Cosmic ray acceleration by supernova shocks

We analyse the results of recent measurements of nonthermal emission from individual supernova remnants (SNRs) and their correspondence to the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is shown that the theory fits these data in a satisfactory way and provides the strong evidences for the efficient CR production in SNRs accompanied by significant magnetic field amplification. Magnetic field amplification leads to considerable increase of CR maximum energy so that the spectrum of CRs accelerated in SNRs is consistent with the requirements for the formation of Galactic CR spectrum up to the energy ∼10¹⁷ eV.     

XMM-Newton survey of non-thermal shell candidates: Preliminary results on DA 530

The investigation of the general properties of non-thermal (NT) X-ray shell supernova remnants (SNRs), of which SN 1006 is the prototype, is important to understand how electrons are accelerated in SNR shocks and what is the origin of cosmic rays. Using the XMM-Newton satellite, we are carrying on a survey of putative non-thermal SNR candidates previously unknown or little studied in the X-ray band, in order to investigate the different manifestations of NT emission in SNR shells. The SNRs we have selected are likely to expand in a low density medium, and therefore to have a low thermal X-ray emission, that usually outshines the non-thermal one. We report here preliminary results obtained on the SNR shell DA 530.     

二次时效对微合金化的Al-Cu-Li 微观组织及力学性能的影响

通过常规力学性能、扫描电镜、透射电镜等测试分析方法研究了T8I6二次时效制度对Mg、Ag和Zn复合微合金化的Al-3.48Cu-1.44Li合金微观组织和力学性能的影响.结果表明,与单级时效相比,二次时效合金强度提高,而塑性略降;合金强度随第三级时效时间的延长进一步提高.最优的合金其抗拉强度(UTS)、屈服强度(YS)和延伸率分别为613.7、564.9 MPa和6.8％.合金的强化相主要为T1相,另有少量的θ'相和S'相.二次时效促进强化相,特别是T1相的二次沉淀,提高合金的强度,同时几乎不损失塑性.     

次流通道对双喉道气动矢量喷管的性能影响研究

为了进一步了解次流通道对双喉道气动矢量喷管(Dual Throat Nozzle,DTN)气动矢量性能的影响,基于二维DTN喷管构型进行了详细的数值模拟研究。结果表明:收扩的次流通道相对于平直的次流通道不会改善DTN喷管的推力矢量性能;随着次流流量增加,DTN的推力矢量角存在一个最大值,超过该值各推力矢量性能均会降低;次流通道宽度对DTN喷管推力矢量性能影响显著:(1)次流宽度不影响所能达到的最大推力矢量角;(2)小的次流宽度在进口总压较高的条件下具有更高的推力矢量角;(3)增大次流宽度能降低次流总压,但达到的矢量角会有所减小。     

电离层顶部电子含量对GNSS电离层层析的影响分析

卫星信号射线上的总电子含量(slant total electron content, STEC)是像素基全球卫星导航系统电离层层析(computerized ionospheric tomography, CIT)建模的必要数据来源，但电离层层析通常忽略1 000 km以上的顶部电子含量，为弄清这部分电子含量对层析结果的影响，利用NeQuick2模型计算站星视线上的STEC与其在电离层区域内的STEC比值来改正原始数据，并分别利用改正前后的STEC进行电离层层析。结果显示，电离层顶部电子含量占比约为10%，白天占比略大于黑夜，与测高仪站的数据相比，改正后的均方根值比改正前提高了20%以上；与Swarm卫星提供的电子剖面数据对比，改正后的层析结果精度较改正前提升了19.6%左右，且该方法受地磁扰动影响较为明显。总的来说，利用CIT进行小尺度电离层探测，可较直观地看出，顶部电子含量对层析结果的影响较大，需要采取相应手段予以剔除。     

A nonlinear background removal method for seismo-ionospheric anomaly analysis under a complex solar activity scenario: A case study of the M9.0 Tohoku earthquake

A precise determination of ionospheric total electron content (TEC) anomaly variations that are likely associated with large earthquakes as observed by global positioning system (GPS) requires the elimination of the ionospheric effect from irregular solar electromagnetic radiation. In particular, revealing the seismo-ionospheric anomalies when earthquakes occurred during periods of high solar activity is of utmost importance. To overcome this constraint, a multiresolution time series processing technique based on wavelet transform applicable to global ionosphere map (GIM) TEC data was used to remove the nonlinear effect from solar radiation for the earthquake that struck Tohoku, Japan, on 11 March, 2011. As a result, it was found that the extracted TEC have a good correlation with the measured solar extreme ultraviolet flux in 26–34 nm (EUV_26–34) and the 10.7 cm solar radio flux (F_10.7). After removing the influence of solar radiation origin in GIM TEC, the analysis results show that the TEC around the forthcoming epicenter and its conjugate were significantly enhanced in the afternoon period of 8 March 2011, 3 days before the earthquake. The spatial distributions of the TEC anomalous and extreme enhancements indicate that the earthquake preparation process had brought with a TEC anomaly area of size approximately 1650 and 5700 km in the latitudinal and longitudinal directions, respectively.     

Solar activity dependence of total electron content derived from GPS observations over Mbarara

Vertical total electron content (VTEC) observed at Mbarara (geographic co-ordinates: 0.60°S, 30.74°E; geomagnetic coordinates: 10.22°S, 102.36°E), Uganda, for the period 2001–2009 have been used to study the diurnal, seasonal and solar activity variations. The daily values of the 10.7 cm radio flux (F_10.7) and sunspot number (R) were used to represent Solar Extreme Ultraviolet Variability (EUV). VTEC is generally higher during high solar activity period for all the seasons and increases from 0600 h LT and reaches its maximum value within 1400 h–1500 h LT. All analysed linear and quadratic fits demonstrate positive VTEC-F_10.7 and positive VTEC-R correlation, with all fits at 0000 h and 1400 h LT being significant with a confidence level of 95% when both linear and quadratic models are used. All the fits at 0600 h LT are insignificant with a confidence level of 95%. Generally, over Mbarara, quadratic fit shows that VTEC saturates during all seasons for F_10.7 more than 200 units and R more than 150 units. The result of this study can be used to improve the International Reference Ionosphere (IRI) prediction of TEC around the equatorial region of the African sector.     

Response of the EIA ionosphere to the 7-8 May 2005 geomagnetic storm

In this paper, response of low latitude ionosphere to a moderate geomagnetic storm of 7–8 May 2005 (SSC: 1920 UT on 7 May with Sym-H minimum, ∼−112 nT around 1600 UT on 8 May) has been investigated using the GPS measurements from a near EIA crest region, Rajkot (Geog. 22.29°N, 70.74°E, Geomag.14°), India. We found a decrease in total electron content (TEC) in 12 h after the onset of the storm, an increase during and after 6 h of Sym-H deep minimum with a decrease below its usual-day level on the second day during the recovery phase of the storm. On 8 May, an increase of TEC is observed after sunset and during post-midnight hours (maximum up to 170%) with the formation of ionospheric plasma bubbles followed by a nearly simultaneous onset of scintillations at L-band frequencies following the time of rapid decrease in Sym-H index (−30 nT/h around 1300 UT).     

Options for mapping foF2

Available long-term and near-real time global and regional maps of foF2 are examined in relation to telecommunication and aeronomy requirements and recommendations are made for the best present-day maps to adopt. In particular, it is shown that current CCIR maps do not meet all requirements and should not necessarily be regarded as standards against which other mappings should be compared.     

Seasonal dependence of TEC and SLAB thickness

Several years of hourly daily GPS measurements of the vertical total electron content (TEC) and of the equivalent slab thickness made at different European locations are analysed by using the linear regression technique to demonstrate the response of these two ionospheric parameters to seasonal variations. It is found that both TEC and slab thickness are highly correlated with season. Analytical relationships are determined expressing the seasonal dependence of the vertical TEC and of the equivalent slab thickness as a function of the seasonal parameter cos χ at noon in each location.