An artificial neural networks (ANN) model is developed to study the observed pattern of local scour at bridge piers using an FHWA (Federal Highway Administration) data set composed of 380 measurements at 56 bridges in 13 states. Various ANN estimates of observed pier scour depth on different choices of input variables are examined. Reducing the number of variables from 14 to 9 has negligible effect on the coefficient of determination, R2, (0.73 vs. 0.72). Further sensitivity analysis indicates that pier scour depth can be estimated using only four variables: pier shape and skew, flow depth and velocity with a coefficient of determination of 0.81, suggesting that inclusion of some variables actually diminishes the quality of ANN predictions of short term observed pattern of scour. The ANN estimates indicate that flow depth and flow velocity make up 66% of the coefficient of determination. 相似文献
The correlations of the δ18Omax in the shallow ice core from the Guliya ice cap on the Tibetan Plateau with the global sea surface temperatures (SST) and height at the 500 hPa over the Northern Hemisphere were analyzed. The correlated regions on oceans that have a significant influence on the δ18Omax in the Guliya ice core are all located in ocean currents, or convergent regions of currents. They are the eastern Equatorial Pacific, the Northern Pacific Current, the Hot Pool in the eastern Indian Ocean, the Mozambique Current, the Northern Atlantic Current, the Canary Current and the Atlantic Equatorial Current. The δ18Omax in the Guliya ice core has negative correlations with the SST located in the lower latitudes, and positive correlations with the SST in the middle latitudes. The correlated areas at the 500 hPa that have a great impact on the δ18Omax are located in the subtropical highs over the mid-low-latitude oceans and the long-wave trough area over Balkhash Lake, where there are marked negative correlations between the heights in those areas and the δ18Omax. The influencing mechanism is displayed by the diversity of the vapor origins transported to the Guliya region. The strengths of the European ridge and the ridge over Baikal Lake have notable positive correlations with the δ18Omax. The two systems indirectly influence the vapor transportation towards the Guliya region by the adjustment of long-wave trough and ridge. 相似文献
The δ18O variations in an 80.36 m ice core retrieved in the accumulation zone of the East Rongbuk Glacier, Mount Qomolangma (Everest), is not consistent with changes of air temperature from both southern and northern slopes of Himalayas, as well as these of the temperature anomalies over the Northern Hemisphere. The negative relationship between the δ18O and the net accumulation records of the ice core suggests the "amount effect" of summer precipitation on the δ18O values in the region. Therefore, the δ18O records of the East Rongbuk ice core should be a proxy of Indian Summer Monsoon intensity, which shows lower δ18O values during strong monsoon phases and higher values during weak phases. 相似文献
Analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the Kodiak Trench, Hydrate Ridge, Monterey Bay Clam Flats, and the Eel River Basin, coupled with the studies of the chemistry of the pore fluids, have shown that these carbonates have grown within the sediment column. Geochemical profiles of pore fluids show that, in deep water seeps (Kodiak Trench—4450 m; Monterey Bay—1000 m; Hydrate Ridge—650 m), δ13C (DIC) values are low (isotopically light), whereas in the Eel River area ( 350–500 m), δ13C (DIC) values are much higher (isotopically heavier). In all cases, the δ13C values indicate that processes of methane oxidation, associated with sulfate reduction, are dominant in the shallow sediments. Data on the isotopic composition of authigenic carbonates found at sites in Kodiak Trench, Eel River Basin South, and Eel River Basin North indicate a variable composition and origin in different geochemical environments. Some of the authigenic carbonates from the study sites show a trend in their δ13C values similar to those of the pore fluids obtained in their vicinity, suggesting formation at relatively shallow depths, but others indicate formation at greater sediment depths. The latter usually consist of high magnesium calcite or dolomite, which, from their high values of δ13C (up to 23‰;) and δ18O (up to 7.5‰), suggest formation in the deeper horizons of the sediments, in the zone of methanogenesis. These observations are in agreement with observations by other workers at Hydrate Ridge, in Monterey Bay, and in the Eel River Basin. 相似文献
The stable isotopic composition of hydrogen and oxygen (δ2H and δ18O) and tritium activity (3H) were monitored in monthly precipitation at two continental stations (Ljubljana, Zagreb) and six stations along the eastern Adriatic coasts of Slovenia and Croatia in the period 2001–2003. Mean air temperatures and amount of precipitation were also recorded.
Distinct differences in both meteorological and isotopic data between the continental and maritime stations were observed. Seasonal variations in δ18O are smaller at the maritime stations than at the continental ones due to smaller seasonal temperature variations. A good correlation between δ18O and δ2H was obtained for each station, and the local meteoric water lines are close to the Global Meteoric Water Line, with a decreasing trend of slope for the south-Adriatic stations. Good correlations between δ18O in monthly precipitation and mean monthly air temperature were observed at all stations. The slope of δ18O vs. T varied between 0.37‰ °C−1 and 0.15‰ °C−1. Mean 3H activity and seasonal variation of 3H activity are smaller at maritime stations than at continental ones. Additionally, 3H activity decreases in the NW–SE direction of the Adriatic coast.
The study of spatial variations over this relatively small area rich in geographical and climatic diversities showed the complexity of the isotopic composition of precipitation and the isotopic data obtained for eight stations, most of them in the karstic area along the Adriatic coast, and gave valuable information for regional hydrological investigations and modelling of isotope variability over the Mediterranean basin. 相似文献
Based on summer observations of stable isotope of precipitation at Muztagata, western China, during 2002-2003, this paper
presents the relationship between δ18O in precipitation and air temperature, and discusses the effect of moisture transport on δ18O in precipitation. Results show that air temperature correlates positively with δ18O in precipitation, and the temperature effect controls the δ18O of precipitation in this area. The Muztagata region exhibits high δ18O values in summer precipitation, similar to those shown at stations in adjacent regions. According to the results of our
model set up to trace the moisture trajectories, the westerlies and local moisture circulation contribute to variations of
oxygen isotopes in precipitation. In addition, the impacts of the moisture transport distance, the moisture transport level,
and the incursion of the polar air mass also influence the variations of δ18O in precipitation. The moisture origins and transport mechanisms also contribute to the variation of δ18O in precipitation at Muztagata. 相似文献
Based on the theoretical modelling of water-rock δD-δ18O isotopic exchange process, the evolution and sources of ore-forming fluid in four metallogenic epochs of the Jinduicheng
superlarge-scale porphyry-type molybdenum deposit were investigated. It was revealed that in the pre-metallogenic and early-metallogenic
epochs, the ore-forming fluid was a residual fluid derived from magmatic water-wall rock interaction at middle to high temperatures
(T = 250–500°C) and lower W/R ratios (0.1> = W/R>0.001), while in the metallogenic and postmetallogenic epochs, the ore-forming
fluid was a residual fluid derived from meteoric water-wall rock interaction at middle to lower temperatures (T = 150–310°C) and relatively high W/R ratios (0.5>W/R≥0.1). The meteoric water played an important role in molybdenum mineralization,
and at the main metallogenic epoch the W/R ratio reached its maximum value.
This project was financially supported by both the National Natural Science Foundation of China and the Key Research Project
of the Ministry of Geology and Mineral Resources of China. 相似文献