111 resultados para AC voltage source
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Using a comprehensive firm-level data set from China spanning the period 1998–2005, this study investigates the relationship between firm size, financing sources, and total factor productivity growth. Controlling for the endogeneity of financing sources, we find that firm size plays an important role in the way financial structure affects the growth process. Domestic bank loans are more effective for bigger firms, while self-raised finance is more beneficial to smaller firms’ growth. We also uncover evidence that ownership mediates the relationship between firm size, finance, and growth.
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Using a comprehensive firm-level dataset spanning the period 1998-2005, this paper provides a thorough investigation of the relationship between firm size, total factor productivity growth and financial structure in China, controlling for the endogeneity of the latter. Generally, it finds financing source matters for firms of different size, and the extent to which financing source matters for firm growth is greater for small firms than big firms. Self-raised finance appears to be most effective in promoting small firms to grow, and bank loan seems to be more supportive to big firms. The relationship between size, finance and growth also depends on ownership. In addition, there exist strong complementarities between formal and informal finance, as well as between indigenous and foreign finance.
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Monitoring land-cover changes on sites of conservation importance allows environmental problems to be detected, solutions to be developed and the effectiveness of actions to be assessed. However, the remoteness of many sites or a lack of resources means these data are frequently not available. Remote sensing may provide a solution, but large-scale mapping and change detection may not be appropriate, necessitating site-level assessments. These need to be easy to undertake, rapid and cheap. We present an example of a Web-based solution based on free and open-source software and standards (including PostGIS, OpenLayers, Web Map Services, Web Feature Services and GeoServer) to support assessments of land-cover change (and validation of global land-cover maps). Authorised users are provided with means to assess land-cover visually and may optionally provide uncertainty information at various levels: from a general rating of their confidence in an assessment to a quantification of the proportions of land-cover types within a reference area. Versions of this tool have been developed for the TREES-3 initiative (Simonetti, Beuchle and Eva, 2011). This monitors tropical land-cover change through ground-truthing at latitude / longitude degree confluence points, and for monitoring of change within and around Important Bird Areas (IBAs) by Birdlife International and the Royal Society for the Protection of Birds (RSPB). In this paper we present results from the second of these applications. We also present further details on the potential use of the land-cover change assessment tool on sites of recognised conservation importance, in combination with NDVI and other time series data from the eStation (a system for receiving, processing and disseminating environmental data). We show how the tool can be used to increase the usability of earth observation data by local stakeholders and experts, and assist in evaluating the impact of protection regimes on land-cover change.
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The inverse problem of determining a spacewise dependent heat source, together with the initial temperature for the parabolic heat equation, using the usual conditions of the direct problem and information from two supplementary temperature measurements at different instants of time is studied. These spacewise dependent temperature measurements ensure that this inverse problem has a unique solution, despite the solution being unstable, hence the problem is ill-posed. We propose an iterative algorithm for the stable reconstruction of both the initial data and the source based on a sequence of well-posed direct problems for the parabolic heat equation, which are solved at each iteration step using the boundary element method. The instability is overcome by stopping the iterations at the first iteration for which the discrepancy principle is satisfied. Numerical results are presented for a typical benchmark test example, which has the input measured data perturbed by increasing amounts of random noise. The numerical results show that the proposed procedure gives accurate numerical approximations in relatively few iterations.
The multinational enterprise as a source of international knowledge flows:Direct evidence from Italy
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This paper examines the determinants of technology transfer between parent firms and their international affiliates, and of knowledge spillovers from those affiliates to host-country firms. Using a unique data set of foreign multinational enterprise (MNE) affiliates based in Italy, we find that affiliate investment in R&D and investment in capital-embodied technology plays a significant role in determining the nature of intra-firm technology flows. However, the basis for any spillovers arising from MNE affiliates does not originate from codified knowledge associated with R&D, but rather from the productivity of the affiliate.
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The recent explosive growth of voice over IP (VoIP) solutions calls for accurate modelling of VoIP traffic. This study presents measurements of ON and OFF periods of VoIP activity from a significantly large database of VoIP call recordings consisting of native speakers speaking in some of the world's most widely spoken languages. The impact of the languages and the varying dynamics of caller interaction on the ON and OFF period statistics are assessed. It is observed that speaker interactions dominate over language dependence which makes monologue-based data unreliable for traffic modelling. The authors derive a semi-Markov model which accurately reproduces the statistics of composite dialogue measurements. © The Institution of Engineering and Technology 2013.
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To fully utilize second-life batteries on the grid system, a hybrid battery scheme needs to be considered for several reasons: the uncertainty over using a single source supply chain for second-life batteries, the differences in evolving battery chemistry and battery configuration by different suppliers to strive for greater power levels, and the uncertainty of degradation within a second-life battery. Therefore, these hybrid battery systems could have widely different module voltage, capacity, and initial state of charge and state of health. In order to suitably integrate and control these widely different batteries, a suitable multimodular converter topology and an associated control structure are required. This paper addresses these issues proposing a modular boost-multilevel buck converter based topology to integrate these hybrid second-life batteries to a grid-tie inverter. Thereafter, a suitable module-based distributed control architecture is introduced to independently utilize each converter module according to its characteristics. The proposed converter and control architecture are found to be flexible enough to integrate widely different batteries to an inverter dc link. Modeling, analysis, and experimental validation are performed on a single-phase modular hybrid battery energy storage system prototype to understand the operation of the control strategy with different hybrid battery configurations.
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DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT
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DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT
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We describe an all-fibre, passive scheme for making extended range interferometric measurements based on the dual wavelength technique. The coherence tuned interferometer network is illuminated with a single superfluorescent fibre source at 1.55 μm and the two wavelengths are synthesised at the output by means of chirped fibre Bragg gratings. We demonstrate an unambiguous sensing range of 270 μm, with a dynamic range of 2.7 × 105.
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Wavelength-locking of a multiwavelength stabilized slotted Fabry-Perot (SFP) laser to a single-mode laser source is experimentally demonstrated. The SFP resonates at channels spaced by similar to 8 nm between 1510 and 1565 nm over a wide range of temperatures and drive currents. Under low-power (<- 20 dBm) external optical injection, wavelength-locking with a sidemode suppression ratio (SMSR) > 25 dB is achieved. A locking width of > 25 GHz and SMSR > 30 dB can be achieved for each locked wavelength channel at injection power > - 16 dBm.
Resumo:
The inverse problem of determining a spacewise-dependent heat source for the parabolic heat equation using the usual conditions of the direct problem and information from one supplementary temperature measurement at a given instant of time is studied. This spacewise-dependent temperature measurement ensures that this inverse problem has a unique solution, but the solution is unstable and hence the problem is ill-posed. We propose a variational conjugate gradient-type iterative algorithm for the stable reconstruction of the heat source based on a sequence of well-posed direct problems for the parabolic heat equation which are solved at each iteration step using the boundary element method. The instability is overcome by stopping the iterative procedure at the first iteration for which the discrepancy principle is satisfied. Numerical results are presented which have the input measured data perturbed by increasing amounts of random noise. The numerical results show that the proposed procedure yields stable and accurate numerical approximations after only a few iterations.