A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory

Compact elliptical galaxies are characterized by small sizes and high stellar densities. They are thought to form through tidal stripping of massive progenitors. However, only a handful of them were known, preventing us from understanding the role played by this mechanism in galaxy evolution. We present a population of 21 compact elliptical galaxies gathered with the Virtual Observatory. Follow-up spectroscopy and data mining, using high-resolution images and large databases, show that all the galaxies exhibit old metal-rich stellar populations different from those of dwarf elliptical galaxies of similar masses but similar to those of more massive early-type galaxies, supporting the tidal stripping scenario. Their internal properties are reproduced by numerical simulations, which result in compact dynamically hot remnants resembling the galaxies in our sample.Comment: 26 pages, 5 figures, 2 tables. Science in press, published in Science Express on 1/Oct/2009. Full resolution figures in the supplementary online material are available from the Science Magazine web-sit

Ab-initio calculation of all-optical time-resolved calorimetry of nanosized systems: Evidence of nanosecond-decoupling of electron and phonon temperatures

The thermal dynamics induced by ultrashort laser pulses in nanoscale systems, i.e. all-optical time-resolved nanocalorimetry is theoretically investigated from 300 to 1.5 K. We report ab-initio calculations describing the temperature dependence of the electron-phonon interactions for Cu nanodisks supported on Si. The electrons and phonons temperatures are found to decouple on the ns time scale at 10 K, which is two orders of magnitude in excess with respect to that found for standard low-temperature transport experiments. By accounting for the physics behind our results we suggest an alternative route for overhauling the present knowledge of the electron-phonon decoupling mechanism in nanoscale systems by replacing the mK temperature requirements of conventional experiments with experiments in the time-domain.Comment: 5 pages, 3 figures. Accepted on Physical Review B

Ward identities for disordered metals and superconductors

This article revisits Ward identities for disordered interacting normal metals and superconductors. It offers a simple derivation based on gauge invariance and recasts the identities in a new form that allows easy analysis of the quasiparticle charge conservation (as e.g. in a normal metal) or non-conservation (as e.g. in a d-wave superconductor).Comment: Discussion of decoherence at T=0 remove

The early days of the Sculptor dwarf spheroidal galaxy

We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in this metallicity range. We carry out a detailed analysis of the chemical abundances of alpha, iron peak, light and heavy elements, and draw comparisons with the Milky Way halo and the ultra faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follows the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the TypeII supernovae. In addition to its value to help refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggestive of a fair proportion of s-process; we discuss the implication for the nucleosynthetic origin of the neutron capture elements.Comment: Replacement after language editio

Thermo-mechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near infrared pump-probe diffraction experiments

The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of metallic nano-disks has been studied by near infrared pump-probe diffraction measurements, over a temporal range spanning from 100 fs to several nanoseconds. The experiments demonstrate that, in these systems, a two-dimensional surface acoustic wave (2DSAW), with a wavevector given by the reciprocal periodicity of the array, can be excited by ~120 fs Ti:sapphire laser pulses. In order to clarify the interaction between the nanodisks and the substrate, numerical calculations of the elastic eigenmodes and simulations of the thermodynamics of the system are developed through finite-element analysis. At this light, we unambiguously show that the observed 2DSAW velocity shift originates from the mechanical interaction between the 2DSAWs and the nano-disks, while the correlated 2DSAW damping is due to the energy radiation into the substrate.Comment: 13 pages, 10 figure

Stellar metallicity gradients of Local Group dwarf galaxies

Aims. We explore correlations between the strength of metallicity gradients in Local Group dwarf galaxies and their stellar mass, star formation history timescales, and environment. Methods. We performed a homogeneous analysis of literature spectroscopic data of red giant stars and determined radial metallicity profiles for 30 Local Group dwarf galaxies. This is the largest compilation of this type to date. Results. The dwarf galaxies in our sample show a variety of metallicity profiles, most of them decreasing with radius and some with rather steep profiles. The derived metallicity gradients as a function of the half-light radius, [Fe/H](R/Re), show no statistical differences when compared with the morphological type of the galaxies, nor with their distance from the Milky Way or M31. No correlations are found with either stellar mass or star formation timescales. In particular, we do not find the linear relation between [Fe/H](R/Re) and the galaxy median age t50, which has been reported in the literature for a set of simulated systems. On the other hand, the high angular momentum in some of our galaxies does not seem to affect the gradient strengths. The strongest gradients in our sample are observed in systems that are likely to have experienced a past merger event. When these merger candidates are excluded, the analysed dwarf galaxies show mild gradients (ã-0.1 dex Re-1) with little scatter between them, regardless of their stellar mass, dynamical state, and their star formation history. These results agree well with different sets of simulations presented in the literature that were analysed using the same method as for the observed dwarf galaxies. Conclusions. The interplay between the multitude of factors that could drive the formation of metallicity gradients likely combine in complex ways to produce in general comparable mild [Fe/H](R/Re) values, regardless of stellar mass and star formation history. The strongest driver of steep gradients seems to be previous dwarf-dwarf merger events in a system

MyD88 and TLR9 dependent immune responses mediate resistance to Leishmania guyanensis infections, irrespective of Leishmania RNA virus burden.

Infections with Leishmania parasites of the Leishmania Viannia subgenus give rise to both localized cutaneous (CL), and metastatic leishmaniasis. Metastasizing disease forms including disseminated (DCL) and mutocutaneous (MCL) leishmaniasis result from parasitic dissemination and lesion formation at sites distal to infection and have increased inflammatory responses. The presence of Leishmania RNA virus (LRV) in L. guyanensis parasites contributes to the exacerbation of disease and impacts inflammatory responses via activation of TLR3 by the viral dsRNA. In this study we investigated other innate immune response adaptor protein modulators and demonstrated that both MyD88 and TLR9 played a crucial role in the development of Th1-dependent healing responses against L. guyanensis parasites regardless of their LRV status. The absence of MyD88- or TLR9-dependent signaling pathways resulted in increased Th2 associated cytokines (IL-4 and IL-13), which was correlated with low transcript levels of IL-12p40. The reliance of IL-12 was further confirmed in IL12AB-/- mice, which were completely susceptible to infection. Protection to L. guyanensis infection driven by MyD88- and TLR9-dependent immune responses arises independently to those induced due to high LRV burden within the parasites

Numerical simulation of the heat transfer in amorphous silicon nitride membrane-based microcalorimeters

Numerical simulations of the two-dimensional ͑2D͒ heat flow in a membrane-based microcalorimeter have been performed. The steady-state isotherms and time-dependent heat flow have been calculated for a wide range of sample and membrane thermal conductivities and heat capacities. In the limit of high internal thermal conductivity and low membrane heat capacity, the sample heat capacity determined using the relaxation method with a single time constant is shown to be exact. The fractional contribution of the square 2D membrane border to the total heat capacity is calculated ͑ϳ24%͒. Analysis of the steady-state isotherms provide the 2D geometric factor ͑10.33͒ linking membrane thermal conductance to thermal conductivity, allowing extraction of the thermal conductivity of either the membrane itself or a sample deposited everywhere on the membrane. For smaller internal thermal conductivity and/or larger membrane heat capacity, systematic errors are introduced into the determination of heat capacity and thermal conductivity of a sample analyzed in the standard ͑single time constant͒ relaxation method, as has been previously shown for one dimension. These errors are due to both the changing contribution of the membrane border and to deviations from the ideal semiadiabatic approximation of the relaxation method. The errors are here calculated as a function of the ratios of thermal conductivity and heat capacity of sample and membrane. The differential method of measurement in which the sample heat capacity is taken as the difference between a relaxation method measurement with and without the sample is shown to give significantly smaller errors than the absolute errors of a single measurement. Under standard usage, high internal thermal conductivity is guaranteed by use of a thermal conduction layer such as Cu. The systematic error in this case is an underestimate of true sample heat capacity by less than 2%. The simulation was extended to thermal conditions where a single time constant relaxation approximation cannot be used, specifically, for a sample with low thermal conductivity. Because of the highly precise geometry of these micromachined devices, a comparison between measured and simulated steady-state and time-dependent temperatures is demonstrated to allow extraction of the heat capacity and thermal conductivity of this sample with less uncertainty due to elimination of the Cu heat capacity

Specific heat of MgB_2 after irradiation

We studied the effect of disorder on the superconducting properties of polycrystalline MgB_2 by specific-heat measurements. In the pristine state, these measurements give a bulk confirmation of the presence of two superconducting gaps with 2 Delta 0 / k_B T_c = 1.3 and 3.9 with nearly equal weights. The scattering introduced by irradiation suppresses T_c and tends to average the two gaps although less than predicted by theory. We also found that by a suitable irradiation process by fast neutrons, a substantial bulk increase of dH_{c2}/dT at T_c can be obtained without sacrificing more than a few degrees in T_c. The upper critical field of the sample after irradiation exceeds 28 T at T goes to 0 K.Comment: 11 pages text, 6 figures, accepted by Journal of Physics: Condensed Matte