Symmetries of the TDNLS equations for weakly nonlinear dispersive MHD waves
NASA Technical Reports Server (NTRS)
Webb, G. M.; Brio, M.; Zank, G. P.
1995-01-01
In this paper we consider the symmetries and conservation laws for the TDNLS equations derived by Hada (1993) and Brio, Hunter and Johnson, to describe the propagation of weakly nonlinear dispersive MHD waves in beta approximately 1 plasmas. The equations describe the interaction of the Alfven and magnetoacoustic modes near the triple umbilic, where the fast magnetosonic, slow magnetosonic and Alfven speeds coincide and a(g)(exp 2) = V(A)(exp 2) where a(g) is the gas sound speed and V(A) is the Alfven speed. We discuss Lagrangian and Hamiltonian formulations, and similarity solutions for the equations.
Dispersive ducting of MHD waves in the plasma sheet - A source of Pi2 wave bursts
NASA Technical Reports Server (NTRS)
Edwin, P. M.; Roberts, B.; Hughes, W. J.
1986-01-01
Fast magnetoacoustic waves can be ducted by plasma inhomogeneities such as the plasma sheet. As this ducting is dispersive an impulsive source will give rise to a well-defined, quasi-periodic wave packet with time-scales determined by the width of the inhomogeneity and characteristic speeds in the wave duct and surrounding medium. The duration of the wave packet depends upon the distance from the source. It is argued that an impulsive source in the plasma sheet at substorm onset will produce a wave packet near earth with characteristics similar to pi2 wave bursts and put this idea forward as a mechanism for the generation of pi2 pulsations.
Multi-dimensional MHD simple waves
Webb, G. M.; Ratkiewicz, R.; Brio, M.; Zank, G. P.
1996-07-20
In this paper we consider a formalism for multi-dimensional simple MHD waves using ideas developed by Boillat. For simple wave solutions one assumes that all the physical variables (the density {rho}, gas pressure p, fluid velocity u, gas entropy S, and magnetic induction B in the MHD case) depend on a single phase function {phi}(r,t). The simple wave solution ansatz and the MHD equations then require that the phase function {phi} satisfies an implicit equation of the form f({phi})=r{center_dot}n({phi})-{lambda}({phi})t, where n({phi})={nabla}{phi}/|{nabla}{phi}| is the wave normal, {lambda}({phi})={omega}/k=-{phi}{sub t}/|{nabla}{phi}| is the normal speed of the wave front, and f({phi}) is an arbitrary differentiable function of {phi}. The formalism allows for more general simple waves than that usually dealt with in which n({phi}) is a constant unit vector that does not vary along the wave front. The formalism has implications for shock formation and wave breaking for multi-dimensional waves.
Simulation of wave interactions with MHD
Batchelor, Donald B; Abla, G; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.
2008-07-01
The broad scientific objectives of the SWIM (Simulation of Wave Interaction with MHD) project are twofold: (1) improve our understanding of interactions that both radio frequency (RF) wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (2) develop an integrated computational system for treating multiphysics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project. The Integrated Plasma Simulator (IPS) has been implemented. Presented here are initial physics results on RF effects on MHD instabilities in tokamaks as well as simulation results for tokamak discharge evolution using the IPS.
Multi-dimensional MHD simple waves
NASA Technical Reports Server (NTRS)
Webb, G. M.; Ratkiewicz, R.; Brio, M.; Zank, G. P.
1995-01-01
In this paper we consider a formalism for multi-dimensional simple MHD waves using ideas developed by Boillat. For simple wave solutions one assumes that all the physical variables (the density rho, gas pressure p, fluid velocity V, gas entropy S, and magnetic induction B in the MHD case) depend on a single phase function phi(r,t). The simple wave solution ansatz and the MHD equations then require that the phase function has the form phi = r x n(phi) - lambda(phi)t, where = n(phi) = Delta phi / (absolute value of Delta phi) is the wave normal and lambda(phi) = omega/k = -phi t / (absolute value of Delta phi) is the normal speed of the wave front. The formalism allows for more general simple waves than that usually dealt with in which n(phi) is a constant unit vector that does not vary along the wave front. The formalism has implications for shock formation for multi-dimensional waves.
Amplitudes of MHD Waves in Sunspots
NASA Astrophysics Data System (ADS)
Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint, Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.; Rajaguru, Paul
2016-05-01
The conversion of p-modes into MHD waves by strong magnetic fields occurs mainly in the sub-photospheric layers. The photospheric signatures of MHD waves are weak due to low amplitudes at the beta=1 equipartion level where mode-conversion occurs. We report on small amplitude oscillations observed in the photosphere with Hinode SOT/SP in which we analyze time series for sunspots ARs 12186 (11.10.2014) and 12434 (17.10.2015). No significant magnetic field oscillations are recovered in the umbra or penumbra in the ME inversion. However, periodicities in the inclination angle are found at the umbral/penumbral boundary with 5 minute periods. Upward propagating waves are indicated in the intensity signals correlated between HMI and AIA at different heights. We compare SP results with the oscillations observed in HMI data. Simultaneous IRIS data shows transition region brightening above the umbral core.
Nonlinear MHD Waves in a Prominence Foot
NASA Astrophysics Data System (ADS)
Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B.
2015-11-01
We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ˜ δn/n). The waves are evident as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5-11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5-14 G. For the typical prominence density the corresponding fast magnetosonic speed is ˜20 km s-1, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.
NONLINEAR MHD WAVES IN A PROMINENCE FOOT
Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B.
2015-11-10
We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ∼ δn/n). The waves are evident as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5–11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5–14 G. For the typical prominence density the corresponding fast magnetosonic speed is ∼20 km s{sup −1}, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.
Dispersive wave emission from wave breaking.
Conforti, Matteo; Trillo, Stefano
2013-10-01
We show that pulses undergoing wave breaking in nonlinear weakly dispersive fibers radiate, owing to phase-matching (assisted by higher-order dispersion) of linear dispersive waves with the shock-wave front. Our theoretical results perfectly explain the radiation observed recently from pulses propagating in the normal dispersion (i.e., nonsolitonic) regime.
Propagation and Dissipation of MHD Waves in Coronal Holes
NASA Astrophysics Data System (ADS)
Dwivedi, B. N.
2006-11-01
bholadwivedi@gmail.com In view of the landmark result on the solar wind outflow, starting between 5 Mm and 20 Mm above the photosphere in magnetic funnels, we investigate the propagation and dissipation of MHD waves in coronal holes. We underline the importance of Alfvén wave dissipation in the magnetic funnels through the viscous and resistive plasma. Our results show that Alfvén waves are one of the primary energy sources in the innermost part of coronal holes where the solar wind outflow starts. We also consider compressive viscosity and thermal conductivity to study the propagation and dissipation of long period slow longitudinal MHD waves in polar coronal holes. We discuss their likely role in the line profile narrowing, and in the energy budget for coronal holes and the solar wind. We compare the contribution of longitudinal MHD waves with high frequency Alfvén waves.
Linear and Nonlinear MHD Wave Processes in Plasmas. Final Report
Tataronis, J. A.
2004-06-01
This program treats theoretically low frequency linear and nonlinear wave processes in magnetized plasmas. A primary objective has been to evaluate the effectiveness of MHD waves to heat plasma and drive current in toroidal configurations. The research covers the following topics: (1) the existence and properties of the MHD continua in plasma equilibria without spatial symmetry; (2) low frequency nonresonant current drive and nonlinear Alfven wave effects; and (3) nonlinear electron acceleration by rf and random plasma waves. Results have contributed to the fundamental knowledge base of MHD activity in symmetric and asymmetric toroidal plasmas. Among the accomplishments of this research effort, the following are highlighted: Identification of the MHD continuum mode singularities in toroidal geometry. Derivation of a third order ordinary differential equation that governs nonlinear current drive in the singular layers of the Alfvkn continuum modes in axisymmetric toroidal geometry. Bounded solutions of this ODE implies a net average current parallel to the toroidal equilibrium magnetic field. Discovery of a new unstable continuum of the linearized MHD equation in axially periodic circular plasma cylinders with shear and incompressibility. This continuum, which we named “accumulation continuum” and which is related to ballooning modes, arises as discrete unstable eigenfrequency accumulate on the imaginary frequency axis in the limit of large mode numbers. Development of techniques to control nonlinear electron acceleration through the action of multiple coherent and random plasmas waves. Two important elements of this program aye student participation and student training in plasma theory.
Vorticity equation for MHD fast waves in geospace environment
NASA Technical Reports Server (NTRS)
Yamauchi, M.; Lundin, R.; Lui, A. T. Y.
1993-01-01
The MHD vorticity equation is modified in order to apply it to nonlinear MHD fast waves or shocks when their extent along the magnetic field is limited. Field-aligned current (FAC) generation is also discussed on the basis of this modified vorticity equation. When the wave normal is not aligned to the finite velocity convection and the source region is spatially limited, a longitudinal polarization causes a pair of plus and minus charges inside the compressional plane waves or shocks, generating a pair of FACs. This polarization is not related to the separation between the electrons and ions caused by their difference in mass, a separation which is inherent to compressional waves. The resultant double field-aligned current structure exists both with and without the contributions from curvature drift, which is questionable in terms of its contribution to vorticity change from the viewpoint of single-particle motion.
Wave-equation dispersion inversion
NASA Astrophysics Data System (ADS)
Li, Jing; Feng, Zongcai; Schuster, Gerard
2017-03-01
We present the theory for wave-equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. The dispersion curves are obtained from Rayleigh waves recorded by vertical-component geophones. Similar to wave-equation traveltime tomography, the complicated surface wave arrivals in traces are skeletonized as simpler data, namely the picked dispersion curves in the phase-velocity and frequency domains. Solutions to the elastic wave equation and an iterative optimization method are then used to invert these curves for 2-D or 3-D S-wave velocity models. This procedure, denoted as wave-equation dispersion inversion (WD), does not require the assumption of a layered model and is significantly less prone to the cycle-skipping problems of full waveform inversion. The synthetic and field data examples demonstrate that WD can approximately reconstruct the S-wave velocity distributions in laterally heterogeneous media if the dispersion curves can be identified and picked. The WD method is easily extended to anisotropic data and the inversion of dispersion curves associated with Love waves.
MHD Wave Modes Resolved in Fine-Scale Chromospheric Magnetic Structures
NASA Astrophysics Data System (ADS)
Verth, G.; Jess, D. B.
2016-02-01
Due to its complex and dynamic fine-scale structure, the chromosphere is a particularly challenging region of the Sun's atmosphere to understand. It is now widely accepted that to model chromospheric dynamics, even on a magnetohydrodynamic (MHD) scale, while also calculating spectral line emission, one must realistically include the effects of partial ionization and radiative transfer in a multi-fluid plasma under non-LTE conditions. Accurate quantification of MHD wave energetics must be founded on a precise identification of the actual wave mode being observed. This chapter focuses on MHD kink-mode identification, MHD sausage mode identification, and MHD torsional Alfvén wave identification. It then reviews progress in determining more accurate energy flux estimations of specific MHD wave modes observed in the chromosphere. The chapter finally examines how the discovery of these MHD wave modes has helped us advance the field of chromospheric magnetoseismology.
Mirror force induced wave dispersion in Alfvén waves
Damiano, P. A.; Johnson, J. R.
2013-06-15
Recent hybrid MHD-kinetic electron simulations of global scale standing shear Alfvén waves along the Earth's closed dipolar magnetic field lines show that the upward parallel current region within these waves saturates and broadens perpendicular to the ambient magnetic field and that this broadening increases with the electron temperature. Using resistive MHD simulations, with a parallel Ohm's law derived from the linear Knight relation (which expresses the current-voltage relationship along an auroral field line), we explore the nature of this broadening in the context of the increased perpendicular Poynting flux resulting from the increased parallel electric field associated with mirror force effects. This increased Poynting flux facilitates wave energy dispersion across field lines which in-turn allows for electron acceleration to carry the field aligned current on adjacent field lines. This mirror force driven dispersion can dominate over that associated with electron inertial effects for global scale waves.
Numerical simulation of propagation of the MHD waves in sunspots
NASA Astrophysics Data System (ADS)
Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky, V.; Collados, M.
2010-11-01
We present results of numerical 3D simulation of propagation of MHD waves in sunspots. We used two self consistent magnetohydrostatic background models of sunspots. There are two main differences between these models: (i) the topology of the magnetic field and (ii) dependence of the horizontal profile of the sound speed on depth. The model with convex shape of the magnetic field lines near the photosphere has non-zero horizorntal perturbations of the sound speed up to the depth of 7.5 Mm (deep model). In the model with concave shape of the magnetic field lines near the photosphere Δ c/c is close to zero everywhere below 2 Mm (shallow model). Strong Alfven wave is generated at the wave source location in the deep model. This wave is almost unnoticeable in the shallow model. Using filtering technique we separated magnetoacoustic and magnetogravity waves. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. The sunspot causes anisotropy of the amplitude distribution along the wavefront and changes the shape of the wavefront. The amplitude of the waves is reduced inside the sunspot. This effect is stronger for the magnetogravity waves than for magnetoacoustic waves. The shape of the wavefront of the magnetogravity waves is distorted stronger as well. The deep model causes bigger anisotropy for both mgnetoacoustic and magneto gravity waves than the shallow model.
Inductive-dynamic magnetosphere-ionosphere coupling via MHD waves
NASA Astrophysics Data System (ADS)
Tu, Jiannan; Song, Paul; Vasyliūnas, Vytenis M.
2014-01-01
In the present study, we investigate magnetosphere-ionosphere/thermosphere (M-IT) coupling via MHD waves by numerically solving time-dependent continuity, momentum, and energy equations for ions and neutrals, together with Maxwell's equations (Ampère's and Faraday's laws) and with photochemistry included. This inductive-dynamic approach we use is fundamentally different from those in previous magnetosphere-ionosphere (M-I) coupling models: all MHD wave modes are retained, and energy and momentum exchange between waves and plasma are incorporated into the governing equations, allowing a self-consistent examination of dynamic M-I coupling. Simulations, using an implicit numerical scheme, of the 1-D ionosphere/thermosphere system responding to an imposed convection velocity at the top boundary are presented to show how magnetosphere and ionosphere are coupled through Alfvén waves during the transient stage when the IT system changes from one quasi steady state to another. Wave reflection from the low-altitude ionosphere plays an essential role, causing overshoots and oscillations of ionospheric perturbations, and the dynamical Hall effect is an inherent aspect of the M-I coupling. The simulations demonstrate that the ionosphere/thermosphere responds to magnetospheric driving forces as a damped oscillator.
Doppler displacements in kink MHD waves in solar flux tubes
NASA Astrophysics Data System (ADS)
Goossens, Marcel; Van Doorsselaere, Tom; Terradas, Jaume; Verth, Gary; Soler, Roberto
Doppler displacements in kink MHD waves in solar flux tubes Presenting author: M. Goossens Co-authors: R. Soler, J. Terradas, T. Van Doorsselaere, G. Verth The standard interpretation of the transverse MHD waves observed in the solar atmosphere is that they are non-axisymmetric kink m=1) waves on magnetic flux tubes. This interpretation is based on the fact that axisymmetric and non-axisymmetric fluting waves do not displace the axis of the loop and the loop as a whole while kink waves indeed do so. A uniform transverse motion produces a Doppler displacement that is constant across the magnetic flux tube. A recent development is the observation of Doppler displacements that vary across the loop. The aim of the present contribution is to show that spatial variations of the Doppler displacements across the loop can be caused by kink waves. The motion associated with a kink wave is purely transverse only when the flux tube is uniform and sufficiently thin. Only in that case do the radial and azimuthal components of displacement have the same amplitude and is the azimuthal component a quarter of a period ahead of the radial component. This results in a unidirectional or transverse displacement. When the flux tube is non-uniform and has a non-zero radius the conditions for the generation of a purely transverse motion are not any longer met. In that case the motion in a kink wave is the sum of a transverse motion and a non-axisymmetric rotational motion that depends on the azimuthal angle. It can produce complicated variations of the Doppler displacement across the loop. I shall discuss the various cases of possible Doppler displacenents that can occur depending on the relative sizes of the amplitudes of the radial and azimuthal components of the displacement in the kink wave and on the orientation of the line of sight.
MHD-waves in the geomagnetic tail: A review
NASA Astrophysics Data System (ADS)
Leonovich, Anatoliy; Mazur, Vitaliy; Kozlov, Daniil
2015-03-01
This article presents the review of experimental and theoretical studies on ultra-lowfrequency MHD oscillations of the geomagnetic tail. We consider the Kelvin-Helmholtz instability at the magnetopause, oscillations with a discrete spectrum in the "magic frequencies"range, the ballooning instability of coupled Alfvén and slow magnetosonic waves, and "flapping" oscillations of the current sheet of the geomagnetic tail. Over the last decade, observations from THEMIS, CLUSTER and Double Star satellites have been of great importance for experimental studies. The use of several spacecraft allows us to study the structure of MHD oscillations with high spatial resolution. Due to this, we can make a detailed comparison between theoretical results and those obtained from multi-spacecraft studies. To make such comparisons in theoretical studies, in turn, we have to use the numerical models closest to the real magnetosphere.
Striae and MHD Waves in Molecular Clouds
NASA Astrophysics Data System (ADS)
Goldsmith, Paul; Heyer, Mark H.; Yildiz, Umut; Snell, Ronald L.; Falgarone, Edith; Pineda, Jorge L.
2017-01-01
The origin of molecular striae aligned along the local magnetic field in the envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J=2-1 emission obtained with the 10m submillimeter telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsibe for the striae features. For both 12CO and 13CO, spatial variations of the J=2-1 to J=1-0 line ratio are small and are not spatially correlated with the striae locations. A medium comprised of small, unresolved cells of CO emission with a filling factor less than 1 is required to explain the average line ratios and brightness temperatures. We propose that the striae features result from the modulation of the velocities and the beam filling factor of the cells, as a result of magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Such waves are likely a common feature of molecular clouds that are sub-Alfvenic and may explain low column density, cirrus-like features that are observed to be aligned along the magnetic field direction.
NASA Astrophysics Data System (ADS)
Walker, A. D. M.
2014-12-01
Magnetohydrodynamic (MHD) waves in the solar wind and magnetosphere are propagated in a medium whose velocity is comparable to or greater than the wave velocity and which varies in both space and time. In the approximation where the scales of the time and space variation are long compared with the period and wavelength, the ray-tracing equations can be generalized and then include an additional first-order differential equation that determines the variation of frequency. In such circumstances the wave can exchange energy with the background: wave energy is not conserved. In such processes the wave action theorem shows that the wave action, defined as the ratio of the wave energy to the frequency in the local rest frame, is conserved. In this paper we discuss ray-tracing techniques and the energy exchange relation for MHD waves. We then provide a unified account of how to deal with energy transport by MHD waves in non-uniform media. The wave action theorem is derived directly from the basic MHD equations for sound waves, transverse Alfvén waves, and the fast and slow magnetosonic waves. The techniques described are applied to a number of illustrative cases. These include a sound wave in a medium undergoing a uniform compression, an isotropic Alfvén wave in a steady-state shear layer, and a transverse Alfvén wave in a simple model of the magnetotail undergoing compression. In each case the nature and magnitude of the energy exchange between wave and background is found.
Vorticity equation for MHD fast waves in geospace environment
Yamauchi, M.; Lundin, R.; Lui, A.T.Y.
1993-08-01
The magnetohydrodynamic (MHD) vorticity equation is modified in order to apply it to nonlinear MHD fast waves or shocks when their extent along the magnetic field is limited. Field-aligned current (FAC) generation is also discussed on the basis of this modified vorticity equation. When the wave normal is not aligned to the finite velocity convection and the source region is spatially limited, a longitudinal polarization (u{sub {perpendicular}}{center_dot}J{sub {perpendicular}}) causes a pair of plus and minus charges inside the compressional plane waves or shocks, generating a pair of FACs. This polarization is not related to the separation between the electrons and ions caused by their difference in mass (i.e., Langmuir mode), a separation which is inherent to compressional waves. The resultant double field-aligned current structure exists both with and without the contributions from curvature drift, which is questionable in terms of its contribution to vorticity change from the viewpoint of single-particle motion. 14 refs., 3 figs.
Is the magnetosphere a lens for MHD waves?
NASA Technical Reports Server (NTRS)
Papadopoulos, K.; Sharma, A. S.; Valdivia, J. A.
1993-01-01
A viewpoint of the magnetosphere as a lens for MHD waves is presented. Using a simple model of the variation of the Alfven speed as proportional to the local magnetic value given by the Earth's dipole field and that due to the magnetopause currents represented by a current loop, it is found that the near-Earth magnetotail, in the range 8-16 R(sub E), is the focus of the magnetospheric lens. This location is found to be quite insensitive to a wide variation of parameters. By using simple diffraction theory analysis it is found that the focal region extends about 1 R(sub E) about the neutral sheet in the north-south plane and 0.2 - 0.5 R(sub E) along the Sun-Earth line. Compressive MHD waves carried by the solar wind or created by the interaction of the wind with the magnetopause can be amplified by a factor of about 100 in the focal region and this has potentially important implications to substorm activity.
Kelvin-Helmholtz Unstable Magnetotail Flow Channels: Deceleration and Radiation of MHD Waves
NASA Astrophysics Data System (ADS)
Turkakin, H.; Mann, I. R.; Rankin, R.
2014-12-01
The Kelvin-Helmholtz instability (KHI) of magnetotail flow channels associated with burstybulk flows (BBFs) is investigated. MHD oscillations of the channel in both kink and sausage modes areinvestigated for KHI, and both the primary and secondary KHIs are found that drive MHD waves. Theseinstabilities are likely to be important for flow channel braking where the KHI removes energy from the flow.At flow speeds above the peak growth rate, the MHD modes excited by KHI develop from surface modesinto propagating modes leading to the radiation of MHD waves from the flow channel. The coupling ofBBF-driven shear flow instabilities to MHD waves presented here represents a new paradigm to explain BBFexcitation of tail flapping. Our model can also explain, for the first time, the generation mechanism for theobservations of waves propagating toward both flanks and emitted from BBF channels in the magnetotail.
Large amplitude MHD waves upstream of the Jovian bow shock
NASA Technical Reports Server (NTRS)
Goldstein, M. L.; Smith, C. W.; Matthaeus, W. H.
1983-01-01
Observations of large amplitude magnetohydrodynamics (MHD) waves upstream of Jupiter's bow shock are analyzed. The waves are found to be right circularly polarized in the solar wind frame which suggests that they are propagating in the fast magnetosonic mode. A complete spectral and minimum variance eigenvalue analysis of the data was performed. The power spectrum of the magnetic fluctuations contains several peaks. The fluctuations at 2.3 mHz have a direction of minimum variance along the direction of the average magnetic field. The direction of minimum variance of these fluctuations lies at approximately 40 deg. to the magnetic field and is parallel to the radial direction. We argue that these fluctuations are waves excited by protons reflected off the Jovian bow shock. The inferred speed of the reflected protons is about two times the solar wind speed in the plasma rest frame. A linear instability analysis is presented which suggests an explanation for many of the observed features of the observations.
Heating of solar and stellar chromospheres and coronae by MHD waves
NASA Technical Reports Server (NTRS)
Musielak, Z. E.
1992-01-01
The two general classes of models that deal with the required heating of stellar chromospheres and coronae assume that outer stellar atmospheres are heated by hydrodynamic or by magnetohydrodynamic (MHD) waves and that these waves are generated by turbulent motions in the stellar convection zones. This paper considers the types of MHD waves and the source of these waves in stars like sun, the efficiency of the generation of MHD waves, and the manner of propagation and energy dissipation of MHD waves. It is shown that the basic criteria for the validity of any theory of MHD wave heating must account for the mean level of heating observed in stellar chromospheres and coronae, and for the range of radiative losses observed for a given spectral type. It is also required that the MHD wave heating theory accounts for the existence of inhomogeneities in stellar atmospheres. The results obtained indicate that magnetic tube waves might supply enough energy for the chromospheric and coronal heating and might also account for the observed range of variations of stellar radiative losses for a given spectral type.
QT dispersion and P wave dispersion in patients with fibromyalgia
Yolbaş, Servet; Yıldırım, Ahmet; Düzenci, Deccane; Karakaya, Bülent; Dağlı, Mustafa Necati; Koca, Süleyman Serdar
2016-01-01
Objective Fibromyalgia (FM) is a chronic disease characterized by widespread pain. Somatic complaints associated with the cardiovascular system, such as chest pain and palpitations, are frequently seen in FM patients. P and QT dispersions are simple and inexpensive measurements reflecting the regional heterogeneity of atrial and ventricular repolarization, respectively. QT dispersion can cause serious ventricular arrhythmias. The aim of the present study was to evaluate QT dispersion and P wave dispersion in patients with FM. Material and Methods The study involved 48 FM patients who fulfilled the established criteria and 32 healthy controls (HC). A standard 12-lead electrocardiogram was performed on all participants. QT dispersion was defined as the difference between the longest and the shortest QT intervals. Similarly, the differences between the shortest and longest P waves were defined as P wave dispersion. Results The QT dispersion and corrected QT dispersion were shorter in the FM group compared with the HC group (p<0.001 for both). In terms of the P wave dispersion value, there was no significant difference between the FM and HC groups (p=0.088). Conclusion Longer QT and P wave dispersions are not problems in patients with FM. Therefore, it may be concluded that fibromyalgia does not include an increased risk of atrial and/or ventricular arrhythmias. PMID:28149660
Dispersive internal long wave models
Camassa, R.; Choi, W.; Holm, D.D.; Levermore, C.D.; Lvov, Y.
1998-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work is a joint analytical and numerical study of internal dispersive water wave propagation in a stratified two-layer fluid, a problem that has important geophysical fluid dynamics applications. Two-layer models can capture the main density-dependent effects because they can support, unlike homogeneous fluid models, the observed large amplitude internal wave motion at the interface between layers. The authors have derived new model equations using multiscale asymptotics in combination with the method they have developed for vertically averaging velocity and vorticity fields across fluid layers within the original Euler equations. The authors have found new exact conservation laws for layer-mean vorticity that have exact counterparts in the models. With this approach, they have derived a class of equations that retain the full nonlinearity of the original Euler equations while preserving the simplicity of known weakly nonlinear models, thus providing the theoretical foundation for experimental results so far unexplained.
Linear MHD Wave Propagation in Time-Dependent Flux Tube. II. Finite Plasma Beta
NASA Astrophysics Data System (ADS)
Williamson, A.; Erdélyi, R.
2014-04-01
The propagation of magnetohydrodynamic (MHD) waves is an area that has been thoroughly studied for idealised static and steady state magnetised plasma systems applied to numerous solar structures. By applying the generalisation of a temporally varying background density to an open magnetic flux tube, mimicking the observed slow evolution of such waveguides in the solar atmosphere, further investigations into the propagation of both fast and slow MHD waves can take place. The assumption of a zero-beta plasma (no gas pressure) was applied in Williamson and Erdélyi ( Solar Phys. 2013, doi:10.1007/s11207-013-0366-9, Paper I) is now relaxed for further analysis here. Firstly, the introduction of a finite thermal pressure to the magnetic flux tube equilibrium modifies the existence of fast MHD waves which are directly comparable to their counterparts found in Paper I. Further, as a direct consequence of the non-zero kinetic plasma pressure, a slow MHD wave now exists, and is investigated. Analysis of the slow wave shows that, similar to the fast MHD wave, wave amplitude amplification takes place in time and height. The evolution of the wave amplitude is determined here analytically. We conclude that for a temporally slowly decreasing background density both propagating magnetosonic wave modes are amplified for over-dense magnetic flux tubes. This information can be very practical and useful for future solar magneto-seismology applications in the study of the amplitude and frequency properties of MHD waveguides, e.g. for diagnostic purposes, present in the solar atmosphere.
Alfven Wave Generated Electron Time Dispersion
NASA Technical Reports Server (NTRS)
Kletzing, C. A.; Hu, S.
2001-01-01
The results from a model of kinetic Alfven waves which includes varying magnetic field and density show that time-dispersed bursts of auroral electrons can be accelerated by Alfven, wave pulses propagating from the magnetosphere to the ionosphere. The modeled electron signatures have similar energy range and temporal structure to those observed on sounding rockets and satellites suggesting that electron time dispersion is generated by Alfven waves.
Plasma wave signatures in the magnetotail reconnection region - MHD simulation and ray tracing
NASA Technical Reports Server (NTRS)
Omura, Yoshiharu; Green, James L.
1993-01-01
An MHD simulation was performed to obtain a self-consistent model of magnetic field and plasma density near the X point reconnection region. The MHD model was used to perform extensive ray tracing calculations in order to clarify the propagation characteristics of the plasma waves near the X point reconnection region. The dynamic wave spectra possibly observed by the Geotail spacecraft during a typical cross-tail trajectory are reconstructed. By comparing the extensive ray tracing calculations with the plasma wave data from Geotail, it is possible to perform a kind of 'remote sensing' to identify the location and structure of potential X point reconnection regions.
On The Role of MHD Waves in Heating Localised Magnetic Structures
NASA Astrophysics Data System (ADS)
Erdélyi, R.; Nelson, C. J.
2016-04-01
Satellite and ground-based observations from e.g. SOHO, TRACE, STEREO, Hinode, SDO and IRIS to DST/ROSA, IBIS, CoMP, STT/CRISP have provided a wealth of evidence of waves and oscillations present in a wide range of spatial scales of the magnetised solar atmosphere. Our understanding about localised solar structures has been considerably changed in light of these high spatial and time resolution observations. However, MHD waves not only enable us to perform sub-resolution magneto-seismology of magnetic waveguides but are also potential candidates to carry and damp the necessary non-thermal energy in these localised waveguides. First, we will briefly outline the basic recent developments in MHD wave theory focussing on linear waves. Next, we discuss the role of the most frequently studied wave classes, including the Alfven, and magneto-acoustic kink and sausage waves. The current theoretical (and often difficult) interpretations of the detected solar atmospheric wave and oscillatory phenomena within the framework of MHD will be shown. Last, the latest reported observational findings of potential MHD wave flux, in terms of localised plasma heating, in the solar atmosphere is discussed, bringing us closer to solve the coronal heating problem.
Advances in Simulation of Wave Interaction with Extended MHD Phenomena
Batchelor, Donald B; Abla, Gheni; D'Azevedo, Ed F; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, Joshua; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Foley, S.; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.
2009-01-01
The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: 1) recent improvements to the IPS, 2) application of the IPS for very high resolution simulations of ITER scenarios, 3) studies of resistive and ideal MHD stability in tokamk discharges using IPS facilities, and 4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.
Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Bonoli, P.; Bramley, Randall B; Breslau, Joshua; Elwasif, Wael R; Foley, S.; Jaeger, Erwin Frederick; Jardin, S. C.; Klasky, Scott A; Kruger, Scott E; Ku, Long-Poe; McCune, Douglas; Ramos, J.; Schissel, David P; Schnack, Dalton D
2009-01-01
The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: (1) recent improvements to the IPS, (2) application of the IPS for very high resolution simulations of ITER scenarios, (3) studies of resistive and ideal MHD stability in tokamak discharges using IPS facilities, and (4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.
Integrated Physics Advances in Simulation of Wave Interactions with Extended MHD Phenomena
Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Fu, GuoYong; Harvey, R. W.; Houlberg, Wayne A; Jaeger, Erwin Frederick; Jardin, S. C.; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; McCune, Douglas; Schissel, D.; Schnack, D.; Wright, J. C.
2007-06-01
The broad scientific objectives of the SWIM (Simulation of Wave Interaction with MHD) project are: (A) To improve our understanding of interactions that both RF wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (B) To develop an integrated computational system for treating multi-physics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project (FSP).
London Dispersion Forces and "The Wave"
NASA Astrophysics Data System (ADS)
Wilcox, C. Jayne
1998-10-01
An analogy is presented likening London dispersion forces to "The Wave", a popular ritual performed by fans attending sports events in large stadia. Similarities between people in the stands and electrons in atoms are emphasized.
Shock-associated MHD waves - A model for interstellar density fluctuations
NASA Technical Reports Server (NTRS)
Spangler, Steven R.
1988-01-01
The possibility that the density fluctuations responsible for radio scintillations could be due to ion-beam-generated MHD waves near interstellar shock waves is discussed. This suggestion is inspired by spacecraft observations which reveal these phenomena near shocks in the solar system. The model quite naturally accounts for the scale on which these fluctuations occur; it is dictated by the wavelength of the unstable waves.
NASA Astrophysics Data System (ADS)
Majid, M. F. M. A.; Apandi, Muhamad Al-Hakim Md; Sabri, M.; Shahril, K.
2016-02-01
As increasing of agricultural and industrial activities each year has led to an increasing in demand for energy. Possibility in the future, the country was not able to offer a lot of energy and power demand. This means that we need to focus on renewable energy to supply the demand for energy. Energy harvesting is among a method that can contribute on the renewable energy. MHD power generator is a new way to harvest the energy especially Ocean wave energy. An experimental investigation was conducted to explore performance of MHD generator. The effect of intensity of NaCl Solution (Sea Water), flow rate of NaCl solution, magnetic strength and magnet position to the current produce was analyzed. The result shows that each factor is give a significant effect to the current produce, because of that each factor need to consider on develop of MHD generator to harvest the wave energy as an alternative way to support the demand for energy.
Weakly relativistic dispersion of Bernstein waves
NASA Technical Reports Server (NTRS)
Robinson, P. A.
1988-01-01
Weakly relativistic effects on the dispersion of Bernstein waves are investigated for waves propagating nearly perpendicular to a uniform magnetic field in a Maxwellian plasma. Attention is focused on those large-wave-vector branches that are either weakly damped or join continuously onto weakly damped branches since these are the modes of most interest in applications. The transition between dispersion at perpendicular and oblique propagation is examined and major weakly relativistic effects can dominate even in low-temperature plasmas. A number of simple analytic criteria are obtained which delimit the ranges of harmonic number and propagation angle within which various types of weakly damped Bernstein modes can exist.
Development of MHD Wave Diagnostic and Models of Coronal Active Regions
NASA Astrophysics Data System (ADS)
Ofman, L.; Thompson, B. J.; Davila, J. M.
2004-05-01
We investigate the generation, propagation, and damping of MHD waves in active regions, with the goal to develop a diagnostic tool of active region structure, dynamics, and stability. We used 3D MHD model to study the generation and the propagation of EIT waves in a simple model of an active regions, and the interaction of EIT waves with the active region magnetic field. We model the oscillation of active region loops numerically using the 3D MHD model active regions. Such oscillations have been recently observed by TRACE. We use photospheric magnetograms as the boundary conditions for the magnetic field model, and construct an initial field using force-free extrapolation. Finite plasma temperature, density, and gravity are included in the model. We construct loop density structures in the model, guided by TRACE and EIT observations in the EUV. We demonstrate that by comparing the results of the MHD models of waves in an active region to observations we will be able to construct a diagnostic tool for the physical properties of the active regions, such as magnetic field and density structure.
NASA Astrophysics Data System (ADS)
Pilipenko, Vyacheslav; Kozyreva, Olga; Fedorov, Evgeniy; Uspenskiy, Mihail; Kauristi, Kirsti
2016-09-01
We have developed a numerical model that yields a steady-state distribution of field components of MHD wave in an inhomogeneous plasma box simulating the realistic magnetosphere. The problem of adequate boundary condition at the ionosphere-magnetosphere interface for coupled MHD mode is considered. To justify the model's assumptions, we have derived the explicit inequality showing when the ionospheric inductive Hall effect can be neglected upon the consideration of Alfven wave reflection from the ionospheric boundaries. The model predicts a feature of the ULF spatial amplitude/phase distribution that has not been noticed by the field line resonance theory: the existence of a region with opposite phase delays on the source side of the resonance. This theoretical prediction is supported by the amplitude-phase latitudinal structures of Pc5 waves observed by STARE radar and IMAGE magnetometers. A gradual decrease in azimuthal wave number m at smaller L-shells was observed at longitudinally separated radar beams.
MODE IDENTIFICATION OF MHD WAVES IN AN ACTIVE REGION OBSERVED WITH HINODE/EIS
Kitagawa, N.; Yokoyama, T.; Imada, S.; Hara, H.
2010-09-20
In order to better understand the possibility of coronal heating by MHD waves, we analyze Fe XII 195.12A data observed with the EUV Imaging Spectrometer on board Hinode. We performed a Fourier analysis of EUV intensity and Doppler velocity time series data in the active region corona. Notable intensity and Doppler velocity oscillations were found for two moss regions out of the five studied, while only small oscillations were found for five apexes of loops. The amplitudes of the oscillations were 0.4%-5.7% for intensity and 0.2-1.2 km s{sup -1} for Doppler velocity. In addition, oscillations of only the Doppler velocity were seen relatively less often in the data. We compared the amplitudes of intensity and those of Doppler velocity in order to identify MHD wave modes and calculated the phase delays between Fourier components of intensity and those of Doppler velocity. The results are interpreted in terms of MHD waves as follows: (1) few kink modes or torsional Alfven mode waves were seen in both moss regions and the apexes of loops, (2) upwardly propagating and standing slow mode waves were found in moss regions, and (3) consistent with previous studies, estimated values of energy flux of the waves were several orders of magnitude lower than that required for heating active regions.
Optical carrier wave shocking: detection and dispersion.
Kinsler, P; Radnor, S B P; Tyrrell, J C A; New, G H C
2007-06-01
Carrier wave shocking is studied using the pseudospectral spatial-domain (PSSD) technique. We describe the shock detection diagnostics necessary for this numerical study and verify them against theoretical shocking predictions for the dispersionless case. These predictions show a carrier envelope phase and pulse bandwidth sensitivity in the single-cycle regime. The flexible dispersion management offered by the PSSD enables us to independently control the linear and nonlinear dispersion. Customized dispersion profiles allow us to analyze the development of both carrier self-steepening and shocks. The results exhibit a marked asymmetry between normal and anomalous dispersion, both in the limits of the shocking regime and in the (near) shocked pulse wave forms. Combining these insights, we offer some suggestions on how carrier shocking (or at least extreme self-steepening) might be realized experimentally.
Eigen-Frequencies of MHD Wave Equations in the Presence of Longitudinal Stratification Density
NASA Astrophysics Data System (ADS)
Esmaeili, Shahriar; Nasiri, Mojtaba; Dadashi, Neda; Safari, Hossein
2015-04-01
Coronal Loops oscillations and MHD waves propagating in solar corona and transition region has been observed by TRACE telescope in 1999. In this Study, the MHD mode oscillations of the coronal plasma are studied. The aim is to identify the effect of structuring such as density on the frequencies of oscillations. We modeled the coronal medium as a zero-plasma with longitudinally density stratification. Magnetic flux tube oscillations are categorized into sausage, kink and torsion modes. The MHD equations are reduced and the governing equation are solved numerically using Finite Element Method. Eigenfrequencies and eigenfunctions are extracted. The torsional mode is analyzed. By changing the stratification parameter the antinodes move towards the footpoints and we also concluded that in the thin tube approximation, leakage modes are propagated.
Guided MHD waves as a coronal diagnostic tool
NASA Technical Reports Server (NTRS)
Roberts, B.
1986-01-01
A description is provided of how fast magnetoacoustic waves are ducted along regions of low Alfven velocity (high density) in the corona, exhibiting a distinctive wave signature which may be used as a diagnostic probe of in situ coronal conditions (magnetic field strength, density inhomogeneity, etc.). Some observational knowledge of the start time of the impulsive wave source, possibly a flare, the start and end times of the generated wave event, and the frequency of the pulsations in that event permits a seismological deduction of the physical properties of the coronal medium in which the wave propagated. With good observations the theory offers a new means of probing the coronal atmosphere.
The generation and damping of propagating MHD kink waves in the solar atmosphere
Morton, R. J.; Verth, G.; Erdélyi, R.; Hillier, A. E-mail: g.verth@sheffield.ac.uk
2014-03-20
The source of the non-thermal energy required for the heating of the upper solar atmosphere to temperatures in excess of a million degrees and the acceleration of the solar wind to hundreds of kilometers per second is still unclear. One such mechanism for providing the required energy flux is incompressible torsional Alfvén and kink magnetohydrodynamic (MHD) waves, which are magnetically dominated waves supported by the Sun's pervasive and complex magnetic field. In particular, propagating MHD kink waves have recently been observed to be ubiquitous throughout the solar atmosphere, but, until now, critical details of the transport of the kink wave energy throughout the Sun's atmosphere were lacking. Here, the ubiquity of the waves is exploited for statistical studies in the highly dynamic solar chromosphere. This large-scale investigation allows for the determination of the chromospheric kink wave velocity power spectra, a missing link necessary for determining the energy transport between the photosphere and corona. Crucially, the power spectra contain evidence for horizontal photospheric motions being an important mechanism for kink wave generation in the quiescent Sun. In addition, a comparison with measured coronal power spectra is provided for the first time, revealing frequency-dependent transmission profiles, suggesting that there is enhanced damping of kink waves in the lower corona.
Dispersive radiation induced by shock waves in passive resonators.
Malaguti, Stefania; Conforti, Matteo; Trillo, Stefano
2014-10-01
We show that passive Kerr resonators pumped close to zero dispersion wavelengths on the normal dispersion side can develop the resonant generation of linear waves driven by cavity (mixed dispersive-dissipative) shock waves. The resonance mechanism can be successfully described in the framework of the generalized Lugiato-Lefever equation with higher-order dispersive terms. Substantial differences with radiation from cavity solitons and purely dispersive shock waves dispersion are highlighted.
NASA Technical Reports Server (NTRS)
Cattell, Cynthia A.
2004-01-01
This grant was focused on research in two specific areas: (1) development of new techniques and software for assimilation, analysis and visualization of data from multiple satellites making in-situ measurements; and (2) determination of the role of MHD waves in energy transport during storms and substorms. Results were obtained in both areas and presented at national meetings and in publications. The talks and papers that were supported in part or fully by this grant are listed in this paper.
Numerical modelling of MHD waves in the solar chromosphere.
Carlsson, Mats; Bogdan, Thomas J
2006-02-15
Acoustic waves are generated by the convective motions in the solar convection zone. When propagating upwards into the chromosphere they reach the height where the sound speed equals the Alfvén speed and they undergo mode conversion, refraction and reflection. We use numerical simulations to study these processes in realistic configurations where the wavelength of the waves is similar to the length scales of the magnetic field. Even though this regime is outside the validity of previous analytic studies or studies using ray-tracing theory, we show that some of their basic results remain valid: the critical quantity for mode conversion is the angle between the magnetic field and the k-vector: the attack angle. At angles smaller than 30 degrees much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In three-dimensions, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low-mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves. The oscillatory power is suppressed in magnetic field concentrations and enhanced in ring-formed patterns around them. The complex interference patterns caused by mode-conversion, refraction and reflection, even with simple incident waves and in simple magnetic field geometries, make direct inversion of observables exceedingly difficult. In a dynamic chromosphere it is doubtful if the determination of mean quantities is even meaningful.
Flare-induced MHD disturbances in the corona - Moreton waves and type 2 shocks
NASA Technical Reports Server (NTRS)
Uchida, Y.
1973-01-01
The propagation in the corona of the magnetohydrodynamic (MHD) disturbance possibly emitted at the explosive stage in the initial phase of a flare is considered. The behavior of the MHD fast-mode wavefront, whose source is located at the flare, is calculated by using eiconal-characteristic method in the High Altitude Observatory (HAO) realistic models of coronal magnetic field and density for the days of some particular flare events. It is shown as the result that the peculiar behavior of Moreton's surface wave and the peculiar appearance in the shape and position of the type 2 burst sources can be consistently understood by considering the refraction, focussing, and formation of shocks of MHD fast-mode disturbance in the actual distribution of Alfven velocity in the corona. Moreton waves seem to appear only when the flare explosion happens to occur at the edge of an active region and faces a low-Alfven-velocity region lying on the surface. The wave, which is initially emitted isotropically is refracted into a direction in which the condition for down-refraction holds to allow chromospheric reentrance of disturbance.
Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere.
Claudepierre, S G; Toffoletto, F R; Wiltberger, M
2016-01-01
We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.
Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere
NASA Astrophysics Data System (ADS)
Claudepierre, S. G.; Toffoletto, F. R.; Wiltberger, M.
2016-01-01
We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.
Dispersive shock waves and modulation theory
NASA Astrophysics Data System (ADS)
El, G. A.; Hoefer, M. A.
2016-10-01
There is growing physical and mathematical interest in the hydrodynamics of dissipationless/dispersive media. Since G.B. Whitham's seminal publication fifty years ago that ushered in the mathematical study of dispersive hydrodynamics, there has been a significant body of work in this area. However, there has been no comprehensive survey of the field of dispersive hydrodynamics. Utilizing Whitham's averaging theory as the primary mathematical tool, we review the rich mathematical developments over the past fifty years with an emphasis on physical applications. The fundamental, large scale, coherent excitation in dispersive hydrodynamic systems is an expanding, oscillatory dispersive shock wave or DSW. Both the macroscopic and microscopic properties of DSWs are analyzed in detail within the context of the universal, integrable, and foundational models for uni-directional (Korteweg-de Vries equation) and bi-directional (Nonlinear Schrödinger equation) dispersive hydrodynamics. A DSW fitting procedure that does not rely upon integrable structure yet reveals important macroscopic DSW properties is described. DSW theory is then applied to a number of physical applications: superfluids, nonlinear optics, geophysics, and fluid dynamics. Finally, we survey some of the more recent developments including non-classical DSWs, DSW interactions, DSWs in perturbed and inhomogeneous environments, and two-dimensional, oblique DSWs.
MHD waves and oscillations in the solar plasma. Introduction.
Erdélyi, Robert
2006-02-15
The Sun's magnetic field is responsible for many spectacularly dynamic and intricate phenomena, such as the 11 year solar activity cycle, the hot and tenuous outer atmosphere called the solar corona, and the continuously expanding stream of solar particles known as the solar wind.Recently, there has been an enormous increase in our understanding of the role of solar magnetism in producing the observed complex atmosphere of the Sun. One such advance has occurred in the detection, by several different high-resolution space instruments on-board the Solar and Heliospheric Observatory and Transition Region and Coronal Explorer satellites, of magnetic waves and oscillations in the solar corona. The new subjects of solar atmospheric and coronal seismology are undergoing rapid development. The aim of this Scientific Discussion Meeting was to address the progress made through observational, theoretical and numerical studies of wave phenomena in the magnetic solar plasma. Major theoretical and observational advances were reported by a wide range of international scientists and pioneers in this field, followed by lively discussions and poster sessions on the many intriguing questions raised by the new results. Theoretical and observational aspects of magnetohydrodynamic waves and oscillations in general, and how these wave phenomena differ in various regions of the Sun, including sunspots, the transient lower atmosphere and the corona (in magnetic loops, plumes and prominences), were addressed through invited review papers and selected poster presentations. The results of these deliberations are collected together in this volume.
Shear wave speed and dispersion measurements using crawling wave chirps.
Hah, Zaegyoo; Partin, Alexander; Parker, Kevin J
2014-10-01
This article demonstrates the measurement of shear wave speed and shear speed dispersion of biomaterials using a chirp signal that launches waves over a range of frequencies. A biomaterial is vibrated by two vibration sources that generate shear waves inside the medium, which is scanned by an ultrasound imaging system. Doppler processing of the acquired signal produces an image of the square of vibration amplitude that shows repetitive constructive and destructive interference patterns called "crawling waves." With a chirp vibration signal, successive Doppler frames are generated from different source frequencies. Collected frames generate a distinctive pattern which is used to calculate the shear speed and shear speed dispersion. A special reciprocal chirp is designed such that the equi-phase lines of a motion slice image are straight lines. Detailed analysis is provided to generate a closed-form solution for calculating the shear wave speed and the dispersion. Also several phantoms and an ex vivo human liver sample are scanned and the estimation results are presented.
Interaction of solitary waves in longitudinal magnetic field in two-fluid MHD
NASA Astrophysics Data System (ADS)
Gavrikov, M. B.; Savelyev, V. V.
2017-01-01
The interaction of solitary waves in a model of two-fluid MHD is studied analytically and numerically in the most general case of waves in cold plasma in longitudinal magnetic field. The distinctive feature of this work is the use of “exact” equations rather than an approximate approach (a model equation). Numerical analysis of the solutions of this system of eight partial differential equations shows that the the interaction of solitary waves found in this case is the same (with great accuracy) as that of solitons, i.e., solitary waves that are solutions of various model equations. The solitary waves considered here transport plasmoids with velocities of the order of the Alfven velocity. The main finite-difference method used here for solving the said equations is a natural generalization of the classical two-step Lax-Wendorff scheme.
Dispersive wave-breaking in coherently driven passive cavities.
Malaguti, Stefania; Bellanca, Gaetano; Trillo, Stefano
2014-04-15
We show that the intracavity field evolving in an externally driven passive Kerr resonator subject to weak normal dispersion undergoes wave-breaking, thus forming dispersive shock waves. At variance with the cavity-less propagation, such dispersive wave-breaking turns out to be strongly favored by cavity bistability and coexisting modulational instability.
Wideband dispersion reversal of lamb waves.
Xu, Kailiang; Ta, Dean; Hu, Bo; Laugier, Pascal; Wang, Weiqi
2014-06-01
Ultrasonic guided waves have been widely acknowledged as the most promising tools for nondestructive evaluation (NDE). However, because of the multimodal dispersion, the received guided modes usually overlap in both time and frequency, which highly complicates the mode separation and signal interpretation. The time-reversal technique can be used to realize the time recompression of the Lamb waves, but because of the multimode excitation and reception, it still may not be able to remove the mode ambiguity and achieve the pure pulse compression. With the goal of overcoming this limitation, a wideband dispersion reversal (WDR) technique is proposed. The technique makes use of a priori knowledge of the guided dispersion characteristics to synthesize the corresponding dispersion reversal excitations, which are able to selectively excite the self-compensation pure mode pulse. The theoretical basis of the technique is thoroughly described. A two-dimensional finite-difference time-domain (2D-FDTD) method is employed to simulate the propagation of two fundamental Lamb modes, the symmetrical S0 and antisymmetrical A0 modes in a steel plate. The proposed method was verified through experimental investigation. Finally, the advantages and potential applications of the method are briefly discussed.
Adaptive dispersion compensation for guided wave imaging
NASA Astrophysics Data System (ADS)
Hall, James S.; Michaels, Jennifer E.
2012-05-01
Ultrasonic guided waves offer the promise of fast and reliable methods for interrogating large, plate-like structures. Distributed arrays of permanently attached, inexpensive piezoelectric transducers have thus been proposed as a cost-effective means to excite and measure ultrasonic guided waves for structural health monitoring (SHM) applications. Guided wave data recorded from a distributed array of transducers are often analyzed and interpreted through the use of guided wave imaging algorithms, such as conventional delay-and-sum imaging or the more recently applied minimum variance imaging. Both imaging algorithms perform reasonably well using signal envelopes, but can exhibit significant performance improvements when phase information is used. However, the use of phase information inherently requires knowledge of the dispersion relations, which are often not known to a sufficient degree of accuracy for high quality imaging since they are very sensitive to environmental conditions such as temperature, pressure, and loading. This work seeks to perform improved imaging with phase information by leveraging adaptive dispersion estimates obtained from in situ measurements. Experimentally obtained data from a distributed array is used to validate the proposed approach.
MHD waves on solar magnetic flux tubes - Tutorial review
NASA Technical Reports Server (NTRS)
Hollweg, Joseph V.
1990-01-01
Some of the highly simplified models that have been developed for solar magnetic flux tubes, which are intense photospheric-level fields confined by external gas pressure but able to vary rapidly with height, are presently discussed with emphasis on the torsional Alfven mode's propagation, reflection, and non-WKB properties. The 'sausage' and 'kink' modes described by the thin flux-tube approximation are noted. Attention is also given to the surface waves and resonance absorption of X-ray-emitting loops, as well as to the results of recent work on the resonant instabilities that occur in the presence of bulk flows.
MHD waves on solar magnetic flux tubes - Tutorial review
NASA Astrophysics Data System (ADS)
Hollweg, Joseph V.
Some of the highly simplified models that have been developed for solar magnetic flux tubes, which are intense photospheric-level fields confined by external gas pressure but able to vary rapidly with height, are presently discussed with emphasis on the torsional Alfven mode's propagation, reflection, and non-WKB properties. The 'sausage' and 'kink' modes described by the thin flux-tube approximation are noted. Attention is also given to the surface waves and resonance absorption of X-ray-emitting loops, as well as to the results of recent work on the resonant instabilities that occur in the presence of bulk flows.
Generalized dispersive wave emission in nonlinear fiber optics.
Webb, K E; Xu, Y Q; Erkintalo, M; Murdoch, S G
2013-01-15
We show that the emission of dispersive waves in nonlinear fiber optics is not limited to soliton-like pulses propagating in the anomalous dispersion regime. We demonstrate, both numerically and experimentally, that pulses propagating in the normal dispersion regime can excite resonant dispersive radiation across the zero-dispersion wavelength into the anomalous regime.
Numerical simulation of MHD shock waves in the solar wind
NASA Technical Reports Server (NTRS)
Steinolfson, R. S.; Dryer, M.
1978-01-01
The effects of the interplanetary magnetic field on the propagation speed of shock waves through an ambient solar wind are examined by numerical solutions of the time-dependent nonlinear equations of motion. The magnetic field always increases the velocity of strong shocks. Although the field may temporarily slow down weak shocks inside 1 AU, it eventually also causes weak shocks to travel faster than they would without the magnetic field at larger distances. Consistent with the increase in the shock velocity, the gas pressure ratio across a shock is reduced considerably in the presence of the magnetic field. The numerical method is used to simulate (starting at 0.3 AU) the large deceleration of a shock observed in the lower corona by ground-based radio instrumentation and the more gradual deceleration of the shock in the solar wind observed by the Pioneer 9 and Pioneer 10 spacecraft.
Experimental, Numerical and Analytical Studies of the MHD-driven plasma jet, instabilities and waves
NASA Astrophysics Data System (ADS)
Zhai, Xiang
This thesis describes a series of experimental, numerical, and analytical studies involving the Caltech magnetohydrodynamically (MHD)-driven plasma jet experiment. The plasma jet is created via a capacitor discharge that powers a magnetized coaxial planar electrodes system. The jet is collimated and accelerated by the MHD forces. We present three-dimensional ideal MHD finite-volume simulations of the plasma jet experiment using an astrophysical magnetic tower as the baseline model. A compact magnetic energy/helicity injection is exploited in the simulation analogous to both the experiment and to astrophysical situations. Detailed analysis provides a comprehensive description of the interplay of magnetic force, pressure, and flow effects. We delineate both the jet structure and the transition process that converts the injected magnetic energy to other forms. When the experimental jet is sufficiently long, it undergoes a global kink instability and then a secondary local Rayleigh-Taylor instability caused by lateral acceleration of the kink instability. We present an MHD theory of the Rayleigh-Taylor instability on the cylindrical surface of a plasma flux rope in the presence of a lateral external gravity. The Rayleigh-Taylor instability is found to couple to the classic current-driven instability, resulting in a new type of hybrid instability. The coupled instability, produced by combination of helical magnetic field, curvature of the cylindrical geometry, and lateral gravity, is fundamentally different from the classic magnetic Rayleigh-Taylor instability occurring at a two-dimensional planar interface. In the experiment, this instability cascade from macro-scale to micro-scale eventually leads to the failure of MHD. When the Rayleigh-Taylor instability becomes nonlinear, it compresses and pinches the plasma jet to a scale smaller than the ion skin depth and triggers a fast magnetic reconnection. We built a specially designed high-speed 3D magnetic probe and
Soliton trapping of dispersive waves in photonic crystal fiber with two zero dispersive wavelengths.
Wang, Weibin; Yang, Hua; Tang, Pinghua; Zhao, Chujun; Gao, Jing
2013-05-06
Based on the generalized nonlinear Schrödinger equation, we present a numerical study of trapping of dispersive waves by solitons during supercontinuum generation in photonic crystal fibers pumped with femtosecond pulses in the anomalous dispersion region. Numerical simulation results show that the generated supercontinuum is bounded by two branches of dispersive waves, namely blue-shifted dispersive waves (B-DWs) and red-shifted dispersive waves (R-DWs). We find a novel phenomenon that not only B-DWs but also R-DWs can be trapped by solitons across the zero-dispersion wavelength when the group-velocity matching between the soliton and the dispersive wave is satisfied, which may led to the generation of new spectral components via mixing of solitons and dispersive waves. Mixing of solitons with dispersive waves has been shown to play an important role in shaping not only the edge of the supercontinuum, but also its central part around the higher zero-dispersion wavelength. Further, we show that the phenomenon of soliton trapping of dispersive waves in photonic crystal fibers with two zero-dispersion wavelengths has a very close relationship with pumping power and the interval between two zero-dispersion wavelengths. In order to clearly display the evolution of soliton trapping of dispersive waves, the spectrogram of output pulses is observed using cross-correlation frequency-resolved optical gating technique (XFROG).
NUMERICAL SIMULATION OF PROPAGATION AND SCATTERING OF THE MHD WAVES IN SUNSPOTS
NASA Astrophysics Data System (ADS)
Parchevsky, K.; Kosovichev, A. G.; Khomenko, E.; Collados, M.
2009-12-01
We present comparison of numerical simulation results of MHD wave propagation in two different magnitostatic models of sunspots refferred to as "deep" and "shallow" models. The "deep" model has convex shape of magnetic field lines near the photosphere and non-zero horizorntal perturbations of the sound speed up to the bottom of the model (7.5 Mm). The "shallow" model has concave shape of the magnetic field lines near the photosphere and horizontally uniform sound speed below 2 Mm. Common feature of MHD waves behaviour in these two models is that for weak magnetic field (less than 1kG at the photosphere) waves reduce their amplitude when they reach the center of the sunspot and restore the amplitude when pass the center. For the "deep" model this effect is bigger than for the "shallow" model. The wave amplitude inside sunspots depends on the strength of the magnetic field. For the "shallow" model with photospheric magnetic field of 2.2 kG the wave amplitude inside the sunspot becomes bigger than outside (opposite to the weak magnetic field). The wave amplitude depends on the distance of the source from the sunspot center. For the "shallow" model and source distance of 9 Mm from the sunspot center the wave amplitude at some moment (when the wavefront passes the sunspot center) becomes bigger inside the sunspot than outside. For the source distance of 12 Mm the wave amplitude remains smaller inside the sunspot than outside for all moments of time. Using filtering technique we separated magnetoacoustic and magnetogravity waves. Simulations show that the sunspot changes the shape of the wave front and amplitude of the f-modes significantly stronger than the p-modes. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. Strong Alfven wave is generated at the wave source location in the "deep" model. This wave exists in the "shallow" model as well, but with
Study on evaluation methods for Rayleigh wave dispersion characteristic
Shi, L.; Tao, X.; Kayen, R.; Shi, H.; Yan, S.
2005-01-01
The evaluation of Rayleigh wave dispersion characteristic is the key step for detecting S-wave velocity structure. By comparing the dispersion curves directly with the spectra analysis of surface waves (SASW) method, rather than comparing the S-wave velocity structure, the validity and precision of microtremor-array method (MAM) can be evaluated more objectively. The results from the China - US joint surface wave investigation in 26 sites in Tangshan, China, show that the MAM has the same precision with SASW method in 83% of the 26 sites. The MAM is valid for Rayleigh wave dispersion characteristic testing and has great application potentiality for site S-wave velocity structure detection.
ON THE PROPERTIES OF SLOW MHD SAUSAGE WAVES WITHIN SMALL-SCALE PHOTOSPHERIC MAGNETIC STRUCTURES
Freij, N.; Ruderman, M. S.; Erdélyi, R.; Dorotovič, I.; Morton, R. J.; Karlovský, V. E-mail: ivan.dorotovic@suh.sk E-mail: m.s.ruderman@sheffield.ac.uk E-mail: robertus@sheffield.ac.uk
2016-01-20
The presence of magnetoacoustic waves in magnetic structures in the solar atmosphere is well-documented. Applying the technique of solar magneto-seismology (SMS) allows us to infer the background properties of these structures. Here, we aim to identify properties of the observed magnetoacoustic waves and study the background properties of magnetic structures within the lower solar atmosphere. Using the Dutch Open Telescope and Rapid Oscillations in the Solar Atmosphere instruments, we captured two series of high-resolution intensity images with short cadences of two isolated magnetic pores. Combining wavelet analysis and empirical mode decomposition (EMD), we determined characteristic periods within the cross-sectional (i.e., area) and intensity time series. Then, by applying the theory of linear magnetohydrodynamics (MHD), we identified the mode of these oscillations within the MHD framework. Several oscillations have been detected within these two magnetic pores. Their periods range from 3 to 20 minutes. Combining wavelet analysis and EMD enables us to confidently find the phase difference between the area and intensity oscillations. From these observed features, we concluded that the detected oscillations can be classified as slow sausage MHD waves. Furthermore, we determined several key properties of these oscillations such as the radial velocity perturbation, the magnetic field perturbation, and the vertical wavenumber using SMS. The estimated range of the related wavenumbers reveals that these oscillations are trapped within these magnetic structures. Our results suggest that the detected oscillations are standing harmonics, and this allows us to estimate the expansion factor of the waveguides by employing SMS. The calculated expansion factor ranges from 4 to 12.
On the Properties of Slow MHD Sausage Waves within Small-scale Photospheric Magnetic Structures
NASA Astrophysics Data System (ADS)
Freij, N.; Dorotovič, I.; Morton, R. J.; Ruderman, M. S.; Karlovský, V.; Erdélyi, R.
2016-01-01
The presence of magnetoacoustic waves in magnetic structures in the solar atmosphere is well-documented. Applying the technique of solar magneto-seismology (SMS) allows us to infer the background properties of these structures. Here, we aim to identify properties of the observed magnetoacoustic waves and study the background properties of magnetic structures within the lower solar atmosphere. Using the Dutch Open Telescope and Rapid Oscillations in the Solar Atmosphere instruments, we captured two series of high-resolution intensity images with short cadences of two isolated magnetic pores. Combining wavelet analysis and empirical mode decomposition (EMD), we determined characteristic periods within the cross-sectional (i.e., area) and intensity time series. Then, by applying the theory of linear magnetohydrodynamics (MHD), we identified the mode of these oscillations within the MHD framework. Several oscillations have been detected within these two magnetic pores. Their periods range from 3 to 20 minutes. Combining wavelet analysis and EMD enables us to confidently find the phase difference between the area and intensity oscillations. From these observed features, we concluded that the detected oscillations can be classified as slow sausage MHD waves. Furthermore, we determined several key properties of these oscillations such as the radial velocity perturbation, the magnetic field perturbation, and the vertical wavenumber using SMS. The estimated range of the related wavenumbers reveals that these oscillations are trapped within these magnetic structures. Our results suggest that the detected oscillations are standing harmonics, and this allows us to estimate the expansion factor of the waveguides by employing SMS. The calculated expansion factor ranges from 4 to 12.
A global 3-D MHD model of the solar wind with Alfven waves
NASA Technical Reports Server (NTRS)
Usmanov, A. V.
1995-01-01
A fully three-dimensional solar wind model that incorporates momentum and heat addition from Alfven waves is developed. The proposed model upgrades the previous one by considering self-consistently the total system consisting of Alfven waves propagating outward from the Sun and the mean polytropic solar wind flow. The simulation region extends from the coronal base (1 R(sub s) out to beyond 1 AU. The fully 3-D MHD equations written in spherical coordinates are solved in the frame of reference corotating with the Sun. At the inner boundary, the photospheric magnetic field observations are taken as boundary condition and wave energy influx is prescribed to be proportional to the magnetic field strength. The results of the model application for several time intervals are presented.
Ultra-High-Resolution Observations of MHD Waves in Photospheric Magnetic Structures
NASA Astrophysics Data System (ADS)
Jess, D. B.; Verth, G.
2016-02-01
This chapter reviews the recent observations of waves and oscillations manifesting in fine-scale magnetic structures in the solar photosphere, which are often interpreted as the "building blocks' of the magnetic Sun. The authors found, through phase relationships between the various waveforms, that small-scale magnetic bright points (MBPs) in the photosphere demonstrated signatures of specific magnetoacoustic waves, in particular the sausage and kink modes. Modern magnetohydrodynamic (MHD) simulations of the lower solar atmosphere clearly show how torsional motions can easily be induced in magnetic elements in the photosphere through the processes of vortical motions and/or buffeting by neighboring granules. The authors detected significant power associated with high-frequency horizontal motions, and suggested that these cases may be especially important in the creation of a turbulent environment that efficiently promotes Alfvén wave dissipation.
Possible signatures of nonlinear MHD waves in the solar wind: UVCS observations and models
NASA Technical Reports Server (NTRS)
Ofman, L.; Romoli, M.; Davila, J. M.; Poletto, G.; Kohl, J.; Noci, G.
1997-01-01
Recent ultraviolet coronagraph spectrometer (UVCS) white light channel observations are discussed. These data indicated quasi-periodic variations in the polarized brightness in the polar coronal holes. The Fourier power spectrum analysis showed significant peaks at about six minutes and possible fluctuations on longer time scales. The observations are consistent with the predictions of the nonlinear solitary-like wave model. The purpose of a planned study on plume and inter-plume regions of coronal holes, motivated by the result of a 2.5 magnetohydrodynamic model (MHD), is explained.
Resonant behaviour of MHD waves on magnetic flux tubes. III - Effect of equilibrium flow
NASA Technical Reports Server (NTRS)
Goossens, Marcel; Hollweg, Joseph V.; Sakurai, Takashi
1992-01-01
The Hollweg et al. (1990) analysis of MHD surface waves in a stationary equilibrium is extended. The conservation laws and jump conditions at Alfven and slow resonance points obtained by Sakurai et al. (1990) are generalized to include an equilibrium flow, and the assumption that the Eulerian perturbation of total pressure is constant is recovered as the special case of the conservation law for an equilibrium with straight magnetic field lines and flow along the magnetic field lines. It is shown that the conclusions formulated by Hollweg et al. are still valid for the straight cylindrical case. The effect of curvature is examined.
Axisymmetric and non-axisymmetric modulated MHD waves in magnetic flux tubes
NASA Astrophysics Data System (ADS)
Chargeishvili, B. B.; Japaridze, D. R.
2016-02-01
Nonlinear modulated both axisymmetric and non-axisymmetric MHD wave propagation in magnetic flux tubes is studied. In the cylindrical coordinates, ordinary differential equation with cubic nonlinearity is derived. In both cases of symmetry, the equation has solitary solutions. Modulation stability of the solutions is studied. The results of the study show that the propagation of axisymmetric soliton causes rising of plasma temperature in peripheral regions of a magnetic flux tube. In the non-axisymmetric case, it gives also temperature rising effect. Results of theoretical study are examined on idealized model of chromospheric spicule.
Numerical Simulation of Propagation and Transformation of the MHD Waves in Sunspots
NASA Astrophysics Data System (ADS)
Parchevsky, Konstantin; Zhao, J.; Kosovichev, A.
2010-05-01
Direct numerical simulation of propagation of MHD waves in stratified medium in regions with non-uniform magnetic field is very important for understanding of scattering and transformation of waves by sunspots. We present numerical simulations of wave propagation through the sunspot in 3D. We compare results propagation in two different magnitostatic models of sunspots refferred to as "deep" and "shallow" models. The "deep" model has convex shape of magnetic field lines near the photosphere and non-zero horizorntal perturbations of the sound speed up to the bottom of the model. The "shallow" model has concave shape of the magnetic field lines near the photosphere and horizontally uniform sound speed below 2 Mm. Waves reduce their amplitude when they reach the center of the sunspot and estore the amplitude when pass the center. For the "deep" model this effect is bigger than for the "shallow" model. The wave amplitude depends on the distance of the source from the sunspot center. For the "shallow" model and source distance of 9 Mm from the sunspot center the wave amplitude at some moment (when the wavefront passes the sunspot center) becomes bigger inside the sunspot than outside. For the source distance of 12 Mm the wave amplitude remains smaller inside the sunspot than outside for all moments of time. Using filtering technique we separated magnetoacoustic and magnetogravity waves. Simulations show that the sunspot changes the shape of the wave front and amplitude of the f-modes significantly stronger than the p-modes. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. We compared simulation results with the wave signals (Green's functions) extracted from the SOHO/MDI data for AR9787.
Dispersive Wave Analysis Using the Chirplet Transform
Kerber, Florian; Luangvilai, Kritsakorn; Kuttig, Helge; Niethammer, Marc; Jacobs, Laurence J.
2007-03-21
Time-frequency representations (TFR) are a widely used tool to analyze signals of guided waves such as Lamb waves. As a consequence of the uncertainty principle, however, the resolution in time and frequency is limited for all existing TFR methods. Due to the multi-modal and dispersive character of Lamb waves, displacement or energy related quantities can only be allocated to individual modes when they are well-separated in the time-frequency plane.The chirplet transform (CT) has been introduced as a generalization of both the wavelet and Short-time Fourier transform (STFT). It offers additional degrees of freedom to adjust time-frequency atoms which can be exploited in a model-based approach to match the group delay of individual modes. Thus, more exact allocation of quantities of interest is possible.The objective of this research is to use a previously developed adaptive algorithm based on the CT for nondestructive evaluation. Both numerically and experimentally generated data for a single aluminum plate is analyzed to determine the accuracy and robustness of the new method in comparison the classical STFT.
Dispersive shock waves in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Smyth, Noel F.
2016-10-01
The propagation of coherent light with an initial step intensity profile in a nematic liquid crystal is studied using modulation theory. The propagation of light in a nematic liquid crystal is governed by a coupled system consisting of a nonlinear Schrödinger equation for the light beam and an elliptic equation for the medium response. In general, the intensity step breaks up into a dispersive shock wave, or undular bore, and an expansion fan. In the experimental parameter regime for which the nematic response is highly nonlocal, this nematic bore is found to differ substantially from the standard defocusing nonlinear Schrödinger equation structure due to the effect of the nonlocality of the nematic medium. It is found that the undular bore is of Korteweg-de Vries equation-type, consisting of bright waves, rather than of nonlinear Schrödinger equation-type, consisting of dark waves. In addition, ahead of this Korteweg-de Vries bore there can be a uniform wavetrain with a short front which brings the solution down to the initial level ahead. It is found that this uniform wavetrain does not exist if the initial jump is below a critical value. Analytical solutions for the various parts of the nematic bore are found, with emphasis on the role of the nonlocality of the nematic medium in shaping this structure. Excellent agreement between full numerical solutions of the governing nematicon equations and these analytical solutions is found.
Overview of the Simulation of Wave Interactions with MHD Project (SWIM)
NASA Astrophysics Data System (ADS)
Batchelor, Donald
2010-11-01
The SWIM center has the scientific objectives of: improving our understanding of interactions that both RF wave and particle sources have on extended-MHD phenomena, improving our capability for predicting and optimizing the performance of burning plasmas, developing an integrated computational system for treating multi-physics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project, addressing mathematics issues related to the multi-scale, coupled physics of RF waves and extended MHD, and optimizing the integrated system on high performance computers. Our Center has now built an end-to-end computational system that allows existing physics codes to be able to function together in a parallel environment and connects them to utility software components and data management systems. We have used this framework to couple together state-of-the-art fusion energy codes to produce a unique and world-class simulation capability. A physicist's overview of the Integrated Plasma Simulator (IPS) will be given and applications described. For example the IPS is being employed to support ITER with operational scenario studies.
A Finite Difference-Augmented Peridynamics Method for Wave Dispersion
2014-10-21
ARL-RP-0531 ● AUG 2015 US Army Research Laboratory A Finite Difference- Augmented Peridynamics Method for Wave Dispersion by...AUG 2015 US Army Research Laboratory A Finite Difference- Augmented Peridynamics Method for Wave Dispersion by Raymond A Wildman and George...Difference- Augmented Peridynamics Method for Wave Dispersion 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S
Localization of Dispersive Alfvén Wave in Solar wind plasmas and Turbulent Spectrum
NASA Astrophysics Data System (ADS)
Sharma, Swati; Sharma, R. P.
2016-07-01
Solar wind turbulence at large inertial scales is well known for decades and believed to consist of Alfvén cascade. The inertial range of Solar wind turbulence can be described by a magnetohydrodynamic model. But at small scales the MHD description is not valid. At scales of the order of proton inertial length, Alfvén cascade excites kinetic Alfvén wave or fast wave or whistler wave that carries wave energy to smaller scales. On the other hand, parallel propagating right(R) and left(L) circularly polarized Alfvén/ ion cyclotron wave in the framework of Hall MHD are also thought to be essential ingredients of the solar wind turbulence. Recently, He et.al[1] have used the magnetic field data from the STEREO spacecraft to calculate the magnetic helicities in the solar wind turbulence and reported the possible existence of Alfvén -cyclotron waves and their coexistence with the right handed polarized fluctuations. In the present article we intend to study the right circularly polarized dispersive Alfvén wave (DAW) and their role in the solar wind turbulence. The inclusion of the Hall term causes the dispersion of the AW which, in the present study, is considered on account of the finite frequency (frequency comparable to ion gyro frequency) of the pump wave. Filamentation instability has been reported to occur for the case of circularly polarized dispersive Alfvén wave (DAW) propagating parallel to ambient magnetic field. In the present study, the instability arises on account of the transverse density perturbations of the acoustic wave that may couple nonlinearly with the Alfvén wave and the driven ponderomotive force sequentially leads to growth of density perturbations. Numerical simulation involves finite difference method for the time domain and pseudo spectral method for the spatial domain. The power spectrum is investigated which shows a steepening for scales larger than the proton inertial length. These findings have been reported by Alexandrova et al
Single-mode dispersive waves and soliton microcomb dynamics
NASA Astrophysics Data System (ADS)
Yi, Xu; Yang, Qi-Fan; Zhang, Xueyue; Yang, Ki Youl; Li, Xinbai; Vahala, Kerry
2017-03-01
Dissipative Kerr solitons are self-sustaining optical wavepackets in resonators. They use the Kerr nonlinearity to both compensate dispersion and offset optical loss. Besides providing insights into nonlinear resonator physics, they can be applied in frequency metrology, precision clocks, and spectroscopy. Like other optical solitons, the dissipative Kerr soliton can radiate power as a dispersive wave through a process that is the optical analogue of Cherenkov radiation. Dispersive waves typically consist of an ensemble of optical modes. Here, a limiting case is studied in which the dispersive wave is concentrated into a single cavity mode. In this limit, its interaction with the soliton induces hysteresis behaviour in the soliton's spectral and temporal properties. Also, an operating point of enhanced repetition-rate stability occurs through balance of dispersive-wave recoil and Raman-induced soliton-self-frequency shift. The single-mode dispersive wave can therefore provide quiet states of soliton comb operation useful in many applications.
Amplitude-dependent Lamb wave dispersion in nonlinear plates.
Packo, Pawel; Uhl, Tadeusz; Staszewski, Wieslaw J; Leamy, Michael J
2016-08-01
The paper presents a perturbation approach for calculating amplitude-dependent Lamb wave dispersion in nonlinear plates. Nonlinear dispersion relationships are derived in closed form using a hyperelastic stress-strain constitutive relationship, the Green-Lagrange strain measure, and the partial wave technique integrated with a Lindstedt-Poincaré perturbation approach. Solvability conditions are derived using an operator formalism with inner product projections applied against solutions to the adjoint problem. When applied to the first- and second-order problems, these solvability conditions lead to amplitude-dependent, nonlinear dispersion corrections for frequency as a function of wavenumber. Numerical simulations verify the predicted dispersion shifts for an example nonlinear plate. The analysis and identification of amplitude-dependent, nonlinear Lamb wave dispersion complements recent research focusing on higher harmonic generation and internally resonant waves, which require precise dispersion relationships for frequency-wavenumber matching.
Phase patterns of dispersive waves from moving localized sources
NASA Astrophysics Data System (ADS)
Svirkunov, P. N.; Kalashnik, M. V.
2014-01-01
A general approach is proposed within which the phase structure of wave perturbations caused by a moving localized source can be described based on the wave dispersion law alone. Applying this approach, a simple analytical expression for the phase surfaces is obtained. It is used to study the details of phase patterns of gravity-capillary waves, the structure of wave trains in the ocean in the wake of a moving tropical hurricane, and the system of lee waves in Earth's atmosphere.
The interaction of chemical dispersants and suspended sediments with crude oil influences the fate and transport of oil spills in coastal waters. A wave tank study was conducted to investigate the effects of chemical dispersants and mineral fines on the dispersion of oil and the ...
Ultrabroadband Dispersive Radiation by Spatiotemporal Oscillation of Multimode Waves.
Wright, Logan G; Wabnitz, Stefan; Christodoulides, Demetrios N; Wise, Frank W
2015-11-27
In nonlinear dynamical systems, qualitatively distinct phenomena occur depending continuously on the size of the bounded domain containing the system. For nonlinear waves, a multimode waveguide is a bounded three-dimensional domain, allowing observation of dynamics impossible in open settings. Here we study radiation emitted by bounded nonlinear waves: the spatiotemporal oscillations of solitons in multimode fiber generate multimode dispersive waves over an ultrabroadband spectral range. This work suggests routes to sources of coherent electromagnetic waves with unprecedented spectral range.
NASA Technical Reports Server (NTRS)
Sakurai, Takashi; Goossens, Marcel; Hollweg, Joseph V.
1991-01-01
The present method of addressing the resonance problems that emerge in such MHD phenomena as the resonant absorption of waves at the Alfven resonance point avoids solving the fourth-order differential equation of dissipative MHD by recourse to connection formulae across the dissipation layer. In the second part of this investigation, the absorption of solar 5-min oscillations by sunspots is interpreted as the resonant absorption of sounds by a magnetic cylinder. The absorption coefficient is interpreted (1) analytically, under certain simplifying assumptions, and numerically, under more general conditions. The observed absorption coefficient magnitude is explained over suitable parameter ranges.
Long Distance Dispersal and Accelerating Waves of Disease: Empirical Relationships
Technology Transfer Automated Retrieval System (TEKTRAN)
Biological invasions have substantial ecological and economic impacts. Classic approaches to modeling biological invasions predict "traveling waves" with invasion fronts of constant velocity that are determined by an organism's reproductive capacity and its dispersal ability. These approaches are ba...
The Foggy EUV Corona and Coronal Heating by MHD Waves from Explosive Reconnection Events
NASA Technical Reports Server (NTRS)
Moore, Ron L.; Cirtain, Jonathan W.; Falconer, David A.
2008-01-01
In 0.5 arcsec/pixel TRACE coronal EUV images, the corona rooted in active regions that are at the limb and are not flaring is seen to consist of (1) a complex array of discrete loops and plumes embedded in (2) a diffuse ambient component that shows no fine structure and gradually fades with height. For each of two not-flaring active regions, found that the diffuse component is (1) approximately isothermal and hydrostatic and (2) emits well over half of the total EUV luminosity of the active-region corona. Here, from a TRACE Fe XII coronal image of another not-flaring active region, the large sunspot active region AR 10652 when it was at the west limb on 30 July 2004, we separate the diffuse component from the discrete loop component by spatial filtering, and find that the diffuse component has about 60% of the total luminosity. If under much higher spatial resolution than that of TRACE (e. g., the 0.1 arcsec/pixel resolution of the Hi-C sounding-rocket experiment proposed by J. W. Cirtain et al), most of the diffuse component remains diffuse rather being resolved into very narrow loops and plumes, this will raise the possibility that the EUV corona in active regions consists of two basically different but comparably luminous components: one being the set of discrete bright loops and plumes and the other being a truly diffuse component filling the space between the discrete loops and plumes. This dichotomy would imply that there are two different but comparably powerful coronal heating mechanisms operating in active regions, one for the distinct loops and plumes and another for the diffuse component. We present a scenario in which (1) each discrete bright loop or plume is a flux tube that was recently reconnected in a burst of reconnection, and (2) the diffuse component is heated by MHD waves that are generated by these reconnection events and by other fine-scale explosive reconnection events, most of which occur in and below the base of the corona where they are
Amplitude Dispersion Compensation for Damage Detection Using Ultrasonic Guided Waves.
Zeng, Liang; Lin, Jing; Huang, Liping; Zhao, Ming
2016-09-30
Besides the phase and group velocities, the amplitude of guided wave mode is also frequency dependent. This amplitude dispersion also influences the performance of guided wave methods in nondestructive evaluation (NDE) and structural health monitoring (SHM). In this paper, the effects of amplitude dispersion to the spectrum and waveform of a propagating wave-packet are investigated. It is shown that the amplitude dispersion results in distortion in the spectrum of guided wave response, and thus influences the waveform of the wave-packet. To remove these effects, an amplitude dispersion compensation method is established on the basis of Vold-Kalman filter and Taylor series expansion. The performance of that method is then investigated by experimental examples. The results show that with the application of the amplitude dispersion compensation, the time reversibility could be preserved, which ensures the applicability of the time reversal method for damage detection. Besides, through amplitude dispersion compensation, the testing resolution of guided waves could be improved, so that the structural features located in the close proximity may be separately identified.
Amplitude Dispersion Compensation for Damage Detection Using Ultrasonic Guided Waves
Zeng, Liang; Lin, Jing; Huang, Liping; Zhao, Ming
2016-01-01
Besides the phase and group velocities, the amplitude of guided wave mode is also frequency dependent. This amplitude dispersion also influences the performance of guided wave methods in nondestructive evaluation (NDE) and structural health monitoring (SHM). In this paper, the effects of amplitude dispersion to the spectrum and waveform of a propagating wave-packet are investigated. It is shown that the amplitude dispersion results in distortion in the spectrum of guided wave response, and thus influences the waveform of the wave-packet. To remove these effects, an amplitude dispersion compensation method is established on the basis of Vold–Kalman filter and Taylor series expansion. The performance of that method is then investigated by experimental examples. The results show that with the application of the amplitude dispersion compensation, the time reversibility could be preserved, which ensures the applicability of the time reversal method for damage detection. Besides, through amplitude dispersion compensation, the testing resolution of guided waves could be improved, so that the structural features located in the close proximity may be separately identified. PMID:27706067
Experimental investigation of two oil dispersion pathways by breaking waves
NASA Astrophysics Data System (ADS)
Li, Cheng; Katz, Joseph
2014-11-01
This experimental study focuses on generation and size distribution of airborne and subsurface oil droplets as breaking surface waves interact with a crude oil slick (MC252 surrogate). Experiments in a specialized wave tank investigate the effects of wave height and wave properties (e.g. spilling vs. plunging), as well as drastically reducing the oil-water interfacial tension by orders of magnitude by introducing dispersant (Coexist 9500-A). This dispersant is applied at varying dispersant-to-oil ratios either by premixing or surface spraying, the latter consistent with typical application. The data include high-speed visualizations of processes affecting the entrainment of subsurface oil and bubbles as well as airborne aerosols. High-speed digital holographic cinematography is employed to track the droplet trajectories, and quantify the droplet size distributions above and below the surface. Introduction of dispersants drastically reduces the size of subsurface droplets to micron and even submicron levels. Ahead of the wave, the 25 μm (our present resolution limit) to 2 mm airborne droplet trajectories are aligned with the wave direction. Behind the wave, these droplets reverse their direction, presumably due to the airflow above the wave. Supported by Gulf of Mexico Research Initiative (GoMRI).
Alfven wave dispersion behavior in single- and multicomponent plasmas
Rahbarnia, K.; Grulke, O.; Klinger, T.; Ullrich, S.; Sauer, K.
2010-03-15
Dispersion relations of driven Alfven waves (AWs) are measured in single- and multicomponent plasmas consisting of mixtures of argon, helium, and oxygen in a magnetized linear cylindrical plasma device VINETA [C. Franck, O. Grulke, and T. Klinger, Phys. Plasmas 9, 3254 (2002)]. The decomposition of the measured three-dimensional magnetic field fluctuations and the corresponding parallel current pattern reveals that the wave field is a superposition of L- and R-wave components. The dispersion relation measurements agree well with calculations based on a multifluid Hall-magnetohydrodynamic model if the plasma resistivity is correctly taken into account.
Rogue waves in a normal-dispersion fiber laser.
Liu, Zhanwei; Zhang, Shumin; Wise, F W
2015-04-01
Experimental evidence of rogue-wave formation in a normal-dispersion ytterbium fiber laser is reported. Spectral filtering is a primary component of pulse-shaping in normal-dispersion lasers, and we find that the choice of filter dramatically influences the distribution of noise-pulse energies produced by these lasers. With an interference filter in the cavity, non-Gaussian distributions with pulses as large as 6 times the significant wave height are observed. These correspond to pulse energies as high as ∼50 nJ. To our knowledge, the results presented are not accounted for by existing theoretical models of rogue-wave formation.
High resolution surface wave dispersion studies in China
Jones, L.E.; Patton, H.J.
1997-11-01
The Los Alamos National Laboratory regional calibration project is actively assembling a database of surface-wave dispersion information for China and surrounding areas. As part of the effort to characterize surface wave dispersion in China, we integrate prior long period results from the University of Colorado with our shorter period dispersion measurements in a high resolution survey of key monitoring areas. Focusing on western China initially, we employ broadband data recorded on CDSN stations, and regional events (m{sub b} 4 and above). Our approach is twofold, employing path specific calibration of key stations and well-recorded reference events, and tomographic inference to provide group velocity curves for regions with sparse station distribution and little seismic activity. Initial dispersion studies at Chinese stations WMQ and LZH show substantial azimuthal variation in dispersion, reinforcing the need for careful determination of source regions for path-specific calibration.
A test of the Hall-MHD model: Application to low-frequency upstream waves at Venus
NASA Technical Reports Server (NTRS)
Orlowski, D. S.; Russell, C. T.; Krauss-Varban, D.; Omidi, N.
1994-01-01
Early studies suggested that in the range of parameter space where the wave angular frequency is less than the proton gyrofrequency and the plasma beta, the ratio of the thermal to magnetic pressure, is less than 1 magnetohydrodynamics provides an adequate description of the propagating modes in a plasma. However, recently, Lacombe et al. (1992) have reported significant differences between basic wave characteristics of the specific propagation modes derived from linear Vlasov and Hall-magnetohydrodynamic (MHD) theories even when the waves are only weakly damped. In this paper we compare the magnetic polarization and normalization magnetic compression ratio of ultra low frequency (ULF) upstream waves at Venus with magnetic polarization and normalized magnetic compression ratio derived from both theories. We find that while the 'kinetic' approach gives magnetic polarization and normalized magnetic compression ratio consistent with the data in the analyzed range of beta (0.5 less than beta less than 5) for the fast magnetosonic mode, the same wave characteristics derived from the Hall-MHD model strongly depend on beta and are consistent with the data only at low beta for the fast mode and at high beta for the intermediate mode.
Kinetic dispersion of Langmuir waves. I. The Langmuir decay instability
NASA Astrophysics Data System (ADS)
Palastro, J. P.; Williams, E. A.; Hinkel, D. E.; Divol, L.; Strozzi, D. J.
2009-09-01
We derive a fully kinetic, three-dimensional dispersion relation for Langmuir waves with a focus on the Langmuir decay instability (LDI). The kinetic dispersion is compared to the standard fluid dispersion found with an equation of state (EOS) closure. The EOS closure fails to capture the intricacies of the nonlinear pressure when high frequency electron plasma waves (EPWs) couple to low frequency ion acoustic waves (IAWs). In particular, we find discrepancies in the kλd scaling of the LDI growth rate, where k is the wavenumber of the incident EPW and λd is the Debye length. As a result, the kinetic dispersion relation for LDI results in instability thresholds that can be in excess of twice those predicted by the fluid theory. Both the fluid and kinetic dispersion relations predict a nonlinear frequency shift due to the beating of the pump and scattered EPWs, but again the kλd scaling of these frequency shifts differ. In addition, the kinetic dispersion predicts a nonlinear reduction in the IAW damping from the three-wave interaction.
Kinetic dispersion of Langmuir waves. I. The Langmuir decay instability
Palastro, J. P.; Williams, E. A.; Hinkel, D. E.; Divol, L.; Strozzi, D. J.
2009-09-15
We derive a fully kinetic, three-dimensional dispersion relation for Langmuir waves with a focus on the Langmuir decay instability (LDI). The kinetic dispersion is compared to the standard fluid dispersion found with an equation of state (EOS) closure. The EOS closure fails to capture the intricacies of the nonlinear pressure when high frequency electron plasma waves (EPWs) couple to low frequency ion acoustic waves (IAWs). In particular, we find discrepancies in the k{lambda}{sub d} scaling of the LDI growth rate, where k is the wavenumber of the incident EPW and {lambda}{sub d} is the Debye length. As a result, the kinetic dispersion relation for LDI results in instability thresholds that can be in excess of twice those predicted by the fluid theory. Both the fluid and kinetic dispersion relations predict a nonlinear frequency shift due to the beating of the pump and scattered EPWs, but again the k{lambda}{sub d} scaling of these frequency shifts differ. In addition, the kinetic dispersion predicts a nonlinear reduction in the IAW damping from the three-wave interaction.
P-wave dispersion: What we know till now?
Aytemir, Kudret; Oto, Ali
2016-01-01
P-wave dispersion is defined as the difference between the maximum and the minimum P-wave duration recorded from multiple different-surface ECG leads. It has been known that increased P-wave duration and P-wave dispersion reflect prolongation of intraatrial and interatrial conduction time and the inhomogeneous propagation of sinus impulses, which are well-known electrophysiologic characteristics in patients with atrial arrhythmias and especially paroxysmal atrial fibrillation. Extensive clinical evaluation of P-wave dispersion has been performed in the assessment of the risk for atrial fibrillation in patients without apparent heart disease, in hypertensives, in patients with coronary artery disease, in patients undergoing coronary artery bypass surgery, in patients with congenital heart diseases, as well as in other groups of patients suffering from various cardiac or non-cardiac diseases. In this paper, we aimed to summarize the measurement methods, current use in different clinical situations, strengths and limitations of the of P-wave dispersion. PMID:27081484
Wave propagation in strongly dispersive superthermal dusty plasma
NASA Astrophysics Data System (ADS)
El-Labany, S. K.; El-Shewy, E. K.; Abd El-Razek, H. N.; El-Rahman, A. A.
2017-04-01
The attributes of acoustic envelope waves in a collisionless dust ion unmagnetized plasmas model composed of cold ions, superthermal electrons and positive-negative dust grains have been studied. Using the derivative expansion technique in a strong dispersive medium, the system model is reduced to a nonlinearly form of Schrodinger equation (NLSE). Rational solution of NLSE in unstable region is responsible for the creation of large shape waves; namely rogue waves. The subjection of instability regions upon electron superthermality (via κ), carrier wave number and dusty grains charge is discussed.
A fractional calculus model of anomalous dispersion of acoustic waves.
Wharmby, Andrew W
2016-09-01
An empirical formula based on viscoelastic analysis techniques that employs concepts from the fractional calculus that was used to model the dielectric behavior of materials exposed to oscillating electromagnetic fields in the radiofrequency, terahertz, and infrared bands. This work adapts and applies the formula to model viscoelastic behavior of materials that show an apparent increase of phase velocity of vibration with an increase in frequency, otherwise known as anomalous dispersion. A fractional order wave equation is derived through the application of the classic elastic-viscoelastic correspondence principle whose analytical solution is used to describe absorption and dispersion of acoustic waves in the viscoelastic material displaying anomalous dispersion in a specific frequency range. A brief discussion and comparison of an alternative fractional order wave equation recently formulated is also included.
Adiabatic theory of solitons fed by dispersive waves
NASA Astrophysics Data System (ADS)
Pickartz, Sabrina; Bandelow, Uwe; Amiranashvili, Shalva
2016-09-01
We consider scattering of low-amplitude dispersive waves at an intense optical soliton which constitutes a nonlinear perturbation of the refractive index. Specifically, we consider a single-mode optical fiber and a group velocity matched pair: an optical soliton and a nearly perfectly reflected dispersive wave, a fiber-optical analog of the event horizon. By combining (i) an adiabatic approach that is used in soliton perturbation theory and (ii) scattering theory from quantum mechanics, we give a quantitative account of the evolution of all soliton parameters. In particular, we quantify the increase in the soliton peak power that may result in the spontaneous appearance of an extremely large, so-called champion soliton. The presented adiabatic theory agrees well with the numerical solutions of the pulse propagation equation. Moreover, we predict the full frequency band of the scattered dispersive waves and explain an emerging caustic structure in the space-time domain.
Particle Scattering off of Right-handed Dispersive Waves
NASA Astrophysics Data System (ADS)
Schreiner, C.; Kilian, P.; Spanier, F.
2017-01-01
Resonant scattering of fast particles off low frequency plasma waves is a major process determining transport characteristics of energetic particles in the heliosphere and contributing to their acceleration. Usually, only Alfvén waves are considered for this process, although dispersive waves are also present throughout the heliosphere. We investigate resonant interaction of energetic electrons with dispersive, right-handed waves. For the interaction of particles and a single wave a variable transformation into the rest frame of the wave can be performed. Here, well-established analytic models derived in the framework of magnetostatic quasi-linear theory can be used as a reference to validate simulation results. However, this approach fails as soon as several dispersive waves are involved. Based on analytic solutions modeling the scattering amplitude in the magnetostatic limit, we present an approach to modify these equations for use in the plasma frame. Thereby we aim at a description of particle scattering in the presence of several waves. A particle-in-cell code is employed to study wave–particle scattering on a micro-physically correct level and to test the modified model equations. We investigate the interactions of electrons at different energies (from 1 keV to 1 MeV) and right-handed waves with various amplitudes. Differences between model and simulation arise in the case of high amplitudes or several waves. Analyzing the trajectories of single particles we find no microscopic diffusion in the case of a single plasma wave, although a broadening of the particle distribution can be observed.
Nonlinear Dispersive ALFVÉN Waves in Magnetoplasmas
NASA Astrophysics Data System (ADS)
Shukla, P. K.; Eliasson, B.; Stenflo, L.; Bingham, R.
2008-03-01
Large amplitude Alfvén waves are frequently found in magnetized space and laboratory plasmas. Our objective here is to discuss the linear and nonlinear properties of dispersive Alfvén waves (DAWs) in a uniform magnetoplasma. We first consider the effects of finite frequency (ω/ωci) and ion gyroradius on inertial and kinetic Alfvén waves, where ωci is the ion gyrofrequency. Next, we focus on nonlinear effects caused by the dispersive Alfvén waves. Such effects include the plasma density enhancement and depression by the Alfvén wave ponderomotive force, nonlinear interactions among the DAWs, the generation of zonal flows by the DAWs, as well as the electron and ion heating due to wave-particle interactions. The relevance of our investigation to the appearance of nonlinear dispersive Alfvén waves in the Earth's auroral acceleration region, in the solar corona, and in the Large Plasma Device (LAPD) at UCLA is discussed.
GENERAL: Periodic folded waves for a (2+1)-dimensional modified dispersive water wave equation
NASA Astrophysics Data System (ADS)
Huang, Wen-Hua
2009-08-01
A general solution, including three arbitrary functions, is obtained for a (2+1)-dimensional modified dispersive water-wave (MDWW) equation by means of the WTC truncation method. Introducing proper multiple valued functions and Jacobi elliptic functions in the seed solution, special types of periodic folded waves are derived. In the long wave limit these periodic folded wave patterns may degenerate into single localized folded solitary wave excitations. The interactions of the periodic folded waves and the degenerated single folded solitary waves are investigated graphically and found to be completely elastic.
Magnetostatic Wave Transducers, Resonators and Dispersion Control
1990-05-01
propagating at microwave frequencies in magnetically biased, liquid phase epitaxial films of Yttrium Iron Garnet (YIG) grown on Gadolinium Gallium Garnet... microwave energy for MSSW propagation along the YIG film. A 25 um-thick 3mm- wide YIG film and 15 um-thick Gadolinium Gallium Garnet (GGG) substrate was...stretching. Methods for providing these time delays include an assortment of fixed cables. ferrite loaded cables. surface acoustic wave iSA W) devices
Curvature-Induced Asymmetric Spin-Wave Dispersion
NASA Astrophysics Data System (ADS)
Otálora, Jorge A.; Yan, Ming; Schultheiss, Helmut; Hertel, Riccardo; Kákay, Attila
2016-11-01
In magnonics, spin waves are conceived of as electron-charge-free information carriers. Their wave behavior has established them as the key elements to achieve low power consumption, fast operative rates, and good packaging in magnon-based computational technologies. Hence, knowing alternative ways that reveal certain properties of their undulatory motion is an important task. Here, we show using micromagnetic simulations and analytical calculations that spin-wave propagation in ferromagnetic nanotubes is fundamentally different than in thin films. The dispersion relation is asymmetric regarding the sign of the wave vector. It is a purely curvature-induced effect and its fundamental origin is identified to be the classical dipole-dipole interaction. The analytical expression of the dispersion relation has the same mathematical form as in thin films with the Dzyalonshiinsky-Moriya interaction. Therefore, this curvature-induced effect can be seen as a "dipole-induced Dzyalonshiinsky-Moriya-like" effect.
Refractive phenomena in the shock wave dispersion with variable gradients
Markhotok, A.; Popovic, S.
2010-06-15
In this article the refraction effects in the weak shock wave (SW) dispersion on an interface with a temperature variation between two mediums are described. In the case of a finite-gradient boundary, the effect of the SW dispersion is remarkably stronger than in the case of a step change in parameters. In the former case the vertical component of velocity for the transmitted SW (the refraction effect) must be taken into account. Results of comparative calculations based on the two-dimensional model corrected for the refraction effect show significant differences in the shapes of the dispersed SW fronts.
Absorption of ultrasound waves during dynamic processes in disperse systems
NASA Astrophysics Data System (ADS)
Kol'tsova, I. S.; Khomutova, A. S.
2016-11-01
Measurements of ultrasound wave absorption are conducted at a frequency of 3 MHz in 3% suspensions of starch, gelatin, and lactose. It is shown that the dynamics of the additional ultrasound wave absorption coefficient in the suspensions carries information on the processes of swelling, dissolution, and the phase and structural periods occurring in the interaction of the disperse and dispersoid phases; it also reflects the influence of the temperature field on these processes.
Mode properties of low-frequency waves: Kinetic theory versus Hall-MHD
NASA Technical Reports Server (NTRS)
Krauss-Varban, D.; Omidi, N.; Quest, K. B.
1994-01-01
In fluid theory, the ordering of low-frequency modes in a homogeneous plasma is based on the phase velocity, since modes do not intersect each other in dispersion diagrams as a function of wavenumber or other parameters. In linear kinetic theory, modes cross each other. Thus a consistent and useful classification should be based on the physical properties of the modes instead. This paper attempts such a classification by documeting the dispersion and general mode properties of the low-frequency waves (omega much less than (OMEGA(sub ci) OMEGA(sub ce) (exp 1/2)), where OMEGA(sub ci), OMEGA(sub ce) are the cyclotron frequencies of the ions and electrons, respectively) in kinetic theory, and by comparing them to the results of two-fluid theory. Kinetic theory gives a seperate Alfven/ion-cyclotron (A/IC) wave with phase speed Omega/k approximately = v(sub A) cos theta for omega much less than OMEGA(sub ci), where v(sub A) is the Alfven velocity and theta the angle of propagation between wave vector k and background magnetic field B(sub o). For a given wavenumber, the magnetosonic mode is a double-valued solution with a singular point in theta, beta parameter space, where beta is the ratio of thermal pressure to magnetic pressure. It is shown that a branch cut starting at the singular point theta approximately 30 deg, beta approximately 3 and leading to larger beta gives a practical and consitent seperation of this double-valued magnetosonic solution. Selection of this branch cut results in a moderately damped fast/magnetos onic and a heavily damped slow/sound wave. A comprehensive review of the polarization, compressibility and other mode properties is given and shown to be consistent with the selected branch cut. At small wavenumbers, the kinetic mode properties typically start to deviate significantly from their fluid counterparts at beta approximately 0.5. At larger beta, there is no longer a consistent correspondence between the fluid and kinetic modes. Kinetic
Dispersion of seed vapor and gas ionization in an MHD second stage combustor and channel
Chang, S.L.; Lottes, S.A.; Bouillard, J.X.
1992-07-01
An approach is introduced for the simulation of a magnetohydrodynamic system consisting of a second stage combustor, a convergent nozzle, and a channel. The simulation uses an Argonne integral combustion flow computer code and another Argonne channel computer code to predict flow, thermal and electric properties in the seed particle laden reacting flow in the system. The combustion code is a general hydrodynamics computer code for two-phase, two-dimensional, turbulent, and reacting flows, based on mass, momentum, and energy conservation laws for gaseous and condensed phases. The channel code is a multigrid three-dimensional computer code for compressible flow subject to magnetic and electric interactions. Results of this study suggests that (1) the processes of seed particle evaporation, seed vapor dispersion, and gas ionization in the reacting flow are critical to the evaluation of the downstream channel performance and (2) particle size, loading, and inlet profile have strong effects on wall deposition and plasma temperature development.
Dispersion of seed vapor and gas ionization in an MHD second stage combustor and channel
Chang, S.L.; Lottes, S.A.; Bouillard, J.X.
1992-01-01
An approach is introduced for the simulation of a magnetohydrodynamic system consisting of a second stage combustor, a convergent nozzle, and a channel. The simulation uses an Argonne integral combustion flow computer code and another Argonne channel computer code to predict flow, thermal and electric properties in the seed particle laden reacting flow in the system. The combustion code is a general hydrodynamics computer code for two-phase, two-dimensional, turbulent, and reacting flows, based on mass, momentum, and energy conservation laws for gaseous and condensed phases. The channel code is a multigrid three-dimensional computer code for compressible flow subject to magnetic and electric interactions. Results of this study suggests that (1) the processes of seed particle evaporation, seed vapor dispersion, and gas ionization in the reacting flow are critical to the evaluation of the downstream channel performance and (2) particle size, loading, and inlet profile have strong effects on wall deposition and plasma temperature development.
Dispersion of seed vapor and gas ionization in an MHD second stage combustor and channel
NASA Astrophysics Data System (ADS)
Chang, S. L.; Lottes, S. A.; Bouillard, J. X.
An approach is introduced for the simulation of a magnetohydrodynamic system consisting of a second stage combustor, a convergent nozzle, and a channel. The simulation uses an Argonne integral combustion flow computer code and another Argonne channel computer code to predict flow, thermal and electric properties in the seed particle laden reacting flow in the system. The combustion code is a general hydrodynamics computer code for two-phase, two-dimensional, turbulent, and reacting flows, based on mass, momentum, and energy conservation laws for gaseous and condensed phases. The channel code is a multigrid three-dimensional computer code for compressible flow subject to magnetic and electric interactions. Results of this study suggests that (1) the processes of seed particle evaporation, seed vapor dispersion, and gas ionization in the reacting flow are critical to the evaluation of the downstream channel performance, and (2) particle size, loading, and inlet profile have strong effects on wall deposition and plasma temperature development.
Partial Wave Dispersion Relations: Application to Electron-Atom Scattering
NASA Technical Reports Server (NTRS)
Temkin, A.; Drachman, Richard J.
1999-01-01
In this Letter we propose the use of partial wave dispersion relations (DR's) as the way of solving the long-standing problem of correctly incorporating exchange in a valid DR for electron-atom scattering. In particular a method is given for effectively calculating the contribution of the discontinuity and/or poles of the partial wave amplitude which occur in the negative E plane. The method is successfully tested in three cases: (i) the analytically solvable exponential potential, (ii) the Hartree potential, and (iii) the S-wave exchange approximation for electron-hydrogen scattering.
The Gaussian Shear Wave in a Dispersive Medium
Parker, Kevin J.; Baddour, Natalie
2014-01-01
Within the field of “imaging the biomechanical properties of tissues,” a number of approaches analyze shear wave propagation initiated by a short radiation force push. Unfortunately, it is experimentally observed that the displacement vs. time curves in lossy tissues are rapidly damped and distorted in ways that confound any simple tracking approach. This paper addresses the propagation, decay, and distortion of pulses in lossy and dispersive media, in order to derive closed form analytic expressions for the propagating pulses. The theory identifies key terms that drive the distortion and broadening of the pulse. Furthermore, the approach taken is not dependent on any particular viscoelastic model of tissue, but instead takes a general first order approach to dispersion. Examples with a Gaussian beam pattern and realistic dispersion parameters are given along with general guidelines for identifying the features of the distorting wave that are the most compact. PMID:24412170
Measurement of elastic wave dispersion on human femur tissue
NASA Astrophysics Data System (ADS)
Strantza, M.; Louis, O.; Polyzos, D.; Boulpaep, F.; Van Hemelrijck, D.; Aggelis, D. G.
2014-03-01
Cortical bone is one of the most complex heterogeneous media exhibiting strong wave dispersion. In such media when a burst of energy goes into the formation of elastic waves the different modes tend to separate according to the velocities of the frequency components as usually occurs in waveguides. In this study human femur specimens were subjected to elastic wave measurements. The main objective of the study is using broadband acoustic emission sensors to measure parameters like wave velocity dispersion and attenuation. Additionally, waveform parameters like the duration, rise time and average frequency, are also examined relatively to the propagation distance as a preparation for acoustic emission monitoring during fracture. To do so, four sensors were placed at adjacent positions on the surface of the cortical bone in order to record the transient response after pencil lead break excitation. The results are compared to similar measurements on a bulk metal piece which does not exhibit heterogeneity at the scale of the propagating wave lengths. It is shown that the microstructure of the tissue imposes a dispersive behavior for frequencies below 1 MHz and care should be taken for interpretation of the signals.
Berryman, J G; Pride, S R
2004-07-28
Laboratory experiments on wave propagation through saturated and partially saturated porous media have often been conducted on porous cylinders that were initially fully saturated and then allowed to dry while continuing to acquire data on the wave behavior. Since it is known that drying typically progresses from outside to inside, a sensible physical model of this process is concentric cylinders having different saturation levels--the simplest example being a fully dry outer cylindrical shell together with a fully wet inner cylinder. We use this model to formulate the equations for wave dispersion in porous cylinders for patchy saturation (i.e. drainage) conditions. In addition to multiple modes of propagation obtained numerically from these dispersion relations, we find two distinct analytical expressions for torsional wave modes. We solve the dispersion relation for torsional waves for two examples: Massillon sandstone and Sierra White granite. The drainage analysis appears to give improved agreement with the data for both these materials.
NASA Astrophysics Data System (ADS)
Antolin, P.; De Moortel, I.; Van Doorsselaere, T.; Yokoyama, T.
2016-10-01
In the highly structured solar corona, resonant absorption is an unavoidable mechanism of energy transfer from global transverse MHD waves to local azimuthal Alfvén waves. Due to its localized nature, direct detection of this mechanism is extremely difficult. Yet, it is the leading theory explaining the observed fast damping of the global transverse waves. However, at odds with this theoretical prediction are recent observations that indicate that in the low-amplitude regime such transverse MHD waves can also appear decay-less, a still unsolved phenomenon. Recent numerical work has shown that Kelvin-Helmholtz instabilities (KHI) often accompany transverse MHD waves. In this work, we combine 3D MHD simulations and forward modeling to show that for currently achieved spatial resolution and observed small amplitudes, an apparent decay-less oscillation is obtained. This effect results from the combination of periodic brightenings produced by the KHI and the coherent motion of the KHI vortices amplified by resonant absorption. Such an effect is especially clear in emission lines forming at temperatures that capture the boundary dynamics rather than the core, and reflects the low damping character of the local azimuthal Alfvén waves resonantly coupled to the kink mode. Due to phase mixing, the detected period can vary depending on the emission line, with those sensitive to the boundary having shorter periods than those sensitive to the loop core. This allows us to estimate the density contrast at the boundary.
Li, Zhengkai; Kepkay, Paul; Lee, Kenneth; King, Thomas; Boufadel, Michel C; Venosa, Albert D
2007-07-01
The interaction of chemical dispersants and suspended sediments with crude oil influences the fate and transport of oil spills in coastal waters. A wave tank study was conducted to investigate the effects of chemical dispersants and mineral fines on the dispersion of oil and the formation of oil-mineral-aggregates (OMAs) in natural seawater. Results of ultraviolet spectrofluorometry and gas chromatography flame ionized detection analysis indicated that dispersants and mineral fines, alone and in combination, enhanced the dispersion of oil into the water column. Measurements taken with a laser in situ scattering and transmissometer (LISST-100X) showed that the presence of mineral fines increased the total concentration of the suspended particles from 4 to 10microl l(-1), whereas the presence of dispersants decreased the particle size (mass mean diameter) of OMAs from 50 to 10microm. Observation with an epifluorescence microscope indicated that the presence of dispersants, mineral fines, or both in combination significantly increased the number of particles dispersed into the water.
Mode separation of Lamb waves based on dispersion compensation method.
Xu, Kailiang; Ta, Dean; Moilanen, Petro; Wang, Weiqi
2012-04-01
Ultrasonic Lamb modes typically propagate as a combination of multiple dispersive wave packets. Frequency components of each mode distribute widely in time domain due to dispersion and it is very challenging to separate individual modes by traditional signal processing methods. In the present study, a method of dispersion compensation is proposed for the purpose of mode separation. This numerical method compensates, i.e., compresses, the individual dispersive waveforms into temporal pulses, which thereby become nearly un-overlapped in time and frequency and can thus be extracted individually by rectangular time windows. It was further illustrated that the dispersion compensation also provided a method for predicting the plate thickness. Finally, based on reversibility of the numerical compensation method, an artificial dispersion technique was used to restore the original waveform of each mode from the separated compensated pulse. Performances of the compensation separation techniques were evaluated by processing synthetic and experimental signals which consisted of multiple Lamb modes with high dispersion. Individual modes were extracted with good accordance with the original waveforms and theoretical predictions.
Spatial Statistics of Deep-Water Ambient Noise; Dispersion Relations for Sound Waves and Shear Waves
2015-09-30
Environmental and system data will also be depth-profiled, including temperature , salinity, pressure and (directly measured) sound speed, along...configurations, and an environmental sensor package [Conductivity- Temperature - Depth sensor (CTD) plus sound speed sensor (SVX)]. The system is untethered...Dispersion Relations for Sound Waves and Shear Waves Michael J. Buckingham Marine Physical Laboratory, Scripps Institution of Oceanography University
Multi-instrument observations of a failed flare eruption associated with MHD waves in a loop bundle
NASA Astrophysics Data System (ADS)
Nisticò, G.; Polito, V.; Nakariakov, V. M.; Del Zanna, G.
2017-03-01
Context. We present observations of a B7.9-class flare that occurred on the 24th January, 2015, using the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO), the EUV Imaging Spectrometer (EIS) and the X-Ray Telescope of Hinode. The flare triggers the eruption of a dense cool plasma blob as seen in AIA 171 Å, which is unable to completely break out and remains confined within a local bundle of active region loops. During this process, transverse oscillations of the threads are observed. The cool plasma is then observed to descend back to the chromosphere along each loop strand. At the same time, a larger diffuse co-spatial loop observed in the hot wavebands of SDO/AIA and Hinode/XRT is formed, exhibiting periodic intensity variations along its length. Aims: The formation and evolution of magnetohydrodynamic (MHD) waves depend upon the values of the local plasma parameters (e.g. density, temperature and magnetic field), which can hence be inferred by coronal seismology. In this study we aim to assess how the observed MHD modes are affected by the variation of density and temperature. Methods: We combined analysis of EUV/X-ray imaging and spectroscopy using SDO/AIA, Hinode/EIS and XRT. Results: The transverse oscillations of the cool loop threads are interpreted in terms of vertically polarised kink oscillations. The fitting procedure applied to the loop displacement time series gives a period of 3.5 to 4 min, and an amplitude of 5 Mm. The oscillations are strongly damped showing very low quality factor (1.5-2), which is defined as the ratio of the damping time and the oscillation period. The weak variation of the period of the kink wave, which is estimated from the fitting analysis, is in agreement with the density variations due to the presence of the plasma blob inferred from the intensity light curve at 171 Å. The coexisting intensity oscillations along the hot loop are interpreted as a slow MHD wave with a period of 10 min and phase
Three-dimensional, time-dependent, MHD model of a solar flare-generated interplanetary shock wave
NASA Technical Reports Server (NTRS)
Dryer, M.; Wu, S. T.; Han, S. M.
1986-01-01
A three-dimensional time-dependent MHD model of the propagation of an interplanetary shock wave into an ambient three-dimensional heliospheric solar wind is initialized with a peak velocity of 1000 km/s at the center of a right circular cone of 18 deg included angle at 18 solar radii. Differences from a previous 2-1/2 simulation (Wu et al., 1983; Gislason et al., 1984; Dryer et al., 1984) include diminuation of the solar peak velocity and concentration of the peak density at each radius. The IMF magnitude starts with high-latitude peaks, and helical-like IMF rotation is noted due to a large-amplitude nonlinear Alfven wave in the shocked plasma.
Dispersion relations for electromagnetic wave propagation in chiral plasmas
Gao, M. X.; Guo, B. Peng, L.; Cai, X.
2014-11-15
The dispersion relations for electromagnetic wave propagation in chiral plasmas are derived using a simplified method and investigated in detail. With the help of the dispersion relations for each eignwave, we explore how the chiral plasmas exhibit negative refraction and investigate the frequency region for negative refraction. The results show that chirality can induce negative refraction in plasmas. Moreover, both the degree of chirality and the external magnetic field have a significant effect on the critical frequency and the bandwidth of the frequency for negative refraction in chiral plasmas. The parameter dependence of the effects is calculated and discussed.
Dispersion-Engineered Traveling Wave Kinetic Inductance Parametric Amplifier
NASA Technical Reports Server (NTRS)
Zmuidzinas, Jonas (Inventor); Day, Peter K. (Inventor)
2014-01-01
A traveling wave kinetic inductance parametric amplifier comprises a superconducting transmission line and a dispersion control element. The transmission line can include periodic variations of its dimension along its length. The superconducting material can include a high normal state resistivity material. In some instances the high normal state resistivity material includes nitrogen and a metal selected from the group consisting of titanium, niobium and vanadium. The traveling wave kinetic inductance parametric amplifier is expected to exhibit a noise temperature below 100 mK/GHz.
Li, Zhengkai; Lee, Kenneth; King, Thomas; Boufadel, Michel C; Venosa, Albert D
2009-05-01
Testing dispersant effectiveness under conditions similar to that of the open environment is required for improvements in operational procedures and the formulation of regulatory guidelines. To this end, a novel wave tank facility was fabricated to study the dispersion of crude oil under regular non-breaking and irregular breaking wave conditions. This wave tank facility was designed for operation in a flow-through mode to simulate both wave- and current-driven hydrodynamic conditions. We report here an evaluation of the effectiveness of chemical dispersants (Corexit EC9500A and SPC 1000) on two crude oils (Medium South American [MESA] and Alaska North Slope [ANS]) under two different wave conditions (regular non-breaking and plunging breaking waves) in this wave tank. The dispersant effectiveness was assessed by measuring the water column oil concentration and dispersed oil droplet size distribution. In the absence of dispersants, nearly 8-19% of the test crude oils were dispersed and diluted under regular wave and breaking wave conditions. In the presence of dispersants, about 21-36% of the crude oils were dispersed and diluted under regular waves, and 42-62% under breaking waves. Consistently, physical dispersion under regular waves produced large oil droplets (volumetric mean diameter or VMD > or = 300 microm), whereas chemical dispersion under breaking waves created small droplets (VMD < or = 50 microm). The data can provide useful information for developing better operational guidelines for dispersant use and improved predictive models on dispersant effectiveness in the field.
Modeling Gravitational Waves to Test GR Dispersion and Polarization
NASA Astrophysics Data System (ADS)
Tso, Rhondale; Chen, Yanbei; Isi, Maximilliano
2017-01-01
Given continued observation runs from the Laser Interferometer Gravitational-Wave Observatory Scientific Collaboration, further gravitational wave (GW) events will provide added constraints on beyond-general relativity (b-GR) theories. One approach, independent of the GW generation mechanism at the source, is to look at modification to the GW dispersion and propagation, which can accumulate over vast distances. Generic modification of GW propagation can also, in certain b-GR theories, impact the polarization content of GWs. To this end, a comprehensive approach to testing the dispersion and polarization content is developed by modeling anisotropic deformations to the waveforms' phase, along with birefringence effects and corollary consequences for b-GR polarizations, i.e., breathing, vector, and longitudinal modes. Such an approach can be mapped to specific theories like Lorentz violation, amplitude birefringence in Chern-Simons, and provide hints at additional theories to be included. An overview of data analysis routines to be implemented will also be discussed.
Ultrasonic wave velocity in the restructuring of disperse media
NASA Astrophysics Data System (ADS)
Koltsova, I. S.; Khomutova, A. S.; Deinega, M. A.
2016-03-01
The ultrasonic wave velocities in the restructuring of disperse media were measured using interference and pulsed techniques and the coefficient of reflection in suspensions of starch, Al2O3, and SiO2 particles, glass bulbs, their porous sediments, and composites of Fe3O4 particles in 10% gelatin aqueous solution at a frequency of 3 MHz. The experiments showed alternating variation in the concentration velocity coefficient during the transition of the dispersed phase concentration from the subpercolation to percolation region. The minimum ultrasonic wave velocity in the region of discrete clusters correlates with the ratio between the particle and matrix densities. The results obtained are explained using the Isakovich, Chaban, Rytov, Biot, Hausdorff, and other theories.
Dispersion of waves in relativistic plasmas with isotropic particle distributions
Shcherbakov, Roman V.
2009-03-15
The dispersion laws of Langmuir and transverse waves are calculated in the relativistic nonmagnetized formalism for several isotropic particle distributions: thermal, power law, relativistic Lorentzian {kappa}, and hybrid {beta}. For Langmuir waves the parameters of superluminal undamped, subluminal damped principal, and higher modes are determined for a range of distribution parameters. The undamped and principal damped modes are found to match smoothly. Principal damped and second damped modes are found not to match smoothly. The presence of maximum wavenumber is discovered above that no longitudinal modes formally exist. The higher damped modes are discovered to be qualitatively different for thermal and certain nonthermal distributions. Consistently with the known results, the Landau damping is calculated to be stronger for nonthermal power-law-like distributions. The dispersion law is obtained for the single undamped transverse mode. The analytic results for the simplest distributions are provided.
Optical dispersive shock waves in defocusing colloidal media
NASA Astrophysics Data System (ADS)
An, X.; Marchant, T. R.; Smyth, N. F.
2017-03-01
The propagation of an optical dispersive shock wave, generated from a jump discontinuity in light intensity, in a defocusing colloidal medium is analysed. The equations governing nonlinear light propagation in a colloidal medium consist of a nonlinear Schrödinger equation for the beam and an algebraic equation for the medium response. In the limit of low light intensity, these equations reduce to a perturbed higher order nonlinear Schrödinger equation. Solutions for the leading and trailing edges of the colloidal dispersive shock wave are found using modulation theory. This is done for both the perturbed nonlinear Schrödinger equation and the full colloid equations for arbitrary light intensity. These results are compared with numerical solutions of the colloid equations.
The dispersion relations of dispersive Alfvén waves in superthermal plasmas
NASA Astrophysics Data System (ADS)
Gaelzer, Rudi; Ziebell, Luiz F.
2014-12-01
The effects of velocity distribution functions (VDFs) that exhibit a power law dependence on the high-energy tail have been the subject of intense research by the space plasma community. Such functions, known as superthermal or kappa distributions, have been found to provide a better fitting to the VDF measured by several spacecraft in the plasma environment of the solar wind. In the literature, the general treatment for waves excited by (bi-)Maxwellian plasmas is well established. However, for kappa distributions, either isotropic or anisotropic, the wave characteristics have been studied mostly for the limiting cases of purely parallel or perpendicular propagation. Contributions for the general case of obliquely propagating waves have been scarcely reported so far. In this work we introduce a mathematical formalism that provides expressions for the dielectric tensor components and subsequent dispersion relations for oblique propagating dispersive Alfvén waves (DAWs) resulting from a kappa VDF. We employ an isotropic distribution, but the methods used here can be easily applied to more general anisotropic distributions, such as the bi-kappa or product-bi-kappa. The effect of the kappa index and thermal corrections on the dispersion relations of DAW is discussed.
The energy associated with MHD waves generation in the solar wind plasma
NASA Technical Reports Server (NTRS)
delaTorre, A.
1995-01-01
Gyrotropic symmetry is usually assumed in measurements of electron distribution functions in the heliosphere. This prevents the calculation of a net current perpendicular to the magnetic field lines. Previous theoretical results derived by one of the authors for a collisionless plasma with isotropic electrons in a strong magnetic field have shown that the excitation of MHD modes becomes possible when the external perpendicular current is non-zero. We consider then that any anisotropic electron population can be thought of as 'external', interacting with the remaining plasma through the self-consistent electromagnetic field. From this point of view any perpendicular current may be due to the anisotropic electrons, or to an external source like a stream, or to both. As perpendicular currents cannot be derived from the measured distribution functions, we resort to Ampere's law and experimental data of magnetic field fluctuations. The transfer of energy between MHD modes and external currents is then discussed.
NASA Astrophysics Data System (ADS)
Salem, C. S.; Sundkvist, D. J.; Bale, S.
2009-12-01
Electromagnetic fluctuations in the inertial range of solar wind MHD turbulence and beyond (up to frequencies of 10Hz) have been studied for the first time using both magnetic field and electric field measurements on Cluster [Bale et al., 2005]. It has been shown that at frequencies above the spectral breakpoint at ~0.4Hz, in the dissipation range, the wave modes become dispersive and are consistent with Kinetic Alfven Waves (KAW). This interpretation, consistent with findings from recent theoretical studies, is based on the simple assumption that the measured frequency spectrum is actually a Doppler shifted wave number spectrum (ω ≈ k Vsw), commonly used in the solar wind and known as Taylor's hypothesis. While Taylor's hypothesis is valid in the inertial range of solar wind turbulence, it may break down in the dissipation range where temporal fluctuations can become important. We recently analyzed the effect of Doppler shift on KAW as well as compressional proton whistler waves [Salem et al., 2009]. The dispersive properties of the KAW and the whistler wave modes, as well as the electric to magnetic field (E/B) ratio, have been determined both analytically and numerically in the plasma and the spacecraft frame, with the goal of directly comparing those analytical/numerical estimates in the spacecraft frame with the data as measured. We revisit here Cluster electric field and magnetic field data in the solar wind using this approach. We focus our analysis on several ambient solar wind intervals with varying plasma parameters, allowing for a statistical study. We show that this technique provides an efficient diagnostics for wave-mode identification in the dissipation/dispersion range of solar wind turbulence.
NASA Astrophysics Data System (ADS)
Louis, Hélène; Odent, Vincent; Louvergneaux, Eric
2016-04-01
Shock waves are well-known nonlinear waves, displaying an abrupt discontinuity. Observation can be made in a lot of physical fields, as in water wave, plasma and nonlinear optics. Shock waves can either break or relax through either catastrophic or regularization phenomena. In this work, we restrain our study to dispersive shock waves. This regularization phenomenon implies the emission of dispersive waves. We demonstrate experimentally and numerically the generation of spatial dispersive shock waves in a nonlocal focusing media. The generation of dispersive shock wave in a focusing media is more problematic than in a defocusing one. Indeed, the modulational instability has to be frustrated to observe this phenomenon. In 2010, the dispersive shock wave was demonstrated experimentally in a focusing media with a partially coherent beam [1]. Another way is to use a nonlocal media [2]. The impact of nonlocality is more important than the modulational instability frustration. Here, we use nematic liquid crystals (NLC) as Kerr-like nonlocal medium. To achieve shock formation, we use the Riemann condition as initial spatial condition (edge at the beam entrance of the NLC cell). In these experimental conditions, we generate, experimentally and numerically, shock waves that relax through the emission of dispersive waves. Associated with this phenomenon, we evidence the emergence of a localized wave that travels through the transverse beam profile. The beam steepness, which is a good indicator of the shock formation, is maximal at the shock point position. This latter follows a power law versus the injected power as in [3]. Increasing the injected power, we found multiple shock points. We have good agreements between the numerical simulations and the experimental results. [1] W. Wan, D. V Dylov, C. Barsi, and J. W. Fleischer, Opt. Lett. 35, 2819 (2010). [2] G. Assanto, T. R. Marchant, and N. F. Smyth, Phys. Rev. A - At. Mol. Opt. Phys. 78, 1 (2008). [3] N. Ghofraniha, L. S
Lamb waves dispersion curves for diamond based piezoelectric layered structure
NASA Astrophysics Data System (ADS)
Sorokin, B. P.; Kvashnin, G. M.; Telichko, A. V.; Novoselov, A. S.; Burkov, S. I.
2016-03-01
The presence of spurious peaks in the amplitude-frequency response of diamond based piezoelectric layered structure was shown. Excitation of such peaks results in deterioration of an useful acoustical signal. It was shown that such spurious peaks should be associated with Lamb waves in a layered structure. By means of FEM analysis, the propagation of acoustic waves of different types in the piezoelectric layered structure "Al/AlN/Mo/(100) diamond" has been investigated in detail. By analyzing the elastic displacement patterns at frequencies from 0 up to 250 MHz, a set of all the possible acoustic waves, especially Lamb modes, have been studied, and dispersive curves of phase velocity have been plotted. A revised classification of Lamb modes has been introduced.
Observation of Dispersive Shock Waves, Solitons, and Their Interactions in Viscous Fluid Conduits.
Maiden, Michelle D; Lowman, Nicholas K; Anderson, Dalton V; Schubert, Marika E; Hoefer, Mark A
2016-04-29
Dispersive shock waves and solitons are fundamental nonlinear excitations in dispersive media, but dispersive shock wave studies to date have been severely constrained. Here, we report on a novel dispersive hydrodynamic test bed: the effectively frictionless dynamics of interfacial waves between two high viscosity contrast, miscible, low Reynolds number Stokes fluids. This scenario is realized by injecting from below a lighter, viscous fluid into a column filled with high viscosity fluid. The injected fluid forms a deformable pipe whose diameter is proportional to the injection rate, enabling precise control over the generation of symmetric interfacial waves. Buoyancy drives nonlinear interfacial self-steepening, while normal stresses give rise to the dispersion of interfacial waves. Extremely slow mass diffusion and mass conservation imply that the interfacial waves are effectively dissipationless. This enables high fidelity observations of large amplitude dispersive shock waves in this spatially extended system, found to agree quantitatively with a nonlinear wave averaging theory. Furthermore, several highly coherent phenomena are investigated including dispersive shock wave backflow, the refraction or absorption of solitons by dispersive shock waves, and the multiphase merging of two dispersive shock waves. The complex, coherent, nonlinear mixing of dispersive shock waves and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows.
Observation of Dispersive Shock Waves, Solitons, and Their Interactions in Viscous Fluid Conduits
NASA Astrophysics Data System (ADS)
Maiden, Michelle D.; Lowman, Nicholas K.; Anderson, Dalton V.; Schubert, Marika E.; Hoefer, Mark A.
2016-04-01
Dispersive shock waves and solitons are fundamental nonlinear excitations in dispersive media, but dispersive shock wave studies to date have been severely constrained. Here, we report on a novel dispersive hydrodynamic test bed: the effectively frictionless dynamics of interfacial waves between two high viscosity contrast, miscible, low Reynolds number Stokes fluids. This scenario is realized by injecting from below a lighter, viscous fluid into a column filled with high viscosity fluid. The injected fluid forms a deformable pipe whose diameter is proportional to the injection rate, enabling precise control over the generation of symmetric interfacial waves. Buoyancy drives nonlinear interfacial self-steepening, while normal stresses give rise to the dispersion of interfacial waves. Extremely slow mass diffusion and mass conservation imply that the interfacial waves are effectively dissipationless. This enables high fidelity observations of large amplitude dispersive shock waves in this spatially extended system, found to agree quantitatively with a nonlinear wave averaging theory. Furthermore, several highly coherent phenomena are investigated including dispersive shock wave backflow, the refraction or absorption of solitons by dispersive shock waves, and the multiphase merging of two dispersive shock waves. The complex, coherent, nonlinear mixing of dispersive shock waves and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows.
Two-dimensional envelope localized waves in the anomalous dispersion regime.
Malaguti, Stefania; Bellanca, Gaetano; Trillo, Stefano
2008-05-15
Narrowband localized wave packets that are nondispersing and nondiffracting in one transverse dimension are characterized in anomalously dispersive media by means of a Fourier approach. Depending on the group velocity, waves with a dispersion relationship characterized by real wavenumbers can be O or X waves, while we also find waves with evanescent wavenumbers.
NASA Astrophysics Data System (ADS)
Li, Zhao; Hudson, Mary; Paral, Jan; Wiltberger, Michael; Turner, Drew
2016-07-01
The 17-18 March 2015 storm is the largest geomagnetic storm in the Van Allen Probes era to date. The Lyon-Fedder-Mobarry global MHD model has been run for this event using ARTEMIS data as solar wind input. The ULF wave power spectral density of the azimuthal electric field and compressional magnetic field is analyzed in the 0.5-8.3 mHz range. The lowest three azimuthal modes account for 70% of the total power during quiet times. However, during high activity, they are not exclusively dominant. The calculation of the radial diffusion coefficient is presented. We conclude that the electric field radial diffusion coefficient is dominant over the magnetic field coefficient by one to two orders of magnitude. This result contrasts with the dominant magnetic field diffusion coefficient used in most 3-D diffusion models.
1-D profiling using highly dispersive guided waves
Volker, Arno; Zon, Tim van
2014-02-18
Corrosion is one of the industries major issues regarding the integrity of assets. Currently, inspections are conducted at regular intervals to ensure a sufficient integrity level of these assets. Cost reduction while maintaining a high level of reliability and safety of installations is a major challenge. There are many situations where the actual defect location is not accessible, e.g., a pipe support or a partially buried pipe. Guided wave tomography has been developed to reconstruct the wall thickness of steel pipes. In case of bottom of the line corrosion, i.e., a single corrosion pit, a simpler approach may be followed. Data is collected in a pitch-catch configuration at the 12 o'clock position using highly dispersive guided waves. After dispersion correction the data collapses to a short pulse, any residual dispersion indicates wall loss. The phase spectrum is used to invert for the wall thickness profile in the circumferential direction, assuming a Gaussian defect profile. The approach is evaluated on numerically simulated and on measured data. The method is intended for rapid, semi-quantitative screening of pipes.
Magnetopause surface waves triggered by a rotating IMF with the global MHD SWMF/BAT-S-RUS model
NASA Astrophysics Data System (ADS)
Andriyas, T.; Spencer, E. A.
2010-12-01
The solar wind driving of magnetopause surface waves is only partly understood. In particular we do not have a picture of the magnetopause surface wave properties and behavior when a magnetic cloud event, which sometimes involves a rotating IMF, impinges on the magnetosphere. Here we investigate the effect of a twisting or rotational IMF under moderate solar wind velocity (about 500 km/s) upon the magnetosphere with the Global MHD BATS-R-US code. Synthetic solar wind data is constructed to simulate the most important features of a magnetic cloud event, but without including shock features. A sinusoidally varying By component accompanied by a cosinusoidally varying Bz component of the IMF is input into the model with magnitude 10-20 nT. The synthetic data is representative of the magnetic cloud event that occurred on October 3-7 2000. We use the results of the simulation to infer the modes, properties, and particularly the phase speed and wavelength of the surface wave structures.
Linear guided waves in a hyperbolic planar waveguide. Dispersion relations
Lyashko, E I; Maimistov, A I
2015-11-30
We have theoretically investigated waveguide modes propagating in a planar waveguide formed by a layer of an isotropic dielectric surrounded by hyperbolic media. The case, when the optical axis of hyperbolic media is perpendicular to the interface, is considered. Dispersion relations are derived for the cases of TE and TM waves. The differences in the characteristics of a hyperbolic and a conventional dielectric waveguide are found. In particular, it is shown that in hyperbolic waveguides for each TM mode there are two cut-off frequencies and the number of propagating modes is always limited. (metamaterials)
Lamb Wave Dispersion Characterization Using Multiplexed Two-Wave Mixing Interferometry
NASA Astrophysics Data System (ADS)
Zhou, Yi; Zhang, Feifei; Krishnaswamy, Sridhar
2003-03-01
In recent work at Northwestern University, Multiplexed Two-Wave Mixing Interferometers (MTWM) have been developed. These systems are able to perform optical detection of ultrasonic motion over an array of points simultaneously. Optical phase gratings are used to create a detection-array of laser beams that are directed to the specimen. The detection array can be arranged in several ways on the test object. The scattered beams from the detection-array are collected and combined with a single reference beam in a photorefractive crystal to form a multiplexed two-wave mixing configuration. Each of the output beams from the photorefractive crystal is imaged on to a separate element of a photodetector array. The resulting MTWM system is capable of providing simultaneous optical detection (with high spatial resolution and sub-nanometer displacement sensitivities) at several points on a test object. The MTWM system can be used in several modes for laser ultrasonic NDE of flaws and materials characterization. In this paper we present recent advances and applications of this technology. An application of the MTWM system for fast recovery of Lamb wave dispersion curves is presented. We obtain the dispersive time-domain Lamb wave signals at multiple source-to-receiver distances. Following the algorithm of Alleyne and Cawley, these time-position domain signals are transformed to the frequency-wavenumber domain using a 2D FFT technique. The MTWM system enables rapid characterization of Lamb wave dispersion.
NASA Astrophysics Data System (ADS)
Gao, Donghong
Interest in utilizing liquid metal film flows to protect the plasma-facing solid structures places increasing demand on understanding the magnetohydrodynamics (MHD) of such flows in a magnetic field with spatial variation. The field gradient effect is studied by a two-dimensional (2D) model in Cartesian coordinates. The thin film flow down an inclined plane in spanwise (z-direction) magnetic field with constant streamwise gradient and applied current is analyzed. The solution to the equilibrium flow shows forcefully the M-shaped velocity profile and dependence of side layer thickness on Ha-1/2 whose definition is based on field gradient. The major part of the dissertation is the numerical simulation of free surface film flows and understanding the results. The VOF method is employed to track the free surface, and the CSF model is combined with VOF method to account for surface dynamics condition. The code is validated with respect to Navier-Stokes solver and MHD implementation by computations of ordinary wavy films, MHD flat films and a colleague proposed film flow. The comparisons are performed against respective experimental, theoretical or numerical solutions, and the results are well matched with them. It is found for the ordinary water falling films, at low frequency and high flowrate, the small forcing disturbance at inlet flowrate develops into big roll waves preceded by small capillary bow waves; at high frequency and low Re, it develops into nearly sinusoidal waves with small amplitude and without fore-running capillary waves. The MHD surface instability is investigated for two kinds of film flows in constant streamwise field gradient: one with spatial disturbance and without surface tension, the other with inlet forcing disturbance and with surface tension. At no surface tension condition, the finite amplitude disturbance is rapidly amplified and degrades to irregular shape. With surface tension to maintain smooth interface, finite amplitude regular waves
Parametric dispersion and amplification of acoustohelicon waves in piezoelectric semiconductors
NASA Astrophysics Data System (ADS)
Neogi, A.; Ghosh, S.
1991-01-01
Assuming that the origin of the nonlinear interaction lies in the second-order optical susceptibility arising from the nonlinear induced current density and using the coupled-mode theory, the parametric dispersion and amplification of acoustohelicon waves is analytically investigated in a longitudinally magnetized piezoelectric semiconductor of noncentrosymmetric nature. The relevant experiments have not been reported. The threshold value of the pump electric field E0th and its corresponding excitation intensity is obtained. The longitudinal magnetic field decreases the required magnitude of E0th for the excitation of parametric amplification. The phenomenon of self-defocusing of the signal in the prevailing case is found to be a consequence of the negative dispersive characteristics exhibited by the acoustohelicon waves. Numerical analyses are performed for an InSb crystal at 77 K, duly irradiated by frequency-doubled pulsed 10.6-μm CO2 lasers. The parametric gain constant is observed to be maximum when the cyclotron frequency ωc attains the magnitude equal to that of ω0, the incident laser frequency (=1.78×1014 s-1 ).
Dispersion properties of compressional electromagnetic waves in quantum dusty magnetoplasmas
Ali, S.; Shukla, P.K.
2006-05-15
A new dispersion relation for low-frequency compressional electromagnetic waves is derived by employing quantum magnetohydrodynamic model and Maxwell equations in cold quantum dusty magnetoplasmas. The latter is composed of inertialess electrons, mobile ions, and immobile charged dust particulates. The dispersion relation for the low-frequency compressional electromagnetic modes is further analyzed for the waves propagating parallel, perpendicular, and oblique to the external magnetic field direction. It is found theoretically and numerically that the quantum parameter {alpha}{sub q}=(n{sub i0}/n{sub e0})({Dirac_h}/2{pi}){sup 2}/(4m{sub e}m{sub i}) affects the real angular frequencies and the phase speeds of the compressional electromagnetic modes. Here, n{sub i0} (n{sub e0}) is the equilibrium number density of the ions (electrons), m{sub e} (m{sub i}) is the electron (ion) mass, and ({Dirac_h}/2{pi}) is the Plank constant divided by 2{pi}.
Radiating dispersive shock waves in non-local optical media
El, Gennady A.
2016-01-01
We consider the step Riemann problem for the system of equations describing the propagation of a coherent light beam in nematic liquid crystals, which is a general system describing nonlinear wave propagation in a number of different physical applications. While the equation governing the light beam is of defocusing nonlinear Schrödinger (NLS) equation type, the dispersive shock wave (DSW) generated from this initial condition has major differences from the standard DSW solution of the defocusing NLS equation. In particular, it is found that the DSW has positive polarity and generates resonant radiation which propagates ahead of it. Remarkably, the velocity of the lead soliton of the DSW is determined by the classical shock velocity. The solution for the radiative wavetrain is obtained using the Wentzel–Kramers–Brillouin approximation. It is shown that for sufficiently small initial jumps the nematic DSW is asymptotically governed by a Korteweg–de Vries equation with the fifth-order dispersion, which explicitly shows the resonance generating the radiation ahead of the DSW. The constructed asymptotic theory is shown to be in good agreement with the results of direct numerical simulations. PMID:27118911
Slow-Mode MHD Wave Penetration into a Coronal Null Point due to the Mode Transmission
NASA Astrophysics Data System (ADS)
Afanasyev, Andrey N.; Uralov, Arkadiy M.
2016-11-01
Recent observations of magnetohydrodynamic oscillations and waves in solar active regions revealed their close link to quasi-periodic pulsations in flaring light curves. The nature of that link has not yet been understood in detail. In our analytical modelling we investigate propagation of slow magnetoacoustic waves in a solar active region, taking into account wave refraction and transmission of the slow magnetoacoustic mode into the fast one. The wave propagation is analysed in the geometrical acoustics approximation. Special attention is paid to the penetration of waves in the vicinity of a magnetic null point. The modelling has shown that the interaction of slow magnetoacoustic waves with the magnetic reconnection site is possible due to the mode transmission at the equipartition level where the sound speed is equal to the Alfvén speed. The efficiency of the transmission is also calculated.
Interpreting Solar EUV Wave Observations from Different Viewing Angles Using an MHD Model
NASA Astrophysics Data System (ADS)
Hoilijoki, S.; Pomoell, J.; Vainio, R.; Palmroth, M.; Koskinen, H. E. J.
2013-09-01
We study the effect of projection and line-of-sight integration on the interpretation of the morphology and kinematics of EUV waves. We have performed a three-dimensional magnetohydrodynamic simulation of a coronal mass ejection (CME) erupting in an environment that mimics the low solar corona and calculated the resulting emission measure of the event from five different viewing angles. Our study provides more quantitative information about the impact of the viewing angle and projection effect on the properties of EUV waves than previous studies on the subject. Analyzing the emission measure of the lower corona reveals wave-like increases that move away from the eruption site, which we interpret as EUV waves. Behind the EUV wave front we can recognize coronal dimming regions. A comparison of the emission measure and calculated density supports the view that EUV waves are true waves. Our results show that the origin of the observed EUV wave is height-dependent, which means that the measured speed and the morphology depend on the viewing direction. Consequently, care should be taken when EUV observations are used to infer the true propagation speeds of EUV wave fronts.
Wave velocity dispersion and attenuation in media exhibiting internal oscillations
NASA Astrophysics Data System (ADS)
Frehner, Marcel; Steeb, Holger; Schmalholz, Stefan M.
2010-05-01
Understanding the dynamical and acoustical behavior of porous and heterogeneous rocks is of great importance in geophysics, e.g. earthquakes, and for various seismic engineering applications, e.g. hydrocarbon exploration. Within a heterogeneous medium oscillations with a characteristic resonance frequency, depending on the mass and internal length of the heterogeneity, can occur. When excited, heterogeneities can self-oscillate with their natural frequency. Another example of internal oscillations is the dynamical behavior of non-wetting fluid blobs or fluid patches in residually saturated pore spaces. Surface tension forces or capillary forces act as the restoring force that drives the oscillation. Whatever mechanism is involved, an oscillatory phenomena within a heterogeneous medium will have an effect on acoustic or seismic waves propagating through such a medium, i.e. wave velocity dispersion and frequency-dependent attenuation. We present two models for media exhibiting internal oscillations and discuss the frequency-dependent wave propagation mechanism. Both models give similar results: (1) The low-frequency (i.e. quasi-static) limit for the phase velocity is identical with the Gassmann-Wood limit and the high-frequency limit is larger than this value and (2) Around the resonance frequency a very strong phase velocity change and the largest attenuation occurs. (1) Model for a homogeneous medium exhibiting internal oscillations We present a continuum model for an acoustic medium exhibiting internal damped oscillations. The obvious application of this model is water containing oscillating gas bubbles, providing the material and model parameters for this study. Two physically based momentum interaction terms between the two inherent constituents are used: (1) A purely elastic term of oscillatory nature that scales with the volume of the bubbles and (2) A viscous term that scales with the specific surface of the bubble. The model is capable of taking into account
NASA Astrophysics Data System (ADS)
Walsh, Braden Michael
Studying and determining crustal structure of the Earth is important for understanding the interior of the Earth. Using methods like receiver functions and surface wave dispersion allows the determination of differences in structure and composition through the crust. Jointly inverting receiver functions and surface wave dispersion reduces the error and over-interpretation of the crustal structure estimation. Receiver functions and surface wave dispersion invert well together because receiver functions are very sensitive to velocity contrasts and vertical travel times, and surface wave dispersion is sensitive to average velocity and insensitive to sharp velocity contrasts. By jointly inverting receiver functions and surface wave dispersion, shear wave velocity profiles can be created to determine the properties of the crustal structure and velocity contrasts. With the use of IRIS Transportable Array stations data throughout the United States, this thesis takes a closer look at the crustal structure of North Dakota through the joint inversion of surface wave dispersion and teleseismic P-wave receiver functions. The receiver functions in North Dakota show shallow sediment effects that affect the joint inversion process. In western North Dakota the Williston basin and in eastern North Dakota the Red River Valley cause ringing effects in the receiver functions. The shallow sediments in North Dakota control and overpower the rest of the crustal signal in the receiver functions, and thus affect the ability of determining the crustal shear wave velocity structure of North Dakota through the joint inversion of receiver functions and surface wave dispersion, thus the use of background geology is necessary.
Lithospheric Thickness Modeled from Long Period Surface Wave Dispersion
Pasyanos, M E
2008-05-15
The behavior of surface waves at long periods is indicative of subcrustal velocity structure. Using recently published dispersion models, we invert surface wave group velocities for lithospheric structure, including lithospheric thickness, over much of the Eastern Hemisphere, encompassing Eurasia, Africa, and the Indian Ocean. Thicker lithosphere under Precambrian shields and platforms are clearly observed, not only under the large cratons (West Africa, Congo, Baltic, Russia, Siberia, India), but also under smaller blocks like the Tarim Basin and Yangtze craton. In contrast, it is found that remobilized Precambrian structures like the Saharan Shield and Sino-Korean Paraplatform do not have well-established lithospheric keels. The thinnest lithospheric thickness is found under oceanic and continental rifts, as well as along convergence zones. We compare our results to thermal models of continental lithosphere, lithospheric cooling models of oceanic lithosphere, lithosphere-asthenosphere boundary (LAB) estimates from S-wave receiver functions, and velocity variations of global tomography models. In addition to comparing results for the broad region, we examine in detail the regions of Central Africa, Siberia, and Tibet. While there are clear differences in the various estimates, overall the results are generally consistent. Inconsistencies between the estimates may be due to a variety of reasons including lateral and depth resolution differences and the comparison of what may be different lithospheric features.
Increased P-wave dispersion a risk for atrial fibrillation in adolescents with anorexia nervosa.
Ertuğrul, İlker; Akgül, Sinem; Derman, Orhan; Karagöz, Tevfik; Kanbur, Nuray
2016-01-01
Studies have shown that a prolonged P-wave dispersion is a risk factor for the development of atrial fibrillation. The aim of this study was to evaluate P-wave dispersion in adolescents with anorexia nervosa at diagnosis. We evaluated electrocardiographic findings, particularly the P-wave dispersion, at initial assessment in 47 adolescents with anorexia nervosa. Comparison of P-wave dispersion between adolescents with anorexia nervosa and controls showed a statistically significant higher P-wave dispersion in patients with anorexia nervosa (72 ± 16.3 msec) when compared to the control group (43.8 ± 9.5 msec). Percent of body weight lost, lower body mass index, and higher weight loss rate in the patients with anorexia nervosa had no effect on P-wave dispersion. Due to the fact that anorexia nervosa has a high mortality rate we believe that cardiac pathologies such as atrial fibrillation must also be considered in the medical evaluation.
The Magnetic Coupling of Chromospheres and Winds From Late Type Evolved Stars: Role of MHD Waves
NASA Astrophysics Data System (ADS)
Airapetian, Vladimir; Leake, James; Carpenter, Kenneth
2015-08-01
Stellar chromospheres and winds represent universal attributes of stars on the cool portion of H-R diagram. In this paper we derive observational constrains for the chromospheric heating and wind acceleration from cool evolved stars and examine the role of Alfven waves as a viable source of energy dissipation and momentum deposition. We use a 1.5D magnetohydrodynamic code with a generalized Ohm's law to study propagation of Alfven waves generated along a diverging magnetic field in a stellar photosphere at a single frequency. We demonstrate that due to inclusion of the effects of ion-neutral collisions in magnetized weakly ionized chromospheric plasma on resistivity and the appropriate grid resolution, the numerical resistivity becomes 1-2 orders of magnitude smaller than the physical resistivity. The motions introduced by non-linear transverse Alfven waves can explain non-thermally broadened and non-Gaussian profiles of optically thin UV lines forming in the stellar chromosphere of α Tau and other late-type giant and supergiant stars. The calculated heating rates in the stellar chromosphere model due to resistive (Joule) dissipation of electric currents on Pedersen resistivity are consistent with observational constraints on the net radiative losses in UV lines and the continuum from α Tau. At the top of the chromosphere, Alfven waves experience significant reflection, producing downward propagating transverse waves that interact with upward propagating waves and produce velocity shear in the chromosphere. Our simulations also suggest that momentum deposition by non-linear Alfven waves becomes significant in the outer chromosphere within 1 stellar radius from the photosphere that initiates a slow and massive winds from red giants and supergiants.
Hartley, D P; Chen, Y; Kletzing, C A; Denton, M H; Kurth, W S
2015-02-01
Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1-0.9 fce). Results from this study indicate that the calculated wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10(-3) nT(2), using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons.
Hartley, D. P.; Chen, Y.; Kletzing, C. A.; Denton, M. H.; Kurth, W. S.
2015-02-17
Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1–0.9 f_{ce}). Results from this study indicate that the calculated wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10⁻³ nT², using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons.
Multiwavelength Studies of MHD Waves in the Solar Chromosphere. An Overview of Recent Results
NASA Astrophysics Data System (ADS)
Jess, D. B.; Morton, R. J.; Verth, G.; Fedun, V.; Grant, S. D. T.; Giagkiozis, I.
2015-07-01
The chromosphere is a thin layer of the solar atmosphere that bridges the relatively cool photosphere and the intensely heated transition region and corona. Compressible and incompressible waves propagating through the chromosphere can supply significant amounts of energy to the interface region and corona. In recent years an abundance of high-resolution observations from state-of-the-art facilities have provided new and exciting ways of disentangling the characteristics of oscillatory phenomena propagating through the dynamic chromosphere. Coupled with rapid advancements in magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly investigate the role waves play in supplying energy to sustain chromospheric and coronal heating. Here, we review the recent progress made in characterising, categorising and interpreting oscillations manifesting in the solar chromosphere, with an impetus placed on their intrinsic energetics.
1D profiling using highly dispersive guided waves
NASA Astrophysics Data System (ADS)
Volker, Arno; van Zon, Tim; Hsu, Mick; Boogert, Lennart
2016-02-01
Corrosion is one of the industries major issues regarding the integrity of assets. Currently inspections are conducted at regular intervals to ensure a sufficient integrity level of these assets. Cost reduction while maintaining a high level of reliability and safety of installations is a major challenge. There are many situations where the actual defect location is not accessible, e.g., a pipe support or a partially buried pipe. In case of bottom of the line corrosion, i.e., a single corrosion pit, a simpler approach may be followed. Guided waves are propagated around the circumference of a pipe. In case of wall loss, the phase of the signal changes which is used to estimate the local wall thickness profile. A special EMAT sensor has been developed, which works in a pit-catch configuration at the 12 o'clock position using highly dispersive guided waves. In order to improve the sensitivity, an inversion in performed on multiple orders of circumferential passes. Experimental results are presented on different pipes containing artificial and real defects.
1D profiling using highly dispersive guided waves
Volker, Arno; Zon, Tim van; Enthoven, Daniel; Verburg, Wesley
2015-03-31
Corrosion is one of the industries major issues regarding the integrity of assets. Currently inspections are conducted at regular intervals to ensure a sufficient integrity level of these assets. Cost reduction while maintaining a high level of reliability and safety of installations is a major challenge. There are many situations where the actual defect location is not accessible, e.g., a pipe support or a partially buried pipe. Guided wave tomography has been developed to reconstruct the wall thickness. In case of bottom of the line corrosion, i.e., a single corrosion pit, a simpler approach may be followed. Data is collected in a pit-catch configuration at the 12 o'clock position using highly dispersive guided waves. The phase spectrum is used to invert for a wall thickness profile in the circumferential direction, assuming a Gaussian defect profile. An EMAT sensor design has been made to measure at the 12 o'clock position of a pipe. The concept is evaluated on measured data, showing good sizing capabilities on a variety simple defect profiles.
Hartley, D. P.; Chen, Y.; Kletzing, C. A.; ...
2015-02-17
Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1–0.9 fce). Results from this study indicate that the calculated wavemore » intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10⁻³ nT², using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons.« less
Rossby wave energy dispersion from tropical cyclone in zonal basic flows
NASA Astrophysics Data System (ADS)
Shi, Wenli; Fei, Jianfang; Huang, Xiaogang; Liu, Yudi; Ma, Zhanhong; Yang, Lu
2016-04-01
This study investigates tropical cyclone energy dispersion under horizontally sheared flows using a nonlinear barotropic model. In addition to common patterns, unusual features of Rossby wave trains are also found in flows with constant vorticity and vorticity gradients. In terms of the direction of the energy dispersion, the wave train can rotate clockwise and elongate southwestward under anticyclonic circulation (ASH), which contributes to the reenhancement of the tropical cyclone (TC). The wave train even splits into two obvious wavelike trains in flows with a southward vorticity gradient (WSH). Energy dispersed from TCs varies over time, and variations in the intensity of the wave train components typically occur in two stages. Wave-activity flux diagnosis and ray tracing calculations are extended to the frame that moves along with the TC to reveal the concrete progress of wave propagation. The direction of the wave-activity flux is primarily determined by the combination of the basic flow and the TC velocity. Along the flux, the distribution of pseudomomentum effectively illustrates the development of wave trains, particularly the rotation and split of wave propagation. Ray tracing involves the quantitative tracing of wave features along rays, which effectively coincide with the wave train regimes. Flows of a constant shear (parabolic meridional variation) produce linear (nonlinear) wave number variations. For the split wave trains, the real and complex wave number waves move along divergent trajectories and are responsible for different energy dispersion ducts.
MHD Modeling of Coronal Large-Amplitude Waves Related to CME Lift-off
NASA Astrophysics Data System (ADS)
Pomoell, J.; Vainio, R.; Kissmann, R.
2008-12-01
We have employed a two-dimensional magnetohydrodynamic simulation code to study mass motions and large-amplitude coronal waves related to the lift-off of a coronal mass ejection (CME). The eruption of the filament is achieved by an artificial force acting on the plasma inside the flux rope. By varying the magnitude of this force, the reaction of the ambient corona to CMEs with different acceleration profiles can be studied. Our model of the ambient corona is gravitationally stratified with a quadrupolar magnetic field, resulting in an ambient Alfvén speed that increases as a function of height, as typically deduced for the low corona. The results of the simulations show that the erupting flux rope is surrounded by a shock front, which is strongest near the leading edge of the erupting mass, but also shows compression near the solar surface. For rapidly accelerating filaments, the shock front forms already in the low corona. Although the speed of the driver is less than the Alfvén speed near the top of the atmosphere, the shock survives in this region as well, but as a freely propagating wave. The leading edge of the shock becomes strong early enough to drive a metric type II burst in the corona. The speed of the weaker part of the shock front near the surface is lower, corresponding to the magnetosonic speed there. We analyze the (line-of-sight) emission measure of the corona during the simulation and recognize a wave receding from the eruption site, which strongly resembles EIT waves in the low corona. Behind the EIT wave, we clearly recognize a coronal dimming, also observed during CME lift-off. We point out that the morphology of the hot downstream region of the shock would be that of a hot erupting loop, so care has to be taken not to misinterpret soft X-ray imaging observations in this respect. Finally, the geometry of the magnetic field around the erupting mass is analyzed in terms of precipitation of particles accelerated in the eruption complex. Field
Simulated Obstructive Sleep Apnea Increases P-Wave Duration and P-Wave Dispersion
Wons, Annette M.; Rossi, Valentina; Bratton, Daniel J.; Schlatzer, Christian; Schwarz, Esther I.; Camen, Giovanni; Kohler, Malcolm
2016-01-01
Background A high P-wave duration and dispersion (Pd) have been reported to be a prognostic factor for the occurrence of paroxysmal atrial fibrillation (PAF), a condition linked to obstructive sleep apnea (OSA). We tested the hypothesis of whether a short-term increase of P-wave duration and Pd can be induced by respiratory manoeuvres simulating OSA in healthy subjects and in patients with PAF. Methods 12-lead-electrocardiography (ECG) was recorded continuously in 24 healthy subjects and 33 patients with PAF, while simulating obstructive apnea (Mueller manoeuvre, MM), obstructive hypopnea (inspiration through a threshold load, ITH), central apnea (AP), and during normal breathing (BL) in randomized order. The P-wave duration and Pd was calculated by using dedicated software for ECG-analysis. Results P-wave duration and Pd significantly increased during MM and ITH compared to BL in all subjects (+13.1ms and +13.8ms during MM; +11.7ms and +12.9ms during ITH; p<0.001 for all comparisons). In MM, the increase was larger in healthy subjects when compared to patients with PAF (p<0.05). Conclusion Intrathoracic pressure swings through simulated obstructive sleep apnea increase P-wave duration and Pd in healthy subjects and in patients with PAF. Our findings imply that intrathoracic pressure swings prolong the intra-atrial and inter-atrial conduction time and therefore may represent an independent trigger factor for the development for PAF. PMID:27071039
Wave Tank Studies On Formation And Transport Of OMA From The Chemically Dispersed Oil
The interaction of chemical dispersants and suspended sediments with crude oil influences the fate and transport of oil spills in coastal waters. A wave tank study was conducted to investigate the effects of chemical dispersants and mineral fines on dispersion of oil, formation ...
Are There Optical Solitary Wave Solutions in Linear Media with Group Velocity Dispersion?
NASA Technical Reports Server (NTRS)
Li, Zhonghao; Zhou, Guosheng
1996-01-01
A generalized exact optical bright solitary wave solution in a three dimensional dispersive linear medium is presented. The most interesting property of the solution is that it can exist in the normal group-velocity-dispersion (GVD) region. In addition, another peculiar feature is that it may achieve a condition of 'zero-dispersion' to the media so that a solitary wave of arbitrarily small amplitude may be propagated with no dependence on is pulse width.
Do dispersive waves play a role in collisionless magnetic reconnection?
Liu, Yi-Hsin; Daughton, W.; Li, H.; Karimabadi, H.; Peter Gary, S.
2014-02-15
Using fully kinetic simulations, we demonstrate that the properly normalized reconnection rate is fast ∼0.1 for guide fields up to 80× larger than the reconnecting field and is insensitive to both the system size and the ion to electron mass ratio. These results challenge conventional explanations of reconnection based on fast dispersive waves, which are completely absent for sufficiently strong guide fields. In this regime, the thickness of the diffusion layer is set predominantly by the electron inertial length with an inner sublayer that is controlled by finite gyro-radius effects. As the Alfvén velocity becomes relativistic for very strong guide fields, the displacement current becomes important and strong deviations from charge neutrality occur, resulting in the build-up of intense electric fields which absorb a portion of the magnetic energy release. Over longer time scales, secondary magnetic islands are generated near the active x-line while an electron inertial scale Kelvin-Helmholtz instability is driven within the outflow. These secondary instabilities give rise to time variations in the reconnection rate but do not alter the average value.
NASA Astrophysics Data System (ADS)
Luo, Zhi; Zeng, Liang; Lin, Jing; Hua, Jiadong
2017-02-01
Dispersion effect of Lamb wave will cause wave-packets to spread out in space and time, making received signals hard to be interpreted. Though the conventional dispersion compensation method can restrain dispersion effect, waveform deformation still remains in the compensated results. To eliminate dispersion effect completely, a reshaped excitation dispersion compensation method is proposed in this paper. The method compensates the dispersed signal to the same shape as the original excitation by generating a reshaped excitation and then mapping the received signal from time domain to distance domain. Simulations and experiments are conducted for the validation of the waveform correction of the reshaped excitation dispersion compensation method. Applied in the traditional delay-and-sum algorithm, the new dispersion compensation method can effectively enhance the resolution of the damage imaging.
NASA Astrophysics Data System (ADS)
Bekki, Naoaki; Shintani, Seine A.
2015-12-01
We consider the Rayleigh-Lamb-type equation for propagating pulsive waves excited by aortic-valve closure at end-systole in the human heart wall. We theoretically investigate the transcendental dispersion equation of pulsive waves for the asymmetrical zero-order mode of the Lamb wave. We analytically find a simple dispersion equation with a universal constant for a small Lamb wavenumber. We show that the simple dispersion equation can qualitatively explain the myocardial noninvasive measurements in vivo of pulsive waves in the human heart wall. We can also consistently estimate the viscoelastic constant of the myocardium in the human heart wall using the simple dispersion equation for a small Lamb wavenumber instead of using a complex nonlinear optimization.
Wang, Zhaojun; Zhou, Xiaoming
2016-12-01
The authors study the wave propagation in continuum acoustic metamaterials whose all or not all of the principal elements of the mass tensor or the scalar compressibility can be negative due to wave dispersion. Their time-domain wave characteristics are particularly investigated by the finite-difference time-domain (FDTD) method, in which algorithms for the Drude and Lorentz dispersion pertinent to acoustic metamaterials are provided necessarily. Wave propagation nature of anisotropic acoustic metamaterials with all admissible material parameters are analyzed in a general manner. It is found that anomalous negative refraction phenomena can appear in several dispersion regimes, and their unique time-domain signatures have been discovered by the FDTD modeling. It is further proposed that two different metamaterial layers with specially assigned dispersions could comprise a conjugate pair that permits wave propagation only at specific points in the wave vector space. The time-domain pulse simulation verifies that acoustic directive radiation capable of modulating radiation angle with the wave frequency can be realized with this conjugate pair. The study provides the detailed analysis of wave propagation in anisotropic and dispersive acoustic mediums, which makes a further step toward dispersion engineering and transient wave control through acoustic metamaterials.
Observation of spin-wave dispersion in Nd-Fe-B magnets using neutron Brillouin scattering
Ono, K. Inami, N.; Saito, K.; Takeichi, Y.; Kawana, D.; Yokoo, T.; Itoh, S.; Yano, M.; Shoji, T.; Manabe, A.; Kato, A.; Kaneko, Y.
2014-05-07
The low-energy spin-wave dispersion in polycrystalline Nd-Fe-B magnets was observed using neutron Brillouin scattering (NBS). Low-energy spin-wave excitations for the lowest acoustic spin-wave mode were clearly observed. From the spin-wave dispersion, we were able to determine the spin-wave stiffness constant D{sub sw} (100.0 ± 4.9 meV.Å{sup 2}) and the exchange stiffness constant A (6.6 ± 0.3 pJ/m)
NASA Astrophysics Data System (ADS)
Sundkvist, David; Krasnoselskikh, V.; Bale, S. D.; Schwartz, S. J.; Soucek, J.; Mozer, F.
2012-01-01
Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.
Packo, Pawel; Uhl, Tadeusz; Staszewski, Wieslaw J
2014-09-01
The paper presents an efficient and accurate method for dispersion curve calculation and analysis of numerical models for guided waves. The method can be used for any arbitrarily selected anisotropic material. The proposed approach utilizes the wave equation and through-thickness-only discretization of anisotropic, layered plates to obtain the Lamb wave characteristics. Thus, layered structures, such as composites, can be analyzed in a straightforward manner. A general framework for the proposed analysis is given, along with application examples. Although these examples are based on the local interaction simulation approach for elastic waves propagation, the proposed methodology can be easily adopted for other methods (e.g., finite elements). The method can be also used to study the influence of discretization parameters on dispersion curves estimates.
Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?
NASA Astrophysics Data System (ADS)
Heyer, M.; Goldsmith, P. F.; Yıldız, U. A.; Snell, R. L.; Falgarone, E.; Pineda, J. L.
2016-10-01
The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J = 2-1 emission obtained with the 10-m Submillimeter Telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J = 2-1 to J = 1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations are generated from the modulation of velocities and beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvénic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.
NASA Astrophysics Data System (ADS)
Mruczkiewicz, M.; Krawczyk, M.
2014-03-01
We study the effect of one-side metallization of a uniform ferromagnetic thin film on its spin-wave dispersion relation in the Damon-Eshbach geometry. Due to the finite conductivity of the metallic cover layer on the ferromagnetic film, the spin-wave dispersion relation may be nonreciprocal only in a limited wave-vector range. We provide an approximate analytical solution for the spin-wave frequency, discuss its validity, and compare it with numerical results. The dispersion is analyzed systematically by varying the parameters of the ferromagnetic film, the metal cover layer and the value of the external magnetic field. The conclusions drawn from this analysis allow us to define a structure based on a 30 nm thick CoFeB film with an experimentally accessible nonreciprocal dispersion relation in a relatively wide wave-vector range.
Li, Zhengkai; Lee, Kenneth; King, Thomas; Boufadel, Michel C; Venosa, Albert D
2008-05-01
Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural environment, including transport and dilution effects. To achieve this goal, Fisheries and Oceans Canada and the US Environmental Protection Agency (EPA) designed and constructed a wave tank system to study chemical dispersant effectiveness under controlled mixing energy conditions (regular non-breaking, spilling breaking, and plunging breaking waves). Quantification of oil dispersant effectiveness was based on observed changes in dispersed oil concentrations and oil-droplet size distribution. The study results quantitatively demonstrated that total dispersed oil concentration and breakup kinetics of oil droplets in the water column were strongly dependent on the presence of chemical dispersants and the influence of breaking waves. These data on the effectiveness of dispersants as a function of sea state will have significant implications in the drafting of future operational guidelines for dispersant use at sea.
Increased P-wave dispersion in patients with newly diagnosed lichen planus
Sahin, Musa; Bilgili, Serap Gunes; Simsek, Hakki; Akdag, Serkan; Akyol, Aytac; Gumrukcuoglu, Hasan Ali; Yaman, Mehmet; Bayram, Yasemin; Karadag, Ayse Serap
2013-01-01
OBJECTIVE: Lichen planus is a chronic inflammatory autoimmune mucocutaneous disease. Recent research has emphasized the strong association between inflammation and both P-wave dispersion and dyslipidemia. The difference between the maximum and minimum P-wave durations on an electrocardiogram is defined as P-wave dispersion. The prolongation of P-wave dispersion has been demonstrated to be an independent risk factor for developing atrial fibrillation. The aim of this study was to investigate P-wave dispersion in patients with lichen planus. METHODS: Fifty-eight patients with lichen planus and 37 age- and gender-matched healthy controls were included in this study. We obtained electrocardiographic recordings from all participants and used them to calculate the P-wave variables. We also assessed the levels of highly sensitive C-reactive protein, which is an inflammatory marker, and the lipid levels for each group. The results were reported as the means ± standard deviations and percentages. RESULTS: The P-wave dispersion was significantly higher in lichen planus patients than in the control group. Additionally, highly sensitive C-reactive protein, LDL cholesterol, and triglyceride levels were significantly higher in lichen planus patients compared to the controls. There was a significant positive correlation between highly sensitive C-reactive protein and P-wave dispersion (r = 0.549, p<0.001) in lichen planus patients. CONCLUSIONS: P-wave dispersion increased on the surface electrocardiographic measurements of lichen planus patients. This result may be important in the early detection of subclinical cardiac involvement. Increased P-wave dispersion, in terms of the tendency for atrial fibrillation, should be considered in these patients. PMID:23778479
Sparse recovery of the multimodal and dispersive characteristics of Lamb waves.
Harley, Joel B; Moura, José M F
2013-05-01
Guided waves in plates, known as Lamb waves, are characterized by complex, multimodal, and frequency dispersive wave propagation, which distort signals and make their analysis difficult. Estimating these multimodal and dispersive characteristics from experimental data becomes a difficult, underdetermined inverse problem. To accurately and robustly recover these multimodal and dispersive properties, this paper presents a methodology referred to as sparse wavenumber analysis based on sparse recovery methods. By utilizing a general model for Lamb waves, waves propagating in a plate structure, and robust l1 optimization strategies, sparse wavenumber analysis accurately recovers the Lamb wave's frequency-wavenumber representation with a limited number of surface mounted transducers. This is demonstrated with both simulated and experimental data in the presence of multipath reflections. With accurate frequency-wavenumber representations, sparse wavenumber synthesis is then used to accurately remove multipath interference in each measurement and predict the responses between arbitrary points on a plate.
MHD waveguides in space plasma
Mazur, N. G.; Fedorov, E. N.; Pilipenko, V. A.
2010-07-15
The waveguide properties of two characteristic formations in the Earth's magnetotail-the plasma sheet and the current (neutral) sheet-are considered. The question of how the domains of existence of different types of MHD waveguide modes (fast and slow, body and surface) in the (k, {omega}) plane and their dispersion properties depend on the waveguide parameters is studied. Investigation of the dispersion relation in a number of particular (limiting) cases makes it possible to obtain a fairly complete qualitative pattern of all the branches of the dispersion curve. Accounting for the finite size of perturbations across the wave propagation direction reveals new additional effects such as a change in the critical waveguide frequencies, the excitation of longitudinal current at the boundaries of the sheets, and a change in the symmetry of the fundamental mode. Knowledge of the waveguide properties of the plasma and current sheets can explain the occurrence of preferred frequencies in the low-frequency fluctuation spectra in the magnetotail. In satellite observations, the type of waveguide mode can be determined from the spectral properties, as well as from the phase relationships between plasma oscillations and magnetic field oscillations that are presented in this paper.
Zonca, F.; Chen, L.
2008-11-01
We briefly discuss the unified theoretical framework that allows explaining a variety of experimental observations with one single 'fishbone-like' dispersion relation. We also point out the relationship of MHD and shear Alfven waves in the kinetic thermal ion frequency gap with microturbulence, Zonal Flows and Geodesic Acoustic Modes, emphasizing its importance in determining long time scale dynamic behaviors in burning plasmas.
Minimizing influence of multi-modes and dispersion of electromagnetic ultrasonic lamb waves.
Zhai, Guofu; Jiang, Tao; Kang, Lei; Wang, Shujuan
2010-12-01
Electromagnetic ultrasonic (EMU) Lamb waves excited by electromagnetic acoustic transducers (EMATs) possess many advantages in NDT. However, their characteristic multi-modes and dispersion are disadvantageous for inspection and restrict further improvements in their real applications. By deducing the excitation equation of EMU Lamb waves, the primary design parameters of EMATs and the characteristic equation of Lamb waves are combined, and excitation curves based on the excitation equation are plotted to aid the design of EMATs. The excitation characteristic of EMU Lamb waves on different thickness of plates is analyzed according to the excitation curves. The influence of multi-modes of EMU Lamb waves is minimized by choosing reasonable operating points and operating zones to excite a single-mode Lamb wave or multi-mode Lamb waves with identical or approximate propagation velocities. The influence of dispersion is minimized by searching corresponding points whose slope of group velocity tends to zero. The validity of the proposed method is verified by experiments.
Luo, Y.; Xu, Y.; Liu, Q.; Xia, J.
2008-01-01
In recent years, multichannel analysis of surface waves (MASW) has been increasingly used for obtaining vertical shear-wave velocity profiles within near-surface materials. MASW uses a multichannel recording approach to capture the time-variant, full-seismic wavefield where dispersive surface waves can be used to estimate near-surface S-wave velocity. The technique consists of (1) acquisition of broadband, high-frequency ground roll using a multichannel recording system; (2) efficient and accurate algorithms that allow the extraction and analysis of 1D Rayleigh-wave dispersion curves; (3) stable and efficient inversion algorithms for estimating S-wave velocity profiles; and (4) construction of the 2D S-wave velocity field map.
Wave dispersion in a counterstreaming, cold, magnetized, electron-positron plasma.
Verdon, M W; Melrose, D B
2008-04-01
The dispersion equation is analyzed for waves in a strongly magnetized, electron-positron plasma in which counterstreaming electrons are cold in their respective rest frames. For propagation parallel to the magnetic field the dispersion equation factorizes into equations for two longitudinal modes and four transverse modes. Instabilities occur in both longitudinal and transverse modes, with the most notable being at low wave numbers where a longitudinal branch has purely imaginary frequency. For oblique propagation at small angles, the modes reconnect at points where the parallel modes intersect, either deviating away from each another, or being separated by a pair of complex modes. In addition, intrinsically oblique branches of the dispersion equation appear. The results are applied to an oscillating model for a pulsar magnetosphere, in which the oscillations are purely temporal with a frequency well below relevant wave frequencies, and in which the counterstreaming becomes highly relativistic. We assume that the medium may be treated as time stationary in treating the wave dispersion and wave growth. The wave properties, including the wave frequency, vary periodically with the phase of the oscillations. The fastest growing instability is when the counterstreaming is nonrelativistic or mildly relativistic. A given wave can experience bursts of growth over many oscillations. Mode coupling associated with the cyclotron resonance may be effective in generating the observed orthogonally polarized modes at phases of the oscillation where the (relativistic) cyclotron and wave frequencies are comparable.
Electromagnetic drift waves dispersion for arbitrarily collisional plasmas
Lee, Wonjae Krasheninnikov, Sergei I.; Angus, J. R.
2015-07-15
The impacts of the electromagnetic effects on resistive and collisionless drift waves are studied. A local linear analysis on an electromagnetic drift-kinetic equation with Bhatnagar-Gross-Krook-like collision operator demonstrates that the model is valid for describing linear growth rates of drift wave instabilities in a wide range of plasma parameters showing convergence to reference models for limiting cases. The wave-particle interactions drive collisionless drift-Alfvén wave instability in low collisionality and high beta plasma regime. The Landau resonance effects not only excite collisionless drift wave modes but also suppress high frequency electron inertia modes observed from an electromagnetic fluid model in collisionless and low beta regime. Considering ion temperature effects, it is found that the impact of finite Larmor radius effects significantly reduces the growth rate of the drift-Alfvén wave instability with synergistic effects of high beta stabilization and Landau resonance.
Formation of wave packets in the Ostrovsky equation for both normal and anomalous dispersion
Grimshaw, Roger; Stepanyants, Yury; Alias, Azwani
2016-01-01
It is well known that the Ostrovsky equation with normal dispersion does not support steady solitary waves. An initial Korteweg–de Vries solitary wave decays adiabatically through the radiation of long waves and is eventually replaced by an envelope solitary wave whose carrier wave and envelope move with different velocities (phase and group velocities correspondingly). Here, we examine the same initial condition for the Ostrovsky equation with anomalous dispersion, when the wave frequency increases with wavenumber in the limit of very short waves. The essential difference is that now there exists a steady solitary wave solution (Ostrovsky soliton), which in the small-amplitude limit can be described asymptotically through the solitary wave solution of a nonlinear Schrödinger equation, based at that wavenumber where the phase and group velocities coincide. Long-time numerical simulations show that the emergence of this steady envelope solitary wave is a very robust feature. The initial Korteweg–de Vries solitary wave transforms rapidly to this envelope solitary wave in a seemingly non-adiabatic manner. The amplitude of the Ostrovsky soliton strongly correlates with the initial Korteweg–de Vries solitary wave. PMID:26997887
Density functional calculations of spin-wave dispersion curves.
NASA Astrophysics Data System (ADS)
Kleinman, Leonard; Niu, Qian
1998-03-01
Extending the density functional method of Kubler et al( J. Kubler et al, J. Phys. F 18, 469 (1983) and J. Phys. Condens. Matter 1, 8155 (1989). ) for calcuating spin density wave ground states (but not making their atomic sphere approximation which requires a constant spin polarization direction in each WS sphere) we dicuss the calculation of frozen spin-wave eigenfunctions and their total energies. From these and the results of Niu's talk, we describe the calculation of spin-wave frequencies.
NASA Astrophysics Data System (ADS)
Luppescu, Gregory C.; Dawson, Alexander J.; Michaels, Jennifer E.
2016-02-01
Although bulk waves have served as the industry standard in nondestructive evaluation for many years, guided waves (Lamb waves in plates) have become the focus of many current research efforts because they are able to interrogate larger areas of a structure in less time. Despite this advantage, guided waves also have characteristics that obfuscate data interpretation. The first property of guided waves that complicates analysis is their dispersive nature: their wave speed is a function of frequency. The second is that they are multimodal: they propagate as multiple symmetric and antisymmetric modes. Using pulse-compression techniques and a priori calculations of theoretical dispersion curves, the dispersive matched filter attempts to take advantage of these otherwise undesirable characteristics by maximizing the autocorrelation for only one mode, ideally increasing both the signal-to-noise ratio and time-resolution of ultrasonic guided wave measurements. In this research, the responses from broadband chirp excitations are recorded from a sparse transducer array after propagation through an aluminum plate containing no damage and simulated damage. Dispersive matched filtering is applied to the measurements and localization images are generated using the delay-and-sum method. Imaging results are compared to those obtained with narrowband tone burst excitations in terms of their ability to detect and localize the different scatterers. Results show that the dispersive matched filter notably improves the quality of the localization images.
Li, Zhengkai; Lee, Kenneth; King, Thomas; Boufadel, Michel C; Venosa, Albert D
2010-09-01
The effectiveness of chemical dispersants (Corexit 9500 and SPC 1000) on heavy fuel oil (IFO180 as test oil) has been evaluated under different wave conditions in a flow-through wave tank. The dispersant effectiveness was determined by measuring oil concentrations and droplet size distributions. An analysis of covariance (ANCOVA) model indicated that wave type and temperature significantly (p<0.05) affected the dynamic dispersant effectiveness (DDE). At higher temperatures (16 degrees C), the test IFO180 was effectively dispersed under breaking waves with a DDE of 90% and 50% for Corexit 9500 and SPC 1000, respectively. The dispersion was ineffective under breaking waves at lower temperature (10 degrees C), and under regular wave conditions at all temperatures (10-17 degrees C), with DDE<15%. Effective chemical dispersion was associated with formation of smaller droplets (with volumetric mean diameters or VMD < or = 200 microm), whereas ineffective dispersion produced large oil droplets (with VMD > or = 400 microm).
Rayleigh-Wave Dispersion Technique for Rapid Subsurface Exploration
1973-04-01
23 Preceding page blank V CONVEJSION FACrOR3, BRITISH To METHIC UNITS OF MEASUREMENT British units of measurement used in this report can...soil layering, P-wave velocity, S-wave velocity, anid density of the media can be made. These param- eters can be determined by borehole sampling
Supercontinuum generation using continuous-wave multiwavelength pumping and dispersion management.
Sylvestre, Thibaut; Vedadi, Armand; Maillotte, Hervé; Vanholsbeeck, Frédérique; Coen, Stéphane
2006-07-01
We experimentally demonstrate that continuous-wave supercontinuum generation in optical fibers can be significantly enhanced by using both multiwavelength pumping and dispersion management. We show by detailed spectral analysis that continuum enhancement is achieved mainly through a combination of Raman-assisted modulation instabilities, soliton compression, and dispersive wave generation. With this technique, an 800 nm wide (from 1.2 to 2.0 microm) 2 W supercontinuum source is reported that uses a three-wavelength pump and a dispersion-tailored four-optical fibers arrangement.
Strongly nonlinear evolution of low-frequency wave packets in a dispersive plasma
NASA Technical Reports Server (NTRS)
Vasquez, Bernard J.
1993-01-01
The evolution of strongly nonlinear, strongly modulated wave packets is investigated in a dispersive plasma using a hybrid numerical code. These wave packets have amplitudes exceeding the strength of the external magnetic field, along which they propagate. Alfven (left helicity) wave packets show strong steepening for p < 1, while fast (fight heIicity) wave packets hardly steepen for any beta. Substantial regions of opposite helicity form on the leading side of steepened Alfven wave packets. This behavior differs qualitatively from that exhibited by the solutions to the derivative nonlinear Schrodinger (DNLS) equation.
Rayleigh-wave dispersive energy imaging using a high-resolution linear radon transform
Luo, Y.; Xia, J.; Miller, R.D.; Xu, Y.; Liu, J.; Liu, Q.
2008-01-01
Multichannel Analysis of Surface Waves (MASW) analysis is an efficient tool to obtain the vertical shear-wave profile. One of the key steps in the MASW method is to generate an image of dispersive energy in the frequency-velocity domain, so dispersion curves can be determined by picking peaks of dispersion energy. In this paper, we propose to image Rayleigh-wave dispersive energy by high-resolution linear Radon transform (LRT). The shot gather is first transformed along the time direction to the frequency domain and then the Rayleigh-wave dispersive energy can be imaged by high-resolution LRT using a weighted preconditioned conjugate gradient algorithm. Synthetic data with a set of linear events are presented to show the process of generating dispersive energy. Results of synthetic and real-world examples demonstrate that, compared with the slant stacking algorithm, high-resolution LRT can improve the resolution of images of dispersion energy by more than 50%. ?? Birkhaueser 2008.
Zhang, S.X.; Chan, L.S.; Xia, J.
2004-01-01
The accuracy and resolution of surface wave dispersion results depend on the parameters used for acquiring data in the field. The optimized field parameters for acquiring multichannel analysis of surface wave (MASW) dispersion images can be determined if preliminary information on the phase velocity range and interface depth is available. In a case study on a fill slope in Hong Kong, the optimal acquisition parameters were first determined from a preliminary seismic survey prior to a MASW survey. Field tests using different sets of receiver distances and array lengths showed that the most consistent and useful dispersion images were obtained from the optimal acquisition parameters predicted. The inverted S-wave velocities from the dispersion curve obtained at the optimal offset distance range also agreed with those obtained by using direct refraction survey.
Pulse compression and dispersion compensation for high- resolution Lamb wave inspection
NASA Astrophysics Data System (ADS)
Hua, J.; Lin, J.; Zeng, L.
2015-07-01
The dispersion of ultrasonic guided waves causes the energy of a signal to spread out in space and time as it propagates, which decreases the performance for damage detection significantly. A lot of signal processing methods have been proposed to reduce the effect of dispersion for this reason. In this paper, with the aim of developing an efficient methodology for high resolution Lamb wave inspection, a pulse compression and dispersion compensation method is established. In this method, broadband excitation and pulse compression technique are introduced to reconstruct the transform function with a high SNR. Subsequently, a scheme is established to alleviate the dispersion effects by performing compensation on the original narrowband excitation signals, and thus the time duration of received wave packet can be compressed during the extracting process. Finally, Numerical simulation and experiment are carried on aluminum specimens to investigate the behavior of the proposed method.
Testing dispersant effectiveness under conditions similar to that of the open environment is required for improvements in operational procedures and the formulation of regulatory guidelines. To this end, a novel wave tank facility was fabricated to study the dispersion of crude ...
Extending dispersive waves theory to use in semi-open systems
NASA Astrophysics Data System (ADS)
Chumakova, Lyubov; Rosales, Ruben; Rzeznik, Andrew; Tabak, Esteban
2015-11-01
In the classical linear dispersive wave theory the sinusoidal waves e i (kx - ωt) carry energy with the group speed cg = dω / dk . This concept is limited to the case where both the frequency ω (k) and the wavenumber k are real. On the other hand, semi-open dispersive systems allow more than just sinusoidal solutions: they can have exponentially blowing up and/or decaying solutions as well. In this talk I will address the questions of what is direction and the speed of the energy propagation for these exponential waves, extend the classical concept of group velocity, and use this theory to construct radiation boundary conditions for semi-open dispersive systems. This approach will be demonstrated on an example of dry hydrostatic troposphere which experiences effective damping due to gravity waves propagating into the stratosphere. RSE, Scottish government.
Urban, Matthew W.; Pislaru, Cristina; Nenadic, Ivan Z.; Kinnick, Randall R.; Greenleaf, James F.
2012-01-01
Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb Wave Dispersion Ultrasound Vibrometry (LDUV) is a shear wave-based method that uses wave velocity dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of wave propagation were measured over the 50–400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb wave model to obtain estimates of the shear elasticity, μ1, and viscosity, μ2 as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb wave model was also studied using simulated data. We demonstrated that wave velocity measurements and Lamb wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle. PMID:23060325
Tuning of acoustic wave dispersion in ferroelectrics—A theoretical study
NASA Astrophysics Data System (ADS)
Chang, Wontae
2017-02-01
Tuning of acoustic wave dispersion in ferroelectrics due to its electrostrictive effect is theoretically investigated. As the acoustic wave is excited electrically in ferroelectrics, the elastic stiffness tensor can be modified by both the linear piezoelectric and nonlinear electrostrictive electromechanical couplings depending on the wave excitation direction of the crystal, where the linear piezoelectric modification has been well characterized and extensively used for the application of piezoelectric-based acoustic wave devices over the past 50 years, but the nonlinear electrostrictive modification, determining the tuning of acoustic wave dispersion in the medium, is still too premature to use the properties in application. For the tuning application, it is essential to know how the electrostrictive strain actually tunes the propagation and displacement of the ferroelectrically active acoustic waves, and this information is currently unavailable. In this paper, the ferroelectrically active acoustic wave propagation and displacement in conjunction with the nonlinear electrostrictive modification are calculated using the plane wave expansion method, and the tunable wave properties associated with the propagation and displacement, are discussed. The electrically excited acoustic wave properties in ferroelectrics are largely modified from the electrostrictive effect, e.g., tuned, excited, vanished, coupled, decoupled, etc., and this should be taken into account in the development of ferroelectric-based acoustic wave devices.
NASA Astrophysics Data System (ADS)
Lotekar, Ajay; Kakad, Amar; Kakad, Bharati
2016-10-01
One-dimensional fluid simulation is performed for the unmagnetized plasma consisting of cold fluid ions and superthermal electrons. Such a plasma system supports the generation of ion acoustic (IA) waves. A standard Gaussian type perturbation is used in both electron and ion equilibrium densities to excite the IA waves. The evolutionary profiles of the IA waves are obtained by varying the superthermal index and the amplitude of the initial perturbation. This simulation demonstrates that the amplitude of the initial perturbation and the superthermal index play an important role in determining the time evolution and the characteristics of the generated IA waves. The initial density perturbation in the system creates charge separation that drives the finite electrostatic potential in the system. This electrostatic potential later evolves into the dispersive and nondispersive IA waves in the simulation system. The density perturbation with the amplitude smaller than 10% of the equilibrium plasma density evolves into the dispersive IA waves, whereas larger density perturbations evolve into both dispersive and nondispersive IA waves for lower and higher superthermal index. The dispersive IA waves are the IA oscillations that propagate with constant ion plasma frequency, whereas the nondispersive IA waves are the IA solitary pulses (termed as IA solitons in the stability region) that propagate with the constant wave speed. The characteristics of the stable nondispersive IA solitons are found to be consistent with the nonlinear fluid theory. To the best of our knowledge, this is the first fluid simulation study that has considered the superthermal distributions for the plasma species to model the electrostatic solitary waves.
Weerasekara, Gihan; Tokunaga, Akihiro; Terauchi, Hiroki; Eberhard, Marc; Maruta, Akihiro
2015-01-12
One of the extraordinary aspects of nonlinear wave evolution which has been observed as the spontaneous occurrence of astonishing and statistically extraordinary amplitude wave is called rogue wave. We show that the eigenvalues of the associated equation of nonlinear Schrödinger equation are almost constant in the vicinity of rogue wave and we validate that optical rogue waves are formed by the collision between quasi-solitons in anomalous dispersion fiber exhibiting weak third order dispersion.
Exchange Coulomb interaction in nanotubes: Dispersion of Langmuir waves
Andreev, P. A. Ivanov, A. Yu.
2015-07-15
The microscopic derivation of the Coulomb exchange interaction for electrons located on the nanotubes is presented. The derivation is based on the many-particle quantum hydrodynamic method. We demonstrate the effect of curvature of the nanocylinders on the force of exchange interaction. We calculate corresponding dispersion dependencies for electron oscillations on the nanotubes.
Modulation theory, dispersive shock waves and Gerald Beresford Whitham
NASA Astrophysics Data System (ADS)
Minzoni, A. A.; Smyth, Noel F.
2016-10-01
Gerald Beresford (GB) Whitham, FRS, (13th December, 1927-26th January, 2014) was one of the leading applied mathematicians of the twentieth century whose work over forty years had a profound, formative impact on research on wave motion across a broad range of areas. Many of the ideas and techniques he developed have now become the standard tools used to analyse and understand wave motion, as the papers of this special issue of Physica D testify. Many of the techniques pioneered by GB Whitham have spread beyond wave propagation into other applied mathematics areas, such as reaction-diffusion, and even into theoretical physics and pure mathematics, in which Whitham modulation theory is an active area of research. GB Whitham's classic textbook Linear and Nonlinear Waves, published in 1974, is still the standard reference for the applied mathematics of wave motion. In honour of his scientific achievements, GB Whitham was elected a Fellow of the American Academy of Arts and Sciences in 1959 and a Fellow of the Royal Society in 1965. He was awarded the Norbert Wiener Prize for Applied Mathematics in 1980.
Measurement of the dispersion and attenuation of cylindrical ultrasonic guided waves in long bone.
Ta, Dean; Wang, Weiqi; Wang, YuanYuan; Le, Lawrence H; Zhou, Yuqing
2009-04-01
Osteoporotic bones are likely to have less cortical bone than healthy bones. The velocities of guided waves propagating in a long cylindrical bone are very sensitive to bone properties and cortical thickness (CTh). This work studies the dispersion and attenuation of ultrasonic guided waves propagating in long cylindrical bone. A hollow cylinder filled with a viscous liquid was used to model the long bone and then to calculate the theoretical phase and group velocities, as well as the attenuation of the waves. The generation and selection of guided wave modes were based on theoretical dispersive curves. The phase velocity and attenuation of cylindrical guided wave modes, such as L(0,1), L(0,2) and L(0,3), were measured in bovine tibia using angled beam transducers at various propagation distances ranging from 75 to 160 mm. The results showed that the phase velocity of the L(0,2) guided wave mode decreased with an increase in CTh. The attenuation of the low cylindrical guided wave modes was a nonlinear function that increased with propagation distance and mode order. The L(0,2) mode had a different attenuation for each CTh. The experimental results were in good agreement with the predicted values. Cylindrical guided waves of low-frequency and low-order have been shown to demonstrate more dispersion and less attenuation and should, therefore, be used to evaluate long bone.
Wave-packet formation at the zero-dispersion point in the Gardner-Ostrovsky equation
NASA Astrophysics Data System (ADS)
Whitfield, A. J.; Johnson, E. R.
2015-05-01
The long-time effect of weak rotation on an internal solitary wave is the decay into inertia-gravity waves and the eventual emergence of a coherent, steadily propagating, nonlinear wave packet. There is currently no entirely satisfactory explanation as to why these wave packets form. Here the initial value problem is considered within the context of the Gardner-Ostrovsky, or rotation-modified extended Korteweg-de Vries, equation. The linear Gardner-Ostrovsky equation has maximum group velocity at a critical wave number, often called the zero-dispersion point. It is found here that a nonlinear splitting of the wave-number spectrum at the zero-dispersion point, where energy is shifted into the modulationally unstable regime of the Gardner-Ostrovsky equation, is responsible for the wave-packet formation. Numerical comparisons of the decay of a solitary wave in the Gardner-Ostrovsky equation and a derived nonlinear Schrödinger equation at the zero-dispersion point are used to confirm the spectral splitting.
Wave-packet formation at the zero-dispersion point in the Gardner-Ostrovsky equation.
Whitfield, A J; Johnson, E R
2015-05-01
The long-time effect of weak rotation on an internal solitary wave is the decay into inertia-gravity waves and the eventual emergence of a coherent, steadily propagating, nonlinear wave packet. There is currently no entirely satisfactory explanation as to why these wave packets form. Here the initial value problem is considered within the context of the Gardner-Ostrovsky, or rotation-modified extended Korteweg-de Vries, equation. The linear Gardner-Ostrovsky equation has maximum group velocity at a critical wave number, often called the zero-dispersion point. It is found here that a nonlinear splitting of the wave-number spectrum at the zero-dispersion point, where energy is shifted into the modulationally unstable regime of the Gardner-Ostrovsky equation, is responsible for the wave-packet formation. Numerical comparisons of the decay of a solitary wave in the Gardner-Ostrovsky equation and a derived nonlinear Schrödinger equation at the zero-dispersion point are used to confirm the spectral splitting.
Mirzanejhad, Saeed; Sohbatzadeh, Farshad; Ghasemi, Maede; Sedaghat, Zeinab; Mahdian, Zeinab
2010-05-15
In this article, the dispersion characteristics of the paraxial (near axis) electromagnetic (EM) waves in a relativistic electron beam guided by the ion channel are investigated. Equilibrium fields such as ion-channel electrostatic field and self-fields of relativistic electron beam are included in this formalism. In accordance with the equilibrium field structure, radial and azimuthal waves are selected as base vectors for EM waves. It is shown that the dispersion of the radially polarized EM and space charge waves are influenced by the equilibrium fields, but azimuthally polarized wave remain unaffected. In some wave number domains, the radially polarized EM and fast space charge waves are coupled. In these regions, instability is analyzed as a function of equilibrium structure. It is shown that the total equilibrium radial force due to the ion channel and electron beam and also relativistic effect play a key role in the coupling of the radially polarized EM wave and space charge wave. Furthermore, some asymptotic behaviors such as weak and strong ion channel, nonrelativistic case and cutoff frequencies are discussed. This instability could be used as an amplification mechanism for radially polarized EM waves in a beam-plasma system where a relativistic electron beam is guided by the ion channel.
Higher order dispersion in the propagation of a gravity wave packet
NASA Technical Reports Server (NTRS)
Yeh, K. C.; Dong, B.
1989-01-01
To the first order of approximation, the complex amplitude of a wave packet in an anisotropic and dispersive medium is convected with the group of velocity. However, a gravity wave is a vector wave. Its wave packet must be formed by superposition of various wave numbers with corresponding frequencies, as is the case for scalar waves, and additionally by superposing many eigenmodes which also depend on the wave number. To represent the vector wave packet self-consistently, it is found that a gradient term must be included in the expansion. For a Guassian wave packet, this gradient term is shown to have important implications on the velocity vector as represented by its hodograph. Numerical results show that the hodograph is influenced by the location of the relative position of interest from the center of a Gaussian pulse. Higher order expansion shows that an initial Gaussian wave packet will retain its Gaussian shape as it propagates, but the pulse will spread in all directions with its major axis undergoing a rotation. Numerical results indicate that these higher order dispersive effects may be marginally observable in the atmosphere.
NASA Astrophysics Data System (ADS)
Adames, Á. F.; Kim, D.
2015-12-01
A linear wave theory for the Madden-Julian Oscillation (MJO), previously developed by Sobel and Maloney, is extended upon in this study. Using column-integrated moisture as a prognostic variable, a dispersion relation is derived that solely depends on the convective adjustment timescale, a parameter that indicates the amount of moisture available for propagation and the distance that free Kelvin waves are able to travel in the presence of dissipation. The dispersion relation adequately describes the MJO's signal in the wavenumber-frequency spectrum and defines the MJO as a dispersive equatorial moist wave with a westward group velocity. On the basis of linear regression analysis of the time varying field of outgoing longwave radiation, it is estimated that that the MJO's group velocity is 2/5 as large as its eastward phase speed. This dispersion is the result of the anomalous winds in the Kelvin and Rossby wave responses modulating the mean distribution of moisture such that the moisture anomaly propagates eastward while wave energy propagates westward. Additionally, it is found that cloud-radiation feedbacks cause growth of the moist wave to be largest at the planetary scales. It is hypothesized that this scale selection mechanism is the result of upper-level cloudiness exhibiting a larger zonal extent than precipitation. The longwave radiative heating from these upper-level clouds causes an expansion of the region of ascent under weak-temperature gradient balance.
Optical gyroscope with controllable dispersion in four wave mixing regime.
NASA Astrophysics Data System (ADS)
Mikhailov, Eugeniy; Wolfe, Owen; Du, Shuangli; Rochester, Simon; Budker, Dmitry; Novikova, Irina
2016-05-01
We present our work towards realization of the fast-light gyroscope prototype, in which the sensitivity enhancement (compared to a regular laser gyroscopes) is achieved by adjusting the intra-cavity dispersion. We discuss schematics and underlying nonlinear effects leading to the negative dispersion in Rb vapor: level structure, optically addressed transitions, and configuration of the resonant cavity. We investigate dependence of the pulling factor (i.e., the ratio of the lasing frequency shift with the change of the cavity length to the equivalent resonance frequency shift in the empty cavity) on pump lasers detunings, power, and density of the atomic vapor. The observation of the pulling factor exceeding unity implies the gyroscope sensitivity improvement over the regular system This work is supported by Naval Air Warfare Center STTR program N68335-11-C-0428.
Microscopic Models for Electromagnetic Wave Propagation in Highly Dispersive Media
1990-06-18
rotations, the effects of pressure and temperature and to show the classes of density fluctuations in I which give spatial dispersion, ie, the k- dependance ...complex plane the response e (co, Q) lives on some Riemann surface which is determined by the k- dependance . 2. Talks and Publications Three talks were...sources of 1- dependance (k- dependance in Fourier transform variables) have been identified. One is bubbles or cavitation which scatter the propagating
Magnetic field effects on nonlocal wave dispersion characteristics of size-dependent nanobeams
NASA Astrophysics Data System (ADS)
Ebrahimi, Farzad; Barati, Mohammad Reza
2017-01-01
In this paper, wave propagation analysis of functionally graded size-dependent nanobeams embedded in elastic foundation exposed to a longitudinal magnetic field is conducted based on nonlocal elasticity theory. Material properties of nanobeam change gradually according to the sigmoid function. Applying an analytical solution, the acoustical and optical dispersion relations are explored for various wave number, nonlocality parameter, material composition, elastic foundation constants and magnetic field intensity. It is found that frequency and phase velocity of waves propagating in S-FGM nanobeam are significantly affected by these parameters. Also the presence of cutoff and escape frequencies in wave propagation analysis of embedded S-FGM nanobeams is investigated.
Nonlinear acoustics in a dispersive continuum: Random waves, radiation pressure, and quantum noise
NASA Astrophysics Data System (ADS)
Cabot, M. A.
The nonlinear interaction of sound with sound is studied using dispersive hydrodynamics which derived from a variational principle and the assumption that the internal energy density depends on gradients of the mass density. The attenuation of sound due to nonlinear interaction with a background is calculated and is shown to be sensitive to both the nature of the dispersion and decay bandwidths. The theoretical results are compared to those of low temperature helium experiments. A kinetic equation which described the nonlinear self-inter action of a background is derived. When a Deybe-type cutoff is imposed, a white noise distribution is shown to be a stationary distribution of the kinetic equation. The attenuation and spectrum of decay of a sound wave due to nonlinear interaction with zero point motion is calculated. In one dimension, the dispersive hydrodynamic equations are used to calculate the Langevin and Rayleigh radiation pressures of wave packets and solitary waves.
NASA Astrophysics Data System (ADS)
De Basabe, Jonás D.; Sen, Mrinal K.; Wheeler, Mary F.
2008-10-01
Recently, there has been an increased interest in applying the discontinuous Galerkin method (DGM) to wave propagation. In this work, we investigate the applicability of the interior penalty DGM to elastic wave propagation by analysing it's grid dispersion properties, with particular attention to the effect that different basis functions have on the numerical dispersion. We consider different types of basis functions that naturally yield a diagonal mass matrix. This is relevant to seismology because a diagonal mass matrix is tantamount to an explicit and efficient time marching scheme. We find that the Legendre basis functions that are traditionally used in the DGM introduce numerical dispersion and anisotropy. Furthermore, we find that using Lagrange basis functions along with the Gauss nodes has attractive advantages for numerical wave propagation.
NASA Astrophysics Data System (ADS)
Barth, M.; Küttner, M.; Köhler, B.; Bamberg, J.; Baron, H.-U.
2012-05-01
There are several approaches for determining the Rayleigh wave dispersion of surface treated materials. Most of them are based either on ultrasonic probes in contact technique or on laser excitation or detection of ultrasound. Disadvantages of these methods for in-service use are coupling problems (contact methods) and very high device costs (laser based methods). The paper presents an immersion technique trying to avoid the disadvantages of the previous approaches for practical use. The High precision Ultrasound Goniometer (HUGO) allows to vary both: the sound beam angles and the distance between the excitation and detection sound beams. Thus, the Rayleigh wave velocity and its dispersion can be determined by two independent methods: by the drop in the reflexion coefficient at the Rayleigh angle and by change in travel time for a given change in travel distance. The dispersion can also be determined for surface skimming longitudinal waves. The application for stress determination in surface treated aero-engine materials is discussed.
Dispersion relations with crossing symmetry for {pi}{pi} D- and F-wave amplitudes
Kaminski, R.
2011-04-01
A set of once subtracted dispersion relations with imposed crossing symmetry condition for the {pi}{pi} D- and F-wave amplitudes is derived and analyzed. An example of numerical calculations in the effective two-pion mass range from the threshold to 1.1 GeV is presented. It is shown that these new dispersion relations impose quite strong constraints on the analyzed {pi}{pi} interactions and are very useful tools to test the {pi}{pi} amplitudes. One of the goals of this work is to provide a complete set of equations required for easy use. Full analytical expressions are presented. Along with the well-known dispersion relations successful in testing the {pi}{pi} S- and P-wave amplitudes, those presented here for the D and F waves give a complete set of tools for analyses of the {pi}{pi} interactions.
NASA Astrophysics Data System (ADS)
Maeda, Takuto; Tsushima, Hiroaki; Furumura, Takashi
2016-04-01
We numerically simulated the propagation of tsunami waves with finite difference methods by using perfectly matched layer (PML) boundary conditions to effectively eliminate artificial reflections from model boundaries. The PML method damps the tsunami height and velocity of seawater only in directions perpendicular to the boundary. Although the additional terms required to implement the PML conditions make the use of the PML technique difficult for linear dispersive tsunami waves, we have proposed an empirical extension of the PML method for modeling dispersive tsunami waves. Even for heterogeneous, realistic bathymetries, numerical tests demonstrated that the PML boundary condition dramatically decreased artificial reflections from model boundaries compared to the use of traditional boundary conditions. The use of PML boundary conditions for numerical modeling of tsunamis is especially useful because it facilitates use of the later phases of tsunamis that would otherwise be compromised by artifacts caused by reflections from model boundaries.
Mid-infrared dispersive waves generation in a birefringent fluorotellurite microstructured fiber
NASA Astrophysics Data System (ADS)
Yao, Chuanfei; Zhao, Zhipeng; Jia, Zhixu; Li, Qing; Hu, Minglie; Qin, Guanshi; Ohishi, Yasutake; Qin, Weiping
2016-09-01
Tunable mid-infrared dispersive waves are generated in a birefringent fluorotellurite microstructured fiber (FTMF) pumped by a 1560 nm femtosecond fiber laser. The FTMF have two zero-dispersion wavelengths (ZDWs) for each polarization axis. The second ZDWs for the fast and slow axes of the FTMF are 2224 and 2042 nm, respectively. As the pump laser is polarized along the fast (or slow) axis of the FTMF, tunable mid-infrared dispersive waves from 2680 to 2725 nm (or from 2260 to 2400 nm) are generated in the FTMF when the Raman soliton meets the second zero-dispersion wavelength of the fast (or slow) axis with increasing the pump power. Our results show that the designed FTMFs are promising nonlinear media for generating tunable mid-infrared light sources.
Pseudospectral modeling and dispersion analysis of Rayleigh waves in viscoelastic media
Zhang, K.; Luo, Y.; Xia, J.; Chen, C.
2011-01-01
Multichannel Analysis of Surface Waves (MASW) is one of the most widely used techniques in environmental and engineering geophysics to determine shear-wave velocities and dynamic properties, which is based on the elastic layered system theory. Wave propagation in the Earth, however, has been recognized as viscoelastic and the propagation of Rayleigh waves presents substantial differences in viscoelastic media as compared with elastic media. Therefore, it is necessary to carry out numerical simulation and dispersion analysis of Rayleigh waves in viscoelastic media to better understand Rayleigh-wave behaviors in the real world. We apply a pseudospectral method to the calculation of the spatial derivatives using a Chebyshev difference operator in the vertical direction and a Fourier difference operator in the horizontal direction based on the velocity-stress elastodynamic equations and relations of linear viscoelastic solids. This approach stretches the spatial discrete grid to have a minimum grid size near the free surface so that high accuracy and resolution are achieved at the free surface, which allows an effective incorporation of the free surface boundary conditions since the Chebyshev method is nonperiodic. We first use an elastic homogeneous half-space model to demonstrate the accuracy of the pseudospectral method comparing with the analytical solution, and verify the correctness of the numerical modeling results for a viscoelastic half-space comparing the phase velocities of Rayleigh wave between the theoretical values and the dispersive image generated by high-resolution linear Radon transform. We then simulate three types of two-layer models to analyze dispersive-energy characteristics for near-surface applications. Results demonstrate that the phase velocity of Rayleigh waves in viscoelastic media is relatively higher than in elastic media and the fundamental mode increases by 10-16% when the frequency is above 10. Hz due to the velocity dispersion of P
Impact of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation
NASA Technical Reports Server (NTRS)
Khazanov, G. V.; Gamayunov, K. V.
2007-01-01
Effect of the ring current ions in the real part of electromagnetic ion Cyclotron wave dispersion relation is studied on global scale. Recent Cluster observations by Engebretson et al. showed that although the temperature anisotropy of is energetic (> 10 keV) ring current protons was high during the entire 22 November 2003 perigee pass, electromagnetic ion cyclotron waves were observed only in conjunction with intensification of the ion fluxes below 1 keV by over an order of magnitude. To study the effect of the ring current ions on the wave dispersive properties and the corresponding global wave redistribution, we use a self-consistent model of interacting ring current and electromagnetic ion cyclotron waves, and simulate the May 1998 storm. The main findings of our simulation can be summarized as follows: First, the plasma density enhancement in the night MLT sector during the main and recovery storm phases is mostly caused by injection of suprathermal plasma sheet H + (approximately < 1 keV), which dominate the thermal plasma density. Second, during the recovery storm phases, the ring current modification of the wave dispersion relation leads to a qualitative change of the wave patterns in the postmidnight-dawn sector for L > 4.75. This "new" wave activity is well organized by outward edges of dense suprathermal ring current spots, and the waves are not observed if the ring current ions are not included in the real part of dispersion relation. Third, the most intense wave-induced ring current precipitation is located in the night MLT sector and caused by modification of the wave dispersion relation. The strongest precipitating fluxes of about 8 X 10(exp 6)/ (cm(exp 2) - s X st) are found near L=5.75, MLT=2 during the early recovery phase on 4 May. Finally, the nightside precipitation is more intense than the dayside fluxes, even if there are less intense waves, because the convection field moves ring current ions into the loss cone on the nightside, but drives
Surface Wave Dispersion Measurements and Tomography from Ambient Seismic Noise Correlation in China
2008-09-30
30 Sep 2008 REPRINT 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER SURFACE WAVE DISPERSION MEASUREMENTS AND TOMOGRAPHY FROM FA8718-07-C-0006 C AMIBIENT...25 September 2008, Portsmouth, VA, Volume I pp 268 - 278. 14. ABSTRACT We perform ambient noise tomography of China using the data from the China...National Seismic Network and global and PASSCAL stations. The results so far are summarized below. (I) Dispersion measurements and tomography . For most of
Acoustic Wave Dispersion and Scattering in Complex Marine Sediment Structures
2014-09-30
summary of the work completed is listed below: • Improvement of Viscous Grain Shearing (VGS) model [1] in collaboration with Mike Buckingham. We show...RESULTS The Viscous Grain Shearing model developed by Mike Buckingham [1] predicts the frequency dependence of compressional and wave speeds...unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2 assumed to be shearing at the grain -to- grain contacts and fluid flow around
On compression and rarefaction waves in a dispersed layer
NASA Astrophysics Data System (ADS)
Teplitskii, Yu. S.; Kovenskii, V. I.
2008-11-01
Mathematical modeling of nonstationary filtration regimes with instantaneous reduction (increase) in the pressure at entry into the granular bed has been carried out within the framework of the two-temperature approximation. The regularities of transmission of rarefaction and compression waves have been investigated. Equations for calculation of the minimum and maximum temperature of the heat-transfer agent in criterial form and of the time of reaching a new stationary state have been obtained.
Seismic wave attenuation and velocity dispersion in UAE carbonates
NASA Astrophysics Data System (ADS)
Ogunsami, Abdulwaheed Remi
Interpreting the seismic property of fluids in hydrocarbon reservoirs at low frequency scale has been a cherished goal of petroleum geophysics research for decades. Lately, there has been tremendous interest in understanding attenuation as a result of fluid flow in porous media. Although interesting, the emerging experimental and theoretical information still remain ambiguous and are practically not utilized for reasons not too obscure. Attenuation is frequency dependent and hard to measure in the laboratory at low frequency. This thesis describes and reports the results of an experimental study of low frequency attenuation and velocity dispersion on a selected carbonate reservoir samples in the United Arab Emirates (UAE). For the low frequency measurements, stress-strain method was used to measure the moduli from which the velocity is derived. Attenuation was measured as the phase difference between the applied stress and the strain. For the ultrasonic component, the pulse propagation method was employed. To study the fluid effect especially at reservoir in situ conditions, the measurements were made dry and saturated with liquid butane and brine at differential pressures of up to 5000 psi with pore pressure held constant at 500 psi. Similarly to what has been documented in the literatures for sandstone, attenuation of the bulk compressibility mode dominates the losses in these dry and somewhat partially saturated carbonate samples with butane and brine. Overall, the observed attenuation cannot be simply said to be frequency dependent within this low seismic band. While attenuation seems to be practically constant in the low frequency band for sample 3H, such conclusion cannot be made for sample 7H. For the velocities, significant dispersion is observed and Gassmann generally fails to match the measured velocities. Only the squirt model fairly fits the velocities, but not at all pressures. Although the observed dispersion is larger than Biot's prediction, the fact
Density Waves in Saturn's Rings: Non-linear Dispersion and Moon Libration Effects
NASA Astrophysics Data System (ADS)
Sremcevic, Miodrag; Stewart, G. R.; Albers, N.; Colwell, J. E.; Esposito, L. W.
2008-05-01
We analyze strong spiral density waves in stellar occultations by Saturn's A ring observed with the Cassini Ultraviolet Imaging Spectrograph (UVIS) and find that waves dispersion relation exhibits a clear deviation from the linear trend. All waves examined here reveal an intrinsic quadratic radial dependence on the wavenumber. We provide evidence that the deviation from the linear trend is caused by the ring's pressure term acting against the self-gravity of the ring particles. From the observed dispersion relation and using the theory of Goldreich and Tremaine (1978, 1979, ApJ) where the pressure is parameterized as p=σ c2, we measure the velocity dispersion c=2-5 mm/s in the A ring. Additionally, in all first order Pandora waves the dispersion relation exhibits a wiggly structure. Comparing 60 stellar UVIS occultations between 2004 and 2008 we infer that this wavenumber oscillation propagates away from the resonance location with a period of about 600 days. This inferred period is consistent with the 3:2 near corotation resonance between Pandora and Mimas (French et al., 2003, Icarus). The observed libration in wavenumber allows us to accurately measure the group velocity in the rings and obtain independent estimates of both surface density and velocity dispersion of the rings.
Dispersion of Lamb waves in a honeycomb composite sandwich panel.
Baid, Harsh; Schaal, Christoph; Samajder, Himadri; Mal, Ajit
2015-02-01
Composite materials are increasingly being used in advanced aircraft and aerospace structures. Despite their many advantages, composites are often susceptible to hidden damages that may occur during manufacturing and/or service of the structure. Therefore, safe operation of composite structures requires careful monitoring of the initiation and growth of such defects. Ultrasonic methods using guided waves offer a reliable and cost effective method for defects monitoring in advanced structures due to their long propagation range and their sensitivity to defects in their propagation path. In this paper, some of the useful properties of guided Lamb type waves are investigated, using analytical, numerical and experimental methods, in an effort to provide the knowledge base required for the development of viable structural health monitoring systems for composite structures. The laboratory experiments involve a pitch-catch method in which a pair of movable transducers is placed on the outside surface of the structure for generating and recording the wave signals. The specific cases considered include an aluminum plate, a woven composite laminate and an aluminum honeycomb sandwich panel. The agreement between experimental, numerical and theoretical results are shown to be excellent in certain frequency ranges, providing a guidance for the design of effective inspection systems.
MnO spin-wave dispersion curves from neutron powder diffraction
Goodwin, Andrew L.; Dove, Martin T.; Tucker, Matthew G.; Keen, David A.
2007-02-15
We describe a model-independent approach for the extraction of spin-wave dispersion curves from powder neutron total scattering data. Our approach is based on a statistical analysis of real-space spin configurations to calculate spin-dynamical quantities. The RMCPROFILE implementation of the reverse Monte Carlo refinement process is used to generate a large ensemble of supercell spin configurations from MnO powder diffraction data collected at 100 K. Our analysis of these configurations gives spin-wave dispersion curves for MnO that agree well with those determined independently using neutron triple-axis spectroscopic techniques.
Observation of dispersive shock waves, solitons, and their interactions in viscous fluid conduits
NASA Astrophysics Data System (ADS)
Anderson, Dalton; Maiden, Michelle; Lowman, Nicholas; Schubert, Marika; Hoefer, Mark
2016-11-01
Dispersive shock waves (DSWs) and solitons are fundamental structures in dispersive hydrodynamics, but studies have been severely constrained. Here we report on a novel testbed called the conduit system where one fluid is moved through another via a fluid pipe with virtually no mass diffusion. The interfacial dynamics of this pipe are conservative and are modeled by a scalar, nonlinear, dispersive wave equation, similar to those describing a superfluid. Resultantly, the interfacial waves are effectively dissipationless, which enables high fidelity observations of coherent phenomena such as large amplitude DSWs. Experiments involving solitons, wavebreaking leading to DSWs, and their interactions will be presented. The results include the refraction and absorption of a soliton by a DSW and the refraction of a DSW by a second DSW, resulting in two-phase behavior. Excellent agreement between nonlinear wave averaging, numerics, and laboratory experiments will be presented. The nonlinear wave dynamics observed in this model system have implications for a broad range of other conservative dispersive hydrodynamic systems. NSF.
Breakup of an oil slick mixed with dispersants by breaking wave
NASA Astrophysics Data System (ADS)
Li, Cheng; Holser, Anne; Katz, Joseph
2013-11-01
After oil spill, coherent oil slick are entrained by breaking ocean waves together with air, which produces a complicated three-phase flow, involving a wide range of length and time scales. The oil droplet size distribution is a crucial factor affecting the physical and chemical dispersion of oil spills, but little is known about oil droplet formation mechanism and droplet size distributions during and immediately after the impact of breaking waves. In our experimental study, we investigate the breakup of an oil slick in a specialized wave tank. The widely used dispersant Coexist 9500-A at different dispersant to oil ratio is used for varying the surface tension of crude oil (MC252 surrogate) in the 10 - 1 to 10 mN/m range. The dispersant is applied either by premixing or surface spraying, the latter consistent with typical application. The results include high-speed images of the oil and bubbles' entrainment, showing the resulting formation of a series of droplet clouds during multiple ``plunges'' associated with a single propagating breaking wave. High-speed inline digital holographic cinematography is employed to quantify the oil droplet size distribution, and the impact of droplet-bubble interactions on the entrainment process for varying Weber numbers, and wave properties, from spilling to plunging breakers. Supported by Gulf of Mexico Research Initiative (GoMRI).
Observation of dispersive shock waves developing from initial depressions in shallow water
NASA Astrophysics Data System (ADS)
Trillo, S.; Klein, M.; Clauss, G. F.; Onorato, M.
2016-10-01
We investigate surface gravity waves in a shallow water tank, in the limit of long wavelengths. We report the observation of non-stationary dispersive shock waves rapidly expanding over a 90 m flume. They are excited by means of a wave maker that allows us to launch a controlled smooth (single well) depression with respect to the unperturbed surface of the still water, a case that contains no solitons. The dynamics of the shock waves are observed at different levels of nonlinearity equivalent to a different relative smallness of the dispersive effect. The observed undulatory behavior is found to be in good agreement with the dynamics described in terms of a Korteweg-de Vries equation with evolution in space, though in the most nonlinear cases the description turns out to be improved over the quasi linear trailing edge of the shock by modeling the evolution in terms of the integro-differential (nonlocal) Whitham equation.
What do we know about shear wave dispersion in normal and steatotic livers?
Parker, Kevin J; Partin, Alexander; Rubens, Deborah J
2015-05-01
A number of new approaches to measure the viscoelastic properties of the liver are now available to clinicians, many involving shear waves. However, we are at an early stage in understanding the physical processes that govern shear wave propagation in normal liver, with more unknowns added when pathologies such as steatosis are present. This technical note focuses on what is known about the characterization of normal and steatotic (or fatty) livers, with a particular focus on dispersion. Some studies in phantoms and mouse livers support the hypothesis that, starting with a normal liver, increasing accumulations of micro- and macrosteatosis will increase the lossy viscoelastic properties of shear waves in a medium. This results in an increased dispersion (or slope) of shear wave speed and attenuation in the steatotic livers. Theoretical and empirical findings across a number of studies are summarized.
NASA Astrophysics Data System (ADS)
Goodman, M. L.
2008-12-01
Analytic solutions of an MHD model that includes an anisotropic, inhomogeneous electrical conductivity tensor containing Hall, Pedersen, and Spitzer conductivities are used to compute resistive heating rates as a function of height z from the photosphere to the lower corona due to dissipation of driven, linear, non- plane waves. The background state of the atmosphere is assumed to be an FAL atmosphere. This state is linearly perturbed by a harmonic perturbation of frequency ν. The height dependence of the perturbation in the presence of the inhomogeneous background state is determined by solving the MHD equations given the harmonic, horizontal, driving magnetic field Bx1 at the photosphere, the constant vertical magnetic field Bz, and the magnetic field strength Bcond(z) that enters the electrical conductivity tensor. The variation of the heating rates per unit volume and mass with ν, Bx1, and Bcond(0) are determined. The heating rates are found to be ∝ Bcond(0)2 Bx12, and to increase with ν. The Pedersen resistivity is ∝ Bcond(0)2. It is several orders of magnitude greater than the Spitzer resistivity in the chromosphere, and determines the rate of heating by Pedersen current dissipation in the chromosphere. The Pedersen current is essentially a proton current in the chromosphere. The onset of Pedersen current dissipation rates large enough to balance the net radiative loss from the chromosphere occurs near the height of the FAL temperature minimum, and is triggered by the product of the electron and proton magnetizations first exceeding unity. The magnetizations and heating rate increase rapidly with height beginning near the temperature minimum. For the special case of Bz = 200 G, Bx1=140 G, and 400 ≤ Bcond(0) ≤ 1500 G the driver frequency for which the period averaged chromospheric heating flux FCh = 5 × 106 ergs-cm-2-sec-1 has the corresponding range of 91 ≥ ν ≥ 25 mHz. Larger magnetic field strengths correspond to lower frequencies for a
Chakrabarti, Nikhil; Maity, Chandan; Schamel, Hans
2011-04-08
Compressional waves in a magnetized plasma of arbitrary resistivity are treated with the lagrangian fluid approach. An exact nonlinear solution with a nontrivial space and time dependence is obtained with boundary conditions as in Harris' current sheet. The solution shows competition among hydrodynamic convection, magnetic field diffusion, and dispersion. This results in a collapse of density and the magnetic field in the absence of dispersion. The dispersion effects arrest the collapse of density but not of the magnetic field. A possible application is in the early stage of magnetic star formation.
Are Ring Current Ions Lost in Electromagnetic Ion Cyclotron Wave Dispersion Relation?
NASA Technical Reports Server (NTRS)
Khazanov, G. V.; Gamayunov, K. V.
2006-01-01
Electromagnetic ion cyclotron (EMIC) waves are widely observed in the inner and outer magnetosphere, at geostationary orbit, at high latitudes along the plasmapause, and at the ionospheric altitudes. Interaction of the Ring Current (RC) ions and EMIC waves causes ion scattering into the loss cone and leads to decay of the RC, especially during the main phase of storms when the RC decay times of about one hour or less are observed. The oblique EMIC waves damp due to Landau resonance with the thermal plasmaspheric electrons, and subsequent transport of the dissipating wave energy into the ionosphere below causes an ionosphere temperature enhancement. Induced scattering of these waves by the plasmaspheric thermal ions leads to ion temperature enhancement, and forms a so-called hot zone near the plasmapause where the temperature of core plasma ions can reach tens of thousands of degrees. Relativistic electrons in the outer radiation belt also interact well with the EMIC waves, and during the main and/or recovery phases of the storms these electrons can easily be scattered into the loss cone over a time scale from several hours to a day. The plasma density distribution in the magnetosphere and the ion content play a critical role in EMIC wave generation and propagation, but the wave dispersion relation in the known RC-EMIC wave interaction models is assumed to be determined by the thermal plasma distribution only. In these models, the modification of the EMIC wave dispersion relation caused by the RC ions is not taken into account, and the RC ions are only treated as a source of free energy in order to generate EMIC waves. At the same time, the RC ions can dominate the thermal magnetospheric content in the night MLT sector at great L shells during the main and/or recovery storm phase. In this study, using our self-consistent RC-EMIC wave model [Khazanov et al., 2006], we simulate the May 1998 storm in order to quantify the global EMIC wave redistribution caused by
Effect of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation
NASA Technical Reports Server (NTRS)
Gamayunov, K. V.; Khazanov, G. V.
2006-01-01
Electromagnetic ion cyclotron (EMIC) waves are widely observed in the inner and outer magnetosphere, at geostationary orbit, at high latitudes along the plasmapause, and at the ionospheric altitudes. Interaction of the Ring Current (RC) ions and EMIC waves causes ion scattering into the loss cone and leads to decay of the RC, especially during the main phase of storms when the RC decay times of about one hour or less are observed. The oblique EMIC waves damp due to Landau resonance with the thermal plasmaspheric electrons, and subsequent transport of the dissipating wave energy into the ionosphere below causes an ionosphere temperature enhancement. Induced scattering of these waves by the plasmaspheric thermal ions leads to ion temperature enhancement, and forms a so-called hot zone near the plasmapause where the temperature of core plasma ions can reach tens of thousands of degrees. Relativistic electrons in the outer radiation belt also interact well with the EMIC waves, and during the main and/or recovery phases of the storms these electrons can easily be scattered into the loss cone over a time scale from several hours to a day. The plasma density distribution in the magnetosphere and the ion content play a critical role in EMIC wave generation and propagation, but the wave dispersion relation in the known RC-EMIC wave interaction models is assumed to be determined by the thermal plasma distribution only. In these models, the modification of the EMIC wave dispersion relation caused by the RC ions is not taken into account, and the RC ions are only treated as a source of free energy in order to generate EMIC waves. At the same time, the RC ions can dominate the thermal magnetospheric content in the night MLT sector at great L shells during the main and/or recovery storm phase. In this study, using our self-consistent RC-EMIC wave model [Khazanov et al., 2006], we simulate the May 1998 storm in order to quantify the global EMIC wave redistribution caused by
Dispersion in Nb microstrip transmission lines at submillimeter wave frequencies
NASA Technical Reports Server (NTRS)
Javadi, H. H. S.; Mcgrath, W. R.; Bumble, B.; Leduc, H. G.
1992-01-01
We have measured the effects of dispersion on the resonant mode frequencies of open-ended Nb-SiO(x)-Nb microstrip transmission lines over a frequency range from 50 to 800 GHz. Submicron Nb/Al-AlOx/Nb Josephson junctions were used as both voltage-controlled oscillators and detectors to sample the high order modes of the resonators. The resonator modes are equally spaced up to about 550 GHz where the mode spacing start to decrease gradually to a minimum above the gap frequency of about 700 GHz and then increases. Results are in good agreement with the expected theoretical behavior based on the Mattis-Bardeen conductivity of the superconductor line.
Nenadic, Ivan Z.; Urban, Matthew W.; Mitchell, Scott A.; Greenleaf, James F.
2011-01-01
Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of Shearwave Dispersion Ultrasound Vibrometry (SDUV), a noninvasive ultrasound based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb wave Dispersion Ultrasound Vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb waves and measure the dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb wave model was fitted to the wave speed dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb wave dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify mechanical properties of soft tissues with a plate-like geometry. PMID:21403186
1D profiling using highly dispersive guided waves
NASA Astrophysics Data System (ADS)
Volker, Arno; Brandenburg, Martijn
2017-02-01
Corrosion is one of the industries major issues regarding the integrity of assets. Currently inspections are conducted at regular intervals to ensure a sufficient integrity level of these assets. There are many situations where the actual defect location is not accessible, e.g., a pipe support or a partially buried pipe. Last year an approach was presented using a phase inversion of guided waves that propagated around the circumference of a pipe. This approach works well for larger corrosion spots, but shows significant under-sizing of small spots due to lack of sufficient phase rotation. In this paper the use of arrival time and amplitude loss of higher order circumferential passes is evaluated. Using higher order passes increases sensitivity for sizing smaller defects. Different defect profiles are assumed and the change in arrival time and amplitude loss are calculated using a wave equation based approach for different defect widths and depths. This produces a differential travel time and amplitude change map as function of defect depth and defect width. The actually measured travel time change and amplitude change produces two contours in these maps. Calculating the intersection point gives the defect dimensions. The contours for amplitude loss and travel time change are quite orthogonal, this yields a good discrimination between deep and shallow defects. The approach is evaluated using experimental data from different pipes contain artificial and real defects.
Propagation and dispersion of whistler waves generated by fast reconnection onset
NASA Astrophysics Data System (ADS)
Singh, Nagendra
2013-02-01
The role of whistler mode during the onset of magnetic reconnection (MR) has been widely suggested, but the manifestations of its highly dispersive and anisotropic propagation properties in reconnection events remain largely unclear. Comparing results from a recently developed theoretical model for reconnection in terms of whistler's dispersive behavior with those reported from laboratory experiments on fast spontaneous magnetic reconnection, we demonstrate that the onset of fast reconnection in electron current layers (ECLs) emits whistler wave packets. The time scale of the explosively fast reconnection events are inversely related to the whistler mode frequencies at the lower end of the whistler frequency band. The wave packets in this frequency band have a characteristic angular dispersion, which marks the initial opening of the reconnection exhaust angle. The multidimensional propagation of the whistler for the reconnection with a strong guide magnetic field is investigated, showing that the measured propagation velocities of the reconnection electric field along the guide field in the Versatile Toroidal Facility at MIT quantitatively compare with the group velocities of the whistler wave packets. The whistler mode dispersive properties measured in laboratory experiments without a guide magnetic field in the magnetic reconnection experiments at Princeton also compare well with the theoretically predicted dispersion of the wave packets depending on the ECL width. Fast normalized reconnection rates extending to ˜0.35 at the MR onset in thin ECLs imply whistler wave propagation away from the onset location. We also present evidences for the whistler wave packets being emitted from reconnection diffusion region as seen in simulations and satellite observations.
Long-distance dispersal and accelerating waves of disease: empirical relationships.
Mundt, Christopher C; Sackett, Kathryn E; Wallace, LaRae D; Cowger, Christina; Dudley, Joseph P
2009-04-01
Classic approaches to modeling biological invasions predict a "traveling wave" of constant velocity determined by the invading organism's reproductive capacity, generation time, and dispersal ability. Traveling wave models may not apply, however, for organisms that exhibit long-distance dispersal. Here we use simple empirical relationships for accelerating waves, based on inverse power law dispersal, and apply them to diseases caused by pathogens that are wind dispersed or vectored by birds: the within-season spread of a plant disease at spatial scales of <100 m in experimental plots, historical plant disease epidemics at the continental scale, the unexpectedly rapid spread of West Nile virus across North America, and the transcontinental spread of avian influenza strain H5N1 in Eurasia and Africa. In all cases, the position of the epidemic front advanced exponentially with time, and epidemic velocity increased linearly with distance; regression slopes varied over a relatively narrow range among data sets. Estimates of the inverse power law exponent for dispersal that would be required to attain the rates of disease spread observed in the field also varied relatively little (1.74-2.36), despite more than a fivefold range of spatial scale among the data sets.
Prolonged P-Wave and QT Dispersion in Children with Inflammatory Bowel Disease in Remission
Yılmaz, Nuh; Kutluk, Günsel; Dedeoğlu, Reyhan; Öztarhan, Kazım; Tulunoğlu, Aras; Şap, Fatih
2017-01-01
Objectives. Ulcerative colitis (UC) and Crohn's disease (CD) are chronic inflammatory bowel diseases (IBD) with unclear underlying aetiologies. Severe cardiac arrhythmias have been emphasised in a few studies on adult IBD patients. This study aimed to investigate the alteration of the P-wave and QT interval dispersion parameters to assess the risk of atrial conduction and ventricular repolarisation abnormalities in pediatric IBD patients. Patients and Methods. Thirty-six IBD patients in remission (UC: 20, CD: 16) aged 3–18 years and 36 age- and sex-matched control patients were enrolled in the study. Twelve-lead electrocardiograms were used to determine durations of P-wave, QT, and corrected QT (QTc) interval dispersion. Transthoracic echocardiograms and 24-hour rhythm Holter recordings were obtained for both groups. Results. The P-wave dispersion, QT dispersion, and QTc interval dispersion (Pdisp, QTdisp, and QTcdisp) were significantly longer in the patient group. The mean values of Pminimum, Pmaximum, and QTcminimum were significantly different between the two groups. The echocardiography and Holter monitoring results were not significantly different between the groups. Furthermore, no differences in these parameters were detected between the CD and UC groups. Conclusion. Results suggest that paediatric IBD patients may carry potential risks for serious atrial and ventricular arrhythmias over time even during remission. PMID:28316985
Dispersion Relation and Numerical Simulation of Hydrodynamic Waves In Mar's Topside Ionosphere
NASA Astrophysics Data System (ADS)
Wang, J.-S.; Nielsen, E.
The dispersion relation for hydrodynamic waves in an ionosphere with at most a weak magnetic field shows, hydrodynamic hybrid waves may be excited in the topside iono- sphere of Mars and Venus owing to fluctuations in the solar wind pressure. The hy- brid waves result from coupling between two different hydrodynamic wave modes: the classic acoustic-gravity wave(AGW) and the newly developed background gradi- ent wave(BGW). Numerical simulations show that these waves will cause wave-like structures in the altitude profiles of the ionospheric plasma density. The wavelength and frequency are various but their prevailing values in Martian ionosphere are about 60km and 0.001-0.0001Hz, respectively. The amplitudes of the plasma density vari- ations decrease nearly exponentially with increasing altitude, and are of the same or- der of the magnitude as the uncertainty on all the previous measurements of Mar- tian ionospheric electron densities. Radio occultation observations at Mars and Venus show electron density fluctuations in the high altitude ionosphere. The fluctuations are mainly noise, but they may in part be caused by hydrodynamic wave activity. To verify wave activity more detailed measurements are required, and may be obtained with the low frequency radar planned for the Mars Express mission.
NASA Astrophysics Data System (ADS)
Dugan, J. P.; Piotrowski, C. C.; Williams, J. Z.
2001-08-01
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.
Nonlinear Acoustics in a Dispersive Continuum: Random Waves, Radiation Pressure, and Quantum Noise.
1983-03-01
Karpman , Nonlinear Waves in Dispersive Media, Pergamon Press, New York, 1975, p. 76. 26. R. Beyers, Nonlinear Acoustics, U.S. Government Printing...20301 U. S. Army Research nffice 2 copies Box 12211 Research Triangle Park tlorth Carolina 27709 Defense Technical Information Center 12 copies Cameron
NASA Technical Reports Server (NTRS)
Wong, H. K.; Goldstein, M. L.
1986-01-01
A class of parametric instabilities of large-amplitude, circularly polarized Alfven waves is considered in which finite frequency (dispersive) effects are included. The dispersion equation governing the instabilities is a sixth-order polynomial which is solved numerically. As a function of K identically equal to k/k-sub-0 (where k-sub-0 and k are the wave number of the 'pump' wave and unstable sound wave, respectively), there are three regionals of instability: a modulation instability at K less than 1, a decay instability at K greater than 1, and a relatively weak and narrow instability at K close to squared divided by v-sub-A squared (where c-sub-s and v-sub-A are the sound and Alfven speeds respectively), the modulational instability occurs when beta is less than 1 (more than 1) for left-hand (right-hand) pump waves, in agreement with the previous results of Sakai and Sonnerup (1983). The growth rate of the decay instability of left-hand waves is greater than the modulational instability at all values of beta. Applications to large-amplitude wave observed in the solar wind, in computer simulations, and in the vicinity of planetary and interplanetary collisionless shocks are discussed.
Three octave spanning supercontinuum by red-shifted dispersive wave in photonic crystal fibers
NASA Astrophysics Data System (ADS)
Sharma, Mohit; Konar, S.
2016-03-01
This article presents a three-layer index guided lead silicate (SF57) photonic crystal fiber which simultaneously promises to yield large effective optical nonlinear coefficient and low anomalous dispersion that makes it suitable for supercontinuum (SC) generation. At an operating wavelength 1550 nm, the typical optimized value of anomalous dispersion and effective nonlinear coefficient turns out to be ~4 ps/km/nm and ~1078 W-1km-1, respectively. Through numerical simulation, it is realized that the designed fiber promises to exhibit three octave spanning SC from 900 to 7200 nm using 50 fs 'sech' optical pulses of 5 kW peak power. Due to the cross-phase modulation and four-wave mixing processes, a long range of red-shifted dispersive wave generated, which assists to achieve such large broadening. In addition, we have investigated the compatibility of SC generation with input pulse peak power increment and briefly discussed the impact of nonlinear processes on SC generation.
NASA Astrophysics Data System (ADS)
Baba, Toshitaka; Takahashi, Narumi; Kaneda, Yoshiyuki; Ando, Kazuto; Matsuoka, Daisuke; Kato, Toshihiro
2015-12-01
Because of improvements in offshore tsunami observation technology, dispersion phenomena during tsunami propagation have often been observed in recent tsunamis, for example the 2004 Indian Ocean and 2011 Tohoku tsunamis. The dispersive propagation of tsunamis can be simulated by use of the Boussinesq model, but the model demands many computational resources. However, rapid progress has been made in parallel computing technology. In this study, we investigated a parallelized approach for dispersive tsunami wave modeling. Our new parallel software solves the nonlinear Boussinesq dispersive equations in spherical coordinates. A variable nested algorithm was used to increase spatial resolution in the target region. The software can also be used to predict tsunami inundation on land. We used the dispersive tsunami model to simulate the 2011 Tohoku earthquake on the Supercomputer K. Good agreement was apparent between the dispersive wave model results and the tsunami waveforms observed offshore. The finest bathymetric grid interval was 2/9 arcsec (approx. 5 m) along longitude and latitude lines. Use of this grid simulated tsunami soliton fission near the Sendai coast. Incorporating the three-dimensional shape of buildings and structures led to improved modeling of tsunami inundation.
Joint inversion of surface wave dispersion and receiver functions for crustal structure in Oklahoma
NASA Astrophysics Data System (ADS)
Guo, Hao
The surge in seismicity in Oklahoma starting in 2008 raises questions about the actual locations of the earthquakes in the upper crust. The key to answering this is an improved crustal model that explains as many observations as possible. Love and Rayleigh wave dispersion, teleseismic P-wave receiver functions and some unique transverse motions observed at distances less than 100 km that are characteristics of rays reverberating in a basin provide data to derive the crustal model. The surface wave dispersion data set consists of over 300,000 Love/Rayleigh phase/group values obtained from ambient noise cross-correlation of BH channels of the 133 Transportable Array (TA) stations of Earthscope to periods as short as 2 seconds. Station coverage is dense enough to perform the tomography on a 25*25 km grid that should be able to image shallow geological structures. In addition, receiver functions were obtained using teleseismic data recorded from 3 US Geological Survey Networks (GS) stations and 6 Oklahoma Seismic Network (OK) stations from 2011 to 2014. The 1-D S-wave velocity models derived by the joint inversion of surface wave dispersion and receiver functions with geological constraints are tested by fitting the independent transverse seismograms. This test also provides constraints on the earthquake depths in relation to the geological structure.
Planetary waves in rotating ionosphere
Khantadze, A. G.; Jandieri, V. G.; Jandieri, G. V.
2008-06-15
The problem of propagation of ultralong planetary waves in the Earth's upper atmosphere is considered. A new exact solution to the MHD equations for the ionosphere is obtained in spherical coordinates with allowance for the geomagnetic field and Earth's rotation. A general dispersion relation is derived for planetary waves in the ionospheric E and F regions, and the characteristic features of their propagation in a weakly ionized ionospheric plasma are discussed.
Andries, J.; Cally, P. S. E-mail: paul.cally@monash.edu
2011-12-20
We provide a fairly general analytic theory for the dispersion and scattering of magnetohydrodynamic waves by longitudinally stratified flux tubes. The theory provides a common framework for, and synthesis of, many previous studies of flux tube oscillations that were carried out under various simplifying assumptions. The present theory focuses on making only a minimal number of assumptions. As a result it thus provides an analytical treatment of several generalizations of existing tube oscillation models. The most important practical cases are inclusion of plasma pressure and possibly buoyancy effects in models of straight non-diverging tubes as applied in coronal seismology, and relaxation of the 'thin tube' approximation in oscillation models of diverging tubes as applied both in the context of p-mode scattering and coronal seismology. In particular, it illustrates the unifying theoretical framework underlying both the description of waves scattered by flux tubes and the dispersion of waves carried along flux tubes.
Measurements of Finite Dust Temperature Effects in the Dispersion Relation of the Dust Acoustic Wave
NASA Astrophysics Data System (ADS)
Snipes, Erica; Williams, Jeremiah
2009-04-01
A dusty plasma is a four-component system composed of ions, electrons, neutral particles and charged microparticles. The presence of these charged microparticles gives rise to new plasma wave modes, including the dust acoustic wave. Recent measurements [1, 2] of the dispersion relationship for the dust acoustic wave in a glow discharge have shown that finite temperature effects are observed at higher values of neutral pressure. Other work [3] has shown that these effects are not observed at lower values of neutral pressure. We present the results of ongoing work examining finite temperature effects in the dispersion relation as a function of neutral pressure. [4pt] [1] E. Thomas, Jr., R. Fisher, and R. L. Merlino, Phys. Plasmas 14, 123701 (2007). [0pt] [2] J. D. Williams, E. Thomas Jr., and L. Marcus, Phys. Plasmas 15, 043704 (2008). [0pt] [3] T. Trottenberg, D. Block, and A. Piel, Phys. Plasmas 13, 042105 (2006).
Rovibrational Wave-Packet Dispersion during Femtosecond Laser Filamentation in Air
Odhner, J. H.; Romanov, D. A.; Levis, R. J.
2009-08-14
An impulsive, femtosecond filament-based Raman technique producing high quality Raman spectra over a broad spectral range (1554.7-4155 cm{sup -1}) is presented. The temperature of gas phase molecules can be measured by temporally resolving the dispersion of impulsively excited vibrational wave packets. Application to laser-induced filamentation in air reveals that the initial rovibrational temperature is 300 K for both N{sub 2} and O{sub 2}. The temperature-dependent wave-packet dynamics are interpreted using an analytic anharmonic oscillator model. The wave packets reveal a 1/e dispersion time of 3.9 ps for N{sub 2} and 2.8 ps for O{sub 2}. Pulse self-compression of temporal features to 8 fs within the filament is directly measured by impulsive vibrational excitation of H{sub 2}.
An investigation into the dispersion of ocean surface waves in sea ice
NASA Astrophysics Data System (ADS)
Collins, Clarence Olin; Rogers, William Erick; Lund, Björn
2017-02-01
This investigation considers theoretical models and empirical studies related to the dispersion of ocean surface gravity waves propagating in ice covered seas. In theory, wave dispersion is related to the mechanical nature of the ice. The change of normalized wavenumber is shown for four different dispersion models: the mass-loading model, an elastic plate model, an elastic plate model extended to include dissipation, and a viscous-layer model. For each dispersion model, model parameters are varied showing the dependence of deviation from open water dispersion on ice thickness, elasticity, and viscosity. In all cases, the deviation of wavenumber from the open water relation is more pronounced for higher frequencies. The effect of mass loading, a component of all dispersion models, tends to shorten the wavelength. The Voigt model of dissipation in an elastic plate model does not change the wavelength. Elasticity in the elastic plate model and viscosity in the viscous-layer model tend to increase the wavelength. The net effect, lengthening or shortening, is a function of the particular combination of ice parameters and wave frequency. Empirical results were compiled and interpreted in the context of these theoretical models of dispersion. A synopsis of previous measurements is as follows: observations in a loose pancake ice in the marginal ice zone, often, though not always, showed shortened wavelengths. Both lengthening and shortening have been observed in compact pancakes and pancakes in brash ice. Quantitative matches to the flexural-gravity model have been found in Arctic interior pack ice and sheets of fast ice.
An investigation into the dispersion of ocean surface waves in sea ice
NASA Astrophysics Data System (ADS)
Collins, Clarence Olin; Rogers, William Erick; Lund, Björn
2016-12-01
This investigation considers theoretical models and empirical studies related to the dispersion of ocean surface gravity waves propagating in ice covered seas. In theory, wave dispersion is related to the mechanical nature of the ice. The change of normalized wavenumber is shown for four different dispersion models: the mass-loading model, an elastic plate model, an elastic plate model extended to include dissipation, and a viscous-layer model. For each dispersion model, model parameters are varied showing the dependence of deviation from open water dispersion on ice thickness, elasticity, and viscosity. In all cases, the deviation of wavenumber from the open water relation is more pronounced for higher frequencies. The effect of mass loading, a component of all dispersion models, tends to shorten the wavelength. The Voigt model of dissipation in an elastic plate model does not change the wavelength. Elasticity in the elastic plate model and viscosity in the viscous-layer model tend to increase the wavelength. The net effect, lengthening or shortening, is a function of the particular combination of ice parameters and wave frequency. Empirical results were compiled and interpreted in the context of these theoretical models of dispersion. A synopsis of previous measurements is as follows: observations in a loose pancake ice in the marginal ice zone, often, though not always, showed shortened wavelengths. Both lengthening and shortening have been observed in compact pancakes and pancakes in brash ice. Quantitative matches to the flexural-gravity model have been found in Arctic interior pack ice and sheets of fast ice.
2008-05-30
use a similar technique with a narrower kernel that they believe to be more representative of realistic surface waves. Spetzler et al. (2001, 2002...Nor and KNET. We measured surface wave spectral amplitudes from the calculations using the same techniques used to measure observed surface waves...The Born approximation techniques discussed in section 3 provide a straightforward, but approximate, way to incorporate scattering and diffraction
Deeba, F.; Ahmad, Zahoor; Murtaza, G.
2010-10-15
A generalized dielectric constant for the electron Bernstein waves using non-Maxwellian distribution functions is derived in a collisionless, uniform magnetized plasma. Using the Neumann series expansion for the products of Bessel functions, we can derive the dispersion relations for both kappa and the generalized (r,q) distributions in a straightforward manner. The dispersion relations now become dependent upon the spectral indices {kappa} and (r,q) for the kappa and the generalized (r,q) distribution, respectively. Our results show how the non-Maxwellian dispersion curves deviate from the Maxwellian depending upon the values of the spectral indices chosen. It may be noted that the (r,q) dispersion relation is reduced to the kappa distribution for r=0 and q={kappa}+1, which, in turn, is further reducible to the Maxwellian distribution for {kappa}{yields}{infinity}.
NASA Astrophysics Data System (ADS)
Heinz-Essen, H.; Grevemeyer, Ingo; Herber, Rolf; Weigel, Wilfried
1998-01-01
An experiment with a newly developed implosive source, located about 1 m above the seafloor at 3665 m depth, revealed a slow interface wave. This wave is attributed to S waves in a soft sediment layer covering the hard rock sub-bottom. Dispersion analysis by means of the multiple-filter technique yields the group velocity as a function of frequency. Model calculations showed that the observed dispersion curve can be reproduced by considering a steep gradient of S velocity within the sediment layer. Nearly perfect agreement of experimental and model data could be achieved with a sediment layer thickness of 21.5 m, an S speed of 225 m s- 1 at the water-sediment interface and an increase by 23 s- 1 within the layer. These values are relatively high compared to data from the literature. However, previous estimates of in situ S-wave velocity have been obtained on old oceanic crust in the vicinity of continents or islands, while our experiment was carried out on young Pacific crust. Therefore, we suggest two mechanisms which could support a relatively high S speed in sediments: (1) the input of hydrothermally generated metalliferous sediments from the adjacent spreading axis; and (2) post-depositional diagenesis which has accelerated the induration of sediments.
Hybrid dispersive media with controllable wave propagation: A new take on smart materials
NASA Astrophysics Data System (ADS)
Bergamini, Andrea E.; Zündel, Manuel; Flores Parra, Edgar A.; Delpero, Tommaso; Ruzzene, Massimo; Ermanni, Paolo
2015-10-01
In this paper, we report on the wave transmission characteristics of a hybrid one dimensional (1D) medium. The hybrid characteristic is the result of the coupling between a 1D mechanical waveguide in the form of an elastic beam, supporting the propagation of transverse waves and a discrete electrical transmission line, consisting of a series of inductors connected to ground through capacitors. The capacitors correspond to a periodic array of piezoelectric patches that are bonded to the beam and that couple the two waveguides. The coupling leads to a hybrid medium that is characterized by a coincidence condition for the frequency/wavenumber value corresponding to the intersection of the branches of the two waveguides. In the frequency range centered at coincidence, the hybrid medium features strong attenuation of wave motion as a result of the energy transfer towards the electrical transmission line. This energy transfer, and the ensuing attenuation of wave motion, is alike the one obtained through internal resonating units of the kind commonly used in metamaterials. However, the distinct shape of the dispersion curves suggests how this energy transfer is not the result of a resonance and is therefore fundamentally different. This paper presents the numerical investigation of the wave propagation in the considered media, it illustrates experimental evidence of wave transmission characteristics and compares the performance of the considered configuration with that of internal resonating metamaterials. In addition, the ability to conveniently tune the dispersion properties of the electrical transmission line is exploited to adapt the periodicity of the domain and to investigate diatomic periodic configurations that are characterized by a richer dispersion spectrum and broader bandwidth of wave attenuation at coincidence. The medium consisting of mechanical, piezoelectric, and analog electronic elements can be easily interfaced to digital devices to offer a novel
Hybrid dispersive media with controllable wave propagation: A new take on smart materials
Bergamini, Andrea E.; Zündel, Manuel; Flores Parra, Edgar A.; Ermanni, Paolo; Delpero, Tommaso; Ruzzene, Massimo
2015-10-21
In this paper, we report on the wave transmission characteristics of a hybrid one dimensional (1D) medium. The hybrid characteristic is the result of the coupling between a 1D mechanical waveguide in the form of an elastic beam, supporting the propagation of transverse waves and a discrete electrical transmission line, consisting of a series of inductors connected to ground through capacitors. The capacitors correspond to a periodic array of piezoelectric patches that are bonded to the beam and that couple the two waveguides. The coupling leads to a hybrid medium that is characterized by a coincidence condition for the frequency/wavenumber value corresponding to the intersection of the branches of the two waveguides. In the frequency range centered at coincidence, the hybrid medium features strong attenuation of wave motion as a result of the energy transfer towards the electrical transmission line. This energy transfer, and the ensuing attenuation of wave motion, is alike the one obtained through internal resonating units of the kind commonly used in metamaterials. However, the distinct shape of the dispersion curves suggests how this energy transfer is not the result of a resonance and is therefore fundamentally different. This paper presents the numerical investigation of the wave propagation in the considered media, it illustrates experimental evidence of wave transmission characteristics and compares the performance of the considered configuration with that of internal resonating metamaterials. In addition, the ability to conveniently tune the dispersion properties of the electrical transmission line is exploited to adapt the periodicity of the domain and to investigate diatomic periodic configurations that are characterized by a richer dispersion spectrum and broader bandwidth of wave attenuation at coincidence. The medium consisting of mechanical, piezoelectric, and analog electronic elements can be easily interfaced to digital devices to offer a novel
Wave-speed dispersion associated with an attenuation obeying a frequency power law.
Buckingham, Michael J
2015-11-01
An attenuation scaling as a power of frequency, |ω|(β), over an infinite bandwidth is neither analytic nor square-integrable, thus calling into question the application of the Kramers-Krönig dispersion relations for determining the frequency dependence of the associated phase speed. In this paper, three different approaches are developed, all of which return the dispersion formula for the wavenumber, K(ω). The first analysis relies on the properties of generalized functions and the causality requirement that the impulse response, k(t), the inverse Fourier transform of -iK(ω), must vanish for t < 0. Second, a wave equation is introduced that yields the phase-speed dispersion associated with a frequency-power-law attenuation. Finally, it is shown that, with minor modification, the Kramers-Krönig dispersion relations with no subtractions (the Plemelj formulas) do in fact hold for an attenuation scaling as |ω|(β), yielding the same dispersion formula as the other two derivations. From this dispersion formula, admissible values of the exponent β are established. Physically, the inadmissible values of β, which include all the integers, correspond to attenuation-dispersion pairs whose Fourier components cannot combine in such a way as to make the impulse response, k(t), vanish for t < 0. There is no upper or lower limit on the value that β may take.
NASA Astrophysics Data System (ADS)
Peureux, Charles; Ardhuin, Fabrice
2016-04-01
The stereo-video reconstuction method [Leckler et al. 2015] allows now for the full reconstruction of 3D frequency-wavenumber spectra of short waves. A new field campaign in 2013 on the Katsiveli platform (Black Sea) provided such spectra in various wind and waves conditions, and particularly a stormy event, after which very mature waves had been generated. The short waves energies are found to be mostly located around a dispersion relation of the form, () ° ----------- ω ⃗k = gktanh(kH)+ ⃗kṡ ⃗Ueff The effective advection velocity [Kirby and Chen 1989] ⃗Ueff(k) integrates contributions from both the Stokes drift and quasi-eulerian current [Groeneweg and Klopman 1998]. We find that the effective drift velocity has a very weak wavenumber dependancy, as a result the eulerian current must be vertically sheared. This shear is relevant to the breaking of small scale waves [Banner and Phillips 1974]. It is possible that in field conditions the wind drift is much less important than in the laboratory. Bibliography Banner, M. L. and Phillips, O. M., On the incipient breaking of small scale waves, J. Fluid Mech., 1974, 65, 647. Groeneweg, J. and Klopman, G., Changes of the mean velocity profiles in the combined wave-current motion described in a GLM formulation, J. Fluid Mech., 1998, 370, 271-296. Kirby, J. T. and Chen, T. M., Surface waves on vertically sheared flows : Approximate dispersion relations, J. Geophys. Res., 1989, 94, 1013. Leckler, F., Ardhuin, F., Peureux, C.,Benetazzo, A., Bergamasco, F. and Dulov, V., Analysis and interpretation of frequency-wavenumber spectra of young wind-waves, J. Phys. Oceanogr., 2015, 45, 2484-2496.
Full 3D dispersion curve solutions for guided waves in generally anisotropic media
NASA Astrophysics Data System (ADS)
Hernando Quintanilla, F.; Lowe, M. J. S.; Craster, R. V.
2016-02-01
Dispersion curves of guided waves provide valuable information about the physical and elastic properties of waves propagating within a given waveguide structure. Algorithms to accurately compute these curves are an essential tool for engineers working in non-destructive evaluation and for scientists studying wave phenomena. Dispersion curves are typically computed for low or zero attenuation and presented in two or three dimensional plots. The former do not always provide a clear and complete picture of the dispersion loci and the latter are very difficult to obtain when high values of attenuation are involved and arbitrary anisotropy is considered in single or multi-layered systems. As a consequence, drawing correct and reliable conclusions is a challenging task in the modern applications that often utilize multi-layered anisotropic viscoelastic materials. These challenges are overcome here by using a spectral collocation method (SCM) to robustly find dispersion curves in the most complicated cases of high attenuation and arbitrary anisotropy. Solutions are then plotted in three-dimensional frequency-complex wavenumber space, thus gaining much deeper insight into the nature of these problems. The cases studied range from classical examples, which validate this approach, to new ones involving materials up to the most general triclinic class for both flat and cylindrical geometry in multi-layered systems. The apparent crossing of modes within the same symmetry family in viscoelastic media is also explained and clarified by the results. Finally, the consequences of the centre of symmetry, present in every crystal class, on the solutions are discussed.
Study on measurement of dispersive characteristics of higher order mode Lamb waves.
Lin, Wei; Fan, Li; Gan, Changming; Xu, Boling; Zhu, Zhemin
2006-12-22
The dispersive characteristics of higher order mode Lamb waves (HOMLW) excited by interdigital transducers (IDT) are measured and analyzed, which are necessary for designing micro-sensor in ultrahigh frequency (UHF). A measurement system is set up, in which dispersive characteristics of HOMLW are obtained by the method of transform between frequency and time domains. The characteristics of amplitude-frequency and phase-frequency of Lamb wave are auto-measured by the system. By IFFT, the pulse response of the IDT device was obtained. Different modes were separated in time domain and dispersive curve of each mode is calculated by FFT. The best mode is chosen to design the micro-sensor in UHF. The phase velocity of HOMLW is greater than the surface wave (SAW) velocity and an oscillator in higher frequency can be made, so the absolute sensitivity of micro-sensor can be increased. In this paper, the dispersive characteristics of HOMLW excited by an IDT in a 127.86 degrees rotated Y-cut, X propagating lithium niobate plate is analyzed. An oscillator using a(13) mode is made, the phase velocity of which is measured about 19,652 m/s when h/lambda=0.94 (h=plate thickness, lambda=wavelength).
Complex dispersion relation of surface acoustic waves at a lossy metasurface
NASA Astrophysics Data System (ADS)
Schwan, Logan; Geslain, Alan; Romero-García, Vicente; Groby, Jean-Philippe
2017-01-01
The complex dispersion relation of surface acoustic waves (SAWs) at a lossy resonant metasurface is theoretically and experimentally reported. The metasurface consists of the periodic arrangement of borehole resonators in a rigid substrate. The theoretical model relies on a boundary layer approach that provides the effective metasurface admittance governing the complex dispersion relation in the presence of viscous and thermal losses. The model is experimentally validated by measurements in the semi-anechoic chamber. The complex SAW dispersion relation is experimentally retrieved from the analysis of the spatial Laplace transform of the pressure scanned along a line at the metasurface. The geometrical spreading of the energy from the speaker is accounted for, and both the real and imaginary parts of the SAW wavenumber are obtained. The results show that the strong reduction of the SAW group velocity occurs jointly with a drastic attenuation of the wave, leading to the confinement of the field close to the source and preventing the efficient propagation of such slow-sound surface modes. The method opens perspectives to theoretically predict and experimentally characterize both the dispersion and the attenuation of surface waves at structured surfaces.
NASA Technical Reports Server (NTRS)
Huang, N. E.; Tung, C.-C.
1977-01-01
The influence of the directional distribution of wave energy on the dispersion relation is calculated numerically using various directional wave spectrum models. The results indicate that the dispersion relation varies both as a function of the directional energy distribution and the direction of propagation of the wave component under consideration. Furthermore, both the mean deviation and the random scatter from the linear approximation increase as the energy spreading decreases. Limited observational data are compared with the theoretical results. The agreement is favorable.
NASA Technical Reports Server (NTRS)
Montgomery, David
1988-01-01
Three areas of study in MHD turbulence are considered. These are the turbulent relaxation of the toroidal Z pinch, density fluctuations in MHD fluids, and MHD cellular automata. A Boolean computer game that updates a cellular representation in parallel and that has macroscopic averages converging to solutions of the two-dimensional MHD equations is discussed.
Imaging ultrasonic dispersive guided wave energy in long bones using linear radon transform.
Tran, Tho N H T; Nguyen, Kim-Cuong T; Sacchi, Mauricio D; Le, Lawrence H
2014-11-01
Multichannel analysis of dispersive ultrasonic energy requires a reliable mapping of the data from the time-distance (t-x) domain to the frequency-wavenumber (f-k) or frequency-phase velocity (f-c) domain. The mapping is usually performed with the classic 2-D Fourier transform (FT) with a subsequent substitution and interpolation via c = 2πf/k. The extracted dispersion trajectories of the guided modes lack the resolution in the transformed plane to discriminate wave modes. The resolving power associated with the FT is closely linked to the aperture of the recorded data. Here, we present a linear Radon transform (RT) to image the dispersive energies of the recorded ultrasound wave fields. The RT is posed as an inverse problem, which allows implementation of the regularization strategy to enhance the focusing power. We choose a Cauchy regularization for the high-resolution RT. Three forms of Radon transform: adjoint, damped least-squares, and high-resolution are described, and are compared with respect to robustness using simulated and cervine bone data. The RT also depends on the data aperture, but not as severely as does the FT. With the RT, the resolution of the dispersion panel could be improved up to around 300% over that of the FT. Among the Radon solutions, the high-resolution RT delineated the guided wave energy with much better imaging resolution (at least 110%) than the other two forms. The Radon operator can also accommodate unevenly spaced records. The results of the study suggest that the high-resolution RT is a valuable imaging tool to extract dispersive guided wave energies under limited aperture.
Investigation of phononic crystals for dispersive surface acoustic wave ozone sensors
NASA Astrophysics Data System (ADS)
Westafer, Ryan S.
The object of this research was to investigate dispersion in surface phononic crystals (PnCs) for application to a newly developed passive surface acoustic wave (SAW) ozone sensor. Frequency band gaps and slow sound already have been reported for PnC lattice structures. Such engineered structures are often advertised to reduce loss, increase sensitivity, and reduce device size. However, these advances have not yet been realized in the context of surface acoustic wave sensors. In early work, we computed SAW dispersion in patterned surface structures and we confirmed that our finite element computations of SAW dispersion in thin films and in one dimensional surface PnC structures agree with experimental results obtained by laser probe techniques. We analyzed the computations to guide device design in terms of sensitivity and joint spectral operating point. Next we conducted simulations and experiments to determine sensitivity and limit of detection for more conventional dispersive SAW devices and PnC sensors. Finally, we conducted extensive ozone detection trials on passive reflection mode SAW devices, using distinct components of the time dispersed response to compensate for the effect of temperature. The experimental work revealed that the devices may be used for dosimetry applications over periods of several days.
NASA Astrophysics Data System (ADS)
Zhang, Guangmin; Gao, Weihang; Song, Gangbing; Song, Yue
2017-02-01
Piezoceramic induced Lamb waves are often used for imaging based damage detection, especially for plate like structures. The dispersion effect of the Lamb waves deteriorates the performance of most of imaging methods, since the waveform of the dispersion signals will spread out. In this paper, an imaging method which can compensate the dispersion is developed. In the proposed method, the phase induced by the propagation distance is compensated firstly. After that, the phase deviation generated by the dispersion effect is compensated. Via the two compensations, the proposed method can derive an accurate location of the target with a clean imaging map. An experiment using a plate like structure with four piezoceramic transducer was conducted. In the experiment, the four piezoceramic sensors were used to obtain the signals of the scatterer that simulated the damage on an aluminum plate. The experimental results show that since the dispersion effect is compensated, the target’s image based on the proposed method is about 10 cm × 14 cm, which is about a quarter of that of using the back-projection imaging method.
Adiabatically tapered hyperbolic metamaterials for dispersion control of high-k waves.
West, Paul R; Kinsey, Nathaniel; Ferrera, Marcello; Kildishev, Alexander V; Shalaev, Vladimir M; Boltasseva, Alexandra
2015-01-14
Hyperbolic metamaterials (HMMs) have shown great promise in the optical and quantum communities due to their extremely large, broadband photonic density of states. This feature is a direct consequence of supporting photonic modes with unbounded k-vectors. While these materials support such high-k waves, they are intrinsically confined inside the HMM and cannot propagate into the far-field, rendering them impractical for many applications. Here, we demonstrate how the magnitude of k-vectors can be engineered as the propagating radiation passes through media of differing dispersion relations (including type II HMMs and dielectrics) in the in-plane direction. The total outcoupling efficiency of waves in the in-plane direction is shown to be on average 2 orders of magnitude better than standard out-of-plane outcoupling methods. In addition, the outcoupling can be further enhanced using a proposed tapered HMM waveguide that is fabricated using a shadowed glancing angle deposition technique; thereby proving the feasibility of the proposed device. Applications for this technique include converting high-k waves to low-k waves that can be out-coupled into free-space and creating extremely high-k waves that are quickly quenched. Most importantly, this method of in-plane outcoupling acts as a bridge through which waves can cross between the regimes of low-k waves in classical dielectric materials and the high-k waves in HMMs with strongly reduced reflective losses.
Soh, Daniel B S; Koplow, Jeffrey P; Moore, Sean W; Schroder, Kevin L; Hsu, Wen L
2010-10-11
In addition to fiber nonlinearity, fiber dispersion plays a significant role in spectral broadening of incoherent continuous-wave light. In this paper we have performed a numerical analysis of spectral broadening of incoherent light based on a fully stochastic model. Under a wide range of operating conditions, these numerical simulations exhibit striking features such as damped oscillatory spectral broadening (during the initial stages of propagation), and eventual convergence to a stationary, steady state spectral distribution at sufficiently long propagation distances. In this study we analyze the important role of fiber dispersion in such phenomena. We also demonstrate an analytical rate equation expression for spectral broadening.
Four-wave mixing stability in hybrid photonic crystal fibers with two zero-dispersion wavelengths.
Sévigny, Benoit; Vanvincq, Olivier; Valentin, Constance; Chen, Na; Quiquempois, Yves; Bouwmans, Géraud
2013-12-16
The four-wave mixing process in optical fibers is generally sensitive to dispersion uniformity along the fiber length. However, some specific phase matching conditions show increased robustness to longitudinal fluctuations in fiber dimensions, which affect the dispersion, even for signal and idler wavelengths far from the pump. In this paper, we present the method by which this point is found, how the fiber design characteristics impact on the stable point and demonstrate the stability through propagation simulations using the non-linear Schrödinger equation.
Wu, Junru; Layman, Christopher; Liu, Jun
2004-02-01
A fundamental mathematical framework for applications of Doublet Mechanics to ultrasound propagation in a discrete material is introduced. A multiscale wave equation, dispersion relation for longitudinal waves, and shear waves are derived. The van Hove singularities and corresponding highest frequency limits for the Mth-order wave equations of longitudinal and shear waves are determined for a widely used microbundle structure. Doublet Mechanics is applied to soft tissue and low-density polyethylene. The experimental dispersion data for soft tissue and low-density polyethylene are compared with results predicted by Doublet Mechanics and an attenuation model based on a Kramers-Kronig relation in classical continuum mechanics.
NASA Astrophysics Data System (ADS)
Wu, Junru; Layman, Christopher; Liu, Jun
2004-02-01
A fundamental mathematical framework for applications of Doublet Mechanics to ultrasound propagation in a discrete material is introduced. A multiscale wave equation, dispersion relation for longitudinal waves, and shear waves are derived. The van Hove singularities and corresponding highest frequency limits for the Mth-order wave equations of longitudinal and shear waves are determined for a widely used microbundle structure. Doublet Mechanics is applied to soft tissue and low-density polyethylene. The experimental dispersion data for soft tissue and low-density polyethylene are compared with results predicted by Doublet Mechanics and an attenuation model based on a Kramers-Kronig relation in classical continuum mechanics.
Dispersion characteristics of spin-electromagnetic waves in planar multiferroic structures
Nikitin, Andrey A.; Ustinov, Alexey B.; Vitko, Vitaliy V.; Semenov, Alexander A.; Mironenko, Igor G.; Belyavskiy, Pavel Yu.; Kalinikos, Boris A.; Stashkevich, Andrey A.; Lähderanta, E.
2015-11-14
A method of approximate boundary conditions is used to derive dispersion relations for spin-electromagnetic waves (SEWs) propagating in thin ferrite films and in multiferroic layered structures. A high accuracy of this method is proven. It was shown that the spin-electromagnetic wave propagating in the structure composed of a thin ferrite film, a thin ferroelectric film, and a slot transmission line is formed as a result of hybridization of the surface spin wave in the ferrite film and the electromagnetic wave in the slot-line. The structure demonstrates dual electric and magnetic field tunability of the SEW spectrum. The electric field tunability is provided by the thin ferroelectric film. Its efficiency increases with an increase in the thicknesses of the ferrite and ferroelectric films and with a decrease in the slot-line gap width. The theory is confirmed by experimental data.
Dispersion relation of electrostatic ion cyclotron waves in multi-component magneto-plasma
Khaira, Vibhooti Ahirwar, G.
2015-07-31
Electrostatic ion cyclotron waves in multi component plasma composed of electrons (denoted by e{sup −}), hydrogen ions (denoted by H{sup +}), helium ions (denoted by He{sup +}) and positively charged oxygen ions (denoted by O{sup +})in magnetized cold plasma. The wave is assumed to propagate perpendicular to the static magnetic field. It is found that the addition of heavy ions in the plasma dispersion modified the lower hybrid mode and also allowed an ion-ion mode. The frequencies of the lower hybrid and ion- ion hybrid modes are derived using cold plasma theory. It is observed that the effect of multi-ionfor different plasma densities on electrostatic ion cyclotron waves is to enhance the wave frequencies. The results are interpreted for the magnetosphere has been applied parameters by auroral acceleration region.
Slow shock and rotational discontinuity in MHD and Hall MHD models with anisotropic pressure
NASA Astrophysics Data System (ADS)
Hau, L.-N.; Wang, B.-J.
2016-07-01
Pressure anisotropy may modify the characteristics of magnetohydrodynamic (MHD) waves, in particular, the slow mode wave and the corresponding shocks and discontinuities. In this study the formation of slow shocks (SSs) in anisotropic plasmas is examined by solving the gyrotropic MHD and Hall MHD equations numerically for one-dimensional Riemann problem. The MHD shocks and discontinuities are generated by imposing a finite normal magnetic field on the Harris type current sheet with a guide magnetic By component. It is shown that anomalous SSs moving faster than the intermediate wave or with positive density-magnetic field correlation may be generated in gyrotropic MHD and Hall MHD models. Moreover, for some parameter values SSs may exhibit upstream wave trains with right-handed polarization in contrast with the earlier prediction that SSs shall possess downstream left-hand polarized wave trains based on the isotropic Hall MHD theory. For the cases of By ≠ 0, SSs with increased density and decreased magnetic field followed by noncoplanar intermediate mode or rotational discontinuity (RD)-like structures similar to the compound SS-RD structures observed in space plasma environments may possibly form in symmetric and asymmetric current layers. The Walén relation of these anomalous RDs without the correction of pressure anisotropy may significantly be violated.
Pasyanos, M E
2005-03-21
This paper presents the results of a large-scale study of surface wave dispersion performed across Eurasia and North Africa. Improvements were made to previous surface wave work by enlarging the study region, increasing path density, improving spatial resolution, and expanding the period range. This study expands the coverage area northwards and eastwards relative to a previous dispersion analysis, which covered only North Africa and the Middle East. We have significantly increased the number of seismograms examined and group velocity measurements made. We have now made good quality dispersion measurements for about 30,000 Rayleigh wave and 20,000 Love wave paths, and have incorporated measurements from several other researchers into the study. A conjugate gradient method was employed for the group velocity tomography, which improved the inversion from the previous study by adopting a variable smoothness. This technique allows us to go to higher resolution where the data allow without producing artifacts. The current results include both Love and Rayleigh wave inversions across the region for periods from 7 to 100 seconds at 1{sup o} resolution. Short period group velocities are sensitive to slow velocities associated with large sedimentary features such as the Caspian Sea, West Siberian Platform, Mediterranean Sea, Bay of Bengal, Tarim Basin, and Persian Gulf. Intermediate periods are sensitive to differences in crustal thickness, such as those between oceanic and continental crust or along orogenic zones and continental plateaus. At longer periods, fast velocities are consistently found beneath cratons while slow upper mantle velocities occur along rift systems, subduction zones, and collision zones such as the Tethys Belt. We have compared the group velocities at various periods with features such as sediment thickness, topographic height, crustal thickness, proximity to plate boundaries, lithospheric age and lithospheric thickness, and find significant
Nonlinear interaction of long dispersive Kelvin waves in deep natural basins
NASA Astrophysics Data System (ADS)
Budnev, Nikolay M.; Lovtsov, Sergey V.; Portyanskaya, Inna A.; Rastegin, Alexey E.; Rubtsov, Valeriy Yu.
2010-05-01
Nonlinear phenomena are of great importance for complete understanding of dynamical processes in fluids. However, direct studies of hydrodynamic equations seem to be very hard just due to nonlinear terms. Many approaches to nonlinear dispersive waves are related to the technique of multiple scales. It is one of most seminal ways to obtain those models that combine possibility of analytic investigation with actual effects of nonlinearity. Consideration of long Kelvin waves within the linear theory is well known issue of geophysical hydrodynamics. An influence of boundary effects leads to dispersion of Kelvin waves. At the same time, mutual balance between dispersive and nonlinear terms in motion equations can provide a formation of stable localized structures so-called solitary waves. When stratification is essential, different vertical modes of oscillation are typically excited. Corresponding analysis of vertical structure for solitary Rossby waves has been developed in many works, mainly due to Redekopp. But proper treatment of large-scale Kelvin waves seems to be not indicated in the literature. The principal aim of our work is to fill this lacuna. The present work has been partially inspired by temperature monitoring data obtained in south area of Lake Baikal. Under conditions of winter stratification, specific displacements of fragments of temperature profile from up to down were observed within upper layer. It is valuable that a shape of moving fragment remains almost undistorted. After ending this temperature decreasing, the temperature profile was rectified to initial shape. In all the years of observations, vertical displacements reach several tens of meters with duration of several days. These phenomena were interpreted as manifestation of long dispersive Kelvin waves, especially due to direction of propagation along the coastline. Regularly observed displacements from up to down may be evidences for nonlinear character of wave dynamics. Indeed, internal
Propagation and Dispersion of Sausage Wave Trains in Magnetic Flux Tubes
NASA Astrophysics Data System (ADS)
Oliver, R.; Ruderman, M. S.; Terradas, J.
2015-06-01
A localized perturbation of a magnetic flux tube produces wave trains that disperse as they propagate along the tube, where the extent of dispersion depends on the physical properties of the magnetic structure, on the length of the initial excitation, and on its nature (e.g., transverse or axisymmetric). In Oliver et al. we considered a transverse initial perturbation, whereas the temporal evolution of an axisymmetric one is examined here. In both papers we use a method based on Fourier integrals to solve the initial value problem. We find that the propagating wave train undergoes stronger attenuation for longer axisymmetric (or shorter transverse) perturbations, while the internal to external density ratio has a smaller effect on the attenuation. Moreover, for parameter values typical of coronal loops axisymmetric (transverse) wave trains travel at a speed 0.75-1 (1.2) times the Alfvén speed of the magnetic tube. In both cases, the wave train passage at a fixed position of the magnetic tube gives rise to oscillations with periods of the order of seconds, with axisymmetric disturbances causing more oscillations than transverse ones. To test the detectability of propagating transverse or axisymmetric wave packets in magnetic tubes of the solar atmosphere (e.g., coronal loops, spicules, or prominence threads) a forward modeling of the perturbations must be carried out.
PROPAGATION AND DISPERSION OF SAUSAGE WAVE TRAINS IN MAGNETIC FLUX TUBES
Oliver, R.; Terradas, J.; Ruderman, M. S.
2015-06-10
A localized perturbation of a magnetic flux tube produces wave trains that disperse as they propagate along the tube, where the extent of dispersion depends on the physical properties of the magnetic structure, on the length of the initial excitation, and on its nature (e.g., transverse or axisymmetric). In Oliver et al. we considered a transverse initial perturbation, whereas the temporal evolution of an axisymmetric one is examined here. In both papers we use a method based on Fourier integrals to solve the initial value problem. We find that the propagating wave train undergoes stronger attenuation for longer axisymmetric (or shorter transverse) perturbations, while the internal to external density ratio has a smaller effect on the attenuation. Moreover, for parameter values typical of coronal loops axisymmetric (transverse) wave trains travel at a speed 0.75–1 (1.2) times the Alfvén speed of the magnetic tube. In both cases, the wave train passage at a fixed position of the magnetic tube gives rise to oscillations with periods of the order of seconds, with axisymmetric disturbances causing more oscillations than transverse ones. To test the detectability of propagating transverse or axisymmetric wave packets in magnetic tubes of the solar atmosphere (e.g., coronal loops, spicules, or prominence threads) a forward modeling of the perturbations must be carried out.
NASA Astrophysics Data System (ADS)
Zulhan, Zulfakriza; Saygin, Erdinc; Cummins, Phil; Widiyantoro, Sri; Nugraha, Andri Dian; Luehr, Birger-G.; Bodin, Thomas
2015-04-01
Our previous study on MERAMEX data (Zulfakriza et al., 2014) obtained features of the tomographic images which correlate well with the surface geology of central Java in periods between 1 to 12 sec. Kendeng Basin and active volcanoes in the central part of this region are clearly imaged with low group velocities with values around 0.8 km/sec, while the carbonate structures in the southern part of the region correspond to higher group velocities in the range of 1.8 to 2.0 km/sec. In this current study, we invert dispersion curves obtained from seismic noise tomography to estimate shear wave-depth profiles of the region. The results are used to discuss the spatial variation of shear wave velocities for a depth range down from the surface to upper crust. Most of the shear wave velocity anomalies, including the upper crustal areas of the Kendeng basin and active volcanoes, are consistent with our previous study of Rayleigh wave group velocities and fit to the regional geology. Keywords: Dispersion Inversion; shear wave velocity; Central Java, Indonesia. Reference: Zulfakriza, Z., Saygin, E., Cummins, P., Widiyantoro, S., Nugraha, A., Luehr, B.-G., Bodin, T., 2014. Upper crustal structure of central Java, Indonesia, from transdimensional seismic ambient noise tomography. Geophys. J. Int. 197.
Soler, Roberto; Terradas, Jaume; Oliver, Ramón; Goossens, Marcel
2013-11-10
Magnetohydrodynamic (MHD) waves are ubiquitously observed in the solar atmosphere. Kink waves are a type of transverse MHD waves in magnetic flux tubes that are damped due to resonant absorption. The theoretical study of kink MHD waves in solar flux tubes is usually based on the simplification that the transverse variation of density is confined to a nonuniform layer much thinner than the radius of the tube, i.e., the so-called thin boundary approximation. Here, we develop a general analytic method to compute the dispersion relation and the eigenfunctions of ideal MHD waves in pressureless flux tubes with transversely nonuniform layers of arbitrary thickness. Results for kink waves are produced and compared with fully numerical resistive MHD eigenvalue computations in the limit of small resistivity. We find that the frequency and resonant damping rate are the same in both ideal and resistive cases. The actual results for thick nonuniform layers deviate from the behavior predicted in the thin boundary approximation and strongly depend on the shape of the nonuniform layer. The eigenfunctions in ideal MHD are very different from those in resistive MHD. The ideal eigenfunctions display a global character regardless of the thickness of the nonuniform layer, while the resistive eigenfunctions are localized around the resonance and are indistinguishable from those of ordinary resistive Alfvén modes. Consequently, the spatial distribution of wave energy in the ideal and resistive cases is dramatically different. This poses a fundamental theoretical problem with clear observational consequences.
Luo, Y.; Xia, J.; Miller, R.D.; Liu, J.; Xu, Y.; Liu, Q.
2008-01-01
Multichannel Analysis of Surface Waves (MASW) analysis is an efficient tool to obtain the vertical shear-wave profile. One of the key steps in the MASW method is to generate an image of dispersive energy in the frequency-velocity domain, so dispersion curves can be determined by picking peaks of dispersion energy. In this paper, we image Rayleigh-wave dispersive energy and separate multimodes from a multichannel record by high-resolution linear Radon transform (LRT). We first introduce Rayleigh-wave dispersive energy imaging by high-resolution LRT. We then show the process of Rayleigh-wave mode separation. Results of synthetic and real-world examples demonstrate that (1) compared with slant stacking algorithm, high-resolution LRT can improve the resolution of images of dispersion energy by more than 50% (2) high-resolution LRT can successfully separate multimode dispersive energy of Rayleigh waves with high resolution; and (3) multimode separation and reconstruction expand frequency ranges of higher mode dispersive energy, which not only increases the investigation depth but also provides a means to accurately determine cut-off frequencies.
S-Wave Dispersion Relations: Exact Left Hand E-Plane Discontinuity from the Born Series
NASA Technical Reports Server (NTRS)
Bessis, D.; Temkin, A.
1999-01-01
We show, for a superposition of Yukawa potentials, that the left hand cut discontinuity in the complex E plane of the (S-wave) scattering amplitude is given exactly, in an interval depending on n, by the discontinuity of the Born series stopped at order n. This also establishes an inverse and unexpected correspondence of the Born series at positive high energies and negative low energies. We can thus construct a viable dispersion relation (DR) for the partial (S-) wave amplitude. The high numerical precision achievable by the DR is demonstrated for the exponential potential at zero scattering energy. We also briefly discuss the extension of our results to Field Theory.
Dark three-sister rogue waves in normally dispersive optical fibers with random birefringence.
Chen, Shihua; Soto-Crespo, Jose M; Grelu, Philippe
2014-11-03
We investigate dark rogue wave dynamics in normally dispersive birefringent optical fibers, based on the exact rational solutions of the coupled nonlinear Schrödinger equations. Analytical solutions are derived up to the second order via a nonrecursive Darboux transformation method. Vector dark "three-sister" rogue waves as well as their existence conditions are demonstrated. The robustness against small perturbations is numerically confirmed in spite of the onset of modulational instability, offering the possibility to observe such extreme events in normal optical fibers with random birefringence, or in other Manakov-type vector nonlinear media.
Chekroun, Mathieu; Minonzio, Jean-Gabriel; Prada, Claire; Laugier, Pascal; Grimal, Quentin
2016-02-01
A method is proposed to evaluate in a non-contact way the phase velocity dispersion curves of circumferential waves around a shell of arbitrary shape immersed in a fluid. No assumptions are made about the thickness or the material of the shell. A geometrical model is derived to describe the shape of the radiated wavefronts in the surrounding fluid, and predict the positions of its centers of curvature. Then the time-reversal principle is applied to recover these positions and to calculate the phase velocity of the circumferential waves. Numerical finite-difference simulations are performed to evaluate the method on a circular and on an elliptic thin shell. Different dispersion curves can be recovered with an error of less than 10%.
Nonlinear effects associated with dispersive Alfvén waves in plasmas
NASA Astrophysics Data System (ADS)
Shukla, P. K.; Stenflo, L.; Bingham, R.; Eliasson, B.
2004-12-01
Large amplitude Alfvén waves are frequently found in magnetized space and laboratory plasmas. Our objective here is to discuss the linear and nonlinear properties of dispersive Alfvén waves (DAWs) in a uniform magnetoplasma. We first consider finite frequency (ω/ωci) and ion gyroradius effects on inertial and kinetic Alfvén waves, where ωci is the ion gyrofrequency. Next, we focus on nonlinear effects caused by DAWs. Such effects include plasma density enhancement and depression by the Alfvén wave ponderomotive force, electron Joule heating by the thermal Alfvén wave force, the generation of zonal flows due to the shear Alfvén wave mode couplings as well as the formation of localized Alfvénic structures and Alfvénic vortices. The relevance of our investigation to the appearance of nonlinear Alfvén waves in the Earth's auroral acceleration region, in the solar corona and in the large plasma device at UCLA is discussed.
Surface Wave Dispersion Measurements and Tomography From Ambient Seismic Noise in China
2007-12-20
and the US Geological Survey in 1986, most of the new stations started operating in early 2000. The bandwiths of the instruments are from 20 Hz to over...predictions from a global 3D model based on earthquake data (Shapiro and Ritzwoller, 2002). However, the HTA -BRVK path, which samples the Tarim Basin...Ritzwoller and Levshin, 1998) to retrieve dispersion curves (blue lines) for Rayleigh waves of station pair AXX-QIZ (upper panels) and HTA -BRVK
Shear wave dispersion behaviors of soft, vascularized tissues from the microchannel flow model
NASA Astrophysics Data System (ADS)
Parker, K. J.; Ormachea, J.; McAleavey, S. A.; Wood, R. W.; Carroll-Nellenback, J. J.; Miller, R. K.
2016-07-01
The frequency dependent behavior of tissue stiffness and the dispersion of shear waves in tissue can be measured in a number of ways, using integrated imaging systems. The microchannel flow model, which considers the effects of fluid flow in the branching vasculature and microchannels of soft tissues, makes specific predictions about the nature of dispersion. In this paper we introduce a more general form of the 4 parameter equation for stress relaxation based on the microchannel flow model, and then derive the general frequency domain equation for the complex modulus. Dispersion measurements in liver (ex vivo) and whole perfused placenta (post-delivery) correspond to the predictions from theory, guided by independent stress relaxation measurements and consideration of the vascular tree structure.
The role of granular shocks in dust-layer dispersal by shock waves
NASA Astrophysics Data System (ADS)
Houim, Ryan; Ugarte, Orlando; Oran, Elaine
2016-11-01
Exactly how dust-layers are lifted and dispersed by shocks has been a longstanding question in compressible multiphase flow. Understanding the mechanism for this, however, is extremely important for early control of dust explosions. We address this problem by numerically solving a set of equations that couples a fully compressible representation of a gas with a kinetic-theory model for a granular medium (see) to simulate a shock propagating along the surface of a dust layer. The results show that the majority of the dispersed dust is lifted by hydrodynamic shear directly behind the shock wave. Simultaneously, large forces are produced behind the shock that compact the dust layer and create a granular shock. The effects from this granular shock on the surface of the dust layer destabilize the gas-dust boundary layer, which, in turn, enhances turbulence and the rate of dust dispersal.
Shear wave dispersion behaviors of soft, vascularized tissues from the microchannel flow model.
Parker, K J; Ormachea, J; McAleavey, S A; Wood, R W; Carroll-Nellenback, J J; Miller, R K
2016-07-07
The frequency dependent behavior of tissue stiffness and the dispersion of shear waves in tissue can be measured in a number of ways, using integrated imaging systems. The microchannel flow model, which considers the effects of fluid flow in the branching vasculature and microchannels of soft tissues, makes specific predictions about the nature of dispersion. In this paper we introduce a more general form of the 4 parameter equation for stress relaxation based on the microchannel flow model, and then derive the general frequency domain equation for the complex modulus. Dispersion measurements in liver (ex vivo) and whole perfused placenta (post-delivery) correspond to the predictions from theory, guided by independent stress relaxation measurements and consideration of the vascular tree structure.
Clobert, J.; Danchin, E.; Dhondt, A.A.; Nichols, J.D.
2001-01-01
The ability of species to migrate and disperse is a trait that has interested ecologists for many years. Now that so many species and ecosystems face major environmental threats from habitat fragmentation and global climate change, the ability of species to adapt to these changes by dispersing, migrating, or moving between patches of habitat can be crucial to ensuring their survival. This book provides a timely and wide-ranging overview of the study of dispersal and incorporates much of the latest research. The causes, mechanisms, and consequences of dispersal at the individual, population, species and community levels are considered. The potential of new techniques and models for studying dispersal, drawn from molecular biology and demography, is also explored. Perspectives and insights are offered from the fields of evolution, conservation biology and genetics. Throughout the book, theoretical approaches are combined with empirical data, and care has been taken to include examples from as wide a range of species as possible.
Legg, Mathew; Yücel, Mehmet K; Kappatos, Vassilios; Selcuk, Cem; Gan, Tat-Hean
2015-09-01
Overhead Transmission Line (OVTL) cables can experience structural defects and are, therefore, inspected using Non-Destructive Testing (NDT) techniques. Ultrasonic Guided Waves (UGW) is one NDT technique that has been investigated for inspection of these cables. For practical use, it is desirable to be able to inspect as long a section of cable as possible from a single location. This paper investigates increasing the UGW inspection range on Aluminium Conductor Steel Reinforced (ACSR) cables by compensating for dispersion using dispersion curve data. For ACSR cables, it was considered to be difficult to obtain accurate dispersion curves using modelling due to the complex geometry and unknown coupling between wire strands. Group velocity dispersion curves were, therefore, measured experimentally on an untensioned, 26.5m long cable and a method of calculating theoretical dispersion curves was obtained. Attenuation and dispersion compensation were then performed for a broadband Maximum Length Sequence (MLS) excitation signal. An increase in the Signal to Noise Ratio (SNR) of about 4-8dB compared to that of the dispersed signal was obtained. However, the main benefit was the increased ability to resolve the individual echoes from the end of the cable and an introduced defect in the form of a cut, which was 7 to at least 13dB greater than that of the dispersed signal. Five echoes were able to be clearly detected using MLS excitation signal, indicating the potential for an inspection range of up to 130m in each direction. To the best of the authors knowledge, this is the longest inspection range for ACSR cables reported in the literature, where typically cables, which were only one or two meter long, have been investigated previously. Narrow band tone burst and Hann windowed tone burst excitation signal also showed increased SNR and ability to resolve closely spaced echoes.
Lamb wave dispersion in a PZT/metal/PZT sandwich plate with imperfect interface
NASA Astrophysics Data System (ADS)
Kurt, Ilkay; Akbarov, Surkay D.; Sezer, Semih
2016-07-01
The Lamb wave dispersion in a PZT/Metal/PZT sandwich plate is investigated by employing the exact linear equations of electro-elastic waves in piezoelectric materials within the scope of the plane-strain state. It is assumed that at the interfaces between the piezoelectric face layers and metal core layer, shear-spring and normal-spring type imperfect conditions are satisfied. The degree of this imperfectness is estimated through the corresponding shear-spring and normal-spring type parameters which appear in the contact condition characterizing the transverse and normal displacements' discontinuity. The corresponding dispersion equation is derived, and as a result of the numerical solution to this equation, the dispersion curves are constructed for the first and second lowest modes in the cases where the material of the face layers is PZT and the material of the middle layer is Steel (St). Consequently, for the PZT/St/PZT sandwich plate, the study of the influence of the problem parameters such as the piezoelectric and dielectric constants, layer thickness ratios, non-dimensional shear-spring, and normal-spring type parameters, is carried out. In particular, it is established that the imperfectness of the contact between the layers of the plate causes a decrease in the values of the wave propagation velocity.
A theoretical study of wave dispersion and thermal conduction for HMX/additive interfaces
NASA Astrophysics Data System (ADS)
Long, Yao; Chen, Jun
2014-04-01
The wave dispersion rule for non-uniform material is useful for ultrasonic inspection and engine life prediction, and also is key in achieving an understanding of the energy dissipation and thermal conduction properties of solid material. On the basis of linear response theory and molecular dynamics, we derive a set of formulas for calculating the wave dispersion rate of interface systems, and study four kinds of interfaces inside plastic bonded explosives: HMX/{HMX, TATB, F2312, F2313}. (HMX: octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine; TATB: 1,3,5-triamino-2,4,6-trinitrobenzene; F2312, F2313: fluoropolymers). The wave dispersion rate is obtained over a wide frequency range from kHz to PHz. We find that at low frequency, the rate is proportional to the square of the frequency, and at high frequency, the rate couples with the molecular vibration modes at the interface. By using the results, the thermal conductivities of HMX/additive interfaces are derived, and a physical model is built for describing the total thermal conductivity of mixture explosives, including HMX multi-particle systems and {TATB, F2312, F2313}-coated HMX.
Dispersion reducing methods for edge discretizations of the electric vector wave equation
NASA Astrophysics Data System (ADS)
Bokil, V. A.; Gibson, N. L.; Gyrya, V.; McGregor, D. A.
2015-04-01
We present a novel strategy for minimizing the numerical dispersion error in edge discretizations of the time-domain electric vector wave equation on square meshes based on the mimetic finite difference (MFD) method. We compare this strategy, called M-adaptation, to two other discretizations, also based on square meshes. One is the lowest order Nédélec edge element discretization. The other is a modified quadrature approach (GY-adaptation) proposed by Guddati and Yue for the acoustic wave equation in two dimensions. All three discrete methods use the same edge-based degrees of freedom, while the temporal discretization is performed using the standard explicit Leapfrog scheme. To obtain efficient and explicit time stepping methods, the three schemes are further mass lumped. We perform a dispersion and stability analysis for the presented schemes and compare all three methods in terms of their stability regions and phase error. Our results indicate that the method produced by GY-adaptation and the Nédélec method are both second order accurate for numerical dispersion, but differ in the order of their numerical anisotropy (fourth order, versus second order, respectively). The result of M-adaptation is a discretization that is fourth order accurate for numerical dispersion as well as numerical anisotropy. Numerical simulations are provided that illustrate the theoretical results.
Analysis of group-velocity dispersion of high-frequency Rayleigh waves for near-surface applications
Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.
2011-01-01
The Multichannel Analysis of Surface Waves (MASW) method is an efficient tool to obtain the vertical shear (S)-wave velocity profile using the dispersive characteristic of Rayleigh waves. Most MASW researchers mainly apply Rayleigh-wave phase-velocity dispersion for S-wave velocity estimation with a few exceptions applying Rayleigh-wave group-velocity dispersion. Herein, we first compare sensitivities of fundamental surface-wave phase velocities with group velocities with three four-layer models including a low-velocity layer or a high-velocity layer. Then synthetic data are simulated by a finite difference method. Images of group-velocity dispersive energy of the synthetic data are generated using the Multiple Filter Analysis (MFA) method. Finally we invert a high-frequency surface-wave group-velocity dispersion curve of a real-world example. Results demonstrate that (1) the sensitivities of group velocities are higher than those of phase velocities and usable frequency ranges are wider than that of phase velocities, which is very helpful in improving inversion stability because for a stable inversion system, small changes in phase velocities do not result in a large fluctuation in inverted S-wave velocities; (2) group-velocity dispersive energy can be measured using single-trace data if Rayleigh-wave fundamental-mode energy is dominant, which suggests that the number of shots required in data acquisition can be dramatically reduced and the horizontal resolution can be greatly improved using analysis of group-velocity dispersion; and (3) the suspension logging results of the real-world example demonstrate that inversion of group velocities generated by the MFA method can successfully estimate near-surface S-wave velocities. ?? 2011 Elsevier B.V.
Micropolar dissipative models for the analysis of 2D dispersive waves in periodic lattices
NASA Astrophysics Data System (ADS)
Reda, H.; Ganghoffer, J. F.; Lakiss, H.
2017-03-01
The computation of the dispersion relations for dissipative periodic lattices having the attributes of metamaterials is an actual research topic raising the interest of researchers in the field of acoustics and wave propagation phenomena. We analyze in this contribution the impact of wave damping on the dispersion features of periodic lattices, which are modeled as beam-lattices. The band diagram structure and damping ratio are computed for different repetitive lattices, based on the homogenized continuum response of the initially discrete lattice architecture, modeled as Kelvin-Voigt viscoelastic beams. Three of these lattices (reentrant hexagonal, chiral diamond, hexachiral lattice) are auxetic metamaterials, since they show negative Poisson's ratio. The effective viscoelastic anisotropic continuum behavior of the lattices is first computed in terms of the homogenized stiffness and viscosity matrices, based on the discrete homogenization technique. The dynamical equations of motion are obtained for an equivalent homogenized micropolar continuum evaluated based on the homogenized properties, and the dispersion relation and damping ratio are obtained by inserting an harmonic plane waves Ansatz into these equations. The comparison of the acoustic properties obtained in the low frequency range for the four considered lattices shows that auxetic lattices attenuate waves at lower frequencies compared to the classical hexagonal lattice. The diamond chiral lattice shows the best attenuation properties of harmonic waves over the entire Brillouin zone, and the hexachiral lattice presents better acoustic properties than the reentrant hexagonal lattice. The range of validity of the effective continuum obtained by the discrete homogenization has been assessed by comparing the frequency band structure of this continuum with that obtained by a Floquet-Bloch analysis.
NASA Astrophysics Data System (ADS)
Akbar, Noreen Sher; Tripathi, D.; Bég, O. Anwar; Khan, Z. H.
2016-11-01
A theoretical investigation of magnetohydrodynamic (MHD) flow and heat transfer of electrically-conducting viscoplastic fluids through a channel is conducted. The robust Casson model is implemented to simulate viscoplastic behavior of fluids. The external magnetic field is oblique to the fluid flow direction. Viscous dissipation effects are included. The flow is controlled by the metachronal wave propagation generated by cilia beating on the inner walls of the channel. The mathematical formulation is based on deformation in longitudinal and transverse velocity components induced by the ciliary beating phenomenon with cilia assumed to follow elliptic trajectories. The model also features velocity and thermal slip boundary conditions. Closed-form solutions to the non-dimensional boundary value problem are obtained under physiological limitations of low Reynolds number and large wavelength. The influence of key hydrodynamic and thermo-physical parameters i.e. Hartmann (magnetic) number, Casson (viscoplastic) fluid parameter, thermal slip parameter and velocity slip parameter on flow characteristics are investigated. A comparative study is also made with Newtonian fluids (corresponding to massive values of plastic viscosity). Stream lines are plotted to visualize trapping phenomenon. The computations reveal that velocity increases with increasing the magnitude of Hartmann number near the channel walls whereas in the core flow region (center of the channel) significant deceleration is observed. Temperature is elevated with greater Casson parameter, Hartmann number, velocity slip, eccentricity parameter, thermal slip and also Brinkmann (dissipation) number. Furthermore greater Casson parameter is found to elevate the quantity and size of the trapped bolus. In the pumping region, the pressure rise is reduced with greater Hartmann number, velocity slip, and wave number whereas it is enhanced with greater cilia length.
NASA Astrophysics Data System (ADS)
Huang, Chia-Lin; Spence, Harlan E.; Singer, Howard J.; Hughes, W. Jeffrey
2010-06-01
To provide critical ULF wave field information for radial diffusion studies in the radiation belts, we quantify ULF wave power (f = 0.5-8.3 mHz) in GOES observations and magnetic field predictions from a global magnetospheric model. A statistical study of 9 years of GOES data reveals the wave local time distribution and power at geosynchronous orbit in field-aligned coordinates as functions of wave frequency, solar wind conditions (Vx, ΔPd and IMF Bz) and geomagnetic activity levels (Kp, Dst and AE). ULF wave power grows monotonically with increasing solar wind Vx, dynamic pressure variations ΔPd and geomagnetic indices in a highly correlated way. During intervals of northward and southward IMF Bz, wave activity concentrates on the dayside and nightside sectors, respectively, due to different wave generation mechanisms in primarily open and closed magnetospheric configurations. Since global magnetospheric models have recently been used to trace particles in radiation belt studies, it is important to quantify the wave predictions of these models at frequencies relevant to electron dynamics (mHz range). Using 27 days of real interplanetary conditions as model inputs, we examine the ULF wave predictions modeled by the Lyon-Fedder-Mobarry magnetohydrodynamic code. The LFM code does well at reproducing, in a statistical sense, the ULF waves observed by GOES. This suggests that the LFM code is capable of modeling variability in the magnetosphere on ULF time scales during typical conditions. The code provides a long-missing wave field model needed to quantify the interaction of radiation belt electrons with realistic, global ULF waves throughout the inner magnetosphere.
Spatial Statistics of Deep-Water Ambient Noise; Dispersion Relations for Sound Waves and Shear Waves
2014-09-30
published, refereed]. 24. M. J. Buckingham and M. S. Garcés, “Airborne acoustics of explosive volcanic eruptions ,” J. Comp. Acoust., 9 (3), 1215-1225...Buckingham, “On the transient solutions of three acoustic wave equations: van Wijngaarden’s equation, Stokes’ equation and the time-dependent diffusion
Propagation and dispersion of transverse wave trains in magnetic flux tubes
Oliver, R.; Terradas, J.; Ruderman, M. S.
2014-07-01
The dispersion of small-amplitude, impulsively excited wave trains propagating along a magnetic flux tube is investigated. The initial disturbance is a localized transverse displacement of the tube that excites a fast kink wave packet. The spatial and temporal evolution of the perturbed variables (density, plasma displacement, velocity, ...) is given by an analytical expression containing an integral that is computed numerically. We find that the dispersion of fast kink wave trains is more important for shorter initial disturbances (i.e., more concentrated in the longitudinal direction) and for larger density ratios (i.e., for larger contrasts of the tube density with respect to the environment density). This type of excitation generates a wave train whose signature at a fixed position along a coronal loop is a short event (duration ≅ 20 s) in which the velocity and density oscillate very rapidly with typical periods of the order of a few seconds. The oscillatory period is not constant but gradually declines during the course of this event. Peak values of the velocity are of the order of 10 km s{sup –1} and are accompanied by maximum density variations of the order of 10%-15% the unperturbed loop density.
Nonlinear coupling of left and right handed circularly polarized dispersive Alfvén wave
Sharma, R. P. Sharma, Swati Gaur, Nidhi
2014-07-15
The nonlinear phenomena are of prominent interests in understanding the particle acceleration and transportation in the interplanetary space. The ponderomotive nonlinearity causing the filamentation of the parallel propagating circularly polarized dispersive Alfvén wave having a finite frequency may be one of the mechanisms that contribute to the heating of the plasmas. The contribution will be different of the left (L) handed mode, the right (R) handed mode, and the mix mode. The contribution also depends upon the finite frequency of the circularly polarized waves. In the present paper, we have investigated the effect of the nonlinear coupling of the L and R circularly polarized dispersive Alfvén wave on the localized structures formation and the respective power spectra. The dynamical equations are derived in the presence of the ponderomotive nonlinearity of the L and R pumps and then studied semi-analytically as well as numerically. The ponderomotive nonlinearity accounts for the nonlinear coupling between both the modes. In the presence of the adiabatic response of the density fluctuations, the nonlinear dynamical equations satisfy the modified nonlinear Schrödinger equation. The equations thus obtained are solved in solar wind regime to study the coupling effect on localization and the power spectra. The effect of coupling is also studied on Faraday rotation and ellipticity of the wave caused due to the difference in the localization of the left and the right modes with the distance of propagation.
NASA Astrophysics Data System (ADS)
Gao, Yan; Sui, Fusheng; Muggleton, Jennifer M.; Yang, Jun
2016-08-01
The dispersion characteristics of axisymmetric (n=0) waves offer a way to gain physical insight into the low-frequency vibrational behaviour of underground pipe systems. Whilst these can be found in the literature, they are generally calculated numerically. Coupled equations of motion for the n=0 waves that propagate in a buried fluid-filled pipe are presented in this paper and, from this, an analytical solution is developed for the fluid-dominated (s=1) wavenumber. The effect of the frictional stress at the pipe-soil interface on the dispersion behaviour of the s=1 wave is characterised by adopting a soil loading matrix. Overall, the fluid loading has a greater effect on the propagation wavespeed compared with the soil loading: for metal pipes, the effect of soil loading is negligible; for plastic pipes, however, simply neglecting the effect of soil loading can lead to a considerable underestimation in the calculation of the wavespeed. The wave attenuation increases significantly at higher frequencies regardless of pipe material resulting from the added damping due to radiation into the soil. Theoretical predictions of the s=1 wavenumber are compared with experimental data measured on an MDPE water pipe. The degree of agreement between prediction and experiment makes clear that, although the wavespeed is only slightly affected by the presence of the frictional stress, the frictional stress at the pipe-soil interface needs to be appropriately taken into account for attenuation predictions.
A comprehensive dispersion model of surface wave phase and group velocity for the globe
NASA Astrophysics Data System (ADS)
Ma, Zhitu; Masters, Guy; Laske, Gabi; Pasyanos, Michael
2014-10-01
A new method is developed to measure Rayleigh- and Love-wave phase velocities globally using a cluster analysis technique. This method clusters similar waveforms recorded at different stations from a single event and allows users to make measurements on hundreds of waveforms, which are filtered at a series of frequency ranges, at the same time. It also requires minimal amount of user interaction and allows easy assessment of the data quality. This method produces a large amount of phase delay measurements in a manageable time frame. Because there is a strong trade-off between the isotropic part of the Rayleigh-wave phase velocity and azimuthal anisotropy, we include the effect of azimuthal anisotropy in our inversions in order to obtain reliable isotropic phase velocity. We use b-splines to combine these isotropic phase velocity maps with our previous group velocity maps to produce an internally consistent global surface wave dispersion model.
Measurement of Thermal Effects in the Dispersion Relation of the Dust Acoustic Wave
NASA Astrophysics Data System (ADS)
Hoyng, Joshua; Williams, Jeremiah
2016-10-01
A complex or dusty plasma is a four-component plasma system composed of ions, electrons, neutral particles and charged microparticles. The presence of these charged microparticles reveals different plasma phenomena, including a new wave mode known as the dust acoustic, or dust density, wave (DAW). The DAW is a low frequency, longitudinal mode that propagates through the microparticle component of the dusty plasma system and is self-excited by the energy from the ions streaming through this component. In recent years the DAW has been the subject of intense study and has provided a way to examine the thermal properties of the microparticle component. In this presentation, we report the results of an experimental study examining the thermal effects in the dispersion relation of this wave mode over a range of neutral gas pressures.
Heeter, R F; Fasoli, A; Testa, D; Sharapov, S; Berk, H L; Breizman, B; Gondhalekar, A; Mantsinen, M
2004-03-23
Experiments are conducted on the JET tokamak to assess the diagnostic potential of MHD active and passive spectroscopy, for the plasma bulk and its suprathermal components, using Alfv{acute e}n Eigenmodes (AEs) excited by external antennas and by energetic particles. The measurements of AE frequencies and mode numbers give information on the bulk plasma. Improved equilibrium reconstruction, in particular in terms of radial profiles of density and safety factor, is possible from the comparison between the antenna driven spectrum and that calculated theoretically. Details of the time evolution of the non-monotonic safety factor profile in advanced scenarios can be reconstructed from the frequency of ICRH-driven energetic particle modes. The plasma effective mass can be inferred from the resonant frequency of externally driven AEs in discharges with similar equilibrium profiles. The stability thresholds and the nonlinear development of the instabilities can give clues on energy and spatial distribution of the fast particle population. The presence of unstable AEs provides lower limits in the energy of ICRH generated fast ion tails. Fast ion pressure gradients and their evolution can be inferred from the stability of AEs at different plasma radial positions. Finally, the details of the AE spectrum in the nonlinear stage can be used to obtain information about the fast particle velocity space diffusion.
NASA Technical Reports Server (NTRS)
Jones, E.; Anliker, M.; Chang, I.
1971-01-01
Investigation of the effects of blood viscosity on dissipation as well as dispersion of small waves in arteries and veins by means of a parametric study. A linearized analysis of axisymmetric waves in a cylindrical membrane that contains a viscous fluid indicates that there are two families of waves: a family of slow waves and one of fast waves. The faster waves are shown to be more sensitive to variations in the elastic properties of the medium surrounding the blood vessels and at high values of the frequency parameter alpha. At low values of alpha the effects of viscosity on attenuation are reversed.
NASA Astrophysics Data System (ADS)
Li, Fucai; Meng, Guang; Ye, Lin; Lu, Ye; Kageyama, Kazuro
2009-09-01
In this paper, the dispersion of Lamb waves in aluminum structures was systematically analyzed to differentiate the mode of each package in Lamb wave signals and localize damage. Piezoelectric transducers were bonded on the surfaces of aluminum structures, functioning as actuator and sensor to excite and acquire Lamb waves, respectively. Wavelet transform was applied to the acquired Lamb wave signals, in which the optimal mother wavelet was selected using the concept of Shannon entropy to obtain the most accurate location of each wave package. The ridge and contour of the Lamb wave signals in the time-scale domain were obtained to distinguish the mode of each wave package and pinpoint these packages for estimating the actual group velocities of dispersion curves and localizing damage. The proposed approach could help search the actual dispersion curves in the excitation frequency band by using only one Lamb wave signal. Ridges in the time-scale domain and the actual group velocities were further used to identify damage in the structures. Results demonstrate that the proposed approaches were effective in dispersion analysis, wave mode differentiation and damage localization.
ERIC Educational Resources Information Center
Kantrowitz, Arthur; Rosa, Richard J.
1975-01-01
Explains the operation of the Magnetohydrodynamic (MHD) generator and advantages of the system over coal, oil or nuclear powered generators. Details the development of MHD generators in the United States and Soviet Union. (CP)
NASA Astrophysics Data System (ADS)
Garth, T.; Rietbrock, A.
2012-12-01
Low velocity structures in the upper slab have been inferred from guided wave studies (e.g Abers 2000) and subsequently resolved by a number of geophysical methods including receiver function analyses and high resolution seismic tomography . These low velocity structures are potentially explained by the presence of hydrous mineral assemblages in the subducted oceanic crust. This supports the long proposed theory that mineral dehydration during subduction may weaken the crust and allow for intermediate depth seismicity. Recently it has been proposed that normal faulting in the slab may provide a mechanism for hydration deep in the slab, as stress changes due to slab bending promotes the downward pumping of fluids (Faccenda et al. 2009). At greater depth, the reactivation of outer rise normal faults has been postulated by Ranero et al. (2005) as a cause Wadati-Benioff zone seismicity. However there is no direct seismological evidence of normal faults at intermediate depths. Here we present seismic evidence that these faults are in fact associated with low velocities, possibly caused by hydrous minerals or the presence of fluids. We analyse dispersive P-wave arrivals from intermediate depth events in Northern Japan. Finite difference wave propagation models are used to constrain the structure related to this dispersion. Dispersion of deeper events (>150 km) can be explained by a low velocity layer (LVL) at the top of the slab acting as a waveguide. This LVL has a thickness of ~8 km, and a 5 - 12% reduction in velocity. Shallower events (70 - 150 km depth) that occur well below the top of the slab also show dispersion. This cannot be attributed to the upper LVL as the event must be on or near to the waveguide for dispersion to occur. Numerical modeling shows that these shallower dispersive events can be explained by very low velocity structures dipping with a normal fault geometry. We propose that these dipping planes might indicate hydrated material along normal
Anisotropy in the Pacific upper mantle from inversion of a surface-wave dispersion dataset
NASA Astrophysics Data System (ADS)
Eddy, C. L.; Ekstrom, G.; Nettles, M.; Gaherty, J. B.
2015-12-01
We present work towards a three-dimensional model of the anisotropic velocity structure of the Pacific upper mantle. Models of seismic anisotropy in oceanic regions provide important constraints on the geometry of strain in the mantle, the nature of the lithosphere-asthenosphere transition, and the possible presence of partial melt in the asthenosphere. The goal of this work is to produce a three-dimensional model of isotropic and anisotropic velocities in the Pacific, which will improve constraints on olivine fabrics and strain geometries in the oceanic upper mantle. Measurements of fundamental-mode dispersion for Rayleigh and Love waves traversing oceanic paths are drawn from the waveform dataset used to construct the global dispersion model GDM52. We develop anisotropic phase-velocity maps of the Pacific basin for Rayleigh and Love waves between 25 s and 250 s and invert the phase-velocity maps for anisotropic velocity structure at depth. The resulting models are radially anisotropic and include the G parameters that are related to the azimuthal anisotropy of vSV. We compare results of these two-step inversions with direct inversions of fundamental-mode phase anomalies for three-dimensional anisotropic structure. In much of the central and western Pacific, vertical gradients in both vS and anisotropy are consistent with the transition from rigid lithosphere to viscously deforming asthenosphere. In future work we plan to incorporate waveform data providing constraints on higher-mode dispersion in the modeling of the three-dimensional anisotropic structure.
Modeling blast waves, gas and particles dispersion in urban and hilly ground areas.
Hank, S; Saurel, R; Le Métayer, O; Lapébie, E
2014-09-15
The numerical simulation of shock and blast waves as well as particles dispersion in highly heterogeneous media such as cities, urban places, industrial plants and part of countries is addressed. Examples of phenomena under study are chemical gas products dispersion from damaged vessels, gas dispersion in urban places under explosion conditions, shock wave propagation in urban environment. A three-dimensional simulation multiphase flow code (HI2LO) is developed in this aim. To simplify the consideration of complex geometries, a heterogeneous discrete formulation is developed. When dealing with large scale domains, such as countries, the topography is considered with the help of elevation data. Meteorological conditions are also considered, in particular regarding complex temperature and wind profiles. Heat and mass transfers on sub-scale objects, such as buildings, trees and other obstacles are considered as well. Particles motion is addressed through a new turbulence model involving a single parameter to describe accurately plumes. Validations against experiments in basic situations are presented as well as examples of industrial and environmental computations.
Gravitational-wave detection by dispersion force modulation in nanoscale parametric amplifiers
NASA Astrophysics Data System (ADS)
Fabrizio, Pinto
2016-05-01
Two infinite parallel plane slabs separated by a gap alter the zero-point-energy of the matter-electromagnetic field system. Generally speaking, the corresponding interaction depends on the reflection properties of the boundaries, and therefore on the dielectric functions of both the slab and gap materials, on the gap width, and on the absolute temperature of the system. Importantly, it is known experimentally that dispersion forces can be modulated in time. This can be achieved by mechanically varying the gap width so as to introduce parametric oscillations. Much more fundamentally, however, dispersion forces can be altered by acting on the dielectric functions involved as is the case in semiconductors. In the optical analogy, a gravitational wave introduces an additional time dependence of the effective gap dielectric function. These elements, already confirmed by direct experimentation or predicted from the Lifshitz theory, support the design of a novel approach to ground-based nanoscale gravitational wave detection based on parametric amplification driven by dispersion force modulation.
NASA Astrophysics Data System (ADS)
Leo, François; Gorza, Simon-Pierre; Safioui, Jassem; Kockaert, Pascal; Coen, Stéphane; Dave, Utsav; Kuyken, Bart; Roelkens, Gunther
2014-06-01
We experimentally and numerically study dispersive wave emission, soliton fission and supercontinuum generation in a silicon wire at telecommunication wavelengths. Through dispersion engineering, we experimentally confirm a previously reported numerical study [1] and show that the emission of resonant radiation from the solitons can lead to the generation of a supercontinuum spanning over 500 nm. An excellent agreement with numerical simulations is observed.
NASA Astrophysics Data System (ADS)
Lambert, Simon A.; Näsholm, Sven Peter; Nordsletten, David; Michler, Christian; Juge, Lauriane; Serfaty, Jean-Michel; Bilston, Lynne; Guzina, Bojan; Holm, Sverre; Sinkus, Ralph
2015-08-01
Wave scattering provides profound insight into the structure of matter. Typically, the ability to sense microstructure is determined by the ratio of scatterer size to probing wavelength. Here, we address the question of whether macroscopic waves can report back the presence and distribution of microscopic scatterers despite several orders of magnitude difference in scale between wavelength and scatterer size. In our analysis, monosized hard scatterers 5 μ m in radius are immersed in lossless gelatin phantoms to investigate the effect of multiple reflections on the propagation of shear waves with millimeter wavelength. Steady-state monochromatic waves are imaged in situ via magnetic resonance imaging, enabling quantification of the phase velocity at a voxel size big enough to contain thousands of individual scatterers, but small enough to resolve the wavelength. We show in theory, experiments, and simulations that the resulting coherent superposition of multiple reflections gives rise to power-law dispersion at the macroscopic scale if the scatterer distribution exhibits apparent fractality over an effective length scale that is comparable to the probing wavelength. Since apparent fractality is naturally present in any random medium, microstructure can thereby leave its fingerprint on the macroscopically quantifiable power-law exponent. Our results are generic to wave phenomena and carry great potential for sensing microstructure that exhibits intrinsic fractality, such as, for instance, vasculature.
Composite Materials NDE Using Enhanced Leaky Lamb Wave Dispersion Data Acquisition Method
NASA Technical Reports Server (NTRS)
Bar-Cohen, Yoseph; Mal, Ajit; Lih, Shyh-Shiuh; Chang, Zensheu
1999-01-01
The leaky Lamb wave (LLW) technique is approaching a maturity level that is making it an attractive quantitative NDE tool for composites and bonded joints. Since it was first observed in 1982, the phenomenon has been studied extensively, particularly in composite materials. The wave is induced by oblique insonification using a pitch-catch arrangement and the plate wave modes are detected by identifying minima in the reflected spectra to obtain the dispersion data. The wave behavior in multi-orientation laminates has been well documented and corroborated experimentally with high accuracy. The sensitivity of the wave to the elastic constants of the material and to the boundary conditions led to the capability to measure the elastic properties of bonded joints. Recently, the authors significantly enhanced the LLW method's capability by increasing the speed of the data acquisition, the number of modes that can be identified and the accuracy of the data inversion. In spite of the theoretical and experimental progress, methods that employ oblique insonification of composites are still not being applied as standard industrial NDE methods. The authors investigated the issues that are hampering the transition of the LLW to industrial applications and identified 4 key issues. The current capability of the method and the nature of these issues are described in this paper.
NASA Astrophysics Data System (ADS)
Bar-Cohen, Yoseph; Mal, Ajit K.; Lih, Shyh-Shiuh; Chang, Zensheu
1999-01-01
The leaky Lamb wave (LLW) technique is approaching a maturity level that is making it an attractive quantitative NDE tool for composites and bonded joints. Since it was first observed in 1982, the phenomenon has been studied extensively, particularly in composite materials. The wave is induced by oblique insonification using a pitch-catch arrangement and the plate wave modes are detected by identifying minima in the reflected spectra to obtain the dispersion data. The wave behavior in multi-orientation laminates has ben well documented and corroborated experimentally with high accuracy. The sensitivity of the wave to the elastic constants of the material and to the boundary conditions led to the capability to measure the elastic properties of bonded joints. Recently, the authors significantly enhanced the LLW method's capability by increasing the speed of the data acquisition, the number of modes that can be identified and the accuracy of the data inversion. In spite of the theoretical and experimental progress, methods that employ oblique insonification of composites are still not being applied as standard industrial NDE methods. The authors investigated the issues that are hampering the transition of the LLW to industrial applications and identified 4 key issues. The current capability of the method and the nature of these issues are described in this paper.
Lambert, Simon A; Näsholm, Sven Peter; Nordsletten, David; Michler, Christian; Juge, Lauriane; Serfaty, Jean-Michel; Bilston, Lynne; Guzina, Bojan; Holm, Sverre; Sinkus, Ralph
2015-08-28
Wave scattering provides profound insight into the structure of matter. Typically, the ability to sense microstructure is determined by the ratio of scatterer size to probing wavelength. Here, we address the question of whether macroscopic waves can report back the presence and distribution of microscopic scatterers despite several orders of magnitude difference in scale between wavelength and scatterer size. In our analysis, monosized hard scatterers 5 μm in radius are immersed in lossless gelatin phantoms to investigate the effect of multiple reflections on the propagation of shear waves with millimeter wavelength. Steady-state monochromatic waves are imaged in situ via magnetic resonance imaging, enabling quantification of the phase velocity at a voxel size big enough to contain thousands of individual scatterers, but small enough to resolve the wavelength. We show in theory, experiments, and simulations that the resulting coherent superposition of multiple reflections gives rise to power-law dispersion at the macroscopic scale if the scatterer distribution exhibits apparent fractality over an effective length scale that is comparable to the probing wavelength. Since apparent fractality is naturally present in any random medium, microstructure can thereby leave its fingerprint on the macroscopically quantifiable power-law exponent. Our results are generic to wave phenomena and carry great potential for sensing microstructure that exhibits intrinsic fractality, such as, for instance, vasculature.
Jugé, Lauriane; Petiet, Anne; Lambert, Simon A; Nicole, Pascal; Chatelin, Simon; Vilgrain, Valerie; Van Beers, Bernard E; Bilston, Lynne E; Sinkus, Ralph
2015-12-01
Magnetic Resonance Elastography (MRE) uses macroscopic shear wave propagation to quantify mechanical properties of soft tissues. Micro-obstacles are capable of affecting the macroscopic dispersion properties of shear waves. Since disease or therapy can change the mechanical integrity and organization of vascular structures, MRE should be able to sense these changes if blood vessels represent a source for wave scattering. To verify this, MRE was performed to quantify alteration of the shear wave speed cs due to the presence of vascular outgrowths using an aortic ring model. Eighteen fragments of rat aorta included in a Matrigel matrix (n=6 without outgrowths, n=6 with a radial outgrowth extent of ~600 µm and n=6 with ~850 µm) were imaged using a 7 Tesla MR scanner (Bruker, PharmaScan). High resolution anatomical images were acquired in addition to multi-frequency MRE (ν = 100, 115, 125, 135 and 150 Hz). Average cs was measured within a ring of ~900 µm thickness encompassing the aorta and were normalized to cs0 of the corresponding Matrigel. The frequency dependence was fit to the power law model cs ~ν(y). After scanning, optical microscopy was performed to visualize outgrowths. Results demonstrated that in presence of vascular outgrowths (1) normalized cs significantly increased for the three highest frequencies (Kruskal-Wallis test, P = 0.0002 at 125 Hz and P = 0.002 at 135 Hz and P = 0.003 at 150 Hz) but not for the two lowest (Kruskal-Wallis test, P = 0.63 at 100 Hz and P = 0.87 at 115 Hz), and (2) normalized cs followed a power law behavior not seen in absence of vascular outgrowths (ANOVA test, P < 0.0001). These results showed that vascular outgrowths acted as micro-obstacles altering the dispersion relationships of propagating shear waves and that MRE could provide valuable information about microvascular changes.
A theory for narrow-banded radio bursts at Uranus - MHD surface waves as an energy driver
NASA Technical Reports Server (NTRS)
Farrell, W. M.; Curtis, S. A.; Desch, M. D.; Lepping, R. P.
1992-01-01
A possible scenario for the generation of the narrow-banded radio bursts detected at Uranus by the Voyager 2 planetary radio astronomy experiment is described. In order to account for the emission burstiness which occurs on time scales of hundreds of milliseconds, it is proposed that ULF magnetic surface turbulence generated at the frontside magnetopause propagates down the open/closed field line boundary and mode-converts to kinetic Alfven waves (KAW) deep within the polar cusp. The oscillating KAW potentials then drive a transient electron stream that creates the bursty radio emission. To substantiate these ideas, Voyager 2 magnetometer measurements of enhanced ULF magnetic activity at the frontside magnetopause are shown. It is demonstrated analytically that such magnetic turbulence should mode-convert deep in the cusp at a radial distance of 3 RU.
Saturn A ring surface mass densities from spiral density wave dispersion behavior
NASA Astrophysics Data System (ADS)
Spilker, Linda J.; Pilorz, Stuart; Lane, Arthur L.; Nelson, Robert M.; Pollard, Benjamin; Russell, Christopher T.
2004-10-01
We have undertaken an analysis of the Voyager photopolarimeter (PPS) stellar occultation data of Saturn's A ring. The Voyager PPS observed the bright star δ Scorpii as it was occulted by Saturn's main rings during the spacecraft flyby of the Saturn system in 1981. The occultation measurement produced a ring profile with radial resolution of approximately 100 m, and radial structure is evident in the profile down to the resolution limit. We have applied an autoregressive technique to the data for estimating the power spectrum as a function of radius, which has allowed us to identify 40 spiral density waves in Saturn's A ring, associated with the strongest torques due to forcing from the moons. The majority of the detected waves are observed to disperse linearly in regions beginning a few kilometers from the resonance location. We have used the dispersion behavior for those waves to calculate local surface mass densities in the vicinity of each wave. We find that the inner three-quarters of the A ring (up to the beginning of the Encke gap) has an average surface mass density of 43.8±7.9 g cm-2, while the outer region has an average surface mass density of 28.3±10.8 g cm-2. The two regions have different mean surface mass densities with a significance of approximately 0.999993, as estimated with a T-statistic, which corresponds to about 4.5 σ. While the mean optical depth of the A ring increases slightly with increasing distance from Saturn, we find that it is not significantly correlated with the surface mass density; the two quantities having a linear Pearson's correlation coefficient of rcorr≈-0.03. The variation of mass density, independent of PPS optical depth, is consistent with previous conjectures that the particle size distribution and composition are not constant across the entire A ring, particularly in the very outer portion. We estimate the mass of Saturn's A ring from our surface mass density estimates as 4.9×10 21 gm, or 8.61×10 -9 of the mass
NASA Astrophysics Data System (ADS)
Seadawy, Aly R.
2017-01-01
The propagation of three-dimensional nonlinear irrotational flow of an inviscid and incompressible fluid of the long waves in dispersive shallow-water approximation is analyzed. The problem formulation of the long waves in dispersive shallow-water approximation lead to fifth-order Kadomtsev-Petviashvili (KP) dynamical equation by applying the reductive perturbation theory. By using an extended auxiliary equation method, the solitary travelling-wave solutions of the two-dimensional nonlinear fifth-order KP dynamical equation are derived. An analytical as well as a numerical solution of the two-dimensional nonlinear KP equation are obtained and analyzed with the effects of external pressure flow.
NASA Astrophysics Data System (ADS)
Fang, Hongjian; Yao, Huajian; Zhang, Haijiang; Huang, Yu-Chih; van der Hilst, Robert D.
2015-06-01
We propose a method to invert surface wave dispersion data directly for 3-D variations of shear wave speed, that is, without the intermediate step of phase or group velocity maps, using frequency-dependent ray tracing and a wavelet-based sparsity-constrained tomographic inversion. A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. This avoids the assumption of great-circle propagation that is used in most surface wave tomographic studies, but which is not appropriate in complex media. To simplify the problem we consider quasi-stratified media with smoothly varying seismic properties. We represent the 3-D shear wave speed model by means of 1-D profiles beneath grid points, which are determined from all dispersion data simultaneously using a wavelet-based sparsity-constrained tomographic method. The wavelet coefficients of the wave speed model are estimated with an iteratively reweighted least squares algorithm, and upon iteration the surface wave ray paths and the data sensitivity matrix are updated using the newly obtained wave speed model. To demonstrate its feasibility, we apply the method to determine the 3-D shallow crustal shear wave speed variations in the Taipei basin of Taiwan using short period interstation Rayleigh wave phase velocity dispersion measurements extracted from the ambient noise cross-correlation method. The results are consistent with previous studies and reveal strong shallow crustal heterogeneity that correlates with surface geology.
NASA Astrophysics Data System (ADS)
Touil, B.; Bendib, A.; Bendib-Kalache, K.
2017-02-01
The longitudinal dielectric function is derived analytically from the relativistic Vlasov equation for arbitrary values of the relevant parameters z = m c 2 / T , where m is the rest electron mass, c is the speed of light, and T is the electron temperature in energy units. A new analytical approach based on the Legendre polynomial expansion and continued fractions was used. Analytical expression of the electron distribution function was derived. The real part of the dispersion relation and the damping rate of electron plasma waves are calculated both analytically and numerically in the whole range of the parameter z . The results obtained improve significantly the previous results reported in the literature. For practical purposes, explicit expressions of the real part of the dispersion relation and the damping rate in the range z > 30 and strongly relativistic regime are also proposed.
Manipulating dispersive wave generation by anomalous self-steepening effect in metamaterials.
Xiang, Yuanjiang; Wu, Jipeng; Dai, Xiaoyu; Wen, Shuangchun; Guo, Jun; Wang, Qingkai
2012-11-19
We present a theoretical investigation of dispersive wave (DW) generation in nonlinear metamaterials (MMs). The role of the anomalous self-steepening (SS) effect, which can be either positive or negative, and the negative SS parameter can have a very large value compared to an ordinary positive-index material, in DW generation is particularly identified. It is demonstrated that the SS effect exerts a great impact on the peak power while has little effect on the frequency shift of DW. For positive third-order dispersion (TOD), the negative SS broadens the pulse spectrum and weakens the DW's peak power significantly, opposite to the case of positive SS. For negative TOD, however, the negative SS narrows the pulse spectrum and enhances the DW's peak power, also opposite to the case of positive SS. The results suggest that the DW generation in nonlinear MMs can be manipulated by SS effect to a large extent.
Onset of dispersion in Nb microstrip transmission lines at submillimeter wave frequencies
NASA Technical Reports Server (NTRS)
Javadi, H. H. S.; Mcgrath, William R.; Bumble, B.; Leduc, Henry G.
1992-01-01
We have measured the dispersion in phase velocity of a Nb-SiO(x)-Nb microstrip transmission line resonator over a frequency range from 50 GHz to 800 GHz. A submicron Nb/Al-AlO(x)/Nb Josephson junction was used as a voltage-controlled oscillator to excite the high order modes in the resonator. The same junction is used as a direct detector resulting in a series of step-like structures in the DC current-voltage characteristic at the position of each mode frequency. The transmission line is dispersionless up to about 500 GHz where the phase velocity begins to decrease. This is well below the gap frequency f(sub g) approx. equals 700 GHz. Results agree qualitatively with the expected theoretical behavior near f(sub g). This onset of dispersion and loss in Nb transmission lines will have a significant impact on the design of submillimeter wave RF circuits.
Evanescent-wave comb spectroscopy of liquids with strongly dispersive optical fiber cavities
NASA Astrophysics Data System (ADS)
Avino, S.; Giorgini, A.; Salza, M.; Fabian, M.; Gagliardi, G.; De Natale, P.
2013-05-01
We demonstrate evanescent-wave fiber cavity-enhanced spectroscopy in the liquid phase using a near-infrared frequency comb. Exploiting strong fiber-dispersion effects, we show that liquid absorption spectra can be recorded without any external dispersive element. The fiber cavity is used both as sensor and spectrometer. The resonance modes are frequency locked to the comb teeth while the cavity photon lifetime is measured over 155 nm, from 1515 nm to 1670 nm, where absorption bands of liquid polyamines are detected as a proof of concept. Our fiber spectrometer lends itself to in situ, real-time chemical analysis in environmental monitoring, biomedical assays, and micro-opto-fluidic systems.
Numerous laboratory test systems have been developed for the comparison of efficacy between various chemical oil dispersant formulations. However, for the assessment of chemical dispersant effectiveness under realistic sea state, test protocols are required to produce hydrodynam...
A dispersive wave pattern on Jupiter's fastest retrograde jet at 20°S
NASA Astrophysics Data System (ADS)
Rogers, J. H.; Fletcher, L. N.; Adamoli, G.; Jacquesson, M.; Vedovato, M.; Orton, G. S.
2016-10-01
A compact wave pattern has been identified on Jupiter's fastest retrograding jet at 20°S (the SEBs) on the southern edge of the South Equatorial Belt. The wave has been identified in both reflected sunlight from amateur observations between 2010 and 2015, thermal infrared imaging from the Very Large Telescope and near infrared imaging from the Infrared Telescope Facility. The wave pattern is present when the SEB is relatively quiescent and lacking large-scale disturbances, and is particularly notable when the belt has undergone a fade (whitening). It is generally not present when the SEB exhibits its usual large-scale convective activity ('rifts'). Tracking of the wave pattern and associated white ovals on its southern edge over several epochs have permitted a measure of the dispersion relationship, showing a strong correlation between the phase speed (-43.2 to -21.2 m/s) and the longitudinal wavelength, which varied from 4.4 to 10.0° longitude over the course of the observations. Infrared imaging sensing low pressures in the upper troposphere suggest that the wave is confined to near the cloud tops. The wave is moving westward at a phase speed slower (i.e., less negative) than the peak retrograde wind speed (-62 m/s), and is therefore moving east with respect to the SEBs jet peak. Unlike the retrograde NEBn jet near °N, which is a location of strong vertical wind shear that sometimes hosts Rossby wave activity, the SEBs jet remains retrograde throughout the upper troposphere, suggesting the SEBs pattern cannot be interpreted as a classical Rossby wave. 2D windspeeds and thermal gradients measured by Cassini in 2000 are used to estimate the quasi-geostrophic potential vorticity gradient as a means of understanding the origin of the a wave. We find that the vorticity gradient is dominated by the baroclinic term and becomes negative (changes sign) in a region near the cloud-top level (400-700 mbar) associated with the SEBs. Such a sign reversal is a necessary (but
Effects of waves on water dispersion in a semi-enclosed estuarine bay
NASA Astrophysics Data System (ADS)
Delpey, M. T.; Ardhuin, F.; Otheguy, P.
2012-04-01
The bay of Saint Jean de Luz - Ciboure is a touristic destination located in the south west of France on the Basque coast. This small bay is 1.5km wide for 1km long. It is semi-enclosed by breakwaters, so that the area is mostly protected from waves except in its eastern part, where wave breaking is regularly observed over a shallow rock shelf. In the rest of the area the currents are generally weak. The bay receives fresh water inflows from two rivers. During intense raining events, the rivers can introduce pollutants in the bay. The input of pollutants combined with the low level dynamic of the area can affect the water quality for several days. To study such a phenomenon, mechanisms of water dispersion in the bay are investigated. The present paper focuses on the effects of waves on bay dynamics. Several field experiments were conducted in the area, combining wave and current measurements from a set of ADCP and ADV, lagrangian difter experiments in the surfzone, salinity and temperature profile measurements. An analysis of this set of various data is provided. It reveals that the bay combines remarkable density stratification due to fresh water inflows and occasionally intense wave-induced currents in the surfzone. These currents have a strong influence on river plume dynamics when the sea state is energetic. Moreover, modifications of hydrodynamics in the bay passes are found to be remarkably correlated with sea state evolutions. This result suggests a significant impact of waves on the bay flushing. To further analyse these phenomena, a three dimensional numerical model of bay hydrodynamics is developed. The model aims at reproducing fresh water inflows combined with wind-, tide- and wave-induced currents and mixing. The model of the bay is implemented using the code MOHID , which has been modified to allow the three dimensional representation of wave-current interactions proposed by Ardhuin et al. [2008b] . The circulation is forced by the wave field modelled
Influence of wavelength-dependent-loss on dispersive wave in nonlinear optical fibers.
Herrera, Rodrigo Acuna
2012-11-01
In this work, we study numerically the influence of wavelength-dependent loss on the generation of dispersive waves (DWs) in nonlinear fiber. This kind of loss can be obtained, for instance, by the acousto-optic effect in fiber optics. We show that this loss lowers DW frequency in an opposite way that the Raman effect does. Also, we see that the Raman effect does not change the DW frequency too much when wavelength-dependent loss is included. Finally, we show that the DW frequency is not practically affected by fiber length.
Tu, Haohua; Lægsgaard, Jesper; Zhang, Rui; Tong, Shi; Liu, Yuan; Boppart, Stephen A.
2013-01-01
We predict and realize the targeted wavelength conversion from the 1550-nm band of a fs Er:fiber laser to an isolated band inside 370-850 nm, corresponding to a blue-shift of 700-1180 nm. The conversion utilizes resonant dispersive wave generation in widely available optical fibers with good efficiency (~7%). The converted band has a large pulse energy (~1 nJ), high spectral brightness (~1 mW/nm), and broad Gaussian-like spectrum compressible to clean transform-limited ~17 fs pulses. The corresponding coherent fiber sources open up portable applications of optical parametric oscillators and dual-output synchronized ultrafast lasers. PMID:24104233
Temperature-dependent gelation process in colloidal dispersions by diffusing wave spectroscopy.
Liu, Jiaxue; Boyko, Volodymyr; Yi, Zhiyong; Men, Yongfeng
2013-11-19
Temperature-dependent microrheology of a concentrated charge-stabilized poly(methyl methacrylate) colloidal dispersion with different salt concentrations was investigated by diffusing wave spectroscopy in backscattering mode. The critical temperature where the system undergoes aggregation and gelation depends upon the particle volume fraction or salt concentration. The viscoelastic properties of the systems have been discussed using Maxwell and Kelvin-Voigt models. Temperature-dependent crossover (G' = G″) frequency has been used to calculate activation energies representing a critical energy of interaction of gel formation.
A dispersion relation in bidust acoustic wave in non uniform stratified plasma
Valdeblanquez, E.
2006-12-04
Low frequencies waves are studied in plasma with two kind of dusty grains. Also considered are stratified plasma with layers of different densities to that of the main plasma. In this analysis each dust species is treated with a simplified model of fluid equations, and electrons and ions are determined by a Boltzmann factor. Relative velocities between each species and the non uniform plasma is considered in order to study instabilities. In cases in which the speed or the density of current of the charged dust grains is zero, the dispersion equation is recovered.
Abla, G
2012-11-09
The Center for Simulation of Wave Interactions with Magnetohydrodynamics (SWIM) project is dedicated to conduct research on integrated multi-physics simulations. The Integrated Plasma Simulator (IPS) is a framework that was created by the SWIM team. It provides an integration infrastructure for loosely coupled component-based simulations by facilitating services for code execution coordination, computational resource management, data management, and inter-component communication. The IPS framework features improving resource utilization, implementing application-level fault tolerance, and support of the concurrent multi-tasking execution model. The General Atomics (GA) team worked closely with other team members on this contract, and conducted research in the areas of computational code monitoring, meta-data management, interactive visualization, and user interfaces. The original website to monitor SWIM activity was developed in the beginning of the project. Due to the amended requirements, the software was redesigned and a revision of the website was deployed into production in April of 2010. Throughout the duration of this project, the SWIM Monitoring Portal (http://swim.gat.com:8080/) has been a critical production tool for supporting the project's physics goals.
NASA Astrophysics Data System (ADS)
Solano-Carrillo, E.; Franco, R.; Silva-Valencia, J.
2010-11-01
We study the effect of crystal-field anisotropy on the dispersion relations of mixed-spin (S,s) alternating chains by using the interacting spin-wave theory and the density-matrix renormalization group algorithm. For the easy-plane anisotropy case we find that the spin-wave results fail to describe the ground-state properties of the systems under consideration, whereas for the easy-axis anisotropy regime the method demonstrates a surprising efficiency showing, for example for the system (S,s)=(3/2,1/2), a discrepancy from the density-matrix renormalization group of about 0.0006% for the ground-state energy and of 2% for the sublattice magnetizations.
Impulsive dispersion of a granular layer by a weak blast wave
NASA Astrophysics Data System (ADS)
Rodriguez, V.; Saurel, R.; Jourdan, G.; Houas, L.
2017-03-01
The dispersion of particles by blast or shock waves induces the formation of coherent structures taking the shape of particle jets. In the present study, a blast wave, issued from an open shock tube, is generated at the center of a granular ring initially confined in a Hele-Shaw cell. With the present experimental setup, solid particle jet formation is clearly observed in a quasi-two-dimensional configuration. In all instances, the jets are initially generated inside the particle ring and thereafter expelled outward. Furthermore, thanks to the two-dimensional experimental configuration, a general study of the main parameters involved in these types of flows can be performed. Among them, the particle diameter, the density of the particles, the initial size of the ring, the shape of the overpressure generated and the surface friction of the Hele-Shaw cell are investigated. Empirical relationships are deduced from experimental results.
Nonlinear effects related to circularly polarized dispersive Alfvén waves
NASA Astrophysics Data System (ADS)
Sharma, Swati; Gaur, Nidhi; Sharma, R. P.
2016-09-01
In situ measurements of solar wind have strongly implicated its turbulent behavior. The observed power spectra report a breakpoint around length scales of the order of ion scales. As one of the responsible mechanisms for the observed steepening in power spectrum, our approach includes a right circularly polarized dispersive Alfvén wave (DAW) with finite frequency correction which, when subjected to transverse collapse/filamentation instability, may possibly result in steepening of spectrum and progressive transfer of energy from larger scales to smaller scales. We have studied the nonlinear effects associated with coupling of DAW with kinetic Alfvén wave in solar wind at 1 A.U. The formation of localized structures provides a clue about the emergence of turbulence. Numerical simulation is performed to study localization and power spectral density of the field and density fluctuations. The results show steeper spectrum indicating transfer of large scale turbulent energy down to small scales.
NASA Technical Reports Server (NTRS)
Kaushik, Dinesh K.; Baysal, Oktay
1997-01-01
Accurate computation of acoustic wave propagation may be more efficiently performed when their dispersion relations are considered. Consequently, computational algorithms which attempt to preserve these relations have been gaining popularity in recent years. In the present paper, the extensions to one such scheme are discussed. By solving the linearized, 2-D Euler and Navier-Stokes equations with such a method for the acoustic wave propagation, several issues were investigated. Among them were higher-order accuracy, choice of boundary conditions and differencing stencils, effects of viscosity, low-storage time integration, generalized curvilinear coordinates, periodic series, their reflections and interference patterns from a flat wall and scattering from a circular cylinder. The results were found to be promising en route to the aeroacoustic simulations of realistic engineering problems.
NASA Astrophysics Data System (ADS)
Wen, Jin; Ma, Chengju; Fan, Wei; Fu, Haiwei
2015-08-01
We numerically investigate the dispersive wave emission and soliton trapping in the process of femtosecond soliton propagation in silicon-on-insulator (SOI) waveguide. The cross-correlation frequency resolved optical gating (X-FROG) technique is employed to analyze the spectral-temporal dynamics of the soliton at different propagation distances. The numerical results show that dispersive wave emission can be blue-shifted (around 1300 nm) or red-shifted (around 1900 nm), which is determined by the dispersion slope for the pump wavelength (1550 nm). In addition, it can be found that red-shifted dispersive wave can supply contribution to the flatness of the supercontinuum generation. Through increasing the peak power of the soliton to 100 W, the soliton trapping can be observed by the edge of dispersive wave, which can be visualized in the form of multi-peak oscillation structure in the spectrogram when not considering the two-photon absorption (TPA). This work opens up the possibility for the realization of dispersive wave emission device in highly integrated circuit.
King, Thomas L; Clyburne, Jason A C; Lee, Kenneth; Robinson, Brian J
2013-06-15
Test facilities such as lab basins and wave tanks are essential when evaluating the use of chemical dispersants to treat oil spills at sea. However, these test facilities have boundaries (walls) that provide an ideal environment for surface (interfacial) film formation on seawater. Surface films may form from surfactants naturally present in crude oil as well as dispersant drift/overspray when applied to an oil spill. The objective of this study was to examine the impact of surface film formation on oil spreading rates in a small scale lab basin and on dispersant effectiveness conducted in a large scale wave tank. The process of crude oil spreading on the surface of the basin seawater was influenced in the presence of a surface film as shown using a 1st order kinetic model. In addition, interfacial film formation can greatly influence chemically dispersed crude oil in a large scale dynamic wave tank.
1988-09-01
decomposed into a series of associated aperiodic solitary waves, as can be achieved for solutions of the KdV equation [11], is still under investigation. 3...The organization of the paper is as follows: In Section 2, we discuss aperiodic and periodic solitary wave solutions of a model equation with...Periodic Solitary Wave Solutions of the Nonlinear Klein Gordon Equation without Dispersion We shall take, as our model equation , the nonlinear Klein
MHD energy fluxes for late type dwarfs
NASA Technical Reports Server (NTRS)
Rosner, R.; Musielak, Z. E.
1987-01-01
The efficiency of MHD wave generation by turbulent motions in stratified stellar atmospheres with embedded uniform magnetic fields is calculated. In contradiction with previous results, it is shown that there is no significant increase in the efficiency of wave generation because of the presence of magnetic fields, at least within the theory's limits of applicability. It is shown that MHD energy fluxes for late-type stars are less than those obtained for acoustic waves in a magnetic-field-free atmosphere, and do not vary enough for a given spectral type in order to explain observed UV and X-ray fluxes. Thus, the results show that MHD energy fluxes obtained if stellar surface magnetic fields are uniform cannot explain the observed stellar coronal emissions.
Construction of the wave operator for non-linear dispersive equations
NASA Astrophysics Data System (ADS)
Tsuruta, Kai Erik
In this thesis, we will study non-linear dispersive equations. The primary focus will be on the construction of the positive-time wave operator for such equations. The positive-time wave operator problem arises in the study of the asymptotics of a partial differential equation. It is a map from a space of initial data X into itself, and is loosely defined as follows: Suppose that for a solution ψlin to the dispersive equation with no non-linearity and initial data ψ +, there exists a unique solution ψ to the non-linear equation with initial data ψ0 such that ψ behaves as ψ lin as t → infinity. Then the wave operator is the map W+ that takes ψ + to ψ0. By its definition, W+ is injective. An important additional question is whether or not the map is also surjective. If so, then every non-linear solution emanating from X behaves, in some sense, linearly as it evolves (this is known as asymptotic completeness). Thus, there is some justification for treating these solutions as their much simpler linear counterparts. The main results presented in this thesis revolve around the construction of the wave operator(s) at critical non-linearities. We will study the "semi-relativistic" Schrodinger equation as well as the Klein-Gordon-Schrodinger system on R2 . In both cases, we will impose fairly general quadratic non-linearities for which conservation laws cannot be relied upon. These non-linearities fall below the scaling required to employ such tools as the Strichartz estimates. We instead adapt the "first iteration method" of Jang, Li, and Zhang to our setting which depends crucially on the critical decay of the non-linear interaction of the linear evolution. To see the critical decay in our problem, careful analysis is needed to treat the regime where one has spatial and/or time resonance.
Mechanical balance laws for fully nonlinear and weakly dispersive water waves
NASA Astrophysics Data System (ADS)
Kalisch, Henrik; Khorsand, Zahra; Mitsotakis, Dimitrios
2016-10-01
The Serre-Green-Naghdi system is a coupled, fully nonlinear system of dispersive evolution equations which approximates the full water wave problem. The system is known to describe accurately the wave motion at the surface of an incompressible inviscid fluid in the case when the fluid flow is irrotational and two-dimensional. The system is an extension of the well known shallow-water system to the situation where the waves are long, but not so long that dispersive effects can be neglected. In the current work, the focus is on deriving mass, momentum and energy densities and fluxes associated with the Serre-Green-Naghdi system. These quantities arise from imposing balance equations of the same asymptotic order as the evolution equations. In the case of an even bed, the conservation equations are satisfied exactly by the solutions of the Serre-Green-Naghdi system. The case of variable bathymetry is more complicated, with mass and momentum conservation satisfied exactly, and energy conservation satisfied only in a global sense. In all cases, the quantities found here reduce correctly to the corresponding counterparts in both the Boussinesq and the shallow-water scaling. One consequence of the present analysis is that the energy loss appearing in the shallow-water theory of undular bores is fully compensated by the emergence of oscillations behind the bore front. The situation is analyzed numerically by approximating solutions of the Serre-Green-Naghdi equations using a finite-element discretization coupled with an adaptive Runge-Kutta time integration scheme, and it is found that the energy is indeed conserved nearly to machine precision. As a second application, the shoaling of solitary waves on a plane beach is analyzed. It appears that the Serre-Green-Naghdi equations are capable of predicting both the shape of the free surface and the evolution of kinetic and potential energy with good accuracy in the early stages of shoaling.
NASA Technical Reports Server (NTRS)
Vanel, Florence O.; Baysal, Oktay
1995-01-01
Important characteristics of the aeroacoustic wave propagation are mostly encoded in their dispersion relations. Hence, a computational aeroacoustic (CAA) algorithm, which reasonably preserves these relations, was investigated. It was derived using an optimization procedure to ensure, that the numerical derivatives preserved the wave number and angular frequency of the differential terms in the linearized, 2-D Euler equations. Then, simulations were performed to validate the scheme and a compatible set of discretized boundary conditions. The computational results were found to agree favorably with the exact solutions. The boundary conditions were transparent to the outgoing waves, except when the disturbance source was close to a boundary. The time-domain data generated by such CAA solutions were often intractable until their spectra was analyzed. Therefore, the relative merits of three different methods were included in the study. For simple, periodic waves, the periodogram method produced better estimates of the steep-sloped spectra than the Blackman-Tukey method. Also, for this problem, the Hanning window was more effective when used with the weighted-overlapped-segment-averaging and Blackman-Tukey methods gave better results than the periodogram method. Finally, it was demonstrated that the representation of time domain-data was significantly dependent on the particular spectral analysis method employed.
NASA Astrophysics Data System (ADS)
Zimmerling, Jörn; Wei, Lei; Urbach, Paul; Remis, Rob
2016-06-01
In this paper we present a Krylov subspace model-order reduction technique for time- and frequency-domain electromagnetic wave fields in linear dispersive media. Starting point is a self-consistent first-order form of Maxwell's equations and the constitutive relation. This form is discretized on a standard staggered Yee grid, while the extension to infinity is modeled via a recently developed global complex scaling method. By applying this scaling method, the time- or frequency-domain electromagnetic wave field can be computed via a so-called stability-corrected wave function. Since this function cannot be computed directly due to the large order of the discretized Maxwell system matrix, Krylov subspace reduced-order models are constructed that approximate this wave function. We show that the system matrix exhibits a particular physics-based symmetry relation that allows us to efficiently construct the time- and frequency-domain reduced-order models via a Lanczos-type reduction algorithm. The frequency-domain models allow for frequency sweeps meaning that a single model provides field approximations for all frequencies of interest and dominant field modes can easily be determined as well. Numerical experiments for two- and three-dimensional configurations illustrate the performance of the proposed reduction method.
Dispersion of Lamb waves under a periodic metal grating in aluminum nitride plates.
Naumenko, Natalya F
2014-09-01
Dispersion of Lamb waves propagating in AlN plates with a periodic Al grating on the top surface and an Al electrode on the bottom surface is investigated using the numerical technique SDA-FEM-SDA, which combines finite element modeling (FEM) analysis of the electrode region with spectral-domain analysis (SDA) of the adjacent multi-layered half-spaces. Characteristics of zero-order and higher-order Lamb waves are presented as functions of plate thickness and spectral frequency, which varies in the first Brillouin zone. The structures of typical Lamb waves are examined via visualization of the instantaneous displacement fields in the AlN plate confined between the grating and the bottom electrode. The mechanism of building hybrid modes, which arise from intermode coupling between the counter-propagating Lamb waves of different symmetry and order, is illustrated by two examples of modes propagating with wavelengths λ = 3p and λ = 4p, where p is the pitch of the grating.
Kundu, Santimoy; Gupta, Shishir
2017-01-01
This theoretical work reports the dispersion and absorption characteristics of horizontally polarized shear wave (SH-wave) in a corrugated medium with void pores sandwiched between two dissimilar half-spaces. The dispersion and absorption equations have been derived in a closed form using the method of separation of variables. It has been established that there are two different kinds of wavefronts propagating in the proposed media. One of the wavefronts depends on the modulus of rigidity of elastic matrix of the medium and satisfies the dispersion equation of SH-waves. The second wavefront depends on the changes in volume fraction of the pores. Numerical computation of the obtained relations has been performed and the results are depicted graphically. The influence of corrugation, sandiness on the phase velocity and the damped velocity of SH-wave has been studied extensively. PMID:28386416
NASA Astrophysics Data System (ADS)
Pandit, Deepak Kr.; Kundu, Santimoy; Gupta, Shishir
2017-02-01
This theoretical work reports the dispersion and absorption characteristics of horizontally polarized shear wave (SH-wave) in a corrugated medium with void pores sandwiched between two dissimilar half-spaces. The dispersion and absorption equations have been derived in a closed form using the method of separation of variables. It has been established that there are two different kinds of wavefronts propagating in the proposed media. One of the wavefronts depends on the modulus of rigidity of elastic matrix of the medium and satisfies the dispersion equation of SH-waves. The second wavefront depends on the changes in volume fraction of the pores. Numerical computation of the obtained relations has been performed and the results are depicted graphically. The influence of corrugation, sandiness on the phase velocity and the damped velocity of SH-wave has been studied extensively.
Zhang, Ya-Ni; Ren, Li-Yong; Gong, Yong-Kang; Li, Xiao-Hui; Wang, Lei-Ran; Sun, Chuan-Dong
2010-06-01
We have proposed a novel type of photonic crystal fiber (PCF) with low dispersion and high nonlinearity for four-wave mixing. This type of fiber is composed of a solid silica core and a cladding with a squeezed hexagonal lattice elliptical airhole along the fiber length. Its dispersion and nonlinearity coefficient are investigated simultaneously by using the full vectorial finite element method. Numerical results show that the proposed highly nonlinear low-dispersion fiber has a total dispersion as low as +/-2.5 ps nm(-1) km(-1) over an ultrabroad wavelength range from 1.43 to 1.8 microm, and the corresponding nonlinearity coefficient and birefringence are about 150 W(-1) km(-1) and 2.5x10(-3) at 1.55 microm, respectively. The proposed PCF with low ultraflattened dispersion, high nonlinearity, and high birefringence can have important application in four-wave mixing.
Supersonic MHD generator system
Rahman, M.A.
1983-11-29
An improved MHD electrical power generating system of the type having a MHD topping cycle and a steam generating bottoming cycle is disclosed. The system typically includes a combustion system, a conventional MHD generator and a first diffuser radiant boiler. The improvement comprises a first supersonic MHD generator and ramjet engine configuration operatively connected in series with each other and with the conventional MHD generator. The first supersonic MHD generator and ramjet engine configuration increase the power output and improve the operating efficiency of the electrical generating system. A diffuser system is also disclosed which is in fluid communication with the supersonic MHD generator and the ramjet engine for collecting bypass plasma gas to be used for heating a second radiant boiler adapted for powering a steam turbine generator.
Methods for the treatment of acoustic and absorptive/dispersive wave field measurements
NASA Astrophysics Data System (ADS)
Innanen, Kristopher Albert Holm
Many recent methods of seismic wave field processing and inversion concern themselves with the fine detail of the amplitude and phase characteristics of measured events. Processes of absorption and dispersion have a strong impact on both; the impact is particularly deleterious to the effective resolution of images created from the data. There is a need to understand the dissipation of seismic wave energy as it affects such methods. I identify: algorithms based on the inverse scattering series, algorithms based on multiresolution analysis, and algorithms based on the estimation of the order of the singularities of seismic data, as requiring this kind of study. As it turns out, these approaches may be cast such that they deal directly with issues of attenuation, to the point where they can be seen as tools for viscoacoustic forward modelling, Q estimation; viscoacoustic inversion, and/or Q compensation. In this thesis I demonstrate these ideas in turn. The forward scattering series is formulated such that a viscoacoustic wave field is represented as an expansion about an acoustic reference; analysis of the convergence properties and scattering diagrams are carried out, and it is shown that (i) the attenuated wave field may be generated by the nonlinear interplay of acoustic reference fields, and (ii) the cumulative effect of certain scattering types is responsible for macroscopic wave field properties: also, the basic form of the absorptive/dispersive inversion problem is predicted. Following this, the impact of Q on measurements of the local regularity of a seismic trace, via Lipschitz exponents, is discussed, with the aim of using these exponents as a means to estimate local Q values. The problem of inverse scattering based imaging and inversion is treated next: I present a simple, computable form for the simultaneous imaging and wavespeed inversion of 1D acoustic wave field data. This method is applied to 1D, normal incidence synthetic data: its sensitivity with
NASA Astrophysics Data System (ADS)
Rham, D. J.; Preistley, K.; Tatar, M.; Paul, A.
2006-12-01
We present group velocity dispersion results from a study of regional fundamental mode Rayleigh and Love waves propagating across Iran and the surrounding region. Data for these measurements comes from field deployments within Iran by the University of Cambridge (GBR) and the Universite Joseph-Fourier (FRA) in conjunction with International Institute of Earthquake Engineering and Seismology (Iran), in addition to data from IRIS and Geofone. 1D path- averaged dispersion measurements have been made for ~5500 source-receiver paths using multiple filter analysis. We combine these observations in a tomographic inversion to produce group velocity images between 10 and 60 s period. Because of the dense path coverage, these images have substantially higher lateral resolution for this region than is currently available from global and regional group velocity studies. We observe variations in short-period wave group velocity which is consistent with the surface geology. Low group velocities (2.00-2.55 km/s) at short periods (10-20 s), for both Rayleigh and Love waves are observed beneath thick sedimentary deposits; The south Caspian Basin, Black Sea, the eastern Mediterranean, the Persian Gulf, the Makran, the southern Turan shield, and the Indus and Gangetic basins. Somewhat higher group velocity (2.80-3.15 km/s for Rayleigh, and 3.00-3.40 km/s for Love) at these periods occur in sediment poor regions, such as; the Turkish-Iranian plateau, the Arabian shield, and Kazakhstan. At intermediate periods (30-40 s) group velocities over most of the region are low (2.65-3.20 km/s for Rayleigh, and 2.80-3.45 km/s for love) compared to Arabia (3.40-3.70 km/s Rayleigh, 3.50-4.0 km/s Love). At longer periods (50-60 s) Love wave group velocities remain low (3.25-3.70 km/s) over most of Iran, but there are even lower velocities (2.80-3.00 km/s) still associated with the thick sediments of the south Caspian basin, the surrounding shield areas have much higher group velocities (3
NASA Astrophysics Data System (ADS)
Su, Han
The northern Mississippi Embayment is characterized by relatively high seismicity at the New Madrid Seismic Zone. Although many studies have focused on specific earthquakes or on the structure at specific locations, the mechanism of the earthquake process has remained an enigma. As part of the Northern Embayment Lithosphere Experiment, we focus on high resolution surface-wave tomography of Love and Rayleigh, phase and group velocities for a study region bounded by 34-40 N latitude and 85-94 W longitude for periods from 2 to 50 seconds by cross-correlating ambient noise from BH channels of the Transportable Array of EarthScope. To test the usefulness of the dispersion, we perform a joint inversion of dispersion and teleseismic P-wave receiver functions for stations in the region. At a few locations, we are able to test the resulting models by comparing predicted to observed broadband recordings of local earthquakes. At these few locations, we find good agreement and also evidence that the Moho is a gradient rather than a sharp discontinuity.
Crustal Structure of Iraq from Receiver Functions and Surface Wave Dispersion
Gok, R; Mahdi, H; Al-Shukri, H; Rodgers, A J
2006-08-31
We report the crustal structure of Iraq, located in the northeastern Arabian plate, estimated by joint inversion of P-wave receiver functions and surface wave group velocity dispersion. Receiver functions were computed from teleseismic recordings at two temporary broadband seismic stations in Mosul (MSL) and Baghdad (BHD), separated by approximately 360 km. Group velocity dispersion curves at the sites were derived from continental-scale tomography of Pasyanos (2006). The inversion results show that the crustal thicknesses are 39 km at MSL and 43 km at BHD. Both sites reveal low velocity surface layers consistent with sedimentary thickness of about 3 km at station MSL and 7 km at BHD, agreeing well with the existing models. Ignoring the sediments, the crustal velocities and thicknesses are remarkably similar between the two stations, suggesting that the crustal structure of the proto-Arabian Platform in northern Iraq was uniform before subsidence and deposition of the sediments in the Cenozoic. Deeper low velocity sediments at BHD are expected to result in higher ground motions for earthquakes.
NASA Astrophysics Data System (ADS)
Keefe, Laurence
2016-11-01
Parabolized acoustic propagation in transversely inhomogeneous media is described by the operator update equation U (x , y , z + Δz) =eik0 (- 1 +√{ 1 + Z }) U (x , y , z) for evolution of the envelope of a wavetrain solution to the original Helmholtz equation. Here the operator, Z =∇T2 + (n2 - 1) , involves the transverse Laplacian and the refractive index distribution. Standard expansion techniques (on the assumption Z << 1)) produce pdes that approximate, to greater or lesser extent, the full dispersion relation of the original Helmholtz equation, except that none of them describe evanescent/damped waves without special modifications to the expansion coefficients. Alternatively, a discretization of both the envelope and the operator converts the operator update equation into a matrix multiply, and existing theorems on matrix functions demonstrate that the complete (discrete) Helmholtz dispersion relation, including evanescent/damped waves, is preserved by this discretization. Propagation-constant/damping-rates contour comparisons for the operator equation and various approximations demonstrate this point, and how poorly the lowest-order, textbook, parabolized equation describes propagation in lined ducts.
Zhang, Y.; Xu, Y.; Xia, J.
2011-01-01
We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable-'open pore', impermeable-'closed pore' and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant-Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im(k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays -f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the -f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.
Germán Rubino, J; Monachesi, Leonardo B; Müller, Tobias M; Guarracino, Luis; Holliger, Klaus
2013-12-01
Oscillatory fluid movements in heterogeneous porous rocks induced by seismic waves cause dissipation of wave field energy. The resulting seismic signature depends not only on the rock compressibility distribution, but also on a statistically averaged permeability. This so-called equivalent seismic permeability does not, however, coincide with the respective equivalent flow permeability. While this issue has been analyzed for one-dimensional (1D) media, the corresponding two-dimensional (2D) and three-dimensional (3D) cases remain unexplored. In this work, this topic is analyzed for 2D random medium realizations having strong permeability fluctuations. With this objective, oscillatory compressibility simulations based on the quasi-static poroelasticity equations are performed. Numerical analysis shows that strong permeability fluctuations diminish the magnitude of attenuation and velocity dispersion due to fluid flow, while the frequency range where these effects are significant gets broader. By comparing the acoustic responses obtained using different permeability averages, it is also shown that at very low frequencies the equivalent seismic permeability is similar to the equivalent flow permeability, while for very high frequencies this parameter approaches the arithmetic average of the permeability field. These seemingly generic findings have potentially important implications with regard to the estimation of equivalent flow permeability from seismic data.
NASA Astrophysics Data System (ADS)
Soomro, R. A.; Weidle, C.; Lebedev, S.; Cristiano, L.; Meier, T. M.
2013-12-01
With the rapid growth in the no. of seismic stations globally, manual data processing for routine analysis as well as determination of seismic observables becomes more and more impractical. Therefore, automated schemes are inevitable to handle these large data volumes. For surface wave tomography, phase velocity dispersion curves of fundamental mode surface waves yield information on the isotropic as well as anisotropic structure of the crust and upper mantle. We measure inter-station phase velocity dispersion curves through cross correlation of vertical component (Rayleigh wave) and transverse component (Love wave) seismograms. We have developed a scheme to automate this well established inter-station method, which automatically selects the smooth parts of observed phase velocity dispersion curves, and thus obtain path average phase velocity dispersion curve of each inter-station path. After testing various parameters for automation of the procedure we finally confined the method to three parameters only, namely (1) difference of the measured phase velocity curve from a background model, (2) a smoothness constraint and (3) a length criterion. We performed rigorous tests to optimize the parameters and obtained optimal values of these three parameters. We successfully applied the method to more than one hundred thousand inter station paths in central and northern Europe which involved more than one million cross correlations on 20 years of the data of the permanent networks. The method was also tested on temporary deployments e.g. TOR, PASSEQ, SVEKALPKO etc, across Europe. After inversion of the fundamental mode phase velocity dispersion curves for both Rayleigh and Love waves, we obtain high resolution anisotropic phase velocity maps for periods between 10 and 250 seconds with a lateral resolution between about 50 to 100 kilometers. Well known features of upper mantle structure in central Europe are well resolved in our phase velocity maps. Distinct differences
P-wave dispersion in patients with Guillain-Barré syndrome.
Demirci, Seden; Arslan, Akif; Yürekli, Vedat Ali; Kutluhan, Süleyman; Koyuncuoğlu, Hasan Rifat; Demirci, Serpil
2017-03-01
Cardiac autonomic dysfunction assessed by the presence of arrhythmia, by the methods, such as heart rate variability or blood pressure variability, and by the electrocardiographic abnormalities is common in Guillain-Barré syndrome (GBS). The goal of present study was to analyze the P-wave dispersion (PWD), which is the non-invasive marker of atrial arrhythmia, in GBS patients and to compare those with healthy individuals. Thirty-five patients with GBS (mean age 53.6 ± 15.5 years) and 35 healthy controls (mean age 49.2 ± 14.1 years) were included to this study. Demographic and clinical information of the patients with GBS were assessed retrospectively. A 12-lead surface electrocardiogram was acquired from all participants. Minimum and maximum P-wave duration and PWD were measured in the patients with GBS and healthy controls. Maximum P-wave duration and PWD were significantly longer, and minimum P-wave duration was significantly lower in the patients with GBS rather than the control group (p = 0.037, p < 0.001, p = 0.007, respectively). GBS disability scores were positively correlated with the maximum P-wave duration (p = 0.015, r = 0.406) and PWD (p = 0.001, r = 0.525). We found that PWD was significantly prolonged in GBS patients compared with the controls. The increased PWD which is cheap, quick, non-invasive and feasible electrocardiographic marker may be related to increased risk for atrial fibrillation in patients with GBS.
Measurement of Lamb waves dispersion curves under narrowband monomode excitation using TV holography
NASA Astrophysics Data System (ADS)
Deán, J. Luis; Fernández, José L.; Doval, Ángel F.; Trillo, Cristina
2006-08-01
Ultrasonic Lamb waves provide a useful means for the nondestructive determination of the material elastic constants of shell structures such as plates, pipes, cans and many others. A new optical technique is described for the measurement of the dispersion curves of Lamb wave modes. The experimental system employs the wedge method for the excitation of Lamb modes in aluminum plates of thickness in the range of a few millimetres. Long tone-bursts are used in order to ensure the generation of narrowband ultrasonic waves. Furthermore, an appropriate selection of the wedge angle allows one to generate only the desired individual Lamb mode. The detection of the surface out-of-plane displacements is performed by our self-developed pulsed TV holography system, which evaluates the optical phase by the Spatial Fourier Transform Method. Inasmuch as a whole-field measurement is realized, the wavelength of the excited mode can be precisely measured from the TV holography displacement maps. On the other hand, the wave frequency is measured by a pointwise method, namely a Michelson speckle interferometer. The phase velocity is directly obtained as the product of these two values. Measurements are done for several frequencies and several Lamb modes, thus yielding a collection of experimental points. By fitting these results to the theoretical Rayleigh-Lamb frequency spectrum, values of the shear wave velocity and the Poisson's ratio of the plate material are obtained. For a better accuracy in the measurements, the longitudinal phase velocity was directly determined by the pulse-echo method. The additional knowledge of the mass density allows one to calculate the Young's modulus.
NASA Astrophysics Data System (ADS)
Shen, Weisen; Ritzwoller, Michael H.; Kang, Dou; Kim, YoungHee; Lin, Fan-Chi; Ning, Jieyuan; Wang, Weitao; Zheng, Yong; Zhou, Longquan
2016-08-01
Using data from more than 2000 seismic stations from multiple networks arrayed throughout China (CEArray, China Array, NECESS, PASSCAL, GSN) and surrounding regions (Korean Seismic Network, F-Net, KNET), we perform ambient noise Rayleigh wave tomography across the entire region and earthquake tomography across parts of South China and Northeast China. We produce isotropic Rayleigh wave group and phase speed maps with uncertainty estimates from 8 to 50 s period across the entire region of study, and extend them to 70 s period where earthquake tomography is performed. Maps of azimuthal anisotropy are estimated simultaneously to minimize anisotropic bias in the isotropic maps, but are not discussed here. The 3D model is produced using a Bayesian Monte Carlo formalism covering all of China, extending eastwards through the Korean Peninsula, into the marginal seas, to Japan. We define the final model as the mean and standard deviation of the posterior distribution at each location on a 0.5° × 0.5° grid from the surface to 150 km depth. Surface wave dispersion data do not strongly constrain internal interfaces, but shear wave speeds between the discontinuities in the crystalline crust and uppermost mantle are well determined. We design the resulting model as a reference model, which is intended to be useful to other researchers as a starting model, to predict seismic wave fields and observables and to predict other types of data (e.g. topography, gravity). The model and the data on which it is based are available for download. In addition, the model displays a great variety and considerable richness of geological and tectonic features in the crust and in the uppermost mantle deserving of further focus and continued interpretation.
Wave dispersion in the hybrid-Vlasov model: Verification of Vlasiator
Kempf, Yann; Pokhotelov, Dimitry; Koskinen, Hannu E. J.; Alfthan, Sebastian von; Palmroth, Minna; Vaivads, Andris
2013-11-15
Vlasiator is a new hybrid-Vlasov plasma simulation code aimed at simulating the entire magnetosphere of the Earth. The code treats ions (protons) kinetically through Vlasov's equation in the six-dimensional phase space while electrons are a massless charge-neutralizing fluid [M. Palmroth et al., J. Atmos. Sol.-Terr. Phys. 99, 41 (2013); A. Sandroos et al., Parallel Comput. 39, 306 (2013)]. For first global simulations of the magnetosphere, it is critical to verify and validate the model by established methods. Here, as part of the verification of Vlasiator, we characterize the low-β plasma wave modes described by this model and compare with the solution computed by the Waves in Homogeneous, Anisotropic Multicomponent Plasmas (WHAMP) code [K. Rönnmark, Kiruna Geophysical Institute Reports No. 179, 1982], using dispersion curves and surfaces produced with both programs. The match between the two fundamentally different approaches is excellent in the low-frequency, long wavelength range which is of interest in global magnetospheric simulations. The left-hand and right-hand polarized wave modes as well as the Bernstein modes in the Vlasiator simulations agree well with the WHAMP solutions. Vlasiator allows a direct investigation of the importance of the Hall term by including it in or excluding it from Ohm's law in simulations. This is illustrated showing examples of waves obtained using the ideal Ohm's law and Ohm's law including the Hall term. Our analysis emphasizes the role of the Hall term in Ohm's law in obtaining wave modes departing from ideal magnetohydrodynamics in the hybrid-Vlasov model.
Dispersion relations and polarizations of low-frequency waves in two-fluid plasmas
Zhao, Jinsong
2015-04-15
Analytical expressions for the dispersion relations and polarizations of low-frequency waves in magnetized plasmas based on two-fluid model are obtained. The properties of waves propagating at different angles (to the ambient magnetic field B{sub 0}) and β (the ratio of the plasma to magnetic pressures) values are investigated. It is shown that two linearly polarized waves—namely, the fast and Alfvén modes in the low-β (β≪1) plasmas, the fast and slow modes in the β∼1 plasmas, and the Alfvén and slow modes in the high-β (β≫1) plasmas—become circularly polarized at the near-parallel (to B{sub 0}) propagation. The negative magnetic-helicity of the Alfvén mode occurs only at small or moderate angles in the low-β plasmas, and the ion cross-helicity of the slow mode is nearly the same as that of the Alfvén mode in the high-β plasmas. It is also shown that the electric polarization δE{sub z}/δE{sub y} decreases with the temperature ratio T{sub e}/T{sub i} for the long-wavelength waves, and the transition between left- and right-hand polarizations of the Alfvén mode in T{sub e}/T{sub i}≠0 plasmas can disappear when T{sub e}/T{sub i}=0. The approximate dispersion relations in the near-perpendicular propagation, low-β, and high-β limits can quite accurately describe the three modes.
Observations of Alfvén and Slow Waves in the Solar Wind near 1 AU
NASA Astrophysics Data System (ADS)
SHI, M. J.; XIAO, C. J.; LI, Q. S.; WANG, H. G.; WANG, X. G.; LI, H.
2015-12-01
Magnetohydrodynamic (MHD) waves play a significant role in the processes of the solar wind acceleration and the coronal heating. Based on the in situ measurements of the WIND spacecraft, some MHD waves in the quiet solar wind are identified with two criteria: (1) the correlation coefficients between velocity and magnetic field perturbations (δ {\\boldsymbol{v}} and δ {\\boldsymbol{B}}) and between thermal pressure and magnetic pressure perturbations (δpt and δpb), and (2) the dispersion relations of MHD waves. A preliminary statistics of those MHD modes is also achieved by selecting and analyzing the WIND data of 42,279 samples (45050.4 hr) in the 23rd solar cycle. It is found that the time fraction of Alfvén waves is 8% in this period, while the existence time of slow waves is 3.4%, and the fast wave is rare. The statistical result also shows that the Alfvén waves have a higher time fraction in fast solar wind, while the occurrence of slow waves is higher in moderate-speed solar wind. This work will provide more clues to understanding MHD activities in the solar wind, as well as the studies of solar wind acceleration and heating.
NASA Astrophysics Data System (ADS)
Tang, Yugang; Liu, Ying; Zhao, Dong
2017-03-01
Based on the nonlocal strain gradient theory and Timoshenko beam model, the properties of wave propagation in a viscoelastic single-walled carbon nanotube (SWCNT) are investigated. The characteristic equations for flexural and shear waves in visco-SWCNTs are established. The influence of the tube size on the wave dispersion is clarified. For a low damping coefficient, threshold diameter for shear wave (SW) is observed, below which the phase velocity of SW is equal to zero, whilst flexural wave (FW) always exists. For a high damping coefficient, SW is absolutely constrained, and blocking diameter for FW is observed, above which the wave propagation is blocked. The effects of the wave number, nonlocal and strain gradient length scale parameters on the threshold and blocking diameters are discussed in detail.
Dispersion and waves in bounded plasmas with subwavelength inhomogeneities: Genesis of MEFIB
Bhattacharjee, Sudeep
2014-02-11
Bounded plasma exhibit many interesting behavior that are not found in plasmas of 'infinite' extent such as space and astrophysical plasmas. Our studies have revealed that the dispersion properties of waves in a bounded magnetoplasma deviates considerably from the predictions of the Clemmow-Mullaly-Allis (CMA) model, giving rise to new regimes of wave propagation and absorption. The anisotropy of the medium dictated by the length scales of plasma nonuniformity and magnetostatic field inhomogeneity lead to rotation of the polarization axis an effect similar to the Cotton-Mouton effect in a magneto-optic medium but with distinct differences due to wave induced resonances. This article highlights some of these interesting effects observed experimentally and corroborated with Monte Carlo simulations. One of the principal outcomes of this research is the genesis of a novel multielement focused ion beam (MEFIB) system that utilizes compact bounded plasmas in a minimum – B field to provide intense focused ion beams of a variety of elements for new research in nanoscience and technology.
Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval
NASA Astrophysics Data System (ADS)
Wirgin, Armand
2016-07-01
The fact that seismologists often make measurements, using natural seismic solicitations, of properties of the Earth on rather large scales (laterally and in terms of depth) has led to interrogations as to whether attenuation of body waves is dispersive and even significant. The present study, whose aim is to clarify these complicated issues, via a controlled thought measurement, concerns the retrieval of a single, real body wave velocity of a simple geophysical configuration (involving two homogeneous, isotropic, non-dissipative media, one occupying the layer, the other the substratum), from its simulated response to pulsed plane wave probe radiation. This inverse problem is solved, at all frequencies within the bandwidth of the pulse. Due to discordance between the models associated with the assumed and trial responses, the imaginary part of the retrieved velocity turns out to be non-nil even when both the layer and substratum are non-lossy, and, in fact, to be all the greater, the larger is the discordance. The reason for this cannot be due to intrinsic attenuation, scattering, or geometrical spreading since these phenomena are absent in the chosen thought experiment, but rather to uncertainty in the measurement model.
NASA Astrophysics Data System (ADS)
Hogg, C. A. R.; Pietrasz, V. B.; Ouellette, N. T.; Koseff, J. R.
2015-12-01
Desalination of seawater offers a source of potable water in arid regions and during drought. However, hypersaline discharge from desalination facilities presents environmental risks, particularly to benthic organisms. The risks posed by salt levels and chemical additives, which can be toxic to local ecosystems, are typically mitigated by ensuring high levels of dilution close to the source. We report on laboratory flume experiments examining how internal waves at the pycnocline of a layered ambient density stratification influence the transport of hypersaline effluent moving as a gravity current down the slope. We found that some of the hypersaline fluid from the gravity current was diverted away from the slope into an intrusion along the pycnocline. A parametric study investigated how varying the energy of the internal wave altered the amount of dense fluid that was diverted into the pycnocline intrusion. The results are compared to an analytical framework that compares the incident energy in the internal wave to potential energy used in diluting the gravity current. These results are significant for desalination effluents because fluid diverted into the intrusion avoids the ecologically sensitive benthic layer and disperses more quickly than if it had continued to propagate along the bed.
Low-Dispersion Scheme for Nonlinear Acoustic Waves in Nonuniform Flow
NASA Technical Reports Server (NTRS)
Baysal, Oktay; Kaushik, Dinesh K.; Idres, Moumen
1997-01-01
The linear dispersion-relation-preserving scheme and its boundary conditions have been extended to the nonlinear Euler equations. This allowed computing, a nonuniform flowfield and a nonlinear acoustic wave propagation in such a medium, by the same scheme. By casting all the equations, boundary conditions, and the solution scheme in generalized curvilinear coordinates, the solutions were made possible for non-Cartesian domains and, for the better deployment of the grid points, nonuniform grid step sizes could be used. It has been tested for a number of simple initial-value and periodic-source problems. A simple demonstration of the difference between a linear and nonlinear propagation was conducted. The wall boundary condition, derived from the momentum equations and implemented through a pressure at a ghost point, and the radiation boundary condition, derived from the asymptotic solution to the Euler equations, have proven to be effective for the nonlinear equations and nonuniform flows. The nonreflective characteristic boundary conditions also have shown success but limited to the nonlinear waves in no mean flow, and failed for nonlinear waves in nonuniform flow.
NASA Astrophysics Data System (ADS)
Umavathi, J. C.; Kumar, J. P.; Gorla, R. S. R.; Gireesha, B. J.
2016-08-01
The longitudinal dispersion of a solute between two parallel plates filled with two immiscible electrically conducting fluids is analyzed using Taylor's model. The fluids in both the regions are incompressible and the transport properties are assumed to be constant. The channel walls are assumed to be electrically insulating. Separate solutions are matched at the interface using suitable matching conditions. The flow is accompanied by an irreversible first-order chemical reaction. The effects of the viscosity ratio, pressure gradient and Hartman number on the effective Taylor dispersion coefficient and volumetric flow rate for an open and short circuit are drawn in the absence and in the presence of chemical reactions. As the Hartman number increases the effective Taylor diffusion coefficient decreases for both open and short circuits. When the magnetic field remains constant, the numerical results show that for homogeneous and heterogeneous reactions, the effective Taylor diffusion coefficient decreases with an increase in the reaction rate constant for both open and short circuits.
NASA Astrophysics Data System (ADS)
Dosso, S. E.; Molnar, S.; Cassidy, J.
2010-12-01
Bayesian inversion of microtremor array dispersion data is applied, with evaluation of data errors and model parameterization, to produce the most-probable shear-wave velocity (VS) profile together with quantitative uncertainty estimates. Generally, the most important property characterizing earthquake site response is the subsurface VS structure. The microtremor array method determines phase velocity dispersion of Rayleigh surface waves from multi-instrument recordings of urban noise. Inversion of dispersion curves for VS structure is a non-unique and nonlinear problem such that meaningful evaluation of confidence intervals is required. Quantitative uncertainty estimation requires not only a nonlinear inversion approach that samples models proportional to their probability, but also rigorous estimation of the data error statistics and an appropriate model parameterization. A Bayesian formulation represents the solution of the inverse problem in terms of the posterior probability density (PPD) of the geophysical model parameters. Markov-chain Monte Carlo methods are used with an efficient implementation of Metropolis-Hastings sampling to provide an unbiased sample from the PPD to compute parameter uncertainties and inter-relationships. Nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a Gaussian error distribution. The most appropriate model parameterization is determined using the Bayesian information criterion (BIC), which provides the simplest model consistent with the resolving power of the data. Parameter uncertainties are found to be under-estimated when data error correlations are neglected and when compressional-wave velocity and/or density (nuisance) parameters are fixed in the inversion. Bayesian inversion of microtremor array data is applied at two sites in British Columbia, the area of highest seismic risk in
Rayleigh wave group velocity dispersion across Northern Africa, Southern Europe and the Middle East
McNamara, D.E.; Walter, W.R.
1997-07-15
THis report presents preliminary results from a large scale study of surface wave group velocity dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave velocity structure within this region by improving the resolution of global surface wave tomographic studies. We hope to accomplish this goal by incorporating regional data at relatively short periods (less than 40 sec), into the regionalization of lateral velocity variation. Due to the sparse distributions of stations and earthquakes throughout the region (Figure 1) we have relied on data recorded at both teleseismic and regions; distances. Also, to date we have concentrated on Rayleigh wave group velocity measurements since valuable measurements can be made without knowledge of the source. In order to obtain Rayleigh wave group velocity throughout the region, vertical component teleseismic and regional seismograms were gathered from broadband, 3-component, digital MEDNET, GEOSCOPE and IRIS stations plus the portable PASSCAL deployment in Saudi Arabia. Figure 1 shows the distribution of earthquakes (black circles) and broadband digital seismic stations (white triangles) throughout southern Europe, the middle east and northern Africa used in this study. The most seismicly active regions of northern Africa are the Atlas mountains of Morocco and Algeria as well as the Red Sea region to the east. Significant seismicity also occurs in the Mediterranean, southern Europe and throughout the high mountains and plateaus of the middle-east. To date, over 1300 seismograms have been analyzed to determine the individual group velocities of 10-150 second Rayleigh waves. Travel times, for each period, are then inverted in a back projection tomographic method in order to determine the lateral group velocity variation throughout the region. These results are preliminary, however, Rayleigh wave group velocity maps for a range of
NASA Astrophysics Data System (ADS)
Tataru, Dragos; Grecu, Bogdan; Zaharia, Bogdan
2014-05-01
Variations in crustal thickness in Romania where determined by joint inversion of P wave receiver functions (RFs) and Rayleigh wave group velocity dispersion. We present new models of shear wave velocity structure of the crust beneath Romanian broad band stations. The data set consist in more than 500 teleseismic earthquake with epicentral distance between 30° and 95°, magnitude greater than 6 and a signal-to-noise ratio greater than 3 for the P-wave pulse. Most epicenters are situated along the northern Pacific Rim and arrive with backazimuths (BAZs) between 0° and 135° at the Romanian seismic network. We combine receiver functions with fundamental-mode of the Rayleigh wave group velocities to further constrain the shear-wave velocity structure.To extract the group velocities we applied the Multiple Filter Technique analysis to the vertical components of the earthquakes recordings. This technique allowed us to identify the Rayleigh wave fundamental mode and to compute the dispersion curves of the group velocities at periods between 10 and 150 s allowing us to resolve shear wave velocities to a depth of 100 km. The time-domain iterative deconvolution procedure of Ligorrıa and Ammon (1999) was employed to deconvolve the vertical component of the teleseismic P waveforms from the corresponding horizontal components and obtain radial and transverse receiver functions at each broadband station. The data are inverted using a joint, linearized inversion scheme (Hermann, 2002) which accounts for the relative influence of each set of observations, and allows a trade-off between fitting the observations, constructing a smooth model, and matching a priori constraints. The results show a thin crust for stations located inside the Pannonian basin (28-30 km) and a thicker crust for those in the East European Platform (36-40 km). The stations within the Southern and Central Carpathian Orogen are characterized by crustal depths of ~35 km. For stations located in the Northern
NASA Astrophysics Data System (ADS)
Brum, J.; Bernal, M.; Gennisson, J. L.; Tanter, M.
2014-02-01
Non-invasive evaluation of the Achilles tendon elastic properties may enhance diagnosis of tendon injury and the assessment of recovery treatments. Shear wave elastography has shown to be a powerful tool to estimate tissue mechanical properties. However, its applicability to quantitatively evaluate tendon stiffness is limited by the understanding of the physics on the shear wave propagation in such a complex medium. First, tendon tissue is transverse isotropic. Second, tendons are characterized by a marked stiffness in the 400 to 1300 kPa range (i.e. fast shear waves). Hence, the shear wavelengths are greater than the tendon thickness leading to guided wave propagation. Thus, to better understand shear wave propagation in tendons and consequently to properly estimate its mechanical properties, a dispersion analysis is required. In this study, shear wave velocity dispersion was measured in vivo in ten Achilles tendons parallel and perpendicular to the tendon fibre orientation. By modelling the tendon as a transverse isotropic viscoelastic plate immersed in fluid it was possible to fully describe the experimental data (deviation<1.4%). We show that parallel to fibres the shear wave velocity dispersion is not influenced by viscosity, while it is perpendicularly to fibres. Elasticity (found to be in the range from 473 to 1537 kPa) and viscosity (found to be in the range from 1.7 to 4 Pa.s) values were retrieved from the model in good agreement with reported results.
NASA Astrophysics Data System (ADS)
Lebedev, E. F.; Ostashev, V. E.; Fortov, V. E.
2004-11-01
Explosive driven MHD generators (EMHD) occupy an intermediate position between destroyed Explosive Flux Compression Generators and solid-propellant- pulsed MHD generators. Studies revealed the negative consequences of destroying a plasma liner through Rayleigh-Taylor instability. The real efficiency of conversion of condensed HE charge chemical energy reaches ~10% if the magnetic field in a MHD channel is approximately 8-10 T. Accommodation of 20-30 linear MHD channels into a toroidal magnet seems to be optimal for EMHD generator design. This device may operate repeatedly with a frequency of up to 6.5×103pps.
Dutta, Jhuma; Ramakrishna, S. Anantha; Lakhtakia, Akhlesh
2015-01-07
The morphology of a columnar thin film (CTF) of silver renders it an effectively biaxially anisotropic continuum. CTFs of silver deposited on one-dimensional gratings of photoresist showed strong blazing action and asymmetrically coupled optical radiation to surface-plasmon-polariton (SPP) waves propagating only along one direction supported by either the CTF/photoresist or the CTF/air interfaces. Homogenization of the CTFs using the Bruggeman formalism revealed them to display hyperbolic dispersion, and the dispersion of SPP waves was adequately described thereby.
Benoit, M H; Nyblade, A A; Pasyanos, M E
2006-01-17
The East African and Ethiopian Plateaus have long been recognized to be part of a much larger topographic anomaly on the African Plate called the African Superswell. One of the few places within the African Superswell that exhibit elevations of less than 1 km is southeastern Sudan and northern Kenya, an area containing both Mesozoic and Cenozoic rift basins. Crustal structure and uppermost mantle velocities are investigated in this area by modeling Rayleigh wave dispersion. Modeling results indicate an average crustal thickness of 25 {+-} 5 km, some 10-15 km thinner than the crust beneath the adjacent East African and Ethiopian Plateaus. The low elevations can therefore be readily attributed to an isostatic response from crustal thinning. Low Sn velocities of 4.1-4.3 km/s also characterize this region.
Kotov, L V; Koptev, M Yu; Anashkina, E A; Muravyev, S V; Andrianov, A V; Kim, A V; Bubnov, M M; Likhachev, M E; Ignat'ev, A D; Lipatov, D S; Gur'yanov, A N
2014-05-30
We have demonstrated a femtosecond erbium-doped fibre laser system built in the master oscillator/power amplifier (MOPA) approach. The final amplifier stage utilises a specially designed large mode area active fibre cladding-pumped by multimode laser diodes. The system is capable of generating submicrojoule pulses at a wavelength near 1.6 μm. We have obtained 530-fs pulses with an energy of 400 nJ. The output of the system can be converted to wavelengths shorter than 1 μm through the generation of dispersive waves in passive nonlinear fibre. We have obtained ultra-short 7-nJ pulses with a spectral width of ∼100 nm and a centre wavelength of 0.9 μm, which can be used as a seed signal in parametric amplifiers in designing petawatt laser systems. (lasers)
Energy dispersive x-ray diffraction of charge density waves via chemical filtering
Feng Yejun; Somayazulu, M. S.; Jaramillo, R.; Rosenbaum, T.F.; Isaacs, E.D.; Hu Jingzhu; Mao Hokwang
2005-06-15
Pressure tuning of phase transitions is a powerful tool in condensed matter physics, permitting high-resolution studies while preserving fundamental symmetries. At the highest pressures, energy dispersive x-ray diffraction (EDXD) has been a critical method for geometrically confined diamond anvil cell experiments. We develop a chemical filter technique complementary to EDXD that permits the study of satellite peaks as weak as 10{sup -4} of the crystal Bragg diffraction. In particular, we map out the temperature dependence of the incommensurate charge density wave diffraction from single-crystal, elemental chromium. This technique provides the potential for future GPa pressure studies of many-body effects in a broad range of solid state systems.
Asymptotic solutions of weakly nonlinear, dispersive wave-propagation problems by Fourier analysis
Srinivasan, R.
1989-01-01
A perturbation method based on Fourier analysis and multiple scales is introduced for solving weakly nonlinear, dispersive wave propagation problems with Fourier transformable initial conditions. Asymptotic solutions are derived for the weakly nonlinear cubic Schroedinger (NLS) equation with variable coefficients and the weakly nonlinear Kortewegde-Vries (KdV) equation; the results for the NLS equation are verified by comparison with numerical solutions. In the special case of constant coefficients, the asymptotic solution for the weakly nonlinear NLS equation agrees to leading order with previously derived results in the literature; in general, this is not true to higher orders. Therefore previous asymptotic results for the strongly nonlinear Schroedinger equation can be valid only for restricted initial conditions. Similar conclusions apply to the KdV equation.
Impact of spatial dispersion, evolution, and selection on Ebola Zaire Virus epidemic waves.
Azarian, Taj; Lo Presti, Alessandra; Giovanetti, Marta; Cella, Eleonora; Rife, Brittany; Lai, Alessia; Zehender, Gianguglielmo; Ciccozzi, Massimo; Salemi, Marco
2015-05-14
Ebola virus Zaire (EBOV) has reemerged in Africa, emphasizing the global importance of this pathogen. Amidst the response to the current epidemic, several gaps in our knowledge of EBOV evolution are evident. Specifically, uncertainty has been raised regarding the potential emergence of more virulent viral variants through amino acid substitutions. Glycoprotein (GP), an essential component of the EBOV genome, is highly variable and a potential site for the occurrence of advantageous mutations. For this study, we reconstructed the evolutionary history of EBOV by analyzing 65 GP sequences from humans and great apes over diverse locations across epidemic waves between 1976 and 2014. We show that, although patterns of spatial dispersion throughout Africa varied, the evolution of the virus has largely been characterized by neutral genetic drift. Therefore, the radical emergence of more transmissible variants is unlikely, a positive finding, which is increasingly important on the verge of vaccine deployment.
Excitation of quasielectrostatic waves in a laboratory magnetoplasma with weak spatial dispersion
Starodubtsev, Mikhail V.; Kostrov, Alexander V.; Nazarov, Vladimir V.; Permitin, German V.
2005-08-01
Short-wavelength quasielectrostatic waves radiated by a small probe in a cold (T{sub e}{approx_equal}0.5 eV) laboratory magnetoplasma are studied in both the upper-hybrid (UH) and the lower-hybrid (LH) frequency ranges. Measured radiation patterns are characterized by resonance cones in the LH range and in the low-frequency part of the UH range (at {omega}<2{omega}{sub c}), while in its high-frequency part (at {omega}>2{omega}{sub c}), a beamed radiation along the external magnetic field is observed. An analysis reveals that the angular resonance is primarily limited by the phase effects caused by weak spatial dispersion.
Yin, Anmin; Wang, Xiaochen; Glorieux, Christ; Yang, Quan; Dong, Feng; He, Fei; Wang, Yanlong; Sermeus, Jan; Van der Donck, Tom; Shu, Xuedao
2017-02-24
A photoacoustic, laser ultrasonics based approach in an Impulsive Stimulated Scattering (ISS) implementation was used to investigate the texture in polycrystalline metal plates. The angular dependence of the 'polycrystalline' surface acoustic wave (SAW) velocity measured along regions containing many grains was experimentally determined and compared with simulated results that were based on the angular dependence of the 'single grain' SAW velocity within single grains and the grain orientation distribution. The polycrystalline SAW velocities turn out to vary with texture. The SAW velocities and their angular variations for {110} texture were found to be larger than that the ones for {111} texture or the strong γ fiber texture. The SAW velocities for {001} texture were larger than for {111} texture, but with almost the same angular dependence. The results infer the feasibility to apply angular SAW angular dispersion measurements by laser ultrasonics for on-line texture monitoring.
NASA Astrophysics Data System (ADS)
Antikainen, Aku; Arteaga-Sierra, Francisco R.; Agrawal, Govind P.
2017-03-01
We show that temporal reflections off a moving refractive index barrier play a major role in the spectral broadening of a dual-wavelength input inside a highly nonlinear, dispersion-decreasing fiber. We also find that a recently developed linear theory of temporal reflections works well in predicting the reflected frequencies. Successive temporal reflections from multiple closely spaced solitons create a blueshifted spectral band, while continuous narrowing of solitons inside the dispersion-decreasing fiber enhances Raman-induced redshifts, leading to supercontinuum generation at relatively low pump powers. We also show how dispersive wave emission can be considered a special case of the more general process of temporal reflections. Hence our findings have implications on all systems able to support solitons.
Dispersion analysis of leaky guided waves in fluid-loaded waveguides of generic shape.
Mazzotti, M; Marzani, A; Bartoli, I
2014-01-01
A fully coupled 2.5D formulation is proposed to compute the dispersive parameters of waveguides with arbitrary cross-section immersed in infinite inviscid fluids. The discretization of the waveguide is performed by means of a Semi-Analytical Finite Element (SAFE) approach, whereas a 2.5D BEM formulation is used to model the impedance of the surrounding infinite fluid. The kernels of the boundary integrals contain the fundamental solutions of the space Fourier-transformed Helmholtz equation, which governs the wave propagation process in the fluid domain. Numerical difficulties related to the evaluation of singular integrals are avoided by using a regularization procedure. To improve the numerical stability of the discretized boundary integral equations for the external Helmholtz problem, the so called CHIEF method is used. The discrete wave equation results in a nonlinear eigenvalue problem in the complex axial wavenumbers that is solved at the frequencies of interest by means of a contour integral algorithm. In order to separate physical from non-physical solutions and to fulfill the requirement of holomorphicity of the dynamic stiffness matrix inside the complex wavenumber contour, the phase of the radial bulk wavenumber is uniquely defined by enforcing the Snell-Descartes law at the fluid-waveguide interface. Three numerical applications are presented. The computed dispersion curves for a circular bar immersed in oil are in agreement with those extracted using the Global Matrix Method. Novel results are presented for viscoelastic steel bars of square and L-shaped cross-section immersed in water.
Linear Analysis of the m=0 Instability for a Visco-resistive Hall MHD Plasma
Oliver, B.V.; Genoni, T.C.; Mehlhorn, T.A.
2006-01-05
We present a comprehensive analysis of the linear dispersion relation for the axisymmetric (m=0) compressible interchange instability of Bennett equilibria in a visco-resistive, Hall MHD plasma. The full anisotropic stress tensor with Braginskii viscous coefficients is considered. The eigenvalues are obtained numerically. For small axial mode number, Hall currents enhance the growth rates, whereas in the limit of high mode number the growth rates are suppressed, eventually resulting in wave cutoff, even in the ideal limit. For the visco-resistive plasma the unstable spectra are weakly dependent on the off-diagonal elements of the stress tensor.
Baik, Chan-Wook Young Ahn, Ho; Kim, Yongsung; Lee, Jooho; Hong, Seogwoo; Hee Choi, Jun; Kim, Sunil; Hun Lee, Sang; Min Kim, Jong; Hwang, Sungwoo; Yeon Jun, So; Yu, SeGi; Lawrence Ives, R.
2014-01-13
A multi-level microstructure is proposed for terahertz slow-wave circuits, with dispersion relation retrieved by scattering parameter measurements. The measured return loss shows strong resonances above the cutoff with negligible phase shifts compared with finite element analysis. Splitting the circuit into multi levels enables a low aspect ratio configuration that alleviates the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles. The dispersion retrieved from the measurement, therefore, corresponds well to the theoretical estimation. The result provides a straightforward way to the precise determination of dispersions in terahertz vacuum electronics.
NASA Astrophysics Data System (ADS)
Zhang, Guo-Bao; Ma, Ruyun
2014-10-01
This paper is concerned with the traveling wave solutions and the spreading speeds for a nonlocal dispersal equation with convolution-type crossing-monostable nonlinearity, which is motivated by an age-structured population model with time delay. We first prove the existence of traveling wave solution with critical wave speed c = c*. By introducing two auxiliary monotone birth functions and using a fluctuation method, we further show that the number c = c* is also the spreading speed of the corresponding initial value problem with compact support. Then, the nonexistence of traveling wave solutions for c < c* is established. Finally, by means of the (technical) weighted energy method, we prove that the traveling wave with large speed is exponentially stable, when the initial perturbation around the wave is relatively small in a weighted norm.
NASA Astrophysics Data System (ADS)
Lee, C. T.; Lee, C. C.
2015-04-01
This paper introduces a systematic approach to investigate a higher order nonlinear dispersive wave equation for modeling different wave modes. We present both the conventional KdV-type soliton and anomaly type solitons for the equation. We also show the conservation laws and Hamiltonian structures for the equation. Our results suggest that the underlying equation has more interacting soliton phenomena than one would have known for the classical KdV and Boussinesq equation.
Mase, A.; Jeong, J.H.; Itakura, A.; Ishii, K.; Miyoshi, S. )
1990-04-01
The Fraunhofer diffraction measurements from a tandem mirror plasma are reported. The successful use of a new multichannel detector array permits a detailed study of {bold k}{minus}{omega} spectra of long-wavelength waves with a few plasma shots. The observed dispersion relations are in good agreement with those of drift wave including a Doppler shift due to {bold E}{times}{bold B} rotation velocity.
NASA Astrophysics Data System (ADS)
Kniskern, T. A.; Warrick, J. A.; Farnsworth, K. L.
2008-12-01
Small rivers with mountainous catchments account for over half of the terrigenous material delivered to the coastal ocean. Dispersal, deposition, and cycling of sediments and associated nutrients ultimately influence shelf carbon budgets. Recent work on collision margins revealed that these small rivers flood during energetic ocean conditions, creating conditions conducive to dispersal of sediments via multiple sediment transport mechanisms. Furthermore, the relative timing of the peak flood and peak wave conditions influences dispersal and depositional patterns. Our study sought to identify patterns of fluvial and oceanic coherence along the US west coast by analyzing 10 years (1996-2006) of NOAA buoy, Climate Prediction Center storm track, and USGS gauge data. Discharge, buoy data, and storm tracks for the Umpqua, Eel, Salinas, and Santa Clara rivers and their adjacent shelves revealed temporal and spatial coherence patterns of wave event and flood magnitude, frequency, and timing. The seasonal period of energetic waves for each river-shelf system began 1-2 months earlier than the flood season (November) and extended 1 month beyond the end of flood season (May). There was also a seasonal disconnect in the timing of peak wave energy (December) and peak floods (January to February). Peak flood activity occurred in January on the Umpqua and Eel Rivers, and in February for the Salinas and Santa Clara Rivers. Flooding and wave events were more frequent and greater in magnitude on the Eel and Umpqua river shelves. The Salinas and Santa Clara rivers displayed lower fluvial inputs, but Salinas River shelf wave events were greater in magnitude. The magnitude and timing of peak waves and peak discharges during floods varied characteristically for each river-shelf system. Peak discharge and peak wave magnitude during floods generally decreased from December to May, indicating that dispersal and depositional patterns vary over the season. Additionally, the timing between
Spin-wave dispersion of nanostructured magnonic crystals with periodic defects
NASA Astrophysics Data System (ADS)
Zhang, V. L.; Lim, H. S.; Ng, S. C.; Kuok, M. H.; Zhou, X.; Adeyeye, A. O.
2016-11-01
The spin-wave dispersions in nanostructured magnonic crystals with periodic defects have been mapped by Brillouin light scattering. The otherwise perfect crystals are one-dimensional arrays of alternating 460nm-wide Ni80Fe20 stripes and 40nm-wide air gaps, where one in ten Ni80Fe20 stripes is a defect of width other than 460 nm. Experimentally, the defects are manifested as additional Brillouin peaks, lying within the first and second bandgaps of the perfect crystal, whose frequencies decrease with increasing defect stripe width. Finite-element calculations, based on a supercell comprising one defect and nine perfect Py stripes, show that the defect modes are localized about the defects, with the localization exhibiting an approximate U-shaped dependence on defect size. Calculations also reveal extra magnon branches and the opening of mini-bandgaps, within the allowed bands of the perfect crystal, arising from Bragg reflections at the boundaries of the shorter supercell Brillouin zone. Simulated magnetization profiles of the band-edge modes of the major and mini-bandgaps reveal their different symmetries and localization properties. The findings could find application in microwave magnonic devices like single-frequency passband spin-wave filters.
P-wave and QT dispersion in patients with conversion disorder
Izci, Filiz; Hocagil, Hilal; Izci, Servet; Izci, Vedat; Koc, Merve Iris; Acar, Rezzan Deniz
2015-01-01
Objective The aim of this study was to investigate QT dispersion (QTd), which is the noninvasive marker of ventricular arrhythmia and sudden cardiac death, and P-wave dispersion, which is the noninvasive marker of atrial arrhythmia, in patients with conversion disorder (CD). Patients and methods A total of 60 patients with no known organic disease who were admitted to outpatient emergency clinic and were diagnosed with CD after psychiatric consultation were included in this study along with 60 healthy control subjects. Beck Anxiety Inventory and Beck Depression Scale were administered to patients and 12-lead electrocardiogram measurements were obtained. Pd and QTd were calculated by a single blinded cardiologist. Results There was no statistically significant difference in terms of age, sex, education level, socioeconomic status, weight, height, and body mass index between CD patients and controls. Beck Anxiety Inventory scores (25.2±10.8 and 3.8±3.2, respectively, P<0.001) and Beck Depression Scale scores (11.24±6.15 and 6.58±5.69, respectively, P<0.01) were significantly higher in CD patients. P-wave dispersion measurements did not show any significant differences between conversion patients and control group (46±5.7 vs 44±5.5, respectively, P=0.156). Regarding QTc and QTd, there was a statistically significant increase in all intervals in conversion patients (416±10 vs 398±12, P<0.001, and 47±4.8 vs 20±6.1, P<0.001, respectively). Conclusion A similar relation to that in literature between QTd and anxiety and somatoform disorders was also observed in CD patients. QTc and QTd were significantly increased compared to the control group in patients with CD. These results suggest a possibility of increased risk of ventricular arrhythmia resulting from QTd in CD patients. Larger samples are needed to evaluate the clinical course and prognosis in terms of arrhythmia risk in CD patients. PMID:25848293
Coupled periodic waves with opposite dispersions in a nonlinear optical fiber
NASA Astrophysics Data System (ADS)
Tsang, S. C.; Nakkeeran, K.; Malomed, Boris A.; Chow, K. W.
2005-05-01
Using the Hirota's method and elliptic θ-functions, we obtain three families of exact periodic (cnoidal) wave solutions for two nonlinear Schrödinger (NLS) equations coupled by XPM (cross-phase-modulation) terms, with a ratio σ of the XPM and SPM (self-phase-modulation) coefficients. Unlike the previous works, we obtain the solutions for the case when the coefficients of the group-velocity-dispersion (GVD) in the coupled equations have opposite signs. In the limit of the infinite period, the solutions with σ > 1 carry over into inverted bound states of bright and dark solitons in the normal- and anomalous-GVD modes (known as "symbiotic solitons"), while the infinite-period solution with σ < 1 is an uninverted bound state (also an unstable one). The case of σ = 2 is of direct interest to fiber-optic telecommunications, as it corresponds to a scheme with a pulse stream in an anomalous-GVD payload channel stabilized by a concomitant strong periodic signal in a mate normal-GVD channel. The case of arbitrary σ may be implemented in a dual-core waveguide. To understand the stability of the coupled waves, we first analytically explore the modulational stability of CW (constant-amplitude) solutions, concluding that they may be completely stable for σ ⩾ 1, provided that the absolute value of the GVD coefficient is smaller in the anomalous-GVD mode than in the normal-GVD one, and certain auxiliary conditions on the amplitudes are met. The stability of the exact cnoidal-wave solutions is tested in direct simulations. We infer that, while, strictly speaking, in the practically significant case of σ = 2 all the solutions are unstable, in many cases the instability may be strongly attenuated, rendering the above-mentioned paired channels scheme usable. In particular, the instability is milder for a smaller period of the wave pattern, and/or if the anomalous GVD is weaker than the normal GVD in the mate channel. When the instability sets in, it first initiates quasi
NASA Astrophysics Data System (ADS)
Rubino, J. Germán.; Caspari, Eva; Müller, Tobias M.; Milani, Marco; Barbosa, Nicolás. D.; Holliger, Klaus
2016-09-01
The presence of stiffness contrasts at scales larger than the typical pore sizes but smaller than the predominant seismic wavelengths can produce seismic attenuation and velocity dispersion in fluid-saturated porous rocks. This energy dissipation mechanism is caused by wave-induced fluid pressure diffusion among the different components of the probed geological formations. In many cases, heterogeneities have elongated shapes and preferential orientations, which implies that the overall response of the medium is anisotropic. In this work, we propose a numerical upscaling procedure that permits to quantify seismic attenuation and phase velocity considering fluid pressure diffusion effects as well as generic anisotropy at the sample's scale. The methodology is based on a set of three relaxation tests performed on a 2-D synthetic rock sample representative of the medium of interest. It provides a complex-valued frequency-dependent equivalent stiffness matrix through a least squares procedure. We also derive an approach for computing various poroelastic fields associated with the considered sample in response to the propagation of a seismic wave with arbitrary incidence angle. Using this approach, we provide an energy-based estimation of seismic attenuation. A comprehensive numerical analysis indicates that the methodology is suitable for handling complex media and different levels of overall anisotropy. Comparisons with the energy-based estimations demonstrate that the dynamic-equivalent viscoelastic medium assumption made by the numerical upscaling procedure is reasonable even in the presence of high levels of overall anisotropy. This work also highlights the usefulness of poroelastic fields for the physical interpretation of seismic wave phenomena in strongly heterogeneous and complex media.
NASA Astrophysics Data System (ADS)
Luo, Yinhe; Xia, Jianghai; Xu, Yixian; Zeng, Chong; Liu, Jiangping
2010-12-01
Love-wave propagation has been a topic of interest to crustal, earthquake, and engineering seismologists for many years because it is independent of Poisson's ratio and more sensitive to shear (S)-wave velocity changes and layer thickness changes than are Rayleigh waves. It is well known that Love-wave generation requires the existence of a low S-wave velocity layer in a multilayered earth model. In order to study numerically the propagation of Love waves in a layered earth model and dispersion characteristics for near-surface applications, we simulate high-frequency (>5 Hz) Love waves by the staggered-grid finite-difference (FD) method. The air-earth boundary (the shear stress above the free surface) is treated using the stress-imaging technique. We use a two-layer model to demonstrate the accuracy of the staggered-grid modeling scheme. We also simulate four-layer models including a low-velocity layer (LVL) or a high-velocity layer (HVL) to analyze dispersive energy characteristics for near-surface applications. Results demonstrate that: (1) the staggered-grid FD code and stress-imaging technique are suitable for treating the free-surface boundary conditions for Love-wave modeling, (2) Love-wave inversion should be treated with extra care when a LVL exists because of a lack of LVL information in dispersions aggravating uncertainties in the inversion procedure, and (3) energy of high modes in a low-frequency range is very weak, so that it is difficult to estimate the cutoff frequency accurately, and "mode-crossing" occurs between the second higher and third higher modes when a HVL exists.
Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.; Liu, J.
2010-01-01
Love-wave propagation has been a topic of interest to crustal, earthquake, and engineering seismologists for many years because it is independent of Poisson's ratio and more sensitive to shear (S)-wave velocity changes and layer thickness changes than are Rayleigh waves. It is well known that Love-wave generation requires the existence of a low S-wave velocity layer in a multilayered earth model. In order to study numerically the propagation of Love waves in a layered earth model and dispersion characteristics for near-surface applications, we simulate high-frequency (>5 Hz) Love waves by the staggered-grid finite-difference (FD) method. The air-earth boundary (the shear stress above the free surface) is treated using the stress-imaging technique. We use a two-layer model to demonstrate the accuracy of the staggered-grid modeling scheme. We also simulate four-layer models including a low-velocity layer (LVL) or a high-velocity layer (HVL) to analyze dispersive energy characteristics for near-surface applications. Results demonstrate that: (1) the staggered-grid FD code and stress-imaging technique are suitable for treating the free-surface boundary conditions for Love-wave modeling, (2) Love-wave inversion should be treated with extra care when a LVL exists because of a lack of LVL information in dispersions aggravating uncertainties in the inversion procedure, and (3) energy of high modes in a low-frequency range is very weak, so that it is difficult to estimate the cutoff frequency accurately, and "mode-crossing" occurs between the second higher and third higher modes when a HVL exists. ?? 2010 Birkh??user / Springer Basel AG.
Current chemical dispersant effectiveness tests for product selection are commonly performed with bench-scale testing apparatus. However, for the assessment of oil dispersant effectiveness under real sea state conditions, test protocols are required to have hydrodynamic conditio...
NASA Astrophysics Data System (ADS)
Mercerat, D.; Ampuero, J.; Nissen-Meyer, T.
2006-12-01
Some problems in global seismology require the computation of synthetic seismograms with particularly high accuracy for waves travelling over very long distances. For instance the R3 and R4 phases (Rayleigh waves propagating twice around the globe) can improve data coverage and provide valuable information about the Earth structure. The spectral element method (SEM) is now widely applied in seismic wave propagation, owing to its often claimed geometrical flexibility and high accuracy. It appears however that a complete theoretical analysis of the dispersion properties of the SEM has been missing, or that existing results have had little exposure in the computational seismology community. We have analyzed the dispersion properties of the spectral element method (SEM) for the wave equation, with an emphasis on practical issues for the numerical modelling of seismic wave propagation. The asymptotic behavior of the dispersion error is given in closed form. We show how to select the polynomial order p, the element size h and the timestep Δ t in order to minimize the computational cost for a given accuracy goal. When the accuracy requirements are stringent, we show that the spectral convergence of the SEM is wasted by the usage of low-order time integration schemes such as Newmark and centered differences. In these cases, we reduce the dispersion error by applying high-order symplectic time schemes developped in astrophysics and molecular dynamics. These schemes are easy to implement in existing codes and have low memory and CPU cost. We show how to select the optimal order of the time scheme that meets a prescribed accuracy while minimizing the computational cost. We will report on our efforts to further optimize the symplectic family for the wave equation, and illustrate the advantages in applications ranging from local to global scale seismic wave propagation. This work is partly funded by SPICE, a Marie-Curie Research and Training Network.
NASA Astrophysics Data System (ADS)
Grünsteidl, Clemens; Veres, István A.; Roither, Jürgen; Burgholzer, Peter; Murray, Todd W.; Berer, Thomas
2013-01-01
We present a laser-ultrasound measurement technique which combines adjustable spatial and temporal modulation of the excitation laser beam. Our method spreads the intensity of an amplitude modulated continuous wave laser over a micro-scale pattern on the sample surface to excite surface acoustic waves. The excitation pattern consists of parallel, equidistant lines and the waves generated from the individual lines interfere on the sample surface. Measurement is done in the spatial-temporal frequency domain allowing the direct determination of dispersion relations. The technique performs with high signal-to-noise-ratios and low peak power densities on the sample.
Soni, Dilip; Sharma, Giriraj; Saxena, Ajay; Jadhav, Akhilesh
2015-07-31
An analytical study on propagation characteristics of longitudinal electro-kinetic (LEK) waves is presented. Based on multi-fluid model of plasma, we have derived a dispersion relation for LEK waves in colloid laden GaN semiconductor plasmas. It is assumed that ions are implanted to form colloids in the GaN sample. The colloids are continuously bombarded by the plasma particles and stick on them, but they acquire a net negative charge due to relatively higher mobility of electrons. It is found from the dispersion relation that the presence of charged colloids not only modifies the existing modes but also supports new novel modes of LEKWs. It is hoped that the study would enhance understanding on dispersion and absorption of LEKWs and help in singling out the appropriate configurations in which GaN crystal would be better suited for fabrication of microwave devices.
NASA Technical Reports Server (NTRS)
Armoundas, A. A.; Osaka, M.; Mela, T.; Rosenbaum, D. S.; Ruskin, J. N.; Garan, H.; Cohen, R. J.
1998-01-01
T-wave alternans and QT dispersion were compared as predictors of the outcome of electrophysiologic study and arrhythmia-free survival in patients undergoing electrophysiologic evaluation. T-wave alternans was a highly significant predictor of these 2 outcome variables, whereas QT dispersion was not.
NASA Astrophysics Data System (ADS)
Maksymov, I. S.; Kostylev, M.
2013-12-01
We propose a rigorous solution to a long-standing problem of the impact of eddy currents on the dispersion relation of surface spin waves propagating in thin conducting magnetic films. Our results confirm the prediction of the Almeida-Mill's exchange-free theory that the inclusion of the eddy-current contribution results in a deviation of the dispersion curve for the fundamental mode from the Damon-Eshbach law and a substantial linewidth broadening in a large wave vector range. We show that the decrease in the spin-wave frequency is due to an increase in the in-plane component of the dynamic magnetic field within the conducting film. The decrease in the frequency is accompanied by a drastic change in the asymmetry of the modal profiles for the waves. This effect is not observable in magneto-insulating films and therefore it is unambiguously attributed to eddy currents that appear in conducting films only. We also show that the wave vector range in which eddy currents affect the dispersion curve is strongly correlated with the value of the film conductivity. This result holds for conducting films with the thickness 10-100 nm, which are considered promising for future magnonic and spintronic applications.
NASA Astrophysics Data System (ADS)
Ma, Xiao; Yang, Dinghui
2017-03-01
The finite-difference method, which is an important numerical tool for solving seismic wave equations, is widely applied in wavefield simulation, wave-equation-based migration and inversion. As the seismic wave phase plays a critical role in forward simulation and inversion, it should be preserved during wavefield simulation. In this paper, we propose a type of phase-preserving stereomodelling method, which is simultaneously symplectic and low numerical dispersive. First, we propose three new time-marching schemes for solving wave equations that are optimal symplectic partitioned Runge-Kutta schemes with minimized phase errors. Relevant simulations on a harmonic oscillator show that even after 200,000 temporal iterations, our schemes can still avoid the phase drifting issue that appears in other symplectic schemes. We use these symplectic schemes as time integrators, and a numerically low dispersive operator called the stereomodelling discrete operator as a spatial discretization approach to solve seismic wave equations. Theoretical analysis on the stability conditions shows that the new methods are more stable than previous methods. We also investigate the numerical dispersion relations of the methods proposed in this study. To further investigate phase accuracy, we compare the numerical solutions generated by the proposed methods with analytic solutions. Several numerical experiments indicate that our proposed methods are efficient for various models and perform well with perfectly matched layer boundary conditions.
NASA Astrophysics Data System (ADS)
De Santi, Francesca; Fraternale, Federico; Tordella, Daniela
2016-03-01
In this study we analyze the phase and group velocity of three-dimensional linear traveling waves in two sheared flows: the plane channel and the wake flows. This was carried out by varying the wave number over a large interval of values at a given Reynolds number inside the ranges 20-100, 1000-8000, for the wake and channel flow, respectively. Evidence is given about the possible presence of both dispersive and nondispersive effects which are associated with the long and short ranges of wavelength. We solved the Orr-Sommerfeld and Squire eigenvalue problem and observed the least stable mode. It is evident that, at low wave numbers, the least stable eigenmodes in the left branch of the spectrum behave in a dispersive manner. By contrast, if the wave number is above a specific threshold, a sharp dispersive-to-nondispersive transition can be observed. Beyond this transition, the dominant mode belongs to the right branch of the spectrum. The transient behavior of the phase velocity of small three-dimensional traveling waves was also considered. Having chosen the initial conditions, we then show that the shape of the transient highly depends on the transition wavelength threshold value. We show that the phase velocity can oscillate with a frequency which is equal to the frequency width of the eigenvalue spectrum. Furthermore, evidence of intermediate self-similarity is given for the perturbation field.
NASA Astrophysics Data System (ADS)
Li, Ping-Wah
1994-12-01
In his paper [J. Acoust. Soc. Am. 77, 2050 (1985)] Blackstock presented a generalized Burgers equation for the propagation of one-dimensional weakly nonlinear waves in various media. His results, and the approach he employed there, however, are limited to harmonic waves. In this paper, we present a general approach to model nonlinear waves of more general wave forms that propagate in media with arbitrary absorption and dispersion relations. The resulting equation is again called the generalized Burgers equation (to follow the terminology of the literature). It is found that steady shock solutions for various media can be described by the corresponding simplified version of the equation. An efficient numerical method by means of spectral analysis is developed for solving the generalized Burgers equation. Typical results exemplified by the case of a sinusoidal wave source are also reported in this paper.
Javan, N. Sepehri Homami, S. H. H.
2015-02-15
Self-guided nonlinear propagation of intense circularly-polarized electromagnetic waves in a hot electron-positron-ion magnetoplasma is studied. Using a relativistic fluid model, a nonlinear equation is derived, which describes the interaction of the electromagnetic wave with the plasma in the quasi-neutral approximation. Transverse Eigen modes, the nonlinear dispersion relation and the group velocity are obtained. Results show that the transverse profile in the case of magnetized plasma with cylindrical symmetry has a radially damping oscillatory form. Effect of applying external magnetic fields, existence of the electron-positron pairs, changing the amplitude of the electromagnetic wave, and its polarization on the nonlinear dispersion relation and Eigen modes are studied.
Observation of linear spin wave dispersion in the reentrant spin glass Fe0.7Al0.3
NASA Astrophysics Data System (ADS)
Shapiro, S. M.; Bao, W.; Raymond, S.; Lee, S. H.; Motoya, K.
Fe0.7Al0.3 is a reentrant spin glass, which undergoes a transition from a paramagnet to a disordered ferromagnet at Tc 500K at a lower temperature the spins progressively freeze and it exhibits a spin-glass-like behavior. In the ferromagnetic phase spin waves with a q2 dispersion are observed at small q, which broaden rapidly and become diffusive beyond a critical wave vector q0. On cooling the spin waves also disappear and a strong elastic central peak develops. For measurements around the (1,1,1) Bragg peak, a new sharp excitation is observed which has a linear dispersion behavior. It disappears above Tc, but persists throughout the spin-glass phase. It is not present in the stoichiometric Fe3Al material.
NASA Astrophysics Data System (ADS)
Selima, Ehab S.; Seadawy, Aly R.; Yao, Xiaohua
2016-12-01
The three-dimensional (3-D) nonlinear and dispersive PDEs system for surface waves propagating at undisturbed water surface under the gravity force and surface tension effects are studied. By applying the reductive perturbation method, we derive the (2 + 1) -dimensions form of the Davey-Stewartson (DS) system for the modulation of 2-D harmonic waves. By using the simplest equation method, we find exact traveling wave solutions and a general form of the multiple-soliton solution of the DS model. The dispersion analysis as well as the conservation law of the DS system are discussed. It is revealed that the consistency of the results with the conservation of the potential energy increases with increasing Ursell parameter. Also, the stability of the ODEs form of the DS system is presented by using the phase portrait method.
Stop and Go – Waves of Tarsier Dispersal Mirror the Genesis of Sulawesi Island
Driller, Christine; Merker, Stefan; Perwitasari-Farajallah, Dyah; Sinaga, Walberto; Anggraeni, Novita; Zischler, Hans
2015-01-01
The Indonesian island of Sulawesi harbors a highly endemic and diverse fauna sparking fascination since long before Wallace’s contemplation of biogeographical patterns in the region. Allopatric diversification driven by geological or climatic processes has been identified as the main mechanism shaping present faunal distribution on the island. There is both consensus and conflict among range patterns of terrestrial species pointing to the different effects of vicariant events on once co-distributed taxa. Tarsiers, small nocturnal primates with possible evidence of an Eocene fossil record on the Asian mainland, are at present exclusively found in insular Southeast Asia. Sulawesi is hotspot of tarsier diversity, whereby island colonization and subsequent radiation of this old endemic primate lineage remained largely enigmatic. To resolve the phylogeographic history of Sulawesi tarsiers we analyzed an island-wide sample for a set of five approved autosomal phylogenetic markers (ABCA1, ADORA3, AXIN1, RAG1, and TTR) and the paternally inherited SRY gene. We constructed ML and Bayesian phylogenetic trees and estimated divergence times between tarsier populations. We found that their arrival at the Proto-Sulawesi archipelago coincided with initial Miocene tectonic uplift and hypothesize that tarsiers dispersed over the region in distinct waves. Intra-island diversification was spurred by land emergence and a rapid succession of glacial cycles during the Plio-Pleistocene. Some tarsier range boundaries concur with spatial limits in other taxa backing the notion of centers of faunal endemism on Sulawesi. This congruence, however, has partially been superimposed by taxon-specific dispersal patterns. PMID:26559527
NASA Astrophysics Data System (ADS)
Nikitenkova, S.; Singh, N.; Stepanyants, Y.
2015-12-01
In this paper, we revisit the problem of modulation stability of quasi-monochromatic wave-trains propagating in a media with the double dispersion occurring both at small and large wavenumbers. We start with the shallow-water equations derived by Shrira [Izv., Acad. Sci., USSR, Atmos. Ocean. Phys. (Engl. Transl.) 17, 55-59 (1981)] which describes both surface and internal long waves in a rotating fluid. The small-scale (Boussinesq-type) dispersion is assumed to be weak, whereas the large-scale (Coriolis-type) dispersion is considered as without any restriction. For unidirectional waves propagating in one direction, only the considered set of equations reduces to the Gardner-Ostrovsky equation which is applicable only within a finite range of wavenumbers. We derive the nonlinear Schrödinger equation (NLSE) which describes the evolution of narrow-band wave-trains and show that within a more general bi-directional equation the wave-trains, similar to that derived from the Ostrovsky equation, are also modulationally stable at relatively small wavenumbers k < kc and unstable at k > kc, where kc is some critical wavenumber. The NLSE derived here has a wider range of applicability: it is valid for arbitrarily small wavenumbers. We present the analysis of coefficients of the NLSE for different signs of coefficients of the governing equation and compare them with those derived from the Ostrovsky equation. The analysis shows that for weakly dispersive waves in the range of parameters where the Gardner-Ostrovsky equation is valid, the cubic nonlinearity does not contribute to the nonlinear coefficient of NLSE; therefore, the NLSE can be correctly derived from the Ostrovsky equation.
Nikitenkova, S; Singh, N; Stepanyants, Y
2015-12-01
In this paper, we revisit the problem of modulation stability of quasi-monochromatic wave-trains propagating in a media with the double dispersion occurring both at small and large wavenumbers. We start with the shallow-water equations derived by Shrira [Izv., Acad. Sci., USSR, Atmos. Ocean. Phys. (Engl. Transl.) 17, 55-59 (1981)] which describes both surface and internal long waves in a rotating fluid. The small-scale (Boussinesq-type) dispersion is assumed to be weak, whereas the large-scale (Coriolis-type) dispersion is considered as without any restriction. For unidirectional waves propagating in one direction, only the considered set of equations reduces to the Gardner-Ostrovsky equation which is applicable only within a finite range of wavenumbers. We derive the nonlinear Schrödinger equation (NLSE) which describes the evolution of narrow-band wave-trains and show that within a more general bi-directional equation the wave-trains, similar to that derived from the Ostrovsky equation, are also modulationally stable at relatively small wavenumbers k < kc and unstable at k > kc, where kc is some critical wavenumber. The NLSE derived here has a wider range of applicability: it is valid for arbitrarily small wavenumbers. We present the analysis of coefficients of the NLSE for different signs of coefficients of the governing equation and compare them with those derived from the Ostrovsky equation. The analysis shows that for weakly dispersive waves in the range of parameters where the Gardner-Ostrovsky equation is valid, the cubic nonlinearity does not contribute to the nonlinear coefficient of NLSE; therefore, the NLSE can be correctly derived from the Ostrovsky equation.
NASA Astrophysics Data System (ADS)
Sina, Nima; Moosavi, Hassan; Aghaei, Hosein; Afrand, Masoud; Wongwises, Somchai
2017-01-01
In this paper, for the first time, a nonlocal Timoshenko beam model is employed for studying the wave dispersion of a fluid-conveying single-walled carbon nanotube on Viscoelastic Pasternak foundation under high and low temperature change. In addition, the phase and group velocity for the nanotube are discussed, respectively. The influences of Winkler and Pasternak modulus, homogenous temperature change, steady flow velocity and damping factor of viscoelastic foundation on wave dispersion of carbon nanotubes are investigated. It was observed that the characteristic of the wave for carbon nanotubes conveying fluid is the normal dispersion. Moreover, implying viscoelastic foundation leads to increasing the wave frequencies.
NASA Astrophysics Data System (ADS)
Treyssède, Fabien
2016-04-01
Elastic guided waves are of interest for the non-destructive evaluation of cables. Such structures are usually helical, multiwired and highly prestressed, which greatly complicates the understanding of wave propagation from a theoretical point of view. A remarkable feature is the occurrence of a missing frequency band in experimental time-frequency diagrams, sometimes referred to as notch frequency in the literature. The central frequency of this band increases under tensile loads. Recently, a numerical model has been proposed to compute the dispersion curves of prestressed helical seven-wire waveguides. Results have shown that the notch frequency indeed corresponds to a curve veering phenomenon between two longitudinal-like modes and that the increase of the notch under tensile loads is mainly due to interwire contact mechanisms. The main goal of this paper is to highlight the origin of this curve veering phenomenon, which is still unexplained up to the author's knowledge. This paper also provides further results which allow us to clarify the accuracy of numerical solutions as well as the influence of contact assumptions. First, the static part of the model, necessary to compute the prestress state including contact effects, is checked from reference analytical solutions. Owing to the importance of contact, the accuracy of results is discussed both in statics and in dynamics. The influence of slip contact conditions is outlined. Then, some numerical tests are conducted by varying the Poisson coefficient and the helix lay angle. These tests allows us to find out that the radial displacement constraint imposed on peripheral wires by the central one in the contact regions constitutes the main source of curve veering. More precisely, it is shown that a similar curve veering does occur for an uncoupled single peripheral wire when constrained by a radially blocked motion localized in its contact zone. Indeed, such a localized boundary condition completely breaks the
Xiao, Qiang; Li, Yuanmin; Guo, Huimei; Zhang, Ge
2015-01-01
Although red cell distribution width (RDW) and P-wave dispersion (Pwd) are strong independent predictors of atrial tachyarrhythmia (ATa), the association between these two factors in the occurrence of ATA has hitherto not been reported. We retrospectively analyzed the cases of ATa patients who underwent Holter monitoring at our hospital from October 2013 to August 2014. Clinical data including RDW and color doppler ultrasonography data were collected, and Pwd was calculated from synchronous recording of P-wave intervals of 12-lead electrocardiograms. Patients were categorized into three groups in ascending order of RDW values. Between-group comparisons yielded significant differences in Pwd, left ventricular diastolic diameter (LVDD), and left atrial diameter (LAD; P < 0.05). Pearson correlation analysis revealed that the RDW level positively correlated with the Kleiger grade of atrial arrhythmia (r = 0.280, P < 0.001), Pwd (r = 0.148, P = 0.001), and LAD (r = 0.297, P < 0.001); Pwd positively correlated with the Kleiger grade of atrial arrhythmia (r = 0.257, P < 0.001), aortic root diameter (r = 0.143, P < 0.002), and LAD (r = 0.201, P < 0.001). Binary logistic multiple regression analysis with ATa as the dependent variable revealed that Pwd [odds ratio (OR) = 1.024], RDW [OR = 1.215], and aortic root diameter [OR = 1.030] were significant risk factors for ATa occurrence. This is the first study to establish a correlation between RDW and Pwd in the occurrence of ATa; however, further prospective studies using large cohorts are required to validate the correlation. PMID:26221382
NASA Astrophysics Data System (ADS)
Harb, M. S.; Yuan, F. G.
2015-03-01
Conventional ultrasound inspection has been a standard non-destructive testing method for providing an in-service evaluation and noninvasive means of probing the interior of a structure. In particular, measurement of the propagation characteristics of Lamb waves allows inspection of plates that are typical components in aerospace industry. A rapid, complete non-contact hybrid approach for excitation and detection of Lamb waves is presented and applied for non-destructive evaluation of composites. An air-coupled transducer (ACT) excites ultrasonic waves on the surface of a composite plate, generating different propagating Lamb wave modes and a laser Doppler vibrometer (LDV) is used to measure the out-of-plane velocity of the plate. This technology, based on direct waveform imaging, focuses on measuring dispersive curves for A0 mode in a composite laminate and its anisotropy. A two-dimensional fast Fourier transform (2D-FFT) is applied to out-of-plane velocity data captured experimentally using LDV to go from the time-spatial domain to frequency-wavenumber domain. The result is a 2D array of amplitudes at discrete frequencies and wavenumbers for A0 mode in a given propagation direction along the composite. The peak values of the curve are then used to construct frequency wavenumber and phase velocity dispersion curves, which are also obtained directly using Snell's law and the incident angle of the excited ultrasonic waves. A high resolution and strong correlation between numerical and experimental results are observed for dispersive curves with Snell's law method in comparison to 2D-FFT method. Dispersion curves as well as velocity curves for the composite plate along different directions of wave propagation are measured. The visual read-out of the dispersion curves at different propagation directions as well as the phase velocity curves provide profiling and measurements of the composite anisotropy. The results proved a high sensitivity of the air-coupled and laser
Extended-MHD modeling of diamagnetic-drift tearing instabilities
NASA Astrophysics Data System (ADS)
King, Jacob; Kruger, Scott
2012-03-01
We use analytics and computations with the NIMROD code to examine tearing stability in large-guide-field slab cases with a nonzero equilibrium pressure gradient. A well known result from drift-reduced MHD is the diamagnetic drift associated with the pressure gradient has a stabilizing influence were the dispersion relation becomes (γ+iφ*e)^3γ(γ+iφ*i)=γrMHD^5 [1]. Here φ*i and φ*e are the ion- and electron-diamagnetic frequencies and γrMHD is the tearing growth rate with a resistive-MHD model. Preliminary computational results with an unreduced extended-MHD model do not produce the expected drift-reduced result. For moderate values of φ*i (φ*i<=3γrMHD), the computations follow the dispersion relation that would result if the ∇pe term were not included in the drift-reduced parallel Ohm's law: (γ+iφ*e)^4(γ+iφ*i)=γrMHD^5. Analytics, guided by computational diagnostics, are used to examine the significant terms in the flux evolution equation and investigate the discrepancy with the drift-reduced result.[4pt] [1] For example Coppi, PoF 7, 1501 (1964); Biskamp, NF 18, 1059 (1978).
Predoi, Mihai Valentin
2014-09-01
The dispersion curves for hollow multilayered cylinders are prerequisites in any practical guided waves application on such structures. The equations for homogeneous isotropic materials have been established more than 120 years ago. The difficulties in finding numerical solutions to analytic expressions remain considerable, especially if the materials are orthotropic visco-elastic as in the composites used for pipes in the last decades. Among other numerical techniques, the semi-analytical finite elements method has proven its capability of solving this problem. Two possibilities exist to model a finite elements eigenvalue problem: a two-dimensional cross-section model of the pipe or a radial segment model, intersecting the layers between the inner and the outer radius of the pipe. The last possibility is here adopted and distinct differential problems are deduced for longitudinal L(0,n), torsional T(0,n) and flexural F(m,n) modes. Eigenvalue problems are deduced for the three modes classes, offering explicit forms of each coefficient for the matrices used in an available general purpose finite elements code. Comparisons with existing solutions for pipes filled with non-linear viscoelastic fluid or visco-elastic coatings as well as for a fully orthotropic hollow cylinder are all proving the reliability and ease of use of this method.
Dispersive shock waves in the Kadomtsev-Petviashvili and two dimensional Benjamin-Ono equations
NASA Astrophysics Data System (ADS)
Ablowitz, Mark J.; Demirci, Ali; Ma, Yi-Ping
2016-10-01
Dispersive shock waves (DSWs) in the Kadomtsev-Petviashvili (KP) equation and two dimensional Benjamin-Ono (2DBO) equation are considered using step like initial data along a parabolic front. Employing a parabolic similarity reduction exactly reduces the study of such DSWs in two space one time (2 + 1) dimensions to finding DSW solutions of (1 + 1) dimensional equations. With this ansatz, the KP and 2DBO equations can be exactly reduced to the cylindrical Korteweg-de Vries (cKdV) and cylindrical Benjamin-Ono (cBO) equations, respectively. Whitham modulation equations which describe DSW evolution in the cKdV and cBO equations are derived and Riemann type variables are introduced. DSWs obtained from the numerical solutions of the corresponding Whitham systems and direct numerical simulations of the cKdV and cBO equations are compared with very good agreement obtained. In turn, DSWs obtained from direct numerical simulations of the KP and 2DBO equations are compared with the cKdV and cBO equations, again with good agreement. It is concluded that the (2 + 1) DSW behavior along self similar parabolic fronts can be effectively described by the DSW solutions of the reduced (1 + 1) dimensional equations.
Hass, Roland; Munzke, Dorit; Ruiz, Salomé Vargas; Tippmann, Johannes; Reich, Oliver
2015-04-01
In turbid biogenic liquid material, like blood or milk, quantitative optical analysis is often strongly hindered by multiple light scattering resulting from cells, particles, or droplets. Here, optical attenuation is caused by losses due to absorption as well as scattering of light. Fiber-based Photon Density Wave (PDW) spectroscopy is a very promising method for the precise measurement of the optical properties of such materials. They are expressed as absorption and reduced scattering coefficients (μ a and μ s', respectively) and are linked to the chemical composition and physical properties of the sample. As a process analytical technology, PDW spectroscopy can sense chemical and/or physical processes within such turbid biogenic liquids, providing new scientific insight and process understanding. Here, for the first time, several bioprocesses are analyzed by PDW spectroscopy and the resulting optical coefficients are discussed with respect to established mechanistic models of the chosen processes. As model systems, enzymatic casein coagulation in milk, temperature-induced starch hydrolysis in beer mash, and oxy- as well as deoxygenation of human donor blood were investigated by PDW spectroscopy. The findings indicate that also for very complex biomaterials (i.e., not well-defined model materials like monodisperse polymer dispersions), obtained optical coefficients allow for the assessment of a structure/process relationship and thus for a new analytical access to biogenic liquid material. This is of special relevance as PDW spectroscopy data are obtained without any dilution or calibration, as often found in conventional spectroscopic approaches.
Dispersion, dissipation and refraction of shock waves in acoustically treated turbofan inlets
NASA Astrophysics Data System (ADS)
Prasad, Dilip; Li, Ding; A. Topol, David
2015-09-01
This paper describes a numerical investigation of the effects of the inlet duct liner on the acoustics of a high-bypass ratio turbofan rotor operating at supersonic tip relative flow conditions. The near field of the blade row is then composed of periodic shocks that evolve spatially both because of the varying mean flow and because of the presence of acoustic treatment. The evolution of this shock system is studied using a Computational Fluid Dynamics-based method incorporating a wall impedance boundary condition. The configuration examined is representative of a fan operating near the takeoff condition. The behavior of the acoustic power and the associated waveforms reveal that significant dispersion occurs to the extent that there are no shocks in the perturbation field leaving the entrance plane of the duct. The effect of wave refraction due to the high degree of shear in the mean flow near the entrance plane of the inlet is examined, and numerical experiments are conducted to show that the incorporation of liners in this region can be highly beneficial. The implications of these results for the design of aircraft engine acoustic liners are discussed.
MHD shocks in coronal mass ejections
NASA Technical Reports Server (NTRS)
Steinolfson, R. S.
1991-01-01
The primary objective of this research program is the study of the magnetohydrodynamic (MHD) shocks and nonlinear simple waves produced as a result of the interaction of ejected lower coronal plasma with the ambient corona. The types of shocks and nonlinear simple waves produced for representative coronal conditions and disturbance velocities were determined. The wave system and the interactions between the ejecta and ambient corona were studied using both analytic theory and numerical solutions of the time-dependent, nonlinear MHD equations. Observations from the SMM coronagraph/polarimeter provided both guidance and motivation and are used extensively in evaluating the results. As a natural consequence of the comparisons with the data, the simulations assisted in better understanding the physical interactions in coronal mass ejections (CME's).
Zhu, Xuefeng; Li, Kun; Zhang, Peng; Zhu, Jie; Zhang, Jintao; Tian, Chao; Liu, Shengchun
2016-01-01
The ability to slow down wave propagation in materials has attracted significant research interest. A successful solution will give rise to manageable enhanced wave–matter interaction, freewheeling phase engineering and spatial compression of wave signals. The existing methods are typically associated with constructing dispersive materials or structures with local resonators, thus resulting in unavoidable distortion of waveforms. Here we show that, with helical-structured acoustic metamaterials, it is now possible to implement dispersion-free sound deceleration. The helical-structured metamaterials present a non-dispersive high effective refractive index that is tunable through adjusting the helicity of structures, while the wavefront revolution plays a dominant role in reducing the group velocity. Finally, we numerically and experimentally demonstrate that the helical-structured metamaterials with designed inhomogeneous unit cells can turn a normally incident plane wave into a self-accelerating beam on the prescribed parabolic trajectory. The helical-structured metamaterials will have profound impact to applications in explorations of slow wave physics. PMID:27198887
Greer, Colleen D; Hodson, Peter V; Li, Zhengkai; King, Thomas; Lee, Kenneth
2012-06-01
Tests of crude oil toxicity to fish are often chronic, exposing embryos from fertilization to hatch to oil solutions prepared using standard mixing procedures. However, during oil spills, fish are not often exposed for long periods and the dynamic nature of the ocean is not easily replicated in the lab. Our objective was to determine if brief exposures of Atlantic herring (Clupea harengus) embryos to dispersed oil prepared by standard mixing procedures was as toxic as oil dispersed in a more realistic model system. Embryos were first exposed to chemically dispersed Alaska North Slope crude and Arabian light crude oil for 2.4 h to 14 d from fertilization to determine if exposure time affected toxicity. Toxicity increased with exposure time, but 2.4-h exposures at realistic concentrations of oil induced blue-sac disease and reduced the percentage of normal embryos at hatch; there was little difference in toxicity between the two oils. Secondly, oil was chemically dispersed in a wave tank to determine if the resultant oil solutions were as toxic to herring embryos as laboratory-derived dispersed oil using a single exposure period of 24 h. Samples taken 15 min postdispersion were more toxic than laboratory-prepared solutions, but samples taken at 5, 30, and 60 min postdispersion were less toxic. Overall, the laboratory- and wave tank-derived solutions of dispersed oil provided similar estimates of toxicity despite differences in the methods for preparing test solutions, suggesting that laboratory and wave tank data are a reliable basis for ecological risk assessments of spilled oil.
NASA Astrophysics Data System (ADS)
Li, Jin Hua; Chan, Hiu Ning; Chiang, Kin Seng; Chow, Kwok Wing
2015-11-01
Breathers and rogue waves of special coupled nonlinear Schrödinger systems (the Manakov equations) are studied analytically. These systems model the orthogonal polarization modes in an optical fiber with randomly varying birefringence. Studies earlier in the literature had shown that rogue waves can occur in these Manakov systems with dispersion and nonlinearity of opposite signs, and that the criterion for the existence of rogue waves correlates closely with the onset of modulation instability. In the present work the Hirota bilinear transform is employed to calculate the breathers (pulsating modes), and rogue waves are obtained as a long wave limit of such breathers. In terms of wave profiles, a 'black' rogue wave (intensity dropping to zero) and the transition to a four-petal configuration are elucidated analytically. Sufficiently strong modulation instabilities of the background may overwhelm or mask the development of the rogue waves, and such thresholds are correlated to actual physical properties of optical fibers. Numerical simulations on the evolution of breathers are performed to verify the prediction of the analytical formulations.
Dave, Utsav D; Ciret, Charles; Gorza, Simon-Pierre; Combrie, Sylvain; De Rossi, Alfredo; Raineri, Fabrice; Roelkens, Gunther; Kuyken, Bart
2015-08-01
We demonstrate the generation of an octave-spanning supercontinuum in InGaP membrane waveguides on a silicon substrate pumped by a 1550-nm femtosecond source. The broadband nature of the supercontinuum in these dispersion-engineered high-index-contrast waveguides is enabled by dispersive wave generation on both sides of the pump as well as by the low nonlinear losses inherent to the material. We also measure the coherence properties of the output spectra close to the pump wavelength and find that the supercontinuum is highly coherent at least in this wavelength range.
Aseeva, N. V. Gromov, E. M.; Tyutin, V. V.
2015-12-15
The dynamics of high-frequency field solitons is considered using the extended nonhomogeneous nonlinear Schrödinger equation with induced scattering from damped low-frequency waves (pseudoinduced scattering). This scattering is a 3D analog of the stimulated Raman scattering from temporal spatially homogeneous damped low-frequency modes, which is well known in optics. Spatial inhomogeneities of secondorder linear dispersion and cubic nonlinearity are also taken into account. It is shown that the shift in the 3D spectrum of soliton wavenumbers toward the short-wavelength region is due to nonlinearity increasing in coordinate and to decreasing dispersion. Analytic results are confirmed by numerical calculations.
NASA Technical Reports Server (NTRS)
Maruschek, Joseph W.; Kory, Carol L.; Wilson, Jeffrey D.
1993-01-01
The frequency-phase dispersion and Pierce on-axis interaction impedance of a ferruled, coupled-cavity, traveling-wave tube (TWT), slow-wave circuit were calculated using the three-dimensional simulation code Micro-SOS. The utilization of the code to reduce costly and time-consuming experimental cold tests is demonstrated by the accuracy achieved in calculating these parameters. A generalized input file was developed so that ferruled coupled-cavity TWT slow-wave circuits of arbitrary dimensions could be easily modeled. The practicality of the generalized input file was tested by applying it to the ferruled coupled-cavity slow-wave circuit of the Hughes Aircraft Company model 961HA TWT and by comparing the results with experimental results.
Kudlinski, A; Pureur, V; Bouwmans, G; Mussot, A
2008-11-01
We study the effect of stimulated Raman scattering on four-wave mixing sidebands generated by pumping in the normal dispersion regime of a photonic crystal fiber. Q-switch nanosecond pulses at 1064 nm are used to generate signal and idler wavelengths by degenerate four-wave mixing. These three waves generate their own Raman Stokes orders, leading to a broadband supercontinuum.
NASA Astrophysics Data System (ADS)
Raphaldini, Breno; Raupp, Carlos F. M.
2015-01-01
The solar dynamo is known to be associated with several periodicities, with the nearly 11/22 yr cycle being the most pronounced one. Even though these quasiperiodic variations of solar activity have been attributed to the underlying dynamo action in the Sun's interior, a fundamental theoretical description of these cycles is still elusive. Here, we present a new possible direction in understanding the Sun's cycles based on resonant nonlinear interactions among magnetohydrodynamic (MHD) Rossby waves. The WKB theory for dispersive waves is applied to magnetohydrodynamic shallow-water equations describing the dynamics of the solar tachocline, and the reduced dynamics of a resonant triad composed of MHD Rossby waves embedded in constant toroidal magnetic field is analyzed. In the conservative case, the wave amplitudes evolve periodically in time, with periods on the order of the dominant solar activity timescale (~11 yr). In addition, the presence of linear forcings representative of either convection or instabilities of meridionally varying background states appears to be crucial in balancing dissipation and thus sustaining the periodic oscillations of wave amplitudes associated with resonant triad interactions. Examination of the linear theory of MHD Rossby waves embedded in a latitudinally varying mean flow demonstrates that MHD Rossby waves propagate toward the equator in a waveguide from -35° to 35° in latitude, showing a remarkable resemblance to the structure of the butterfly diagram of the solar activity. Therefore, we argue that resonant nonlinear magnetohydrodynamic Rossby wave interactions might significantly contribute to the observed cycles of magnetic solar activity.
NASA Astrophysics Data System (ADS)
Zhang, H.; Fang, H.; Yao, H.; Maceira, M.; van der Hilst, R. D.
2014-12-01
Recently, Zhang et al. (2014, Pure and Appiled Geophysics) have developed a joint inversion code incorporating body-wave arrival times and surface-wave dispersion data. The joint inversion code was based on the regional-scale version of the double-difference tomography algorithm tomoDD. The surface-wave inversion part uses the propagator matrix solver in the algorithm DISPER80 (Saito, 1988) for forward calculation of dispersion curves from layered velocity models and the related sensitivities. The application of the joint inversion code to the SAFOD site in central California shows that the fault structure is better imaged in the new model, which is able to fit both the body-wave and surface-wave observations adequately. Here we present a new joint inversion method that solves the model in the wavelet domain constrained by sparsity regularization. Compared to the previous method, it has the following advantages: (1) The method is both data- and model-adaptive. For the velocity model, it can be represented by different wavelet coefficients at different scales, which are generally sparse. By constraining the model wavelet coefficients to be sparse, the inversion in the wavelet domain can inherently adapt to the data distribution so that the model has higher spatial resolution in the good data coverage zone. Fang and Zhang (2014, Geophysical Journal International) have showed the superior performance of the wavelet-based double-difference seismic tomography method compared to the conventional method. (2) For the surface wave inversion, the joint inversion code takes advantage of the recent development of direct inversion of surface wave dispersion data for 3-D variations of shear wave velocity without the intermediate step of phase or group velocity maps (Fang et al., 2014, Geophysical Journal International). A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. We will test the new joint
Essama, Bedel Giscard Onana; Atangana, Jacques; Frederick, Biya Motto; Mokhtari, Bouchra; Eddeqaqi, Noureddine Cherkaoui; Kofane, Timoleon Crepin
2014-09-01
We investigate the behavior of the electromagnetic wave that propagates in a metamaterial for negative index regime. Second-order dispersion and cubic-quintic nonlinearities are taken into account. The behavior obtained for negative index regime is compared to that observed for absorption regime. The collective coordinates technique is used to characterize the light pulse intensity profile at some frequency ranges. Five frequency ranges have been pointed out. The perfect combination of second-order dispersion and cubic nonlinearity leads to a robust soliton at each frequency range for negative index regime. The soliton peak power progressively decreases for absorption regime. Further, this peak power also decreases with frequency. We show that absorption regime can induce rogue wave trains generation at a specific frequency range. However, this rogue wave trains generation is maintained when the quintic nonlinearity comes into play for negative index regime and amplified for absorption regime at a specific frequency range. It clearly appears that rogue wave behavior strongly depends on the frequency and the regime considered. Furthermore, the stability conditions of the electromagnetic wave have also been discussed at frequency ranges considered for both negative index and absorption regimes.
NASA Astrophysics Data System (ADS)
Schramm, K. A.; Bilek, S. L.; Patton, H. J.; Abbott, R. E.; Stead, R.; Pancha, A.; White, R.
2009-12-01
Earth structure plays an important role in the generation of seismic waves for all sources. Nowhere is this more evident than at near-surface depths where man-made sources, such as explosions, are conducted. For example, short-period Rayleigh waves (Rg) are excited and propagate in the upper 2 km of Earth's crust. The importance of Rg in the generation of S waves from explosion sources through near-source scattering depends greatly on the shear-wave velocity structure at very shallow depths. Using three distinct datasets, we present a very broadband Rayleigh-wave phase velocity dispersion curve for the Yucca Flat (YF) region of the Nevada Test Site (NTS). The first dataset consists of waveforms of historic NTS explosions recorded on regional seismic networks and will provide information for the lowest frequencies (0.06-0.3 Hz). The second dataset is comprised of waveforms from a non-nuclear explosion on YF recorded at near-local distances and will be used for mid-range frequencies (0.2-1.5 Hz). The third dataset contains high-frequency waveforms recorded from refraction microtremor surveys on YF. This dataset provides information between 1.5 and 60 Hz. Initial results from the high frequency dataset indicate velocities range from 0.45-0.9 km/s at 1.5 Hz and 0.25-0.45 km/s at 60 Hz. The broadband nature of the dispersion curve will allow us to invert for the shear-wave velocity structure to 10 km depth, with focus on shallow depths where nuclear tests were conducted in the YF region. The velocity model will be used by researchers as a tool to aid the development of new explosion source models that incorporate shear wave generation. The new model can also be used to help improve regional distance yield estimation and source discrimination for small events.
Askari, Nasim; Eslami, Esmaeil; Mirzaie, Reza
2015-11-15
The photonic band gap of obliquely incident terahertz electromagnetic waves in a one-dimensional plasma photonic crystal is studied. The periodic structure consists of lossless dielectric and inhomogeneous plasma with a parabolic density profile. The dispersion relation and the THz wave transmittance are analyzed based on the electromagnetic equations and transfer matrix method. The dependence of effective plasma frequency and photonic band gap characteristics on dielectric and plasma thickness, plasma density, and incident angle are discussed in detail. A theoretical calculation for effective plasma frequency is presented and compared with numerical results. Results of these two methods are in good agreement.
Di, Kai; Zhang, Vanessa Li; Lim, Hock Siah; Ng, Ser Choon; Kuok, Meng Hau; Qiu, Xuepeng; Yang, Hyunsoo
2015-02-02
Employing Brillouin spectroscopy, strong interfacial Dzyaloshinskii-Moriya interactions have been observed in an ultrathin Pt/CoFeB film. Our micromagnetic simulations show that spin-wave nonreciprocity due to asymmetric surface pinning is insignificant for the 0.8 nm-thick CoFeB film studied. The observed high asymmetry of the monotonic spin wave dispersion relation is thus ascribed to strong Dzyaloshinskii-Moriya interactions present at the Pt/CoFeB interface. Our findings should further enhance the significance of CoFeB as an important material for magnonic and spintronic applications.
Trudel, Ken; Belore, Randy C; Mullin, Joseph V; Guarino, Alan
2010-09-01
This study determined the limiting oil viscosity for chemical dispersion of oil spills under simulated sea conditions in the large outdoor wave tank at the US National Oil Spill Response Test Facility in New Jersey. Dispersant effectiveness tests were completed using crude oils with viscosities ranging from 67 to 40,100 cP at test temperature. Tests produced an effectiveness-viscosity curve with three phases when oil was treated with Corexit 9500 at a dispersant-to-oil ratio of 1:20. The oil viscosity that limited chemical dispersion under simulated at-sea conditions was in the range of 18,690 cP to 33,400 cP. Visual observations and measurements of oil concentrations and droplet size distributions in the water under treated and control slicks correlated well with direct measurements of effectiveness. The dispersant effectiveness versus oil viscosity relationship under simulated at sea conditions at Ohmsett was most similar to those from similar tests made using the Institut Francais du Pétrole and Exxon Dispersant Effectiveness (EXDET) test methods.
Makarov, V A; Petnikova, V M; Shuvalov, V V
2015-09-30
Three unusual classes of particular analytical solutions to a system of four nonlinear equations are found for slowly varying complex amplitudes of circularly polarised components of the electric field. The system describes the self-action and interaction of two elliptically polarised plane waves collinearly propagating in an isotropic medium with second-order frequency dispersion and spatial dispersion of cubic nonlinearity. The solutions correspond to self-consistent combinations of two elliptically polarised cnoidal waves whose mutually orthogonal polarisation components vary in accordance with pairwise identical laws during propagation. At the same time, the amplitudes of the component with the same circular polarisation are proportional to two different elliptic Jacobi functions with the same periods. (nonlinear optical phenomena)
Sun, Ruoyu; Jin, Dongchen; Tan, Fangzhou; Wei, Shouyu; Hong, Chang; Xu, Jia; Liu, Jiang; Wang, Pu
2016-10-03
We report a high-power all-fiber-integrated femtosecond chirped pulse amplification system operating at 1064 nm, which consists of a dispersive wave source, a fiber stretcher, a series of ytterbium-doped amplifiers and a chirped volume Bragg grating (CVBG) compressor. The dispersive wave is generated by an erbium-doped mode-locked fiber laser with frequency shifted to the 1 μm region in a highly nonlinear fiber. With three stages of ytterbium-doped amplification, the average output power is scaled up to 125 W. Through CVBG, the pulse duration is compressed from 525 ps to 566 fs, the average output power of 107 W with a high compression efficiency of 86% is achieved, and the measured repetition rate is 17.57 MHz, corresponding to the peak power of 10.8 MW.
NASA Astrophysics Data System (ADS)
Attygalle, M.; Lim, C.; Nirmalathas, A.
2005-01-01
This paper presents a scheme by which multiple wavelength-division-multiplexed millimeter-wave (mm-wave) signals in the range of 30 GHz can be generated from a single monolithic semiconductor laser for applications in optically fed mm-wave networks or fiber radio networks. The mm-wave signals are generated using dual optical modes separated by a mm-wave frequency, obtained from spectrum slicing the output from a stable multimode hybrid mode-locked semiconductor laser. In this scheme, self-heterodyne detection at a high-speed photodetector achieves the photonic upconversion of low-data-rate signals to mm-wave frequencies without the need for electronic mixing. Experimental results show the generation of up to 14 WDM channels using a single laser. The phase noise of electrical signals generated by photonic upconversion of these signals is less than -94 dBc/Hz at 100-kHz offset frequency across the wavelengths. Also presented is the transmission of 155-Mb/s binary-phase-shift-keyed data signals at 30-GHz frequency over 10 km of single-mode fiber at different wavelengths using dual-mode signals. The results confirm that a bit-error rate of 10-^9 can be easily achieved. The dispersion tolerance of the dual-mode signals is evaluated using simulation and an analytical model and compared with other mm-wave signal generation techniques.
Benisti, D; Strozzi, D J; Gremillet, L
2007-05-08
The kinetic nonlinear dispersion relation, and frequency shift {delta}{omega}{sub srs}, of a plasma wave driven by stimulated Raman scattering (SRS) are presented. Our theoretical calculations are fully electromagnetic, and use an adiabatic expression for the electron susceptibility which accounts for the change in phase velocity as the wave grows. When k{lambda}{sub D} {approx}> 0.35 (k being the plasma wave number and {lambda}{sub D} the Debye length), {delta}{omega}{sub srs} is significantly larger than could be inferred by assuming that the wave is freely propagating. Our theory is in excellent agreement with 1-D Eulerian Vlasov-Maxwell simulations when 0.3 {le} k{lambda}{sub D} {le} 0.58, and allows discussion of previously proposed mechanisms for Raman saturation. In particular, we find that no 'loss of resonance' of the plasma wave would limit the Raman growth rate, and that saturation through a phase detuning between the plasma wave and the laser drive is mitigated by wave number shifts.
NASA Astrophysics Data System (ADS)
Beghein, C.; Lebedev, S.; van der Hilst, R.
2005-12-01
Interstation dispersion curves can be used to obtain regional 1D profiles of the crust and upper mantle. Unlike phase velocity maps, dispersion curves can be determined with small errors and for a broad frequency band. We want to determine what features interstation surface wave dispersion curves can constrain. Using synthetic data and the Neighbourhood Algorithm, a direct search approach that provides a full statistical assessment of model uncertainites and trade-offs, we investigate how well crustal and upper mantle structure can be recovered with fundamental Love and Rayleigh waves. We also determine how strong are the trade-offs between the different parameters and what depth resolution can we expect to achieve with the current level of precision of this type of data. Synthetic dispersion curves between approximately 7 and 340s were assigned realistic error bars, i.e. an increase of the relative uncertainty with the period but with an amplitude consistent with the one achieve in ``real'' measurements. These dispersion curves were generated by two types of isotropic model differing only by their crustal structure. One represents an oceanic region (shallow Moho) and the other corresponds to an archean continental area with a larger Moho depth. Preliminary results show that while the Moho depth, the shear-velocity structure in the transition zone, between 200 and 410km depth, and between the base of the crust and 50km depth are generally well recovered, crustal structure and Vs between between 50 and 200km depth are more difficult to constrain with Love waves or Rayleigh waves alone because of some trade-off between the two layers. When these two layers are put together, the resolution of Vs between 50 and 100km depth apperas to improve. Stucture deeper than the transition zone is not constrained by the data because of a lack of sensitivity. We explore the possibility of differentiating between an upper and lower crust as well, and we investigate whether a joint
2011-09-30
anisotropic turbulence and dispersive waves in different environments , test them, compare them with data and implement them in ocean models. In this project...stratification and/or a solid body rotation. We have also performed computer simulations with an idealized circulation model of quasi-two-dimensional...member of a team on Martian planetary boundary layer at the International Space Science Institute and was responsible for reviewing turbulence models
Colman, Pierre; Cestier, Isabelle; Willinger, Amnon; Combrié, Sylvain; Lehoucq, Gaëlle; Eisenstein, Gadi; De Rossi, Alfredo
2011-07-15
We investigate four-wave mixing (FWM) in GaInP 1.5 mm long dispersion engineered photonic crystal waveguides. We demonstrate an 11 nm FWM bandwidth in the CW mode and a conversion efficiency of -24 dB in the quasi-CW mode. For picosecond pump and probe pulses, we report a 3 dB parametric gain and nearly a -5 dB conversion efficiency at watt-level peak pump powers.
Chow, K K; Shu, C; Lin, Chinlon; Bjarklev, A
2005-10-31
We demonstrate extinction ratio improvement by using pump-modulated four-wave mixing in a dispersion-flattened nonlinear photonic crystal fiber. A 6-dB improvement in the extinction ratio of a degraded return-to-zero signal has been achieved. A power penalty improvement of 3 dB at 10(-9) bit-error-rate level is obtained in the 10 Gb/s bit-error-rate measurements.
NASA Astrophysics Data System (ADS)
Li, Xiaobo; Dong, Liangguo; Zhao, Qun
2014-12-01
Seismic wave propagation in patchy-saturated porous media is studied by numerical simulation in time domain at the seismic frequency band (1-1000 Hz). The models consist of hundreds of representative elementary volumes (REVs), where the REV is partially saturated with water and gas pockets. Seismic modelling experiments are implemented in a traditional way, with ‘periodic’ boundary conditions applied to get rid of undrained boundary conditions at the outer edges of the REVs. The characteristics of confining pressure, induced pore pressure, solid particle velocities and Darcy filtration velocities are analysed. The snapshots show that strong pore pressure gradients are generated across the interface between gas and water phases, and significant fluid flow occurs. The conversion of a fast P-wave into a dissipating slow P-wave takes place at seismic frequencies, and the converted slow P-wave diffuses strongly in both gas- and water-saturated phases. These numerical results can help us to understand the loss mechanism at seismic frequencies. Then, P-wave attenuation and velocity dispersion of a heterogeneous REV are calculated during traditional seismic modelling at seismic frequencies. The numerical results show good agreement with theoretical predictions obtained from patchy saturation theory. Furthermore, the effects of different fluid distributions on P-wave attenuation and velocity dispersion are analysed numerically. A series of experiments are implemented by considering large, small and random gas-patchy inclusions. The decrease of gas pocket size makes the peak frequency move towards high frequencies. Random distribution of gas patches may affect both the peak attenuation and peak frequencies. Seismic attenuation caused by Biot global flow, elastic scattering and wave-induced fluid flow (WIFF) associated with patchy saturation are computed numerically. The results show that the contribution of Biot’s global flow and scattering to the overall attenuation
Hummel, David; Ivan, Lucian
2017-03-15
A "dirty bomb" is a type of radiological dispersal device (RDD) that has been the subject of significant safety and security concerns given the disruption that would result from a postulated terrorist attack. Assessing the risks of radioactive dose in a hypothetical scenario requires models that can accurately predict dispersion in a realistic environment. Modelling a RDD is complicated by the fact that the most important phenomena occur over vastly disparate spatial and temporal length scales. Particulate dispersion in the air is generally considered on scales of hundreds to thousands of meters, and over periods of minutes and hours. Dispersion models are extremely sensitive, however, to the particle size and source characterization, which are determined in distances measured in micrometers to meters, over milliseconds or less. This study examines the extent to which the explosive blast determines the transport of contaminant particles relative to the atmospheric wind over distances relevant to "near-field" dispersion problems (i.e., hundreds of meters), which are relevant to urban environments. Our results indicate that whether or not the effect of the blast should be included in a near-field dispersion model is largely dependent on the size of the contaminant particle. Relatively large particles (i.e., >40 μm in diameter), which are most likely to be produced by a RDD, penetrate the leading shock front, thereby avoiding the reverse blast wind. Consequently, they travel much farther than suspended aerosols (<10 μm) before approaching the ambient wind velocity. This suggests that, for these "near-field" dispersion problems in urban environments, the transport of contaminants from the blast wave may be integral to accurately predicting their dispersion.
Esfandyari-Kalejahi, A.; Ebrahimi, V.
2014-03-15
We have derived generalized dispersion relations for longitudinal waves in collisionless thermal plasma using linear Vlasov-Poisson kinetic model and nonextensive distributions for electrons. The Maxwellian limit of the dispersion relations, where the q-nonextensive parameter tends to one, is calculated. The generalized dispersion relations are reduced to polynomials for some specific values of q. The well-known modes of oscillations such as the Langmuir and electron acoustic waves have been obtained by solving the dispersion relations. Some new modes of oscillation are also found. Finally, the dependence of the oscillation modes and damps on q is discussed.
Kim, Young H; Song, Sung-Jin; Kwon, Sung-Duk; Cheong, Yong-Moo; Jung, Hyun-Kyu
2004-04-01
A plate of Inconel 600 was interrogated using the resonant ultrasound spectroscopy (RUS) and the reflected leaky Lamb waves (LLW). It was found that the plate used in the present work has anisotropy in its material properties by the RUS. The longitudinal and the transverse wave velocities of the Inconel 600 plate were determined by the RUS, ultrasonic pulse-echo method and cut-off frequencies of the LLWs. The wave velocities in the direction of thickness determined by the RUS under the assumption of the orthotropic symmetry were quite similar to those obtained by other methods, the pulse-echo method and from cut-off frequencies. The reflected LLW from the plate was measured with varying the incident angle. The dispersion curves obtained from the reflected LLWs show good agreement with the theoretical calculation in general. The mismatches may be caused by anisotropy of the plate.
Guo, Xiao; Wei, Peijun; Lan, Man; Li, Li
2016-08-01
The effects of functionally graded interlayers on dispersion relations of elastic waves in a one-dimensional piezoelectric/piezomagnetic phononic crystal are studied in this paper. First, the state transfer equation of the functionally graded interlayer is derived from the motion equation by the reduction of order (from second order to first order). The transfer matrix of the functionally graded interlayer is obtained by solving the state transfer equation with the spatial-varying coefficient. Based on the transfer matrixes of the piezoelectric slab, the piezomagnetic slab and the functionally graded interlayers, the total transfer matrix of a single cell is obtained. Further, the Bloch theorem is used to obtain the resultant dispersion equations of in-plane and anti-plane Bloch waves. The dispersion equations are solved numerically and the numerical results are shown graphically. Five kinds of profiles of functionally graded interlayers between a piezoelectric slab and a piezomagnetic slab are considered. It is shown that the functionally graded interlayers have evident influences on the dispersion curves and the band gaps.
NASA Astrophysics Data System (ADS)
Kim, K. Y.; Jeon, K. M.; Hong, M. H.; Park, Young-gyu
2011-02-01
To locate anomalous features including seepage pathways through the Daeryong earth-fill dam, P and Rayleigh waves were recorded along a 250-m profile on the crest of the dam. Seismic energy was generated using a 5-kg sledgehammer and detected by 24 4.5-Hz vertical-axis geophones installed at 3-m intervals. P-wave and apparent S-wave velocities of the reservoir dam and underlying bedrock were then inverted from first-arrival traveltimes and dispersion curves of Rayleigh waves, respectively. Apparent dynamic Poisson's ratios as high as 0.46 were obtained at the base of the dam near its north-east end, where an outlet conduit occurs, and in the clay core body near the south-west end of the profile where the dam was repeatedly grouted to abate seepage before our survey. These anomalies of higher Poisson's ratios in the upper part of clay core were also associated with effusion of grout on the downstream slope of the dam during post-survey grouting to abate leakage. Combining P-wave traveltime tomography and inversion of Rayleigh wave velocities was very effective in detecting potential pathways for seepage and previous grouted zones in this earthen dam.
C Kubrusly, Alan; M B Braga, Arthur; von der Weid, Jean Pierre
2016-10-01
The propagation speed of ultrasonic waves in pre-stressed media can be evaluated either at the natural or initial frames of reference. In this paper general equations that can be applied to the partial wave technique are presented in order to obtain the dispersion spectra of acoustoelastic Lamb waves in anisotropic plates in either frame of reference. Employing these equations, dispersion curves for the fundamental modes in a pre-stressed transversely isotropic aluminum plate were numerically obtained in both reference frames under longitudinal and transverse loading with the material transverse axis along each of the Cartesian directions, as well as the propagation along a non-principal direction. Results confirm that due to the material natural anisotropy, the speed variation depends not only on the pre-stress direction but also on the material orientation as well as on the polarization of the propagating mode. Similar to bulk waves, the relationship between the speed at the natural and initial frames is a function of the load direction.
NASA Astrophysics Data System (ADS)
Islam, Md. Saiful; Sultana, Jakeya; Rana, Sohel; Islam, Mohammad Rakibul; Faisal, Mohammad; Kaijage, Shubi F.; Abbott, Derek
2017-03-01
In this paper, we present a porous-core circular photonic crystal fiber (PC-CPCF) with ultra-low material loss for efficient terahertz wave transmission. The full vector finite element method with an ideally matched layer boundary condition is used to characterize the wave guiding properties of the proposed fiber. At an operating frequency of 1 THz, simulated results exhibit an extremely low effective material loss of 0.043 cm-1, higher core power fraction of 47% and ultra-flattened dispersion variation of 0.09 ps/THz/cm. The effects of important design properties such as single mode operation, confinement loss and effective area of the fiber are investigated in the terahertz regime. Moreover, the proposed fiber can be fabricated using the capillary stacking or sol-gel technique and be useful for long distance transmission of terahertz waves.
NASA Astrophysics Data System (ADS)
Zhang, H.; Thurber, C. H.; Maceira, M.; Roux, P.
2013-12-01
The crust around the San Andreas Fault Observatory at depth (SAFOD) has been the subject of many geophysical studies aimed at characterizing in detail the fault zone structure and elucidating the lithologies and physical properties of the surrounding rocks. Seismic methods in particular have revealed the complex two-dimensional (2D) and three-dimensional (3D) structure of the crustal volume around SAFOD and the strong velocity reduction in the fault damage zone. In this study we conduct a joint inversion using body-wave arrival times and surface-wave dispersion data to image the P-and S-wave velocity structure of the upper crust surrounding SAFOD. The two data types have complementary strengths - the body-wave data have good resolution at depth, albeit only where there are crossing rays between sources and receivers, whereas the surface waves have very good near-surface resolution and are not dependent on the earthquake source distribution because they are derived from ambient noise. The body-wave data are from local earthquakes and explosions, comprising the dataset analyzed by Zhang et al. (2009). The surface-wave data are for Love waves from ambient noise correlations, and are from Roux et al. (2011). The joint inversion code is based on the regional-scale version of the double-difference (DD) tomography algorithm tomoDD. The surface-wave inversion code that is integrated into the joint inversion algorithm is from Maceira and Ammon (2009). The propagator matrix solver in the algorithm DISPER80 (Saito, 1988) is used for the forward calculation of dispersion curves from layered velocity models. We examined how the structural models vary as we vary the relative weighting of the fit to the two data sets and in comparison to the previous separate inversion results. The joint inversion with the 'optimal' weighting shows more clearly the U-shaped local structure from the Buzzard Canyon Fault on the west side of SAF to the Gold Hill Fault on the east side.
NASA Astrophysics Data System (ADS)
Hoefer, Mark A.
This thesis examines nonlinear wave phenomena, in two physical systems: a Bose-Einstein condensate (BEC) and thin film ferromagnets where the magnetization dynamics are excited by the spin momentum transfer (SMT) effect. In the first system, shock waves generated by steep gradients in the BEC wavefunction are shown to be of the disperse type. Asymptotic and averaging methods are used to determine shock speeds and structure in one spatial dimension. These results are compared with multidimensional numerical simulations and experiment showing good, qualitative agreement. In the second system, a model of magnetization dynamics due to SMT is presented. Using this model, nonlinear oscillating modes---nano-oscillators---are found numerically and analytically using perturbative methods. These results compare well with experiment. A Bose-Einstein condensate (BEC) is a quantum fluid that gives rise to interesting shock wave nonlinear dynamics. Experiments depict a BEC that exhibits behavior similar to that of a shock wave in a compressible gas, e.g. traveling fronts with steep gradients. However, the governing Gross-Pitaevskii (GP) equation that describes the mean field of a BEC admits no dissipation hence classical dissipative shock solutions do not explain the phenomena. Instead, wave dynamics with small dispersion is considered and it is shown that this provides a mechanism for the generation of a dispersive shock wave (DSW). Computations with the GP equation are compared to experiment with excellent agreement. A comparison between a canonical 1D dissipative and dispersive shock problem shows significant differences in shock structure and shock front speed. Numerical results associated with laboratory experiments show that three and two-dimensional approximations are in excellent agreement and one dimensional approximations are in qualitative agreement. The interaction of two DSWs is investigated analytically and numerically. Using one dimensional DSW theory it is argued
NASA Astrophysics Data System (ADS)
Faccio, Daniele; Clerici, Matteo; Averchi, Alessandro; Lotti, Antonio; Jedrkiewicz, Ottavia; Dubietis, Audrius; Tamosauskas, Gintaras; Couairon, Arnaud; Bragheri, Francesca; Papazoglou, Dimitris; Tzortzakis, Stelios; di Trapani, Paolo
2008-09-01
We study ultrashort laser-pulse propagation and filamentation dynamics in dispersive Kerr media. We identify the regime for which the filamentation threshold (Pth) is considerably higher than the critical power (Pcr) for monochromatic beam collapse in pure Kerr media. In particular, we compare the threshold for the formation of filaments with that for the formation of X -waves. At powers Pcr
dispersion, and no filaments or X -waves are formed. At P⩾Pth , we observe X -wave formation and a weak filamentation regime. At P≫Pth , we observe both X -waves and fully formed filaments.
On Wave-Ice Interaction in the Arctic Marginal Ice Zone: Dispersion, Attenuation, and Ice Response
2016-06-01
transfer ) equation: D Dt =� 3 This describes the conservation of wave action (spectral density divided by frequency) where... energy as waves interact with ice. These mechanisms are typically split into two broad categories: 1) conservative (Sice,c) and (2) non-conservative...many individual mechanisms of wave ice interaction and thus, like attenuation, is bulk property. Whereas the mechanisms described above are
Interstellar MHD Turbulence and Star Formation
NASA Astrophysics Data System (ADS)
Vázquez-Semadeni, Enrique
This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior, causing it to behave approximately isobarically, in spite of spanning several orders of magnitude in density and temperature. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability (TI) in the atomic gas and of moderately-to-strongly supersonic motions in the roughly isothermal cold atomic and molecular components. Within this context, we discuss: (1) the production and statistical distribution of turbulent density fluctuations in both isothermal and polytropic media; (2) the nature of the clumps produced by TI, noting that, contrary to classical ideas, they in general accrete mass from their environment in spite of exhibiting sharp discontinuities at their boundaries; (3) the density-magnetic field correlation (and, at low densities, lack thereof) in turbulent density fluctuations, as a consequence of the superposition of the different wave modes in the turbulent flow; (4) the evolution of the mass-to-magnetic flux ratio (MFR) in density fluctuations as they are built up by dynamic compressions; (5) the formation of cold, dense clouds aided by TI, in both the hydrodynamic (HD) and the magnetohydrodynamic (MHD) cases; (6) the expectation that star-forming molecular clouds are likely to be undergoing global gravitational contraction, rather than being near equilibrium, as generally believed, and (7) the regulation of the star formation rate (SFR) in such gravitationally contracting clouds by stellar feedback which, rather than keeping the clouds from collapsing, evaporates and disperses
Yamamoto, Takashi; Mori, Takayoshi; Sakamoto, Taiji; Kurokawa, Kenji; Tomita, Shigeru; Tsubokawa, Makoto
2010-09-20
We show that any optical pulse train recovers its original waveform after passing through a group velocity dispersion (GVD) device when the total GVD value of the device is equal to an integral multiple of 1/(2πf(rep)(2)), where f(rep) is the repetition rate of the optical pulse train. In addition, we detail our proposed GVD measurement method, or optical phase-modulation (PM) method, which utilizes a sinusoidally PM continuous wave (CW) light as a probe light. The total GVD B(2) of a device under test (DUT) is derived by using a very simple equation, |B(2)|=1/(2πf(null)(2)), where f(null) is the smallest modulation frequency at which the sinusoidally PM light becomes CW light again after passing through the DUT.
NASA Astrophysics Data System (ADS)
Helfenstein-Didier, C.; Andrade, R. J.; Brum, J.; Hug, F.; Tanter, M.; Nordez, A.; Gennisson, J.-L.
2016-03-01
The shear wave velocity dispersion was analyzed in the Achilles tendon (AT) during passive dorsiflexion using a phase velocity method in order to obtain the tendon shear modulus (C 55). Based on this analysis, the aims of the present study were (i) to assess the reproducibility of the shear modulus for different ankle angles, (ii) to assess the effect of the probe locations, and (iii) to compare results with elasticity values obtained with the supersonic shear imaging (SSI) technique. The AT shear modulus (C 55) consistently increased with the ankle dorsiflexion (N = 10, p < 0.05). Furthermore, the technique showed a very good reproducibility (all standard error of the mean values <10.7 kPa and all coefficient of variation (CV) values ⩽0.05%). In addition, independently from the ankle dorsiflexion, the shear modulus was significantly higher in the proximal location compared to the more distal one. The shear modulus provided by SSI was always lower than C55 and the difference increased with the ankle dorsiflexion. However, shear modulus values provided by both methods were highly correlated (R = 0.84), indicating that the conventional shear wave elastography technique (SSI technique) can be used to compare tendon mechanical properties across populations. Future studies should determine the clinical relevance of the shear wave dispersion analysis, for instance in the case of tendinopathy or tendon tear.
NASA Astrophysics Data System (ADS)
Wang, Hsiao-Chuan; Fleming, Simon; Lee, Yung-Chun; Law, Susan; Swain, Michael; Xue, Jing
2009-09-01
Laser ultrasonic nondestructive evaluation (NDE) methods have been proposed to replace conventional in vivo dental clinical diagnosis tools that are either destructive or incapable of quantifying the elasticity of human dental enamel. In this work, a laser NDE system that can perform remote measurements on samples of small dimensions is presented. A focused laser line source is used to generate broadband surface acoustic wave impulses that are detected with a simplified optical fiber interferometer. The measured surface wave velocity dispersion spectrum is in turn used to characterize the elasticity of the specimen. The NDE system and the analysis technique are validated with measurements of different metal structures and then applied to evaluate human dental enamel. Artificial lesions are prepared on the samples to simulate different states of enamel elasticity. Measurement results for both sound and lesioned regions, as well as lesions of different severity, are clearly distinguishable from each other and fit well with physical expectations and theoretical value. This is the first time, to the best of our knowledge, that a laser-based surface wave velocity dispersion technique is successfully applied on human dental enamel, demonstrating the potential for noncontact, nondestructive in vivo detection of the development of carious lesions.
NASA Astrophysics Data System (ADS)
Xia, Ya-Rong; Xin, Xiang-Peng; Zhang, Shun-Li
2017-01-01
This paper mainly discusses the (2+1)-dimensional modified dispersive water-wave (MDWW) system which will be proved nonlinear self-adjointness. This property is applied to construct conservation laws corresponding to the symmetries of the system. Moreover, via the truncated Painlevé analysis and consistent tanh-function expansion (CTE) method, the soliton-cnoidal periodic wave interaction solutions and corresponding images will be eventually achieved. Supported by National Natural Science Foundation of China under Grant Nos. 11371293, 11505090, the Natural Science Foundation of Shaanxi Province under Grant No. 2014JM2-1009, Research Award Foundation for Outstanding Young Scientists of Shandong Province under Grant No. BS2015SF009 and the Science and Technology Innovation Foundation of Xi’an under Grant No. CYX1531WL41
NASA Technical Reports Server (NTRS)
Retallick, F. D.
1980-01-01
Directly-fired, separately-fired, and oxygen-augmented MHD power plants incorporating a disk geometry for the MHD generator were studied. The base parameters defined for four near-optimum-performance MHD steam power systems of various types are presented. The finally selected systems consisted of (1) two directly fired cases, one at 1920 K (2996F) preheat and the other at 1650 K (2500 F) preheat, (2) a separately-fired case where the air is preheated to the same level as the higher temperature directly-fired cases, and (3) an oxygen augmented case with the same generator inlet temperature of 2839 (4650F) as the high temperature directly-fired and separately-fired cases. Supersonic Mach numbers at the generator inlet, gas inlet swirl, and constant Hall field operation were specified based on disk generator optimization. System pressures were based on optimization of MHD net power. Supercritical reheat stream plants were used in all cases. Open and closed cycle component costs are summarized and compared.
Single-arm three-wave interferometer for measuring dispersion of short lengths of fiber.
Galle, Michael A; Mohammed, Waleed S; Qian, Li; Smith, Peter W
2007-12-10
We present a simple fiber-based single-arm spectral interferometer to measure directly the second-order dispersion parameter of short lengths of fiber (< 50 cm). The standard deviation of the measured dispersion on a 39.5-cm-long SMF28(TM) fiber is 1x10(-4) ps/nm, corresponding to 1% relative error, without employing any curve fitting. Our technique measures the second-order dispersion by examining the envelope of the interference pattern produced by three reflections: two from the facets of the test fiber and one from a mirror placed away from the fiber facet at a distance that introduces the same group delay as the test fiber at the measured wavelength. The operational constraints on system parameters, such as required bandwidth, wavelength resolution, and fiber length, are discussed in detail. Experimental verification of this technique is carried out via comparison of measurements of single mode fiber (SMF28(TM)) with published data and via comparison of measurements of a dispersion compensating fiber with those taken using conventional techniques. Moreover, we used this new technique to measure the dispersion coefficient of a 45-cm-long twin-hole fiber over a 70 nm bandwidth. It is the first time dispersion measurement on this specialty fiber is reported.
Laser-powered MHD generators for space application
NASA Technical Reports Server (NTRS)
Jalufka, N. W.
1986-01-01
Magnetohydrodynamic (MHD) energy conversion systems of the pulsed laser-supported detonation (LSD) wave, plasma MHD, and liquid-metal MHD (LMMHD) types are assessed for their potential as space-based laser-to-electrical power converters. These systems offer several advantages as energy converters relative to the present chemical, nuclear, and solar devices, including high conversion efficiency, simple design, high-temperature operation, high power density, and high reliability. Of these systems, the Brayton cycle liquid-metal MHD system appears to be the most attractive. The LMMHD technology base is well established for terrestrial applications, particularly with regard to the generator, mixer, and other system components. However, further research is required to extend this technology base to space applications and to establish the technology required to couple the laser energy into the system most efficiently. Continued research on each of the three system types is recommended.
Ebrahimi, V.; Esfandyari-Kalejahi, A.
2014-09-15
In this paper, first we represent the differences between spatial and temporal dispersions and their dependence on the measurement techniques for electrostatic waves in unmagnetized collisionless plasma. Then, three different experimental data are compared to the solutions of exact nonextensive dispersion relations for electron-ion and pair plasma. The results confirm the existence of new acoustic plasma waves. Furthermore, these comparisons yield a Maxwellian and a nonextensive plasma with nonextensive parameter q larger than one, and a Maxwellian plasma with some abnormal dispersion properties.
Chekroun, M; Le Marrec, L; Abraham, O; Durand, O; Villain, G
2009-12-01
Rayleigh waves measurements are used to characterise cover concrete and mortar in the frequency range 60-180 kHz. At these frequencies, the wavelength is comparable to the size of the aggregates, and waves propagate in a multiple scattering regime. Acquired signals are then difficult to interpret due to an important incoherent part. The method proposed here is the study of the coherent waves, obtained by averaging signals over several configurations of disorder. Coherent waves give information on an equivalent homogeneous medium. To acquire a large amount of measurements with accuracy, an optimised piezoelectric source is used with a laser interferometer for reception. Adapted signal processing technique are presented to evaluate the coherent phase and group velocities and also the coherent attenuation parameter. The sensitivity of these three parameters with the properties of concrete is discussed, as well as the necessity to use coherent waves to obtain accurate results.
Maroof, R.; Ali, S.; Mushtaq, A.; Qamar, A.
2015-11-15
Linear properties of high and low frequency waves are studied in an electron-positron-ion (e-p-i) dense plasma with spin and relativity effects. In a low frequency regime, the magnetohydrodynamic (MHD) waves, namely, the magnetoacoustic and Alfven waves are presented in a magnetized plasma, in which the inertial ions are taken as spinless and non-degenerate, whereas the electrons and positrons are treated quantum mechanically due to their smaller mass. Quantum corrections associated with the spin magnetization and density correlations for electrons and positrons are re-considered and a generalized dispersion relation for the low frequency MHD waves is derived to account for relativistic degeneracy effects. On the basis of angles of propagation, the dispersion relations of different modes are discussed analytically in a degenerate relativistic plasma. Numerical results reveal that electron and positron relativistic degeneracy effects significantly modify the dispersive properties of MHD waves. Our present analysis should be useful for understanding the collective interactions in dense astrophysical compact objects, like, the white dwarfs and in atmosphere of neutron stars.
Yang, Taotao; Shu, Chester; Lin, Chinlon
2005-07-11
We have developed a depolarization technique to achieve polarization-insensitive wavelength conversion using four-wave mixing in an optical fiber. A maximum conversion efficiency of -11.79 dB was achieved over a 3 dB bandwidth of 26 nm in a 100-m-long dispersion-flattened photonic crystal fiber. The polarization-dependent conversion efficiency was less than 0.38 dB and the measured power penalty for a 10 Gbit/s NRZ signal was 1.9 dB. The relation between the conversion efficiency and the degree of polarization of the pump was also formulated.
Symmetry, Statistics and Structure in MHD Turbulence
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2007-01-01
Here, we examine homogeneous MHD turbulence in terms of truncated Fourier series. The ideal MHD equations and the associated statistical theory of absolute equilibrium ensembles are symmetric under P, C and T. However, the presence of invariant helicities, which are pseudoscalars under P and C, dynamically breaks this symmetry. This occurs because the surface of constant energy in phase space has disjoint parts, called components: while ensemble averages are taken over all components, a dynamical phase trajectory is confined to only one component. As the Birkhoff-Khinchin theorem tells us, ideal MHD turbulence is thus non-ergodic. This non-ergodicity manifests itself in low-wave number Fourier modes that have large mean values (while absolute ensemble theory predicts mean values of zero). Therefore, we have coherent structure in ideal MHD turbulence. The level of non-ergodicity and amount of energy contained in the associated coherent structure depends on the values of the helicities, as well as on the presence, or not, of a mean magnetic field and/or overall rotation. In addition to the well known cross and magnetic helicities, we also present a new invariant, which we call the parallel helicity, since it occurs when mean field and rotation axis are aligned. The question of applicability of these results to real (i.e., dissipative) MHD turbulence is also examined. Several long-time numerical simulations on a 64(exp 3) grid are given as examples. It is seen that coherent structure begins to form before decay dominates over nonlinearity. The connection of these results with inverse spectral cascades, selective decay, and magnetic dynamos is also discussed.
Analytic studies of dispersive properties of shear Alfvén and acoustic wave spectra in tokamaks
Chavdarovski, Ilija; Zonca, Fulvio
2014-05-15
The properties of the low frequency shear Alfvén and acoustic wave spectra in toroidal geometry are examined analytically and numerically considering wave particle interactions with magnetically trapped and circulating particles, using the theoretical model described in [I. Chavdarovski and F. Zonca, Plasma Phys. Controlled Fusion 51, 115001 (2009)] and following the framework of the generalized fishbone-like dispersion relation. Effects of trapped particles as well as diamagnetic effects on the frequencies and damping rates of the beta-induced Alfvén eigenmodes, kinetic ballooning modes and beta-induced Alfvén-acoustic eigenmodes are discussed and shown to be crucial to give a proper assessment of mode structure and stability conditions. Present results also demonstrate the mutual coupling of these various branches and suggest that frequency as well as mode polarization are crucial for their identification on the basis of experimental evidence.
Analytic studies of dispersive properties of shear Alfvén and acoustic wave spectra in tokamaks
NASA Astrophysics Data System (ADS)
Chavdarovski, Ilija; Zonca, Fulvio
2014-05-01
The properties of the low frequency shear Alfvén and acoustic wave spectra in toroidal geometry are examined analytically and numerically considering wave particle interactions with magnetically trapped and circulating particles, using the theoretical model described in [I. Chavdarovski and F. Zonca, Plasma Phys. Controlled Fusion 51, 115001 (2009)] and following the framework of the generalized fishbone-like dispersion relation. Effects of trapped particles as well as diamagnetic effects on the frequencies and damping rates of the beta-induced Alfvén eigenmodes, kinetic ballooning modes and beta-induced Alfvén-acoustic eigenmodes are discussed and shown to be crucial to give a proper assessment of mode structure and stability conditions. Present results also demonstrate the mutual coupling of these various branches and suggest that frequency as well as mode polarization are crucial for their identification on the basis of experimental evidence.
NASA Astrophysics Data System (ADS)
Ball, J. S.; Sheehan, A. F.; Stachnik, J. C.; Collins, J. A.
2012-12-01
Surface wave dispersion measurements, receiver functions and seafloor compliance data were jointly inverted to produce shear velocity profiles at Ocean Bottom Seismic (OBS) stations off the South Island of New Zealand. Receiver function analysis of OBS data presents a technical challenge due largely to the presence of multiply scattered reverberations in the water and low-velocity sediments at OBS sites. Teleseismic arrivals from interfaces of tectonic interest are obscured by sediment-converted shear waves and water column multiples. Mitigation of these effects typically requires accurate characterization of sediment layer shear velocities and thicknesses. The seismic properties of the sediment column can be probed using shallow mode-converted shear arrivals and the seafloor's response to ocean loading from infragravity waves (seafloor compliance). Data for this study were acquired in 2009-2010 by the Marine Observations of Anisotropy Near Aotearoa (MOANA) experiment, which deployed 30 broadband OBS and differential pressure gauges (DPGs) off the South Island of New Zealand. Seafloor compliance was calculated from MOANA DPG pressure and OBS vertical component acceleration power spectra at periods between 50-250s. The resulting compliance values range from 10-10-10-8 Pa-1 and are sensitive to changes in shear modulus at depths that increase with forcing period. Receiver functions were estimated using events of high SNR from epicentral distances of 30-90 degrees. Forward modeling utilized full-wavefield synthetic seismograms to account for the OBS location at the boundary between acoustic and elastic media. Rayleigh wave group velocity dispersion curves at periods from 6-30s were derived from ambient noise tomography. A Bayesian Markov Chain Monte Carlo algorithm was implemented to estimate shear velocity profiles, crustal and sediment thicknesses using these combined observations. Preliminary sediment thickness estimates range from 400m on the Challenger plateau to
Anisotropic MHD model and some solutions
Kuznetsov, V. D.; Dzhalilov, N. S.
2010-09-15
MHD waves and instabilities in a collisionless anisotropic-pressure plasma are analyzed in an anisotropic MHD model based on the 16-moment approximation, and the results are found to agree well with those obtained in the low-frequency limit of the kinetic model. It is shown that accounting for heat fluxes leads to an asymmetry in the phase velocities of the wave modes with respect to the heat flux direction and also to a strong interaction between the modes, especially between the backward ones (those that propagate in a direction opposite to that of the heat flux). A correct description of the mirror instability is given. The resonant interaction of three backward modes-fast acoustic, fast magnetosonic, and slow acoustic-under the conditions for the onset of the classical firehose instability triggers a new type of instability the growth rate of which is faster than the maximum growth rate of the conventional firehose instability. The results prove that, in contrast to the familiar Chew-Goldberger-Low approximate model, the anisotropic MHD approach provides a correct description of the large-scale dynamics of collisionless anisotropic plasmas (such as solar corona, solar wind, and ionospheric and magnetospheric plasmas).
Ge Xingjun; Zhong Huihuang; Qian Baoliang; Zhang Jun; Fan Yuwei; Shu Ting; Liu Jinliang
2009-11-15
The method for calculating the dispersion relations of the slow-wave structures (SWSs) with arbitrary geometrical structures is studied in detail by using the Fourier series expansion. In addition, dispersive characteristics and longitudinal resonance properties of the SWSs with the cosinusoidal, trapezoidal, and rectangular corrugations are analyzed by numerical calculation. Based on the above discussion, a comparison on an L-band coaxial relativistic backward wave oscillator (BWO) and an L-band coaxial BWO with a coaxial extractor is investigated in detail with particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). Furthermore, experiments are carried out at the TORCH-01 accelerator under the low guiding magnetic field. At diode voltage of 647 kV, beam current of 9.3 kA, and guiding magnetic field strength of 0.75 T, the microwave is generated with power of 1.07 GW, mode of TM{sub 01}, and frequency of 1.61 GHz. That is the first experimental report of the L-band BWO.
Numerical simulation for treatment of dispersive shallow water waves with Rosenau-KdV equation
NASA Astrophysics Data System (ADS)
Ak, Turgut; Battal Gazi Karakoc, S.; Triki, Houria
2016-10-01
In this paper, numerical solutions for the Rosenau-Korteweg-de Vries equation are studied by using the subdomain method based on the sextic B-spline basis functions. Numerical results for five test problems including the motion of single solitary wave, interaction of two and three well-separated solitary waves of different amplitudes, evolution of solitons with Gaussian and undular bore initial conditions are obtained. Stability and a priori error estimate of the scheme are discussed. A comparison of the values of the obtained invariants and error norms for single solitary wave with earlier results is also made. The results show that the present method is efficient and reliable.
NASA Technical Reports Server (NTRS)
Bar-Cohen, Y.; Mal, A.; Chang, Z.
1998-01-01
The phenomenon of Leaky Lamb Wave (LLW) in composite materials was first observed in 1982 using a Schlieren system. It has been studied extensively by numerous investigators and successfully shown to be an effective quantitative NDE tool.
Lakhin, V. P.; Sorokina, E. A. E-mail: vilkiae@gmail.com; Ilgisonis, V. I.; Konovaltseva, L. V.
2015-12-15
A set of reduced linear equations for the description of low-frequency perturbations in toroidally rotating plasma in axisymmetric tokamak is derived in the framework of ideal magnetohydrodynamics. The model suitable for the study of global geodesic acoustic modes (GGAMs) is designed. An example of the use of the developed model for derivation of the integral conditions for GGAM existence and of the corresponding dispersion relation is presented. The paper is dedicated to the memory of academician V.D. Shafranov.
Proceedings of the workshop on nonlinear MHD and extended MHD
1998-12-01
Nonlinear MHD simulations have proven their value in interpreting experimental results over the years. As magnetic fusion experiments reach higher performance regimes, more sophisticated experimental diagnostics coupled with ever expanding computer capabilities have increased both the need for and the feasibility of nonlinear global simulations using models more realistic than regular ideal and resistive MHD. Such extended-MHD nonlinear simulations have already begun to produce useful results. These studies are expected to lead to ever more comprehensive simulation models in the future and to play a vital role in fully understanding fusion plasmas. Topics include the following: (1) current state of nonlinear MHD and extended-MHD simulations; (2) comparisons to experimental data; (3) discussions between experimentalists and theorists; (4) /equations for extended-MHD models, kinetic-based closures; and (5) paths toward more comprehensive simulation models, etc. Selected papers have been indexed separately for inclusion in the Energy Science and Technology Database.
Wang, Xiang-Hua; Yin, Wen-Yan; Chen, Zhi Zhang David
2013-09-09
The one-step leapfrog alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is reformulated for simulating general electrically dispersive media. It models material dispersive properties with equivalent polarization currents. These currents are then solved with the auxiliary differential equation (ADE) and then incorporated into the one-step leapfrog ADI-FDTD method. The final equations are presented in the form similar to that of the conventional FDTD method but with second-order perturbation. The adapted method is then applied to characterize (a) electromagnetic wave propagation in a rectangular waveguide loaded with a magnetized plasma slab, (b) transmission coefficient of a plane wave normally incident on a monolayer graphene sheet biased by a magnetostatic field, and (c) surface plasmon polaritons (SPPs) propagation along a monolayer graphene sheet biased by an electrostatic field. The numerical results verify the stability, accuracy and computational efficiency of the proposed one-step leapfrog ADI-FDTD algorithm in comparison with analytical results and the results obtained with the other methods.
NASA Astrophysics Data System (ADS)
Liu, Shuyong; Jiang, J.; Parr, Nicola
2016-09-01
Water loss in distribution systems is a global problem for the water industry and governments. According to the international water supply association (IWSA), as a result of leaks from distribution pipes, 20% to 30% of water is lost while in transit from treatment plants to consumers. Although governments have tried to push the water industry to reduce the water leaks, a lot of experts have pointed out that a wide use of plastic pipes instead of metal pipes in recent years has caused difficulties in the detection of leaks using current acoustic technology. Leaks from plastic pipes are much quieter than traditional metal pipes and comparing to metal pipes the plastic pipes have very different coupling characteristics with soil, water and surrounding structures, such as other pipes, road surface and building foundations. The dispersion characteristics of wave propagating along buried plastic pipes are investigated in this paper using finite element and boundary element based models. Both empty and water- filled pipes were considered. Influences from nearby pipes and building foundations were carefully studied. The results showed that soil condition and nearby structures have significant influences on the dispersion characteristics of wave propagating along buried plastic pipes.
Magnetohydrodynamic Waves in an Asymmetric Magnetic Slab
NASA Astrophysics Data System (ADS)
Allcock, Matthew; Erdélyi, Robert
2017-02-01
Analytical models of solar atmospheric magnetic structures have been crucial for our understanding of magnetohydrodynamic (MHD) wave behaviour and in the development of the field of solar magneto-seismology. Here, an analytical approach is used to derive the dispersion relation for MHD waves in a magnetic slab of homogeneous plasma enclosed on its two sides by non-magnetic, semi-infinite plasma with different densities and temperatures. This generalises the classic magnetic slab model, which is symmetric about the slab. The dispersion relation, unlike that governing a symmetric slab, cannot be decoupled into the well-known sausage and kink modes, i.e. the modes have mixed properties. The eigenmodes of an asymmetric magnetic slab are better labelled as quasi-sausage and quasi-kink modes. Given that the solar atmosphere is highly inhomogeneous, this has implications for MHD mode identification in a range of solar structures. A parametric analysis of how the mode properties (in particular the phase speed, eigenfrequencies, and amplitudes) vary in terms of the introduced asymmetry is conducted. In particular, avoided crossings occur between quasi-sausage and quasi-kink surface modes, allowing modes to adopt different properties for different parameters in the external region.
NASA Astrophysics Data System (ADS)
Ball, J. S.; Sheehan, A. F.; Stachnik, J. C.; Lin, F.; Collins, J. A.
2013-12-01
We have developed a joint Monte Carlo inversion of teleseismic receiver functions, seafloor compliance, and Rayleigh wave dispersion and apply it here to ocean bottom seismic (OBS) data from offshore New Zealand. With this method we estimate sediment and crustal thickness and shear velocity structure beneath the Bounty Trough and the Tasman Sea flanking the South Island of New Zealand. Teleseismic receiver functions and surface wave dispersion measurements provide complementary constraints on shear velocity structure and interface depths beneath seismic stations. At ocean bottom seismic (OBS) stations the interpretation of these measurements is complicated by strong sediment reverberations that obscure deeper impedance contrasts such as the Moho. In principle, the seafloor's response to ocean loading from infragravity waves (seafloor compliance) can be used to determine shallow shear velocity information. This velocity information can subsequently be used to better model the receiver function reverberations, allowing deeper interfaces of tectonic interest to be resolved. Data for this study were acquired in 2009-2010 by the Marine Observations of Anisotropy Near Aotearoa (MOANA) experiment, which deployed 30 broadband OBS and differential pressure gauges (DPGs) off the South Island of New Zealand. High-frequency (5Hz) receiver functions were estimated using multitaper cross-correlation for events in a 30-90 degree epicentral distance range. Coherence-weighted stacks binned by epicentral distance were produced in the frequency domain to suppress noise. Seafloor compliance was measured using multitaper pressure and acceleration spectra averaged from 120 days of continuous data without large transient events. Seafloor compliance measurements on the order of 10-9 Pa-1 are sensitive to shear velocity structure in the uppermost 5km of the crust and sediments. Rayleigh dispersion measurements were obtained at periods of 6-27s from ambient noise cross correlation. Sediment
NASA Astrophysics Data System (ADS)
Aquino-López, A.; Mousatov, A.; Markov, M.; Kazatchenko, E.
2015-05-01
This paper presents a new approach for simulating P- and S-wave velocities, and electrical conductivity in shaly-sand rocks and determining the shale spatial distribution (dispersed and/or structural shales). In this approach, we used the effective medium method and hierarchical model for clastic formations. We treat shaly-sand formations as porous natural-composite materials containing: solid grains (such as quartz, feldspars and structural shale) and pores completely filled with a mixture of hydrocarbon, water and dispersed shale. For calculating the effective elastic properties and electrical conductivity of this composite, we have applied the multi-component self-consistent effective media approximation (EMA) method. We simulate the elastic velocities and electrical conductivity for clastic formations in two steps. Firstly, we calculate the effective properties of mixture (combination of water, hydrocarbon and dispersed shale) filling the pores. Then we find the effective elastic and electrical conductivity properties of formation constituted of solid grains (quartz and structural shale) and pores with the effective properties determined in the previous step. We considered that all components are represented by ellipsoids. The aspect ratios (shapes) of grains and pores; are defined as a porosity function obtained for the model of clean sand formations. Modeling results have demonstrated that the shapes of both shale components (dispersed and structural) weakly affect the effective elastic velocities and electrical conductivity of shaly-sand formation and can be approximated by flatted ellipsoids. The model proposed has been used to determine the volumes of dispersed and structural shales for two sets of published experimental data obtained from the cores. For determining the shale distribution, we have performed the joint inversion of the following physical properties: P-, S-wave velocities, total porosity, and total shale volume. Additionally, we have
Xu, Kailiang; Minonzio, Jean-Gabriel; Ta, Dean; Hu, Bo; Wang, Weiqi; Laugier, Pascal
2016-10-01
The 2-D Fourier transform analysis of multichannel signals is a straightforward method to extract the dispersion curves of guided modes. Basically, the time signals recorded at several positions along the waveguide are converted to the wavenumber-frequency space, so that the dispersion curves (i.e., the frequency-dependent wavenumbers) of the guided modes can be extracted by detecting peaks of energy trajectories. In order to improve the dispersion curve extraction of low-amplitude modes propagating in a cortical bone, a multiemitter and multireceiver transducer array has been developed together with an effective singular vector decomposition (SVD)-based signal processing method. However, in practice, the limited number of positions where these signals are recorded results in a much lower resolution in the wavenumber axis than in the frequency axis. This prevents a clear identification of overlapping dispersion curves. In this paper, a sparse SVD (S-SVD) method, which combines the signal-to-noise ratio improvement of the SVD-based approach with the high wavenumber resolution advantage of the sparse optimization, is presented to overcome the above-mentioned limitation. Different penalty constraints, i.e., l1 -norm, Frobenius norm, and revised Cauchy norm, are compared with the sparse characteristics. The regularization parameters are investigated with respect to the convergence property and wavenumber resolution. The proposed S-SVD method is investigated using synthetic wideband signals and experimental data obtained from a bone-mimicking phantom and from an ex-vivo human radius. The analysis of the results suggests that the S-SVD method has the potential to significantly enhance the wavenumber resolution and to improve the extraction of the dispersion curves.
2006-09-01
Plasmatron // The 15th International Conference on 16 N I MHD Energy Conversion and the 6th International Workshop on MagnetoPlasma Aerodynamics, IVTAN...series. 1 2. FACILITY The principal scheme of High Frequency Plasmatron is given in Fig.88, and basic specifications in the Table 1. The high-frequency...CHAMBER OF HF- PLASMATRON Statement of the problem Detailed diagnostics of plasma jet flow is required for any type of studies in HF- plasmatron . Gas flow in
2007-11-02
model the Power Conversion Unit (gas reactor + nozzle and MHD channel), and the cross sections derived from Task 1.. The configuration extends ...8 1.1 Project Objectives 8 1.2 Report Organization 9 Tables and Figures 10 2 PROJECT DESCRIPTION 11 3 REFLECTOR MODELING 13 3.1 Symbols...outlet. This conclusion remains true even if the effect of dissociation and attachment are included in the numerical model . Furthermore, a
NASA Astrophysics Data System (ADS)
Caldwell, Warren B.; Klemperer, Simon L.; Rai, Shyam S.; Lawrence, Jesse F.
2009-11-01
Seismic shear-wave velocities are sensitive to the partial melts that should be present in the Himalayan orogen if low-viscosity channel flow is active at the present day. We analyzed regional earthquakes in the western Himalaya and Tibet recorded on 16 broadband seismometers deployed across the NW Indian Himalaya, from the Indian platform to the Karakoram Range. We used a multiple filter technique to calculate the group velocity dispersion of fundamental-mode Rayleigh waves, and then inverted the dispersion records to obtain separate one-dimensional shear-wave velocity models for five geologic provinces: the Tibetan plateau, Ladakh arc complex, Indus Tsangpo suture zone, Tethyan Himalaya, and Himalayan thrust belt. Our velocity models show a low-velocity layer (LVL) with 7-17% velocity reduction centered at ~ 30 km depth and apparently continuous from the Tethyan Himalaya to the Tibetan plateau. This LVL shows good spatial correspondence with observations of low resistivity from magnetotelluric studies along the same profile. Of the possible explanations for low velocity and low resistivity in the mid-crust, only the presence of melts or aqueous fluids (or both) satisfactorily explains both sets of observations. Elevated heat flow observed in the NW Himalaya implies that if aqueous fluids are present in the mid-crust, then the mid-crust is well above its solidus. Comparison of our results with laboratory measurements and theoretical models suggests 3-7% melt is present in a channel in the upper-middle crust of the NW Himalaya at the present day, and the physical conditions to enable active channel flow may be present.
Torsional wave propagation in solar tornadoes
NASA Astrophysics Data System (ADS)
Vasheghani Farahani, S.; Ghanbari, E.; Ghaffari, G.; Safari, H.
2017-02-01
Aims: We investigate the propagation of torsional waves in coronal structures together with their collimation effects in the context of magnetohydrodynamic (MHD) theory. The interplay of the equilibrium twist and rotation of the structure, e.g. jet or tornado, together with the density contrast of its internal and external media is studied to shed light on the nature of torsional waves. Methods: We consider a rotating magnetic cylinder embedded in a plasma with a straight magnetic field. This resembles a solar tornado. In order to express the dispersion relations and phase speeds of the axisymmetric magnetohydrodynamic waves, the second-order thin flux tube approximation is implemented for the internal medium and the ideal MHD equations are implemented for the external medium. Results: The explicit expressions for the phase speed of the torsional wave show the modification of the torsional wave speed due to the equilibrium twist, rotation, and density contrast of the tornado. The speeds could be either sub-Alfvénic or ultra-Alfvénic depending on whether the equilibrium twist or rotation is dominant. The equilibrium twist increases the phase speed while the equilibrium rotation decreases it. The good agreement between the explicit versions for the phase speed and that obtained numerically proves adequate for the robustness of the model and method. The density ratio of the internal and external media also play a significant role in the speed and dispersion. Conclusions: The dispersion of the torsional wave is an indication of the compressibility of the oscillations. When the cylinder is rotating or twisted, in contrast to when it only possesses a straight magnetic field, the torsional wave is a collective mode. In this case its phase speed is determined by the Alfvén waves inside and outside the tornado.
Broken Ergodicity in MHD Turbulence in a Spherical Domain
NASA Technical Reports Server (NTRS)
Shebalin, John V.; wang, Yifan
2011-01-01
Broken ergodicity (BE) occurs in Fourier method numerical simulations of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence. Although naive statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that low-wave-number coefficients have non-zero mean values that can be very large compared to the associated standard deviation. In other words, large-scale coherent structure (i.e., broken ergodicity) in homogeneous MHD turbulence can spontaneously grow out of random initial conditions. Eigenanalysis of the modal covariance matrices in the probability density functions of ideal statistical theory leads to a theoretical explanation of observed BE in homogeneous MHD turbulence. Since dissipation is minimal at the largest scales, BE is also relevant for resistive magnetofluids, as evidenced in numerical simulations. Here, we move beyond model magnetofluids confined by periodic boxes to examine BE in rotating magnetofluids in spherical domains using spherical harmonic expansions along with suitable boundary conditions. We present theoretical results for 3-D and 2-D spherical models and also present computational results from dynamical simulations of 2-D MHD turbulence on a rotating spherical surface. MHD turbulence on a 2-D sphere is affected by Coriolus forces, while MHD turbulence on a 2-D plane is not, so that 2-D spherical models are a useful (and simpler) intermediate stage on the path to understanding the much more complex 3-D spherical case.
Harmonic Response of the Organ of Corti: Results for Wave Dispersion
NASA Astrophysics Data System (ADS)
Foucaud, Simon; Michon, Guilhem; Morlier, Joseph; Gourinat, Yves
2011-11-01
Inner ear is a remarkable multiphysical system and its modelling is a great challenge. The approach used in this paper aims to reproduce physic with a realistic description of the radial cross section of the cochlea. A 2D-section of the organ of Corti is fully described. Wavenumbers and corresponding modes of propagation are calculated taking into account passive structural responses. The study is extended to six cross sections of the organ of Corti and a large frequency bandwidth from 100 Hz to 3 kHz. Dispersion curves reveal the influence of fluid structure interactions with a dispersive behavior at high frequencies. Longitudinal mechanical coupling provides new interacting modes of propagation.
NASA Astrophysics Data System (ADS)
Hsu, Keng-Tsang; Cheng, Chia-Chi; Tao, Hung-Yu; Chiang, Chih-Hung
2017-02-01
Surface waves generated by an impact are used to assess depth of deterioration for concrete plate. The proposed method uses one receiver positioned away from the impacting source. The spectrogram of the group velocity obtained from the signal recorded from the receiver is calculated by Short-Time Fourier Transform and the reassignment technique. Experiments were conduct on the concrete plate with top mortar layer to simulate concrete with serious aggregate segregation and bleeding. In the experiment, the responses corresponding to different source-receiver distance were explored. The results were shown by both slowness spectrogram and velocity profile. In the slowness spectrogram, substantial increase of velocity at low frequency domain is found. The velocity profile shows the change of wave speed is at the wave length about 1.2 times the mortar thickness. The results also show the lower velocity corresponding to the weak layer may be identified for source-receiver distance as short as 0.5 m but the wave speed may be underestimated.
Incorporating floating surface objects into a fully dispersive surface wave model
NASA Astrophysics Data System (ADS)
Orzech, Mark D.; Shi, Fengyan; Veeramony, Jayaram; Bateman, Samuel; Calantoni, Joseph; Kirby, James T.
2016-06-01
The shock-capturing, non-hydrostatic, three-dimensional (3D) finite-volume model NHWAVE was originally developed to simulate wave propagation and landslide-generated tsunamis in finite water depth (Ma, G., Shi, F., Kirby, J. T., 2012. Ocean Model. 43-44, 22-35). The model is based on the incompressible Navier-Stokes equations, in which the z-axis is transformed to a σ-coordinate that tracks the bed and surface. As part of an ongoing effort to simulate waves in polar marginal ice zones (MIZs), the model has now been adapted to allow objects of arbitrary shape and roughness to float on or near its water surface. The shape of the underside of each floating object is mapped onto an upper σ-level slightly below the surface. In areas without floating objects, this σ-level continues to track the surface and bed as before. Along the sides of each floating object, an immersed boundary method is used to interpolate the effects of the object onto the neighboring fluid volume. Provided with the object's shape, location, and velocity over time, NHWAVE determines the fluid fluxes and pressure variations from the corresponding accelerations at neighboring cell boundaries. The system was validated by comparison with analytical solutions and a VOF model for a 2D floating box and with laboratory measurements of wave generation by a vertically oscillating sphere. A steep wave simulation illustrated the high efficiency of NHWAVE relative to a VOF model. In a more realistic MIZ simulation, the adapted model produced qualitatively reasonable results for wave attenuation, diffraction, and scattering.
NASA Astrophysics Data System (ADS)
Ebrahimi, Farzad; Dabbagh, Ali
2017-02-01
Main object of the present research is an exact investigation of wave propagation responses of smart rotating magneto-electro-elastic (MEE) graded nanoscale plates. In addition, effective material properties of functionally graded (FG) nanoplate are presumed to be calculated using the power-law formulations. Also, it has been tried to cover both softening and stiffness-hardening behaviors of nanostructures by the means of employing nonlocal strain gradient theory (NSGT). Due to increasing the accuracy of the presented model in predicting shear deformation effects, a refined higher-order plate theory is introduced. In order to cover the most enormous circumstances, maximum amount of load generated by plate’s rotation is considered. Furthermore, utilizing a developed form of Hamilton’s principle, containing magneto-electric effects, the nonlocal governing equations of MEE-FG rotating nanoplates are derived. An analytical solution is obtained to solve the governing equations and validity of the solution method is proven by comparing results from present method with those of former attempts. At last, outcomes are plotted in the framework of some figures to show the influences of various parameters such as wave number, nonlocality, length scale parameter, magnetic potential, electric voltage, gradient index and angular velocity on wave frequency, phase velocity and escape frequency of the examined nanoplate.
Conmy, Robyn N; Coble, Paula G; Farr, James; Wood, A Michelle; Lee, Kenneth; Pegau, W Scott; Walsh, Ian D; Koch, Corey R; Abercrombie, Mary I; Miles, M Scott; Lewis, Marlon R; Ryan, Scott A; Robinson, Brian J; King, Thomas L; Kelble, Christopher R; Lacoste, Jordanna
2014-01-01
In situ fluorometers were deployed during the Deepwater Horizon (DWH) Gulf of Mexico oil spill to track the subsea oil plume. Uncertainties regarding instrument specifications and capabilities necessitated performance testing of sensors exposed to simulated, dispersed oil plumes. Dynamic ranges of the Chelsea Technologies Group AQUAtracka, Turner Designs Cyclops, Satlantic SUNA and WET Labs, Inc. ECO, exposed to fresh and artificially weathered crude oil, were determined. Sensors were standardized against known oil volumes and total petroleum hydrocarbons and benzene-toluene-ethylbenzene-xylene measurements-both collected during spills, providing oil estimates during wave tank dilution experiments. All sensors estimated oil concentrations down to 300 ppb oil, refuting previous reports. Sensor performance results assist interpretation of DWH oil spill data and formulating future protocols.
NASA Astrophysics Data System (ADS)
Zheng, Dan; Li, Hongyi; Shen, Yang; Tan, Jing; Ouyang, Longbin; Li, Xinfu
2016-01-01
The crustal and upper mantle velocity structure in the northeastern Tibetan Plateau is obtained from joint analysis of receiver functions and Rayleigh wave dispersions. The resulting velocity model reveals a close correlation between the thick (>60 km) crust and the presence of an intracrustal low-velocity zone beneath the Qiangtang and Songpan-Ganzi terranes as well as the northwestern Qilian orogen. However, the high Vp/Vs ratio of the crust is found only beneath the Qiangtang and Songpan-Ganzi terranes. The crustal low velocity zone does not appear in the west Qinling and southeastern Qilian orogens, which have a relatively thin (˜50 km) crust, indicating that crustal channel flow is not the primary mechanism by which the northeastern Tibetan Plateau grows. A continuous low velocity zone from the mid-to-lower crust down to 160 km beneath the eastern Kunlun fault suggests an induced local mantle upwelling after partial detachment of the lithosphere.
NASA Technical Reports Server (NTRS)
Meyers, Steven D.; Kelly, B. G.; O'Brien, J. J.
1993-01-01
Wavelet analysis is a relatively new technique that is an important addition to standard signal analysis methods. Unlike Fourier analysis that yields an average amplitude and phase for each harmonic in a dataset, the wavelet transform produces an instantaneous estimate or local value for the amplitude and phase of each harmonic. This allows detailed study of nonstationary spatial or time-dependent signal characteristics. The wavelet transform is discussed, examples are given, and some methods for preprocessing data for wavelet analysis are compared. By studying the dispersion of Yanai waves in a reduced gravity equatorial model, the usefulness of the transform is demonstrated. The group velocity is measured directly over a finite range of wavenumbers by examining the time evolution of the transform. The results agree well with linear theory at higher wavenumber but the measured group velocity is reduced at lower wavenumbers, possibly due to interaction with the basin boundaries.
Su, Shih-Wei; Lu, Zhen-Kai; Gou, Shih-Chuan; Liao, Wen-Te
2016-01-01
Cavity quantum electrodynamics (CQED) has played a central role in demonstrating the fundamental principles of the quantum world, and in particular those of atom-light interactions. Developing fast, dynamical and non-mechanical control over a CQED system is particularly desirable for controlling atomic dynamics and building future quantum networks at high speed. However conventional mirrors do not allow for such flexible and fast controls over their coupling to intracavity atoms mediated by photons. Here we theoretically investigate a novel all-optical CQED system composed of a binary Bose-Einstein condensate (BEC) sandwiched by two atomic ensembles. The highly tunable atomic dispersion of the CQED system enables the medium to act as a versatile, all-optically controlled atomic mirror that can be employed to manipulate the vacuum-induced diffraction of matter-wave superradiance. Our study illustrates a innovative all-optical element of atomtroics and sheds new light on controlling light-matter interactions. PMID:27748413
NASA Astrophysics Data System (ADS)
Su, Shih-Wei; Lu, Zhen-Kai; Gou, Shih-Chuan; Liao, Wen-Te
2016-10-01
Cavity quantum electrodynamics (CQ