PM2.5/PM10 ratio characteristics over urban sites of India

The PM_2.5/PM₁₀ ratio (PM_2.5 and PM₁₀ are defined as mass concentration of particles having aerodynamic diameter less than 2.5 and 10 µm respectively) is one of the important parameters in understanding the severity of the fine mode surface particulate matter pollution. The present study characterises PM_2.5/PM₁₀ ratio estimates from eight Indian urban sites with varying levels of urbanization. Five years (2015–2019) of collocated PM_2.5, PM₁₀, and meteorological (ambient temperature, relative humidity (RH), and wind speed) measurements are used to understand the spatial and temporal variability in the PM_2.5/PM₁₀ ratio at different scales and to investigate its relationship with meteorological parameters. Over the study sites, the seasonal mean PM_2.5/PM₁₀ ratio varied between 0.31 ± 0.08 (mean ± standard deviation) and 0.65 ± 0.13. Seasonally, the highest PM_2.5/PM₁₀ ratio was observed during winter and post-monsoon seasons. Sites in the Indo-Gangetic Plain (IGP) exhibited higher PM levels (PM_2.5 and PM₁₀) and higher PM_2.5/PM₁₀ ratios than the corresponding values recorded at other sites. The seasonal mean PM_2.5/PM₁₀ ratio estimated (over the study sites) using MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) ranged between 0.25 ± 0.08 and 0.77 ± 0.16, and exhibited consistent overestimation (when compared to values derived from measurements) during winter and pre-monsoon seasons. Grossly, the PM_2.5/PM₁₀ ratio exhibited a weak association with meteorological parameters. Interestingly, despite variations in geography, population, anthropogenic activities and PM concentrations across seasons and sites, the PM_2.5/PM₁₀ ratio showed low variability.     

Variation of monthly mean foF2 and hmF2 over a mid latitude station during the period 1997–2006

Ionosonde data of a mid latitude station Novosibirsk (Geog. Lat. 54.6°N, Geog. Long. 83.2°E) has been analyzed for the years 1997–2006 that covers the major part of solar cycle 23. Our results show the presence of winter anomaly in the daytime F2 layer critical frequency during different phases of solar activity. Results also reveal a semiannual variation of foF₂ with two maxima and a minimum that always appears in summer. While the first maximum is in the spring equinox, the second one is found to shift from autumn to winter with the increase of solar activity. The maximum height of F2 layer during the daytime shows variation with the solar activity. It is higher during the higher activity periods and lower during the periods of low activity. Results of ionosonde observations have been compared with those obtained from IRI-2007 model and it is found that model reproduces gross features of foF₂ variation. However, the modeled hmF₂ variations during equinoxes are significantly different from the ones derived using the ionosonde data. The model also underestimates the hmF₂ values.     

A Digital System for Accurate Time Sector Division of a Spin-Stabilized Vehicle

This paper describes an aspect system flown on PIONEERS VI and VII2 which incorporates an extremely accurate adaptive digital computer in order to define rigorously equal time intervals which are submultiples of the spacecraft spin period. The several submultiples which compose the complete spin period exhibit equality to within 2.5 parts in 105. This system has potential applications in other experiments involving the study of the angular dependence of cosmic radiation and other physical phenomena being measured by a single directional detector mounted on spin-stabilized spacecraft. Included here are the scientific goals for this experiment, system restraints, and the generalized system operation. Some details on specific logic and hardware implementation for the Pioneer experiments are included along with in-flight performance evaluation of the system aboard PIONEER VI.     

电传飞控系统地面维护检测方法研究与探讨

某先进高级教练机采用典型电传飞控系统架构,本文通过对该型飞机电传飞控系统的组成和工作原理的分析,研究了该型飞机飞控系统地面的检测维护方法,并从系统检测维护的角度对电传飞控系统设计和优化提出了建议。     

Keeping up with remote sensing and GI advances—Policy and legal perspectives

Technological advances in remote sensing capabilities, wider participation of commercial firms and the possibilities of ‘processing’ spatial data to create value-added information have given rise to a range of policy and legal issues in the geographic information (GI) field. How far satellite images can still be considered a ‘public good’, conflicts between commercial and national interests is becoming a major issue, especially where security is concerned, sovereignty and the rights of sensed states, shutter control vs transparency is debated, data access, IPR and infringement of privacy becoming more relevant are all discussed. At the same time, the societal and public good of GI is well accepted with innumerable national and international examples. It is clear that societies would greatly benefit from the proper use of GI. A multilateral debate to formulate a GI policy that will take account of these while ensuring that the full benefits of remote sensing are available to society is called for.     

油气混相回流泵送密封结构启动过程摩擦磨损性能试验

针对航空发动机轴承腔油气混相回流泵送密封（OG-RPS）结构启动过程中转速低于开启转速时密封端面易发生摩擦磨 损问题，采用Plint摩擦磨损试验机进行了摩擦学性能试验。选择浸锑石墨和浸树脂石墨2种典型软环，18Cr 2 Ni 4 WA钢、表面喷涂 Al 2 O 3 陶瓷和表面喷涂Cr 2 O 3 陶瓷3种典型硬环，改变转速和载荷模拟密封启动过程的速度和端面比压变化，监测密封端面摩擦系 数和温度，并与机械密封结构试验数据进行对比。结果表明：螺旋槽能有效提升摩擦副润滑特性，减少表面磨损，大幅降低摩擦系 数和温升，最高可分别降低73.02%和63.41%；表面喷涂陶瓷能有效提高密封面抗磨损性能，其摩擦面更平滑；对摩擦副组对浸树 脂石墨和表面喷涂陶瓷更容易获得超低摩擦系数（C OF <0.01）。研究结果可为航空发动机轴承腔OG-RPS密封环设计选材和性能 优化提供数据支撑。     

A comprehensive study on middle atmospheric thermal structure over a tropic and sub-tropic stations

The general characteristics of middle atmospheric thermal structure have been studied by making use of the Rayleigh lidar data collected over the period of about four years (1998–2001). Here, the data has been used from two different stations in the Indian sub-continent in tropics (Gadanki; 13.5°N, 79.2°E) and in sub-tropics (Mt. Abu; 24.5°N, 72.7°E). The observed monthly mean temperature profiles are compared with different model atmospheres (CIRA-86 and MSISE-90). We observed, the mean temperature profiles have closer agreement with MSISE-90 than CIRA-86. The temperature profiles measured by lidar and HALOE satellite overpass nearby lidar site are generally in agreement with each other. The systematic and statistical errors in deriving temperature are found to be uniform for both the stations, as 1 K at 50 km, 3 K at 60 km and 10 K at 70 km. The special features of mesospheric temperature inversion (MTI) and double stratopause structure (DBS) are also addressed for both the stations.     

基于西门子611D的力矩电机控制技术

简要介绍了力矩电机在航空制造设备的应用及控制技术要求。着重介绍了基于西门子611D全数字伺服控制下,力矩电机驱动参数的配置及速度环、位置环的优化,为力矩电机的控制技术应用提供了实践基础。     

A PC based test system for an on-board computer

This paper presents a robust method of testing a processor based on-board computer used in the Indian remote sensing satellite (IRS-1C). The novelty of this scheme lies in a judicious mix of software and hardware approaches adopted to realise this PC-based system. All the electrical interfaces (like telemetry, Telecommand, timer and star sensor) are simulated. They are fabricated as add-on cards to PC-AT (ISAbus). The on-board computer controls two star sensors apart from handling three telemetry streams and accepting more than one hundred Telecommands     

Onboard Attitude Error Computation for Automatic Spin Axis Control of Bhaskara

The Indian experimental remote sensing satellite, Bhaskara, uses two horizon crossing sensors mounted at 45° and 135° with respect to spin axis for onboard roll error computation and automatic control of the spin axis orientation within 3° of the orbit normal. A new method for roll error computation and control and digital hardware for the same are described. The system has flexibility to vary the threshold, to adapt to altitude variations and various mission requirements, and to work with a single horizon sensor. Flight performance of the system is satisfactory.