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- Artículo de Publicación PeriódicaOptimal control of a batch bioreactor: a study on the use of an imperfect model(2001-12) Dondo, Rodolfo G.; Marqués, Dardo
Ver más "This paper presents a numerical study on the performance degradation of a batch bioreactor optimal control strategy when the model used to compute such strategy shows wide variations from the real process. The optimal control was computed using a model that, when exposed to large variations of the control inputs, presents large departures from real process behavior. An improved model based on published experiments was proposed. A new optimal policy was calculated and the behavior of this model when controlled with the earlier policy was studied. Although the earlier control showed a performance degradation with respect to the real optimal control, degradation was modest, and the results are superior to these obtained with other control strategies."Ver más - Artículo de Publicación PeriódicaAn inference engine based on fuzzy logic for uncertain and imprecise expert reasoning(2002-07) D'Aquila, Raimundo; Crespo Crespo, Cecilia; Mate, J. L.; Pazos, J.
Ver más "This paper addresses the development and computational implementation of an inference engine based on a full fuzzy logic, excluding only imprecise quantifiers, for handling uncertainty and imprecision in rule-based expert systems. The logical model exploits some connectives of Lukasiewicz’s infinite multi-valued logic and is mainly founded on the work of L.A. Zadeh and J.F. Baldwin. As it is oriented to expert systems, the inference engine was developed to be as knowledge domain independent as possible, while having satisfactory computational efficiency (...)."Ver más - Artículo de Publicación PeriódicaThe evolutionary minority game with local coordination(2003) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J.
Ver más "We discuss a modification of the evolutionary minority game (EMG) in which agents are placed in the nodes of a regular or a random graph. A neighborhood for each agent can thus be defined and a modification of the usual relaxation dynamics can be made in which each agent updates her decision depending upon her neighborhood. We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood. We find the surprising result that in the EMG a better coordination (a lower frustration) can be achieved if agents base their actions on local information disregarding the global trend in the self-segregation process."Ver más - Artículo de Publicación PeriódicaLearning and imitation: transitional dynamics in variants of the BAM(2004) Heymann, D.; Perazzo, Roberto P. J.; Schuschny, A. R.
Ver más "We study the dynamics of self-organized systems when disturbed by shocks. For this purpose, we consider extensions of the “Bar Attendance Model” [1] (BAM), which provides a stylized setting for the analysis of the emergence of coordination in the behavior of a large collection of agents. We represent the learning process of the agents through genetic algorithms, which respond to global (publicly available) information. In addition, we allow the actions of agents to be influenced by local information, as expressed in the behavior and performance of neighboring individuals. In the context of the BAM, we show that, in the event of a shock, the imitation behavior may become widespread and generate a contagion cascade which mimics a collective panic. We use this framework to represent features of the dynamics of an actual bank run."Ver más - Artículo de Publicación PeriódicaPerformance of non-fibre based dispersion compensation for long-haul 10.7 Gbit/s DWDM transmission(2004) Grosz, Diego; Maywar, D. N.; Küng, A. P.; Agarwal, A.; Banerjee, S.
Ver más "Non-fibre based in-line dispersion compensation is employed to achieve long-haul transmission of 80 channels at 10.7 Gbit=s bit rate over 1200 km of LEAF fibre. Average system margins of more than 4 dB and small transmission are demonstrated. The additional penalty incurred by the periodic nature of the dispersion compensator is assessed."Ver más - Artículo de Publicación PeriódicaDoubly periodic dispersion maps for 10 and 40 Gbit/s ultra-long-haul transmission(2004-09) Grosz, Diego; Banerjee, S.; Agarwal, A.; Küng, A. P.; Maywar, D. N.
Ver más "Optical transmission employing doubly periodic dispersion maps at 10 and 40 Gbit/s data rates is reported. The implications of these transmission results in providing added degrees of flexibility in network design, in particular, in applications such as optical add-drops and hybrid data rate systems, are discussed. "Ver más - Artículo de Publicación PeriódicaUncertainty relation for the optimization of optical-fiber transmission systems simulations(2005) Tolisano, T.; Callegari, Fulvio A.; Grosz, Diego; Fragnito, Hugo L.; Rieznik, Andrés
Ver más “The mathematical inequality which in quantum mechanics gives rise to the uncertainty principle between two non commuting operators is used to develop a spatial step-size selection algorithm for the Split-Step Fourier Method (SSFM) for solving Generalized Non-Linear Schrödinger Equations (G-NLSEs). Numerical experiments are performed to analyze the efficiency of the method in modeling optical-fiber communications systems, showing its advantages relative to other algorithms.”Ver más - Artículo de Publicación PeriódicaStochastic resonance and brownian ratchets(2005) Fendrik, Alejandro J.; Romanelli, Lilia; Perazzo, Roberto P. J.
Ver más "We discuss the connections between Brownian ratchets (BR) and stochastic resonance (SR). We consider a periodic potential energy landscape with no left–right symmetry that is driven by an external force which can be derived from a potential that is periodic both in time and space. We show that this system presents two thermal enhancements within two different windows of the temperature. One is associated with a ‘‘coherent diffusion’’ by which particles jump back and forth between the minima of the periodic potential in synchrony with the external driving. The other is instead associated with a ‘‘coherent directional transport’’ by which particles hop synchronically from one minimum of the ratchet to the next. We calculate the current and the diffusion coefficients and show how transport undergoes a resonant enhancement. While the former is always present, the second only appears when left–right symmetry is broken."Ver más - Artículo de Publicación PeriódicaOrder and disorder in the local evolutionary minority game(2005) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J.
Ver más "We study a modification of the Evolutionary Minority Game (EMG) in which agents are placed in the nodes of a regular or a random graph. A neighborhood for each agent can thus be defined and a modification of the usual relaxation dynamics can be made in which each agent updates her decision scheme depending upon the options made in her immediate neighborhood. We name this model the Local Evolutionary Minority Game (LEMG). We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood.We focus our discussion in a one-dimensional system and perform a detailed comparison of the results obtained from the random relaxation dynamics of the LEMG and from a linear chain of interacting spin-like variables with temperature. We provide a physical interpretation of the surprising result that in the LEMG a better coordination (a lower frustration) is achieved if agents base their actions on local information.We show how the LEMG can be regarded as a model that gradually interpolates between a fully ordered, antiferromagnetic-like system, and a fully disordered system that can be assimilated to a spin glass."Ver más - Artículo de Publicación PeriódicaUniform stability properties of switched systems with switchings governed by digraphs(2005-05) Mancilla-Aguilar, J. L.; García Galiñanes, Rafael; Sontag, E.; Wang, Y.
Ver más "Characterizations of various uniform stability properties of switched systems described by differential inclusions, and whose switchings are governed by a digraph, are developed. These characterizations are given in terms of stability properties of the system with restricted switchings and also in terms of Lyapunov functions."Ver más - Artículo de Publicación PeriódicaAn extension of LaSalle’s invariance principle for switched systems(2006) Mancilla-Aguilar, J. L.; García Galiñanes, Rafael
Ver más "This paper addresses invariance principles for a certain class of switched nonlinear systems. We provide an extension of LaSalle’s Invariance Principle for these systems and state asymptotic stability criteria. We also present some related results that deal with the compactness of the trajectories of these switched systems and that are interesting by their own."Ver más - Artículo de Publicación PeriódicaImpact of DCF properties on system design(2006) Essiambre, René-Jean; Winzer, Peter J.; Grosz, Diego
Ver más "The dispersion-compensating ﬁber is an important optical element of current and future optical networks. In this paper, we review the impact that various properties of dispersion-compensating ﬁbers has on the performance of optical communication systems."Ver más - Artículo de Publicación PeriódicaFoundations and applications for secure triggers(2006-02) Futoransky, Ariel; Kargieman, Emiliano; Sarraute, Carlos; Waissbein, Ariel
Ver más "Imagine there is certain content we want to maintain private until some particular event occurs, when we want to have it automatically disclosed. Suppose furthermore, that we want this done in a (possibly) malicious host. Say, the conﬁdential content is a piece of code belonging to a computer program that should remain ciphered and then “be triggered” (i.e., deciphered and executed) when the underlying system satisﬁes a preselected condition which must remain secret after code inspection. In this work we present diﬀerent solutions for problems of this sort, using diﬀerent “declassiﬁcation” criteria, based on a primitive we call secure triggers. We establish the notion of secure triggers in the universally-composable security framework of [Canetti 2001] and introduce several examples. Our examples demonstrate that a new sort of obfuscation is possible. Finally, we motivate its use with applications in realistic scenarios."Ver más - Artículo de Publicación PeriódicaPiet: a GIS-OLAP implementation(2007) Vaisman, Alejandro Ariel; Gómez, Leticia Irene; Kuijpers, Bart; Escribano, Ariel
Ver más "Data aggregation in Geographic Information Systems (GIS) is a desirable feature, although only marginally present in commercial systems, which also fail to provide integration between GIS and OLAP (On Line Analytical Processing). With this in mind, we have developed Piet, a system that makes use of a novel query processing technique: first, a process called sub-polygonization decomposes each thematic layer in a GIS, into open convex polygons; then, another process computes and stores in a database the overlay of those layers for later use by a query processor. We describe the implementation of Piet, and provide experimental evidence that overlay precomputation can outperform GIS systems that employ indexing schemes based on R-trees."Ver más - Artículo de Publicación PeriódicaWhy nestedness in mutualistic networks?(2007) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J.; Devoto, Mariano; Medan, Diego; Zimmermann, Martín; Delbue, Ana María
Ver más "We investigate the relationship between the nested organization of mutualistic systems and their robustness against the extinction of species. We establish that a nested pattern of contacts is the best possible one as far as robustness is concerned, but only when the least linked species have the greater probability of becoming extinct. We introduce a coefficient that provides a quantitative measure of the robustness of a mutualistic system."Ver más - Artículo de Publicación PeriódicaTwo classes of bipartite networks: nested biological and social systems(2008) Burgos, Enrique; Ceva, Horacio; Hernández, Laura; Perazzo, Roberto P. J.; Devoto, Mariano; Medan, Diego
Ver más "Bipartite graphs have received some attention in the study of social networks and of biological mutualistic systems. A generalization of a previous model is presented, that evolves the topology of the graph in order to optimally account for a given Contact Preference Rule between the two guilds of the network. As a result, social and biological graphs are classified as belonging to two clearly different classes. Projected graphs, linking the agents of only one guild, are obtained from the original bipartite graph. The corresponding evolution of its statistical properties is also studied. An example of a biological mutualistic network is analyzed in detail, and it is found that the model provides a very good fitting of all the main statistical features. The model also provides a proper qualitative description of the same features observed in social webs, suggesting the possible reasons underlying the difference in the organization of these two kinds of bipartite networks."Ver más - Artículo de Publicación PeriódicaMicrofluidic device concept based on microoscillator dynamics at a liquid–liquid interface(2008) Allievi, Alejandro
Ver más "Oscillating microbeams and microplates have been used extensively as sensing components for property detection in fluids. In liquids, their quality factor Q is drastically decreased, thus affecting a microsensor’s resolution. To improve the Q-factor, we present a novel concept based on the positive use of surface tension on a mechanical oscillator composed of a microbeam–microplate assembly suspended at a liquid–liquid interface in a microfluidic channel. An analytical model is developed to investigate rotational dynamics of such an assembly..."Ver más - Artículo de Publicación PeriódicaCausality study and numerical response of the magnetic permeability as a function of the frequency of ferrites using Kramers–Kronig relations(2008) Fano, Walter Gustavo; Boggi, Silvina; Razzitte, Adrián C.
Ver más "In this paper, the numerical treatment of magnetic loss of NiZn, MnZn, Ni2Y, and NiZnCu ferrite and their composites, by using Krameres–Kronig relations, is investigated. The complex magnetic permeability spectra for ferromagnetic materials have been studied. Due to the principle of causality and time independence in the relation between magnetic induction B and magnetic field H, the real and the imaginary part of the complex magnetic permeability are mutually dependent, and the correlation is given by the Krameres–Kronig equations. Through them, it is possible to measure the real component of the complex magnetic permeability, assuming the real component is given, and by the Hilbert transform, the imaginary part of the magnetic permeability can be calculated. Magnetic circuit model has been studied theoretically, focusing on the model’s poles in the complex plane to verify the principle of causality and the temporary independence."Ver más - Artículo de Publicación PeriódicaTime delay properties of stochastics-resonance information transmission line(2008) Ibáñez, Santiago Agustín; Fendrik, Alejandro J.; Fierens, Pablo Ignacio; Grosz, Diego; Perazzo, Roberto P. J.
Ver más "In this paper we analyze the properties of a chain of forward-coupled bi-stable over-damped oscillators. It is well known that this system displays stochastic resonance and behaves as a transmission line when an adequate amount of noise is added to each oscillator, and the first oscillator is driven by a periodic (sine) modulating signal. By driving the first oscillator with a modulated sequence of random non-return-to-zero (NRZ) bits, we start by showing that the system exhibits a stochastic-resonance behavior. Then we show that bit delays can be adjusted by either changing the amount of noise and/or the coupling intensity between adjacent oscillators. We find that the system can be regarded as a tunable delay line for a broad range of noise and coupling parameters, a feature that may find applications in information processing and bit regeneration."Ver más - Artículo de Publicación PeriódicaDiseño de observadores en modos cuasi-deslizantes vía LMIs(2008-07) Fraguío, Alberto Javier; Mancilla-Aguilar, J. L.; Zanini, Aníbal
Ver más "En este trabajo se presenta un observador robusto por modos cuasi-deslizantes para plantas con modelo nominal lineal e incertidumbres/pertubaciones de cierta clase particular. Las señales utilizadas para la estimación del vector de estados se suponen contaminadas con ruido del que sólo se conocen cotas. El diseño del observador se plantea como un problema de factibilidad LMI (Linear Matrix Inequalities) y se encuentran cotas para el error de estimación que pueden ser calculadas a priori. Posteriormente el diseño del observador se reformula como un problema de optimización GEVP (Generalized Eigen Value Problem) con el objeto de minimizar las cotas del error de estimación. El trabajo incluye un ejemplo numérico y simulaciones de un brazo robótico con un eje manejado por un motor de corriente continua."Ver más