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901.
902.
In full waveform inversion (FWI), Hessian information of the misfit function is of vital importance for accelerating the convergence of the inversion; however, it usually is not feasible to directly calculate the Hessian matrix and its inverse. Although the limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) or Hessian-free inexact Newton (HFN) methods are able to use approximate Hessian information, the information they collect is limited. The two methods can be interlaced because they are able to provide Hessian information for each other; however, the performance of the hybrid iterative method is dependent on the effective switch between the two methods. We have designed a new scheme to realize the dynamic switch between the two methods based on the decrease ratio (DR) of the misfit function (objective function), and we propose a modified hybrid iterative optimization method. In the new scheme, we compare the DR of the two methods for a given computational cost, and choose the method with a faster DR. Using these steps, the modified method always implements the most efficient method. The results of Marmousi and over thrust model testings indicate that the convergence with our modified method is significantly faster than that in the L-BFGS method with no loss of inversion quality. Moreover, our modified outperforms the enriched method by a little speedup of the convergence. It also exhibits better efficiency than the HFN method. 相似文献
903.
904.
905.
Based on the estimation of greenhouse gases (GHG) emissions and carbon sequestration of the total conversion of marshlands (TMC), marshlands conversion to paddy fields (MCPFs) and marshlands conversion to uplands (MCULs), this study revealed the contribution to the global warming mitigation (CGWM) of paddy fields versus uplands converted from marshlands in the Sanjiang Plain (excluding the Muling‐Xingkai Plain on south of Wanda Mountain), Heilongjiang Province, northeast China. The results showed that the total area of MCPFs and MCULs was 504.23 × 103 ha between 1982 and 2005. The CGWM per unit area was 45.53 t CO2eq/ha for MCPFs and that was 23.95 t CO2eq/ha for MCULs, with an obvious 47.40% reduction. The MCPFs and MCULs ecosystems acted as the carbon sink all of the year. As far as CGWM per unit area is concerned, MCPFs mitigated the greenhouse effect which was greater than MCULs. And it was effective that the implementation of the uplands transformed into paddy fields in Northeast China with regard to marshlands protection and croplands (including paddy fields and uplands) reclamation. 相似文献
906.
绩溪县洪坑板岩砚石矿的岩性、成分、物理化学性能特征分析 总被引:1,自引:0,他引:1
赋存于中元古代大谷运组上段地层中的绩溪县洪坑板岩类砚石,通过与歙砚石~歙县龙头石及江西龙尾石、九江石、大畈石、玉山石的物理化学参数测试资料对比分析,歙砚石其原岩均为泥砂质构造沉积岩,但岩性、成分、物理化学性能特征存在一定差异,与歙砚石—龙尾石属于不同成因机制的砚石。 相似文献
907.
Cheng-Bang An Shi-Chen Tao Jiaju Zhao Fa-Hu Chen Yanbin Lv Weimiao Dong Hu Li Yongtao Zhao Ming Jin Zongli Wang 《Journal of Paleolimnology》2013,49(2):145-154
Surface and fossil pollen samples were collected to reconstruct the vegetation and environment since 30.7 cal ka BP in the Lake Balikun Basin, northwest China. This record demonstrates that the region was occupied by four vegetation communities during the interval 30.7–9.0 cal ka BP, including desert steppe (30.7–25.1 cal ka BP), Amaranthaceae-Asteraceae desert (25.1–17.7 cal ka BP), Amaranthaceae-Artemisia-Asteraceae desert (17.7–12.8 cal ka BP) and Amaranthaceae desert (12.8–9.0 cal ka BP), corresponding to relatively humid, the coldest and driest, cold and dry, and colder and drier conditions, respectively. The reconstructions of vegetation and environmental changes around Lake Balikun do not support the interpretation of an extremely humid LGM in Central Asia, challenging the cold-moist (glacial), warm-dry (interglacial) pattern of late Quaternary environmental change in Central Asia. The Last Glacial Maximum was cold and dry, and similarly harsh conditions continued into the early Holocene. 相似文献
908.
Using Contextualized Geographically Weighted Regression to Model the Spatial Heterogeneity of Land Prices in Beijing,China 总被引:3,自引:0,他引:3
Geographically Weighted Regression (GWR) is a method of spatial statistical analysis allowing the modeled relationship between a response variable and a set of covariates to vary geographically across a study region. Its use of geographical weighting arises from the expectation that observations close together by distance are likely to share similar characteristics. In practice, however, two points can be geographically close but socially distant because the contexts (or neighborhoods) within which they are situated are not alike. Drawing on a previous study of geographically and temporally weighted regression, in this article we develop what we describe as contextualized Geographically Weighted Regression (CGWR), applying it to the field of hedonic house price modeling to examine spatial heterogeneity in the land parcel prices of Beijing, China. Contextual variables are incorporated into the analysis by adjusting the geographical weights matrix to measure proximity not only by distance but also with respect to an attribute space defined by measures of each observation's neighborhood. Comparing CGWR with GWR suggests that adding the contextual information improves the model fit. 相似文献
909.
基于2012—2019年兰州地区146个区域自动气象站小时降水数据,从不同时间尺度分析兰州地区近8 a降水精细化特征。结论如下:(1)2012—2019年,兰州地区年均降水量总体呈"北少南多、外多内少"的空间分布特征;年降水量具有明显的年际变化,2018年降水异常偏多46%,而2015、2017年降水异常偏少,尤其2015年偏少30%。(2)兰州地区降水主要集中在7—8月,受环流形势影响,7—8月南部降水明显多于北部,其余月份南北降水差异不明显。(3)兰州地区降水量和降水范围分别表现为"朝少夕多"、"夜大日小"的日变化特征;受海拔高度影响,城区降水量总体比山区小,且因热岛效应,城区降水主要集中在午后至傍晚前后,多为对流性降水,而山区降水日分布较为均匀,整体日波动较小。(4)安宁区短时强降水发生频次最高,但短时强降水频发的站点出现在皋兰县六合站和永登县徐家磨村站,永登县是兰州地区短时强降水预报需重点关注的地区。 相似文献
910.
基于2012—2019年兰州地区146个区域自动气象站小时降水数据,从不同时间尺度分析兰州地区近8 a降水精细化特征。结论如下:(1)2012—2019年,兰州地区年均降水量总体呈"北少南多、外多内少"的空间分布特征;年降水量具有明显的年际变化,2018年降水异常偏多46%,而2015、2017年降水异常偏少,尤其2015年偏少30%。(2)兰州地区降水主要集中在7—8月,受环流形势影响,7—8月南部降水明显多于北部,其余月份南北降水差异不明显。(3)兰州地区降水量和降水范围分别表现为"朝少夕多"、"夜大日小"的日变化特征;受海拔高度影响,城区降水量总体比山区小,且因热岛效应,城区降水主要集中在午后至傍晚前后,多为对流性降水,而山区降水日分布较为均匀,整体日波动较小。(4)安宁区短时强降水发生频次最高,但短时强降水频发的站点出现在皋兰县六合站和永登县徐家磨村站,永登县是兰州地区短时强降水预报需重点关注的地区。 相似文献