A numerical model of beach morphological evolution due to waves and currents in the vicinity of coastal structures   总被引：2，自引：0，他引：2  

Pham Thanh Nam  Magnus Larson  Hans Hanson  Le Xuan Hoan 《Coastal Engineering》2011

A numerical model was developed of beach morphological evolution in the vicinity of coastal structures. The model includes five sub-models for random wave transformation, surface roller development, nearshore wave-induced currents, sediment transport, and morphological evolution. The model was validated using high-quality data sets obtained during experiments with a T-head groin and a detached breakwater in the basin of the Large-scale Sediment Transport Facility at the Coastal and Hydraulics Laboratory in Vicksburg, Miss, USA. The simulations showed that the model reproduced well the wave conditions, wave-induced currents, and beach morphological evolution in the vicinity of coastal structures. Both salient and tombolo formation behind a T-head groin and a detached breakwater were simulated with good agreement compared to the measurements.  相似文献   

Sources of continental magmatism adjacent to the late Archean Kolar Suture Zone,south India: distinct isotopic and elemental signatures of two late Archean magmatic series     

E. J. Krogstad  G. N. Hanson  V. Rajamani 《Contributions to Mineralogy and Petrology》1995,122(1-2):159-173

 Conspicuous Nd, Sr and Pb isotopic differences exist between the Archean gneiss terranes adjoining the suture at the Kolar Schist Belt, south India. These gneisses, which are the deformed equivalents of plutonic and volcanic rocks, have known or inferred igneous ages of 2630 to 2530 Ma. Initial isotopic ratios of Nd, Sr and Pb suggest that metaplutonic gneisses west of the Kolar Schist Belt were emplaced into, and variably contaminated by, an evolved continental crust that formed prior to 3200 Ma. Felsic metaigneous gneisses that occur as slivers on the western margin of the schist belt have an isotopic character similar to that of the metaplutonic rocks on the same side of the Kolar Schist Belt. On the east side of the Kolar Schist Belt the isotopic evidence suggests that the 2530 Ma granitic gneisses were not derived from or contaminated by an older continental crust. Their source probably evolved with a Nd isotopic composition similar to that of typical Archean mantle, but became light rare earth element enriched after 2900 to 2700 Ma. The inferred tectonic setting for the west side of the Kolar Schist Belt is an Andean continental magmatic arc. For the east side of the Kolar Schist Belt, a possible Phanerozoic analog is an evolved island arc, such as Japan. Received: 24 June 1994/Accepted: 9 January 1995  相似文献   

Evaluating the Effectiveness of Ground Water Extraction Systems   总被引：2，自引：0，他引：2  

Jennifer L. Haley  Bill Hanson  Carl Enfield  John Glass 《Ground Water Monitoring & Remediation》1991,11(1):119-124

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Large-scale rhyolite peperites (Jurassic, southern Chile)     

Richard E. Hanson  Terry J. Wilson 《Journal of Volcanology and Geothermal Research》1993,54(3-4)

Development of a Jurassic volcano-tectonic rift basin in the southern Andes created a setting in which thick, rhyolitic volcaniclastic sequences accumulated in submarine environments and were penetrated by hypabyssal intrusions during or shortly after deposition. In the Ultima Esperanza District of southern Chile, extensive masses of peperite were produced when rhyolite magma underwent quenching, disruption, and commingling with wet, unconsolidated sediments during intrusion at shallow levels beneath the sea floor. The peperite forms discordant intrusive masses with volumes of up to several cubic kilometers, in which large, widely spaced, coherent rhyolite feeder pods are surrounded by, and grade into closely packed and dispersed peperite. Closely packed peperite consists of tightly fitting clasts separated by sediment-filled fractures. In dispersed peperite, the sediment forms a matrix surrounding large masses of fractured rhyolite and smaller more widely separated rhyolite clasts; evidence of in situ quench fragmentation is well preserved on both outcrop and thin-section scales. Thin sections show that clast margins and, in some cases, entire small clasts underwent cooling-contraction granulation, releasing shards of quenched rhyolite and fragments of phenocrysts into the adjacent sediment.Interaction between magma and wet sediment was non-explosive and involved fluidization of the host sediments, creating space for the intruding magma and causing pervasive injection of highly mobile sediment along thermal contraction cracks in quench-fragmented rhyolite. The ability of the magma to undergo complex intermixing with large volumes of sediment, with widespread preservation of in situ fragmentation textures, is interpreted to reflect a relatively low magma viscosity, presumably caused by retention of volatiles in the magma at the ambient pressures involved.Beds of redeposited peperite within the rift-basin fill indicate that some of the intrusive peperite masses reached the sea floor, undergoing slumping and mass flow. The peperites were thus an important local source of coarse-grained debris during the evolution of the basin.  相似文献   

The potential effects of climate change on ecosystem processes and cattle production on U.S. rangelands     

B. B. Baker  J. D. Hanson  R. M. Bourdon  J. B. Eckert 《Climatic change》1993,25(2):97-117

In spite of the uncertainties of potential climate change, a scientific consensus is emerging that increasing concentrations of atmospheric CO₂ could alter global temperatures and precipitation patterns. Changes in global climate as predicted by General Circulation Models (GCM) could therefore, have profound implications for global agriculture. The objective of this study was to assess the impacts of potential climate change on livestock and grassland production in the major producing regions of the United States. Simulation sites were selected for the study on the basis of the region's economic dependence on rangeland livestock production. Five thirty-year simulations were conducted on each site using the Simulation of Production and Utilization of Rangelands model and Colorado Beef Cattle Production Model. Climate change files were obtained by combining historic weather data from each site with predicted output from three GCM's. Results from nominal runs were compared with the three climate change scenarios and a doubled CO₂ run. The magnitude and direction of ecosystem response to climate change varied among the GCM's and by geographic region. Simulations demonstrated that changes in temperature and precipitation patterns caused an increase in above-ground net primary production for most sites. Increased decomposition rates were recorded for northern regions. Similarly, animal production in northern regions increased, implying an increase in economic survivability. However, because decreases in animal production indicators were recorded for the southern regions, economic survivability in southern regions is less certain.  相似文献   

Development and deployment of a precision underwater positioning system for in situ laser Raman spectroscopy in the deep ocean     

Sheri N. White  William Kirkwood  Alana Sherman  Mark Brown  Richard Henthorn  Karen Salamy  Peter Walz  Edward T. Peltzer  Peter G. Brewer 《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(12):2376-2389

The field of ocean geochemistry has recently been expanded to include in situ laser Raman spectroscopic measurements in the deep ocean. While this technique has proved to be successful for transparent targets, such as fluids and gases, difficulty exists in using deep submergence vehicle manipulators to position and control the very small laser spot with respect to opaque samples of interest, such as many rocks, minerals, bacterial mats, and seafloor gas hydrates. We have developed, tested, and successfully deployed by remotely operated vehicle (ROV) a precision underwater positioner (PUP) which provides the stability and precision movement required to perform spectroscopic measurements using the Deep Ocean Raman In situ Spectrometer (DORISS) instrument on opaque targets in the deep ocean for geochemical research. The positioner is also adaptable to other sensors, such as electrodes, which require precise control and positioning on the seafloor. PUP is capable of translating the DORISS optical head with a precision of 0.1 mm in three dimensions over a range of at least 15 cm, at depths up to 4000 m, and under the normal range of oceanic conditions (T, P, current velocity). The positioner is controlled, and spectra are obtained, in real time via Ethernet by scientists aboard the surface vessel. This capability has allowed us to acquire high quality Raman spectra of targets such as rocks, shells, and gas hydrates on the seafloor, including the ability to scan the laser spot across a rock surface in sub-millimeter increments to identify the constituent mineral grains. These developments have greatly enhanced the ability to obtain in situ Raman spectra on the seafloor from an enormous range of specimens.  相似文献   

Learning about Feminism in Digital Spaces: online methodologies and participatory mapping     

Jessica McLean  Sophia Maalsen  Alana Grech 《The Australian geographer》2016,47(2):157-177

Collaborative online research offers opportunities and constraints for geographers. This article critically appraises a collaborative research process that we used to illuminate spatial and political dynamics of feminism contained within the online group ‘Destroy the Joint’ (DTJ). A mostly Australian initiative of over 74 000 Facebook members, DTJ aims to end sexism and misogyny in multiple ways. It operates as a meeting place, discussion forum, and umbrella organisation for numerous micro-campaigns that change in response to broader social, cultural and political contexts, and occur in online and offline spaces. We formed a collaborative research agreement with the moderators of DTJ to reflect on its work, asking participants to put themselves on a map and complete a survey. Participatory GIS and survey-based research operated in the real and the more-than-real spaces that contain paradoxical possibilities. We use the term more-than-real to highlight the excesses of digital spaces: the affect that social media generates, and is generated by, characterises the more-than-real, where extremes in productive and corrosive relations can permeate. Survey results showed diverse appreciations of DTJ's multiple activist tactics (across seemingly ‘superficial’ and ‘meaningful’ interventions), and creative ideas for future campaigns. Mapping revealed both dispersed networks and urban activist concentrations. Nevertheless, after an initial peak of interest and enthusiasm for reflecting on DTJ, the reporting back of research findings to DTJ followers did not garner significant interest. This article tracks that collaborative research trajectory. Intentions to build a hybrid research collective were not realised because of how the more-than-real affords possibilities and limitations. The politics of ‘giving-back’ within the more-than-real are critically engaged with in this appraisal of an experimental online collaboration.  相似文献   

Simulation and Analysis of Conjunctive Use with MODFLOW's Farm Process     

R. T. Hanson  W. Schmid  C. C. Faunt  B. Lockwood 《Ground water》2010,48(5):674-689

The extension of MODFLOW onto the landscape with the Farm Process (MF-FMP) facilitates fully coupled simulation of the use and movement of water from precipitation, streamflow and runoff, groundwater flow, and consumption by natural and agricultural vegetation throughout the hydrologic system at all times. This allows for more complete analysis of conjunctive use water-resource systems than previously possible with MODFLOW by combining relevant aspects of the landscape with the groundwater and surface water components. This analysis is accomplished using distributed cell-by-cell supply-constrained and demand-driven components across the landscape within “water-balance subregions” comprised of one or more model cells that can represent a single farm, a group of farms, or other hydrologic or geopolitical entities. Simulation of micro-agriculture in the Pajaro Valley and macro-agriculture in the Central Valley are used to demonstrate the utility of MF-FMP. For Pajaro Valley, the simulation of an aquifer storage and recovery system and related coastal water distribution system to supplant coastal pumpage was analyzed subject to climate variations and additional supplemental sources such as local runoff. For the Central Valley, analysis of conjunctive use from different hydrologic settings of northern and southern subregions shows how and when precipitation, surface water, and groundwater are important to conjunctive use. The examples show that through MF-FMP's ability to simulate natural and anthropogenic components of the hydrologic cycle, the distribution and dynamics of supply and demand can be analyzed, understood, and managed. This analysis of conjunctive use would be difficult without embedding them in the simulation and are difficult to estimate a priori.  相似文献   

Improvements of a dynamic global vegetation model and simulations of carbon and water at an upland-oak forest   总被引：1，自引：0，他引：1  

毛嘉富  王斌  戴永久 《大气科学进展》2007,24(2):311-322

The interest in the development and improvement of dynamic global vegetation models （DGVMs）, which have the potential to simulate fluxes of carbon, water and nitrogen, along with changes in the vegetation dynamics, within an integrated system, has been increasing. In this paper, some numerical schemes and a higher resolution soil texture dataset were employed to improve the Sheffield Dynamic Global Vegetation Model （SDGVM）. Using eddy covariance-based measurements, we then tested the standard version of the SDGVM and the modified version of the SDGVM. Detailed observations of daily carbon and water fluxes made at the upland oak forest on the Walker Branch Watershed in Tennessee, USA offered a unique opportunity for these comparisons. The results revealed that the modified version of the SDGVM did a reasonable job of simulating the carbon and water flux and the variation of soil water content （SWC）. However, at the end of the growing season, it failed to simulate the effect of the limitations on the soil respiration dynamics and as a result underestimated this respiration. It was also noted that the modified version overestimated the increase in the SWC following summer rainfall, which was attributed to an inadequate representation of the ground water and thermal cycle.  相似文献   

Experimental investigation of Ostwald-ripening rates of forsterite in the haplobasaltic system     

Youngdo Park  Ben Hanson 《Journal of Volcanology and Geothermal Research》1999,90(1-2)

The rate of Ostwald ripening of forsterite is experimentally measured in a haplobasaltic melt (SiO₂–Al₂O₃–CaO–MgO). The goal of the experiments is to determine if the rate of Ostwald ripening is sufficient to affect textural development in crystallizing magmas of a basaltic composition. With preequilibrated charges, experiments were run isothermally so that all textural changes could be ascribed to Ostwald ripening. An increase of crystal size from 3.5 μm to 14 μm (in average) has been observed during 10 days. Glass compositions were identical in all charges, indicating that the observed increase in average crystal size is not the results of chemical disequilibrium but the results of Ostwald ripening. Due to the constraints on experimental duration, the rate-limiting process (i.e., diffusion control or reaction control) could not be determined. Our experimental results, however, demonstrate that the rate of Ostwald ripening in basaltic rocks is sufficient to be of fundamental importance in the development of textures in igneous rocks. These results strongly suggest that Ostwald ripening, as well as nucleation and crystal growth, should be considered in analyses of textures in igneous rocks.  相似文献