895 resultados para Markov chains. Convergence. Evolutionary Strategy. Large Deviations


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The simulation of a power system such as the More Electric Aircraft is a complex problem. There are conflicting requirements of the simulation, for example in order to reduce simulation run-times, power ratings that need to be established over long periods of the flight can be calculated using a fairly coarse model, whereas power quality is established over relatively short periods with a detailed model. An important issue is to establish the requirements of the simulation work at an early stage. This paper describes the modelling and simulation strategy adopted for the UK TIMES project, which is looking into the optimisation of the More Electric Aircraft from a system level. Essentially four main requirements of the simulation work have been identified, resulting in four different types of simulation. Each of the simulations is described along with preliminary models and results.

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We introduce self-interested evolutionary market agents, which act on behalf of service providers in a large decentralised system, to adaptively price their resources over time. Our agents competitively co-evolve in the live market, driving it towards the Bertrand equilibrium, the non-cooperative Nash equilibrium, at which all sellers charge their reserve price and share the market equally. We demonstrate that this outcome results in even load-balancing between the service providers. Our contribution in this paper is twofold; the use of on-line competitive co-evolution of self-interested service providers to drive a decentralised market towards equilibrium, and a demonstration that load-balancing behaviour emerges under the assumptions we describe. Unlike previous studies on this topic, all our agents are entirely self-interested; no cooperation is assumed. This makes our problem a non-trivial and more realistic one.

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This work introduces a Gaussian variational mean-field approximation for inference in dynamical systems which can be modeled by ordinary stochastic differential equations. This new approach allows one to express the variational free energy as a functional of the marginal moments of the approximating Gaussian process. A restriction of the moment equations to piecewise polynomial functions, over time, dramatically reduces the complexity of approximate inference for stochastic differential equation models and makes it comparable to that of discrete time hidden Markov models. The algorithm is demonstrated on state and parameter estimation for nonlinear problems with up to 1000 dimensional state vectors and compares the results empirically with various well-known inference methodologies.

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Mathematics Subject Classification: 30B10, 30B30; 33C10, 33C20

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This paper contrasts the effects of trade, inward FDI and technological development upon the demand for skilled and unskilled workers in the UK. By focussing on industry level data panel data on smaller firms, the paper also contrasts these effects with those generated by large scale domestic investment. The analysis is placed within the broader context of shifts in British industrial policy, which has seen significant shifts from sectoral to horizontal measures and towards stressing the importance of SMEs, clusters and new technology, all delivered at the regional scale. This, however, is contrasted with continued elements of British and EU regional policy which have emphasised the attraction of inward investment in order to alleviate regional unemployment. The results suggest that such policies are not naturally compatible; that while both trade and FDI benefit skilled workers, they have adverse effects on the demand for unskilled labour in the UK. At the very least this suggests the need for a range of policies to tackle various targets (including in this case unemployment and social inclusion) and the need to integrate these into a coherent industrial strategy at various levels of governance, whether regional and/or national. This has important implications for the form of any 'new' industrial policy.

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Developing novel heterojunction photocatalysts is a powerful strategy for improving the separation efficiency of photogenerated charge carriers, which is attracting the intense research interest in photocatalysis. Herein we report a highly efficient hetero/nanojunction consisting of Ag2CO3 nanoparticles grown on layered g-C3N4 nanosheets synthesized via a facile and template free in situ precipitation method. The UV–vis diffuse reflectance studies revealed that the synthesized Ag2CO3/g-C3N4 hetero/nanojunctions exhibit a broader and stronger light absorption in the visible light region, which is highly beneficial for absorbing the visible light in the solar spectrum. The optimum photocatalytic activity of Ag2CO3/g-C3N4 at a weight content of 10% Ag2CO3 for the degradation of Rhodamine B was almost 5.5 and 4 times as high as that of the pure Ag2CO3 and g-C3N4, respectively. The enhanced photocatalytic activity of the Ag2CO3/g-C3N4 hetero/nanojunctions is due to synergistic effects including the strong visible light absorption, large specific surface area, and high charge transfer and separation efficiency. More importantly, the high photostability and low use of the noble metal silver which reduces the cost of the material. Therefore, the synthesized Ag2CO3/g-C3N4 hetero/nanojunction photocatalyst is a promising candidate for energy storage and environment protection applications.

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A great number of strategy tools are being taught in strategic management modules. These tools are available to managers for use in facilitating strategic decision making and enhancing the strategy development process in their organisations. A number of studies have been published examining which are the most popular tools; however there is little empirical evidence on how their utilisation influences the strategy process. This paper is based on a large scale international survey on the strategy development process, and seeks to examine the impact of a particular strategy tool, the Balanced Scorecard (BSC), upon the strategy process. Recently, it has been suggested that as a strategy tool, the BSC can influence all elements of the strategy process. The results of this study indicate that although there are significant differences in some elements of the strategy process between the organisations that have implemented the BSC and those that have not, the impact is not comprehensive. © 2011 Operational Research Society Ltd. All rights reserved.

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Large-scale mechanical products, such as aircraft and rockets, consist of large numbers of small components, which introduce additional difficulty for assembly accuracy and error estimation. Planar surfaces as key product characteristics are usually utilised for positioning small components in the assembly process. This paper focuses on assembly accuracy analysis of small components with planar surfaces in large-scale volume products. To evaluate the accuracy of the assembly system, an error propagation model for measurement error and fixture error is proposed, based on the assumption that all errors are normally distributed. In this model, the general coordinate vector is adopted to represent the position of the components. The error transmission functions are simplified into a linear model, and the coordinates of the reference points are composed by theoretical value and random error. The installation of a Head-Up Display is taken as an example to analyse the assembly error of small components based on the propagation model. The result shows that the final coordination accuracy is mainly determined by measurement error of the planar surface in small components. To reduce the uncertainty of the plane measurement, an evaluation index of measurement strategy is presented. This index reflects the distribution of the sampling point set and can be calculated by an inertia moment matrix. Finally, a practical application is introduced for validating the evaluation index.

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A tanulmány célja, hogy azonosítsa azokat a tényezőket, amelyek befolyásolják az élelmiszer-gazdasági kis- és közepes vállalkozások szerződéseinek teljesülését a Közép-magyarországi régióban. Számításaink megerősítik Guo-Jolly [2008] eredményeit, amely szerint a szerződések tartalmi elemeinek kulcsszerepük van a szerződések teljesülésében. Továbbá a vállalatvezetői képességek, a vállalati és tranzakciós jellemzők szintén jelentős hatást gyakorolnak a szerződések teljesülésére. Érdekes módon az ágazatspecifikus jellemzőknek csak korlátozott szerepük van a szerződések teljesülésének magyarázatában. / === / The paper analyses the contractual relations and contract fulfilment of small and medium-sized firms along the food chain, in the central region of Hungary, using survey data. The estimates also reveal that contract fulfilment is significantly affected by the design of the contract. They confirm that an important role in contract fulfilment is played by corporate and managerial attributes and transaction characteristics. Interestingly, branch-specific characteristics play only a limited role in explaining contract fulfilment.

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A tanulmánykötet a globális értékláncok névvel fémjelezett jelenséget veszi górcső alá. A fókuszban a multinacionális vállalatcsoportok ill. a nemzetközi cégek állnak. A tíz tanulmány különböző megközelítések alapján betekintést ad abba, hogy hogyan ragadhatják meg és vizsgálhatják a kutatók a globális értékláncokat a vállalatok, ill. vezetőik nézőpontjából, mi következik a kutatási eredményekből a vállalatok vezetői számára, és milyen következményei vannak a globális értékláncok karakteres és terjedő jelenlétének a nemzetgazdaságok gazdasági politikáit formálókra. A tanulmánykötet szerzői a 2012/2013.tanév tavaszi félévében a Nemzetközi üzleti gazdaságtan c. PhD kurzus hallgatói voltak. ______ The working paper is to provide a Hungarian language overview on the research finding s on Global Value Chain and global factory. The phenomenon behind them is recognized but under researched in Hungary. The chapters of the working paper are to cover as many angles and perspectives of Global Value Chain as many it is possible. Each chapter is based on a published English language paper. Theoretical and conceptual issues, considerations of MNEs and small- and medium sized enterprises and that of national policies are discussed. Authors of the working paper attended the International Business PhD course in the spring semester of 2012/2013.