Feature extension and matching for mobile robot global localization

This paper introduces an indoor global localization method by extending and matching features. In the proposed method, the environment is partitioned into convex subdivisions. Local extended maps of the subdivisions are then built by exten- ding features to constitute the local extended map set. While the robot is moving in the environment, the local extended map of the current local environment is established and then matched with the local extended map set. Therefore, global localization in an indoor environment can be achieved by integrating the position and ori- entation matching rates. Both theoretical analysis and comparison experimental result are provided to verify the effectiveness of the proposed method for global localization.

High-resolution reconstruction of April-September precipitation and major extreme droughts in China over the past∼530 years

Extreme drought events have increased,causing serious losses and damage to the social economy under current warming conditions.However,short-term meteorological data limit our understanding and projection of these extremes.With the accumulation of proxy data,especially tree-ring data,large-scale precipitation field reconstruction has provided opportunities to explore underlying mechanisms further.Using point-by-point regression,we reconstructed the April-September precipitation field in China for the past~530 years on the basis of 590 proxy records,including 470 tree-ring width chronologies and 120 drought/flood indices.Our regression models explained average 50%of the variance in precipitation.In the statistical test on calibration and verification,our models passed the significance level that assured reconstruction quality.The reconstruction data performed well,showing consistency and better quality than previously reported reconstructions.The first three leading modes of variability in the reconstruction revealed the main distribution modes of precipitation over China.Wet/drought and extremely wet/drought years accounted for 12.81%/10.92%(68 years/58 years)and 1.69%/3.20%(9 years/17 years)of the past~530 years in China,respectively.Major extreme drought events can be identified explicitly in our reconstruction.The detailed features of the Chongzhen Great Drought(1637-1643),the Wanli Great Drought(1585-1590),and the Ding-Wu Great Famine(1874-1879),indicated the existence of potentially different underlying mechanisms that need further exploration.Although further improvements can be made for remote uninhabited areas and large deserts,our gridded reconstruction of April-September precipitation in China over the past~530 years can provide a solid database for studies on the attribution of climate change and the mechanism of extreme drought events.

Exhumation history and preservation of the Jiaojia giant gold deposit, Jiaodong Peninsula

The Jiaojia giant gold deposit is the largest gold deposit in China, with a total gold reserve of approximately 1200 t.Until now, the knowledge of the exhumation history of post-mineralization period is limited, in particular for the low-temperature thermochronology studies of samples below-1000 m. In this work, we combined zircon fission-track(ZFT) and apatite fission-track(AFT) dating of samples between-1100 and-2000 m to determine the post-mineralization cooling and exhumation history of the Jiaojia giant gold deposit. The ZFT ages ranged from 144.2±6.3 to 124.4±5.5 Ma, representing the cooling period and the disturbance of ore-forming fluid. The AFT ages ranged from 28.1±2.6 to 16.2±1.0 Ma, recording the exhumation and cooling processes. With reference to previous low-temperature thermochronology studies in the Jiaojia goldfield, we estimated the exhumation rate and amount of the Jiaojia giant gold deposit and reconstructed its exhumation and preservation history. The exhumation history was divided into four stages, rapid exhumation(~120–95 Ma), relatively slow exhumation(~95–50 Ma),slow exhumation(~50–30 Ma) and relatively rapid exhumation(since 30 Ma). Each stage corresponds to geological events related to the basin-mountain coupling that have occurred since the Cretaceous in the Jiaodong area, namely, a strong tectonic extension and volcanic eruption in the Jiaolai Basin, subsidence of the Jiaolai Basin and Wangshi Group molasse sedimentary,tectonic quiescence, and the Linqu Group basalt eruption of the Jiaobei uplift. Our results show that the exhumation of the Jiaojia giant gold deposit is ~5.2±1.2 km and the orebody erosion degree is relatively low, indicating huge prospecting potential deep in the Jiaojia giant gold deposit. These findings have significance and practical value for deep prospecting in the Jiaodong area.