顾及轨道误差BDS/GPS实时钟差融合估计的观测权函数设计

实时钟差产品是高精度广域差分位置服务(亚米级、分米级、厘米级)的基础产品,本文针对BDS/GPS轨道精度差异,设计了一种顾及轨道精度差异观测权函数,优化了实时钟差估计的随机模型,在此基础上基于非差法实现了BDS/GPS联合的实时钟差估计。采用MGEX和iGMAS跟踪站的实时观测数据进行实时钟差解算,并与iGMAS产品综合中心提供的事后精密钟差产品进行了比较分析。结果表明:基于该方法估计的钟差精度对单GPS、单BDS和BDS/GPS融合都有提高,其中BDS钟差精度整体较GPS更为显著,提高幅度约12.8%,其中IGSO/MEO更为突出,提高幅度约20%,验证了方法的有效性。     

陆态网测站高精度解算分区方案

中国大陆构造环境监测网络由260个连续全球定位系统观测站点和2 000个不定期全球定位系统观测站点构成,一般采用GAMIT或Bernese高精度数据处理软件进行处理。由于GAMIT及Bernese软件对测站数处理能力的限制,必须对陆态网连续运行基准站进行分区解算。针对这一问题,为研究不同分区方案对陆态网解算精度的影响,该文基于全国55个陆态网络连续运行基准站数据,采用整网解算方案以及间距分区法和区域子网划分法分别进行解算,并以整网解算结果作为标准值,对比两种分区方案与整网解算方案的基线长度差及坐标差。结果表明,间距分区方案解算精度比区域子网划分方案精度高,可实现对陆态网分区的高精度解算。最后利用间距分区法对全国240个陆态网络连续运行基准站进行分区解算,得到了较高精度的解算结果。     

青岛湾有机质污染带小型底栖生物群落的研究

本文是1990年6月至10月,对青岛湾东侧有机质污染潮间带的小型底栖动物群落的研究结果。结果指出海洋线虫与多毛类小头虫的数量消长完全一致,它们保持着共栖或互利的共生关系。共鉴定出海洋线虫20种,其中6种占总丰度的90％。依据种类组成计算的Simpsion和Shannon-Wiener多样性指数,以及线虫与桡足类、小头虫与其他多毛类的数量比值指明,该有机质污染带正向着半污染带过渡。     

Verification of a VOF-based two-phase flow model for wave breaking and wave–structure interactions

The objective of the present study is to develop a volume of fluid (VOF)-based two-phase flow model and to discuss the applicability of the model to the simulation of wave–structure interactions. First, an overview of the development of VOF-type models for applications in the field of coastal engineering is presented. The numerical VOF-based two-phase flow model has been developed and applied to the simulations of wave interactions with a submerged breakwater as well as of wave breaking on a slope. Numerical results are then compared with laboratory experimental data in order to verify the applicability of the numerical model to the simulations of complex interactions of waves and permeable coastal structures, including the effects of wave breaking. It is concluded that the two-phase flow model with the aid of the advanced VOF technique can provide with acceptably accurate numerical results on the route to practical purposes.     

An efficient finite–discrete element method for quasi‐static nonlinear soil–structure interaction problems

An efficient finite–discrete element method applicable for the analysis of quasi‐static nonlinear soil–structure interaction problems involving large deformations in three‐dimensional space was presented in this paper. The present method differs from previous approaches in that the use of very fine mesh and small time steps was not needed to stabilize the calculation. The domain involving the large displacement was modeled using discrete elements, whereas the rest of the domain was modeled using finite elements. Forces acting on the discrete and finite elements were related by introducing interface elements at the boundary of the two domains. To improve the stability of the developed method, we used explicit time integration with different damping schemes applied to each domain to relax the system and to reach stability condition. With appropriate damping schemes, a relatively coarse finite element mesh can be used, resulting in significant savings in the computation time. The proposed algorithm was validated using three different benchmark problems, and the numerical results were compared with existing analytical and numerical solutions. The algorithm performance in solving practical soil–structure interaction problems was also investigated by simulating a large‐scale soft ground tunneling problem involving soil loss near an existing lining. Copyright © 2011 John Wiley & Sons, Ltd.     

Simulating the spatial diffusion of memes on social media networks

This article reports the findings from simulating the spatial diffusion processes of memes over social media networks by using the approach of agent-based modeling. Different from other studies, this article examines how space and distance affect the diffusion of memes. Simulations were carried out to emulate and to allow assessment of the different levels of efficiency that memes spread spatially and temporally. Analyzed network structures include random networks and preferential attachment networks. Simulated spatial processes for meme diffusion include independent cascade models and linear threshold models. Both simulated and real-world social networks were used in the analysis. Findings indicate that the numbers of information sources and opinion leaders affect the processes of meme diffusion. In addition, geography is still important in the processes of spatial diffusion of memes over social media networks.     

Hydrological alterations from water infrastructure development in the Mekong floodplains

The Mekong floodplains, which encompasses the region from Kratie Township in Central Cambodia to the Vietnamese East Sea, is a region of globally renown agricultural productivity and biodiversity. The construction of 135 dams across the Mekong basin and the development of delta‐based flood prevention systems have caused public concern given possible threats on the stability of agricultural and ecological systems in the floodplains. Mekong dams store water upstream and regulate flow seasonality, while in situ flood prevention systems re‐distribute water retention capacity in the floodplains. The main aim of this paper is to evaluate possible impacts of the recent development of both hydropower dams and flood prevention systems on hydrological regimes in the Mekong floodplains. An analysis of measured daily and hourly water level data for key stations in the Mekong floodplains from Kratie to the river mouth in Vietnam was conducted. Hydropower dam information was obtained from the hydropower database managed by the Mekong River Commission, and the MODIS satellite imagery was used to detect changes in flooding extent related to the operation of flood prevention systems in the Vietnam Mekong Delta. Results indicate that the upper part of the floodplains, the Cambodian floodplains, may buffer upstream dam impacts to the Vietnam Mekong Delta. Flood prevention up to date has had the greatest effect on the natural hydrological regime of the Mekong floodplains, evidenced by a significant increase of water level rise and fall rates in the upper delta and causing water levels in the middle delta to increase. The development of flood prevention systems has also effected spatial distribution of flooding as indicated via a time series analysis of satellite imagery. While this development leads to increase localized agricultural productivity, our historical data analysis indicates that development of one region detrimentally affects other regions within the delta, which could increase the risk of future conflicts among regions, economic sectors and the ecological value of these important floodplains. Copyright © 2016 John Wiley & Sons, Ltd.     

Participants’ livelihoods compatible with conservation programs: evidence from China’s grain-for-green program in northern Shaanxi Province

GeoJournal - As the largest conservation program and payments for ecosystem services in China, the grain-for-green program (GGP) has substantially changed land use and cover, and reduced soil...     

1996~2017年枯水期地下水排泄对洞庭湖水量均衡的贡献及其时间变异性

地下水排泄在湖泊水量及营养盐均衡中发挥着重要作用,其中地下水向湖泊排泄的量化是关键,但目前对其时间变异性的研究却十分薄弱.针对这一科学问题,以长江中游重要调蓄湖泊-洞庭湖为例,通过收集1996~2017年洞庭湖流域的水文和气象数据,基于质量平衡模型,查明地下水排泄对洞庭湖水量均衡的贡献以及地下水向洞庭湖排泄强度随时间的变化.结果显示:（1）枯水期时地下水排泄量为（0.17~1.51）亿m3/d,地下水排泄强度为38.74~207.26 mm/d,地下水排泄对湖泊水量均衡的贡献为8.70%~30.37%;（2）地下水排泄量、地下水排泄强度、地下水排泄对湖泊水量均衡的贡献在1996~2017年间均呈现出明显的先降低再升高的变化趋势,三峡水库蓄水后至三峡工程全面竣工初期的地下水排泄相较于三峡水库蓄水前和三峡工程全面运行后显著降低;（3）三峡工程运行对长江水位及地下水位的改变可能是引起湖底地下水排泄时间变异性的重要原因.为洞庭湖区域的水量均衡提供了新的认识,也为今后洞庭湖区域水资源开发利用和区域生态安全管理提供了理论支撑.      

近53年石家庄地区气温稳定通过10℃的农业气候资源变化特征

以17个气象站1960—2012年的观测资料,利用趋势分析, Mann Kendall检验,Morlet小波分析等方法,分析了石家庄地区气温稳定通过10 ℃的农业气候资源变化特征,结果表明：近53年气温稳定通过10 ℃的初日以14 d/10a的趋势提前,终日以1.1 d/10a的趋势后延,持续日数以2.5 d/10a的趋势增加,积温以64.5 ℃〖DK〗·d/10a的趋势增加,降水量无明显变化,日照时数以53.4 h/10a的趋势减少;各要素的时间序列除降水外均存在不同程度的突变,终日、持续日数、积温以及日照时数的突变较为显著,终日在2007年后后延显著,持续日数在1998年后显著增多,积温在2000年后显著增加,日照时数在1993年后显著减少;通过Morlet小波分析发现,各要素在近53年中存在周期性变化规律,初日和期间积温存在准2～4年的振荡周期,终日存在准2～3年的振荡周期,持续日数存在准2年的振荡周期。降水量存在准3年和准3～7年的振荡周期,日照时数存在准2～3年的振荡周期。石家庄地区气温稳定通过10 ℃的农业气候资源变化使作物的生长发育提前,生长周期变短,日照时数减少对作物生长有一定的不利影响。