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161.
This paper investigates the ionospheric and geomagnetic responses during the 28 March 2005 and 14 May 2005 Sumatran earthquakes using GPS and magnetometer stations located in the near zone of the epicenters. These events occurred during low solar and geomagnetic activity. TEC oscillations with periods of 5–10 min were observed about 10–24 min after the earthquakes and have horizontal propagation velocities of 922–1259 m/s. Ionospheric disturbances were observed at GPS stations located to the northeast of the epicenters, while no significant disturbances were seen relatively east and south of the epicenters. The magnetic field measurements show rapid fluctuations of 4–5 s shortly after the earthquake, followed by a Pc5 pulsation of 4.8 min about 11 min after the event. The correlation between the ionospheric and geomagnetic responses shows a good agreement in the period and time lag of the peak disturbance arrival, i.e. about 11–13 min after the earthquake.  相似文献   
162.
In this paper,dynamic simulation of a beam-like structure with a transverse open crack subjected to a random moving mass oscillator is investigated.The simultaneous effect of a crack and a random oscillator has not been addressed up to now.The crack in the beam at different locations and with different depths is considered as one group of damage,each as an individual imperfection.In addition,bearing immobility is considered as another type of problem in the beam.Mass, stiffness,damping and velocity of th...  相似文献   
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164.
The main objective of this study is to develop algorithms for calculating the air surface temperature (AST). This study also aims to analyze and investigate the effects of greenhouse gases (GHGs) on the AST value in Peninsular Malaysia. Multiple linear regression is used to achieve the objectives of the study. Peninsular Malaysia has been selected as the research area because it is among the regions of tropical Southeast Asia with the greatest humidity, pockets of heavy pollution, rapid economic growth, and industrialization. The predicted AST was highly correlated (R = 0.783) with GHGs for the 6-year data (2003–2008). Comparisons of five stations in 2009 showed close agreement between the predicted AST and the observed AST from AIRS, especially in the wet season (within 1.3 K). The in situ data ranged from 1 to 2 K. Validation results showed that AST (R = 0.776–0.878) has values nearly the same as the observed AST from AIRS. We found that O3 during the wet season was indicated by a strongly positive beta coefficient (0.264–0.992) with AST. The CO2 yields a reasonable relationship with temperature with low to moderate beta coefficient (?0.065 to 0.238). The O3, CO2, and environmental variables experienced different seasonal fluctuations that depend on weather conditions and topography. The concentration of gases and pollution were the highest over industrial zones and overcrowded cities, and the dry season was more polluted compared with the wet season. These results indicate the advantage of using the satellite AIRS data and a correlation analysis to investigate the effect of atmospheric GHGs on AST over Peninsular Malaysia. An algorithm that is capable of retrieving Peninsular Malaysian AST in all weather conditions with total uncertainties ranging from 1 to 2 K was developed.  相似文献   
165.
Stope stability is a key factor for the success of a mining operation. To optimise ore productivity while maintaining stope stability, the mining block/stope must be extracted in stages. Ore dilution will occur if the stope is not properly excavated/blasted. This study examines stope stability during mining in three stages, where the height of each stage stope is 10 m. The paper also presents simulation analysis of a typical steeply dipping tabular orebody at 1200 m depth below the surface, which is common in many Canadian underground hard rock mines. Numerical modelling analysis was conducted using the finite element program, RS2D, where the non-linear elasto-plastic Mohr-Coulomb failure criterion was adopted. The rock reinforcement system (i.e. cable bolts) was modelled/installed in the stope footwall after each mining stage to strengthen access drifts and stabilise the rock mass around the stope that was disturbed by mining activity. Results are discussed in terms of depth of failure zones, total deformation and axial forces in cable bolts with respect to mining stage.  相似文献   
166.
Determination of the geometry and the dimensions of a cave is an important factor considered for planning geotechnical, archeological, speleological studies, and quarrying activities. In recent years, researchers have raised an increasing number of questions related to the shape and size of cavities using 2D geoelectrical resistivity imaging techniques. The inverse model is valuable in detecting the location and extent of subterranean cavities. In this study, a 2D geoelectrical resistivity imaging technique is employed to determine the geometry of a known subterranean cavity. The results provided valuable information and demonstrated the effectiveness of the technique for exploring the size of cavities.  相似文献   
167.
Groundwater stored in the deep seated sedimentary aquifers is the most important source of water supply. The lack of sufficient groundwater recharge and the overdependence on groundwater might lead to unavailability of this precious natural resource if proper management practices are not adopted. Finite difference modelling using the MODFLOW program was carried out in the east of Riyadh city to simulate the groundwater level conditions under different abstraction scenarios. The simulated aquifer system combines the Wasia and Biyadh aquifer (composed of sandstone) and Aruma aquifer (limestone) which lies between 24°30'00"- 25°30'00" N and longitudes 47°00'00"- 48°00'00"E. The transmissivity and storage coefficient values of Biyadh aquifer are 7.0x10-3 to 7.0x10-2 m2/day and 3.7x10-4 to 9.4x10-4 respectively. The transmissivity and storage coefficient values of Wasia aquifer ranges from 6.7x10-3 to 8.5x10-2 m2/day and 2x10-4 to 2.3x10-4 respectively. The model calibration involved altering the values of model input parameters to match field conditions within certain acceptable limits to forecast the aquifer response over a period of 35 years (2015-2050). The modelling grid consisted of 20 and 24 columns with the grids spacing of 4 km for the small grids and 6 km for large grids. The results showed that though the Wasia aquifer was productive, it showed a large decline in water levels if water abstraction continued at the present rate. If the existing trends of groundwater withdraw continues; the piezometric heads in Wasia and Biyadh aquifers will decline by the year 2050. A reduction in 25% of the existing groundwater pumping rate in the well field will minimize the rate of groundwater decline in the aquifer to a considerable extent.  相似文献   
168.
169.
Jizan is one of the Saudi Arabian coastal cities endowed with diverse natural settings, which includes Ash Shuqayq in the north, Turfah in the centre and Jizan in the South. This work analysed specific environmental characteristics, such as spits, sabkhas and wadis. Assessments used Landsat imagery to examine coastal change between 1973 and 2011. The cumulative temporal change identified regression trends given by coefficients of determination that explained a significant percentage of data variation for Jizan (R 2 = 69%) and Turfah (R 2 = 72%), while Ash Shuqayq was insignificant (R 2 = 14%). Inter-survey results predicted future change, although trends were not significant, i.e. Jizan (R 2 = 22%), Turfah (R 2 = 14%) and Ash Shuqayq (R 2 = 3 and 61% with outlying value removed). Aerial photos showed regional coastal changes, which included a maximum accretion of 36.4 m and maximum erosion of 12.9 m. These are scientifically effective techniques to monitor regional coastal change, i.e. erosion and accretion and identified rates of 0.59, 1.80 and 3.53 myr?1 for Ash Shuqayq, Turfah and Jizan. Changes were linked to infrastructure developments, e.g. tourism, port development and natural causes, e.g. spit formations and wadi outfalls.  相似文献   
170.
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