The effect of gravitational tides on dwarf spheroidal galaxies

The effect of the local environment on the evolution of dwarf spheroidal galaxies is poorly understood. We have undertaken a suite of simulations to investigate the tidal impact of the Milky Way on the chemodynamical evolution of dwarf spheroidals that resemble present day classical dwarfs using the SPH code GEAR. After simulating the models through a large parameter space of potential orbits the resulting properties are compared with observations from both a dynamical point of view, but also from the, often neglected, chemical point of view. In general, we find that tidal effects quench the star formation even inside gas-endowed dwarfs. Such quenching, may produce the radial distribution of dwarf spheroidals from the orbits seen within large cosmological simulations. We also find that the metallicity gradient within a dwarf is gradually erased through tidal interactions as stellar orbits move to higher radii. The model dwarfs also shift to higher $\langle$[Fe/H]$\rangle$/L ratios, but only when losing $>$$20\%$ of stellar mass.Comment: A&A accepte

The post-infall evolution of a satellite galaxy

As galaxy simulations increase in resolution more attention is being paid towards the evolution of dwarf galaxies and how the simulations compare to observations. Despite this increasing resolution we are however, far away from resolving the interactions of satellite dwarf galaxies and the hot coronae which surround host galaxies. We describe a new method which focuses only on the local region surrounding an infalling dwarf in an effort to understand how the hot baryonic halo will alter the chemodynamical evolution of dwarf galaxies. Using this method we examine how a dwarf, similar to Sextans dwarf spheroidal, evolves in the corona of a Milky Way like galaxy. We find that even at high perigalacticons the synergistic interaction between ram pressure and tidal forces transform a dwarf into a stream, suggesting that Sextans was much more massive in the past in order survive its perigalacticon passage. In addition the large confining pressure of the hot corona allows gas that was originally at the outskirts to begin forming stars, initially forming stars of low metallicity compared to the dwarf evolved in isolation. This increase in star formation eventually allows a dwarf galaxy to form more metal rich stars compared to one in isolation, but only if the dwarf retains gas for a sufficiently long period of time. In addition, dwarfs which formed substantial numbers of stars post-infall will have a slightly elevated [Mg/Fe] at high metallicity ([Fe/H] -1.5).Comment: 29 pages, 26 figures, A&A accepte

Experimental rig for measuring lubricant film thickness in rolling bearings

Electrical capacitance has been applied in the past for measuring the lubricant film thickness in rolling element bearings. The main difficulty arises from the fact that the measured capacitance is a combination of the capacitances of many rolling elements, which come in contact with both the inner and outer rings. Besides, the capacitance of the Hertzian contact itself and the surrounding area must also be separated. It results in a complex system which, in order to be solved for the film thickness at a particular location on the bearing many approximations have to be made. In the present study the authors use an experimental rig in which the capacitance of a single ball can be isolated. Moreover the capacitance of the ball – inner ring and ball – outer ring contacts can be measured separately

Chemical evolution of bulges at high redshift

We present a new class of hydrodynamical models for the formation of bulges (either massive elliptical galaxies or classical bulges in spirals) in which we implement detailed prescriptions for the chemical evolution of H, He, O and Fe. Our results hint toward an outside-in formation in the context of the supernovae-driven wind scenario. The build-up of the chemical properties of the stellar populations inhabiting the galactic core is very fast. Therefore we predict a non significant evolution of both the mass-metallicity and the mass-[alpha/Fe] relations after the first 0.5 - 1 Gyr. In this framework we explain how the observed slopes, either positive or negative, in the radial gradient of the mean stellar [alpha/Fe], and their apparent lack of any correlation with all the other observables, can arise as a consequence of the interplay between star formation and metal-enhanced internal gas flows.Comment: 4 pages, 6 figures, to appear on the IAU Symposium 245 Proceedings, Eds. M. Bureau, E. Athanassoula, B. Barbu

Interacting networks in social landscapes: a devo-evo approach to socialcultural dynamics

Can the study of epigenetics, physiology, and cognitive science contribute to the investigation and understanding of social-cultural systems while respecting the autonomy of social research? I present a developmental system theory (DST) approach, which takes the unit of analysis to be the system of self-sustaining interactions among multiple biological, psychological, and social resources. On this view, the cybernetic architecture of the networks that constitute the system channels development so that different trajectories lead to convergent end states, accounting for the system's developmental stability as well as shedding light on the conditions that lead to departures from typical outcomes. Based on previous work, which is extended here, I suggest that Waddington's epigenetic landscape metaphor, which was built to illustrate the relationship between genetic networks and embryological development, is a useful tool for thinking about the temporal dynamics of social systems, capturing some important features of social stability and change at different scales and levels of social organization. I discuss five social systems using the landscape metaphor and explore the implications of this DST approach for investigating the relations between sociocultural development and evolution

Firedec: a two-channel finite-resolution image deconvolution algorithm

We present a two-channel deconvolution method that decomposes images into a parametric point-source channel and a pixelized extended-source channel. Based on the central idea of the deconvolution algorithm proposed by Magain, Courbin & Sohy (1998), the method aims at improving the resolution of the data rather than at completely removing the point spread function (PSF). Improvements over the original method include a better regularization of the pixel channel of the image, based on wavelet filtering and multiscale analysis, and a better controlled separation of the point source vs. the extended source. In addition, the method is able to simultaneously deconvolve many individual frames of the same object taken with different instruments under different PSF conditions. For this purpose, we introduce a general geometric transformation between individual images. This transformation allows the combination of the images without having to interpolate them. We illustrate the capability of our algorithm using real and simulated images with complex diffraction-limited PSF.Comment: Accepted in A&A. An application of the technique to real data is available in Cantale et al. http://arxiv.org/abs/1601.05192v