ITER纵场磁体馈线温度场分析

ITER超导托卡马克装置在运行之前要对磁体线圈及馈线系统进行冷却降温,以达到超导体工作所需的低温环境.文中利用大型有限元分析软件ANSYS的温度场分析模块,对纵场磁体馈线系统的降温过程进行模拟仿真,得到了不同时刻馈线上的温度分布情况.在得出冷却过程中馈线上的温度变化之后,又根据稳定状态时的温度分布对结构进行了热应力分析...     

Inhibition of amyloid aggregation by formation of helical assemblies

The formation of amyloid aggregates is responsible for a wide range of diseases, including Alzheimer's and Parkinson's disease. Although the amyloid-forming proteins have different structures and sequences, all undergo a conformational change to form amyloid aggregates that have a characteristic cross-β-structure. The mechanistic details of this process are poorly understood, but different strategies for the development of inhibitors of amyloid formation have been proposed. In most cases, chemically diverse compounds bind to an elongated form of the protein in a β-strand conformation and thereby exert their therapeutic effect. However, this approach could favor the formation of prefibrillar oligomeric species, which are thought to be toxic. Herein, we report an alternative approach in which a helical coiled-coil-based inhibitor peptide has been designed to engage a coiled-coil-based amyloid-forming model peptide in a stable coiled-coil arrangement, thereby preventing rearrangement into a β-sheet conformation and the subsequent formation of amyloid-like fibrils. Moreover, we show that the helix-forming peptide is able to disassemble mature amyloid-like fibrils.     

Effective noise estimation and filtering from correlated multiple-coil MR data

Modern magnetic resonance (MR) imaging protocols based on multiple-coil acquisitions have carried on a new attention to noise and signal statistical modeling, as long as most of the existing techniques for data processing are model based. In particular, nonaccelerated multiple-coil and GeneRalized Autocalibrated Partially Parallel Acquisitions (GRAPPA) have brought noncentral-χ (nc-χ) statistics into stake as a suitable substitute for traditional Rician distributions. However, this model is only valid when the signals received by each coil are roughly uncorrelated. The recent literature on this topic suggests that this is often not the case, so nc-χ statistics are in principle not adequate. Fortunately, such model can be adapted through the definition of a set of effective parameters, namely, an effective noise power (greater than the actual power of thermal noise in the Radio Frequency receiver) and an effective number of coils (smaller than the actual number of RF receiving coils in the system). The implications of these artifacts in practical algorithms have not been discussed elsewhere. In the present paper, we aim to study their actual impact and suggest practical rules to cope with them. We define the main noise parameters in this context, introducing a new expression for the effective variance of noise which is of capital importance for the two image processing problems studied: first, we propose a new method to estimate the effective variance of noise from the composite magnitude signal of MR data when correlations are assumed. Second, we adapt several model-based image denoising techniques to the correlated case using the noise estimation techniques proposed. We show, through a number of experiments with synthetic, phantom, and in vivo data, that neglecting the correlated nature of noise in multiple-coil systems implies important errors even in the simplest cases. At the same time, the proper statistical characterization of noise through effective parameters drives to improved accuracy (both qualitatively and quantitatively) for both of the problems studied.     

共轴三线圈磁场的均匀性

给出用平行共轴不等大等电流的三个圆线圈形成匀强磁场的方法．文中给出了三线圈形成匀强磁场的条件,并且通过数值计算全面分析了三线圈磁场的均匀性．与Helmholtz线圈磁场比较显示,三线圈的磁场无论在强度方面,还是在磁场均匀性方面都明显优于Helmholtz线圈的磁场．     

Eddy current simulation in thick cylinders of finite length induced by coils of arbitrary geometry

Eddy currents are inevitably induced when time-varying magnetic field gradients interact with the metallic structures of a magnetic resonance imaging (MRI) scanner. The secondary magnetic field produced by this induced current degrades the spatial and temporal performance of the primary field generated by the gradient coils. Although this undesired effect can be minimized by using actively and/or passively shielded gradient coils and current pre-emphasis techniques, a residual eddy current still remains in the MRI scanner structure. Accurate simulation of these eddy currents is important in the successful design of gradient coils and magnet cryostat vessels. Efficient methods for simulating eddy currents are currently restricted to cylindrical-symmetry. The approach presented in this paper divides thick conducting cylinders into thin layers (thinner than the skin depth) and expresses the current density on each as a Fourier series. The coupling between each mode of the Fourier series with every other is modeled with an inductive network method. In this way, the eddy currents induced in realistic cryostat surfaces by coils of arbitrary geometry can be simulated. The new method was validated by simulating a canonical problem and comparing the results against a commercially available software package. An accurate skin depth of 2.76 mm was calculated in 6 min with the new method. The currents induced by an actively shielded x-gradient coil were simulated assuming a finite length cylindrical cryostat consisting of three different conducting materials. Details of the temporal-spatial induced current diffusion process were simulated through all cryostat layers, which could not be efficiently simulated with any other method. With this data, all quantities that depend on the current density, such as the secondary magnetic field, are simply evaluated.     

Detection of Multiple Samples Based on AlGaN/GaN High Electron Mobility Transistors and Magnetic Microbeads

Semiconductor biochemical sensors are regarded as robust tools for the detection of various targets. However, re‐use of these sensors is one of the major obstacles hindering further development. To address this problem, a multi‐objective platform was developed based on magnetic beads and the AlGaN/GaN high electron mobility transistor (MBs AlGaN/GaN HEMT) device. Since the magnetic beads are capable of being fixed and released by inductance coils, the platform enables repeatability and multi‐objectivity during testing. To validate the advantages of the platform, metal ions and prostate specific antigen (PSA) were used. In this study, a platform sensing biochemical responses with a sensor was demonstrated to show the characteristics of reusability, multi‐target sensing, and simplicity, resulting in its promising prospects for widespread applications.     

ITER 聚变装置内部线圈导体高纯铜管机械性能研究

对ITER 装置内部线圈(IVC)中,管内矿物绝缘导体(SSMIC)中的无氧铜管在常温、高温下的机械性能进行了研究。结果显示高纯铜的机械性能满足设计要求,抗拉强度和屈服强度在常温、高温下均有提高。此结果为ITER 内部线圈导体的设计与性能分析提供了数据参考。     

HL-2M 装置环向场线圈匝间绝缘工艺研究

HL-2M tokamak adopts the demountable toroidal field coils (TFCs) structure in order to assemble the vacuum vessel chamber and poloidal field coils (PFCs) integrally. TFCs are subjected to high shear force, which require high electrical performance and adhesive strength between the inter turn insulation and the copper plate. Baking and curing impregnated glass cloth and epoxy glass cloth under different pressure, then adhesive properties have been researched by shear tests. The results show that there are some differences in the adhesive properties between the turn to turn insulation and the copper plate under different structural combinations and different pressures. Appropriate structural combination and pressure of hot baking and curing were selected for TFCs.     

托卡马克聚变堆中环向磁场超导线圈的磁弹性弯曲与稳定性

本文针对托卡马克装置中超导载流磁体的磁弹性弯曲与稳定性问题，运用Ｂｉｏｔ－Ｓａｖａｒｔ定律和曲梁弯曲理论，给出了其环向磁场的超导载流线圈结构在自身电流产生的磁力作用下的磁弹性力学模型。所得到的控制方程反映了磁场与线圈变形之间的非线性耦合作用，全面描述了结构的轴向拉伸、绕轴扭转、面内弯曲和面外弯曲等各种变形模式。本文采用半解析半数值方法对控制方程进行了定量求解，获得了有关线圈形变和内力分布的定量结果。通过其面外弯曲变形与外加电流的非线性关系，应用Ｓｏｕｔｈｗｅｌ图，给出了线圈在磁弹性相互作用下发生磁弹性失稳的临界电流值，并讨论了临界电流随环向磁场线圈个数变化的规律     

全超导托卡马克极向场超导线圈的失超检测

EAST装置做为全超导托卡马克装置,其纵场和极向场线圈全部由超导磁体组成,所以进行安全,准确,有效的超导线圈的失超保护是装置安全运行的首要环节.由于等离子体电流的建立必须由极向场线圈系统提供极快速的磁通变化,随之产生较高的交流损耗使得极向场线圈很容易发生失超.如何对快速交变脉冲磁场下的超导线圈进行有效的失超检测,这在世界上也无先例可循.EAST装置的失超检测系统经过几十轮单饼超导线圈实验及多轮装置正式放电实验后逐步建立和完善起来,并已通过工程验收满足了装置实验运行要求.本文主要介绍了EAST装置失超检测系统的基本结构和检测原理,重点阐述了极向场超导磁体失超检测的设计方法及实验结果。