Climate changes associated with high-amplitude <Emphasis Type="Italic">Sq</Emphasis> geomagnetic variations

When the solar irradiance propagates between the outer magnetospheric regions and the ionosphere, dynamic processes of the magnetosphere-ionosphere-thermosphere system are affected at the lower end of their paths by the interaction of radiation with the neutral troposphere. The main target of this work is to investigate the relationship between the diurnal magnetic field variations resulting from solar activities and the variation in the troposphere temperature. Meteorological and geomagnetic data acquired from different observatories located in Egypt, Portugal and Slovakia in a long-term and daily-term scales were analyzed.     

Electromagnetic effects on the orbital motion of a charged spacecraft

This paper deals with the effects of electromagnetic forces on the orbital motion of a spacecraft.The electrostatic charge which a spacecraft generates on its surface in the Earth’s magnetic field will be subject to a perturbative Lorentz force.A model incorporating all Lorentz forces as a function of orbital elements has been developed on the basis of magnetic and electric fields.This Lorentz force can be used to modify or perturb the spacecraft’s orbits.Lagrange’s planetary equations in the Gauss variational form are derived using the Lorentz force as a perturbation to a Keplerian orbit.Our approach incorporates orbital inclination and the true anomaly.The numerical results of Lagrange’s planetary equations for some operational satellites show that the perturbation in the orbital elements of the spacecraft is a second order perturbation for a certain value of charge.The effect of the Lorentz force due to its magnetic component is three times that of the Lorentz force due to its electric component.In addition,the numerical results confirm that the strong effects are due to the Lorentz force in a polar orbit,which is consistent with realistic physical phenomena that occur in polar orbits.The results confirm that the magnitude of the Lorentz force depends on the amount of charge.This means that we can use artificial charging to create a force to control the attitude and orbital motion of a spacecraft.     

United Arab Emirates limestones: impact of petrography on thermal behavior

The thermal behavior of selected limestones from representative localities of the United Arab Emirates is investigated for their suitability for soft-burnt lime production. The limestone samples were collected from the Ghalilah, Musandam, Shauiba, Muthaymimah, Dammam and Asmari formations. The samples were characterized for petrography, mineral and chemical composition, together with physico-mechanical characteristics. Investigative methods included transmitted light microscopy (TLM), cathodoluminescence (CLM) and scanning electron microscopy (SEM), as well as X-ray micro-tomography (μ-CT), XRD, XRF and Archimedes method. The limestone samples were fired in an electrical muffle furnace for 0.25, 0.5, 1 and 2 hours at 800, 900, 1,000 and 1,100 °C. After firing the lime grains were tested to determine their hydration rate and microfabric. The Ghalilah and Musandam limes show the lowest and highest maximum hydration rates, respectively, due mainly to the impure nature of the former, and the smaller lime crystallites and dominance of post-calcination micro-cracks of the latter. The Dammam and Asmari limes preserve a “ghost” microfabric of the original limestone. Higher allochem contents impose lower activation energy requirements for calcination, which implies earlier calcination of the allochems. The Musandam, Shauiba and Muthaymimah limestones may be useful for the production of reactive soft-burnt lime under the applied firing conditions, however, the Dammam and Asmari limestones need more advanced calcination conditions than the applied ones. The Ghalilah limestone was found to be unsuitable for the production of lime.     

巴基斯坦山达克矿区ASTER遥感数据、蚀变信息提取及找矿预测

巴基斯坦查盖火山岩浆岩带属于特提斯成矿域的重要组成部分之一,是巴基斯坦境内最重要的斑岩型铜矿带,但目前其相关的遥感研究还较少,制约了对该成矿带的找矿潜力分析。笔者等以山达克矿床及其周边为研究区,对先进星载热辐射与反射辐射计(Advanced Spaceborne Thermal Emission and Reflection Radiometer, ASTER)数据进行RBD (Relative absorption band depth)比值假彩色合成、主成分分析、光谱角制图等处理,获得蚀变遥感异常信息分布特征,通过对蚀变特征和主要控矿要素进行遥感研究,建立了山达克矿床遥感找矿模型并开展成矿预测,为该成矿带矿产勘查提供借鉴。根据建立的遥感找矿模型,圈定了找矿预测靶区10处。对矿区东矿体和矿区北部的2个靶区进行野外验证,证实了提取结果与实际地质事实吻合较好,对矿区岩石样品进行光谱实测,表明样品实测光谱曲线与标准矿物光谱曲线的吸收特征位置高度相似,证实了研究区绢云母化、青磐岩化等蚀变较强且分布较广。结果表明本次研究提取的矿化蚀变结果可信度较高,可为后续找矿勘查工作提供参考。     

Inverse geochemical modeling of groundwater salinization in Azraq Basin,Jordan

The aim is to define the mechanism of chemical reactions that are responsible for the salinization of the Azraq basin along groundwater flow path, using inverse modeling technique by PHREEQC Interactive 2.8 for Windows. The chemical analysis of representative groundwater samples was used to predict the causes of salinization of groundwater. In addition, the saturation indices analysis was used to characterize the geochemical processes that led to the dissolution of mineral constituents within the groundwater aquifer system. According to the modeling results, it was noted that the groundwater at the recharge area was undersaturated with respect to calcite, dolomite, gypsum, anhydrite, and halite. Thus, the water dissolved these minerals during water rock interaction, and therefore, the concentration of Ca, Mg, Na, and SO₄ increased along the groundwater flow path. Furthermore, the groundwater at the discharge area was oversaturated with respect to calcite and dolomite. This meant that the water would precipitate these minerals along the flow path, while the water was undersaturated with respect to gypsum and halite throughout the simulated path; this showed the dissolution processes that take place during water-rock interaction. Therefore, the salinity of the groundwater increased significantly along the groundwater flow paths.     

Late Cryogenian arc-related volcaniclastic metasediment successions at Wadi Hammuda,Central Eastern Desert,Egypt: geology and geochemistry

Wadi Hammuda is dominated by a variety of low grade regionally metamorphosed volcaniclastic metasediments pertaining to two different geotectonic settings and intruded by arc and late collision granitic rocks. Thus, the volcaniclastic metasediments which form extensive outcrops are considered as a member of island arc assemblages. This paper deals with the petrography, geochemistry, and tectonic setting of the island arc volcaniclastic metasediment rock units. The volcaniclastic metasediments consist of interbedded metagreywackes, metasiltstones, metamudstones, and schists as well as metapyroclastics. They are well foliated, crenulated and tightly folded, metamorphosed, and intruded by granitic rocks. Geochemical data support the petrographic classification and reveal that these volcaniclastic metasediments are generally low-K, essentially tholeiitic in character, with the exception of some metasediments and metapyroclastics which exhibits calc-alkaline and tholeiitic affinities and represent the first stage of island arc volcanism. The overthrusted oceanic lithosphere blocks with fragments of the fore arc and/or back-arc marginal basins volcaniclastic metasediments were incorporated among the island arc volcanics which supported by tectonically relationship between the different rock units in the study area. Contemporaneous with this deformation event, Wadi Hammuda was subjected to low grade regional metamorphism and the rocks document an early phase of shearing and/or foliation. Occasionally minor folds were developed particularly in the metasediments and schists. The subsequent emplacement of the syn-tectonic granites (tonalites and granodiorites) resulted in minor local thrusts. During the regional thrusting event which preceded the emplacement of the late-tectonic granites (alkali feldspar granites) and affected the whole region, low grade successions cover the study area similar to the Meatiq volcaniclastic metasediments.     

A typical weathering profile of granitic rock in Johor,Malaysia based on joint characterization

Arabian Journal of Geosciences - One of the most important challenges in the study of slope stability, foundation, and excavation in rocks is understanding the weathering states. This issue is more...     

Nuclear geophysical logging for Gondwana coal exploration: a case study at Phulbari Coal Basin, northern part of Bangladesh

Different methods of lithology predictions from geophysical data have been developed in the last 15 years, among which the conventional logs are as follows: sonic, neutron–neutron, natural gamma, and density (backscattered gamma–gamma). This article concentrates on the nuclear geophysical suite, in particular, gamma and gamma–gamma logging, which, to date, provide the most accurate geophysical means of identifying coal seams and estimating their thickness. From the gamma and gamma–gamma logs of boreholes AEN 002, 007, 044, 045, 063, 085, and 105, which were carried out at the Phulbari Coal Basin of Bangladesh, two coal seams—upper and main with two lower seams of limited occurrence and of varying thickness—were identified, together with their regional occurrence.