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931.
François Farges 《Physics and Chemistry of Minerals》1994,20(7):504-514
The thermal annealing (300–1700 K) of two metamict zircons (Ampagabe, Madagascar and Näegy, Japan) has been studied using X-Ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) at Zr K-edge. Two stages of thermal annealing within the aperiodic zircon are evidenced between 293 and 1700 K. The first stage (up to 600° C) shows a decrease of the a
0-cell parameter from 6.674 (at 300° C) to 6.610 (at 600° C)± 0.005 Å. In that temperature range, the average local environment around Zr (presence of VIIZr and d(Zr-Zr) 3.3–3.6 Å) shows a weak, but significant increase of the Zr-Zr correlations located at 3.3–3.4 Å, undetectable by XRD. At temperatures up to 700° C (stage 2), the XRD-Bragg component arising from crystalline zircon increases in magnitude, whereas, Zr-K EXAFS analysis indicates a progressive VIIZrVIIIZr transition, associated with a recovery of the crystalline zircon medium-range environment. For both techniques, the zircon structure is fully recovered at annealing temperatures up to 900° C.Electrostatic modelings suggest that the VIIIZrVIIZr transition observed in zircon with increasing alpha-decay damage creates significantly overbonded oxygen atoms around Zr. With increasing temperature, those oxygen atoms are better bonded to VIIZr, due to the thermal expansion of the Zr-O bond. The congruent recovery of the zircon structure should therefore be favoured with increasing temperature. On the other hand, the metamict network can be also partially reorganized around 400–500° C, with the creation of Zr-rich domains, as measured by EXAFS. However, the growth of these domains after 3 hours annealing affects only minor portions of the aperiodic network. This model is corroborated by a similar thermal behaviour observed for a synthetic sol-gel of ZrO2 · SiO2 composition. 相似文献
932.
TheUBV photometry of the detached F-type eclipsing binary BK Pegasi is presented. The light curve solution by a simple spherical model assumption suggests that a slightly hotter, larger and more luminous primary was eclipsed during the primary minimum. Combined with the radial velocity curves in Popper (1983), it was used to determine anew the system's parameters. The age and the metal abundance of the system were estimated as (3.3 ± 0.2) × 109 yr andz = 0.028 ± 0.003 from a comparison with the new grids of stellar models and the isochrones by Schalleret al. (1993). The distance of the system was estimated as 290 pc. 相似文献
933.
Many controversial questions about the shape and evolution of city size distributions can be solved if reliable, large and comparable set of data are used for several countries. We provide new empirical evidence by using the large data base Geopolis, which has strictly comparable figures for all towns and cities of the world over 10,000 inhabitants between 1950 and 1990. A Pareto model is used for identifying as metropolises one or a few large cities for each national urban system. From those data, two empirical power laws are established, linking the size of the metropolises to the size of their national urban system. The first is a transversal law: for a set of countries at a given date, the share of population concentrated in metropolises tends to decrease when larger countries are considered. The second law, which is longitudinal, shows that metropolises in the past have grown in a systematic way more rapidly than the rest of their urban system, invalidating Gibrat's urban growth model. Such empirical regularities could help for predicting the future of nowadays observed metropolisation trends. 相似文献
934.
Landslide susceptibility mapping (LSM) is important for catastrophe management in the mountainous regions. They focus on generating susceptibility maps beginning from landslide inventories and considering the main predisposing parameters. The aim of this study was to assess the susceptibility of the occurrence of debris flows in the Zêzere River basin and its surrounding area using logistic regression (LR) and frequency ratio (FR) models. To achieve this, a landslide inventory map was created using historical information, satellite imagery, and extensive field works. One hundred landslides were mapped, of which 75% were randomly selected as training data, while the remaining 25% were used for validating the models. The landslide influence factors considered for this study were lithology, elevation, slope gradient, slope aspect, plan curvature, profile curvature, normalized difference vegetation index (NDVI), distance to roads, topographic wetness index (TWI), and stream power index (SPI). The relationships between landslide occurrence and these factors were established, and the results were then evaluated and validated. Validation results show that both methods give acceptable results [the area under curve (AUC) of success rates is 83.71 and 76.38 for LR and FR, respectively]. Furthermore, the AUC results for prediction accuracy revealed that LR model has the highest predictive performance (AUC of predicted rate?=?80.26). Hence, it is concluded that the two models showed reasonably good accuracy in predicting the landslide susceptibility in the study area. These two models have the potential to aid planners in development and land-use planning and to offer tools for hazard mitigation measures. 相似文献
935.
Konopásek Jiří Janoušek Vojtěch Oyhantçabal Pedro Sláma Jiří Ulrich Stanislav 《International Journal of Earth Sciences》2018,107(5):1859-1894
International Journal of Earth Sciences - Early Neoproterozoic metaigneous rocks occur in the central part of the Kaoko–Dom Feliciano–Gariep orogenic system along the coasts of the... 相似文献
936.
Wang Ji-Peng Luan Ji-Yuan Gao Xu-Guang Liu Tai-Heng Andò Edward François Bertrand 《Acta Geotechnica》2022,17(11):4799-4821
Acta Geotechnica - The mechanical behaviours of unsaturated soils are highly related to the water content and pore water and air distributions. Under the context of climate change, geo-disasters... 相似文献
937.
Geomagnetism and Aeronomy - In this paper, using the Total Electron Content (TEC) data obtained from GUAM (13.58° N, 144.86° E) and PNGM (2.04° S, 147.36° E) Global Positioning... 相似文献
938.
Natural Hazards - The high seismicity and tectonic activity of the study area located in a near-fault region in Gölyaka, Düzce, results in a bedrock geometry highly complex in the sense... 相似文献
939.
Azarafza Mohammad Koçkar Mustafa K. Zhu Hong-Hu 《Geotechnical and Geological Engineering》2022,40(4):1751-1764
Geotechnical and Geological Engineering - The preliminary responses on stability assessment are very effective in discontinuous rock slope stabilisations, which geo-mechanical empirical... 相似文献
940.