3,848 research outputs found

    Measurement of the transverse momentum spectrum of the Higgs boson decaying into WW with the CMS experiment

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    DiÔ¨Äerential and integrated Ô¨Āducial cross sections measured using the Higgs to W+W‚ąí leptonic decays are presented as a function of the Higgs boson production. The measurements are performed using proton-proton collisions at a centre-of-mass energy of 8TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.4fb‚ąí1. The Higgs boson transverse momentum is reconstructed using the lepton pair transverse momentum and missing transverse momentum, which originates from the presence of two neutrinos in the Ô¨Ānal state. The diÔ¨Äerential cross section is measured as a function of the Higgs boson transverse momentum in a Ô¨Āducial phase space deÔ¨Āned to match the experimental acceptance in terms of the lepton kinematics and event topology. The measurements are compared to theoretical calculations

    Frustration and sound attenuation in structural glasses

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    Three classes of harmonic disorder systems (Lennard-Jones like glasses, percolators above threshold, and spring disordered lattices) have been numerically investigated in order to clarify the effect of different types of disorder on the mechanism of high frequency sound attenuation. We introduce the concept of frustration in structural glasses as a measure of the internal stress, and find a strong correlation between the degree of frustration and the exponent alpha that characterizes the momentum dependence of the sound attenuation Gamma(Q)Gamma(Q)‚ČÉ\simeqQőĪQ^\alpha. In particular, alpha decreases from about d+1 in low-frustration systems (where d is the spectral dimension), to about 2 for high frustration systems like the realistic glasses examined.Comment: Revtex, 4 pages including 4 figure

    Relaxation processes in harmonic glasses?

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    A relaxation process, with the associated phenomenology of sound attenuation and sound velocity dispersion, is found in a simulated harmonic Lennard-Jones glass. We propose to identify this process with the so called microscopic (or instantaneous) relaxation process observed in real glasses and supercooled liquids. A model based on the memory function approach accounts for the observation, and allows to relate to each others: 1) the characteristic time and strength of this process, 2) the low frequency limit of the dynamic structure factor of the glass, and 3) the high frequency sound attenuation coefficient, with its observed quadratic dependence on the momentum transfer.Comment: 11 pages, 3 figure

    Resilience Assessment : International Best Practice Principles

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    PURPOSE This document sets out international best-practice principles for resilience assessment being undertaken within an impact assessment (IA) of some project, plan, programme, or policy (in this context, its function may be different to that of a self-standing resilience assessment). Resilience assessment can contribute to impact assessment by defining specific disturbances that can lead to failure of natural, social, and engineered systems. The disturbance can be caused either by the proposed action, factors beyond the influence of proposed action, or combination of both. The impact assessment can consider all these factors within one coherent framework. It can identify synergies and knock-on effects that can cause potential system failures, and advise on interventions that avoid failures in the critical functions of the system BACKGROUND Resilience assessment evaluates the structure and function of a system of focus (hereafter ‚Äėfocal system‚Äô) and, in the context of an impact assessment, focuses on the effects of the proposed action on the resilience of that focal system. The focal system can include: socio-ecological, biophysical, engineering, technological, or other components. Resilience assessment should ideally examine the consequences of the proposed action in combination with internal or external factors that may collectively influence the resilience of the focal system (e.g., biophysical system change caused by global warming on engineered structures)

    Potential Energy Landscape and Long Time Dynamics in a Simple Model Glass

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    We analyze the properties of a Lennard-Jones system at the level of the potential energy landscape. After an exhaustive investigation of the topological features of the landscape of the systems, obtained studying small size sample, we describe the dynamics of the systems in the multi-dimensional configurational space by a simple model. This consider the configurational space as a connected network of minima where the dynamics proceeds by jumps described by an appropriate master equation. Using this model we are able to reproduce the long time dynamics and the low temperature regime. We investigate both the equilibrium regime and the off-equilibrium one, finding those typical glassy behavior usually observed in the experiments such as: {\it i)} stretched exponential relaxation, {\it ii)} temperature-dependent stretching parameter, {\it iii)} breakdown of the Stokes-Einstein relation, and {\it iv)} appearance of a critical temperature below which one observes deviation from the fluctuation-dissipation relation as consequence of the lack of equilibrium in the system.Comment: 11 pages (Latex), 9 ps figure

    Connected Network of Minima as a Model Glass: Long Time Dynamics

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    A simple model to investigate the long time dynamics of glass-formers is presented and applied to study a Lennard-Jones system in supercooled and glassy phases. According to our model, the point representing the system in the configurational phase space performs harmonic vibrations around (and activated jumps between) minima pertaining to a connected network. Exploiting the model, in agreement with the experimental results, we find evidence for: i) stretched relaxational dynamics; ii) a strong T-dependence of the stretching parameter; iii) breakdown of the Stokes-Einstein law.Comment: 4 pages (Latex), 4 eps figure

    Evidence of short time dynamical correlations in simple liquids

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    We report a molecular dynamics (MD) study of the collective dynamics of a simple monatomic liquid -interacting through a two body potential that mimics that of lithium- across the liquid-glass transition. In the glassy phase we find evidences of a fast relaxation process similar to that recently found in Lennard-Jones glasses. The origin of this process is ascribed to the topological disorder, i.e. to the dephasing of the different momentum QQ Fourier components of the actual normal modes of vibration of the disordered structure. More important, we find that the fast relaxation persists in the liquid phase with almost no temperature dependence of its characteristic parameters (strength and relaxation time). We conclude, therefore, that in the liquid phase well above the melting point, at variance with the usual assumption of {\it un-correlated} binary collisions, the short time particles motion is strongly {\it correlated} and can be described via a normal mode expansion of the atomic dynamics.Comment: 7 pages, 7 .eps figs. To appear in Phys. Rev.

    Energy landscape, two-level systems and entropy barriers in Lennard-Jones clusters

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    We develop an efficient numerical algorithm for the identification of a large number of saddle points of the potential energy function of Lennard- Jones clusters. Knowledge of the saddle points allows us to find many thousand adjacent minima of clusters containing up to 80 argon atoms and to locate many pairs of minima with the right characteristics to form two-level systems (TLS). The true TLS are singled out by calculating the ground-state tunneling splitting. The entropic contribution to all barriers is evaluated and discussed.Comment: 4 pages, RevTex, 2 PostScript figure
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