Bright Regions Research Articles

An unbiased estimator of the full-sky CMB angular power spectrum at large scales using neural networks

ABSTRACT Accurate estimation of the cosmic microwave background (CMB) angular power spectrum is enticing due to the prospect for precision cosmology it presents. Galactic foreground emissions, however, contaminate the CMB signal and need to be subtracted reliably in order to lessen systematic errors on the CMB temperature estimates. Typically, bright foregrounds in a region lead to further uncertainty in temperature estimates in the area even after some foreground removal technique is performed and hence determining the underlying full-sky angular power spectrum poses a challenge. We explore the feasibility of utilizing artificial neural networks to predict the angular power spectrum of the full-sky CMB temperature maps from the observed angular power spectrum of the partial sky in which CMB temperatures in some bright foreground regions are masked. We present our analysis at large angular scales with two different masks. We produce unbiased predictions of the full-sky angular power spectrum and recover the underlying theoretical power spectrum using neural networks. Our predictions are also uncorrelated to a large extent. We further show that the multipole-space covariances of the predictions of full-sky spectra made by the artificial neural networks are much smaller than those of the estimates obtained using the pseudo-Cℓ method.

Star formation in the nearby dwarf galaxy DDO 53: interplay between gas accretion and stellar feedback

ABSTRACT We present the results of a multiwavelength study of the nearby dwarf galaxy DDO 53 – a relatively isolated member of the M 81 group. We analyse the atomic and ionized gas kinematics (based on the observations with Fabry–Perot interferometer in H α line and archival data in H i 21 cm line), distribution, excitation, and oxygen abundance of the ionized gas (based on the long-slit and integral-field spectroscopy and on imaging with narrow-band filters), and their relation with the young massive stars (based on archival HST data). We detect a faint 2-kpc sized supershell of ionized gas surrounding the galaxy. Most probably, this structure represents a large-scale gas outflow, however, it could be also created by the ionizing quanta leaking from star-forming regions to the marginally detected atomic hydrogen surrounding the galactic disc. We analyse the properties of the anomalous H i in the north part of the galaxy and find that its peculiar kinematics is also traced by ionized gas. We argue that this H i feature is related to the accreting gas cloud captured from the intergalactic medium or remaining after the merger event occurred >1 Gyr ago. The infalling gas produces shocks in the interstellar medium and could support the star formation activity in the brightest region in DDO 53.

Strain-Induced Alternating Photoluminescence Segmentation in Hexagonal Monolayer Tungsten Disulfide Grown by Physical Vapor Deposition.

Two-dimensional semiconductors exhibit strong light emission under optical or electrical pumping due to quantum confinement and large exciton binding energies. The regulation of the light emission shows great application potential in next-generation optoelectronic devices. Herein, by the physical vapor deposition strategy, we synthesize monolayer hexagonal-shaped WS2, and its photoluminescence intensity mapping show three-fold symmetric patterns with alternating bright and dark regions. Regardless of the length of the edges, all domains with S-terminated edges show lower photoluminescence intensity, while all regions with W-terminated edges exhibit higher photoluminescence intensity. The photoluminescence segmentation mechanism is studied in detail by employing Raman spectroscopy, atomic force microscopy, high-resolution transmission electron microscopy, and Kelvin probe force microscopy, and it is found to originate from different strain distributions in the S-terminated region and the W-terminated region. The optical band gap determined by the photoluminescence in the dark region is ∼2 meV lower than that in the bright region, implying that more strain is stored in the S-terminated region than in the W-terminated region. The photoluminescence segmentation vanishes in transferred hexagonal-shaped WS2 from the initial substrate to a fresh silicon substrate, further confirming the physical mechanism. Our results provide guidance for tuning the optical properties of two-dimensional semiconductors by controllable strain engineering.

Neuromorphic System for Edge Information Encoding: Emulating Retinal Center-Surround Antagonism by Li-Ion-Mediated Highly Interactive Devices.

Center-surround antagonism, a key mechanism in the retina, contributes to the encoding of edge contrast rather than of the overall information on a visual image. Here, a neuromorphic system consisting of multiple ionic devices is built, where each device has a lithium cobalt oxide channel arranged on a common lithium phosphorus oxynitride electrolyte. Because of the migration of Li ions between the channels through the electrolyte, the devices are highly interactive, as is seen with retinal neurons. On the basis of the excitation of single devices and device-to-device inhibition, the system successfully emulates the antagonistic center-surround receptive field and the Mach band effect in which perceived contrast is enhanced at the edges between dark and bright regions. Furthermore, a two-dimensional array system is simulated to implement edge detection for real images. This scheme enables computer vision tasks with simple and effective operations, owing to the intrinsic properties of the materials employed.

The Fornax3D project: Planetary nebulae catalogue and independent distance measurements to Fornax cluster galaxies

Extragalactic planetary nebulae (PNe) offer a way to determine the distance to their host galaxies thanks to the nearly universal shape of the planetary nebulae luminosity function (PNLF). Accurate PNe distance measurements rely on obtaining well-sampled PNLFs and the number of observed PNe scales with the encompassed stellar mass. This means either disposing of wide-field observations or focusing on the bright central regions of galaxies. In this work we take this second approach and conduct a census of the PNe population in the central regions of galaxies in the Fornax cluster, using VLT/MUSE data for the early-type galaxies observed over the course of the Fornax3D survey. Using such integral-field spectroscopic observations to carefully separate the nebular emission from the stellar continuum, we isolated [O III] 5007 Å sources of interest, filtered out unresolved impostor sources or kinematic outliers, and present a catalogue of 1350 unique PNe sources across 21 early-type galaxies, which includes their positions, [O III] 5007 Å line magnitudes, and line-of-sight velocities. Using the PNe catalogued within each galaxy, we present independently derived distance estimates based on the fit to the entire observed PNLF observed while carefully accounting for the PNe detection incompleteness. With these individual measurements, we arrive at an average distance to the Fornax cluster itself of 19.86 ± 0.32 Mpc (μPNLF = 31.49 ± 0.04 mag). Our PNLF distance measurements agree well with previous distances based on surface brightness fluctuations, finding no significant systematic offsets between the two methods as otherwise reported in previous studies.

Underwater image enhancement method based on color correction and three-interval histogram stretching

Since the attenuation and absorption of light in the water medium and the influence of the tiny suspended particles, underwater images are degraded and suffer from color cast and low contrast. An underwater image enhancement method based on color correction and three-interval histogram stretching is proposed to handle these issues. Firstly, a color correction method based on sub-interval linear transformation is designed to achieve color correction. Meanwhile, using the three adaptive sub-histograms equalization algorithm to enhance the contrast, and then the resulting images of the above-mentioned methods are combined by the multi-scale fusion. Final experiments demonstrate the proposed method can improve the image contrast, obtain the details of the bright and dark regions of the image, rich color, and finally output high-quality images.

Good and bad boundaries in ultrasound compounding: preserving anatomic boundaries while suppressing artifacts

PurposeUltrasound compounding is to combine sonographic information captured from different angles and produce a single image. It is important for multi-view reconstruction, but as of yet there is no consensus on best practices for compounding. Current popular methods inevitably suppress or altogether leave out bright or dark regions that are useful and potentially introduce new artifacts. In this work, we establish a new algorithm to compound the overlapping pixels from different viewpoints in ultrasound.MethodsInspired by image fusion algorithms and ultrasound confidence, we uniquely leverage Laplacian and Gaussian pyramids to preserve the maximum boundary contrast without overemphasizing noise, speckles, and other artifacts in the compounded image, while taking the direction of the ultrasound probe into account. Besides, we designed an algorithm that detects the useful boundaries in ultrasound images to further improve the boundary contrast.ResultsWe evaluate our algorithm by comparing it with previous algorithms both qualitatively and quantitatively, and we show that our approach not only preserves both light and dark details, but also somewhat suppresses noise and artifacts, rather than amplifying them. We also show that our algorithm can improve the performance of downstream tasks like segmentation.ConclusionOur proposed method that is based on confidence, contrast, and both Gaussian and Laplacian pyramids appears to be better at preserving contrast at anatomic boundaries while suppressing artifacts than any of the other approaches we tested. This algorithm may have future utility with downstream tasks such as 3D ultrasound volume reconstruction and segmentation.

A Plasmoid model for the Sgr A* Flares Observed With Gravity and CHANDRA

Abstract The Galactic Center black hole Sgr A* shows significant variability and flares in the submillimeter, infrared, and X-ray wavelengths. Owing to its exquisite resolution in the IR bands, the GRAVITY experiment for the first time spatially resolved the locations of three flares and showed that a bright region moves in ellipse-like trajectories close to, but offset from, the black hole over the course of each event. We present a model for plasmoids that form during reconnection events and orbit in the coronal region around a black hole to explain these observations. We utilize general-relativistic radiative-transfer calculations that include effects from finite light travel time, plasmoid motion, particle acceleration, and synchrotron cooling, and obtain a rich structure in the flare light curves. This model can naturally account for the observed motion of the bright regions observed by the GRAVITY experiment and the offset between the center of the centroid motion and the position of the black hole. It also explains why some flares may be double peaked while others have only a single peak and uncovers a correlation between the structure in the light curve and the location of the flare. Finally, we make predictions for future observations of flares from the inner accretion flow of Sgr A* that will provide a test of this model.

A High-resolution View of Fast Radio Burst Host Environments

Abstract We present Hubble Space Telescope ultraviolet and infrared observations of eight fast radio burst (FRB) host galaxies with subarcsecond localizations, including the hosts of three known repeating FRBs. We quantify their spatial distributions and locations with respect to their host galaxy light distributions, finding that they occur at moderate host-normalized offsets of 1.4r e ([0.6, 2.1]r e ; 68% interval) and on fainter regions of their hosts in terms of IR light but overall trace the radial distribution of IR light in their galaxies. The FRBs in our tested distribution do not clearly trace the distributions of any other transient population with known progenitors and are statistically distinct from the locations of LGRBs, H-poor SLSNe, SGRBs, and Ca-rich transients. We further find that most FRBs are not in regions of elevated local star formation rates and stellar mass surface densities in comparison to the mean global values of their hosts. We also place upper limits on the IR flux at the FRB positions of m IR ≳ 24.8–27.6 AB mag, constraining both satellite and background galaxies to luminosities well below the host luminosity of FRB 121102. We find that 5/8 FRB hosts exhibit clear spiral arm features in IR light, and that the positions of all well-localized FRBs located in such hosts are consistent with their spiral arms, although not on their brightest regions. Our results do not strongly support the primary progenitor channel of FRBs being connected with either the most massive (stripped-envelope) stars or events that require kicks and long delay times (neutron star mergers).

Visible and infrared image fusion using an efficient adaptive transition region extraction technique

In order to track a targeted environment, concealed weapon detection, navigation and military require various imaging modalities, for instance, visible image (VI) and infrared (IR) image. These modalities provide additional details. Complementary information from these images need to be fused into a single image for improved situational awareness. Hence, an ideal fused image should assimilate the essential bright information from the IR image and retain much of the original visual information from the VI. To achieve this, a region based image fusion technique using an efficient adaptive transition region extraction (ATRE) strategy is suggested in this paper. For the first time, the transition region extraction based approach is brought into the context of visible and infrared image fusion. This method is beneficial because it overcomes the problems of noise sensitivity, poor contrast and blurring effects associated with the conventional pixel-based methods. The proposed ATRE technique is used to efficiently extract the bright object regions from the IR image and retain much of the visual background regions from the VI. An adaptive parameter is introduced for accurate segmentation. A region mapping process is followed to get the fused image. Our technique is tested on standard fusion datasets. Image inspection and objective fusion indices are utilized to validate the results. They are compared with conventional and current pixel based and region based fusion techniques. The outcomes reveal that the suggested technique is comparable or better than state-of-the-art fusion techniques.

Toward Precision Cosmology with Improved PNLF Distances Using VLT-MUSEI. Methodology and Tests

Abstract The [O iii] λ5007 planetary nebula luminosity function (PNLF) is an established distance indicator that has been used for more than 30 yr to measure the distances of galaxies out to ∼15 Mpc. With the advent of the Multi-Unit Spectroscopic Explorer on the Very Large Telescope (MUSE) as an efficient wide-field integral-field spectrograph, the PNLF method is due for a renaissance, as the spatial and spectral information contained in the instrument’s data cubes provides many advantages over classical narrowband imaging. Here we use archival MUSE data to explore the potential of a novel differential emission-line filter (DELF) technique to produce spectrophotometry that is more accurate and more sensitive than other methods. We show that DELF analyses are superior to classical techniques in high surface brightness regions of galaxies, and we validate the method both through simulations and via the analysis of data from two early-type galaxies (NGC 1380 and NGC 474) and one late-type spiral (NGC 628). We demonstrate that with adaptive optics support or under excellent seeing conditions, the technique is capable of producing precision (≲0.05 mag) [O iii] photometry out to distances of 40 Mpc while providing discrimination between planetary nebulae and other emission-line objects such as H ii regions, supernova remnants, and background galaxies. These capabilities enable us to use MUSE to measure precise PNLF distances beyond the reach of Cepheids and the tip of the red giant branch method and become an additional tool for constraining the local value of the Hubble constant.

ACCESS and LRG-BEASTS: A Precise New Optical Transmission Spectrum of the Ultrahot Jupiter WASP-103b

Abstract We present a new ground-based optical transmission spectrum of the ultrahot Jupiter WASP-103b ( T eq = 2484 K). Our transmission spectrum is the result of combining five new transits from the ACCESS survey and two new transits from the LRG-BEASTS survey with a reanalysis of three archival Gemini/GMOS transits and one VLT/FORS2 transit. Our combined 11-transit transmission spectrum covers a wavelength range of 3900–9450 Å with a median uncertainty in the transit depth of 148 parts per million, which is less than one atmospheric scale height of the planet. In our retrieval analysis of WASP-103b’s combined optical and infrared transmission spectrum, we find strong evidence for unocculted bright regions (4.3σ) and weak evidence for H2O ( 1.9 σ ), HCN ( 1.7 σ ), and TiO ( 2.1 σ ), which could be responsible for WASP-103b’s observed temperature inversion. Our optical transmission spectrum shows significant structure that is in excellent agreement with the extensively studied ultrahot Jupiter WASP-121b, for which the presence of VO has been inferred. For WASP-103b, we find that VO can only provide a reasonable fit to the data if its abundance is implausibly high and we do not account for stellar activity. Our results highlight the precision that can be achieved by ground-based observations and the impacts that stellar activity from F-type stars can have on the interpretation of exoplanet transmission spectra.

AN AUTOMATIC EXTRACTION METHOD FOR ANTARCTIC SUBGLACIAL LAKE BASED ON RADIO ECHO SOUNDING DATA

Abstract. Detection of subglacial lakes and interpretation their hydrological connectivity is of great importance to understanding the mass balance of Antarctic ice sheet. Over the past five decades, a large number of Radio Echo Sounding (RES) data has been collected in Antarctica. However, the identification of subglacial lakes based on RES data mainly relies on visual interpretation due to the lack of quantitative indicators for subglacial lakes distinguishing. To solve this problem, an automatic subglacial lakes detection method based on the reflective characteristics of B-scan echogram is proposed in this paper. Firstly, the echo strength of the original radar echogram is corrected for the dielectric attenuation and geometric spreading in the ice. Secondly, the original radar echogram is binarized to preserve the bright subglacial lake region, and the thickness of bright pixels is measured along the direction of A-scan. Thirdly, the thickness, the variance of the thickness in the neighbourhood and the corrected echo strength are used to obtain the response value for the subglacial lake. Finally, a threshold for the response value is determined to detect subglacial lakes. It is found that the proposed method can determine the location of the subglacial lake in Antarctica's Gamburtsev Province (AGAP) region with high accuracy.

Dy3+ doped Y2MoO6 nanopowders for white light emission: Spectroscopic and transport properties for optoelectronic and energy harvesting applications

In this communication, we report the white light emitting Dy3+ ions doped Y2MoO6 (YMO) nanopowders (NPs) prepared via green combustion synthesis route by utilizing the Aloe vera (AV) gel as surfactant. For the convenient to the readers, we represent Y2MoO6:Dy3+ as YMOD. The cubic structure of the YMOD is confirmed by the results of powder X-ray diffraction (PXRD). The energy band gap values are studied by diffuse reflectance spectra (DRS) plots and the observed values are found to be in the range of 3.33–3.43 eV. The block-like structures of the fabricated nanopowders is analyzed by means of scanning electron microscope (SEM) images. Transmission electron microscope (TEM) images are castoff to evaluate the particle size of the prepared powders. The crystallinity and interplanar spacing are analyzed by means of selected area diffraction (SAED) and high-resolution TEM (HRTEM) images respectively. In order to study the luminescence behaviour of the fabricated powders, the photoluminescence spectra are recorded in the range of 400–675 nm under 386 nm excitation wavelength. There are three prominent peaks positioned at 480, 575 and 637 nm which are corresponding to the 4F9/2 → 6H15/2, 13/2 and 11/2 respectively. The direct current conductivity is studied in the temperature range from 30 to 400 °C. The DC conductivity of NPs increases with increase in temperature. The color emission of the fabricated powders is studied by means of color diagrams namely, CIE and CCT. It is noticed from the color diagrams that, the emission color lies in the bright white region (0.33, 0.33) which is a characteristic emission of the Dy3+ doped powders. The obtained CCT value (5426 K) indicates that the prepared powders can be effectively utilized for cool LED sources in the indoor lighting applications. The average color purity (CP) values are found to be 80%. The quantum efficiency of the prepared nanopowders is found to be ~86.82%. The above findings substantiate the ability of YMO: Dy3+ phosphor to be used in photovoltaic and display device applications.

Influence of linking units on the photo responsive studies of azobenzene liquid Crystals: Application in optical storage devices

In this paper, we report on the photoisomerization process of three series of photosensitive bent-core liquid crystals with a lateral chlorine atom in the central resorcinol core and various linkers. The effect of linkers, such as benzoate ester, biphenyl, cinnamate, Schiff base and stilbene on the photoisomerization and thermal back relaxation have been studied using UV–Vis spectroscopy. Resorcinol with benzoate ester showed the longest thermal back relaxation of 7 h, whereas, the bent-cores with the stilbene linker rendered the shortest relaxation time of 4 h. The compiled results suggest the influence of linkers, central resorcinol core and position of the azobenzene moiety on the photoisomerization. Additionally, optical storage device fabricated using cinnamate containing bent-core LC (A3), showed the visibility of bright and dark regions in a crossed polarizers upon illumination at λ = 365 nm, indicating the changes from the ordered to disordered state. The observed properties of constructed device demonstrate the potential application of reported azobenzene derivatives in optical storage devices.

Higher-voltage asymmetric-electrolyte metal-air batteries

Higher-voltage asymmetric-electrolyte metal-air batteries

Oil Spill Identification and Monitoring from Sentinel-1 Sar Satellite Earth Observations: a Machine Learning Approach

Identification of an oil spill is essential to evaluate the potential spread and float from the source to coastal terrains, and their continued monitoring is essential for managing the environmental protection actions to confine the pollution and avoid further damage. The SAR sensor is perceived as the most significant remote sensing apparatus for the oil slick examination. One of the main aspects of oil spreading over sea surface is that it dampens the capillary waves and so, the backscatter radio waves are suppressed. As a result, oil spills are represented as black spots, while the brighter regions are usually related with unspoiled polluted sea areas. Additionally, the wide coverage that the sensor can provide is highly significant including long-range fate, as well as contextual information, such as sensitive coastal areas or vessels, which can be enclosed in the acquired image. However, oceanic natural phenomena such as low wind speed regions, weed beds and algae blooms, wave shadows behind land, grease ice, etc. can also be depicted as dark spots. These dark regions are commonly categorized as “look-alikes and their discrimination is very challenging. Machine Learning techniques are the most appropriate choice to classify oil spills and look-alikes. In the present work, a comparison between decision trees models and NN is performed to identify and extract the appropriate set of features characterizing an oil spill allowing effective evolution monitoring and setting up proper emergency actions.

Advances in Bessel image sharpness analysis

This paper introduces advances in the use of Bessel functions (cylinder functions) in achieving optimal sharpness of shapes delineated by collections of holes (dark valley regions) and bright regions in different areas of a video frame in terms of 4D voxels (grayscale video frame picture elements with coordinates (x, y, g, t) at location x, y with intensity g, and elapsed time t). An image hole is an island of low voxel intensities surrounded by varying voxel intensity peaks. The basic approach is to identify dominant collections of lights (high voxel intensity peaks) and darks (low voxel intensity clusters) in video frames. A main finding in this paper is that surface objects (recorded in images) are sharper wherever there are preponderant contrasting differences between image lights and darks. These contrasting differences lead to the highly accurate detection of shape holes (dark valleys) that delineate surface shapes recorded in sequences of video frames. With the use of cylindrical Bessel functions introduced by F. W. Bessel in 1824, contrasting differences between peaks and valleys can be measured in terms of voxel intensities and voxel indices.

An improved algorithm using weighted guided coefficient and union self‐adaptive image enhancement for single image haze removal

The visibility of outdoor images is usually significantly degraded by haze. Existing dehazing algorithms, such as dark channel prior (DCP) and colour attenuation prior (CAP), have made great progress and are highly effective. However, they all suffer from the problems of dark distortion and detailed information loss. This paper proposes an improved algorithm for single-image haze removal based on dark channel prior with weighted guided coefficient and union self-adaptive image enhancement. First, a weighted guided coefficient method with sampling based on guided image filtering is proposed to refine the transmission map efficiently. Second, the k-means clustering method is adopted to calibrate the original image into bright and non-bright colour areas and form a transmission constraint matrix. The constraint matrix is then marked by connected-component labelling, and small bright regions are eliminated to form an atmospheric light constraint matrix, which can suppress the halo effect and optimize the atmospheric light. Finally, an adaptive linear contrast enhancement algorithm with a union score is proposed to optimize restored images. Experimental results demonstrate that the proposed algorithm can overcome the problems of image distortion and detailed information loss and is more efficient than conventional dehazing algorithms.

Speckle-dependent accuracy in phase-sensitive optical coherence tomography.

Phase-sensitive optical coherence tomography (OCT) is used to measure motion in a range of techniques, such as Doppler OCT and optical coherence elastography (OCE). In phase-sensitive OCT, motion is typically estimated using a model of the OCT signal derived from a single reflector. However, this approach is not representative of turbid samples, such as tissue, which exhibit speckle. In this study, for the first time, we demonstrate, through theory and experiment that speckle significantly lowers the accuracy of phase-sensitive OCT in a manner not accounted for by the OCT signal-to-noise ratio (SNR). We describe how the inaccuracy in speckle reduces phase difference sensitivity and introduce a new metric, speckle brightness, to quantify the amount of constructive interference at a given location in an OCT image. Experimental measurements show an almost three-fold degradation in sensitivity between regions of high and low speckle brightness at a constant OCT SNR. Finally, we apply these new results in compression OCE to demonstrate a ten-fold improvement in strain sensitivity, and a five-fold improvement in contrast-to-noise by incorporating independent speckle realizations. Our results show that speckle introduces a limit to the accuracy of phase-sensitive OCT and that speckle brightness should be considered to avoid erroneous interpretation of experimental data.