oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 9 )

2019 ( 429 )

2018 ( 519 )

2017 ( 535 )

Custom range...

Search Results: 1 - 10 of 325392 matches for " S. Costanza "
All listed articles are free for downloading (OA Articles)
Page 1 /325392
Display every page Item
Initial values for Riccati ODEs from variational PDEs
Costanza, Vicente;Rivadeneira, Pablo S.;
Computational & Applied Mathematics , 2011, DOI: 10.1590/S1807-03022011000200005
Abstract: the recently discovered variational pdes (partial differential equations) for finding missing boundary conditions in hamilton equations of optimal control are applied to the extended-space transformation of time-variant linear-quadratic regulator (lqr) problems. these problems become autonomous but with nonlinear dynamics and costs. the numerical solutions to the pdes are checked against the analytical solutions to the original lqr problem. this is the first validation of the pdes in the literature for a nonlinear context. it is also found that the initial value of the riccati matrix can be obtained from the spatial derivative of the hamiltonian flow, which satisfies the variational equation. this last result has practical implications when implementing two-degrees-of freedom control strategies for nonlinear systems with generalized costs.
Adsorption-desorption kinetics with multiple site occupation
S. Manzi,G. Costanza,V. D. Pereyra
Revista mexicana de física , 2005,
Abstract:
Estimating pure diffusion contributions in alkaline pulping processes
Costanza,Vicente; Costanza,Pedro;
Latin American applied research , 2002,
Abstract: a model that predicts isothermal alkali diffusion and reaction with acetyl groups in moist wood chips was derived and approximated. system parameters were estimated from unsteady-state experimental data. simulation results reinforce the idea that the diffusion effect is not fully exploited in pulping processes. traditionally, digestion is conducted at high temperature, where delignification reaction kinetics is enhanced and the reaction effect is predominant. this approach is being reviewed by modern industry since energy and environmental savings associated with low temperature operation might compensate for high-yield productivity. the concentration of alkali at the center of the chip is a measure of the completeness of wood deacetylation, which translates into the aptitude of the final product for pulping purposes. this concentration is predicted here from the solution to a pair of coupled ode's. since alternatives combining both low and high-temperature processes are being studied, the results in this paper provide basic data for optimization analysis.
Estimating pure diffusion contributions in alkaline pulping processes
Vicente Costanza,Pedro Costanza
Latin American applied research , 2002,
Abstract: A model that predicts isothermal alkali diffusion and reaction with acetyl groups in moist wood chips was derived and approximated. System parameters were estimated from unsteady-state experimental data. Simulation results reinforce the idea that the diffusion effect is not fully exploited in pulping processes. Traditionally, digestion is conducted at high temperature, where delignification reaction kinetics is enhanced and the reaction effect is predominant. This approach is being reviewed by modern industry since energy and environmental savings associated with low temperature operation might compensate for high-yield productivity. The concentration of alkali at the center of the chip is a measure of the completeness of wood deacetylation, which translates into the aptitude of the final product for pulping purposes. This concentration is predicted here from the solution to a pair of coupled ODE's. Since alternatives combining both low and high-temperature processes are being studied, the results in this paper provide basic data for optimization analysis.
Numerical solution of the variational PDEs arising in optimal control theory
Costanza, Vicente;Troparevsky, Maria I.;Rivadeneira, Pablo S.;
Computational & Applied Mathematics , 2012, DOI: 10.1590/S1807-03022012000100003
Abstract: an iterative method based on picard's approach to odes' initial-value problems is proposed to solve first-order quasilinear pdes with matrix-valued unknowns, in particular, the recently discovered variational pdes for the missing boundary values in hamilton equations of optimal control. as illustrations the iterative numerical solutions are checked against the analytical solutions to some examples arising from optimal control problems for nonlinear systems and regular lagrangians in finite dimension, and against the numerical solution obtained through standard mathematical software. an application to the (n + 1)-dimensional variational pdes associated with the n-dimensional finite-horizon time-variant linear-quadratic problem is discussed, due to the key role the lqr plays in two-degrees-of freedom control strategies for nonlinear systems with generalized costs. mathematical subject classification: primary: 35f30; secondary: 93c10.
Adsorption-Desorption Kinetics: A Review of a Classical Problem
S. Manzi,R. E. Belardinelli,G. Costanza,V. D. Pereyra
Physics , 2008,
Abstract: In this work we have analyzed the adsorption-desorption kinetics in the framework of the lattice gas model. We have shown that the coefficients representing the transition probabilities must be carefully chosen even when they fulfill the principle of detailed balance, otherwise the observables arising from the kinetics present anomalous behavior. We have demonstrated that when the adsorption $A_i$ and desorption $D_i$ coefficients are linearly related through a parameter $\gamma$, there are values of lateral interaction, $V$, that lead to bad behavior in the kinetics. We have shown a phase diagram for the allowed values of $V$ and $\gamma$, concluding that detailed balance does not guarantee a correct physical behavior of the observables obtained from the rate equations like adsorption isotherms, sticking coefficients and thermal desorption spectra. Alternatively, we have introduced a description of the adsorption-desorption processes based in a simple but consistent energetic argument that leads to a correct behavior of the observables without physical inconsistencies.
Optimal state-feedback regulation of the hydrogene evolution reactions
Costanza,V.;
Latin American applied research , 2005,
Abstract: a control strategy is developed in order to keep processes based on the hydrogen evolution reactions (her) near operational steady states. the problem is treated in the context of optimal control for nonlinear systems subject to quadratic cost objectives. the original dynamics is shown to be accurately approximated by a bilinear model without increasing the dimension, so the state variables retain their physical meaning. finite and infinite horizon optimal control strategies are developed, based on the hamiltonian formalism, and introducing a novel approach for working on-line with generalized riccati differential equations and the associated costate dynamics. when there exists a final penalty on the state deviation, then a first order quasi-linear partial differential equation is discovered and solved for the riccati matrix. the observability problem is also treated, since the natural state (electrode surface coverage) can not be measured continuously. the output variable (current density) is fed into a high-gain nonlinear observer based on lyapunov's stability considerations. the whole approach allows for (in general time-dependent) state-feedback control.
Visions of Alternative (Unpredictable) Futures and Their Use in Policy Analysis
Robert Costanza
Ecology and Society , 2000,
Abstract: The most critical task facing humanity today is the creation of a shared vision of a sustainable and desirable society, one that can provide permanent prosperity within the biophysical constraints of the real world in a way that is fair and equitable to all of humanity, to other species, and to future generations. Recent work with businesses and communities indicates that creating a shared vision is the most effective engine for change in the desired direction, yet most effort in "futures modeling" has focused on extrapolating past trends rather than envisioning alternative futures. Science and economics as applied to policy are in conflict more often over alternative visions of the world than purely "scientific" disagreements. Likewise, governance has gotten bogged down in mediating short term conflicts between special interests rather than its more basic role of creating broadly shared visions that can guide dispute resolution. This paper addresses the question of what policies are most appropriate for society now, given alternative visions of the future and the enormous uncertainty about the reality of the assumptions underlying these visions. Four specific visions are laid out as being representative of the major alternatives. For each vision the benefits of achieving the vision, the assumptions that would have to be true in order for it to be achieved, and the implications of it being attempted but not achieved are explored. It is argued that dealing with uncertainty about the nature of the world, its carrying capacity for humans, the impacts of climate change, and other aspects of its future can best be done at this level of future visions and assumptions, not at more detailed levels (like the parameter uncertainty in models). Application of this vision/uncertainty analysis can help us both to design the future society we want and to maximize the chances of our getting there safely.
Optimal state-feedback regulation of the hydrogene evolution reactions
V. Costanza
Latin American applied research , 2005,
Abstract: A control strategy is developed in order to keep processes based on the hydrogen evolution reactions (HER) near operational steady states. The problem is treated in the context of Optimal Control for nonlinear systems subject to quadratic cost objectives. The original dynamics is shown to be accurately approximated by a bilinear model without increasing the dimension, so the state variables retain their physical meaning. Finite and infinite horizon optimal control strategies are developed, based on the Hamiltonian formalism, and introducing a novel approach for working on-line with generalized Riccati differential equations and the associated costate dynamics. When there exists a final penalty on the state deviation, then a first order quasi-linear partial differential equation is discovered and solved for the Riccati matrix. The observability problem is also treated, since the natural state (electrode surface coverage) can not be measured continuously. The output variable (current density) is fed into a high-gain nonlinear observer based on Lyapunov's stability considerations. The whole approach allows for (in general time-dependent) state-feedback control.
Gammaherpesvirus Latency Accentuates EAE Pathogenesis: Relevance to Epstein-Barr Virus and Multiple Sclerosis
Costanza Casiraghi,Iryna Shanina,Sehyun Cho,Michael L. Freeman,Marcia A. Blackman,Marc S. Horwitz
PLOS Pathogens , 2012, DOI: 10.1371/journal.ppat.1002715
Abstract: Epstein-Barr virus (EBV) has been identified as a putative environmental trigger of multiple sclerosis (MS), yet EBV's role in MS remains elusive. We utilized murine gamma herpesvirus 68 (γHV-68), the murine homolog to EBV, to examine how infection by a virus like EBV could enhance CNS autoimmunity. Mice latently infected with γHV-68 developed more severe EAE including heightened paralysis and mortality. Similar to MS, γHV-68EAE mice developed lesions composed of CD4 and CD8 T cells, macrophages and loss of myelin in the brain and spinal cord. Further, T cells from the CNS of γHV-68 EAE mice were primarily Th1, producing heightened levels of IFN-γ and T-bet accompanied by IL-17 suppression, whereas a Th17 response was observed in uninfected EAE mice. Clearly, γHV-68 latency polarizes the adaptive immune response, directs a heightened CNS pathology following EAE induction reminiscent of human MS and portrays a novel mechanism by which EBV likely influences MS and other autoimmune diseases.
Page 1 /325392
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.