一种基于时态密度的倾斜分布数据流聚类算法

为解决倾斜分布的数据流聚类这一难题,提出了时态密度概念,给出其度量,揭示了其包括可增量计算在内的一系列数学性质;设计了时态密度树结构,提高了聚类时的存储和检索效率;设计了能够以实时或异步方式捕捉数据倾斜分布的数据流时态特征的聚类算法TDCA(temporal density based clustering algorithm),其时间复杂度为O(c×m×lgm).实验结果表明,该算法不仅有较强的功能,而且具有较好的规模可伸缩性.

基于时态密度特征的改进数据流聚类算法

针对经典Clu Stream聚类算法的在线微簇聚类过程中限制微簇数量的增长,对微簇进行强制合并,使其在线聚类结果受到影响,导致数据流聚类质量不高,且难以适应海量大数据等问题,提出一种基于时态密度特征的改进Clu Stream聚类算法.首先,提出微簇时态密度的概念,并用其对微簇进行描述;其次,提出新的微簇删除、合并的机制,能够根据在线微簇的情况动态地添加微簇的数量;最后,应用并行化的框架将算法并行化,以适应海量实时大数据的需求.通过在人工数据集和真实数据集上的对比实验表明,改进后的数据流聚类算法相较于Clu Stream算法能够得到更高质量的聚类结果.

时态数据的变粒度分段存储策略及其效益分析

根据时态数据库用户对数据厚今薄古的需求特点，该文提出变粒度分段存储技术，将一个对象的历史分为３个时期，分介质、变粒度存储．文章讨论了分段存储的特殊数据结构、时代转移算法和压缩采样算法．基于微机实用参数的定量分析表明，这一技术将时态存储密度和时态查询速度提高了一个数量级.

基于仿射传播的进化数据流在线聚类算法

为提高数据流聚类的精度和时效性,提出一种具有时态特征与近邻传播思想的高效数据流聚类算法(TCAPStream).该算法利用改进的WAP将新检测到的类模式合并到聚类模型中,同时利用微簇时态密度表征数据流的时态演化特征,并提出在线动态删除机制对微簇进行维护,使算法模型既能体现数据流的时态特征,又能反映数据流的分布特性,得到更精确的聚类结果.实验结果表明,该算法在多个人工数据集和真实数据集上不仅具有良好的聚类效果,而且具有较好的伸缩性和可扩展性.

一种新的雷达信号实时分选方法

针对现有实时分选方法依赖滑动窗(单次处理脉冲数)的选取、分选效率低以及分选结果存在严重增批现象等缺陷,将脉冲串的接收视为数据流过程,从而设计了一种基于进化数据流聚类的雷达信号实时分选框架。该框架分为在线处理和离线分析两个阶段,通过引入时态密度特征避免了主观上对滑动窗长度的选取,并利用衰变检测和噪声点检测来提高在线聚类的效率。离线阶段通过对历史快照的分析可以判明雷达的活动情况,并将属于一部雷达的脉冲批组进行关联。仿真实验表明了该框架的有效性和可行性。

基于倾斜分布的变流速数据流聚类算法

处理倾斜分布特征的数据流聚类算法TDCA存在聚类速度与内存利用率上的不足,且变流速的数据流环境对聚类结果的质量有严重影响。针对上述问题,提出一种数据流聚类算法GR-Stream。采用网格单元作为数据点的聚集形式,以基于R-tree的扩展数据结构作为组织网格单元的索引结构,在此基础上引入剪枝策略,并调整数据点进入树的方式。在真实数据集KDD-CUP99上进行测试,结果表明,与TDCA算法相比,该算法在聚类过程中可以提高40%的访问速度,应用剪枝策略节省至少一半的内存使用量,同时在变流速的数据流环境下将聚类结果的平均纯度保持在90%以上。

Effects of Planting Density, Duration of Disclosing Plastic Film and Nitrogen Fertilization on the Growth Dynamics of Rapeseed under No-tillage Cultivation

[ Objective] This study was to understend the optimized combination of planting density, duration of disclosing plastic film and nitrogen fertilization under no-tillage cultivation. [ Method] Quadratic polynomial regression and saturated D-optimal design were employed to investigate the effects of planting density, duration of disclosing plastic film and nitrogen fertilization on the dynamics growth of rapeseed under no-tillage cultivation.[ Result] Within the experimental range, the growth dynamics of no-tillage cultivated rapeseed assumed a rise-fall tend. For the effects to the growth dynamics of no-tillage cultivated rapeseed, nitrogen application amount was higher than planting density and duration of disclosing plastic film. The interaction effect between planting density and duration of disclosing plastic film was higher than that between nitrogen application amount and planting density, and between nitrogen application amount and duration of disclosing plastic film. [ Conclusion] The optimized combination of these factors for dynamic growth of rapeseed under no-tillage cultivation was determined to be： planting density of per hectare 154 925 individuals, duration of disclosing plastic film of 110 d, nitrogen application amount of 315 kg/hm^2.

Experimental and Theoretical Investigation on Excited State Intramolecular Proton Transfer Coupled Charge Transfer Reaction of Baicalein

The excited state intramolecular proton transfer （ESIPT） coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the absorption peak from S1 excited state both in the experi-mental and calculated absorption spectra indicates that S1 is a dark state. The dark excited state S1 results in the very weak fluorescence of solid baicalein in the experiment. The fron- tier molecular orbital and the charge difference densities of baicalein show clearly that the S1 state is a charge-transfer state whereas the S2 state is a locally excited state. The only one stationary point on the potential energy profile of excited state suggests that the ESIPT reaction of baicalein is a barrierless process.

Hydrogen Bonding Effects on the Photophysical Properties of 2,3-dihydro-3-keto- 1H-pyrido[3,2,1-kl] phenothiazine

Time-dependent density functional theory （TDDFT） and femtosecond transient absorption spectroscopy were used to investigate the photophysical properties of 2,3-dihydro-3-keto-lH- pyrido[3,2,1-kl]phenothiazine （PTZ4） and 3-keto-lH-pyrido[3,2,1-kl]phenothiazine （PTZ5）. The calculated results obtained from TDDFT suggest that the red-shifts of the absorption spectra of these two fluorophores in methanol are due to the formation of hydrogen-bonded complexes at the ground state. Four conformers of PTZ4 were obtained by TDDFT. The two fluorescence peaks of PTZ4 in tetrahydrofuran （THF） came from the ICT states of the four conformers. The fluorescence of PTZ4 in THF showed a dependence on the excitation wavelength because of butterfly bending. The excited state dynamics of PTZ4 in THF and methanol were obtained by transient absorption spectroscopy. The lifetime of the excited PTZ4 in methanol was 53.8 ps, and its relaxation from the LE state to the ICT state was completed within several picoseconds. The short lifetime of excited PTZ4 in methanol was due to the formation of out-of-plane model hydrogen bonds between PTZ4 and methanol at the excited state.

Electronic and Transport Properties of Carbon Nanotubes with Impurities and Structure Disorder

Electron relaxation time and density of states near the Fermi level were calculated for ＂dirty＂ carbon nanotubes taking into account multiple elastic electrons scattering on impurities and structural inhomogeneities of a short-range order type. A possible explanation of low-temperature behavior of density of states and electrical conductivity depending on defect structure, impurities and chirality is presented.

Effect of Solvent Polarity on Excited-State Double Proton Transfer Process of 1,5-Dihydroxyanthraquinone

The excited-state double proton transfer(ESDPT)properties of 1,5-dihydroxyanthraquinone(1,5-DHAQ)in various solvents were investigated using femtosecond transient absorption spectroscopy and the DFT/TDDFT method.The steady-state fluorescence spectra in toluene,tetrahydrofuran(THF)and acetonitrile(ACN)solvents presented that the solvent polarity has an effect on the position of the ESDPT fluorescence emission peak for the 1,5-DHAQ system.Transient absorption spectra show that the increasing polarity of the solvent accelerates the rate of excited state dynamics.Calculated potential energy curves analysis further verified the experimental results.The ESDPT barrier decreases gradually with the increase of solvent polarity from toluene,THF to ACN solvent.It is convinced that the increase of solvent polarity can promote the occurrence of the ESDPT dynamic processes for the 1,5-DHAQ system.This work clarifies the mechanism of the influence of solvent polarity on the ESDPT process of 1,5-DHAQ,which provides novel ideas for design and synthesis of new hydroxyanthraquinone derivatives.

Quantitative conditions for time evolution in terms of the von Neumann equation

The adiabatic theorem describes the time evolution of the pure state and gives an adiabatic approximate solution to the Schrrdinger equation by choosing a single eigenstate of the Hamiltonian as the initial state. In quantum systems, states are divided into pure states （unite vectors） and mixed states （density matrices, i.e., positive operators with trace one）. Accordingly, mixed states have their own corresponding time evolution, which is described by the von Neumann equation. In this paper, we discuss the quantitative conditions for the time evolution of mixed states in terms of the von Neumann equation. First, we introduce the definitions for uniformly slowly evolving and δ-uniformly slowly evolving with respect to mixed states, then we present a necessary and sufficient condition for the Hamiltonian of the system to be uniformly slowly evolving and we obtain some upper bounds for the adiabatic approximate error. Lastly, we illustrate our results in an example.