Accessibility and Network Structures in the German Commuting

A great deal of attention has recently been paid to the analysis of the structure and evolution of (complex) networks, starting from pioneering contributions in the physical and social sciences—and more recently in the regional and transportation sciences—mainly concerning the relevance of highly connected nodes (hubs). The presence of hubs identifies a network as Scale-Free (SF), because of its intrinsic characteristic of exhibiting power-law distributions in its connectivity structure, and thus highly heterogeneous patterns. The focus of this paper is to explore the homogeneous vs. heterogeneous characteristics of the German commuting network, by focusing on the role of accessibility. The concept of accessibility has a long tradition in the transport economics literature, starting with the fundamental works by Hansen in the 1950’s and later on by Weibull in the 1980’s. These authors defined accessibility as the potential of opportunities for spatial interaction. Accessibility conceived in this manner should also capture spatial structure effects and thus the network configuration properties, such as connectivity. This conventional accessibility function—in the light of the related economic activities—is be used as a suitable instrument to identify the major German hub/attraction nodes. As the functional form in this potential accessibility, the power-decay function will be considered—in addition to the negative exponential function—in order to explore the spatial configuration patterns, i.e. whether people perceive commuting cost in log-like way. The connectivity network analysis will then be developed as a benchmark to testing the results emerging from the spatial-economic analysis. In our application we consider home-to-work commuters travelling between 439 German districts, for the year 2002. The final results seem to highlight the tendency, in Germany, towards a multi-nodality network, where accessibility can play a fundamental role.     

The spatial organization of accessibility and functional hierarchy: The case of Israel

Accessibility is a well-known basic term in spatial science and planning and is inherently related to functional aspects of places and regions. Although previous studies have examined functional systems and spatial accessibility few have attended to the association among them across geographical scales. Our study attempts to fill this gap. Using the space syntax methodology, spatial accessibility was analyzed for the entire national road network of Israel across different geographic scales – from local culminating in the national scale. The analysis was based on angular segment analyses of the road center-line network. Following this, the correlation between spatial accessibility across scales and functional performance of employment and commuting flows was examined.The study findings show a significant correspondence and exposes transitions between local, regional and national spatio-functional systems. First, a significant correlation between local (2 km radius) accessibility levels of settlements with the number of employees and commuters. Second, the regional/metropolitan system (10–15 km radius) accessibility is highly correlated to the emergence of the main employment centers. Third, the main metropolitan areas are integrated at higher scale (from 30 km radius) and form together a core region characterized by high accessibility as well as well connectivity through commuting flows. In contrast, no substantial commuting flows were found within the periphery, as well as between periphery-core. The findings show clearly that this functional structure corresponds to the multi-scale accessibility levels of settlements. We conclude that the core region functions at multiple scales (local-regional-national) while the periphery functions mostly at a local scale.     

改进生成对抗网络在场景图像转换中的应用

本文针对不同场景图像之间的转换问题,提出了一种改进的生成对抗网络模型,能够生成高质量的目标场景图像.在生成目标图像过程中存在因为向下采样而丢失原图像空间位置信息的现象,因此本文设计了一个包含跳跃连接和残差块的生成网络,通过在网络中加入多个跳跃连接部分,将图像的空间位置信息在网络中保持传递.同时为提高训练过程中生成图像在结构上的稳定性,引入SSIM图像结构相似指数,作为结构重建损失,以指导模型生成更优结构的目标图像.此外,为使得转换后的目标场景图像保留更多的色彩细节,加入了身份保持损失,明显增强了目标生成图像的色彩表现力.实验结果表明,本文所提的改进生成对抗网络模型能够在场景图像转换中得到有效地应用.     

Modeling interregional commodity flows with incorporating network autocorrelation in spatial interaction models: An application of the US interstate commodity flows

Spatial interaction models are frequently used to predict and explain interregional commodity flows. Studies suggest that the effects of spatial structure significantly influence spatial interaction models, often resulting in model misspecification. Competing destinations and intervening opportunities have been used to mitigate this issue. Some recent studies also show that the effects of spatial structure can be successfully modeled by incorporating network autocorrelation among flow data. The purpose of this paper is to investigate the existence of network autocorrelation among commodity origin–destination flow data and its effect on model estimation in spatial interaction models. This approach is demonstrated using commodity origin–destination flow data for 111 regions of the United States from the 2002 Commodity Flow Survey. The results empirically show how network autocorrelation affects modeling interregional flows and can be successfully captured in spatial autoregressive model specifications.     

Extensions and generalizations of smoothed perturbation analysis ina generalized semi-Markov process framework

Under a very general framework, both in terms of finite-time performance measures and system structure, the authors derive smoothed perturbation analysis (SPA) estimators and prove their unbiasedness. The commuting condition, which has been key in previous work, is not required a priori, and thus the framework includes such systems as the GI/G/1/K queue and multiclass queueing networks, which do not satisfy the commuting condition. The generality achieved is traded off against the fact that the estimator is not always easily implementable on a single sample path. The use of the commuting condition in a local sense is proposed to help simplify the estimators derived: queueing and multiclass queueing networks are used as illustrative examples. For a simple multiclass closed queueing network, some simulation results are provided. When the commuting condition is satisfied globally, the framework allows the recovery of previous results on IPA and SPA estimators as corollaries of the main theorems     

空间数据立方体多维信息空间分析实例*

多维信息空间分析是构筑数字城市最为关键的技术之一,而空间数据立方体是解决这个关键技术问题的有效途径;提出了空间数据立方体的分析操作主要由概括分析、局部分析、全局分析和旋转分析组成,简单介绍了这些分析操作功能和结构;在分析操作过程中,采用具体分析功能和例子数据相结合的直观方式列举了多维信息的缓冲区分析、连接分析、网络分析实例.     

一种针对路口监控图像的区域分割方法

针对智能交通系统中对交通路口场景理解的需求,提出一种基于线特征先验和凸包损失函数的空间分割网络,目标是对斑马线以及斑马线所围路口区域进行精确检测和分割。利用公安交通管理系统平台采集并标注路口数据集;引入线特征先验,将RGBL图像作为网络输入,为深度学习实例分割提供显著的物体边缘特征以加强深度网络对图像特征学习的针对性;在分割网络中引入SCNN网络结构,构成空间分割网络以增强网络对空间结构的学习;引入凸包二值交叉熵动态损失函数来优化网络的输出精度。实验结果表明,该空间分割网络对斑马线及路口区域的检测正确率和分割完整度和精确度都有了显著的提升。     

Mixed Attention Densely Residual Network for Single Image Super-Resolution

Recent applications of convolutional neural networks (CNNs) in single image super-resolution (SISR) have achieved unprecedented performance. However, existing CNN-based SISR network structure design consider mostly only channel or spatial information, and cannot make full use of both channel and spatial information to improve SISR performance further. The present work addresses this problem by proposing a mixed attention densely residual network architecture that can make full and simultaneous use of both channel and spatial information. Specifically, we propose a residual in dense network structure composed of dense connections between multiple dense residual groups to form a very deep network. This structure allows each dense residual group to apply a local residual skip connection and enables the cascading of multiple residual blocks to reuse previous features. A mixed attention module is inserted into each dense residual group, to enable the algorithm to fuse channel attention with laplacian spatial attention effectively, and thereby more adaptively focus on valuable feature learning. The qualitative and quantitative results of extensive experiments have demonstrate that the proposed method has a comparable performance with other state-of-the-art methods.     

基于哈希锁定的网络传输异常序列监测仿真

为有效提升传统网络传输异常序列监测方法的处理效率,提出基于哈希锁定的网络传输异常序列监测方法。利用随机投影的哈希函数将高维空间数据转换为低维空间数据,并利用网络传输序列的多元数量值函数,组建网络传输结构模型。对网络传输结构模型进行流量时频采样以及时间序列分析,结合FIR滤波器对其进行流量抗干扰处理,通过高阶累计的振荡衰减,对输出的滤波数据进行特征搜索及提取,实现基于哈希锁定的网络传输异常序列监测。仿真结果表明,所提方法具有较强的抗干扰性,并且能够确保网络的稳定运行。     

A template-based approach for the generation of abstractable and reducible models of featured networks

We investigate the relationship between symmetry reduction and inductive reasoning when applied to model checking networks of featured components. Popular reduction techniques for combatting state space explosion in model checking, like abstraction and symmetry reduction, can only be applied effectively when the natural symmetry of a system is not destroyed during specification. We introduce a property which ensures this is preserved, open symmetry. We describe a template-based approach for the construction of open symmetric Promela specifications of featured systems. For certain systems (safely featured parameterised systems) our generated specifications are suitable for conversion to abstract specifications representing any size of network. This enables feature interaction analysis to be carried out, via model checking and induction, for systems of any number of featured components. In addition, we show how, for any balanced network of components, by using a graphical representation of the features and the process communication structure, a group of permutations of the underlying state space of the generated specification can be determined easily. Due to the open symmetry of our Promela specifications, this group of permutations can be used directly for symmetry reduced model checking.The main contributions of this paper are an automatic method for developing open symmetric specifications which can be used for generic feature interaction analysis, and the novel application of symmetry detection and reduction in the context of model checking featured networks.We apply our techniques to a well known example of a featured network – an email system.     

空间位置的关联分析及其向量化表示方法

理解地理空间位置的空间相关性,对于地理信息检索、推荐系统,城市交通管理,居民出行模式探究等应用研究具有重要支撑作用.为更具体表义空间位置及其关联关系,本文基于多种居民出行轨迹数据,提出一种基于深度学习的空间位置向量化表示方法,而后通过空间位置向量的向量运算,可计算得到空间位置的关联程度.首先将长、短距离出行轨迹进行匹配连接,构建大规模交通网络,覆盖多种出行模式,得到对不同位置间空间关联信息的完整识别.然后基于图神经网络模型,本文提出融合位置特征与轨迹信息的空间向量化表示方法,并优化其训练学习中节点采样方法,提高空间向量的表达能力.最后以北京市共享单车轨迹数据与公共交通路网数据进行实证分析,实验结果表明基于本文提出方法生成的空间向量在空间位置的关联分析、聚类分析中相比DeepMove等已有方法拥有更好的效果.     

基于多级时空域3D卷积的换脸视频检测方法

近年来,视频换脸技术发展迅速。该技术可被用于伪造视频来影响政治行动和获得不当利益,从而给社会带来严重危害,目前已经引起了各国政府和舆论的广泛关注。本文通过分析现有的主流视频换脸生成技术和检测技术,指出当前主流的生成方法在时域和空域中均具有伪造痕迹和生成损失。而当前基于神经网络检测合成人脸视频的算法大部分方法只考虑了空域的单幅图像特征,并且在实际检测中有明显的过拟合问题。针对目前检测方法的不足,本文提出一种高效的基于时空域结合的检测算法。该方法同时对视频换脸生成结果在空域与时域中的伪造痕迹进行捕捉,其中,针对单帧的空域特征设计了全卷积网络模块,该模块采用3D卷积结构,能够精确地提取视频帧阵列中每帧的伪造痕迹;针对帧阵列的时域特征设计了卷积长短时记忆网络模块,该模块能够检测伪造视频帧之间的时序伪造痕迹;最后,根据特征分类设计特征网络金字塔网络结构,该结构能够融合不同尺寸的时空域特征,通过多尺度融合来提高分类效果,并减少过拟合现象。与现有方法相比,该方法在训练中的收敛效果和分类效果方面有明显优势。除此之外,我们在保证检测准确率的前提下采用较少的参数,相比现有结构而言训练效率更高。     

Temporal dynamics of the impact of land use on modal disparity in commuting efficiency

Urban land use is known to affect commuting efficiency according to the excess commuting framework. However, most studies do not include temporal dynamics, and those that do, focus on decadal, yearly, or daily temporal resolutions. However, commuting is not a stationary spatial process. Since people leave home and start their jobs at different times of the day and since traffic congestion varies throughout the day, neglecting hourly dynamics can misestimate commuting efficiency in a region and lead to erroneous policy implications. Another important issue often overlooked in the past is the modal disparity in commuting efficiency and how it evolves during the day. To overcome these limitations, this research examines the commuting efficiency variation by car and public transport by six one-hour periods between 5 AM and 11 AM in Warsaw, Poland, using travel survey data and travel times generated from GPS-based big data for cars and from GTFS for public transport. We develop four different groups of modeling scenarios: no disaggregation, disaggregation by time, disaggregation by mode, and disaggregation by time and mode. Therefore, excess commuting and modal disparity metrics are applied for a total of 21 specific time and mode combinations. The results suggest that commuting efficiency is worst during the 8–9 AM period for both modes, and that public transport users are more efficient after 7 AM. Hourly variations in the excess commuting metrics imply that policy makers should examine ways to encourage flexible work hours to distribute work starts and to increase public transport frequencies in the off-peak.     

Expressive program verification via structured specifications

Conventional specifications typically have a flat structure that is based primarily on the underlying logic. Such specifications lack structures that could provide better guidance to the verification process. In this work, we propose to add three new structures to a specification framework for separation logic to achieve a more precise and better guided verification for pointer-based programs. The newly introduced structures empower users with more control over the verification process in the following ways: (1) case analysis can be invoked to take advantage of disjointedness conditions in the logic, (2) early, as opposed to late, instantiation can minimise the use of existential quantification and (3) novel formulae structuring can provide better reuse of the verification process. Initial experiments have shown that structured specifications can lead to more precise verification without incurring any performance overhead. To support our proposal, we shall illustrate the usage of structured specifications in the context of proving termination and we will briefly outline the impact of our proposal on a recent development focussed on verifying the FreeRTOS scheduler Ferreira et al. (Int. J. Softw. Tools Technol. Trans. 2014).     

空间活跃度网络模型构建与特性研究

基于现实网络拓扑的时变特征,利用Twitter数据集构建了在线社交网络,分析发现网络中用户的活跃度分布独立于时间尺度,并且网络的度分布与边长分布均具有异质性。结合该网络的特点,提出了一种空间活跃度网络模型。模型中网络的拓扑变化受节点活跃度和偏好连边概率影响,通过统计特性分析验证了机制的准确性。为了研究时变网络的动力学过程,在空间活跃度网络中进行了随机游走,得到节点活跃度越大、平均首达时间越短的结论。最后在基于最短路径的搜索策略下研究了偏好连边幂指数与平均搜索时间的关系,发现在空间活跃度网络中使搜索效率最高的幂指数在2左右。该活跃度网络模型可应用于时变网络。     

拓扑服务中融合GIS与拓扑发现技术的研究

传统的网络拓扑服务通过拓扑发现技术,描述了网络节点间的逻辑连接关系,基于GIS技术的网络拓扑服务,则体现了网络传输线路、网络节点间的空间连接关系。对这二种网络拓扑服务的实现展开研究,提出一种将两者相融合的方法,将网络资源及其拓扑关系视图化,以便于网络资源的保存、查询、管理,在计算机上实现准确真实的空间分析和可视化表达,实现了两者的优势互补,为网络资源利用,故障检测、定位、修复提供一种全新、强大的辅助工具。     

基于社团结构的复杂网络抗毁性测度

综合复杂网络连通度和社团结构的抗毁性测度,提出了一种新的基于社团结构的复杂网络抗毁性测度,既考虑网络的整体效能,又联系了网络本身的社团结构性。另一方面,为了更加有效地攻击网络的社团,提出一种基于社团的选择性攻击方式,移除较少的节点就使网络中的社团崩溃。通过仿真分析表明,基于社团的复杂网络抗毁性测度更加全面客观地衡量了网络的抗毁性,基于社团的选择性攻击更加有效地破坏了网络的社团结构性。     

Specifications of distributed programs

This paper discusses informal specifications of distributed programs, that is, programs that reside at nodes connected by a network. Such programs often have performance requirements, such as high availability and concurrency, that make it difficult to specify their behavior. These requirements often have an effect on the functional behavior of a program, forcing designers to change their initial expectations. In this paper we show how to give user-oriented specifications of the functional behavior of programs with such requirements. We propose a structure for specifications that distinguishes expected and desirable effects from undesirable ones. We believe that this distinction is an important one for both users and implementers of a system, and that it makes the specifications easier to understand. We illustrate our approach by giving example specifications of several distributed programs that have been described in the literature.     

Effectiveness of spatial representation in the formation of network communities: experimental study on community organizer

In this paper, we present and discuss Community Organizer, a system designed to support network communities. The main characteristic of Community Organizer is the use of spatial representations for the relationships among community members including the communications exchanged among these members. These spatial representations reflect the degree of closeness of interests and concerns among the members, and are intended to provide users with clues on how to form network communities. In order to investigate the effectiveness of the proposed spatial representations, we conducted experiments with two different versions of the software. One version offered meaningful spatial representations while the other version did not. The subjects who used the former software version felt a greater sense of ‘community’, enjoyed using the software more, and actively used it longer than the subjects using the latter software version (control condition). These results indicated that the proposed spatial representations are effective in supporting network community formation.     

Algebraic analysis of the topological properties of a banyan network and its application in fault-tolerant switching networks

In this paper, we introduce abstract algebraic analysis of the topological structure of a banyan network, which has become the baseline for most switching networks. The analysis provides the following key results: (1) The switching elements of a switching stage are arranged in order, that is, each stage of a banyan network consists of a series of a cyclic group. (2) The links between switching stages implement a homomorphism relationship in terms of self-routing. Therefore, we can recover the misrouting of a detour fault link by providing adaptive self-routing. (3) The cyclic group of a stage is a subgroup of that of the next stage, so that every stage and its adjacent stage make up a factor group. Based on this analysis, we introduce a cyclic banyan network that is more reliable than other switching networks. We present mathematical analysis of the reliability of the switching network to allow quantitative comparison against other switching networks.