Death valley regional ground-water flow model calibration using optimal parameter estimation methods and geoscientific information systems     

Frank A. D'Agnese  Claudia C. Faunt  Mary C. Hill  A. Keith Turner 《Advances in water resources》1999,22(8):2555

A regional-scale, steady-state, saturated-zone ground-water flow model was constructed to evaluate potential regional ground-water flow in the vicinity of Yucca Mountain, Nevada. The model was limited to three layers in an effort to evaluate the characteristics governing large-scale subsurface flow. Geoscientific information systems (GSIS) were used to characterize the complex surface and subsurface hydrogeologic conditions of the area, and this characterization was used to construct likely conceptual models of the flow system. Subsurface properties in this system vary dramatically, producing high contrasts and abrupt contacts. This characteristic, combined with the large scale of the model, make zonation the logical choice for representing the hydraulic-conductivity distribution. Different conceptual models were evaluated using sensitivity analysis and were tested by using nonlinear regression to determine parameter values that are optimal, in that they provide the best match between the measured and simulated heads and flows. The different conceptual models were judged based both on the fit achieved to measured heads and spring flows, and the plausibility of the optimal parameter values. One of the conceptual models considered appears to represent the system most realistically. Any apparent model error is probably caused by the coarse vertical and horizontal discretization.  相似文献   

A closure study of sub-micrometer aerosol particle hygroscopic behaviour   总被引：2，自引：0，他引：2  

Erik Swietlicki  Jingchuan Zhou  Olle H. Berg  Bengt G. Martinsson  Gran Frank  Sven-Inge Cederfelt  Ulrike Dusek  Axel Berner  Wolfram Birmili  Alfred Wiedensohler  Brett Yuskiewicz  Keith N. Bower 《Atmospheric Research》1999,50(3-4)

The hygroscopic properties of sub-micrometer aerosol particles were studied in connection with a ground-based cloud experiment at Great Dun Fell, in northern England in 1995. Hygroscopic diameter growth factors were measured with a Tandem Differential Mobility Analyser (TDMA) for dry particle diameters between 35 and 265 nm at one of the sites upwind of the orographic cloud. An external mixture consisting of three groups of particles, each with different hygroscopic properties, was observed. These particle groups were denoted less-hygroscopic, more-hygroscopic and sea spray particles and had average diameter growth factors of 1.11–1.15, 1.38–1.69 and 2.08–2.21 respectively when taken from a dry state to a relative humidity of 90%. Average growth factors increased with dry particle size. A bimodal hygroscopic behaviour was observed for 74–87% of the cases depending on particle size. Parallel measurements of dry sub-micrometer particle number size distributions were performed with a Differential Mobility Particle Sizer (DMPS). The inorganic ion aerosol composition was determined by means of ion chromatography analysis of samples collected with Berner-type low pressure cascade impactors at ambient conditions. The number of ions collected on each impactor stage was predicted from the size distribution and hygroscopic growth data by means of a model of hygroscopic behaviour assuming that only the inorganic substances interacted with the ambient water vapour. The predicted ion number concentration was compared with the actual number of all positive and negative ions collected on the various impactor stages. For the impactor stage which collected particles with aerodynamic diameters between 0.17–0.53 μm at ambient relative humidity, and for which all pertinent data was available for the hygroscopic closure study, the predicted ion concentrations agreed with the measured values within the combined measurement and model uncertainties for all cases but one. For this impactor sampling occasion, the predicted ion concentration was significantly higher than the measured. The air mass in which this sample was taken had undergone extensive photochemical activity which had probably produced hygroscopically active material other than inorganic ions, such as organic oxygenated substances.  相似文献   

Cosmological obscuration by galactic dust: effects of dust evolution     

Frank J. Masci  Rachel L. Webster 《Monthly notices of the Royal Astronomical Society》1999,305(4):937-945

  相似文献   

Collateral consequences of the inhomogeneous distribution of short-lived radionuclides in the solar nebula     

Robert H. NICHOLS  Frank A. PODOSEK  Brad S. MEYER  Cristine L. JENNINGS 《Meteoritics & planetary science》1999,34(6):869-884

Abstract— The presence of several short-lived (now extinct) radionuclides in the early solar system demands that they were synthesized and added to preexisting solar system materials shortly (on a time scale on the order of the relevant radionuclide lifetime) before formation of solar system solids. For diverse reasons, it is often suggested that the solar system distributions of these radionuclides were radically heterogeneous, perhaps because of the late addition. Much attention has been given to the astrophysical circumstances that might govern the synthesis and distribution of these short-lived radionuclides, but comparatively little attention has been devoted to the distribution of cosynthesized isotopes. The focus of this paper is a systematic, quantitative evaluation of the collateral consequences in stable and long-lived isotopes that might be expected if short-lived radionuclides, in particular ²⁶Al or ⁵³Mn, were injected at their canonical levels and inhomogeneously distributed in the early solar system. We mix model massive star yields of Meyer et al. (1995) and Woosley and Weaver (1995) into a reservoir of cosmic composition, as tabulated by Anders and Grevesse (1989). To mitigate the effects of systematic deviations that may be present in these mixtures due to uncertainties in model stellar yields, we follow Timmes and Clayton (1996) and also mix into a “renormalized” proxy solar system composition computed from a galactic chemical evolution model based primarily on the stellar yields of Woosley and Weaver (1995). The results are very unfavorable to the likelihood of heterogeneously distributed ²⁶Al derived from supernova ejecta. If a massive star is invoked to account for ²⁶Al, its ejecta must have been rather uniformly distributed, as inferred from the lack of measured collateral anomalies in several elements, notably Ca, Cr, and Ni. Conversely, if ²⁶Al were indeed radically heterogeneously distributed, some other nucleosynthetic source more efficient at producing ²⁶Al is required. In principle, a similar statement applies to ⁵³Mn, but the situation is more complicated. The inferred anomalies at ⁵³Cr will depend not only on how much ⁵³Mn is added by a heterogeneous component, but also more sensitively on the contributions to the associated stable nuclides, ⁵³Cr, ⁵²Cr, and ⁵⁰Cr. Consideration of predicted collateral anomalies provides no direct support for heterogeneously distributed supernova-derived ⁵³Mn, but the required quantity of supernova contribution, and thus also the collateral anomalies, are much less for ⁵³Mn than for ²⁶Al. With allowance for model calculation uncertainties, it could be argued that anomalies collateral to heterogeneous ⁵³Mn might be small enough to have evaded detection.  相似文献   

The K‐primed approach to high‐pressure equations of state     

Frank D. Stacey 《Geophysical Journal International》2000,143(3):621-628

  相似文献   

Long-term records of erosional change from marine ferromanganese crusts     

R. Keith O’Nions  Martin Frank 《Journal of Earth System Science》2000,109(1):171-180

Ferromanganese crusts from the Atlantic, Indian and Pacific Oceans record the Nd and Pb isotope compositions of the water masses from which they form as hydrogenous precipitates. The¹⁰Be/⁹Be-calibrated time series for crusts are compared to estimates based on Co-contents, from which the equatorial Pacific crusts studied are inferred to have recorded ca. 60 Ma of Pacific deep water history. Time series of ɛNd show that the oceans have maintained a strong provinciality in Nd isotopic composition, determined by terrigenous inputs, over periods of up to 60 Ma. Superimposed on the distinct basin-specific signatures are variations in Nd and Pb isotope time series which have been particularly marked over the last 5 Ma. It is shown that changes in erosional inputs, particularly associated with Himalayan uplift and the northern hemisphere glaciation have influenced Indian and Atlantic Ocean deep water isotopic compositions respectively. There is no evidence so far for an imprint of the final closure of the Panama Isthmus on the Pb and Nd isotopic composition in either Atlantic or Pacific deep water masses.  相似文献   

Variations of continental discharge pattern in space and time: implications from the Laptev Sea continental margin, Arctic Siberia     

Hans Peter Kleiber  Frank Niessen 《International Journal of Earth Sciences》2000,89(3):605-616

Variations in sediment input and distribution to the Laptev Sea continental margin during the Holocene and Termination I could be identified based on radiocarbon dated magnetic susceptibility logs and sediment thickness in high-resolution seismic profiles. Magnetic susceptibility of surface samples reveals an increased input of magnetic grains to the Laptev Sea deriving from the Anabar and Khatanga river catchments. Exposed magnetite schists and volcanic rocks of the Anabar shield and Putoran Plateau, respectively, function as major source of magnetic material. The distribution of magnetic susceptibility in association with the thickness of the Holocene sediments indicates bottom-current induced sediment transport guided by major submarine valleys on the Laptev Sea shelf. The sites of filled paleoriver channels identified in the seismic profiles suggest that during the Late Weichselian sea-level lowstand river runoff continued through four of the major valleys on the exposed Laptev Sea shelf. The sediments at the top of the lowstand deposits in front of the Anabar-Khatanga valley, represented in the seismic profiles by prograding deltas, are characterized by outstandingly high magnetic susceptibility values. Radiocarbon datings approximate the deposition of these high magnetic sediments between 10 and 13.4 ka. It is suggested that this increased input of magnetic material is related to the deglaciation of the Anabar shield and the Putoran Plateau and thus support their glaciation during marine isotope stage (MIS) 2.  相似文献   

Long-Term Temperature Trends and Tree Growth in the Taymir Region of Northern Siberia   总被引：2，自引：0，他引：2  

Gordon C. Jacoby  Nikolai V. Lovelius  Oleg I. Shumilov  Oleg M. Raspopov  Juri M. Karbainov  David C. Frank 《Quaternary Research》2000,53(3):312

The northernmost conifers in the world are located well above the Arctic Circle in the Taymir region of northern Siberia and have been recording the thermal environment for centuries to millennia. The trees respond to temperatures beyond the narrow season of actual cambial cell division by means of root growth, photosynthesis, lignification of cell walls, and other biochemical processes. Data from annual tree-ring widths are used to reconstruct May–September mean temperatures for the past four centuries. These warm-season temperatures correlate with annual temperatures and indicate unusual warming in the 20th century. However, there is a loss of thermal response in ring widths since about 1970. Previously the warmer temperatures induced wider rings. Most major warming and cooling trends are in agreement with other high-latitude temperature reconstructions based on tree-ring analyses with some regional differences in timing of cooling in the late 18th century and of warming in the late 19th century.  相似文献   

Health effects from the sun's ultraviolet radiation and ozone as a stratospheric sunscreen     

Frank R. de Gruijl 《Global Change & Human Health》2000,1(1):26-40

  相似文献   

Importance of seagrass as a carbon source for heterotrophic bacteria in a subtropical estuary (Florida Bay)     

Clayton J. Williams  Rudolf Jaffé  William T. Anderson  Frank J. Jochem 《Estuarine, Coastal and Shelf Science》2009

A stable carbon isotope approach was taken to identify potential organic matter sources incorporated into biomass by the heterotrophic bacterial community of Florida Bay, a subtropical estuary with a recent history of seagrass loss and phytoplankton blooms. To gain a more complete understanding of bacterial carbon cycling in seagrass estuaries, this study focused on the importance of seagrass-derived organic matter to pelagic, seagrass epiphytic, and sediment surface bacteria. Particulate organic matter (POM), seagrass epiphytic, seagrass (Thalassia testudinum) leaf, and sediment surface samples were collected from four Florida Bay locations with historically different organic matter inputs, macrophyte densities, and primary productivities. Bulk (observed and those reported previously) and compound-specific bacterial fatty acid δ¹³C values were used to determine important carbon sources to the estuary and benthic and pelagic heterotrophic bacteria. The δ¹³C values of T. testudinum green leaves with epiphytes removed ranged from −9.9 to −6.9‰. Thalassia testudinum δ¹³C values were significant more enriched in ¹³C than POM, epiphytic, and sediment samples, which ranged from −16.4 to −13.5, −16.2 to −9.6, and −16.7 to −11.0‰, respectively. Bacterial fatty acid δ¹³C values (measured for br14:0, 15:0, i15:0, a15:0, br17:0, and 17:0) ranged from −25.5 to −8.2‰. Assuming a −3‰ carbon source fractionation from fatty acid to whole bacteria, pelagic, epiphytic, and sediment bacterial δ¹³C values were generally more depleted in ¹³C than T. testudinum δ¹³C values, more enriched in ¹³C than reported δ¹³C values for mangroves, and similar to reported δ¹³C values for algae. IsoSource mixing model results indicated that organic matter derived from T. testudinum was incorporated by both benthic and pelagic bacterial communities, where 13–67% of bacterial δ¹³C values could arise from consumption of seagrass-derived organic matter. The IsoSource model, however, failed to discriminate clearly the fraction of algal (0–86%) and mangrove (0–42%) organic matter incorporated by bacterial communities. These results indicate that pelagic, epiphytic, and sediment surface bacteria consumed organic matter from a variety of sources. Bacterial communities incorporated consistently seagrass-derived organic matter, the dominant macrophyte in Florida Bay, but seagrass δ¹³C values alone could not account fully for bacterial δ¹³C values.  相似文献