Using GPS-TEC data to calibrate VTEC computed with the IRI model over Nigeria

This paper presents the development of a Total Electron Content (TEC) map for the Nigerian ionosphere. In this work, TEC measurements obtained from the AFRL-SCINDA GPS (Air Force Research Laboratory-Scintillation Network Decision Aid, Global Positioning System) equipment installed at Nsukka (6.87°N, 7.38°E) are used to adapt the International Reference Ionosphere (IRI) model for the Nigerian Ionosphere. The map is being developed as a computer program (implemented in the MATLAB programming language) that shows spatial and temporal representations of TEC for the Nigerian ionosphere. The method is aimed at showing how the IRI model can be used to estimate VTEC over wide areas by incorporating GPS measurements. This method is validated by using GPS VTEC data collected from a station in Ilorin (8.50°N, 4.55°E).     

On the variabilities of the Total Electron Content (TEC) over the Indian low latitude sector

The Total Electron Content (TEC) from four locations in the Indian sector namely, Trivandrum (8.47°N, 76.91°E, Geomag.0.63°S, 0.3° dip), Waltair (17.7° N, 83.3°E, Geomag. 6.4°N, 20° dip), Bhopal (23.28°N, 77.34°E, Geomag.14.26°N, 33.2° dip), and Delhi (28.58°N, 77.21°E, Geomag.19.2°N, 43.4° dip) during a low sunspot year of 2004 are used to study the variabilities of the TEC. The day time TEC values are higher over Waltair and Bhopal compared to those at Trivandrum and Delhi. Considerable day-to-day variations in the diurnal values of TEC are observed at the anomaly crest locations. The observed GPS-TEC has been compared with the IRI-2007 model derived TEC considering three different options (IRI-2001, IRI-2001 corrected and Ne-Quick) available in the model for the topside electron density. The TEC derived with Ne-Quick and IRI-01 corrected options show better agreement with GPS-TEC while the TEC from IRI-01 method shows larger deviations. From the correlation analysis carried out between TEC value at 1300 h LT and solar indices parameters namely sunspot number (SSN), F10.7 and EUV, it is observed that the correlation is more during equinoctial months and less during summer months. The correlation coefficients observed over the anomaly locations, Bhopal and Delhi are lower compared to those at Trivandrum and Waltair.     

Ti_2AlNb基合金电子束焊接头的显微组织

利用透射电子显微镜和能谱,研究电子束焊接过程中Ti_2AlNb基合金显微组织演变过程以及焊缝区组成、焊后热处理对接头显微组织的影响.结果表明:焊接过程中焊缝区Al元素损失较为严重,这有利于B_2相的形成而不利于O相的形成,使得接头焊缝区主要由B_2和α_2两相组成;在随后的热处理过程中,焊缝区的B_2相转变为β相和板条状的O相,使焊缝区由α_2、O和β相组成.     

Dark Matter Particle Explorer:The First Chinese Cosmic Ray and Hard γ-ray Detector in Space

The Dark Matter Particle Explorer (DAMPE) mission is one of the five scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Science (CAS) approved in 2011. The main scientific objective of DAMPE is to detect electrons and photons in the range of 5GeV-10TeV with unprecedented energy resolution (1.5% at 100GeV) in order to identify possible Dark Matter (DM) signatures. It will also measure the flux of nuclei up to above 500TeV with excellent energy resolution (40% at 800GeV), which will bring new insights to the origin and propagation high energy cosmic rays. With its excellent photon detection capability, the DAMPE mission is well placed for new discoveries in high energy-ray astronomy as well.      

辅助加热温度对铝合金厚板FSW焊缝成形的影响

对铝合金厚板搅拌摩擦焊（FSW）而言,焊缝底部金属温度低、流动能力差是导致焊缝成形困难的主要原因。为此,本研究采用辅助加热的方式对待焊母材底部进行预热,分析辅助加热温度对厚板搅拌摩擦焊焊缝成形的影响。结果表明,随着辅助加热温度从20℃升高至80℃时,焊缝成形质量先变好后变差,宏观表现为焊缝内部焊核区宽度、高度及面积呈现先增大后减小的趋势,而疏松区面积呈现先减小后增大的趋势。其中,当辅助加热温度为40℃时,焊缝成形质量最好,焊核区尺寸最大,疏松区消失;而当辅助加热温度升高至80℃时,焊缝成形质量最差,疏松区面积最大。研究认为,其主要原因是添加合适的辅助加热温度可显著提高焊核区塑性金属的峰值温度及高温停留时间,塑性金属流动能力明显提高,焊缝成形质量得到极大改善。焊核区塑性金属的迁移方式由沿搅拌针表面向焊缝上部高温区迁移向挤压焊核区周边冷金属横向迁移转变。但是,当辅助加热温度太高时,焊核区塑性金属迁移方式开始转变为原始的沿搅拌针表面向焊缝上部高温区迁移,且此迁移程度有明显增大的趋势,导致焊缝内部疏松区缺陷再次出现。     

Spectral characteristics of electron fluxes at L < 2 under the Radiation Belts

The paper presents the analysis of experimental data on electron fluxes with energies 10 keV–10 MeV. Data were obtained during 1978–2005 years in different space experiments (COSMOS-900, MIR Space Station, ACTIVE, SAMPEX, CORONAS-I, CORONAS-F, NOAA POES-17, TATYANA and others). Two areas of electron flux enhancements are studied in the paper: the near-equatorial (L < 1.2) zone and the middle-latitude (1.2 < L < 1.9) zone. It is shown that electron flux enhancements are regularly registered at L < 2 and the observed formations have some typical features. Electron peaks at L < 1.2 appear sporadically while peaks at 1.2 < L < 1.9 are observed regularly. The approximations of spectra by several functions including kappa-function are presented.     

小束斑电子束脉冲轰击偏压电源的研制

为了获得一种性价比较高的电子束表面处理技术,采用定频调压电路,研制出一种新型偏压脉冲电源。这种电源由偏压主电路拓扑、偏压变压器和偏压整流滤波电路组成,其中偏压主电路由偏压基值发生电路和偏压脉冲发生电路组成。偏压基值发生电路控制偏压脉冲基值,偏压脉冲发生电路控制偏压脉冲频率和占空比。脉冲偏压电源的脉冲基值、脉冲频率、占空比均连续可调,相应实现脉冲束流的幅值、束流频率和占空比的调节。检测分析了脉冲偏压电源的输出电压波形,带载时的输出束流波形,并观察分析了电子束轰击后钨合金组织变化规律。结果表明所研制的脉冲偏压电源输出电压稳定、可调性好,能满足小束斑脉冲电子束轰击工艺的要求。     

昆明上空电离层D区电子密度季节变化的首次观测分析

通过分析2008年8月至2009年7月昆明站(25.6°N, 103.8°E) 中频(MF)雷达观测数据, 研究了太阳活动低年电离层D区电子密度的季节变化特性,发现D区电子密度主要呈现半年变化特征, 即在春秋季电子密度较大, 而在夏冬季则较小, 这与国际参考电离层(IRI)预测的年变化趋势不一致, 但与昆明站电离层测高仪的最低回波频率f_min的观测结果相符. 同时比较了D区电子密度半年变化与纬向风半年变化的关系, 发现二者之间保持了非常一致的变化趋势并对这种一致性的内在原因进行了分析.      

GNSS radio tomography of the ionosphere: The problem with essentially incomplete data

We discuss the specific features of the spatiotemporal radio tomography of ionospheric electron density based on the data from high orbiting global navigational satellite system (GNSS). The main peculiarities are four-dimensionality of the problem and essential incompleteness of input data. The approach suggested for the solution of this problem is based on the search for the solution with minimal Sobolev’s norm (the most smooth solution), which provides, in particular, smooth extension of the solution to the area where no input data is available. Methods and algorithms for the solution of the problem are developed, and the resolution of the proposed technique is estimated. Examples of global and regional radio tomographic imaging based on GNSS data are presented. The obtained results are compared with the data of ionosondes and with the results of radio tomography based on the radio transmissions from low-orbiting satellites.     

减压直流等离子体射流电子温度的双静电探针测量

建立了一套双静电探针诊断系统,用于检测在气流量为4.2 slm、弧电流为80 A、真空室压力为165Pa的条件下纯氩直流非转移弧等离子体射流的电子温度及其分布。结果表明:发生器出口处射流中心的电子温度约为14 500 K,射流中电子温度随离开发生器出口的轴向或径向距离的增加而单调降低;径向电子温度梯度约为263 K/mm,轴向电子温度梯度为69 K/mm;射流中电子温度随弧电流增加而单调上升。