Small Axial Ratios Research Articles

Experimental and numerical investigations on seismic behavior of spiral stirrup-confined square concrete-filled steel tubular columns

To investigate the seismic behavior of spiral stirrup-confined square concrete-filled steel tubular (SS-CFST) columns, ten square CFST columns, including eight SS-CFST columns and two ordinary CFST columns were experimentally studied through the cyclic loading tests. The critical test variables included the axial load ratio, spiral pitch, and longitudinal reinforcement ratio. First, the seismic behavior of the SS-CFST columns was herein discussed and clarified based on the failure modes, hysteretic response, skeleton curves, load-bearing capacity, strength and stiffness degradation, ductility and energy dissipation. Then, a total of 53 full-scale finite element (FE) models were established for parameter analysis of SS-CFST columns. The experimental and numerical results showed that the expansion deformation, necking and fracture of spiral stirrup were not formed when the SS-CFST columns were damaged, but the confinement effect effectively reduced the concrete fragmentation, alleviated the buckling of steel tube and longitudinal rebar, and limited the expansion of internal cracks. In the range of n=0.20–0.50, the ductility of SS-CFST columns significantly decreased with an increase in the axial load ratio, despite the stable bearing capacity and good energy dissipation of the columns. Moreover, unlike SS-CFST columns with high axial load ratio, spiral stirrup can only slightly improve the load-bearing capacity of SS-CFST columns with small axial load ratio (nt≤0.35). Compared with ordinary CFST columns, the strength degradation, ductility, collapse resistance, and energy dissipation of SS-CFST columns were significantly improved except for lateral stiffness, and the ultimate drift ratio of all SS-CFST columns in the test was greater than 3.00%. Furthermore, for SS-CFST columns, increasing the longitudinal reinforcement ratio can improve the lateral load-bearing capacity and stiffness. Finally, the formulas established in this paper can be adopted to assess the lateral load-bearing capacity of SS-CFST columns.

Low-Sidelobe-Level Circularly Polarized Short Leaky-Wave Antenna With A-Shaped Element Based on Substrate Integrated Image Guide

In this letter, a low-sidelobe-level (SLL) circularly polarized (CP) leaky-wave antenna with A-shaped elements is proposed based on substrate integrated image guide (SIIG). The A-shaped CP radiating element consists of a horizontal linearly polarized (LP) structure and a vertical LP structure. The horizontal LP wave and the vertical LP wave can be excited by a pair of inclined transversal metal strip patches and a longitudinal metal strip patch, respectively. Their phases are orthogonal and amplitudes can be controlled to be equal by adjusting the tilted angle of the horizontal LP structure and the length of the vertical LP structure. Moreover, the longitudinal metal strip patch is modified to the V-shaped strip patch, which can realize the field cancellation, thereby achieving the boresight radiation for such a leaky-wave antenna. Furthermore, a low SLL is realized by controlling the aperture-field distribution to obtain the desired amplitude distribution and the relatively small axial ratio. In addition, because of the short waveguide wavelength of the SIIG, this feedline can be used to achieve the small interelement spacing and element size, thereby realizing the short length of the array. The measured peak gain of this antenna is 12.3 dBic, the SLL is –19.1 dB and the efficiency is 92.3% at the center frequency of 14 GHz.

Seismic behavior of multi-cell steel reinforced concrete columns: Experimental study

In order to investigate the seismic behavior of multi-cell steel reinforced concrete (MSRC) columns, an experimental study of five large-size MSRC columns various in axial load ratio, cross-sectional structures and loading directions was conducted under axial loading and lateral cyclic loading. The failure mode, bearing capacity, ductility, residual deformation, bearing capacity degeneration and energy dissipation capacity were analyzed based on experimental study. The results showed that the damage developments of specimens with multi-cell steel under a large axial load ratio and a small axial load ratio were similar, while the damage developments of specimens with open steel showed significant differences. Meanwhile, the specimens with multi-cell steel exhibited larger bearing capacity, slower bearing capacity degeneration, better energy dissipation capacity and more stable behavior under different axial load ratios compared to specimens with open steel. However, the bearing capacities of specimens with multi-cell steel showed a sudden decline after the peak point and the ductility index was smaller than that of specimens with open steel. While when the confinement effects on concrete in different regions of cross-section were reasonably designed, the post peak behavior of specimens with multi-cell steel will be significantly improved. Based on the experimental results, a fiber-based method considering concrete in different regions experiencing different confinement effects was proposed to predict the backbone curves of five specimens. The predicted curves showed good agreement with the test curves. The errors of the peak bearing capacity and peak displacement ranged from −8.3% to 5% and −10% to −14%.

Low-Profile Wideband Spiral Antenna With a Circular HIS Reflector Composed of Homogenous Fan-Shaped Patch Elements

A low-profile spiral antenna backed by a circular high-impedance surface (HIS) reflector composed of homogeneous (CirHISRhomo) fan-shaped patch elements is investigated. The total antenna height from the bottom of the CirHISRhomo to the spiral antenna is very small: 0.09 wavelength at a lowest design frequency of 3 GHz. It is revealed that the CirHISRhomo contributes to a constant input impedance and a small axial ratio (AR) across the design frequency range of 3–10 GHz (the fractional bandwidth is approximately 108%). For comparison, the AR for the spiral antenna backed by a conventional perfect electric conducting reflector is also presented. The analysis results are verified by the measured results of the fabricated antenna.

Single-Feed Circularly Polarized Microstrip Antenna With Bethe Holes on the Radiating Patch

A novel single-feed (SF) circularly polarized (CP) microstrip antenna with Bethe holes on the radiating patch is introduced. The proposed antenna provides a small axial ratio (AR) over a relatively large frequency range and the CP quality is good over a wide range of radiation angle. The structure is of a single layer, providing easy fabrication at low cost.

Optimum design of helical antennas by genetic algorithm

AbstractThe genetic algorithm is employed to obtain optimal designs for helical antennas that, over the frequency range of operation, provide considerably smaller axial ratio, higher gain, and an appreciably wider overall bandwidth than the conventional axial mode helices with the same size. Also, for nearly equal bandwidth and peak directivity, the new design provides a 2 to1 reduction in size. For these helical antennas the pitch angle and radius, which are constant in conventional helices, vary continuously along the length; pitch angle increases while radius decreases. Genetic algorithm is used to determine variations of these parameters such that maximum directivity and minimum axial ratio are simultaneously achieved over the largest frequency range. Radiation properties of optimized helices, including far‐field pattern, axial ratio, and directivity, are examined numerically over a wide range of frequencies. Empirical design equations are provided. A 12‐turn prototype optimized helix is constructed and measured. Comparison of measured and simulated radiation patterns shows excellent agreement.

Shear-compression tests of URM walls: Various setups and their influence on experimental results

Current design codes provide empirical equations for the drift capacity of unreinforced masonry (URM) walls that are based on results of quasi-static cyclic shear-compression tests. Yet different experimental campaigns have used various approaches of imposing fixed-fixed boundary conditions at the wall top which may affect the test results. This article investigates, by means of numerical simulations, the influence of experimental setups on the force and drift capacities of in-plane loaded URM walls subjected to double-fixed conditions. It is shown that controlling the shear span or the top rotation while keeping the axial force constant leads to very similar results. Controlling the axial elongation at the top of the wall results for walls subjected to a small axial load ratio in an increase and for walls subjected to a large axial load ratio in a decrease in axial load with increasing drift demands. Testing a wall with half the height applying cantilever boundary conditions is not recommended as the stiff loading beam at the wall top changes the failure mode and leads to significantly larger drift capacities.

Design and Analysis of Dual Band Circularly Polarized Stacked Patch Antenna for GPS Application

In communications, antennas are the very important equipments are necessary to generate a communication system. Antennas are used in several applications like satellite communications etc. The design specifications of the antenna are considered using the transmission line model and designed with stacked square patches for multiple band operation with improved impedance matching. The Diagonal feed divides the given field into two orthogonal modes with equal magnitude and equal phase shift. The feed position is then optimized to attain the small axial ratio necessary to attain circular polarization at required frequency. The antenna has been designed at two different frequency bands with center frequencies of 1575 MHz and 1176 MHz. So the dual band circular polarization has been successfully incorporated into two square patches.

THE ABUNDANCE OF X-SHAPED RADIO SOURCES. I. VLA SURVEY OF 52 SOURCES WITH OFF-AXIS DISTORTIONS

Cheung identified a sample of 100 candidate X-shaped radio galaxies using the NRAO FIRST survey; these are small-axial-ratio extended radio sources with off-axis emission. Here we present radio images of 52 of these sources that have been made from archival Very Large Array data with resolution of about 1 arcsec. Fifty-one of the 52 were observed at 1.4 GHz, seven were observed at 1.4 GHz and 5 GHz, and one was observed only at 5 GHz. We also present overlays of the SDSS red images for 48 of the sources, and DSS II overlays for the remainder. Optical counterparts have been identified for most sources, but there remain a few empty fields. Our higher resolution VLA images along with FIRST survey images of the sources in the sample reveal that extended extragalactic radio sources with small axial ratios are largely (60%) cases of double radio sources with twin lobes that have off-axis extensions, usually with inversion-symmetric structure. The available radio images indicate that at most 20% sources might be genuine X-shaped radio sources that could have formed by a restarting of beams in a new direction following an interruption and axis flip. The remaining 20% are in neither of these categories. The implications of this result for the gravitational wave background are discussed in Roberts, Saripalli, and Subrahmanyan.

X-Shaped Radio Galaxies and the Nanohertz Gravitational Wave Background

AbstractCoalescence of supermassive black holes (SMBHs) in galaxy mergers is potentially the dominant contributor to the low frequency gravitational wave background (GWB). It was proposed by Merritt & Ekers that X-shaped radio galaxies are signposts of such coalescences and that their abundance might be used to predict the magnitude of the GWB. Cheung identified a sample of 100 candidate X-shaped radio galaxies using the NRAO FIRST survey; these are small-axial-ratio extended radio sources with off-axis emission. In Roberts et al. we made radio images of 52 of these sources with resolution of about 1 arcsecond using archival Very Large Array data. Fifty-one of the 52 were observed at 1.4 GHz, seven were observed at 1.4 and 5 GHz, and one was observed only at 5 GHz. Our higher resolution VLA images along with FIRST survey images of the sources in the sample reveal that extended extragalactic radio sources with small axial ratios are largely (60%) cases of double radio sources with twin lobes that have off-axis extensions, usually with inversion-symmetric structure. The available radio images indicate that at most 20% of sources might be genuine X-shaped radio sources that could have formed by a restarting of beams in a new direction following an interruption and axis flip. The remaining 20% are in neither of these categories.These images indicate that at most a small fraction of the candidates might be genuine X-shaped radio sources that were formed by a restarting of beams in a new direction following a major merger, or by spin drift caused by BH-BH interaction. This suggests that fewer than 1.3% of extended radio sources appear to be candidates for genuine axis reorientations (“spin flips”), or 2.2% if possible “axis drift” sources are included, much smaller than the 7% suggested by Leahy & Parma. Thus, the associated GWB may be substantially smaller than previous estimates. These results can be used to normalize detailed calculations of the SMBH coalescence rate and the GWB.

Estimation of absolute magnitude-dependent Galactic model parameters in intermediate latitude with SDSS and SCUSS

Based on the Sloan Digital Sky Survey and South Galactic Cap of u-band Sky Survey (SCUSS) early data, we use a star count method to estimate the Galactic structure parameters in an intermediate latitude with 10 180 main-sequence (MS) stars in an absolute magnitude interval of 4 ≤ Mr ≤ 13. We divide the absolute magnitude into five intervals, 4 ≤ Mr < 5, 5 ≤ Mr < 6, 6 ≤ Mr < 8, 8 ≤ Mr < 10 and 10 ≤ Mr ≤ 13, and estimate the Galactic structure parameters in each absolute magnitude interval to explore their possible variation with the absolute magnitude. Our study shows that the parameters depend on absolute magnitude. For the thin disc, the intrinsic faint MS stars have large local space density and they tend to stay close to the Galactic plane. A plausible explanation is that faint MS stars with long lifetime experience and long gravitational interaction time result in a short scaleheight. However, for the thick disc, the parameters show a complex trend with absolute magnitude, which may imply the complicated original of the thick disc. For the halo, the intrinsic faint MS stars have large local density and small axial ratio, which indicate a flattened inner halo and a more spherical outer halo.

A SEARCH FOR MODERATE-REDSHIFT SURVIVORS FROM THE POPULATION OF LUMINOUS COMPACT PASSIVE GALAXIES AT HIGH REDSHIFT

From a search of a ~ 2400 square degree region covered by both the SDSS and UKIDSS databases, we have attempted to identify galaxies at z ~ 0.5 that are consistent with their being essentially unmodified examples of the luminous passive compact galaxies found at z ~ 2.5. After isolating good candidates via deeper imaging, we further refine the sample with Keck moderate-resolution spectroscopy and laser-guide-star adaptive-optics imaging. For 4 of the 5 galaxies that so far remain after passing through this sieve, we analyze plausible star-formation histories based on our spectra in order to identify galaxies that may have survived with little modification from the population formed at high redshift. We find 2 galaxies that are consistent with having formed > 95% of their mass at z > 5. We attempt to estimate masses both from our stellar population determinations and from velocity dispersions. Given the high frequency of small axial ratios, both in our small sample and among samples found at high redshifts, we tentatively suggest that some of the more extreme examples of passive compact galaxies may have prolate morphologies.

Stacked Tri-Band Circularly Polarized Microstrip Patch Antenna for CNSS Applications

This paper proposes a novel stacked tri-band circularly polarized antenna which has three independent ports. To obtain tri-band operation, a stacked three layers of microstrip antenna working at different frequency is presented. Each of them is fed by dual feed probes. The simulated results show that the antenna can cover Compass Navigation Satellite System CNSS B3 1.268 GHz, L band 1.615 GHz and S band 2.49 GHz. The proposed antenna has achieved a bandwidth of 3.1%, 6.8% and 2.3% at each band, respectively. It exhibits small axial ratio under 3dB in three bands for the CNSS applications. Details of the proposed antenna design and results for the obtained tri-band circularly polarized performances are presented and discussed.

Package-Platformed Linear/Circular Polarization Reconfigurable Antenna Using an Integrated Silicon RF MEMS Switch

This letter presents a K-band polarization reconfigurable antenna integrated with a silicon radio frequency MEMS switch into the form of a compact package. The proposed antenna can change its state from linear polarization (LP) to circular polarization (CP) by actuating the MEMS switch, which controls the configuration of the coupling ring slot. Low-loss quartz is used for a radiating patch substrate and at the same time for a packaging lid by stacking it onto the MEMS substrate, which can increase the system integrity. The fabricated antenna shows broadband impedance matching and exhibits high axial ratios better than 15 dB in the LP and small axial ratios in the CP, with a minimum value of 0.002 dB at 20.8 GHz in the K-band.

Viscoelastic Fluids Originated from Enhanced Solubility of Sodium Laurate in Cetyl Trimethyl Ammonium Bromide Micelles through Cooperative Self-Assembly

Sodium laurate (SL), which is otherwise sparingly soluble in water at room temperature, forms viscoelastic fluids when mixed with cationic cetyl trimethylammonium bromide (CTAB) micelles. This originates from a cooperative assembly of CTAB and SL through electrostatic interaction and the ability of the tetralkyl ammonium headgroup in decreasing the Kraft point of SL. Addition of SL to CTAB induces the formation of rod-like micelles, the length of which can be controlled by the composition of the mixture. The effects of electrostatic repulsion of ionic moieties and steric repulsion of hydrocarbon chains in controlling the packing of surfactant molecules within the aggregate have been identified. The variation in the optimum interfacial area occupied by the surfactant as a function of electrolyte concentration is consistent with the model predicted by Nagarajan. Small angle neutron scattering studies indicate that the micelles undergo composition dependent uniaxial growth without any significant change in the cross section radius, in the absence of electrolytes. However, in the presence of NaCl, both the length and cross section radius of the elongated micelles are sensitive to composition. At small axial ratio, these micelles behave like Newtonian fluids, while long polymer-like micelles show shear thinning behavior. The dynamic rheological responses of long micelles are consistent with a Maxwell type viscoelastic behavior.

Fabrication of Circular Polarization Antenna on PEI/BSTZ Composite Substrate for the Application of UHF-RFID Reader

The dielectric characteristics of poly(ether imide) (BSTZ) composites are developed. A circular polarization (CP) antenna with a simple structure is designed on a PEI/BSTZ composite substrate for the applications of ultrahigh frequency (UHF) band radio-frequency identification (RFID) readers. Two rectangular stubs on the proposed circular patch of RFID antennas are used to tune the impedance matching effect and to improve the axial ratio performance. The proposed CP antennas are successfully fabricated on the PEI/BSTZ composite substrates, and an antenna with a similar structure is also fabricated on the FR4 substrate for comparison. In this study, we demonstrate that the CP antenna fabricated on the PEI/BSTZ substrate has better characteristics and is smaller than that fabricated on the FR4 substrate. The antenna fabricated on the PEI/BSTZ composite substrate also has a larger impedance bandwidth and a smaller axial ratio than the antennas fabricated on the FR4 substrate.

High Precision Transport Properties of Cylinders by the Boundary Element Method

In this work we apply the boundary element method to obtain very precise computations of the hydrodynamic transport properties for rectangular, sphero, and open cylinders. This work numerically solves the exact integral equations for Stokes flow with stick boundary conditions and includes the tensor values for the translational and rotational diffusion coefficients, and the intrinsic viscosity for three types of cylinders with axial ratios between 1 and 100. We describe the properties of the triangular tessellations that yield essentially numerically exact properties, with estimated uncertainties of 0.07% or better. The data are summarized by fairly simple mathematical expressions as a function of the axial ratio of the cylinders which are constructed to satisfy the correct asymptotic expressions, yielding formulas that are valid for 1 ≤ p < ∞. The end effects for the three different types of caps are discussed—such end effects are noticeable for small axial ratios and become unimportant for large axial ratios. The open cylinders behave in a similar fashion to the closed end cylinders, despite the absence of caps. For the intrinsic viscosity, we introduce a new formula with correct asymptotic limits and high accuracy at unit axial ratio which greatly improves the description over traditional expressions derived from slender body theory. We compare our results with previous formulas available in the literature for different types of cylinders and conclude that, except for the path integral method results, most previous work has significant inaccuracies. The expressions obtained in this work, will be useful in the description of the transport properties of interesting macromolecular structures such as carbon nanotubes, microtubules, and viruses.

Galaxy Morphologies in the Hubble Ultra Deep Field: Dominance of Linear Structures at the Detection Limit

Galaxies in the Hubble Ultra Deep Field (UDF) larger than 10 pixels (0.3 arcsec) have been classified according to morphology and their photometric properties are presented. There are 269 spirals, 100 ellipticals, 114 chains, 126 double-clump, 97 tadpole, and 178 clump-cluster galaxies. We also catalogued 30 B-band and 13 V-band drop-outs and calculated their star formation rates. Chains, doubles, and tadpoles dominate the other types at faint magnitudes. The fraction of obvious bars among spirals is ~10 percent, a factor of 2-3 lower than in other deep surveys. The distribution function of axial ratios for elliptical galaxies is similar to that seen locally, suggesting that ellipticals relaxed quickly to a standardized shape. The distribution of axial ratios for spiral galaxies is significantly different than locally, having a clear peak at ~0.55 instead of a nearly flat distribution. The fall-off at small axial ratio occurs at a higher value than locally, indicating thicker disks by a factor of ~2. The fall-off at high axial ratio could be from intrinsic triaxial shapes or selection effects. Inclined disks should be more highly sampled than face-on disks near the surface brightness limit of a survey. Simple models and data distributions demonstrate these effects. The decreased numbers of obvious spiral galaxies at high redshifts could be partly the result of surface brightness selection.

A Design of a Leaky Waveguide Crossed-Slot Linear Array with a Matching Element by the Method of Moments with Numerical-Eigenmode Basis Functions

A waveguide crossed-slot linear array with a matching element is accurately analyzed and designed by the method of moments using numerical-eigenmode basis functions developed by the authors. The rounded ends of crossed-slots are accurately modeled in the analysis. The initial values of the slot parameters determined by a model with assumption of periodicity of field are modified and refined by the full-wave finite-array analysis for uniform excitation and small axial ratio. As an example, an 8-element linear array is designed at 11.85 GHz, which radiates a circularly polarized wave at a beam-tilting angle of 50 degrees. The radiation pattern, the frequency characteristics of the reflection and the axial ratio are compared between the analysis and the measurement and they agree very well. The calculated and measured axial ratio at the beam direction are 0.1 dB and 1.7dB, respectively. This method provides a basic and powerful design tool for slotted waveguide arrays.

Quadrifilar helix antenna with parasitic helical strips

AbstractAn omnidirectional quadrifilar helix antenna (QHA) with parasitic helical strips for circular polarization (CP) is proposed and experimentally investigated for handheld mobile terminals. This antenna is small in size, low cost, and lightweight. The mutual coupling effect between the grounded helical strips and the feeding helical arms provides a good impedance match, a smaller axial ratio, and wider hemispherical coverage. The impedance bandwidth corresponding to SWR&lt;2 and bandwidth with respect to the axial ratio &lt;3 dB are found to be 39% and 160 MHz at 3.64 GHz, respectively. © 2001 John Wiley &amp; Sons, Inc. Microwave Opt Technol Lett 30: 128–130, 2001.