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21.
Chen Jing Vinod Jayan S. Indraratna Buddhima Ngo Ngoc Trung Gao Rui Liu Yangzepeng 《Acta Geotechnica》2022,17(9):3977-3993
Acta Geotechnica - This paper presents the results of Discrete Element Modelling (DEM) which quantitively examine the effect of coal fouling on the deformation and degradation of ballast upon... 相似文献
22.
Craig L. Patterson Fernando Cadena Rajib Sinha Dzung Kim Ngo‐Kidd Abbas Ghassemi E. Radha Krishnan 《Ground Water Monitoring & Remediation》2013,33(2):44-52
Methyl‐tertiary butyl ether (MTBE) is often found in groundwater as a result of gasoline spills and leaking underground storage tanks. An extrapolation of occurrence data in 2008 estimated at least one detection of MTBE in approximately 165 small and large public water systems serving 896,000 people nationally (United States Environmental Protection Agency [U.S. EPA] 2008). The objective of this collaborative field study was to evaluate a small groundwater treatment system to determine the effectiveness of ultraviolet (UV)/ozone treatment in removing MTBE from contaminated drinking water wells. A pilot‐scale advanced oxidation process (AOP) system was tested to evaluate the oxidation efficiency of MTBE and intermediates under field conditions. This system used ozone as an oxidizer in the presence of UV light at hydraulic retention times varying from 1 to 3 min. MTBE removal efficiencies approaching 97% were possible with this system, even with low retention times. The intermediate t‐butyl alcohol (TBA) was removed to a lesser extent (71%) under the same test conditions. The main intermediate formed in the oxidation process of the contaminated groundwater in these studies was acetone. The concentrations of the other anticipated intermediates t‐butyl formate (TBF), isopropyl alcohol (IPA), methyl acetate (MAc), and possible co‐occurring aromatics (BTEX) in the effluent were negligible. 相似文献
23.
Canada’s Near-Earth Object Surveillance Satellite (NEOSSat), set to launch in early 2012, will search for and track Near-Earth Objects (NEOs), tuning its search to best detect objects with a < 1.0 AU. In order to construct an optimal pointing strategy for NEOSSat, we needed more detailed information in the a < 1.0 AU region than the best current model (Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.M., Levison, H.F., Michel, P., Metcalfe, T.S. [2002]. Icarus 156, 399–433) provides. We present here the NEOSSat-1.0 NEO orbital distribution model with larger statistics that permit finer resolution and less uncertainty, especially in the a < 1.0 AU region. We find that Amors = 30.1 ± 0.8%, Apollos = 63.3 ± 0.4%, Atens = 5.0 ± 0.3%, Atiras (0.718 < Q < 0.983 AU) = 1.38 ± 0.04%, and Vatiras (0.307 < Q < 0.718 AU) = 0.22 ± 0.03% of the steady-state NEO population. Vatiras are a previously undiscussed NEO population clearly defined in our integrations, whose orbits lie completely interior to that of Venus. Our integrations also uncovered the unexpected production of retrograde orbits from main-belt asteroid sources; this retrograde NEA population makes up ?0.1% of the steady-state NEO population. The relative NEO impact rate onto Mercury, Venus, and Earth, as well as the normalized distribution of impact speeds, was calculated from the NEOSSat-1.0 orbital model under the assumption of a steady-state. The new model predicts a slightly higher Mercury impact flux. 相似文献
24.
Abstract— Late Eocene tektite material from DSDP site 612 is composed of angular to spherical tektites and microtektites containing abundant vesicles and a few unmelted to partially melted mineral inclusions. The major element compositions of the 612-tektites are generally comparable to those of North American tektites, but the physical features suggest that the DSDP-612 tektites were formed by less severe shock melting. The 87Sr/86Sr and 143Nd/144Nd compositions of 612-tektites: a) show much wider ranges than the tightly constrained group of North American tektites and microtektites, and b) are significantly different from those of other groups of tektites. The existence of large isotopic variations in tektites from DSDP site 612 requires that they were formed from a chemically and isotopically heterogeneous material in a regime that is distinctive from that of other groups of tektites. TNDCHUR and TSrUR model ages of the 612-tektites indicate that they were formed from a crustal source of late Precambrian mean age (800–1000 Ma) which in middle Palaeozoic time (?400 Ma) was further enriched in Rb/Sr during sedimentary processes. These source characteristics suggest that the impact which produced the 612-tektites occurred in rocks of the Appalachian orogeny or sediments derived from this orogenic belt. Potential source materials for both 612-tektites and North American tektites are present on the eastern and southeastern part of the North American continent and its adjacent shelf. The distinct isotopic differences between 612-tektites and North American tektites indicate that the two groups of tektites were either formed by the impact of more than one bolide in the same general area, or by a single impact event that sampled different layers. 相似文献
25.
Shelley Gustafson Angela Joehl Cadena Chinh Cong Ngo Ammar Kawash Ienkate Saenghkaew Paul Hartman 《Climatic change》2018,149(1):91-106
Climate change is increasingly affecting rural areas worldwide. The Lower Mekong Basin (LMB) is at particular risk due to heat stress, changing rainfall patterns, rising sea levels, and more frequent and extreme climatic events. It is imperative that local-level adaptation plans are developed in a manner that builds resilience to these growing threats. Strategies for developing adaptation plans tend to comprise predominantly science-led or predominantly community-led processes. This study examines an approach that balances inputs from both processes in characterizing community vulnerability as a component of the adaptation planning workflow. Evaluation sites are located within four distinct sub-regions of the LMB: the Vietnam Mekong Delta, the Annamite Mountains of Lao PDR, the Cambodia central lowlands, and the mid-elevation forests of northern Thailand. Our results indicate that by merging science-based data with community-level perspective, knowledge gaps from both sides are filled and a more comprehensive understanding of vulnerability is factored into adaptation planning. 相似文献
26.
Harry Y. McSween Edward M. Stolper Lawrence A. Taylor Richard A. Muntean G. Davis O&#x;Kelley James S. Eldridge Swarajranjan Biswas Hung T. Ngo Michael E. Lipschutz 《Earth and Planetary Science Letters》1979,45(2):275-284
Allan Hills (ALHA) 77005 is a newly discovered, unique achondrite from Antarctica. Petrologic similarities with the shergottites in terms of mineralogy, oxidation state, inferred source region composition, shock metamorphic effects and shock ages suggest a genetic relationship. Volatile to involatile element ratios (e.g. K/U, Rb/U, Cs/U, Tl/U) and abundances of other trace elements support this hypothesis. ALHA 77005 may be a cumulate that crystallized from a liquid parental to those from which the shergottites crystallized; alternatively it may be a sample of the type of source peridotite from which shergottite parent liquids were derived by partial melting. Chemical similarities with terrestrial ultramafic rocks suggest that this unique meteorite provides an additional sample of the only other solar system body known to have basalt source regions chemically similar to the upper mantle of the Earth. 相似文献
27.
Earthquakes that occur on the territory of Vietnam and especially in the South China Sea are a major hazard to the Vietnam population and infrastructure because of possible destruction and tsunamis, like those took place there in earlier times according to geological data. Therefore, in the early 2000s, the government of Vietnam decided to modernize and expand the network of seismological observations on the territory of the republic. First, it was planned to modernize the seismic network in Vietnam with 20 broadband seismic stations and then increase that number to 30. This raised the problem of the optimal arrangement of these stations in the country to predict earthquakes and study the structure of the crust and upper mantle of Vietnam. The map of Vietnam clearly shows the impossibility of constructing a single optimal observation network to locate earthquake hypocenters over the entire territory, because it is strongly elongated from north to south. Any seismological observation network for such an entire territory will not be optimal. In this case, we can speak about improving local observation networks for some areas, such as the north, center, and south of the country. This work estimates the efficiency (distribution of the minimum representative magnitudes and the error in determining the coordinates of earthquake hypocenters) for the new network of seismological observations in Vietnam, consisting of 30 stations. To improve the quality of the network in central and southern Vietnam, six more seismic stations are proposed. Such a network will allow more accurate determination of the hypocenter parameters in central and southern Vietnam. During the construction of the optimal network configuration, one of the main problems was the choice of an effective network radius. The formula for determining the optimal radius in the seismic observation network is obtained for the case of a uniform distribution of hypocenters in a certain cylindrical region based on the radius of the base and height of this cylinder. In this work, it follows from the formula that the radius of the optimal network should be no less than the radius of the hypocentral region. In our case, the choice of network radius is confined within the state borders and coastline of Vietnam. These restrictions are taken into account in the calculations to optimize the number of seismic stations and the configuration of their location in the country. 相似文献
28.
Unbonded fibre‐reinforced elastomeric isolator (U‐FREI) is relatively new seismic base isolator in which fibre layers are used as reinforcement to replace steel shims as are normally used in conventional isolators. Further, the top and bottom end steel connector plates of conventional isolators are also removed. In general, the horizontal response of U‐FREI is nonlinear because of reduction in contact area due to rollover deformation and reduction in shear modulus of isolator under large deformation. Thus, evaluation of horizontal stiffness of U‐FREI is a challenging problem. Most previous studies were focused on the investigation of horizontal response of scaled models of U‐FREIs with low shape factors. A few analytical approaches were suggested for predicting the horizontal response of U‐FREI; but their results were not in good agreement with experimental observations. In the present study, the horizontal responses of prototype U‐FREIs are evaluated under a constant vertical pressure and cyclic loading using both experiments and finite element analysis. Prototype U‐FREIs with different shear moduli and with different shape factors are considered. Finite element simulations of corresponding bonded FREIs are also performed under the same loadings as in U‐FREIs. A rational analytical approach including the influence of rollover deformation and simultaneous reduction in shear modulus is proposed as a basic analytical tool for predicting the horizontal stiffness of FREIs (both bonded and unbonded). It is in reasonably good agreement with the results obtained from experiments and numerical analysis. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
29.
Phan Trong Trinh Hoang Quang Vinh Nguyen Van Huong Ngo Van Liem 《Central European Journal of Geosciences》2013,5(2):223-235
Based on remote sensing, geological data, geomorphologic analysis, and field observations, we determine the fault system which is a potential source of earthquakes in Hoa-Binh reservoir. It is the sub-meridian fault system composed of fault segments located in the central part of the eastern and western flanks of the Quaternary Hoa-Binh Graben: the Hoa-Binh 1 fault is east-dipping (75–80°), N-S trending, 4 km long, situated in the west of the Hoa-Binh Graben, and the Hoa-Binh 2 is a west-dipping (75–80°), N-S trending; 8.4 km long fault, situated in the east of the Hoa-Binh Graben. The slip rate of normal fault in Hoa-Binh hydropower dam was estimated at 0.3–1.1 mm/yr. The Maximum Credible Earthquake (MCE) and Peak Ground Acceleration (PGA) in the Hoa-Binh hydropower dam have been assessed. The estimated MCE of HB.1 and HB.2 is 5.6 and 6.1 respectively, and the maximum PGA at Hoa-Binh dam is 0.30 g and 0.40 g, respectively. The assessment of seismic hazard in Hoa-Binh reservoir is a typical example of seismic hazards of a large dam constructed in an area of low seismicity and lack of law of seismic attenuation. 相似文献
30.
Binh T. Pham Indra Prakash Khabat Khosravi Kamran Chapi Phan T. Trinh Trinh Q. Ngo 《国际地球制图》2013,28(13):1385-1407
AbstractIn this study, the main goal is to compare the predictive capability of Support Vector Machines (SVM) with four Bayesian algorithms namely Naïve Bayes Tree (NBT), Bayes network (BN), Naïve Bayes (NB), Decision Table Naïve Bayes (DTNB) for identifying landslide susceptibility zones in Pauri Garhwal district (India). First, landslide inventory map was built using 1295 historical landslide data, then in total sixteen influencing factors were selected and tested for landslide susceptibility modelling. Performance of the model was evaluated and compared using Statistical based index methods, Area under the Receiver Operating Characteristic (ROC) curve named AUC, and Chi-square method. Analysis results show that that the SVM has the highest prediction capability, followed by the NBT, DTNBT, BN and NB, respectively. Thus, this study confirms that the SVM is one of the benchmark models for the assessment of susceptibility of landslides. 相似文献