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.     

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.     

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.     

分治策略在卫星数据交换控制中的应用

基于并行技术对卫星数据流控制进行了研究,利用分治策略设计一种并行架构的卫星数据流控制方式.这种并行进行的通信方式与以往卫星采用的顺序轮询下位机的通信方式相比,可大大缩短与所有下位机完成通信所花费的时间,为中心计算机节约出大量的系统时间,让中心计算机可以利用更多的时间进行卫星姿态控制与轨道计算.     

A surface reflectance correction model to improve the retrieval of MISR aerosol optical depth supported by MODIS data

Combined use of different satellite sensors are known to improve retrievals of aerosol optical depth (AOD). In this study, we propose a new method for retrieving Multi-angle Imaging SpectroRadiometer (MISR) AOD data supported by Moderate Resolution Imaging Spectroradiometer (MODIS) data in Jiangsu Province, China, over the period of 2016–2018 using MODIS L1B, bidirectional reflectance distribution function (BRDF), MISR 1B2T, and ground-measured AOD data. This method is based on the surface reflectance determined by the MODIS V5.2 algorithm. Through the observation angle and spectral conversion between different sensors, the MISR AOD can be obtained. The correlation coefficient (R) and root-mean-square error (RMSE) between the retrieved MISR and ground-measured AOD data varied between different seasons. The accuracy of the MISR AOD retrieval was notably improved after correcting the MISR surface reflectance. Therefore, the method proposed in this study is feasible for the retrieval of MISR AOD supported by MODIS data, and will be applicable to atmospheric environmental monitoring over large areas in the future.     

A holistic approach to the monitoring of land cover changes in Sri Lanka using intermediate remote sensing techniques

Heavy social and economic pressure on the available land resources in Sri Lanka are causing major land-cover changes. They need to be assessed to serve as input data for decision-making processes e.g. in agricultural or ecological planning.The Sri Lanka/Swiss Satellite Imagery Interpretation Project has developed a holistic approach to the mapping and monitoring of the land-use and the land-cover changes. The method applies intermediate level technology and is based on a benchmark/masking technique using satellite images, aerial photography and field surveys.The regular monitoring of changes of land-use types as a whole, e.g. forests, is part of the approach as well as the periodic assessment of changes within a specific land category, e.g. the seasonally cultivated riceland.The activities have to be transferred from the level of scientific research to the actual application within a reasonable time frame using the local resources. Discussed are also some of the problems inherent in the implementation of remote sensing activities in a so-called Third World country.     

The use of MODIS 250 m bands to improve the MODIS 1 km ocean color atmospheric correction algorithm in turbid water

“Clear water” is a scale-dependent concept, so it is more likely to successfully find the “clear water” from images with smaller scale than that with larger scale data. In this study, an optimal spectral relationship of moderate-resolution imaging spectroradiometer (MODIS) 250 m and 1 km resolution data at near-infrared bands (OSRLM) is constructed for converting pseudo “clear water” reflectance at 859 nm to those at 748 and 869 nm. According to scale effects, the satellite-observed pseudo “clear water” reflectance is greater than 5.18%, larger than that derived from OSRLM model. An atmospheric correction model for MODIS 1km data using pseudo “clear water” reflectance of MODIS 250 m data (ACMM) was developed for improving the performance of traditional “clear water” atmospheric correction model (CWAC). The model validation results indicate that ACMM model has a better performance than CWAC model. By comparison, the uncertainty decreases by 19.18% in the use of ACMM model over CWAC model for deriving water-leaving reflectance in Taihu Lake, China. This uncertainty is significantly reduced in water-leaving reflectance estimation due to partial removal of scale effects on “clear water”. These findings imply that satellite-derived aerosol scattering contribution at smaller scale usually has a better performance than that at larger scale.     

Tolerance of chufa (Cyperus esculentus L.) plants,representing the higher plant compartment in bioregenerative life support systems,to super-optimal air temperatures

Plants intended to be included in the photosynthesizing compartment of the bioregenerative life support system (BLSS) need to be studied in terms of both their production parameters under optimal conditions and their tolerance to stress factors that might be caused by emergency situations. The purpose of this study was to investigate tolerance of chufa (Cyperus esculentus L.) plants to the super-optimal air temperature of 45 ± 1 °C as dependent upon PAR (photosynthetically active radiation) intensity and the duration of the exposure to the stress factor. Chufa plants were grown hydroponically, on expanded clay, under artificial light. The nutrient solution was Knop’s mineral medium. Until the plants were 30 days old, they had been grown at 690 μmol m⁻² s⁻¹ PAR and air temperature 25 °C. Thirty-day-old plants were exposed to the temperature 45 °C for 6 h, 20 h, and 44 h at PAR intensities 690 μmol m⁻² s⁻¹ and 1150 μmol m⁻² s⁻¹. The exposure to the damaging air temperature for 44 h at 690 μmol m⁻² s⁻¹ PAR caused irreversible damage to PSA, resulting in leaf mortality. In chufa plants exposed to heat shock treatment at 690 μmol m⁻² s⁻¹ PAR for 6 h and 20 h, respiration exceeded photosynthesis, and CO₂ release in the light was recorded. Functional activity of photosynthetic apparatus, estimated from parameters of pulse-modulated chlorophyll fluorescence in Photosystem 2 (PS 2), decreased 40% to 50%. After the exposure to the stress factor was finished, functional activity of PSA recovered its initial values, and apparent photosynthesis (P_apparent) rate after a 20-h exposure to the stress factor was 2.6 times lower than before the elevation of the temperature. During the first hours of plant exposure to the temperature 45 °C at 1150 μmol m⁻² s⁻¹ PAR, respiration rate was higher than photosynthesis rate, but after 3–4 h of the exposure, photosynthetic processes exceeded oxidative ones and CO₂ absorption in the light was recorded. At the end of the 6-h exposure, P_apparent rate was close to that recorded prior to the exposure, and no significant changes were observed in the functional activity of PSA. At the end of the 20-h exposure, P_apparent rate was close to its initial value, but certain parameters of the functional activity of PSA decreased 25% vs. their initial values. During the repair period, the parameters of external gas exchange recovered their initial values, and parameters of pulse-modulated chlorophyll fluorescence were 20–30% higher than their initial values. Thus, exposure of chufa plants to the damaging temperature of the air for 20 h did not cause any irreversible damage to the photosynthetic apparatus of plants at either 690 μmol m⁻² s⁻¹ or 1150 μmol m⁻² s⁻¹ PAR, and higher PAR intensity during the heat shock treatment enhanced heat tolerance of the plants.