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51.
52.
R. Whitley T. V. Hromadka II 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(1):51-63
A basic problem in hydrology is computing confidence levels for the value of the T-year flood when it is obtained from a Log
Pearson III distribution in terms of estimated mean, estimated standard deviation, and estimated skew. In an important paper
Chowdhury and Stedinger [1991] suggest a possible formula for approximate confidence levels, involving two functions previously
used by Stedinger [1983] and a third function, λ, for which asymptotic estimates are given. This formula is tested [Chowdhury
and Stedinger, 1991] by means of simulations, but these simulations assume a distribution for the sample skew which is not,
for a single site, the distribution which the sample skew is forced to have by the basic hypothesis which underlies all of
the analysis, namely that the maximum discharges have a Log Pearson III distribution. Here we test these approximate formulas
for the case of data from a single site by means of simulations in which the sample skew has the distribution which arises
when sampling from a Log Pearson III distribution. The formulas are found to be accurate for zero skew but increasingly inaccurate
for larger common values of skew. Work in progress indicates that a better choice of λ can improve the accuracy of the formula. 相似文献
53.
Wen-Jong Chang Ellen M. Rathje Kenneth H. Stokoe II Brady R. Cox 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):723
A dynamic full scale testing program was performed to quantitatively assess the effectiveness of prefabricated vertical drains as a liquefaction countermeasure. The testing program involved a new in situ liquefaction testing technique, which uses a large hydraulic vibrator to generate waves propagating through an embedded instrumentation area to measure the coupled soil-pore water response. The effectiveness of prefabricated vertical drains is assessed experimentally by comparing the pore pressure generation, pore pressure dissipation, and settlement from two reconstituted soil specimens; one without a drain in place and the other with a single drain installed. Because the prefabricated drain was installed during the specimen preparation process, no accompanying densification during installation occurred. Therefore, the effect of drainage alone was evaluated. The testing results show that the drainage provided by prefabricated drains can significantly reduce pore pressure generation, accelerate post-shaking pore pressure dissipation, and limit associated settlement. The outcome also shows that the new developed in situ liquefaction testing technique can be an alternative to quantitatively evaluate the effects of various liquefaction remediation techniques. 相似文献
54.
The presence of large amounts of gas and/or liquid hydrocarbon seepage in near surface sediments can produce distinct features
including an irregular topography (on several scales, ranging from meters to kilometers); seismically transparent/chaotic
sediments; oil staining; gas plumes; sediments containing elevated concentrations of extractable organic matter, organic carbon,
and calcium carbonate; associated brine seepage and anoxic conditions; extensive bacterial mats; hydrate formation and decomposition;
and dense chemoautotrophic communities. Although no single characteristic is always uniquely associated with seepage, the
co-occurrence of several of these features is strongly suggestive of an area being exposed to non-indigenous upward migrating
hydrocarbons. 相似文献
55.
Laurel A. Zahn Jeremy T. Claisse Jonathan P. Williams Chelsea M. Williams Daniel J. Pondella II 《Marine Ecology》2016,37(4):770-785
Understanding species distributions and their community structure is increasingly important when taking an ecosystem‐based approach to conservation and management. However, knowledge of the distribution and community structure of species in mid‐range trophic levels (e.g. macroinvertebrates) is lacking in most marine ecosystems. Our study aimed to examine the spatial distribution and community‐level biogeographic patterns of common kelp forest–rocky reef macroinvertebrates in Southern California and to evaluate the effects of environmental gradients on these communities. Quantitative SCUBA surveys were used to estimate macroinvertebrate densities at 92 sites from 2008–2012. Non‐metric multidimensional scaling was used to evaluate spatial patterns of macroinvertebrate communities among Regions. We found that kelp forest–rocky reef macroinvertebrate communities are distinct among different island and mainland regions, and their community patterns exhibited a strong relationship with an environmental gradient (i.e. sea surface temperature) even after controlling for geographic distance between sites. High abundances of urchin species (Strongylocentrotus purpuratus and Strongylocentrotus franciscanus) were strong drivers of regional differences. Macroinvertebrate community patterns were driven by characteristic species that were typically more prevalent at warmer or colder sites. Our results provide the first quantitative analysis of macroinvertebrate community structure within the California kelp forest ecosystem. We also describe the distribution and abundance of 92 conspicuous kelp forest‐rocky reef macroinvertebrates among nine pre‐defined Regions. This study provides important preliminary information on these macroinvertebrate species that will be directly useful to inform management of invertebrate fisheries and spatial protection of marine resources. 相似文献
56.
Eric N. Powell Robert D. Barber Mahlon C. Kennicutt II Susan E. Ford 《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(12):915
Petroleum seep mussels are often exposed to high hydrocarbon concentrations in their natural habitat and, thus, offer the opportunity to examine the relationship between parasitism, disease and contaminant exposure under natural conditions. This is the first report on the histopathology of cold-seep mussels. Seep mussels were collected by submersible from four primary sites in the Gulf of Mexico, lease blocks Green Canyon (GC) 184, GC-234, GC-233, and Garden Banks 425 in 550–650 m water depth. Five types of parasites were identified in section: (1) gill “rosettes” of unknown affinity associated with the gill bacteriocytes, (2) gill “inclusions” similar to chlamydia/rickettsia inclusions, (3) extracellular gill ciliates, (4) body “inclusions” that also resemble chlamydial/rickettsial inclusions, and (5) Bucephalus-like trematodes. Comparison to shallow-water mytilids demonstrates that: (1) both have similar parasite faunas; (2) seep mytilids are relatively heavily parasitized; and (3) infection intensities are extremely high in comparison to shallow-water mytilids for Bucephalus and chlamydia/rickettsia. In this study, the lowest prevalence for chlamydia/rickettsia was 67%. Prevalences of 100% were recorded from three populations. Bucephalus prevalence was 70% in three of 10 populations. The parasite fauna was highly variable between populations. Some important parasites were not observed in some primary sites. Even within primary sites, some important parasites were not observed in some populations. Bucephalus may exert a significant influence on seep mussel population dynamics. Forty percent of the populations in this study are severely reproductively compromised by Bucephalus infection. Only a fraction of petroleum seep mussel populations are maintaining the entire beta-level population structure of this species. Variation in two parasites, gill ciliates and Bucephalus, explained most of the variation in PAH body burden between mussel populations. PAHs are known to be sequestered preferentially in gametic tissue. Bucephalus would be expected to reduce overall body burden, at high infection intensities, by replacing gametic tissue. PAH concentrations exceeded 1 ppm in 4 of 9 populations, a ratio significantly higher than the 8 of 30 mussel locales in the NOAA Mussel Watch Program. Only five Mussel Watch locales exceeded the highest value for a petroleum seep population. Digestive gland and gill tissue atrophy were not significantly correlated with PAH body burden, even though some populations were characterized by body burdens exceeding 1 ppm, suggesting that seep mussels may not be as sensitive to PAH exposure as are some shallow-water mytilid populations. 相似文献
57.
A. K. Tripathi R. P. Singhal K. P. Singh O. N. Singh II 《Earth, Moon, and Planets》2013,110(1-2):11-27
Pitch-angle diffusion coefficients of electrons have been calculated for resonant interaction with electrostatic electron-cyclotron harmonic (ECH) waves using quasi linear diffusion theory. Calculations have been performed for the planets Earth and Jupiter at three radial distances for each planet. Electron precipitation fluxes have also been calculated and compared with observed fluxes. At Earth, electrons of energy ≤200 eV may be put on strong diffusion at L = 10. At lower L values, observed ECH wave amplitudes are insufficient to put electrons on strong diffusion. At Jupiter, electrons can be put on strong diffusion at all L values. However, the energy of electrons which may be put on strong diffusion decreases from about 1 keV at L = 7 to ~100 eV at L = 17. It is concluded that ECH waves may be partly responsible for diffuse auroral precipitation of low energy electrons at Jupiter for lower L values. At Earth contribution of ECH waves to diffuse aurora is quite small. 相似文献
58.
59.
Penka Pavlova Kostadinka Markova Stephan Tanev Joseph S. Davis 《International Journal of Salt Lake Research》1998,7(4):357-368
Data on biota and nutrients in solar ponds of a saltworks near Burgas, Bulgaria, were obtained. Surveys of the biota were
undertaken, and records from management officials gave information on biological and physical conditions related to salt production.
The decrease in the quality and quantity of sodium chloride harvested that began 10 to 15 years before the study, may be related
to the high levels of plankton, combined nitrogen and phosphate, and the large accretion of bottom sediments and density of
benthic communities. Biological management can improve the quality and quantity of the sodium chloride produced by the saltworks. 相似文献
60.
The field deployment of a heated distributed temperature sensor (DTS) for over three years has revealed two obstacles to estimating soil moisture (θ) that may hamper subsurface DTS applications as well as use of other subsurface thermal probes. The first observed obstacle was a hysteretic response of the DTS sensor. The relationship between θ and the temperature response (?T) within the cable was not only dependent on θ of the soil, but also on the previous wetting and drying cycles leading to that state. The second observed obstacle was soil structure healing. Soil structure healing causes the relationship between ?T and θ to evolve through time; this calibration curve becomes flatter, or less sensitive, as the surrounding soil makes better contact with the cable. Effects of the hysteretic response of the instrument and soil structure healing are largely the result of small gaps between the cable and soil. These small gaps can be approximated by a contact resistance between the cable and soil. In this article we characterize the occurrence of hysteretic and soil structure healing effects from field data and parameterize contact resistance by simulating heat transfer using a numerical modelling approach Copyright © 2015 John Wiley & Sons, Ltd. 相似文献