晶体振荡器的应用及发展MCXO晶振的必要性

介绍了晶体振荡器在国内外的广泛应用和ＭＣＸＯ晶振的原理方案及其较之ＴＣＸＯ晶振的各种优越性。ＭＣＸＯ晶体振荡器结合了ＳＣ切等特殊晶体的特性及微型计算机技术，对晶体振荡器和高准确度频率源的长远发展有重要意义。     

一种新型恒温—温补晶体振荡器

提出了一种ＯＣＸＯ的恒温控制方法。该方法是利用乙醇的沸点制成换态式恒温箱。这种温度控制方法既可以用作中准确度的ＯＣＸＯ，又可以作为精密双层控温ＯＣＸＯ的外层恒温装置，还可以与简单的温补线路结合，构成高准确度的ＯＴＣＸＯ。     

一种专用的晶体振荡器电路M101及其应用

传统的晶体振荡器大都是采用以三极管为主的分立元件搭起来的,这种晶体振荡器的准确度可达到1×10-9/d以上的老化指标和10-10/τ以上的频率稳定性,应用也很广泛,但是它的线路比较复杂,不便于小型化,对于准确要求在1×10-8/d或低于1×10-8/d的晶体振荡器,可以采用一种新型的集成电路M101来实现.它的线路实现起来简单,可靠性高,开机特性(用AT切晶体,在稳定的室温下不加温控线路)可达到1×10-7/d专用集成电路主要介绍M101的使用情况.     

一种新型的微机补偿晶体振荡器及开发系统

提出了一种新型的以微处理器为核心的AT切温度补偿晶体振荡器 (MCXO)的设计思想 ,说明了其开发系统的原理 ,给出了最后的实验结果。使用该开发系统得到的这种振荡器可以工作在 - 40℃～ 85℃的环境内 ,频率—温度稳定性≤± 5× 10 - 7。     

抗振晶体振荡器的仿真设计CSCD

本文介绍了利用仿真软件进行抗振晶体振荡器设计的方法,通过建立晶体振荡器结构仿真模型,对其力学特性进行深入细致的分析,并在此基础上对比分析减振材料的剪切模量和被减振物质量对晶体振荡器抗振性能的影响,优化晶体振荡器减振结构。然后,根据仿真设计制做了抗振晶体振荡器,并进行了随机振动试验。结果表明,试验现象与仿真结果基本一致,验证了仿真分析的有效性,且振动下晶体振荡器相位噪声达到-145d Bc/Hz@1k Hz,极大地提高了晶体振荡器的抗振性能。     

一种新型微机补偿晶体振荡器

提出了一种以微处理器 +单一A/D、D/A数据处理芯片的新型微机补偿晶体振荡器。该温补晶振的频率稳定度≤± 2× 10 -7(- 4 5℃～ +85℃ ) ,体积 35× 2 4× 10mm3 ,平均功耗≤ 30mW。     

加速度对晶体振荡器的影响及补偿技术研究

晶体振荡器作为基准频率源,在电子设备中发挥着重要作用。晶体振荡器对加速度具有敏感性,振动、冲击、离心力等作用均会导致其输出频率失稳。讨论了加速度影响晶体振荡器频率及相噪的机理,介绍了目前降低加速度效应的常用措施,并提出一种基于数字补偿系统的新方法。     

单片机数字温度补偿晶体振荡器的研究

讨论应用单片微型计算机对晶体振荡器进行数字温度补偿的原理,给出系统方框图和单片微机程序流程图,也对校准值的插值运算作了介绍,在-20～+50℃温度范围内,获得了小于±1×10~(-7)频率稳定度的温补晶体振荡器。     

基于C8051F061的微机补偿晶体振荡器

设计了一种基于C8051F061芯片的新型微机补偿晶体振荡器(简称MCXO).由于C8051F061单片机丰富的硬件资源、同时充分发挥了软件的作用使得本设计具有结构简单、体积小、功耗低、开机预热时间短等优点,主要技术指标为:频率温度稳定度为±5×10-8(-40℃～+85℃),体积为(35×23×10)mm3,平均功耗不大于60mW.     

具有良好压控特性的压控晶体振荡器的设计

介绍了一种具有良好压控特性的晶体振荡器的设计方法。阐述了产生压控晶体振荡器压控特性非线性的原因,介绍了VCXO设计过程中主要元件的选择和设计,并且设计和制作了一个工作频率为10MHZ,具有一个粗调节压控端和一个微调节压控端的压控晶体振荡器。该电路通过MAX828来改善VCXO的电压控制范围及压控线性。实验证明了该设计的正确性。     

超小型高可靠高稳定晶体振荡器

介绍体积仅为３０ｍｍ×３０ｍｍ×４０ｍｍ，重量仅为５０ｇ，适用于宇航系统的新型高稳定、高可靠频率源的研制情况。给出各项技术指标的测试结果。     

Highlights about the performances of storm-time TEC modelling techniques for low/equatorial and mid-latitude locations

A statistical evaluation of storm-time total electron content (TEC) modelling techniques over various latitudes of the African sector and surrounding areas is presented. The source of observational TEC data used in this study is the Global Navigation Satellite Systems (GNSS), specifically the Global Positioning Systems (GPS) receiver networks. For each selected receiver station, three different storm-time models based on empirical orthogonal functions (EOF) analysis, non-linear regression analysis (NLRA) and Artificial neural networks (ANN), were implemented. Storm-time GPS TEC data used for both development and validation of the models was selected based on the storm criterion of $\mathit{Dst}?-50$ nT or $K_p?4$ to take into account both coronal mass ejections (CMEs) and co-rotating interaction regions (CIRs) driven storms, respectively. To make an independent test of the models, storm periods considered for validation were excluded from datasets used during the implementation of the models and results are compared with observations, monthly median values, and International Reference Ionosphere (IRI-2016) predictions. Considering GPS TEC as reference, a statistical analysis performed over six storm periods reserved for validation revealed that ANN model is about 10%, 26%, and 58% more accurate than EOF, NLRA, and IRI models, respectively. It was further found that, EOF model performs 15%, and 44% better than NLRA, and IRI models, respectively, while NLRA is 25% better than IRI. On the other hand, results are also discussed referring to the background ionosphere represented by monthly median TEC (MM TEC) and statistics are provided. Moreover, strengths and weaknesses of each model are highlighted.     

ECR中和器改进试验研究

目前国内电子回旋共振(ECR)中和器的研究存在电子束流不能连续引出的问题,为此通过改进中和器天线结构及优化电子引出孔径来改善中和器的性能。试验结果表明：中和器结构改进及优化后其电子束流可以随着接触电压的升高而连续变化,同时提高了中和器的推进剂利用效率、降低了电子产生损耗。推进剂利用效率和电子产生损耗在中和器结构改进前后分别为1.278 9和194.573 W/A,1.659 8和126.3 W/A。试验还通过静电探针诊断出中和器耦合天线附近等离子体密度分布在1.72×10¹⁷~12.1×10¹⁷ m^-3范围内。     

High-velocity impact experiments needed to improve our understanding of the asteroids

The lifetime of almost all the asteroids against catastrophic impact events is less than the age of the solar system, implying that the asteroids can be considered as outcomes of catastrophic collisions. Therefore to understand their physical properties (structure, shape, rotation, regolith development) and their family memberships (since families are generated by the escape of breakup fragments), a systematic knowledge of the outcomes of catastrophic impacts under a variety of conditions seems needed. In particular, interesting fields to be explored by laboratory experiments are: the dependence of the critical energy densities associated with various degrees of fragmentation on the target's size and composition; the velocity distribution of the fragments and the inelasticity of the process in different cases; the shape of the fragments and its possible correlation with other quantities; the way a dust- or regolith-covered target affects the collisional outcomes; the angular momentum partitioning and the rotation of the fragments. On this latter problem very few experimental results are presently available; on the other hand, the rotation of small asteroids presents several intriguing “anomalies”.

A significant progress of our understanding of asteroid collisional evolution and related phenomena can be provided by new laboratory experiments of collisional breakup. The targets should have spherical and/or irregular shape (up to axial ratios of the order of 2), and should be made of (possibly different) geological materials. The interesting projectile velocities are of the order of the relative velocities commonly found among asteroids, i.e., in the range 1 to 10 Kms⁻¹. In order to get catastrophic collisions, the ratio of the projectile kinetic energy to the target mass (≡E/M) has to be chosen within a “critical” range (for basalt targets, from 10⁶ to 10⁸ erg/g). In some particular cases, this kind of experiments has been already performed in past (Gault and Wedekind [10]; Fujiwara et al. [7]; Fujiwara and Tsukamoto [9]); however the generalization of the results to a wide range of experimental conditions is lacking, and many problems of outstanding importance to model asteroid evolution are still completely open.     

Exploration of groundwater potential zones mapping for hard rock region in the Jakham river basin using geospatial techniques and aquifer parameters

Geospatial techniques are useful to understand the groundwater resources assessment, development, and management. Groundwater mapping is essential to counter the excessive withdrawal of groundwater and fulfil the need of drinking, irrigation water in hard rock areas. Currently, the main problem is facing the groundwater level is decreasing due to less rainfall, climate changes and increasing demand, which is under in the hot zones. This results can be more useful for future challenges, sustainable development and demand to Jakham river basin. The main objective of this paper to demarcated the groundwater potential zones (GWPZ) using geospatial techniques for the hard rock region with the reference of aquifer parameters. In this paper, we have used to total eight thematic layers such as geomorphology, land use, soil, topographic elevation, slope, post-monsoon groundwater level (GWL), net recharge, and transmissivity, which are prepared from satellite data and field verification. All thematic layers were integrated for assigning the weights to demarcation of the groundwater potential zones in the RS and GIS environment. The selected thematic layers and features were assigned weightage and normalized by the analytic hierarchy process (AHP) technique. Finally, the thematic layers were systematically integrated using weighted overlay analysis within a GIS environment. We have classified into five GWPZ classes i.e. very high, high, moderate, low, and very low for basin area using GIS, and AHP methods. The study area result indicated that high and moderate zone, which is confined in the central part of the basin, covers 2.43 % and 43.88 % area, respectively. The low (49.21 %) and very low (4.25%) GW potential zone is under the confined aquifer in the high slope and rock outcrops formations near the basin boundary. The final GWPZ map was validated with groundwater level fluctuation data, which illustrates the accuracy of the adopted approach. This unique approach and conclusions of this work may also help to develop the framework and policies for swiftly analyzing groundwater recharge planning, development and locating the artificial recharge structures in the other semi-arid, arid and hard rock regions.     

利用神经网络逆控制系统提高 Turbo码译码性能

对Turbo码译码逆模型建立问题,提出使用神经网络结构的非线性滤波器来建立Turbo码译码自适应逆模型.采用最优常系数比例因子统计得到Turbo码期望衰减系数,通过利用期望衰减系数训练神经网络非线性自回归外输入NARX滤波器,建立全局范围内的Turbo码译码逆输入输出映射模型.在线性逆控制系统中采用该自适应逆模型,与非线性逆控制结构的自适应逆控制系统相比,具有系统结构简单、运算量小等特点.仿真结果表明在信噪比大于0?dB时,该自适应逆模型算法收敛迅速、稳定,计算误差保持在较小的范围之内.自适应逆译码模型从译码机理角度提供了一种改善译码性能的新途径.     

Using cross-correlation techniques to assess the validity of AP8 at low altitude

Background effects, such as single event upsets, are used as proxy data sets to evaluate AP8 at low altitude. The approach is to use a 2-D (longitude and latitude) cross-correlation between the background data set and the current-epoch AP8 predicted fluxes. The technique can be used to determine the energy of the particle that is producing a particular effect. This cross-correlation technique shows that using AP8 with a present-epoch magnetic field model accurately predicts the present location of the South Atlantic Anomaly proton flux enhancement and that a dual-peaked intensity structure above 100 MeV in the model is an artifact of AP8 and its interpolation routines.