757 research outputs found
Rearranged Stochastic Heat Equation
The purpose of this work is to provide an explicit construction of a strong
Feller semigroup on the space of probability measures over the real line that
additionally maps bounded measurable functions into Lipschitz continuous
functions, with a Lipschitz constant that blows up in an integrable manner in
small time. Our construction relies on a rearranged version of the stochastic
heat equation on the circle driven by a coloured noise. Formally, this
stochastic equation writes as a reflected equation in infinite dimension, a
topic that is known to be challenging. Under the action of the rearrangement,
the solution is forced to live in a space of quantile functions that is
isometric to the space of probability measures on the real line. We prove the
equation to be solvable by means of an Euler scheme in which we alternate flat
dynamics in the space of random variables on the circle with a rearrangement
operation that projects back the random variables onto the subset of quantile
functions. A first challenge is to prove that this scheme is tight. A second
one is to provide a consistent theory for the limiting reflected equation and
in particular to interpret in a relevant manner the reflection term. The last
step in our work is to establish the aforementioned Lipschitz property of the
semigroup by adapting earlier ideas from the Bismut-Elworthy-Li formula in
stochastic analysis
Taille de la population dâAvahi laniger dans la rĂ©serve dâAmbodiriana-Manompana, Nord-est de Madagascar
Avahi laniger est le seul lĂ©murien nocturne appartenant Ă la famille des Indriidae qui habite les forĂȘts humides de lâest de Madagascar (Mittermeier et. al., 2010) dont une partie disparaĂźt chaque annĂ©e (exploitation du bois, pratique du «tavy» ou culture sur brĂ»lis) (Beaucent and Fayolle, 2011; Lehman and Wright, 2000). La fragmentation et la destruction de leur habitat ainsi que la chasse menacent la survie de
nombreuses espĂšces de lĂ©muriens incluant celle de A. laniger (Jenkins et. al., 2011; Rakotondravony and Rabenandrasana, 2011; Anderson, Rowcliffe and Cowlishaw, 2007). Nous avons rĂ©alisĂ©, entre fin Avril et Mai 2012, une Ă©tude de densitĂ© de la population de A. laniger au sein de lâaire protĂ©gĂ©e de Manompana-Ambodiriana afin dâestimer la taille de la population totale et de dĂ©terminer lâimpact du projet de conservation menĂ©e par lâAssociation de DĂ©fense de la ForĂȘt dâAmbodiriana (ADEFA) qui recherche lâĂ©volution dĂ©mographique Ă moyen terme de cette espĂšce."LABEX" TULIP: (ANR-10-LABX-41), fct fellowship: (SFRH/BD/64875/2009)
Evaluating postoperative rotator cuff healing: Prospective comparison of MRI and ultrasound
AbstractBackgroundThe objective of this prospective comparative single centre study was to compare postoperative rotator cuff healing rates as assessed by magnetic resonance imaging (MRI) versus ultrasonography (US).Material and methodsBetween October 2012 and February 2013, 61 patients underwent arthroscopic repair of postero-superior rotator cuff tears. Each patient underwent MRI and US 6 months later. The findings were assessed independently by two observers. We compared intra-observer and inter-observer levels of agreement regarding healing rates assessed by MRI and US.ResultsIntra-observer agreement regarding the MRI interpretation was 95% (Îș coefficient, 0.83) for one observer and 98% (Îș coefficient, 0.94) for the other. Values of Îș for inter-observer agreement ranged across readings from 0.76 to 0.90. When MRI was taken as the reference, US had 80% sensitivity and 98% specificity.DiscussionMRI and US provide similar assessments of postoperative rotator cuff healing, although US is less sensitive. Intra-observer and inter-observer agreements are very good.Level of evidenceIII
Large Deviations Analysis for Distributed Algorithms in an Ergodic Markovian Environment
We provide a large deviations analysis of deadlock phenomena occurring in
distributed systems sharing common resources. In our model transition
probabilities of resource allocation and deallocation are time and space
dependent. The process is driven by an ergodic Markov chain and is reflected on
the boundary of the d-dimensional cube. In the large resource limit, we prove
Freidlin-Wentzell estimates, we study the asymptotic of the deadlock time and
we show that the quasi-potential is a viscosity solution of a Hamilton-Jacobi
equation with a Neumann boundary condition. We give a complete analysis of the
colliding 2-stacks problem and show an example where the system has a stable
attractor which is a limit cycle
Probabilistic analysis of the upwind scheme for transport
We provide a probabilistic analysis of the upwind scheme for
multi-dimensional transport equations. We associate a Markov chain with the
numerical scheme and then obtain a backward representation formula of
Kolmogorov type for the numerical solution. We then understand that the error
induced by the scheme is governed by the fluctuations of the Markov chain
around the characteristics of the flow. We show, in various situations, that
the fluctuations are of diffusive type. As a by-product, we prove that the
scheme is of order 1/2 for an initial datum in BV and of order 1/2-a, for all
a>0, for a Lipschitz continuous initial datum. Our analysis provides a new
interpretation of the numerical diffusion phenomenon
Targeting intratumoral B cells with rituximab in addition to CHOP in angioimmunoblastic T-cell lymphoma. A clinicobiological study of the GELA.
Background In angioimmunoblastic T-cell lymphoma, symptoms linked to B-lymphocyte activation are common, and variable numbers of CD20(+) large B-blasts, often infected by Epstein-Barr virus, are found in tumor tissues. We postulated that the disruption of putative B-T interactions and/or depletion of the Epstein-Barr virus reservoir by an anti-CD20 monoclonal antibody (rituximab) could improve the clinical outcome produced by conventional chemotherapy. DESIGN AND METHODS: Twenty-five newly diagnosed patients were treated, in a phase II study, with eight cycles of rituximab + chemotherapy (R-CHOP21). Tumor infiltration, B-blasts and Epstein-Barr virus status in tumor tissue and peripheral blood were fully characterized at diagnosis and were correlated with clinical outcome. RESULTS: A complete response rate of 44% (95% CI, 24% to 65%) was observed. With a median follow-up of 24 months, the 2-year progression-free survival rate was 42% (95% CI, 22% to 61%) and overall survival rate was 62% (95% CI, 40% to 78%). The presence of Epstein-Barr virus DNA in peripheral blood mononuclear cells (14/21 patients) correlated with Epstein-Barr virus score in lymph nodes (P<0.004) and the detection of circulating tumor cells (P=0.0019). Despite peripheral Epstein-Barr virus clearance after treatment, the viral load at diagnosis (>100 copy/ÎŒg DNA) was associated with shorter progression-free survival (P=0.06). Conclusions We report here the results of the first clinical trial targeting both the neoplastic T cells and the microenvironment-associated CD20(+) B lymphocytes in angioimmunoblastic T-cell lymphoma, showing no clear benefit of adding rituximab to conventional chemotherapy. A strong relationship, not previously described, between circulating Epstein-Barr virus and circulating tumor cells is highlighted
A non-hybrid method for the PDF equations of turbulent flows on unstructured grids
In probability density function (PDF) methods of turbulent flows, the joint
PDF of several flow variables is computed by numerically integrating a system
of stochastic differential equations for Lagrangian particles. A set of
parallel algorithms is proposed to provide an efficient solution of the PDF
transport equation, modeling the joint PDF of turbulent velocity, frequency and
concentration of a passive scalar in geometrically complex configurations. An
unstructured Eulerian grid is employed to extract Eulerian statistics, to solve
for quantities represented at fixed locations of the domain (e.g. the mean
pressure) and to track particles. All three aspects regarding the grid make use
of the finite element method (FEM) employing the simplest linear FEM shape
functions. To model the small-scale mixing of the transported scalar, the
interaction by exchange with the conditional mean model is adopted. An adaptive
algorithm that computes the velocity-conditioned scalar mean is proposed that
homogenizes the statistical error over the sample space with no assumption on
the shape of the underlying velocity PDF. Compared to other hybrid
particle-in-cell approaches for the PDF equations, the current methodology is
consistent without the need for consistency conditions. The algorithm is tested
by computing the dispersion of passive scalars released from concentrated
sources in two different turbulent flows: the fully developed turbulent channel
flow and a street canyon (or cavity) flow. Algorithmic details on estimating
conditional and unconditional statistics, particle tracking and particle-number
control are presented in detail. Relevant aspects of performance and
parallelism on cache-based shared memory machines are discussed.Comment: Accepted in Journal of Computational Physics, Feb. 20, 200
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