Search results for "stochastic"
showing 10 items of 1018 documents
Predator population depending on lemming cycles
2016
In this paper, a Langevin equation for predator population with multiplicative correlated noise is analyzed. The noise source, which is a nonnegative random pulse noise with regulated periodicity, corresponds to the prey population cycling. The increase of periodicity of noise affects the average predator density at the stationary state.
Stochastic dynamics and mean field approach in a system of three interacting species
2008
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. Afterwar…
DOSE DEPENDENT SURVIVAL RESPONSE IN CHRONIC MYELOID LEUKEMIA UNDER CONTINUOUS AND PULSED TARGETED THERAPY
2010
A simulative study of cancer growth dynamics in patients affected by Chronic Myeloid Leukemia (CML), under the effect of a targeted dosedependent continuous or pulsed therapy, is presented. We have developed a model for the dynamics of CML in which thestochastic evolution of white blood cell populations are simulated by adopting a Monte Carlo approach. Several scenarios in the evolutionary dynamics of white blood cells, as a consequence of the efficacy of the different modelled therapies, pulsed or continuous, are described. The best results, in terms of a permanent disappearance of the leukemic phenotype, are achieved with a continuous therapy and higher dosage. However, our findings demon…
Role of the colored noise in a FitzHugh-Nagumo system driven by a periodic signal
2007
During these last years the interest in neuronal dynamics increased. The study of this kind of system has been carried out by using the FitzHugh-Nagumo (FHN) model that is a simplified modification of the Hodgkin-Huxley model. Many interesting phenomena can be observed in the presence of fluctuations: modification of detection threshold by manipulation of noisy parameters (FHN model), noise-induced activation and coeherence resonance for suitable noise amplitude (absence of periodic signal), resonant activation for high periodic signals and noise reduction, intrinsic stochastic resonance (ISR) in Hodgkin-Huxley neuron and the enhancement of a weak signal by tuning the subthreshold intrinsic…
Non-linear Correlation Coefficients for pushover analysis
2013
Aiming to put forward an improvement on Multimodal Pushover Analysis, a modified version of the modal correlation rule that takes into account the non-linear behavior of structures is proposed. The modification is primarily based on using the correlation coefficients consistent with the mechanical and dynamical properties of the hysteretic oscillators utilized in the MPA method, i.e. determined taking into account the second order statistics pertinent to the non-linear oscillators. Initially, the new correlation coefficients are evaluated by Monte Carlo Simulations (MCS), assuming a spectrum-compatible representation of the seismic input. The results of a large numerical parametric analysis…
Modeling of spanish household electrical consumptions: Simplified and detailed stochastic approach in trnsys environment
2013
The initial assessment of electric energy demands of a building is a key element in the design process, that should be integrated in the earlier stages of the design of a net zero energy building. The objective of the study is the creation of predictive models of household electrical consumptions in the Mediterranean/Spanish climate and its implementation in TRNSYS 17 environment. The models offer both a simplified level of analysis, based on average seasonal electrical consumptions trends and a stochastic in-depth level for the simulation of peak loads through the compiling of multiple TRNSYS types.
Constrained Robust MultiObjective Optimization for Reactive Design in Distribution Systems
2006
This paper presents a new formulation including robustness of solution of constrained multiobjective design or reactive power compensation. The algorithm used for optimization is the NSGA-II (Non dominated Sorting Genetic Algorithm II) with a special crowded comparison operator for constraints handling. The need for including the issue of robustness of solutions derives from the simple observation that loads are uncertain in distribution systems and their estimation is often affected by errors. In design problems it is desirable to consider the loads with a certain range of variation. In this paper the NSGA-II algorithm is applied to efficiently solve the issue and the solutions attained co…
A New Meta-Heuristic Multi-Objective Approach For Optimal Dispatch of Dispersed and Renewable Generating Units in Power Distribution Systems
2011
The application of stochastic methods in engineering research and optimization has been increasing over the past few decades. Ant Colony Optimization, in particular, has been attracting growing attention as a promising approach both in discrete and continuous domains. The present work proposes a multi-objective Ant Colony Optimization for continuous domains showing good convergence properties and uniform coverage of the non-dominated front. These properties have been proved both with mathematical test functions and with a complex real world problem. Besides the second part of the chapter presents the application of the new algorithm to the problem of optimal dispatch of dispersed power gene…
Texture Synthesis for Digital Restoration in the Bit-Plane Representation
2007
In this paper we propose a new approach to handle the problem of restoration of grayscale textured images. The purpose is to recovery missing data of a damaged area. The key point is to decompose an image in its bit-planes, and to process bits rather than pixels. We propose two texture synthesis methods for restoration. The first one is a random generation process, based on the conditional probability of bits in the bit-planes. It is designed for images with stochastic textures. The second one is a best-matching method, running on each bit-plane, that is well suited to synthesize periodic patterns. Results are compared with a state-of-the-art restoration algorithm.
Transfer Entropy Analysis of Pulse Arrival Time - Heart Period Interactions during Physiological Stress
2022
Although Heart Period (HP) variability is the most widely used measure to assess cardiovascular oscillations, its evaluation combined with that of Pulse Arrival Time (PAT) variability may provide additional information about cardiac dynamics and cardiovascular interactions. In this study, we computed the transfer entropy from PAT to HP in 76 subjects monitored at rest and during orthostatic and mental stress using both a model-free (k- Nearest Neighbors) and a linear parametric estimator. Our results show how the information flow between these two variables depends on the physiological condition and how the nonlinear measure captures more information than the linear one during orthostatic s…