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关键词： 光纤光学   三维加速度传感器   光纤光栅  

摘要： 提出了一种基于光纤光栅(FBG)的一体式三维加速度传感器。该传感器以十字梁为弹性体,采用有限元分析方法研究了弹性体的应变分布特征,5个光纤光栅按照特定的规则被封装在梁的表面。通过将两两组合的光纤光栅波长漂移量的差值作为传感器不同振动方向的输出信号,实现三维加速度的低耦合测量及温度补偿。振动测试结果表明,该传感器在x、y和z方向的谐振频率分别为2000,1920,1160 Hz,工作频带分别为20~1400 Hz、20~1300 Hz和10~800 Hz,在x、y和z方向的灵敏度分别为1.36,1.70,1.31 pm/g。该传感器具有良好的线性度、弱耦合性和温度补偿能力。

关键词： 相位光栅   衍射   衍射效率   分光功能  

摘要： 利用相干叠加思想推导了平面波通过相位型光栅的衍射表达式.结果表明,相位光栅衍射可以实现将最大衍射光强集中在具有分光功能的±1级,克服了振幅光栅衍射中具有最大衍射光强的0级无分光功能的缺陷.讨论了相位层引入的相位、光栅占空比对±1级衍射光强的影响.利用相干叠加思想得到的衍射公式物理意义明确,便于掌握,并可应用于其他衍射结构.

关键词： Laser absorption spectroscopy   DFB laser   Multi-pass absorption cell   FMCW ranging  

摘要： Small changes in mirror displacement cause variations in the reflection pattern and corresponding optical path length in a multi-pass absorption cell. Herein, we propose a path length calibration-free laser absorption spectrometer based on a frequency modulated continuous wave (FMCW) ranging system. The absorption coefficient of atmospheric oxygen and the optical path length in a multi-pass absorption cell were measured using direct absorption spectroscopy and an FMCW ranging system, respectively. Further, the measured optical path length in the multi-pass absorption cell was compared with ray-tracing simulations. In addition, we demonstrated that the optical absorption coefficients measured by the direct absorption spectroscopy were not affected by changes in the distance between mirrors.

关键词： 激光告警   大视场   光斑中心   曲线拟合   非均匀性校正  

摘要： 针对国内现有激光告警系统波段范围较窄、视场角小等问题,设计并搭建一种光栅衍射型宽波段大视场二维激光告警系统,可实现100°大视场角、450 nm~1600 nm范围波段内对来袭激光进行探测,同时测得来袭激光的二维方向信息及波长信息。通过对系统采集的图片进行分析,设计两点校正算法对探测器进行非均匀性校正,并进行衍射光斑中心提取,最后根据激光告警原理计算求得来袭激光的方位角、俯仰角及波长信息。实验选用波长为1313 nm的激光器对宽波段大视场的二维激光告警系统进行测试,结果显示角度分辨率≤0.67°。

关键词： 弥散张量成像   血管性帕金森综合征   帕金森病  

摘要： 目的探讨磁共振弥散张量成像(DTI)定量测量在血管性帕金森综合征(VP)与帕金森病(PD)的鉴别诊断中的应用价值。方法收集并评价15例VP及与之相匹配的16例PD患者的运动功能(UPDRS-Ⅲ),进行DTI成像扫描,并对感兴趣点进行定量测量后进行统计学分析。结果VP组双侧红核、双侧黑质致密带、左侧苍白球、左侧壳核FA值均较PD组明显降低(P<0.05);VP组双侧红核、双侧黑质致密带、右侧黑质网状带、右侧扣带回ADC值较PD组明显升高(P<0.05)。结论利用DTI成像定量测量红核及黑质致密带FA及ADC值在VP及PD鉴别诊断中具有一定参考价值。

关键词： 波叠加法   非唯一性   体积速度   相对误差   位置优化  

摘要： 本文提出一种有效满足声场整体计算精度需求且能保证声场唯一解的改进方法。该方法在单极子波叠加法的基础上,以分析波数范围内重构前后体积速度相对误差为目标函数,以同形缩小系数为优化变量对声源所在曲面位置进行优化选取,再通过辐射体内部添加适量额外的单极子源可有效保证声场的唯一解。两个数值算例表明:对于脉动球源,球心处添加一个单极子源的改进波叠加法可以有效避免解的非唯一性问题,且具有非常高的计算效率及精度;对于复杂几何体,以体积速度相对误差为目标函数优化得到的单极子源位置,添加附加源后可求得声场的唯一解,且满足整体计算精度要求。

关键词： 皮秒放大器   光子晶体光纤   光栅   脉冲展宽   二次谐波产生  

摘要： 具有高平均功率的皮秒级脉冲激光在工业加工、空间探测等领域具有重要的应用。但是锁模产生的皮秒种子光因脉冲宽度窄、单脉冲能量低,难以直接通过传统的行波放大实现功率的高效提升,因此也限制了输出脉冲的非线性频率转换效率。文中通过光栅啁啾脉冲展宽器和狭缝,将中心波长为1 030 nm、脉冲宽度7 ps、重复频率52 MHz的光纤锁模种子光脉冲宽度展宽至32 ps,且将其光谱宽度控制在1.1 nm,利用两个空气包层光子晶体光纤放大器将功率放大至190 W。最后通过温度相位匹配LiB_(3)O_(5)晶体实现了平均功率为103.1 W的绿光皮秒脉冲输出,光束质量因子1.17,二次谐波转换效率54.3%。

关键词： 考试分数   义务教育学校   期中考试   学生学习成绩   回归教育   纸笔考试   央视网   期末考试  

摘要： 2021年8月30日,在教育部新闻发布会上,教育部基础教育司司长吕玉刚强调,《关于加强义务教育学校考试管理的通知》明确小学一、二年级不进行纸笔考试,其他年级由学校每学期组织一次期末考试;初中年级从不同学科实际出发,可适当安排一次期中考试。(2021年8月30日《央视网》)长期以来,考试分数是很多老师和家长衡量、考核学生学习成绩和能力的重要标准,一旦学生考试分数拖了班级平均分,有的老师往往会焦急不已。

关键词： Bond Gruneisen parameter   Quasi-harmonic   EXAFS   Thermal expansion   Einstein frequency   Gallium arsenide  

摘要： The bond Gruneisen parameter of gallium arsenide's first shell was directly evaluated using temperature dependent Extended X-ray Absorption Fine Structure (EXAFS) data. A quasi-harmonic approach based on the anharmonic contribution to parallel Mean Square Relative Displacement (MSRD) has led to a positive and weakly temperature-dependent linear bond Gruneisen parameter (GP) of GaAs in the entire region (14-300 K). For all temperatures, we report linear bond GPs greater than those retrieved with EXAFS using an anharmonic Einstein model. The comparison with volumic Gruneisen parameters given by diffraction or dilatometric techniques shows a significant difference which could be attributed to the different definitions used to connect frequency and bond length (or lattice parameter). These results are an evidence of the inadequacy of the quasi-harmonic model to deal with local properties using EXAFS.

关键词： galaxies: active   galaxies: evolution   galaxies: haloes  

摘要： The co-evolution between central supermassive black holes (BHs), their host galaxies, and dark matter haloes is still a matter of intense debate. Present theoretical models suffer from large uncertainties and degeneracies, for example, between the fraction of accreting sources and their characteristic accretion rate. In recent work, we showed that active galactic nuclei (AGNs) clustering represents a powerful tool to break degeneracies when analysed in terms of mean BH mass, and that AGN bias at fixed stellar mass is largely independent of most of the input parameters, such as the AGN duty cycle and the mean scaling between BH mass and host galaxy stellar mass. In this paper, we take advantage of our improved semi-empirical methodology and recent clustering data derived from large AGN samples at z similar to 1.2, demonstrate that the AGN bias as a function of host galaxy stellar mass is a crucial diagnostic of the BH-galaxy connection, and is highly dependent on the scatter around the BH mass-galaxy mass scaling relation and on the relative fraction of satellite and central active BHs. Current data at z similar to 1.2 favour relatively high values of AGN in satellites, pointing to a major role of disc instabilities in triggering AGN, unless a high minimum host halo mass is assumed. The data are not decisive on the magnitude/covariance of the BH-galaxy scatter at z similar to 1.2 and intermediate host masses M-star less than or similar to 10(11) M-star. However, future surveys like Euclid/LSST will be pivotal in shedding light on the BH-galaxy co-evolution.