54 research outputs found
A forward--backward stochastic algorithm for quasi-linear PDEs
We propose a time-space discretization scheme for quasi-linear parabolic
PDEs. The algorithm relies on the theory of fully coupled forward--backward
SDEs, which provides an efficient probabilistic representation of this type of
equation. The derivated algorithm holds for strong solutions defined on any
interval of arbitrary length. As a bypass product, we obtain a discretization
procedure for the underlying FBSDE. In particular, our work provides an
alternative to the method described in [Douglas, Ma and Protter (1996) Ann.
Appl. Probab. 6 940--968] and weakens the regularity assumptions required in
this reference.Comment: Published at http://dx.doi.org/10.1214/105051605000000674 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Stopped diffusion processes: boundary corrections and overshoot
For a stopped diffusion process in a multidimensional time-dependent domain
\D, we propose and analyse a new procedure consisting in simulating the
process with an Euler scheme with step size and stopping it at
discrete times in a modified domain, whose boundary has
been appropriately shifted. The shift is locally in the direction of the inward
normal at any point on the parabolic boundary of \D, and its
amplitude is equal to where
stands for the diffusion coefficient of the process. The procedure is
thus extremely easy to use. In addition, we prove that the rate of convergence
w.r.t. for the associated weak error is higher than without shifting,
generalizin g previous results by \cite{broa:glas:kou:97} obtained for the one
dimensional Brownian motion. For this, we establish in full generality the
asymptotics of the triplet exit time/exit position/overshoot for the discretely
stopped Euler scheme. Here, the overshoot means the distance to the boundary of
the process when it exits the domain. Numerical experiments support these
results.Comment: 39 page
Non Linear Singular Drifts and Fractional Operators: when Besov meets Morrey and Campanato
Within the global setting of singular drifts in Morrey-Campanato spaces
presented in [6], we study now the H{\"o}lder regularity properties of the
solutions of a transport-diffusion equation with nonlinear singular drifts that
satisfy a Besov stability property. We will see how this Besov information is
relevant and how it allows to improve previous results. Moreover, in some
particular cases we show that as the nonlinear drift becomes more regular, in
the sense of Morrey-Campanato spaces, the additional Besov stability property
will be less useful
Heat kernel of supercritical SDEs with unbounded drifts
Let and . Consider the following SDE in
:where is a -dimensional
rotationally invariant -stable process, and are H\''older continuous functions in space,
with respective order such that , uniformly in . Here may be unbounded.When is
bounded and uniformly elliptic, we show that the unique solution of
the above SDE admits a continuous density, which enjoys sharp two-sided
estimates. We also establish sharp upper-bound for the logarithmic derivative.
{In particular, we cover the whole \textit{supercritical} range .} Our proof is based on \textit{ad hoc} parametrix expansions and
probabilistic techniques
On Multidimensional stable-driven Stochastic Differential Equations with Besov drift
We establish well-posedness results for multidimensional non degenerate
-stable driven SDEs with time inhomogeneous singular drifts in
L^r-B^{--1+}_{p,q} with < 1 and in (1, 2], where L^r
and B^{--1+}_{p,q} stand for Lebesgue and Besov spaces respectively.
Precisely, we first prove the well-posedness of the corresponding martingale
problem and then give a precise meaning to the dynamics of the SDE. Our results
rely on the smoothing properties of the underlying PDE, which is investigated
by combining a perturbative approach with duality results between Besov spaces
Trends in Cancer Incidence in Different Antiretroviral Treatment-Eras amongst People with HIV
Despite cancer being a leading comorbidity amongst individuals with HIV, there are limited data assessing cancer trends across different antiretroviral therapy (ART)-eras. We calculated age-standardised cancer incidence rates (IRs) from 2006–2021 in two international cohort collaborations (D:A:D and RESPOND). Poisson regression was used to assess temporal trends, adjusted for potential confounders. Amongst 64,937 individuals (31% ART-naïve at baseline) and 490,376 total person-years of follow-up (PYFU), there were 3763 incident cancers (IR 7.7/1000 PYFU [95% CI 7.4, 7.9]): 950 AIDS-defining cancers (ADCs), 2813 non-ADCs, 1677 infection-related cancers, 1372 smoking-related cancers, and 719 BMI-related cancers (groups were not mutually exclusive). Age-standardised IRs for overall cancer remained fairly constant over time (8.22/1000 PYFU [7.52, 8.97] in 2006–2007, 7.54 [6.59, 8.59] in 2020–2021). The incidence of ADCs (3.23 [2.79, 3.72], 0.99 [0.67, 1.42]) and infection-related cancers (4.83 [4.2, 5.41], 2.43 [1.90, 3.05]) decreased over time, whilst the incidence of non-ADCs (4.99 [4.44, 5.58], 6.55 [5.67, 7.53]), smoking-related cancers (2.38 [2.01, 2.79], 3.25 [2.63–3.96]), and BMI-related cancers (1.07 [0.83, 1.37], 1.88 [1.42, 2.44]) increased. Trends were similar after adjusting for demographics, comorbidities, HIV-related factors, and ART use. These results highlight the need for better prevention strategies to reduce the incidence of NADCs, smoking-, and BMI-related cancers
Discrétisations associées à un processus dans un domaine et Schémas numériques probabilistes pour les EDP paraboliques quasi-linéaires
PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
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