Normal Reflection Research Articles

The Dark Side of Iapetus: Additional Evidence for an Exogenous Origin

The saturnian satellite Iapetus presents one of the most unusual appearances of any object in the Solar System: one hemisphere is about 10 times as bright as the other. The origin of the dark hemisphere—which reflects only a few percent of the solar radiation falling on it—has historically been one of the great puzzles of planetary science. From a map produced from previously unstudied, archived Voyager images obtained in the near ultraviolet region of the spectrum, we show that the interface between the bright and dark material is gradual. The ultraviolet (0.34 μm) normal reflectance gradually changes from ∼0.55 to less than 0.03 over a distance of about 1500 km. We present the first color map of Iapetus, showing there is a gradual change in color at the interface between the two hemispheres. This change is highly correlated with the change in albedo. This result supports a spectral mixing model in which the dark and bright sides are the spectral endmembers, and the interface represents a progressive enrichment of a dark red chromophore. Our results are most consistent with a model originally proposed by Cruikshank et al . (1983, Icarus 53 90-104) and Bell et al. (1985, Icarus 61, 192-207). In this model, exogenously produced material from Phoebe impacts the leading side of Iapetus and volatizes the icy component to leave a dark red lag deposit consisting of material from Phoebe and a preexisting nonvolatile constituent that is similar to the D-type material found on Hyperion and D-type asteroids.

Some remarks on approximation of solutions of SDE's with reflecting boundary conditions

Let D be either a convex domain in R d or a domain satisfying the conditions (A) and (B) considered by Lions and Sznitman (1981) and Saisho (1987). We estimate the rate of convergence for Euler scheme for stochastic differential equations in D with normal reflection at the boundary of the form ▪ where W is a d-dimensional Wiener process.

Increased echodensity of myocardial wall in the diabetic heart: An ultrasound tissue characterization study

We sought to characterize myocardial echodensity in asymptomatic patients with insulin-dependent diabetes and normal conventional two-dimensional echocardiographic findings to determine whether ultrasound tissue characterization can detect ultrastructural changes in myocardium, such as an increase in collagen content. Fibrosis alters the acoustic properties of the heart in animals and humans, and these changes are detectable by cardiac tissue characterization with ultrasound. Early changes detected in the diabetic heart include increased interstitial collagen deposition. Using two-dimensional echocardiography, we evaluated 26 asymptomatic patients with insulin-dependent diabetes with normal regional and global rest function, and 17 age- and gender-matched control subjects. By selection, all diabetic patients were normotensive and had negative maximal exercise stress test results to avoid the confounding effects of hypertension and coronary artery disease. Using an echocardiographic instrument implemented at the Institute of Clinical Physiology, we performed an on-line radiofrequency analysis to obtain quantitative operator-independent measurements of the integrated back-scatter signal of the ventricular septum and posterior wall. The integrated values of the radiofrequency signal from the myocardial wall were normalized for those from the pericardial interface and were expressed as percentages (integrated backscatter index). Diabetic patients showed a significant increase in myocardial echodensity both in the septum ([mean +/- SD] 36.6 +/- 8.1 vs. 23.6 +/- 4.4, p < 0.0001) and posterior wall (21.2 +/- 5.3 vs. 18.4 +/- 3.7, p < 0.001). By individual patient analysis, 17 patients exceeded the 95% confidence limits for normal myocardial echocardiographic reflectivity found in normal subjects, and only 3 had a relatively abnormal transmitral Doppler filling pattern (E/A ratio), mainly consisting of an abnormally increased late peak flow velocity (65% vs. 11%, p < 0.001). The increased myocardial intensity was similar in patients with (n = 16) and without (n = 10) noncardiac complications, such as retinopathy or nephropathy (37.5 +/- 7.9% vs. 35.0 +/- 8.3%, p = 0.35). Abnormally increased myocardial echodensity, possibly related to collagen deposition, can be detected in asymptomatic diabetic patients with normal rest function. Theoretically, this finding might be considered a very early preclinical alteration potentially related to subsequent development of diabetic cardiomyopathy.

Stability of surface reconstructions on silicon during RT deposition of Si submonolayers

Surface reconstruction stability of different surface phases formed by Al and Sb on Si(111) and Si(100) surfaces has been studied by monitoring the attenuation of the low-energy electron diffraction normal and extra reflections during room temperature deposition of Si submonolayers. The variety of surface phases under consideration and extensive information background regarding their atomic structure have enabled us to recognize the relationship between the stability of surface phases and their structure.

Multichannel seismic image of the crustal thinning at the NE Iberian Margin combining normal and wide angle reflection data

The seismic image of the Moho at the transition from the NE Iberian Peninsula to the Western Mediterranean Sea is investigated using coincident steep and wide‐angle reflection data merged into a single stacked and migrated section. The multichannel analysis of onshore/offshore large‐aperture data provides new insight on the deep structure in areas where the steep sections lack penetration, and reveals that the crust undergoes a strong but continuous thinning along the flanks of the Valencia trough. The combined seismic image indicates that almost half of the continental crust (14–15 km) is lost in less than 60 km horizontal distance.

Nonequilibrium in normal-conductor/superconductor microconstrictions.

By high-current injection from a point contact into bulk superconducting Ta a nonequilibrium state is produced that may be described as a normal bubble within the superconductor half-space. In driving the diameter of this bubble by the external bias we observe two different types of oscillatory behavior of the conductance. At zero magnetic field the quasiparticle current across the droplet is modulated due to geometrical resonances by multiple Andreev and normal reflections. At magnetic fields somewhat below the critical field, the superconducting surrounding of the normal region forms a symmetric dc SQUID. The magnetic flux through the normal region thus modulates a small supercurrent contribution. Equal numerical values of the bubble diameter are obtained by quantitative evaluation of both effects.

Quasiparticle transport and induced superconductivity in InAs-AlSb quantum wells with Nb electrodes

Current transport through InAs-AlSb quantum wells contacted with superconducting Nb electrodes shows strong evidence for the presence of multiple Andreev reflections (AR's). The efficiency of the multiple AR process is greatly enhanced by the specular normal reflection of electrons at the backplane of the quantum well, thereby permitting multiple AR attempts. Superconductivity observed for sufficiently narrow inter-electrode gaps is interpreted as the result of phase-coherent multiple AR's. Series-connected multi-junction InAs-Nb arrays have been constructed by contracting the InAs-AlSb quantum well with a periodic grating of superconducting Nb electrodes with sub-micrometer spacings. They showed superconductivity at sufficiently low temperatures, in one case as high as 4.2 K. Above the transition temperatures, strong precursors of the superconductivity were observed, in the form of dramatically enhanced zero-bias conductances, decreasing with increasing temperature, but larger by about a factor on the order 10 4 than the fluctuation-induced precursors of thin BCS films. Weak magnetic fields restored non-zero resistance values; the increase in resistance with increasing magnetic field contained a component periodic in the magnetic field, with a period corresponding to a flux per grating cell of only a fraction ( ≈ 1 5 − 1 2 ) of a conventional flux quantum. The observations are interpreted in terms of the formation of a flux cell superlattice.

Multiple Andreev and elastic interface scattering in superconductor-normal-metal-superconductor junctions.

Current-voltage characteristics of superconductor-normal-metal-superconductor junctions are calculated. Multiple Andreev reflections and the effect of normal elastic scattering at the superconductor-normal-metal interfaces are considered. The normal reflections of quasiparticles appear due to the mismatches in Fermi velocities and effective masses of superconductors and weak link. The wave-packet solution of nonequilibrium time-dependent Bogoliubov--de Gennes equations was obtained with the help of the boundary conditions on the wave function of the quasiparticle. At voltages of interest for multiple Andreev reflections (eV2\ensuremath{\Delta}), the result is applied to the rather thick weak links where the density of bound Andreev states is small.

The detection of thin embedded layers using normal incidence ultrasound

A theoretical investigation of the use of normal incidence ultrasonic reflection measurements for the detection and characterization of thin layers embedded between two much thicker media has been carried out. It has been shown that the form of the relationship between the normal incidence longitudinal reflection coefficient and frequency is defined by the reflection coefficients at zero frequency and at half the resonance frequency of the layer. The reflection coefficient at zero frequency is solely a function of the impedances of the media on either side of the layer, while that at half the resonance frequency of the layer is a function of the impedances of all three media. In general, the sensitivity of the reflection coefficient to the presence of the layer increases as the product of frequency and layer thickness increases, the maximum sensitivity being at half the resonance frequency of the layer. Unfortunately, with thin layers, it is generally not practical to test at this frequency. However, the reflection coefficient curve can, in principle, be reconstructed from data measured at lower frequencies and the sensitivity of the reflection coefficient at lower frequencies to the characteristics of the layer can be predicted from the sensitivity at half the resonance frequency. The sensitivity is also critically dependent on the relative impedances of the three media and is generally greatest when the half spaces on either side of the layer have the same impedance. With favourable impedances, it is possible to detect layers whose thickness is a small fraction of the wavelength of the ultrasonic waves employed. However, with other combinations of impedances, the detection of much thicker layers is not possible.

In situ Rapid-Scan Spectrophotometry of Solution-Phase Species Generated on the Surface of a Rotating Disk Electrode

A rapid scan spectrophotometer has been coupled to a rotating disk electrode (RDE) to enable acquisition of potential difference near normal incidence UV-visible reflection absorption spectra of electrogenerated species in the diffusion boundary layer. The (correlated) noise associated with the wobbling of the RDE and other imperfections could be eliminated by synchronizing the rotation angle of the disk, with respect to an arbitrary fixed point, and the initiation of each spectral scan. This strategy was implemented by employing a signal generated by an optical sensor coupled to the rotating shaft as a primary source to drive the grating/galvanometer unit of a Harrick rapid scan spectrophotometer

A Photometric Study of Enceladus

We have supplemented Voyager imaging data from Enceladus (limited to phase angles of 13°-43°) with recent Earth-based CCD observations to obtain an improved determination of the Bond albedo, to construct an albedo map of the satellite, and to constrain parameters in Hapke's (1986, Icarus 67, 264-280) photometric equation. A major result is evidence of regional variations in the physical properties of Enceladus' surface. The average global photometric properties are described by single scattering albedo ω̄ o = 0.998 ± 0.001, macroscopic roughness parameter θ̄ = 6 ± 1°, and Henyey-Greenstein asymmetry parameter g = -0.399 ± 0.005. The value of θ̄ is smaller than the 14° found by fitting whole-disk data, which include all terrains on Enceladus. The opposition surge amplitude B o = 0.21 ± 0.07 and regolith compaction parameter h = 0.014 ± 0.02 are loosely constrained by the scarcity of and uncertainty in near-opposition observations. From the solar phase curve we determine the geometric albedo of Enceladus pv = 0.99 ± 0.06 and phase integral q = 0.92 ± 0.05, which correspond to a spherical albedo A = p v q = 0.91 ± 0.1. Since the spectrum of Enceladus is fairly flat (D. P. Cruikshank, 1980, Icarus 41, 246-258; B. J. Buratti, 1984, Icarus 59, 392-405), we can approximate the Bond albedo A B with the spherical albedo. Our photometric analysis is summarized in terms of an albedo map which generally reproduces the satellite's observed lightcurve and indicates that normal reflectances range from 0.9 on the leading hemisphere to 1.4 on the trailing one. The albedo map also reveals an albedo variation of 15% from longitudes 170° to 200°, corresponding to the boundary between the leading and trailing hemispheres.

Modelling of blast loading on aboveground structures—II. Internal blast and ground shock

Recent studies of the nature and structural effects of confined explosions, contact blast and explosion-induced ground shock are presented. High explosive blast is distinguished from that due to a gaseous deflagration. The effects of confinement and venting are considered in the evaluation of dynamic loads. Maxima for the initial internal blast pressure can be estimated from the scaled blast data or theoretical analyses of normal blast wave reflection from a rigid wall. Semi-empirical relations and prediction methods for gas pressures for many types of internal explosions including high explosives, gas mixtures and dust suspensions are given on the basis of pseudo-static character. The loading of a contact explosion and the associated effects on a concrete target are determined as functions of charge weight, concrete strength and member thickness. In the final part, the evaluation of both airblast-induced ground shock and directly transmitted motion are included in simple form without considering the soil-structure interaction.

Specular optical activity and specular gyrotropic linear dichroism in semiconductors

Observations of rotation of the plane of polarisation of linearly polarised light on normal reflection and in transmission for single pass and forward-backward configurations are reported in GaAs. Spectral dependence of the rotation is measured at wavelengths close to the band gap.

On approximation of solutions of multidimensional SDE's with reflecting boundary conditions

Let D be either a convex domain in R d or a domain satisfying the conditions (A) and (B) considered by Lions and Sznitman [7] and Saisho [11]. We estimate the rate of L p convergence for Euler and Euler–Peano schemes for stochastic differential equations in D with normal reflection at the boundary of the form X t=X 0+∫ t 0f(X s) dW s+∫ t 0g(X s) ds+K t,t∈ R + , where W is a d-dimensional Wiener process. As a consequence we give the rate of almost sure convergence for these schemes.

Modification of the Blonder, Tinkham and Klapwijk expressions for Andreev and normal reflection coefficients due to a finite-thickness barrier at the normal metal-superconductor interface

Amplitudes of normal and Andreev reflections for a normal metal-arbitrary potential barrier-superconductor system are derived with explicitly expressed contributions due to the superconductivity and due to the barrier at the interface. General results are illustrated by the example of a rectangular potential barrier. For somevalues of barrier parameters the results are expressively different from the ones predicted by the standard Blonder, Tinkham and Klapwijk model with a delta-functional barrier at the interface.

In situ spectral reflectance monitoring of III-V epitaxy

Near normal incidence spectral reflectance was used to monitor the growth of ALAs, GaAs, and AlGaAs films by metalorganic chemical vapor deposition in real time. The simultaneous acquisition of reflectance data over a wide spectral bandwidth allows compositional discrimination between layers and greater thickness sensitivity than single wavelength measurements. The potential of this technique for application to device structures was demonstrated by moni-toring the fabrication of AlAs/AlGaAs visible distributed Bragg reflectors.

Hydration Behavior of Na-Smectite Crystals Synthesized at High Pressure and High Temperature

AbstractHydration behavior of Na-smectite crystals synthesized at a pressure of 5.5 GPa and temperatures of 1400°–1500°C was examined by X-ray powder diffraction at various relative humidities (RH) in the range of 0–100%. The basal spacing of the Na-smectite crystal increased stepwise with increase in RH. The reflections observed were only normal reflections of a single or dual hydration states of smectite. No irrational, intermediate, or asymmetrical reflections were observed. The simple hydration behavior, not known for natural smectite with fine particle sizes and low crystallinity, indicates that the Na-smectite crystals are as perfect as common inorganic crystals with an ordered structure.

Structural and FTIR spectroscopic studies of gel-xerogel-oxide transitions of SnO2 and SnO2: Sb powders and dip-coated films prepared via inorganic sol-gel route

Sb doped and undoped SnO2 thin solid coatings were prepared by the dip-coating technique via the sol-gel route. Aqueous gels of undoped compound were made by using a SnCl4 precursor and doping was achieved through the addition of SbCl3 in the concentration range 1–10 mol%. Fourier transform infrared (FTIR), ATR and near normal reflectance spectroscopic techniques were utilized to determine the vibrational spectra of aqueous gels, xerogels and oxides of Sb doped and undoped compounds. Analysis of the corresponding FTIR spectra revealed the existence of Sb-O modes at 770 cm−1. The drying of both types of gel was accompanied by the formation of hydrogen bonds of medium strength wit the OH-O length about 2.7–2.8 Å. Some properties of pure and Sb doped oxide powders formed in the temperature range ≤1000°C were measured by the thermogravimetry, X-ray diffraction and FTIR spectroscopic techniques. The doping brought about a broadening of the X-ray diffraction peaks. The reflectivity of the samples increased in the spectral range 4000-600 cm−1 up to 60%, due to the formation of plasma modes. Thin solids films were made by the dip-coating method. The efficiency of the dip-coating process was 0.02–0.1 μm per dipping, depending on the viscosity of the gel. The electrical resistivity of the doped SnO2 coatings was about 1.2 × 10−2 ω cm and thus comparable to the electrical resistivity of the alkoxide derived Sb doped SnO2. Doping decreased visible transmittance ∼5% but infrared reflectance increased up to 40%, depending on the film thickness.

Shape, surface reflectance, illuminant direction and illuminant intensity from images with shading

AbstractA method is proposed for estimating shape, surface reflectance, illuminant direction and illuminant intensity from images with shading. First, an n x m image data matrix I is constructed from n pixel image inten‐sity data through m frames by moving a light source arbitrarily. Using the Lambertian assumption, the image data matrix I can be written as the product of two matrices N and S; N represents the surface normal and surface reflectance, and S represents the illuminant direction and illuminant intensity. Based on this for‐mulation, a singular value decomposition technique is employed and one of the following two constraints is used to factorize the image data matrix.One is the constraint of surface reflectance which can be used when there are at least 6 pixels in the images, where the surface reflectance is constant. The other is the constraint of illuminant intensity which can be used when there are at least 6 frames among the images, where the illuminant intensity is constant.As the number of images with shading increases, the estimation errors become smaller even if the images are taken in a noisy environment. The proposed method can also treat self shadows and cast shadows without assumptions. The effectiveness of the proposed method is demonstrated through computer simulation, performance analysis and laboratory experiment.

乾海苔のあいまい画像計測データと多変量分析による等級鑑別(&lt;特集&gt;ファジィ画像情報処理)

Grading of dried seaweed by subjective sense inspection of an expert(an inspector of grade) generally includes fuzziness or ambiguity. Although our final purpose would develop an automatic grading machine of dried seaweed, this paper aims to get fundamental knowledge on how to objectively discriminate the grade of dried seaweed as a first stage. In order to know features of graded dried seaweed, first, the statistics has been taken in terms of X, Y, Z of CIE three stimulus' values and normal reflection rate R obtained from image processing equipments and so on. As results of Investigating the relation between the grade and the fundamental statistics, an average of X(color tone), an average of Y(brightness), standard deviations of X and Y have been proved to increase with a lowering of seaweed's grade. On the other hand, a normal reflection rate(gloss) has a tendency to decrease with a lowering of grade. Next, the principal component analysis which is one of the multivariate analysis was carried out so as to examine the features of discrimination by the expert again. As a result, it was shown that ranking of dried seaweed by gains of principal components has a good agreement with grading of sense inspection by the expert. Moreover, after making the criterion of each grade by discrimination analysis of Mahalanobis' generalized distance, by using test samples for verification we inspected them to be belong to which grade. As a result, the comparatively good discrimination was obtained.