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排序方式: 共有219条查询结果,搜索用时 281 毫秒
81.
Ijaz Ahmad Ahmad Zulfiqar Lisa Mona Mahmood Syed Amer Ali Asad Rehman Obaid Ur 《Water Resources》2019,46(6):894-909
Water Resources - Snow cover dynamics play an important role in the hydrological characteristics of Upper Indus Basin (UIB) of Pakistan in terms of seasonal accumulation and depletions. The current... 相似文献
82.
Hafiz U. Rehman Tahseenullah Khan Hao‐Yang Lee Sun‐Lin Chung Mamoru Murata M. Qasim Jan 《Island Arc》2019,28(6)
We report Permian (ca. 272 Ma ±5.4 Ma) felsic dykes that intrude into the Neoproterozoic (ca. 750 Ma) magmatic suite of the Nagar Parkar Igneous Complex (NPIC), the western extension of the Malani Igneous Suite (MIS). The NPIC consists of Neoproterozoic basement amphibolites and granites (riebeckite–aegirine gray granites and the biotite–hornblende pink granites), all of which are intruded by several generations of mafic and felsic dykes. Granitic magmatism occurred in the Late Neoproterozoic (ca. 750 Ma) due to the subduction‐, followed by the rift‐related tectonic regime during the breakup of the Rodinia supercontinent. U–Th–Pb zircon and monazite CHIME age data of 700–800 Ma from the earlier generation porphyritic felsic dykes suggest the dyke intrusion was coeval or soon after the emplacement of the host granites. Our findings of Permian age orthophyric felsic dykes provide new insights for the prevalence of active tectonics in the MIS during late Paleozoic. Textural features and geochemistry also make the orthophyric dykes distinct from the early‐formed porphyritic dykes and the host granites. Our newly obtained age data combined with geochemistry, suggest the existence of magmatism along the western margin of India (peri‐Gondwana margin) during Permian. Like elsewhere in the region, the Permian magmatism in the NPIC could be associated with the rifting of the Cimmerian micro‐continents from the Gondwana. 相似文献
83.
Multitemporal NOAA/AVHRR NDVI images and monthly temperature and precipitation data were obtained across Yangtze River basin
covering the period 1981–2001. The spatial and temporal patterns of NDVI are the same, while spatial analysis shows that the
NDVI is influenced by the vegetation types growing in the study regions, and NDVI presents an increasing trend during the
study period in the whole basin. The climate indicators play an important role in the changes of vegetation cover in the river
basin. In the two Indicators, temperature has a significant effect on the NDVI values than precipitation in the whole basin.
However, in the 11 subbasins, the different rules are shown in different subbasins. 相似文献
84.
Olfa Abid Alya Sellami-Kammoun Habib Ayadi Zaher Drira Abderrahmen Bouain Lotfi Aleya 《Estuarine, Coastal and Shelf Science》2008
The distribution of protein and carbohydrate concentrations of the particulate matter (size fraction: 0.45–160 μm) was studied, from 22 January 2003 to 02 December 2003, in three ponds of increasing salinity in the Sfax solar saltern (Tunisia). The coupling of N/P: DIN (DIN = NO2− + NO3− + NH4+) to DIP (DIP = PO43−) with P/C: protein/carbohydrates ratios along salinity gradient allowed the discrimination of three types of ecosystems. Pond A1 (mean salinity: 45.0 ± 5.4) having marine characteristics showed enhanced P/C ratios during a diatom bloom. N/P and P/C ratios were closely coupled throughout the sampling period, suggesting that the nutritional status is important in determining the seasonal change in the phytoplankton community in pond A1. In pond A16 (mean salinity: 78.7 ± 8.8), despite the high nitrate load, P/C ratios were overall lower than in pond A1. This may be explained by the fact that dinoflagellates, which were the most abundant phytoplankton in pond A16 might be strict heterotrophs and/or mixotrophs, and so they may have not contributed strongly to anabolic processes. Also, N/P and P/C ratios were uncoupled, suggesting that cells in pond A16 were stressed due to the increased salinity caused by water evaporation, and so cells synthesized reserve products such as carbohydrates. In pond M2 (mean salinity: 189.0 ± 13.8), P/C levels were higher than those recorded in either pond A1 or A16. N/P and P/C were more coupled than in pond A16. Species in the hypersaline pond seemed paradoxally less stressed than in pond A16, suggesting that salt-tolerant extremophile species overcome hypersaline constraints and react metabolically by synthesizing carbohydrates and proteins. 相似文献
85.
A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance between two pipes in length. The novel strategy is utilized in offshore areas instead of a single flow line. In this regard, there are only a handful of experimental and numerical studies investigating the effect of scour below a piggyback pipeline under steady current. Hence, this study focuses on examining the influential factors on scouring due to steady current including the pipe diameter and the gap between pipes through numerical simulations and experimental tests. Accordingly, at the first phase of the research, a single pipe was established and tested in laboratory to compare the results with those of an empirical equation. After finishing experimental verifications,piggyback pipelines were also assembled to study the scouring under steady current conditions. It was concluded that by increasing the gap distance between the pipes, the maximum scour depth decreases; however, an increase in the small pipe's diameter results in a larger maximum scour depth. Secondly, numerical simulations were carried out using the FLOW-3D software which was found to be a suitable tool for the numerical investigation of this study.Finally, the numerical results have been compared with the corresponding experimental data and a relatively good agreement was achieved between them. 相似文献
86.
87.
Water pollution is a source of danger to the health of people living in developing countries such as Pakistan. The main industries
located at various industrial zones of Pakistan cause water pollution, which ultimately result in various diseases. The aim
of the present study was to study the concentrations of essential and toxic metals (Na, K, Cu, Zn, Fe, Ca, Pb and As) in the
drained water of three main industrial estates of Pakistan, i.e., Industrial Estate No. 1 Peshawar, Small Industrial Estate
No. 2 Gujranwala, Industrial Estate Hattar Haripur, and in Warsak Canal (industrially pure water) with the help of atomic
absorption spectroscopy and flame emission spectroscopy. The study showed high Pb and As levels originating from industries.
The concentrations of Pb and As ranged from 0.04 to 0.942 mg/L in all the samples. These have been extensively used for irrigation
since the last five decades. The elevated concentrations of heavy metals are continuously entering into the food chain through
agriculture leading to serious health hazards and a threat to the sustainability of local ecosystem. 相似文献
88.
89.
Farhat?AbbasEmail author Iqra?Rehman Muhammad?Adrees Muhammad?Ibrahim Farhan?Saleem Shafaqat?Ali Muhammad?Rizwan Muhammad?Raza?Salik 《Theoretical and Applied Climatology》2018,131(3-4):1101-1117
This study examines the variability and change in the patterns of climatic extremes experienced in Indus-Delta of Sindh province of Pakistan, comprising regions of Karachi, Badin, Mohenjodaro, and Rohri. The homogenized daily minimum and maximum temperature and precipitation data for a 36-year period were used to calculate 13 and 11 indices of temperature and precipitation extremes with the help of RClimDex, a program written in the statistical software package R. A non-parametric Mann–Kendall test and Sen’s slope estimates were used to determine the statistical significance and magnitude of the calculated trend. Temperatures of summer days and tropical nights increased in the region with overall significant warming trends for monthly maximum temperature as well as for warm days and nights reflecting dry conditions in the study area. The warm extremes and nighttime temperature indices showed greater trends than cold extremes and daytime indices depicting an overall warming trends in the Delta. Historic decrease in the acreage of major crops and over 33% decrease in agriculture credit for Sindh are the indicators of adverse impacts of warmer and drier weather on Sindh agriculture. Trends reported for Karachi and Badin are expected to decrease rice cultivation, hatching of fisheries, and mangroves forest surrounding these cities. Increase in the prevailing temperature trends will lead to increasingly hotter and drier summers resulting to constraints on cotton, wheat, and rice yield in Rohri and Mohenjodaro areas due to increased crop water requirements that may be met with additional groundwater pumping; nonetheless, the depleted groundwater resources would have a direct impact on the region’s economy. 相似文献
90.
S. A. Khan X. Liu H. Li Y. Zhu W. Fan P. Zhou Z. ur Rehman 《International Journal of Environmental Science and Technology》2016,13(11):2597-2608
Lead and cadmium are the two widely recognized toxic metals, with known ecological risk to freshwater fish in contaminated ecosystems. However, their effect at environmentally realistic level in a mixture has been rarely investigated. In the present study, serum metabolic responses of Crucian carp exposed to Pb (30 µgL?1), Cd (100 µgL?1) and Pb+Cd (30 + 100 µgL?1) for 21 days were investigated by 1H NMR-based metabolomics. The metabolic responses were compared to control by multivariate techniques (PCA, PLS-DA and OPLS-DA), and metabolites that significantly contributed to the variation were identified. Metal dependent metabolic responses revealed a decline of alanine, lysine and tyrosine in Pb exposed fish, indicating changes in neurotransmitters, and amino acid metabolism, while fish exposed to Cd showed significant decrease in lysine, isoleucine, leucine, alanine and increase in 3-hydroxybutyrate, acetone, lactate, choline, inosine, guanosine and threonine. The coexposure of Pb and Cd had additive effect on metabolic profile with increase in pyruvate, guanosine and inosine. The overall metabolic changes due to Pb and Cd were characterized by disturbed energy metabolism, impaired osmotic regulation and a shift from aerobic to anaerobic respiration. Moreover, 1H NMR-based metabolomics was proved to be a powerful tool in elucidating the toxic effects of environmental pollutants and underlying mechanism. 相似文献