用于晶体生长的地基无容器悬浮技术

空间微重力环境下几乎无对流和沉降,可为晶体生长提供一个相对稳定和均一的理想环境,易于得到尺寸较大的高质量单晶。但是,空间结晶实验成功率低,费用昂贵,实验机会受限。因此,研发各种空间微重力环境地基模拟技术具有重要意义。目前可用于晶体生长的地基无容器悬浮技术主要有空气动力悬浮、静电悬浮、电磁悬浮、液体界面悬浮、超声悬浮和磁场悬浮技术等。这些地基模拟技术可实现晶体的无容器悬浮生长,避免器壁对晶体生长的不良影响,提高晶体质量,为解决X射线单晶衍射技术中的瓶颈问题提供新途径,还可为在地基进行结晶动力学和机理研究提供简单易行的方法。从技术原理、优势、缺陷及在结晶(特别是蛋白质结晶)中的应用4个方面对这些技术逐一进行了介绍和评述。重点介绍了液体界面悬浮、超声悬浮和磁场悬浮技术这3种用于蛋白质晶体生长的较为成熟的地基无容器悬浮技术。     

A superconducting magnetic levitation device for the transport of light payloads

A device for the frictionless transport of light payloads, e.g., silicon wafers, using superconducting magnetic levitation has been demonstrated. The device consists of an array of rigidly connected carrier magnets levitating above a corresponding array of superconducting discs. Silicon wafers placed on the carrier have been linearly transported with velocities up to 50 cm/s. The configuration provides for excellent lateral stability. Studies of the height and lateral friction effects (caused by flux pinning) were measured as a function of payload mass. Future applications may include the frictionless transport of silicon wafers in vacuum environments.     

基于力失衡的二维主动磁悬浮驱动方法分析与测试

提出一种基于力失衡的磁悬浮驱动系统,并对外磁场主动驱动设计一种神经网络PID(Proportion Integration Differentiation)控制方法,可以有效应对非线性、模型参数不明确的复杂驱动系统。实验结果表明,该控制算法解决了基于模型控制方法中被控对象与稳态工作点之间偏差增大、跟踪性能迅速恶化等问题,实现了磁性小球在二维空间中的稳定悬浮与高精度可控运动。可应用于工业领域细长管道内壁非破坏式质量检测、管道内部清淤和医疗领域血管、肠腔内的检查和手术。     

Magnetic Levitation With High-Tc Superconducting Thin Films

The levitation force between a permanent magnet and a superconducting thin film was investigated experimentally. The configuration consisted of a cylindrical NdFeB permanent magnet placed above a circular YBa₂Cu₃O_7– disk with common cylinder axis. Precise measurements were made of the vertical force F _z and the magnetic stiffness _z as a function of the magnet–superconductor separation at 77 K. Several features contrasting the levitation force produced using bulk superconductors were observed. Thin films produced very high values for F _z and _z per unit volume of superconducting material. The hysteretic behavior of F _z during decreasing and increasing separation resulted in loops of nearly symmetrical shape, which also contain a peak in the repulsive force branch. The observations are analyzed and explained with good quantitative agreement using recent theories for flux penetration in thin superconductors in transverse magnetic fields.     

单轴式声悬浮的物理特性

采用边界元方法对单轴式声悬浮过程中的人射声场计算,揭示了样品在声悬浮过程中的受力特性,结果表明,提高声源强度,降低重力水平或者采用密度大声速小的气体介质有利于提高声悬浮能力,另外,采用适当曲率半径和较大截面半径的凹球面反射端能够提高模式4下靠近反射面的一个悬浮位置的悬浮性能。     

高效磁悬浮变频离心式冷水机组的研制

对磁悬浮变频离心式压缩机高效、无油、高可靠性的特点进行介绍,并着重介绍一款采用该压缩机开发的新型冷水机组。该型机组在额定工况下性能系数可达6.19,远高于GB 19577—2004《冷水机组能效限定值及能源效率等级》中的一级能耗,部分负荷性能系数更可达到9.79,为GB 19577—2004限定值的2倍。     

磁力金属带传动的传动特性分析

介绍了磁力金属带传动的工作原理,分析和探讨了其有效拉力、线速度及弹性滑动率等传动性能,并通过实验测定了相关性能参数。结果表明,磁力金属带传动主要是利用磁场吸引力与初拉力的耦合作用来增加摩擦力进而传递运动和动力的,其传动效率可达95%～98%,而弹性滑动率一般在0.1%以下。     

The interminable adolescence of superconductivity

Seventy-seven years after its discovery, superconductivity has failed to mature into a practical technology because we in America have lacked the curiosity to understand it, the imagination to appreciate it, and the spirit of enterprise to develop it. We are about to miss our last chance to regain technical leadership and economic security if we continue to pretend that higher-T _c materials alone will change the situation.     

磁悬浮转子真空计混合磁悬浮建模与控制研究

针对磁悬浮转子真空计的永磁-电磁混合磁悬浮系统,考虑其磁悬浮结构中的永磁体影响,计算了磁悬浮轴向的磁场分布,建立了混合磁悬浮系统的频域模型。设计了永磁电流刚度系数与永磁位移刚度系数,用来表征线圈电流、转子距下线圈的距离及永磁体参数对混合磁悬浮系统的影响,并依据这两个参数对悬浮系统的设计做出限制与规定。设计了模拟比例-积分-微分控制电路以进行悬浮控制。最后按照此控制模型在真空下用测量头进行压力测量实验。实验结果表明,根据设计的混合磁悬浮模型的线圈参数与安装位置,在模拟比例-积分-微分控制电路的控制下,可以完成9×10^-5～1 Pa的压力测量。     

计量级磁悬浮转子真空计技术研究

磁悬浮转子真空计为国际公认的高真空范围溯源/传递标准,因其优良的计量特性和化学惰性,广泛应用于航空航天、核工业、半导体和高端装备制造等领域。针对高真空范围传递标准国产化需求,开展了永磁偏置转子稳定悬浮、转子轴向位移精确测量、转子转速衰减速率动力学模型构建及高精度检测等关键技术研究,为计量级磁悬浮转子真空计研制、实现高真空范围真空量值溯源/传递国际等效,进而建立我国现代先进的真空计量技术体系奠定基础。     

Dynamics of magnetophoretic separation of a suspension of slightly magnetic microparticles in a high-gradient field of a magnetized rod

A macroscopic model of the process of magnetophoretic separation of slightly magnetic particles from a suspension under the action of a high-gradient magnetic field with account for the particle size is proposed. The mechanisms of separation of dia- and paramagnetic particles from a narrow fluid layer in an inhomogeneous field of a magnetized rod have been investigated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 221–226, March–April, 2009.     

Design of the DEMO Fusion Reactor Following ITER

Runs of the NSTAB nonlinear stability code show there are many three-dimensional (3D) solutions of the advanced tokamak problem subject to axially symmetric boundary conditions. These numerical simulations based on mathematical equations in conservation form predict that the ITER international tokamak project will encounter persistent disruptions and edge localized mode (ELMS) crashes. Test particle runs of the TRAN transport code suggest that for quasineutrality to prevail in tokamaks a certain minimum level of 3D asymmetry of the magnetic spectrum is required which is comparable to that found in quasiaxially symmetric (QAS) stellarators. The computational theory suggests that a QAS stellarator with two field periods and proportions like those of ITER is a good candidate for a fusion reactor. For a demonstration reactor (DEMO) we seek an experiment that combines the best features of ITER, with a system of QAS coils providing external rotational transform, which is a measure of the poloidal field. We have discovered a configuration with unusually good quasisymmetry that is ideal for this task.     

单轴式声悬浮的实验研究及数值模拟分析

采用自行研制的单轴式声悬浮装置,实现了密度为7.9g/cm3的钢球的稳定悬浮.采用有限元方法对两种不同形状谐振腔的声场进行了数值计算和模拟,结果表明采用凹球面形反射面能有效提高悬浮性能;同时解释了实验过程中小球沿凹球面壁运动的现象,对进一步研究声悬浮装置结构对悬浮性能的影响有一定的借鉴意义.