A Spatially Periodic Solute Boundary for MT3DMS and PHT3D          下载免费PDF全文

Tariq Laattoe  Vincent E. A. Post  Adrian D. Werner 《Ground water》2017,55(3):419-427

The assumption of spatial repetition is commonly made when producing bedform scale models of the hyporheic zone. Two popular solute transport codes, MT3DMS and PHT3D, do not currently provide the necessary boundary condition required to simulate spatial periodicity in hyporheic zone transport problems. In this study, we develop a spatially periodic boundary (SPB) for solutes that is compatible with a SPB that was previously developed for MODFLOW to simulate the flow component of spatially periodic problems. The approach is ideal for simulating groundwater flow and transport patterns under repeating surface features, such as ripples or dunes on the bottom of a lake or stream. The appropriate block‐centered finite‐difference approach to implement the boundary is presented and the necessary source code modifications are discussed. The performance of the solute SPB, operating in conjunction with the groundwater flow SPB, is explored through comparison of a multi‐bedform hyporheic‐zone model with a single bedform variant. The new boundary conditions perform well in situations where both dispersive effects and lateral seepage flux in the underflow regime beneath the hyporheic zone are minimal.  相似文献   

Scanning anisotropy parameters in horizontal transversely isotropic media          下载免费PDF全文

Nabil Masmoudi  Alexey Stovas  Tariq Alkhalifah 《Geophysical Prospecting》2017,65(4):981-991

The horizontal transversely isotropic model, with arbitrary symmetry axis orientation, is the simplest effective representative that explains the azimuthal behaviour of seismic data. Estimating the anisotropy parameters of this model is important in reservoir characterisation, specifically in terms of fracture delineation. We propose a travel‐time‐based approach to estimate the anellipticity parameter η and the symmetry axis azimuth ? of a horizontal transversely isotropic medium, given an inhomogeneous elliptic background model (which might be obtained from velocity analysis and well velocities). This is accomplished through a Taylor's series expansion of the travel‐time solution (of the eikonal equation) as a function of parameter η and azimuth angle ?. The accuracy of the travel time expansion is enhanced by the use of Shanks transform. This results in an accurate approximation of the solution of the non‐linear eikonal equation and provides a mechanism to scan simultaneously for the best fitting effective parameters η and ?, without the need for repetitive modelling of travel times. The analysis of the travel time sensitivity to parameters η and ? reveals that travel times are more sensitive to η than to the symmetry axis azimuth ?. Thus, η is better constrained from travel times than the azimuth. Moreover, the two‐parameter scan in the homogeneous case shows that errors in the background model affect the estimation of η and ? differently. While a gradual increase in errors in the background model leads to increasing errors in η, inaccuracies in ?, on the other hand, depend on the background model errors. We also propose a layer‐stripping method valid for a stack of arbitrary oriented symmetry axis horizontal transversely isotropic layers to convert the effective parameters to the interval layer values.  相似文献   

Traffic ‐and Industry‐Related Air Pollution Exposure Assessment in an Asian Megacity          下载免费PDF全文

Muhammad Usman Alvi  Farrukh Chishtie  Imran Shahid  Tariq Mahmud  Riaz Hussain 《洁净——土壤、空气、水》2018,46(1)

Like other Asian countries, Pakistan is facing the issue of air pollution due to rapid urbanization, enormous transportation increases, and other related human activities. Moreover, continuously increasing emission sources have not only raised pollutant concentrations but also their types, thus damaging both human health and the environment. Faisalabad is the third largest megacity of Pakistan and its state of air quality is getting worse due to factors such as industrialization, high traffic volumes, and extensive fossil‐fuel‐burning activities. This review article aims to highlight the present status of air pollution in this city with special reference to particulate matter, elemental profiles, gaseous pollutants, organic–inorganic particulate contents as well as their sources. The concentration levels of these entities were also compared with other national and international cities, and related environmental standards. It is found that current levels of these pollutants are beyond safety limits as specified by various environment protection agencies and organizations. Several weak aspects and gaps are also identified along with suggestions for improvements of the present situation and directions for future research.  相似文献   

Offshore Carbonate Facies Characterization and Reservoir Quality of Miocene Rocks in the Southern Margin of South China Sea     

Hammad Tariq JANJUHAH  Abubaker ALANSARI 《《地质学报》英文版》2020,94(5):1547-1561

Carbonate rocks are important hydrocarbon reservoirs around the globe and in Southeast Asia a key one, particularly, is the Central Luconia province. Understanding the internal characteristics, distribution, geometry and lateral extent of these rocks is essential for exploration and production success. Detailed work on Miocene carbonate reservoir facies, north of Bintulu, offshore Sarawak includes qualitative and quantitative analysis of photomicrographs and reservoir quality, considering especially microporosity. Stratigraphically, these carbonates are known as Cycles IV and V and are represented by eight major facies types (F-1 to F-8]. They comprise: coated grain packstone (F-1) (av. ? = 3%, av. Kh = 0.5 mD) (av = Average; ? = total porosity, and Kh = permeability); massive coral lime grainstone (F-2) (av. ? = 14.7%, av. Kh = 6 mD); oncolite lime grain-dominated packstone (F-3) (av. ? = 10%, av. Kh = 4 mD); skeletal lime/dolo-packstone (F-4) (av. ? = 15%, av. Kh = 4.6 mD); coral (platy) lime mud-dominated packstone (F-5) (av. ? = 4%, av. Kh = 0.5 mD); coral (branching) lime-dominated pack-grainstone (F-6) (av. ? = 15%, av. Kh = 1 mD); cross-bedded skeletal lime packstone (F-7) (av. ? = 20%, av. Kh = 2 mD); and bioturbated carbonate mudstone/chalk (F-8) (av. ? = 8%, av. Kh = 0.8 mD). Study of thin sections reveals that red algae, foraminifera, and corals are the dominant fossil components with a minor admixture of skeletal fragments of echinoderms, bivalves, bryozoans, and green algae. All parameters, e.g., facies characterization, petrography, porosity–permeability value, and microporosity value were utilized to obtain a reliable reservoir quality. The microporosity value was quantified using digital image analysis software and is significant for recognition of good reservoir quality. Consideration of the presence of microporosity against the total porosity in the carbonate rocks has improved the correlation coefficient (R2) value, which has increased from 0.51 to 0.82.  相似文献   

Automated morphological classification of galaxies based on projection gradient nonnegative matrix factorization algorithm     

I. M. Selim  Mohamed Abd El Aziz 《Experimental Astronomy》2017,43(2):131-144

The development of automated morphological classification schemes can successfully distinguish between morphological types of galaxies and can be used for studies of the formation and subsequent evolution of galaxies in our universe. In this paper, we present a new automated machine supervised learning astronomical classification scheme based on the Nonnegative Matrix Factorization algorithm. This scheme is making distinctions between all types roughly corresponding to Hubble types such as elliptical, lenticulars, spiral, and irregular galaxies. The proposed algorithm is performed on two examples with different number of image (small dataset contains 110 image and large dataset contains 700 images). The experimental results show that galaxy images from EFIGI catalog can be classified automatically with an accuracy of ～93% for small and ～92% for large number. These results are in good agreement when compared with the visual classifications.  相似文献   

Analysis of drought condition and risk in Peninsular Malaysia using Standardised Precipitation Index   总被引：2，自引：0，他引：2  

Wan Zawiah Wan Zin  Abdul Aziz Jemain  Kamarulzaman Ibrahim 《Theoretical and Applied Climatology》2013,111(3-4):559-568

Contrary to the belief that Peninsular Malaysia experiences wet condition throughout the year, prolonged dry condition has lately become a recurrent phenomenon in this region. As a result, country's agricultural sector and water resources have been under severe constraints from this situation. To get a clearer picture of the dry condition in Peninsular Malaysia, the Standardised Precipitation Index, based on the data of monthly rainfall from 50 stations, is derived. Spatial analysis is used to illustrate the percentage of occurrences of dry and very dry events. To evaluate the potential risk due to the dry conditions, we modelled the joint distribution of severity and duration of dry condition by means of bivariate copula. Several copula models were tested, and the model, which best represents the relationship between severity and duration, is determined using Akaike information criterion. Based on the results, the return period for the drought severity, based on the longest duration of drought at each station, can be estimated. This enables the drought risk to be calculated, thus planning on the measures to minimise the impact of a prolonged drought to the societies, which can be done by the relevant authorities.  相似文献   

Wavefield dependency on virtual shifts in the source location     

Tariq Alkhalifah 《Geophysical Prospecting》2011,59(4):627-634

The wavefield dependence on a virtual shift in the source location can provide information helpful in velocity estimation and interpolation. However, the second‐order partial differential equation (PDE) that relates changes in the wavefield form (or shape) to lateral perturbations in the source location depends explicitly on lateral derivatives of the velocity field. For velocity models that include lateral velocity discontinuities this is problematic as such derivatives in their classical definition do not exist. As a result, I derive perturbation partial differential wave equations that are independent of direct velocity derivatives and thus, provide possibilities for wavefield shape extrapolation in complex media. These PDEs have the same structure as the wave equation with a source function that depends on the background (original source) wavefield. The solutions of the perturbation equations provide the coefficients of a Taylor's series type expansion for the wavefield. The new formulas introduce changes to the background wavefield only in the presence of lateral velocity variation or in general terms velocity variations in the perturbation direction. The accuracy of the representation, as demonstrated on the Marmousi model, is generally good.  相似文献   

Angle gathers in wave‐equation imaging for transversely isotropic media     

Tariq Alkhalifah  Sergey Fomel 《Geophysical Prospecting》2011,59(3):422-431

In recent years, wave‐equation imaged data are often presented in common‐image angle‐domain gathers as a decomposition in the scattering angle at the reflector, which provide a natural access to analysing migration velocities and amplitudes. In the case of anisotropic media, the importance of angle gathers is enhanced by the need to properly estimate multiple anisotropic parameters for a proper representation of the medium. We extract angle gathers for each downward‐continuation step from converting offset‐frequency planes into angle‐frequency planes simultaneously with applying the imaging condition in a transversely isotropic with a vertical symmetry axis (VTI) medium. The analytic equations, though cumbersome, are exact within the framework of the acoustic approximation. They are also easily programmable and show that angle gather mapping in the case of anisotropic media differs from its isotropic counterpart, with the difference depending mainly on the strength of anisotropy. Synthetic examples demonstrate the importance of including anisotropy in the angle gather generation as mapping of the energy is negatively altered otherwise. In the case of a titled axis of symmetry (TTI), the same VTI formulation is applicable but requires a rotation of the wavenumbers.  相似文献   

A comparison of IBC with 1997 UBC for modal response spectrum analysis in standard-occupancy buildings     

Tariq M. Nahhas 《地震工程与工程振动(英文版)》2011,10(1):99-113

This paper presents a comparison of the seismic forces generated from a Modal Response Spectrum Analysis (MRSA) by applying the provisions of two building codes, the 1997 Uniform Building Code (UBC) and the 2000-2009 International Building Code (IBC), to the most common ordinary residential buildings of standard occupancy. Considering IBC as the state of the art benchmark code, the primary concern is the safety of buildings designed using the UBC as compared to those designed using the IBC. A sample of four buildings with different layouts and heights was used for this comparison. Each of these buildings was assumed to be located at four different geographical sample locations arbitrarily selected to represent various earthquake zones on a seismic map of the USA, and was subjected to code-compliant response spectrum analyses for all sample locations and for five different soil types at each location. Response spectrum analysis was performed using the ETABS software package. For all the cases investigated, the UBC was found to be significantly more conservative than the IBC. The UBC design response spectra have higher spectral accelerations, and as a result, the response spectrum analysis provided a much higher base shear and moment in the structural members as compared to the IBC. The conclusion is that ordinary office and residential buildings designed using UBC 1997 are considered to be overdesigned, and therefore they are quite safe even according to the IBC provisions.  相似文献   

Dynamics of arsenic adsorption in the targeted arsenic-safe aquifers in Matlab, south-eastern Bangladesh: Insight from experimental studies   总被引：1，自引：0，他引：1  

Clare Robinson  Mattias von Brömssen  Prosun BhattacharyaSara Häller  Annelie BivénMohammed Hossain  Gunnar JacksKazi Matin Ahmed  M. Aziz HasanRoger Thunvik 《Applied Geochemistry》2011,26(4):624-635

Targeting shallow low-As aquifers based on sediment colour may be a viable solution for supplying As-safe drinking water to rural communities in some regions of Bangladesh and West Bengal in India. The sustainability of this solution with regard to the long-term risk of As-safe oxidized aquifers becoming enriched with As needs to be assessed. This study focuses on the adsorption behaviour of shallow oxidized sediments from Matlab Region, Bangladesh, and their capacity to attenuate As if cross-contamination of the oxidized aquifers occurs. Water quality analyses of samples collected from 20 tube-wells in the region indicate that while there may be some seasonal variability, the groundwater chemistry in the reduced and oxidized aquifers was relatively stable from 2004 to 2009. Although sediment extractions indicate a relatively low amount of As in the oxidized sediments, below 2.5 mg kg⁻¹, batch isotherm experiments show that the sediments have a high capacity to adsorb As. Simulations using a surface complexation model that considers adsorption to amorphous Fe(III) oxide minerals only, under-predict the experimental isotherms. This suggests that a large proportion of the adsorption sites in the oxidized sediments may be associated with crystalline Fe(III) oxides, Mn(IV) and Al(III) oxides, and clay minerals. Replicate breakthrough column experiments conducted with lactose added to the influent solution demonstrate that the high adsorption capacity of the oxidized sediments may be reduced if water drawn down into the oxidized aquifers contains high levels of electron donors such as reactive dissolved organic C.  相似文献