493 research outputs found

    Exact quasinormal modes for a special class of black holes

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    Analytic exact expressions for the quasinormal modes of scalar and electromagnetic perturbations around a special class of black holes are found in d\ge3 dimensions. It is shown that, the size of the black hole provides a bound for the angular momentum of the perturbation. Quasinormal modes appear when this bound is fulfilled, otherwise the excitations become purely damped.Comment: 8 pages, no figures. Slightly updated version of the plenary talk given at the General Relativity Conference: "50 Years of FaMAF and Workshop on Global Problems in Relativity", hosted during November 2006 at FaMAF, Universidad Nacional de Cordoba, Cordoba, Argentina

    Colour analysis of degraded parchment

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    Multispectral imaging was employed to collect data on the degradation of an 18th century parchment by a series of physical and chemical treatments. Each sample was photographed before and after treatment by a monochrome digital camera with 21 narrow-band filters. A template-matching technique was used to detect the circular holes in each sample and a four-point projective transform to register the 21 images. Colour accuracy was verified by comparison of reconstructed spectra with measurements by spectrophotometer

    The D^4 R^4 term in type IIB string theory on T^2 and U-duality

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    We propose a manifestly U-duality invariant modular form for the D^4 R^4 interaction in type IIB string theory compactified on T^2. It receives perturbative contributions upto two loops, and non-perturbative contributions from D-instantons and (p,q) string instantons wrapping T^2. We provide evidence for this modular form by showing that the coefficients at tree level and at one loop precisely match those obtained using string perturbation theory. Using duality, parts of the perturbative amplitude are also shown to match exactly the results obtained from eleven dimensional supergravity compactified on T^3 at one loop. Decompactifying the theory to nine dimensions, we obtain a U-duality invariant modular form, whose coefficients at tree level and at one loop agree with string perturbation theory.Comment: 25 pages, LaTe

    A Preliminary Note On The Development Of Certain Lenticels

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    Regular quantum graphs

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    We introduce the concept of regular quantum graphs and construct connected quantum graphs with discrete symmetries. The method is based on a decomposition of the quantum propagator in terms of permutation matrices which control the way incoming and outgoing channels at vertex scattering processes are connected. Symmetry properties of the quantum graph as well as its spectral statistics depend on the particular choice of permutation matrices, also called connectivity matrices, and can now be easily controlled. The method may find applications in the study of quantum random walks networks and may also prove to be useful in analysing universality in spectral statistics.Comment: 12 pages, 3 figure

    Influence de la variation de la température de combustion dans un moteur Diesel sur les émissions de polluants (NOx et suies)

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    Le problème majeur du moteur Diesel est la pollution due aux émissions de gaz polluants tels que le monoxyde de carbone (CO), les hydrocarbures imbrûlés (HC), les particules (suies) et les oxydes d'azote (NOx). Ces polluants ont une influence néfaste sur la santé de l'homme et l’environnement. L’objectif de cette étude est d’évaluer l’influence de la variation de la température au niveau de la chambre de combustion du moteur Diesel sur les émissions des polluants NOx et suies. De ce fait, une investigation numérique a été effectuée par l’utilisation du code KIVA-3 –Lite. A un régime de 1400 tpm du moteur Diesel et à une forte charge, il a été constaté une influence de la variation de la température des  composants de la chambre de combustion sur les émissions des polluants (NOx et suies). A la température (T°) de 300 °K au niveau de la culasse, les concentrations du NOx et des suies étaient respectivement de 9,36 et 0,62 gr/kg-f et à la T° de 900°K au sein du même composant, les émissions de NOx ont diminué (3,05 gr/kg-f ) mais celles des suies étaient stables (0,75 gr/kg-f). Au niveau de la paroi du cylindre de la chambre de combustion et à une T° de 300 °K, les concentrations de NOx et suies étaient respectivement de 7,68 et 0,66 gr/kg-f par contre à la T° de 625 °K, les émissions de NOx et des suies étaient constantes (8,18 et 0,66 gr/kg-f). La performance du moteur Diesel, en cours, et les nouvelles réglementations ont réduit les émissions des polluants (NOx et suies).Mots clés : Moteur Diesel, pollution, émissions, suies, oxydes d’azote

    The importance of accessible information in promoting the inclusion of people with an intellectual disability

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    People with an intellectual disability experience high levels of social exclusion and a range of health inequalities. Increased inclusion and participation in healthcare decision making have been identified as key to promoting inclusion in health and social care. However, achieving these objectives requires increased recognition of the communication and health literacy needs of individuals with an intellectual disability and consideration of the appropriateness of the information currently provided. In this article, we report the results of a pre-COVID-19 qualitative study exploring the provision and use of accessible information to support the healthcare inclusion of individuals with an intellectual disability. A total of 35 clinicians participated in focus group discussions, and 10 people with intellectual disabilities and 10 carers were interviewed regarding their experiences of using accessible health-related information. Qualitative data analysis using a framework approach highlighted the crucial role of communication partners when using accessible information, deficits in current National Health Service (NHS: UK’s publicly funded health care system) information provision in the UK, and possible broader relevance of accessible resources. The implications of these findings for the provision of accessible information in a post-COVID-19 environment are explored, and recommendations are made for the increased integration and theory-driven research to inform the provision, content, and use of health-related information, especially the provision of online information, in the future

    Domain wall partition functions and KP

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    We observe that the partition function of the six vertex model on a finite square lattice with domain wall boundary conditions is (a restriction of) a KP tau function and express it as an expectation value of charged free fermions (up to an overall normalization).Comment: 16 pages, LaTeX2

    Automorphic properties of low energy string amplitudes in various dimensions

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    This paper explores the moduli-dependent coefficients of higher derivative interactions that appear in the low-energy expansion of the four-graviton amplitude of maximally supersymmetric string theory compactified on a d-torus. These automorphic functions are determined for terms up to order D^6R^4 and various values of d by imposing a variety of consistency conditions. They satisfy Laplace eigenvalue equations with or without source terms, whose solutions are given in terms of Eisenstein series, or more general automorphic functions, for certain parabolic subgroups of the relevant U-duality groups. The ultraviolet divergences of the corresponding supergravity field theory limits are encoded in various logarithms, although the string theory expressions are finite. This analysis includes intriguing representations of SL(d) and SO(d,d) Eisenstein series in terms of toroidally compactified one and two-loop string and supergravity amplitudes.Comment: 80 pages. 1 figure. v2:Typos corrected, footnotes amended and small clarifications. v3: minor corrections. Version to appear in Phys Rev
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