1,721,104 research outputs found
Studies of open charm, charmonium and bottomonium production at LHCb
No full textStudies of quarkonium and charm production in the forward region provide important tests of NRQCD. During 2010 and 2011 the LHCb experiment has collected a dataset corresponding to an integrated luminosity of 1 fb in proton-proton collisions at = 7 TeV. We present studies of the production of open charm, charmonium, and bottomonium states and compare the results to recent theoretical predictions. We also present measurements of double charm production, performed for the first time at a hadron collider
Gravitational instability and fragmentation of self-gravitating accretion disks
No full textWe know from observations that supermassive black holes (SMBH) of masses up to 10^{10} \msol existed in quasars when the universe was only about years old. The rapid formation of SMBHs can be understood as the outcome of the collision of two large gas-rich galaxies followed by disk accretion. This model relies on a large enough turbulent viscosity in the disk. We show in a linear stability analysis of thin self-gravitating viscous disks that the gravitational instability can drive a turbulence generating the -viscosity. For simulating a self-gravitating accretion disk in polar coordinates the hydrodynamics code NIRVANA2.0 is adapted for our needs which includes cooling. The results are disk fragmentation, strong accretion at the inner radial boundary of the calculation domain and strong outflow at the outer boundary which both come about by interactions between clumps. The accretion time scale for a disk mass of 6\ex{8} \msol in a radial extent of 29 \pc to 126 \pc is about 1.2\ex{7} \yr, corresponding to a viscosity parameter . We can confirm the -viscosity interpretation by the turbulent velocity and length scale and by the scaling of the accretion time scale. All this supports the SMBH-formation model
Hyperon Production in Proton-Nucleus Collisions at 42 GeV Center of Mass Energy
No full textThe subject of this thesis is a measurement of hyperon production ratios which is of special interest as a reference on Quark Gluon Plasma search. The data used in this analysis have been taken with a minimum bias trigger at the fixed target experiment HERA-B, which uses the 920 GeV proton beam of the HERA storage ring at DESY. , and hyperons produced in collisions using carbon and tungsten wires as targets were reconstructed. Hyperon ratios are presented for the rapidity range (where they where measured), extrapolated to the whole phase space and to . The main results at are (error including systematic error) and (statistical uncertainty only) for the carbon target. These values are compared to proton--nucleus and nucleus--nucleus data above and below HERA-B energies and are comparable with both. In the rapidity range the ratio is significantly different for the two target materials, whereas extrapolated to the whole phase space it is not. A possible explanation in terms of multiple scatterings in the nucleus is given. The distribution of the particle--anti-particle asymmetry versus Feynman's scaling variable using the carbon target is found to be in good agreement with measurements from pion--nucleus reactions at 500 GeV -beam energy
Inclusive particle production
No full textThe LHCb detector has a unique pseudorapidity coverage and low transverse momentum theshold. These properties allow for measurements providing unique insight into particle production in the forward region at the LHC. The latest LHCb soft-QCD results, the measurements of charged particle multiplicity at 7 TeV and the measurement of the production ratios at 0.9 TeV and 7 TeV are presented. These results offer an important input to the understanding of baryon transport and of the hadronization process in a kinematical range where QCD models have large uncertainties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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