Scaled penalization of Brownian motion with drift and the Brownian ascent

We study a scaled version of a two-parameter Brownian penalization model introduced by Roynette-Vallois-Yor in arXiv:math/0511102. The original model penalizes Brownian motion with drift $h\in\mathbb{R}$ by the weight process ${\big(\exp(\nu S_t):t\geq 0\big)}$ where $\nu\in\mathbb{R}$ and $\big(S_t:t\geq 0\big)$ is the running maximum of the Brownian motion. It was shown there that the resulting penalized process exhibits three distinct phases corresponding to different regions of the $(\nu,h)$-plane. In this paper, we investigate the effect of penalizing the Brownian motion concurrently with scaling and identify the limit process. This extends a result of Roynette-Yor for the ${\nu<0,~h=0}$ case to the whole parameter plane and reveals two additional "critical" phases occurring at the boundaries between the parameter regions. One of these novel phases is Brownian motion conditioned to end at its maximum, a process we call the Brownian ascent. We then relate the Brownian ascent to some well-known Brownian path fragments and to a random scaling transformation of Brownian motion recently studied by Rosenbaum-Yor.Comment: 32 pages; made additions to Section

DISTRIBUTIONS ISOTOPIQUES DES PRODUITS DE TRANSFERTS TRÈS INÉLASTIQUES ENTRE IONS LOURDS

On compare les distributions isotopiques expérimentales des produits de transfert très inélastiques obtenus par les réactions 40Ca (284 MeV) + 40Ca et 40Ar (295 MeV) + 232Th

Probing pre-formed alpha particles in the ground state of nuclei

In this Letter, we report on alpha particle emission through the nuclear break-up in the reaction 40Ca on a 40Ca target at 50A MeV. It is observed that, similarly to nucleons, alpha particles can be emitted to the continuum with very specific angular distribution during the reaction. The alpha particle properties can be understood as resulting from an alpha cluster in the daughter nucleus that is perturbed by the short range nuclear attraction of the collision partner and emitted. A time-dependent theory that describe the alpha particle wave-function evolution is able to reproduce qualitatively the observed angular distribution. This mechanism offers new possibilities to study alpha particle properties in the nuclear medium.Comment: 4 pages, 3 figure

Invariance of the white noise for KdV

We prove the invariance of the mean 0 white noise for the periodic KdV. First, we show that the Besov-type space \hat{b}^s_{p, \infty}, sp <-1, contains the support of the white noise. Then, we prove local well-posedness in \hat{b}^s_{p, \infty} for p= 2+, s = -{1/2}+ such that sp <-1. In establishing the local well-posedness, we use a variant of the Bourgain spaces with a weight. This provides an analytical proof of the invariance of the white noise under the flow of KdV obtained in Quastel-Valko.Comment: 18 pages. To appear in Comm. Math. Phy

ÉTUDE DE L'INTERACTION DE NEUTRONS DE 14 MeV SUR 238U

Le spectre d'énergie des neutrons secondaires a été observé par temps de vol de 800 keV à 14 MeV. La distribution angulaire a été étudiée de 30° à 150°. A partir des spectres expérimentaux, on a déduit les spectres de fission et d'évaporation, puis déterminé la température des noyaux excités. Une évaluation du coefficient de densité de niveaux a été faite à partir du modèle du gaz de Fermi.The fast neutron interaction of 238U has been studied by measuring the secondary neutron spectrum as a function of angle (30° ⩽ θ ⩽ 150°). The measurements were made by the time-of-flight method and spectra were observed over the energy range 800 keV-14 MeV. From experimental data, the fission and evaporation spectra have been deduced. The Fermi-gas model and the calculated temperature were used to determine the nuclear level density coefficient

Resuspension of carbon dust collected in Tore Supra and exposed to turbulent airflow Controlled experiments and comparison with model

International audienceThis work presents the results of experiments conducted with carbon microparticles collected in the tokamak Tore Supra in order to characterize their resuspension behaviour from a stainless-steel substrate when exposed to turbulent airflow. Experiments were conducted in a wind tunnel with controlled velocity profiles and monitored environmental conditions. A consequent amount of dust has been collected in the vessel of the tokamak and a bimodal particle size distribution of samples is first demonstrated. Comparison with resuspension of alumina powders with equivalent particle size distributions under turbulent airflow is also discussed. Results for both carbon and alumina microparticles are then compared to a theoretical resuspension model. Data reveal that exposing multilayer deposits with bimodal particle size distributions to low-speed flows (i.e. 3-10 m/s) induces a significant reduction of the mobilized fractions compared to what was predicted by the model. In addition, results helped to highlight some limitations in the model to physically describe changes in the adhesive strength that can occur with a polydisperse deposit. © 2014 Published by Elsevier B.V