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   

Observational evidence for stellar mass black holes     

Tariq Shahbaz 《Journal of Astrophysics and Astronomy》1999,20(3-4):197-210

I review the evidence for stellar mass black holes in the Galaxy. The unique properties of the soft X-ray transient (SXTs) have provided the first opportunity for detailed studies of the mass-losing star in low-mass X-ray binaries. The large mass functions of these systems imply that the compact object has a mass greater than the maximum mass of a neutron star, strengthening the case that they contain black holes. The results and techniques used are discussed. I also review the recent study of a comparison of the luminosities of black hole and neutron star systems which has yielded compelling evidence for the existence of event horizons.  相似文献   

Geotechnical assessment of cut slopes in the landslide-prone Himalayas: rock mass characterization and simulation approach     

Siddique  Tariq  Mondal  M. E. A.  Pradhan  S. P.  Salman  M.  Sohel  M. 《Natural Hazards》2020,104(1):413-435

Natural Hazards - The roadway networks serve as arteries for the ongoing socio-economic activities within the Himalayan region. The perilous conditions of geologically active and fragile terrain...  相似文献   

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郑扣根  潘云鹤 《中国地理科学(英文版)》1999,9(2):159-165

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Anisotropy parameter inversion in vertical axis of symmetry media using diffractions          下载免费PDF全文

Umair bin Waheed  Alexey Stovas  Tariq Alkhalifah 《Geophysical Prospecting》2017,65(1):194-203

Diffractions play a vital role in seismic processing as they can be utilized for high‐resolution imaging applications and analysis of subsurface medium properties like velocity. They are particularly valuable for anisotropic media as they inherently possess a wide range of dips necessary to resolve the angular dependence of velocity. However, until recently, the focus of diffraction imaging or inversion algorithms have been only on the isotropic approximation of the subsurface. Using diffracted waves, we develop a framework to invert for the effective η model. This effective model is obtained through scanning over possible effective η values and selecting the one that best fits the observed moveout curve for each diffractor location. The obtained effective η model is then converted to an interval η model using a Dix‐type inversion formula. The inversion methodology holds the potential to reconstruct the true η model with sufficiently high accuracy and resolution properties. However, it relies on an accurate estimation of diffractor locations, which in turn requires good knowledge of the background velocity model. We test the effectiveness and applicability of our method on the vertical transverse isotropic Marmousi model. The inversion results yield a reasonable match even for the complex Marmousi model.  相似文献   

Analysis of the traveltime sensitivity kernels for an acoustic transversely isotropic medium with a vertical axis of symmetry          下载免费PDF全文

Ramzi Djebbi  René‐Édouard Plessix  Tariq Alkhalifah 《Geophysical Prospecting》2017,65(1):22-34

In anisotropic media, several parameters govern the propagation of the compressional waves. To correctly invert surface recorded seismic data in anisotropic media, a multi‐parameter inversion is required. However, a tradeoff between parameters exists because several models can explain the same dataset. To understand these tradeoffs, diffraction/reflection and transmission‐type sensitivity‐kernels analyses are carried out. Such analyses can help us to choose the appropriate parameterization for inversion. In tomography, the sensitivity kernels represent the effect of a parameter along the wave path between a source and a receiver. At a given illumination angle, similarities between sensitivity kernels highlight the tradeoff between the parameters. To discuss the parameterization choice in the context of finite‐frequency tomography, we compute the sensitivity kernels of the instantaneous traveltimes derived from the seismic data traces. We consider the transmission case with no encounter of an interface between a source and a receiver; with surface seismic data, this corresponds to a diving wave path. We also consider the diffraction/reflection case when the wave path is formed by two parts: one from the source to a sub‐surface point and the other from the sub‐surface point to the receiver. We illustrate the different parameter sensitivities for an acoustic transversely isotropic medium with a vertical axis of symmetry. The sensitivity kernels depend on the parameterization choice. By comparing different parameterizations, we explain why the parameterization with the normal moveout velocity, the anellipitic parameter η, and the δ parameter is attractive when we invert diving and reflected events recorded in an active surface seismic experiment.  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