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SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing several magnetometers at different heights along the vertical direction,we could simultaneously obtain the synthetic gradiometers with different baselines.By using the traditional signal-to-noise ratio(SNR) as a performance index,we successfully obtain an optimal baseline for the magnetocardiography(MCG) measurement in a magnetically shielded room(MSR).Finally,we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR.The SNR about 38 dB is obtained in the recorded MCG signal. 相似文献
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Performance study of aluminum shielded room for ultra-low-field magnetic resonance imaging based on SQUID:Simulations and experiments 下载免费PDF全文
The aluminum shielded room has been an important part of ultra-low-field magnetic resonance imaging(ULF MRI)based on the superconducting quantum interference device(SQUID). The shielded room is effective to attenuate the external radio-frequency field and keep the extremely sensitive detector, SQUID, working properly. A high-performance shielded room can increase the signal-to-noise ratio(SNR) and improve image quality. In this study, a circular coil with a diameter of 50 cm and a square coil with a side length of 2.0 m was used to simulate the magnetic fields from the nearby electric apparatuses and the distant environmental noise sources. The shielding effectivenesses(SE) of the shielded room with different thicknesses of aluminum sheets were calculated and simulated. A room using 6-mm-thick aluminum plates with a dimension of 1.5 m×1.5 m×2.0 m was then constructed. The SE was experimentally measured by using three-axis SQUID magnetometers, with tranisent magnetic field induced in the aluminum plates by the strong pre-polarization pulses. The results of the measured SE agreed with that from the simulation. In addition, the introduction of a 0.5-mm gap caused the obvious reduction of SE indicating the importance of door design. The nuclear magnetic resonance(NMR) signals of water at 5.9 kHz were measured in free space and in a shielded room, and the SNR was improved from 3 to 15. The simulation and experimental results will help us design an aluminum shielded room which satisfies the requirements for future ULF human brain imaging. Finally, the cancellation technique of the transient eddy current was tried, the simulation of the cancellation technique will lead us to finding an appropriate way to suppress the eddy current fields. 相似文献
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引入跨股氨基酸队的方法进行β-发夹结构的设计,序列[R1G2T3F4W5V6d-P7S8V9N10Y11F12, β2] 中包含二个氨基酸对V6V9和F4Y11,并以d-P7S8作转角来稳定结构.多肽合成采用Fmoc/But固相合成方法.圆二色谱研究显示,β2在202 nm呈现正峰,在217.5 nm处呈负峰,为β转角和β折叠共同贡献的叠加,是典型的β-发夹结构圆二色谱特征.红外光谱研究进一步验证了圆二色谱的结果,表明β2在溶液中主要以β-发夹结构存在. 相似文献
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建立了一种盖印法加工纸基微流控芯片的方法。滤纸经烷基烯酮二聚体(AKD)的正己烷溶液浸泡,以三乙醇胺溶液为阻断试剂,用绘图软件设计芯片图案并制作光敏印章,用带有芯片图案的印章将阻断试剂盖印在滤纸表面。滤纸在105 ℃烘箱中加热10 min后,非盖印区域呈疏水性,盖印区域呈亲水性,从而形成液体流动通道。考察了疏水试剂浓度、阻断试剂的选择及配比、盖印分辨率等因素对纸芯片性能的影响。制得的纸芯片用于亚硝酸钠溶液的比色分析,获得良好的线性关系。该方法具有成本低廉、操作简便快速等特点,在制备廉价易普及的纸芯片方面有一定应用前景。 相似文献
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在中国聚变工程实验堆(CFETR)真空室最新设计尺寸下,利用蒙特卡洛中子输运程序(MCNP)建立一维中子学模型,在2GW 的聚变功率下进行了计算。分析了中子反射材料ZrH2 对中子的屏蔽效果,发现200mm 的反射层可以屏蔽94.3%的中子通量和94.9%的中子核热。研究CFETR 在运行10 个满功率年(FPY)和20FPY 后,对应不同中子壁载荷的最小屏蔽包层厚度。结果显示,装置运行10FPY 后中子壁载荷在1.0MW·m−2、1.5MW·m−2、 2.5MW·m−2 时所对应的最小屏蔽包层厚度分别为44cm、53cm、65cm;而在装置运行20FPY 后,则需要在径向方向更厚的屏蔽包层才能满足中子屏蔽要求。屏蔽包层的尺寸优化将为目前阶段的CFETR 先进包层设计提供参考。 相似文献
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TEMPORAL CHARACTERIZATION OF LASER PULSES FROM JIGUANG-I LASER FACILITY WITH A COMPACT DUAL FUNCTION AUTOCORRELATOR 下载免费PDF全文
An optical pulse autocorrelator for rapid and slow scanning is described in this paper. Using an audio loudspeaker on one arm, an interferometric rapid-scanning signal of the output from a high-repetition laser oscillator is obtained. However, by adjusting the positions of the mirrors and using a step-motor on another arm, the intensity autocorrelation function of the output from a low-repetition laser amplifier can be easily measured. Using all-reflecting optics and an adequate nonlinear crystal, the whole instrument is very compact and has been used to measure sub-20 fs light pulses in both configurations with excellent agreement. In the slow-scanning configuration, a pulse train as long as 500ps has been determined. Using this autocorrelator, the home-made JIGUANG-I CPA laser facility was characterized for its pulse duration evolution. 相似文献
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Fetal magnetocardiography (MCG) is a sophisticated non-invasive technique for the fetal heart diagnosis. We constructed a multichannel fetal MCG system based on a novel superconducting quantum interference device (SQUID) direct readout scheme called SQUID bootstrap circuit (SBC). The system incorporates four SBC gradiometers for the signal detection and three SBC magnetometers as the references. The fetal MCG signal at a 28-weeks’ gestation was measured. By the fetal MCG signal separation and average, the P-wave and QRS complex can be clearly identified. These results indicate that the SBC is one of the most promising techniques for the fetal MCG recordings. 相似文献
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