Elliptical Aperture Research Articles

Best Image with Elliptical Synthetic Obscured Apertures

It is well established that synthetic apertures of various shapes are superior to a single aperture in improving the overall performance of optical systems.In this research, a set of elliptical synthetic obstructed apertures was used in place of the ellipse synthetic obstructed apertures that was used previously and the calculation of the point spread function to assess the performance of the optical system and reduce the diffraction values from it previously, according to the results, an improvement was observed in the optical system with array of elliptical synthetic obstructed apertures.

Influence of the Laser Heat Treatment on the AA5754-H32 strain path during hydraulic bulge tests

The hydraulic bulge test represents an effective experimental method to characterise sheet metals since the equivalent strains before failure are much larger than those measured during tensile testing and there is nearly no frictional effect on the results. Recently this test has been proposed not only for extracting data concerning the equi-biaxial strain condition, but to determine the forming limit diagram (FLD) in the range of positive minor strains. In the proposed methodology, different strain paths can be obtained by merely using a test blank having two holes with a suitable geometry and position to be tested, without the need of dies with elliptical apertures. However, a carrier sheet is necessary, thus implying results may be affected by friction effects. This paper proposes a new methodology for the determination of the right side of the Forming Limit Curve (FLC), based on the adoption of local heat treatments aimed at determining different strain paths on the blank to be tested while using the classical circular die for bulge tests. In particular, the formability of the alloy AA5754-H32 was investigated; 3D Finite Element simulations were conducted setting different laser strategies and monitoring the resulting strain path. Results revealed that the proposed methodology supports obtaining many additional points in the right side of the FLC, thus being effective and friction free.

Identification and Mitigation of a Vibrational Telescope Systematic with Application to Spitzer

Abstract We observed Proxima Centauri with the Spitzer Space Telescope Infrared Array Camera five times in 2016 and 2017 to search for transits of Proxima Centauri b. Following standard analysis procedures, we found three asymmetric, transit-like events that are now understood to be vibrational systematics. This systematic is correlated with the width of the point-response function (PRF), which we measure with rotated and nonrotated-Gaussian fits with respect to the detector array. We show that the systematic can be removed with a novel application of an adaptive elliptical-aperture photometry technique, and compare the performance of this technique with fixed and variable circular-aperture photometry, using both BiLinearly Interpolated Subpixel Sensitivity (BLISS) maps and nonbinned Pixel-Level Decorrelation (PLD). With BLISS maps, elliptical photometry results in a lower standard deviation of normalized residuals, and reduced or similar correlated noise when compared to circular apertures. PLD prefers variable, circular apertures, but generally results in more correlated noise than BLISS. This vibrational effect is likely present in other telescopes and Spitzer observations, where correction could improve results. Our elliptical apertures can be applied to any photometry observations, and may be even more effective when applied to more circular PRFs than Spitzer’s.

Two new species of Caulobothrium (Cestoda: "Tetraphyllidea") from the duckbill eagle ray, Aetomylaeus bovinus (Myliobatiformes: Myliobatidae), off Senegal with new insights on morphological features of the genus.

Two new species of the cestode genus Caulobothrium, collected from the duckbill eagle ray, Aetomylaeus bovinus, off Senegal, are described. Although postulated as sister taxa in an earlier molecular phylogenetic analysis, Caulobothrium multispelaeum n. sp. and Caulobothrium katzi n. sp., respectively, are among the smallest and largest members of the genus. The smaller species is unique among its congeners in possessing unusual medial longitudinal grooves along the dorsal and ventral surfaces of its strobila that develop into a tandem series of elliptical apertures on the posterior proglottids. The inner surfaces of these apertures stained positively with McManus' periodic acid Schiff in a manner similar to that seen in members of the distantly related lecanicephalidean genus Elicilacunosus. The larger species differs from its congeners in size, number of proglottids, and arrangement of bothridial loculi. Both new species were found to possess a small apical sucker on the anterior margin of each of their bothridia. Scanning electron microscopy (SEM) and frontal sections of a bothridium of Caulobothrium tetrascaphium suggests that this species also bears an apical sucker. Examination of the hologenophore of the species provisionally referred to as Caulobothrium n. sp. 5 in the earlier molecular analysis indicates it is conspecific with the recently described Caulobothrium pedunculatum, which was also determined to possess bothridial apical suckers. This leads us to suspect that this feature may be found to occur in all members of the genus. SEM of specimens of Caulobothrium for the first time indicates their bothridial surfaces are covered with filitriches of various sizes but lack spinitriches; spinitriches were seen only on the cephalic peduncle of C. katzi n. sp. The geographic distribution and host associations of Caulobothrium are expanded to include data now available for all species. The diagnosis of the genus is revised to include all of this information.

An Analytical Evaluation of the Shielding Effectiveness of Enclosures Containing Complex Apertures

Analytical methods are significantly useful tools for engineers in computational modeling. These methods provide fast simulations, while preserving physical meaning. In this paper, a full analytical formulation is developed based on the circuit approach, also known as Intermediate Level Circuit Model (ILCM), to evaluate the shielding effectiveness (SE) of metallic structures. The proposal focuses on rectangular enclosures containing apertures of complex geometrical shape, illuminated by an external plane wave. The enclosure is taken as a short-circuited waveguide. The aperture is treated as a transmission line with an intrinsic impedance that depends on the aperture polarizability, according to Bethe’s theory of small holes. The formulation easily takes into account high-order resonant modes and different apertures, such as circular, elliptical, round-ended and cross-shaped apertures. The ILCM technique reveals good agreement with a numerical full-wave method for various configurations of enclosures, covering a large range of frequencies from 0.5 GHz to 2.5 GHz, thus offering perspectives for parametric and/or optimization SE studies.

Fabrication of metal nanorod arrays using anodic porous alumina mask with elliptical apertures prepared by lattice conversion process

Highly ordered Au nanorod arrays were fabricated using anodic porous alumina with elliptical nanoholes as an evaporation mask and applied as a substrate for measurements of surface-enhanced Raman scattering (SERS) spectra. Shape of nanoholes in anodic porous alumina obtained by self-ordering anodization process is usually circular. In the present study, elliptical nanoholes ordered in rectangular lattice were successfully fabricated by lattice conversion process using naturally ordered anodic porous alumina. The Au nanorod arrays were fabricated by thermal evaporation using the obtained anodic porous alumina. The SERS activity of the Au nanorods were higher than that of a circular Au nanodots.

Aperture elongation of the femoral tunnel on the lateral cortex in anatomical double-bundle anterior cruciate ligament reconstruction using the outside-in technique.

In anatomical anterior cruciate ligament reconstruction surgery using the outside-in technique, the aperture of the femoral lateral cortex may become elliptical.Retrospective cross-sectional studyTo evaluate the extent of elliptical eccentricity in lateral apertures relative to aperture positioning and clinical failure rate in anatomical anterior cruciate ligament double-bundle reconstruction using outside-in technique.In 75 patients, the aperture elongation factor was defined as the ratio of the major axis of the elliptical aperture to the drill size. Using the lateral epicondyle as a reference point, the lateral femur was divided into sections by distance and angle, and the minimum area was evaluated to assess the relationship between the elongation factor and aperture position of the lateral cortex for each bundle. The incidence and associated clinical performance regarding cortical button migration were also investigated.Aperture elongation factors were 120.2 ± 13.3% and 120.0 ± 16.3% on the anteromedial (AM) and posterolateral (PL) sides, respectively. Femoral tunnel elongation was smallest when the entry point axis were both between 30 to 60° and distance was between 10 to 20 mm and 0 to 10 mm on the AM and PL sides, respectively. During the postoperative follow-up period, intra-tunnel migration was confirmed in 4 of 75 cases (5.3%). Fixation failure neither affected clinical scores nor knee laxity.Areas of minimum elongation for each bundle on both AM and PL sides were found anteroproximally to the lateral epicondyle and positioned near each other. Elongation did not directly affect the clinical outcome.Level of evidence grade: prognostic level III

Выбор схемы подкрепления параболической антенны из композиционных материалов с эллиптической линией раскрыва

Being prepared foThe problems of designing and calculating reinforced shells of revolution made of composite materials as constituent elements of parabolic antennas with an elliptical aperture line having a focal parameter value of not more than 0.03 m are examined in this paper. The structural layout schemes of reflectors of the parabolic-type mirror spacecraft antennas are reviewed. A technique for designing a bearing frame for reinforcing the reflector shell using numerical analysis based on the finite element method is presented. The technique is based on the assessment of the stiffness parameters of the structural elements of the reflector located between the annular ribs. It utilizes optimization in order to achieve a constant gradient of changes in the stiffness parameters. The deformability of the reflector design that uses a modern high-modulus composite material is evaluated. A finished product is presented as the result of the application of the technique. An assessment of manufacturing and design errors is performed based on the experimental data. The proposed approach to the design of reflectors with an elliptical aperture line eliminates warping of the molded product and deformation during operation such as twisting in the form of a propeller. The results of the study can be used for designing reflectors of spacecraft mirror antennas with a narrow radiation pattern that meet strict requirements of the accuracy of the reflecting surface geometry as well as mass restrictions.

Polarization Multiplexing Terahertz Metasurfaces through Spatial Femtosecond Laser‐Shaping Fabrication

AbstractTerahertz (THz) metasurface has emerged as a powerful technique to fully modulate the wavefronts of THz radiation. To improve the information storage capability and enhance the encryption security of THz metasurface holograms, smart metasurface designs, and fabrications for polarization multiplexing are essential. In this study, two kinds of polarization multiplexing THz metasurfaces are fabricated through the slit‐based spatial modulation of femtosecond laser. Controllable elliptical aperture arrays can easily and flexibly be fabricated on gold films by adjusting the width and position of the slit combined with the laser pulse energy. Based on the Pancharatnam–Berry phase and amplitude modulation, respectively, THz metasurfaces, with two independent target phases or amplitude profiles, are obtained. A variety of information can be processed under different polarization states through these THz metasurfaces. This method allows flexible and efficient customization of THz metasurfaces because of the high‐speed fabrication and reproducibility as well as precise control of elliptical apertures location on the surface.

LOW SLL PATTERN OF ELLIPTICAL APERTURE ARRAY BASED ON INNOVATIVE OPTIMIZATION METHOD

LOW SLL PATTERN OF ELLIPTICAL APERTURE ARRAY BASED ON INNOVATIVE OPTIMIZATION METHOD

Synthesis of Monopulse Antenna Patterns for Elliptical Phased Array Antennas With Different Peak Sidelobes Along the Principal Planes

This paper deals with the synthesis of monopulse antenna patterns, sum and difference ones, for planar phased array antennas with an elliptical aperture boundary featuring unequal ultra-low peak sidelobe levels (PSLLs) for the two principal planes of its far field. The used synthesis method is the iterative Fourier transform (IFT) approach. The elliptical planar phased array antenna involved in this synthesis contains 3656 open-ended waveguide radiating elements arranged in a triangular element grid and has an aperture width and height of 50λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and 25λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , respectively, where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength at X-band center frequency 1.0f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The simulated monopulse pattern results will be compared with those of a 4680-element rectangular planar phased array antenna having the same width, height, radiator type and triangular grid as the elliptical array antenna. The monopulse patterns of the rectangular array antenna meet the same unequal ultra-low PSLL requirements as those of the elliptical array antenna. It will be shown that the elliptical array antenna with a slightly enlarged aperture containing 4170 elements features on receive comparable or even better far-field performance characteristics as that of the rectangular array antenna. All reported far-field pattern simulations take mutual coupling between the array elements into account.

Adaptive elliptical aperture photometry: A software package for high-cadence ground-based photometry

Context.Modern space telescopes are currently providing high-precision light curves for a large fraction of the sky, such that many new variable stars are being discovered. However, some stars have periodic variability with periods on the order of minutes and require high-cadence photometry to probe the physical mechanisms responsible. A cadence of less than a minute is often required to remove Nyquist ambiguities and confirm rapid variability, which forces observers to obtain high-cadence ground-based photometry.Aims.We aim to provide a modern software package to reduce ground-based photometric time series data and deliver optimised (differential) light curves. To produce high-quality light curves, which maximise the amplitude signal-to-noise ratio of short-period variability in a Fourier spectrum, we require adaptive elliptical aperture photometry as this represents a significant advantage compared to aperture photometry using circular apertures of fixed radii.Methods.The methodology of our code and its advantages are demonstrated using high-cadence ground-based photometry from the South African Astronomical Observatory (SAAO) of a confirmed rapidly oscillating Ap (roAp) star. Furthermore, we employed our software package to search for rapid oscillations in three candidate roAp stars.Results.We demonstrate that our pipeline represents a significant improvement in the quality of light curves, and we make it available to the community for use with different instruments and observatories. We search for and demonstrate the lack of high-frequency roAp pulsations to a limit of ∼1 mmag usingBdata in the three Ap stars HD 158596, HD 166542, and HD 181810.Conclusions.We demonstrate the significant improvement in the extraction of short-period variability caused by high-frequency pulsation modes, and discuss the implication of null detections in three Ap stars.

Generating Ultrabroadband Deep-UV Radiation and Sub-10 nm Gap by Hybrid-Morphology Gold Antennas.

We experimentally investigate the interaction between hybrid-morphology gold optical antennas and a few-cycle Ti:sapphire laser up to ablative intensities, demonstrating rich nonlinear plasmonic effects and promising applications in coherent frequency upconversion and nanofabrication technology. The two-dimensional array of hybrid antennas consists of elliptical apertures combined with bowties in its minor axis. The plasmonic resonance frequency of the bowties is red-shifted with respect to the laser central frequency and thus mainly enhances the third harmonic spectrum at long wavelengths. The gold film between two neighboring elliptical apertures forms an hourglass-shaped structure, which acts as a "plasmonic lens" and thus strongly reinforces surface currents into a small area. This enhanced surface current produces a rotating magnetic field that deeply penetrates into the substrate. At resonant frequency, the magnetic field is further intensified by the bowties. The resonant frequency of the hourglass is blueshifted with respect to the laser central frequency. Consequently, it spectacularly extends the third harmonic spectrum toward short wavelengths. The resultant third harmonic signal ranges from 230 to 300 nm, much broader than the emission from a sapphire crystal. In addition, the concentration of surface current within the neck of the hourglass antenna results in a structural modification through laser ablation, producing sub-10 nm sharp metallic gaps. Moreover, after laser illumination the optical field hotspots are imprinted around the antennas, allowing us to confirm the subwavelength enhancement of the electric near-field intensity.

Parametric geometry analysis for circular-aperture off-axis parabolic mirror segment

We investigated the geometrical characteristics of circular-aperture off-axis parabolic (OAP) mirror segments to clarify the meaning of the loosely defined word “center” used in the literature and in documents to describe OAPs. We proposed the elliptical aperture center of an OAP as the definition of the center. The off-axis distance (OAD) is the vertical distance from the reference optical axis to the aperture center. In addition, the OAD can be varied depending on the desired center of a circular aperture to select the part of a parallel beam for focusing. The radius of the circular aperture becomes the minor-axis semidiameter of the elliptical aperture of the OAP. These geometrical parameters were systematically defined, derived, and/or analyzed in the context of optical engineering applications. Based on a set of those fundamental parameters, an intrinsic datum point utilizing the deepest point on the OAP surface was presented. The datum point provides a well-defined reference co-ordinate frame for locating or aligning an OAP within various astronomical telescope designs, instrument manufacturing and assembly processes, and optical system alignment and testing applications.

Theory of diffraction of vortex beams from structured apertures and generation of elegant elliptical vortex Hermite-Gaussian beams.

In this work, a comprehensive analytic study of the diffraction of vortex beams from structured apertures is presented. We formulate the near- and far-field diffraction of a vortex beam from an aperture having an arbitrary functionality in the Cartesian coordinates by two general and different approaches. We show that each of the resulting diffraction patterns can be determined by a number of successive derivatives of the 2D Fourier transform of the corresponding hypothetical aperture function or equally can be obtained by a summation of 2D Fourier transforms of the corresponding modified aperture function. We implement both introduced analytic approaches in predicting the diffraction of a vortex beam from an elliptic Gaussian aperture, an elliptic Gaussian phase mask, and a hyperbolic Gaussian phase mask in the near- and far-field regimes. It is shown that the predicted diffraction patterns by both these approaches are exactly the same. It is shown that the diffraction of a vortex beam from an elliptic Gaussian aperture at the far-field regime forms a light beam that belongs to a family of light beams we call elegant elliptical vortex Hermite-Gaussian beams. In addition, the diffractions of a vortex beam from a Fresnel zone plate in general form for the on- and off-axis situations are formulated, and sinusoidal and binary zone plates are investigated in detail. Our general analytic formula can be used for a large variety of apertures including off-center situations and asymmetrical cases.

Mesh Generation of Elliptical Aperture Reflectors

AbstractOffset-feed elliptical aperture reflectors have better mechanical and electrical performance than circular aperture reflectors and are an inevitable trend for the future development of high...

A-PHOT: a new, versatile code for precision aperture photometry

Aims. We present A-PHOT, a new publicly available code for performing aperture photometry on astronomical images, that is particularly well suited for multi-band extragalactic surveys. Methods.A-PHOT estimates the fluxes emitted by astronomical objects within a chosen set of circular or elliptical apertures. Unlike other widely used codes, it runs on predefined lists of detected sources, allowing for repeated measurements on the same list of objects on different images. This can be very useful when forced photometric measurement on a given position is needed. A-PHOT can also estimate morphological parameters and a local background flux, and compute on-the-fly individual optimized elliptical apertures, in which the signal-to-noise ratio is maximized. Results. We check the performance of A-PHOT on both synthetic and real test datasets: we explore a simulated case of a space-based high-resolution imaging dataset, investigating the input parameter space to optimize the accuracy of the performance, and we exploit the CANDELS GOODS-South data to compare the A-PHOT measurements with those from the survey legacy catalogs, finding good agreement overall. Conclusions.A-PHOT proves to a useful and versatile tool for quickly extracting robust and accurate photometric measurements and basic morphological information of galaxies and stars, with the advantage of allowing for various measurements of fluxes at any chosen position without the need of a full detection run, and for determining the basic morphological features of the sources.

Electric Field Integral Equation-Based Synthesis of Elliptical-Domain Metasurface Antennas

A method based on the electric field integral equation is proposed for synthesizing planar metasurface (MTS) antennas built on elliptical apertures. The MTS is modeled with a modulated tensorial surface impedance. Entire-domain basis functions are used to discretize efficiently the currents as well as the surface impedance, allowing a quasi-direct computation of the surface impedance from the desired radiation pattern. The corresponding surface currents are combined with the near-field radiation from a constant reactance to derive the surface impedance of the MTS. The obtained algorithm is, therefore, systematic and can be applied to generate arbitrary radiation patterns, with control on the amplitude, phase, and polarization. Numerical validation of the proposed technique illustrates the effectiveness of the method.

Femoral tunnel widening is similar between anteromedial portal and transtibial techniques following single-bundle anterior cruciate ligament reconstruction: a systematic review and meta-analysis.

In anterior cruciate ligament (ACL) reconstruction, there is concern regarding the potential risk of femoral tunnel widening in the anteromedial portal (AMP) technique due to the acute graft-bending angle at the aperture and the more elliptical aperture shape of the femoral tunnel compared to the transtibial (TT) techniques. Therefore, the aim of the current systematic review and meta-analysis was to compare the femoral tunnel widening between the AMP and TT techniques in patients who underwent ACL reconstruction. It should be included the studies that reported on femoral tunnel widening in patients who underwent single-bundle ACL reconstruction, using soft-tissue tendon graft, with AMP and/or TT techniques. Two reviewers independently recorded data from each study, including the sample size and magnitude of tunnel widening after ACL reconstruction. Twenty-one studies were finally included in this meta-analysis. The pooled changes of absolute millimeters of tunnel widening from the immediate postoperative status to the last follow-up did not differ significantly between the AMP and TT techniques at both the aperture [3.31mm, 95% confidence interval (CI) 1.7-5.0. mm versus 2.9mm, 95% CI 2.4-3.4mm, P = n.s.] and the midportion (3.5mm, 95% CI 0.8-6.3mm versus 3.0mm, 95% CI 2.2-3.9mm, P = n.s.) of the femoral tunnel. No significant difference was observed between the two techniques in the relative percentage of femoral tunnel widening (AMP; 28.8%, 95% CI 14.8-42.9% vs. TT; 29.7%, 95% CI 15.6-43.7%, P = n.s.). No significant difference in femoral tunnel widening was observed between the AMP and TT techniques, both in absolute millimeter and relative percentage, in patients who underwent single-bundle ACL reconstruction. This finding could alleviate the potential concerns associated with femoral tunnels being wider for the AMP than for the TT technique. III.

Design of a wideband transmissive linear-to-circular polarization converter based on a metasurface

A wideband transmissive linear-to-circular polarization converter based on an anisotropic metasurface is proposed, which consists of three layers of conductive pattern layers separated by two dielectric layers, each conductive pattern layer consists of a square array of elliptical loop apertures. For the long axis of each loop aperture is tilted 45° from the vertical direction, and it is an orthogonal anisotropic structure with a pair of mutually perpendicular symmetric axes u and v along ± 45° directions with respect to y axis direction. Numerical simulation results show that the polarization converter can realize linear-to-circular polarization conversion at x and y polarized incidences in the frequency range from 10.73 to 16.13 GHz with a relative bandwidth of 40.2%. A detailed analysis for the polarization conversion was presented, and an effective formula was deduced, which can be used to calculate the cross- and co-polarization transmission coefficients at x and y polarized incidences according to the two transmission coefficients at u and v polarized incidences. Finally, one experiment was carried out, and a good agreement was observed between measured and simulated results.