Surface Brightness Fluctuations from archival ACS images: a stellar population and distance study

We derive Surface Brightness Fluctuations (SBF) and integrated magnitudes in the V- and I-bands using Advanced Camera for Surveys (ACS) archival data. The sample includes 14 galaxies covering a wide range of physical properties: morphology, total absolute magnitude, integrated color. We take advantage of the latter characteristic of the sample to check existing empirical calibrations of absolute SBF magnitudes both in the I- and V-passbands. Additionally, by comparing our SBF and color data with the Teramo-SPoT simple stellar population models, and other recent sets of population synthesis models, we discuss the feasibility of stellar population studies based on fluctuation magnitudes analysis. The main result of this study is that multiband optical SBF data and integrated colors can be used to significantly constrain the chemical composition of the dominant stellar system in the galaxy, but not the age in the case of systems older than 3 Gyr. SBF color gradients are also detected and analyzed. These SBF gradient data, together with other available data, point to the existence of mass dependent metallicity gradients in galaxies, with the more massive objects showing a non--negligible SBF versus color gradient. The comparison with models suggests that such gradients imply more metal rich stellar populations in the galaxies' inner regions with respect to the outer ones.Comment: ApJ Accepte

Geologic Map and Structural Development of the Noerthernmost Sur-Nacimiento Fault Zone, Central California Coast

The Sur-Nacimiento fault exposed along the central California coast (United States) juxtaposes the Salinian block arc against the Nacimiento block accretionary complex, cuts out the majority of the forearc basin and western arc, and requires a minimum of 150 km of orogen-normal crustal excision within the Mesozoic California convergent margin. Despite this significant strain, the kinematic evolution of the Sur-Nacimiento fault remains poorly understood, with diverse hypotheses suggesting sinistral, dextral, thrust, or normal displacement along the fault. This Late Cretaceous–Paleogene strain history is complicated by the location of the fault within a belt of subparallel faults that have accommodated significant Oligocene and younger dextral displacement between the Pacific and North American plates. In the vicinity of Big Creek along the Big Sur coast, steeply bounded bedrock enclaves of Salinian block affinity are enclosed within Nacimiento block mélange, and have been used to support multiple kinematic models for Late Cretaceous–Eocene Sur-Nacimiento slip. The work presented here targets coastal outcrops from McWay Falls to Gamboa Point, where our new mapping documents Salinian enclaves within Franciscan mélange along several steeply NE-dipping strands of the fault. Between these strands, bedding-parallel gouge zones as much as 2 m wide dip 50°–70°NE and display P-Y fabrics and asymmetric blocks indicating dextral displacement. Kinematic analysis of 401 individual outcrop-scale brittle faults and Y-plane surfaces record dominantly NW-SE extension and NE-SW shortening oblique to the strike of the Sur-Nacimiento fault. At McWay Falls, shear-sense indicators in mylonitic calcite marble found along the McWay fault yield top-South thrust displacement of Salinian basement over Salinian sedimentary rocks. South of the McWay fault, Salinian sedimentary rocks are overturned adjacent to and within strands of the Sur-Nacimiento fault, and display a subvertical E-W–striking disjunctive cleavage. These results are consistent with pre-Miocene N-S shortening or dextral transpression adjacent to the Sur-Nacimiento fault, followed by 8–11 km of Neogene dextral slip along the Gamboa fault that reactivated preexisting NW-SE–striking structures along this segment of the Sur-Nacimiento fault. This study highlights the multiple episodes of deformation along the Sur-Nacimiento fault that obscure the fault’s early slip evolution with respect to the juxtaposition of the Salinian and Nacimiento blocks, as well as the potential that dextral reactivation of the Sur-Nacimiento fault may partially accommodate differential displacement along the San Gregorio–Hosgri fault

Amino acid transport in thermophiles: characterization of an arginine-binding protein in Thermotoga maritima

Members of the periplasmic binding protein superfamily are involved in the selective passage of ligands through bacterial cell membranes. The hyperthermophilic eubacterium Thermotoga maritima was found to encode a highly stable and specific periplasmic arginine-binding protein (TM0593). Following signal sequence removal and overexpression in Escherichia coli, TM0593 was purified by thermoprecipitation and affinity chromatography. The ultra-stable protein with a monomeric molecular weight of 27.7 kDa was found to exist as both a homodimer and homotrimer at appreciable concentrations even under strongly denaturing conditions, with an estimated transition temperature of 116 °C. Its multimeric structure may provide further evidence of the importance of quaternary structure in the movement of nutrients across bacterial membranes. Purified and refolded TM0593 was further characterized by fluorescence spectroscopy, mass spectrometry, and circular dichroism to demonstrate the specificity of the protein for arginine and to elucidate structural changes associated with arginine binding. The protein binds arginine with a dissociation constant of 20 mM as determined by surface plasmon resonance measurements. Due to its high thermodynamic stability, TM0593 may serve as a scaffold for the creation of a robust fluorescent biosensor

The effects of Non-Gaussian initial conditions on the structure and substructure of Cold Dark Matter halos

We study the structure and substructure of halos obtained in N-body simulations for a Lambda Cold Dark Matter (LCDM) cosmology with non-Gaussian initial conditions (NGICs). The initial statistics are lognormal in the gravitational potential field with positive (LNp) and negative (LNn) skewness; the sign of the skewness is conserved by the density field, and the power spectrum is the same for all the simulations. Our aim is not to test a given non-Gaussian statistics, but to explore the generic effect of positive- and negative-skew statistics on halo properties. From our low-resolution simulations, we find that LNp (LNn) halos are systematically more (less) concentrated than their Gaussian counterparts. This result is confirmed by our Milky Way- and cluster-sized halos resimulated with high-resolution. In addition, they show inner density profiles that depend on the statistics: the innermost slopes of LNp (LNn) halos are steeper (shallower) than those obtained from the corresponding Gaussian halos. A subhalo population embedded in LNp halos is more susceptible to destruction than its counterpart inside Gaussian halos. On the other hand, subhalos in LNn halos tend to survive longer than subhalos in Gaussian halos. The spin parameter probability distribution of LNp (LNn) halos is skewed to smaller (larger) values with respect to the Gaussian case. Our results show how the statistics of the primordial density field can influence some halo properties, opening this the possibility to constrain, although indirectly, the primordial statistics at small scale.Comment: 15 pages, 8 figures. Slight corrections after referee report. To appear in ApJ, v598, November 20, 200

Detection of Radial Surface Brightness Fluctuation and Color Gradients in elliptical galaxies with ACS

We study surface brightness fluctuations (SBF) in a sample of 8 elliptical galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when available -- are presented. Galaxy surface brightness profiles are determined as well. We present the first SBF--broadband color calibration for the ACS/WFC F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies. We detect and study in detail the SBF variations within individual galaxies as a probe of possible changes in the underlying stellar populations. Inspecting both the SBF and color gradients in comparison to model predictions, we argue that SBF, and SBF-gradients, can in principle be used for unraveling the different evolutionary paths taken by galaxies, though a more comprehensive study of this issue would be required. We confirm that the radial variation of galaxy stellar population properties should be mainly connected to the presence of radial chemical abundance gradients, with the outer galaxy regions being more metal poor than the inner ones.Comment: 47 pages, 13 figures, ApJ, accepte

The relevance of BRAF G469A mutation in determining the response to therapy in metastatic melanoma

N.A

The Pafah1b Complex Interacts with the Reelin Receptor VLDLR

Reelin is an extracellular protein that directs the organization of cortical structures of the brain through the activation of two receptors, the very low-density lipoprotein receptor (VLDLR) and the apolipoprotein E receptor 2 (ApoER2), and the phosphorylation of Disabled-1 (Dab1). Lis1, the product of the Pafah1b1 gene, is a component of the brain platelet-activating factor acetylhydrolase 1b (Pafah1b) complex, and binds to phosphorylated Dab1 in response to Reelin. Here we investigated the involvement of the whole Pafah1b complex in Reelin signaling and cortical layer formation and found that catalytic subunits of the Pafah1b complex, Pafah1b2 and Pafah1b3, specifically bind to the NPxYL sequence of VLDLR, but not to ApoER2. Compound Pafah1b1(+/−);Apoer2(−/−) mutant mice exhibit a reeler-like phenotype in the forebrain consisting of the inversion of cortical layers and hippocampal disorganization, whereas double Pafah1b1(+/−);Vldlr(−/−) mutants do not. These results suggest that a cross-talk between the Pafah1b complex and Reelin occurs downstream of the VLDLR receptor

The CHilean Automatic Supernova sEarch (CHASE)

The CHASE project started in 2007 with the aim of providing young southern supernovae (SNe) to the Carnegie Supernova Project (CSP) and Millennium Center for Supernova Studies (MCSS) follow-up programs. So far CHASE has discovered 33 SNe with an average of more than 2.5 SNe per month in 2008. In addition to the search we are carrying out a follow-up program targeting bright SNe. Our fully automated data reduction allows us to follow the evolution on the light curve in real time, triggering further observations if something potentially interesting is detectedComment: 4 pages, 2 figures, conference proceedin