Thin accretion disc with a corona in a central magnetic field

We study the steady-state structure of an accretion disc with a corona surrounding a central, rotating, magnetized star. We assume that the magneto-rotational instability is the dominant mechanism of angular momentum transport inside the disc and is responsible for producing magnetic tubes above the disc. In our model, a fraction of the dissipated energy inside the disc is transported to the corona via these magnetic tubes. This energy exchange from the disc to the corona which depends on the disc physical properties is modified because of the magnetic interaction between the stellar magnetic field and the accretion disc. According to our fully analytical solutions for such a system, the existence of a corona not only increases the surface density but reduces the temperature of the accretion disc. Also, the presence of a corona enhances the ratio of gas pressure to the total pressure. Our solutions show that when the strength of the magnetic field of the central neutron star is large or the star is rotating fast enough, profiles of the physical variables of the disc significantly modify due to the existence of a corona.Comment: Accepted for publication in Astrophysics & Space Scienc

Atomic X-ray Spectroscopy of Accreting Black Holes

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian Journal of Physics, in pres

The uses of coherent structure (Dryden Lecture)

The concept of coherent structure in turbulent flow is a revolutionary idea which is being developed by evolutionary means. The main objective of this review is to list some solid achievements, showing what can be done by using the concept of coherent structure that cannot be done without it. The nature of structure is described in terms of some related concepts, including celerity, topology, and the phenomenon of coalescence and splitting of structure. The main emphasis is on the mixing layer, as the one flow whose structure is well enough understood so that technical applications are now being made in problems of mixing and chemistry. An attempt is made to identify some conceptual and experimental obstacles that stand in the way of progress in other technically important flows, particularly the turbulent boundary layer. A few comments are included about the role of structure in numerical simulations and in current work on manipulation and control of turbulent flow. Some recent developments are cited which suggest that the time is nearly right for corresponding advances to occur in turbulence modeling

A novel 65 kDa RNA-binding protein in squid presynaptic terminals

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Neuroscience 166 (2010): 73-83, doi:10.1016/j.neuroscience.2009.12.005.A polyclonal antibody (C4), raised against the head domain of chicken myosin Va, reacted strongly towards a 65 kDa polypeptide (p65) on western blots of extracts from squid optic lobes but did not recognize the heavy chain of squid myosin V. This peptide was not recognized by other myosin Va antibodies, nor by an antibody specific for squid myosin V. In an attempt to identify it, p65 was purified from optic lobes of Loligo plei by cationic exchange and reverse phase chromatography. Several peptide sequences were obtained by mass spectroscopy from p65 cut from SDS-PAGE gels. BLAST analysis and partial matching with ESTs from a Loligo pealei data bank indicated that p65 contains consensus signatures for the hnRNP A/B family of RNA-binding proteins. Centrifugation of post mitochondrial extracts from optic lobes on sucrose gradients after treatment with RNase gave biochemical evidence that p65 associates with cytoplasmic RNP complexes in an RNA-dependent manner. Immunohistochemistry and immunofluorescence studies using the C4 antibody showed partial co-labeling with an antibody against squid synaptotagmin in bands within the outer plexiform layer of the optic lobes and at the presynaptic zone of the stellate ganglion. Also, punctate labeling by the C4 antibody was observed within isolated optic lobe synaptosomes. The data indicate that p65 is a novel RNA-binding protein located to the presynaptic terminal within squid neurons and may have a role in synaptic localization of RNA and its translation or processing.REL, JCR and JEM received financial support from the Fundação de Amparo à Pesquisa do Estado de Sao Paulo (FAPESP), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the Fundação de Apoio ao Ensino, Pesquisa e Assistência do Hospital das Clínicas da FMRP-USP (FAEPA). JAD received financial support from the RI-INBRE Program Grant #P20RR016457 from the Nation Center for Research Resources, NIH, Bethesda, MD. DTPL, LC, SBFT, EJRV and MMAB were recipients of research fellowships from FAPESP and CNPq. REL and JEM received Productivityin- Research fellowships from CNPq

Cardiovascular risk factors in patients with spondyloarthritis from Northern European and Mediterranean countries: An ancillary study of the ASAS-COMOSPA project

Objectives: The objectives of this study were: (1) to compare the prevalence of cardiovascular disease and cardiovascular risk factors among different phenotypes of spondyloarthritis (SpA); (2) to assess the differences in cardiovascular disease and cardiovascular risk factors between two geographical areas, i.e. Northern Europe vs. Mediterranean region; (3) to identify potential predictive factors for high Framingham Risk Score regarding disease features in SpA and geographical area. Methods: Ancillary analysis of the international, multicentric, observational, cross-sectional ASAS-COMOSPA study. Cardiovascular disease and cardiovascular risk factors were compared depending on SpA phenotype and geographical regions. Potential factors associated with higher cardiovascular risk (i.e. Framingham Risk Score) were determined by a multiple logistic regression. Results: The most frequent cardiovascular risk factor and cardiovascular disease were smoking (31.2%) and ischemic heart disease (3.2%), respectively. Regarding SpA phenotype, axial SpA patients showed significantly lower prevalence (P < 0.05) of hypertension (19.2% vs. 33.8% vs. 26.6% for axial, peripheral and mixed phenotypes, respectively), type 2 diabetes mellitus (4.3% vs. 8.5% vs. 7.4%), dyslipidemia (13.9% vs. 28.4% vs. 15.2%) and ischemic heart disease (2.4% vs. 7.0% vs. 3.2%). Regarding geographical area, a higher frequency of hypertension (34.7% vs. 19.4%,), dyslipidemia (19.3% vs. 14.4%), obesity (29.3% vs. 20.7%) and ischemic heart disease (6.2% vs. 1.8%) was observed for Northern Europe vs. Mediterranean Region, respectively. Conclusions: Our results suggest that SpA phenotype and geographical area are associated with the prevalence of cardiovascular risk factors and the cardiovascular risk itself, observed in patients in the ASAS-COMOSPA cohort

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters