Organic carbon mobilization in a Bangladesh aquifer explained by seasonal monsoon-driven storativity changes     

Britta Planer-Friedrich  Cornelia Härtig  Heidi Lissner  Jörg Steinborn  Elke Süß  M. Qumrul Hassan  Anwar Zahid  Mahmood Alam  Broder Merkel 《Applied Geochemistry》2012

Currently, the most widely accepted hypothesis to explain high As concentrations in Bangladesh groundwaters is that dissolved organic C (DOC) reduces solid Fe (hydr)oxides and mobilizes sorbed arsenate. The nature of the DOC and its release mechanism are still controversial. Based on weekly to biweekly sampling over the course of one monsoon cycle at six monitoring wells of different depths, it is proposed that storativity changes drive natural DOC release from clay–peat layers to the adjacent aquifers. With a decrease in hydraulic heads during the dry season, total mineralization and DOC concentrations increased. With the onset of the rainy season and an increase in hydraulic heads, release of clay–peat derived components stopped and vertical water displacement due to groundwater recharge from rainwater occurred, causing aquifer flushing and a decrease in total mineralization and DOC concentrations. Total As and DOC concentrations correlated over depth. However, at the depth of maximum concentrations, the As peak was observed during the rainy season. At present, the reason for this inverse seasonal trend between As and DOC is unclear. Higher mineralization or DOC concentrations could lead to increased As sorption or the increased arsenite release is a time-lag abiotic or microbial response to the DOC peak. The vulnerability of the Pleistocene aquifer towards increased As concentrations was found to be much higher than previously assumed. Though sorption capacities were determined to be higher than in the Holocene aquifer, probably due to intact Fe (hydr)oxides, long-term continuous As input from overlying clay and peat layers by the proposed seasonal storativity changes has led to increased aqueous As concentrations of 85 μg/L, considerably higher than drinking water standards. Until now, aquifer and especially aquitard and aquiclude hydraulics have not been considered sufficiently when attempting to explain As mobilization in Bangladesh.  相似文献   

Magnetoacoustic solitons in dense astrophysical electron-positron-ion plasmas     

S. Hussain  S. Mahmood  A. Mushtaq 《Astrophysics and Space Science》2013,346(2):359-366

Nonlinear magnetoacoustic waves in dense electron-positron-ion plasmas are investigated by using three fluid quantum magnetohydrodynamic model. The quantum mechanical effects of electrons and positrons are taken into account due to their Fermionic nature (to obey Fermi statistics) and quantum diffraction effects (Bohm diffusion term) in the model. The reductive perturbation method is employed to derive the Korteweg-de Vries (KdV) equation for low amplitude magnetoacoustic soliton in dense electron-positron-ion plasmas. It is found that positron concentration has significant impact on the phase velocity of magnetoacoustic wave and on the formation of single pulse nonlinear structure. The numerical results are also illustrated by taking into account the plasma parameters of the outside layers of white dwarfs and neutron stars/pulsars.  相似文献   

A continuous time delay-difference type model (CTDDM) applied to stock assessment of the southern Atlantic albacore <Emphasis Type="Italic">Thunnus alalunga</Emphasis>     

廖宝超  刘群  张魁  韩亚楠 《中国海洋湖沼学报》2016,34(5):977-984

A continuous time delay-diff erence model (CTDDM) has been established that considers continuous time delays of biological processes. The southern Atlantic albacore (Thunnus alalunga) stock is the one of the commercially important tuna population in the marine world. The age structured production model (ASPM) and the surplus production model (SPM) have already been used to assess the albacore stock. However, the ASPM requires detailed biological information and the SPM lacks the biological realism. In this study, we focus on applying a CTDDM to the southern Atlantic albacore (T. alalunga) species, which provides an alternative method to assess this fishery. It is the first time that CTDDM has been provided for assessing the Atlantic albacore (T. alalunga) fishery. CTDDM obtained the 80% confidence interval of MSY (maximum sustainable yield) of (21 510 t, 23 118t). The catch in 2011 (24 100 t) is higher than the MSY values and the relative fishing mortality ratio (F ₂₀₁₁/F _MSY) is higher than 1.0. The results of CTDDM were analyzed to verify the proposed methodology and provide reference information for the sustainable management of the southern Atlantic albacore stock. The CTDDM treats the recruitment, the growth, and the mortality rates as all varying continuously over time and fills gaps between ASPM and SPM in this stock assessment.  相似文献   

Direct displacement-based design of special concentrically-braced frames in near-fault regions     

Mahmood Yahyai  Bahram Rezayibana 《Bulletin of Earthquake Engineering》2015,13(10):2945-2971

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Rate of Carbon Storage in Soil of Natural and Degraded Mangrove Forest in Peninsular Malaysia          下载免费PDF全文

Zhila Hemati  Mahmood Hossain  Chijioke U. Emenike  Mohamad Zakaria Rozainah 《洁净——土壤、空气、水》2015,43(4):614-619

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Crop Residues Mulch as Organic Weed Management Strategy in Maize          下载免费PDF全文

Azhar Mahmood  Muhammad Zahid Ihsan  Abdul Khaliq  Saddam Hussain  Zahid Ata Cheema  Muhammad Naeem  Ihsanullah Daur  Hafiz Athar Hussain  Fahad Alghabari 《洁净——土壤、空气、水》2016,44(3):317-324

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Experimental study on local scour around single oblong pier fitted with a collar in a 180 degree flume bend     

Alireza MASJEDI  Mahmood SHAFaEI BEJESTAN  Abdolkarim ESFANDI 《国际泥沙研究》2010,25(3):304-312

In this work, investigation on the development of local scour around an oblong pier in a 180 degree flume bend is presented. Scour hole can cause failure of the bridge especially during the river floods. In this study, the use of oblong collars for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. Tests were conducted using one oblong pier in positions of 60degree under one flow conditions. The study was conducted using a physical hydraulic model operated under clear-water conditions in cohesionless bed material. In this study, the time development of the local scour around the oblong pier fitted with and without collar plates was studied. Investigated was the effect of size and elevation collar on the time development of scour and its efficacy at preventing scour at a bridge pier. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. It was observed that, as the minimum depth of scour occurs for the square collar at width of 3B placed at elevation of 0.1B below the bed and the size of a collar plate increases, the scour decreases. Measuring depth of scouring based on experimental observation, an empirical relation is developed with regression coefficient 95%.  相似文献   

Impacts of future land cover and climate change on the water balance in northern Iran     

Sharif Joorabian Shooshtari  Mehdi Gholamalifard  Mahmood Azari  Roberto Serrano-Notivoli  Juan Ignacio López-Moreno 《水文科学杂志》2017,62(16):2655-2673

We evaluated the potential impacts of future land cover change and climate variability on hydrological processes in the Neka River basin, northern Iran. This catchment is the main source of water for the intensively cultivated area of Neka County. Hydrological simulations were conducted using the Soil and Water Assessment Tool. An ensemble of 17 CMIP5 climate models was applied to assess changes in temperature and precipitation under the moderate and high emissions scenarios. To generate the business-as-usual scenario map for year 2050 we used the Land Change Modeler. With a combined change in land cover and climate, discharge is expected to decline in all seasons except the end of autumn and winter, based on the inter-model average and various climate models, which illustrated a high degree of uncertainty in discharge projections. Land cover change had a minor influence on discharge relative to that resulting from climate change.  相似文献   

Appraisal of Anchor Arrangement and Size on Sand-Geogrid Interaction in Direct Shear     

Abdi  Mahmood Reza  Chafjiri  Mehdi Pour-Ramazan 《Geotechnical and Geological Engineering》2022,40(9):4761-4773

Geotechnical and Geological Engineering - Soil–reinforcement interaction is a major factor in the analysis and design of reinforced earth structures. In current research the effects of...  相似文献   

Optimization of design parameters for controlled rocking steel braced dual-frames     

Ghasemi  Sobhan  Nezamabadi  M. Firoozi  Moghadam  Abdolreza S.  Hosseini  Mahmood 《地震工程与工程振动(英文版)》2022,21(4):1053-1068

Earthquake Engineering and Engineering Vibration - A controlled rocking concentrically steel braced frame (CR-CSBF) is introduced as an alternative to conventional methods to prevent major...  相似文献