950 resultados para Turbulent flows


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This article enquires into the causes of union growth and decline by analysing flows in and out of membership at the level of 70 Swiss union locals over 2006-2008. Gross flows in union membership are much larger than the resulting net changes: annual membership turnover of 10 per cent is a surprisingly constant feature across unions. Net changes in membership are primarily determined by inflows: successful and languishing union locals differ in their entry rates, whereas exit rates are similar. Variance in union locals' entry rates is not usefully explained by the labour market context, but by differences in union strategy.

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Every year, debris flows cause huge damage in mountainous areas. Due to population pressure in hazardous zones, the socio-economic impact is much higher than in the past. Therefore, the development of indicative susceptibility hazard maps is of primary importance, particularly in developing countries. However, the complexity of the phenomenon and the variability of local controlling factors limit the use of processbased models for a first assessment. A debris flow model has been developed for regional susceptibility assessments using digital elevation model (DEM) with a GIS-based approach.. The automatic identification of source areas and the estimation of debris flow spreading, based on GIS tools, provide a substantial basis for a preliminary susceptibility assessment at a regional scale. One of the main advantages of this model is its workability. In fact, everything is open to the user, from the data choice to the selection of the algorithms and their parameters. The Flow-R model was tested in three different contexts: two in Switzerland and one in Pakistan, for indicative susceptibility hazard mapping. It was shown that the quality of the DEM is the most important parameter to obtain reliable results for propagation, but also to identify the potential debris flows sources.

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Aquest document de treball mira d'establir un nou camp d'investigació a la cruïlla entre els fluxos de migració i d'informació i comunicació. Hi ha diversos factors que fan que valgui la pena adoptar aquesta perspectiva. El punt central és que la migració internacional contemporània és incrustada en la dinàmica de la societat de la informació, seguint models comuns i dinàmiques interconnectades. Per consegüent, s'està començant a identificar els fluxos d'informació com a qüestions clau en les polítiques de migració. A més, hi ha una manca de coneixement empíric en el disseny de xarxes d'informació i l'ús de les tecnologies d'informació i comunicació en contextos migratoris. Aquest document de treball també mira de ser una font d'hipòtesis per a investigacions posteriors.

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The paper analyses the regional flows of domestic tourism that took place in Spain in year 2000, contributing to the state of knowledge on tourism required by authorities and private firms when faced with decision making, for example, for regional infrastructure planning. Although tourism is one of the main income-generating economic activities in Spain, domestic tourism has received little attention in the literature compared to inbound tourism. The paper uses among others, gravitational model tools and concentration indices, to analyse regional concentration of both domestic demand and supply; tourism flows among regions, and the causes that may explain the observed flows and attractiveness between regions. Among the most remarkable results are the high regional concentration of demand and supply, and the role of population and regional income as explanatory variables. Also remarkable are the attractiveness of own region and neighbour ones, and that domestic tourism may be acting as a regional income redistributing activity

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TCP flows from applications such as the web or ftp are well supported by a Guaranteed Minimum Throughput Service (GMTS), which provides a minimum network throughput to the flow and, if possible, an extra throughput. We propose a scheme for a GMTS using Admission Control (AC) that is able to provide different minimum throughput to different users and that is suitable for "standard" TCP flows. Moreover, we consider a multidomain scenario where the scheme is used in one of the domains, and we propose some mechanisms for the interconnection with neighbor domains. The whole scheme uses a small set of packet classes in a core-stateless network where each class has a different discarding priority in queues assigned to it. The AC method involves only edge nodes and uses a special probing packet flow (marked as the highest discarding priority class) that is sent continuously from ingress to egress through a path. The available throughput in the path is obtained at the egress using measurements of flow aggregates, and then it is sent back to the ingress. At the ingress each flow is detected using an implicit way and then it is admission controlled. If it is accepted, it receives the GMTS and its packets are marked as the lowest discarding priority classes; otherwise, it receives a best-effort service. The scheme is evaluated through simulation in a simple "bottleneck" topology using different traffic loads consisting of "standard" TCP flows that carry files of varying sizes

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In previous work we proposed a multi-objective traffic engineering scheme (MHDB-S model) using different distribution trees to multicast several flows. In this paper, we propose a heuristic algorithm to create multiple point-to-multipoint (p2mp) LSPs based on the optimum sub-flow values obtained with our MHDB-S model. Moreover, a general problem for supporting multicasting in MPLS networks is the lack of labels. To reduce the number of labels used, a label space reduction algorithm solution is also considered

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We show that any transversally complete Riemannian foliation &em&F&/em& of dimension one on any possibly non-compact manifold M is tense; namely, (M,&em&F&/em&) admits a Riemannian metric such that the mean curvature form of &em&F&/em& is basic. This is a partial generalization of a result of Domínguez, which says that any Riemannian foliation on any compact manifold is tense. Our proof is based on some results of Molino and Sergiescu, and it is simpler than the original proof by Domínguez. As an application, we generalize some well known results including Masa's characterization of tautness.

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The development of susceptibility maps for debris flows is of primary importance due to population pressure in hazardous zones. However, hazard assessment by processbased modelling at a regional scale is difficult due to the complex nature of the phenomenon, the variability of local controlling factors, and the uncertainty in modelling parameters. A regional assessment must consider a simplified approach that is not highly parameter dependant and that can provide zonation with minimum data requirements. A distributed empirical model has thus been developed for regional susceptibility assessments using essentially a digital elevation model (DEM). The model is called Flow-R for Flow path assessment of gravitational hazards at a Regional scale (available free of charge under www.flow-r.org) and has been successfully applied to different case studies in various countries with variable data quality. It provides a substantial basis for a preliminary susceptibility assessment at a regional scale. The model was also found relevant to assess other natural hazards such as rockfall, snow avalanches and floods. The model allows for automatic source area delineation, given user criteria, and for the assessment of the propagation extent based on various spreading algorithms and simple frictional laws.We developed a new spreading algorithm, an improved version of Holmgren's direction algorithm, that is less sensitive to small variations of the DEM and that is avoiding over-channelization, and so produces more realistic extents. The choices of the datasets and the algorithms are open to the user, which makes it compliant for various applications and dataset availability. Amongst the possible datasets, the DEM is the only one that is really needed for both the source area delineation and the propagation assessment; its quality is of major importance for the results accuracy. We consider a 10m DEM resolution as a good compromise between processing time and quality of results. However, valuable results have still been obtained on the basis of lower quality DEMs with 25m resolution.

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Using a new dataset on capital account openness, we investigate why equity return correlations changed over the last century. Based on a new, long-run dataset on capital account regulations in a group of 16 countries over the period 1890-2001, we show that correlations increase as financial markets are liberalized. These findings are robust to controlling for both the Forbes-Rigobon bias and global averages in equity return correlations. We test the robustness of our conclusions, and show that greater synchronization of fundamentals is not the main cause of increasing correlations. These results imply that the home bias puzzle may be smaller than traditionally claimed.

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Rock slope instabilities are implicitly linked to the supply of sediment and debris recharging channels prone to debris flow. Hence, the incorporation of bedrock structure and terrain morphology can be relevant in the analysis of sediment budget and debris flow hazard assessment. Here, the mode of debris production of the Manival catchment (northern French Alps) is documented by the study of its morphostructural aspects extracted from high resolution DEM. Terrain implication in the process of debris supply is evaluated by: a) A systematic classification of the major morphological units based on the slope gradient that enables a spatial analysis of zones of debris production and deposition. b) A detailed structural analysis performed on DEM in order to identify potential unstable slopes. c) An analysis of the gullies orientation that informs in term of structural control of the sources zones. d) Localisation of high density joints sets that document about whether sources of continuous debris production are controlled by the structural setting of the catchment. These DEM-based indicators can be used as proxies for assessing the influences of the current topography and enable to quantify a degree of susceptibility to mass wasting and hillslope erosion activity. This present contribution suggests some directions for characterizing sediment flux dynamic in small alpine catchment.

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External knowledge is an important input for the innovation process of firms. Increasingly, this knowledge is likely to originate fromoutside of their national borders. This explains the preoccupationof policymakers with stimulating local technology transfers coming from international firms. We find that firms that have access to the international technology market are more likely to transfer technology to the local economy. In doing so, we qualify the traditional assertion that multinational firms are more likelyto transfer technology to the local economy. Once controlled for the superior access to the international technology market that multinationals enjoy, we find that these firms are not more likelyto transfer technology to the local economy compared to exportingor local firms that have access to the international technology market. In summary, the main result of this paper is that it isnot so much the international character of the firms, but rathertheir access to the international technology market that is important for generating external knowledge transfers to the local economy.

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This paper presents a stylized model of international trade and asset price bubbles. Its central insight is that bubbles tend to appear and expand in countries where productivity is low relative to the rest of the world. These bubbles absorb local savings, eliminating inefficient investments and liberating resources that are in part used to invest in high productivity countries. Through this channel, bubbles act as a substitute for international capital flows, improving the international allocation of investment and reducing rate-of-return differentials across countries. This view of asset price bubbles could eventually provide a simple account of some real world phenomenae that have been difficult to model before, such as the recurrence and depth of financial crises or their puzzling tendency to propagate across countries.

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In this paper we carefully link knowledge flows to and from a firm s innovation process with this firm s investment decisions. Three types of investments are considered: investments in applied research, investments in basic research, and investments in intellectual property protection. Only when basic research is performed, can the firm effectively access incoming knowledge flows and these incoming spillovers serve to increase the efficiency of own applied research. The firm can at the same time influence outgoing knowledge flows, improving appropriability of its innovations, by investing in protection. Our results indicate that firms with small budgets for innovation will not invest in basic research. This occurs in the short run, when the budget for know-how creation is restricted, or in the long-run, when market opportunities are low, when legal protection is not very important, or, when the pool of accessible and relevant external know-how is limited. The ratio of basic to applied research is non-decreasing in the size of the pool of accessible external know-how, the size and opportunity of the market, and, the effectiveness of intellectual property rights protection. This indicates the existence of economies of scale in basic research due to external market related factors. Empirical evidence from a sample of innovative manufacturing firms in Belgium confirms the economies of scale in basic research as a consequence of the firm s capacity to access external knowledge flows and to protectintellectual property, as well as the complementarity between legal and strategic investments.

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The standard deviations of capital flows to emerging countries are 80 percent higher than those to developed countries. First, we show that very little of this difference can be explained by more volatile fundamentals or by higher sensitivity to fundamentals. Second, we show that most of the difference in volatility can be accounted for by three characteristics of capital flows: (i) capital flows to emerging countries are more subject to occasional large negative shocks ( crises ) than those to developed countries, (ii) shocks are subject to contagion, and (iii) the most important one shocks to capital flows to emerging countries are more persistent than those to developed countries. Finally, we study a number of country characteristics to determine which are most associated with capital flow volatility. Our results suggest that underdevelopment of domestic financial markets, weak institutions, and low income per capita, are all associated with capital flow volatility.