Time synchronization is one of the important aspects in wireless sensor networks. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. There are various applicati...Time synchronization is one of the important aspects in wireless sensor networks. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. There are various applications such as seismic study, military applications, pollution monitoring where sensor nodes require synchronized time. Time synchronization is mandatory for many wireless sensor networks protocols such as MAC protocols and also important for TDMA scheduling for proper duty cycle coordination. Time synchronization is a stimulating problem in wireless sensor networks because each node has its own local clock which keeps on varying due to variation in the oscillator frequency. The oscillator frequency is time varying due to ambient conditions which leads to re-synchronization of nodes time and again. This re-synchronization process is energy consuming whereas energy is constraints in WSN. This paper proposes a novel cluster based time synchronization technique for wireless sensor networks in which cluster head rotation is based on minimum clock offset. Simulation results based on energy analysis of the proposed model demonstrate that proposed novel cluster based time synchronization technique reduces the energy consumption and also the synchronization error compared with other existing protocols.展开更多
针对传统聚类算法存在样本形状及孤立点敏感的问题,提出基于修剪树的优化聚类中心(Optimized Clustering Center Based on Trimmed Tree,OCT)算法.该算法自适应地寻找裁剪尺寸来修剪并分割最小生成树为森林,获取森林全部叶子结点并再次...针对传统聚类算法存在样本形状及孤立点敏感的问题,提出基于修剪树的优化聚类中心(Optimized Clustering Center Based on Trimmed Tree,OCT)算法.该算法自适应地寻找裁剪尺寸来修剪并分割最小生成树为森林,获取森林全部叶子结点并再次构造最小生成树,根据预设簇数n,修剪最小生成树的n-1条最长边,得到包含n棵树的森林,计算森林中每棵树的质心并将其置为初始类簇聚类中心.在仿真数据集和真实数据集上的测试结果表明,OTC算法的平均识别率分别为98.8%和95.7%,平均耗时为57 ms和10.53 ms.展开更多
土地利用、土地利用变化和林业(LULUCF)关联的碳问题是影响适应和减缓气候变化的重要问题。厘清近20年来LULUCF涉及林业碳科学的国际研究进展,对作好响应气候变化的林业政策制定及调整具有重要意义。本文应用CiteSpace分析工具,以Web of...土地利用、土地利用变化和林业(LULUCF)关联的碳问题是影响适应和减缓气候变化的重要问题。厘清近20年来LULUCF涉及林业碳科学的国际研究进展,对作好响应气候变化的林业政策制定及调整具有重要意义。本文应用CiteSpace分析工具,以Web of Science数据库1999—2018年的175篇文献为研究对象,运用知识图谱分析,归纳了LULUCF林业碳问题的研究趋势。结果表明:①'制度和方法的改进''林业管理行为'和'环境目标'3大类群是当前LULUCF的研究主题。②德国、意大利、英国和美国是研究LULUCF的主要国家,分别侧重于研究毁林、林业项目、经济成本问题和部门响应机制。③LULUCF社会科学的研究重点是土地利用管理、政策制度的响应机制和减缓气候变化的信贷等经济调节杠杆问题,主要方法是以情景分析法和一般均衡模型为代表的工程管理学与经济学方法。本文对于中国LULUCF未来的研究提供了相关建议:完善LULUCF碳核算基础方法和土地利用及动态变化监测的理论及手段,重视林业管理项目的科学评估及其对林业政策调整的指导作用,加快推进LULUCF碳预算及土地利用部门针对减排方案的制订。展开更多
文摘Time synchronization is one of the important aspects in wireless sensor networks. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. There are various applications such as seismic study, military applications, pollution monitoring where sensor nodes require synchronized time. Time synchronization is mandatory for many wireless sensor networks protocols such as MAC protocols and also important for TDMA scheduling for proper duty cycle coordination. Time synchronization is a stimulating problem in wireless sensor networks because each node has its own local clock which keeps on varying due to variation in the oscillator frequency. The oscillator frequency is time varying due to ambient conditions which leads to re-synchronization of nodes time and again. This re-synchronization process is energy consuming whereas energy is constraints in WSN. This paper proposes a novel cluster based time synchronization technique for wireless sensor networks in which cluster head rotation is based on minimum clock offset. Simulation results based on energy analysis of the proposed model demonstrate that proposed novel cluster based time synchronization technique reduces the energy consumption and also the synchronization error compared with other existing protocols.
文摘针对传统聚类算法存在样本形状及孤立点敏感的问题,提出基于修剪树的优化聚类中心(Optimized Clustering Center Based on Trimmed Tree,OCT)算法.该算法自适应地寻找裁剪尺寸来修剪并分割最小生成树为森林,获取森林全部叶子结点并再次构造最小生成树,根据预设簇数n,修剪最小生成树的n-1条最长边,得到包含n棵树的森林,计算森林中每棵树的质心并将其置为初始类簇聚类中心.在仿真数据集和真实数据集上的测试结果表明,OTC算法的平均识别率分别为98.8%和95.7%,平均耗时为57 ms和10.53 ms.
文摘高精度、高分辨率的地形地貌数据是活动构造定量研究的重要基础数据。传统研究方法中,通过航卫片或遥感影像解译只能获取二维平面特征,中等分辨率DEM(5~10m网格单元)只适用于大尺度三维地貌特征的提取。激光雷达测量(Light Detection and Ranging,LiDAR)技术可直接对地貌进行高精度、全方位的三维地表形态测量,为活动构造研究提供了精细的地貌形态数据,有助于深化对断裂带地表破裂过程和断裂活动特性的理解。文中选取青藏高原东北缘香山-天景山断裂带西段的景泰小红山断裂中一段断错地貌明显的断裂段作为研究对象,基于高精度LiDAR数据生成了景泰小红山断裂0.3m高分辨率的数字高程模型(DEM),沿断裂带详细识别并测量了地貌标志(冲沟、山脊和阶地)的断错位移,获得了地貌标志的82个水平位移和62个垂直位移,并分析了不同方向上的位移丛集特征。结果显示,沿断裂的水平与垂直位移均可识别出5个丛集,其中最小丛集可能指示最新一次地震的同震位移,而其它位移丛集则反映了断裂带多次地震活动累积的结果。通过对多个断错标志的水平和垂直位移合成的滑动矢量进行分析,可以看出该断层段的运动习性具有分段不均匀特征,不同段落的倾滑矢量有一定的差异。
文摘土地利用、土地利用变化和林业(LULUCF)关联的碳问题是影响适应和减缓气候变化的重要问题。厘清近20年来LULUCF涉及林业碳科学的国际研究进展,对作好响应气候变化的林业政策制定及调整具有重要意义。本文应用CiteSpace分析工具,以Web of Science数据库1999—2018年的175篇文献为研究对象,运用知识图谱分析,归纳了LULUCF林业碳问题的研究趋势。结果表明:①'制度和方法的改进''林业管理行为'和'环境目标'3大类群是当前LULUCF的研究主题。②德国、意大利、英国和美国是研究LULUCF的主要国家,分别侧重于研究毁林、林业项目、经济成本问题和部门响应机制。③LULUCF社会科学的研究重点是土地利用管理、政策制度的响应机制和减缓气候变化的信贷等经济调节杠杆问题,主要方法是以情景分析法和一般均衡模型为代表的工程管理学与经济学方法。本文对于中国LULUCF未来的研究提供了相关建议:完善LULUCF碳核算基础方法和土地利用及动态变化监测的理论及手段,重视林业管理项目的科学评估及其对林业政策调整的指导作用,加快推进LULUCF碳预算及土地利用部门针对减排方案的制订。
