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311.
312.
Jessie M. Doyle Ryan A. Hill Scott G. Leibowitz Joseph L. Ebersole 《Journal of the American Water Resources Association》2023,59(5):1099-1114
Channel dimensions (width and depth) at varying flows influence a host of instream ecological processes, as well as habitat and biotic features; they are a major consideration in stream habitat restoration and instream flow assessments. Models of widths and depths are often used to assess climate change vulnerability, develop endangered species recovery plans, and model water quality. However, development and application of such models require specific skillsets and resources. To facilitate acquisition of such estimates, we created a dataset of modeled channel dimensions for perennial stream segments across the conterminous United States. We used random forest models to predict wetted width, thalweg depth, bankfull width, and bankfull depth from several thousand field measurements of the National Rivers and Streams Assessment. Observed channel widths varied from <5 to >2000 m and depths varied from <2 to >125 m. Metrics of watershed area, runoff, slope, land use, and more were used as model predictors. The models had high pseudo R2 values (0.70–0.91) and median absolute errors within ±6% to ±21% of the interquartile range of measured values across 10 stream orders. Predicted channel dimensions can be joined to 1.1 million stream segments of the 1:100 K resolution National Hydrography Dataset Plus (version 2.1). These predictions, combined with a rapidly growing body of nationally available data, will further enhance our ability to study and protect aquatic resources. 相似文献
313.
A patient in whom intrauterine fetal cytomegalovirus (CMV) infection was diagnosed at approximately 25 weeks' gestation is presented. The fetus was evaluated by serial fetal blood samplings and ultrasound examinations. The fetus manifested evidence of severe thrombocytopenia and hepatic inflammation, with recovery over a period of approximately 8 weeks. The initial sonographic findings of marked fetal ascites and cardiomegaly gradually resolved; ventriculomegaly developed during the third trimester. At delivery, the baby was morphologically normal with the exception of mild ventriculomegaly. Cord blood was negative for CMV IgM but urine was culture-positive for CMV. At age 3, the child has a severe but stable unilateral hearing deficit and is otherwise developmentally normal. This case demonstrates the utility of serial ultrasound and fetal blood sampling in the prenatal diagnosis and management of fetal CMV infection. 相似文献
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315.
Nicola A. Clark Mark Williams Daniel J. Hill Patrick G. Quilty John L. Smellie Jan Zalasiewicz Melanie J. Leng Michael A. Ellis 《Die Naturwissenschaften》2013,100(8):699-722
We evaluate the available palaeontological and geochemical proxy data from bivalves, bryozoans, silicoflagellates, diatoms and cetaceans for sea surface temperature (SST) regimes around the nearshore Antarctic coast during the late Neogene. These fossils can be found in a number of shallow marine sedimentary settings from three regions of the Antarctic continent, the northern Antarctic Peninsula, the Prydz Bay region and the western Ross Sea. Many of the proxies suggest maximum spring–summer SSTs that are warmer than present by up to 5 °C, which would result in reduced seasonal sea ice. The evidence suggests that the summers on the Antarctic shelf during the late Neogene experienced most of the warming, while winter SSTs were little changed from present. Feedbacks from changes in summer sea ice cover may have driven much of the late Neogene ocean warming seen in stratigraphic records. Synthesized late Neogene and earliest Quaternary Antarctic shelf proxy data are compared to the multi-model SST estimates of the Pliocene Model Intercomparison Project (PlioMIP) Experiment 2. Despite the fragmentary geographical and temporal context for the SST data, comparisons between the SST warming in each of the three regions represented in the marine palaeontological record of the Antarctic shelf and the PlioMIP climate simulations show a good concordance. 相似文献
316.
Kristal A. Huggins Kristen J. Navara Mary T. Mendonça Geoffrey E. Hill 《Die Naturwissenschaften》2010,97(7):637-644
Carotenoid pigments produce yellow, orange, and red integumentary color displays that can serve as reliable signals of health
and condition. In many birds and fish, individuals gain competitive or mating advantages by ingesting and utilizing large
quantities of carotenoid pigments. Carotenoid pigments serve as antioxidants, performing important functions as free-radical
scavengers. The beneficial effects of carotenoid pigments are well documented, but rarely have researchers considered potential
detrimental effects of high-level accumulation of carotenoids. We maintained American goldfinches (Carduelis tristis) on high- or low-carotenoid diets through molt and tested for damage to the liver and skeletal muscle. High intake of carotenoids
had no measurable effect on liver enzymes but caused an increase in creatine kinase, an indicator of skeletal muscle breakdown,
and a reduction in vertical flight performance, a measure of skeletal muscle integrity. The detrimental effects of high-level
carotenoid accumulation were approximately equivalent to the negative effects of removing carotenoids from the diet. The adverse
effects observed in this study have important implications for theories of the function and evolution of colorful plumage. 相似文献
317.
John Kaihong KAM 《环境科学学报(英文版)》1992,4(1):39-42
Data acquired in the area of Environmental Sciences are by their very nature often discontinuous and abrupt. As such, the mathematical theories of catastrophe and chaos may be of use in analyzing such scientific data and in formulating mathematical models. 相似文献
318.
319.
The nitroaromatic compounds 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and 2,4-dinitroanisole (DNAN) are potential environmental contaminants and their transformations under a variety of environmental conditions are consequently of great interest. One possible method to safely degrade these nitrocompounds is alkaline hydrolysis. A mechanism of the initial stages of this reaction was investigated computationally. Simulations of UV-VIS and NMR spectra for this mechanism were also produced. The results obtained were compared to available experimental data on the alkaline hydrolysis of TNT and suggest that the formation of Meisenheimer complexes and an anion of TNT are potential first-step intermediates in the reaction path. As the reaction proceeds, computational results indicate that polynegative complexes dominate the degradation pathway, followed by cycles of carbon chain opening and breaking. A second possible pathway was identified that leads to polymeric products through Janovsky complex formation. Results from this study indicate that the order of increasing resistance to alkaline hydrolysis is TNT, DNT and DNAN. 相似文献
320.
Antonious G Hill R Ross K Coolong T 《Journal of environmental science and health. Part. B》2012,47(5):369-378
Endosulfan 3 EC, a mixture of α- and β-stereo isomers, was sprayed on field-grown pepper, melon, and sweet potato plants at the recommended rate of 0.44 kg A.I. acre(-1). Plant tissue samples (leaves, fruits, or edible roots) were collected 1 h to 30 days following spraying and analyzed for endosulfan isomers (α- and β-isomers). Analysis of samples was accomplished using a gas chromatograph (GC) equipped with a mass detector in total ion mode. The results indicated the formation of endosulfan sulfate as the major metabolite of endosulfan sulfite and the relatively higher persistence of the β-isomers as compared to the α-isomer. The initial total residues (α- and β-isomers plus endosulfan sulfate) were higher on leaves than on fruits. On pepper and melon fruits, the α-isomer, which is the more toxic to mammals, dissipated faster (T(1/2) = 1.22 and 0.95 d, respectively) than the less toxic β-isomer (T(1/2) = 3.0 and 2.5 d, respectively). These results confirm the greater loss of the α-isomer compared to the β-isomer, which can ultimately impact endosulfan dissipation in the environment. Additionally, the higher initial residues of endosulfan on pepper and sweet potato leaves should be considered of great importance for timing field operations and the safe entry of harvesters due to the high mammalian toxicity of endosulfan. 相似文献