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.     

涡桨教练机螺旋桨设计关键技术分析

涡桨教练机以其完美的节油特性越来越受用户青睐,本文就涡桨教练机推进部件螺旋桨的设计技术进行探讨。简要介绍了提高螺旋桨效率的一般技术,重点围绕提高螺旋桨效率以及影响全机气动特性的关键技术展开分析。     

DZ22高温合金复杂应力疲劳强度研究

一、疲劳强度计算方法的建立　　定向凝固镍基高温合金 DZ2 2是一种正交各向异性材料 ,对于各向异性材料 ,由于偏轴向拉剪和剪拉耦合的存在 ,形状改变与体积变化无法分开 ,仅考虑剪切应变能不足以说明各向异性材料的失效 ,还需要考虑体积改变能。据此认为 Tsia- Wu理论 [1 ] 较 Hill理论 [2 ] 更能有效地反应各向异性材料的失效 ,并根据 Tsai- Wu理论导出一个疲劳强度的计算方法。Tsai- Wu假设各向异性材料在应力空间中的破坏表面可表示为一个高阶张量多项式 ,并提出了以二阶张量多项式为破坏准则的计算方法 ,即Fijσiσj+ Fiσi =1 ( …     

New approach for suppression of FM jamming in GPS receivers

A new approach is proposed for the suppression of FM jammers in C/A code GPS receivers. This approach is based on the cascading of the augmented-state approximate conditional mean (ASACM) filter and the discrete wavelet transform (DWT) filter. An ASACM filter for single interference suppression in spread-spectrum systems has been reported in the recent literature. However, the formulation of the ASACM filter and its performance analysis is lacking in the case of suppression of multiple FM interferences. The ASACM filter is formulated here for the suppression of multiple FM jammers. Further, a DWT filter using biorthogonal wavelet is suggested for the suppression of FM jammers. Finally, these two filters are cascaded to get an optimum performance for higher jammer to signal ratio, which is of importance in the GPS, for the case of suppression of multiple FM jammers. The performance of the proposed filters is analyzed through simulation examples for the suppression of single and multiple FM jammers in GPS receivers     

Mechanical properties of ANTRIX balloon film and fabrication of single cap large volume balloons

The zero pressure plastic balloons used for high altitude studies are generally made from polyethylene material. Tensile properties of the thin film polymer are the key parameters for material selection due to extremely low temperature of −90 °C encountered by the balloons in the tropopause region during the ascent at equatorial latitudes. The physical and structural properties of the material determine the uniformity of the stress distribution over the entire shell. Load stresses from the suspended load propagate via load tapes heat sealed along with the gore seals as per the balloon design. A balance between this heat seal strength and the film strength is a desirable property of the basic resin in terms of the bubble strength, gauge uniformity, and long-term storage properties. In addition, the design of the top shell of the balloon and its stress distribution play an important role since only a fraction of the balloon is deployed during the filling operation and the ascent. In this paper we describe the mechanical properties of the ‘ANTRIX’ film developed by us and the optimized design of single cap balloons, which have been successfully used in our experiments over the past 5 years.     

涡轮盘的破裂分析

某烟气轮机涡轮盘发生了盘缘断裂掉块事故,某航空发动机Ⅰ级涡轮盘也大量发生槽底裂纹的故障。我们对这两个盘的盘体和槽底部分用轴对称和平面8节点等参元有限元法对温度场(包括瞬态温度场)与应力场进行了计算,从而对涡轮盘在不同工作状态下的应力分布及故障原因进行了分析。本文着重阐述冷却条件对于涡轮应力分布是十分重要的,同时,不应忽视轮缘的应力水平,在某特定工作状态下,轮缘的应力值可能远远超过轮心,而且循环的应力幅值也很大,且由于载荷与几何形状的复杂性,在轮缘与榫齿的过渡段上出现较大的应力集中,往往成为裂纹源区;本文最后分析了轮缘残余应力形成及对槽底径向裂纹的生成与扩展的影响。     

Space capsule recovery—Evaluation of risk factors, safety plans and procedures and design of experiments for systems qualification

The Indian Space capsule (SRE-1) launched aboard PSLV-C7 rocket, was recovered successfully in the Bay of Bengal on January 22, 2007 after its orbital sojourn of 12 days. Apart from serving as a platform for micro-gravity experiments, SRE-1 demonstrated ISRO's capability in the field of orbital reentry and recovery technologies. Satish Dhawan Space Centre (SDSC SHAR), the Spaceport of India was given the prime responsibility of assessment of mission risk, formulation and execution of safety plans and procedures, design and conduct of trials for validating the mission-critical sub-systems as well as the physical recovery of the capsule. To achieve these objectives, a number of drop tests were designed and conducted by SDSC SHAR involving real time computer network, ground-based tracking and telemetry stations, communication systems, safety and material handling systems, target identification and recovery systems. Dissemination of relevant information and coordination with multiple external organizations such as Indian Coast Guard, Indian Air Force and Indian Navy is an important aspect of these experiments. This paper delineates the methodologies designed and implemented at SDSC SHAR for validating those critical systems whose functionality finally culminated in the success of the mission, enabling India to join the elite group of nations with reentry module recovery capability.     

Transitional Flow and Heat Transfer Characteristics in a Rectangular Duct with Stagger-arrayed Short Pin Fins

This article describes an experimental study on friction and heat transfer performances of a transitional airflow in a rectangular channel with stagger-arrayed short pin fins. Friction factors, average Nusselt numbers and overall thermal performances of the transitional flow are obtained. The experimental study has showed that the pin fins enhance the heat transfer performance significantly, however increasing the flow frictional resistance considerably. After comparing the experimental results with the published data in references, it can be concluded that, in the transitional flow region, the pin fin channels of the proposed geometrical configuration could lead to a significant improvement of an overall thermal performance; for instance, the convective heat transfer performance is increased by at least 68%. By contrast, in the fully turbulent flow region, the ability of the proposed pin fin channels to increase heat transfer performances decreases as the Reynolds number increases. When Re > 6 000, the overall thermal performance becomes lower than the others.     

A study on TEC reduction during the tail phase of the 21st June 2020 annular solar eclipse

Ionospheric response during the annular solar eclipse of June 21, 2020, has been examined in terms of the Total Electron Content (TEC) obtained from six Global Positioning System (GPS) receivers positioned in the Chinese-Taiwanese region. We have shown TEC variation from satellites designated by PRNs (Pseudo-Random Noise code) 2, 6, and 19. PRN wise TEC trend was observed to depend upon satellite-pass trajectory to the receiver's location during the eclipse period. A time lag of ~15–30 min is also observed in maximum TEC decrement after the phase of maximum eclipse. Instead of the percentage of eclipse magnitude, a reduction in TEC is seen more for the station for which the orbital track of respective satellites was in closer view relative to receivers for more hours of eclipse window. Additionally, the eclipse day diurnal variations are compared with the pre-eclipse day TEC trend, and observed results show a clear decrease in TEC values at all chosen stations after the eclipse onset then reached the lowest value a few minutes afterward the maximum eclipse phase.     

The Indian EO Programme-national and global drivers

The Indian Earth Observations Program, over the past three decades, has been mainly driven by the national need for natural resources management, environment monitoring and disaster support. With an array of seven Indian Earth Observation Satellites, national development support has been provided through a well-knit institutional framework of a National Natural Resources Management System (NNRMS). A wide variety of applications have been developed as an inter-agency effort over the past 15 years. Now, the capacity of the programme has extended into the global arena and is providing operational data services to the global user community. Positioning of relevant policy guidelines for the EO program to contribute to national endeavor and its transitioning for global outreaching and development of a commercial enterprise — both at national and global levels has been an area of constant attention within ISRO.Issues related to defining the space and data acquisition as a national “public ground”, costing of data products and services and evolving a commercial Earth Observation policy have been addressed for providing the overall thrust of the Indian Earth Observations program. The paper discusses the evolution of the policy in the early stages and its transition today to support a two-pronged strategy of supporting national development support and at the same time, developing a commercial program. The paper also illustrates the success of these policy endeavors through specific cases of applications and development of value added services. The paper also brings out the potential policy adjustments that will be called for in the coming years.