非金属低温杜瓦装置的研制

报道了一种非金属杜瓦装置的研制,以满足高温超导磁悬浮车系统对液氮低温容器的要求。这种长方体低温容器采用无磁非金属材料制备,从而可以避免由涡流导致的阻力和热损耗,以及由磁性导致的吸引力等不利于高温超导磁悬浮车系统的影响。容器的液氮损耗率为0.55L/h。综合性能测试表明,该非金属杜瓦可以作为高温超导磁浮车低温容器的理想选择之一。     

广东科学中心高温超导磁悬浮车设计与制作

广东科学中心交通世界展馆的高温超导磁悬浮车演示模型,由支架、永磁轨道、超导磁悬浮小车、直线电机和控制系统构成。∞形轨道长19m,包含直线、圆曲线、缓和曲线、坡道,轨道沿线布置直线电机线圈和光电传感器。磁悬浮小车为两节联挂,每节小车车体由两个低温液氮容器和一个直线电机动子组成,每个液氮容器中包含6块YBCO超导块材。磁悬浮小车可以在轨道上连续运行,自控系统能够对小车进行启动、加速、减速、定位停车等运行控制,运行模式分自动行驶和手动操作两种。     

真空管道HTS侧浮系统对直线电机推力的影响

为提高真空管道高温超导(HTS)磁悬浮列车系统的自由悬浮运行速度,提出了侧浮式高温超导磁悬浮系统.通过实验对该系统环线运行下的动态过程进行了研究,结果表明,磁浮车在环线运行中,因离心力和重力作用产生横向位移和垂直位移,通过实验和仿真研究了该动态过程对直线电机驱动性能的影响,结果表明,随着垂直位移和横向位移的减小,直线电机起动推力逐渐增大;当垂直位移为5 mm,横向位移小于10 mm时,磁浮车偏离电机中心引起的驱动力变化影响不大.使列车保持较高的驱动稳定性,为侧浮式真空管道高温超导磁浮车初始悬浮位置设计提供参考.     

面向超导钉扎磁浮的液氮液位检测方法研究现状

高温超导钉扎磁浮制式以悬浮导向一体化、自稳定、无需控制等优势得到了越来越多的关注.与其他磁浮制式不同,高温超导钉扎磁浮制式采用块状高温超导材料作为车载悬浮体,需要低温液体液氮作为悬浮单元的制冷剂,冷却方式为浴冷,因此实时监测液氮液面,保证液面平稳是未来超导钉扎磁浮车运行维护的首要需求.本文从车载高温超导YBaCuO块材所需的液氮环境及其配套的液氮容器功能和结构出发,结合我们近期的基于卡尔曼滤波(Kalman filtering,KF)滤波算法的铂电阻传感器液氮液位计研究工作,对6种低温液位检测方法的基础原理、特征及检测精度的对比分析,总结示出包括铂电阻阵列方式在内的3种适用于超导钉扎磁浮列车在线检测系统的液氮液位检测方法,用于推进我国2021年1月13日正式启用的高温超导钉扎高速磁浮工程化样车应用发展.     

高温超导磁浮系统中的振动耗能法制动分析

为了实现磁浮车的无接触的制动,本文提出一种振动耗能的方法.该方法通过人为使得轨道磁场分布不均衡,从而将运行磁浮车体运动方向上的动能转化为与其垂直方向上的阻尼振动,以消耗运行车体的动能并使车体减速.文中忽略空气阻力,采用理论分析与计算机仿真的方法讨论了轨道磁场分布不均对车体振动特性的影响.最后在西南交通大学真空管道高温超导磁浮系统实验平台上实验验证了该方法对车体运行速度的影响,为将来的真空管道磁浮交通系统的设计提供参考.     

车载高温超导磁悬浮系统的设计

介绍车载高温超导磁悬浮系统的设计问题。为了完成系统的设计 ,首先进行了单块和多块YBCO高温超导体块材的悬浮力的研究 ,同时考虑了 YBCO高温超导体块材的选取问题。设计的目标是稳定悬浮 350 kg,采用 8个车载液氮低温容器 ,这种容器是底壁仅 3mm厚的长方体形的。     

35kV/90MVA高温超导限流器低温系统

35kV/90MVA高温超导限流器的低温系统是一个开放式的液氮制冷系统,包括一个环形不锈钢杜瓦、真空绝热管、压力及温度传感器、低温阀门以及监控系统.高温超导磁体放置在杜瓦中;监控系统检测杜瓦内液氮的液面,并控制往杜瓦内进行补液.杜瓦内蒸发的氮气通过真空绝热管道直接排放到大气中.分别对不同工况下的液氮蒸发量进行了测量.进...     

一种新式单倾角高温超导磁悬浮车永磁道岔设计

高温超导(HTS)磁悬浮列车是下一代新型磁悬浮交通工具的备选方案之一。非接触轮轨系统使得轨道道岔面临诸多问题。给出了一种单倾角永磁体结构的新型机械永磁道岔结构。在使用单倾角永磁体装配永磁道岔时,两相邻永磁体之间的楔形缝隙用于调整永磁轨道在水平面上的曲率,以适应磁悬浮车变道目的。成功推导出了单倾角永磁体的几何尺寸、倾角大小和永磁道岔最小转弯半径之间的关系数学表达式并通过仿真计算进行了初步验证。计算结果表明,当永磁道岔换轨时,这种微小的差别不足于影响高温超导磁悬浮车的运行稳定性。     

时变外磁场中高温超导块材导向力性能的数值模拟

基于Bean临界态模型,针对目前的高温超导磁悬浮车系统,提出了一种模拟计算方法,该方法可计算在时变外磁场中块材导向力的衰减变化情况。通过对时变外磁场中块材温度、俘获磁通以及导向力等参数变化情况的实验结果和计算结果的对比,证实了该模拟计算方法的有效性。该模拟计算方法可用于定性研究高温超导块材的导向力性能在时变外磁场作用下的变化情况,为高温超导磁悬浮车的研究和工程实践提供了较为重要的科学依据。     

高真空多层绝热低温容器真空丧失后的传热研究

高真空多层绝热低温容器的绝热夹层发生完全的真空丧失事故后,由于自然对流换热的原因,其绝热夹层的漏热量会急剧增加.在搭建了高真空多层绝热低温容器完全真空丧失后的传热研究实验台的基础上,使用于燥氮气为破空介质、液氮为低温介质,进行了多次高真空多层绝热低温容器的完全真空丧失实验.重点研究了低温容器液位及绝热材料层数的变化对其...     

Electronic topological transition in zinc metal? A 67Zn-Mössbauer investigation

The question concerning the existence of an electronic topological transition (ETT) in Zn metal under quasi-hydrostatic pressure at ～6.6 GPa caused a considerable controversy in the literature. We briefly review low-temperature ⁶⁷Zn-Mössbauer data and scalar-relativistic augmented plane wave calculations and give a consistent interpretation in terms of an ETT. To highlight some important aspects of the controversy two theoretical and two experimental publications will be discussed in more detail. At present the existence of an ETT in Zn metal is disputed both from an experimental and from a theoretical point of view. The suggestion of a transition to a commensurate spin-density wave at ～6.6 GPa instead of an ETT may reconcile the seemingly contradictory results of ⁶⁷Zn-Mössbauer experiments at 4.2 K and of room temperature inelastic neutron scattering measurements. However, it does not explain the anomalies found in theoretical calculations performed for Zn metal in this pressure range. Considerable experimental and theoretical efforts are required to confirm - or rule out - a spin-density-wave transition.     

永磁轨道上方高温超导块材各向异性对悬浮力弛豫特性的影响

采用顶部熔融织构生长法制备的高温超导块材YBCO通常有5个生长区域．通过捕获磁通实验研究,人们发现高温超导块材内部生长区域及边界的捕获磁通能力不同,存在明显的各向异性．面向高温超导磁悬浮应用,本文比较研究了3块不同的高温超导块材YBCO组合在永磁轨道上方悬浮力弛豫特性．实验结果表明,无论场冷还是零场冷情况,块材籽晶生长...     

Electronic-topological transition and shear stability of the β alloys Ni-Al and TiNi

On the basis of a numerical calculation of the band contributions to the shear moduli, this paper discusses a hypothesis expressed earlier that the premartensitic softening of the lattice in Ni-Al and TiNi alloys is caused by the approach of the latter to an electronic-topological transition (ETT). It is found in both alloys that the ETT effects are substantially different in the different shear moduli: They are strong in the modulus C′ (especially in Ni-Al) and weak in C ₄₄. It can be concluded from this result that the observed premartensitic softening of C′ in Ni-Al and TiNi can actually be caused by the approach to the ETT point. At the same time, the anomalous temperature dependence of C ₄₄ observed in TiNi is apparently not associated with ETT effects. Fiz. Tverd. Tela (St. Petersburg) 39, 972–976 (June 1997)     

Levitation force relaxation under reloading in a HTS Maglev system

The loading capacity of the high-temperature superconducting (HTS) Maglev vehicle is an important parameter in the practical application. It is closely related to the levitation force of the HTS bulk. Many papers reported that the levitation force showed the relaxation characteristic. Because different loads cause different levitation gaps and different applied magnetic fields, the levitation force relaxations under the different loads are not the same. In terms of cylindrical YBCO bulk levitated over the permanent magnetic guideway, the relationship between the levitation force relaxation and the reloading is investigated experimentally in this paper. The decrement, the decrement rate and the relaxation rate of the levitation force are calculated, respectively. This work might be helpful for studying the loading capacity of the HTS Maglev vehicle.     

高温超导磁悬浮深冷测试系统设计

介绍一种使用 G- M制冷机实现深冷环境的高温超导磁悬浮测试系统。高温超导体块材YBa Cu O被固定在制冷机冷头上 ,其温度通过温度控制器可以控制在 1 0 0 K到 40 K范围内。永久磁体 Nd Fe B固定在位于 YBa Cu O上方高温超导磁悬浮测试系统的垂直运动部件上 ,并在计算机控制下作垂直运动以改变它与 YBa Cu O之间的距离。同时 ,计算机采集数据得到 YBa Cu O与 Nd Fe B之间悬浮力与距离的关系。通过温度设定 ,可得到 YBa Cu O在不同温度下的悬浮性能。     

Two-dimensional agnor evaluation as a prognostic variable in urinary bladder carcinoma: a different approach via total agnor area/nucleus area per cell

Traditional criterions are not sufficient to predict accurately the recurrence of transitional cell carcinoma of the urinary bladder. Therefore, we aimed to evaluate the AgNORs via total AgNOR area/nucleus area (TAA/NA) for each cell as a prognostic parameter, in TCC of urinary bladder. Tumor tissues of 20 consecutive cases of male bladder cancer patients were divided into two groups as middle differentiated (LG) and high grade (HG). The extra-tumoral tissue (ETT) samples of 10 males served as control group. A second control group (HC) consisted of five healthy and normal bladder tissue samples. The 3 microm of sections from each paraffin embedded tumoral, extra-tumoral and normal tissue samples served as patient and control groups. After deparaffinization and rehydratation steps, silver (AgNO(3)) staining of nucleolar organizer regions-associated proteins (AgNORs) was performed. Instead of Giemsa stain, we used Hematoxylin for contra staining. The images of the 100 analyzable nuclei from each tissue sample, transferred by means of a video camera and video capture card from microscope and recorded onto a computer. Software was prepared in Delphi language for analysis. Mean (E+02) TAA/NA values of HC, ETT, LG and HG groups were 6.97+2.80, 5.70+1.82, 7.80+3.22 and 9.24+3.88, respectively. Statistical comparisons have shown significant differences between all groups.In conclusion, mean TAA/NA per cell has a potential to be a prognostic parameter. Therefore, further evaluation of big patient series will be useful.     

Effect of strain-induced electronic topological transitions on the superconducting properties of [Formula: See Text] thin films

We propose a Ginzburg-Landau phenomenological model for the dependence of the critical temperature on microscopic strain in tetragonal high-[Formula: See Text] cuprates. Such a model is in agreement with the experimental results for LSCO under epitaxial strain, as well as with the hydrostatic pressure dependence of [Formula: See Text] in most cuprates. In particular, a nonmonotonic dependence of [Formula: See Text] on hydrostatic pressure, as well as on in-plane or apical microstrain, is derived. From a microscopic point of view, such results can be understood as due to the proximity to an electronic topological transition (ETT). In the case of LSCO, we argue that such an ETT can be driven by a strain-induced modification of the band structure, at constant hole content, at variance with a doping-induced ETT, as is usually assumed.     

Influence of pressure on electron spectra of metals and semiconductors

Abstract

We have already reported the results of direct observations of electron-topological phase transition (ETT) in cadmium'. The appearance of new dHvA-frequencies corresponding to the Fermi surface (FS) change, i.e. restoring of folding of hole “monster” and electron “needle” appearance is observed under pressure. In t h i s report we are going to enlarge on the ETT consequences study in cadmium-on the advent of anomalous electronic features in transverse magnetoresistance and thermoelectric power.     

Electronic topological transition in metastable Al-Ge solid solutions

Al-rich Al-Ge solid solutions synthesized under high pressure demonstrate physical properties strikingly different from those of pure Al. In particular, enhanced superconductivity temperature (T_c), anomalies in the phonon spectra and decrease of the Debye temperature have been observed. We show from first-principles, based on calculations of the electronic spectra and Fermi surfaces of Al-Ge substitutional solid solutions, that an electronic topological transition (ETT) takes place in the system. We predict anomalies in transport properties to be revealed experimentally for Al-Ge solid solutions with the Ge concentration ≈10 at.%. The influence of the ETT on the thermodynamic properties of the system is discussed and, in particular, concentration dependence of the Debye temperature is reproduced in good agreement with experiment.     

Effect of strain-induced electronic topological transitions on the superconducting properties of La 2 - x Sr x CuO 4 thin films

We propose a Ginzburg-Landau phenomenological model for the dependence of the critical temperature on microscopic strain in tetragonal high-T _c cuprates. Such a model is in agreement with the experimental results for LSCO under epitaxial strain, as well as with the hydrostatic pressure dependence of T _c in most cuprates. In particular, a nonmonotonic dependence of T _c on hydrostatic pressure, as well as on in-plane or apical microstrain, is derived. From a microscopic point of view, such results can be understood as due to the proximity to an electronic topological transition (ETT). In the case of LSCO, we argue that such an ETT can be driven by a strain-induced modification of the band structure, at constant hole content, at variance with a doping-induced ETT, as is usually assumed. Received 1st October 2001 and Received in final form 5 December 2001