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超导电动悬浮列车以超导磁体作为核心部件, 具有环境影响小、 高速下自稳定、 安全性能好等优点, 已成为高速轨道交通的重要发展方向之一. 然而, 传统的磁体线圈结构存在绕组内磁场过于集中的问题, 导致磁体的临界电流下降显著, 列车的悬浮及安全性能也受到影响. 针对现有悬浮磁体结构自场集中导致的临界电流衰减问题,本文提出了一种梯形高温超导磁体线圈结构. 建立了一种可以提升磁体临界电流计算效率的均质自洽模型, 设计了梯形结构线圈的结构参数并完成了磁体线圈的绕制. 实验和计算结果表明, 自洽模型计算的磁体临界电流与实验测量值吻合良好, 验证了模型的准确性. 利用该模型对日本山梨试验线上的全尺寸车载高温超导磁体进行了结构优化设计. 研究发现, 优化后的车载磁体绕组内磁场集中程度明显下降, 车载磁体的临界电流及目标区域的磁场强度显著提高. 本研究相关成果可为电动悬浮列车车载磁体的结构设计提供参考. 相似文献
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本文设计了用于关节成像的1.5T超导核磁共振成像(MRI)主磁体的电磁结构与机械支撑结构.首先计算了主磁体成像区域及磁体周围的电磁场分布.在此基础上,采用电磁-结构耦合方法计算了主磁体与支撑结构中的应力、应变分布情况.同时分析了不同的支撑材料对磁体应力/应变的影响.给出了1.5T超导MRI主磁体支撑结构的设计标准. 相似文献
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Anischenko I. V. Osipov M. A. Pokrovskii S. V. Abin D. A. Starikovskii A. S. Rudnev I. A. 《Physics of Atomic Nuclei》2021,84(12):1982-1990
Physics of Atomic Nuclei - Stacked composite high-temperature superconducting tapes (HTS tapes) are advanced material for development of magnetic levitation systems such as levitation transport,... 相似文献
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E. A. Brui A. V. Shchelokova A. V. Sokolov A. P. Slobozhanyuk A. E. Andreychenko V. A. Fokin P. A. Belov I. V. Melchakova 《JETP Letters》2018,108(6):423-427
A hybrid metasurface realized by a double array of brass wires inserted into two high-permittivity dielectric slabs at both sides was used to perform a magnetic resonance spectroscopy experiment at a 1.5 T clinical magnetic resonance scanner. The metasurface coupled inductively to a transceive birdcage body coil located within the scanner’s bore. The metasurface demonstrated an enhancement of the signal-to-noise ratio of the magnetic resonance spectroscopy experiment in vitro. Up to a signal-to-noise ratio gain of 7.4 for choline and creatine spectral lines was observed in the presence of the metasurface compared to the body coil alone. 相似文献
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A phantom with T1 and T2 relaxation times encompassing normal liver and liver lesions was constructed to evaluate fast magnetic resonance pulse sequences using TR from 21-100 milliseconds, TE 12-60 milliseconds and flip angles from 5 degrees-90 degrees. Ten of these fast MR sequences were then selected and compared with conventional spin-echo sequences in normal volunteers (n = 3) and in patients with liver lesions (n = 6). Subjectively, the fast MR sequences eliminated motion artefacts. Objectively, 8 of 10 fast sequences had signal-to-noise ratios comparable to spin-echo imaging whereas only 2 of 10 had contrast-to-noise ratios that were similar to spin-echo imaging. This preliminary study, performed at 1.5 Tesla, does not show any clear-cut advantage of fast imaging over spin-echo imaging in the detection of liver lesions. The use of a liver tissue equivalent phantom provides a rapid, practical approach in evaluation of fast scans. 相似文献
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K. M. Horton M. S. Levey F. A. Owl-Smith R. G. Azizkhan M. L. Schiebler 《Magnetic resonance imaging》1989,7(6):689-691
We present here the first report of an extraskeletal metastasizing presacral chordoma found in a child. MRI of this large lesion showed heterogeneous signal intensity on both the SE 550/30 and on SE 2440/100 images. MRI demonstrated this mass to be separate from the sacrum and provided nonionizing cross-sectional imaging prior to attempted surgical resection. 相似文献
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We have previously reported that the T1 and T2 of experimental clots at 0.47 T varies considerably depending upon the method used in their preparation. However, these studies, while relevant to midfield imaging, may not reflect accurately the behavior of such thrombi at higher field strengths. Accordingly, we studied the T1 and T2 at 1.5 T of experimental thrombi prepared by several methods and compared these results with the relaxation times of clinical deep venous thrombi measured in situ in patients. The relationship between the T2 values for the different clot preparation methods was different at 1.5 T than at 0.47 T. The combined use of thrombin and epsilon-amino caproic acid produced thrombi with T1 and T2 indistinguishable from clinical deep venous thrombi. 相似文献
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F C Simm R C Semelka M Recht M Deimling G Lenz G A Laub 《Magnetic resonance imaging》1992,10(1):41-47
T2-weighted images are considered the most sensitive for lesion detection at high field; however, long imaging time is problematic. Accordingly, the authors compared four breath-hold T2 or T2* weighted sequences comprising T2*-weighted FLASH, T2*-weighted PSIF, T2-weighted rapid spin echo (RASE), and T2-weighted Turbo-FLASH (Turbo) in 20 different healthy volunteers, 10 at 1.0 T and 10 at 1.5 T with reference to regular T2-weighted spin echo. Images were evaluated quantitatively by liver signal to noise (S/N) and spleen-liver signal difference to noise (SD/N) ratios and qualitatively for presence of artifacts and image quality. Data were evaluated for 1.0 T and 1.5 T separately and combined. In the combined evaluation, T2*-FLASH had good S/N (23.1 + 5.1) but low SD/N (2.9 + 1.7) and suffered from susceptibility artifacts. T2* PSIF had good S/N (28.1 + 10.0) and moderate SD/N (6.0 + 2.4), but occasionally had heterogeneous signal intensity. Flow signal void was an attractive feature. T2 RASE had very low S/N (4.4 + 1.9) and low SD/N (2.3 + 1.1) and suffered from flow artifacts. T2-Turbo had good S/N (24.6 + 8.6) and SD/N (8.9 + 2.5). Flow signal void was present, but small matrix size decreased image quality. The results of our study suggest that T2*-PSIF and T2-Turbo have good S/N and SD/N and fair image quality which may be clinically useful for breath-hold T2-weighted sequences of the liver. 相似文献
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Dzik-Jurasz AS Wolber J Prock T Collins DJ Leach MO Rowland IJ 《Magnetic resonance imaging》2001,19(6):839-844
19F-MR-imaging has been used to quantitate albumin concentration in a phantom at 1.5 T. The experimentally derived relationship between albumin concentration and the T1 relaxation time of a fluorinated marker, tetrafluorosuccinic acid (TFSA) was used to calculate the albumin concentration from a quantitative 19F T1 map acquired using a gradient echo sequence. There was close correlation between calculated and actual BSA concentrations (r = 0.99, SE = 0.15). The potentially interfering effect of paramagnetic species on T1 relaxation times was also investigated. Relaxivity data show that albumin concentration measurements should be performed prior to any contrast agent administration. 相似文献
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第二代(RE)BCO高温超导带可以进行切割和堆叠以形成叠层状的复合导体结构,具备磁化后捕获强磁场的潜力.脉冲磁化条件下,叠层导体会受到电-磁-热多物理场作用,易对高温超导带的力学稳定性造成不利影响.本文基于电磁场H格式和热传导方程对叠层导体进行了多场耦合建模分析,同时结合有限元方法,分析了圆柱形叠层导体脉冲磁化过程中的应力分布特性.结果显示,环向拉应力是叠层导体的主要破坏因素.环向应力的主导成分为热应力,其变化趋势与热应力变化高度吻合.热应力在叠层内部处于较低水平,表现为拉应力,沿半径逐渐变更为压缩应力,在边缘区域达到峰值-34 MPa,随后转变为拉应力,并在边界处达到峰值38 MPa,峰值时间点都位于升磁阶段,降磁阶段峰值不断降低. 相似文献
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实现了Nd^3+掺杂的氟化物玻璃的光纤激光输出。首次研究了不同输出耦合下的激光输出特性。并获得了激光输出渴谱随泵浦功率的变化过程。 相似文献
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《Magnetic resonance imaging》1995,13(1):81-88
The objective of this study was to determine correlation between structural anatomy and surface coil spin-echo MR imaging of the rat kidney and the effect of hydration state on MR signal intensities of the cortex and medulla. Twelve rats were studied in a pilot study with a 3-inch surface coil in a 1.5 T magnet under five different states of hydration. Serum and urine osmolality measurements were obtained immediately prior to each scan. Signal intensity measurements were made from both T1- and T2-weighted images of the cortex and medulla of both kidneys in each state of hydration. Gross and histological anatomy of the rat kidneys was correlated with the MR images. Four distinct layers were detected in vivo on MRI images of the rat kidney; these correlated with the histological layers. T1-weighted cortico-medullary differentiation was most pronounced at 48 h dehydration; T2 cortico-medullary differentiation was greatest at 72 h of dehydration. We concluded that different parts of the mammalian nephron can be identified by MR imaging and that cortico-medullary differentiation is affected by the hydration state of the animal. 相似文献
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An interferometric method has been used to measure the isothermal bulk modulus (the reciprocal of the compressibility) of solid xenon at zero pressure for several temperatures. It is the first time that an elastic constant of this substance has been measured at a temperature below 10 K. The smoothed results are (37.9 ± 0.5) kbars at 4.2 K, (29.6 ± 0.5) kbars at 65.6 K, and (28.2 ± 0.5) kbars at 77 K. 相似文献
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Gong Ya-Qian J. R. Birch E. A. M. Baker A. E. Costley 《International Journal of Infrared and Millimeter Waves》1983,4(1):135-143
The results of a determination of the optical constants of n-type indium antimonide at 1.5K in the spectral region between 4 and 40 cm–1 are presented. The absorption spectrum was determined by the two thickness method, while the refraction spectrum was determined both by an extension of the two thickness method and by an analysis of a channel spectrum. The errors involved in the application of these approximate methods are discussed. The material measured was of detector quality and, therefore, the results are relevant to the design of near millimetre wavelength detectors with optimised performance.Gong Ya-Qian is on leave of absence from Shanghai Institute of Applied Physics 相似文献
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随着温度的降低,超导块材表现出的超导特性也随之变化.本文结合现有实际应用的车载超导块材冷却方法,通过改变气压的方式营造过冷液氮温度条件,探究块材组合与Halbach轨道之间的悬浮特性.由于实验测量存在一定局限性,只能完成部分工况条件下的研究.为了更加系统全面的研究,本文对过冷状态下超导块材的悬浮特性进行仿真计算,通过与实验结果对比来确定仿真参数.结果显示,仿真计算与实验数据吻合度较高,为后期的研究工作提供了仿真工具. 相似文献
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Teh K de Zanche N Wild JM 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,185(1):164-172
The presence and diagnosis of radiation damping could have major implications in NMR experiments with hyperpolarised gases, where accurate knowledge of the flip angle is imperative. In this work radiation damping was observed and investigated in a low-pass birdcage resonator (Q=250) with samples of hyperpolarised 3He at 1.5 T. With an initially highly polarised (P=38%) sample of 3He in a spherical cell, the observed FID had a distorted line shape with a spectral line width that was three times that of the same sample in a virtually depolarised state (1 Hz line width for P<1%). Moreover a linear relation between the sample's magnetisation (M0) and the line width of the spectrum was observed which is indicative of radiation damping. With highly polarised samples, significant radiation damping was observed and the effect was a lower than expected rate of depletion of M0 in RF flip angle calibration experiments, which led to significant underestimate of the RF flip angle. To our knowledge this is the first report of radiation damping in a birdcage resonator with samples hyperpolarised or otherwise. Experimental observation of radiation damping could be used as means of measuring coil efficiency as an alternative to the geometrical filling factor (eta) the definition of which is open to question for a birdcage resonator. Estimates of the birdcage filling factor from the measured damping time constants (eta(RD)=0.4%) are compared to those derived from electromagnetic energy ratios (eta(E)=1.6%) and metallic sphere frequency shift methods (eta(fs)=1.4%). These figures are much lower than the simple volume geometrical upper limit of eta(v)=3.7% derived from the ratio of cell volume to total coil volume (shield included). The physical explanation for this shortfall is that the bulk of the magnetic energy stored in the birdcage is spatially distributed predominantly between the rungs and the shield, and not in the coil centre where the sample is placed and where the B1+ field has its highest spatial homogeneity. 相似文献