Showing papers on "Reflection (physics) published in 2009"

Reflection images from ambient seismic noise

Abstract: One application of seismic interferometry is to retrieve the impulse response (Green's function) from crosscorrelation of ambient seismic noise. Various researchers show results for retrieving the surface-wave part of the Green's function. However, reflection retrieval has proven more challenging. We crosscorrelate ambient seismic noise, recorded along eight parallel lines in the Sirte basin east of Ajdabeya, Libya, to obtain shot gathers that contain reflections. We take advantage of geophone groups to suppress part of the undesired surface-wave noise and apply frequency-wavenumber filtering before crosscorrelation to suppress surface waves further. After comparing the retrieved results with data from an active seismic exploration survey along the same lines, we use the retrieved reflection data to obtain a migrated reflection image of the subsurface.

Optical scanning device and image forming apparatus

Abstract: A common photodetecting unit detects a plurality of beams scanned by a plurality of polyhedral reflection mirrors provided in a multiple stages with a common rotation axis, and generates a synchronization detection signal based on detected beams. The reflection mirrors make a predetermined angle θ1 in a direction of rotation of the reflection mirrors. When time between two consecutive synchronization detection signals on a time line generated by the common photodetecting unit is ti, where i is a positive integer equal to or smaller than number of split beams, at least one of ti is different from others.

Broadband moth-eye antireflection coatings fabricated by low-cost nanoimprinting

Abstract: Subwavelength scale antireflection moth-eye structures in silicon were fabricated by a wafer-scale nanoimprint technique and demonstrated an average reflection of 1% in the spectral range from 400 to 1000 nm at normal incidence. An excellent antireflection property out to large incident angles is shown with the average reflection below 8% at 60°. Pyramid array gave an almost constant average reflection of about 10% for an incident angle up to 45° and concave-wall column array produced an approximately linear relation between the average reflection and the incident angles. The technique is promising for improving conversion efficiencies of silicon solar cells.

Observing angular deviations in the specular reflection of a light beam

Abstract: The Law of Reflection of a light ray incident upon a mirror (θin = θout) was first formulated by Euclid around 300 bc in his book Catoptrics1; it has been a tenet of geometrical optics ever since. However, more recently, a small angular deviation of the Law of Reflection has been predicted for a physical light beam when this is regarded as the implementation of a ray2,3,4,5. The deviation is a diffractive consequence of the angular dependence of the reflectivity and should occur for any mirror with less than 100% reflectivity. We report here experimental proof of this angular deviation by determining the direction of an optical beam after reflection from an air–glass interface, using a position detector with nanometre resolution. Our results are relevant for angular metrology in general and cantilever-based surface microscopies in particular. Analogous angular deviations are expected for reflection of acoustic waves and quantum matter waves. A small angular deviation of the law of reflection has been previously predicted for a light beam, and is a consequence of the angular dependence of the reflectivity. Experimental proof of such a deviation at near-infrared wavelengths is now reported.

EUV Wave Reflection from a Coronal Hole

Abstract: We report on the detection of EUV wave reflection from a coronal hole, as observed by the Solar Terrestrial Relations Observatory mission. The EUV wave was associated with a coronal mass ejection (CME) erupting near the disk center. It was possible to measure the kinematics of the reflected waves for the first time. The reflected waves were generally slower than the direct wave. One of the important implications of the wave reflection is that the EUV transients are truly a wave phenomenon. The EUV wave reflection has implications for CME propagation, especially during the declining phase of the solar cycle when there are many low-latitude coronal holes.

Planar metamaterial with transmission and reflection that depend on the direction of incidence

Abstract: We report that normal incidence reflection and transmission of circularly polarized electromagnetic waves from and through planar split-ring microwave metamaterials with chiral symmetry breaking depends on the incidence direction and handedness of circular polarization. The effect has a resonant nature and is linked to the lack of mirror symmetry in the metamaterial pattern leading to a polarization-sensitive excitation of electric and magnetic dipolar responses in the meta-molecules. It has striking phenomenological resemblance with the reflective circular dichroism of high-temperature “anyon” superconductors.

Study on x-ray spectra of obscured active galactic nuclei based on monte carlo simulation—an interpretation of observed wide-band spectra

Abstract: Monte Carlo simulation is one of the best tools to study the complex spectra of Compton-thick active galactic nuclei (AGNs) and to figure out the relation between their nuclear structures and X-ray spectra. We have simulated X-ray spectra of Compton-thick AGNs obscured by an accretion torus whose structure is characterized by a half-opening angle, an inclination angle of the torus relative to the observer, and a column density along the equatorial plane. We divided the simulated spectra into three components: one direct component, an absorbed reflection component, and an unabsorbed reflection component. We then deduced the dependences of these components on the parameters describing the structure of the torus. Our simulation results were applied to fit the wide-band spectrum of the Seyfert 2 galaxy Mrk 3 obtained by Suzaku. The spectral analysis indicates that we observe the nucleus along a line of sight intercepting the torus near its edge, and the column density along the equatorial plane was estimated to be ~1024 cm–2. Using this model, we can estimate the luminosities of both the direct emission and the emission irradiating the surrounding matter. This is useful to find the time variability and time lag between the direct and reflected light.

Antenna device, radome, and spurious radiation wave preventing method

Abstract: PROBLEM TO BE SOLVED: To provide an antenna device, a radome and a spurious wave radiation preventing method, for preventing an electromagnetic wave transmitted through the outer surface of a reflection mirror from an antenna rear surface direction from sneaking into the front of the reflection mirror at low cost. SOLUTION: The antenna device has: an antenna body having a radiator 14, a reflection plate 12 for reflecting an electromagnetic wave radiated from the radiator 14 in a predetermined direction, and a shroud 13 provided on the circumferential edge of the radiation plate; and a radome 11 for covering the antenna body so as to be put on from the shroud 13 side wherein a flat surface 11a having the same shape as that of an opening of the reflection plate 12 and a sidewall 11b surrounding the part exhibit a cap shape. An electromagnetic absorber 20 is installed astride the boundary between the flat surface 11a and the sidewall 11b on a side of the radome 11 which opposes the antenna body, and the electromagnetic absorber 20 abuts on an end of the shroud 13. COPYRIGHT: (C)2010,JPO&INPIT

Diffraction imaging by multifocusing

Abstract: Correct identification of geologic discontinuities, such as faults, pinch-outs, and small-size scattering objects, is a primary challenge of the seismic method. Seismic response from these objects is encoded in diffractions. Our method images local heterogeneities of the subsurface using diffracted seismic events. The method is based on coherent summation of diffracted waves arising in media that include interface discontinuities and local velocity heterogeneities. This is done using a correlation procedure that coherently focuses diffraction energy on a seismic section by flattening diffraction events using a new local-time-correction formula to parameterize diffraction traveltime curves. This time correction, which is based on the multifocusing method, depends on two parameters: the emergent angle and the radius of curvature of the diffracted wavefront. These parameters are estimated directly from prestack seismic traces. The diffraction multifocusing stack (DMFS) can separate diffracted and reflected energy on a stacked section by focusing diffractions to the diffraction location and defocusing the reflection energy over a large area.

Electromagnetic boundary and its realization with anisotropic metamaterial.

Abstract: A set of boundary conditions requiring vanishing of the normal components of the D and B vectors at the boundary surface is introduced and labeled as that of DB boundary Basic properties of the DB boundary are studied in this paper Reflection of an arbitrary plane wave, incident with a complex propagation vector, is analyzed for the planar DB boundary It is shown that waves polarized transverse electric (TE) and transverse magnetic (TM) with respect to the normal of the boundary are reflected as from respective perfect electric conductor and perfect magnetic conductor planes The basic problem of current source above the planar DB boundary is solved by applying TE and TM decomposition for the source Realization of the DB boundary in terms of an interface of uniaxially anisotropic metamaterial half-space with zero axial medium parameters is considered It is also shown that such a medium with small axial parameters acts as a spatial filter for waves incident at the interface which could be used for narrowing the beam of a directive antenna Application of DB boundary as an isotropic soft surface with low interaction between antenna apertures also appears possible

The seismic reflection inverse problem

Abstract: The seismic reflection method seeks to extract maps of the Earth's sedimentary crust from transient near-surface recording of echoes, stimulated by explosions or other controlled sound sources positioned near the surface. Reasonably accurate models of seismic energy propagation take the form of hyperbolic systems of partial differential equations, in which the coefficients represent the spatial distribution of various mechanical characteristics of rock (density, stiffness, etc). Thus the fundamental problem of reflection seismology is an inverse problem in partial differential equations: to find the coefficients (or at least some of their properties) of a linear hyperbolic system, given the values of a family of solutions in some part of their domains. The exploration geophysics community has developed various methods for estimating the Earth's structure from seismic data and is also well aware of the inverse point of view. This article reviews mathematical developments in this subject over the last 25 years, to show how the mathematics has both illuminated innovations of practitioners and led to new directions in practice. Two themes naturally emerge: the importance of single scattering dominance and compensation for spectral incompleteness by spatial redundancy.

Constraints on turbulent pressure in the X-ray halos of giant elliptical galaxies from resonant scattering

Abstract: The dense cores of X-ray emitting gaseous halos of large elliptical galaxies with temperatures below about 0.8 keV show two prominent Fe XVII emission features, which provide a sensitive diagnostic tool to measure the effects of resonant scattering. We present here high-resolution spectra of five bright nearby elliptical galaxies, obtained with the Reflection Grating Spectrometers (RGS) on the XMM-Newton satellite. The spectra for the cores of four of the galaxies show the Fe XVII line at 15.01 Angstrom being suppressed by resonant scattering. The data for NGC 4636 in particular allow the effects of resonant scattering to be studied in detail and to prove that the 15.01 Angstrom line is suppressed only in the dense core and not in the surrounding regions. Using deprojected density and temperature profiles for this galaxy obtained with the Chandra satellite, we model the radial intensity profiles of the strongest resonance lines, accounting for the effects of resonant scattering, for different values of the characteristic turbulent velocity. Comparing the model to the data, we find that the isotropic turbulent velocities on spatial scales smaller than about 1 kpc are less than 100 km/s and the turbulent pressure support in the galaxy core is smaller than 5% of the thermal pressure at the 90% confidence level, and less than 20% at 95% confidence. Neglecting the effects of resonant scattering in spectral fitting of the inner 2 kpc core of NGC 4636 will lead to underestimates of the chemical abundances of Fe and O by ~10-20%.

Simple and efficient method for specularity removal in an image.

Abstract: For dielectric inhomogeneous objects, the perceived reflections are the linear combinations of diffuse and specular reflection components. Specular reflection plays an important role in the fields of image analysis, pattern recognition, and scene synthesis. Several methods for the separation of the diffuse and the specular reflection components have been presented based on image segmentation or local interaction of neighboring pixels. We propose a simple and effective method for specularity removal in a single image on the level of each individual pixel. The chromaticity of diffuse reflection is approximately estimated by employing the concept of modified specular-free image, and the specular component is adjusted according to the criterion of smooth color transition along the boundary of diffuse and specular regions. Experimental results indicate that the proposed method is promising when compared with other state-of-the-art techniques, in both separation accuracy and running speed.

Analysing the pattern of pulse waves in arterial networks: a time-domain study

Abstract: The mechanisms underlying the shape of pulse waves in the systemic arterial network are studied using the time-domain, one-dimensional (1-D) equations of blood flow in compliant vessels. The pulse waveform at an arbitrarylocationinthenetworkisinitiallyseparatedintoaperipheralcomponentthatdependsonthecardiacoutput, total compliance and total peripheral resistance of the network, and a conduit component governed by reflections at the junctions of the large conduit arteries and at the aortic valve. The dynamics of the conduit component are then analysed using a new algorithm that describes all the waves generated in the linear 1-D model network by a single wavefront starting at the root. This algorithm allows one to systematically follow all the waves arriving at the measuring site and identify all the reflection sites that these waves have visited. Application of this method to the pulse waves simulated using a 1-D model of the largest 55 systemic arteries in the human demonstrates that peripheral components make a larger contribution to aortic pressure waveforms than do the conduit components. Conduit components are closely related to the outflow from the left ventricle in early systole. Later in the cardiac cycle, they are the result of reflections at the arterial junctions and aortic valve. The number of reflected waves increases approximately as 3 m , with m being the number of reflection sites encountered. The pressure changes associated with these waves can be positive or negative but their absolute values tend to decrease exponentially. As a result, wave activity is minimal during late diastole, when the peripheral components of pressure and the flow are dominant,andaorticpressurestendtoaspace-independentvaluedeterminedbythecardiacoutput,totalcompliance and total peripheral resistance. The results also suggest that pulse-wave propagation is the mechanism by which the arterial system reaches the mean pressure dictated by the cardiac output and total resistance that is required to perfuse the microcirculation. The total compliance determines the rate at which this pressure is restored when the system has departed from its equilibrium state of steady oscillation. This study provides valuable information on

Evaluation of Noninvasive Methods to Assess Wave Reflection and Pulse Transit Time From the Pressure Waveform Alone

Abstract: Accurate quantification of pressure wave reflection requires separation of pressure in forward and backward components to calculate the reflection magnitude as the ratio of the amplitudes backward and forward pressure. To do so, measurement of aortic flow in addition to the pressure wave is mandatory, a limitation that can be overcome by replacing the unknown flow wave by an (uncalibrated) triangular estimate. Another extended application of this principle is the derivation of aortic pulse transit time from a single pulse recording. We verified these approximation techniques for reflection magnitude and transit time using carotid pressure and aortic flow waveforms measured noninvasively in the Asklepios Study (> 2500 participants; 35 to 55 years of age). A triangular flow approximation using timing information from the measured aortic flow waveform yielded moderate agreement between reference and estimated reflection magnitude (R-2 = 0.55). Approximating the flow by a more physiological waveform significantly improved these results (R-2 = 0.74). Aortic transit time was assessed using pressure and measured or approximated flow waveforms, and results were compared with carotid-femoral transit times measured by Doppler ultrasound. Agreement between estimated and reference transit times was moderate (R-2 < 0.29). Both for reflection magnitude and transit time, agreement between reference and approximated values further decreased when the approximated flow waveform was obtained using timing information from the pressure waveform. We conclude that, in our Asklepios population, results from pressure-based approximative methods to derive reflection magnitude or aortic pulse transit time differ substantially from the values obtained when using both measured pressure and flow information.

Measurement of mechanical properties of bone material in vitro by ultrasound reflection: Methodology and comparison with ultrasound transmission

Abstract: An ultrasound reflection technique was designed and implemented to study the mechanical properties of bone material. The technique uses the fact that an ultrasound beam produced in water undergoes total internal reflection off a bone sample at a critical angle formally related to the velocity of a pressure wave in bone. When the plane of scattering is rotated around the normal to the sample surface, the critical angle varies with a periodic dependence dictated by the intrinsic symmetry of the bone structure at the point being examined. Most current measurements of sound velocity are made using transmission techniques. A double-blind intercomparison between this technique and a transmission technique, which was previously validated against tensile mechanical testing, was performed for samples of isotropic materials and of human cortical bone. Strong correlations were found for both sets of samples. For the isotropic materials the velocities were approximately equal, but for bone they were on average 11% higher in reflection than in transmission. This was the result both of the higher frequency employed in reflection (3.5 rather than 2.25 MHz) and of the different effects of sample imperfections on the two measurements. In particular, the reflection technique used in this work studied the surface of the sample, but the ultrasound beam in the transmission method propagated through its interior. In assessing the mechanical properties of bone specimens by ultrasound, the reflection technique samples a discrete bone surface element and the transmission method analyzes the entire volume of the specimen. Thus the reflection technique may yield a measure of the mechanical property of bone trabeculae that is largely unaffected by the mass of the entire specimen, but mass and the structural density of the specimen affect the transmission method.

Light source device, and lighting system

Abstract: PROBLEM TO BE SOLVED: To provide a light source device capable of sufficiently attaining high luminance in comparison with a conventional light source device.SOLUTION: In the light source device including a solid light source 5 for emitting light of a designated wavelength among a wavelength range from ultraviolet light to visible light, and a phosphor layer 2 containing at least one kind or more of phosphors which is excited with excited light from the solid light source 5 and emits fluorescence of a wavelength longer than the wavelength emitted from the solid light source 5 and not substantially containing a resin component, the solid light source 5 and the phosphor layer 2 are spatially arranged at a separated location, and the fluorescence is extracted from a face among faces of the phosphor layer 2, wherein the excited light from the solid light source 5 is incident, by using a reflection method. A base board 6 having light reflectivity and thermal conductivity is arranged on a face opposite to a side where the excited light is incident, among the faces of the phosphor layer 2, and the phosphor layer 2 is connected to the base board 6 at a connection section 7 made of a material having light reflectivity, thermal conductivity, and fluidity.

Improved sample characterization in terahertz reflection imaging and spectroscopy

Abstract: For imaging applications involving biological subjects, the strong attenuation of terahertz radiation by water means that terahertz pulsed imaging is most likely to be successfully implemented in a reflection geometry. Many terahertz reflection geometry systems have a window onto which the sample is placed – this window may introduce unwanted reflections which interfere with the reflection of interest from the sample. In this paper we derive a new approach to account for the effects of these reflections and illustrate its success with improved calculations of sample optical properties.

Counting graphene layers on glass via optical reflection microscopy

Abstract: We show that optical reflection microscopy is a reliable method to simultaneously locate and count graphene layers deposited on bulk, transparent substrates such as soda-lime glass. The visible contrast in optical reflection versus graphene layer number is resolvable on bulk substrates. A simple Fresnel theory based on the universal optical conductance of graphene layers accurately models optical reflection images taken at a wavelength of 550±5 nm. We directly count one to nine layers of graphene using reflection microscopy.

Experimental study on a plane shock wave accelerating a gas bubble

Abstract: A detailed experimental study of the interaction between a planar shock wave and an isolated spherical gas inhomogeneity is presented here. Different configurations have been considered: a shock wave moving from one gas into another, of similar density, lower density and one of higher density. Sequences of shadowgraph pictures obtained during the same run provided useful insights into several mechanisms such as shock wave reflection, refraction and focusing, distortion of the bubble interface, and vortex formation. Based on these sequences, the changes with time in the characteristic bubble sizes were plotted and the results showed that the influence of the shock wave Mach number is significantly greater in the case of light gas bubbles. The displacement of the inhomogeneity relative to the surrounding gas was determined and compared to Rudinger and Somers’ model. In all the cases studied, although the measurements were found to agree well with the theoretical predictions, in the initial acceleration phas...

Electromagnetic Wave Scattering From Layered Structures With an Arbitrary Number of Rough Interfaces

Abstract: A closed-form first-order perturbative solution to the problem of electromagnetic scattering from a layered structure with an arbitrary number of rough interfaces is presented in this paper. Following the classical scheme employed to deal with a rough surface, a perturbative expansion of the fields in the rough-interface layered structure is performed, assuming that roughness heights and slopes are small enough. In this manner, in the first-order approximation, the geometric randomness of the corrugated interfaces is translated into random current sheets imposed on the unperturbed (flat) interfaces and radiating in the unperturbed (flat boundaries) layered media. The scattered field is then represented as the sum of up- and down-going waves, and a systematic approach that involves the use of matrix formalism and generalized reflection/transmission coefficients is employed. This approach permits us to avoid the necessity of the cumbersome Green function formalism. The demonstration of the consistency of the presented solution is analytically provided, showing that the proposed solution reduces to the corresponding existing ones when the stratification geometry reduces to the simplified ones considered by the other authors.

Internal wave beam propagation in non-uniform stratifications

Abstract: In addition to being observable in laboratory experiments, internal wave beams are reported in geophysical settings, which are characterized by non-uniform density stratifications. Here, we perform a combined theoretical and experimental study of the propagation of internal wave beams in non-uniform density stratifications. Transmission and reflection coefficients, which can differ greatly for different physical quantities, are determined for sharp density-gradient interfaces and finite-width transition regions, accounting for viscous dissipation. Thereafter, we consider even more complex stratifications to model geophysical scenarios. We show that wave beam ducting can occur under conditions that do not necessitate evanescent layers, obtaining close agreement between theory and quantitative laboratory experiments. The results are also used to explain recent field observations of a vanishing wave beam at the Keana Ridge, Hawaii.

Spiral-type terahertz antennas and the manifestation of the Mushiake principle.

Abstract: We report on the experimental and theoretical study of the resonant eigenmodes of spiral-type terahertz antennas. The analysis is carried out for a varying number of spiral windings. For larger numbers the structure possesses a self-complementary property which allows the application of the Mushiake principle predicting that the impedance of such structures is half the impedance of free space. This permits to observe an equal and frequency independent reflection and transmission coefficient. This property makes the spiral-type terahertz antenna not only a fascinating example of a medium supporting strong resonances in the long wavelength limit but also a medium which can be easily and reasonably homogenized at higher frequencies. This is in stark contrast to most of the existing metamaterials.

Color display device and method for manufacturing the same

Abstract: Disclosed is a color display device containing plural pixels on a substrate, each pixel is composed of plural sub-pixels which emit lights different in wavelength in the visible range and a white sub-pixel, the plural sub-pixels and the white sub-pixel each have a white organic electroluminescence layer interposed between an optically semitransparent reflection layer and a light reflection layer, the optical distance between the optically semitransparent reflection layer and the light reflection layer in each of the plural sub-pixels forms a resonator having a distance for resonating emitted light, and the optical distance between the optically semitransparent reflection layer and the light reflection layer in the white sub-pixel is longer than the maximum optical distance between the optically semitransparent reflection layer and the light reflection layer in each of the plural sub-pixels.

Flat focusing lens designs having minimized reflection based on coordinate transformation techniques

Abstract: Two-dimensional far-zone focusing lenses are designed using the coordinate transformation approach that feature minimized reflections from the lens boundaries. A flat lens of trapezoidal cross section completely converts incident waves with cylindrical wavefronts into transmitted waves with planar wavefronts. A rectangular lens with reduced non-magnetic material parameters that incorporates a nonlinear coordinate transformation features a significantly reduced amount of reflections compared with the non-magnetic lens based on a linear transformation. The improved reflection performance of each new lens design is verified using a full-wave finite-element analysis and compared with previously reported transformation optical lenses.

Phase-Noise-Compensated Optical Frequency-Domain Reflectometry

Abstract: The theory of phase-noise-compensated optical frequency-domain reflectometry (PNC-OFDR), a novel type of optical frequency-domain reflectometry (OFDR) with a measurement range much longer than the laser coherence length, is described, and the signal and noise spectral densities are deduced for a discussion of signal-to-noise ratio (SNR). The analysis of PNC-OFDR shows the possibility of obtaining a high SNR by using many reference signals for phase-noise compensation. By using a ldquoconcatenately generated phaserdquo (CGP), only a single auxiliary interferometer is needed for phase-noise compensation, and other reference signals can be easily generated by performing a calculation based on signal use obtained from the single auxiliary interferometer. An experimental investigation shows the feasibility of using CGPs for PNC-OFDR by dividing the fiber under test into several sections for phase-noise compensation. Moreover, the influence of strong reflection events on Rayleigh backscattering is discussed by considering the dead zone caused by a fiber/air Fresnel reflection. It is shown theoretically that a dead zone that has no influence on the neighboring section can be achieved by using suitable parameters in an actual system.