400 research outputs found
The visibility of the Galactic bulge in optical surveys. Application to the Gaia mission
The bulge is a region of the Galaxy which is of tremendous interest for
understanding Galaxy formation. However, measuring photometry and kinematics in
it raises several inherent issues, like high extinction in the visible and
severe crowding. Here we attempt to estimate the problem of the visibility of
the bulge at optical wavelengths, where large CCD mosaics allow to easily cover
wide regions from the ground, and where future astrometric missions are
planned. Assuming the Besancon Galaxy model and high resolution extinction
maps, we estimate the stellar density as a function of longitude, latitude and
apparent magnitude and we deduce the possibility of reaching and measuring
bulge stars. The method is applied to three Gaia instruments, the BBP and MBP
photometers, and the RVS spectrograph. We conclude that, while in the BBP most
of the bulge will be accessible, in the MBP there will be a small but
significant number of regions where bulge stars will be detected and accurately
measured in crowded fields. Assuming that the RVS spectra may be extracted in
moderately crowded fields, the bulge will be accessible in most regions apart
from the strongly absorbed inner plane regions, because of high extinction, and
in low extinction windows like the Baades's window where the crowding is too
severe.Comment: 11 pages, 9 figures, accepted for publication in A&A, latex using A&A
macro
Stellar density distribution in the NIR on the Galactic plane at longitudes 15-27 deg. Clues for the Galactic bar ?
12 pages, 15 figures, accepted by A&AGarzon et al. (1997), Lopez-Corredoira et al. (1999) and Hammersley et al. (2000)have identified in TMGS and DENIS data a large excess of stars at l=27 deg andb=0 deg which might correspond to an in-plane bar. We compared near infraredCAIN star counts and simulations from the Besancon Model of Galaxy on 15 fieldsbetween 15 deg and 45 deg in longitude and -2 deg and 2 deg in latitude.Comparisons confirm the existence of an overdensity at longitudes lower than 27deg which is inhomogeneous and decreases very steeply off the Galactic plane.The observed excess in the star distribution over the predicted density is evenhigher than 100%. Its distance from the sun is estimated to be lower than 6kpc. If this overdensity corresponds to the stellar population of the bar, weestimate its half-length to 3.9 +/ -0.4 kpc and its angle from the Sun-centerdirection to 45 +/- 9 degrees
A synthetic view on structure and evolution of the Milky Way
Since the Hipparcos mission and recent large scale surveys in the optical and
the near-infrared, new constraints have been obtained on the structure and
evolution history of the Milky Way. The population synthesis approach is a
useful tool to interpret such data sets and to test scenarios of evolution of
the Galaxy. We present here new constraints on evolution parameters obtained
from the Besancon model of population synthesis and analysis of optical and
near-infrared star counts. The Galactic potential is computed
self-consistently, in agreement with Hipparcos results and the observed
rotation curve. Constraints are posed on the outer bulge structure, the warped
and flared disc, the thick disc and the spheroid populations. The model is
tuned to produce reliable predictions in the visible and the near-infrared in
wide photometric bands from U to K. Finally, we describe applications such as
photometric and astrometric simulations and a new classification tool based on
a Bayesian probability estimator, which could be used in the framework of
Virtual Observatories. As examples, samples of simulated star counts at
different wavelengths and directions are also given.Comment: 20 pages, 12 figures, latex using A&A macros, version corrected from
the original version published in A&A 409, 523 (2003) with erratum. Model
accessible at http://www.obs-besancon.fr/modele/model2003.htm
Collision Dynamics and Solvation of Water Molecules in a Liquid Methanol Film
Environmental molecular beam experiments are used to examine water
interactions with liquid methanol films at temperatures from 170 K to 190 K. We
find that water molecules with 0.32 eV incident kinetic energy are efficiently
trapped by the liquid methanol. The scattering process is characterized by an
efficient loss of energy to surface modes with a minor component of the
incident beam that is inelastically scattered. Thermal desorption of water
molecules has a well characterized Arrhenius form with an activation energy of
0.47{\pm}0.11 eV and pre-exponential factor of 4.6 {\times} 10^(15{\pm}3)
s^(-1). We also observe a temperature dependent incorporation of incident water
into the methanol layer. The implication for fundamental studies and
environmental applications is that even an alcohol as simple as methanol can
exhibit complex and temperature dependent surfactant behavior.Comment: 8 pages, 5 figure
Oxygen abundances in the Galactic Bulge: evidence for fast chemical enrichment
AIMS: We spectroscopically characterize the Galactic Bulge to infer its star
formation timescale, compared to the other Galactic components, through the
chemical signature on its individual stars.
METHODS: We derived iron and oxygen abundances for 50 K giants in four fields
towards the Galactic bulge. High resolution (R=45,000) spectra for the target
stars were collected with FLAMES-UVES at the VLT.
RESULTS: Oxygen, as measured from the forbidden line at 6300 \AA, shows a
well-defined trend with [Fe/H], with [O/Fe] higher in bulge stars than in thick
disk ones, which were known to be more oxygen enhanced than thin disk stars.
CONCLUSIONS: These results support a scenario in which the bulge formed
before and more rapidly than the disk, and therefore the MW bulge can be
regarded as a prototypical old spheroid, with a formation history similar to
that of early-type (elliptical) galaxies.Comment: A&A Letters, in pres
Novel Graphene Electrode for Retinal Implants: An in vivo Biocompatibility Study
Evaluating biocompatibility is a core essential step to introducing a new material as a candidate for brain-machine interfaces. Foreign body reactions often result in glial scars that can impede the performance of the interface. Having a high conductivity and large electrochemical window, graphene is a candidate material for electrical stimulation with retinal prosthesis. In this study, non-functional devices consisting of chemical vapor deposition (CVD) graphene embedded onto polyimide/SU-8 substrates were fabricated for a biocompatibility study. The devices were implanted beneath the retina of blind P23H rats. Implants were monitored by optical coherence tomography (OCT) and eye fundus which indicated a high stability in vivo up to 3 months before histology studies were done. Microglial reconstruction through confocal imaging illustrates that the presence of graphene on polyimide reduced the number of microglial cells in the retina compared to polyimide alone, thereby indicating a high biocompatibility. This study highlights an interesting approach to assess material biocompatibility in a tissue model of central nervous system, the retina, which is easily accessed optically and surgically.This project has received funding from the European Unionâs Horizon 2020 research and innovation programme under grant agreement No. 785219 (GrapheneCore2) and No. 881603 (GrapheneCore3). DN has received funding from the doctoral school of Cerveau, cognition, comportement (3C) of Sorbonne UniversitĂ©. SP was also supported by the French state funds managed by the Agence Nationale de la Recherche within the Programme Investissements dâAvenir, LABEX LIFESENSES (ANR-10-LABX-65) and IHU FOReSIGHT (ANR-18-IAHU-0001). This work has made use of the Spanish ICTS Network MICRONANOFABS partially supported by MICINN and the ICTS âNANBIOSIS,â more specifically by the Micro-NanoTechnology Unit of the CIBER in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN) at the IMB-CNM
On the growth of nonuniform lattices in pinched negatively curved manifolds
We study the relation between the exponential growth rate of volume in a
pinched negatively curved manifold and the critical exponent of its lattices.
These objects have a long and interesting story and are closely related to the
geometry and the dynamical properties of the geodesic flow of the manifold
Microlensing as a probe of the Galactic structure; 20 years of microlensing optical depth studies
Microlensing is now a very popular observational astronomical technique. The
investigations accessible through this effect range from the dark matter
problem to the search for extra-solar planets. In this review, the techniques
to search for microlensing effects and to determine optical depths through the
monitoring of large samples of stars will be described. The consequences of the
published results on the knowledge of the Milky-Way structure and its dark
matter component will be discussed. The difficulties and limitations of the
ongoing programs and the perspectives of the microlensing optical depth
technique as a probe of the Galaxy structure will also be detailed.Comment: Accepted for publication in General Relativity and Gravitation.
General Relativity and Gravitation in press (2010) 0
MOB1 Mediated Phospho-recognition in the Core Mammalian Hippo Pathway.
The Hippo tumor suppressor pathway regulates organ size and tissue homoeostasis in response to diverse signaling inputs. The core of the pathway consists of a short kinase cascade: MST1 and MST2 phosphorylate and activate LATS1 and LATS2, which in turn phosphorylate and inactivate key transcriptional coactivators, YAP1 and TAZ (gene WWTR1). The MOB1 adapter protein regulates both phosphorylation reactions firstly by concurrently binding to the upstream MST and downstream LATS kinases to enable the trans phosphorylation reaction, and secondly by allosterically activating the catalytic function of LATS1 and LATS2 to directly stimulate phosphorylation of YAP and TAZ. Studies of yeast Mob1 and human MOB1 revealed that the ability to recognize phosphopeptide sequences in their interactors, Nud1 and MST2 respectively, was critical to their roles in regulating the Mitotic Exit Network in yeast and the Hippo pathway in metazoans. However, the underlying rules of phosphopeptide recognition by human MOB1, the implications of binding specificity for Hippo pathway signaling, and the generality of phosphopeptide binding function to other human MOB family members remained elusive.Employing proteomics, peptide arrays and biochemical analyses, we systematically examine the phosphopeptide binding specificity of MOB1 and find it to be highly complementary to the substrate phosphorylation specificity of MST1 and MST2. We demonstrate that autophosphorylation of MST1 and MST2 on several threonine residues provides multiple MOB1 binding sites with varying binding affinities which in turn contribute to a redundancy of MST1-MOB1 protein interactions in cells. The crystal structures of MOB1A in complex with two favored phosphopeptide sites in MST1 allow for a full description of the MOB1A phosphopeptide-binding consensus. Lastly, we show that the phosphopeptide binding properties of MOB1A are conserved in all but one of the seven MOB family members in humans, thus providing a starting point for uncovering their elusive cellular functions
Promiscuous targeting of bromodomains by bromosporine identifies BET proteins as master regulators of primary transcription response in leukemia
Bromodomains (BRDs) have emerged as compelling targets for cancer therapy. The development of selective and potent BET (bromo and extra-terminal) inhibitors and their significant activity in diverse tumor models have rapidly translated into clinical studies and have motivated drug development efforts targeting non-BET BRDs. However, the complex multidomain/subunit architecture of BRD protein complexes complicates predictions of the consequences of their pharmacological targeting. To address this issue, we developed a promiscuous BRD inhibitor [bromosporine (BSP)] that broadly targets BRDs (including BETs) with nanomolar affinity, creating a tool for the identification of cellular processes and diseases where BRDs have a regulatory function. As a proof of principle, we studied the effects of BSP on leukemic cell lines known to be sensitive to BET inhibition and found, as expected, strong antiproliferative activity. Comparison of the modulation of transcriptional profiles by BSP after a short exposure to the inhibitor resulted in a BET inhibitor signature but no significant additional changes in transcription that could account for inhibition of other BRDs. Thus, nonselective targeting of BRDs identified BETs, but not other BRDs, as master regulators of context-dependent primary transcription response.The Structural Genomics Consortium is a registered charity (no. 1097737) that receives funds from AbbVie, Bayer Pharma AG, Boehringer Ingelheim, Canada Foundation for Innovation, Eshelman Institute for Innovation, Genome Canada, Innovative Medicines Initiative (EU/EFPIA) (ULTRA-DD grant 115766), Janssen, Merck & Co., Novartis Pharma AG, Ontario Ministry of Economic Development and Innovation, Pfizer, SĂŁo Paulo Research Foundation (FAPESP), Takeda, and Wellcome Trust (092809/Z/10/Z). P.F., S.P., and C.-Y.W. were supported by a Wellcome Career Development Fellowship (095751/Z/11/Z). A.-C.G. is the Canada Research Chair in Functional Proteomics and the Lea Reichmann Chair in Cancer Proteomics and was supported by the Canadian Institutes of Health Research (foundation grant FDN143301). J.-P.L. was supported by a Cancer Research Society (Canada) Scholarship for the Next Generation of Scientists
- âŠ