99 research outputs found

    Cooperative conflict detection and resolution of civil unmanned aerial vehicles in metropolis

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    Unmanned air vehicles have recently attracted attention of many researchers because of their potential civil applications. A systematic integration of unmanned air vehicles in non-segregated airspace is required that allows safe operation of unmanned air vehicles along with other manned aircrafts. One of the critical issues is conflict detection and resolution. This article proposes to solve unmanned air vehicles’ conflict detection and resolution problem in metropolis airspace. First, the structure of metropolis airspace in the coming future is studied, and the airspace conflict problem between different unmanned air vehicles is analyzed by velocity obstacle theory. Second, a conflict detection and resolution framework in metropolis is proposed, and factors that have influences on conflict-free solutions are discussed. Third, the multi-unmanned air vehicle conflict resolution problem is formalized as a nonlinear optimization problem with the aim of minimizing overall conflict resolution consumption. The safe separation constraint is further discussed to improve the computation efficiency. When the speeds of conflict-involved unmanned air vehicles are equal, the nonlinear safe separation constraint is transformed into linear constraints. The problem is solved by mixed integer convex programming. When unmanned air vehicles are with unequal speeds, we propose to solve the nonlinear optimization problem by stochastic parallel gradient descent–based method. Our approaches are demonstrated in computational examples

    A Cross-Domain Alliance Authentication Scheme based on Bilinear Group

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    Abstract: With the development of grid computing, cloud computing and other large distributed network technology, users need them to provide services of unlimited space and unlimited speed. In order to meeting this request of users, all the domains in these large distributed networks need coordination for each other. For ensuring the safety to access resources in all domains, we propose a crossdomain union authentication scheme. We compute a large prime cyclic group by elliptic curve, and use the direct decomposition of this group to decompose automorphism groups,and design an signcryption scheme between domains by bilinear of automorphism group to achieve cross-domain union authentication. This scheme overcome the complexity of certificate transmission and bottlenecks in the scheme of PKI-based, and it can trace the entities and supports two-way entities anonymous authentication, which avoid the domain certificate authority counterfeiting its member to access cross-domain resources. Analyses show that its advantages on security and communication-consumption

    Giant right atrial cystic hamartoma: a case report and literature review

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    An 11-year-old boy presenting with palpitation and chest distress was found to have gross cardiomegaly on chest radiography. Subsequent echocardiography revealed an intramural giant cystic mass in the right atrium. An operative measure was planned to prevent acute cardiac tamponade and right coronary artery obstruction. The patient successfully underwent open cystectomy to remove the mass, which was located on the front wall of the right atrium and extended to the atrioventricular appendage. Histopathological examination confirmed a cystic hamartoma. To the best of our knowledge, this is the first reported case of a giant cystic hamartoma located on the right atrium
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