Geo-spatial dynamics of snowcover and hydro-meteorological parameters of Astore basin,UIB, HKH Region,Pakistan     

Ijaz Ahmad  Zulfiqar Ahmad  Siraj Munir  Obaid-ur-Rehman  Syed Roshaan Ali Shah  Yasir Shabbir 《Arabian Journal of Geosciences》2018,11(15):419

Snowcover dynamics and associated accumulation and depletion of snowcover along with its spatial and temporal scale mainly constitute hydrological phenomena of the given basin and are mostly controlled by the local climate variables. Snow accumulation and melting time and duration determine the cyclic volume of water resources and downstream availability. In this study, snowcover area (SCA) was extracted from remotely sensed Moderate Resolution Imaging Spectroradiometer (MODIS) snow products (MOD10A2) for the period 2000–2016. Data for hydro-meteorological parameters was obtained from relevant departments acquired through their field stations. The analysis of 16-year satellite data shows that there is a slight increase in cryospheric area at high altitude. In Astore basin, the study concluded that 15–20% of the basin area is covered by glacier and snowcover may reach around 90–95% of the basin area due to accumulation of seasonal snow from the westerly wind circulation. Analysis of hydro-meteorological parameters showed significant correlation between temperatures (T_max, T_min) and river runoff while no significant correlation was observed between river runoff and rainfall. Similarly, significant inverse correlation was found between river runoff and Astore mean snowcover. At sub-altitudinal zone level (zones 1, 2, 3), river runoff has significant correlation with snowcover. Analysis of 20-year climate data along with river runoff depicts that river runoff is a general phenomenon of snowmelt when minimum temperature starts to rise above 4 °C during mid of April. The study highlights the importance and interdependence of meteorological parameters and snowcover dynamics in determining the hydrological characteristics of Astore Basin.  相似文献   

Magnetic equilibria resulting from a helically symmetric kink instability     

Farhad Ali  Alfred Sneyd 《地球物理与天体物理流体动力学》2013,107(3-4):221-248

Abstract

This paper explores magnetic equilibria which could result from the kink instability in a cylindrical magnetic flux tube. We examine a variety of cylindrical magnetic equilibria which are susceptible to the kink, and simulate its evolution in a frictional fluid. We assume that the evolution takes place under conditions of helical symmetry, so the problem becomes effectively two-dimensional. The initial cylindrical equilibrium field is specified in terms of its twist function k(r) = B _θ/(rB_z ) and for a variety of k(r) functions we calculate linear growth rates for the kink instability, assuming that it develops under helical symmetry with pitch τ. We find that the growth rate is sensitive to the value of τ.

We simulate nonlinear evolution of the kink using a Lagrangian frictional code which constrains the field to have helical symmetry of a given pitch τ. Ideal MHD is assumed and the plasma pressure is taken to be small in order to mimic conditions in the solar corona. In some cases the flux tube evolves to a new smooth helically symmetric equilibrium which involves a relatively small change in the maximum electric current. In other cases there is evidence of current-sheet formation.  相似文献   

A semi-analytical model for estimating seismic behavior of buried steel pipes at bend point under propagating waves     

Miad Saberi  Farhad Behnamfar  Mahmood Vafaeian 《Bulletin of Earthquake Engineering》2013,11(5):1373-1402

A buried pipe extends over long distances and passes through soils with different properties. In the event of an earthquake, the same pipe experiences a variable ground motion along its length. At bends, geometrically a more complicated problem exists where seismic waves propagating in a certain direction affect pipe before and after bend differently. Studying these different effects is the subject of this paper. Two variants for modeling of pipe, a beam model and a beam-shell hybrid model are examined. The surrounding soil is modeled with the conventional springs in both models. A suitable boundary condition is introduced at the ends of the system to simulate the far field. Effects of angle of incidence in the horizontal and vertical planes, angle of pipe bend, soil type, diameter to thickness ratio, and burial depth ratio on pipe strains at bend are examined thoroughly. It is concluded that extensional strains are highest at bends and these strains increase with the angle of incidence with the vertical axis. The pipe strains attain their peaks when pipe bend is around $135^{\circ }$ and exceed the elastic limit in certain cases especially in stiffer soils, but remain below the rupture limit. Then equations for predicting the seismic response of the buried pipe at bend are developed using the analytical data calculated above and regression analysis. It is shown that these semi-analytical equations predict the response with very good accuracy saving much time and effort.  相似文献   

Characterization and Purification of Membrane‐Bound Azoreductase From Azo Dye Degrading Shewanella sp. Strain IFN4          下载免费PDF全文

Muhammad Imran  Fayek Negm  Sabir Hussain  Muhammad Ashraf  Muhammad Ashraf  Zulfiqar Ahmad  Muhammad Arshad  David E. Crowley 《洁净——土壤、空气、水》2016,44(11):1523-1530

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Geomorphology of the Alluvial Sediments and Bedrock in an Intermontane Basin: Application of Variogram Modeling to Electrical Resistivity Soundings     

Adnan Ahmad Khan  Asam Farid  Gulraiz Akhter  Khyzer Munir  James Small  Zulfiqar Ahmad 《Surveys in Geophysics》2016,37(3):579-599

The study describes a methodology used to integrate legacy resistivity data with limited geological data in order to build three-dimensional models of the near subsurface. Variogram analysis and inversion techniques more typically found in the petroleum industry are applied to a set of 1D resistivity data taken from electrical surveys conducted in the 1980s. Through careful integration with limited geological data collected from boreholes and outcrops, the resultant model can be visualized in three dimensions to depict alluvium layers as lithological and structural units within the bedrock. By tuning the variogram parameters to account for directionality, it is possible to visualize the individual lithofacies and geomorphological features in the subsurface. In this study, an electrical resistivity data set collected as part of a groundwater study in an area of the Peshawar basin in Pakistan has been re-examined. Additional lithological logs from boreholes throughout the area have been combined with local outcrop information to calibrate the data. Tectonic activity during the Himalayan orogeny has caused uplift in the area and generated significant faulting in the bedrock resulting in the formation of depressions which are identified by low resistivity values representing clays. Paleo-streams have reworked these clays which have been eroded and replaced by gravel–sand facies along paleo-channels. It is concluded that the sediments have been deposited as prograding fan-shaped bodies and lacustrine deposits with interlayered gravel–sand and clay–silt facies. The Naranji area aquifer system has thus been formed as a result of local tectonic activity with fluvial erosion and deposition and is characterized by coarse sediments with high electrical resistivities.  相似文献   

Blind prediction of in-plane and out-of-plane responses for a thin singly reinforced concrete flanged wall specimen     

Farhad Dashti  Rajesh P. Dhakal  Stefano Pampanin 《Bulletin of Earthquake Engineering》2018,16(1):427-458

This paper describes the blind prediction carried out to simulate the response of a thin reinforced concrete wall tested under uni-directional (in-plane) quasi-static reverse cyclic loading. The specimen was a singly reinforced T-shaped wall panel with a shear-span ratio of 3.7. The response of the test specimen was simulated prior to the release of test results using a finite element model which had already been verified for its capabilities in capturing different failure patterns of rectangular walls, particularly out-of-plane instability. The numerical model predicted a flexural dominated response for the specimen accompanied by considerable out-of-plane deformations. The blind prediction report, submitted in advance to the principal investigator of the experimental campaign, included lateral load-top displacement response of the specimen, maximum out-of-plane deformation corresponding to each drift level, evolution of out-of-plane displacements throughout in-plane loading, response of the longitudinal reinforcement at the section exhibiting the maximum out-of-plane deformation, and von Mises as well as reinforcement stress distribution at some key points of the wall response. Furthermore, a parametric study was carried out addressing the effects of shear-span ratio, reinforcement eccentricity and axial load ratio on the wall response. Results of the numerical simulation that had been included in the blind prediction report have been compared with the experimental measurements indicating that the evolution of the out-of-plane deformation was well captured by the model.  相似文献   

A three-dimensional drift pushover method for unsymmetrical plan buildings     

Mehdi Karimi  Farhad Behnamfar 《Bulletin of Earthquake Engineering》2018,16(11):5397-5424

The drift pushover analysis method for tall and regular buildings is extended in this paper to the third dimension. The focus of study is on the structures with important torsional response. For this purpose, 10, 15, 20 and 30-story steel moment frame buildings having unsymmetrical plans with 5–30% eccentricity ratios are studied. For evaluation of accuracy, nonlinear dynamic response of the buildings is determined under a consistent suit of earthquake ground motions. The maxima of the story drifts and shears and cumulative plastic hinge rotations of stories are calculated under the ground motions and their averages along with those of the modal pushover procedure are compared with the results of the presented method. The comparative analysis establishes the good accuracy of the three dimensional drift pushover method.  相似文献   

Smoothed response spectra including soil-structure interaction effects     

Behnamfar  Farhad  Babaei  Amir H.  Ghandil  Mehdi 《地震工程与工程振动(英文版)》2020,19(1):37-51

Elastic response spectra that take into account the effects of soil-structure interaction on soft soils are developed. The response spectra are calculated utilizing a 3 DOF system including deformations of the superstructure and foundation. The equations of motion of the system are solved using direct integration under normalized earthquake records. Statistical processing of the results is implemented resulting in response spectra for "short and dense buildings with low interaction", "short and dense buildings with high interaction", "tall and light buildings with low interaction" and "tall and light buildings with high interaction". The resulting response spectra are smoothed and discussed.  相似文献   

Geo-Spatial Dynamics of Snow Cover and Hydro-Meteorological Parameters of Hunza Basin,HKH Region,Pakistan     

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   

Trace Metals Accumulation and Antioxidants Profiling in Two Maize Genotypes Against Sewage and Textile Wastewater Treatment     

Zoya Zafar  Javaid Akhtar  Muhammad Amjad  Muhammad Anwar‐ul‐Haq  Zulfiqar Ahmed Saqib 《洁净——土壤、空气、水》2019,47(7)

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