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Sample records for propagating planar wave

  1. Experimental study of multichromatic terahertz wave propagation through planar micro-channels

    DOE PAGES

    Shin, Young-Min -Min; Northern Illinois Univ., Dekalb, IL; Fermi National Accelerator Lab.; ...

    2012-04-10

    Previous theoretical and numerical studies [Y. M. Shin and L. R. Barnett, Appl. Phys. Lett. 92, 091501 (2008) and Y. M. Shin et al., Appl. Phys. Lett. 93, 221504 (2008)] have reported that a planar micro-channel with an asymmetric corrugation array supports strongly confined propagation of broadband THz plasmonic waves. The highly broad spectral response is experimentally demonstrated in the near-THz regime of 0.19-0.265 THz. Signal reflection and transmission tests on the three designed micro-channels including directional couplers resulted in a full-width-half-maximum bandwidth of ~ 50-60GHz with an insertion loss of approximately -5 dB, which is in good agreement withmore » simulation data. As a result, these micro-structures can be utilized for free electron beam and electronic/optic integrated devices« less

  2. Experimental study of multichromatic terahertz wave propagation through planar micro-channels

    SciTech Connect

    Shin, Young-Min -Min; Baig, Anisullah; Barchfeld, Robert; Gamzina, Diana; Barnett, Larry R.; Luhmann, Jr., Neville C.

    2012-04-10

    Previous theoretical and numerical studies [Y. M. Shin and L. R. Barnett, Appl. Phys. Lett. 92, 091501 (2008) and Y. M. Shin et al., Appl. Phys. Lett. 93, 221504 (2008)] have reported that a planar micro-channel with an asymmetric corrugation array supports strongly confined propagation of broadband THz plasmonic waves. The highly broad spectral response is experimentally demonstrated in the near-THz regime of 0.19-0.265 THz. Signal reflection and transmission tests on the three designed micro-channels including directional couplers resulted in a full-width-half-maximum bandwidth of ~ 50-60GHz with an insertion loss of approximately -5 dB, which is in good agreement with simulation data. As a result, these micro-structures can be utilized for free electron beam and electronic/optic integrated devices

  3. Experimental investigation of the propagation of a planar shock wave through a two-phase gas-liquid medium

    NASA Astrophysics Data System (ADS)

    Chauvin, A.; Jourdan, G.; Daniel, E.; Houas, L.; Tosello, R.

    2011-11-01

    We conducted a series of shock tube experiments to study the influence of a cloud of water droplets on the propagation of a planar shock wave. In a vertically oriented shock tube, the cloud of droplets was released downwards into the air at atmospheric pressure while the shock wave propagated upwards. Two shock wave Mach numbers, 1.3 and 1.5, and three different heights of clouds, 150 mm, 400 mm, and 700 mm, were tested with an air-water volume fraction and a droplet diameter fixed at 1.2% and 500 μm, respectively. From high-speed visualization and pressure measurements, we analyzed the effect of water clouds on the propagation of the shock wave. It was shown that the pressure histories recorded in the two-phase gas-liquid mixture are different from those previously obtained in the gas-solid case. This different behavior is attributed to the process of atomization of the droplets, which is absent in the gas-solid medium. Finally, it was observed that the shock wave attenuation was dependent on the exchange surface crossed by the shock combined with the breakup criterion.

  4. Propagation and stability of quantum dust-ion-acoustic shock waves in planar and nonplanar geometry

    SciTech Connect

    Masood, W.; Siddiq, M.; Nargis, Shahida; Mirza, Arshad M.

    2009-01-15

    Dust-ion-acoustic (DIA) shock waves are studied in an unmagnetized quantum plasma consisting of electrons, ions, and dust by employing the quantum hydrodynamic (QHD) model. In this context, a Korteweg-deVries-Burger (KdVB) equation is derived by employing the small amplitude perturbation expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. It is found that the strength of the quantum DIA shock wave is maximum for spherical, intermediate for cylindrical, and minimum for the planar geometry. The effects of quantum Bohm potential, dust concentration, and kinematic viscosity on the quantum DIA shock structure are also investigated. The temporal evolution of DIA KdV solitons and Burger shocks are also studied by putting the dissipative and dispersive coefficients equal to zero, respectively. The effects of the quantum Bohm potential on the stability of the DIA shock is also investigated. The present investigation may be beneficial to understand the dissipative and dispersive processes that may occur in the quantum dusty plasmas found in microelectronic devices as well as in astrophysical plasmas.

  5. Vibrational eigenvalues and eigenfunctions for planar acetylene by wave-packet propagation, and its mode-selective infrared excitation

    NASA Astrophysics Data System (ADS)

    Liu, Li; Muckerman, James T.

    1997-09-01

    Vibrational eigenvalues with estimated errors <5×10-2 cm-1 and their corresponding eigenfunctions for J=0 5D (planar) acetylene modeled by the Halonen-Child-Carter potential-energy surface are obtained using an energy-shifted, imaginary-time Lanczos propagation of symmetry-adapted wave packets. A lower resolution (˜4 cm-1) vibrational eigenspectrum of the system is also calculated by the Fourier transform of the autocorrelation of an appropriate wave packet. The eigenvalues from both approaches are in excellent agreement. The wave function of the molecule is represented in a direct-product discrete variable representation (DVR) with nearly 300 000 grid points. Our results are compared with the previously reported theoretical and experimental values. We use our 69 computed eigenstates as a basis to perform an optimal control simulation of selective two-photon excitation of the symmetric CH-stretch mode with an infrared, linearly polarized, transform-limited, and subpicosecond-picosecond laser pulse. The resulting optimal laser pulses, which are then tested on the full DVR grid, fall within the capabilities of current powerful, subpicosecond, and tunable light sources.

  6. Wave Propagation Program

    SciTech Connect

    McCandless, Kathleen; Petersson, Anders; Nilsson, Stefan; Sjogreen, Bjorn

    2007-01-08

    WPP is a massively parallel, 3D, C++, finite-difference elastodynamic wave propagation code. Typical applications for wave propagation with WPP include: evaluation of seismic event scenarios and damage from earthquakes, non-destructive evaluation of materials, underground facility detection, oil and gas exploration, predicting the electro-magnetic fields in accelerators, and acoustic noise generation. For more information, see User’s Manual [1].

  7. Roughening of a propagating planar crack front

    NASA Astrophysics Data System (ADS)

    Åström, J. A.; Alava, M. J.; Timonen, J.

    2000-08-01

    A numerical model of the front of a planar crack propagating between two connected elastic plates is investigated. The plates are modeled as square lattices of elastic beams. The plates are connected by similar but breakable beams with a randomly varying stiffness. The crack is driven by pulling both plates at one end in Mode I at a constant rate. We find ζ=1/3, z=4/3, and β=1/4 for the roughness, dynamical, and growth exponents, respectively, that describe the front behavior. This is similar to continuum limit analyses based on a perturbative stress-intensity treatment of the front [H. Gao and J. R. Rice, J. Appl. Mech. 56, 828 (1989)]. We discuss the differences to recent experiments.

  8. Linear guided waves in a hyperbolic planar waveguide. Dispersion relations

    SciTech Connect

    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)

  9. Nonlinear Wave Propagation

    DTIC Science & Technology

    2009-02-09

    of parameters. Hence one expects that the solutions of the two equations , PES and NLS, are comparable. In Fig. 3 we plot the two solutions for...power saturated term, in the PES equation ) have stable soliton solutions or mode-locking evolution. In general the solitons are found to be unstable...literature. Generally speaking, the above lattice equations omitting nonlinear terms have solutions propagating along z direction, i.e., ψ(r, z) = e−iµzϕ(r

  10. Reconstruction of nonlinear wave propagation

    DOEpatents

    Fleischer, Jason W; Barsi, Christopher; Wan, Wenjie

    2013-04-23

    Disclosed are systems and methods for characterizing a nonlinear propagation environment by numerically propagating a measured output waveform resulting from a known input waveform. The numerical propagation reconstructs the input waveform, and in the process, the nonlinear environment is characterized. In certain embodiments, knowledge of the characterized nonlinear environment facilitates determination of an unknown input based on a measured output. Similarly, knowledge of the characterized nonlinear environment also facilitates formation of a desired output based on a configurable input. In both situations, the input thus characterized and the output thus obtained include features that would normally be lost in linear propagations. Such features can include evanescent waves and peripheral waves, such that an image thus obtained are inherently wide-angle, farfield form of microscopy.

  11. Wave propagation in ballistic gelatine.

    PubMed

    Naarayan, Srinivasan S; Subhash, Ghatu

    2017-01-23

    Wave propagation characteristics in long cylindrical specimens of ballistic gelatine have been investigated using a high speed digital camera and hyper elastic constitutive models. The induced transient deformation is modelled with strain rate dependent Mooney-Rivlin parameters which are determined by modelling the stress-strain response of gelatine at a range of strain rates. The varying velocity of wave propagation through the gelatine cylinder is derived as a function of prestress or stretch in the gelatine specimen. A finite element analysis is conducted using the above constitutive model by suitably defining the impulse imparted by the polymer bar into the gelatine specimen. The model results are found to capture the experimentally observed wave propagation characteristics in gelatine effectively.

  12. Nonlinear Wave Propagation.

    DTIC Science & Technology

    1987-11-23

    generalized wave equation (GWE) when (z) 0 (1-Z2)/2: - X(z). (1.5) The compatibility condition required for the existence of solutions to these B~icklund...Phys. tion of a class of nonlocal nonlinear evolution equations , A 15 (1982) 781. INS *47, Clarkson University (1985), to be published in J. Math... semilinear form. The above approach will fail if there exist linearizable quasilinear equations which can not be mapped to a semilinear from. It is shown in

  13. Propagation and excitation of multiple surface waves

    NASA Astrophysics Data System (ADS)

    Faryad, Muhammad

    Surface waves are the solutions of the frequency-domain Maxwell equations at the planar interface of two dissimilar materials. The time-averaged Poynting vector of a surface wave (i) has a significant component parallel to the interface and (ii) decays at sufficiently large distances normal to the interface. If one of the partnering materials is a metal and the other a dielectric, the surface waves are called surface plasmon-polariton (SPP) waves. If both partnering materials are dielectric, with at least one being periodically nonhomogeneous normal to the interface, the surface waves are called Tamm waves; and if that dielectric material is also anisotropic, the surface waves are called Dyakonov--Tamm waves. SPP waves also decays along the direction of propagation, whereas Tamm and Dyakonov--Tamm waves propagate with negligible losses. The propagation and excitation of multiple SPP waves guided by the interface of a metal with a periodically nonhomogeneous sculptured nematic thin film (SNTF), and the interface of a metal with a rugate filter were theoretically investigated. The SNTF is an anisotropic material with a permittivity dyadic that is periodically nonhomogeneous in the thickness direction. A rugate filter is also a periodically nonhomogeneous dielectric material; however, it is an isotropic material. Multiple SPP waves of the same frequency but with different polarization states, phase speeds, attenuation rates, and spatial field profiles were found to be guided by a metal/SNTF interface, a metal/rugate-filter interface, and a metal slab in the SNTF. Multiple Dyakonov--Tamm waves of the same frequency but different polarization states, phase speeds, and spatial field profiles were found to be guided by a structural defect in an SNTF, and by a dielectric slab in an SNTF. The characteristics of multiple SPP and Dyakonov--Tamm waves were established by the investigations on canonical boundary-value problems. The Turbadar-Kretschmann-Raether (TKR) and the

  14. Planar and nonplanar ion acoustic shock waves in relativistic degenerate astrophysical electron-positron-ion plasmas

    SciTech Connect

    Ata-ur-Rahman,; Qamar, A.; Ali, S.; Mirza, Arshad M.

    2013-04-15

    We have studied the propagation of ion acoustic shock waves involving planar and non-planar geometries in an unmagnetized plasma, whose constituents are non-degenerate ultra-cold ions, relativistically degenerate electrons, and positrons. By using the reductive perturbation technique, Korteweg-deVries Burger and modified Korteweg-deVries Burger equations are derived. It is shown that only compressive shock waves can propagate in such a plasma system. The effects of geometry, the ion kinematic viscosity, and the positron concentration are examined on the ion acoustic shock potential and electric field profiles. It is found that the properties of ion acoustic shock waves in a non-planar geometry significantly differ from those in planar geometry. The present study has relevance to the dense plasmas, produced in laboratory (e.g., super-intense laser-dense matter experiments) and in dense astrophysical objects.

  15. Wave equations for pulse propagation

    SciTech Connect

    Shore, B.W.

    1987-06-24

    Theoretical discussions of the propagation of pulses of laser radiation through atomic or molecular vapor rely on a number of traditional approximations for idealizing the radiation and the molecules, and for quantifying their mutual interaction by various equations of propagation (for the radiation) and excitation (for the molecules). In treating short-pulse phenomena it is essential to consider coherent excitation phenomena of the sort that is manifest in Rabi oscillations of atomic or molecular populations. Such processes are not adequately treated by rate equations for excitation nor by rate equations for radiation. As part of a more comprehensive treatment of the coupled equations that describe propagation of short pulses, this memo presents background discussion of the equations that describe the field. This memo discusses the origin, in Maxwell's equations, of the wave equation used in the description of pulse propagation. It notes the separation into lamellar and solenoidal (or longitudinal and transverse) and positive and negative frequency parts. It mentions the possibility of separating the polarization field into linear and nonlinear parts, in order to define a susceptibility or index of refraction and, from these, a phase and group velocity. The memo discusses various ways of characterizing the polarization characteristics of plane waves, that is, of parameterizing a transverse unit vector, such as the Jones vector, the Stokes vector, and the Poincare sphere. It discusses the connection between macroscopically defined quantities, such as the intensity or, more generally, the Stokes parameters, and microscopic field amplitudes. The material presented here is a portion of a more extensive treatment of propagation to be presented separately. The equations presented here have been described in various books and articles. They are collected here as a summary and review of theory needed when treating pulse propagation.

  16. X-Ray Propagation in Tapered Planar Waveguide

    NASA Astrophysics Data System (ADS)

    Dolocan, Andrei; van der Veen, J. Friso

    The present paper focuses on the tapered planar waveguide solution for an initial given wave form. The algorithm is constructed in distributions space such that the calculations can be actually computed by taking some hypothesis regarding the mode series which appear. The whole argument leads to the conclusion that the wave is compressed towards the waveguide in the direction of tilting, leading thereafter to a focusing phenomena. We present two alternative constructions in order to compute the convolution which gives the wave inside the waveguide. The hypothesis are providing results in good approximation with the real evolution of the field within the definition domain.

  17. Partially coherent fundamental Gaussian wave generated by a fluctuating planar current source.

    PubMed

    Seshadri, S R

    2010-06-01

    The propagation characteristics of a spatially localized electromagnetic wave produced by a planar current source of different states of spatial coherence are analyzed by the use of a Gaussian Schell-model source. A linearly polarized fundamental electromagnetic Gaussian wave with the electric field perpendicular to the direction of propagation is treated. The effects of the degree of coherence of the source distribution on the radiation intensity distribution and the total radiated power are determined.

  18. Wave Propagation in Bimodular Geomaterials

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Maria; Pasternak, Elena; Dyskin, Arcady; Pelinovsky, Efim

    2016-04-01

    Observations and laboratory experiments show that fragmented or layered geomaterials have the mechanical response dependent on the sign of the load. The most adequate model accounting for this effect is the theory of bimodular (bilinear) elasticity - a hyperelastic model with different elastic moduli for tension and compression. For most of geo- and structural materials (cohesionless soils, rocks, concrete, etc.) the difference between elastic moduli is such that their modulus in compression is considerably higher than that in tension. This feature has a profound effect on oscillations [1]; however, its effect on wave propagation has not been comprehensively investigated. It is believed that incorporation of bilinear elastic constitutive equations within theory of wave dynamics will bring a deeper insight to the study of mechanical behaviour of many geomaterials. The aim of this paper is to construct a mathematical model and develop analytical methods and numerical algorithms for analysing wave propagation in bimodular materials. Geophysical and exploration applications and applications in structural engineering are envisaged. The FEM modelling of wave propagation in a 1D semi-infinite bimodular material has been performed with the use of Marlow potential [2]. In the case of the initial load expressed by a harmonic pulse loading strong dependence on the pulse sign is observed: when tension is applied before compression, the phenomenon of disappearance of negative (compressive) strains takes place. References 1. Dyskin, A., Pasternak, E., & Pelinovsky, E. (2012). Periodic motions and resonances of impact oscillators. Journal of Sound and Vibration, 331(12), 2856-2873. 2. Marlow, R. S. (2008). A Second-Invariant Extension of the Marlow Model: Representing Tension and Compression Data Exactly. In ABAQUS Users' Conference.

  19. Avalanches and clusters in planar crack front propagation.

    PubMed

    Laurson, Lasse; Santucci, Stephane; Zapperi, Stefano

    2010-04-01

    We study avalanches in a model for a planar crack propagating in a disordered medium. Due to long-range interactions, avalanches are formed by a set of spatially disconnected local clusters, the sizes of which are distributed according to a power law with an exponent tau{a}=1.5. We derive a scaling relation tau{a}=2tau-1 between the local cluster exponent tau{a} and the global avalanche exponent tau . For length scales longer than a crossover length proportional to the Larkin length, the aspect ratio of the local clusters scales with the roughness exponent of the line model. Our analysis provides an explanation for experimental results on planar crack avalanches in Plexiglas plates, but the results are applicable also to other systems with long-range interactions.

  20. Analytical description of partially coherent propagation and absorption losses in x-ray planar waveguides.

    PubMed

    Tsanaktsidis, K J; Paganin, D M; Pelliccia, D

    2013-06-01

    We present an analytical approach to describe field propagation along a planar x-ray waveguide (WG) in the presence of absorption losses. The method utilizes the complete expression for the complex index of refraction in solving the Helmholtz equation describing the guided modes. In this way, the propagation modes for the WG are no longer imposed to be standing waves and the energy flow from the core to the cladding, a consequence of the absorption in the cladding, can be calculated. In addition, the method accurately describes the field coupling between a plane wave and the WG, reproducing the self-imaging phenomenon. The case of partially coherent illumination has also been calculated for a realistic laboratory x-ray source.

  1. Whistler wave propagation in a large magnetoplasma

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.

    1976-01-01

    A large collisionless quiescent plasma source is developed for investigating the phase and amplitude distribution of antenna-launched whistler waves in a specified parameter regime relating wave frequency to electron cyclotron frequency. Wave dispersion is studied both by interferometer techniques with monochromatic waves and by propagation of short phase-coherent wave bursts. The wave damping mechanism is examined by propagating perfectly ducted whistler waves. The dispersion of single frequency waves and wave packets is demonstrated. Trough ducting for wave frequency to electron cyclotron frequency ratio greater than 1/2 is verified, and new eigenmodes in nonuniform plasmas at ratio values less than 1/2 are observed. It is shown that geometric effects due to ray divergence and wave refraction dominate over collisional damping.

  2. Slow wave propagation in soft adhesive interfaces.

    PubMed

    Viswanathan, Koushik; Sundaram, Narayan K; Chandrasekar, Srinivasan

    2016-11-16

    Stick-slip in sliding of soft adhesive surfaces has long been associated with the propagation of Schallamach waves, a type of slow surface wave. Recently it was demonstrated using in situ experiments that two other kinds of slow waves-separation pulses and slip pulses-also mediate stick-slip (Viswanathan et al., Soft Matter, 2016, 12, 5265-5275). While separation pulses, like Schallamach waves, involve local interface detachment, slip pulses are moving stress fronts with no detachment. Here, we present a theoretical analysis of the propagation of these three waves in a linear elastodynamics framework. Different boundary conditions apply depending on whether or not local interface detachment occurs. It is shown that the interface dynamics accompanying slow waves is governed by a system of integral equations. Closed-form analytical expressions are obtained for the interfacial pressure, shear stress, displacements and velocities. Separation pulses and Schallamach waves emerge naturally as wave solutions of the integral equations, with oppositely oriented directions of propagation. Wave propagation is found to be stable in the stress regime where linearized elasticity is a physically valid approximation. Interestingly, the analysis reveals that slow traveling wave solutions are not possible in a Coulomb friction framework for slip pulses. The theory provides a unified picture of stick-slip dynamics and slow wave propagation in adhesive contacts, consistent with experimental observations.

  3. Experimental Measurements of Two-dimensional Planar Propagating Edge Flames

    NASA Technical Reports Server (NTRS)

    Villa-Gonzalez, Marcos; Marchese, Anthony J.; Easton, John W.; Miller, Fletcher J.

    2007-01-01

    The study of edge flames has received increased attention in recent years. This work reports the results of a recent study into two-dimensional, planar, propagating edge flames that are remote from solid surfaces (called here, free-layer flames, as opposed to layered flames along floors or ceilings). They represent an ideal case of a flame propagating down a flammable plume, or through a flammable layer in microgravity. The results were generated using a new apparatus in which a thin stream of gaseous fuel is injected into a low-speed laminar wind tunnel thereby forming a flammable layer along the centerline. An airfoil-shaped fuel dispenser downstream of the duct inlet issues ethane from a slot in the trailing edge. The air and ethane mix due to mass diffusion while flowing up towards the duct exit, forming a flammable layer with a steep lateral fuel concentration gradient and smaller axial fuel concentration gradient. We characterized the flow and fuel concentration fields in the duct using hot wire anemometer scans, flow visualization using smoke traces, and non-reacting, numerical modeling using COSMOSFloWorks. In the experiment, a hot wire near the exit ignites the ethane air layer, with the flame propagating downwards towards the fuel source. Reported here are tests with the air inlet velocity of 25 cm/s and ethane flows of 967-1299 sccm, which gave conditions ranging from lean to rich along the centerline. In these conditions the flame spreads at a constant rate faster than the laminar burning rate for a premixed ethane air mixture. The flame spread rate increases with increasing transverse fuel gradient (obtained by increasing the fuel flow rate), but appears to reach a maximum. The flow field shows little effect due to the flame approach near the igniter, but shows significant effect, including flow reversal, well ahead of the flame as it approaches the airfoil fuel source.

  4. Surface acoustic wave propagation in graphene

    NASA Astrophysics Data System (ADS)

    Thalmeier, Peter; Dóra, Balázs; Ziegler, Klaus

    2010-01-01

    Surface acoustic wave (SAW) propagation is a powerful method to investigate two-dimensional (2D) electron systems. We show how SAW observables are influenced by coupling to the 2D massless Dirac electrons of graphene and argue that Landau oscillations in SAW propagation can be observed as function of gate voltage for constant field. Contrary to other transport measurements, the zero-field SAW propagation gives the wave-vector dependence of graphene conductivity for small wave numbers. We predict a crossover from Schrödinger to Dirac-like behavior as a function of gate voltage, with no attenuation in the latter for clean samples.

  5. Numerical investigation of the effects of shear waves in transcranial photoacoustic tomography with a planar geometry

    PubMed Central

    Wang, Lihong V.

    2012-01-01

    Abstract. Using a recently developed reconstruction method for photoacoustic tomography (PAT) valid for a planar measurement geometry parallel to a layered medium, we investigate the effects of shear wave propagation in the solid layer upon the ability to estimate Fourier components of the object. We examine this ability as a function of the thickness of the layer supporting shear waves as well as of the incidence angle of the field in the planewave representation. Examples are used to demonstrate the importance of accounting for shear waves in transcranial PAT. Error measures are introduced to quantify the error found when omitting shear waves from the forward model in PAT. PMID:22734745

  6. Making and Propagating Elastic Waves: Overview of the new wave propagation code WPP

    SciTech Connect

    McCandless, K P; Petersson, N A; Nilsson, S; Rodgers, A; Sjogreen, B; Blair, S C

    2006-05-09

    We are developing a new parallel 3D wave propagation code at LLNL called WPP (Wave Propagation Program). WPP is being designed to incorporate the latest developments in embedded boundary and mesh refinement technology for finite difference methods, as well as having an efficient portable implementation to run on the latest supercomputers at LLNL. We are currently exploring seismic wave applications, including a recent effort to compute ground motions for the 1906 Great San Francisco Earthquake. This paper will briefly describe the wave propagation problem, features of our numerical method to model it, implementation of the wave propagation code, and results from the 1906 Great San Francisco Earthquake simulation.

  7. Asymptotic wave propagation in excitable media.

    PubMed

    Bernus, Olivier; Vigmond, Edward

    2015-07-01

    Wave shape and velocity are important issues in reaction-diffusion systems, and are often the result of competition in media with heterogeneous conduction properties. Asymptotic wave front propagation at maximal conduction velocity has been previously reported in the context of anisotropic cardiac tissue, but it is unknown whether this is a universal property of excitable tissues where conduction velocity can be locally modulated by mechanisms other than anisotropy. Here, we investigate the impact of conduction heterogeneities and boundary effects on wave propagation in excitable media. Following a theoretical analysis, we find that wave-front cusps occur where local velocity is reduced and that asymptotic wave fronts propagate at the maximal translational conduction velocity. Simulations performed in different reaction-diffusion systems, including cardiac tissue, confirm our theoretical findings. We conclude that this property can be found in a wide range of reaction-diffusion systems with excitable dynamics and that asymptotic wave-front shapes can be predicted.

  8. Radio wave propagation and acoustic sounding

    NASA Astrophysics Data System (ADS)

    Singal, S. P.

    Radio wave propagation of the decimetric and centimetric waves depends to a large extent on the boundary layer meteorological conditions which give rise to severe fadings, very often due to multipath propagation. Sodar is one of the inexpensive remote sensing techniques which can be employed to probe the boundary layer structure. In the paper a historical perspective has been given of the simultaneously conducted studies on radio waves and sodar at various places. The radio meteorological information needed for propagation studies has been clearly spelt out and conditions of a ray path especially in the presence of a ducting layer have been defined as giving rise to fading or signal enhancement conditions. Finally the potential of the sodar studies to obtain information about the boundary layer phenomena has been stressed, clearly spelling out the use of acoustic sounding in radio wave propagation studies.

  9. Propagation of waves along an impedance boundary

    NASA Technical Reports Server (NTRS)

    Wenzel, A. R.

    1974-01-01

    A theoretical analysis of the scalar wave field due to a point source above a plane impedance boundary is presented. A surface wave is found to be an essential component of the total wave field. It is shown that, as a result of ducting of energy by the surface wave, the amplitude of the total wave near the boundary can be greater than it would be if the boundary were perfectly reflecting. Asymptotic results, valid near the boundary, are obtained both for the case of finite impedance (the soft-boundary case) and for the limiting case in which the impedance becomes infinite (the hard-boundary case). In the latter, the wave amplitude in the farfield decreases essentially inversely as the horizontal propagation distance; in the former (if the surface-wave term is neglected), it decreases inversely as the square of the horizontal propagation distance.

  10. Longitudinal nonlinear wave propagation through soft tissue.

    PubMed

    Valdez, M; Balachandran, B

    2013-04-01

    In this paper, wave propagation through soft tissue is investigated. A primary aim of this investigation is to gain a fundamental understanding of the influence of soft tissue nonlinear material properties on the propagation characteristics of stress waves generated by transient loadings. Here, for computational modeling purposes, the soft tissue is modeled as a nonlinear visco-hyperelastic material, the geometry is assumed to be one-dimensional rod geometry, and uniaxial propagation of longitudinal waves is considered. By using the linearized model, a basic understanding of the characteristics of wave propagation is developed through the dispersion relation and in terms of the propagation speed and attenuation. In addition, it is illustrated as to how the linear system can be used to predict brain tissue material parameters through the use of available experimental ultrasonic attenuation curves. Furthermore, frequency thresholds for wave propagation along internal structures, such as axons in the white matter of the brain, are obtained through the linear analysis. With the nonlinear material model, the authors analyze cases in which one of the ends of the rods is fixed and the other end is subjected to a loading. Two variants of the nonlinear model are analyzed and the associated predictions are compared with the predictions of the corresponding linear model. The numerical results illustrate that one of the imprints of the nonlinearity on the wave propagation phenomenon is the steepening of the wave front, leading to jump-like variations in the stress wave profiles. This phenomenon is a consequence of the dependence of the local wave speed on the local deformation of the material. As per the predictions of the nonlinear material model, compressive waves in the structure travel faster than tensile waves. Furthermore, it is found that wave pulses with large amplitudes and small elapsed times are attenuated over shorter spans. This feature is due to the elevated

  11. Inward propagating chemical waves in Taylor vortices

    NASA Astrophysics Data System (ADS)

    Thompson, Barnaby W.; Novak, Jan; Wilson, Mark C. T.; Britton, Melanie M.; Taylor, Annette F.

    2010-04-01

    Advection-reaction-diffusion (ARD) waves in the Belousov-Zhabotinsky reaction in steady Taylor-Couette vortices have been visualized using magnetic-resonance imaging and simulated using an adapted Oregonator model. We show how propagating wave behavior depends on the ratio of advective, chemical and diffusive time scales. In simulations, inward propagating spiral flamelets are observed at high Damköhler number (Da). At low Da, the reaction distributes itself over several vortices and then propagates inwards as contracting ring pulses—also observed experimentally.

  12. Inward propagating chemical waves in Taylor vortices.

    PubMed

    Thompson, Barnaby W; Novak, Jan; Wilson, Mark C T; Britton, Melanie M; Taylor, Annette F

    2010-04-01

    Advection-reaction-diffusion (ARD) waves in the Belousov-Zhabotinsky reaction in steady Taylor-Couette vortices have been visualized using magnetic-resonance imaging and simulated using an adapted Oregonator model. We show how propagating wave behavior depends on the ratio of advective, chemical and diffusive time scales. In simulations, inward propagating spiral flamelets are observed at high Damköhler number (Da). At low Da, the reaction distributes itself over several vortices and then propagates inwards as contracting ring pulses--also observed experimentally.

  13. Wave propagation into the middle atmosphere

    NASA Technical Reports Server (NTRS)

    Hirota, I.

    1989-01-01

    Recent observations of various types of waves propagating into the middle atmosphere are reviewed. Emphasis is made on the excitation processes in the lower atmosphere and their vertical propagation through the background flow as a function of the latitude, height and season. The following subjects are discussed: (1) Vertical propagation of quasi-stationary forced Rossby waves into the winter stratosphere in connection with the sudden warming; (2) Spectral distribution and seasonal characteristics of normal mode (free) Rossby waves and the asymmetry of the Northern and Southern Hemispheres; and (3) Seasonal variation of internal gravity waves in the middle atmosphere. Further discussions are presented for future studies based on accumulated observational data during the MAP period.

  14. Turbulent Transitions in Optical Wave Propagation

    NASA Astrophysics Data System (ADS)

    Pierangeli, D.; Di Mei, F.; Di Domenico, G.; Agranat, A. J.; Conti, C.; DelRe, E.

    2016-10-01

    We report the direct observation of the onset of turbulence in propagating one-dimensional optical waves. The transition occurs as the disordered hosting material passes from being linear to one with extreme nonlinearity. As the response grows, increased wave interaction causes a modulational unstable quasihomogeneous flow to be superseded by a chaotic and spatially incoherent one. Statistical analysis of high-resolution wave behavior in the turbulent regime unveils the emergence of concomitant rogue waves. The transition, observed in a photorefractive ferroelectric crystal, introduces a new and rich experimental setting for the study of optical wave turbulence and information transport in conditions dominated by large fluctuations and extreme nonlinearity.

  15. RF Wave Propagation and Scattering in Tokamaks

    NASA Astrophysics Data System (ADS)

    Horton, Wendell; Goniche, Marc; Arefiev, Alex; Peysson, Yves; Ekedahl, Annika; InstituteFusion Studies Collaboration; IRFM CEA Collaboration

    2016-10-01

    The propagation, scattering and absorption of the lower hybrid and electron cyclotron RF waves used to control fusion plasmas is reviewed. Drift wave turbulence driven by the steep ion and electron temperature gradients in H-mode divertor tokamaks produces strong scattering of the RF waves used for heating and plasma currents drive Both the 3-5GHz lower-hybrid (LH) and the 170GHZ electron cyclotron (EC) waves experience scattering and diffraction as propagating through the statistically complex density of the plasma. Ray equations are used to calculate the spread of the rays and the associated change in the parallel phase, polarization and group velocity of the RF waves in the propagation through the fusion plasma. A Fokker Planck equation for the phase space of the RF plasmons is one method to describe the spread of the RF wave power in the complex geometry of a divertor tokamak using the ray tracing codes. The evolution of the electron distribution function from the resonant electron-wave interactions is summarized for several scenarios. The resulting X-ray spectrum is broaden giving better agreement with the measured X-ray spectrum than that calculated in the absence of the turbulent scattering of the RF waves. M. Goniche et al., and Tore Supra Team, Phys. Plasmas 21, 2014.

  16. A study of helical and planar waves on sea urchin sperm flagella, with a theory of how they are generated.

    PubMed

    Woolley, D M; Vernon, G G

    2001-04-01

    When the spermatozoon of Echinus esculentus swims in sea water containing methyl cellulose (viscosity 1.5--4 Pa s), its flagellum may generate either a helical or a planar waveform, each type being stable. The helical wave, which is dextral, is complicated by the concurrent passage of miniature waves along it. These miniature waves have a pulsatile origin in the neck region of the spermatozoon. Our videotape analysis indicates that there are two pulses of mechanical activity for each true cycle of the helical wave. (The true helical frequency was obtained from the apparent wave frequency and the roll frequency of the sperm head, the latter being detectable in some sperm when lit stroboscopically.) The planar wave has a meander shape. During the propagation of planar waves, the sliding displacements are adjustable in either direction; moribund flagella can undergo unrestricted sliding. The planar waves are, in fact, exactly planar only at interfaces. Otherwise, there tend to be torsions in the interbend segments between planar bends. Mechanical stimulation of the flagellum can cause a sudden transition from the helical to the planar waveform. To account for the two modes of beating, we advance the hypothesis that circumferential linkages yield beyond a threshold strain. Whether this yield point is exceeded, we suggest, depends upon the balance between the active shear force and the external viscosity (among other factors). We propose that a subthreshold force originates in one array and then triggers the other dynein arrays circumferentially, but unidirectionally, around the base of the flagellum; whereas a suprathreshold force provokes bi-directional circumferential triggering. These may be the two patterns of activation that result in helical and planar waveforms, respectively. The transition from helical to planar bending may result from an increment in the force produced by the dynein motors. The pulsatile origin of the helical wave resembles behaviour described

  17. Propagation of shock waves through clouds

    NASA Astrophysics Data System (ADS)

    Zhou, Xin Xin

    1990-10-01

    The behavior of a shock wave propagating into a cloud consisting of an inert gas, water vapor and water droplets was investigated. This has particular application to sonic bangs propagating in the atmosphere. The finite different method of MacCormack is extended to solve the one and two dimensional, two phase flow problems in which mass, momentum and energy transfers are included. The FCT (Fluid Corrected Transport) technique developed by Boris and Book was used in the basic numerical scheme as a powerful corrective procedure. The results for the transmitted shock waves propagating in a one dimensional, semi infinite cloud obtained by the finite difference approach are in good agreement with previous results by Kao using the method characteristics. The advantage of the finite difference method is its adaptability to two and three dimensional problems. Shock wave propagation through a finite cloud and into an expansion with a 90 degree corner was investigated. It was found that the transfer processes between the two phases in two dimensional flow are much more complicated than in the one dimensional flow cases. This is mainly due to the vortex and expansion wave generated at the corner. In the case considered, further complications were generated by the reflected shock wave from the floor. Good agreement with experiment was found for one phase flow but experimental data for the two phase case is not yet available to validate the two phase calculations.

  18. Wave propagation in metamaterial lattice sandwich plates

    NASA Astrophysics Data System (ADS)

    Fang, Xin; Wen, Jihong; Yin, Jianfei; Yu, Dianlong

    2016-04-01

    This paper designed a special acoustic metamaterial 3D Kagome lattice sandwich plate. Dispersion properties and vibration responses of both traditional plate and metamaterial plate are investigated based on FEA methods. The traditional plate does not have low-frequency complete bandgaps, but the metamaterial plate has low-frequency complete bandgap (at 620Hz) coming from the symmetrical local cantilever resonators. The bandgap frequency is approximate to the first-order natural frequency of the oscillator. Complex wave modes are analyzed. The dispersion curves of longitudinal waves exist in the flexural bandgap. The dispersion properties demonstrate the metamaterial design is advantageous to suppress the low-frequency flexural wave propagation in lattice sandwich plate. The flexural vibrations near the bandgap are also suppressed efficiently. The longitudinal excitation stimulates mainly longitudinal waves and lots of low-frequency flexural vibration modes are avoided. Furthermore, the free edge effects in metamaterial plate provide new method for damping optimizations. The influences of damping on vibrations of the metamaterial sandwich plate are studied. Damping has global influence on the wave propagation; stronger damping will induce more vibration attenuation. The results enlighten us damping and metamaterial design approaches can be unite in the sandwich plates to suppress the wave propagations.

  19. Lamb-type waves generated by a cylindrical bubble oscillating between two planar elastic walls

    NASA Astrophysics Data System (ADS)

    Doinikov, A. A.; Mekki-Berrada, F.; Thibault, P.; Marmottant, P.

    2016-04-01

    The volume oscillation of a cylindrical bubble in a microfluidic channel with planar elastic walls is studied. Analytical solutions are found for the bulk scattered wave propagating in the fluid gap and the surface waves of Lamb-type propagating at the fluid-solid interfaces. This type of surface wave has not yet been described theoretically. A dispersion equation for the Lamb-type waves is derived, which allows one to evaluate the wave speed for different values of the channel height h. It is shown that for h<λt, where λt is the wavelength of the transverse wave in the walls, the speed of the Lamb-type waves decreases with decreasing h, while for h on the order of or greater than λt, their speed tends to the Scholte wave speed. The solutions for the wave fields in the elastic walls and in the fluid are derived using the Hankel transforms. Numerical simulations are carried out to study the effect of the surface waves on the dynamics of a bubble confined between two elastic walls. It is shown that its resonance frequency can be up to 50% higher than the resonance frequency of a similar bubble confined between two rigid walls.

  20. Lamb-type waves generated by a cylindrical bubble oscillating between two planar elastic walls

    PubMed Central

    Mekki-Berrada, F.; Thibault, P.; Marmottant, P.

    2016-01-01

    The volume oscillation of a cylindrical bubble in a microfluidic channel with planar elastic walls is studied. Analytical solutions are found for the bulk scattered wave propagating in the fluid gap and the surface waves of Lamb-type propagating at the fluid–solid interfaces. This type of surface wave has not yet been described theoretically. A dispersion equation for the Lamb-type waves is derived, which allows one to evaluate the wave speed for different values of the channel height h. It is shown that for h<λt, where λt is the wavelength of the transverse wave in the walls, the speed of the Lamb-type waves decreases with decreasing h, while for h on the order of or greater than λt, their speed tends to the Scholte wave speed. The solutions for the wave fields in the elastic walls and in the fluid are derived using the Hankel transforms. Numerical simulations are carried out to study the effect of the surface waves on the dynamics of a bubble confined between two elastic walls. It is shown that its resonance frequency can be up to 50% higher than the resonance frequency of a similar bubble confined between two rigid walls. PMID:27274695

  1. Lamb-type waves generated by a cylindrical bubble oscillating between two planar elastic walls.

    PubMed

    Doinikov, A A; Mekki-Berrada, F; Thibault, P; Marmottant, P

    2016-04-01

    The volume oscillation of a cylindrical bubble in a microfluidic channel with planar elastic walls is studied. Analytical solutions are found for the bulk scattered wave propagating in the fluid gap and the surface waves of Lamb-type propagating at the fluid-solid interfaces. This type of surface wave has not yet been described theoretically. A dispersion equation for the Lamb-type waves is derived, which allows one to evaluate the wave speed for different values of the channel height h. It is shown that for h<λt, where λt is the wavelength of the transverse wave in the walls, the speed of the Lamb-type waves decreases with decreasing h, while for h on the order of or greater than λt, their speed tends to the Scholte wave speed. The solutions for the wave fields in the elastic walls and in the fluid are derived using the Hankel transforms. Numerical simulations are carried out to study the effect of the surface waves on the dynamics of a bubble confined between two elastic walls. It is shown that its resonance frequency can be up to 50% higher than the resonance frequency of a similar bubble confined between two rigid walls.

  2. Antenna Construction and Propagation of Radio Waves.

    ERIC Educational Resources Information Center

    Marine Corps Inst., Washington, DC.

    Developed as part of the Marine Corps Institute (MCI) correspondence training program, this course on antenna construction and propagation of radio waves is designed to provide communicators with instructions in the selection and/or construction of the proper antenna(s) for use with current field radio equipment. Introductory materials include…

  3. Shallow water sound propagation with surface waves.

    PubMed

    Tindle, Chris T; Deane, Grant B

    2005-05-01

    The theory of wavefront modeling in underwater acoustics is extended to allow rapid range dependence of the boundaries such as occurs in shallow water with surface waves. The theory allows for multiple reflections at surface and bottom as well as focusing and defocusing due to reflection from surface waves. The phase and amplitude of the field are calculated directly and used to model pulse propagation in the time domain. Pulse waveforms are obtained directly for all wavefront arrivals including both insonified and shadow regions near caustics. Calculated waveforms agree well with a reference solution and data obtained in a near-shore shallow water experiment with surface waves over a sloping bottom.

  4. Propagation of seismic waves in tall buildings

    USGS Publications Warehouse

    Safak, E.

    1998-01-01

    A discrete-time wave propagation formulation of the seismic response of tall buildings is introduced. The building is modeled as a layered medium, similar to a layered soil medium, and is subjected to vertically propagating seismic shear waves. Soil layers and the bedrock under the foundation are incorporated in the formulation as additional layers. Seismic response is expressed in terms of the wave travel times between the layers, and the wave reflection and transmission coefficients at the layer interfaces. The equations account for the frequency-dependent filtering effects of the foundation and floor masses. The calculation of seismic response is reduced to a pair of simple finite-difference equations for each layer, which can be solved recursively starting from the bedrock. Compared to the commonly used vibration formulation, the wave propagation formulation provides several advantages, including simplified calculations, better representation of damping, ability to account for the effects of the soil layers under the foundation, and better tools for identification and damage detection from seismic records. Examples presented show the versatility of the method. ?? 1998 John Wiley & Sons, Ltd.

  5. Large-scale Globally Propagating Coronal Waves.

    PubMed

    Warmuth, Alexander

    Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the "classical" interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which "pseudo waves" are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.

  6. Planar shock wave sliding over a water layer

    NASA Astrophysics Data System (ADS)

    Rodriguez, V.; Jourdan, G.; Marty, A.; Allou, A.; Parisse, J.-D.

    2016-08-01

    In this work, we conduct experiments to study the interaction between a horizontal free water layer and a planar shock wave that is sliding over it. Experiments are performed at atmospheric pressure in a shock tube with a square cross section (200× 200 mm^2) for depths of 10, 20, and 30 mm; a 1500-mm-long water layer; and two incident planar shock waves having Mach numbers of 1.11 and 1.43. We record the pressure histories and high-speed visualizations to study the flow patterns, surface waves, and spray layers behind the shock wave. We observe two different flow patterns with ripples formed at the air-water interface for the weaker shock wave and the dispersion of a droplet mist for the stronger shock wave. From the pressure signals, we extract the delay time between the arrival of the compression wave into water and the shock wave in air at the same location. We show that the delay time evolves with the distance traveled over the water layer, the depth of the water layer, and the Mach number of the shock wave.

  7. Speeding up tsunami wave propagation modeling

    NASA Astrophysics Data System (ADS)

    Lavrentyev, Mikhail; Romanenko, Alexey

    2014-05-01

    Trans-oceanic wave propagation is one of the most time/CPU consuming parts of the tsunami modeling process. The so-called Method Of Splitting Tsunami (MOST) software package, developed at PMEL NOAA USA (Pacific Marine Environmental Laboratory of the National Oceanic and Atmospheric Administration, USA), is widely used to evaluate the tsunami parameters. However, it takes time to simulate trans-ocean wave propagation, that is up to 5 hours CPU time to "drive" the wave from Chili (epicenter) to the coast of Japan (even using a rather coarse computational mesh). Accurate wave height prediction requires fine meshes which leads to dramatic increase in time for simulation. Computation time is among the critical parameter as it takes only about 20 minutes for tsunami wave to approach the coast of Japan after earthquake at Japan trench or Sagami trench (as it was after the Great East Japan Earthquake on March 11, 2011). MOST solves numerically the hyperbolic system for three unknown functions, namely velocity vector and wave height (shallow water approximation). The system could be split into two independent systems by orthogonal directions (splitting method). Each system can be treated independently. This calculation scheme is well suited for SIMD architecture and GPUs as well. We performed adaptation of MOST package to GPU. Several numerical tests showed 40x performance gain for NVIDIA Tesla C2050 GPU vs. single core of Intel i7 processor. Results of numerical experiments were compared with other available simulation data. Calculation results, obtained at GPU, differ from the reference ones by 10^-3 cm of the wave height simulating 24 hours wave propagation. This allows us to speak about possibility to develop real-time system for evaluating tsunami danger.

  8. Wave Propagation in Polymers, Part II

    NASA Astrophysics Data System (ADS)

    Newlander, David C.; Charest, Jacques A.; Lilly, Martin D.; Eisler, Robert D.

    1999-06-01

    Work reported in a previous study (Wave Propagations in Polymers, Part I, J.A. Charest, M.D. Lilly, 44th ARA Meeting Munich, Germany Sept. 17-20, 1993) discussed gas gun plane wave impact work and the measurements of stress wave profiles in Polycarbonate at around 2 kbars. The wave profiles were obtained using combined carbon and PVDF thin film stress gauges. The results showed amplitude attenuation and dispersion effects which were neither expected nor predictable from available hydrocode models. The data have been revisited using a modified material model and the PUFF74 computer code. These new wave profile calculations show remarkable agreement with the previous experiments in Polycarbonate. The model treats the material as viscoelastic-plastic using methods developed by Bade (Dynamic Response Model for PMMA, W. L. Bade, AVCO Systems Division, TR K500-74-WLB-204, Oct. 1, 1974). The measured and calculated results are quite different from those exhibited by PMMA at similar impact conditions. This work is expected to further our understanding of the processes that control wave propagation in highly-compressible and viscoelastic/viscoplastic media. It is also expected to provide clues on the effects of high strain rates on properties such as the modulus of elasticity, strength, and material loading behavior.

  9. Surface acoustic wave propagation in graphene film

    SciTech Connect

    Roshchupkin, Dmitry Plotitcyna, Olga; Matveev, Viktor; Kononenko, Oleg; Emelin, Evgenii; Irzhak, Dmitry; Ortega, Luc; Zizak, Ivo; Erko, Alexei; Tynyshtykbayev, Kurbangali; Insepov, Zinetula

    2015-09-14

    Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.

  10. Surface acoustic wave propagation in graphene film

    NASA Astrophysics Data System (ADS)

    Roshchupkin, Dmitry; Ortega, Luc; Zizak, Ivo; Plotitcyna, Olga; Matveev, Viktor; Kononenko, Oleg; Emelin, Evgenii; Erko, Alexei; Tynyshtykbayev, Kurbangali; Irzhak, Dmitry; Insepov, Zinetula

    2015-09-01

    Surface acoustic wave (SAW) propagation in a graphene film on the surface of piezoelectric crystals was studied at the BESSY II synchrotron radiation source. Talbot effect enabled the visualization of the SAW propagation on the crystal surface with the graphene film in a real time mode, and high-resolution x-ray diffraction permitted the determination of the SAW amplitude in the graphene/piezoelectric crystal system. The influence of the SAW on the electrical properties of the graphene film was examined. It was shown that the changing of the SAW amplitude enables controlling the magnitude and direction of current in graphene film on the surface of piezoelectric crystals.

  11. VLF/LF long wave propagation study

    NASA Astrophysics Data System (ADS)

    Verplanck, P.; Kahler, R. C.; Donohoe, J. B.

    1981-11-01

    A program of ARCAS rocket measurements provided field strength data from 0 to 75 km altitude, in both Transverse Magnetic (TM) and Transverse Electric (TE) polarizations. Sky wave parameters related to survivable ground wave communications were measured at a frequency of 100 kHz, and a method of communicating with short (ground wave) pulses was demonstrated on a 230 km propagation path. Measurements were made in New York state, and in Brazil, to further define the nature of pulse reflections from ionospheric heights below the classical D-region. Instrumentation was developed to detect small changes in 100 kHz ground wave propagation velocity which might correlate with tropospheric conditions. Preliminary mechanical considerations indicate that it might be possible to deploy long center-fed dipole antennas from an Earth satellite. The program of high-resolution ionosounding with TM pulses in Greenland was augmented by transmitting TE pulses from an unused powerline at Thule Air Base. It was demonstrated that the effects of ionospheric disturbances can now be observed simultaneously with both polarizations. Input resistances and reactances of the powerline antenna were measured as functions of frequency in preparation for a follow-on program of long range propagation tests.

  12. Wave propagation in spatially modulated tubes

    NASA Astrophysics Data System (ADS)

    Ziepke, A.; Martens, S.; Engel, H.

    2016-09-01

    We investigate wave propagation in rotationally symmetric tubes with a periodic spatial modulation of cross section. Using an asymptotic perturbation analysis, the governing quasi-two-dimensional reaction-diffusion equation can be reduced into a one-dimensional reaction-diffusion-advection equation. Assuming a weak perturbation by the advection term and using projection method, in a second step, an equation of motion for traveling waves within such tubes can be derived. Both methods predict properly the nonlinear dependence of the propagation velocity on the ratio of the modulation period of the geometry to the intrinsic width of the front, or pulse. As a main feature, we observe finite intervals of propagation failure of waves induced by the tube's modulation and derive an analytically tractable condition for their occurrence. For the highly diffusive limit, using the Fick-Jacobs approach, we show that wave velocities within modulated tubes are governed by an effective diffusion coefficient. Furthermore, we discuss the effects of a single bottleneck on the period of pulse trains. We observe period changes by integer fractions dependent on the bottleneck width and the period of the entering pulse train.

  13. Review of the role of dielectric anisotropy in Dyakonov surface-wave propagation

    NASA Astrophysics Data System (ADS)

    Nelatury, Sudarshan R., II; Polo, John A., Jr.; Lakhtakia, Akhlesh

    2008-08-01

    Surface waves (SWs) are localized waves that travel along the planar interface between two different mediums when certain dispersion relations are satisfied. If both mediums have purely dielectric constitutive properties, the characteristics of SW propagation are determined by the anisotropy of both mediums. Surface waves are then called Dyakonov SWs (DSWs), after Dyakonov who theoretically established the possibility of SW propagation at the planar interface of an isotropic dielectric and a positive uniaxial dielectric. Since then, DSW propagation guided by interfaces between a variety of dielectrics has been studied. With an isotropic dielectric on one side, the dielectric on the other side of the interface can be not only positive uniaxial but also biaxial. DSW propagation can also occur along an interface between two uniaxial or biaxial dielectrics that are twisted about a common axis with respect to each other but are otherwise identical. Recently, DSW propagation has been studied taking (i) uniaxial dielectrics such as calomel and dioptase crystals; (ii) biaxial dielectrics such as hemimorphite, crocoite, tellurite, witherite, and cerussite; and (iii) electro-optic materials such as potassium niobate. With materials that are significantly anisotropic, the angular regime of directions for DSW propagation turns out to be narrow. In the case of naturally occurring crystals, one has to accept the narrow angular existence domain (AED). However, exploiting the Pockels effect not only facilitates dynamic electrical control of DSW propagation, but also widens the AED for DSW propagation.

  14. Lattice Boltzmann model for wave propagation.

    PubMed

    Zhang, Jianying; Yan, Guangwu; Shi, Xiubo

    2009-08-01

    A lattice Boltzmann model for two-dimensional wave equation is proposed by using the higher-order moment method. The higher-order moment method is based on the solution of a series of partial differential equations obtained by using multiscale technique and Chapman-Enskog expansion. In order to obtain the lattice Boltzmann model for the wave equation with higher-order accuracy of truncation errors, we removed the second-order dissipation term and the third-order dispersion term by employing the moments up to fourth order. The reversibility in time appears owing to the absence of the second-order dissipation term and the third-order dispersion term. As numerical examples, some classical examples, such as interference, diffraction, and wave passing through a convex lens, are simulated. The numerical results show that this model can be used to simulate wave propagation.

  15. Propagating wave correlations in complex systems

    NASA Astrophysics Data System (ADS)

    Creagh, Stephen C.; Gradoni, Gabriele; Hartmann, Timo; Tanner, Gregor

    2017-01-01

    We describe a novel approach for computing wave correlation functions inside finite spatial domains driven by complex and statistical sources. By exploiting semiclassical approximations, we provide explicit algorithms to calculate the local mean of these correlation functions in terms of the underlying classical dynamics. By defining appropriate ensemble averages, we show that fluctuations about the mean can be characterised in terms of classical correlations. We give in particular an explicit expression relating fluctuations of diagonal contributions to those of the full wave correlation function. The methods have a wide range of applications both in quantum mechanics and for classical wave problems such as in vibro-acoustics and electromagnetism. We apply the methods here to simple quantum systems, so-called quantum maps, which model the behaviour of generic problems on Poincaré sections. Although low-dimensional, these models exhibit a chaotic classical limit and share common characteristics with wave propagation in complex structures.

  16. Mechanical Surface Waves Accompany Action Potential Propagation

    NASA Astrophysics Data System (ADS)

    Machta, Benjamin; El Hady, Ahmed

    2015-03-01

    The action potential (AP) is the basic mechanism by which information is transmitted along neuronal axons. Although the excitable nature of axons is understood to be primarily electrical, many experimental studies have shown that a mechanical displacement of the axonal membrane co-propagates with the electrical signal. While the experimental evidence for co-propagating mechanical waves is diverse and compelling, there is no consensus for their physical underpinnings. We present a model in which these mechanical displacements arise from the driving of mechanical surface waves, in which potential energy is stored in elastic deformations of the neuronal membrane and cytoskeleton while kinetic energy is stored in the movement of the axoplasmic fluid. In our model these surface waves are driven by the traveling wave of electrical depolarization that characterizes the AP, altering the electrostatic forces across the membrane as it passes. Our model allows us to predict the shape of the displacement that should accompany any traveling wave of voltage, including the well-characterized AP. We expect our model to serve as a framework for understanding the physical origins and possible functional roles of these AWs in neurobiology. See Arxiv/1407.7600

  17. Seismic wave propagation in cracked porous media

    NASA Astrophysics Data System (ADS)

    Pointer, Tim; Liu, Enru; Hudson, John A.

    2000-07-01

    The movement of interstitial fluids within a cracked solid can have a significant effect on the properties of seismic waves of long wavelength propagating through the solid. We consider three distinct mechanisms of wave-induced fluid flow: flow through connections between cracks in an otherwise non-porous material, fluid movement within partially saturated cracks, and diffusion from the cracks into a porous matrix material. In each case the cracks may be aligned or randomly oriented, leading, respectively, to anisotropic or isotropic wave speeds and attenuation factors. In general, seismic velocities exhibit behaviour that is intermediate between that of empty cracks and that of isolated liquid-filled cracks if fluid flow is significant. In the range of frequencies for which considerable fluid flow occurs there is high attenuation and dispersion of seismic waves. Fluid flow may be on either a wavelength scale or a local scale depending on the model and whether the cracks are aligned or randomly oriented, resulting in completely different effects on seismic wave propagation. A numerical analysis shows that all models can have an effect over the exploration seismic frequency range.

  18. Wave Propagation in Jointed Geologic Media

    SciTech Connect

    Antoun, T

    2009-12-17

    Predictive modeling capabilities for wave propagation in a jointed geologic media remain a modern day scientific frontier. In part this is due to a lack of comprehensive understanding of the complex physical processes associated with the transient response of geologic material, and in part it is due to numerical challenges that prohibit accurate representation of the heterogeneities that influence the material response. Constitutive models whose properties are determined from laboratory experiments on intact samples have been shown to over-predict the free field environment in large scale field experiments. Current methodologies for deriving in situ properties from laboratory measured properties are based on empirical equations derived for static geomechanical applications involving loads of lower intensity and much longer durations than those encountered in applications of interest involving wave propagation. These methodologies are not validated for dynamic applications, and they do not account for anisotropic behavior stemming from direcitonal effects associated with the orientation of joint sets in realistic geologies. Recent advances in modeling capabilities coupled with modern high performance computing platforms enable physics-based simulations of jointed geologic media with unprecedented details, offering a prospect for significant advances in the state of the art. This report provides a brief overview of these modern computational approaches, discusses their advantages and limitations, and attempts to formulate an integrated framework leading to the development of predictive modeling capabilities for wave propagation in jointed and fractured geologic materials.

  19. Simulations of Seismic Wave Propagation on Mars

    NASA Astrophysics Data System (ADS)

    Bozdağ, Ebru; Ruan, Youyi; Metthez, Nathan; Khan, Amir; Leng, Kuangdai; van Driel, Martin; Wieczorek, Mark; Rivoldini, Attilio; Larmat, Carène S.; Giardini, Domenico; Tromp, Jeroen; Lognonné, Philippe; Banerdt, Bruce W.

    2017-03-01

    We present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust (Sohl and Spohn in J. Geophys. Res., Planets 102(E1):1613-1635, 1997). For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE (Komatitsch and Tromp in Geophys. J. Int. 149(2):390-412, 2002a; 150(1):303-318, 2002b) against the 2D axisymmetric wave propagation solver AxiSEM (Nissen-Meyer et al. in Solid Earth 5(1):425-445, 2014) at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on ray theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars' northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D (Fichtner et al. Geophys. J. Int. 179:1703-1725, 2009) based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. We conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.

  20. Local stability analysis for a planar shock wave

    NASA Technical Reports Server (NTRS)

    Salas, M. D.

    1984-01-01

    A procedure to study the local stability of planar shock waves is presented. The procedure is applied to a Rankine-Hugoniot shock in a divergent/convergent nozzle, to an isentropic shock in a divergent/convergent nozzle, and to Rankine-Hugoniot shocks attached to wedges and cones. It is shown that for each case, the equation governing the shock motion is equivalent to the damped harmonic oscillator equation.

  1. Seismic Wave Propagation on the Tablet Computer

    NASA Astrophysics Data System (ADS)

    Emoto, K.

    2015-12-01

    Tablet computers widely used in recent years. The performance of the tablet computer is improving year by year. Some of them have performance comparable to the personal computer of a few years ago with respect to the calculation speed and the memory size. The convenience and the intuitive operation are the advantage of the tablet computer compared to the desktop PC. I developed the iPad application of the numerical simulation of the seismic wave propagation. The numerical simulation is based on the 2D finite difference method with the staggered-grid scheme. The number of the grid points is 512 x 384 = 196,608. The grid space is 200m in both horizontal and vertical directions. That is the calculation area is 102km x 77km. The time step is 0.01s. In order to reduce the user waiting time, the image of the wave field is drawn simultaneously with the calculation rather than playing the movie after the whole calculation. P and S wave energies are plotted on the screen every 20 steps (0.2s). There is the trade-off between the smooth simulation and the resolution of the wave field image. In the current setting, it takes about 30s to calculate the 10s wave propagation (50 times image updates). The seismogram at the receiver is displayed below of the wave field updated in real time. The default medium structure consists of 3 layers. The layer boundary is defined by 10 movable points with linear interpolation. Users can intuitively change to the arbitrary boundary shape by moving the point. Also users can easily change the source and the receiver positions. The favorite structure can be saved and loaded. For the advance simulation, users can introduce the random velocity fluctuation whose spectrum can be changed to the arbitrary shape. By using this application, everyone can simulate the seismic wave propagation without the special knowledge of the elastic wave equation. So far, the Japanese version of the application is released on the App Store. Now I am preparing the

  2. Wave propagation in axially moving periodic strings

    NASA Astrophysics Data System (ADS)

    Sorokin, Vladislav S.; Thomsen, Jon Juel

    2017-04-01

    The paper deals with analytically studying transverse waves propagation in an axially moving string with periodically modulated cross section. The structure effectively models various relevant technological systems, e.g. belts, thread lines, band saws, etc., and, in particular, roller chain drives for diesel engines by capturing both their spatial periodicity and axial motion. The Method of Varying Amplitudes is employed in the analysis. It is shown that the compound wave traveling in the axially moving periodic string comprises many components with different frequencies and wavenumbers. This is in contrast to non-moving periodic structures, for which all components of the corresponding compound wave feature the same frequency. Due to this "multi-frequency" character of the wave motion, the conventional notion of frequency band-gaps appears to be not applicable for the moving periodic strings. Thus, for such structures, by frequency band-gaps it is proposed to understand frequency ranges in which the primary component of the compound wave attenuates. Such frequency band-gaps can be present for a moving periodic string, but only if its axial velocity is lower than the transverse wave speed, and, the higher the axial velocity, the narrower the frequency band-gaps. The revealed effects could be of potential importance for applications, e.g. they indicate that due to spatial inhomogeneity, oscillations of axially moving periodic chains always involve a multitude of frequencies.

  3. Planar Submillimeter-Wave Mixer Technology with Integrated Antenna

    NASA Technical Reports Server (NTRS)

    Chattopadhyay, Gautam; Mehdi, Imran; Gill, John J.; Lee, Choonsup; lombart, Muria L.; Thomas, Betrand

    2010-01-01

    High-performance mixers at terahertz frequencies require good matching between the coupling circuits such as antennas and local oscillators and the diode embedding impedance. With the availability of amplifiers at submillimeter wavelengths and the need to have multi-pixel imagers and cameras, planar mixer architecture is required to have an integrated system. An integrated mixer with planar antenna provides a compact and optimized design at terahertz frequencies. Moreover, it leads to a planar architecture that enables efficient interconnect with submillimeter-wave amplifiers. In this architecture, a planar slot antenna is designed on a thin gallium arsenide (GaAs) membrane in such a way that the beam on either side of the membrane is symmetric and has good beam profile with high coupling efficiency. A coplanar waveguide (CPW) coupled Schottky diode mixer is designed and integrated with the antenna. In this architecture, the local oscillator (LO) is coupled through one side of the antenna and the RF from the other side, without requiring any beam sp litters or diplexers. The intermediate frequency (IF) comes out on a 50-ohm CPW line at the edge of the mixer chip, which can be wire-bonded to external circuits. This unique terahertz mixer has an integrated single planar antenna for coupling both the radio frequency (RF) input and LO injection without any diplexer or beamsplitters. The design utilizes novel planar slot antenna architecture on a 3- mthick GaAs membrane. This work is required to enable future multi-pixel terahertz receivers for astrophysics missions, and lightweight and compact receivers for planetary missions to the outer planets in our solar system. Also, this technology can be used in tera hertz radar imaging applications as well as for testing of quantum cascade lasers (QCLs).

  4. Modeling Propagation of Shock Waves in Metals

    SciTech Connect

    Howard, W M; Molitoris, J D

    2005-08-19

    We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P {approx} 300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and shear modulus depend on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and shear modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that give the correct detonation velocity and C-J pressure (P {approx} 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov.

  5. 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.

  6. Truncation and Accumulated Errors in Wave Propagation

    NASA Astrophysics Data System (ADS)

    Chiang, Yi-Ling F.

    1988-12-01

    The approximation of the truncation and accumulated errors in the numerical solution of a linear initial-valued partial differential equation problem can be established by using a semidiscretized scheme. This error approximation is observed as a lower bound to the errors of a finite difference scheme. By introducing a modified von Neumann solution, this error approximation is applicable to problems with variable coefficients. To seek an in-depth understanding of this newly established error approximation, numerical experiments were performed to solve the hyperbolic equation {∂U}/{∂t} = -C 1(x)C 2(t) {∂U}/{∂x}, with both continuous and discontinuous initial conditions. We studied three cases: (1) C1( x)= C0 and C2( t)=1; (2) C1( x)= C0 and C2( t= t; and (3) C 1(x)=1+( {solx}/{a}) 2 and C2( t)= C0. Our results show that the errors are problem dependent and are functions of the propagating wave speed. This suggests a need to derive problem-oriented schemes rather than the equation-oriented schemes as is commonly done. Furthermore, in a wave-propagation problem, measurement of the error by the maximum norm is not particularly informative when the wave speed is incorrect.

  7. Sound wave propagation through glow discharge plasma

    NASA Astrophysics Data System (ADS)

    Stepaniuk, Vadim P.

    This work investigates the use of glow discharge plasma for acoustic wave manipulation. The broader goal is the suppression of aerodynamic noise using atmospheric glow discharge plasma as a sound barrier. Part of the effort was devoted to the development of a system for the generation of a large volume stable DC glow discharge in air both at atmospheric and at reduced pressures. The single tone sound wave propagation through the plasma was systematically studied. Attenuation of the acoustic wave passing through the glow discharge was measured for a range of experimental conditions including different discharge currents, electrode configurations, air pressures and sound frequencies including audible sound and ultrasound. Sound attenuation by glow discharge plasma as high as -28 dB was recorded in the experiments. Two types of possible mechanisms were considered that can potentially cause the observed sound attenuation. One is a global mechanism and the other is a local mechanism. The global mechanism considered is based on the reflection and refraction of acoustic wave due to the gas temperature gradients that form around the plasma. The local mechanism, on the other hand, is essentially the interaction of the acoustic wave with the plasma as it propagates inside the discharge and it can be viewed as a feedback system. Detailed temperature measurements, using laser-induced Rayleigh scattering technique, were carried out in the glow discharge plasma in order to evaluate the role of global mechanism in the observed attenuation. These measurements were made for a range of conditions in the atmospheric glow discharge. Theoretical analysis of the sound attenuation was carried out to identify the physical mechanism for the observed sound attenuation by plasma. It was demonstrated that the global mechanism is the dominant mechanism of sound attenuation. As a result of this study, the potentials and limitations of the plasma noise suppression technology were determined and

  8. Determination of complex permittivity from propagation constant measurement with planar transmission lines

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A new two-standard calibration procedure is outlined for determining the complex permittivity of materials from the propagation constant measured with planar transmission lines. Once calibrated, a closed-form expression for the material permittivity is obtained. The effects of radiation and conducto...

  9. Fracturing from highly deviated and horizontal wells: Numerical analysis of non-planar fracture propagation

    SciTech Connect

    Olson, J.E.

    1995-12-31

    Fracturing from horizontal and highly deviated wells can often result in complex, non-planar fracture geometry. A two-dimensional model was developed to analyze the effects of non-planar fracture propagation for different in situ boundary conditions and hydraulic fracturing parameters. Numerical simulations show that curving fracture geometry reduces created fracture length compared to a planar fracture and causes a fracture width restriction at the wellbore. Reduction in fracture length can reduce expected well stimulation effects and jeopardize well economics. Near-wellbore width restrictions increase fracture treating pressure and may cause wellbore screen-out during the proppant stages of a fracturing treatment. The negative impact of non-planar geometry can be mitigated with short perforated intervals, high viscosity fracturing fluids, proper wellbore alignment and pre-pad proppant slugs for near-wellbore erosion.

  10. Elastic Wave Propagation and Generation in Seismology

    NASA Astrophysics Data System (ADS)

    Lees, Jonathan M.

    The majority of mature seismologists of my generation were introduced to theoretical seismology via classic textbooks written in the early 1980s. Since this generation has matured and taken the mantle of teaching seismology to a new generation, several new books have been put forward as replacements, or alternatives, to the original classical texts. The target readers of the new texts range from beginner through intermediate to more advanced, although all have been attempts to improve upon what is now considered standard convention in quantitative seismology. To this plethora of choices we now have a new addition by Jose Pujol, titledElastic Wave Propagation and Generation in Seismology.

  11. Elastic Wave Propagation Mechanisms in Underwater Acoustic Environments

    DTIC Science & Technology

    2015-09-30

    Elastic wave propagation mechanisms in underwater acoustic environments Scott D. Frank Marist College Department of Mathematics Poughkeepsie...conversion from elastic propagation to acoustic propagation, and intense interface waves on underwater acoustic environments with elastic bottoms... acoustic energy in the water column. Elastic material parameters will be varied for analysis of the dissipation of water column acoustic energy

  12. Wave propagation in polymers. Part II

    NASA Astrophysics Data System (ADS)

    Newlander, C. D.; Cherest, J. A.; Lilly, M. C.; Eisler, R. D.

    2000-04-01

    Wave profile measurements made in Polycarbonate at around 2.2 kbars were previously reported showing dispersion and amplitude attenuation that were neither expected nor predicted from available models. This data is being re-visited here and analyzed using a modified material model and the PUFF74 computer code. The new computation shows remarkable agreement with the experiments. The modeling treated the material as a visco-elastic/plastic medium using the method developed by Bade. This work is expected to further our understanding of wave propagation in highly compressible and visco-elastic/plastic media. It is also expected to provide insights on the role of strain rate effects on material properties such as elastic moduli, strengths and loading behaviors.

  13. Seismic wave propagation in granular media

    NASA Astrophysics Data System (ADS)

    Tancredi, Gonzalo; López, Francisco; Gallot, Thomas; Ginares, Alejandro; Ortega, Henry; Sanchís, Johnny; Agriela, Adrián; Weatherley, Dion

    2016-10-01

    Asteroids and small bodies of the Solar System are thought to be agglomerates of irregular boulders, therefore cataloged as granular media. It is a consensus that many asteroids might be considered as rubble or gravel piles.Impacts on their surface could produce seismic waves which propagate in the interior of these bodies, thus causing modifications in the internal distribution of rocks and ejections of particles and dust, resulting in a cometary-type comma.We present experimental and numerical results on the study of propagation of impact-induced seismic waves in granular media, with special focus on behavior changes by increasing compression.For the experiment, we use an acrylic box filled with granular materials such as sand, gravel and glass spheres. Pressure inside the box is controlled by a movable side wall and measured with sensors. Impacts are created on the upper face of the box through a hole, ranging from free-falling spheres to gunshots. We put high-speed cameras outside the box to record the impact as well as piezoelectic sensors and accelerometers placed at several depths in the granular material to detect the seismic wave.Numerical simulations are performed with ESyS-Particle, a software that implements the Discrete Element Method. The experimental setting is reproduced in the numerical simulations using both individual spherical particles and agglomerates of spherical particles shaped as irregular boulders, according to rock models obtained with a 3D scanner. The numerical experiments also reproduces the force loading on one of the wall to vary the pressure inside the box.We are interested in the velocity, attenuation and energy transmission of the waves. These quantities are measured in the experiments and in the simulations. We study the dependance of these three parameters with characteristics like: impact speed, properties of the target material and the pressure in the media.These results are relevant to understand the outcomes of impacts in

  14. Artificial birefringent metallic planar structures for terahertz wave polarization manipulation.

    PubMed

    Wang, Lei; Jiang, Suhua; Hu, Haifeng; Song, Haomin; Zeng, Wei; Gan, Qiaoqiang

    2014-01-15

    We propose an artificial birefringent terahertz (THz) device constructed by subwavelength L-shaped hole arrays on a single metallic layer. This structure is able to work as a polarizer when the incident frequency is between the cut-off frequencies of two eigenmodes. When the incident wave is beyond cut-off frequencies of these two modes, it can be designed as an efficient half- or quarter-wave plate with extraordinary transmission properties. A big effective index difference from 0.254 to 0.768 is obtained using a subwavelength-thick planar structure, which can reduce the thickness of the device to one tenth of conventional quartz birefringent crystals for THz waves.

  15. Propagation of gravity waves across the tropopause

    NASA Astrophysics Data System (ADS)

    Bense, Vera; Spichtinger, Peter

    2015-04-01

    The tropopause region is characterised by strong gradients in various atmospheric quantities that exhibit different properties in the troposphere compared to the stratosphere. The temperature lapse rate typically changes from negative to near-zero values resulting in a strong increase in stability. Accordingly, the buoyancy frequency often undergoes a jump at the tropopause. Analysis of radiosounding data also shows the existence of a strong inversion layer (tropopause inversion layer, TIL) characterised by a strong maximum in buoyancy frequency just above the tropopause, see e.g. Birner et al. (2002). Additionally, the magnitude of the vertical wind shear of the horizontal wind maximizes at the tropopause and the region also exhibits characteristical gradients of trace gases. Vertically propagating gravity waves can be excited in the troposphere by several mechanisms, e.g. by flow over topography (e.g. Durran, 1990), by jets and fronts (for a recent review: Plougonven and Zhang, 1990) or by convection (e.g. Clark et al., 1986). When these waves enter the tropopause region, their properties can be changed drastically by the changing stratification and strong wind shear. Within this work, the EULAG (Eulerian/semi-Lagrangian fluid solver, see e.g. Smolarkiewicz and Margolin, 1997) model is used to investigate the impact of the tropopause on vertically propagating gravity waves excited by flows over topography. The choice of topography (sine-shaped mountains, bell-shaped mountain) along with horizontal wind speed and tropospheric value of buoyancy frequency determine the spectrum of waves (horizontal and vertical wavelengths) that is excited in the tropsphere. In order to analyse how these spectra change for several topographies when a tropopause is present, we investigate different idealized cases in a two-dimensional domain. By varying the vertical profiles of buoyancy frequency (step-wise vs. continuos change, including TIL) and wind shear, the tropopause

  16. Calibration of seismic wave propagation in Kuwait

    SciTech Connect

    Al-Awadhi, J; Endo, E; Fryall, F; Harris, D; Mayeda, K; Rodgers, A; Ruppert, S; Sweeney, J

    1999-07-23

    The Kuwait Institute of Scientific Research (KISR), the USGS and LLNL are collaborating to calibrate seismic wave propagation in Kuwait and surrounding regions of the northwest Arabian Gulf using data from the Kuwait National Seismic Network (KNSN). Our goals are to develop local and regional propagation models for locating and characterizing seismic events in Kuwait and portions of the Zagros mountains close to Kuwait. The KNSN consists of 7 short-period stations and one broadband (STS-2) station. Constraints on the local velocity structure may be derived from joint inversions for hypocenters of local events and the local velocity model, receiver functions from three-component observations of teleseisms, and surface wave phase velocity estimated from differential dispersion measurements made across the network aperture. Data are being collected to calibrate travel-time curves for the principal regional phases for events in the Zagros mountains. The available event observations span the distance range from approximately 2.5 degrees to almost 9 degrees. Additional constraints on structure across the deep sediments of the Arabian Gulf will be obtained from long-period waveform modeling.

  17. WAVE: Interactive Wave-based Sound Propagation for Virtual Environments.

    PubMed

    Mehra, Ravish; Rungta, Atul; Golas, Abhinav; Ming Lin; Manocha, Dinesh

    2015-04-01

    We present an interactive wave-based sound propagation system that generates accurate, realistic sound in virtual environments for dynamic (moving) sources and listeners. We propose a novel algorithm to accurately solve the wave equation for dynamic sources and listeners using a combination of precomputation techniques and GPU-based runtime evaluation. Our system can handle large environments typically used in VR applications, compute spatial sound corresponding to listener's motion (including head tracking) and handle both omnidirectional and directional sources, all at interactive rates. As compared to prior wave-based techniques applied to large scenes with moving sources, we observe significant improvement in runtime memory. The overall sound-propagation and rendering system has been integrated with the Half-Life 2 game engine, Oculus-Rift head-mounted display, and the Xbox game controller to enable users to experience high-quality acoustic effects (e.g., amplification, diffraction low-passing, high-order scattering) and spatial audio, based on their interactions in the VR application. We provide the results of preliminary user evaluations, conducted to study the impact of wave-based acoustic effects and spatial audio on users' navigation performance in virtual environments.

  18. Circular polarization of obliquely propagating whistler wave magnetic field

    SciTech Connect

    Bellan, P. M.

    2013-08-15

    The circular polarization of the magnetic field of obliquely propagating whistler waves is derived using a basis set associated with the wave partial differential equation. The wave energy is mainly magnetic and the wave propagation consists of this magnetic energy sloshing back and forth between two orthogonal components of magnetic field in quadrature. The wave electric field energy is small compared to the magnetic field energy.

  19. Propagation of waves of acoustic frequencies in curved ducts

    NASA Technical Reports Server (NTRS)

    Rostafinski, W.

    1973-01-01

    The propagation of waves of acoustic frequencies in curved ducts is studied for the first four modes. The analysis makes use of Bessel functions to construct curves of wave number in the duct versus imposed wave number. The results apply to ducts of arbitrary width and arbitrary radii of curvature. The characteristics of motion in a bend are compared with propagation of waves in a straight duct, and important differences in the behavior of waves are noted.

  20. Calibration of seismic wave propagation in Jordan

    SciTech Connect

    Al-Husien, A; Amrat, A; Harris, D; Mayeda, K; Nakanishi, K; Rodgers, A; Ruppert, S; Ryall, F; Skinnell, K; Yazjeen, T

    1999-07-23

    The Natural Resources Authority of Jordan (NRA), the USGS and LLNL have a collaborative project to improve the calibration of seismic propagation in Jordan and surrounding regions. This project serves common goals of CTBT calibration and earthquake hazard assessment in the region. These objectives include accurate location of local and regional earthquakes, calibration of magnitude scales, and the development of local and regional propagation models. In the CTBT context, better propagation models and more accurately located events in the Dead Sea rift region can serve as (potentially GT5) calibration events for generating IMS location corrections. The detection and collection of mining explosions underpins discrimination research. The principal activity of this project is the deployment of two broadband stations at Hittiyah (south Jordan) and Ruweishid (east Jordan). These stations provide additional paths in the region to constrain structure with surface wave and body wave tomography. The Ruweishid station is favorably placed to provide constraints on Arabian platform structure. Waveform modeling with long-period observations of larger earthquakes will provide constraints on 1-D velocity models of the crust and upper mantle. Data from these stations combined with phase observations from the 26 short-period stations of the Jordan National Seismic Network (JNSN) may allow the construction of a more detailed velocity model of Jordan. The Hittiyah station is an excellent source of ground truth information for the six phosphate mines of southern Jordan and Israel. Observations of mining explosions collected by this station have numerous uses: for definition of templates for screening mining explosions, as ground truth events for calibrating travel-time models, and as explosion populations in development and testing discriminants. Following previously established procedures for identifying explosions, we have identified more than 200 explosions from the first 85 days of

  1. Three-dimensional modeling of propagating precipitation waves.

    PubMed

    Tinsley, Mark R; Collison, Darrell; Showalter, Kenneth

    2015-06-01

    A general three-dimensional model for propagating precipitation waves is presented. Structural features identified in experimental studies of propagating waves in the AlCl3/NaOH and NaAl(OH)4/HCl systems are described by the 3D model. Two forms of precipitate with different physical properties play key mechanistic roles in the wave propagation. Experimentally observed circular and spiral waves are simulated by the 3D model, as well as wave annihilation on the collision of two waves.

  2. Some Numerical Experiments on Detonation Wave Propagation

    NASA Technical Reports Server (NTRS)

    Cambier, Jean-Luc; Edwards, Thomas A. (Technical Monitor)

    1995-01-01

    In this paper we present the results of a series of numerical experiments done on the propagation and initiation of a detonation wave. The calculations are performed in one-dimension, with considerable grid resolution. Of particular interest are the following questions: (1) the nature of periodic and chaotic instabilities generated by the wave; (2) the influence of the grid resolution on these instabilities; (3) the influence of the 'quality' of the numerical scheme; and (4) the influence of 'noise'. In the calculations, we use a second-order Total Variation Diminishing (TVD) scheme as the basic numerical method, with grid spacings as low as a fraction of a micron. Detonations waves are generated at the closed end of a tube, and allowed to propagate for approximately 20 cm. The required energy for successful initiation of the detonation will be measured for different cases of grid resolution and numerical schemes. A modified version of the TVD scheme has also been devised, which allows for much lower numerical diffusion of the radical species in the exponentially growing region behind the shock. The effect of this modification will be demonstrated. Oscillations in peak pressure and induction length are seen to develop in some cases: the oscillations can go through a sequence of modes, from a regular, high frequency mode to a low frequency mode with period doubling. A chaotic regime can also be obtained. General conclusions on the quality of algorithms will be presented. We will also discuss the performance of a version of the code developed on the IBM SP2 parallel computer.

  3. Properties of elastic waves in quasiregular structures with planar defects

    NASA Astrophysics Data System (ADS)

    Aynaou, H.; Velasco, V. R.; Nougaoui, A.; El Boudouti, E. H.; Bria, D.

    2002-07-01

    We have studied the elastic waves in quasiregular structures following the Fibonacci and Rudin-Shapiro sequences, and having planar defects, that is breaks of the quasiregular structure in different parts of the system. It is seen that the different kinds of defects produce effects on different ranges of the frequency spectrum, and can introduce more localized states in the gaps, or modify the frequencies of the states in the gaps. We have also studied the phase time and transmission coefficients, thus seeing how these localized modes can be used as frequency filters.

  4. Wave propagation in predator-prey systems

    NASA Astrophysics Data System (ADS)

    Fu, Sheng-Chen; Tsai, Je-Chiang

    2015-12-01

    In this paper, we study a class of predator-prey systems of reaction-diffusion type. Specifically, we are interested in the dynamical behaviour for the solution with the initial distribution where the prey species is at the level of the carrying capacity, and the density of the predator species has compact support, or exponentially small tails near x=+/- ∞ . Numerical evidence suggests that this will lead to the formation of a pair of diverging waves propagating outwards from the initial zone. Motivated by this phenomenon, we establish the existence of a family of travelling waves with the minimum speed. Unlike the previous studies, we do not use the shooting argument to show this. Instead, we apply an iteration process based on Berestycki et al 2005 (Math Comput. Modelling 50 1385-93) to construct a set of super/sub-solutions. Since the underlying system does not enjoy the comparison principle, such a set of super/sub-solutions is not based on travelling waves, and in fact the super/sub-solutions depend on each other. With the aid of the set of super/sub-solutions, we can construct the solution of the truncated problem on the finite interval, which, via the limiting argument, can in turn generate the wave solution. There are several advantages to this approach. First, it can remove the technical assumptions on the diffusivities of the species in the existing literature. Second, this approach is of PDE type, and hence it can shed some light on the spreading phenomenon indicated by numerical simulation. In fact, we can compute the spreading speed of the predator species for a class of biologically acceptable initial distributions. Third, this approach might be applied to the study of waves in non-cooperative systems (i.e. a system without a comparison principle).

  5. Hybrid Metameterials Enable Fast Electrical Modulation Of Freely Propagating Terahertz Waves

    SciTech Connect

    Chen, Hou-tong; O' Hara, John F; Taylor, Antoinette J

    2008-01-01

    We demonstrate fast electrical modulation of freely propagating THz waves at room temperature using hybrid metamaterial devices. the devices are planar metamaterials fabricated on doped semiconducor epitaxial layers, which form hybrid metamaterial - Schottky diode structures. With an applied ac voltage bias, we show modulation of THz radiation at inferred frequencies over 2 MHz. The modulation speed is limited by the device depletion capacitance which may be reduced for even faster operation.

  6. A geometric singular perturbation approach for planar stationary shock waves

    NASA Astrophysics Data System (ADS)

    Wang, Zhuopu; Zhang, Jiazhong; Ren, Junheng; Aslam, Muhammad Nauman

    2015-08-01

    The non-linear non-equilibrium nature of shock waves in gas dynamics is investigated for the planar case. Along each streamline, the Euler equations with non-equilibrium pressure are reduced to a set of ordinary differential equations defining a slow-fast system, and geometric singular perturbation theory is applied. The proposed theory shows that an orbit on the slow manifold corresponds to the smooth part of the solution to the Euler equation, where non-equilibrium effects are negligible; and a relaxation motion from the unsteady to the steady branch of the slow manifold corresponds to a shock wave, where the flow relaxes from non-equilibrium to equilibrium. Recognizing the shock wave as a fast motion is found to be especially useful for shock wave detection when post-processing experimental measured or numerical calculated flow fields. Various existing shock detection methods can be derived from the proposed theory in a rigorous mathematical manner. The proposed theory provides a new shock detection method based on its non-linear non-equilibrium nature, and may also serve as the theoretical foundation for many popular shock wave detection techniques.

  7. Regional Wave Propagation in Southeastern United States

    NASA Astrophysics Data System (ADS)

    Jemberie, A. L.; Langston, C. A.

    2003-12-01

    Broad band seismograms from the April 29, 2003, M4.6 Fort Payne, Alabama earthquake are analyzed to infer mechanisms of crustal wave propagation, crust and upper mantle velocity structure in southeastern United States, and source parameters of the event. In particular, we are interested in producing deterministic models of the distance attenuation of earthquake ground motions through computation of synthetic seismograms. The method first requires constraining the source parameters of an earthquake and then modeling the amplitude and times of broadband arrivals within the waveforms to infer appropriate layered earth models. A first look at seismograms recorded by stations outside the Mississippi Embayment (ME) show clear body phases such P, sP, Pnl, Sn and Lg. The ME signals are qualitatively different from others because they have longer durations and large surface waves. A straightforward interpretation of P wave arrival times shows a typical upper mantle velocity of 8.18 km/s. However, there is evidence of significantly higher P phase velocities at epicentral distances between 400 and 600km, that may be caused by a high velocity upper mantle anomaly; triplication of P-waves is seen in these seismograms. The arrival time differences between regional P and the depth phase sP at different stations are used to constrain the depth of the earthquake. The source depth lies between 9.5 km and 13km which is somewhat more shallow than the network location that was constrained to 15km depth. The Fort Payne earthquake is the largest earthquake to have occurred within the Eastern Tennessee Seismic Zone.

  8. Wave propagation in a random medium

    NASA Technical Reports Server (NTRS)

    Lee, R. W.; Harp, J. C.

    1969-01-01

    A simple technique is used to derive statistical characterizations of the perturbations imposed upon a wave (plane, spherical or beamed) propagating through a random medium. The method is essentially physical rather than mathematical, and is probably equivalent to the Rytov method. The limitations of the method are discussed in some detail; in general they are restrictive only for optical paths longer than a few hundred meters, and for paths at the lower microwave frequencies. Situations treated include arbitrary path geometries, finite transmitting and receiving apertures, and anisotropic media. Results include, in addition to the usual statistical quantities, time-lagged functions, mixed functions involving amplitude and phase fluctuations, angle-of-arrival covariances, frequency covariances, and other higher-order quantities.

  9. Propagation of nonlinearly generated harmonic spin waves in microscopic stripes

    SciTech Connect

    Rousseau, O.; Yamada, M.; Miura, K.; Ogawa, S.; Otani, Y.

    2014-02-07

    We report on the experimental study of the propagation of nonlinearly generated harmonic spin waves in microscopic CoFeB stripes. Using an all electrical technique with coplanar waveguides, we find that two kinds of spin waves can be generated by nonlinear frequency multiplication. One has a non-uniform spatial geometry and thus requires appropriate detector geometry to be identified. The other corresponds to the resonant fundamental propagative spin waves and can be efficiently excited by double- or triple-frequency harmonics with any geometry. Nonlinear excited spin waves are particularly efficient in providing an electrical signal arising from spin wave propagation.

  10. Wave propagation in sandwich panels with a poroelastic core.

    PubMed

    Liu, Hao; Finnveden, Svante; Barbagallo, Mathias; Arteaga, Ines Lopez

    2014-05-01

    Wave propagation in sandwich panels with a poroelastic core, which is modeled by Biot's theory, is investigated using the waveguide finite element method. A waveguide poroelastic element is developed based on a displacement-pressure weak form. The dispersion curves of the sandwich panel are first identified as propagating or evanescent waves by varying the damping in the panel, and wave characteristics are analyzed by examining their motions. The energy distributions are calculated to identify the dominant motions. Simplified analytical models are also devised to show the main physics of the corresponding waves. This wave propagation analysis provides insight into the vibro-acoustic behavior of sandwich panels lined with elastic porous materials.

  11. Acoustoelastic lamb wave propagation in a homogeneous, isotropic aluminum plate

    SciTech Connect

    Gandhi, Navneet; Michaels, Jennifer E.; Lee, Sang Jun

    2011-06-23

    The effect of stress on Lamb wave propagation is relevant to both nondestructive evaluation and structural health monitoring because of changes in received signals due to both the associated strain and the acoustoelastic effect. A homogeneous plate that is initially isotropic becomes anisotropic under uniaxial stress, and dispersion of propagating waves becomes directionally dependent. The problem is similar to Lamb wave propagation in an anisotropic plate, except the fourth order tensor in the resulting wave equation does not have the same symmetry as that for the unstressed anisotropic plate, and the constitutive equation relating incremental stress to incremental strain is more complicated. Here we consider the theory of acoustoelastic Lamb wave propagation and show how dispersion curves shift anisotropically for an aluminum plate under uniaxial tension. Theoretical predictions of changes in phase velocity as a function of propagation direction are compared to experimental results for a single wave mode.

  12. Oscillations above sunspots: Evidence for propagating waves?

    NASA Astrophysics Data System (ADS)

    O'Shea, E.; Muglach, K.; Fleck, B.

    2002-05-01

    We present results of an analysis of time series data observed in sunspot umbral regions. The data were obtained in the context of the SOHO Joint Observing Program (JOP) 97 in September 2000. This JOP included the Coronal Diagnostic Spectrometer (CDS) and the Michelson Doppler Imaging (MDI) instrument, both part of SOHO, the TRACE satellite and various ground based observatories. The data was analysed by using both Fourier and wavelet time series analysis techniques. We find that oscillations are present in the umbra at all temperatures investigated, from the temperature minimum as measured by TRACE 1700 Å up to the upper corona as measured by CDS Fe Xvi 335 Å (log T=6.4 K). Oscillations are found to be present with frequencies in the range of 5.4 mHz (185 s) to 8.9 mHz (112 s). Using the techniques of cross-spectral analysis time delays were found between low and high temperature emission suggesting the possibility of both upward and downward wave propagation. It is found that there is typically a good correlation between the oscillations measured at the different emission temperatures, once the time delays are taken into account. We find umbral oscillations both inside and outside of sunspot plume locations which indicates that umbral oscillations can be present irrespective of the presence of these sunspot plumes. We find that a number of oscillation frequencies can exist co-spatially and simultaneously i.e. for one pixel location three different frequencies at 5.40, 7.65 and 8.85 mHz were measured. We investigate the variation of the relative amplitudes of oscillation with temperature and find that there is a tendency for the amplitudes to reach a maximum at the temperature of O Iii (and less typically O V and Mg Ix) and then to decrease to reach a minimum at the temperature of Mg X (log T=6.0 K), before increasing again at the temperature of Fe Xvi. We discuss a number of possible theoretical scenarios that might explain these results. From a measurement of

  13. Pressure wave propagation studies for oscillating cascades

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.

    1992-01-01

    The unsteady flowfield around an oscillating cascade of flat plates is studied using a time marching Euler code. Exact solutions based on linear theory serve as model problems to study pressure wave propagation in the numerical solution. The importance of using proper unsteady boundary conditions, grid resolution, and time step is demonstrated. Results show that an approximate non-reflecting boundary condition based on linear theory does a good job of minimizing reflections from the inflow and outflow boundaries and allows the placement of the boundaries to be closer than cases using reflective boundary conditions. Stretching the boundary to dampen the unsteady waves is another way to minimize reflections. Grid clustering near the plates does a better job of capturing the unsteady flowfield than cases using uniform grids as long as the CFL number is less than one for a sufficient portion of the grid. Results for various stagger angles and oscillation frequencies show good agreement with linear theory as long as the grid is properly resolved.

  14. Pressure wave propagation studies for oscillating cascades

    NASA Technical Reports Server (NTRS)

    Huff, Dennis L.

    1992-01-01

    The unsteady flow field around an oscillating cascade of flat plates is studied using a time marching Euler code. Exact solutions based on linear theory serve as model problems to study pressure wave propagation in the numerical solution. The importance of using proper unsteady boundary conditions, grid resolution, and time step is demonstrated. Results show that an approximate non-reflecting boundary condition based on linear theory does a good job of minimizing reflections from the inflow and outflow boundaries and allows the placement of the boundaries to be closer than cases using reflective boundary conditions. Stretching the boundary to dampen the unsteady waves is another way to minimize reflections. Grid clustering near the plates does a better job of capturing the unsteady flow field than cases using uniform grids as long as the CFL number is less than one for a sufficient portion of the grid. Results for various stagger angles and oscillation frequencies show good agreement with linear theory as long as the grid is properly resolved.

  15. Effect of Resolution on Propagating Detonation Wave

    SciTech Connect

    Menikoff, Ralph

    2014-07-10

    Simulations of the cylinder test are used to illustrate the effect of mesh resolution on a propagating detonation wave. For this study we use the xRage code with the SURF burn model for PBX 9501. The adaptive mesh capability of xRage is used to vary the resolution of the reaction zone. We focus on two key properties: the detonation speed and the cylinder wall velocity. The latter is related to the release isentrope behind the detonation wave. As the reaction zone is refined (2 to 15 cells for cell size of 62 to 8μm), both the detonation speed and final wall velocity change by a small amount; less than 1 per cent. The detonation speed decreases with coarser resolution. Even when the reaction zone is grossly under-resolved (cell size twice the reaction-zone width of the burn model) the wall velocity is within a per cent and the detonation speed is low by only 2 per cent.

  16. Understanding and Prediction of Nonlinear Effects in Wave Propagation

    DTIC Science & Technology

    2013-02-20

    by a JONSWAP wave spectrum with a significant wave height of Hs = 4m, a peak period of Tp =8s and an enhancement parameter =3.0. The time...for public release; distribution is unlimited In ocean wave-field evolution, nonlinear effects affect the propagation velocity of each wave component...exceeding wave height and/or wave crest height probability functions for wide ranges of nonlinear spectrum parameters, which will enable the

  17. Polydimethylsiloxane membranes for millimeter-wave planar ultra flexible antennas

    NASA Astrophysics Data System (ADS)

    Tiercelin, Nicolas; Coquet, Philippe; Sauleau, Ronan; Senez, Vincent; Fujita, Hiroyuki

    2006-11-01

    We present here the use of polydimethylsiloxane (PDMS) membranes as a new soft polymer substrate (ɛr ap 2.67 at 77 GHz) for the realization of ultra-flexible millimeter-wave printed antennas thanks to the extremely low Young's modulus (EPDMS < 2 MPa). Ultimately this peculiar property enables one to design wide-angle mechanically beam-steering antennas and flexible conformal antennas. The experimental characterization of PDMS material in V- and W-bands highlights high loss tangent values (tanδ ap 0.04 at 77 GHz). Thus micromachining techniques have been developed to reduce dielectric losses for antenna applications at millimeter waves. Here the antenna performance is demonstrated in the 60 GHz band by considering a single microstrip patch antenna supported by a PDMS membrane over an air-filled cavity. After a brief description of the design approach using the method of moments (MoM) and the finite-difference time-domain (FDTD) technique, the technological processes are described in detail. The input impedance and radiation patterns of the prototype are in good agreement with numerical simulations. The radiation efficiency of the micromachined antenna is equal to 60% and is in the same order as that obtained with conventional polymer bulk substrates such as Duroids. These results confirm the validity of the new technological process and assembly procedure, and demonstrate that PDMS membranes can be used to realize low-loss planar membrane-supported millimeter-wave printed circuits and radiating structures.

  18. Analysis and Synthesis of Leaky-Wave Devices in Planar Technology

    NASA Astrophysics Data System (ADS)

    Martinez Ros, Alejandro Javier

    The work developed along this doctoral thesis has been focused on the analysis and synthesis of microwave devices in planar technology. In particular, several types of devices based on the radiation mechanism of leaky waves have been studied. Typically, the radiation properties in leaky-wave devices are determined by the complex propagation constant of the leaky mode, wherein the phase constant is responsible for the pointing angle and the leakage rate for the intensity of the radiated fields. In this manner, by controlling both amplitude and phase of the leaky mode, an effective control over the device's radiation diagram can be obtained. Moreover, with the purpose of efficiently obtaining the leaky mode's radiation properties as function of the main geometrical parameters of the structure, several modal tools based on the transverse resonance analysis of the structure have been performed. In order to demonstrate this simultaneous control over the complex propagation constant in planar technology, several types of leaky-wave devices, including antennas (LWAs), multiplexors and near-field focusing systems, have been designed and manufactured in the technology of substrate integrated waveguide (SIW). This recently proposed technology, allows the design of devices based on classical waveguide technology with standard manufacturing techniques used for printed circuit board (PCB) designs. In this way, most of the parts that form a communication system can be integrated into a single substrate, thus reducing its cost and providing a more robust and compact device, which has less losses compared to other planar technologies such as the microstrip. El trabajo llevado a cabo durante la realizacion de esta tesis doctoral, se ha centrado en el analisis y sintesis de dispositivos de microondas en tecnologia planar. En concreto, se han estudiado diferentes tipos de dispositivos basados en radiacion por ondas de fuga "leaky waves", en los cuales las propiedades de radiacion

  19. Wave-propagation formulation of seismic response of multistory buildings

    USGS Publications Warehouse

    Safak, E.

    1999-01-01

    This paper presents a discrete-time wave-propagation method to calculate the seismic response of multistory buildings, founded on layered soil media and subjected to vertically propagating shear waves. Buildings are modeled as an extension of the layered soil media by considering each story as another layer in the wave-propagation path. The seismic response is expressed in terms of wave travel times between the layers and wave reflection and transmission coefficients at layer interfaces. The method accounts for the filtering effects of the concentrated foundation and floor masses. Compared with commonly used vibration formulation, the wave-propagation formulation provides several advantages, including simplicity, improved accuracy, better representation of damping, the ability to incorporate the soil layers under the foundation, and providing better tools for identification and damage detection from seismic records. Examples are presented to show the versatility and the superiority of the method.

  20. Voltage modulation of propagating spin waves in Fe

    SciTech Connect

    Nawaoka, Kohei; Shiota, Yoichi; Miwa, Shinji; Tamura, Eiiti; Tomita, Hiroyuki; Mizuochi, Norikazu; Shinjo, Teruya; Suzuki, Yoshishige

    2015-05-07

    The effect of a voltage application on propagating spin waves in single-crystalline 5 nm-Fe layer was investigated. Two micro-sized antennas were employed to excite and detect the propagating spin waves. The voltage effect was characterized using AC lock-in technique. As a result, the resonant field of the magnetostatic surface wave in the Fe was clearly modulated by the voltage application. The modulation is attributed to the voltage induced magnetic anisotropy change in ferromagnetic metals.

  1. Propagation of Axially Symmetric Detonation Waves

    SciTech Connect

    Druce, R L; Roeske, F; Souers, P C; Tarver, C M; Chow, C T S; Lee, R S; McGuire, E M; Overturf, G E; Vitello, P A

    2002-06-26

    We have studied the non-ideal propagation of detonation waves in LX-10 and in the insensitive explosive TATB. Explosively-driven, 5.8-mm-diameter, 0.125-mm-thick aluminum flyer plates were used to initiate 38-mm-diameter, hemispherical samples of LX-10 pressed to a density of 1.86 g/cm{sup 3} and of TATB at a density of 1.80 g/cm{sup 3}. The TATB powder was a grade called ultrafine (UFTATB), having an arithmetic mean particle diameter of about 8-10 {micro}m and a specific surface area of about 4.5 m{sup 2}/g. Using PMMA as a transducer, output pressure was measured at 5 discrete points on the booster using a Fabry-Perot velocimeter. Breakout time was measured on a line across the booster with a streak camera. Each of the experimental geometries was calculated using the Ignition and Growth Reactive Flow Model, the JWL++ Model and the Programmed Burn Model. Boosters at both ambient and cold (-20 C and -54 C) temperatures have been experimentally and computationally studied. A comparison of experimental and modeling results is presented.

  2. Stratospheric constituent response to vertically propagating equatorial waves

    NASA Astrophysics Data System (ADS)

    Salby, Murry L.

    1988-02-01

    Planetary-scale equatorial waves play an important role in the dynamics of the tropical atmosphere. They are believed to be excited in unsteady convective heating in the tropical troposphere. From convective centers in the intertropical convergence zone (ITCZ), equatorial waves propagate vertically into the upper atmosphere where they are eventually absorbed, e.g., through radiative dissipation. A spectrum of vertically propagating Kelvin waves was revealed to be trapped about the equator, radiating vertically out of the tropical troposphere. Two other Kelvin waves were found with phase velocities 2 and 4 times as fast. The ultrafast Kelvin waves move at nearly 120 m/s and are seen to propagate to the highest altitude observed by Nimbus-7 LIMS. Each class has the form of a Kelvin wave, a Gaussian centered on the equator and propagating vertically, and all satisfy the dispersion relationship for equatorial Kelvin waves. These vertically propagating Kelvin waves account for a substantial fraction of the temperature variability in the tropical stratosphere. In combination, they lead to temperature fluctuations in excess of 5K in the upper stratosphere and mesosphere. Because several chemical constituents are photochemically controlled in this region, vertically propagating Kelvin waves are expected to lead to variations in the abundances of such species.

  3. Wave propagation in laminated orthotropic circular cylindrical shells

    NASA Technical Reports Server (NTRS)

    Srinivas, S.

    1976-01-01

    An exact three-dimensional analysis of wave propagation in laminated orthotropic circular cylindrical-shells is developed. Numerical results are presented for three-ply shells, and for various axial wave lengths, circumferential wave numbers, and thicknesses. Results from a thin shell theory and a refined approximate theory are compared with the exact results.

  4. ON THE SOURCE OF PROPAGATING SLOW MAGNETOACOUSTIC WAVES IN SUNSPOTS

    SciTech Connect

    Prasad, S. Krishna; Jess, D. B.; Khomenko, Elena

    2015-10-10

    Recent high-resolution observations of sunspot oscillations using simultaneously operated ground- and space-based telescopes reveal the intrinsic connection between different layers of the solar atmosphere. However, it is not clear whether these oscillations are externally driven or generated in situ. We address this question by using observations of propagating slow magnetoacoustic waves along a coronal fan loop system. In addition to the generally observed decreases in oscillation amplitudes with distance, the observed wave amplitudes are also found to be modulated with time, with similar variations observed throughout the propagation path of the wave train. Employing multi-wavelength and multi-instrument data, we study the amplitude variations with time as the waves propagate through different layers of the solar atmosphere. By comparing the amplitude modulation period in different layers, we find that slow magnetoacoustic waves observed in sunspots are externally driven by photospheric p-modes, which propagate upward into the corona before becoming dissipated.

  5. Studies of Gravity Wave Propagation in the Middle Atmosphere.

    DTIC Science & Technology

    2014-09-26

    34 . . . . . • * * . , . • :’ . . . , ",.,,- -. ’’’ " . ’-- o p - %"""" * " AFOSR.TR. 85-0505 physical dynamics,inc. PD-NW-85-330R L n STUDIES OF GRAVITY WAVE PROPAGATION IN...8217.. , .,- - -. ( %’. , .;: :..............,....... .-... . ~.b .. .. - ..... ,......... ..-. ....-.. PD-NW-85-330R STUDIES OF GRAVITY WAVE PROPAGATION...Include SewftY CsuiclUon STUDIES OF GRAVITY WAVE PROPAGATION IN THE MIDD E 12. PERSONAL AUTHORE) TMOPHU. r Timothy J. Dunkerton a13a. TYPE OF REPORT I3k

  6. Analysis of guided wave propagation in a tapered composite panel

    NASA Astrophysics Data System (ADS)

    Wandowski, Tomasz; Malinowski, Pawel; Moll, Jochen; Radzienski, Maciej; Ostachowicz, Wieslaw

    2015-03-01

    Many studies have been published in recent years on Lamb wave propagation in isotropic and (multi-layered) anisotropic structures. In this paper, adiabatic wave propagation phenomenon in a tapered composite panel made out of glass fiber reinforced polymers (GFRP) will be considered. Such structural elements are often used e.g. in wind turbine blades and aerospace structures. Here, the wave velocity of each wave mode does not only change with frequency and the direction of wave propagation. It further changes locally due to the varying cross-section of the GFRP panel. Elastic waves were excited using a piezoelectric transducer. Full wave-field measurements using scanning Laser Doppler vibrometry have been performed. This approach allows the detailed analysis of elastic wave propagation in composite specimen with linearly changing thickness. It will be demonstrated here experimentally, that the wave velocity changes significantly due to the tapered geometry of the structure. Hence, this work motivates the theoretical and experimental analysis of adiabatic mode propagation for the purpose of Non-Destructive Testing and Structural Health Monitoring.

  7. T-wave generation and propagation: a comparison between data and spectral element modeling.

    PubMed

    Jamet, Guillaume; Guennou, Claude; Guillon, Laurent; Mazoyer, Camille; Royer, Jean-Yves

    2013-10-01

    T-waves are underwater acoustic waves generated by earthquakes. Modeling of their generation and propagation is a challenging problem. Using a spectral element code-SPECFEM2D, this paper presents the first realistic simulations of T-waves taking into account major aspects of this phenomenon: The radiation pattern of the source, the propagation of seismic waves in the crust, the seismic to acoustic conversion on a non-planar seafloor, and the propagation of acoustic waves in the water column. The simulated signals are compared with data from the mid-Atlantic Ridge recorded by an array of hydrophones. The crust/water interface is defined by the seafloor bathymetry. Different combinations of water sound-speed profiles and sub-seafloor seismic velocities, and frequency content of the source are tested. The relative amplitudes, main arrival-times, and durations of simulated T-phases are in good agreement with the observed data; differences in the spectrograms and early arrivals are likely due to too simplistic source signals and environmental model. These examples demonstrate the abilities of the SPECFEM2D code for modeling earthquake generated T-waves.

  8. Local effects of gravity wave propagation and saturation

    NASA Technical Reports Server (NTRS)

    Fritts, D. C.

    1985-01-01

    In recent years, gravity waves were recognized to play a major role in the dynamics of the middle atmosphere. Perhaps the major effect of such motions are the reversal of the vertical shear of the mean zonal wind and the occurrence of a large turbulent diffusivity in the mesosphere due to gravity wave saturation. Yet, despite the importance of these gravity wave effects, the processes and the consequences of gravity wave propagation and saturation are only beginning to be understood in detail. The linear saturation theory predicts drag and turbulent diffusion due to saturating wave motion. This theory, however, fails to address a number of issues that are certain to be important for gravity wave propagation and saturation in the middle atmosphere. These issues, including wave transience, wave superposition, local convective adjustment, and nonlinearity, are discussed.

  9. Simulation of guided wave propagation near numerical Brillouin zones

    NASA Astrophysics Data System (ADS)

    Kijanka, Piotr; Staszewski, Wieslaw J.; Packo, Pawel

    2016-04-01

    Attractive properties of guided waves provides very unique potential for characterization of incipient damage, particularly in plate-like structures. Among other properties, guided waves can propagate over long distances and can be used to monitor hidden structural features and components. On the other hand, guided propagation brings substantial challenges for data analysis. Signal processing techniques are frequently supported by numerical simulations in order to facilitate problem solution. When employing numerical models additional sources of errors are introduced. These can play significant role for design and development of a wave-based monitoring strategy. Hence, the paper presents an investigation of numerical models for guided waves generation, propagation and sensing. Numerical dispersion analysis, for guided waves in plates, based on the LISA approach is presented and discussed in the paper. Both dispersion and modal amplitudes characteristics are analysed. It is shown that wave propagation in a numerical model resembles propagation in a periodic medium. Consequently, Lamb wave propagation close to numerical Brillouin zone is investigated and characterized.

  10. Acoustoelastic Lamb Wave Propagation in Biaxially Stressed Plates (Preprint)

    DTIC Science & Technology

    2012-03-01

    particularly as compared to most bulk wave NDE methods, Lamb wave are particularly sensitive to changes in the propagation environment, such as... Wilcox , and J. E. Michaels, “Efficient temperature compensation strategies for guided wave structural health monitoring,” Ultrasonics, 50, pp. 517...Liu, “Effects of residual stress on guided waves in layered media,” Rev. Prog. Quant. NDE , 17, D. O. Thompson and D. E. Chimenti (Eds.), Plenum Press

  11. On the Propagation and Interaction of Spherical Blast Waves

    NASA Technical Reports Server (NTRS)

    Kandula, Max; Freeman, Robert

    2007-01-01

    The characteristics and the scaling laws of isolated spherical blast waves have been briefly reviewed. Both self-similar solutions and numerical solutions of isolated blast waves are discussed. Blast profiles in the near-field (strong shock region) and the far-field (weak shock region) are examined. Particular attention is directed at the blast overpressure and shock propagating speed. Consideration is also given to the interaction of spherical blast waves. Test data for the propagation and interaction of spherical blast waves emanating from explosives placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure.

  12. Wave Propagation in Isotropic Media with Two Orthogonal Fracture Sets

    NASA Astrophysics Data System (ADS)

    Shao, S.; Pyrak-Nolte, L. J.

    2016-10-01

    Orthogonal intersecting fracture sets form fracture networks that affect the hydraulic and mechanical integrity of a rock mass. Interpretation of elastic waves propagated through orthogonal fracture networks is complicated by guided modes that propagate along and between fractures, by multiple internal reflections, as well as by scattering from fracture intersections. The existence of some or all of these potentially overlapping modes depends on local stress fields that can preferentially close or open either one or both sets of fractures. In this study, an acoustic wave front imaging system was used to examine the effect of bi-axial loading conditions on acoustic wave propagation in isotropic media containing two orthogonal fracture sets. From the experimental data, orthogonal intersecting fracture sets support guided waves that depend on fracture spacing and fracture-specific stiffnesses. In addition, fracture intersections have stronger effects on propagating wave fronts than merely the superposition of the effects of two independent fractures because of energy partitioning among transmitted/reflected waves, scattered waves and guided modes. Interpretation of the properties of fractures or fracture sets from seismic measurements must consider non-uniform fracture stiffnesses within and among fracture sets, as well as considering the striking effects of fracture intersections on wave propagation.

  13. Spectral solution of acoustic wave-propagation problems

    NASA Technical Reports Server (NTRS)

    Kopriva, David A.

    1990-01-01

    The Chebyshev spectral collocation solution of acoustic wave propagation problems is considered. It is shown that the phase errors decay exponentially fast and that the number of points per wavelength is not sufficient to estimate the phase accuracy. Applications include linear propagation of a sinusoidal acoustic wavetrain in two space dimensions, and the interaction of a sound wave with the bow shock formed by placing a cylinder in a uniform Mach 4 supersonic free stream.

  14. Computational Modeling of Wave Propagation in a Geophysical Domain

    DTIC Science & Technology

    2008-10-01

    finite element software with desktop computing hardware. 8. References 1. Pujol , J., Elastic Wave Propagation and Generation in Seismology ...half-space loading with an impact and develops a general closed-form solution against which to compare the computational results. These results... generic problem of a seismic wave that is generated at a source, propagates through a media, and is measured at a receiver. Some researchers are

  15. Teaching Wave Propagation and the Emergence of Viete's Formula

    ERIC Educational Resources Information Center

    Cullerne, J. P.; Goekjian, M. C. Dunn

    2012-01-01

    The well-known result for the frequency of a simple spring-mass system may be combined with elementary concepts like speed = wavelength x frequency to obtain wave propagation speeds for an infinite chain of springs and masses (masses "m" held apart at equilibrium distance "a" by springs of stiffness "gamma"). These propagation speeds are dependent…

  16. Subwavelength confined terahertz waves on planar waveguides using metallic gratings.

    PubMed

    You, Borwen; Lu, Ja-Yu; Chang, Wei-Lun; Yu, Chin-Ping; Liu, Tze-An; Peng, Jin-Long

    2013-03-11

    A terahertz plasmonic waveguide is experimentally demonstrated using a plastic ribbon waveguide integrated with a diffraction metal grating to approach subwavelength-scaled confinement and long-distance delivery. Appropriately adjusting the metal-thickness and the periodical slit width of a grating greatly improves both guiding ability and field confinement in the hybrid waveguide structure. The measured lateral decay length of the bound terahertz surface waves on the hybrid waveguide can be reduced to less than λ/4 after propagating a waveguide of around 50mm-long in length. The subwavelength-confined field is potentially advantageous to biomolecular sensing or membrane detection because of the long interaction length between the THz field and analytes.

  17. Time dependent wave envelope finite difference analysis of sound propagation

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1984-01-01

    A transient finite difference wave envelope formulation is presented for sound propagation, without steady flow. Before the finite difference equations are formulated, the governing wave equation is first transformed to a form whose solution tends not to oscillate along the propagation direction. This transformation reduces the required number of grid points by an order of magnitude. Physically, the transformed pressure represents the amplitude of the conventional sound wave. The derivation for the wave envelope transient wave equation and appropriate boundary conditions are presented as well as the difference equations and stability requirements. To illustrate the method, example solutions are presented for sound propagation in a straight hard wall duct and in a two dimensional straight soft wall duct. The numerical results are in good agreement with exact analytical results.

  18. Generation and propagation of Alfvenic waves in spicules

    NASA Astrophysics Data System (ADS)

    De Pontieu, B.; Okamoto, T. J.; Rouppe van der Voort, L.; Hansteen, V. H.; Carlsson, M.

    2011-12-01

    Both spicules and Alfven waves have recently been implicated in playing a role in the heating of the outer atmosphere. Yet we do not know how spicules or Alfven waves are generated. Here we focus on the properties of Alfvenic waves in spicules and their role in forming spicules. We use high-resolution observations taken with the Solar Optical Telescope onboard Hinode, and with the CRISP Fabry-Perot Interferometer at the Swedish Solar Telescope (SST) in La Palma to study the generation and propagation of Alfvenic waves in spicules and their disk counterparts. Using automated detection algorithms to identify propagating waves in limb spicules, we find evidence for both up- and downward propagating as well as standing waves. Our data suggests significant reflection of waves in and around spicules and provides constraints for theoretical models of spicules and wave propagation through the chromosphere. We also show observational evidence (using SST data) of the generation of Alfven waves and the role they play in forming spicules.

  19. Influence of Plasma Pressure Fluctuation on RF Wave Propagation

    NASA Astrophysics Data System (ADS)

    Liu, Zhiwei; Bao, Weimin; Li, Xiaoping; Liu, Donglin; Zhou, Hui

    2016-02-01

    Pressure fluctuations in the plasma sheath from spacecraft reentry affect radio-frequency (RF) wave propagation. The influence of these fluctuations on wave propagation and wave properties is studied using methods derived by synthesizing the compressible turbulent flow theory, plasma theory, and electromagnetic wave theory. We study these influences on wave propagation at GPS and Ka frequencies during typical reentry by adopting stratified modeling. We analyzed the variations in reflection and transmission properties induced by pressure fluctuations. Our results show that, at the GPS frequency, if the waves are not totally reflected then the pressure fluctuations can remarkably affect reflection, transmission, and absorption properties. In extreme situations, the fluctuations can even cause blackout. At the Ka frequency, the influences are obvious when the waves are not totally transmitted. The influences are more pronounced at the GPS frequency than at the Ka frequency. This suggests that the latter can mitigate blackout by reducing both the reflection and the absorption of waves, as well as the influences of plasma fluctuations on wave propagation. Given that communication links with the reentry vehicles are susceptible to plasma pressure fluctuations, the influences on link budgets should be taken into consideration. supported by the National Basic Research Program of China (No. 2014CB340205) and National Natural Science Foundation of China (No. 61301173)

  20. Ocean Acoustic Propagation Measurements and Wave Propagation in Random Media

    DTIC Science & Technology

    1993-04-01

    medium focus follows closely the prediction of Spivack and Uscinski3 5 . Using numerical solutions to the 4th moment equation, the (I’, Z) dependence...32(1), 71-89 (1985). 13. B.J. Uscinski, C. Macaskill and M. Spivack , "Path integrals for wave intensity fluctuations in random media," J. Sound and...intensity in a turbulent atmosphere-- the distribution function," Soy. Phys. JETP 47(6), 1028-1030 (1978). 35. M. Spivack and BJ. Uscinski, "Accurate

  1. Planar millimeter wave radar frontend for automotive applications

    NASA Astrophysics Data System (ADS)

    Grubert, J.; Heyen, J.; Metz, C.; Stange, L. C.; Jacob, A. F.

    2003-05-01

    A fully integrated planar sensor for 77 GHz automotive applications is presented. The frontend consists of a transceiver multichip module and an electronically steerable microstrip patch array. The antenna feed network is based on a modified Rotman-lens and connected to the array in a multilayer approach offering higher integration. Furthermore, the frontend comprises a phase lock loop to allow proper frequency-modulated continuous wave (FMCW) radar operation. The latest experimental results verify the functionality of this advanced frontend design featuring automatic cruise control, precrash sensing and cut-in detection. These promising radar measurements give reason to a detailed theoretical investigation of system performance. Employing commercially available MMIC various circuit topologies are compared based on signal-tonoise considerations. Different scenarios for both sequential and parallel lobing hint to more advanced sensor designs and better performance. These improvements strongly depend on the availability of suitable MMIC and reliable packaging technologies. Within our present approach possible future MMIC developments are already considered and, thus, can be easily adapted by the flexible frontend design. Es wird ein integrierter planarer Sensor für 77 GHz Radaranwendungen vorgestellt. Das Frontend besteht aus einem Sende- und Empfangs-Multi-Chip-Modul und einer elektronisch schwenkbaren Antenne. Das Speisenetzwerk der Antenne basiert auf einer modifizierten Rotman- Linse. Für eine kompakte Bauweise sind Antenne und Speisenetzwerk mehrlagig integriert. Weiterhin umfasst das Frontend eine Phasenregelschleife für eine präzise Steuerung des frequenzmodulierten Dauerstrichradars. Die aktuellen Messergebnisse bestätigen die Funktionalit¨at dieses neuartigen Frontend-Designs, das automatische Geschwindigkeitsregelung, Kollisionswarnung sowie Nahbereichsüberwachung ermöglicht. Die Qualität der Messergebnisse hat weiterf

  2. Propagation of surface waves and waveguide modes guided by a dielectric slab inserted in a sculptured nematic thin film

    SciTech Connect

    Faryad, Muhammad; Lakhtakia, Akhlesh

    2011-01-15

    Wave propagation guided by a dielectric slab inserted in a sculptured nematic thin film (SNTF) was studied theoretically. Two types of guided waves can be identified: (i) surface (Dyakonov-Tamm) waves guided by one or both of the two planar interfaces of the dielectric slab and the SNTF, and (ii) waveguide modes in the dielectric waveguide formed by the slab with the SNTF as the cladding. As the thickness of the dielectric slab is increased, the number of waveguide modes increases. If the slab thickness is less than twice the e-folding distance into the dielectric slab, the Dyakonov-Tamm waves propagate coupled to both interfaces; the coupling decreases and eventually vanishes as the slab thickness increases, so that Dyakonov-Tamm waves are guided by the individual dielectric-SNTF interfaces independently. The chosen structure supports the propagation of Dyakonov-Tamm waves in all directions, in contrast to the restricted range of propagation supported by a single SNTF-dielectric interface. Propagation of both Dyakonov-Tamm waves and waveguide modes should occur in practice with negligible attenuation, in contrast to that of surface-plasmon-polariton waves that are guided when the dielectric slab is replaced by a metal slab.

  3. Propagation of surface waves and waveguide modes guided by a dielectric slab inserted in a sculptured nematic thin film

    NASA Astrophysics Data System (ADS)

    Faryad, Muhammad; Lakhtakia, Akhlesh

    2011-01-01

    Wave propagation guided by a dielectric slab inserted in a sculptured nematic thin film (SNTF) was studied theoretically. Two types of guided waves can be identified: (i) surface (Dyakonov-Tamm) waves guided by one or both of the two planar interfaces of the dielectric slab and the SNTF, and (ii) waveguide modes in the dielectric waveguide formed by the slab with the SNTF as the cladding. As the thickness of the dielectric slab is increased, the number of waveguide modes increases. If the slab thickness is less than twice the e-folding distance into the dielectric slab, the Dyakonov-Tamm waves propagate coupled to both interfaces; the coupling decreases and eventually vanishes as the slab thickness increases, so that Dyakonov-Tamm waves are guided by the individual dielectric-SNTF interfaces independently. The chosen structure supports the propagation of Dyakonov-Tamm waves in all directions, in contrast to the restricted range of propagation supported by a single SNTF-dielectric interface. Propagation of both Dyakonov-Tamm waves and waveguide modes should occur in practice with negligible attenuation, in contrast to that of surface-plasmon-polariton waves that are guided when the dielectric slab is replaced by a metal slab.

  4. Controlling wave propagation through nonlinear engineered granular systems

    NASA Astrophysics Data System (ADS)

    Leonard, Andrea

    We study the fundamental dynamic behavior of a special class of ordered granular systems in order to design new, structured materials with unique physical properties. The dynamic properties of granular systems are dictated by the nonlinear, Hertzian, potential in compression and zero tensile strength resulting from the discrete material structure. Engineering the underlying particle arrangement of granular systems allows for unique dynamic properties, not observed in natural, disordered granular media. While extensive studies on 1D granular crystals have suggested their usefulness for a variety of engineering applications, considerably less attention has been given to higher-dimensional systems. The extension of these studies in higher dimensions could enable the discovery of richer physical phenomena not possible in 1D, such as spatial redirection and anisotropic energy trapping. We present experiments, numerical simulation (based on a discrete particle model), and in some cases theoretical predictions for several engineered granular systems, studying the effects of particle arrangement on the highly nonlinear transient wave propagation to develop means for controlling the wave propagation pathways. The first component of this thesis studies the stress wave propagation resulting from a localized impulsive loading for three different 2D particle lattice structures: square, centered square, and hexagonal granular crystals. By varying the lattice structure, we observe a wide range of properties for the propagating stress waves: quasi-1D solitary wave propagation, fully 2D wave propagation with tunable wave front shapes, and 2D pulsed wave propagation. Additionally the effects of weak disorder, inevitably present in real granular systems, are investigated. The second half of this thesis studies the solitary wave propagation through 2D and 3D ordered networks of granular chains, reducing the effective density compared to granular crystals by selectively placing wave

  5. WAVE PROPAGATION AND JET FORMATION IN THE CHROMOSPHERE

    SciTech Connect

    Heggland, L.; Hansteen, V. H.; Carlsson, M.; De Pontieu, B.

    2011-12-20

    We present the results of numerical simulations of wave propagation and jet formation in solar atmosphere models with different magnetic field configurations. The presence in the chromosphere of waves with periods longer than the acoustic cutoff period has been ascribed to either strong inclined magnetic fields, or changes in the radiative relaxation time. Our simulations include a sophisticated treatment of radiative losses, as well as fields with different strengths and inclinations. Using Fourier and wavelet analysis techniques, we investigate the periodicity of the waves that travel through the chromosphere. We find that the velocity signal is dominated by waves with periods around 5 minutes in regions of strong, inclined field, including at the edges of strong flux tubes where the field expands, whereas 3 minute waves dominate in regions of weak or vertically oriented fields. Our results show that the field inclination is very important for long-period wave propagation, whereas variations in the radiative relaxation time have little effect. Furthermore, we find that atmospheric conditions can vary significantly on timescales of a few minutes, meaning that a Fourier analysis of wave propagation can be misleading. Wavelet techniques take variations with time into account and are more suitable analysis tools. Finally, we investigate the properties of jets formed by the propagating waves once they reach the transition region, and find systematic differences between the jets in inclined-field regions and those in vertical field regions, in agreement with observations of dynamic fibrils.

  6. Propagation of acoustic waves in multifractional polydisperse gas suspension

    NASA Astrophysics Data System (ADS)

    Gubaidullin, D. A.; Teregulova, E. A.

    2017-01-01

    The propagation of acoustic waves in multifractional polydisperse gas suspension is studied. A mathematical model is presented, the dispersion equation is obtained, dispersion curves are calculated. The influence of the particle size and the parameters of the dispersed phase for multifractional gas mixture with ice particles, aluminum and sand on dissipation and dispersion of sound waves is analyzed.

  7. Relationship between directions of wave and energy propagation for cold plasma waves

    NASA Technical Reports Server (NTRS)

    Musielak, Zdzislaw E.

    1986-01-01

    The dispersion relation for plasma waves is considered in the 'cold' plasma approximation. General formulas for the dependence of the phase and group velocities on the direction of wave propagation with respect to the local magnetic field are obtained for a cold magnetized plasma. The principal cold plasma resonances and cut-off frequencies are defined for an arbitrary angle and are used to establish basic regimes of frequency where the cold plasma waves can propagate or can be evanescent. The relationship between direction of wave and energy propagation, for cold plasma waves in hydrogen atmosphere, is presented in the form of angle diagrams (angle between group velocity and magnetic field versus angle between phase velocity and magnetic field) and polar diagrams (also referred to as 'Friedrich's diagrams') for different directions of wave propagation. Morphological features of the diagrams as well as some critical angles of propagation are discussed.

  8. Influence of atmospheric structure and topography on infrasonic wave propagation

    NASA Astrophysics Data System (ADS)

    Lacanna, G.; Ichihara, M.; Iwakuni, M.; Takeo, M.; Iguchi, M.; Ripepe, M.

    2014-04-01

    The effects of topography and atmospheric structures on infrasonic wave propagation from a volcanic source were investigated using observations and numerical modeling. This paper presents the first long-term observational data set showing spatiotemporal variations in patterns of infrasound propagation at distances of up to 60 km from a persistently active infrasound source (Sakurajima Volcano, Japan). The data show that the amplitudes of infrasonic waves received at distant stations relative to those received at a reference station close to the source can vary up to an order of magnitude over short time intervals and short distances and that they do not follow the theoretical geometric decay expected for homogeneous media. Moreover, waveforms also change significantly in both time and space. Numerical simulations were performed using a two-dimensional finite difference time domain (2-D FDTD) method. Effects of atmospheric structure and topography are included in a vertical section parallel to the wave propagation direction. The simulation successfully reproduced the variations of amplitudes and waveforms. Results are interpreted in terms of wave refraction due to sound and wind speed gradients and wave diffraction at topographic barriers. Our numerical results indicate that both atmospheric and topographic propagation effects are nonnegligible. To evaluate the propagation effects and determine source processes in spatially and temporally varying infrasound data, atmospheric data with a time resolution higher than is currently available are required. If the data are available, the present results suggest that the propagation effects could be evaluated using 2-D FDTD modeling at realistic calculation times.

  9. Numerical simulation of wave propagation in cancellous bone.

    PubMed

    Padilla, F; Bossy, E; Haiat, G; Jenson, F; Laugier, P

    2006-12-22

    Numerical simulation of wave propagation is performed through 31 3D volumes of trabecular bone. These volumes were reconstructed from high synchrotron microtomography experiments and are used as the input geometry in a simulation software developed in our laboratory. The simulation algorithm accounts for propagation into both the saturating fluid and bone but absorption is not taken into account. We show that 3D simulation predicts phenomena observed experimentally in trabecular bones : linear frequency dependence of attenuation, increase of attenuation and speed of sound with the bone volume fraction, negative phase velocity dispersion in most of the specimens, propagation of fast and slow wave depending on the orientation of the trabecular network compared to the direction of propagation of the ultrasound. Moreover, the predicted attenuation is in very close agreement with the experimental one measured on the same specimens. Coupling numerical simulation with real bone architecture therefore provides a powerful tool to investigate the physics of ultrasound propagation in trabecular structures.

  10. 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.

  11. Shear horizontal (SH) ultrasound wave propagation around smooth corners.

    PubMed

    Petcher, P A; Burrows, S E; Dixon, S

    2014-04-01

    Shear horizontal (SH) ultrasound guided waves are being used in an increasing number of non-destructive testing (NDT) applications. One advantage SH waves have over some wave types, is their ability to propagate around curved surfaces with little energy loss; to understand the geometries around which they could propagate, the wave reflection must be quantified. A 0.83mm thick aluminium sheet was placed in a bending machine, and a shallow bend was introduced. Periodically-poled magnet (PPM) electromagnetic acoustic transducers (EMATs), for emission and reception of SH waves, were placed on the same side of the bend, so that reflected waves were received. Additional bending of the sheet demonstrated a clear relationship between bend angles and the reflected signal. Models suggest that the reflection is a linear superposition of the reflections from each bend segment, such that sharp turns lead to a larger peak-to-peak amplitude, in part due to increased phase coherence.

  12. Electron acceleration in the ionosphere by obliquely propagating electromagnetic waves

    NASA Astrophysics Data System (ADS)

    Burke, William J.; Ginet, Gregory P.; Heinemann, Michael A.; Villalon, Elena

    The paper presents an analysis of the relativistic equations of motion for electrons in magnetized plasma and externally imposed electromagnetic fields that propagate at arbitrary angles to the background magnetic field. The relativistic Lorentz equation for a test electron moving under the influence of an electromagnetic wave in a cold magnetized plasma and wave propagation through the ionospheric 'radio window' are examined. It is found that at wave energy fluxes greater than 10 to the 8th mW/sq m, initially cold electrons can be accelerated to energies of several MeV in less than a millisecond. Plans to test the theoretical results with rocket flights are discussed.

  13. Modelling propagation of deflagration waves out of hot spots

    NASA Astrophysics Data System (ADS)

    Partom, Yehuda

    2015-06-01

    It is widely accepted that shock initiation and detonation of heterogeneous explosives come about by a two-step process known as ignition and growth. In the first step a shock sweeping an explosive cell (control volume) creates hot spots that become ignition sites. In the second step deflagration waves (or burn waves) propagate out of those hot spots and transform the reactant in the cell into reaction products. The macroscopic (or average) reaction rate of the reactant in a cell depends on the speed of those deflagration waves and on the average distance between neighbouring hot spots. Here we simulate the propagation of deflagration waves out of hot spots on the mesoscale in axial symmetry using a 2D hydrocode, to which we add heat conduction and bulk reaction. The propagation speed of the deflagration wave depends on both pressure and temperature, where pressure dependence is dominant at low shock level, and temperature dependence is dominant at a higher shock level. From the simulation we obtain deflagration (or burn) fronts emanating out of the hot spots. For intermediate shock levels the deflagration waves consume the explosive between hot spots. For higher shock levels the deflagration waves strengthen to become detonation waves on the mesoscale. From the simulation results we extract average deflagration wave speeds and show how they depend on reaction rate and on other material parameters.

  14. Diurnal Variability and Kelvin Wave Propagation Through Maritime Continent

    NASA Astrophysics Data System (ADS)

    Flatau, M. K.; Baranowski, D. B.; Flatau, P. J.; Matthews, A. J.

    2014-12-01

    The 10 year series of the equatorial Kelvin waves obtained from the analysis of TRMM precipitation were examined to evaluate the impact of the diurnal variability of convection on the wave propagation through Maritime Continent. The convection in the Kelvin waves appears to be strongly phase locked in the area of the Maritime continent with the pronounced afternoon maximum. The diurnal phase locking is also evident as Kelvin waves propagate trough the Indian Ocean basin, suggesting that at least some Kelvin waves in this area are forced by the diurnally varying heat source related either to the convection over the land such as Eastern Africa or Madagascar, or over ocean areas with the high SST variability. We examine the hypothesis that the "matching" of the convective phase of the waves with the afternoon maximum of convection over Sumatra influences the wave strength after it crosses the Maritime Continent and can contribute to MJO propagation. The observational results based on observed Kelvin waves are supported by the results of the shallow water model of the interaction of the dry Kelvin wave with the diurnally oscillating heat source.

  15. Longitudinally propagating traveling waves of the mammalian tectorial membrane.

    PubMed

    Ghaffari, Roozbeh; Aranyosi, Alexander J; Freeman, Dennis M

    2007-10-16

    Sound-evoked vibrations transmitted into the mammalian cochlea produce traveling waves that provide the mechanical tuning necessary for spectral decomposition of sound. These traveling waves of motion that have been observed to propagate longitudinally along the basilar membrane (BM) ultimately stimulate the mechano-sensory receptors. The tectorial membrane (TM) plays a key role in this process, but its mechanical function remains unclear. Here we show that the TM supports traveling waves that are an intrinsic feature of its visco-elastic structure. Radial forces applied at audio frequencies (2-20 kHz) to isolated TM segments generate longitudinally propagating waves on the TM with velocities similar to those of the BM traveling wave near its best frequency place. We compute the dynamic shear storage modulus and shear viscosity of the TM from the propagation velocity of the waves and show that segments of the TM from the basal turn are stiffer than apical segments are. Analysis of loading effects of hair bundle stiffness, the limbal attachment of the TM, and viscous damping in the subtectorial space suggests that TM traveling waves can occur in vivo. Our results show the presence of a traveling wave mechanism through the TM that can functionally couple a significant longitudinal extent of the cochlea and may interact with the BM wave to greatly enhance cochlear sensitivity and tuning.

  16. Nonlinear electron magnetohydrodynamics physics. II. Wave propagation and wave-wave interactions

    SciTech Connect

    Urrutia, J. M.; Stenzel, R. L.; Strohmaier, K. D.

    2008-04-15

    The propagation of low-frequency whistler modes with wave magnetic field exceeding the ambient field is investigated experimentally. Such nonlinear waves are excited with magnetic loop antennas whose axial field is aligned with the background magnetic field and greatly exceeds its strength. The oscillatory antenna field excites propagating wave packets with field topologies alternating between whistler spheromaks and mirrors. The propagation speed of spheromaks is observed to decrease with amplitude while that of mirrors increases with amplitude. The field distribution varies with amplitude: Spheromaks contract axially while mirrors spread out compared to linear whistlers. Consequently, the peak magnetic field and current densities in spheromaks exceed that of mirrors. Wave-wave interactions of nonlinear whistler modes is also studied. Counterpropagating spheromaks collide inelastically and form a stationary field-reversed configuration. The radius of the toroidal current ring depends on current and can be larger than that of the loop antenna. A tilted field-reversed configuration precesses in the direction of the electron drift. The free magnetic energy is dissipated in the plasma volume and converted into electron heat.

  17. Solitary wave propagation through two-dimensional treelike structures.

    PubMed

    Falls, William J; Sen, Surajit

    2014-02-01

    It is well known that a velocity perturbation can travel through a mass spring chain with strongly nonlinear interactions as a solitary and antisolitary wave pair. In recent years, nonlinear wave propagation in 2D structures have also been explored. Here we first consider the propagation of such a velocity perturbation for cases where the system has a 2D "Y"-shaped structure. Here each of the three pieces that make up the "Y" are made of a small mass spring chain. In addition, we consider a case where multiple "Y"-shaped structures are used to generate a "tree." We explore the early time dynamical behavior associated with the propagation of a velocity perturbation initiated at the trunk and at the extremities for both cases. We are looking for the energy transmission properties from one branch to another of these "Y"-shaped structures. Our dynamical simulations suggest the following broad observations: (i) for strongly nonlinear interactions, mechanical energy propagation resembles pulse propagation with the energy propagation being dispersive in the linear case; (ii) for strong nonlinear interactions, the tree-like structure acts as an energy gate showing preference for large perturbations in the system while the behavior of the linear case shows no such preference, thereby suggesting that such structures can possibly act as switches that activate at sufficiently high energies. The study aspires to develop insights into the nature of nonlinear wave propagation through a network of linear chains.

  18. Propagation and amplitude decay mechanisms of internal solitary waves

    NASA Astrophysics Data System (ADS)

    Wang, Ling-ling; Wang, Chun-ling; Tang, Hong-wu; Chen, Hong

    2016-12-01

    In this paper, a modified dynamic coherent eddy model (DCEM) of large eddy simulation is applied to study internal solitary waves in a numerical flume. The model was verified by physical experiment and applied to investigate the potential influence factors on internal wave amplitude. In addition, we discussed the energy loss of internal solitary wave as well as hydrodynamics in the propagation. The results of our study show that (1) Step-depth is the most sensitive factor on wave amplitude for the "step-pool" internal wave generation method and the wave amplitudes obey a linear increase with step depth, and the increase rate is about 0.4. (2) Wave energy loss obeys a linear decrease with the propagation distance and its loss rate of large amplitude waves is smaller than that of small amplitude waves. (3) Loss of kinetic energy in wave valley is larger than that near the interface due to relative high fluctuating frequency. (4) Discovered boundary jet-flow can intensify the bottom shear, which might be one of the mechanisms of substance transportation, and the boundary layers of jet flows are easily influenced by the adjacent waves.

  19. Wave propagation in fiber composite laminates, part 2

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.; Liber, T.

    1976-01-01

    An experimental investigation was conducted to determine the wave propagation characteristics, transient strains and residual properties in unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicone rubber projectiles at velocities up to 250 MS-1. The predominant wave is flexural, propagating at different velocities in different directions. In general, measured wave velocities were higher than theoretically predicted values. The amplitude of the in-plane wave is less than ten percent of that of the flexural wave. Peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers. The dynamics of impact were also studied with high speed photography.

  20. Spatial damping of propagating sausage waves in coronal cylinders

    NASA Astrophysics Data System (ADS)

    Guo, Ming-Zhe; Chen, Shao-Xia; Li, Bo; Xia, Li-Dong; Yu, Hui

    2015-09-01

    Context. Sausage modes are important in coronal seismology. Spatially damped propagating sausage waves were recently observed in the solar atmosphere. Aims: We examine how wave leakage influences the spatial damping of sausage waves propagating along coronal structures modeled by a cylindrical density enhancement embedded in a uniform magnetic field. Methods: Working in the framework of cold magnetohydrodynamics, we solve the dispersion relation (DR) governing sausage waves for complex-valued, longitudinal wavenumber k at given real angular frequencies ω. For validation purposes, we also provide analytical approximations to the DR in the low-frequency limit and in the vicinity of ωc, the critical angular frequency separating trapped from leaky waves. Results: In contrast to the standing case, propagating sausage waves are allowed for ω much lower than ωc. However, while able to direct their energy upward, these low-frequency waves are subject to substantial spatial attenuation. The spatial damping length shows little dependence on the density contrast between the cylinder and its surroundings, and depends only weakly on frequency. This spatial damping length is of the order of the cylinder radius for ω ≲ 1.5vAi/a, where a and vAi are the cylinder radius and the Alfvén speed in the cylinder, respectively. Conclusions: If a coronal cylinder is perturbed by symmetric boundary drivers (e.g., granular motions) with a broadband spectrum, wave leakage efficiently filters out the low-frequency components.

  1. Wave propagation in elastic medium with heterogeneous quadratic nonlinearity

    SciTech Connect

    Tang Guangxin; Jacobs, Laurence J.; Qu Jianmin

    2011-06-23

    This paper studies the one-dimensional wave propagation in an elastic medium with spatially non-uniform quadratic nonlinearity. Two problems are solved analytically. One is for a time-harmonic wave propagating in a half-space where the displacement is prescribed on the surface of the half-space. It is found that spatial non-uniformity of the material nonlinearity causes backscattering of the second order harmonic, which when combined with the forward propagating waves generates a standing wave in steady-state wave motion. The second problem solved is the reflection from and transmission through a layer of finite thickness embedded in an otherwise linearly elastic medium of infinite extent, where it is assumed that the layer has a spatially non-uniform quadratic nonlinearity. The results show that the transmission coefficient for the second order harmonic is proportional to the spatial average of the nonlinearity across the thickness of the layer, independent of the spatial distribution of the nonlinearity. On the other hand, the coefficient of reflection is proportional to a weighted average of the nonlinearity across the layer thickness. The weight function in this weighted average is related to the propagating phase, thus making the coefficient of reflection dependent on the spatial distribution of the nonlinearity. Finally, the paper concludes with some discussions on how to use the reflected and transmitted second harmonic waves to evaluate the variance and autocorrelation length of nonlinear parameter {beta} when the nonlinearity distribution in the layer is a stochastic process.

  2. Wave Propagation Through The Far Infrared Beamline At The CLS

    SciTech Connect

    Reininger, R.; May, T.

    2004-05-12

    One of the beamlines to become operational in the first phase at the Canadian Light Source will be dedicated to high resolution spectroscopy in the far infrared (FIR). The beamline includes three ellipsoidal mirrors and several plane mirrors that transport the beam from the bending magnet source to the FIR spectrometer. The F-number of the spectrometer is matched by the beamline optics, which relay the light via intermediate foci rather than by collimation used in mid infrared beamlines. The beamline has been designed using regular ray tracing and by propagating the electric fields generated at the magnet through the beamline optics. The fields were calculated using SRW and the propagations were performed with SRW, which assumes ideal lenses, and with a wave propagating program using the real optical surfaces. The simulations, based on wave propagation, show the significant diffraction effects at both the foci and optical surfaces due to the small electron beam, beamline aperture, and mirrors sizes.

  3. Impact of mountain gravity waves on infrasound propagation

    NASA Astrophysics Data System (ADS)

    Damiens, Florentin; Lott, François; Millet, Christophe

    2016-04-01

    Linear theory of acoustic propagation is used to analyze how mountain waves can change the characteristics of infrasound signals. The mountain wave model is based on the integration of the linear inviscid Taylor-Goldstein equation forced by a nonlinear surface boundary condition. For the acoustic propagation we solve the wave equation using the normal mode method together with the effective sound speed approximation. For large-amplitude mountain waves we use direct numerical simulations to compute the interactions between the mountain waves and the infrasound component. It is shown that the mountain waves perturb the low level waveguide, which leads to significant acoustic dispersion. The mountain waves also impact the arrival time and spread of the signals substantially and can produce a strong absorption of the wave signal. To interpret our results we follow each acoustic mode separately and show which mode is impacted and how. We also show that the phase shift between the acoustic modes over the horizontal length of the mountain wave field may yield to destructive interferences in the lee side of the mountain, resulting in a new form of infrasound absorption. The statistical relevance of those results is tested using a stochastic version of the mountain wave model and large enough sample sizes.

  4. Asymmetric wave propagation in nonlinear systems.

    PubMed

    Lepri, Stefano; Casati, Giulio

    2011-04-22

    A mechanism for asymmetric (nonreciprocal) wave transmission is presented. As a reference system, we consider a layered nonlinear, nonmirror-symmetric model described by the one-dimensional discrete nonlinear Schrödinger equation with spatially varying coefficients embedded in an otherwise linear lattice. We construct a class of exact extended solutions such that waves with the same frequency and incident amplitude impinging from left and right directions have very different transmission coefficients. This effect arises already for the simplest case of two nonlinear layers and is associated with the shift of nonlinear resonances. Increasing the number of layers considerably increases the complexity of the family of solutions. Finally, numerical simulations of asymmetric wave packet transmission are presented which beautifully display the rectifying effect.

  5. Geometric effects on stress wave propagation.

    PubMed

    Johnson, K L; Trim, M W; Horstemeyer, M F; Lee, N; Williams, L N; Liao, J; Rhee, H; Prabhu, R

    2014-02-01

    The present study, through finite element simulations, shows the geometric effects of a bioinspired solid on pressure and impulse mitigation for an elastic, plastic, and viscoelastic material. Because of the bioinspired geometries, stress wave mitigation became apparent in a nonintuitive manner such that potential real-world applications in human protective gear designs are realizable. In nature, there are several toroidal designs that are employed for mitigating stress waves; examples include the hyoid bone on the back of a woodpecker's jaw that extends around the skull to its nose and a ram's horn. This study evaluates four different geometries with the same length and same initial cross-sectional diameter at the impact location in three-dimensional finite element analyses. The geometries in increasing complexity were the following: (1) a round cylinder, (2) a round cylinder that was tapered to a point, (3) a round cylinder that was spiraled in a two dimensional plane, and (4) a round cylinder that was tapered and spiraled in a two-dimensional plane. The results show that the tapered spiral geometry mitigated the greatest amount of pressure and impulse (approximately 98% mitigation) when compared to the cylinder regardless of material type (elastic, plastic, and viscoelastic) and regardless of input pressure signature. The specimen taper effectively mitigated the stress wave as a result of uniaxial deformational processes and an induced shear that arose from its geometry. Due to the decreasing cross-sectional area arising from the taper, the local uniaxial and shear stresses increased along the specimen length. The spiral induced even greater shear stresses that help mitigate the stress wave and also induced transverse displacements at the tip such that minimal wave reflections occurred. This phenomenon arose although only longitudinal waves were introduced as the initial boundary condition (BC). In nature, when shearing occurs within or between materials

  6. Wave propagation in a plate after impact by a projectile

    NASA Technical Reports Server (NTRS)

    El-Raheb, M.; Wagner, P.

    1987-01-01

    The wave propagation in a circular plate after impact by a cylindrical projectile is studied. In the vicinity of impact, the pressure is computed numerically. An intense pressure pulse is generated that peaks 0.2 microns after impact, then drops sharply to a plateau. The response of the plate is determined adopting a modal solution of Mindlin's equations. Velocity and acceleration histories display both propagating and dispersive features.

  7. Efficient counter-propagating wave acoustic micro-particle manipulation

    NASA Astrophysics Data System (ADS)

    Grinenko, A.; Ong, C. K.; Courtney, C. R. P.; Wilcox, P. D.; Drinkwater, B. W.

    2012-12-01

    A simple acoustic system consisting of a pair of parallel singe layered piezoelectric transducers submerged in a fluid used to form standing waves by a superposition of two counter-propagating waves is reported. The nodal positions of the standing wave are controlled by applying a variable phase difference to the transducers. This system was used to manipulate polystyrene micro-beads trapped at the nodal positions of the standing wave. The demonstrated good manipulation capability of the system is based on a lowering of the reflection coefficient in a narrow frequency band near the through-thickness resonance of the transducer plates.

  8. Propagating spectroscopy of backward volume spin waves in a metallic FeNi film

    SciTech Connect

    Sato, N.; Ishida, N.; Kawakami, T.; Sekiguchi, K.

    2014-01-20

    We report a propagating spin wave spectroscopy for a magnetostatic backward volume spin wave in a metallic Fe{sub 19}Ni{sub 81} film. We show that the mutual-inductance between two independent antennas detects a small but clear propagation signal of backward volume spin waves. All experimental data are consistent with the time-domain propagating spin-wave spectroscopy. The control of propagating backward spin wave enables to realize the miniaturize spin-wave circuit.

  9. Special Course on Acoustic Wave Propagation

    DTIC Science & Technology

    1979-08-01

    l.Recipient’s Reference 2.Originator’s Reference 3.Further Reference 4.Security Classification of Document AGARD-R-686 ISBN 92-835-0248-5 UNCLASSIFIED 5...3L t’acoustique eat d’Ariatote (384-322 av. .Y.C.) qui a effectud una classification des diffdrentes branches de l’acoustique en cansacrant une part...silence a cotia- tique at balistique. DepuiS la econde guerre mondiale de tres nombreux travaux Sur la propagation acoustique dans les fluides et das

  10. Spherical Wave Propagation in a Nonlinear Elastic Medium

    SciTech Connect

    Korneev, Valeri A.

    2009-07-01

    Nonlinear propagation of spherical waves generated by a point-pressure source is considered for the cases of monochromatic and impulse primary waveforms. The nonlinear five-constant elastic theory advanced by Murnaghan is used where general equations of motion are put in the form of vector operators, which are independent of the coordinate system choice. The ratio of the nonlinear field component to the primary wave in the far field is proportional to ln(r) where r is a propagation distance. Near-field components of the primary field do not contribute to the far field of nonlinear component.

  11. Polarization controlled directional propagation of Bloch surface wave.

    PubMed

    Kovalevich, Tatiana; Boyer, Philippe; Suarez, Miguel; Salut, Roland; Kim, Myun-Sik; Herzig, Hans Peter; Bernal, Maria-Pilar; Grosjean, Thierry

    2017-03-06

    Bloch surface waves (BSWs) are recently developing alternative to surface plasmon polaritons (SPPs). Due to dramatically enhanced propagation distance and strong field confinement these surface states can be successfully used in on-chip all-optical integrated devices of increased complexity. In this work we propose a highly miniaturized grating based BSW coupler which is gathering launching and directional switching functionalities in a single element. This device allows to control with polarization the propagation direction of Bloch surface waves at subwavelength scale, thus impacting a large panel of domains such as optical circuitry, function design, quantum optics, etc.

  12. Ultrasonic guided wave propagation in pipes with elbows

    NASA Astrophysics Data System (ADS)

    Breon, Luke J.

    Guided wave inspection of pipelines is an important and growing area of Non-Destructive Evaluation (NDE). This technique can be used for remote inspection or monitoring of buried pipelines, or pipelines with insulation. Guided waves are sensitive to flaws such as corrosion pits and cracks. They can be used to locate flaws existing on either the outer or the inner surface of a pipe. Guided wave energy focusing can be performed to concentrate guided wave energy at particular combinations of circumferential and axial locations in straight pipes. When it can be used, this practice enhances the circumferential resolution of defects. Elbows in a piping system are sufficiently disruptive to guided wave energy that the focusing methods used in practical inspections of straight pipe have not been extended to the region beyond an elbow. Counter-intuitively, elbows with a 45 degree bend are more harmful to guided waves than those with a 90 degree bend. A simple and elegant explanation for this phenomenon is provided in this dissertation. Theoretical advancements to guided wave physics propagating around an elbow have tended to be few and slow. This is at least partly due to the complexity of the mathematics involved in the conventional description of guided wave mechanics. Parametric focusing for pipes with bends has not been previously possible as it is for straight sections of pipes. While some techniques such as time-reversal mirrors and blind finite-element-method modeling have existed for focusing beyond elbows, these techniques have been limited and largely of academic value. Also, the understanding of wave behavior in a pipe elbow has in the past been generally unclear. Consequently, signal interpretation has also been very limited for guided waves initiating in, or returning from, the far side of an elbow. A new approach to understanding guided wave propagation is developed in this work. This understanding consists of the idea that the pathway a guided wave will take

  13. Voltage induced mechanical/spin wave propagation over long distances

    NASA Astrophysics Data System (ADS)

    Chen, C.; Barra, A.; Mal, A.; Carman, G.; Sepulveda, A.

    2017-02-01

    We simulated the generation and propagation of spin waves (SWs) using two excitation methods, namely, magnetic field and voltage induced strain. A fully coupled non-linear magnetoelastic model, combining Landau-Lifshitz-Gilbert with elastodynamic equations, is used to study the propagation characteristics of SWs in magnetoelastic materials. Simulation results show that for excitation frequencies above ferromagnetic resonance (FMR), SWs excited by voltage induced strain propagate over longer distances compared to SWs excited by magnetic field. In addition, strain mediated SWs exhibit loss characteristics, which are relatively independent of the magnetic losses (Gilbert damping). Moreover, it is also shown that strain induced SWs can also be excited at frequencies below FMR.

  14. Maxwell Equation for the Coupled Spin-Charge Wave Propagation

    SciTech Connect

    Bernevig, B.Andrei; Yu, Xiaowei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-01-15

    We show that the dissipationless spin current in the ground state of the Rashba model gives rise to a reactive coupling between the spin and charge propagation, which is formally identical to the coupling between the electric and the magnetic fields in the 2 + 1 dimensional Maxwell equation. This analogy leads to a remarkable prediction that a density packet can spontaneously split into two counter propagation packets, each carrying the opposite spins. In a certain parameter regime, the coupled spin and charge wave propagates like a transverse 'photon'. We propose both optical and purely electronic experiments to detect this effect.

  15. Propagation of sound waves in tubes of noncircular cross section

    NASA Technical Reports Server (NTRS)

    Richards, W. B.

    1986-01-01

    Plane-acoustic-wave propagation in small tubes with a cross section in the shape of a flattened oval is described. Theoretical descriptions of a plane wave propagating in a tube with circular cross section and between a pair of infinite parallel plates, including viscous and thermal damping, are expressed in similar form. For a wide range of useful duct sizes, the propagation constant (whose real and imaginary parts are the amplitude attenuation rate and the wave number, respectively) is very nearly the same function of frequency for both cases if the radius of the circular tube is the same as the distance between the parallel plates. This suggests that either a circular-cross-section model or a flat-plate model can be used to calculate wave propagation in flat-oval tubing, or any other shape tubing, if its size is expressed in terms of an equivalent radius, given by g = 2 x (cross-sectional area)/(length of perimeter). Measurements of the frequency response of two sections of flat-oval tubing agree with calculations based on this idea. Flat-plate formulas are derived, the use of transmission-line matrices for calculations of plane waves in compound systems of ducts is described, and examples of computer programs written to carry out the calculations are shown.

  16. MULTI-LAYER STUDY OF WAVE PROPAGATION IN SUNSPOTS

    SciTech Connect

    Felipe, T.; Khomenko, E.; Collados, M.; Beck, C.

    2010-10-10

    We analyze the propagation of waves in sunspots from the photosphere to the chromosphere using time series of co-spatial Ca II H intensity spectra (including its line blends) and polarimetric spectra of Si I {lambda}10,827 and the He I {lambda}10,830 multiplet. From the Doppler shifts of these lines we retrieve the variation of the velocity along the line of sight at several heights. Phase spectra are used to obtain the relation between the oscillatory signals. Our analysis reveals standing waves at frequencies lower than 4 mHz and a continuous propagation of waves at higher frequencies, which steepen into shocks in the chromosphere when approaching the formation height of the Ca II H core. The observed nonlinearities are weaker in Ca II H than in He I lines. Our analysis suggests that the Ca II H core forms at a lower height than the He I {lambda}10,830 line: a time delay of about 20 s is measured between the Doppler signal detected at both wavelengths. We fit a model of linear slow magnetoacoustic wave propagation in a stratified atmosphere with radiative losses according to Newton's cooling law to the phase spectra and derive the difference in the formation height of the spectral lines. We show that the linear model describes well the wave propagation up to the formation height of Ca II H, where nonlinearities start to become very important.

  17. Propagation of elastic waves through textured polycrystals: application to ice.

    PubMed

    Maurel, Agnès; Lund, Fernando; Montagnat, Maurine

    2015-05-08

    The propagation of elastic waves in polycrystals is revisited, with an emphasis on configurations relevant to the study of ice. Randomly oriented hexagonal single crystals are considered with specific, non-uniform, probability distributions for their major axis. Three typical textures or fabrics (i.e. preferred grain orientations) are studied in detail: one cluster fabric and two girdle fabrics, as found in ice recovered from deep ice cores. After computing the averaged elasticity tensor for the considered textures, wave propagation is studied using a wave equation with elastic constants c=〈c〉+δc that are equal to an average plus deviations, presumed small, from that average. This allows for the use of the Voigt average in the wave equation, and velocities are obtained solving the appropriate Christoffel equation. The velocity for vertical propagation, as appropriate to interpret sonic logging measurements, is analysed in more details. Our formulae are shown to be accurate at the 0.5% level and they provide a rationale for previous empirical fits to wave propagation velocities with a quantitative agreement at the 0.07-0.7% level. We conclude that, within the formalism presented here, it is appropriate to use, with confidence, velocity measurements to characterize ice fabrics.

  18. Propagation of elastic waves through textured polycrystals: application to ice

    PubMed Central

    Maurel, Agnès; Lund, Fernando; Montagnat, Maurine

    2015-01-01

    The propagation of elastic waves in polycrystals is revisited, with an emphasis on configurations relevant to the study of ice. Randomly oriented hexagonal single crystals are considered with specific, non-uniform, probability distributions for their major axis. Three typical textures or fabrics (i.e. preferred grain orientations) are studied in detail: one cluster fabric and two girdle fabrics, as found in ice recovered from deep ice cores. After computing the averaged elasticity tensor for the considered textures, wave propagation is studied using a wave equation with elastic constants c=〈c〉+δc that are equal to an average plus deviations, presumed small, from that average. This allows for the use of the Voigt average in the wave equation, and velocities are obtained solving the appropriate Christoffel equation. The velocity for vertical propagation, as appropriate to interpret sonic logging measurements, is analysed in more details. Our formulae are shown to be accurate at the 0.5% level and they provide a rationale for previous empirical fits to wave propagation velocities with a quantitative agreement at the 0.07–0.7% level. We conclude that, within the formalism presented here, it is appropriate to use, with confidence, velocity measurements to characterize ice fabrics. PMID:27547099

  19. Off-axis propagation of Ultrasonic Guided Waves in Thin Orthotropic Layers: Theoretical Analysis and Dynamic Holographic Imaging Measurement

    SciTech Connect

    Telschow, Kenneth Louis; Deason, Vance Albert; Mukdadi, O.; Datta, S. K.

    2001-11-01

    The elastic properties of many materials in sheet or plate form can be approximated with orthotropic symmetry. In many sheet material manufacturing industries (e.g., the paper industry), manufacturers desire knowledge of certain anisotropic elastic properties in the sheet for handling and quality issues. Ultrasonic wave propagation in plate materials forms a method to determine the anisotropic elastic properties in a nondestructive manner. This work explores exact and approximate analysis methods of ultrasonic guided wave propagation in thin layers, explicitly dealing with orthotropic symmetry and propagation off-axis with respect to the manufacturing direction. Recent advances in full-field ultrasonic imaging methods, based on dynamic holography, allow simultaneous measurement of the plate wave motion in all planar directions within a single image. Results from this laser ultrasonic imaging approach are presented that record the lowest anti-symmetric (flexural) mode wavefront in a single image without scanning. Specific numerical predictions for flexural wave propagation in two distinctly different types of paper are presented and compared with direct imaging measurements. Very good agreement is obtained for the lowest anti-symmetric plate mode using paper properties independently determined by a third party. Complete determination of the elastic modulus tensor for orthotropic layers requires measurement of other modes in addition to the lowest anti-symmetric. Theoretical predictions are presented for other guided wave modes [extensional (S), flexural (A), and shear-horizontal (SH)] in orthotropic plates with emphasis on propagation in all planar directions. It is shown that there are significant changes in the dispersion characterization of these modes at certain frequencies (including off-axis mode coupling) that can be exploited to measure additional in-plane elastic moduli of thin layers. At present, the sensitivity of the imaging measurement approach limits

  20. Plate damage identification using wave propagation and impedance methods.

    SciTech Connect

    Wait, J. R.; Park, G. H.; Sohn, H.; Farrar, C. R.

    2004-01-01

    This paper illustrates an integrated approach for identifying structural damage in an aluminum plate. Piezoelectric (PZT) materials are used to actuatehense the dynamic response of the structure. Two damage identification techniques are integrated in this study, including Lamb wave propagations and impedance methods. In Lamb wave propagations, one PZT launches an elastic wave through the structure, and responses are measured by an array of PZT sensors. The changes in both wave attenuation and reflection are used to detect and locate the damage. The impedance method monitors the variations in structural mechanical impedance, which is coupled with the electrical impedance of the PZT. Both methods operate in high frequency ranges at which there are measurable changes in structural responses even for incipient damage such as small cracks or loose connections. This paper summarizes two methods used for damage identification, experimental procedures, and additional issues that can be used as a guideline for future investigations.

  1. Interactive propagation of photosensitive chemical waves on two circular routes.

    PubMed

    Nakata, Satoshi; Morishima, Sayaka; Kitahata, Hiroyuki

    2006-03-16

    The propagation of chemical waves in the photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated using an excitable field composed of two rings in slight contact, which were drawn using computer software and then projected on a film soaked with BZ solution using a liquid-crystal projector. When the initial phase difference between the two chemical waves in the individual rings was smaller than a critical value, this initial value was maintained after collision of the chemical waves. However, when the initial phase difference was larger than this critical value, the phase difference converged to the same value after the second collision. The critical value increased with an increase in the thickness of the rings. These experimental results on the geometry of the excitable field are discussed in relation to the nature of chemical wave propagation. These results suggest that the photosensitive BZ reaction may be useful for creating spatiotemporal patterns that depend on the geometric arrangement of excitable fields.

  2. The rarefaction wave propagation in transparent windows

    NASA Astrophysics Data System (ADS)

    Glam, B.; Porat, E.; Horovitz, Y.; Yosef-Hai, A.

    2017-01-01

    The radial (lateral) rarefaction wave velocity of polymethyl methacrylate (PMMA) and Lithium Fluoride (LiF) windows were studied by plate impact experiments that were carried out at Soreq NRC up to a pressure of 146 kbar in the PMMA and 334 kbar in the LiF. The windows were glued to Lead targets that were impacted by a copper impactor. The VISAR measurement was done in the window interface with the target. This information was utilized to identify the radial rarefaction arrival time at the center of different diameter windows after the shock event, and served as a measurement to the radial wave velocity in the shocked material. It was found that for both windows, LiF or PMMA, the measured radial wave velocity increases with the pressure. Furthermore, this velocity is significantly higher compared to the expected longitudinal sound velocity at the same pressure, calculated by the Steinberg EOS in the PMMA and by ab initio calculation in the LiF. Here we present the experimental results and a comparison with analytical calculation of the sound velocity using the Steinberg EOS.

  3. A New Physics-Based Modeling of Multiple Non-Planar Hydraulic Fractures Propagation

    SciTech Connect

    Zhou, Jing; Huang, Hai; Deo, Milind; Jiang, Shu

    2015-10-01

    Because of the low permeability in shale plays, closely spaced hydraulic fractures and multilateral horizontal wells are generally required to improve production. Therefore, understanding the potential fracture interaction and stress evolution is critical in optimizing fracture/well design and completion strategy in multi-stage horizontal wells. In this paper, a novel fully coupled reservoir flow and geomechanics model based on the dual-lattice system is developed to simulate multiple non-planar fractures propagation. The numerical model from Discrete Element Method (DEM) is used to simulate the mechanics of fracture propagations and interactions, while a conjugate irregular lattice network is generated to represent fluid flow in both fractures and formation. The fluid flow in the formation is controlled by Darcy’s law, but within fractures it is simulated by using cubic law for laminar flow through parallel plates. Initiation, growth and coalescence of the microcracks will lead to the generation of macroscopic fractures, which is explicitly mimicked by failure and removal of bonds between particles from the discrete element network. We investigate the fracture propagation path in both homogeneous and heterogeneous reservoirs using the simulator developed. Stress shadow caused by the transverse fracture will change the orientation of principal stress in the fracture neighborhood, which may inhibit or alter the growth direction of nearby fracture clusters. However, the initial in-situ stress anisotropy often helps overcome this phenomenon. Under large in-situ stress anisotropy, the hydraulic fractures are more likely to propagate in a direction that is perpendicular to the minimum horizontal stress. Under small in-situ stress anisotropy, there is a greater chance for fractures from nearby clusters to merge with each other. Then, we examine the differences in fracture geometry caused by fracturing in cemented or uncemented wellbore. Moreover, the impact of

  4. A Study of Alfven Wave Propagation and Heating the Chromosphere

    NASA Astrophysics Data System (ADS)

    Tu, J.; Song, P.

    2013-12-01

    Alfven wave propagation, reflection and heating of the solar atmosphere are studied for a one-dimensional solar atmosphere by self-consistently solving plasma and neutral fluid equations and Maxwell's equations with incorporation of the Hall effect, strong electron-neutral, electron-ion, and ion-neutral collisions. The governing equations are very stiff because of the strong coupling between the charged and neutral fluids. We have developed a numerical model based on an implicit backward difference formula (BDF2) of second order accuracy both in time and space to overcome the stiffness. A non-reflecting boundary condition is applied to the top boundary of the simulation domain so that the wave reflection within the domain due to the density gradient can be unambiguously determined. It is shown that the Alfven waves are partially reflected throughout the chromosphere. The reflection is increasingly stronger at higher altitudes and the strongest reflection occurs at the transition region. The waves are damped in the lower chromosphere dominantly through Joule dissipation due to electron collisions with neutrals and ions. The heating resulting from the wave damping is strong enough to balance the radiation energy loss for the quiet chromosphere. The collisional dissipation of the Alfven waves in the weakly collisional corona is negligible. The heating rates are larger for weaker background magnetic fields. In addition, higher frequency waves are subject to heavier damping. There is an upper cutoff frequency, depending on the background magnetic field, above which the waves are completely damped. At the frequencies below which the waves are not strongly damped, the waves may be strongly reflected at the transition region. The reflected waves interacting with the upward propagating waves may produce power at their double frequencies, which leads to more damping. Due to the reflection and damping, the energy flux of the waves transmitted to the corona is one order of

  5. Design Optimization and Simulation of Wave Propagation in Metamaterials

    DTIC Science & Technology

    2014-09-24

    AFRL-OSR-VA-TR-2014-0232 Design Optimizations Simulation of Wave Propagation in Metamaterials Robert Freund MASSACHUSETTS INSTITUTE OF TECHNOLOGY...In Metamaterials FA9550-11-1-0141 FA9550-11-1-0141 Freund, Robert Peraire, Jaime Nguyen, Cuong Massachusetts Institute of Technology 77...cannot be achieved with conventional materials. For instance, metamaterials can be designed to bend electromagnetic waves around an object so that

  6. Analysis of wave propagation in periodic 3D waveguides

    NASA Astrophysics Data System (ADS)

    Schaal, Christoph; Bischoff, Stefan; Gaul, Lothar

    2013-11-01

    Structural Health Monitoring (SHM) is a growing research field in the realm of civil engineering. SHM concepts are implemented using integrated sensors and actuators to evaluate the state of a structure. Within this work, wave-based techniques are addressed. Dispersion effects for propagating waves in waveguides of different materials are analyzed for various different cross-sections. Since analytical theory is limited, a general approach based on the Waveguide Finite Element Method is applied. Numerical results are verified experimentally.

  7. Estimating propagation velocity through a surface acoustic wave sensor

    DOEpatents

    Xu, Wenyuan; Huizinga, John S.

    2010-03-16

    Techniques are described for estimating the propagation velocity through a surface acoustic wave sensor. In particular, techniques which measure and exploit a proper segment of phase frequency response of the surface acoustic wave sensor are described for use as a basis of bacterial detection by the sensor. As described, use of velocity estimation based on a proper segment of phase frequency response has advantages over conventional techniques that use phase shift as the basis for detection.

  8. Effects of ionospheric disturbances on high latitude radio wave propagation

    NASA Astrophysics Data System (ADS)

    Larsen, T. R.

    The effects of anomalous high-latitude ionization on radio wave propagation are described for the main types of disturbances, that is, sudden ionospheric disturbances, relativistic electron events, magnetic storms, auroral disturbances, and polar cap events. Examples of radio wave characteristics for such conditions are given for the frequencies between the very low (3-3000 Hz) and high (3-30 MHz) frequency domains.

  9. Surface waves generated by charged particle bunch moving along the edge of semi-infinite planar wire grid

    NASA Astrophysics Data System (ADS)

    Vorobev, Viktor V.; Tyukhtin, Andrey V.; Galyamin, Sergey N.

    2017-04-01

    Surface waves generated by a charged-particle bunch at the semi-infinite planar periodic wire structure are analyzed. It is supposed that the bunch moves parallel to the edge of the structure. The influence of the grid is described by the averaged boundary conditions. The analytical results are given for a general case, which takes into account the finite period and wires radius. It is shown that the surface waves excited by the bunch propagate along wires with the speed of light in vacuum. The number and the structure of these surface waves depend on relative location of the bunch path and the grid. One type of wave is always excited, but its magnitude decreases with distance from the bunch path to the structure edge. If the bunch projection falls on the half-plane occupied by wires, then additionally three surface waves are generated: two of them are equivalent to ones excited by the bunch moving along infinite wire grid and another one represents the surface wave reflected from the edge. The analysis of the surface waves shows that their structure allows for determination of the length of the bunch. Typical numerical results are presented.

  10. Regulation of Spontaneous Propagating Waves in the Embryonic Mouse Brainstem

    PubMed Central

    Bosma, Martha M.

    2017-01-01

    Spontaneous activity (SA) modulates many aspects of neural development, including neuronal phenotype, axon path-finding and synaptic connectivity. In the embryonic mouse brainstem, SA initially is recorded in isolated cells at embryonic day (E) 9.5, and 48 h later takes the form of propagating waves. The majority of these waves originate from one midline initiation zone (InZ), which is situated within the developing serotonergic raphe. InZ cells express a t-type calcium channel, are depolarized, and have high membrane resistance, the combination of which allows spontaneous depolarization. Propagating events require signaling at metabotropic 5-HT receptors; a possible source could be 5-HT released by newly differentiating 5-HT neurons. At E11.5, waves propagate throughout the hindbrain, with some events crossing into the midbrain. At E12.5, lateral cells (further than 150 μm from the midline) up-regulate expression of a K channel that increases resting conductance and hyperpolarizes them, preventing the propagation of waves laterally. At the same stage, cells in the isthmus up-regulate t-type calcium channels, permitting more events to cross into the midbrain, some of which form recurring loops of activity that are able to keep intracellular calcium levels high for many minutes. At E13.5, caudal hindbrain cells hyperpolarize utilizing the same K conductance, and 24 h later, at E14.5, the InZ hyperpolarizes and no longer undergoes spontaneous events. Thus, 5-HT receptor-dependent propagating waves in the embryonic brainstem are generated and propagated by regulation of membrane conductance. We discuss these mechanisms, and the possible role of this SA in neuronal development. PMID:28101007

  11. Impact of Fog on Electromagnetic Wave Propagation

    NASA Astrophysics Data System (ADS)

    Morris, Jonathon; Fleisch, Daniel

    2002-04-01

    This experiment was designed to explore the impact of fog on electromagnetic radiation, in particular microwaves and infrared light. For years law enforcement agencies have used microwave radiation (radar guns) to measure the speed of vehicles, and the last ten years has seen increased use of LIDAR, which uses 905-nm infrared radiation rather than microwaves. To evaulate the effect of fog on the operation of these devices, we have constructed a fog chamber with microwave and optical portals to allow light from a HeNe laser and 10.6-GHz microwaves to propagate through various densities of fog. Data is acquired using Vernier Logger Pro and analyzed using MATLAB and Mathematica. Using the attenuation of the laser light to determine fog density, the impact of fog on the signal-to-noise ratio of both microwave and IR devices may be quantified, and the maximum useful range may be calculated.

  12. Skewon field and cosmic wave propagation

    NASA Astrophysics Data System (ADS)

    Ni, Wei-Tou

    2014-03-01

    We study the propagation of the Hehl-Obukhov-Rubilar skewon field in weak gravity field/dilute matter or with weak violation of the Einstein Equivalence Principle (EEP), and further classify it into Type I and Type II skewons. From the dispersion relation we show that no dissipation/no amplification condition implies that the additional skewon field must be of Type II. For Type I skewon field, the dissipation/amplification is proportional to the frequency and the CMB spectrum would deviate from Planck spectrum. From the high precision agreement of the CMB spectrum with 2.755 K Planck spectrum, we constrain the Type I cosmic skewon field |χijkl(SkI)| to ⩽ a few ×10-35. The skewon part of constitutive tensor constructed from asymmetric metric is of Type II, hence it is allowed. This study may also be applied to macroscopic electrodynamics in the case of laser pumped medium or dissipative medium.

  13. Excitation and Propagation of Electromagnetic Waves: RBSP Observation and Modeling

    NASA Astrophysics Data System (ADS)

    Zhou, Q.; Xiao, F.; Yang, C.; Liu, S.; Spence, H. E.; Geoffrey, R.; Funsten, H. O.; Blake, J. B.; Baker, D. N.; Wygant, J. R.

    2015-12-01

    During the recovery phase of the geomagnetic storm on 30-31 March 2013, Van Allen Probe A detected enhanced magnetosonic (MS) waves in a broad range of L = 1.8-4.7 and magnetic local time (MLT) = 17-22 h, with a frequency range ˜10-100 Hz. In the meanwhile, distinct proton ring distributions with peaks at energies of ˜10 keV, were also observed in L = 3.2-4.6 and L = 5.0-5.6. Using a subtracted bi-Maxwellian distribution to model the observed proton ring distribution, we perform three-dimensional ray tracing to investigate the instability, propagation, and spatial distribution of MS waves. Numerical results show that nightside MS waves are produced by proton ring distribution and grow rapidly from the source location L = 5.6 to the location L = 5.0 but remain nearly stable at locations L < 5.0. Moreover, waves launched toward lower L shells with different initial azimuthal angles propagate across different MLT regions with divergent paths at first, then gradually turn back toward higher L shells and propagate across different MLT regions with convergent paths. The current results further reveal that MS waves are generated by a ring distribution of ˜10 keV proton and proton ring in one region can contribute to the MS wave power in another region.

  14. Wave propagation in carbon nanotubes under shear deformation

    NASA Astrophysics Data System (ADS)

    Dong, K.; Wang, X.

    2006-06-01

    This paper reports the results of an investigation on the effect of shear deformations on wave propagation in carbon nanotubes embedded in an elastic matrix. A multi-walled carbon nanotube is considered as a multiple shell coupled together through van der Waals forces between two adjacent tubes. The surrounding matrix is considered as a spring element defined by the Winkler model. Using the variational calculus of Hamilton's principle, dynamic governing equations considering the shear deformation and rotary inertia terms are derived. Numerical examples describe the effects of shear deformation, rotary inertia and elastic matrix on the velocity, the critical frequency, the cut-off frequency and the amplitude ratio of wave propagation in multi-walled carbon nanotubes embedded in an elastic matrix, respectively. The results obtained show that wave propagation in carbon nanotubes appears in a critical frequency or a cut-off frequency for different wave modes; the effect of shear deformation decreases the value of critical frequency; the critical frequency increases as the matrix stiffness increases; the inertia rotary has an obvious influence on the wave velocity for some wave modes in the higher frequency region.

  15. Effect of fuel stratification on detonation wave propagation

    NASA Astrophysics Data System (ADS)

    Masselot, Damien; Fievet, Romain; Raman, Venkat

    2016-11-01

    Rotating detonation engines (RDEs) form a class of pressure-gain combustion systems of higher efficiency compared to conventional gas turbine engines. One of the key features of the design is the injection system, as reactants need to be continuously provided to the detonation wave to sustain its propagation speed. As inhomogeneities in the reactant mixture can perturb the detonation wave front, premixed fuel jet injectors might seem like the most stable solution. However, this introduces the risk of the detonation wave propagating through the injector, causing catastrophic failure. On the other hand, non-premixed fuel injection will tend to quench the detonation wave near the injectors, reducing the likelihood of such failure. Still, the effects of such non-premixing and flow inhomogeneities ahead of a detonation wave have yet to be fully understood and are the object of this study. A 3D channel filled with O2 diluted in an inert gas with circular H2 injectors is simulated as a detonation wave propagates through the system. The impact of key parameters such as injector spacing, injector size, mixture composition and time variations will be discussed. PhD Candidate.

  16. Stress Wave Propagation in Two-dimensional Buckyball Lattice

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Zheng, Bowen

    2016-11-01

    Orderly arrayed granular crystals exhibit extraordinary capability to tune stress wave propagation. Granular system of higher dimension renders many more stress wave patterns, showing its great potential for physical and engineering applications. At nanoscale, one-dimensionally arranged buckyball (C60) system has shown the ability to support solitary wave. In this paper, stress wave behaviors of two-dimensional buckyball (C60) lattice are investigated based on square close packing and hexagonal close packing. We show that the square close packed system supports highly directional Nesterenko solitary waves along initially excited chains and hexagonal close packed system tends to distribute the impulse and dissipates impact exponentially. Results of numerical calculations based on a two-dimensional nonlinear spring model are in a good agreement with the results of molecular dynamics simulations. This work enhances the understanding of wave properties and allows manipulations of nanoscale lattice and novel design of shock mitigation and nanoscale energy harvesting devices.

  17. Linear and nonlinear propagation of water wave groups

    NASA Technical Reports Server (NTRS)

    Pierson, W. J., Jr.; Donelan, M. A.; Hui, W. H.

    1992-01-01

    Results are presented from a study of the evolution of waveforms with known analytical group shapes, in the form of both transient wave groups and the cloidal (cn) and dnoidal (dn) wave trains as derived from the nonlinear Schroedinger equation. The waveforms were generated in a long wind-wave tank of the Canada Centre for Inland Waters. It was found that the low-amplitude transients behaved as predicted by the linear theory and that the cn and dn wave trains of moderate steepness behaved almost as predicted by the nonlinear Schroedinger equation. Some of the results did not fit into any of the available theories for waves on water, but they provide important insight on how actual groups of waves propagate and on higher-order effects for a transient waveform.

  18. Stress Wave Propagation in Two-dimensional Buckyball Lattice

    PubMed Central

    Xu, Jun; Zheng, Bowen

    2016-01-01

    Orderly arrayed granular crystals exhibit extraordinary capability to tune stress wave propagation. Granular system of higher dimension renders many more stress wave patterns, showing its great potential for physical and engineering applications. At nanoscale, one-dimensionally arranged buckyball (C60) system has shown the ability to support solitary wave. In this paper, stress wave behaviors of two-dimensional buckyball (C60) lattice are investigated based on square close packing and hexagonal close packing. We show that the square close packed system supports highly directional Nesterenko solitary waves along initially excited chains and hexagonal close packed system tends to distribute the impulse and dissipates impact exponentially. Results of numerical calculations based on a two-dimensional nonlinear spring model are in a good agreement with the results of molecular dynamics simulations. This work enhances the understanding of wave properties and allows manipulations of nanoscale lattice and novel design of shock mitigation and nanoscale energy harvesting devices. PMID:27892963

  19. Propagating Stress Waves During Epithelial Expansion

    NASA Astrophysics Data System (ADS)

    Banerjee, Shiladitya; Utuje, Kazage J. C.; Marchetti, M. Cristina

    2015-06-01

    Coordinated motion of cell monolayers during epithelial wound healing and tissue morphogenesis involves mechanical stress generation. Here we propose a model for the dynamics of epithelial expansion that couples mechanical deformations in the tissue to contractile activity and polarization in the cells. A new ingredient of our model is a feedback between local strain, polarization, and contractility that naturally yields a mechanism for viscoelasticity and effective inertia in the cell monolayer. Using a combination of analytical and numerical techniques, we demonstrate that our model quantitatively reproduces many experimental findings [Nat. Phys. 8, 628 (2012)], including the buildup of intercellular stresses, and the existence of traveling mechanical waves guiding the oscillatory monolayer expansion.

  20. Wave Propagation through Axially Symmetric Dielectric Shells.

    DTIC Science & Technology

    1981-06-01

    1-8 2..2 Sc lr .o en i.. . . . . ..........eo oe e .eoe. o. eeeeo. oo....... 2 1 1.2 Baekground: Analytical Methods Based on Flat Sheet Appr oatei...Fields Near a Radome Consist of Constituent Waves. 1-2 - -t . -__-_-_-_-_-_-_..._._._._._._. 1.2 BACKGROUND: ANALYTICAL METHODS BASED ON FLAT SHEET...2.4.2. So A2 ikR x (4 ) = (K-1) E feik Cos2 dado dz (2-100) x 2 R2 o where = (aa - ap cos - zz’) R - 1 (2-101) and -11 = [6 (a+6p)-6 (a-6p)-a 1. (2

  1. Elastic wave propagation in finitely deformed layered materials

    NASA Astrophysics Data System (ADS)

    Galich, Pavel I.; Fang, Nicholas X.; Boyce, Mary C.; Rudykh, Stephan

    2017-01-01

    We analyze elastic wave propagation in highly deformable layered media with isotropic hyperelastic phases. Band gap structures are calculated for the periodic laminates undergoing large deformations. Compact explicit expressions for the phase and group velocities are derived for the long waves propagating in the finitely deformed composites. Elastic wave characteristics and band gaps are shown to be highly tunable by deformation. The influence of deformation on shear and pressure wave band gaps for materials with various composition and constituent properties are studied, finding advantageous compositions for producing highly tunable complete band gaps in low-frequency ranges. The shear wave band gaps are influenced through the deformation induced changes in effective material properties, whereas pressure wave band gaps are mostly influenced by deformation induced geometry changes. The wide shear wave band gaps are found in the laminates with small volume fractions of a soft phase embedded in a stiffer material; pressure wave band gaps of the low-frequency range appear in the laminates with thin highly compressible layers embedded in a nearly incompressible phase. Thus, by constructing composites with a small amount of a highly compressible phase, wide complete band gaps at the low-frequency range can be achieved; furthermore, these band gaps are shown to be highly tunable by deformation.

  2. Seismic Wave Propagation in Stratified Media

    NASA Astrophysics Data System (ADS)

    Frazer, Neil

    In order to fully appreciate this book, it is necessary to recall some of the recent history of body wave seismology. Until the late 1960s, most of our knowledge of subsurface structure came from travel time studies. Pekeris [1948] and Haskell [1953] had shown how to model seismic data, but existing computers limited the use of their methods to the computation of dispersion curves for simple earth models. Then Helmberger [1968] used the Cagniard-de Hoop method [de Hoop, 1960] to model refraction arrivals and thereby demonstrated the practicality of seismic modeling in the time domain. The Cagniard-de Hoop method is a generalized ray method, which means (in practical terms) that it is good for synthesizing first motions but not so good for the later parts of the seismogram. Accordingly, Fuchs and Muller [1971] returned to the methods of Pekeris and Haskell and showed that with large modern computers, the whole seismogram could be synthesized. However, problems remained, because Haskell matrices are numerically unstable when used to synthesize SV body waves. Methods of overcoming this instability were found (and are still being found), but they are all, with the possible exception of the methods of Schmidt and Tango [1986] and of Chin et al. [1984], complicated, difficult to program, and lacking in physical insight.

  3. 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.

  4. Self-consistent evolution of tissue damage under stress wave propagation

    SciTech Connect

    Amendt, P; Glinsky, M; Kaufman, Y; London, R A; Sapir, M; Strauss, M

    1999-01-14

    Laser-initiated stress waves are reflected from tissue boundaries, thereby inducing tensile stresses, which are responsible for tissue damage. A self-consistent model of tissue failure evolution induced by stress wave propagation is considered. The failed tissue is represented by an ensemble of spherical voids and includes the effect of nucleation, growth and coalescence of voids under stress wave tension. Voids nucleate around impurities and grow according to an extended Rayleigh model that includes the effects of surface tension, viscosity and acoustic emission at void collapse. The damage model is coupled self-consistently to a one-dimensional planar hydrodynamic model of stress waves generated by a short pulse laser. We considered the problem of a bipolar wave generated by a short pulse laser absorbed on a free boundary of an aqueous system. The propagating wave includes a tensile component, which interacts with the impurities of exponential distribution in dimension, impurity density ({approximately}10{sup 8} cm{sup -3}) void and an ensemble of voids is generated. For moderate growth reduces the tensile wave component and causes the pressure to oscillate between tension and compression. For low impurity density ({approximately}10{sup 6} cm{sup -3} ) the bubbles grow on a long time scale (5-10 {micro}sec) relative to the wave interaction time ({approximately}100 nsec). At later times the growing bubbles interact with each other causing pressure oscillations and delay the system from reaching the 1 bar ambient compression pressure. This effect increases considerably the bubble lifetime consistent with experiments. At the collapse stage small bubbles collapse earlier and induce pressures, which reduce the collapse time of the larger bubbles.

  5. A compendium of millimeter wave propagation studies performed by NASA

    NASA Technical Reports Server (NTRS)

    Kaul, R.; Rogers, D.; Bremer, J.

    1977-01-01

    Key millimeter wave propagation experiments and analytical results were summarized. The experiments were performed with the Ats-5, Ats-6 and Comstar satellites, radars, radiometers and rain gage networks. Analytic models were developed for extrapolation of experimental results to frequencies, locations, and communications systems.

  6. Electromagnetic wave propagation in rain and polarization effects

    PubMed Central

    OKAMURA, Sogo; OGUCHI, Tomohiro

    2010-01-01

    This paper summarizes our study on microwave and millimeter-wave propagation in rain with special emphasis on the effects of polarization. Starting from a recount of our past findings, we will discuss developments with these and how they are connected with subsequent research. PMID:20551593

  7. Wave propagation in turbulent media: use of convergence acceleration methods.

    PubMed

    Baram, A; Tsadka, S; Azar, Z; Tur, M

    1988-06-01

    We propose the use of convergence acceleration methods for the evaluation of integral expressions of an oscillatory nature, often encountered in the study of optical wave propagation in the turbulent atmosphere. These techniques offer substantial savings in computation time with appreciable gain in accuracy. As an example, we apply the Levin u acceleration scheme to the problem of remote sensing of transversal wind profiles.

  8. Normal Wave Propagation Velocity in a Static Web.

    DTIC Science & Technology

    1986-12-01

    34 " " ’ . " . " . " " . " , " " . " -" " " " . " " . " " " " . " * . - " " " , 4 . " . " . " " " . " " "." "-" "." " . . . . . " " " " -w A- INah . . . . . . - - 1 NORMAL WAVE PROPAGATION VELOCITY IN A STATIC WEB By

  9. Frozen Gaussian approximation for 3-D seismic wave propagation

    NASA Astrophysics Data System (ADS)

    Chai, Lihui; Tong, Ping; Yang, Xu

    2017-01-01

    We present a systematic introduction on applying frozen Gaussian approximation (FGA) to compute synthetic seismograms in 3-D earth models. In this method, seismic wavefield is decomposed into frozen (fixed-width) Gaussian functions, which propagate along ray paths. Rather than the coherent state solution to the wave equation, this method is rigorously derived by asymptotic expansion on phase plane, with analysis of its accuracy determined by the ratio of short wavelength over large domain size. Similar to other ray-based beam methods (e.g. Gaussian beam methods), one can use relatively small number of Gaussians to get accurate approximations of high-frequency wavefield. The algorithm is embarrassingly parallel, which can drastically speed up the computation with a multicore-processor computer station. We illustrate the accuracy and efficiency of the method by comparing it to the spectral element method for a 3-D seismic wave propagation in homogeneous media, where one has the analytical solution as a benchmark. As another proof of methodology, simulations of high-frequency seismic wave propagation in heterogeneous media are performed for 3-D waveguide model and smoothed Marmousi model, respectively. The second contribution of this paper is that, we incorporate the Snell's law into the FGA formulation, and asymptotically derive reflection, transmission and free surface conditions for FGA to compute high-frequency seismic wave propagation in high contrast media. We numerically test these conditions by computing traveltime kernels of different phases in the 3-D crust-over-mantle model.

  10. Frozen Gaussian approximation for three-dimensional seismic wave propagation

    NASA Astrophysics Data System (ADS)

    Chai, Lihui; Tong, Ping; Yang, Xu

    2016-09-01

    We present a systematic introduction on applying frozen Gaussian approximation (FGA) to compute synthetic seismograms in three-dimensional earth models. In this method, seismic wavefield is decomposed into frozen (fixed-width) Gaussian functions, which propagate along ray paths. Rather than the coherent state solution to the wave equation, this method is rigorously derived by asymptotic expansion on phase plane, with analysis of its accuracy determined by the ratio of short wavelength over large domain size. Similar to other ray-based beam methods (e.g. Gaussian beam methods), one can use relatively small number of Gaussians to get accurate approximations of high-frequency wavefield. The algorithm is embarrassingly parallel, which can drastically speed up the computation with a multicore-processor computer station. We illustrate the accuracy and efficiency of the method by comparing it to the spectral element method for a three-dimensional (3D) seismic wave propagation in homogeneous media, where one has the analytical solution as a benchmark. As another proof of methodology, simulations of high-frequency seismic wave propagation in heterogeneous media are performed for 3D waveguide model and smoothed Marmousi model respectively. The second contribution of this paper is that, we incorporate the Snell's law into the FGA formulation, and asymptotically derive reflection, transmission and free surface conditions for FGA to compute high-frequency seismic wave propagation in high contrast media. We numerically test these conditions by computing traveltime kernels of different phases in the 3D crust-over-mantle model.

  11. Corrigendum and addendum. Modeling weakly nonlinear acoustic wave propagation

    DOE PAGES

    Christov, Ivan; Christov, C. I.; Jordan, P. M.

    2014-12-18

    This article presents errors, corrections, and additions to the research outlined in the following citation: Christov, I., Christov, C. I., & Jordan, P. M. (2007). Modeling weakly nonlinear acoustic wave propagation. The Quarterly Journal of Mechanics and Applied Mathematics, 60(4), 473-495.

  12. The Propagation of Slow Wave Potentials in Pea Epicotyls.

    PubMed Central

    Stahlberg, R.; Cosgrove, D. J.

    1997-01-01

    Slow wave potentials are considered to be electric long-distance signals specific for plants, although there are conflicting ideas about a chemical, electrical, or hydraulic mode of propagation. These ideas were tested by comparing the propagation of hydraulic and electric signals in epicotyls of pea (Pisum sativum L). A hydraulic signal in the form of a defined step increase in xylem pressure (Px) was applied to the root of intact seedlings and propagated nearly instantly through the epicotyl axis while its amplitude decreased with distance from the pressure chamber. This decremental propagation was caused by a leaky xylem and created an axial Px gradient in the epicotyl. Simultaneously along the epicotyl surface, depolarizations appeared with lag times that increased acropetally with distance from the pressure chamber from 5 s to 3 min. When measured at a constant distance, the lag times increased as the size of the applied pressure steps decreased. We conclude that the Px gradient in the epicotyl caused local depolarizations with acropetally increasing lag times, which have the appearance of an electric signal propagating with a rate of 20 to 30 mm min-1. This static description of the slow wave potentials challenges its traditional classification as a propagating electric signal. PMID:12223601

  13. Wave propagation of myocardial stretch: correlation with myocardial stiffness.

    PubMed

    Pislaru, Cristina; Pellikka, Patricia A; Pislaru, Sorin V

    2014-01-01

    The mechanism of flow propagation during diastole in the left ventricle (LV) has been well described. Little is known about the associated waves propagating along the heart walls. These waves may have a mechanism similar to pulse wave propagation in arteries. The major goal of the study was to evaluate the effect of myocardial stiffness and preload on this wave transmission. Longitudinal late diastolic deformation and wave speed (Vp) of myocardial stretch in the anterior LV wall were measured using sonomicrometry in 16 pigs. Animals with normal and altered myocardial stiffness (acute myocardial infarction) were studied with and without preload alterations. Elastic modulus estimated from Vp (E VP; Moens-Korteweg equation) was compared to incremental elastic modulus obtained from exponential end-diastolic stress-strain relation (E SS). Myocardial distensibility and α- and β-coefficients of stress-strain relations were calculated. Vp was higher at reperfusion compared to baseline (2.6 ± 1.3 vs. 1.3 ± 0.4 m/s; p = 0.005) and best correlated with E SS (r2 = 0.80, p < 0.0001), β-coefficient (r2 = 0.78, p < 0.0001), distensibility (r2 = 0.47, p = 0.005), and wall thickness/diameter ratio (r2 = 0.42, p = 0.009). Elastic moduli (E VP and E SS) were strongly correlated (r2 = 0.83, p < 0.0001). Increasing preload increased Vp and E VP and decreased distensibility. At multivariate analysis, E SS, wall thickness, and end-diastolic and systolic LV pressures were independent predictors of Vp (r2 model = 0.83, p < 0.0001). In conclusion, the main determinants of wave propagation of longitudinal myocardial stretch were myocardial stiffness and LV geometry and pressure. This local wave speed could potentially be measured noninvasively by echocardiography.

  14. Wave Propagation in the Vicinities of Rock Fractures Under Obliquely Incident Wave

    NASA Astrophysics Data System (ADS)

    Zou, Yang; Li, Jianchun; He, Lei; laloui, Lyesse; Zhao, Jian

    2016-05-01

    Though obliquely incident plane wave across rock fractures has been extensively investigated by theoretical analysis, the quantitative identification of each wave emerged from fractures has not been achieved either in numerical simulation or laboratory experiment. On the other hand, there are no theoretical results describing the stress/velocity state of the rocks beside a fracture. The superposition of the multiple waves propagating in the media results in the variation of the stress/velocity state. To understand the superposition of the wave components in the adjacent rocks of a facture, based on the geometrical analysis of the wave paths, the lag times among passing waves at an arbitrary point are determined. The normalised critical distances from the fracture to the measuring locations where the corresponding harmonic waves depart from other waves for a certain duration are then derived. Discussion on the correction for an arbitrary incident wave is then carried out considering the changes of the duration of the reflected and transmitted waves. Under the guidance of the analysis, wave superposition is performed for theoretical results and separated waves are obtained from numerical model. They are demonstrated to be consistent with each other. The measurement and the data processing provide an approach for wave separation in a relatively unbounded media. In addition, based on the mechanical analysis on the wave front, an indirect wave separation method is proposed which provides a possibility for laboratory experiments of wave propagation with an arbitrary incident angle.

  15. Propagation of longitudinal thermoplastic waves in layered structures

    NASA Astrophysics Data System (ADS)

    Li, Chen; Cetinkaya, Cetin

    2000-05-01

    The recent advances in photonics and laser instrumentation have been creating a favorable environment for thermal-based elastic wave generation techniques and their applications in various fields, such as nondestructive testing and smart structures. The main advantages of laser-based NDE include noncontact evaluation, freedom for complex surface geometry, high spatial and temporal resolution, easy access to cavities, and fast scanning. Two disadvantages are that the laser-based method requires a good physical understanding of thermoelastic wave propagation in solids, which is considerably more complicated than elastic wave propagation, and more complicated instrumentation needed for data collection. In an idealized solid, thermal energy is transported by two different mechanisms: by quantized electronic excitations, which are called free electrons, and the quanta of lattice vibrations, which are called phonons. These quanta undergo collisions of a dissipative nature, giving rise to thermal resistance in the medium. A relaxation time is associated with the average communication time between these collisions for the commencement of resistive flow. There are a number of optical methods available for elastic wave generation and detection. The most commonly utilized techniques include interferometric and noninterferometric techniques, optical heterodyning, differential interferometry, and time-delay interferometry. In the current work, a transfer matrix formulation including the second sound effect is developed for a thermoelastic layer. The second sound effect is included to eliminate the thermal wave travelling with infinite velocity as predicted by the diffusion heat transfer model, and, consequently, the immediate arrival of waves. Utilizing this formulation and the periodic systems framework, the attenuation and propagation properties of one-dimensional thermoelastic wave in both continuum and layered structures are studied. A perturbation analysis is carried out

  16. Wave propagation in one-dimensional microscopic granular chains

    NASA Astrophysics Data System (ADS)

    Lin, Wei-Hsun; Daraio, Chiara

    2016-11-01

    We employ noncontact optical techniques to generate and measure stress waves in uncompressed, one-dimensional microscopic granular chains, and support our experiments with discrete numerical simulations. We show that the wave propagation through dry particles (150 μm radius) is highly nonlinear and it is significantly influenced by the presence of defects (e.g., surface roughness, interparticle gaps, and misalignment). We derive an analytical relation between the group velocity and gap size, and define bounds for the formation of highly nonlinear solitary waves as a function of gap size and axial misalignment.

  17. Effects of D region ionization on radio wave propagation

    NASA Technical Reports Server (NTRS)

    Larsen, T. R.

    1979-01-01

    The effects of anomalous D region ionization upon radio wave propagation are described for the main types of disturbances: sudden ionospheric disturbances, relativistic electron events, magnetic storms, auroral disturbances, polar cap events, and stratospheric warmings. Examples of radio wave characteristics for such conditions are given for the frequencies between the extremely low (3-3000 Hz) and high (3-30 MHz) frequency domains. Statistics on the disturbance effects and radio wave data are given in order to contribute towards the evaluation of possibilities for predicting the radio effects.

  18. Lightning location with variable radio wave propagation velocity

    NASA Astrophysics Data System (ADS)

    Liu, Zhongjian; Koh, Kuang Liang; Mezentsev, Andrew; Sugier, Jacqueline; Fullekrug, Martin

    2016-04-01

    Lightning discharges can be located by triangulation of their broadband electromagnetic pulses in long-baseline (~500 km) radio receiver networks. Here we apply the time of arrival difference (TOA) method to electric field recordings with a low frequency radio receiver array consisting of four stations in western Europe. The electromagnetic wave propagation velocity at low radio frequencies is an important input parameter for the TOA calculation and it is normally assumed to be equal to the speed of light. However, the radio wave propagation depends for example on the frequency, ground conductivity and the ionospheric height and small variations can cause location differences from hundreds to thousands of meters, as demonstrated in this study. The radio wave propagation from two VLF transmissions at 20.9 kHz and 23.4 kHz are compared. The results show that the apparent phase velocities are 0.6% slower and 0.5% faster than the speed of light respectively. As a result, a variable velocity is implemented in the TOA method using continuously recorded data on the 8th August 2014, when a mesoscale convective system developed over central France. The lightning locations inferred with a variable wave propagation velocity are more clustered than those using a fixed velocity. The distribution of the lightning velocities in a given geographic area fits a normal distribution that is not centred at the speed of light. As a result, representative velocities can be calculated for smaller regions to generate a velocity map over a larger area of enhanced lightning activity. These results suggest a connection with the ground elevation and/or surface conductivity that might have an impact on the observed wave propagation velocities.

  19. Enhanced traveling wave amplification of co-planar slow wave structure by extended phase-matching

    SciTech Connect

    Palm, Andrew; Sirigiri, Jagadishwar; Shin, Young-Min

    2015-09-15

    The electron beam co-propagating with slow waves in a staggered double grating array (SDGA) efficiently amplifies millimeter and sub-millimeter waves over a wide spectrum. Our theoretical and numerical analyses show that the power amplification in the fundamental passband is enhanced by the extended beam-wave phase-matching. Particle-in-cell simulations on the SDGA slow wave structure, designed with 10.4 keV and 50–100 mA sheet beam, indicate that maintaining beam-wave synchronization along the entire length of the circuit improves the gain by 7.3% leading to a total gain of 28 dB, corresponding to 62 W saturated power at the middle of operating band, and a 3-dB bandwidth of 7 GHz with 10.5% at V-band (73.5 GHz center frequency) with saturated peak power reaching 80 W and 28 dB at 71 GHz. These results also show a reasonably good agreement with analytic calculations based on Pierce small signal gain theory.

  20. Surface wave propagation in non-ideal plasmas

    NASA Astrophysics Data System (ADS)

    Pandey, B. P.; Dwivedi, C. B.

    2015-03-01

    The properties of surface waves in a partially ionized, compressible magnetized plasma slab are investigated in this work. The waves are affected by the non-ideal magnetohydrodynamic (MHD) effects which causes finite drift of the magnetic field in the medium. When the magnetic field drift is ignored, the characteristics of the wave propagation in a partially ionized plasma fluid is similar to the fully ionized ideal MHD except now the propagation properties depend on the fractional ionization as well as on the compressibility of the medium. The phase velocity of the sausage and kink waves increases marginally (by a few per cent) due to the compressibility of the medium in both ideal as well as Hall-diffusion-dominated regimes. However, unlike ideal regime, only waves below certain cut-off frequency can propagate in the medium in Hall dominated regime. This cut-off for a thin slab has a weak dependence on the plasma beta whereas for thick slab no such dependence exists. More importantly, since the cut-off is introduced by the Hall diffusion, the fractional ionization of the medium is more important than the plasma compressibility in determining such a cut-off. Therefore, for both compressible as well incompressible medium, the surface modes of shorter wavelength are permitted with increasing ionization in the medium. We discuss the relevance of these results in the context of solar photosphere-chromosphere.

  1. Experimental and theoretical study of Rayleigh-Lamb wave propagation

    NASA Technical Reports Server (NTRS)

    Rogers, Wayne P.; Datta, Subhendu K.; Ju, T. H.

    1990-01-01

    Many space structures, such as the Space Station Freedom, contain critical thin-walled components. The structural integrity of thin-walled plates and shells can be monitored effectively using acoustic emission and ultrasonic testing in the Rayleigh-Lamb wave frequency range. A new PVDF piezoelectric sensor has been developed that is well suited to remote, inservice nondestructive evaluation of space structures. In the present study the new sensor was used to investigate Rayleigh-Lamb wave propagation in a plate. The experimental apparatus consisted of a glass plate (2.3 m x 25.4 mm x 5.6 mm) with PVDF sensor (3 mm diam.) mounted at various positions along its length. A steel ball impact served as a simulated acoustic emission source, producing surface waves, shear waves and longitudinal waves with dominant frequencies between 1 kHz and 200 kHz. The experimental time domain wave-forms were compared with theoretical predictions of the wave propagation in the plate. The model uses an analytical solution for the Green's function and the measured response at a single position to predict response at any other position in the plate. Close agreement was found between the experimental and theoretical results.

  2. Excitation of coherent propagating spin waves by pure spin currents

    PubMed Central

    Demidov, Vladislav E.; Urazhdin, Sergei; Liu, Ronghua; Divinskiy, Boris; Telegin, Andrey; Demokritov, Sergej O.

    2016-01-01

    Utilization of pure spin currents not accompanied by the flow of electrical charge provides unprecedented opportunities for the emerging technologies based on the electron's spin degree of freedom, such as spintronics and magnonics. It was recently shown that pure spin currents can be used to excite coherent magnetization dynamics in magnetic nanostructures. However, because of the intrinsic nonlinear self-localization effects, magnetic auto-oscillations in the demonstrated devices were spatially confined, preventing their applications as sources of propagating spin waves in magnonic circuits using these waves as signal carriers. Here, we experimentally demonstrate efficient excitation and directional propagation of coherent spin waves generated by pure spin current. We show that this can be achieved by using the nonlocal spin injection mechanism, which enables flexible design of magnetic nanosystems and allows one to efficiently control their dynamic characteristics. PMID:26818232

  3. Spiral Calcium Wave Propagation and Annihilation in Xenopus laevis Oocytes

    NASA Astrophysics Data System (ADS)

    Lechleiter, James; Girard, Steven; Peralta, Ernest; Clapham, David

    1991-04-01

    Intracellular calcium (Ca2+) is a ubiquitous second messenger. Information is encoded in the magnitude, frequency, and spatial organization of changes in the concentration of cytosolic free Ca2+. Regenerative spiral waves of release of free Ca2+ were observed by confocal microscopy in Xenopus laevis oocytes expressing muscarinic acetylcholine receptor subtypes. This pattern of Ca2+ activity is characteristic of an intracellular milieu that behaves as a regenerative excitable medium. The minimal critical radius for propagation of focal Ca2+ waves (10.4 micrometers) and the effective diffusion constant for the excitation signal (2.3 x 10-6 square centimeters per second) were estimated from measurements of velocity and curvature of circular wavefronts expanding from foci. By modeling Ca2+ release with cellular automata, the absolute refractory period for Ca2+ stores (4.7 seconds) was determined. Other phenomena expected of an excitable medium, such as wave propagation of undiminished amplitude and annihilation of colliding wavefronts, were observed.

  4. Quasinormal modes and classical wave propagation in analogue black holes

    SciTech Connect

    Berti, Emanuele; Cardoso, Vitor; Lemos, Jose P.S.

    2004-12-15

    Many properties of black holes can be studied using acoustic analogues in the laboratory through the propagation of sound waves. We investigate in detail sound wave propagation in a rotating acoustic (2+1)-dimensional black hole, which corresponds to the 'draining bathtub' fluid flow. We compute the quasinormal mode frequencies of this system and discuss late-time power-law tails. Because of the presence of an ergoregion, waves in a rotating acoustic black hole can be superradiantly amplified. We also compute superradiant reflection coefficients and instability time scales for the acoustic black hole bomb, the equivalent of the Press-Teukolsky black hole bomb. Finally we discuss quasinormal modes and late-time tails in a nonrotating canonical acoustic black hole, corresponding to an incompressible, spherically symmetric (3+1)-dimensional fluid flow.

  5. Torsional wave propagation in multiwalled carbon nanotubes using nonlocal elasticity

    NASA Astrophysics Data System (ADS)

    Arda, Mustafa; Aydogdu, Metin

    2016-03-01

    Torsional wave propagation in multiwalled carbon nanotubes is studied in the present work. Governing equation of motion of multiwalled carbon nanotube is obtained using Eringen's nonlocal elasticity theory. The effect of van der Waals interaction coefficient is considered between inner and outer nanotubes. Dispersion relations are obtained and discussed in detail. Effect of nonlocal parameter and van der Waals interaction to the torsional wave propagation behavior of multiwalled carbon nanotubes is investigated. It is obtained that torsional van der Waals interaction between adjacent tubes can change the rotational direction of multiwalled carbon nanotube as in-phase or anti-phase. The group and escape velocity of the waves converge to a limit value in the nonlocal elasticity approach.

  6. Simulation of wave propagation in three-dimensional random media

    NASA Technical Reports Server (NTRS)

    Coles, William A.; Filice, J. P.; Frehlich, R. G.; Yadlowsky, M.

    1993-01-01

    Quantitative error analysis for simulation of wave propagation in three dimensional random media assuming narrow angular scattering are presented for the plane wave and spherical wave geometry. This includes the errors resulting from finite grid size, finite simulation dimensions, and the separation of the two-dimensional screens along the propagation direction. Simple error scalings are determined for power-law spectra of the random refractive index of the media. The effects of a finite inner scale are also considered. The spatial spectra of the intensity errors are calculated and compared to the spatial spectra of intensity. The numerical requirements for a simulation of given accuracy are determined for realizations of the field. The numerical requirements for accurate estimation of higher moments of the field are less stringent.

  7. S-Wave Normal Mode Propagation in Aluminum Cylinders

    USGS Publications Warehouse

    Lee, Myung W.; Waite, William F.

    2010-01-01

    Large amplitude waveform features have been identified in pulse-transmission shear-wave measurements through cylinders that are long relative to the acoustic wavelength. The arrival times and amplitudes of these features do not follow the predicted behavior of well-known bar waves, but instead they appear to propagate with group velocities that increase as the waveform feature's dominant frequency increases. To identify these anomalous features, the wave equation is solved in a cylindrical coordinate system using an infinitely long cylinder with a free surface boundary condition. The solution indicates that large amplitude normal-mode propagations exist. Using the high-frequency approximation of the Bessel function, an approximate dispersion relation is derived. The predicted amplitude and group velocities using the approximate dispersion relation qualitatively agree with measured values at high frequencies, but the exact dispersion relation should be used to analyze normal modes for full ranges of frequency of interest, particularly at lower frequencies.

  8. Obliquely Propagating Electromagnetic Waves in Magnetized Kappa Plasmas

    NASA Astrophysics Data System (ADS)

    Gaelzer, R.

    2015-12-01

    The effects of velocity distribution functions (VDFs) that exhibit a power-law dependence on the high-energy tail have been the subjectof intense research by the space plasma community. Such functions, known as kappa or superthermal distributions, have beenfound to provide a better fitting to the VDF measured by spacecraft in the solar wind. One of the problems that is being addressed on this new light is the temperature anisotropy of solar wind protons and electrons. An anisotropic kappa VDF contains a large amount of free energy that can excite waves in the solar wind. Conversely, the wave-particle interaction is important to determine the shape of theobserved particle distributions.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 electromagnetic waves have been scarcely reported so far. The absence of a general treatment prevents a complete analysis of the wave-particle interaction in kappa plasmas, since some instabilities, such as the firehose, can operate simultaneously both in the parallel and oblique directions.In a recent work [1], we have obtained expressions for the dielectric tensor and dispersion relations for the low-frequency, quasi-perpendicular dispersive Alfvén waves resulting from a kappa VDF. In the present work, we generalize the formalism introduced by [1] for the general case of electrostatic and/or electromagnetic waves propagating in a kappa plasma in any frequency range and for arbitrary angles.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. [1] R. Gaelzer and L. F. Ziebell, Journal of Geophysical Research 119, 9334

  9. Ultralong propagation of a surface plasmon polariton wave within an ultrawide bandwidth via phase-sensitive optical parametric amplification.

    PubMed

    Izadi, Mohammad Amin; Nouroozi, Rahman

    2017-04-15

    The propagation length enhancement of surface plasmon polariton (SPP) waves could lead to practical applications. This Letter proposes the numerically verified phase-sensitive nonlinear χ(2)-based optical parametric amplification (OPA) for ultralong propagation of a SPP wave within an ultrawide bandwidth. The strong nonlinear interaction between the SPP mode and the hybrid guided mode, which limits the length enhancement, is mitigated in a silver-coated linearly chirped periodically poled lithium niobate planar waveguide via slowly phase-matched OPA. Obtained results indicate an ultralong propagation length for a SPP mode of about 4 cm when a 135 MW/cm pump intensity is launched. The acceptance bandwidth of the amplified SPP shows its dependency on the pump intensity; for a pump intensity range between 70 and 135 MW/cm, the acceptance bandwidth is still ultrawide, varying from 28 to 18 nm, respectively.

  10. Attenuation of propagating spin wave induced by layered nanostructures

    NASA Astrophysics Data System (ADS)

    Sekiguchi, K.; Vader, T. N.; Yamada, K.; Fukami, S.; Ishiwata, N.; Seo, S. M.; Lee, S. W.; Lee, K. J.; Ono, T.

    2012-03-01

    Spin wave attenuation in the layered [FeNi/Pt]6/FeNi thin films was investigated by the time-domain electrical measurement. The spin-wave waveform was detected with an asymmetric coplanar strip transmission line, as an induced voltage flowing into a fast oscilloscope. We report that the amplitude of a spin-wave packet was systematically changed by controlling the thickness of a platinum layer, up to a maximum change of 50%. The virtues of spin wave, ultrafast propagation velocity and non-reciprocal emission, are preserved in this manner. This means that the Pt layer can manipulate an arbitral power-level of spin-wave input signal (reliable attenuator).

  11. Nonlinear propagation of stress waves during high speed cutting

    NASA Astrophysics Data System (ADS)

    Jiang, Yifei; Zhang, Jun; He, Yong; Liu, Hongguang; Zhao, Wanhua

    2016-11-01

    Stress waves induced by high speed cutting (HSC) were demonstrated visually, and the dependence of their nonlinear propagation characteristics on cutting speed was studied. The time-resolved photoelasticity imaging technique in the bright-field mode was used to observe stress waves in the workpiece, and the obtained photoelastic images were evaluated semi-quantitatively. The experimental results were quantitatively reproduced via the lattice model, which helped explain our observations by analyzing the superposition of stress waves. According to the further simulation, we find that as the cutting speed increases, the stress intensity of the workpiece near the cutting tool is not in a linear enhancement process, with strong distortion of stress field under the superposition of different stress wave components. These help us have a deep understanding about the HSC mechanism under stress waves' effects.

  12. LF radio wave propagation at equatorial regions

    NASA Astrophysics Data System (ADS)

    Boudjada, Mohammed Y.; Sawas, Sami; Galopeau, Patrick H. M.; Eichelberger, Hans; Schwingenschuh, Konrad

    2016-04-01

    We analyse night-side electric field observations recorded by the ICE experiment onboard the DEMETER micro-satellite. We show the presence of multiple spaced frequency bands between 30 kHz and 500 kHz, and sometimes in the range 3 MHz - 3.5 MHz, the upper frequency of the instrument. The frequency bandwidth is found to be less than 5 kHz and the time duration about several minutes. The frequency bands are recorded close to the equatorial plane, when the satellite latitudes extend between -05° and +05°. Particular enhancements occur at two geographical longitudes: 130°E and 160°W. Those LF radio waves may be associated to density irregularities in the equatorial region. These irregularities are occurring along the ray path between the emission source region and the satellite. We discuss in this study the locations where such frequency bands are generated, and we show that the observed spectral features may be comparable to the kilometric continuum radiation which is considered as a non-thermal radio emission.

  13. Conversion of evanescent Lamb waves into propagating waves via a narrow aperture edge.

    PubMed

    Yan, Xiang; Yuan, Fuh-Gwo

    2015-06-01

    This paper presents a quantitative study of conversion of evanescent Lamb waves into propagating in isotropic plates. The conversion is substantiated by prescribing time-harmonic Lamb displacements/tractions through a narrow aperture at an edge of a semi-infinite plate. Complex-valued dispersion and group velocity curves are employed to characterize the conversion process. The amplitude coefficient of the propagating Lamb modes converted from evanescent is quantified based on the complex reciprocity theorem via a finite element analysis. The power flow generated into the plate can be separated into radiative and reactive parts made on the basis of propagating and evanescent Lamb waves, where propagating Lamb waves are theoretically proved to radiate pure real power flow, and evanescent Lamb waves carry reactive pure imaginary power flow. The propagating power conversion efficiency is then defined to quantitatively describe the conversion. The conversion efficiency is strongly frequency dependent and can be significant. With the converted propagating waves from evanescent, sensors at far-field can recapture some localized damage information that is generally possessed in evanescent waves and may have potential application in structural health monitoring.

  14. Generation of planar blast waves using carbon nanotubes-poly-dimethylsiloxane optoacoustic transducer

    NASA Astrophysics Data System (ADS)

    Moon, C.; Fan, X.; Ha, K.; Kim, D.

    2017-01-01

    We have generated planar blast waves over the large area using carbon nanotubes(CNT)-poly-dimethylsiloxane(PDMS) optoacoustic transducer. Pulse laser is absorbed by CNT and converted to heat, and the heat is transferred to PDMS inducing its thermal expansion and blast wave generation. To theoretically describe the planar blast wave generation, we build one-dimensional simulation model and find analytical solutions for temperature and pressure distributions. The analytical solution validated by the experimental data sheds light on how to improve the performance of the new transducer. Resonance of acoustic waves inside the transducer is also discussed. The new optoacoustic transducer optimized based on the fundamental understandings will be useful in generating high quality blast waves for research and industrial applications.

  15. Generation and propagation of nonlinear internal waves in Massachusetts Bay

    USGS Publications Warehouse

    Scotti, A.; Beardsley, R.C.; Butman, B.

    2007-01-01

    During the summer, nonlinear internal waves (NLIWs) are commonly observed propagating in Massachusetts Bay. The topography of the area is unique in the sense that the generation area (over Stellwagen Bank) is only 25 km away from the shoaling area, and thus it represents an excellent natural laboratory to study the life cycle of NLIWs. To assist in the interpretation of the data collected during the 1998 Massachusetts Bay Internal Wave Experiment (MBIWE98), a fully nonlinear and nonhydrostatic model covering the generation/shoaling region was developed, to investigate the response of the system to the range of background and driving conditions observed. Simplified models were also used to elucidate the role of nonlinearity and dispersion in shaping the NLIW field. This paper concentrates on the generation process and the subsequent evolution in the basin. The model was found to reproduce well the range of propagation characteristics observed (arrival time, propagation speed, amplitude), and provided a coherent framework to interpret the observations. Comparison with a fully nonlinear hydrostatic model shows that during the generation and initial evolution of the waves as they move away from Stellwagen Bank, dispersive effects play a negligible role. Thus the problem can be well understood considering the geometry of the characteristics along which the Riemann invariants of the hydrostatic problem propagate. Dispersion plays a role only during the evolution of the undular bore in the middle of Stellwagen Basin. The consequences for modeling NLIWs within hydrostatic models are briefly discussed at the end.

  16. Mechanical constraint converts planar waves into helices on tunicate and sea urchin sperm flagella.

    PubMed

    Ishijima, Sumio

    2012-01-01

    The change in the flagellar waves of spermatozoa from a tunicate and sea urchins was examined using high-speed video microscopy to clarify the regulation of localized sliding between doublet microtubules in the axoneme. When the tunicate Ciona spermatozoa attached to a coverslip surface by their heads in seawater or they moved in seawater with increased viscosity, the planar waves of the sperm flagella were converted into left-handed helical waves. On the other hand, conversion of the planar waves into helical waves in the sea urchin Hemicentrotus spermatozoa was not seen in seawater with an increased viscosity as well as in ordinary seawater. However, the sea urchin Clypeaster spermatozoa showed the conversion, albeit infrequently, when they thrust their heads into seawater with an increased viscosity. The chirality of the helical waves of the Clypeaster spermatozoa was right-handed. When Ciona spermatozoa swam freely near a glass surface, they moved in relatively large circular paths (yawing motion). There was no difference in the proportion of spermatozoa yawing in either a clockwise or counterclockwise direction when viewed from above, which was also different from that of the sea urchin spermatozoa. These observations suggest that the planar waves generally observed on the sperm flagella are mechanically regulated, although their stability must depend on the Ca(2+) concentration in the cell. Furthermore, the chirality of the helical waves may be determined by the intracellular Ca(2+) concentration and changed by transmitting the localized active sliding between the doublet microtubules around the axoneme in an alternative direction.

  17. Efficient way to convert propagating waves into guided waves via gradient wire structures.

    PubMed

    Chu, Hong Chen; Luo, Jie; Lai, Yun

    2016-08-01

    We propose a method for the design of gradient wire structures that are capable of converting propagating waves into guided waves along the wire. The conversion process is achieved by imposing an additional wave vector to the scattered waves via the gradient wire structure, such that the wave vector of scattered waves is beyond the wave number in the background medium. Thus, the scattered waves turn into evanescent waves. We demonstrate that two types of gradient wire structures, with either a gradient permittivity and a fixed radius, or a gradient radius and a fixed permittivity, can both be designed to realize such a wave conversion effect. The principle demonstrated in our work has potential applications in various areas including nanophotonics, silicone photonics, and plasmonics.

  18. Impact of coronary bifurcation morphology on wave propagation

    PubMed Central

    Rivolo, Simone; Hadjilucas, Lucas; Sinclair, Matthew; van Horssen, Pepijn; van den Wijngaard, Jeroen; Wesolowski, Roman; Chiribiri, Amedeo; Smith, Nicolas P.

    2016-01-01

    The branching pattern of the coronary vasculature is a key determinant of its function and plays a crucial role in shaping the pressure and velocity wave forms measured for clinical diagnosis. However, although multiple scaling laws have been proposed to characterize the branching pattern, the implications they have on wave propagation remain unassessed to date. To bridge this gap, we have developed a new theoretical framework by combining the mathematical formulation of scaling laws with the wave propagation theory in the pulsatile flow regime. This framework was then validated in multiple species using high-resolution cryomicrotome images of porcine, canine, and human coronary networks. Results demonstrate that the forward well-matchedness (no reflection for pressure/flow waves traveling from the coronary stem toward the microcirculation) is a salient feature in the coronary vasculature, and this result remains robust under many scenarios of the underlying pulse wave speed distribution assumed in the network. This result also implies a significant damping of the backward traveling waves, especially for smaller vessels (radius, <0.3 mm). Furthermore, the theoretical prediction of increasing area ratios (ratio between the area of the mother and daughter vessels) in more symmetric bifurcations found in the distal circulation was confirmed by experimental measurements. No differences were observed by clustering the vessel segments in terms of transmurality (from epicardium to endocardium) or perfusion territories (left anterior descending, left circumflex, and right coronary artery). PMID:27402665

  19. Ultrasonic Surface Wave Propagation and Interaction with Surface Defects

    NASA Astrophysics Data System (ADS)

    Fan, Y.; Dixon, S.; Edwards, R. S.; Jian, X.

    2007-03-01

    Electromagnetic acoustic transducers (EMATs) are non-contact ultrasonic transducers capable of generating wideband surface acoustic waves on metallic samples. We describe some lab based ultrasonic measurements using EMATs to generate wideband, low frequency (approximately 50-500kHz) ultrasonic surface waves on a number of samples including aluminum billets and sections of rail track that contain simulated defects. A stabilized Michelson interferometer has been used to measure accurately the absolute out-of-plane displacement of the ultrasonic waves generated on the sample, which propagate along the sample to interact with a simulated surface breaking defect. Transient finite element analysis has been used to model the ultrasonic wave propagation on the sample and the interaction of these waves with surface breaking defects. These simulations compare very favorably with the experimental results obtained using the Michelson interferometer to measure the out-of-plane displacement of the surface waves. We describe different approaches that can be used to determine the depth and presence of the crack. The non-contact nature of EMATs and the pitch-catch test geometry that we propose to use for testing make them especially suitable for online detection and depth gauging of surface breaking cracks at high inspection speeds.

  20. Dynamics and Predictability of Deep Propagating Atmospheric Gravity Waves

    NASA Astrophysics Data System (ADS)

    Doyle, J.; Fritts, D. C.; Smith, R.; Eckermann, S. D.

    2012-12-01

    An overview will be provided of the first field campaign that attempts to follow deeply propagating gravity waves (GWs) from their tropospheric sources to their mesospheric breakdown. The DEEP propagating gravity WAVE experiment over New Zealand (DEEPWAVE-NZ) is a comprehensive, airborne and ground-based measurement and modeling program focused on providing a new understanding of GW dynamics and impacts from the troposphere through the mesosphere and lower thermosphere (MLT). This program will employ the new NSF/NCAR GV (NGV) research aircraft from a base in New Zealand in a 6-week field measurement campaign in June-July 2014. The NGV will be equipped with new lidar and airglow instruments for the DEEPWAVE measurement program, providing temperatures and vertical winds spanning altitudes from immediately above the NGV flight altitude (~13 km) to ~100 km. The region near New Zealand is chosen since all the relevant GW sources occur strongly here, and upper-level winds in austral winter permit GWs to propagate to very high altitudes. Given large-amplitude GWs that propagate routinely into the MLT, the New Zealand region offers an ideal natural laboratory for studying these important GW dynamics and effects impacting weather and climate over a much deeper atmospheric layer than previous campaigns have attempted (0-100 km altitude). The logistics of making measurements in the vicinity of New Zealand are potentially easier than from the Andes and Drake Passage region. A suite of GW-focused modeling and predictability tools will be used to guide NGV flight planning to GW events of greatest scientific significance. These models will also drive scientific interpretation of the GW measurements, together providing answers to the key science questions posed by DEEPWAVE about GW dynamics, morphology, predictability and impacts from 0-100 km. Preliminary results will be presented from high-resolution and adjoint models applied over areas featuring deep wave propagation. The high

  1. RESONANTLY DAMPED PROPAGATING KINK WAVES IN LONGITUDINALLY STRATIFIED SOLAR WAVEGUIDES

    SciTech Connect

    Soler, R.; Verth, G.; Goossens, M.; Terradas, J.

    2011-07-20

    It has been shown that resonant absorption is a robust physical mechanism for explaining the observed damping of magnetohydrodynamic kink waves in the solar atmosphere due to naturally occurring plasma inhomogeneity in the direction transverse to the direction of the magnetic field. Theoretical studies of this damping mechanism were greatly inspired by the first observations of post-flare standing kink modes in coronal loops using the Transition Region and Coronal Explorer. More recently, these studies have been extended to explain the attenuation of propagating coronal kink waves observed by the Coronal Multi-Channel Polarimeter. In the present study, for the first time we investigate the properties of propagating kink waves in solar waveguides including the effects of both longitudinal and transverse plasma inhomogeneity. Importantly, it is found that the wavelength is only dependent on the longitudinal stratification and the amplitude is simply a product of the two effects. In light of these results the advancement of solar atmospheric magnetoseismology by exploiting high spatial/temporal resolution observations of propagating kink waves in magnetic waveguides to determine the length scales of the plasma inhomogeneity along and transverse to the direction of the magnetic field is discussed.

  2. SPATIAL DAMPING OF PROPAGATING KINK WAVES IN PROMINENCE THREADS

    SciTech Connect

    Soler, R.; Oliver, R.; Ballester, J. L.

    2011-01-10

    Transverse oscillations and propagating waves are frequently observed in threads of solar prominences/filaments and have been interpreted as kink magnetohydrodynamic (MHD) modes. We investigate the spatial damping of propagating kink MHD waves in transversely nonuniform and partially ionized prominence threads. Resonant absorption and ion-neutral collisions (Cowling's diffusion) are the damping mechanisms taken into account. The dispersion relation of resonant kink waves in a partially ionized magnetic flux tube is numerically solved by considering prominence conditions. Analytical expressions of the wavelength and damping length as functions of the kink mode frequency are obtained in the thin tube and thin boundary approximations. For typically reported periods of thread oscillations, resonant absorption is an efficient mechanism for the kink mode spatial damping, while ion-neutral collisions have a minor role. Cowling's diffusion dominates both the propagation and damping for periods much shorter than those observed. Resonant absorption may explain the observed spatial damping of kink waves in prominence threads. The transverse inhomogeneity length scale of the threads can be estimated by comparing the observed wavelengths and damping lengths with the theoretically predicted values. However, the ignorance of the form of the density profile in the transversely nonuniform layer introduces inaccuracies in the determination of the inhomogeneity length scale.

  3. Effects of dissipation on propagation of surface electromagnetic and acoustic waves

    NASA Astrophysics Data System (ADS)

    Nagaraj, Nagaraj

    With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. With this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. The first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an effort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. A dielectric-metal-dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metal-dielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectric-metal-dielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. An equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a Kronig-Penny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. In the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the metal plates, I derive a dispersion equation that gives

  4. The impact of positrons beam on the propagation of super freak waves in electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Ali Shan, S.; El-Tantawy, S. A.

    2016-07-01

    In this work, we examine the nonlinear propagation of planar ion-acoustic freak waves in an unmagnetized plasma consisting of cold positive ions and superthermal electrons subjected to cold positrons beam. For this purpose, the reductive perturbation method is used to derive a nonlinear Schrödinger equation (NLSE) for the evolution of electrostatic potential wave. We determine the domain of the plasma parameters where the rogue waves exist. The effect of the positron beam on the modulational instability of the ion-acoustic rogue waves is discussed. It is found that the region of the modulational stability is enhanced with the increase of positron beam speed and positron population. Second as positrons beam increases the nonlinearities of the plasma system, large amplitude ion acoustic rogue waves are pointed out. The present results will be helpful in providing a good fit between the theoretical analysis and real applications in future laboratory plasma experiments.

  5. Propagation of VLF waves through the equatorial anomaly

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Cairo, L.

    1980-12-01

    The propagation characteristics of artificial VLF waves (NBA, 24.0 kHz) through the equatorial ionosphere have been studied by means of data obtained onboard the FR-1 satellite at 750 km altitude over Latin America. Large latitudinal variations of the vertical component of the wave normal generally appear in the evening at geomagnetic latitudes of 10 to 15 deg, and they also appear on most of the passes examined at night at latitudes of 5 to 10 deg. Ray and wave normal directions of the VLF waves are computed in various models of field-aligned equatorial anomaly. The latitudinal variations in the evening are due to large negative latitudinal gradients of electron density associated with the equatorial anomaly, and the latitudinal variations at night are due to relatively small density gradients.

  6. Asymptotic analysis of numerical wave propagation in finite difference equations

    NASA Technical Reports Server (NTRS)

    Giles, M.; Thompkins, W. T., Jr.

    1983-01-01

    An asymptotic technique is developed for analyzing the propagation and dissipation of wave-like solutions to finite difference equations. It is shown that for each fixed complex frequency there are usually several wave solutions with different wavenumbers and the slowly varying amplitude of each satisfies an asymptotic amplitude equation which includes the effects of smoothly varying coefficients in the finite difference equations. The local group velocity appears in this equation as the velocity of convection of the amplitude. Asymptotic boundary conditions coupling the amplitudes of the different wave solutions are also derived. A wavepacket theory is developed which predicts the motion, and interaction at boundaries, of wavepackets, wave-like disturbances of finite length. Comparison with numerical experiments demonstrates the success and limitations of the theory. Finally an asymptotic global stability analysis is developed.

  7. Wave speed propagation measurements on highly attenuative heated materials

    SciTech Connect

    Moore, David G.; Ober, Curtis C.; Rodacy, Phil J.; Nelson, Ciji L.

    2015-09-19

    Ultrasonic wave propagation decreases as a material is heated. Two factors that can characterize material properties are changes in wave speed and energy loss from interactions within the media. Relatively small variations in velocity and attenuation can detect significant differences in microstructures. This paper discusses an overview of experimental techniques that document the changes within a highly attenuative material as it is either being heated or cooled from 25°C to 90°C. The experimental set-up utilizes ultrasonic probes in a through-transmission configuration. The waveforms are recorded and analyzed during thermal experiments. To complement the ultrasonic data, a Discontinuous-Galerkin Model (DGM) was also created which uses unstructured meshes and documents how waves travel in these anisotropic media. This numerical method solves particle motion travel using partial differential equations and outputs a wave trace per unit time. As a result, both experimental and analytical data are compared and presented.

  8. Surface wave propagation in thin silver films under residual stress

    NASA Astrophysics Data System (ADS)

    Njeh, Anuar; Wieder, Thomas; Schneider, D.; Fuess, Hartmut; Ben Ghozlen, M. H.

    Investigations using surface acoustic waves provide information on the elastic properties of thin films. Residual stresses change the phase velocity of the surface waves. We have calculated phase velocity and dispersion of surface waves in thin silver films with a strong [111]-fibre texture. A non-linear description of surface waves propagating along the [110]-direction of the substrate has been developed on the basis of an acoustoelastic theory, taking into account residual stresses. The relative change delta_v/v of the velocity v was found to be lin-ear for large excitation frequencies. The dispersion curves were measured using a photoa-coustic method. For sputtered polycrystalline thin silver films we found good agreement be-tween the experimental and calculated dispersion curves for frequencies up to 225 MHz.

  9. Elastic wave propagation through a material with voids

    NASA Astrophysics Data System (ADS)

    Wright, Thomas W.

    1998-10-01

    An exact mathematical analogy exists between plane wave propagation through a material with voids and axial wave propagation along a circular cylindrical rod with radial shear and inertia. In both cases the internal energy can be regarded as a function of a displacement gradient, an internal variable, and the gradient of the internal variable. In the rod the internal variable represents radial strain, and in the material with voids it is related to changes in void volume fraction. In both cases kinetic energy is associated not only with particle translation, but also with the internal variable. In the rod this microkinetic energy represents radial inertia ; in the material with voids it represents dilitational inertia around the voids. Thus, the basis for the analogy is that in both cases there are two kinematic degrees of freedom, the Lagrangians are identical in form, and therefore, the Euler-Lagrange equations are also identical in form. Of course, the constitutive details and the internal length scales for the two cases are very different, but insight into the behavior of rods can be transferred directly to interpreting the effects of wave propagation in a material with voids. The main result is that just as impact on the end of a rod produces a pulse that first travels with the longitudinal wave speed and then transfers the bulk of its energy into a dispersive wave that travels with the bar speed (calculated using Youngs modulus), so impact on the material with voids produces a pulse that also begins with the longitudinal speed but then transfers to a slower dispersive wave whose speed is determined by an effective longitudinal modulus. The rate of transfer and the strength of the dispersive effect depend on the details in the two cases.

  10. Hilbert space inverse wave imaging in a planar multilayer environment.

    PubMed

    Lehman, Sean K

    2005-05-01

    Most diffraction tomography (DT) algorithms use a homogeneous Green function (GF) regardless of the medium being imaged. This choice is usually motivated by practical considerations: analytic inversions in standard geometries (Cartesian, spherical, etc.) are significantly simplified by the use of a homogeneous GF, estimating a nonhomogeneous GF can be very difficult, as can incorporating a nonhomogeneous GF into standard DT algorithms. Devaney has circumvented these issues by developing a purely numerical DT inversion algorithm [A. J. Devaney and M. Dennison, Inverse Probl. 19, 855-870 (2003)] that is independent of measurement system geometry, number of frequencies used in the reconstruction, and GF. A planar multilayer GF has been developed for use in Devaney's "Hilbert space" algorithm and used in a proof-of-principle nondestructive evaluation (NDE) experiment to image noninvasively a flaw in an aluminum/copper planar multilayer medium using data collected from an ultrasonic measurement system. The data were collected in a multistatic method with no beamforming: all focusing through the multilayer was performed mathematically "after-the-fact," that is, after the data were collected.

  11. Modeling anomalous surface - wave propagation across the Southern Caspian basin

    SciTech Connect

    Priestly, K.F.; Patton, H.J.; Schultz, C.A.

    1998-01-09

    The crust of the south Caspian basin consists of 15-25 km of low velocity, highly attenuating sediment overlying high velocity crystalline crust. The Moho depth beneath the basin is about 30 km as compared to about 50 km in the surrounding region. Preliminary modeling of the phase velocity curves shows that this thick sediments of the south Caspian basin are also under-lain by a 30-35 km thick crystalline crust and not by typical oceanic crust. This analysis also suggest that if the effect of the over-pressuring of the sediments is to reduce Poissons` ratio, the over-pressured sediments observed to approximately 5 km do not persist to great depths. It has been shown since 1960`s that the south Caspian basin blocks the regional phase Lg. Intermediate frequency (0.02-0.04 Hz) fundamental mode Raleigh waves propagating across the basin are also severely attenuated, but the low frequency surface waves are largely unaffected. This attenuation is observed along the both east-to-west and west-to-east great circle paths across the basin, and therefore it cannot be related to a seismograph site effect. We have modeled the response of surface waves in an idealized rendition of the south Caspian basin model using a hybrid normal mode / 2-D finite difference approach. To gain insight into the features of the basin which cause the anomalous surface wave propagation, we have varied parameters of the basin model and computed synthetic record sections to compare with the observed seismograms. We varied the amount of mantel up-warp, the shape of the boundaries, the thickness and shear wave Q of the sediments and mantle, and the depth of the water layer. Of these parameters, the intermediate frequency surface waves are most severely affected by the sediments thickness and shear wave attenuation. fundamental mode Raleigh wave phase velocities measure for paths crossing the basin are extremely low.

  12. Magnetic resonance imaging of shear wave propagation in excised tissue.

    PubMed

    Bishop, J; Poole, G; Leitch, M; Plewes, D B

    1998-01-01

    The propagation of shear waves in ex vivo tissue samples, agar/gel phantoms, and human volunteers was investigated. A moving coil apparatus was constructed to generate low acoustic frequency shear perturbations of 50 to 400 Hz. Oscillating gradients phase-locked with the shear stimulus were used to generate a series of phase contrast images of the shear waves at different time-points throughout the wave cycle. Quantitative measurements of wave velocity and attenuation were obtained to evaluate the effects of temperature, frequency, and tissue anisotropy. Results of these experiments demonstrate significant variation in shear wave behavior with tissue type, whereas frequency and anisotropic behavior was mixed. Temperature-dependent behavior related mainly to the presence of fat. Propagation velocities ranged from 1 to 5 m/sec, and attenuation coefficients of from 1 to 3 nepers/unit wavelength, depending on tissue type. These results confirm the potential of elastic imaging attributable to the intrinsic variability of elastic properties observed in normal tissue, although some difficulty may be experienced in clinical implementation because of viscous attenuation in fat.

  13. Wave Propagation in Discontinuous Media by the Scattering Matrix Method

    NASA Astrophysics Data System (ADS)

    Perino, A.; Orta, R.; Barla, G.

    2012-09-01

    Propagation of elastic waves in discontinuous media is studied in this paper by the scattering matrix method (SMM). An electromagnetic transmission line analogy is also used to set up the mathematical model. The SMM operates in the frequency domain and allows for all wave polarizations (P, SV and SH). Rock masses are examples of discontinuous media in which the discontinuities (fractures or joints) influence wave propagation. Both elastic and viscoelastic joints are considered and the latter are described by Kelvin-Voigt, Maxwell and Burgers models. Rock joints with Coulomb slip behavior are also analyzed, by applying the averaging principle of Caughy (J Appl Mech 27:640-643, 1960). The evaluation of the effects of periodic discontinuities in a homogeneous medium is presented by introducing the concept of Bloch waves. The dispersion curves of these waves are useful to explain the existence of frequency bands of strong attenuation, also in the case of lossless (perfectly elastic) structures. Simple expressions of transmission and reflection coefficients are obtained. Finally, the SMM results are compared with those computed via the distinct element method (DEM). The comparisons are performed on a medium with joints with Coulomb slip behavior and the agreement is satisfactory, although the SMM must be applied in conjunction with the equivalent linearization technique. Even if the DEM is much more general, the SMM in these simple cases is extremely faster and provides a higher physical insight.

  14. Wave propagation in a moving cold magnetized plasma

    NASA Astrophysics Data System (ADS)

    Hebenstreit, H.

    1980-03-01

    Polarization relations and dispersion equations are derived for media that are electrically anisotropic in the comoving frame. Three-dimensional calculations for media at rest recover the known dispersion equations, i.e., Astrom's dispersion equation for magnetized cold plasmas and Fresnel's wave normal equation for uniaxial crystals. An analogous four-dimensional calculation yields the generalization to moving media. The dispersion equations so obtained for moving gyrotropic media are then discussed qualitatively for various special media and special directions of wave propagation. Finally, the polarization relations are specialized to media gyrotropic in the comoving frame.

  15. A numerical formulation for nonlinear ultrasonic waves propagation in fluids.

    PubMed

    Vanhille, C; Campos-Pozuelo, C

    2004-08-01

    A finite-difference algorithm is developed for analysing the nonlinear propagation of pulsed and harmonic ultrasonic waves in fluid media. The time domain model allows simulations from linear to strongly nonlinear plane waves including weak shock. Effects of absorption are included. All the harmonic components are obtained from only one solving process. The evolution of any original signal can be analysed. The nonlinear solution is obtained by the implicit scheme via a fast linear solver. The numerical model is validated by comparison to analytical data. Numerical experiments are presented and commented. The effect of the initial pulse shape on the evolution of the pressure waveform is especially analysed.

  16. Wave propagation in a quasi-chemical equilibrium plasma

    NASA Technical Reports Server (NTRS)

    Fang, T.-M.; Baum, H. R.

    1975-01-01

    Wave propagation in a quasi-chemical equilibrium plasma is studied. The plasma is infinite and without external fields. The chemical reactions are assumed to result from the ionization and recombination processes. When the gas is near equilibrium, the dominant role describing the evolution of a reacting plasma is played by the global conservation equations. These equations are first derived and then used to study the small amplitude wave motion for a near-equilibrium situation. Nontrivial damping effects have been obtained by including the conduction current terms.

  17. Propagation of waves in a medium with high radiation pressure

    NASA Technical Reports Server (NTRS)

    Bisnovatyy-Kogan, G. S.; Blinnikov, S. I.

    1979-01-01

    The propagation and mutual transformation of acoustic and thermal waves are investigated in media with a high radiative pressure. The equations of hydrodynamics for matter and the radiative transfer equations in a moving medium in the Eddington approximation are used in the investigation. Model problems of waves in a homogeneous medium with an abrupt jump in opacity and in a medium of variable opacity are presented. The characteristic and the times of variability are discussed. Amplitude for the brightness fluctuations for very massive stars are discussed.

  18. Electrostatic wave propagation and trapping near the magnetic equator

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1985-01-01

    Results of a two-dimensional ray tracing computer code, based on Snell's law, for electrostatic wave propagation in a dipole magnetic field are discussed. A survey of possible ray paths varying a wide range of parameters is conducted for low-harmonic Bernstein modes in a high-density plasma. It is shown that the ray paths exhibit similarity with radial distance and that there exists the possibility of two classes of wave statistics of the equator: a broad emission region extending to about + or - 4 deg and a class of events restricted to the smaller region of 1-2 deg about the magnetic equator. The regulating parameter between these two types of events is the transition energy from the isotropic background electrons to the unstable distribution of superthermals. Ray paths for propagation in the magnetic equatorial plane are considered and an explanation is given for ray focusing in the equatorial plane based on electron gyroradius considerations.

  19. Wave propagation in non-Gaussian random media

    NASA Astrophysics Data System (ADS)

    Franco, Mariano; Calzetta, Esteban

    2015-01-01

    We develop a compact perturbative series for acoustic wave propagation in a medium with a non-Gaussian stochastic speed of sound. We use Martin-Siggia and Rose auxiliary field techniques to render the classical wave propagation problem into a ‘quantum’ field theory one, and then frame this problem within the so-called Schwinger-Keldysh of closed time-path (CTP) formalism. Variation of the so-called two-particle irreducible (2PI) effective action (EA), whose arguments are both the mean fields and the irreducible two point correlations, yields the Schwinger-Dyson and the Bethe-Salpeter equations. We work out the loop expansion of the 2PI CTP EA and show that, in the paradigmatic problem of overlapping spherical intrusions in an otherwise homogeneous medium, non-Gaussian corrections might be much larger than Gaussian ones at the same order of loops.

  20. Fracture Phenomena in Foams: From Film Instability to Wave Propagation

    NASA Astrophysics Data System (ADS)

    Hilgenfeldt, Sascha; Stewart, Peter

    2016-11-01

    Injection of a gas into a gas/liquid foam is known to give rise to instability phenomena on a variety of time and length scales. Macroscopically, one observes a propagating gas-filled structure that can display properties of liquid finger propagation as well as of fracture in solids. The observation of both large-scale, finger-like cracks (without film breakage) and brittle cleavage phenomena (consisting of successive film ruptures) is explained through careful modeling of phenomena ranging from thin-film instabilities to friction between bubbles and confining plates. Whereas we use a network approach with full representation of the foam microstructure to model the cracks, we also derive a continuum limit description in order to investigate possible modes of wave propagation and their feedback on the fracture process.

  1. Computational study of nonlinear plasma waves: 1: Simulation model and monochromatic wave propagation

    NASA Technical Reports Server (NTRS)

    Matda, Y.; Crawford, F. W.

    1974-01-01

    An economical low noise plasma simulation model is applied to a series of problems associated with electrostatic wave propagation in a one-dimensional, collisionless, Maxwellian plasma, in the absence of magnetic field. The model is described and tested, first in the absence of an applied signal, and then with a small amplitude perturbation, to establish the low noise features and to verify the theoretical linear dispersion relation at wave energy levels as low as 0.000,001 of the plasma thermal energy. The method is then used to study propagation of an essentially monochromatic plane wave. Results on amplitude oscillation and nonlinear frequency shift are compared with available theories. The additional phenomena of sideband instability and satellite growth, stimulated by large amplitude wave propagation and the resulting particle trapping, are described.

  2. The effect of microscale random Alfven waves on the propagation of large-scale Alfven waves

    NASA Astrophysics Data System (ADS)

    Namikawa, T.; Hamabata, H.

    1983-04-01

    The ponderomotive force generated by random Alfven waves in a collisionless plasma is evaluated taking into account mean magnetic and velocity shear and is expressed as a series involving spatial derivatives of mean magnetic and velocity fields whose coefficients are associated with the helicity spectrum function of random velocity field. The effect of microscale random Alfven waves through ponderomotive and mean electromotive forces generated by them on the propagation of large-scale Alfven waves is also investigated.

  3. Simplified theory of large-amplitude wave propagation

    NASA Technical Reports Server (NTRS)

    Kim, H.

    1976-01-01

    An orbit perturbation procedure was applied to the description of monochromatic, large-amplitude, electrostatic plasma wave propagation. In the lowest order approximation, untrapped electrons were assumed to follow constant-velocity orbits and trapped electrons were assumed to execute simple harmonic motion. The deviations of these orbits from the actual orbits were regarded as perturbations. The nonlinear damping rate and frequency shift were then obtained in terms of simple functions. The results are in good agreement with previous less approximate analyses.

  4. Monograph on propagation of sound waves in curved ducts

    NASA Technical Reports Server (NTRS)

    Rostafinski, Wojciech

    1991-01-01

    After reviewing and evaluating the existing material on sound propagation in curved ducts without flow, it seems strange that, except for Lord Rayleigh in 1878, no book on acoustics has treated the case of wave motion in bends. This monograph reviews the available analytical and experimental material, nearly 30 papers published on this subject so far, and concisely summarizes what has been learned about the motion of sound in hard-wall and acoustically lined cylindrical bends.

  5. Wave propagation in the chromosphere and transition region

    NASA Technical Reports Server (NTRS)

    Steffens, S.; Deubner, F.-L.; Fleck, B.; Wilhelm, K.; Harrison, R.; Gurman, J.

    1997-01-01

    The results from a joint observing program involving the solar ultraviolet measurement of emitted radiation (SUMER), the coronal diagnostic spectrometer (CDS) and the extreme-ultraviolet imaging telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO) are presented. These operations were coordinated with ground-based observations at the vacuum tower telescope at Izana (Tenerife). The purpose was to characterize the wave propagation properties in the solar atmosphere, from the photosphere through the chromosphere into the transition region.

  6. Spin Wave Propagation in Non-Uniform Magnetic Fields

    DTIC Science & Technology

    2006-11-01

    set-up. The yttrium iron garnet ( YIG ) film strip is magnetized to saturation by a z − dependent static field ( )H z . The microstrip transducer is...time- and space-resolved measurements of spin wave pulse propagation properties in a magnetic film strip magnetized to saturation with non-uniform...EXPERIMENT Figure 1 shows a schematic of the experimental set- up. The magnetic medium was a yttrium iron garnet ( YIG ) film strip cut from a

  7. Acoustic Bloch Wave Propagation in a Periodic Waveguide

    DTIC Science & Technology

    1991-07-24

    electrical conductivity. In the quantum theory, the electron is represented by De Broglie/ Schr ~ dinger matter waves which propagate in an electrical conductor...waveguide loaded with a periodic array of rigid spheres. They based their approach on the Webster horn equation and compared the results of a strained...governing equations , we simply use the dissi- pative equations in the limit as the heat conductivity and viscosity approach zero. In such a limit the

  8. Horizontal propagation of Gravity Waves in the ionosphere

    NASA Astrophysics Data System (ADS)

    Chum, J.; Base, J.; Hruska, F.; Buresova, D.; McKinnell, L. A.; Athieno, R.

    2010-12-01

    Using a multi-point Continuous Doppler sounding system we investigate propagation directions and velocities of Gravity Waves (GWs) in the ionosphere at altitudes from ~150 km to ~250 km. The velocities and directions are computed from the time delays between the observations of corresponding GWs at different reflection points that correspond to various sounding paths. We focused on the GWs that produce an S-shaped trace in Doppler shift spectrograms since it is know that these patterns are formed if the disturbances (waves) mainly propagate in the horizontal plane. The S-shaped signatures also make it possible to estimate the errors of measurements. The system that we used was developed in the Institute of Atmospheric Physics, Czech Republic and has been operated in the western part of the Czech Republic. A statistical study based on the analysis of about 100 events during the last solar minimum show that the analyzed GWs propagate with typical horizontal velocities from ~100 to ~200 m/s. The north-south component of GW velocities depends on the season and/or daytime. At the same time, it has an opposite sign than the north-south component of neutral winds calculated by the HWM07 model. A similar system was also installed in the South Africa, close to Cape Town at the end of May 2010. The first results of the observation of GW propagation in the ionosphere over the South Africa will also be presented.

  9. Radio Wave Propagation Handbook for Communication on and Around Mars

    NASA Technical Reports Server (NTRS)

    Ho, Christian; Golshan, Nasser; Kliore, Arvydas

    2002-01-01

    This handbook examines the effects of the Martian environment on radio wave propagation on Mars and in the space near the planet. The environmental effects include these from the Martian atmosphere, ionosphere, global dust storms, aerosols, clouds, and geomorphologic features. Relevant Martian environmental parameters were extracted from the measurements of Mars missions during the past 30 years, especially from Mars Pathfinder and Mars Global Surveyor. The results derived from measurements and analyses have been reviewed through an extensive literature search. The updated parameters have been theoretically analyzed to study their effects on radio propagation. This handbook also provides basic information about the entire telecommunications environment on and around Mars for propagation researchers, system engineers, and link analysts. Based on these original analyses, some important recommendations have been made, including the use of the Martian ionosphere as a reflector for Mars global or trans-horizon communication between future Martian colonies, reducing dust storm scattering effects, etc. These results have extended our wave propagation knowledge to a planet other than Earth; and the tables, models, and graphics included in this handbook will benefit telecommunication system engineers and scientific researchers.

  10. Lamb waves propagation in layered piezoelectric/piezomagnetic plates.

    PubMed

    Ezzin, Hamdi; Ben Amor, Morched; Ben Ghozlen, Mohamed Hédi

    2017-04-01

    A dynamic solution is presented for the propagation of harmonic waves in magneto-electro-elastic plates composed of piezoelectric BaTiO3(B) and magnetostrictive CoFe2O4(F) material. The state-vector approach is employed to derive the propagator matrix which connects the field variables at the upper interface to those at the lower interface of each layer. The ordinary differential approach is employed to determine the wave propagating characteristics in the plate by imposing the traction-free boundary condition on the top and bottom surfaces of the layered plate. The dispersion curves of the piezoelectric-piezomagnetic plate are shown for different thickness ratios. The numerical results show clearly the influence of different stacking sequences as well as thickness ratio on dispersion curves and on magneto-electromechanical coupling factor. These findings could be relevant to the analysis and design of high-performance surface acoustic wave (SAW) devices constructed from piezoelectric and piezomagnetic materials.

  11. Equivalent Continuum Modeling for Shock Wave Propagation in Jointed Media

    SciTech Connect

    Vorobiev, O; Antoun, T

    2009-12-11

    This study presents discrete and continuum simulations of shock wave propagating through jointed media. The simulations were performed using the Lagrangian hydrocode GEODYN-L with joints treated explicitly using an advanced contact algorithm. They studied both isotropic and anisotropic joint representations. For an isotropically jointed geologic medium, the results show that the properties of the joints can be combined with the properties of the intact rock to develop an equivalent continuum model suitable for analyzing wave propagation through the jointed medium. For an anisotropically jointed geologic medium, they found it difficult to develop an equivalent continuum (EC) model that matches the response derived from mesoscopic simulation. They also performed simulations of wave propagation through jointed media. Two appraoches are suggested for modeling the rock mass. In one approach, jointed are modeled explicitly in a Lagrangian framework with appropriate contact algorithms used to track motion along the interfaces. In the other approach, the effect of joints is taken into account using a constitutive model derived from mesoscopic simulations.

  12. Instability and Wave Propagation in Structured 3D Composites

    NASA Astrophysics Data System (ADS)

    Kaynia, Narges; Fang, Nicholas X.; Boyce, Mary C.

    2014-03-01

    Many structured composites found in nature possess undulating and wrinkled interfacial layers that regulate mechanical, chemical, acoustic, adhesive, thermal, electrical and optical functions of the material. This research focused on the complex instability and wrinkling pattern arising in 3D structured composites and the effect of the buckling pattern on the overall structural response. The 3D structured composites consisted of stiffer plates supported by soft matrix on both sides. Compression beyond the critical strain led to complex buckling patterns in the initially straight plates. The motivation of our work is to elaborate the formation of a system of prescribed periodic scatterers (metamaterials) due to buckling, and their effect to interfere wave propagation through the metamaterial structures. Such metamaterials made from elastomers enable large reversible deformation and, as a result, significant changes of the wave propagation properties. We developed analytical and finite element models to capture various aspects of the instability mechanism. Mechanical experiments were designed to further explore the modeling results. The ability to actively alter the 3D composite structure can enable on-demand tunability of many different functions, such as active control of wave propagation to create band-gaps and waveguides.

  13. Spin-wave propagation in ultra-thin YIG based waveguides

    NASA Astrophysics Data System (ADS)

    Collet, M.; Gladii, O.; Evelt, M.; Bessonov, V.; Soumah, L.; Bortolotti, P.; Demokritov, S. O.; Henry, Y.; Cros, V.; Bailleul, M.; Demidov, V. E.; Anane, A.

    2017-02-01

    Spin-wave propagation in microfabricated 20 nm thick, 2.5 μm wide Yttrium Iron Garnet (YIG) waveguides is studied using propagating spin-wave spectroscopy (PSWS) and phase resolved micro-focused Brillouin Light Scattering (μ-BLS) spectroscopy. We demonstrate that spin-wave propagation in 50 parallel waveguides is robust against microfabrication induced imperfections and extract spin-wave propagation parameters for the Damon-Eshbach configuration in a wide range of excitation frequencies. As expected from its low damping, YIG allows for the propagation of spin waves over long distances; the attenuation lengths is 25 μm at μ 0 H = 45 mT. Moreover, direct mapping of spin waves by μ-BLS allows us to reconstruct the spin-wave dispersion relation and to confirm the multi-mode propagation in the waveguides, glimpsed by propagating spin-wave spectroscopy.

  14. The excitation and detection of lamb waves with planar coil electromagnetic acoustic transducers.

    PubMed

    Wilcox, Paul D; Lowe, Michael J S; Cawley, Peter

    2005-12-01

    Planar coil electromagnetic acoustic transducers (EMATs) are investigated for the excitation and detection of Lamb waves in nonferromagnetic metallic wave-guides. Such EMATs are attractive for certain applications due to their omni-directional sensitivity to wave modes with predominantly in-plane surface displacement, such as the So Lamb wave mode. A model is developed that enables the modal content of the radiated Lamb wave field from a transmitting EMAT to be calculated, and the output voltage from a receiving EMAT to be predicted when a Lamb wave mode is incident on it. The predictions from this model are compared with experimental data obtained from 12 different EMATs tested on a 5-mm thick aluminum plate, and good agreement is obtained. The model then is used to analyze the different effects that contribute to the overall Lamb wave modal sensitivity of an EMAT. The relationship between coil geometry and wavelength is examined.

  15. Quasi-optical theory of relativistic surface-wave oscillators with one-dimensional and two-dimensional periodic planar structures

    SciTech Connect

    Ginzburg, N. S.; Zaslavsky, V. Yu.; Malkin, A. M.; Sergeev, A. S.

    2013-11-15

    Within the framework of a quasi-optical approach, we develop 2D and 3D self-consistent theory of relativistic surface-wave oscillators. Presenting the radiation field as a sum of two counter-propagating wavebeams coupled on a shallow corrugated surface, we describe formation of an evanescent slow wave. Dispersion characteristics of the evanescent wave following from this method are in good compliance with those found from the direct cst simulations. Considering excitation of the slow wave by a sheet electron beam, we simulate linear and nonlinear stages of interaction, which allows us to determine oscillation threshold conditions, electron efficiency, and output coupling. The transition from the model of surface-wave oscillator operating in the π-mode regime to the canonical model of relativistic backward wave oscillator is considered. We also described a modified scheme of planar relativistic surface-wave oscillators exploiting two-dimensional periodic gratings. Additional transverse propagating waves emerging on these gratings synchronize the emission from a wide sheet rectilinear electron beam allowing realization of a Cherenkov millimeter-wave oscillators with subgigawatt output power level.

  16. A Kinetic Approach to Propagation and Stability of Detonation Waves

    NASA Astrophysics Data System (ADS)

    Monaco, R.; Bianchi, M. Pandolfi; Soares, A. J.

    2008-12-01

    The problem of the steady propagation and linear stability of a detonation wave is formulated in the kinetic frame for a quaternary gas mixture in which a reversible bimolecular reaction takes place. The reactive Euler equations and related Rankine-Hugoniot conditions are deduced from the mesoscopic description of the process. The steady propagation problem is solved for a Zeldovich, von Neuman and Doering (ZND) wave, providing the detonation profiles and the wave thickness for different overdrive degrees. The one-dimensional stability of such detonation wave is then studied in terms of an initial value problem coupled with an acoustic radiation condition at the equilibrium final state. The stability equations and their initial data are deduced from the linearized reactive Euler equations and related Rankine-Hugoniot conditions through a normal mode analysis referred to the complex disturbances of the steady state variables. Some numerical simulations for an elementary reaction of the hydrogen-oxygen chain are proposed in order to describe the time and space evolution of the instabilities induced by the shock front perturbation.

  17. Low frequency piezoresonance defined dynamic control of terahertz wave propagation

    PubMed Central

    Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G.; Bhalla, Amar S.; Guo, Ruyan

    2016-01-01

    Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators. PMID:27901070

  18. Guided wave propagation in porous unidirectional carbon fiber reinforced plastic

    NASA Astrophysics Data System (ADS)

    Dobmann, Nicolas; Bach, Martin

    2017-02-01

    Networks of piezoelectric transducers mounted on aircraft structures for Acousto Ultrasonics (AU) purposes are designed to be applied during the service life of the aircraft. The approach to integrate these sensor networks already during the manufacture of carbon fiber reinforced plastic (CFRP) host structures prompts ideas to achieve an additional benefit by their application for cure monitoring, thus extending their use to the manufacturing chain. This benefit could be extended even further if guided waves generated by AU sensor networks could be used for porosity testing extensively applied for CFRP aircraft structures. In light of this, an experimental study was conducted to investigate effects of porosity on the propagation of guided waves in a basic configuration of unidirectional CFRP. Several samples were manufactured at different porosity levels by variation of the processing pressure. Wave fields were acquired using an ultrasonic scanning device. In the present work, phase velocities are chosen as best measurable and quantifiable propagation feature and the approach for the analysis of phase velocities in porosity samples is outlined. First results are presented and discussed regarding the influence of porosity on guided wave phase velocity and basic applicability for porosity testing of aircraft structures.

  19. Experiment to Study Alfven Wave Propagation in Plasma Loops

    NASA Astrophysics Data System (ADS)

    Kendall, Mark; Bellan, Paul

    2010-11-01

    Arched plasma-filled twisted magnetic flux tubes are generated in the laboratory using pulsed power techniques (J.F. Hansen, S.K.P. Tripathi, P.M. Bellan, 2004). Their structure and time evolution exhibit similarities with both solar coronal loops and spheromaks. We are now developing a method to excite propagating torsional Alfven wave modes in such plasma loops by superposing a ˜10kA, ˜100ns current pulse upon the ˜50kA, 10μs main discharge current that flows along the ˜20cm long, 2cm diameter arched flux tube. To achieve this high power 100ns pulse, a magnetic pulse compression technique based on saturable reactors is employed. A low power prototype has been successfully tested, and design and construction of a full-power device is nearing completion. The full-power device will compress an initial 2μs pulse by a factor of nearly 20; the final stage utilizes a water-filled transmission line with ultra-low inductance to attain the final timescale. This new pulse device will subsequently be used to investigate interactions between Alfven waves and the larger-scale loop evolution; one goal will be to directly image the wave using high-speed photography. Attention will be paid to wave propagation including dispersion and reflection, as well as dissipation mechanisms and possible energetic particle generation.

  20. Low frequency piezoresonance defined dynamic control of terahertz wave propagation

    NASA Astrophysics Data System (ADS)

    Dutta, Moumita; Betal, Soutik; Peralta, Xomalin G.; Bhalla, Amar S.; Guo, Ruyan

    2016-11-01

    Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated. In this article we provide an experimental demonstration of phase modulation of THz beam by operating a ferroelectric single crystal LiNbO3 film device at the piezo-resonance. The piezo-resonance, excited by an external a.c. electric field, develops a coupling between electromagnetic and lattice-wave and this coupling governs the wave propagation of the incident THz beam by modulating its phase transfer function. We report the understanding developed in this work can facilitate the design and fabrication of a family of resonance-defined highly sensitive and extremely low energy sub-millimeter wave sensors and modulators.

  1. Nonlinear Propagation of Planet-Generated Tidal Waves

    NASA Technical Reports Server (NTRS)

    Rafikov, R. R.

    2002-01-01

    The propagation and evolution of planet-generated density waves in protoplanetary disks is considered. The evolution of waves, leading to shock formation and wake dissipation, is followed in the weakly nonlinear regime. The 2001 local approach of Goodman and Rafikov is extended to include the effects of surface density and temperature variations in the disk as well as the disk cylindrical geometry and nonuniform shear. Wave damping due to shocks is demonstrated to be a nonlocal process spanning a significant fraction of the disk. Torques induced by the planet could be significant drivers of disk evolution on timescales of approx. 10(exp 6)-10(exp 7) yr, even in the absence of strong background viscosity. A global prescription for angular momentum deposition is developed that could be incorporated into the study of gap formation in a gaseous disk around the planet.

  2. Vibration response and harmonic wave propagation of ultrasonic arc drivers

    NASA Astrophysics Data System (ADS)

    Smithmaitrie, Pruittikorn; DeHaven, J. G.; Higuchi, K.; Tzou, H. S.

    2007-02-01

    A piezoelectric curvilinear arc driver designed for an ultrasonic curvilinear motor is evaluated in this study. A design of piezoelectric curvilinear arc driver is proposed and its governing equations, vibration behaviour and wave propagation are investigated. Then, analysis of forced vibration response or driving characteristics to harmonic excitations in the modal domain is conducted. Finite element modelling and analysis of the arc driver are also discussed. Analytical results of free vibration characteristics are compared favourably with the finite element results. Harmonic analyses of the three finite element models reveal changes of dynamic behaviours of three models and also imply operating frequencies with a significant travelling wave component. Parametric study of mathematical and finite element simulation results suggests that stable travelling waves can be generated to drive a rotor on the proposed curvilinear arc motor system.

  3. Determination of particle size distributions from acoustic wave propagation measurements

    SciTech Connect

    Spelt, P.D.; Norato, M.A.; Sangani, A.S.; Tavlarides, L.L.

    1999-05-01

    The wave equations for the interior and exterior of the particles are ensemble averaged and combined with an analysis by Allegra and Hawley [J. Acoust. Soc. Am. {bold 51}, 1545 (1972)] for the interaction of a single particle with the incident wave to determine the phase speed and attenuation of sound waves propagating through dilute slurries. The theory is shown to compare very well with the measured attenuation. The inverse problem, i.e., the problem of determining the particle size distribution given the attenuation as a function of frequency, is examined using regularization techniques that have been successful for bubbly liquids. It is shown that, unlike the bubbly liquids, the success of solving the inverse problem is limited since it depends strongly on the nature of particles and the frequency range used in inverse calculations. {copyright} {ital 1999 American Institute of Physics.}

  4. An experimental study of shock wave propagation through a polyester film

    NASA Astrophysics Data System (ADS)

    Eliasson, Veronica; Jeon, Hongjoo

    2016-11-01

    A polyester film is available in a variety of uses such as packaging, protective overlay, barrier protection, and other industrial applications. In the current study, shock tube experiments are performed to study the influence of a polyester film on the propagation of a planar shock wave. A conventional shock tube is used to create incident shock Mach numbers of Ms = 1.34 and 1.46. A test section of the shock tube is designed to hold a 0.009 mm, 0.127 mm, 0.254 mm, or 0.508 mm thick polyester film (Dura-Lar). High-temporal resolution schlieren photography is used to visualize the shock wave mitigation caused by the polyester film. In addition, four pressure transducers are used to measure the elapsed time of arrival and overpressure of the shock wave both upstream and downstream of the test section. Results show that the transmitted shock wave in the polyester film is clearly observed and the transmitted shock Mach number is decreased by increasing film thickness. This study is supported by the National Science Foundation under Grant No. CBET-1437412.

  5. Ultra-Scalable Algorithms for Large-Scale Uncertainty Quantification in Inverse Wave Propagation

    DTIC Science & Technology

    2016-03-04

    associated uncertainty, the heterogeneity of a medium or shape of a scatterer from reflected/transmitted waves (acoustic, elastic, electromagnetic ) at very...elastic, and electromagnetic wave propagation; discontinuous Petrov Galerkin method; volume integral equations; fast multipole method; FFT; inverse...reflected/transmitted waves (acoustic, elastic, electromagnetic ) at very large scale. The resulting Bayesian wave inverse propagation problem has been

  6. Zero-group-velocity propagation of electromagnetic wave through nanomaterial

    NASA Astrophysics Data System (ADS)

    Fan, Taian

    This research will investigate the problem on the propagation of electromagnetic wave through a specific nanomaterial. The nanomaterial analyzed is a material consisting of a field of Pt nanorods. This field of Pt nanorods are deposited on a substrate which consists of a RuO2 nano structure. When the nanorod is exposed to an electron beam emitted by a TEM (Transmission electron microscopy). A wave disturbance has been observed. A video taken within the chamber shows a wave with a speed in the scale of um/s (10-6 m/s), which is 14 orders of magnitude lower than speed of light in free space (approximate 3x108 m/s ). A physical and mathematical model is developed to explain this phenomenon. Due to the process of fabrication, the geometry of the decorated Pt nanorod field is assumed to be approximately periodic. The nanomaterials possess properties similar to a photonic crystal. Pt, as a noble metal, shows dispersive behaviours that is different from those ones of a perfect or good conductors. A FDTD algorithm is implemented to calculate the band diagram of the nanomaterials. To explore the dispersive properties of the Pt nanorod field, the FDTD algorithm is corrected with a Drude Model. The analysis of the corrected band diagram illustrates that the group velocity of the wave packet propagating through the nanomaterial can be positive, negative or zero. The possible zero-group velocity is therefore used to explain the extremely low velocity of wave (wave envelope) detected in the TEM.

  7. Low frequency guided plate wave propagation in fiber reinforced composites

    SciTech Connect

    Lih, S.S.; Mal, A.K.; Bar-Cohen, Y.

    1995-12-31

    The behavior of low frequency guided waves in composite laminates was studied theoretically and experimentally. The objective of this study is to develop a contact-coupling ultrasonic method of determining of the stiffness constants of composite materials. The solution for the low frequency guided wave modes was derived from exact and approximate plate theories. A parametric study was curried out to examine the influence of variations in the elastic stiffness constants on the guided wave modes. A comparison was made between the measured and calculated group velocities to corroborate the theoretical calculations. The experimental setup consisted of a contact coupled pair of transmitting and receiving transducers using pulsed waves and a broadband ultrasonic system. Graphite/epoxy laminates were tested by transmitting the wave along various angles of propagation with the fibers. The received signals were analyzed to determine the group velocity of the low frequency wave modes. Test results have shown a very, good agreement of the calculated and measured elastic constants.

  8. Generation, propagation, and breaking of internal solitary waves.

    PubMed

    Grue, John

    2005-09-01

    Tidal, two-layer flow over topography generates a kink of the interface separating an upstream interfacial elevation from a depression above the topography. Upstream undular bores and solitary waves of large amplitude are generated from the interfacial kink. The waves propagate upstream when the tide turns. Interfacial simulations of this kind of generation process fit with the observations at Knight Inlet in British Columbia, in the Sulu Sea experiment, and undular bores generated by internal tides in the Strait of Gibraltar. Fully nonlinear interfacial computations compare successfully with experimental observations of solitary waves in the laboratory and in the field for wave amplitudes ranging from small to maximal values. The waves exhibit only minor sensitivity to a finite thickness of the pycnocline. Analytical solitary waves are recaptured in the small amplitude limit. Shear-induced breaking appears first in the top part of the pycnocline and is expressed in terms of the Richardson number. Convective breaking in the top part of the water column occurs beyond a threshold amplitude when a pronounced stratification continues all the way to the ocean surface.

  9. ENERGY CONTENT AND PROPAGATION IN TRANSVERSE SOLAR ATMOSPHERIC WAVES

    SciTech Connect

    Goossens, M.; Van Doorsselaere, T.; Soler, R.; Verth, G.

    2013-05-10

    Recently, a significant amount of transverse wave energy has been estimated propagating along solar atmospheric magnetic fields. However, these estimates have been made with the classic bulk Alfven wave model which assumes a homogeneous plasma. In this paper, the kinetic, magnetic, and total energy densities and the flux of energy are computed for transverse MHD waves in one-dimensional cylindrical flux tube models with a piecewise constant or continuous radial density profile. There are fundamental deviations from the properties for classic bulk Alfven waves. (1) There is no local equipartition between kinetic and magnetic energy. (2) The flux of energy and the velocity of energy transfer have, in addition to a component parallel to the magnetic field, components in the planes normal to the magnetic field. (3) The energy densities and the flux of energy vary spatially, contrary to the case of classic bulk Alfven waves. This last property has the important consequence that the energy flux computed with the well known expression for bulk Alfven waves could overestimate the real flux by a factor in the range 10-50, depending on the flux tube equilibrium properties.

  10. Propagation of photosensitive chemical waves on the circular routes.

    PubMed

    Kitahata, Hiroyuki; Yamada, Akiko; Nakata, Satoshi; Ichino, Takatoshi

    2005-06-09

    The propagation of chemical waves in the photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated using an excitable field in the shape of a circular ring or figure "8" that was drawn by computer software and then projected on a film soaked with BZ solution using a liquid-crystal projector. For a chemical wave in a circular reaction field, the shape of the chemical wave was investigated depending on the ratio of the inner and outer radii. When two chemical waves were generated on a field shaped like a figure "8" (one chemical wave in each circle) as the initial condition, the location of the collision of the waves either was constant or alternated depending on the degree of overlap of the two circular rings. These experimental results were analyzed on the basis of a geometrical discussion and theoretically reproduced on the basis of a reaction-diffusion system using a modified Oregonator model. These results suggest that the photosensitive BZ reaction may be useful for creating spatio-temporal patterns depending on the geometric arrangement of excitable fields.

  11. Higher order acoustoelastic Lamb wave propagation in stressed plates.

    PubMed

    Pei, Ning; Bond, Leonard J

    2016-11-01

    Modeling and experiments are used to investigate Lamb wave propagation in the direction perpendicular to an applied stress. Sensitivity, in terms of changes in velocity, for both symmetrical and anti-symmetrical modes was determined. Codes were developed based on analytical expressions for waves in loaded plates and they were used to give wave dispersion curves. The experimental system used a pair of compression wave transducers on variable angle wedges, with set separation, and variable frequency tone burst excitation, on an aluminum plate 0.16 cm thick with uniaxial applied loads. The loads, which were up to 600 με, were measured using strain gages. Model results and experimental data are in good agreement. It was found that the change in Lamb wave velocity, due to the acoustoelastic effect, for the S1 mode exhibits about ten times more sensitive, in terms of velocity change, than the traditional bulk wave measurements, and those performed using the fundamental Lamb modes. The data presented demonstrate the potential for the use of higher order Lamb modes for online industrial stress measurement in plate, and that the higher sensitivity seen offers potential for improved measurement systems.

  12. Optical Properties and Wave Propagation in Semiconductor-Based Two-Dimensional Photonic Crystals

    SciTech Connect

    Agio, Mario

    2002-12-31

    This work is a theoretical investigation on the physical properties of semiconductor-based two-dimensional photonic crystals, in particular for what concerns systems embedded in planar dielectric waveguides (GaAs/AlGaAs, GaInAsP/InP heterostructures, and self-standing membranes) or based on macro-porous silicon. The photonic-band structure of photonic crystals and photonic-crystal slabs is numerically computed and the associated light-line problem is discussed, which points to the issue of intrinsic out-of-lane diffraction losses for the photonic bands lying above the light line. The photonic states are then classified by the group theory formalism: each mode is related to an irreducible representation of the corresponding small point group. The optical properties are investigated by means of the scattering matrix method, which numerically implements a variable-angle-reflectance experiment; comparison with experiments is also provided. The analysis of surface reflectance proves the existence of selection rules for coupling an external wave to a certain photonic mode. Such rules can be directly derived from symmetry considerations. Lastly, the control of wave propagation in weak-index contrast photonic-crystal slabs is tackled in view of designing building blocks for photonic integrated circuits. The proposed designs are found to comply with the major requirements of low-loss propagation, high and single-mode transmission. These notions are then collected to model a photonic-crystal combiner for an integrated multi-wavelength-source laser.

  13. Planar waveguide yields mm-wave monopulse comparators

    NASA Astrophysics Data System (ADS)

    Syrigos, H.; Crossland, D.; van Wyck, B.

    1984-03-01

    The miniature monopulse comparator assemblies are machined from small split blocks of aluminum 3.000 in. in diameter and 0.375 in. thick at 94 GHz; at 35 GHz, the dimensions are 3.500 in. and 0.750 in., respectively. A computerized milling machine ensures very close control of the machining tolerances. The feed distribution lines are designed on the top of the comparator block without introducing waveguide runs. This allows the four balanced output ports to be distributed from their wide separation inside the comparator to a small cluster for proper feedhorn excitation. It is noted that these signals are then coupled to a unique multimode scalar feed horn through a sensitive resonant cavity. The horn throat of this feed is circular and sufficiently large to accommodate the HE(11) mode for the sum and HE(01) and HE(21) for the difference modes. It is pointed out that miniature monopulse comparators for 35 and 94 GHz employ planar waveguide technology to give a performance that is equivalent to much larger designs.

  14. Initiation of detonation by steady planar incident shock waves

    NASA Astrophysics Data System (ADS)

    Edwards, D. H.; Thomas, G. O.; Williams, T. L.

    1981-11-01

    The initiation of detonation by planar shocks is studied in a vertical shock tube in which a removable diaphragm allows the generated shock to be transmitted into the gas mixture, without any reflection at the interface. Streak schlieren photography confirms that a quasi-steady shock reaction complex is formed prior to the shock acceleration phase. The steady phase enabled the induction delay time to be measured in a direct manner, and microwave interferometry, along with pressure transducers, gave an accurate value for the delay time. The shock acceleration was determined from the locus of the exothermic reaction zone, and it is shown that the time coherence of energy release between particles entering the shock front at different times leads to the formation of reactive centers which are characteristic of mild ignition. Ignition delay data obtained by the incident shock method for oxyacetylene, diluted with nitrogen, are compared with those obtained by the reflected shock technique and shown to have advantages in high heat capacity systems.

  15. Wave propagation in fluid-saturated porous media

    NASA Astrophysics Data System (ADS)

    Ren, Jiaxiang

    The wave propagation in fluid-saturated porous media is studied by solving the Biot equations, the governing equations for the motion of the porous medium. Methods are devised to solve the Biot equations for different problems and medium models. The problem of the reflection and transmission at an interface is solved by using the eigen-analysis of the Biot equations. The displacement-stress vectors in the media on both sides of the interface are represented by corresponding upgoing and downgoing wave vectors which are then linked by the boundary conditions on the interface. The reflection and transmission coefficients are extracted from the proportionalities between the upgoing and downgoing waves. For an incident fast wave or shear wave, the reflection and transmission coefficients for the reflected and transmitted slow waves are very sensitive to frequency and interface permeability (kappasb{I}); while those for the reflected and transmitted fast waves and shear waves are not, except when incident angles are close to and greater than critical angles. For sandstones, the amplitudes of the reflected and transmitted slow waves could be several percent of the amplitude of the incident fast wave or shear wave. Higher interface permeabilities favor the generation of the slow wave. The slow waves generated at an open interface (kappasb{I}->infty) and a sealed interface (kappasb{I}=0) could be one-order different in amplitude. The reflection and transmission at an interface have been extended to the model composed of multi-layers of porous media. An algorithm based on the compact finite-difference method is developed for 2-D seismic modeling. The compact finite-difference method is used to estimate the spatial derivatives in the Biot equations, with a 6sp{th}-order accuracy. It needs fewer grid intervals to represent a mono-wavelength function than the traditional 2sp{nd}-order central-difference method. Therefore, the algorithm based on the compact finite

  16. Fluctuations in millimeter-wave signals propagated through inclement weather

    NASA Astrophysics Data System (ADS)

    Bohlander, Ronald A.; McMillan, Robert W.; Patterson, E. M.; Clifford, Steven F.; Hill, Reginald J.

    1988-05-01

    Results are presented from measurements of the effects of inclement weather on the fluctuations in amplitude and phase of millimeter-wave (MMW) signals propagated through the atmosphere. These measurements were made at frequencies near 116, 140, 173, and 230 GHz at a site near Champaign-Urbana, Illinois, in a community chosen for its exceptional flatness and lack of terrain features that might perturb the atmosphere. It was found that this inclement weather fluctuations are generally smaller than those observed in clear air under sunny conditions, and are also smaller than the corresponding effects observed at visible and near-infrared wavelengths. Typical values of the intensity standard deviation observed (in 20-s intervals) were 1 percent in rain, 0.2 percent in fog, and 1.5-2.5 percent in snow. Typical values of the standard deviation of wavefront angle-of-arrival were 40, 5, 4, and 1 microrad from clear air, snow, rain, and fog, respectively. It was also found that rain has the greatest effect on MMW transmission, causing large, slow changes in received signal strength as a function of rain rate. It should also be noted that rain caused the only observed loss of the propagation link, during a thunderstorm in which the rain rate was as high as 60 mm/h. It is concluded that, in general, millimeter-wave radiation propagates well in adverse weather, with rain causing the major problems observed during this series of measurements.

  17. Evolution of the average steepening factor for nonlinearly propagating waves.

    PubMed

    Muhlestein, Michael B; Gee, Kent L; Neilsen, Tracianne B; Thomas, Derek C

    2015-02-01

    Difficulties arise in attempting to discern the effects of nonlinearity in near-field jet-noise measurements due to the complicated source structure of high-velocity jets. This article describes a measure that may be used to help quantify the effects of nonlinearity on waveform propagation. This measure, called the average steepening factor (ASF), is the ratio of the average positive slope in a time waveform to the average negative slope. The ASF is the inverse of the wave steepening factor defined originally by Gallagher [AIAA Paper No. 82-0416 (1982)]. An analytical description of the ASF evolution is given for benchmark cases-initially sinusoidal plane waves propagating through lossless and thermoviscous media. The effects of finite sampling rates and measurement noise on ASF estimation from measured waveforms are discussed. The evolution of initially broadband Gaussian noise and signals propagating in media with realistic absorption are described using numerical and experimental methods. The ASF is found to be relatively sensitive to measurement noise but is a relatively robust measure for limited sampling rates. The ASF is found to increase more slowly for initially Gaussian noise signals than for initially sinusoidal signals of the same level, indicating the average distortion within noise waveforms occur more slowly.

  18. Transient processes in the parametric interaction of counter-propagating waves

    SciTech Connect

    Slabko, V V; Rasskazova, E V; Tkachenko, V A; Moskalev, A K; Popov, A K; Myslivets, S A

    2015-12-31

    We present a comparative analysis of transient processes in media with a negative refractive index for the parametric interaction of co- and counter-propagating waves. The transient time for the interaction of counter-propagating waves is shown to considerably exceed that for the interaction of co-propagating waves. In the case of counter-propagating waves, we present fitting results for the generated wave amplitude as a function of time and for the transient time vs. the amplitude of the pump wave and the length of the medium. (optical metamaterials)

  19. Shock wave propagation along constant sloped ocean bottoms.

    PubMed

    Maestas, Joseph T; Taylor, Larissa F; Collis, Jon M

    2014-12-01

    The nonlinear progressive wave equation (NPE) is a time-domain model used to calculate long-range shock propagation using a wave-following computational domain. Current models are capable of treating smoothly spatially varying medium properties, and fluid-fluid interfaces that align horizontally with a computational grid that can be handled by enforcing appropriate interface conditions. However, sloping interfaces that do not align with a horizontal grid present a computational challenge as application of interface conditions to vertical contacts is non-trivial. In this work, range-dependent environments, characterized by sloping bathymetry, are treated using a rotated coordinate system approach where the irregular interface is aligned with the coordinate axes. The coordinate rotation does not change the governing equation due to the narrow-angle assumption adopted in its derivation, but care is taken with applying initial, interface, and boundary conditions. Additionally, sound pressure level influences on nonlinear steepening for range-independent and range-dependent domains are used to quantify the pressures for which linear acoustic models suffice. A study is also performed to investigate the effects of thin sediment layers on the propagation of blast waves generated by explosives buried beneath mud line.

  20. Ray Tracing Modeling of Gravity Wave Propagation and Dissipation

    NASA Astrophysics Data System (ADS)

    Vadas, Sharon; Crowley, Geoff

    In this paper, we describe a ray trace model which calculates the wavevector, location and phase of a gravity wave (GW) as it propagates in the lower atmosphere and thermosphere. If used for a discreet transient source (such as a deep convective plume), we describe how this model can calculate the body forcing and the heat/cooling that are created when the GWs within a wave packet dissipate in the thermosphere from kinematic viscosity and thermal diffusivity. Although the body force calculation requires only the divergence of the momentum flux, the heat/cooling calculation requires the reconstructed GW field (e.g., density, velocity perturbations), which in turn requires the GW dissipative polarization relations. We describe these relations. We then describe the results of a recent study involving GWs identified from TIDDBIT HF Doppler sounder data taken at Wallops Island, VI, USA. Using this ray trace model, we determine if the unusual neutral wind profile measured by a rocket experiment at high altitudes (~290-370 km) could have been caused by the propagation and dissipation of several waves observed by TIDDBIT at lower altitudes.

  1. Synthetic observations of wave propagation in a sunspot umbra

    SciTech Connect

    Felipe, T.; Socas-Navarro, H.; Khomenko, E.

    2014-11-01

    Spectropolarimetric temporal series from Fe I λ6301.5 Å and Ca II infrared triplet lines are obtained by applying the Stokes synthesis code NICOLE to a numerical simulation of wave propagation in a sunspot umbra from MANCHA code. The analysis of the phase difference between Doppler velocity and intensity core oscillations of the Fe I λ6301.5 Å line reveals that variations in the intensity are produced by opacity fluctuations rather than intrinsic temperature oscillations, except for frequencies between 5 and 6.5 mHz. On the other hand, the photospheric magnetic field retrieved from the weak field approximation provides the intrinsic magnetic field oscillations associated to wave propagation. Our results suggest that this is due to the low magnetic field gradient of our sunspot model. The Stokes parameters of the chromospheric Ca II infrared triplet lines show striking variations as shock waves travel through the formation height of the lines, including emission self-reversals in the line core and highly abnormal Stokes V profiles. Magnetic field oscillations inferred from the Ca II infrared lines using the weak field approximation appear to be related with the magnetic field strength variation between the photosphere and the chromosphere.

  2. Electronically nonadiabatic wave packet propagation using frozen Gaussian scattering

    SciTech Connect

    Kondorskiy, Alexey D.; Nanbu, Shinkoh

    2015-09-21

    We present an approach, which allows to employ the adiabatic wave packet propagation technique and semiclassical theory to treat the nonadiabatic processes by using trajectory hopping. The approach developed generates a bunch of hopping trajectories and gives all additional information to incorporate the effect of nonadiabatic coupling into the wave packet dynamics. This provides an interface between a general adiabatic frozen Gaussian wave packet propagation method and the trajectory surface hopping technique. The basic idea suggested in [A. D. Kondorskiy and H. Nakamura, J. Chem. Phys. 120, 8937 (2004)] is revisited and complemented in the present work by the elaboration of efficient numerical algorithms. We combine our approach with the adiabatic Herman-Kluk frozen Gaussian approximation. The efficiency and accuracy of the resulting method is demonstrated by applying it to popular benchmark model systems including three Tully’s models and 24D model of pyrazine. It is shown that photoabsorption spectrum is successfully reproduced by using a few hundreds of trajectories. We employ the compact finite difference Hessian update scheme to consider feasibility of the ab initio “on-the-fly” simulations. It is found that this technique allows us to obtain the reliable final results using several Hessian matrix calculations per trajectory.

  3. A study on compressive shock wave propagation in metallic foams

    NASA Astrophysics Data System (ADS)

    Wang, Zhihua; Zhang, Yifen; Ren, Huilan; Zhao, Longmao

    2010-02-01

    Metallic foam can dissipate a large amount of energy due to its relatively long stress plateau, which makes it widely applicable in the design of structural crashworthiness. However, in some experimental studies, stress enhancement has been observed when the specimens are subjected to intense impact loads, leading to severe damage to the objects being protected. This paper studies this phenomenon on a 2D mass-spring-bar model. With the model, a constitutive relationship of metal foam and corresponding loading and unloading criteria are presented; a nonlinear kinematics equilibrium equation is derived, where an explicit integration algorithm is used to calculate the characteristic of the compressive shock wave propagation within the metallic foam; the effect of heterogeneous distribution of foam microstructures on the shock wave features is also included. The results reveal that under low impact pulses, considerable energy is dissipated during the progressive collapse of foam cells, which then reduces the crush of objects. When the pulse is sufficiently high, on the other hand, stress enhancement may take place, especially in the heterogeneous foams, where high peak stresses usually occur. The characteristics of compressive shock wave propagation in the foam and the magnitude and location of the peak stress produced are strongly dependent on the mechanical properties of the foam material, amplitude and period of the pulse, as well as the homogeneity of the microstructures. This research provides valuable insight into the reliability of the metallic foams used as a protective structure.

  4. Workshop on Research Techniques in Wave Propagation and Scattering

    NASA Astrophysics Data System (ADS)

    Varadan, V. V.; Varadan, V. K.

    1983-05-01

    A Workshop/Symposium on Research Techniques in Wave Propagation and Scattering was held at the Ohio State University October 18-21, 1982. This workshop was co-sponsored with the generous financial support of the U.S. Army Research Office, U.S. Office of Naval Research, the Center for Welding Research, O.S.U., and the Department of Engineering Mechanics, O.S.U. The workshop format consisted of a core of a general lectures of fifty minutes duration each and several shorter contributions that were of twenty minutes duration each. In addition, there were three panel discussions. The general lectures were of an expository nature on fundamental concepts and basic analytical/numerical techniques for the solution of wave scattering and propagation problems. The speakers were noted for their contribution to these techniques and in many cases have pioneered the techniques that they elaborated upon. These lectures were invaluable to the participants since they were of a pedagogical nature and easily understood by even those not very familiar with the particular method. The written version of many of these lectures will appear in a four volume Handbook on Acoustic, Electromagnetic and Elastic Wave Scattering to be published by North Holland as a separate project.

  5. Double porosity modeling in elastic wave propagation for reservoir characterization

    SciTech Connect

    Berryman, J. G., LLNL

    1998-06-01

    Phenomenological equations for the poroelastic behavior of a double porosity medium have been formulated and the coefficients in these linear equations identified. The generalization from a single porosity model increases the number of independent coefficients from three to six for an isotropic applied stress. In a quasistatic analysis, the physical interpretations are based upon considerations of extremes in both spatial and temporal scales. The limit of very short times is the one most relevant for wave propagation, and in this case both matrix porosity and fractures behave in an undrained fashion. For the very long times more relevant for reservoir drawdown,the double porosity medium behaves as an equivalent single porosity medium At the macroscopic spatial level, the pertinent parameters (such as the total compressibility) may be determined by appropriate field tests. At the mesoscopic scale pertinent parameters of the rock matrix can be determined directly through laboratory measurements on core, and the compressibility can be measured for a single fracture. We show explicitly how to generalize the quasistatic results to incorporate wave propagation effects and how effects that are usually attributed to squirt flow under partially saturated conditions can be explained alternatively in terms of the double-porosity model. The result is therefore a theory that generalizes, but is completely consistent with, Biot`s theory of poroelasticity and is valid for analysis of elastic wave data from highly fractured reservoirs.

  6. Propagation and Reflection of Diffusionless Torsional Waves in a Sphere

    NASA Astrophysics Data System (ADS)

    Maffei, S.; Jackson, A.

    2015-12-01

    The magnetohydrodynamics of stars and planetary cores is usually dominated by the overwhelming importance of rotation compared to other forces. Under these conditions the fluid motions are characterized by a strong invariance along the rotation axis. In the presence of a background magnetic field, magnetohydrodynamic oscillations can be triggered. Among these, of particular interest are the torsional waves, azimuthal perturbations of the fluid that are axisymmetric and invariant along the vertical direction. Their periods depend solely on the intensity of the magnetic field component aligned with the radial direction of propagation. As the detection of the fundamental period could constrain the magnetic field intensity in the Earth's outer core there is a long history of attempted detection of torsional waves from geomagnetic data. There is however a fundamental lack of knowledge concerning the propagation and reflection properties of these waves, as observational studies suggests behaviors that are different from theoretical expectations. In particular, recent findings (Gillet et al., 2011) suggest the lack of reflection at the equator and at the rotation axis. Through numerical simulation and analytical techniques we analyze the temporal evolution of diffusionless torsional waves in spherical geometry, with particular attention on the reflection at the equator and the pseudo-reflection at the rotation axis. We develop a novel analytical solution to the torsional wave eigenvalue problem whose behavior at the boundaries helps us to illustrate the meaning of the boundary conditions. Furthermore we find that for any acceptable magnetic background field, reflections at both boundaries are allowed and we illustrate how the WKBJ approximation is an efficient tool for investigating them.

  7. Propagating Waves of Directionality and Coordination Orchestrate Collective Cell Migration

    PubMed Central

    Zaritsky, Assaf; Kaplan, Doron; Hecht, Inbal; Natan, Sari; Wolf, Lior; Gov, Nir S.; Ben-Jacob, Eshel; Tsarfaty, Ilan

    2014-01-01

    The ability of cells to coordinately migrate in groups is crucial to enable them to travel long distances during embryonic development, wound healing and tumorigenesis, but the fundamental mechanisms underlying intercellular coordination during collective cell migration remain elusive despite considerable research efforts. A novel analytical framework is introduced here to explicitly detect and quantify cell clusters that move coordinately in a monolayer. The analysis combines and associates vast amount of spatiotemporal data across multiple experiments into transparent quantitative measures to report the emergence of new modes of organized behavior during collective migration of tumor and epithelial cells in wound healing assays. First, we discovered the emergence of a wave of coordinated migration propagating backward from the wound front, which reflects formation of clusters of coordinately migrating cells that are generated further away from the wound edge and disintegrate close to the advancing front. This wave emerges in both normal and tumor cells, and is amplified by Met activation with hepatocyte growth factor/scatter factor. Second, Met activation was found to induce coinciding waves of cellular acceleration and stretching, which in turn trigger the emergence of a backward propagating wave of directional migration with about an hour phase lag. Assessments of the relations between the waves revealed that amplified coordinated migration is associated with the emergence of directional migration. Taken together, our data and simplified modeling-based assessments suggest that increased velocity leads to enhanced coordination: higher motility arises due to acceleration and stretching that seems to increase directionality by temporarily diminishing the velocity components orthogonal to the direction defined by the monolayer geometry. Spatial and temporal accumulation of directionality thus defines coordination. The findings offer new insight and suggest a basic

  8. Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation.

    PubMed

    Jing, Yun; Tao, Molei; Clement, Greg T

    2011-01-01

    A wave-vector-frequency-domain method is presented to describe one-directional forward or backward acoustic wave propagation in a nonlinear homogeneous medium. Starting from a frequency-domain representation of the second-order nonlinear acoustic wave equation, an implicit solution for the nonlinear term is proposed by employing the Green's function. Its approximation, which is more suitable for numerical implementation, is used. An error study is carried out to test the efficiency of the model by comparing the results with the Fubini solution. It is shown that the error grows as the propagation distance and step-size increase. However, for the specific case tested, even at a step size as large as one wavelength, sufficient accuracy for plane-wave propagation is observed. A two-dimensional steered transducer problem is explored to verify the nonlinear acoustic field directional independence of the model. A three-dimensional single-element transducer problem is solved to verify the forward model by comparing it with an existing nonlinear wave propagation code. Finally, backward-projection behavior is examined. The sound field over a plane in an absorptive medium is backward projected to the source and compared with the initial field, where good agreement is observed.

  9. PROPAGATION AND STABILITY OF SUPERLUMINAL WAVES IN PULSAR WINDS

    SciTech Connect

    Mochol, Iwona; Kirk, John G. E-mail: john.kirk@mpi-hd.mpg.de

    2013-07-01

    Nonlinear electromagnetic waves with superluminal phase velocity can propagate in the winds around isolated pulsars, and around some pulsars in binary systems. Using a short-wavelength approximation, we find and analyze an integrable system of equations that govern their evolution in spherical geometry. A confined mode is identified that stagnates to finite pressure at large radius and can form a precursor to the termination shock. Using a simplified criterion, we find this mode is stable for most isolated pulsars, but may be unstable if the external pressure is high, such as in the pulsar wind nebulae in starburst galaxies and in W44. Pulsar winds in eccentric binary systems, such as PSR 1259-63, may go through phases with stable and unstable electromagnetic precursors, as well as phases in which the density is too high for these modes to propagate.

  10. Excitation wave propagation in a patterned multidomain cardiac tissue

    NASA Astrophysics Data System (ADS)

    Kudryashova, N. N.; Teplenin, A. S.; Orlova, Y. V.; Agladze, K. I.

    2015-06-01

    Electrospun fibrous mats are widely used in the contemporary cardiac tissue engineering as the substrates for growing cardiac cells. The substrate with chaotically oriented nanofibers leads to the growth of cardiac tissue with randomly oriented, but internally morphologically anisotropic clusters or domains. The domain structure affects the stability of the excitation propagation and we studied the stability of the propagating excitation waves versus the average size of the domains and the externally applied excitation rate. In an experimental model based on neonatal rat cardiac tissue monolayers, as well as in the computer simulations, we have found that an increase in domain sizes leads to the decrease in the critical stimulation frequencies, thus evidencing that larger domains are having a higher arrhythmogenic effect.

  11. Propagation of spiral waves pinned to circular and rectangular obstacles.

    PubMed

    Sutthiopad, Malee; Luengviriya, Jiraporn; Porjai, Porramain; Phantu, Metinee; Kanchanawarin, Jarin; Müller, Stefan C; Luengviriya, Chaiya

    2015-05-01

    We present an investigation of spiral waves pinned to circular and rectangular obstacles with different circumferences in both thin layers of the Belousov-Zhabotinsky reaction and numerical simulations with the Oregonator model. For circular objects, the area always increases with the circumference. In contrast, we varied the circumference of rectangles with equal areas by adjusting their width w and height h. For both obstacle forms, the propagating parameters (i.e., wavelength, wave period, and velocity of pinned spiral waves) increase with the circumference, regardless of the obstacle area. Despite these common features of the parameters, the forms of pinned spiral waves depend on the obstacle shapes. The structures of spiral waves pinned to circles as well as rectangles with the ratio w/h∼1 are similar to Archimedean spirals. When w/h increases, deformations of the spiral shapes are observed. For extremely thin rectangles with w/h≫1, these shapes can be constructed by employing semicircles with different radii which relate to the obstacle width and the core diameter of free spirals.

  12. Wave propagation, scattering and emission in complex media

    NASA Astrophysics Data System (ADS)

    Jin, Ya-Qiu

    I. Polarimetric scattering and SAR imagery. EM wave propagation and scattering in polarimetric SAR interferometry / S. R. Cloude. Terrain topographic inversion from single-pass polarimetric SAR image data by using polarimetric stokes parameters and morphological algorithm / Y. Q. Jin, L. Luo. Road detection in forested area using polarimetric SAR / G. W. Dong ... [et al.]. Research on some problems about SAR radiometric resolution / G. Dong ... [et al.]. A fast image matching algorithm for remote sensing applications / Z. Q. Hou ... [et al.]. A new algorithm of noised remote sensing image fusion based on steerable filters / X. Kang ... [et al.]. Adaptive noise reduction of InSAR data based on anisotropic diffusion models and their applications to phase unwrapping / C. Wang, X. Gao, H. Zhang -- II. Scattering from randomly rough surfaces. Modeling tools for backscattering from rough surfaces / A. K. Fung, K. S. Chen. Pseudo-nondiffracting beams from rough surface scattering / E. R. Méndez, T. A. Leskova, A. A. Maradudin. Surface roughness clutter effects in GPR modeling and detection / C. Rappaport. Scattering from rough surfaces with small slopes / M. Saillard, G. Soriano. Polarization and spectral characteristics of radar signals reflected by sea-surface / V. A. Butko, V. A. Khlusov, L. I. Sharygina. Simulation of microwave scattering from wind-driven ocean surfaces / M. Y. Xia ... [et al.]. HF surface wave radar tests at the Eastern China Sea / X. B. Wu ... [et al.] -- III. Electromagnetics of complex materials. Wave propagation in plane-parallel metamaterial and constitutive relations / A. Ishimaru ... [et al.]. Two dimensional periodic approach for the study of left-handed metamaterials / T. M. Grzegorczyk ... [et al.]. Numerical analysis of the effective constitutive parameters of a random medium containing small chiral spheres / Y. Nanbu, T. Matsuoka, M. Tateiba. Wave propagation in inhomogeneous media: from the Helmholtz to the Ginzburg -Landau equation / M

  13. Micromechanics of Seismic Wave Propagation in Granular Rocks

    NASA Astrophysics Data System (ADS)

    Nihei, Kurt Toshimi

    1992-09-01

    This thesis investigates the details of seismic wave propagation in granular rocks by examining the micromechanical processes which take place at the grain level. Grain contacts are identified as the primary sites of attenuation in dry and fluid-saturated rocks. In many sedimentary rocks such as sandstones and limestones, the process of diagenesis leaves the grains only partially cemented together. When viewed at the micron scale, grain contacts are non-welded interfaces similar in nature to large scale joints and faults. Using a lumped properties approximation, the macroscopic properties of partially cemented grain contacts are modeled using a displacement-discontinuity boundary condition. This model is used to estimate the magnitude and the frequency dependence of the grain contact scattering attenuation for an idealized grain packing geometry. Ultrasonic P- and S-wave group velocity and attenuation measurements on sintered glass beads, alundum, and Berea sandstones were performed to determine the effects of stress, frequency, and pore fluid properties in granular materials with sintered and partially sintered grain contacts. P - and S-wave attenuation displayed the same overall trends for tests with n-decane, water, silicone oil, and glycerol. The magnitudes of the attenuation coefficients were, in general, higher for S-waves. The experimental measurements reveal that viscosity-dependent attenuation dominates in material with sintered grain contacts. Viscosity-dependent attenuation is also observed in Berea sandstone but only at hydrostatic stresses in excess of 15 MPa where the grain contacts are highly stiffened. Fluid surface chemistry-related attenuation was observed in Berea sandstone loaded uniaxially. These measurements suggest that attenuation in fluid-saturated rocks with partially cemented grain contacts is dependent on both the fluid properties and the state of stress at the grain contacts. A numerical method for simulating seismic wave propagation in

  14. Wave propagation downstream of a high power helicon in a dipolelike magnetic field

    SciTech Connect

    Prager, James; Winglee, Robert; Roberson, B. Race; Ziemba, Timothy

    2010-01-15

    The wave propagating downstream of a high power helicon source in a diverging magnetic field was investigated experimentally. The magnetic field of the wave has been measured both axially and radially. The three-dimensional structure of the propagating wave is observed and its wavelength and phase velocity are determined. The measurements are compared to predictions from helicon theory and that of a freely propagating whistler wave. The implications of this work on the helicon as a thruster are also discussed.

  15. Gravity Wave Variances and Propagation Derived from AIRS Radiances

    NASA Technical Reports Server (NTRS)

    Gong, Jie; Wu, Dong L.; Eckermann, S. D.

    2012-01-01

    As the first gravity wave (GW) climatology study using nadir-viewing infrared sounders, 50 Atmospheric Infrared Sounder (AIRS) radiance channels are selected to estimate GW variances at pressure levels between 2-100 hPa. The GW variance for each scan in the cross-track direction is derived from radiance perturbations in the scan, independently of adjacent scans along the orbit. Since the scanning swaths are perpendicular to the satellite orbits, which are inclined meridionally at most latitudes, the zonal component of GW propagation can be inferred by differencing the variances derived between the westmost and the eastmost viewing angles. Consistent with previous GW studies using various satellite instruments, monthly mean AIRS variance shows large enhancements over meridionally oriented mountain ranges as well as some islands at winter hemisphere high latitudes. Enhanced wave activities are also found above tropical deep convective regions. GWs prefer to propagate westward above mountain ranges, and eastward above deep convection. AIRS 90 field-of-views (FOVs), ranging from +48 deg. to -48 deg. off nadir, can detect large-amplitude GWs with a phase velocity propagating preferentially at steep angles (e.g., those from orographic and convective sources). The annual cycle dominates the GW variances and the preferred propagation directions for all latitudes. Indication of a weak two-year variation in the tropics is found, which is presumably related to the Quasi-biennial oscillation (QBO). AIRS geometry makes its out-tracks capable of detecting GWs with vertical wavelengths substantially shorter than the thickness of instrument weighting functions. The novel discovery of AIRS capability of observing shallow inertia GWs will expand the potential of satellite GW remote sensing and provide further constraints on the GW drag parameterization schemes in the general circulation models (GCMs).

  16. Deep vertical propagation of mountain waves above Scandinavia

    NASA Astrophysics Data System (ADS)

    Dörnbrack, A.; Witschas, B.; Rahm, S.; Gisinger, S.; Rapp, M.; Baumgarten, G.; Stober, G.; Luebken, F. J.; Achtert, P.; Ehard, B.; Gumbel, J.; Kivi, R.; Wagner, J.

    2014-12-01

    The project "Investigation of the life cycle of gravity waves"(GW-LCYCLE) is part of the German research initiative ROMIC (Role of theMiddle atmosphere In Climate) funded by the ministry of research. Inclose cooperation with Scandinavian partners as the Stockholm Universityand the Finnish Meteorological Institute a first field phase wasconducted in November/December 2013. The field program combinedground-based observations of tropospheric and lower stratospheric flowand stratospheric and mesospheric temperature by lidars and radars atAlomar (N) and at Esrange (S) with airborne and balloonborneobservations. Northern Scandinavia was chosen since the westerly flowacross the mountains is often aligned with the polar night jetpermitting gravity waves (GWs) to propagate into the middle atmosphere.From 2 until 14 December 2013, 24 flight hours of the DLR Falcon flownin four intensive observing periods (IOPs) provided in-situ andremote-sensing observations of atmospheric wind, temperature, watervapour and other trace gases (e.g. CO, N2O, O3) in the vicinity of thetropopause. During three IOPs, the airborne observations were supportedby 3 hourly simultaneous radiosonde launches from Andøya (N), Esrange(S) and Sodankylä (FIN). Additionally, 1.5 hourly high-frequencyradiosonde launches were conducted from the Arena Arctica at Kirunaairport with two systems (Väisälä and GRAW)and different balloonfillings to obtain different ascent rates.During GW-LCYCLE, the atmospheric flow above the Scandinavian mountainswas observed under distinct meteorological conditions enabling orattenuating the deep vertical propagation of mountain-induced gravitywaves. The presentation juxtaposes two different cases and analyses theassociated meteorological conditions. The unique combination of airbornetropospheric wind lidar measurements, flight level data, high-frequencyradiosonde profiles and the ground-based lidar observations allow acomprehensive study of deeply propagating gravity waves

  17. Radio wave propagation at frequencies exceeding MUF-F2 in the short wave band

    NASA Technical Reports Server (NTRS)

    Ashkaliyev, Y. F.; Bocharov, V. I.

    1972-01-01

    The results of measurements of field strength and signal/noise ratio on experimental ionospheric-scattering short wave radio links are presented. It is shown that the seasonal and diurnal variations of field strength are determined by features of solar and meteoric activity. The role of the sporadic E-layer in propagation of short radio waves at frequencies exceeding MUF-F2 is noted.

  18. Investigation of guided waves propagation in pipe buried in sand

    SciTech Connect

    Leinov, Eli; Cawley, Peter; Lowe, Michael J.S.

    2014-02-18

    The inspection of pipelines by guided wave testing is a well-established method for the detection of corrosion defects in pipelines, and is currently used routinely in a variety of industries, e.g. petrochemical and energy. When the method is applied to pipes buried in soil, test ranges tend to be significantly compromised because of attenuation of the waves caused by energy radiating into the soil. Moreover, the variability of soil conditions dictates different attenuation characteristics, which in-turn results in different, unpredictable, test ranges. We investigate experimentally the propagation and attenuation characteristics of guided waves in pipes buried in fine sand using a well characterized full scale experimental apparatus. The apparatus consists of an 8 inch-diameter, 5.6-meters long steel pipe embedded over 3 meters of its length in a rectangular container filled with fine sand, and an air-bladder for the application of overburden pressure. Longitudinal and torsional guided waves are excited in the pipe and recorded using a transducer ring (Guided Ultrasonics Ltd). Acoustic properties of the sand are measured independently in-situ and used to make model predictions of wave behavior in the buried pipe. We present the methodology and the systematic measurements of the guided waves under a range of conditions, including loose and compacted sand. It is found that the application of overburden pressure modifies the compaction of the sand and increases the attenuation, and that the measurement of the acoustic properties of sand allows model prediction of the attenuation of guided waves in buried pipes with a high level of confidence.

  19. Propagation of unsteady waves in an elastic layer

    NASA Astrophysics Data System (ADS)

    Kuznetsova, E. L.; Tarlakovskii, D. V.; Fedotenkov, G. V.

    2011-10-01

    We consider a plane problem of propagation of unsteady waves in a plane layer of constant thickness filled with a homogeneous linearly elastic isotropic medium in the absence of mass forces and with zero initial conditions. We assume that, on one of the layer boundaries, the normal stresses are given in the form of the Dirac delta function, the tangential stresses are zero, and the second boundary is rigidly fixed. The problem is solved by using the Laplace transform with respect to time and the Fourier transform with respect to the longitudinal coordinate. The normal displacements at an arbitrary point are obtained in the form of finite sums.

  20. Magnetostatic volume wave propagation in multilayer YIG/GGG structures

    NASA Astrophysics Data System (ADS)

    Adam, J. D.; Daniel, M. R.

    1984-09-01

    The growth of multiple epitaxial YIG film structures using epitaxial GGG spacer layers is described. Samarium doping of the epitaxial GGG was used to reduce its lattice mismatch with the GGG substrate to less than 0.002 A and both double and triple YIG films were grown on 50 mm diameter GGG substrates. Measured and calculated results for magnetostatic wave propagation in three different examples are given, i.e., FVWs in double and triple YIG layer structures and BVWs in a four YIG layer structure. In these cases agreement between measurements and calculations was excellent.

  1. Dispersion relations for electromagnetic wave propagation in chiral plasmas

    SciTech Connect

    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.

  2. Regular Wave Propagation Out of Noise in Chemical Active Media

    SciTech Connect

    Alonso, S.; Sendina-Nadal, I.; Perez-Munuzuri, V.; Sancho, J. M.; Sagues, F.

    2001-08-13

    A pacemaker, regularly emitting chemical waves, is created out of noise when an excitable photosensitive Belousov-Zhabotinsky medium, strictly unable to autonomously initiate autowaves, is forced with a spatiotemporal patterned random illumination. These experimental observations are also reproduced numerically by using a set of reaction-diffusion equations for an activator-inhibitor model, and further analytically interpreted in terms of genuine coupling effects arising from parametric fluctuations. Within the same framework we also address situations of noise-sustained propagation in subexcitable media.

  3. Regular wave propagation out of noise in chemical active media.

    PubMed

    Alonso, S; Sendiña-Nadal, I; Pérez-Muñuzuri, V; Sancho, J M; Sagués, F

    2001-08-13

    A pacemaker, regularly emitting chemical waves, is created out of noise when an excitable photosensitive Belousov-Zhabotinsky medium, strictly unable to autonomously initiate autowaves, is forced with a spatiotemporal patterned random illumination. These experimental observations are also reproduced numerically by using a set of reaction-diffusion equations for an activator-inhibitor model, and further analytically interpreted in terms of genuine coupling effects arising from parametric fluctuations. Within the same framework we also address situations of noise-sustained propagation in subexcitable media.

  4. Particle velocity non-uniformity and steady-wave propagation

    NASA Astrophysics Data System (ADS)

    Meshcheryakov, Yu. I.

    2017-03-01

    A constitutive equation grounded in dislocation dynamics is shown to be incapable of describing the propagation of shock fronts in solids. Shock wave experiments and theoretical investigations motivate an additional collective mechanism of stress relaxation that should be incorporated into the model through the standard deviation of the particle velocity, which is found to be proportional to the strain rate. In this case, the governing equation system results in a second-order differential equation of square non-linearity. Solution to this equation and calculations for D16 aluminum alloy show a more precise coincidence of the theoretical and experimental velocity profiles.

  5. Propagation analysis of forward degenerate four-wave mixing

    NASA Astrophysics Data System (ADS)

    Maruani, A.

    1980-05-01

    The problem of forward degenerate four-wave mixing in one- and two-photon absorbing media is shown to be analytically solvable for all current experimental conditions. The resonant interaction is studied in detail, and optical Kerr effect, auto and induced two-photon absorption, and nonlinear gain are taken explicitly into account. It is demonstrated how the Kerr effect limits the efficiency of the process. Around a two-photon resonance, the problem of the nearly parallel propagation of two beams undergoing auto and induced two-photon absorption is solved. The solutions are obtained in a form simple enough to allow numerical computations on a programmable calculator.

  6. Interaction of High Frequency Acoustic Waves and Optical Waves Propagating in Single Mode Fibers.

    NASA Astrophysics Data System (ADS)

    de Paula, Ramon Perez

    This paper develops a frequency dependent model for the acousto-optic interaction with a single mode fiber of acoustic waves having wavelengths comparable to the fiber diameter. This paper also presents optical techniques for experimental observation and measurement of such effects. The acoustic waves are both normally and obliquelly incident on the fiber. The solutions to the elastic problem studied here are constructed using scalar and vector potentials. The principal strains induced by a plane wave propagating in a fluid is calculated through the solution of the wave equation and the associated boundary condition. The optical beam propagation is analyzed starting with Maxwell's, equations and the required solution for single mode (degenerate double mode) propagation is presented. For the perturbed fiber the anisotropic solution is discussed. The optical indicatrix is derived from the electric energy density, with the major axis parallel to the induced principal strains obtained from the solution of the elastic problem. The solution of the optical indicatrix equation (index ellipsoid) yields two independent propagation modes that are linear polarized plane waves with two different propagation velocities. The induced phase shift and birefringence are calculated from the index ellipsoid. The birefringence and phase shift are also measured experimentally using a fiber optic interferometer and a fiber optic polariscope. The experimental apparatus is discussed in detail and the techniques used to make the measurements are presented. The results are separated into two parts: first, the results for ultrasonic waves of normal incidence are presented, theoretical and experimental results are discussed, and the two compared; second, the results for angular incidence are presented in the same format as above, and compared with the results for perpendicular incidence.

  7. Discretizing singular point sources in hyperbolic wave propagation problems

    NASA Astrophysics Data System (ADS)

    Petersson, N. Anders; O'Reilly, Ossian; Sjögreen, Björn; Bydlon, Samuel

    2016-09-01

    We develop high order accurate source discretizations for hyperbolic wave propagation problems in first order formulation that are discretized by finite difference schemes. By studying the Fourier series expansions of the source discretization and the finite difference operator, we derive sufficient conditions for achieving design accuracy in the numerical solution. Only half of the conditions in Fourier space can be satisfied through moment conditions on the source discretization, and we develop smoothness conditions for satisfying the remaining accuracy conditions. The resulting source discretization has compact support in physical space, and is spread over as many grid points as the number of moment and smoothness conditions. In numerical experiments we demonstrate high order of accuracy in the numerical solution of the 1-D advection equation (both in the interior and near a boundary), the 3-D elastic wave equation, and the 3-D linearized Euler equations.

  8. Discretizing singular point sources in hyperbolic wave propagation problems

    DOE PAGES

    Petersson, N. Anders; O'Reilly, Ossian; Sjogreen, Bjorn; ...

    2016-06-01

    Here, we develop high order accurate source discretizations for hyperbolic wave propagation problems in first order formulation that are discretized by finite difference schemes. By studying the Fourier series expansions of the source discretization and the finite difference operator, we derive sufficient conditions for achieving design accuracy in the numerical solution. Only half of the conditions in Fourier space can be satisfied through moment conditions on the source discretization, and we develop smoothness conditions for satisfying the remaining accuracy conditions. The resulting source discretization has compact support in physical space, and is spread over as many grid points as themore » number of moment and smoothness conditions. In numerical experiments we demonstrate high order of accuracy in the numerical solution of the 1-D advection equation (both in the interior and near a boundary), the 3-D elastic wave equation, and the 3-D linearized Euler equations.« less

  9. Discretizing singular point sources in hyperbolic wave propagation problems

    SciTech Connect

    Petersson, N. Anders; O'Reilly, Ossian; Sjogreen, Bjorn; Bydlon, Samuel

    2016-06-01

    Here, we develop high order accurate source discretizations for hyperbolic wave propagation problems in first order formulation that are discretized by finite difference schemes. By studying the Fourier series expansions of the source discretization and the finite difference operator, we derive sufficient conditions for achieving design accuracy in the numerical solution. Only half of the conditions in Fourier space can be satisfied through moment conditions on the source discretization, and we develop smoothness conditions for satisfying the remaining accuracy conditions. The resulting source discretization has compact support in physical space, and is spread over as many grid points as the number of moment and smoothness conditions. In numerical experiments we demonstrate high order of accuracy in the numerical solution of the 1-D advection equation (both in the interior and near a boundary), the 3-D elastic wave equation, and the 3-D linearized Euler equations.

  10. Ultrasonic wave propagation in concentrated slurries--the modelling problem.

    PubMed

    Challis, Richard E; Pinfield, Valerie J

    2014-09-01

    The suspended particle size distribution in slurries can, in principle, be estimated from measured ultrasonic wave attenuation across a frequency band in the 10s of MHz range. The procedure requires a computational model of wave propagation which incorporates scattering phenomena. These models fail at high particle concentrations due to hydrodynamic effects which they do not incorporate. This work seeks an effective viscosity and density for the medium surrounding the particles, which would enable the scattering model predictions to match experimental data for high solids loading. It is found that the required viscosity model has unphysical characteristics leading to the conclusion that a simple effective medium modification to the ECAH/LB is not possible. The paper confirms the successful results which can be obtained using core-shell scattering models, for smaller particles than had previously been studied, and outlines modifications to these which would permit rapid computation of sufficient stability to support fast particle sizing procedures.

  11. Seismic wave propagation effects in the upper volcanic edifice

    NASA Astrophysics Data System (ADS)

    Martínez Montesinos, Beatriz; Bean, Chris; Lokmer, Ivan

    2015-04-01

    A seismogram contains information about the seismic source and the wave path. Understanding the path effect is important for both source inversions and geophysical imagery. In the case of volcanoes, the correct interpretation of the signals helps us to determine their internal state. For instance, long-period events are commonly associated to magma movements in resonant conduits. We present an application of the adjoint methodology proposed in Tromp et al. [2004] to study the seismic wave propagation effects in the upper volcanic edifice. We do this by calculating sensitivity kernels, that is, investigating the sensitivity of different parts of a seismogram to different parts of the velocity model. In particular, we examine the influence of near-surface low-velocity volcanic structure to the recorded signals. We use the SPECFEM 2D software, a two-dimensional elastic wave propagation code based on the spectral-element method, to simulate examples for Mount Etna, Italy. We calculate synthetic seismograms in 2D heterogeneous models with topography, for the sources with different dominant frequency and locations. Then, we calculate the adjoint wavefield by time-reversing the calculated seismograms and "playing" them back into the medium as simultaneous seismic sources at the original receiver positions. In the last step, by combining the forward and adjoint wavefields, we calculate the traveltime sensitivity kernels of Mount Etna. In order to be able to capture a complex wave travel path, we examine the sensitivity of different parts of a seismic wavefield, that is, different time-window on a seimogram to different parts of the structural models. Preliminary results show the importance of the velocity structure at the near surface on the recorded traces. This means that we cannot ignore the heterogeneity of the upper volcanic edifice at the time of the interpretation of the recorded signals.

  12. Acoustic wave propagation in high-pressure system.

    PubMed

    Foldyna, Josef; Sitek, Libor; Habán, Vladimír

    2006-12-22

    Recently, substantial attention is paid to the development of methods of generation of pulsations in high-pressure systems to produce pulsating high-speed water jets. The reason is that the introduction of pulsations into the water jets enables to increase their cutting efficiency due to the fact that the impact pressure (so-called water-hammer pressure) generated by an impact of slug of water on the target material is considerably higher than the stagnation pressure generated by corresponding continuous jet. Special method of pulsating jet generation was developed and tested extensively under the laboratory conditions at the Institute of Geonics in Ostrava. The method is based on the action of acoustic transducer on the pressure liquid and transmission of generated acoustic waves via pressure system to the nozzle. The purpose of the paper is to present results obtained during the research oriented at the determination of acoustic wave propagation in high-pressure system. The final objective of the research is to solve the problem of transmission of acoustic waves through high-pressure water to generate pulsating jet effectively even at larger distances from the acoustic source. In order to be able to simulate numerically acoustic wave propagation in the system, it is necessary among others to determine dependence of the sound speed and second kinematical viscosity on operating pressure. Method of determination of the second kinematical viscosity and speed of sound in liquid using modal analysis of response of the tube filled with liquid to the impact was developed. The response was measured by pressure sensors placed at both ends of the tube. Results obtained and presented in the paper indicate good agreement between experimental data and values of speed of sound calculated from so-called "UNESCO equation". They also show that the value of the second kinematical viscosity of water depends on the pressure.

  13. Anti-plane transverse waves propagation in nanoscale periodic layered piezoelectric structures.

    PubMed

    Chen, A-Li; Yan, Dong-Jia; Wang, Yue-Sheng; Zhang, Chuanzeng

    2016-02-01

    In this paper, anti-plane transverse wave propagation in nanoscale periodic layered piezoelectric structures is studied. The localization factor is introduced to characterize the wave propagation behavior. The transfer matrix method based on the nonlocal piezoelectricity continuum theory is used to calculate the localization factor. Additionally, the stiffness matrix method is applied to compute the wave transmission spectra. A cut-off frequency is found, beyond which the elastic waves cannot propagate through the periodic structure. The size effect or the influence of the ratio of the internal to external characteristic lengths on the cut-off frequency and the wave propagation behavior are investigated and discussed.

  14. Full wave propagation modelling in view to integrated ICRH wave coupling/RF sheaths modelling

    NASA Astrophysics Data System (ADS)

    Jacquot, Jonathan; Bobkov, Volodymyr; Colas, Laurent; Heuraux, Stéphane; Křivská, Alena; Lu, Lingfeng; Noterdaeme, Jean-Marie

    2015-12-01

    RF sheaths rectification can be the reason for operational limits for Ion Cyclotron Range of Frequencies (ICRF) heating systems via impurity production or excessive heat loads. To simulate this process in realistic geometry, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code is a minimal set of coupled equations that computes self-consistently wave propagation and DC plasma biasing. The present version of its wave propagation module only deals with the Slow Wave assumed to be the source of RF sheath oscillations. However the ICRF power coupling to the plasma is due to the fast wave (FW). This paper proposes to replace this one wave equation module by a full wave module in either 2D or 3D as a first step towards integrated modelling of RF sheaths and wave coupling. Since the FW is propagative in the main plasma, Perfectly Matched Layers (PMLs) adapted for plasmas were implemented at the inner side of the simulation domain to absorb outgoing waves and tested numerically with tilted B0 in Cartesian geometry, by either rotating the cold magnetized plasma dielectric tensors in 2D or rotating the coordinate vector basis in 3D. The PML was further formulated in cylindrical coordinates to account for for the toroidal curvature of the plasma. Toroidal curvature itself does not seem to change much the coupling. A detailed 3D geometrical description of Tore Supra and ASDEX Upgrade (AUG) antennas was included in the coupling code. The full antenna structure was introduced, since its toroidal symmetry with respect to the septum plane is broken (FS bars, toroidal phasing, non-symmetrical structure). Reliable convergence has been obtained with the density profile up to the leading edge of antenna limiters. Parallel electric field maps have been obtained as an input for the present version of SSWICH.

  15. Propagation of partially coherent fields through planar dielectric boundaries using angle-impact Wigner functions I. Two dimensions.

    PubMed

    Petruccelli, Jonathan C; Alonso, Miguel A

    2007-09-01

    We examine the angle-impact Wigner function (AIW) as a computational tool for the propagation of nonparaxial quasi-monochromatic light of any degree of coherence past a planar boundary between two homogeneous media. The AIWs of the reflected and transmitted fields in two dimensions are shown to be given by a simple ray-optical transformation of the incident AIW plus a series of corrections in the form of differential operators. The radiometric and leading six correction terms are studied for Gaussian Schell-model fields of varying transverse width, transverse coherence, and angle of incidence.

  16. The various manifestations of collisionless dissipation in wave propagation

    NASA Astrophysics Data System (ADS)

    Benisti, Didier; Morice, Olivier; Gremillet, Laurent

    2012-10-01

    In this talk, we provide a theoretical description of collisionless dissipation [1], for an electrostatic wave propagating in a three-dimensional plasma, from the linear regime when it simply amounts to Landau damping, to the strongly nonlinear one when it significantly affects the wave group velocity, both, along and across the local wave number. We, moreover, discuss the impact of dissipation on the longitudinal and transverse extent of the wave packet, which allows us to reinterpret previously published kinetic simulations [2-4]. Finally, we illustrate our results on a two-dimensional simulation of stimulated Raman scattering.[4pt] [1] D. B'enisti, O. Morice, and L. Gremillet, Phys. Plasmas 16, 063110 (2012). [2] J. E. Fahlen, B. J. Winjum, T. Grismayer, and W. B. Mori, Phys. Rev. Lett. 102, 245002 (2009). [3] J. W. Banks, R. L. Berger, S. Brunner, B. I. Cohen, and J. A. F. Hittinger, Phys. Plasmas 18, 052102 (2011). [4] J. E. Fahlen, B. J. Winjum, T. Grismayer, and W. B. Mori, Phys. Rev. E 83, 045501(R) (2011).

  17. Elastic wave propagation in bone in vivo: methodology.

    PubMed

    Cheng, S; Timonen, J; Suominen, H

    1995-04-01

    The purpose of this study was to investigate the usefulness of elastic wave propagation (EWP) in estimating the mechanical properties (elasticity) of human tibia. The test group was composed of 78-yr-old women assigned to high (n = 19) and low (n = 17) bone mineral density (BMD) groups as measured at the calcaneus by the 125I-photon absorption method. The EWP apparatus consisted of an impact-producing hammer with a force strain gauge and two accelerometers positioned on the bone. Results for nylon and acrylic were used to calibrate the apparatus. Polyvinyl chloride (PVC) solid rods and tubes of various diameters were used to evaluate the relationship between the elastic wave velocity and cross-sectional area. The density and the cross-sectional area of tibia were measured by the computerized tomographic (CT) method at the same intersection points as velocity recordings. The velocities in tibia of bending waves produced by the mechanical hammer were found to depend on the density, area moment of inertia, and density-dependent elastic constants of bone. It is important to account for the changes of these quantities along the bone. It is suggested that the velocity of elastic waves and various indices derived there from provide inexpensive ways of evaluating the elastic properties of bone.

  18. Plasma and radio waves from Neptune: Source mechanisms and propagation

    NASA Technical Reports Server (NTRS)

    Wong, H. K.

    1994-01-01

    This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

  19. Wave speed propagation measurements on highly attenuative heated materials

    DOE PAGES

    Moore, David G.; Ober, Curtis C.; Rodacy, Phil J.; ...

    2015-09-19

    Ultrasonic wave propagation decreases as a material is heated. Two factors that can characterize material properties are changes in wave speed and energy loss from interactions within the media. Relatively small variations in velocity and attenuation can detect significant differences in microstructures. This paper discusses an overview of experimental techniques that document the changes within a highly attenuative material as it is either being heated or cooled from 25°C to 90°C. The experimental set-up utilizes ultrasonic probes in a through-transmission configuration. The waveforms are recorded and analyzed during thermal experiments. To complement the ultrasonic data, a Discontinuous-Galerkin Model (DGM) wasmore » also created which uses unstructured meshes and documents how waves travel in these anisotropic media. This numerical method solves particle motion travel using partial differential equations and outputs a wave trace per unit time. As a result, both experimental and analytical data are compared and presented.« less

  20. Simulation of seismic wave propagation for reconnaissance in machined tunnelling

    NASA Astrophysics Data System (ADS)

    Lambrecht, L.; Friederich, W.

    2012-04-01

    During machined tunnelling, there is a complex interaction chain of the involved components. For example, on one hand the machine influences the surrounding ground during excavation, on the other hand supporting measures are needed acting on the ground. Furthermore, the different soil conditions are influencing the wearing of tools, the speed of the excavation and the safety of the construction site. In order to get information about the ground along the tunnel track, one can use seismic imaging. To get a better understanding of seismic wave propagation for a tunnel environment, we want to perform numerical simulations. For that, we use the spectral element method (SEM) and the nodal discontinuous galerkin method (NDG). In both methods, elements are the basis to discretize the domain of interest for performing high order elastodynamic simulations. The SEM is a fast and widely used method but the biggest drawback is it's limitation to hexahedral elements. For complex heterogeneous models with a tunnel included, it is a better choice to use the NDG, which needs more computation time but can be adapted to tetrahedral elements. Using this technique, we can perform high resolution simulations of waves initialized by a single force acting either on the front face or the side face of the tunnel. The aim is to produce waves that travel mainly in the direction of the tunnel track and to get as much information as possible from the backscattered part of the wave field.

  1. Lateral wave propagation in a three-layered medium

    NASA Astrophysics Data System (ADS)

    Dunn, John M.

    1986-09-01

    The effect of an intervening layer on a lateral wave which propagates along the interface between two different electrical media is considered. The lateral wave travels down from a time-harmonic electric dipole source in the upper region, through the middle region, and parallel to the interface between the middle and lower regions. It is assumed that the magnitude of the wavenumber in the upper medium is much greater than that of the middle, which in turn is much greater than that of the lower. The middle layer affects the lateral wave in two ways. It multiplies the usual lateral wave results by an overall factor which depends on the thickness of the slab and the electrical properties of the three media. It also changes at what distance the transition from intermediate to far field behavior occurs. Typically, the presence of the slab increases the magnitude of the fields near the transmitter, but leads to smaller field strengths in the far field region. The formulas are derived in two ways. The first utilizes an iterative procedure based on impedance boundary conditions and boundary layer theory. The second uses the more traditional steepest descent evaluation of the exact integrals available for the problem.

  2. Evolution of the derivative skewness for nonlinearly propagating waves.

    PubMed

    Reichman, Brent O; Muhlestein, Michael B; Gee, Kent L; Neilsen, Tracianne B; Thomas, Derek C

    2016-03-01

    The skewness of the first time derivative of a pressure waveform, or derivative skewness, has been used previously to describe the presence of shock-like content in jet and rocket noise. Despite its use, a quantitative understanding of derivative skewness values has been lacking. In this paper, the derivative skewness for nonlinearly propagating waves is investigated using analytical, numerical, and experimental methods. Analytical expressions for the derivative skewness of an initially sinusoidal plane wave are developed and, along with numerical data, are used to describe its behavior in the preshock, sawtooth, and old-age regions. Analyses of common measurement issues show that the derivative skewness is relatively sensitive to the effects of a smaller sampling rate, but less sensitive to the presence of additive noise. In addition, the derivative skewness of nonlinearly propagating noise is found to reach greater values over a shorter length scale relative to sinusoidal signals. A minimum sampling rate is recommended for sinusoidal signals to accurately estimate derivative skewness values up to five, which serves as an approximate threshold indicating significant shock formation.

  3. Longitudinal elastic wave propagation characteristics of inertant acoustic metamaterials

    NASA Astrophysics Data System (ADS)

    Kulkarni, Prateek P.; Manimala, James M.

    2016-06-01

    Longitudinal elastic wave propagation characteristics of acoustic metamaterials with various inerter configurations are investigated using their representative one-dimensional discrete element lattice models. Inerters are dynamic mass-amplifying mechanical elements that are activated by a difference in acceleration across them. They have a small device mass but can provide a relatively large dynamic mass presence depending on accelerations in systems that employ them. The effect of introducing inerters both in local attachments and in the lattice was examined vis-à-vis the propagation characteristics of locally resonant acoustic metamaterials. A simple effective model based on mass, stiffness, or their combined equivalent was used to establish dispersion behavior and quantify attenuation within bandgaps. Depending on inerter configurations in local attachments or in the lattice, both up-shift and down-shift in the bandgap frequency range and their extent are shown to be possible while retaining static mass addition to the host structure to a minimum. Further, frequency-dependent negative and even extreme effective-stiffness regimes are encountered. The feasibility of employing tuned combinations of such mass-delimited inertant configurations to engineer acoustic metamaterials that act as high-pass filters without the use of grounded elements or even as complete longitudinal wave inhibitors is shown. Potential device implications and strategies for practical applications are also discussed.

  4. Regional wave propagation using the discontinuous Galerkin method

    NASA Astrophysics Data System (ADS)

    Wenk, S.; Pelties, C.; Igel, H.; Käser, M.

    2012-08-01

    We present an application of the discontinuous Galerkin (DG) method to regional wave propagation. The method makes use of unstructured tetrahedral meshes, combined with a time integration scheme solving the arbitrary high-order derivative (ADER) Riemann problem. The ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain. The ADER-DG method is benchmarked for the accurate radiation of elastic waves excited by an explosive and a shear dislocation source. We compare real data measurements with synthetics of the 2009 L'Aquila event (central Italy). We take advantage of the geometrical flexibility of the approach to generate a European model composed of the 3-D EPcrust model, combined with the depth-dependent ak135 velocity model in the upper-mantle. The results confirm the applicability of the ADER-DG method for regional scale earthquake simulations, which provides an alternative to existing methodologies.

  5. Regional wave propagation using the discontinuous Galerkin method

    NASA Astrophysics Data System (ADS)

    Wenk, S.; Pelties, C.; Igel, H.; Käser, M.

    2013-01-01

    We present an application of the discontinuous Galerkin (DG) method to regional wave propagation. The method makes use of unstructured tetrahedral meshes, combined with a time integration scheme solving the arbitrary high-order derivative (ADER) Riemann problem. This ADER-DG method is high-order accurate in space and time, beneficial for reliable simulations of high-frequency wavefields over long propagation distances. Due to the ease with which tetrahedral grids can be adapted to complex geometries, undulating topography of the Earth's surface and interior interfaces can be readily implemented in the computational domain. The ADER-DG method is benchmarked for the accurate radiation of elastic waves excited by an explosive and a shear dislocation source. We compare real data measurements with synthetics of the 2009 L'Aquila event (central Italy). We take advantage of the geometrical flexibility of the approach to generate a European model composed of the 3-D EPcrust model, combined with the depth-dependent ak135 velocity model in the upper mantle. The results confirm the applicability of the ADER-DG method for regional scale earthquake simulations, which provides an alternative to existing methodologies.

  6. A Phased-Array Stimulator System for Studying Planar and Curved Cardiac Activation Wave Fronts

    PubMed Central

    Abbas, Rashida A.; Lin, Shien Fong; Mashburn, David; Xu, Junkai; Wikswo, John P.

    2009-01-01

    Wave front propagation in cardiac tissue is affected greatly by the geometry of the wave front. We describe a computer-controlled stimulator system that creates reproducible wave fronts of a predetermined shape and orientation for the investigation of the effects of wave front geometry. We conducted demonstration experiments on isolated perfused rabbit hearts, which were stained with the voltage-sensitive dye, di-4-ANEPPS. The wave fronts were imaged using a laser and a CCD camera. The stimulator and imaging systems have been used to characterize the relationship between wave front velocity and fiber orientation. This approach has potential applications in investigating curvature effects, testing numerical models of cardiac tissue, and creating complex wave fronts using one-, twoor three-dimensional electrode arrays. PMID:18232365

  7. Propagation of nonlinear, radiatively damped longitudinal waves along magnetic flux tubes in the solar atmosphere

    NASA Technical Reports Server (NTRS)

    Herbold, G.; Ulmschneider, P.; Spruit, H. C.; Rosner, R.

    1985-01-01

    For solar magnetic flux tubes three types of waves are compared: longitudinal MHD tube waves, acoustic tube waves propagating in the same tube geometry but with rigid walls and ordinary acoustic waves in plane geometry. It is found that the effect of the distensibility of the tube is small and that longitudinal waves are essentially acoustic tube waves. Due to the tube geometry there is considerable difference between longitudinal waves or acoustic tube waves and ordinary acoustic waves. Longitudinal waves as well as acoustic tube waves show a smaller amplitude growth, larger shock formation heights, smaller mean chromospheric temperature but a steeper dependence of the temperature gradient on wave period.

  8. Modelling Mechanical Wave Propagation: Guidelines and Experimentation of a Teaching-Learning Sequence

    ERIC Educational Resources Information Center

    Fazio, Claudio; Guastella, Ivan; Sperandeo-Mineo, Rosa Maria; Tarantino, Giovanni

    2008-01-01

    The present paper reports the design process and the experimentation of a teaching-learning sequence about the concept of mechanical wave propagation and the role played by media where waves are propagating. The sequence focuses on the central issue of the relationships between observable phenomena, like macroscopic behaviours of waves, and their…

  9. Parametric Excitations of Fast Plasma Waves by Counter-propagating Laser Beams

    SciTech Connect

    G. Shvets; N.J. Fisch

    2001-03-19

    Short- and long-wavelength plasma waves can become strongly coupled in the presence of two counter-propagating laser pump pulses detuned by twice the cold plasma frequency. What makes this four-wave interaction important is that the growth rate of the plasma waves occurs much faster than in the more obvious co-propagating geometry.

  10. A Problem-Based Approach to Elastic Wave Propagation: The Role of Constraints

    ERIC Educational Resources Information Center

    Fazio, Claudio; Guastella, Ivan; Tarantino, Giovanni

    2009-01-01

    A problem-based approach to the teaching of mechanical wave propagation, focused on observation and measurement of wave properties in solids and on modelling of these properties, is presented. In particular, some experimental results, originally aimed at measuring the propagation speed of sound waves in metallic rods, are used in order to deepen…

  11. Model test research of breakwater core material influence on wave propagation

    NASA Astrophysics Data System (ADS)

    Wang, Deng-ting; Sun, Tian-ting; Chen, Wei-qiu; Zhu, Jia-ling

    2016-10-01

    The interaction between waves and porous breakwater has an important theoretical significance and great application value of engineering. In this paper, the tests of the core material's influence in rubble mound breakwater on wave propagation are carried out. The relations among the transmitted wave height, incident wave element, and breakwater width are discussed. The calculation formula is obtained. The test results show that different core materials have obvious influence on wave propagation.

  12. Numerical Simulations of Upstream Propagating Solitary Waves and Wave Breaking In A Stratified Fjord

    NASA Astrophysics Data System (ADS)

    Stastna, M.; Peltier, W. R.

    In this talk we will discuss ongoing numerical modeling of the flow of a stratified fluid over large scale topography motivated by observations in Knight Inlet, a fjord in British Columbia, Canada. After briefly surveying the work done on the topic in the past we will discuss our latest set of simulations in which we have observed the gener- ation and breaking of three different types of nonlinear internal waves in the lee of the sill topography. The first type of wave observed is a large lee wave in the weakly strat- ified main portion of the water column, The second is an upward propagating internal wave forced by topography that breaks in the strong, near-surface pycnocline. The third is a train of upstream propagating solitary waves that, in certain circumstances, form as breaking waves consisting of a nearly solitary wave envelope and a highly unsteady core near the surface. Time premitting, we will comment on the implications of these results for our long term goal of quantifying tidally driven mixing in Knight Inlet.

  13. On the accurate simulation of tsunami wave propagation

    NASA Astrophysics Data System (ADS)

    Castro, C. E.; Käser, M.; Toro, E. F.

    2009-04-01

    A very important part of any tsunami early warning system is the numerical simulation of the wave propagation in the open sea and close to geometrically complex coastlines respecting bathymetric variations. Here we are interested in improving the numerical tools available to accurately simulate tsunami wave propagation on a Mediterranean basin scale. To this end, we need to accomplish some targets, such as: high-order numerical simulation in space and time, preserve steady state conditions to avoid spurious oscillations and describe complex geometries due to bathymetry and coastlines. We use the Arbitrary accuracy DERivatives Riemann problem method together with Finite Volume method (ADER-FV) over non-structured triangular meshes. The novelty of this method is the improvement of the ADER-FV scheme, introducing the well-balanced property when geometrical sources are considered for unstructured meshes and arbitrary high-order accuracy. In a previous work from Castro and Toro [1], the authors mention that ADER-FV schemes approach asymptotically the well-balanced condition, which was true for the test case mentioned in [1]. However, new evidence[2] shows that for real scale problems as the Mediterranean basin, and considering realistic bathymetry as ETOPO-2[3], this asymptotic behavior is not enough. Under these realistic conditions the standard ADER-FV scheme fails to accurately describe the propagation of gravity waves without being contaminated with spurious oscillations, also known as numerical waves. The main problem here is that at discrete level, i.e. from a numerical point of view, the numerical scheme does not correctly balance the influence of the fluxes and the sources. Numerical schemes that retain this balance are said to satisfy the well-balanced property or the exact C-property. This unbalance reduces, as we refine the spatial discretization or increase the order of the numerical method. However, the computational cost increases considerably this way

  14. Planar Superconducting Millimeter-Wave/Terahertz Channelizing Filter

    NASA Technical Reports Server (NTRS)

    Ehsan, Negar; U-yen, Kongpop; Brown, Ari; Hsieh, Wen-Ting; Wollack, Edward; Moseley, Samuel

    2013-01-01

    This innovation is a compact, superconducting, channelizing bandpass filter on a single-crystal (0.45 m thick) silicon substrate, which operates from 300 to 600 GHz. This device consists of four channels with center frequencies of 310, 380, 460, and 550 GHz, with approximately 50-GHz bandwidth per channel. The filter concept is inspired by the mammalian cochlea, which is a channelizing filter that covers three decades of bandwidth and 3,000 channels in a very small physical space. By using a simplified physical cochlear model, and its electrical analog of a channelizing filter covering multiple octaves bandwidth, a large number of output channels with high inter-channel isolation and high-order upper stopband response can be designed. A channelizing filter is a critical component used in spectrometer instruments that measure the intensity of light at various frequencies. This embodiment was designed for MicroSpec in order to increase the resolution of the instrument (with four channels, the resolution will be increased by a factor of four). MicroSpec is a revolutionary wafer-scale spectrometer that is intended for the SPICA (Space Infrared Telescope for Cosmology and Astrophysics) Mission. In addition to being a vital component of MicroSpec, the channelizing filter itself is a low-resolution spectrometer when integrated with only an antenna at its input, and a detector at each channel s output. During the design process for this filter, the available characteristic impedances, possible lumped element ranges, and fabrication tolerances were identified for design on a very thin silicon substrate. Iterations between full-wave and lumped-element circuit simulations were performed. Each channel s circuit was designed based on the availability of characteristic impedances and lumped element ranges. This design was based on a tabular type bandpass filter with no spurious harmonic response. Extensive electromagnetic modeling for each channel was performed. Four channels

  15. Direct observation of a propagating, planar-waveguide surface mode in a discontinuous film of metal nanoparticles.

    PubMed

    Soller, B J; Hall, D G

    2000-08-01

    We report the observation of p-polarized guided waves that propagate confined to the surface of a two-dimensional array of silver (Ag) nanoparticles of average particle diameter and film thickness of approximately 400 and 154 nm, respectively, and comparable interparticle spacing. We interpret resonant features in the attenuated total reflection angular spectrum as arising from the excitation of guided waves in our discontinuous samples. The excitation of these waves is a direct consequence of the interaction of the light field with the localized resonance of the conduction electrons in the individual metal nanoparticles.

  16. Making waves: initiation and propagation of corticothalamic Ca2+ waves in vivo.

    PubMed

    Stroh, Albrecht; Adelsberger, Helmuth; Groh, Alexander; Rühlmann, Charlotta; Fischer, Sebastian; Schierloh, Anja; Deisseroth, Karl; Konnerth, Arthur

    2013-03-20

    Corticothalamic slow oscillations of neuronal activity determine internal brain states. At least in the cortex, the electrical activity is associated with large neuronal Ca(2+) transients. Here we implemented an optogenetic approach to explore causal features of the generation of slow oscillation-associated Ca(2+) waves in the in vivo mouse brain. We demonstrate that brief optogenetic stimulation (3-20 ms) of a local group of layer 5 cortical neurons is sufficient for the induction of global brain Ca(2+) waves. These Ca(2+) waves are evoked in an all-or-none manner, exhibit refractoriness during repetitive stimulation, and propagate over long distances. By local optogenetic stimulation, we demonstrate that evoked Ca(2+) waves initially invade the cortex, followed by a secondary recruitment of the thalamus. Together, our results establish that synchronous activity in a small cluster of layer 5 cortical neurons can initiate a global neuronal wave of activity suited for long-range corticothalamic integration.

  17. Ultrasound shear wave simulation based on nonlinear wave propagation and Wigner-Ville Distribution analysis

    NASA Astrophysics Data System (ADS)

    Bidari, Pooya Sobhe; Alirezaie, Javad; Tavakkoli, Jahan

    2017-03-01

    This paper presents a method for modeling and simulation of shear wave generation from a nonlinear Acoustic Radiation Force Impulse (ARFI) that is considered as a distributed force applied at the focal region of a HIFU transducer radiating in nonlinear regime. The shear wave propagation is simulated by solving the Navier's equation from the distributed nonlinear ARFI as the source of the shear wave. Then, the Wigner-Ville Distribution (WVD) as a time-frequency analysis method is used to detect the shear wave at different local points in the region of interest. The WVD results in an estimation of the shear wave time of arrival, its mean frequency and local attenuation which can be utilized to estimate medium's shear modulus and shear viscosity using the Voigt model.

  18. Vortex Rossby wave propagation in baroclinic tropical cyclone-like vortices

    NASA Astrophysics Data System (ADS)

    Gao, Cen; Zhu, Ping

    2016-12-01

    This study extends the vortex Rossby wave (VRW) propagation theory into baroclinic tropical cyclone-like vortices. Dispersion relation, group velocities, and stagnation radius/height of propagating wave packets in baroclinic conditions are derived using the Wenzel-Kramers-Brillouin approximation. It is found that the VRW dispersion relation in baroclinic vortices in isentropic coordinates has the same mathematical form as that in barotropic vortices in pseudoheight coordinates. However, baroclinicity causes the vertical wave number to increase as wave packets propagate upward, resulting in different wave propagation features from those in barotropic vortices. The stagnation radius and level are constrained by a "critical" surface where the initial central angular phase velocity equals the angular velocity of the vortex. Depending on the specific structure of vortex basic-state baroclinicity and positions where asymmetries are located, the excited waves can either be trapped vertically and behave like those in barotropic conditions or effectively propagate upward but with their radial propagation largely suppressed.

  19. Dispersion characteristics of spin-electromagnetic waves in planar multiferroic structures

    SciTech Connect

    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.

  20. Experimental research on dust lifting by propagating shock wave

    NASA Astrophysics Data System (ADS)

    Żydak, P.; Oleszczak, P.; Klemens, R.

    2017-03-01

    The aim of the presented work was to study the dust lifting process from a layer of dust behind a propagating shock wave. The experiments were conducted with the use of a shock tube and a specially constructed, five-channel laser optical device enabling measurements at five positions located in one vertical plane along the height of the tube. The system enabled measurements of the delay in lifting up of the dust from the layer, and the vertical velocity of the dust cloud was calculated from the dust concentration measurements. The research was carried out for various initial conditions and for three fractions of black coal dust. In the presented tests, three shock wave velocities: 450, 490 and 518 m/s and three dust layer thicknesses, equal to 1.0, 1.5 and 2.0 mm, were taken into consideration. On the grounds of the obtained experimental results, it was assumed that the vertical component of the lifted dust velocity is a function of the dust particle diameter, the velocity of the air flow in the channel, the layer thickness and the dust bulk density. It appeared, however, that lifting up of the dust from the thick layers, thicker than 1 mm, is a more complex process than that from thin layers and still requires further research. A possible explanation is that the shock wave action upon the thick layer results in its aggregation in the first stage of the dispersing process, which suppresses the dust lifting process.

  1. Propagation of global shear Alfven waves in gyrokinetic tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Nishimura, Y.; Lin, Z.; Holod, I.; Chen, L.; Decyk, V.; Klasky, S.; Ma, K.; Adams, M.; Ethier, S.; Hahm, T.; Lee, W.; Lewandowski, J.; Rewoldt, G.; Wang, W.

    2006-04-01

    Employing the electromagnetic gyrokinetic simulation models, Alfven wave dynamics in global tokamak geometry is studied. Based on a small parameter expansion by the square-root of the electron-ion mass ratio, the fluid-kinetic hybrid electron model solves the adiabatic response in the lowest order and solves the kinetic response in the higher orders. We verify the propagation of shear Alfven waves in the absence of drives or damping mechanisms by perturbing the magnetic field lines at t=0 in a global eigenmode structure. The Alfven wave experiences continuum damping. In the presence of energetic particles, excitations of toroidal Alfven eigenmode (TAE) is expected within the frequency gap. With the ηi gradient drive, at a critical β value, the kinetic ballooning mode (KBM) is excited below the ideal MHD limit. W.W.Lee et al., Phys. Plasmas 8, 4435 (2001). Z.Lin and L.Chen, Phys. Plasmas 8, 1447 (2001). J.A.Tataronis and W. Grossman, Z. Phys. 14, 203 (1973). C.Z.Cheng, L.Chen, and M.S.Chance, Ann.Phys. 161, 21 (1984). C.Z.Cheng, Nucl. Fusion 22, 773 (1982).

  2. Application of the Parareal Algorithm for Acoustic Wave Propagation

    SciTech Connect

    Mercerat, Diego; Guillot, Laurent; Vilotte, Jean-Pierre

    2009-09-09

    We present an application of the parareal algorithm to solve wave propagation problems in the time domain. The parareal algorithm is based on a decomposition of the integration time interval in time slices. It involves a serial prediction step based on a coarse approximation, and a correction step (computed in parallel) based on a fine approximation within each time slice. In our case, the spatial discretization is based on a spectral element approximation which allows flexible and accurate wave simulations in complex geological media. Fully explicit time advancing schemes are classically used for both coarse and fine solvers.In a first stage, we solve the 1D acoustic wave equation in an homogeneous medium in order to test stability and convergence properties of the parareal algorithm. We confirmed the stability problems outlined by Bal and Farhat et al. for hyperbolic problems. These stability issues are mitigated by a time-discontinuous Galerkin discretization of the coarse solver. It may also involve a coarser spatial discretization (hp-refinement) which helps to preserve stability and allows more significant computer savings. Besides, we explore the contribution of elastodynamic homogenization to build consistent coarse grid solvers. Extension to 2D/3D realistic geological media is an ongoing work.

  3. FDTD Simulation on Terahertz Waves Propagation Through a Dusty Plasma

    NASA Astrophysics Data System (ADS)

    Wang, Maoyan; Zhang, Meng; Li, Guiping; Jiang, Baojun; Zhang, Xiaochuan; Xu, Jun

    2016-08-01

    The frequency dependent permittivity for dusty plasmas is provided by introducing the charging response factor and charge relaxation rate of airborne particles. The field equations that describe the characteristics of Terahertz (THz) waves propagation in a dusty plasma sheath are derived and discretized on the basis of the auxiliary differential equation (ADE) in the finite difference time domain (FDTD) method. Compared with numerical solutions in reference, the accuracy for the ADE FDTD method is validated. The reflection property of the metal Aluminum interlayer of the sheath at THz frequencies is discussed. The effects of the thickness, effective collision frequency, airborne particle density, and charge relaxation rate of airborne particles on the electromagnetic properties of Terahertz waves through a dusty plasma slab are investigated. Finally, some potential applications for Terahertz waves in information and communication are analyzed. supported by National Natural Science Foundation of China (Nos. 41104097, 11504252, 61201007, 41304119), the Fundamental Research Funds for the Central Universities (Nos. ZYGX2015J039, ZYGX2015J041), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20120185120012)

  4. Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media

    NASA Astrophysics Data System (ADS)

    Schmidt, Felix; Wagner, Norman; Lünenschloß, Peter; Toepfer, Hannes; Dietrich, Peter; Kaliorias, Andreas; Bumberger, Jan

    2015-04-01

    The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric

  5. Frequency Domain Modelling of Electromagnetic Wave Propagation in Layered Media

    NASA Astrophysics Data System (ADS)

    Schmidt, Felix; Lünenschloss, Peter; Mai, Juliane; Wagner, Norman; Töpfer, Hannes; Bumberger, Jan

    2016-04-01

    The amount of water in porous media such as soils and rocks is a key parameter when water resources are under investigation. Especially the quantitative spatial distribution and temporal evolution of water contents in soil formations are needed. In high frequency electromagnetic applications soil water content is quantitatively derived from the propagation behavior of electromagnetic waves along waveguides embedded in soil formations. The spatial distribution of the dielectric material properties along the waveguide can be estimated by numerical solving of the inverse problem based on the full wave forward model in time or frequency domain. However, current approaches mostly neglect or approximate the frequency dependence of the electromagnetic material properties of transfer function of the waveguide. As a first prove of concept a full two port broadband frequency domain forward model for propagation of transverse electromagnetic (TEM) waves in coaxial waveguide has been implemented. It is based on the propagation matrix approach for layered transmission line sections. Depending on the complexity of the material different models for the frequency dependent complex permittivity were applied. For the validation of the model a broadband frequency domain measurement with network analyzer technique was used. The measurement is based on a 20 cm long 50 Ohm 20/46 coaxial transmission line cell considering inhomogeneous material distributions. This approach allows (i) an increase of the waveguide calibration accuracy in comparison to conventional TDR based technique and (ii) the consideration of the broadband permittivity spectrum of the porous material. In order to systematic analyze the model, theoretical results were compared with measurements as well as 3D broadband finite element modeling of homogeneous and layered media in the coaxial transmission line cell. Defined standards (Teflon, dry glass beads, de-ionized water) were placed inside the line as the dielectric

  6. DETERMINATION OF TRANSVERSE DENSITY STRUCTURING FROM PROPAGATING MAGNETOHYDRODYNAMIC WAVES IN THE SOLAR ATMOSPHERE

    SciTech Connect

    Arregui, I.; Asensio Ramos, A.

    2013-06-01

    We present a Bayesian seismology inversion technique for propagating magnetohydrodynamic transverse waves observed in coronal waveguides. The technique uses theoretical predictions for the spatial damping of propagating kink waves in transversely inhomogeneous coronal waveguides. It combines wave amplitude damping length scales along the waveguide with theoretical results for resonantly damped propagating kink waves to infer the plasma density variation across the oscillating structures. Provided that the spatial dependence of the velocity amplitude along the propagation direction is measured and the existence of two different damping regimes is identified, the technique would enable us to fully constrain the transverse density structuring, providing estimates for the density contrast and its transverse inhomogeneity length scale.

  7. Effects of non-extensive electrons and positive /negative dust particles on modulational instability of dust-ion-acoustic solitary waves in non-planar geometry

    NASA Astrophysics Data System (ADS)

    Eghbali, M.; Farokhi, B.; Eslamifar, M.

    2017-01-01

    The nonlinear propagation of cylindrical and spherical dust-ion-acoustic (DIA) envelope solitary waves in unmagnetized dusty plasma consisting of dust particles with opposite polarity and non-extensive distribution of electron is investigated. By using the reductive perturbation method, the modified nonlinear Schrödinger (NLS) equation in cylindrical and spherical geometry is obtained. The modulational instability (MI) of DIA waves governed by the NLS equation is also presented. The effects of different ranges of the non-extensive parameter q on the MI are studied. The growth rate of the MI is also given for different values of q. It is found that the basic features of the DIA waves are significantly modified by non-extensive electron distribution, polarity of the net dust-charge number density and non-planar geometry.

  8. Near-planar TS waves and longitudinal vortices in channel flow - Nonlinear interaction and focussing

    NASA Technical Reports Server (NTRS)

    Hall, Philip; Smith, Frank T.

    1990-01-01

    The nonlinear interaction between planar or near-planar Tollmien-Schlichting waves and longitudinal vortices, induced or input, is considered theoretically for channel flows at high Reynolds numbers. Several kinds of nonlinear interaction, dependent on the input amplitudes and wavenumbers or on previously occurring interactions, are found and inter-related. The first, Type 1, is studied the most here and it usually produces spanwise focusing of both the wave and the vortex motion, within a finite scaled time, along with enhancement of both their amplitudes. This then points to the nonlinear interaction Type 2 where new interactive effects come into force to drive the wave and the vortex nonlinearly. Types 3, 4 correspond to still higher amplitudes, with 3 being related to 2, while 4 is connected with a larger-scale interaction 5 studied in an allied paper. Both 3, 4 are subsets of the full three-dimensional triple-deck-lie interaction, 6. The strongest nonlinear interactions are those of 4, 5, 6 since they alter the mean-flow profile substantially, i.e., by an O(1) relative amount. All the types of nonlinear interaction, however, can result in the formation of focused responses in the sense of spanwise concentrations and/or amplifications of vorticity and wave amplitude.

  9. Near-planar TS waves and longitudinal vortices in channel flow: Nonlinear interaction and focusing

    NASA Technical Reports Server (NTRS)

    Hall, P.; Smith, F. T.

    1989-01-01

    The nonlinear interaction between planar or near-planar Tollmien-Schlichting waves and longitudinal vortices, induced or input, is considered theoretically for channel flows at high Reynolds numbers. Several kinds of nonlinear interaction, dependent on the input amplitudes and wavenumbers or on previously occurring interactions, are found and inter-related. The first, Type 1, is studied the most here and it usually produces spanwise focusing of both the wave and the vortex motion, within a finite scaled time, along with enhancement of both their amplitudes. This then points to the nonlinear interaction Type 2 where new interactive effects come into force to drive the wave and the vortex nonlinearly. Types 3, 4 correspond to still higher amplitudes, with 3 being related to 2, while 4 is connected with a larger-scale interaction 5 studied in an allied paper. Both 3, 4 are subsets of the full three-dimensional triple-deck-lie interaction, 6. The strongest nonlinear interactions are those of 4, 5, 6 since they alter the mean-flow profile substantially, i.e., by an 0(1) relative amount. All the types of nonlinear interaction however can result in the formation of focussed responses in the sense of spanwise concentrations and/or amplifications of vorticity and wave amplitude.

  10. TROTT computer program for two-dimensional stress wave propagation, volume 3

    NASA Astrophysics Data System (ADS)

    Seaman, L.; Curran, D. R.

    1980-04-01

    TROTT is a Lagrangian finite-difference computer program for calculating two dimensional stress wave propagation through solid, porous, and composite materials. The stress waves may be caused by impact, detonation of an explosive, or a prescribed velocity. The calculational procedure is the standard leapfrog method of von Neumann and Richtmyer, using artificial viscosity to smooth shock fronts. Quadrilateral or triangular cells are used. The momentum relations are derived by treating the cells as finite elements. Axisymmetric or planar flow can be handled. The constitutive relations include the standard Mie-Gruneisen equation-of-state and elastic-plastic, work-hardening deviator stress relations. A polytropic gas and detonating flow relations are provided for explosives. Ductile and brittle fracture and shear banding are provided by nucleation and growth models. Porous materials can be represented by a cap plasticity model. A model for layered composites is also present. The code is constructed for easy insertion of additional material models. The number of extra variables required for each cell for a material model can be specified on an input card. This manual includes many sample problems, a derivation of the flow equations, and a discussion of material models.

  11. Coupling layers regularizes wave propagation in stochastic neural fields

    NASA Astrophysics Data System (ADS)

    Kilpatrick, Zachary P.

    2014-02-01

    We explore how layered architectures influence the dynamics of stochastic neural field models. Our main focus is how the propagation of waves of neural activity in each layer is affected by interlaminar coupling. Synaptic connectivities within and between each layer are determined by integral kernels of an integrodifferential equation describing the temporal evolution of neural activity. Excitatory neural fields, with purely positive connectivities, support traveling fronts in each layer, whose speeds are increased when coupling between layers is considered. Studying the effects of noise, we find coupling reduces the variance in the position of traveling fronts, as long as the noise sources to each layer are not completely correlated. Neural fields with asymmetric connectivity support traveling pulses whose speeds are decreased by interlaminar coupling. Again, coupling reduces the variance in traveling pulse position. Asymptotic analysis is performed using a small-noise expansion, assuming interlaminar connectivity scales similarly.

  12. Propagation mechanism of laser-supported detonation wave

    NASA Astrophysics Data System (ADS)

    Fujiwara, T.; Tsujioka, M.

    1991-01-01

    Modeling and numerical analysis for a flowfield caused by intense laser absorption are done, where a propagation phenomenon called LSD (Laser-Supported Detonation) appears. The problem is formulated on the basis of microscopic physics and chemistry including several elementary reactions and an absorption process called inverse bremsstrahlung. To take account of thermal-nonequilibrium in plasma where electron temperature dominates other phenomena, the electron/heavy-particle two-temperature model is used. Utilizing a time splitting technique, the problem treating the interaction between flowfield and radiation field is divided into a chemically-frozen gasdynamics and a radiation-absorption-induced chemical reaction. By this technique, the initial stage of an LSD wave is simulated.

  13. Vibration and wave propagation characteristics of multisegmented elastic beams

    NASA Technical Reports Server (NTRS)

    Nayfeh, Adnan H.; Hawwa, Muhammad A.

    1990-01-01

    Closed form analytical solutions are derived for the vibration and wave propagation of multisegmented elastic beams. Each segment is modeled as a Timoshenko beam with possible inclusion of material viscosity, elastic foundation and axial forces. Solutions are obtained by using transfer matrix methods. According to these methods formal solutions are first constructed which relate the deflection, slope, moment and shear force of one end of the individual segment to those of the other. By satisfying appropriate continuity conditions at segment junctions, a global 4x4 matrix results which relates the deflection, slope, moment and shear force of one end of the beam to those of the other. If any boundary conditions are subsequently invoked on the ends of the beam one gets the appropriate characteristic equation for the natural frequencies. Furthermore, by invoking appropriate periodicity conditions the dispersion relation for a periodic system is obtained. A variety of numerical examples are included.

  14. A wave action equation for water waves propagating on vertically sheared flows

    NASA Astrophysics Data System (ADS)

    Quinn, Brenda; Toledo, Yaron; Shrira, Victor

    2015-04-01

    The coexistence of motions of different scales in oceans and other natural water basins presents a challenge for their dynamic modeling. For water waves on currents, an asymptotic procedure exploiting the separation of scales allows the modeling of two motions of a qualitatively different nature, the fast shortwaves on the surface and the dynamics of the slow, long currents. Most wave forecast models are based on the wave action equation which is a conservation equation which takes into account the propagation of the wave energy in geographic space, shoaling, refraction, diffraction and also source terms which account for generation, wave-wave interactions and dissipation of the energy. Water waves almost always propagate on currents with a vertical structure such as currents directed towards the beach accompanied by an under-current directed back toward the deep sea or wind-induced currents which change magnitude with depth due to viscosity effects. On larger scales they also change their direction due to the Coriolis force as described by the Ekman spiral. This implies that the existing wave models, which assume vertically-averaged currents, is an approximation which is far from realistic. In recent years, ocean circulation models have significantly improved with the capability to model vertically-sheared current profiles in contrast with the earlier vertically-averaged current profiles. Further advancements have coupled wave action models to circulation models to relate the mutual effects between the two types of motion. Restricting wave models to vertically-averaged current profiles is obviously problematic in these cases and the primary goal of this work is to derive and examine a general wave action equation which accounts for this shortcoming. Combining two previous theoretical approaches [Voronovich, 1976; Skop, 1987], the developed wave action formulation greatly improves the representation of linear wave-current interaction in the case of tidal inlets

  15. Optimised prefactored compact schemes for linear wave propagation phenomena

    NASA Astrophysics Data System (ADS)

    Rona, A.; Spisso, I.; Hall, E.; Bernardini, M.; Pirozzoli, S.

    2017-01-01

    A family of space- and time-optimised prefactored compact schemes are developed that minimise the computational cost for given levels of numerical error in wave propagation phenomena, with special reference to aerodynamic sound. This work extends the approach of Pirozzoli [1] to the MacCormack type prefactored compact high-order schemes developed by Hixon [2], in which their shorter Padé stencil from the prefactorisation leads to a simpler enforcement of numerical boundary conditions. An explicit low-storage multi-step Runge-Kutta integration advances the states in time. Theoretical predictions for spatial and temporal error bounds are derived for the cost-optimised schemes and compared against benchmark schemes of current use in computational aeroacoustic applications in terms of computational cost for a given relative numerical error value. One- and two-dimensional test cases are presented to examine the effectiveness of the cost-optimised schemes for practical flow computations. An effectiveness up to about 50% higher than the standard schemes is verified for the linear one-dimensional advection solver, which is a popular baseline solver kernel for computational physics problems. A substantial error reduction for a given cost is also obtained in the more complex case of a two-dimensional acoustic pulse propagation, provided the optimised schemes are made to operate close to their nominal design points.

  16. Modes in light wave propagating in semiconductor laser

    NASA Technical Reports Server (NTRS)

    Manko, Margarita A.

    1994-01-01

    The study of semiconductor laser based on an analogy of the Schrodinger equation and an equation describing light wave propagation in nonhomogeneous medium is developed. The active region of semiconductor laser is considered as optical waveguide confining the electromagnetic field in the cross-section (x,y) and allowing waveguide propagation along the laser resonator (z). The mode structure is investigated taking into account the transversal and what is the important part of the suggested consideration longitudinal nonhomogeneity of the optical waveguide. It is shown that the Gaussian modes in the case correspond to spatial squeezing and correlation. Spatially squeezed two-mode structure of nonhomogeneous optical waveguide is given explicitly. Distribution of light among the laser discrete modes is presented. Properties of the spatially squeezed two-mode field are described. The analog of Franck-Condon principle for finding the maxima of the distribution function and the analog of Ramsauer effect for control of spatial distribution of laser emission are discussed.

  17. Radio-wave propagation for space communications systems

    NASA Technical Reports Server (NTRS)

    Ippolito, L. J.

    1981-01-01

    The most recent information on the effects of Earth's atmosphere on space communications systems is reviewed. The design and reliable operation of satellite systems that provide the many applications in space which rely on the transmission of radio waves for communications and scientific purposes are dependent on the propagation characteristics of the transmission path. The presence of atmospheric gases, clouds, fog, precipitation, and turbulence causes uncontrolled variations in the signal characteristics. These variations can result in a reduction of the quality and reliability of the transmitted information. Models and other techniques are used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz have been reviewed. Particular emphasis has been placed on the effects of precipitation on the Earth/space path, including rain attenuation, and ice particle depolarization. Other factors are sky noise, antenna gain degradation, scintillations, and bandwidth coherence. Each of the various propagation factors has an effect on design criteria for communications systems. These criteria include link reliability, power margins, noise contribution, modulation and polarization factors, channel cross talk, error rate, and bandwidth limitations.

  18. Waves of DNA: Propagating excitations in extended nanoconfined polymers

    NASA Astrophysics Data System (ADS)

    Klotz, Alexander R.; de Haan, Hendrick W.; Reisner, Walter W.

    2016-10-01

    We use a nanofluidic system to investigate the emergence of thermally driven collective phenomena along a single polymer chain. In our approach, a single DNA molecule is confined in a nanofluidic slit etched with arrays of embedded nanocavities; the cavity lattice is designed so that a single chain occupies multiple cavities. Fluorescent video-microscopy data shows fluctuations in intensity between cavities, including waves of excess fluorescence that propagate across the cavity-straddling molecule, corresponding to propagating fluctuations of contour overdensity in the cavities. The transfer of DNA between neighboring pits is quantified by examining the correlation in intensity fluctuations between neighboring cavities. Correlations grow from an anticorrelated minimum to a correlated maximum before decaying, corresponding to a transfer of contour between neighboring cavities at a fixed transfer time scale. The observed dynamics can be modeled using Langevin dynamics simulations and a minimal lattice model of coupled diffusion. This study shows how confinement-based sculpting of the polymer equilibrium configuration, by renormalizing the physical system into a series of discrete cavity states, can lead to new types of dynamic collective phenomena.

  19. Propagation of Electromagnetic Waves in Two Dimensionally Periodic Media

    NASA Astrophysics Data System (ADS)

    Dong, Tian-Lin

    1985-12-01

    The propagation of electromagnetic waves in two dimensionally periodic structure is systematically investigated, to provide the basic theory for two dimensionally modulated dielectric waveguide. A canonical two dimensionally periodic medium of infinite extent, whose dielectic constant varies sinusoidally in two orthogonal directions, is first examined. The charact solutions are represented exactly by a double Fourier series which is known as the Floquet solution. The harmonic amplitudes of the Floquet solution are determined by a five-term recurrence relation in the vector form, properly taking into account the hybrid-mode nature of the propagation problem. The five-term recurrence relation is then treated by different approaches so that clear physical pictures and practical numerical methods can be obtained. The characteristic solutions for two dimensionally periodic medium are then applied to the boundary-value problem of multi-layer dielectric waveguides containing a finite layer of periodic medium. As an example, the guidance problems are analysed and the numerical analysis of the dispersion characteristics are then carried out. Besides the canonical medium as a model, more general two dimensionally periodic medium are also discussed.

  20. Stress Wave Propagation Across a Rock Mass with Two Non-parallel Joints

    NASA Astrophysics Data System (ADS)

    Chai, S. B.; Li, J. C.; Zhang, Q. B.; Li, H. B.; Li, N. N.

    2016-10-01

    A rock mass includes a number of joints, which govern the mechanical behavior of the rock mass and greatly affect stress wave propagation. Generally, joints do not parallel with each other, resulting in multiple wave reflections between joints and complex wave propagation process in rock masses. The present study presents an approach to analyze stress wave propagation through a rock mass with two non-parallel joints when the angle between the two joints is <10°. For incident P-wave impinging on this kind of rock mass, multiple reflections take place between the two joints. Meanwhile, transmitted waves are generated and propagate successively away from the joints. The mathematical expressions for P-wave propagation across the two joints are established in time domain by analyzing the wave field in the rock mass. By comparing with the result from numerical simulation, the new approach is proved to be effective to analyze wave propagation across two non-parallel joints, where the influence of joint tips on wave propagation is neglected. Parametric studies show that the joint stiffness, joint angle and frequency of incident wave have different effects on transmission and reflection coefficients.

  1. On propagation of electromagnetic and gravitational waves in the expanding Universe

    NASA Astrophysics Data System (ADS)

    Gladyshev, V. O.

    2016-07-01

    The purpose of this study was to obtain an equation for the propagation time of electromagnetic and gravitational waves in the expanding Universe. The velocity of electromagnetic waves propagation depends on the velocity of the interstellar medium in the observer's frame of reference. Gravitational radiation interacts weakly with the substance, so electromagnetic and gravitational waves propagate from a remote astrophysical object to the terrestrial observer at different time. Gravitational waves registration enables the inverse problem solution - by the difference in arrival time of electromagnetic and gravitational-wave signal, we can determine the characteristics of the emitting area of the astrophysical object.

  2. Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves.

    PubMed

    Sun, Shulin; He, Qiong; Xiao, Shiyi; Xu, Qin; Li, Xin; Zhou, Lei

    2012-04-01

    The arbitrary control of electromagnetic waves is a key aim of photonic research. Although, for example, the control of freely propagating waves (PWs) and surface waves (SWs) has separately become possible using transformation optics and metamaterials, a bridge linking both propagation types has not yet been found. Such a device has particular relevance given the many schemes of controlling electromagnetic waves at surfaces and interfaces, leading to trapped rainbows, lensing, beam bending, deflection, and even anomalous reflection/refraction. Here, we demonstrate theoretically and experimentally that a specific gradient-index meta-surface can convert a PW to a SW with nearly 100% efficiency. Distinct from conventional devices such as prism or grating couplers, the momentum mismatch between PW and SW is compensated by the reflection-phase gradient of the meta-surface, and a nearly perfect PW-SW conversion can happen for any incidence angle larger than a critical value. Experiments in the microwave region, including both far-field and near-field characterizations, are in excellent agreement with full-wave simulations. Our findings may pave the way for many applications, including high-efficiency surface plasmon couplers, anti-reflection surfaces, light absorbers, and so on.

  3. Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves

    NASA Astrophysics Data System (ADS)

    Sun, Shulin; He, Qiong; Xiao, Shiyi; Xu, Qin; Li, Xin; Zhou, Lei

    2012-05-01

    The arbitrary control of electromagnetic waves is a key aim of photonic research. Although, for example, the control of freely propagating waves (PWs; refs , , , , , ) and surface waves (SWs; refs , , , ) has separately become possible using transformation optics and metamaterials, a bridge linking both propagation types has not yet been found. Such a device has particular relevance given the many schemes of controlling electromagnetic waves at surfaces and interfaces, leading to trapped rainbows, lensing, beam bending, deflection, and even anomalous reflection/refraction. Here, we demonstrate theoretically and experimentally that a specific gradient-index meta-surface can convert a PW to a SW with nearly 100% efficiency. Distinct from conventional devices such as prism or grating couplers, the momentum mismatch between PW and SW is compensated by the reflection-phase gradient of the meta-surface, and a nearly perfect PW-SW conversion can happen for any incidence angle larger than a critical value. Experiments in the microwave region, including both far-field and near-field characterizations, are in excellent agreement with full-wave simulations. Our findings may pave the way for many applications, including high-efficiency surface plasmon couplers, anti-reflection surfaces, light absorbers, and so on.

  4. Modeling the propagation of electromagnetic waves over the surface of the human body

    NASA Astrophysics Data System (ADS)

    Vendik, I. B.; Vendik, O. G.; Kirillov, V. V.; Pleskachev, V. V.; Tural'chuk, P. A.

    2016-12-01

    The results of modeling and an experimental study of electromagnetic (EM) waves in microwave range propagating along the surface of the human body have been presented. The parameters of wave propagation, such as the attenuation and phase velocity, have also been investigated. The calculation of the propagation of EM waves by the numerical method FDTD (finite difference time domain), as well as the use of the analytical model of the propagation of the EM wave along flat and curved surfaces has been fulfilled. An experimental study on a human body has been conducted. It has been shown that creeping waves are slow and exhibit a noticeable dispersion, while the surface waves are dispersionless and propagate at the speed of light in free space. A comparison of the results of numerical simulation, analytical calculation, and experimental investigations at a frequency of 2.55 GHz has been carried out.

  5. Stationary propagation of a wave segment along an inhomogeneous excitable stripe

    NASA Astrophysics Data System (ADS)

    Gao, Xiang; Zhang, Hong; Zykov, Vladimir; Bodenschatz, Eberhard

    2014-03-01

    We report a numerical and theoretical study of an excitation wave propagating along an inhomogeneous stripe of an excitable medium. The stripe inhomogeneity is due to a jump of the propagation velocity in the direction transverse to the wave motion. Stationary propagating wave segments of rather complicated curved shapes are observed. We demonstrate that the stationary segment shape strongly depends on the initial conditions which are used to initiate the excitation wave. In a certain parameter range, the wave propagation is blocked at the inhomogeneity boundary, although the wave propagation is supported everywhere within the stripe. A free-boundary approach is applied to describe these phenomena which are important for a wide variety of applications from cardiology to information processing.

  6. Explicit schemes for time propagating many-body wave functions

    NASA Astrophysics Data System (ADS)

    Frapiccini, Ana Laura; Hamido, Aliou; Schröter, Sebastian; Pyke, Dean; Mota-Furtado, Francisca; O'Mahony, Patrick F.; Madroñero, Javier; Eiglsperger, Johannes; Piraux, Bernard

    2014-02-01

    Accurate theoretical data on many time-dependent processes in atomic and molecular physics and in chemistry require the direct numerical ab initio solution of the time-dependent Schrödinger equation, thereby motivating the development of very efficient time propagators. These usually involve the solution of very large systems of first-order differential equations that are characterized by a high degree of stiffness. In this contribution, we analyze and compare the performance of the explicit one-step algorithms of Fatunla and Arnoldi. Both algorithms have exactly the same stability function, therefore sharing the same stability properties that turn out to be optimum. Their respective accuracy, however, differs significantly and depends on the physical situation involved. In order to test this accuracy, we use a predictor-corrector scheme in which the predictor is either Fatunla's or Arnoldi's algorithm and the corrector, a fully implicit four-stage Radau IIA method of order 7. In this contribution, we consider two physical processes. The first one is the ionization of an atomic system by a short and intense electromagnetic pulse; the atomic systems include a one-dimensional Gaussian model potential as well as atomic hydrogen and helium, both in full dimensionality. The second process is the decoherence of two-electron quantum states when a time-independent perturbation is applied to a planar two-electron quantum dot where both electrons are confined in an anharmonic potential. Even though the Hamiltonian of this system is time independent the corresponding differential equation shows a striking stiffness which makes the time integration extremely difficult. In the case of the one-dimensional Gaussian potential we discuss in detail the possibility of monitoring the time step for both explicit algorithms. In the other physical situations that are much more demanding in term of computations, we show that the accuracy of both algorithms depends strongly on the degree

  7. Propagation of impact-induced shock waves in porous sandstone using mesoscale modeling

    NASA Astrophysics Data System (ADS)

    GÜLdemeister, Nicole; WÜNnemann, Kai; Durr, Nathanael; Hiermaier, Stefan

    2013-01-01

    Abstract-Generation and <span class="hlt">propagation</span> of shock <span class="hlt">waves</span> by meteorite impact is significantly affected by material properties such as porosity, water content, and strength. The objective of this work was to quantify processes related to the shock-induced compaction of pore space by numerical modeling, and compare the results with data obtained in the framework of the Multidisciplinary Experimental and Modeling Impact Research Network (MEMIN) impact experiments. We use mesoscale models resolving the collapse of individual pores to validate macroscopic (homogenized) approaches describing the bulk behavior of porous and water-saturated materials in large-scale models of crater formation, and to quantify localized shock amplification as a result of pore space crushing. We carried out a suite of numerical models of <span class="hlt">planar</span> shock <span class="hlt">wave</span> <span class="hlt">propagation</span> through a well-defined area (the "sample") of porous and/or water-saturated material. The porous sample is either represented by a homogeneous unit where porosity is treated as a state variable (macroscale model) and water content by an equation of state for mixed material (ANEOS) or by a defined number of individually resolved pores (mesoscale model). We varied porosity and water content and measured thermodynamic parameters such as shock <span class="hlt">wave</span> velocity and particle velocity on meso- and macroscales in separate simulations. The mesoscale models provide additional data on the heterogeneous distribution of peak shock pressures as a consequence of the complex superposition of reflecting rarefaction <span class="hlt">waves</span> and shock <span class="hlt">waves</span> originating from the crushing of pores. We quantify the bulk effect of porosity, the reduction in shock pressure, in terms of Hugoniot data as a function of porosity, water content, and strength of a quartzite matrix. We find a good agreement between meso-, macroscale models and Hugoniot data from shock experiments. We also propose a combination of a porosity compaction model (ɛ-α model) that was</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EJPh...38b5209Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EJPh...38b5209Y"><span id="translatedtitle">Understanding the power reflection and transmission coefficients of a plane <span class="hlt">wave</span> at a <span class="hlt">planar</span> interface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ye, Qian; Jiang, Yikun; Lin, Haoze</p> <p>2017-03-01</p> <p>In most textbooks, after discussing the partial transmission and reflection of a plane <span class="hlt">wave</span> at a <span class="hlt">planar</span> interface, the power (energy) reflection and transmission coefficients are introduced by calculating the normal-to-interface components of the Poynting vectors for the incident, reflected and transmitted <span class="hlt">waves</span>, separately. Ambiguity arises among students since, for the Poynting vector to be interpreted as the energy flux density, on the incident (reflected) side, the electric and magnetic fields involved must be the total fields, namely, the sum of incident and reflected fields, instead of the partial fields which are just the incident (reflected) fields. The interpretation of the cross product of partial fields as energy flux has not been obviously justified in most textbooks. Besides, the plane <span class="hlt">wave</span> is actually an idealisation that is only ever found in textbooks, then what do the reflection and transmission coefficients evaluated for a plane <span class="hlt">wave</span> really mean for a real beam of limited extent? To provide a clearer physical picture, we exemplify a light beam of finite transverse extent by a fundamental Gaussian beam and simulate its reflection and transmission at a <span class="hlt">planar</span> interface. Due to its finite transverse extent, we can then insert the incident fields or reflected fields as total fields into the expression of the Poynting vector to evaluate the energy flux and then power reflection and transmission coefficients. We demonstrate that the power reflection and transmission coefficients of a beam of finite extent turn out to be the weighted sum of the corresponding coefficients for all constituent plane <span class="hlt">wave</span> components that form the beam. The power reflection and transmission coefficients of a single plane <span class="hlt">wave</span> serve, in turn, as the asymptotes for the corresponding coefficients of a light beam as its width expands infinitely.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19582074','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19582074"><span id="translatedtitle">Analytical theory of <span class="hlt">wave</span> <span class="hlt">propagation</span> through stacked fishnet metamaterials.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Marqués, R; Jelinek, L; Mesa, F; Medina, F</p> <p>2009-07-06</p> <p>This work analyzes the electromagnetic <span class="hlt">wave</span> <span class="hlt">propagation</span> through periodically stacked fishnets from zero frequency to the first Wood's anomaly. It is shown that, apart from Fabry-Perot resonances, these structures support two transmission bands that can be backward under the appropriate conditions. The first band starts at Wood's anomaly and is closely related to the well-known phenomena of extraordinary transmission through a single fishnet. The second band is related to the resonances of the fishnet holes. In both cases, the in-plane periodicity of the fishnet cannot be made electrically small, which prevents any attempt of homogenization of the structure along the fishnet planes. However, along the normal direction, even with very small periodicity transmission is still possible. An homogenization procedure can then be applied along this direction, thus making that the structure can behave as a backward-<span class="hlt">wave</span> transmission line for such transmission bands. Closed-form design formulas will be provided by the analytical formulation here presented. These formulas have been carefully validated by intensive numerical computations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999GeoJI.136..431J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999GeoJI.136..431J"><span id="translatedtitle">P-SV-<span class="hlt">wave</span> <span class="hlt">propagation</span> in heterogeneous media: grid method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jianfeng, Zhang; Tielin, Liu</p> <p>1999-02-01</p> <p>We present a new numerical modelling algorithm for P-SV-<span class="hlt">wave</span> <span class="hlt">propagation</span> in heterogeneous media, which is named the grid method in this paper. Similar to the finite-element method in the discretization of a numerical mesh, the grid method is flexible in incorporating surface topography and curved interfaces. The grid method, in the same way as the staggered-grid finite-difference scheme, is developed from the first-order velocity-stress hyperbolic system of elastic <span class="hlt">wave</span> equations. The free-surface conditions are satisfied naturally for the grid method. The method, with its small numerical dispersion and good stability, is of high accuracy and low computational cost. Each time step needs 34M+N multiplication operations and 26M+N addition operations for N nodes and M triangular grids. In this paper, the triangular grid method is discussed in detail, and the numerical dispersion, stability criterion and numerical simulations are presented. The grid method based on triangular grids and quadrangular grids is also studied here.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFMNG43B0570S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFMNG43B0570S"><span id="translatedtitle">Simulation of 3D Global <span class="hlt">Wave</span> <span class="hlt">Propagation</span> Through Geodynamic Models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schuberth, B.; Piazzoni, A.; Bunge, H.; Igel, H.; Steinle-Neumann, G.</p> <p>2005-12-01</p> <p>This project aims at a better understanding of the forward problem of global 3D <span class="hlt">wave</span> <span class="hlt">propagation</span>. We use the spectral element program "SPECFEM3D" (Komatitsch and Tromp, 2002a,b) with varying input models of seismic velocities derived from mantle convection simulations (Bunge et al., 2002). The purpose of this approach is to obtain seismic velocity models independently from seismological studies. In this way one can test the effects of varying parameters of the mantle convection models on the seismic <span class="hlt">wave</span> field. In order to obtain the seismic velocities from the temperature field of the geodynamical simulations we follow a mineral physics approach. Assuming a certain mantle composition (e.g. pyrolite with CMASF composition) we compute the stable phases for each depth (i.e. pressure) and temperature by system Gibbs free energy minimization. Elastic moduli and density are calculated from the equations of state of the stable mineral phases. For this we use a mineral physics database derived from calorimetric experiments (enthalphy and entropy of formation, heat capacity) and EOS parameters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19830028229','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19830028229"><span id="translatedtitle">Ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in two-phase media: Spherical inclusions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Fu, L. S.; Sheu, Y. C.</p> <p>1983-01-01</p> <p>The scattering theory, recently developed via the extended method of equivalent inclusion, is used to study the <span class="hlt">propagation</span> of time-harmonic <span class="hlt">waves</span> in two-phase media of elastic matrix with randomly distributed elastic spherical inclusion materials. The elastic moduli and mass density of the composite medium are determined as functions of frequencies when given properties and concentration of the spheres and the matrix. Velocity and attenuation of ultrasonic <span class="hlt">waves</span> in two-phase media are determined for cases of distributed spheres and localized damage. An averaging theorem that requires the equivalence of the strain energy and the kinetic energy between the effective medium and the original matrix with spherical inhomogeneities is employed to derive the effective moduli and mass density. The functional dependency of these quantities upon frequencies and concentration provides a method of data analysis in ultrasonic evaluation of material properties. Numerical results or moduli, velocity and/or attenuation as functions of concentration of inclusion material, or porosity, are graphically displayed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003PApGe.160..509W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003PApGe.160..509W"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">Propagation</span>, Scattering and Imaging Using Dual-domain One-way and One-return <span class="hlt">Propagators</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wu, R.-S.</p> <p></p> <p>- Dual-domain one-way <span class="hlt">propagators</span> implement <span class="hlt">wave</span> <span class="hlt">propagation</span> in heterogeneous media in mixed domains (space-wavenumber domains). One-way <span class="hlt">propagators</span> neglect <span class="hlt">wave</span> reverberations between heterogeneities but correctly handle the forward multiple-scattering including focusing/defocusing, diffraction, refraction and interference of <span class="hlt">waves</span>. The algorithm shuttles between space-domain and wavenumber-domain using FFT, and the operations in the two domains are self-adaptive to the complexity of the media. The method makes the best use of the operations in each domain, resulting in efficient and accurate <span class="hlt">propagators</span>. Due to recent progress, new versions of dual-domain methods overcame some limitations of the classical dual-domain methods (phase-screen or split-step Fourier methods) and can <span class="hlt">propagate</span> large-angle <span class="hlt">waves</span> quite accurately in media with strong velocity contrasts. These methods can deliver superior image quality (high resolution/high fidelity) for complex subsurface structures. One-way and one-return (De Wolf approximation) <span class="hlt">propagators</span> can be also applied to <span class="hlt">wave</span>-field modeling and simulations for some geophysical problems. In the article, a historical review and theoretical analysis of the Born, Rytov, and De Wolf approximations are given. A review on classical phase-screen or split-step Fourier methods is also given, followed by a summary and analysis of the new dual-domain <span class="hlt">propagators</span>. The applications of the new <span class="hlt">propagators</span> to seismic imaging and modeling are reviewed with several examples. For seismic imaging, the advantages and limitations of the traditional Kirchhoff migration and time-space domain finite-difference migration, when applied to 3-D complicated structures, are first analyzed. Then the special features, and applications of the new dual-domain methods are presented. Three versions of GSP (generalized screen <span class="hlt">propagators</span>), the hybrid pseudo-screen, the wide-angle Padé-screen, and the higher-order generalized screen <span class="hlt">propagators</span> are discussed. Recent</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009PhDT........56D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009PhDT........56D"><span id="translatedtitle">High-order finite element methods for seismic <span class="hlt">wave</span> <span class="hlt">propagation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Basabe Delgado, Jonas De Dios</p> <p></p> <p>Purely numerical methods based on the Finite Element Method (FEM) are becoming increasingly popular in seismic modeling for the <span class="hlt">propagation</span> of acoustic and elastic <span class="hlt">waves</span> in geophysical models. These methods offer a better control on the accuracy and more geometrical flexibility than the Finite Difference methods that have been traditionally used for the generation of synthetic seismograms. However, the success of these methods has outpaced their analytic validation. The accuracy of the FEMs used for seismic <span class="hlt">wave</span> <span class="hlt">propagation</span> is unknown in most cases and therefore the simulation parameters in numerical experiments are determined by empirical rules. I focus on two methods that are particularly suited for seismic modeling: the Spectral Element Method (SEM) and the Interior-Penalty Discontinuous Galerkin Method (IP-DGM). The goals of this research are to investigate the grid dispersion and stability of SEM and IP-DGM, to implement these methods and to apply them to subsurface models to obtain synthetic seismograms. In order to analyze the grid dispersion and stability, I use the von Neumann method (plane <span class="hlt">wave</span> analysis) to obtain a generalized eigenvalue problem. I show that the eigenvalues are related to the grid dispersion and that, with certain assumptions, the size of the eigenvalue problem can be reduced from the total number of degrees of freedom to one proportional to the number of degrees of freedom inside one element. The grid dispersion results indicate that SEM of degree greater than 4 is isotropic and has a very low dispersion. Similar dispersion properties are observed for the symmetric formulation of IP-DGM of degree greater than 4 using nodal basis functions. The low dispersion of these methods allows for a sampling ratio of 4 nodes per wavelength to be used. On the other hand, the stability analysis shows that, in the elastic case, the size of the time step required in IP-DGM is approximately 6 times smaller than that of SEM. The results from the analysis</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.7373G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.7373G"><span id="translatedtitle">Seismic <span class="hlt">wave</span> <span class="hlt">propagation</span> on heterogeneous systems with CHAPEL</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gokhberg, Alexey; Fichtner, Andreas</p> <p>2014-05-01</p> <p>Simulations of seismic <span class="hlt">wave</span> <span class="hlt">propagation</span> play a key role in the exploration of the Earth's internal structure, the prediction of earthquake-induced ground motion, and numerous other applications. In order to harness modern heterogeneous HPC systems, we implement a spectral-element discretization of the seismic <span class="hlt">wave</span> equation using the emerging parallel programming language Chapel. High-performance massively parallel computing systems are widely used for solving seismological problems. A recent trend in the evolution of such systems is a transition from homogeneous architectures based on the conventional CPU to faster and more energy-efficient heterogeneous architectures that combine CPU with the special purpose GPU accelerators. These new heterogeneous architectures have much higher hardware complexity and are thus more difficult to program. Therefore transition to heterogeneous computing systems widens the well known gap between the performance of the new hardware and the programmers' productivity. In particular, programming heterogeneous systems typically involves a mix of various programming technologies like MPI, CUDA, or OpenACC. This conventional approach increases complexity of application code, limits its portability and reduces the programmers' productivity. We are approaching this problem by introducing a unified high-level programming model suitable for both conventional and hybrid architectures. Our model is based on the Partitioned Global Address Space (PGAS) paradigm used by several modern parallel programming languages. We implemented this model by extending Chapel, the emerging parallel programming language created at Cray Inc. In particular, we introduced the language abstractions for GPU-based domain mapping and extended the open source Chapel compiler (version 1.8.0) with facilities designed to translate Chapel high-level parallel programming constructs into CUDA kernels. We used this extended Chapel implementation to re-program the package for the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SPIE.9064E..1JL','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SPIE.9064E..1JL"><span id="translatedtitle">Local computational strategies for predicting <span class="hlt">wave</span> <span class="hlt">propagation</span> in nonlinear media</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Leamy, Michael J.; Autrusson, Thibaut B.; Staszewski, Wieslaw J.; Uhl, Tadeusz; Packo, Pawel</p> <p>2014-03-01</p> <p>Two local computational strategies for modeling elastic <span class="hlt">wave</span> <span class="hlt">propagation</span>, namely the Local Interaction Simulation Approach (LISA) and Cellular Automata for Elastodynamics (CAFE), are compared and contrasted in analyzing bulk <span class="hlt">waves</span> in two-dimensional nonlinear media. Each strategy formulates the problem from the perspective of a cell and its local interactions with other cells, leading to robust treatments of anisotropy, heterogeneity, and nonlinearity. The local approach also enables straight-forward parallelization on high performance computing clusters. While the two share a common local perspective, they differ in two major respects. The first is that CAFE employs both rectangular and triangular cells, while LISA considers only rectangular. The second is that LISA appeared much earlier than CAFE (early 1990's versus late 2000's), and as such has been developed to a much greater degree with a multitude of material models, cell-to-cell interactions, loading possibilities, and boundary treatments. A hybrid approach which combines the two is of great interest since the non-uniform mesh capability of the CAFE triangular cell can be readily coupled to LISA's rectangular grids, taking advantage of the built-in LISA features on the uniform portion of the domain. For linear material domains, the hybrid implementation appears straight-forward since both methods have been shown to recover the same equations in the rectangular case. For nonlinear material domains, the formulations cannot be put into a one-to-one correspondence, and hybrid implementation may be more problematic. This paper addresses these differences by first presenting the underlying formulations, and then computing results for growth of a second harmonic in an introduced bulk pressure <span class="hlt">wave</span>. Rectangular cells are used in both LISA and CAFE. Results from both approaches are compared to an approximate, analytical solution based on a two-scale field representation. Differences in the LISA and CAFE computed</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5205640','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5205640"><span id="translatedtitle">Chemical fluctuations associated with vertically <span class="hlt">propagating</span> equatorial Kelvin <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Salby, M.L.; Callaghan, P. ); Soloman, S. NOAA, Boulder, CO ); Garcia, R.R. )</p> <p>1990-11-20</p> <p>Satellite retrievals of ozone and nitrogen dioxide from the Nimbus-7 Limb Infrared Monitor of the Stratosphere (LIMS) reveal distinct spectral features which are collocated in frequency with Kelvin <span class="hlt">wave</span> temperature fluctuations. These features represent a significant component of the unsteady variance in retrievals of O{sub 3} and nighttime NO{sub 2} in the tropics and are very similar to Kelvin <span class="hlt">wave</span> temperature disturbances. Chemical fluctuations occur symmetrically about the equator, in phase across the tropics, and <span class="hlt">propagate</span> downward, all consistent with the behavior of equatorial Kelvin <span class="hlt">waves</span>. The phase structure of ozone perturbations mirrors that of temperature fluctuations in the upper stratosphere and mesosphere, only shifted 180{degree}. The regular phase tilt with altitude disappears in the middle to lower stratosphere, where it is replaced by more or less barotropic behavior. That change in phase structure marks a transition fromn photochemical control in the upper stratosphere and mesosphere to dynamical control in the lower stratosphere. Fluctuations in ozone are consistent with dynamical and chemical mechanisms operating on that species. The response of ozone in a detailed photochemical calculation driven by observed temperature variability locks into agreement with the observed ozone variability above about 4 mbar, where O{sub 3} is under photochemical control. At lower altitudes, vertical transport is able to explain both the magnitude and phase of the observed fluctuations in ozone. The same considerations have only mixed success in explaining the observed variability of nitrogen dioxide. The amplitude of nighttime NO{sub 2} fluctuations is underestimated in the photochemical calculation by about a factor of 2. Although large enough to explain the discrepancy, contributions from vertical transport have the wrong phase.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010PhDT.........1M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010PhDT.........1M"><span id="translatedtitle">Earthquake source properties and <span class="hlt">wave</span> <span class="hlt">propagation</span> in Eastern North America</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Magalhaes de Matos Viegas Fernandes, Gisela Sofia</p> <p></p> <p>The study of intraplate earthquakes is fundamental for the understanding of the physics of faulting, seismic hazard assessment, and nuclear monitoring, but large to moderate well recorded intraplate earthquakes are scarce. I use the best recorded earthquake in Eastern North America (ENA)---the Mw 5.0 20 April 2002, Au Sable Forks, NY, earthquake and its aftershock sequence to investigate <span class="hlt">wave</span> <span class="hlt">propagation</span> and earthquake source properties in ENA. The Au Sable Forks epicenter is located near the boundary of two distinct geological provinces Appalachian (New England) and Grenville (New York). Existing regional one-dimensional (1D) crustal models were derived from seismic surveys or from sparse ground-motions recordings from regional moderate earthquakes. I obtain improved 1D crustal models for these two provinces by forward modeling, for the first time, multi-path high-quality ground-motions of a moderate earthquake in ENA. Using Au Sable Forks earthquake records at 16 stations (epicentral distances < 400 km) at intermediate frequencies (<1 Hz), I generate synthetic seismograms using the frequency-<span class="hlt">wave</span> number method. The new models improve the fit of synthetics to data at all 6 stations in the Grenville province and at 5 of the 10 stations in the Appalachian province. I identify complex <span class="hlt">wave</span> paths along the boundary between the provinces, and 3% azimuthal anisotropy in the Appalachian crust. It is unknown how much earthquake source properties depend on the tectonic setting in which the earthquakes occur. Debate exists regarding the invariance of stress drop with earthquake size in ENA, and whether earthquakes in intraplate regions have higher stress drops than those in more tectonically active regions. I estimate source parameters for 22 earthquakes (M1-M5) of the Au Sable Forks sequence, using two alternative methods: a direct <span class="hlt">wave</span> method (Empirical Green's Function) and a coda <span class="hlt">wave</span> method (Coda Ratio) applied for the first time to small magnitude earthquakes. Both</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890005714','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890005714"><span id="translatedtitle">Nonlinear interaction of near-<span class="hlt">planar</span> TS <span class="hlt">waves</span> and longitudinal vortices in boundary-layer transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, F. T.</p> <p>1988-01-01</p> <p>The nonlinear interactions that evolve between a <span class="hlt">planar</span> or nearly <span class="hlt">planar</span> Tollmien-Schlichting (TS) <span class="hlt">wave</span> and the associated longitudinal vortices are considered theoretically for a boundary layer at high Reynolds number. The vortex flow is either induced by the TS nonlinear forcing or is input upstream, and similarly for the nonlinear <span class="hlt">wave</span> development. Three major kinds of nonlinear spatial evolution, Types 1-3, are found. Each can start from secondary instability and then become nonlinear, Type 1 proving to be relatively benign but able to act as a pre-cursor to the Types 2, 3 which turn out to be very powerful nonlinear interactions. Type 2 involves faster stream-wise dependence and leads to a finite-distance blow-up in the amplitudes, which then triggers the full nonlinear 3-D triple-deck response, thus entirely altering the mean-flow profile locally. In contrast, Type 3 involves slower streamwise dependence but a faster spanwise response, with a small TS amplitude thereby causing an enhanced vortex effect which, again, is substantial enough to entirely alter the meanflow profile, on a more global scale. Streak-like formations in which there is localized concentration of streamwise vorticity and/or <span class="hlt">wave</span> amplitude can appear, and certain of the nonlinear features also suggest by-pass processes for transition and significant changes in the flow structure downstream. The powerful nonlinear 3-D interactions 2, 3 are potentially very relevant to experimental findings in transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16371710','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16371710"><span id="translatedtitle">Coherent <span class="hlt">propagation</span> of white X-rays in a <span class="hlt">planar</span> waveguide.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fuhse, Christian; Ollinger, Christoph; Kalbfleisch, Sebastian; Salditt, Tim</p> <p>2006-01-01</p> <p>The far-field diffraction pattern of a front-coupled <span class="hlt">planar</span> waveguide supporting two guided modes has been measured using a white X-ray beam. Interference of the guided modes leads to a characteristic variation of the far-field diffraction pattern for different photon energies. The experiment verifies the predicted properties of the guided modes, shows that these modes superpose coherently, and demonstrates that the electromagnetic field downstream of the waveguide is significantly different from that expected for a hypothetical small slit of the same size.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22255220','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22255220"><span id="translatedtitle">Study of performance and <span class="hlt">propagation</span> characteristics of wire and <span class="hlt">planar</span> structures around human body.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Aroul, A L Praveen; Bhatia, Dinesh</p> <p>2011-01-01</p> <p>Continued miniaturization of electronic devices and technological advancements in wireless communications has made wearable body-centric telemedicine systems viable. Antennas play a crucial role in characterizing the efficiency and reliability of these systems. The performance characteristics such as the radiation pattern, gain, efficiency of the antennas get adversely affected due to the presence of lossy human body tissues. In this paper we investigate the above mentioned performance parameters and radio frequency transmission properties of wire and <span class="hlt">planar</span> structures operating at ISM frequency band of 2.40-2.50 GHz in the proximity of human body.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA225559','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA225559"><span id="translatedtitle">Formation and <span class="hlt">Propagation</span> of Love <span class="hlt">Waves</span> in a Surface Layer with a P-<span class="hlt">Wave</span> Source</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1990-04-01</p> <p>AD- A225 559 GL-TR-90-0100 Formation and <span class="hlt">Propagation</span> of Love <span class="hlt">Waves</span> in a Surface Layer with a P-<span class="hlt">Wave</span> Source A. L. Florence S. A. Miller PTh FILE COP...describing outgoing <span class="hlt">waves</span> is (p(r,t) = - f(s) s = t - (r- a)/ cr (27) In terms of the function f(s), the displacement, velocity, and stresses are cr r2...28) cr r2 (29) CyrpC2 - +2(1- 2,0) ’ + = 1 -1 (r2 (30) ce P21 - I -M I= I$ C(2r )x + ) (31) in which 1) is Poisson’s ratio. For a given cavity wall</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/972072','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/972072"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">propagation</span> in photonic crystals and metamaterials: Surface <span class="hlt">waves</span>, nonlinearity and chirality</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wang, Bingnan</p> <p>2009-01-01</p> <p>Photonic crystals and metamaterials, both composed of artificial structures, are two interesting areas in electromagnetism and optics. New phenomena in photonic crystals and metamaterials are being discovered, including some not found in natural materials. This thesis presents my research work in the two areas. Photonic crystals are periodically arranged artificial structures, mostly made from dielectric materials, with period on the same order of the wavelength of the working electromagnetic <span class="hlt">wave</span>. The <span class="hlt">wave</span> <span class="hlt">propagation</span> in photonic crystals is determined by the Bragg scattering of the periodic structure. Photonic band-gaps can be present for a properly designed photonic crystal. Electromagnetic <span class="hlt">waves</span> with frequency within the range of the band-gap are suppressed from <span class="hlt">propagating</span> in the photonic crystal. With surface defects, a photonic crystal could support surface modes that are localized on the surface of the crystal, with mode frequencies within the band-gap. With line defects, a photonic crystal could allow the <span class="hlt">propagation</span> of electromagnetic <span class="hlt">waves</span> along the channels. The study of surface modes and waveguiding properties of a 2D photonic crystal will be presented in Chapter 1. Metamaterials are generally composed of artificial structures with sizes one order smaller than the wavelength and can be approximated as effective media. Effective macroscopic parameters such as electric permittivity ϵ, magnetic permeability μ are used to characterize the <span class="hlt">wave</span> <span class="hlt">propagation</span> in metamaterials. The fundamental structures of the metamaterials affect strongly their macroscopic properties. By designing the fundamental structures of the metamaterials, the effective parameters can be tuned and different electromagnetic properties can be achieved. One important aspect of metamaterial research is to get artificial magnetism. Metallic split-ring resonators (SRRs) and variants are widely used to build magnetic metamaterials with effective μ < 1 or even μ < 0. Varactor based</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ASAJ..118.2667C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ASAJ..118.2667C"><span id="translatedtitle">Modeling elastic <span class="hlt">wave</span> <span class="hlt">propagation</span> in kidney stones with application to shock <span class="hlt">wave</span> lithotripsy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cleveland, Robin O.; Sapozhnikov, Oleg A.</p> <p>2005-10-01</p> <p>A time-domain finite-difference solution to the equations of linear elasticity was used to model the <span class="hlt">propagation</span> of lithotripsy <span class="hlt">waves</span> in kidney stones. The model was used to determine the loading on the stone (principal stresses and strains and maximum shear stresses and strains) due to the impact of lithotripsy shock <span class="hlt">waves</span>. The simulations show that the peak loading induced in kidney stones is generated by constructive interference from shear <span class="hlt">waves</span> launched from the outer edge of the stone with other <span class="hlt">waves</span> in the stone. Notably the shear <span class="hlt">wave</span> induced loads were significantly larger than the loads generated by the classic Hopkinson or spall effect. For simulations where the diameter of the focal spot of the lithotripter was smaller than that of the stone the loading decreased by more than 50%. The constructive interference was also sensitive to shock rise time and it was found that the peak tensile stress reduced by 30% as rise time increased from 25 to 150 ns. These results demonstrate that shear <span class="hlt">waves</span> likely play a critical role in stone comminution and that lithotripters with large focal widths and short rise times should be effective at generating high stresses inside kidney stones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1814120S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1814120S"><span id="translatedtitle">Seismic <span class="hlt">wave</span> <span class="hlt">propagation</span> through an extrusive basalt sequence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sanford, Oliver; Hobbs, Richard; Brown, Richard; Schofield, Nick</p> <p>2016-04-01</p> <p>Layers of basalt flows within sedimentary successions (e.g. in the Faeroe-Shetland Basin) cause complex scattering and attenuation of seismic <span class="hlt">waves</span> during seismic exploration surveys. Extrusive basaltic sequences are highly heterogeneous and contain strong impedance contrasts between higher velocity crystalline flow cores (˜6 km s-1) and the lower velocity fragmented and weathered flow crusts (3-4 km s-1). Typically, the refracted <span class="hlt">wave</span> from the basaltic layer is used to build a velocity model by tomography. This velocity model is then used to aid processing of the reflection data where direct determination of velocity is ambiguous, or as a starting point for full waveform inversion, for example. The model may also be used as part of assessing drilling risk of potential wells, as it is believed to constrain the total thickness of the sequence. In heterogeneous media, where the scatter size is of the order of the seismic wavelength or larger, scattering preferentially traps the seismic energy in the low velocity regions. This causes a build-up of energy that is guided along the low velocity layers. This has implications for the interpretation of the observed first arrival of the seismic <span class="hlt">wave</span>, which may be a biased towards the low velocity regions. This will then lead to an underestimate of the velocity structure and hence the thickness of the basalt, with implications for the drilling of wells hoping to penetrate through the base of the basalts in search of hydrocarbons. Using 2-D acoustic finite difference modelling of the guided <span class="hlt">wave</span> through a simple layered basalt sequence, we consider the relative importance of different parameters of the basalt on the seismic energy <span class="hlt">propagating</span> through the layers. These include the proportion of high to low velocity material, the number of layers, their thickness and the roughness of the interfaces between the layers. We observe a non-linear relationship between the ratio of high to low velocity layers and the apparent velocity</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JPhCS.656a2023K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JPhCS.656a2023K"><span id="translatedtitle">Study on Pressure <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in a Liquid Containing Spherical Bubbles in a Rectangular Duct</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kawahara, Junya; Watanabe, Masao; Kobayashi, Kazumichi</p> <p>2015-12-01</p> <p>Pressure <span class="hlt">wave</span> <span class="hlt">propagation</span> in a liquid containing several bubbles is numerically investigated. We simulate liner plane <span class="hlt">wave</span> <span class="hlt">propagation</span> in a liquid containing 10 spherical bubbles in a rectangular duct with the equation of motion for N spherical bubbles. The sound pressures of the reflected <span class="hlt">waves</span> from the rigid walls are calculated by using the method of images. The result shows that the phase velocity of the pressure <span class="hlt">wave</span> <span class="hlt">propagating</span> in the liquid containing 10 spherical bubbles in the duct agrees well with the low-frequency speed of sound in a homogeneous bubbly liquid.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20706372','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20706372"><span id="translatedtitle">Characteristics of surface-<span class="hlt">wave</span> and volume-<span class="hlt">wave</span> plasmas produced with internally mounted large-area <span class="hlt">planar</span> microwave launcher</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Nagatsu, Masaaki; Naito, Katsutoshi; Ogino, Akihisa; Ninomiya, Keigo; Nanko, Shohei</p> <p>2005-10-17</p> <p>We studied discharge characteristics of microwave plasmas excited with a large-area <span class="hlt">planar</span> microwave launcher installed internally in a 600-mm-diam cylindrical vacuum chamber. With the microwave power less than roughly 400 W, we demonstrated the large volumetric volume-<span class="hlt">wave</span> plasma (VWP) spread in the entire chamber at a pressure of 14-27 Pa in He. Above 400 W, the plasma discharge made a sudden transition to higher-density, uniform surface-<span class="hlt">wave</span> plasma (SWP) having a spatial uniformity of {+-}3.5% over 300 mm in diameter. Electron energy probability functions in the downstream region were studied using Langmuir probe measurements with Druyvesteyn method in both the SWP and VWP discharges.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18156170','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18156170"><span id="translatedtitle">Origin and <span class="hlt">propagation</span> of individual slow <span class="hlt">waves</span> along the intact feline small intestine.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lammers, Wim J E P; Stephen, Betty</p> <p>2008-03-01</p> <p>The pattern of <span class="hlt">propagation</span> of slow <span class="hlt">waves</span> in the small intestine is not clear. Specifically, it is not known whether <span class="hlt">propagation</span> is determined by a single dominant ICC-MP (Interstitial cells of Cajal located in the Myenteric Plexus) pacemaker unit or whether there are multiple active pacemakers. To determine this pattern of <span class="hlt">propagation</span>, waveforms were recorded simultaneously from 240 electrodes distributed along the whole length of the intact isolated feline small intestine. After the experiments, the <span class="hlt">propagation</span> patterns of successive individual slow <span class="hlt">waves</span> were analysed. In the intact small intestine, there was only a single slow <span class="hlt">wave</span> pacemaker unit active, and this was located at or 6-10 cm from the pyloric junction. From this site, slow <span class="hlt">waves</span> <span class="hlt">propagated</span> in the aboral direction at gradually decreasing velocities. The majority of slow <span class="hlt">waves</span> (73%) reached the ileocaecal junction while the remaining <span class="hlt">waves</span> were blocked. Ligation of the intestine at one to four locations led to: (a) decrease in the distal frequencies; (b) disappearance of distal <span class="hlt">propagation</span> blocks; (c) increase in velocities; (d) emergence of multiple and unstable pacemaker sites; and (e) <span class="hlt">propagation</span> from these sites in the aboral and oral directions. In conclusion, in the quiescent feline small intestine a single pacemaker unit dominates the organ, with occasional <span class="hlt">propagation</span> blocks of the slow <span class="hlt">waves</span>, thereby producing the well-known frequency gradient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24094454','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24094454"><span id="translatedtitle">Finite element modeling of impulsive excitation and shear <span class="hlt">wave</span> <span class="hlt">propagation</span> in an incompressible, transversely isotropic medium.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rouze, Ned C; Wang, Michael H; Palmeri, Mark L; Nightingale, Kathy R</p> <p>2013-11-15</p> <p>Elastic properties of materials can be measured by observing shear <span class="hlt">wave</span> <span class="hlt">propagation</span> following localized, impulsive excitations and relating the <span class="hlt">propagation</span> velocity to a model of the material. However, characterization of anisotropic materials is difficult because of the number of elasticity constants in the material model and the complex dependence of <span class="hlt">propagation</span> velocity relative to the excitation axis, material symmetries, and <span class="hlt">propagation</span> directions. In this study, we develop a model of <span class="hlt">wave</span> <span class="hlt">propagation</span> following impulsive excitation in an incompressible, transversely isotropic (TI) material such as muscle. <span class="hlt">Wave</span> motion is described in terms of three <span class="hlt">propagation</span> modes identified by their polarization relative to the material symmetry axis and <span class="hlt">propagation</span> direction. Phase velocities for these <span class="hlt">propagation</span> modes are expressed in terms of five elasticity constants needed to describe a general TI material, and also in terms of three constants after the application of two constraints that hold in the limit of an incompressible material. Group <span class="hlt">propagation</span> velocities are derived from the phase velocities to describe the <span class="hlt">propagation</span> of <span class="hlt">wave</span> packets away from the excitation region following localized excitation. The theoretical model is compared to the results of finite element (FE) simulations performed using a nearly incompressible material model with the five elasticity constants chosen to preserve the essential properties of the material in the incompressible limit. <span class="hlt">Propagation</span> velocities calculated from the FE displacement data show complex structure that agrees quantitatively with the theoretical model and demonstrates the possibility of measuring all three elasticity constants needed to characterize an incompressible, TI material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoRL..4310034H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoRL..4310034H"><span id="translatedtitle"><span class="hlt">Propagation</span> and linear mode conversion of magnetosonic and electromagnetic ion cyclotron <span class="hlt">waves</span> in the radiation belts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Horne, Richard B.; Miyoshi, Yoshizumi</p> <p>2016-10-01</p> <p>Magnetosonic <span class="hlt">waves</span> and electromagnetic ion cyclotron (EMIC) <span class="hlt">waves</span> are important for electron acceleration and loss from the radiation belts. It is generally understood that these <span class="hlt">waves</span> are generated by unstable ion distributions that form during geomagnetically disturbed times. Here we show that magnetosonic <span class="hlt">waves</span> could be a source of EMIC <span class="hlt">waves</span> as a result of <span class="hlt">propagation</span> and a process of linear mode conversion. The converse is also possible. We present ray tracing to show how magnetosonic (EMIC) <span class="hlt">waves</span> launched with large (small) <span class="hlt">wave</span> normal angles can reach a location where the <span class="hlt">wave</span> normal angle is zero and the <span class="hlt">wave</span> frequency equals the so-called crossover frequency whereupon energy can be converted from one mode to another without attenuation. While EMIC <span class="hlt">waves</span> could be a source of magnetosonic <span class="hlt">waves</span> below the crossover frequency, magnetosonic <span class="hlt">waves</span> could be a source of hydrogen band <span class="hlt">waves</span> but not helium band <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S23C2742P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S23C2742P"><span id="translatedtitle">The imprint of crustal density heterogeneities on seismic <span class="hlt">wave</span> <span class="hlt">propagation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Plonka, A.; Fichtner, A.</p> <p>2015-12-01</p> <p>We present the results of a set of numerical experiments designed to observe the imprint of three-dimensional density heterogeneities on a seismogram. To compute the full seismic wavefield in a three-dimensional heterogeneous medium, we use numerical <span class="hlt">wave</span> <span class="hlt">propagation</span> based on a spectral-element discretization of the seismic <span class="hlt">wave</span> equation. We consider a 2000 by 1000 km wide and 500 km deep spherical section, with the one-dimensional Earth model PREM, altered so that the crust is 40 km thick and all the parameters in the crust are constant, as a background. Onto the uppermost 40 km of the underlying one-dimensional model we superimpose three-dimensional randomly generated velocity and density heterogeneities of various correlation lengths. We use different random realizations of heterogeneity distribution. We compare the synthetic seismograms for three-dimensional velocity and density structure with three-dimensional velocity structure and one-dimensional density kept as PREM, calculating relative amplitude differences and time shifts as functions of time and frequency. The misfits in time shift and amplitude for different frequency bands, epicentral distances and medium complexities are then stacked into histograms and statistically analysed. We observe strong dependency on frequency of density-related amplitude difference. We also conclude potential sensitivity to distant density structures, and that scattering is essential to observe significant density imprint on a seismogram. The possible density-related bias in velocity and attenuation for regional tomographic models is calculated using mean misfit values for given epicentral distances. Whereas the bias in velocity does not exceed 0.5% of the model value, the density-related change in attenuation may be as big as 71% of the model value for the mean amplitude difference in the highest frequency band. The results suggest that density imprint on a seismogram is not negligible and with further theoretical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120016254','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120016254"><span id="translatedtitle">Theory of a Traveling <span class="hlt">Wave</span> Feed for a <span class="hlt">Planar</span> Slot Array Antenna</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rengarajan, Sembiam</p> <p>2012-01-01</p> <p><span class="hlt">Planar</span> arrays of waveguide-fed slots have been employed in many radar and remote sensing applications. Such arrays are designed in the standing <span class="hlt">wave</span> configuration because of high efficiency. Traveling <span class="hlt">wave</span> arrays can produce greater bandwidth at the expense of efficiency due to power loss in the load or loads. Traveling <span class="hlt">wave</span> <span class="hlt">planar</span> slot arrays may be designed with a long feed waveguide consisting of centered-inclined coupling slots. The feed waveguide is terminated in a matched load, and the element spacing in the feed waveguide is chosen to produce a beam squinted from the broadside. The traveling <span class="hlt">wave</span> <span class="hlt">planar</span> slot array consists of a long feed waveguide containing resonant-centered inclined coupling slots in the broad wall, coupling power into an array of stacked radiating waveguides orthogonal to it. The radiating waveguides consist of longitudinal offset radiating slots in a standing <span class="hlt">wave</span> configuration. For the traveling <span class="hlt">wave</span> feed of a <span class="hlt">planar</span> slot array, one has to design the tilt angle and length of each coupling slot such that the amplitude and phase of excitation of each radiating waveguide are close to the desired values. The coupling slot spacing is chosen for an appropriate beam squint. Scattering matrix parameters of resonant coupling slots are used in the design process to produce appropriate excitations of radiating waveguides with constraints placed only on amplitudes. Since the radiating slots in each radiating waveguide are designed to produce a certain total admittance, the scattering (S) matrix of each coupling slot is reduced to a 2x2 matrix. Elements of each 2x2 S-matrix and the amount of coupling into the corresponding radiating waveguide are expressed in terms of the element S11. S matrices are converted into transmission (T) matrices, and the T matrices are multiplied to cascade the coupling slots and waveguide sections, starting from the load end and proceeding towards the source. While the use of non-resonant coupling slots may provide an</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhPl...24a2108K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhPl...24a2108K"><span id="translatedtitle">Parametric decay of a parallel <span class="hlt">propagating</span> monochromatic whistler <span class="hlt">wave</span>: Particle-in-cell simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ke, Yangguang; Gao, Xinliang; Lu, Quanming; Wang, Shui</p> <p>2017-01-01</p> <p>In this paper, by using one-dimensional (1-D) particle-in-cell simulations, we investigate the parametric decay of a parallel <span class="hlt">propagating</span> monochromatic whistler <span class="hlt">wave</span> with various <span class="hlt">wave</span> frequencies and amplitudes. The pump whistler <span class="hlt">wave</span> can decay into a backscattered daughter whistler <span class="hlt">wave</span> and an ion acoustic <span class="hlt">wave</span>, and the decay instability grows more rapidly with the increase of the frequency or amplitude. When the frequency or amplitude is sufficiently large, a multiple decay process may occur, where the daughter whistler <span class="hlt">wave</span> undergoes a secondary decay into an ion acoustic <span class="hlt">wave</span> and a forward <span class="hlt">propagating</span> whistler <span class="hlt">wave</span>. We also find that during the parametric decay a considerable part of protons can be accelerated along the background magnetic field by the enhanced ion acoustic <span class="hlt">wave</span> through the Landau resonance. The implication of the parametric decay to the evolution of whistler <span class="hlt">waves</span> in Earth's magnetosphere is also discussed in the paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5658','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5658"><span id="translatedtitle">Inversion of Head <span class="hlt">Wave</span> Traveltimes for Three-Dimensional <span class="hlt">Planar</span> Structure</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Aldridge, D.F.; Oldenburg, D.W.</p> <p>1999-03-31</p> <p>Inversion of head <span class="hlt">wave</span> arrival times for three-dimensional (3D) <span class="hlt">planar</span> structure is formulated as a constrained parameter optimization problem, and solved via linear programming techniques. The earth model is characterized by a set of homogeneous and isotropic layers bounded by plane, dipping interfaces. Each interface may possess arbitrary strike and dip. Predicted data consists of traveltimes of critically refracted <span class="hlt">waves</span> formed on the plane interfaces of the model. The nonlinear inversion procedure is iterative; an initial estimate of the earth model is refined until an acceptable match is obtained between observed and predicted data. Inclusion of a priori constraint information, in the form of inequality relations satisfied by the model parameters, assists the algorithm in converging toward a realistic solution. Although the 3D earth model adopted for the inversion procedure is simple, the algorithm is quite useful in two particular contexts: (i) it can provide an initial model estimate suitable for subsequent improvement by more general techniques (i.e., traveltime tomography), and (ii) it is an effective analysis tool for investigating the power of areal recording geometries for detecting and resolving 3D dipping <span class="hlt">planar</span> structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040074324&hterms=numerical+methods+applications&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dnumerical%2Bmethods%2Bapplications','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040074324&hterms=numerical+methods+applications&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dnumerical%2Bmethods%2Bapplications"><span id="translatedtitle">An Investigation of <span class="hlt">Wave</span> <span class="hlt">Propagations</span> in Discontinuous Galerkin Method</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hu, Fang Q.</p> <p>2004-01-01</p> <p>Analysis of the discontinuous Galerkin method has been carried out for one- and two-dimensional system of hyperbolic equations. Analytical, as well as numerical, properties of <span class="hlt">wave</span> <span class="hlt">propagation</span> in a DGM scheme are derived and verified with direct numerical simulations. In addition to a systematic examination of the dissipation and dispersion errors, behaviours of a DG scheme at an interface of two different grid topologies are also studied. Under the same framework, a quantitative discrete analysis of various artificial boundary conditions is also conducted. Progress has been made in numerical boundary condition treatment that is closely related to the application of DGM in aeroacoustics problems. Finally, Fourier analysis of DGM for the Convective diffusion equation has also be studied in connection with the application of DG schemes for the Navier-Stokes equations. This research has resulted in five(5) publications, plus one additional manuscript in preparation, four(4) conference presentations, and three(3) departmental seminars, as summarized in part II. Abstracts of papers are given in part 111 of this report.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9799E..06B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9799E..06B"><span id="translatedtitle">Parametric study of <span class="hlt">wave</span> <span class="hlt">propagation</span> in hierarchical auxetic perforated metamaterials</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Billon, K.; Ouisse, M.; Sadoulet-Reboul, E.; Scarpa, F.; Collet, M.</p> <p>2016-04-01</p> <p>The understanding of <span class="hlt">wave</span> <span class="hlt">propagation</span> in a metamaterial with hierarchical, auxetic rectangular perforations is presented in this work. The metamaterial is a 2D structure with chaining horizontal and vertical perforations exhibiting auxetic in-plane behaviour. The unit cell of this lattice is identified as the reference level 0. Hierarchical structures are composed of structural elements which themselves have structure. At level 0, 4 rigid squares are present in the unit cell. In each square, the reference structure is used by applying a scale ratio to obtain the level 1. The same strategy is used to reach the upper level in each subunit. A geometric parametric investigation of these rectangular perforations using a numerical asymptotic homogenisation finite element approach is done. Some numerical eigenvalue tools are used for the dispersion analysis of this structure. It is first observed that the total width of Band gaps increases with the hierarchy. The porosity induced by the perforations is taken into account in the mechanical properties. The symmetry of the geometry in the x-y plane allow to define the entire geometry of the unit cell using only 2 parameters: the void aspect ratio, the intercell spacing and the hierarchy level. When decreasing the intercell spacing, the total width of Band gaps increases and the effective stiffness in x and y directions decrease, allowing for increased rotations of the rigid squares, so auxetic behaviour is greater. Hierarchical levels shift from isotropic to orthotropic, hierarchical levels are always auxetic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AIPC.1581..332B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AIPC.1581..332B"><span id="translatedtitle">Guided <span class="hlt">wave</span> <span class="hlt">propagation</span> and scattering in pipeworks comprising elbows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bakkali, Marouane El; Lhémery, Alain; Baronian, Vahan; Berthelot, François</p> <p>2014-02-01</p> <p>Guided <span class="hlt">waves</span> (GW) are used to inspect pipeworks in various industries. Specific features of pipeworks lead to complex scattering phenomena. Simulations tools able to handle such a complexity must be developed to help interpretation and to optimize testing configurations. They must handle both long range <span class="hlt">propagation</span> and local scattering phenomena. Here, a modal formulation is derived to deal with pipeworks comprising arbitrarily curved elbows linking otherwise straight pipes. First, the semi-analytic finite element method is extended in curvilinear coordinates to predict guided modes in elbows. Then, GW scattering at the junction of a straight pipe with an elbow is investigated. Modal solutions in both parts being known, the mode matching method is derived to compute modal reflection and transmission coefficients given as elements of a scattering matrix. Further, the global scattering matrix of a pipework comprising an arbitrary number of elbows linking straight pipes is considered. A general formulation presented in this conference series is used which handles multiple scattering phenomena that possibly arise. Interestingly, the computation of both modal solution and the scattering matrix with mode-matching method only requires meshing the pipe section. Examples illustrate the various steps.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005JPCM...17.4245A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005JPCM...17.4245A"><span id="translatedtitle"><span class="hlt">Propagation</span> and localization of acoustic <span class="hlt">waves</span> in Fibonacci phononic circuits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aynaou, H.; El Boudouti, E. H.; Djafari-Rouhani, B.; Akjouj, A.; Velasco, V. R.</p> <p>2005-07-01</p> <p>A theoretical investigation is made of acoustic <span class="hlt">wave</span> <span class="hlt">propagation</span> in one-dimensional phononic bandgap structures made of slender tube loops pasted together with slender tubes of finite length according to a Fibonacci sequence. The band structure and transmission spectrum is studied for two particular cases. (i) Symmetric loop structures, which are shown to be equivalent to diameter-modulated slender tubes. In this case, it is found that besides the existence of extended and forbidden modes, some narrow frequency bands appear in the transmission spectra inside the gaps as defect modes. The spatial localization of the modes lying in the middle of the bands and at their edges is examined by means of the local density of states. The dependence of the bandgap structure on the slender tube diameters is presented. An analysis of the transmission phase time enables us to derive the group velocity as well as the density of states in these structures. In particular, the stop bands (localized modes) may give rise to unusual (strong normal) dispersion in the gaps, yielding fast (slow) group velocities above (below) the speed of sound. (ii) Asymmetric tube loop structures, where the loops play the role of resonators that may introduce transmission zeros and hence new gaps unnoticed in the case of simple diameter-modulated slender tubes. The Fibonacci scaling property has been checked for both cases (i) and (ii), and it holds for a periodicity of three or six depending on the nature of the substrates surrounding the structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhLA..381..636L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhLA..381..636L"><span id="translatedtitle">Bohm potential effect on the <span class="hlt">propagation</span> of electrostatic surface <span class="hlt">wave</span> in semi-bounded quantum plasmas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Myoung-Jae; Jung, Young-Dae</p> <p>2017-02-01</p> <p>High frequency electrostatic <span class="hlt">wave</span> <span class="hlt">propagation</span> in a dense and semi-bounded electron quantum plasma is investigated with consideration of the Bohm potential. The dispersion relation for the surface mode of quantum plasma is derived and numerically analyzed. We found that the quantum effect enhances the frequency of the <span class="hlt">wave</span> especially in the high <span class="hlt">wave</span> number regime. However, the frequency of surface <span class="hlt">wave</span> is found to be always lower than that of the bulk <span class="hlt">wave</span> for the same quantum <span class="hlt">wave</span> number. The group velocity of the surface <span class="hlt">wave</span> for various quantum <span class="hlt">wave</span> number is also obtained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005PhRvB..72g5405D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005PhRvB..72g5405D"><span id="translatedtitle"><span class="hlt">Planar</span> metal plasmon waveguides: frequency-dependent dispersion, <span class="hlt">propagation</span>, localization, and loss beyond the free electron model</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dionne, J. A.; Sweatlock, L. A.; Atwater, H. A.; Polman, A.</p> <p>2005-08-01</p> <p>A numerical analysis of surface plasmon dispersion, <span class="hlt">propagation</span>, and localization on smooth lossy films is presented. Particular attention is given to determining wavelength-dependent behavior of thin Ag slab waveguides embedded in a symmetric SiO2 environment. Rather than considering Ag as a damped free electron gas, the metal is defined by the experimentally determined optical constants of Johnson and Christy and Palik. As in free electron gas models, analytic dispersion results indicate a splitting of plasmon modes—corresponding to symmetric and antisymmetric field distributions—as film thickness is decreased below 50nm . However, unlike free electron gas models, the surface plasmon <span class="hlt">wave</span> vector remains finite at resonance with the antisymmetric-field plasmon converging to a pure photon mode for very thin films. In addition, allowed excitation modes are found to exist between the bound and radiative branches of the dispersion curve. The <span class="hlt">propagation</span> characteristics of all modes are determined, and for thin films (depending upon electric field symmetry), <span class="hlt">propagation</span> distances range from microns to centimeters in the near infrared. <span class="hlt">Propagation</span> distances are correlated with both the field decay (skin depth) and energy density distribution in the metal and surrounding dielectric. While the energy density of most long-range surface plasmons exhibits a broad spatial extent with limited confinement in the waveguide, it is found that high-field confinement does not necessarily limit <span class="hlt">propagation</span>. In fact, enhanced <span class="hlt">propagation</span> is observed for silver films at ultraviolet wavelengths despite strong field localization in the metal. The surface plasmon characteristics described in this paper provide a numerical springboard for engineering nanoscale metal plasmon waveguides, and the results may provide a new avenue for integrated optoelectronic applications.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21576626','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21576626"><span id="translatedtitle">SPATIAL DAMPING OF <span class="hlt">PROPAGATING</span> KINK <span class="hlt">WAVES</span> DUE TO RESONANT ABSORPTION: EFFECT OF BACKGROUND FLOW</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Soler, R.; Goossens, M.; Terradas, J.</p> <p>2011-06-20</p> <p>Observations show the ubiquitous presence of <span class="hlt">propagating</span> magnetohydrodynamic (MHD) kink <span class="hlt">waves</span> in the solar atmosphere. <span class="hlt">Waves</span> and flows are often observed simultaneously. Due to plasma inhomogeneity in the direction perpendicular to the magnetic field, kink <span class="hlt">waves</span> are spatially damped by resonant absorption. The presence of flow may affect the <span class="hlt">wave</span> spatial damping. Here, we investigate the effect of longitudinal background flow on the <span class="hlt">propagation</span> and spatial damping of resonant kink <span class="hlt">waves</span> in transversely nonuniform magnetic flux tubes. We combine approximate analytical theory with numerical investigation. The analytical theory uses the thin tube (TT) and thin boundary (TB) approximations to obtain expressions for the wavelength and the damping length. Numerically, we verify the previously obtained analytical expressions by means of the full solution of the resistive MHD eigenvalue problem beyond the TT and TB approximations. We find that the backward and forward <span class="hlt">propagating</span> <span class="hlt">waves</span> have different wavelengths and are damped on length scales that are inversely proportional to the frequency as in the static case. However, the factor of proportionality depends on the characteristics of the flow, so that the damping length differs from its static analog. For slow, sub-Alfvenic flows the backward <span class="hlt">propagating</span> <span class="hlt">wave</span> gets damped on a shorter length scale than in the absence of flow, while for the forward <span class="hlt">propagating</span> <span class="hlt">wave</span> the damping length is longer. The different properties of the <span class="hlt">waves</span> depending on their direction of <span class="hlt">propagation</span> with respect to the background flow may be detected by the observations and may be relevant for seismological applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/822058','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/822058"><span id="translatedtitle">Electromagnetic <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Two-Dimensional Photonic Crystals</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Foteinopoulou, Stavroula</p> <p>2003-01-01</p> <p>In this dissertation, they have undertaken the challenge to understand the unusual <span class="hlt">propagation</span> properties of the photonic crystal (PC). The photonic crystal is a medium where the dielectric function is periodically modulated. These types of structures are characterized by bands and gaps. In other words, they are characterized by frequency regions where <span class="hlt">propagation</span> is prohibited (gaps) and regions where <span class="hlt">propagation</span> is allowed (bands). In this study they focus on two-dimensional photonic crystals, i.e., structures with periodic dielectric patterns on a plane and translational symmetry in the perpendicular direction. They start by studying a two-dimensional photonic crystal system for frequencies inside the band gap. The inclusion of a line defect introduces allowed states in the otherwise prohibited frequency spectrum. The dependence of the defect resonance state on different parameters such as size of the structure, profile of incoming source, etc., is investigated in detail. For this study, they used two popular computational methods in photonic crystal research, the Finite Difference Time Domain method (FDTD) and the Transfer Matrix Method (TMM). The results for the one-dimensional defect system are analyzed, and the two methods, FDTD and TMM, are compared. Then, they shift their attention only to periodic two-dimensional crystals, concentrate on their band properties, and study their unusual refractive behavior. Anomalous refractive phenomena in photonic crystals included cases where the beam refracts on the ''wrong'' side of the surface normal. The latter phenomenon, is known as negative refraction and was previously observed in materials where the <span class="hlt">wave</span> vector, the electric field, and the magnetic field form a left-handed set of vectors. These materials are generally called left-handed materials (LHM) or negative index materials (NIM). They investigated the possibility that the photonic crystal behaves as a LHM, and how this behavior relates with the observed</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/945525','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/945525"><span id="translatedtitle">Supersonic Heat <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Laser-Produced Underdense Plasma for Efficient X-Ray Generation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tanabe, M; Nishimura, H; Fujioka, S; Nagai, K; Iwamae, A; Ohnishi, N; Fournier, K B; Girard, F; Primout, M; Villette, B; Tobin, M; Mima, K</p> <p>2008-06-12</p> <p>We have observed supersonic heat <span class="hlt">wave</span> <span class="hlt">propagation</span> in a low-density aerogel target ({rho} {approx} 3.2 mg/cc) irradiated at the intensity of 4 x 10{sup 14} W/cm{sup 2}. The heat <span class="hlt">wave</span> <span class="hlt">propagation</span> was measured with a time-resolved x-ray imaging diagnostics, and the results were compared with simulations made with the two-dimensional radiation-hydrodynamic code, RAICHO. <span class="hlt">Propagation</span> velocity of the ionization front gradually decreased as the <span class="hlt">wave</span> <span class="hlt">propagates</span> into the target. The reason of decrease is due to increase of laser absorption region as the front <span class="hlt">propagates</span> and interplay of hydrodynamic motion and reflection of laser <span class="hlt">propagation</span>. These features are well reported with the simulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17022204','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17022204"><span id="translatedtitle">Study of noise <span class="hlt">propagation</span> and the effects of insufficient numbers of projection angles and detector samplings for iterative reconstruction using <span class="hlt">planar</span>-integral data.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, B; Zeng, G L</p> <p>2006-09-01</p> <p>A rotating slat collimator can be used to acquire <span class="hlt">planar</span>-integral data. It achieves higher geometric efficiency than a parallel-hole collimator by accepting more photons, but the <span class="hlt">planar</span>-integral data contain less tomographic information that may result in larger noise amplification in the reconstruction. Lodge evaluated the rotating slat system and the parallel-hole system based on noise behavior for an FBP reconstruction. Here, we evaluate the noise <span class="hlt">propagation</span> properties of the two collimation systems for iterative reconstruction. We extend Huesman's noise <span class="hlt">propagation</span> analysis of the line-integral system to the <span class="hlt">planar</span>-integral case, and show that approximately 2.0(D/dp) SPECT angles, 2.5(D/dp) self-spinning angles at each detector position, and a 0.5dp detector sampling interval are required in order for the <span class="hlt">planar</span>-integral data to be efficiently utilized. Here, D is the diameter of the object and dp is the linear dimension of the voxels that subdivide the object. The noise <span class="hlt">propagation</span> behaviors of the two systems are then compared based on a least-square reconstruction using the ratio of the SNR in the image reconstructed using a <span class="hlt">planar</span>-integral system to that reconstructed using a line-integral system. The ratio is found to be proportional to the square root of F/D, where F is a geometric efficiency factor. This result has been verified by computer simulations. It confirms that for an iterative reconstruction, the noise tradeoff of the two systems is not only dependent on the increase of the geometric efficiency afforded by the <span class="hlt">planar</span> projection method, but also dependent on the size of the object. The <span class="hlt">planar</span>-integral system works better for small objects, while the line-integral system performs better for large ones. This result is consistent with Lodge's results based on the FBP method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19730021203','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19730021203"><span id="translatedtitle">A critical survey of <span class="hlt">wave</span> <span class="hlt">propagation</span> and impact in composite materials</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Moon, F. C.</p> <p>1973-01-01</p> <p>A review of the field of stress <span class="hlt">waves</span> in composite materials is presented covering the period up to December 1972. The major properties of <span class="hlt">waves</span> in composites are discussed and a summary is made of the major experimental results in this field. Various theoretical models for analysis of <span class="hlt">wave</span> <span class="hlt">propagation</span> in laminated, fiber and particle reinforced composites are surveyed. The anisotropic, dispersive and dissipative properties of stress pulses and shock <span class="hlt">waves</span> in such materials are reviewed. A review of the behavior of composites under impact loading is presented along with the application of <span class="hlt">wave</span> <span class="hlt">propagation</span> concepts to the determination of impact stresses in composite plates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28389057','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28389057"><span id="translatedtitle">Acoustic <span class="hlt">wave</span> <span class="hlt">propagation</span> in bubbly flow with gas, vapor or their mixtures.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Yuning; Guo, Zhongyu; Gao, Yuhang; Du, Xiaoze</p> <p>2017-03-29</p> <p>Presence of bubbles in liquids could significantly alter the acoustic <span class="hlt">waves</span> in terms of <span class="hlt">wave</span> speed and attenuation. In the present paper, acoustic <span class="hlt">wave</span> <span class="hlt">propagation</span> in bubbly flows with gas, vapor and gas/vapor mixtures is theoretically investigated in a wide range of parameters (including frequency, bubble radius, void fraction, and vapor mass fraction). Our finding reveals two types of <span class="hlt">wave</span> <span class="hlt">propagation</span> behavior depending on the vapor mass fraction. Furthermore, the minimum <span class="hlt">wave</span> speed (required for the closure of cavitation modelling in the sonochemical reactor design) is analyzed and the influences of paramount parameters on it are quantitatively discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24726796','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24726796"><span id="translatedtitle">Experimental observation of cumulative second-harmonic generation of lamb <span class="hlt">waves</span> <span class="hlt">propagating</span> in long bones.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Zhenggang; Liu, Dan; Deng, Mingxi; Ta, Dean; Wang, Weiqi</p> <p>2014-07-01</p> <p>The experimental observation of cumulative second-harmonic generation of fundamental Lamb <span class="hlt">waves</span> in long bones is reported. Based on the modal expansion approach to waveguide excitation and the dispersion characteristics of Lamb <span class="hlt">waves</span> in long bones, the mechanism underlying the generation and accumulation of second harmonics by <span class="hlt">propagation</span> of the fundamental Lamb <span class="hlt">waves</span> was investigated. An experimental setup was established to detect the second-harmonic signals of Lamb <span class="hlt">wave</span> <span class="hlt">propagation</span> in long bones in vitro. Through analysis of the group velocities of the received signals, the appropriate fundamental Lamb <span class="hlt">wave</span> modes and the duration of the second-harmonic signals could be identified. The integrated amplitude of the time-domain second-harmonic signal was introduced and used to characterize the efficiency of second-harmonic generation by fundamental Lamb <span class="hlt">wave</span> <span class="hlt">propagation</span>. The results indicate that the second-harmonic signal generated by fundamental Lamb <span class="hlt">waves</span> <span class="hlt">propagating</span> in long bones can be observed clearly, and the effect was cumulative with <span class="hlt">propagation</span> distance when the fundamental Lamb <span class="hlt">wave</span> mode and the double-frequency Lamb <span class="hlt">wave</span> mode had the same phase velocities. The present results may be important in the development of a new method to evaluate the status of long bones using the cumulative second harmonic of ultrasonic Lamb <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRD..122.1423E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRD..122.1423E"><span id="translatedtitle">Horizontal <span class="hlt">propagation</span> of large-amplitude mountain <span class="hlt">waves</span> into the polar night jet</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ehard, Benedikt; Kaifler, Bernd; Dörnbrack, Andreas; Preusse, Peter; Eckermann, Stephen D.; Bramberger, Martina; Gisinger, Sonja; Kaifler, Natalie; Liley, Ben; Wagner, Johannes; Rapp, Markus</p> <p>2017-02-01</p> <p>We analyze a large-amplitude mountain <span class="hlt">wave</span> event, which was observed by a ground-based lidar above New Zealand between 31 July and 1 August 2014. Besides the lidar observations, European Centre for Medium-Range Weather Forecasts (ECMWF) data, satellite observations, and ray tracing simulations are utilized in this study. It is found that the <span class="hlt">propagation</span> of mountain <span class="hlt">waves</span> into the middle atmosphere is influenced by two different processes at different stages of the event. At the beginning of the event, instabilities in a weak wind layer cause <span class="hlt">wave</span> breaking in the lower stratosphere. During the course of the event the mountain <span class="hlt">waves</span> <span class="hlt">propagate</span> to higher altitudes and are refracted southward toward the polar night jet due to the strong meridional shear of the zonal wind. As the <span class="hlt">waves</span> <span class="hlt">propagate</span> out of the observational volume, the ground-based lidar observes no mountain <span class="hlt">waves</span> in the mesosphere. Ray tracing simulations indicate that the mountain <span class="hlt">waves</span> <span class="hlt">propagated</span> to mesospheric altitudes south of New Zealand where the polar night jet advected the <span class="hlt">waves</span> eastward. These results underline the importance of considering horizontal <span class="hlt">propagation</span> of gravity <span class="hlt">waves</span>, e.g., when analyzing locally confined observations of gravity <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5353470','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5353470"><span id="translatedtitle"><span class="hlt">Propagation</span> of electromagnetic <span class="hlt">wave</span> packets in iron-yttrium garnet plates and films</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Visatskas, A.V.; Ivashka, V.P.; Meshkauskas, I.I.</p> <p>1987-10-01</p> <p>The <span class="hlt">propagation</span> of <span class="hlt">wave</span> packets and harmonic <span class="hlt">waves</span> in iron-yttrium garnet (YIG) polycrystalline plates and single-crystalline films is studied. The basic parameters of the <span class="hlt">waves</span> are determined with the use of the equations for a flat waveguide and also the equations of magnetostatics. The theoretical results agree well with the experimental results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.tmp..434S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.tmp..434S"><span id="translatedtitle"><span class="hlt">Propagation</span> and attenuation of inhomogeneous <span class="hlt">waves</span> in double-porosity dual-permeability materials</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharma, M. D.</p> <p>2016-11-01</p> <p>This study considers the <span class="hlt">propagation</span> of harmonic plane <span class="hlt">waves</span> in a double-porosity dual-permeability solid saturated with single viscous fluid. Christoffel system is obtained to explain the existence of three longitudinal <span class="hlt">waves</span> and a transverse <span class="hlt">wave</span> in the medium considered. Each <span class="hlt">wave</span> is identified with a complex velocity, which is resolved for inhomogeneous <span class="hlt">propagation</span> to calculate the phase velocity and attenuation of the <span class="hlt">wave</span>. Pore-fluid pressures are expressed in terms of velocities of solid particles corresponding to the <span class="hlt">propagation</span> of three longitudinal <span class="hlt">waves</span>. Then, transfer rate of pore-fluid between two porosities induced by each longitudinal <span class="hlt">wave</span> is calculated as a function of its complex velocity. Numerical example is solved to study the dispersion in phase velocity and attenuation for each of the four <span class="hlt">waves</span>. Effects of pore-fluid viscosity, <span class="hlt">wave</span>-inhomogeneity and composition of double porosity on inhomogeneous <span class="hlt">propagation</span> are analysed graphically. Transfer rate of pore-fluid, induced by each of the three longitudinal <span class="hlt">waves</span>, is calculated as a periodic waveform. Variations in the fluid-flow profile are exhibited for different values of pore-fluid viscosity, skeleton permeability, <span class="hlt">wave</span>-frequency and <span class="hlt">wave</span>-inhomogeneity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.208..737S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.208..737S"><span id="translatedtitle"><span class="hlt">Propagation</span> and attenuation of inhomogeneous <span class="hlt">waves</span> in double-porosity dual-permeability materials</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharma, M. D.</p> <p>2017-02-01</p> <p>This study considers the <span class="hlt">propagation</span> of harmonic plane <span class="hlt">waves</span> in a double-porosity dual-permeability solid saturated with single viscous fluid. Christoffel system is obtained to explain the existence of three longitudinal <span class="hlt">waves</span> and a transverse <span class="hlt">wave</span> in the medium considered. Each <span class="hlt">wave</span> is identified with a complex velocity, which is resolved for inhomogeneous <span class="hlt">propagation</span> to calculate the phase velocity and attenuation of the <span class="hlt">wave</span>. Pore-fluid pressures are expressed in terms of velocities of solid particles corresponding to the <span class="hlt">propagation</span> of three longitudinal <span class="hlt">waves</span>. Then, transfer rate of pore-fluid between two porosities induced by each longitudinal <span class="hlt">wave</span> is calculated as a function of its complex velocity. Numerical example is solved to study the dispersion in phase velocity and attenuation for each of the four <span class="hlt">waves</span>. Effects of pore-fluid viscosity, <span class="hlt">wave</span>-inhomogeneity and composition of double porosity on inhomogeneous <span class="hlt">propagation</span> are analysed graphically. Transfer rate of pore-fluid, induced by each of the three longitudinal <span class="hlt">waves</span>, is calculated as a periodic waveform. Variations in the fluid-flow profile are exhibited for different values of pore-fluid viscosity, skeleton permeability, <span class="hlt">wave</span>-frequency and <span class="hlt">wave</span>-inhomogeneity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/AD1010149','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/AD1010149"><span id="translatedtitle">Highly Nonlinear <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Elastic Woodpile Periodic Structures</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2016-08-03</p> <p>attenuated over time (again, we briefly discuss the relevant features in Supple- mental Material [41]). We now explore this nanopteronic waveform more...formation of genuinely traveling <span class="hlt">waves</span> composed of a strongly-localized solitary <span class="hlt">wave</span> on top of a small amplitude oscillatory tail. This type of <span class="hlt">wave</span>...manipulat- ing highly nonlinear stress <span class="hlt">waves</span> at will, including high <span class="hlt">wave</span> attenuation and spontaneous formation of novel traveling <span class="hlt">waves</span> after an impact</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22482452','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22482452"><span id="translatedtitle">Coupled pulsating and cellular structure in the <span class="hlt">propagation</span> of globally <span class="hlt">planar</span> detonations in free space</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Han, Wenhu; Gao, Yang; Wang, Cheng; Law, Chung K.</p> <p>2015-10-15</p> <p>The globally <span class="hlt">planar</span> detonation in free space is numerically simulated, with particular interest to understand and quantify the emergence and evolution of the one-dimensional pulsating instability and the two-dimensional cellular structure which is inherently also affected by pulsating instability. It is found that the pulsation includes three stages: rapid decay of the overdrive, approach to the Chapman-Jouguet state and emergence of weak pulsations, and the formation of strong pulsations; while evolution of the cellular structure also exhibits distinct behavior at these three stages: no cell formation, formation of small-scale, irregular cells, and formation of regular cells of a larger scale. Furthermore, the average shock pressure in the detonation front consists of fine-scale oscillations reflecting the collision dynamics of the triple-shock structure and large-scale oscillations affected by the global pulsation. The common stages of evolution between the cellular structure and the pulsating behavior, as well as the existence of shock-front pressure oscillation, suggest highly correlated mechanisms between them. Detonations with period doubling, period quadrupling, and chaotic amplitudes were also observed and studied for progressively increasing activation energies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFD.H4005Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFD.H4005Z"><span id="translatedtitle">Laboratory measurements of the effect of internal <span class="hlt">waves</span> on sound <span class="hlt">propagation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Likun; Swinney, Harry L.; Lin, Ying-Tsong</p> <p>2016-11-01</p> <p>The fidelity of acoustic signals used in communication and imaging in the oceans is limited by density fluctuations arising from many sources, particularly from internal <span class="hlt">waves</span>. We present results from laboratory experiments on sound <span class="hlt">propagation</span> through an internal <span class="hlt">wave</span> field produced by a <span class="hlt">wave</span> generator consisting of multiple oscillating plates. The fluid density as a function of height is measured and used to determine the sound speed as a function of the height. Sound pulses from a transducer <span class="hlt">propagate</span> through the fluctuating stratified density field and are detected to determine sound refraction, pulse arrival time, and sound signal distortion. The results are compared with sound ray model and numerical models of underwater sound <span class="hlt">propagation</span>. The laboratory experiments can explore the parameter dependence by varying the fluid density profile, the sound pulse signal, and the internal <span class="hlt">wave</span> amplitude and frequency. The results lead to a better understanding of sound <span class="hlt">propagation</span> through and scattered by internal <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26880545','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26880545"><span id="translatedtitle">A circuit mechanism for the <span class="hlt">propagation</span> of <span class="hlt">waves</span> of muscle contraction in Drosophila.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fushiki, Akira; Zwart, Maarten F; Kohsaka, Hiroshi; Fetter, Richard D; Cardona, Albert; Nose, Akinao</p> <p>2016-02-15</p> <p>Animals move by adaptively coordinating the sequential activation of muscles. The circuit mechanisms underlying coordinated locomotion are poorly understood. Here, we report on a novel circuit for the <span class="hlt">propagation</span> of <span class="hlt">waves</span> of muscle contraction, using the peristaltic locomotion of Drosophila larvae as a model system. We found an intersegmental chain of synaptically connected neurons, alternating excitatory and inhibitory, necessary for <span class="hlt">wave</span> <span class="hlt">propagation</span> and active in phase with the <span class="hlt">wave</span>. The excitatory neurons (A27h) are premotor and necessary only for forward locomotion, and are modulated by stretch receptors and descending inputs. The inhibitory neurons (GDL) are necessary for both forward and backward locomotion, suggestive of different yet coupled central pattern generators, and its inhibition is necessary for <span class="hlt">wave</span> <span class="hlt">propagation</span>. The circuit structure and functional imaging indicated that the commands to contract one segment promote the relaxation of the next segment, revealing a mechanism for <span class="hlt">wave</span> <span class="hlt">propagation</span> in peristaltic locomotion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21538161','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21538161"><span id="translatedtitle"><span class="hlt">Propagation</span> of terahertz <span class="hlt">waves</span> in an atmospheric pressure microplasma with Epstein electron density profile</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yuan Chengxun; Zhou Zhongxiang; Zhang, Jingwen W.; Sun Hongguo; Wang He; Du Yanwei; Xiang Xiaoli</p> <p>2011-03-15</p> <p><span class="hlt">Propagation</span> properties of terahertz (THz) <span class="hlt">waves</span> in a bounded atmospheric-pressure microplasma (AMP) are analyzed in this study. A modified Epstein profile model is used to simulate the electron density distribution caused by the plasma sheaths. By introducing the dielectric constant of a Drude-Lorentz model and using the method of dividing the plasma into a series of subslabs with uniform electron density, the coefficients of power reflection, transmission, and absorption are derived for a bounded microplasma structure. The effects of size of microplasma, electron density profile, and collision frequency on the <span class="hlt">propagation</span> of THz <span class="hlt">waves</span> are analyzed numerically. The results indicate that the <span class="hlt">propagation</span> of THz <span class="hlt">waves</span> in AMPs depend greatly on the above three parameters. It is demonstrated that the THz <span class="hlt">wave</span> can play an important role in AMPs diagnostics; meanwhile, the AMP can be used as a novel potential tool to control THz <span class="hlt">wave</span> <span class="hlt">propagation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22471836','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22471836"><span id="translatedtitle">Solitary fast magnetosonic <span class="hlt">waves</span> <span class="hlt">propagating</span> obliquely to the magnetic field in cold collisionless plasma</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kichigin, G. N.</p> <p>2016-01-15</p> <p>Solutions describing solitary fast magnetosonic (FMS) <span class="hlt">waves</span> (FMS solitons) in cold magnetized plasma are obtained by numerically solving two-fluid hydrodynamic equations. The parameter domain within which steady-state solitary <span class="hlt">waves</span> can <span class="hlt">propagate</span> is determined. It is established that the Mach number for rarefaction FMS solitons is always less than unity. The restriction on the <span class="hlt">propagation</span> velocity leads to the limitation on the amplitudes of the magnetic field components of rarefaction solitons. It is shown that, as the soliton <span class="hlt">propagates</span> in plasma, the transverse component of its magnetic field rotates and makes a complete turn around the axis along which the soliton <span class="hlt">propagates</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ShWav..25..347W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ShWav..25..347W"><span id="translatedtitle">Experimental study on the interaction of <span class="hlt">planar</span> shock <span class="hlt">wave</span> with polygonal helium cylinders</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, M.; Si, T.; Luo, X.</p> <p>2015-07-01</p> <p>The evolution of a polygonal helium cylinder impacted by a <span class="hlt">planar</span> weak shock <span class="hlt">wave</span> is investigated experimentally. Three different polygonal interface shapes including a square, an equilateral triangle and a diamond are formed by the soap film technique, where thin pins are used as edges to connect the adjacent sides of soap films. Shock tube experiments are conducted to obtain sequences of schlieren images using a high-speed video camera. In each case, the development of the <span class="hlt">wave</span> system and the evolution of the polygonal helium cylinder subjected to a <span class="hlt">planar</span> shock <span class="hlt">wave</span> with a Mach number of are obtained in a single test. For comparison, numerical simulations are also performed using the two-dimensional and axisymmetric vectorized adaptive solver (VAS2D). The variations of the interface properties including the displacement, the length and the height of the distorted interfaces in the three cases are given. For the square helium cylinder, two counter-rotating vortices connected by a thin link can be observed. The height of the distorted interface always increases, and its length first decreases and then increases. In the triangle case, an air jet is formed quickly and moves downwards within the volume and eventually encounters the downstream interface, resulting in a bulge on the downstream interface. In the diamond case, the upstream interface quickly forms a re-entrant air jet similar to that in the triangle case, and the downstream interface becomes flat. The circulation in the three cases is calculated numerically, revealing the main driving mechanism of the development of the shocked polygonal interface. This work exhibits the great potential of the experimental method in studying shock-polygonal interface interactions in the case of slow/fast (air/helium) situations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25911148','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25911148"><span id="translatedtitle">Analysis of second-harmonic generation by primary ultrasonic guided <span class="hlt">wave</span> <span class="hlt">propagation</span> in a piezoelectric plate.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Deng, Mingxi; Xiang, Yanxun</p> <p>2015-08-01</p> <p>The effect of second-harmonic generation (SHG) by primary ultrasonic guided <span class="hlt">wave</span> <span class="hlt">propagation</span> is analyzed, where the nonlinear elastic, piezoelectric, and dielectric properties of the piezoelectric plate material are considered simultaneously. The formal solution of the corresponding second-harmonic displacement field is presented. Theoretical and numerical investigations clearly show that the SHG effect of primary guided <span class="hlt">wave</span> <span class="hlt">propagation</span> is highly sensitive to the electrical boundary conditions of the piezoelectric plate. The results obtained may provide a means through which the SHG efficiency of ultrasonic guided <span class="hlt">wave</span> <span class="hlt">propagation</span> can effectively be regulated by changing the electrical boundary conditions of the piezoelectric plate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/970653','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/970653"><span id="translatedtitle">Characterization of Heat-<span class="hlt">Wave</span> <span class="hlt">Propagation</span> through Laser-Driven Ti-Doped Underdense Plasma</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tanabe, M; Nishimura, H; Ohnishi, N; Fournier, K B; Fujioka, S; Iwamae, A; Hansen, S B; Nagai, K; Girard, F; Primout, M; Villette, B; Brebion, D; Mima, K</p> <p>2009-02-23</p> <p>The <span class="hlt">propagation</span> of a laser-driven heat-<span class="hlt">wave</span> into a Ti-doped aerogel target was investigated. The temporal evolution of the electron temperature was derived by means of Ti K-shell x-ray spectroscopy, and compared with two-dimensional radiation hydrodynamic simulations. Reasonable agreement was obtained in the early stage of the heat-<span class="hlt">wave</span> <span class="hlt">propagation</span>. In the later phase, laser absorption, the <span class="hlt">propagation</span> of the heat <span class="hlt">wave</span>, and hydrodynamic motion interact in a complex manner, and the plasma is mostly re-heated by collision and stagnation at the target central axis.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ApPhL.103g1904L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ApPhL.103g1904L"><span id="translatedtitle">Anisotropic <span class="hlt">propagation</span> and upper frequency limitation of terahertz <span class="hlt">waves</span> in graphene</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, XiaoYi; Wang, FengChao; Wu, HengAn</p> <p>2013-08-01</p> <p>Transverse <span class="hlt">wave</span> <span class="hlt">propagation</span> in single-layer graphene sheet (SLGS) is studied via molecular dynamics simulation, continuum, and non-continuum analysis. We found that the <span class="hlt">propagation</span> of transverse <span class="hlt">waves</span> with frequency over 3 THz is remarkably chirality-dependent. Furthermore, the <span class="hlt">wave</span> <span class="hlt">propagation</span> in zigzag direction remains undistorted only when the frequency is below 16 THz, while this threshold is 10 THz in the armchair direction. The minimum permissible wavelength is proposed to explain the frequency limitation due to non-continuity. Our findings lead to an improved fundamental understanding on the vibration of graphene-based nanodevices and have potential applications in design and fabrication of nanoelectromechanical systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...362..157V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...362..157V"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">propagation</span> in a 2D nonlinear structural acoustic waveguide using asymptotic expansions of wavenumbers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vijay Prakash, S.; Sonti, Venkata R.</p> <p>2016-02-01</p> <p>Nonlinear acoustic <span class="hlt">wave</span> <span class="hlt">propagation</span> in an infinite rectangular waveguide is investigated. The upper boundary of this waveguide is a nonlinear elastic plate, whereas the lower boundary is rigid. The fluid is assumed to be inviscid with zero mean flow. The focus is restricted to non-<span class="hlt">planar</span> modes having finite amplitudes. The approximate solution to the acoustic velocity potential of an amplitude modulated pulse is found using the method of multiple scales (MMS) involving both space and time. The calculations are presented up to the third order of the small parameter. It is found that at some frequencies the amplitude modulation is governed by the Nonlinear Schrödinger equation (NLSE). The first objective here is to study the nonlinear term in the NLSE. The sign of the nonlinear term in the NLSE plays a role in determining the stability of the amplitude modulation. Secondly, at other frequencies, the primary pulse interacts with its higher harmonics, as do two or more primary pulses with their resultant higher harmonics. This happens when the phase speeds of the <span class="hlt">waves</span> match and the objective is to identify the frequencies of such interactions. For both the objectives, asymptotic coupled wavenumber expansions for the linear dispersion relation are required for an intermediate fluid loading. The novelty of this work lies in obtaining the asymptotic expansions and using them for predicting the sign change of the nonlinear term at various frequencies. It is found that when the coupled wavenumbers approach the uncoupled pressure-release wavenumbers, the amplitude modulation is stable. On the other hand, near the rigid-duct wavenumbers, the amplitude modulation is unstable. Also, as a further contribution, these wavenumber expansions are used to identify the frequencies of the higher harmonic interactions. And lastly, the solution for the amplitude modulation derived through the MMS is validated using these asymptotic expansions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1030251','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1030251"><span id="translatedtitle">Stress <span class="hlt">wave</span> <span class="hlt">propagation</span> in a composite beam subjected to transverse impact.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Lu, Wei-Yang; Song, Bo; Jin, Huiqing</p> <p>2010-08-01</p> <p>Composite materials, particularly fiber reinforced plastic composites, have been extensively utilized in many military and industrial applications. As an important structural component in these applications, the composites are often subjected to external impact loading. It is desirable to understand the mechanical response of the composites under impact loading for performance evaluation in the applications. Even though many material models for the composites have been developed, experimental investigation is still needed to validate and verify the models. It is essential to investigate the intrinsic material response. However, it becomes more applicable to determine the structural response of composites, such as a composite beam. The composites are usually subjected to out-of-plane loading in applications. When a composite beam is subjected to a sudden transverse impact, two different kinds of stress <span class="hlt">waves</span>, longitudinal and transverse <span class="hlt">waves</span>, are generated and <span class="hlt">propagate</span> in the beam. The longitudinal stress <span class="hlt">wave</span> <span class="hlt">propagates</span> through the thickness direction; whereas, the <span class="hlt">propagation</span> of the transverse stress <span class="hlt">wave</span> is in-plane directions. The longitudinal stress <span class="hlt">wave</span> speed is usually considered as a material constant determined by the material density and Young's modulus, regardless of the loading rate. By contrast, the transverse <span class="hlt">wave</span> speed is related to structural parameters. In ballistic mechanics, the transverse <span class="hlt">wave</span> plays a key role to absorb external impact energy [1]. The faster the transverse <span class="hlt">wave</span> speed, the more impact energy dissipated. Since the transverse <span class="hlt">wave</span> speed is not a material constant, it is not possible to be calculated from stress-<span class="hlt">wave</span> theory. One can place several transducers to track the transverse <span class="hlt">wave</span> <span class="hlt">propagation</span>. An alternative but more efficient method is to apply digital image correlation (DIC) to visualize the transverse <span class="hlt">wave</span> <span class="hlt">propagation</span>. In this study, we applied three-pointbending (TPB) technique to Kolsky compression bar to facilitate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998PhDT.......166G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998PhDT.......166G"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">propagation</span> in tyres and the resultant noise radiation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gi-Jeon, Kim</p> <p></p> <p>Tyre noise has become an increasingly important road traffic noise source. This is because other sources on the vehicle, such as the air intake system, the exhaust system and the engine, have tended to become relatively quieter. This situation forces the tyre noise component to be reduced in order to achieve a reduction in the overall traffic noise level. In the research reported here, vibration, sound radiation and sound transmission of a passenger car radial tyre were investigated. The first half of this thesis discusses the vibration characteristics using two methods; (1)FEM to analysis modal behaviour in detail, (2)Analytical models to interpret the FEM results. These methods have both advantages and disadvantages in investigating tyre vibration. Combining the two methods is necessary in order to a fully understand the vibration behaviour of a tyre. Dispersion relationships and the related frequency of tyre modes is analysed by FEM and the flexural <span class="hlt">wave</span> <span class="hlt">propagation</span> in the tyre shell and the sound radiation of the tyre wall by flexural modes is analyzed using plate and shell theory. The second part of this thesis discusses the radiation and transmission of tyre noise. To predict the radiation of sound with only a knowledge of the surface vibration velocity, the experimental Green's functions were estimated by using the acoustic reciprocity principle. This technique was also applied to separate airborne structure borne noise for identification of the transmission path of tyre noise into a vehicle cabin and quantification of the relative contribution of various regions of the vibrating tyre surface to vehicle interior noise. The application of acoustic reciprocity for the tyre noise problem was verified and compared with BEM analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ACP....16.8447K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ACP....16.8447K"><span id="translatedtitle">On the climatological probability of the vertical <span class="hlt">propagation</span> of stationary planetary <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Karami, Khalil; Braesicke, Peter; Sinnhuber, Miriam; Versick, Stefan</p> <p>2016-07-01</p> <p>We introduce a diagnostic tool to assess a climatological framework of the optimal <span class="hlt">propagation</span> conditions for stationary planetary <span class="hlt">waves</span>. Analyzing 50 winters using NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research) reanalysis data we derive probability density functions (PDFs) of positive vertical <span class="hlt">wave</span> number as a function of zonal and meridional <span class="hlt">wave</span> numbers. We contrast this quantity with classical climatological means of the vertical <span class="hlt">wave</span> number. Introducing a membership value function (MVF) based on fuzzy logic, we objectively generate a modified set of PDFs (mPDFs) and demonstrate their superior performance compared to the climatological mean of vertical <span class="hlt">wave</span> number and the original PDFs. We argue that mPDFs allow an even better understanding of how background conditions impact <span class="hlt">wave</span> <span class="hlt">propagation</span> in a climatological sense. As expected, probabilities are decreasing with increasing zonal <span class="hlt">wave</span> numbers. In addition we discuss the meridional <span class="hlt">wave</span> number dependency of the PDFs which is usually neglected, highlighting the contribution of meridional <span class="hlt">wave</span> numbers 2 and 3 in the stratosphere. We also describe how mPDFs change in response to strong vortex regime (SVR) and weak vortex regime (WVR) conditions, with increased probabilities of the <span class="hlt">wave</span> <span class="hlt">propagation</span> during WVR than SVR in the stratosphere. We conclude that the mPDFs are a convenient way to summarize climatological information about planetary <span class="hlt">wave</span> <span class="hlt">propagation</span> in reanalysis and climate model data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JaJAP..54gHF02M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JaJAP..54gHF02M"><span id="translatedtitle">Two-<span class="hlt">wave</span> <span class="hlt">propagation</span> in in vitro swine distal ulna</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mano, Isao; Horii, Kaoru; Matsukawa, Mami; Otani, Takahiko</p> <p>2015-07-01</p> <p>Ultrasonic transmitted <span class="hlt">waves</span> were obtained in an in vitro swine distal ulna specimen, which mimics a human distal radius, that consists of interconnected cortical bone and cancellous bone. The transmitted waveforms appeared similar to the fast <span class="hlt">waves</span>, slow <span class="hlt">waves</span>, and overlapping fast and slow <span class="hlt">waves</span> measured in the specimen after removing the surface cortical bone (only cancellous bone). In addition, the circumferential <span class="hlt">waves</span> in the cortical bone and water did not affect the fast and slow <span class="hlt">waves</span>. This suggests that the fast-and-slow-<span class="hlt">wave</span> phenomenon can be observed in an in vivo human distal radius.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22567590','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22567590"><span id="translatedtitle">Feasibility of optical coherence elastography measurements of shear <span class="hlt">wave</span> <span class="hlt">propagation</span> in homogeneous tissue equivalent phantoms.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Razani, Marjan; Mariampillai, Adrian; Sun, Cuiru; Luk, Timothy W H; Yang, Victor X D; Kolios, Michael C</p> <p>2012-05-01</p> <p>In this work, we explored the potential of measuring shear <span class="hlt">wave</span> <span class="hlt">propagation</span> using optical coherence elastography (OCE) based on a swept-source optical coherence tomography (OCT) system. Shear <span class="hlt">waves</span> were generated using a 20 MHz piezoelectric transducer (circular element 8.5 mm diameter) transmitting sine-<span class="hlt">wave</span> bursts of 400 μs, synchronized with the OCT swept source wavelength sweep. The acoustic radiation force (ARF) was applied to two gelatin phantoms (differing in gelatin concentration by weight, 8% vs. 14%). Differential OCT phase maps, measured with and without the ARF, demonstrate microscopic displacement generated by shear <span class="hlt">wave</span> <span class="hlt">propagation</span> in these phantoms of different stiffness. We present preliminary results of OCT derived shear <span class="hlt">wave</span> <span class="hlt">propagation</span> velocity and modulus, and compare these results to rheometer measurements. The results demonstrate the feasibility of shear <span class="hlt">wave</span> OCE (SW-OCE) for high-resolution microscopic homogeneous tissue mechanical property characterization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25704900','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25704900"><span id="translatedtitle">Analyzing critical <span class="hlt">propagation</span> in a reaction-diffusion-advection model using unstable slow <span class="hlt">waves</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kneer, Frederike; Obermayer, Klaus; Dahlem, Markus A</p> <p>2015-02-01</p> <p>The effect of advection on the <span class="hlt">propagation</span> and in particular on the critical minimal speed of traveling <span class="hlt">waves</span> in a reaction-diffusion model is studied. Previous theoretical studies estimated this effect on the velocity of stable fast <span class="hlt">waves</span> and predicted the existence of a critical advection strength below which <span class="hlt">propagating</span> <span class="hlt">waves</span> are not supported anymore. In this paper, an analytical expression for the advection-velocity relation of the unstable slow <span class="hlt">wave</span> is derived. In addition, the critical advection strength is calculated taking into account the unstable slow <span class="hlt">wave</span> solution. We also analyze a two-variable reaction-diffusion-advection model numerically in a wide parameter range. Due to the new control parameter (advection) we can find stable <span class="hlt">wave</span> <span class="hlt">propagation</span> in the otherwise non-excitable parameter regime, if the advection strength exceeds a critical value. Comparing theoretical predictions to numerical results, we find that they are in good agreement. Theory provides an explanation for the observed behaviour.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhPl...24a2107F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhPl...24a2107F"><span id="translatedtitle">Effects of external magnetic field on oblique <span class="hlt">propagation</span> of ion acoustic cnoidal <span class="hlt">wave</span> in nonextensive plasma</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Farhad Kiyaei, Forough; Dorranian, Davoud</p> <p>2017-01-01</p> <p>Effects of the obliqueness and the strength of external magnetic field on the ion acoustic (IA) cnoidal <span class="hlt">wave</span> in a nonextensive plasma are investigated. The reductive perturbation method is employed to derive the corresponding KdV equation for the IA <span class="hlt">wave</span>. Sagdeev potential is extracted, and the condition of generation of IA <span class="hlt">waves</span> in the form of cnoidal <span class="hlt">waves</span> or solitons is discussed in detail. In this work, the domain of allowable values of nonextensivity parameter q for generation of the IA cnoidal <span class="hlt">wave</span> in the plasma medium is considered. The results show that only the compressive IA <span class="hlt">wave</span> may generate and <span class="hlt">propagate</span> in the plasma medium. Increasing the strength of external magnetic field will increase the frequency of the <span class="hlt">wave</span> and decrease its amplitude, while increasing the angle of <span class="hlt">propagation</span> will decrease the frequency of the <span class="hlt">wave</span> and increase its amplitude.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22072444','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22072444"><span id="translatedtitle">The interaction between two <span class="hlt">planar</span> and nonplanar quantum electron acoustic solitary <span class="hlt">waves</span> in dense electron-ion plasmas</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>EL-Labany, S. K.; El-Mahgoub, M. G.; EL-Shamy, E. F.</p> <p>2012-06-15</p> <p>The interaction between two <span class="hlt">planar</span> and nonplanar (cylindrical and spherical) quantum electron acoustic solitary <span class="hlt">waves</span> (QEASWs) in quantum dense electron-ion plasmas has been studied. The extended Poincare-Lighthill-Kuo method is used to obtain <span class="hlt">planar</span> and nonplanar phase shifts after the interaction of the two QEASWs. The change of phase shifts and trajectories for QEASWs due to the effect of the different geometries, the quantum corrections of diffraction, and the cold electron-to-hot electron number density ratio are discussed. It is shown that the interaction of the QEASWs in <span class="hlt">planar</span> geometry, cylindrical geometry, and spherical geometry are different. The present investigation may be beneficial to understand the interaction between two <span class="hlt">planar</span> and nonplanar QEASWs that may occur in the quantum plasmas found in laser-produced plasmas as well as in astrophysical plasmas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26274641','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26274641"><span id="translatedtitle">How <span class="hlt">planar</span> optical <span class="hlt">waves</span> can be made to climb dielectric steps.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hammer, Manfred; Hildebrandt, Andre; Förstner, Jens</p> <p>2015-08-15</p> <p>We show how to optically connect guiding layers at different elevations in a 3-D integrated photonic circuit. Transfer of optical power carried by <span class="hlt">planar</span>, semi-guided <span class="hlt">waves</span> is possible without reflections or radiation losses, and over large vertical distances. This functionality is realized through simple step-like folds of high-contrast dielectric slab waveguides, in combination with oblique <span class="hlt">wave</span> incidence, and fulfilling a resonance condition. Radiation losses vanish, and polarization conversion is suppressed for TE <span class="hlt">wave</span> incidence beyond certain critical angles. This can be understood by fundamental arguments resting on a version of Snell's law. The two 90° corners of a step act as identical partial reflectors in a Fabry-Perot-like resonator setup. By selecting the step height, i.e., the distance between the reflectors, one realizes resonant states with full transmission. Rigorous quasi-analytical simulations for typical silicon/silica parameters demonstrate the functioning. Combinations of several step junctions can lead to other types of optical on-chip connects, e.g., U-turn- or bridge-like configurations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22220724','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22220724"><span id="translatedtitle"><span class="hlt">Propagation</span> of sound <span class="hlt">waves</span> through a spatially homogeneous but smoothly time-dependent medium</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hayrapetyan, A.G.; Grigoryan, K.K.; Petrosyan, R.G.; Fritzsche, S.</p> <p>2013-06-15</p> <p>The <span class="hlt">propagation</span> of sound through a spatially homogeneous but non-stationary medium is investigated within the framework of fluid dynamics. For a non-vortical fluid, especially, a generalized <span class="hlt">wave</span> equation is derived for the (scalar) potential of the fluid velocity distribution in dependence of the equilibrium mass density of the fluid and the sound <span class="hlt">wave</span> velocity. A solution of this equation for a finite transition period τ is determined in terms of the hypergeometric function for a phenomenologically realistic, sigmoidal change of the mass density and sound <span class="hlt">wave</span> velocity. Using this solution, it is shown that the energy flux of the sound <span class="hlt">wave</span> is not conserved but increases always for the <span class="hlt">propagation</span> through a non-stationary medium, independent of whether the equilibrium mass density is increased or decreased. It is found, moreover, that this amplification of the transmitted <span class="hlt">wave</span> arises from an energy exchange with the medium and that its flux is equal to the (total) flux of the incident and the reflected <span class="hlt">wave</span>. An interpretation of the reflected <span class="hlt">wave</span> as a <span class="hlt">propagation</span> of sound backward in time is given in close analogy to Feynman and Stueckelberg for the <span class="hlt">propagation</span> of anti-particles. The reflection and transmission coefficients of sound <span class="hlt">propagating</span> through a non-stationary medium is analyzed in more detail for hypersonic <span class="hlt">waves</span> with transition periods τ between 15 and 200 ps as well as the transformation of infrasound <span class="hlt">waves</span> in non-stationary oceans. -- Highlights: •Analytically exact study of sound <span class="hlt">propagation</span> through a non-stationary medium. •Energy exchange between the non-stationary medium and the sound <span class="hlt">wave</span>. •Transformation of hypersonic and ultrasound frequencies in non-stationary media. •<span class="hlt">Propagation</span> of sound backward in time in close analogy to anti-particles. •Prediction of tsunamis both in spatially and temporally inhomogeneous oceans.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/503587','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/503587"><span id="translatedtitle">Self-consistent simulation of a <span class="hlt">planar</span> electron-cyclotron-<span class="hlt">wave</span>-resonance discharge</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Krimke, R.; Urbassek, H.M.</p> <p>1997-06-01</p> <p>A discharge heated inductively by resonant absorption of electron cyclotron <span class="hlt">waves</span> discharge is modeled in a <span class="hlt">planar</span> geometry. The simulation algorithm is based on a kinetic particle-in-cell (PIC/MC) simulation of the plasma properties; the electromagnetic field is calculated macroscopically using the Appleton{endash}Hartree theory for the dielectric tensor. The results are checked against a simplified analytical theory and experimental data by B. Pfeiffer [J. Appl. Phys. {bold 37}, 1624,1628 (1966)] for a 15 mTorr argon discharge. As a result, we show that an inhomogeneous density profile in the discharge strongly affects the electromagnetic fields in the plasma. Power deposition is calculated both in and outside of the resonance. {copyright} {ital 1997 American Institute of Physics.}</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SoPh..291.1369B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SoPh..291.1369B"><span id="translatedtitle"><span class="hlt">Propagation</span> of Long-Wavelength Nonlinear Slow Sausage <span class="hlt">Waves</span> in Stratified Magnetic Flux Tubes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barbulescu, M.; Erdélyi, R.</p> <p>2016-05-01</p> <p>The <span class="hlt">propagation</span> of nonlinear, long-wavelength, slow sausage <span class="hlt">waves</span> in an expanding magnetic flux tube, embedded in a non-magnetic stratified environment, is discussed. The governing equation for surface <span class="hlt">waves</span>, which is akin to the Leibovich-Roberts equation, is derived using the method of multiple scales. The solitary <span class="hlt">wave</span> solution of the equation is obtained numerically. The results obtained are illustrative of a solitary <span class="hlt">wave</span> whose properties are highly dependent on the degree of stratification.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA482175','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA482175"><span id="translatedtitle">A Model for the <span class="hlt">Propagation</span> of Nonlinear Surface <span class="hlt">Waves</span> over Viscous Muds</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2007-07-05</p> <p>Coastal Geosciences Hsiao, S.V., Shemdin , O.H., 1980. Interaction of ocean <span class="hlt">waves</span> with a soft Program (AS; award N00014-03-1-0200). Dr. Johan C...locate/coastaleng A model for the <span class="hlt">propagation</span> of nonlinear surface <span class="hlt">waves</span> over viscous muds James M. Kaihatu a,, Alexandru Sheremet b K. Todd Holland c...The effect of a thin viscous fluid-mud layer on nearshore nonlinear <span class="hlt">wave</span> - <span class="hlt">wave</span> interactions is studied using a parabolic frequency-domain nonlinear</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26093440','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26093440"><span id="translatedtitle">Elastic parabolic equation solutions for oceanic T-<span class="hlt">wave</span> generation and <span class="hlt">propagation</span> from deep seismic sources.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Frank, Scott D; Collis, Jon M; Odom, Robert I</p> <p>2015-06-01</p> <p>Oceanic T-<span class="hlt">waves</span> are earthquake signals that originate when elastic <span class="hlt">waves</span> interact with the fluid-elastic interface at the ocean bottom and are converted to acoustic <span class="hlt">waves</span> in the ocean. These <span class="hlt">waves</span> <span class="hlt">propagate</span> long distances in the Sound Fixing and Ranging (SOFAR) channel and tend to be the largest observed arrivals from seismic events. Thus, an understanding of their generation is important for event detection, localization, and source-type discrimination. Recently benchmarked seismic self-starting fields are used to generate elastic parabolic equation solutions that demonstrate generation and <span class="hlt">propagation</span> of oceanic T-<span class="hlt">waves</span> in range-dependent underwater acoustic environments. Both downward sloping and abyssal ocean range-dependent environments are considered, and results demonstrate conversion of elastic <span class="hlt">waves</span> into water-borne oceanic T-<span class="hlt">waves</span>. Examples demonstrating long-range broadband T-<span class="hlt">wave</span> <span class="hlt">propagation</span> in range-dependent environments are shown. These results confirm that elastic parabolic equation solutions are valuable for characterization of the relationships between T-<span class="hlt">wave</span> <span class="hlt">propagation</span> and variations in range-dependent bathymetry or elastic material parameters, as well as for modeling T-<span class="hlt">wave</span> receptions at hydrophone arrays or coastal receiving stations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAP...119u4902Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAP...119u4902Y"><span id="translatedtitle">Numerical and experimental study of Lamb <span class="hlt">wave</span> <span class="hlt">propagation</span> in a two-dimensional acoustic black hole</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yan, Shiling; Lomonosov, Alexey M.; Shen, Zhonghua</p> <p>2016-06-01</p> <p>The <span class="hlt">propagation</span> of laser-generated Lamb <span class="hlt">waves</span> in a two-dimensional acoustic black-hole structure was studied numerically and experimentally. The geometrical acoustic theory has been applied to calculate the beam trajectories in the region of the acoustic black hole. The finite element method was also used to study the time evolution of <span class="hlt">propagating</span> <span class="hlt">waves</span>. An optical system based on the laser-Doppler vibration method was assembled. The effect of the focusing <span class="hlt">wave</span> and the reduction in <span class="hlt">wave</span> speed of the acoustic black hole has been validated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22086264','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22086264"><span id="translatedtitle">ANALYTIC APPROXIMATE SEISMOLOGY OF <span class="hlt">PROPAGATING</span> MAGNETOHYDRODYNAMIC <span class="hlt">WAVES</span> IN THE SOLAR CORONA</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Goossens, M.; Soler, R.; Arregui, I.</p> <p>2012-12-01</p> <p>Observations show that <span class="hlt">propagating</span> magnetohydrodynamic (MHD) <span class="hlt">waves</span> are ubiquitous in the solar atmosphere. The technique of MHD seismology uses the <span class="hlt">wave</span> observations combined with MHD <span class="hlt">wave</span> theory to indirectly infer physical parameters of the solar atmospheric plasma and magnetic field. Here, we present an analytical seismological inversion scheme for <span class="hlt">propagating</span> MHD <span class="hlt">waves</span>. This scheme uses the observational information on wavelengths and damping lengths in a consistent manner, along with observed values of periods or phase velocities, and is based on approximate asymptotic expressions for the theoretical values of wavelengths and damping lengths. The applicability of the inversion scheme is discussed and an example is given.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930049673&hterms=dependance&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Ddependance','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930049673&hterms=dependance&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Ddependance"><span id="translatedtitle">Parametric instabilities of large amplitude Alfven <span class="hlt">waves</span> with obliquely <span class="hlt">propagating</span> sidebands</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vinas, A. F.; Goldstein, M. L.</p> <p>1992-01-01</p> <p>This paper presents a brief report on properties of the parametric decay and modulational, filamentation, and magnetoacoustic instabilities of a large amplitude, circularly polarized Alfven <span class="hlt">wave</span>. We allow the daughter and sideband <span class="hlt">waves</span> to <span class="hlt">propagate</span> at an arbitrary angle to the background magnetic field so that the electrostatic and electromagnetic characteristics of these <span class="hlt">waves</span> are coupled. We investigate the dependance of these instabilities on dispersion, plasma/beta, pump <span class="hlt">wave</span> amplitude, and <span class="hlt">propagation</span> angle. Analytical and numerical results are compared with numerical simulations to investigate the full nonlinear evolution of these instabilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.7839G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.7839G"><span id="translatedtitle">Peculiarities of the <span class="hlt">Propagation</span> of Supersonic Seismic <span class="hlt">Waves</span> to the Upper Atmosphere.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gavrilov, Nikolai M.; Kshevetskii, Sergey P.</p> <p>2016-04-01</p> <p>Seismic <span class="hlt">waves</span> generated before and after earthquakes produce vertical and horizontal motion of the Earth's surface. The perturbations can <span class="hlt">propagate</span> upwards and produce variations and oscillations of atmospheric characteristics at different altitudes. One of the mechanisms of such ionospheric perturbations is <span class="hlt">propagation</span> of acoustic-gravity <span class="hlt">waves</span> (AGWs) in the atmosphere caused by seismic excitations at the ground surface. The main difficulties in such explanation are high phase speeds of surface seismic <span class="hlt">waves</span>, much exceeding the sound speed in the atmosphere near the ground. The strongest ground seismic <span class="hlt">waves</span> are the surface Rayleigh <span class="hlt">waves</span>, having phase speeds 3 - 4 km/s (sometimes up to 10 km/s). Traditional theory of atmospheric AGWs predicts that such supersonic excitation should produce not <span class="hlt">propagating</span>, but trapped (or evanescent) gravity <span class="hlt">wave</span> modes with amplitudes exponentially decaying with altitude. This can raise questions about the importance of seismic-excited supersonic <span class="hlt">waves</span> in the formation of ionospheric disturbances. In the present study, we use the recently developed nonlinear numerical Whole-altitude Acoustic-Gravity <span class="hlt">Wave</span> Model (WAGWM) to simulate <span class="hlt">propagation</span> of supersonic <span class="hlt">wave</span> modes from the ground to the upper atmosphere. The WAGWM is a three-dimensional model and uses the plain geometry. It calculates atmospheric velocity components and deviations of temperature, pressure, and density from their background values. Gavrilov and Kshevetskii (2014) described the set of used nonlinear three-dimensional equations of continuity, motion and heat balance. At the upper boundary z = 500 km we assume zero vertical velocity and zero vertical gradients of the other <span class="hlt">wave</span> parameters. In the present research, we made calculations in rectangle region of the atmosphere and assume horizontal periodicity of <span class="hlt">wave</span> solutions. Variations of vertical velocity produced by <span class="hlt">propagating</span> seismic <span class="hlt">waves</span> at the Earth's surface serve to force the <span class="hlt">waves</span> in the model. Calculations</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AIPC.1806o0005M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AIPC.1806o0005M"><span id="translatedtitle">Numerical simulation of ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in fiber reinforced plastic using image-based modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mizokami, Naoya; Nakahata, Kazuyuki; Ogi, Keiji; Yamawaki, Hisashi; Shiwa, Mitsuharu</p> <p>2017-02-01</p> <p>The use of fiber reinforced plastics (FRPs) as structural components has significantly increased in recent years. FRPs are made of stacks of plies, each of which is reinforced by fibers. When modeling ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in FRPs, it is important to introduce three-dimensional mesoscopic and microscopic structures to account for the anisotropy and heterogeneity caused by fiber orientation and the lay-up of laminates. In this study, a finite element method using an image-based modeling is applied to simulation of ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in a carbon FRP (CFRP). Here, the elastic stiffness of a single ply is determined using a homogenization method, where a CFRP microstructure is incorporated on the basis of a two-scale asymptotic expansion. The <span class="hlt">wave</span> <span class="hlt">propagation</span> in a CFRP specimen composed of unidirectionally aligned fibers is calculated, and the simulation results are compared to visualization results obtained for ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> using a laser scanning device.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1259966','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1259966"><span id="translatedtitle">Conical <span class="hlt">wave</span> <span class="hlt">propagation</span> and diffraction in two-dimensional hexagonally packed granular lattices</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chong, C.; Kevrekidis, P. G.; Ablowitz, M. J.; Ma, Yi-Ping</p> <p>2016-01-25</p> <p>We explore linear and nonlinear mechanisms for conical <span class="hlt">wave</span> <span class="hlt">propagation</span> in two-dimensional lattices in the realm of phononic crystals. As a prototypical example, a statically compressed granular lattice of spherical particles arranged in a hexagonal packing configuration is analyzed. Upon identifying the dispersion relation of the underlying linear problem, the resulting diffraction properties are considered. Analysis both via a heuristic argument for the linear <span class="hlt">propagation</span> of a <span class="hlt">wave</span> packet and via asymptotic analysis leading to the derivation of a Dirac system suggests the occurrence of conical diffraction. This analysis is valid for strong precompression, i.e., near the linear regime. For weak precompression, conical <span class="hlt">wave</span> <span class="hlt">propagation</span> is still possible, but the resulting expanding circular <span class="hlt">wave</span> front is of a nonoscillatory nature, resulting from the complex interplay among the discreteness, nonlinearity, and geometry of the packing. Lastly, the transition between these two types of <span class="hlt">propagation</span> is explored.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2722927','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2722927"><span id="translatedtitle">Surface Current Density Mapping for Identification of Gastric Slow <span class="hlt">Wave</span> <span class="hlt">Propagation</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Bradshaw, L. A.; Cheng, L. K.; Richards, W. O.; Pullan, A. J.</p> <p>2009-01-01</p> <p>The magnetogastrogram records clinically relevant parameters of the electrical slow <span class="hlt">wave</span> of the stomach noninvasively. Besides slow <span class="hlt">wave</span> frequency, gastric slow <span class="hlt">wave</span> <span class="hlt">propagation</span> velocity is a potentially useful clinical indicator of the state of health of gastric tissue, but it is a difficult parameter to determine from noninvasive bioelectric or biomagnetic measurements. We present a method for computing the surface current density (SCD) from multichannel magnetogastrogram recordings that allows computation of the <span class="hlt">propagation</span> velocity of the gastric slow <span class="hlt">wave</span>. A moving dipole source model with hypothetical as well as realistic biomagnetometer parameters demonstrates that while a relatively sparse array of magnetometer sensors is sufficient to compute a single average <span class="hlt">propagation</span> velocity, more detailed information about spatial variations in <span class="hlt">propagation</span> velocity requires higher density magnetometer arrays. Finally, the method is validated with simultaneous MGG and serosal EMG measurements in a porcine subject. PMID:19403355</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1259966-conical-wave-propagation-diffraction-two-dimensional-hexagonally-packed-granular-lattices','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1259966-conical-wave-propagation-diffraction-two-dimensional-hexagonally-packed-granular-lattices"><span id="translatedtitle">Conical <span class="hlt">wave</span> <span class="hlt">propagation</span> and diffraction in two-dimensional hexagonally packed granular lattices</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Chong, C.; Kevrekidis, P. G.; Ablowitz, M. J.; ...</p> <p>2016-01-25</p> <p>We explore linear and nonlinear mechanisms for conical <span class="hlt">wave</span> <span class="hlt">propagation</span> in two-dimensional lattices in the realm of phononic crystals. As a prototypical example, a statically compressed granular lattice of spherical particles arranged in a hexagonal packing configuration is analyzed. Upon identifying the dispersion relation of the underlying linear problem, the resulting diffraction properties are considered. Analysis both via a heuristic argument for the linear <span class="hlt">propagation</span> of a <span class="hlt">wave</span> packet and via asymptotic analysis leading to the derivation of a Dirac system suggests the occurrence of conical diffraction. This analysis is valid for strong precompression, i.e., near the linear regime. Formore » weak precompression, conical <span class="hlt">wave</span> <span class="hlt">propagation</span> is still possible, but the resulting expanding circular <span class="hlt">wave</span> front is of a nonoscillatory nature, resulting from the complex interplay among the discreteness, nonlinearity, and geometry of the packing. Lastly, the transition between these two types of <span class="hlt">propagation</span> is explored.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24960005','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24960005"><span id="translatedtitle">Sea <span class="hlt">wave</span> <span class="hlt">propagation</span> from offshore to Maputo's coast. Application to longshore sediment transport assessment.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Viola, Cristina N A; Grifoll, Manel; Palalane, Jaime; Oliveira, Tiago C A</p> <p>2014-01-01</p> <p>This study aims to characterize the <span class="hlt">wave</span> climate near the coastal region of Maputo (Mozambique), and to provide a first assessment of the sediment transport load in this area. A time-series of 13 years' worth of offshore <span class="hlt">wave</span> data, obtained from reanalysis products, was <span class="hlt">propagated</span> to the coast. <span class="hlt">Wave</span> <span class="hlt">propagation</span> was performed using Linear <span class="hlt">Wave</span> theory and the numerical model, Simulating <span class="hlt">WAves</span> Nearshore (SWAN). <span class="hlt">Propagations</span> with SWAN were carried out considering different scenarios in order to evaluate the influence of parameters such as wind, tidal level, frequency spectrum and numerical mesh resolution on <span class="hlt">wave</span> characteristics along the coast. The prevalent <span class="hlt">waves</span> <span class="hlt">propagated</span> came from between east and southwest directions. Results from linear <span class="hlt">propagation</span> were used to estimate the potential longshore sediment transport. The Coastal Engineering Research Center formula was applied for a stretch of beach in the Machangulo Peninsula. A net potential rate of longitudinal sediment transport (of the order of 10(5) m(3)/year, along an extension of the coast of 21 km) was directed northwards, and was consistent with the frequent <span class="hlt">wave</span> directions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1367963','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1367963"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">Propagation</span> through a Viscous Incompressible Fluid Contained in an Initially Stressed Elastic Tube</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Atabek, H. B.; Lew, H. S.</p> <p>1966-01-01</p> <p>To have a better understanding of the flow of blood in arteries a theoretical analysis of the pressure <span class="hlt">wave</span> <span class="hlt">propagation</span> through a viscous incompressible fluid contained in an initially stressed tube is considered. The fluid is assumed to be Newtonian. The tube is taken to be elastic and isotropic. The analysis is restricted to tubes with thin walls and to <span class="hlt">waves</span> whose wavelengths are very large compared with the radius of the tube. It is further assumed that the amplitude of the pressure disturbance is sufficiently small so that nonlinear terms of the inertia of the fluid are negligible compared with linear ones. Both circumferential and longitudinal initial stresses are considered; however, their origins are not specified. Initial stresses enter equations as independent parameters. A frequency equation, which is quadratic in the square of the <span class="hlt">propagation</span> velocity is obtained. Two out of four roots of this equation give the velocity of <span class="hlt">propagation</span> of two distinct outgoing <span class="hlt">waves</span>. The remaining two roots represent incoming <span class="hlt">waves</span> corresponding to the first two <span class="hlt">waves</span>. One of the <span class="hlt">waves</span> <span class="hlt">propagates</span> more slowly than the other. As the circumferential and/or longitudinal stress of the wall increases, the velocity of <span class="hlt">propagation</span> and transmission per wavelength of the slower <span class="hlt">wave</span> decreases. The response of the fast <span class="hlt">wave</span> to a change in the initial stress is on the opposite direction. PMID:19210972</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992JSV...158...93K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992JSV...158...93K"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">propagation</span> in randomly stratified media and the law of large numbers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kotulski, Z.</p> <p>1992-10-01</p> <p>The <span class="hlt">propagation</span> of scalar harmonic <span class="hlt">waves</span> through a randomly stratified slab is investigated. The transition matrix method is applied for the analysis of the problem. To obtain the effective parameters of the material of the slab the law of large numbers for non-commuting products is applied. The results are illustrated with the numerical example of the <span class="hlt">propagation</span> of elastic <span class="hlt">waves</span> in steel-titanium laminate in an aluminium environment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20860281','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20860281"><span id="translatedtitle">Short wavelength quantum electrodynamical correction to cold plasma-<span class="hlt">wave</span> <span class="hlt">propagation</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Lundin, J.; Brodin, G.; Marklund, M.</p> <p>2006-10-15</p> <p>The effect of short wavelength quantum electrodynamic (QED) correction on plasma-<span class="hlt">wave</span> <span class="hlt">propagation</span> is investigated. The effect on plasma oscillations and on electromagnetic <span class="hlt">waves</span> in an unmagnetized as well as a magnetized plasma is investigated. The effects of the short wavelength QED corrections are most evident for plasma oscillations and for extraordinary modes. In particular, the QED correction allow plasma oscillations to <span class="hlt">propagate</span>, and the extraordinary mode loses its stop band. The significance of our results is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750022814','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750022814"><span id="translatedtitle">Theoretical and experimental studies of space-related plasma <span class="hlt">wave</span> <span class="hlt">propagation</span> and resonance phenomena</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Crawford, F. W.</p> <p>1975-01-01</p> <p>A ten year summary was given of university research on the nature and characteristics of space related plasma resonance phenomena, whistler <span class="hlt">propagation</span> in laboratory plasmas, and theoretical and experimental studies of plasma <span class="hlt">wave</span> <span class="hlt">propagation</span>. Data are also given on long delayed echoes, low frequency instabilities, ionospheric heating, and backscatter, and pulse <span class="hlt">propagation</span>. A list is included of all conference papers, publications, and reports resulting from the study.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/674556','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/674556"><span id="translatedtitle">Effects of pore fluids in the subsurface on ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Seifert, Patricia Katharina</p> <p>1998-05-01</p> <p>This thesis investigates ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in unconsolidated sands in the presence of different pore fluids. Laboratory experiments have been conducted in the sub-MHz range using quartz sand fully saturated with one or two liquids. Elastic <span class="hlt">wave</span> <span class="hlt">propagation</span> in unconsolidated granular material is computed with different numerical models: in one-dimension a scattering model based on an analytical <span class="hlt">propagator</span> solution, in two dimensions a numerical approach using the boundary integral equation method, in three dimensions the local flow model (LFM), the combined Biot and squirt flow theory (BISQ) and the dynamic composite elastic medium theory (DYCEM). The combination of theoretical and experimental analysis yields a better understanding of how <span class="hlt">wave</span> <span class="hlt">propagation</span> in unconsolidated sand is affected by (a) homogeneous phase distribution; (b) inhomogeneous phase distribution, (fingering, gas inclusions); (c) pore fluids of different viscosity; (d) wettabilities of a porous medium. The first study reveals that the main ultrasonic P-<span class="hlt">wave</span> signatures, as a function of the fraction on nonaqueous-phase liquids in initially water-saturated sand samples, can be explained by a 1-D scattering model. The next study investigates effects of pore fluid viscosity on elastic <span class="hlt">wave</span> <span class="hlt">propagation</span>, in laboratory experiments conducted with sand samples saturated with fluids of different viscosities. The last study concentrates on the wettability of the grains and its effect on elastic <span class="hlt">wave</span> <span class="hlt">propagation</span> and electrical resistivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25618089','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25618089"><span id="translatedtitle"><span class="hlt">Propagation</span> of time-reversed Lamb <span class="hlt">waves</span> in bovine cortical bone in vitro.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lee, Kang Il; Yoon, Suk Wang</p> <p>2015-01-01</p> <p>The present study aims to investigate the <span class="hlt">propagation</span> of time-reversed Lamb <span class="hlt">waves</span> in bovine cortical bone in vitro. The time-reversed Lamb <span class="hlt">waves</span> were successfully launched at 200 kHz in 18 bovine tibiae through a time reversal process of Lamb <span class="hlt">waves</span>. The group velocities of the time-reversed Lamb <span class="hlt">waves</span> in the bovine tibiae were measured using the axial transmission technique. They showed a significant correlation with the cortical thickness and tended to follow the theoretical group velocity of the lowest order antisymmetrical Lamb <span class="hlt">wave</span> fairly well, consistent with the behavior of the slow guided <span class="hlt">wave</span> in long cortical bones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/947757','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/947757"><span id="translatedtitle">FY08 LDRD Final Report A New Method for <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Elastic Media LDRD Project Tracking Code: 05-ERD-079</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Petersson, A</p> <p>2009-01-29</p> <p>The LDRD project 'A New Method for <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Elastic Media' developed several improvements to the traditional finite difference technique for seismic <span class="hlt">wave</span> <span class="hlt">propagation</span>, including a summation-by-parts discretization which is provably stable for arbitrary heterogeneous materials, an accurate treatment of non-<span class="hlt">planar</span> topography, local mesh refinement, and stable outflow boundary conditions. This project also implemented these techniques in a parallel open source computer code called WPP, and participated in several seismic modeling efforts to simulate ground motion due to earthquakes in Northern California. This research has been documented in six individual publications which are summarized in this report. Of these publications, four are published refereed journal articles, one is an accepted refereed journal article which has not yet been published, and one is a non-refereed software manual. The report concludes with a discussion of future research directions and exit plan.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27657478','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27657478"><span id="translatedtitle">Fourier Transform Ultrasound Spectroscopy for the determination of <span class="hlt">wave</span> <span class="hlt">propagation</span> parameters.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pal, Barnana</p> <p>2017-01-01</p> <p>The reported results for ultrasonic <span class="hlt">wave</span> attenuation constant (α) in pure water show noticeable inconsistency in magnitude. A "<span class="hlt">Propagating-Wave</span>" model analysis of the most popular pulse-echo technique indicates that this is a consequence of the inherent <span class="hlt">wave</span> <span class="hlt">propagation</span> characteristics in a bounded medium. In the present work Fourier Transform Ultrasound Spectroscopy (FTUS) is adopted to determine ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> parameters, the <span class="hlt">wave</span> number (k) and attenuation constant (α) at 1MHz frequency in tri-distilled water at room temperature (25°C). Pulse-echo signals obtained under same experimental conditions regarding the exciting input signal and reflecting boundary wall of the water container for various lengths of water columns are captured. The Fast Fourier Transform (FFT) components of the echo signals are taken to compute k, α and r, the reflection constant at the boundary, using Oak Ridge and Oxford method. The results are compared with existing literature values.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21632054','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21632054"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">propagation</span> in protein microtubules modeled as orthotropic elastic shells including transverse shear deformations.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Daneshmand, Farhang; Ghavanloo, Esmaeal; Amabili, Marco</p> <p>2011-07-07</p> <p><span class="hlt">Wave</span> <span class="hlt">propagation</span> along the microtubules is one of the issues of major concern in various microtubule cellular functions. In this study, the general <span class="hlt">wave</span> <span class="hlt">propagation</span> behavior in protein microtubules is investigated based on a first-order shear deformation shell theory for orthotropic materials, with particular emphasis on the role of strongly anisotropic elastic properties of microtubules. According to experimental observation, the first-order shear deformation theory is used for the modeling of microtubule walls. A general displacement representation is introduced and a type of coupled polynomial eigenvalue problem is developed. Numerical examples describe the effects of shear deformation and rotary inertia on <span class="hlt">wave</span> velocities in orthotropic microtubules. Finally, the influences of the microtubule shear modulus, axial external force, effective thickness and material temperature dependency on <span class="hlt">wave</span> velocities along the microtubule protofilaments, helical pathway and radial directions are elucidated. Most results presented in the present investigation have been absent from the literature for the <span class="hlt">wave</span> <span class="hlt">propagation</span> in microtubules.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22181524','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22181524"><span id="translatedtitle">Laser-driven plasma beat-<span class="hlt">wave</span> <span class="hlt">propagation</span> in a density-modulated plasma.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gupta, Devki Nandan; Nam, In Hyuk; Suk, Hyyong</p> <p>2011-11-01</p> <p>A laser-driven plasma beat <span class="hlt">wave</span>, <span class="hlt">propagating</span> through a plasma with a periodic density modulation, can generate two sideband plasma <span class="hlt">waves</span>. One sideband moves with a smaller phase velocity than the pump plasma <span class="hlt">wave</span> and the other <span class="hlt">propagates</span> with a larger phase velocity. The plasma beat <span class="hlt">wave</span> with a smaller phase velocity can accelerate modest-energy electrons to gain substantial energy and the electrons are further accelerated by the main plasma <span class="hlt">wave</span>. The large phase velocity plasma <span class="hlt">wave</span> can accelerate these electrons to higher energies. As a result, the electrons can attain high energies during the acceleration by the plasma <span class="hlt">waves</span> in the presence of a periodic density modulation. The analytical results are compared with particle-in-cell simulations and are found to be in reasonable agreement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhPl...24a3518N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhPl...24a3518N"><span id="translatedtitle">Correlation of <span class="hlt">wave</span> <span class="hlt">propagation</span> modes in helicon plasma with source tube lengths</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Niu, Chen; Zhao, Gao; Wang, Yu; Liu, Zhongwei; Chen, Qiang</p> <p>2017-01-01</p> <p>Helicon <span class="hlt">wave</span> plasma demonstrates lots of advantages in high coupling efficiency, high density, and low magnetic field. However, the helicon <span class="hlt">wave</span> plasma still meets challenges in applications of material deposition, surface treatment, and electromagnetic thrusters owing to the changeable coupled efficiency and the remarkable non-uniformity. In this paper, we explore the <span class="hlt">wave</span> <span class="hlt">propagation</span> characterization by the B-dot probe in various lengths of source tubes. We find that in a long source tube the standing <span class="hlt">wave</span> appears under the antenna zone, while the traveling <span class="hlt">wave</span> is formed out of the antenna region. The apparent modulation of <span class="hlt">wave</span> amplitude is formed in upstream rather than in downstream of the antenna. In a short source tube, however, there is only standing <span class="hlt">wave</span> <span class="hlt">propagation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMSM41F2548K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMSM41F2548K"><span id="translatedtitle">Investigations into the Influence of Heavy Ions on EMIC <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in the Earth's Magnetosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keller, S.; Kim, E. H.; Johnson, J.</p> <p>2015-12-01</p> <p>Geomagnetic pulsations in the Pc1 frequency range (0.2 to 5.0 Hz), which are known as electromagnetic ion cyclotron (EMIC) <span class="hlt">waves</span>, are often observed at magnetically conjugate locations by spacecraft in the equatorial magnetosphere and ground-based stations. One difficulty in linking the <span class="hlt">propagation</span> of detected radiation between these regions is the presence of stop bands near the heavy ion cyclotron resonance locations. Recent full <span class="hlt">wave</span> calculations (Kim and Johnson, Full <span class="hlt">wave</span> modeling of EMIC <span class="hlt">waves</span> in the Earth's magnetosphere, 2015 AGU fall meeting) demonstrate how EMIC <span class="hlt">waves</span> <span class="hlt">propagate</span> to higher magnetic latitudes in an electron-proton-He+ plasma. However, while the heavy ion concentration can be large during the solar maximum and geomagnetic storms, they adopted a 5% He+ plasma. In this study, we explore the roles of heavy ion (He+ and O+) concentrations on the levels of EMIC <span class="hlt">wave</span> energy that reach lower altitudes using a two-dimensional, finite element, full <span class="hlt">wave</span> model. The Poynting flux and polarization of the emissions are used to monitor the <span class="hlt">propagation</span> and absorption of <span class="hlt">wave</span> energy, as well as mode coupling between left- and right-hand circularly polarized modes. Due to the increase in heavy ion populations in the magnetosphere, the consequences that geomagnetic storms have on EMIC <span class="hlt">wave</span> <span class="hlt">propagation</span> are also discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2679998','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2679998"><span id="translatedtitle"><span class="hlt">Propagating</span> <span class="hlt">Waves</span> of Activity in the Neocortex: What They Are, What They Do</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>WU, JIAN-YOUNG; HUANG, XIAOYING; ZHANG, CHUAN</p> <p>2009-01-01</p> <p>The development of voltage-sensitive dyes (VSD) and fast optical imaging techniques have brought us a new tool for examining spatiotemporal patterns of population neuronal activity in the neocortex. <span class="hlt">Propagating</span> <span class="hlt">waves</span> have been observed during almost every type of cortical processing examined by VSD imaging or electrode arrays. These <span class="hlt">waves</span> provide subthreshold depolarization to individual neurons and increase their spiking probability. Therefore, the <span class="hlt">propagation</span> of the <span class="hlt">waves</span> sets up a spatiotemporal framework for increased excitability in neuronal populations, which can help to determine when and where the neurons are likely to fire. In this review, first discussed is <span class="hlt">propagating</span> <span class="hlt">waves</span> observed in various systems and possible mechanisms for generating and sustaining these <span class="hlt">waves</span>. Then discussed are <span class="hlt">wave</span> dynamics as an emergent behavior of the population activity that can, in turn, influence the activity of individual neurons. The functions of spontaneous and sensory-evoked <span class="hlt">waves</span> remain to be explored. An important next step will be to examine the interaction between dynamics of <span class="hlt">propagating</span> <span class="hlt">waves</span> and functions in the cortex, and to verify if cortical processing can be modified when these <span class="hlt">waves</span> are altered. PMID:18997124</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006SunGe...1b..25A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006SunGe...1b..25A"><span id="translatedtitle">Generation Mechanism and <span class="hlt">Propagation</span> Features of the Ionospheric Weather Forming ULF Electromagnetic <span class="hlt">Wave</span> Structures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aburjania, G. D.; Chargazia, Kh. Z.; Khantadze, A. G.; Lominadze, J. G.</p> <p>2006-12-01</p> <p>Results of theoretical investigation of the dynamics of generation and <span class="hlt">propagation</span> of planetary (with wavelengths 103 km and more) weather-forming Ultra-Low Frequency (ULF) electromagnetic <span class="hlt">wave</span> structures in the dissipative ionosphere are given in this paper. It is established that the global factor, acting permanently in the ionosphere spatial inhomogeneity and curvature of the geomagnetic field and inhomogeneity of angular velocity of the Earth's rotation generates the fast and slow planetary ULF electromagnetic <span class="hlt">waves</span>. The <span class="hlt">waves</span> <span class="hlt">propagate</span> along the parallels to the east as well as to the west. In the E-region the fast <span class="hlt">waves</span> have phase velocities of (2-20) km/s-1 and frequencies of (10^-1-10^-4) Hz; the slow <span class="hlt">waves</span> <span class="hlt">propagate</span> with local wind velocities and have frequencies (10^-4-10^-6) Hz. In the F-region the fast ULF electromagnetic <span class="hlt">waves</span> <span class="hlt">propagate</span> with phase velocities of tens-hundreds km/s-1 and their frequencies are in the range of (10-10^-3) Hz. The large-scale <span class="hlt">waves</span> are weakly damped. The <span class="hlt">waves</span> generate the geomagnetic field perturbations from several tens to several hundreds nT and more. It is established that planetary ULF electromagnetic <span class="hlt">waves</span>, at their interaction with the local shear winds, can self-localize in the form of nonlinear solitary vortices, moving along the latitude circles westward as well as eastward.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4525157','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4525157"><span id="translatedtitle">Investigating Alfvénic <span class="hlt">wave</span> <span class="hlt">propagation</span> in coronal open-field regions</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Morton, R. J.; Tomczyk, S.; Pinto, R.</p> <p>2015-01-01</p> <p>The physical mechanisms behind accelerating solar and stellar winds are a long-standing astrophysical mystery, although recent breakthroughs have come from models invoking the turbulent dissipation of Alfvén <span class="hlt">waves</span>. The existence of Alfvén <span class="hlt">waves</span> far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic <span class="hlt">waves</span> throughout the solar atmosphere has been confirmed. However, the presence of atmospheric Alfvénic <span class="hlt">waves</span> does not, alone, provide sufficient support for <span class="hlt">wave</span>-based models; the existence of counter-<span class="hlt">propagating</span> Alfvénic <span class="hlt">waves</span> is crucial for the development of turbulence. Here, we demonstrate that counter-<span class="hlt">propagating</span> Alfvénic <span class="hlt">waves</span> exist in open coronal magnetic fields and reveal key observational insights into the details of their generation, reflection in the upper atmosphere and outward <span class="hlt">propagation</span> into the solar wind. The results enhance our knowledge of Alfvénic <span class="hlt">wave</span> <span class="hlt">propagation</span> in the solar atmosphere, providing support and constraints for some of the recent Alfvén <span class="hlt">wave</span> turbulence models. PMID:26213234</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22224191','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22224191"><span id="translatedtitle">Nonlinear <span class="hlt">propagation</span> of Rossby-Khantadze electromagnetic planetary <span class="hlt">waves</span> in the ionospheric E-layer</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Futatani, S.; Horton, W.; Kaladze, T. D.</p> <p>2013-10-15</p> <p>Nonlinear vortex <span class="hlt">propagation</span> of electromagnetic coupled Rossby and Khantadze planetary <span class="hlt">waves</span> in the weakly ionized ionospheric E-layer is investigated with numerical simulations. Large scale, finite amplitude vortex structures are launched as initial conditions at low, mid, and high latitudes. For each k-vector the linear dispersion relation has two eigenmodes corresponding to the slow magnetized Rossby <span class="hlt">wave</span> and the fast magnetic Khantadze <span class="hlt">wave</span>. Both <span class="hlt">waves</span> <span class="hlt">propagate</span> westward with local speeds of the order of 10–20 m/s for the slow <span class="hlt">wave</span> and of the order of 500–1000 km/s for the fast <span class="hlt">wave</span>. We show that for finite amplitudes there are dipole solitary structures emitted from the initial conditions. These structures are neutrally stable, nonlinear states that avoid radiating <span class="hlt">waves</span> by <span class="hlt">propagating</span> faster than the corresponding linear <span class="hlt">wave</span> speeds. The condition for these coherent structures to occur is that their amplitudes are such that the nonlinear convection around the core of the disturbance is faster than the linear <span class="hlt">wave</span> speed for the corresponding dominant Fourier components of the initial disturbance. The presence of the solitary vortex states is indicative of an initial strong disturbance such as that from a solar storm or a tectonic plate movement. We show that for generic, large amplitude initial disturbances both slow and fast vortex structures <span class="hlt">propagate</span> out of the initial structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2636873','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2636873"><span id="translatedtitle">On <span class="hlt">Propagation</span> of Excitation <span class="hlt">Waves</span> in Moving Media: The FitzHugh-Nagumo Model</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ermakova, Elena A.; Shnol, Emmanuil E.; Panteleev, Mikhail A.; Butylin, Andrey A.; Volpert, Vitaly; Ataullakhanov, Fazoil I.</p> <p>2009-01-01</p> <p>Background Existence of flows and convection is an essential and integral feature of many excitable media with <span class="hlt">wave</span> <span class="hlt">propagation</span> modes, such as blood coagulation or bioreactors. Methods/Results Here, <span class="hlt">propagation</span> of two-dimensional <span class="hlt">waves</span> is studied in parabolic channel flow of excitable medium of the FitzHugh-Nagumo type. Even if the stream velocity is hundreds of times higher that the <span class="hlt">wave</span> velocity in motionless medium (), steady <span class="hlt">propagation</span> of an excitation <span class="hlt">wave</span> is eventually established. At high stream velocities, the <span class="hlt">wave</span> does not span the channel from wall to wall, forming isolated excited regions, which we called “restrictons”. They are especially easy to observe when the model parameters are close to critical ones, at which <span class="hlt">waves</span> disappear in still medium. In the subcritical region of parameters, a sufficiently fast stream can result in the survival of excitation moving, as a rule, in the form of “restrictons”. For downstream excitation <span class="hlt">waves</span>, the axial portion of the channel is the most important one in determining their behavior. For upstream <span class="hlt">waves</span>, the most important region of the channel is the near-wall boundary layers. The roles of transversal diffusion, and of approximate similarity with respect to stream velocity are discussed. Conclusions These findings clarify mechanisms of <span class="hlt">wave</span> <span class="hlt">propagation</span> and survival in flow. PMID:19212435</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26482393','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26482393"><span id="translatedtitle"><span class="hlt">Propagation</span> of ultrasonic Love <span class="hlt">waves</span> in nonhomogeneous elastic functionally graded materials.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kiełczyński, P; Szalewski, M; Balcerzak, A; Wieja, K</p> <p>2016-02-01</p> <p>This paper presents a theoretical study of the <span class="hlt">propagation</span> behavior of ultrasonic Love <span class="hlt">waves</span> in nonhomogeneous functionally graded elastic materials, which is a vital problem in the mechanics of solids. The elastic properties (shear modulus) of a semi-infinite elastic half-space vary monotonically with the depth (distance from the surface of the material). The Direct Sturm-Liouville Problem that describes the <span class="hlt">propagation</span> of Love <span class="hlt">waves</span> in nonhomogeneous elastic functionally graded materials is formulated and solved by using two methods: i.e., (1) Finite Difference Method, and (2) Haskell-Thompson Transfer Matrix Method. The dispersion curves of phase and group velocity of surface Love <span class="hlt">waves</span> in inhomogeneous elastic graded materials are evaluated. The integral formula for the group velocity of Love <span class="hlt">waves</span> in nonhomogeneous elastic graded materials has been established. The effect of elastic non-homogeneities on the dispersion curves of Love <span class="hlt">waves</span> is discussed. Two Love <span class="hlt">wave</span> waveguide structures are analyzed: (1) a nonhomogeneous elastic surface layer deposited on a homogeneous elastic substrate, and (2) a semi-infinite nonhomogeneous elastic half-space. Obtained in this work, the phase and group velocity dispersion curves of Love <span class="hlt">waves</span> <span class="hlt">propagating</span> in the considered nonhomogeneous elastic waveguides have not previously been reported in the scientific literature. The results of this paper may give a deeper insight into the nature of Love <span class="hlt">waves</span> <span class="hlt">propagation</span> in elastic nonhomogeneous functionally graded materials, and can provide theoretical guidance for the design and optimization of Love <span class="hlt">wave</span> based devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26213234','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26213234"><span id="translatedtitle">Investigating Alfvénic <span class="hlt">wave</span> <span class="hlt">propagation</span> in coronal open-field regions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Morton, R J; Tomczyk, S; Pinto, R</p> <p>2015-07-27</p> <p>The physical mechanisms behind accelerating solar and stellar winds are a long-standing astrophysical mystery, although recent breakthroughs have come from models invoking the turbulent dissipation of Alfvén <span class="hlt">waves</span>. The existence of Alfvén <span class="hlt">waves</span> far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic <span class="hlt">waves</span> throughout the solar atmosphere has been confirmed. However, the presence of atmospheric Alfvénic <span class="hlt">waves</span> does not, alone, provide sufficient support for <span class="hlt">wave</span>-based models; the existence of counter-<span class="hlt">propagating</span> Alfvénic <span class="hlt">waves</span> is crucial for the development of turbulence. Here, we demonstrate that counter-<span class="hlt">propagating</span> Alfvénic <span class="hlt">waves</span> exist in open coronal magnetic fields and reveal key observational insights into the details of their generation, reflection in the upper atmosphere and outward <span class="hlt">propagation</span> into the solar wind. The results enhance our knowledge of Alfvénic <span class="hlt">wave</span> <span class="hlt">propagation</span> in the solar atmosphere, providing support and constraints for some of the recent Alfvén <span class="hlt">wave</span> turbulence models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22271284','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22271284"><span id="translatedtitle"><span class="hlt">Propagating</span> and reflecting of spin <span class="hlt">wave</span> in permalloy nanostrip with 360° domain wall</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zhang, Senfu; Mu, Congpu; Zhu, Qiyuan; Zheng, Qi; Liu, Xianyin; Wang, Jianbo; Liu, Qingfang</p> <p>2014-01-07</p> <p>By micromagnetic simulation, we investigated the interaction between <span class="hlt">propagating</span> spin <span class="hlt">wave</span> (or magnonic) and a 360° domain wall in a nanostrip. It is found that <span class="hlt">propagating</span> spin <span class="hlt">wave</span> can drive a 360° domain wall motion, and the velocity and direction are closely related to the transmission coefficient of the spin <span class="hlt">wave</span> of the domain wall. When the spin <span class="hlt">wave</span> passes through the domain wall completely, the 360° domain wall moves toward the spin <span class="hlt">wave</span> source. When the spin <span class="hlt">wave</span> is reflected by the domain wall, the 360° domain wall moves along the spin <span class="hlt">wave</span> <span class="hlt">propagation</span> direction. Moreover, when the frequency of the spin <span class="hlt">wave</span> is coincident with that of the 360° domain wall normal mode, the 360° domain wall velocity will be resonantly enhanced no matter which direction the 360 DW moves along. On the other hand, when the spin <span class="hlt">wave</span> is reflected from the moving 360° domain wall, we observed the Doppler effect clearly. After passing through a 360° domain wall, the phase of the spin <span class="hlt">wave</span> is changed, and the phase shift is related to the frequency. Nevertheless, phase shift could be manipulated by the number of 360° domain walls that spin <span class="hlt">wave</span> passing through.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23363084','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23363084"><span id="translatedtitle">Simulations of ultrasound <span class="hlt">propagation</span> in random arrangements of elliptic scatterers: occurrence of two longitudinal <span class="hlt">waves</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mézière, Fabien; Muller, Marie; Dobigny, Blandine; Bossy, Emmanuel; Derode, Arnaud</p> <p>2013-02-01</p> <p>Ultrasound <span class="hlt">propagation</span> in clusters of elliptic (two-dimensional) or ellipsoidal (three-dimensional) scatterers randomly distributed in a fluid is investigated numerically. The essential motivation for the present work is to gain a better understanding of ultrasound <span class="hlt">propagation</span> in trabecular bone. Bone microstructure exhibits structural anisotropy and multiple <span class="hlt">wave</span> scattering. Some phenomena remain partially unexplained, such as the <span class="hlt">propagation</span> of two longitudinal <span class="hlt">waves</span>. The objective of this study was to shed more light on the occurrence of these two <span class="hlt">waves</span>, using finite-difference simulations on a model medium simpler than bone. Slabs of anisotropic, scattering media were randomly generated. The coherent <span class="hlt">wave</span> was obtained through spatial and ensemble-averaging of the transmitted wavefields. When varying relevant medium parameters, four of them appeared to play a significant role for the observation of two <span class="hlt">waves</span>: (i) the solid fraction, (ii) the direction of <span class="hlt">propagation</span> relatively to the scatterers orientation, (iii) the ability of scatterers to support shear <span class="hlt">waves</span>, and (iv) a continuity of the solid matrix along the <span class="hlt">propagation</span>. These observations are consistent with the hypothesis that fast <span class="hlt">waves</span> are guided by the locally plate/bar-like solid matrix. If confirmed, this interpretation could significantly help developing approaches for a better understanding of trabecular bone micro-architecture using ultrasound.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22518783','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22518783"><span id="translatedtitle">APPARENT CROSS-FIELD SUPERSLOW <span class="hlt">PROPAGATION</span> OF MAGNETOHYDRODYNAMIC <span class="hlt">WAVES</span> IN SOLAR PLASMAS</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kaneko, T.; Yokoyama, T.; Goossens, M.; Doorsselaere, T. Van; Soler, R.; Terradas, J.; Wright, A. N.</p> <p>2015-10-20</p> <p>In this paper we show that the phase-mixing of continuum Alfvén <span class="hlt">waves</span> and/or continuum slow <span class="hlt">waves</span> in the magnetic structures of the solar atmosphere as, e.g., coronal arcades, can create the illusion of <span class="hlt">wave</span> <span class="hlt">propagation</span> across the magnetic field. This phenomenon could be erroneously interpreted as fast magnetosonic <span class="hlt">waves</span>. The cross-field <span class="hlt">propagation</span> due to the phase-mixing of continuum <span class="hlt">waves</span> is apparent because there is no real <span class="hlt">propagation</span> of energy across the magnetic surfaces. We investigate the continuous Alfvén and slow spectra in two-dimensional (2D) Cartesian equilibrium models with a purely poloidal magnetic field. We show that apparent superslow <span class="hlt">propagation</span> across the magnetic surfaces in solar coronal structures is a consequence of the existence of continuum Alfvén <span class="hlt">waves</span> and continuum slow <span class="hlt">waves</span> that naturally live on those structures and phase-mix as time evolves. The apparent cross-field phase velocity is related to the spatial variation of the local Alfvén/slow frequency across the magnetic surfaces and is slower than the Alfvén/sound velocities for typical coronal conditions. Understanding the nature of the apparent cross-field <span class="hlt">propagation</span> is important for the correct analysis of numerical simulations and the correct interpretation of observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhPro..70..122D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhPro..70..122D"><span id="translatedtitle">Lamb <span class="hlt">wave</span> <span class="hlt">Propagation</span> in Functionally Graded Piezoelectric Material Created by Internal Temperature Gradient</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dammak, Y.; Thomas, J. H.; Ghozlen, M. H. Ben</p> <p></p> <p>This work presents a theoretical study of the <span class="hlt">propagation</span> behavior of lamb <span class="hlt">wave</span> in a functionally graded piezoelectric material (FGPM). The piezoelectric material is polarized when the six fold symmetry axis is put along the <span class="hlt">propagation</span> direction x1 and the material properties change gradually perpendicularly to the plate. The FGPM behavior is created by forming a temperature variation across the plate. The ordinary differential equation (ODE) and the Stiffness Matrix Method (SMM) are used to investigate the <span class="hlt">propagation</span> of the lowest-order symmetric (S0) and antisymmetric (A0) Lamb <span class="hlt">wave</span> modes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19750044633&hterms=dependance&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Ddependance','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19750044633&hterms=dependance&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Ddependance"><span id="translatedtitle">Nonlinear <span class="hlt">propagation</span> of a <span class="hlt">wave</span> packet in a hard-walled circular duct</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nayfeh, A. H.</p> <p>1975-01-01</p> <p>The method of multiple scales is used to derive a nonlinear Schroedinger equation for the temporal and spatial modulation of the amplitudes and the phases of <span class="hlt">waves</span> <span class="hlt">propagating</span> in a hard-walled circular duct. This equation is used to show that monochromatic <span class="hlt">waves</span> are stable and to determine the amplitude dependance of the cutoff frequencies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760011291','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760011291"><span id="translatedtitle">Nonlinear <span class="hlt">propagation</span> of a <span class="hlt">wave</span> packet in a hard-walled circular duct</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nayfeh, A. H.</p> <p>1974-01-01</p> <p>The method of multiple scales is used to derive a nonlinear Schroedinger equation for the temporal and spatial modulation of the amplitudes and the phases of <span class="hlt">waves</span> <span class="hlt">propagating</span> in a hard-walled circular duct. This equation is used to show that monochromatic <span class="hlt">waves</span> are stable and to determine the amplitude dependance of the cut off frequencies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPhCS.766a2031Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.766a2031Z"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">Propagation</span> by Way of Exponential B-Spline Galerkin Method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zorsahin Gorgulu, M.; Dag, I.; Irk, D.</p> <p>2016-10-01</p> <p>In this paper, the exponential B-spline Galerkin method is set up for getting the numerical solution of the Burgers’ equation. Two numerical examples related to shock <span class="hlt">wave</span> <span class="hlt">propagation</span> and travelling <span class="hlt">wave</span> are studied to illustrate the accuracy and the efficiency of the method. Obtained results are compared with some early studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=space+AND+travel&pg=5&id=EJ983107','ERIC'); return false;" href="http://eric.ed.gov/?q=space+AND+travel&pg=5&id=EJ983107"><span id="translatedtitle">Causal <span class="hlt">Wave</span> <span class="hlt">Propagation</span> for Relativistic Massive Particles: Physical Asymptotics in Action</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Berry, M. V.</p> <p>2012-01-01</p> <p>Wavepackets representing relativistic quantum particles injected into a half-space, from a source that is switched on at a definite time, are represented by superpositions of plane <span class="hlt">waves</span> that must include negative frequencies. <span class="hlt">Propagation</span> is causal: it is a consequence of analyticity that at time t no part of the <span class="hlt">wave</span> has travelled farther than…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19960021412&hterms=solar+wind+power&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dsolar%2Bwind%2Bpower','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19960021412&hterms=solar+wind+power&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dsolar%2Bwind%2Bpower"><span id="translatedtitle">Non-WKB Alfven <span class="hlt">waves</span> in the solar wind: <span class="hlt">Propagation</span> and reflection of pulses</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hollweg, J. V.</p> <p>1995-01-01</p> <p>The non-WKB <span class="hlt">propagation</span> of Alfven <span class="hlt">waves</span> has been studied either for harmonic <span class="hlt">waves</span>, or in terms of the evolution of power spectra. Here we present analytical and numerical solutions for the <span class="hlt">propagation</span> of pulses, the goal being to understand how <span class="hlt">waves</span> reflect in a smoothly varying medium. We here limit our discussion to a radial magnetic field. If we launch an outward-<span class="hlt">propagating</span> delta function, it leaves behind an inward-propagaing signal which is roughly a square <span class="hlt">wave</span> whose amplitude is proportional to the area under the initial pulse. The inward-<span class="hlt">propagating</span> signal also reflects, producing an outward <span class="hlt">propagating</span> pulse which is roughly triangular in shape and which grows with time. These signals also oscillate if v is less than v(A), but they grow if v is greater than v(A). The result reported by us earlier, that the 'ingoing Elsasser variable' can have outgoing phase, is now understood to be a consequence of interference. The inward-<span class="hlt">propagating</span> signal depends to lowest order on the integral of the outgoing <span class="hlt">waves</span> which have preceded it. Thus the ingoing signal can be expected to develop as a random walk. This will affect the radial evolution of cross-helicity in the solar wind.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AdSpR..59.1962E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AdSpR..59.1962E"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">propagation</span> in strongly dispersive superthermal dusty plasma</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>El-Labany, S. K.; El-Shewy, E. K.; Abd El-Razek, H. N.; El-Rahman, A. A.</p> <p>2017-04-01</p> <p>The attributes of acoustic envelope <span class="hlt">waves</span> 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 <span class="hlt">waves</span>; namely rogue <span class="hlt">waves</span>. The subjection of instability regions upon electron superthermality (via κ), carrier <span class="hlt">wave</span> number and dusty grains charge is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMNH31C3883B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMNH31C3883B"><span id="translatedtitle">Modeling of acoustic and gravity <span class="hlt">waves</span> <span class="hlt">propagation</span> through the atmosphere with spectral element method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brissaud, Q.; Garcia, R.; Martin, R.; Komatitsch, D.</p> <p>2014-12-01</p> <p>Low-frequency events such as tsunamis generate acoustic and gravity <span class="hlt">waves</span> which quickly <span class="hlt">propagate</span> in the atmosphere. Since the atmospheric density decreases exponentially as the altitude increases and from the conservation of the kinetic energy, those <span class="hlt">waves</span> see their amplitude raise (to the order of 105 at 200km of altitude), allowing their detection in the upper atmosphere. Various tools have been developed through years to model this <span class="hlt">propagation</span>, such as normal modes modeling or to a greater extent time-reversal techniques, but none offer a low-frequency multi-dimensional atmospheric <span class="hlt">wave</span> modelling.A modeling tool is worthy interest since there are many different phenomena, from quakes to atmospheric explosions, able to <span class="hlt">propagate</span> acoustic and gravity <span class="hlt">waves</span>. In order to provide a fine modeling of the precise observations of these <span class="hlt">waves</span> by GOCE satellite data, we developed a new numerical modeling tool.Starting from the SPECFEM program that already <span class="hlt">propagate</span> <span class="hlt">waves</span> in solid, porous or fluid media using a spectral element method, this work offers a tool with the ability to model acoustic and gravity <span class="hlt">waves</span> <span class="hlt">propagation</span> in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source.Atmospheric attenuation is required in a proper modeling framework since it has a crucial impact on acoustic <span class="hlt">wave</span> <span class="hlt">propagation</span>. Indeed, it plays the role of a frequency filter that damps high-frequency signals. The bottom forcing feature has been implemented due to its ability to easily model the coupling with the Earth's or ocean's surface (that vibrates when a surface <span class="hlt">wave</span> go through it) but also huge atmospheric events.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850054272&hterms=appraisal+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dappraisal%2Btheory','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850054272&hterms=appraisal+theory&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dappraisal%2Btheory"><span id="translatedtitle">Geometric effects of global lateral heterogeneity on long-period surface <span class="hlt">wave</span> <span class="hlt">propagation</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lay, T.; Kanamori, H.</p> <p>1985-01-01</p> <p>The present investigation has the objective to document examples of anomalous long-period surface <span class="hlt">wave</span> amplitude behavior and to provide a preliminary appraisal of the effects of global lateral heterogeneity on surface <span class="hlt">wave</span> <span class="hlt">propagation</span> from a ray theory perspective. Attention is given to remarkable long-period surface <span class="hlt">wave</span> anomalies described in literature, an equidistance azimuthal plot centered on the Iranian source region, Rayleigh <span class="hlt">wave</span> and Love <span class="hlt">wave</span> spectra for the 256-s period arrivals for the Tabas earthquake, constrained moment tensor and fault model inversion solutions ofr Iranian earthquakes, aspects of surface <span class="hlt">wave</span> ray tracing, and a table of Rayleigh <span class="hlt">wave</span> amplitude anomalies for Iranian earthquakes. Surface <span class="hlt">wave</span> ray-tracing calculations for models of global phase velocity variations proposed by Nakanishi and Anderson (1984) are found to show that large-amplitude anomalies will be observed for Love and Rayleigh <span class="hlt">waves</span> with periods of 100-250 s.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004GeoJI.158.1067A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004GeoJI.158.1067A"><span id="translatedtitle">Acoustic <span class="hlt">waves</span> generated from seismic surface <span class="hlt">waves</span>: <span class="hlt">propagation</span> properties determined from Doppler sounding observations and normal-mode modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Artru, Juliette; Farges, Thomas; Lognonné, Philippe</p> <p>2004-09-01</p> <p>Since 1960, experiments have shown that perturbations of the ionosphere can occur after earthquakes, by way of dynamic coupling between seismic surface <span class="hlt">waves</span> and the atmosphere. The atmospheric <span class="hlt">wave</span> is amplified exponentially while <span class="hlt">propagating</span> upwards due to the decrease of density, and interaction with the ionospheric plasma leads to clearly identified signals on both ground-based or satellite ionospheric measurements. In 1999 and 2000, after an upgrade of the HF Doppler sounder, the Commisariat à l'Énergie Atomique systematically recorded these effects in the ionosphere with the Francourville (France) network, by measuring vertical oscillations of ionospheric layers with the Doppler technique. Normal-mode theory extended to a solid Earth with an atmosphere allows successful modelling of such signals, even if this 1-D approach is probably too crude, especially in the solid Earth, where 20 s surface <span class="hlt">waves</span> see large lateral variations in the crust. The combination of observations and simulations provides a new tool to determine acoustic gravity <span class="hlt">wave</span> <span class="hlt">propagation</span> characteristics from the ground to ionospheric height. Observed velocity and amplification of the atmospheric <span class="hlt">waves</span> show good agreement from the ground up to moderate sounding altitudes (140-150 km); however, at higher altitudes the <span class="hlt">propagation</span> speed is found to be much smaller than predicted and attenuation is underestimated. This shows that the standard formalism of acoustic gravity <span class="hlt">waves</span> in the atmosphere cannot efficiently describe <span class="hlt">propagation</span> in the ionized atmosphere. Further work is needed to characterize the <span class="hlt">propagation</span> of acoustic <span class="hlt">waves</span> in this altitude range: we believe that seismic <span class="hlt">waves</span> can provide a well-constrained source for such study.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1611873K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1611873K"><span id="translatedtitle">Generation and <span class="hlt">propagation</span> of stick-slip <span class="hlt">waves</span> over a fault with rate-independent friction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Karachevtseva, Iuliia; Dyskin, Arcady; Pasternak, Elena</p> <p>2014-05-01</p> <p>Earthquakes generated at faults are either produced by rapid (sometimes supersonic) <span class="hlt">propagation</span> of shear cracks/ruptures along the fault or originated in the stick-slip sliding over the fault. In some cases, supersonic (faster than the shear <span class="hlt">wave</span> velocity) <span class="hlt">propagation</span> of earthquake-generating shear ruptures or sliding is observed. This gave rise to the concept of supersonic shear crack <span class="hlt">propagation</span>, much researched in the literature. Here we consider another mechanisms of supersonic sliding <span class="hlt">propagation</span>. We concentrate on the stick-slip sliding as the earthquake mechanism. It is conventionally assumed that the mechanism of stick-slip lies in intermittent change between static and kinetic friction and the rate dependence of the friction coefficient. However the accumulation of elastic energy in the sliding plates on both sides of the fault can produce oscillations in the velocity of sliding even if the friction coefficient is constant. These oscillations resemble stick-slip movement, but they manifest themselves in terms of sliding velocity rather than displacement. Furthermore, over long faults the sliding exhibits <span class="hlt">wave</span>-like <span class="hlt">propagation</span>. We developed a model that shows that the zones of non-zero sliding velocities <span class="hlt">propagate</span> along the fault with the velocity of p-<span class="hlt">wave</span>. The mechanism of such fast movement is in the fact that sliding of every element of the rock at the fault surface creates normal (tensile/compressive) stresses in the neighbouring elements (normal stresses on the planes normal to the fault surface). The strains associated with these stresses are controlled by the Young's modulus rather than shear modulus resulting in the p-<span class="hlt">wave</span> velocity of <span class="hlt">propagation</span> of the sliding zone. This results in the observed supersonic (with respect to the s-<span class="hlt">waves</span>) <span class="hlt">propagation</span> of the apparent shear rupture. Keywords: Stick-slip, Rate-independent friction, Supersonic <span class="hlt">propagation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMSM13D2543S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMSM13D2543S"><span id="translatedtitle"><span class="hlt">Propagation</span> and Damping of Kinetic Alfven <span class="hlt">Waves</span> Generated During Magnetic Reconnection</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharma, P.; Shay, M. A.; Haggerty, C. C.; Parashar, T.</p> <p>2015-12-01</p> <p>Magnetospheric <span class="hlt">waves</span> have the potential to convert to Kinetic Alfven <span class="hlt">Waves</span> (KAW) at scales close to the ion larmor radius and the electron inertial length. At this length scale, it is observed that KAW generated at reconnection <span class="hlt">propagates</span> super-Alfvenically and the <span class="hlt">wave</span> is responsible for the parallel <span class="hlt">propagation</span> of the Hall magnetic field near the separatrice from the magnetotial region. The pointing flux associated with this Hall magnetic field is also consistent with observed Cluster data observations [1]. An important question is whether this KAW energy will be able to <span class="hlt">propagate</span> all the way to the Earth, creating aurora associated with a substorm. If this KAW <span class="hlt">propagation</span> can be well understood, then this will provide valuable insight as to the relative timing of substorm onset versus reconnection onset in the magnetotail. The difficulty currently is that the nonlinear damping of KAW is not well understood even in a homogenous system, let alone more realistic magnetotail geometries including changes to density, magnetic field strength, and magnetic orientation. We study the <span class="hlt">propagation</span>, dispersion, and damping of these KAWs using P3D, a kinetic particle-in-cell (PIC) simulation code. Travelling <span class="hlt">waves</span> are initialized based on a fluid model and allowed to <span class="hlt">propagate</span> for substantial time periods. Damping of the <span class="hlt">waves</span> are compared with Landau damping predictions. The <span class="hlt">waves</span> are simulated in both homogenous and varying equilibrium meant to determine the effect on <span class="hlt">propagation</span>. Implications for energetic electron production and Poynting flux input into the ionosphere are discussed. [1] Shay, M. A., J. F. Drake, J. P. Eastwood, and T. D. Phan, Super-Alfvenic <span class="hlt">propagation</span> of substorm reconnection signatures and Poynting flux,, Physics Review Letters, Vol. 107, 065001, 2011.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997SPD....28.0120F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997SPD....28.0120F"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">Propagation</span> in the Chromosphere and Transition Region: Where Have All the Shock <span class="hlt">Waves</span> Gone?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fleck, B.; Steffens, S.; Deubner, F.-L.; Wilhelm, K.; Harrison, R.; Gurman, J.</p> <p>1997-05-01</p> <p>We present first results from a joint observing program (SOHO JOP 26) involving SUMER, CDS and EIT on SOHO, coordinated with ground-based observations at the Vacuum Tower Telescope at Iza{\\ n}a, Tenerife. The objective of this study is to characterize the <span class="hlt">wave</span> <span class="hlt">propagation</span> properties in the solar atmosphere, from the photosphere through the chromosphere up into the transition region. Particular emphasis is laid on the 3-min shock <span class="hlt">waves</span> observed in the Ca II K line. How do they impact the transition region and what signature do they leave there and in the lower corona? The ground-based measurements comprise high resolution time series (both filtergrams and spectrograms) in Ca II K, Hα and Mgb_2. With SUMER we ran four sequences covering different temperature regimes: a) O I 1302, O I 1306, Si II 1309, C I 1311, C II 1334, C II 1335, b) Si I 1256, N V 1242, O V 629 c) He I 584, C III 1175, O I 1152, d) H I 1025, O VI 1031, O VI 1037. With CDS we took spectral time series in O VI 554, He I 584, He II 607, Mg IX 368, and O V 629 as well as wide-slit (90x240'') ``movies'' in He I 584, Mg IX 368 and O V 629, while EIT ran sub-field high cadence sequences in He II 304.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JaJAP..52hJN25R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JaJAP..52hJN25R"><span id="translatedtitle">Plasma Instability and <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Gate-Controlled GaN Conduction Channels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rudin, Sergey; Rupper, Greg</p> <p>2013-08-01</p> <p>The plasma <span class="hlt">wave</span> in the conduction channel of a semiconductor heterostructure high electron mobility transistor (HEMT) can be excited at frequencies significantly higher than the cut-off frequency in a short channel device. The hydrodynamic model predicts a resonance response to applied harmonic signal at the plasma oscillation frequency. When either the ac voltage induced in the channel by the signal at the gate or the current applied at the drain or source contact are not very small, the plasma <span class="hlt">waves</span> in the semiconductor channel will <span class="hlt">propagate</span> as a shock <span class="hlt">wave</span>. The device can be used either as a detector or a tunable source of terahertz range radiation. Using the parameters appropriate for the GaN channel we show that in both configurations the charge flow develops shock <span class="hlt">waves</span> due to hydrodynamic nonlinearities. In a sufficiently wide channel the <span class="hlt">wave</span> <span class="hlt">propagation</span> separates into two or more different bands giving a two-dimensional structure to the <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26871174','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26871174"><span id="translatedtitle">Self-similar <span class="hlt">propagation</span> of Hermite-Gauss water-<span class="hlt">wave</span> pulses.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fu, Shenhe; Tsur, Yuval; Zhou, Jianying; Shemer, Lev; Arie, Ady</p> <p>2016-01-01</p> <p>We demonstrate both theoretically and experimentally <span class="hlt">propagation</span> dynamics of surface gravity water-<span class="hlt">wave</span> pulses, having Hermite-Gauss envelopes. We show that these <span class="hlt">waves</span> <span class="hlt">propagate</span> self-similarly along an 18-m <span class="hlt">wave</span> tank, preserving their general Hermite-Gauss envelopes in both the linear and the nonlinear regimes. The measured surface elevation <span class="hlt">wave</span> groups enable observing the envelope phase evolution of both nonchirped and linearly frequency chirped Hermite-Gauss pulses, hence allowing us to measure Gouy phase shifts of high-order Hermite-Gauss pulses for the first time. Finally, when increasing pulse amplitude, nonlinearity becomes essential and the second harmonic of Hermite-Gauss <span class="hlt">waves</span> was observed. We further show that these generated second harmonic bound <span class="hlt">waves</span> still exhibit self-similar Hermite-Gauss shapes along the tank.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005JThSc..14..329K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005JThSc..14..329K"><span id="translatedtitle">A study of the weak shock <span class="hlt">wave</span> <span class="hlt">propagating</span> over a porous wall/cavity system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kim, H. D.; Jung, S. J.; Aoki, T.; Setoguchi, T.</p> <p>2005-12-01</p> <p>The present computational study addresses the attenuation of the shock <span class="hlt">wave</span> <span class="hlt">propagating</span> in a duct, using a porous wall/cavity system. In the present study, a weak shock <span class="hlt">wave</span> <span class="hlt">propagating</span> over the porous wall/cavity system is investigated with computational fluid dynamics. A total variation diminishing scheme is employed to solve the unsteady, two-dimensional, compressible, Navier-Stokes equations. The Mach number of an initial shock <span class="hlt">wave</span> is changed in the range from 1.02 to 1.12. Several different types of porous wall/cavity systems are tested to investigate the passive control effects. The results show that wall pressure strongly fluctuates due to diffraction and reflection processes of the shock <span class="hlt">waves</span> behind the incident shock <span class="hlt">wave</span>. From the results, it is understood that for effective alleviation of tunnel impulse <span class="hlt">waves</span>, the length of the perforated region should be sufficiently long.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SMaS...25k5043A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SMaS...25k5043A"><span id="translatedtitle">Ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> of flexible piezoelectric polymer for tactile actuator: simulation and experiment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Akther, Asma; Kafy, Abdullahil; Zhai, Lindong; Kim, Hyun Chan; Shishir, MD Imrul Reza; Kim, Jaehwan</p> <p>2016-11-01</p> <p>This study deals with ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> on a piezoelectric polymer substrate for tactile actuator. On the piezoelectric polymer substrate, a pair of interdigital transductor (IDT) electrodes is patterned by lift-off process and a resonator is made by exciting the IDTs. A standing <span class="hlt">wave</span> is generated between the pair of IDT electrodes, of which the wavelength matches with the distance between two IDTs. The standing ultrasonic <span class="hlt">waves</span> can give different textures to the users. The <span class="hlt">wave</span> <span class="hlt">propagation</span> in this periodic structure on the polymer substrate is studied by harmonic and transient analysis. Vertical displacement and induced voltage at the output IDT electrode are calculated and the ultrasonic <span class="hlt">wave</span> generation is experimentally verified. The proposed concept of tactile actuator based on ultrasonic <span class="hlt">wave</span> is explained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010MS%26E...10a2120W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010MS%26E...10a2120W"><span id="translatedtitle">3D dynamic simulation of crack <span class="hlt">propagation</span> in extracorporeal shock <span class="hlt">wave</span> lithotripsy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wijerathne, M. L. L.; Hori, Muneo; Sakaguchi, Hide; Oguni, Kenji</p> <p>2010-06-01</p> <p>Some experimental observations of Shock <span class="hlt">Wave</span> Lithotripsy(SWL), which include 3D dynamic crack <span class="hlt">propagation</span>, are simulated with the aim of reproducing fragmentation of kidney stones with SWL. Extracorporeal shock <span class="hlt">wave</span> lithotripsy (ESWL) is the fragmentation of kidney stones by focusing an ultrasonic pressure pulse onto the stones. 3D models with fine discretization are used to accurately capture the high amplitude shear shock <span class="hlt">waves</span>. For solving the resulting large scale dynamic crack <span class="hlt">propagation</span> problem, PDS-FEM is used; it provides numerically efficient failure treatments. With a distributed memory parallel code of PDS-FEM, experimentally observed 3D photoelastic images of transient stress <span class="hlt">waves</span> and crack patterns in cylindrical samples are successfully reproduced. The numerical crack patterns are in good agreement with the experimental ones, quantitatively. The results shows that the high amplitude shear <span class="hlt">waves</span> induced in solid, by the lithotriptor generated shock <span class="hlt">wave</span>, play a dominant role in stone fragmentation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27739865','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27739865"><span id="translatedtitle">Observation of Wood's anomalies on surface gravity <span class="hlt">waves</span> <span class="hlt">propagating</span> on a channel.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schmessane, Andrea</p> <p>2016-09-01</p> <p>I report on experiments demonstrating the appearance of Wood's anomalies in surface gravity <span class="hlt">waves</span> <span class="hlt">propagating</span> along a channel with a submerged obstacle. Space-time measurements of surface gravity <span class="hlt">waves</span> allow one to compute the stationary complex field of the <span class="hlt">wave</span> and the amplitude growth of localized and <span class="hlt">propagative</span> modes over all the entire channel, including the scattering region. This allows one to access the near and far field dynamics, which constitute a new and complementary way of observation of mode resonances of the incoming <span class="hlt">wave</span> displaying Wood's anomalies. Transmission coefficient, dispersion relations and normalized <span class="hlt">wave</span> energy of the incoming <span class="hlt">wave</span> and the excited mode are measured and found to be in good agreement with theoretical predictions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1036305','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1036305"><span id="translatedtitle">A Full-<span class="hlt">wave</span> Model for <span class="hlt">Wave</span> <span class="hlt">Propagation</span> and Dissipation in the Inner Magnetosphere Using the Finite Element Method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ernest Valeo, Jay R. Johnson, Eun-Hwa and Cynthia Phillips</p> <p>2012-03-13</p> <p>A wide variety of plasma <span class="hlt">waves</span> play an important role in the energization and loss of particles in the inner magnetosphere. Our ability to understand and model <span class="hlt">wave</span>-particle interactions in this region requires improved knowledge of the spatial distribution and properties of these <span class="hlt">waves</span> as well as improved understanding of how the <span class="hlt">waves</span> depend on changes in solar wind forcing and/or geomagnetic activity. To this end, we have developed a two-dimensional, finite element code that solves the full <span class="hlt">wave</span> equations in global magnetospheric geometry. The code describes three-dimensional <span class="hlt">wave</span> structure including mode conversion when ULF, EMIC, and whistler <span class="hlt">waves</span> are launched in a two-dimensional axisymmetric background plasma with general magnetic field topology. We illustrate the capabilities of the code by examining the role of plasmaspheric plumes on magnetosonic <span class="hlt">wave</span> <span class="hlt">propagation</span>; mode conversion at the ion-ion and Alfven resonances resulting from external, solar wind compressions; and <span class="hlt">wave</span> structure and mode conversion of electromagnetic ion cyclotron <span class="hlt">waves</span> launched in the equatorial magnetosphere, which <span class="hlt">propagate</span> along the magnetic field lines toward the ionosphere. We also discuss advantages of the finite element method for resolving resonant structures, and how the model may be adapted to include nonlocal kinetic effects.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27167307','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27167307"><span id="translatedtitle">One-Directional Fluidic Flow Induced by Chemical <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in a Microchannel.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Arai, Miyu; Takahashi, Kazuhiro; Hattori, Mika; Hasegawa, Takahiko; Sato, Mami; Unoura, Kei; Nabika, Hideki</p> <p>2016-05-26</p> <p>A one-directional flow induced by chemical <span class="hlt">wave</span> <span class="hlt">propagation</span> was investigated to understand the origin of its dynamic flow. A cylindrical injection port was connected with a straight <span class="hlt">propagation</span> channel; the chemical <span class="hlt">wave</span> was initiated at the injection port. Chemical <span class="hlt">waves</span> <span class="hlt">propagated</span> with a constant velocity irrespective of the channel width, indicating that the dynamics of the chemical <span class="hlt">waves</span> were governed by a geometry-independent interplay between the chemical reaction and diffusion. In contrast, the velocity of the one-directional flow was dependent on the channel width. Furthermore, enlargement of the injection port volume increased the flow velocity and volume flux. These results imply that the one-directional flow in the microchannel is due to a hydrodynamic effect induced in the injection port. Spectroscopic analysis of a pH indicator revealed the simultaneous behavior between the pH increase near the injection port and the one-directional flow. Hence, we can conclude that the one-directional flow in the microchannel with chemical <span class="hlt">wave</span> <span class="hlt">propagation</span> was caused by a proton consumption reaction in the injection port, probably through liquid volume expansion by the reaction products and the reaction heat. It is a characteristic feature of the present system that the hydrodynamic flow started from the chemical <span class="hlt">wave</span> initiation point and not the <span class="hlt">propagation</span> wavefront, as observed for previous systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004JAP....96.1993W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004JAP....96.1993W"><span id="translatedtitle">Nonlinear anisotropic description for shocked single crystals: Thermoelastic response and pure mode <span class="hlt">wave</span> <span class="hlt">propagation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Winey, J. M.; Gupta, Y. M.</p> <p>2004-08-01</p> <p>An anisotropic continuum framework for describing the nonlinear thermoelastic response of shocked single crystals has been developed. Using this framework, the <span class="hlt">propagation</span> of large amplitude stress <span class="hlt">waves</span> along arbitrary directions in crystals of any symmetry can be examined. We developed an incremental approach, where the reference state for the dynamical variables and the material properties is updated throughout the calculation. Results from our incremental approach are in excellent agreement with the results from a finite strain formulation. Using a finite-difference <span class="hlt">wave</span> <span class="hlt">propagation</span> code, we performed numerical simulations of large amplitude elastic <span class="hlt">wave</span> <span class="hlt">propagation</span> in single crystals. Results of impact loading simulations for quartz and sapphire single crystals are presented. The framework developed was also useful for examining the <span class="hlt">propagation</span> of pure mode nonlinear <span class="hlt">waves</span> for various crystal symmetries. Our calculations showed that pure longitudinal <span class="hlt">waves</span> resulted from impact loading along any rotational symmetry axis for all crystal symmetry classes. Differences between pure mode <span class="hlt">wave</span> <span class="hlt">propagation</span> for linear and nonlinear elastic deformation are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/875673','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/875673"><span id="translatedtitle">Supersonic <span class="hlt">propagation</span> of ionization <span class="hlt">waves</span> in an under-dense, laser-produced plasma</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Constantin, C; Back, C A; Fournier, K B; Gregori, G; Landen, O L; Glenzer, S H; Dewald, E L; Miller, M C</p> <p>2004-10-22</p> <p>We observe a laser-driven supersonic ionization <span class="hlt">wave</span> heating a mm-scale plasma of sub-critical density up to 2-3 keV electron temperatures. <span class="hlt">Propagation</span> velocities initially 10 times the sound speed were measured by means of time-resolved x-ray imaging diagnostics. The measured ionization <span class="hlt">wave</span> trajectory is modeled analytically and by a 2D radiation-hydrodynamics code. The comparison to the modeling suggests that nonlocal heat transport effects may contribute to the attenuation of the heat <span class="hlt">wave</span> <span class="hlt">propagation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15950030','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15950030"><span id="translatedtitle">Lamb <span class="hlt">waves</span> <span class="hlt">propagation</span> in elastic plane layers with a joint strip.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Predoi, Mihai Valentin; Rousseau, Martine</p> <p>2005-06-01</p> <p>The Lamb <span class="hlt">waves</span> are used for the ultrasonic characterization of welds because of their relative long-range <span class="hlt">propagation</span>. In this paper, a simplified model of a weld-strip between two identical semi-infinite elastic layers is investigated. The reflected and transmitted ultrasonic fields are expressed by modal series whose coefficients are obtained by application of orthogonality relation. Comparisons with solutions obtained by finite elements <span class="hlt">wave</span> <span class="hlt">propagation</span> simulations are made. The energy balance between the incident and the scattered <span class="hlt">waves</span> is also used to verify the accuracy of the obtained modal amplitudes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3948613','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3948613"><span id="translatedtitle">Spherical <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in a Poroelastic Medium with Infinite Permeability: Time Domain Solution</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ozyazicioglu, Mehmet</p> <p>2014-01-01</p> <p>Exact time domain solutions for displacement and porepressure are derived for <span class="hlt">waves</span> emanating from a pressurized spherical cavity, in an infinitely permeable poroelastic medium with a permeable boundary. Cases for blast and exponentially decaying step pulse loadings are considered; letter case, in the limit as decay constant goes to zero, also covers the step (uniform) pressure. Solutions clearly show the <span class="hlt">propagation</span> of the second (slow) p-<span class="hlt">wave</span>. Furthermore, Biot modulus Q is shown to have a pronounced influence on <span class="hlt">wave</span> <span class="hlt">propagation</span> characteristics in poroelastic media. Results are compared with solutions in classical elasticity theory. PMID:24701190</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4738718','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4738718"><span id="translatedtitle">Rescaled Local Interaction Simulation Approach for Shear <span class="hlt">Wave</span> <span class="hlt">Propagation</span> Modelling in Magnetic Resonance Elastography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Packo, P.; Staszewski, W. J.; Uhl, T.</p> <p>2016-01-01</p> <p>Properties of soft biological tissues are increasingly used in medical diagnosis to detect various abnormalities, for example, in liver fibrosis or breast tumors. It is well known that mechanical stiffness of human organs can be obtained from organ responses to shear stress <span class="hlt">waves</span> through Magnetic Resonance Elastography. The Local Interaction Simulation Approach is proposed for effective modelling of shear <span class="hlt">wave</span> <span class="hlt">propagation</span> in soft tissues. The results are validated using experimental data from Magnetic Resonance Elastography. These results show the potential of the method for shear <span class="hlt">wave</span> <span class="hlt">propagation</span> modelling in soft tissues. The major advantage of the proposed approach is a significant reduction of computational effort. PMID:26884808</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhRvB..95b0407S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhRvB..95b0407S"><span id="translatedtitle">Nonreciprocal <span class="hlt">propagation</span> of surface acoustic <span class="hlt">wave</span> in Ni/LiNbO 3</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sasaki, R.; Nii, Y.; Iguchi, Y.; Onose, Y.</p> <p>2017-01-01</p> <p>We investigated surface acoustic <span class="hlt">wave</span> <span class="hlt">propagation</span> in a Ni/LiNbO3 hybrid device. We found that the absorption and phase velocity are dependent on the sign of the <span class="hlt">wave</span> vector, which indicates that the surface acoustic <span class="hlt">wave</span> <span class="hlt">propagation</span> has nonreciprocal characteristics induced by simultaneous breaking of time-reversal and spatial inversion symmetries. The nonreciprocity was reversed by 180∘ rotation of the magnetic field. The origin of the nonreciprocity is ascribed to interference of shear-type and longitudinal-type magnetoelastic couplings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/AD1006842','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/AD1006842"><span id="translatedtitle">Fast Multiscale Algorithms for <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Heterogeneous Environments</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2016-01-07</p> <p>guaranteed. In support of this goal we have developed: (i.) convenient implementations of optimal local radiation boundary sequences for isotropic <span class="hlt">waves</span>...this goal we have developed: (i.) convenient implementations of optimal local radiation boundary sequences for isotropic <span class="hlt">waves</span>, with implementations...Modeling and Numerical Analysis, (05 2012): 545. doi: Thomas Hagstrom. HIGH-ORDER RADIATION BOUNDARY CONDITIONS FORSTRATIFIED MEDIA AND CURVILINEAR</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983RaRLR..29..505O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983RaRLR..29..505O"><span id="translatedtitle">Anomalous <span class="hlt">propagation</span> of Omega VLF <span class="hlt">waves</span> near the geomagnetic equator</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ohtani, A.; Kikuchi, T.; Nozaki, K.; Kurihara, N.; Kuratani, Y.; Ohse, M.</p> <p>1983-09-01</p> <p>Omega HAIKU, REUNION, and LIBERIA signals were received and anomalous <span class="hlt">propagation</span> characteristics were obtained near the geomagnetic equator. Short-period fluctuations were found in the phase of the HAIKU 10.2 kHz signal in November 1979 and in the phase and amplitude of the HAIKU 13.6 kHz signal in November 1981. These cyclic fluctuations are in close correlation with the phase cycle slippings, which occur most frequently when the receiver is located at 6 S geomagnetic latitude. On the basis of anisotropic waveguide mode theory indicating much less attenuation in WE <span class="hlt">propagation</span> than in EW <span class="hlt">propagation</span> at the geomagnetic equator, it is concluded that the short-period fluctuations in the phase and amplitude are due to interference between the short-path and the long-path signals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22496220','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22496220"><span id="translatedtitle">RF <span class="hlt">wave</span> <span class="hlt">propagation</span> and scattering in turbulent tokamak plasmas</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Horton, W. Michoski, C.; Peysson, Y.; Decker, J.</p> <p>2015-12-10</p> <p>Drift <span class="hlt">wave</span> turbulence driven by the steep electron and ion temperature gradients in H-mode divertor tokamaks produce scattering of the RF <span class="hlt">waves</span> used for heating and current drive. The X-ray emission spectra produced by the fast electrons require the turbulence broaden RF <span class="hlt">wave</span> spectrum. Both the 5 GHz Lower Hybrid <span class="hlt">waves</span> and the 170 GHz electron cyclotron [EC] RF <span class="hlt">waves</span> experience scattering and diffraction by the electron density fluctuations. With strong LHCD there are bifurcations in the coupled turbulent transport dynamics giving improved steady-state confinement states. The stochastic scattering of the RF rays makes the prediction of the distribution of the rays and the associated particle heating a statistical problem. Thus, we introduce a Fokker-Planck equation for the probably density of the RF rays. The general frame work of the coupled system of coupled high frequency current driving rays with the low-frequency turbulent transport determines the profiles of the plasma density and temperatures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993JGR....98.5291H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993JGR....98.5291H"><span id="translatedtitle"><span class="hlt">Propagation</span> of electromagnetic <span class="hlt">waves</span> parallel to the magnetic field in the nightside Venus ionosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huba, J. D.; Rowland, H. L.</p> <p>1993-03-01</p> <p>The <span class="hlt">propagation</span> of electromagnetic <span class="hlt">waves</span> parallel to the magnetic field in the nightside Venus ionosphere is presented in a theoretical and numerical analysis. The model assumes a source of electromagnetic radiation in the Venus atmosphere, such as that produced by lightning. Specifically addressed is <span class="hlt">wave</span> <span class="hlt">propagation</span> in the altitude range z = 130-160 km at the four frequencies detectable by the Pioneer Venus Orbiter Electric Field Detector: 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz. Parameterizations of the <span class="hlt">wave</span> intensities, peak electron density, and Poynting flux as a function of magnetic field are presented. The <span class="hlt">waves</span> are found to <span class="hlt">propagate</span> most easily in conditions of low electron density and high magnetic field. The results of the model are consistent with observational data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21797512','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21797512"><span id="translatedtitle">Lattice Boltzmann method for multimode <span class="hlt">wave</span> <span class="hlt">propagation</span> in viscoelastic media and in elastic solids.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Frantziskonis, George N</p> <p>2011-06-01</p> <p>This paper reports the lattice Boltzmann method (LBM) based formulation for viscoelastic fluids with both volumetric and shear viscoelasticity. The relaxation limit of the viscoelastic fluid formulation yields the LBM for elastic solids with both volumetric or pressure (p) and shear (s) <span class="hlt">wave</span> <span class="hlt">propagation</span> modes. The reflection of a two-dimensional p <span class="hlt">wave</span> from an obstacle (wedge) inclined to the <span class="hlt">propagation</span> direction of the p <span class="hlt">wave</span> is studied together with the convergence and stability behavior of the LBM as the lattice size and lattice time step decrease. The model is capable of accurately predicting the mode change (p to s) due to the reflection. The model provides a unique unified approach capable of simulating fluids, viscoelastic fluids, and solids within a single LBM framework, thus avoiding interface problems between different simulation methods. The paper concentrates on the <span class="hlt">wave</span> <span class="hlt">propagation</span> part of the model, in the quasielastic regime.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...631783W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...631783W"><span id="translatedtitle">Spin-<span class="hlt">wave</span> <span class="hlt">propagation</span> steered by electric field modulated exchange interaction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Sheng; Guan, Xiawei; Cheng, Xiaomin; Lian, Chen; Huang, Ting; Miao, Xiangshui</p> <p>2016-09-01</p> <p>Combined ab initio and micromagnetic simulations are carried out to demonstrate the feasibility on the electrical manipulation of spin-<span class="hlt">wave</span> <span class="hlt">propagation</span> in ultrathin Fe films. It is discovered that the exchange interaction can be substantially weakened under the influence of electric field applied perpendicular to the magnetic film surface. Furthermore, we demonstrate that the electric field modified exchange constant could effectively control the <span class="hlt">propagation</span> of spin <span class="hlt">waves</span>. To be specific, an external applied electric field of 5 V/nm can effectively weaken exchange interaction by 80% and is sufficient to induce nearly twofold change of the wavenumber. This discovery may open a door to energy-efficient local manipulation of the spin <span class="hlt">wave</span> <span class="hlt">propagation</span> utilizing electric fields, which is crucial for both fundamental research and spin <span class="hlt">wave</span> based logic applications.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <center> <div class="footer-extlink text-muted"><small>Some links on this page may take you to non-federal websites. 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