磁悬浮列车与超导

据悉,在不久的将来,建造从北京到上海的长距离磁悬浮列车,到那时,乘坐磁悬浮列车从上海到北京只需4个小时. 超导是超导电性的简称,它是指金属、合金及其氧化物的电阻变为零的性质.自1911年荷兰物理学家昂纳斯(H.K.Onnes)发现低温超导现象以来,对超导的研究和应用,特别是1986年后高温超导的研究和应用,已取得重大进展.     

空间高频交变磁场对超导块材悬浮力影响研究

高温超导磁悬浮装置,如磁悬浮列车和磁悬浮轴承在高速运行时,空间磁场交变及不均匀性扰动会引发超导块材内部损耗并影响性能,传统均匀时变磁场实验研究及仿真模拟无法满足实际工程应用情况.本文通过设计不同永磁阵列得到不同波形,在高速系统驱动下得到不同交变频率下超导块材损耗特性,发现全波型损耗较半波型损耗高,并研究了不同磁场构型悬浮力衰减特性,可为高速超导磁浮应用提供实验依据.     

超导涡旋玻璃

超导涡旋系统的性质丰富多彩，对它的理论和实验研究已积累了大量的新知识，以致形成了凝聚态物理的一个新分支－涡旋物理学，涡旋固体可以是玻璃态或结晶态，其强度直接联系超导应用的主要参数之一的临界电流密度，使这一研究有浓厚的应用背景，文章试图深入浅出地介绍超导涡旋玻璃的基本内容与特征，着重于其存在的物理基础和证据。希望这一涉及多种物理分支学科，使用多种专门理论工具和精巧实验方法研究出来的新物态为更多的读者     

低温超导物理学中的重要实验史话

综观超导发展史，实验既是创立超导理论的基础，也是检验超导理论的惟一手段。正是实验的发展，不断揭示了超导的各种新现象，日益加深着人们对超导电性的认识，促进了超导物理学的发展和应用。文章回顾了低温超导发展过程中的一些重要实验，探讨了这些实验的思想及其对超导发展的重要促进作用。通过对超导实验历史材料的研究，我们不仅可以学到科研技能和了解科学新现象的发现过程，而且可以学到正确的科研态度和方法。     

强耦合超导理论的物理基础(Ⅰ)

本刊曾经发表了“超导临界温度理论综述”（７卷２期）与“超导微观理论及其进展浅说”（７卷５期）．前文侧重于超导微观理论的最新进展，后文侧重于早期微观理论的介绍．本期及下期将连续两期刊登“强耦合超导理论的物理基础”．该文将超导微观理论的物理图象以及从弱耦合到强耦合的发展作了深入浅出的介绍．     

超导限流器的性能检测方法研究

超导限流器是研究最为活跃的一种超导电力装置,也是被认为可以率先达到实际应用的一种超导电力装置。但是要将超导限流器应用到电力系统中仍然有若干关键问题需要解决,其中对其试验、检测方法及其主要设备的规范化研究就是一个很重要的方面。文中从超导限流器的电磁特性出发,总结了超导限流器的特性试验、检测方法,并重点介绍了超导限流器的短路试验。     

空芯大气隙高温超导直线电机电磁力实验研究

直线电机是一种无需中间传动装置而直接将电磁力转换为线性运动的特种电机,在交通运输领域具有广泛的应用前景.将高温超导技术与电机理论相结合,能够有效利用超导材料的强载流能力与高场特性提高直线电机的输出能力.本文提出了一种应用于超导磁悬浮列车牵引的空芯高温超导直线电机,首先建立空芯高温超导直线电机的二维有限元模型对电机结构参数进行初步探索,并完成了超导直线电机样机的设计与制作.通过搭建实验测试平台完成了空芯高温超导直线电机定子磁场和电磁力的实验测试.有限元计算结果与实验数据有较好的一致性,验证了模型的有效性,并利用该模型研究了定子电流,超导线圈电流以及电机气隙对电机推进力输出的影响.本文的相关成果将促进超高速磁浮交通领域关键驱动技术的研究与发展.     

夸克物质中的色超导性理论简介

夸克-夸克通过单胶子交换的相互作用在其反对称态上是相互吸引的,在致密夸克物质里,这种吸引相互作用会导致费米面上的双夸克凝聚,这就是所谓的夸克配对或色超导现象。本文介绍了夸克配对或色超导现象的基本知识和一些新进展。色超导是一个对称性自发破坏现象,有非常丰富的破缺方式,我们介绍了色超导对称性及其自发破坏模式的分析方法,介绍了怎样计算色超导体两个最基本的变量：能隙和迈斯纳质量。然后我们介绍了描述色超导现象的有效理论。最后是这些理论的一个应用,即计算色超导体里的中微子发射率以及其它输运性质。本文可以作为研究夸克物质理论的入门参考资料。     

夸克物质中的色超导性理论简介(英文)

夸克-夸克通过单胶子交换的相互作用在其反对称态上是相互吸引的,在致密夸克物质里,这种吸引相互作用会导致费米面上的双夸克凝聚,这就是所谓的夸克配对或色超导现象。本文介绍了夸克配对或色超导现象的基本知识和一些新进展。色超导是一个对称性自发破坏现象,有非常丰富的破缺方式,我们介绍了色超导对称性及其自发破坏模式的分析方法,介绍了怎样计算色超导体两个最基本的变量:能隙和迈斯纳质量。然后我们介绍了描述色超导现象的有效理论。最后是这些理论的一个应用,即计算色超导体里的中微子发射率以及其它输运性质。本文可以作为研究夸克物质理论的入门参考资料。     

我国高温超导材料研究进展

本文概述了我国在高温超导材料研究方面的最新进展，较系统地介绍了超导块材和薄膜的制备方法及性能，并简单地介绍了高温超导材料在超导量子干涉器件、超导天线、磁屏蔽和磁通变换器等方面的应用．     

Effectiveness of blowing for improving the high-speed trains aerodynamics

The promising method of drag reduction with the use of micro-blowing through the streamlined surface has been proposed for its use to the external surface of high-speed train. The advantages of high-speed train as an object of micro-blowing application are introduced. The corresponding RANS-based mathematical model is elaborated, and the computations of the external flow around a long train body are performed. Predictions of the turbulent boundary layer over penetrable surface with different modes of micro-blowing have been presented and analyzed. The developed modifications of mathematical model of turbulence have been used to take into account the micro-blowing influence in the inner region of turbulent boundary layer. The obtained results of parametric analysis of drag reduction depending on the area of permeable sections, intensity of micro-blowing, and high-speed train length have been analyzed. In particular, the dependence between drag reduction effect and length of train body with realized micro-blowing as well as its intensity is established. Realization of micro-blowing with blowing velocity just 0.25 % of train speed (V = 100 m/s) on the 70 % of the streamlined surface area for just one train carriage (L = 25 m) allows one to reduce the aerodynamic drag (including the most actual friction and head-tail pressure components) of the whole train (L = 200 m) by about 5.25 %, so in case of micro-blowing realization on all its 8 carriages, the train’s aerodynamic drag can be reduced approximately by 42 %.     

Simulation for influence of train failure on railway traffic flow and research on train operation adjusting strategies using cellular automata

Many complex train operation plans are being implemented in practice because more and more railway transit networks have been constructed and put into use, and thus a certain train’s failure will cause more harmful influence on the efficiency and safety of the overall railway transit system. In this paper, a new cellular automaton model is proposed. In this model, two control schemes are introduced to simulate the characteristic behaviors of railway traffic flow when a train breaks down for traction failure, stops, and later be rescued by its first following train. The simulation results prove that the proposed model is able to simulate the occurrence of train failure and reproduce the complex behaviors of train movement in railway transit system. Two train operation adjusting strategies are proposed and tested later with this model. Simulation results show that increments in train operation interval after the train failure bring more benefits than decrements in maximum velocity and that with proper parameters both strategies can serve to reduce the severity of delay and go-and-stop waves to a lower level.     

高架桥声屏障高度对列车气动特性影响的数值模拟

采用计算流体力学方法对高架桥声屏障高度影响高速列车空气动力特性进行数值研究.通过网格划分、湍流模型选取、边界条件设置等来提高数值计算精度.结果表明,当高速列车运行在下风向时,头车、中间车上的侧向力随着声屏障高度增加而逐渐下降.头车所受的侧翻力矩在整车中最大,且随着声屏障高度的增加而逐渐减小.随着声屏障高度的增加,上风向工况下中间车受到的侧翻力矩要大于下风向工况.上、下风向工况下高速列车气动特性差异主要是由于流动空腔中列车所处的相对位置不同,改变了车体表面的压力分布,从而改变了车体所受到的气动力、力矩.     

Conclusive evidence of an attosecond pulse train observed with the mode-resolved autocorrelation technique

We report on the direct observation of an attosecond pulse train with a mode-resolved autocorrelation technique. The chirp among the three harmonic fields is specified by analyzing two-photon above-threshold ionization spectra of electrons, resulting in a pulse duration that should be shorter than 450 as, which is, to our knowledge, the first determination of the chirp in the attosecond pulse train with an autocorrelation technique. These results will open the way to full characterization of an attosecond pulse train with its envelope.     

Dynamic analysis of a coupled high-speed train and bridge system subjected to collision load

A dynamic analysis model is established for a coupled high-speed train and bridge system subjected to collision-load. A 7×32 m simply-supported high-speed railway bridge with box girders is considered as an illustrating case study. A high-speed China-Star train is traveling on the bridge. The time history curve of a drifting-floe collision force is obtained from a field experiment and introduced as the excitation load on the bridge piers. Then, the dynamic response of the coupled train–bridge system subjected to the measured drifting-floe collision is calculated. Afterwards, the running safety indices such as derailment factor, offload factor and lateral wheel-rail force of train vehicles are investigated. The results show that the dynamic response of the bridge subjected to a collision load is much greater than the one without a collision, resulting in a big influence on the running safety of high-speed trains. For the case study, a critical train speed curve is proposed to evaluate the running safety of train vehicles on the bridge under drifting-floe collision with various intensities.     

来流Mach数连续变化下的激波串运动特性

为了研究入射激波变化的隔离段内激波串的运动特性,设计并搭建了直连式变Mach数实验系统,捕捉了相同来流Mach数变化速率、不同背压变化速率下激波串的运动行为,揭示了入射激波与背压同时变化对激波串运动的影响机理。入射激波与背压同时变化时,共有3个方面的因素会影响激波串整体的上下游运动趋势,其一,Mach数变化,Mach数增大导致激波串向下游运动,该影响随Mach数增大逐渐减弱;其二,背景波系移动,背景激波反射点靠近激波串前缘时,可能引起激波串的突跳;其三,背压压比变化,背压压比增大时激波串向上游运动,该影响随背压压比增大逐渐增强。三方面因素共同作用下激波串表现出复杂的运动。      

The relationship between energy consumption and train delay in railway traffic

Based on deterministic NaSch model, we propose a new cellular automation model for simulating train movement. In the proposed model, the reaction time of driver/train equipment is considered. Our study is focused on the additional energy consumption arising by train delay around a traffic bottle (station). The simulation results demonstrate that the proposed model is suitable for simulating the train movement under high speed condition. Further, we discuss the relationship between the additional energy consumption and some factors which affect the formation of train delay, such as the maximum speed of trains and the station dwell time etc.     

Tunable subpicosecond electron-bunch-train generation using a transverse-to-longitudinal phase-space exchange technique

We report on the experimental generation of a train of subpicosecond electron bunches. The bunch train generation is accomplished using a beam line capable of exchanging the coordinates between the horizontal and longitudinal degrees of freedom. An initial beam consisting of a set of horizontally separated beamlets is converted into a train of bunches temporally separated with tunable bunch duration and separation. The experiment reported in this Letter unambiguously demonstrates the conversion process and its versatility.     

Modeling and Simulation for Urban Rail Traffic Problem Based on Cellular Automata

Based on the Nagel-Schreckenberg model, we propose a new cellular automata model to simulate the urban rail traffic flow under moving block system and present a new minimum instantaneous distance formula under pure moving block. We also analyze the characteristics of the urban rail traffic flow under the influence of train density, station dwell times, the length of train, and the train velocity. Train delays can be decreased effectively through flexible departure intervals according to the preceding train type before its departure. The results demonstrate that a suitable adjustment of the current train velocity based on the following train velocity can greatly shorten the minimum departure intervals and then increase the capacity of rail transit.