Temporal evolution analysis of storm-enhanced density during an intense magnetic storm on March 2015

An intense Storm Enhancement Density (SED) event with the magnetic storm occurred on 17–24 March 2015 has been investigated. The morphological character of the SED during different phase of the magnetic storm is examined and compared with the non-storm time. Three intensity indexes, i.e., “general” SED index, “heavy” SED index and “severe” SED index, are defined to represent the intensity of SED respectively represented by the numbers of the ionospheric total electron content (TEC) grids with TEC > 60 TECu, TEC > 80 TECu and TEC > 100 TECu. The temporal evolution of the SED intensity indexes during a time span covering the non-storm time and the magnetic storm time have also been investigated. The SED exhibits a shape with two parallel slender troughs in the middle and low latitudes during the non-storm time and then gradually develops into an ellipse structure as the development of magnetic storm. The intensity of SED and the fluctuation of the TEC evolution are generally corresponding to the fluctuation of Dst index. The analyzing results enrich our understanding of the temporal and spatial evolution of the ionospheric SED.     

Influence of uniaxial tensile pre-strain on forming limit curve by using biaxial tensile test

This paper focused on the effect of pre-strain on forming limit curves (FLC) of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach. Based on Swift model and Yld2000-2d yield criterion, the dimensions of cruciform specimen was optimized through applying finite element method for increasing the strain at specimen center. After that, with the recommended specimen size, the cruciform specimen was tested under various stroke ratios to experimentally characterize the limit strains under different pre-strain levels. Subsequently, the biaxial tensile tests were simulated by Abaqus to obtain the limit strains and validate the material models. It can be observed in both experiments and simulations that the pre-strained uniaxial tension followed by plane tension or equi-biaxial tension can improve the formability of sheet metals. Besides, the strain path change affects the trend of first derivative of strain rate difference between neighboring points with respect to time. An early increase occurred and then fell back to the stable value, the steady evolution continued until to a new increase reaching the critical value. The M–K prediction approach was simulated to verify the influence of pre-strain on FLC. It can be found that the early increase peaks of the major strain incremental ratio rose with the amplitude of pre-strain. Finally, the phenomenon of pseudolocalization caused by the strain path change was explained through evolution of stress state inside the groove.     

On the detection of anomalous seismo-ionospheric behavior in the presence of space weather stimuli for large earthquakes

Anomalous behavior of ionospheric total electron content (TEC) prior to earthquake has been observed in many studies. Evidence of such seismo-ionospheric coupling effects suggests that it is plausible to rely on TEC signatures for early earthquake warning. However, the detection of pre-earthquake TEC anomalies (PETA) has not been adopted in practice due to two pertinent issues. Firstly, the effects of space weather activity can affect TEC levels and cause anomalous behavior in the TEC. Usually arbitrary thresholds are set for space weather indices to eliminate TEC anomaly due to space weather effects. Secondly, the choice regarding moving time-window length used to characterise background variation of TEC within the statistical envelope approach has an effect on detection of PETA. While the rule-of-thumb in selecting the moving window length is to have a time window capable of capturing background variability and short-term fluctuations, the length of the time window used in the literature varies with little justification. In this study, a critical examination is conducted on the statistical envelope approach and in particular, to eliminate the effect of space weather activity without the use of arbitrary space indices to detect PETA. A two-part PETA identification procedure is proposed, consisting of wavelet analyses isolating non-earthquake TEC contributions, followed by the statistical envelope method using a moving window length standardized based on observed periodicities and statistical implications is suggested. The approach is tested on a database of 30 large earthquakes (M?≥?7.0). The proposed procedure shows that PETA can be detected prior to earthquakes at higher confidence levels without the need to separately check for space weather activity. More importantly, the procedure was able to detect PETA for studies where it was previously reported that PETA could not be detected or detected convincingly.     

Near real-time PPP-based monitoring of the ionosphere using dual-frequency GPS/BDS/Galileo data

Ionosphere delay is very important to GNSS observations, since it is one of the main error sources which have to be mitigated even eliminated in order to determine reliable and precise positions. The ionosphere is a dispersive medium to radio signal, so the value of the group delay or phase advance of GNSS radio signal depends on the signal frequency. Ground-based GNSS stations have been used for ionosphere monitoring and modeling for a long time. In this paper we will introduce a novel approach suitable for single-receiver operation based on the precise point positioning (PPP) technique. One of the main characteristic is that only carrier-phase observations are used to avoid particular effects of pseudorange observations. The technique consists of introducing ionosphere ambiguity parameters obtained from PPP filter into the geometry-free combination of observations to estimate ionospheric delays. Observational data from stations that are capable of tracking the GPS/BDS/GALILEO from the International GNSS Service (IGS) Multi-GNSS Experiments (MGEX) network are processed. For the purpose of performance validation, ionospheric delays series derived from the novel approach are compared with the global ionospheric map (GIM) from Ionospheric Associate Analysis Centers (IAACs). The results are encouraging and offer potential solutions to the near real-time ionosphere monitoring.     

残余V元素对1Crl8Ni9Ti钢板组织与性能的影响

通过试验详细论述了1Crl8Ni9Ti钢中不同残余V含量对材料固溶状态的组织及400℃、500℃长期时效后对组织、晶间腐蚀和室温、高温性能的影响。从而得出结论适量V的存在对1Crl8Ni9Ti钢板组织影响不大,对抗晶间腐蚀性能稍有提高,对室温、高温抗拉强度、屈服强度稍有提高,塑性稍有降低。     

Study of TEC changes during geomagnetic storms occurred near the crest of the equatorial ionospheric ionization anomaly in the Indian sector

GPS satellites data obtained at Bhopal (23.16° N, 77.36° E, geomagnetic latitude 14.23° N) India were analyzed to study the TEC changes during several geomagnetic storms (−300 nT < Dst < −50 nT) occurred in 2005–2007. We had segregated the storms according to the Dst value, i.e. moderate storms (−100 nT < Dst ? −50 nT), strong storms (−150 nT < Dst < −100 nT), and severe storms (Dst less than −150 nT). Total of 21 geomagnetic storms (10 moderate, 9 strong, 2 severe) are considered for the present study. Deviation in vertical total electron content (VTEC) during the main phase of the storm was found to be associated with the prompt penetration of electric field originated due to the under-shielding and over-shielding conditions for almost all geomagnetic storms discussed in this paper. For most of the storms VTEC shows the positive percentage deviation during the main phase while it shows positive as well as the negative deviation during the recovery phase of the storms. The −80% deviation in VTEC was found for geomagnetic storm occurred on July 17, 2005 and the negative trend continued for recovery phase of the storm. This was mainly due to the thermospheric composition changes by Joule heating effect at auroral latitudes that generate electric field disturbance at low latitudes. Traveling ionospheric disturbances (TIDs) were responsible for the formation of wave like nature in VTEC for the storms occurred on May 15, 2005, whereas it was not observed for storm occurred on August 24, 2005.     

耐碱棉纸中含铁量的测定方法

用Ｎ２ＯＣ２Ｈ２原子吸收法来测定某型导弹热电池耐碱棉纸中的铁含量。并对测定条件和干扰困素进行了综合考虑。该测定方法具有很好的灵敏度，很好的精确度、干扰少、选择性和重现性好等优点。相对标准偏差ＲＳＤ＜１．０％（ｎ＝１０）。标准加入回收率均在９８％～１０２％（ｎ＝３）范围内。完全适用于耐碱棉纸中的含铁量的控制和样品系统分析。在实际应用中取得了很好的效果。     

The impact of large solar events on the total electron content of the ionosphere at mid latitudes

Ionospheric disturbances associated with solar activity may occur via two basic mechanisms. The first is related to the direct impact on the ionosphere of EUV photons from a flare, and the second by prompt electric field penetration into the magnetosphere during geomagnetic storms. In this paper we examine the possibility that these two mechanisms may have an impact at mid latitudes by calculating the total electron content (TEC) from GPS stations in Mexico during several large X-ray flares. We have found that indeed large, complex flares, which are well located, may affect the mid latitude ionosphere. In fact, in the solar events of July 14, 2000 and April 2001 storms, ionospheric disturbances were observed to increase up to 138 and 150 TECu, respectively, due to the influence of EUV photons. Also, during the solar events of July 2000, April 2001, Halloween 2003, January 2005 and December 2006, there are large ionospheric disturbances (up to 393 TECu in the Halloween Storms), due to prompt penetration electric field, associated with CME producing geomagnetic storm.     

近红外光谱测定NEPE胶组分含量

研究了近红外光谱测定NEPE胶中硝化甘油、丁三醇三硝酸酯、聚乙二醇含量的方法,采用相关系数、显变分析、间隔偏最小二乘法、遗传算法等方法选择波长,对相关实验条件和影响因素进行了研究.实验结果表明,数据平移处理可以有效改善样品吸光度与浓度之间的相关性;遗传算法选择波长优于相关系数法和间隔偏最小二乘法,显变分析不适合于本项研究;近红外光谱法快速测定NEPE胶组分含量的结果与标准分析方法的测定结果一致,两者相差小于1%;水分含量的变化、正常加热操作对NEPE胶组分含量测定的影响不明显.     

月球电离层掩星探测研究

日本SELENE/KAGUYA探测任务提供了研究月球电离层的机会。采用无线电掩星探测技术和趋势外推算法,消除地球电离层和行星际等离子体的干扰影响,残余的信号相位信息的变化反映了月球电离层的信息,估算出月球周围附近近似对称分布的稀薄电离层中电子总含量(TEC)约为每立方米10-14个。