Dwarf Galaxies in the MATLAS Survey: Hubble Space Telescope Observations of the Globular Cluster System in the Ultra-diffuse Galaxy MATLAS-2019

Ultra-diffuse galaxies (UDGs) are very-low-surface-brightness galaxies with large effective radii. Spectroscopic measurements of a few UDGs have revealed a low dark-matter content based on the internal motion of stars or globular clusters (GCs). This is in contrast to the large number of GCs found for these systems, from which it would be expected to correspond to a large dark-matter halo mass. Here we present HST+ACS observations for the UDG MATLAS-2019 in the NGC 5846 group. Using the F606W and F814W filters, we trace the GC population two magnitudes below the peak of the GC luminosity function (GCLF). Employing Bayesian considerations, we identify 26 ± 6 GCs associated with the dwarf, yielding a large specific frequency of S N = 58 ± 14. We use the turnover of the GCLF to derive a distance of 21 ± 2 Mpc, which is consistent with the NGC 5846 group of galaxies. Due to the superior image quality of the HST, we are able to resolve the GCs and measure their sizes, which are consistent with the sizes of GCs around Local Group galaxies. Using the linear relation between the total mass of galaxies and of GCs, we derive a halo mass of 0.9 ± 0.2 × 1011 M ⊙ (M ⊙/L ⊙ > 1000). The high abundance of GCs, together with the small uncertainties, make MATLAS-2019 one of the most extreme UDGs, which likely sets an upper limit of the number of GCs for UDGs.

Improved Error Reduction and Hybrid Input Output Algorithms for Phase Retrieval by including a Sparse Dictionary Learning-Based Inpainting Method

The phase retrieval (PR), reconstructing an object from its Fourier magnitudes, is equivalent to a nonlinear inverse problem. In this paper, we proposed a two-step algorithm that traditional ER/HIO iteration plays as the coarse feature reconstruction, whereas the KSVD-based inpainting technique deals with the fine feature set accordingly. Since the KSVD allows the content of oversampled dictionary with sparse representation to adaptively fit a given set of object examples, as long as the ER/HIO algorithms provide decent object estimation at early stage, the pixels violating the object constraint can be restored with superior image quality. The numerical analyses demonstrated the effectiveness of ER + KSVD and HIO + KSVD through multiple independent initial Fourier phases. With its versatility and simplicity, the proposed method can be generalized to be implemented with more PR state-of-the-arts.

Watermarking in dot-diffusion halftones using adaptive class-matrix and error diffusion

Digital halftoning deals with transforming a gray or color image into its binary version which is useful in printing applications. Dot diffusion is one of the prominent halftone methods which can yield superior image quality with parallel processing capabilities. In this paper, a rapid watermarking algorithm is proposed for dot-diffusion halftone images using adaptive class-matrix selection and modified error diffusion kernels. To process the image using an adaptive class matrix, the processing order of the class matrix is reversed and transposed, and for error diffusion the coefficients are replaced with different weights. For decoding, an effective strategy is proposed based on a correlation analysis and halftone statistics. The proposed strategy can successfully embed and decode the binary watermark from a single dot-diffused halftone image. From the experimental results, the proposed method is found to be effective in terms of good decoding accuracy, imperceptibility and robustness against various printed distortions.

Sparse interferometric Stokes imaging under the polarization constraint (Polarized SARA)

ABSTRACT We develop a novel algorithm for sparse imaging of Stokes parameters in radio interferometry under the polarization constraint. The latter is a physical non-linear relation between the Stokes parameters, imposing the polarization intensity as a lower bound on the total intensity. To solve the joint inverse Stokes imaging problem including this bound, we leverage epigraphical projection techniques in convex optimization and we design a primal–dual method offering a highly flexible and parallelizable structure. In addition, we propose to regularize each Stokes parameter map through an average sparsity prior in the context of a reweighted analysis approach (SARA). The resulting method is dubbed Polarized SARA. Using simulated observations of M87 with the Event Horizon Telescope, we demonstrate that imposing the polarization constraint leads to superior image quality. For the considered data sets, the results also indicate better performance of the average sparsity prior in comparison with the widely used Cotton–Schwab clean algorithm and other total variation based priors for polarimetric imaging. Our matlab code is available online on GitHub.

Randomized study of digital single-operator cholangioscope compared to fiberoptic single-operator cholangioscope in a novel cholangioscopy bench model

Background and study aims Cholangiopancreatoscopy is utilized for diagnosis and therapy of pancreaticobiliary disorders. a fully-disposable, digital, single-operator cholangioscope (DSOC) was developed with high image resolution and wide field-of-view. This bench study compared the new DSOC to the previous semi-disposable, fiber-optic cholangioscope (FSOC) prior to the clinical availability of the DSOC system. Methods Five experts performed one practice run followed by randomized runs comparing DSOC to FSOC in a biliary tract model consisting of three fixed left-intrahepatic tracts (LIHD), and variable common bile duct (CBD) and right-intrahepatic tracts (RIHD) with seven total lesions in multiple configurations. Timed runs aimed to visualize and target each lesion using miniature biopsy forceps. Definitions: visual success, visualizing targets; targeting success, touching target with forceps; complete run, touching seven targets within 20 minutes. Image quality, ease-of-use, and time to completion were recorded. Results Thirty-seven evaluable runs (20 DSOC, 17 FSOC) were completed. DSOC was superior to FSOC in Visual (99 % vs. 67 %, P < 0.001) and targeting success (6.6 vs. 4.5, P = 0.009), proportion of complete runs (13 /20 vs. 0 /17, P < 0.001) and time of run (10.1 min vs. 15.4 min, P < 0.001). For fixed LIHD, DSOC achieved higher targeting success compared to FSOC (2.6 vs. 1.1, P < 0.001) with no difference in RIHD and CBD targets (4.0 vs. 3.4, P = 0.39). Investigators reported superior image quality and ease-of-use with DSOC. Conclusions In this model, DSOC performed superiorly to FSOC in image quality, visualization, and maneuverability. The model could potentially be utilized for training endoscopists less experienced with cholangiopancreatoscopy.

Comparison of B-Mode with B-Flow Sonography for the Evaluation of Femoral Arteries in Infants

Purpose To evaluate femoral arteries (FAs) in infants in the context of catheter angiography with B-mode (BMS) and B-flow sonography (BFS) and to compare both methods for vessel delineation and reliability of vessel diameter measurements. Methods 21 consecutive infants who underwent ultrasound for the evaluation of FAs before or after cardiac catheterization were retrospectively included in this study. The diameter of the FAs and the maximum length of the vessel section displayed on a single ultrasound plane were recorded by two radiologists for BMS and BFS. The visual image quality was rated by one observer. Statistics included intraclass correlation coefficient, Bland-Altman analysis, Fisher´s exact test and t-test. Results The intraobserver as well as interobserver correlation was excellent for BMS (0.7922 and 0.6521) and BFS (0.8094 and 0.7637). The Bland-Altman analysis revealed limits of agreement for BMS between +/–0.73 mm (intraobserver) and +/–0.55 mm (interobserver) and for BFS between +/–0.83 mm (intraobserver) and +/–0.7 mm (interobserver). BFS allowed visualization of a longer stretch of the FA than BMS (length 3.54 +/–0.85 vs. 2.21 +/–0.9 cm, p < 0.0001). The image quality was significantly higher for BFS (p = 0.0043). Conclusion Since BFS shows excellent reproducibility for vessel measurements and superior image quality in infants, if available, BFS should be included in standard protocols when realistic measurements are required. Key Points Citation Format