Azimuthal Pattern Research Articles

Time‐frequency analysis based on curvelet transforms with time skewing

ABSTRACTOil and gas exploration gradually changes to the deep and complex areas. The quality of seismic data restricts the effective application of conventional time‐frequency analysis technology, especially in the case of low signal‐to‐noise ratio. To address this problem, we propose a curvelet‐based time‐frequency analysis method, which is suitable for seismic data, and takes into account the lateral variation of seismic data. We first construct a kind of curvelet adapted to seismic data. By adjusting the rotation mode of the curvelet in the form of time skewing, the scale parameter can be directly related to the frequency of the seismic data. Therefore, the curvelet coefficients at different scales can reflect the time‐frequency information of the seismic data. Then, the curvelet coefficients, which represent the dominant azimuthal pattern, are converted to the time‐frequency domain. Since the curvelet transform is a kind of sparse representation for the signal, the screening process of the dominant coefficient masks most of the random noise, which enables the method to adapt for the low signal‐to‐noise ratio data. Results of synthetic and field data experiments using the proposed method demonstrate that it is a good approach to identify weak signals from strong noise in the time‐frequency domain.

PIV-based characterization of puffs in transitional pipe flow

High frame rate stereo-PIV was conducted on circular cross sections of pipe flow to examine velocity variations inside turbulent puffs. A registration method was developed to recognize strong ejections of fluid from the wall near a puff’s trailing edge, and the method was employed to determine ensemble averages of multiple puff occurrences. Both individual puff reconstructions and the ensemble average revealed that these ejections were accompanied consistently by a hairpin vortex that was, in turn, frequently part of a streamwise-aligned hairpin sequence. This sequence is associated with a region that starts near the wall one diameter upstream of the puff’s trailing edge and spreads to the center of the pipe at the trailing edge before shrinking back towards the wall over the next three diameters downstream. The sequence is accompanied by additional hairpins and disturbances that extend over the pipe cross section already by the trailing-edge location. The puff data were used also to search for azimuthal modal patterns within streamwise velocity variations. These modal patterns were shown to be a robust feature of experimental puffs. Upstream patterns were typically disrupted by the trailing edge ejection and hairpin, resulting in downstream patterns of different mode and character. On average, modal patterns existed over longer distances than those identified previously in numerical simulations.

Artificial Immune System with Negative Selection Applied to Facial Biometry Based on Binary Pattern Characteristics

This work aims to explore resources and alternatives for 3D facial biometry using Binary Patterns. A 3D facial geometry image is converted into two 2D representations, appointed as descriptors: A Depth Map and an Azimuthal Projection Distance Image. The first is known as traditional facial geometry, and the second is normal facial geometry that is able to capture the information of different geometries. The characteristics of Local Binary Patterns, Local Phase Quantisers and Gabor Binary Patterns were used with the Depth Map and Azimuthal Projection Distance Image to produce six new facial descriptors: 3D Local Binary Patterns, Local Azimuthal Binary Patterns, Local Depth Phase Quantisers, Local Azimuthal Phase Patterns, and Local Depth Gabor Binary Pattern Magnitudes and Phases. Then, this work uses the immune concept to propose a new approach to realize facial biometry, where the eight new facial descriptors were applied to an Artificial Intelligence algorithm named Artificial Immune Systems of Negative Selection. The analysis of the results shows the efficiency, robustness, precision and reliability of this approach, encouraging further research in this area.

High-Speed Free-Space Optical Continuous Variable-Quantum Key Distribution Based on Kramers–Kronig Scheme

We propose and experimentally investigate a high-speed Kramers–Kronig (KK) scheme based continuous-variable quantum key distribution (CV-QKD) system over a free-space optical (FSO) channel. The atmospheric turbulence channel is emulated by three spatial light modulators on which three randomly generated azimuthal phase patterns yielding Andrews’ spectrum are recorded. The proposed KK scheme enables a low-complexity implementation, insensitivity to laser phase noise, low detection noise, and accurate channel transmittance monitoring. In addition, eight state CV-QKD protocols and 10-channels wavelength-division multiplexing (WDM) scheme are experimentally verified to obtain a high secure key rate. In our experiment, the minimum transmittance of 0.6 is required to guarantee the secure transmission, and a total SKR of 2.1 Gb/s can be obtained at the mean transmittance in weak turbulence regime.

Constraining the Dip of Shallow, Shallowly Dipping Thrust Events Using Long‐Period Love Wave Radiation Patterns: Applications to the 25 October 2010 Mentawai, Indonesia, and 4 May 2018 Hawaii Island Earthquakes

AbstractConstraining precise faulting geometry for shallow, shallowly dipping thrust earthquakes is a common challenge. Plate boundary megathrust faults near the trench and décollement faults beneath volcanic islands and nappes may dip only a few degrees. Long‐period point source moment tensor waveform inversions provide limited resolution of shallow fault dip angle. The possibility of splay faulting requires precise dip estimation. High sensitivity to dip is provided by long‐period Love wave amplitude azimuthal radiation patterns, which undergo rapid change from four lobed to two lobed as dip decreases from 10° to 0°. Modeling variability in Love wave nodal amplitudes allows the dip to be determined to within a few degrees. This is demonstrated for the 25 October 2010 Mentawai (MWW 7.8) tsunami earthquake, which ruptured the 2.0–5.0° dipping megathrust beneath the shallow sedimentary wedge offshore of Indonesia, and the 4 May 2018 Hawaii Island (MWW 6.9) thrust earthquake, which ruptured the 2.5–7.5° dipping décollement under the island flank.

Combined effect of surface roughness and pressure-dependent viscosity over couple-stress squeeze film lubrication between circular stepped plates

In this paper, the effect of surface roughness and pressure-dependent viscosity over couple-stresses squeeze film lubrication between circular stepped plates is studied. The modified average Reynolds equation is derived for the one-dimensional roughness structures, namely the radial roughness pattern and azimuthal roughness pattern. Modified equations for the nondimensional pressure, load-carrying capacity, and nondimensional squeeze film time are obtained. Also, the obtained results of our study for some special cases are compared with the previously published smooth surface case, and the results are found to be in very good agreement. It is observed that, one-dimensional azimuthal (radial) roughness pattern on the rough circular stepped plate increases (decreases) the load-carrying capacity and the squeeze film time as compared to the smooth case.

The unstable eastern flank of Mt. Etna volcano (Italy): First results of a GNSS-based network at its southeastern edge

Two small geodetic subnetworks were established in 2010 and in 2014, respectively, along the southeastern edge of the unstable eastern flank of Mt. Etna volcano. These networks have been monitored since late 2014 with GNSS techniques by the GEOmatic_laboratory of Earth Science Section of the University of Catania. The resulting horizontal velocity field allowed us to observe a westward decay of the rate and a different azimuthal pattern of motion between the two networks. We suggest that both features are due to active deformation of the Nizzeti faults. We also observed that the deforming region is not entirely confined by the Tremestieri-San Gregorio-Acitrezza fault zones, but it extends southwards. Areal upgrades of the networks as well as the scheduling of measurements at least on a monthly basis will improve our knowledge of the current deformation pattern of the investigated area.

Effects of Surface Roughness on Conical Squeeze Film Bearings with Micropolar fluid

In the current paper, a hypothetical analysis of the impact of surface roughness on squeeze film lubrication of rough conical bearing using Micropolar fluid is examined using Eringen’sMicropolar fluid model. The generalized averaged Reynolds type equation for roughness has been determined analytically using the Christensen’s stochastic theory of roughness effects and the closed form expressions are obtained for the fluid film pressure, load carrying capacity and squeezing time. Further, the impacts of surface roughness using micropolar fluids on the squeeze film lubrication of rough conical bearings has been discussed and according to the outcomes arrived, pressure, load carrying capacity and squeezing time increases for azimuthal roughness pattern and decreases for radial roughness patterns comparatively to the smooth case.

Combined effect of piezo-viscous dependency and Couple Stresses on Squeeze-Film Characteristics of Rough Annular Plates

In this paper the combined effect of piezo viscous dependency and couple stresses on the performance of squeeze film characteristic of the Rough annular plates has been studied. The modified Reynolds equations are obtained for the two roughness structure in one-dimensional surface, namely radial roughness pattern and Azimuthal roughness pattern. The results has been presented numerically. It is observed that the effect of radial (azimuthal) roughness pattern on the bearing surface decrease (increase) the pressure, load carrying capacity, and approach of squeeze film time.

Analysis of effect of magneto-hydrodynamic, couple-stress and roughness on conical bearing

The current paper explains the effect of couple stress fluid between the conical bearing when magnetic field and surface roughness is applied jointly. Modified Reynolds equation is acquired for various roughness patterns. Various parameters are tested on both these roughness pattern and the results are presented in the current paper. It is observed that non dimensional pressure, load carrying capacity and squeeze film time increases for magnetic field and couple stress increases. We also noticed that all these non-dimensional parameters increases for higher values of Azimuthal pattern, whereas in Radial roughness pattern these parameters decreases.

Resolving the Polarized Dust Emission of the Disk around the Massive Star Powering the HH 80–81 Radio Jet

Abstract Here we present deep (16 μJy beam−1), very high (40 mas) angular resolution 1.14 mm, polarimetric, Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protostar driving the HH 80–81 radio jet. The observations clearly resolve the disk oriented perpendicularly to the radio jet, with a radius of ≃0.″171 (∼291 au at 1.7 kpc distance). The continuum brightness temperature, the intensity profile, and the polarization properties clearly indicate that the disk is optically thick for a radius of R ≲ 170 au. The linear polarization of the dust emission is detected almost all along the disk, and its properties suggest that dust polarization is produced mainly by self-scattering. However, the polarization pattern presents a clear differentiation between the inner (optically thick) part of the disk and the outer (optically thin) region of the disk, with a sharp transition that occurs at a radius of ∼0.″1 (∼170 au). The polarization characteristics of the inner disk suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 μm. The outer part of the disk has a clear azimuthal pattern but with a significantly higher polarization fraction compared to the inner disk. This pattern is broadly consistent with the self-scattering of a radiation field that is beamed radially outward, as expected in the optically thin outer region, although contribution from non-spherical grains aligned with respect to the radiative flux cannot be excluded.

Inversion of water cloud lidar returns using the azimuthal dependence of the cross-polarization signal.

The contrast in the azimuthal pattern of cross-polarized lidar data is used directly to retrieve the extinction coefficient profile of water droplet clouds. Using a Monte Carlo simulation, we demonstrate that there is a simple mathematical relationship between the optical depth and the contrast of the cross-polarization azimuthal pattern. This relationship is independent of the water cloud droplet size, cloud position, and extinction profile. The derivation of the extinction profile of a water droplet cloud is obtained directly using the simple mathematical relationship without performing lidar equation inversion. The technique is limited to spherical particles.

Four-Dimensionally Multiplexed Eight-State Continuous-Variable Quantum Key Distribution Over Turbulent Channels

We experimentally demonstrate an eight-state continuous-variable quantum key distribution (CV-QKD) over atmospheric turbulence channels. The high secret key rate (SKR) is enabled by 4-D multiplexing of 96 channels, i.e., six-channel wavelength-division multiplexing, four-channel orbital angular momentum multiplexing, two-channel polarization multiplexing, and two-channel spatial-position multiplexing. The atmospheric turbulence channel is emulated by a spatial light modulator on which a series of azimuthal phase patterns yielding Andrews’ spectrum are recorded. A commercial coherent receiver is implemented at Bob's side, followed by a phase noise cancellation stage, where channel transmittance can be monitored accurately and phase noise can be effectively eliminated. Compared to four-state CV-QKD, eight-state CV-QKD protocol potentially provides a better performance by offering higher SKR, better excess noise tolerance, and longer secure transmission distance. In our proposed CV-QKD system, the minimum transmittances of 0.24 and 0.26 are required for OAM states of 2 (or –2) and 6 (or –6), respectively, to guarantee the secure transmission. A maximum SKR of 3.744 Gb/s is experimentally achievable, while a total SKR of 960 Mb/s can be obtained in case of mean channel transmittances.

Double-parton scattering effects in associated production of charm mesons and dijets at the LHC

We calculate several differential distributions for the production of charm and dijets. Both single-parton scattering (SPS) and double-parton scattering (DPS) contributions are calculated in the $k_T$-factorization approach. The Kimber-Martin-Ryskin unintegrated parton distributions are used in our calculations. Relatively low cuts on jet transverse momenta are imposed to enhance the double-parton scattering mechanism contribution. We find dominance of the DPS contribution over the SPS one. We have found regions of the phase space where the SPS contribution is negligible compared to the DPS contribution. The distribution in transverse momentum of charm quark/antiquark or charmed mesons can be used to observe transition from the dominance of DPS at low transvsverse momenta to the dominance of SPS at large transverse momenta. Very distinct azimuthal correlation patterns (for $c \bar{c}$, $c\mathrm{\textit{-jet}}$, $\mathrm{\textit{jet-jet}}$, $D^0\mathrm{\textit{-jet}}$, $D^0 D^0$) are predicted as a result of the competition of the SPS and DPS mechanisms.

Wideband Frequency-Domain and Space-Domain Pattern Reconfigurable Circular Antenna Array

This paper presents a wideband circular antenna array with a frequency-domain and space-domain reconfigurable radiation pattern. A wideband circular array antenna is designed with omnidirectional radiation pattern, in azimuth direction, throughout the whole frequency band. The antenna array consists of eight TEM horn antennas. The antenna array exhibits an omnidirectional azimuthal radiation pattern when all eight ports are excited with signals of the same magnitude and phase. The antenna array is fed through eight reconfigurable bandstop filters and a power splitter. This enables it to provide an omnidirectional azimuthal pattern along with a single directional pattern null in a given spatial direction and at a certain frequency. Both the spatial direction and the frequency can be altered. The antenna works from 0.8 to 3 GHz. The antenna array will be useful in combating interference in wideband communication systems. It will also be of value in surveillance military applications.

Surrogate Bicycle Design for Millimeter-Wave Automotive Radar Pre-Collision Testing

This paper discusses the development of a surrogate bicycle target for evaluating the effectiveness of vehicular autonomous emergency braking (AEB)/ pre-collision systems (PCSs) that uses 77-GHz radar systems in detecting bicyclists on the road. The design objective of the surrogate bicycle is to produce similar optical appearance and radar response in a 76–78 GHz band as a real bicycle selected based on its popularity (in 2014) in the United States. In addition, the surrogate bicyclist needs to be able to withstand the impact of the test vehicle traveling at 30 mph (or 48 kph) should it fail to detect the surrogate target. Our design approach differs from the only other surrogate bicyclist developed by a European research group in that our surrogate bicyclist produces similar radar response as a real bicyclist over the entire 360° of azimuth angles. Our design approach began with experimental characterizing the radar cross section (RCS) patterns of real bikes of different types as well as identifying RCS contributions of different parts on a bike via accurate simulations, which were also used for design optimizations. The RCS performance of the fabricated surrogate bicycle was verified via 360° azimuth pattern measurement comparison with a real bicycle. Its physical performance was tested via actual field testing on a test track with two commercial vehicles equipped with AEB and PCS systems.

An Embedded Lightweight Folded Printed Quadrifilar Helix Antenna: UAV telemetry and remote control systems

An embedded folded, printed, quadrifilar helix antenna (FPQHA) with a wide-angle coverage for unmanned aerial vehicles (UAVs) telemetry and remote control systems is presented in this article. The novelty of this design is that the FPQHA needs to be designed carefully due to UAV tail dimensions and weight constraints while maintaining a high performance to be integrated in the inner part of the UAV tail fuselage to reduce aerodynamic drag. The radiating terminal, formed by a folded, printed, four-helix, radiating section and a compact feeding network, is designed to provide left-handed, circular polarization (LHCP). The complete design offers a very homogeneous pattern in azimuth with a very good axial-ratio (AR) level over a wide range of elevation angles. The use of low-loss and lightweight materials is also an advantage of this design. The wide radiation pattern favors its use for multielement communication systems. Finally, the antenna performance results are obtained mounted inside a UAV tail platform.

Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

AbstractThe thick, seismically fast lithospheric keels underlying continental cores (cratons) are thought to have formed in the Precambrian and resisted subsequent tectonic destruction. A consensus is emerging from a variety of disciplines that keels are vertically stratified, but the processes that led to their development remain uncertain. Eastern Canada is a natural laboratory to study Precambrian lithospheric formation and evolution. It comprises the largest Archean craton in the world, the Superior Craton, surrounded by multiple Proterozoic orogenic belts. To investigate its lithospheric structure, we construct a frequency‐dependent anisotropic seismic model of the region using Rayleigh waves from teleseismic earthquakes recorded at broadband seismic stations across eastern Canada. The joint interpretation of phase velocity heterogeneity and azimuthal anisotropy patterns reveals a seismically fast and anisotropically complex Superior Craton. The upper lithosphere records fossilized Archean tectonic deformation: anisotropic patterns align with the orientation of the main tectonic boundaries at periods ≤110 s. This implies that cratonic blocks were strong enough to sustain plate‐scale deformation during collision at 2.5 Ga. Cratonic lithosphere with fossil anisotropy partially extends beneath adjacent Proterozoic belts. At periods sensitive to the lower lithosphere, we detect fast, more homogenous, and weakly anisotropic material, documenting postassembly lithospheric growth, possibly in a slow or stagnant convection regime. A heterogeneous, anisotropic transitional zone may also be present at the base of the keel. The detection of multiple lithospheric fabrics at different periods with distinct tectonic origins supports growing evidence that cratonization processes may be episodic and are not exclusively an Archean phenomenon.

Can we assume insignificant temporal changes in spatial variations of sap flux for year-round individual tree transpiration estimates? A case study on Cryptomeria japonica in central Taiwan

Although spatial variations in sap flux changed seasonally in cedar trees, neglecting these seasonal changes generally resulted in less than 10% errors in year-round tree transpiration estimates. Spatial and temporal variations in sap flux (F d ) affect the accuracy of year-round individual tree water use (Q) estimates. We aimed to determine seasonal changes in radial and azimuthal variations in F d and to evaluate their potential impacts on year-round Q estimates for humid subtropical forest trees. We measured F d using 38 probes in eight Cryptomeria japonica trees in Taiwan from July 2010 to May 2011. During the study period, the ratio of inner F d to outermost F d (R r ) ranged between 0.29 and 0.68. The ratio of mean outermost F d to that at one direction (R a ) ranged between 0.36 and 1.89. The seasonal patterns were inconsistent among individuals. We compared year-round Q estimates derived from multi-sensor measurements (Q m ) with those derived from measurements at a certain position with constant correction factors for radial (Q r ) or azimuthal (Q a ) patterns of F d determined from the summer measurements. This simple exercise revealed consistent relationships between Q m and Q r year-round (<10% error), suggesting that seasonal changes in the radial profiles of F d had little effect on Q estimates. Although using a constant correction factor for azimuthal variations led to 20–40% errors in Q a of some individuals with large azimuthal variations (i.e., CV > 0.49), five out of eight individuals had less than 10% errors in their Q a estimates. These results suggested that constant correction factors can be used for radial variations in year-round Q estimates, but are not applicable for azimuthal variations in individuals showing large azimuthal variations of F d .

High-speed free-space optical continuous-variable quantum key distribution enabled by three-dimensional multiplexing.

A high-speed four-state continuous-variable quantum key distribution (CV-QKD) system, enabled by wavelength-division multiplexing, polarization multiplexing, and orbital angular momentum (OAM) multiplexing, is studied in the presence of atmospheric turbulence. The atmospheric turbulence channel is emulated by two spatial light modulators (SLMs) on which two randomly generated azimuthal phase patterns yielding Andrews' spectrum are recorded. The phase noise is mitigated by the phase noise cancellation (PNC) stage, and channel transmittance can be monitored directly by the D.C. level in our PNC stage. After the system calibration, a total SKR of >1.68 Gbit/s can be reached in the ideal system, featured with lossless channel and free of excess noise. In our experiment, based on commercial photodetectors, the minimum transmittances of 0.21 and 0.29 are required for OAM states of 2 (or -2) and 6 (or -6), respectively, to guarantee the secure transmission, while a total SKR of 120 Mbit/s can be obtained in case of mean transmittances.