单频GPS接收机天线扼流圈的研制与测试

讨论了多路径效应对GPS共视比对的影响及削弱其影响的方法。结合综合原子时项目的需求,研制了适用于单频GPS接收机的天线扼流圈,并用零基线比对方法进行了测试。结果表明,研制的天线扼流圈可有效地削弱多路径效应的影响,并可明显地改善单频GPS接收机NTSCGPS-1的抗干扰能力。     

利用“黄海芯1号”55K SNP芯片评估凡纳滨对虾选育群体的遗传多样性与基因组近交水平

凡纳滨对虾的主要选育目标分为两个方面: 一是培育具有较强抗病、抗逆性的“高抗系”(GK),二是培育具有快速生长特性的“快大系”(KD)。然而, 国内缺少针对这两个选育群体的遗传多样性特别是基因组近交水平的调查分析研究。基于液相芯片“黄海芯1号”(55 K SNP)的基因分型数据, 首次分析了GK (1 064尾个体)和KD (564尾个体)选育群体的遗传结构和遗传多样性, 调查了连续性纯合片段(ROH)的基因组分布特征, 并重点评估了两个群体的基因组近交水平。PCA及进化树分析表明GK及KD群体可明确分层, 亲缘关系热图表明KD群体内个体间的亲缘关系比GK群体更近。GK群体包括的家系数量更多, 导致其遗传多样性高于KD群体; 两群体间的F_st为0.09, 存在中等遗传分化。GK和KD群体每个ROH的平均长度分别为(1.70±0.34) Mb和(1.65±0.38) Mb, 每个样本ROH的平均数量分别为1.98±1.30和2.07±1.37。GK和KD群体0.8~1.25 Mb长度的ROH占比分别为11.41%和19.17%, 表明KD群体的选育历史比GK群体更长。两个群体>2.25 Mb长度的ROH片段占比分别为10.26和9.74%, 表明两个群体短期内未发生近亲交配。七种基因组近交系数评估结果表明, KD群体的近交水平高于GK群体。不依赖基础群体等位基因频率的F_ROH和F_HOM方法可准确地评价育种群体的真实近交水平, 而F_VR1、F_YA1和F_LH1等依赖基础群体等位基因频率的方法可以用来比较群体及个体间的相对近交水平。上述结果为准确地评估育种群体的近交水平和优化育种方案提供了重要参考依据。     

The application of the self-tuning neural network PID controller on the ship roll reduction in random waves

In this paper, we present a mathematical model including seakeeping and maneuvering characteristics to analyze the roll reduction for a ship traveling with the stabilizer fin in random waves. The self-tuning PID controller based on the neural network theory is applied to adjust optimal stabilizer fin angles to reduce the ship roll motion in waves. Two multilayer neural networks, including the system identification neural network (NN1) and the parameter self-tuning neural network (NN2), are adopted in the study. The present control technique can save the time for searching the optimal PID gains in any sea states. The simulation results show that the present developed self-tuning PID control scheme based on the neural network theory is indeed quite practical and sufficient for the ship roll reduction in the realistic sea.     

Micromechanical investigation of the particle size effect on the shear strength of uncrushable granular materials

Particle size strongly influences the shear strength of granular materials. However, previous studies of the particle size effect have focused mainly on the macroscopic behavior of granular materials, neglecting the associated micro-mechanism. In this study, the effect of particle size on the shear strength of uncrushable granular materials in biaxial testing is investigated using the discrete element method (DEM). First, a comprehensive calibration against experimental results is conducted to obtain the DEM parameters for two types of quartz sand. Then, a series of biaxial tests are simulated on sands with parallel particle size distributions to investigate the effect of particle size on macro- and microscopic behaviors. Finally, by adopting the rolling resistance method and the clump method, irregular-shaped particles are simulated to investigate how the particle size effect will be influenced by the particle shape. Simulation results demonstrate that (1) the peak shear strength increases with particle size, whereas the residual shear strength is independent of particle size; (2) the thickness of the shear band increases with the particle size, but its ratio decreases with particle size; (3) the particle size effect can be explained by the increase of friction utilization ratio with particle size; and (4) the particle size effect is more significant in granular materials that consist of particles with higher angularity.