Late Neogene radiolarian absence event in the southern South China Sea and its paleoceanographic implication

Down-core variations of radiolarians at ODP Site 1143 in the southern South China Sea （SCS） are presented for the last 12 Myr. The fluctuations of radiolarian abundances since the Late Miocene can be divided into three stages： a high abundance stage at 12-5.96 Myr, a radiolarian absent stage at 5.96-3.30 Myr and a gradual increasing stage after 3.30 Myr. The three stages correspond to the forming and vicissitudes of the Western Pacific Warm Pool （WPWP） and the Eastern Asian Summer Monsoon （EASM）. The radiolarian absence event （RAE） was also absent of diatom and occurred nearly simultaneously with the closures of the Panama Isthmus and the Indonesian seaway, which probably caused the reorganization of oceanic circulation systems. Accompanied this circulation reorganization was the weakening of the WPWP and the EASM, which probably led to a weakened upwelling in the southern SCS. In addition dissolved silica （Dsi） content in surface seawater might be very low during 5.96-3.30 Myr due to the ＂biogenic bloom＂ event, which consumed a large amount of Dsi in the surface seawater. All these factors together might lead to a great decrease of siliceous production in the southern SCS and consequently caused the RAE. Moreover, the dissolution of siliceous skeletons might also influence the abundance of radiolarians.     

Late Neogene radiolarian absence event in the southern South China Sea and its paleoceanographic implication

Down-core variations of radiolarians at ODP Site 1143 in the southern South China Sea (SCS) are presented for the last 12 Myr. The ?uctuations of radiolarian abundances since the Late Miocene can be divided into three stages: a high abundance stage at 12–5.96 Myr, a radiolarian absent stage at 5.96–3.30 Myr and a gradual increasing stage after 3.30 Myr. The three stages correspond to the forming and vicissitudes of the Western Paci?c Warm Pool (WPWP) and the Eastern Asian Summer Monsoon (EASM). The radiolarian absence event (RAE) was also absent of diatom and occurred nearly imultaneously with the closures of the Panama Isthmus and the Indonesian seaway, which probably caused the reorganization of oceanic circulation systems. Accompanied this circulation reorganization was the weakening of the WPWP and the EASM, which probably led to a weakened upwelling in the southern SCS. In addition dissolved silica (Dsi) content in surface seawater might be very low during 5.96–3.30 Myr due to the ‘‘biogenic bloom” event, which consumed a large amount of Dsi in the surface seawater. All these factors together might lead to a great decrease of siliceous production in the southern SCS and consequently caused the RAE. Moreover, the dissolution of siliceous skeletons might also in?uence the abundance of radiolarians.     

Energy transfer process between Eu3+ and wide-band-gap SnO2 nanocrystals in silica films studied by photoluminescence excitation and time-resolved photoluminescence techniques

Eu3+ions embedded in silica thin films codoped with SnO2 nanocrystals were fabricated by sol–gel and spin-coating methods.SnO2 nanocrystals with controllable sizes were synthesized through precisely controlling the Sn concentrations.The influences of doping and annealing conditions on the photoluminescence intensity from SnO2 nanocrystals are systematically investigated.The effective energy transfer from the defect states of SnO2nanocrystals to nearby Eu3+ions has revealed by the selective photoluminescence excitation spectra.The efficiency of the Forster resonance energy transfer is evaluated by the time-resolved photoluminescence measurements,which is about 29.1%based on the lifetime tests of the SnO2emission.     

1981—2000年内蒙古中部地区植被净初级生产量变化研究

基于AVHRR GLOPEM NPP数据集及相应时段的气候数据集,通过对逐个像元信息的提取与分析,研究了1981—2000年内蒙古中部地区植被净初级生产量退化的状况及其与气候变化的相关性。结果显示:1)该区植被净初级生产量的空间分布大致由东向西呈减少的趋势,年际变化比较明显,尤其是在1990—2000年,减少率达10.32gC/m2.a;2)1981—2000年,植被净初级生产量年际变化的区域差异比较明显;3)植被净初级生产量年际变化与气候因子年际变化的相关性存在比较明显的区域差异;4)不同植被类型对气候变化表现出不同的响应特征,该区降水量年际变化对植被的影响要高于气温年际变化对其的影响。本研究有助于了解内蒙古中部地区植被净初级生产量退化的状况以及影响其退化的气候因素,可为退化植被的生态修复提供有意义的参考。     

MEEMD-DBA-based short term traffic flow prediction

Aiming at the problem that ensemble empirical mode decomposition(EEMD) method can not completely neutralize the added noise in the decomposition process, which leads to poor reconstruction of decomposition results and low accuracy of traffic flow prediction, a traffic flow prediction model based on modified ensemble empirical mode decomposition(MEEMD), double-layer bidirectional long-short term memory(DBiLSTM) and attention mechanism is proposed. Firstly, the intrinsic mode functions(IMFs) and r...     

基于约束跟随理论的消防无人机水枪喷嘴跟踪控制

利用无人机（Unmanned Aerial Vehicle，UAV）参与灭火是解决城市高层建筑消防问题的一种有效手段.针对无人机云台运动的控制问题，提出一种基于约束跟随理论的云台水枪喷嘴跟踪控制策略.根据高层建筑实际灭火需求，设计了云台水枪喷嘴两自由度驱动结构，采用Denavit-Hartenberg（D-H）方法对云台系统进行建模并由此完成云台运动学方程的建立.根据拉格朗日方程构建云台无约束动力学模型，把云台水枪喷嘴的期望轨迹作为约束，在不引入诸如拉格朗日乘数等任何变量或伪变量的情况下，基于Udwadia-Kalaba方程得到可以满足约束跟随需要的驱动转矩解析式，实现状态连续反馈控制，以达到水枪喷嘴轨迹跟踪的目的.为了减小跟踪误差，采用 Baumgarte 约束违约法进行稳定性处理，并在MATLAB/Simulink环境下对其轨迹跟踪控制进行仿真. 搭建以数字信号处理器（Digital Signal Processor， DSP）为控制核心的实验平台进行轨迹跟踪控制实验.仿真和实验结果表明，基于约束跟随理论的轨迹跟踪控制算法能够有效地完成跟踪任务并实现对期望轨迹的高精度跟踪.     

A hint from phosphine complex: The π back-bonding in cobalt-phosphorene composite enables enhanced electrocatalytic performance

Regulating the electronic structure of the metal electrocatalyst is fundamental for its performance optimizing. The electronic states of the active metal centers are highly dependent on their coordination environment, especially when bonding is formed. The π back-bonding can induce great electron density redistribution around metals, yet it is barely applied in electrocatalyst design. Herein we electrodeposited metallic cobalt on black phosphorus(BP)nanosheets, forming BP-Co with a unique π back...     

The effect of surface-free energy and microstructure on the condensation mechanism of water vapor

Obtaining high-water-yield drinking water in arid areas without consuming energy is still a global challenge.Since water vapor is ubiquitous, atmospheric water harvesting technologies are undoubtedly one of the most promising candidates. A typical water condensation process is analyzed in this paper(nucleation, self-growth,coalescence and sliding). The mechanisms of interactions between adsorbate and water vapor are discussed.The effect of surface-free energy and microstructure on water vapor co...