Physical and geometrical parameters of VCBS XIII: HIP 105947     

Suhail Gumaan Masda  Mashhoor Ahmed Al-Wardat  Jiyaulla Khan Moula Khan Pathan 《天文和天体物理学研究(英文版)》2018,(6)

The best physical and geometrical parameters of the main sequence close visual binary system(CVBS), HIP 105947, are presented. These parameters have been constructed conclusively using Al-Wardat's complex method for analyzing CVBSs, which is a method for constructing a synthetic spectral energy distribution(SED) for the entire binary system using individual SEDs for each component star. The model atmospheres are in its turn built using the Kurucz(ATLAS9) line-blanketed plane-parallel models. At the same time, the orbital parameters for the system are calculated using Tokovinin's dynamical method for constructing the best orbits of an interferometric binary system. Moreover, the mass-sum of the components, as well as the ?θ and ?ρ residuals for the system, is introduced. The combination of Al-Wardat's and Tokovinin's methods yields the best estimations of the physical and geometrical parameters. The positions of the components in the system on the evolutionary tracks and isochrones are plotted and the formation and evolution of the system are discussed.  相似文献   

Geochemical and oxygen isotope perspective of a new R chondrite Dhofar 1671: Affinity with ordinary chondrites          下载免费PDF全文

Arshad Ali  Sobhi J. Nasir  Iffat Jabeen  Ahmed Al Rawas  Neil R. Banerjee  Gordon R. Osinski 《Meteoritics & planetary science》2017,52(9):1991-2003

Dhofar 1671 is a relatively new meteorite that previous studies suggest belongs to the Rumuruti chondrite class. Major and REE compositions are generally in agreement with average values of the R chondrites (RCs). Moderately volatile elements such as Se and Zn abundances are lower than the R chondrite values that are similar to those in ordinary chondrites (OCs). Porphyritic olivine pyroxene (POP), radial pyroxene (RP), and barred olivine (BO) chondrules are embedded in a proportionately equal volume of matrix, one of the characteristic features of RCs. Microprobe analyses demonstrate compositional zoning in chondrule and matrix olivines showing Fa‐poor interior and Fa‐rich outer zones. Precise oxygen isotope data for chondrules and matrix obtained by laser‐assisted fluorination show a genetic isotopic relationship between OCs and RCs. On the basis of our data, we propose a strong affinity between these groups and suggest that OC chondrule precursors could have interacted with a ¹⁷O‐rich matrix to form RC chondrules (i.e., ?¹⁷O shifts from ~1‰ to ~3‰). These interactions could have occurred at the same time as “exotic” clasts in brecciated samples formed such as NWA 10214 (LL3–6), Parnallee (LL3), PCA91241 (R3.8–6), and Dhofar 1671 (R3.6). We also infer that the source of the oxidation and ¹⁷O enrichment is the matrix, which may have been enriched in ¹⁷O‐rich water. The abundance of matrix in RCs relative to OCs, ensured that these rocks would be apparently more oxidized and appreciably ¹⁷O‐enriched. In situ analysis of Dhofar 1671 is recommended to further strengthen the link between OCs and RCs.  相似文献   

Prawn postlarvae fishing in coastal Bangladesh: Challenges for sustainable livelihoods   总被引：1，自引：0，他引：1  

Nesar Ahmed  Max Troell  Edward H. Allison  James F. Muir 《Marine Policy》2010,34(2):218-227

Fishing for prawn (Macrobrachium rosenbergii) postlarvae is a major contributor to the livelihoods of the coastal poor in Bangladesh, including women. A study of coastal livelihoods along the lower Pasur River in southwest Bangladesh indicates that on average 40% of total annual income comes from postlarvae fishing during the few months involved. However, indiscriminate fishing of wild postlarvae, with high levels of by-catch, has an impact on biodiversity in coastal ecosystems. This has provoked imposition of restrictions on postlarvae collection. The ban has, however, not been firmly enforced because of the lack of alternative livelihoods for coastal poor. A conceptual framework, drawn from an approach to poverty reduction known as the sustainable livelihoods approach, is applied to understanding the role of prawn postlarvae fishing. Evidence from this study suggests that postlarvae fishers faced a number of livelihood constraints, including poor livelihood assets. This paper concludes that wider livelihood options need to be found for postlarvae fishers to support their livelihoods.  相似文献   

Gravity map of Kalabsha area, northwest of Aswan Lake, and its structural significance     

E.M. Abdelrahman  A. Tealeb  H.A. Ahmed 《Journal of Geodynamics》1991,14(1-4)

A detailed gravity survey was carried out in one of the seismo-active areas at the northwestern region of the High Dam Lake (Kalabsha area) to study its subsurface structure. In order to understand the seismicity of the area, the establishment of a geodynamic model from geological and geodetic data is of great importance. After a series of adjustments and corrections of the measured gravity data, free-air and Bouguer anomaly maps were constructed for the Kalabsha area, and several interpretation techniques were applied to analyse these anomalies. The results of the analysis indicate that the Kalabsha area is affected by several faults trending mainly E-W and N-S. The active area located west of Gebel Marawa is bounded by a set of faults striking NE-SW, N-S and E-W. The throws of these faults range from 160 to 370 m.The minimum depth to the basement complex is about 200 m and its maximum depth is around 600 m. The thickness of the sedimentary column (Nubia sandstone) in the Kalabsha area decreases due west and increases toward the southern and eastern parts of the area. The results explain the tectonic framework of the area well.  相似文献   

Drought and human adjustment in Saudi Arabia   总被引：1，自引：0，他引：1  

Abdulla Ahmed Al-Taher 《GeoJournal》1994,33(4):411-422

Drought is one of the natural hazards which causes death and damage for property particularly in drylands of the world. Drought as a natural hazard tends to limit and disrupt human activities. On the other hand, man has tried to adjust his living conditions to this hazard. The adjustment to drought is different from one country to another. Adjustment to drought is affected by culture, income, and by the political system in the country. In the case of Saudi Arabia adjustment to drought hazard is usually the work of both individuals, and government. The Saudi Arabian government has spent large sums of money to reduce impact of drought hazard.  相似文献   

On the distribution of rainfall over the Sultanate of Oman     

Ahmed Abdalla Ahmed Babikir Dr. 《GeoJournal》1985,11(2):165-172

Rainfall distribution over the Sultanate of Oman is analysed. Data from seven recently installed weather stations as well as supporting data from scattered sources were used. Distribution maps were drawn. NW and NE winter wind meet resulting in troughs and rainfall on the Mountains and Coastal Strips. Summer monsoon wind dominates the S. Central areas of overlap receive light showers from both summer monsoons and winter local troughs. Heavier amounts of rainfall are generally associated with high altitude.  相似文献   

Wind gradients at meteor heights over mid-latitude stations     

P. C. S. Devara  G. Chandrasekhar  M. I. Ahmed 《Journal of Earth System Science》1986,95(3):427-434

The gradients of amplitude and phase of diurnal and semidiurnal components of zonal and meridional winds in the height intervals of 80–90 km and 90–100 km are studied using the meteor wind radar data collected at Atlanta (34°N, 84°W) during the period August 1974–March 1978. The results are compared with those at Adelaide (35°S, 139°E). It is found that the gradients vary in an opposite manner between the two height intervals.  相似文献   

A petrographic and fluid inclusion comparison of silver-poor and silver-rich zinc-lead ores,N.E. Washington State     

Philip E. Brown  Gaafar A. Ahmed 《Mineralium Deposita》1986,21(2):156-163

Many of the zinc-lead deposits of NE Washington State are poorly known examples of Mississippi Valley Type (MVT) mineralization. This study compares inclusion fluids from the Josephine Breccia ores with the later cross-cutting sulfide-bearing quartz veins. The breccia ores are cemented mainly by open space fillings of dolomite, sphalerite, quartz, galena, jasperoid and calcite. Replacement is of minor importance. Ore and gangue deposition occurred over the range 150–250 °C with most of the temperatures less than 200 °C. The aqueous brines typically contain 17–23 equivalent weight percent NaCl with often substantial amounts of Ca and/or Mg chlorides. Homogenization temperatures do not delineate any cooling or paragenetic sequence. The cross-cutting vein quartz contains CO₂-rich inclusions with overall densities usually less than 0.7 g/cc and homogenization temperatures from 250–325 °C. Sulfur isotope analyses yield two populations with the quartz vein ores being lighter (<13 permil CDT) than the average for the conformable ores. The later veins are not remobilized MVT sulfides but represent a separate, high-silver period of mineralization.  相似文献   

The non-linear seismic response of AGR core graphite brick slices—correlation of experimental and analytical results     

Khalid Ahmed  Stefan Stojko 《地震工程与结构动力学》1987,15(2):159-188

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Ulvöspinel in native iron-bearing assemblages and the origin of these assemblages in basalts from Ovifak,Greenland, and Bühl,Federal Republic of Germany     

Olaf Medenbach  Ahmed ElGoresy 《Contributions to Mineralogy and Petrology》1982,80(4):358-366

Euhedral crystals of ulvöspinel are found in many of the native-iron-bearing xenoliths from the basalt of Bühl near Kassel (West Germany) and Ovifak on Disko Island (West Greenland). The typical assemblage of these xenoliths at both localities is: native Fe, troilite, cohenite, ulvöspinel, ilmenite, olivine, and plagioclase, as well as silicate glass containing droplets of former Fe and troilite melt. The ulvöspinel subsolidus textures and intergrowths also indicate identical cooling histories for the xenoliths in both cases. Ulvöspinel crystallized after the formation of iron, but still above the Fe-FeS eutectic at 988° C. A subsequent strong drop in oxygen fugacity revealed partial breakdown of ulvöspinel according to the reaction .Microprobe analyses of a Bühl xenolith indicate that ulvöspinel contains up to 4.7 w.t.% MnO, while olivine compositions correspond to Fa_64–74Fo_12–24Te_12–15. The entire xenolith contains 1.9 w.t.% MnO. This fact, together with the geological evidence and the occurrence of corroded quartz relicts within some of the xenoliths provides clear evidence for reduction under near-surface conditions in a blast-furnace-like process. The reducing agent was coal from the Tertiary seams cut by the erupting basalt, while the xenolith source material most probably was spherosiderite, which is very common in the coals and would explain the high MnO content. Consequently, the presence of cohenite is not necessarily an indicator of high pressure.The analogies between the Bühl and Ovifak localities and their xenoliths strongly suggest a similar formation through near surface reduction and not derivation from the mantle.  相似文献