Rational scale of urban rail transit network based on system dynamics

Urban rail transit(URT) has been playing an important role in urban sustainable development with its advantages of high speed,large capacity,high efficiency and low pollution.Estimating URT network scale is the key to ensure the scientificity and feasibility of its construction.The existing studies on rational scale of URT network have not dealt with the interaction of supply and demand.This paper describes the establishment of a system dynamics model of rational URT network scale determination,considering the interaction between URT construction and city social economic development as well as the dynamic equilibrium of capital supply and traffic demand,and the verification of the model validity by applying it to the case of Wuhan City's URT construction.

Effects of Reduced Frequency on Network Configuration and Synchronization Transition

Synchronization of networked phase oscillators depends essentially on the correlation between the topological structure of the graph and the dynamical property of the elements. We propose the concept of ＇reduced frequency＇, a measure which can quantify natural frequencies of each pair of oscillators. Then we introduce an evolving network whose linking rules are controlled by its own dynamical property. The simulation results indicate that when the linking probability positively correlates with the reduced frequency, the network undergoes a first-order phase transition. Meanwhile, we discuss the circumstance under which an explosive synchronization can be ignited. The numerical results show that the peculiar butterfly shape correlation between frequencies and degrees of the nodes contributes to an explosive synchronization transition.

Analysis of Transit Network Design Using GIS and Honeybee Algorithm in the City of Sanandaj, Iran

Public transit planning is a user-oriented problem, respectful of financial issues and involves different stakeholders such as the general public, the transportation provider and the local government. One of the main components of public transit planning is the transit network design (TND) problem. This research is an attempt to perform transit network design and analysis in the city of Sanandaj, Iran using the capabilities of GIS and Honeybee algorithm. Objectives of this study are formulating a multi-objective model of the TND problem, developing a GIS-based procedure for solving the TND problem and examination of the solutions using artificial metaheuristic methods such as honeybee algorithm. The transit network design approach in this research, aims to reduce the walking distance, the total travel distance and the total number of stops needed for a suitable transit service in Sanandaj, Iran. One of the contributions of this research is developing a transit network design with utilizing a spectrum of GIS software modelling functionalities and using the abilities of the artificial intelligence in modelling and assessment of the transit network.

Transit Network Design Using GIS and Ant Colony Optimization in Sanandaj

The public transit system in Sanandaj has been under review and modification for the last several years. The goal is to reduce the traffic congestion and the share of private car usage in the city and increase the very low share of the public transit. The bus routes in Sanandaj are not connected. There is no connected transit network with the ability to transfer between the routes in locations outside of the downtown terminal. The routes mostly connect the downtown core directly to the peripheries without providing travel options for passengers between peripheries. Although there has been some improvement in the transit system, lack of service in many populated districts of Sanandaj and town nearby makes the transit system unpopular and unreliable. This research is an attempt to provide solutions for the transit network design (TND) problem in Sanandaj using the capabilities of GIS and artificial intelligence methods. GIS offers several tools that enable the decision-makers to investigate the spatial correlations between different features. One of the contributions of this research is developing a transit network design with utilizing a spectrum of GIS software modeling functionalities. The visual ability of GIS is used to generate TNDs. Many studies focus on artificial intelligence as the main method to generate the TNDs, but the focus of this research is to combine GIS and artificial intelligence capabilities in order to generate a multi-objective GIS-based procedure to construct different bus network designs and explore and evaluate them to find the suitable transit network alternative.

Phase Transition in Recovery Process of Complex Networks

The dynamic characteristic of complex network failure and recovery is one of the main research topics in complex networks. Real world systems such as traffic jams and Internet recovery could be described by the complex network theory. We propose a model to study the recovery process in complex networks. Two different recovery mechanisms are considered in three kinds of networks： external recovery and internal recovery. By simulating the process of the nodes recovery in networks, it is found that the system exhibits the feature of first-order phase transition only when the external recovery is considered. Internal recovery cannot induce such a kind of transitions. As external recovery and internal recovery coexist on networks, the systems will retain the most efficient part of external recovery and internal recovery. Meanwhile, a hysteresis could be observed when increasing or decreasing the failure probability. Finally, a largest degree node protection strategy is proposed for improving the robustness of networks.

Phase Transitions of Majority-Vote Model on Modular Networks

We investigate the phase transitions behavior of the majority-vote model with noise on a topology that consists of two coupled random networks. A parameter p is used to measure the degree of modularity, defined as the ratio of intermodular to intramodular connectivity. For the networks of strong modularity （small p）, as the level of noise f increases, the system undergoes successively two transitions at two distinct critical noises, fc1 and fc2. The first transition is a discontinuous jump from a coexistence state of parallel and antiparallel order to a state that only parallel order survives, and the second one is continuous that separates the ordered state from a disordered state. As the network modularity worsens, fc1 becomes smaller and fc1 does not change, such that the antiparallel ordered state will vanish if p is larger than a critical value of pc. We propose a mean-field theory to explain the simulation results.

Four Types of Percolation Transitions in the Cluster Aggregation Network Model

We study the percolation transition in a one-species cluster aggregation network model, in which the parameter α describes the suppression on the cluster sizes. It is found that the model can exhibit four types of percolation transitions, two continuous percolation transitions and two discontinuous ones. Continuous and discontinuous percolation transitions can be distinguished from each other by the largest single jump. Two types of continuous percolation transitions show different behaviors in the time gap. Two types of discontinuous percolation transitions are different in the time evolution of the cluster size distribution. Moreover, we also find that the time gap may also be a measure to distinguish different discontinuous percolations in this model.

城市轨道交通网络系统效率评价指标改进

为提高城市轨道交通网络系统效率评价指标的可比性和完备性,引入有效行程速度和有效客流密度的概念,改进了网络系统效率评价指标,并以重庆市中心城区2017年和2019年运营的城市轨道交通线网为例验证了改进后评价指标的科学性和可操作性。研究表明:既有评价指标由于显著受到线网服务范围的影响,且未体现网络的投入产出效率,无法直接作为网络结构优化的目标函数;改进后的系统效率评价指标能够综合反映剔除线网服务范围影响后的网络结构性能和投入产出效率,且存在理论上的最优值;平衡网络中节点换乘时间和路段行程时间,并适度加密城市核心区域的轨道交通线路和站点,是持续提升网络系统效率的2个重要手段。

相邻城市综合交通系统建模中轨道交通接驳公交线网的快速构建方法

针对既有城市轨道交通线网客流预测模型在郊区简化的做法,为提高建模精度,提出一种在Visum软件中利用GTFS和COM快速构建相邻城市综合交通模型中轨道交通接驳公交线网的方法。该方法基于COM接口对Visum软件进行二次开发,快速构建出交通小区与不同类型轨道交通车站之间GTFS格式的公交线路,并结合组成公交线路的路段运行时间及停站时间,按照一定的发车频率构建出公交线路的时刻表及车次;也考虑了出行小区至轨道交通车站的距离在合理步行范围之内时对乘客出行方式选择的影响。经过实例验证,采用该方法不但可以快速构建出研究区域内各个交通小区至不同类型轨道交通车站的接驳公交线路,增加乘客出行选择的同时提高建模工作的效率,而且可以较为精确地计算接驳公交的出行时间,提高模型的精度。

城轨车辆网络通信实训平台的建设与优化设计

在城市轨道交通车辆运营中,网络通信系统是城轨车辆的核心关键系统,它关系到车辆的可靠运行。文章分析了城轨车辆网络通信实训平台建设的必要性,提出了建设的总体目标,实现了城轨车辆网络通信实训平台的建设,并对该平台进行了优化设计,为城轨车辆网络通信实训平台的建设提供了参考。

基于强化学习的CBTC系统信息安全风险评估方法

城市轨道交通属于十分重要的基础设施,具有较高的安全苛求特性,其核心的列车运行控制系统信息安全是当前的研究热点。该文采用了复杂网络和强化学习等方法,研究了当前城市轨道交通中应用最为广泛的基于通信的列车运行控制(Communication Based Train Control,CBTC)系统的信息安全风险。分析了CBTC系统的信息安全风险要素;基于复杂网络理论构建了CBTC系统的信息域模型;研究了CBTC系统的信息安全风险量化方法,并基于强化学习评估了系统最严峻的风险面。经过实例验证,提出的方法能够有效评估CBTC系统的信息安全。

轨道交通多制式专用移动通信系统互联互通方案研究

为适应“四网融合”发展趋势,干线铁路、城际铁路、市域铁路、城市轨道交通等的专用移动通信系统之间存在互联互通需求。通过分析城市轨道交通专用移动通信系统业务,对比GSM-R、LTE、5G-R等移动通信技术制式的频率和技术特点,提出城市轨道交通专用移动通信系统互联互通方案。采用LTE网络承载关键业务通信服务(MCX)系统,分别从列车控制业务和调度通信业务两方面,设计采用MCX的LTE与GSM-R、5G-R网络互联互通方案,并给出LTE跨核心网漫游切换以及采用MCX的LTE跨核心网漫游切换测试方案,以提高专用移动通信系统运营的安全性及服务水平,促进多层次轨道交通网络融合发展。

基于广义优先关系网络的全自动运行系统故障应急处置方案研究

全自动运行系统是未来城市轨道交通的主流发展方向。出于安全和应急响应及时性等因素考虑,目前我国多数全自动运行线路仍在列车运行时安排人员值守,与行车相关的应急预案和现场处置方案仍沿袭传统处置经验,未能结合系统新功能特点建立与之匹配的“无人化”或“少人化”的应急预案体系。文章采用广义优先关系网络,对城市轨道交通运营的一般应急处置流程进行模块化建模和量化处理,为全自动运行系统应急处置方案的构建提供一种建模方法,同时以时效性、决策质量为评价目标,实现对应急处置方案的评价和优化,并以列车运行实际突发故障事件为案例,通过建模、分析、评价和方案优化,验证文章所提出的全自动运行模式下应急处置模式构建方法的合理性。

城市轨道交通宽窄融合专网无线系统应用研究

随着城市轨道交通系统对可靠通信需求的提升,宽窄融合专网无线系统成为了关键技术。文中围绕该系统在城市轨道交通中的应用,分析了系统设计、面临的挑战及优化策略。研究表明,通过技术创新和网络优化,宽窄融合网络能有效提高城市轨道交通运营效率和乘客体验,同时确保通信的安全性和系统的可靠性。

Estimation method for a skip-stop operation strategy for urban rail transit in China

The skip-stop operation strategy （SOS） is rarely applied to Chinese urban rail transit networks because it is a simple scheme and a less universally popular transportation service. However, the SOS has performance advantages, in that the total trip time can be reduced depending on the number of skipped stations, crowds of passengers can be rapidly evacuated at congested stations in peak periods, and the cost to transit companies is reduced. There is a contradiction between reducing the trip time under the SOS and increasing the passengers＇ waiting times under an all-stop scheme. Given this situation, the three objectives of our study were to minimize the waiting and trip times of all passengers and the travel times of trains. A comprehensive estimation model is presented for the SOS. The mechanism through which the trip time for all passengers is affected by the SOS is analyzed in detail. A 0-I integer programming formulation is established for the three objectives, and is solved using a tabu search algorithm. Finally, an example is presented to demonstrate that the estimation method for the SOS is capable of optimizing the timetable and operation schemes for a Chinese urban rail transit network.

Structural and robustness properties of smart-city transportation networks

The concept of smart city gives an excellent resolution to construct and develop modern cities, and also demands infrastructure construction. How to build a safe, stable, and highly efficient public transportation system becomes an important topic in the process of city construction. In this work, we study the structural and robustness properties of transportation networks and their sub-networks. We introduce a complementary network model to study the relevance and complementarity between bus network and subway network. Our numerical results show that the mutual supplement of networks can improve the network robustness. This conclusion provides a theoretical basis for the construction of public traffic networks, and it also supports reasonable operation of managing smart cities.

A Molecular Description of Superconductivity of Sulfur Hydride and Related Systems under High-Pressure Conditions

It has been shown that the recently discovered sulfur trihydride (H3S) can be considered as a superconductor with a transition temperature Tc of 203 Kelvin (K) at 155 GigaPascals (GPa). This is the highest Tc value reported for any superconductor. The established superconductivity occurs via the formation of a molecular system with sulfur atoms arranged on a body-centered cubic lattice. It has been generally accepted that the high Tc value is the result of an efficient electron-phonon interaction. The responsible substance formed by H2S under high pressure, may be considered as a compound with H3S stoichiometry creating an impressive network with hydrogens. We will focus on the hydrogen bonding between sulfur and hydrogens demonstrating a symmetrical arrangement. The geometry of the individual radical compound in relation to corresponding systems will be discussed. Ab initio calculations based on a linear three-center two-, three- and four-electron type of bonding clearly visualized in combination with the dynamics of the Van’t Hoff concept, as described by us in various papers, give a good description of this exclusive network. We also discuss the superconductivity of related phosphorus hydrides and focus on the stability and geometrical differences with respect to the H3S system. These differences are significant, demonstrating the diversity in various structures in showing superconductivity.

Optimisation of a Bus Network Configuration and Frequency Considering the Common Lines Problem

Public transportation network reorganisation can be a key measure in designing more efficient networks and increasing the number of passengers. To date, several authors have proposed models for the “transit route network design problem” (TRNDP), and many of them use a transit assignment model as one component. However, not all models have considered the “common lines problem,” which is an essential feature in transit network assignment and is based on the concept that the fastest way to get to a destination is to take the first vehicle arriving among an “attractive” set of lines. Thus, we sought to reveal the features of considering the common lines problem by comparing results with and without considering the problem in a transit assignment model. For comparison, a model similar to a previous one was used, formulated as a bi-level optimisation problem, the upper problem of which is described as a multi-objective problem. As a result, although the solutions with and without considering the common lines showed almost the same Pareto front, we confirmed that a more direct service is provided if the common lines problem is considered whereas a less direct service is provided if it is not. With a small network case study, we found that considering the common lines problem in the TRNDP is important as it allows operators to provide more direct services.

Building Traversing NAT IPv6 Tunnel Gateway System Relies on Netfilter/Iptable Framework

The transition from IPv4 to IPv6 is doomed to be a long process. The network Address translation （NAT） technology is used very popularly in IPv4 network to make up the shortage of network address. It is a desiderated problem to make the users behind NAT gateway to access to IPv6 networks. By studying the transition technology from IPv4 to IPv6 and introducing NAT technology in IPv6, a scenario is put forward through 6to4 tunnel The scenario is implemented and the gateway system＇s performance is analyzed.

T2T和T2G混合网络中的功率分配算法

现有功率分配算法大多基于理想信道状态信息(CSI)实现性能优化,在列车对列车(T2T)双移动端通信场景中并不适用.针对城市轨道交通系统T2T和车地(T2G)混合网络场景,引入CSI反馈延时,研究非理想状态时仍可保障通信质量的功率分配算法.考虑单蜂窝用户复用单T2T用户对情况,以T2G用户传输速率总和最大化为优化目标,构建多约束条件下的功率分配模型.首先,根据分步思想将非凸模型简化为最优分配功率计算和最佳复用用户匹配2个子模型;其次,利用线性规划分析可行域内目标函数的最优解及最优值,并通过二分法求解最优分配功率;最后,筛选出可行复用对集合后,利用匈牙利算法进行二分图匹配.仿真结果表明:该算法兼顾城市轨道交通系统中T2T通信中断概率约束和T2G用户传输速率,且可实现1.0 ms内的CSI反馈延时.