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41.
Tarek Ben Hassen Juan‐Luis Klein Diane‐Gabrielle Tremblay 《The Canadian geographer》2011,55(4):439-456
This article analyzes the mechanisms through which metropolitan governance is established in Montreal's aeronautics sector, one of the most important and innovative industries in the region. The article also examines the role of lead firms, socio‐economic actors, and public agencies from a territorial point of view. It is established that on the one hand the existence of a small number of prime producers at the local level facilitates productive linkages among businesses through subcontracting, and on the other hand, the intensive participation of intermediate socio‐economic agencies and organizations ensures a metropolitan anchoring of the sector and creates a strong territorial identity among the players. 相似文献
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Ground-supported steel tanks experienced extensive damage in past earthquakes. The failure of tanks in earthquakes may cause severe environmental damage and economic losses. This study deals with the evaluation of the elastic buckling of above-ground steel tanks anchored to the foundation due to seismic shaking. The proposed nonlinear static procedure is based on the capacity spectrum method (CSM) utilized for the seismic evaluation of buildings. Different from the standard CSM, the results are not the base shear and the maximum displacement of a characteristic point of the structure but the minimum value of the horizontal peak ground acceleration (PGA) that produces buckling in the tank shell. Three detailed finite element models of tank-liquid systems with height to diameter ratios H/D of 0.40, 0.63, and 0.95 are used to verify the methodology. The 1997 UBC design spectrum and response spectra of records of the 1986 El Salvador and 1966 Parkfield earthquakes are used as seismic demand. The estimates of the PGA for the occurrence of first elastic buckling obtained with the proposed nonlinear static procedure were quite accurate compared with those calculated with more elaborate dynamic buckling studies. For all the cases considered, the proposed methodology yielded slightly smaller values of the critical PGA for the first elastic buckling compared to the dynamic buckling results. 相似文献
43.
This essay considers the ways in which the reception of Virgil's Georgics in eighteenth-century English verse may inform, enrich and complicate present-day readings of Virgil, focusing on questions raised by readers’ detection of wit or humorousness in Virgil and by the critical aim of discovering poetic unity in the Georgics. 相似文献
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Xabier Pontevedra-Pombal Tim M. Mighall Juan C. Nóvoa-Muñoz Eva Peiteado-Varela José Rodríguez-Racedo Eduardo García-Rodeja Antonio Martínez-Cortizas 《Journal of archaeological science》2013
The analysis of environmental archives from across the world has demonstrated that human perturbation of the geochemical cycles of trace metals and the resultant atmospheric metal contamination date back, at least, several millennia. However, an understanding of the local processes and timing of changes in trace metal deposition is also essential for a proper global interpretation. The Iberian Peninsula was a major mining area since prehistoric times and the analysis of environmental archives provides a good opportunity to improve our understanding of the history of mining and metallurgy in Europe. We present the results from three 14C dated peat cores from the Xistral Mountains (NW Iberia). These records are used to reconstruct past atmospheric deposition of Ni, Zn, As, and Cd. The chronology of the changes in concentrations and metal accumulation rates was found to be concordant in the three bogs, and showed great similarity to total Pb, Hg, and Pb isotope ratios as determined in previous investigations. They present a consistent view of changes in atmospheric pollution and the importance of metals in the development of human societies, especially: i) the first evidence of atmospheric metal pollution 3400 years ago, which is simultaneous with the expansion of the Atlantic Bronze Koine; ii) a pollution event between 2350 and 2150 years ago, associated to the development of so-called Celtic culture (local Late Iron Age); iii) a dramatic increase of metal fluxes in Roman times; iv) a severe and rapid increase in the last 250 years corresponding to the beginning of the industrial revolution in Europe, reflecting the emergence of the new dominant sources of pollution, and v) the increase of long range atmospheric transport of pollutants. Our data suggest that all detected ancient (until ca. 1450 cal BP) periods of enhanced Ni, Zn, As, and Cd accumulation may have had an anthropogenic origin, related to the onset and development of mining and metallurgy. 相似文献
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Alzira is situated in a cut-off meander loop of the Rio Júcar. Geo-archaeological study shows that the Islamic city wall was built during the second quarter of the 11th century AD, at a time when the river had a low-amplitude and low-energy flood regime. After mid-century, overbank silts began to invade the city as peak flood discharge increased, with a spate of destructive floods reflected by high-energy deposits during the late 11th century. Urban expansion within the city wall is dated to the later 11th or early 12th century, interrupted by local abandonment and moderate-energy flood silts. Major construction during the mid-12th century was followed by protracted abandonment (after a siege in AD 1171?) and further, moderate-energy flood silts that redistributed occupation and collapse debris. Reoccupation, during the late 14th century, was terminated by catastrophic floods in 1517 and 1571, after which much of the western end of Alzira was not rebuilt. Following further flood catastrophes during the 17th century, parts of the central walled city remained abandoned until the 19th century. with new occupation atop flood sands of yet another disaster in 1864. The change in flood regime after 1150 was a result of deforestation of the watershed, but progradation of a downstream tributary fan after 1517 created an unstable, aggrading floodplain increasingly prone to severe flooding. Climatic anomalies were responsible for periods of recurrent severe floods, archaeologically verified during the 11th and 12th centuries, and historically documented, beginning in 1318. The geo-archaeological methodology illuminates the constructional and settlement history of Alzira, allows distinction of fluvial and cultural components, and provides the necessary microstratigraphic detail and dating control to document the true complexity of alluvial processes during the last 1000 years. 相似文献
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Juan R.I. Cole Nikki R. Keddie William Millward Mehrdad R. Izady 《Iranian studies》1989,22(2-3):189-194