1,720,979 research outputs found
Perturbative and non-perturbative aspects of heavy-quark fragmentation
No full textWe describe a new approach to heavy-quark fragmentation which is based on a resummed perturbative calculation and parametrization of power corrections, concentrating on the z -> 1 limit, where the heavy meson carries a large fraction of the momentum of the initial quark. It is shown that the leading power corrections in this region are controlled by the scale m(1-z). Renormalon analysis is then used to extend the perturbative treatment of soft and collinear radiation to the non-perturbative regime. Theoretical predictions are confronted with data on B-meson production in e+e- annihilation
Heavy-Quark Fragmentation
No full textWe study perturbative and non-perturbative aspects of heavy-quark fragmentation into hadrons, emphasizing the large-x region, where x is the energy fraction of the detected hadron. We first prove that when the moment index N and the quark mass m get large simultaneously with the ratio (N Lambda/m) fixed, the fragmentation function depends on this ratio alone. This opens up the way to formulate the non-perturbative contribution to the fragmentation function at large N as a shape function of m(1-x) which is convoluted with the Sudakov-resummed perturbative result. We implement this resummation and the parametrization of the corresponding shape function using Dressed Gluon Exponentiation. The Sudakov exponent is calculated in a process independent way from a generalized splitting function which describes the emission probability of an off-shell gluon off a heavy quark. Non-perturbative corrections are parametrized based on the renormalon structure of the Sudakov exponent. They appear in moment space as an exponential factor, with a leading contribution scaling as (N Lambda/m) and corrections of order (N Lambda/m)^3 and higher. Finally, we analyze in detail the case of B-meson production in e+e- collisions, confronting the theoretical predictions with LEP experimental data by fitting them in moment space.We study perturbative and non-perturbative aspects of heavy-quark fragmentation into hadrons, emphasizing the large- x region, where x is the energy fraction of the detected hadron. We first prove that when the moment index N and the quark mass m get large simultaneously with the ratio NΛ / m fixed, the fragmentation function depends on this ratio alone. This opens up the way to formulate the non-perturbative contribution to the fragmentation function at large N as a shape function of m (1− x ) which is convoluted with the Sudakov-resummed perturbative result. We implement this resummation and the parametrization of the corresponding shape function using Dressed Gluon Exponentiation. The Sudakov exponent is calculated in a process independent way from a generalized splitting function which describes the emission probability of an off-shell gluon off a heavy quark. Non-perturbative corrections are parametrized based on the renormalon structure of the Sudakov exponent. They appear in moment space as an exponential factor, with a leading contribution scaling as NΛ / m and corrections of order ( NΛ / m ) 3 and higher. Finally, we analyze in detail the case of B -meson production in e + e − collisions, confronting the theoretical predictions with LEP experimental data by fitting them in moment space.We study perturbative and non-perturbative aspects of heavy-quark fragmentation into hadrons, emphasizing the large-x region, where x is the energy fraction of the detected hadron. We first prove that when the moment index N and the quark mass m get large simultaneously with the ratio (N Lambda/m) fixed, the fragmentation function depends on this ratio alone. This opens up the way to formulate the non-perturbative contribution to the fragmentation function at large N as a shape function of m(1-x) which is convoluted with the Sudakov-resummed perturbative result. We implement this resummation and the parametrization of the corresponding shape function using Dressed Gluon Exponentiation. The Sudakov exponent is calculated in a process independent way from a generalized splitting function which describes the emission probability of an off-shell gluon off a heavy quark. Non-perturbative corrections are parametrized based on the renormalon structure of the Sudakov exponent. They appear in moment space as an exponential factor, with a leading contribution scaling as (N Lambda/m) and corrections of order (N Lambda/m)^3 and higher. Finally, we analyze in detail the case of B-meson production in e+e- collisions, confronting the theoretical predictions with LEP experimental data by fitting them in moment space
Power corrections in deep inelastic structure functions at large Bjorken x
No full textWe study power corrections to the spin-averaged structure functions F2 and FL in the semi-inclusive region. The dramatic breakdown of the operator product expansion at large Bjorken x due to the formation of a narrow jet with invariant mass W (W2=Q2(1?x)/x) calls for an alternative approach. Our main conjecture is that the dominant contribution at each twist is the one which mixes under renormalization with the leading twist (ultraviolet dominance). At twist two the dominant perturbative corrections at large x due to soft and collinear radiation can be factorized into a jet function. From the ultraviolet dominance conjecture it follows that the twist two parton distribution as well as the jet function actually factorize to any order in the twist expansion. This factorization suggests that non-perturbative corrections 1/W2n exponentiate together with the leading twist. We verify explicitly, at the level of a single dressed gluon, the cancellation between ambiguities due to infrared renormalons in the twist-two coefficient functions and those due to the ultraviolet divergence of twist-four matrix elements. Independently of the renormalon analysis, we show that the dominant contribution to twist four at large x is associated with a twist-two like configuration: the final states are identical to those of twist two, whereas the initial states differ just by additional partons carrying small momentum fractions. This picture is consistent with the ultraviolet dominance conjecture
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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