Time filter

Source Type

Agapie A.,Academy of Economic Studies Bucharest | Agapie A.,Institute of Mathematical Statistics and Applied Mathematics
Physica A: Statistical Mechanics and its Applications | Year: 2010

3D cellular automata can be analyzed by means of finite homogeneous Markov chains. If the automaton is allowed to change only one cell per iteration, and the transition probability depends linearly on the number of ones in the neighborhood, the Markov chain has two attractors at all zeroes and all ones. Otherwise-and this is the case we tackle-the chain is ergodic, thus allowing for the search of stationary distributions. This proves cumbersome in the general case, still, under detailed balance equation, the stationary distribution can be derived in closed form. The probability of a particular state is found to be exponential in the number of zero-one borders within the configuration. © 2010 Elsevier B.V. All rights reserved.


Agapie A.,Academy of Economic Studies Bucharest | Agapie A.,Institute of Mathematical Statistics and Applied Mathematics
International Journal of Computer Mathematics | Year: 2010

The evolutionary algorithms discussed in this paper do not use crossover, nor mutation. Instead, they estimate and evolve a marginal probability distribution, the only distribution responsible for generating new populations of chromosomes. So far, the analysis of this class of algorithms was confined to proportional selection and additive decomposable functions. Dropping both assumptions, we consider here truncation selection and non-separable problems with polynomial number of distinct fitness values. The emergent modelling is half theoretical - with respect to selection, completely characterized by stochastic calculus - and half empirical - concerning the generation of new individuals. For the latter operator, we sample the chromosomes arbitrarily, one for each selected level of fitness. That is the break-symmetry point, making the difference between the finite and infinite population cases, and ensuring the convergence of the model.


Radulescu M.,Institute of Mathematical Statistics and Applied Mathematics | Radulescu C.Z.,National Institute for Research and Development in Microtechnologies
Studies in Informatics and Control | Year: 2015

The paper presents a minimum risk model, inspired from the financial portfolio theory, for the selection of a software vendor. The performance of the software products offered by potential software vendors is evaluated by several experts regarding several criteria. The minimum risk model has several constraints. One of the constraints is a complementarity constraint. Other constraints are connected with the available budget and the expected performance of the software products. A procedure for solving the minimum risk model is presented and a numerical example is analyzed. © ICI Bucharest * 2010 - 2015.


Marinoschi G.,Institute of Mathematical Statistics and Applied Mathematics
AIP Conference Proceedings | Year: 2011

We consider a nonlinear diffusion parabolic equation with transport in which the coefficient of time derivative u vanishes on a subset of positive measure of the space domain. The aim of the paper is to identify this coefficient on the basis of known data for the solution. © 2011 American Institute of Physics.


Iannelli M.,University of Trento | Marinoschi G.,Institute of Mathematical Statistics and Applied Mathematics
Mathematical Methods in the Applied Sciences | Year: 2013

The basic linear model for describing an age structured population spreading in a limited habitat is considered with the purpose of investigating an approximation procedure based on parabolic regularization. In fact, a viscosity model is introduced by considering an appropriate approximating regularized parabolic problem and it is proved that the sequence of the approximating solutions tends to the solution to the original problem. The advantage of this approach is that it leads to the numerical solution of a parabolic problem that has more stable solutions than the hyperbolic-parabolic original problem and avoids the restrictions (compatibility conditions) needed to treat the latter. Moreover, for the solution of the approximating problem, it is possible to take advantage of established software packages dedicated to parabolic problems. Some examples of the approach are provided using COMSOL Multiphysics. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.


Popescu D.,Institute of Mathematical Statistics and Applied Mathematics
Proceedings of the Romanian Academy Series A - Mathematics Physics Technical Sciences Information Science | Year: 2010

I consider a great lipid vesicle filled with an aqueous solution of a solute, for which its membrane is impermeable. Because of the mechanical tension induced by the osmotic flow, the vesicle swells up to a critical size, triggering a transient lipidic pore when it is introduced into a hypotonic aqueous medium. In this paper, we will obtain the differential equations of the vesicle dynamics, which is in fact a periodic process due to osmotic gradient and transbilayer pore appearance. We will also analyse the characteristic parameters of this process: swelling time, pore lifetime, number of cycles, the length time of vesicle activity, material quantity leaked out during a cycle. In the end, we present the condition to design a n-cycles working vesicle and propose some biotechnological applications.


Gandolfi A.,CNR Institute of Neuroscience | Iannelli M.,University of Trento | Marinoschi G.,Institute of Mathematical Statistics and Applied Mathematics
Journal of Mathematical Biology | Year: 2011

We propose a model with age and space structure for the evolution of the supra-basal epidermis. The model includes different types of cells: proliferating cells, differentiated cells, corneous cells, and apoptotic cells. We assume that all cells move with the same velocity and that the local volume fraction, occupied by the cells is constant in space and time. This hypothesis, based on experimental evidence, allows us to determine a constitutive equation for the cell velocity. We focus on the stationary case of the problem, that takes the form of a quasi-linear evolution problem of first order, and we investigate conditions under which there is a solution. © 2010 Springer-Verlag.


Pelican E.,Ovidius University | Vernic R.,Ovidius University | Vernic R.,Institute of Mathematical Statistics and Applied Mathematics
International Journal of Computer Mathematics | Year: 2013

Used to model dependency in a multivariate setting with given marginals, Sarmanov's family of distributions creates difficulties when it comes to statistical inference. In this paper, we study maximum-likelihood procedures for estimating Sarmanov's distribution parameters for two different models: Under model I, we make use of a random data sample of volume m observed from an n-dimensional random vector, while model II consists of the first n dependent univariate random variables from a discrete-time stochastic process to which we try to fit Sarmanov's distribution starting from the corresponding n-tuple of observed values. To estimate some specific parameters, the use of the method of moments based on the covariance/correlation coefficient is also suggested. We illustrate these methods on simulated data and discuss the results. © 2013 Copyright Taylor and Francis Group, LLC.


Dumitrescu H.,Institute of Mathematical Statistics and Applied Mathematics | Cardos V.,Institute of Mathematical Statistics and Applied Mathematics
11th World Congress on Computational Mechanics, WCCM 2014, 5th European Conference on Computational Mechanics, ECCM 2014 and 6th European Conference on Computational Fluid Dynamics, ECFD 2014 | Year: 2014

In urban areas the wind is very turbulent and unstable with fast changes in direction and velocity. In these environments, the use of small vertical axis wind turbines (VAWT) becomes increasingly attractive due to several advantages over horizontal axis wind turbines (HAWT). However, such designs have received much less attention than the more common propeller-type designs and the understanding of same aspects of their operation remains, to this day, incomplete. This is particularly true of their starting characteristics. Indeed, same authors heuristically maintain that they cannot start without external assistance. This paper reviews the cause of the inability of the low solidity fixed pitch vertical axis wind turbines to self start, and investigates the way of overcoming this draw back.


Radulescu C.Z.,National Institute for Research and Development in Microtechnologies | Radulescu M.,Institute of Mathematical Statistics and Applied Mathematics
Studies in Informatics and Control | Year: 2012

In this paper is presented a decision support tool for crop planning under risk. The software tool is based on a portfolio selection model for crop planning. The portfolio selection model is a minimum financial risk model. It takes into account climate risk and market risk. The decision variable describes the land allocation to crops. The model was solved with the MINLP solver from GAMS. The decision support tool has an interface that facilitates the construction of the input data collection and the user parameters. It gives a flexible way of working and is mainly user oriented. Numerical results obtained with this Decision Support tool are analyzed.

Loading Institute of Mathematical Statistics and Applied Mathematics collaborators
Loading Institute of Mathematical Statistics and Applied Mathematics collaborators