Analysis of Urban Atmosphere Plume Concentration Fluctuations   总被引：1，自引：1，他引：0  

Dennis Finn  Kirk L. Clawson  Roger G. Carter  Jason D. Rich  Chris Biltoft  Martin Leach 《Boundary-Layer Meteorology》2010,136(3):431-456

Concentration variability in the fast-response tracer dataset for continuous, near-surface, point source releases in the urban core from the Joint Urban 2003 field study is analyzed. Concentration variability for conditionally and unconditionally sampled time series is characterized by probability densities, concentration fluctuation intensity, skewness, and kurtosis. Significant day-night differences in plume dispersion are observed. Relative to daytime, nighttime plumes were more likely to have reduced concentration fluctuation intensities, higher normalized surface concentrations, suppressed vertical mixing, and a greater prevalence of Gaussian-like distributions rather than log-normal or mixed mode distributions. This was in spite of the similar stability and turbulence conditions in the urban core for day and night. The potential roles of flow meander and thermal stability in explaining these differences are examined. Probability densities of concentration are found to be a strong function of fluctuation intensity. There are few differences in probability densities between day and night when classified by fluctuation intensity. There are no appreciable differences between conditional and unconditional probability densities and only small differences between conditional and unconditional sampling statistics relative to the larger differences usually observed in more homogeneous settings. Fluctuation intensity, skewness, and kurtosis are higher for the daytime experiments, and closer to the source, but show little difference between conditional and unconditional results over most of their range of values. The log-normal distribution provides a better overall fit to a broader range of the dataset than the exponential or clipped-normal distributions.  相似文献   

GRI: focusing on the evolving violent universe     

Jürgen Knödlseder  Peter von Ballmoos  Filippo Frontera  Angela Bazzano  Finn Christensen  Margarida Hernanz  Cornelia Wunderer 《Experimental Astronomy》2009,23(1):121-138

The gamma-ray imager (GRI) is a novel mission concept that will provide an unprecedented sensitivity leap in the soft gamma-ray domain by using for the first time a focusing lens built of Laue diffracting crystals. The lens will cover an energy band from 200–1,300 keV with an effective area reaching 600 cm². It will be complemented by a single reflection multilayer coated mirror, extending the GRI energy band into the hard X-ray regime, down to ∼10 keV. The concentrated photons will be collected by a position sensitive pixelised CZT stack detector. We estimate continuum sensitivities of better than 10^− 7 ph cm^− 2s^− 1keV^− 1 for a 100 ks exposure; the narrow line sensitivity will be better than 3 × 10^− 6 ph cm^− 2s^− 1 for the same integration time. As focusing instrument, GRI will have an angular resolution of better than 30 arcsec within a field of view of roughly 5 arcmin—an unprecedented achievement in the gamma-ray domain. Owing to the large focal length of 100 m of the lens and the mirror, the optics and detector will be placed on two separate spacecrafts flying in formation in a high elliptical orbit. R&D work to enable the lens focusing technology and to develop the required focal plane detector is currently underway, financed by ASI, CNES, ESA, and the Spanish Ministery of Education and Science. The GRI mission has been proposed as class M mission for ESAs Cosmic Vision 2015–2025 program. GRI will allow studies of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the universe. All authors are on behalf of a large international collaboration The GRI mission has been proposed as an international collaboration between (in alphabetical order) Belgium (CSR), China (IHEP, Tsinghua Univ.), Denmark (DNSC, Southern Univ.), France (CESR, APC, ILL, CSNSM, IAP, LAM), Germany (MPE), Ireland (UCD School of Physics), Italy (INAF/IASF Rome, Bologna, Milano, Palermo; INAF/OA Brera, Roma; UNIFE, CNR/IMEM), Poland (NCAC), Portugal (Combra Univ., Evora Univ.), Russia (SINP, MSU, Ioffe Inst.), Spain (IEEC-CSIC-IFAE, CNM-IMB), the Netherlands (SRON, Utrecht Univ.), Turkey (Sabanci Univ.), United Kingdom (Univ. of Southampton, MSSL, RAL, Edinburgh Univ.), and the United States of America (SSL UC Berkeley, Argonne National Lab., MSFC, GSFC, US NRL).  相似文献   

Submersed macrophyte effects on nutrient exchanges in riverine sediments     

Cathleen Wigand  Melissa Finn  Stuart Findlay  David Fischer 《Estuaries and Coasts》2001,24(3):398-406

Submersed macrophytes are important in nutrient cycling in marine and lacustrine systems, although their in nutrient exchange in tidally-influenced riverine systems is not well studied. In the laboratory, plants significantly lowered porewater nutrient pools of riverine sediments compared with bare controls. Deep-rootedVallisneria americana lowered the porewater nutrients to a greater extent than the shallow-rootedPotamogeton pectinatus. V. americana showed significantly higher tissue nutrient content (N in roots, P in leaves) thanP. pectinatus. porewater nutrients in the river increased from spring to summer (1995) when vegetation was at its peak (for porewater PO₄-P, p<0.05). In 1996, porewater nutrients were higher during peak plant biomass in the summer than in the fall (for porewater PO₄-P, p<0.05). In the summer (1995) vegetated patches had significantly greater porewater PO₄-P than bare patches. We hypothesize that the concentrating of particulates in riverine grassbeds and subsequent microbial processing may provide an indirect source of nutrients for submersed macrophytes. In tidally-influenced riverine systems, biological mechanisms such as root uptake of nutrients and lateral oxygen release may be masked by the interaction of physical forces (i.e., tides, currents) with the structure of the grassbeds.  相似文献   

Development and validation of an estuarine biotic integrity index   总被引：1，自引：0，他引：1  

Linda A. Deegan  John T. Finn  Suzanne G. Ayvazian  Cheryl A. Ryder-Kieffer  John Buonaccorsi 《Estuaries and Coasts》1997,20(3):601-617

We tested hypotheses about how estuarine fish assemblages respond to habitat degradation and then integrated these responses into an overall index, the Estuarine Biotic Integrity Index (EBI), which summarized observed changes. Fish assemblages (based on trawl catches) and habitat quality were measured monthly or biweekly at nine sites in two estuaries from March 1988 to June 1990. Submerged aquatic vegetation habitats were classified as low or medium quality based on year-round measurements of chemical and physical characteristics (phytoplankton blooms; macroalgae; dissolved oxygen; nutrients; dredged channels). We tested 15 metrics and selected 8 for inclusion in the EBI: total number of species, dominance, fish abundance (number or biomass), number of nursery species, number of estuarine spawning species, number of resident species, proportion of benthic-associated fishes, and proportion abnormal or diseased. Fish assemblages in low-quality sites had lower number of species, density, biomass, and dominance compared with medium-quality sites. Fish abundance peaked in July and August, and was lowest in January to March. The seasonal cycle in low-quality sites was damped compared with medium-quality sites. Abundances of fishes using estuaries as a spawning and nursery area and of benthic species were lower in low-quality sites compared to medium-quality sites. The individual metrics and the overall index correlated with habitat degradation. The EBI based on biomass did not do better than the EBI based on number, indicating that the extra effort to obtain biomass may not be warranted. We suggest the EBI is a useful indicator of estuarine ecosystem status because it reflects the relationship between anthropogenic alterations in estuarine ecosystems and the status of higher trophic levels.  相似文献   

Analysis of ground motions at Treasure Island site during the 1989 Loma Prieta earthquake   总被引：1，自引：0，他引：1  

W. D. Liam Finn  Carlos E. Ventura  Guoxi Wu 《Soil Dynamics and Earthquake Engineering》1993,12(7)

Site response analyses and coherence studies were conducted at the Treasure Island site where surface motions were recorded during the Loma Prieta earthquake. The analyses were conducted using a nonlinear dynamic effective stress method which took into account the effects of the liquefaction that occured at the site. The rock motions recorded at nearby Yerba Buena Island were used as input motions. Computed and recorded ground motions transverse to the direction of wave propagation and associated response spectra were in good agreement. Agreement was also good in the radial direction, except in certain frequency bands higher than 1·25 Hz. Coherence studies showed that some of these discrepancies may be due to low coherence between the Treasure Island and Yerba Buena motions in these same frequency bands.  相似文献   

IMPROVING THE INTERPRETATION OF GEOGRAPHICAL CANONICAL CORRELATION MODELS     

Mark S. Monmonier  Fay Evanko Finn 《The Professional geographer》1973,25(2):140-142

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Load distribution in large pile groups under static and dynamic loading     

J. Dowling  W. D. L. Finn  C. E. Ventura  M. Taiebat 《Bulletin of Earthquake Engineering》2016,14(6):1461-1474

Research on the action of pile groups in resisting lateral loading is usually based on analysis, field and centrifuge tests of small pile groups. The interaction between piles in these groups is modelled by modifying the lateral resistance p–y curves developed for a single pile using row dependent reduction factors or a group factor for the entire group to simulate the effect of soil–pile–soil interaction. The modifying factors for the p–y curves and the appropriate group factors for pile groups are based entirely on static tests and there is no direct verification that these factors are appropriate to handle the dynamic loading of earthquake induced ground motions. In this paper we investigate the interaction effects between piles under static and seismic loading using the computer program VERSAT-P3D, which uses an equivalent linear constitutive model for the soil. The analytical procedure is calibrated using data from a static field load test on a single pile. Several pile groups, 2 × 2, 3 × 3, 4 × 4, 5 × 5, 8 × 8, 10 × 10, 10 × 2 and 15 × 2 were analysed for the study. Each group was subjected to static pushover and earthquake loading and the distribution of static and dynamic shear forces at various lateral displacements were evaluated. The study shows that the distribution of load within a pile group under dynamic loading varies significantly from the distribution under static loading and is strongly load intensity dependent. Current practice assumes that the distributions are similar.  相似文献   

A Holocene pollen and diatom record from Vanderlin Island, Gulf of Carpentaria, lowland tropical Australia   总被引：1，自引：0，他引：1  

Matiu Prebble  Robin Sim  Jan Finn  David Fink 《Quaternary Research》2005,64(3):357-371

Sedimentary, palynological and diatom data from a dunefield lake deposit in the interior of Vanderlin Island in the Gulf of Carpentaria are presented. Prior to the formation of present perennial lake conditions, the intensified Australian monsoon associated with the early Holocene marine transgression allowed Cyperaceae sedges to colonise the alluvial margins of an expansive salt flat surrounded by an open Eucalyptus woodland. As sea level stabilised between 7500 and 4500 cal yr B.P. coastal dunes ceased to develop allowing dense Melaleuca forest to establish in a Restionaceae swamp. Dune-sand input into the swamp was diminished further as the increasingly dense vegetation prevented fluvial and aeolian transported sand arriving from coastal sources. This same process impounded the drainage basin allowing a perennial lake to form between 5500 and 4000 cal yr B.P. Myriophyllum and other aquatic taxa colonised the lake periphery under the most extensive woodland recorded for the Holocene. The palynological data support an effective precipitation model proposed for northern Australia that suggests more variable conditions in the late Holocene. A more precise measure of effective precipitation change is provided by diatom-based inferences that indicate few changes in lake hydrology. Such interpretations are explained in terms of palynological sensitivity to adjustments in local fire regimes where regional precipitation change may only be recorded indirectly through fire promoting mechanisms, including intensified ENSO periodicity and human impact.  相似文献   

Plume Dispersion in Low-Wind-Speed Conditions During Project Sagebrush Phase 2, with Emphasis on Concentration Variability     

D. Finn  R. G. Carter  R. M. Eckman  J. D. Rich  Z. Gao  H. Liu 《Boundary-Layer Meteorology》2018,169(1):67-91

Eight short-range, open-terrain SF₆ tracer tests in low wind speeds were conducted during Phase 2 of Project Sagebrush using continuous releases. Four tests were made during very unstable conditions in July and August 2016, and four during very stable conditions in October 2016. All tests featured 10-min averaging and 1-Hz sampling of tracer concentrations together with an extensive suite of meteorological measurements. We find that the uncertainty in well-mixed daytime measurements of tracer concentrations, using the absolute value of the relative percentage difference in collocated duplicate samplers, approaches a downwind limit of about 7–8%. Concentration variability in collocated sampling, due to stochastic factors and independent of measurement uncertainty, increases the total observational uncertainty closer to the source from about 20% (daytime) to 40% (very stable conditions). Longer averaging periods moderately reduce the concentration variability. The data indicate that the large increase in concentration variability is linked with the suppression of turbulent mixing, small eddy length scales, and meandering in very stable conditions. These results should be considered when comparing observations with model predictions in evaluations.  相似文献