3,342 research outputs found
On the uniqueness for the spatially homogeneous Boltzmann equation with a strong angular singularity
We prove an inequality on the Wasserstein distance with quadratic cost
between two solutions of the spatially homogeneous Boltzmann equation without
angular cutoff, from which we deduce some uniqueness results. In particular, we
obtain a local (in time) well-posedness result in the case of (possibly very)
soft potentials. A global well-posedeness result is shown for all regularized
hard and soft potentials without angular cutoff. Our uniqueness result seems to
be the first one applying to a strong angular singularity, except in the
special case of Maxwell molecules.
Our proof relies on the ideas of Tanaka: we give a probabilistic
interpretation of the Boltzmann equation in terms of a stochastic process. Then
we show how to couple two such processes started with two different initial
conditions, in such a way that they almost surely remain close to each other
Cannabis through the looking glass: chemo- and enantio-selective separation of phytocannabinoids by enantioselective ultra high performance supercritical fluid chromatography
By using the Inverted Chirality Columns Approach (ICCA) we have developed an enantioselective UHPSFC method to determine the enantiomeric excess (ee) of (-)-Î(9)-THC in medicinal marijuana (BedrocanÂź). The ee was high (99.73%), but the concentration of the (+)-enantiomer (0.135%) was not negligible, and it is worth a systematic evaluation of bioactivity
Relational reasoning via probabilistic coupling
Probabilistic coupling is a powerful tool for analyzing pairs of
probabilistic processes. Roughly, coupling two processes requires finding an
appropriate witness process that models both processes in the same probability
space. Couplings are powerful tools proving properties about the relation
between two processes, include reasoning about convergence of distributions and
stochastic dominance---a probabilistic version of a monotonicity property.
While the mathematical definition of coupling looks rather complex and
cumbersome to manipulate, we show that the relational program logic pRHL---the
logic underlying the EasyCrypt cryptographic proof assistant---already
internalizes a generalization of probabilistic coupling. With this insight,
constructing couplings is no harder than constructing logical proofs. We
demonstrate how to express and verify classic examples of couplings in pRHL,
and we mechanically verify several couplings in EasyCrypt
Continuity of Optimal Control Costs and its application to Weak KAM Theory
We prove continuity of certain cost functions arising from optimal control of
affine control systems. We give sharp sufficient conditions for this
continuity. As an application, we prove a version of weak KAM theorem and
consider the Aubry-Mather problems corresponding to these systems.Comment: 23 pages, 1 figures, added explanations in the proofs of the main
theorem and the exampl
The Arbuscular Mycorrhizal Fungus Glomus viscosum Improves the Tolerance to Verticillium Wilt in Artichoke by Modulating the Antioxidant Defense Systems
Verticillium wilt, caused by the fungal pathogen Verticillium dahliae, is the most severe disease that threatens artichoke (Cynara scolymus L.) plants. Arbuscular mycorrhizal fungi (AMF) may represent a useful biological control strategy against this pathogen attack, replacing chemical compounds that, up to now, have been not very effective. In this study, we evaluated the effect of the AMF Glomus viscosum Nicolson in enhancing the plant tolerance towards the pathogen V. dahliae. The role of the ascorbate-glutathione (ASC-GSH) cycle and other antioxidant systems involved in the complex network of the pathogen-fungi-plant interaction have been investigated. The results obtained showed that the AMF G. viscosum is able to enhance the defense antioxidant systems in artichoke plants affected by V. dahliae, alleviating the oxidative stress symptoms. AMF-inoculated plants exhibited significant increases in ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and superoxide dismutase (SOD) activities, a higher content of ascorbate (ASC) and glutathione (GSH), and a decrease in the levels of lipid peroxidation and hydrogen peroxide (H2O2). Hence, G. viscosum may represent an effective strategy for mitigating V. dahliae pathogenicity in artichokes, enhancing the plant defense systems, and improving the nutritional values and benefit to human health
On the speed of approach to equilibrium for a collisionless gas
We investigate the speed of approach to Maxwellian equilibrium for a
collisionless gas enclosed in a vessel whose wall are kept at a uniform,
constant temperature, assuming diffuse reflection of gas molecules on the
vessel wall. We establish lower bounds for potential decay rates assuming
uniform bounds on the initial distribution function. We also obtain a
decay estimate in the spherically symmetric case. We discuss with particular
care the influence of low-speed particles on thermalization by the wall.Comment: 22 pages, 1 figure; submitted to Kinetic and Related Model
Celebrating Cercignani's conjecture for the Boltzmann equation
Cercignani's conjecture assumes a linear inequality between the entropy and
entropy production functionals for Boltzmann's nonlinear integral operator in
rarefied gas dynamics. Related to the field of logarithmic Sobolev inequalities
and spectral gap inequalities, this issue has been at the core of the renewal
of the mathematical theory of convergence to thermodynamical equilibrium for
rarefied gases over the past decade. In this review paper, we survey the
various positive and negative results which were obtained since the conjecture
was proposed in the 1980s.Comment: This paper is dedicated to the memory of the late Carlo Cercignani,
powerful mind and great scientist, one of the founders of the modern theory
of the Boltzmann equation. 24 pages. V2: correction of some typos and one
ref. adde
On Strong Convergence to Equilibrium for the Boltzmann Equation with Soft Potentials
The paper concerns - convergence to equilibrium for weak solutions of
the spatially homogeneous Boltzmann Equation for soft potentials (-4\le
\gm<0), with and without angular cutoff. We prove the time-averaged
-convergence to equilibrium for all weak solutions whose initial data have
finite entropy and finite moments up to order greater than 2+|\gm|. For the
usual -convergence we prove that the convergence rate can be controlled
from below by the initial energy tails, and hence, for initial data with long
energy tails, the convergence can be arbitrarily slow. We also show that under
the integrable angular cutoff on the collision kernel with -1\le \gm<0, there
are algebraic upper and lower bounds on the rate of -convergence to
equilibrium. Our methods of proof are based on entropy inequalities and moment
estimates.Comment: This version contains a strengthened theorem 3, on rate of
convergence, considerably relaxing the hypotheses on the initial data, and
introducing a new method for avoiding use of poitwise lower bounds in
applications of entropy production to convergence problem
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