Invariant expectations and vanishing of bounded cohomology for exact groups

We study exactness of groups and establish a characterization of exact groups in terms of the existence of a continuous linear operator, called an invariant expectation, whose properties make it a weak counterpart of an invariant mean on a group. We apply this operator to show that exactness of a finitely generated group $G$ implies the vanishing of the bounded cohomology of $G$ with coefficients in a new class of modules, which are defined using the Hopf algebra structure of $\ell_1(G)$.Comment: Final version, to appear in the Journal of Topology and Analysi

Calibration of the mixing-length theory for convective white dwarf envelopes

A calibration of the mixing-length parameter in the local mixing-length theory (MLT) is presented for the lower part of the convection zone in pure-hydrogen-atmosphere white dwarfs. The parameterization is performed from a comparison of three-dimensional (3D) CO5BOLD simulations with a grid of one-dimensional (1D) envelopes with a varying mixing-length parameter. In many instances, the 3D simulations are restricted to the upper part of the convection zone. The hydrodynamical calculations suggest, in those cases, that the entropy of the upflows does not change significantly from the bottom of the convection zone to regions immediately below the photosphere. We rely on this asymptotic entropy value, characteristic of the deep and adiabatically stratified layers, to calibrate 1D envelopes. The calibration encompasses the convective hydrogen-line (DA) white dwarfs in the effective temperature range 6000 ≤ T eff (K) ≤15, 000 and the surface gravity range 7.0 ≤ log g ≤ 9.0. It is established that the local MLT is unable to reproduce simultaneously the thermodynamical, flux, and dynamical properties of the 3D simulations. We therefore propose three different parameterizations for these quantities. The resulting calibration can be applied to structure and envelope calculations, in particular for pulsation, chemical diffusion, and convective mixing studies. On the other hand, convection has no effect on the white dwarf cooling rates until there is a convective coupling with the degenerate core below T eff ~ 5000 K. In this regime, the 1D structures are insensitive to the MLT parameterization and converge to the mean 3D results, hence they remain fully appropriate for age determinations

Pure-helium 3D model atmospheres of white dwarfs

We present the first grid of 3D simulations for the pure-helium atmospheres of DB white dwarfs. The simulations were computed with the CO5BOLD radiation-hydrodynamics code and cover effective temperatures and surface gravities between 12 000 K ≲ Teff ≲ 34 000 K and 7.5 ≤ log g (cgs units) ≤ 9.0, respectively. In this introductory work, synthetic spectra calculated from the 3D simulations are compared to appropriate 1D model spectra under a differential approach. This results in the derivation of 3D corrections for the spectroscopically derived atmospheric parameters of DB stars with respect to the 1D ML2/α = 1.25 mixing-length parametrization. No significant Teff corrections are found for the V777 Her instability strip region, and therefore no 3D revision is expected for the empirical blue and red edges of the strip. However, large log g corrections are found in the range 12 000 K < Teff < 23 000 K for all log g values covered by the 3D grid. These corrections indicate that 1D model atmospheres overpredict log g, reminiscent of the results found from 3D simulations of pure-hydrogen white dwarfs. The next step will be to compute 3D simulations with mixed helium and hydrogen atmospheres to comprehend the full implications for the stellar parameters of DB and DBA white dwarfs

The pathogenesis of Staphylococcus epidermidis biofilm-associated infections: the host and the pathogen perspective

Book of Abstracts of CEB Annual Meeting 2017info:eu-repo/semantics/publishedVersio

A first new look into the interaction of Staphylococcus epidermidis biofilm-released cells with the host immune system

The widespread application of indwelling medical devices in the clinical setting, together with the remarkable ability of the commensal Staphylococcus epidermidis to adhere to these surfaces and form biofilms, has given to this bacterium the recognition of being a leading causative agent of nosocomial infections. Biofilms lifecycle is currently divided into 4 main steps: initial adhesion, accumulation, maturation and, disassembly. Biofilm disassembly, the release of the cells within the biofilm into the involving environment, is the less understood of all steps despite its involvement in the development of several serious acute infections such as endocarditis, bacteremia and pneumonia. Hence, due to its important consequences in human health and disease, the study of the cells released from S. epidermidis biofilms is crucial to create effective therapeutic strategies against these serious infections. For that reason, in order to better characterize S. epidermidis biofilm-released cells, we assessed their cell properties by determining 1) the expression of key genes involved in initial adhesion, biofilm regulation and disassembly, 2) the total protein profile, 3) the susceptibility to routinely used antibiotics for the treatment of staphylococcal infection, and 4) the adhesion ability to coated and uncoated surfaces. Additionally, 5) the interaction of these cells with the host immune system was also assessed using an intravenous mouse infection model. Planktonic and biofilm cells were also used for comparison purposes. Our results revealed that S. epidermidis biofilm-released cells share some particular features with planktonic cells, such as expression of psmβ, but at the same time share some features similar to biofilms, such as high antibiotic tolerance. Moreover, although these shared features, the cells released from the S. epidermidis biofilms produced a unique protein that is not detected in the other assessed phenotypes. Additionally, S. epidermidis biofilm-released cells elicit a different in vivo response than their planktonic counterparts, by stimulating a lower production of inflammatory chemokines KC and MCP-1, and interleukine-6 as well. Altogether, these results indicate that this particular phenotype may present some advantageous features allowing a more effective host colonization and infection spreading. Thus, the targeting of the particular properties of the biofilm-released cells could present new opportunities to more effectively prevent the pathologic events associated with dissemination of cells from a biofilm to more distant sites.This work was funded by Fundação para a Ciência e a Tecnologia (The Foundation for Science and Technology: FCT) and COMPETE (Programa Operacional Factores de Competitividade) grants PTDC/BIA-MIC/113450/2009 and FCOMP-01-0124-FEDER-014309. AF and VC were funded by FCT fellowship SFRH/BD/62359/2009 and SFRH/BD/78235/2011, respectively

Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data

A sample of 4208 objects with magnitude 15 < g* < 22 and colors of main sequence A stars has been selected from 370 square degrees of Sloan Digital Sky Survey (SDSS) commissioning observations. The data is from two long, narrow stripes, each with an opening angle of greater than 60 deg, at Galactic latitudes 36 < abs(b) < 63 on the celestial equator. An examination of the sample's distribution shows that these stars trace considerable substructure in the halo. Large overdensities of A-colored stars in the North at (l,b,R) = (350, 50, 46 kpc) and in the South at (157, -58, 33 kpc) and extending over tens of degrees are present in the halo of the Milky Way. Using photometry to separate the stars by surface gravity, both structures are shown to contain a sequence of low surface gravity stars consistent with identification as a blue horizontal branch (BHB). Both structures also contain a population of high surface gravity stars two magnitudes fainter than the BHB stars, consistent with their identification as blue stragglers (BSs). From the numbers of detected BHB stars, lower limits to the implied mass of the structures are 6x10^6 M_sun and 2x10^6 M_sun. The fact that two such large clumps have been detected in a survey of only 1% of the sky indicates that such structures are not uncommon in the halo. Simple spheroidal parameters are fit to a complete sample of the remaining unclumped BHB stars and yield (at r < 40 kpc) a fit to a halo distribution with flattening (c/a = 0.65+/-0.2) and a density falloff exponent of alpha = -3.2+/-0.3.Comment: AASTeX v5_0, 26 pages, 1 table, 20 figures, ApJ accepte