频率源短期频率稳定度的新表征——沃尔什正弦方差

通过对频率源稳定度的时域测量进行极低频谱分析是一种有效方法。哈德玛方差的传递函数由于具有选频特性,因而可用来进行频率源相对频率噪声谱S_y(f)分析。本文从最佳“频窗”传递函数出发,利用沃尔什函数的性质,获得了频率短期稳定度的新表征——沃尔什正弦方差。它能够充分发挥微型计算机优良的数值计算和系统控制功能,灵活、方便地获得频率源短期稳定度的各种表征,特别在测试S_y(f)时,基本克服了哈德玛方差传递函数的谐波及其旁瓣所带来的误差,并可通过数据复用大大缩短测试时间。文中给出了沃尔什正弦方差与阿仑方差及哈德玛方差的关系,指出它在获取频率短期稳定度方面具有内在含义。     

星载原子钟性能分析方法比较研究

卫星导航时间系统是影响导航系统性能的决定性因素。原子时钟作为频率标准,能够产生高准确度和高稳定度的标准频率信号,可以实现精确计时。因此在导航卫星上广泛使用原子钟作为频率标准。讨论了原子时钟频率稳定度的Allan方差、重叠Allan方差、Hadamard方差及重叠Hadamard方差算法,并对GPS卫星真实数据进行了频率稳定度分析。得出了不同的GPS卫星,星载卫星钟的稳定度不同。对于同一种类的GPS卫星,卫星钟的稳定度也存在差异,且GPS BLOCK IIR卫星具有较好的频率稳定度。     

双TWSTFT链路北斗站间时间频率传递:钟差阿伦方差的置信区间计算

卫星双向时间频率传递(TWSTFT)是我国北斗卫星导航系统(BDS)中实现地面站之间时间频率传递的重要方法.不同于通常的站间时频传递系统,BDS的一些地面站之间通过两颗地球静止轨道卫星实现了双TWSTFT独立比对链路.基于此双链路特征,我们之前的研究表明,通过有效分离钟差阿伦方差与测量噪声阿伦方差,可降低测量噪声对站间钟差频率稳定度评估(阿伦方差表示)的影响.本文在假设测量噪声为相位白噪声,钟差噪声为频率白噪声的情况下,推导给出了BDS双TWSTFT链路分离测量噪声阿伦方差获得的站间钟差阿伦方差置信区间的计算方法.对BDS实测数据分析表明,平滑时间=1 s时,通过双TWSTFT链路可获得的站间钟差的阿伦偏差(阿伦方差的平方根)的置信区间上限为3.2481012(置信度0.95).相比之下,通过单TWSTFT链路直接获得的站间钟差的阿伦偏差仅为(8.59–8.91)×1011(=1 s).本文结果进一步表明,利用两条独立比对链路,可以将测量噪声阿伦方差与钟差阿伦方差进行有效分离,从而减少测量噪声对钟差频率稳定度评估结果的影响.     

Sφ（f）谱密度分析在可编程计数器上的实现

本文简述频率稳定度在频域中的表征和用Hadmard 方差进行相位噪声谱密度S_φ(f)分析原理.从而提出用可编程计数器进行相位噪声谱密度测量分析和计算的方法.     

正交解调Pound-Drever-Hall激光稳频技术实验研究

为了提高激光器的频率稳定度,设计了基于正交解调原理的Pound-Drever-Hall(PDH)稳频系统。该系统采用直接数字频率合成器同步产生三路同频正弦和余弦信号,其中一路正弦信号用作电光相位调制器的驱动信号,另两路正弦和余弦信号同时用作相位解调的参考信号。解调所得PDH稳频系统的误差信号用于反馈调节激光器腔长,使得激光器频率自动稳定到Fabry-Perot(F-P)参考腔的谐振频率上。建立了正交解调PDH稳频实验系统,实验结果表明,在1.5 h稳频时间内,激光器的频率漂移不超过±0.13 MHz,根据Allan方差计算得到其频率稳定度优于1.2×10^-11。这种稳频激光器可用作合成波绝对距离干涉测量系统的理想光源。     

石英晶体振荡器频率测量结果不确定度评定

石英晶体振荡器简称为晶振,由于其体积小、重量轻、可靠性高、频率稳定度高等优点,广泛应用于家用电器和通信设备中。为了保证使用设备的性能,常需对石英晶体振荡器的频率准确度、短期频率稳定度、日老化率计量特性进行校准,通过对石英晶体振荡器的三种频率测量结果的不确定度评定,表征其测量结果的质量能够完全满足量值溯源要求,校准结果可信。     

频标传递的研究

介绍频标的传递以及副载波频标的,石英晶体频率稳定度的测量。     

有限测量二级方差估值的不确定度

有限次（ｍ次）测量二级方差的估值σ２Δｙ（τ，ｍ）随机地偏离其真值〈σ２Δｙ（τ）〉，相对偏差为Δ．讨论了这种随机不确定性的统计特性；推导出求算标准方差σ２（Δ）的表达式；引用幂律谱噪声模型计算了由各单项噪声产生的不确定度，并与阿仑方差估值的不确度进行比较．     

10·6μCO_2激光器频率稳定度的初步研究

报告叙述了10.6μCO_2激光器的稳频原理。对激光器频率不稳定的各种因素进行了分析,在普通实验室条件下,引起CO_2激光频率起伏的主要因素是:环境温度的变化、机械振动及电源的不稳定等外界騒扰。采取一定措施,对这些因素进行控制,利用鑑频器和示波器对激光器短期稳定度以及用“频率分析仪”对长期稳定度进行了测量,初步结果是短期稳定度为1×10~(10)量级(0.1秒内),长期稳定度为3×10~7量级(7小时内)。     

相位差法测量激光束频率稳定度的研究

本文提出一种测量激光束频率稳定度的新方法(相位差法),采用光外差技术,测量两光束的光程不同而引起的相位差,在所设计的光路中,激光管的频率变化将使两光束的相位差随着变化,从而使本方法得以实现。本文从理论上推导了激光管的频率稳定度△f/f_0与两光束相位差的变化之间的关系,叙述了实验装置,进行了比对测试,理论与实验都得到了一致的结果。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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