344 research outputs found

    A trace finite element method for a class of coupled bulk-interface transport problems

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    In this paper we study a system of advection-diffusion equations in a bulk domain coupled to an advection-diffusion equation on an embedded surface. Such systems of coupled partial differential equations arise in, for example, the modeling of transport and diffusion of surfactants in two-phase flows. The model considered here accounts for adsorption-desorption of the surfactants at a sharp interface between two fluids and their transport and diffusion in both fluid phases and along the interface. The paper gives a well-posedness analysis for the system of bulk-surface equations and introduces a finite element method for its numerical solution. The finite element method is unfitted, i.e., the mesh is not aligned to the interface. The method is based on taking traces of a standard finite element space both on the bulk domains and the embedded surface. The numerical approach allows an implicit definition of the surface as the zero level of a level-set function. Optimal order error estimates are proved for the finite element method both in the bulk-surface energy norm and the L2L^2-norm. The analysis is not restricted to linear finite elements and a piecewise planar reconstruction of the surface, but also covers the discretization with higher order elements and a higher order surface reconstruction

    The Sky is the Limit? The Determinants and Constraints of European Airports' Commercial Revenues

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    This study investigates the determinants of commercial and retail airport revenues as well as revenues from real estate operations. Cross-sectional OLS, 2SLS and robust regression models of European airports identify a number of significant drivers of airport revenues. Aviation revenues per passenger are mainly determined by the national income per capita in which the airport is located, the percentage of leisure travelers and the size of the airport proxied by total aviation revenues. Main drivers of commercial revenues per passenger include the total number of passengers passing through the airport, the ratio of commercial to total revenues, the national income, the share of domestic and leisure travelers and the total number of flights. These results are in line with previous findings of a negative influence of business travelers on commercial revenues per passenger. We also find that a high amount of retail space per passenger is generally associated with lower commercial revenues per square meter confirming decreasing marginal revenue effects. Real estate revenues per passenger are positively associated with national income per capita at airport location, share of intra-EU passengers and percent delayed flights. Overall, aviation and non-aviation revenues appear to be strongly interlinked, underlining the potential for a comprehensive airport management strategy above and beyond mere cost minimization of the aviation sector.Commercial revenues, non-aviation activities, European airports, regression analysis

    Flying for a buck or two: Low-cost Carriers in Australia and New Zealand

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    Over the past few decades, the traditional aviation market has seen significant developments. Traditional “legacy“ carriers have been challenged by new no/low-frills, low cost carriers. While these new airlines have a relatively long history in North America, more recently they successively emerged in markets such as Europe, Asia, Oceania and Africa. The business model of low cost carriers has revolutionized air travel, and both media and academics paid ample attention to these in America and Europe. However, academic literature pertaining to the development of low cost carriers in Australia and New Zealand is scarce. Thus, this paper offers a brief history of low cost carriers in this region, and compares the business models of low cost carriers currently operating in and between Australia and New Zealand. The paper concludes that low cost carriers in this region differ from American and European low cost carriers, in part due to the geography of the countries. The main differences are the levels of in-flight service, and the fact that Australian and New Zealand low cost carriers operate on longer distances, such as coast-to-coast domestic flights in Australia, trans-Tasman flights, and flights to the South Pacific islands, and increasingly to Asia

    Multi-vortices are Wall Vortices: A Numerical Proof

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    We study the Abrikosov-Nielsen-Olesen multi-vortices. Using a numerical code we are able to solve the vortex equations with winding number up to n=25,000. We can thus check the wall vortex conjecture previously made in hep-th/0507273 and hep-th/0507286. The numerical results show a remarkable agreement with the theoretical predictions.Comment: 22 pages, 18 figure

    Adapt or Become Extinct!:The Case for a Unified Framework for Deployment-Time Optimization

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    The High-Performance Computing ecosystem consists of a large variety of execution platforms that demonstrate a wide diversity in hardware characteristics such as CPU architecture, memory organization, interconnection network, accelerators, etc. This environment also presents a number of hard boundaries (walls) for applications which limit software development (parallel programming wall), performance (memory wall, communication wall) and viability (power wall). The only way to survive in such a demanding environment is by adaptation. In this paper we discuss how dynamic information collected during the execution of an application can be utilized to adapt the execution context and may lead to performance gains beyond those provided by static information and compile-time adaptation. We consider specialization based on dynamic information like user input, architectural characteristics such as the memory hierarchy organization, and the execution profile of the application as obtained from the execution platform\u27s performance monitoring units. One of the challenges of future execution platforms is to allow the seamless integration of these various kinds of information with information obtained from static analysis (either during ahead-of-time or just-in-time) compilation. We extend the notion of information-driven adaptation and outline the architecture of an infrastructure designed to enable information flow and adaptation through-out the life-cycle of an application

    Gestational age and the risk of autism spectrum disorder in Sweden, Finland, and Norway: A cohort study

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    Introduction The complex etiology of autism spectrum disorder (ASD) is still unresolved. Preterm birth ( Author summaryWhy was this study done? Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by persistent impairments in social communication and restricted and repetitive behaviors. The etiology remains unresolved. Length of gestation, including preterm birth, has been linked to risk of ASD, but reliable estimates of risks for the whole range of gestational ages (GAs) are lacking. The primary objective of this study was to provide a detailed and robust description of ASD risk across the entire range of GA while taking fetal sex and size at birth into account. What did the researchers do and find? This study was based on population-based data from national medical registries in three Nordic countries-Sweden, Finland, and Norway-and included 3,526,174 singletons born 1995 to 2015. Relative risks (RRs) of ASD by GA at birth were estimated with log binominal regression. The RR of ASD increased by each week of GA, pre- as well as postterm, from 40 to 24 weeks of gestation and from 40 to 44 weeks of gestation, independently of sex and birth weight for GA. What do these findings mean? On a population level, the risks of ASD were increased in children born either pre- or postterm, including children born close to week 40. We found that the risk of ASD increased weekly, with each week further away from 40 weeks of gestation.Peer reviewe
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