Surface acoustic wave propagation in graphene film
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.
Mechanical surface waves accompany action potential propagation.
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
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.
Surface waves propagating on a turbulent flow
NASA Astrophysics Data System (ADS)
Gutiérrez, Pablo; AumaÃ®tre, 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.
Mechanical Surface Waves Accompany Action Potential Propagation
NASA Astrophysics Data System (ADS)
Machta, Benjamin; El Hady, Ahmed
2015-03-01
The action potential (AP) is the basic mechanism by which information is transmitted along neuronal axons. Although the excitable nature of axons is understood to be primarily electrical, many experimental studies have shown that a mechanical displacement of the axonal membrane co-propagates with the electrical signal. While the experimental evidence for co-propagating mechanical waves is diverse and compelling, there is no consensus for their physical underpinnings. We present a model in which these mechanical displacements arise from the driving of mechanical surface waves, in which potential energy is stored in elastic deformations of the neuronal membrane and cytoskeleton while kinetic energy is stored in the movement of the axoplasmic fluid. In our model these surface waves are driven by the traveling wave of electrical depolarization that characterizes the AP, altering the electrostatic forces across the membrane as it passes. Our model allows us to predict the shape of the displacement that should accompany any traveling wave of voltage, including the well-characterized AP. We expect our model to serve as a framework for understanding the physical origins and possible functional roles of these AWs in neurobiology. See Arxiv/1407.7600
Surface wave propagation across the USArray
NASA Astrophysics Data System (ADS)
Foster, A. E.; Ekstrom, G.; Hjorleifsdottir, V.
2010-12-01
We present Love and Rayleigh wave phase-velocity models at discrete periods between 25 and 100 s from the inversion of phase measurements. Phase measurements are made on an updated set of USArray TA data using a two-station method that has been corrected for the estimated wavefront arrival angle. Arrival angles are estimated using a “mini-array” method, which additionally calculates the local phase velocity for each event recorded in a mini array. By minimizing the misfit between observed and predicted phase within the mini array, we find the best-fit local phase velocity, which is then used to predict the phase in a grid search for apparent source locations. The trial sources have fixed epicentral distance but varied arrival angles with respect to the mini array, and the optimal apparent source corresponds to the arrival angle. Correcting the two-station method for the arrival angle produces small (around 1%) changes in phase velocity. In the inversion results, these changes are most significant along the Pacific coast at shorter periods, as a result of refraction at the ocean-continent transition. The local phase-velocity estimates are combined to make independent phase-velocity models for comparison with the inversion results. For Rayleigh waves at all periods, the two models have similar size, location, and strength of anomalies. Higher noise levels in Love wave data are apparent in both models; they show similar velocities and large anomalies, but smaller anomalies are below the noise levels at short periods. Still, the overall quality and quantity of data available allow us to investigate the errors associated with the two-station method, and the effect the duration and complexity of wave propagation has on these errors. We examine the consistency of wave propagation using the estimated arrival angles for multiple events recorded at the same stations. This is repeated with synthetic events, calculated using the spectral element method of Komatitsch and
Surface wave propagation characteristics in atmospheric pressure plasma column
NASA Astrophysics Data System (ADS)
Pencheva, M.; Benova, E.; Zhelyazkov, I.
2007-04-01
In the typical experiments of surface wave sustained plasma columns at atmospheric pressure the ratio of collision to wave frequency (ν/ω) is much greater than unity. Therefore, one might expect that the usual analysis of the wave dispersion relation, performed under the assumption ν/ω = 0, cannot give adequate description of the wave propagation characteristics. In order to study these characteristics we have analyzed the wave dispersion relationship for arbitrary ν/ω. Our analysis includes phase and wave dispersion curves, attenuation coefficient, and wave phase and group velocities. The numerical results show that a turning back point appears in the phase diagram, after which a region of backward wave propagation exists. The experimentally observed plasma column is only in a region where wave propagation coefficient is higher than the attenuation coefficient. At the plasma column end the electron density is much higher than that corresponding to the turning back point and the resonance.
Electromagnetic Wave Propagation over Oil-Covered Sea Surface
NASA Astrophysics Data System (ADS)
Yang, Chao; Jin, Wei; Guo, Li-Xin
2012-07-01
An exhaustive analysis of electromagnetic wave propagation over an oil-covered sea surface in an evaporation duct environment is studied in comparison with those of the oil-free sea surface. Instead of using the traditional rms height formula, which only considers the oil-free sea surface, we reduce the rms height of a one-dimensional oil-covered sea surface based on the Pierson-Moskowitz sea spectrum. Then, the electromagnetic wave propagation over the oil-covered sea surface in an evaporation duct environment with different wind speeds and frequencies is discussed by the parabolic equation for a fully oil-covered sea surface. In addition, the influence of the fractional filling factor on the electromagnetic wave propagation over non-fully oil-covered sea surface is also investigated. The results show that the oil film can reduce the sea surface roughness and strengthen the trapping effect in an evaporation duct environment.
Estimating propagation velocity through a surface acoustic wave sensor
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.
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.
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.
Modeling anomalous surface - wave propagation across the Southern Caspian basin
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.
Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves.
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
Unidirectional propagation of magnetostatic surface spin waves at a magnetic film surface
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
2014-12-08
An analytical expression for the amplitudes of magnetostatic surface spin waves (MSSWs) propagating 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 propagate along the direction of −H{sup →}×n{sup →}, where n{sup →} is the surface normal. This unidirectional propagation 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-wave devices such as isolators and spin-wave diodes.
Effect of near-surface topography on high-frequency Rayleigh-wave propagation
NASA Astrophysics Data System (ADS)
Wang, Limin; Xu, Yixian; Xia, Jianghai; Luo, Yinhe
2015-05-01
Rayleigh waves, which are formed due to interference of P- and Sv-waves near the free surface, propagate along the free surface and vanish exponentially in the vertical direction. Their propagation is strongly influenced by surface topography. Due to the high resolution and precision requirements of near-surface investigations, the high-frequency Rayleigh waves are usually used for near-surface structural detecting. Although there are some numerical studies on high-frequency Rayleigh-wave propagation on topographic free surface, detailed analysis of characters of high-frequency Rayleigh-wave propagation on topographic free surface remains untouched. Hence, research of propagation of Rayleigh waves on complex topographic surface becomes critical for Rayleigh-wave methods in near-surface applications. To study the propagation of high-frequency Rayleigh waves 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 propagation of high-frequency Rayleigh waves on these two topographic surfaces by finite-difference method. Soon afterwards, we analyze the propagation character of high-frequency Rayleigh waves 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 waves is more distinct than influence of uplifted topography. Rayleigh waves produce new scattering body waves 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 waves is lost. The uplifted topography with gentle slope produces similar
Single crystal metal wedges for surface acoustic wave propagation
Fisher, Edward S.
1982-01-01
An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.
Single crystal metal wedges for surface acoustic wave propagation
Fisher, E.S.
1980-05-09
An ultrasonic testing device has been developed to evaluate flaws and inhomogeneities in the near-surface region of a test material. A metal single crystal wedge is used to generate high frequency Rayleigh surface waves in the test material surface by conversion of a slow velocity, bulk acoustic mode in the wedge into a Rayleigh wave at the metal-wedge test material interface. Particular classes of metals have been found to provide the bulk acoustic modes necessary for production of a surface wave with extremely high frequency and angular collimation. The high frequency allows flaws and inhomogeneities to be examined with greater resolution. The high degree of angular collimation for the outgoing ultrasonic beam permits precision angular location of flaws and inhomogeneities in the test material surface.
Wave propagation in photonic crystals and metamaterials: Surface waves, nonlinearity and chirality
Wang, Bingnan
2009-01-01
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 wave. The wave propagation 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 waves with frequency within the range of the band-gap are suppressed from propagating 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 propagation of electromagnetic waves 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 wave propagation 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
Geometric effects of global lateral heterogeneity on long-period surface wave propagation
NASA Technical Reports Server (NTRS)
Lay, T.; Kanamori, H.
1985-01-01
The present investigation has the objective to document examples of anomalous long-period surface wave amplitude behavior and to provide a preliminary appraisal of the effects of global lateral heterogeneity on surface wave propagation from a ray theory perspective. Attention is given to remarkable long-period surface wave anomalies described in literature, an equidistance azimuthal plot centered on the Iranian source region, Rayleigh wave and Love wave spectra for the 256-s period arrivals for the Tabas earthquake, constrained moment tensor and fault model inversion solutions ofr Iranian earthquakes, aspects of surface wave ray tracing, and a table of Rayleigh wave amplitude anomalies for Iranian earthquakes. Surface wave ray-tracing calculations for models of global phase velocity variations proposed by Nakanishi and Anderson (1984) are found to show that large-amplitude anomalies will be observed for Love and Rayleigh waves with periods of 100-250 s.
Siemens, M.; Li, Q.; Murnane, M.; Kapteyn, H.; Yang, R.; Anderson, E.; Nelson, K.
2009-03-02
We study ultrahigh frequency surface acoustic wave propagation in nickel-on-sapphire nanostructures. The use of ultrafast, coherent, extreme ultraviolet beams allows us to extend optical measurements of propagation dynamics of surface acoustic waves to frequencies of nearly 50 GHz, corresponding to wavelengths as short as 125 nm. We repeat the measurement on a sequence of nanostructured samples to observe surface acoustic wave dispersion in a nanostructure series for the first time. These measurements are critical for accurate characterization of thin films using this technique.
Visualization of terahertz surface waves propagation on metal foils
Wang, Xinke; Wang, Sen; Sun, Wenfeng; Feng, Shengfei; Han, Peng; Yan, Haitao; Ye, Jiasheng; Zhang, Yan
2016-01-01
Exploitation of surface plasmonic devices (SPDs) in the terahertz (THz) band is always beneficial for broadening the application potential of THz technologies. To clarify features of SPDs, a practical characterization means is essential for accurately observing the complex field distribution of a THz surface wave (TSW). Here, a THz digital holographic imaging system is employed to coherently exhibit temporal variations and spectral properties of TSWs activated by a rectangular or semicircular slit structure on metal foils. Advantages of the imaging system are comprehensively elucidated, including the exclusive measurement of TSWs and fall-off of the time consumption. Numerical simulations of experimental procedures further verify the imaging measurement accuracy. It can be anticipated that this imaging system will provide a versatile tool for analyzing the performance and principle of SPDs. PMID:26729652
Visualization of terahertz surface waves propagation on metal foils.
Wang, Xinke; Wang, Sen; Sun, Wenfeng; Feng, Shengfei; Han, Peng; Yan, Haitao; Ye, Jiasheng; Zhang, Yan
2016-01-01
Exploitation of surface plasmonic devices (SPDs) in the terahertz (THz) band is always beneficial for broadening the application potential of THz technologies. To clarify features of SPDs, a practical characterization means is essential for accurately observing the complex field distribution of a THz surface wave (TSW). Here, a THz digital holographic imaging system is employed to coherently exhibit temporal variations and spectral properties of TSWs activated by a rectangular or semicircular slit structure on metal foils. Advantages of the imaging system are comprehensively elucidated, including the exclusive measurement of TSWs and fall-off of the time consumption. Numerical simulations of experimental procedures further verify the imaging measurement accuracy. It can be anticipated that this imaging system will provide a versatile tool for analyzing the performance and principle of SPDs. PMID:26729652
Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma
Niknam, A. R.; Taheri Boroujeni, S.; Khorashadizadeh, S. M.
2013-12-15
The propagation of surface waves on a semi-bounded quantum plasma in the presence of the external magnetic field and collisional effects is investigated by using quantum magnetohydrodynamics model. A general analytical expression for the dispersion relation of surface waves is obtained by considering the boundary conditions. It is shown that, in some special cases, the obtained dispersion relation reduces to the results reported in previous works. It is also indicated that the quantum, external magnetic field and collisional effects can facilitate the propagation of surface waves on a semi-bounded plasma. In addition, it is found that the growth rate of the surface wave instability is enhanced by increasing the collision frequency and plasmonic parameter.
On Lamb wave propagation from small surface explosions in the atmospheric boundary layer
ReVelle, D.O.; Kulichkov, S.N.
1998-12-31
The problem of Lamb waves propagation from small explosions in the atmospheric boundary layer are discussed. The results of lamb waves registrations from surface explosions with yields varied from 3 tons up to a few hundred tons (TNT equivalent) are presented. The source-receiver distances varied from 20 km up to 310 km. Most of the explosions were conducted during the evening and early morning hours when strong near-surface temperature and wind inversions existed. The corresponding profiles of effective sound velocity are presented. Some of the explosions had been realized with 15 minute intervals between them when morning inversion being destroyed. Corresponding transformation of Lamb waves was observed. The Korteveg-de Vrize equation to explain experimental data on Lamb waves propagation along earth surface is used.
Luo, Si; Yang, Hangbo; Yang, Yuanqing; Zhao, Ding; Chen, Xingxing; Qiu, Min; Li, Qiang
2015-01-01
Surface plasmon polaritons (SPPs) propagating at metal nanostructures play an important role in breaking the diffraction limit. Chemically synthesized single-crystalline metal nanoplates with atomically flat surfaces provide favorable features compared with traditional polycrystalline metal films. The excitation and propagation of leaky SPPs on micrometer sized (10–20 μm) and thin (30 nm) gold nanoplates are investigated utilizing leakage radiation microscopy. By varying polarization and excitation positions of incident light on apexes of nanoplates, wave-vector (including propagation constant and propagation direction) distributions of leaky SPPs in Fourier planes can be controlled, indicating tunable SPP propagation. These results hold promise for potential development of chemically synthesized single-crystalline metal nanoplates as plasmonic platforms in future applications. PMID:26302955
Hung, Yu-Ju; Lin, I-Sheng
2016-07-11
This paper reports a novel approach to the direct observation of Bloch surface waves, wherein a layer of fluorescent material is deposited directly on the surface of a semi-infinite periodic layered cell. A set of surface nano-gratings is used to couple pumping light to Bloch surface waves, while the sample is rotated until the pumping light meets the quasi-phase matching conditions. This study investigated the directional propagation of waves on stripe and circular one-dimensional grating structures by analyzing the dispersion relationship of the first two eigen modes. Our results demonstrate the efficacy of the proposed scheme in visualizing Bloch surface waves, which could be extended to a variety of other devices. PMID:27410869
NASA Astrophysics Data System (ADS)
Kolínský, Petr; Fuchs, Florian; Gröschl, Gidera; Bokelmann, Götz; AlpArray Working Group
2016-04-01
We utilize array beamforming techniques to investigate deterministic surface waves from regional and teleseismic earthquakes. Because the signal is well recognized and the fundamental mode for both Love and Rayleigh waves is separated before the beamforming, instead of searching for energy of all possible signals, we identify the frequency dependence of surface wave phase velocity and the true backazimuths of propagation. Using the dense AlpArray seismic broadband network distributed in the greater Alpine region across Europe with interstation distances around 40 km, we consider each station as a centre of an array of neighboring 5 to 6 stations. This allows us to calculate the local phase velocity dispersion curves for individual regions with diameter of approximately 80 - 100 km. By the beamforming, phase velocities are corrected for the true propagation backazimuth, which is slightly frequency dependent for each event. We invert the dispersion curves for S and P wave velocity distribution with depth. Measuring the phase velocity from different events distributed around the world, azimuthal dependence of the phase velocity is estimated and thus anisotropy constrained for particular depths. Beamforming of the signals in the time window sliding along the coda after the fundamental mode allows us to detect deterministic late surface-wave signals coming from certain directions dissimilar from the direct fundamental mode backazimuths for some of the events - these can be considered as surface wave reflections from lateral heterogeneities and vertical boundaries.
Fujii, Satoshi; Shikata, Shinichi; Uemura, Tomoki; Nakahata, Hideaki; Harima, Hiroshi
2005-10-01
Diamond films with various crystal qualities were grown by chemical vapor deposition on silicon wafers. Their crystallinity was characterized by Raman scattering and electron backscattering diffraction. By fabricating a device structure for surface acoustic wave (SAW) using these diamond films, the propagation loss was measured at 1.8 GHz and compared with the crystallinity. It was found that the propagation loss was lowered in relatively degraded films having small crystallites, a narrow distribution in the diamond crystallite size, and preferential grain orientation. This experiment clarifies diamond film characteristics required for high-frequency applications in SAW filters. PMID:16382634
Ciliary metachronal wave propagation on the compliant surface of Paramecium cells.
Narematsu, Naoki; Quek, Raymond; Chiam, Keng-Hwee; Iwadate, Yoshiaki
2015-12-01
Ciliary movements in protozoa exhibit metachronal wave-like coordination, in which a constant phase difference is maintained between adjacent cilia. It is at present generally thought that metachronal waves require hydrodynamic coupling between adjacent cilia and the extracellular fluid. To test this hypothesis, we aspirated a Paramecium cell using a micropipette which completely sealed the surface of the cell such that no fluid could pass through the micropipette. Thus, the anterior and the posterior regions of the cell were hydrodynamically decoupled. Nevertheless, we still observed that metachronal waves continued to propagate from the anterior to the posterior ends of the cell, suggesting that in addition to hydrodynamic coupling, there are other mechanisms that can also transmit the metachronal waves. Such transmission was also observed in computational modeling where the fluid was fully decoupled between two partitions of a beating ciliary array. We also imposed cyclic stretching on the surface of live Paramecium cells and found that metachronal waves persisted in the presence of cyclic stretching. This demonstrated that, in addition to hydrodynamic coupling, a compliant substrate can also play a critical role in mediating the propagation of metachronal waves. PMID:26616106
Guided wave propagation in metallic and resin plates loaded with water on single surface
NASA Astrophysics Data System (ADS)
Hayashi, Takahiro; Inoue, Daisuke
2016-02-01
Our previous papers reported dispersion curves for leaky Lamb waves in a water-loaded plate and wave structures for several typical modes including quasi-Scholte waves [1,2]. The calculations were carried out with a semi-analytical finite element (SAFE) method developed for leaky Lamb waves. This study presents SAFE calculations for transient guided waves including time-domain waveforms and animations of wave propagation in metallic and resin water-loaded plates. The results show that non-dispersive and non-attenuated waves propagating along the interface between the fluid and the plate are expected for effective non-destructive evaluation of such fluid-loaded plates as storage tanks and transportation pipes. We calculated transient waves in both steel and polyvinyl chloride (PVC) plates loaded with water on a single side and input dynamic loading from a point source on the other water-free surface as typical examples of metallic and resin plates. For a steel plate, there exists a non-dispersive and non-attenuated mode, called the quasi-Scholte wave, having an almost identical phase velocity to that of water. The quasi-Scholte wave has superior generation efficiency in the low frequency range due to its broad energy distribution across the plate, whereas it is localized near the plate-water interface at higher frequencies. This means that it has superior detectability of inner defects. For a PVC plate, plural non-attenuated modes exist. One of the non-attenuated modes similar to the A0 mode of the Lamb wave in the form of a group velocity dispersion curve is promising for the non-destructive evaluation of the PVC plate because it provides prominent characteristics of generation efficiency and low dispersion.
Propagation of detonation wave in hydrogen-air mixture in channels with sound-absorbing surfaces
NASA Astrophysics Data System (ADS)
Bivol, G. Yu.; Golovastov, S. V.; Golub, V. V.
2015-12-01
The possibility of using sound-absorbing surfaces for attenuating the intensity of detonation waves propagating in hydrogen-air mixtures has been experimentally studied in a cylindrical detonation tube open at one end, with an explosive initiated by spark discharge at the closed end. Sound-absorbing elements were made of an acoustic-grade foamed rubber with density of 0.035 g/cm3 containing open pores with an average diameter of 0.5 mm. The degree of attenuation of the detonation wave front velocity was determined as dependent on the volume fraction of hydrogen in the gas mixture.
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
NASA Astrophysics Data System (ADS)
Thoma, Carsten Hilmar
1997-12-01
The coupling of stress and strain fields to electric fields present in anisotropic piezoelectric crystals makes them ideal for use as electromechanical transducers in a wide variety of applications. In recent years such crystals have been utilized to produce surface acoustic wave devices for signal processing applications, in which an applied metallic grating both transmits and receives, through the piezoelectric effect, electromechanical surface waves. The design of such interdigital transducers requires an accurate knowledge of wave propagation and reflection. The presence of the metal grating in addition to its ideal transduction function, by means of electrical and mechanical loading, also introduces a velocity shift as well as reflection into substrate surface waves. We seek to obtain a consistent formulation of the wave behavior due to the electrical and mechanical loading of the substrate crystal by the metallic grating. A perturbative solution up to second order in h//lambda is developed, where h is the maximum grating height and λ the acoustic wavelength. For the operating frequencies and physical parameters of modern surface acoustic wave devices such an analysis will provide an adequate description of device behavior in many cases, thereby circumventing the need for more computationally laborious methods. Numerical calculations are presented and compared with available experimental data.
Experimental Study on Wave Propagation Across a Rock Joint with Rough Surface
NASA Astrophysics Data System (ADS)
Chen, X.; Li, J. C.; Cai, M. F.; Zou, Y.; Zhao, J.
2015-11-01
Joints are an important mechanical feature of rock masses. Their effect on wave propagation is significant in characterizing dynamic behaviors of discontinuous rock masses. An experimental study on wave propagation across artificial rock joint was carried out to reveal the relation between the transmission coefficient and the contact situation of the joint surface. The modified split Hopkinson pressure bar apparatus was used in this study while all the bars and specimens were norite cored from the same site. One surface of the specimens with a number of notches was adopted to simulate the artificial rough joint. Two strain gauges were mounted on each pressure bar at a specific spacing. The incident, reflected and transmitted waves across the joints were obtained using a wave separation method. Comparisons of the transmission coefficients were made under two different conditions: with the same joint thickness but different contact area ratios, and with the same contact area ratio but different joint thicknesses. The results show the effects of contact area ratio and thickness of joints on wave transmission.
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.
Kong, Zhi; Wei, Peijun; Jiao, Fengyu
2016-07-01
The effective propagation constants of elastic waves in an inhomogeneous medium with randomly distributed parallel cylindrical nanofibers are studied. First, the surface energy theory proposed by Huang and Wang (Handbook of Micromechanics and Nanomechanics, 2013) is used to derive the nontraditional boundary conditions on the surfaces of the nanoholes and the interfaces between the nanofibers and the host. Then, the scattering matrix of individual scatterer (cylindrical hole or nanofiber) is derived from the nontraditional boundary condition. The total wave field is obtained by considering the multiple scattering processes among the dispersive scatterers. The configuration average of the total wave field results in the coherent waves or the averaged waves. By using the corrected Linton-Martin formula, the effective propagation constants (effective speed and effective attenuation) of the coherent waves are estimated. The in-plane waves (P and SV waves) and the anti-plane waves (SH wave) are considered, respectively, and the numerical results are shown graphically. Apart from the effects of surface elasticity, the effects of inertia of surface/interface and the effects of residual surface tension (which are often ignored in the previous literature) are also considered. Moreover, the influences of the nonsymmetric parts of in-plane surface stress and the out-of-plane parts of the surface stress are both discussed first based on the numerical examples. These investigations show the underestimation and overestimation of effective propagation constants caused by various simplifications. PMID:27475172
NASA Astrophysics Data System (ADS)
Tang, Gongbin; Han, Tao; Chen, Jing; Zhang, Benfeng; Omori, Tatsuya; Hashimoto, Ken-ya
2016-07-01
In this paper, we propose the use of the “longitudinal resonance condition” for the characterization of the two-dimensional propagation of surface acoustic waves (SAWs) in periodic grating structures, and also show a procedure for extracting parameters required in the behavior model from the full-wave analysis. The condition is given by β xp = π, where p is the grating period and β x is the wavenumber of the grating mode in the longitudinal direction (x). This is based on the fact that in conventional SAW resonators, acoustic resonances including transverse ones occur when β x is real but the longitudinal resonance condition is mostly satisfied. The longitudinal resonance condition is applied to a simple model, and the wavenumber β y in the lateral direction (y) is expressed as a simple function of the angular frequency ω. The full-wave analysis is applied for SAWs propagating in an infinite grating on a 128°YX-LiNbO3 substrate, and the anisotropy parameter γ is extracted by the fitting with the derived equation. The fitted result agrees well with the original numerical result. It is also indicated that γ estimated by this technique is significantly different from the value estimated without taking the effects of the grating structure into account.
Stafford, L.; Margot, J.; Moisan, M.; Khare, R.; Donnelly, V. M.
2009-01-12
Electron energy distribution functions (EEDFs) were measured in a 50 mTorr oxygen plasma column sustained by propagating surface waves. Trace-rare-gas-optical-emission spectroscopy was used to derive EEDFs by selecting lines to extract ''electron temperature''(T{sub e}) corresponding to either lower energy electrons that excite high-lying levels through stepwise excitation via metastable states or higher energy electrons that excite emission directly from the ground state. Lower energy T{sub e}'s decreased from 8 to 5.5 eV with distance from the wave launcher, while T{sub e}{approx_equal}6 eV for higher energy electrons and T{sub e}>20 eV for a high-energy tail. Mechanisms for such EEDFs are discussed.
Energy Science and Technology Software Center (ESTSC)
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 Users Manual [1].
Propagation of pulsed surface spin-wave signals at millikelvin temperatures
NASA Astrophysics Data System (ADS)
van Loo, Arjan; Morris, Richard; Karenowska, Alexy
Propagating microwave-frequency magnons in magnetic films attract increasing attention on account of their potential interface with superconducting quantum circuit and qubit systems. Their rich dynamics and slow speeds make magnons an interesting addition to the circuit quantum electrodynamics toolbox and, at the same time, superconducting circuit technology promises to be a powerful tool in the investigation of their quantum properties. We have studied the propagation of pulsed surface spin-wave signals over millimeter distances in yttrium iron garnet waveguides at ~ 10 mK . Input microwave pulses and pulse trains with various envelope shapes were applied to an inductive input antenna, and the resulting magnons were detected by an output antenna of identical design. The shape of the output signal was observed to depend on the frequency content (carrier and pulse shape) of the input pulse. By performing measurements at varying frequencies and magnetic fields we have been able to map out the dispersion relation for surface magnon modes. These experiments were undertaken as a first step towards coupling propagating magnons in thin films to other quantum systems with microwave-frequency transition energies, and superconducting qubits in particular. The authors acknowledge support from the EPSRC (EP/K032690/1).
Marine Atmospheric Surface Layer and Its Application to Electromagnetic Wave Propagation
NASA Astrophysics Data System (ADS)
Wang, Q.
2015-12-01
An important application of the atmospheric surface layer research is to characterize the near surface vertical gradients in temperature and humidity in order to predict radar and radio communication conditions in the environment. In this presentation, we will give an overview of a new research initiative funded under the Office of Naval Research (ONR) Multi-University Research Initiative (MURI): the Coupled Air-Sea Processes and EM Ducting Research (CASPER). The objective is to fully characterize the marine atmospheric boundary layer (MABL) as an electromagnetic (EM) propagation environment with the emphasis of spatial and temporal heterogeneities and surface wave/swell effects, both of which contravene the underlying assumptions of Monin-Obukhov Similarity Theory (MOST) used in coupled environmental forecast models. Furthermore, coastal variability in the inversion atop the MABL presents a challenge to forecast models and also causes practical issues in EM prediction models. These issues are the target of investigation of CASPER. CASPER measurement component includes two major field campaigns: CASPER-East (2015 Duck, NC) and CASPER-West (2018 southern California). This presentation will show the extensive measurements to be made during the CASPER -East field campaign with the focus on the marine atmospheric surface layer measurements with two research vessels, two research aircraft, surface flux buoy, wave gliders, ocean gliders, tethered balloons, and rawinsondes. Unlike previous research on the marine surface layer with the focus on surface fluxes and surface flux parameterization, CASPER field campaigns also emphasize of the surface layer profiles and the validation of the surface layer flux-profile relationship originally derived over land surfaces. Results from CASPER pilot experiment and preliminary results from CASPER-East field campaign will be discussed.
On the Use of Fractal Surfaces to Understand Seismic Wave Propagation in Layered Basalt Sequences
NASA Astrophysics Data System (ADS)
Nelson, Catherine E.; Hobbs, Richard W.; Rusch, Roxanne
2015-07-01
The aim of this study is to better understand how a layered basalt sequence affects the propagation of a seismic wave, which has implications for sub-basalt seismic imaging. This is achieved by the construction of detailed, realistic models of basalt sequences, using data derived directly from outcrop analogues. Field data on the surface roughness of basaltic lava flows were captured using terrestrial laser scanning and satellite remote sensing. The fractal properties of the surface roughness were derived, and it can be shown that the lava flow surface is fractal over length scales up to approximately 2 km. The fractal properties were then used to construct synthetic lava flow surfaces using a von Karman power spectrum, and the resulting surfaces were then stacked to create a synthetic lava flow sequence. P-wave velocity data were then added, and the resulting model was used to generate synthetic seismic data. The resulting stacked section shows that the ability to resolve the internal structure of the lava flows is quickly lost due to scattering and attenuation by the basalt pile. A further result from generating wide-angle data is that the appearance of a lower-velocity layer below the basalt sequence may be caused by destructive interference within the basalt itself.
Influence of rigid boundary on the propagation of torsional surface wave in an inhomogeneous layer
NASA Astrophysics Data System (ADS)
Gupta, Shishir; Sultana, Rehena; Kundu, Santimoy
2015-02-01
The present work illustrates a theoretical study on the effect of rigid boundary for the propagation of torsional surface wave in an inhomogeneous crustal layer over an inhomogeneous half space. It is believed that the inhomogeneity in the half space arises due to hyperbolic variation in shear modulus and density whereas the layer has linear variation in shear modulus and density. The dispersion equation has been obtained in a closed form by using Whittaker's function, which shows the variation of phase velocity with corresponding wave number. Numerical results show the dispersion equations, which are discussed and presented by means of graphs. Results in some special cases are also compared with existing solutions available from analytical methods, which show a close resemblance. It is also observed that, for a layer over a homogeneous half space, the velocity of torsional waves does not coincide with that of Love waves in the presence of the rigid boundary, whereas it does at the free boundary. Graphical user interface (GUI) software has been developed using MATLAB 7.5 to generalize the effect of various parameter discussed.
NASA Astrophysics Data System (ADS)
El-Dib, Yusry O.
1995-10-01
Resonances of interfacial waves in a nonlinear interfacial instability of two superposed electrified fluids stressed by a time-dependent electric field are studied. Two subharmonic resonances have been distinguished and investigated. Based on the method of multiple-scale expansion, for a small amplitude of periodic field, two parametric nonlinear Schrodinger equations are derived to describe the propagation of capillary waves on the fluid interface in the resonance cases. A classical nonlinear Schrodinger equation is derived in the nonresonant case. A temporal solution for a travelling wave is obtained analytically. The necessary and sufficient conditions for stability are obtained. It is found that the stability criteria are significantly affected by the amplitude of the temporal solution. Further the formula for the surface elevation is obtained in each case. Numerical calculations show that the constant electric field plays a dual role in the stability analysis. It is observed that the field frequency changes the mechanism due to the dual role of the electric field.
Ginzburg, N. S.; Malkin, A. M.; Zheleznov, I. V.; Sergeev, A. S.
2013-06-15
By using a quasi-optical approach, we study propagation of evanescent waves along a periodically corrugated surface and their excitation by relativistic electron beams. Under assumption of a shallow (in the scale of period) corrugation, the dispersion equation for normal waves is derived and two particular cases are studied. In the first case, the wave frequency is far from the Bragg resonance; therefore, the evanescent wave propagation can be described by using the impedance approximation with deceleration of the zeroth spatial harmonic. The second case takes place at the frequencies close to the Bragg resonance. There, the field can be represented as two counter-propagating quasi-optical wave beams, which are coupled on the corrugated surface and form an evanescent normal wave. With regard to the interaction with an electron beam, the first case corresponds to the convective instability that can be used for amplification of radiation, while the second case corresponds to the absolute instability used in surface-wave oscillators. This paper is focused on studying main features of amplifier schemes, such as the increments, electron efficiency, and formation of a self-consistent spatial structure of the radiated field. For practical applications, the feasibility of realization of relativistic surface-wave amplifiers in the submillimeter wavelength range is estimated.
FE simulation of laser generated surface acoustic wave propagation in skin.
L'Etang, Adèle; Huang, Zhihong
2006-12-22
Advances in laser ultrasonics have opened new possibilities in medical applications, such as the characterization of skin properties. This paper describes the development of a multilayered finite element model (FEM) using ANSYS to simulate the propagation of laser generated thermoelastic surface acoustic waves (SAWs) through skin and to generate signals one would expect to observe without causing thermal damage to skin. A transient thermal analysis is developed to simulate the thermal effect of the laser source penetrating into the skin. The results from the thermal analysis are subsequently applied as a load to the structural analysis where the out-of-plane displacement responses are analysed in models with varying dermis layer thickness. PMID:16814352
NASA Astrophysics Data System (ADS)
Liu, Tianyun; Zhao, Chongbin; Duan, Yunling
2012-08-01
This paper presents a systematic and efficient method, namely the generalized transfer matrix method, for evaluating the dispersion curves and eigenfunctions of surface waves in multilayered azimuthally anisotropic half-space. Apart from avoiding the well-known numerical difficulties associated with the existing Thomson-Haskell method, the generalized transfer matrix method possesses the robust determination of independent polarization vectors by using the singular value decomposition (SVD) approach, the explicit inversion of the 6 × 6 eigencolumn matrix without any resort to numerical inversion and the efficient computation of eigenfunctions for layered azimuthally anisotropic media. By means of straightforward transformations, the generalized transfer matrix method leads to a twofold recursive algorithm: (1) for the recursive computation of phase velocities it starts from the bottom half-space to the top layer and (2) for the recursive solution of eigenfunctions it starts from the top layer to the bottom half-space. While keeping the simplicity of the Thomson-Haskell transfer matrix method, the generalized transfer matrix method is of unconditional stability and computational efficiency. The related numerical examples demonstrate that the generalized transfer matrix method is a powerful and robust tool for simulating the propagation of elastic surface waves in the layered azimuthally anisotropic half-space.
Sankaranarayanan, Subramanian K R S; Bhethanabotla, Venkat R
2009-03-01
We develop a 3-D finite element model of a focused surface acoustic wave (F-SAW) device based on LiNbO(3) to analyze the wave generation and propagation characteristics for devices operating at MHz frequencies with varying applied input voltages. We compare the F-SAW device to a conventional SAW device with similar substrate dimensions and transducer finger periodicity. SAW devices with concentrically shaped focused interdigital transducer fingers (F-IDTs) are found to excite waves with high intensity and high beam-width compression ratio, confined to a small localized area. F-SAW devices are more sensitive to amplitude variations at regions close to the focal point than conventional SAW devices having uniform IDT configuration. We compute F-SAW induced streaming forces and velocity fields by applying a successive approximation technique to the Navier-Stokes equation (Nyborg's theory). The maximum streaming force obtained at the focal point varies as the square of the applied input voltage. Computed streaming velocities at the focal point in F-SAW devices are at least an order of magnitude higher than those in conventional SAW devices. Simulated frequency response indicates higher insertion losses in F-SAW devices than in conventional devices, reflecting their greater utility as actuators than as sensors. Our simulation findings suggest that F-SAW devices can be utilized effectively for actuation in microfluidic applications involving diffusion limited transport processes. PMID:19411221
NASA Astrophysics Data System (ADS)
Vadas, Sharon L.; Makela, Jonathan J.; Nicolls, Michael J.; Milliff, Ralph F.
2015-11-01
In this paper, we derive the atmospheric gravity waves (GWs) and acoustic waves excited by an ocean surface wave packet with frequency ωF and duration χ in an f plane, isothermal, windless, and inviscid atmosphere. This packet is modeled as a localized vertical body force with Gaussian depth σz. The excited GW spectrum has discrete intrinsic frequencies (ωIr) at ωF and ωF±2π/χ ("sum" and "difference") and has a "continuum" of frequencies for ωIr<ωF+2π/χ. The momentum flux spectrum peaks at ωIr˜ωF and decreases rapidly as ωIr decreases. To simulate the effect these GWs have on the thermosphere, we present a new scheme whereby we sprinkle N GW spectra in the ocean wave packet region, ray trace the GWs, and reconstruct the GW field. We model the GWs excited by ocean wave packets with horizontal wavelengths of λH = 190 km, periods of τF = 2π/ωF = 14 - 20 min and χ = 30 - 50 min. The excited GWs begin to arrive at z = 250 km at t ˜ 75 - 80 min. Those with the largest temperature perturbations T' have large ωIr and arrive at t ˜ 90 - 130 min. If |α|=ωF+2π/χ is a solution of the GW dispersion relation and |α| is less than the buoyancy frequency at z = 250 km, the sum and highest-frequency continuum GWs have much larger phase speeds and arrive 50-60 min earlier with larger T' than the GWs with frequency ωF. For a packet with λH = 190 km, τF = 14 min, χ = 30 min, and height h0=1.3 m, the maximum T' at z = 250 km is ˜9, 22, and 40 K for σz = 1, 2, and 4 m, respectively.
NASA Astrophysics Data System (ADS)
Lindner, Gerhard
2008-06-01
The propagation of surface acoustic waves (SAWs) along solid-liquid interfaces depends sensitively on the properties of the liquid covering the solid surface and may result in a momentum transfer into the liquid and thus a propulsion effect via acoustic streaming. This review gives an overview of the design of different SAW devices used for the sensing of liquids and the basic mechanisms of the interaction of SAWs with overlaying liquids. In addition, applications of devices based on these phenomena with respect to touch sensing and the measurement of liquid properties such as density, viscosity or the composition of mixed liquids are described, including microfabricated as well as macroscopic devices made from non-piezoelectric materials. With respect to the rapidly growing field of acoustic streaming applications, recent developments in the movement of nanolitre droplets on a single piezoelectric chip, the rather macroscopic approaches to the acoustic pumping of liquids in channels and recent attempts at numerical simulations of acoustic streaming are reported.
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.
NASA Technical Reports Server (NTRS)
Manning, Robert M.
2008-01-01
Long-range, over-the-horizon (transhorizon) radio wave propagation is considered for the case of the Moon. In the event that relay satellites are not available or otherwise unwarranted for use, transhorizon communication provides for a contingency or backup option for non line-of-sight lunar surface exploration scenarios. Two potential low-frequency propagation mechanisms characteristic of the lunar landscape are the lunar regolith and the photoelectron induced plasma exosphere enveloping the Moon. Although it was hoped that the regolith would provide for a spherical waveguide which could support a trapped surface wave phenomena, it is found that, in most cases, the regolith is deleterious to long range radio wave propagation. However, the presence of the plasma of the lunar exosphere supports wave propagation and, in fact, surpasses the attenuation of the regolith. Given the models of the regolith and exosphere adopted here, it is recommended that a frequency of 1 MHz be considered for low rate data transmission along the lunar surface. It is also recommended that further research be done to capture the descriptive physics of the regolith and the exospheric plasma so that a more complete model can be obtained. This comprehensive theoretical study is based entirely on first principles and the mathematical techniques needed are developed as required; it is self-contained and should not require the use of outside resources for its understanding.
NASA Astrophysics Data System (ADS)
Glushkov, Evgeny; Glushkova, Natalia; Lammering, Rolf; Eremin, Artem; Neumann, Mirko N.
2011-01-01
Experimental and theoretical investigations of Lamb wave excitation and sensing using piezo patch transducers and the laser vibrometer technique have been performed, aiming at the development of adequate mathematical and computer models for the interpretation of sensing data and for the choice of optimal parameters for structural health monitoring. The proposed models are validated by experimental results. Furthermore, a methodology is presented which allows for the determination of central frequencies at which maximal values of the structural response spectrum can be expected in the case of wave propagation monitoring with laser vibrometry.
Propagation of surface waves in two-plasma systems bounded by a metallic enclosure
NASA Astrophysics Data System (ADS)
Margot, Joëlle; Stafford, Luc; Johnston, Tudor W.
1999-10-01
The excitation of surface waves (SW) has been the object of intensive research over the last twenty to thirty years because of their interest in sustaining plasmas under various experimental conditions and configurations. Since the pioneering work having reported the theoretical existence of surface waves in 1959 (Trivelpiece and Gould), it is commonly believed that such waves only exist in plasmas bounded by a dielectric layer. However, some recent numerical and experimental investigations by the groups of Birdsall and Sugai, respectively, indicate that surface waves can be excited in plasmas bounded by a metallic enclosure, the plasma sheath then acting as a dielectric layer. In this presentation, we generalize the theory of surface waves to plasma-plasma-metal configurations in cylindrical geometry. Using a full electromagnetic approach in the cold plasma approximation, we search for SW or pseudo-SW solutions (i.e. solutions that tend toward pure surface waves when the permittivity of the outer plasma approaches unity). We thus determine the dispersion and attenuation characteristics of the waves. We explore situations in which the inner plasma column is either overdense or underdense and we investigate the influence of a magnetic field axial to the plasma columns.
Propagation of a fluidization - combustion wave
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.
Kowalewski, Markus Mukamel, Shaul
2015-07-28
Femtosecond Stimulated Raman Spectroscopy (FSRS) signals that monitor the excited state conical intersections dynamics of acrolein are simulated. An effective time dependent Hamiltonian for two C—H vibrational marker bands is constructed on the fly using a local mode expansion combined with a semi-classical surface hopping simulation protocol. The signals are obtained by a direct forward and backward propagation of the vibrational wave function on a numerical grid. Earlier work is extended to fully incorporate the anharmonicities and intermode couplings.
NASA Astrophysics Data System (ADS)
Kowalewski, Markus; Mukamel, Shaul
2015-07-01
Femtosecond Stimulated Raman Spectroscopy (FSRS) signals that monitor the excited state conical intersections dynamics of acrolein are simulated. An effective time dependent Hamiltonian for two C—H vibrational marker bands is constructed on the fly using a local mode expansion combined with a semi-classical surface hopping simulation protocol. The signals are obtained by a direct forward and backward propagation of the vibrational wave function on a numerical grid. Earlier work is extended to fully incorporate the anharmonicities and intermode couplings.
Seismic wave propagation through surface basalts - implications for coal seismic surveys
NASA Astrophysics Data System (ADS)
Sun, Weijia; Zhou, Binzhong; Hatherly, Peter; Fu, Li-Yun
2010-02-01
Seismic reflection surveying is one of the most widely used and effective techniques for coal seam structure delineation and risk mitigation for underground longwall mining. However, the ability of the method can be compromised by the presence of volcanic cover. This problem arises within parts of the Bowen and Sydney Basins of Australia and seismic surveying can be unsuccessful. As a consequence, such areas are less attractive for coal mining. Techniques to improve the success of seismic surveying over basalt flows are needed. In this paper, we use elastic wave-equation-based forward modelling techniques to investigate the effects and characteristics of seismic wave propagation under different settings involving changes in basalt properties, its thickness, lateral extent, relative position to the shot position and various forms of inhomogeneity. The modelling results suggests that: 1) basalts with high impedance contrasts and multiple flows generate strong multiples and weak reflectors; 2) thin basalts have less effect than thick basalts; 3) partial basalt cover has less effect than full basalt cover; 4) low frequency seismic waves (especially at large offsets) have better penetration through the basalt than high frequency waves; and 5) the deeper the coal seams are below basalts of limited extent, the less influence the basalts will have on the wave propagation. In addition to providing insights into the issues that arise when seismic surveying under basalts, these observations suggest that careful management of seismic noise and the acquisition of long-offset seismic data with low-frequency geophones have the potential to improve the seismic results.
NASA Astrophysics Data System (ADS)
Tian, Y.; Shen, W.; Ritzwoller, M. H.
2013-12-01
Ambient noise cross-correlation analysis has been widely used to investigate the continental lithosphere, but the method has been applied much less to study the oceanic lithosphere due to the relative shortage of continuous ocean bottom seismic measurements. The Cascadia Initiative experiment possesses a total of 62 ocean bottom seismometers that spans much of the Juan de Fuca plate and provides data to investigate both the structure and evolution of the oceanic lithosphere near the Juan De Fuca ridge and the characteristics of surface waves and overtones propagating within the oceanic lithosphere. We produce ambient noise cross correlations for the first year of Cascadia OBS data for both the vertical and the horizontal components. The observed empirical Green's functions are first used to test the hypothesis that the near-ridge phase speeds can be described by a simple age-dependent formula, which we invert for an age-dependent shear wave speed model (Figure 1a). A shallow low shear velocity zone with a velocity minimum at about 20km depth is observed in Vsv and the lithosphere thickens with age faster than predicted by a half-space conductive cooling model (Figure 1b). To further understand the oceanic surface waves, we analyze the first higher mode Rayleigh waves that propagate within the Juan De Fuca plate and emerge on the North American continent and investigate the existence of radial anisotropy beneath the ridge by exploring the Rayleigh and Love wave Green's functions. The results of the study are summarized with the age-dependent shear velocity model along with some preliminary observations of both Love wave and higher mode Rayleigh waves.
NASA Astrophysics Data System (ADS)
Zou, Qingping; Hay, Alex E.; Bowen, Anthony J.
2003-08-01
Theoretical predictions of the vertical structure of wave motion over a sloping seabed are compared with field observations close to the bed in the nearshore zone. Of particular interest is the effect of the local slope on the magnitude and phase of the vertical velocity. Field measurements of near-bed velocity profiles on a 2° bed slope were obtained using a coherent Doppler profiler. The surface elevation was measured by a colocated, upward looking, acoustic sounder. Results are presented from two intervals of different wave energy levels during a storm event: for wave height/water depth ratios smaller than 0.3 and for Ursell numbers smaller than 0.6. The local comparisons of magnitude and phase between the vertical velocity and surface elevation measurements are in good agreement with linear theory for a sloping bed, but differ greatly from that for a horizontal bottom, especially in the lower water column. The sloping bottom, however, has little effect on the horizontal velocity. Linear theory appears to adequately describe the transfer function between the surface elevation and the near-bed velocities, not only at the peak frequencies but also at their harmonics. However, in relatively shallow water the local transformations of free and forced waves at the harmonic frequencies are indistinguishable in the lower water column. Therefore, given surface elevation measurements at a particular location (which reflect the integrated effects of nonlinearities associated with wave shoaling), the vertical structure of the third moments of velocity fields estimated from linear theory is in reasonable agreement with the observations. Both theory and observations show that the skewness and asymmetry of the vertical velocity are subject to significant bottom slope effects, whereas those of horizontal velocity are not.
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.
Du, Huijing; Xu, Zhiliang; Anyan, Morgen; Kim, Oleg; Leevy, W. Matthew; Shrout, Joshua D.; Alber, Mark
2012-01-01
This work describes a new, to our knowledge, strategy of efficient colonization and community development where bacteria substantially alter their physical environment. Many bacteria move in groups, in a mode described as swarming, to colonize surfaces and form biofilms to survive external stresses, including exposure to antibiotics. One such bacterium is Pseudomonas aeruginosa, which is an opportunistic pathogen responsible for both acute and persistent infections in susceptible individuals, as exampled by those for burn victims and people with cystic fibrosis. Pseudomonas aeruginosa often, but not always, forms branched tendril patterns during swarming; this phenomena occurs only when bacteria produce rhamnolipid, which is regulated by population-dependent signaling called quorum sensing. The experimental results of this work show that P. aeruginosa cells propagate as high density waves that move symmetrically as rings within swarms toward the extending tendrils. Biologically justified cell-based multiscale model simulations suggest a mechanism of wave propagation as well as a branched tendril formation at the edge of the population that depends upon competition between the changing viscosity of the bacterial liquid suspension and the liquid film boundary expansion caused by Marangoni forces. Therefore, P. aeruginosa efficiently colonizes surfaces by controlling the physical forces responsible for expansion of thin liquid film and by propagating toward the tendril tips. The model predictions of wave speed and swarm expansion rate as well as cell alignment in tendrils were confirmed experimentally. The study results suggest that P. aeruginosa responds to environmental cues on a very short timescale by actively exploiting local physical phenomena to develop communities and efficiently colonize new surfaces. PMID:22947877
Wave propagation in isogrid structures
NASA Astrophysics Data System (ADS)
Reynolds, Whitney D.; Doyle, Derek; Arritt, Brandon
2011-04-01
This work focuses on an analysis of wave propagation in isogrid structures as it relates to Structural Health Monitoring (SHM) methods. Assembly, integration, and testing (AI&T) of satellite structures in preparation for launch includes significant time for testing and reworking any issues that may arise. SHM methods are being investigated as a means to validate the structure during assembly and truncate the number of tests needed to qualify the structure for the launch environment. The most promising of these SHM methods uses an active wave-based method in which an actuator propagates a Lamb wave through the structure; the Lamb wave is then received by a sensor and evaluated over time to detect structural changes. To date this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and joining features. Previous studies have been conducted in simplified ribbed structures, giving initial insight into the complex wave propagation phenomena. In this work, the study has been extended numerically to the isogrid plate case. Wave propagation was modeled using commercial finite element analysis software. The results of the analyses offer further insight into the complexities of wave propagation in isogrid structures.
NASA Astrophysics Data System (ADS)
Foster, Anna E.
observation of bands of arrival-angle anomalies crossing the footprint of the USArray Transportable array in the propagation direction. These bands of deviations may result from heterogeneous velocity structure within the array, or on the larger source-to-array path. We use two global tomographic models to predict arrival-angle anomaly patterns, with both ray-theory-based prediction methods and measurements on synthetic waveforms calculated using SPECFEM3D Globe, a finite element package. We show that both models predict well the long-wavelength patterns of anomalies observed, but not the short-wavelength variations. Experiments with crustal structure indicate that greater heterogeneity is needed in the models. Predictions from the spectral-element-method synthetic waveforms contain the type of complexity seen in the observed patterns, and not obtained with the ray-theoretical methods, indicating that full synthetics are needed to compare model predictions to observed arrival-angle anomalies. We further examine possible overtone interference in the mini-array arrival-angle and local phase-velocity measurements for Love waves at long periods. Love wave fundamental-mode and higher-mode waves at the same period travel with similar group velocity, making them difficult to separate; the waves have different phase velocities, resulting in a beating interference pattern that oscillates with distance. We show this interference pattern for single-station, two-station, and mini-array phase-velocity measurements. Using measurements on synthetic waveforms calculated using both mode summation and SPECFEM3D Globe, we show that contamination of single-station measurements can largely be explained by interference between the fundamental and first-higher mode only. Interference causes small variations in the single-station phase velocity, up to 1%, and the oscillations about the expected values are asymmetric. The two array-based measurement techniques can be thought of as a spatial gradient
NASA Astrophysics Data System (ADS)
Chen, Jing; Zhang, Qiaozhen; Han, Tao; Zhou, Liu; Tang, Gongbin; Liu, Boquan; Ji, Xiaojun
2015-08-01
The surface acoustic wave (SAW) propagating characteristics of Y-cut nano LiNbO3 (LN) film on SiO2/LN substrate have been theoretically calculated. The simulated results showed a shear horizontal (SH) SAW with enhanced electromechanical coupling factor K2 owing to a dimensional effect of the nanoscale LN film. However, a Rayleigh SAW and two other resonances related to thickness vibrations caused spurious responses for wideband SAW devices. These spurious waves could be fully suppressed by properly controlling structural parameters including the electrode layer height, thickness, and the Euler angle (θ) of the LN thin film. Finally, a pure SH SAW was obtained with a wide θ range, from 0° to 5° and 165° to 180°. The largest K2 achieved for the pure SH SAW was about 35.1%. The calculated results demonstrate the promising application of nano LN film to the realization of ultra-wideband SAW devices.
Light propagation in local and linear media: Fresnel-Kummer wave surfaces with 16 singular points
NASA Astrophysics Data System (ADS)
Favaro, Alberto; Hehl, Friedrich W.
2016-01-01
It is known that the Fresnel wave surfaces of transparent biaxial media have four singular points, located on two special directions. We show that, in more general media, the number of singularities can exceed 4. In fact, a highly symmetric linear material is proposed whose Fresnel surface exhibits 16 singular points. Because for every linear material the dispersion equation is quartic, we conclude that 16 is the maximum number of isolated singularities. The identity of Fresnel and Kummer surfaces, which holds true for media with a certain symmetry (zero skewon piece), provides an elegant interpretation of the results. We describe a metamaterial realization for our linear medium with 16 singular points. It is found that an appropriate combination of metal bars, split-ring resonators, and magnetized particles can generate the correct permittivity, permeability, and magnetoelectric moduli. Lastly, we discuss the arrangement of the singularities in terms of Kummer's 166 configuration of points and planes. An investigation parallel to ours, but in linear elasticity, is suggested for future research.
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.
NASA Astrophysics Data System (ADS)
Luo, Cong; Friederich, Wolfgang
2016-04-01
Realistic shallow seismic wave propagation simulation is an important tool for studying induced seismicity (e.g., during geothermal energy development). However over a long time, there is a significant problem which constrains computational seismologists from performing a successful simulation conveniently: pre-processing. Conventional pre-processing has often turned out to be inefficient and unrobust because of the miscellaneous operations, considerable complexity and insufficiency of available tools. An integrated web-based platform for shallow seismic wave propagation simulation has been built. It is aiming at providing a user-friendly pre-processing solution, and cloud-based simulation abilities. The main features of the platform for the user include: revised digital elevation model (DEM) retrieving and processing mechanism; generation of multi-layered 3D shallow Earth model geometry (the computational domain) with user specified surface topography based on the DEM; visualization of the geometry before the simulation; a pipeline from geometry to fully customizable hexahedral element mesh generation; customization and running the simulation on our HPC; post-processing and retrieval of the results over cloud. Regarding the computational aspect, currently the widely accepted specfem3D is chosen as the computational package; packages using different types of elements can be integrated as well in the future. According to our trial simulation experiments, this web-based platform has produced accurate waveforms while significantly simplifying and enhancing the pre-processing and improving the simulation success rate.
NASA Technical Reports Server (NTRS)
Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei; Kim, Yoonkee; Hunt, William D.
1995-01-01
A potential application for piezoelectric films substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on /001/-cut group of (110) zone axes-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(sup 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on /001/-cut GaAs samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. It was found that near the group of (110) zone axes propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the (100) direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.
NASA Technical Reports Server (NTRS)
Kim, Yoonkee; Hunt, William D.; Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei
1995-01-01
A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut <110> -propagating GaAs substrates are investigated in this article, including SAW Velocity effective piezoelectric coupling constant, propagation loss. diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films or different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(exp 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2, or Si3N4 on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the <110> propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the <100> direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.
NASA Astrophysics Data System (ADS)
Altshuler, Gennady; Manor, Ofer
2016-07-01
We use both theory and experiment to study the response of thin and free films of a partially wetting liquid to a MHz vibration, propagating in the solid substrate in the form of a Rayleigh surface acoustic wave (SAW). We generalise the previous theory for the response of a thin fully wetting liquid film to a SAW by including the presence of a small but finite three phase contact angle between the liquid and the solid. The SAW in the solid invokes a convective drift of mass in the liquid and leaks sound waves. The dynamics of a film that is too thin to support the accumulation of the sound wave leakage is governed by a balance between the drift and capillary stress alone. We use theory to demonstrate that a partially wetting liquid film, supporting a weak capillary stress, will spread along the path of the SAW. A partially wetting film, supporting an appreciable capillary stress, will however undergo a concurrent dynamic wetting and dewetting at the front and the rear, respectively, such that the film will displace, rather than spread, along the path of the SAW. The result of the theory for a weak capillary stress is in agreement with the previous experimental and theoretical studies on the response of thin silicon oil films to a propagating SAW. No corresponding previous results exist for the case of an appreciable capillary stress. We thus complement the large capillary limit of our theory by undertaking an experimental procedure where we explore the response of films of water and a surfactant solutions to a MHz SAW, which is found to be in qualitative agreement with the theory at this limit.
Reconstruction of nonlinear wave propagation
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.
NASA Technical Reports Server (NTRS)
Harker, K. J.
1975-01-01
The generation of ULF waves by ground-based magnetic and electric dipoles is studied with a simplified model consisting of three adjoining homogeneous regions representing the groud, the vacuum (free space) region, and the ionosphere. The system is assumed to be immersed in a homogeneous magnetic field with an arbitrary tilt angle. By the use of Fourier techniques and the method of stationary phase, analytic expressions are obtained for the field strength of the compressional Alfven waves in the ionosphere. Expressions are also obtained for the strength of the torsional Alfven wave in the ionosphere and the ULF magnetic field at ground level. Numerical results are obtained for the compressional Alfven-wave field strength in the ionosphere with a nonvertical geomagnetic field and for the ULF magnetic field at ground level for a vertical geomagnetic field.
Seismic wave propagation modeling
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.
Wave propagation in solids and fluids
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.
Chen, Jing Zhang, Qiaozhen; Han, Tao; Zhou, Liu; Tang, Gongbin; Liu, Boquan; Ji, Xiaojun
2015-08-15
The surface acoustic wave (SAW) propagating characteristics of Y-cut nano LiNbO{sub 3} (LN) film on SiO{sub 2}/LN substrate have been theoretically calculated. The simulated results showed a shear horizontal (SH) SAW with enhanced electromechanical coupling factor K{sup 2} owing to a dimensional effect of the nanoscale LN film. However, a Rayleigh SAW and two other resonances related to thickness vibrations caused spurious responses for wideband SAW devices. These spurious waves could be fully suppressed by properly controlling structural parameters including the electrode layer height, thickness, and the Euler angle (θ) of the LN thin film. Finally, a pure SH SAW was obtained with a wide θ range, from 0° to 5° and 165° to 180°. The largest K{sup 2} achieved for the pure SH SAW was about 35.1%. The calculated results demonstrate the promising application of nano LN film to the realization of ultra-wideband SAW devices.
NASA Astrophysics Data System (ADS)
Gallego, A.; Ito, G.; Dunn, R. A.
2013-08-01
Surface wave studies of the Reykjanes Ridge (RR) and the Iceland hotspot have imaged an unusual and enigmatic pattern of two zones of negative radial anisotropy on each side of the RR. We test previously posed and new hypotheses for the origin of this anisotropy, by considering lattice preferred orientation (LPO) of olivine A-type fabric in simple models with 1-D, layered structures, as well as in 2-D and 3-D geodynamic models with mantle flow and LPO evolution. Synthetic phase velocities of Love and Rayleigh waves traveling parallel to the ridge axis are produced and then inverted to mimic the previous seismic studies. Results of 1-D models show that strong negative radial anisotropy can be produced when olivine a axes are preferentially aligned not only vertically but also subhorizontally in the plane of wave propagation. Geodynamic models show that negative anisotropy on the sides of the RR can occur when plate spreading impels a corner flow, and in turn a subvertical alignment of olivine a axes, on the sides of the ridge axis. Mantle dehydration must be invoked to form a viscous upper layer that minimizes the disturbance of the corner flow by the Iceland mantle plume. While the results are promising, important discrepancies still exist between the observed seismic structure and the predictions of this model, as well as models of a variety of types of mantle flow associated with plume-ridge interaction. Thus, other factors that influence seismic anisotropy, but not considered in this study, such as power-law rheology, water, melt, or time-dependent mantle flow, are probably important beneath the Reykjanes Ridge.
SH wave propagation in piezoelectric coupled plates.
Wang, Quan
2002-05-01
The propagation of shear horizontal (SH) wave in a piezoelectric coupled plate is investigated in this paper. Full account is taken of the piezoelectric coupling effect to the isotropic metal core in the mathematical model. One of the applications of this research is in the damage detection of the host metal structure from the wave propagation signal excited by the piezoelectric layer which is surface bonded on the surface of a metal core. This research is distinct from the previous works on SH propagation in piezoelectric structures because the piezoelectric materials were used as the core structure in the previous studies, and the potential of the studies was mainly on time-delay devices. The dispersive characteristics and the mode shapes of the transverse displacement and the electric potential of the piezoelectric layer are theoretically derived. The results from numerical simulations show that the phase velocity of the plate structure tends to the bulk shear wave velocity of the host metal core at high wavenumber when the shear wave velocity of host plate is larger than that of PZT bonded on it. Furthermore, there are three asymptotic solutions of wave propagation when the shear wave velocity of the host plate is smaller than that of PZT. The mode shape of the electric potential of the piezoelectric layer changes from the quadratic shape at lower wavenumber and with thinner piezoelectric layer to the shape with more zero nodes at higher wavenumber and with thicker piezoelectric layer. These findings are significant in the application of wave propagation in piezoelectric coupled structures. PMID:12046935
Effect of surface deposits on electromagnetic waves propagating in uniform ducts
NASA Technical Reports Server (NTRS)
Baumeister, Kenneth J.
1990-01-01
A finite-element Galerkin formulation was used to study the effect of material surface deposits on the reflective characteristics of straight uniform ducts with PEC (perfectly electric conducting) walls. Over a wide frequency range, the effect of both single and multiple surface deposits on the duct reflection coefficient were examined. The power reflection coefficient was found to be significantly increased by the addition of deposits on the wall.
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.
Non-Hermitian quantum mechanics: wave packet propagation on autoionizing potential energy surfaces.
Moiseyev, N; Scheit, S; Cederbaum, L S
2004-07-01
The correspondence between the time-dependent and time-independent molecular dynamic formalisms is shown for autoionizing processes. We demonstrate that the definition of the inner product in non-Hermitian quantum mechanics plays a key role in the proof. When the final state of the process is dissociative, it is technically favorable to introduce a complex absorbing potential into the calculations. The conditions which this potential should fulfill are briefly discussed. An illustrative numerical example is presented involving three potential energy surfaces. PMID:15260598
Propagation characteristics of magnetostatic waves: A review
NASA Astrophysics Data System (ADS)
Parekh, J. P.
1983-01-01
This paper reviews the propagation characteristics of guided magnetostatic waves (MSW's) in a YIG film magnetized beyond saturation. There exist three guided magnetostatic wave-types, viz., magnetostatic surface waves (MSSW's) and magnetostatic forward and backward volume waves (MSFVW's and MSBVW's). The orientation of the internal bias field determines the particular wave-type that can be supported by the YIG film. The frequency spectrum of the volume waves coincides with that over which magnetostatic plane waves are of the homogeneous variety. The frequency spectrum of the MSSW's is located immediately above the MSVW spectrum. MSW's are dispersive, with the dispersion properties alterable through modification in boundary conditions. The most explored dispersion control technique employs the placement of a ground plane somewhat above the YIG film surface. This dispersion control technique, which provides one method of realizing nondispersive MSW propagation, raises the upper bound of the MSSW spectrum but does not affect the bounds of the MSVW spectrum. Numerical computations illustrating the dispersion and polarization characteristics of MSW's are presented.
NASA Astrophysics Data System (ADS)
Qian, Lirong; Li, Cuiping; Li, Mingji; Wang, Fang; Yang, Baohe
2014-11-01
Propagation characteristics of surface acoustic wave (SAW) in periodic (AlN/ZnO)N/diamond multilayer structures were theoretically investigated using effective permittivity method. The phase velocity Vp, electromechanical coupling coefficient K2, and temperature coefficient of frequency (TCF) of the Sezawa mode are analyzed for different thicknesses-to-wavelength H/λ, thickness ratios of AlN to ZnO Rh, and periods of alternating ZnO and AlN layers N. Results show that, comparing with AlN/ZnO/diamond multilayer structure, the periodic (AlN/ZnO)N/diamond multilayer structure (N ≥ 2) shows excellent electromechanical coupling and temperature stable characteristics with significantly improved K2 and TCF. The largest coupling coefficient of 3.0% associated with a phase velocity of 5726 m/s and a TCF of -29.2 ppm/°C can be reached for Rh = 0.2 and N = 2. For a low TCF of -24.4 ppm/°C, a large coupling coefficient of 2.0% associated with a phase velocity of 7058 m/s can be obtained for Rh = 1.0 and N = 5. The simulated results can be used to design the low loss and good temperature stability SAW devices of gigahertz-band application.
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.
Wave propagation in modified gravity
NASA Astrophysics Data System (ADS)
Lindroos, Jan Ø.; Llinares, Claudio; Mota, David F.
2016-02-01
We investigate the propagation of scalar waves induced by matter sources in the context of scalar-tensor theories of gravity which include screening mechanisms for the scalar degree of freedom. The usual approach when studying these theories in the nonlinear regime of cosmological perturbations is based on the assumption that scalar waves travel at the speed of light. Within general relativity this approximation is valid and leads to no loss of accuracy in the estimation of observables. We find, however, that mass terms and nonlinearities in the equations of motion lead to propagation and dispersion velocities significantly different from the speed of light. As the group velocity is the one associated with the propagation of signals, a reduction of its value has direct impact on the behavior and dynamics of nonlinear structures within modified gravity theories with screening. For instance, the internal dynamics of galaxies and satellites submerged in large dark matter halos could be affected by the fact that the group velocity is smaller than the speed of light. It is therefore important, within such a framework, to take into account the fact that different parts of a galaxy will see changes in the environment at different times. A full nonstatic analysis may be necessary under those conditions.
NASA Astrophysics Data System (ADS)
Ghorbanpour Arani, A.; Roudbari, M. A.
2014-11-01
This paper investigates the electro-thermal nonlocal wave propagation of fluid-conveying single-walled Boron Nitride nanotubes (SWBNNTs) using nonlocal piezoelasticity with surface stress, initial stress and Knudsen-dependent flow velocity effect. SWBNNT is embedded in a vicsoelastic medium which is simulated as visco-Pasternak foundation. Using Euler-Bernoulli beam (EBB) model, Hamilton's principle and nonlocal piezoelasticity theory, the higher order governing equation is derived. A detailed parametric study is conducted, focusing on the combined effects of the electric parameters, viscoelastic medium, initial stress, surface stress, Knudsen number (Kn) and small scale on the wave propagation behaviour of the fluid-conveying SWBNNT. The results show that for smaller values of wave number the dispersion relation for different fluid viscosities seems to be similar. At the higher values of wave numbers, increase in the wave frequency values is remarkable due to increase in fluid viscosity. The electric field as a smart controller, surface effect, initial stress, temperature change and slip velocity effect have significant role on the wave frequency. The results of this work is hoped to be of use in design and manufacturing of smart MEMS/NEMS in advanced medical applications such as drug delivery systems with great applications in biomechanics.
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.
NASA Astrophysics Data System (ADS)
Yankin, S.; Talbi, A.; Du, Y.; Gerbedoen, J.-C.; Preobrazhensky, V.; Pernod, P.; Bou Matar, O.
2014-06-01
We study both theoretically and experimentally the interaction of surface elastic waves with 2D surface phononic crystal (PnC) on a piezoelectric substrate. A rigorous analysis based on 3D finite element method is conducted to calculate the band structure of the PnC and to analyze the transmission spectrum (module and phase). Interdigital transducers (IDTs) are considered for electrical excitation and detection, and absorbing boundary conditions are used to suppress wave's reflection from the edges. The PnCs are composed of an array of 20 Nickel cylindrical pillars arranged in a square lattice symmetry, and deposited on a LiNbO3 substrate (128°Y cut-X propagating) between two dispersive IDTs. We investigate by means of band diagrams and transmission spectrum the opening band-gaps originating from pillars resonant modes and from Bragg band-gap. The physical parameters that influence and determine their appearance are also discussed. Experimental validation is achieved through electrical measurement of the transmission characteristics, including amplitude and phase.
3D Elastic Seismic Wave Propagation Code
Energy Science and Technology Software Center (ESTSC)
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.
Zhang, Sijia; Gu, Bin; Zhang, Hongbin; Feng, Xi-Qiao; Pan, Rongying; Alamusi; Hu, Ning
2016-03-01
The propagation of Love waves in the structure consisting of a nanosized piezoelectric film and a semi-infinite elastic substrate is investigated in the present paper with the consideration of surface effects. In our analysis, surface effects are taken into account in terms of the surface elasticity theory and the electrically-shorted conditions are adopted on the free surface of the piezoelectric film and the interface between the film and the substrate. This work focuses on the new features in the dispersion relations of different modes due to surface effects. It is found that with the existence of surface effects, the frequency dispersion of Love waves shows the distinct dependence on the thickness and the surface constants when the film thickness reduces to nanometers. In general, phase velocities of all dispersion modes increase with the decrease of the film thickness and the increase of the surface constants. However, surface effects play different functions in the frequency dispersions of different modes, especially for the first mode dispersion. Moreover, different forms of Love waves are observed in the first mode dispersion, depending on the presence of the surface effects on the surface and the interface. PMID:26678787
Voltage modulation of propagating spin waves in Fe
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.
NASA Astrophysics Data System (ADS)
Li, Li; Wei, P. J.
2015-03-01
The propagation behaviour of Love wave in an initially stressed functionally graded magnetic-electric-elastic half-space carrying a homogeneous layer is investigated. The material parameters in the substrate are assumed to vary exponentially along the thickness direction only. The velocity equations of Love wave are derived on the electrically or magnetically open circuit and short circuit boundary conditions, based on the equations of motion of the graded magnetic-electric-elastic mate- rial with the initial stresses and the free traction boundary conditions of surface and the continuous boundary conditions of interface. The dispersive curves are obtained numerically and the influences of the initial stresses and the material gradient index on the dispersive curves are dis- cussed. The investigation provides a basis for the development of new functionally graded magneto-electro-elastic surface wave devices.
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.
Modeling Propagation of Shock Waves in Metals
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.
Manipulating Water Wave Propagation via Gradient Index Media
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
On the propagation of acceleration waves in incompressible hyperelastic solids
NASA Astrophysics Data System (ADS)
Gültop, T.
2003-07-01
The conditions for the propagation of acceleration waves (sound waves) in incompressible elastic media undergoing finite deformation are investigated. The incompressible hyperelastic solid media is considered in accordance with the general constitutive theory of materials subject to internal mechanical constraints. The equation of motion of acceleration waves is obtained using the theory of singular surfaces. A general comparison is made between the magnitudes of the propagation speeds of waves in incompressible and unconstrained solid media by the use of Mandel's inequalities. The magnitudes of the speeds of propagation of acceleration waves in the incompressible hyperelastic material classes of neo-Hookean, Mooney-Rivlin, and St. Venant-Kirchhoff solids are determined. Comparisons are made of the specific results concerning the magnitudes of wave propagation speeds making use of the corresponding material parameters.
Propagation Dynamics of Airy Water-Wave Pulses.
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
Ignatovich, V. K.
2009-01-15
It is shown that neutron surface waves do not exist. The difference between the neutron wave mechanics and the wave physics of electromagnetic and acoustic processes, which allows the existence of surface waves, is analyzed.
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.
Making and Propagating Elastic Waves: Overview of the new wave propagation code WPP
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.
Propagation of shock waves through petroleum suspensions
NASA Astrophysics Data System (ADS)
Mukuk, K. V.; Makhkamov, S. M.; Azizov, K. K.
1986-01-01
Anomalous shock wave propagation through petroleum with a high paraffin content was studied in an attempt to confirm the theoretically predicted breakdown of a forward shock wave into oscillating waves and wave packets as well as individual solitons. Tests were performed in a shock tube at 10, 20, and 50 to 60 C, with pure kerosene as reference and with kerosene + 5, 10, 15, and 20% paraffin. The addition of paraffin was found to radically alter the rheodynamic characteristics of the medium and, along with it, the pattern of shock wave propagation. The integro-differential equation describing a one dimensional hydraulic shock process in viscoelastic fluids is reduced to the Burgers-Korteweg-deVries equation, which is solved numerically for given values of the system parameters. The results indicate that the theory of shock wave propagation through such an anomalous suspension must be modified.
NASA Astrophysics Data System (ADS)
Ratilal, Purnima; Makris, Nicholas C.
2002-11-01
Analytic expressions for the mean field propagated through a stratified ocean with random volume or sufrace inhomogeneities of arbitrary size compared to the wavelength are derived from a wave guide scattering model stemming from Green's theorem. It is found that multiple scattering through inhomogeneities in the forward direction can be succinctly expressed in terms of modal attenuation and dispersion coefficients under widely satisfied conditions. The inhomogeneities can have an arbitrary distribution in depth so that the model can realistically apply to scattering from internal waves, bubbles, fish, seafloor and seasurface roughness as well as sub-bottom anomalies. An understanding of the coherence of the forward scattered field can be gained by analogy with the formation of optical mirages in low-grazing angle forward scatter from random surfaces.
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.
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
Calibration of seismic wave propagation in Kuwait
Al-Awadhi, J; Endo, E; Fryall, F; Harris, D; Mayeda, K; Rodgers, A; Ruppert, S; Sweeney, J
1999-07-23
The Kuwait Institute of Scientific Research (KISR), the USGS and LLNL are collaborating to calibrate seismic wave propagation in Kuwait and surrounding regions of the northwest Arabian Gulf using data from the Kuwait National Seismic Network (KNSN). Our goals are to develop local and regional propagation models for locating and characterizing seismic events in Kuwait and portions of the Zagros mountains close to Kuwait. The KNSN consists of 7 short-period stations and one broadband (STS-2) station. Constraints on the local velocity structure may be derived from joint inversions for hypocenters of local events and the local velocity model, receiver functions from three-component observations of teleseisms, and surface wave phase velocity estimated from differential dispersion measurements made across the network aperture. Data are being collected to calibrate travel-time curves for the principal regional phases for events in the Zagros mountains. The available event observations span the distance range from approximately 2.5 degrees to almost 9 degrees. Additional constraints on structure across the deep sediments of the Arabian Gulf will be obtained from long-period waveform modeling.
Overview of near millimeter wave propagation
NASA Astrophysics Data System (ADS)
Flood, W. A.
1981-02-01
Near millimeter wave (NMMW) propagation problems are divided into three classes: propagation through homogeneous, turbid, and turbulent atmospheres. These classical forms include anomalous water vapor absorption in a homogeneous atmosphere as well as scintillation phenomena associated with propagation through severe weather and 'dirty battlefield' environments. Examples of the existing, inadequate, scintillation data base are given and the lack of supporting meteorological data noted. Carefully designed NMMW scintillation experiments with equally carefully designed micro-meteorological support are needed.
Longitudinal nonlinear wave propagation through soft tissue.
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
Calibration of seismic wave propagation in Jordan
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
All electrical propagating spin wave spectroscopy with broadband wavevector capability
NASA Astrophysics Data System (ADS)
Ciubotaru, F.; Devolder, T.; Manfrini, M.; Adelmann, C.; Radu, I. P.
2016-07-01
We developed an all electrical experiment to perform the broadband phase-resolved spectroscopy of propagating spin waves in micrometer sized thin magnetic stripes. The magnetostatic surface spin waves are excited and detected by scaled down to 125 nm wide inductive antennas, which award ultra broadband wavevector capability. The wavevector selection can be done by applying an excitation frequency above the ferromagnetic resonance. Wavevector demultiplexing is done at the spin wave detector thanks to the rotation of the spin wave phase upon propagation. A simple model accounts for the main features of the apparatus transfer functions. Our approach opens an avenue for the all electrical study of wavevector-dependent spin wave properties including dispersion spectra or non-reciprocal propagation.
Electromagnetic wave propagation characteristics in unimolecular reactions
NASA Astrophysics Data System (ADS)
Liu, Xingpeng; Huang, Kama
2016-01-01
Microwave-assisted chemical reactions have attracted interests because of their benefits for enhancement of reaction rates. However, the problems, such as hot spots and thermal runaway, limit the application of microwaves in the chemical industry. To study the characteristics of electromagnetic wave propagation in a chemical reaction is critical to solve the problems. The research on the characteristics of electromagnetic wave propagation in the unimolecular reaction that is a simple model reaction, can be generalized to the research in a chemical reaction. The approximate expressions of the attenuation and dispersion characteristics of electromagnetic wave propagation in the unimolecular reaction are derived by the nonlinear propagation theory. Specially, when the reaction rate is zero, the derived approximate expressions can be reduced to the formulas in low-loss dispersive media. Moreover, a 1D mold is used to validate the feasibility of the approximate expressions. The influences of the reaction rate and initial reactant concentration on the characteristics are obtained.
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.
The Propagation of Radio Waves
NASA Astrophysics Data System (ADS)
Budden, K. G.
1988-08-01
Preface; 1. The ionosphere and magnetosphere; 2. The basic equations; 3. The constitutive relations; 4. Magnetoionic theory I. Polarisation and refractive index; 5. Magnetoionic theory II. Rays and group velocity; 6. Stratified media. The booker quartic; 7. Slowly varying medium. The W.K.B. solution; 8. The Airy integral function and the Stokes phenomenon; 9. Integration by steepest descents; 10. Ray tracing in a loss-free stratified medium; 11. Reflection and transmission coefficients; 12. Ray theory results for isotropic ionosphere; 13. Ray theory results for anisotropic plasmas; 14. General ray tracing; 15. Full wave solutions for isotropic ionosphere; 16. Coupled wave eqations; 17. Coalescence of couling points; 18. Full wave methods for anisotropic stratified media; 19. Applications of full wave methods; Answers to problems; Bibliography; Index of definitions of the more important symbols; Subject and name index.
Variational principle for nonlinear wave propagation in dissipative systems.
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
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.
Propagation of polarized waves in inhomogeneous media.
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
Propagating precipitation waves: experiments and modeling.
Tinsley, Mark R; Collison, Darrell; Showalter, Kenneth
2013-12-01
Traveling precipitation waves, including counterrotating spiral waves, are observed in the precipitation reaction of AlCl3 with NaOH [Volford, A.; et al. Langmuir 2007, 23, 961 - 964]. Experimental and computational studies are carried out to characterize the wave behavior in cross-section configurations. A modified sol-coagulation model is developed that is based on models of Liesegang band and redissolution systems. The dynamics of the propagating waves is characterized in terms of growth and redissolution of a precipitation feature that travels through a migrating band of colloidal precipitate. PMID:24191642
Chabchoub, A.; Kibler, B.; Finot, C.; Millot, G.; Onorato, M.; Dudley, J.M.; Babanin, A.V.
2015-10-15
The dynamics of waves in weakly nonlinear dispersive media can be described by the nonlinear Schrödinger equation (NLSE). An important feature of the equation is that it can be derived in a number of different physical contexts; therefore, analogies between different fields, such as for example fiber optics, water waves, plasma waves and Bose–Einstein condensates, can be established. Here, we investigate the similarities between wave propagation in optical Kerr media and water waves. In particular, we discuss the modulation instability (MI) in both media. In analogy to the water wave problem, we derive for Kerr-media the Benjamin–Feir index, i.e. a nondimensional parameter related to the probability of formation of rogue waves in incoherent wave trains.
Propagating waves can explain irregular neural dynamics.
Keane, Adam; Gong, Pulin
2015-01-28
Cortical neurons in vivo fire quite irregularly. Previous studies about the origin of such irregular neural dynamics have given rise to two major models: a balanced excitation and inhibition model, and a model of highly synchronized synaptic inputs. To elucidate the network mechanisms underlying synchronized synaptic inputs and account for irregular neural dynamics, we investigate a spatially extended, conductance-based spiking neural network model. We show that propagating wave patterns with complex dynamics emerge from the network model. These waves sweep past neurons, to which they provide highly synchronized synaptic inputs. On the other hand, these patterns only emerge from the network with balanced excitation and inhibition; our model therefore reconciles the two major models of irregular neural dynamics. We further demonstrate that the collective dynamics of propagating wave patterns provides a mechanistic explanation for a range of irregular neural dynamics, including the variability of spike timing, slow firing rate fluctuations, and correlated membrane potential fluctuations. In addition, in our model, the distributions of synaptic conductance and membrane potential are non-Gaussian, consistent with recent experimental data obtained using whole-cell recordings. Our work therefore relates the propagating waves that have been widely observed in the brain to irregular neural dynamics. These results demonstrate that neural firing activity, although appearing highly disordered at the single-neuron level, can form dynamical coherent structures, such as propagating waves at the population level. PMID:25632135
Propagation of plate acoustic waves in contact with fluid medium
NASA Astrophysics Data System (ADS)
Ghatadi Suraji, Nagaraj
The characteristics of acoustic waves propagating in thin piezoelectric plates in the presence of a fluid medium contacting one or both of the plate surfaces are investigated. If the velocity of plate wave in the substrate is greater than velocity of bulk wave in the fluid, then a plate acoustic wave (PAW) traveling in the substrate will radiate a bulk acoustic wave (BAW) in the fluid. It is found that, under proper conditions, efficient conversion of energy from plate acoustic waves to bulk acoustic waves and vice versa can be obtained. For example, using the fundamental anti symmetric plate wave mode (A0 mode) propagating in a lithium niobate substrate and water as the fluid, total mode conversion loss (PAW to BAW and back from BAW to PAW) of less than 3 dB has been obtained. This mode conversion principle can be used to realize miniature, high efficiency transducers for use in ultrasonic flow meters. Similar type of transducer based on conversion of energy from surface acoustic wave (SAW) to bulk acoustic wave (BAW) has been developed previously. The use of plate waves has several advantages. Since the energy of plate waves is present on both plate surfaces, the inter digital transducer (IDT) can be on the surface opposite from that which is in contact with the fluid. This protects the IDT from possible damage due to the fluid and also simplifies the job of making electrical connections to the IDT. Another advantage is that one has wider choice of substrate materials with plate waves than is the case with SAWs. Preliminary calculations indicate that the mode conversion principle can also be used to generate and detect ultrasonic waves in air. This has potential applications for realizing transducers for use in non-contact ultrasonic's. The design of an ASIC (Application Specific Integrated Circuit) chip containing an amplifier and frequency counter for use with ultrasonic transducers is also presented in this thesis.
Mattei, S.; Boudreault, O.; Stafford, L.; Khare, R.; Donnelly, V. M.
2011-06-01
Phase-sensitive microwave interferometry and trace-rare-gas optical emission spectroscopy were used to measure the line-integrated electron density, n{sub e}, and electron temperature, T{sub e}, in a high-density chlorine plasma sustained in a quartz discharge tube (inner diameter = 6 mm) by an electromagnetic surface wave at 2.45 GHz. For pressures in the 0.1-1 Torr range, n{sub e} decreased nearly linearly along the tube's z-axis down to the critical density for surface wave propagation, where the plasma decayed abruptly. At lower pressures (< 50 mTorr), however, the plasma extended well beyond this critical point, after which n{sub e} decreased quasiexponentially toward the end of the plasma column. The length of this expansion region increased with decreasing pressure, going from {approx}8 cm at 5 mTorr to {approx}1 cm at 50 mTorr. T{sub e} was nearly independent of the axial position in the main plasma region and strongly decreased in the expansion region at lower pressures. The Cl{sub 2} percent dissociation, {tau}{sub D}, obtained from the calibrated Cl{sub 2} (306 nm)-to-Xe (828 nm) emission ratio, displayed behavior similar to that of n{sub e} and T{sub e}. For example, at 5 mTorr, {tau}{sub D} was close to 100% near the wave launcher and {approx}70% at 0.5 cm from the end of the plasma column.
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.
Globally propagating waves in the solar corona
NASA Astrophysics Data System (ADS)
Warmuth, Alexander
2011-12-01
High-cadence space-based observations, available for over a decade now, have revealed globally propagating wave-like disturbances in the solar corona. These coronal waves have now been imaged in a wide range of spectral channels, yielding a wealth of information. Still, no consensus on their physical nature has been reached yet. While many findings are consistent with fast-mode MHD waves and/or shocks, other characteristics have given rise to alternative models which involve magnetic reconfiguration in the framework of an erupting coronal mass ejection. In this paper, the observational signatures of coronal waves will be reviewed, and the different physical interpretations of coronal waves and how they are motivated by observations will be discussed. Finally, the potential of using coronal waves as a diagnostic tool for the corona will be shown.
Alfven Wave Propagation in Inhomogeneous Plasmas
NASA Astrophysics Data System (ADS)
Sears, Stephanie
Damping of Alfven waves is one of the most likely mechanisms for ion heating in the solar corona. Density gradients have significant but poorly-understood effects on energy transfer and Alfven wave propagation in partially ionized plasmas, such as those found in the solar chromosphere. Reflection of Alfven waves at density and magnetic field gradients can give rise to turbulence which sustains particle heating. The density profile in the Hot hELIcon eXperiment (HELIX) varies strongly with radius, giving access to a wide range of Alfven dynamics across the plasma column and providing an ideal environment to observe Alfven wave-driven particle heating. A new internal wave-launching antenna, situated at the edge of the high-density core and the density-gradient region of HELIX has been used to excite low-frequency waves in argon plasma. The propagation behavior of the launched waves was measured with a small-scale (smaller than the ion gyroradius) magnetic sense coil at multiple radial locations across the plasma column (from the high-density core through the density gradient region). Time-resolved laser induced fluorescence (LIF) and Langmuir probe measurements also yield insight into the plasma response to the perturbation. This dissertation presents cross-spectral and wavelet analysis of low-frequency waves in a helicon plasma with a strong density gradient. Building on the work of Houshmandyar, shear Alfven waves were launched in a helicon plasma source with a strong density gradient. Alfven wave turbulence is suggested from phase angle and wavelet analysis of magnetic sense coil probe measurements. The perturbation wavelength derived from phase angle measurements is consistent with predictions from the full Alfven wave dispersion relation (taking electron Landua damping, electron-ion collisions, and finite frequency effects into account). Time-resolved LIF measurements across the plasma column suggest ion heating where the turbulence is strongest. Time
Wave propagation in complex coordinates
NASA Astrophysics Data System (ADS)
Horsley, S. A. R.; King, C. G.; Philbin, T. G.
2016-04-01
We give an interpretation for the use of complex spatial coordinates in electromagnetism, in terms of a family of closely related inhomogeneous media. Using this understanding we find that the phenomenon of reflection can be related to branch cuts in the wave that originate from poles of ε (z) at complex positions. Demanding that these branch cuts disappear, we derive a new large family of inhomogeneous media that are reflectionless for a single angle of incidence. Extending this property to all angles of incidence leads us to a generalized form of the Pöschl Teller potentials that in general include regions of loss and gain. We conclude by analyzing our findings within the phase integral (WKB) method, and find another very large family of isotropic planar media that from one side have a transmission of unity and reflection of zero, for all angles of incidence.
Methods in wave propagation and scattering
NASA Astrophysics Data System (ADS)
Braunisch, Henning
2001-11-01
Aspects of wave propagation and scattering with an emphasis on specific applications in engineering and physics are examined. Frequency-domain methods prevail. Both forward and inverse problems are considered. Typical applications of the method of moments to rough surface three-dimensional (3-D) electromagnetic scattering require a truncation of the surface considered and call for a tapered incident wave. A proposed special choice of polarization vectors removes an irregularity at the origin of the wavenumber space and leads to a wave that is optimal in a least squared error sense. An analytical solution is presented for the electromagnetic induction problem of magnetic diffusion into and scattering from a permeable, highly but not perfectly conducting prolate spheroid under axial excitation, expressed in terms of an infinite matrix equation. The solution is based on separation of variables and matching boundary conditions where the prolate spheroidal wavefunctions with complex wavenumber parameter are expanded in terms of spherical harmonics. A general broadband rational function approximation technique is developed and demonstrated. We treat special cases and provide numerical reference data for the induced magnetic dipole moment or, equivalently, the magnetic polarizability factor. The magnetoquasistatic response of a distribution of an arbitrary number of interacting small conducting and permeable objects is also investigated. Useful formulations are provided for expressing the magnetic dipole moment of conducting and permeable objects of general shape. An alternative to Tikhonov regularization for deblurring and inverse diffraction, based on a local extrapolation scheme, is described, analyzed, and illustrated numerically for the cases of continuation of fields obeying Laplace and Helmholtz equations. The problem of inferring unknown geometry and material parameters of a wave-guide model from noisy samples of the associated modal dispersion curves is
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…
Surface waves on Saturn's magnetopause
NASA Astrophysics Data System (ADS)
Masters, A.; Achilleos, N.; Cutler, J. C.; Coates, A. J.; Dougherty, M. K.; Jones, G. H.
2012-05-01
Waves on the surface of a planetary magnetopause promote energy transport into the magnetosphere, representing an important aspect of solar wind-magnetosphere coupling. At Saturn's magnetopause it has been proposed that growth of the Kelvin-Helmholtz (K-H) instability produces greater wave activity on the dawn side of the surface than on the dusk side. We test this hypothesis using data taken by the Cassini spacecraft during crossings of Saturn's magnetopause. Surface orientation perturbations are primarily controlled by the local magnetospheric magnetic field orientation, and are generally greater at dusk than at dawn. 53% of all crossings were part of a sequence of regular oscillations arising in consecutive surface normals that is strong evidence for tailward propagating surface waves, with no detectable local time asymmetry in this phenomenon. We estimate the dominant wave period to be ∼5 h at dawn and ∼3 h at dusk. The role played by the magnetospheric magnetic field, tailward wave propagation, and the dawn-dusk difference in wave period suggests that K-H instability is a major wave driving mechanism. Using linear K-H theory we estimate the dominant wavelength to be ∼10 Saturn radii (RS) and amplitude to be ∼1 RS at both dawn and dusk, giving propagation speeds of ∼30 and ∼50 km s-1 at dawn and dusk, respectively. The lack of the hypothesized dawn-dusk asymmetry in wave activity demonstrates that we need to revise our understanding of the growth of the K-H instability at Saturn's magnetopause, which will have implications for the study of other planetary magnetospheres.
Wave propagation analysis using the variance matrix.
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
Large-scale Globally Propagating Coronal Waves
NASA Astrophysics Data System (ADS)
Warmuth, Alexander
2015-09-01
Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the "classical" interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which "pseudo waves" are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.
Propagation of seismic waves in tall buildings
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.
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
Ionic wave propagation along actin filaments.
Tuszyński, J A; Portet, S; Dixon, J M; Luxford, C; Cantiello, H F
2004-04-01
We investigate the conditions enabling actin filaments to act as electrical transmission lines for ion flows along their lengths. We propose a model in which each actin monomer is an electric element with a capacitive, inductive, and resistive property due to the molecular structure of the actin filament and viscosity of the solution. Based on Kirchhoff's laws taken in the continuum limit, a nonlinear partial differential equation is derived for the propagation of ionic waves. We solve this equation in two different regimes. In the first, the maximum propagation velocity wave is found in terms of Jacobi elliptic functions. In the general case, we analyze the equation in terms of Fisher-Kolmogoroff modes with both localized and extended wave characteristics. We propose a new signaling mechanism in the cell, especially in neurons. PMID:15041636
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.
Global propagation of body waves revealed by seismic interferometry (Invited)
NASA Astrophysics Data System (ADS)
Nishida, K.
2013-12-01
Seismic interferometry has now been applied to the exploration of the Earth's interior at scales ranging from local to global. Most studies have used surface-wave propagation. Recently, some studies have focused on body wave propagation on local and regional scales but not on a global scale. In this study, we succeed in extracting global body wave propagation(of P, PP, PKP, S, SS, ScS, P‧P‧, etc. waves) using seismic hum with frequency-wave number filtering in the range of 5 to 40 mHz. Although the observed body wave propagation is similar to that of the corresponding components of Green's functions, there are two differences between them: the lack of reflection phases in the observation and the dominance of shear-coupled PL waves in the observation. These differences originate from the dominance of shear-traction sources on the Earth's surface, which causes the breakdown of equipartition among modes with different radial orders. To discuss the differences quantitatively, we developed a new method to synthesize cross-spectra between a pair of stations with an assumption of spatially homogeneous distribution of random sources, which are characterized by effective horizontal traction and effective pressure. At first, we estimated power spectra of the effective pressure and the effective shear traction by fitting the synthetic spectra to the observed ones. The results show dominance of random shear traction from 5 to 20 mHz, which is consistent with past studies. Next, we synthesized cross-correlation functions with the source model. The synthetic spectra can reconstruct the two observed features: the lack of reflection phases and the dominance of shear-coupled PL waves. The source characteristics are crucial for the body wave exploration in further studies.
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.
Gerdes, Frank; Finette, Steven
2012-10-01
A modeling and simulation study is performed in a littoral ocean waveguide subject to uncertainty in four quantities: source depth, tidal forcing, initial thermocline structure, and sediment sound speed. In this partially known shelf-break environment, tidal forcing over a density-stratified water column produces internal tides and solitary wave packets. The resulting uncertainty in the space-time oceanographic field is mapped into the sound speed distribution which, in turn, introduces uncertainty into the acoustic wave field. The latter is treated as a stochastic field whose intensity is described by a polynomial chaos expansion. The expansion coefficients are estimated through constrained multivariate linear regression, and an analysis of the chaos coefficients provides insight into the relative contribution of the uncertain acoustic and oceanographic quantities. Histograms of acoustic intensity are estimated and compared to a reference solution obtained through Latin Hypercube sampling. A sensitivity analysis is performed to illustrate the relative importance of the four contributions of incomplete information about the environment. The simulation methodology represents an end-to-end analysis approach including both oceanographic and acoustic field uncertainty where the latter is quantified using stochastic basis expansions in the form of a polynomial chaos representation. PMID:23039422
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.
Nonlinear guided wave propagation in prestressed plates.
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
Wave propagation in spatially modulated tubes.
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
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.
Lattice Boltzmann model for wave propagation.
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. PMID:19792280
Seismic Wave Propagation Along Fracture Intersections
NASA Astrophysics Data System (ADS)
Abell, B.; Pyrak-Nolte, L. J.; Knobloch, J.
2012-12-01
Past research has shown that fractures support guided-modes such as coupled Rayleigh waves as well as confined modes such as Love waves and leaky-mode compressional waves. We demonstrated experimentally that fracture intersections support a mode that is similar to interface waves but propagates at speeds below the Rayleigh wave for low applied load. In this experimental study, we demonstrated that at low stress, fracture intersections support highly-localized wedge waves whose existence depends on stress and source-receiver polarization. Wedge waves (W.W.) were propagated along the orthogonal edge of aluminum samples. The sample measured 100 x 150 x 150 mm and was machined with two orthogonal fractures, intersecting at the center, such that four independent pieces of aluminum could be measured independently or pieced together. Seismic measurements were performed for two cases: (1) two right angle blocks in contact to examine the stress dependence of two corners in contact and (2) four right angle blocks in contact to study the behavior of four intersecting corners in contact. Seismic transducers with a central frequency of 1MHz were used to propagate shear (S) waves along the corners of the blocks that form an intersection, along the fractures and through the bulk. Measurements were made with the shear transducers polarized at 0, 45, 90 and 135 deg. to the direction of loading for a range (0 to 66 kN) of applied normal loads. When only two blocks were in contact, a W.W. was observed traveling at speeds between 2650 m/s and 3000 m/s. This is below the Rayleigh speed (2830 m/s) for low stress. As the applied load was increased, the wave speed increased, indicating a change in the local stiffness. Although an increase in speed was observed for both polarizations, the measured speed was lower for 135 deg. polarization indicating that the local stiffness of the top wedge was dramatically different than the bottom aluminum block. All four blocks were also examined under
Obliquely propagating dust-density waves
NASA Astrophysics Data System (ADS)
Piel, A.; Arp, O.; Klindworth, M.; Melzer, A.
2008-02-01
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.
Solitons in wave propagation and spin systems
NASA Astrophysics Data System (ADS)
Loutsenko, Igor
1999-10-01
This thesis consists of three parts: In the first part, a solution of the restricted Hadamard problem is presented. The classical Hadamard problem consists in determining (up to equivalence) all the second order differential operators which satisfy Huygens' Principle in the narrow sense. Physically, such operators describe systems where the diffusion of waves is absent and where signals propagate with maximal velocity. Unlike the original principle of superposition of secondary waves, which holds for all wave propagation phenomena, Huygens' principle in the narrow sense of Hadamard applies only to a very restricted range of wave processes, with sharp signals. We present a new class of Huygens' operators on Minkowski space-time and establish a new link between Huygens' principle and the solitons of the Korteveg-de Vries equation. In the second part, a new class of exactly solvable models in statistical mechanics is presented. We study the connections between the soliton solutions of certain integrable nonlinear equations (hierarchies of equations) and the thermodynamic quantities of one-dimensional Ising models with different types of interactions between spins. The exact solvability of these models can be traced back to this connection. We consider a model linked to soliton solutions of the Korteveg de Vries and of the B-type Kadomtsev-Petiashvili hierarchies. A connection between these Ising chains and random matrix models is considered as well. In the third part, we study solitonic mechanisms of exciton superfluidity. We provide a theoretical explanation of recent experiments on the propagation of excitons in semiconductors. In these experiments, the excitonic transport under the action of a laser pulse has been studied. It turned out that under certain conditions this transport becomes anomalous and the excitons propagate through the crystal in a wave packet without diffusion. We propose a model for this phenomenon which relies on the presence of an exciton
Wave Propagation in Jointed Geologic Media
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.
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
An experimental investigation of wave propagation in fractured brittle material
NASA Astrophysics Data System (ADS)
Patel, Bibhuti Bhusan
An experimental method for visualizing and analyzing the propagation of plate stress waves in a brittle plate is developed. A procedure has been developed to cast Break-Away glass (a low molecular weight polystyrene material) plate specimens in an open mold. The specimens are loaded with short duration (200 [...]s) stress pulses on one edge by an electromagnetic stress wave generator. The propagating stress waves generate out-of-plane deformations on the specimen surface, which are observed using Twyman-Green interferometry. The fringe patterns created by the propagating stress waves are captured using a high speed camera - pulsing laser combination at 4[...]s intervals.A generalized "Fringe Analysis Procedure" is developed to subtract the reference interferogram from the subsequent interferograms. The "Fringe Analysis Procedure" employs a fringe edge detection algorithm to obtain the sharp edge lines of the fringes in an interferogram. A digitizer is used to extract points on these edge lines and assign them fringe numbers. The "griddata" option in the commercial software "Matlab" is utilized to interpolate the deformation field on to the nodes of a uniform grid. The field values at these nodes in the reference image are then subtracted from corresponding values in the subsequent images to obtain the actual deformation patterns generated by the propagating stress waves. The "Fringe Analysis Procedure" has eliminated the subjective element introduced by human judgment in manual fringe tracing procedures.The developed experimental method and the image analysis technique is used to investigate the propagation of stress waves in Break-Away glass plate specimens.
Shock wave propagation in glow discharges
NASA Astrophysics Data System (ADS)
Ganguly, B. N.
1998-10-01
The modification of acoustic shock wave propagation characteristics in a 25 cm long positive column low pressure (10 to 50 Torr), low current density (2 to 10 mA/cm^2) argon and N2 dc discharges have been measured by laser beam deflection technique. The simultaneous multi point shock velocity, dispersion and damping have been measured both inside and outside the glow discharge region. The local shock velocity is found to increase with the increased propagation path length through the discharge; for Mach number greater than 1.7 the upstream velocity exceeded the downstream velocity in contrast to the opposite behavior in neutral gas. The damping and dispersion are also dependent on the propagation distance. The recovery of the shock dispersion and damping in the post discharge region, for a given discharge condition, are functions of the initial Mach number. The optical measurement of the wall and the gas (rotational) temperatures suggest the observed shock features can not be solely explained by the gas heating in a self sustained discharge. The results are similar for both Ar and N2 discharges showing that vibrational excitation and relaxation are not essential^1. The explanation of the observed weak shock propagation properties in a glow discharge appears to require long range cooperative interactions that enhance heavy particle collisional energy transfer rates for the measured discharge conditions. Unlike collisional shock wave propagation in highly ionized plasmas^2,3, the exact energy coupling mechanism between the nonequilibrium weakly ionized plasma and shock is not understood. 1. A.I. Osipov and A.V. Uvarov, Sov. Phys. Usp. 35, 903 (1992) and other references there in. 2. M. Casanova, O. Larroche and J-P Matte, Phys. Rev. Lett. 67, 2143 (1991). 3. M.C.M. van de Sanden, R. van den Bercken and D.C. Schram, Plasma Sources Sci.Technol. 3, 511 (1994).
S-Wave Normal Mode Propagation in Aluminum Cylinders
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.
The Propagation of Slow Wave Potentials in Pea Epicotyls.
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
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.
Propagating wave pattern on a falling liquid curtain.
Le Grand-Piteira, N; Brunet, P; Lebon, L; Limat, L
2006-08-01
A regular pattern of surface waves is observed on a liquid curtain falling from a horizontal, wetted tube, maintained between two vertical wires. Since the upper boundary is not constrained in the transverse direction, the top of the curtain enters a pendulum-like motion, when the flow rate is progressively reduced, coupled to the propagation of curtain undulations, structured as a checkerboard. This structure is formed by two patterns of propagating waves. In some sense, these propagating patterns replace the stationary pattern of liquid columns observed at a lower flow rate. Measurements of phase velocity, frequency, and wavelength are reported. The data are in agreement with a simple dimensional argument suggesting that the wave velocity is proportional to the surface tension divided by the mass flux of liquid per unit length. This scaling is also that followed by the fluid velocity at the so-called transonic point, i.e., the point where the fluid velocity equals that of sinuous waves. We finally discuss the implications of these results for the global stability of liquid curtains. PMID:17025537
Undulations from amplified low frequency surface waves
Coutant, Antonin; Parentani, Renaud
2014-04-15
We study the linear scattering of gravity waves in longitudinal inhomogeneous stationary flows. When the flow becomes supercritical, it is known that counterflow propagating shallow waves are blocked and converted into deep waves. Here we show that in the zero-frequency limit, the reflected waves are amplified in such a way that the free surface develops an undulation, i.e., a zero-frequency wave of large amplitude with nodes located at specific places. This amplification involves negative energy waves and implies that flat surfaces are unstable against incoming perturbations of arbitrary small amplitude. The relation between this instability and black hole radiation (the Hawking effect) is established.
Seismic Wave Propagation Simulation using Circular Hough Transform
NASA Astrophysics Data System (ADS)
Miah, K.; Potter, D. K.
2012-12-01
Synthetic data generation by numerically solving a two-way wave equation is an essential part of seismic tomography, especially in full-waveform inversion. Finite-difference and finite-element are the two common methods of seismic wave propagation modeling in heterogeneous media. Either time or frequency domain representation of wave equation is used for these simulations. Hanahara and Hiyane [1] proposed and implemented a circle-detection algorithm based on the Circular Hough transform (CHT) to numerically solve a two-dimensional wave equation. The Hough transform is generally used in image processing applications to identify objects of various shapes in an image [2]. In this abstract, we use the Circular Hough transform to numerically solve an acoustic wave equation, with the purpose to identify and locate primaries and multiples in the transform domain. Relationships between different seismic events and the CHT parameter are also investigated. [1] Hanahara, K. and Hiyane, M., A Circle-Detection Algorithm Simulating Wave Propagation, Machine Vision and Applications, vol. 3, pp. 97-111, 1990. [2 ] Petcher, P. A. and Dixon, S., A modified Hough transform for removal of direct and reflected surface waves from B-scans, NDT & E International, vol. 44, no. 2, pp. 139-144, 2011.
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.
Ultrasonic wave propagation in cortical bone mimics
NASA Astrophysics Data System (ADS)
Dodd, Simon P.; Cunningham, James L.; Miles, Anthony W.; Humphrey, Victor F.; Gheduzzi, Sabina
2004-10-01
Understanding the velocity and attenuation of ultrasonic waves in cortical bone is important for studies of osteoporosis and fractures. In particular, propagation in free- and water-loaded acrylic plates, with a thickness range of around 1-6 mm, has been widely used to mimic cortical bone behavior. A theoretical investigation of Lamb mode propagation at 200 kHz in free- and water-loaded acrylic plates revealed a marked difference in the form of their velocity and attenuation dispersion curves as a function of frequency thickness product. In experimental studies, this difference between free and loaded plates is not seen. Over short measurement distances, the results for both free and loaded plates are consistent with previous modeling and experimental studies: for thicker plates (above 3-4 mm), the velocity calculated using the first arrival signal is a lateral wave comparable with the longitudinal velocity. As the plate thickness decreases, the velocity approaches the S0 Lamb mode value. WAVE2000 modeling of the experimental setup agrees with experimental data. The data are also used to test a hypothesis that for thin plates the velocity approaches the corresponding S0 Lamb mode velocity at large measurement distances or when different arrival time criteria are used. [Work supported by Action Medical Research.
Wave envelopes method for description of nonlinear acoustic wave propagation.
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
Radio wave propagation in pulsar magnetospheres
NASA Astrophysics Data System (ADS)
Petrova, S. A.; Lyubarskii, Yu. E.
Pulsar magnetospheres are known to contain an ultrarelativistic highly magnetized plasma which streams along the open magnetic lines. The radio emission observed from pulsars is believed to originate sufficiently deep in the open field line tube, so that the characteristics of outgoing waves can be influenced by propagation in the magnetospheric plasma. Refraction of radio waves in pulsar magnetospheres appears to be efficient. The effect not only influences the observed pulse width and its frequency dependency. It can alter the apparent spatial structure of pulsar emission region which can be derived from the observations of pulsar interstellar scintillations. Transverse ray separation versus pulse longitude calculated allowing for magnetospheric refraction appears to be in qualitative agreement with that observed. In particular, the nonmonotonic character of the curve can be attributed to nonmonotonic distribution of the plasma number density across the open field line tube which makes the rays emitted at different spatial locations deviate in the opposite directions. Proceeding from the frequency dependence of refraction some predictions are made about the frequency evolution of the apparent spatial structure of pulsar emission region. Magnetospheric refraction can also determine the profile shape giving rise to ray grouping into separate components. It will be demonstrated that the salient features of profile morphology can be explained within the frame of a primordial hollow-cone emission model taking into account refraction of rays in pulsar plasma. Then the frequency evolution of profile structure is naturally interpreted as a consequence of frequency dependence of refraction. As the waves propagate in the magnetospheric plasma their polarization also evolves essentially. In the vicinity of the emission region normal waves are linearly polarized and propagate independently, with the polarization plane following the orientation of the local magnetic field. As
Lightning location with variable radio wave propagation velocity
NASA Astrophysics Data System (ADS)
Liu, Zhongjian; Koh, Kuang Liang; Mezentsev, Andrew; Sugier, Jacqueline; Fullekrug, Martin
2016-04-01
Lightning discharges can be located by triangulation of their broadband electromagnetic pulses in long-baseline (~500 km) radio receiver networks. Here we apply the time of arrival difference (TOA) method to electric field recordings with a low frequency radio receiver array consisting of four stations in western Europe. The electromagnetic wave propagation velocity at low radio frequencies is an important input parameter for the TOA calculation and it is normally assumed to be equal to the speed of light. However, the radio wave propagation depends for example on the frequency, ground conductivity and the ionospheric height and small variations can cause location differences from hundreds to thousands of meters, as demonstrated in this study. The radio wave propagation from two VLF transmissions at 20.9 kHz and 23.4 kHz are compared. The results show that the apparent phase velocities are 0.6% slower and 0.5% faster than the speed of light respectively. As a result, a variable velocity is implemented in the TOA method using continuously recorded data on the 8th August 2014, when a mesoscale convective system developed over central France. The lightning locations inferred with a variable wave propagation velocity are more clustered than those using a fixed velocity. The distribution of the lightning velocities in a given geographic area fits a normal distribution that is not centred at the speed of light. As a result, representative velocities can be calculated for smaller regions to generate a velocity map over a larger area of enhanced lightning activity. These results suggest a connection with the ground elevation and/or surface conductivity that might have an impact on the observed wave propagation velocities.
Simulation of 3D Seismic Wave Propagation with Volcano Topography
NASA Astrophysics Data System (ADS)
Ripperger, J.; Igel, H.; Wassermann, J.
2001-12-01
We investigate the possibilities of using three-dimensional finite difference (FD) methods for numerical simulation of the seismic wave field at active volcanoes. We put special emphasis on the implementation of the boundary conditions for free surface topography. We compare two different approaches to solve the free surface boundary conditions. The algorithms are implemented on parallel hardware and have been tested for correctness and stability. We apply them to smooth artificial topographies and to the real topography of Mount Merapi, Indonesia. We conclude, that grid stretching type methods (e.g. Hestholm & Ruud, 1994) are not well suited for realistic volcano topography as they tend to become unstable for large topographic gradients. The representation of topography through staircase shaped grids (Ohminato & Chouet, 1997) results in stable calculations, while demanding very fine gridding. The simulations show the effects of a three-dimensional surface topography on elastic wave propagation. Ground motion at the surface is severely affected by topography. If neglected, this may jeopardize attempts to determine source location by analyzing particle motion. Numerical studies like this can help to understand wave propagation phenomena observed on field recordings in volcano seismology. Future studies will aim at separating the wave effects of internal scattering, topography and sources (tremors, tectonic events, pyroclastic flows).
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.
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.
Elastic Wave Propagation and Generation in Seismology
NASA Astrophysics Data System (ADS)
Lees, Jonathan M.
The majority of mature seismologists of my generation were introduced to theoretical seismology via classic textbooks written in the early 1980s. Since this generation has matured and taken the mantle of teaching seismology to a new generation, several new books have been put forward as replacements, or alternatives, to the original classical texts. The target readers of the new texts range from beginner through intermediate to more advanced, although all have been attempts to improve upon what is now considered standard convention in quantitative seismology. To this plethora of choices we now have a new addition by Jose Pujol, titledElastic Wave Propagation and Generation in Seismology.
Investigation into stress wave propagation in metal foams
NASA Astrophysics Data System (ADS)
Li, Lang; Xue, Pu; Chen, Yue
2015-09-01
The aim of this study is to investigate stress wave propagation in metal foams under high-speed impact loading. Three-dimensional Voronoi model is established to represent real closed-cell foam. Based on the one-dimensional stress wave theory and Voronoi model, a numerical model is developed to calculate the velocity of elastic wave and shock wave in metal foam. The effects of impact velocity and relative density of metal foam on the stress wave propagation in metal foams are explored respectively. The results show that both elastic wave and shock wave propagate faster in metal foams with larger relative density; with increasing the impact velocity, the shock wave propagation velocity increase, but the elastic wave propagation is not sensitive to the impact velocity.
Propagation and attenuation of Rayleigh waves in generalized thermoelastic media
NASA Astrophysics Data System (ADS)
Sharma, M. D.
2014-01-01
This study considers the propagation of Rayleigh waves in a generalized thermoelastic half-space with stress-free plane boundary. The boundary has the option of being either isothermal or thermally insulated. In either case, the dispersion equation is obtained in the form of a complex irrational expression due to the presence of radicals. This dispersion equation is rationalized into a polynomial equation, which is solvable, numerically, for exact complex roots. The roots of the dispersion equation are obtained after removing the extraneous zeros of this polynomial equation. Then, these roots are filtered out for the inhomogeneous propagation of waves decaying with depth. Numerical examples are solved to analyze the effects of thermal properties of elastic materials on the dispersion of existing surface waves. For these thermoelastic Rayleigh waves, the behavior of elliptical particle motion is studied inside and at the surface of the medium. Insulation of boundary does play a significant role in changing the speed, amplitude, and polarization of Rayleigh waves in thermoelastic media.
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
NASA Astrophysics Data System (ADS)
Lehner, M.; Jungen, M.
2015-02-01
A three-dimensional wave packet method, based on Lanczos tridiagonalization of the Hamiltonian, is introduced and applied to the three-particle predissociation of rotating D3 and H3 3{{ }2}{{A}\\prime } (2sa1\\prime ). The time-dependent propagation calculations on the (diabatic) ground state potential energy surfaces include the non-adiabatic transition from the excited initial state. Results for the eight lowest vibrational levels are presented as Dalitz plots and compared to momentum correlation measurements.
Wave propagation in random granular chains.
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
WAVE: Interactive Wave-based Sound Propagation for Virtual Environments.
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
Fujita, Fuminori; Mizuno, Katsunori; Matsukawa, Mami
2013-12-01
Wave propagation in a trabecular bone was experimentally investigated using an acoustic tube. For the purposes of this study, a cubic sample was gradually filed so the waveform change due to the sample thickness could be observed. The initial sample showed clear two-wave separation. As the sample became thinner, the fast and slow waves gradually overlapped. The apparent frequencies and amplitudes of the fast waves obtained from the time domain data decreased significantly for the smaller thicknesses. This indicates an increase in the apparent attenuation at the initial stage of the propagation. Next the authors investigated the distribution of the ultrasonic field after the transmission through the cancellous bone sample. In addition to a large aperture receiver, a needle-type ultrasonic transducer was used to observe the ultrasonic field. Within an area of the same size of the large transducer, the waveforms retrieved with the needle sensor exhibited high spatial variations; however, the averaged waveform in the plane was similar to the waveform obtained with the large aperture receiver. This indicates that the phase cancellation effect on the surface of the large aperture receiver can be one of the reasons for the strong apparent attenuation observed at the initial stages of the propagation. PMID:25669289
On the generation of internal wave modes by surface waves
NASA Astrophysics Data System (ADS)
Harlander, Uwe; Kirschner, Ian; Maas, Christian; Zaussinger, Florian
2016-04-01
Internal gravity waves play an important role in the ocean since they transport energy and momentum and the can lead to mixing when they break. Surface waves and internal gravity waves can interact. On the one hand, long internal waves imply a slow varying shear current that modifies the propagation of surface waves. Surface waves generated by the atmosphere can, on the other hand, excite internal waves by nonlinear interaction. Thereby a surface wave packet consisting of two close frequencies can resonate with a low frequency internal wave (Phillips, 1966). From a theoretical point of view, the latter has been studied intensively by using a 2-layer model, i.e. a surface layer with a strong density contrast and an internal layer with a comparable weak density contrast (Ball, 1964; Craig et al., 2010). In the present work we analyse the wave coupling for a continuously stratified fluid using a fully non-linear 2D numerical model (OpenFoam) and compare this with laboratory experiments (see Lewis et al. 1974). Surface wave modes are used as initial condition and the time development of the dominant surface and internal waves are studied by spectral and harmonic analysis. For the simple geometry of a box, the results are compared with analytical spectra of surface and gravity waves. Ball, F.K. 1964: Energy transfer between external and internal gravity waves. J. Fluid Mech. 19, 465. Craig, W., Guyenne, P., Sulem, C. 2010: Coupling between internal and surface waves. Natural Hazards 57, 617-642. Lewis, J.E., Lake, B.M., Ko, D.R.S 1974: On the interaction of internal waves and surfacr gravity waves, J. Fluid Mech. 63, 773-800. Phillips, O.M. 1966: The dynamics of the upper ocean, Cambridge University Press, 336pp.
The effect of source's shape for seismic wave propagation
NASA Astrophysics Data System (ADS)
Tanaka, S.; Mikada, H.; Goto, T.; Takekawa, J.; Onishi, K.; Kasahara, J.; Kuroda, T.
2009-12-01
In conventional simulation of seismic wave propagation, the source which generates signals is usually given by a point force or by a particle velocity at a point. In practice, seismic wave is generated by signal generators with finite volume and width. Since seismic lines span a distance up to hundreds meter to several kilometers, many people conducted seismic survey and data processing with the assumption that the size of signal generator is negligible compared with survey scale. However, there are no studies that tells how the size of baseplate influences generated seismic waves. Such estimations, therefore, are meaningful to consider the scale of generator. In this sense, current seismic processing might require a theoretical background about the seismic source for further detailed analysis. The main purpose of this study is to investigate the impact of seismic source’s shape to resultant wave properties, and then estimate how effective the consideration about the scale of signal generator is for analyzing the seismic data. To evaluate source’s scale effect, we performed finite element analysis with the 3D model including the baseplate of source and the heterogeneous ground medium. We adopted a finite element method (FEM) and chose the code named “MD Nastran” (MSC Software Ver.2008) to calculate seismic wave propagation. To verify the reliability of calculation, we compared the result of FEM and that of finite-difference method (FDM) with wave propagating simulation of isotropic and homogeneous model with a point source. The amplitude and phase of those two were nearly equal each other. We considered the calculation of FEM is accurate enough and can be performed in the following calculations. As the first step, we developed a simple point source model and a baseplate model. The point source model contains only the ground represented by an elastic medium. The force generating the signal is given at the nodal point of the surface in this case. On the other
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.
Propagation of Buoyancy Waves Through the Magnetosphere
NASA Astrophysics Data System (ADS)
Wolf, R.; Schutza, A. M.; Toffoletto, F. R.
2015-12-01
THEMIS observations analyzed by E. V. Panov and collaborators have shown that, when an earthward-moving plasma-sheet flow burst encounters the quasi-dipolar region of the magnetosphere, the plasma that formed the burst often oscillates a few times before coming to rest. The observed oscillation periods seem in good agreement with the frequency calculated theoretically for a thin filament oscillating in the same region. However, since a thin filament is an extreme idealization of a real flow burst, we have investigated the relationship between thin-filament oscillations and the normal modes of a 2D plasma system that is analogous to the magnetosphere. We have developed an analytic model of the normal modes of an idealized plasma configuration that consists of a wedge with circular field lines. For that system, the low-frequency wave obeys a one-dimensional differential equation that is essentially the same as the equation describing buoyancy oscillations in the neutral atmosphere. An important term in the neutral-atmosphere equation is proportional to the square of ωb, which is called the "buoyancy frequency" or "Brunt-Väisälä frequency", and the corresponding quantity in the plasma equation is exactly the square of the fundamental oscillation frequency of a thin filament. In both cases, a buoyancy wave of frequency ω propagates in the region where ωb>ω, but is evanescent in the region where ωb<ω. A thin-filament code has been used to calculate the buoyancy frequency in different regions of the magnetosphere, as represented by a force-balanced configuration based on a Tsyganenko model. The results suggest that, if the braking of a bursty bulk flow produces an oscillation at the buoyancy frequency at about 10 RE, it may generate a buoyancy wave that can propagate earthward to the plasmapause.
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).
Interactions between two propagating waves in rat visual cortex.
Gao, X; Xu, W; Wang, Z; Takagaki, K; Li, B; Wu, J-Y
2012-08-01
Sensory-evoked propagating waves are frequently observed in sensory cortex. However, it is largely unknown how an evoked propagating wave affects the activity evoked by subsequent sensory inputs, or how two propagating waves interact when evoked by simultaneous sensory inputs. Using voltage-sensitive dye imaging, we investigated the interactions between two evoked waves in rat visual cortex, and the spatiotemporal patterns of depolarization in the neuronal population due to wave-to-wave interactions. We have found that visually-evoked propagating waves have a refractory period of about 300 ms, within which the response to a subsequent visual stimulus is suppressed. Simultaneous presentation of two visual stimuli at different locations can evoke two waves propagating toward each other, and these two waves fuse. Fusion significantly shortens the latency and half-width of the response, leading to changes in the spatial profile of evoked population activity. The visually-evoked propagating wave may also be suppressed by a preceding spontaneous wave. The refractory period following a propagating wave and the fusion between two waves may contribute to visual sensory processing by modifying the spatiotemporal profile of population neuronal activity evoked by sensory events. PMID:22561730
Propagation of sound waves in drill strings
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
di Sarra, Alcide; Fuà, Daniele; Meloni, Daniela
2013-04-01
This study is based on measurements made at ENEA Station for Climate Observations (35.52° N, 12.63° E, 50 m asl) on the island of Lampedusa, in the Southern part of the Central Mediterranean. A quasi periodic oscillation of aerosol optical depth, column water vapour, shortwave (SW) and photosynthetic active radiation (PAR) is observed to occur during the morning of 7 September 2005. The quasi-periodic wave is present from about 6 to 10 UT, with solar zenith angles (SZA) varying between 77.5° and 37.2° . In this period the aerosol optical depth at 500 nm, ?, varies between 0.29 and 0.41; the column water vapour, cwv, varies between 2.4 and 2.8 cm. The oscillations of ? and cwv are in phase, while the modulation of the downward surface irradiances is in opposition of phase with respect to ? and cwv. The period of the oscillation is about 13 min. The oscillation is attributed to the propagation of a gravity wave which modulates the structure of the planetary boundary layer. The measured aerosol optical properties are typical of cases dominated by Saharan dust, with the Ångström exponent comprised between 0.5 and 0.6. The backtrajectory analysis for that day shows that airmasses overpass Northern Libya (trajectories arriving below 2000 m), Tunisia and Northern Algeria (trajectories arriving above 2000 m), carrying Saharan dust particles to Lampedusa. The combined modulation of downward irradiance, water vapour column, and aerosol optical depth is used to estimate the aerosol effect on the irradiance. From the irradiance-optical depth relation, the aerosol surface direct forcing efficiency (FE) is derived, under the assumption that during the measurement interval the aerosol microphysical properties do not appreciably change. As a first step, all SW irradiances are reported to the same cwv content (2.6 cm), by using radiative transfer model calculations. Reference curves describing the downward SW and PAR irradiances are constructed by using measurements obtained
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.
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.
Zabolotin, V.V.; Uvarova, L.A.
2015-03-10
A numerical simulation of the interaction of laser radiation with dispersed particles in the course of propagation of breather in the surface layer of the liquid breather was performed. The shape and amplitude of the acoustic signal formed in this interaction were obtained. Two acoustic signals, before and after the impact of a breather on the process of optical sound generation, were compared. Results of the comparison showed that the breather spreading over the surface of the liquid medium affecst the acoustic signal and its effect must be considered in the measurements.
Spin-wave propagation and transformation in a thermal gradient
NASA Astrophysics Data System (ADS)
Obry, Björn; Vasyuchka, Vitaliy I.; Chumak, Andrii V.; Serga, Alexander A.; Hillebrands, Burkard
2012-11-01
The influence of a thermal gradient on the propagation properties of externally excited dipolar spin waves in a magnetic insulator waveguide is investigated. It is shown that spin waves propagating towards a colder region along the magnetization direction continuously reduce their wavelength. The wavelength increase of a wave propagating into a hotter region was utilized to realize its decomposition in the partial waveguide modes which are reflected at different locations. This influence of temperature on spin-wave properties is mainly caused by a change in the saturation magnetization and yields promising opportunities for the manipulation of spin waves in spin-caloritronic applications.
Effect of Resolution on Propagating Detonation Wave
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.
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
Surface waves on Saturn's magnetopause
NASA Astrophysics Data System (ADS)
Masters, A.; Achilleos, N.; Cutler, J. C.; Coates, A. J.; Dougherty, M. K.
2011-10-01
Waves on the surface of a planetary magnetopause lead to the transport of energy into the magnetosphere, making them an important aspect of solar wind-magnetosphere coupling. In the case of Saturn's magnetosphere it has been proposed that the growth of the Kelvin-Helmholtz (K-H) instability produces greater wave activity on the dawn side of the magnetopause than on the dusk side. Here we test this hypothesis using data taken by the Cassini spacecraft during 520 magnetopause crossings. We determine the surface normal for 477 of the crossings and show that perturbations of the surface orientation are predominantly in the direction perpendicular to the local magnetospheric magnetic field, due to the stabilizing influence of magnetic tension forces. There are two most likely orientations with respect to the magnetospheric magnetic field, and 45% of the crossings were part of a clear oscillation of consecutive normals. The only local time asymmetry in the surface orientation is a greater level of normal perturbations at dusk than at dawn. These results suggest that surface waves on Saturn's magnetopause are ubiquitous, and the K-H instability is the most plausible driving mechanism. The waves generally propagate tailward, with a typical period, wavelength, speed, and amplitude of 4 hrs, 10 Saturn radii (RS), 50 km s-1, and 1 RS, respectively. The lack of the hypothesized dawn-dusk asymmetry in wave activity means that we need to revise our understanding of the growth of the K-H instability at Saturn's magnetopause, which will have implications for the study of other planetary magnetospheres.
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.
Generation, propagation, and breaking of internal solitary waves.
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
Dynamics of propagating front into sand ripples under regular waves.
Lebunetel-Levaslot, J; Jarno-Druaux, A; Ezersky, A B; Marin, F
2010-09-01
The results of an experimental study of pattern formation on sandy bottom under the action of regular harmonic surface waves are reported. It is found that two modes of pattern formation occur: sand ripples form uniformly on the whole bottom or from localized nucleation sites. In the second regime, the ripples appear in isolated regions (patches) increasing in size, and front propagation speed is measured. A simple dynamical model based on the Ginzburg-Landau equation is proposed to explain the characteristics of patches. PMID:21230122
NASA Astrophysics Data System (ADS)
Nakahara, Motonao; Nagayama, Kunihito
1999-06-01
Pressure enhancement of the generated shock waves in water has been found, when pulse laser energy is transmitted through an optical fiber whose end surface is intentionally roughened. More effective high-pressure shock generation can be possible by the aluminum coating on the roughened fiber surface. In case of the moderate laser energy of about 50 mJ input to the fiber, it is found that the phenomena are dependent on (1) the roughness, (2) the fiber diameter, and (3) the ambient medium. Shock wave generation can be detected successively by the laser input, but found to degrade down. Cavitation bubbles have also been observed after each shot. When the fiber end is in air, an intense and long-stretched flash can be observed. We have observed the phenomena by the pulse laser shadowgraphy.
The impact of density heterogeneities on seismic wave propagation
NASA Astrophysics Data System (ADS)
Płonka, Agnieszka; Fichtner, Andreas
2014-05-01
Using 3D numerical simulations of seismic wave propagation in heterogeneous media, we systematically compare the imprints of heterogeneities of different type (and particularly density heterogeneities) on synthetic seismograms. Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convective motion in the mantle. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravity provide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling, making strong assumptions on the origin of structural heterogeneities, which may not necessarily be true. We propose to develop a seismic tomography technique that directly inverts for density, using complete seismograms rather than arrival times of certain waves only. The first task in this challenge is to systematically study the imprints of density on synthetic seismograms. In this context, our study aims to compare the significance of density heterogeneities relative to velocity heterogeneities, and to design a numerical experiment with a source-receiver configuration particularly sensitive to density. To compute the full seismic wavefield in a 3D heterogeneous medium without making significant approximations, we use numerical wave propagation based on a spectral-element discretization of the seismic wave equation. We consider a 2000 by 1000 km wide and 500 km deep spherical section, with the 1D Earth model ak135 as a background. Onto this we superimpose 3D Gaussian-shaped perturbations of different type (P, SV, SH velocities and density) for depths in the range from 10 km to 70 km. The choice of depth in which the 3D heterogeneities were placed (10 km - 70 km) was dictated by the surface wave sensitivity to density. For each depth we perform 4 wave propagation simulations corresponding to 4 different types of heterogeneities, and calculate surface wave sensitivity
Lamb wave propagation in vibrating structures for effective health monitoring
NASA Astrophysics Data System (ADS)
Lu, Xubin; Soh, Chee Kiong; Avvari, Panduranga Vittal
2015-03-01
Lamb wave based Structural Health Monitoring (SHM) has received much attention during the past decades for its broad coverage and high sensitivity to damage. Lamb waves can be used to locate and quantify damage in static structures successfully. Nonetheless, structures are usually subjected to various external vibrations or oscillations. Not many studies are reported in the literature concerning the damage detecting ability of Lamb wave in oscillating structures which turns out to be a pivotal issue in the practical application of the SHM technique. For this reason in this study, the propagating capability of Lamb waves in a vibrating thin aluminum plate is examined experimentally. Two circular shaped piezoelectric wafer active transducers are surface-bonded on the aluminum plate where one acted as an actuator and another as a sensor. An arbitrary waveform generator is connected to the actuator for the generation of a windowed tone burst on the aluminum plate. An oscilloscope is connected to the sensor for receiving the traveled waves. An external shaker is used to generate out-of-plane external vibration on the plate structure. Time of flight (TOF) is a crucial parameter in most Lamb wave based SHM studies, which measures wave traveling time from the actuator to sensor. In the present study the influence of the external vibrations on the TOF is investigated. Experiments are performed under different boundary conditions of the plate, such as free-free and fixed by gluing. The effects of external vibrations in the frequency range between 10 Hz to 1000 Hz are analyzed. Comparisons are carried out between the resulting Lamb wave signals from the vibrating plate for different boundary conditions. Experimental results show that the external vibrations in relatively low frequency range do not change the TOF during the application of Lamb wave based SHM.
Wave propagation in damage assessment of ground anchors
NASA Astrophysics Data System (ADS)
Zima, B.; Rucka, M.
2015-07-01
The inspection possibilities of ground anchors are limited to destructive test such as pull-out test. Guided wave propagation gives an opportunity to develop an inspection system dedicated to determine the condition of inspected element without violation of their integrity. In this paper the experimental study on wave propagation in laboratory models of ground anchors are presented. Experiments were conducted for different bonding lengths and different frequencies of excitation. Waves were generated by a piezoelectric actuator and the laser vibrometry technique was used to register velocity signals. For all tested anchors it was possible to identify the boundary between steel and concrete based on the registered reflections in wave propagation signals.
Deep vertical propagation of mountain waves above Scandinavia
NASA Astrophysics Data System (ADS)
Dörnbrack, Andreas; Gisinger, Sonja; Rapp, Markus; Witschas, Benjamin; Ehard, Benedikt; Wagner, Johannes; Achtert, Peggy; Stober, Gunter; Kivi, Rigel; Gumbel, Jörg
2015-04-01
propagating gravity waves from the Earth's surface to the mesosphere.
Wave-propagation formulation of seismic response of multistory buildings
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.
Superluminal propagation of solitary kinklike waves in amplifying media.
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
Wave propagation in polar elastic superlattices
NASA Astrophysics Data System (ADS)
Green, W. A.; Green, E. Rhian
1994-08-01
This paper examines the passband and stop band regions for time-periodic waves travelling normal to the layering through an infinite medium composed of alternating layers of two different elastic materials. The materials are such that the elastic energy density is a function of the strains and the strain gradients and, in consequence, a deformation gives rise to both the usual Cauchy stress and to a hyperstress or couple-stress. Such materials can exhibit a non-uniform wrinkling deformation at a free surface and similar non-uniform deformations can arise at interfaces between two different media. The presence of the strain derivatives in the elastic energy function introduces a natural length scale l into the material and the depth of the non-uniform deformation is of the order of this length scale. This model can give rise to enhanced elastic response when the layer depths are comparable with l and it is of interest as a possible mathematical model of nanolayered structures. The model also includes a non-standard set of continuity conditions at material interfaces. These arise from the elastic interaction energy of the two materials at the boundary and their effect is localized in a boundary layer whose depth is of order l. The periodic layering gives rise to displacements which are periodic with a frequency-dependent wave number, the Floquet wave number. Dispersion curves, relating circular frequency to the Floquet wave number, are obtained for different ratios of the layer depth to the natural length l and for different values of the elastic interface coupling parameters.
Electronically nonadiabatic wave packet propagation using frozen Gaussian scattering
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.
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.
Electronically nonadiabatic wave packet propagation using frozen Gaussian scattering.
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. PMID:26395683
Propagation of Long-Wavelength Nonlinear Slow Sausage Waves in Stratified Magnetic Flux Tubes
NASA Astrophysics Data System (ADS)
Barbulescu, M.; Erdélyi, R.
2016-05-01
The propagation of nonlinear, long-wavelength, slow sausage waves in an expanding magnetic flux tube, embedded in a non-magnetic stratified environment, is discussed. The governing equation for surface waves, which is akin to the Leibovich-Roberts equation, is derived using the method of multiple scales. The solitary wave solution of the equation is obtained numerically. The results obtained are illustrative of a solitary wave whose properties are highly dependent on the degree of stratification.
Seismic wave propagation effects in the upper volcanic edifice
NASA Astrophysics Data System (ADS)
Martínez Montesinos, Beatriz; Bean, Chris; Lokmer, Ivan
2015-04-01
A seismogram contains information about the seismic source and the wave path. Understanding the path effect is important for both source inversions and geophysical imagery. In the case of volcanoes, the correct interpretation of the signals helps us to determine their internal state. For instance, long-period events are commonly associated to magma movements in resonant conduits. We present an application of the adjoint methodology proposed in Tromp et al. [2004] to study the seismic wave propagation effects in the upper volcanic edifice. We do this by calculating sensitivity kernels, that is, investigating the sensitivity of different parts of a seismogram to different parts of the velocity model. In particular, we examine the influence of near-surface low-velocity volcanic structure to the recorded signals. We use the SPECFEM 2D software, a two-dimensional elastic wave propagation code based on the spectral-element method, to simulate examples for Mount Etna, Italy. We calculate synthetic seismograms in 2D heterogeneous models with topography, for the sources with different dominant frequency and locations. Then, we calculate the adjoint wavefield by time-reversing the calculated seismograms and "playing" them back into the medium as simultaneous seismic sources at the original receiver positions. In the last step, by combining the forward and adjoint wavefields, we calculate the traveltime sensitivity kernels of Mount Etna. In order to be able to capture a complex wave travel path, we examine the sensitivity of different parts of a seismic wavefield, that is, different time-window on a seimogram to different parts of the structural models. Preliminary results show the importance of the velocity structure at the near surface on the recorded traces. This means that we cannot ignore the heterogeneity of the upper volcanic edifice at the time of the interpretation of the recorded signals.
Modeling of the Lunar Global Seismic Wave Propagation
NASA Astrophysics Data System (ADS)
Toyokuni, G.; Takenaka, H.; Ishihara, Y.; Zhao, D.
2012-12-01
We calculate global seismic wave propagation on cross sections of the realistic whole Lunar structure models. The U.S. Apollo missions installed five seismometers on the lunar surface. Seismograms obtained during 1969 to 1977 have widely been used for investigation of the lunar interior. For example, many researchers have been working on construction of the 1-D structure models (e.g., Nakamura, 1983, textit{JGR}; Garcia et al., 2011, textit{PEPI}). Zhao et al. (2008, textit{Chinese Sci. Bull.}) further estimated the 3-D velocity structure of the Moon by applying seismic tomography to the moonquake traveltime data. Now the Japanese next lunar mission ``SELENE-II'' is planning installation of broad-band seismometers, which are expected to greatly increase resolution of the lunar interior images. Looking back on investigation history of the Earth's interior, our knowledge has been enhanced by mutual progress of observation and numerical methods. Increased enthusiasm for the Moon exploration in recent years strongly requires developing a method for numerical modeling of global seismic wave propagation based on our current knowledge of the lunar interior. We have been constructing numerical schemes using the finite-difference method (FDM) for accurate and efficient modeling of global seismic wave propagation through realistic Earth models with lateral heterogeneity (e.g., Toyokuni et al., 2005, textit{GRL}; Toyokuni & Takenaka, 2006, textit{EPS}). Our scheme calculates the 3-D equations of seismic waves in spherical coordinates only on a 2-D cross section of the whole Earth including a seismic source and receivers (``spherical 2.5-D FDM''), which enables global waveform modeling with a similar computation time and memory as for 2-D modeling with consideration of full 3-D geometrical spreading. This time we apply it to model global seismic wave propagation in the whole Moon. In the presentation, we will show numerical examples using 1-D models by Nakamura (1983, textit
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
Ion stochastic heating by obliquely propagating magnetosonic waves
Gao Xinliang; Lu Quanming; Wu Mingyu; Wang Shui
2012-06-15
The ion motions in obliquely propagating Alfven waves with sufficiently large amplitudes have already been studied by Chen et al.[Phys. Plasmas 8, 4713 (2001)], and it was found that the ion motions are stochastic when the wave frequency is at a fraction of the ion gyro-frequency. In this paper, with test particle simulations, we investigate the ion motions in obliquely propagating magnetosonic waves and find that the ion motions also become stochastic when the amplitude of the magnetosonic waves is sufficiently large due to the resonance at sub-cyclotron frequencies. Similar to the Alfven wave, the increase of the propagating angle, wave frequency, and the number of the wave modes can lower the stochastic threshold of the ion motions. However, because the magnetosonic waves become more and more compressive with the increase of the propagating angle, the decrease of the stochastic threshold with the increase of the propagating angle is more obvious in the magnetosonic waves than that in the Alfven waves.
Millimeter wave propagation measurements from an orbiting earth satellite.
NASA Technical Reports Server (NTRS)
Ippolito, L. J.
1973-01-01
Major results of the millimeter wave propagation measurements conducted with the ATS-5 satellite are reviewed. The impact of these results on millimeter wave communications systems design is outlined. Advanced millimeter wave flight experiments currently under development for the ATS-F satellite are also discussed, and their main characteristics are summarized.
Peculiarities of the Propagation of Supersonic Seismic Waves to the Upper Atmosphere.
NASA Astrophysics Data System (ADS)
Gavrilov, Nikolai M.; Kshevetskii, Sergey P.
2016-04-01
Seismic waves generated before and after earthquakes produce vertical and horizontal motion of the Earth's surface. The perturbations can propagate upwards and produce variations and oscillations of atmospheric characteristics at different altitudes. One of the mechanisms of such ionospheric perturbations is propagation of acoustic-gravity waves (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 waves, much exceeding the sound speed in the atmosphere near the ground. The strongest ground seismic waves are the surface Rayleigh waves, 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 propagating, but trapped (or evanescent) gravity wave modes with amplitudes exponentially decaying with altitude. This can raise questions about the importance of seismic-excited supersonic waves in the formation of ionospheric disturbances. In the present study, we use the recently developed nonlinear numerical Whole-altitude Acoustic-Gravity Wave Model (WAGWM) to simulate propagation of supersonic wave 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 wave parameters. In the present research, we made calculations in rectangle region of the atmosphere and assume horizontal periodicity of wave solutions. Variations of vertical velocity produced by propagating seismic waves at the Earth's surface serve to force the waves in the model. Calculations
Application of a finite difference technique to thermal wave propagation
NASA Technical Reports Server (NTRS)
Baumeister, K. J.
1975-01-01
A finite difference formulation is presented for thermal wave propagation resulting from periodic heat sources. The numerical technique can handle complex problems that might result from variable thermal diffusivity, such as heat flow in the earth with ice and snow layers. In the numerical analysis, the continuous temperature field is represented by a series of grid points at which the temperature is separated into real and imaginary terms. Next, computer routines previously developed for acoustic wave propagation are utilized in the solution for the temperatures. The calculation procedure is illustrated for the case of thermal wave propagation in a uniform property semi-infinite medium.
Application of a finite difference technique to thermal wave propagation
NASA Technical Reports Server (NTRS)
Baumeister, K. J.
1975-01-01
A finite difference formulation is presented for thermal wave propagation resulting from periodic heat sources. The numerical technique can handle complex problems that might result from variable thermal diffusivity, such as heat flow in the earth with ice and snow layers. In the numerical analysis, the continuous temperature field is represented by a series of grid points at which the temperature is separated into real and imaginary terms. Computer routines previously developed for acoustic wave propagation are utilized in the solution for the temperatures. The calculation procedure is illustrated for the case of thermal wave propagation in a uniform property semi-infinite medium.
Surface Acoustic Wave Microfluidics
NASA Astrophysics Data System (ADS)
Yeo, Leslie Y.; Friend, James R.
2014-01-01
Fluid manipulations at the microscale and beyond are powerfully enabled through the use of 10-1,000-MHz acoustic waves. A superior alternative in many cases to other microfluidic actuation techniques, such high-frequency acoustics is almost universally produced by surface acoustic wave devices that employ electromechanical transduction in wafer-scale or thin-film piezoelectric media to generate the kinetic energy needed to transport and manipulate fluids placed in adjacent microfluidic structures. These waves are responsible for a diverse range of complex fluid transport phenomena - from interfacial fluid vibration and drop and confined fluid transport to jetting and atomization - underlying a flourishing research literature spanning fundamental fluid physics to chip-scale engineering applications. We highlight some of this literature to provide the reader with a historical basis, routes for more detailed study, and an impression of the field's future directions.
Do cyanobacteria swim using traveling surface waves?
Ehlers, K M; Samuel, A D; Berg, H C; Montgomery, R
1996-01-01
Bacteria that swim without the benefit of flagella might do so by generating longitudinal or transverse surface waves. For example, swimming speeds of order 25 microns/s are expected for a spherical cell propagating longitudinal waves of 0.2 micron length, 0.02 micron amplitude, and 160 microns/s speed. This problem was solved earlier by mathematicians who were interested in the locomotion of ciliates and who considered the undulations of the envelope swept out by ciliary tips. A new solution is given for spheres propagating sinusoidal waveforms rather than Legendre polynomials. The earlier work is reviewed and possible experimental tests are suggested. Images Fig. 1 PMID:8710872
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.
Study on tsunami generation and propagation in a large scale wave flume
NASA Astrophysics Data System (ADS)
Schimmels, Stefan; Venkatachalam, Sriram; Didenkulova, Ira
2015-04-01
In this paper we study very long, i.e. real tsunami-like wave generation in a large scale wave flume using a piston type wave maker. Waves of periods between 30 s and more than 100 s were generated at 1 m water depth using two different approaches: (i) deriving the wave board motion directly by integration of the water surface elevation, composed of a different number of solitons (sech2 waves) and (ii) using an iterative self correcting method (SCM). The importance of very long wave generation instead of solitary waves and the necessity for long testing facilities is discussed and results from GWK experiments are presented for single pulses (elongated solitons), N-waves and real tsunami records, either approximated as a combination of solitons or applying the SCM to the time series directly. The possibility to study propagation, shoaling and run-up of these waves over a slope in a 300-meter long large wave flume (GWK), Hannover is dicsussed. Experimental data of long wave propagation in the flume are compared with numerical simulations performed within the fully nonlinear potential flow theory and KdV equations. Shoaling and run-up of waves on different mild slopes is studied hypothetically using nonlinear shallow water theory. The paper ends with the conclusions about the feasibility of using large scale experimental facility (GWK) to study tsunami wave propagation and run-up.
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.
Apparent Cross-field Superslow Propagation of Magnetohydrodynamic Waves in Solar Plasmas
NASA Astrophysics Data System (ADS)
Kaneko, T.; Goossens, M.; Soler, R.; Terradas, J.; Van Doorsselaere, T.; Yokoyama, T.; Wright, A. N.
2015-10-01
In this paper we show that the phase-mixing of continuum Alfvén waves and/or continuum slow waves in the magnetic structures of the solar atmosphere as, e.g., coronal arcades, can create the illusion of wave propagation across the magnetic field. This phenomenon could be erroneously interpreted as fast magnetosonic waves. The cross-field propagation due to the phase-mixing of continuum waves is apparent because there is no real propagation 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 propagation across the magnetic surfaces in solar coronal structures is a consequence of the existence of continuum Alfvén waves and continuum slow waves 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 propagation is important for the correct analysis of numerical simulations and the correct interpretation of observations.
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.
Ultrafast Imaging of Surface Plasmons Propagating on a Gold Surface
Gong, Yu; Joly, Alan G.; Hu, Dehong; El-Khoury, Patrick Z.; Hess, Wayne P.
2015-05-13
We record time-resolved nonlinear photoemission electron microscopy (tr-PEEM) images of propagating surface plasmons (PSPs) launched from a lithographically patterned rectangular trench on a flat gold surface. Our tr-PEEM scheme involves a pair of identical, spatially separated, and interferometrically-locked femtosecond laser pulses. Power dependent PEEM images provide experimental evidence for a sequential coherent nonlinear photoemission process, in which one laser source creates a PSP polarization state through a linear interaction, and the second subsequently probes the prepared state via two photon photoemission. The recorded time-resolved movies of a PSP allow us to directly measure various properties of the surface-bound wave packet, including its carrier wavelength (785 nm) and group velocity (0.95c). In addition, tr-PEEM in concert with finite-difference time domain simulations together allow us to set a lower limit of 75 μm for the decay length of the PSP on a 100 nm thick gold film.
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.
Spectral solution of acoustic wave-propagation problems
NASA Technical Reports Server (NTRS)
Kopriva, David A.
1990-01-01
The Chebyshev spectral collocation solution of acoustic wave propagation problems is considered. It is shown that the phase errors decay exponentially fast and that the number of points per wavelength is not sufficient to estimate the phase accuracy. Applications include linear propagation of a sinusoidal acoustic wavetrain in two space dimensions, and the interaction of a sound wave with the bow shock formed by placing a cylinder in a uniform Mach 4 supersonic free stream.
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…
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
Wave propagation in sandwich panels with a poroelastic core.
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. PMID:24815252
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.
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.
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)
Self-similar propagation of Hermite-Gauss water-wave pulses.
Fu, Shenhe; Tsur, Yuval; Zhou, Jianying; Shemer, Lev; Arie, Ady
2016-01-01
We demonstrate both theoretically and experimentally propagation dynamics of surface gravity water-wave pulses, having Hermite-Gauss envelopes. We show that these waves propagate self-similarly along an 18-m wave tank, preserving their general Hermite-Gauss envelopes in both the linear and the nonlinear regimes. The measured surface elevation wave groups enable observing the envelope phase evolution of both nonchirped and linearly frequency chirped Hermite-Gauss pulses, hence allowing us to measure Gouy phase shifts of high-order Hermite-Gauss pulses for the first time. Finally, when increasing pulse amplitude, nonlinearity becomes essential and the second harmonic of Hermite-Gauss waves was observed. We further show that these generated second harmonic bound waves still exhibit self-similar Hermite-Gauss shapes along the tank. PMID:26871174
Isomorphic surface acoustic waves on multilayer structures
NASA Astrophysics Data System (ADS)
Hunt, William D.
2001-03-01
There has been growing interest in recent years over the investigation of bulk acoustic waves (BAWs) which propagate along certain directions in anisotropic crystals with a minimum of diffraction. One application of these BAWs is for multichannel acousto-optic devices. The fact that the beams propagate with the minimum diffraction implies that the channels in such a device can be closely packed. Since surface acoustic waves (SAWs) are constrained to be within roughly one acoustic wavelength from the surface, the possibility exists to deposit thin films of isotropic or anisotropic material on the substrate and embue the aggregate multilayer structure with properties not present in the beginning substrate material. The characteristic investigated in this article is the velocity anisotropy which, as is known, predominates SAW diffraction. Specifically, we present a method whereby self-collimating SAWs can be generated on surfaces even though the substrate material itself does not exhibit this behavior. We discuss the particular case of a ZnO layer on (001)-cut <110>-propagating GaAs for which a fair amount of slowness surface data exists. Finally, using angular spectrum of plane waves diffraction theory, we present data which substantiate the claim that self-collimating can more accurately be viewed as isomorphic because the SAW beam profile can propagate without changing its shape.
Viscoelastic representation of surface waves in patchy saturated poroelastic media
NASA Astrophysics Data System (ADS)
Zhang, Yu; Xu, Yixian; Xia, Jianghai; Ping, Ping; Zhang, Shuangxi
2014-08-01
Wave-induced flow is observed as the dominated factor for P wave propagation at seismic frequencies. This mechanism has a mesoscopic scale nature. The inhomogeneous unsaturated patches are regarded larger than the pore size, but smaller than the wavelength. Surface wave, e.g., Rayleigh wave, which propagates along the free surface, generated by the interfering of body waves is also affected by the mesoscopic loss mechanisms. Recent studies have reported that the effect of the wave-induced flow in wave propagation shows a relaxation behavior. Viscoelastic equivalent relaxation function associated with the wave mode can describe the kinetic nature of the attenuation. In this paper, the equivalent viscoelastic relaxation functions are extended to take into account the free surface for the Rayleigh surface wave propagation in patchy saturated poroelastic media. Numerical results for the frequency-dependent velocity and attenuation and the time-dependent dynamical responses for the equivalent Rayleigh surface wave propagation along an interface between vacuum and patchy saturated porous media are reported in the low-frequency range (0.1-1,000 Hz). The results show that the dispersion and attenuation and kinetic characteristics of the mesoscopic loss effect for the surface wave can be effectively represented in the equivalent viscoelastic media. The simulation of surface wave propagation within mesoscopic patches requires solving Biot's differential equations in very small grid spaces, involving the conversion of the fast P wave energy diffusion into the Biot slow wave. This procedure requires a very large amount of computer consumption. An efficient equivalent approach for this patchy saturated poroelastic media shows a more convenient way to solve the single phase viscoelastic differential equations.
Millimetre-wave propagation in the evaporation duct
NASA Astrophysics Data System (ADS)
Levy, M. F.; Craig, K. H.
1990-03-01
Recent developments in propagation modeling based on the Parabolic Equation Method allow the forecasting of two-dimensional antenna coverage diagrams at millimeter wavelengths, in a dispersive atmosphere with arbitrary two-dimensional variation of the refractive index. The model was applied successfully to mm-wave propagation in the evaporation duct. The evaporation duct height is not sufficient to characterize mm-wave propagation, and information on the water vapor content is essential for the correct modeling of atmospheric absorption. Turbulence simulations were carried out, showing marked scintillation, effects in the evaporation duct. The method can be applied to arbitrary refractivity spectra, and gives a complete numerical description of the field statistics.
The propagation of spark-produced N waves through turbulence
NASA Technical Reports Server (NTRS)
Lipkens, Bart
1994-01-01
A model experiment was designed and built to simulate the propagation of sonic booms through atmospheric turbulence. The setup of the model experiment is described briefly. Measurements of the N waves after they propagated across the turbulent velocity field reveal the same waveform distortion and change in rise time as for sonic booms. The data from the model experiment is used to test sonic boom models. Some models yield predictions for the waveform distortion, while others give estimates of the rise time of the sonic booms. A new theoretical model for the propagation of plane N waves through a turbulent medium is described.
Surface electromagnetic wave equations in a warm magnetized quantum plasma
Li, Chunhua; Yang, Weihong; Wu, Zhengwei; Chu, Paul K.
2014-07-15
Based on the single-fluid plasma model, a theoretical investigation of surface electromagnetic waves in a warm quantum magnetized inhomogeneous plasma is presented. The surface electromagnetic waves are assumed to propagate on the plane between a vacuum and a warm quantum magnetized plasma. The quantum magnetohydrodynamic model includes quantum diffraction effect (Bohm potential), and quantum statistical pressure is used to derive the new dispersion relation of surface electromagnetic waves. And the general dispersion relation is analyzed in some special cases of interest. It is shown that surface plasma oscillations can be propagated due to quantum effects, and the propagation velocity is enhanced. Furthermore, the external magnetic field has a significant effect on surface wave's dispersion equation. Our work should be of a useful tool for investigating the physical characteristic of surface waves and physical properties of the bounded quantum plasmas.
NASA Astrophysics Data System (ADS)
Wang, Yanbin; Takenaka, Hiroshi; Jiang, Xianghua; Lei, Jianshe
2013-03-01
The whole-Moon model was recently proposed by re-analyzing of lunar seismic data, which presumes efficient propagation of seismic waves within the Moon. However, common seismic body-wave or surface-wave phases observed for earthquake are absent or very weak in lunar seismic signals characterized by strong reverberations and coda. Hence, the process of seismic wave propagation in the Moon's interior is not well understood from limited lunar seismic data. We present numerical simulations of seismic body wave propagation in the whole Moon based on recently published whole-Moon model. Seismic wave equations are solved in a 2-D cross-section of spherical Moon with a staggered grid pseudospectral and finite difference hybrid method. Our simulation results provide the processes of seismic body wave propagation in the whole Moon for both deep and shallow moonquakes with sequential wavefield snapshots and synthetic waveforms. Effects of lateral heterogeneity on seismic wave propagation were investigated by simulations for a Moon tomographic model. Comparisons with the observed Apollo seismograms show that simulations predicted the arrivals of direct P and S waves and reproduced the reverberating nature of both direct and secondary waves. However, modelling with only the 1-D or tomographic model does not seem to be enough to produce the slow decay of energy in observations if other possible factors, such as scattering, are not considered in the model. Comparisons between different focal mechanisms suggest that great differences can be seen for the direct waves, but the structure model contributes significantly to the overall characteristics of synthetic seismograms. Numerical simulations demonstrated efficient propagation and interactions with various interfaces of seismic body waves within the whole Moon. Seismic energy propagating in the near surface low-velocity layer formed trapped waves, which propagate along the surface and appear as reverberations in the waveforms
Low Frequency Guided Plate Waves Propagation in Fiber Reinforced Composites
NASA Technical Reports Server (NTRS)
Lih, S-S.; Bar-Cohen, Y.
1995-01-01
Conventional destructive techniques for the determination of the elastic stiffness constants of composite materials can be costly and often inaccurate. Reliable nondestructive evaluation methods for monitoring the integrity of composite materials and structures are needed. Guided wave propagation in isotropic plate have been studied. Studies on the low frequency symmetric guide waves are presented.
WAVE PROPAGATION AND JET FORMATION IN THE CHROMOSPHERE
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.
Impact induced solitary wave propagation through a woodpile structure
NASA Astrophysics Data System (ADS)
Kore, R.; Waychal, A.; Agarwal, S.; Yadav, P.; Uddin, Ahsan; Sahoo, N.; Shelke, A.
2016-02-01
In this paper, we investigate solitary wave propagation through a one-dimensional woodpile structure excited by low and high velocity impact. Woodpile structures are a sub-class of granular metamaterial, which supports propagation of nonlinear waves. Hertz contact law governs the behavior of the solitary wave propagation through the granular media. Towards an experimental study, a woodpile structure was fabricated by orthogonally stacking cylindrical rods. A shock tube facility has been developed to launch an impactor on the woodpile structure at a velocity of 30 m s-1. Embedded granular chain sensors were fabricated to study the behavior of the solitary wave. The impact induced stress wave is studied to investigate solitary wave parameters, i.e. contact force, contact time, and solitary wave velocity. With the aid of the experimental setup, numerical simulations, and a theoretical solution based on the long wavelength approximation, formation of the solitary wave in the woodpile structure is validated to a reasonable degree of accuracy. The nondispersive and compact supported solitary waves traveling at sonic wave velocity offer unique properties that could be leveraged for application in nondestructive testing and structural health monitoring.
Relationship between directions of wave and energy propagation for cold plasma waves
NASA Technical Reports Server (NTRS)
Musielak, Zdzislaw E.
1986-01-01
The dispersion relation for plasma waves is considered in the 'cold' plasma approximation. General formulas for the dependence of the phase and group velocities on the direction of wave propagation with respect to the local magnetic field are obtained for a cold magnetized plasma. The principal cold plasma resonances and cut-off frequencies are defined for an arbitrary angle and are used to establish basic regimes of frequency where the cold plasma waves can propagate or can be evanescent. The relationship between direction of wave and energy propagation, for cold plasma waves in hydrogen atmosphere, is presented in the form of angle diagrams (angle between group velocity and magnetic field versus angle between phase velocity and magnetic field) and polar diagrams (also referred to as 'Friedrich's diagrams') for different directions of wave propagation. Morphological features of the diagrams as well as some critical angles of propagation are discussed.
Analysis of spurious bulk waves in ball surface wave device.
Ishikawa, Satoru; Cho, Hideo; Tsukahara, Yusuke; Nakaso, Noritaka; Yamanaka, Kazushi
2003-01-01
We analyzed the acoustic waves propagating in a sphere to establish a useful guideline for the design of NDE apparatus and ball surface acoustic wave (SAW) device exploiting the diffraction-free propagation of SAW on a sphere. First, we calculated the laser-generated acoustic displacements both under ablation condition and under thermoelastic condition and verified experimentally the validity of the calculation. Next, the acoustic waves excited by out-of-plane stress and those excited by in-plane stress were compared. The results showed that when the out-of-plane stress was applied, the relative amplitudes of the bulk waves to that of the SAW were larger and the number of bulk waves was larger than that when the in-plane stress was applied, while the SAW had similar waveforms in each case. The ratio of the relative amplitude of the bulk waves for the out-of-plane stress and the in-plane stress was 3.1:1 at phi(1)=90 degrees and 1.67:1 at phi(1)=0 degrees. The large amplitude for the out-of-plane stress can be explained by wide directivities of bulk waves. Consequently, we found that it is necessary for ball SAW device to select a piezoelectric material and form of interdigital transducer so that the in-plane stress becomes dominant. PMID:12464407
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.
Simulation of the elastic wave propagation in anisotropic microstructures
NASA Astrophysics Data System (ADS)
Bryner, Juerg; Vollmann, Jacqueline; Profunser, Dieter M.; Dual, Jurg
2007-06-01
For the interpretation of optical Pump-Probe Measurements on microstructures the wave propagation in anisotropic 3-D structures with arbitrary geometries is numerically calculated. The laser acoustic Pump-Probe technique generates bulk waves in structures in a thermo-elastic way. This method is well established for non-destructive measurements of thin films with an indepth resolution in the order of 10 nm. The Pump-Probe technique can also be used for measurements, e.g. for quality inspection of three-dimensional structures with arbitrary geometries, like MEMS components. For the interpretation of the measurements it is necessary that the wave propagation in the specimen to be inspected can be calculated. Here, the wave propagation for various geometries and materials is investigated. In the first part, the wave propagation in isotropic axisymmetric structures is simulated with a 2-D finite difference formulation. The numerical results are verified with measurements of macroscopic specimens. In a second step, the simulations are extended to 3-D structures with orthotopic material properties. The implemented code allows the calculation of the wave propagation for different orientations of the material axes (orientation of the orthotropic axes relative to the geometry of the structure). Limits of the presented algorithm are discussed and future directions of the on-going research project are presented.
Wave propagation in bianisotropic metamaterials: angular selective transmission.
Chang, Po-Han; Kuo, Chih-Yu; Chern, Ruey-Lin
2014-10-20
We investigate the basic features of wave propagation in bianisotropic metamaterials characterized by asymmetric magnetoelectric tensors with zero diagonal elements. The wave propagation is described by a biquadratic dispersion relation with two elliptically polarized eigenwaves. In particular, the bianisotropic media may possess a hybrid character of the elliptic and hyperbolic dispersions. For a wave incident from vacuum onto a bianisotropic medium, there exist an ordinary and an inversion critical angle, leading to angular selective transmission. A standard and a complementary type of angular selective transmissions are illustrated with the incidence of Gaussian beams based on Fourier integral formulation. PMID:25401604
Global propagation of body waves revealed by cross-correlation analysis of seismic hum
NASA Astrophysics Data System (ADS)
Nishida, K.
2013-05-01
Seismic interferometry has now been applied to the exploration of the Earth's interior at scales ranging from local to global. Most studies have used surface-wave propagation. Recently, some studies have focused on body wave propagation on local and regional scales but not on a global scale. In this study, we succeed in extracting global body wave propagation(of P, PP, PKP, S, SS, ScS, P'P', etc. waves) using seismic hum with frequency-wave number filtering in the range of 5 to 40 mHz. Although the observed body wave propagation is similar to that of the corresponding components of Green's functions, there are two differences between them: the lack of reflection phases in the observation and the dominance of shear-coupled PL waves in the observation. These differences originate from the dominance of shear-traction sources on the Earth's surface, which causes the breakdown of equipartition among modes with different radial orders. For further studies of body wave exploration by seismic interferometry, these differences should be considered.
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"
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.
Propagation of electromagnetic wave in dusty plasma and the influence of dust size distribution
NASA Astrophysics Data System (ADS)
Li, Hui; Wu, Jian; Zhou, Zhongxiang; Yuan, Chengxun
2016-07-01
The effect of charged dust particle and their size distribution on the propagation of electromagnetic wave in a dusty plasma is investigated. It is shown that the additional collision mechanism provided by charged dust particles can significantly alter the electromagnetic properties of a plasma, leading to the appearance of attenuation of electromagnetic wave through dusty plasma. The attenuation coefficient mainly depends on the dust density, radius, and the charge numbers on the dust surface. The results described here will be used to enhance understanding of electromagnetic wave propagation processed in space and laboratory dusty plasma.
Synaptically Generated Wave Propagation in Excitable Neural Media
NASA Astrophysics Data System (ADS)
Bressloff, P. C.
1999-04-01
We study the propagation of solitary waves in a one-dimensional network of excitable integrate-and-fire neurons with axo-dendritic synaptic coupling. We show that for small axonal delays there exists a stable solitary wave, and derive a power scaling law for the velocity as a function of the coupling. In the case of large axonal delays and fast synapses we establish that the solitary wave can destabilize via a Hopf bifurcation in the firing times.
Depth propagation and surface construction in 3-D vision.
Georgeson, Mark A; Yates, Tim A; Schofield, Andrew J
2009-01-01
In stereo vision, regions with ambiguous or unspecified disparity can acquire perceived depth from unambiguous regions. This has been called stereo capture, depth interpolation or surface completion. We studied some striking induced depth effects suggesting that depth interpolation and surface completion are distinct stages of visual processing. An inducing texture (2-D Gaussian noise) had sinusoidal modulation of disparity, creating a smooth horizontal corrugation. The central region of this surface was replaced by various test patterns whose perceived corrugation was measured. When the test image was horizontal 1-D noise, shown to one eye or to both eyes without disparity, it appeared corrugated in much the same way as the disparity-modulated (DM) flanking regions. But when the test image was 2-D noise, or vertical 1-D noise, little or no depth was induced. This suggests that horizontal orientation was a key factor. For a horizontal sine-wave luminance grating, strong depth was induced, but for a square-wave grating, depth was induced only when its edges were aligned with the peaks and troughs of the DM flanking surface. These and related results suggest that disparity (or local depth) propagates along horizontal 1-D features, and then a 3-D surface is constructed from the depth samples acquired. The shape of the constructed surface can be different from the inducer, and so surface construction appears to operate on the results of a more local depth propagation process. PMID:18977239
Wave propagation on a random lattice
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.
Mantle compression affects seismic wave propagation
NASA Astrophysics Data System (ADS)
Schultz, Colin
2014-02-01
To try to understand the direction of motion of the Earth's mantle, which lies hidden beneath tens of kilometers of crust, researchers have relied on the property of seismic anisotropy. When seismic shear waves pass through some types of materials, known as anisotropic materials, the speed of the wave can vary depending on the direction in which it is moving. Traditionally, scientists have assumed that the direction in which waves move more quickly aligns with the direction of mantle motion. For subduction zones, however, this general rule seemed to break down—a discrepancy exists between numerical model simulations and observed seismic data.
NASA Technical Reports Server (NTRS)
Anderson, D. L.
1984-01-01
Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown.
Local Wave Propagation in the Kachchh Basin, India: Synergy With the New Madrid Seismic Zone
NASA Astrophysics Data System (ADS)
Langston, C. A.; Kang, D.; Bodin, P.; Horton, S.
2002-12-01
Aftershocks of the Mw7.6 Bhuj earthquake are used to infer velocity structure and the nature of wave propagation within the Kachchh Basin, India. The data were collected from a joint MAEC/ISTAR deployment of seismographs within 3 weeks of the main event and from existing broadband stations in the region under the India Meteorological Department. Waveforms are available from events that span the entire thickness of the crust and display a variety of wave propagation effects due to low-velocity near-surface site structure and larger structure of the Mesozoic Kachchh basin. These effects include near-site, high frequency reverberations in P and S waves, Sp and Ps mode conversions, PL waves within the Mesozoic basin, basin S multiples, and surface waves. Surface wave group velocity dispersion yields estimates of basin shear wave velocity, and when coupled to analysis of large observed Sp conversions, give a migrated image of stratigraphy within the Banni plains that agrees favorably with published stratigraphy. Identification of basin structure effects allows constraints to be placed on aftershock source depths that are needed in evaluating standard earthquake locations. Structure models are used to construct Green's functions for determining source parameters through waveform modeling. Although stations of the aftershock network were situated on a variety of sites that varied from consolidated Mesozoic bedrock to unconsolidated recent sediments, all stations show major wave propagation effects due to basin fill that must be included in source parameter estimation. These effects seen in India have many similarities to wave propagation effects observed within the Mississippi embayment from microearthquakes in the New Madrid Seismic Zone (NMSZ) of the central U.S. Joint waveform studies are motivating new ways of understanding wave propagation and source processes within both areas.
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.
Nonlinear electron magnetohydrodynamics physics. II. Wave propagation and wave-wave interactions
Urrutia, J. M.; Stenzel, R. L.; Strohmaier, K. D.
2008-04-15
The propagation of low-frequency whistler modes with wave magnetic field exceeding the ambient field is investigated experimentally. Such nonlinear waves are excited with magnetic loop antennas whose axial field is aligned with the background magnetic field and greatly exceeds its strength. The oscillatory antenna field excites propagating wave packets with field topologies alternating between whistler spheromaks and mirrors. The propagation speed of spheromaks is observed to decrease with amplitude while that of mirrors increases with amplitude. The field distribution varies with amplitude: Spheromaks contract axially while mirrors spread out compared to linear whistlers. Consequently, the peak magnetic field and current densities in spheromaks exceed that of mirrors. Wave-wave interactions of nonlinear whistler modes is also studied. Counterpropagating spheromaks collide inelastically and form a stationary field-reversed configuration. The radius of the toroidal current ring depends on current and can be larger than that of the loop antenna. A tilted field-reversed configuration precesses in the direction of the electron drift. The free magnetic energy is dissipated in the plasma volume and converted into electron heat.
NASA Astrophysics Data System (ADS)
Brissaud, Q.; Garcia, R.; Martin, R.; Komatitsch, D.
2014-12-01
Low-frequency events such as tsunamis generate acoustic and gravity waves which quickly propagate in the atmosphere. Since the atmospheric density decreases exponentially as the altitude increases and from the conservation of the kinetic energy, those waves see their amplitude raise (to the order of 105 at 200km of altitude), allowing their detection in the upper atmosphere. Various tools have been developed through years to model this propagation, such as normal modes modeling or to a greater extent time-reversal techniques, but none offer a low-frequency multi-dimensional atmospheric wave modelling.A modeling tool is worthy interest since there are many different phenomena, from quakes to atmospheric explosions, able to propagate acoustic and gravity waves. In order to provide a fine modeling of the precise observations of these waves by GOCE satellite data, we developed a new numerical modeling tool.Starting from the SPECFEM program that already propagate waves in solid, porous or fluid media using a spectral element method, this work offers a tool with the ability to model acoustic and gravity waves propagation in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source.Atmospheric attenuation is required in a proper modeling framework since it has a crucial impact on acoustic wave propagation. Indeed, it plays the role of a frequency filter that damps high-frequency signals. The bottom forcing feature has been implemented due to its ability to easily model the coupling with the Earth's or ocean's surface (that vibrates when a surface wave go through it) but also huge atmospheric events.
Three-dimensional finite-element modeling of wave propagation in a transversely isotropic medium
Sun, Y.F.; Teng, Y.C.
1994-12-31
In this research, the authors present the numerical results of three-dimensional finite element modeling of elastic wave propagation in a half space of a transversely isotropic medium. The input physical parameters are taken from the physical model used by Chang and Gardner (1992). The synthetic seismograms of the three displacement components along the axis at an azimuth of 45{degree} to the fracture orientation on the surface are shown. Snapshots taken on the free surface are illustrated which are the displacement fields with polarization in the direction perpendicular to the fracture orientation. These snapshots show clearly the elliptical patterns demonstrating the effects of anisotropy on wave propagation. Four waves, namely, the fast and slow S-waves and the fast and slow P-waves, can be clearly observed.
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
3D simulation of seismic wave propagation around a tunnel using the spectral element method
NASA Astrophysics Data System (ADS)
Lambrecht, L.; Friederich, W.
2010-05-01
We model seismic wave propagation in the environment of a tunnel for later application to reconnaissance. Elastic wave propagation can be simulated by different numerical techniques such as finite differences and pseudospectral methods. Their disadvantage is the lack of accuracy on free surfaces, numerical dispersion and inflexibility of the mesh. Here we use the software package SPECFEM3D_SESAME in an svn development version, which is based on the spectral element method (SEM) and can handle complex mesh geometries. A weak form of the elastic wave equation leads to a linear system of equations with a diagonal mass matrix, where the free surface boundary of the tunnel can be treated under realistic conditions and can be effectively implemented in parallel. We have designed a 3D external mesh including a tunnel and realistic features such as layers and holes to simulate elastic wave propagation in the zone around the tunnel. The source is acting at the tunnel surface so that we excite Rayleigh waves which propagate to the front face of the tunnel. A conversion takes place and a high amplitude S-wave is radiated in the direction of the tunnel axis. Reflections from perturbations in front of the tunnel can be measured by receivers implemented on the tunnel face. For a shallow tunnel the land surface has high influence on the wave propagation. By implementing additional receivers at this surface we intent to improve the prediction. It shows that the SEM is very capable to handle the complex geometry of the model and especially incorporates the free surfaces of the model.
NASA Astrophysics Data System (ADS)
Riobóo, Rafael J. Jiménez; Prieto, Carlos; Cuscó, Ramón; Artús, Lluís; Boney, Chris; Bensaoula, Abdelhak; Yamaguchi, Tomohiro; Nanishi, Yasushi
2013-05-01
Temperature-dependent surface acoustic wave (SAW) propagation velocity and temperature coefficient of frequency (TCF) have been determined for the first time in InxGa1-xN alloys by means of high-resolution Brillouin spectroscopy (HRBS). HRBS offers an alternative way of determining TCF. The obtained TCF values present a non-linear behavior with the In concentration. TCF of pure InN (-13.75 ppm/K) is similar to those of AlN and GaN (-19 and -17.7 ppm/K, respectively). InxGa1-xN samples exhibit frequency values that are very stable against temperature changes, which makes InxGa1-xN a good candidate for current SAW-based technological applications.
A superconducting qubit coupled to propagating acoustic waves
NASA Astrophysics Data System (ADS)
Gustafsson, Martin V.; Aref, Thomas; Frisk Kockum, Anton; Ekström, Maria K.; Johansson, Göran; Delsing, Per
2015-03-01
Mechanical devices in the quantum regime have so far consisted mainly of suspended resonators, where standing modes can be populated with quanta of vibrational energy. We present a fundamentally different system, where the mechanical excitation is not restricted to a specific mode and location. Instead, we demonstrate strong non-classical coupling between propagating phonons and a superconducting qubit. The qubit is fabricated on a piezoelectric substrate, and is designed to interact with Surface Acoustic Waves (SAWs) in the gigahertz frequency range. A separate on-chip transducer allows us to launch SAWs toward the qubit from a distance and pick up SAW phonons that the qubit reflects and emits. In a series of experiments where the qubit is addressed both electrically and acoustically, we show that the qubit couples much more strongly to SAWs than to any electrical modes. The low speed of sound sets phonons apart from photons as a medium for transporting quantum information, and should enable real-time manipulation of propagating quanta. The short acoustic wavelength and strong piezoelectric coupling should also allows regimes of interaction to be explored which cannot be reached in photonic systems.
Detection of Electromechanical Wave Propagation Using Synchronized Phasor Measurements
NASA Astrophysics Data System (ADS)
Suryawanshi, Prakash; Dambhare, Sanjay; Pramanik, Ashutosh
2014-01-01
Considering electrical network as a continuum has become popular for electromechanical wave analysis. This paper reviews the concept of electromechanical wave propagation. Analysis of large number of generator ring system will be an easy way to illustrate wave propagation. The property of traveling waves is that the maximum and minimum values do not occur at the same time instants and hence the difference between these time delays can be easily calculated. The homogeneous, isotropic 10 generator ring system is modeled using electromagnetic transient simulation programs. The purpose of this study is to investigate the time delays and wave velocities using Power System Computer Aided Design (PSCAD)/Electromagnetic Transient Program (EMTP). The disturbances considered here are generator disconnections and line trips.
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.
Experiments and Numerical Investigations of Wave Propagation In Thermal Plumes.
NASA Astrophysics Data System (ADS)
Laudenbach, N.; Christensen, U. R.
In laboratory experiments thermal plumes are created by injecting hot corn syrup into a column of cold syrup. The viscosity contrast is up to a factor of 1000. Solitary waves, that propagate upwards in the plume conduit, are generated by enhancing the injection rate for a few seconds. For the measurement of the thermal structure of the plume we have implemented a method based on the deflection of a laser beam passing through the plume. Continuous scanning provides a new radial temperature profile each second, which allows detailed studies of the thermal structure of solitary waves. A PIV - (particle image volecimetry) method provides the velocity structure of the thermal plume. Measurements were taken for plume heads, conduits and propagating waves. Comparison between experimental results and numerical 2-D axisymmetric simulations shows a good agreement of the temperature profiles and velocity fields in the plume conduit and waves. Because of thermal diffusion, the conduit widens with height, while its central temperature decreases. The solitary waves start with the same temperature as the unperturbed conduit, however, we find that the temperature in the waves decreases less rapide with rising height. This can be explained by the faster upward propagation and the trapping of fluid within the soliton. If solitary waves exists in mantle plumes, this would imply that they arrive at the bottom of the lithosphere with a larger excess temperature than what the plumes normally exhibits. Especially for weak hotspots solitary waves could have strong influence on the variation of melt generation with time.
Propagation of electromagnetic waves in a weakly ionized dusty plasma
NASA Astrophysics Data System (ADS)
Jia, Jieshu; Yuan, Chengxun; Gao, Ruilin; Wang, Ying; Liu, Yaoze; Gao, Junying; Zhou, Zhongxiang; Sun, Xiudong; Wu, Jian; Li, Hui; Pu, Shaozhi
2015-11-01
Propagation properties of electromagnetic (EM) waves in weakly ionized dusty plasmas are the subject of this study. Dielectric relation for EM waves propagating at a weakly ionized dusty plasma is derived based on the Boltzmann distribution law while considering the collision and charging effects of dust grains. The propagation properties of EM energy in dusty plasma of rocket exhaust are numerically calculated and studied, utilizing the parameters of rocket exhaust plasma. Results indicate that increase of dust radius and density enhance the reflection and absorption coefficient. High dust radius and density make the wave hardly transmit through the dusty plasmas. Interaction enhancements between wave and dusty plasmas are developed through effective collision frequency improvements. Numerical results coincide with observed results by indicating that GHz band wave communication is effected by dusty plasma as the presence of dust grains significantly affect propagation of EM waves in the dusty plasmas. The results are helpful to analyze the effect of dust in plasmas and also provide a theoretical basis for the experiments.
Geometric effects on stress wave propagation.
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
Spin-wave propagation steered by electric field modulated exchange interaction.
Wang, Sheng; Guan, Xiawei; Cheng, Xiaomin; Lian, Chen; Huang, Ting; Miao, Xiangshui
2016-01-01
Combined ab initio and micromagnetic simulations are carried out to demonstrate the feasibility on the electrical manipulation of spin-wave propagation in ultrathin Fe films. It is discovered that the exchange interaction can be substantially weakened under the influence of electric field applied perpendicular to the magnetic film surface. Furthermore, we demonstrate that the electric field modified exchange constant could effectively control the propagation of spin waves. To be specific, an external applied electric field of 5 V/nm can effectively weaken exchange interaction by 80% and is sufficient to induce nearly twofold change of the wavenumber. This discovery may open a door to energy-efficient local manipulation of the spin wave propagation utilizing electric fields, which is crucial for both fundamental research and spin wave based logic applications. PMID:27587083
Spin-wave propagation steered by electric field modulated exchange interaction
Wang, Sheng; Guan, Xiawei; Cheng, Xiaomin; Lian, Chen; Huang, Ting; Miao, Xiangshui
2016-01-01
Combined ab initio and micromagnetic simulations are carried out to demonstrate the feasibility on the electrical manipulation of spin-wave propagation in ultrathin Fe films. It is discovered that the exchange interaction can be substantially weakened under the influence of electric field applied perpendicular to the magnetic film surface. Furthermore, we demonstrate that the electric field modified exchange constant could effectively control the propagation of spin waves. To be specific, an external applied electric field of 5 V/nm can effectively weaken exchange interaction by 80% and is sufficient to induce nearly twofold change of the wavenumber. This discovery may open a door to energy-efficient local manipulation of the spin wave propagation utilizing electric fields, which is crucial for both fundamental research and spin wave based logic applications. PMID:27587083
NASA Astrophysics Data System (ADS)
Tang, Qiuyan; Wang, Jing; Lv, Pin; Sun, Quan
2015-10-01
Propagation simulation method and choosing mesh grid are both very important to get the correct propagation results in wave optics simulation. A new angular spectrum propagation method with alterable mesh grid based on the traditional angular spectrum method and the direct FFT method is introduced. With this method, the sampling space after propagation is not limited to propagation methods no more, but freely alterable. However, choosing mesh grid on target board influences the validity of simulation results directly. So an adaptive mesh choosing method based on wave characteristics is proposed with the introduced propagation method. We can calculate appropriate mesh grids on target board to get satisfying results. And for complex initial wave field or propagation through inhomogeneous media, we can also calculate and set the mesh grid rationally according to above method. Finally, though comparing with theoretical results, it's shown that the simulation result with the proposed method coinciding with theory. And by comparing with the traditional angular spectrum method and the direct FFT method, it's known that the proposed method is able to adapt to a wider range of Fresnel number conditions. That is to say, the method can simulate propagation results efficiently and correctly with propagation distance of almost zero to infinity. So it can provide better support for more wave propagation applications such as atmospheric optics, laser propagation and so on.
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
Parabolic approximation method for fast magnetosonic wave propagation in tokamaks
Phillips, C.K.; Perkins, F.W.; Hwang, D.Q.
1985-07-01
Fast magnetosonic wave propagation in a cylindrical tokamak model is studied using a parabolic approximation method in which poloidal variations of the wave field are considered weak in comparison to the radial variations. Diffraction effects, which are ignored by ray tracing mthods, are included self-consistently using the parabolic method since continuous representations for the wave electromagnetic fields are computed directly. Numerical results are presented which illustrate the cylindrical convergence of the launched waves into a diffraction-limited focal spot on the cyclotron absorption layer near the magnetic axis for a wide range of plasma confinement parameters.
Globally propagating waves in the solar corona -an introduction
NASA Astrophysics Data System (ADS)
Warmuth, Alexander
Globally propagating wave-like disturbances have been observed in the solar chromosphere since the 1960s. These "Moreton waves" were interpreted as the ground tracks of dome-shaped waves that expand through the corona and sweep over the chromosphere. However, only the recent decade has seen detailed analysis of these phenomena, prompted by the availability of coronal imaging data from numerous spaced-based instruments, most famously SOHO/EIT. Globally propagating coronal waves have now been observed in a wide range of spectral channels, yielding a wealth of information. Still, no consensus on their physical nature has been reached. While many findings have supported the "classical" interpretation of the disturbances -fast-mode MHD waves which are propagating in the solar corona and which may be shocked -other characteristics have given rise to alternative models which involve magnetic reconfiguration in the framework of a CME eruption. I will review the different observational signatures of coronal waves, as well as associated phenomena such as metric type II radio bursts. Furthermore, I will discuss the different physical interpretations of coronal waves and how they are supported by observations. Finally, I will consider how some of the lingering controversies might be resolved by observations.
Experiments and numerical investigations of wave propagation in thermal plumes
NASA Astrophysics Data System (ADS)
Laudenbach, N.
2001-12-01
In laboratory experiments thermal plumes are created by injecting hot corn syrup into a column of cold syrup. The viscosity contrast is up to a factor of 1000. Solitary waves, that propagate upwards in the plume conduit, are generated by enhancing the injection rate for a few seconds. For the measurement of the thermal structure of the plume we have implemented a method based on the deflection of a laser beam passing through the plume. Continuous scanning provides a new radial temperature profile each second, which allows detailed studies of the thermal structure of solitary waves. A PIV - (particle image volecimetry) method provides the velocity structure of the thermal plume. Measurements were taken for plume heads, conduits and propagating waves. Comparison between experimental results and numerical 2-D axisymmetric simulations shows a good agreement of the temperature profiles and velocity fields in the plume conduit and waves. Because of thermal diffusion, the conduit widens with height, while its central temperature decreases. The solitary waves start with the same temperature as the unperturbed conduit, however, we find that the temperature in the waves decreases less rapide with rising height. This can be explained by the faster upward propagation and the trapping of fluid within the soliton. If solitary waves exists in mantle plumes, this would imply that they arrive at the bottom of the lithosphere with a larger excess temperature than what the plumes normally exhibits, which could explain strong variations of melt generation with time.
High Frequency Elastic Wave Propagation in Media with a Microstructure
NASA Astrophysics Data System (ADS)
Tie, B.; Aubry, D.; Mouronval, A.-S.; Solas, D.; Thébault, J.; Tian, B.-Y.
2010-05-01
This contribution deals with the theoretical analysis and numerical modeling of elastic wave propagation in media with a microstructure. Two kinds of media are considered: polycrystalline material and honeycomb core sandwich shells, in which elastic waves are triggered by transient signals that result in large frequency ranges including high frequencies. Our theoretical and numerical investigations aim at understanding and simulating the interactions between the microstructure of those media and the wave propagation phenomena, when the characteristic lengths of the microstructure and the involved shortest wavelengths have roughly the same scale. In this paper, some key mechanisms of interaction between the considered microstructures and the elastic waves are highlighted. In polycrystalline superalloys, the misorientation distribution and the average grain size are considered, as they can alter pressure/shear wave propagation and also the permeability to ultrasonic waves monitored to perform non-destructive testing. For the flexure behavior of honeycomb core sandwich shells, the fundamental role played by the honeycomb cells, especially in high frequency domain, is analyzed. Relevant numerical modeling that provides a promising way to quantify micro-structure/wave interactions is presented. The important issue of how to take into account these micro-scale interactions in a homogenized macro-scale modeling is also discussed.
Propagation of polarized millimeter waves through falling snow.
Brien, S G; Goedecke, G H
1988-06-15
Propagation of coherent linearly polarized waves through falling snow is calculated for two monodisperse and one polydisperse model snowstorms for fixed orientation and for random orientation of the snow crystals, at a 10-mm wavelength, utilizing a theoretical model based on the Foldy-Lax model. Results for linearly polarized waves incident on oriented monodispersions and polydispersions exhibit a marked damped oscillatory behavior as a function of propagation distance for the copolarized and cross-polarized intensities. For the polydispersion, a simple approximation for the dependence of the forward scattering matrix elements on snow crystal size is also obtained. PMID:20531776
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.
Direct observation of negative-index microwave surface waves.
Dockrey, J A; Horsley, S A R; Hooper, I R; Sambles, J R; Hibbins, A P
2016-01-01
Waves propagating in a negative-index material have wave-front propagation (wavevector, k) opposite in direction to that of energy flow (Poynting vector, S). Here we present an experimental realisation at microwave frequencies of an analogous surface wave phenomenon whereby a metasurface supports a surface mode that has two possible wavevector eigenstates within a narrow band of frequencies: one that supports surface waves with positive mode index, and another that supports surface waves with negative mode index. Phase sensitive measurements of the near-field of surface waves across the metasurface show the contrasting spatial evolution of the two eigenstates, providing a unique opportunity to directly observe the negative-index phenomenon. PMID:26903284
Direct observation of negative-index microwave surface waves
NASA Astrophysics Data System (ADS)
Dockrey, J. A.; Horsley, S. A. R.; Hooper, I. R.; Sambles, J. R.; Hibbins, A. P.
2016-02-01
Waves propagating in a negative-index material have wave-front propagation (wavevector, k) opposite in direction to that of energy flow (Poynting vector, S). Here we present an experimental realisation at microwave frequencies of an analogous surface wave phenomenon whereby a metasurface supports a surface mode that has two possible wavevector eigenstates within a narrow band of frequencies: one that supports surface waves with positive mode index, and another that supports surface waves with negative mode index. Phase sensitive measurements of the near-field of surface waves across the metasurface show the contrasting spatial evolution of the two eigenstates, providing a unique opportunity to directly observe the negative-index phenomenon.
Direct observation of negative-index microwave surface waves
Dockrey, J. A.; Horsley, S. A. R.; Hooper, I. R.; Sambles, J. R.; Hibbins, A. P.
2016-01-01
Waves propagating in a negative-index material have wave-front propagation (wavevector, k) opposite in direction to that of energy flow (Poynting vector, S). Here we present an experimental realisation at microwave frequencies of an analogous surface wave phenomenon whereby a metasurface supports a surface mode that has two possible wavevector eigenstates within a narrow band of frequencies: one that supports surface waves with positive mode index, and another that supports surface waves with negative mode index. Phase sensitive measurements of the near-field of surface waves across the metasurface show the contrasting spatial evolution of the two eigenstates, providing a unique opportunity to directly observe the negative-index phenomenon. PMID:26903284
Propagating spectroscopy of backward volume spin waves in a metallic FeNi film
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.
Local interaction modeling for acousto-ultrasonic wave propagation
NASA Astrophysics Data System (ADS)
Lee, B. C.; Staszewski, Wieslaw J.
2002-07-01
Damage detection in metallic structures has been the subject of many investigations. Recent developments have shown applications of acousto-ultrasonic and Lamb wave testing. Lamb wave inspection is based on theory of longitudinal waves propagating in plates. In general, the principles of acousto-ultrasonic and Lamb wave inspection techniques are similar. Damage in a structure is identified by a change in the output signal. Previous studies show that even simple input signals can lead to complex output waves, which are difficult to interpret. It is clear that knowledge and understanding of wave propagation in analyzed structures can ease the interpretation of damage detection results. The paper reports an application of local interaction modeling of acousto-ultrasonic waves in metallic structures. The focus of the analysis is on one-dimensional interactions between different material boundaries. This includes modeling of acousto-ultrasonic waves in piezoceramic, adhesive glue and copper in an actuator/sensor configuration. The study also involves experimental validation of the simulation results. The method shows the potential for modeling of acousto-ultrasonic waves in complex media for damage detection applications.
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.
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.
Propagation of elastic waves through textured polycrystals: application to ice
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
NASA Astrophysics Data System (ADS)
Kim, Seulong; Kim, Kihong
2016-06-01
Bi-isotropic media, which include isotropic chiral media and Tellegen media as special cases, are the most general form of linear isotropic media where the electric displacement and the magnetic induction are related to both the electric field and the magnetic intensity. In inhomogeneous bi-isotropic media, electromagnetic waves of two different polarizations are coupled to each other. In this paper, we develop a generalized version of the invariant imbedding method for the study of wave propagation in arbitrarily inhomogeneous stratified bi-isotropic media, which can be used to solve the coupled wave propagation problem accurately and efficiently. We verify the validity and usefulness of the method by applying it to several examples, including the wave propagation in a uniform chiral slab, the surface wave excitation in a bilayer system made of a layer of Tellegen medium and a metal layer, and the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations in inhomogeneous Tellegen media. In contrast to the case of ordinary isotropic media, we find that the surface wave excitation and the mode conversion occur for both s and p waves in bi-isotropic media.
Two-wave propagation in in vitro swine distal ulna
NASA Astrophysics Data System (ADS)
Mano, Isao; Horii, Kaoru; Matsukawa, Mami; Otani, Takahiko
2015-07-01
Ultrasonic transmitted waves 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 waves, slow waves, and overlapping fast and slow waves measured in the specimen after removing the surface cortical bone (only cancellous bone). In addition, the circumferential waves in the cortical bone and water did not affect the fast and slow waves. This suggests that the fast-and-slow-wave phenomenon can be observed in an in vivo human distal radius.
Elandt, Ryan B; Shakeri, Mostafa; Alam, Mohammad-Reza
2014-02-01
Here we show that a nonlinear resonance between oceanic surface waves caused by small seabed features (the so-called Bragg resonance) can be utilized to create the equivalent of lenses and curved mirrors for surface gravity waves. Such gravity wave lenses, which are merely small changes to the seafloor topography and therefore are surface noninvasive, can focus or defocus the energy of incident waves toward or away from any desired focal point. We further show that for a broadband incident wave spectrum (i.e., a wave group composed of a multitude of different-frequency waves), a polychromatic topography (occupying no more than the area required for a monochromatic lens) can achieve a broadband lensing effect. Gravity wave lenses can be utilized to create localized high-energy wave zones (e.g., for wave energy harvesting or creating artificial surf zones) as well as to disperse waves in order to create protected areas (e.g., harbors or areas near important offshore facilities). In reverse, lensing of oceanic waves may be caused by natural seabed features and may explain the frequent appearance of very high amplitude waves in certain bodies of water. PMID:25353576
Alfven Wave Propagation in Young Stellar Systems
NASA Astrophysics Data System (ADS)
Humienny, Ray; Fatuzzo, Marco
Young stellar systems have disks that are threaded by magnetic field lines with an hourglass geometry. These fields funnel ionizing cosmic rays (CRs) into the system. However, the effect is offset by magnetic mirroring. An previous analysis considered how the presence of magnetic turbulence moving outward from the disk would effect the propagation of cosmic-rays, and in turn, change the cosmic-ray ionization fraction occurring within the disk. This work indicated that turbulence reduces the overall flux of cosmic-rays at the disk, which has important consequences for both chemical processes and planet formation that occur within these environments. However, the analysis assumed ideal MHD condition in which the gas is perfectly coupled to the magnetic field. We explore here the validity of this assumption by solving the full equations governing the motion of both ions and neutral within the system.
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.
Propagation of guided waves through weak penetrable scatterers.
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
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.
Three-wave coupling coefficients for perpendicular wave propagation in a magnetized plasma
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.
Propagating Stress Waves During Epithelial Expansion
NASA Astrophysics Data System (ADS)
Banerjee, Shiladitya; Utuje, Kazage J. C.; Marchetti, M. Cristina
2015-06-01
Coordinated motion of cell monolayers during epithelial wound healing and tissue morphogenesis involves mechanical stress generation. Here we propose a model for the dynamics of epithelial expansion that couples mechanical deformations in the tissue to contractile activity and polarization in the cells. A new ingredient of our model is a feedback between local strain, polarization, and contractility that naturally yields a mechanism for viscoelasticity and effective inertia in the cell monolayer. Using a combination of analytical and numerical techniques, we demonstrate that our model quantitatively reproduces many experimental findings [Nat. Phys. 8, 628 (2012)], including the buildup of intercellular stresses, and the existence of traveling mechanical waves guiding the oscillatory monolayer expansion.
Impulsive Wave Propagation within Magmatic Conduits with Axial Symmetry
NASA Astrophysics Data System (ADS)
De Negri Leiva, R. S.; Arciniega-Ceballos, A.; Scheu, B.; Dingwell, D. B.; Sanchez-Sesma, F. J.
2013-12-01
We implemented Trefftz's method to simulate wave propagation 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 wave 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 wave field of volcanic conduit dynamics.
Numerical simulations of blast/shock wave propagations after nuclear explosions
NASA Astrophysics Data System (ADS)
Song, Seungho; Choi, Jung-Il; Li, Yibao; Lee, Changhoon
2013-11-01
Pressure waves develop immediately after nuclear explosions and start to move outward from the fireball. The most of initial damages are caused by the blast waves. We performed the blast wave propagations by solving two-dimensional and axisymmetric Euler equations. For shock capturing, inviscid fluxes are discretized using a variant of the piecewise parabolic method (PPM) and an approximate Riemann solver based on Roe's method is used. A clean air burst of fireball above the ground zero is considered. The initial condition of fireball is given at the point of breakaway that shock waves are appeared on the surface of the fireball. The growth of fireball is also calculated by solving one-dimensional radiation hydrodynamics (RHD) equation from point explosion. Characteristics of the blast wave propagations due to the various heights of burst and amount of the nuclear detonations are investigated. The results of parametric studies will be shown in the final presentation. Supported by Agency for Defense Development.
The propagation of horizontally polarized shear waves in plates bordered with viscous liquid.
Gitis, Alexander; Sauer, Dirk Uwe
2016-09-01
Requirements for ultrasonic horizontally polarized shear waves based viscosity sensors and their applicability for continuous in-line measurement are presented and discussed. The results reveal, that sensors using non-piezoelectric plates as well as wave guides and sensing surface have application-oriented advantages in corrosive and hot liquids. For such non-piezoelectric plate sensors, the dispersion relations are found and the linking equation among propagation velocity as well as attenuation coefficient and Newtonian liquid parameters are obtained. The findings show that in presence of viscous liquids the propagation parameters of horizontally polarized shear waves (HPSW) in non-piezoelectric plate change and a viscosity depending attenuation occurs. It is shown that the measurement sensitivity, in physical terms, of the investigated device highly depends on plate thickness, shear wave impedance of the plate material, and the shear wave impedance of the ambient liquid. Further, reasonable geometrical optimizations and suited plate materials are discussed. PMID:27423968
SH0 Guided Wave Interaction with a Crack Aligned in the Propagation Direction in a Plate
NASA Astrophysics Data System (ADS)
Ratassepp, M.; Lowe, M. J. S.
2009-03-01
Ultrasonic guided waves are currently of interest for structural health monitoring of large structures such as storage tanks and pipelines. This study focuses on the scattering of the fundamental horizontal shear (SH0) mode at a through-thickness notch or crack in a plate whose alignment is in the direction of the wave propagation. The reflection and diffraction of the wave at a crack are examined using 2D finite element simulations. It is shown that the main reflection is generated by Rayleigh-like surface waves created on the faces of the crack, which radiate energy back into the plate. The amplitudes of the reflected and diffracted signals are verified experimentally.
Propagation of acoustic pulses in random gravity wave fields
NASA Astrophysics Data System (ADS)
Millet, Christophe; de La Camara, Alvaro; Lott, François
2015-11-01
A linear solution modeling the interaction between an incoming acoustic wave and a randomly perturbed atmosphere is developed, using the normal mode method. The wave mode structure is determined by a sound speed profile that is confining. The environmental uncertainty is described by a stochastic field obtained with a multiwave stochastic parameterization of gravity waves (GW). Using the propagating modes of the unperturbed atmosphere, the wave propagation problem is reduced to solving a system of ordinary differential equations. We focus on the asymptotic behavior of the transmitted waves in the weakly heterogeneous regime. In this regime, the coupling between the acoustic pulse and the randomly perturbed waveguides is weak and the propagation distance must be large enough for the wave to experience significant scattering. A general expression for the pressure far-field is derived in terms of saddle-point contributions. The saddle-points are obtained from a WKB approximation of the vertical eigenvalue problem. We present preliminary results that show how statistics of the transmitted signal are related to some eigenvalues and how an ``optimal'' GW field can trigger large deviations in the acoustic signals. The present model is used to explain the variability of infrasound signals.
Propagation characteristics of electromagnetic waves in concrete
NASA Astrophysics Data System (ADS)
Halabe, Udaya B.; Maser, Kenneth; Kausel, Eduardo
1989-03-01
This research develops models which can predict the velocity and attenuation of electromagnetic waves in concrete as a function of frequency, temperature, moisture content, chloride content and concrete mix constituents. These models were proposed to predict the electromagnetic properties of concrete by aggregating the electromagnetic properties of its constituents. Water and the dissolved salt are the constituents having the most prominent effect on the dielectric behavior of concrete. A comparative study of three existing three-phase mixture models was carried out. Numerical results were generated using the most representative Discrete model. These results have shown that the real part of complex concrete permittivity (and therefore the velocity of electromagnetic waves) is independent of salinity or frequency in the 0.6 to 3.0 GHz frequency range. On the other hand, these results show that the attenuation coefficient and dielectric conductivity vary almost linearly with frequency in this same frequency range. The real part of concrete permittivity and the attenuation coefficient also show a linear dependence with respect to the degree of saturation of water in the concrete mixture. This suggests that future research should focus on approximating the complex models presented in this research by simple equations.
Harhad, Nadia; El-Kettani, Mounsif Ech-Cherif; Djelouah, Hakim; Izbicki, Jean-Louis; Predoi, Mihai Valentin
2014-03-01
Guided waves propagation in immersed plates with irregular surfaces has potential application to detection and assessment of the extent, depth and pattern of the irregularity. The complexity of the problem, due to the large number of involved parameters, has limited the number of existing studies. The simplest case of irregularities of practical interest is the two-dimensional corrosion profile. Even this case is in general so complex, that one can extract several amplitude dominant periodic surfaces only by using a Fourier spectrum of the surface. Guided waves in plates, with one or both free surfaces having periodic perturbations of different shapes, have been presented in specialized literature. In this paper is studied the propagation of Lamb waves in an aluminum plate with a periodic grooved surface on only one side and immersed in water. The interaction between an incident Lamb wave and the grating gives rise to retro-converted waves. Preliminary numerical simulation by the finite element method is performed in order to obtain key parameters for the experiments. It is shown that retro-converted waves radiating into the water are detectable although their amplitudes are small. The phonon relation is verified for the leaky Lamb modes. The damping coefficients of the leaky Lamb modes in the grooved immersed plate are evaluated. PMID:24262677
Ray Tracing Study of Magnetospheric ULF Wave Propagation.
NASA Astrophysics Data System (ADS)
Zhang, Xinbo
1993-01-01
A semi-empirical plasma density model and Mead -Fairfield magnetic field model are incorporated into a 3-D ray tracing code to study magnetospheric ULF wave propagation from the subsolar magnetopause. The ray-tracing of Pc3 compressional waves from the magnetosheath reveals that the magnetosphere can present a major propagation barrier to the penetration of these waves to the plasmasphere. This barrier is the ion-ion cutoff between the He^+ and O ^+ gyroresonances. As a result of the frequency -dependent location of this cutoff, the magnetosphere behaves like a filter for Pc3 compressional waves, and only the low frequency components can penetrate to the inner magnetosphere. These results are in agreement with previous satellite observations. This 'filter action' strongly depends on the relative concentration of He^+ and O^+ and is, therefore, sensitive to solar and magnetic activity. The study of the propagation characteristics of Pc3 transverse Alfven waves shows that these waves cannot penetrate to low Earth altitudes for wave frequencies above about approximately 0.03 hz. The configuration of the refractive index reveals an O^+-He^+ associated cutoff located between the assumed wave source in the equatorial magnetopause and the Earth. When the O^+ concentration is removed from the plasma composition, the barrier no longer exists, and waves with much higher frequencies than 0.03 Hz can penetrate to low altitudes. The result that the 0.03 Hz or lower frequency Alfven waves can be guided to the low altitudes agrees with ground-based power spectrum observations at high latitudes. The ray tracing study of Pc 1-2 waves reproduces earlier results (Rauch and Roux, 1982) for an H ^+-He^+ two-ion-species plasma, i.e. Pc 1-2 left hand polarized Alfven mode waves originating at equatorial geostationary orbit, below He ^+ gyrofrequency, are guided to the ground. However, our ray tracing study shows that previous Pc 1-2 ray tracing results are only valid in the absence of O
Multidimensional detonation propagation modeled via nonlinear shock wave superposition
NASA Astrophysics Data System (ADS)
Higgins, Andrew; Mehrjoo, Navid
2010-11-01
Detonation waves in gases are inherently multidimensional due to their cellular structure, and detonations in liquids and heterogeneous solids are often associated with instabilities and stochastic, localized reaction centers (i.e., hot spots). To explore the statistical nature of detonation dynamics in such systems, a simple model that idealizes detonation propagation as an ensemble of interacting blast waves originating from spatially random point sources has been proposed. Prior results using this model exhibited features that have been observed in real detonating systems, such as anomalous scaling between axisymmetric and two-dimensional geometries. However, those efforts used simple linear superposition of the blast waves. The present work uses a model of blast wave superposition developed for multiple-source explosions (the LAMB approximation) that incorporates the nonlinear interaction of shock waves analytically, permitting the effect of a more physical model of blast wave interaction to be explored. The results are suggestive of a universal behavior in systems of spatially randomized energy sources.
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.
Wave Turbulence on Water Surface
NASA Astrophysics Data System (ADS)
Nazarenko, Sergey; Lukaschuk, Sergei
2016-03-01
We overview the wave turbulence approach by example of one physical system: gravity waves on the surface of an infinitely deep fluid. In the theoretical part of our review, we derive the nonlinear Hamiltonian equations governing the water-wave system and describe the premises of the weak wave turbulence theory. We outline derivation of the wave-kinetic equation and the equation for the probability density function, and most important solutions to these equations, including the Kolmogorov-Zakharov spectra corresponding to a direct and an inverse turbulent cascades, as well as solutions for non-Gaussian wave fields corresponding to intermittency. We also discuss strong wave turbulence as well as coherent structures and their interaction with random waves. We describe numerical and laboratory experiments, and field observations of gravity wave turbulence, and compare their results with theoretical predictions.
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.
Surface acoustic wave microfluidics
Ding, Xiaoyun; Li, Peng; Lin, Sz-Chin Steven; Stratton, Zackary S.; Nama, Nitesh; Guo, Feng; Slotcavage, Daniel; Mao, Xiaole; Shi, Jinjie; Costanzo, Francesco; Huang, Tony Jun
2014-01-01
The recent introduction of surface acoustic wave (SAW) technology onto lab-on-a-chip platforms has opened a new frontier in microfluidics. The advantages provided by such SAW microfluidics are numerous: simple fabrication, high biocompatibility, fast fluid actuation, versatility, compact and inexpensive devices and accessories, contact-free particle manipulation, and compatibility with other microfluidic components. We believe that these advantages enable SAW microfluidics to play a significant role in a variety of applications in biology, chemistry, engineering, and medicine. In this review article, we discuss the theory underpinning SAWs and their interactions with particles and the contacting fluids in which they are suspended. We then review the SAW-enabled microfluidic devices demonstrated to date, starting with devices that accomplish fluid mixing and transport through the use of travelling SAW; we follow that by reviewing the more recent innovations achieved with standing SAW that enable such actions as particle/cell focusing, sorting, and patterning. Finally, we look forward and appraise where the discipline of SAW microfluidics could go next. PMID:23900527
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
NASA Astrophysics Data System (ADS)
Martin, Roland; Brissaud, Quentin; Garcia, Raphael; Komatitsch, Dimitri
2015-04-01
During low-frequency events such as tsunamis, acoustic and gravity waves are generated and quickly propagate in the atmosphere. Due to the exponential decrease of the atmospheric density with the altitude, the conservation of the kinetic energy imposes that the amplitude of those waves increases (to the order of 105 at 200km of altitude), which allows their detection in the upper atmosphere. This propagation bas been modelled for years with different tools, such as normal modes modeling or to a greater extent time-reversal techniques, but a low-frequency multi-dimensional atmospheric wave modelling is still crucially needed. A modeling tool is worth of interest since there are many different sources, as earthquakes or atmospheric explosions, able to propagate acoustic and gravity waves. In order to provide a fine modeling of the precise observations of these waves by GOCE satellite data, we developed a new numerical modeling tool. By adding some developments to the SPECFEM package that already models wave propagation in solid, porous or fluid media using a spectral element method, we show here that acoustic and gravity waves propagation can now be modelled in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source. The bottom forcing feature has been implemented to easily model the coupling with the Earth's or ocean's vibrating surfaces but also huge atmospheric events. Atmospheric attenuation is also introduced since it has a crucial impact on acoustic wave propagation. Indeed, it plays the role of a frequency filter that damps high-frequency signals.
Propagation and generation of waves in solar atmosphere
NASA Astrophysics Data System (ADS)
Routh, Swati
The fact that the temperature increases with height in the solar atmosphere has been known for many years. To maintain this temperature increase, sources of heating must be present in the atmosphere. One of the most important, and still unsolved, problems in solar physics is to identify the basic physical processes that are responsible for this heating, and explain solar activities caused by the heating. It is also observationally well-established that the solar atmosphere shows a broad range of oscillations that are different in magnetic and non-magnetic regions of the atmosphere. The oscillations are driven by propagating waves, which cause the atmosphere to oscillate at its natural (cutoff) frequency. Since different waves have different cutoff frequencies, it is important to have a method that would allow determining such cutoffs for the solar atmosphere. In this PhD dissertation, the concept of cutoff frequency is extended to inhomogeneous atmospheres, and a general method to determine the cutoff frequency is presented. The method leads to new forms of wave equations obtained for all wave variables, and allows deriving the cutoff frequency without formally solving the wave equations. The main result is that the derived cutoff frequency is a local quantity and that its value at a given atmospheric height determines the frequency that waves must have in order to be propagating at this height. The developed method is general enough, so that it can be used to establish theoretical bases for studying the propagation and generation of different waves in the solar atmosphere. Acoustic waves play an important role in the heating of magnetic-free regions of the solar atmosphere. To determine the propagation conditions for these waves in the non-isothermal solar atmosphere, the method is used to obtain the resulting acoustic cutoff frequency. This new cutoff frequency is a local quantity and it generalizes Lamb's acoustic cutoff frequency that was obtained for an
Computational strategy for modeling radio wave propagation in lossy circular waveguides
Moses, Ronald; Cai, D Michael
2008-01-01
The propagation of radio waves in lossy waveguides and tunnels has been researched extensively for many years as can be seen in the detailed book by Wait. The mathematics used to model waveguides for communications is essentially the same as that needed to model radio frequency (RF) propagation in simple tunnels. The presence or lack of conductors inside a waveguide or tunnel is a key driver in the nature of the solutions one will find for a particular application, Delogne. When there are conductors passing through a waveguide or tunnel, the simplest modes of propagation are surface-guided waves following the conductor and typically enabling long-range transmission. A tunnel containing a core conductor can act rather like a coaxial cable, propagating waves at a nearly constant speed, regardless of frequency. Conversely, a tunnel or waveguide without internal conductors is subject to very different wave patterns, resulting in a much more complex propagation analysis. Holloway et al. presented an exhaustive study of RF propagation in circular structures embedded in lossy surroundings. The work of Holloway et al. is the basis for this paper, where we discuss application of their computational techniques and present refinements gleaned from our work on similar problems.
Numerical simulation of surface waves instability on a homogeneous grid
NASA Astrophysics Data System (ADS)
Korotkevich, Alexander O.; Dyachenko, Alexander I.; Zakharov, Vladimir E.
2016-05-01
We performed full-scale numerical simulation of instability of weakly nonlinear waves on the surface of deep fluid. We show that the instability development leads to chaotization and formation of wave turbulence. Instability of both propagating and standing waves was studied. We separately studied pure capillary wave, that was unstable due to three-wave interactions and pure gravity waves, that were unstable due to four-wave interactions. The theoretical description of instabilities in all cases is included in the article. The numerical algorithm used in these and many other previous simulations performed by the authors is described in detail.
Sawtooth-Control Mechanism using Toroidally Propagating Ion-Cyclotron-Resonance Waves in Tokamaks
Graves, J. P.; Coda, S.; Chapman, I.
2009-02-13
The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the magnetic field determines stability when the rational q=1 surface resides within a narrow region centered about the shifted fundamental cyclotron resonance.
Electromagnetic wave propagation in rain and polarization effects
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
Corrigendum and addendum. Modeling weakly nonlinear acoustic wave propagation
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.
A k-Space Method for Moderately Nonlinear Wave Propagation
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
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.
Nonlinearities of waves propagating over a mild-slope beach: laboratory and numerical results
NASA Astrophysics Data System (ADS)
Rocha, Mariana V. L.; Michallet, Hervé; Silva, Paulo A.; Cienfuegos, Rodrigo
2014-05-01
As surface gravity waves propagate from deeper waters to the shore, their shape changes, primarily due to nonlinear wave interactions and further on due to breaking. The nonlinear effects amplify the higher harmonics and cause the oscillatory flow to transform from nearly sinusoidal in deep water, through velocity-skewed in the shoaling zone, to velocity asymmetric in the inner-surf and swash zones. In addition to short-wave nonlinearities, the presence of long waves and wave groups also results in a supplementary wave-induced velocity and influences the short-waves. Further, long waves can themselves contribute to velocity skewness and asymmetry at low frequencies, particularly for very dissipative mild-slope beach profiles, where long wave shoaling and breaking can also occur. The Hydralab-IV GLOBEX experiments were performed in a 110-m-long flume, with a 1/80 rigid-bottom slope and allowed the acquisition of high-resolution free-surface elevation and velocity data, obtained during 90-min long simulations of random and bichromatic wave conditions, and also of a monochromatic long wave (Ruessink et al., Proc. Coastal Dynamics, 2013). The measurements are compared to numerical results obtained with the SERR-1D Boussinesq-type model, which is designed to reproduce the complex dynamics of high-frequency wave propagation, including the energy transfer mechanisms that enhance infragravity-wave generation. The evolution of skewness and asymmetry along the beach profile until the swash zone is analyzed, relatively to that of the wave groupiness and long wave propagation. Some particularities of bichromatic wave groups are further investigated, such as partially-standing long-wave patterns and short-wave reformation after the first breakpoint, which is seen to influence particularly the skewness trends. Decreased spectral width (for random waves) and increased modulation (for bichromatic wave groups) are shown to enhance energy transfers between super- and sub
Wave Propagation of Myocardial Stretch: Correlation with Myocardial Stiffness
Pislaru, Cristina; Pellikka, Patricia A.; Pislaru, Sorin V.
2015-01-01
The mechanism of flow propagation during diastole in the left ventricle (LV) has been well described. Little is known about the associated waves propagating along the heart wall s. These waves may have a mechanism similar to pulse wave propagation in arteries. The major goal of the study was to evaluate the effect of myocardial stiffness and preload on this wave transmission. Methods Longitudinal late diastolic deformation and wave speed (Vp) of myocardial stretch in the anterior LV wall were measured using sonomicrometry in sixteen pigs. Animals with normal and altered myocardial stiffness (acute myocardial infarction) were studied with and without preload alterations. Elastic modulus estimated from Vp (EVP; Moens-Korteweg equation) was compared to incremental elastic modulus obtained from exponential end -diastolic stress-strain relation (ESS). Myocardial distensibility and α-and β-coefficients of stress-strain relations were calculated. Results Vp was higher at reperfusion compared to baseline (2.6±1.3 m/s vs. 1.3±0.4 m/s; p=0.005) and best correlated with ESS (r 2=0.80, p<0.0001), β-coefficient (r2=0.78, p<0.0001), distensibility (r2=0.47, p=0.005), and wall thickness/diameter ratio (r2=0.42, p=0.009). Elastic moduli (EVP and ESS) were strongly correlated (r2=0.83, p<0.0001). Increasing preload increased Vp and EVP and decreased distensibility. At multivariate analysis, ESS, wall thickness, and end-diastolic and systolic LV pressures were independent predictors of Vp (r2model=0.83, p<0.0001). Conclusions The main determinants of wave propagation of longitudinal myocardial stretch were myocardial stiffness and LV geometry and pressure. This local wave speed could potentially be measured noninvasively by echocardiography. PMID:25193091
Anisotropic electromagnetic wave propagation modeling using parabolic approximations
NASA Astrophysics Data System (ADS)
Brent, R. I.; Siegmann, W. L.; Jacobson, M. J.; Jacyna, G. M.
1990-12-01
A new method for the investigation of anisotropic electromagnetic wave propagation in the atmosphere is developed using parabolic approximations. Model equations for the electric field components are formulated which include the effects of both the inhomogeneous atmosphere and the static magnetic field of the earth. Application of parabolic-type approximations produces different systems of coupled parabolic equations. Each is valid for different relative magnitudes of components of the electric field. All admissible cases are then synthesized into one system which can be numerically examined, yielding solutions without a priori knowledge of electric field ratios. A specific example is presented and examined to understand static magnetic field effects on electromagnetic wave propagation. The influences of the earth's magnetic field are discussed and displayed in terms of electric components and the Poynting vector. Results demonstrate that the geomagnetic field can significantly influence HF atmospheric propagation.
Magnetoelastic surface waves in auxetic structure
NASA Astrophysics Data System (ADS)
Maruszewski, B.; Drzewiecki, A.; Starosta, R.
2010-06-01
In modern technologies searching materials of peculiar features is of a fundamental interest for many researchers and engineers. Negative Poisson's ratio materials and structures expand transversely when stretching axially. Nowadays, there is an increasing interest in the development of these novel materials called auxetics. We are interested not only in their mechanical properties, but also in their interaction with external physical fields, e.g. electromagnetic field. It is expected that magnetoelastic surface waves propagation has essential meaning in many other physical and biomechanical applications. The paper aims at investigating propagation of magnetoelastic surface waves along an auxetic elastic halfspace in the presence of an external magnetic field of various orientations related to the limiting plane. Dispersion and existence conditions of those waves have been calculated and analyzed in order to present new features of described interactions. It has occurred that the dispersion properties in the case of the Rayleigh-like magnetoelastic surface waves are significantly different for the auxetic material compared to materials of positive Poisson's ratio.
Oblique propagation, wave particle interaction and particle distribution function
NASA Astrophysics Data System (ADS)
Osmane, Adnane; Hamza, A. M.; Meziane, Karim
Recent results from the Cluster mission have stimulated theoretical investigations and simulations to explain ion distribution functions observed in the quasi-perp bow shock. High-time resolution observations have revealed distributions of gyrating ions that are gyrophase-bunched. When not produced at the shock, such distributions are believed to be resulting from interactions between field-aligned beams and low frequency beamdriven waves . The Conventional models used to account for such distributions assume that the waves are purely transverse, and that they propagate parallel to the ambient magnetic eld. However observations indicate that these waves are propagating obliquely with respect to the ambient magnetic eld [Meziane et al., 2001]. A theoretical investigation of the non-relativistic wave-particle interaction in a background magnetic eld with the electromagnetic wave propagating obliquely has been addressed previously, resulting in a dynamical system describing the wave interaction with a single ion in the absence of dissipation mechanisms. [Hamza et al., 2005] This dynamical system has been numerically integrated to construct the ion distribution functions by seeding the particles with di erent initial conditions. We compute the particle orbits and simulate the time evolution of the distribution functions based on Liouville's theorem of phase space density conservation. It will be shown that the trapping which is due to the oblique propagation of the wave, gives an explanation for gyrophase-bunching and unstable distributions in velocity space which could trigger instabilities such as firehose and mirror. Therefore this exercise provide insights on the particle dynamics and onset of waves away from the shock. Meziane, K., C. Mazelle, R.P. Lin, D. LeQueau, D.E. Larson, G.K. Parks, R.P. Lepping (2001), Three dimensional observations of gyrating ions distributions far upstream from the Earth's bow shock and their association with low-frequency waves, J
Excitation of propagating spin waves with global uniform microwave fields
NASA Astrophysics Data System (ADS)
Au, Y.; Davison, T.; Ahmad, E.; Keatley, P. S.; Hicken, R. J.; Kruglyak, V. V.
2011-03-01
We demonstrate a magnonic architecture that converts global free-space uniform microwaves into spin waves propagating in a stripe magnonic waveguide. The architecture is based upon dispersion mismatch between the narrow magnonic waveguide and a wide "antenna" patch, both patterned from the same magnetic film. The spin waves injected into the waveguide travel to distances as large as several tens of micrometers. The antennas can be placed at multiple positions on a magnonic chip and used to excite mutually coherent multiple spin waves for magnonic logic operations. This demonstration paves way for "magnonics" to become a pervasive technology for information processing.
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.
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.
A study of helical Lamb wave propagation on two hollow cylinders with imperfect contact conditions
NASA Astrophysics Data System (ADS)
Balvantin, A.; Baltazar, A.; Kim, J.-Y.
2013-01-01
The effects of varying interfacial conditions between two contacting hollow cylinders on the propagation of helical Lamb waves are studied. Experiments were carried out on two aluminum hollow cylinders (114 mm in outer-diameter and 6 mm of wall thickness) axially loaded by a horizontal press to control contact interfacial stiffness. An ultrasonic measurement setup using broadband transducers, with semispherical contact probes coupled to the cylinders surface, in a pitchcatch configuration is presented. Time-frequency representation (TFR) is employed to accurately perform mode identification of ultrasonic captured signals. The effect of different interfacial contact conditions in mechanically joined cylinders into propagation parameters of helical Lamb waves is studied. Finally, a comparison of sensitivity, between Lamb waves in straight and helical propagating paths, under different interfacial conditions is presented.
Wave Propagation in the Vicinities of Rock Fractures Under Obliquely Incident Wave
NASA Astrophysics Data System (ADS)
Zou, Yang; Li, Jianchun; He, Lei; laloui, Lyesse; Zhao, Jian
2016-05-01
Though obliquely incident plane wave across rock fractures has been extensively investigated by theoretical analysis, the quantitative identification of each wave emerged from fractures has not been achieved either in numerical simulation or laboratory experiment. On the other hand, there are no theoretical results describing the stress/velocity state of the rocks beside a fracture. The superposition of the multiple waves propagating in the media results in the variation of the stress/velocity state. To understand the superposition of the wave components in the adjacent rocks of a facture, based on the geometrical analysis of the wave paths, the lag times among passing waves at an arbitrary point are determined. The normalised critical distances from the fracture to the measuring locations where the corresponding harmonic waves depart from other waves for a certain duration are then derived. Discussion on the correction for an arbitrary incident wave is then carried out considering the changes of the duration of the reflected and transmitted waves. Under the guidance of the analysis, wave superposition is performed for theoretical results and separated waves are obtained from numerical model. They are demonstrated to be consistent with each other. The measurement and the data processing provide an approach for wave separation in a relatively unbounded media. In addition, based on the mechanical analysis on the wave front, an indirect wave separation method is proposed which provides a possibility for laboratory experiments of wave propagation with an arbitrary incident angle.
Surface wave acoustics of granular packing under gravity
NASA Astrophysics Data System (ADS)
Clement, Eric; Bonneau, Lenaic; Andreotti, Bruno
2009-06-01
Due to the non-linearity of Hertzian contacts, the speed of sound in granular matter increases with pressure. For a packing under gravity and in the presence of a free surface, bulk acoustic waves cannot propagate due to the inherent refraction toward the surface (the mirage effect). Thus, only modes corresponding to surface waves (Raleigh-Hertz modes) are able to propagate the acoustic signal. First, based on a non-linear elasticity model, we describe the main features associated to these surface waves. We show that under gravity, a granular packing is from the acoustic propagation point of view an index gradient waveguide that selects modes of two distinct families i.e. the sagittal and transverse waves localized in the vicinity of the free surface. A striking feature of these surface waves is the multi-modal propagation: for both transverse and sagittal waves, we show the existence of a infinite but discrete series of propagating modes. In each case, we determine the mode shape and and the corresponding dispersion relation. In the case of a finite size system, a geometric waveguide is superimposed to the index gradient wave guide. In this later case, the dispersion relations are modified by the appearance of a cut-off frequency that scales with depth. The second part is devoted to an experimental study of surface waves propagating in a granular packing confined in a long channel. This set-up allows to tune a monomodal emission by taking advantage of the geometric waveguide features combined with properly designed emitters. For both sagittal and transverses waves, we were able to isolate a single mode (the fundamental one) and to plot the dispersion relation. This measurements agree well with the Hertzian scaling law as predicted by meanfield models. Furthermore, it allows us to determine quantitatively relations on the elastic moduli. However, we observe that our data yield a shear modulus abnormally weak when compared to several meanfield predictions.
Surface wave acoustics of granular packing under gravity
Clement, Eric; Andreotti, Bruno; Bonneau, Lenaic
2009-06-18
Due to the non-linearity of Hertzian contacts, the speed of sound in granular matter increases with pressure. For a packing under gravity and in the presence of a free surface, bulk acoustic waves cannot propagate due to the inherent refraction toward the surface (the mirage effect). Thus, only modes corresponding to surface waves (Raleigh-Hertz modes) are able to propagate the acoustic signal. First, based on a non-linear elasticity model, we describe the main features associated to these surface waves. We show that under gravity, a granular packing is from the acoustic propagation point of view an index gradient waveguide that selects modes of two distinct families i.e. the sagittal and transverse waves localized in the vicinity of the free surface. A striking feature of these surface waves is the multi-modal propagation: for both transverse and sagittal waves, we show the existence of a infinite but discrete series of propagating modes. In each case, we determine the mode shape and and the corresponding dispersion relation. In the case of a finite size system, a geometric waveguide is superimposed to the index gradient wave guide. In this later case, the dispersion relations are modified by the appearance of a cut-off frequency that scales with depth. The second part is devoted to an experimental study of surface waves propagating in a granular packing confined in a long channel. This set-up allows to tune a monomodal emission by taking advantage of the geometric waveguide features combined with properly designed emitters. For both sagittal and transverses waves, we were able to isolate a single mode (the fundamental one) and to plot the dispersion relation. This measurements agree well with the Hertzian scaling law as predicted by meanfield models. Furthermore, it allows us to determine quantitatively relations on the elastic moduli. However, we observe that our data yield a shear modulus abnormally weak when compared to several meanfield predictions.
Active micromixer using surface acoustic wave streaming
Branch; Darren W. , Meyer; Grant D. , Craighead; Harold G.
2011-05-17
An active micromixer uses a surface acoustic wave, preferably a Rayleigh wave, propagating on a piezoelectric substrate to induce acoustic streaming in a fluid in a microfluidic channel. The surface acoustic wave can be generated by applying an RF excitation signal to at least one interdigital transducer on the piezoelectric substrate. The active micromixer can rapidly mix quiescent fluids or laminar streams in low Reynolds number flows. The active micromixer has no moving parts (other than the SAW transducer) and is, therefore, more reliable, less damaging to sensitive fluids, and less susceptible to fouling and channel clogging than other types of active and passive micromixers. The active micromixer is adaptable to a wide range of geometries, can be easily fabricated, and can be integrated in a microfluidic system, reducing dead volume. Finally, the active micromixer has on-demand on/off mixing capability and can be operated at low power.
Acoustic Measurement of Surface Wave Damping by a Meniscus
NASA Astrophysics Data System (ADS)
Michel, Guillaume; Pétrélis, François; Fauve, Stéphan
2016-04-01
We investigate the reflection of gravity-capillary surface waves by a plane vertical barrier. The size of the meniscus is found to strongly affect reflection: the energy of the reflected wave with a pinned contact line is around twice the one corresponding to a fully developed meniscus. To perform these measurements, a new experimental setup similar to an acousto-optic modulator is developed and offers a simple way to measure the amplitude, frequency and direction of propagation of surface waves.
Simulating tsunami propagation in fjords with long-wave models
NASA Astrophysics Data System (ADS)
Løvholt, F.; Glimsdal, S.; Lynett, P.; Pedersen, G.
2015-03-01
Tsunamis induced by rock slides constitute a severe hazard towards coastal fjord communities. Fjords are narrow and rugged with steep slopes, and modeling the short-frequency and high-amplitude tsunamis in this environment is demanding. In the present paper, our ability (and the lack thereof) to simulate tsunami propagation and run-up in fjords for typical wave characteristics of rock-slide-induced waves is demonstrated. The starting point is a 1 : 500 scale model of the topography and bathymetry of the southern part of Storfjorden fjord system in western Norway. Using measured wave data from the scale model as input to numerical simulations, we find that the leading wave is moderately influenced by nonlinearity and dispersion. For the trailing waves, dispersion and dissipation from the alongshore inundation on the traveling wave become more important. The tsunami inundation was simulated at the two locations of Hellesylt and Geiranger, providing a good match with the measurements in the former location. In Geiranger, the most demanding case of the two, discrepancies are larger. The discrepancies may be explained by a combinations of factors, such as the accumulated errors in the wave propagation along large stretches of the fjord, the coarse grid resolution needed to ensure model stability, and scale effects in the laboratory experiments.
Excitation of coherent propagating spin waves by pure spin currents
NASA Astrophysics Data System (ADS)
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.
Excitation of coherent propagating spin waves by pure spin currents.
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
Nonlinear wave propagation in strongly coupled dusty plasmas.
Veeresha, B M; Tiwari, S K; Sen, A; Kaw, P K; Das, A
2010-03-01
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. PMID:20365882
Nonlinear wave propagation in strongly coupled dusty plasmas
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.
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.
Attenuation characteristics of nonlinear pressure waves propagating in pipes
NASA Technical Reports Server (NTRS)
Shih, C. C.
1974-01-01
A series of experiments was conducted to investigate temporal and spatial velocity distributions of fluid flow in 3-in. open-end pipes of various lengths up to 210 ft, produced by the propagation of nonlinear pressure waves of various intensities. Velocity profiles across each of five sections along the pipes were measured as a function of time with the use of hot-film and hot-wire anemometers for two pressure waves produced by a piston. Peculiar configurations of the velocity profiles across the pipe section were noted, which are uncommon for steady pipe flow. Theoretical consideration was given to this phenomenon of higher velocity near the pipe wall for qualitative confirmation. Experimentally time-dependent velocity distributions along the pipe axis were compared with one-dimensional theoretical results obtained by the method of characteristics with or without diffusion term for the purpose of determining the attenuation characteristics of the nonlinear wave propagation in the pipes.
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.
Wave propagation in square granular crystals with spherical interstitial intruders
NASA Astrophysics Data System (ADS)
Szelengowicz, I.; Kevrekidis, P. G.; Daraio, C.
2012-12-01
We investigate the propagation and scattering of highly nonlinear waves in granular systems composed of spheres in contact arranged in a square packing, and study how the presence of small and light spherical interstitial defects, also referred to as intruders, affects the wave propagation. The effects of a single defect are investigated experimentally and compared to numerical simulations, showing very good quantitative agreement. Transmitted and scattered waves are formed, whose characteristics depend on the material properties of the defect in relation to the properties of the particles in the lattice. Experiments and numerical simulations reveal that stiffer defects are more efficient at redistributing energy outside the impacted chain and soft defects induce a localization of the energy at the defect. Finally, the effects of the presence of two defects, placed diagonally or aligned in the square packing are also investigated, as well as how their interaction depends on their relative positions.
Excitation of coherent propagating spin waves by pure spin currents
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
Quasinormal modes and classical wave propagation in analogue black holes
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.
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
Observations of rossby wave propagation in the Northeast Atlantic with topex/poseidon altimetry
NASA Astrophysics Data System (ADS)
Cipollini, P.; Cromwell, D.; Quartly, G. D.
1998-11-01
A technique is described to observe Rossby waves in the oceans using altimeter data, which makes use of longitude/time diagrams of sea surface height anomalies at a given latitude, relying on the zonal propagation of those waves. By means of the Fast Fourier and Radon Transforms of the longitude/time diagrams it is possible to locate the spectral components corresponding to wave propagation and to give an approximate estimation of some of their characteristics such as their height and speed. The results obtained by using data from the TOPEX/POSEIDON radar altimeters in the Northeast Atlantic highlight a narrow `preferred' zonal band of propagation for Rossby waves around 33°-34° N. The speeds of the dominant signals at different latitudes have been computed both in Fourier space and in Radon space: they are in good agreement with the prediction of a revised theory of Rossby wave propagation, which has recently been introduced to explain the discrepancy between observed wave speeds and the speeds computed from the classical theory.
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.
ATS-6 mm-wave propagation experiment
NASA Technical Reports Server (NTRS)
Davis, C. C.; Ekstrom, P. A.
1976-01-01
Attenuation on a Space-to-Earth path was measured at 20 GHz for a ground terminal at approximately 1 km elevation in an arid (16 cm annual precipitation) region of eastern Washington state. Precipitation intensity and radiometric sky temperature at 20 GHz were also measured. Attenuation greater than 1 dB was observed only in the presence of wet snow on antenna surfaces. Ten thousand (10,000) hours of radiometric sky temperature data recorded over an 18-month period indicated atmospheric attenuation of 5 to 7 dB during two instances of rain intensity of approximately 1 inch per hour.
Two layer asymptotic model for the wave propagation in the presence of vorticity
NASA Astrophysics Data System (ADS)
Kazakova, M. Yu; Noble, P.
2016-06-01
In the present study, we consider the system of two layers of the immiscible constant density fluids which are modeled by the full Euler equations. The domain of the flow is infinite in the horizontal directions and delimited above by a free surface. Bottom topography is taken into account. This is a simple model of the wave propagation in the ocean where the upper layer corresponds to the (thin) layer of fluid above the thermocline whereas the lower layer is under the thermocline. Though even this simple framework is computationally too expensive and mathematically too complicated to describe efficiently propagation of waves in the ocean. Modeling assumption such as shallowness, vanishing vorticity and hydrostatic pressure are usually made to get the bi-layer shallow water models that are mathematically more manageable. Though, they cannot describe correctly the propagation of both internal and free surface waves and dispersive/non hydrostatic must be added. Our goal is to consider the regime of medium to large vorticities in shallow water flow. We present the derivation of the model for internal and surface wave propagation in the case of constant and general vorticities in each layer. The model reduces to the classical Green-Naghdi equations in the case of vanishing vorticities.
Propagation Dynamics of Nonspreading Cosine-Gauss Water-Wave Pulses.
Fu, Shenhe; Tsur, Yuval; Zhou, Jianying; Shemer, Lev; Arie, Ady
2015-12-18
Linear gravity water waves are highly dispersive; therefore, the spreading of initially short wave trains characterizes water surface waves, and is a universal property of a dispersive medium. Only if there is sufficient nonlinearity does this envelope admit solitary solutions which do not spread and remain in fixed forms. Here, in contrast to the nonlinear localized wave packets, we present both theoretically and experimentally a new type of linearly nondispersive water wave, having a cosine-Gauss envelope, as well as its higher-order Hermite cosine-Gauss variations. We show that these waves preserve their width despite the inherent dispersion while propagating in an 18-m wave tank, accompanied by a slowly varying carrier-envelope phase. These wave packets exhibit self-healing; i.e., they are restored after bypassing an obstacle. We further demonstrate that these nondispersive waves are robust to weakly nonlinear perturbations. In the strong nonlinear regime, symmetry breaking of these waves is observed, but their cosine-Gauss shapes are still approximately preserved during propagation. PMID:26722925
Propagation Dynamics of Nonspreading Cosine-Gauss Water-Wave Pulses
NASA Astrophysics Data System (ADS)
Fu, Shenhe; Tsur, Yuval; Zhou, Jianying; Shemer, Lev; Arie, Ady
2015-12-01
Linear gravity water waves are highly dispersive; therefore, the spreading of initially short wave trains characterizes water surface waves, and is a universal property of a dispersive medium. Only if there is sufficient nonlinearity does this envelope admit solitary solutions which do not spread and remain in fixed forms. Here, in contrast to the nonlinear localized wave packets, we present both theoretically and experimentally a new type of linearly nondispersive water wave, having a cosine-Gauss envelope, as well as its higher-order Hermite cosine-Gauss variations. We show that these waves preserve their width despite the inherent dispersion while propagating in an 18-m wave tank, accompanied by a slowly varying carrier-envelope phase. These wave packets exhibit self-healing; i.e., they are restored after bypassing an obstacle. We further demonstrate that these nondispersive waves are robust to weakly nonlinear perturbations. In the strong nonlinear regime, symmetry breaking of these waves is observed, but their cosine-Gauss shapes are still approximately preserved during propagation.
Generation and propagation of nonlinear internal waves in Massachusetts Bay
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.
Propagating and localized surface plasmons in Ag nanostructures
NASA Astrophysics Data System (ADS)
Dabrowski, Maciej; Dai, Yanan; Petek, Hrvoje
Plasmonic excitations strongly depend on the size, geometry and dielectric environment of nanoscale metals. Here, we study an epitaxially grown Ag nanostructures on Si(001) and Si(111) surfaces by Low Energy Electron Microscopy/Photoemission Electron Microscopy (LEEM/PEEM). Using the combination of LEEM and broadly tunable femtosecond laser excited multiphoton PEEM we image how single crystalline metallic nanostructures form and how plasmon excitations depend on the particle structure and laser excitation parameters. For Ag pyramids with the dimensions of few hundreds nanometers, dipolar and quadrupolar localized surface plasmons are observed. For Ag wires with several micrometer lengths, both localized and propagating surface plasmons can be excited, depending on the polarization, particle orientation and energy of the excitation. Finally, in larger Ag islands, several micrometers in size, the interference patterns are created by plasmon waves excited at the island edges. In addition to plasmonic response, light diffraction patterns around the Ag nanostrutures are discussed.
Existence and uniqueness of stabilized propagating wave segments in wave front interaction model
NASA Astrophysics Data System (ADS)
Guo, Jong-Shenq; Ninomiya, Hirokazu; Tsai, Je-Chiang
2010-02-01
Recent experimental studies of photosensitive Belousov-Zhabotinskii reaction have revealed the existence of propagating wave segments. The propagating wave segments are unstable, but can be stabilized by using a feedback control to continually adjust the excitability of the medium. Experimental studies also indicate that the locus of the size of a stabilized wave segment as a function of the excitability of the medium gives the excitability boundary for the existence of 2D wave patterns with free ends in excitable media. To study the properties of this boundary curve, we use the wave front interaction model proposed by Zykov and Showalter. This is equivalent to study a first order system of three ordinary differential equations which includes a singular nonlinearity. Using two different reduced first order systems of two ordinary differential equations, we first show the existence of wave segments for any given propagating velocity. Then the wave profiles can be classified into two types, namely, convex and non-convex types. More precisely, when the normalized propagating velocity is small, we show that the wave profile is of convex type, while the wave profile is of non-convex type when the normalized velocity is close to 1.
Numerical investigation of seismic wave propagation in fracture systems
NASA Astrophysics Data System (ADS)
Yi, Weidong
The geometric features and physical characteristics of fractures in rock masses are often considered major factors controlling the production of oil and gas. Therefore, it is important to detect fractures in oil and gas reservoirs. Of the various geophysical methods, seismic methods are particularly attractive for fracture detection and imaging because of the sensitivity of elastic waves to the mechanical compliance associated with fractures. Based on the effects of fracture on the velocities and amplitudes of seismic waves, several studies have shown the potential for using seismic tomography and vertical seismic profiling (VSP) techniques to characterize fracture systems in reservoirs. In this thesis, seismic wave propagation through a fracture system is numerically investigated by the finite-difference method. When seismic waves propagate in a medium with single fractures of infinite and finite length, the head wave and the dispersive interface waves (symmetric and antisymmetric modes) along the fracture are strongly excited by the explosion source if the seismic source is moved close to the fracture with low stiffness. In a fracture waveguide, fracture channel waves are supported by the waveguide, even in the absence of a velocity contrast between the fracture waveguide and surrounding host rock. The particular modes generated strongly depend on the polarization of the seismic source. When the seismic source is vertically (horizontally) polarized, antisymmetric (symmetric) modes are excited. In addition, if the thickness of the fracture waveguide increases, a complex particle motion of the fracture channel waves develops because the fracture channel waves partly couple with the interface waves along the fractures. For seismic wave propagation through a multi-fracture system consisting of equally spaced fractures, both an explicit fracture model and an equivalent transversely isotropic (TI) medium model were used to model the fracture system. In comparison to
Voronoi based microstructure modelling for elastic wave propagation
NASA Astrophysics Data System (ADS)
Shivaprasad, S.; Balasubramaniam, Krishnan; Krishnamurthy, C. V.
2016-02-01
Ultrasonic assessment of materials and defects are affected by microstructural parameters like grain size and texture. When a beam of ultrasound propagates in a polycrystalline medium, it undergoes extensive scattering by grains, grain boundaries and other microstructural features such as dislocations, voids, micro cracks etc. To understand the role of anisotropy and grain size distribution on an ultrasonic beam, a model system is proposed for carrying out ultrasonic wave propagation in a model characterized by grain size distribution and grain orientation distribution. A 2D polycrystalline medium constructed using Voronoi tessellations with a specific grain size distribution is considered and orientational averaging studies are carried out.
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
Constitutive modeling for blast-induced wave propagation
NASA Astrophysics Data System (ADS)
Drumm, E. C.
1985-03-01
The description of stress-time history acting on a buried structure is a major source of error in the analysis of underground structures to weapons loadings. The stress wave propagating spherically from the weapon is attenuated as it travels from the source. This attenuation is a function of the inelastic response of the soil, and results in an increase in the loading rise time or decrease in the loading rate. Since the inelastic soil response is a function of the loading rate, a wave propagation analysis should be conducted to determine the stresses on the structure. At the interface between the soil and structure, the stress is modified further by soil-structure interaction effects. Thus, the stress on the structure is a function of both the structural and soil properties as well as the distance traveled by the stress wave. These related phenomena can be included in a numerical analysis, but the accuracy depends on the constitutive representation of the materials. One-dimensional wave propagation experiments and impact tests with various soils are reviewed, and the attenuation as a function of the soil stress-strain response is discussed.
Homogenized Tomographic Models: a Tool for Efficient Numerical Modeling of Seismic Wave Propagation
NASA Astrophysics Data System (ADS)
Landes, M.; Capdeville, Y.; Shapiro, N.; Guilbert, J.
2013-12-01
Full seismic waveforms are frequently used to characterize details of seismic sources and to discriminate their origin. Prediction of realistic waveforms requires developing algorithms for fast and reliable simulation of seismic wave propagation in 3D models of Earth. Classical 3D seismic tomographic models often use a layered parameterization. However, computing exact wave propagation in layered models may result in mesh complexity and long computing time. These difficulties become crucial when considering regional scales with operational interests. The aim of our study is to develop a parameterization of seismic tomographic models adapted for efficient numerical modeling of the wave propagation within a given frequency range. We use a 'homogenization' approach to construct models smoothed at scale naturally imposed by their propagation characteristics at target frequencies. We start with defining a basis of continuous and smooth functions with a Principal Component Analysis based on the statistic of the homogenized CUB2 tomographic model. Then, we invert surface phase and the group velocities deduced from global tomographic maps with a Monte Carlo method to generate smooth depth profiles with a controlled number of unknowns at all grid points. The set of these profiles form a smooth 3D seismic velocity model designed for numerical wave propagation.
Extraction of near-surface properties for a lossy layered medium using the propagator matrix
Mehta, K.; Snieder, R.; Graizer, V.
2007-01-01
Near-surface properties play an important role in advancing earthquake hazard assessment. Other areas where near-surface properties are crucial include civil engineering and detection and delineation of potable groundwater. From an exploration point of view, near-surface properties are needed for wavefield separation and correcting for the local near-receiver structure. It has been shown that these properties can be estimated for a lossless homogeneous medium using the propagator matrix. To estimate the near-surface properties, we apply deconvolution to passive borehole recordings of waves excited by an earthquake. Deconvolution of these incoherent waveforms recorded by the sensors at different depths in the borehole with the recording at the surface results in waves that propagate upwards and downwards along the array. These waves, obtained by deconvolution, can be used to estimate the P- and S-wave velocities near the surface. As opposed to waves obtained by cross-correlation that represent filtered version of the sum of causal and acausal Green's function between the two receivers, the waves obtained by deconvolution represent the elements of the propagator matrix. Finally, we show analytically the extension of the propagator matrix analysis to a lossy layered medium for a special case of normal incidence. ?? 2007 The Authors Journal compilation ?? 2007 RAS.
Large-scale spatiotemporal spike patterning consistent with wave propagation in motor cortex.
Takahashi, Kazutaka; Kim, Sanggyun; Coleman, Todd P; Brown, Kevin A; Suminski, Aaron J; Best, Matthew D; Hatsopoulos, Nicholas G
2015-01-01
Aggregate signals in cortex are known to be spatiotemporally organized as propagating waves across the cortical surface, but it remains unclear whether the same is true for spiking activity in individual neurons. Furthermore, the functional interactions between cortical neurons are well documented but their spatial arrangement on the cortical surface has been largely ignored. Here we use a functional network analysis to demonstrate that a subset of motor cortical neurons in non-human primates spatially coordinate their spiking activity in a manner that closely matches wave propagation measured in the beta oscillatory band of the local field potential. We also demonstrate that sequential spiking of pairs of neuron contains task-relevant information that peaks when the neurons are spatially oriented along the wave axis. We hypothesize that the spatial anisotropy of spike patterning may reflect the underlying organization of motor cortex and may be a general property shared by other cortical areas. PMID:25994554
Large-scale spatiotemporal spike patterning consistent with wave propagation in motor cortex
Takahashi, Kazutaka; Kim, Sanggyun; Coleman, Todd P.; Brown, Kevin A.; Suminski, Aaron J.; Best, Matthew D.; Hatsopoulos, Nicholas G.
2015-01-01
Aggregate signals in cortex are known to be spatiotemporally organized as propagating waves across the cortical surface, but it remains unclear whether the same is true for spiking activity in individual neurons. Furthermore, the functional interactions between cortical neurons are well documented but their spatial arrangement on the cortical surface has been largely ignored. Here we use a functional network analysis to demonstrate that a subset of motor cortical neurons in non-human primates spatially coordinate their spiking activity in a manner that closely matches wave propagation measured in the beta oscillatory band of the local field potential. We also demonstrate that sequential spiking of pairs of neuron contains task-relevant information that peaks when the neurons are spatially oriented along the wave axis. We hypothesize that the spatial anisotropy of spike patterning may reflect the underlying organization of motor cortex and may be a general property shared by other cortical areas. PMID:25994554
Multichannel analysis of surface waves
Park, C.B.; Miller, R.D.; Xia, J.
1999-01-01
The frequency-dependent properties of Rayleigh-type surface waves can be utilized for imaging and characterizing the shallow subsurface. Most surface-wave analysis relies on the accurate calculation of phase velocities for the horizontally traveling fundamental-mode Rayleigh wave acquired by stepping out a pair of receivers at intervals based on calculated ground roll wavelengths. Interference by coherent source-generated noise inhibits the reliability of shear-wave velocities determined through inversion of the whole wave field. Among these nonplanar, nonfundamental-mode Rayleigh waves (noise) are body waves, scattered and nonsource-generated surface waves, and higher-mode surface waves. The degree to which each of these types of noise contaminates the dispersion curve and, ultimately, the inverted shear-wave velocity profile is dependent on frequency as well as distance from the source. Multichannel recording permits effective identification and isolation of noise according to distinctive trace-to-trace coherency in arrival time and amplitude. An added advantage is the speed and redundancy of the measurement process. Decomposition of a multichannel record into a time variable-frequency format, similar to an uncorrelated Vibroseis record, permits analysis and display of each frequency component in a unique and continuous format. Coherent noise contamination can then be examined and its effects appraised in both frequency and offset space. Separation of frequency components permits real-time maximization of the S/N ratio during acquisition and subsequent processing steps. Linear separation of each ground roll frequency component allows calculation of phase velocities by simply measuring the linear slope of each frequency component. Breaks in coherent surface-wave arrivals, observable on the decomposed record, can be compensated for during acquisition and processing. Multichannel recording permits single-measurement surveying of a broad depth range, high levels of
Numerical modeling of nonlinear acoustic-gravity wave propagation in the whole atmosphere
NASA Astrophysics Data System (ADS)
Gavrilov, Nikolai M.; Kshevetskii, Sergey P.
According to present knowledge, acoustic-gravity waves (AGWs) observed in the upper atmosphere may be generated near the Earth surface due to different sources and propagate upwards. Algorithms for two- and three-dimensional numerical simulation of vertical propagation and breaking of nonlinear AGWs from the Earth's surface to the upper atmosphere were developed recently. The algorithms of the solution of fluid dynamic equations use finite-difference analogues of basic conservation laws. This approach allows us to select physically correct generalized wave solutions of the nonlinear equations. Horizontally moving periodical horizontal sinusoidal structures of vertical velocity on the Earth’s surface serve as AGW sources in the model. Numerical simulation was made in a region of the Earth atmosphere with dimensions up to several thousand kilometers horizontally and 500 km vertically. Vertical profiles of the mean temperature, density, molecular viscosity and thermal conductivity are specified from standard models of the atmosphere. Calculations are made for different amplitudes, horizontal wavelengths and speeds of wave sources at the bottom boundary of the model. It is shown that after “switch on” tropospheric source atmospheric waves very quickly (for several minutes) may propagate to high altitudes (up to 100 km). When AGW amplitudes increase with height, waves may break down in the middle and upper atmosphere. Instability and dissipation of wave energy may lead to formations of wave accelerations of the mean winds and to creations of wave-induced jet flows in the middle and upper atmosphere. Nonlinear interactions may lead to instabilities of the initial wave and to the creation of smaller-scale structures. These smaller inhomogeneities may increase temperature and wind gradients and enhance the wave energy dissipation. Thus, the increase in AGW amplitudes in the upper atmosphere may occur at a much slower pace than the increase in amplitudes of
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.
Experimental study of wave propagation dynamics of binary distillation columns
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.
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.
Mapping of spin wave propagation in a one-dimensional magnonic crystal
NASA Astrophysics Data System (ADS)
Ordóñez-Romero, César L.; Lazcano-Ortiz, Zorayda; Drozdovskii, Andrey; Kalinikos, Boris; Aguilar-Huerta, Melisa; Domínguez-Juárez, J. L.; Lopez-Maldonado, Guillermo; Qureshi, Naser; Kolokoltsev, Oleg; Monsivais, Guillermo
2016-07-01
The formation and evolution of spin wave band gaps in the transmission spectrum of a magnonic crystal have been studied. A time and space resolved magneto inductive probing system has been used to map the spin wave propagation and evolution in a geometrically structured yttrium iron garnet film. Experiments have been carried out using (1) a chemically etched magnonic crystal supporting the propagation of magnetostatic surface spin waves, (2) a short microwave pulsed excitation of the spin waves, and (3) direct spin wave detection using a movable magneto inductive probe connected to a synchronized fast oscilloscope. The results show that the periodic structure not only modifies the spectra of the transmitted spin waves but also influences the distribution of the spin wave energy inside the magnonic crystal as a function of the position and the transmitted frequency. These results comprise an experimental confirmation of Bloch's theorem in a spin wave system and demonstrate good agreement with theoretical observations in analogue phononic and photonic systems. Theoretical prediction of the structured transmission spectra is achieved using a simple model based on microwave transmission lines theory. Here, a spin wave system illustrates in detail the evolution of a much more general physical concept: the band gap.
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.
High-order Two-way Artificial Boundary Conditions for Nonlinear Wave Propagation with Backscattering
NASA Technical Reports Server (NTRS)
Fibich, Gadi; Tsynkov, Semyon
2000-01-01
When solving linear scattering problems, one typically first solves for the impinging wave in the absence of obstacles. Then, by linear superposition, the original problem is reduced to one that involves only the scattered waves driven by the values of the impinging field at the surface of the obstacles. In addition, when the original domain is unbounded, special artificial boundary conditions (ABCs) that would guarantee the reflectionless propagation of waves have to be set at the outer boundary of the finite computational domain. The situation becomes conceptually different when the propagation equation is nonlinear. In this case the impinging and scattered waves can no longer be separated, and the problem has to be solved in its entirety. In particular, the boundary on which the incoming field values are prescribed, should transmit the given incoming waves in one direction and simultaneously be transparent to all the outgoing waves that travel in the opposite direction. We call this type of boundary conditions two-way ABCs. In the paper, we construct the two-way ABCs for the nonlinear Helmholtz equation that models the laser beam propagation in a medium with nonlinear index of refraction. In this case, the forward propagation is accompanied by backscattering, i.e., generation of waves in the direction opposite to that of the incoming signal. Our two-way ABCs generate no reflection of the backscattered waves and at the same time impose the correct values of the incoming wave. The ABCs are obtained for a fourth-order accurate discretization to the Helmholtz operator; the fourth-order grid convergence is corroborated experimentally by solving linear model problems. We also present solutions in the nonlinear case using the two-way ABC which, unlike the traditional Dirichlet boundary condition, allows for direct calculation of the magnitude of backscattering.
Electromagnetic wave propagation in a random distribution of C{sub 60} molecules
Moradi, Afshin
2014-10-15
Propagation of electromagnetic waves in a random distribution of C{sub 60} molecules are investigated, within the framework of the classical electrodynamics. Electronic excitations over the each C{sub 60} molecule surface are modeled by a spherical layer of electron gas represented by two interacting fluids, which takes into account the different nature of the π and σ electrons. It is found that the present medium supports four modes of electromagnetic waves, where they can be divided into two groups: one group with shorter wavelength than the light waves of the same frequency and the other with longer wavelength than the free-space radiation.
Seismic wave propagation in fully anisotropic axisymmetric media
NASA Astrophysics Data System (ADS)
van Driel, Martin; Nissen-Meyer, Tarje
2014-11-01
We present a numerical method to compute 3-D elastic waves in fully anisotropic axisymmetric media. This method is based on a decomposition of the wave equation into a series of uncoupled 2-D equations for which the dependence of the wavefield on the azimuth can be solved analytically. Four independent equations up to quadrupole order appear as solutions for moment-tensor sources located on the symmetry axis while single forces can be accommodated by two separate solutions up to dipole order. This decomposition gives rise to an efficient solution of the 3-D wave equation in a 2-D axisymmetric medium. First, we prove the validity of the decomposition of the wavefield in the presence of general anisotropy. Then we use it to derive the reduced 2-D equations of motions and discretize them using the spectral element method. Finally, we benchmark the numerical implementation for global wave propagation at 1 Hz and consider inner core anisotropy as an application for high-frequency wave propagation in anisotropic media at frequencies up to 2 Hz.
High Harmonic Fast Wave Propagation and Heating on NSTX
NASA Astrophysics Data System (ADS)
Parker, J. B.; Phillips, C. K.; Hosea, J. C.; Valeo, E. J.; Wilson, J. R.; Harvey, R. W.
2007-11-01
Recent experiments on the National Spherical Torus Experiment (NSTX) show that the high harmonic fast wave (HHFW) core heating efficiency depends on the antenna phasing and plasma conditions. [1]. Power losses in the edge due to rf sheath formation or other parasitic absorption processes could occur if the waves propagate nearly parallel to the wall in the edge regions and intersect nearby vessel structures. To investigate this possibility, the 3D HHFW propagation in NSTX has been studied both analytically and numerically with the ray tracing code GENRAY. Initial calculations show that for certain values of the launched parallel wave number and magnetic field, the waves in NSTX are launched at a shallow angle to the vessel wall. In contrast, for ICRF heating in C-Mod or ITER, the initial ray trajectories tend to be more radially oriented. Comparisons of the GENRAY results with 2D TORIC full wave simulations for the power deposition will also be discussed. [1] See invited talk by J. C. Hosea this meeting.
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.
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.
Backward propagating acoustic waves in single gold nanobeams
NASA Astrophysics Data System (ADS)
Jean, Cyril; Belliard, Laurent; Becerra, Loïc; Perrin, Bernard
2015-11-01
Femtosecond pump-probe spectroscopy has been carried out on suspended gold nanostructures with a rectangular cross section lithographed on a silicon substrate. With a thickness fixed to 110 nm and a width ranging from 200 nm to 800 nm , size dependent measurements are used to distinguish which confined acoustic modes are detected. Furthermore, in order to avoid any ambiguity due to the measurement uncertainties on both the frequency and size, pump and probe beams are also spatially shifted to detect guided acoustic phonons. This leads us to the observation of backward propagating acoustic phonons in the gigahertz range ( ˜3 GHz ) in such nanostructures. While backward wave propagation in elastic waveguides has been predicted and already observed at the macroscale, very few studies have been done at the nanoscale. Here, we show that these backward waves can be used as the unique signature of the width dilatational acoustic mode.
Numerical modelling of nonlinear full-wave acoustic propagation
NASA Astrophysics Data System (ADS)
Velasco-Segura, Roberto; Rendón, Pablo L.
2015-10-01
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.
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.
Numerical modelling of nonlinear full-wave acoustic propagation
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.
Wave propagation modeling with non-Markov phase screens.
Charnotskii, Mikhail
2016-04-01
A recently introduced [J. Opt. Soc. Am. A30, 479 (2013)10.1364/JOSAA.30.000479JOAOD61084-7529] sparse spectrum (SS) model of statistically homogeneous random fields makes it possible to generate 3D samples of refractive-index fluctuations with prescribed spectral density at a very reasonable computational cost. The SS technique can be used in the framework of the split-step Fourier method for numerical simulation of wave propagation in turbulence. It allows generation of the phase screen samples that are free from the limitations of the Markov approximation, which is commonly used for theoretical description and numerical modeling of optical waves propagation through turbulence. We investigate statistics of these phase screens and present a numerical algorithm for their generation. PMID:27140765
Studies of the propagation of Low Frequency (LF) radio waves
NASA Astrophysics Data System (ADS)
Warrington, E. M.; Jones, T. B.
1993-05-01
Low frequency (30-300 kHz) radio waves can propagate to great distances with little attenuation in the cavity formed by the earth and the ionosphere. Because of the relatively high frequency at LF, many active propagation modes can occur between the transmitter and receiver. Changes in the ionospheric conductivity or reflection height can influence the phase and amplitude of these modes and, hence, produce mutual interference. Because of these interference effects, the propagation is less stable than at VLF and the received field strength becomes more difficult to predict. In the present investigation, the WAVEHOP program was employed in conjunction with a range of ionospheric models to estimate the receiver field strength over a number of experimental paths. The predicted values were compared with those measured in an attempt to validate the ionospheric models and the method of calculation.
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.
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.
Size-Dependent Behavior of Love Wave Propagation in a Nanocoating
NASA Astrophysics Data System (ADS)
Li, Yong-Dong; Lee, Kang-Yong
The effect of surface/interface stress on mechanical behaviors may become remarkable when the characteristic size of a structure decreases to nanoscale. Various problems have been analyzed to reveal the size-dependent mechanical behaviors of nano structures with curved surfaces/interfaces. In this work, the problem of planar surfaces/interfaces is addressed. The generalized Young-Laplace equation is presented for a planar interface and the propagation behavior of Love wave in a nanocoating is discussed. Parametric studies indicate that if the surface effect of the nanocoating is considered the phase velocity of Love wave shows notable size-dependency on both the nanocoating thickness and the wavelength. When these two sizes are both in nanoscale, the phase velocity further depends on the relative size between them. In addition, increasing the residual surface stress may reduce the phase velocity of Love wave.
Frequency and wavelength prediction of ultrasonic induced liquid surface waves.
Mahravan, Ehsan; Naderan, Hamid; Damangir, Ebrahim
2016-12-01
A theoretical investigation of parametric excitation of liquid free surface by a high frequency sound wave is preformed, using potential flow theory. Pressure and velocity distributions, resembling the sound wave, are applied to the free surface of the liquid. It is found that for impinging wave two distinct capillary frequencies will be excited: One of them is the same as the frequency of the sound wave, and the other is equal to the natural frequency corresponding to a wavenumber equal to the horizontal wavenumber of the sound wave. When the wave propagates in vertical direction, mathematical formulation leads to an equation, which has resonance frequency equal to half of the excitation frequency. This can explain an important contradiction between the frequency and the wavelength of capillary waves in the two cases of normal and inclined interaction of the sound wave and the free surface of the liquid. PMID:27566141
Simplified theory of large-amplitude wave propagation
NASA Technical Reports Server (NTRS)
Kim, H.
1976-01-01
An orbit perturbation procedure was applied to the description of monochromatic, large-amplitude, electrostatic plasma wave propagation. In the lowest order approximation, untrapped electrons were assumed to follow constant-velocity orbits and trapped electrons were assumed to execute simple harmonic motion. The deviations of these orbits from the actual orbits were regarded as perturbations. The nonlinear damping rate and frequency shift were then obtained in terms of simple functions. The results are in good agreement with previous less approximate analyses.
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.
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.
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.
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.
The effect of microscale random Alfven waves on the propagation of large-scale Alfven waves
NASA Astrophysics Data System (ADS)
Namikawa, T.; Hamabata, H.
1983-04-01
The ponderomotive force generated by random Alfven waves in a collisionless plasma is evaluated taking into account mean magnetic and velocity shear and is expressed as a series involving spatial derivatives of mean magnetic and velocity fields whose coefficients are associated with the helicity spectrum function of random velocity field. The effect of microscale random Alfven waves through ponderomotive and mean electromotive forces generated by them on the propagation of large-scale Alfven waves is also investigated.
Equivalent Continuum Modeling for Shock Wave Propagation in Jointed Media
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.
Instability and Wave Propagation in Structured 3D Composites
NASA Astrophysics Data System (ADS)
Kaynia, Narges; Fang, Nicholas X.; Boyce, Mary C.
2014-03-01
Many structured composites found in nature possess undulating and wrinkled interfacial layers that regulate mechanical, chemical, acoustic, adhesive, thermal, electrical and optical functions of the material. This research focused on the complex instability and wrinkling pattern arising in 3D structured composites and the effect of the buckling pattern on the overall structural response. The 3D structured composites consisted of stiffer plates supported by soft matrix on both sides. Compression beyond the critical strain led to complex buckling patterns in the initially straight plates. The motivation of our work is to elaborate the formation of a system of prescribed periodic scatterers (metamaterials) due to buckling, and their effect to interfere wave propagation through the metamaterial structures. Such metamaterials made from elastomers enable large reversible deformation and, as a result, significant changes of the wave propagation properties. We developed analytical and finite element models to capture various aspects of the instability mechanism. Mechanical experiments were designed to further explore the modeling results. The ability to actively alter the 3D composite structure can enable on-demand tunability of many different functions, such as active control of wave propagation to create band-gaps and waveguides.
Scattered surface wave energy in the seismic coda
Zeng, Y.
2006-01-01
One of the many important contributions that Aki has made to seismology pertains to the origin of coda waves (Aki, 1969; Aki and Chouet, 1975). In this paper, I revisit Aki's original idea of the role of scattered surface waves in the seismic coda. Based on the radiative transfer theory, I developed a new set of scattered wave energy equations by including scattered surface waves and body wave to surface wave scattering conversions. The work is an extended study of Zeng et al. (1991), Zeng (1993) and Sato (1994a) on multiple isotropic-scattering, and may shed new insight into the seismic coda wave interpretation. The scattering equations are solved numerically by first discretizing the model at regular grids and then solving the linear integral equations iteratively. The results show that scattered wave energy can be well approximated by body-wave to body wave scattering at earlier arrival times and short distances. At long distances from the source, scattered surface waves dominate scattered body waves at surface stations. Since surface waves are 2-D propagating waves, their scattered energies should in theory follow a common decay curve. The observed common decay trends on seismic coda of local earthquake recordings particular at long lapse times suggest that perhaps later seismic codas are dominated by scattered surface waves. When efficient body wave to surface wave conversion mechanisms are present in the shallow crustal layers, such as soft sediment layers, the scattered surface waves dominate the seismic coda at even early arrival times for shallow sources and at later arrival times for deeper events.
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
Propagation of extensional waves in a piezoelectric semiconductor rod
NASA Astrophysics Data System (ADS)
Zhang, C. L.; Wang, X. Y.; Chen, W. Q.; Yang, J. S.
2016-04-01
We studied the propagation of extensional waves in a thin piezoelectric semiconductor rod of ZnO whose c-axis is along the axis of the rod. The macroscopic theory of piezoelectric semiconductors was used which consists of the coupled equations of piezoelectricity and the conservation of charge. The problem is nonlinear because the drift current is the product of the unknown electric field and the unknown carrier density. A perturbation procedure was used which resulted in two one-way coupled linear problems of piezoelectricity and the conservation of charge, respectively. The acoustic wave and the accompanying electric field were obtained from the equations of piezoelectricity. The motion of carriers was then determined from the conservation of charge using a trigonometric series. It was found that while the acoustic wave was approximated by a sinusoidal wave, the motion of carriers deviates from a sinusoidal wave qualitatively because of the contributions of higher harmonics arising from the originally nonlinear terms. The wave crests become higher and sharper while the troughs are shallower and wider. This deviation is more pronounced for acoustic waves with larger amplitudes.
CIP-MOC Modeling of Seismic Wave Propagation in Elastic Media
NASA Astrophysics Data System (ADS)
Yoshimi, M.
2004-12-01
In many fields such as hydrodynamics and MHD, the CIP method, an upwind difference hyperbolic equation solver, has widely been employed for advection calculation. The CIP scheme was constructed considering that an advected property and its spatial derivative follow same advection equation. This effects low numerical dispersion and relaxed CFL condition in the advection calculation. In the present work, we developed a CIP-MOC (CIP with method of characteristics) scheme for seismic wave propagation in 3D elastic heterogeneous media with flat free surface. 3D elastic wave equations in velocity-stress formulation and their spatial derivatives, as well, are converted into sets of 1D advection equations and non-advection equations for each direction (x,y,z in Cartesian coodinate system) with the method of characteristics. Since the Riemann invariant of each advection equation consists of stress and velocity, updatings of velocity and stress are simultaneous and a collocated grid system is employed. A free surface is modeled as a zero-stress surface. A reflection free boundary is installed by considering no incident wave comes from outside of the boundary. A double coupled seismic point source is introduced as external point stresses. Overall scheme is made up of multiphases employing time-splitting and directional-splitting techniques. Each time step is composed of three directional updating phases each for wave propagation in x, y and z direction. Each directional updating phase is made up of advection phase and non-advection phase. In the advection phase, advection equations are solved with the CIP method. In the non-advection phases, non-advetion equations and boundary conditions are evaluated with central finite differences. We conducted CIP-MOC seismic wave propagation simulations in a half-space, layered and fully heterogeneous media for embedded point source. By comparing our products with those produced with discrete wavenumber method and finite difference method
A computational study of laser-supported detonation waves propagating up an oblique incident beam
NASA Astrophysics Data System (ADS)
Bohn, C. L.; Crawford, M. L.
1987-01-01
A series of numerical experiments was conducted to study the propagation of laser-supported detonation waves (LSDWs) in the case that a CO2 laser beam strikes an aluminum surface obliquely in air. A reflected shock formed at the aluminum surface was more prominent at higher angles of incidence theta of the beam, but otherwise the hydrodynamics of the plasma and the LSDW were insensitive to theta. Furthermore, the total impulse delivered to the aluminum varied approximately as 1/cos theta, a result that can be modeled with elementary blast-wave theory.
Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals
Stavroula Foteinopoulou
2003-12-12
In this dissertation, they have undertaken the challenge to understand the unusual propagation 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 propagation is prohibited (gaps) and regions where propagation 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 wave 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
Resonance wave pumping with surface waves
NASA Astrophysics Data System (ADS)
Carmigniani, Remi; Gharib, Morteza; Violeau, Damien; Caltech-ENPC Collaboration
2015-11-01
The valveless impedance pump enables the production or amplification of a flow without the use of integrated mobile parts, thus delaying possible failures. It is usually composed of fluid-filled flexible tubing, closed by solid tubes. The flexible tube is pinched at an off-centered position relative to the tube ends. This generates a complex wave dynamic that results in a pumping phenomenon. It has been previously reported that pinching at intrinsic resonance frequencies of the system results in a strong pulsating flow. A case of a free surface wave pump is investigated. The resonance wave pump is composed of a rectangular tank with a submerged plate separating the water into a free surface and a recirculation rectangular section connected through two openings at each end of the tank. A paddle placed at an off-center position above the submerged plate is controlled in a heaving motion with different frequencies and amplitudes. Similar to the case of valveless impedance pump, we observed that near resonance frequencies strong pulsating flow is generated with almost no oscillations. A linear theory is developed to pseudo-analytically evaluate these frequencies. In addition, larger scale applications were simulated using Smoothed Particle Hydrodynamic codes.
Distortion of surface plasmon polariton propagation on graphene due to chemical potential variation
NASA Astrophysics Data System (ADS)
Amanatiadis, Stamatios; Kantartzis, Nikolaos
2016-04-01
The variation of graphene chemical potential owing to surface plasmon polariton excitation and its influence on the propagation properties of the latter is systematically examined in this paper. Although the chemical potential is controlled via a constant electric field bias, the excitation of the highly confined surface wave can considerably affect it, thus disrupting the wave natural propagation. To this aim, the propagation properties of the surface wave are extracted to reliably estimate the aforesaid distortion effect with regard to frequency. Numerical results, obtained in terms of an accurate finite-difference time-domain scheme, certify this interesting convention. Furthermore, the electrodynamic forces on the free electrons of the graphene layer are calculated to justify the electrostatic assumption.
Study on the electromagnetic waves propagation characteristics in partially ionized plasma slabs
NASA Astrophysics Data System (ADS)
Wang, Zhi-Bin; Li, Bo-Wen; Nie, Qiu-Yue; Wang, Xiao-Gang; Kong, Fan-Rong
2016-05-01
Propagation characteristics of electromagnetic (EM) waves in partially ionized plasma slabs are studied in this paper. Such features are significant to applications in plasma antennas, blackout of re-entry flying vehicles, wave energy injection to plasmas, and etc. We in this paper developed a theoretical model of EM wave propagation perpendicular to a plasma slab with a one-dimensional density inhomogeneity along propagation direction to investigate essential characteristics of EM wave propagation in nonuniform plasmas. Particularly, the EM wave propagation in sub-wavelength plasma slabs, where the geometric optics approximation fails, is studied and in comparison with thicker slabs where the geometric optics approximation applies. The influences of both plasma and collisional frequencies, as well as the width of the plasma slab, on the EM wave propagation characteristics are discussed. The results can help the further understanding of propagation behaviours of EM waves in nonuniform plasma, and applications of the interactions between EM waves and plasmas.
Experiment to Study Alfven Wave Propagation in Plasma Loops
NASA Astrophysics Data System (ADS)
Kendall, Mark; Bellan, Paul
2010-11-01
Arched plasma-filled twisted magnetic flux tubes are generated in the laboratory using pulsed power techniques (J.F. Hansen, S.K.P. Tripathi, P.M. Bellan, 2004). Their structure and time evolution exhibit similarities with both solar coronal loops and spheromaks. We are now developing a method to excite propagating torsional Alfven wave modes in such plasma loops by superposing a ˜10kA, ˜100ns current pulse upon the ˜50kA, 10μs main discharge current that flows along the ˜20cm long, 2cm diameter arched flux tube. To achieve this high power 100ns pulse, a magnetic pulse compression technique based on saturable reactors is employed. A low power prototype has been successfully tested, and design and construction of a full-power device is nearing completion. The full-power device will compress an initial 2μs pulse by a factor of nearly 20; the final stage utilizes a water-filled transmission line with ultra-low inductance to attain the final timescale. This new pulse device will subsequently be used to investigate interactions between Alfven waves and the larger-scale loop evolution; one goal will be to directly image the wave using high-speed photography. Attention will be paid to wave propagation including dispersion and reflection, as well as dissipation mechanisms and possible energetic particle generation.
NASA Astrophysics Data System (ADS)
Song, Fei
Honeycomb sandwich structures have been widely used in marine and aerospace applications due to their high strength/stiffness-to-weight ratio. However, an excessive load or repeated loading in the core tends to induce debonding along the skin-core interface, threatening the integrity and safety of the whole structure. This dissertation focuses on development of guided wave strategies for health monitoring of honeycomb sandwich structures, based on a piezoelectric actuator/sensor network. The honeycomb sandwich panels, which are composed of aluminum alloy (T6061) skins and hexagonal-celled Nomex core, are specifically considered in the study. First, elastic wave propagation mechanism in honeycomb sandwich structures is numerically and experimentally investigated, based on a piezoelectric actuator/sensor system. Influences of cell geometry parameters upon wave propagation are also discussed. Some wave propagation characteristics, such as wave group velocity dispersion relation and mode tuning capabilities, in the honeycomb composite panels are experimentally characterized. Secondly, effects of skin-core debonding upon the leaky guided wave propagation in honeycomb sandwich structures are studied by the finite element simulation. An appropriate signal difference coefficient is defined to represent the differential features caused by debonding. By means of probability analysis of differential features of transmitted guided waves and the image fusion, the final image of the structure is constructed with improved detection precision. A multilevel sensor network strategy is proposed to detect multiple debondings in the honeycomb sandwich structure. Thirdly, an analytical model considering coupled piezo-elastodynamics is developed to quantitatively describe dynamic load transfer between a surface-bonded piezoelectric wafer actuator and a prestressed plate. The finite element method is used to evaluate the accuracy of the analytical prediction. Effects of prestresses on the
Efficient techniques for wave-based sound propagation in interactive applications
NASA Astrophysics Data System (ADS)
Mehra, Ravish
Sound propagation techniques model the effect of the environment on sound waves and predict their behavior from point of emission at the source to the final point of arrival at the listener. Sound is a pressure wave produced by mechanical vibration of a surface that propagates through a medium such as air or water, and the problem of sound propagation can be formulated mathematically as a second-order partial differential equation called the wave equation. Accurate techniques based on solving the wave equation, also called the wave-based techniques, are too expensive computationally and memory-wise. Therefore, these techniques face many challenges in terms of their applicability in interactive applications including sound propagation in large environments, time-varying source and listener directivity, and high simulation cost for mid-frequencies. In this dissertation, we propose a set of efficient wave-based sound propagation techniques that solve these three challenges and enable the use of wave-based sound propagation in interactive applications. Firstly, we propose a novel equivalent source technique for interactive wave-based sound propagation in large scenes spanning hundreds of meters. It is based on the equivalent source theory used for solving radiation and scattering problems in acoustics and electromagnetics. Instead of using a volumetric or surface-based approach, this technique takes an object-centric approach to sound propagation. The proposed equivalent source technique generates realistic acoustic effects and takes orders of magnitude less runtime memory compared to prior wave-based techniques. Secondly, we present an efficient framework for handling time-varying source and listener directivity for interactive wave-based sound propagation. The source directivity is represented as a linear combination of elementary spherical harmonic sources. This spherical harmonic-based representation of source directivity can support analytical, data
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.
ATS-F Comsat Millimeter Wave Propagation Experiment
NASA Technical Reports Server (NTRS)
Westerlund, L. H.; Levatich, J. L.; Buige, A.
1973-01-01
The ATS-F Comsat Millimeter Wave Propagation Experiment has been designed to gather statistical data on the attenuation caused by rain at millimeter wave frequencies. These data will be used to determine system design parameters for future communications satellite systems operating at frequencies above 10 GHz. The experiment has 39 ground terminals transmitting at 13.2 or 17.8 GHz to a transponder on board the ATS-F satellite. The transponder retransmits these signals at 4 GHz to a central earth terminal which records their amplitudes once each second. The data will be analyzed to provide probabilities of attenuation as functions of parameters such as rainfall, location, and time. These probabilities can then be used to determine the required power margins of millimeter wave communications systems. Techniques of overcoming severe attenuation such as site diversity and the use of a spot beam to increase the power level at selected locations will also be evaluated.
Multiscale simulation of 2D elastic wave propagation
NASA Astrophysics Data System (ADS)
Zhang, Wensheng; Zheng, Hui
2016-06-01
In this paper, we develop the multiscale method for simulation of elastic wave propagation. Based on the first-order velocity-stress hyperbolic form of 2D elastic wave equation, the particle velocities are solved first ona coarse grid by the finite volume method. Then the stress tensor is solved by using the multiscale basis functions which can represent the fine-scale variation of the wavefield on the coarse grid. The basis functions are computed by solving a local problem with the finite element method. The theoretical formulae and description of the multiscale method for elastic wave equation are given in more detail. The numerical computations for an inhomogeneous model with random scatter are completed. The results show the effectiveness of the multiscale method.
Paraxial WKB Method Applied to the Lower Hybrid Wave Propagation
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.
Determination of particle size distributions from acoustic wave propagation measurements
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.}
Large amplitude compression and shear wave propagation in an elastomer
NASA Astrophysics Data System (ADS)
Gupta, Y. M.; Murri, W. J.; Henley, D.
1982-04-01
Experimental techniques have been developed to measure the high strain-rate compression and shear response of Solithane 113. Compression and shear wave profiles have been measured in specimens compressed to 20% (compressive stresses ˜1.2 GPa). The compressive profiles are nearly steady and the compressive stress-strain response is typical of a compliant material. The shear wave profiles are dispersive and show attenuation with propagation. Analyses of these wave profiles will be presented. Shear moduli vary from 0.35 GPa to 0.8 GPa for the compression range examined to date. These values are within a factor of two of the static shear moduli in the glassy state. The data described here have been used to calculate the high strain rate compressive and shear stress-strain curves for Solithane 113.
Holography with standing surface plasma waves
NASA Technical Reports Server (NTRS)
Cowan, J. J.
1974-01-01
Holography with standing surface plasma waves, where both reference and object beams propagate in opposite directions, has been investigated using an Al reflection grating coated with evaporated As2S3 layers. The image, which appears only for p-polarization and at certain critical angles, is enhanced by the Lippman-Bragg effect and by an increase in intensity over ordinary holography approximately equal to the absolute value of the real part of the dielectric constant for Al. Also considered is holography with object light alone in photoresist layers, using the beam-splitting properties of the grating.
Combined wave propagation analysis of earthquake recordings from borehole and building sensors
NASA Astrophysics Data System (ADS)
Petrovic, B.; Parolai, S.; Dikmen, U.; Safak, E.; Moldobekov, B.; Orunbaev, S.
2015-12-01
In regions highly exposed to natural hazards, Early Warning Systems can play a central role in risk management and mitigation procedures. To improve at a relatively low cost the spatial resolution of regional earthquake early warning (EEW) systems, decentralized onsite EEW and building monitoring, a wireless sensing unit, the Self-Organizing Seismic Early Warning Information Network (SOSEWIN) was developed and further improved to include the multi-parameter acquisition. SOSEWINs working in continuous real time mode are currently tested on various sites. In Bishkek and Istanbul, an instrumented building is located close to a borehole equipped with downhole sensors. The joint data analysis of building and borehole earthquake recordings allows the study of the behavior of the building, characteristics of the soil, and soil-structure interactions. The interferometric approach applied to recordings of the building response is particularly suitable to characterize the wave propagation inside a building, including the propagation velocity of shear waves and attenuation. Applied to borehole sensors, it gives insights into velocity changes in different layers, reflections and mode conversion, and allows the estimation of the quality factor Qs. We used combined building and borehole data from the two test sites: 1) to estimate the characteristics of wave propagation through the building to the soil and back, and 2) to obtain an empirical insight into soil-structure interactions. The two test sites represent two different building and soil types, and soil structure impedance contrasts. The wave propagation through the soil to the building and back is investigated by the joint interferometric approach. The propagation of up and down-going waves through the building and soil is clearly imaged and the reflection of P and S waves from the earth surface and the top of the building identified. An estimate of the reflected and transmitted energy amounts is given, too.
Deterministic forward scatter from surface gravity waves.
Deane, Grant B; Preisig, James C; Tindle, Chris T; Lavery, Andone; Stokes, M Dale
2012-12-01
Deterministic structures in sound reflected by gravity waves, such as focused arrivals and Doppler shifts, have implications for underwater acoustics and sonar, and the performance of underwater acoustic communications systems. A stationary phase analysis of the Helmholtz-Kirchhoff scattering integral yields the trajectory of focused arrivals and their relationship to the curvature of the surface wave field. Deterministic effects along paths up to 70 water depths long are observed in shallow water measurements of surface-scattered sound at the Martha's Vineyard Coastal Observatory. The arrival time and amplitude of surface-scattered pulses are reconciled with model calculations using measurements of surface waves made with an upward-looking sonar mounted mid-way along the propagation path. The root mean square difference between the modeled and observed pulse arrival amplitude and delay, respectively, normalized by the maximum range of amplitudes and delays, is found to be 0.2 or less for the observation periods analyzed. Cross-correlation coefficients for modeled and observed pulse arrival delays varied from 0.83 to 0.16 depending on surface conditions. Cross-correlation coefficients for normalized pulse energy for the same conditions were small and varied from 0.16 to 0.06. In contrast, the modeled and observed pulse arrival delay and amplitude statistics were in good agreement. PMID:23231099
NASA Astrophysics Data System (ADS)
Bernardino, M. J.; Jones, C. H.
2013-12-01
Past seismic studies attempting to image the lithosphere underneath the Sierra Nevada and to constrain the geometry of the upper mantle Isabella anomaly, a high wave-speed body underneath the western foothills of the range, have observed complex behavior in teleseismic and regional waveforms recorded at stations within the range. Notably, a 1993 teleseismic mini-array recorded multipath P-wave arrivals, topographic reflections, and scattered energy ~25 km west of the Sierran crest. These effects suggest wave propagation through strongly heterogeneous lithosphere complicated by near-surface phenomena. Multipathing and other complex wave propagation are indicative of strong variations in wavespeed, which in turn reflect structural complexity important in understanding the genesis of the Isabella anomaly. However, determining the extent of such propagative behavior in and underneath the Sierra Nevada has not been studied. We investigate the behavior of teleseismic P-waves using vertical-component receiver functions in an effort to better understand the extent of complex waveforms as a first tool in better constraining the geographic region(s) where sufficiently complex lithospheric structure exists. We expect that the presence of sufficiently high velocity gradients should result in P-wave multipath arrivals from events that skirt the perimeter of the Isabella anomaly from certain backazimuths. We deconvolve regionally beamed vertical P-waveforms from individual vertical component P-waves. This effectively recovers variability in the P waveforms that is normally lost in typical single-station radial- and transverse-component receiver function analyses. Vertical P-wave beams are constructed using dbxcor, a waveform correlation algorithm developed by G. Pavlis. Seismic data for the northern and central Sierra Nevada are from the 2005-2007 Sierra Nevada Earthscope Project (SNEP) and further supplemented by many permanent and temporary stations including the Earthscope
NASA Astrophysics Data System (ADS)
Shi, Yang; Kun-De, Yang; Yi-Xin, Yang; Yuan-Liang, Ma
2015-04-01
The evaporation duct which forms above the ocean surface has a significant influence on electromagnetic wave propagation above 2 GHz over the ocean. The effects of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation are investigated, both in numerical simulation and experimental observation methods, in this paper. Firstly, the features of the horizontal inhomogeneity of the evaporation duct are discussed. Then, two typical inhomogeneous cases are simulated and compared with the homogeneous case. The result shows that path loss is significantly higher than that in the homogeneous case when the evaporation duct height (EDH) at the receiver is lower than that at the transmitter. It is also concluded that the horizontal inhomogeneity of the evaporation duct has a significant influence when the EDH is low or when the electromagnetic wave frequency is lower than 13 GHz. Finally, experimental data collected on a 149-km long propagation path in the South China Sea in 2013 are used to verify the conclusion. The experimental results are consistent with the simulation results. The horizontal inhomogeneity of evaporation duct should be considered when modeling electromagnetic wave propagation over the ocean. Project supported by the National Natural Science Foundation of China (Grant No. 11174235) and the Fundamental Research Funds for the Central Universities (Grant No. 3102014JC02010301).
Phonon wave propagation in ballistic-diffusive regime
NASA Astrophysics Data System (ADS)
Tang, Dao-Sheng; Hua, Yu-Chao; Nie, Ben-Dian; Cao, Bing-Yang
2016-03-01
Wide applications of ultra-short pulse laser technique in micromachining and thermophysical properties' measurements make the study on ultrafast transient thermal transport necessarily essential. When the characteristic time is comparable to the phonon relaxation time, phonons propagate in ballistic-diffusive regime and thermal wave occurs. Here, ultrafast transient phonon transport is systematically investigated based on the Monte Carlo (MC) simulations, the Cattaneo-Vernotte (C-V) model, and the phonon Boltzmann transport equation (BTE). It is found that remarkable differences exist between the C-V model and the MC simulations when describing the evolution of the thermal wave excited by the ultra-short heat pulse. The C-V model predicts a non-dispersive dissipative thermal wave, while the MC simulation with Lambert emission predicts a dispersive dissipative thermal wave. Besides, different phonon emissions can significantly influence the evolution of the thermal wave in the MC simulations. A modified C-V model with a time- and position-dependent effective thermal conductivity is derived based on the phonon BTE to characterize the evolution of the transport regime from ballistic to diffusive. The integrations on moments of the distribution function cause the loss of the information of the phonon distribution in wave vector space, making the macroscopic quantities incomplete when describing the ballistic transport processes and corresponding boundary conditions. Possible boundary conditions for the phonon BTE in practice are also discussed on different heating methods.
Study of MHD Effects on Surface Waves in Liquid Gallium
NASA Astrophysics Data System (ADS)
Fox, W.; Ji, H.; Pace, D.; Rappaport, H.
2001-10-01
The liquid metal experiment (LMX) at the Princeton Plasma Physics Laboratory has been constructed to study magnetohydrodynamic (MHD) effects on the propagation of surface waves in liquid metals in an imposed horizontal magnetic field. The physics of liquid metal is of interest generally as a regime of small magnetic Reynolds number MHD and more specifically contributes basic knowledge to the applications of liquid lithium walls in a fusion reactor. Surface waves are driven by a wave driver controlled by a PC-based Labview system. A non-invasive diagnostic measures surface fluctuations at multiple locations accurately by reflecting an array of lasers off the surface and onto a screen recorded by an ICCD camera. The real part of the dispersion relation has been measured precisely and agrees well with a linear theory, revealing the role of surface oxidation. Experiments have also confirmed that a transverse magnetic field does not affect wave propagation, and have qualitatively observed MHD damping (a non-zero imaginary component of the dispersion relation) of waves propagating in a parallel magnetic field. Planned upgrades to LMX will enable quantitative measurement of this MHD damping rate as well as experiments on two-dimensional waves and nonlinear waves. Implications to the liquid metal wall concept in fusion reactors will be discussed.
NASA Astrophysics Data System (ADS)
Singh, Baljeet
2016-01-01
The present paper is concerned with the propagation of plane waves in a rotating, transversely isotropic, two-temperature generalized thermoelastic solid half-space without energy dissipation. The governing equations are solved to show the existence of three plane waves in the x-z plane. The reflection of these plane waves from a thermally insulated free surface is also studied to obtain a system of three non-homogeneous equations in reflection coefficients of the reflected waves. The speeds and reflection coefficients are computed for a particular model of the half-space. The speeds and reflection coefficients of plane waves are shown graphically to observe the effects of anisotropy, two temperatures and rotation.
Effect of beam pre-bunching on gain and efficiency in a surface wave-pumped free electron laser
NASA Astrophysics Data System (ADS)
Sharma, Suresh C.; Sharma, Jyotsna; Bhasin, Anuradha; Walia, Ritu; Walia
2012-12-01
A pre-bunched relativistic electron beam (REB) counter-propagating to the surface wave in the vacuum region Compton backscatters the surface wave into a high-frequency coherent radiation. Plasma supports the surface wave that acquires a large wave number k 0 z around pump wave frequency $\\omega _0 = {{\\omega _p } {/ {\\vphantom {{\\omega _p } {\\sqrt 2 }}} \\kern-\
Shallow seismic surface waves analysis across a tectonic fault
NASA Astrophysics Data System (ADS)
Gazdova, R.; Vilhelm, J.; Kolinsky, P.
2011-12-01
When performing a seismic survey of a shallow medium, we record wave motion which can be excited by a sledge hammer blow on the ground surface. The recorded wave motion is a complex combination of different types of waves, propagating directly from the source to the receiver, reflecting from velocity boundaries, passing through multiple layers or forming dispersive surface waves. We can use all of these wave types to identify the structure of the medium. In the presented contribution we deal with interpretation of surface waves. In contrast with body waves, the surface wave velocity is frequency-dependent. This property is called dispersion, and the dependence of the velocity on the frequency is known as the dispersion curve. The measured dispersion of the surface waves can be used to assess the structural velocity distribution in the layered medium, through which the waves propagate. We analyze surface waves recorded within the geophysical survey of the paleoseismological trench site over the Hluboka tectonic fault, Czech Republic, Central Europe. The surface waves in frequency range 15 - 70 Hz were recorded by the three component geophones with the active (sledge hammer) source. Group velocities are analyzed by the program SVAL which is based on the multiple filtering technique. It is a standard method of the Fourier transform-based frequency-time analysis. The spectrum of each record is multiplied by weighting functions centered at many discrete frequencies. Five local envelope maxima of all quasiharmonic components obtained by the inverse Fourier transform are found and their propagation times determined. These maxima are assigned to different modes of direct surface waves as well as to possible reflected, converted and multipathed modes. Filtered fundamental modes at pairs of geophones are correlated and phase velocities of surface waves are computed from the delays of propagation times of all quasiharmonic components. From the dispersion curves the shear wave
NASA Astrophysics Data System (ADS)
Gavrilov, Nikolai M.; Kshevetskii, Sergey P.
2015-11-01
We performed numerical simulations of nonlinear AGW propagation to the middle and upper atmosphere from a plane wave forcing at the Earth's surface with period τ = 2 × 103 s. After activating the surface wave forcing, initial pulse of acoustic and very long gravity modes in a few minutes can reach altitudes above 100 km. Dissipation of this initial pulse produces substantial mean heating and wave-induced mean winds at altitudes above 200 km. This may influence AGW propagation and produce enhanced vertical gradients of temperature, horizontal velocity and increased wave dissipation in the lower part of the wave-induced mean flows helping their downward expansions. Later, AGWs may produce layers of convective instability and peaks of the wave-induced jets at altitudes 100-120 km. Shorter AGWs with smaller horizontal wave speeds produce smaller mean heating and wave-induced mean velocities in the upper atmosphere at fixed amplitudes and periods of the surface wave excitation. Numerical simulation of nonlinear AGW propagation helps better understanding the details of dynamical and thermal influence of waves coming from the troposphere on the mean temperature and wind in the middle and upper atmosphere.
Excitation, propagation and damping of helicon waves in a high density, low temperature plasma
NASA Astrophysics Data System (ADS)
Caneses, J. F.; Blackwell, B. D.
2015-11-01
The MAGnetized Plasma Interaction Experiment (MAGPIE) is a helicon linear plasma device built to study fusion relevant plasma-surface interactions. In this work, we investigate helicon wave propagation in high density (1018-1019 m-3) low temperature (2-4 eV) magnetized (50-200 G) hydrogen plasma produced by a half-helical antenna operated at 7 MHz and 20 kW. Using the cold dielectric tensor with collisional terms (electron-neutral and Coulomb), helicon wave damping is calculated along the length of MAGPIE using a WKB approximation. Comparison with experiment indicates that wave damping, under these conditions, is entirely collisional. Numerical results from a fully electromagnetic wave code and 2D wavefield measurements indicate that helicon waves are excited at the plasma edge by the antenna's transverse current straps while the helical straps play a secondary role. These waves propagate towards the center of the discharge along the whistler wave ray direction (19 degrees to the background magnetic field), interfere on-axis and form the axial interference pattern commonly observed in helicon devices.
Switchable nonlinear metasurfaces for absorbing high power surface waves
NASA Astrophysics Data System (ADS)
Kim, Sanghoon; Wakatsuchi, Hiroki; Rushton, Jeremiah J.; Sievenpiper, Daniel F.
2016-01-01
We demonstrate a concept of a nonlinear metamaterial that provides power dependent absorption of incident surface waves. The metasurface includes nonlinear circuits which transform it from a low loss to high loss state when illuminated with high power waves. The proposed surface allows low power signals to propagate but strongly absorbs high power signals. It can potentially be used on enclosures for electric devices to protest against damage. We experimentally verify that the nonlinear metasurface has two distinct states controlled by the incoming signal power. We also demonstrate that it inhibits the propagation of large signals and dramatically decreases the field that is leaked through an opening in a conductive enclosure.
Shock wave propagation along constant sloped ocean bottoms.
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
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.
A study on compressive shock wave propagation in metallic foams
NASA Astrophysics Data System (ADS)
Wang, Zhihua; Zhang, Yifen; Ren, Huilan; Zhao, Longmao
2010-02-01
Metallic foam can dissipate a large amount of energy due to its relatively long stress plateau, which makes it widely applicable in the design of structural crashworthiness. However, in some experimental studies, stress enhancement has been observed when the specimens are subjected to intense impact loads, leading to severe damage to the objects being protected. This paper studies this phenomenon on a 2D mass-spring-bar model. With the model, a constitutive relationship of metal foam and corresponding loading and unloading criteria are presented; a nonlinear kinematics equilibrium equation is derived, where an explicit integration algorithm is used to calculate the characteristic of the compressive shock wave propagation within the metallic foam; the effect of heterogeneous distribution of foam microstructures on the shock wave features is also included. The results reveal that under low impact pulses, considerable energy is dissipated during the progressive collapse of foam cells, which then reduces the crush of objects. When the pulse is sufficiently high, on the other hand, stress enhancement may take place, especially in the heterogeneous foams, where high peak stresses usually occur. The characteristics of compressive shock wave propagation in the foam and the magnitude and location of the peak stress produced are strongly dependent on the mechanical properties of the foam material, amplitude and period of the pulse, as well as the homogeneity of the microstructures. This research provides valuable insight into the reliability of the metallic foams used as a protective structure.
Double porosity modeling in elastic wave propagation for reservoir characterization
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.
Ray Tracing Modeling of Gravity Wave Propagation and Dissipation
NASA Astrophysics Data System (ADS)
Vadas, Sharon; Crowley, Geoff
In this paper, we describe a ray trace model which calculates the wavevector, location and phase of a gravity wave (GW) as it propagates in the lower atmosphere and thermosphere. If used for a discreet transient source (such as a deep convective plume), we describe how this model can calculate the body forcing and the heat/cooling that are created when the GWs within a wave packet dissipate in the thermosphere from kinematic viscosity and thermal diffusivity. Although the body force calculation requires only the divergence of the momentum flux, the heat/cooling calculation requires the reconstructed GW field (e.g., density, velocity perturbations), which in turn requires the GW dissipative polarization relations. We describe these relations. We then describe the results of a recent study involving GWs identified from TIDDBIT HF Doppler sounder data taken at Wallops Island, VI, USA. Using this ray trace model, we determine if the unusual neutral wind profile measured by a rocket experiment at high altitudes (~290-370 km) could have been caused by the propagation and dissipation of several waves observed by TIDDBIT at lower altitudes.
Electromagnetic wave propagation through an overdense magnetized collisional plasma layer
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.
Propagation of three-dimensional electron-acoustic solitary waves
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.
Synthetic observations of wave propagation in a sunspot umbra
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.
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.
Transition from 1D to 2D Laser-Induced Ultrasonic Wave Propagation in an Extended Plate
NASA Astrophysics Data System (ADS)
Laloš, Jernej; Požar, Tomaž; Možina, Janez
2016-05-01
Optodynamic interaction between a laser pulse and the surface of an opaque, solid elastic object produces transient waves that propagate and reverberate within the object. They can be, in general, categorized into three distinctive types which are all formed through different mechanisms: ablation-induced waves, light-pressure-induced waves, and thermoelastic waves. In this paper, out-of-plane displacements of such waves are simulated at the epicentral position on the opposite side of an extended plane-parallel elastic plate. Wave propagation is mathematically described by Green's transfer functions convolved with suitable time profiles of the incoming laser pulses. The simulated size of the circularly symmetric laser-illuminated area on the plate surface is varied to show the limit-to-limit transition of the displacement waveforms: from a 2D point source to an infinite 1D source.
PROPAGATION AND STABILITY OF SUPERLUMINAL WAVES IN PULSAR WINDS
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.
Propagation of spiral waves pinned to circular and rectangular obstacles
NASA Astrophysics Data System (ADS)
Sutthiopad, Malee; Luengviriya, Jiraporn; Porjai, Porramain; Phantu, Metinee; Kanchanawarin, Jarin; Müller, Stefan C.; Luengviriya, Chaiya
2015-05-01
We present an investigation of spiral waves pinned to circular and rectangular obstacles with different circumferences in both thin layers of the Belousov-Zhabotinsky reaction and numerical simulations with the Oregonator model. For circular objects, the area always increases with the circumference. In contrast, we varied the circumference of rectangles with equal areas by adjusting their width w and height h . For both obstacle forms, the propagating parameters (i.e., wavelength, wave period, and velocity of pinned spiral waves) increase with the circumference, regardless of the obstacle area. Despite these common features of the parameters, the forms of pinned spiral waves depend on the obstacle shapes. The structures of spiral waves pinned to circles as well as rectangles with the ratio w /h ˜1 are similar to Archimedean spirals. When w /h increases, deformations of the spiral shapes are observed. For extremely thin rectangles with w /h ≫1 , these shapes can be constructed by employing semicircles with different radii which relate to the obstacle width and the core diameter of free spirals.
Micromagnetic calculation of spin wave propagation for magnetologic devices
NASA Astrophysics Data System (ADS)
Bance, Simon; Schrefl, Thomas; Hrkac, Gino; Goncharov, Alexander; Allwood, Dan A.; Dean, Julian
2008-04-01
The propagation of magnetic wave packets in magnetic nanowires was calculated as a function of wire width, field strength, field ramp time, field area size, and geometry of a magnetic nanowire. Spin waves are excited locally by applying a small perturbation in the magnetization in a 20nm wide region. A wave packet is emitted from the input region and travels along the wire with a velocity of 740m/s. The finite element micromagnetic simulations show that wave packets can be guided along a bent nanostructure without losses due to geometry; amplitude and frequency are exactly the same as in a straight wire with equal distance between excitation point and probe. The wave amplitude was found to decrease with increasing rise time of the excitation field with an upper limit of 100ps. For a Permalloy wire with a thickness of 10nm, the frequency peak changes from 10GHz in a wire with 60nm width to 6GHz in a wire with 140nm width.
Fabric dependence of wave propagation in anisotropic porous media
Cowin, Stephen C.; Cardoso, Luis
2012-01-01
Current diagnosis of bone loss and osteoporosis is based on the measurement of the Bone Mineral Density (BMD) or the apparent mass density. Unfortunately, in most clinical ultrasound densitometers: 1) measurements are often performed in a single anatomical direction, 2) only the first wave arriving to the ultrasound probe is characterized, and 3) the analysis of bone status is based on empirical relationships between measurable quantities such as Speed of Sound (SOS) and Broadband Ultrasound Attenuation (BUA) and the density of the porous medium. However, the existence of a second wave in cancellous bone has been reported, which is an unequivocal signature of poroelastic media, as predicted by Biot’s poroelastic wave propagation theory. In this paper the governing equations for wave motion in the linear theory of anisotropic poroelastic materials are developed and extended to include the dependence of the constitutive relations upon fabric - a quantitative stereological measure of the degree of structural anisotropy in the pore architecture of a porous medium. This fabric-dependent anisotropic poroelastic approach is a theoretical framework to describe the microarchitectural-dependent relationship between measurable wave properties and the elastic constants of trabecular bone, and thus represents an alternative for bone quality assessment beyond BMD alone. PMID:20461539
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).
Global Propagation of Gravity Waves Generated with the Whole Atmosphere Transfer Function Model
NASA Astrophysics Data System (ADS)
Mayr, H. G.; Talaat, E. R.; Wolven, B. C.
2012-12-01
three distinct classes of waves: (1) Lamb waves that propagate in the thermosphere with about 800 m/s, strongly dissipated by molecular viscosity. (2) Waves reflected from the Earth surface, which return in narrow propagation cones to the thermosphere with velocities of about 200 m/s. (3) Waves that are ducted through the lower atmosphere and leak back into the thermosphere, where they propagate with about 300 m/s, virtually without dissipation. Waves from the leaking duct, with short propagation velocity, thus can propagate from the auroral region to equatorial latitudes, and this has been observed. The TFM has been applied to simulate AGW patterns during magnetic sub-storm activity observed with the Dynamics Explorer (DE) spacecraft. The TFM can readily be employed also to simulate AGW generated with excitation sources in the lower atmosphere, and efforts are underway to resurrect the model with present day advanced computers and analysis software [e.g., Porter et al., AGU, 2008].
Metasurface transformation for surface wave control.
Martini, E; Mencagli, M; Maci, S
2015-08-28
Metasurfaces (MTSs) constitute a class of thin metamaterials used for controlling plane waves and surface waves (SWs). At microwave frequencies, they are constituted by a metallic texture with elements of sub-wavelength size printed on thin grounded dielectric substrates. These structures support the propagation of SWs. By averaging the tangential fields, the MTSs can be characterized through homogenized isotropic or anisotropic boundary conditions, which can be described through a homogeneous equivalent impedance. This impedance can be spatially modulated by locally changing the size/orientation of the texture elements. This allows for a deformation of the SW wavefront which addresses the local wavevector along not-rectilinear paths. The effect of the MTS modulation can be analysed in the framework of transformation optics. This article reviews theory and implementation of this MTS transformation and shows some examples at microwave frequencies. PMID:26217056
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
Ultrafast microfluidics using surface acoustic waves
Yeo, Leslie Y.; Friend, James R.
2009-01-01
We demonstrate that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and micro∕bioparticle manipulation schemes. We show that sessile drops can be translated rapidly on planar substrates or fluid can be pumped through microchannels at 1–10 cm∕s velocities, which are typically one to two orders quicker than that afforded by current microfluidic technologies. Through symmetry-breaking, azimuthal recirculation can be induced within the drop to drive strong inertial microcentrifugation for micromixing and particle concentration or separation. Similar micromixing strategies can be induced in the same microchannel in which fluid is pumped with the SAW by merely changing the SAW frequency to rapidly switch the uniform through-flow into a chaotic oscillatory flow by exploiting superpositioning of the irradiated sound waves from the sidewalls of the microchannel. If the flow is sufficiently quiescent, the nodes of the transverse standing wave that arises across the microchannel also allow for particle aggregation, and hence, sorting on nodal lines. In addition, the SAW also facilitates other microfluidic capabilities. For example, capillary waves excited at the free surface of a sessile drop by the SAW underneath it can be exploited for micro∕nanoparticle collection and sorting at nodal points or lines at low powers. At higher powers, the large accelerations off the substrate surface as the SAW propagates across drives rapid destabilization of the drop free surface giving rise to inertial liquid jets that persist over 1–2 cm in length or atomization of the entire drop to produce 1–10 μm monodispersed aerosol droplets, which can be exploited for ink-jet printing, mass spectrometry interfacing, or pulmonary drug delivery. The atomization of polymer∕protein solutions
Air-ground interface: Surface waves, surface impedance and acoustic-to-seismic coupling coefficient
NASA Technical Reports Server (NTRS)
Daigle, Gilles; Embleton, Tony
1990-01-01
In atmospheric acoustics, the subject of surface waves has been an area of discussion for many years. The existence of an acoustic surface wave is now well established theoretically. The mathematical solution for spherical wave propagation above an impedance boundary includes the possibility of a contribution that possesses all the standard properties for a surface wave. Surface waves exist when the surface is sufficiently porous, relative to its acoustical resistance, that it can influence the airborne particle velocity near the surface and reduce the phase velocity of sound waves in air at the surface. This traps some of the sound energy in the air to remain near the surface as it propagates. Above porous grounds, the existence of surface waves has eluded direct experimental confirmation (pulse experiments have failed to show a separate arrival expected from the reduced phase speed) and indirect evidence for its existence has appeared contradictory. The experimental evidence for the existence of an acoustical surface wave above porous boundaries is reviewed. Recent measurements including pulse experiments are also described. A few years ago the acoustic impedance of a grass-covered surface was measured in the frequency range 30 to 300 Hz. Here, further measurements on the same site are discussed. These measurements include core samples, a shallow refractive survey to determine the seismic velocities, and measurements of the acoustic-to-seismic coupling coefficient.
Wave-measurement capabilities of the surface contour radar and the airborne oceanographic lidar
NASA Technical Reports Server (NTRS)
Walsh, Edward J.; Hancock, David W., III; Hines, Donald E.; Swift, Robert N.; Scott, John F.
1987-01-01
The 36-gigahertz surface contour radar and the airborne oceanographic lidar were used in the SIR-B underflight mission off the coast of Chile in October 1984. The two systems and some of their wave-measurement capabilities are described. The surface contour radar can determine the directional wave spectrum and eliminate the 180-degree ambiguity in wave propagation direction that is inherent in some other techniques such as stereophotography and the radar ocean wave spectrometer. The Airborne Oceanographic Lidar can acquire profile data on the waves and produce a spectrum that is close to the nondirectional ocean-wave spectrum for ground tracks parallel to the wave propagation direction.
Wave propagation downstream of a high power helicon in a dipolelike magnetic field
NASA Astrophysics Data System (ADS)
Prager, James; Ziemba, Timothy; Winglee, Robert; Roberson, B. Race
2010-01-01
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.
Wave propagation downstream of a high power helicon in a dipolelike magnetic field
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.
Investigation of guided waves propagation in pipe buried in sand
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.
Dispersion relations for electromagnetic wave propagation in chiral plasmas
Gao, M. X.; Guo, B. Peng, L.; Cai, X.
2014-11-15
The dispersion relations for electromagnetic wave propagation in chiral plasmas are derived using a simplified method and investigated in detail. With the help of the dispersion relations for each eignwave, we explore how the chiral plasmas exhibit negative refraction and investigate the frequency region for negative refraction. The results show that chirality can induce negative refraction in plasmas. Moreover, both the degree of chirality and the external magnetic field have a significant effect on the critical frequency and the bandwidth of the frequency for negative refraction in chiral plasmas. The parameter dependence of the effects is calculated and discussed.
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
Particle velocity non-uniformity and steady-wave propagation
NASA Astrophysics Data System (ADS)
Meshcheryakov, Yu. I.
2016-05-01
A constitutive equation grounded in dislocation dynamics is shown to be incapable of describing the propagation of shock fronts in solids. Shock wave experiments and theoretical investigations motivate an additional collective mechanism of stress relaxation that should be incorporated into the model through the standard deviation of the particle velocity, which is found to be proportional to the strain rate. In this case, the governing equation system results in a second-order differential equation of square non-linearity. Solution to this equation and calculations for D16 aluminum alloy show a more precise coincidence of the theoretical and experimental velocity profiles.
Passive models of viscothermal wave propagation in acoustic tubes.
Bilbao, Stefan; Harrison, Reginald; Kergomard, Jean; Lombard, Bruno; Vergez, Christophe
2015-08-01
A continued fraction expansion to the immittances defining viscothermal wave propagation in a cylindrical tube has been presented recently in this journal, intended as a starting point for time domain numerical method design. Though the approximation has the great benefit of passivity, or positive realness under truncation, its convergence is slow leading to approximations of high order in practice. Other passive structures, when combined with optimisation methods, can lead to good accuracy over a wide frequency range, and for relatively low order. PMID:26328672
LOCA simulation: analysis of rarefaction waves propagating through geometric singularities
Crouzet, Fabien; Faucher, Vincent; Galon, Pascal; Piteau, Philippe; Izquierdo, Patrick
2012-07-01
The propagation of a transient wave through an orifice is investigated for applications to Loss Of Coolant Accident in nuclear plants. An analytical model is proposed for the response of an orifice plate and implemented in the EUROPLEXUS fast transient dynamics software. It includes an acoustic inertial effect in addition to a quasi-steady dissipation term. The model is experimentally validated on a test rig consisting in a single pipe filled with pressurized water. The test rig is designed to generate a rapid depressurization of the pipe, by means of a bursting disk. The proposed model gives results which compare favourably with experimental data. (authors)
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.
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.
Wave Propagation in a Green-Naghdi Thermoelastic Solid with Diffusion
NASA Astrophysics Data System (ADS)
Singh, Baljeet
2013-03-01
The Green and Naghdi theory of thermoelasticity is applied to study plane-wave propagation in an elastic solid with thermo-diffusion. The governing equations of an elastic solid with generalized thermo-diffusion are solved to show the existence of three coupled longitudinal waves and a shear vertical (SV) wave in a two-dimensional model of the solid with thermo-diffusion. The reflection of plane waves from a thermally insulated stress-free surface of an elastic solid with thermo-diffusion is also studied. A non-homogeneous system of four equations in reflection coefficients is obtained. The speeds of the plane waves are computed numerically and plotted against frequency for a particular range. The complex absolute values of the reflection coefficients of all reflected waves are computed numerically and plotted against the angle of incidence of the striking wave at the free surface. The effects of diffusion parameters are shown graphically for speeds and reflection coefficients of plane waves.
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.
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.
Elastic Wave Propagation in Concrete and Continuous Wavelet Transform
Chiang, C.-H.; Gi, Y.-F.; Pan, C.-L.; Cheng, C.-C.
2005-04-09
Elastic wave methods, such as the ultrasonic pulse velocity and the impact echo, are often subject to multiple reflections at the boundaries of various constituents of concrete. Current study aims to improve the feature identification of elastic wave propagation due to buried objects in concrete slabs and cylinders. Embedded steel reinforcement, steel and PVC tubes, wooden disks, and rubber spheres are tested. The received signals are analyzed using continuous wavelet transform. As a result, signals are decomposed into distinctive frequency bands with transient information preserved. The interpretation of multiple reflections at different boundary conditions thus becomes more straightforward. Features related to reflections from steel bar, PVC tube, and steel tube can be readily identified in the magnitude plot of wavelet coefficients. Vibration modes of the concrete slab corresponding to different buried objects can also be separated based on corresponding time duration.
Elastic Wave Propagation in Concrete and Continuous Wavelet Transform
NASA Astrophysics Data System (ADS)
Chiang, Chih-Hung; Gi, Yu-Fung; Pan, Chi-Ling; Cheng, Chia-Chi
2005-04-01
Elastic wave methods, such as the ultrasonic pulse velocity and the impact echo, are often subject to multiple reflections at the boundaries of various constituents of concrete. Current study aims to improve the feature identification of elastic wave propagation due to buried objects in concrete slabs and cylinders. Embedded steel reinforcement, steel and PVC tubes, wooden disks, and rubber spheres are tested. The received signals are analyzed using continuous wavelet transform. As a result, signals are decomposed into distinctive frequency bands with transient information preserved. The interpretation of multiple reflections at different boundary conditions thus becomes more straightforward. Features related to reflections from steel bar, PVC tube, and steel tube can be readily identified in the magnitude plot of wavelet coefficients. Vibration modes of the concrete slab corresponding to different buried objects can also be separated based on corresponding time duration.
Measurements on wave propagation characteristics of spiraling electron beams
NASA Technical Reports Server (NTRS)
Singh, A.; Getty, W. D.
1976-01-01
Dispersion characteristics of cyclotron-harmonic waves propagating on a neutralized spiraling electron beam immersed in a uniform axial magnetic field are studied experimentally. The experimental setup consisted of a vacuum system, an electron-gun corkscrew assembly which produces a 110-eV beam with the desired delta-function velocity distribution, a measurement region where a microwave signal is injected onto the beam to measure wavelengths, and a velocity analyzer for measuring the axial electron velocity. Results of wavelength measurements made at beam currents of 0.15, 1.0, and 2.0 mA are compared with calculated values, and undesirable effects produced by increasing the beam current are discussed. It is concluded that a suitable electron beam for studies of cyclotron-harmonic waves can be generated by the corkscrew device.
Numerical solutions of acoustic wave propagation problems using Euler computations
NASA Technical Reports Server (NTRS)
Hariharan, S. I.
1984-01-01
This paper reports solution procedures for problems arising from the study of engine inlet wave propagation. The first problem is the study of sound waves radiated from cylindrical inlets. The second one is a quasi-one-dimensional problem to study the effect of nonlinearities and the third one is the study of nonlinearities in two dimensions. In all three problems Euler computations are done with a fourth-order explicit scheme. For the first problem results are shown in agreement with experimental data and for the second problem comparisons are made with an existing asymptotic theory. The third problem is part of an ongoing work and preliminary results are presented for this case.
Electromagnetic Effects on Wave Propagation in an Isotropic Micropolar Plate
NASA Astrophysics Data System (ADS)
Shaw, S.; Mukhopadhyay, B.
2015-11-01
The generalized theory of thermoelasticity is applied to study the propagation of plane harmonic waves in an infinitely long, isotropic, micropolar plate in the presence of a uniform magnetic field. The present analysis also includes the thermal relaxation time, electric displacement current, and the coupling of heat transfer and microrotation of the material. To determine the effect of the presence of thermal as well as magnetic fields on the phase velocity, two potential functions are used, and more general dispersive relations are obtained for symmetric and antisymmetric modes. The results for the cases of coupled thermoelasticity, magnetoelasticity, micropolar thermoelasticity, and classical micropolar elasticity as special cases are derived. The changes in the phase velocity and attenuation coefficient with the wave number are shown graphically.
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.
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.
Pang, Yu; Liu, Yu-Shan; Liu, Jin-Xi; Feng, Wen-Jie
2016-04-01
In this paper, SH bulk/surface waves propagating in the corresponding infinite/semi-infinite piezoelectric (PE)/piezomagnetic (PM) and PM/PE periodically layered composites are investigated by two methods, the stiffness matrix method and the transfer matrix method. For a semi-infinite PE/PM or PM/PE medium, the free surface is parallel to the layer interface. Both PE and PM materials are assumed to be transversely isotropic solids. Dispersion equations are derived by the stiffness/transfer matrix methods, respectively. The effects of electric-magnetic (ME) boundary conditions at the free surface and the layer thickness ratios on dispersion curves are considered in detail. Numerical examples show that the results calculated by the two methods are the same. The dispersion curves of SH surface waves are below the bulk bands or inside the frequency gaps. The ratio of the layer thickness has an important effect not only on the bulk bands but also on the dispersion curves of SH surface waves. Electric and magnetic boundary conditions, respectively, determine the dispersion curves of SH surface waves for the PE/PM and PM/PE semi-infinite structures. The band structures of SH bulk waves are consistent for the PE/PM and PM/PE structures, however, the dispersive behaviors of SH surface waves are indeed different for the two composites. The realization of the above-mentioned characteristics of SH waves will make it possible to design PE/PM acoustic wave devices with periodical structures and achieve the better performance. PMID:26836289
Propagation of nonlinear waves over submerged step: wave separation and subharmonic generation
NASA Astrophysics Data System (ADS)
Monsalve, Eduardo; Maurel, Agnes; Pagneux, Vincent; Petitjeans, Philippe
2015-11-01
Water waves can be described in simplified cases by the Helmholtz equation. However, even in these cases, they present a high complexity, among which their dispersive character and their nonlinearities are the subject of the present study. Using Fourier Transform Profilometry, we study experimentally the propagation of waves passing over a submerged step. Because of the small water depth after the step, the wave enters in a nonlinear regime. In the shallow water region, the second harmonic leads to two types of waves: bound waves which are slaves of the fundamental frequency with wavenumber 2 k (ω) , and free waves which propagate according to the usual dispersion relation with wavenumber k (2 ω) . Because of the presence of these two waves, beats are produced at the second harmonic with characteristic beat length. In this work, for the first time we extended this analysis to the third and higher harmonics. Next, the region after the step is limited to a finite size L with a reflecting wall. For certain frequencies and L- values, the spectral component becomes involved, with the appearance of sub harmonics. This regime is analyzed in more details, suggesting a transition to a chaotic and quasi-periodic wave behavior.
Visualization of non-propagating Lamb wave modes for fatigue crack evaluation
NASA Astrophysics Data System (ADS)
An, Yun-Kyu; Sohn, Hoon
2015-03-01
This article develops a non-propagating Lamb wave mode (NPL) imaging technique for fatigue crack visualization. NPL has a great potential for crack evaluation in that it significantly contributes local mode amplitudes in the vicinity of a crack without spatial propagation. Such unique physical phenomenon is theoretically proven and experimentally measured through laser scanning. Although its measurement is a quite challenging work due to the fact that it is quite localized and coexists with complex propagating Lamb wave modes, a NPL filter proposed in this article overcomes the technical challenge by eliminating all propagating Lamb modes from laser scanned full Lamb wavefields. Through the NPL filtering process, only fatigue crack-induced NPLs can be measured and retained. To verify such physical observation and the corresponding NPL filter, a real micro fatigue crack is created by applying repeated tensile loading, and its detectability is tested using a surface-mounted piezoelectric transducer for generating Lamb waves and a laser Doppler vibrometer for measuring the corresponding responses. The experimental results confirm that even an invisible fatigue crack can be instantaneously visualized and effectively evaluated through the proposed NPL measurement and filtering processes.
Frequency nonreciprocity of surface spin wave in permalloy thin films
NASA Astrophysics Data System (ADS)
Gladii, O.; Haidar, M.; Henry, Y.; Kostylev, M.; Bailleul, M.
2016-02-01
Surface spin waves in thin permalloy films are studied by means of propagative-spin-wave spectroscopy. We observe a systematic difference of up to several tens of MHz when comparing the frequencies of counterpropagating waves. This frequency nonreciprocity effect is modeled using an analytical dipole-exchange theory that considers the mutual influence of nonreciprocal spin wave modal profiles and differences in magnetic anisotropies at the two film surfaces. At moderate film thickness (20 nm and below), the frequency nonreciprocity scales linearly with the wave vector and quadratically with the thickness, whereas a more complex nonmonotonic behavior is observed at larger thickness. Our paper suggests that surface wave frequency nonreciprocity can be used as an accurate spectroscopic probe of magnetic asymmetries in thin ferromagnetic films.
The Millikan shaking experiments and high-frequency seismic wave propagation in Southern California
NASA Astrophysics Data System (ADS)
Tanimoto, Toshiro; Okamoto, Taro
2014-08-01
In order to study high-frequency seismic wave propagation, seismic wavefields generated by resonant-shaking experiments of the Millikan Library, on the campus of California Institute Technology (Pasadena, California, USA), were analysed. Because the resonant shaking frequencies are 1.12 Hz (the east-west direction) and 1.64 Hz (the north-south direction), this active-source experiment can provide opportunities for studying high-frequency seismic wave propagation in Southern California. Because they are very narrow frequency band data, the analyses must be quite different from ordinary time-domain analyses. We show, theoretically, that the signals must be dominated by surface waves. Adopting this surface wave assumption, we proceed to make two separate analyses, one on spectral amplitude and the other on phase. We present a new method to derive group velocity from phase based on the cross correlations between the station in the Millikan Library (MIK) and stations in the regional network. Our results support that an active-source experiment by resonant shaking of a building is a feasible approach for high-frequency seismic wave studies.
The correlation of VLF propagation variations with atmospheric planetary-scale waves
NASA Technical Reports Server (NTRS)
Cavalieri, D. J.; Deland, R. J.; Potemra, T. A.; Gavin, R. F.
1973-01-01
Variations in the received daytime phase of long distance, cesium-controlled, VLF transmission were compared to the height variations of the 10-mb isobaric surface during the first three months of 1965 and 1969. The VLF phase values are also compared to height variations of constant electron densities in the E-region and to variations of f-min which have been shown to be well correlated with planetary-scale variations in the stratosphere by Deland and Cavalieri (1973). The VLF phase variations show good correlation with these previous ionospheric measurements and with the 10-mb surfaces. The planetary scale waves in the stratosphere are shown to be travelling on the average eastward in 1965 and westward in 1969. These correlations are interpreted as due to the propagation of travelling planetary scale waves with westward tilted wave fronts. Upward energy transport due to the vertical structure of those waves is also discussed. These correlations provide further evidence for the coupling between the lower ionosphere at about 70 km altitude (the daytime VLF reflection height and the stratosphere, and they demonstrate the importance of planetary wave phenomena to VLF propagation.
Simulation of seismic wave propagation for reconnaissance in machined tunnelling
NASA Astrophysics Data System (ADS)
Lambrecht, L.; Friederich, W.
2012-04-01
During machined tunnelling, there is a complex interaction chain of the involved components. For example, on one hand the machine influences the surrounding ground during excavation, on the other hand supporting measures are needed acting on the ground. Furthermore, the different soil conditions are influencing the wearing of tools, the speed of the excavation and the safety of the construction site. In order to get information about the ground along the tunnel track, one can use seismic imaging. To get a better understanding of seismic wave propagation for a tunnel environment, we want to perform numerical simulations. For that, we use the spectral element method (SEM) and the nodal discontinuous galerkin method (NDG). In both methods, elements are the basis to discretize the domain of interest for performing high order elastodynamic simulations. The SEM is a fast and widely used method but the biggest drawback is it's limitation to hexahedral elements. For complex heterogeneous models with a tunnel included, it is a better choice to use the NDG, which needs more computation time but can be adapted to tetrahedral elements. Using this technique, we can perform high resolution simulations of waves initialized by a single force acting either on the front face or the side face of the tunnel. The aim is to produce waves that travel mainly in the direction of the tunnel track and to get as much information as possible from the backscattered part of the wave field.
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.
Propagation of dissolution/precipitation waves in porous media
Novak, C.F.
1992-01-01
The transport of a chemically reactive fluid through a permeable medium is governed by many classes of chemical interactions. Dissolution/precipitation (D/P) reactions are among the interactions of primary importance because of their significant influence on the mobility of aqueous ions. In general, D/P reactions lead to the propagation of coherent waves. This paper provides an overview of the types of wave phenomena observed in one-dimensional (1D) and two-dimensional (2D) porous media for systems in which mineral D/P is the dominant type of chemical reaction. It is demonstrated that minerals dissolve in sharp waves in 1D advection-dominated transport, and that these waves separate zones of constant chemical compositions in the aqueous and mineral phases. Analytical solutions based on coherence methods are presented for solving 1D advection-dominated transport problems with constant and variable boundary conditions. Numerical solutions of diffusion-dominated transport in porous media show that sharp D/P fronts occur in this system as well. A final example presents a simple dual-porosity system with advection in an idealized fracture and solute diffusion into an adjacent porous matrix. The example illustrates the delay of contaminant release from the 2D domain due to a combination of physical retardation and chemical retardation.
Full wave propagation modelling in view to integrated ICRH wave coupling/RF sheaths modelling
NASA Astrophysics Data System (ADS)
Jacquot, Jonathan; Bobkov, Volodymyr; Colas, Laurent; Heuraux, Stéphane; Křivská, Alena; Lu, Lingfeng; Noterdaeme, Jean-Marie
2015-12-01
RF sheaths rectification can be the reason for operational limits for Ion Cyclotron Range of Frequencies (ICRF) heating systems via impurity production or excessive heat loads. To simulate this process in realistic geometry, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating (SSWICH) code is a minimal set of coupled equations that computes self-consistently wave propagation and DC plasma biasing. The present version of its wave propagation module only deals with the Slow Wave assumed to be the source of RF sheath oscillations. However the ICRF power coupling to the plasma is due to the fast wave (FW). This paper proposes to replace this one wave equation module by a full wave module in either 2D or 3D as a first step towards integrated modelling of RF sheaths and wave coupling. Since the FW is propagative in the main plasma, Perfectly Matched Layers (PMLs) adapted for plasmas were implemented at the inner side of the simulation domain to absorb outgoing waves and tested numerically with tilted B0 in Cartesian geometry, by either rotating the cold magnetized plasma dielectric tensors in 2D or rotating the coordinate vector basis in 3D. The PML was further formulated in cylindrical coordinates to account for for the toroidal curvature of the plasma. Toroidal curvature itself does not seem to change much the coupling. A detailed 3D geometrical description of Tore Supra and ASDEX Upgrade (AUG) antennas was included in the coupling code. The full antenna structure was introduced, since its toroidal symmetry with respect to the septum plane is broken (FS bars, toroidal phasing, non-symmetrical structure). Reliable convergence has been obtained with the density profile up to the leading edge of antenna limiters. Parallel electric field maps have been obtained as an input for the present version of SSWICH.
NASA Astrophysics Data System (ADS)
Grant, S. D. T.; Jess, D. B.; Moreels, M. G.; Morton, R. J.; Christian, D. J.; Giagkiozis, I.; Verth, G.; Fedun, V.; Keys, P. H.; Van Doorsselaere, T.; Erdélyi, R.
2015-06-01
We present observational evidence of compressible MHD wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four wavelength bands using the Dunn Solar Telescope. Employing Fourier and wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations. The intensity and area fluctuations exhibit a range of periods from 181 to 412 s, with an average period ˜290 s, consistent with the global p-mode spectrum. Intensity and area oscillations present in adjacent bandpasses were found to be out of phase with one another, displaying phase angles of 6.°12, 5.°82, and 15.°97 between the 4170 Å continuum-G-band, G-band-Na i D1, and Na i D1-Ca ii K heights, respectively, reiterating the presence of upwardly propagating sausage-mode waves. A phase relationship of ˜0° between same-bandpass emission and area perturbations of the pore best categorizes the waves as belonging to the “slow” regime of a dispersion diagram. Theoretical calculations reveal that the waves are surface modes, with initial photospheric energies in excess of 35,000 W m-2. The wave energetics indicate a substantial decrease in energy with atmospheric height, confirming that magnetic pores are able to transport waves that exhibit appreciable energy damping, which may release considerable energy into the local chromospheric plasma.
Propagating waves separate two states of actin organization in living cells
Schroth-Diez, Britta; Gerwig, Silke; Ecke, Mary; Hegerl, Reiner; Diez, Stefan; Gerisch, Günther
2009-01-01
Propagating actin waves are dynamic supramolecular structures formed by the self-assembly of proteins within living cells. They are built from actin filaments together with single-headed myosin, the Arp2∕3 complex, and coronin in a defined three-dimensional order. The function of these waves in structuring the cell cortex is studied on the substrate-attached surface of Dictyostelium cells by the use of total internal reflection fluorescence (TIRF) microscopy. Actin waves separate two areas of the cell cortex from each other, which are distinguished by the arrangement of actin filaments. The Arp2∕3 complex dominates in the area enclosed by a wave, where it has the capacity of building dendritic structures, while the proteins prevailing in the external area, cortexillin I and myosin-II, bundle actin filaments and arrange them in antiparallel direction. Wave propagation is accompanied by transitions in the state of actin with a preferential period of 5 min. Wave generation is preceded by local fluctuations in actin assembly, some of the nuclei of polymerized actin emanating from clathrin-coated structures, others emerging independently. The dynamics of phase transitions has been analyzed to provide a basis for modeling the nonlinear interactions that produce spatio-temporal patterns in the actin system of living cells. PMID:20514132
Propagation of 3D nonlinear waves over complex bathymetry using a High-Order Spectral method
NASA Astrophysics Data System (ADS)
Gouin, Maïté; Ducrozet, Guillaume; Ferrant, Pierre
2016-04-01
Scattering of regular and irregular surface gravity waves propagating over a region of arbitrary three-dimensional varying bathymetry is considered here. The three-dimensional High-Order Spectral method (HOS) with an extension to account for a variable bathymetry is used. The efficiency of the model has been proved to be conserved even with this extension. The method is first applied to a bathymetry consisting of an elliptical lens, as used in the Vincent and Briggs (1989) experiment. Incident waves passing across the lens are transformed and a strong convergence region is observed after the elliptical mound. The wave amplification depends on the incident wave. Numerical results for regular and irregular waves are analysed and compared with other methods and experimental data demonstrating the efficiency and practical applicability of the present approach. Then the method is used to model waves propagating over a real bathymetry: the canyons of Scripps/La Jolla in California. The implementation of this complex bathymetry in the model is presented, as well as the first results achieved. They will be compared to the ones obtained with another numerical model.
Anti-plane transverse waves propagation in nanoscale periodic layered piezoelectric structures.
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
Sound radiation from an infinite elastic cylinder with dual-wave propagation-intensity distributions
NASA Technical Reports Server (NTRS)
Fuller, C. R.
1988-01-01
The radiation of sound from an elastic cylindrical shell filled with fluid and supporting multiwave propagation is studied analytically. Combinations of supersonic and subsonic shell waves are considered. The radiated field is mapped by using acoustic intensity vectors evaluated at various locations. Both time averaged and instantaneous intensity are investigated. The acoustic intensity is seen to vary markedly with axial distance down the cylinder. The effect is shown to be associated with cross terms in the intensity relations, and its magnitude and location to depend upon the relative phase and amplitudes of individual waves. Subsonic shell waves are demonstrated to interact strongly with supersonic shell waves to cause a large modification in the radiated intensity distributions near the shell surface.
Retarded condensate freezing propagation on superhydrophobic surfaces patterned with micropillars
NASA Astrophysics Data System (ADS)
Zhao, Yugang; Yang, Chun
2016-02-01
Previous studies have shown ice delay on nano-structured or hierarchical surfaces with nanoscale roughness. Here we report retarded condensate freezing on superhydrophobic silicon substrates fabricated with patterned micropillars of small aspect ratio. We further investigated the pillar size effects on freezing propagation. We found that the velocity of freezing propagation on the surface patterned with proper micropillars can be reduced by one order of magnitude, compared to that on the smooth untreated silicon surface. Additionally, we developed an analytical model to describe the condensate freezing propagation on a structured surface with micropillars and the model predictions were compared with our experimental results.
Evolution of the derivative skewness for nonlinearly propagating waves.
Reichman, Brent O; Muhlestein, Michael B; Gee, Kent L; Neilsen, Tracianne B; Thomas, Derek C
2016-03-01
The skewness of the first time derivative of a pressure waveform, or derivative skewness, has been used previously to describe the presence of shock-like content in jet and rocket noise. Despite its use, a quantitative understanding of derivative skewness values has been lacking. In this paper, the derivative skewness for nonlinearly propagating waves is investigated using analytical, numerical, and experimental methods. Analytical expressions for the derivative skewness of an initially sinusoidal plane wave are developed and, along with numerical data, are used to describe its behavior in the preshock, sawtooth, and old-age regions. Analyses of common measurement issues show that the derivative skewness is relatively sensitive to the effects of a smaller sampling rate, but less sensitive to the presence of additive noise. In addition, the derivative skewness of nonlinearly propagating noise is found to reach greater values over a shorter length scale relative to sinusoidal signals. A minimum sampling rate is recommended for sinusoidal signals to accurately estimate derivative skewness values up to five, which serves as an approximate threshold indicating significant shock formation. PMID:27036276
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.
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.
Surface acoustic wave oxygen sensor
NASA Technical Reports Server (NTRS)
Collman, James P.; Oglesby, Donald M.; Upchurch, Billy T.; Leighty, Bradley D.; Zhang, Xumu; Herrmann, Paul C.
1994-01-01
A surface acoustic wave (SAW) device that responds to oxygen pressure was developed by coating a 158 MHz quartz surface acoustic wave (SAW) device with an oxygen binding agent. Two types of coatings were used. One type was prepared by dissolving an oxygen binding agent in a toluene solution of a copolymer containing the axial ligand. A second type was prepared with an oxygen binding porphyrin solution containing excess axial ligand without a polymer matrix. In the polymer based coatings, the copolymer served to provide the axial ligand to the oxygen binding agent and as a coating matrix on the surface of the SAW device. The oxygen sensing SAW device has been shown to bind oxygen following a Langmuir isotherm and may be used to measure the equilibrium constant of the oxygen binding compound in the coating matrix.
Surface wave chemical detector using optical radiation
Thundat, Thomas G.; Warmack, Robert J.
2007-07-17
A surface wave chemical detector comprising at least one surface wave substrate, each of said substrates having a surface wave and at least one measurable surface wave parameter; means for exposing said surface wave substrate to an unknown sample of at least one chemical to be analyzed, said substrate adsorbing said at least one chemical to be sensed if present in said sample; a source of radiation for radiating said surface wave substrate with different wavelengths of said radiation, said surface wave parameter being changed by said adsorbing; and means for recording signals representative of said surface wave parameter of each of said surface wave substrates responsive to said radiation of said different wavelengths, measurable changes of said parameter due to adsorbing said chemical defining a unique signature of a detected chemical.
Instationary compaction wave propagation in highly porous cohesive granular media
NASA Astrophysics Data System (ADS)
Gunkelmann, Nina; Ringl, Christian; Urbassek, Herbert M.
2016-04-01
We study the collision of a highly porous granular aggregate of adhesive μm-sized silica grains with a hard wall using a granular discrete element method. A compaction wave runs through the granular sample building up an inhomogeneous density profile. The compaction is independent of the length of the aggregate, within the regime of lengths studied here. Also short pulses, as they might be exerted by a piston pushing the granular material, excite a compaction wave that runs through the entire material. The speed of the compaction wave is larger than the impact velocity but considerably smaller than the sound speed. The wave speed is related to the compaction rate at the colliding surface and the average slope of the linear density profile.
Instationary compaction wave propagation in highly porous cohesive granular media
NASA Astrophysics Data System (ADS)
Gunkelmann, Nina; Ringl, Christian; Urbassek, Herbert M.
2016-07-01
We study the collision of a highly porous granular aggregate of adhesive \\upmu m-sized silica grains with a hard wall using a granular discrete element method. A compaction wave runs through the granular sample building up an inhomogeneous density profile. The compaction is independent of the length of the aggregate, within the regime of lengths studied here. Also short pulses, as they might be exerted by a piston pushing the granular material, excite a compaction wave that runs through the entire material. The speed of the compaction wave is larger than the impact velocity but considerably smaller than the sound speed. The wave speed is related to the compaction rate at the colliding surface and the average slope of the linear density profile.
Effects of branched defect geometry on the propagation of Rayleigh waves
NASA Astrophysics Data System (ADS)
Hernandez-Valle, F.; Clough, A. R.; Dutton, B.; Edwards, R. S.
2014-02-01
Rayleigh waves can be used for characterisation of surface-breaking defects, giving a measure of the depth and the angle of propagation of a defect with simple (i.e. single crack) geometry. However, surface breaking defects will often grow with a more complicated geometry. We present here results of experimental measurements using laser generated and detected Rayleigh waves on aluminium samples containing machined slots with varied branched geometries. The signal enhancement found in the near-field, and the reflection and transmission of different wavemodes can be used to position the defect and gain an idea of its geometry. This research can be applied to monitor components prone to developing stress corrosion cracking (branched-like defects). Results are shown of the near-field interactions of Rayleigh waves with this type of cracking in stainless steel pipe samples, in order to resolve the spatial extent and geometric alignment of those defects.
Finite Larmor Radius approximation for waves propagation in cylindrical plasma configurations
NASA Astrophysics Data System (ADS)
Galeotti, Laura; Ceccherini, Francesco; Brambilla, Marco; Barnes, Daniel C.; Pegoraro, Francesco
2011-10-01
We present an analytical derivation in cylindrical geometry of the Finite Larmor Radius approximation for the wave equations in the cyclotron frequency range and show a set of numerical results obtained with a new extended version of the code FELICE, which allows for arbitrary profiles of field, densities and temperatures. Obtaining a cylindrical FLR approximation is of great relevance for studying the wave propagation in plasma configurations like FRC's and theta-pinches in particular. The generic configuration we consider can be divided in the radial direction in two regions, i.e, a ``plasma region'' and a ``vacuum region''. In the former the wave propagation is computed numerically from the FRL approximation found, in the latter instead a general analytical solution has been calculated and implemented in the code. A detailed description on how to ensure both the overall causality of the propagation process and the correct matching conditions for the antenna surface and the vacuum/plasma surface is shown as well.
NASA Astrophysics Data System (ADS)
Isliker, Heinz; Chatziantonaki, Ioanna; Tsironis, Christos; Vlahos, Loukas
2012-09-01
We analyze the propagation of electron-cyclotron waves, their absorption and current drive when neoclassical tearing modes (NTMs), in the form of magnetic islands, are present in a tokamak plasma. So far, the analysis of the wave propagation and power deposition in the presence of NTMs has been performed mainly in the frame of an axisymmetric magnetic field, ignoring any effects from the island topology. Our analysis starts from an axisymmetric magnetic equilibrium, which is perturbed such as to exhibit magnetic islands. In this geometry, we compute the wave evolution with a ray-tracing code, focusing on the effect of the island topology on the efficiency of the absorption and current drive. To increase the precision in the calculation of the power deposition, the standard analytical flux-surface labeling for the island region has been adjusted from the usual cylindrical to toroidal geometry. The propagation up to the O-point is found to be little affected by the island topology, whereas the power absorbed and the driven current are significantly enhanced, because the resonant particles are bound to the small volumes in between the flux surfaces of the island. The consequences of these effects on the NTM evolution are investigated in terms of the modified Rutherford equation.
Zhu, Bo O.; Chen, Ke; Jia, Nan; Sun, Liang; Zhao, Junming; Jiang, Tian; Feng, Yijun
2014-01-01
Transmission and reflection are two fundamental properties of the electromagnetic wave propagation through obstacles. Full control of both the magnitude and phase of the transmission and reflection independently are important issue for free manipulation of electromagnetic wave propagation. Here we employed the equivalent principle, one fundamental theorem of electromagnetics, to analyze the required surface electric and magnetic impedances of a passive metasurface to produce either arbitrary transmission magnitude and phase or arbitrary reflection magnitude and phase. Based on the analysis, a tunable metasurface is proposed. It is shown that the transmission phase can be tuned by 360° with the unity transmissivity or the transmissivity can be tuned from 0 to 1 while the transmission phase is kept around 0°. The reflection magnitude and phase can also been tuned similarly with the proposed metasurface. The proposed design may have many potential applications, such as the dynamic EM beam forming and scanning.
NASA Astrophysics Data System (ADS)
Belov, E.; Blachman, M.; Britan, A.; Sadot, O.; Ben-Dor, G.
2015-11-01
A simple experimental technique, based on pressure transducers, capable of measuring the stress wave that propagates along the solid phase of a granular column after being hit head-on by a plane shock wave is presented. The technique is based on installing couples of gauges at different cross-sections along the granular column in such a way that one transducer measures the overall pressure acting on it while the other measures only the pressure exerted on it by the gaseous phase of the granular column. By means of the presented experimental technique the time histories of the stresses normal to the shock tube walls and data on the stress wave attenuation as it propagates downstream towards the shock tube end wall were obtained.
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…
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…
Parametric Excitations of Fast Plasma Waves by Counter-propagating Laser Beams
G. Shvets; N.J. Fisch
2001-03-19
Short- and long-wavelength plasma waves can become strongly coupled in the presence of two counter-propagating laser pump pulses detuned by twice the cold plasma frequency. What makes this four-wave interaction important is that the growth rate of the plasma waves occurs much faster than in the more obvious co-propagating geometry.
Magnonic crystal wave guide with large spin-wave propagation velocity in CoFeB
NASA Astrophysics Data System (ADS)
Schwarze, T.; Grundler, D.
2013-06-01
Propagating spin-wave spectroscopy is reported for two-dimensional CoFeB antidot lattices (ADLs) with perpendicular-to-plane magnetization. The magnonic crystals consist of square lattices of 190 nm diameter holes with different periods p. At p = 600 nm, the velocity vg of long wavelength spin-waves is reduced compared to the unpatterned reference film by up to about 30%. However, a large vg is regained when we leave out a column of nanoholes in the ADLs. Such a magnonic crystal wave guide is found to support faster spin waves than a CoFeB stripe of the same geometrical width, making the finding interesting for spin-wave guiding in integrated magnonics.
Some wave-particle effects on large-scale Alfven wave propagation and damping
NASA Technical Reports Server (NTRS)
Siregar, E.; Goldstein, M. L.
1995-01-01
Phase mixing can reduce greatly the torsional Alfven wave's dissipation length for propagation in complex magnetic field-line geometries. This phase mixing causes significant energy transfers from large to small scales where a conversion from ordered wave energy into a particle kinetic form occurs. This conversion during its initial stages is an entropy conserving process well described by Vlasov theory, Nonlinear stages of wave-particle resonance, particle trapping, and collisional resistivity are often invoked as processes eventually responsible for converting ordered wave motions into random thermal motion. Strictly speaking, this entropy producing phase cannot be described within Vlasov theory, and the large-scale effects of these microscopic events resides at the difficult frontier between generalized fluid and kinetic theories. We attempt to describe certain aspects of such resonances within the framework of fluid theory focusing on torsional Alfven wave energy transport and deposition within flux tubes.
Dual differential interferometer for measurements of broadband surface acoustic waves
NASA Technical Reports Server (NTRS)
Turner, T. M.; Claus, R. O.
1981-01-01
A simple duel interferometer which uses two pairs of orthogonally polarized optical beams to measure both the amplitude and direction of propagation of broadband ultrasonic surface waves is described. Each pair of focused laser probe beams is used in a separate wideband differential interferometer to independently detect the component of surface wave motion along one direction on the surface. By combining the two output signals corresponding to both components, the two dimensional surface profile and its variation as a function of time is determined.
Coronal Seismology: The Search for Propagating Waves in Coronal Loops
NASA Astrophysics Data System (ADS)
Schad, Thomas A.; Seeley, D.; Keil, S. L.; Tomczyk, S.
2007-05-01
We report on Doppler observations of the solar corona obtained in the Fe XeXIII 1074.7nm coronal emission line with the HAO Coronal Multi-Channel Polarimeter (CoMP) mounted on the NSO Coronal One Shot coronagraph located in the Hilltop Facility of NSO/Sacramento Peak. The COMP is a tunable filtergraph instrument that records the entire corona from the edge of the occulting disk at approximately 1.03 Rsun out to 1.4 Rsun with a spatial resolution of about 4” x 4”. COMP can be rapidly scanned through the spectral line while recording orthogonal states of linear and circular polarization. The two dimensional spatial resolution allows us to correlate temporal fluctuations observed in one part of the corona with those seen at other locations, in particular along coronal loops. Using cross spectral analysis we find that the observations reveal upward propagating waves that are characterized by Doppler shifts with rms velocities of 0.3 km/s, peak wave power in the 3-5 mHz frequency range, and phase speeds 1-3 Mm/s. The wave trajectories are consistent with the direction of the magnetic field inferred from the linear polarization measurements. We discuss the phase and coherence of these waves as a function of height in the corona and relate our findings to previous observations. The observed waves appear to be Alfvenic in character. "Thomas Schad was supported through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program." Daniel Seeley was supported through the National Solar Observatory Research Experience for Teachers (RET) site program, which is funded by the National Science Foundation RET program.
Acoustic Measurement of Surface Wave Damping by a Meniscus.
Michel, Guillaume; Pétrélis, François; Fauve, Stéphan
2016-04-29
We investigate the reflection of gravity-capillary surface waves by a plane vertical barrier. The size of the meniscus is found to strongly affect reflection: the energy of the reflected wave with a pinned contact line is around twice the one corresponding to a fully developed meniscus. To perform these measurements, a new experimental setup similar to an acousto-optic modulator is developed and offers a simple way to measure the amplitude, frequency and direction of propagation of surface waves. PMID:27176523
NASA Astrophysics Data System (ADS)
Li, Jiasong; Wang, Shang; Manapuram, Ravi Kiran; Singh, Manmohan; Menodiado, Floredes M.; Aglyamov, Salavat; Emelianov, Stanislav; Twa, Michael D.; Larin, Kirill V.
2013-12-01
We demonstrate the use of phase-stabilized swept-source optical coherence tomography to assess the propagation of low-amplitude (micron-level) waves induced by a focused air-pulse system in tissue-mimicking phantoms, a contact lens, a silicone eye model, and the mouse cornea in vivo. The results show that the wave velocity can be quantified from the analysis of wave propagation, thereby enabling the estimation of the sample elasticity using the model of surface wave propagation for the tissue-mimicking phantoms. This noninvasive, noncontact measurement technique involves low-force methods of tissue excitation that can be potentially used to assess the biomechanical properties of ocular and other delicate tissues in vivo.
Broadband transverse electric surface wave in silicene
NASA Astrophysics Data System (ADS)
Ukhtary, M. Shoufie; Nugraha, Ahmad R. T.; Hasdeo, Eddwi H.; Saito, Riichiro
2016-08-01
Transverse electric (TE) surface wave in silicine is theoretically investigated. The TE surface wave in silicene is found to exhibit better characteristics compared with that in graphene, in terms of a broader frequency range and more confinement to the surface which originate from the buckled structure of silicene. We found that even undoped silicene can support the TE surface wave. We expect the similar characteristics of the TE surface wave in other two-dimensional materials that have a slightly buckled honeycomb lattice.
Propagating Waves of Self-assembly in Organosilane Monolayers
Douglas,J.; Efimenko, K.; Fischer, D.; Phelan, F.; Genzer, J.
2007-01-01
Wavefronts associated with reaction-diffusion and self-assembly processes are ubiquitous in the natural world. For example, propagating fronts arise in crystallization and diverse other thermodynamic ordering processes, in polymerization fronts involved in cell movement and division, as well as in the competitive social interactions and population dynamics of animals at much larger scales. Although it is often claimed that self-sustaining or autocatalytic front propagation is well described by mean-field 'reaction-diffusion' or 'phase field' ordering models, it has recently become appreciated from simulations and theoretical arguments that fluctuation effects in lower spatial dimensions can lead to appreciable deviations from the classical mean-field theory (MFT) of this type of front propagation. The present work explores these fluctuation effects in a real physical system. In particular, we consider a high-resolution near-edge x-ray absorption fine structure spectroscopy (NEXAFS) study of the spontaneous frontal self-assembly of organosilane (OS) molecules into self-assembled monolayer (SAM) surface-energy gradients on oxidized silicon wafers. We find that these layers organize from the wafer edge as propagating wavefronts having well defined velocities. In accordance with two-dimensional simulations of this type of front propagation that take fluctuation effects into account, we find that the interfacial widths w(t) of these SAM self-assembly fronts exhibit a power-law broadening in time, w(t) {approx} t{sup {beta}}, rather than the constant width predicted by MFT. Moreover, the observed exponent values accord rather well with previous simulation and theoretical estimates. These observations have significant implications for diverse types of ordering fronts that occur under confinement conditions in biological or materials-processing contexts.
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)
Experimental research on dust lifting by propagating shock wave
NASA Astrophysics Data System (ADS)
Żydak, P.; Oleszczak, P.; Klemens, R.
2016-05-01
The aim of the presented work was to study the dust lifting process from a layer of dust behind a propagating shock wave. The experiments were conducted with the use of a shock tube and a specially constructed, five-channel laser optical device enabling measurements at five positions located in one vertical plane along the height of the tube. The system enabled measurements of the delay in lifting up of the dust from the layer, and the vertical velocity of the dust cloud was calculated from the dust concentration measurements. The research was carried out for various initial conditions and for three fractions of black coal dust. In the presented tests, three shock wave velocities: 450, 490 and 518 m/s and three dust layer thicknesses, equal to 1.0, 1.5 and 2.0 mm, were taken into consideration. On the grounds of the obtained experimental results, it was assumed that the vertical component of the lifted dust velocity is a function of the dust particle diameter, the velocity of the air flow in the channel, the layer thickness and the dust bulk density. It appeared, however, that lifting up of the dust from the thick layers, thicker than 1 mm, is a more complex process than that from thin layers and still requires further research. A possible explanation is that the shock wave action upon the thick layer results in its aggregation in the first stage of the dispersing process, which suppresses the dust lifting process.
The propagation of sound waves in drill strings
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.