4,110 research outputs found
Measurement of the transverse momentum spectrum of the Higgs boson decaying into WW with the CMS experiment
Differential and integrated fiducial cross sections measured using the Higgs to W+W− 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−1. 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 final state. The differential cross section is measured as a function of the Higgs boson transverse momentum in a fiducial phase space defined 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
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 . 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?
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
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 ‘focal system’) 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
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
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
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
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
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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