Azimuthal Pattern Research Articles

Centrality dependence of soft photon production and its collective flow in Au+Au collisions at sNN=200 GeV

Direct photons coming from heavy-ion collisions are of particular interest since once produced, they are unmodified, thus carrying information about the space–time evolution and properties of the hot and dense medium produced in such collisions. We present new results on the centrality dependence of soft single photon production in s N N = 200 GeV Au+Au collisions. Photons are measured down to p T = 400 GeV / c via conversion of real photons into e + e − pairs in the detector material. Our measurement of the photon p T spectra indicates that the spectral shape does not depend on centrality. In addition, the azimuthal emission patterns of photons carry additional information on their production mechanisms. Previously published PHENIX results [2] indicate that the 2nd order Fourier coefficient ( v 2 ) is positive for p T < 4 GeV / c , which is qualitatively explained by hydrodynamical model calculations, but not quantitatively. The 3rd order Fourier coefficient ( v 3 ) of photons has been proposed as a critical additional handle to understand the photon emission. We found that the v 3 of photons is positive for p T < 4 GeV / c , and both the strength and shape of v 3 are comparable to those of hadrons, similarly to the case of v 2 . We report the latest results on the centrality dependence of the soft photon production and the v 3 coefficients in Au+Au collisions at s N N = 200 GeV . These measurements provide stringent tests of the hydrodynamic space–time evolution as a function of the collision geometry.

Azimuthal emission patterns ofK+and ofK−mesons in Ni + Ni collisions near the strangeness production threshold

Azimuthal emission patterns of $K^\pm$ mesons have been measured in Ni + Ni collisions with the FOPI spectrometer at a beam kinetic energy of 1.91 A GeV. The transverse momentum $p_{T}$ integrated directed and elliptic flow of $K^{+}$ and $K^{-}$ mesons as well as the centrality dependence of $p_{T}$ - differential directed flow of $K^{+}$ mesons are compared to the predictions of HSD and IQMD transport models. The data exhibits different propagation patterns of $K^{+}$ and $K^{-}$ mesons in the compressed and heated nuclear medium and favor the existence of a kaon-nucleon in-medium potential, repulsive for $K^{+}$ mesons and attractive for $K^{-}$ mesons.

Highly c-axis oriented ZnO:Ni thin film nanostructure by RF magnetron sputtering: Structural, morphological and magnetic studies

Nickel doped zinc oxide (ZnO:Ni) thin films with different Ni concentrations were deposited on silicon substrates at 400°C by reactive magnetron sputtering using a mixture of Ar and O2 gases. The X-ray diffraction and azimuthal patterns of the ZnO:Ni were carried out, and the quality of the strong preferred orientation of crystalline columns in the direction [001] perpendicular to the substrate surface were analysed. The grain size, distribution, and homogeneity of the thin film surfaces were studied by FE-SEM. The EDX and mapping confirmed that the Ni is incorporated into ZnO uniformly. The microstructure of the textured columns was analysed by TEM and HRTEM analyses. The average thickness and length of the columns were found to be about 50nm and 600nm, respectively. The rise of ferromagnetism by the influence of Ni content was studied by VSM magnetic studies at room temperature.

Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

The lowermost few hundreds of kilometres of the Earth's mantle are elastically anisotropic; seismic velocities vary with direction of propagation and polarization. Observations of strong seismic anisotropy correlate with regions where subducted slab material is expected. In this study, we evaluate the hypothesis that crystal preferred orientation (CPO) in a slab, as it impinges on the core–mantle boundary, is the cause of the observed anisotropy. Next, we determine if fast polarization directions seen by shear waves can be mapped to directions of geodynamic flow. This approach is similar to our previous study performed for a 2-D geodynamic model. In this study, we employ a 3-D geodynamic model with temperature-dependent viscosity and kinematic velocity boundary conditions defined at the surface of the Earth to create a broad downwelling slab. Tracers track the deformation that we assume to be accommodated by dislocation creep. We evaluate the models for the presence of perovskite or post-perovskite and for different main slip systems along which dislocation creep may occur in post-perovskite [(100),(010) and (001)]—resulting in four different mineralogical models of CPO. Combining the crystal pole orientations with single crystal elastic constants results in seismically distinguishable models of seismic anisotropy. The models are evaluated against published seismic observations by analysing different anisotropic components: the radial anisotropy, the splitting for (sub-)vertical phases (i.e. azimuthal anisotropy), and the splitting for subhorizontal phases. The patterns in radial anisotropy confirm our earlier results in 2-D. Observations of radial anisotropy and splitting in subhorizontal phases are mostly consistent with our models of post-perovskite with (010)-slip and (001)-slip. Our model of (001)-slip predicts stronger splitting than for (010)-slip for horizontally propagating phases in all directions. The strongest seismic anisotropy in this model occurs where the slab impinges on the core–mantle boundary. The azimuthal anisotropy pattern for (001)-slip shows fast axis directions at the edges of the slab (sub-)parallel to flow directions, suggesting horizontal flows may be mapped out in the lowermost mantle using seismic observations.

The stability of a thin water layer over a rotating disk revisited

The flow driven by a rotating disk of a thin fluid layer in a fixed cylindrical casing is studied by direct numerical simulation and experimental flow visualizations. The characteristics of the flow are first briefly discussed but the focus of this work is to understand the transition to the primary instability. The primary bifurcation is 3D and appears as spectacular sharp-cornered polygonal patterns located along the shroud. The stability diagram is established experimentally in a (Re, G plane, where G is the aspect ratio of the cavity and Re the rotational Reynolds number and confirmed numerically. The number of vortices scales well with the Ekman number based on the water depth, which confirms the existence of a Stewartson layer along the external cylinder. The critical mixed Reynolds number is found to be constant as in other rotating flows involving a shear-layer instability. Hysteresis cycles are observed highlighting the importance of the spin-up and spin-down processes. In some particular cases, a crossflow instability appears under the form of high azimuthal wave number spiral patterns, similar to those observed in a rotor-stator cavity with throughflow and coexists with the polygons. The DNS calculations confirm the experimental results under the flat free surface hypothesis.

The TerraSAR-X Staring Spotlight Mode Concept

The paper investigates the possibility to enhance the TerraSAR-X (TSX) azimuth resolution by means of staring spotlight imaging in combination with an extended azimuth pattern steering. The current TSX spotlight modes are briefly reviewed, and the azimuth steering limitations are discussed. Based on a realistic TSX azimuth pattern simulation and performance estimation using a Kepler orbit and the WGS84 reference ellipsoid, the key performance parameters are estimated for an increasing azimuth pattern steering angle span. The azimuth ambiguity performance is identified to be the driving performance parameter. Experimental TSX staring spotlight high-resolution images are presented. They demonstrate and verify the envisaged performance estimation. The paper concludes with a concept for a high-resolution TSX staring spotlight mode that serves as baseline for the upcoming operational implementation.

Enhanced Photoresponsivity of a Germanium Single-Nanowire Photodetector Confined within a Superwavelength Metallic Slit

Single nanowire photodetectors (SNPDs) have recently gained much attention due to their unique photonic and electronic properties. We design a germanium SNPD confined inside a silver slit and demonstrate that properly engineering the slit into superwavelength scale is able to dramatically enhance the SNPD photoresponsivity to transverse electric incidence. The light absorption by this rationally designed device can be over 3.7 times that of its subwavelength counterpart based on plasmonic resonance under transverse magnetic incidence. An extensive investigation on polarization dependence, field profile, photon flux distribution, and azimuthal absorption pattern in the SNPD reveals that the underlying mechanism responsible for the significant performance enhancement is the optimal light–nanowire coupling, benefiting from strong interference-directed light concentration inside the slit cavity. This work provides us new insights, beyond the mostly studied plasmonic enhancement effects, into photoresponsivity...

Effect of surface roughness on magneto-hydrodynamic squeeze-film characteristics between a sphere and a porous plane surface

Purpose– The purpose of this article is to analyse the effects of surface roughness on the magneto-hydrodynamic (MHD) squeeze-film characteristics between a sphere and a porous plane surface, which have not been studied so far.Design/methodology/approach– The analytical model takes into account the effect of porosity by assuming that the flow in the porous matrix obeys modified Darcy's law. The stochastic MHD Reynold's type equation is derived by using the Christensen's stochastic method developed for hydrodynamic lubrication of rough surfaces. Two types of one-dimensional surface roughness (radial and azimuthal) patterns are considered.Findings– The expressions for the mean MHD squeeze-film pressure and mean load-carrying capacity are obtained numerically. The results are shown graphically for selected representative parametric values. It is found that the response time increases significantly for the MHD case as compared to the corresponding non-conducting lubricants. The effect of roughness parameter is to increase/decrease the load-carrying capacity and the response time for azimuthal/radial roughness patterns as compared to the smooth case. Also, the effect of porous parameter is to decrease the load-carrying capacity and response time as compared to the solid case.Originality/value– In this paper, an attempt has been made to analyse the combined effects of surface roughness and permeability on the MHD squeeze-film characteristics between a sphere and a plane surface.

Isolation enhancement in wideband dual‐polarised suspended plate antenna with modified T‐type probes

An isolation enhancement technique for a wideband (1.71–2.17 GHz) and ±45° linear dual-polarised suspended plate antenna is proposed. Isolation (S 12, S 21) between channels is improved by making extensions on suspended plates (SPs) 1–2 and inserting a vertical ungrounded vertical wall under SP-1. The modified T-type probes in this design provide better coupling and return losses (S 11, S 22) for wideband operation. Based on the numerical simulations and measurements, it is observed that 8.2 ± 0.5 dBi gain and 66° ± 6° symmetric azimuth and elevation radiation patterns are obtained. Return losses ≤ − 15 dB and isolation ≤ − 30 dB are achieved in the entire band. This antenna is suitable for base stations of mobile wireless communication systems (PCS, DCS and IMTS ).

Effect of Surface Roughness and Viscosity-Pressure Dependency on the Couple Stress Squeeze Film Characteristics of Parallel Circular Plates

Combined effects of surface roughness and viscosity-pressure dependency on the couple stress squeeze film characteristics of parallel circular plates are presented. On the basis of Christensen’s stochastic theory, two types of one-dimensional roughness structures, namely, the radial roughness and azimuthal roughness patterns, are considered and the stochastic modified Reynolds equation for these two types of roughness patterns is derived for Stokes couple stress fluid by taking into account variation of viscosity with pressure. The standard perturbation technique is employed to solve the averaged Reynolds equation and closed form expressions for the mean fluid film pressure, load carrying capacity, and squeeze film time are obtained. It is found that the effects of couple stresses and viscosity-pressure dependency are to increase the load carrying capacity, and squeeze film time for both types of roughness patterns. The effect of azimuthal (radial) roughness pattern is to increase (decrease) these squeeze film characteristics as compared to the corresponding smooth case.

AN ULTRA-WIDEBAND QUASI-PLANAR ANTENNA WITH ENHANCED GAIN

A new ultra-wideband antenna with enhanced and nearly constant gain is presented. This quasi-planar antenna is composed of a CPW-fed printed monopole and a short horn, both made out of a single substrate. The measurements demonstrate an almost ∞at peak gain of 5:5dBi § 0:7dB from 2.5GHz to 15GHz with the average gain difierence in XZ plane is roughly 2dB up to 8GHz, which further rise to 6dB at 10GHz. The antenna also has a nearly linear phase response in this band. Well tested performance both in frequency and time domains, along with broad azimuth pattern, results in minimal ringing of a radiated pulse. The new antenna is suitable for establishing good line of sight link for UWB transmission and other broadband applications.

Decade Bandwidth Circularly Polarized Antenna Array

A circularly polarized antenna array design comprising of a feed network that splits an input signal into four orthogonal (0°, 90°, 180°, and 270°) phased signals with equal magnitudes and connected to four anti-podal Vivaldi antennas sequentially rotated by 90° is presented. The proposed antenna array yields 10-dB return loss and 3-dB axial ratio bandwidths from 1-10 GHz. The symmetrical structure gives the antenna array almost identical azimuth and elevation radiation patterns. Pulse reception from various angles show equi-amplitude outputs and very little distortion. The proposed design is suited for high-resolution microwave imaging systems.

Constraints on the tectonic evolution of the westernmost Mediterranean and northwestern Africa from shear wave splitting analysis

The westernmost Mediterranean mantle and lithosphere have evolved into their current configuration due to complex interactions between the African and Eurasian plates. To help unravel the regional tectonics, we use new broadband seismic data across the Gibraltar arc and into southern Morocco to infer azimuthal seismic anisotropy and flow patterns for the upper mantle based on shear wave splitting analysis. A deep (>600km) earthquake in April 2010 was recorded by the array and allowed us to compare 31 direct S measurements with 235 teleseismic SK(K)S events from 3years of deployment. The patterns of apparent fast polarization orientations and delay times suggest three major tectonic domains when interpreted jointly with recent tomographic images of the subducted slab: (1) a subducted slab related toroidal flow domain centered upon the Alboran Sea and southern Spain, leading to complex splits, (2), a region where the west African craton deflects mantle flow in the Anti-Atlas and High Plateaux, and, (3), an intermediate domain across the central High Atlas. Across the axis of the mountain belt a coherent, regional maximum of delay times is observed for both S and SKS splitting measurements, with polarizations predominantly parallel to the strike. We interpret this as possible SW–NE channeling of mantle flow beneath the region with a thinned lithosphere and slow seismic velocities beneath the central High Atlas Mountains.

Orientation of solar wind dynamic pressure phase fronts

Orientation of structures in the solar wind plays an important role when attempting to use upstream observations at L1 for prediction of subsequent conditions near the Earth. In this study, the relationship between solar wind dynamic pressure forcing and geosynchronous magnetic field response is used to determine a very large set of lagged correlations between the ACE and GOES satellites. Effects due to tilted solar wind structures are explored using the dispersion of arrival times relative to a simple phase plane model. Assuming that structure phase‐front normal vectors were located in the GSE‐xy plane, we found a characteristic azimuth of 15°. Similar analysis carried out with velocity scaling according to the Parker spiral model did not produce an improved fit. Binning by average interplanetary magnetic field (IMF) orientation produced a clear pattern in characteristic azimuth, with phase‐front normals perpendicular to both the predominant Parker spiral orientation and the less common ortho‐spiral configuration. An empirical relationship was found to predict phase‐front normal azimuth over the entire range of observed IMF azimuths. The effects of lateral displacement from the Sun‐Earth line in the GSE‐z direction are comparable to those for GSE‐y, indicating that solar wind structures are often significantly inclined with respect to the ecliptic plane.

Secondary Surveillance Radar Antenna [Antenna Designer's Notebook

This paper deals with a secondary surveillance radar (SSR) array antenna, which is intended for a system combining the secondary surveillance radar antenna and the primary surveillance radar antenna. It describes the patch array elements and the synthesis for the secondary surveillance radar array, considering both elevation and azimuth patterns for sum, difference, and sidelobe-suppression beams, and suspended stripline couplers. The utilization of multilayer techniques allows the connection of layers with patch radiating elements and layers with beamforming networks.

Low-Profile Automotive Antenna for Omnidirectional Vertical Polarized Signal Reception

A low-profile antenna is designed for a WiBro vertical polarized signal. The proposed antenna is packaged and installed on the roof of a vehicle. The low-profile configuration is inspired from a zero-phase constant that realizes a horizontal magnetic loop current distribution equivalent to a vertical electric current distribution. With the proposed antenna, a wide bandwidth is achieved by overcoming the narrow bandwidth characteristics of an antenna with a zero-phase constant. The antenna was designed using a large conductive plate to simulate the vehicle roof in the electromagnetic simulation, thereby dramatically reducing simulation time. The results are comparable to the experimental results of an antenna on a vehicle's roof. The unpackaged and packaged antennas' radiation patterns are first measured in an anechoic chamber. Azimuth patterns are measured by installing the packaged antenna on the vehicle's roof. Simulations agree with experimental data where the vertically polarized signal is successfully received with a reasonable gain and efficiency in a WiBro band.

Novel radiation pattern reconfigurable antenna with six beam choices

This article presents a novel radiation pattern reconfigurable antenna with six beam choices, which works in 5.2 GHz wireless local area network (WLAN) frequency band. The designed antenna has good impedance matching at the resonant frequency. The beam can be reconfigured to six different directions, and each main lobe of six azimuth patterns has a half power beam width (HPBW) of about 60°. The antenna can cover all directions in the azimuth plane (XY-plane) by controlling the states (ON or OFF) of six switches. Simulation and measurement have been carried out to validate the design and experimental results demonstrate that the proposed antenna has the capacity to provide the pattern reconfigurability.

Azimuthal Distributions of K + Mesons in Heavy-Ion Collisions

Strange mesons are considered to be sensitive to in-medium modifications. Theory predicts a repulsive K+N potential and an attractive K−N potential in dense matter. A repulsive K+N potential would repel the K+ mesons from the bulk of the nucleons and therefore cause a preferred out-of-plane emission of K+ mesons at midrapidity and a directed flow opposite to the nucleons at target and projectile rapidity. One of observables to probe in-medium effects is the azimuthal emission pattern of K+ mesons in heavy ion collisions. KaoS collaboration has measured the azimuthal distributions of K+ mesons in Au + Au reactions at 1.5 A GeV and Ni + Ni reactions at 1.93 A GeV. Data show that K+ mesons exhibit a pronounced enhancement at \({\phi = {90}^\circ}\) , i.e. perpendicular to the reaction plane. The data have also been fitted using the first two components of a Fourier series to get the directed flow v1 and elliptic flow v2. We used the quantum molecular dynamics model based on the covariant kaon dynamics to simulate the Au + Au collisions at 1.5 A GeV and the Ni + Ni collisions at 1.93 A GeV, to analyze the azimuthal distributions of K+ mesons, and to calculate v1 and v2 of K+ mesons. Calculated results with a repulsive in-medium K+N potential can reasonably describe the features of KaoS data. This indicates that the azimuthal distribution is one of sensitive probes to extract information on in-medium properties at high densities.

Indirect Coupling Method of Chip Impedance Matched Dipole Antenna for UHF RFID Tag

Radio Frequency Identification is the wireless technology that uses radio waves to automatically identify items within certain proximity. This process involves tagging items with a transmitter which will send bursts of information. Passive RFID tag consists of a microchip connected with an antenna. The passive tag uses the electromagnetic pulse from readers as a power source to transmit its identifier. So proper impedance matching between the antenna and the chip is very important in passive RFID tag design. The RFID system performance characteristics and the range of a tag depend on the impedance matching. A load impedance of RFID microchip is a nonlinear whose complex part varies with the frequency and the input power [2]. This paper presents simulated results of a UHF RFID dipole antenna and inductively coupled with a small rectangular loop. Such a design provides controlled values of inductive reactance that is required for obtaining good impedance match of the antenna to microchip. The proposed dipole antenna is simple and robust in design, which enables low-cost while realization. General Terms Return-loss, 3D Radiation Pattern, 2D Azimuth and Elevation Radiation Pattern, S-Parameters.

Effect of surface roughness on magneto‐hydrodynamic couple‐stress squeeze film lubrication between circular stepped plates

ABSTRACTIn this paper, a theoretical analysis of the problem of magneto‐hydrodynamic couple‐stress squeeze film lubrication between rough circular stepped plates is presented. The modified averaged Reynolds equation is derived for the two types of one‐dimensional roughness structures, namely the radial roughness pattern and the azimuthal roughness pattern. The closed‐form expressions are obtained for the mean squeeze film pressure, load‐carrying capacity and squeeze film time. The results are presented for different operating parameters. It is observed that the effect of azimuthal (radial) roughness pattern on the bearing surface is to increase (decrease) the mean load‐carrying capacity and squeeze film time. The applied magnetic field increases the load‐carrying capacity and lengthens the squeezing time. Copyright © 2012 John Wiley &amp; Sons, Ltd.