387 research outputs found

    Paramater estimation for the McKean-Vlasov stochastic differential equation

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    We consider the problem of parameter estimation for a stochastic McKean-Vlasov equation, and the associated system of weakly interacting particles. We first establish consistency and asymptotic normality of the offline maximum likelihood estimator for the interacting particle system in the limit as the number of particles N→∞N\rightarrow\infty. We then propose an online estimator for the parameters of the McKean-Vlasov SDE, which evolves according to a continuous-time stochastic gradient descent algorithm on the asymptotic log-likelihood of the interacting particle system. We prove that this estimator converges in L1\mathbb{L}^1 to the stationary points of the asymptotic log-likelihood of the McKean-Vlasov SDE in the joint limit as N→∞N\rightarrow\infty and t→∞t\rightarrow\infty, under suitable assumptions which guarantee ergodicity and uniform-in-time propagation of chaos. We then demonstrate, under the additional assumption of global strong concavity, that our estimator converges in L2\mathbb{L}^2 to the unique maximiser of this asymptotic log-likelihood function, and establish an L2\mathbb{L}^2 convergence rate. We also obtain analogous results under the assumption that, rather than observing multiple trajectories of the interacting particle system, we instead observe multiple independent replicates of the McKean-Vlasov SDE itself or, less realistically, a single sample path of the McKean-Vlasov SDE and its law. Our theoretical results are demonstrated via two numerical examples, a linear mean field model and a stochastic opinion dynamics model

    Selective sonographic screening for developmental dysplasia of the hip – increasing trends in late diagnosis

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    There are concerns that selective sonographic screening for developmental dysplasia of the hip (DDH) may be suboptimal. Our aim was to test this hypothesis by identifying trends in presentation and surgical treatment in patients with DDH. This is a retrospective review of children born between 1997-2018 who were treated surgically for DDH at our sub- regional paediatric orthopaedic unit. Demographic data, risk factors, age of diagnosis and surgical treatments were analysed. Late diagnosis was defined as greater than 4 months. 103 children (14 male, 89 female) underwent surgery. 93 hips were operated for dislocation and 21 for dysplasia. 13 patients presented with bilateral hip dislocations. The median age at diagnosis was 10 months (95% CI: 4-15). 62/103 (60.2%) were diagnosed late (after 4 months) and the median age for diagnosis in this group was 18.5 months (95% CI: 16-20.5). Significantly more patients were referred late (p=0.0077). The presence of risk factors (breech presentation or family history) was associated with early diagnosis. Over the duration of our study the operation rate per 1000 live births gradually increased, and on Poisson regression analysis there was a statistically significant increasing trend towards late diagnosis in recent years (p=0.0237), which necessitated more aggressive surgical management. In the UK, the current selective sonographic screening programme for DDH has shown a deterioration over the years of this study and this questions its current effectiveness. It appears that the majority of irreducible hip dislocations are diagnosed late, with an increased need for surgical management

    Towards 5G Software-Defined Ecosystems: Technical Challenges, Business Sustainability and Policy Issues

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    Techno-economic drivers are creating the conditions for a radical change of paradigm in the design and operation of future telecommunications infrastructures. In fact, SDN, NFV, Cloud and Edge-Fog Computing are converging together into a single systemic transformation termed “Softwarization” that will find concrete exploitations in 5G systems. The IEEE SDN Initiative1 has elaborated a vision, an evolutionary path and some techno-economic scenarios of this transformation: specifically, the major technical challenges, business sustainability and policy issues have been investigated. This white paper presents: 1) an overview on the main techno-economic drivers steering the “Softwarization” of telecommunications; 2) an introduction to the Open Mobile Edge Cloud vision (covered in a companion white paper); 3) the main technical challenges in terms of operations, security and policy; 4) an analysis of the potential role of open source software; 5) some use case proposals for proof-of-concepts; and 6) a short description of the main socio-economic impacts being produced by “Softwarization”. Along these directions, IEEE SDN is also developing of an open catalogue of software platforms, toolkits, and functionalities aiming at a step-by-step development and aggregation of test-beds/field-trials on SDNNFV- 5G

    Brokering justice: global indigenous rights and struggles over hydropower in Nepal

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    This article explores the dynamics of brokerage at the intersection between the justice conceptions enshrined in global norms and the notions of justice asserted in specific socio-environmental struggles. Using the case of a small hydropower project in Nepal, we trace the attempts of an indigenous activist to enrol villagers in his campaign against the background of villagers’ everyday negotiations with the hydropower company. The study shows how global norms, such as indigenous peoples’ rights, may fail to gain traction on the ground or even become sources of injustice in particular contexts

    Amadurecimento e qualidade pĂłs-colheita de kiwis gold3.

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    Enhanced Graph Rewriting Systems for Complex Software Domain

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    International audienceMethodologies for correct by construction reconfigurations can efficiently solve consistency issues in dynamic software architecture. Graph-based models are appropriate for designing such architectures and methods. At the same time, they may be unfit to characterize a system from a non functional perspective. This stems from efficiency and applicability limitations in handling time-varying characteristics and their related dependencies. In order to lift these restrictions, an extension to graph rewriting systems is proposed herein. The suitability of this approach, as well as the restraints of currently available ones, are illustrated, analysed and experimentally evaluated with reference to a concrete example. This investigation demonstrates that the conceived solution can: (i) express any kind of algebraic dependencies between evolving requirements and properties; (ii) significantly ameliorate the efficiency and scalability of system modifications with respect to classic methodologies; (iii) provide an efficient access to attribute values; (iv) be fruitfully exploited in software management systems; (v) guarantee theoretical properties of a grammar, like its termination
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