利用宽带信号统计的鱼群资源量反演方法

针对鱼群资源量反演问题,建立了一种基于宽带回波信号统计的反演方法。首先考虑自然状态下鱼群活动的随机性,并通过回波信号波形简化,实现了对鱼群宽带回波脉冲压缩输出信号的建模。然后以信号强度变异系数作为统计特征量,完成了统计特征量与鱼群资源量的数值关系模型的推导。仿真与海试实验结果表明该方法能有效实现鱼群资源量的反演,且比已有的窄带反演方法误差更小、统计所需样本更少。与主流的回波积分法相比,该方法不依赖鱼群先验知识,且无需计算声呐信号的绝对声学量,具有很好的应用潜力。      

基于Matlab的同态滤波器的优化设计

介绍同态滤波器的基本原理,基于Matlab软件,设计了适用的同态滤波器模型,并给出了其表达式参数,在此基础上,将同态滤波方法应用到彩色图像的光照补偿和对比度增强中。结果表明:经处理后的图像,局部对比度增强效果明显,较好地保持了图像的原始面貌,取得了预期的理想滤波效果。基于Matlab的同态滤波,能更好地适合人眼的视觉特性,提供了图像分析与判读的一种新方法。     

基于线阵CCD的迈克耳孙干涉仪条纹计数器

通过CCD图像传感器对光干涉信号进行捕捉与采集,并将捕捉信号送至ARM微控制器,利用芯片内部的A/D转换单元将模拟信号转换成数字信号,然后对数字信号进行分析、变换、测量处理,将干涉图像、干涉环变换方向及计数结果显示在液晶屏上,该方法消除了人工记录干涉圆环数目时因疲劳而产生的计数误差,提高了测量精度.     

兰州充气谱仪的焦平面探测系统

在兰州充气谱仪上,设计安装了一套新的焦平面探测系统,该系统包括飞行时间(TOF) 探测器、盒型硅(Si-box) 探测器阵列和反符合(Veto) 探测器3 部分。Si-box 探测器阵列是由3 块位置灵敏硅探测器(PSSD) 和8 块周边硅探测器(SSD) 构成,它对注入核的 衰变的探测效率达到80% 左右。Si-box 探测器阵列与TOF 探测器关联可以有效区分注入信号和 衰变信号。Veto 探测器与Si-box 探测器阵列和TOF 探测器关联可以反符合掉高能轻粒子对注入信号和 衰变信号的干扰。简要介绍了PSSD 的能量和位置刻度方法。这套探测器系统已经应用于40Ca+175Lu 和40Ca+169Tm 的实验。实验结果表明,该探测器系统具备很好的本底抑制能力,能够给出干净的a衰变能谱,结合能量-时间-位置关联测量方法可以实现对单原子的探测和鉴别,总体上达到了预期的设计要求。A new designed focal plane detection system was mounted at the gas-filled recoil separator at Institute of Modern Physics, Chinese Academy of Sciences, which consisted of a time-of-flight (TOF) detector, a silicon-box (Sibox) detector array and a silicon veto detector. Three position sensitive silicon detectors (PSSD) were surrounded by eight side silicon detectors (SSD) without position sensitive, forming a box of the detector open from the front side. The detection efficiency for -decays of implanted nuclei was about 80%. The anticoincidence condition for the signals from the TOF detector and Si-box detector array was used to distinguish between the pulses originating from the implanted nuclei and their -decays. The veto detector information was used to discriminate events due to high-energy charged particles．External energy calibration and position calibration of PSSD are described concisely in this work. This systemhas been used in experiments of 40Ca+175Lu and 40Ca+169Tm. Clean a-decay spectra obtained in these reactions indicated the detection system has a good performance in background suppression. Evaporation residues can be identified by the energy-time-position correlation method. On the whole, the new designed focal plane detection system has achieved thedesign requirements.     

A Small Signal Equivalent Circuit Model for Resonant Tunnelling Diode

We report a resonant tunnelling diode （RTD） small signal equivalent circuit model consisting of quantum capacitance and quantum inductance. The model is verified through the actual InAs/In0.53Ga0.47As/AlAs RTD fabricated on an InP substrate. Model parameters are extracted by fitting the equivalent circuit model with ac measurement data in three different regions of RTD current-voltage （I-V） characteristics. The electron lifetime, representing the average time that the carriers remain in the quasibound states during the tunnelling process, is also calculated to be 2.09ps.     

188Tl的πh9/2(○×)νi13/2扁椭球转动带的旋称反转研究

利用能量为170MeV的35Cl束流,通过157Gd(35Cl,4n)熔合蒸发反应研究了188Tl的高自旋态能级结构.依据实验结果建立了188Tl基于πh9/2(○×)νi13/2组态的转动带.根据双奇Tl核能级结构的相似性,指定了188Tlπh9/2(○×)νi13/2扁椭球转动带的自旋值.结果表明在188Tl中,πh9/2(○×)νi13/2扁椭球转动带在低自旋区具有旋称反转性质.利用包含了质子-中子剩余相互作用的准粒子-转子模型,定性地解释了πh9/2(○×)νi13/2扁椭球转动带的低自旋区旋称反转现象.     

充气反冲核谱仪焦平面探测阵列的GEANT4模拟

充气反冲核谱仪(SHANS)是目前国内合成缺中子锕系新核素、研究重核素α衰变性质的重要实验装置。为进一步提高焦平面探测阵列对重核素α衰变粒子和射线的探测效率,计划对现有探测装置进行升级。本文的主要工作是采用基于蒙特卡罗方法的GEANT4软件对现有的谱仪探测器阵列进行模拟,并与实验测量数据进行比较,以验证程序的准确性。结果表明,新探测系统对α衰变粒子的探测效率可达到88%左右,对能量在1 MeV的$\gamma$射线全能峰的探测效率约为7%。     

一种多滤波器组合导航数据融合方法

针对组合导航系统中使用单天线GPS接收机时导致姿态角不易收敛的问题,提出了一种互补滤波器和卡尔曼滤波器相结合的数据融合算法。该方法首先通过MEMS惯性传感器与磁强计设计了一种互补滤波算法。针对载体在变速运动过程中加速度计的倾角测量值有较大误差,影响互补滤波器输出精度的问题,通过GPS接收机和加速度计设计了卡尔曼滤波模型,将卡尔曼滤波器输出速度的微分量反馈给互补滤波器,实现了对互补滤波器中载体运动加速度的补偿。基于以上解算方法,以FPGA为核心处理器设计了组合导航系统并进行了车载实验。实验中,该方法有效补偿了汽车变速过程中的倾角测量误差,证明了该方法的有效性。     

STRUCTURE AND MAGNETIC PROPERTIES OF NITRIDES R3Fe29-xCrxN4

A systematic investigation of nitrides R₃Fe_29-xCr_xN₄(R=Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. The nitrogen concentration in the nitride R₃Fe_29-xCr_xN_y was determined to be y=4. Nitrogenation leads to a relative volume expansion of about 5.3%. The lattice constants and unit cell volume decrease with in creasing rare earth atomic number from Nd to Dy, reflecting the lanthanide contraction. In average, the increase of Curie temperature upon nitrogenation is about 200 K, compared with its parent compound. The nitrogenation also results in a remarkable improvement in the saturation magnetization and anisotropy fields for R₃Fe_29-xCr_xN₄ at 4.2 K and room temperature, comp ared with their parent compounds. A spin reorientation of Nd₃Fe_24.5 Cr_4.5N₄ occurs at around 368 K, which is 138 K higher than that of Nd₃Fe_24.5Cr_4.5.Magnetohistory effects of R₃Fe_29-xCr_xN₄(R=Nd and Sm) are observed in a low field of 0.04 T. First order magneti zation process occurs in Sm₃Fe_24.0Cr_5.0N₄ in magnetic fields of around 3.0 T at 4.2 K. After nitrogenation the easy magnetization direction of Sm₃Fe_24.0Cr_5.0 is changed from the easy cone structure to the uniaxial. The excellent intrinsic magnetic properties of Sm₃Fe_24.0Cr_5.0N₄ make this compound a hopeful candidate for new high performance permanent magnets.