DEM simulation of impact force exerted by granular flow on rigid structures   总被引：3，自引：1，他引：2  

H. Teufelsbauer  Y. Wang  S. P. Pudasaini  R. I. Borja  W. Wu 《Acta Geotechnica》2011,6(3):119-133

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Pollen analyses from a 50 000‐yr rodent midden series in the southern Atacama Desert (25° 30′ S)     

Antonio Maldonado  Julio L. Betancourt  Claudio Latorre  Carolina Villagran 《第四纪科学杂志》2005,20(5):493-507

Precipitation in northern Chile is controlled by two great wind belts—the southern westerlies over the southern Atacama and points south (> 24° S) and the tropical easterlies over the northern and central Atacama Desert (16–24° S). At the intersection of these summer and winter rainfall regimes, respectively, is a Mars‐like landscape consisting of expansive surfaces devoid of vegetation (i.e. absolute desert) except in canyons that originate high enough to experience runoff once every few years. Pollen assemblages from 39 fossil rodent middens in one of these canyons, Quebrada del Chaco (25° 30′ S), were used to infer the history of vegetation and precipitation at three elevations (2670–2800 m; 3100–3200 m; 3450–3500 m) over the past 50 000 years. When compared to modern conditions and fossil records to the north and south, the pollen evidence indicates more winter precipitation at > 52, 40–33, 24–17 k cal. yr BP, more precipitation in both seasons at 17–14 k cal. yr BP, and more summer precipitation from 14–11 k cal. yr BP. Younger middens are scarce at Quebrada del Chaco, and the few Holocene samples indicate hyperarid conditions comparable to today. The only exception is a pollen assemblage that indicates a brief but significant interlude of increased winter precipitation in the last millennium. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

A double-yield-surface plasticity theory for transversely isotropic rocks     

Zhao  Yang  Borja  Ronaldo I. 《Acta Geotechnica》2022,17(11):5201-5221

Acta Geotechnica - We present a double-yield-surface plasticity theory for transversely isotropic rocks that distinguishes between plastic deformation through the solid matrix and localized...  相似文献   

Trends and anomalies in sea-surface temperature,observed over the last 60 years,within the southeastern Bay of Biscay     

Nerea Goikoetxea  Ángel Borja  Almudena Fontán  Manuel González  Victoriano Valencia 《Continental Shelf Research》2009,29(8):1060-1069

The Oceanographic Society of Gipuzkoa has recorded daily sea-surface temperature (SST) measurements, since 2nd July 1946, on a (nearly) daily basis. Sixty years of SST measurements (1947–2007) have been considered, in order to analyse the hydrographic trends and anomalies at the southeastern Bay of Biscay. The study reviews initially the consistency and reliability of the time-series; and trends and anomaly patterns. Then, the periodicity of the series; a reference period, for analysing seasonality during the period 2001–2007; and oceano-meteorological coupling within the period 2001–2007, with reference to the baseline period, have been determined. Within this context, a slight cooling trend has been observed for the whole of the time-series, in contrast to the warming over the last three-decadal period. Regarding the periodicity of the series, several cycles have been identified, with periods of about 8, 11 and 18 years; these represent the influence of climate cycles over the (local) SST series. Additionally, seasonal anomaly patterns between 2001 and 2007 have been examined based upon the selected reference period (1980–2002). Several extreme seasonal events have been observed, such as warm summer SST values in 2003 and 2006 and cold winter values in 2005. Such events can be explained by the “deseasonality” phenomenon, observed throughout the study period. In addition to the direct influence of atmospherical parameters, such as air temperature and irradiance on SST, dynamical variables (turbulence and upwelling–downwelling) account also for this coupling. Overall, despite the marginal location and surface character of the time-series, it reveals anomalies that agree with those described for larger zones of the northeastern Atlantic Ocean; hence, it can be characterised as being a reliable and representative long-term SST series.  相似文献   

A Marine Biotic Index to Establish the Ecological Quality of Soft-Bottom Benthos Within European Estuarine and Coastal Environments   总被引：34，自引：0，他引：34  

A. Borja  J. Franco  V. Prez 《Marine pollution bulletin》2000,40(12):1235-1114

In this paper, a marine Biotic Index (BI) for soft-bottom benthos of European estuarine and coastal environments is proposed. This is derived from the proportions of individual abundance in five ecological groups, which are related to the degree of sensitivity/tolerance to an environmental stress gradient. The main difference with previously published indices is the use of a simple formula that produces a continuous Biotic Coefficient (BC) – which makes it more suitable for statistical analysis, in opposition with previous discreet biotic indices – not affected by subjectivity. Relationships between this coefficient and a complementary BI with several environmental variables are discussed. Finally, a validation of the proposed index is made with data from systems affected by recent human disturbances, showing that different anthropogenic changes in the environment can be detected through the use of this BI.  相似文献   

Genomics in marine monitoring: New opportunities for assessing marine health status     

Sarah J. Bourlat  Angel Borja  Jack Gilbert  Martin I. Taylor  Neil Davies  Stephen B. Weisberg  John F. Griffith  Teresa Lettieri  Dawn Field  John Benzie  Frank Oliver Glöckner  Naiara Rodríguez-Ezpeleta  Daniel P. Faith  Tim P. Bean  Matthias Obst 《Marine pollution bulletin》2013

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Multiphysics hillslope processes triggering landslides   总被引：4，自引：3，他引：1  

Ronaldo I. Borja  Xiaoyu Liu  Joshua A. White 《Acta Geotechnica》2012,7(4):261-269

In 1996, a portion of a highly instrumented experimental catchment in the Oregon coast range failed as a large debris flow from heavy rain. For the first time, we quantify the 3-D multiphysical aspects that triggered this event, including the coupled sediment deformation-fluid flow processes responsible for mobilizing the slope failure. Our analysis is based on a hydromechanical continuum model that accounts for the loss of sediment strength due to increased saturation as well as the frictional drag exerted by the moving fluid. Our studies highlight the dominant role that bedrock topography and rainfall history played in defining the failure mechanism, as indicated by the location of the scarp zone that was accurately predicted by our 3-D continuum model.  相似文献   

Assessing reference conditions and physico-chemical status according to the European Water Framework Directive: a case-study from the Basque Country (Northern Spain)     

Bald J  Borja A  Muxika I  Franco J  Valencia V 《Marine pollution bulletin》2005,50(12):1508-1522

The European Water Framework Directive requires the development of new and accurate methodologies, addressing the assessment of the physico-chemical status of transitional and coastal waters; these are considered by the Directive as the supporting elements for the final evaluation of the Ecological Quality Status.

This contribution develops new approaches in the determination of the physico-chemical status, solving some problems detected in previous contributions, i.e.: (a) fitting the classification of water bodies and typologies, by means of the stretching of the typologies, according to the natural salinity gradient of types; (b) defining reference conditions, based upon the new approach to typologies, (c) proposing accurate multivariate methodologies, in determining the physico-chemical status of the transitional and coastal waters, based upon the defined typologies and references; and (d) discussion of the results obtained by reference to methodological aspects and water quality evolution in the Basque Country, Spain (as a case-study), during the last decade.  相似文献   

Capturing strain localization behind a geosynthetic‐reinforced soil wall     

Timothy Y. Lai  Ronaldo I. Borja  Blaise G. Duvernay  Richard L. Meehan 《国际地质力学数值与分析法杂志》2003,27(5):425-451

This paper presents the results of finite element (FE) analyses of shear strain localization that occurred in cohesionless soils supported by a geosynthetic‐reinforced retaining wall. The innovative aspects of the analyses include capturing of the localized deformation and the accompanying collapse mechanism using a recently developed embedded strong discontinuity model. The case study analysed, reported in previous publications, consists of a 3.5‐m tall, full‐scale reinforced wall model deforming in plane strain and loaded by surcharge at the surface to failure. Results of the analysis suggest strain localization developing from the toe of the wall and propagating upward to the ground surface, forming a curved failure surface. This is in agreement with a well‐documented failure mechanism experienced by the physical wall model showing internal failure surfaces developing behind the wall as a result of the surface loading. Important features of the analyses include mesh sensitivity studies and a comparison of the localization properties predicted by different pre‐localization constitutive models, including a family of three‐invariant elastoplastic constitutive models appropriate for frictional/dilatant materials. Results of the analysis demonstrate the potential of the enhanced FE method for capturing a collapse mechanism characterized by the presence of a failure, or slip, surface through earthen materials. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Structural control considering soil–structure interaction effects     

H. Allison Smith  Wen-Hwa Wu  Ronaldo I. Borja 《地震工程与结构动力学》1994,23(6):609-626

A discussion of the effects of Soil-Structure Interaction (SSI) on the formulation of active structural control algorithms is presented. Two approaches for incorporating SSI effects in linear optimal control theory are developed: one which performs the control analysis on a structure with a fixed base and then considers the effects of SSI on the controlled structural response; and another which performs the control analysis using a structural equation of motion reformulated to include SSI effects. The two control formulations are studied and compared using a single-degree-of-freedom structure supported through a rigid foundation resting on a linear, elastic half-space. Results show that control effectiveness is affected by the approach used in formulating the equations of motion of the interacting system.  相似文献