3,511 research outputs found

    Reliable and timely event notification for publish/subscribe services over the internet

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    The publish/subscribe paradigm is gaining attention for the development of several applications in wide area networks (WANs) due to its intrinsic time, space, and synchronization decoupling properties that meet the scalability and asynchrony requirements of those applications. However, while the communication in a WAN may be affected by the unpredictable behavior of the network, with messages that can be dropped or delayed, existing publish/subscribe solutions pay just a little attention to addressing these issues. On the contrary, applications such as business intelligence, critical infrastructures, and financial services require delivery guarantees with strict temporal deadlines. In this paper, we propose a framework that enforces both reliability and timeliness for publish/subscribe services over WAN. Specifically, we combine two different approaches: gossiping, to retrieve missing packets in case of incomplete information, and network coding, to reduce the number of retransmissions and, consequently, the latency. We provide an analytical model that describes the information recovery capabilities of our algorithm and a simulation-based study, taking into account a real workload from the Air Traffic Control domain, which evidences how the proposed solution is able to ensure reliable event notification over a WAN within a reasonable bounded time window. © 2013 IEEE

    Development of a geological model useful for the study of the natural hazards in urban environments. An example from the eastern sector of Rome (Italy)

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    Detailed knowledge of the subsoil setting is an extremely important issue for a correct risk reduction policy, especially when dealing with urban areas hosting cultural heritage, which enhance risk conditions even at low geo-hazard levels, as in the case of Rome. In general, the reliability of risk assessments related to geo-hazards is strictly dependent on the resolution of the reference geological model. The study presented here exemplifies an integrated methodology aimed at refining the knowledge of the geological setting in unique urban environments, such as the city of Rome, where canonical approaches are limited by the scarcity of outcrops and ad-hoc geognostic surveys may be expensive and time-consuming. The methodology used in the study is based on a critical review of available geological, stratigraphic, archeological and historical-archival data. The integration of such data, properly stored, managed and analysed in a GIS environment, made it possible to: i) better frame the geological setting of a wide sector of the eastern part of Rome; and, in particular, ii) focus on buried natural morphologies (i.e. valleys) strongly modified by progressive urbanisation that determined their filling with huge thickness of backfills, which often represent a critical geotechnical issue. A detailed geological model was thus developed. The model shows slight but significant differences with respect to already available official maps, emphasising the need for carrying out in-depth analyses of already existing data from different sources, in order to collect thematic data to be used for effective land management policies

    Single-tree detection in high-density LiDAR data from UAV-based survey

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    UAV-based LiDAR survey provides very-high-density point clouds, which involve very rich information about forest detailed structure, allowing for detection of individual trees, as well as demanding high computational load. Single-tree detection is of great interest for forest management and ecology purposes, and the task is relatively well solved for forests made of single or largely dominant species, and trees having a very evident pointed shape in the upper part of the canopy (in particular conifers). Most authors proposed methods based totally or partially on search of local maxima in the canopy, which has poor performance for species that have flat or irregular upper canopy, and for mixed forests, especially where taller trees hide smaller ones. Such considerations apply in particular to Mediterranean hardwood forests. In such context, it is imperative to use the whole volume of the point cloud, however keeping computational load tractable. The authors propose the use of a methodology based on modelling the 3D-shape of the tree, which improves performance w.r.t to maxima-based models. A case study, performed on a hazel grove, is provided to document performance improvement on a relatively simple, but significant, case

    Redefining the organization of the public water supply sector: an analysisof costs and performance in the Portuguese market

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    CEMSThe role of regulators in the public sector has never been so challenging. Their function of identifying and amending costs misallocations within operators’ financial statements is constantly threatened by operational inefficiencies and abuses of the local government funds. While encouraging investments, regulators have to deal with the local economic and political situation. Portugal is suffering from a critical fiscal recession that is alarmingly constraining the government budget. On top of this, the municipalities are lowering tariffs to gain citizens’ consensus, creating unsustainable public debts. This paper aims at facilitating the detection of these flaws through the implementation of a financial model, to in turn enhance operators’ sustainability while protecting citizens’ interests

    The Seiberg-Witten map for non-commutative pure gravity and vacuum Maxwell theory

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    In this paper the Seiberg-Witten map is first analyzed for non-commutative Yang-Mills theories with the related methods, developed in the literature, for its explicit construction, that hold for any gauge group. These are exploited to write down the second-order Seiberg-Witten map for pure gravity with a constant non-commutativity tensor. In the analysis of pure gravity when the classical space-time solves the vacuum Einstein equations, we find for three distinct vacuum solutions that the corresponding non-commutative field equations do not have solution to first order in non-commutativity, when the Seiberg-Witten map is eventually inserted. In the attempt of understanding whether or not this is a peculiar property of gravity, in the second part of the paper, the Seiberg-Witten map is considered in the simpler case of Maxwell theory in vacuum in the absence of charges and currents. Once more, no obvious solution of the non-commutative field equations is found, unless the electromagnetic potential depends in a very special way on the wave vector.Comment: Misprints corrected. References adde

    Experimental Shape Sensing and Load Identification on a Stiffened Panel: A Comparative Study

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    The monitoring of loads and displacements during service life is proving to be crucial for developing a modern Structural Health Monitoring framework. The continuous monitoring of these physical quantities can provide fundamental information on the actual health status of the structure and can accurately guide pro-active condition-based maintenance operations, thus reducing the maintenance costs and extending the service life of the monitored structures. Pushed by these needs and by the simultaneous development in the field of strain sensing technologies, several displacement reconstruction and load identification methods have been developed that are based on discrete strain measurements. Among the different formulations, the inverse Finite Element Method (iFEM), the Modal Method (MM) and the 2-step method, the latter being the only one able to also compute the loads together with the displacements, have emerged as the most accurate and reliable ones. In this paper, the formulation of the three methods is summarized in order to set the numerical framework for a comparative study. The three methods are tested on the reconstruction of the external load and of the displacement field of a stiffened aluminium plate starting from experimentally measured strains. A fibre optic sensing system has been used to measure surface strains and an optimization procedure has been performed to provide the best fibre pattern, based on five lines running along the stiffeners’ direction and with a back-to-back measuring scheme. Additional sensors are used to measure the applied force and the plate’s deflection in some locations. The comparison of the results obtained by each method proves the extreme accuracy and reliability of the iFEM in the reconstruction of the deformed shape of the panel. On the other hand, the Modal Method leads to a good reconstruction of the displacements, but also exhibits a sensitivity to the choice of the modes considered for the specific application. Finally, the 2-step approach is able to correctly identify the loads and to reconstruct the displacements with an accuracy that depends on the modeling of the experimental setup

    Shape Sensing for an UAV Composite Half-Wing: Numerical Comparison between Modal Method and Ko’s Displacement Theory

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    Shape sensing is the reconstruction of the displacement field of a structure from some discrete surface strain measurements and is a key technology for structural health monitoring. Aim of this paper is to compare two approaches to shape sensing that have been shown to be more efficient, especially for aircraft structures applications, in terms of required input strain measurements, the Ko’s Displacement Theory and the Modal Method. Object of the shape-sensing analysis is the half-wing of a multirotor UAV. The approaches are summarized in order to set the framework for the numerical comparative in-vestigation. Then, the multirotor UAV is presented and a finite element model of its half-wing is used to simulate the static response to straight-and-level flight conditions. For a given common set of surface strain measurement points, Ko’s Displacement Theory and the Modal Method are compared in terms of accuracy of the reconstructed half-wing deflection and twist angle. The Modal Method is shown to be more accurate than Ko’s Displacement Theory, especially for the evaluation of the deflection field. Further numerical analyses show that the Modal Method is in-fluenced by the set of mode shapes included in the analysis and that excellent reconstructed de-flections can be obtained with a reduced number of sensors, thus assessing the approach as an ef-ficient shape-sensing tool for aircraft structures real applications
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