光泵磁共振实验探讨

本文讨论了在光泵磁共振实验中，地磁场垂直分量的抵消、样品泡所在处恒定磁场的确定和实验中的干扰信号等问题。阐明了地磁场垂直分量不被抵消情况下，对实验结果的影响；在实验中采用利用一种元素测量样品所在处磁场的方法，准确确定样品泡所在处的恒定磁场；最后对实验中的干扰信号进行了分析。     

垂直磁场对光抽运信号的影响

保持扫场和垂直磁场合成的叠加磁场大小一定,定量研究了地磁场的垂直分量抵消不同时叠加磁场方向变化角度Δθ对光抽运信号幅度的影响.结果表明:光抽运信号幅度随叠加磁场方向变化角度Δθ的增大而增大,当Δθ=180°时,即地磁场的垂直分量完全抵消时,光抽运信号幅度最大,并用量子理论的观点解释了这一规律.     

光磁共振实验测量地磁场方法的探究

在对光磁共振实验原理深入了解的基础上,对光磁共振测量地磁场的诸多方法进行了比较研究,分析了外加水平及竖直方向磁场对共振条件的影响,提出了利用光磁共振实验直接测量地磁场的改进方法.在不抵消地磁场竖直分量的情况下,只改变电流方向而不改变其大小得出前后2次共振频率的平方差与电流的线性关系,进而拟合直线得出斜率,计算出地磁场分量的大小,从而避免了抵消法测地磁场竖直分量带来的误差.     

磁场对光抽运信号的影响

在做光泵磁共振实验时,分别研究了竖直线圈和水平线圈产生的磁场对光抽运信号的影响,并做出了它们之间的关系曲线.由此曲线计算了北京地磁场的垂直分量为(0.0881±0.0015)×10-4T,估算出北京地磁场的水平分量约为0.425×10-4T.同时,这项工作对于区分光抽运信号和磁共振吸收信号也有一定的帮助.     

光泵磁共振中确定地磁水平分量方向的改进方法

讨论了光泵磁共振实验中亥姆霍兹线圈产生的磁场方向与地磁场水平分量方向的一致程度对实验结果的影响,并分析了传统确定方向一致的方法的不足.通过调节光泵磁共振仪的摆放方向,观察共振信号的分开程度来确定仪器摆放方向与地磁场水平分量方向之间的夹角,当分开程度最小时,对应仪器方向与地磁场水平分量方向相互平行.     

磁场对光轴运信号的影响

摘 要;在做光泵磁共振实验时,分别研究了竖直线圈和水平线圈产生的磁场对光抽运信号的影响．并做出了它们之间的关系曲线．由此曲线计算了北京地磁场的垂直分量为（0. 0881±0·0015）×10-4T ,估算出北京地磁场的水平分量约为 0．425 ×10-4T．同时,这项工作对于区分光抽运信号和磁共振吸收信号也有一定的帮助．     

光抽运信号与线圈电流的关系

分别固定水平线圈和垂直线圈的电流后,在不同的光抽运信号下测定了铷样品吸收池的透射光强度与垂直线圈和水平线圈电流的关系曲线．得到了只有在正常光抽运信号下,透射光强度才与cos^2θ成正比的结论．指出了只有在正常光抽运信号下,地磁场的垂直分量被垂直线圈的磁场抵消时,吸收池的透射光强度才最强．     

利用光泵磁共振实验测量重庆地区地磁场

通过光泵磁共振实验设计,对水平场、扫场信号、地磁场不同组合情况下的光泵磁共振信号进行了观测和记录,利用线性拟合的方法测算出铷原子的因子,测算误差只有0.24％；采用固定射频测地磁场的实验方法测得重庆地区的地磁场为0.391 8 GS.该应用实验成果丰富了创新性、实用性实验教学内容.     

光磁共振实验中测量gF值方法的改进

采用与示波 步的扫描场探测光抽运和光磁共振,使光抽运峰和磁共振峰稳定;用扫描场抵消地磁场水平分量,从而使光抽运峰和光磁共振峰分开而容易判断,改进测量ｇＦ值的方法并对惯用测量方法的缺陷进行分析。     

光泵磁共振实验中测量地磁场水平分量的方法

基于光泵磁共振实验过程中光抽运信号和磁共振信号出现的条件，阐述了3种测量地磁场水平分量的方法．通过实验，验证了用这3种方法所得到的测量结果是一致的．这项工作对于理解光抽运信号和磁共振吸收信号有一定帮助．     

基于PASCO实验平台的地球磁场测量

基于PASCO实验平台的软件和计算机接口,利用高灵敏度磁场传感器对地球磁场的强度及磁倾角等相关参量进行测量与分析。实验结果表明,该测量方法操作简单,精确度较高,实用性很强。通过轻松的实验过程对地球磁场等不易感知的弱磁场有了一个清晰直观的认识。     

带电粒子在地磁场中的运动

用计算机模拟的方法研究了地磁场中带电粒子的运动特性,绘制了粒子轨迹曲线,对粒子运动进行了分析,解释了地磁场的磁瓶效应和辐射带.     

基于磁通门和时域数字鉴频的磁场锁定系统

永磁型磁共振仪器的磁体易受温度和其他环境磁场干扰,造成主磁场波动,进而影响仪器测量的重复性和准确性.本文讨论了两种解决磁场波动的锁定方法：一方面,通过磁通门传感器对环境波动引起的瞬态磁场进行高灵敏探测,然后采用现场可编程门阵列进行实时处理并计算磁场补偿量;另一方面,针对环境温度变化引起的缓慢磁场偏移,则采用时域数字鉴频锁场方法,在对锁样品进行射频激发后,将磁共振信号通过混频变换到较低的频率范围,再转换为方波,然后直接送入现场可编程门阵列进行周期测量,并计算磁场补偿量.将两种方法获得的磁场补偿量叠加后,再转换为电流信号驱动安装在磁体上的B₀补偿线圈,并研制了一套磁场锁定系统,以实现对磁场的锁定. 在0.5 T食品快检磁共振分析仪上进行测试验证,结果显示当受到瞬态干扰时,可将磁场稳定在±4 Hz（对应磁场为±0.093 9 μT）范围内,同时也可以精准测量温度造成的磁场偏移,该结果验证了本文磁场锁定方法的可行性.     

利用地磁场综合模型CM4分析中国大陆地区地磁场变化

第四代地磁场综合模型CM4是迄今为止将地磁场的内源场和外源场分离得最为彻底的数学模型.利用该模型结合Taylor多项式模型,基于1960—2000年期间中国大陆地区的实测数据,计算并分析了以10a为间隔的内源场和外源场的变化情况,通过将1960—1990年的所有磁异常点归算至2000年以分析地壳磁异常场的总体分布趋势.结果显示:地磁北向分量X的内源场强度总体呈逐年减弱的趋势,从1960年到2000年共下降了约750nT,外源场强度总体呈先增强后减弱的趋势,共下降了约32nT;地磁东向分量Y的内源场强度总体呈先减弱后增强的趋势,1960—2000年期间共上升了约40nT,外源场强度总体呈先减弱后增强再减弱的趋势,共上升了约3.8nT;地磁垂直分量Z的内源场变化趋势与Y分量类似,共上升了约600nT,外源场总体呈先减弱后增强的趋势,共上升了约4.6nT.对于地壳磁异常场,X分量、Z分量、地磁总强度F和地磁水平分量H在中国大陆地区都为负异常分布,X分量和H分量的负异常强度随经度增加而减弱,Z分量和F分量则相反;Y分量和磁偏角D的分布较为类似,在中国的中西部大部分地区为正异常,强度随经度增加而减弱,磁倾角I主要以负异常为主,负异常强度随经度增加而增强.     

Avian magnetoreception model realized by coupling a magnetite-based mechanism with a radical-pair-based mechanism

Many animal species have been proven to use the geomagnetic field for their navigation, but the biophysical mechanism of magnetoreception has remained enigmatic. In this paper, we present a special biophysical model that consists of magnetite-based and radical-pair-based mechanisms for avian magnetoreception. The amplitude of the resultant magnetic field around the magnetic particles corresponds to the geomagnetic field direction and affects the yield of singlet/triplet state products in the radical-pair reactions. Therefore, in the proposed model, the singlet/triplet state product yields are related to the geomagnetic field information for orientational detection. The resultant magnetic fields corresponding to two materials with different magnetic properties are analyzed under different geomagnetic field directions. The results show that ferromagnetic particles in organisms can provide more significant changes in singlet state products than superparam- agnetic particles, and the period of variation for the singlet state products with an included angle in the geomagnetic field is approximately 180 when the magnetic particles are ferromagnetic materials, consistent with the experimental results obtained from the avian magnetic compass. Further, the calculated results of the singlet state products in a reception plane show that the proposed model can explain the avian magnetoreception mechanism with an inclination compass.     

Multi-bubble motion behavior of uniform magnetic field based on phase field model

Aiming at the interaction and coalescence of bubbles in gas–liquid two-phase flow, a multi-field coupling model was established to simulate deformation and dynamics of multi-bubble in gas–liquid two-phase flow by coupling magnetic field, phase field, continuity equation, and momentum equation. Using the phase field method to capture the interface of two phases, the geometric deformation and dynamics of a pair of coaxial vertical rising bubbles under the applied uniform magnetic field in the vertical direction were investigated. The correctness of results is verified by mass conservation method and the comparison of the existing results. The results show that the applied uniform magnetic field can effectively shorten the distance between the leading bubble and the trailing bubble, the time of bubbles coalescence, and increase the velocity of bubbles coalescence. Within a certain range, as the intensity of the applied uniform magnetic field increases, the velocity of bubbles coalescence is proportional to the intensity of the magnetic field, and the time of bubbles coalescence is inversely proportional to the intensity of the magnetic field.     

Experiment on relationship between the magnetic gradient of low-carbon steel and its stress

In geomagnetic field, a series of tensile experiments on the low-carbon steel sticks were carried out. A special homemade detector was used to measure the magnetic gradient on the material surface. The results showed that the relationship between the magnetic gradient and the stress varied with different conditions of measurement. There was no obvious correlation between the magnetic gradient and the tensile stress if the sample remained on the material test machine. If the sample was taken off from the machine, the measured magnetic gradient was linear with the prior maximum stress. In Nanjing, PR China, a place of 32°N latitude, the slope of the linear relationship was about 67 (uT/m)/MPa. This offered a new method of non-destructive stress testing by measuring the magnetic gradient on the ferromagnetic component surface. The prior maximum applied stress of the sample could be tested by measuring the present surface magnetic gradient. Actually this phenomenon was the metal magnetic memory (MMM). The magnetic gradient near the stress concentration zone of the sample, the necking point, was much larger than other area. Thus, the hidden damage in the ferromagnetic component could be detected early by measuring the magnetic gradient distribution on its surface. In addition, the magnetic memory signal gradually weakened as the sample was taken off and laid aside. Therefore, it was effective for a given period of time to detect the stress or stress concentration based on the MMM testing.     

利用金刚石氮-空位色心精确测量弱磁场的探索

基于金刚石氮-空位色心对精确测量微弱静磁场进行了探索.金刚石氮-空位色心电子自旋的退相干时间高度依赖于外磁场,而不同的退相干特征时间对磁场的灵敏度不同.对金刚石氮-空位色心电子自旋在不同强度外磁场下的退相干过程进行模拟,得到不同退相干特征时间与磁场大小的高准确度关系,提出了基于响应度最高的退相干特征时间测量静态弱磁场大小和方向的方法,并分析了该方法测量静态弱磁场的灵敏度,证明该方法的测量灵敏度比一般磁场测量仪器更高.     

利用电子自旋共振测量地磁场强度及磁倾角

利用射频段电子自旋共振实验仪,采用恒定磁场正、反向时共振信号等间距及共振条件,精确地测量了延安地区的地磁场强度及磁倾角.