14 research outputs found

    Towards scalable optimal traffic control

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    International audienceThis paper deals with scalable control of traffic lights in urban traffic networks. Optimization is done in real time, so as to take into account variable traffic demands.At each cycle of the traffic lights, the optimization concerns times instants where each traffic light starts and ends its green phase: this allows to describe both the duty-cycle and the phase shifts.First, we formulate a global optimization problem, which can be cast as a mixed-integer linear program. To overcome the complexity of this centralized approach, we also propose a decentralized suboptimal algorithm, whose simplicity allows on-line implementation. Simulations show the effectiveness of the proposed strategies

    Towards scalable optimal traffic control

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    International audienceThis paper deals with scalable control of traffic lights in urban traffic networks. Optimization is done in real time, so as to take into account variable traffic demands.At each cycle of the traffic lights, the optimization concerns times instants where each traffic light starts and ends its green phase: this allows to describe both the duty-cycle and the phase shifts.First, we formulate a global optimization problem, which can be cast as a mixed-integer linear program. To overcome the complexity of this centralized approach, we also propose a decentralized suboptimal algorithm, whose simplicity allows on-line implementation. Simulations show the effectiveness of the proposed strategies

    An efficient one-step-ahead optimal control for urban signalized traffic networks based on an averaged Cell-Transmission model

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    International audience— This paper presents a model for large urban traffic networks, based on the well-known macroscopic Cell Transmission Model. We start by describing the dynamics of traffic flow at signalized intersections. Then we develop an average-based approximation of such a system, that we use to build our control algorithm as a linear optimization problem. Simulation results validate the averaged approach and show the effectiveness of the proposed control strategy

    Contrôle de vaste réseau de trafic

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    The thesis focuses on traffic lights control in large scale urban networks. It starts off with a study of macroscopic modeling based on the Cell Transmission model. We formulate a signalized version of such a model in order to include traffic lights’ description into the dynamics. Moreover, we introduce two simplifications of the signalized model towards control design, one that is based on the average theory and considers duty cycles of traffic lights, and a second one that describes traffic lights trajectories with the time instants of the rising and falling edges of a binary signals. We use numerical simulations to validate the models with respect to the signalized Cell Transmission model, and microsimulations (with the software Aimsun), to validate the same model with respect to realistic vehicles’ behavior.We propose two control algorithms based on the two models above mentioned. The first one, that uses the average Cell Transmission model, considers traffic lights’ duty cycles as controlled variables and it is formulated as an optimization problem of standard traffic measures. We analyze such a problem and we show that it is equivalent to a convex optimization problem, so ensuring its computational efficiency. We analyze its performance with respect to a best-practice control scheme both in MatLab simulations and in Aimsun simulations that emulate a large portion of Grenoble, France. The second proposed approach is an optimization problem in which the decision variables are the activation and deactivation time instants of every traffic lights. We employ the Big-M modeling technique to reformulate such a problem as a mixed integer linear program, and we show via numerical simulations that the expressivity of it can lead to improvements of the traffic dynamics, at the price of the computational efficiency of the control scheme.To pursue the scalability of the proposed control techniques we develop two iterative distributed approaches to the traffic lights control problem. The first, based on the convex optimization above mentioned, uses the dual descent technique and its provably optimal, that is, it gives the same solution of the centralized optimization. The second, based on the mixed integer problem aforesaid, is a suboptimal algorithm that leads to substantial improvements by means of the computational efficiency with respect to the related centralized problem. We analyze via numerical simulations the convergence speed of the iterative algorithms, their computational burden and their performance regarding traffic metrics.The thesis is concluded with a study of the traffic lights control algorithm that is employed in several large intersections in Grenoble. We present the working principle of such an algorithm, detailing technological and methodological differences with our proposed approaches. We create into Aimsun the scenario representing the related part of the city, also reproducing the control algorithm and comparing its performance with the ones given by one of our approaches on the same scenario.La thèse concerne le contrôle de feux tricolores dans de larges réseaux urbains. Le point de départ est l’étude d’un modèle macroscopique se basant sur le Cell Transmission model. Nous avons formulé une version du modèle intégrant les feux tricolores à sa dynamique. De plus, nous avons introduit deux simplifications à ce modèle orientées vers la conception des techniques de contrôle ; la première se base sur la théorie de la moyenne et considère le pourcentage de vert des feux tricolores, la seconde décrit les trajectoires des feux tricolores en utilisant les instants d’activation et de désactivation d’un signal binaire. Nous utilisons des simulations numériques pour valider les modèles en les comparant avec le Cell Transmisson model intégrant les feux tricolores, ainsi que des simulations microscopiques (avec le logiciel Aimsun) afin de valider les mêmes modèles en les comparant cette fois-ci à un comportement réaliste des véhicules.Nous proposons deux techniques de contrôle à partir des deux modèles mentionnés ci-dessus. Le premier, qui utilise le modèle moyen de transmission de véhicules, considère les pourcentages de vert des feux tricolores comme variables contrôlées, et il est formulé comme un problème d'optimisation des mesures de trafic standards. Nous analysons un tel problème et nous montrons que cela équivaut à un problème d'optimisation convexe, afin d'assurer son efficacité de calcul. Nous analysons sa performance par rapport à un best-practice control à la fois dans des simulations MatLab, et dans des simulations microscopiques, avec un modèle Aimsun qui reproduit une grande partie de Grenoble, en France. La deuxième approche proposée est un problème d'optimisation dans lequel les variables contrôlées sont les instants d'activation et de désactivation de chaque feu tricolore. Nous utilisons la technique de modélisation Big-M dans le but de formuler un tel problème comme un programme linéaire avec variables entières, et nous montrons par des simulations numériques que l’expressivité de cette optimisation conduit à des améliorations de la dynamique du trafic, au prix de l'efficacité de calcul.Pour poursuivre la scalabilité des techniques de contrôle proposées nous développons deux algorithmes itératifs pour le problème de contrôle des feux de signalisation. Le premier, basé sur l'optimisation convexe mentionnée ci-dessus, utilise la technique dual descent et nous prouvons qu’il est optimal, i.e., il donne la même solution que l'optimisation centralisée. Le second, basé sur le problème d’optimisation entier susmentionné, est un algorithme sous-optimal qui mène à des améliorations substantielles par rapport au problème centralisé connexe, concernant l'efficacité de calcul. Nous analysons par des simulations numériques la vitesse de convergence des algorithmes itératifs, leur charge de calcul et leurs performances en matière de mesure du trafic.La thèse est conclue avec une étude de l'algorithme de contrôle des feux de circulation qui est utilisé dans plusieurs grandes intersections dans Grenoble. Nous présentons le principe de fonctionnement d'un tel algorithme, en détaillant les différences technologiques et méthodologiques par rapport aux approches proposées. Nous créons dans Aimsun le scénario représentant la partie intéressée de la ville, en reproduisant également l'algorithme de contrôle et en comparant ses performances avec celles de l'une de nos approches sur le même scénario

    Distributed Optimal Traffic Lights Design for Large-Scale Urban Networks

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    International audienceIn this paper we deal with the problem of dynamical assignment of traffic lights schedules in large-scale urban networks. We present a model for signalized traffic networks, based on the Cell Transmission Model, and then a simplified model based on averaging theory. The control objective is to improve traffic, optimizing traffic indexes such as total travel distance and density balancing. We design a scheme that decides the duty cycles of traffic lights, by solving a convex program. The optimization is done in real time, at each cycle of traffic lights, so as to take into account variable traffic demands. The scalability problem is tackled through the synthesis of a distributed optimization algorithm; this reduces the computational load significantly, since the large optimization problem is broken into small local subproblems, whose size does not grow with the size of the network, together with iterative exchanges of messages with few neighbor subproblems. The perfomance of the proposed approach is evaluated via numerical simulations in two different scenarios: a macroscopic (MatLab-based) Manhattan grid and a microscopic scenario (based on Aimsun simulator) reproducing a portion of the city of Grenoble, France

    Corporate income tax subjects

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    Il tema della soggettività tributaria delle persone giuridiche è alquanto discusso poiché non corrisponde con la personalità giuridica di diritto civile. Nel presente contributo viene sviluppata un’indagine tesa all’individuazione dei principi generali che governano il fenomeno della soggettività passiva dell’imposta sul reddito delle società in Italia analizzandone l’evoluzione nel tempo.The topic of corprate income tax subjectivity has been long time discussed because it doesn’t correspond with legal personality in civil law. This essay develops a research on general principles of corporate income tax in Italy, analyzing its evolution during the time

    Distributed Optimal Traffic Lights Design for Large-Scale Urban Networks

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    Acute renal failure in orthopaedic surgery.

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    Orthopaedic diseases affect a broad spectrum of patients, and many of these have concomitant medical problems that may differ from those of the general surgical population. Acute postoperative renal failure is thought to arise secondary to acute tubular necrosis from volume depletion, reduction in glomerular filtration rate, hypotension, and nephrotoxic drugs. If acute renal failure occurs and necessitates hemodialysis, morbidity and mortality are significantly increased. To enhance the literature, we performed this study to review the rates and risk factors for acute renal failure in orthopaedic surgery. This information may be useful for orthopaedic surgeons and treating physicians during the rehabilitation stage, to provide a rationale to stratify a patient's risk of acute renal failure or death on the basis of perioperative medical factors and type of surgery, or for improved perioperative monitoring, better surveillance, and preventive measures to reduce this risk
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