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Showing papers on "Reflection (physics) published in 2005"


Book
01 Jan 2005
TL;DR: In this paper, the basic theory of anisotropic wave propagation is discussed and a velocity analysis and parameter estimation for VTI media is presented. And P-wave imaging is performed in transversely isotropic media.
Abstract: 1. Elements of basic theory of anisotropic wave propagation. 2. Influence of anisotropy on point-source radiation and AVO analysis. 3. Normal-moveout velocity in layered anisotropic media. 4. Nonhyperbolic reflection moveout. 5. Reflection moveout of mode-converted waves. 6. P-wave time-domain signatures in transversely isotropic media. 7. Velocity analysis and parameter estimation for VTI media. 8. P-wave imaging for VTI media.

672 citations


Journal ArticleDOI
TL;DR: In this article, a model of the global properties of Alfven waves in the solar atmosphere and the fast solar wind is presented, where linear non-WKB wave transport equations are solved from the photosphere to a distance past the orbit of the Earth, for wave periods ranging from 3 s to 3 days.
Abstract: We present a comprehensive model of the global properties of Alfven waves in the solar atmosphere and the fast solar wind. Linear non-WKB wave transport equations are solved from the photosphere to a distance past the orbit of the Earth, and for wave periods ranging from 3 s to 3 days. We derive a radially varying power spectrum of kinetic and magnetic energy fluctuations for waves propagating in both directions along a superradially expanding magnetic flux tube. This work differs from previous models in three major ways. (1) In the chromosphere and low corona, the successive merging of flux tubes on granular and supergranular scales is described using a two-dimensional magnetostatic model of a network element. Below a critical flux-tube merging height the waves are modeled as thin-tube kink modes, and we assume that all of the kink-mode wave energy is transformed into volume-filling Alfven waves above the merging height. (2) The frequency power spectrum of horizontal motions is specified only at the photosphere, based on prior analyses of G-band bright point kinematics. Everywhere else in the model the amplitudes of outward and inward propagating waves are computed with no free parameters. We find that the wave amplitudes in the corona agree well with off-limb nonthermal line-width constraints. (3) Nonlinear turbulent damping is applied to the results of the linear model using a phenomenological energy loss term. A single choice for the normalization of the turbulent outer-scale length produces both the right amount of damping at large distances (to agree with in situ measurements) and the right amount of heating in the extended corona (to agree with empirically constrained solar wind acceleration models). In the corona, the modeled heating rate differs by more than an order of magnitude from a rate based on isotropic Kolmogorov turbulence.

484 citations


Journal ArticleDOI
TL;DR: In this paper, a large sample of type 1 active galactic nuclei (AGN) spectra taken with XMM-Newton was used to fit both the conventional model (a power law and black body) and the relativistically-blurred photoionized disc reflection model of Ross and Fabian.
Abstract: We present a large sample of type 1 active galactic nuclei (AGN) spectra taken with XMM-Newton, and fit them with both the conventional model (a power law and black body) and the relativistically-blurred photoionized disc reflection model of Ross and Fabian (2005). We find the disc reflection model is a better fit. The disc reflection model successfully reproduces the continuum shape, including the soft excess, of all the sources. The model also reproduces many features that would conventionally be interpreted as absorption edges. We are able to use the model to infer the properties of the sources; specifically that the majority of black holes in the sample are strongly rotating and that there is a deficit in sources with an inclination > 70 degrees. We conclude that the disc reflection model is an important tool in the study of AGN X-ray spectra.

378 citations


Journal ArticleDOI
TL;DR: In this paper, a grid-based numerical scheme for tracking the evolution of monotonically advancing interfaces, via finite-difference solution of the eikonal equation, known as the fast marching method (FMM), is presented.
Abstract: The accurate prediction of seismic traveltimes is required in many areas of seismology, including the processing of seismic reflection profiles, earthquake location, and seismic tomography at a variety of scales. In this paper, we present two seismic applications of a recently developed grid-based numerical scheme for tracking the evolution of monotonically advancing interfaces, via finite-difference solution of the eikonal equation, known as the fast marching method (FMM). Like most other practical grid-based techniques, FMM is only capable of locating the first-arrival phase in continuous media; however, its combination of unconditional stability and rapid computation make it a truly practical scheme for velocity fields of arbitrary complexity. The first application of FMM that we present focuses on the prediction of multiple reflection and refraction phases in complex 2D layered media. By treating each layer that the wavefront enters as a separate computational domain, we show that sequential application of FMM can be used to track phases comprising any number of reflection and transmission branches in media of arbitrary complexity. We also show that the use of local grid refinement in the source neighbourhood, where wavefront curvature is high, significantly improves the accuracy of the scheme with little extra computational expense. The second application of FMM that we consider is in the context of 3D teleseismic tomography, which uses relative traveltime residuals from distant earthquakes to image wavespeed variations in the Earth’s crust and upper mantle beneath a seismic array. Using teleseismic data collected in Tasmania, we show that FMM can rapidly and robustly calculate two-point traveltimes from an impinging teleseismic wavefront to a receiver array located on the surface, despite the presence of significant lateral variations in wavespeed in the intervening crust and upper mantle. Combined with a rapid subspace inversion method, the new FMM based tomographic scheme is shown to be extremely efficient and robust.

230 citations


Journal ArticleDOI
TL;DR: In this paper, the analysis of coherent radar sounding echoes from polar ice sheets can provide information suitable for classifying the subglacial environment, including smooth seawater, smooth saturated sediments, accreted marine ice, rough bottom crevasses, mixed conditions with partial subglice water, and dry frozen conditions.
Abstract: [1] Analysis of coherent radar sounding echoes from polar ice sheets can provide information suitable for classifying the subglacial environment. Echoes from a general interface consist of both specularly reflected and diffusely scattered contributions. Specular reflection results from smooth uniform interfaces, whereas diffuse scattering results from rough nonuniform interfaces and inhomogeneous media. This article discusses how these phenomena are important to the acquisition and analysis of coherent radar sounding data. Reflection results are presented from airborne surveys conducted in 1987 over the downstream portions of Whillans Ice Stream and Ice Stream C, West Antarctica. Additionally, reflection and scattering analyses along with new results are presented for repeat profiles flown in 2001 over Ice Stream C. Analysis methods include using echo amplitudes to compute reflection coefficients which are used for inferring the dielectric properties of the subglacial material. Echo phase analysis provides the locations of dominant scattering centers which relate to reflection or scattering from the interface as well as provide interface roughness estimates. Comparison of low- and high-resolution imaging obtained from synthetic aperture radar techniques indicates a reflecting and/or scattering interface. Combining the results from these independent analyses provides classification of the subglacial environment. Classified regions include smooth seawater, smooth saturated sediments, accreted marine ice, rough bottom crevasses, mixed conditions with partial subglacial water, and dry frozen conditions.

223 citations


Journal ArticleDOI
TL;DR: In this paper, wave transmission on rubble mound structures has been subject for more flume tests in the DELOS programme and simultaneously an existing database has been increased extensively by receiving data from other researchers in the world.

220 citations


Patent
12 May 2005
TL;DR: In this article, an ultrasonic diagnostic apparatus that can recognize a nature variation on a blood vessel wall that varies according to types of disease including aneurysm, collagen disease, and diabetes and their severity, and can perform non-invasive diagnosis easily and accurately.
Abstract: PROBLEM TO BE SOLVED: To provide an ultrasonic diagnostic apparatus that can recognize a nature variation on a blood vessel wall that varies according to types of disease including aneurysm, collagen disease, and diabetes and their severity, and can perform non-invasive diagnosis easily and accurately SOLUTION: An ultrasonic driving equipment 11 sends a wave transmission command to an ultrasonic probe 12 The ultrasonic probe 12 transmits an ultrasonic wave vertically against a beating blood vessel and receives a reflection echo generated by the Doppler effect A wave receiving circuit 13 amplifies the reflection echo A comparison circuit 14 extracts a Doppler signal in the reflection echo A noise filter circuit 15 eliminates noises in the Doppler signal A frequency-voltage converter circuit 16 converts a frequency of the Doppler signal into a voltage A calculation means 17 obtains a fractal dimension of a voltage output wave form of the reflection echo by fractal analysis using the box counting method An output means 18 outputs a result calculated by the calculation means 17 COPYRIGHT: (C)2005,JPO&NCIPI

194 citations


Journal ArticleDOI
TL;DR: In this paper, a textured surface is used as an electronically steerable leaky wave antenna, by coupling energy into a leaky band, and tuning the surface to change the radiation angle.
Abstract: A resonant texture allows the impedance of a metal surface to be changed from an electric conductor to a magnetic conductor, or any boundary condition in between. Varactor diodes incorporated into the structure allow electronic control the reflection phase and the surface wave properties. This tunable textured surface is used as an electronically steerable leaky wave antenna, by coupling energy into a leaky wave band, and tuning the surface to change the radiation angle. With a simple optimization algorithm, the beam can be electronically scanned over a wide range in both the forward and backward directions. Because the surface geometry provides multiple degrees of freedom per half wavelength, it allows independent control of the magnitude and phase of the surface wave radiation, so the antenna can be programmed to have a large effective aperture over the entire scan range. Radiation in the backward direction can also be understood in terms of a backward band, which can be measured directly from the surface reflection properties.

172 citations


Journal ArticleDOI
TL;DR: In this paper, a nonlinear supersymmetric σ-model is used to derive closed-form analytic expressions for the distribution of reflection probability in a generic disordered system.
Abstract: We review recent progress in analysing wave scattering in systems with both intrinsic chaos and/or disorder and internal losses, when the scattering matrix is no longer unitary. By mapping the problem onto a nonlinear supersymmetric σ-model, we are able to derive closed-form analytic expressions for the distribution of reflection probability in a generic disordered system. One of the most important properties resulting from such an analysis is statistical independence between the phase and the modulus of the reflection amplitude in every perfectly open channel. The developed theory has far-reaching consequences for many quantities of interest, including local Green functions and time delays. In particular, we point out the role played by absorption as a sensitive indicator of mechanisms behind the Anderson localization transition. We also provide a random-matrix-based analysis of S-matrix and impedance correlations for various symmetry classes as well as the distribution of transmitted power for systems with broken time-reversal invariance, completing previous works on the subject. The results can be applied, in particular, to the experimentally accessible impedance and reflection in a microwave or an ultrasonic cavity attached to a system of antennas.

148 citations


Journal ArticleDOI
TL;DR: In this paper, wave reflection, transmission, and propagation in Timoshenko beams together with wave analysis of vibrations in timoshenko beam structures are derived, and the transmission and reflection matrices for various discontinuities on a Timoshenko beam are derived.
Abstract: This paper concerns wave reflection, transmission, and propagation in Timoshenko beams together with wave analysis of vibrations in Timoshenko beam structures. The transmission and reflection matrices for various discontinuities on a Timoshenko beam are derived. Such discontinuities include general point supports, boundaries, and changes in section. The matrix relations between the injected waves and externally applied forces and moments are also derived. These matrices can be combined to provide a concise and systematic approach to vibration analysis of Timoshenko beams or complex structures consisting of Timoshenko beam components. The approach is illustrated with several numerical examples.

128 citations


Journal ArticleDOI
Baljeet Singh1
TL;DR: In this paper, the reflection coefficients of P and SV waves from free surface of an elastic solid with thermodiffusion are considered and boundary conditions are solved to obtain a system of four non-homogeneous equations for reflection coefficients.
Abstract: The governing equations for generalized thermodiffusion in an elastic solid are solved. There exists three kinds of dilatational waves and a Shear Vertical (SV) wave in a two-dimensional model of the solid. The reflection phenomena of P and SV waves from free surface of an elastic solid with thermodiffusion is considered. The boundary conditions are solved to obtain a system of four non-homogeneous equations for reflection coefficients. These reflection coefficients are found to depend upon the angle of incidence of P and SV waves, thermodiffusion parameters and other material constants. The numerical values of modulus of the reflection coefficients are presented graphically for different values of thermodiffusion parameters. The dimensional velocities of various plane waves are also computed for different material constants.

Journal ArticleDOI
TL;DR: In this article, the ability of a shear wave reflection (WR) method to monitor microstructural changes of Portland cement mortar during hydration was investigated, and it was shown that the wave reflection measurements are governed primarily by the degree of the interparticle bonding of the cement particles as calculated from the specific contact area of a simulated microstructure.

Journal ArticleDOI
TL;DR: In this paper, the angular dependent reflection coefficients of different building materials were determined using terahertz time-domain spectroscopy in transmission geometry and Fresnel's equations, which is more efficient than a set of measurements in reflection geometry for different angles.
Abstract: To obtain realistic models for propagation channels in future pico-cellular indoor terahertz communication systems it is necessary to know the reflective properties of building materials found in a typical office environment. The angular dependent reflection coefficients of different building materials were determined using terahertz time-domain spectroscopy in transmission geometry and Fresnel's equations. This approach is more efficient than a set of measurements in reflection geometry for different angles. Verification of the method with a set of such reflection measurements shows an excellent agreement.

Journal ArticleDOI
TL;DR: In this paper, surface displacements, surface strain, rocking, and energy partitioning during reflection-of-plane waves in a fluid-saturated poroelastic half-space are discussed.

Journal ArticleDOI
TL;DR: In this article, the authors show that remote sensing of internal waves by marine seismic reflection methods can provide quantitative information on internal wave energy and its spatial variability at high lateral resolution and full ocean depth over large volumes of the ocean.
Abstract: [1] Internal waves affect many important dynamical processes in the ocean, but in situ observations of internal waves are infrequent and spatially sparse. Here we show that remote sensing of internal waves by marine seismic reflection methods can provide quantitative information on internal wave energy and its spatial variability at high lateral resolution and full ocean depth over large volumes of the ocean. Seismic images of the Norwegian Sea water column show reflections that capture snapshots of finestructure displacements due to internal waves. Horizontal wave number spectra derived from digitized reflection horizons in the open ocean compare favorably to the Garrett-Munk tow spectrum of oceanic internal wave displacements. Spectra within 10 km laterally and 200 m vertically of the continental slope show enhanced energy likely associated with internal wave-sloping boundary interactions.

Journal ArticleDOI
TL;DR: A continuous electromagnetic metal planar metamaterial, which resembles a "fish scale" structure, which is highly transparent to electromagnetic radiation throughout a broad spectral range and becomes completely "invisible" at some frequency inflicting no transmission losses and phase delay.
Abstract: We report on a continuous electromagnetic metal planar metamaterial, which resembles a "fish scale" structure. Apart from the one isolated wavelength, it is highly transparent to electromagnetic radiation throughout a broad spectral range and becomes completely "invisible" at some frequency inflicting no transmission losses and phase delay. When the structure is superimposed on a metallic mirror it becomes a good broadband reflector everywhere apart from one wavelength where the reflectivity is small. At this wavelength the reflected wave shows no phase change with respect to the incident wave, thus resembling a reflection from a hypothetical zero refractive index material, or "magnetic wall." We also discovered that the structure acts as a local field concentrator and a resonant "amplifier" of losses in the underlying dielectric.

Journal ArticleDOI
TL;DR: In this article, the authors considered a two-dimensional inverse scattering problem of determining a sound-soft obstacle from the far field pattern and established uniqueness within a class of polygonal domains by means of a single incoming plane wave.
Abstract: We consider a two-dimensional inverse scattering problem of determining a sound-soft obstacle from the far field pattern and, under a non-trapping condition, we establish uniqueness within a class of polygonal domains by means of a single incoming plane wave. Moreover, we will show similar uniqueness in the sound-hard case by means of two incoming plane waves. The key is the analyticity of the solution of the scattering problem and the reflection of solutions.

Journal ArticleDOI
TL;DR: In this paper, the authors used an enhanced signal processing technique to improve the detection of leaks using an artificial generation of pressure waves using a solenoid valve, rather than relying upon natural sources of fluid excitation.
Abstract: This paper describes progress on a new technique to detect pipeline features and leaks using signal processing of a pressure wave measurement. Previous work (by the present authors) has shown that the analysis of pressure wave reflections in fluid pipe networks can be used to identify specific pipeline features such as open ends, closed ends, valves, junctions, and certain types of bends. It was demonstrated that by using an extension of cross-correlation analysis, the identification of features can be achieved using fewer sensors than are traditionally employed. The key to the effectiveness of the technique lies in the artificial generation of pressure waves using a solenoid valve, rather than relying upon natural sources of fluid excitation. This paper uses an enhanced signal processing technique to improve the detection of leaks. It is shown experimentally that features and leaks can be detected around a sharp bend and up to seven reflections from features/leaks can be detected, by which time the wave has traveled over 95 m. The testing determined the position of a leak to within an accuracy of 5%, even when the location of the reflection from a leak is itself dispersed over a certain distance and, therefore, does not cause an exact reflection of the wave.

Journal ArticleDOI
TL;DR: In this paper, the authors considered the propagation of a plane electromagnetic wave in a medium with a piecewise constant axion field and showed that the reflection and transmission of a wave at an interface between the two media is sensitive to the difference of the axion values.

Patent
12 Apr 2005
TL;DR: A reflector has a curved part covering the light source and a pair of end parts extending at the two sides of the curved part, the inside surface of each end part has a plurality of substantially parallel projections or depressions.
Abstract: A reflector has a curved part covering the light source and a pair of end parts extending at the two sides of the curved part. The inside surface of each end part has a plurality of substantially parallel projections or depressions. The light-guiding plate has an incident surface and an emission surface substantially perpendicular to the incident surface, the incident surface having a plurality of projections or depressions extending substantially parallel to the emission surface. Also, the reflection surface of the light-guiding plate has projections.

Proceedings ArticleDOI
18 Sep 2005
TL;DR: In this paper, a quantitative methodology for the optimization of the acoustic mirror layer stack is proposed, and the influence of the mirror structure on the trapping of both longitudinal and shear wave energy is discussed.
Abstract: The overall performance of bulk acoustic wave (BAW) filters is dominated by the effective coupling coefficient and the quality factor of the constituting BAW resonators. Whereas the effective coupling coefficient and its dependency on the layer stack is quite accurately modeled with a simple one-dimensional acousto-electric model (e.g. Masonstransmission line model), the prediction and optimization of the resonators quality factor - particularly for solidly mounted resonators (SMR) - completely fails with this model: whereas a calculation of the acoustic reflectance of a standard quarter-wavelength mirror stack leads to theoretical Q-factors well above 10000, experimental SMR devices with this type of mirror show values of typically well below 1000. This discrepancy is commonly explained by either visco-elastic loss in the materials and/or laterally leaking waves leaving the active resonator area. However, we have found a new, far more important loss mechanism relating to shear waves generated in the device. These waves can be created by injection from the resonators border area as well as by reflection/refraction of longitudinal waves at non-perpendicular angle of incidence to a material interface. In this paper, a quantitative methodology for the optimization of the acoustic mirror layer stack will be proposed. The influence of the mirror structure on the trapping of both longitudinal and shear wave energy will be discussed based on this very simple approach. Trade-offs with respect to the other important device parameters, such as effective coupling coefficient, temperature coefficient of frequency (TCF) and purity of the electrical response, are analyzed. The usefulness of this approach for the optimization of resonator Q-values will be proven by experimental results demonstrating Q-factors of 1500 and higher.

Proceedings ArticleDOI
24 Feb 2005
TL;DR: In this paper, a shape from polarization (SFP) method was used to reconstruct surface shapes of specular metallic objects by using the refractive index of the surface, a relationship between the degree of polarization and the reflection angle can be established.
Abstract: We propose a new application of « Shape from Polarization » method to reconstruct surface shapes of specular metallic objects. Studying the polarization state of the reflected light is very useful to get information on the surface normals. After reflection, an unpolarized light wave becomes partially linearly polarized. Such a wave, can be described by its three parameters: intensity, degree of polarization, and angle of polarization. By using the refractive index of the surface, a relationship between the degree of polarization and the reflection angle can be established. Unfortunately, the relation commonly used for dielectrics, cannot be applied since the refractive index of metallic surfaces is complex. To get a similar relation, we apply a usual approximation valid in the visible region. The Fresnel reflectance model can also provide a relationship between the angle of polarization and the incidence plane orientation. Thus, the reflection angle and the incidence plane orientation give the surface normals. The shape is finally computed by integrating the normals with a relaxation algorithm. Applications on metallic objects made by stamping and polishing are also described, and show the efficiency of our system to discriminate shape defects. Future works will consist in integrating the system into an automatic process of defects detection.

Patent
01 Dec 2005
TL;DR: In this article, a reflection preventing material includes substrate having a surface on which a convex/concave pattern of a cycle smaller than the shortest wavelength of the incident light is formed in x direction and y direction and satisfies Expression (1) below.
Abstract: A reflection preventing material includes substrate having a surface on which a convex/concave pattern of a cycle smaller than the shortest wavelength of the incident light is formed in x direction and y direction and satisfies Expression (1) below: (1) wherein λmin is the shortest wavelength of the incident light, θimax is the maximum incident angle of the incident light, ni is the refraction index of the incident medium, Λx is the cycle of the convex/concave pattern in the x direction, and Λy is the cycle of the convex/concave pattern in the y direction. Thus, it is possible to suppress generation of diffractive light of short wavelength light component in a wide wavelength range.

Journal ArticleDOI
TL;DR: To understand how short-wave behavior near the peak modifies the predictions of the long-wave theory, this paper solves the scattering problem in the 2-D cochlear model.
Abstract: The theory of coherent reflection filtering explains the empirical form of the cochlear reflectance by showing how it emerges from the coherent “backscattering” of forward-traveling waves by impedance perturbations in the mechanics of the cochlear partition. Since the theory was developed using the one-dimensional (1-D) transmission-line model of the cochlea, an obvious logical shortcoming is the failure of the long-wavelength approximation near the peak of the traveling wave, where coherent backscattering is purported to occur. Indeed, existing theory suggests that wave reflection may be strongly suppressed in the short-wave regime. To understand how short-wave behavior near the peak modifies the predictions of the long-wave theory, this paper solves the scattering problem in the 2-D cochlear model. The 2-D problem is reduced to a 1-D wave equation and the solution expressed as an infinite series in which successive terms arise via multiple scattering within the cochlea. The cochlear reflectance is computed in response-matched models constructed by solving the inverse problem to control for variations in mechanical tuning among models of different heights and dimensionality. Reflection from the peak region is significantly enhanced by the short-wave hydrodynamics, but other conclusions of the 1-D analysis—such as the predicted relation between emission group delay and the wavelength of the traveling wave—carry over with only minor modifications. The results illustrate the important role of passive hydromechanical effects in shaping otoacoustic emissions and cochlear tuning.

Journal ArticleDOI
TL;DR: In this article, the relative importance of different contributions to transport of light gases in single walled carbon nanotubes, using methane and hydrogen as examples, is examined using molecular dynamics simulation with atomistic models of the nanotube wall, from which the diffusive and viscous contributions are resolved using a recent approach that provides an explicit expression for the latter.
Abstract: We examine here the relative importance of different contributions to transport of light gases in single walled carbon nanotubes, using methane and hydrogen as examples. Transport coefficients at 298 K are determined using molecular dynamics simulation with atomistic models of the nanotube wall, from which the diffusive and viscous contributions are resolved using a recent approach that provides an explicit expression for the latter. We also exploit an exact theory for the transport of Lennard-Jones fluids at low density considering diffuse reflection at the tube wall, thereby permitting the estimation of Maxwell coefficients for the wall reflection. It is found that reflection from the carbon nanotube wall is nearly specular, as a result of which slip flow dominates, and the viscous contribution is small in comparison, even for a tube as large as 8.1 nm in diameter. The reflection coefficient for hydrogen is 3-6 times as large as that for methane in tubes of 1.36 nm diameter, indicating less specular reflection for hydrogen and greater sensitivity to atomic detail of the surface. This reconciles results showing that transport coefficients for hydrogen and methane, obtained in simulation, are comparable in tubes of this size. With increase in adsorbate density, the reflection coefficient increases, suggesting that adsorbate interactions near the wall serve to roughen the local potential energy landscape perceived by fluid molecules.

Journal ArticleDOI
TL;DR: In this article, an analytical-numerical technique for the solution of the two-dimensional electromagnetic plane-wave scattering by a finite set of perfectly conducting circular cylinders buried in a dielectric half-space is presented.
Abstract: An analytical-numerical technique, for the solution of the two-dimensional electromagnetic plane-wave scattering by a finite set of perfectly conducting circular cylinders buried in a dielectric half-space, is presented. The problem is solved for both the near- and the far-field regions, for TM and TE polarizations. The diffracted field is represented in terms of a superposition of cylindrical waves and use is made of the plane-wave spectrum to take into account the reflection and transmission of such waves by the interface. The validity of the approach is confirmed by comparisons with results available in the literature, with very good agreement. The multiple interactions between two buried cylinders have been studied by considering both the induced currents and the scattered field diagrams. Applications of the method to objects of arbitrary cross-section simulated by a suitable configuration of circular cylinders are shown.

Journal ArticleDOI
TL;DR: Results of measurements of the bidirectional reflection function of snow for the solar zenith angle close to 54/spl deg/ are compared with a recently developed snow optical model based on the representation of snow grains as fractal particles.
Abstract: Results of measurements of the bidirectional reflection function of snow for the solar zenith angle close to 54/spl deg/ are compared with a recently developed snow optical model based on the representation of snow grains as fractal particles. The model has a high accuracy out of the principal plane for the observation zenith angles smaller than 60/spl deg/. However, the accuracy is reduced in the principal plane. Specular light reflection by partially oriented snow plates on the snow surface not accounted for by the model can play a role for measurements in the principal plane. The model discussed can be used for the grain size retrieval using both ground and spaceborne measurements of the snow reflectance. This is supported by a high accuracy of the model in a broad spectral range 545-2120 nm as demonstrated in this work.

Journal ArticleDOI
TL;DR: The invasive nature of electrodes placed into sound fields is examined, and a scattering model is developed which is able to predict the acoustic pressure as a function of position over a disk-like electrode substrate.
Abstract: The invasive nature of electrodes placed into sound fields is examined. In particular, perturbations of the sound field due to the presence of the electrode support are explored. The effect of an electrode on the drive sound field (at approximately 23 kHz) is shown to be negligible under the conditions investigated in this paper. However, scattering of shock waves produced by cavity collapse is shown to exhibit a significant effect. To demonstrate this, multibubble sonoluminescence (MBSL) and electrochemical erosion measurements are employed. These measurements show an enhancement, due to the reflection by the solid/liquid boundary at the electrode support, of pressure pulses emitted when cavitation bubbles collapse. To first order, this effect can be accounted for by a correction factor. However, this factor requires accurate knowledge of the acoustic impedance of the interface and the electrolyte media. These are measured for two commonly employed substrates (soda glass and epoxy resin, specifically Epofix). A scattering model is developed which is able to predict the acoustic pressure as a function of position over a disk-like electrode substrate. The effects of shock wave reflection and materials employed in the electrode construction are used to clarify the interpretation of the results obtained from different sonoelectrochemical experiments. Given the widespread experimentation involving the insertion of electrodes (or other sensors) into ultrasonic fields, this work represents a significant development to aid the interpretation of the results obtained.

Journal ArticleDOI
TL;DR: It is predicted that layered structures that include the so-called double-negative metamaterials can demonstrate a giant lateral Goos-Hänchen shift of the scattered beam accompanied by a splitting of the reflected and transmitted beams due to the resonant excitation of surface waves at the interfaces between the conventional and double- negative materials.
Abstract: We study the electromagnetic beam reflection from layered structures that include the so-called double-negative metamaterials, also called left-handed metamaterials. We predict that such structures can demonstrate a giant lateral Goos-Hanchen shift of the scattered beam accompanied by a splitting of the reflected and transmitted beams due to the resonant excitation of surface waves at the interfaces between the conventional and double-negative materials as well as due to the excitation of leaky modes in the layered structures. The beam shift can be either positive or negative, depending on the type of the guided waves excited by the incoming beam. We also perform finite-difference time-domain simulations and confirm the major effects predicted analytically.

Journal ArticleDOI
TL;DR: In this article, the dispersion curves for toroidal structures have been calculated using a finite element method, as there is no available analytical solution, and the factors affecting the transmission and reflection behavior have been identified by studying a straight-curved-straight structure both numerically and experimentally.
Abstract: The practical testing of pipes in a pipe network has shown that there are issues concerning the propagation of ultrasonic guided waves through bends. It is therefore desirable to improve the understanding of the reflection and transmission characteristics of the bend. First, the dispersion curves for toroidal structures have been calculated using a finite element method, as there is no available analytical solution. Then the factors affecting the transmission and reflection behavior have been identified by studying a straight-curved-straight structure both numerically and experimentally. The frequency dependent transmission behavior obtained is explained in terms of the modes propagating in the straight and curved sections of the pipe.