Anomalous diffusion in correlated continuous time random walks

We demonstrate that continuous time random walks in which successive waiting times are correlated by Gaussian statistics lead to anomalous diffusion with mean squared displacement ~t^{2/3}. Long-ranged correlations of the waiting times with power-law exponent alpha (0<alpha<=2) give rise to subdiffusion of the form ~t^{alpha/(1+alpha)}. In contrast correlations in the jump lengths are shown to produce superdiffusion. We show that in both cases weak ergodicity breaking occurs. Our results are in excellent agreement with simulations.Comment: 6 pages, 6 figures. Slightly revised version, accepted to J Phys A as a Fast Track Communicatio

Optimizing persistent random searches

We consider a minimal model of persistent random searcher with short range memory. We calculate exactly for such searcher the mean first-passage time to a target in a bounded domain and find that it admits a non trivial minimum as function of the persistence length. This reveals an optimal search strategy which differs markedly from the simple ballistic motion obtained in the case of Poisson distributed targets. Our results show that the distribution of targets plays a crucial role in the random search problem. In particular, in the biologically relevant cases of either a single target or regular patterns of targets, we find that, in strong contrast with repeated statements in the literature, persistent random walks with exponential distribution of excursion lengths can minimize the search time, and in that sense perform better than any Levy walk.Comment: 4 pages, 4 figure

In vivo anomalous diffusion and weak ergodicity breaking of lipid granules

Combining extensive single particle tracking microscopy data of endogenous lipid granules in living fission yeast cells with analytical results we show evidence for anomalous diffusion and weak ergodicity breaking. Namely we demonstrate that at short times the granules perform subdiffusion according to the laws of continuous time random walk theory. The associated violation of ergodicity leads to a characteristic turnover between two scaling regimes of the time averaged mean squared displacement. At longer times the granule motion is consistent with fractional Brownian motion.Comment: 4 pages, 4 figures, REVTeX. Supplementary Material. Physical Review Letters, at pres

Genetic markers in clinical subtypes of juvenile idiopathic arthritis

Poster presentatationInternational audienc

Quantitative analysis of single particle trajectories: mean maximal excursion method

An increasing number of experimental studies employ single particle tracking to probe the physical environment in complex systems. We here propose and discuss new methods to analyze the time series of the particle traces, in particular, for subdiffusion phenomena. We discuss the statistical properties of mean maximal excursions, i.e., the maximal distance covered by a test particle up to time t. Compared to traditional methods focusing on the mean squared displacement we show that the mean maximal excursion analysis performs better in the determination of the anomalous diffusion exponent. We also demonstrate that combination of regular moments with moments of the mean maximal excursion method provides additional criteria to determine the exact physical nature of the underlying stochastic subdiffusion processes. We put the methods to test using experimental data as well as simulated time series from different models for normal and anomalous dynamics, such as diffusion on fractals, continuous time random walks, and fractional Brownian motion.Comment: 10 pages, 7 figures, 2 tables. NB: Supplementary material may be found in the downloadable source file

Aproximación 2-D a la eficacia del apantallamiento de carcasas metálicas

In this work an approximated method to obtain Shielding Effectiveness of metallic enclosures with an aperture is evaluated. The method consists of the analysis of the 2-D transversal cut of the structure through a numerical method. A Finite Element Method based CAD tool, has been used in order to obtain the results for the susceptibility analysis of the structure. To obtain the level of energy coupling between the inner and outer part of the cavity an empirical formula is used. Shielding Effectiveness of metallic enclosures with different sizes and apertures has been analysed and good agreement has been found between the 2-D approximated method and measurements. This tool can be used to study shielding properties of materials and the effects of enclosure contents, PCBs, I/O devices, etc.Este trabajo ha sido financiado por la Fundación Séneca, Agencia Regional de Ciencia y Tecnología, a través del proyecto 00700/PPC/04