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排序方式: 共有143条查询结果,搜索用时 15 毫秒
91.
Xueliang Wang Luqing Zhang Jixin Ding Qingfeng Meng Javed Iqbal Lihui Li Zhifa Yang 《Environmental Earth Sciences》2014,72(11):4639-4652
This study shows a rockfall susceptibility assessment at local scale in north Beijing of China, including the identification of rockfall sources onsite by terrain and rock discontinuities analysis and run-out distance prediction by Rocfall? simulation. Two types of rockfall were defined including one type on the cliffs with long inclined slopes and another type on the road slopes with low height. Two historical rockfall events were used to back-calibrating the parameters used for run-out distance simulation. Based on the work, rockfall susceptibility map at local scale was created in GIS, which was compared with the map obtained at regional scale (entire Huairou district scale). Due to the difference of approaches applied, procedure of assessment and types of source data acquired, the two resulting rockfall susceptibility maps are proved to be different. Still, both of them are useful and could be used at different level’s decision for rockfall prevention and mitigation. Different types of uncertainties exist in the study of rockfall susceptibility assessment. To reduce the uncertainties, studies on both approaches and techniques are suggested. 相似文献
92.
Muhammad Nauman Malik Mehdi Murtuza Iqbal Asif Bakar Muhammad Saifullah Abu Brahim Aissa Dk Nur Afiqah Jalwati Puteri Amer Farhan Rafique 《地下水科学与工程》2014,7(4):373-382
In many circumstances involving heat and mass transfer issues, it is considered impractical to measure the input flux and the resulting state distribution in the domain. Therefore, the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative. Adaptive state estimator (ASE) is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique, thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters. The ASE is particularly designed for a system that encompasses independent unknowns and /or random switching of input and measurement biases. The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE, which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10% in 2-dimensional problems. Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios. Results also show that ASE enjoys a better estimation performance than its competitor, Recursive Least Square Estimator (RLSE) due to its larger error tolerance in greater process noise regimes. ASE’s inherent deficiency of being slower than the RLSE, resulting from the complexity of algorithm, was also noticed. The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location. 相似文献
93.
94.
Although previous literature have considered Southern Oscillation Index (SOI), Indian Dipole, and SST as the major teleconnection patterns to explain the variability of summer monsoon rainfall over India. South Asia low pressure and Indian Ocean high are the centers of action that dominates atmospheric circulations in Indian continent. This paper examines the possible impact of South Asian low pressure distribution on the variability of summer monsoon rainfall of India using centers of action approach. Our analysis demonstrates that the explanation of summer monsoon rainfall variability over Central India is improved significantly if the SOI is replaced by South Asian low heat. This contribution also explains the physical mechanisms to establish the relationships between the South Asian low heat and regional climate by examining composite maps of large-scale circulation fields using NCEP/NCAR Reanalysis data. 相似文献
95.
M. Z. Iqbal 《水文研究》2008,22(23):4609-4619
Oxygen and deuterium isotopes in precipitation were analysed to define local isotopic trends in Iowa, US. The area is far inland from an oceanic source and the observed averages of δ18O and δ D are ? 6·43‰ and ? 41·35‰ for Ames, ? 7·53‰ and ? 51·33‰ for Cedar Falls, and ? 6·01‰ and ? 38·19‰ for Iowa City, respectively. Although these data generally follow global trends, they are different when compared to a semi‐arid mid‐continental location in North Platt, Nebraska. The local meteoric water lines of Iowa are δ D = 7·68 δ18O + 8·0 for Ames, δ D = 7·62 δ18O + 6·07 for Cedar Falls, and δ D = 7·78 δ18O + 8·61 for Iowa City. The current Iowa study compares well with a study conducted in Ames, Iowa, 10 years earlier. The differences between Iowa and Nebraska studies are attributed to a variable climate across the northern Great Plains ranging from sub‐humid in the east to semi‐arid in the west. Iowa being further east in the region is more strongly influenced by a moist sub‐humid to humid climate fed by the tropical air stream from the Gulf of Mexico. The average d‐excess values are 10·06‰ for Ames, 8·92‰ for Cedar Falls and 9·92‰ for Iowa City. Eighty seven percent of the samples are within the global d‐excess range of 0‰ and 20‰. The results are similar to previous studies, including those by National Atmospheric Deposition Programs and International Atomic Energy Agency. It appears that the impact of recycled water or secondary evaporation on δ18O values of area precipitation is minimal. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
96.
97.
We have studied periodic orbits generated by Lagrangian solutions of the restricted three body problem when one of the primaries
is an oblate body. We have determined the periodic orbits for different values of μ, h and A (h is energy constant, μ is mass ratio of the two primaries and A is an oblateness factor). These orbits have been determined by giving displacements along the tangent and normal to the mobile
coordinates as defined by Karimov and Sokolsky (Celest. Mech. 46:335, 1989). These orbits have been drawn by using the predictor-corrector method. We have also studied the effect of oblateness by
taking some fixed values of μ, A and h. As starters for our method, we use some known periodic orbits in the classical restricted three body problem. 相似文献
98.
Kafeel Ahmad Zafar Iqbal Khan Asma Ashfaq Muhammad Ashraf Nudrat Aisha Akram Muhammad Sher Hazoor Ahmad Shad Vincenzo Tufarelli Antonio Lonigro Mariano Fracchiolla Eugenio Cazzato 《Environmental Earth Sciences》2017,76(8):322
Bio-concentration of elements such as Mo, As, Se, Fe, Cu, Zn, Ni and Pb was analyzed in spring onion (Allium fistulosum L.) in three different locations of central Punjab, Pakistan. At location GW, relatively low level of hazardous elements was found in spring onion, suggesting that groundwater is a safe source of water for irrigating food crops. The pH of soil at wastewater irrigation was found less acidic (pH 7.4) than the other sites. The range of concentration in the different samples of spring onion was as follows: 6.15–8.16 mg kg?1 for Mo, 2.77–4.28 mg kg?1 for As, 0.395–0.705 mg kg?1 for Se, 36.73–48.17 mg kg?1 for Fe, 10.58–16.26 mg kg?1 for Cu, 28.87–39.79 mg kg?1 for Zn, 6.66–8.75 mg kg?1 for Ni and 4.33–6.09 mg kg?1 for Pb, respectively. High bio-concentration of Zn (15.37) from soil to spring onion was found at canal water irrigated location. The estimated daily intake of metal for spring onion was less, but the health risk index was higher than 1 for Mo, As, Cu, Pb and Ni, respectively. This was due to higher proportion of spring onion in diet, which consequently increased the health risk index for metals. Therefore, it is recommended to avoid growing vegetables in untreated urban and rural wastewater containing elevated amounts of metals. 相似文献
99.
100.
S. N. Jamal M. Z. Iqbal M. Athar 《International Journal of Environmental Science and Technology》2006,3(4):411-416
A greenhouse experiment was conducted to determine the phytotoxic effect of aluminum and chromium on the germination and early growth of two wheat (Triticum aestivum) varieties Anmol and Kiran. Seed were treated with 40, 80, 120 and 160 ppm of aluminum and chromium solution individually and in combined form. Observations were made on seed germination, root, shoot and seedling length, and dry biomass. Seed germination and dry biomass showed no effect of aluminum, chromium and combined treatment. Root, shoot and seedling length of both the varieties showed significant (P<0.05) decrease as compared to control. The growth was also reduced as the concentration of aluminum and chromium increased. Seedling length decreased in both the varieties at all the concentration of different treatment of aluminum, chromium and combined treatment. Attempts are being made in different laboratories to construct novel plants using genetic manipulation technologies that may have a greater tolerance to the presence of toxic metals. The results of the present study may help in understanding the mechanisms involved and their possible use in pytoremediation. 相似文献