Showing papers on "Reflection (physics) published in 1994"

Dynamic Behavior of Materials

Abstract: Dynamic Deformation and Waves. Elastic Waves. Plastic Waves. Shock Waves. Shock Waves: Equations of State. Differential Form of Conservation Equations and Numerical Solutions to More Complex Problems. Shock Wave Attenuation, Interaction, and Reflection. Shock Wave-Induced Phase Transformations and Chemical Changes. Explosive-Material Interactions. Detonation. Experimental Techniques: Diagnostic Tools. Experimental Techniques: Methods to Produce Dynamic Deformation. Plastic Deformation at High Strain Rates. Plastic Deformation in Shock Waves. Shear Bands (Thermoplastic Shear Instabilities). Dynamic Fracture. Applications. Indexes.

On the Wave Theory in Heat Conduction

Abstract: This work contains three major components: a thorough review on the research emphasizing engineering applications of the thermal wave theory, special features in thermal wave propagation, and the thermal wave model in relation to the microscopic two-step model. For the sake of convenience, the research works are classified according to their individual emphases. Special features in thermal wave propagation include the sharp wavefront and rate effects, the thermal shock phenomenon, the thermal resonance phenomenon, and reflections and refractions of thermal waves across a material interface. By employing the dual-phase-lag concept, we show that the energy equation may be reduced to that governing the heat transport through the metal lattice in the microscopic two-step model

Nonspecular x-ray reflection from rough multilayers.

Abstract: X-ray reflection from periodical multilayers with randomly rough interfaces has been described within the distorted-wave Born approximation. The method is suitable for calculating both specular x-ray reflection and nonspecular (diffuse) scattering. In this paper, both in-plane and vertical correlations of the roughness profiles have been considered and it has been demonstrated that the vertical roughness correlation substantially affects the nonspecular scattering. The theory can explain resonant effects observed in the beam scattered nonspecularly from a periodical multilayer. The theoretical approach has been used for the study of interfacial roughness in a long-periodic AlAs/GaAs multilayer and good agreement has been achieved between the experimental results and the theory.

Some simple ideas on X-ray reflection and grazing-incidence diffraction from thin surfactant films

Abstract: For Langmuir films of long linear amphiphilic molecules at the air-water interface, grazing-incidence diffraction data resolved in terms of both the horizontal and vertical components of the scattering angle can be evaluated to a fair level of detail by means of a slide rule. Specular reflection data require more sophisticated means although some rules of thumb can be formulated.

Modeling wide-angle seismic data for crustal structure: Southeastern Grenville Province

Abstract: A modeling methodology for obtaining two-dimensional (2-D) crustal structure from wide-angle seismic data is applied to data from the southeastern Grenville Province. Pre-modeling steps include (1) assignment of arrival pick uncertainties for appropriate data fitting and weighting using an empirical relationship based on signal-to-noise ratio, (2) using a modified form of travel time reciprocity to avoid unreasonable levels of model heterogeneity, and (3) identifying data unsuitable for 2-D modeling. The goal of the travel time inversion-amplitude modeling approach is to obtain a minimum-structure and minimum-parameter model that takes into account both horizontal and vertical variations in the resolution of typical wide-angle data. Each step of a layer-stripping procedure involves a series of inversions in which a one-dimensional or simple starting model is improved with additional velocity and/or interface nodes until a satisfactory trade-off between travel time fit, parameter resolution and complete ray coverage of all source-receiver pairs is achieved. Using zero vertical-velocity gradient layers and head waves during preliminary first-arrival inversion can (1) decrease the number of intermediate models, (2) allow greater lateral heterogeneity to be imaged, and (3) simplify incorporation of amplitude modeling constraints into the final model. Using amplitude-distance curves allows quantitative modeling of the relative amplitude and offset variations of phases. Discrepancies between observed and calculated reflection amplitudes are used to infer fundamental, non step-like velocity changes at layer boundaries. Later arrivals due to unresolved velocity anomalies are modeled using reflecting segments that “float” within the model without an associated velocity structure. These reflectors provide a spatial image like that obtained from vertical-incidence reflection data, as opposed to a velocity image. The model of Grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in nearby deep reflection data. A crustal-scale zone of wide-angle reflectors with an average easterly apparent dip of 13° defines a major Grenvillian terrane boundary.

The photonic band edge optical diode

Abstract: Using numerical methods, we study pulse propagation near the band edge of a one‐dimensional photonic band gap material with a spatial gradiation in the linear refractive index, together with a nonlinear medium response. We find that such a structure can result in unidirectional pulse propagation. That is, the field will be transmitted for, say, a left‐to‐right direction of propagation, while for right‐to‐left nearly complete reflection occurs. This behavior constitutes the operational mechanism for a passive optical diode.

Radiative transfer in nonuniformly refracting layered media: atmosphere–ocean system

Abstract: We have applied the discrete-ordinate method to solve the radiative-transfer problem pertaining to a system consisting of two strata with different indices of refraction. The refraction and reflection at the interface are taken into account. The relevant changes (as compared with the standard problem with a constant index of refraction throughout the medium) in formulation and solution of the radiative-transfer equation, including the proper application of interface and boundary conditions, are described. Appropriate quadrature points (streams) and weights are chosen for the interface-continuity relations. Examples of radiative transfer in the coupled atmosphere-ocean system are provided. To take into account the region of total reflection in the ocean, additional angular quadrature points are required, compared with those used in the atmosphere and in the refractive region of the ocean that communicates directly with the atmosphere. To verify the model we have tested for energy conservation. We also discuss the effect of the number of streams assigned to the refractive region and the total reflecting region on the convergence. Our results show that the change in the index of refraction between the two strata significantly affects the radiation field. The radiative-transfer model we present is designed for application to the atmosphere-ocean system, but it can be applied to other systems that need to consider the change in the index of refraction between two strata.

Reflection and transmission behaviour of building materials at 60 GHz

Abstract: Mobile radio communications at very high data rates require wide bandwidths which are only available at very high frequency bands. In order to model millimetre wave radio scenarios profound knowledge of the reflection and transmission properties of building materials is required. For a variety of typical smooth and rough building materials reflection scattering, bistatic reflection and transmission measurements have been carried out at 50 GHz. This document introduces briefly the basic physical principles of reflection and transmission as well as the used measuring technique. The measurement results are presented graphically and in tabular form. Additionally, the comparison of measured and calculated profiles is given, using a heuristic approach for permittivity estimation.

Errors induced by the neglect of polarization in radiance calculations for rayleigh-scattering atmospheres

Abstract: Although neglecting polarization and replacing the rigorous vector radiative transfer equation by its approximate scalar counterpart has no physical background, it is a widely used simplification when the incident light is unpolarized and only the intensity of the reflected light is to be computed. We employ accurate vector and scalar multiple-scattering calculations to perform a systematic study of the errors induced by the neglect of polarization in radiance calculations for a homogeneous, plane-parallel Rayleigh-scattering atmosphere (with and without depolarization) above a Lambertian surface. Specifically, we calculate percent errors in the reflected intensity for various directions of light incidence and reflection, optical thicknesses of the atmosphere, single-scattering albedos, depolarization factors, and surface albedos. The numerical data displayed can be used to decide whether or not the scalar approximation may be employed depending on the parameters of the problem. We show that the errors decrease with increasing depolarization factor and/or increasing surface albedo. For conservative or nearly conservative scattering and small surface albedos, the errors are maximum at optical thicknesses of about 1. The calculated errors may be too large for some practical applications, and, therefore, rigorous vector calculations should be employed whenever possible. However, if approximate scalar calculations are used, we recommend to avoid geometries involving phase angles equal or close to 0 deg and 90 deg, where the errors are especially significant. We propose a theoretical explanation of the large vector/scalar differences in the case of Rayleigh scattering. According to this explanation, the differences are caused by the particular structure of the Rayleigh scattering matrix and come from lower-order (except first-order) light scattering paths involving right scattering angles and right-angle rotations of the scattering plane.

Reflection of Ocean Surface Gravity Waves from a Natural Beach

Abstract: The energy of seaward and shoreward propagating ocean surface gravity waves on a natural beach was estimated with data from an army of 24 bottom-mounted pressure sensors in 13-m water depth, 2 km from the North Carolina coast. Consistent with a parameterization of surface wave reflection from a plane sloping beach by Miche, the ratio of seaward to shoreward propagating energy in the swell-sea frequency band (0.044–0.20 Hz) decreased with increasing wave frequency and increasing wave height, and increased with increasing beach-face slope. Although most incident swell-sea energy dissipated in the surf zone, reflection was sometimes significant (up to 18% of the incident swell-sea energy) when the beach face was steep (at high tide) and the wave field was dominated by low-energy, low-frequency swell. Frequency-directional spectra show that reflection of swell and sea was approximately specular. The ratio of seaward to shoreward propagating energy in the infragravity frequency band (0.010–0.044 Hz) v...

Surface light source device and liquid crystal display

Abstract: A wedge shaped parallelized light flux element made of a light scattering guide of an emitting directionality has a specified ranged effective scattering irradiation parameter and correlation distance "a". A light incident into the parallelized light flux element from a fluorescent lamp arranged facing a light incident surface of the parallelized light flux element is emitted from a light output surface as a parallelized light flux G1 by composite factors including forward scattering of the inside, repeated reflection on wedge shaped two sides, critical angular condition and boundary face transmittance for the light output surface. A total amount of parallel light flux G1 emitted from the parallel light flux emitting section F is reflected on a two side prism surface of two prism reflection element PR thereby being converted into sectional area enlarged light fluxes G2 and G3. They are incident on a liquid crystal panel LP through a light diffusion plate DF, and utilized as a backlight. Reflective appearance of a light supply source for supplying a light to the light scattering guide is prevented by forming a reverse slope portion or the like on back surface of the light output surface in adjacent to the light incident surface of the parallelized light flux element.

Constant Q attenuation of subsurface radar pulses

Abstract: Q is a measure of the energy stored to the energy dissipated in a propagating wave and can be estimated from the ratio of attenuation and frequency. For seismic waves, Q has been found to be essentially independent of frequency. As a result, attenuation is an approximately linear function of frequency and the impulse response function of the earth. Hence, the distortion of a seismic pulse as it propagates can be described by a single parameter. Laboratory measurements show that the attenuation of radio waves in some geological materials can also be approximated by a linear function of frequency over the bandwidths of typical subsurface radar pulses. We define a new parameter Q* to describe the slope of this linear region. The impulse response of the transfer function for a given value of Q* differs from that of the same value of Q only in total amplitude. Thus the change of shape of a radar pulse as it travels through these materials can also be described by a single parameter. The constant Q* model succe...

Diffuse-reflectance model for smooth dielectric surfaces

Abstract: A reflectance model that accurately predicts diffuse reflection from smooth inhomogeneous dielectric surfaces as a function of both viewing angle and angle of incidence is proposed. Utilizing results of radiative-transfer theory for subsurface multiple scattering, this new model precisely accounts for how incident light and the distribution of subsurface scattered light are influenced by Fresnel attenuation and Snell refraction at a smooth air–dielectric surface boundary. Whereas similar assumptions about subsurface scattering and Fresnel attenuation have been made in previous research on diffuse-reflectance modeling, the proposed model combines these assumptions in a different way and yields a more accurate expression for diffuse reflection that is shown to account for a number of empirical observations not predicted by existing models. What is particularly new about this diffuse-reflectance model is the resulting significant dependence on the viewing angle with respect to the surface normal. This dependence on the viewing angle explains distinctive properties of the behavior of diffuse reflection from smooth dielectric objects, properties not accounted for by existing diffuse-reflection models. Among these properties are prominent diffuse-reflection maxima effects occurring on objects when incident point-source illumination is greater than 50° relative to viewing, including the range from 90° to 180°, where the light source is behind the object with respect to viewing. For this range of incident illumination there is significant deviation from Lambertian behavior over a large portion of most smooth dielectric object surfaces, which makes it important for the computer vision community to be aware of such effects during incorporation of reflectance models into implementation of algorithms such as shape-from-shading. A number of experimental results are presented that verify the proposed diffuse-reflectance model.

Theory of seismic diffractions

Abstract: This book is devoted to one important aspect of development of physical foundations of the seismic method — the theory of edge diffraction phenomena. Thoese phenomena occur when conditions of the regular wave reflection/transmission change sharply. Though these phenomena drew the attention of many scientist for many decades, their real influence on the resolution ability of the seismic method was truly understood rather recently due to interpretation of seismic data in block structures. Clearly, to develop seismic method for investigation of such structures without developing the theory of edge diffraction phenomena is impossible. The latter is the aim of this book. The seismic method is based on the fundamental laws of continuum mechanics. These laws describe the behavior of wavefields on the microscopic level, i.e., in the form of differential equations of motion. Integrating these equations under some initial conditions or boundary conditions, makes possible acquisition of all necessary information on the wavefield in the given situation. However, the working base of the seismic method consists of not only the differential equations of motion themselves but of some general and simple enough consequences of their solutions, which are formulated in the form of physical principles and l aws. The latter include the concepts of wave, Fermat’s principle, the law of conservation of the energy flux, and the reflection/transmission laws. Essentially these laws and principles must form a system of concepts sufficient for the solution of some class of typical interpretation problems. In fact, these principles and laws form the physical fo ndation of the seismic method.

Projection type color liquid crystal optical apparatus

Abstract: A light source optical system for projection 1, dichroic mirrors 21, 22 disposed to have a predetermined included angle β, a reflection type liquid crystal optical element blocks 31-33 each including a closely contacted converging lens and having a reflection surface and a projection optical system 4 are provided, wherein the normal line of a dichroic mirror surface and the optical axis of incident light form an included angle α; the normal line of the reflection surface and the optical axis of incident light form an included angle γ; light emitted from a light source is color-separated so as to become color lights; the color lights are rendered to be parallel light beams, and are modulated and reflected by means of the reflection type liquid crystal optical elements; the reflected light beams are color-synthesized; and the color-synthesized light is projected through a projection lens. A projection type color liquid crystal optical apparatus having a compact shape and a high brightness is obtainable.

Probing porous media with first and second sound. II. Acoustic properties of water‐saturated porous media

Abstract: The ultrasonic properties (reflection/transmission and bulk attenuation/speed) of porous and permeable media saturated with a Newtonian fluid, namely water, are considered. The frequency dependence of the transmission amplitudes of pulses is measured through a slab of thickness d1, repeated for another slab of thickness d2 for a given material. With these two measurements on two different thicknesses, it is possible in principle to separate bulk losses from reflection/transmission losses for compressional waves in these materials. The bulk properties are calculated from the Biot theory for which all of the input parameters have been measured separately; the attenuations are particularly sensitive to the values of Λ, determined from second‐sound attenuation measurements reported in the companion article. There is excellent quantitative agreement between the theoretical and experimental values in the cases considered; there are no adjustable parameters involved. The reflection and transmission coefficients ...

Imaging of short ocean wind waves: a critical theoretical review

Abstract: Optical techniques to measure the small-scale shape of the ocean surface, i.e., the short wind waves, are theoretically reviewed. The well-known shape-from-shading and shape-from-stereo paradigms from computer vision are applied to a specular reflecting surface such as the ocean surface and are used to study a variety of techniques. The analysis shows that most techniques for the imaging of short wind waves, such as Stilwell photography and various stereo techniques, have significant deficiencies. Stereophotography is plagued by insufficient height resolution for small waves and by the problem that, because of the specular nature of reflection at the water surface, features seen in one image are not necessarily found in the other (correspondence problem). Techniques based on light reflection (shape from reflection) are useful only for deriving wave-slope statistics, and techniques based on light refraction (shape from refraction) are found to be most suitable for wave slope imaging.

Nonstationary flows and shock waves

Abstract: 1. Introduction 2. Shock waves on earth and in space 3. Transition fronts 4. One-dimensional flows in a simple shock tube 5. Shock tubes with area change 6. Boundary-layer effects 7. Two-dimensional studies of oblique shock-wave reflection and diffraction 8. Spherical and cylindrical shock-tube analogues and flow simulation 10. Dusty-gas shock tube 11. Real-gas effects on shock-tube flows 12. Implosion waves and applications 13. Shock-tube construction and instrumentation 14. Closing comments Index

Reflection Z‐scan technique for measurements of optical properties of surfaces

Abstract: Spatial modification of a Gaussian beam by reflection on a surface of a high‐absorbing material is investigated experimentally. A theoretical description in a geometrical‐optics approach is given. The usefulness and sensitivity of the method for applications in measuring laser induced surface deformation and Kerr‐like nonlinear coefficients is discussed.

Observation of velocity-tuned resonances in the reflection of atoms from an evanescent light grating.

Abstract: We report on the observation of velocity-tuned (doppleron) resonances in the grazing-incidence reflection of thermal sodium atoms from a moving evanescent light grating created by interference between two counterpropagating laser beams. The relative velocity between the atoms and the grating can be varied continuously by adjusting the frequency of one laser. We observe an exchange of photons between copropagating and counterpropagating fields in an evanescent light grating. The results are in general agreement with a dressed-state model for the diffraction of atoms from such a grating.

Transmission and reflection characteristics at concrete block walls in the UHF bands proposed for future PCS

Abstract: Buildings such as warehouses, supermarkets and retail department stores typically have walls constructed from concrete (cinder) blocks. The web and void design of the individual blocks and their arrangement within a wall creates a periodic structure, which exhibits frequency dependent transmission and reflections characteristics in the UHF bands proposed for future Personal Communication Systems (PCS). For higher frequencies, higher order Floquet modes excited at the periodic structure can propagate away from the wall, suggesting that significant power can be carried away from the wall in non-specular directions. Indoor propagation prediction models must consider the non-specular paths exited by walls with a periodic nature in order to account for all of the scattered power. In this work, plane wave reflection and transmission characteristics for typical concrete block walls are examined theoretically and experimentally to determine the frequency dependence of the specularly and non-specularly transmitted and reflected fields. >

Band structure for the propagation of elastic waves in superlattices

Abstract: A 2×2 transfer matrix approach is used to study the elastic response of multilayered systems. Superlattices with a period of n layers are considered to calculate the dispersion relations of the normal modes for both longitudinal and transverse waves, and the reflectivity of longitudinal modes for finite and semi‐infinite structures. Numerical results of the dispersion relation for a two‐ and three‐layer period superlattice are presented to show the band structure of wave propagation. For transverse waves, it is considered that the single layer may support surface modes and it is found that their interaction with those of the adjacent layers also yield a band structure. The calculated reflectivity of longitudinal elastic waves for the semi‐inifinite superlattices resembles the allowed and forbidden regions of the dispersion relations. The theoretical reflectivity curves of sound waves are compared with the experimental results for the three‐layer systems. A good agreement between theory and experiment is obtained.

Pulsed beam propagation in inhomogeneous medium

Abstract: Pulsed beams (PB) are localized space-time wavepackets that propagate along ray trajectories. This paper deals with general PB solutions in inhomogeneous medium. We derive an approximate form of the time-dependent wave equation (termed the wavepacket equation), valid within a moving space-time window that brackets the wavepacket, and then construct its exact PB solutions. This is done first in a free-space and latter on in a general smoothly varying medium where the propagation trajectories are curved. We also determine the reflection and transmission laws at curved interfaces. These new PBs are related to the so called complex source pulsed beams which are exact solutions in free-space, but they have more general form that admits wavepacket astigmatism and medium inhomogeneity. Since they maintain their wavepacket structure throughout the propagation process they are identified as eigen-wavepacket solutions of the time dependent wave equation. >

The Arzacq-Western Pyrenees ECORS Deep Seismic Profile

Abstract: In late 1989, a 100-km-long vertical seismic reflection profile was recorded in the western Pyrenees from the French-Spanish border, at the limit between the Axial Zone and the Mendibelza Paleozoic massif, to the deep Arzacq domain of the Aquitaine basin.

Reconnaisance studies of moisture in the subsurface with GPR

Abstract: The ground wave in GPR can be used for reconnaissance studies of moisture in the subsurface. Wave velocity depends on moisture via the dielectric properties of the material. When using a small antenna separation, the ground wave may be superimposed by the air wave. On the other hand, the ground wave decays fast with distance. As a consequence, the ground wave can be observed in the radargram only within a limited antenna separation. We begin the field studies with a wide angle reflection and refraction 0NARR) measurement to identify the ground wave, to determine its velocity and to fmd the optimal antenna separation. This separation is kept throughout a profile when tracing out the lateral variation of ground wave velocity. The free volumetric water content is determined from the dielectric properties of subsurface matter by an empirical relation of Topp et al. (1980). Field data are usually influenced by several factors, such as antenna frequency, antenna separation and small inhomogeneties near the surface. Moisture in the subsurface can be determined more accurately using lower antenna frequencies in a humid subsurface than vice versa. We used the Pulse EKKO IV radar system with 50 and 200 MHz antennas for the field measurements. Reconnaissance studies of moisture with GPR ground wave are non-destructive, free of radiation hazard, fast and suitable for both soft and hard subsurface.