98 research outputs found
Cyclic Fluctuations, Climatic Changes and Role of Noise in Planktonic Foraminifera in the Mediterranean Sea
The study of Planktonic Foraminifera abundances permits to obtain climatic
curves on the basis of percentage ratio between tropical and temperate/polar
forms. Climatic changes were controlled by several phenomena as: (i)
Milankovitch's cycles, produced by variations of astronomical parameters such
as precession, obliquity and eccentricity; (ii) continental geodynamic
evolution and orogenic belt; (iii) variations of atmospheric and oceanic
currents; (iv) volcanic eruptions; (v) meteor impacts. But while astronomical
parameters have a quasi-regular periodicity, the other phenomena can be
considered as "noise signal" in natural systems. The interplay between cyclical
astronomical variations, the "noise signal" and the intrinsic nonlinearity of
the ecologic system produces strong glacial or interglacial period according to
the stochastic resonance phenomenon.Comment: 6 pages, 4 figure
Environmental Noise and Nonlinear Relaxation in Biological Systems
We analyse the effects of environmental noise in three different biological
systems: (i) mating behaviour of individuals of \emph{Nezara viridula} (L.)
(Heteroptera Pentatomidae); (ii) polymer translocation in crowded solution;
(iii) an ecosystem described by a Verhulst model with a multiplicative L\'{e}vy
noise.Comment: 32 pages; In "Ecological Modeling" by Ed. Wen-Jun Zhang. ISBN:
978-1-61324-567-5. - Nova Science Publishers, New York, 201
Exploring the protective function of positivity and regulatory emotional self-efficacy in time of pandemic covid-19
Despite several empirical studies on the 2019 coronavirus disease (COVID-19) pandemic that have highlighted its detrimental effect on individuals’ mental health, the identification of psychological factors that may moderate its impact on individuals’ behavior and well-being remains partly unexplored. The present study was conceived to examine the mediation role of regulatory emotional self-efficacy in the relationship between positivity and anxiety, depression, and perceived self-efficacy in complying with the containment measures to contrast the COVID-19 spread. Furthermore, the moderation role of age was tested. A sample of 1258 participants (64.2% women; Mage = 42.09, SD = 13.62) enrolled from the Italian general population answered an online survey aimed at investigating the role of individual differences in facing the COVID-19 pandemic. We opted for a snowball recruiting procedure to find participants. The online survey was disseminated through email invitation and using social media platforms (i.e., Facebook, Instagram). A multi-group path analysis model was performed using Mplus 8.4 to explore the hypothesized relations among variables. The following criteria were employed to evaluate the goodness of fit: χ2 likelihood ratio statistic, CFI and TLI > 0.95, RMSEA < 0.06 and SRMR < 0.08. The findings corroborated the protective role of both positivity and regulatory emotional self-efficacy in reducing individuals’ anxiety and depressive symptoms, as well as in fostering individuals’ capabilities in complying with the containment measures imposed by the government to reduce the risk of illness and to contain the spread of the virus COVID-19. Specifically, regulatory emotional self-efficacy beliefs partially mediated the relations between positivity and anxiety and depressive symptoms and fully mediated the effect of positivity on perceived self-efficacy beliefs in complying with the containment measures. These paths were equal across ages. The results of the present study appear relevant to implementing psychological interventions aimed to reduce the deleterious effects of the COVID-19 pandemic on mental health through the promotion of individuals’ optimistic orientation and emotion regulation
Gestione sostenibile delle foreste Mediterranee e uso energetico delle biomasse forestali residuali
he book describes the reasons that led the Regional Department of Rural and Territorial Development to take part in the PROFORBIOMED Project. They can be summarized by the need to dispose of a tool for the sustainable management of all the state-owned forests of the Region. As a matter of fact, the Project aims at developing a model of sustainable forest management, through the recovery and reuse of wood scraps from ordinary
silvicultural operations, to be used for the production of power and heat inside of a process adopting natural renewable energy sources.
The main actions taken and the methodologies adopted are described, as well as the principles and instruments required for the setting up and execution of the work. Some of the most relevant are: the drafting of “Forest Management Plans”, the “Short Supply Chain” and the “Biomass Traceability Protocol”, together with the application of “Best Practices” of Management and the “Monitoring of impacts” caused by the woody biomass extraction procedures.
The “forest – wood – energy” chain developed and proposed is exclusively related to the territory pertaining to one municipality, and with CHP plants fed with biomass exclusively produced within the territory of each municipality, in strict compliance with the “sustainable forest management” principles, as well as with the fundamental principle of “short supply chain”. For these reasons the CHP plans proposed shall be sized according to the biomass available in each municipality, with the possibility of integrating residual forest biomass with other waste wood resources potentially available in the territory and coming from prunings in agricultural activities.
Therefore, the replicable model prepared and proposed by PROFORBIOMED aims at appraising from the economic point of view a waste product, such is currently considered the residual forest biomass from the forests of Sicily, and at the same time significantly improving the natural environment, thanks to the reduction in oil consumption
Noise delayed decay of unstable states: theory versus numerical simulations
We study the noise delayed decay of unstable nonequilibrium states in
nonlinear dynamical systems within the framework of the overdamped Brownian
motion model. We give the exact expressions for the decay times of unstable
states for polynomial potential profiles and obtain nonmonotonic behavior of
the decay times as a function of the noise intensity for the unstable
nonequilibrium states. The analytical results are compared with numerical
simulations.Comment: 9 pages, 6 figures, in press in J. Phys.
Active Brownian Motion Models and Applications to Ratchets
We give an overview over recent studies on the model of Active Brownian
Motion (ABM) coupled to reservoirs providing free energy which may be converted
into kinetic energy of motion. First, we present an introduction to a general
concept of active Brownian particles which are capable to take up energy from
the source and transform part of it in order to perform various activities. In
the second part of our presentation we consider applications of ABM to ratchet
systems with different forms of differentiable potentials. Both analytical and
numerical evaluations are discussed for three cases of sinusoidal,
staircase-like and Mateos ratchet potentials, also with the additional loads
modeled by tilted potential structure. In addition, stochastic character of the
kinetics is investigated by considering perturbation by Gaussian white noise
which is shown to be responsible for driving the directionality of the
asymptotic flux in the ratchet. This \textit{stochastically driven
directionality} effect is visualized as a strong nonmonotonic dependence of the
statistics of the right versus left trajectories of motion leading to a net
current of particles. Possible applications of the ratchet systems to molecular
motors are also briefly discussedComment: 12 pages, 17 figure
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
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