from a full-wave analysis

Electromagnetic surface modes in structured perfect-conductor surfaces.

Abstract: Surface-bound modes in metamaterials forged by drilling periodic hole arrays in perfect-conductor surfaces are investigated by means of both analytical techniques and rigorous numerical solution of Maxwell's equations. It is shown that these metamaterials cannot be described in general by local, frequency-dependent permittivities and permeabilities for small periods compared to the wavelength, except in certain limiting cases that are discussed in detail. New related metamaterials are shown to exhibit exciting optical properties that are elucidated in the light of our simple analytical approach.

Generalized Stokes parameters of random electromagnetic beams

Abstract: A generalization of the Stokes parameters of a random electromagnetic beam is introduced. Unlike the usual Stokes parameters, which depend on one spatial variable, the generalized Stokes parameters, depend on two spatial variables. They obey precise laws of propagation, both in free space and in any linear medium, whether deterministic or random. With the help of the generalized Stokes parameters, the changes in the ordinary Stokes parameters upon propagation can be determined. Numerical examples of such changes are presented. The generalized Stokes parameters contain information not only about the polarization properties of the beam but also about its coherence properties. We illustrate this fact by expressing the degree of coherence of the electromagnetic beam in terms of one of the generalized Stokes parameters.

Propagation of spontaneously actuated pulsive vibration in human heart wall and in vivo viscoelasticity estimation

Abstract: Though myocardial viscoelasticity is essential in the evaluation of heart diastolic properties, it has never been noninvasively measured in vivo. By the ultrasonic measurement of the myocardial motion, we have already found that some pulsive waves are spontaneously excited by aortic-valve closure (AVC) at end-systole (To). These waves may serve as an ideal source of the intrinsic heart sound caused by AVC. In this study, using a sparse sector scan, in which the beam directions are restricted to about 16, the pulsive waves were measured almost simultaneously at about 160 points set along the heart wall at a sufficiently high frame rate. The consecutive spatial phase distributions, obtained by the Fourier transform of the measured waves, clearly revealed wave propagation along the heart wall for the first time. The propagation time of the wave along the heart wall is very small (namely, several milliseconds) and cannot be measured by conventional equipment. Based on this phenomenon, we developed a means to measure the myocardial viscoelasticity in vivo. In this measurement, the phase velocity of the wave is determined for each frequency component. By comparing the dispersion of the phase velocity with the theoretical one of the Lamb wave (the plate flexural wave), which propagates along the viscoelastic plate (heart wall) immersed in blood, the instantaneous viscoelasticity is determined noninvasively. This is the first report of such noninvasive determination. In in vivo experiments applied to five healthy subjects, propagation of the pulsive wave was clearly visible in all subjects. For the 60-Hz component, the typical propagation speed rapidly decreased from 5 m/s just before the time of AVC (t = To - 8 ms) to 3 m/s at t = To + 10 ms. In the experiments, it was possible to determine the viscosity more precisely than the elasticity. The typical value of elasticity was about 24-30 kPa arid did not change around the time of AVC. The typical transient values of viscosity decreased rapidly from 400 Pa/spl middot/s at t = To - 8 ms to 70 Pa-s at t = To + 10 ms. The measured shear elasticity and viscosity in this study are comparable to those obtained for the human tissues using audio frequency in in vitro experiments reported in the literature.

The degeneration of internal waves in lakes with sloping topography

Abstract: In a laboratory study, we quantified the temporal energy flux associated with the degeneration of basin-scale internal waves in closed basins. The system is two-layer stratified and subjected to a single forcing event creating available potential energy at time zero. A downscale energy transfer was observed from the wind-forced basin-scale motions to the turbulent motions, where energy was lost due to high-frequency internal wave breaking along sloping topography. Under moderate forcing conditions, steepening of nonlinear basin-scale wave components was found to produce a high-frequency solitary wave packet that contained as much as 20% of the available potential energy introduced by the initial condition. The characteristic lengthscale of a particular solitary wave was less than the characteristic slope length, leading to wave breaking along the sloping boundary. The ratio of the steepening timescale required for the evolution of the solitary waves to the travel time until the waves shoaled controlled their development and degeneration within the domain. The energy loss along the slope, the mixing efficiency, and the breaker type were modeled using appropriate forms of an internal Iribarren number, defined as the ratio of the boundary slope to the wave slope (amplitude/wavelength). This parameter allows generalization to the oceanographic context. Analysis of field data shows the portion of the internal wave spectrum for lakes, between motions at the basin and buoyancy scales, to be composed of progressive waves: both weakly nonlinear waves (sinusoidal profile with frequencies near 10 24 Hz) and strongly nonlinear waves (hyperbolic‐secant-squared profile with frequencies near 10 23 Hz). The results suggest that a periodically forced system may sustain a quasi-steady flux of 20% of the potential energy introduced by the surface wind stress to the benthic boundary layer at the depth of the pycnocline.

A laboratory investigation into the seismic velocities of methane gas hydrate‐bearing sand

Abstract: Remote seismic methods, which measure the compressional wave (P wave) velocity (Vp) and shear wave (S wave) velocity (Vs), can be used to assess the distribution and concentration of marine gas hydrates in situ. However, interpreting seismic data requires an understanding of the seismic properties of hydrate-bearing sediments, which has proved problematic because of difficulties in recovering intact hydrate-bearing sediment samples and in performing valid laboratory tests. Therefore a dedicated gas hydrate resonant column (GHRC) was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both Vp and Vs made at frequencies and strains relevant to marine seismic investigations. Thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested. The results show a bipartite relationship between velocities and hydrate pore saturation, with a marked transition between 3 and 5% hydrate pore saturation for both Vp and Vs. This suggests that methane hydrate initially cements sand grain contacts then infills the pore space. These results show in detail for the first time, using a resonant column, how hydrate cementation affects elastic wave properties in quartz sand. This information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation.

Subwavelength light bending by metal slit structures.

Abstract: We discuss how light can be efficiently bent by nanoscale-width slit waveguides in metals. The discussion is based on accurate numerical solutions of Maxwell's equations. Our results, using a realistic model for silver at optical wavelengths, show that good right-angle bending transmission can be achieved for wavelengths lambda> 600 nm. An approximate stop-band at lower wavelengths also occurs, which can be partly understood in terms of a dispersion curve analysis. The bending efficiency is shown to correlate with a focusing effect at the inner bend corner. Finally, we show that good bending transmission can even arise out of U-turn structures.

On radar imaging of current features: 1. Model and comparison with observations

Abstract: [1] A new radar imaging model of ocean current features is proposed. The simulated normalized radar cross section (NRCS) takes into account scattering from ‘‘regular’’ surfaces (by means of resonant Bragg scattering and specular reflections) and scattering from breaking waves. The description of background wind waves and their transformation in nonuniform medium is based on solution of the wave action conservation equation. Wave breaking plays a key role in the radar imaging model. Breaking waves scatter radio waves (thus directly contributing to the NRCS), provide energy dissipation in wind waves (thus defining the wave spectrum of intermediate scale waves), and generate short surface waves (thus affecting Bragg scattering). Surface current, surfactants accumulated in the convergence zone, and varying wind field are considered as the main sources for the NRCS manifestations of current features. The latter source can result from transformation of atmospheric boundary layer over the sea surface temperature front. It is shown that modulation of wave breaking significantly influences both radar returns and short wind waves. In the range of short gravity waves related to Ku- X-, and C-bands, the modulation of Bragg waves through wave breaking is the governing mechanism. The model is tested against well-controlled experiments including JOWIP, SARSEX, and CoastWatch-95. A reasonably good agreement between model and observations is obtained.

Generalized nonlinear Schrödinger equation for dispersive susceptibility and permeability: application to negative index materials.

Abstract: A new generalized nonlinear Schr\"odinger equation describing the propagation of ultrashort pulses in bulk media exhibiting frequency dependent dielectric susceptibility and magnetic permeability is derived and used to characterize wave propagation in a negative index material. The equation has new features that are distinct from ordinary materials ($\ensuremath{\mu}=1$): the linear and nonlinear coefficients can be tailored through the linear properties of the medium to attain any combination of signs unachievable in ordinary matter, with significant potential to realize a wide class of solitary waves.

Time-lapse travel time change of multiply scattered acoustic waves

Abstract: Existing techniques in correlation spectroscopy, such as coda wave interferometry and diffusing acoustic wave spectroscopy, determine the average motion of scatterers or change in the propagation velocity from the temporal change of multiply scattered sound. However, neither of them gives an indication of the spatial extent of the change in the medium. This study is an extension of the technique coda wave interferometry, where multiply scattered waves are used to determine the change in the wave field due to a localized perturbation in the propagation velocity. Here, the propagation of multiply scattered sound is described using the diffusion approximation, which allows the cross-correlation function of the unperturbed and perturbed wave fields to be related to the localized change in the propagation velocity. The technique is tested numerically for two-dimensional (2D) acoustic waves using synthetic seismograms calculated using finite-differences before and after a small perturbation in the propagation velocity has been introduced. Despite the relatively small size and magnitude of the change, multiple scattering greatly amplifies small perturbations, making changes in the phase or travel time of the wave field visible in the later-arriving waveforms. Potential applications of this technique include nondestructive evaluation of inhomogeneous materials and time-lapse monitoring of volcanoes and highly heterogeneous reservoirs.

Stabilizing the Benjamin–Feir instability

Abstract: The Benjamin–Feir instability is a modulational instability in which a uniform train of oscillatory waves of moderate amplitude loses energy to a small perturbation of other waves with nearly the same frequency and direction. The concept is well established in water waves, in plasmas and in optics. In each of these applications, the nonlinear Schrodinger equation is also well established as an approximate model based on the same assumptions as required for the derivation of the Benjamin–Feir theory: a narrow-banded spectrum of waves of moderate amplitude, propagating primarily in one direction in a dispersive medium with little or no dissipation. In this paper, we show that for waves with narrow bandwidth and moderate amplitude, any amount of dissipation (of a certain type) stabilizes the instability. We arrive at this stability result first by proving it rigorously for a damped version of the nonlinear Schrodinger equation, and then by confirming our theoretical predictions with laboratory experiments on waves of moderate amplitude in deep water. The Benjamin–Feir instability is often cited as the first step in a nonlinear process that spreads energy from an initially narrow bandwidth to a broader bandwidth. In this process, sidebands grow exponentially until nonlinear interactions eventually bound their growth. In the presence of damping, this process might still occur, but our work identifies another possibility: damping can stop the growth of perturbations before nonlinear interactions become important. In this case, if the perturbations are small enough initially, then they never grow large enough for nonlinear interactions to become important.

Wave propagation through elastic porous media containing two immiscible fluids

Abstract: [1] Acoustic wave phenomena in porous media containing multiphase fluids have received considerable attention in recent years because of an increasing scientific awareness of poroelastic behavior in groundwater aquifers. To improve quantitative understanding of these phenomena, a general set of coupled partial differential equations was derived to describe dilatational wave propagation through an elastic porous medium permeated by two immiscible fluids. These equations, from which previous models of dilatational wave propagation can be recovered as special cases, incorporate both inertial coupling and viscous drag in an Eulerian frame of reference. Two important poroelasticity concepts, the linearized increment of fluid content and the closure relation for porosity change, originally defined for an elastic porous medium containing a single fluid, also are generalized for a two-fluid system. To examine the impact of relative fluid saturation and wave excitation frequency (50, 100, 150, and 200 Hz) on free dilatational wave behavior in unconsolidated porous media, numerical simulations of the three possible modes of wave motion were conducted for Columbia fine sandy loam containing either an air-water or oil-water mixture. The results showed that the propagating (P1) mode, which results from in-phase motions of the solid framework and the two pore fluids, moves with a speed equal to the square root of the ratio of an effective bulk modulus to an effective density of the fluid-containing porous medium, regardless of fluid saturation and for both fluid mixtures. The nature of the pore fluids exerts a significant influence on the attenuation of the P1 wave. In the air-water system, attenuation was controlled by material density differences and the relative mobilities of the pore fluids, whereas in the oil-water system an effective kinematic shear viscosity of the pore fluids was the controlling parameter. On the other hand, the speed and attenuation of the two diffusive modes (P2, resulting from out-of-phase motions of the solid framework and the fluids, and P3, the result of capillary pressure fluctuations) were closely associated with an effective dynamic shear viscosity of the pore fluids. The P2 and P3 waves also had the same constant value of the quality factor, and by comparison of our results with previous research on these two dilatational wave modes in sandstones, both were found to be sensitive to the state of consolidation of the porous medium.

Relationship between stationary planetary wave activity and the East Asian winter monsoon

Abstract: [1] The variability of both the stationary planetary wave activity and the East Asian winter monsoon is strongly associated with the thermal contrast between oceans and landmasses. In this study, we explore the interannual relationship between the monsoon and the wave activity defined by an index of the difference in the divergence of EliassenPalm flux between 50� N at 500 hPa and 40� N at 300 hPa. It is found that, compared to the winters of low wave activity, the equatorward propagation of planetary waves in the middle and upper troposphere is stronger in the high wave activity winters. During these high activity winters, the upward wave propagation from the troposphere into the stratosphere becomes weaker. This is accompanied by a smaller perturbation in the polar vortex, which tends to be colder and stronger. In the meantime, the East Asian westerly jet stream, the East Asian trough, the Siberian high, and the Aleutian low all become weaker apparently. In particular, the weakening of the Siberian high and the Aleutian low decreases the northeasterly wind over East Asia, leading to a warming condition in the region especially in northeastern Asia. A further analysis reveals that the zonal wavenumber-2 pattern of planetary waves contributes dominantly to the variability of the East Asian winter monsoon.

Phase measurement of atomic resolution image using transport of intensity equation.

Abstract: t Since the Transport Intensity Equation (TIE) has been applied to electron microscopy only recently, there are controversial discussions in the literature regarding the theoretical concepts underlying the equation and the practical techniques to solve the equation. In this report we explored some of the issues regarding the TIE, especially bearing electron microscopy in mind, and clarified that: (i) the TIE for electrons exactly corresponds to the Schrodinger equation for high-energy electrons in free space, and thus the TIE does not assume weak scattering; (ii) the TIE can give phase information at any distance from the specimen, not limited to a new field; (iii) information transfer in the TIE for each spatial frequency g will be multiplied by g 2 and thus low frequency components will be dumped more with respect to high frequency components; (vi) the intensity derivative with respect to the direction of wave propagation is well approximated by using a set of three symmetric images; and (v) a substantially larger defocus distance than expected before can be used for high-resolution electron microscopy. In the second part of this report we applied the TIE down to atomic resolution images to obtain phase information and verified the following points experimentally: (i) although low frequency components are attenuated in the TIE, all frequencies will be recovered satisfactorily except the very low frequencies; and (ii) using a reconstructed phase and the measured image intensity we can correct effectively the defects of imaging, such as spherical aberrations as well as partial coherence.

Evaluation of quasi-linear diffusion coefficients for whistler mode waves in a plasma with arbitrary density ratio

Abstract: [1] Techniques are presented for efficiently evaluating quasi-linear diffusion coefficients for whistler mode waves propagating according to the full cold plasma index of refraction. In particular, the density ratio ωpe/Ωe can be small, which favors energy diffusion. This generalizes an approach, previously used for high-density hiss and electromagnetic ion cyclotron waves, of identifying (and omitting) ranges of wavenormal angle θ that are incompatible with cyclotron resonant frequencies ω occurring between sharp cutoffs of the modeled wave frequency spectrum. This requires a detailed analysis of the maximum and minimum values of the refractive index as a function of ω and θ, as has previously been performed in the high-density approximation. Sample calculations show the effect of low-density ratio on the pitch angle and energy diffusion coefficients modeling the effect of chorus waves on radiation belt electrons. The high-density approximation turns out to be quite robust, especially when the upper frequency cutoff is small compared with Ωe. The techniques greatly reduce the amount of computation needed for a sample calculation, while taking into account all resonant harmonic numbers n up to ±∞.