结合时间相关度与课程搭配度的课程推荐方法

针对现有课程推荐系统存在过度依赖用户对课程的评分、未考虑用户兴趣随时间变化以及忽略了用户已学课程和推荐课程之间的搭配问题,提出一种基于时间相关度与课程搭配度的TIMR课程推荐模型。TIMR模型一方面采用课程观看进度代替课程评分,并将时间相关度函数应用于课程间的相似度计算;另一方面利用课程的共同被选频率,构建课程搭配度函数;然后将时间相关度与课程搭配度融合起来产生预测评分。为了验证TIMR模型的有效性,分别在TM数据集、CN数据集和MOOC数据集进行实验。实验表明,与现有推荐方法UserCF、ItemCF、LFM、PR、MPR、SMCR相比,TIMR在Precision、Recall、F1_score指标上均有明显提升,对于提高推荐质量具有明显的优势。

一种基于时间相关度的盲分离方法

本文从信号的相关性出发,提出信号时间相关度的定义,并证明了时间相关度定义具有如下性质:一组独立源信号的线性混合信号其时间相关度介于源信号中时间相关度的最小值和最大值之间。本文根据这一定义及性质,利用矩阵广义特征值理论,建立时间相关度的广义特征值问题,通过求解此广义特征值问题的特征矢量,从而达到分离信号的目的。本文算法适用于瞬时混合模型,仿真结果证明本算法可以应用与灰度图像的分离及复杂混合环境中声音的分离,计算简单,性能良好,效果真实可靠。

基于时间相关度和覆盖权重的协同过滤推荐算法

基于物品的协同过滤(IBCF)在计算相似度和预测评分时为所有物品分配相同的权重,提供的推荐往往不能同时具有良好的预测精度和分类精度。因此,文中提出基于时间相关度和覆盖权重的协同过滤算法(TCWCF)。将时间相关度函数应用于物品间的相似度计算,提高推荐的预测精度。同时构建覆盖度函数,融入预测评分阶段,提高推荐的分类精度。在MovieLens数据集上的实验表明,TCWCF性能优于IBCF和其它相关算法,可以同时为目标用户提供具有良好预测精度和分类精度的满意推荐。

基于事件-时间关联模型的话题跟踪研究

针对话题跟踪的任务是从时序新闻报道流中实时识别和挖掘相关于特定新闻话题的报道,本文提出一种事件-时间关联模型(EventTime Relation Model,ETRM)用来展开话题跟踪研究。ETRM将相关报道的时间属性引入向量空间模型,话题跟踪过程中将话题与相关报道相同特征项的时间相关度应用于相关性判定机制,同时基于时间的分布属性调整特征向量的权重分配,实现话题模型的自适应学习更新。实验采用DET曲线评测系统性能,结果显示相比于传统的话题模型,ETRM能够更加准确地追踪到话题焦点演化趋势,有效提高了话题跟踪系统的性能。

Probabilistic durability assessment approach of deteriorating RC bridges

A stochastic finite element computational methodology for probabilistic durability assessment of deteriorating reinforced concrete（RC） bridges by considering the time-and space-dependent variabilities is presented.First,finite element analysis with a smeared cracking approach is implemented.The time-dependent bond-slip relationship between steel and concrete,and the stress-strain relationship of corroded steel bars are considered.Secondly,a stochastic finite element-based computational framework for reliability assessment of deteriorating RC bridges is proposed.The spatial and temporal variability of several parameters affecting the reliability of RC bridges is considered.Based on the data reported by several researchers and from field investigations,the Monte Carlo simulation is used to account for the uncertainties in various parameters,including local and general corrosion in rebars,concrete cover depth,surface chloride concentration,chloride diffusion coefficient,and corrosion rate.Finally,the proposed probabilistic durability assessment approach and framework are applied to evaluate the time-dependent reliability of a girder of a RC bridge located on the Tianjin Binhai New Area in China.

MULTIVARIATE ABSOLUTE DEGREE OF GREY INCIDENCE BASED ON DISTRIBUTION CHARACTERISTICS OF POINTS

The analysis result of absolute degree of grey incidence for multivariate time series is often inconsistent with the qualitative analysis. To overcome this shortage, a multivariate absolute degree of grey incidence based on distribution characteristics of points is proposed. Based on the geometric description of multivariate time se- ries, the neighborhood extrema are extracted in the different regions, and a characteristic point set is constructed. Then according to the distribution of the characteristic point set, a characteristic point sequence reflecting the ge- ometric features of multivariate time series is obtained. The incidence analysis between multivariate time series is transformed into the relational analysis between characteristic point sequences, and a grey incidence model is established. The model possesses the properties of translational invariance, transpose and rank transform invari- ance, and satisfies the grey incidence analysis axioms. Finally, two cases are studied and the results prove the ef- fectiveness of the model.

Stochastic Resonance in a Bacterium Growth System Subjected to Colored Noises

We present the logistic growth model to study the stochastic resonance （SR） in a bacterium growth system under the simultaneous action of two external multiplicative cross-correlation noises and periodic external forcing. The expression of the signal-to-noise ratio （SNR） for a bacterium growth system is derived by using the theory of SNR in the adiabatic limit. Based on SNR, we discuss the effects of self-correlation time τ1 and τ2, cross-correlation time 3-3 and cross-correlation strength λ on the SNR. It is found that the self-correlation time τ1 and τ2, and cross-correlation strength λ enhance the SR of the bacterium growth system, while cross-correlation time τ3 weakens the SR of the bacterium growth system.

Oscillation in frequency of tropical cyclones passing Taiwan and Hainan Islands and the relationship with summer monsoon

The temporal variations in the frequency of tropical cyclones (TCs) traversing the Taiwan and Hainan Islands (TH islands), were analyzed using a best-track TC dataset from the Joint Typhoon Warning Center for the period 1945-2007. Results show that the oscillations were interannual and interdecadal on the timescales of 2-8 and 8-12 years, respectively. It is also shown that the number of TCs formed in the western North Pacific basin (WNP) and of those traversing the TH islands varied intraseasonally. These results also held for typhoons traversing the TH islands, although the oscillations were less apparent. This study identified interrelationships between the frequency of TCs making landfall on the TH islands and the East Asia summer monsoon (EASM), the South Asia summer monsoon (SASM), and the South China Sea summer monsoon (SCSSM). The SCSSM significantly influenced the number of TCs traversing Hainan Island, but had little influence on the number of TCs traversing Taiwan Island. By contrast, the SASM influenced the numbers of TCs traversing both of the TH islands, shown by correlation coefficients of 0.41 for Taiwan Island and -0.25 for Hainan Island. In addition, the frequency of TC landfall on Taiwan Island increased during years of enhanced EASM, as indicated by a correlation coefficient of 0.4.

Detecting the Relationship Between Summer Rainfall Anomalies in Eastern China and the SSTA in the Global Domain with a New Significance Test Method

It is suggested that the multiple samples in a correlation map or a set of correlation maps should be examined with significance tests as per the Bernoulli probability model. Therefore, both the contemporaneous and lag correlations of summertime precipitation R in any one of the three regions of Northern China （NC）, the Changjiang-Huaihe River Valley （CHRV）, and Southern China （SC） with the SSTA in the global domain have been tested in the present article, using our significance test method and the method proposed by Livezey and Chen （1983） respectively. Our results demonstrate that the contemporaneous correlations of sum- mer R in CHRV with the SSTA are larger than those in NC. Significant correlations of SSTA with CHRV R are found to be in some warm SST regions in the tropics, whereas those of SSTA with NC R, which are opposite in sign as compared to the SSTA-CHRVR correlations, are found to be in some regions where the mean SSTs are low. In comparison with the patterns of the contemporaneous correlations, the 1 to 12 month lag correlations between NC R and SSTA, and those between CHRV summer R and SSTA show similar patterns, including the magnitudes and signs, and the spatial distributions of the coefficients. However, the summer rainfall in SC is not well correlated with the SSTA, no matter how long the lag interval is. The results derived from the observations have set up a relationship frame connecting the precipitation anomalies in NC, CHRV, and SC with the SSTA in the global domain, which is critically useful for our understanding and predicting the climate variabilities in different parts of China. Both NC and CHRV summer R are connected with E1 Nifio events, showing a ‘- -＇pattern in an E1 Nifio year and a‘＋ ＋＇ pattern in the subsequent year. Key words summer precipitation; eastern China; global sea surface

Lump Solutions of Kadomtsev-Petviashvili I Equation in Non-uniform Media

N-lump solutions of the Kadomtsev-Petviashvili I equation in non-uniform media are derived through the inverse scattering transform. The obtained solutions describe lump waves with time-dependent amplitudes and velocities. Dynamics of l-lump wave and interactions of two lump wave are illustrated.

Effects of internal waves on signal temporal correlation length in the South China Sea

We simulated the temporal correlation of sound transmission using a two-dimensional advective frozen-ocean model with temperature data from a temperature sensor array on a propagation path in the South China Sea （SCS） Experiment 2009, and investigated the relationships of temporal correlation length, source-receiver range, and maximal sound speed fluctuation mainly caused by the solitary internal waves. We found that the temporal correlation length is -h2-power dependent on source-receiver range and -0.9-power dependent on maximal sound speed fluctuation. The empirical relationship is deduced from one-day environmental measurements in a limited area, needing more works and verification in the future with more acoustic data. But the relationship is useful in many applications in the area of SCS Experiment 2009.

Exact Analytical Solutions in Bose-Einstein Condensates with Time-Dependent Atomic Scattering Length

In the paper, the generalized Riccati equation rational expansion method is presented. Making use of the method and symbolic computation, we present three families of exact analytical solutions of Bose-Einstein condensates with the time-dependent interatomic interaction in an expulsive parabolic potential. Then the dynamics of two anlytical solutions are demonstrated by computer simulations under some selectable parameters including the Feshbach-managed nonlinear coefficient and the hyperbolic secant function coefficient.

Effects of Colored Noise on Periodic Orbits in a One-Dimensional Map

Noise can induce inverse period-doubling transition and chaos. The effects of the colored noise on periodic orbits, of the different periodic sequences in the logistic map, are investigated. It is found that the dynamical behaviors of the orbits, induced by an exponentially correlated colored noise, are different in the mergence of transition, and the effects of the noise intensity on their dynamical behaviors are different from the effects of the correlation time of noise. Remarkably, the noise can induce new periodic orbits, namely, two new orbits emerge in the period-four sequence at the bifurcation parameter value μ = 3.5, four new orbits in the period-eight sequence at μ= 3.55, and three new orbits in the period-six sequence at μ = 3.846, respectively. Moreover, the dynamical behaviors of the new orbits clearly show the resonancelike response to the colored noise.

New Correlation Ratio in Chemistry and Biology with Respect to Time and Magnetic Field

The authors reviewed the influence of various factors--inductive, mesomeric and steric effects, and magnetic fields and time correlation ratio. The authors offered the new correlation ratio in Chemistry and Biology with respect to time and magnetic field. The proposed formula takes into account the influence of the magnetic field on the correlation ratio.

Analyzing Dynamics of a Bright Soliton in Bose-Einstein Condensates with Time-Dependent Atomic Scattering Length

We analyze the dynamics of a bright soliton in atomic scattering length in an expulsive parabolic potential. Bose-Einstein condensates （BECs） with time-dependent Under a safe ravage of parameters in which the Gross-Pitaevskii （GP） equation is effective in one dimension, our results show that, the dynamics of the bright soliton can be classed into two phases, depending on the value of the scattering length. Meanwhile, there exists a critical value of the absolute value of the atomic scattering length, below which, the dynamics of the bright soliton is very regular. Those phenomena can be useful for developing concrete applications of the nonlinear matter waves. We also obtain the orbital equation of the bright soliton and get some interesting data which may be useful for the experimental observation of the bright soliton and the application of the atom laser with manipulated intensity.

Chill injury in the eggs of the migratory locust, Locusta migratoria （Orthoptera： Acrididae）： the time-temperature relationship with high-temperature interruption

Mortality of the overwintering egg of the migratory locust, Locustamigratoria L., was attributed to chill injury because of its occurrence well above the egg' ssupercooling point. In this study, two parameters, upper limit of chill injury zone (ULCIZ) and sumof the injurious temperature (SIT), were used to examine the locust egg's cold hardiness. The valueof ULCIZ for the locust egg is 1.06 ± 0.54℃, and the SIT is -329.7 (hour ? degree). Thesuperoxide dismutase (SOD) and catalase (CAT) activities changed dramatically after cold stress,indicating that oxygen and hydroxide free radicals are probably efficiently detoxified at lowtemperatures. It was suggested that the nature of chill injury in locust egg might be a complex ofmetabolic disorder and a non-proportional decrease in enzymatic reaction and transports, because theLDH activity at low temperature increased significantly and the ATPase activity decreased withprolonged duration of exposure to low temperatures. The results from high temperature interruptionrevealed that the high temperature intervals significantly increased the survival of locust eggs.

Spatio-temporal evolution of population and urbanization in the countries along the Belt and Road 1950–2050

This paper uses data for the period 1950-2050 compiled by the United Nations Population Division together with methods including spatial autocorrelation analysis, hie- rarchical cluster analysis and the standard deviational ellipse, to analyze the spatio-temporal evolution of population and urbanization in the 75 countries located along the routes of the Silk Road Economic Belt and the 21st-century Maritime Silk Road, to identify future popula- tion growth and urbanization hotspots. The results reveal the following： First, in 2015, the majority of Belt and Road countries in Europe, South Asia and Southeast Asia had high population densities, whereas most countries in Central Asia, North Africa and West Asia, as well as Russia and Mongolia, had low population densities; the majority of countries in South Asia, Southeast Asia, Central Asia, West Asia and North Africa had rapid population growth, whereas many countries in Europe had negative population growth; and five Belt and Road countries are in the initial stage of urbanization, 44 countries are in the acceleration stage of urbanization, and 26 are in the terminal stage of urbanization. Second, in the century from 1950 to 2050, the mean center of the study area＇s population is consistently located in the border region between India and China. Prior to 2000, the trajectory of the mean center was from northwest to southeast, but from 2000 it is on a southward trajectory, as the population of the study area becomes more concentrated. Future population growth hotspots are predicted to be in South Asia, West Asia and Southeast Asia, and hotspot countries for the period 2015-2030 include India, China, Pakistan and Indonesia, though China will move into nega- tive population growth after 2030. Third, the overall urban population of Belt and Road coun- tries increased from 22% in 1950 to 49% in 2015, and it is expected to gradually catch up with the world average, reaching 64% in 2050. The different levels of urbanization in different countries display significant spatial dependency, and in the hundred-year period under con-sideration, this dependency increases before eventually weakening. Fourth, between 2015 and 2030, urban population hotspots will include Thailand, China, Laos and Albania, while Kuwait, Cyprus, Qatar and Estonia will be urban ＂coldspots.＂ Fifth, there were 293 cities with populations over 1 million located along the Belt and Road in 2015, but that number Js ex- pected to increase to 377 by 2030. Of those, 43 will be in China, with many of the others located in India, Indonesia and the eastern Mediterranean.

Phase asynchrony between flare index and sunspot activity

In this paper, the relative phase relationship between flare index and sunspot activity （sunspot numbers and sunspot areas） is investigated. It is found that （i） the flare index and sunspot activity are asynchronous in phase space at all period scales, and the former lags behind the latter, which implies our results are supported for the integral response model; （ii） their different definitions and physical meanings may be a major reason for their phase asynchrony between them, and the solar flare activity favor to be related to the magnetic complex rather than magnetic strength.

Semi-linear Wave Equations with Effective Damping

The authors study the Cauchy problem for the semi-linear damped wave equation utt-△u＋b（t）ut=f（u）,u（0,χ）=u0（χ）,ut（0,χ）=u1（χ） in any space dimension n ≥ 1. It is assumed that the time-dependent damping term b（t）〉 0 is effective, and in particular tb（t） →∞ as t →∞. The global existence of small energy data solutions for｜f（u）｜≈｜u｜^p in the supercritical case of p 〉 1＋ 2/n and p ≤n/n-2 for n ≥ 3 is proved.

Breather Dynamics of the Sine-Gordon Equation

This paper studies the adiabatic dynamics of the breather soliton of the sine-Gordon equation. The integrals of motion are found and then used in soliton perturbation theory to derive the differential equation governing the soliton velocity. Time-dependent functions arise and their properties are studied. These functions are found to be bounded and periodic and affect the soliton velocity. The soliton velocity is numerically plotted against time for different combinations of initial velocities and perturbation terms.