114 research outputs found
Source coding with escort distributions and Renyi entropy bounds
We discuss the interest of escort distributions and R\'enyi entropy in the
context of source coding. We first recall a source coding theorem by Campbell
relating a generalized measure of length to the R\'enyi-Tsallis entropy. We
show that the associated optimal codes can be obtained using considerations on
escort-distributions. We propose a new family of measure of length involving
escort-distributions and we show that these generalized lengths are also
bounded below by the R\'enyi entropy. Furthermore, we obtain that the standard
Shannon codes lengths are optimum for the new generalized lengths measures,
whatever the entropic index. Finally, we show that there exists in this setting
an interplay between standard and escort distributions
A simple probabilistic construction yielding generalized entropies and divergences, escort distributions and q-Gaussians
We give a simple probabilistic description of a transition between two states
which leads to a generalized escort distribution. When the parameter of the
distribution varies, it defines a parametric curve that we call an escort-path.
The R\'enyi divergence appears as a natural by-product of the setting. We study
the dynamics of the Fisher information on this path, and show in particular
that the thermodynamic divergence is proportional to Jeffreys' divergence.
Next, we consider the problem of inferring a distribution on the escort-path,
subject to generalized moments constraints. We show that our setting naturally
induces a rationale for the minimization of the R\'enyi information divergence.
Then, we derive the optimum distribution as a generalized q-Gaussian
distribution
An entropic view of Pickands' theorem
It is shown that distributions arising in Renyi-Tsallis maximum entropy
setting are related to the Generalized Pareto Distributions (GPD) that are
widely used for modeling the tails of distributions. The relevance of such
modelization, as well as the ubiquity of GPD in practical situations follows
from Balkema-De Haan-Pickands theorem on the distribution of excesses (over a
high threshold). We provide an entropic view of this result, by showing that
the distribution of a suitably normalized excess variable converges to the
solution of a maximum Tsallis entropy, which is the GPD. This highlights the
relevance of the so-called Tsallis distributions in many applications as well
as some relevance to the use of the corresponding entropy.Comment: 4 pages, accepted to ISIT0
Array processing with model adequation
This paper is an introduction to the array processing problems analysed in this
special issue . The objective is twofold . First, to give a simple mathematical model
and a formalism ranging the applications presented in the issue . Second, to give
some elements on several "classic" methods of array processing, classic in the
sense that they do not take into account model errors problems .Cet article constitue une introduction aux problĂšmes de calibration en traitement d'antenne analysĂ©s dans ce numĂ©ro spĂ©cial. Il a un double objet: d'une part donner un modĂšle mathĂ©matique simple et un formalisme unique couvrant l'ensemble des applications prĂ©sentĂ©es dans ce document; et d'autre part donner quelques Ă©lĂ©ments sur plusieurs mĂ©thodes "classiques" en traitement d'antenne, classiques dans le sens oĂč elles ne tiennent pas compte des problĂšmes d'erreurs de modĂšl
On some entropy functionals derived from R\'enyi information divergence
We consider the maximum entropy problems associated with R\'enyi -entropy,
subject to two kinds of constraints on expected values. The constraints
considered are a constraint on the standard expectation, and a constraint on
the generalized expectation as encountered in nonextensive statistics. The
optimum maximum entropy probability distributions, which can exhibit a
power-law behaviour, are derived and characterized. The R\'enyi entropy of the
optimum distributions can be viewed as a function of the constraint. This
defines two families of entropy functionals in the space of possible expected
values. General properties of these functionals, including nonnegativity,
minimum, convexity, are documented. Their relationships as well as numerical
aspects are also discussed. Finally, we work out some specific cases for the
reference measure and recover in a limit case some well-known entropies
On a (\beta,q)-generalized Fisher information and inequalities involving q-Gaussian distributions
In the present paper, we would like to draw attention to a possible
generalized Fisher information that fits well in the formalism of nonextensive
thermostatistics. This generalized Fisher information is defined for densities
on Just as the maximum R\'enyi or Tsallis entropy subject to
an elliptic moment constraint is a generalized q-Gaussian, we show that the
minimization of the generalized Fisher information also leads a generalized
q-Gaussian. This yields a generalized Cram\'er-Rao inequality. In addition, we
show that the generalized Fisher information naturally pops up in a simple
inequality that links the generalized entropies, the generalized Fisher
information and an elliptic moment. Finally, we give an extended Stam
inequality. In this series of results, the extremal functions are the
generalized q-Gaussians. Thus, these results complement the classical
characterization of the generalized q-Gaussian and introduce a generalized
Fisher information as a new information measure in nonextensive
thermostatistics.Comment: v2: corrected equation (A5
Experimental Study of electron acceleration by plasma beat-waves with Nd lasers
International audienceWe have observed the acceleration of electrons by a beat-wave generated in a deuterium plasma by two Nd-YAG and Nd-YLF laser wavelengths. Electrons injected at an energy of 3.3 MeV are observed to be accelerated up to 4.7 MeV after the plasma. The energy gain is compatible with a peak electric field of the order of 1.2 GV/m. The experiment has been performed with different injection energies, from 2.5 to 3.3 MeV, with different plasma dimensions, and with different laser intensitie
RNA interference therapeutics targeting angiotensinogen ameliorate preeclamptic phenotype in rodent models
Preeclampsia, with the hallmark features of new-onset hypertension and proteinuria after 20 weeks of gestation, is a major cause of fetal and maternal morbidity and mortality. Studies have demonstrated a role for the renin-angiotensin system (RAS) in its pathogenesis; however, small-molecule RAS blockers are contraindicated because of fetal toxicity. We evaluated whether siRNA targeting maternal hepatic angiotensinogen (Agt) could ameliorate symptoms of preeclampsia without adverse placental or fetal effects in 2 rodent models. The first model used a cross of females expressing human Agt with males expressing human renin, resulting in upregulation of the circulating and uteroplacental RAS. The second model induced ischemia/reperfusion injury and subsequent local and systemic inflammation by surgically reducing placental blood flow midgestation (reduced uterine perfusion pressure [RUPP]). These models featured hypertension, proteinuria, and fetal growth restriction, with altered biomarkers. siRNA treatment ameliorated the preeclamptic phenotype in both models, reduced blood pressure, and improved intrauterine growth restriction, with no observed deleterious effects on the fetus. Treatment also improved the angiogenic balance and proteinuria in the transgenic model, and it reduced angiotensin receptor activating antibodies in both. Thus, an RNAi therapeutic targeting Agt ameliorated the clinical sequelae and improved fetal outcomes in 2 rodent models of preeclampsia
Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up
Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated
Rapid Acoustic Survey for Biodiversity Appraisal
Biodiversity assessment remains one of the most difficult challenges encountered by ecologists and conservation biologists. This task is becoming even more urgent with the current increase of habitat loss. Many methodsâfrom rapid biodiversity assessments (RBA) to all-taxa biodiversity inventories (ATBI)âhave been developed for decades to estimate local species richness. However, these methods are costly and invasive. Several animalsâbirds, mammals, amphibians, fishes and arthropodsâproduce sounds when moving, communicating or sensing their environment. Here we propose a new concept and method to describe biodiversity. We suggest to forego species or morphospecies identification used by ATBI and RBA respectively but rather to tackle the problem at another evolutionary unit, the community level. We also propose that a part of diversity can be estimated and compared through a rapid acoustic analysis of the sound produced by animal communities. We produced α and ÎČ diversity indexes that we first tested with 540 simulated acoustic communities. The α index, which measures acoustic entropy, shows a logarithmic correlation with the number of species within the acoustic community. The ÎČ index, which estimates both temporal and spectral dissimilarities, is linearly linked to the number of unshared species between acoustic communities. We then applied both indexes to two closely spaced Tanzanian dry lowland coastal forests. Indexes reveal for this small sample a lower acoustic diversity for the most disturbed forest and acoustic dissimilarities between the two forests suggest that degradation could have significantly decreased and modified community composition. Our results demonstrate for the first time that an indicator of biological diversity can be reliably obtained in a non-invasive way and with a limited sampling effort. This new approach may facilitate the appraisal of animal diversity at large spatial and temporal scales
- âŠ