An efficient calibration method for SQUID measurement system using three orthogonal Helmholtz coils

For a practical superconducting quantum interference device(SQUID) based measurement system,the Tesla/volt coefficient must be accurately calibrated.In this paper,we propose a highly efficient method of calibrating a SQUID magnetometer system using three orthogonal Helmholtz coils.The Tesla/volt coefficient is regarded as the magnitude of a vector pointing to the normal direction of the pickup coil.By applying magnetic fields through a three-dimensional Helmholtz coil,the Tesla/volt coefficient can be directly calculated from magnetometer responses to the three orthogonally applied magnetic fields.Calibration with alternating current(AC) field is normally used for better signal-to-noise ratio in noisy urban environments and the results are compared with the direct current(DC) calibration to avoid possible effects due to eddy current.In our experiment,a calibration relative error of about 6.89 × 10-4is obtained,and the error is mainly caused by the non-orthogonality of three axes of the Helmholtz coils.The method does not need precise alignment of the magnetometer inside the Helmholtz coil.It can be used for the multichannel magnetometer system calibration effectively and accurately.     

基于高温超导SQUID的低场核磁共振研究

采用一高温超导射频量子干涉器(HTS rf-SQUID)作为信号探测器件,研究了多种液体样品的低场核磁共振信号。通过改变测量场(简称Bm)的大小,可以探测到质子拉莫频率(简称fL)从2Hz到40kHz的信号。由于在低场核磁共振中,Bm的均匀性能很好的得到满足,因而可能得到很窄的谱线宽度。实验发现,对自来水样品,在7μT以下均可接近谱线的自然宽度。同时,在低场核磁共振条件下,样品的化学位移很小以至于消失,因而可以研究"纯"的异核间的自旋耦合谱。作者研究了低场下2,2,2-三氟乙醇的低场自旋耦合谱。另外,作者首次采用SQUID在户外探测到地球磁场下的核磁共振现象,并研究了地球磁场的涨落对测量的影响,为SQUID的低场核磁共振研究开辟了一个新的研究方向。     

基于曲率滤波和视觉显著性的红外小目标检测

红外成像因具有隐蔽性强、环境适应能力强和抗干扰能力强等优点,被广泛用于军事和民用领域。为了实现对红外小目标的高精度检测,提出了一种基于曲率滤波和视觉显著性相结合的红外小目标检测算法。首次将曲率滤波引入红外小目标检测中,对图像中的背景进行估计,然后将背景估计结果与原图像进行差分,使得图像中的大部分背景被显著抑制。为了减小残余的部分高强度杂波对目标的正确检测产生影响,利用形态学方法将高强度杂波移除。为了进一步提高目标的检测精度,提出了一种局部对比度算法进行杂波抑制及目标增强。最后,采用自适应阈值分割方法得到显著的小目标。对本文所提算法与其他算法在5个数据集上进行了比较分析,结果表明,本文算法的信杂比(SCR)与背景抑制因子(BSF)远高于其他算法,在检测率和误报率方面也明显优于其他算法。     

业务相关性对排队性能的影响及其意义

以TES法和洗牌法为依据，通过一系列计算机模拟实验，分析了业务相关性与排队性能之间的关系．指出：业务的相关性对排队性能有着重大的影响，对于无限排队系统，业务的长时相关性决定着排队系统的性能；而在有限排队情况下，短时相关性的影响相对大一些，且起作用的主要是相邻数据的相关性的强弱，因此短时相关性和长时相关性都不容忽略．     

Effect of HTS Superconductors on Homogeneity of Measurement Field in Low Field Nuclear Magnetic Resonance Detection

In recent years, superconducting quantum interference devices （SQUIDs） have been demonstrated to be useful in the low field nuclear magnetic resonance （NMR） measurements. The high temperature superconducting （HTS） SQUID used in our experiments has a frequency-independent sensitivity of 40-50fT/Hz^1/2. When a liquid nitrogen cooled LC circuit is employed to form a tuned circuit with the SQUID, the sensitivity of the system can be further enhanced. The LC circuit consists of a capacitor and a coil made of copper wire or HTS tape, which is inductively coupled to the SQUID. However, the homogeneity of the measurement field deteriorates because of the HTS tape coil in the proximity of the sample. In contrast, the thin film SQUID with a washer area of 1 cm^2 has no effect on the NMR signal. Therefore, the impairment of the measurement field homogeneity in the case of different superconducting elements nearby is discussed by examining the free induction decay signals at 9 kHz. It is found that a square superconducting film with an area of i cm^2 may compensate for the inhomogeneity of the measurement field after the adjustment of its position.     

Multichannel fetal magnetocardiography using SQUID bootstrap circuit

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.     

无粘性颗粒堆底的应力分布

从弹性理论出发，推导出了变系数弹性模型。利用此模型，计算了二维沙堆式样里的应力分布，得到了试样底面应力分布曲线有低陷的结论，并用不同方法验证了模型的稳定性与准确性。     

高职院校心理教育的问题及策略分析

随着我国在教育方面的重视度愈来愈高，高职院校心理教育问题也逐渐得到重视，心理健康教育是大学生全面发展的重要组成，对大学生心理健康教育进行加强是树立良好健康心理素质的重要途径。     

YBa2Cu3Ox(123)超导体的微波焊接及其对微观结构的影响

对Ｙ－系（１２３）相超导材料的微波焊接进行了初步研究，结果表明微波快速焊接后的试样，经９６０℃空气中退火１５ｈ后炉冷，其Ｔ_c可恢复至８９．７Ｋ，比焊接前试样的Ｔ_c低１．６Ｋ。利用电子探针对焊接前后样品的显微结构进行了比较，发现焊区组织致密，但在后处理过程中超导相发生了再结晶，导致焊缝变宽，气孔因聚集而变大。同时用电子微探针分析仪发现，焊接后焊区普遍存在Ｙ₂ＢａＣｕＯ_x相、Ｂａ_2-yＣｕ_{y 关键词：}