Azimuthal Pattern Research Articles

Azimuthal anisotropy of Rayleigh waves beneath the Tibetan Plateau and adjacent areas

The crustal and upper mantle azimuthal anisotropy of the Tibetan Plateau and adjacent areas was studied by Rayleigh wave tomography. We collected sufficient broadband digital seismograms traversing the Tibetan Plateau and adjacent areas from available stations, including especially some data from the temporary stations newly deployed in Yunnan, eastern Tibet, and western Sichuan. They made an adequate path coverage in most regions to achieve a reasonable resolution for the inversion. The model resolution tests show that the anisotropic features of scope greater than 400 km and strength greater than 2% are reliable. The azimuthal anisotropy pattern inside the Tibetan Plateau was similar to the characteristic of tectonic partition. The crustal anisotropy strength is greater than 2% in most regions of East Tibet, and the anisotropy shows clockwise rotation surrounding the eastern Himalayan syntaxis. Vertically, the anisotropy direction indicates a coherent pattern within the upper crust, lower crust, and lithosphere mantle of the Tibetan Plateau, which also is consistent with GPS velocity field and SKS fast polarization directions. The result supports that the crust-mantle deformation beneath the Tibetan Plateau is vertically coherent. The anisotropy strength of crust and lithospheric upper mantle in Yunnan outside the Tibetan Plateau is lower than 2%, so SKS splitting from core-mantle boundary to station should largely be attributed to the anisotropy of asthenosphere.

Ionization and shielding of interface states in native p+-Si/SiO2 probed by electric field induced second harmonic generation

Electric field induced second harmonic measurements applying femtosecond laser pulses (1.59 eV, 80±5 fs, 80 MHz) to substantially boron doped p+-Si/SiO2 interfaces reveal a temporal evolution of the second harmonic (SH) signal, which differs drastically from that of weakly doped samples. A significant initial SH signal is observed in native p+-Si/SiO2 interfaces for boron doping concentrations >7.5×1017 cm−3. This SH signal is attributed to a built-in interfacial electric field E0 generated by the doping induced accumulation of charges at the Si/SiO2 interface following the ionization of interface defect states. A sign reversal is observed in the azimuthal SH anisotropy pattern of the initial SH signal relative to that of the saturated SH signal in p+-Si/SiO2 indicating that the doping related and electron induced interfacial field components oppose each other. Furthermore, the intensity dependence of the initial SH signal in p+-Si/SiO2 is found to be nonquadratic and, in particular, shows a nonmonotonic behavior at incident intensities above ∼60 GW/cm2. These observations are attributed to ultrafast screening of E0 caused by linearly as well as nonlinearly photoexcited electron-hole pairs.

RAPIDITY AND AZIMUTHAL CORRELATION PATTERNS IN NUCLEON-NUCLEON AND RELATIVISTIC HEAVY ION COLLISIONS AT $\sqrt{s} = 200\, {\rm GeV}$

Rapidity and azimuthal correlation patterns for nucleon and relativistic heavy ion collisions are systematically studied by using PYTHIA for pp collisions, RQMD and AMPT for Au − Au collisions at [Formula: see text], respectively. The results show that the measures are sensitive to the collision particles, system size and production mechanism of the system.

Azimuthal flow patterns produced by annular swirling jets

Azimuthal flow patterns produced by annular swirling jets

Magnetospheric Convection near a Drainage Plume

We report on equatorial convection associated with a plasmaspheric drainage plume using simultaneous observations from five satellites. During the early recovery phase of the July 2000 Bastille Day magnetic storm, the Extreme Ultraviolet sensor on the Magnetopause‐to‐Aurora Global Exploration satellite detected the plume near 16:00–17:00 magnetic local time extending outward to L ≈ 2.8. The plasmaspheric boundary was near L = 2 at other local times. We mapped simultaneously measured ionospheric plasma drifts from ROCSAT‐1 and three Defense Meteorological Satellite Program (DMSP) spacecraft along magnetic field lines to infer equatorial convection velocities in the inner magnetosphere. The zonal component of convection derived from ROCSAT‐1 ion‐drift measurements had a sharp, positive azimuthal gradient near the plume’s boundaries, reversing direction from westward to eastward. The meridional profile of horizontal velocities deduced from DMSP measurements shows a large, westward‐flowing subauroral polarization stream (SAPS) located outside the plasmapause. The peak velocity of the SAPS centered at a radial distance of L ≈ 2.8 with a full width of ∼1 RE. In the inertial frame of reference, equatorial plasmas flowed toward the plume from both its day and evening sides, suggesting a negative gradient in the equatorial azimuthal velocity that was largest near the plume’s outermost boundary. These observations provide new evidence about diversion of SAPS plasma flows and distinctive azimuthal velocity patterns in the vicinity of plasmaspheric plumes.

Combined effects of surface roughness and couple stresses on squeeze film lubrication between porous circular stepped plates

In this paper, combined effects of surface roughness and couple stresses on squeeze film lubrication between porous circular stepped plates is analysed. In the context of Christensen stochastic theory for the study of surface roughness two types of one-dimensional surface roughness pattern, viz., azimuthal roughness pattern and radial roughness pattern are considered. The stochastic modified Reynolds equation for these two types of roughness patterns is derived for the couple-stress fluid. The Beavers-Joseph slip boundary condition on the fluid-porous interface is utilized. Closed form expressions for the mean load carrying capacity and squeeze film time are obtained. It is found that the squeeze film characteristics are improved for the azimuthal surface roughness pattern. However, the performance of the squeeze film bearing suffers due to the presence of radial roughness pattern.

Wide band planar modified triangular monopole antennas

AbstractVarious new configurations of planar triangular monopole antennas have been investigated. Effect of flaring angle of planar triangular monopole antennas on the bandwidth has been studied. A compact configuration of vertex chopped equilateral triangular monopole antenna has been proposed for ultra wide bandwidth ratio of 9.2:1. Orthogonal vertex chopped equilateral triangular monopole antenna is proposed for obtaining the improved azimuthal omnidirectional radiation pattern. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 628–632, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22214

Spherical-earth Fréchet sensitivity kernels

We outline a method that enables the efficient computation of exact Frechet sensitivity kernels for a non-gravitating 3-D spherical earth model. The crux of the method is a 2-D weak formulation for determining the 3-D elastodynamic response of the earth model to both a moment-tensor and a point-force source. The sources are decomposed into their monopole, dipole and quadrupole constituents, with known azimuthal radiation patterns. The full 3-D response and, therefore, the 3-D waveform sensitivity kernel for an arbitrary source–receiver geometry, can be reconstructed from a series of six independent 2-D solutions, which may be obtained using a spectral-element or other mesh-based numerical method on a 2-D, planar, semicircular domain. This divide-and-conquer, 3-D to 2-D reduction strategy can be used to compute sensitivity kernels for any seismic phase, including grazing and diffracted waves, at relatively low computational cost.

Omnidirectional Cylindrical Electromagnetic Bandgap Antenna With Dual Polarization

This paper describes the method of design of an electromagnetic bandgap antenna. This antenna is able to radiate in vertical, horizontal, and dual polarization with an omnidirectional pattern in azimuth. Through the given abacuses, it is possible to conceive the structure to obtain specific performances in each polarization. To illustrate this purpose, a dual polarization antenna, operating in the lower HiperLAN frequency band, i.e., 5.15-5.35 GHz, is presented.

Magnetic flares in Active Galactic Nuclei: modeling the iron Kα line

AbstractThe X‐ray spectra of Active Galactic Nuclei (AGN) are complex and vary rapidly in time as seen in recent observations. Magnetic flares above the accretion disk can account for the extreme variability of AGN. They also explain the observed iron Kα fluorescence lines. We present radiative transfer modeling of the X‐ray reflection due to emission from magnetic flares close to the marginally stable orbit. The hard X‐ray primary radiation coming from the flare source illuminates the accretion disk. A Compton reflection/reprocessed component coming from the disk surface is computed for different emission directions. We assume that the density structure remains adjusted to the hydrostatic equilibrium without external illumination because the flare duration is only a quarter‐orbit. The model takes into account the variations of the incident radiation across the hot spot underneath the flare source. The integrated spectrum seen by a distant observer is computed for flares at different orbital phases close to the marginally stable orbit of a Schwarzschild black hole and of a maximally rotating Kerr black hole. The calculations include relativistic and Doppler corrections of the spectra using a ray tracing technique. We explore the practical possibilities to map out the azimuthal irradiation pattern of the inner accretion disks and conclude that the next generation of X‐ray satellites should reveal this structure from iron Kα line profiles and X‐ray lightcurves. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The nature of the volcanic activity at Loki: Insights from Galileo NIMS and PPR data

Loki is the largest patera and the most energetic hotspot on Jupiter's moon Io, in turn the most volcanically active body in the Solar System, but the nature of the activity remains enigmatic. We present detailed analysis of Galileo Near-Infrared Mapping Spectrometer (NIMS) and PhotoPolarimeter/Radiometer (PPR) observations covering the 1.5–100 μm wavelength range during the I24, I27, and I32 flybys. The general pattern of activity during these flybys is consistent with previously proposed models of a resurfacing wave periodically crossing a silicate lava lake. In particular our analysis of the I32 NIMS observations shows, over much of the observed patera, surface temperatures and implied ages closely matching those expected for a wave advancing counterclockwise at 0.94–1.38 km/day. The age pattern is different than other published analyses which do not show as clearly this azimuthal pattern. Our analysis also shows two additional distinctly different patera surfaces. The first is located along the inner and outer margins where components with a 3.00–4.70-μm color temperature of 425 K exist. The second is located at the southwestern margin where components with a 550-K color temperature exist. Although the high temperatures could be caused by disruption of a lava lake crust, some additional mechanism is required to explain why the southwest margin is different from the inner or outer ones. Finally, analysis of the temperature profiles across the patera reveal a smoothness that is difficult to explain by simple lava cooling models. Paradoxically, at a subpixel level, wide temperature distributions exist which may be difficult to explain by just the presence of hot cracks in the lava crust. The resurfacing wave and lava cooling models explain well the overall characteristics of the observations. However, additional physical processes, perhaps involving heat transport by volatiles, are needed to explain the more subtle features.

Relaxation of Azimuthal Flow Pattern from Ring to Bell Shape through Two-Dimensional Turbulence Triggered by Diocotron Instability

Experimentally observed dynamics of vortex patches, as generated by the diocotron instability in a magnetized pure electron plasma, is examined in terms of the power spectra of the distributions of...

Radar Cross-Section Measurements of a Full-Scale Aircraft Duct/Engine Structure

Cavity radar cross-section (RCS) data are measured from a full-sized generic aircraft duct/engine mock-up experimental apparatus. Details of the experimental measurements and characterization of the RCS from a generic aircraft engine inlet with a fan assembly embedded inside are described. The experimental results reveal that the azimuthal RCS patterns from an aircraft engine inlet with fan components embedded inside are very complex

Crack azimuths on Europa: Sequencing of the northern leading hemisphere

Nonsynchronous rotation of Europa should result in a periodic change in stress azimuths at any given location, which may result in a corresponding change in crack azimuths. An early study seemed to provide evidence for such variation within a crack sequence in the northern trailing hemisphere. However, more recent work with higher‐resolution imagery resulted in a more complete sequence of cracks in the region and showed that the azimuth variation with time was not systematic. Similar results were found in the southern leading region. Here we investigate whether the northern leading region contains a crack record, on the basis of crosscutting relationships, that is adequate to indicate nonsynchronous rotation. As in the previous studies of other regions, we find no clear evidence of nonsynchronous rotation within crack azimuth patterns. However, there are other lines of evidence in support of nonsynchronous rotation. Therefore the lack of a continuous pattern of azimuth change with time is likely due to only a few cracks forming per cycle, thus hiding any discernable signal from nonsynchronous rotation in those regions. In that case, the cracks would have formed over numerous cycles of nonsynchronous rotation. The study also reveals a distinctive distribution of crack azimuths, with gaps at certain values. This distribution may reflect a combination of observation selection due to illumination and less‐favorable cracking orientations.

Measurements of diffuse backscattering Mueller matrices of turbid media

We report on the development of a method that records spatially dependent intensity patterns of polarized light that arise from illuminating a turbid media with a polarized laser beam and being diffusely backscattered. Our technique employs polarized light from a He–Ne laser ( λ = 632.8 nm ) which is focused onto the surface of the scattering medium. A surface area of approximately 2×2 cm centered on the light input point is imaged through polarization analysis optics onto a CCD camera. The Mueller matrix is reconstructed by 49 intensity measurements with various orientations of polarizer and analyzer. The measured Mueller matrix of polystyrene spheres was compared with the theory result of incoherent scattering of light by spheres. The experimental and theory results are in excellent agreement. It appears that the azimuthal patterns of the Mueller matrix are determined by the symmetry of the turbid media.

Hysteretic gravity-wave bifurcation in a highly turbulent swirling flow

We report on experimental observations of a gravity-wave instability forced by a highly turbulent free-surface Taylor–Couette flow. Bistability and hysteresis are observed at the bifurcation from a turbulent base state, with an axisymmetric mean flow, to a turbulent gravity-wave state, with an azimuthal pattern related to the mean flow and free surface. We show that the critical Reynolds number at which the wave state appears is not sharply defined as it depends on turbulent fluctuations.

Morphological Development of Oriented Isotactic Polypropylene in the Presence of a Nucleating Agent

The morphological development of sheared isotactic polypropylene (iPP) containing different amounts of sodium benzoate (SB) has been investigated using wide- and small-angle X-ray scattering techniques. The microbeam of synchrotron radiation allows us to gain, precisely and efficiently, the local morphology at a given position with a good spatial resolution. The morphological distributions such as crystallinity, fractions of α-form and β-form crystals, crystal size, and orientation functions can therefore be well constructed through the shear field or temperature gradient. The distribution of crystallinity is changed from a U-shape without SB to an almost flat with SB, in company with a minimum fraction of α-form crystal and a maximum fraction of β-form crystal. The epitaxial growth of branched lamellae in the presence of SB is confirmed from the orientation functions of two axes using wide-angle diffraction. The effect of SB on the molecular orientation is understood from the orientation function of c-axis and the azimuthal patterns of small-angle scattering. It is found that both the molecular orientation and the lamellar orientation of the α-form crystal are increased with increasing SB. The thickness of crystalline lamellae with respect to flow direction is found to increase with increasing SB in the whole range from shear zone to core center. A slight declination of crystalline lamellae has been observed in the presence of SB.

Spiral Cavity Backing Effects on Pattern Symmetry and Modal Contamination

The majority of reported results on lossless, cavity-backed planar spiral antennas do not provide a good indication of higher-order modal contamination or azimuthal pattern symmetry. These parameters are crucial for determining the purity of the radiated far field and, thus, the actual bandwidth. Effects of the spiral backing on these parameters are studied in this letter. It is demonstrated that the best backing for the printed spiral remains the conventional absorber loaded cavity. The addition of either perfect magnetic or perfect electric (PEC/PMC) backing contributes to the overall pattern asymmetry of the antenna, even if some other far-field parameters such as gain are improved. However, we show that for a simple and inexpensive horizontally fed slot spiral, the far-field modal purity and gain can be improved with various counter- or cowound slot spiral backings.

Shear-wave splitting around the Eifel hotspot: evidence for a mantle upwelling

SummaryWe present the results of a shear-wave splitting analysis across the Eifel hotspot in west-central Europe. Our data set includes 18 permanent European broadband stations and 102 temporary Eifel broadband and short-period stations. We observe variations in splitting at most permanent stations, but are not able to model them reliably with unique dipping-axis or two-layer anisotropy models. We prefer instead a single-layer model with a horizontal fast axis to approximate the first-order anisotropy, which varies smoothly between stations. We observe a first-order parabolic pattern in fast polarization azimuth around the hotspot, which suggests that a lattice preferred orientation (LPO) of olivine fast axes exists in the asthenosphere as a result of the interaction between the slowly WSW-moving Eurasian plate and a mantle upwelling beneath the Eifel volcanic fields. The minority of the variation not explained by this model correlates with rapid lateral changes in splitting, and is interpreted as a result of additional anisotropy and/or the effects of dynamic recrystallization associated with LPO development in the region of corner flow near the conduit. Our parabolic asthenospheric flow (PAF) interpretation is consistent with Eifel geological, tomographic, receiver function, global absolute plate motion, electrical conductivity anisotropy, and geochemical studies, as well as with splitting studies in the Great Basin and around Hawaii.We suggest that the Eifel upwelling is sporadic, and a result of a low excess upwelling temperature and/or varying crustal stresses that periodically shift and facilitate eruption. The PAF pattern we observe neither suggests nor rules out anisotropy in the conduit associated with a wet Eifel upwelling.We use our optimum PAF model parameters to calculate a Eurasian plate speed of 12 km Ma−1, which is consistent with the recent HS3-NUVEL1A speed of 19 ± 14 km Ma−1.

Theory and analysis of adaptive cylindrical array antenna for ultrawideband wireless communications

In this paper, the principle of cylindrical array beamforming based on ultrawideband impulse (UWBI) signals is introduced. A cylindrical array antenna is composed of a number of vertically aligned and concentric circular subarrays of equal radius and equal number of array elements. Theory, analysis, and computer simulation of the cylindrical array antenna are presented based on UWBI signals with the time variation of a generalized Gaussian pulse (GGP). The radiation pattern of the cylindrical array antenna is derived in terms of the inverse Fourier transform of the radiated far-zone GGP signal. The radiation pattern results in different azimuth and elevation beam patterns such as peak amplitude pattern, peak power pattern, and energy pattern. Computer plots of these antenna patterns are generated for different design parameters such as array radius, interelement spacing distance, frequency bandwidth, and steering angle. The phenomenon of beamwidth broadening associated with electronic beamsteering is analyzed, and the resolution angle for the cylindrical array antenna is derived too. Beamforming based on UWBI signals provides a tradeoff between array dimensions, frequency bandwidth, and steering angle for achieving a high angular resolution capability in the azimuth plane as well as in the elevation plane. Such a tradeoff is attractive in practice for UWBI communications, indoor (multimedia) communications, radar, and localization systems.