87,680 research outputs found
Perturbative renormalization factors and O(a^{2}) corrections for lattice four-fermion operators with improved fermion/gluon actions
No full textIn this work we calculate the corrections to the amputated Green's functions of 4-fermion operators, in 1-loop Lattice Perturbation theory. One of the novel aspects of our calculations is that they are carried out to O(a^2) (a: lattice spacing). We employ the Wilson/clover action for massless fermions (also applicable for the twisted mass action in the chiral limit) and a family of Symanzik improved actions for gluons. Our calculations have been carried out in a general covariant gauge. Results have been obtained for several popular choices of values for the Symanzik coefficients. While our Green's function calculations regard any pointlike 4-fermion operators which do not mix with lower dimension ones, we pay particular attention to DF=2 operators, both Parity Conserving and Parity Violating (F: flavour). We compute the perturbative renormalization constants for a complete basis of 4-fermion operators and we study their mixing pattern. For some of the actions considered here, even O(a^0) results did not exist in the literature to date. The correction terms which we calculate are essential ingredients for minimizing the lattice artifacts which are present in non-perturbative evaluations of renormalization constants with the RI'-MOM method. Our perturbative results, for the matrix elements of DF=2 operators and for the corresponding renormalization matrices, depend on a large number of parameters: coupling constant, number of colors, lattice spacing, external momentum, clover parameter, Symanzik coefficients, gauge parameter. To make these results most easily accessible, we have included them in the distribution package of this paper, as an ASCII file named: 4-fermi.m; the file is best perused as Mathematica input. The main results of this work have been applied to improve non-perturbative estimates of the B_K-parameter in N_F=2 twisted mass lattice QCD
O(a^2) corrections to 1-loop matrix elements of 4-fermion operators with improved fermion/gluon actions
No full textWe calculate the corrections to the amputated Green's functions of 4-fermion operators, in 1-loop Lattice Perturbation theory. The novel aspect of our calculations is that they are carried out to second order in the lattice spacing, O(a^2). We employ the Wilson/clover action for massless fermions (also applicable for the twisted mass action in the chiral limit) and the Symanzik improved action for gluons. Our calculations have been carried out in a general covariant gauge. Results have been obtained for several popular choices of values for the Symanzik coefficients (Plaquette, Tree-level Symanzik, Iwasaki, TILW and DBW2 action). We pay particular attention to ΔF=2 operators, both Parity Conserving and Parity Violating (F stands for flavour: S, C, B). We study the mixing pattern of these operators, to O(a^2), using the appropriate projectors. Our results for the corresponding renormalization matrices are given as a function of a large number of parameters: coupling constant, clover parameter, number of colors, lattice spacing, external momentum and gauge parameter. The O(a^2) correction terms (along with our previous O(a^2) calculation of ZΨ) are essential ingredients for minimizing the lattice artifacts which are present in non-perturbative evaluations of renormalization constants with the RI'-MOM method. A longer write-up of this work, including non-perturbative results, is in preparation together with members of the ETM Collaboration
O(a^2) corrections to the one-loop propagator and bilinears of clover fermions with Symanzik improved gluons
No full textWe calculate corrections to the fermion propagator and to the Green's functions of all fermion bilinear operators of the form (Psi) over bar Gamma Psi, to one-loop in perturbation theory. We employ the Wilson/clover action for fermions and the Symanzik improved action for gluons. The novel aspect of our calculations is that they are carried out to second order in the lattice spacing, O (a(2)). Consequently, they have addressed a number of new issues, most notably the appearance of loop integrands with strong IR divergences (convergent only beyond 6 dimensions). Such integrands are not present in O (a(1)) improvement calculations; there, IR divergent terms are seen to have the same structure as in the O (a(0)) case, by virtue of parity under integration, and they can thus be handled by well-known techniques. We explain how to correctly extract the full O (a(2)) dependence; in fact, our method is generalizable to any order in a. The O (a(2)) corrections to the quark propagator and Green's functions computed in this paper are useful to improve the nonperturbative RI-MOM determination of renormalization constants for quark bilinear operators. Our results depend on a large number of parameters: coupling constant, number of colors, lattice spacing, external momentum, clover parameter, Symanzik coefficients, gauge parameter. To make these results most easily accessible to the reader, we have included them in the distribution package of this paper, as an ASCII file named: Oa2results. m; the file is best perused as Mathematica input
Variations on the Author
No full text“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
[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
Analyzing a turbulent pipe flow via the one-point structure tensors: Vorticity crawlers and streak shadows
No full textAbstractEfforts to identify and visualize near-wall structures typically focus on the region y+≳5, where large-scale structures with significant turbulent kinetic energy content reside, such as the high-speed and low-speed streaks associated with sweep and ejection events. While it is true that the level of the turbulent kinetic energy drops to zero as one approaches the wall, the organization of near-wall turbulence does not end at y+≈5. Large-scale structures with significant streamwise extent and spatial organization exist even in the immediate proximity of the wall y+<5. These coherent structures have received less attention so far, but it would be both useful and enlightening to bring them to focus in order, on one hand, to understand them, but also to analyze their interaction with the energetic structures that reside at somewhat higher distances from the wall.We have recently developed a rigorous mathematical and computational framework that can be used for the calculation of the turbulence structure tensors in arbitrary flow configurations. In this work, we use this new framework to compute, for the first time, the structure tensors in a fully-developed turbulent pipe flow. We perform Direct Numerical Simulation (DNS) at Reynolds number Reb=5300, based on the bulk velocity and the pipe diameter. We demonstrate the diagnostic properties of the structure tensors, by analyzing the DNS results with a focus on the near-wall structure of the turbulence. We develop a new eduction technique, based on the instantaneous values of the structure tensors, for the identification of inactive structures (i.e. large-scale structures without significant turbulent kinetic energy). This leads to the visualization of “vorticity crawlers”
and “streak shadows”, large-scale structures with low energy content in the extreme vicinity of the wall. Furthermore, comparison with traditional eduction techniques (such as instantaneous iso-surfaces of turbulent kinetic energy) shows that the structure-based eduction method seamlessly captures the large-scale energetic structures further away from the wall. We then show that the one-point structure tensors reflect the morphology of the inactive structures in the extreme vicinity of the wall and that of the energy-containing large-scale structures further away from the wall. The emerging complete picture of large-scale structures helps explain the near-wall profiles of all the one-point structure tensors and is likely to have an impact in the further development of Structure-Based Models (SBMs) of turbulence
On the Electronic and Optical Properties of Metal-Organic Frameworks: Case Study of MIL-125 and MIL-125-NH2
No full textThe photoactive MIL-125 and MIL-125-NH Metal-Organic Frameworks (MOFs), despite a very similar crystalline structure, exhibit different optically behaviour. Luminescence in MIL-125 decays in about 1 ns while for its amino counterpart the lifetime of the charge-carriers is at least one order of magnitude larger. The origin of this difference is the key element for understanding the photocatalytic behaviour of MIL-125-NH2 when associated with active nanoparticles, behaviour that is completely absent in MIL-125. By performing advancedab-initio electronic structure calculations, we find that charge-carriers interact differently in the two MOFs with subsequent effects on the luminescence lifetimes and their catalytic performances. To confirm the predictions of our model we synthesized a novel material in the MIL-125 family, MIL-125-NH2-[10%](OH)2, and confirm that our theory correctly predicts a faster decay compared to MIL-125-NH2.</div
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
John F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
Designing Interactions. On the Use of Digital Technologies in the Musealisation of Difficult Built Heritage
No full textThe paper aims at reflecting on the curatorial strategies and design solutions that are being applied in the musealisation projects of difficult heritage sites, with a particular focus on the actual and potential contribution that digital technologies could bring in this complex field. To critically evaluate and assess the opportunities and criticalities implied, the text draws on the comparison between two emblematic examples that sit at opposite extremes in the use of digital technologies in their museum and exhibition design: the former Horsens State Penitentiary (Denmark), today hosting the Fængselsmuseet, and the Museo di Storia della Psichiatria in Italy, at the former San Lazzaro Psychiatric Hospital in Reggio Emilia (Italy)
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