Optical Color Gradients in Star-Forming Ring Galaxies

We compute radial color gradients produced by an outwardly propagating circular wave of star formation and compare our results with color gradients observed in the classical ring galaxy, the ``Cartwheel''. We invoke two independent models of star formation in the ring galaxies. The first one is the conventional density wave scenario, in which an intruder galaxy creates a radially propagating density wave accompanied by an enhanced star formation following the Schmidt law. The second scenario is a pure self-propagating star formation model, in which the intruder only sets off the first burst of stars at the point of impact. Both models give essentially the same results. Systematic reddening of B-V, V-K colors towards the center, such as that observed in the Cartwheel, can be obtained only if the abundance of heavy elements in the star-forming gas is a few times below solar. The B-V and V-K color gradients observed in the Cartwheel can be explained as a result of mixing of stellar populations born in a star-forming wave propagating through a low-metallicity gaseous disk, and a pre-existing stellar disk of the size of the gaseous disk with color properties typical to those observed in nearby disk galaxies.Comment: 16 pages, 12 figures; accepted for publication in the Astrophysical Journa

Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85

This work is part of a series of papers devoted to investigate the evolution of cluster galaxies during their infall. In the present article we imaged in NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z = 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2 deeper than 2MASS. We use these images to unveil asymmetries in the outskirts of a sample of bright galaxies and develop a new asymmetry index, alpha_An, which allows to quantify the degree of disruption by the relative area occupied by the tidal features on the plane of the sky. We measure the asymmetries for a subsample of 41 large area objects finding clear asymmetries in ten galaxies, most of them being in groups and pairs projected at different clustercentric distances, some of them located beyond R500 . Combining information on the Hi-gas content of blue galaxies and the distribution of sub-structures across Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful tool to confirm that tidal mechanisms are indeed present and are currently affecting a fraction of galaxies in Abell 85. However, when comparing our deep NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in this cluster, we discard the presence of tidal 1 interactions down to our detection limit. Our results suggest that ram-pressure stripping is at the origin of such spectacular disruptions. We conclude that across a complex cluster like Abell 85, environment mechanisms, both gravitational and hydrodynamical, are playing an active role in driving galaxy evolution.Comment: 30 pages, 13 figures, Accepted for Publication in A

Surface Brightness Gradients Produced by the Ring Waves of Star Formation

We compute surface brightness profiles of galactic disks for outwardly propagating waves of star formation with a view to investigate the stellar populations in ring galaxies. We consider two mechanisms which can create outwardly propagating star forming rings in a purely gaseous disk --- a self-induced wave and a density wave. We show that the surface brightness profiles produced by both scenarios of ring formation are similar and are strongly sensitive to the velocity of the wave. The results of our computations are compared with the observational quantities sensitive to the young and old stellar populations in the ring galaxies A0035-335 (the Cartwheel galaxy) and VIIZw466. The best fit to the observed radial H_alpha surface brightness distribution in the Cartwheel galaxy is obtained for a wave velocity of about 90 km/s. The red continuum brightness of the ring can be fully explained by the evolving stars present in the trailing part of the wave. However the red continuum brightness in regions internal to the ring indicates that the wave of star formation propagates in a pre-existing stellar disk in the Cartwheel. The H_alpha and K-band surface brightness profiles in VIIZw466 match the values expected from stellar populations produced by a wave of star formation propagating in a purely gaseous disk very well. We conclude that VIIZw466 is probably experiencing the first event of star formation in the disk.Comment: Uses aas2pp4.sty and epsfig.sty, 15 pages To appear in Astrophysical Journal, March 10, 199

Star formation history of the post-collisional Cartwheel galaxy using Astrosat/UVIT FUV images

We present the results obtained by analysing new Astrosat/UVIT far ultraviolet (FUV) image of the collisional-ring galaxy Cartwheel. The FUV emission is principally associated with the star-forming outer ring, with no UV detection from the nucleus and inner ring. A few sources are detected in the region between the inner and the outer rings, all of which lie along the spokes. The FUV fluxes from the detected sources are combined with aperture-matched multi-band photometric data from archival images to explore the post-collision star formation history of the Cartwheel. The data were corrected for extinction using Av derived from the Balmer decrement ratios and commonly used extinction curves. We find that the ring regions contain stellar populations of wide range of ages, with the bulk of the FUV emission coming from non-ionizing stars, formed over the last 20 to 150 Myr, that are ~25 times more massive than the ionizing populations. On the other hand, regions belonging to the spokes have negligible current star formation, with the age of the dominant older population systematically increasing as its distance from the outer ring increases. The presence of populations of a wide range of ages in the ring suggests that the stars formed in the wave in the past were dragged along it to the current position of the ring. We derive an average steady star formation rate, SFR=5 Msun/yr, over the past 150 Myr, with an increase to ~18 Msun/yr in the recent 10 Myr.Comment: 16 pages, to appear in MNRA

Multi-Scale Convolutional Neural Network for Accurate Corneal Segmentation in Early Detection of Fungal Keratitis.

Microbial keratitis is an infection of the cornea of the eye that is commonly caused by prolonged contact lens wear, corneal trauma, pre-existing systemic disorders and other ocular surface disorders. It can result in severe visual impairment if improperly managed. According to the latest World Vision Report, at least 4.2 million people worldwide suffer from corneal opacities caused by infectious agents such as fungi, bacteria, protozoa and viruses. In patients with fungal keratitis (FK), often overt symptoms are not evident, until an advanced stage. Furthermore, it has been reported that clear discrimination between bacterial keratitis and FK is a challenging process even for trained corneal experts and is often misdiagnosed in more than 30% of the cases. However, if diagnosed early, vision impairment can be prevented through early cost-effective interventions. In this work, we propose a multi-scale convolutional neural network (MS-CNN) for accurate segmentation of the corneal region to enable early FK diagnosis. The proposed approach consists of a deep neural pipeline for corneal region segmentation followed by a ResNeXt model to differentiate between FK and non-FK classes. The model trained on the segmented images in the region of interest, achieved a diagnostic accuracy of 88.96%. The features learnt by the model emphasize that it can correctly identify dominant corneal lesions for detecting FK

Determination of the action type of hydrate formation inhibitors by their infrared spectra

In this paper, differences of infrared spectra of hydrate formation inhibitors of thermodynamic and kinetic action types were investigated. The method was proposed for determining the action type of a hydrate formation inhibitor by its infrared spectrum. The relevance of the proposed method is due to its expressiveness in comparison with the testing of inhibitors in laboratory tests. It is proposed to use the method of Fourier transform infrared spectrometry. The method allows us to obtain data on the molecular and intermolecular interactions of the substance under study. The spectra obtained in the mode of attenuated total reflection were analyzed by the principal component analysis and the regression method of projection on latent structures, which are related to chemometric methods of analysis and make it possible to identify the key features of the inhibitor compositions that affect the mechanism of their action. The separation of the sample of infrared spectra of the studied inhibitors into two subgroups, which represent two different types of inhibitor action, was obtained. The principal component analysis makes it possible to identify the key features of the compositions of reagents that affect the mechanism of their action. For kinetic inhibitors, a characteristic ratio of the amplitudes of vibrations of the –OH and N–H functional groups in the internal standard of the spectrum was revealed. It is shown that the decisive factor in the division of inhibitors into groups is the difference between the resonant vibration frequencies corresponding to the valence vibrations of C–O, C–N bonds and the resonant vibration frequencies of organofluorine compounds. At the same time, the similarity in the amplitude of the indicated spectral regions was noted. For the group of thermodynamic inhibitors, the most influential bands in the IR spectrum were the bands of symmetric and asymmetric stretching vibrations of the C–H bonds in the CH2 and CH3 groups. There was a significant increase in the amplitude in the spectral range of 2950–2750 cm–1 compared with the signal amplitude in the regions of 3300–3400 cm–1 and 1200–1100 cm–1, also found in the spectra of this group of inhibitors. The method of projection on latent structures was used to develop a regression model to determine the mechanism of action of the studied inhibitors. The proposed method allows for express determination of the action type of hydrate formation inhibitors. Results could be used in oilfield chemistry to determine the action type of hydrate formation inhibitors used to prevent the formation of gas hydrates during the production, preparation or transportation of hydrocarbons

Sorption Properties of Clay and Pectin-Containing Hydrogels

As is known, polymeric polyelectrolyte hydrogels are superabsorbents that are capable of absorbing moisture in amounts many times greater than their own mass. Numerous studies have shown that besides water absorption and retention, they can also be effectively used as sorbents to purify water from heavy metals. In many works, attempts are made to improve the sorption properties of polyelectrolyte hydrogels by creating polymer composites based on them. Organic/inorganic composite materials frequently exhibited desired hybrid performance superior to their individual components and cost-efficient characteristics. The composites derived from natural polysaccharides and inorganic clay minerals are of special interest by virtue of their unique commercial and environmental advantages, which means that the design and development of environmentally friendly superabsorbents, introducing natural ingredients, have long been necessary. In this paper, we consider polymer hydrogels based on a copolymer of acrylic acid and acrylamide filled with pectin and bentonite. The aim of this study is to investigate the influence of chemical conditions on hydrogels and their composites, kinetic, and absorption behavior toward metal ions in the presence of the chelating agent. In this chapter, an investigation of the kinetic patterns of swelling, deswelling, and sorption of the hydrogels and their composites will be presented