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Sample records for propagating planar wave

  1. In-plane propagation of electromagnetic waves in planar metamaterials

    NASA Astrophysics Data System (ADS)

    Yi, Changhyun; Rhee, Joo Yull; Kim, Ki Won; Lee, YoungPak

    2016-08-01

    Some planar metamaterials (MMs) or subwavelength antenna/hole arrays have a considerable amount of in-plane propagation when certain conditions are met. In this paper, the in-plane propagation caused by a wave incident on a MM absorber was studied by using a finite-difference time-domain (FDTD) technique. By using a FDTD simulation, we were able to observe a nonnegligible amount of in-plane propagation after the incident wave had arrived at the surface of the planar structure and gradually decreased propagation of the electromagnetic wave in the planar direction gradually decreased. We performed the FDTD simulation carefully to reproduce valid results and to verify the existence of in-plane propagation. For verification of the in-plane propagation explicitly, Poynting vectors were calculated and visualized inside the dielectric substrate between the metallic back-plate and an array of square patches. We also investigated several different structures with resonators of various shapes and found that the amount of facing edges of adjacent metallic patches critically determined the strength of the in-plane propagation. Through this study, we could establish the basis for the existence of in-plane propagation in MMs.

  2. Optical wave propagation in epitaxial Nd:Y2O3 planar waveguides.

    PubMed

    Li, Wei; Webster, Scott E; Kumaran, Raveen; Penson, Shawn; Tiedje, Thomas

    2010-02-01

    Optical wave propagation in neodymium-doped yttrium oxide (Nd:Y(2)O(3)) films grown on R-plane sapphire substrates by molecular beam epitaxy has been studied by the prism coupler method. The measurements yield propagation loss data, the refractive index, and the dispersion relation. The refractive index of the Nd:Y(2)O(3) at 632.8 nm is found to be 1.909, and the lowest propagation loss measured is 0.9 +/- 0.2 cm(-1) at 1046 nm with a polymethyl methacrylate top cladding layer on a film with 6 nm root mean square surface roughness. The loss measurements suggest that the majority loss of this planar waveguide sample is scatter from surface roughness that can be described by the model of Payne and Lacey [Opt. Quantum Electron. 26, 977 (1994)].

  3. 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.; 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 withmore » simulation data. As a result, these micro-structures can be utilized for free electron beam and electronic/optic integrated devices« less

  4. 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

  5. A new matrix formulation of classical electrodynamics. Part 3: Wave propagation through a multilayer dielectric medium with planar boundaries

    NASA Astrophysics Data System (ADS)

    Bocker, R. P.

    1993-10-01

    A new approach for solving electromagnetic wave propagation problems is currently being developed at the Naval Command, Control and Ocean Surveillance Center (NCCOSC), RDT and E Division (NRaD). This new approach is based upon an eight by eight matrix representation of the Maxwell field equations. In addition, a computer software package based on this matrix representation of electromagnetic theory is also being written and tested at NRaD to handle a variety of scenarios involving electromagnetic wave propagation through matter. This software package is referred to as the MATURE Program. MATURE is the acronym for matrix approach to understanding relativistic electrodynamics. The MATURE program is written in MATLAB code for use on a Sun 4 SPARCstation 2 workstation. Under Independent Research (IR) FY 92 funding, this matrix approach was successfully employed in solving problems dealing with electromagnetic wave propagation through dielectric, crystalline, linear electro-optic, and magneto-optic materials of infinite extent. Under the Office of Naval Research (ONR) FY 93 funding, this matrix formulation was extended to handle problems involving wave propagation through multilayer dielectric media with planar boundaries. Presented in this technical document is the underlying theory of this matrix approach. Several numerical examples, based on the use of the MATURE program, are also included to illustrate the use of the matrix approach in solving electromagnetic wave propagation problems.

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

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

    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.

  7. 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.

  8. Wave propagation phenomena

    NASA Astrophysics Data System (ADS)

    Groenenboom, P. H. L.

    The phenomenon of wave propagation is encountered frequently in a variety of engineering disciplines. It has been realized that for a growing number of problems the solution can only be obtained by discretization of the boundary. Advantages of the Boundary Element Method (BEM) over domain-type methods are related to the reduction of the number of space dimensions and of the modelling effort. It is demonstrated how the BEM can be applied to wave propagation phenomena by establishing the fundamental relationships. A numerical solution procedure is also suggested. In connection with a discussion of the retarded potential formulation, it is shown how the wave propagation problem can be cast into a Boundary Integral Formulation (BIF). The wave propagation problem in the BIF can be solved by time-successive evaluation of the boundary integrals. The example of pressure wave propagation following a sodium-water reaction in a Liquid Metal cooled Fast Breeder Reactor steam generator is discussed.

  9. 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].

  10. Electromagnetic inhomogeneous waves at planar boundaries: tutorial.

    PubMed

    Frezza, Fabrizio; Tedeschi, Nicola

    2015-08-01

    In this review paper, we summarize the fundamental properties of inhomogeneous waves at the planar interface between two media. We point out the main differences between the wave types: lateral waves, surface waves, and leaky waves. We analyze each kind of inhomogeneous wave, giving a quasi-optical description and explaining the physical origin of some of their properties.

  11. Generation of whistler-wave heated discharges with planar resonant RF networks.

    PubMed

    Guittienne, Ph; Howling, A A; Hollenstein, Ch

    2013-09-20

    Magnetized plasma discharges generated by a planar resonant rf network are investigated. A regime transition is observed above a magnetic field threshold, associated with rf waves propagating in the plasma and which present the characteristics of whistler waves. These wave heated regimes can be considered as analogous to conventional helicon discharges, but in planar geometry.

  12. Fundamentals of Seismic Wave Propagation

    NASA Astrophysics Data System (ADS)

    Chapman, Chris

    2004-08-01

    Presenting a comprehensive introduction to the propagation of high-frequency body-waves in elastodynamics, this volume develops the theory of seismic wave propagation in acoustic, elastic and anisotropic media to allow seismic waves to be modelled in complex, realistic three-dimensional Earth models. The book is a text for graduate courses in theoretical seismology, and a reference for all academic and industrial seismologists using numerical modelling methods. Exercises and suggestions for further reading are included in each chapter.

  13. A nonlinear wave equation in nonadiabatic flame propagation

    SciTech Connect

    Booty, M.R.; Matalon, M.; Matkowsky, B.J.

    1988-06-01

    The authors derive a nonlinear wave equation from the diffusional thermal model of gaseous combustion to describe the evolution of a flame front. The equation arises as a long wave theory, for values of the volumeric heat loss in a neighborhood of the extinction point (beyond which planar uniformly propagating flames cease to exist), and for Lewis numbers near the critical value beyond which uniformly propagating planar flames lose stability via a degenerate Hopf bifurcation. Analysis of the equation suggests the possibility of a singularity developing in finite time.

  14. 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.

  15. Transhorizon propagation of decameter waves

    NASA Astrophysics Data System (ADS)

    Kalinin, Yu. K.; Shchelkalin, A. V.

    2013-04-01

    Solutions to the problem of the point source field in a spherically layered medium are analyzed. For a three-layer waveguide model, a solution in the form of the Watson integral was used. A consideration of the singularities in the plane of the integration variable made it possible to represent the integral as a superposition of three waves. Two of them are connected with the interaction of the primary spherical wave with the lower convex and upper concave interfaces. The third wave is connected with the alternate action with both interfaces. The fourth wave is caused by the interaction between the primary wave and random inhomogeneities of the external medium (the ionosphere). Here, simulation was carried out based on Green equations. The considered unique data of flight measurements of the point source field strength indicate the efficiency of simulating the transhorizon propagation of decameter waves based on the superposition of all four aforesaid wave packets.

  16. Seismic wave propagation modeling

    SciTech Connect

    Jones, E.M.; Olsen, K.B.

    1998-12-31

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). A hybrid, finite-difference technique was developed for modeling nonlinear soil amplification from three-dimensional, finite-fault radiation patters for earthquakes in arbitrary earth models. The method was applied to the 17 January 1994 Northridge earthquake. Particle velocities were computed on a plane at 5-km depth, immediately above the causative fault. Time-series of the strike-perpendicular, lateral velocities then were propagated vertically in a soil column typical of the San Fernando Valley. Suitable material models were adapted from a suite used to model ground motions at the US Nevada Test Site. The effects of nonlinearity reduced relative spectral amplitudes by about 40% at frequencies above 1.5 Hz but only by 10% at lower frequencies. Runs made with source-depth amplitudes increased by a factor of two showed relative amplitudes above 1.5 Hz reduced by a total of 70% above 1.5 Hz and 20% at lower frequencies. Runs made with elastic-plastic material models showed similar behavior to runs made with Masing-Rule models.

  17. Wave propagation in solids and fluids

    SciTech Connect

    Davis, J. L.

    1988-01-01

    The fundamental principles of mathematical analysis for wave phenomena in gases, solids, and liquids are presented in an introduction for scientists and engineers. Chapters are devoted to oscillatory phenomena, the physics of wave propagation, partial differential equations for wave propagation, transverse vibration of strings, water waves, and sound waves. Consideration is given to the dynamics of viscous and inviscid fluids, wave propagation in elastic media, and variational methods in wave phenomena. 41 refs.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  19. 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.

  20. 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.

  1. 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.

  2. Planar and non-planar dust ion-acoustic solitary waves in a quantum dusty electronegative plasma

    NASA Astrophysics Data System (ADS)

    Tasnim, S.; Islam, S.; Mamun, A. A.

    2012-03-01

    A theoretical investigation has been made on nonlinear propagation of planar and non-planar solitary waves in a quantum dusty electronegative plasma, whose constituents are quantum electrons, positive ions, negative ions, and arbitrarily charged stationary dust. The reductive perturbation method has been used to derive the Korteweg-de Vries and modified Korteweg-de Vries equations for studying the basic features of solitary waves, which are associated with both positive and negative ion dynamics. The effects of quantum parameter (H), positive and negative ion mass ratio (μin), as well as dust and positive ion number densities (β) on the basic features (polarity, height, and width) of planar solitary waves have been studied. It has been also found that the properties of dust ion-acoustic solitary waves in non-planar cylindrical or spherical geometry differ from those in planar one-dimensional geometry. The implications of our results in space (viz., interstellar compact objects like neutron stars) and laboratory experiments (e.g., intense laser solid density plasma experiments) have been briefly discussed.

  3. Wave equations for pulse propagation

    NASA Astrophysics Data System (ADS)

    Shore, B. W.

    1987-06-01

    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.

  4. 3D Elastic Seismic Wave Propagation Code

    1998-09-23

    E3D is capable of simulating seismic wave propagation in a 3D heterogeneous earth. Seismic waves are initiated by earthquake, explosive, and/or other sources. These waves propagate through a 3D geologic model, and are simulated as synthetic seismograms or other graphical output.

  5. Active Wave Propagation and Sensing in Plates

    NASA Technical Reports Server (NTRS)

    Ghoshal, Anindya; Martin, William N.; Sundaresan, Mannur J.; Schulz, Mark J.; Ferguson, Frederick

    2001-01-01

    Health monitoring of aerospace structures can be done using an active interrogation approach with diagnostic Lamb waves. Piezoelectric patches are often used to generate the waves, and it is helpful to understand how these waves propagate through a structure. To give a basic understanding of the actual physical process of wave propagation, a model is developed to simulate asymmetric wave propagation in a panel and to produce a movie of the wave motion. The waves can be generated using piezoceramic patches of any size or shape. The propagation, reflection, and interference of the waves are represented in the model. Measuring the wave propagation is the second important aspect of damage detection. Continuous sensors are useful for measuring waves because of the distributed nature of the sensor and the wave. Two sensor designs are modeled, and their effectiveness in measuring acoustic waves is studied. The simulation model developed is useful to understand wave propagation and to optimize the type of sensors that might be used for health monitoring of plate-like structures.

  6. Wave propagation in magnetic fluids

    NASA Astrophysics Data System (ADS)

    Cissoko, Mahdy

    1987-08-01

    This paper deals within the relativistic framework with the wave propagation in magnetizable fluids, assumed to be perfect, magnetically soft, isotropic, and inhomogeneous with an arbitrary isotropic law χ=χ(T,r,||b||2) (χ,T,r,||b|| being the magnetic susceptibility, the proper temperature, the proper material density, and the strength of the magnetic field, respectively). The characteristic manifolds of the flow are determined in a very elegant and rigorous manner which avoids the extensive algebraic manipulations one usually encounters in the classical methods of characteristics. It is shown that in a magnetic medium there exists a hyperbolic region of nonsteady flows of magnetizable fluids. This implies the existence of magnetosonic waves of the same kind as in nonmagnetic fluids (χ or μ=const), that is, as in ordinary magnetohydrodynamics. However, in magnetic fluids there is the possibility of the development of instabilities similar to that which arise in nonmagnetic fluids with transverse and longitudinal pressure [M. Cissoko, Ann. Mat. Pura Appl. 111, 331 (1976)].

  7. Propagation of a fluidization - combustion wave

    SciTech Connect

    Pron, G.P.; Gusachenko, L.K.; Zarko, V.E.

    1994-05-01

    A fluidization-combustion wave propagating through a fixed and initially cool bed was created by igniting coal at the top surface of the bed. The proposed physical interpretation of the phenomenon is in qualitative agreement with the experimental dependences of the characteristics of the process on determining parameters. A kindling regime with forced wave propagation is suggested.

  8. 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.

  9. Pulse Wave Propagation in the Arterial Tree

    NASA Astrophysics Data System (ADS)

    van de Vosse, Frans N.; Stergiopulos, Nikos

    2011-01-01

    The beating heart creates blood pressure and flow pulsations that propagate as waves through the arterial tree that are reflected at transitions in arterial geometry and elasticity. Waves carry information about the matter in which they propagate. Therefore, modeling of arterial wave propagation extends our knowledge about the functioning of the cardiovascular system and provides a means to diagnose disorders and predict the outcome of medical interventions. In this review we focus on the physical and mathematical modeling of pulse wave propagation, based on general fluid dynamical principles. In addition we present potential applications in cardiovascular research and clinical practice. Models of short- and long-term adaptation of the arterial system and methods that deal with uncertainties in personalized model parameters and boundary conditions are briefly discussed, as they are believed to be major topics for further study and will boost the significance of arterial pulse wave modeling even more.

  10. Numerical wave propagation in ImageJ.

    PubMed

    Piedrahita-Quintero, Pablo; Castañeda, Raul; Garcia-Sucerquia, Jorge

    2015-07-20

    An ImageJ plugin for numerical wave propagation is presented. The plugin provides ImageJ, the well-known software for image processing, with the capability of computing numerical wave propagation by the use of angular spectrum, Fresnel, and Fresnel-Bluestein algorithms. The plugin enables numerical wave propagation within the robust environment provided by the complete set of built-in tools for image processing available in ImageJ. The plugin can be used for teaching and research purposes. We illustrate its use to numerically recreate Poisson's spot and Babinet's principle, and in the numerical reconstruction of digitally recorded holograms from millimeter-sized and pure phase microscopic objects.

  11. Radiation of planar electromagnetic waves by a line source in anisotropic metamaterials

    NASA Astrophysics Data System (ADS)

    Cheng, Qiang; Jiang, Wei Xiang; Cui, Tie Jun

    2010-08-01

    We show experimentally that a line source in an anisotropic metamaterial directly radiates planar electromagnetic waves instead of cylindrical waves, when one component of the permeability tensor approaches zero. The impedance of this material can be perfectly matched to that of free space, which can significantly reduce the reflections between the source and the superstrate, as in traditional highly directive antennas based on zero index metamaterials. Such a unique property determines the two-way propagation of electromagnetic waves excited by a line source, instead of all-way propagation. From this feature, a highly directive emission of electromagnetic waves is achieved using the anisotropic metamaterial with arbitrary shape. We have designed and fabricated the anisotropic metamaterial in the microwave region, and observed the generation of plane waves and their highly directive emission. The proposed plane-wave emission is independent of the shape variance of the anisotropic metamaterial, which can be utilized in the design of conformal antennas.

  12. 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.

  13. 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.

  14. 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.

  15. Controls on flood and sediment wave propagation

    NASA Astrophysics Data System (ADS)

    Bakker, Maarten; Lane, Stuart N.; Costa, Anna; Molnar, Peter

    2015-04-01

    The understanding of flood wave propagation - celerity and transformation - through a fluvial system is of generic importance for flood forecasting/mitigation. In association with flood wave propagation, sediment wave propagation may induce local erosion and sedimentation, which will affect infrastructure and riparian natural habitats. Through analysing flood and sediment wave propagation, we gain insight in temporal changes in transport capacity (the flood wave) and sediment availability and transport (the sediment wave) along the river channel. Heidel (1956) was amongst the first to discuss the progressive lag of sediment concentration behind the corresponding flood wave based on field measurements. Since then this type of hysteresis has been characterized in a number of studies, but these were often based on limited amount of floods and measurement sites, giving insufficient insight into associated forcing mechanisms. Here, as part of a project concerned with the hydrological and geomorphic forcing of sediment transfer processes in alpine environments, we model the downstream propagation of short duration, high frequency releases of water and sediment (purges) from a flow intake in the Borgne d'Arolla River in south-west Switzerland. A total of >50 events were measured at 1 minute time intervals using pressure transducers and turbidity probes at a number of sites along the river. We show that flood and sediment wave propagation can be well represented through simple convection diffusion models. The models are calibrated/validated to describe the set of measured waves and used to explain the observed variation in wave celerity and diffusion. In addition we explore the effects of controlling factors including initial flow depth, flood height, flood duration, bed roughness, bed slope and initial sediment concentration, on the wave propagation processes. We show that the effects of forcing mechanisms on flood and sediment wave propagation will lead to different

  16. Supersaturation of vertically propagating internal gravity waves

    NASA Technical Reports Server (NTRS)

    Lindzen, Richard S.

    1988-01-01

    The usual assumption that vertically propagating internal gravity waves will cease growing with height once their amplitudes are such as to permit convective instability anywhere within the wave is reexamined. Two factors lead to amplitude limitation: (1) wave clipping associated with convective mixing, and (2) energetic constraints associated with the rate at which the wave can supply energy to the convection. It is found that these two factors limit supersaturation to about 50 percent for waves with short horizontal wavelengths and high relative phase speeds. Usually the degree of supersaturation will be much less. These factors also lead to a gradual, rather than sudden, cessation of wave growth with height.

  17. 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.

  18. 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

  19. Atmospheric millimeter wave propagation model

    NASA Astrophysics Data System (ADS)

    Liebe, H. J.

    1983-12-01

    The neutral atmosphere is characterized for the frequency range from 1 to 300 GHz as nonturbulent propagation medium. Attenuation and propagation delay effects are predicated from meteorological data sets: pressure, temperature, humidity, suspended particle concentration, and rain rate. The physical data base of the propagation model consists of four terms: (1) resonance information for 30 water vapor and 48 oxygen absorption lines in the form of intensity coefficients and center frequency for each line; (2) a composite (oxygen, water vapor, and nitrogen) continum spectrum; (3) a hydrosol attenuation term for haze, fog, and cloud conditions; and (4) a rain attenuation model. Oxygen lines extend into the mesosphere, where they behave in a complicated manner due to the Zeeman effect.

  20. 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.

  1. Faraday Pilot-Waves: Generation and Propagation

    NASA Astrophysics Data System (ADS)

    Galeano-Rios, Carlos; Milewski, Paul; Nachbin, André; Bush, John

    2015-11-01

    We examine the dynamics of drops bouncing on a fluid bath subjected to vertical vibration. We solve a system of linear PDEs to compute the surface wave generation and propagation. Waves are triggered at each bounce, giving rise to the Faraday pilot-wave field. The model captures several of the behaviors observed in the laboratory, including transitions between a variety of bouncing and walking states, the Doppler effect, and droplet-droplet interactions. Thanks to the NSF.

  2. Harmonic plane wave propagation in gyroelectric media

    NASA Astrophysics Data System (ADS)

    Hillion, Pierre

    2006-05-01

    We analyse the behaviour of harmonic plane waves in unbounded gyroelectric media once the refractive index in the direction of propagation is known from the Fresnel equation. We get, for the electric and magnetic fields, analytical expressions simple enough to use in a plane wave spectrum representation of more structured electromagnetic fields in these media. We also discuss the reflection and refraction of harmonic plane waves at the boundary between an isotropic medium and a gyroelectric material.

  3. Planar and non-planar ion acoustic shock waves in electron positron ion plasmas

    NASA Astrophysics Data System (ADS)

    Masood, Waqas; Jehan, Nusrat; Mirza, Arshad M.; Sakanaka, P. H.

    2008-06-01

    Ion acoustic shock waves (IASW's) are studied in an unmagnetized plasma consisting of electrons, positrons and adiabatically hot positive ions. This is done by deriving the Kortweg-deVries-Burger (KdVB) equation under 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 ion acoustic shock wave is maximum for spherical, intermediate for cylindrical, and minimum for planar geometry. It is observed that the positron concentration, ratio of ion to electron temperature, and the plasma kinematic viscosity significantly modifies the shock structure. Finally, it is found that the temporal evolution of the non-planar IASW's is quite different by comparison with the planar geometry. The relevance of the present study with regard to the dense astrophysical environments is also pointed out.

  4. Electrostatic lower hybrid waves excited by electromagnetic whistler mode waves scattering from planar magnetic-field-aligned plasma density irregularities

    NASA Technical Reports Server (NTRS)

    Bell, T. F.; Ngo, H. D.

    1990-01-01

    This paper presents a theoretical model for electrostatic lower hybrid waves excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and the topside ionosphere, where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. In this model, the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. Results indicate that high-amplitude short-wavelength (5 to 100 m) quasi-electrostatic whistler mode waves can be excited when electromagnetic whistler mode waves scatter from small-scale planar magnetic-field-aligned plasma density irregularities in the topside ionosphere and magnetosphere.

  5. Propagation of polarized waves in inhomogeneous media.

    PubMed

    Charnotskii, Mikhail

    2016-07-01

    A parabolic equation for electromagnetic wave propagation in a random medium is extended to include the depolarization effects in the narrow-angle, forward-scattering setting. Closed-form parabolic equations for propagation of the coherence tensor are derived under a Markov approximation model. For a general partially coherent and partially polarized beam wave, this equation can be reduced to a system of ordinary differential equations, allowing a simple numeric solution. An analytical solution exists for statistically homogeneous waves. Estimates based on the perturbation solution support the common knowledge that the depolarization at the optical frequencies is negligible for atmospheric turbulence propagation. These results indicate that the recently published theory [Opt. Lett.40, 3077 (2015)10.1364/OL.40.003077] is not valid for atmospheric turbulence. PMID:27409697

  6. Instability of a planar expansion wave.

    PubMed

    Velikovich, A L; Zalesak, S T; Metzler, N; Wouchuk, J G

    2005-10-01

    An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion wave in an ideal gas, like a rippled shock wave, typically produces decaying oscillations of all fluid variables. Its behavior, however, is different at large and small values of the adiabatic exponent gamma. At gamma > 3, the mass modulation amplitude delta(m) in a rippled expansion wave exhibits a power-law growth with time alpha(t)beta, where beta = (gamma - 3)/(gamma - 1). This is the only example of a hydrodynamic instability whose law of growth, dependent on the equation of state, is expressed in a closed analytical form. The growth is shown to be driven by a physical mechanism similar to that of a classical Richtmyer-Meshkov instability. In the opposite extreme gamma - 1 < 1, delta(m) exhibits oscillatory growth, approximately linear with time, until it reaches its peak value approximately (gamma - 1)(-1/2), and then starts to decrease. The mechanism driving the growth is the same as that of Vishniac's instability of a blast wave in a gas with low . Exact analytical expressions for the growth rates are derived for both cases and favorably compared to hydrodynamic simulation results.

  7. Instability of a planar expansion wave

    NASA Astrophysics Data System (ADS)

    Velikovich, A. L.; Zalesak, S. T.; Metzler, N.; Wouchuk, J. G.

    2005-10-01

    An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion wave in an ideal gas, like a rippled shock wave, typically produces decaying oscillations of all fluid variables. Its behavior, however, is different at large and small values of the adiabatic exponent γ . At γ>3 , the mass modulation amplitude δm in a rippled expansion wave exhibits a power-law growth with time ∝ tβ , where β= (γ-3) / (γ-1) . This is the only example of a hydrodynamic instability whose law of growth, dependent on the equation of state, is expressed in a closed analytical form. The growth is shown to be driven by a physical mechanism similar to that of a classical Richtmyer-Meshkov instability. In the opposite extreme γ-1≪1 , δm exhibits oscillatory growth, approximately linear with time, until it reaches its peak value ˜ (γ-1)-1/2 , and then starts to decrease. The mechanism driving the growth is the same as that of Vishniac’s instability of a blast wave in a gas with low γ . Exact analytical expressions for the growth rates are derived for both cases and favorably compared to hydrodynamic simulation results.

  8. Instability of a planar expansion wave.

    PubMed

    Velikovich, A L; Zalesak, S T; Metzler, N; Wouchuk, J G

    2005-10-01

    An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion wave in an ideal gas, like a rippled shock wave, typically produces decaying oscillations of all fluid variables. Its behavior, however, is different at large and small values of the adiabatic exponent gamma. At gamma > 3, the mass modulation amplitude delta(m) in a rippled expansion wave exhibits a power-law growth with time alpha(t)beta, where beta = (gamma - 3)/(gamma - 1). This is the only example of a hydrodynamic instability whose law of growth, dependent on the equation of state, is expressed in a closed analytical form. The growth is shown to be driven by a physical mechanism similar to that of a classical Richtmyer-Meshkov instability. In the opposite extreme gamma - 1 < 1, delta(m) exhibits oscillatory growth, approximately linear with time, until it reaches its peak value approximately (gamma - 1)(-1/2), and then starts to decrease. The mechanism driving the growth is the same as that of Vishniac's instability of a blast wave in a gas with low . Exact analytical expressions for the growth rates are derived for both cases and favorably compared to hydrodynamic simulation results. PMID:16383532

  9. Instability of a planar expansion wave

    SciTech Connect

    Velikovich, A.L.; Zalesak, S.T.; Metzler, N.; Wouchuk, J.G.

    2005-10-01

    An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion wave in an ideal gas, like a rippled shock wave, typically produces decaying oscillations of all fluid variables. Its behavior, however, is different at large and small values of the adiabatic exponent {gamma}. At {gamma}>3, the mass modulation amplitude {delta}m in a rippled expansion wave exhibits a power-law growth with time {proportional_to}t{sup {beta}}, where {beta}=({gamma}-3)/({gamma}-1). This is the only example of a hydrodynamic instability whose law of growth, dependent on the equation of state, is expressed in a closed analytical form. The growth is shown to be driven by a physical mechanism similar to that of a classical Richtmyer-Meshkov instability. In the opposite extreme {gamma}-1<<1, {delta}m exhibits oscillatory growth, approximately linear with time, until it reaches its peak value {approx}({gamma}-1){sup -1/2}, and then starts to decrease. The mechanism driving the growth is the same as that of Vishniac's instability of a blast wave in a gas with low {gamma}. Exact analytical expressions for the growth rates are derived for both cases and favorably compared to hydrodynamic simulation results.

  10. 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.

  11. 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.

  12. 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…

  13. Wave propagation analysis using the variance matrix.

    PubMed

    Sharma, Richa; Ivan, J Solomon; Narayanamurthy, C S

    2014-10-01

    The propagation of a coherent laser wave-field through a pseudo-random phase plate is studied using the variance matrix estimated from Shack-Hartmann wavefront sensor data. The uncertainty principle is used as a tool in discriminating the data obtained from the Shack-Hartmann wavefront sensor. Quantities of physical interest such as the twist parameter, and the symplectic eigenvalues, are estimated from the wavefront sensor measurements. A distance measure between two variance matrices is introduced and used to estimate the spatial asymmetry of a wave-field in the experiment. The estimated quantities are then used to compare a distorted wave-field with its undistorted counterpart. PMID:25401243

  14. 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.

  15. 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.

  16. Solitary wave propagation influenced by submerged breakwater

    NASA Astrophysics Data System (ADS)

    Wang, Jin; Zuo, Qi-hua; Wang, Deng-ting; Shukrieva, Shirin

    2013-10-01

    The form of Boussinesq equation derived by Nwogu (1993) using velocity at an arbitrary distance and surface elevation as variables is used to simulate wave surface elevation changes. In the numerical experiment, water depth was divided into five layers with six layer interfaces to simulate velocity at each layer interface. Besides, a physical experiment was carried out to validate numerical model and study solitary wave propagation. "Water column collapsing" method (WCCM) was used to generate solitary wave. A series of wave gauges around an impervious breakwater were set-up in the flume to measure the solitary wave shoaling, run-up, and breaking processes. The results show that the measured data and simulated data are in good agreement. Moreover, simulated and measured surface elevations were analyzed by the wavelet transform method. It shows that different wave frequencies stratified in the wavelet amplitude spectrum. Finally, horizontal and vertical velocities of each layer interface were analyzed in the process of solitary wave propagation through submerged breakwater.

  17. 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.

  18. Mechanical surface waves accompany action potential propagation.

    PubMed

    El Hady, Ahmed; Machta, Benjamin B

    2015-01-01

    Many diverse studies have shown that a mechanical displacement of the axonal membrane accompanies the electrical pulse defining the action potential (AP). We present a model for these mechanical displacements as arising from the driving of surface wave modes in which potential energy is stored in elastic properties of the neuronal membrane and cytoskeleton while kinetic energy is carried by the axoplasmic fluid. In our model, these surface waves are driven by the travelling wave of electrical depolarization characterizing the AP, altering compressive electrostatic forces across the membrane. This driving leads to co-propagating mechanical displacements, which we term Action Waves (AWs). Our model allows us to estimate the shape of the AW that accompanies any travelling wave of voltage, making predictions that are in agreement with results from several experimental systems. Our model can serve as a framework for understanding the physical origins and possible functional roles of these AWs. PMID:25819404

  19. Mechanical surface waves accompany action potential propagation

    NASA Astrophysics Data System (ADS)

    El Hady, Ahmed; Machta, Benjamin B.

    2015-03-01

    Many diverse studies have shown that a mechanical displacement of the axonal membrane accompanies the electrical pulse defining the action potential (AP). We present a model for these mechanical displacements as arising from the driving of surface wave modes in which potential energy is stored in elastic properties of the neuronal membrane and cytoskeleton while kinetic energy is carried by the axoplasmic fluid. In our model, these surface waves are driven by the travelling wave of electrical depolarization characterizing the AP, altering compressive electrostatic forces across the membrane. This driving leads to co-propagating mechanical displacements, which we term Action Waves (AWs). Our model allows us to estimate the shape of the AW that accompanies any travelling wave of voltage, making predictions that are in agreement with results from several experimental systems. Our model can serve as a framework for understanding the physical origins and possible functional roles of these AWs.

  20. Propagation characteristics of acoustic waves in snow

    NASA Astrophysics Data System (ADS)

    Capelli, Achille; Kapil, Jagdish Chandra; Reiweger, Ingrid; Schweizer, Jürg; Or, Dani

    2015-04-01

    Acoustic emission analysis is a promising technique for monitoring snow slope stability with potential for application in early warning systems for avalanches. Current research efforts focus on identification and localization of acoustic emission features preceding snow failure and avalanches. However, our knowledge of sound propagation characteristics in snow is still limited. A review of previous studies showed that significant gaps exist and that the results of the various studies are partly contradictory. Furthermore, sound velocity and attenuation have been determined for the frequency range below 10 kHz, while recent snow failure experiments suggest that the peak frequency is in the ultrasound range between 30 kHz to 500 kHz. We therefore studied the propagation of pencil lead fracture (PLF) signals through snow in the ultrasound frequency range. This was achieved by performing laboratory experiments with columns of artificially produced snow of varying density and temperature. The attenuation constant was obtained by varying the size of the columns to eliminate possible influences of the snow-sensor coupling. The attenuation constant was measured for the entire PLF burst signal and for single frequency components. The propagation velocity was calculated from the arrival time of the acoustic signal. We then modelled the sound propagation for our experimental setup using Biot's model for wave propagation in porous media. The Model results were in good agreement with our experimental results. For the studied samples, the acoustic signals propagated as fast and slow longitudinal waves, but the main part of the energy was carried by the slow waves. The Young's modulus of our snow samples was determined from the sound velocity. This is highly relevant, as the elastic properties of snow are not well known.

  1. 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.

  2. Nonlinear guided wave propagation in prestressed plates.

    PubMed

    Pau, Annamaria; Lanza di Scalea, Francesco

    2015-03-01

    The measurement of stress in a structure presents considerable interest in many fields of engineering. In this paper, the diagnostic potential of nonlinear elastic guided waves in a prestressed plate is investigated. To do so, an analytical model is formulated accounting for different aspects involved in the phenomenon. The fact that the initial strains can be finite is considered using the Green Lagrange strain tensor, and initial and final configurations are not merged, as it would be assumed in the infinitesimal strain theory. Moreover, an appropriate third-order expression of the strain energy of the hyperelastic body is adopted to account for the material nonlinearities. The model obtained enables to investigate both the linearized case, which gives the variation of phase and group velocity as a function of the initial stress, and the nonlinear case, involving second-harmonic generation as a function of the initial state of stress. The analysis is limited to Rayleigh-Lamb waves propagating in a plate. Three cases of initial prestress are considered, including prestress in the direction of the wave propagation, prestress orthogonal to the direction of wave propagation, and plane isotropic stress.

  3. Wave propagation in spatially modulated tubes.

    PubMed

    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.

  4. 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.

  5. Nonlinear guided wave propagation in prestressed plates.

    PubMed

    Pau, Annamaria; Lanza di Scalea, Francesco

    2015-03-01

    The measurement of stress in a structure presents considerable interest in many fields of engineering. In this paper, the diagnostic potential of nonlinear elastic guided waves in a prestressed plate is investigated. To do so, an analytical model is formulated accounting for different aspects involved in the phenomenon. The fact that the initial strains can be finite is considered using the Green Lagrange strain tensor, and initial and final configurations are not merged, as it would be assumed in the infinitesimal strain theory. Moreover, an appropriate third-order expression of the strain energy of the hyperelastic body is adopted to account for the material nonlinearities. The model obtained enables to investigate both the linearized case, which gives the variation of phase and group velocity as a function of the initial stress, and the nonlinear case, involving second-harmonic generation as a function of the initial state of stress. The analysis is limited to Rayleigh-Lamb waves propagating in a plate. Three cases of initial prestress are considered, including prestress in the direction of the wave propagation, prestress orthogonal to the direction of wave propagation, and plane isotropic stress. PMID:25786963

  6. Wave propagation in spatially modulated tubes.

    PubMed

    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. PMID:27608990

  7. Surface waves propagating on a turbulent flow

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Pablo; Aumaître, Sébastien

    2016-02-01

    We study the propagation of monochromatic surface waves on a turbulent flow of liquid metal, when the waves are much less energetic than the background flow. Electromagnetic forcing drives quasi-two-dimensional turbulence with strong vertical vorticity. To isolate the surface-wave field, we remove the surface deformation induced by the background turbulent flow using coherent-phase averaging at the wave frequency. We observe a significant increase in wavelength, when the latter is smaller than the forcing length scale. This phenomenon has not been reported before and can be explained by multiple random wave deflections induced by the turbulent velocity gradients. The shift in wavelength thus provides an estimate of the fluctuations in deflection angle. Local measurements of the wave frequency far from the wavemaker do not reveal such systematic behavior, although a small shift is visible. Finally, we quantify the damping enhancement induced by the turbulent flow and compare it to the existing theoretical predictions. Most of them suggest that the damping increases as the square of the Froude number, whereas our experimental data show a linear increase with the Froude number. We interpret this linear relationship as a balance between the time for a wave to cross a turbulent structure and the turbulent mixing time. The larger the ratio of these two times, the more energy is extracted from the wave. We conclude with possible mechanisms for energy exchange.

  8. 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.

  9. Obliquely propagating dust-density waves

    SciTech Connect

    Piel, A.; Arp, O.; Klindworth, M.; Melzer, A.

    2008-02-15

    Self-excited dust-density waves are experimentally studied in a dusty plasma under microgravity. Two types of waves are observed: a mode inside the dust volume propagating in the direction of the ion flow and another mode propagating obliquely at the boundary between the dusty plasma and the space charge sheath. The dominance of oblique modes can be described in the frame of a fluid model. It is shown that the results fom the fluid model agree remarkably well with a kinetic electrostatic model of Rosenberg [J. Vac. Sci. Technol. A 14, 631 (1996)]. In the experiment, the instability is quenched by increasing the gas pressure or decreasing the dust density. The critical pressure and dust density are well described by the models.

  10. 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.

  11. 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.

  12. 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).

  13. 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

  14. 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...

  15. Propagation of a constant velocity fission wave

    NASA Astrophysics Data System (ADS)

    Deinert, Mark

    2011-10-01

    The ideal nuclear fuel cycle would require no enrichment, minimize the need fresh uranium, and produce few, if any, transuranic elements. Importantly, the latter goal would be met without the reprocessing. For purely physical reasons, no reactor system or fuel cycle can meet all of these objectives. However, a traveling-wave reactor, if feasible, could come remarkably close. The concept is simple: a large cylinder of natural (or depleted) uranium is subjected to a fast neutron source at one end, the neutrons would transmute the uranium downstream and produce plutonium. If the conditions were right, a self-sustaining fission wave would form, producing yet more neutrons which would breed more plutonium and leave behind little more than short-lived fission products. Numerical studies have shown that fission waves of this type are also possible. We have derived an exact solution for the propagation velocity of a fission wave through fertile material. The results show that these waves fall into a class of traveling wave phenomena that have been encountered in other systems. The solution places a strict conditions on the shapes of the flux, diffusive, and reactive profiles that would be required for such a phenomenon to persist. The results are confirmed numerically.

  16. 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.

  17. Wave propagation in negative index materials

    NASA Astrophysics Data System (ADS)

    Aylo, Rola

    Properties of electromagnetic propagation in materials with negative permittivities and permeabilities were first studied in 1968. In such metamaterials, the electric field vector, the magnetic field vector, and the propagation vector form a left hand triad, thus the name left hand materials. Research in this area was practically non-existent, until about 10 years ago, a composite material consisting of periodic metallic rods and split-ring resonators showed left-handed properties. Because the dimension of the constituents of the metamaterial are small compared to the operating wavelength, it is possible to describe the electromagnetic properties of the composite using the concept of effective permittivity and permeability. In this dissertation, the basic properties of electromagnetic propagation through homogenous left hand materials are first studied. Many of the basic properties of left hand materials are in contrast to those in right hand materials, viz., negative refraction, perfect lensing, and the inverse Doppler effect. Dispersion relations are used to study wave propagation in negative index materials. For the first time to the best of our knowledge, we show that a reduced dispersion relation, obtained from the frequency dependence of the propagation constant by neglecting a linear frequency dependent term, obeys causality. Causality of the propagation constant enables us to use a novel and simple operator formalism approach to derive the underlying partial differential equations for baseband and envelope wave propagation. Various tools for understanding and characterizing left-handed materials are thereafter presented. The transfer matrix method is used to analyze periodic and random structures composed of positive and negative index materials. By random structures we mean randomness in layer position, index of refraction, and thickness. As an application of alternating periodic negative index and positive index structures, we propose a novel sensor using

  18. Common omissions and misconceptions of wave propagation in turbulence: discussion.

    PubMed

    Charnotskii, Mikhail

    2012-05-01

    This review paper addresses typical mistakes and omissions that involve theoretical research and modeling of optical propagation through atmospheric turbulence. We discuss the disregard of some general properties of narrow-angle propagation in refractive random media, the careless use of simplified models of turbulence, and omissions in the calculations of the second moment of the propagating wave. We also review some misconceptions regarding short-exposure imaging, propagation of polarized waves, and calculations of the scintillation index of the beam waves.

  19. Counterstreaming magnetized plasmas. II. Perpendicular wave propagation

    SciTech Connect

    Tautz, R.C.; Schlickeiser, R.

    2006-06-15

    The properties of longitudinal and transverse oscillations in magnetized symmetric counterstreaming Maxwellian plasmas with equal thermal velocities for waves propagating perpendicular to the stream direction are investigated on the basis of Maxwell equations and the nonrelativistic Vlasov equation. With the constraint of vanishing particle flux in the stream direction, three distinct dispersion relations are known, which are the ordinary-wave mode, the Bernstein wave mode, and the extraordinary electromagnetic wave mode, where the latter two are only approximations. In this article, all three dispersion relations are evaluated for a counterstreaming Maxwellian distribution function in terms of the hypergeometric function {sub 2}F{sub 2}. The growth rates for the ordinary-wave mode are compared to earlier results by Bornatici and Lee [Phys. Fluids 13, 3007 (1970)], who derived approximate results, whereas in this article the exact dispersion relation is solved numerically. The original results are therefore improved and show differences of up to 21% to the results obtained in this article.

  20. Wave envelopes method for description of nonlinear acoustic wave propagation.

    PubMed

    Wójcik, J; Nowicki, A; Lewin, P A; Bloomfield, P E; Kujawska, T; Filipczyński, L

    2006-07-01

    A novel, free from paraxial approximation and computationally efficient numerical algorithm capable of predicting 4D acoustic fields in lossy and nonlinear media from arbitrary shaped sources (relevant to probes used in medical ultrasonic imaging and therapeutic systems) is described. The new WE (wave envelopes) approach to nonlinear propagation modeling is based on the solution of the second order nonlinear differential wave equation reported in [J. Wójcik, J. Acoust. Soc. Am. 104 (1998) 2654-2663; V.P. Kuznetsov, Akust. Zh. 16 (1970) 548-553]. An incremental stepping scheme allows for forward wave propagation. The operator-splitting method accounts independently for the effects of full diffraction, absorption and nonlinear interactions of harmonics. The WE method represents the propagating pulsed acoustic wave as a superposition of wavelet-like sinusoidal pulses with carrier frequencies being the harmonics of the boundary tone burst disturbance. The model is valid for lossy media, arbitrarily shaped plane and focused sources, accounts for the effects of diffraction and can be applied to continuous as well as to pulsed waves. Depending on the source geometry, level of nonlinearity and frequency bandwidth, in comparison with the conventional approach the Time-Averaged Wave Envelopes (TAWE) method shortens computational time of the full 4D nonlinear field calculation by at least an order of magnitude; thus, predictions of nonlinear beam propagation from complex sources (such as phased arrays) can be available within 30-60 min using only a standard PC. The approximate ratio between the computational time costs obtained by using the TAWE method and the conventional approach in calculations of the nonlinear interactions is proportional to 1/N2, and in memory consumption to 1/N where N is the average bandwidth of the individual wavelets. Numerical computations comparing the spatial field distributions obtained by using both the TAWE method and the conventional approach

  1. Wave envelopes method for description of nonlinear acoustic wave propagation.

    PubMed

    Wójcik, J; Nowicki, A; Lewin, P A; Bloomfield, P E; Kujawska, T; Filipczyński, L

    2006-07-01

    A novel, free from paraxial approximation and computationally efficient numerical algorithm capable of predicting 4D acoustic fields in lossy and nonlinear media from arbitrary shaped sources (relevant to probes used in medical ultrasonic imaging and therapeutic systems) is described. The new WE (wave envelopes) approach to nonlinear propagation modeling is based on the solution of the second order nonlinear differential wave equation reported in [J. Wójcik, J. Acoust. Soc. Am. 104 (1998) 2654-2663; V.P. Kuznetsov, Akust. Zh. 16 (1970) 548-553]. An incremental stepping scheme allows for forward wave propagation. The operator-splitting method accounts independently for the effects of full diffraction, absorption and nonlinear interactions of harmonics. The WE method represents the propagating pulsed acoustic wave as a superposition of wavelet-like sinusoidal pulses with carrier frequencies being the harmonics of the boundary tone burst disturbance. The model is valid for lossy media, arbitrarily shaped plane and focused sources, accounts for the effects of diffraction and can be applied to continuous as well as to pulsed waves. Depending on the source geometry, level of nonlinearity and frequency bandwidth, in comparison with the conventional approach the Time-Averaged Wave Envelopes (TAWE) method shortens computational time of the full 4D nonlinear field calculation by at least an order of magnitude; thus, predictions of nonlinear beam propagation from complex sources (such as phased arrays) can be available within 30-60 min using only a standard PC. The approximate ratio between the computational time costs obtained by using the TAWE method and the conventional approach in calculations of the nonlinear interactions is proportional to 1/N2, and in memory consumption to 1/N where N is the average bandwidth of the individual wavelets. Numerical computations comparing the spatial field distributions obtained by using both the TAWE method and the conventional approach

  2. Millimeter-wave planar integrated circuits and subsystems

    NASA Astrophysics Data System (ADS)

    Chang, K.

    Millimeter-wave planar ICs based on microstrip line, suspended strip line and fin line design approaches are described, including the performance properties of the materials involved and numerical models for the functioning of the ICs. Techniques for designing mixers and tailored transition steps between each of the types of planar ICs are discussed, along with mixer configurations. A general theory of IC active sources is presented and illustrated for Gunn and IMPATT oscillators and amplifiers. Design guidelines for frequency multipliers are discussed, along with IC switches and phase shifters and other components, such as dc blocks and broadside couplers, couplers, filters and multiplexers, and circulators. Finally, IC subsystems, i.e., receivers, transceivers, and QPSK exciter/modulator subsystems are described, and future trends are projected.

  3. Nonlinear acoustic wave propagation in atmosphere

    NASA Technical Reports Server (NTRS)

    Hariharan, S. I.

    1985-01-01

    A model problem that simulates an atmospheric acoustic wave propagation situation that is nonlinear is considered. The model is derived from the basic Euler equations for the atmospheric flow and from the regular perturbations for the acoustic part. The nonlinear effects are studied by obtaining two successive linear problems in which the second one involves the solution of the first problem. Well posedness of these problems is discussed and approximations of the radiation boundary conditions that can be used in numerical simulations are presented.

  4. Nonlinear acoustic wave propagation in atmosphere

    NASA Technical Reports Server (NTRS)

    Hariharan, S. I.

    1986-01-01

    In this paper a model problem is considered that simulates an atmospheric acoustic wave propagation situation that is nonlinear. The model is derived from the basic Euler equations for the atmospheric flow and from the regular perturbations for the acoustic part. The nonlinear effects are studied by obtaining two successive linear problems in which the second one involves the solution of the first problem. Well-posedness of these problems is discussed and approximations of the radiation boundary conditions that can be used in numerical simulations are presented.

  5. 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

  6. 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

  7. Wave propagation in random granular chains.

    PubMed

    Manjunath, Mohith; Awasthi, Amnaya P; Geubelle, Philippe H

    2012-03-01

    The influence of randomness on wave propagation in one-dimensional chains of spherical granular media is investigated. The interaction between the elastic spheres is modeled using the classical Hertzian contact law. Randomness is introduced in the discrete model using random distributions of particle mass, Young's modulus, or radius. Of particular interest in this study is the quantification of the attenuation in the amplitude of the impulse associated with various levels of randomness: two distinct regimes of decay are observed, characterized by an exponential or a power law, respectively. The responses are normalized to represent a vast array of material parameters and impact conditions. The virial theorem is applied to investigate the transfer from potential to kinetic energy components in the system for different levels of randomness. The level of attenuation in the two decay regimes is compared for the three different sources of randomness and it is found that randomness in radius leads to the maximum rate of decay in the exponential regime of wave propagation. PMID:22587093

  8. Wave propagation in random granular chains.

    PubMed

    Manjunath, Mohith; Awasthi, Amnaya P; Geubelle, Philippe H

    2012-03-01

    The influence of randomness on wave propagation in one-dimensional chains of spherical granular media is investigated. The interaction between the elastic spheres is modeled using the classical Hertzian contact law. Randomness is introduced in the discrete model using random distributions of particle mass, Young's modulus, or radius. Of particular interest in this study is the quantification of the attenuation in the amplitude of the impulse associated with various levels of randomness: two distinct regimes of decay are observed, characterized by an exponential or a power law, respectively. The responses are normalized to represent a vast array of material parameters and impact conditions. The virial theorem is applied to investigate the transfer from potential to kinetic energy components in the system for different levels of randomness. The level of attenuation in the two decay regimes is compared for the three different sources of randomness and it is found that randomness in radius leads to the maximum rate of decay in the exponential regime of wave propagation.

  9. 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

  10. 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. PMID:26357093

  11. 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.

  12. Kink Wave Propagation in Thin Isothermal Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    Lopin, I. P.; Nagorny, I. G.; Nippolainen, E.

    2014-08-01

    We investigated the propagation of kink waves in thin and isothermal expanding flux tubes in cylindrical geometry. By using the method of radial expansion for fluctuating variables we obtained a new kink wave equation. We show that including the radial component of the tube magnetic field leads to cutoff-free propagation of kink waves along thin flux tubes.

  13. 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).

  14. 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.

  15. Wave Propagation in Fractured Anisotropic Media

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Discontinuities such as fractures, joints and faults occur in the Earth's crusts in a variety of rock types. While much theoretical, experimental and computational research have examined seismic wave propagation in fractured isotropic rock, few experimental studies have investigated seismic wave propagation in fractured anisotropic media. The co-existence of fractures and layers can complicate the interpretation of seismic properties because of the discrete guided modes that propagate along or are confined by the fractures. In this study, we use seismic arrays and acoustic wavefront imaging techniques to examine the competing sources of seismic anisotropy from fractures and from layers. Samples with textural anisotropy (100 mm x 100 mm x 100 mm) were fabricated from garolite, an epoxy - cloth laminate, with layer thickness 0f ~ 0.5 mm. Two sets of fractured samples were fabricated: (1) two single fractured samples with one fracture either parallel or (and) perpendicular to layers, and (2) four multi-fractured samples with 5 parallel fractures oriented either parallel, 30 degrees, 60 degrees or perpendicular to the layers. An intact sample containing no fractures was used as a standard orthorhombic medium for reference. Seismic arrays were used on the first set of samples to measure bulk waves and fracture interface waves as a function of stress. The seismic array contained two compressional and five shear-wave source-receiver pairs with a central frequency of 1 MHz. Shear wave transducers were polarized both perpendicular and parallel to the layering as well as to the fracture. Measurements were made for a range of stresses (0.4 - 4MPa). From these measurements it was observed that a fractured layered medium appears more isotropic or anisotropic than the orthorhombic background, depending on the orientation of the fracture relative to layers. The matrix anisotropy was recovered by increasing the normal stress on a fracture (i.e., by closing the fracture). For the

  16. An investigation into Voigt wave propagation for optical sensing

    NASA Astrophysics Data System (ADS)

    Mackay, Tom G.

    2013-09-01

    In the nonsingular case of optical propagation in a linear, homogeneous, anisotropic, dielectric material, two independent plane waves, with orthogonal polarizations and different phase speeds, can propagate in a given direction. However, in certain dissipative biaxial materials there are particular directions along which these two waves coalesce to form a single plane wave. This coalescent Voigt wave represents the singular case. Most conspicuously, the amplitude of Voigt waves are linearly dependent upon propagation direction. A porous nanostructured thin film which supports Voigt wave propagation was investigated, with a view to possible optical sensing applications. The directions along which Voigt waves propagate can be highly sensitive to the refractive index of a fluid which infiltrates this porous material. Indeed, in our theoretical studies sensitivities which compare favourably to those of surface-plasmon-polariton-based optical sensors were found.

  17. 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.

  18. 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.

  19. Anisotropic propagation of Ca2+ waves in isolated cardiomyocytes.

    PubMed Central

    Engel, J; Fechner, M; Sowerby, A J; Finch, S A; Stier, A

    1994-01-01

    Digital imaging microscopy of fluor-3 fluorescence was used to study the propagation of intracellular Ca2+ waves in isolated adult rat cardiomyocytes from 17 to 37 degrees C. Ca2+ waves spread in both transverse and longitudinal direction of a myocyte. Transverse propagation was pronounced in waves starting from a focus at the edge of a myocyte and in waves following an irregular, curved path (spiral waves). For the former type of waves, propagation velocities were determined. Both transverse and longitudinal wave components propagated at constant velocity ranging from 30 to 125 micron/s. Myocytes were anisotropic with respect to wave propagation: waves propagated faster in the longitudinal than in the transverse direction. The ratio between longitudinal and transverse velocity increased from 1.30 at 17 degrees C to 1.55 at 37 degrees C. Apparent activation energies for transverse and longitudinal wave propagation were estimated to be -20 kJ/mol, suggesting that these processes are limited by diffusion of Ca2+. Direction-dependent propagation velocities are interpreted to result from the highly ordered structure of the myocytes, especially from the anisotropic arrangement of diffusion obstacles such as myofilaments and mitochondria. Images FIGURE 1 FIGURE 2 FIGURE 4 PMID:8075316

  20. Wave Propagation in Expanding Cell Layers

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    The coordinated migration of groups of cells drives important biological processes, such as wound healing and morphogenesis. In this talk we present a minimal continuum model of an expanding cell monolayer coupling elastic deformations to myosin-based activity in the cells. The myosin-driven contractile activity is quantified by the chemical potential difference for the process of ATP hydrolysis by myosin motors. A new ingredient of the model is a feedback of the local strain rate of the monolayer on contractility that naturally yields a mechanism for viscoelasticity of the cellular medium. By combining analytics and numerics we show that this simple model reproduces qualitatively many experimental findings, including the build-up of contractile stresses at the center of the cell monolayer, and the existence of traveling mechanical waves that control spreading dynamics and stress propagation in the cell monolayer. KJCU and MCM were supported by the NSF through grants DMR-1004789 and DGE-1068780.

  1. 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.

  2. Models and Observations of Shock Wave Propagation in Volcanic Settings

    NASA Astrophysics Data System (ADS)

    Anderson, J.; Johnson, J. B.; Ruiz, M. C.; Steele, A.

    2013-12-01

    High-amplitude air waves (shock waves) propagate nonlinearly; although this strongly affects recorded signals, it is not commonly modeled in studies of volcanic explosions. Failure to account for the shock wave component of air waves can lead to underestimation of source power and inaccurate source times. Additionally, propagation effects can significantly alter waveforms from the original source signals. In order to permit more accurate studies of shock wave sources, we examine modeling techniques and observations of shock waves. Shock wave signals begin with strong, abrupt compressions that, compared to typical sound waves, propagate and decay more quickly. Because of the high-amplitude discontinuities, numerical methods that are commonly used to study linear sound waves become unstable and inaccurate when applied to shock waves. We discuss the use of other techniques that are capable of modeling shock wave propagation. Equations relating wave speed to the difference of various physical quantities across the shock (such as pressure, density, and particle velocity) are useful for modeling these waves. Addressing the shock explicitly as such, in conjunction with use of traditional numerical methods for the remainder of the signal, permits modeling of full shock waveforms. Additionally, we present examples of recorded volcanic signals that propagate nonlinearly and demonstrate propagation effects on amplitude, waveform, and spectrum.

  3. 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.

  4. 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.

  5. 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.

  6. A study for the propagation of electromagnetic waves over imperfect ground planes based on Schelkunoff integrals

    NASA Astrophysics Data System (ADS)

    Dyab, Walid Mohamed Galal

    A new formulation for the analysis of propagation of electromagnetic waves over imperfectly conducting planar surfaces is proposed. The classical approach for the analysis of this problem uses the Sommerfeld formulation. In Sommerfeld formulation, the wave function corresponding to a point source is expanded in terms of the propagation constants of the various waves in the radial direction from the source. This gives rise to the well-known Sommerfeld integrals which are highly oscillatory and slowly-decaying in nature, especially when the source is mounted just on top of a planar boundary between two media of arbitrary conductivity. In addition, the nature of the convergence for these integrals is extremely slow and may not yield stable results. In this dissertation we present an approach, developed originally by Schelkunoff, which expands the wave function in terms of the waves emanating perpendicular to the planar interface, not parallel to it as in Sommerfeld formulation. Expressions are given for both cases of vertical and horizontal electric dipoles on top of a planar interface. The debatable nature of this problem is unavoidable, thus a detailed analytical comparison between the Sommerfeld integrals and the expressions derived here is given. Based on the study given in this dissertation, the true rationale in relating the work of Zenneck and Sommerfeld to the relatively new field of surface plasmons is exposed. A detailed literature study as well as an analytical critique of the field of plasmonics and its relation to Sommerfeld-Zenneck surface waves is presented. Finally, some applications of the new formulation are discussed using numerical simulations.

  7. Linear and nonlinear acoustic wave propagation in the atmosphere

    NASA Technical Reports Server (NTRS)

    Hariharan, S. I.; Yu, Ping

    1988-01-01

    The investigation of the acoustic wave propagation theory and numerical implementation for the situation of an isothermal atmosphere is described. A one-dimensional model to validate an asymptotic theory and a 3-D situation to relate to a realistic situation are considered. In addition, nonlinear wave propagation and the numerical treatment are included. It is known that the gravitational effects play a crucial role in the low frequency acoustic wave propagation. They propagate large distances and, as such, the numerical treatment of those problems become difficult in terms of posing boundary conditions which are valid for all frequencies.

  8. Patterns of spiral wave attenuation by low-frequency periodic planar fronts

    NASA Astrophysics Data System (ADS)

    de la Casa, Miguel A.; de la Rubia, F. Javier; Ivanov, Plamen Ch.

    2007-03-01

    There is evidence that spiral waves and their breakup underlie mechanisms related to a wide spectrum of phenomena ranging from spatially extended chemical reactions to fatal cardiac arrhythmias [A. T. Winfree, The Geometry of Biological Time (Springer-Verlag, New York, 2001); J. Schutze, O. Steinbock, and S. C. Muller, Nature 356, 45 (1992); S. Sawai, P. A. Thomason, and E. C. Cox, Nature 433, 323 (2005); L. Glass and M. C. Mackey, From Clocks to Chaos: The Rhythms of Life (Princeton University Press, Princeton, 1988); R. A. Gray et al., Science 270, 1222 (1995); F. X. Witkowski et al., Nature 392, 78 (1998)]. Once initiated, spiral waves cannot be suppressed by periodic planar fronts, since the domains of the spiral waves grow at the expense of the fronts [A. N. Zaikin and A. M. Zhabotinsky, Nature 225, 535 (1970); A. T. Stamp, G. V. Osipov, and J. J. Collins, Chaos 12, 931 (2002); I. Aranson, H. Levine, and L. Tsimring, Phys. Rev. Lett. 76, 1170 (1996); K. J. Lee, Phys. Rev. Lett. 79, 2907 (1997); F. Xie, Z. Qu, J. N. Weiss, and A. Garfinkel, Phys. Rev. E 59, 2203 (1999)]. Here, we show that introducing periodic planar waves with long excitation duration and a period longer than the rotational period of the spiral can lead to spiral attenuation. The attenuation is not due to spiral drift and occurs periodically over cycles of several fronts, forming a variety of complex spatiotemporal patterns, which fall into two distinct general classes. Further, we find that these attenuation patterns only occur at specific phases of the descending fronts relative to the rotational phase of the spiral. We demonstrate these dynamics of phase-dependent spiral attenuation by performing numerical simulations of wave propagation in the excitable medium of myocardial cells. The effect of phase-dependent spiral attenuation we observe can lead to a general approach to spiral control in physical and biological systems with relevance for medical applications.

  9. 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

  10. Asymptotic Stability of Planar Rarefaction Waves for the Relaxation Approximation of Conservation Laws in Several Dimensions

    NASA Astrophysics Data System (ADS)

    Luo, Tao

    1997-01-01

    This paper concerns the large time behavior toward planar rarefaction waves of solutions for the relaxation approximation of conservation laws in several dimensions. It is shown that a planar rarefaction wave is nonlinear stable in the sense that it is an asymptotic attractor for the relaxation approximation of conservation laws.

  11. Subspace model identification of guided wave propagation in metallic plates

    NASA Astrophysics Data System (ADS)

    Kim, Junhee; Kim, Kiyoung; Sohn, Hoon

    2014-03-01

    In this study, a data-driven subspace system identification approach is proposed for modeling guided wave propagation in plate media. In the data-driven approach, the subspace system identification estimates a mathematical model fitted to experimentally measured data, but the black-box model identified captures the dynamics of wave propagation. To demonstrate the versatility of the black-box model, wave motions in various shapes of aluminum plates are investigated in the study. In addition, a waveform predictor and temperature change indicator are proposed as applications of the black-box models, to further promote the modeling approach to guided wave propagation.

  12. Hypersonic evanescent waves generated with a planar spiral coil.

    PubMed

    Stevenson, A C; Araya-Kleinsteuber, B; Sethi, R S; Mehta, H M; Lowe, C R

    2003-09-01

    A planar spiral coil has been used to induce hypersonic evanescent waves in a quartz substrate with the unique ability to focus the acoustic wave down onto the chemical recognition layer. These special sensing conditions were achieved by investigating the application of a radio frequency current to a coaxial waveguide and spiral coil, so that wideband repeating electrical resonance conditions could be established over the MHz to GHz frequency range. At a selected operating frequency of 1.09 GHz, the evanescent wave depth of a quartz crystal hypersonic resonance is reduced to 17 nm, minimising unwanted coupling to the bulk fluid. Verification of the validity of the hypersonic resonance was carried out by characterising the system electrically and acoustically: Impedance calculations of the combined coil and coaxial waveguide demonstrated an excellent fit to the measured data, although above 400 MHz a transition zone was identified where unwanted impedance is parasitic of the coil influence efficiency, so the signal-to-noise ratio is reduced from 3000 to 300. Acoustic quartz crystal resonances at intervals of precisely 13.2138 MHz spacing, from the 6.6 MHz ultrasonic range and onto the desired hypersonic range above 1 GHz, were incrementally detected. Q factor measurements demonstrated that reductions in energy lost from the resonator to the fluid interface were consistent with the anticipated shrinkage of the evanescent wave with increasing operating frequency. Amplitude and frequency reduction in contact with a glucose solution was demonstrated at 1.09 GHz. The complex physical conditions arising at the solid-liquid interface under hypersonic entrainment are discussed with respect to acceleration induced slippage, rupture, longitudinal and shear radiation and multiphase relaxation affects.

  13. General constitutive model for supercooled liquids: anomalous transverse wave propagation.

    PubMed

    Mizuno, Hideyuki; Yamamoto, Ryoichi

    2013-03-01

    A transverse acoustic wave propagates through supercooled liquids in an anomalous manner: for a macroscopic wave number k, the wave propagates long distances, as in elastic solids, whereas it attenuates rapidly for a mesoscopic to microscopic wave number k, as in viscous liquids. In this work, we theoretically describe this anomalous wave propagation using the hydrodynamics of the two-mode Maxwell constitutive model, which were determined independently from the mechanical properties under oscillatory shear strains. To ensure that the Maxwell model can be applied down to a microscopic length scale, we extended it to a k-dependent equation, taking into account the recently reported k dependences of the shear viscosity and modulus [A. Furukawa and H. Tanaka, Phys. Rev. Lett. 103, 135703 (2009); A. Furukawa H. Tanaka Phys. Rev. E 84, 061503 (2011)]. The anomalous wave propagation in supercooled liquids can also be understood in terms of a linear coupling of many independent normal modes, as in amorphous solids. PMID:23496725

  14. 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.

  15. 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.

  16. Propagation of compression waves in bubbly liquid with hydrate formation

    NASA Astrophysics Data System (ADS)

    Shagapov, V. Sh.; Lepikhin, S. A.; Chiglintsev, I. A.

    2010-06-01

    The dynamics of planar one-dimensional shock waves applied to the available experimental data for the water-Freon system is studied on the basis of the theoretical model of the bubbly liquid refined with regard for a possible hydrate formation. A scheme is proposed for considering the fragmentation of bubbles in the shock wave, which is one of the main factors of the intensification of the hydrate formation process with the growth of the shock wave amplitude.

  17. 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.

  18. Superluminal propagation of solitary kinklike waves in amplifying media.

    PubMed

    Janowicz, Maciej; Mostowski, Jan

    2006-04-01

    It is shown that solitary-wave, kinklike structures can propagate superluminally in two- and four-level amplifying media with strongly damped oscillations of coherences. This is done by solving analytically the Maxwell-Bloch equations in the kinetic limit. It is also shown that the true wave fronts--unlike the pseudo wave fronts of the kinks--must propagate with velocity c, so that no violation of special relativity is possible. The conditions of experimental verification are discussed. PMID:16711948

  19. Two cortical circuits control propagating waves in visual cortex.

    PubMed

    Wang, Wenxue; Campaigne, Clay; Ghosh, Bijoy K; Ulinski, Philip S

    2005-12-01

    Visual stimuli produce waves of activity that propagate across the visual cortex of fresh water turtles. This study used a large-scale model of the cortex to examine the roles of specific types of cortical neurons in controlling the formation, speed and duration of these waves. The waves were divided into three components: initial depolarizations, primary propagating waves and secondary waves. The maximal conductances of each receptor type postsynaptic to each population of neurons in the model was systematically varied and the speed of primary waves, durations of primary waves and total wave durations were measured. The analyses indicate that wave formation and speed are controlled principally by feedforward excitation and inhibition, while wave duration is controlled principally by recurrent excitation and feedback inhibition. PMID:16284712

  20. Manipulating Water Wave Propagation via Gradient Index Media

    PubMed Central

    Wang, Zhenyu; Zhang, Pei; Nie, Xiaofei; Zhang, Yongqiang

    2015-01-01

    It is challenging to realise the perfect manipulation of water waves within a broad range of frequencies. By extending conformal transformation principles to water waves, their propagation can be controlled via gradually varying water depths, permitting the realisation of a desired refractive index profile for linear water surface waves. Wave bending, directional wave emission and wave focusing are analysed experimentally with accompanying simulations. The results demonstrate desired wave manipulations within a broad range of frequencies, confirming the accuracy and effectiveness of conformal transformation for water waves. PMID:26603312

  1. [Propagation of shear waves in the muscle tissue].

    PubMed

    Afanas'eva, D A; Tsaturian, A K

    2010-01-01

    A mathematical model of the propagation of acoustic shear waves in muscle tissue is considered. The muscle is modelled by an incompressible transversely isotropic viscoelastic continuum with quasi-one-dimensional active tension. Two types of shear waves in an infinite medium have been established. The waves of the second type (transverse) propagate without attenuation even when myofibril viscosity is taken into account. A problem of standing transverse waves in a rectangular layer has been investigated numerically. The values of the problem parameters have been found for which the active tension or muscle tonus is easily estimated from the characteristics of standing waves. This value is informative for the diagnosis of muscle state.

  2. Ultrathin multi-band planar metamaterial absorber based on standing wave resonances.

    PubMed

    Peng, Xiao-Yu; Wang, Bing; Lai, Shumin; Zhang, Dao Hua; Teng, Jing-Hua

    2012-12-01

    We present a planar waveguide model and a mechanism based on standing wave resonances to interpret the unity absorptions of ultrathin planar metamaterial absorbers. The analytical model predicts that the available absorption peaks of the absorber are corresponding to the fundamental mode and only its odd harmonic modes of the standing wave. The model is in good agreement with numerical simulation and can explain the main features observed in typical ultrathin planar metamaterial absorbers. Based on this model, ultrathin planar metamaterial absorbers with multi-band absorptions at desired frequencies can be easily designed.

  3. 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.

  4. Wave propagation in a medium with cavities

    NASA Astrophysics Data System (ADS)

    Adler, Pierre; Pazdniakou, Aliaksei

    2016-04-01

    The detection and imaging of cavities is still difficult, but it generates a lot of interest because of its potential applications. We have developed a code based on Lattice Springs and Lattice Boltzmann which can calculate wave propagation through a three dimensional composite medium. The theoretical background of these techniques will only be briefly addressed during the talk. The solid phase may have properties which are variable in space; the solid matrix may contain voids of arbitrary shapes which are filled or not with a mixture of air and water. In addition some of the voids may be empty. The surface of the ground is also arbitrary and it may be hilly. The source may be either a disturbance applied to a region of the solid phase or an overpressure applied to a particular cavity. In both cases, the disturbance and the overpressure can be arbitrary in time. Several sources can be simultaneously employed. Any region can be recorded, but a particular attention is paid to surface signals since they are the ones which are usually measured. The code is parallelized. Systematic applications of this tool have been done in order to analyse the response of a medium containing cavities to various signals. This complete parametric study has analyzed the most important parameters. The shape and the nature of the source have been addressed first; step functions of a limited or of an infinite duration have been studied and they are shown to result in simpler outputs than Ricker functions. The position of the source with respect to the ground surface has been varied. If it is deep, the reflection of the initial signal with the surface complicates the analysis of the surface measurements. The distance between the source and the cavity does not appear to be a critical parameter as long as the signal remains sufficiently large when it interacts with the cavity. Moreover, when this distance is large, the signal is transformed into a plane wave. The influence of the shape of the

  5. Impact of propagating and standing waves on cavitation appearance.

    PubMed

    Kenis, Alexander M; Grinfeld, Javier; Zadicario, Eyal; Vitek, Shuki

    2012-01-01

    Standing waves play a significant role in the appearance of cavitation phenomena. The goal of this study was to investigate the effect that the relation between standing and propagating waves in a focused field has on acoustic bubble cloud formation. Measurements of the cavitation signals were performed on five different configurations of a hemispheric phased array transducer (230 kHz) representing a wide range of relations between propagating and standing waves. The results show that configurations with a larger propagating component induce bubble clouds at lower pressures than configurations with a larger standing component.

  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. Propagation Dynamics of Airy Water-Wave Pulses.

    PubMed

    Fu, Shenhe; Tsur, Yuval; Zhou, Jianying; Shemer, Lev; Arie, Ady

    2015-07-17

    We observe the propagation dynamics of surface gravity water waves, having an Airy function envelope, in both the linear and the nonlinear regimes. In the linear regime, the shape of the envelope is preserved while propagating in an 18-m water tank, despite the inherent dispersion of the wave packet. The Airy wave function can propagate at a velocity that is slower (or faster if the Airy envelope is inverted) than the group velocity. Furthermore, the introduction of the Airy wave packet as surface water waves enables the observation of its position-dependent chirp and cubic-phase offset, predicted more than 35 years ago, for the first time. When increasing the envelope of the input Airy pulse, nonlinear effects become dominant, and are manifested by the generation of water-wave solitons. PMID:26230797

  8. 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. PMID:24116530

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Seismic-acoustic finite-difference wave propagation algorithm.

    SciTech Connect

    Preston, Leiph; Aldridge, David Franklin

    2010-10-01

    An efficient numerical algorithm for treating earth models composed of fluid and solid portions is obtained via straightforward modifications to a 3D time-domain finite-difference algorithm for simulating isotropic elastic wave propagation.

  14. 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.

  15. Lamb wave propagation in negative Poisson's ratio composites

    NASA Astrophysics Data System (ADS)

    Remillat, Chrystel; Wilcox, Paul; Scarpa, Fabrizio

    2008-03-01

    Lamb wave propagation is evaluated for cross-ply laminate composites exhibiting through-the-thickness negative Poisson's ratio. The laminates are mechanically modeled using the Classical Laminate Theory, while the propagation of Lamb waves is investigated using a combination of semi analytical models and Finite Element time-stepping techniques. The auxetic laminates exhibit well spaced bending, shear and symmetric fundamental modes, while featuring normal stresses for A 0 mode 3 times lower than composite laminates with positive Poisson's ratio.

  16. 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…

  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. Shear wave propagation in anisotropic soft tissues and gels.

    PubMed

    Namani, Ravi; Bayly, Philip V

    2009-01-01

    The propagation of shear waves in soft tissue can be visualized by magnetic resonance elastography (MRE) to characterize tissue mechanical properties. Dynamic deformation of brain tissue arising from shear wave propagation may underlie the pathology of blast-induced traumatic brain injury. White matter in the brain, like other biological materials, exhibits a transversely isotropic structure, due to the arrangement of parallel fibers. Appropriate mathematical models and well-characterized experimental systems are needed to understand wave propagation in these structures. In this paper we review the theory behind waves in anisotropic, soft materials, including small-amplitude waves superimposed on finite deformation of a nonlinear hyperelastic material. Some predictions of this theory are confirmed in experimental studies of a soft material with controlled anisotropy: magnetically-aligned fibrin gel. PMID:19963987

  19. Hybrid simulation of wave propagation in the Io plasma torus

    NASA Astrophysics Data System (ADS)

    Stauffer, B. H.; Delamere, P. A.; Damiano, P. A.

    2015-12-01

    The transmission of waves between Jupiter and Io is an excellent case study of magnetosphere/ionosphere (MI) coupling because the power generated by the interaction at Io and the auroral power emitted at Jupiter can be reasonably estimated. Wave formation begins with mass loading as Io passes through the plasma torus. A ring beam distribution of pickup ions and perturbation of the local flow by the conducting satellite generate electromagnetic ion cyclotron waves and Alfven waves. We investigate wave propagation through the torus and to higher latitudes using a hybrid plasma simulation with a physically realistic density gradient, assessing the transmission of Poynting flux and wave dispersion. We also analyze the propagation of kinetic Alfven waves through a density gradient in two dimensions.

  20. 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)

  1. Left/right asymmetry in Dyakonov-Tamm-wave propagation guided by a topological insulator and a structurally chiral material

    NASA Astrophysics Data System (ADS)

    Chiadini, Francesco; Fiumara, Vincenzo; Mackay, Tom G.; Scaglione, Antonio; Lakhtakia, Akhlesh

    2016-11-01

    The propagation of Dyakonov-Tamm waves guided by the planar interface of an isotropic topological insulator and a structurally chiral material, both assumed to be nonmagnetic, was investigated by numerically solving the associated canonical boundary-value problem. The topologically insulating surface states of the topological insulator were quantitated via a surface admittance {γ }{{TI}}, which significantly affects the phase speeds and the spatial profiles of the Dyakonov-Tamm waves. Most significantly, it is possible that a Dyakonov-Tamm wave propagates co-parallel to a vector {u} in the interface plane, but no Dyakonov-Tamm wave propagates anti-parallel to {u}. The left/right asymmetry, which vanishes for {γ }{{TI}}=0, is highly attractive for one-way on-chip optical communication.

  2. The propagation and growth of whistler mode waves generated by electron beams in earth's bow shock

    NASA Technical Reports Server (NTRS)

    Tokar, R. L.; Gurnett, D. A.

    1985-01-01

    In this study, the propagation and growth of whistler mode waves generated by electron beams within earth's bow shock is investigated using a planar model for the bow shock and a model electron distribution function. Within the shock, the model electron distribution function possesses a field-aligned T greater than T beam that is directed toward the magnetosheath. Waves with frequencies between about 1 and 100 Hz with a wide range of wave normal angles are generated by the beam via Landau and anomalous cyclotron resonances. However, because the growth rate is small and because the wave packets traverse the shock quickly, these waves do not attain large amplitudes. Waves with frequencies between about 30 and 150 Hz with a wide range of wave normal angles are generated by the beam via the normal cyclotron resonance. The ray paths for most of these waves are directed toward the solar wind although some wave packets, due to plasma convection travel transverse to the shock normal. These wave packets grow to large amplitudes because they spend a long time in the growth region. The results suggest that whistler mode noise within the shock should increase in amplitude with increasing upstream theta sub Bn. The study provides an explanation for the origin of much of the whistler mode turbulence observed at the bow shock.

  3. Autoresonant propagation of incoherent light-waves.

    PubMed

    Barak, Assaf; Lamhot, Yuval; Friedland, Lazar; Segev, Mordechai

    2010-08-16

    We study, theoretically and experimentally, the evolution of optical waves with randomly-fluctuating phases in a spatially chirped nonlinear directional coupler. As the system crosses its linear resonance, we observe collective self-phase-locking (autoresonance) of all mutually-incoherent waves, each with its own pump, and simultaneous amplification until the pumps are exhausted. We show that the autoresonant transition in this system exhibits a sharp threshold, common to all mutually-incoherent waves comprising the light beam.

  4. 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.

  5. 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.

  6. Time Reversal Mirrors and Cross Correlation Functions in Acoustic Wave Propagation

    NASA Astrophysics Data System (ADS)

    Fishman, Louis; Jonsson, B. Lars G.; de Hoop, Maarten V.

    2009-03-01

    In time reversal acoustics (TRA), a signal is recorded by an array of transducers, time reversed, and then retransmitted into the configuration. The retransmitted signal propagates back through the same medium and retrofocuses on the source that generated the signal. If the transducer array is a single, planar (flat) surface, then this configuration is referred to as a planar, one-sided, time reversal mirror (TRM). In signal processing, for example, in active-source seismic interferometry, the measurement of the wave field at two distinct receivers, generated by a common source, is considered. Cross correlating these two observations and integrating the result over the sources yield the cross correlation function (CCF). Adopting the TRM experiments as the basic starting point and identifying the kinematically correct correspondences, it is established that the associated CCF signal processing constructions follow in a specific, infinite recording time limit. This perspective also provides for a natural rationale for selecting the Green's function components in the TRM and CCF expressions. For a planar, one-sided, TRM experiment and the corresponding CCF signal processing construction, in a three-dimensional homogeneous medium, the exact expressions are explicitly calculated, and the connecting limiting relationship verified. Finally, the TRM and CCF results are understood in terms of the underlying, governing, two-way wave equation, its corresponding time reversal invariance (TRI) symmetry, and the absence of TRI symmetry in the associated one-way wave equations, highlighting the role played by the evanescent modal contributions.

  7. 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.

  8. Wave propagation in reconfigurable magneto-elastic kagome lattice structures

    NASA Astrophysics Data System (ADS)

    Schaeffer, Marshall; Ruzzene, Massimo

    2015-05-01

    The paper discusses the wave propagation characteristics of two-dimensional magneto-elastic kagome lattices. Mechanical instabilities caused by magnetic interactions are exploited in combination with particle contact to bring about changes in the topology and stiffness of the lattices. The analysis uses a lumped mass system of particles, which interact through axial and torsional elastic forces as well as magnetic forces. The propagation of in-plane waves is predicted by applying Bloch theorem to lattice unit cells with linearized interactions. Elastic wave dispersion in these lattices before and after topological changes is compared, and large differences are highlighted.

  9. Nonlinear propagation and control of acoustic waves in phononic superlattices

    NASA Astrophysics Data System (ADS)

    Jiménez, Noé; Mehrem, Ahmed; Picó, Rubén; García-Raffi, Lluís M.; Sánchez-Morcillo, Víctor J.

    2016-05-01

    The propagation of intense acoustic waves in a one-dimensional phononic crystal is studied. The medium consists in a structured fluid, formed by a periodic array of fluid layers with alternating linear acoustic properties and quadratic nonlinearity coefficient. The spacing between layers is of the order of the wavelength, therefore Bragg effects such as band gaps appear. We show that the interplay between strong dispersion and nonlinearity leads to new scenarios of wave propagation. The classical waveform distortion process typical of intense acoustic waves in homogeneous media can be strongly altered when nonlinearly generated harmonics lie inside or close to band gaps. This allows the possibility of engineer a medium in order to get a particular waveform. Examples of this include the design of media with effective (e.g., cubic) nonlinearities, or extremely linear media (where distortion can be canceled). The presented ideas open a way towards the control of acoustic wave propagation in nonlinear regime. xml:lang="fr"

  10. Plasma wave propagation with a plasma density gradient

    SciTech Connect

    Cho, Guangsup; Choi, Eun-Ha; Uhm, Han Sup

    2011-03-15

    Plasma waves with the plasma diffusion velocity u{sub n} due to a plasma density gradient are described in a positive column plasma. The ion wave is generated by the perturbation of the operating frequency 10{sup 6} s{sup -1} and it propagates with the group velocity u{sub g{approx}}c{sub s}{sup 2}/u{sub n{approx}}(10{sup 5}-10{sup 6}) m/s, where c{sub s} is the acoustic velocity in a fine tube fluorescent lamp, while the electron wave cannot be generated with a turbulence of low frequency less than the electron oscillation frequency {omega}{sub pe}. The propagation of the lighting signal observed in long tube fluorescent lamps is well understood with the propagation of ion waves occurring along the plasma density gradient.

  11. Finite Element Modeling of Guided Wave Propagation in Plates

    NASA Astrophysics Data System (ADS)

    Kumar KM, Manoj; Ramaswamy, Sivaramanivas; Kommareddy, Vamshi; Baskaran, Ganesan; Zongqi, Sun; Kirkire, Gautam

    2006-03-01

    This paper aims at developing a numerical model for guided wave propagation in plates and the interaction of modes with defects using Finite Element Modeling (FEM). Guided waves propagate as extensional, flexural and torsional waves. Theoretically, these modes are infinite in number, but only some of these propagate and the others are attenuated. The dispersion curves for a structure reveal the plausibility of these modes. In this paper, FEM is used to examine interaction of first few symmetric and anti-symmetric modes independently with the cracks of various sizes in a plate. A time-frequency representation of the acquired guided wave mode signals will be discussed to show the mode sensitivity with crack size.

  12. On the propagation of plane waves above an impedance surface

    NASA Technical Reports Server (NTRS)

    Zhong, F. H.; Vanmoorhem, W. K.

    1990-01-01

    The propagation of grazing incidence plane waves along a finite impedance boundary is investigated. A solution of the semi-infinite problem, where a harmonic motion, parallel to the boundary, is imposed along a line perpendicular to the boundary, is obtained. This solution consists of quasiplane waves, waves moving parallel to the boundary with amplitude and phase variations perpendicular to the boundary. Several approximations to the full solution are considered.

  13. Wave propagation on a random lattice

    SciTech Connect

    Sahlmann, Hanno

    2010-09-15

    Motivated by phenomenological questions in quantum gravity, we consider the propagation of a scalar field on a random lattice. We describe a procedure to calculate the dispersion relation for the field by taking a limit of a periodic lattice. We use this to calculate the lowest order coefficients of the dispersion relation for a specific one-dimensional model.

  14. 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.

  15. Propagating waves in visual cortex: a large-scale model of turtle visual cortex.

    PubMed

    Nenadic, Zoran; Ghosh, Bijoy K; Ulinski, Philip

    2003-01-01

    This article describes a large-scale model of turtle visual cortex that simulates the propagating waves of activity seen in real turtle cortex. The cortex model contains 744 multicompartment models of pyramidal cells, stellate cells, and horizontal cells. Input is provided by an array of 201 geniculate neurons modeled as single compartments with spike-generating mechanisms and axons modeled as delay lines. Diffuse retinal flashes or presentation of spots of light to the retina are simulated by activating groups of geniculate neurons. The model is limited in that it does not have a retina to provide realistic input to the geniculate, and the cortex and does not incorporate all of the biophysical details of real cortical neurons. However, the model does reproduce the fundamental features of planar propagating waves. Activation of geniculate neurons produces a wave of activity that originates at the rostrolateral pole of the cortex at the point where a high density of geniculate afferents enter the cortex. Waves propagate across the cortex with velocities of 4 microm/ms to 70 microm/ms and occasionally reflect from the caudolateral border of the cortex. PMID:12567015

  16. Impact of gravity waves on long-range infrasound propagation

    NASA Astrophysics Data System (ADS)

    Millet, Christophe; Lott, François; De La Camara, Alvaro

    2016-04-01

    In this work we study infrasound propagation in acoustic waveguides that support a finite number of propagating modes. We analyze the effects of gravity waves on these acoustic waveguides. Testing sound propagation in such perturbed fields can potentially be used to improve the gravity wave models. A linear solution modeling the interaction between an incoming acoustic wave and a randomly perturbed atmosphere is developed, using the forward-scattering approximation. The wave mode structure is determined by the effective sound speed profile which is strongly affected by gravity wave breaking. The random perturbations are described by a stochastic field predicted by a multiwave stochastic parameterization of gravity waves, which is operational in the LMDz climate model. The justification for this approach is two fold. On the one hand, the use of a few monochromatic waves mimics the observations of rather narrow-banded gravity wave packets in the lower stratosphere. On the other hand, the stochastic sampling of the gravity wave field and the random choice of wave properties deals with the inherent unpredictability of mesoscale dynamics from large scale conditions provided by the meteorological reanalysis. The transmitted acoustic signals contain a stable front and a small-amplitude incoherent coda. A general expression for the stable front is derived in terms of saddle-point contributions. The saddle-points are obtained from a WKB approximation of the vertical eigenvalue problem. This approach extract the dominant effects in the acoustic - gravity wave interaction. We present results that show how statistics of the transmitted signal are related to a few saddle-points and how the GW field can trigger large deviations in the acoustic signals. While some of the characteristics of the stable front can be directly related to that of a few individual gravity waves, it is shown that the amount of the launched gravity waves included in climate models can be estimated using

  17. 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.

  18. 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.

  19. Scattering effects on lower hybrid wave propagation

    NASA Astrophysics Data System (ADS)

    Bertelli, N.; Phillips, C. K.; Valeo, E. J.; Wilson, J. R.; Baek, S. G.; Bonoli, P. T.; Parker, R. R.; Wallace, G.; Wright, J. C.; Harvey, R. W.; Smirnov, A. P.

    2012-10-01

    The effects of edge plasma density fluctuations on the scattering of lower hybrid (LH) waves are studied. Scattering can improve the penetration of LH waves into the plasma core due to the k upshift that occurs through the poloidal field (because the rotation of k induces a finite poloidal mode number). Scattering can also inhibit wave penetration depending on the density fluctuation levels, resulting in enhanced collisional absorption of the waves in the SOL at high density. These two effects might contribute, respectively, to resolving the ``spectral gap'' problem [Bonoli P. T. and R. C. Englade, Phys. Fluids 9 (1986) 2937] and the ``density limit'' in the efficiency of LHCD [Wallace G. et al., Phys. Plasmas 17 (2010) 082508]. The scattering model used is based on the work of Bonoli and Ott [Phys. Fluids 25 (1982) 361] that introduces an electromagnetic wave kinetic equation solved by a Monte Carlo technique. This equation has been implemented in the ray tracing code GENRAY, which explicitly includes the SOL region. A detailed analysis of this scattering model will be presented in comparison with the experimental observations of LHCD for Alcator C-Mod tokamak.

  20. 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.

  1. 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

  2. Amplitude-Preserving Propagator and its Applications in Computational Wave Propagation and Seismic Imaging

    NASA Astrophysics Data System (ADS)

    Eslaminia, Mehran

    A novel method is developed to approximately solve acoustic wave equation in the frequency domain. The key idea of the method is to partition the domain into smaller subdomains and solve for the wavefield in each subdomain sequentially, which is facilitated by special interface (continuity) conditions. The sequential solution is performed in two steps: First the downward propagating wavefield is computed considering only downward propagation and transmission at the interfaces. The wavefield is then corrected by adding the upward propagating wavefield resulting from reflections and body forces. It is shown that the proposed method results in accurate amplitudes for downward propagation and primary reflections and is hence called the Amplitude-Preserving Propagator. This novel wave propagator leads to three disparate contributions in large scale computational wave modeling and seismic imaging: forward modeling, migration imaging and full waveform inversion. Forward Modeling: The amplitude-preserving propagator is implemented as a preconditioner to iteratively solve the Helmholtz equation. The effectiveness of the proposed preconditioner is studied using various numerical experiments. We show three significant properties of the proposed preconditioner. First, number of iterations grows very slowly with increasing frequency which is a significant advantage compared to other methods, e.g. sweeping preconditioner. Second, the mesh size (i.e. number of elements per wavelength) does not change number of iterations. Third, and the most important one, the computational time is much less than many other preconditioners. Migration Imaging: In the context of migration imaging, the amplitude-preserving propagator is implemented as an efficient forward solver to perform wave propagation simulation in the frequency domain. We show that the propagator results in a new migration algorithm that is almost as accurate as full-wave migration, while being significantly more efficient

  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. Investigation of plasma waves propagation around traversible wormhole's throat

    NASA Astrophysics Data System (ADS)

    Ramezani-Arani, Reza; Mirzaee, Ali Reza; Abdoli-Arani, Abbas

    2015-01-01

    The ? formalism of general relativity is used in a preliminary investigation of waves propagating in a plasma around the throat of traversible wormhole. The relativistic two-fluid equations are used to take account of gravitational effects due to the throat of traversible wormhole. Here, a local approximation is used to investigate the one-dimensional electromagnetic waves radial propagation near the throat of wormhole. We use approximation near by the throat of wormhole for one-dimensional radial propagation. The dispersion relations for the transverse and longitudinal electromagnetic waves are obtained. Finally, the components of stress-energy tensor and the zero tidal force, and so flaring-out condition for traversible wormhole metric are calculated.

  5. 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

  6. Localization of angular momentum in optical waves propagating through turbulence.

    PubMed

    Sanchez, Darryl J; Oesch, Denis W

    2011-12-01

    This is the first in a series of papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. The scope of this first paper is much narrower. Here, we demonstrate that atmospheric turbulence can impart non-trivial angular momentum to beams and that this non-trivial angular momentum is highly localized. Furthermore, creation of this angular momentum is a normal part of propagation through atmospheric turbulence. PMID:22273930

  7. Localization of angular momentum in optical waves propagating through turbulence.

    PubMed

    Sanchez, Darryl J; Oesch, Denis W

    2011-12-01

    This is the first in a series of papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. The scope of this first paper is much narrower. Here, we demonstrate that atmospheric turbulence can impart non-trivial angular momentum to beams and that this non-trivial angular momentum is highly localized. Furthermore, creation of this angular momentum is a normal part of propagation through atmospheric turbulence.

  8. Variational principle for nonlinear wave propagation in dissipative systems.

    PubMed

    Dierckx, Hans; Verschelde, Henri

    2016-02-01

    The dynamics of many natural systems is dominated by nonlinear waves propagating through the medium. We show that in any extended system that supports nonlinear wave fronts with positive surface tension, the asymptotic wave-front dynamics can be formulated as a gradient system, even when the underlying evolution equations for the field variables cannot be written as a gradient system. The variational potential is simply given by a linear combination of the occupied volume and surface area of the wave front and changes monotonically over time. PMID:26986334

  9. Variational principle for nonlinear wave propagation in dissipative systems.

    PubMed

    Dierckx, Hans; Verschelde, Henri

    2016-02-01

    The dynamics of many natural systems is dominated by nonlinear waves propagating through the medium. We show that in any extended system that supports nonlinear wave fronts with positive surface tension, the asymptotic wave-front dynamics can be formulated as a gradient system, even when the underlying evolution equations for the field variables cannot be written as a gradient system. The variational potential is simply given by a linear combination of the occupied volume and surface area of the wave front and changes monotonically over time.

  10. Variational principle for nonlinear wave propagation in dissipative systems

    NASA Astrophysics Data System (ADS)

    Dierckx, Hans; Verschelde, Henri

    2016-02-01

    The dynamics of many natural systems is dominated by nonlinear waves propagating through the medium. We show that in any extended system that supports nonlinear wave fronts with positive surface tension, the asymptotic wave-front dynamics can be formulated as a gradient system, even when the underlying evolution equations for the field variables cannot be written as a gradient system. The variational potential is simply given by a linear combination of the occupied volume and surface area of the wave front and changes monotonically over time.

  11. A mm-wave planar microcavity structure for electron linear accelerator system

    SciTech Connect

    Kang, Y.W.; Kustom, R.; Mills, F.; Mavrogenes, G.; Henke, H.

    1993-07-01

    The muffin-tin cavity structure is planar and well suited for mm-wave accelerator with silicon etching techniques. A constant impedance traveling-wave structure is considered for design simplicity. The RF parameters are calculated and the shunt impedance is compared with the shunt impedance of a disk loaded cylindrical structure.

  12. Pc1 propagation in the ionospheric duct: wave vector determination

    NASA Astrophysics Data System (ADS)

    Nomura, Reiko; Glassmeier, Karl-Heinz; Narita, Yasuhito; Plaschke, Fedinand; Mann, Ian

    2013-04-01

    Pc1 geomagnetic pulsations (Pc1) are believed to propagate as fast mode waves in the ionospheric duct. Previous studies tried to locate the Pc1 source region with different methods using the characteristics of the ionospheric duct propagation (e.g., polarization method and amplitude distributions). However, no observational study of the wave vectors and the dispersion relations in the Pc1 source region has been compared with the results estimated from model calculations of the Pc1 ionospheic duct propagation. We have investigated propagation directions of Pc1 pulsations in the ionospheric duct with the 2D Wave Telescope technique. For our study, we used ground-based measurements of Pc1 pulsations from 27 May 2011, observed at 17 different stations of the Canadian magnetometer network CARISMA (www.carisma.ca). These multi-point measurements allow to derive detailed information directly on the wave propagation directions. We also show the dispersion relation of the Pc1 pulsations in the ionospheric duct.

  13. On the propagation of Voigt waves in energetically active materials

    NASA Astrophysics Data System (ADS)

    Mackay, Tom G.; Lakhtakia, Akhlesh

    2016-11-01

    If Voigt-wave propagation is possible in a dissipative anisotropic dielectric material characterised by the permittivity dyadic \\mathop{\\varepsilon }\\limits\\raise{2pt=}, then it is also possible in the analogous energetically active material characterised by the permittivity dyadic \\mathop{\\tilde{\\varepsilon }}\\limits\\raise{2pt=}, where \\mathop{\\tilde{\\varepsilon }}\\limits\\raise{2pt=} is the hermitian conjugate of \\mathop{\\varepsilon }\\limits\\raise{2pt=}. This symmetry follows directly from a theoretical analysis of the necessary and sufficient conditions for Voigt-wave propagation in anisotropic materials. As a consequence of this symmetry, a porous dissipative material that exhibits Voigt-wave propagation can be used to construct a material that allows the propagation of Voigt waves with attendant linear gain in amplitude with propagation distance, by means of infiltration with an electrically or optically activated dye, for example. This phenomenon is captured by the Bruggeman formalism for homogenised composite materials based on isotropic dielectric component materials that are randomly distributed as oriented spheroidal particles.

  14. Spectral-Element Simulations of Wave Propagation in Porous Media

    NASA Astrophysics Data System (ADS)

    Morency, C.; Tromp, J.

    2007-12-01

    Biot theory has been extensively used in the petroleum industry, where seismic surveys are performed to determine the physical properties of reservoir rocks. The theory is also of broad general interest when a physical understanding of the coupling between solid and fluid phases is desired. One fundamental result of Biot theory is the prediction of a second compressional wave, which attenuates rapidly, often referred to as "type II" or "Biot's slow compressional wave", in addition to the classical fast compressional and shear waves. The mathematical formulation of wave propagation in porous media developed by Biot is based upon the principle of virtual work, ignoring processes at the microscopic level. Moreover, even if the Biot formulations are claimed to be valid for non-uniform porosity, gradients in porosity are not explicitly incorporated in the original theory. More recent studies focused on averaging techniques to derive the macroscopic porous medium equations from the microscale, and made an attempt to derive an expression for the change in porosity, but there is still room for clarification of such an expression, and to properly integrate the effects of gradients in porosity. We aim to present a straightforward derivation of the main equations describing wave propagation in porous media, with a particular emphasis on the effects of gradients in porosity. We also present a two dimensional numerical implementation of these equations using a spectral-element method. Finally, we have performed different benchmarks to validate our method, involving acoustic-poroelastic waves interaction and wave propagation in heterogenous porous media.

  15. 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.

  16. The influence of polarization on millimeter wave propagation through rain

    NASA Technical Reports Server (NTRS)

    Bostian, C. W.; Stutzman, W. L.

    1972-01-01

    A program for the measurement and analysis of the depolarization and differential attenuation that occur when millimeter wave signals propagate through rain is described. Initial data are taken along a 1.43 km path at 17.65 GHz and a supporting theoretical model is developed to relate the propagation effects to rainfall rate and wind velocity. A block diagram of the overall experiment is included. It consists of: (1) an RF system (millimeter wave transmitter and receiver), (2) transmitting and receiving antennas, (3) a weather system with rain gauges, wind sensors, and drop counters, and (4) a digital control, processing, and data storage system.

  17. 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.

  18. Numerical study on pressure wave propagation in a mercury loop

    SciTech Connect

    Kogawa, Hiroyuki; Hasegawa, Shoichi; Futakawa, Masatoshi; Riemer, Bernie; Wendel, Mark W; Haines, John R

    2008-01-01

    On-beam tests were carried out at the Los Alamos Neutron Science Center Weapons Neutron Research (LANSCE WNR) facility in June 2005 to investigate pressure wave mitigation in mercury targets for the MW-class spallation neutron sources under international collaboration between US Spallation Neutron Source (SNS) and Japanese Spallation Neutron Source (JSNS). A mercury loop was used for the target, a so-called In-Beam Bubbling Test Loop (IBBTL). The loop consists of the rectangular pipe of 25 mm x 50 mm^2 in cross section, 1.5 mm in wall thickness and 2 m in total length approximately. The SNS team set 8 strain sensors on the pipe wall to measure the strain propagation caused by the pressure wave. The maximum strain appeared at 350 mm apart from the proton-bombarded point at 5.5 ms after the proton bombardment. It is known that the propagation velocity of the pressure wave in mercury is ca. 1500 m/s and that of the stress wave in stainless steel is ca. 5000 m/s. However, the apparent wave propagation velocity in the IBBTL was lower than those velocities and was observed to be 65 m/s. Numerical analysis was carried out to understand the strain propagation in the pipe wall of the IBBTL. Numerical results showed that the maximum strain at 350 mm apart from the beam spot appeared at 5.5 ms after proton bombardment in good agreement with experimental results.

  19. 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.

  20. Multi-layer Study of Wave Propagation in Sunspots

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

    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 λ10,827 and the He I λ10,830 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 λ10,830 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.

  1. Holographic measurement of wave propagation in axi-symmetric shells

    NASA Technical Reports Server (NTRS)

    Evensen, D. A.; Aprahamian, R.; Jacoby, J. L.

    1972-01-01

    The report deals with the use of pulsed, double-exposure holographic interferometry to record the propagation of transverse waves in thin-walled axi-symmetric shells. The report is subdivided into sections dealing with: (1) wave propagation in circular cylindrical shells, (2) wave propagation past cut-outs and stiffeners, and (3) wave propagation in conical shells. Several interferograms are presented herein which show the waves reflecting from the shell boundaries, from cut-outs, and from stiffening rings. The initial response of the shell was nearly axi-symmetric in all cases, but nonsymmetric modes soon appeared in the radial response. This result suggests that the axi-symmetric response of the shell may be dynamically unstable, and thus may preferentially excite certain circumferential harmonics through parametric excitation. Attempts were made throughout to correlate the experimental data with analysis. For the most part, good agreement between theory and experiment was obtained. Occasional differences were attributed primarily to simplifying assumptions used in the analysis. From the standpoint of engineering applications, it is clear that pulsed laser holography can be used to obtain quantitative engineering data. Areas of dynamic stress concentration, stress concentration factors, local anomalies, etc., can be readily determined by holography.

  2. 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

  3. A space-time discretization procedure for wave propagation problems

    NASA Technical Reports Server (NTRS)

    Davis, Sanford

    1989-01-01

    Higher order compact algorithms are developed for the numerical simulation of wave propagation by using the concept of a discrete dispersion relation. The dispersion relation is the imprint of any linear operator in space-time. The discrete dispersion relation is derived from the continuous dispersion relation by examining the process by which locally plane waves propagate through a chosen grid. The exponential structure of the discrete dispersion relation suggests an efficient splitting of convective and diffusive terms for dissipative waves. Fourth- and eighth-order convection schemes are examined that involve only three or five spatial grid points. These algorithms are subject to the same restrictions that govern the use of dispersion relations in the constructions of asymptotic expansions to nonlinear evolution equations. A new eighth-order scheme is developed that is exact for Courant numbers of 1, 2, 3, and 4. Examples are given of a pulse and step wave with a small amount of physical diffusion.

  4. Propagation of guided waves through weak penetrable scatterers.

    PubMed

    Maurel, Agnès; Mercier, Jean-François

    2012-03-01

    The scattering of a scalar wave propagating in a waveguide containing weak penetrable scatterers is inspected in the Born approximation. The scatterers are of arbitrary shape and present a contrast both in density and in wavespeed (or bulk modulus), a situation that can be translated in the context of SH waves, water waves, or transverse electric/transverse magnetic polarized electromagnetic waves. For small size inclusions compared to the waveguide height, analytical expressions of the transmission and reflection coefficients are derived, and compared to results of direct numerical simulations. The cases of periodically and randomly distributed inclusions are considered in more detail, and compared with unbounded propagation through inclusions. Comparisons with previous results valid in the low frequency regime are proposed. PMID:22423685

  5. Propagation of guided waves through weak penetrable scatterers.

    PubMed

    Maurel, Agnès; Mercier, Jean-François

    2012-03-01

    The scattering of a scalar wave propagating in a waveguide containing weak penetrable scatterers is inspected in the Born approximation. The scatterers are of arbitrary shape and present a contrast both in density and in wavespeed (or bulk modulus), a situation that can be translated in the context of SH waves, water waves, or transverse electric/transverse magnetic polarized electromagnetic waves. For small size inclusions compared to the waveguide height, analytical expressions of the transmission and reflection coefficients are derived, and compared to results of direct numerical simulations. The cases of periodically and randomly distributed inclusions are considered in more detail, and compared with unbounded propagation through inclusions. Comparisons with previous results valid in the low frequency regime are proposed.

  6. 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

  7. 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.

  8. Three-wave coupling coefficients for perpendicular wave propagation in a magnetized plasma

    SciTech Connect

    Brodin, G.; Stenflo, L.

    2015-10-15

    The resonant interaction between three waves in a uniform magnetized plasma is reconsidered. Starting from previous kinetic expressions, we limit our investigation to waves propagating perpendicularly to the external magnetic field. It is shown that reliable results can only be obtained in the two-dimensional case, i.e., when the wave vectors have both x and y components.

  9. 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

  10. 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.

  11. 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.

  12. Interface Conditions for Wave Propagation Through Mesh Refinement Boundaries

    NASA Technical Reports Server (NTRS)

    Choi, Dae-II; Brown, J. David; Imbiriba, Breno; Centrella, Joan; MacNeice, Peter

    2002-01-01

    We study the propagation of waves across fixed mesh refinement boundaries in linear and nonlinear model equations in 1-D and 2-D, and in the 3-D Einstein equations of general relativity. We demonstrate that using linear interpolation to set the data in guard cells leads to the production of reflected waves at the refinement boundaries. Implementing quadratic interpolation to fill the guard cells eliminates these spurious signals.

  13. Interface conditions for wave propagation through mesh refinement boundaries

    NASA Astrophysics Data System (ADS)

    Choi, Dae-Il; David Brown, J.; Imbiriba, Breno; Centrella, Joan; MacNeice, Peter

    2004-01-01

    We study the propagation of waves across fixed mesh refinement boundaries in linear and nonlinear model equations in 1-D and 2-D, and in the 3-D Einstein equations of general relativity. We demonstrate that using linear interpolation to set the data in guard cells leads to the production of reflected waves at the refinement boundaries. Implementing quadratic interpolation to fill the guard cells suppresses these spurious signals.

  14. Classical chaos in nonseparable wave propagation problems

    NASA Astrophysics Data System (ADS)

    Palmer, David R.; Brown, Michael G.; Tappert, Frederick D.; Bezdek, Hugo F.

    1988-06-01

    Numerical calculations show that acoustic ray paths in a weakly range-dependent deterministic ocean model exhibit chaotic behavior, that is, have an exponentially sensitive dependence on initial conditions. Since the ray equations define a nonautonomous Hamiltonian system with one degree of freedom, these results may be understood in terms of recent advances in classical chaos. The Hamiltonian structure of ray equations in general suggests that chaotic ray trajectories will be present in all types of linear wave motion in geophysics when variables do not separate, as in laterally inhomogeneous media.

  15. Group velocity and nonlinear dispersive wave propagation.

    NASA Technical Reports Server (NTRS)

    Hayes, W. D.

    1973-01-01

    By the use of a Hamiltonian formulation, a basic group velocity is defined as the derivative of frequency with respect to wavenumber keeping action density constant, and is shown to represent an incremental action velocity in the general nonlinear case. The stability treatment of Whitham and Lighthill is extended to several dimensions. The water-wave analysis of Whitham (1967) is extended to two space dimensions, and is shown to predict oblique-mode instabilities for kh smaller than 1.36. A treatment of Lighthill's (1965) solution in the one-dimensional elliptic case resolves the problem of the energy distribution in the solution past the critical time.

  16. Modification of Spin Wave Propagation by Current Injection

    NASA Astrophysics Data System (ADS)

    Ono, Teruo

    2010-03-01

    We studied the effect of an electric current on the spin wave propagation in magnetic wires, and found the following two effects. (i) Current injection changes the velocity of spin wave; the velocity is increased or decreased depending on the current polarity. (ii) Current injection modifies the attenuation length of spin wave; the attenuation length of spin wave can increase when the spin waves and electrons move in the same direction. The first finding can be interpreted as the time-domain observation of the spin-wave Doppler shift by current injection [1]. The second effect is thought to be affected by the nonadiabaticity of the spin transfer torque and thus can be used to estimate the nonadiabaticity [2]. [4pt] [1] V. Vlaminck and M. Bailleul, Science 322, (2008) 410. [0pt] [2] S. M. Seo, K. J. Lee, H. Yang, and T. Ono, Phys. Rev. Lett. 102, (2009) 147202.

  17. Nonlinear wave propagation in constrained solids subjected to thermal loads

    NASA Astrophysics Data System (ADS)

    Nucera, Claudio; Lanza di Scalea, Francesco

    2014-01-01

    The classical mathematical treatment governing nonlinear wave propagation in solids relies on finite strain theory. In this scenario, a system of nonlinear partial differential equations can be derived to mathematically describe nonlinear phenomena such as acoustoelasticity (wave speed dependency on quasi-static stress), wave interaction, wave distortion, and higher-harmonic generation. The present work expands the topic of nonlinear wave propagation to the case of a constrained solid subjected to thermal loads. The origin of nonlinear effects in this case is explained on the basis of the anharmonicity of interatomic potentials, and the absorption of the potential energy corresponding to the (prevented) thermal expansion. Such "residual" energy is, at least, cubic as a function of strain, hence leading to a nonlinear wave equation and higher-harmonic generation. Closed-form solutions are given for the longitudinal wave speed and the second-harmonic nonlinear parameter as a function of interatomic potential parameters and temperature increase. The model predicts a decrease in longitudinal wave speed and a corresponding increase in nonlinear parameter with increasing temperature, as a result of the thermal stresses caused by the prevented thermal expansion of the solid. Experimental measurements of the ultrasonic nonlinear parameter on a steel block under constrained thermal expansion confirm this trend. These results suggest the potential of a nonlinear ultrasonic measurement to quantify thermal stresses from prevented thermal expansion. This knowledge can be extremely useful to prevent thermal buckling of various structures, such as continuous-welded rails in hot weather.

  18. Local propagation speed constrained estimation of the slowness vector from non-planar array observations.

    PubMed

    Nouvellet, Adrien; Roueff, François; Le Pichon, Alexis; Charbit, Maurice; Vergoz, Julien; Kallel, Mohamed; Mejri, Chourouq

    2016-01-01

    The estimation of the slowness vector of infrasound waves propagating across an array is a critical process leading to the determination of parameters of interest such as the direction of arrival. The sensors of an array are often considered to be located in a horizontal plane. However, due to topography, the altitudes of the sensors are not identical and introduce a bias on the estimate if neglected. However, the unbiased 3D estimation procedure, while suppressing the bias, leads to an increase of the variance. Accounting for an a priori constraint on the slowness vector significantly reduces the variance and could therefore improve the performance of the estimation if the introduced bias by incorrect a priori information remains negligible. This study focuses on measuring the benefits of this approach with a thorough investigation of the bias and variance of the constrained 3D estimator, which is not available in the existing literature. This contribution provides such computations based on an asymptotic Gaussian approximation. Simulations are carried out to assess the theoretical results both with synthetic and real data. Thus, a constrained 3D estimator is proposed yielding the best bias/variance compromise if good knowledge of the propagation wave speed is accessible. PMID:26827049

  19. Modeling ocean wave propagation under sea ice covers

    NASA Astrophysics Data System (ADS)

    Zhao, Xin; Shen, Hayley H.; Cheng, Sukun

    2015-02-01

    Operational ocean wave models need to work globally, yet current ocean wave models can only treat ice-covered regions crudely. The purpose of this paper is to provide a brief overview of ice effects on wave propagation and different research methodology used in studying these effects. Based on its proximity to land or sea, sea ice can be classified as: landfast ice zone, shear zone, and the marginal ice zone. All ice covers attenuate wave energy. Only long swells can penetrate deep into an ice cover. Being closest to open water, wave propagation in the marginal ice zone is the most complex to model. The physical appearance of sea ice in the marginal ice zone varies. Grease ice, pancake ice, brash ice, floe aggregates, and continuous ice sheet may be found in this zone at different times and locations. These types of ice are formed under different thermal-mechanical forcing. There are three classic models that describe wave propagation through an idealized ice cover: mass loading, thin elastic plate, and viscous layer models. From physical arguments we may conjecture that mass loading model is suitable for disjoint aggregates of ice floes much smaller than the wavelength, thin elastic plate model is suitable for a continuous ice sheet, and the viscous layer model is suitable for grease ice. For different sea ice types we may need different wave ice interaction models. A recently proposed viscoelastic model is able to synthesize all three classic models into one. Under suitable limiting conditions it converges to the three previous models. The complete theoretical framework for evaluating wave propagation through various ice covers need to be implemented in the operational ocean wave models. In this review, we introduce the sea ice types, previous wave ice interaction models, wave attenuation mechanisms, the methods to calculate wave reflection and transmission between different ice covers, and the effect of ice floe breaking on shaping the sea ice morphology

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. A k-space method for moderately nonlinear wave propagation.

    PubMed

    Jing, Yun; Wang, Tianren; Clement, Greg T

    2012-08-01

    A k-space method for moderately nonlinear wave propagation in absorptive media is presented. The Westervelt equation is first transferred into k-space via Fourier transformation, and is solved by a modified wave-vector time-domain scheme. The present approach is not limited to forward propagation or parabolic approximation. One- and two-dimensional problems are investigated to verify the method by comparing results to analytic solutions and finite-difference time-domain (FDTD) method. It is found that to obtain accurate results in homogeneous media, the grid size can be as little as two points per wavelength, and for a moderately nonlinear problem, the Courant-Friedrichs-Lewy number can be as large as 0.4. Through comparisons with the conventional FDTD method, the k-space method for nonlinear wave propagation is shown here to be computationally more efficient and accurate. The k-space method is then employed to study three-dimensional nonlinear wave propagation through the skull, which shows that a relatively accurate focusing can be achieved in the brain at a high frequency by sending a low frequency from the transducer. Finally, implementations of the k-space method using a single graphics processing unit shows that it required about one-seventh the computation time of a single-core CPU calculation.

  6. Wave propagation of functionally graded material plates in thermal environments.

    PubMed

    Sun, Dan; Luo, Song-Nan

    2011-12-01

    The wave propagation of an infinite functionally graded plate in thermal environments is studied using the higher-order shear deformation plate theory. The thermal effects and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the plate surface and varied in the thickness direction only. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Considering the effects of transverse shear deformation and rotary inertia, the governing equations of the wave propagation in the functionally graded plate are derived by using the Hamilton's principle. The analytic dispersion relation of the functionally graded plate is obtained by solving an eigenvalue problem. Numerical examples show that the characteristics of wave propagation in the functionally graded plate are relates to the volume fraction index and thermal environment of the functionally graded plate. The influences of the volume fraction distributions and temperature on wave propagation of functionally graded plate are discussed in detail. The results carried out can be used in the ultrasonic inspection techniques and structural health monitoring.

  7. A k-Space Method for Moderately Nonlinear Wave Propagation

    PubMed Central

    Jing, Yun; Wang, Tianren; Clement, Greg T.

    2013-01-01

    A k-space method for moderately nonlinear wave propagation in absorptive media is presented. The Westervelt equation is first transferred into k-space via Fourier transformation, and is solved by a modified wave-vector time-domain scheme. The present approach is not limited to forward propagation or parabolic approximation. One- and two-dimensional problems are investigated to verify the method by comparing results to analytic solutions and finite-difference time-domain (FDTD) method. It is found that to obtain accurate results in homogeneous media, the grid size can be as little as two points per wavelength, and for a moderately nonlinear problem, the Courant–Friedrichs–Lewy number can be as large as 0.4. Through comparisons with the conventional FDTD method, the k-space method for nonlinear wave propagation is shown here to be computationally more efficient and accurate. The k-space method is then employed to study three-dimensional nonlinear wave propagation through the skull, which shows that a relatively accurate focusing can be achieved in the brain at a high frequency by sending a low frequency from the transducer. Finally, implementations of the k-space method using a single graphics processing unit shows that it required about one-seventh the computation time of a single-core CPU calculation. PMID:22899114

  8. Evolution of the temporal slope density function for waves propagating according to the inviscid Burgers equation.

    PubMed

    Muhlestein, Michael B; Gee, Kent L

    2016-02-01

    An exact formulation for the evolution of the probability density function of the time derivative of a waveform (slope density) propagating according to the one-dimensional inviscid Burgers equation is given. The formulation relies on the implicit Earnshaw solution and therefore is only valid prior to shock formation. As explicit examples, the slope density evolution of an initially sinusoidal plane wave, initially Gaussian-distributed planar noise, and an initially triangular wave are presented. The triangular wave is used to examine weak-shock limits without violating the theoretical assumptions. It is also shown that the moments of the slope density function as a function of distance may be written as an expansion in terms of the moments of the source slope density function. From this expansion, approximate expressions are presented for the above cases as well as a specific non-Gaussian noise case intended to mimic features of jet noise. Finally, analytical predictions of the propagation of initially Gaussian-distributed noise are compared favorably with plane-wave tube measurements.

  9. 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

  10. 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.

  11. Wave propagation in a chiral fluid: an undergraduate study

    NASA Astrophysics Data System (ADS)

    Garel, Thomas

    2003-09-01

    We study the propagation of electromagnetic waves in a chiral fluid, where the molecules are described by a simplified version of the Kuhn coupled oscillator model. The eigenmodes of Maxwell's equations are circularly polarized waves. The application of a static magnetic field further leads to a magnetochiral term in the index of refraction of the fluid, which is independent of the wave polarization. A similar result holds when absorption is taken into account. Interference experiments and photochemical reactions have recently demonstrated the existence of the magnetochiral term. The comparison with Faraday rotation in an achiral fluid emphasizes the different symmetry properties of the two effects.

  12. Wave propagation within some non-homogeneous continua

    NASA Astrophysics Data System (ADS)

    Antonio Tamarasselvame, Nirmal; Buisson, Manuel; Rakotomanana, Lalaonirina R.

    We investigate the elastic wave propagation within a non-homogeneous continuum according to W. Noll. After some preliminaries in geometry approach suggested by E. Cartan, the linear momentum equation of so-called weakly continuous medium is written. A first example illustrates the modal analysis of an axisymmetric non-homogeneous thick tube. The overall solution is the product of an attenuating exponential response with Kummer's functions. The second example deals with a Timoshenko beam involving transversal displacement and angular rotation of section. We observe the presence of various waves with spatial attenuation, either for the displacement or the section rotation, together with the occurring waves at different scale levels.

  13. Smoothed Particle Hydrodynamics for water wave propagation in a channel

    NASA Astrophysics Data System (ADS)

    Omidvar, Pourya; Norouzi, Hossein; Zarghami, Ahad

    2015-01-01

    In this paper, Smoothed Particle Hydrodynamics (SPH) is used to simulate the propagation of waves in an intermediate depth water channel. The major advantage of using SPH is that no special treatment of the free surface is required, which is advantageous for simulating highly nonlinear flows with possible wave breaking. The SPH method has an option of different formulations with their own advantages and drawbacks to be implemented. Here, we apply the classical and Arbitrary Lagrange-Euler (ALE) formulation for wave propagation in a water channel. The classical SPH should come with an artificial viscosity which stabilizes the numerical algorithm and increases the accuracy. Here, we will show that the use of classical SPH with an artificial viscosity may cause the waves in the channel to decay. On the other hand, we will show that using the ALE-SPH algorithm with a Riemann solver is more stable, and in addition to producing the pressure fields with much less numerical noise, the waves propagate in the channel without dissipation.

  14. 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.

  15. 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.

  16. Modelling of waves propagation on irregular surfaces using ray tracing and GTD approaches: Application to head waves simulation in TOFD inspections for NDT

    NASA Astrophysics Data System (ADS)

    Ferrand, Adrien; Darmon, Michel; Chatillon, Sylvain; Deschamps, Marc

    2014-04-01

    The Time of Flight Diffraction (TOFD) technique is a classical ultrasonic method used in ultrasonic non-destructive evaluation, which allows a precise positioning and a quantitative size evaluation of cracks in the inspected material. Among the typical phenomena arising in the current TOFD inspection, the so-called "head wave" is the first contribution reaching the receiver. The head wave propagation on a planar interface is well known and identified as a critical refraction taking place on the material surface. On irregular surfaces, it has been shown that the head wave results from the melting of surface and bulk waves mechanisms and that surface irregularities are responsible for numerous diffractions of the incident head wave. To simulate such behaviour, a model has been developed using a ray tracing technique based on time of flight minimization (generalized Fermat's principle). It enables the calculation of the ray path and the corresponding time of flight of all waves propagating in the material, including the head wave. To obtain a complete propagation model for these waves (both trajectory and amplitude), the integration of Geometrical Theory of Diffraction (GTD) models is currently performed by coupling them with the ray-based approach discussed above.

  17. 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.

  18. Propagation of electromagnetic waves in P T -symmetric hyperbolic structures

    NASA Astrophysics Data System (ADS)

    Shramkova, O. V.; Tsironis, G. P.

    2016-07-01

    We investigate theoretically and numerically the propagation of electromagnetic waves in P T -symmetric periodic stacks composed of hyperbolic metamaterial layers separated by dielectric media with balanced loss and gain. We derive the characteristic frequencies governing the dispersion properties of the eigenwaves of P T -symmetric semiconductor-dielectric stacks. By tuning the loss/gain level and thicknesses of the layers, we study the evolution of the dispersion dependencies. We show that the effective-medium approach does not adequately describe the propagating waves in the P T -symmetric hypercrystals, even for wavelengths that are about 100 times larger than the period of the stack. We demonstrate the existence of anisotropic transmission resonances and above-unity reflection in P T -symmetric hyperbolic systems. The P T -symmetry-breaking transition of the scattering matrix is strongly influenced by the constitutive and geometrical parameters of the layers and the angles of wave incidence.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. Obliquely propagating magnetosonic waves in multicomponent quantum magnetoplasma

    NASA Astrophysics Data System (ADS)

    Masood, W.; Mushtaq, A.

    2008-06-01

    Linear properties of obliquely propagating magnetosonic waves (both fast and slow) in multicomponent (electron-positron-ion ( e- p- i) and dust-electron-ion ( d- e- i)) quantum magnetoplasma are studied. It is found that the quantum Bohm potential term significantly changes the propagation of fast and slow magnetosonic waves in both e- p- i and d- e- i quantum plasmas. The variation of the dispersion characteristics with the increase/decrease of positron concentration in e- p- i and dust concentration in d- e- i quantum magnetoplasma is explored. Finally, the effect of angle θ (that the ambient magnetic field makes with the x-axis) on the dispersion properties of magnetosonic waves in multicomponent quantum magnetoplasma is investigated. The relevance of the present investigation to the dense astrophysical environments and microelectronic devices is also pointed out.

  4. Nonlinear wave propagation in strongly coupled dusty plasmas

    SciTech Connect

    Veeresha, B. M.; Tiwari, S. K.; Sen, A.; Kaw, P. K.; Das, A.

    2010-03-15

    The nonlinear propagation of low-frequency waves in a strongly coupled dusty plasma medium is studied theoretically in the framework of the phenomenological generalized hydrodynamic (GH) model. A set of simplified model nonlinear equations are derived from the original nonlinear integrodifferential form of the GH model by employing an appropriate physical ansatz. Using standard perturbation techniques characteristic evolution equations for finite small amplitude waves are then obtained in various propagation regimes. The influence of viscoelastic properties arising from dust correlation contributions on the nature of nonlinear solutions is discussed. The modulational stability of dust acoustic waves to parallel perturbation is also examined and it is shown that dust compressibility contributions influenced by the Coulomb coupling effects introduce significant modification in the threshold and range of the instability domain.

  5. Calculation of the spin-wave spectra in planar magnonic crystals with metallic overlayers

    NASA Astrophysics Data System (ADS)

    Sokolovskyy, M. L.; Klos, J. W.; Mamica, S.; Krawczyk, M.

    2012-04-01

    Planar one-dimensional magnonic crystals of nanoscale lattice constant having different types of overlayers, dielectric and metallic, are studied. The dynamics of magnetization is described by the Landau-Lifshitz equation, which is solved using the plane-wave method. The calculations are performed with the nonuniform dynamic dipolar field. At the same time, the finite thickness of the studied structures is taken into account. New possibilities for shaping dispersion relations of spin waves and magnonic bandgaps in planar magnonic crystals by adding metallic/dielectric overlayers on the top of it are found.

  6. 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

  7. Wave packet propagation across barriers by semiclassical initial value methods

    NASA Astrophysics Data System (ADS)

    Petersen, Jakob; Kay, Kenneth G.

    2015-07-01

    Semiclassical initial value representation (IVR) formulas for the propagator have difficulty describing tunneling through barriers. A key reason is that these formulas do not automatically reduce, in the classical limit, to the version of the Van Vleck-Gutzwiller (VVG) propagator required to treat barrier tunneling, which involves trajectories that have complex initial conditions and that follow paths in complex time. In this work, a simple IVR expression, that has the correct tunneling form in the classical limit, is derived for the propagator in the case of one-dimensional barrier transmission. Similarly, an IVR formula, that reduces to the Generalized Gaussian Wave Packet Dynamics (GGWPD) expression [D. Huber, E. J. Heller, and R. Littlejohn, J. Chem. Phys. 89, 2003 (1988)] in the classical limit, is derived for the transmitted wave packet. Uniform semiclassical versions of the IVR formulas are presented and simplified expressions in terms of real trajectories and WKB penetration factors are described. Numerical tests show that the uniform IVR treatment gives good results for wave packet transmission through the Eckart and Gaussian barriers in all cases examined. In contrast, even when applied with the proper complex trajectories, the VVG and GGWPD treatments are inaccurate when the mean energy of the wave packet is near the classical transmission threshold. The IVR expressions for the propagator and wave packet are cast as contour integrals in the complex space of initial conditions and these are generalized to potentially allow treatment of a larger variety of systems. A steepest descent analysis of the contour integral formula for the wave packet in the present cases confirms its relationship to the GGWPD method, verifies its semiclassical validity, and explains results of numerical calculations.

  8. 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.

  9. 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.

  10. Constraining Gravitational-Wave Propagation Speed with Multimessenger Observations

    NASA Astrophysics Data System (ADS)

    Nishizawa, Atsushi; Nakamura, Takashi

    2015-04-01

    Detection of gravitational waves (GW) provides us an opportunity to test general relativity in strong and dynamical regimes of gravity. One of the tests is checking whether GW propagates with the speed of light or not. This test is crucial because the velocity of GW has not ever been directly measured. Propagation speed of a GW can deviate from the speed of light due to the modification of gravity, graviton mass, and the nontrivial spacetime structure such as extra dimensions and quantum gravity effects. Here we report a simple method to measure the propagation speed of a GW by directly comparing arrival times between gravitational waves, and neutrinos from supernovae or photons from short gamma-ray bursts. As a result, we found that the future multimessenger observations of a GW, neutrinos, and photons can test the GW propagation speed with the precision of 10-16, improving the previous suggestions by 8-10 orders of magnitude. We also propose a novel method that distinguishes the true signal due to the deviation of GW propagation speed from the speed of light and the intrinsic time delay of the emission at a source by looking at the redshift dependence. A. N. is supported by JSPS Postdoctoral Fellowships for Research Abroad.

  11. Propagating and Localized Surface Waves in Metamaterial Stacks

    NASA Astrophysics Data System (ADS)

    Peng, Ruwen; Bao, Yongjun; Tang, Zhaohui; Gao, Feng; Zhang, Zhijian; Sun, Weihua; Wu, Xin; Wang, Mu

    2009-03-01

    We demonstrate the interference effect between propagating and localized surface modes of electromagnetic wave in metamaterial stacks, which leads to a transmission extremum. When radiation is incident on a metal surface perforated with an array of ring-shaped subwavelength apertures, the phase difference between the propagating surface Bloch wave and the localized surface wave can be tailored by the geometrical parameters of the array so as to affect the shape of the transmission spectrum. Above the resonant frequency of the aperture, interference between the surface waves leads to a minimum in the transmission spectrum, whereas below it, the interference leads to a maximum. While in multiple metamaterial stacks with hole arrays, the coupling of surface electromagnetic wave yields a new resonant mode with increasing quality factor of the transmission peak. We suggest that these features provide flexibility in engineering surface wave-based all-optical devices. Reference: Y. J. Bao, R. W. Peng, D. J. Shu, Mu Wang, X. Lu, J. Shao, W. Lu,and N. B. Ming, Phys. Rev. Lett. (2008) 101, 087401.

  12. Broad frequency-band characterizations of electromagnetic energy propagation in planar thin-film transmission lines

    NASA Astrophysics Data System (ADS)

    Kim, Dongchul; Eo, Yungseon

    2014-04-01

    Thin-film transmission lines are experimentally characterized in the frequency range from 10 MHz to 110 GHz. Scattering (S-) parameters for several test lines are measured. Then, two important transmission line parameters ( i.e., the propagation constant and characteristic impedance) are determined in the measured frequency range. The resonances, which are inevitable in a practical experimental environment, are carefully eliminated by de-embedding parasitic effects and by determining the frequency-variant dielectric permittivity based on the Debye model. Based on the experimental work, we showed that the conventional skin-effect model may not be accurate for high-frequencies. Further, the 3-dimensional (3D) numerical field solver does not reflect the radiation loss at high-frequency. Finally, in the millimeter (mm)-wave region, all the three loss mechanisms due to the skin-effect, dielectric polarization, and electromagnetic radiation have to be taken into account.

  13. 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.

  14. 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. PMID:27472616

  15. Electron plasma wave propagation in external-electrode fluorescent lamps

    SciTech Connect

    Cho, Guangsup; Kim, Jung-Hyun; Jeong, Jong-Mun; Hong, Byoung-Hee; Koo, Je-Huan; Choi, Eun-Ha; Verboncoeur, John P.; Uhm, Han Sup

    2008-01-14

    The optical propagation observed along the positive column of external electrode fluorescent lamps is shown to be an electron plasma wave propagating with the electron thermal speed of (kT{sub e}/m){sup 1/2}. When the luminance of the lamp is 10 000-20 000 cd/m{sup 2}, the electron plasma temperature and the plasma density in the positive column are determined to be kT{sub e}{approx}1.26-2.12 eV and n{sub o}{approx}(1.28-1.69)x10{sup 17} m{sup -3}, respectively.

  16. 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

  17. 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.

  18. 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

  19. Broadband and total autocollimation of spin waves using planar magnonic crystals

    NASA Astrophysics Data System (ADS)

    Kumar, D.; Adeyeye, A. O.

    2015-04-01

    We present a systematic study of spin wave autocollimation in planar magnonic crystals comprising of antidot arrays in nanoscale permalloy (Py: Ni80Fe20) thin films. It is shown that a careful design of such crystals can allow for the autocollimation of the entire spin wave spectrum without any significant evanescence or any drop in the group velocity. These developments allow us access to spin wave beams which do not disperse or converge outside a waveguide. Collimated spin wave beams would be essential in applications such as dense signal routing and multiplexing in higher dimensional magnonic systems.

  20. Broadband and total autocollimation of spin waves using planar magnonic crystals

    SciTech Connect

    Kumar, D.; Adeyeye, A. O.

    2015-04-14

    We present a systematic study of spin wave autocollimation in planar magnonic crystals comprising of antidot arrays in nanoscale permalloy (Py: Ni{sub 80}Fe{sub 20}) thin films. It is shown that a careful design of such crystals can allow for the autocollimation of the entire spin wave spectrum without any significant evanescence or any drop in the group velocity. These developments allow us access to spin wave beams which do not disperse or converge outside a waveguide. Collimated spin wave beams would be essential in applications such as dense signal routing and multiplexing in higher dimensional magnonic systems.

  1. Rayleigh wave propagation method for the characterization of a thin layer of biomaterials

    PubMed Central

    Kazemirad, Siavash; Mongeau, Luc

    2013-01-01

    An experimental method based on Rayleigh wave propagation was developed for quantifying the frequency-dependent viscoelastic properties of a small volume of expensive biomaterials over a broad frequency range. Synthetic silicone rubber and gelatin materials were fabricated and tested to evaluate the proposed method. Planar harmonic Rayleigh waves at different frequencies, from 80 to 4000 Hz, were launched on the surface of a sample composed of a substrate with known material properties coated with a thin layer of the soft material to be characterized. A transfer function method was used to obtain the complex Rayleigh wavenumber. An inverse wave propagation problem was solved and a complex nonlinear dispersion equation was obtained. The complex shear and elastic moduli of the sample materials were then calculated through the numerical solution of the obtained dispersion equation using the measured wavenumbers. The results were in good agreement with those of a previous independent study. The proposed method was found to be reliable and cost effective for the measurement of viscoelastic properties of a thin layer of expensive biomaterials, such as phonosurgical biomaterials, over a wide frequency range. PMID:23742382

  2. 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.

  3. Observations of acoustic surface waves in outdoor sound propagation

    NASA Astrophysics Data System (ADS)

    Albert, Donald G.

    2003-05-01

    Acoustic surface waves have been detected propagating outdoors under natural conditions. Two critical experimental conditions were employed to ensure the conclusive detection of these waves. First, acoustic pulses rather than a continuous wave source allowed an examination of the waveform shape and avoided the masking of wave arrivals. Second, a snow cover provided favorable ground impedance conditions for surface waves to exist. The acoustic pulses were generated by blank pistol shots fired 1 m above the snow. The resultant waveforms were measured using a vertical array of six microphones located 60 m away from the source at heights between 0.1 and 4.75 m. A strong, low frequency ``tail'' following the initial arrival was recorded near the snow surface. This tail, and its exponential decay with height (z) above the surface (~e-αz), are diagnostic features of surface waves. The measured attenuation coefficient α was 0.28 m-1. The identification of the surface wave is confirmed by comparing the measured waveforms with waveforms predicted by the theoretical evaluation of the explicit surface wave pole term using residue theory.

  4. Experimental study of wave propagation dynamics of multicomponent distillation columns

    SciTech Connect

    Ting, J.; Helfferich, F.G.; Hwang, Y.L.; Graham, G.K.; Keller, G.E. II

    1999-10-01

    Distillation columns with sharp separations exhibit severely nonlinear behavior, which has been known to cause difficulties in column control and design. Such a column is characterized by sharp composition and temperature variations in the column. Previously, the binary distillation case was thoroughly analyzed using a nonlinear wave theory and such an analysis was experimentally validated. For multicomponent distillation, the complicated nonlinear dynamics of the movement and interference of multiple sharp composition variations can be elucidated with a coherent-wave theory developed earlier for general countercurrent separation processes. With a ternary alcohol mixture, the present study has experimentally verified the theory by demonstrating the existence and propagation of constant-pattern coherent waves in a 50-tray stripping column in response to a step disturbance of feed composition, feed flow rate, or reboiler heat supply. The study has also tested the theory's predictions of composition profile, wave velocities, and asymmetric dynamics.

  5. Experimental studies of fast wave propagation in DIII-D

    SciTech Connect

    Ikezi, H.; Pinsker, R.I.; Chiu, S.C.; deGrassie, J.S.

    1995-06-01

    Fast Alfven waves radiated from the phased array antenna in the DIII-D tokamak and used for heating and current drive are studied by employing a B-loop array mounted on the vacuum vessel wall. The wave propagation direction controlled by the antenna phasing is clearly observed. A small divergence of the rays arising from the anisotropic nature of the fast wave is found. Comparison with a ray tracing code confirms that the ray position calculated by the code is accurate up to at least one toroidal turn of the rays. Conservation of Rk{sub t} which is a basic assumption in computer codes is tested. Although the upshift of toroidal wavenumber k{sub t} at small major radius R is confirmed, Rk{sub t} is not well conserved. A mass density interferometer is demonstrated by employing the extraordinary fast wave.

  6. Experimental study of wave propagation dynamics of binary distillation columns

    SciTech Connect

    Hwang, Y.L.; Graham, G.K.; Keller, G.E. II; Ting, J.; Helfferich, F.G.

    1996-10-01

    High-purity distillation columns are typically difficult to control because of their severely nonlinear behavior reflected by their sharp composition and temperature profiles. The dynamic behavior of such a column, as characterized by the movement of its sharp profile, was elucidated by a nonlinear wave theory established previously. With binary alcohol mixtures, this study provides an experimental observation of such wave-propagation dynamics of a 40-tray stripping column and a 50-tray fractionation column in response to step disturbances of feed composition, feed flow rate, and reboiler heat supply. These experimental results have verified that the sharp profile in a high-purity column moves as a constant-pattern wave and that the nonlinear wave theory predicts its velocity satisfactorily with very simple mathematics. Results also demonstrate the asymmetric dynamics of the transitions between two steady states.

  7. Laser characterization of ultrasonic wave propagation in random media.

    PubMed

    Scales, John A; Malcolm, Alison E

    2003-04-01

    Lasers can be used to excite and detect ultrasonic waves in a wide variety of materials. This allows the measurement of absolute particle motion without the mechanical disturbances of contacting transducers. In an ultrasound transmission experiment, the wave field is usually accessible only on the boundaries of a sample. Using optical methods, one can measure the surface wave field, in effect, within the scattering region. Here, we describe noncontacting (laser source and detector) measurements of ultrasonic wave propagation in randomly heterogeneous rock samples. By scanning the surface of the sample, we can directly visualize the complex dynamics of diffraction, multiple scattering, mode conversion, and whispering gallery modes. We will show measurements on rock samples that have similar elastic moduli and intrinsic attenuation, but different grain sizes, and hence, different scattering strengths. The intensity data are well fit by a radiative transfer model, and we use this fact to infer the scattering mean free path. PMID:12786520

  8. Matter wave propagation using the Fourier optics approach

    NASA Astrophysics Data System (ADS)

    Shayganmanesh, M.; Hematizadeh, A.

    2016-09-01

    In this paper propagation of matter wave of particles is modeled using the Fourier optics approach. In first step the Schrödinger equation of quantum mechanics is used to find the wave function of the particle. In the second step Fourier optics is employed to model the diffraction of the wave function of the particle through single and double slits. The results of the calculations are presented as graphs of diffraction patterns. The results of the presented method are compared to the existing results in the literature (with different methods) to check the validity of the introduced model. It is shown that the Fourier optics approach is applicable to matter wave of particles in diffraction through slits.

  9. Propagating spin waves in YIG micro-channel on Silicon

    NASA Astrophysics Data System (ADS)

    Chen, Jilei; Che, Ping; Tu, Sa; Zhang, Yan; Qin, Jun; Bi, Lei; Liu, Chuanpu; Liao, Zhimin; Yu, Dapeng; Yu, Haiming; Fert Beijing Research Institute Team; University Of Electronic Science; Technology Of China Team; Peking University Collaboration

    Recently the utilization of spin waves in the field of information processing has been widely developed because it is free of Joule heat dissipation and beneficial to miniaturization of the magnon based devices. Here we study spin waves in yttrium iron garnet (YIG) with a low damping property. The YIG film is fabricated on silicon substrate using pulsed laser deposition and the measured FMR linewidth is only a few Gauss. Using ebeam lithography, we are able to pattern the YIG film into a micro-channel and integrate sub-meter waveguides to generate and detect spin waves of wavelength down to 1 μm or below. We show results of propagating spin waves in the YIG micro-channel measured by the S12 parameter of the vector network analyzer.

  10. PROPAGATION OF GRAVITY WAVES IN A CONVECTIVE LAYER

    SciTech Connect

    Onofri, M.; Vecchio, A.; Veltri, P.; De Masi, G.

    2012-02-10

    We perform numerical simulations of gravity mode propagation in a convective layer to investigate the observed association between small spatial scales and low frequencies in the photospheric velocity fields. According to the linear theory, when the fluid layer is convectively unstable, gravity modes are evanescent waves. However, in simple two-dimensional numerical settings, we find that when the equilibrium structure is modified by coherent large-scale convective motions, the waves injected at the bottom of the layer are no longer evanescent. In this situation, gravity waves can be detected at the surface of the layer. In our simplified model the injected wave's frequency remains unchanged, but its amplitude has a spatial modulation determined by the convective structure. This result may explain some analyses done with the proper orthogonal decomposition method of the solar surface velocity field even though solar convection is far more complex than the convection model considered here.

  11. 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.

  12. Obliquely propagating electromagnetic waves in magnetized kappa plasmas

    NASA Astrophysics Data System (ADS)

    Gaelzer, R.; Ziebell, L. F.

    2016-02-01

    Velocity distribution functions (VDFs) that exhibit a power-law dependence on the high-energy tail have been the subject of intense research by the plasma physics community. Such functions, known as kappa or superthermal distributions, have been found to provide a better fitting to the VDFs 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. In the literature, the general treatment for waves excited by (bi-)Maxwellian plasmas is well-established. However, for kappa distributions, the wave characteristics have been studied mostly for the limiting cases of purely parallel or perpendicular propagation, relative to the ambient magnetic field. Contributions to 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 can operate simultaneously both in the parallel and oblique directions. In a recent work, Gaelzer and Ziebell [J. Geophys. Res. 119, 9334 (2014)] 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, the formalism is generalized for the general case of electrostatic and/or electromagnetic waves propagating in a kappa plasma in any frequency range and for arbitrary angles. An isotropic distribution is considered, but the methods used here can be easily applied to more general anisotropic distributions such as the bi-kappa or product-bi-kappa.

  13. 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.

  14. 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.

  15. 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.

  16. Effect of propagation on pulsed four-wave mixing

    NASA Astrophysics Data System (ADS)

    Weisman, P.; Wilson-Gordon, A. D.; Friedmann, H.

    2000-05-01

    We examine the effect of propagation on the resonance Rabi sideband of the four-wave mixing (FWM) spectrum, obtained when short temporally displaced pump and probe pulses interact with an optically thick medium of two-level atoms. We find that the dependence of the time-integrated FWM signal on the pump-probe delay is considerably altered by propagation. In particular, the logarithm of the FWM signal, for the case where the probe precedes the pump, deviates from linearity and may even increase over a range of values. An explanation is given in terms of the overlap of the pump envelope with the coherent response of the atomic system to the probe, both of which are modified on propagation.

  17. Resonance absorption of propagating fast waves in a cold plasma

    NASA Technical Reports Server (NTRS)

    Hollweg, Joseph V.

    1990-01-01

    Absorption of propagating waves impinging on a surface in which the plasma and magnetic field may change is investigated by examining in depth the problem of a combination of cold plasma, uniform magnetic field and a surface density which varies linearly from zero at the left end to some finite value at the right end, beyond which the density is constant. Two cases are considered: one in which the plasma is a vacuum everywhere to the left of the surface (which may correspond to coronal conditions) and one in which the plasma density jumps to a very large value to the left of the surface (which may mimic the magnetosphere with the dense region at the left corresponding to the plasmasphere). A complete discussion of the resonance absorption of propagating fast waves for the case considered by Kiveloson and Southwood (1986) is presented, emphasizing approximate analytical results whenever possible; these results are then compared with exact numerical solutions.

  18. Numerical modelling of nonlinear full-wave acoustic propagation

    SciTech Connect

    Velasco-Segura, Roberto Rendón, Pablo L.

    2015-10-28

    The various model equations of nonlinear acoustics are arrived at by making assumptions which permit the observation of the interaction with propagation of either single or joint effects. We present here a form of the conservation equations of fluid dynamics which are deduced using slightly less restrictive hypothesis than those necessary to obtain the well known Westervelt equation. This formulation accounts for full wave diffraction, nonlinearity, and thermoviscous dissipative effects. A two-dimensional, finite-volume method using Roe’s linearisation has been implemented to obtain numerically the solution of the proposed equations. This code, which has been written for parallel execution on a GPU, can be used to describe moderate nonlinear phenomena, at low Mach numbers, in domains as large as 100 wave lengths. Applications range from models of diagnostic and therapeutic HIFU, to parametric acoustic arrays and nonlinear propagation in acoustic waveguides. Examples related to these applications are shown and discussed.

  19. 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.

  20. Numerical simulation of shock wave propagation in flows

    NASA Astrophysics Data System (ADS)

    Rénier, Mathieu; Marchiano, Régis; Gaudard, Eric; Gallin, Louis-Jonardan; Coulouvrat, François

    2012-09-01

    Acoustical shock waves propagate through flows in many situations. The sonic boom produced by a supersonic aircraft influenced by winds, or the so-called Buzz-Saw-Noise produced by turbo-engine fan blades when rotating at supersonic speeds, are two examples of such a phenomenon. In this work, an original method called FLHOWARD, acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction, is presented. It relies on a scalar nonlinear wave equation, which takes into account propagation in a privileged direction (one-way approach), with diffraction, flow, heterogeneous and nonlinear effects. Theoretical comparison of the dispersion relations between that equation and parabolic equations (standard or wide angle) shows that this approach is more precise than the parabolic approach because there are no restrictions about the angle of propagation. A numerical procedure based on the standard split-step technique is used. It consists in splitting the nonlinear wave equation into simpler equations. Each of these equations is solved thanks to an analytical solution when it is possible, and a finite differences scheme in other cases. The advancement along the propagation direction is done with an implicit scheme. The validity of that numerical procedure is assessed by comparisons with analytical solutions of the Lilley's equation in waveguides for uniform or shear flows in linear regime. Attention is paid to the advantages and drawbacks of that method. Finally, the numerical code is used to simulate the propagation of sonic boom through a piece of atmosphere with flows and heterogeneities. The effects of the various parameters are analysed.

  1. Absorption of planar waves in a draining bathtub

    SciTech Connect

    Oliveira, Ednilton S.; Dolan, Sam R.; Crispino, Luis C. B.

    2010-06-15

    We present an analysis of the absorption of acoustic waves by a black hole analogue in (2+1) dimensions generated by a fluid flow in a draining bathtub. We show that the low-frequency absorption length is equal to the acoustic hole circumference and that the high-frequency absorption length is 4 times the ergoregion radius. For intermediate values of the wave frequency, we compute the absorption length numerically and show that our results are in excellent agreement with the low- and high-frequency limits. We analyze the occurrence of superradiance, manifested as negative partial absorption lengths for corotating modes at low frequencies.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Estimation of the propagation characteristics of elastic waves propagating through a partially saturated sand soil

    NASA Astrophysics Data System (ADS)

    Nakayama, M.; Kawakata, H.; Doi, I.; Takahashi, N.

    2015-12-01

    Recently, landslides due to heavy rain and/or earthquakes have been increasing and severe damage occurred in Japan in some cases (e.g., Chigira et al., 2013, Geomorph.). One of the principle factors activating landslides is groundwater. Continuous measurements of moisture in soil and/or pore pressure are performed to investigate the groundwater behavior. However, such measurements give information on only local behavior of the groundwater. To monitor the state of target slope, it is better to measure signals affected by the behavior of groundwater in a widely surrounding region. The elastic waves propagating through the medium under the target slope are one of candidates of such signals. In this study, we measure propagating waves through a sand soil made in laboratory, injecting water into it from the bottom. We investigate the characteristics of the propagating waves. We drop sand particles in a container (750 mm long, 300 mm wide and 400 mm high) freely and made a sand soil. The sand soil consists of two layers. One is made of larger sand particles (0.2-0.4 mm in diameter) and the other is made of smaller sand particles (0.05-0.2 mm in diameter). The dry density of these sand layers is about 1.45 g/cm3. We install a shaker for generating elastic waves, accelerometers and pore pressure gauges in the sand soil. We apply small voltage steps repeatedly, and we continuously measure elastic waves propagating through the sand soil at a sampling rate of 51.2 ksps for a period including the water injection period. We estimate the spatio-temporal variation in the maximum cross-correlation coefficients and the corresponding time lags, using template waveforms recorded in the initial period as references. The coefficient for the waveforms recorded at the accelerometer attached to the tip of the shaker is almost stable in high values with a slight decrease down to 0.94 in the period when the sand particles around the shaker are considered to become wet. On the other hand

  8. 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.

  9. 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.

  10. Theoretical Methods for Wave Propagation across Jointed Rock Masses

    NASA Astrophysics Data System (ADS)

    Perino, A.; Zhu, J. B.; Li, J. C.; Barla, G.; Zhao, J.

    2010-11-01

    Different methods are presently available for the analysis of wave propagation across jointed rock masses with the consideration of multiple wave reflections between joints. These methods can be divided into two categories. One is based on the displacement discontinuity model for representing rock joints, where the displacements across a joint are discontinuous and the tractions are continuous, and the other is the equivalent medium method. For the first category, there are three methods, i.e., method of characteristics (MC), scattering matrix method (SMM) and virtual wave source method (VWS). MC solves the equation of motion by using the theory of characteristic curves. SMM is based on the definition of the scattering matrix in which the reflection and transmission coefficients of a set of joints are stored. VWS method replaces the joints in the rock mass with a virtual concept. For the second category, equivalent medium model treats the problem in the frame of continuum mechanics and simplifies it from an explicit wave propagation equation. The objective of this paper is to review and compare these theoretical methods. The comparison shows that the four solutions agree very well with each other. Some additional considerations about the advantages and disadvantages of these methods are also given in the paper.

  11. 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.

  12. 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.}

  13. Propagation of acoustic waves in the partly ionized interstellar medium

    NASA Astrophysics Data System (ADS)

    Chalov, S. V.

    2014-07-01

    The properties of linear acoustic waves propagating in the interstellar medium, which is a mixture of electron-proton plasma and hydrogen atoms, are studied analytically. The plasma component interacts with hydrogen atoms through resonant charge exchange between the atoms and protons. To make the problem tractable, only short-wavelength disturbances are considered. Namely, the wavelength is assumed to be small as compared with the mean free path of atoms with respect to charge exchange. It is shown that short waves are damped out due to the charge exchange process, and the magnitude of decrement increases with the cross-section for charge exchange, number density of atoms and sound speed. In the first approximation, decrement does not depend on the wavelength, and acoustic waves are dispersionless. The advantage of our model is fully kinetic treatment of the interstellar atom motion.

  14. Paraxial WKB Method Applied to the Lower Hybrid Wave Propagation

    SciTech Connect

    Bertelli, N; Poli, E; Harvey, R; Wright, J C; Bonoli, P T; Phillips, C K; Simov, A P; Valeo, E

    2012-07-12

    The paraxial WKB (pWKB) approximation, also called beam tracing method, has been employed in order to study the propagation of lower hybrid (LH) waves in a tokamak plasma. Analogous to the well-know ray tracing method, this approach reduces Maxwell's equations to a set of ordinary differential equations, while, in addition, retains the effects of the finite beam cross-section, and, thus, the effects of diffraction. A new code, LHBEAM (Lower Hybrid BEAM tracing), is presented, which solves the pWKB equations in tokamak geometry for arbitrary launching conditions and for analytic and experimental plasma equilibria. In addition, LHBEAM includes linear electron Landau damping for the evaluation of the absorbed power density and the reconstruction of the wave electric field in both the physical and Fourier space. Illustrative LHBEAM calculations are presented along with a comparison with the ray tracing code GENRAY and the full wave solver TORIC-LH.

  15. On a method computing transient wave propagation in ionospheric regions

    NASA Technical Reports Server (NTRS)

    Gray, K. G.; Bowhill, S. A.

    1978-01-01

    A consequence of an exoatmospheric nuclear burst is an electromagnetic pulse (EMP) radiated from it. In a region far enough away from the burst, where nonlinear effects can be ignored, the EMP can be represented by a large-amplitude narrow-time-width plane-wave pulse. If the ionosphere intervenes the origin and destination of the EMP, frequency dispersion can cause significant changes in the original pulse upon reception. A method of computing these dispersive effects of transient wave propagation is summarized. The method described is different from the standard transform techniques and provides physical insight into the transient wave process. The method, although exact, can be used in approximating the early-time transient response of an ionospheric region by a simple integration with only explicit knowledge of the electron density, electron collision frequency, and electron gyrofrequency required. As an illustration of the method, it is applied to a simple example and contrasted with the corresponding transform solution.

  16. 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.

  17. 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.

  18. 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.

  19. 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. PMID:16253005

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

    SciTech Connect

    Mario Agio

    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.

  1. Wave energy converter effects on wave propagation: A sensitivity study in Monterey Bay, CA

    NASA Astrophysics Data System (ADS)

    Chang, G.; Jones, C. A.; Roberts, J.; Magalen, J.; Ruehl, K.; Chartrand, C.

    2014-12-01

    The development of renewable offshore energy in the United States is growing rapidly and wave energy is one of the largest resources currently being evaluated. The deployment of wave energy converter (WEC) arrays required to harness this resource could feasibly number in the hundreds of individual devices. The WEC arrays have the potential to alter nearshore wave propagation and circulation patterns and ecosystem processes. As the industry progresses from pilot- to commercial-scale it is important to understand and quantify the effects of WECs on the natural nearshore processes that support a local, healthy ecosystem. To help accelerate the realization of commercial-scale wave power, predictive modeling tools have been developed and utilized to evaluate the likelihood of environmental impact. At present, direct measurements of the effects of different types of WEC arrays on nearshore wave propagation are not available; therefore wave model simulations provide the groundwork for investigations of the sensitivity of model results to prescribed WEC characteristics over a range of anticipated wave conditions. The present study incorporates a modified version of an industry standard wave modeling tool, SWAN (Simulating WAves Nearshore), to simulate wave propagation through a hypothetical WEC array deployment site on the California coast. The modified SWAN, referred to as SNL-SWAN, incorporates device-specific WEC power take-off characteristics to more accurately evaluate a WEC device's effects on wave propagation. The primary objectives were to investigate the effects of a range of WEC devices and device and array characteristics (e.g., device spacing, number of WECs in an array) on nearshore wave propagation using SNL-SWAN model simulations. Results showed that significant wave height was most sensitive to variations in WEC device type and size and the number of WEC devices in an array. Locations in the lee centerline of the arrays in each modeled scenario showed the

  2. Wave propagation in media having negative permittivity and permeability

    NASA Astrophysics Data System (ADS)

    Ziolkowski, Richard W.; Heyman, Ehud

    2001-11-01

    Wave propagation in a double negative (DNG) medium, i.e., a medium having negative permittivity and negative permeability, is studied both analytically and numerically. The choices of the square root that leads to the index of refraction and the wave impedance in a DNG medium are determined by imposing analyticity in the complex frequency domain, and the corresponding wave properties associated with each choice are presented. These monochromatic concepts are then tested critically via a one-dimensional finite difference time domain (FDTD) simulation of the propagation of a causal, pulsed plane wave in a matched, lossy Drude model DNG medium. The causal responses of different spectral regimes of the medium with positive or negative refractive indices are studied by varying the carrier frequency of narrowband pulse excitations. The smooth transition of the phenomena associated with a DNG medium from its early-time nondispersive behavior to its late-time monochromatic response is explored with wideband pulse excitations. These FDTD results show conclusively that the square root choice leading to a negative index of refraction and positive wave impedance is the correct one, and that this choice is consistent with the overall causality of the response. An analytical, exact frequency domain solution to the scattering of a wave from a DNG slab is also given and is used to characterize several physical effects. This solution is independent of the choice of the square roots for the index of refraction and the wave impedance, and thus avoids any controversy that may arise in connection with the signs of these constituents. The DNG slab solution is used to critically examine the perfect lens concept suggested recently by Pendry. It is shown that the perfect lens effect exists only under the special case of a DNG medium with ɛ(ω)=μ(ω)=-1 that is both lossless and nondispersive. Otherwise, the closed form solutions for the field structure reveal that the DNG slab converts

  3. Surface Wave Propagation on a Laterally Heterogeneous Earth

    NASA Astrophysics Data System (ADS)

    Tromp, Jeroen

    1992-01-01

    Love and Rayleigh waves propagating on the surface of the Earth exhibit path, phase and amplitude anomalies as a result of the lateral heterogeneity of the mantle. In the JWKB approximation, these anomalies can be determined by tracing surface wave trajectories, and calculating phase and amplitude anomalies along them. A time- or frequency -domain JWKB analysis yields local eigenfunctions, local dispersion relations, and conservation laws for the surface wave energy. The local dispersion relations determine the surface wave trajectories, and the energy equations determine the surface wave amplitudes. On an anisotrophic Earth model the local dispersion relation and the local vertical eigenfunctions depend explicitly on the direction of the local wavevector. Apart from the usual dynamical phase, which is the integral of the local wavevector along a raypath, there is an additional variation is phase. This additional phase, which is an analogue of the Berry phase in adiabatic quantum mechanics, vanishes in a waveguide with a local vertical two-fold symmetry axis or a local horizontal mirror plane. JWKB theory breaks down in the vicinity of caustics, where neighboring rays merge and the surface wave amplitude diverges. Based upon a potential representation of the surface wave field, a uniformly valid Maslov theory can be obtained. Surface wave trajectories are determined by a system of four ordinary differential equations which define a three-dimensional manifold in four-dimensional phase space (theta,phi,k_theta,k _phi), where theta is colatitude, phi is longitude, and k_theta and k _phi are the covariant components of the wavevector. There are no caustics in phase space; it is only when the rays in phase space are projected onto configuration space (theta,phi), the mixed spaces (k_theta,phi ) and (theta,k_phi), or onto momentum space (k_theta,k _phi), that caustics occur. The essential strategy is to employ a mixed or momentum space representation of the wavefield in

  4. Experimental investigation of a mm-wave planar antenna

    NASA Astrophysics Data System (ADS)

    Lambrakakis, Georgios D.

    1990-06-01

    This thesis investigates a new mm-wave Bilateral Slot Line (BSL) antenna and its relation to the Linearly Tapered Slot Antenna (LTSA). The BSL antenna consists of a tapered double-sided slotline and can be viewed as two identical LTSAs sandwiched back to back. Dielectric substrates with permittivities of 2.33 and 6.0 were used to construct these antennas. The theoretical background, the design, and the performance in the frequency range 5 to 9 GHz of the new microwave integrated circuit antenna is presented. The effects of several parameters such as dielectric constant, stripline and slotline characteristic impedance, antenna structure, and transition scheme on the radiation patterns and return loss were experimentally investigated. Some relationships between the width of stripline and slotline, their characteristic impedance and the dielectric constant are reported. Guidelines are laid to design the LTSA and BSL antennas.

  5. Multiphase flow, deformation and wave propagation in porous media

    NASA Astrophysics Data System (ADS)

    Pazdniakou, A.; Adler, P. M.

    2010-12-01

    Our goals are to determine some of the most important macroscopic properties of porous media whether they are dry or saturated by one or two fluids such as permeabilities, solid deformations and acoustic velocities. Therefore, one needs to calculate fluid flow through the pores and the deformation of the solid matrix. Single and multiphase flows are determined by Lattice Boltzmann Models (LBM) where fluid motion is described in terms of a discretized particle distribution function which obeys a Lattice Boltzmann Equation equivalent to the Navier-Stokes equations at the macroscopic level. Complex boundary conditions can be easily treated by LBM which makes it convenient for flow simulations in porous media. Applications to the determination of the absolute permeability and of the relative permeabilities in complex media are given as well as examples of transient phenomena. Elastic deformations of the solid matrix whether they are static or time dependent can be determined by Lattice Spring Models (LSM). The solid matrix is represented by a regular cubic lattice whose points are connected by springs which are either linear (between the lattice points) or angular (between the linear springs). The spring set is selected in order to obtain an equivalent isotropic solid. The elastic properties of the medium can be calculated from the elastic energy stored in the elementary cell. A mass can be assigned to the lattice points. Applications to the determination of the macroscopic Young modulus and Poisson ratio of porous solids are given as well as direct simulations of wave propagation through dry porous solids. In order to study wave propagation in porous media containing one or two fluids, the LBM and LSM codes are coupled by using a momentum exchange algorithm which equates the velocities and the normal stresses at the solid-fluid interface. Then, two different methods can be used to study wave propagation. In the first direct method, a pressure variation is induced at a

  6. Electromagnetic wave propagation through an overdense magnetized collisional plasma layer

    NASA Astrophysics Data System (ADS)

    Thoma, C.; Rose, D. V.; Miller, C. L.; Clark, R. E.; Hughes, T. P.

    2009-08-01

    The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth's upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.

  7. 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.

  8. Poleward propagation of parametric subharmonic instability-induced inertial waves

    NASA Astrophysics Data System (ADS)

    Xie, Xiaohui; Liu, Qian; Shang, Xiaodong; Chen, Guiying; Wang, Dongxiao

    2016-03-01

    This study presents two sets of current records obtained from the South China Sea and satellite altimeter data, and it suggests that near-inertial waves induced by parametric subharmonic instability (PSI) associated with internal tides can be transported poleward beyond their critical latitude φc by background geostrophic flow (BGF). The two mooring locations were poleward of φc (≈14°N) for diurnal subharmonics (0.5D1; half diurnal frequency D1); however, both of the current records revealed clear signals at 0.5D1. The enhanced subinertial motion at 0.5D1 exhibited a fortnightly spring-neap cycle but did not agree with that of D1, indicating that it may not be generated via PSI associated with the local D1. Observations from the altimeter data and a ray-tracing simulation suggested that these nonlocally generated 0.5D1 waves may be excited near their φc, after which they propagated poleward under the role of the BGF to the observation site with a latitude higher than φc. The poleward propagation of near-inertial waves can produce elevated vertical shears; thus, it may play an important role in enhancing the local turbulent mixing.

  9. 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.

  10. Electromagnetic wave propagation through an overdense magnetized collisional plasma layer

    SciTech Connect

    Thoma, C.; Rose, D. V.; Miller, C. L.; Clark, R. E.; Hughes, T. P.

    2009-08-15

    The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth's upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.

  11. 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.

  12. Electronically nonadiabatic wave packet propagation using frozen Gaussian scattering

    NASA Astrophysics Data System (ADS)

    Kondorskiy, Alexey D.; Nanbu, Shinkoh

    2015-09-01

    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.

  13. Propagation of three-dimensional electron-acoustic solitary waves

    SciTech Connect

    Shalaby, M.; El-Sherif, L. S.; El-Labany, S. K.; Sabry, R.

    2011-06-15

    Theoretical investigation is carried out for understanding the properties of three-dimensional electron-acoustic waves propagating in magnetized plasma whose constituents are cold magnetized electron fluid, hot electrons obeying nonthermal distribution, and stationary ions. For this purpose, the hydrodynamic equations for the cold magnetized electron fluid, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear evolution equation, Zkharov-Kuznetsov (ZK) equation, in the small- but finite- amplitude regime. The ZK equation is solved analytically and it is found that it supports both solitary and blow-up solutions. It is found that rarefactive electron-acoustic solitary waves strongly depend on the density and temperature ratios of the hot-to-cold electron species as well as the nonthermal electron parameter. Furthermore, there is a critical value for the nonthermal electron parameter, which decides whether the electron-acoustic solitary wave's amplitude is decreased or increased by changing various plasma parameters. Importantly, the change of the propagation angles leads to miss the balance between the nonlinearity and dispersion; hence, the localized pulses convert to explosive/blow-up pulses. The relevance of this study to the nonlinear electron-acoustic structures in the dayside auroral zone in the light of Viking satellite observations is discussed.

  14. Synthetic Observations of Wave Propagation in a Sunspot Umbra

    NASA Astrophysics Data System (ADS)

    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.

  15. 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. PMID:25480048

  16. 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.

  17. 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.

  18. a New Approach to Bulk Wave Propagation in Anisotropic Media.

    NASA Astrophysics Data System (ADS)

    Tverdokhlebov, Andrey

    A new approach to a theoretical description of ultrasonic bulk wave propagation through anisotropic media is developed from the retarded potential representation which was obtained for the Green's function of the elastic wave equation in anisotropic media. The general formulation of the problem and the method of solution are presented. On the basis of the theoretical development, a quantitative model was obtained that yields and properly describes all major features of the phenomena of an anisotropic filter influence. A comparison with other contemporary methods and models for the quantitative evaluation of the bulk wave propagation in anisotropic media is outlined and briefly discussed. The experimental proof of principle was established by ultrasonic measurements performed on centrifugally cast stainless steel (CCSS) and unidirectional graphite fiber -epoxy composite specimens. The experimental technique used a skip-distance arrangement of the identical quasi -point probes serving as a sender and a receiver. Consistent experimental results were attained allowing us to consider the suggested experimental arrangements as a basis for the future development of NDE technique for anisotropic material characterization. Three different types of pilot computer software were developed from this generalized retarded potential model. The results of the simulation runs turn out to be self- and mutually consistent and supported by experiments. The phenomena, such as beam skewing, beam splitting, beam focusing, unsymmetrical beams and other anisotropic effects, some of which have been already known from earlier experimental observations, emerge as computational results of the software developed from the model.

  19. 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.

  20. Anomalous wave propagation across the South Caspian Basin

    SciTech Connect

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

    1997-10-01

    The Caspian basin blocks the propagation of the regional seismic phase Lg and this has importance consequences for seismic discrimination in the Middle East. Intermediate period surface waves propagating across the basin are also severely affected. In a separate study we have developed a crustal model of the south Caspian basin and the surrounding region. The crust of the basin consists of 15-25 km of low velocity, highly attenuating sediments lying on high velocity crystalline crust. The Moho beneath the basin is at a depth of about 30 km as compared to about 50 km in the surrounding region. In this study we used an idealized rendition of this crustal model to compute hybrid normal mode finite difference synthetic seismograms to identify the features of the Caspian basin which lead to the seismic blockage. Of the various features of the basin, the thickness and attenuation of the sediments appear to be the dominant blocking mechanism.

  1. 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.

  2. Non-reciprocal elastic wave propagation in spatiotemporal periodic structures

    NASA Astrophysics Data System (ADS)

    Trainiti, G.; Ruzzene, M.

    2016-08-01

    We study longitudinal and transverse wave propagation in beams with elastic properties that are periodically varying in space and time. Spatiotemporal modulation of the elastic properties breaks mechanical reciprocity and induces one-way propagation. We follow an analytic approach to characterize the non-reciprocal behavior of the structures by analyzing the symmetry breaking of the dispersion spectrum, which results in the formation of directional band gaps and produces shifts of the first Brillouin zone limits. This approach allows us to relate position and width of the directional band gaps to the modulation parameters. Moreover, we identify the critical values of the modulation speed to maximize the non-reciprocal effect. We numerically verify the theoretical predictions by using a finite element model of the modulated beams to compute the transient response of the structure. We compute the two-dimensional Fourier transform of the collected displacement fields to calculate numerical band diagrams, showing excellent agreement between theoretical and numerical dispersion diagrams.

  3. Orbital angular momentum in optical waves propagating through distributed turbulence.

    PubMed

    Sanchez, Darryl J; Oesch, Denis W

    2011-11-21

    This is the second of two papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. In the companion paper, it is shown that propagation through atmospheric turbulence can create non-trivial angular momentum. Here, we extend the result and demonstrate that this momentum is, at least in part, orbital angular momentum. Specifically, we demonstrate that branch points (in the language of the adaptive optic community) indicate the presence of photons with non-zero OAM. Furthermore, the conditions required to create photons with non-zero orbital angular momentum are ubiquitous. The repercussions of this statement are wide ranging and these are cursorily enumerated. PMID:22109489

  4. Orbital angular momentum in optical waves propagating through distributed turbulence.

    PubMed

    Sanchez, Darryl J; Oesch, Denis W

    2011-11-21

    This is the second of two papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. In the companion paper, it is shown that propagation through atmospheric turbulence can create non-trivial angular momentum. Here, we extend the result and demonstrate that this momentum is, at least in part, orbital angular momentum. Specifically, we demonstrate that branch points (in the language of the adaptive optic community) indicate the presence of photons with non-zero OAM. Furthermore, the conditions required to create photons with non-zero orbital angular momentum are ubiquitous. The repercussions of this statement are wide ranging and these are cursorily enumerated.

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

    PubMed Central

    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. PMID:21302985

  6. Effect of tube ovalling on pressure wave propagation speed.

    PubMed

    Anderson, A; Johnson, G R

    1990-01-01

    For physiological and other flows it is often assumed that the pressure pulse wave speed is given by the classic Moens-Korteweg expression and this may be used, for example, to assist in the determination of in vivo blood vessel wall incremental Young's modulus. A number of physical factors affecting the value of this wave speed have been reviewed in the literature, but the effect of slight ovalling of the tube cross-section is rarely mentioned. The analysis for a tube of elliptic cross-section shows that even a very small degree of ovalling can cause quite substantial reductions in Young mode wave propagation velocities compared with the classic Moens-Korteweg expression. Bending-induced changes in cross-section shape with internal pressure increase the apparent elasticity of the tube wall. Experimental confirmation is provided by waterhammer wave speed measurements in a copper tube that has been ovalled by coiling. Even though the Young mode is not dominant in this case, as it would be for a physiological case, the measured wave speed is quite clearly less than the Moens-Korteweg theory and it can be shown that the small degree of measured tube ovality explains this.

  7. 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

  8. 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).

  9. 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

  10. 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.

  11. Sources and propagation of atmospherical acoustic shock waves

    NASA Astrophysics Data System (ADS)

    Coulouvrat, François

    2012-09-01

    Sources of aerial shock waves are numerous and produce acoustical signals that propagate in the atmosphere over long ranges, with a wide frequency spectrum ranging from infrasonic to audible, and with a complex human response. They can be of natural origin, like meteors, lightning or volcanoes, or human-made as for explosions, so-called "buzz-saw noise" (BSN) from aircraft engines or sonic booms. Their description, modeling and data analysis within the viewpoint of nonlinear acoustics will be the topic of the present lecture, with focus on two main points: the challenges of the source description, and the main features of nonlinear atmospheric propagation. Inter-disciplinary aspects, with links to atmospheric and geo-sciences will be outlined. Detailed description of the source is very dependent on its nature. Mobile supersonic sources can be rotating (fan blades of aircraft engines) or in translation (meteors, sonic boom). Mach numbers range from transonic to hypersonic. Detailed knowledge of geometry is critical for the processes of boom minimization and audible frequency spectrum of BSN. Sources of geophysical nature are poorly known, and various mechanisms for explaining infrasound recorded from meteors or thunderstorms have been proposed. Comparison between recorded data and modeling may be one way to discriminate between them. Moreover, the nearfield of these sources is frequently beyond the limits of acoustical approximation, or too complex for simple modeling. A proper numerical description hence requires specific matching procedures between nearfield behavior and farfield propagation. Nonlinear propagation in the atmosphere is dominated by temperature and wind stratification. Ray theory is an efficient way to analyze observations, but is invalid in various situations. Nonlinear effects are enhanced locally at caustics, or in case of grazing propagation over a rigid surface. Absorption, which controls mostly the high frequency part of the spectrum contained

  12. 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.

  13. Obliquely propagating dust-acoustic waves in dense quantum magnetoplasmas

    SciTech Connect

    Khan, S. A.; Masood, W.; Siddiq, M.

    2009-01-15

    Two-dimensional, obliquely propagating nonlinear quantum dust-acoustic waves in dense magnetized plasmas are investigated on the basis of a quantum hydrodynamic model. In this regard, the Zakharov-Kuznetsov (ZK) equation is derived using the small amplitude approximation method. The extended hyperbolic tangent method is employed to obtain solitary and explosive solutions of the ZK equation. It is found that the quantum effects related to the Bohm potential, dust concentration, external magnetic field, and obliqueness significantly modify the amplitude and width of both solitary and explosive pulses. The relevance of the study to dense plasmas is also discussed.

  14. 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.

  15. Oblique propagation of nonlinear electrostatic waves in dense astrophysical magnetoplasmas

    SciTech Connect

    Masood, W.; Siddiq, M.; Rizvi, H.

    2011-10-15

    Nonlinear quantum ion-acoustic waves in dense dissipative as well as non-dissipative magnetized plasmas are investigated employing the quantum hydrodynamic model. In this regard, Zakharov Kuznetsov Burgers equation is derived in quantum plasmas, for the first time, using the small amplitude perturbation expansion method. The unique features of nonlinear electrostatic structures in pure electron-ion quantum magnetoplasma are highlighted and the parametric domain of the applicability of the model is unequivocally expressed. The present study may be useful to understand the nonlinear propagation characteristics of electrostatic shock and solitary structures in dense astrophysical systems where the quantum effects are expected to dominate.

  16. Millimeter-wave propagation measurements at the Ballistic Research Laboratory

    NASA Astrophysics Data System (ADS)

    Wallace, H. Bruce

    1988-05-01

    Results of measurements made with radars from 35 to 217 GHz of near-earth propagation in rain, fog, snow, and humidity are presented. The effects of water vapor are characterized by an attenuation coefficient that is a function of vapor pressure or absolute humidity. Backscatter contributes significantly to the adverse effect of rain on mm-wave radars because the droplet sizes become comparable to signal wavelengths. Path losses from fogs, haze, or clouds, are caused by both absorption and scattering by water droplets. Attenuation due to falling snow is difficult to link to and single characteristics.

  17. Propagating speed of primordial gravitational waves and inflation

    NASA Astrophysics Data System (ADS)

    Cai, Yong; Wang, Yu-Tong; Piao, Yun-Song

    2016-08-01

    We show that if the propagating speed of gravitational waves (GWs) gradually diminishes during inflation, the power spectrum of primordial GWs will be strongly blue, while that of the primordial scalar perturbation may be unaffected. We also illustrate that such a scenario is actually a disformal dual to the superinflation, but it does not have the ghost instability. The blue tilt obtained is 0

  18. Light wave propagation through a dilaton-Maxwell domain wall

    NASA Astrophysics Data System (ADS)

    Morris, J. R.; Schulze-Halberg, A.

    2015-10-01

    We consider the propagation of electromagnetic waves through a dilaton-Maxwell domain wall of the type introduced by Gibbons and Wells [G. W. Gibbons and C. G. Wells, Classical and Quantum Gravity 11, 2499 (1994)]. It is found that if such a wall exists within our observable Universe, it would be absurdly thick, or else have a magnetic field in its core which is much stronger than observed intergalactic fields. We conclude that it is highly improbable that any such wall is physically realized.

  19. Oblique propagation of nonlinear electrostatic waves in dense astrophysical magnetoplasmas

    NASA Astrophysics Data System (ADS)

    Masood, W.; Rizvi, H.; Siddiq, M.

    2011-10-01

    Nonlinear quantum ion-acoustic waves in dense dissipative as well as non-dissipative magnetized plasmas are investigated employing the quantum hydrodynamic model. In this regard, Zakharov Kuznetsov Burgers equation is derived in quantum plasmas, for the first time, using the small amplitude perturbation expansion method. The unique features of nonlinear electrostatic structures in pure electron-ion quantum magnetoplasma are highlighted and the parametric domain of the applicability of the model is unequivocally expressed. The present study may be useful to understand the nonlinear propagation characteristics of electrostatic shock and solitary structures in dense astrophysical systems where the quantum effects are expected to dominate.

  20. Obliquely propagating dust-acoustic waves in dense quantum magnetoplasmas

    NASA Astrophysics Data System (ADS)

    Khan, S. A.; Masood, W.; Siddiq, M.

    2009-01-01

    Two-dimensional, obliquely propagating nonlinear quantum dust-acoustic waves in dense magnetized plasmas are investigated on the basis of a quantum hydrodynamic model. In this regard, the Zakharov-Kuznetsov (ZK) equation is derived using the small amplitude approximation method. The extended hyperbolic tangent method is employed to obtain solitary and explosive solutions of the ZK equation. It is found that the quantum effects related to the Bohm potential, dust concentration, external magnetic field, and obliqueness significantly modify the amplitude and width of both solitary and explosive pulses. The relevance of the study to dense plasmas is also discussed.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  3. 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.

  4. Phase resolved near-field imaging of propagating waves in infrared tapered slot antennas

    NASA Astrophysics Data System (ADS)

    Florence, Louis A.; Kinzel, Edward C.; Olmon, Robert L.; Ginn, James C.; Raschke, Markus B.; Boreman, Glenn D.

    2012-11-01

    Tapered slot antennas (TSAs) consist of a planar non-resonant structure which couples incident radiation to a propagating waveguide mode. They are commonly used at microwave and radio frequencies because they are fundamentally broadband and have small profiles. Because of their planar layout and broadband response they have recently been scaled to infrared frequencies where they have advantages for sensing and energy harvesting. We use scattering-type scanning near-field optical microscopy (s-SNOM) to study the mode transformation of two types of TSA operating in the thermal infrared (λ0 = 10.6 μm) with respect to electric field amplitude and phase. The results agree well with simulation showing both the phase reversal across the tapered slot and the traveling of wave fronts along the tapered slot, yet they also reveal high sensitivity of device performance to inhomogeneities in the geometry or illumination. This study will aid future design and analysis of practical non-resonant antennas operating at optical and infrared frequencies.

  5. Planar channelling of relativistic electrons in half-wave silicon crystal and corresponding radiation

    NASA Astrophysics Data System (ADS)

    Takabayashi, Y.; Bagrov, V. G.; Bogdanov, O. V.; Pivovarov, Yu L.; Tukhfatullin, T. A.

    2016-07-01

    New experimental data on planar channeling of 255 MeV electrons in a 0.74 µm Si Half-Wave Crystal (HWC) obtained at SAGA-LS facility are presented. The computer simulation showed that the angular distribution of electrons after penetration through the HWC revealed the number of unknown before peculiarities is connected with specific electron trajectories in HWC. These specific trajectories lead to specific radiation, the properties of which are analyzed.

  6. High-Frequency Wave Propagation by the Segment Projection Method

    NASA Astrophysics Data System (ADS)

    Engquist, Björn; Runborg, Olof; Tornberg, Anna-Karin

    2002-05-01

    Geometrical optics is a standard technique used for the approximation of high-frequency wave propagation. Computational methods based on partial differential equations instead of the traditional ray tracing have recently been applied to geometrical optics. These new methods have a number of advantages but typically exhibit difficulties with linear superposition of waves. In this paper we introduce a new partial differential technique based on the segment projection method in phase space. The superposition problem is perfectly resolved and so is the problem of computing amplitudes in the neighborhood of caustics. The computational complexity is of the same order as that of ray tracing. The new algorithm is described and a number of computational examples are given, including a simulation of waveguides.

  7. Wave propagation in reconfigurable broadband gain metamaterials at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Fan, Yifeng; Nagarkoti, Deepak S.; Rajab, Khalid Z.; Hao, Yang; Zhang, Hao Chi; Cui, Tie Jun

    2016-05-01

    The wave dispersion characteristics for loop array-based metamaterials were analyzed, based on the general transmission line model of a one-dimensional host medium interacting with a chain of coupled loops. By relating the wave propagation constant and the effective parameters of the coupled host medium, we showed that an active medium embedded with non-Foster loaded loop array can be designed to exhibit broadband negative material parameters with positive gain. Accounting for all interactions, the stability of the active medium was investigated, further yielding necessary design specifications for the non-Foster loads. Subsequently, an experimental demonstration was provided to verify the theoretical analysis, showing that stable reconfigurable broadband gain metamaterials at microwave frequencies can be obtained with proper negative impedance converter design.

  8. 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.

  9. 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.

  10. Active elastic metamaterials for subwavelength wave propagation control

    NASA Astrophysics Data System (ADS)

    Chen, Y. Y.; Huang, G. L.

    2015-06-01

    Recent research activities in elastic metamaterials demonstrate a significant potential for subwavelength wave propagation control owing to their interior locally resonant mechanism. The growing technological developments in electro/magnetomechanical couplings of smart materials have introduced a controlling degree of freedom for passive elastic metamaterials. Active elastic metamaterials could allow for a fine control of material physical behavior and thereby induce new functional properties that cannot be produced by passive approaches. In this paper, two types of active elastic metamaterials with shunted piezoelectric materials and electrorheological elastomers are proposed. Theoretical analyses and numerical validations of the active elastic metamaterials with detailed microstructures are presented for designing adaptive applications in band gap structures and extraordinary waveguides. The active elastic metamaterial could provide a new design methodology for adaptive wave filters, high signal-to-noise sensors, and structural health monitoring applications.

  11. Laboratory Measurement of Guided Wave (Krauklis Wave) Propagation Within a Fluid-Saturated Fracture

    NASA Astrophysics Data System (ADS)

    Nakagawa, S.; Korneev, V. A.

    2013-12-01

    A fluid-saturated flat channel between two solid half-spaces (i.e. a fracture) is known to support a guided wave called the Krauklis wave. In the field, this wave can potentially be used to examine the size and connectivity of natural and hydraulically induced fractures from a borehole. Krauklis waves propagate primarily within the fluid part of a fracture, can have very low velocity and large attenuation, and are very dispersive at low frequencies. We conducted laboratory measurements of the velocity of Krauklis waves using analogue fracture models at frequencies below 1 kHz. The models consisted of (1) two concentric aluminum cylinders with a water-filled gap and (2) a pair of rectangular aluminum plates containing a thin water-filled gap (tri-layer mode). In the latter, the water was contained by an o-ring along the edge of the plates. The velocity of the waves propagating within the models was determined both from waveforms in the time domain measured along the wave path and from acoustic resonances in the system. The results indicated that the waves measured from the cylindrical model were not dispersive at frequencies below 400 Hz, with a phase velocity of ~250 m/s. In contrast, the tri-layer model exhibited strongly dispersive velocity at measured frequencies of 7.5 Hz-500 Hz, with the lowest phase velocity being ~14 m/s at 7.5 Hz. These measurements agree well with our theoretical model predictions.

  12. 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

  13. Propagation of elastic waves in hexagonal crystals with fiber texture

    NASA Astrophysics Data System (ADS)

    Yang, Liyong; Turner, Joseph A.

    2005-09-01

    Many cold-working processes for polycrystalline metals cause alignment of the grains with a single symmetry axis called fiber texture. The existence of a preferred orientation of the grains has a big influence on the propagation and scattering of ultrasonic waves, which are often used for materials inspection. Knowledge of the wave attenuation of such textured materials is of both theoretical and practical interest to nondestructive testing and materials characterization. In this presentation, the quantitative relations between fiber texture and wave attenuations of hexagonal crystals are presented. The texture is characterized by a Gaussian distribution function that contains a single parameter that governs the transition of the texture from statistically isotropic to fiber texture. Under this assumption, the materials of interest have a varying degree of transverse isotropy representatives of processing conditions. Simple expressions for the attenuations of the three modes of waves are given in a concise representation. Finally, numerical results are presented and discussed in terms of the directional, frequency, and texture dependence. The results presented are expected to improve the understanding of the microstructure evolution during thermomechanical processing. [Work supported by DOE.

  14. Experimental studies of fast wave propagation in DIII-D

    SciTech Connect

    Ikezi, H.; Pinsker, R.I.; Chiu, S.C.; deGrassie, J.S.

    1996-02-01

    Fast Alfv{acute e}n waves radiated from the phased array antenna in the DIII-D tokamak and used for heating and current drive are studied by employing a {dot {ital B}}-loop array mounted on the vacuum vessel wall. The wave propagation direction controlled by the antenna phasing is clearly observed. A small divergence of the rays arising from the anisotropic nature of the fast wave is found. Comparison with a ray tracing code confirms that the ray position calculated by the code is accurate up to at least one toroidal turn of the rays. Conservation of {ital Rk}{sub t} which is a basic assumption in computer codes is tested. Although the upshift of toroidal wavenumber {ital k}{sub t} at small major radius {ital R} is confirmed, {ital Rk}{sub {ital t}} is not well conserved. A mass density interferometer is demonstrated by employing the extraordinary fast wave. {copyright} {ital 1996 American Institute of Physics.}

  15. 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.

  16. 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. PMID:26518526

  17. 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.

  18. Links between detonation wave propagation and reactive flow models.

    SciTech Connect

    Swift, D. C.; White, S. J.

    2002-01-01

    An accurate reactive flow model is necessary to be able to predict the initiation properties of explosives by complicated shock structures, but a very fine the spatial resolution is needed in reactive flow to reproduce the detailed dynamics of a detonation wave. However, it is not often necessary to use a reactive flow model to simulate the motion of a fully-developed detonation wave. In many situations the same results can be obtained with a coarse computational mesh using programmed burn techniques. In the WBL model [Lambourn89,Swift93], an eikonal detonation wave propagates through a body of explosive at a speed which depends on the curvature of the wave. The model describes the motion of the leading shock of the detonation wave. Here we use the level set method for integrating the WBL equations in time [Collyer98,Bdzil93,Osher88,Aslam98]. This method is attractive because complicated detonation wave shapes can be represented simply. It was found possible to initialize the level set field by a set of source points derived from a reactive flow simulation, by taking 'trigger states' from the reactive flow. The level set scheme was generalized further to take account of motion of the material behind the detonation wave, allowing it to be used for simulations coupled with reactive flow, where detonation may propagate through preshocked and moving material. The modified level set scheme was implemented in 1D and 2D Lagrangian hydrocodes. Trial calculations were performed of initiation and detonation in the TATB-based explosive LX-17, using the Lee - Tarver model. A CJ detonation was simulated in order to verify that the modified level set algorithm operated correctly. The detonation speed was in very good agreement with the expected value. Single-shock initiation was simulated. The position - time history of the leading shock from the coupled model was in excellent agreement with full reactive flow; the pressure profiles were similar but not identical, because of the

  19. Role of Hydraulic Geometry in Flood Wave Propagation

    NASA Astrophysics Data System (ADS)

    Orlandini, S.

    2010-12-01

    The role of hydraulic geometry in flood wave propagation is investigated by using a diffusion wave model with inertial effects. Power function relationships W = a’Qb’ and kS = r’Qy’ are used to reproduce the at-a-station variations of water-surface width W and Gauckler-Strickler conductance coefficient kS (the inverse of Manning resistance coefficient) with flow discharge Q. Downstream variations of coefficients a’ and r’ are not considered in this study. The considered hydraulic geometry relationships are incorporated into a diffusion wave model in which the term (1 - Ve2), Ve being the Vedernikov number, multiplies the Hayami’s diffusivity Q/(2WS0), S0 being the channel bed slope. This mathematical model is solved numerically by using a matched artificial diffusivity method. Numerical experiments are carried out by evaluating peak attenuation and mean peak celerity of flood waves propagating along channel reaches characterized by coefficients a’ and r’ equal to the average values observed in natural rivers, by all the combinations of exponents b’ and y’ laying in the range 0-0.5, and by values of S0 laying in the range 0.000125-0.032. It is found that: (1) peak attenuation and mean peak celerity display the minimum values for b’ = 0.5 and y’ = 0, (2) for high values of y’, Ve displays values greater than 1 indicating physical instability of flood waves, and (3) around the condition b’ = 0 and y’ = 0, for high values of Q/W and low values of S0, the Peclet number Pe (evaluated over the channel reach length) displays values less than 2 indicating unrealistic hydraulic diffusion (more storage effects than those produced by a reservoir). The region of the plane b’y’ representing relevant flood waves lays therefore between the instability region Ve > 1, where unstable flood waves are physically possible but rarely observed in natural channels and not reproducible with the considered model, and the region of unrealistic diffusion Pe

  20. Numerical Homogenization of Jointed Rock Masses Using Wave Propagation Simulation

    NASA Astrophysics Data System (ADS)

    Gasmi, Hatem; Hamdi, Essaïeb; Bouden Romdhane, Nejla

    2014-07-01

    Homogenization in fractured rock analyses is essentially based on the calculation of equivalent elastic parameters. In this paper, a new numerical homogenization method that was programmed by means of a MATLAB code, called HLA-Dissim, is presented. The developed approach simulates a discontinuity network of real rock masses based on the International Society of Rock Mechanics (ISRM) scanline field mapping methodology. Then, it evaluates a series of classic joint parameters to characterize density (RQD, specific length of discontinuities). A pulse wave, characterized by its amplitude, central frequency, and duration, is propagated from a source point to a receiver point of the simulated jointed rock mass using a complex recursive method for evaluating the transmission and reflection coefficient for each simulated discontinuity. The seismic parameters, such as delay, velocity, and attenuation, are then calculated. Finally, the equivalent medium model parameters of the rock mass are computed numerically while taking into account the natural discontinuity distribution. This methodology was applied to 17 bench fronts from six aggregate quarries located in Tunisia, Spain, Austria, and Sweden. It allowed characterizing the rock mass discontinuity network, the resulting seismic performance, and the equivalent medium stiffness. The relationship between the equivalent Young's modulus and rock discontinuity parameters was also analyzed. For these different bench fronts, the proposed numerical approach was also compared to several empirical formulas, based on RQD and fracture density values, published in previous research studies, showing its usefulness and efficiency in estimating rapidly the Young's modulus of equivalent medium for wave propagation analysis.

  1. Causal theories of evolution and wave propagation in mathematical physics

    SciTech Connect

    Kranys, M. )

    1989-11-01

    There are still many phenomena, especially in continuum physics, that are described by means of parabolic partial differential equations whose solution are not compatible with the causality principle. Compatibility with this principle is required also by the theory of relativity. A general form of hyperbolic operators for the most frequently occurring linear governing equations in mathematical physics is written down. It is then easy to convert any given parabolic equation to the hyperbolic form without necessarily entering into the cause of the inadequacy of the governing equation. The method is verified on the well-known example of Timoshenko's correction of the Bernoulli-Euler-Rayleigh beam equation for flexural motion. The Love-Rayleigh fourth-order differential equations for the longitudinal and torsional wave propagation in the rod is generalized with this method. The hyperbolic version (not to mention others) of the linear Korteweg-deVries equation and of the telegraph equation governing electromagnetic wave propagation through relaxing material are given. Lagrangians of all the equations studied are listed. For all the reasons given the author believes the hyperbolic governing equations to be physically and mathematically more realistic and adequate.

  2. 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.

  3. 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.

  4. 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…

  5. 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…

  6. Propagation of Long Extensional Nonlinear Waves in a Hyper-Elastic Layer

    NASA Astrophysics Data System (ADS)

    Teymür, Mevlüt

    Propagation of small but finite amplitude waves in a nonlinear hyper-elastic plate of uniform thickness is considered. By employing a perturbation expansion, extensional waves are examined under the long wave limit. It is shown that the asymptotic wave field is governed by a Korteweg-DeVries (K-dV) equation. Then the propagation characteristics of the asymptotic waves are discussed via the well known solutions of the K-dV equation.

  7. Propagation of stationary Rossby waves in the Martian lower atmosphere

    NASA Astrophysics Data System (ADS)

    Ghosh, Priyanka; Thokuluwa, Ramkumar

    The Martian lower atmospheric (-1.5 km to 29.3 km) temperature, measured by radio occultation technique during the Mars Global Surveyor (MGS) mission launched by US in November 1996, at the Northern winter hemispheric latitude of about 63(°) N clearly shows a statistically significant (above 95 percent confidential level white noise) and strong 3.5-day oscillation during 1-10 January 2006. This strong signal occurs in the longitudinal sectors of 0-30(°) E and 190-230(°) E but statistically insignificant in almost all the other longitudes. This 180 degree separation between the two peaks of occurrence of strong 3.5 day oscillation indicates that this may be associated with zonal wave number 2 structure global scale wave. At the lowest height of -1.5 km, the power observed in the longitude of 0-30(°) E is 50 K (2) and it increased gradually to the maximum power of 130 K (2) at the height of 0.8 - 1.7 km. Above this height, the power decreased monotonously and gradually to insignificant level at the height of 3.7 km (20 K (2) ). This gradual decrease of power above the height of 1.7 km indicates that radiative damping (infra red cooling due to large abundance of CO _{2} molecules and dust particles) would have played an important role in the dissipation of waves. The height and longitudinal profiles of phase of the 3.5-day wave indicate that this wave is a vertically standing and eastward propagating planetary wave respectively. Since the statistically significant spectral amplitude occurs near the high topography structures, it seems that the wave is generated by flows over the topography. In the Northern winter, it is possible that the large gradient of temperature between the low and high latitudes would lead to flow of winds from the tropical to polar latitudes. Due to the Coriolis effect, this flow would in turn move towards the right and incite wave generation when the air flows over the high topographic structures. This lead to speculate that the observed 3

  8. 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.

  9. Anisotropic effects on ultrasonic guided waves propagation in composite bends.

    PubMed

    Yu, Xudong; Ratassepp, Madis; Rajagopal, Prabhu; Fan, Zheng

    2016-12-01

    Ultrasonic guided waves have proven to be attractive to the long-range testing of composite laminates. As complex-shaped composite components are increasingly incorporated in high-performance structures, understanding of both anisotropic and geometric effects on guided waves propagation is needed to evaluate their suitability for the non-destructive testing (NDT) of such complex structures. This paper reports the Semi-Analytical Finite Element (SAFE) simulations revealing the capability of energy confinement carried by two types of guided modes in 90° carbon fiber/epoxy (CF/EP) bends. Existence of the phenomenon is cross-validated by both 3D Finite Element (FE) modeling and experimental measurements. The physics of such energy trapping effect is explained in view of geometric variation and anisotropic properties, and the frequency effect on the extent of energy concentration is discussed. Finally, the feasibility of using such confined guided waves for rapid inspection of bent composite plate structures is also discussed. PMID:27518426

  10. 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)

  11. Love wave propagation in functionally graded piezoelectric material layer.

    PubMed

    Du, Jianke; Jin, Xiaoying; Wang, Ji; Xian, Kai

    2007-03-01

    An exact approach is used to investigate Love waves in functionally graded piezoelectric material (FGPM) layer bonded to a semi-infinite homogeneous solid. The piezoelectric material is polarized in z-axis direction and the material properties change gradually with the thickness of the layer. We here assume that all material properties of the piezoelectric layer have the same exponential function distribution along the x-axis direction. The analytical solutions of dispersion relations are obtained for electrically open or short circuit conditions. The effects of the gradient variation of material constants on the phase velocity, the group velocity, and the coupled electromechanical factor are discussed in detail. The displacement, electric potential, and stress distributions along thickness of the graded layer are calculated and plotted. Numerical examples indicate that appropriate gradient distributing of the material properties make Love waves to propagate along the surface of the piezoelectric layer, or a bigger electromechanical coupling factor can be obtained, which is in favor of acquiring a better performance in surface acoustic wave (SAW) devices.

  12. The propagation of sound waves in drill strings

    SciTech Connect

    Drumheller, D.S. ); Knudsen, S.D. )

    1995-04-01

    Deep wells are commonly drilled while steering the drill bit. The steering process is completely controlled by the drilling-rig operator. A key element of this procedure is the measurement and communication of navigation information from the bottom of the well to the operator. Pressure pulses modulated onto the flow of the drill fluid are now employed in some cases to communicate this information. However, data rates are only a few binary bits per second with this method. This drastically limits the quantity of data available to the operator. As an alternative method, elastic waves generated within the steel drill string can be used as a carrier signal to transmit data. The drill string is commonly assembled from 10-m segments of threaded pipe and forms a periodic structure. The elastic wavelengths of interest are shorter than this periodic length. Consequently, these waves undergo significant dispersion. This paper presents new data for the propagation of elastic waves in a 2-km drill string. The influence of aperiodicity in the drill string, rotation of the drill string, and noise levels are studied in detail. The data verify a method for reducing the attenuation of a carrier signal by a factor of 2.

  13. Coherence of acoustic modes propagating through shallow water internal waves

    NASA Astrophysics Data System (ADS)

    Rouseff, Daniel; Turgut, Altan; Wolf, Stephen N.; Finette, Steve; Orr, Marshall H.; Pasewark, Bruce H.; Apel, John R.; Badiey, Mohsen; Chiu, Ching-Sang; Headrick, Robert H.; Lynch, James F.; Kemp, John N.; Newhall, Arthur E.; von der Heydt, Keith; Tielbuerger, Dirk

    2002-04-01

    The 1995 Shallow Water Acoustics in a Random Medium (SWARM) experiment [Apel et al., IEEE J. Ocean. Eng. 22, 445-464 (1997)] was conducted off the New Jersey coast. The experiment featured two well-populated vertical receiving arrays, which permitted the measured acoustic field to be decomposed into its normal modes. The decomposition was repeated for successive transmissions allowing the amplitude of each mode to be tracked. The modal amplitudes were observed to decorrelate with time scales on the order of 100 s [Headrick et al., J. Acoust. Soc. Am. 107(1), 201-220 (2000)]. In the present work, a theoretical model is proposed to explain the observed decorrelation. Packets of intense internal waves are modeled as coherent structures moving along the acoustic propagation path without changing shape. The packets cause mode coupling and their motion results in a changing acoustic interference pattern. The model is consistent with the rapid decorrelation observed in SWARM. The model also predicts the observed partial recorrelation of the field at longer time scales. The model is first tested in simple continuous-wave simulations using canonical representations for the internal waves. More detailed time-domain simulations are presented mimicking the situation in SWARM. Modeling results are compared to experimental data.

  14. Wave propagation in a dynamic system of soft granular materials.

    PubMed

    Harada, Shusaku; Takagi, Shu; Matsumoto, Yoichiro

    2003-06-01

    The wave propagation in a dynamic system of soft elastic granules is investigated theoretically and numerically. The perturbation theory for simple fluids is applied to the elastic granular system in order to relate the elastic properties of individual particles with the "thermodynamic" quantities of the system. The properties of a piston-driven shock are derived from the obtained thermodynamic relations and the Rankine-Hugoniot relations. The discrete particle simulation of a piston-driven shock wave in a granular system is performed by the discrete element method. From theoretical and numerical results, the effect of the elastic properties of a particle on shock properties is shown quantitatively. Owing to the finite duration of the interparticle contact, the compressibility factor of the elastic granular system decreases in comparison with that of the hard-sphere system. In addition, the relation between the internal energy and the granular temperature changes due to the energy preserved with the elastic deformation of the particle. Consequently, the shock properties in soft particles are considerably different from those in the hard-sphere system. We also show the theoretical prediction of the speed of sound in soft particles and discuss the effect of the elasticity on an acoustic wave. PMID:16241219

  15. 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.

  16. 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.

  17. A ray tracing model of gravity wave propagation and breakdown in the middle atmosphere

    NASA Technical Reports Server (NTRS)

    Schoeberl, M. R.

    1985-01-01

    Lindzen (1981, 1984) has considered the effects of monochromatic, steady gravity waves propagating into the upper atmosphere. These waves reach such large amplitudes in the mesosphere that they become convectively unstable. The wave is effectively dissipated by the convection, and the pseudomomentum carried by the wave is transferred to the basic flow. The net effect is to accelerate the background flow to the phase speed of the breaking gravity wave. Schoeberl et al. (1983) have discussed modifications to Lindzen's parameterization. The present paper has the objective to develop a type of parameterization scheme for wave breaking that, in principle, can handle lateral wave propagation. Ray tracing is used to follow the gravity wave packets through varying wind conditions. The theory considered uses both the propagation properties of the wave packet and the concept of the conservation of wave action density to determine the local amplitude and position of the wave packet.

  18. 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

  19. The effect of random Alfven waves on the propagation of hydromagnetic waves in a finite-beta plasma

    NASA Technical Reports Server (NTRS)

    Hamabata, Hiromitsu; Namikawa, Tomikazu

    1990-01-01

    Using first-order smoothing theory, Fourier analysis and perturbation methods, the evolution equation of the wave spectrum as well as the nonlinear forces generated by random Alfven waves in a finite-beta plasma with phenomenological Landau-damping effects are obtained. The effect of microscale random Alfven waves on the propagation of large-scale hydromagnetic waves is also investigated by solving the mean-field equations. It is shown that parallel-propagating random Alfven waves are modulationally stable and that obliquely propagating random Alfven waves can be modulationally unstable when the energy of random waves is converted to slow magnetoacoustic waves that can be Landau-damped, providing a dissipation mechanism for the Alfven waves.

  20. 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.

  1. An updated model for millimeter wave propagation in moist air

    NASA Astrophysics Data System (ADS)

    Liebe, H. J.

    1985-10-01

    A practical atmospheric Millimeter-Wave Propagation Model is formulated that predicts attenuation, delay, and noise properties of moist air for frequencies up to 1000 GHz. Input variables are height distributions (0-30 km) of pressure, temperature, humidity, and suspended droplet concentration along an anticipated radio path. Spectroscopic data consists of more than 450 parameters describing local O2 and H2O absorption lines complemented by continuum spectra for dry air, water vapor, and hydrosols. For a model limited to frequencies below GHz, the number of spectroscopic parameters can be reduced to less than 200. Recent laboratory measurements at 138 GHz absolute attenuation rates for simulated air with water vapor pressures up to saturation allow the formulation of an improved, though empirical water vapor continuum. Model predictions are compared with selected (2.5-430 GHz) data from both laboratory and field experiments. In general, good agreement is obtained.

  2. A nonlinear model of ionic wave propagation along microtubules.

    PubMed

    Satarić, M V; Ilić, D I; Ralević, N; Tuszynski, Jack Adam

    2009-06-01

    Microtubules (MTs) are important cytoskeletal polymers engaged in a number of specific cellular activities including the traffic of organelles using motor proteins, cellular architecture and motility, cell division and a possible participation in information processing within neuronal functioning. How MTs operate and process electrical information is still largely unknown. In this paper we investigate the conditions enabling MTs to act as electrical transmission lines for ion flows along their lengths. We introduce a model in which each tubulin dimer is viewed as an electric element with a capacitive, inductive and resistive characteristics arising due to polyelectrolyte nature of MTs. Based on Kirchhoff's laws taken in the continuum limit, a nonlinear partial differential equation is derived and analyzed. We demonstrate that it can be used to describe the electrostatic potential coupled to the propagating localized ionic waves. PMID:19259657

  3. 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.

  4. Wave propagation in granular chains with local resonances

    NASA Astrophysics Data System (ADS)

    Bonanomi, Luca; Theocharis, Georgios; Daraio, Chiara

    2015-03-01

    We study wave propagation in a chain of spherical particles containing a local resonator. The resonant particles are made of an aluminum outer spherical shell and a steel inner mass connected by a polymeric plastic structure acting as a spring. We characterize the dynamic response of individual particles and the transmitted linear spectra of a chain of particles in contact. A wide band gap is observed both in theoretical and experimental results. We show the ability to tune the acoustic transmission by varying the contact interaction between particles. Higher driving amplitude leads to the generation of nonlinearities both in the response of a single particle and that of the whole chain. For a single resonant particle, we observe experimentally a resonant frequency downshift, which follows a complex nonlinear behavior. In the chain of particles, nonlinearity leads to the generation of nonlinear harmonics and the presence of localized modes inside the band gap.

  5. Variational structure of inverse problems in wave propagation and vibration

    SciTech Connect

    Berryman, J.G.

    1995-03-01

    Practical algorithms for solving realistic inverse problems may often be viewed as problems in nonlinear programming with the data serving as constraints. Such problems are most easily analyzed when it is possible to segment the solution space into regions that are feasible (satisfying all the known constraints) and infeasible (violating some of the constraints). Then, if the feasible set is convex or at least compact, the solution to the problem will normally lie on the boundary of the feasible set. A nonlinear program may seek the solution by systematically exploring the boundary while satisfying progressively more constraints. Examples of inverse problems in wave propagation (traveltime tomography) and vibration (modal analysis) will be presented to illustrate how the variational structure of these problems may be used to create nonlinear programs using implicit variational constraints.

  6. Converging spherical wave propagation in a hemispherical solid lens

    NASA Astrophysics Data System (ADS)

    Zhang, Yaoju; Ye, Xuehua; Chen, Junfeng

    2006-06-01

    The propagation of converging spherical waves through a hemispherical solid lens (HSL) is studied, and the multiple reflections inside the HSL are considered. It is found that the reflectivity and transmissivity have an oscillatory behaviour related to the optical radius of the HSL. When the refractive index of the HSL is smaller than that of the sample, the small mismatch in refractive indices is preferable for transmission-mode microscopy. But when the refractive index of the HSL is larger than that of the sample, the reflectivity increases rapidly as the mismatch in refractive indices and the converging angle of incident light increase, the larger mismatch and converging angle are useful for reflection-mode microscopy. The magnitude of the whole reflectivity and its modulation depth are strongly sensitive to the incident polarization, which is also discussed.

  7. Seismoelectric wave propagation numerical modelling in partially saturated materials

    NASA Astrophysics Data System (ADS)

    Warden, S.; Garambois, S.; Jouniaux, L.; Brito, D.; Sailhac, P.; Bordes, C.

    2013-09-01

    To better understand and interpret seismoelectric measurements acquired over vadose environments, both the existing theory and the wave propagation modelling programmes, available for saturated materials, should be extended to partial saturation conditions. We propose here an extension of Pride's equations aiming to take into account partially saturated materials, in the case of a water-air mixture. This new set of equations was incorporated into an existing seismoelectric wave propagation modelling code, originally designed for stratified saturated media. This extension concerns both the mechanical part, using a generalization of the Biot-Gassmann theory, and the electromagnetic part, for which dielectric permittivity and electrical conductivity were expressed against water saturation. The dynamic seismoelectric coupling was written as a function of the streaming potential coefficient, which depends on saturation, using four different relations derived from recent laboratory or theoretical studies. In a second part, this extended programme was used to synthesize the seismoelectric response for a layered medium consisting of a partially saturated sand overburden on top of a saturated sandstone half-space. Subsequent analysis of the modelled amplitudes suggests that the typically very weak interface response (IR) may be best recovered when the shallow layer exhibits low saturation. We also use our programme to compute the seismoelectric response of a capillary fringe between a vadose sand overburden and a saturated sand half-space. Our first modelling results suggest that the study of the seismoelectric IR may help to detect a sharp saturation contrast better than a smooth saturation transition. In our example, a saturation contrast of 50 per cent between a fully saturated sand half-space and a partially saturated shallow sand layer yields a stronger IR than a stepwise decrease in saturation.

  8. Analyses of Impedance Microstructure and Wave Propagation Characteristics in Rocks

    NASA Astrophysics Data System (ADS)

    Prasad, M.; Mukerji, T.

    2002-12-01

    Seismic methods are our primary tools to image subsurface structures and to derive information about microstructural properties at subsurface that are pertinent to exploration. However, velocity - physical property transforms are mostly empirical or qualitative in nature, mainly because microstructural descriptions are qualitative. Although, sedimentary systems produce distinctive textures that influence physical properties and seismic signatures, these textures are not quantified in terms comparable to seismic. We present a method to quantify microsctructure in terms of acoustic impedance and show how these microstructural impedance maps can be used to analyze wave propagation characteristics in rocks. Using image analyses techniques, the texture of the calibrated scanned images is quantified by spatial autocorrelation functions and binary morphological operations. Parametric modeling of the empirical autocorrelation functions is used to estimate the textural anisotropy. We quantify microstructural impedance anisotropy and compare these textural maps to ultrasonic velocity anisotropy measurements. Inclusion based effective medium theory is used to upscale the impedances at the microstructural scale to the core plug scale. In the example of optically opaque kerogen-rich shales, we find that 1. Acoustic impedance in kerogen shales increases with shale maturity, 2. Impedance measured on a micrometer scale and centimeter scale match well, indicating that seismic wave propagation are controlled by the microtexture 3. With increasing maturity, there is a transition from kerogen supported to grain supported framework We thank the Fraunhofer Institute for Nondestructive Testing (IZfP) for use of AM facilities, Walter Arnold (IZfP) for discussions about acoustic microscopy, ARCO and SRB Project for support. This work was performed under the auspices of National Science Foundation (Grant No. EAR 0074330) and Department of Energy (Award No. DE-FC26-01BC15354).

  9. Radio-wave propagation for space communications systems

    NASA Astrophysics Data System (ADS)

    Ippolito, L. J.

    1981-02-01

    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.

  10. 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.

  11. Topology-based hexahedral regular meshing for wave propagation

    NASA Astrophysics Data System (ADS)

    Fousse, Allan; Bertrand, Yves; Rodrigues, Dominique

    2000-10-01

    Numeric simulations allow the study of physical phenomenon that are impossible or difficult to realize in the real world. As an example, it is not conceivable to cause an atomic explosion or an earthquake for exploring the effects on a building or a flood barrier. To be realistic, this kind of simulation (waves propagation), must take into account all the characteristics of the domain where it takes place, and more particularly the tri-dimensional aspect. Therefore, numericians need not only a three-dimensional model of the domain, but also a meshing of this domain. In the case we use finite differences based methods, this meshing must be hexahedral and regular. Moreover, new developments on the numerical propagation code provides tools for using meshes that interpolate the interior subdivisions of the domain. However, the manual generation of this kind of meshing is a long and difficult process. This is why to improve and simplify this work, we propose a semi-automatic algorithm based on a block subdivision. It makes use of the dissociation between the geometrical and topological aspects. Indeed, with our topological model a regular hexahedral meshing is far easier to generate. This meshing geometry can be supplied by a geometric model, with reconstruction, interpolation or parameterization methods, but it is anyway completely guided by the topological model. The result is a software presently used by the Commissariat a` l'Energie Atomique in several full-size studies, and notably for the framework of the Comprehensive Test Ban Treaty.

  12. The analysis of optical wave beams propagation in lens systems

    NASA Astrophysics Data System (ADS)

    Kazakov, I.; Mosentsov, S.; Moskaletz, O.

    2016-08-01

    In this paper some aspects of the formation and propagation of optical wave beams in lens systems were considered. As an example, the two-lens optical information processing system was considered. Analysis of the two-lens optical circuit has been made with a systems approach perspective. As part of the radio-optical analogies had been applied certain provisions of the theory of dynamical systems to the spatial optical system. The lens system is represented as a simple series-connected optical elements with known spatial impulse response. General impulse response of such a system has been received, as well as consider some special cases of the impulse response. The question of the relationship between the parameters and the size of the input aperture lenses for undistorted transmission of the optical signal has been considered. Analysis of the energy loss resulting from the finite aperture of the lens. It's based on an assessment of the fraction of radiation that propagates beyond the lens. Analysis showed that the energy losses depend explicitly on the following parameters: radiation wavelength, distance between input aperture and lens, and ratio of the input aperture and lens aperture. With the computer help simulation the dependence of losses was shown on the above parameters

  13. Annual report 1992/93, FOA 38. Radio systems and wave propagation

    NASA Astrophysics Data System (ADS)

    Mildh, I. M.

    1994-01-01

    The main objective of the division of Radio Systems and Wave Propagation is to carry out research and development in the field of secure and robust radio communications for Sweden's national defense. This is the Annual Report for fiscal year 1992/93 of the Division of Radio Systems and Wave Propagation. The division is responsible for research and development of secure radio communication for information transmission. We are also responsible for wave propagation research within a frequency range from LF to SHF. We carry out applied research in fields like antijamming systems, modulation, error correcting codes, wave propagation and digital signal processing. The wave propagation research is carried out by basic research so the demands from new techniques and new radio systems for accurate propagation models can be achieved.

  14. 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.

  15. Study of performance and propagation characteristics of wire and planar structures around human body.

    PubMed

    Aroul, A L Praveen; Bhatia, Dinesh

    2011-01-01

    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 planar structures operating at ISM frequency band of 2.40-2.50 GHz in the proximity of human body.

  16. 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

    2012-05-01

    The arbitrary control of electromagnetic waves is a key aim of photonic research. Although, for example, the control of freely propagating waves (PWs) 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. PMID:22466746

  17. 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.

  18. CONDITIONS FOR TRANSVERSE WAVES PROPAGATION ALONG THIN MAGNETIC FLUX TUBES ON THE SUN

    SciTech Connect

    Lopin, Igor; Nagorny, Ivan

    2013-09-10

    The propagation of kink waves in the thin gravity stratified flux tubes with a generalized magnetic field distribution model is considered in cylindrical geometry. The new kink wave equations for both wave variables are obtained. It is shown that the inclusion of the radial component of an unperturbed tube magnetic field sufficiently transforms the conditions for the propagation of transverse waves. It is demonstrated that, for the models of isothermal and polytropic atmosphere in the tube and its environment, the propagation of kink waves along thin magnetic flux tubes is cutoff-free.

  19. Nonlinear interaction of near-planar TS waves and longitudinal vortices in boundary-layer transition

    NASA Technical Reports Server (NTRS)

    Smith, F. T.

    1988-01-01

    The nonlinear interactions that evolve between a planar or nearly planar Tollmien-Schlichting (TS) wave 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 wave 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 wave 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.

  20. 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.

  1. The effect of load on guided wave propagation.

    PubMed

    Chen, Feng; Wilcox, Paul D

    2007-12-01

    The motivation for this work is the development of load measurement techniques based on the velocity of propagating guided waves in structural members such as cable and rail. A finite element technique for modelling the dispersion characteristics of guided waves in a waveguide of arbitrary cross section subjected to axial load is presented. The results from the FE model are compared to results obtained from a simple Euler-Bernoulli beam model. A dimensionless measure of the sensitivity of phase and group velocity to load is defined as the fractional change in velocity divided by the applied strain. At frequency waveguide-characteristic-dimension products (fd) of greater than around 1 for phase velocity and 5 for group velocity the sensitivity to strain levels likely to be encountered in engineering materials is strain independent (indicating that the change in velocity is proportional to strain) and decreases with increasing frequency. In this fd range, phase velocity increases under tensile loading and group velocity decreases. For waveguides with simple cross sections, such as plates and circular rods, it is shown that the Euler-Bernoulli beam model provides acceptable results over the majority of the fd range where there is measurable sensitivity to load. However, for waveguides with more complex cross sections such as rail, the Euler-Bernoulli beam model is less satisfactory. In particular, it does not predict the subtleties of the sensitivity of certain modes at high frequencies, nor any sensitivity for the torsional fundamental mode. PMID:17904605

  2. Numerical Simulation of Shock Wave Propagation in Fractured Cortical Bone

    NASA Astrophysics Data System (ADS)

    Padilla, Frédéric; Cleveland, Robin

    2009-04-01

    Shock waves (SW) are considered a promising method to treat bone non unions, but the associated mechanisms of action are not well understood. In this study, numerical simulations are used to quantify the stresses induced by SWs in cortical bone tissue. We use a 3D FDTD code to solve the linear lossless equations that describe wave propagation in solids and fluids. A 3D model of a fractured rat femur was obtained from micro-CT data with a resolution of 32 μm. The bone was subject to a plane SW pulse with a peak positive pressure of 40 MPa and peak negative pressure of -8 MPa. During the simulations the principal tensile stress and maximum shear stress were tracked throughout the bone. It was found that the simulated stresses in a transverse plane relative to the bone axis may reach values higher than the tensile and shear strength of the bone tissue (around 50 MPa). These results suggest that the stresses induced by the SW may be large enough to initiate local micro-fractures, which may in turn trigger the start of bone healing for the case of a non union.

  3. Ultrasonic wave propagation in two-phase media: Spherical inclusions

    NASA Technical Reports Server (NTRS)

    Fu, L. S.; Sheu, Y. C.

    1983-01-01

    The scattering theory, recently developed via the extended method of equivalent inclusion, is used to study the propagation of time-harmonic waves 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 waves 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.

  4. Modeling of weak blast wave propagation in the lung.

    PubMed

    D'yachenko, A I; Manyuhina, O V

    2006-01-01

    Blast injuries of the lung are the most life-threatening after an explosion. The choice of physical parameters responsible for trauma is important to understand its mechanism. We developed a one-dimensional linear model of an elastic wave propagation in foam-like pulmonary parenchyma to identify the possible cause of edema due to the impact load. The model demonstrates different injury localizations for free and rigid boundary conditions. The following parameters were considered: strain, velocity, pressure in the medium and stresses in structural elements, energy dissipation, parameter of viscous criterion. Maximum underpressure is the most suitable wave parameter to be the criterion for edema formation in a rabbit lung. We supposed that observed scattering of experimental data on edema severity is induced by the physiological variety of rabbit lungs. The criterion and the model explain this scattering. The model outlines the demands for experimental data to make an unambiguous choice of physical parameters responsible for lung trauma due to impact load.

  5. Analytical theory of wave propagation through stacked fishnet metamaterials.

    PubMed

    Marqués, R; Jelinek, L; Mesa, F; Medina, F

    2009-07-01

    This work analyzes the electromagnetic wave propagation 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-wave 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.

  6. 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/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://hdl.handle.net/2060/19930018539','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930018539"><span id="translatedtitle">Broadband millimeter-<span class="hlt">wave</span> GaAs transmitters and receivers using <span class="hlt">planar</span> bow-tie antennas</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Konishi, Y.; Kamegawa, M.; Case, M.; Yu, R.; Rodwell, M. J. W.; York, R. A.; Rutledge, D. B.</p> <p>1992-01-01</p> <p>We report broadband monolithic transmitters and receivers IC's for mm-<span class="hlt">wave</span> electromagnetic measurements. The IC's use nonlinear transmission lines (NLTL) and sampling circuits as picosecond pulse generators and detectors. The pulses are radiated and received by <span class="hlt">planar</span> monolithic bow-tie antennas, collimated with silicon substrate lenses and off-axis parabolic reflectors. Through Fourier transformation of the received pulse, 30-250 GHz free space gain-frequency measurements are demonstrated with an accuracy approximately = 0.17 dB, RMS.</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/2015JSV...339..196M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSV...339..196M"><span id="translatedtitle">A symplectic analytical <span class="hlt">wave</span> based method for the <span class="hlt">wave</span> <span class="hlt">propagation</span> and steady state forced vibration of rectangular thin plates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Yongbin; Zhang, Yahui; Kennedy, David</p> <p>2015-03-01</p> <p>A semi-analytical method is used to investigate the <span class="hlt">wave</span> <span class="hlt">propagation</span> characteristics and steady state forced vibration response for rectangular thin plates. By way of a rigorous but simple derivation, the governing differential equations for transverse vibration of rectangular thin plates are first converted into Hamiltonian canonical equations. Following the method of separation of variables, a symplectic eigenproblem is formed whose solution gives analytically the dispersion equation and the <span class="hlt">wave</span> mode shape. Using the <span class="hlt">wave</span> modes, i.e. the <span class="hlt">wave</span> <span class="hlt">propagation</span> parameters and <span class="hlt">wave</span> shapes, and combining the directly excited <span class="hlt">waves</span>, the <span class="hlt">wave</span> <span class="hlt">propagation</span> within the plate and the <span class="hlt">wave</span> reflection at the boundary, the forced response of the plate can be computed in the <span class="hlt">wave</span> domain with high precision and high efficiency. The present method is based on the basic elasticity equations of the plate, and can give the symplectic analytical solutions for the <span class="hlt">wave</span> modes for any combination of simple boundary conditions along the plate edges. The present method eliminates the limitation of the traditional analytical <span class="hlt">wave</span> <span class="hlt">propagation</span> method which can only obtain <span class="hlt">wave</span> modes for plates with two opposite edges simply supported. In contrast to numerical <span class="hlt">wave</span> <span class="hlt">propagation</span> methods, the present method provides symplectic analytical solutions for the <span class="hlt">wave</span> modes, and hence the computations are of high precision and well conditioned. Also, continuously distributed external forces can be easily considered. In the numerical examples, the <span class="hlt">wave</span> <span class="hlt">propagation</span> characteristics are analyzed for plates with three different combinations of boundary conditions, i.e. with two opposite edges either both simply supported, or both clamped, or one simply supported and the other clamped. The steady state forced responses are also computed for plates excited by point forces, as well as for line and area distributed forces, for the three combinations of boundary conditions. Comparison of the present results with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V13H..02D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V13H..02D"><span id="translatedtitle">Impulsive <span class="hlt">Wave</span> <span class="hlt">Propagation</span> within Magmatic Conduits with Axial Symmetry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>De Negri Leiva, R. S.; Arciniega-Ceballos, A.; Scheu, B.; Dingwell, D. B.; Sanchez-Sesma, F. J.</p> <p>2013-12-01</p> <p>We implemented Trefftz's method to simulate <span class="hlt">wave</span> <span class="hlt">propagation</span> in a fluid-solid system aimed to represent a magmatic conduit. Assuming axial symmetry, a set of multipoles is used to build a complete system of <span class="hlt">wave</span> functions for both the solid and the fluid. These functions are solutions of the elastodynamic equations that govern the motions in the fluid and the solid, respectively. The conduit can be closed or open and the exterior elastic domain may be unlimited or with an exterior boundary. In order to find the functions coefficients, boundary conditions (null shear and continuity of pressures and normal velocities) are satisfied in the least squares sense. The impulsive nature of the source is considered using Fourier analysis. Despite the simplicity of the formulation our results display a rich variety of behaviors. In fact, for a uniform infinite cylinder we reproduced the analytical solution. Moreover, this approach allows establishing some important effects of conduit geometry, including changes of sections. Lateral effects and bump resonances are well resolved. We compared our numerical calculations with results obtained from experimental simulations of volcanic explosions in which rapid depressurization induces fragmentation of volcanic rocks. These experiments are performed within a shock-tube apparatus at room temperature and various pressures using Argon (Ar) gas, particles and pumice samples of different porosities, from Popocatepetl volcano. The mechanical system is well characterized and the dynamics of the explosive process is monitored with high precision piezoelectric sensors located at the pipe surface. The combination of analytical and experimental approaches is very useful to understand the seismic <span class="hlt">wave</span> field of volcanic conduit dynamics.</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('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('https://www.ncbi.nlm.nih.gov/pubmed/18079827','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18079827"><span id="translatedtitle">Vector-based plane-<span class="hlt">wave</span> spectrum method for the <span class="hlt">propagation</span> of cylindrical electromagnetic fields.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shi, S; Prather, D W</p> <p>1999-11-01</p> <p>We present a vector-based plane-<span class="hlt">wave</span> spectrum (VPWS) method for efficient <span class="hlt">propagation</span> of cylindrical electromagnetic fields. In comparison with electromagnetic <span class="hlt">propagation</span> integrals, the VPWS method significantly reduces time of <span class="hlt">propagation</span>. Numerical results that illustrate the utility of this method are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014HEDP...11...75G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014HEDP...11...75G"><span id="translatedtitle">Spatially-resolved X-ray scattering measurements of a <span class="hlt">planar</span> blast <span class="hlt">wave</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gamboa, E. J.; Keiter, P. A.; Drake, R. P.; Falk, K.; Montgomery, D. S.; Benage, J. F.</p> <p>2014-06-01</p> <p>We present X-ray scattering measurements characterizing the spatial temperature and ionization profile of a blast <span class="hlt">wave</span> driven in a near-solid density foam. Several-keV X-rays scattered from a laser-driven blast <span class="hlt">wave</span> in a carbon foam. We resolved the scattering in high resolution in space and wavelength to extract the plasma conditions along the <span class="hlt">propagation</span> direction of the blast <span class="hlt">wave</span>. We infer temperatures of 20-40 eV and ionizations of 2-4 in the shock and rarefaction regions of the blast <span class="hlt">wave</span>. This range of measured ionization states allows for a detailed comparison between different models for the bound-free scattering. FLYCHK simulations of the temperature-ionization balance generally agree with the experimental values in the shocked region while consistently underestimating the ionization in the rarefaction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2720971','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2720971"><span id="translatedtitle">Critical scale of <span class="hlt">propagation</span> influences dynamics of <span class="hlt">waves</span> in a model of excitable medium</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Starobin, Joseph M; Danford, Christopher P; Varadarajan, Vivek; Starobin, Andrei J; Polotski, Vladimir N</p> <p>2009-01-01</p> <p>Background Duration and speed of <span class="hlt">propagation</span> of the pulse are essential factors for stability of excitation <span class="hlt">waves</span>. We explore the <span class="hlt">propagation</span> of excitation <span class="hlt">waves</span> resulting from periodic stimulation of an excitable cable to determine the minimal stable pulse duration in a rate-dependent modification of a Chernyak-Starobin-Cohen reaction-diffusion model. Results Various pacing rate dependent features of <span class="hlt">wave</span> <span class="hlt">propagation</span> were studied computationally and analytically. We demonstrated that the complexity of responses to stimulation and evolution of these responses from stable <span class="hlt">propagation</span> to <span class="hlt">propagation</span> block and alternans was determined by the proximity between the minimal level of the recovery variable and the critical excitation threshold for a stable solitary pulse. Conclusion These results suggest that critical <span class="hlt">propagation</span> of excitation <span class="hlt">waves</span> determines conditions for transition to unstable rhythms in a way similar to unstable cardiac rhythms. Established conditions were suitably accurate regardless of rate dependent features and the magnitude of the slopes of restitution curves. PMID:19589165</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://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/2015JPhD...48J5301L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JPhD...48J5301L"><span id="translatedtitle">Ultrathin <span class="hlt">planar</span> chiral metasurface for controlling gradient phase discontinuities of circularly polarized <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>Liu, Yahong; Zhou, Xin; Song, Kun; Wang, Mei; Zhao, Xiaopeng</p> <p>2015-09-01</p> <p>We develop a gradient phase discontinuities ultrathin <span class="hlt">planar</span> metasurface based on chiral branched gammadion structure (CBGS) that provides extreme control of electromagnetic wavefronts across single-sheet design. The introduction of the branch can provide antiparallel magnetic moment, which tunes the chirality of the CBGS. In the CBGS metasurface, the transmission phase of a circularly polarized <span class="hlt">wave</span> can be varied from  -180° to +180°. We experimentally demonstrate a beam-refracting CBGS metasurface with refracting a normally incident plane <span class="hlt">wave</span> to an angle of 17°. The performances of the proposed metasurface at oblique incidence are also presented. The CBGS metasurface can find a wide range of applications over the entire electromagnetic spectrum including single-surface lenses, fully controlling light in direction, and polarization controlling devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9816E..0DK','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9816E..0DK"><span id="translatedtitle">Sol-gel derived optical waveguide films: technological platform for development of <span class="hlt">planar</span> evanescent <span class="hlt">wave</span> sensors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Karasiński, Paweł</p> <p>2015-12-01</p> <p>Plane evanescent <span class="hlt">wave</span> sensors are being developed for over thirty years. However, their full development is somehow limited by the lack of relatively cheap and stable waveguide layers of high refractive index, low optical losses and at the same time resistance to the impact of chemical substances. The paper involves waveguide layers SiO2:TiO2 of high refractive index (˜1.81) satisfying these criteria, fabricated via sol-gel method and dip-coating technique. The parameters of the waveguide layers SiO2:TiO2 were determined using elipsometric and spectrophotometric methods. The presented waveguide layers have excellent optical properties and are suitable for the application in the <span class="hlt">planar</span> evanescent <span class="hlt">wave</span> sensors technology. For the best waveguide SiO2:TiO2 layers, the obtained level of optical loss was below 0.2 dB/cm.</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('http://www.ncbi.nlm.nih.gov/pubmed/27367122','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27367122"><span id="translatedtitle">Tunable dual-band asymmetric transmission for circularly polarized <span class="hlt">waves</span> with graphene <span class="hlt">planar</span> chiral metasurfaces.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Zhancheng; Liu, Wenwei; Cheng, Hua; Chen, Shuqi; Tian, Jianguo</p> <p>2016-07-01</p> <p>The asymmetric transmission effect has attracted great interest due to its wide modern optical applications. In this Letter, we present the underlying theory, the design specifications, and the simulated demonstration of tunable dual-band asymmetric transmission for circularly polarized <span class="hlt">waves</span> with a graphene <span class="hlt">planar</span> chiral metasurface. The spectral position of the asymmetric peak is linearly dependent on the Fermi energy and can be controlled by changing the Fermi energy. The success of tunable dual-band asymmetric transmission can be attributed to the enantiomerically sensitive plasmonic excitations of the graphene metasurface. This work offers a further step in developing tunable asymmetric transmission of circularly polarized <span class="hlt">waves</span> for applications in detectors and other polarization-sensitive electromagnetic devices. PMID:27367122</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/cgi-bin/nph-data_query?bibcode=2016EGUGA..1814120S&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..1814120S&link_type=ABSTRACT"><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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21251355','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21251355"><span id="translatedtitle"><span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Exponentially Varying Cross-Section Rods and Vibration Analysis</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Nikkhah-Bahrami, Mansour; Loghmani, Masih; Pooyanfar, Mostafa</p> <p>2008-09-01</p> <p>In this paper vibration as <span class="hlt">propagating</span> <span class="hlt">waves</span> is used to calculate frequencies of exponentially varying cross-section rods with various boundary conditions. From <span class="hlt">wave</span> standpoint, vibrations <span class="hlt">propagate</span>, reflect and transmit in structures. The <span class="hlt">propagation</span> and reflection matrices are combined to provide a concise and systematic approach to free longitudinal vibration analysis of exponentially varying cross-section rods. The results are compared with another method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21282120','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21282120"><span id="translatedtitle"><span class="hlt">Wave</span> amplification by a relativistic electron beam in a <span class="hlt">planar</span> electrostatic system with sinusoidal-ripple boundary</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zhang Shichang</p> <p>2009-09-15</p> <p>Primary study is devoted to the amplification mechanism of electromagnetic fast <span class="hlt">wave</span> by a relativistic electron beam in a <span class="hlt">planar</span> electrostatic system, where the superplate of two parallel metallic plates is corrugated with sinusoidal ripples and connected to a negative voltage, while the subplate is smooth and grounded. In the system the electrostatic field governs the electrons to move along approximately sinusoidal trajectories and pumps the kinetic energy of electrons to the <span class="hlt">wave</span>. Under exclusion of the space-charge <span class="hlt">wave</span> effect and the Smith-Purcell effect, the fast <span class="hlt">wave</span> gets relativistic Doppler upshift frequency and gain by extracting energy from a sheet electron beam, which is very similar to that in a free-electron laser pumped by a magnetostatic wiggler. Formulas derived and numerical analysis indicate that the amplification mechanism of <span class="hlt">wave</span> pumped by the <span class="hlt">planar</span> electrostatic system with sinusoidal ripples is favorable for a mildly relativistic electron beam to generate terahertz <span class="hlt">wave</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016DPS....4820302S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016DPS....4820302S"><span id="translatedtitle">On the Extraordinary <span class="hlt">Propagation</span> of the Janus 2:1 Density <span class="hlt">Wave</span>: Synergy between Density <span class="hlt">Waves</span> and Viscous Overstability</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stewart, Glen R.; Albers, Nicole; Esposito, Larry W.</p> <p>2016-10-01</p> <p>The effective damping produced by particle collisions prevents most spiral density <span class="hlt">waves</span> in Saturn's rings from <span class="hlt">propagating</span> more than about 100 km from their resonance location. The Janus 2:1 density <span class="hlt">wave</span> defies the usual behavior and appears to alternatively grow and decay in amplitude repeatedly as it <span class="hlt">propagates</span> into regions of larger mean optical depth before finally disappearing over 500 km from the resonance location. Borderies et al. (1985) suggested that the effective viscous coefficients in dense rings might lead to <span class="hlt">wave</span> growth rather than damping. Salo et al. (2001) used N-body simulations to constrain the surface density dependence of the shear and bulk viscosity in the rings and applied them to the study of axisymmetric viscous overstable <span class="hlt">waves</span>. We modify the formalism used by Latter and Ogilvie (2009) to model the nonlinear <span class="hlt">propagation</span> of viscous overstable <span class="hlt">waves</span> and apply it to model the <span class="hlt">propagation</span> of the Janus 2:1 density <span class="hlt">wave</span>. Normal optical depth profiles obtained from Cassini UVIS observations of stellar occultations are used to constrain the mean optical depth variation with ring radius as well as the variation of the <span class="hlt">wave</span> amplitude. We find that the viscous overstability can indeed explain how the <span class="hlt">wave</span> amplitude can alternately grow and decay repeatedly as the <span class="hlt">wave</span> <span class="hlt">propagates</span> into higher optical depth regions. Detailed modeling of the Janus 2:1 density <span class="hlt">wave</span> profile should allow us to place new constraints on the viscous properties of Saturn's inner B ring.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSemi..35e4006J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSemi..35e4006J"><span id="translatedtitle"><span class="hlt">Planar</span> Schottky varactor diode and corresponding large signal model for millimeter-<span class="hlt">wave</span> applications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jie, Huang; Qian, Zhao; Hao, Yang; Junrong, Dong; Haiying, Zhang</p> <p>2014-05-01</p> <p>A GaAs-based <span class="hlt">planar</span> Schottky varactor diode (PSVD) is successfully developed to meet the demand of millimeter-<span class="hlt">wave</span> harmonic generation. Based on the measured S-parameter, I-V and C-V characteristics, an accurate and reliable extraction method of the millimeter-<span class="hlt">wave</span> large signal equivalent circuit model of the PSVD is proposed and used to extract the model parameters of two PSVDs with Schottky contact areas of 160 μm2 and 49 μm2, respectively. The simulated S-parameter, I-V and C-V performances of the proposed physics-based model are in good agreement with the measured one over the frequency range from 0.1 to 40 GHz for wide operation bias range from -10 to 0.6 V for these two PSVDs. The proposed equivalent large signal circuit model of this PSVD has been proven to be reliable and can potentially be used to design microwave circuits., <span class="hlt">planar</span> Schottky varactor diode</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983STIN...8412416S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983STIN...8412416S"><span id="translatedtitle">Initial decay of flow properties of <span class="hlt">planar</span>, cylindrical and spherical blast <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>Sadek, H. S. I.; Gottlieb, J. J.</p> <p>1983-10-01</p> <p>Analytical expressions are presented for the initial decay of all major flow properties just behind <span class="hlt">planar</span>, cylindrical, and spherical shock <span class="hlt">wave</span> fronts whose trajectories are known as a function of either distance versus time or shock overpressure versus distance. These expressions give the time and/or distance derivatives of the flow properties not only along constant time and distance lines but also along positive and negative characteristic lines and a fluid-particle path. Conventional continuity, momentum and energy equations for the nonstationary motion of an inviscid, non-heat conducting, compressible gas are used in their derivation, along with the equation of state of a perfect gas. All analytical expressions are validated by comparing the results to those obtained indirectly from known self-similar solutions for <span class="hlt">planar</span>, cylindrical and spherical shock-<span class="hlt">wave</span> flows generated both by a sudden energy release and by a moving piston. Futhermore, time derivatives of pressure and flow velocity are compared to experimental data from trinitrotoluene (TNT), pentolite, ammonium nitrate-fuel oil (ANFO) and propane-oxygen explosions, and good agreement is obtained.</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('http://adsabs.harvard.edu/abs/1994PhFl....6.2177S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994PhFl....6.2177S"><span id="translatedtitle">On one-dimensional <span class="hlt">planar</span> and nonplanar shock <span class="hlt">waves</span> in a relaxing gas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharma, V. D.; Radha, Ch.</p> <p>1994-06-01</p> <p>The paper examines the evolutionary behavior of shock <span class="hlt">waves</span> of arbitrary strength <span class="hlt">propagating</span> through a relaxing gas in a duct with spatially varying cross section. An infinite system of transport equations, governing the strength of a shock <span class="hlt">wave</span> and the induced discontinuities behind it, are derived in order to study the kinematics of the shock front. The infinite system of transport equations, when subjected to a truncation approximation, provides an efficient system of only finite number of ordinary differential equations describing the shock <span class="hlt">propagation</span> problem. The analysis, which accounts for the dynamical coupling between the shock fronts and the flow behind them, describes correctly the nonlinear steepening effects of the flow behind the shocks. Effects of relaxation on the evolutionary behavior of shocks are discussed. The first-order truncation approximation accurately describes the decay behavior of weak shocks; the usual decay laws for weak shocks in a nonrelaxing gas are exactly recovered. The results concerning shocks of arbitrary strength are compared with the characteristic rule. In the limit of vanishing shock strength, the transport equation for the first-order induced discontinuity leads to an exact description of an acceleration <span class="hlt">wave</span>. In the strong shock limit, the second-order truncation criterion leads to a <span class="hlt">propagation</span> law for imploding shocks which is in agreement (within 5% error) with the Guderley's exact similarity solution.</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://ntrs.nasa.gov/search.jsp?R=19810065274&hterms=electromagnetic+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Delectromagnetic%2Bwaves','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19810065274&hterms=electromagnetic+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Delectromagnetic%2Bwaves"><span id="translatedtitle">Instabilities of low frequency, parallel <span class="hlt">propagating</span> electromagnetic <span class="hlt">waves</span> in the earth's foreshock region</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sentman, D. D.; Edmiston, J. P.; Frank, L. A.</p> <p>1981-01-01</p> <p>An instability analysis is presented for parallel and antiparallel <span class="hlt">propagating</span> electromagnetic <span class="hlt">waves</span> generated by reflected and diffuse suprathermal ions upstream of the earth's bow shock. Calculations are performed on the basis of upstream particle observations made by the ISEE 1 Quadrispheric Lepedea instrument and low-energy electron measurements made by the ISEE 1 electron spectrometer for a single period. The electromagnetic dispersion relation is computed and the unstable modes and growth times of the fastest growing <span class="hlt">waves</span> are determined. It is found that the reflected ions destabilize the plasma most strongly at a <span class="hlt">wave</span> frequency 0.1 that of the ion gyrofrequency by a resonant ion beam instability for <span class="hlt">waves</span> <span class="hlt">propagating</span> upstream and by a nonresonant firehose-like instability for <span class="hlt">waves</span> <span class="hlt">propagating</span> downstream. The diffuse ions also destabilize the plasma most strongly at the same frequency by means of resonant instabilities of both right- and left-hand polarized <span class="hlt">waves</span> <span class="hlt">propagating</span> away from the bow shock.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22482452','SCIGOV-STC'); return false;" href="http://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/2015PhFl...27j6101H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhFl...27j6101H"><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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Han, Wenhu; Gao, Yang; Wang, Cheng; Law, Chung K.</p> <p>2015-10-01</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('https://www.ncbi.nlm.nih.gov/pubmed/18190931','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18190931"><span id="translatedtitle">A <span class="hlt">propagating</span> heat <span class="hlt">wave</span> model of skin electroporation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pliquett, Uwe; Gusbeth, Ch; Nuccitelli, Richard</p> <p>2008-03-21</p> <p>The main barrier to transdermal drug delivery in human skin is the stratum corneum. Pulsed electric fields (PEFs) of sufficient amplitude can create new aqueous pathways across this barrier and enhance drug delivery through the skin. Here, we describe a model of pore formation between adjacent corneocytes that predicts the following sequence of events: (1) the PEF rapidly charges the stratum corneum near the electrode until the transepidermal potential difference is large enough to drive water into a small region of the stratum corneum, creating new aqueous pathways. (2) PEFs then drive a high current density through this newly created electropore to generate Joule heating that warms the pore perimeter. (3) This temperature rise at the perimeter increases the probability of further electroporation there as the local sphingolipids reach their phase transition temperature. (4) This heat-generated <span class="hlt">wave</span> of further electroporation <span class="hlt">propagates</span> outward until the surface area of the pore becomes so large that the reduced current density no longer generates sufficient heat to reach the phase transition temperature of the sphingolipids. (5) Cooling and partial recovery occurs after the field pulse. This process yields large, high permeability regions in the stratum corneum at which molecules can more readily cross this skin barrier. We present a model for this process that predicts that the initial radius of the first aqueous pathway is approximately 5nm for a transdermal voltage of 60V at room temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/23030928','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/23030928"><span id="translatedtitle"><span class="hlt">Propagation</span> of electromagnetic <span class="hlt">waves</span> in stochastic helical media.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mendez, David; Reyes, J Adrian</p> <p>2012-09-01</p> <p>We have developed a model for studying the axial <span class="hlt">propagation</span> of elliptically polarized electromagnetic <span class="hlt">waves</span> in a spatially random helical media. We start by writing Maxwell equations for a structurally chiral medium whose dielectric permittivities, polar, and helical angles contain both a stochastic contribution and a deterministic one. We write the electromagnetic equations into a Marcuvitz-Schwigner representation to transform them afterward in a simpler expression by using the Oseen transformation. We exhibit that in the Oseen frame the Marcuvitz-Schwigner equations turns out to be a linear vector stochastic system of differential equations with multiplicative noise. Applying to the resulting equation a formalism for treating stochastic differential equations, we find the governing equations for the first moments of the electromagnetic field amplitudes for a general autocorrelation function for the system diffractive indexes, and calculate their corresponding band structure for a particular spectral noise density. We have shown that the average resulting electromagnetic fields exhibit a decaying exponential dependence which stems from by dissipation and the presence of qualitative modifications in the band structure including a considerable widening of the band gap and the existence of new local maxima for the modes without a band gap. PMID:23030928</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003SPIE.5047..202M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003SPIE.5047..202M"><span id="translatedtitle">Damage detection in structures from vibration and <span class="hlt">wave</span> <span class="hlt">propagation</span> data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mal, Ajit K.; Ricci, Fabrizio; Gibson, Steve; Banerjee, Sauvik</p> <p>2003-07-01</p> <p>Development of efficient tools to successfully localize and characterize hidden damage in critical structural components is an important task in the design and construction of structural health monitoring systems in aging as well as new structures. In this paper two methodologies for damage identification and localization will be presented. The first is an automatic numerical scheme using a state space system identification approach and the second is based on certain damage correlation indices associated with changes in the frequency response of the structure in presence of flaws. In each case, the structure is to be instrumented with an array of sensors to record its dynamic response including vibration and <span class="hlt">wave</span> <span class="hlt">propagation</span> effects. To determine the type and location of an unknown defect, the sensor data detected is used to identify a new system, which then is compared to a database of state-space models to find the nearest match. The second method deals with the definition of a set of damage correlation indices obtained from the frequency response analysis of the structure. Two types of indices have been considered. The first uses the correlation between the responses of the defect free and damaged structure at the same point, and the second uses correlation at two different points. The potential application of the general approach in developing health monitoring systems in defects-critical structures is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992PhDT.......103S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992PhDT.......103S"><span id="translatedtitle">Spectral analysis of <span class="hlt">wave</span> <span class="hlt">propagation</span> in connected waveguides</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Srinivasan, Gopalakrishnan</p> <p>1992-01-01</p> <p>The spectral element method combined with the Fast Fourier Transform (FFT) is a powerful and versatile tool for analysis of <span class="hlt">wave</span> <span class="hlt">propagation</span> problems in connected structures. They are formulated entirely in the frequency domain and use matrix assembly procedures analogous to the finite element method. This thesis extends the approach to connected structures involving non-uniformities and discontinuities. To handle situations involving deep waveguides, spectral elements are formulated based on the higher order waveguide theories of Timoshenko beam and Mindlin-Herrmann rod. Approximate tapered elements (derived using a frequency domain Ritz method) are formulated to handle situations involving member cross-section variations. For waveguides with embedded discontinuities like cracks and holes, the irregular behavior near the discontinuity is isolated by performing Local/Global analysis via the super spectral element concept. Efficient computation of the super element stiffness is the key to the success of the method and it is addressed directly. The formulated element is verified by comparison with the conventional finite element solution. Some interesting problems involving joints, cracks and holes are solved. One of the distinct advantages of the spectral approach is the capability to perform inverse problems. The concept is demonstrated with some illustrative examples involving multiple boundaries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004APS..MARS19006P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004APS..MARS19006P&link_type=ABSTRACT"><span id="translatedtitle">Image formation by and <span class="hlt">wave</span> <span class="hlt">propagation</span> in a photonic crystal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Parimi, Patanjali; Vodo, Plarenta; Wentao, Lu; di Gennaro, Emiliano; Sridhar, Srinivas</p> <p>2004-03-01</p> <p>Negative refraction and imaging by a flat slab of a material are two of the important consequences of lefthanded electromagnetism. In our recent work we have demonstrated negative refraction and imaging by photonic crystals in the microwave frequency range [1]. The details of image formation are intriguing and urge its investigation. We have carried out microwave measurements in a parallel plate waveguide made of a pair of metallic plates. The Photonic crystal is made of alumina rods arranged on a square lattice such that the electric field is parallel to the axis of the rods. The detector is a dipole antenna which is inserted into the waveguide from outside. HP 8510C network analyzer is used to measure the complex transmission coefficient . The intensity maps of vs. probe position are obtained by scanning the probe using an x-y robot, both inside and outside the crystal. The results suggest Bloch <span class="hlt">wave</span> <span class="hlt">propagation</span> inside the crystal and that the image formation requires a better understanding than a simple ray diagram following geometric optics. [1] P. V. Parimi et al., Nature, 426, 404 (2003).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016Ap%26SS.361..143K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016Ap%26SS.361..143K&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Propagation</span> and damping of slow MHD <span class="hlt">waves</span> in a flowing viscous coronal plasma</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kumar, Nagendra; Kumar, Anil; Murawski, K.</p> <p>2016-04-01</p> <p>We investigate the <span class="hlt">propagation</span> of slow MHD <span class="hlt">waves</span> in a flowing viscous solar coronal plasma. The compressive viscosity and steady flow along and opposite to the <span class="hlt">wave</span> <span class="hlt">propagation</span> are taken into account to study the damping of slow <span class="hlt">waves</span>. We numerically solve the MHD equations by MacCormack method to examine the effect of steady flow on the damping of slow MHD <span class="hlt">waves</span> in viscous solar coronal plasma. Amplitude of velocity perturbation and damping time of slow <span class="hlt">waves</span> decrease with the increase in the value of Mach number. Flow causes a phase shift in the perturbed velocity amplitude and an increase in <span class="hlt">wave</span> period. The damping of slow <span class="hlt">waves</span> in flowing viscous plasma is stronger than the damping of <span class="hlt">waves</span> in viscous plasma. Slow <span class="hlt">wave</span> in backward flow damps earlier than the <span class="hlt">wave</span> in forward flow.</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://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>Stavroula Foteinopoulou</p> <p>2003-12-12</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://adsabs.harvard.edu/abs/2009ChPhL..26g6202C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009ChPhL..26g6202C"><span id="translatedtitle">CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Orientation and Rate Dependence of <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Shocked Beta-SiC from Atomistic Simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cheng, Qin; Wu, Heng-An; Wang, Yu; Wang, Xiu-Xi</p> <p>2009-07-01</p> <p>The orientation dependence of <span class="hlt">planar</span> <span class="hlt">wave</span> <span class="hlt">propagation</span> in beta-SiC is studied via the molecular dynamics (MD) method. Simulations are implemented under impact loadings in four main crystal directions, i.e., (100), (110), (111), and (112). The dispersion of stress states in different directions increases with rising impact velocity, which implies the anisotropic characteristic of shock <span class="hlt">wave</span> <span class="hlt">propagation</span> for beta-SiC materials. We also obtain the Hugoniot relations between the shock <span class="hlt">wave</span> velocity and the impact velocity, and find that the shock velocity falls into a plateau above a threshold of impact velocity. The shock velocity of the plateaux is dependent on the shock directions, while (111) and (112) can be regarded as equivalent directions as they almost reach the same plateau. A comparison between the atomic stress from MD and the stress from Rankine-Hugoniot jump conditions is also made, and it is found that they agree with each other very well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAG...116...93W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAG...116...93W"><span id="translatedtitle">Effect of near-surface topography on high-frequency Rayleigh-<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>Wang, Limin; Xu, Yixian; Xia, Jianghai; Luo, Yinhe</p> <p>2015-05-01</p> <p>Rayleigh <span class="hlt">waves</span>, which are formed due to interference of P- and Sv-<span class="hlt">waves</span> near the free surface, <span class="hlt">propagate</span> along the free surface and vanish exponentially in the vertical direction. Their <span class="hlt">propagation</span> is strongly influenced by surface topography. Due to the high resolution and precision requirements of near-surface investigations, the high-frequency Rayleigh <span class="hlt">waves</span> are usually used for near-surface structural detecting. Although there are some numerical studies on high-frequency Rayleigh-<span class="hlt">wave</span> <span class="hlt">propagation</span> on topographic free surface, detailed analysis of characters of high-frequency Rayleigh-<span class="hlt">wave</span> <span class="hlt">propagation</span> on topographic free surface remains untouched. Hence, research of <span class="hlt">propagation</span> of Rayleigh <span class="hlt">waves</span> on complex topographic surface becomes critical for Rayleigh-<span class="hlt">wave</span> methods in near-surface applications. To study the <span class="hlt">propagation</span> of high-frequency Rayleigh <span class="hlt">waves</span> on topographic free surface, two main topographic models are designed in this study. One of the models contains a depressed topographic surface, and another contains an uplifted topographic surface. We numerically simulate the <span class="hlt">propagation</span> of high-frequency Rayleigh <span class="hlt">waves</span> on these two topographic surfaces by finite-difference method. Soon afterwards, we analyze the <span class="hlt">propagation</span> character of high-frequency Rayleigh <span class="hlt">waves</span> on such topographic models, and compare the variations on its energy and frequency before and after passing the topographic region. At last, we discuss the relationship between the variations and topographical steepness of each model. Our numerical results indicate that influence of depressed topography for high-frequency Rayleigh <span class="hlt">waves</span> is more distinct than influence of uplifted topography. Rayleigh <span class="hlt">waves</span> produce new scattering body <span class="hlt">waves</span> during passing the depressed topography with reduction of amplitude and loss of high-frequency components. Moreover, the steeper the depressed topography is, the more energy of Rayleigh <span class="hlt">waves</span> is lost. The uplifted topography with gentle slope produces similar</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011ApJ...734...80S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011ApJ...734...80S"><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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Soler, R.; Terradas, J.; Goossens, M.</p> <p>2011-06-01</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-Alfvénic 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://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('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/18239707','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18239707"><span id="translatedtitle">Design rules for phase-matched terahertz surface electromagnetic <span class="hlt">wave</span> generation by optical rectification in a nonlinear <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>Musin, Roman R; Xing, Qirong; Li, Yanfeng; Hu, Minglie; Chai, Lu; Wang, Qingyue; Mikhailova, Yuliya M; Nazarov, Maksim M; Shkurinov, Alexander P; Zheltikov, Aleksei M</p> <p>2008-02-01</p> <p>The theory of guided <span class="hlt">waves</span> in metal-dielectric <span class="hlt">planar</span> multilayer structures is applied to reduce the loss and maximize optical nonlinearity for efficient terahertz-field generation in a surface electromagnetic <span class="hlt">wave</span> by femtosecond laser pulses confined in a (chi)((2)) nonlinear <span class="hlt">planar</span> waveguide. For typical parameters of thin-film polymer waveguides and metal-dielectric interfaces, the optimal size of the (chi)((2)) waveguide core providing the maximum efficiency of terahertz plasmon-field generation is shown to be less than the wavelength of the optical pump field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000JDE...163..198Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000JDE...163..198Z"><span id="translatedtitle">Nonlinear Stability of Strong <span class="hlt">Planar</span> Rarefaction <span class="hlt">Waves</span> for the Relaxation Approximation of Conservation Laws in Several Space Dimensions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhao, Huijiang</p> <p>2000-04-01</p> <p>In this paper, we show that a strong <span class="hlt">planar</span> rarefaction <span class="hlt">wave</span> is nonlinear stable, namely it is an attractor for the relaxation approximation of the scalar conservation laws in several space dimensions. Compared with former results obtained by T. P. Liu (1987, Comm. Math. Phys.108, 153-175) and T. Luo (1997, J. Differential Equations133, 255-279), our main novelty lies in the fact that the <span class="hlt">planar</span> rarefaction <span class="hlt">waves</span> do not need to be small, and in the one-dimensional case, the initial disturbance can also be chosen arbitrarily large.</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/23967920','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23967920"><span id="translatedtitle">Ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in thermoviscous moving fluid confined by heating pipeline and flow measurement performance.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Yong; Huang, Yiyong; Chen, Xiaoqian</p> <p>2013-09-01</p> <p>Ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in thermoviscous fluid with pipeline shear mean flow in the presence of a temperature gradient is investigated. On the assumption of irrotational and axisymmetric <span class="hlt">wave</span> <span class="hlt">propagation</span>, a mathematical formulation of the convected <span class="hlt">wave</span> equation is proposed without simplification in the manner of Zwikker and Kosten. A method based on the Fourier-Bessel theory, which is complete and orthogonal in Lebesgue space, is introduced to convert the <span class="hlt">wave</span> equations into homogeneous algebraic equations. Then numerical calculation of the axial wavenumber is presented. In the end, <span class="hlt">wave</span> attenuation in laminar and turbulent flow is numerically studied. Meanwhile measurement performance of an ultrasonic flow meter is parametrically analyzed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/23967920','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/23967920"><span id="translatedtitle">Ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in thermoviscous moving fluid confined by heating pipeline and flow measurement performance.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Yong; Huang, Yiyong; Chen, Xiaoqian</p> <p>2013-09-01</p> <p>Ultrasonic <span class="hlt">wave</span> <span class="hlt">propagation</span> in thermoviscous fluid with pipeline shear mean flow in the presence of a temperature gradient is investigated. On the assumption of irrotational and axisymmetric <span class="hlt">wave</span> <span class="hlt">propagation</span>, a mathematical formulation of the convected <span class="hlt">wave</span> equation is proposed without simplification in the manner of Zwikker and Kosten. A method based on the Fourier-Bessel theory, which is complete and orthogonal in Lebesgue space, is introduced to convert the <span class="hlt">wave</span> equations into homogeneous algebraic equations. Then numerical calculation of the axial wavenumber is presented. In the end, <span class="hlt">wave</span> attenuation in laminar and turbulent flow is numerically studied. Meanwhile measurement performance of an ultrasonic flow meter is parametrically analyzed. PMID:23967920</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('https://www.ncbi.nlm.nih.gov/pubmed/21935152','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21935152"><span id="translatedtitle"><span class="hlt">Wave</span> turbulence in integrable systems: nonlinear <span class="hlt">propagation</span> of incoherent optical <span class="hlt">waves</span> in single-mode fibers.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Suret, Pierre; Picozzi, Antonio; Randoux, Stéphane</p> <p>2011-08-29</p> <p>We study theoretically, numerically and experimentally the nonlinear <span class="hlt">propagation</span> of partially incoherent optical <span class="hlt">waves</span> in single mode optical fibers. We revisit the traditional treatment of the <span class="hlt">wave</span> turbulence theory to provide a statistical kinetic description of the integrable scalar NLS equation. In spite of the formal reversibility and of the integrability of the NLS equation, the weakly nonlinear dynamics reveals the existence of an irreversible evolution toward a statistically stationary state. The evolution of the power spectrum of the field is characterized by the rapid growth of spectral tails that exhibit damped oscillations, until the whole spectrum ultimately reaches a steady state. The kinetic approach allows us to derive an analytical expression of the damped oscillations, which is found in agreement with the numerical simulations of both the NLS and kinetic equations. We report the experimental observation of this peculiar relaxation process of the integrable NLS equation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/21935152','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/21935152"><span id="translatedtitle"><span class="hlt">Wave</span> turbulence in integrable systems: nonlinear <span class="hlt">propagation</span> of incoherent optical <span class="hlt">waves</span> in single-mode fibers.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Suret, Pierre; Picozzi, Antonio; Randoux, Stéphane</p> <p>2011-08-29</p> <p>We study theoretically, numerically and experimentally the nonlinear <span class="hlt">propagation</span> of partially incoherent optical <span class="hlt">waves</span> in single mode optical fibers. We revisit the traditional treatment of the <span class="hlt">wave</span> turbulence theory to provide a statistical kinetic description of the integrable scalar NLS equation. In spite of the formal reversibility and of the integrability of the NLS equation, the weakly nonlinear dynamics reveals the existence of an irreversible evolution toward a statistically stationary state. The evolution of the power spectrum of the field is characterized by the rapid growth of spectral tails that exhibit damped oscillations, until the whole spectrum ultimately reaches a steady state. The kinetic approach allows us to derive an analytical expression of the damped oscillations, which is found in agreement with the numerical simulations of both the NLS and kinetic equations. We report the experimental observation of this peculiar relaxation process of the integrable NLS equation. PMID:21935152</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016IJT....37..101G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016IJT....37..101G"><span id="translatedtitle">Laser-Generated Rayleigh <span class="hlt">Waves</span> <span class="hlt">Propagating</span> in Transparent Viscoelastic Adhesive Coating/Metal Substrate Systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guan, Yi-jun; Sun, Hong-xiang; Yuan, Shou-qi; Zhang, Shu-yi; Ge, Yong</p> <p>2016-10-01</p> <p>We have established numerical models for simulating laser-generated Rayleigh <span class="hlt">waves</span> in coating/substrate systems by a finite element method and investigated the <span class="hlt">propagation</span> characteristics of Rayleigh <span class="hlt">waves</span> in systems concerning the viscoelasticity and transparency of adhesive coatings. In this way, we have studied the influence of the mechanical properties of the coating, such as the elastic moduli, viscoelastic moduli, coating thickness, transparency, and coating material, on the <span class="hlt">propagation</span> characteristics of the Rayleigh <span class="hlt">waves</span>. The results show that the <span class="hlt">propagation</span> characteristics of the Rayleigh <span class="hlt">waves</span> can be divided into low- and high-frequency parts. The high-frequency <span class="hlt">propagation</span> characteristics of the Rayleigh <span class="hlt">wave</span> are closely related to the properties of the adhesive coating.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21538161','SCIGOV-STC'); return false;" href="http://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('http://adsabs.harvard.edu/abs/1998DyAtO..27...91W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998DyAtO..27...91W"><span id="translatedtitle">Atmospheric <span class="hlt">wave</span> <span class="hlt">propagation</span> in heterogeneous flow: basic flow controls on tropical—extratropical interaction and equatorial <span class="hlt">wave</span> modification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Webster, Peter J.; Chang, Hai-Ru</p> <p>1998-01-01</p> <p>It is noted that <span class="hlt">wave</span> <span class="hlt">propagation</span> in the atmosphere and error <span class="hlt">propagation</span> in numerical models appear to have preferred geographical loci. However, these paths appear to be more associated with the low frequency background state of the atmosphere than the location of the <span class="hlt">wave</span> source. Theoretical and numerical models are used to determine the control the basic state has on <span class="hlt">wave</span> <span class="hlt">propagation</span> both between the extratropica and the tropics (and vice versa) and within the tropics. Basic states with horizontal and vertical shear as well as longitudinal stretching deformation are studied. It is shown that strong horizontal shear embedded in equatorial easterlies confines modes close to the equator. Weak shear in westerly tropical flow allows modes to project into the extratropics. That is, the degree of equatorial trapping is diminished. Negative stretching deformation acts to trap modes longitudinally so that the western sides of the westerly ducts are accumulation regions. Negative vertical shear inhibits vertical <span class="hlt">propagation</span> while positive shear enhances <span class="hlt">propagation</span>. It is concluded that the basic state is the determining factor in the observed patterns of <span class="hlt">waves</span> and the locations of errors in numerical weather prediction and climate models. Of particular interest are the westerly duct regions of the eastern Pacific Ocean and the Atlantic Ocean. These regions appear to act as <span class="hlt">wave</span> attractors for both equatorially trapped modes and extratropical modes <span class="hlt">propagating</span> towards the equator and also are regions of enhanced vertical <span class="hlt">propagation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24770473','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24770473"><span id="translatedtitle">The stimulus-evoked population response in visual cortex of awake monkey is a <span class="hlt">propagating</span> <span class="hlt">wave</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Muller, Lyle; Reynaud, Alexandre; Chavane, Frédéric; Destexhe, Alain</p> <p>2014-04-28</p> <p><span class="hlt">Propagating</span> <span class="hlt">waves</span> occur in many excitable media and were recently found in neural systems from retina to neocortex. While <span class="hlt">propagating</span> <span class="hlt">waves</span> are clearly present under anaesthesia, whether they also appear during awake and conscious states remains unclear. One possibility is that these <span class="hlt">waves</span> are systematically missed in trial-averaged data, due to variability. Here we present a method for detecting <span class="hlt">propagating</span> <span class="hlt">waves</span> in noisy multichannel recordings. Applying this method to single-trial voltage-sensitive dye imaging data, we show that the stimulus-evoked population response in primary visual cortex of the awake monkey <span class="hlt">propagates</span> as a travelling <span class="hlt">wave</span>, with consistent dynamics across trials. A network model suggests that this reliability is the hallmark of the horizontal fibre network of superficial cortical layers. <span class="hlt">Propagating</span> <span class="hlt">waves</span> with similar properties occur independently in secondary visual cortex, but maintain precise phase relations with the <span class="hlt">waves</span> in primary visual cortex. These results show that, in response to a visual stimulus, <span class="hlt">propagating</span> <span class="hlt">waves</span> are systematically evoked in several visual areas, generating a consistent spatiotemporal frame for further neuronal interactions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4015334','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4015334"><span id="translatedtitle">The stimulus-evoked population response in visual cortex of awake monkey is a <span class="hlt">propagating</span> <span class="hlt">wave</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>Muller, Lyle; Reynaud, Alexandre; Chavane, Frédéric; Destexhe, Alain</p> <p>2014-01-01</p> <p><span class="hlt">Propagating</span> <span class="hlt">waves</span> occur in many excitable media and were recently found in neural systems from retina to neocortex. While <span class="hlt">propagating</span> <span class="hlt">waves</span> are clearly present under anaesthesia, whether they also appear during awake and conscious states remains unclear. One possibility is that these <span class="hlt">waves</span> are systematically missed in trial-averaged data, due to variability. Here we present a method for detecting <span class="hlt">propagating</span> <span class="hlt">waves</span> in noisy multichannel recordings. Applying this method to single-trial voltage-sensitive dye imaging data, we show that the stimulus-evoked population response in primary visual cortex of the awake monkey <span class="hlt">propagates</span> as a travelling <span class="hlt">wave</span>, with consistent dynamics across trials. A network model suggests that this reliability is the hallmark of the horizontal fibre network of superficial cortical layers. <span class="hlt">Propagating</span> <span class="hlt">waves</span> with similar properties occur independently in secondary visual cortex, but maintain precise phase relations with the <span class="hlt">waves</span> in primary visual cortex. These results show that, in response to a visual stimulus, <span class="hlt">propagating</span> <span class="hlt">waves</span> are systematically evoked in several visual areas, generating a consistent spatiotemporal frame for further neuronal interactions. PMID:24770473</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015A%26A...581A.112A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015A%26A...581A.112A"><span id="translatedtitle">Characterizing the <span class="hlt">propagation</span> of gravity <span class="hlt">waves</span> in 3D nonlinear simulations of solar-like stars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alvan, L.; Strugarek, A.; Brun, A. S.; Mathis, S.; Garcia, R. A.</p> <p>2015-09-01</p> <p>Context. The revolution of helio- and asteroseismology provides access to the detailed properties of stellar interiors by studying the star's oscillation modes. Among them, gravity (g) modes are formed by constructive interferences between progressive internal gravity <span class="hlt">waves</span> (IGWs), <span class="hlt">propagating</span> in stellar radiative zones. Our new 3D nonlinear simulations of the interior of a solar-like star allows us to study the excitation, <span class="hlt">propagation</span>, and dissipation of these <span class="hlt">waves</span>. Aims: The aim of this article is to clarify our understanding of the behavior of IGWs in a 3D radiative zone and to provide a clear overview of their properties. Methods: We use a method of frequency filtering that reveals the path of individual gravity <span class="hlt">waves</span> of different frequencies in the radiative zone. Results: We are able to identify the region of <span class="hlt">propagation</span> of different <span class="hlt">waves</span> in 2D and 3D, to compare them to the linear raytracing theory and to distinguish between <span class="hlt">propagative</span> and standing <span class="hlt">waves</span> (g-modes). We also show that the energy carried by <span class="hlt">waves</span> is distributed in different planes in the sphere, depending on their azimuthal <span class="hlt">wave</span> number. Conclusions: We are able to isolate individual IGWs from a complex spectrum and to study their <span class="hlt">propagation</span> in space and time. In particular, we highlight in this paper the necessity of studying the <span class="hlt">propagation</span> of <span class="hlt">waves</span> in 3D spherical geometry, since the distribution of their energy is not equipartitioned in the sphere.</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/cgi-bin/nph-data_query?bibcode=2016JSV...362..157V&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016JSV...362..157V&link_type=ABSTRACT"><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('http://adsabs.harvard.edu/abs/2016ApPhA.122..328S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApPhA.122..328S"><span id="translatedtitle">Experimental verification of manipulating <span class="hlt">propagation</span> directions of transmitted <span class="hlt">waves</span> in asymmetric acoustic transmission</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Hong-xiang; Zhang, Shu-yi; Yuan, Shou-qi; Xia, Jian-ping</p> <p>2016-04-01</p> <p>The manipulation of the <span class="hlt">propagation</span> directions of the transmitted <span class="hlt">waves</span> in an acoustic system with asymmetric acoustic transmission is investigated numerically and experimentally, in which the system consists of a brass plate and a periodical grating immersed in water. It is experimentally demonstrated that the <span class="hlt">propagation</span> angles of the transmitted <span class="hlt">waves</span> are close to those of ±1-order diffractions in the pass-band of the asymmetric acoustic transmission, and thus, the manipulation of the <span class="hlt">propagation</span> directions of the transmitted <span class="hlt">waves</span> is realized by adjusting the grating period and plate thickness. Our scheme may open up an avenue to the design of tunable unidirectional acoustic devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26406044','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26406044"><span id="translatedtitle">Wall stress and deformation analysis in a numerical model of pulse <span class="hlt">wave</span> <span class="hlt">propagation</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>He, Fan; Hua, Lu; Gao, Lijian</p> <p>2015-01-01</p> <p>To simulate pulse <span class="hlt">wave</span> <span class="hlt">propagation</span>, we set up a <span class="hlt">wave</span> <span class="hlt">propagation</span> model using blood-wall interaction in previous work. In this paper, our purpose is to investigate wall stress and deformation of the <span class="hlt">wave</span> <span class="hlt">propagation</span> model. The finite element method is employed for solving the governing equations of blood and wall. Our results suggest that there are two peaks in the circumferential stress and strain distributions of the normal model. The stress and strain values change with the varieties of different factors, such as wall thickness and vessel diameter. The results indicate that different parameters of fluid and tube wall have remarked impact on wall stress and deformation. PMID:26406044</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22395478','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22395478"><span id="translatedtitle">Unidirectional <span class="hlt">propagation</span> of magnetostatic surface spin <span class="hlt">waves</span> at a magnetic film surface</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wong, Kin L.; Bao, Mingqiang E-mail: caross@mit.edu; Lin, Yen-Ting; Wang, Kang L.; Bi, Lei; Wen, Qiye; Zhang, Huaiwu; Chatelon, Jean Pierre; Ross, C. A. E-mail: caross@mit.edu</p> <p>2014-12-08</p> <p>An analytical expression for the amplitudes of magnetostatic surface spin <span class="hlt">waves</span> (MSSWs) <span class="hlt">propagating</span> in opposite directions at a magnetic film surface is presented. This shows that for a given magnetic field H, it is forbidden for an independent MSSW to <span class="hlt">propagate</span> along the direction of −H{sup →}×n{sup →}, where n{sup →} is the surface normal. This unidirectional <span class="hlt">propagation</span> property is confirmed by experiments with both permalloy and yttrium iron garnet films of different film thicknesses, and has implications in the design of spin-<span class="hlt">wave</span> devices such as isolators and spin-<span class="hlt">wave</span> diodes.</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> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26406044','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26406044"><span id="translatedtitle">Wall stress and deformation analysis in a numerical model of pulse <span class="hlt">wave</span> <span class="hlt">propagation</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>He, Fan; Hua, Lu; Gao, Lijian</p> <p>2015-01-01</p> <p>To simulate pulse <span class="hlt">wave</span> <span class="hlt">propagation</span>, we set up a <span class="hlt">wave</span> <span class="hlt">propagation</span> model using blood-wall interaction in previous work. In this paper, our purpose is to investigate wall stress and deformation of the <span class="hlt">wave</span> <span class="hlt">propagation</span> model. The finite element method is employed for solving the governing equations of blood and wall. Our results suggest that there are two peaks in the circumferential stress and strain distributions of the normal model. The stress and strain values change with the varieties of different factors, such as wall thickness and vessel diameter. The results indicate that different parameters of fluid and tube wall have remarked impact on wall stress and deformation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25911148','PUBMED'); return false;" href="http://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. PMID:25911148</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/20861157','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/20861157"><span id="translatedtitle">Obliquely <span class="hlt">Propagating</span> Dust-Density Plasma <span class="hlt">Waves</span> in the Presence of an Ion Beam</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Piel, A.; Klindworth, M.; Arp, O.; Melzer, A.; Wolter, M.</p> <p>2006-11-17</p> <p>Self-excited dust-density <span class="hlt">waves</span> are experimentally studied in a dusty plasma under microgravity. Two types of <span class="hlt">waves</span> are observed: a mode inside the dust volume <span class="hlt">propagating</span> in the direction of the ion flow and a new mode <span class="hlt">propagating</span> obliquely at the boundary between the dusty plasma and the space-charge sheath. A model for dust-density <span class="hlt">waves</span> <span class="hlt">propagating</span> at an arbitrary angle with respect to the ion-flow direction is presented, which explains the preference for oblique or parallel modes as a function of ion velocity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22072444','SCIGOV-STC'); return false;" href="http://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('http://adsabs.harvard.edu/abs/2012PhPl...19f2105E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhPl...19f2105E"><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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>EL-Labany, S. K.; EL-Shamy, E. F.; El-Mahgoub, M. G.</p> <p>2012-06-01</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 Poincaré-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('http://www.osti.gov/scitech/biblio/1030251','SCIGOV-STC'); return false;" href="http://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/cgi-bin/nph-data_query?bibcode=2015JaJAP..54gHF02M&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015JaJAP..54gHF02M&link_type=ABSTRACT"><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('http://www.osti.gov/scitech/biblio/503587','SCIGOV-STC'); return false;" href="http://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/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/cgi-bin/nph-data_query?bibcode=2016PhRvA..93a3826W&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016PhRvA..93a3826W&link_type=ABSTRACT"><span id="translatedtitle">Plasmon-soliton <span class="hlt">waves</span> in <span class="hlt">planar</span> slot waveguides. II. Results for stationary <span class="hlt">waves</span> and stability analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walasik, Wiktor; Renversez, Gilles; Ye, Fangwei</p> <p>2016-01-01</p> <p>We describe the results of the two methods we developed to calculate the stationary nonlinear solutions in one-dimensional plasmonic slot waveguides made of a finite-thickness nonlinear dielectric core surrounded by metal regions. These two methods are described in detail in the preceding article [Walasik and Renversez, preceding paper, Phys. Rev. A 93, 013825 (2016)], 10.1103/PhysRevA.93.013825. For symmetric waveguides, we provide the nonlinear dispersion curves obtained using the two methods and compare them. We describe the well-known low-order modes and higher modes that were not described before. All the modes are classiffied into two families: modes with or without nodes. We also compare nonlinear modes with nodes with the linear modes in similar linear slot waveguides with a homogeneous core. We recover the symmetry breaking Hopf bifurcation of the first symmetric nonlinear mode toward an asymmetric mode and we show that some of the higher modes also exhibit a bifurcation. We study the behavior of the bifurcation of the fundamental mode as a function of the permittivities of the metal cladding and of the nonlinear core. We demonstrate that the bifurcation can be obtained at low power levels in structures with optimized parameters. Moreover, we provide the dispersion curves for asymmetric nonlinear slot waveguides. Finally, we give results concerning the stability of the fundamental symmetric mode and the asymmetric mode that bifurcates from it using both theoretical argument and numerical <span class="hlt">propagation</span> simulations from two different full-vector methods. We also investigate the stability properties of the first antisymmetric mode using our two numerical <span class="hlt">propagation</span> methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22220724','SCIGOV-STC'); return false;" href="http://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('http://adsabs.harvard.edu/abs/1986JGR....91.6367O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1986JGR....91.6367O"><span id="translatedtitle">Solitary <span class="hlt">wave</span> <span class="hlt">propagation</span> in a fluid conduit within a viscous matrix</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Olson, Peter; Christensen, Ulrich</p> <p>1986-05-01</p> <p>Conduits of low-viscosity, buoyant fluid imbedded in a highly viscous matrix have been used to model the dynamics of magma transport in vertical dikes and within zones of partial melt. The theory predicts that disturbances can <span class="hlt">propagate</span> along the conduit in the form of large-amplitude <span class="hlt">waves</span>. A set of experiments have been made to investigate the behavior of this system. Uniform, vertical conduits of low-viscosity liquid (dilute aqueous solutions of ethyl alcohol and sucrose) were established in a column of high-viscosity, high-density matrix fluid (concentrated sucrose solution). Perturbations were introduced in the form of pulses of conduit liquid. Two classes of travelling disturbances were observed: slowly <span class="hlt">propagating</span>, periodic <span class="hlt">wave</span> trains, and fast <span class="hlt">propagating</span> solitary <span class="hlt">waves</span>. The slow, periodic <span class="hlt">waves</span> form during the development of a conduit, behind an ascending diapir. The fast, solitary <span class="hlt">waves</span> form in response to disturbances introduced into fully developed conduits. Both of these <span class="hlt">wave</span> types are correctly predicted by the theory. Measurements were made of solitary <span class="hlt">wave</span> <span class="hlt">propagation</span> speed versus <span class="hlt">wave</span> volume in two different conduit liquids over a wide range of background (undisturbed) conduit flux. Satisfactory agreement was found between the measured and the theoretical <span class="hlt">propagation</span> speeds except in two limits. For very large <span class="hlt">wave</span> volumes the observed <span class="hlt">propagation</span> was always faster than expected. This deviation may be due to finite <span class="hlt">wave</span> slope effects and to departures from Poiseuille flow in the conduit which are not included in the theory. For very thin conduits the observed <span class="hlt">propagation</span> was generally slower than expected, an effect that can be attributed to mass diffusion between the conduit fluid and the matrix. Overall, our results indicate that the two-fluid models of magma transport are adequate for describing the behavior of homogeneous, nondiffusive systems.</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.ncbi.nlm.nih.gov/pubmed/26093440','PUBMED'); return false;" href="http://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. PMID:26093440</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.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://ntrs.nasa.gov/search.jsp?R=19820050324&hterms=transverse+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dtransverse%2Bwaves','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19820050324&hterms=transverse+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dtransverse%2Bwaves"><span id="translatedtitle">Numerical experimentation on spherically symmetric one-dimensional magnetohydrodynamic /MHD/ <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>Han, S. M.; Wu, S. T.; Nakagawa, Y.</p> <p>1982-01-01</p> <p>Radial <span class="hlt">propagation</span> of one-dimensional magnetohydrodynamic (MHD) <span class="hlt">waves</span> are analyzed numerically on the basis of the Implicit-Continuous-Fluid-Eulerian (ICE) scheme. Accuracy of the numerical method and other properties are tested through the study of MHD <span class="hlt">wave</span> <span class="hlt">propagation</span>. The three different modes of MHD <span class="hlt">waves</span> (i.e., fast-, slow- and Alfven (transverse) mode) are generated by applying physically consistent boundary perturbations derived from MHD compatibility relations. It is shown that the resulting flow following these <span class="hlt">waves</span> depend upon the relative configurations of the initial magnetic field and boundary perturbations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22027745','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22027745"><span id="translatedtitle">Spin effects on the instability and <span class="hlt">propagation</span> modes of electrostatic plasma <span class="hlt">waves</span> in quantum plasmas</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ki, Dae-Han; Jung, Young-Dae</p> <p>2011-09-19</p> <p>The effects of the electron spin interaction on the pure instability and <span class="hlt">propagation</span> modes of the quantum electrostatic <span class="hlt">waves</span> are investigated in cold quantum electron plasmas. It is found that the influence of the electron spin interaction increases the group velocity of the <span class="hlt">propagation</span> mode of the quantum electrostatic <span class="hlt">wave</span>. In addition, it is shown that the electron spin interaction enhances the growth rate of the instability mode of the quantum electrostatic <span class="hlt">wave</span>. It is also found that the effects of the electron spin interaction would be more important in the domain of small Fermi <span class="hlt">wave</span> numbers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22086264','SCIGOV-STC'); return false;" href="http://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('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('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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/pages/biblio/1259966-conical-wave-propagation-diffraction-two-dimensional-hexagonally-packed-granular-lattices','SCIGOV-DOEP'); return false;" href="http://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.; 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. 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('http://adsabs.harvard.edu/abs/2012SMaS...21g5001P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012SMaS...21g5001P"><span id="translatedtitle">Lamb <span class="hlt">wave</span> <span class="hlt">propagation</span> modelling and simulation using parallel processing architecture and graphical cards</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paćko, P.; Bielak, T.; Spencer, A. B.; Staszewski, W. J.; Uhl, T.; Worden, K.</p> <p>2012-07-01</p> <p>This paper demonstrates new parallel computation technology and an implementation for Lamb <span class="hlt">wave</span> <span class="hlt">propagation</span> modelling in complex structures. A graphical processing unit (GPU) and computer unified device architecture (CUDA), available in low-cost graphical cards in standard PCs, are used for Lamb <span class="hlt">wave</span> <span class="hlt">propagation</span> numerical simulations. The local interaction simulation approach (LISA) <span class="hlt">wave</span> <span class="hlt">propagation</span> algorithm has been implemented as an example. Other algorithms suitable for parallel discretization can also be used in practice. The method is illustrated using examples related to damage detection. The results demonstrate good accuracy and effective computational performance of very large models. The <span class="hlt">wave</span> <span class="hlt">propagation</span> modelling presented in the paper can be used in many practical applications of science and engineering.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26871145','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26871145"><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="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chong, C; Kevrekidis, P G; Ablowitz, M J; Ma, Yi-Ping</p> <p>2016-01-01</p> <p>Linear and nonlinear mechanisms for conical <span class="hlt">wave</span> <span class="hlt">propagation</span> in two-dimensional lattices are explored 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. 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('http://www.ncbi.nlm.nih.gov/pubmed/24960005','PUBMED'); return false;" href="http://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. PMID:24960005</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhPl...20c2115L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhPl...20c2115L"><span id="translatedtitle">The mixed Wentzel-Kramers-Brillouin-full-<span class="hlt">wave</span> approach and its application to lower hybrid <span class="hlt">wave</span> <span class="hlt">propagation</span> and absorption</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lu, Z. X.; Zonca, F.; Cardinali, A.</p> <p>2013-03-01</p> <p>The mixed Wentzel-Kramers-Brillouin (WKB)-full-<span class="hlt">wave</span> approach for the calculation of the 2D mode structure in tokamak plasmas is further developed based on our previous work [A. Cardinali and F. Zonca, Phys. Plasmas 10, 4199 (2003) and Z. X. Lu et al., Phys. Plasmas 19, 042104 (2012)]. A new scheme for theoretical analysis and numerical implementation of the mixed WKB-full-<span class="hlt">wave</span> approach is formulated, based on scale separation and asymptotic analysis. Besides its capability to efficiently investigate the initial value problem for 2D mode structures and linear stability, in this work, the mixed WKB-full-<span class="hlt">wave</span> approach is extended to the investigation of radio frequency <span class="hlt">wave</span> <span class="hlt">propagation</span> and absorption, e.g., lower hybrid <span class="hlt">waves</span>. As a novel method, its comparison with other approaches, e.g., WKB and beam tracing methods, is discussed. Its application to lower hybrid <span class="hlt">wave</span> <span class="hlt">propagation</span> in concentric circular tokamak plasmas using typical FTU discharge parameters is also demonstrated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AIPC.1685i0009N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AIPC.1685i0009N"><span id="translatedtitle">Simulation of blast <span class="hlt">wave</span> <span class="hlt">propagation</span> from source to long distance with topography and atmospheric effects</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nguyen-Dinh, Maxime; Gainville, Olaf; Lardjane, Nicolas</p> <p>2015-10-01</p> <p>We present new results for the blast <span class="hlt">wave</span> <span class="hlt">propagation</span> from strong shock regime to the weak shock limit. For this purpose, we analyse the blast <span class="hlt">wave</span> <span class="hlt">propagation</span> using both Direct Numerical Simulation and an acoustic asymptotic model. This approach allows a full numerical study of a realistic pyrotechnic site taking into account for the main physical effects. We also compare simulation results with first measurements. This study is a part of the french ANR-Prolonge project (ANR-12-ASTR-0026).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ChJME..28.1222L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ChJME..28.1222L"><span id="translatedtitle"><span class="hlt">Propagation</span> of electromagnetic <span class="hlt">wave</span> in coaxial conical transverse electromagnetic <span class="hlt">wave</span> cell</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Xingxun; Zhang, Tao; Qi, Wangquan</p> <p>2015-11-01</p> <p>In order to solve the problem of broadband field probes calibration with only selected discrete frequencies above 1 GHz, a sweep-frequency calibration technology based on a coaxial conical(co-conical) cell is researched. Existing research is only qualitative because of the complexity of theoretical calculations. For designing a high performance cell, a mathematic model of high-order modes transmission is built according to the geometrical construction of co-conical. The associated Legendre control functions of high-order modes are calculated by using recursion methodology and the numerical calculation roots are presented with different half angles of inner and outer conductor. Relationship between roots and high-order modes transmission is analyzed, when the half angles of inner conductor and outer conductor are θ 1=1.5136° and θ 2=8° respectively, the co-conical cell has better performance for fewer transmitting high-order modes. The <span class="hlt">propagation</span> process of the first three transmitting modes <span class="hlt">wave</span> is simulated in CST-MWS software from the same structured co-conical. The simulation plots show that transmission of high-order modes appears with electromagnetic <span class="hlt">wave</span> reflection, then different high-order mode transmission has different cut-off region and each cut-off region is determined by its cut-off wavelength. This paper presents numerical calculation data and theoretical analysis to design key structural parameters for the co-conical transverse electromagnetic <span class="hlt">wave</span> cell(co-conical TEM cell).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22167199','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22167199"><span id="translatedtitle">GLOBAL AND LOCAL CUTOFF FREQUENCIES FOR TRANSVERSE <span class="hlt">WAVES</span> <span class="hlt">PROPAGATING</span> ALONG SOLAR MAGNETIC FLUX TUBES</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Routh, S.; Musielak, Z. E.; Hammer, R. E-mail: zmusielak@uta.edu</p> <p>2013-01-20</p> <p>It is a well-established result that the <span class="hlt">propagation</span> of linear transverse <span class="hlt">waves</span> along a thin but isothermal magnetic flux tube is affected by the existence of the global cutoff frequency, which separates the <span class="hlt">propagating</span> and non-<span class="hlt">propagating</span> <span class="hlt">waves</span>. In this paper, the <span class="hlt">wave</span> <span class="hlt">propagation</span> along a thin and non-isothermal flux tube is considered and a local cutoff frequency is derived. The effects of different temperature profiles on this local cutoff frequency are studied by considering different power-law temperature distributions, as well as the semi-empirical VAL C model of the solar atmosphere. The obtained results show that the conditions for <span class="hlt">wave</span> <span class="hlt">propagation</span> strongly depend on the temperature gradients. Moreover, the local cutoff frequency calculated for the VAL C model gives constraints on the range of <span class="hlt">wave</span> frequencies that are <span class="hlt">propagating</span> in different parts of the solar atmosphere. These theoretically predicted constraints are compared to observational data and are used to discuss the role played by transverse tube <span class="hlt">waves</span> in the atmospheric heating and dynamics, and in the excitation of solar atmospheric oscillations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012APS..DPPCP8108G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012APS..DPPCP8108G"><span id="translatedtitle">Spatially-resolved x-ray scattering measurements of a <span class="hlt">planar</span> blast <span class="hlt">wave</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gamboa, E. J.; Montgomery, D. S.; Benage, J. F.; Falk, K.; Kuranz, C. C.; Keiter, P. A.; Drake, R. P.</p> <p>2012-10-01</p> <p>In many laboratory astrophysics experiments, intense laser irradiation creates novel material conditions with large, one-dimensional gradients in the temperature, density, and ionization state. X-ray Thomson scattering is a powerful technique for measuring these plasma parameters. However, the scattered signal is typically measured with little or no spatial resolution, which limits the ability to diagnose inhomogeneous plasmas. We report on the development of a new imaging x-ray Thomson spectrometer (IXTS) for the Omega laser facility. The diffraction of x-rays from a toroidally curved crystal creates high-resolution images that are spatially resolved along a one-dimensional profile while spectrally dispersing the radiation. An experiment is described in which we used the IXTS to measure the spatial temperature profile of a novel system. A low-density carbon foam was irradiated with intensities on the order of 10^15 W/cm^2, launching a <span class="hlt">planar</span> blast <span class="hlt">wave</span>. After a delay of several nanoseconds, x-rays created from irradiation of a nickel foil, scattered at 90 and were recorded by the IXTS. The resulting spatially resolved scattering spectra were analyzed to extract the temperature profile across the blast <span class="hlt">wave</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19890064628&hterms=isothermal+compression&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2528%2Bisothermal%2Bcompression','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19890064628&hterms=isothermal+compression&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2528%2Bisothermal%2Bcompression"><span id="translatedtitle"><span class="hlt">Propagating</span> and nonpropagating compression <span class="hlt">waves</span> in an isothermal atmosphere with uniform horizontal magnetic field</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Musielak, Z. E.; Moore, R. L.; Suess, S. T.; An, C.-H.</p> <p>1989-01-01</p> <p>Full analytical solutions to the <span class="hlt">wave</span> equations for steady vertical compression <span class="hlt">waves</span> in an isothermal hydrostatic atmosphere with a uniform horizontal magnetic field are presented. It is shown that, in the steady state approach, the behavior of upward <span class="hlt">waves</span> and downward <span class="hlt">waves</span> is very different. It is shown that the finding of Thomas (1983), indicating that the cutoff frequency for vertically <span class="hlt">propagating</span> magnetoacoustic <span class="hlt">waves</span> in an isothermal atmosphere with a horizontal magnetic field is the same for isothermal atmosphere with no magnetic field, is true only for the downward <span class="hlt">waves</span>.</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://adsabs.harvard.edu/abs/1999JPhD...32.2578J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999JPhD...32.2578J"><span id="translatedtitle">Shock <span class="hlt">wave</span> and material vapour plume <span class="hlt">propagation</span> during excimer laser ablation of aluminium samples</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeong, S. H.; Greif, R.; Russo, R. E.</p> <p>1999-10-01</p> <p>A probe beam deflection technique was utilized to measure the <span class="hlt">propagation</span> of a shock <span class="hlt">wave</span> and material vapour plume generated during excimer laser ablation of aluminium samples. The measured transit time of the laser-induced shock <span class="hlt">wave</span> was compared with the prediction based on an ideal blast-<span class="hlt">wave</span> model, using the Sedov-Taylor solution. The prediction of the incident laser energy converted into the laser-induced gasdynamic flow utilizing this blast-<span class="hlt">wave</span> model overestimated the efficiency, even under conditions when the measured shock-<span class="hlt">wave</span> velocity follows the correct model relation. The <span class="hlt">propagation</span> of material vapour was measured from the deflection of the probe beam at later times. The <span class="hlt">propagation</span> velocity of material vapour ranged from 20-40 m s-1 with a greater velocity near the target surface.</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> </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://www.ncbi.nlm.nih.gov/pubmed/18997124','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/18997124"><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="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wu, Jian-Young; Xiaoying Huang; Chuan Zhang</p> <p>2008-10-01</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/2013PhPl...20j2903F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhPl...20j2903F"><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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Futatani, S.; Horton, W.; Kaladze, T. D.</p> <p>2013-10-01</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('http://www.ncbi.nlm.nih.gov/pubmed/26213234','PUBMED'); return false;" href="http://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>2015-01-01</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> <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.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> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22224191','SCIGOV-STC'); return false;" href="http://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('http://adsabs.harvard.edu/abs/2016gac..conf..371G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016gac..conf..371G"><span id="translatedtitle">Electromagnetic <span class="hlt">waves</span> <span class="hlt">propagation</span> nearby rotating gravitating astrophysical object with atmosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gladyshev, V. O.; Tereshin, A. A.; Fomin, I. V.; Chelnokov, M. B.; Kauts, V. L.; Gladysheva, T. M.; Bazleva, D. D.</p> <p></p> <p>The aim of the article to explore the effects of gravitational lensing and attraction of electromagnetic radiation in the description of the <span class="hlt">propagation</span> of radiation nearby the atmospheres of rotating astrophysical objects.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22271284','SCIGOV-STC'); return false;" href="http://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('http://adsabs.harvard.edu/abs/2014AGUFMSH53C..07H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMSH53C..07H"><span id="translatedtitle">Observation of Counter <span class="hlt">Propagating</span> Alfven <span class="hlt">Waves</span> with Perpendicular Polarizations and the Associated Proton Kinetics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>He, J.; Pei, Z. T.; Wang, L.; Tu, C. Y.; Marsch, E.; Yao, S.</p> <p>2014-12-01</p> <p>It is believed that MHD turbulence cascading is mainly caused by the collisions between Alfven <span class="hlt">waves</span>, which <span class="hlt">propagate</span> oppositely and are polarized perpendicularly to each other. Nonlinear interaction will vanish if the counter-<span class="hlt">propagating</span> Alfven <span class="hlt">waves</span> have their polarization aligned with each other. However, the Alfven <span class="hlt">waves</span> satisfying these collision criteria have not yet been found in the solar wind observations. Here we report the existence of Alfven <span class="hlt">waves</span> with opposite <span class="hlt">propagation</span> and non-aligned polarization in the solar wind. In one case of anti-sunward magnetic sector, with RTN as the coordinates, the magnetic fluctuations in T-component (BT) are anti-correlated with the velocity fluctuations in T-component (VT), while BR and BN fluctuations are in positive correlation with VR and VN fluctuations, respectively. These features suggest a possible nonlinear interaction between outward <span class="hlt">propagating</span> Alfven <span class="hlt">wave</span> with polarization in T-direction and inward <span class="hlt">propagating</span> Alfven <span class="hlt">wave</span> with polarization in R&N-directions. Moreover, the associated proton kinetics shows the existence of field-aligned sunward beam rather than anti-sunward beam, which may indicate a parallel Landau heating by sunward kinetic Alfven <span class="hlt">waves</span>. A statistical study including more cases is also conducted.</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('http://www.osti.gov/scitech/biblio/22518783','SCIGOV-STC'); return false;" href="http://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://www.osti.gov/scitech/biblio/21072683','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21072683"><span id="translatedtitle">Parametric instabilities of parallel <span class="hlt">propagating</span> incoherent Alfven <span class="hlt">waves</span> in a finite ion beta plasma</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Nariyuki, Y.; Hada, T.; Tsubouchi, K.</p> <p>2007-12-15</p> <p>Large amplitude, low-frequency Alfven <span class="hlt">waves</span> constitute one of the most essential elements of magnetohydrodynamic (MHD) turbulence in the fast solar wind. Due to small collisionless dissipation rates, the <span class="hlt">waves</span> can <span class="hlt">propagate</span> long distances and efficiently convey such macroscopic quantities as momentum, energy, and helicity. Since loading of such quantities is completed when the <span class="hlt">waves</span> damp away, it is important to examine how the <span class="hlt">waves</span> can dissipate in the solar wind. Among various possible dissipation processes of the Alfven <span class="hlt">waves</span>, parametric instabilities have been believed to be important. In this paper, we numerically discuss the parametric instabilities of coherent/incoherent Alfven <span class="hlt">waves</span> in a finite ion beta plasma using a one-dimensional hybrid (superparticle ions plus an electron massless fluid) simulation, in order to explain local production of sunward <span class="hlt">propagating</span> Alfven <span class="hlt">waves</span>, as suggested by Helios/Ulysses observation results. Parameter studies clarify the dependence of parametric instabilities of coherent/incoherent Alfven <span class="hlt">waves</span> on the ion and electron beta ratio. Parametric instabilities of coherent Alfven <span class="hlt">waves</span> in a finite ion beta plasma are vastly different from those in the cold ions (i.e., MHD and/or Hall-MHD systems), even if the collisionless damping of the Alfven <span class="hlt">waves</span> are neglected. Further, ''nonlinearly driven'' modulational instability is important for the dissipation of incoherent Alfven <span class="hlt">waves</span> in a finite ion beta plasma regardless of their polarization, since the ion kinetic effects let both the right-hand and left-hand polarized <span class="hlt">waves</span> become unstable to the modulational instability. The present results suggest that, although the antisunward <span class="hlt">propagating</span> dispersive Alfven <span class="hlt">waves</span> are efficiently dissipated through the parametric instabilities in a finite ion beta plasma, these instabilities hardly produce the sunward <span class="hlt">propagating</span> <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998iwpn.book.....D&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998iwpn.book.....D&link_type=ABSTRACT"><span id="translatedtitle">Introduction to <span class="hlt">Wave</span> <span class="hlt">Propagation</span> in Nonlinear Fluids and Solids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drumheller, Douglas S.</p> <p>1998-02-01</p> <p><span class="hlt">Waves</span> occur widely in nature and have innumerable commercial uses. <span class="hlt">Waves</span> are responsible for the sound of speech, meteors igniting the atmosphere, radio and television broadcasting, medical diagnosis using ultrasound. This book provides a thorough, modern introduction to the study of linear and nonlinear <span class="hlt">waves</span>. Beginning with fundamental concepts of motion, the book goes on to discuss linear and nonlinear mechanical <span class="hlt">waves</span>, thermodynamics, and constitutive models for a variety of gases, liquids, and solids. Among the important areas of research and application are impact analysis, shock <span class="hlt">wave</span> research, explosive detonation, nonlinear acoustics, and hypersonic aerodynamics. Students at an advanced undergraduate/graduate level will find this text a clear and comprehensive introduction to the study of nonlinear <span class="hlt">wave</span> phenomena, and it will also be valuable as a professional reference in engineering and applied physics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1033866','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1033866"><span id="translatedtitle">Mode conversion by symmetry breaking of <span class="hlt">propagating</span> spin <span class="hlt">waves</span>.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Clausen, P.; Vogt, K.; Schultheiss, H.; Schafer, S.; Obry, B.; Wolf, G.; Pirro, P.; Leven, B.; Hillebrands, B.</p> <p>2011-10-01</p> <p>We study spin-<span class="hlt">wave</span> transport in a microstructured Ni{sub 81}Fe{sub 19} waveguide exhibiting broken translational symmetry. We observe the conversion of a beam profile composed of symmetric spin-<span class="hlt">wave</span> width modes with odd numbers of antinodes n = 1, 3,... into a mixed set of symmetric and asymmetric modes. Due to the spatial homogeneity of the exciting field along the used microstrip antenna, quantized spin-<span class="hlt">wave</span> modes with an even number n of antinodes across the stripe's width cannot be directly excited. We show that a break in translational symmetry may result in a partial conversion of even spin-<span class="hlt">wave</span> waveguide modes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20692675','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20692675"><span id="translatedtitle"><span class="hlt">Propagation</span> of elastic <span class="hlt">waves</span> in an anisotropic functionally graded hollow cylinder in vacuum.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Baron, Cécile</p> <p>2011-02-01</p> <p>As a non-destructive, non-invasive and non-ionizing evaluation technique for heterogeneous media, the ultrasonic method is of major interest in industrial applications but especially in biomedical fields. Among the unidirectionally heterogeneous media, the continuously varying media are a particular but widespread case in natural materials. The first studies on laterally varying media were carried out by geophysicists on the Ocean, the atmosphere or the Earth, but the teeth, the bone, the shells and the insects wings are also functionally graded media. Some of them can be modeled as <span class="hlt">planar</span> structures but a lot of them are curved media and need to be modeled as cylinders instead of plates. The present paper investigates the influence of the tubular geometry of a waveguide on the <span class="hlt">propagation</span> of elastic <span class="hlt">waves</span>. In this paper, the studied structure is an anisotropic hollow cylinder with elastic properties (stiffness coefficients c(ij) and mass density ρ) functionally varying in the radial direction. An original method is proposed to find the eigenmodes of this waveguide without using a multilayered model for the cylinder. This method is based on the sextic Stroh's formalism and an analytical solution, the matricant, explicitly expressed under the Peano series expansion form. This approach has already been validated for the study of an anisotropic laterally-graded plate (Baron et al., 2007; Baron and Naili, 2010) [6,5]. The dispersion curves obtained for the radially-graded cylinder are compared to the dispersion curves of a corresponding laterally-graded plate to evaluate the influence of the curvature. Preliminary results are presented for a tube of bone in vacuum modelling the in vitro conditions of bone strength evaluation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/20692675','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/20692675"><span id="translatedtitle"><span class="hlt">Propagation</span> of elastic <span class="hlt">waves</span> in an anisotropic functionally graded hollow cylinder in vacuum.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Baron, Cécile</p> <p>2011-02-01</p> <p>As a non-destructive, non-invasive and non-ionizing evaluation technique for heterogeneous media, the ultrasonic method is of major interest in industrial applications but especially in biomedical fields. Among the unidirectionally heterogeneous media, the continuously varying media are a particular but widespread case in natural materials. The first studies on laterally varying media were carried out by geophysicists on the Ocean, the atmosphere or the Earth, but the teeth, the bone, the shells and the insects wings are also functionally graded media. Some of them can be modeled as <span class="hlt">planar</span> structures but a lot of them are curved media and need to be modeled as cylinders instead of plates. The present paper investigates the influence of the tubular geometry of a waveguide on the <span class="hlt">propagation</span> of elastic <span class="hlt">waves</span>. In this paper, the studied structure is an anisotropic hollow cylinder with elastic properties (stiffness coefficients c(ij) and mass density ρ) functionally varying in the radial direction. An original method is proposed to find the eigenmodes of this waveguide without using a multilayered model for the cylinder. This method is based on the sextic Stroh's formalism and an analytical solution, the matricant, explicitly expressed under the Peano series expansion form. This approach has already been validated for the study of an anisotropic laterally-graded plate (Baron et al., 2007; Baron and Naili, 2010) [6,5]. The dispersion curves obtained for the radially-graded cylinder are compared to the dispersion curves of a corresponding laterally-graded plate to evaluate the influence of the curvature. Preliminary results are presented for a tube of bone in vacuum modelling the in vitro conditions of bone strength evaluation. PMID:20692675</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhyE...70..176D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhyE...70..176D"><span id="translatedtitle"><span class="hlt">Planar</span> electromagnetic band-gap structure based on graphene</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dong, Yanfei; Liu, Peiguo; Yin, Wen-Yan; Li, Gaosheng; Yi, Bo</p> <p>2015-06-01</p> <p>Electromagnetic band-gap structure with slow-<span class="hlt">wave</span> effect is instrumental in effectively controlling electromagnetic <span class="hlt">wave</span> <span class="hlt">propagation</span>. In this paper, we theoretically analyze equivalent circuit model of electromagnetic band-gap structure based on graphene and evaluate its potential applications. Graphene electromagnetic band-gap based on parallel <span class="hlt">planar</span> waveguide is investigated, which display good characteristics in dynamically adjusting the electromagnetic <span class="hlt">wave</span> <span class="hlt">propagation</span> in terahertz range. The same characteristics are retrieved in a spiral shape electromagnetic band-gap based on coplanar waveguide due to tunable conductivity of graphene. Various potential terahertz <span class="hlt">planar</span> devices are expected to derive from the prototype structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998ApSS..127.1029J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998ApSS..127.1029J"><span id="translatedtitle"><span class="hlt">Propagation</span> of the shock <span class="hlt">wave</span> generated from excimer laser heating of aluminum targets in comparison with ideal blast <span class="hlt">wave</span> theory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeong, S. H.; Greif, R.; Russo, R. E.</p> <p>1998-05-01</p> <p><span class="hlt">Propagation</span> of the shock <span class="hlt">wave</span> generated during pulsed laser heating of aluminum targets was measured utilizing a probe beam deflection technique. The transit time of the laser-generated shock <span class="hlt">wave</span> was compared with that predicted from the Sedov-Taylor solution for an ideal spherical blast <span class="hlt">wave</span>. It was found that the most important parameters for the laser-generated shock <span class="hlt">wave</span> to be consistent with the theoretically predicted <span class="hlt">propagation</span> are the ambient pressure and the laser beam spot size. The prediction for laser energy conversion into the laser-induced vapor flow using the Sedov-Taylor solution overestimated the energy coupling efficiency, indicating a difference between a laser-induced gas-dynamic flow and an ideal blast <span class="hlt">wave</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006ShWav..15..341N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006ShWav..15..341N"><span id="translatedtitle">Head-on Collision of a Detonation with a <span class="hlt">Planar</span> Shock <span class="hlt">Wave</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ng, H. D.; Botros, B. B.; Chao, J.; Yang, J. M.; Nikiforakis, N.; Lee, J. H. S.</p> <p>2006-09-01</p> <p>The phenomenon that occurs when a Chapman Jouguet (CJ) detonation collides with a shock <span class="hlt">wave</span> is discussed. Assuming a one-dimensional steady <span class="hlt">wave</span> configuration analogous to a <span class="hlt">planar</span> shock shock frontal interaction, analytical solutions of the Rankine Hugoniot relationships for the transmitted detonation and the transmitted shock are obtained by matching the pressure and particle velocity at the contact surface. The analytical results indicate that there exist three possible regions of solutions, i.e. the transmitted detonation can have either strong, weak or CJ solution, depending on the incident detonation and shock strengths. On the other hand, if we impose the transmitted detonation to have a CJ solution followed by a rarefaction fan, the boundary conditions are also satisfied at the contact surface. The existence of these multiple solutions is verified by an experimental investigation. It is found that the experimental results agree well with those predicted by the second <span class="hlt">wave</span> interaction model and that the transmitted detonation is a CJ detonation. Unsteady numerical simulations of the reactive Euler equations with both simple one-step Arrhenius kinetic and chain-branching kinetic models are also carried out to look at the transient phenomena and at the influence of a finite reaction thickness of a detonation <span class="hlt">wave</span> on the problem of head-on collision with a shock. From all the computational results, a relaxation process consisting of a quasi-steady period and an overshoot for the transmitted detonation subsequent to the head-on collisions can be observed, followed by the asymptotic decay to a CJ detonation as predicted theoretically. For unstable pulsating detonations, it is found that, due to the increase in the thermodynamic state of the reactive mixture caused by the shock, the transmitted pulsating detonation can become more stable with smaller amplitude and period oscillation. These observations are in good agreement with experimental evidence obtained</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012TATJ...10..Pe7N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012TATJ...10..Pe7N"><span id="translatedtitle"><span class="hlt">Propagation</span> of Curved Detonation <span class="hlt">Waves</span> Stabilized in Annular Channels with a Rectangular Cross-section</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakayama, Hisahiro; Takahiro Moriya; Kasahara, Jiro; Matsuo, Akiko; Sasamoto, Yuya; Funaki, Ikkoh</p> <p></p> <p>Visualization experiments employing rectangular cross-section curved channels were performed in order to examine the fundamental characteristics of a curved detonation <span class="hlt">wave</span> <span class="hlt">propagating</span> stably through an annular channel. A stoichiometric ethylene-oxygen mixture gas and five types of curved channels with different inner radii of curvature were used. The detonation <span class="hlt">waves</span> <span class="hlt">propagating</span> in the curved channels were curved due to the expansion <span class="hlt">waves</span> from the inner walls of the curved channels. The ratio of the inner radius of curved channel (ri) to the normal detonation cell width (λ) was an important factor determining the stability of the curved detonation <span class="hlt">waves</span>. The detonation <span class="hlt">propagation</span> mode in the curved channels transitioned from unstable to stable in the range 14 ≤ ri/λ ≤ 26. The normal detonation velocity (Dn) of the curved detonation <span class="hlt">wave</span> <span class="hlt">propagating</span> stably in a curved channel was approximately formulated. The approximated Dn given by the formula agreed well with the experimental results. The front shock shape of the curved detonation <span class="hlt">wave</span> could be reconstructed accurately using the formula. The value of Dn nondimensionalized by the Chapman-Jouguet detonation velocity became a function of the local curvature of the curved detonation <span class="hlt">wave</span> (κ) nondimensionalized by λ regardless of the shape of curved channel. The front shock shapes of the detonation <span class="hlt">waves</span> in the stable mode became similar to each other under constant ri/λ conditions.</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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