Equivalent comparison and analysis between different nominal frequencies

We analyze the phenomena of phase group synchronization between the different nominal frequency signals and propose a new theory of the equivalent comparison between them. The exact expression of the equivalent comparison is deduced. High resolution frequency measurement and phase comparison can be realized using this theory with the divider. For avoiding the frequency mixing, multiplication and synthesis, the system phase noise is improved and the higher resolution comparison and measurement are achieved between the different nominal frequencies by theory.     

Research and application of regular phenomenon between periodic signals

The phase change between periodic signals is regular. Research on the regular phenomenon between periodic signals is helpful to improve the precision of some measurements and develop some new measurement methods. So it is necessary to analyze the characteristics of the greatest common factor frequency and the least common multiple period universally existing in periodic signals. The regulation of the quantitative phase shift resolution between periodic signals is presented.The cause of difference in phase characteristics between periodic signals is explained well. In this paper we propose different application prospects based on the regular phenomenon between periodic signals, with focusing on the methods for high precision frequency measurement and transient stability measurement. The experimental results are satisfactory.     

Analysis and experimental concepts of the vibrating wire alignment technique

The vibrating wire alignment technique is a method which, by measuring the spatial distribution of a magnetic field, can achieve very high alignment accuracy. The vibrating wire alignment technique can be applied to fiducializing magnets and the alignment of accelerator straight section components, and it is a necessary supplement to conventional alignment methods. This article gives a systematic summary of the vibrating wire alignment technique, including vibrating wire model analysis, system frequency calculation, wire sag calculation, and the relation between wire amplitude and magnetic induction intensity. On the basis of this analysis, this article outlines two existing alignment methods, one based on magnetic field measurement and the other on amplitude and phase measurements. Finally, some basic experimental issues are discussed.     

1.57μm半导体激光器长期频率稳定性研究

为满足星载二氧化碳激光雷达对种子光源频率长期稳定的需求,基于自由空间体吸收池结合频率调制光谱技术的方法建立了激光稳频理论模型,通过仿真优化系统设计参数搭建了一套稳频激光器,研究了体吸收池引入的多光束干涉噪声,通过调整调制频率为吸收池干涉条纹自由光谱范围整数倍的方法抑制了干涉噪声的影响,实现了激光器频率抖动峰峰值约为150kHz,长期频率稳定度在10000s时低于1×10~(-11),满足了星载激光雷达的应用需求。     

玩具材料在四种人体模拟液中特定元素迁移方法探讨

选择塑料、纺织品和油漆涂层三类常见玩具材料,采用模拟胃液、酸性汗液、碱性汗液和唾液浸泡提取样品,使用ICP-AES法测试提取液中17种欧盟玩具新指令限制元素(铝、锑、砷、钡、硼、镉、铬、钴、铜、铅、锰、汞、镍、硒、锶、锡、锌)迁移量,试验了前处理过程中不同振荡频率对金属元素迁移量的影响。试验结果表明：胃液对金属元素溶出能力最大,汗液溶出能力最弱,样品提取过程中,恒温水浴振荡器振荡频率在80-160U/min范围内时,特定元素溶出量基本不受振荡频率的影响。     

双材料单伸臂叠合梁的界面滑移与自振特性分析

将叠合梁划分为接触区和分离区,接触区界面间的摩擦作用会对叠合梁的滑移、刚度和自振频率产生影响。本文给出了单伸臂叠合梁在均布荷载和集中力作用下,考虑叠合界面摩擦作用的滑移应变和滑移分布的表达式;推导了考虑叠合界面间摩擦力及摩擦力产生的抵抗弯矩共同作用下的截面刚度。假设梁按等波长和等刚度两种形式自由振动,运用传递矩阵法推导出了单伸臂叠合梁自振频率的计算公式。最后,基于一个钢-混凝土组合与叠合试验梁的算例分析了滑移沿梁长的分布及自振频率。结果表明:随界面间摩擦系数的增大,接触区界面的滑移值逐渐减小;摩擦效应对叠合梁自振频率的影响随阶次的升高越来越明显。     

高径比对砂岩单轴压缩声发射特性的影响研究

岩石尺寸效应对声发射特性的影响对于利用声发射技术监测岩石失稳破坏具有重要的实践意义。本文选择不同高径比的长石细砂岩试样开展单轴压缩声发射试验,探讨尺寸效应对岩石声发射事件数、振铃计数、峰值频率等声发射特性参数的影响。研究结果表明:根据岩石试件撞击数的增长速率,将试件破坏阶段分为突变期、平静期、爆发期三个阶段,随着岩石试件高径比增加,声发射的撞击数相应增加,增加趋势与试件高径比的增加呈近似线性相关关系;随着岩石试件高径比的减小,振铃计数突变期时间占比相应减小,平静期振铃计数也相应减小;岩石试件的加载破坏的峰值频率主要呈现高频和低频两个集中分布区,随着高径比减小,岩石试件加载破坏的峰值频率逐渐由低频区向高频区过渡,同时峰值频率的离散性也在增加。试验成果丰富了岩石声发射特性的基础数据,并可为实际工程中声发射技术的实践应用提供参考。     

不同索力斜拉索的主共振瞬时相频特性

考虑拉索垂度及几何非线性,研究了不同索力拉索的瞬时相频特性。利用斜拉索面内分布激励下的运动控制方程,采用多尺度法对微分方程进行摄动求解,分别得到面内、外主共振响应的近似解析式,再采用Hilbert变换得到响应与激励的瞬时相位差及其幅值。研究了不同索力下,响应与激励的瞬时相位差的变化规律及其原因。研究表明:面外主共振响应与激励间保持恒定的相位差,而面内响应与激励的瞬时相位差与索弹性参数和垂度等有关,微小的索力变化可能导致瞬时相频特性的明显改变。主要原因是面内响应的近似解中存在两倍频项和漂移项,前者使响应瞬时相位在单个周期内出现两次正负交替,后者决定面内响应与激励瞬时相位差的最大值及其变化规律。     

Highly birefringent octagonal photonic crystal fibers with two zero-dispersion wavelengths

A new highly birefringent octagonal photonic crystal fiber(Hi-Bi OPCF) with a rectangular array of four elliptical airholes in the fiber core region is proposed and analyzed using the full-vector finite element method with anisotropic perfect match layer absorbing boundaries.Numerical results show that the phase birefringence of the photonic crystal fiber(PCF) reaches 3.43×10-2 at the wavelength of 1 550 nm.Moreover,two zero-dispersion wavelengths are achieved in the visible and near infrared wavelength regions for one polarization state but not in the other.     

Instantaneous frequency measurement based on transversal microwave filters with high resolution

We propose a novel photonic technique for microwave frequency measurement based on transversal microwave filters with high resolution. Two parallel microwave filters with sine and cosine frequency responses are obtained by cross gain modulation in a single semiconductor optical amplifier, which introduces two different frequency responses to achieve an amplitude comparison function. We also demonstrate a proof- of-concept experiment. The measurement error is less than ±0.04 GHz for the first band range of 0–3.45 GHz and less than ±0.03 GHz for the second band range of 3.45–5.8 GHz. Our scheme is found to be capable of being extended for larger frequency range measurements using a shorter fiber length.