Using more than three million Landsat satellite images, this research developed the first global impervious surface area (GISA) dataset from 1972 to 2019. Based on 120,777 independent and random reference sites from 270 cities all over the world, the omission error, commission error, and F-score of GISA are 5.16%, 0.82%, and 0.954, respectively. Compared to the existing global datasets, the merits of GISA include: (1) It provided the global ISA maps before the year of 1985, and showed the longest time span (1972–2019) and the highest accuracy (in terms of a large number of randomly selected and third-party validation sample sets); (2) it presented a new global ISA mapping method including a semi-automatic global sample collection, a locally adaptive classification strategy, and a spatio-temporal post-processing procedure; and (3) it extracted ISA from the whole global land area (not from an urban mask) and hence reduced the underestimation. Moreover, on the basis of GISA, the long time series global urban expansion pattern (GUEP) has been calculated for the first time, and the pattern of continents and representative countries were analyzed. The two new datasets (GISA and GUEP) produced in this study can contribute to further understanding on the human’s utilization and reformation to nature during the past half century, and can be freely download from http://irsip.whu.edu.cn/resources/dataweb.php.
Shear-crack model with a cohesive zone (or breakdown zone) is appropriate for the analysis of a fault surface in which slip distribution is strongly nonuniform. As the slipped portion advances, slip-weakening occurs over the so-called cohesive zone, a distance behind the fault tip. For a prescribed strength vs. displacement constitutive relation, however, the zone structure is difficult to determine by an analytical method except for some simple cases, thus it often requires a certain numerical procedure. This work proposes a numerical procedure to obtain approximated solutions of the problem by combining a series of elastic solutions derived bySmith (1974). The series is linearly combined and the unknown coefficients are determined by a nonlinear least square method. This method can fit a wide range of prescribed strength vs. displacement relations which may be simple algebraic relations or curves obtained by laboratory tests. By examining the residual errors and in comparison with a derived result in which linear stress is assumed within the zone, it could be concluded that the results provide good accuracy. Moreover, because the results are written in formulae, they can be easily referred to or used. By fitting constitutive curves in many different shapes, it is found that the stress distribution within the zone is more sensitive to the constitutive curve shape than the displacement. The most interesting fact is that the zone size is not sensitive to the curve shape, i.e., the zone size can be estimated by $$R = 3\mu \zeta \upsilon _c /\{ 2(1 - \upsilon )(\tau _c - \tau _f )\}$$ with ζ=1±0.11 for most cases. 相似文献
To investigate the strength of frictional sliding and stability of mafic lower crust, we conducted experiments on oven-dried gabbro gouge of 1 mm thick sandwiched between country rock pieces (with gouge inclined 35° to the sample axis) at slip rates of 1.22 × 10− 3 mm/s and 1.22 × 10− 4 mm/s and elevated temperatures up to 615 °C. Special attention has been paid to whether transition from velocity weakening to velocity strengthening occurs due to the elevation of temperature.Two series of experiments were conducted with normal stresses of 200 MPa and 300 MPa, respectively. For both normal stresses, the friction strengths are comparable at least up to 510 °C, with no significant weakening effect of increasing temperature. Comparison of our results with Byerlee's rule on a strike slip fault with a specific temperature profile in the Zhangbei region of North China shows that the strength given by experiments are around that given by Byerlee's rule and a little greater in the high temperature range.At 200 MPa normal stress, the steady-state rate dependence a − b shows only positive values, probably still in the “run-in” process where velocity strengthening is a common feature. With a normal stress of 300 MPa, the values of steady-state rate dependence decreases systematically with increasing temperature, and stick-slip occurred at 615 °C. Considering the limited displacement, limited normal stress applied and the effect of normal stress for the temperatures above 420 °C, it is inferred here that velocity weakening may be the typical behaviour at higher normal stress for temperature above 420 °C and at least up to 615 °C, which covers most of the temperature range in the lower crust of geologically stable continental interior. For a dry mafic lower crust in cool continental interiors where frictional sliding prevails over plastic flow, unstable slip nucleation may occur to generate earthquakes. 相似文献
Accumulation and distribution of heavy metals and phosphorus in sediments impact water quality. There has been an increasing concern regarding fish health in the St. Lucie Estuary, which is related to increased inputs of nutrients and metals in recent decades. To investigate vertical changes of contaminants (P, Cd, Cr, Co, Cu, Ni, Pb, Zn, and Mn) in sediments of the St. Lucie Estuary in South Florida, 117 layer samples from six of the 210 to 420 cm depth cores were analyzed for their total and water-soluble P and heavy metals, clay, total Fe, Al, K, Ca, Mg, Na, and pH. Principal component analysis (PCA) was used in two sets of analytical data (total and water-soluble contaminant concentrations) to document changes of contaminants in each core of sediments. The PCA of total contaminants and minerals resulted in two factors (principal components). The first and second factors accounted for 61.7 and 17.2 % of the total variation in all variables, and contrast indicators associated with contaminants of P, Cd, Co, Cr, Ni, Pb, Zn, and Mn and accumulation of Fe and Al oxides, respectively. The first factor could be used for overall assessment of P and heavy metal contamination, and was higher in the upper 45–90 cm than the lower depths of each core. The concentrations of P and heavy metals in the surface layers of sediments significantly increased, as compared with those in the sediments deeper than 45–90 cm. The PCA of water-soluble contaminants developed two factors. The second factor (Cu–P) was higher in the upper than the lower depths of the sediment, whereas the highest score of the first factor (Cd–Co–Cr–Ni–Pb–Zn–Mn) occurred below 100 cm. The water-soluble Cu and P concentrations were mainly dependent on their total concentrations in the sediments, whereas the water-soluble Cd, Co, Cr, Ni, Pb, Zn, and Mn concentrations were mainly controlled by pH. 相似文献
1 Introduction Alunite [KAl3(SO4)2(OH)6] is a very important non-ferrous metal resource, so many countries throughout the world have made great investments in research on the mechanism of its formation, its geological characteristics and applications. O… 相似文献