1,721,005 research outputs found
Use of stochastic sources for the lattice determination of light quark physics
No full textIn this paper we investigate the benefits of using Z(2) ⊗ Z(2) single timeslice stochastic sources for the calculation of light quark physics on the lattice. Meson 2-point correlators measured using sources stochastic in only spin and those stochastic in both spin and colour indices are compared to point source correlators on the unit gauge and on a 163 × 32 Domain Wall QCD ensemble. It is found that the use of stochastic sources gives a considerable improvement in statistics for the same computational cost. The neutral kaon mixing matrix element BK is also calculated on this ensemble with stochastic sources, but we conclude that the stochastic method offers no significant advantage over the traditional gauge-fixed wall source approach which already offers an exact volume average. We also discuss the application to semileptonic form factors in conjunction with partially twisted boundary conditions
A lattice computation of the first moment of the kaon's distribution amplitude
No full textWe present a lattice computation of the first moment of the kaon's leading-twist distribution amplitude. The results were computed using ensembles with 2+1 dynamical flavours with the domain wall fermion action and Iwasaki gauge action from the RBC and UKQCD joint dataset. The first moment is non-zero because of SU(3)-breaking effects, and we find that we are able to measure these effects very clearly. We observe the expected chiral behaviour and finally obtain , which agrees very well with results obtained using sum-rules, but with a significantly smaller error. We discuss the systematic uncertainties in detail and explain the prospects for their further reduction. In particular, we are implementing a programme of non-perturbative renormalization to improve the precision on the normalization of the lattice operators (currently performed perturbatively) and are repeating the calculation on a large lattice (243×64 as compared to the present 163×32 lattice).<br/
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
K(l3) form factor with N(f) = 2+1 dynamical domain wall fermions
No full textWe present the latest results from the UKQCD/RBC collaborations for the Kl3 form factor from simulations with 2+1 avours of dynamical domain wall quarks. Simulations are performed on lattices with two different volumes and four values of the light quark mass, allowing for an extrapolation to the chiral limit. The analysis includes a thorough investigation into the sources of systematic error in our ts. After interpolating to zero momentum transfer, we obtain f+(0) = 0:964(5) (or Df = -0.013(5)) which, when combined with the latest experimental results for Kl3 decays, leads to |Vus| = 0.2249(14)
The decay constants fD and fDs in the continuum limit of N=2+1 domain wall lattice QCD
No full textWe present results for the decay constants of the D and D s mesons computed in lattice QCD with N f = 2 + 1 dynamical flavours. The simulations are based on RBC/UKQCD’s domain wall ensembles with both physical and unphysical light-quark masses and lattice spacings in the range 0.11-0.07 fm. We employ the domain wall discretisation for all valence quarks.<br/
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
Hadronic form factors in lattice QCD at small and vanishing momentum transfer
No full textThe introduction of partially twisted boundary conditions allows weak and electromagnetic form factors to be evaluated at specified values of the hadronic momenta (and hence momentum transfers) in lattice simulations. We present and demonstrate this technique for the computation of the K ? ? semileptonic form factor at zero momentum transfer and for the electromagnetic form factor of the pion at arbitrarily small momentum transfers. These exploratory computations are carried out in full QCD with 3 flavours of sea quarks, but with only two values of mu = md which limits our ability to perform the chiral extrapolations. The results should therefore be viewed primarily as a demonstration of the feasibility of the method. For the K ? ? form factor we compare the new technique to the conventional approach and for the pion form factor we assess our results for very small momentum transfer with the help of chiral perturbation theory
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