Maddalena Nonato - Academia.edu (original) (raw)

Uploads

Papers by Maddalena Nonato

Demand-adaptive transit systems (DAS) display features of both traditional fixed-line bus service... more Demand-adaptive transit systems (DAS) display features of both traditional fixed-line bus services and purely on-demand systems, that is, they offer demand- responsive services within the framework of traditional scheduled bus transportation. Similarly to most transportation systems dedicated to serve several demands with the same vehicle, demand-adaptive transit systems involve a complex set of planning activities made up of many interrelated

In this paper new exible collective transportation system are presented. The proposed system is s... more In this paper new exible collective transportation system are presented. The proposed system is suitable in the urban or interurban setting, and conjugate a traditional line transportation system with an on demand system. Several variants of the model are discussed, and for each variant a mathematical model is proposed. Solution approaches are also illustrated.

In this paper we discuss Demand Adaptive Systems (DAS) which are intended as a hybrid public tran... more In this paper we discuss Demand Adaptive Systems (DAS) which are intended as a hybrid public transportation system that integrates traditional bus transportation and on demand service, DAS lines regularly serve a given set of compulsory stops according to a predefined schedule and regardless of current demand. Between a compulsory stop and the next, optional stops can be activated on

Procedia - Social and Behavioral Sciences, 2014

Modern societies rely upon massive supplies of large amounts of commodities, some of which imply ... more Modern societies rely upon massive supplies of large amounts of commodities, some of which imply the use of hazardous materials (hazmat). A crucial step in the hazmat life cycle is transportation. An accident en route is a "low probability -high consequences" event and much effort has been devoted to the development of risk mitigation strategies. In this paper we are concerned with hazmat transportation by truck on a road network, where several alternative itineraries from origin to destination are worthy of choice. Given a set of origin-destination pairs and the hazmat quantities to be transported for each pair, the road network topology, and the cost and the risk of each arc, the aim is to reduce the total risk related to the hazmat itineraries, hopefully not to a sensitive detriment of cost. In a mixed urban setting, the shortest path is often a risky one. Whenever possible, the network administrator imposes to each driver a specific itinerary with lower risk. If not possible, the network administrator may enforce some restrictions regarding network usage, such as forbidding hazmat transit on some links or imposing tolls. Within this framework, we propose a new method that diverts vehicles from their shortest (and risky) path from origin to destination by forcing each vehicle to pass through an intermediate check point, so called gateway. We face the problem of selecting the location of a given number of gateways among a larger number of potential locations and assigning a gateway to each vehicle such that the total risk is minimized. Once gateways are located and assigned, the "rational" driver will travel along the shortest path from its origin to its assigned gateway, and then from such a gateway to its destination. While previous studies have experimentally demonstrated the risk mitigation efficacy of our strategy, the issue of the cost of the solutions has never been analyzed in depth. In this work we describe how to efficiently compute the Pareto frontier given by the non dominated solutions with respect to total risk and total cost on realistic instances taken from the literature, and we present computational results showing that the solution yielded by our method represents a very good compromise between the two criteria, since it achieves substantial risk mitigation while providing an efficient trade off with cost.

Transportation Research Part C: Emerging Technologies, 2013

ABSTRACT

collection center paper container glass container metal container wood container Problem descript... more collection center paper container glass container metal container wood container Problem description: operations • Users convey waste to their nearest collection center and dispose it into the appropriate container • Once a container is full the collection center issues a service request consisting in emptying the full container • The company operates a swap between a full container and an empty one, disposing the waste in the nearest disposal center • The swap takes place when the collection center is closed: the removal and substitution of a container may take place in different moments and not necessarily in this order

2007 15th International Conference on Software, Telecommunications and Computer Networks, 2007

This paper proposes a method to improve the performance of a low-density parity-check code, by se... more This paper proposes a method to improve the performance of a low-density parity-check code, by selectively removing some cycles from the associated bipartite graph. The method is based on a modified version of breadth-first search (BFS) algorithm, that we call modified BFS (MBFS). Throughout the paper we will give a detailed description of the algorithm and analytically study its complexity. Simulation results will show that applying MBFS to a given code leads to significant improvement of its performance.

INFORMS Journal on Computing, 2005

ABSTRACT The demand-adaptive systems studied in this paper attempt to offer demand-responsive ser... more ABSTRACT The demand-adaptive systems studied in this paper attempt to offer demand-responsive services within the framework of traditional scheduled bus transportation: Users call to request service between two given points and, in so doing, induce detours in the vehicle routes; at the same time, though, a given set of compulsory stops is always served according to a predefined schedule, regardless of the current set of active requests. The model developed to select requests and determine the routing of the vehicle yields a difficult formulation but with a special structure that may be used to develop efficient algorithms. In this paper, we develop, test, and compare several solution strategies for the single line-single vehicle problem that belong to two general meta-heuristic classes, memory-enhanced greedy randomized multistart constructive procedures, and tabu search methods. Hybrid meta-heuristics combining the two methods are also analyzed.

IEEE Transactions on Communications, 2000

Low-density parity-check (LDPC) codes are gaining interest for high data rate applications in bot... more Low-density parity-check (LDPC) codes are gaining interest for high data rate applications in both terrestrial and spatial communications. They can be designed and studied through a bipartite graph whose characteristics affect the performance. This paper proposes a low-complexity method to improve the performance of LDPC codes by selectively removing some cycles from the associated bipartite graph. The method is based on a modified version of the breadth first search (BFS) algorithm that we call modified BFS (MBFS), which is applied to find cycles, and a greedy procedure to eliminate them. Throughout the paper we will give a detailed description of the algorithm proposed and analytically study its complexity. Simulation results show that this girth conditioning method applied to some classes of codes, whose structure allows further optimization, can lead to a significative complexity reduction and a performance improvements with respect to other methods.

Electronic Notes in Discrete Mathematics, 2004

Annals of Operations Research, 2012

Demand-Adaptive Systems (DAS) display features of both traditional fixed-line bus services and pu... more Demand-Adaptive Systems (DAS) display features of both traditional fixed-line bus services and purely on-demand systems such as dial-a-ride, that is they offer demand-responsive services within the framework of traditional scheduled bus transportation. A DAS bus line serves, on one hand, a given a set of compulsory stops according to a predefined schedule specifying the time windows associated to each, providing the traditional use of the transit line, without requiring any reservation. On the other hand, passengers may also issue requests for transportation between two desired, optional, stops, which induces detours in the vehicle routes. The design of a DAS line is a complex planning operation that requires to determine not only its design in terms of selecting the compulsory stops, but also its master schedule in terms of the time windows associated to the compulsory stops. Designing a DAS thus combines elements of strategic and tactical planning. In this paper we focus on determining a master-schedule for a single DAS line. We propose a mathematical description and a solution framework based on the estimation of a number of statistical parameters of the demand and the DAS line service. Results of numerical experiments are also given and analyzed. Cooperation as problem-solving and algorithm-design strategy is widely used to build methods addressing complex discrete optimization problems. In most cooperative-search algorithms, the explicit cooperation scheme yields a dynamic process not deliberately controlled by the algorithm design but inflecting the global behaviour of the cooperative solution strategy. The paper presents an overview of explicit cooperation mechanisms and describes issues related to the associated dynamic processes and the emergent computation they often generate. It also identifies a number of research directions into cooperation mechanisms, strategies for dynamic learning, automatic guidance, and selfadjustment, and the associated emergent computation processes.

IEEE Wireless Communications, 2000

The high quality standards required by third-generation systems can be reached only by way of a c... more The high quality standards required by third-generation systems can be reached only by way of a careful tuning of all the parameters of antenna configurations. However, concerns about exposure to electromagnetic fields should also be taken into account when designing telecommunication networks. In this article we investigate how parallel cooperative meta-heuristics provide the means to achieve both goals: devising a