24 research outputs found
Hubble Space Telescope survey of the Perseus Cluster -III: The effect of local environment on dwarf galaxies
We present the results of a Hubble Space Telescope (HST) study of dwarf
galaxies in the outer regions of the nearby rich Perseus Cluster, down to M_V =
-12, and compare these with the dwarf population in the cluster core from our
previous HST imaging. In this paper we examine how properties such as the
colour magnitude relation, structure and morphology are affected by environment
for the lowest mass galaxies. Dwarf galaxies are excellent tracers of the
effects of environment due to their low masses, allowing us to derive their
environmentally based evolution, which is more subtle in more massive galaxies.
We identify 11 dwarf elliptical (dE) and dwarf spheroidal (dSph) galaxies in
the outer regions of Perseus, all of which are previously unstudied. We measure
the (V-I)_0 colours of our newly discovered dEs, and find that these dwarfs lie
on the same red sequence as those in the cluster core. The morphologies of
these dwarfs are examined by quantifying their light distributions using CAS
parameters, and we find that dEs in the cluster outskirts are on average more
disturbed than those in the core, with =0.13\pm0.09 and =0.18\pm0.08,
compared to =0.02\pm0.04, =0.01\pm0.07 for those in the core. Based on
these results, we infer that these objects are ``transition dwarfs'', likely in
the process of transforming from late-type to early type galaxies as they
infall into the cluster, with their colours transforming before their
structures. When we compare the number counts for both the core and outer
regions of the cluster, we find that below M_V = -12, the counts in the outer
regions of the cluster exceed those in the core. This is evidence that in the
very dense region of the cluster, dwarfs are unable to survive unless they are
sufficiently massive to prevent their disruption by the cluster potential and
interactions with other galaxies.Comment: 14 pages, 11 figures. MNRAS accepte
The dynamical state of bars in cluster dwarf galaxies: The cases of NGC 4483 and NGC 4516
Dwarf barred galaxies are the perfect candidates for hosting slowly-rotating bars. They are common in dense environments and they have a relatively shallow potential well, making them prone to heating by interactions. When an interaction induces bar formation, the bar should rotate slowly. They reside in massive and centrally-concentrated dark matter halos, which slow down the bar rotation through dynamical friction. While predictions suggest that slow bars should be common, measurements of bar pattern speed, using the Tremaine-Weinberg method, show that bars are mostly fast in the local Universe. We present a photometric and kinematic characterisation of bars hosted by two dwarf galaxies in the Virgo Cluster, NGC 4483 and NGC 4516. We derive the bar length and strength using the Next Generation Virgo Survey imaging and the circular velocity, bar pattern speed, and rotation rate using spectroscopy from the Multi Unit Spectroscopic Explorer. Including the previously studied galaxy IC 3167, we compare the bar properties of the three dwarf galaxies with those of their massive counterparts from literature. Bars in the dwarf galaxies are shorter and weaker, and rotate slightly slower with respect to those in massive galaxies. This could be due to a different bar formation mechanism and/or to a large dark matter fraction in the centre of dwarf galaxies. We show that it is possible to push the application of the Tremaine-Weinberg method to the galaxy low mass regime
A Simulative and Experimental Approach for the Design and Optimization of Atmospheric Pressure Low Power RF Thermal Plasma Processes
Based on the comparison of simulative and experimental data, an approach is presented for the design and optimization of processes assisted by low power atmospheric pressure Radio Frequency (RF) thermal plasmas. High Speed Imaging (HSI), Schlieren Imaging (SI), and temperature measurement on the surface of the substrate are performed to characterize the effect of the interaction of the RF torch effluent with a substrate placed downstream of the torch outlet. The related processes are simulated in 2-D axisymmetric and 3-D domains for different operating conditions, for the plasma generation region and for the downstream region, respectively. The comparison of numerical and experimental results is used to in depth characterize and investigate the behavior of the effluent of the RF torch
Schlieren imaging: a powerful tool for atmospheric plasma diagnostic
Schlieren imaging has been widely used in science and technology to investigate phenomena occurring in transparent media. In particular, it has proven to be a powerful tool in fundamental studies and process optimization for atmospheric pressure plasma diagnostics, providing qualitative and (in some cases) also quantitative information on the fluid-dynamic characteristics of plasmas generated by many different types of sources. However, obtaining significant and reliable results by schlieren imaging can be challenging, especially when considering the variety of geometries and applications of atmospheric pressure plasma sources. Therefore, it is necessary to adopt solutions that can address the specific issues of different plasma-assisted processes. In this paper, an overview on the use of the schlieren imaging technique for atmospheric pressure plasma characterization is presented. In the first part, the physical principles behind this technique and the different setups that can be adopted to perform it are presented. In the second part, examples of schlieren imaging applied to different kinds of atmospheric pressure plasmas (non-equilibrium plasma jets, plasma actuators for flow control and thermal plasma sources) are presented, showing how it was used to characterize the fluid-dynamic behavior of plasma-assisted processes and reporting best practices in performing this diagnostic technique
Cannabinoids, inner ear, hearing and tinnitus: a neuroimmunological perspective
Cannabis has been used for centuries for recreational and therapeutic purposes. Whereas, the recreative uses are based on the psychotropic effect of some of its compounds, its therapeutic effects range over a wide spectrum of actions, most of which target the brain or the immune system. Several studies have found cannabinoid receptors in the auditory system, both at peripheral and central levels, thus raising the interest in cannabinoid signaling in hearing, and especially in tinnitus, which is affected also by anxiety, memory, and attention circuits where cannabinoid effects are well described. Available studies on animal models of tinnitus suggest that cannabinoids are not likely to be helpful in tinnitus treatment and could even be harmful. However, the pharmacology of cannabinoids is very complex, and most studies focused on neural CB1R-based responses. Cannabinoid effects on the immune system (where CB2Rs predominate) are increasingly recognized as essential in understanding nervous system pathological responses, and data on immune cannabinoid targets have emerged in the auditory system as well. In addition, nonclassical cannabinoid targets (such as TRP channels) appear to play an important role in the auditory system as well. This review will focus on neuroimmunological mechanisms for cannabinoid effects and their possible use as protective and therapeutic agents in the ear and auditory system, especially in tinnitus