Thermal bending of thin, anisotropic, clamped elliptic plates     

P.A.A Laura  C.A Rossit 《Ocean Engineering》1998,26(5):485-488

The present note deals with the exact analytical solution of thermal bending of clamped, anisotropic, elliptic plates in the case where the thermal field is given by an expression of the type T(x,y,z)=z(Ax²+Cxy+By²).The problem is of basic interest in some ocean and mechanical structural systems since anisotropic materials are commonly used in those fields. Obviously the case of an orthotropic material constitutes a particular situation of the problem under study.  相似文献   

Trace element and molecular markers of organic carbon dynamics along a shelf–basin continuum in sediments of the western Arctic Ocean     

Laura L. Belicka  Robie W. Macdonald  H. Rodger Harvey 《Marine Chemistry》2009,115(1-2):72-85

Molecular organic biomarkers together with trace element composition were investigated in sediments east of Barrow Canyon in the western Arctic Ocean to determine sources and recycling of organic carbon in a continuum from the shelf to the basin. Algal biomarkers (polyunsaturated and short-chain saturated fatty acids, 24-methylcholesta-5,24(28)-dien-3β-ol, dinosterol) highlight the substantial contribution of organic matter from water column and sea-ice primary productivity in shelf environments, while redox markers such as acid volatile sulfide (AVS), Mn, and Re indicate intense metabolism of this material leading to sediment anoxia. Shelf sediments also receive considerable inputs from terrestrial organic carbon, with biomarker composition suggesting the presence of multiple pools of terrestrial organic matter segregated by age/lability or hydrodynamic sorting. Sedimentary metabolism was not as intense in slope sediments as on the shelf; however, sufficient labile organic matter is present to create suboxic and anoxic conditions, at least intermittently, as organic matter is focused towards the slope. Basin sediments also showed evidence for episodic delivery of labile organic carbon inputs despite the strong physical controls of water depth and sea-ice cover. Principal components analysis of the lipid biomarker data was used to estimate fractions of preserved recalcitrant (of terrestrial origin) and labile (of marine origin) organic matter in the sediments, with ranges of 12–79%, 14–45%, and 37–66% found for the shelf, slope, and basin cores, respectively. On average, the relative preserved terrestrial organic matter in basin sediments was 56%, suggesting exchange of organic carbon between nearshore and basin environments in the western Arctic.  相似文献   

Numerical modelling of the potential effects of a dam on a coastal aquifer in S. Spain     

M. L. Calvache  S. Ibáñez  C. Duque  W. Martín‐Rosales  M. López‐Chicano  J. C. Rubio  A. González  C. Viseras 《水文研究》2009,23(9):1268-1281

This study presents the results of a three‐dimensional variable‐density numerical modelling of the Motril‐Salobreña coastal aquifer and the possible effects of the entry into service in May 2005 of the Rules Dam, located just 17 km from the coast. Present parameters of the Motril‐Salobreña aquifer show that the system's conditions are very similar to a natural regime. The dam will substantially alter aquifer recharge, as the entry flow through the alluvial sediments of the Guadalfeo River will be entirely cut off or drastically reduced. Different scenarios reproducing the possible evolution of the aquifer under operation of the Rules Dam have been modelled. In most cases, results indicate that the conditions of the aquifer would worsen, with a general advance of the freshwater–saltwater interface. The area with most risk of saltwater intrusion is the old mouth of the Guadalfeo River, where the mixing zone could advance 1200 m inland. It is proposed that maintaining a 5–6 Mm³ year^?1 ‘ecological flow’ in the Guadalfeo River could prevent this saline advance. This application demonstrates that variable‐density models are potentially useful tools for estimating the effects of dams on the hydrodynamic and hydrochemical conditions of a coastal aquifer. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Impact of wildfire on source water contributions in Devil Creek,CA: evidence from end‐member mixing analysis     

Helen Y. Jung  Terri S. Hogue  Laura K. Rademacher  Tom Meixner 《水文研究》2009,23(2):183-200

A geochemical and end‐member mixing analysis (EMMA) is undertaken in Devil Canyon catchment, located in southern California, to further understanding of watershed behaviour and source water contributions after an acute and extensive wildfire. Physical and chemical transformations in post‐fire watersheds are known to increase overland flow and decrease infiltration, mainly due to formation of a hydrophobic layer at, or near, the soil surface. However, less is known about subsurface flow response in burned watersheds. The current study incorporates EMMA to evaluate and quantify source water contributions before, and after, a catchment affected by wildfires in southern California during the fall of 2003. Pre‐ and post‐fire stream water data were available at several sampling sites within the catchment, allowing the identification of contributing water sources at varying spatial scales. Proposed end‐member observations (groundwater, overland flow, shallow subsurface flow) were also collected to constrain and develop the catchment mixing model. Post‐fire source water changes are more evident in the smaller and faster responding sub‐basin (interior sampling point). Early post‐fire storm events are dominated by overland flow with no significant soil water or groundwater flow contribution. Inter‐storm streamwater in this smaller basin shows an increase in groundwater and a decrease in soil water. In the larger, baseflow‐dominated system, source water components appear less affected by fire. A slight increase in lateral flow is observed with only a slight decrease in baseflow. Changes in the post‐fire flow regimes affect nutrient loading and chemical response of the basin. Relatively rapid recovery of the chaparral ecosystem is evidenced, with active re‐growth and evapotranspiration evidenced by the fourth post‐fire rainy season. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Photochemical changes in chemical markers of sedimentary organic matter source and age     

Lawrence M. Mayer  Linda L. Schick  Thomas S. Bianchi  Laura A. Wysocki 《Marine Chemistry》2009,113(1-2):123-128

Several chemical markers of organic matter source and age are shown to be susceptible to light-induced alteration. To test for the photochemical lability of markers previously employed for sediments from the Louisiana coastal zone, we subjected sediments under resuspension conditions to simulated sunlight, and monitored changes in C:N and Br:OC ratios, δ¹³C, Δ¹⁴C, and lignin composition. Markers of terrigenous origin (high C:N, lignin) decreased and δ¹³C became enriched in sediments containing primarily terrigenous organic matter, while a marker of marine organic matter (Br:OC) decreased in samples containing significant contributions from this source. Preferential loss of ¹⁴C from all sediments indicated enhanced photochemical lability of organic matter of relatively recent origin, consistent with the changes in chemical markers. Most, but not all, experimental alterations are consistent with field distributions of these markers. Relatively small experimental changes in the markers in combination with confounding processes in the environment, however, prevent these parallel trends from providing any more than a consistency test for the importance of photochemical reactions in this region.  相似文献   

Macrofaunal density and biomass in the Campeche Canyon, Southwestern Gulf of Mexico     

Elva Escobar Briones  Erika Laura Estrada Santilln  Pierre Legendre 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2679

The composition, density and community structure of the benthic macrofauna were investigated in sediments of the Campeche Canyon in the SW Gulf of Mexico. Total macrofaunal density ranged from 9466±2736 ind m⁻² at the continental shelf station to 1550±195 ind m⁻² in the canyon. Density values significantly diminished with distance from the coast and depth; only a few stations in the center of the canyon displayed larger density values (E-37 with 4666±1530 ind m⁻², E-36 with 5791±642 ind m⁻² and E-26 with 6925±2258 ind m⁻²). Densities were positively correlated to organic nitrogen in the sediment (r=0.82) and coarse silt (r=0.43), and negatively with depth (r=−0.74) and distance from the coast (r=−0.68). At all stations, the polychaete worms contributed most to the multi-species community structure. The nematodes and Foraminifera displayed their highest densities in the center of the canyon. The biomass values declined significantly with depth. We conclude that the macrofauna density and biomass changed in response to organic matter contents in the sediment, both with distance from the coast and with depth.  相似文献   

The Tully–Fisher relation and its evolution with redshift in cosmological simulations of disc galaxy formation     

Laura Portinari  Jesper Sommer-Larsen 《Monthly notices of the Royal Astronomical Society》2007,375(3):913-924

  相似文献   

Geochemical arguments for identifying second‐order sea‐level changes in hemipelagic carbonate ramp deposits     

Idoia Rosales  Santiago Quesada  Sergio Robles 《地学学报》2006,18(4):233-240

Second‐order transgressive–regressive (T–R) cycles, previously recognized using sedimentological criteria in Lower Jurassic hemipelagic deposits from northern Spain, are distinguishable based upon bulk‐rock organic geochemistry [total organic carbon (TOC) and hydrogen index (HI)] and the stable carbon isotope compositions from belemnite rostra. There is a coincidence between regressions and decreasing δ¹³C_bel, TOC and HI values, and between transgressions and increasing δ¹³C_bel, TOC and HI values. The δ¹⁸O and Mg/Ca records from the belemnite rostra are not always in phase with the T–R cycles. The δ¹⁸O_bel record reveals, however, a prominent excursion towards higher values within the spinatum Zone that correlates, according to our results, with a regression and with negative shifts in Mg/Ca, δ¹³C_bel and TOC. On the other hand, an excursion in the δ¹⁸O_bel towards lower values in the serpentinus Zone also correlates with a peak transgression and with positive shifts in Mg/Ca, δ¹³C_bel and TOC. These two excursions have been identified in other European regions as geochemical perturbations of the same characteristics. This suggests a link between second‐order relative sea‐level changes and variations in seawater geochemistry that may reflect local and regional palaeoceanographic perturbations in sea‐water temperature, salinity and water circulation during the Early Jurassic. Terra Nova, 18, 233–240, 2006  相似文献   

Vulnerability assessment for loss of access to drinking water due to extreme weather events   总被引：1，自引：0，他引：1  

Jeanne Luh  Elizabeth C. Christenson  Aizhan Toregozhina  David A. Holcomb  Tucker Witsil  Laura R. Hamrick  Edema Ojomo  Jamie Bartram 《Climatic change》2015,133(4):665-679

  相似文献   

An instrument for commissioning the active and adaptive optics of modern telescopes: the Infrared Test Camera for the Large Binocular Telescope     

Italo Foppiani  John M. Hill  Matteo Lombini  Giovanni Bregoli  Giuseppe Cosentino  Emiliano Diolaiti  Thomas M. Herbst  Giancarlo Innocenti  Daniel Meschke  Douglas L. Miller  Ralf-Rainer Rohloff  Laura Schreiber 《Experimental Astronomy》2011,31(2-3):115-130

We describe the design, integration, and operation of the infrared test cameras for the commissioning of the Large Binocular Telescope. The design and construction phase lasted slightly more than one year from February 2007 to April 2008 and was the result of a joint collaboration among INAF Osservatorio Astronomico di Bologna, Università di Bologna Dipartimento di Astronomia (Italy) and the Max-Planck-Institut für Astronomie (Heidelberg, Germany). Thereafter, the camera was delivered to the LBT Observatory (USA) for commissioning of the telescope active optics and, more recently, for commissioning of the first light adaptive optics.  相似文献