26,245 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 Ligeron® in the context of the Vicaria project (Leonado da Vinci – 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
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
Multi-scale processes in metapopulations : Contributions of stage structure, rescue effect, and correlated extinctions
Peer reviewedPublisher PD
Partition function of free conformal higher spin theory
We compute the canonical partition function Z of non-interacting conformal
higher spin (CHS) theory viewed as a collection of free spin s CFT's in R^d. We
discuss in detail the 4-dimensional case (where s=1 is the standard Maxwell
vector, s=2 is the Weyl graviton, etc.), but also present a generalization for
all even dimensions d. Z may be found by counting the numbers of conformal
operators and their descendants (modulo gauge identities and equations of
motion) weighted by scaling dimensions. This conformal operator counting method
requires a careful analysis of the structure of characters of relevant
(conserved current, shadow field and conformal Killing tensor) representations
of the conformal algebra so(d,2). There is also a close relation to massless
higher spin partition functions with alternative boundary conditions in
AdS_{d+1}. The same partition function Z may also be computed from the CHS path
integral on a curved S^1 x S^{d-1} background. This allows us to determine a
simple factorized form of the CHS kinetic operator on this conformally flat
background. Summing the individual conformal spin contributions Z_s over all
spins we obtain the total partition function of the CHS theory. We also find
the corresponding Casimir energy and show that it vanishes if one uses the same
regularization prescription that implies the cancellation of the total
conformal anomaly a-coefficient. This happens to be true in all even dimensions
d >= 2.Comment: 39 pages, v2 typos corrected and comments adde
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