4,559 research outputs found
Sticky Particles and Stochastic Flows
Gaw\c{e}dzki and Horvai have studied a model for the motion of particles
carried in a turbulent fluid and shown that in a limiting regime with low
levels of viscosity and molecular diffusivity, pairs of particles exhibit the
phenomena of stickiness when they meet. In this paper we characterise the
motion of an arbitrary number of particles in a simplified version of their
model
Dispersion and collapse in stochastic velocity fields on a cylinder
The dynamics of fluid particles on cylindrical manifolds is investigated. The
velocity field is obtained by generalizing the isotropic Kraichnan ensemble,
and is therefore Gaussian and decorrelated in time. The degree of
compressibility is such that when the radius of the cylinder tends to infinity
the fluid particles separate in an explosive way. Nevertheless, when the radius
is finite the transition probability of the two-particle separation converges
to an invariant measure. This behavior is due to the large-scale
compressibility generated by the compactification of one dimension of the
space
Stopping power of hot QCD plasma
The partonic energy loss has been calculated taking both the hard and soft
contributions for all the processes, revealing the importance of the
individual channels. Cancellation of the intermediate separation scale has been
exhibited. Subtleties related to the identical final state partons have
properly been taken into account. The estimated collisional loss is compared
with its radiative counter part. We show that there exists a critical energy
() below which the collisional loss is more than its radiative
counterpart. In addition, we present closed form formulas for both the
collision probabilities and the stopping power ()Comment: revised version, section added, 9pages with 5 figure
Recommended from our members
Reassessment of the evolution of wheat chromosomes 4A, 5A, and 7B.
Key messageComparison of genome sequences of wild emmer wheat and Aegilops tauschii suggests a novel scenario of the evolution of rearranged wheat chromosomes 4A, 5A, and 7B. Past research suggested that wheat chromosome 4A was subjected to a reciprocal translocation T(4AL;5AL)1 that occurred in the diploid progenitor of the wheat A subgenome and to three major rearrangements that occurred in polyploid wheat: pericentric inversion Inv(4AS;4AL)1, paracentric inversion Inv(4AL;4AL)1, and reciprocal translocation T(4AL;7BS)1. Gene collinearity along the pseudomolecules of tetraploid wild emmer wheat (Triticum turgidum ssp. dicoccoides, subgenomes AABB) and diploid Aegilops tauschii (genomes DD) was employed to confirm these rearrangements and to analyze the breakpoints. The exchange of distal regions of chromosome arms 4AS and 4AL due to pericentric inversion Inv(4AS;4AL)1 was detected, and breakpoints were validated with an optical Bionano genome map. Both breakpoints contained satellite DNA. The breakpoints of reciprocal translocation T(4AL;7BS)1 were also found. However, the breakpoints that generated paracentric inversion Inv(4AL;4AL)1 appeared to be collocated with the 4AL breakpoints that had produced Inv(4AS;4AL)1 and T(4AL;7BS)1. Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 either originated sequentially, and Inv(4AL;4AL)1 was produced by recurrent chromosome breaks at the same breakpoints that generated Inv(4AS;4AL)1 and T(4AL;7BS)1, or Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 originated simultaneously. We prefer the latter hypothesis since it makes fewer assumptions about the sequence of events that produced these chromosome rearrangements
Statistical Analysis of a Semilinear Hyperbolic System Advected by a White in Time Random Velocity Field
We study a system of semilinear hyperbolic equations passively advected by
smooth white noise in time random velocity fields. Such a system arises in
modeling non-premixed isothermal turbulent flames under single-step kinetics of
fuel and oxidizer. We derive closed equations for one-point and multi-point
probability distribution functions (PDFs) and closed form analytical formulas
for the one point PDF function, as well as the two-point PDF function under
homogeneity and isotropy. Exact solution formulas allows us to analyze the
ensemble averaged fuel/oxidizer concentrations and the motion of their level
curves. We recover the empirical formulas of combustion in the thin reaction
zone limit and show that these approximate formulas can either underestimate or
overestimate average concentrations when reaction zone is not tending to zero.
We show that the averaged reaction rate slows down locally in space due to
random advection induced diffusion; and that the level curves of ensemble
averaged concentration undergo diffusion about mean locations.Comment: 18 page
Polymer transport in random flow
The dynamics of polymers in a random smooth flow is investigated in the
framework of the Hookean dumbbell model. The analytical expression of the
time-dependent probability density function of polymer elongation is derived
explicitly for a Gaussian, rapidly changing flow. When polymers are in the
coiled state the pdf reaches a stationary state characterized by power-law
tails both for small and large arguments compared to the equilibrium length.
The characteristic relaxation time is computed as a function of the Weissenberg
number. In the stretched state the pdf is unstationary and exhibits
multiscaling. Numerical simulations for the two-dimensional Navier-Stokes flow
confirm the relevance of theoretical results obtained for the delta-correlated
model.Comment: 28 pages, 6 figure
Validité discriminante d'épreuves de dépistage de la dyslexie chez des enfants de CE2-CM1
La dyslexie est un trouble spécifique du langage écrit. Les recherches menées sur l'origine de la dyslexie ont conduit à de multiples hypothèses (i.e. hypothèse phonologique, hypothèse du traitement auditif temporel, hypothèse cérébelleux, etc.). Cette diversité des hypothèses a engendré des traitements multiples et variés et, aujourd'hui, les praticiens expriment le besoin d'un outil d'aide au diagnostic de la dyslexie prenant en compte l'ensemble des déficits de l'enfant afin de proposer une rééducation adaptée. Ce papier présente la conception d'un test préliminaire contenant les épreuves d'évaluation de la dyslexie les plus représentatives de la littérature et les premiers résultats concernant la validité discriminante de ce test préliminaire chez des enfants en âge scolaire (8-10 ans)
Stochastic Lagrangian Particle Approach to Fractal Navier-Stokes Equations
In this article we study the fractal Navier-Stokes equations by using
stochastic Lagrangian particle path approach in Constantin and Iyer
\cite{Co-Iy}. More precisely, a stochastic representation for the fractal
Navier-Stokes equations is given in terms of stochastic differential equations
driven by L\'evy processes. Basing on this representation, a self-contained
proof for the existence of local unique solution for the fractal Navier-Stokes
equation with initial data in \mW^{1,p} is provided, and in the case of two
dimensions or large viscosity, the existence of global solution is also
obtained. In order to obtain the global existence in any dimensions for large
viscosity, the gradient estimates for L\'evy processes with time dependent and
discontinuous drifts is proved.Comment: 19 page
Exposure Opportunity: The Advantages of Including Men in Analyses of Female-Related Risk Factors
Abstract Intuitively, researchers do not include subjects who do not have the opportunity to be exposed, such as men in studies on oral contraceptives (OCs). We aimed to explore in which situations it is nevertheless beneficial to do so. We considered the effect of including men in case-control analyses of 8 different hypothetical data sets on the effect of OC use and venous thrombosis. In all scenarios, OC use was the exposure of interest, sex the factor that determined exposure opportunity, and air travel another risk factor. In some of these scenarios, sex and air travel were included as confounders or effect modifiers. Logistic regression was used to estimate odds ratios. Standard errors of the estimated log odds ratios, including and excluding men, were compared. We also studied the effect of including men using data from 1999–2004 from a case-control study on risk factors for venous thrombosis, conducted in the Netherlands. In all hypothetical examples, and in the real-data study, addition of men to the analysis yielded the same odds ratios when correctly adjusting for confounding. Moreover, use of additional subjects often led to more precise estimates. We suggest that subjects who do not have the opportunity to be exposed should not routinely be excluded from epidemiologic studies
- …