Geochemical characteristics of hadal sediment in the northern Yap Trench     

Huang  Yuhuan  Sun  Chengjun  Yang  Guipeng  Yue  Xin&#;an  Jiang  Fenghua  Cao  Wei  Yin  Xiaofei  Guo  Chaonan  Niu  Jiaohong  Ding  Haibing 《中国海洋湖沼学报》2020,38(3):650-664

Journal of Oceanology and Limnology - Two sediment cores were retrieved in the hadal zone of the Yap Trench, and their concentrations of six major elements Mg, Al, Ca, Ti, Mn and Fe and nine trace...  相似文献   

Ionospheric and receiver DCB-constrained multi-GNSS single-frequency PPP integrated with MEMS inertial measurements     

Zhouzheng Gao  Wenbin Shen  Hongping Zhang  Xiaoji Niu 《Journal of Geodesy》2017,91(11):1351-1366

Single-frequency precise point positioning (SF-PPP) is a potential precise positioning technique due to the advantages of the high accuracy in positioning after convergence and the low cost in operation. However, there are still challenges limiting its applications at present, such as the long convergence time, the low reliability, and the poor satellite availability and continuity in kinematic applications. In recent years, the achievements in the dual-frequency PPP have confirmed that its performance can be significantly enhanced by employing the slant ionospheric delay and receiver differential code bias (DCB) constraint model, and the multi-constellation Global Navigation Satellite Systems (GNSS) data. Accordingly, we introduce the slant ionospheric delay and receiver DCB constraint model, and the multi-GNSS data in SF-PPP modular together. In order to further overcome the drawbacks of SF-PPP in terms of reliability, continuity, and accuracy in the signal easily blocking environments, the inertial measurements are also adopted in this paper. Finally, we form a new approach to tightly integrate the multi-GNSS single-frequency observations and inertial measurements together to ameliorate the performance of the ionospheric delay and receiver DCB-constrained SF-PPP. In such model, the inter-system bias between each two GNSS systems, the inter-frequency bias between each two GLONASS frequencies, the hardware errors of the inertial sensors, the slant ionospheric delays of each user-satellite pair, and the receiver DCB are estimated together with other parameters in a unique Kalman filter. To demonstrate its performance, the multi-GNSS and low-cost inertial data from a land-borne experiment are analyzed. The results indicate that visible positioning improvements in terms of accuracy, continuity, and reliability can be achieved in both open-sky and complex conditions while using the proposed model in this study compared to the conventional GPS SF-PPP.  相似文献   

Spatial and temporal variation of vegetation phenology and its response to climate changes in Qaidam Basin from 2000 to 2015   总被引：1，自引：0，他引：1  

Yang Fu  Hui Chen  Huihui Niu  Siqi Zhang  Yi Yang 《地理学报(英文版)》2018,28(4):400-414

Based on TIMESAT 3.2 platform, MODIS NDVI data (2000–2015) of Qaidam Basin are fitted, and three main phenological parameters are extracted with the method of dynamic threshold, including the start of growth season (SGS), the end of growth season (EGS) and the length of growth season (LGS). The spatial and temporal variation of vegetation phenology and its response to climate changes are analyzed respectively. The conclusions are as follows: (1) SGS is mainly delayed as a whole. Areas delayed are more than the advanced in EGS, and EGS is a little delayed as a whole. LGS is generally shortened. (2) With the altitude rising, SGS is delayed, EGS is advanced, and LGS is shortened and phenophase appears a big variation below 3000 m and above 5000 m. (3) From 2000 to 2015, the temperature appears a slight increase along with a big fluctuation, and the precipitation increases evidently. (4) Response of phenophase to precipitation is not obvious in the low elevation humid regions, where SGS arrives early and EGS delays; while, in the upper part of the mountain regions, SGS delays and EGS advances with temperature rising, SGS arrives early and EGS delays with precipitation increasing.  相似文献   

Evolution and spatial characteristics of tourism field strength of cities linked by high-speed rail (HSR) network in China     

Degen Wang  Yu Niu  Feng Sun  Kaiyong Wang  Jia Qian  Feng Li 《地理学报(英文版)》2017,27(7):835-856

Traffic is an indispensable prerequisite for a tourism system. The “four vertical and four horizontal” HSR network represents an important milestone of the “traffic revolution” in China. It will affect the spatial pattern of tourism accessibility in Chinese cities, thus substantially increasing their power to attract tourists and their radiation force. This paper examines the evolution and spatial characteristics of the power to attract tourism of cities linked by China’s HSR network by measuring the influence of accessibility of 338 HSR-linked cities using GIS analysis. The results show the following. (1) The accessibility of Chinese cities is optimized by the HSR network, whose spatial pattern of accessibility exhibits an obvious traffic direction and causes a high-speed rail-corridor effect. (2) The spatial pattern of tourism field strength in Chinese cities exhibits the dual characteristics of multi-center annular divergence and dendritic diffusion. Dendritic diffusion is particularly more obvious along the HSR line. The change rate of urban tourism field strength forms a high-value corridor along the HSR line and exhibits a spatial pattern of decreasing area from the center to the outer limit along the HSR line. (3) The influence of the higher and highest tourism field strength areas along the HSR line is most significant, and the number of cities that distribute into these two types of tourism field strengths significantly increases: their area expands by more than 100%. HSR enhances the tourism field strength value of regional central cities, and the radiation range of tourism attraction extends along the HSR line.  相似文献   

Identification of paralytic shellfish toxin-producing microalgae using machine learning and deep learning methods     

Xu  Wei  Niu  Jie  Gan  Wenyu  Gou  Siyu  Zhang  Shuai  Qiu  Han  Jiang  Tianjiu 《中国海洋湖沼学报》2022,40(6):2202-2217

Journal of Oceanology and Limnology - Paralytic shellfish poisoning (PSP) microalgae, as one of the harmful algal blooms, causes great damage to the offshore fishery, marine culture, and marine...  相似文献   

煤层滑覆顶板水文地质工程地质特征     

牛志刚 《煤田地质与勘探》1992,20(1):47-49

豫西诸煤田主采煤层二₁煤层顶板非原生顶板,而是滑动构造的滑覆体。其由下而上可分为断层带、破碎带、裂隙带。它的水文地质条件简单,但工程地质条件复杂。岩石破碎,力学强度指标较低,回采中顶板不易管理。按其稳定性可分为较稳定的、不稳定的和极不稳定的三类,且以后两类为主,对这些顶板管理的基本措施是:短工作面,控顶距,快速推进,及时放顶,正常循环,不放大炮。   相似文献   

陆面面积平均通量的参数化问   总被引：5，自引：0，他引：5  

牛国跃  洪钟祥  孙菽芬  叶卓佳 《气候与环境研究》1997,2(3):210-221

目前,气候和大气边界层物理研究中一个十分重要的研究方向就是面积平均通量的参数化问题。本文对这一研究方向中存在的问题、可能的解决方法和目前的研究进展情况进行了阐述,简要介绍了非均匀陆面影响的高度及其尺度划分,阐述了混合高度、参考层高度（观测高度和模式第一层高度）、近地层高度、内边界层高度、平衡层高度、粗糙度副层和边界层高度等之间的关系及其在非均匀尺度划分中的作用,并且阐述了整体输送公式在不同尺度的非均匀陆面中存在的问题及相应的可能解决办法。同时还对中尺度的非均匀陆面驱动的一类非经典中尺度环流的参数化,即中尺度通量的参数化问题进行了评述。最后针对内蒙古草原实验和青藏高原实验等具体问题,提出了边界层观测和非均匀陆面参数化方法的几点问题。  相似文献   

黄河万家寨水库右岸岩溶渗漏问题   总被引：1，自引：1，他引：0  

方宗贤  李仲春  牛世豫  胡兴林  高玉生 《中国岩溶》1986,5(4):273-287

<正> 万家寨水库位于黄河北干流上游段,坝型为混凝土重力坝,坝高约90米,总库容约9.7亿立方米。从五十年代起直到八十年代初,几个单位对本工程曾相继进行了大量地质勘察工作,并对其作过初步设计。三十年来,各家一致认为万家寨水库不存在永久性岩溶渗漏。本文就此问题谈一点认识,不妥之处,欢迎批评指正。   相似文献   

论粗粒料的E-μ模型     

郭见杨  黄胜生  喻小生 《岩土力学》1983,4(1):17-24

本文在大三轴试验成果基础上,对在我国广泛采用的粗粒材料的E-μ模型存在的问题进行了分析。指出,模型中采用（σ1-σ3）f=R（σ1-σ3）ul的关系是多余的,反而给计算带来误差,模型中μi和σ3成半对数关系也不是唯一的。为了完善这个模型,作者建议了更适用的关系式。  相似文献   

自由网平差的经典方法及扩展应用     

牛卓立 《测绘工程》1999,8(4):40-43

采用经典的最小二乘参数平差结果为一个特解,进而以坐标系定位参数为参数求出自由网的最小范数解。之后,以若干工程实例列举了除变形监测网以外的扩展应用。  相似文献