A high-resolution environmental change record since 19 cal ka BP in Pumoyum Co,southern Tibet

A 380-cm-long sediment core was acquired from the deep water area of Pumoyum Co, southern Tibet. Twenty-five plant residue samples were selected, and organic carbon stable isotopes were obtained using the AMS ¹⁴C chronological method. The ¹⁴C age and carbon reservoir effect were calibrated with surface sedimentation rate measurements using ²¹⁰Pb dating. Results showed that the core sediment deposited over 19 cal ka BP. Based on a multi-proxy analysis of TOC and IC contents, grain size and pollen assemblage data, the palaeoclimatic evolution of Pumoyum Co was reconstructed since the last glacial. Pumoyum Co was a shallow lake prior to 16.2 cal ka BP; although the glacier around the lake began to melt due to increasing temperatures, climate was still cold and dry. In the interval of 16.2–11.8 cal ka BP, the sedimentary environment fluctuated drastically and frequently. Two cold-events occurred at 14.2 and 11.8 cal ka BP, and these may correspond to the Older Dryas and the Younger Dryas events, respectively. After 11.8 cal ka BP, Pumoyun Co developed into the deep lake as it is now. The lake water temperature was relatively lower at that time because of influx of cold water from glacial meltwater entering the lake. As a result, the multi-proxy indicators showed no sign of warm conditions. Comparisons between the sedimentary record of Pumoyum Co with that of other lakes of the same age in southern Tibet indicate a warmer climate following the last deglaciation influenced the southeastern Tibetan Plateau. These results imply that the southwest Asian monsoon gradually became stronger since the deglaciation during its expansion to the inner plateau. The glacial-supplied water of the lake responded sensitively to cold-events. The entire southern Tibet region was dominantly influenced climatically by the southwest Asian monsoon during the Holocene.     

基于粒计算的商业数据流概念漂移特征选择

商业数据流具有动态性、漂移性等特性,概念漂移特征选择是数据流挖掘的重要工作之一.本文从数据流的特点和概念漂移特性出发,提出了数据流的概念形式化分析流程和基于粒计算构建数据流的概念形式化描述模型;商业数据流的概念漂移实际上取决于其概念外延的变化,文中使用包括外延偶合度和内涵偶合度在内的概念偶合度来描述概念间的相似性;经过粒化的数据流由概念格来表示,进而通过概念格对的松弛偶合度来分析数据流特征;结合概念偶合分析和数据流变化特征,阐述了一种基于数据流概念格对的松弛匹配偶合度算法,并据此分析概念格对来选择数据流的漂移特征.通过实例验证、评价了特征选择,证明其有效性.     

捷联惯导用挠性陀螺静态漂移误差建模

运用极轴翻滚试验,研究了捷联惯导系统使用的动力调谐式挠性陀螺的静态漂移误差的建模方法。仿真分析和试验验证表明,本方法具有建模准确、估计参数较多,对试验数据异常值不敏感等优点,具有较强的实用性。     

大兴安岭北端地形因子对针叶林土壤黑碳储量的影响

[目的]气候变化对人类社会发展产生的影响受到了世界各国的广泛关注,提高森林生态系统的固碳潜力被认为是经济可行且有效减缓大气二氧化碳(CO2)浓度的重要途径之一,大兴安岭地区森林生态系统的黑碳储量在全球碳循环和碳汇方面具有重要的作用.研究大兴安岭不同地形因子条件下土壤黑碳的储藏分布特征,为区域森林土壤黑碳储量准确估算和森...     

参数H＞1/2分式布朗运动的随机微分方程的弱解

讨论了赫尔斯特参数H＞1/2的一个可加分式布朗运动,其中漂移系数不连续的随机微分方程弱解的存在性,并根据分式布朗运动条件下的Girsanov定理证明了这个结果.     

热-力-电耦合下天线罩电性能仿真及分析

在实际飞行工况下,热力载荷会改变高速飞行器天线罩原有的电磁特性,从而影响制导性能。提出了一种基于六面体网格划分的热-力-电耦合模型及仿真方法,可准确表征高速飞行工况下天线罩介电温漂和结构变形对电性能的影响。基于天线罩热-力-电共享网格模型,首先通过瞬态热仿真得到天线罩响应温度场,通过静力分析得到天线罩结构变形场。然后,将天线罩介电温漂和结构变形准确传递到其电磁仿真模型中,并采用三维射线跟踪法计算其电性能。最后通过一个典型算例对高速飞行工况下天线罩电性能的变化进行仿真和分析,结果表明电性能变化非常明显,也进一步说明了所提方法的可行性和研究的必要性。     

灰色广义Verhulst模型的构建及其应用

一般认为,灰色Verhulst模型(grey verhulst model,简称GVM)适用于具有单峰或饱和S形的序列.然而,在利用GVM建模时,模拟值有时会出现"漂移"现象,使得模型精度变差.针对这一问题,将常数项引入GVM模型,构建了灰色广义Verhulst模型(grey generalized verhulst model,简称GGVM),并在参数的不同分类下,借助灰色建模序列的非负性,完整地给出了灰色广义Verhulst模型的时间响应式及其还原值.将GGVM与GVM模型分别对四个单峰型序列建模,发现GGVM能有效地解决GVM模型模拟值出现的“漂移”现象.在实证部分,利用新模型对江苏省石油与天然气的基础储量进行建模分析,并与GVM模型、数据分组处理算法比较,验证了GGVM在模拟及预测时的优势.     

磁盘表面形貌对润滑剂分布及磁头／磁盘之间润滑剂转移的影响

磁盘表层润滑剂在磁头与磁盘之间转移会影响磁头飞行的稳定性．本文采用改进后的粗粒珠簧模型,运用分子动力学方法,研究了磁盘上类金刚石薄膜（diamondlikecarbon,DLC）层粗糙度和磁盘表面凸起对润滑剂在磁盘表面分布及磁头／磁盘之间润滑剂转移的影响．研究结果表明,DLC层粗糙度对润滑膜平均厚度及磁盘表层粗糙度的影响很小;磁盘表面凸起对磁盘表层润滑剂分布的影响明显．类金刚石薄膜层的粗糙度和磁盘表层凸起均可增加转移到磁头上的润滑剂的体积．但磁盘表层粗糙度对磁头／磁盘之间润滑剂转移量的影响明显低于由磁盘表层凸起导致的磁头／磁盘之间润滑剂的转移量．     

全息光栅干涉法测量曲面形貌的理论研究

基于光栅原理，提出一种可用于任意曲面形貌测量的全息光栅干涉的新方法，给出了光学原理实验系统，系统中采用氦氖激光为光源，反射型柱面全息衍射光栅为标准器，并用计算机软、硬件对光栅信号进行细分处理．实验表明，系统可获得较宽的动态范围和较高的分辨率，可用于测量曲面形貌．