The effect of salinity-dependent hydraulic conductivity on saltwater intrusion episodes   总被引：2，自引：0，他引：2  

E. Mehnert  A.A. Jennings 《Journal of Hydrology》1985,80(3-4):283-297

The ionic strength of percolating water can greatly alter a soil's hydraulic conductivity. This appears to be the result of dispersion and/or swelling of clay particles, and can alter hydraulic conductivity by several orders of magnitude.

In this paper, the potential effects of salinity-dependent changes in hydraulic conductivity during saltwater intrusions are analyzed. Results are presented to show that this can increase the degree to which brackish water will penetrate a coastal aquifer. This can also increase the width of the dispersed salt front, and can lead to a much greater circulation of saltwater within the intruding saltwater toe. These results may help to explain field observations that have previously been attributed to “scale-dependent” dispersivity and domain heterogeneity.  相似文献   

Monitoring Moisture Migration in the Vadose Zone with Resistivity   总被引：1，自引：0，他引：1  

William F. Kean  Muriel Jennings Waller  H. Richard Layson 《Ground water》1987,25(5):562-571

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Oceanographic Change and Terrestrial Human Impacts in a Post A.D. 1400 Sediment Record from the Southwest Iceland Shelf     

A.E. Jennings  S. Hagen  J. Harðardóttir  R. Stein  A.E.J. Ogilvie  I. Jónsdóttir 《Climatic change》2001,48(1):83-100

Environmental proxies of soil erosion on Iceland, and oceanographic conditions on the adjacent shelf, were measured on a 50 cm box core taken from the southwest Iceland shelf in 1993 during cruise 93030 of the Canadian ship, CSS Hudson. These data, covering the last several centuries, are compared with the documentary record of sea-ice changes around Iceland since A.D. 1600. The site is under the influence of the Irminger Current, which carries warm, saline, Atlantic water northward along the shelf. Because of the relative warmth of this current, sea ice rarely occurs off southwest Iceland, even during the most severe sea-ice intervals of the historical record. In severe sea-ice years, however, the ice drifts clockwise around Iceland from the northeast and east and, in rare cases, reaches the southern coasts (Ogilvie, 1992). The chronology of the core was established by converting the basal radiocarbon date to calendar years and assuming a linear sedimentation rate from the base of the core to the year of collection, 1993. Organic carbon, stable C and O isotope ratios, planktonic foraminiferal assemblages, and sediment magnetic parameters were measured on samples from the core, plotted against calendar years and compared to the Icelandic sea-ice index. The environmental proxies suggest that increased soil erosion, reduced salinity, and, possibly, decreased marine productivity prevailed during the severe sea-ice interval lasting from the last quarter of the eighteenth century to around 1920. Such a situation could develop with climatic cooling, increased storminess, and loss of vegetation cover to stabilise the soil. Although the core site generally lies outside the sea-ice limits, the evidence clearly shows the influence of sea ice and fresh water, and is sensitive to the overall climatic deterioration manifested by the sea-ice record.  相似文献   

Modelling potential impacts of bottom trawl fisheries on soft sediment biogeochemistry in the North Sea†     

Daniel E Duplisea  Simon Jennings  Stephen J Malcolm  Ruth Parker  David B Sivyer 《Geochemical transactions》2001,2(1):1-6

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The San Fernando California earthquake     

George W. Housner  Paul C. Jennings 《地震工程与结构动力学》1972,1(1):5-31

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Forced vibration of a tall steel-frame building     

P. C. Jennings  R. B. Matthiesen  J. Brent Hoerner 《地震工程与结构动力学》1972,1(2):107-132

The dynamic properties of the twenty-two-story, steel-frame San Diego Gas and Electric Company Building in San Diego, California, have been determined experimentally in a series of co-operative tests between the California Institute of Technology and the University of California at Los Angeles. The building was vibrated by two eccentric mass exciters capable of frequencies up to 10 c/sec and forces as much as 5000 Ib each. The natural frequencies, associated mode shapes and the amounts of damping were determined for the first six modes of vibration in each of the two translational directions, and also in torsion. The mode shapes and frequencies showed, in general, the regularity and uniformity that appears typical of many tall buildings, but the three fundamental modes (nominally NS, EW and torsion) of the structure showed a coupling of translational and rotational components to a degree that was unexpected in a building whose structural frame is essentially symmetric. It is believed that this may be a consequence of the exceptionally small differences among the three fundamental frequencies. The damping in the first eighteen modes of the structure varied from 1.6 to 4.4 per cent, with a slight tendency for the larger values to be associated with the higher modes. Of the simpler damping models that might be used for analysis of the building, constant modal damping appears most appropriate and stiffness or mass proportional damping would not be realistic.  相似文献   

Position of the Gulf Stream influences lake nitrate concentrations in SW Ireland     

Eleanor Jennings  Norman Allott 《Aquatic Sciences - Research Across Boundaries》2006,68(4):482-489

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Cloud condensation nuclei measurements at Mace Head, Ireland, over the period 1994–2002     

Luke Reade  S.G. Jennings  Gobnait McSweeney 《Atmospheric Research》2006,82(3-4):610

Analyses of cloud condensation nuclei (CCN) number concentrations (cm^− 3) measured at the Mace Head Atmospheric Research Station, near Carna, County Galway, Ireland, using a DH Associates Model M1 static thermal diffusion cloud chamber over the period from March 1994 to September 2002 are presented in this work. Air masses are defined as being ‘marine’ if they originate from a wind direction of 180–300° and ‘continental’ air masses are defined as originating from a wind direction of 45–135°. Air masses without such filtering were classified as ‘undefined’ air masses. Air masses were found to be dominated by marine sector air, re-affirming Mace Head as a baseline atmospheric research station. CCN levels for specific air masses at Mace Head were found to be comparable with earlier studies both at Mace Head and elsewhere. Monthly averaged clean marine (wind direction of 180–300° and black carbon absorption coefficient < 1.425 Mm^− 1) CCN and marine CCN varied between 15–247 cm^− 3 and 54–670 cm^− 3, respectively. As expected, significant increases in number concentration were found in continentally sourced CCN over that of marine CCN and were found to follow a log-normal distribution significantly tighter than that of clean marine air masses. No significant trend was found for CCN over the 9-year period. While polluted continental air masses showed a slight increase in CCN concentrations over the winter months, most likely due to increased fuel usage and a lower mixed boundary layer, the dominance of marine sector air arriving at Mace Head, which generally consists of background CCN concentrations, reduced seasonal differences for polluted air. Marine air showed a distinct seasonal pattern, with elevated values occurring over the spring and summer seasons. This is thought to be due to enhanced biogenic aerosol production as a result of phytoplankton bloom activity in the North Atlantic.  相似文献   

Structural identification using linear models and earthquake records     

James L. Beck  Paul C. Jennings 《地震工程与结构动力学》1980,8(2):145-160

The problem of determining linear models of structures from seismic response data is investigated using ideas from the theory of system identification. The approach is to determine the optimal estimates of the model parameters by minimizing a selected measure-of-fit between the responses of the structure and the model. Because earthquake records are normally available from only a small number of locations in a structure, and because of noise in the records, it is necessary in practice to estimate parameters of the dominant modes in the records, rather than the stiffness and damping matrices of the linear model. A new algorithm is developed to determine the optimal estimates of the modal parameters. After tests with simulated data, the method is applied to a multi-storey building using records from the 1971 San Fernando earthquake in California. New information is obtained concerning the properties of the lower modes of the building and the time-varying character of the equivalent linear parameters.  相似文献   

Honey, I cooled the cods: Modelling the effect of temperature on the structure of Boreal/Arctic fish ecosystems     

John G. Pope  Jannike Falk-Pedersen  Simon Jennings  Jake C. Rice  Henrik Gislason  Niels Daan   《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):2097

Historically colder regions of the North Atlantic had fisheries dominated by only a few fish species; principally cod and capelin. Possible population dynamic mechanisms that lead to such dominance are investigated by considering how a charmingly simple published multispecies model of the North Sea would react if the system operated at a lower temperature. The existing model equations were modified to describe temperature effects on growth, fecundity and recruitment and the model was rerun based on typical temperatures for the North Sea and a colder system. The results suggest that total fish biomass in the colder system increases but the community is more vulnerable to a given rate of fishing mortality. In the colder system, within species density dependence is reduced but relative predation rates are higher. Consequently, intermediate-sized species are vulnerable to relatively high levels of predation throughout their life history and tend to be excluded, leading to a system dominated by small and large species. The model helps to explain how temperature may govern coexistence and competitive exclusion in fish communities and accounts for the observed dominance of small and large species in Boreal/Arctic ecosystems.  相似文献