Descripción: In this note we give some remarks and improvements on our recent paper [5] about an optimization problem for the p-Laplace operator that were motivated by some discussion that we had with Prof. Cianchi. © 2009 Elsevier Ltd. All rights reserved.

Descripción: Fil:Marenco, J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: In this paper we study the optimization problem for the first eigenvalue of the p-Laplacian plus a potential V with respect to V, when the potential is restricted to a bounded, closed and convex Bet of Lq(Ω).

Descripción: We present a new positive lower bound for the minimum value taken by a polynomial P with integer coefficients in k variables over the standard simplex of Rk, assuming that P is positive on the simplex. This bound depends only on the number of variables k, the degree d and the bitsize τ of the coefficients of P and improves all the previous bounds for arbitrary polynomials which are positive over the simplex. © 2010 Elsevier Ltd. All rights reserved.

Descripción: We consider the optimization problem of minimizing ∫Ω G (| ∇ u |) d x in the class of functions W1, G (Ω), with a constraint on the volume of {u > 0}. The conditions on the function G allow for a different behavior at 0 and at ∞. We consider a penalization problem, and we prove that for small values of the penalization parameter, the constrained volume is attained. In this way we prove that every solution u is locally Lipschitz continuous and that the free boundary, ∂ {u > 0} ∩ Ω is smooth. © 2007 Elsevier Inc. All rights reserved.

Descripción: Chromatic scheduling polytopes arise as solution sets of the bandwidth allocation problem in certain radio access networks supplying wireless access to voice/data communication networks to customers with individual communication demands. This bandwidth allocation problem is a special chromatic scheduling problem; both problems are N P-complete and, furthermore, there exist no polynomial-time algorithms with a fixed quality guarantee for them. As algorithms based on cutting planes are shown to be successful for many other combinatorial optimization problems, the goal is to apply such methods to the bandwidth allocation problem. For that, knowledge on the associated polytopes is required. The present paper contributes to this issue, introducing new classes of valid inequalities based on variations and extensions of the covering-clique inequalities presented in [J. Marenco, Chromatic scheduling polytopes coming from the bandwidth allocation problem in point-to-multipoint radio access systems, Ph.D. Thesis, Universidad de Buenos Aires, Argentina, 2005; J. Marenco, A. Wagler, Chromatic scheduling polytopes coming from the bandwidth allocation problem in point-to-multipoint radio access systems, Annals of Operations Research 150-1 (2007) 159-175]. We discuss conditions ensuring that these inequalities define facets of chromatic scheduling polytopes, and we show that the associated separation problems are N P-complete. © 2008 Elsevier B.V. All rights reserved.

Descripción: The yeast Yarrowia lipolytica accumulates oils and is able to produce extracellular lipases when growing in different carbon sources including glycerol, the principal by-product of the biodiesel industry. In this study, biomass production of a novel mutant strain of Y. lipolytica was statistically optimized by Response Surface Methodology in media containing biodiesel-derived glycerol as main carbon source. This strain exhibited distinctive morphological and fatty acid profile characteristics, and showed an increased extracellular lipase activity. An organic source of nitrogen and the addition of 1.0 g/l olive oil were necessary for significant lipase production. Plackett-Burman and Central Composite Statistical Designs were employed for screening and optimization of fermentation in shaken flasks cultures, and the maximum values obtained were 16.1 g/l for biomass and 12.2 Units/ml for lipase, respectively. Optimized batch bioprocess was thereafter scaled in aerated bioreactors and the values reached for lipase specific activity after 95 % of the glycerol had been consumed, were three-fold higher than those obtained in shaken flasks cultures. A sustainable bioprocess to obtain biomass and extracellular lipase activity was attained by maximizing the use of the by-products of biodiesel industry.

Descripción: In this paper we study the problem of minimizing the Sobolev trace Rayleigh quotient ∥u∥W1,p(ω)p/∥u∥Lq(∂ω)p among functions that vanish in a set contained on the boundary ∂ ω of given boundary measure.We prove existence of extremals for this problem, and analyze some particular cases where information about the location of the optimal boundary set can be given. Moreover, we further study the shape derivative of the Sobolev trace constant under regular perturbations of the boundary set. © 2011 Elsevier Inc.

Descripción: We consider the optimization problem of minimizing ∫Ω | ∇ u |p d x with a constraint on the volume of { u > 0 }. We consider a penalization problem, and we prove that for small values of the penalization parameter, the constrained volume is attained. In this way we prove that every solution u is locally Lipschitz continuous and that the free boundary, ∂ { u > 0 } ∩ Ω, is smooth. © 2006 Elsevier Inc. All rights reserved.

Descripción: Background: The vast computational resources that became available during the past decade enabled the development and simulation of increasingly complex mathematical models of cancer growth. These models typically involve many free parameters whose determination is a substantial obstacle to model development. Direct measurement of biochemical parameters in vivo is often difficult and sometimes impracticable, while fitting them under data-poor onditions may result in biologically implausible values. Results: We discuss different methodological approaches to estimate parameters in complex biological models. We make use of the high computational power of the Blue Gene technology to perform an extensive study of the parameter space in a model of avascular tumor growth. We explicitly show that the landscape of the cost function used to optimize the model to the data has a very rugged surface in parameter space. This cost function has many local minima with unrealistic solutions, including the global minimum corresponding to the best fit. Conclusions: The case studied in this paper shows one example in which model parameters that optimally fit the data are not necessarily the best ones from a biological point of view. To avoid force-fitting a model to a dataset, we propose that the best model parameters should be found by choosing, among suboptimal parameters, those that match criteria other than the ones used to fit the model. We also conclude that the model, data and optimization approach form a new complex system and point to the need of a theory that addresses this problem more generally. © 2010 Fernandez Slezak et al.

Descripción: In this work we study a particular way of dealing with interference in combinatorial optimization models representing wireless communication networks. In a typical wireless network, co-channel interference occurs whenever two overlapping antennas use the same frequency channel, and a less critical interference is generated whenever two overlapping antennas use adjacent channels. This motivates the formulation of the minimum-adjacency vertex coloring problem which, given an interference graph G representing the potential interference between the antennas and a set of prespecified colors/channels, asks for a vertex coloring of G minimizing the number of edges receiving adjacent colors. We propose an integer programming model for this problem and present three families of facet-inducing valid inequalities. Based on these results, we implement a branch-and-cut algorithm for this problem, and we provide promising computational results. © 2011 Elsevier B.V. All rights reserved.

Descripción: Background: Resolving the kinetics of agonist binding events separately from the subsequent channel gating processes requires the ability of applying and removing the agonist before channel gating occurs. No reported system has yet achieved pulses shorter than 100 μs, necessary to study nicotinic ACh receptor or AMPA receptor activation. Methodology/Principal Findings: Solution exchange systems deliver short agonist pulses by moving a sharp interface between a control and an experimental solution across a channel preparation. We achieved shorter pulses by means of an exchange system that combines a faster flow velocity, narrower partition between the two streams, and increased velocity and bandwidth of the movement of the interface. The measured response of the entire system was fed back to optimize the voltage signal applied to the piezoelectric actuator overcoming the spurious oscillations arising from the mechanical resonances when a high bandwidth driving function was applied. Optimization was accomplished by analyzing the transfer function of the solution exchange system. When driven by optimized command pulses the enhanced system provided pulses lasting 26 ± 1 μs and exchanging 93 ± 1% of the solution, as measured in the open tip of a patch pipette. Conclusions/Significance: Pulses of this duration open the experimental study of the molecular events that occur between the agonist binding and the opening of the channel. © 2012 Auzmendi et al.

Descripción: The base chromosome number of x = 11 is the most probable in all the subtribes included in tribe Phaseoleae, although some aneuploid reduction is evident in Collaea and Galactia (Diocleinae) and chromosome duplications are seen in Amphicarpaea, Cologania and Glycine (Glycininae). The aims of this study were to improve the cytological knowledge of some species of Collaea and Galactia and to examine the anomalous counts reported for Calopogonium (Glycininae) and verify its taxonomic position. In addition, a molecular phylogeny was constructed using nuclear ribosomal DNA sequences (internal transcribed spacer region), and the chromosome number was optimized on the topology. In this work, the chromosome counts for Galactia lindenii, Galactia decumbens and Collaea cipoensis (all 2n = 20), and Calopogonium sericeum (2n = 22) are reported for the first time. The new reports for Galactia and Collaea species are in agreement with the chromosome number proposed for subtribe Diocleinae. The study rejects the concept of a cytologically anomalous Calopogonium and, based on the phylogenetic analysis, corroborates the position of this genus within subtribe Glycininae. The ancestral basic chromosome number of x = 11 proposed for Phaseoleae is in agreement with the evolutionary pathway of chromosome numbers analysed in this work. © 2008 The Linnean Society of London.

Descripción: A Three-Dimensional Finite Volume Arbitrary Lagrangian-Eulerian simulation code was developed to study different plasma physics problems in 3D+t. The code is based on a complex multi-component species program with transport and radiation terms written and applied to plasma and fusion physics problems. The integration domain is represented with a structured irregular mesh, with fixed connectivity made of hexahedral cells. Coordinates and velocities are assigned to cell vertices. After each calculation cycle, mesh vertices are moved arbitrary over the fluid. The adaptive method consists of shifting mesh vertices over the fluid in order to keep a reasonable mesh structure and increase the spatial resolution where the physical solution demands. The code was a valuable tool for parametric study of different physical problems, mainly optimization of Plasma Focus Machine, detonation and propagation of thermonuclear reactions, and Kelvin-Helmholtz instabilities in the boundary layer of the terrestrial magnetopause. © 2009 IOP Publishing Ltd.

Descripción: We study the dependence on the subset A ⊂ Ω of the Sobolev trace constant for functions defined in a bounded domain Ω that vanish in the subset A. First we find that there exists an optimal subset that makes the trace constant smaller among all the subsets with prescribed and positive Lebesgue measure. In the case that Ω is a ball we prove that there exists an optimal hole that is spherically symmetric. In the case p = 2 we prove that every optimal hole is spherically symmetric. Then, we study the behavior of the best constant when the hole is allowed to have zero Lebesgue measure. We show that this constant depends continuously on the subset and we discuss when it is equal to the Sobolev trace constant without the vanishing restriction. © 2005 Elsevier SAS. All rights reserved.

Descripción: We study a cost function for the aggregate behavior of all the agents involved in the minority game (MG) or the bar attendance model (BAM). The cost function allows us to define a deterministic, synchronous dynamic that yields results that have the main relevant features than those of the probabilistic, sequential dynamics used for the MG or the BAM. We define a temperature through a Langevin approach in terms of the fluctuations of the average attendance. We prove that the cost function is an extensive quantity that can play the role of an internal energy of the many-agent system while the temperature so defined is an intensive parameter. We compare the results of the thermal perturbation to the deterministic dynamics and prove that they agree with those obtained with the MG or BAM in the limit of very low temperature. © 2002 The American Physical Society.

Descripción: The effective spectrum of the hard x-ray output of a Mather-type tabletop plasma focus device was determined from attenuation data on metallic samples using commercial radiographic film coupled to a Gd2 O2 S:Tb phosphor intensifier screen. It was found that the radiation has relevant spectral components in the 40-150 keV range, with a single maximum around 60-80 keV. The radiation output allows for 50 ns resolution, good contrast, and introspective imaging of metallic objects even through metallic walls. A numerical estimation of the induced voltage on the focus during the compressional stage is briefly discussed. © 2007 American Institute of Physics.

Descripción: We consider the optimization problem of minimizing ∫Ω G (| ∇ u |) + λ χ{u > 0} d x in the class of functions W1, G (Ω) with u - φ0 ∈ W01, G (Ω), for a given φ0 ≥ 0 and bounded. W1, G (Ω) is the class of weakly differentiable functions with ∫Ω G (| ∇ u |) d x < ∞. The conditions on the function G allow for a different behavior at 0 and at ∞. We prove that every solution u is locally Lipschitz continuous, that it is a solution to a free boundary problem and that the free boundary, Ω ∩ ∂ {u > 0}, is a regular surface. Also, we introduce the notion of weak solution to the free boundary problem solved by the minimizers and prove the Lipschitz regularity of the weak solutions and the C1, α regularity of their free boundaries near "flat" free boundary points. © 2008 Elsevier Inc. All rights reserved.

Descripción: • Premise of the study: A new infrafamilial circumscription of the Verbenaceae with eight tribes: Casselieae, Citharexyleae, Duranteae, Lantaneae, Neospartoneae, Petreeae, Priveae, and Verbeneae, has been recently proposed, on the basis of molecular phylogenetic studies. Two genera, Dipyrena and Rhaphithamnus, remain unplaced. The aim of this work is to reconstruct the evolutionary history of morphological characters traditionally employed in the classification of the Verbenaceae, with special attention to tribes Verbeneae and Lantaneae. • Methods: Twenty-one characters, related to habit and vegetative morphology, inflorescence and floral morphology, ovary and fruit morphology, as well as chromosome number, were optimized over a molecular phylogeny of Verbenaceae. • Key Results: All tribes are supported by at least one morphological trait except tribes Duranteae and Citharexyleae. Suffrutescent habit, sessile flowers, and four cluses are synapomorphies for tribe Verbeneae. Gynoecium with short style and entire stigma are synapomorphic traits for tribe Lantaneae. Sessile flowers and unicarpellate ovaries are morphological synapomorphies for the new tribe Neospartoneae. Suffrutescent habit is a synapomorphic trait for tribe Priveae. Homothetic pleiobotrya and absence of the adaxial staminode are synapomorphic traits for tribe Casselieae. Undivided fleshy fruits are probably a synapomorphic trait for tribe Petreeae. Putative plesiomorphies for the ancestor of the Verbenaceae are discussed as well as synapomorphic traits within other Verbenaceae clades. • Conclusions: Many of the characters traditionally employed in classification have proven to be very homoplastic, or have been shown not to support relationships within the family. Moreover, traditional assumptions concerning character polarity have in some cases been shown to be incorrect. © 2012 Botanical Society of America.

Descripción: The competition between chemical equilibrium, for example protonation, and physical interactions determines the molecular organization and functionality of biological and synthetic systems. Charge regulation by displacement of acid-base equilibrium induced by changes in the local environment provides a feedback mechanism that controls the balance between electrostatic, van der Waals, steric interactions and molecular organization. Which strategies do responsive systems follow to globally optimize chemical equilibrium and physical interactions? We address this question by theoretically studying model layers of end-grafted polyacids. These layers spontaneously form self-assembled aggregates, presenting domains of controlled local pH and whose morphologies can be manipulated by the composition of the solution in contact with the film. Charge regulation stabilizes micellar domains over a wide range of pH by reducing the local charge in the aggregate at the cost of chemical free energy and gaining in hydrophobic interactions. This balance determines the boundaries between different aggregate morphologies. We show that a qualitatively new form of organization arises from the coupling between physical interactions and protonation equilibrium. This optimization strategy presents itself with polyelectrolytes coexisting in two different and well-defined protonation states. Our results underline the need of considering the coupling between chemical equilibrium and physical interactions due to their highly nonadditive behavior. The predictions provide guidelines for the creation of responsive polymer layers presenting self-organized patterns with functional properties and they give insights for the understanding of competing interactions in highly inhomogeneous and constrained environments such as those relevant in nanotechnology and those responsible for biological cells function.