975 resultados para Covering Radius


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Models of different degrees of complexity are found in the literature for the estimation of lightning striking distances and attractive radius of objects and structures. However, besides the oversimplifications of the physical nature of the lightning discharge on which most of them are based, till recently the tridimensional structure configuration could not be considered. This is an important limitation, as edges and other details of the object affect the electric field and, consequently, the upward leader initiation. Within this context, the Self-consistent leader initiation and propagation model (SLIM) proposed by Becerra and Cooray is state-of-the-art leader inception and propagation leader model based on the physics of leader discharges which enables the tridimensional geometry of the structure to be taken into account. In this paper, the model is used for estimating the striking distance and attractive radius of power transmission lines. The results are compared with those obtained from the electrogeometric and Eriksson's models. © 2003-2012 IEEE.

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Eighteen months into the implementation of the 2008-2009 biennial strategic work programme, the Economic Commission for Latin America and the Caribbean (ECLAC) Subregional Headquarters for the Caribbean continues to focus on strengthening the delivery of activities through regular internal meetings with programme and research staff and consultations with member countries and other partner institutions. The scaling up of efforts advocating for more evidence-based development policy-making is being advanced utilizing the resources provided through the implementation of an additional seven extrabudgetary-funded projects. This effort is being undertaken in collaboration and in consultation with our major international and regional development partners – United Nations Development Programme (UNDP), United Nations Development Fund for Women (UNIFEM), United Nations Population Fund (UNFPA), United Nations Children’s Fund (UNICEF), Caribbean Community (CARICOM), Caribbean Development Bank (CDB), Organisation of Eastern Caribbean States (OECS), Association of Caribbean States (ACS), Inter-American Development Bank (IDB), World Bank, Department for International Development (DFID), Caribbean Community Climate Change Centre (CCCCC). and others. In

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The focus of the activities of the Economic Commission for Latin America and the Caribbean/Caribbean Development and Cooperation Committee (ECLAC/CDCC) secretariat during the 2006-2007 biennium continued to be on assistance to member governments of the subregion with policy-making and development strategies, especially on issues relevant to the promotion of the economic, social, and environmental dimensions of development in the Caribbean. The Subregional Headquarters for the Caribbean worked closely with member countries of the CDCC in an effort to ensure the relevance of outputs which would inform policy options. This involved the strengthening of partnerships with both regional and subregional institutions and relevant agencies of the United Nations system working in the Caribbean. A major decision was taken to refocus the operational aspects of the secretariat to ensure that they were relevant to the development goals of its members. This involved the introduction of a thematic approach to the work of the office. One of the changes resulting from this was the restructuring and renaming of the Caribbean Documentation Centre. The Caribbean Knowledge Management Centre (CKMC), as it is now known, has changed its emphasis from organizing and disseminating documents, and is now a more proactive partner in the research undertaken by staff and other users of the service. The CKMC manages the ECLAC website, the public face of the organization. Newsletters and all other documents, including Information and Communications Technology (ICT) profiles of selected countries, prepared by the secretariat, are now available online at the ECLAC/CDCC website www.eclacpos.org . The Caribbean Knowledge Management Portal was launched at a meeting of information specialists in St. Vincent and the Grenadines in 2007. In addition to reaching a wider public, this measure was introduced as a means of reducing the cost of printing or disseminating publications. In spite of the unusually high vacancy rate, at both the international and local levels, during the biennium, the subregional headquarters accomplished 98 per cent of the 119 outputs earmarked for the period. Using vacant positions to carry out the assignments was not an easy task, given the complexity in recruiting qualified and experienced persons for short periods. Nevertheless, consultancy services and short-term replacement staff greatly aided the delivery of these outputs. All the same, 35 work months remained unused during the biennium, leaving 301 work months to complete the outputs. In addition to the unoccupied positions, the work of the subprogramme was severely affected by the rising cost of regional and subregional travel which limited the ability of staff to network and interact with colleagues of member countries. This also hampered the outreach programme carried out mainly through ad hoc expert group meetings. In spite of these shortcomings, the period proved to be successful for the subprogramme as it engaged the attention of member countries in its work either through direct or indirect participation. Staff members completed 36 technical papers plus the reports of the meetings and workshops. A total of 523 persons, representing member countries, participated in the 18 intergovernmental and expert meetings convened by the secretariat in the 24-month period. In its effort to build technical capacity, the subprogramme convened 15 workshops/seminars which offered training for 446 persons.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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PTFE foils were irradiated with different ion beams (Xe, Au and U) with energies up to 1.5 GeV and fluences between 1 x 10(8) and 1 x 10(13) ions/cm(2) at room temperature. The induced modifications in the polymer were analyzed by FTIR, UV-Vis spectroscopy, and XRD. In the FTIR spectra, the CF2 degradation accompanied by the formation of CF3 terminal and side groups were observed. In the UV-Vis spectra, the observed increase in the absorption at UV wavelengths is an indication of polymer carbonization. From XRD, the amorphization of the material was evidenced by the decrease in the intensity of the main diffraction peak. An exponential fit of the intensity of the IR absorption peaks resulted in the following values: 2.9 +/- 0.8; 4.5 +/- 0.9 and 5.6 +/- 0.8 nm for the latent track radius after irradiation with Xe, Au and U beams, respectively. (C) 2011 Elsevier B.V. All rights reserved.

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Many bird species take recesses during incubation, and while the nests are unattended, the eggs may both be vulnerable to predation and reach suboptimal temperatures for embryo development. Perhaps to avoid these negative possibilities, some birds cover their eggs with materials when they depart from nests. We examined experimentally, using the ground-nesting Kentish plover as model species, whether egg-covering allows egg temperatures to remain within optimal limits for embryogenesis in unattended nests, thus reducing the requirements of contact incubation, and simultaneously maintain the eggs' camouflage. There was a negative relationship between nest attendance and ambient temperature, but only during mid-morning, the period of the day when egg-covering was most frequent. Indeed, during mid-morning egg-covering not only served to better camouflage the eggs, but also to maintain egg temperatures within optimal thermal thresholds for embryogenesis while the nests remained unattended. During other periods of the day, covered eggs in unattended nests overheated (e.g., afternoon) or did not reach the optimal temperature for embryogenesis (e.g., early morning). During periods in which eggs may be uncovered to alleviate overheating, unattended nests may be easier to locate by predators, because the eggs are less well camouflaged. Therefore, camouflage and appropriate thermal environment are inseparable functions of egg-covering in the ground-nesting Kentish plover.

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We analyse the secular effects of a long-lived Galactic spiral structure on the stellar orbits with mean radii close to the corotation resonance. By test-particle simulations and different spiral potential models with parameters constrained on observations, we verified the formation of a minimum with amplitude ∼30–40 per cent of the background disc stellar density at corotation. Such a minimum is formed by the secular angular momentum transfer between stars and the spiral density wave on both sides of corotation. We demonstrate that the secular loss (gain) of angular momentum and decrease (increase) of mean orbital radius of stars just inside (outside) corotation can counterbalance the opposite trend of exchange of angular momentum shown by stars orbiting the librational points L4/5 at the corotation circle. Such secular processes actually allow steady spiral waves to promote radial migration across corotation. We propose some pieces of observational evidence for the minimum stellar density in the Galactic disc, such as its direct relation to the minimum in the observed rotation curve of the Galaxy at the radius r ∼ 9 kpc (for R0 = 7.5 kpc), as well as its association with a minimum in the distribution of Galactic radii of a sample of open clusters older than 1Gyr. The closeness of the solar orbit adius to the corotation resonance implies that the solar orbit lies inside a ring of minimum surface density (stellar + gas). This also implies a correction to larger values for the estimated total mass of the Galactic disc, and consequently, a greater contribution of the disc componente to the inner rotation curve of the Galaxy.