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631.
632.
This article describes a methodology to monitor dynamic vertical sub-centimeter displacement, of a GPS antenna. The dynamic
movement of an antenna is determined by choosing the appropriate reference satellite for measurement differencing and by applying
a FFT filter on the double-difference phase residuals. The validity of the method depends on the time variations of the GPS
residuals and errors, such as, receiver noise, atmospheric contribution, multipath effects, and the antenna movement. This
research is under development and results for simulated motion are presented here. ? 2002 Wiley Periodicals, Inc. 相似文献
633.
634.
Ana Navas 《地球表面变化过程与地形》1990,15(8):709-715
In order to investigate the rate of dissolution of gypsiferous rocks under natural conditions in streams of the Ebro river basin, 55 dissolution trials were carried out with spheres of alabastrine gypsum placed in flowing water. Experimental conditions involved flow velocities between 0·3 and 1·2 m s?1, electrical conductivities between 0·3 and 1·9 dS m?1, and the saturation indices of gypsum between ?2·1 and ?0·33. Mean values of dissolution rate obtained vary from 104 to 226 gm?2 h?1. This loss of mass corresponded to a volume of gypsum of between 393 and 853mmm?2 year?1. The factors most affecting the dissolution of gypsum are in descending order of importance: flow velocity > electrical conductivity > gypsum saturation. 相似文献
635.
Dilce F. Rossetti Ana M. Góes Márcio M. Valeriano Maria Carolina C. Miranda 《第四纪科学杂志》2008,23(2):121-135
Marajó Island is located in a passive continental margin that evolved from rifting associated with the opening of the Equatorial South Atlantic Ocean in the Late Jurassic/Early Cretaceous period. This study, based on remote sensing integrated with sedimentology, as well as subsurface and seismographic data available from the literature, allows discussion of the significance of tectonics during the Quaternary history of marginal basins. Results show that eastern Marajó Island contains channels with evidence of tectonic control. Mapping of straight channels defined four main groups of lineaments (i.e. NNE–SSW, NE–SW, NW–SE and E–W) that parallel main normal and strike‐slip fault zones recorded for the Amazon region. Additionally, sedimentological studies of late Quaternary and Holocene deposits indicate numerous ductile and brittle structures within stratigraphic horizons bounded by undeformed strata, related to seismogenic deformation during or shortly after sediment deposition. This conclusion is consistent with subsurface Bouguer mapping suggestive of eastern Marajó Island being still part of the Marajó graben system, where important fault reactivation is recorded up to the Quaternary. Together with the recognition of several phases of fault reactivation, these data suggest that faults developed in association with rift basins might remain active in passive margins, imposing important control on development of depositional systems. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
636.
The Patos Lagoon estuary is an important environment for the life cycle of many species, including the pink shrimp Farfantepenaeus paulensis. This area acts as a nursery ground for the shrimp larvae, which are spawned in a coastal area and transported into the lagoon during spring and early summer (September to December). Harvesting of shrimp occurs from January to May, and yields have varied from around 1,000 to 8,000 tons year?1. This study is based on analysis of river discharge, pink shrimp catches, and wind velocity time series from 1964 to 2004. Negative correlation between pink shrimp catches and river runoff reflects the influence of discharge on the lagoon circulation and, consequently, on the intrusion of salt water and larvae. When river discharge is below average, landward currents forced by SW winds can enhance larval transport into the estuarine area, leading to an increase in pink shrimp captures. Above average river input would force a seaward flow that works as a barrier to ingress of larvae. This is unusual when compared to many other estuarine systems, and the main factor that accounts for this behavior is the morphology (choking) of Patos Lagoon. Interannual variability related to El Niño/Southern Oscillation events also influence pink shrimp production in this area. Low/high shrimp catches are related to El Niño (flood)/La Niña (drought) events. Wind can also impact production through its effect on the southward displacement of larvae from the spawning area. Long-term trends indicate an increase in river discharge around 20 m3 s?1year?1 and a decrease in shrimp catches on the order of 57 tons year?1. 相似文献
637.
Fabrizio Murgia Riccardo Biddau Alessandro Concas Roberto Demontis Luca Fanfani Zeno Heilmann Cristian Lai Giuditta Lecca Eva Lorrai Marino Marrocu Vittorio Alessandro Marrone Laura Muscas Elisaveta Peneva Andrea Piras Massimo Pisu Gabriella Pusceddu Guido Satta Daniela Theis Andrea Vacca Paolo Valera Ana Melina Vallenilla Ferrara Ernesto Bonomi 《Earth Science Informatics》2009,2(1-2):5-21
GRIDA3 (Shared Resources Manager for Environmental Data Analysis and Applications) is a multidisciplinary project designed to deliver an integrated system to forge solutions to some environmental challenges such as the constant increase of polluted sites, the sustainability of natural resources usage and the forecast of extreme meteorological events. The GRIDA3 portal is mainly based on Web 2.0 technologies and EnginFrame framework. The portal, now at an advanced stage of development, provides end-users with intuitive Web-interfaces and tools that simplify job submission to the underneath computing resources. The framework manages the user authentication and authorization, then controls the action and job execution into the grid computing environment, collects the results and transforms them into an useful format on the client side. The GRIDA3 Portal framework will provide a problem-solving platform allowing, through appropriate access policies, the integration and the sharing of skills, resources and tools located at multiple sites across federated domains. 相似文献
638.
Jos A. Lpez-Sez Antonio Blanco-Gonzlez Lourdes Lpez-Merino M. Blanca Ruiz-Zapata Miriam Dorado-Valio Sebastin Prez-Díaz Ana Valdeolmillos Francesc Burjachs 《Quaternary International》2009,200(1-2):90
Correlations between ecological and cultural changes occurred during a short period between the end of Subboreal and the beginning of Subatlantic in the Amblés Valley (Ávila, central Spain) are analyzed, taking into account palaeopalynological and archaeological data. Plant dynamics from pollen analyses, both from archaeological sites and peat bogs, have been interpreted in relation to human settlements and the transformation of economic practices. These provided a comprehensive hypothesis on human/climate interactions at the beginning of the 1st millennium cal BC. There was an ecological crisis in the region that lasted for a century (ca. 850–760 cal BC). This was especially sharp due to both the geographical constraints of the area and its previous agrarian history. This event implied a sudden and abrupt climatic change from xeric and warm conditions (Subboreal) to more humid and cooler ones (Subatlantic). Environmental stress derived from climatic crisis could be an important factor in the explanation of the historical process, whose main consequences were both the origin of the Iron Age peasant villages and the end of the ‘dehesa’ type landscape. 相似文献
639.
Ana C. Londoo 《Geomorphology》2008,99(1-4):13-25
Earthworks of assumed age and their initial and current morphologies provide an ideal basis for developing and testing models for long-term landform erosion. Inca agricultural terraces abandoned at 1532 A.D in the drylands of southern Peru may be used to document morphological changes since the abandonment. The objective of this research is to determine the erosion pattern and process to estimate the erosion rate.The development of rills and channels on the Inca agricultural terraces is evidence for erosion by wash processes on slopes where the anchoring effect of vegetation is absent and loose material is available for removal. The pattern and amount of erosion from 1532–2005 A.D. is estimated by comparing elevation models of the observed morphology and reconstructed models of the original morphology of the Inca terraces. The results show that in areas of sediment accumulation surface elevation increased up to 0.5 m. Elevation lowering on the terrace treads was 0.7 m at maximum, and a temporally and spatially averaged lowering rate was 0.094 mm yr− 1. This gives insights about how the rate of erosion occurs on currently disturbed lands in arid environments where soil resources are scarce and lands are prone to desertification. 相似文献
640.
Flood response to rainfall variability during the last 2000 years inferred from the Taravilla Lake record (Central Iberian Range, Spain) 总被引:2,自引:0,他引:2
Ana Moreno Blas L. Valero-Garcés Penélope González-Sampériz Mayte Rico 《Journal of Paleolimnology》2008,40(3):943-961
A sedimentological, geochemical and palynological study of the Taravilla Lake sequence (Central Iberian Range, NE Spain) provides
a detailed record of allochthonous terrigenous layers that intercalate within the lacustrine sediments over the last 2000 years.
These terrigenous layers are interpreted as the result of extreme hydrological events that caused higher clastic input to
the basin. Anthropogenic influence caused by fires or deforestation is rejected as the main factor generating these layers
because human impact, inferred from the pollen reconstruction, was minimal when the terrigenous layers reached their greatest
frequency. The reconstructed occurrence of these events in the Taravilla Lake record is coherent with the paleoflood history
of the Tagus River, characterized by a notable increase of extreme events at the beginning of the Little Ice Age. The Taravilla
record suggests a relationship between the occurrence of extreme hydrological events, solar variability, and the North Atlantic
Oscillation for the NE Iberian Peninsula. 相似文献