Improvement In Angular Resolution Research Articles

A hybrid approach to event reconstruction for atmospheric Cherenkov Telescopes combining machine learning and likelihood fitting

The imaging atmospheric Cherenkov technique provides potentially the highest angular resolution achievable in astronomy at energies above the X-ray waveband. High-resolution measurements provide the key to progress on many of the major questions in high energy astrophysics, including the sites and mechanisms of particle acceleration to PeV energies. The huge potential of the next-generation CTA observatory in this regard can be realised with the help of improved algorithms for the reconstruction of the air-shower direction and energy.Hybrid methods combining maximum-likelihood-fitting techniques with neural networks represent a particularly promising approach and have recently been successfully applied for the reconstruction of astrophysical neutrinos. Here, we present the FreePACT algorithm, a hybrid reconstruction method for IACTs. In this, making use of the neural ratio estimation technique from the field of likelihood-free inference, the analytical likelihood used in traditional image likelihood fitting is replaced by a neural network that approximates the charge probability density function for each pixel in the camera.The performance of this improved algorithm is demonstrated using simulations of the planned CTA southern array. For this setupFreePACT provides significant performance improvements over analytical likelihood techniques, with improvements in angular and energy resolution of 25% or more over a wide energy range and an angular resolution as low as 40′′ at energies above 50TeV for observations at 20° zenith angle. It also yields more accurate estimations of the uncertainties on the reconstructed parameters and significantly speeds up the reconstruction compared to analytical likelihood techniques while showing the same stability with respect to changes in the observation conditions. Therefore, the FreePACT method is a promising upgrade over the current state-of-the-art likelihood event reconstruction techniques.

DanceCam: atmospheric turbulence mitigation in wide-field astronomical images with short-exposure video streams

ABSTRACT We introduce a novel technique to mitigate the adverse effects of atmospheric turbulence on astronomical imaging. Utilizing a video-to-image neural network trained on simulated data, our method processes a sliding sequence of short-exposure (∼0.2 s) stellar field images to reconstruct an image devoid of both turbulence and noise. We demonstrate the method with simulated and observed stellar fields, and show that the brief exposure sequence allows the network to accurately associate speckles to their originating stars and effectively disentangle light from adjacent sources across a range of seeing conditions, all while preserving flux to a lower signal-to-noise ratio than an average stack. This approach results in a marked improvement in angular resolution without compromising the astrometric stability of the final image.

Wearable Loop Sensors for Knee Flexion Monitoring: Dynamic Measurements on Human Subjects.

Goals: We have recently introduced a new class of wearable loop sensors for joint flexion monitoring that overcomes limitations in the state-of-the-art. Our previous studies reported a proof-of-concept on a cylindrical phantom limb, under static scenarios and with a rigid sensor. In this work, we evaluate our sensors, for the first time, on human subjects, under dynamic scenarios, using a flexible textile-based prototype tethered to a network analyzer. An untethered version is also presented and validated on phantoms, aiming towards a fully wearable design. Methods: Three dynamic activities (walking, brisk walking, and full flexion/extension, all performed in place) are used to validate the tethered sensor on ten (10) adults. The untethered sensor is validated upon a cylindrical phantom that is bent manually at random speed. A calibration mechanism is developed to derive the sensor-measured angles. These angles are then compared to gold-standard angles simultaneously captured by a light detection and ranging (LiDAR) depth camera using root mean square error (RMSE) and Pearson's correlation coefficient as metrics. Results: We find excellent correlation (≥ 0.981) to gold-standard angles. The sensor achieves an RMSE of 4.463° ± 1.266° for walking, 5.541° ± 2.082° for brisk walking, 3.657° ± 1.815° for full flexion/extension activities, and 0.670° ± 0.366° for the phantom bending test. Conclusion: The tethered sensor achieves similar to slightly higher RMSE as compared to other wearable flexion sensors on human subjects, while the untethered version achieves excellent RMSE on the phantom model. Concurrently, our sensors are reliable over time and injury-safe, and do not obstruct natural movement. Our results set the ground for future improvements in angular resolution and for realizing fully wearable designs, while maintaining the abovementioned advantages over the state-of-the-art.

Deep Learning-Based Angular Resolution Improvement in Planar Sensor Array

Deep Learning-Based Angular Resolution Improvement in Planar Sensor Array

Алгоритм оценки углов прихода сигналов в системе распределенных некогерентных автомобильных радаров

The present paper is focused on processing of signals from multiple sensors in non-coherent mode that provide improvement of angular resolution of close targets compared to single radar. The low-complexity technique of Direction-of-Arrival (DoA) estimation in Automotive Distributed Non-Coherent Multi-Radar Systems in the case of short length of snapshots is proposed. This technique consists of three main stages: beam-scanning procedure, transformation of the received signals of two radars to the unified coordinate system, and joint DoA estimation algorithm. The DoA method is represented by two approaches: (i) the Capon method modified for joint signal processing; (ii) low-complexity algorithm based on theory of auto-compensator. Performance of the system is investigated on the base of Monte-Carlo simulation. Current algorithm shows improvement of system performance of distributed non-coherent multi-radar systems compared to single radar.

300: An ACA 870 μm Continuum Survey of Orion Protostars and Their Evolution

We present an 870 μm continuum survey of 300 protostars from the Herschel Orion Protostar Survey using the Atacama Compact Array (ACA). These data measure protostellar flux densities on envelope scales ≤8000 au (20″) and resolve the structure of envelopes with 1600 au (4″) resolution, a factor of 3–5 improvement in angular resolution over existing single-dish 870 μm observations. We compare the ACA observations to Atacama Large Millimeter/submillimeter Array 12 m array observations at 870 μm with ∼0.″1 (40 au) resolution. Using the 12 m data to measure the fluxes from disks and the ACA data within 2500 au to measure the combined disk plus envelope fluxes, we calculate the 12 m/ACA 870 μm flux ratios. Our sample shows a clear evolution in this ratio. Class 0 protostars are mostly envelope-dominated with ratios <0.5. In contrast, Flat Spectrum protostars are primarily disk-dominated with ratios near 1, although with a number of face-on protostars dominated by their envelopes. Class I protostars span the range from envelope to disk-dominated. The increase in ratio is accompanied by a decrease in the envelope fluxes and estimated mass infall rates. We estimate that 80% of the mass is accreted during the envelope-dominated phase. We find that the 12 m/ACA flux ratio is an evolutionary indicator that largely avoids the inclination and foreground extinction dependence of spectral energy distribution-based indicators.

Improvement of angular rotation measurement resolution and sensitivity based on an SU(1,1) interferometer with intensity sum detection

In order to realize the enhancement of angular rotation measurement sensitivity, a new scheme based on an SU(1,1) interferometer with intensity sum detection has been proposed. A coherent beam carrying orbital angular momentum (OAM) enters into the SU(1,1) interferometer where the Dove prisms are inserted. By taking full advantage of the two outports and employing intensity sum detection, the angular rotation measurement sensitivity can be enhanced by higher gain, photon number and OAM. Meanwhile, resolution can be improved while the pump beam carries OAM. The angular rotation measurement sensitivity of the SU(1,1) interferometer can beat standard quantum limit ), and it still can be optimal when photon depletion inside this interferometer is the same.

Radio astronomy and Space science in Azores: Enhancing the Atlantic VLBI infrastructure cluster

Radio astronomy and Space Infrastructures in the Azores have a great scientific and industrial interest because they benefit from a unique geographical location in the middle of the North Atlantic allowing a vast improvement in the sky coverage. This fact obviously has a very high added value for: i) the establishment of space tracking and communications networks for the emergent global small satellite fleets ii) it is invaluable to connect the radio astronomy infrastructure networks in Africa, Europe and America continents using Very Large Baseline Interferometry (VLBI) techniques, iii) it allows excellent potential for monitoring space debris and Near Earth Objects (NEOs). There is in S. Miguel island a 32-metre SATCOM antenna that could be integrated in advanced VLBI networks and be capable of additional Deep Space Network ground support. This paper explores the space science opportunities offered by the upgrade of the S. Miguel 32-metre SATCOM antenna into a world-class infrastructure for radio astronomy and space exploration: it would enable a Deep Space Network mode and would constitute a key space facility for data production, promoting local digital infrastructure investments and the testing of cutting-edge information technologies. Its Atlantic location also enables improvements in angular resolution, provides many baselines in East–West and North–South directions connecting the emergent VLBI stations in America to Europe and Africa VLBI arrays therefore contributing for greater array imaging capabilities especially for sources or well studied fields close to or below the celestial equator, where ESO facilities, ALMA, SKA and its precursors do or will operate and observe in the coming decades.

Training artificial neural networks for precision orientation and strain mapping using 4D electron diffraction datasets

Techniques for training artificial neural networks (ANNs) and convolutional neural networks (CNNs) using simulated dynamical electron diffraction patterns are described. The premise is based on the following facts. First, given a suitable crystal structure model and scattering potential, electron diffraction patterns can be simulated accurately using dynamical diffraction theory. Secondly, using simulated diffraction patterns as input, ANNs can be trained for the determination of crystal structural properties, such as crystal orientation and local strain. Further, by applying the trained ANNs to four-dimensional diffraction datasets (4D-DD) collected using the scanning electron nanodiffraction (SEND) or 4D scanning transmission electron microscopy (4D-STEM) techniques, the crystal structural properties can be mapped at high spatial resolution. Here, we demonstrate the ANN-enabled possibilities for the analysis of crystal orientation and strain at high precision and benchmark the performance of ANNs and CNNs by comparing with previous methods. A factor of thirty improvement in angular resolution at 0.009˚ (0.16 mrad) for orientation mapping, sensitivity at 0.04% or less for strain mapping, and improvements in computational performance are demonstrated.

Foveation Pipeline for 360° Video-Based Telemedicine.

Pan-tilt-zoom (PTZ) and omnidirectional cameras serve as a video-mediated communication interface for telemedicine. Most cases use either PTZ or omnidirectional cameras exclusively; even when used together, images from the two are shown separately on 2D displays. Conventional foveated imaging techniques may offer a solution for exploiting the benefits of both cameras, i.e., the high resolution of the PTZ camera and the wide field-of-view of the omnidirectional camera, but displaying the unified image on a 2D display would reduce the benefit of “omni-” directionality. In this paper, we introduce a foveated imaging pipeline designed to support virtual reality head-mounted displays (HMDs). The pipeline consists of two parallel processes: one for estimating parameters for the integration of the two images and another for rendering images in real time. A control mechanism for placing the foveal region (i.e., high-resolution area) in the scene and zooming is also proposed. Our evaluations showed that the proposed pipeline achieved, on average, 17 frames per second when rendering the foveated view on an HMD, and showed angular resolution improvement on the foveal region compared with the omnidirectional camera view. However, the improvement was less significant when the zoom level was 8× and more. We discuss possible improvement points and future research directions.

Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the Core of the Phoenix Cluster

Abstract We present new, deep observations of the Phoenix cluster from Chandra, the Hubble Space Telescope, and the Karl Jansky Very Large Array. These data provide an order-of-magnitude improvement in depth and/or angular resolution over previous observations at X-ray, optical, and radio wavelengths. We find that the one-dimensional temperature and entropy profiles are consistent with expectations for pure-cooling models. In particular, the entropy profile is well fit by a single power law at all radii, with no evidence for excess entropy in the core. In the inner ∼10 kpc, the cooling time is shorter than any other known cluster by an order of magnitude, while the ratio of the cooling time to freefall time (t cool/t ff) approaches unity, signaling that the intracluster medium is unable to resist multiphase condensation on kpc scales. The bulk of the cooling in the inner ∼20 kpc is confined to a low-entropy filament extending northward from the central galaxy, with t cool/t ff ∼ 1 over the length of the filament. In this filament, we find evidence for ∼1010 M ⊙ in cool (∼104 K) gas (as traced by the [O ii]λλ3726,3729 doublet), which is coincident with the low-entropy filament and absorbing soft X-rays. The bulk of this cool gas is draped around and behind a pair of X-ray cavities, presumably bubbles that have been inflated by radio jets. These data support a picture in which active galactic nucleus feedback is promoting the formation of a multiphase medium via uplift of low-entropy gas, either via ordered or chaotic (turbulent) motions.

Design of conical Wolter-I geometry with sectioned secondary mirrors for x-ray telescopes

Conical Wolter-I geometry is employed for many x-ray telescopes to lower their cost and fabrication difficulty at the expense of angular resolution. Owing to the conic error, the angular resolution of conical Wolter-I geometry is much worse than that of Wolter-I geometry, especially for the telescopes with large diameter. We optimized the conical Wolter-I geometry to significantly improve the angular resolution. We designed a conical Wolter-I geometry with sectioned secondary mirrors. Based on the normal conical Wolter-I geometry, we divided the secondary mirror into two equal sections along the optical axis. In this case, the collecting area was reduced by 5% because of the interval between the two sections. Meanwhile, the conic error was reduced by about 50%, indicating a great improvement in angular resolution. Regarding our improvement in the thermal slumping technique, it is feasible to fabricate sectioned mirrors, thus improving the angular resolution by 50% at the cost of a 5%-reduction in collecting area. In addition, a hybrid geometry, comprising the sectioned and nonsectioned geometries, is proposed as an alternative for x-ray telescopes with a large amount of nested shells, to obtain both a large collecting area and decent angular resolution.

The Radio Sky at Meter Wavelengths: m-mode Analysis Imaging with the OVRO-LWA

Abstract A host of new low-frequency radio telescopes seek to measure the 21 cm transition of neutral hydrogen from the early universe. These telescopes have the potential to directly probe star and galaxy formation at redshifts 20 ≳ z ≳ 7 but are limited by the dynamic range they can achieve against foreground sources of low-frequency radio emission. Consequently, there is a growing demand for modern, high-fidelity maps of the sky at frequencies below 200 MHz for use in foreground modeling and removal. We describe a new wide-field imaging technique for drift-scanning interferometers: Tikhonov-regularized m-mode analysis imaging. This technique constructs images of the entire sky in a single synthesis imaging step with exact treatment of wide-field effects. We describe how the CLEAN algorithm can be adapted to deconvolve maps generated by m-mode analysis imaging. We demonstrate Tikhonov-regularized m-mode analysis imaging using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) by generating eight new maps of the sky north of δ = −30° with 15′ angular resolution at frequencies evenly spaced between 36.528 and 73.152 MHz and ∼800 mJy beam−1 thermal noise. These maps are a 10-fold improvement in angular resolution over existing full-sky maps at comparable frequencies, which have angular resolutions ≥2°. Each map is constructed exclusively from interferometric observations and does not represent the globally averaged sky brightness. Future improvements will incorporate total power radiometry, improved thermal noise, and improved angular resolution due to the planned expansion of the OVRO-LWA to 2.6 km baselines. These maps serve as a first step on the path to the use of more sophisticated foreground filters in 21 cm cosmology incorporating the measured angular and frequency structure of all foreground contaminants.

Spatial and Angular Resolution Enhancement of Light Fields Using Convolutional Neural Networks.

Light field imaging extends the traditional photography by capturing both spatial and angular distribution of light, which enables new capabilities, including post-capture refocusing, post-capture aperture control, and depth estimation from a single shot. Micro-lens array (MLA) based light field cameras offer a cost-effective approach to capture light field. A major drawback of MLA based light field cameras is low spatial resolution, which is due to the fact that a single image sensor is shared to capture both spatial and angular information. In this paper, we present a learning based light field enhancement approach. Both spatial and angular resolution of captured light field is enhanced using convolutional neural networks. The proposed method is tested with real light field data captured with a Lytro light field camera, clearly demonstrating spatial and angular resolution improvement.

Study of Negative-Ion TPC Using μ-PIC for Directional Dark Matter Search

Negative-ion time projection chambers(TPCs) have been studied for low-rate and high-resolution applications such as dark matter search experiments. Recently, a full volume fiducialization in a self-triggering TPC was realized. This innovative technology demonstrated a significant reduction in the background with MWPC-TPCs. We studied negative-ion TPC using the μ-PIC+GEM system and obtained sufficient gas gain with CS2 gas and SF6 gas at low pressures. We expect an improvement in detector sensitivity and angular resolution with better electronics.

The Highly Collimated Radio Jet of HH 80–81: Structure and Nonthermal Emission

Abstract Radio emission from protostellar jets is usually dominated by free–free emission from thermal electrons. However, in some cases, it has been proposed that nonthermal emission could also be present. This additional contribution from nonthermal emission has been inferred through negative spectral indices at centimeter wavelengths in some regions of the radio jets. In the case of HH 80–81, one of the most powerful protostellar jets known, linearly polarized emission has also been detected, revealing that the nonthermal emission is of synchrotron nature from a population of relativistic particles in the jet. This result implies that an acceleration mechanism should be taking place in some parts of the jet. Here, we present new high sensitivity and high angular resolution radio observations at several wavelengths (in the 3–20 cm range) of the HH 80–81 radio jet. These new observations represent an improvement in sensitivity and angular resolution by a factor of ∼10 with respect to previous observations. This allows us to resolve the morphology of the radio jet and to study the different emission mechanisms involved through spectral index maps. We conclude that synchrotron emission in this jet arises from an extended component detected at low frequencies and from the termination points of the jet, where strong shocks against the ambient medium can produce efficient particle acceleration.

Application of the pattern matching approach for EBSD calibration and orientation mapping, utilising dynamical EBSP simulations

In this paper an alternative method of off-line Kikuchi pattern centre calibration and orientation mapping, utilising the cross-correlation between entire experimental patterns and dynamical simulated patterns is applied and evaluated. To demonstrate the improvement in angular resolution compared to Hough transform based methods, EBSD datasets of a silicon monocrystal were analysed using both, classical and the presented cross-correlation based method, which revealed significant enhancement of angular resolution for the refined method. The mean misorientation over the monocrystalline sample was found to be up to one order of magnitude lower compared to common methods, with an angular resolution of up to 0.06° indicating a substantial gain in orientation precision. The pattern centres were determined for a number of patterns on the map, using pattern matching refinement as well. Subsequently, a multiple linear regression model was computed to correlate pattern centre positions (XPC, YPC) and detector distances (ZSSD) to x- and y-coordinates on the map by means of plane equations. Employing this method, a reduction of orientation noise was achieved in highly deformed Silicon crystals with large intragranular orientation ranges. Furthermore, it was shown that the cross correlation coefficient CC can be used as a parameter indicating the pattern quality and hence can be utilised to create a pseudo greyscale image of the surface, showing grain boundaries and also depicting lattice distortions.

Direct transfer of classical non-separable states into hybrid entangled two photon states

Hybrid entangled states, having entanglement between different degrees-of-freedom (DoF) of a particle pair, are of great interest for quantum information science and communication protocols. Among different DoFs, the hybrid entangled states encoded with polarization and orbital angular momentum (OAM) allow the generation of qubit-qudit entangled states, macroscopic entanglement with very high quanta of OAM and improvement in angular resolution in remote sensing. Till date, such hybrid entangled states are generated by using a high-fidelity polarization entangled states and subsequent imprinting of chosen amount of OAM using suitable mode converters such as spatial light modulator in complicated experimental schemes. Given that the entangled sources have feeble number of photons, loss of photons during imprinting of OAM using diffractive optical elements limits the use of such hybrid states for practical applications. Here we report, on a simple generic experimental scheme to generate hybrid entangled states in polarization and OAM through direct transfer of classical non-separable states of the pump beam in parametric down conversion process. As a proof of principle, using local non-separable pump states of OAM mode l = 3, we have produced quantum hybrid entangled states with entanglement witness parameter of ~1.25 ± 0.03 violating by 8 standard deviation.

Energetic particle imaging: The evolution of techniques in imaging high‐energy neutral atom emissions

AbstractEnergetic neutral atom imaging instruments have been flown on a variety of space missions to satisfy a variety of science requirements. In this paper we discuss the most recent developments that lead to improvements in energy range, angular resolution, and background rejection for the high‐energy range, as represented in the past by the Cassini magnetosphere imaging instrument Ion and Neutral Camera, the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) mission High‐Energy Neutral Atom instrument, and to some degree the IMAGE mission Medium‐Energy Neutral Atom instrument. The new approaches discussed here rely on the use of ultrathin foils without UV filters and on very high speed coincidence logic to reduce accidentals from intense background sources. We present laboratory results demonstrating an electrostatic design that meets the coincidence timing requirements, position, and scattering performance consistent with angular resolution (full width at half maximum) of ~2° for hydrogen above 10 keV and a hydrogen energy threshold ≤1 keV.

Angle-invariant imaging using a total internal reflection virtual aperture.

Conventional lens stops, implemented with an absorptive physical aperture, have an angle-dependent projection that introduces field dependent loss and reduces diffraction-limited resolution. Retro-telephoto lenses obtain uniform response using aberration vignetting, but this results in low wide-angle resolution and significant lens volume. However, an angle-independent "virtual" aperture can be created by total internal reflection (TIR) from a thin low index layer inside the lens. We apply this to monocentric wide-angle imaging and find a simple relationship between the filtering layer index and radius and the resulting lens F/#. We provide two detailed designs of lenses with 12 mm focal length and a F/2.5 TIR stop, one using a low index adhesive within a solid fixed-focus lens, the other using an air cavity within an adjustable focus lens. We show the designs provide absolutely uniform resolution and light collection over an angle range of 84° and 106°, respectively, resulting in a dramatic improvement of both light collection and angular resolution per unit volume over conventional wide-angle lenses.