Online-Computation Approach to Optimal Control of Noise-Affected Nonlinear Systems with Continuous State and Control Spaces

© 2007 EUCA.A novel online-computation approach to optimal control of nonlinear, noise-affected systems with continuous state and control spaces is presented. In the proposed algorithm, system noise is explicitly incorporated into the control decision. This leads to superior results compared to state-of-the-art nonlinear controllers that neglect this influence. The solution of an optimal nonlinear controller for a corresponding deterministic system is employed to find a meaningful state space restriction. This restriction is obtained by means of approximate state prediction using the noisy system equation. Within this constrained state space, an optimal closed-loop solution for a finite decision-making horizon (prediction horizon) is determined within an adaptively restricted optimization space. Interleaving stochastic dynamic programming and value function approximation yields a solution to the considered optimal control problem. The enhanced performance of the proposed discrete-time controller is illustrated by means of a scalar example system. Nonlinear model predictive control is applied to address approximate treatment of infinite-horizon problems by the finite-horizon controller

Evidence from satellite altimetry for small-scale convection in the mantle

Small scale convection can be defined as that part of the mantle circulation in which upwellings and downwellings can occur beneath the lithosphere within the interiors of plates, in contrast to the large scale flow associated with plate motions where upwellings and downwellings occur at ridges and trenches. The two scales of convection will interact so that the form of the small scale convection will depend on how it arises within the large scale flow. Observations based on GEOS-3 and SEASAT altimetry suggest that small scale convection occurs in at least two different ways

Una alpargata en Barracas

A partir de los trabajos de investigación arqueológica en situaciones de rescate, se intervino en la obra de construcción del edificio Ombú, nueva sede de la empresa Metrogas, ubicada en la calle Lamadrid 1360 del barrio de Barracas. En esa localización funcionó el gasómetro que sirvió para el alumbrado barrial desde finales del siglo XIX. A pocos metros, se ubica la Fábrica de Alpargatas desde 1883. Posteriormente a la extracción del elemento de la excavación, se intervino para demostrar la necesidad del trabajo interdisciplinario acorde a la conservación preventiva de hallazgos que incrementan las “colecciones museológicas”. Se puntualizará la intervención sobre una alpargata. Para caracterizarla en detalle se la recuperó y estabilizó devolviéndole la unidad potencial necesaria para dejarla en condiciones óptimas para el almacenaje en la Reserva Técnica o el montaje en una exhibición. Para identificar el objeto se requirió de la selección y clasificación sistemática del material por parte del arqueólogo y del conocimiento del conservador para su individualización y recuperación. Gracias a este trabajo articulado se obtuvo un beneficio pleno del material de excavación optimizándose los resultados y logrando una correcta recuperación del objeto.Tópico 2: Conservación y restauración de pinturas, cueros, textiles y metales

Synthetic aperture radar (SAR)-based mapping of volcanic flows: Manam Island, Papua New Guinea

International audienceWe present new radar-based techniques for efficient identification of surface changes generated by lava and pyroclastic flows, and apply these to the 1996 eruption of Manam Volcano, Papua New Guinea. Polarimetric L- and P-band airborne synthetic aperture radar (SAR) data, along with a C-band DEM, were acquired over the volcano on 17 November 1996 during a major eruption sequence. The L-band data are analyzed for dominant scattering mechanisms on a per pixel basis using radar target decomposition techniques. A classification method is presented, and when applied to the L-band polarimetry, it readily distinguishes bare surfaces from forest cover over Manam volcano. In particular, the classification scheme identifies a post-1992 lava flow in NE Valley of Manam Island as a mainly bare surface and the underlying 1992 flow units as mainly vegetated surfaces. The Smithsonian's Global Volcanism Network reports allow us to speculate whether the bare surface is a flow dating from October or November in the early part of the late-1996 eruption sequence. This work shows that fully polarimetric SAR is sensitive to scattering mechanism changes caused by volcanic resurfacing processes such as lava and pyroclastic flows. By extension, this technique should also prove useful in mapping debris flows, ash deposits and volcanic landslides associated with major eruptions

Adaptive dynamic resource allocation in annual eusocial insects: Environmental variation will not necessarily promote graded control

Background: According to the classical model of Macevicz and Oster, annual eusocial insects should show a clear dichotomous "bang-bang" strategy of resource allocation; colony fitness is maximised when a period of pure colony growth (exclusive production of workers) is followed by a single reproductive period characterised by the exclusive production of sexuals. However, in several species graded investment strategies with a simultaneous production of workers and sexuals have been observed. Such deviations from the "bang-bang" strategy are usually interpreted as an adaptive (bet-hedging) response to environmental fluctuations such as variation in season length or food availability. To generate predictions about the optimal investment pattern of insect colonies in fluctuating environments, we slightly modified Macevicz and Oster's classical model of annual colony dynamics and used a dynamic programming approach nested into a recurrence procedure for the solution of the stochastic optimal control problem. Results: 1) The optimal switching time between pure colony growth and the exclusive production of sexuals decreases with increasing environmental variance. 2) Yet, for reasonable levels of environmental fluctuations no deviation from the typical bang-bang strategy is predicted. 3) Model calculations for the halictid bee Lasioglossum malachurum reveal that bet-hedging is not likely to be the reason for the graded allocation into sexuals versus workers observed in this species. 4) When environmental variance reaches a critical level our model predicts an abrupt change from dichotomous behaviour to graded allocation strategies, but the transition between colony growth and production of sexuals is not necessarily monotonic. Both, the critical level of environmental variance as well as the characteristic pattern of resource allocation strongly depend on the type of function used to describe environmental fluctuations. Conclusion: Up to now bet-hedging as an evolutionary response to variation in season length has been the main argument to explain field observations of graded resource allocation in annual eusocial insect species. However, our model shows that the effect of moderate fluctuations of environmental conditions does not select for deviation from the classical bang-bang strategy and that the evolution of graded allocation strategies can be triggered only by extreme fluctuations. Detailed quantitative observations on resource allocation in eusocial insects are needed to analyse the relevance of alternative explanations, e.g. logistic colony growth or reproductive conflict between queen and workers, for the evolution of graded allocation strategies

Cultural patterns: heritage of the Matanza-Riachuelo watershed, Buenos Aires province

The valuation criteria of the national, provincial and municipal cultural heritage is a cultural pattern among which the collective and restrictive aspects used for their designation take precedence. The analysis of the legally protected assets in the 14 municipalities that are part of the Matanza-Riachuelo watershed enables the identification of the established cultural patterns. The urban-formal spaces become representative of a national identity, whereas the marginal-informal spaces are their opposite. In this investigation, we spatialized the protected assets of the watershed and we assessed their location in formal and informal spaces and through time, in order to identify the cultural pattern. The practice of protecting, preserving and conserving heritage assets representative of the tension between central and peripheral areas, becomes an empowering tool of the national identity.Los criterios de valoración del patrimonio nacional, provincial y municipal se presentan como patrones culturales en donde priman aspectos estandarizados y restrictivos para su nombramiento. El análisis del patrimonio protegido de los 14 municipios que forman parte de la cuenca Matanza-Riachuelo, se presenta como punto de partida para identificar los patrones culturales establecidos, en donde los espacios urbanos-formales se vuelven representativos de la identidad nacional y los espacios marginales-informales su contracara. En este trabajo espacializamos los bienes protegidos de la cuenca y analizamos la proporción de patrimonio en los espacios formales e informales y a lo largo del tiempo, con el fin de identificar el patrón cultural establecido. La práctica de proteger, preservar y conservar los bienes patrimoniales, que surge de la tensión entre las áreas centrales y periféricas, se vuelve una herramienta fortalecedora de la identidad de una nación.Fil: Garcia, Analia. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Departamento de Ciencias Antropológicas; Argentina. Universidad Nacional de Lanús; ArgentinaFil: Weissel, Marcelo Norman. Universidad Maimonides. Area de Invest.biomédicas y Biotecnológicas. Cent.d/est.biomedic.,biotecn.,ambient.y Diagnost.. Departamento de Ecología y Cs.ambientales; Argentina. Fundación de Historia Natural Félix de Azara; ArgentinaFil: Guida Johnson, Bárbara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Zuleta, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Maimónides; Argentin

Finite-Horizon Optimal State Feedback Control of Nonlinear Stochastic Systems Based on a Minimum Principle

In this paper, an approach to the finite-horizon optimal state-feedback control problem of nonlinear, stochastic, discrete-time systems is presented. Starting from the dynamic programming equation, the value function will be approximated by means of Taylor series expansion up to second-order derivatives. Moreover, the problem will be reformulated, such that a minimum principle can be applied to the stochastic problem. Employing this minimum principle, the optimal control problem can be rewritten as a two-point boundary-value problem to be solved at each time step of a shrinking horizon. To avoid numerical problems, the two-point boundary-value problem will be solved by means of a continuation method. Thus, the curse of dimensionality of dynamic programming is avoided, and good candidates for the optimal state-feedback controls are obtained. The proposed approach will be evaluated by means of a scalar example system. © 2006 IEEE

Crustal structure and rift flank uplift of the Adare Trough, Antarctica

The Adare Trough, located 100 km northeast of Cape Adare, Antarctica, represents the extinct third arm of a Tertiary spreading ridge between East and West Antarctica. It is characterized by pronounced asymmetric rift flanks elevated up to over 2 km above the trough's basement, accompanied by a large positive mantle Bouguer anomaly. On the basis of recently acquired seismic reflection and ship gravity data, we invert mantle Bouguer anomalies from the Adare Trough and obtain an unexpectedly large oceanic crustal thickness maximum of 9–10.5 km underneath the extinct ridge. A regional positive residual basement depth anomaly between 1 and 2.5 km in amplitude characterizes ocean crust from offshore Victoria Land to the Balleny Islands and north of Iselin Bank. The observations and models indicate that the mid/late Tertiary episode of slow spreading between East and West Antarctica was associated with a mantle thermal anomaly. The increasing crustal thickness toward the extinct ridge indicates that this thermal mantle anomaly may have increased in amplitude through time during the Adare spreading episode. This scenario is supported by a mantle convection model, which indicates the formation and strengthening of a major regional negative upper mantle density anomaly in the southwest Pacific in the last 50 million years. The total amount of post-26 Ma extension associated with Adare Trough normal faulting was about 7.5 km, in anomalously thick oceanic crust with a lithospheric effective elastic thickness (EET) between 3.5 and 5 km. This corresponds to an age between 3 and 5 million years based on a thermal boundary layer model and supports a scenario in which the Adare Trough formed soon after spreading between East and West Antarctica ceased, confined to relatively weak lithosphere with anomalously thick oceanic crust. There is little evidence for major subsequent structural activity in the Adare trough area from the available seismic data, indicating that this part of the West Antarctic Rift system became largely inactive in the early Miocene, with the exception of minor structural reactivation which is visible in the seismic data as offsets up to end of the early Pliocene

Synthetic aperture radar (SAR)-based mapping of volcanic flows: Manam Island, Papua New Guinea

We present new radar-based techniques for efficient identification of surface changes generated by lava and pyroclastic flows, and apply these to the 1996 eruption of Manam Volcano, Papua New Guinea. Polarimetric L- and P-band airborne synthetic aperture radar (SAR) data, along with a C-band DEM, were acquired over the volcano on 17 November 1996 during a major eruption sequence. The L-band data are analyzed for dominant scattering mechanisms on a per pixel basis using radar target decomposition techniques. A classification method is presented, and when applied to the L-band polarimetry, it readily distinguishes bare surfaces from forest cover over Manam volcano. In particular, the classification scheme identifies a post-1992 lava flow in NE Valley of Manam Island as a mainly bare surface and the underlying 1992 flow units as mainly vegetated surfaces. The Smithsonian's Global Volcanism Network reports allow us to speculate whether the bare surface is a flow dating from October or November in the early part of the late-1996 eruption sequence. This work shows that fully polarimetric SAR is sensitive to scattering mechanism changes caused by volcanic resurfacing processes such as lava and pyroclastic flows. By extension, this technique should also prove useful in mapping debris flows, ash deposits and volcanic landslides associated with major eruptions