时空相关的混载校车路径问题邻域搜索

为节约混载校车路径问题求解过程中邻域解搜索的时间,引入时空距离和时空相关度概念,将邻域搜索空间限定在合理的范围内。该算法首先计算站点间的时空距离,再附加上简单约束的预判断,从而得到时空相关度矩阵。然后对于任意学生乘车站点,将其他可能与之直接相连的站点按照时空相关度排序,形成一个邻接列表。在邻域搜索过程中,通过限定邻接列表长度,仅尝试最终接受概率较大的一部分移动操作,以此缩小邻域搜索空间,从而提高算法效率。在国际标准案例上的测试结果表明,基于时空相关度的搜索策略能在基本不降低求解质量的情况下,平均节省50%以上的求解时间。

无线传感器网络中基于时间分段拟合的高效查询处理算法

以数据为中心的分布式传感器网络,用户经常对感兴趣的传感区域提交查询命令,如获取区域F在某个给定时间段内的感知数据;由于传感器网络依赖高密度部署节点以及高采样频率提高监测精确度,存在大量冗余数据,因此,有效地保证查询数据准确性,减少大量冗余数据传输能量消耗,是目前亟需解决的问题;文中提出一种单个节点传感数据时间分段拟合算法,对给定查询时间进行分段拟合,寻找满足误差阀值的拟合模型集合;理论分析和实验结果表明,文章提出的基于时间分段拟合的高效查询处理算法能节省大量数据传输能耗,返回满足用户精度要求的查询结果.

一种无线传感器网络中基于时间分段拟合的高效查询处理算法

以数据为中心的分布式传感器网络,用户经常对感兴趣的传感区域提交查询命令,如获取区域F在某个给定时间段内的感知数据。由于传感器网络依赖高密度部署节点以及高采样频率提高了监测精确度,存在大量冗余数据,因此,有效地保证查询数据准确性,减少大量冗余数据传输能量消耗,是目前亟需解决的问题。本文提出一种单个节点传感数据时间分段拟合算法,对给定查询时间进行分段拟合,寻找满足误差阈值的拟合模型集合。理论分析和实验结果表明,本文提出的基于时间分段拟合的高效查询处理算法能节省大量数据传输能耗,返回满足用户精度要求的查询结果。

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.

A numerical study of a turbulent mixing layer and its generated noise

A direct numerical simulation of a turbulent mixing layer with the Reynolds number 500 and the convective Mach number 0.6 is performed and the results obtained are used to study the turbulent flow field and its generated noise.In the present simulation,the numerical techniques of absorbing buffer zones,artificial convection velocity and spatial filtering are used to achieve nonreflecting boundary conditions.The self-similarity is used to validate the present numerical simulations.The large-scale coherent structures are plotted together with the acoustic waves,which demonstrates the directivity of acoustic waves.The Lighthill's source and space-time correlations are further investigated.The main contributions to mixing noise are identified in terms of large-scale coherent structures,Lighthill's source and space-time correlations.

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.

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.