Evolution of the ISM of Starburst galaxies: the SN heating efficiency

The interstellar medium heated by SN explosions may acquire an expansion velocity larger than the escape velocity and leave the galaxy through a supersonic wind. SN ejecta are transported out of the galaxies by such winds which thus affect the chemical evolution of the galaxies. The effectiveness of the processes mentioned above depends on the heating efficiency (HE) of the SNe, that is a matter of debate. We have constructed a simple semi-analytic model, considering the essential ingredients of a SB environment which is able to qualitatively trace the thermalisation history of the ISM in a SB region and determine the HE evolution. We find that, as long as the mass-loss rate of the clouds remains larger than the rate at which the SNRs interact one with each other, the SN heating efficiency remains very small, as radiative cooling of the gas dominates. We conclude that the HE value has a time-dependent trend that is sensitive to the initial conditions of the system.Comment: 17 pages, 18 figures, A&A accepte

Studying a dual-species BEC with tunable interactions

We report on the observation of controllable spatial separation in a dual-species Bose-Einstein condensate (BEC) with $^{85}$Rb and $^{87}$Rb. Interparticle interactions between the different components can change the miscibility of the two quantum fluids. In our experiments, we clearly observe the immiscible nature of the two simultaneously Bose-condensed species via their spatial separation. Furthermore the $^{85}$Rb Feshbach resonance near 155 G is used to change them between miscible and immiscible by tuning the $^{85}$Rb scattering length. Our apparatus is also able to create $^{85}$Rb condensates with up to $8\times10^4$ atoms which represents a significant improvement over previous work

Mapping the structural diversity of C60 carbon clusters and their infrared spectra

The current debate about the nature of the carbonaceous material carrying the infrared (IR) emission spectra of planetary and proto-planetary nebulae, including the broad plateaus, calls for further studies on the interplay between structure and spectroscopy of carbon-based compounds of astrophysical interest. The recent observation of C60 buckminsterfullerene in space suggests that carbon clusters of similar size may also be relevant. In the present work, broad statistical samples of C60 isomers were computationally determined without any bias using a reactive force field, their IR spectra being subsequently obtained following local optimization with the density-functional-based tight-binding theory. Structural analysis reveals four main structural families identified as cages, planar polycyclic aromatics, pretzels, and branched. Comparison with available astronomical spectra indicates that only the cage family could contribute to the plateau observed in the 6-9 micron region. The present framework shows great promise to explore and relate structural and spectroscopic features in more diverse and possibly hydrogenated carbonaceous compounds, in relation with astronomical observations

On the Influence of Magnetic Fields on the Structure of Protostellar Jets

We here present the first results of fully three-dimensional (3-D) MHD simulations of radiative cooling pulsed (time-variable) jets for a set of parameters which are suitable for protostellar outflows. Considering different initial magnetic field topologies in approximate $equipartition$ with the thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which permeating the jet and the ambient medium; and (iii) a purely toroidal field permeating only the jet, we find that the overall morphology of the pulsed jet is not very much affected by the presence of the different magnetic field geometries in comparison to a nonmagnetic calculation. Instead, the magnetic fields tend to affect essentially the detailed structure and emission properties behind the shocks at the head and at the pulse-induced internal knots, particularly for the helical and toroidal geometries. In these cases, we find, for example, that the $H_\alpha$ emissivity behind the internal knots can be about three to four times larger than that of the purely hydrodynamical jet. We also find that some features, like the nose cones that often develop at the jet head in 2-D calculations involving toroidal magnetic fields, are smoothed out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections (for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar

Role of Endoplasmic Reticulum Stress Response Signaling in T Cells: A Dissertation

T cells play a central role in cellular-mediated immunity and must become activated to participate as effector cells in the immune response. The activation process is highly intricate and involves stimulation of a number of downstream signaling pathways enabling T cells to proliferate and produce cytokines that are vital for proper effector function. This increase in protein production and protein folding activity adds to the normal physiological strain on cellular machinery. One cellular compartment that has generated a mechanism to mitigate the stress induced by increased protein production is the endoplasmic reticulum (ER). In general, an increase in cellular production of proteins that overwhelms a cell’s protein folding capability can alter ER homeostasis and lead to ER stress. To counteract this stress, an adaptive cellular mechanism known as the ER stress response (ERSR) is initiated. The ERSR allows a cell to cope with normal physiological stress within the ER caused by increased protein translation. In this dissertation, we show that in vitro and in vivoT cell activation involving T cell receptor (TCR) ligation in the presence of costimulation initiates the physiological ERSR. Interestingly, the ERSR was also activated in T cells exposed only to TCR ligation, a treatment known to induce the ‘non-responsive’ states of anergy and tolerance. We further identified a key component of the downstream TCR signaling pathway, protein kinase C (PKC), as an initiator of physiological ERSR signaling, thus revealing a previously unknown role for this serine/threonine protein kinase in T cells. Therefore, induction of the physiological ERSR through PKC signaling may be an important ‘preparatory’ mechanism initiated during the early activation phase of T cells. If ER stress is persistent and ER homeostasis is not reestablished, physiological ER stress becomes pathological and initiates cellular death pathways through ER stress-induced apoptotic signaling. We further present data demonstrating that absence of functional Gimap5, a putative GTPase implicated to play a role in TCR signaling and maintenance of overall T cell homeostasis, leads to pathological ER stress and apoptosis. Using the BioBreeding diabetes-prone (BBDP) rat, a model for type 1 diabetes (T1D), we link pathological ER stress and ER stress-induced apoptotic signaling to the observed T cell lymphopenic phenotype of the animal. By depleting the ER stress apoptotic factor CHOP with siRNA, we were able to protect Gimap5-/-BBDP rat T cells from ER stress-induced death. These findings indicate a direct relationship between Gimap5 and maintenance of ER homeostasis for T cell survival. Overall, our findings suggest that the ERSR is activated by physiological and pathological conditions that disrupt T cell homeostasis. TCR signaling that leads to PKC activation initiates a physiological ERSR, perhaps in preparation for a T cell response to antigen. In addition, we also describe an example of pathological ERSR induction in T cells. Namely, we report that the absence of functional Gimap5 protein in T cells causes CHOP-dependent ER stress-induced apoptosis, perhaps initiated by deregulation of TCR signaling. This indicates a dual role for TCR signaling and regulation in the initiation of both the physiological and pathological ERSR. Future research that provides insights into the molecular mechanisms that govern ERSR induction in TCR signaling and regulation may lead to development of therapeutic modalities for treatment of immune-mediated diseases such as T1D