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1.
Beyond world cities: Central America in a global space of flows 总被引：1，自引：0，他引：1
Central America is a region without a world city. Traditionally, the region's national projects have been based upon openness to the world economy: how do the region's contemporary transnational projects connect to the world economy under the new conditions of openness that is contemporary globalization? Focusing upon advanced producer services, three connections into the world city network are identified: global service firms operating directly in Central American cities, local service firms operating indirectly through extra-regional world cities and global service firms operating through Latin American regional offices. Miami is confirmed as the primary world city through which Central America connects into the world economy 相似文献
2.
Elastic finite element models are applied to investigate the effects of topography and medium heterogeneities on the surface deformation and the gravity field produced by volcanic pressure sources. Changes in the gravity field cannot be interpreted only in terms of gain of mass disregarding the ground deformation of the rocks surrounding the source. Contributions to gravity changes depend also on surface and subsurface mass redistribution driven by dilation of the volcanic source. Both ground deformation and gravity changes were firstly evaluated by solving a coupled axisymmetric problem to estimate the effects of topography and medium heterogeneities. Numerical results show significant discrepancies in the ground deformation and gravity field compared to those predicted by analytical solutions, which disregard topography, elastic heterogeneities and density subsurface structures. With this in mind, we reviewed the expected gravity changes accompanying the 1993–1997 inflation phase on Mt Etna by setting up a fully 3-D finite element model in which we used the real topography, to include the geometry, and seismic tomography, to infer the crustal heterogeneities. The inflation phase was clearly detected by different geodetic techniques (EDM, GPS, SAR and levelling data) that showed a uniform expansion of the overall volcano edifice. When the gravity data are integrated with ground deformation data and a coupled FEM modelling was solved, a mass intrusion could have occurred at depth to justify both ground deformation and gravity observations. 相似文献
3.
Internal structure of Ustica volcanic complex (Italy) based on a 3D inversion of magnetic data 总被引：1，自引：0，他引：1
A ground magnetic study of Ustica Island was performed to provide new insights into subsurface tectonic and volcanic structures.
The total-intensity anomaly field, obtained after a data-reduction procedure, shows the presence of a W–E-striking magnetic
anomaly in the middle of the island and another two intense anomalies, which seem to continue offshore, in the southwestern
and the northeastern sides, respectively. The detected anomalies were analyzed by a quadratic programming (QP) algorithm to
obtain a 3D subsurface magnetization distribution. The volcano magnetization model reveals the presence of intensely magnetized
volumes, interpreted as the feeding systems of the main eruptive centers of the island, which roughly follow the trend of
the main regional structural lineaments. These findings highlight how regional tectonics has strongly affected the structural
and magmatic evolution of the Ustica volcanic complex producing preferential ways for magma ascent. 相似文献
4.
Tadeu José Pereira Gilda Silva Maria José Costa José Lino Costa 《Estuarine, Coastal and Shelf Science》2011
The Lusitanian toadfish, Halobatrachus didactylus (Bloch and Schneider, 1801), is a subtropical sound-producing marine teleost that inhabits estuaries and other brackish water ecosystems in its northern distribution area. The relative isolation of populations within estuaries may cause important modifications in the bio-ecology of this species. The males of this species present two morphotypes which are more accurately distinguishable during the reproductive season. In the Tagus estuary population, the two types of reproductive males were present: type I, the “characteristic” morphotype, and type II, the alternative morphotype. The opportunistic males had more developed testis while type I males had more developed accessory glands. Type I males presented more developed swimbladders and larger body size and live longer than type II males. On the contrary, type II males grew faster and matured earlier. The feeding habits of the two male morphotypes were similar during the reproductive season but differences were found between reproductive specimens and non-reproductive specimens. The diet of reproductive specimens was mainly composed of benthic prey in contrast to predominance of nectobenthic prey in the diet of non-reproductive specimens. The females of H. didactylus generally had an intermediate pattern between the two male morphotypes. The percentage of type II males tended to be higher in denser areas of the estuary. In comparison with populations from different size ecosystems, smaller ecosystems revealed important modifications on the bio-ecology of the species due to the increased competition for nesting sites and mating partners, favouring alternative male tactics. 相似文献
5.
Paula Chainho Gilda Silva Michael F. Lane José L. Costa Tadeu Pereira Carla Azeda Pedro R. Almeida Inês Metelo Maria J. Costa 《Estuaries and Coasts》2010,33(6):1314-1326
Long-term monitoring studies are needed to understand changes in ecosystem status when restoration measures are implemented.
A long-term data series (1996–2007) of the Tagus estuary (Portugal) intertidal and subtidal benthic communities was collected
in a degraded area where mitigation measures were implemented. Multivariate analysis was used to analyze spatial and temporal
patterns in benthic community composition and trends in five benthic community metrics (i.e., taxonomic richness, density,
biomass, Shannon–Wiener diversity and the AMBI index) were also examined. The results revealed a clear separation between
intertidal and subtidal assemblages, although they had 50% of taxa in common, including the most abundant. Significant positive
trends were found for all metrics showing that both intertidal and subtidal communities responded to the restoration measures
implemented. Nevertheless, biotic indices need some adaptation before being universally applied to intertidal and subtidal
habitats. 相似文献
6.
F. Greco G. Currenti G. D’Agostino A. Germak R. Napoli A. Pistorio C. Del Negro 《Bulletin of Volcanology》2012,74(7):1745-1756
To achieve a balance between uncertainty and efficiency in gravity measurements, we have investigated the applicability of combined measurements of absolute and relative gravity as a hybrid method for volcano monitoring. Between 2007 and 2009, three hybrid gravity surveys were conducted at Mt Etna volcano, in June 2007, July 2008, and July 2009. Absolute gravity data were collected with two absolute gravimeters, which represent the state of the art in recent advances in ballistic gravimeter technology: (1) the commercial instrument FG5#238 and (2) the prototype instrument IMGC-02. We carried out several field surveys and confirmed that both the absolute gravimeters can still achieve a 10 μGal or better uncertainty even when they are operated in severe environmental conditions. The use of absolute gravimeters in a field survey of the summit area of Mt Etna is unprecedented. The annual changes of the gravity measured over 2007–2008 and 2008–2009 provide unequivocal evidence that during the 2007–2009 period, two main phenomena of subsurface mass redistribution occurred in distinct sectors of the volcano, accompanying different eruptive episodes. From 2007 to 2008, a gravity change of ?60?μGal was concentrated around the North-East Rift. This coincided with a zone affected by strong extensional tectonics, and hence might have been related to the opening of new voids. Between 2008 and 2009, a North-South elongate feature with a maximum gravity change of +80?μGal was identified in the summit craters area. This is interpreted to indicate recharge of a deep-intermediate magma storage zone, which could have occurred when the 2008–2009 eruption was still ongoing. 相似文献
7.
Over 20 million forest farmers practice slash and burn agriculture in the forests of the Congo Basin (Bahuchet and de Maret, 1995. State of Indigenous Populations Living in Rainforest Areas, European Commission DG XI Environment, Brussels). They rely on the long dry season (December–February north of the equator) to ensure that their new fields, cleared from regrowth forest, burn sufficiently well to deposit nutrients into the soil and to minimize the labor required to prepare the field for planting. Data from the Ituri forest in northeastern Democratic Republic of Congo show that the strength of the annual dry season (a) has a direct positive impact on the size of fields cleared each year by slash and burn farmers, and consequently on food production and the severity of the subsequent year's pre-harvest hunger period; and (b) is inversely related to total annual rainfall. These results suggest that the 1 mm/d increase in rainfall predicted for much of the Congo Basin by the 2050s may cause a basin wide increase in the frequency of heavy rains during the dry season, causing a reduction in the size of slash and burn farmers’ fields, and potentially a substantial increase in the food insecurity of poor rural families across the region. 相似文献
8.
Modelling the long‐term deformation of the sedimentary substrate of Mt. Etna volcano (Italy) 
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下载免费PDF全文 This study investigates in detail the deformation events that have affected the sedimentary successions forming the substrate of Mt. Etna volcano (Italy). Based on the geometric reconstruction of a buried sedimentary marker, we have been able to identify and quantify the effects of three different mechanisms of deformation that have affected the area in the last 600 ka. Numerical results from Finite Element Method (FEM) applied to model viscoelastic deformation suggest the occurrence of a crustal doming process originating at the mantle‐crust transition (~16 km). We propose that the source of deformation is related to the diapiric uprise of hydrothermal material originating in altered ocean‐like crust and its emplacement at a shallower level in the crust. This process has great relevance in the volcanic system and should be considered for the full assessment of its origin and evolution. 相似文献
9.
Rosalba Napoli Gilda Currenti Ciro Del Negro Agnese Di Stefano Filippo Greco Enzo Boschi 《Bulletin of Volcanology》2011,73(9):1311-1322
Significant changes in the local magnetic field marked the resumption of eruptive activity at Stromboli volcano on February
27, 2007. After differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal
thermal noise using temperature data, we identified step-like changes of 1–4 nT coincident with the opening of eruptive fissures
in the upper part of the Sciara del Fuoco. The magnetic variations detected at two stations are closely related to the propagation
of a shallow NE–SW magmatic intrusion extending beyond the summit craters area. These observations are consistent with those
calculated using piezomagnetic models in which stress-induced changes in rock magnetization are produced by the magmatic intrusion.
No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced
magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal
state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern can be related
to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field
was evaluated. This allowed us to estimate the rheological properties of the medium; in particular, an average viscosity ranging
between 1016 and 1017 Pa⋅s was a relaxation time τ of about 38 days. 相似文献
10.
A. Bonaccorso S. Calvari G. Currenti C. Del Negro G. Ganci A. Linde R. Napoli S. Sacks A. Sicali 《Bulletin of Volcanology》2013,75(2):1-12
We investigated the eruptive episodes that occurred at Etna volcano on 15 November 2011 and 18 March 2012 using different types of data. We present novel data from two recently installed strainmeters that recorded unique signals during the lava fountain phases of these events. The strainmeter data, integrated with those recorded by the magnetic network, and with satellite and ground thermal data, allowed us to follow the path of a gas-rich magma batch from the source inside the volcano to the surface and atmosphere. The amplitude ratio of the volumetric strain changes constrained the storage depth of the magma feeding the lava fountains above 1.5 km below sea level. Magnetic data revealed an attempted shallow lateral intrusion, whereas ground and satellite thermal data furnished a quantification of the total erupted volumes of ～2.2?×?106?m3 for the 15 November event and ～3.0?×?106?m3 for the 18 March event. Despite different durations of the explosive and effusive phases of the two lava fountain events, the total erupted volume was quite similar, suggesting the emptying of a shallow storage system displaying a steady behaviour. 相似文献