Cellular Automaton for Realistic Modelling of Landslides

A numerical model is developed for the simulation of debris flow in landslides over a complex three dimensional topography. The model is based on a lattice, in which debris can be transferred among nearest neighbors according to established empirical relationships for granular flows. The model is then validated by comparing a simulation with reported field data. Our model is in fact a realistic elaboration of simpler ``sandpile automata'', which have in recent years been studied as supposedly paradigmatic of ``self-organized criticality''. Statistics and scaling properties of the simulation are examined, and show that the model has an intermittent behavior.Comment: Revised version (gramatical and writing style cleanup mainly). Accepted for publication by Nonlinear Processes in Geophysics. 16 pages, 98Kb uuencoded compressed dvi file (that's the way life is easiest). Big (6Mb) postscript figures available upon request from [email protected] / [email protected]

Analysis strategy for the SM Higgs boson search in the four-lepton final state in CMS

The current status of the searches for the SM Higgs boson in the $H$$\rightarrow$$ZZ^{(*)}$$\rightarrow$$4\ell$ decay channel with the CMS experiment is presented. The selection cuts for suppressing the backgrounds while keeping very high signal efficiencies are described, along with the data-driven algorithms implemented to estimate the background yields and the systematic uncertainties. With an integrated luminosity of $1.66 \mathrm{fb}^{-1}$, upper limits at 95% CL on the SM-like Higgs cross section $\times$ branching ratio exclude cross sections from about one to two times the expected value from the Standard Model in the range $150 < m_{H} < 420 \mathrm{GeV}$. No evidence for the existence of the SM Higgs boson has been found so far.Comment: "Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 5 figures.

Dispersion of passive tracers in closed basins: beyond the diffusion coefficient

We investigate the spreading of passive tracers in closed basins. If the characteristic length scale of the Eulerian velocities is not very small compared with the size of the basin the usual diffusion coefficient does not give any relevant information about the mechanism of spreading. We introduce a finite size characteristic time $\tau(\delta)$ which describes the diffusive process at scale $\delta$. When $\delta$ is small compared with the typical length of the velocity field one has $\tau(\delta) \sim \lambda^{-1}$, where $\lambda$ is the maximum Lyapunov exponent of the Lagrangian motion. At large $\delta$ the behavior of $\tau(\delta)$ depends on the details of the system, in particular the presence of boundaries, and in this limit we have found a universal behavior for a large class of system under rather general hypothesis. The method of working at fixed scale $\delta$ makes more physical sense than the traditional way of looking at the relative diffusion at fixed delay times. This technique is displayed in a series of numerical experiments in simple flows.Comment: 14 pages RevTeX, 9 PS figures, in press on Physics of Fluid