26,233 research outputs found
Bunch coherence in parametric X-ray radiation
The amplitude of Parametric X-ray radiation emitted coherently by a bunch of
electrons crossing a crystal (CPXR) is calculated. When the bunch density is
modulated with a longitudinal period close to the X-ray wavelenght,
constructive many-electron interferences enhance the intensity by Nb *
|F(K)|^2, where Nb is the number of electrons in the bunch, F(K) the bunch form
factor and K a specified wave vector. CPXR can be used to test the
microbunching in a X-ray free-electron laser.Comment: 6 pages, no figure. Presented at NATO Advanced Research Workshop on
Electron-Photon Interaction in Dense Media (Nor Hamberd, Armenia, 25-29 June,
2001
VICARIA: An e-Learning System for Risk Assessment
An e-learning system in the risk assessment engineering domain has been developed by a consortium led by LigeronÂź in the context of the Vicaria project (Leonado da Vinci â N° PP 118018). The e-learning platform: www.vicaria.fr has been implemented and hosted by OVH in compliance with SCORM (Shareable Content Object Reference Model) standard. The Vicaria modules contents have been defined according to an investigation performed in different European countries, particularly in France, to gather the user requirements. The Vicaria contents dedicated mainly to the environmental risks and ICPE are now available for use in French. The issue of the performed work and the e-learning system specifics are partly summarized in this pape
Second Order Noncommutative Corrections to Gravity
In this work, we calculate the leading order corrections to general
relativity formulated on a canonical noncommutative spacetime. These
corrections appear in the second order of the expansion in theta. First order
corrections can only appear in the gravity-matter interactions. Some
implications are briefly discussed.Comment: 10 page
Absence of a true long-range orbital order in a two-leg Kondo ladder
We investigate, through the density-matrix renormalization group and the
Lanczos technique, the possibility of a two-leg Kondo ladder present an
incommensurate orbital order. Our results indicate a staggered short-range
orbital order at half-filling. Away from half-filling our data are consistent
with an incommensurate quasi-long-range orbital order. We also observed that an
interaction between the localized spins enhances the rung-rung current
correlations.Comment: 7 pages, 6 figures, changed the introduction and added some
discussion
Secalonic acid A from Pseudoparmelia sphaerospora (Nyl.) Hale and P. hypomilta (FĂ©e) Hale (Parmeliaceae)
Secalonic acid A, a yellow pigment from fungal metabolism, was isolated from the lichens Pseudoparmelia sphaerospora and P. hypomilta. From P. sphaerospora was also isolated the depsidone hypostictic acid. The structure of these compounds was determined by spectroscopic methods and comparison with literature data
A numerical finite size scaling approach to many-body localization
We develop a numerical technique to study Anderson localization in
interacting electronic systems. The ground state of the disordered system is
calculated with quantum Monte-Carlo simulations while the localization
properties are extracted from the ``Thouless conductance'' , i.e. the
curvature of the energy with respect to an Aharonov-Bohm flux. We apply our
method to polarized electrons in a two dimensional system of size . We
recover the well known universal one
parameter scaling function without interaction. Upon switching on the
interaction, we find that is unchanged while the system flows toward
the insulating limit. We conclude that polarized electrons in two dimensions
stay in an insulating state in the presence of weak to moderate
electron-electron correlations.Comment: 5 pages, 4 figure
Noncommutative General Relativity
We define a theory of noncommutative general relativity for canonical
noncommutative spaces. We find a subclass of general coordinate transformations
acting on canonical noncommutative spacetimes to be volume-preserving
transformations. Local Lorentz invariance is treated as a gauge theory with the
spin connection field taken in the so(3,1) enveloping algebra. The resulting
theory appears to be a noncommutative extension of the unimodular theory of
gravitation. We compute the leading order noncommutative correction to the
action and derive the noncommutative correction to the equations of motion of
the weak gravitation field.Comment: v2: 10 pages, Discussion on noncommutative coordinate transformations
has been changed. Corresponding changes have been made throughout the pape
Oscillating behaviour of the spectrum for a plasmonic problem in a domain with a rounded corner
We investigate the eigenvalue problem in a 2D domain divided into two regions
. We are interested in situations where takes positive
values on and negative ones on . Such problems appear
in time harmonic electromagnetics in the modeling of plasmonic technologies. In
a recent work [15], we highlighted an unusual instability phenomenon for the
source term problem associated with : for certain
configurations, when the interface between the subdomains
presents a rounded corner, the solution may depend critically on the value of
the rounding parameter. In the present article, we explain this property
studying the eigenvalue problem . We provide an asymptotic
expansion of the eigenvalues and prove error estimates. We establish an
oscillatory behaviour of the eigenvalues as the rounding parameter of the
corner tends to zero. We end the paper illustrating this phenomenon with
numerical experiments.Comment: Mathematical Modelling and Numerical Analysis (ESAIM: M2AN),
09/12/2016. arXiv admin note: text overlap with arXiv:1304.478
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