The outbreak of Yantze vole ( Microtus fortis) population in Dongting Lake region is closely related to the evolvement of lake beaches,because the deposition of lake sediments results in the expansion of lake beaches,...The outbreak of Yantze vole ( Microtus fortis) population in Dongting Lake region is closely related to the evolvement of lake beaches,because the deposition of lake sediments results in the expansion of lake beaches,which provides the possibility of the increase of the vole's population. Reclaiming farmland from lake via building cofferdams,eliminating snails by building cofferdams for eradicating schistosomiasis,and over-hunting predators in the region cause the voles becoming a pest after the 1970s. In recent years,the Three Gorges Project and the conversion from farmland into lake have had deep impacts on the environment in the lake region. The dispatching of the down flow rate by the project has induced the expansion of the low and medium level beaches in the lake region,while converting farmland into lake directly has induced the expansion of the lake beaches,both of which have expanded the potential habitats of the vole's population. Therefore,more attention should be paid to the quantitative variation trend of the vole's population in the future.展开更多
In the paper, Ding projective modules and Ding projective complexes are considered. In particular, it is proven that Ding projective complexes are precisely the complexes X for which each Xm is a Ding projective R-mod...In the paper, Ding projective modules and Ding projective complexes are considered. In particular, it is proven that Ding projective complexes are precisely the complexes X for which each Xm is a Ding projective R-module for all m ∈ Z.展开更多
基金Supported by the National Natural Science Foundation(30870402,31170396)Key Knowledge Innovation Project of Chinese Academy of Sciences(KSCX-EW-N-05)
文摘The outbreak of Yantze vole ( Microtus fortis) population in Dongting Lake region is closely related to the evolvement of lake beaches,because the deposition of lake sediments results in the expansion of lake beaches,which provides the possibility of the increase of the vole's population. Reclaiming farmland from lake via building cofferdams,eliminating snails by building cofferdams for eradicating schistosomiasis,and over-hunting predators in the region cause the voles becoming a pest after the 1970s. In recent years,the Three Gorges Project and the conversion from farmland into lake have had deep impacts on the environment in the lake region. The dispatching of the down flow rate by the project has induced the expansion of the low and medium level beaches in the lake region,while converting farmland into lake directly has induced the expansion of the lake beaches,both of which have expanded the potential habitats of the vole's population. Therefore,more attention should be paid to the quantitative variation trend of the vole's population in the future.
基金Supported by National Natural Science Foundation of China(Grant Nos.11561039 and 11761045)Natural Science Foundation of Gansu Province of China(Grant No.17JR5RA091)
文摘In the paper, Ding projective modules and Ding projective complexes are considered. In particular, it is proven that Ding projective complexes are precisely the complexes X for which each Xm is a Ding projective R-module for all m ∈ Z.
文摘修正极坐标表示(Modified Polar Representation,MPR)实现了近场定位与远场测向模型的统一表达,克服了定位或测向对目标距离先验信息的依赖,巧妙地规避了传统坐标系下因远场距离模糊及距离-角度相互耦合导致的定位精度下降.然而现有MPR定位方法存在性能和稳健性不足、边界条件不清晰等问题,无法满足工程应用的实际需求.本文从子空间的角度着手以求解MPR下的时差(Time Difference Of Arrival,TDOA)定位问题,将角度和逆距离的估计分离到两个正交的空间,从而提高算法性能和稳健性.首先利用零空间投影消除逆距离以求解角度的最优估计,然后再代回原方程求解逆距离.在求解逆距离估计时,考虑角度估计误差使得矩阵出现秩亏,可通过向矩阵非零特征值对应的子空间投影解决秩亏的问题,再由加权最小二乘直接求得逆距离的最优估计.与现有研究中最优闭式解广义信赖域子问题(Generalized Trust Region Sub-problem,GTRS)相比,分析和仿真实验都证实所提算法具有更好的性能和大噪声场景下的稳健性.本文还分析了包括所提算法在内的现有基于MPR的TDOA定位算法的局限性,明确了不同算法对最小传感器数量和适用场景的的要求,为工程中算法的选择提供参考.
