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131.
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133.
Nirmala D. Desouza Baby Simon Muhammad S. Qureshi 《Meteorology and Atmospheric Physics》2011,114(3-4):107-121
The evolutionary characteristics of a dust storm over Oman on 2 February 2008 were studied by analyzing the weather associated with it. The National Center for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis wind flow pattern at 1,000?hPa showed a clockwise and outward wind flow pattern over the study region, a manifestation of a high-pressure cold air mass. In addition, ground truth observations for surface temperature and surface winds showed cold northerly winds until the early morning of 2 February 2008. A strong wind shear resulted from differences in wind speed between warm air and trapped cold air. This vertical wind shear enhanced instability. Furthermore, the weakening of the inversion in the lower troposphere and the formation of a mixed layer due to transfer of horizontal momentum from upper air towards the surface led to strong surface winds. These strong winds lifted a large amount of dust particles off the ground, resulting in the dust event of 2 February 2008. 相似文献
134.
Muhammad Ilyas Agus Sudaryanto Iwan Eka Setiawan Tomohiko Isobe Shin Takahashi 《Marine pollution bulletin》2011,62(1):89-98
A total of 33 surficial sediments from riverine and coastal waters from Surabaya, Indonesia were analyzed for PCBs and BFRs. Concentrations of PCBs (62 congeners), PBDEs (14 congeners) and HBCDs (3 isomers) varied from <DL-420, <DL-35 and <DL-5.4 ng g−1 dw, respectively. Higher concentrations of these compounds were found in riverine than coastal sediments. Their levels and distribution were influenced by proximity to the point sources and TOC. The predominant congeners were CB-153, -28, -138, -149, -180, -33 and BDE-209, -207, -206, -197, -196, -183, -99, -47 for PCBs and PBDEs, respectively, and γ-isomer for HBCDs. Debromination of BDE-209 might be taking place producing lower toxic congeners in sediment. Levels of PCBs in riverine sediments were comparable with some polluted areas worldwide, but PBDEs and HBCDs were lower. Hazard assessment of PCBs indicated possible toxic potential, particularly in areas close to point sources. 相似文献
135.
Muhammad Umer Altaf Arnold W. Heemink Martin Verlaan Ibrahim Hoteit 《Ocean Dynamics》2011,61(8):1093-1105
The Dutch continental shelf model (DCSM) is a shallow sea model of entire continental shelf which is used operationally in
the Netherlands to forecast the storm surges in the North Sea. The forecasts are necessary to support the decision of the
timely closure of the moveable storm surge barriers to protect the land. In this study, an automated model calibration method,
simultaneous perturbation stochastic approximation (SPSA) is implemented for tidal calibration of the DCSM. The method uses
objective function evaluations to obtain the gradient approximations. The gradient approximation for the central difference
method uses only two objective function evaluation independent of the number of parameters being optimized. The calibration
parameter in this study is the model bathymetry. A number of calibration experiments is performed. The effectiveness of the
algorithm is evaluated in terms of the accuracy of the final results as well as the computational costs required to produce
these results. In doing so, comparison is made with a traditional steepest descent method and also with a newly developed
proper orthogonal decomposition-based calibration method. The main findings are: (1) The SPSA method gives comparable results
to steepest descent method with little computational cost. (2) The SPSA method with little computational cost can be used
to estimate large number of parameters. 相似文献
136.
Geochemical characterisation of 18 crude oils from the Potwar Basin (Upper Indus), Pakistan is carried out in this study. Their relative thermal maturities, environment of deposition, source of organic matter (OM) and the extent of biodegradation based on the hydrocarbon (HC) distributions are investigated. A detailed oil-oil correlation of the area is established. Gas chromatography-mass spectrometry (GC-MS) analyses and bulk stable carbon and hydrogen isotopic compositions of saturated and aromatic HC fractions reveals three compositional groups of oils. Most of the oils from the basin are typically generated from shallow marine source rocks. However, group A contains terrigenous OM deposited under highly oxic/fluvio-deltaic conditions reflected by high pristane/phytane (Pr/Ph), C30 diahopane/C29Ts, diahopane/hopane and diasterane/sterane ratios and low dibenzothiophene (DBT)/phenanthrene (P) ratios. The abundance of C19-tricyclic and C24-tetracyclic terpanes are consistent with a predominant terrigenous OM source for group A. Saturated HC biomarker parameters from the rest of the oils show a predominant marine origin, however groups B and C are clearly separated by bulk δ13C and δD and the distributions of the saturated HC fractions supporting variations in source and environment of deposition of their respective source rocks. Moreover, various saturated HC biomarker ratios such as steranes/hopanes, diasteranes/steranes, C23-tricyclic/C30 hopane, C28-tricyclic/C30 hopane, total tricyclic terpanes/hopanes and C31(R + S)/C30 hopane show that two different groups are present. These biomarker ratios show that group B oils are generated from clastic-rich source rocks deposited under more suboxic depositional environments compared to group C oils. Group C oils show a relatively higher input of algal mixed with terrigenous OM, supported by the abundance of extended tricyclic terpanes (up to C41+) and steranes.Biomarker thermal maturity parameters mostly reached to their equilibrium values indicating that the source rocks for Potwar Basin oils must have reached the early to peak oil generation window, while aromatic HC parameters suggest up to late oil window thermal maturity. The extent of biodegradation of the Potwar Basin oils is determined using various saturated HC parameters and variations in bulk properties such as API gravity. Groups A and C oils are not biodegraded and show mature HC profiles, while some of the oils from group B show minor levels of biodegradation consistent with high Pr/n-C17, Ph/n-C18 and low API gravities. 相似文献
137.
A. Maimun A. Priyanto A.H. Muhammad C.C. Scully Z.I. Awal 《Ocean Engineering》2011,38(11-12):1291-1299
This paper presents an experimental investigation on the manoeuvring characteristics of a pusher-barge system for deep (H/d>3) and shallow water (H/d=1.3) condition. Since, the operation of pusher-barge mainly concentrates on confined waters, there is a need to predict and analyze the manoeuvring characteristic of the system for a safe and acceptable performance. A time domain simulation programme was developed for this purpose. A series of model experiments were carried out to determine the hydrodynamic coefficients using a planar motion mechanism (PMM). The time domain simulation shows the manoeuvring characteristic in the form of turning circle trajectories and zig-zag manoeuvre based on the hydrodynamic coefficients, which were derived based on experimental results. The manoeuvring characteristics in shallow and deep water conditions were compared through the simulation results. A comparison of simulation results based on experimental and empirical driven coefficients for both conditions shows that the experimental coefficients gave better manoeuvring characteristics for both turning circle trajectories and zig-zag manoeuvre. 相似文献
138.
Nirmala Devidas Desouza Rajnish Kurchania Muhammad Shums Qureshi 《Meteorology and Atmospheric Physics》2013,122(1-2):47-54
Dust storms commonly occur during the pre-monsoon (summer) season in north and northwest parts of India. Characteristics of dust events of the pressure gradient type are well understood. However, comprehensive studies on mechanism of convective dust storms in India are few. A convective dust storm which occurred on 21 April 2010 in association with a western disturbance over North India was hence studied. In the absence of in situ data, we used available satellite data to study the event. Dust storm that occurred on 20 April 2010 on the surface of the Thar Desert transported dust to northern and northwestern parts of India (Rajasthan, Haryana, Delhi and some parts of Uttar Pradesh). This formed a background of aerosols that affected the thunderstorm formed in association with western disturbance and the strong updraft in the thunderstorm carried the dust lingering in the atmosphere to higher altitudes. Large amount of aerosols carried to higher altitude suppressed the chance of precipitation by affecting the cloud top microphysics. Enhancement in evaporation due to an increase in aerosol concentration and strong downdrafts during dissipation of the thunderstorm resulted in emission of dust particles which led to the convective dust event of 21 April 2010. 相似文献
139.
Reservoir Quality Assessment of the Upper Permian Chhidru Formation,Salt and Surghar Ranges,Pakistan
Muhammad ZAHIR Muhammad AWAIS Mukhtiar GHANI Mohibullah MOHIBULLAH Osman SALAD HERSI Irfan U. JAN Sajjad AHMAD Hamid IQBAL 《《地质学报》英文版》2021,95(6):2120-2137
The Late Permian succession of the Upper Indus Basin in northeastern Pakistan is represented by the carbonate-dominated Zaluch Group, which consists of the Amb, Wargal and Chhidru formations, which accumulated on the southwestern shelf of the Paleo-Tethys Ocean, north of the hydrocarbon-producing Permian strata of the Arabian Peninsula. The reservoir properties of the mixed clastic-carbonate Chhidru Formation (CFm) are evaluated based on petrography, using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD) techniques. The diagenetic features are recognized, ranging from marine (isopachous fibrous calcite, micrite), through meteoric (blocky calcite-I, neomorphism and dissolution) to burial (poikilotopic cement, blocky calcite-II-III, fractures, fracture-filling, and stylolites). Major porosity types include fracture and moldic, while inter- and intra-particle porosities also exist. Observed visual porosity ranges from 1.5%–7.14% with an average of 5.15%. The sandstone facies (CMF-4) has the highest average porosity of 10.7%, whereas the siliciclastic grainstone microfacies (CMF-3) shows an average porosity of 5.3%. The siliciclastic mudstone microfacies (CMF-1) and siliciclastic wacke-packestone microfacies (CMF-2) show the lowest porosities of 4.8% and 5.0%, respectively. Diagenetic processes like cementation, neomorphism, stylolitization and compaction have reduced the primary porosities; however, processes of dissolution and fracturing have produced secondary porosity. On average, the CFm in the Nammal Gorge, Salt Range shows promise and at Gula Khel Gorge, Trans-Indus, the lowest porosity. 相似文献
140.
Soomro Riaz Ahmed Iqbal Saleem Shah Muhammad Ali Iqbal Talat 《Journal of Seismology》2022,26(5):1039-1049
Journal of Seismology - We present a P-wave minimum 1D velocity model for central and northern Pakistan along with station delays. The velocity model and appropriate station delays are obtained... 相似文献