Active Brownian Particles. From Individual to Collective Stochastic Dynamics

We review theoretical models of individual motility as well as collective dynamics and pattern formation of active particles. We focus on simple models of active dynamics with a particular emphasis on nonlinear and stochastic dynamics of such self-propelled entities in the framework of statistical mechanics. Examples of such active units in complex physico-chemical and biological systems are chemically powered nano-rods, localized patterns in reaction-diffusion system, motile cells or macroscopic animals. Based on the description of individual motion of point-like active particles by stochastic differential equations, we discuss different velocity-dependent friction functions, the impact of various types of fluctuations and calculate characteristic observables such as stationary velocity distributions or diffusion coefficients. Finally, we consider not only the free and confined individual active dynamics but also different types of interaction between active particles. The resulting collective dynamical behavior of large assemblies and aggregates of active units is discussed and an overview over some recent results on spatiotemporal pattern formation in such systems is given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte

Ecological Complex Systems

Main aim of this topical issue is to report recent advances in noisy nonequilibrium processes useful to describe the dynamics of ecological systems and to address the mechanisms of spatio-temporal pattern formation in ecology both from the experimental and theoretical points of view. This is in order to understand the dynamical behaviour of ecological complex systems through the interplay between nonlinearity, noise, random and periodic environmental interactions. Discovering the microscopic rules and the local interactions which lead to the emergence of specific global patterns or global dynamical behaviour and the noises role in the nonlinear dynamics is an important, key aspect to understand and then to model ecological complex systems.Comment: 13 pages, Editorial of a topical issue on Ecological Complex System to appear in EPJ B, Vol. 65 (2008

Evolutionary dynamics of imatinib-treated leukemic cells by stochastic approach

The evolutionary dynamics of a system of cancerous cells in a model of chronic myeloid leukemia (CML) is investigated by a statistical approach. Cancer progression is explored by applying a Monte Carlo method to simulate the stochastic behavior of cell reproduction and death in a population of blood cells which can experience genetic mutations. In CML front line therapy is represented by the tyrosine kinase inhibitor imatinib which strongly affects the reproduction of leukemic cells only. In this work, we analyze the effects of a targeted therapy on the evolutionary dynamics of normal, first-mutant and cancerous cell populations. Several scenarios of the evolutionary dynamics of imatinib-treated leukemic cells are described as a consequence of the efficacy of the different modeled therapies. We show how the patient response to the therapy changes when an high value of the mutation rate from healthy to cancerous cells is present. Our results are in agreement with clinical observations. Unfortunately, development of resistance to imatinib is observed in a proportion of patients, whose blood cells are characterized by an increasing number of genetic alterations. We find that the occurrence of resistance to the therapy can be related to a progressive increase of deleterious mutations.Comment: Submitted to Central European Journal of Physic

Stochastic dynamics and mean field approach in a system of three interacting species

The spatio-temporal dynamics of three interacting species, two preys and one predator, in the presence of two different kinds of noise sources is studied. To describe the spatial distributions of the species we use a model based on Lotka-Volterra equations. A correlated dichotomous noise acts on \beta, the interaction parameter between the two preys, and a multiplicative white noise affects directly the dynamics of each one of the three species. We study the time behaviour of the three species in single site for different values of the multiplicative noise intensity, finding noise-induced oscillations of the three species densities with an anticorrelated behaviour of the two preys. Afterwards, by considering a spatially extended system formed by a two-dimensional lattice with N sites and applying a mean field approach, we get the corresponding moment equations in Gaussian approximation. Within this formalism we obtain the time behaviour of the first and second order moments for different values of multiplicative noise intensity, with \beta(t) subject to the same dichotomous noise source. Finally, we compare our results with those obtained by using a coupled map lattice model, consisting of a time discrete version of the Lotka-Volterra equations.Comment: 21 pages, 7 figures. Submitted to Centr. Eur. J. Phy

Evidence of stochastic resonance in the mating behavior of Nezara viridula (L.)

We investigate the role of the noise in the mating behavior between individuals of Nezara viridula (L.), by analyzing the temporal and spectral features of the non-pulsed type female calling song emitted by single individuals. We have measured the threshold level for the signal detection, by performing experiments with the calling signal at different intensities and analyzing the insect response by directionality tests performed on a group of male individuals. By using a sub-threshold signal and an acoustic Gaussian noise source, we have investigated the insect response for different levels of noise, finding behavioral activation for suitable noise intensities. In particular, the percentage of insects which react to the sub-threshold signal, shows a non-monotonic behavior, characterized by the presence of a maximum, for increasing levels of the noise intensity. This constructive interplay between external noise and calling signal is the signature of the non-dynamical stochastic resonance phenomenon. Finally, we describe the behavioral activation statistics by a soft threshold model which shows stochastic resonance. We find that the maximum of the ensemble average of the input-output cross-correlation occurs at a value of the noise intensity very close to that for which the behavioral response has a maximum.Comment: 6 pages, 4 figures, to appear in EPJ B (2008

Thermal and inertial resonances in DNA unzipping

Single-molecule experiments combined with alternate forces are able to provide useful information not present in standard constant-force and -velocity pulling protocols. Here, we study the effects of such forces in the DNA mechanical unzipping by using an extension of the Peyrard-Bishop-Dauxois model. By changing the damping regime in the dynamical equations, we obtained two resonant mechanisms in both the mean time and the mean force of unzipping. One is thermally assisted and it is characterized by a matching between the period of the external force and the mean unzipping time of the DNA chain, while the other depends on the inertial properties of the system. Both mechanisms are studied systematically under different opening protocols and different parameters of the system. The main results here presented contribute in characterizing and finding optimized conditions in DNA unzipping experiments

Exposure to neighborhood danger and adolescents’ externalizing behavior problems: The protective role of parental self-efficacy

Adolescence represents a critical period for the development of externalizing behavior problems (EXT; Loeber & Hay, 1997; Moffitt, 1993). Several factors are responsible for the vulnerability of adolescents to EXT, including temperamental and environmental characteristics. Regarding the latter, several studies has shown that the exposure to neighbourhood violence is associated to adolescents’ EXT (Gorman-Smith & Tolan, 1998; Scarpa, 2001). While most studies have documented this relation in samples from the United States, little research is available in the Italian context. One example, Bacchini et al. (2001) in a sample of 489 adolescents in Naples, found that high levels of community violence were associated to antisocial behaviors. In the present study, we examined whether mothers’ perceptions of neighborhood danger are related to adolescents’ EXT and whether maternal perceived self-efficacy in controlling high risk behaviors (MPSE-Risk) moderates this relation. Based on previous studies that have shown that MPSE-Risk significantly reduce adolescents’ EXT (Ceravolo, 2014; Mahabee-Gittens et al., 2011) and on Bandura (1997)’s conceptualization of parental self-efficacy as beliefs in their own caregiving capabilities as well as in managing challenging familial demands, we hypothesized that MPSE-Risk operate as a protective factor especially in challenging circumstances, such as living in a dangerous neighbourhood. Altogether, 100 mothers from Rome and 95 mothers from Naples provided data (Mage of mother = 44.01 years; SD= 5.43; Mage of child =13.18 years, SD=0.66; 50,3% boys). Mother reported measures were used to asses MPSE-Risk, Exposure to neighborhood danger and adolescents’ EXT. Hierarchical linear regressions were conducted to examine the effect of gender, socioeconomic status, MPSE-Risk and their interaction on EXT. Results showed that MPSE-Risk buffered the detrimental effect of the exposure to a neighborhood perceived as dangerous on EXT, representing a protective factor against the development of EXT especially in dangerous neighbourhood. Implications for further research are discussed

Perception of school climate, academic performance and risk behaviors in adolescence

Previous studies support the relevance of students’ perception of positive and negative school climate to learning processes and adolescents’ adjustment. School climate is affected by both the interactions that are established within the classroom, and by the teachers’ behaviors. This study has the overall objective of investigating the relationship between the perception of positive and negative school climate and students’ (mal)adjustment during adolescence. Participants were 105 Italian adolescents (52.5% boys, mean age = 15.56, SD = .77) who responded for 15 consecutive days (ecological momentary assessment) to questions related to their perception of positive and negative school climate (Time 1). After one year (Time 2), students’ academic performance reported by mothers and fathers and adolescents’ self-reported propensity to engage in risk behaviors were examined. Four hierarchical regression models were implemented considering the mean and the instability levels (RMSSD) of the perception of positive and negative school climate as independent variables and, respectively, academic performance and risk behaviors as dependent variables. Results suggest that a higher perception of positive school climate and its instability predict higher academic performance one year later, while a higher perception of negative school climate and its instability predict higher risk behaviors. This study provides an innovative perspective to reflect on the relationship between students’ perceptions of school climate and adolescents’ (mal)adjustment

Exposure to neighborhood danger and adolescents’ externalizing behavior problems: The protective role of parental self-efficacy.

Adolescence represents a critical period for the development of externalizing behavior problems (EXT; Loeber & Hay, 1997; Moffitt, 1993). Several factors are responsible for the vulnerability of adolescents to EXT, including temperamental and environmental characteristics. Regarding the latter, several studies has shown that the exposure to neighbourhood violence is associated to adolescents’ EXT (Gorman-Smith & Tolan, 1998; Scarpa, 2001). While most studies have documented this relation in samples from the United States, little research is available in the Italian context. One example, Bacchini et al. (2001) in a sample of 489 adolescents in Naples, found that high levels of community violence were associated to antisocial behaviors. In the present study, we examined whether mothers’ perceptions of neighborhood danger are related to adolescents’ EXT and whether maternal perceived self-efficacy in controlling high risk behaviors (MPSE-Risk) moderates this relation. Based on previous studies that have shown that MPSE-Risk significantly reduce adolescents’ EXT (Ceravolo, 2014; Mahabee-Gittens et al., 2011) and on Bandura (1997)’s conceptualization of parental self-efficacy as beliefs in their own caregiving capabilities as well as in managing challenging familial demands, we hypothesized that MPSE-Risk operate as a protective factor especially in challenging circumstances, such as living in a dangerous neighbourhood. Altogether, 100 mothers from Rome and 95 mothers from Naples provided data (Mage of mother = 44.01 years; SD= 5.43; Mage of child =13.18 years, SD=0.66; 50,3% boys). Mother reported measures were used to asses MPSE-Risk, Exposure to neighborhood danger and adolescents’ EXT. Hierarchical linear regressions were conducted to examine the effect of gender, socioeconomic status, MPSE-Risk and their interaction on EXT. Results showed that MPSE-Risk buffered the detrimental effect of the exposure to a neighborhood perceived as dangerous on EXT, representing a protective factor against the development of EXT especially in dangerous neighbourhood. Implications for further research are discussed

Anger, Sadness, Anxiety, Happiness, and Self-Efficacy Beliefs about Emotion Regulation: A Mobile Ecological Momentary Assessment with Italian Adolescents

Previous studies suggest that the association between emotion regulation and adolescent adjustment may depend on the type of emotion being managed (Feng et al., 2009), on the extent to which adolescents feel capable of modulating their emotional experiences (Bandura et al., 2003), and on the level of instability of the emotional experience (Maciejewski et al., 2015). In the present study we examined (1) how reciprocal associations between anger, anxiety, sadness, and happiness, and selfefficacy in managing such emotions differed between adolescents throughout their daily lives; and (2) how daily fluctuations in emotional experiences and self-efficacy regulating emotions affected one another. This study included 103 Italian adolescents (53% males; Mage = 16.77, SD = .78). Data were gathered with a mobile ecological momentary assessment. For 15 days, adolescents were prompted via mobile-phones to respond to questions about whether they were feeling angry, sad, anxious, and happy, and how much they believed they were capable of regulating that emotion in that moment (Bandura et al., 2003). Adolescents experienced all examined emotions at low to moderate levels across the study period. Overall, adolescents with higher self-efficacy managing anger, sadness, and anxiety had lower overall anger, sadness, and anxiety, whereas adolescents with high anger, sadness, and anxiety felt no self-efficacy over the entire 15-day period. Teens with higher overall levels of selfefficacy managing happiness experienced higher overall happiness, and teens with the lowest overall levels of happiness felt no self-efficacy in managing happiness. Moreover, if a teen felt higher than usual self-efficacy managing sadness or expressing happiness on a typical day, they also felt less sadness and more happiness than usual on that day, and vice-a-versa. This study contributes to clarify the importance of emotion specificity and of self-efficacy about emotion regulation when clarifying the role of emotion regulation over adolescent adjustment