1,898 research outputs found
Dispersion in optical fibers and timing for particle identification
In the framework of the TOF Wall laser calibration system of the HARP
experiment, a study of time dispersion properties of mono-mode and multi-mode
optical fibers in the green band (532 nm) has been carried out. Dispersion less
than 4 ps/m has been obtained with 10 m core diameter fibers.Comment: 2 pages, 1 .ps figure, moriond.sty included. Talk given at the
XXXVIIth Rencontres de Moriond on Electroweak Interactions and Unified
Theories, Les Arcs, France, 9-16 Mar 200
Long time stability of small amplitude Breathers in a mixed FPU-KG model
In the limit of small couplings in the nearest neighbor interaction, and
small total energy, we apply the resonant normal form result of a previous
paper of ours to a finite but arbitrarily large mixed Fermi-Pasta-Ulam
Klein-Gordon chain, i.e. with both linear and nonlinear terms in both the
on-site and interaction potential, with periodic boundary conditions. An
existence and orbital stability result for Breathers of such a normal form,
which turns out to be a generalized discrete Nonlinear Schr\"odinger model with
exponentially decaying all neighbor interactions, is first proved. Exploiting
such a result as an intermediate step, a long time stability theorem for the
true Breathers of the KG and FPU-KG models, in the anti-continuous limit, is
proven.Comment: Substantial revision in the presentation. Stability time scale
slightly modifie
An extensive adiabatic invariant for the Klein-Gordon model in the thermodynamic limit
We construct an extensive adiabatic invariant for a Klein-Gordon chain in the
thermodynamic limit. In particular, given a fixed and sufficiently small value
of the coupling constant , the evolution of the adiabatic invariant is
controlled up to times scaling as for any large enough
value of the inverse temperature . The time scale becomes a stretched
exponential if the coupling constant is allowed to vanish jointly with the
specific energy. The adiabatic invariance is exhibited by showing that the
variance along the dynamics, i.e. calculated with respect to time averages, is
much smaller than the corresponding variance over the whole phase space, i.e.
calculated with the Gibbs measure, for a set of initial data of large measure.
All the perturbative constructions and the subsequent estimates are consistent
with the extensive nature of the system.Comment: 60 pages. Minor corrections with respect to the first version. To
appear in Annales Henri Poincar\'
Approximation of small-amplitude weakly coupled oscillators with discrete nonlinear Schrodinger equations
Small-amplitude weakly coupled oscillators of the Klein-Gordon lattices are
approximated by equations of the discrete nonlinear Schrodinger type. We show
how to justify this approximation by two methods, which have been very popular
in the recent literature. The first method relies on a priori energy estimates
and multi-scale decompositions. The second method is based on a resonant normal
form theorem. We show that although the two methods are different in the
implementation, they produce equivalent results as the end product. We also
discuss applications of the discrete nonlinear Schrodinger equation in the
context of existence and stability of breathers of the Klein--Gordon lattice
Existence and continuous approximation of small amplitude breathers in 1D and 2D Klein--Gordon lattices
We construct small amplitude breathers in 1D and 2D Klein--Gordon infinite
lattices. We also show that the breathers are well approximated by the ground
state of the nonlinear Schroedinger equation. The result is obtained by
exploiting the relation between the Klein Gordon lattice and the discrete Non
Linear Schroedinger lattice. The proof is based on a Lyapunov-Schmidt
decomposition and continuum approximation techniques introduced in [7],
actually using its main result as an important lemma
Dynamic and Transparent Analysis of Commodity Production Systems
We propose a framework that provides a programming interface to perform
complex dynamic system-level analyses of deployed production systems. By
leveraging hardware support for virtualization available nowadays on all
commodity machines, our framework is completely transparent to the system under
analysis and it guarantees isolation of the analysis tools running on its top.
Thus, the internals of the kernel of the running system needs not to be
modified and the whole platform runs unaware of the framework. Moreover, errors
in the analysis tools do not affect the running system and the framework. This
is accomplished by installing a minimalistic virtual machine monitor and
migrating the system, as it runs, into a virtual machine. In order to
demonstrate the potentials of our framework we developed an interactive kernel
debugger, nicknamed HyperDbg. HyperDbg can be used to debug any critical kernel
component, and even to single step the execution of exception and interrupt
handlers.Comment: 10 pages, To appear in the 25th IEEE/ACM International Conference on
Automated Software Engineering, Antwerp, Belgium, 20-24 September 201
FPU phenomenon for generic initial data
The well known FPU phenomenon (lack of attainment of equipartition of the
mode--energies at low energies, for some exceptional initial data) suggests
that the FPU model does not have the mixing property at low energies. We give
numerical indications that this is actually the case. This we show by computing
orbits for sets of initial data of full measure, sampled out from the
microcanonical ensemble by standard Montecarlo techniques. Mixing is tested by
looking at the decay of the autocorrelations of the mode--energies, and it is
found that the high--frequency modes have autocorrelations that tend instead to
positive values. Indications are given that such a nonmixing property survives
in the thermodynamic limit. It is left as an open problem whether mixing
obtains within time--scales much longer than the presently available ones
Tail resonances of FPU q-breathers and their impact on the pathway to equipartition
Upon initial excitation of a few normal modes the energy distribution among
all modes of a nonlinear atomic chain (the Fermi-Pasta-Ulam model) exhibits
exponential localization on large time scales. At the same time resonant
anomalies (peaks) are observed in its weakly excited tail for long times
preceding equipartition. We observe a similar resonant tail structure also for
exact time-periodic Lyapunov orbits, coined q-breathers due to their
exponential localization in modal space. We give a simple explanation for this
structure in terms of superharmonic resonances. The resonance analysis agrees
very well with numerical results and has predictive power. We extend a
previously developed perturbation method, based essentially on a
Poincare-Lindstedt scheme, in order to account for these resonances, and in
order to treat more general model cases, including truncated Toda potentials.
Our results give qualitative and semiquantitative account for the superharmonic
resonances of q-breathers and natural packets
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