Paolo Paradisi - Academia.edu (original) (raw)

Papers by Paolo Paradisi

International Journal of Environment and Pollution, 2014

Back-trajectory techniques are extensively used to identify the most probable source locations, s... more Back-trajectory techniques are extensively used to identify the most probable source locations, starting from the known pollutants concentration data at some receptor sites. In this paper, we review the trajectory statistical methods (TSMs) that are most used in literature for source identification, which are essentially based on the concept of residence time (RT), and we introduce a novel statistical method. To validate this method, artificial receptor data at two receptor sites are derived from numerical simulations with a given aerial source, using the Lagrangian dispersion model (LSM) FLEXPART in forward mode. Then the RTs are computed using again the model FLEXPART, but in backward mode. Then, the new statistical methodology, which is based on the use of peak concentration events, is applied to reconstruct the spatial distribution of emission sources. Our approach requires simulation times shorter than those required in other methods and could overcome the problem of ghost sources.

Central European Journal of Physics, 2009

An approach to intermittent systems based on renewal processes is reviewed. The Waiting Times (WT... more An approach to intermittent systems based on renewal processes is reviewed. The Waiting Times (WTs) between events are the main variables of interest in intermittent systems. A crucial role is played by the class of critical events, characterized by Non-Poisson statistics and non-exponential WT distribution. A particular important case is given by WT distributions with power tail. Critical events play a crucial role in the behavior of a property known as Renewal Aging. Focusing on the role of critical events, the relation between superstatistics and non-homogeneous Poisson processes is discussed, and the role of Renewal Aging is illustrated by comparing a Non-Poisson model with a Poisson one, both of them modulated by a periodic forcing. It is shown that the analysis of Renewal Aging is sensitive to the presence of critical events and that this property can be exploited to detect Non-Poisson statistics in a time series. As a consequence, it is claimed that, apart from the characterization of superstatistical features such as the distribution of the intensive parameter or the separation of the time scales, the Renewal Aging property can give some effort to better determine the role of Non-Poisson critical events in intermittent systems.

Physica A: Statistical Mechanics and its Applications, 2002

We present a variety of models of random walk, discrete in space and time, suitable for simulatin... more We present a variety of models of random walk, discrete in space and time, suitable for simulating random variables whose probability density obeys a space-time fractional di usion equation.

A method of time series analysis based on the aging properties of renewal processes is introduced... more A method of time series analysis based on the aging properties of renewal processes is introduced. The method compute the amount of renewal aging in a time series. It is shown that the method allows to distinguish between systems with a renewal dynamics from those driven by slow modulation of the parameters. The application of the method to Blinking Quantum Dots shows a maximum of renewal aging. This excludes the possibility of interpreting the dynamics as a slow modulation process and indicates a possible modelling approach in the renewal perspective.

Frontiers in Physiology, 2010

Resting-state EEG signals undergo rapid transition processes (RTPs) that glue otherwise stationar... more Resting-state EEG signals undergo rapid transition processes (RTPs) that glue otherwise stationary epochs. We study the fractal properties of RTPs in space and time, supporting the hypothesis that the brain works at a critical state. We discuss how the global intermittent dynamics of collective excitations is linked to mentation, namely non-constrained non-taskoriented mental activity.

Complexus Mundi - Emergent Patterns in Nature, 2006

Reports on Mathematical Physics, 2012

Scaling laws for the diffusion generated by three different random walk models are reviewed. The ... more Scaling laws for the diffusion generated by three different random walk models are reviewed. The random walks, defined on a one-dimensional lattice, are driven by renewal intermittent events with non-Poisson statistics and inverse power-law tail in the distribution of the inter-event or waiting times, so that the event sequences are characterized by self-similarity. Intermittency is a ubiquitous phenomenon in many complex systems and the power exponent of the waiting time distribution, denoted as complexity index, is a crucial parameter characterizing the system's complexity. It is shown that different scaling exponents emerge from the different random walks, even if the self-similarity, i.e. the complexity index, of the underlying event sequence remains the same. The direct evaluation of the complexity index from the time distribution is affected by the presence of added noise and secondary or spurious events. It is possible to minimize the effect of spurious events by exploiting the scaling relationships of the random walk models. This allows to get a reliable estimation of the complexity index and, at the same time, a confirmation of the renewal assumption. An application to turbulence data is shown to explain the basic ideas of this approach.

Physics of Life Reviews, 2013

Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 2001

... Pergamon PII: S14641909(01)000065 Phys ... In particular, y,l being the maximum point of pa, ... more ... Pergamon PII: S14641909(01)000065 Phys ... In particular, y,l being the maximum point of pa, it turns out that &quot;, 0 (A1) if B Oand ,,=OifB=0. where DB is the symbol of the Feller operator Do: References D =IrIae2(signtc)B7r 2 The explicit expression of Do, acting on a function (z), in ...

Physical review. E, Statistical, nonlinear, and soft matter physics, 2006

We consider two different approaches, to which we refer to as renewal and modulation, to generate... more We consider two different approaches, to which we refer to as renewal and modulation, to generate time series with a nonexponential distribution of waiting times. We show that different time series with the same waiting time distribution are not necessarily statistically equivalent, and might generate different physical properties. Renewal generates aging and anomalous scaling, while modulation yields no significant aging and either ordinary or anomalous diffusion, according to the dynamic prescription adopted. We show, in fact, that the physical realization of modulation generates two classes of events. The events of the first class are determined by the persistent use of the same exponential time scale for an extended lapse of time, and consequently are numerous; the events of the second class are identified with the abrupt changes from one to another exponential prescription, and consequently are rare. The events of the second class, although rare, determine the scaling of the di...

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2009

We study the electroencephalogram ͑EEG͒ of 30 closed-eye awake subjects with a technique of analy... more We study the electroencephalogram ͑EEG͒ of 30 closed-eye awake subjects with a technique of analysis recently proposed to detect punctual events signaling rapid transitions between different metastable states. After single-EEG-channel event detection, we study global properties of events simultaneously occurring among two or more electrodes termed coincidences. We convert the coincidences into a diffusion process with three distinct rules that can yield the same only in the case where the coincidences are driven by a renewal process. We establish that the time interval between two consecutive renewal events driving the coincidences has a waiting-time distribution with inverse power-law index Ϸ 2 corresponding to ideal 1 / f noise. We argue that this discovery, shared by all subjects of our study, supports the conviction that 1 / f noise is an optimal communication channel for complex networks as in art or language and may therefore be the channel through which the brain influences complex processes and is influenced by them.

$Research paper thumbnail of The fractional Fick's law for non-local transport processes$

Physica A: Statistical Mechanics and its Applications, 2001

Fick's law is extensively adopted as a model for standard di usion processes. However, requiring ... more Fick's law is extensively adopted as a model for standard di usion processes. However, requiring separation of scales, it is not suitable for describing non-local transport processes. We discuss a generalized non-local Fick's law derived from the space-fractional di usion equation generating the LÃ evy-Feller statistics. This means that the fundamental solutions can be interpreted as LÃ evy stable probability densities (in the Feller parameterization) with index (1 ¡ 62) and skewness Â (|Â|62 − ). We explore the possibility of deÿning an equivalent local di usivity by displaying a few numerical case studies concerning the relevant quantities ( ux and gradient). It turns out that the presence of asymmetry (Â = 0) plays a fundamental role: it produces shift of the maximum location of the probability density function and gives raise to phenomena of counter-gradient transport.

Physica A: Statistical Mechanics and its Applications, 2006

We study the effects of an external periodic perturbation on a Poisson rate process, with special... more We study the effects of an external periodic perturbation on a Poisson rate process, with special attention to the perturbation-induced sojourn-time patterns. We show that these patterns correspond to turning a memory-less sequence into a sequence with memory. The memory effects are stronger the slower the perturbation. The adoption of a de-trending technique, applied with no caution, might generate the

Nonlinear Processes in Geophysics, 2012

We investigate the time intermittency of turbulent transport associated with the birth-death of s... more We investigate the time intermittency of turbulent transport associated with the birth-death of self-organized coherent structures in the atmospheric boundary layer. We apply a threshold analysis on the increments of turbulent fluctuations to extract sequences of rapid acceleration events, which is a marker of the transition between self-organized structures.

Journal of Statistical Mechanics: Theory and Experiment, 2009

Thus, an analysis based on the WT histogram and/or on scaling methods has to be considered with s... more Thus, an analysis based on the WT histogram and/or on scaling methods has to be considered with some care when dealing with perturbed intermittent systems.

Journal of Physics: Conference Series, 2011

We study the superposition of a non-Poisson renewal process with the presence of a superimposed P... more We study the superposition of a non-Poisson renewal process with the presence of a superimposed Poisson noise. The non-Poisson renewals mark the passage between metastable states in system with self-organization. We propose methods to measure the amount of information due to the two independent processes independently, and we see that a superficial study based on the survival probabilities yield stretched-exponential relaxations. Our method is in fact able to unravel the inverse-power law relaxation of the isolated non-Poisson processes, even when noise is present. We provide examples of this behavior in system of diverse nature, from blinking nano-crystals to weak turbulence. Finally we focus our discussion on events extracted from human electroencephalograms, and we discuss their connection with emerging properties of integrated neural dynamics, i.e. consciousness.