Microscopy and rock magnetism of fine grain-size titanomagnetite from the Jacupiranga Alkaline Complex,Brazil: unearthing Ti-magnesioferrite nanoparticles     

Luis M. Alva-Valdivia  María de la Luz Rivas-Sánchez  Jesús Arenas-Alatorre  Avto Goguitchaishvili  Omar Ferreira Lopes 《Geofísica Internacional》2013,52(2):93-110

Very fine samples from the mineralized zones of the Jacupiranga complex at the Cajati mine were selected for crystallographic identification of Ti-magnesioferrite (TMf) nanostructures embedded in titanomagnetite (TM) using high-resolution transmission electron microscopy (TEM). A magnetic concentrate obtained of pyroxenite samples (sites 4 to 7) was reduced and divided into fractions of distinct range sizes: 26±2 μm, 19±1 μm, 13±1 μm, 9±1 μm, 6±1 μm and 6-0.1 μm. The mineralized samples of carbonatite and pyroxenite were characterized by X-ray diffraction, transmitted and reflected light microscope, and scanning electron microscope with multielemental analysis. The finest magnetic concentrate sample (MC₆) was analyzed under high-resolution transmitted electron microscopy (TEM) and high angle annular dark field and Raman spectroscopy. Magnetic properties were measured for the distinct granulometric fractions, showing drastic changes when grain sizes go beyond the frontier from micro to nanometer sizes. Frequency-dependent magnetic susceptibility percentage (÷_fd%) report higher values (10.2%) for the finer fractions (6±1 μm and 6-0.1 μm) attributed to dominant fractions of superparamagnetic particles. Nanometer and < 6 μm grain size TMf in TM particles require a magnetic field up to 249 mT to reach saturation during the isothermal remanent magnetization experiment. Coercivity and remanent magnetization of these samples increase when the particle size decreases, probably due to parallel coupling effects. Magnetic susceptibility versus temperature experiments were conducted two times on the same (< 35 nm) sample, showing that the repetition during the second heating is probably due to the formation of new TMf nanoparticles and growth of those already present during the first heating process.  相似文献   

Atomic structures and energies of grain boundaries in Mg2SiO4 forsterite from atomistic modeling     

Omar Adjaoud  Katharina Marquardt  Sandro Jahn 《Physics and Chemistry of Minerals》2012,39(9):749-760

Grain boundaries influence many physical and chemical properties of crystalline materials. Here, we perform molecular dynamics simulations to study the structure of a series of [100] symmetric tilt grain boundaries in Mg₂SiO₄ forsterite. The present results show that grain boundary energies depend significantly on misorientation angle. For small misorientation angles (up to 22°), grain boundary structures consist of an array of partial edge dislocations with Burgers vector $\frac{1}{2}[001]$ associated with stacking faults and their energies can be readily fit with a model which adds the Peach-Koehler equation to the Read-Shockley dislocation model for grain boundaries. The core radius of partial dislocations and the spacing between the partials derived from grain boundary energies show that the transition from low- to high-angle grain boundaries occurs for a misorientation angle between 22° and 32°. For high misorientation angles (32.1° and 60.8°), the cores of dislocations overlap and form repeated structural units. Finally, we use a low energy atomic configuration obtained by molecular dynamics for the misorientation of 12.18° as input to simulate a high-resolution transmission electron microscopy (HRTEM) image. The simulated image is in good agreement with an observed HRTEM image, which indicates the power of the present approach to predict realistic atomic structures of grain boundaries in complex silicates.  相似文献   

A probabilistic model to improve reconciliation of estimated and actual grade in open-pit mining     

Ali Parhizkar  Mohamad Ataei  Parviz Moarefvand  Vamegh Rasouli 《Arabian Journal of Geosciences》2012,5(6):1279-1288

Many of the open-pit mines suffer from the lack of reconciliation between estimated and actual grades. In a mining operation, grade reconciliation is the comparison between the values of the estimated grade calculated in exploration stage and the actual grade obtained from more reliable data such as blast holes?? samples. Many different factors affect the degree of reconciliation in a mining operation. In this paper, the factors related to estimated grade which affect the reconciliation process in the exploration stage of the orebody are investigated. These factors constitute the sources of uncertainty for the upcoming phases of the mining life. Among these parameters, the inherent variability, statistical uncertainty, and systematic uncertainty are the most important factors. In this work, these parameters are studied in further detail, and, accordingly, for each of these uncertainties, a correction factor is determined in the proposed model. The model was applied to the study of real data taken from an iron open-pit mine in Iran. The results of the case study indicated that the systematic uncertainty, inherent variability, and statistical uncertainty are, in order, the main sources of uncertainty on grade reconciliation process. Applying the correction factors to estimated grade values has increased the amount of grade reconciliation from 10%, at original condition, to 50%, at new condition, in the case study.  相似文献   

Solar Flare Prediction Using Advanced Feature Extraction, Machine Learning, and Feature Selection   总被引：2，自引：0，他引：2  

Omar W. Ahmed  Rami Qahwaji  Tufan Colak  Paul A. Higgins  Peter T. Gallagher  D. Shaun Bloomfield 《Solar physics》2013,283(1):157-175

Novel machine-learning and feature-selection algorithms have been developed to study: i) the flare-prediction-capability of magnetic feature (MF) properties generated by the recently developed Solar Monitor Active Region Tracker (SMART); ii) SMART’s MF properties that are most significantly related to flare occurrence. Spatiotemporal association algorithms are developed to associate MFs with flares from April 1996 to December 2010 in order to differentiate flaring and non-flaring MFs and enable the application of machine-learning and feature-selection algorithms. A machine-learning algorithm is applied to the associated datasets to determine the flare-prediction-capability of all 21 SMART MF properties. The prediction performance is assessed using standard forecast-verification measures and compared with the prediction measures of one of the standard technologies for flare-prediction that is also based on machine-learning: Automated Solar Activity Prediction (ASAP). The comparison shows that the combination of SMART MFs with machine-learning has the potential to achieve more accurate flare-prediction than ASAP. Feature-selection algorithms are then applied to determine the MF properties that are most related to flare occurrence. It is found that a reduced set of six MF properties can achieve a similar degree of prediction accuracy as the full set of 21 SMART MF properties.  相似文献   

Probabilistic earthquake risk assessment using CAPRA: application to the city of Barcelona, Spain   总被引：2，自引：2，他引：0  

Mabel C. Marulanda  Martha L. Carreño  Omar D. Cardona  Mario G. Ordaz  Alex H. Barbat 《Natural Hazards》2013,69(1):59-84

The risk evaluation model CAPRA (Comprehensive Approach to Probabilistic Risk Assessment) is a techno-scientific methodology and information platform, composed of tools for evaluating and communicating risk at various territorial levels. The model allows evaluating losses on exposed elements using probabilistic metrics, such as the loss exceedance curve, the expected annual loss and the probable maximum loss, useful for multi-hazard risk analyses. In this article, the process of probabilistic seismic risk analysis is described, explaining the main features of the CAPRA modules of hazard, vulnerability and risk estimation applied to the city of Barcelona, Spain. In addition, according to the physical risk results and the information on the socioeconomic indicators of the city, this article presents the holistic evaluation of seismic risk, which is a valuable result to facilitate the integrated risk management by the different stakeholders involved in risk reduction decision making.  相似文献   

Composition and source identification of polycyclic aromatic hydrocarbons in mangrove sediments of Peninsular Malaysia: indication of anthropogenic input   总被引：1，自引：1，他引：0  

Muhammad Raza  Mohamad Pauzi Zakaria  Nor Rasidah Hashim  Un Hyuk Yim  Narayanan Kannan  Sung Yong Ha 《Environmental Earth Sciences》2013,70(6):2425-2436

This is a comprehensive study of the composition, origin and sources of specific polycyclic aromatic hydrocarbons (PAHs) in sediments of mangrove estuary in the western part of Peninsular Malaysia. Mangrove sediments were analyzed for 17 PAHs by gas chromatography–mass spectrometry. Total PAH concentrations in the sediments ranged from 20 to 112 ng/g on a dry-weight basis. High molecular weight PAHs were abundant in the sediments. Parent PAH ratios revealed that pyrogenic input has important contribution to the sedimentary PAHs. Ratios of alkylated PAHs indicate that the sedimentary PAHs were influenced by petrogenic PAHs, which implies that petrogenic input has contribution to the sedimentary PAHs but that it is not a major factor in distribution of PAHs within the estuary. Combustion-derived PAHs show a positive and very strong correlation with total PAHs (R ² = 0.926, p < 0.05). Total methylphenanthrenes show very weak correlation with total PAHs (R ² = 0.0928, p < 0.05). The PAH concentrations were found to increase with distance from the upstream of the estuary to the coastal area of the Straits of Malacca. For the assessment of sediment contamination using biological thresholds, none of the individual studied PAH compounds exceeded the values of the effect range low–effect range median guideline and the threshold effects level–probable effects level guideline. This study demonstrates that the sediments of the mangrove ecosystem facing the Straits of Malacca and Sumatra are influenced by anthropogenic PAH inputs as a result of human activities such as biomass burning, vehicle emissions and boating activities.  相似文献   

Groundwater resources assessment using integrated geophysical techniques in the southwestern region of Peninsular Malaysia   总被引：2，自引：0，他引：2  

Mohamed S. E. Juanah  Shaharin Ibrahim  Wan Nor Azmin Sulaiman  Puziah Abdul Latif 《Arabian Journal of Geosciences》2013,6(11):4129-4144

Combined geophysical techniques such as multi-electrode resistivity, induced polarization, and borehole geophysical techniques were carried out on volcano-sedimentary rocks in the north of Gemas as part of the groundwater resource’s investigations. The result identifies four resistivity units: the tuffaceous mudstone, tuffaceous sandstone, the tuff bed, and the shale layer. Two types of aquifer systems in terms of storage were identified within the area: one within a fracture system (tuff), which is the leaky area through which vertical flow of groundwater occurs, and an intergranular property of the sandy material of the aquifer which includes sandstone and tuffaceous sandstone. The result also reveals that the aquifer occupies a surface area of about 3,250,555 m² with a mean depth of 43.71 m and a net volume of 9.798?×?10⁷?m³. From the approximate volume of the porous zone (28 %) and the total aquifer volume, a usable capacity of (274.339?±?30.177)?×?10⁷?m³ of water in the study area can be deduced. This study provides useful information that can be used to develop a much broader understanding of the nature of groundwater potential in the area and their relationship with the local geology.  相似文献   

Inverted basin analysis and geological modeling, Razzak Oil Field, Western Desert, Egypt     

Mohamed Salah Sedek  Omar Mohamed Mohamed Al Mahdy 《Arabian Journal of Geosciences》2013,6(7):2261-2283

This paper deals with a geological modeling based on seismic and well data of the Razzak Oil Field, located in northwestern desert of Egypt aimed mainly at improving the knowledge on inversion tectonics in the sedimentary basin corresponding to the oil field. Contour maps of significant seismic horizons corresponding to the top of Meso-Cenozoic formations which represent the stratigraphic traps of the oil field (top Apollonia, top Abu Roash “G,” top Bahariya, and top Alamein) are presented. The final model consists of geological cross-sections showing the inversion basin in the Razzak Oil Field. From the seismic data interpretation and modeling, we have different results matching with regional tectonic and transcurrent motion model. There are two main fault trends: the first one was northeast–southwest matching the Jurassic rift where the Jurassic is characterized by normal faults that formed in conjunction with the opening of the Neo-Tethys, and the other fault trend is northwest–southeast matching with Cretaceous faults. This is followed by a period of compressive tectonism (Syrian Arc deformation) in which two of the Jurassic normal faulted blocks (one at the northern part and the other at the southern part of the Qattara–Alamein ridge in the Razzak field) are reactivated as reverse faulted by Eocene–Early Oligocene time.  相似文献   

Sources of sedimentary PAHs in tropical Asian waters: Differentiation between pyrogenic and petrogenic sources by alkyl homolog abundance   总被引：2，自引：0，他引：2  

Mahua Saha  Kaoruko Mizukawa  Hideshige Takada  Mohamad P. Zakaria  Bui Cach Tuyen  Ruchaya Boonyatumanond  Badal Bhattacharya  Touch Seang Tana 《Marine pollution bulletin》2009,58(2):189-200

We collected surface sediment samples from 174 locations in India, Indonesia, Malaysia, Thailand, Vietnam, Cambodia, Laos, and the Philippines and analyzed them for polycyclic aromatic hydrocarbons (PAHs) and hopanes. PAHs were widely distributed in the sediments, with comparatively higher concentrations in urban areas (∑PAHs: ∼1000 to ∼100 000 ng/g-dry) than in rural areas (∼10 to ∼100 g-dry), indicating large sources of PAHs in urban areas. To distinguish petrogenic and pyrogenic sources of PAHs, we calculated the ratios of alkyl PAHs to parent PAHs: methylphenanthrenes to phenanthrene (MP/P), methylpyrenes + methylfluoranthenes to pyrene + fluoranthene (MPy/Py), and methylchrysenes + methylbenz[a]anthracenes to chrysene + benz[a]anthracene (MC/C). Analysis of source materials (crude oil, automobile exhaust, and coal and wood combustion products) gave thresholds of MP/P = 0.4, MPy/Py = 0.5, and MC/C = 1.0 for exclusive combustion origin. All the combustion product samples had the ratios of alkyl PAHs to parent PAHs below these threshold values. Contributions of petrogenic and pyrogenic sources to the sedimentary PAHs were uneven among the homologs: the phenanthrene series had a greater petrogenic contribution, whereas the chrysene series had a greater pyrogenic contribution. All the Indian sediments showed a strong pyrogenic signature with MP/P ≈ 0.5, MPy/Py ≈ 0.1, and MC/C ≈ 0.2, together with depletion of hopanes indicating intensive inputs of combustion products of coal and/or wood, probably due to the heavy dependence on these fuels as sources of energy. In contrast, sedimentary PAHs from all other tropical Asian cities were abundant in alkylated PAHs with MP/P ≈ 1-4, MPy/Py ≈ 0.3-1, and MC/C ≈ 0.2-1.0, suggesting a ubiquitous input of petrogenic PAHs. Petrogenic contributions to PAH homologs varied among the countries: largest in Malaysia whereas inferior in Laos. The higher abundance of alkylated PAHs together with constant hopane profiles suggests widespread inputs of automobile-derived petrogenic PAHs to Asian waters.  相似文献