CHROMITE MINING IN PAKISTAN     

Akhtar H. Siddiqi 《The Professional geographer》1968,20(5):342-345

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Acute ecological risk associated with soot deposition: a Persian Gulf case study     

Mukhtasor  Rehan Sadiq  Tahir Husain  Brian Veitch  Neil Bose 《Ocean Engineering》2001,28(9)

Many studies have been carried out in the past to provide solutions to the threat of chemicals to the ecosystem. However, the basic scientific capability to predict the risk of adverse effects on the ecological system has not kept pace with society's increasing demand for uses of chemicals. As a scientific methodology for quantifying the risk to the environment associated with exposure to chemicals, ecological risk assessment is increasingly important in environmental problem solving. The purpose of this paper is to present a methodology for conducting ecological risk assessment using deterministic and probabilistic approaches. A systematic discussion on elements of ecological risk assessment is presented. A framework of ecological risk assessment is explained with the help of the Persian Gulf environmental problem as a case study. The study was based on the output of a long-range transport model of soot deposition in the Gulf. Results of the assessment using the deterministic and probabilistic approaches are discussed.  相似文献   

Impact of land cover change on land surface temperature: A case study of Spiti Valley     

Pankaj Kumar  Arif Husain  Ram Babu Singh  Manish Kumar 《山地科学学报》2018,15(8):1658-1670

Land surface temperature(LST) is the skin temperature of the earth surface. LST depends on the amount of sunlight received by any geographical area. Apart from sun light, LST is also affected by the land cover, which leads to change in land surface temperature. Impact of land cover change(LCC) on LST has been assessed using Landsat TM5, Landsat 8 TIRS/OLI and Digital Elevation Model(ASTER) for Spiti Valley, Himachal Pradesh, India. In the present study, Spiti valley was divided into three altitudinal zones to check the pattern of changing land cover along different altitudes and LST was calculated for all the four land cover categories extracted from remote sensing data for the years of 1990 and 2015. Matrix table was used as a technique to evaluate the land cover change between two different years. Matrix table shows that as a whole, about 2,151,647 ha(30%) area of Spiti valley experienced change in land cover in the last 25 years. The result also shows vegetation and water bodies increased by 107,560.2 ha(605.87%) and 45 ha(0.98%), respectively. Snow cover and barren land decreased by 19,016.5 ha(23.92%) and 88,589(14.14%), during the study period. A significant increase has been noticed in vegetation amongst all land cover types. Minimum, maximum and mean LST for three altitudinal zones have been calculated. The mean LST recorded was 11℃ in 1990 but it rose by 2℃ and reached to 13℃ in 2015. Changes in LST were obtained for each land cover categories. The mean temperature of different land cover types was calculated by averaging value of all pixels of a given land cover types. The mean LST of vegetation, barren land, snow cover and water body increased by 6℃, 9℃, 1℃, and 7℃, respectively. Further, relationships between LST, Normalized Difference Snow Index(NDSI), and Normalised Difference Vegetation Index(NDVI) were established using Linear Regression.  相似文献   

GIS-based high-resolution spatial interpolation of precipitation in mountain–plain areas of Upper Pakistan for regional climate change impact studies     

Muhammad Waseem Ashiq  Chuanyan Zhao  Jian Ni  Muhammad Akhtar 《Theoretical and Applied Climatology》2010,99(3-4):239-253

In this study, the baseline period (1960–1990) precipitation simulation of regional climate model PRECIS is evaluated and downscaled on a monthly basis for northwestern Himalayan mountains and upper Indus plains of Pakistan. Different interpolation models in GIS environment are used to generate fine scale (250?×?250 m²) precipitation surfaces from PRECIS precipitation data. Results show that the multivariate extension model of ordinary kriging that uses elevation as secondary data is the best model especially for monsoon months. Model results are further compared with observations from 25 meteorological stations in the study area. Modeled data show overall good correlation with observations confirming the ability of PRECIS to capture major precipitation features in the region. Results for low and erratic precipitation months, September and October, are however showing poor correlation with observations. During monsoon months (June, July, August) precipitation pattern is different from the rest of the months. It increases from south to north, but during monsoon maximum precipitation is in the southern regions of the Himalayas, and extreme northern areas receive very less precipitation. Modeled precipitation toward the end of the twenty-first century under A2 and B2 scenarios show overall decrease during winter and increase in spring and monsoon in the study area. Spatially, both scenarios show similar pattern but with varying magnitude. In monsoon, the Himalayan southern regions will have more precipitation, whereas northern areas and southern plains will face decrease in precipitation. Western and south western areas will suffer from less precipitation throughout the year except peak monsoon months. T test results also show that changes in monthly precipitation over the study area are significant except for July, August, and December. Result of this study provide reliable basis for further climate change impact studies on various resources.  相似文献   

Muslim geographic thought and the influence of Greek philosophy     

Akhtar Husain Siddiqi 《GeoJournal》1995,37(1):9-15

The Arabs acquired Greek geographical and astronomical knowledge in the eighth century, when the works of Ptolemy and other Greek philosophers were translated into Arabic. Muslim scholars learned Greek scientific thought and accepted these views as working theories necessary for further scientific inquiry. Muslim scholars were impressed by the Greek point of view, but they added to scientific knowledge in each succeeding generation. In the spirit of objective research, the scientific work of the Muslim scholars was progressive. They were ready to receive the truth from any source, even if that source be foreign. As Western thought became dominant in the Islamic areas in the thirteenth century, Muslim scholars' interest in geography and other natural sciences declined.  相似文献   

The duration of volcanism in Mare Serenitatis     

O.A. Schaeffer  L. Husain  G.A. Schaeffer 《Earth and Planetary Science Letters》1976,31(3):358-368

The crystallization ages of a suite of Apollo 17 basalts from four different stations have been measured using the³⁹Ar-⁴⁰Ar stepwise heating technique. The rocks analyzed include all principal petrographic types found at Apollo 17 landing site. A correlation between the ages and the petrographic type exists; plagioclase-poikilitic ilmenite basalts are youngest and olivine porphyritic ilmenite basalts are the oldest. The duration of volcanism in Mare Serenitatis is about 200 m.y., the same as observed for Mare Imbrium, and less than observed for Mare Tranquillitatis, 400 m.y. A relationship between duration of volcanism and gravity anomalies is noted. The cosmic ray exposure ages (in m.y.) for various locations range as: station 4, 58–315; station 5, 85–440; station 6, 110; station 8, 90–160.  相似文献   

⁴⁰Ar-³⁹Ar age of the Shergotty achondrite and implications for its post-shock thermal history     

D.D. Bogard  Liaquat Husain  L.E. Nyquist 《Geochimica et cosmochimica acta》1979,43(7):1047-1055

Analyses of ⁴⁰Ar-³⁹Ar have been made on a whole rock sample and a maskelynite (feldspar) separate of the shocked Shergotty achondrite. The maskelynite gave a plateau age of 254 ± 10 Myr. The whole rock sample gave a complex release with apparent ages between 240 and 640 Myr. The slightly younger Rb-Sr isochron age of 165 Myr for Shergotty (Nyquistet al., 1978) suggests that the maskelynite as well as the whole rock was incompletely degassed. Reasonable Ar diffusion characteristics for Shergotty for shock heating temperatures of <400°C indicate D/a² of 10^?11?10^?13 sec^?1. The time required to lose 95% of the ⁴⁰Ar from the plagioclase would be ~10³–10⁴ yr. When this gas diffusion time is introduced into a thermal model of a cooling ejecta blanket of variable thickness, a post-shock cooling time of ? 10³ yr and a burial depth of ? 300 m are indicated for Shergotty. These conclusions are not seriously affected by uncertainties in the thermal model. Most likely the shock event occurred ~ 165 Myr ago, but no earlier than 250 Myr ago, when the Shergotty parent object experienced a collision in the asteroid belt. As a result of that collision, feldspar was converted to maskelynite, the K-Ar and Rb-Sr ages were completely or nearly completely reset, and the Shergotty meteorite was heated to <400°C and left to cool slowly inside the parent body.  相似文献   

Gondwana Sediment of Bangladesh and its Correlation With Those of Other Regions of the World on the Basis of Spore-Pollen     

Afia Akhtar 《Gondwana Research》2001,4(2)

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Korteweg-de Vries equation for ion acoustic soliton with negative ions in the presence of nonextensive electrons     

S. Ali Shan  N. Akhtar 《Astrophysics and Space Science》2013,346(2):367-374

Korteweg-de Vries (KdV) equation for electrostatic ion acoustic wave in a three component plasma containing positive and negative ions along with the nonextensive electrons is derived. Fast and slow ion acoustic modes which propagate with different velocities are excited. The effects of variation of quantities like q (nonextensive parameter), Q (mass ratio of positive to negative ion), μ (electron to positive ion number density ratio), θ _i (positive ion to electron temperature ratio) and θ _n (negative ion to electron temperature ratio) have been presented for fast and slow ion acoustic modes. Both compressive and rarefactive solitons are observed. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as on nonextensive electron parameter.  相似文献   

Ion acoustic solitary waves in electron-positron-ion magneto-rotating Lorentzian plasmas     

S. Hussain  N. Akhtar  S. Mahmood 《Astrophysics and Space Science》2013,348(2):475-481

Nonlinear ion acoustic solitary wave structures in electron-positron-ion (e-p-i) magnetized rotating plasmas is studied. The electron and positron species are assumed to be nonthermal and follow the kappa distribution function. The Korteweg de Vries (kdV) equation is derived by employing the reductive perturbation technique for solitary wave in the nonlinear regime. The variation in the amplitude and width of the solitary wave are discussed with the effects of positron concentration, temperature ratio of kappa distributed electrons to positrons, spectral index of the positrons, direction of propagation of the wave with magnetic field and effective gyrofrequency of the rotating nonthermal plasmas. The numerical results are also presented for illustration.  相似文献