Nonreflecting stratifications

1990 ◽  
Vol 68 (9) ◽  
pp. 738-742 ◽  
Author(s):  
John Lekner
Keyword(s):  
Analytic Property ◽  
Frequent Occurrence ◽  
Angle Of Incidence ◽  
Reflection Amplitude

Electromagnetic, acoustic, and particle waves are specularly reflected by planar inhomogeneities (stratifications). A brief review is given of the cases in which zero reflection is known to occur. In general these are rare, but stratifications that are symmetric with respect to inversion about their midplane have an analytic property of the reflection amplitude that makes zero reflection a frequent occurrence. Examples are given of the locii of zero reflection in the angle of incidence – thickness plane of some symmetric stratifications. For uniform layers the zero reflection locii can be classified into Malus–Brewster–Green type and interference type, but this distinction does not hold in general.

scholarly journals Note on the iridescent colours of birds and insects

1911 ◽  
Vol 85 (582) ◽  
pp. 598-605 ◽  
Keyword(s):  
Frequent Occurrence ◽  
Angle Of Incidence ◽  
Similar Paper ◽  
Animal World

Considerable interest attaches to the origin of certain forms of brilliant colouring which are of frequent occurrence in the animal world, though hardly represented among plants. The colours in question are those which are not due to ordinary pigment, and which change with the angle of incidence of the light. The most brilliant examples are to be found amongst birds and insects. Fishes, and a few reptiles, exhibit colours of the.same kind, but not so conspicuously. During the last 10 or 12 years I have examined some hundreds of cases of this sort of colour production, and quite recently Michelson has published investigations on the same subject, and refers to a somewhat similar paper by Walter, “Oberflächen and Schillerfarben,” dated 1895, of the existence of which I was not before aware.

On: “Reflection of spherical seismic waves in elastic layered media” by P. M. Krail and H. Brysk (GEOPHYSICS, June 1983, p. 655–664).

Geophysics ◽  
1984 ◽  
Vol 49 (5) ◽  
pp. 588-589
Author(s):  
Stephen H. Danbom ◽  
S. Norman Domenico
Keyword(s):  
Seismic Waves ◽  
Spherical Wave ◽  
Petroleum Exploration ◽  
Radius Of Curvature ◽  
Model Parameters ◽  
Angle Of Incidence ◽  
Reflection Amplitude ◽  
Half Wavelength ◽  
Bright Spots ◽  
Amplitude Versus

This paper develops the wavefront curvature correction for the plane‐wave Zoeppritz coefficients. The authors imply that seismic reflection amplitude versus angle of incidence does not enhance detection of pore‐fluid‐caused amplitude anomalies (“bright spots”) as proposed in the scientific literature by Backus et al (1982), Ostrander (1982), and Stolt (1981). We believe certain parts of this discussion are incorrect. Points of disagreement are as follows. (1) The model parameters associated with Figure 6 (especially the values for the brine‐filled sandstone) are unrealistic and are not taken from Domenico (1977) as the authors have indicated. (2) The conclusion “… it is clear that the CMP gather by itself fails as a gas indicator” based on Figure 6 is incorrect. (3) A reflecting spherical wave having a radius of curvature equal to approximately one‐half wavelength (kr = 3) requires a shallow reflector unreasonable for petroleum exploration.

Electron Channeling Patterns

1977 ◽  
Vol 35 ◽  
pp. 12-13
Author(s):  
David C. Joy
Keyword(s):  
Electron Diffraction ◽  
Incidence Angle ◽  
Photographic Plate ◽  
Diffraction Effect ◽  
Angle Of Incidence ◽  
Bulk Single Crystal ◽  
Time Resolved ◽  
Electron Channeling ◽  
Spatially Resolved ◽  
Large Bulk

Electron channeling patterns (ECP) were first found by Coates (1967) while observing a large bulk, single crystal of silicon in a scanning electron microscope. The geometric pattern visible was shown to be produced as a result of the changes in the angle of incidence, between the beam and the specimen surface normal, which occur when the sample is examined at low magnification (Booker, Shaw, Whelan and Hirsch 1967).A conventional electron diffraction pattern consists of an angularly resolved intensity distribution in space which may be directly viewed on a fluorescent screen or recorded on a photographic plate. An ECP, on the other hand, is produced as the result of changes in the signal collected by a suitable electron detector as the incidence angle is varied. If an integrating detector is used, or if the beam traverses the surface at a fixed angle, then no channeling contrast will be observed. The ECP is thus a time resolved electron diffraction effect. It can therefore be related to spatially resolved diffraction phenomena by an application of the concepts of reciprocity (Cowley 1969).

Electron-Channelling Patterns: Principles and Techniques

1976 ◽  
Vol 34 ◽  
pp. 400-401
Author(s):  
David C. Joy
Keyword(s):  
Crystal Structure ◽  
Electron Flux ◽  
Lattice Structure ◽  
Incident Beam ◽  
Bloch Wave ◽  
Crystalline Solid ◽  
Angle Of Incidence ◽  
Electron Channelling ◽  
Regular Arrangement ◽  
Backscattered Signals

In a crystalline solid the regular arrangement of the lattice structure influences the interaction of the incident beam with the specimen, leading to changes in both the transmitted and backscattered signals when the angle of incidence of the beam to the specimen is changed. For the simplest case the electron flux inside the specimen can be visualized as the sum of two, standing wave distributions of electrons (Fig. 1). Bloch wave 1 is concentrated mainly between the atom rows and so only interacts weakly with them. It is therefore transmitted well and backscattered weakly. Bloch wave 2 is concentrated on the line of atom centers and is therefore transmitted poorly and backscattered strongly. The ratio of the excitation of wave 1 to wave 2 varies with the angle between the incident beam and the crystal structure.

The Microstructure of Steatite (Protoenstatite)

1985 ◽  
Vol 43 ◽  
pp. 236-237
Author(s):  
W. E. Lee ◽  
A. H. Heuer
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Magnesium Silicate ◽  
Beam Current ◽  
Glassy Matrix ◽  
Angle Of Incidence ◽  
X Ray ◽  
Mechanical And Electrical Properties ◽  
Argon Ions ◽  
High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

On resolving fine periodic microstructures in the optical microscope

1989 ◽  
Vol 47 ◽  
pp. 364-365
Author(s):  
W.S. Putnam ◽  
C. Viney
Keyword(s):  
Liquid Crystalline ◽  
Numerical Aperture ◽  
Polarized Light ◽  
Normal Incidence ◽  
Optical Microscope ◽  
Angle Of Incidence ◽  
Resolution Limit ◽  
Crystalline Materials ◽  
Periodic Microstructures ◽  
Liquid Crystalline Materials

Many sheared liquid crystalline materials (fibers, films and moldings) exhibit a fine banded microstructure when observed in the polarized light microscope. In some cases, for example Kevlar® fiber, the periodicity is close to the resolution limit of even the highest numerical aperture objectives. The periodic microstructure reflects a non-uniform alignment of the constituent molecules, and consequently is an indication that the mechanical properties will be less than optimal. Thus it is necessary to obtain quality micrographs for characterization, which in turn requires that fine detail should contribute significantly to image formation.It is textbook knowledge that the resolution achievable with a given microscope objective (numerical aperture NA) and a given wavelength of light (λ) increases as the angle of incidence of light at the specimen surface is increased. Stated in terms of the Abbe resolution criterion, resolution improves from λ/NA to λ/2NA with increasing departure from normal incidence.

Sun Load Analysis and Testing on Automotive Front Lighting Products

2020 ◽  
pp. 116-122
Author(s):  
Emre Öztürk ◽  
Mehmet Aktaş ◽  
Tunç Şenyüz
Keyword(s):  
Prolonged Exposure ◽  
Hot Spot ◽  
Load Test ◽  
Angle Of Incidence ◽  
The Sun ◽  
Solar Simulator ◽  
Automotive Lighting ◽  
Inclination Angles ◽  
Plastic Parts ◽  
Load Simulation

The purpose of this research is to reach good correlation between sun load simulation and solar focusing test for exterior automotive lighting products. Light coming from sun is highly collimated (parallel rays) and focusable from lenses with concave structure. Focusing incidence leads to a hot spot on lens surrounding plastic parts which may cause melting failures at high temperature zones. Sun load simulation is performing to eliminate risk of discoloration, deformation, out gassing, coating failures and fire with prolonged exposure from field. Irradiance values in W/m2 defined in simulation as heat source depending of an angle of incidence of the sun radiation. At first step, simulation is performing with 5 degree intervals to define the critical zones then intervals decreased to 2 degree to detect the critical azimuth and inclination angles. Critical azimuth and inclination angles is checking with ray trace analysis to check the bouncing of sun rays and possible solution to eliminate focuses with design solutions. After numerical analysis to release and validate the automotive lighting products regarding the sun load test, measurement with first parts is necessary. Measurement is performing for all critical angles which have been detected at simulation with thermal camera under ultra high-collimation solar simulator. Measured temperatures are settled according to environment conditions and correlation is checking with simulations.

Distribution of Orofacial Clefts and Frequent Occurrence of an Unusual Cleft Variant in the Rift Valley of Kenya

2006 ◽  
Author(s):  
Richard Spritz ◽  
Thomas Arnold ◽  
Samuel Buonocore ◽  
David Carter ◽  
Tasha Fingerlin ◽  
...  
Keyword(s):  
Rift Valley ◽  
Frequent Occurrence ◽  
Orofacial Clefts

Technical and radiographic considerations for magnetic resonance imaging–guided focused ultrasound capsulotomy

2020 ◽  
pp. 1-9 ◽  
Author(s):  
Benjamin Davidson ◽  
Karim Mithani ◽  
Yuexi Huang ◽  
Ryan M. Jones ◽  
Maged Goubran ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Focused Ultrasound ◽  
Neurosurgical Procedures ◽  
Lesion Volume ◽  
Angle Of Incidence ◽  
Resonance Imaging ◽  
Radiographic Findings ◽  
Compulsive Disorder ◽  
Skull Thickness

OBJECTIVEMagnetic resonance imaging–guided focused ultrasound (MRgFUS) is an emerging treatment modality that enables incisionless ablative neurosurgical procedures. Bilateral MRgFUS capsulotomy has recently been demonstrated to be safe and effective in treating obsessive-compulsive disorder (OCD) and major depressive disorder (MDD). Preliminary evidence has suggested that bilateral MRgFUS capsulotomy can present increased difficulties in reaching lesional temperatures as compared to unilateral thalamotomy. The authors of this article aimed to study the parameters associated with successful MRgFUS capsulotomy lesioning and to present longitudinal radiographic findings following MRgFUS capsulotomy.METHODSUsing data from 22 attempted MRgFUS capsulotomy treatments, the authors investigated the relationship between various sonication parameters and the maximal temperature achieved at the intracranial target. Lesion volume and morphology were analyzed longitudinally using structural and diffusion tensor imaging. A retreatment procedure was attempted in one patient, and their postoperative imaging is presented.RESULTSSkull density ratio (SDR), skull thickness, and angle of incidence were significantly correlated with the maximal temperature achieved. MRgFUS capsulotomy lesions appeared similar to those following MRgFUS thalamotomy, with three concentric zones observed on MRI. Lesion volumes regressed substantially over time following MRgFUS. Fractional anisotropy analysis revealed a disruption in white matter integrity, followed by a gradual return to near-baseline levels concurrent with lesion regression. In the patient who underwent retreatment, successful bilateral lesioning was achieved, and there were no adverse clinical or radiographic events.CONCLUSIONSWith the current iteration of MRgFUS technology, skull-related parameters such as SDR, skull thickness, and angle of incidence should be considered when selecting patients suitable for MRgFUS capsulotomy. Lesions appear to follow morphological patterns similar to what is seen following MRgFUS thalamotomy. Retreatment appears to be safe, although additional cases will be necessary to further evaluate the associated safety profile.

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