In vivo diffusion tensor imaging of thoracic and cervical rat spinal cord at 7 T

In vivo diffusion tensor imaging (DTI) of rat cervical and thoracic spinal cord was performed using a three-element phased array coil at 7 T. The magnetic field was shimmed over the spinal cord in real time using an in-house developed automatic algorithm. Echo planar imaging (EPI)-based diffusion-weighted images (DWIs) were acquired with 21 gradient encoding directions. The DWIs were tensor encoded, and diffusion tensor metrics, fractional anisotropy (FA), mean diffusivity (MD), longitudinal diffusivity (λ₀) and transverse diffusivity (λ) were determined for both white matter (WM) and gray matter (GM). The results on six normal rats indicated no significant differences in the diffusion tensor metrics between thoracic and cervical regions. However, the DTI-derived metrics in cervical spinal cord from our study are somewhat different from the published results in rats. The possible reasons for these differences are suggested.     

引入电流负反馈后电路输出阻抗变化的测试难点及解决方案

引入电流负反馈会使放大电路的输出电阻变大,这种变化在实验测量时几乎没有出现。我们在分析原因后,提出了一种简单、易行的解决方案,并且对电路参数进行了合理化设计,使实验效果非常理想。     

A strip-shield improves the efficiency of a solenoid coil in probes for high-field solid-state NMR of lossy biological samples

A strip-shield inserted between a high inductance double-tuned solenoid coil and the glass tube containing the sample improves the efficiency of probes used for high-field solid-state NMR experiments on lossy aqueous samples of proteins and other biopolymers. A strip-shield is a coil liner consisting of thin copper strips layered on a PTFE (polytetrafluoroethylene) insulator. With lossy samples, the shift in tuning frequency is smaller, the reduction in Q, and RF-induced heating are all significantly reduced when the strip-shield is present. The performance of 800 MHz ¹H/¹⁵N and ¹H/¹³C double-resonance probes is demonstrated on aqueous samples of membrane proteins in phospholipid bilayers.     

雷电流测量专用柔性无磁芯大型Rogowski线圈

 为了解决小型Rogowski线圈无法测量柱状高塔的自然雷电流波形的问题,提出了采用大型Rogowski线圈测量高塔雷电流的方案,研究设计了柔性骨架无磁芯大型Rogowski线圈,去除磁芯和外加积分器,通过增加线圈匝数获得高电感,以实现测量结果的自积分,降低了微分型Rogowski线圈需要额外积分器的难度。Rogowski线圈的标定表明,线圈具有良好的积分特性,采用输出误差系统辨识模型对Rogowski线圈输出波形进行了校正补偿,提高了测量波形的准确度,增大了高塔自然雷电流精确测量的可能性。     

高温超导线圈在大电流下稳定性的数值仿真

在电力应用中,超导磁体可能会因为线圈工作于过流状态而失超,也可能会因为交流损耗而导致失超.为此,我们模拟了一个磁体在大电流过载下的稳定性情况.我们使用了一个建立在热传导方程和麦克斯韦方程基础上的差分数值计算方法来得出磁体内部的温度分布.我们对各种不同的电流冲击情况进行了考察,我们的模型可以使磁体设计者在实际制作之前能够估计一个比较安全的操作电流水平,有着广泛的实用价值.     

Performance comparison using the GUESS mixture to evaluate counter-current chromatography instruments

Comparing the performance of different counter-current chromatography (CCC) J-type centrifuges has and will always be difficult. This is due to the number of variables such as speed of rotation, swung radius, β-value, column bore, column length that can be chosen during the design of an instrument. This situation is further complicated by the implication that some of these variables are intrinsically linked, such that if one is changed another or others can also change. The chromatographer has no influence on these hardware parameters once the instrument designer has chosen them. However, the chromatographer wants a CCC column that retains the most liquid stationary phase in order to achieve the best separation of the components in a mixture. What matters most is column performance in terms of: sample loading per injection, speed of separation, purity of target and yield of target. The instrument that has the best performance in all these areas is called a “high-performance” CCC system. This paper demonstrates to the modern chromatographer that a “high-performance” CCC instrument has shorter, lower volume columns that are rotated faster to provide quicker separations, even with the same sample loading.     

Interconversion of Planar Networks and Vesicles Triggered by Temperature

Dumbbell‐shaped amphiphiles based on an elongated rod segment can self‐assemble into planar networks with in‐plane hexagonally ordered pores in aqueous solution. On increasing temperature, the 2D networks change into hollow capsules passing through the closed sheets as an intermediate structure due to a LCST behavior of the oligoether dendritic exterior. The primary driving force for this interesting feature seems to originate from a consequence of the energy balance between hydrophobic interactions of anisotropic rod segments and alkyl chains, and repulsive interactions between dissimilar blocks. This dynamic structural variation triggered by external stimuli in a self‐assembling system can provide a useful strategy to create smart supramolecular materials and biomimetic systems.

     

BOTDA光纤传感技术在光纤环圈质量评估中的应用

在分析光纤环对陀螺整体性能影响的基础上,提出将BOTDA光纤传感技术用于光纤环质量检测。通过对光纤环的在线检测、热应力检测和骨架性能影响测试,能及时发现并消除光纤绕制中的应力尖峰及换层现象,消除由骨架、热应力引起的光纤应力曲线反转现象。     

一种可拆装式的脑外科手术用磁共振成像线圈

在临床磁共振成像(MRI)应用中,射频线圈的设计是非常关键的,针对不同的应用目的,合适的线圈能获得质量更好的图像. 有的应用需要线圈提供均匀性较好的射频场,而有的应用则需要线圈在特定区域内提供高的信噪比(SNR). 但是线圈很难同时得到好的射频场（B₁场）、空间均匀性和高的SNR,需要根据实际应用情况进行折衷设计. 针对MRI在脑外科手术中的应用特点,设计并制作了一种新颖的、适用于脑外科手术的MRI接收和发射共用射频线圈. 该线圈采用可分拆式结构,在脑外科手术支架上可以进行反复组装和拆卸,减少了MRI对医生手术的影响. 仿真结果和人体成像实验表明,该线圈能产生均匀的射频场、有较高的SNR和较大的成像范围,满足脑外科手术的需要.     

Designing shielded radio-frequency phased-array coils for magnetic resonance imaging

In this paper, an approach to the design of shielded radio-frequency (RF) phased-array coils for magnetic resonance imaging (MRI) is proposed. The target field method is used to find current densities distributed on primary and shield coils. The stream function technique is used to discretize current densities and to obtain the winding patterns of the coils. The corresponding highly ill-conditioned integral equation is solved by the Tikhonov regularization with a penalty function related to the minimum curvature. To balance the simplicity and smoothness with the homogeneity of the magnetic field of the coil’s winding pattern, the selection of a penalty factor is discussed in detail.