软模成型高硅氧纤维/酚醛树脂复合材料性能

采用硅橡胶热膨胀软模成型工艺制备高硅氧/酚醛防热材料,并用扫描电镜观察断面形貌,对比传统模压材料孔隙率和性能,对其密度及拉伸强度的离散系数进行分析。结果表明:软膜成型材料表面富有光泽;材料孔隙率低,接近"0";材料的密度和拉伸强度的离散系数分别为0. 09%和1. 95%,远小于传统模压成型材料相应的离散系数。     

Morphological studies on ionospheric VHF scintillations over an Indian low latitude station during a solar cycle period (2001–2010)

The amplitude scintillations data recorded at 244 MHz from the geostationary satellite, FLEETSAT (73°E) at a low latitude station, Waltair (17.7°N, 83.3°E) during the ten year period of high to low solar activity from 2001 to 2010 is considered to study the occurrence characteristics of the VHF scintillations. A close association between the intense scintillations on VHF signals during pre-midnight hours, associated with range type of spread-F on ionograms and a relatively weak and slow fading scintillations during post-midnight hours associated with frequency type of spread-F is observed during the relatively high sunspot years from 2001 to 2004, whereas during the low sunspot years from 2005 to 2010 the scintillation activity as well as spread-F activity are found to be minimum. During both the high and low sunspot years, it is observed that the maximum scintillation activity occurs during equinoctial months followed by winter with the minimum occurrence during summer months. The annual mean percentage occurrence of scintillations is found to be clearly associated with the variations in the annual mean sunspot number. The nocturnal variations in the occurrence of scintillations show the onset of scintillation activity starts from 19:00 h LT with maximum of occurrence around 21:00 h LT. A clear semiannual variation in the occurrence of scintillations is observed during pre-midnight hours with two peaks in equinoctial months of March/April and September/October. The number of scintillation patches observed is found to be more during pre-midnight hours compared to those during post-midnight hours. The most probable scintillation patch duration lies around 30 min. Further, it is also found that the number of scintillation patches with durations of 60 min and more decreases with the increase in the patch duration. It is also observed in general that the scintillation activity is inhibited during geomagnetic disturbed days.     

A comparative study of ionospheric spread-F and scintillation at low- and mid-latitudes in China during the 24th solar cycle

The spread-F echo of ionograms and scintillation of satellite signal propagation along the Earth-space path are two typical phenomena induced by ionospheric irregularities. In this study, we obtained spread-F data from HF (high frequency) digital ionosonde and scintillation index (S4) data from L-band and UHF receivers at low- and mid-latitudes in China during the 24th solar cycle. These four sites were located at Haikou (HK) (20°N, 110.34°E), Kunming (KM) (25.64°N, 103.72°E), Qingdao (QD) (36.24°N, 120.42°E), and Manzhouli (MZL) (49.56°N, 117.52°E). We used these data to investigate spread-F and scintillation occurrence percentages and variations with local time, season, latitude and solar activity. A comparative study of spread-F and scintillation occurrence rates has been made. The main conclusions are as follows: (a) FSF occurred mostly during post-midnight, while RSF and scintillation appeared mainly during pre-midnight at HK and KM; (b) FSF occurrence rates were larger at QD and MZL than expected; (c) the FSF occurrence percentages were anti-correlated with solar activity at HK and KM; meanwhile RSF and scintillation occurrence rates increased with the increase of solar activity at this two sites; (d) the highest FSF occurrence rates mostly appeared during the summer months, while RSF and scintillation occurred mostly in the equinoctial months at HK and KM; (e) the scintillation occurrence was usually associated with the appearance of RSF, probably due to a different physical mechanism comparing with FSF. Some of these results verified the conclusions of previous papers, whereas some show slight difference. These results are important in understanding ionospheric irregularities variations characteristic at low- and mid-latitudes in China.     

Latitudinal features of Total Electron Content over the African and European longitude sector following the St. Patrick’s day storm of 2015

GNSS TEC values have been obtained from 18 stations distributed from the magnetic equator to nearly 80°N magnetic dip in the African and west-European longitude sector corresponding to the March 17–18, 2015 geomagnetic storm. Significantly depleted ionosphere have been observed at stations north of 50°N geographic on March 18, 2015 following the above storm over a longitude swath 11.9°–21°E covering the Eastern Africa and Western European longitude sector. High ROTI values were noted on March 17^th at locations around 80°N magnetic dip. Two prominent peaks in PCN were noted around 09:00 UT and 14:00 UT on March 17, 2015 and around 15:00 UT on March 18, 2015. Daytime thermospheric (O/N₂) ratio was markedly less on March 18th at latitudes above 60°N geographic which is suggested to be the major driver behind depleted high latitude ionosphere during the recovery phase of the storm on March 18, 2015.     

连续分布百分位值和百分率的区间估计和假设检验

提出了一种对连续分布百分位值和百分率(或可靠度)进行区间估计和假设检验的理论与方法。并对Weibull分布、对数正态分布、极值分布等常用的两参数分布和三参数分布进行了详细讨论。该方法不仅适用于完全数据,而且还适用于不完全数据和无失效数据。     

Statistical seismo-ionospheric precursors of M7.0+ earthquakes in Circum-Pacific seismic belt by GPS TEC measurements

The Circum-Pacific seismic belt is the region heavily affected by earthquakes in the world. The relationship between earthquake (e.g., the geographic location, occurrence time, magnitude, and focal depth) and ionospheric anomalies in the belt was investigated using 100 M7.0+ earthquakes during 2006–2015. The ground-based GPS measurements and global ionosphere map (GIM) data were used for the analyses of the ionospheric variations preceding the earthquakes. The results indicated that the occurrence rate of total electron content (TEC) anomalies was proportional to the magnitude and inversely proportional to the focal depth to a certain degree, and the occurrence frequency of anomalies had a rising trend with the days getting close to the main shock. The occurrence rate of TEC anomalies in the Southern hemisphere was larger than that in the Northern hemisphere. Besides, the spatial characteristics of TEC anomalies showed that the anomalies in low-middle latitudes did not coincide with the epicenter, sometimes the anomalies were also observed in the corresponding conjugated region. However, the TEC anomalies in the high latitude usually appeared around the epicenter and within the seismogenic zone while no TEC anomalies appeared in the conjugated area. These results may have potential applications to the earthquake prediction in the Circum-Pacific seismic belt.     

固体发动机界面结构试件脱粘健康监测研究

以复合材料壳体和绝热层脱粘模型试件为对象,利用粘贴于壳体外表面的压电主动激励传感器,基于高频机电阻抗方法,对模拟药柱/绝热层界面脱粘的结构健康状态监测进行了数值仿真和实验研究,得出了不同脱粘损伤工况下的导纳频谱曲线,计算了能表征脱粘程度的平均绝对偏差损伤指标。结果表明,高频机电阻抗方法可利用粘贴于壳体外表面的压电传感器有效地识别内部结构的界面脱粘,相比于传统检测方法,能实现实时的结构健康监测,损伤指标能量化表征脱粘程度,实验采用的两种压电传感器中,MFC传感器较PZT传感器更适合于曲面固体发动机壳体脱粘检测,为开展实际工况下的固体发动机药柱结构界面脱粘损伤监检测工作提供理论与技术支撑。     

层合板干涉螺接分层损伤及其临界干涉量

复合材料层合板的干涉配合连接具有优越的性能,是飞机复合材料结构连接的发展趋势。然而,层合板在干涉连接过程中易出现分层损伤。针对以上问题,采用理论建模与有限元模拟方法研究了碳纤维增强树脂基复合材料(CFRP)层合板干涉螺接过程中的分层损伤及其临界干涉量。首先,对CFRP层合板的干涉螺接工艺过程和分层损伤进行力学行为分析;然后,基于虚功原理,建立了各层界面的分层损伤临界轴向力计算模型,结合插钉力与干涉量间的关系,建立临界干涉量的预测模型,求得分层损伤的临界干涉量;最后,采用ABAQUS有限元软件对CFRP层合板干涉螺接过程进行数值模拟,应用内聚力单元建立层合板层间界面,模拟了CFRP层合板在不同干涉量时的分层损伤机理,并通过扫描电子显微镜(SEM)实验观测了细观分层损伤。研究结果显示:干涉量是影响CFRP层合板分层损伤的主要工艺参数;层合板中越靠下边的层间界面,其不产生分层损伤的临界轴向力和临界干涉量越小,即越容易产生分层损伤。     

SAA域选划对天基探测卫星影响简析

通过仿真计算南大西洋异常区(SAA)高能粒子的通量与能量,分析不同通量阈值与能量阈值对SAA空间分布的影响,并以科学实验卫星为研究对象,对其历经SAA的时间百分比进行连续24 h和6个月的统计,获得了SAA对卫星常规运行的工作时间影响。结果表明:在50 MeV能量阈值条件下,500 cm~(-2)?s~(-1)较100 cm~(-2)?s~(-1)通量阈值对SAA空间分布的影响范围在纬度上相差约23.35%,经度上相差约27.06%,历经SAA时间上缩短约48.0%;在100 cm~(-2)?s~(-1)通量阈值条件下,150 MeV较50 MeV能量阈值对SAA空间分布的影响范围在纬度上相差约13.86%,经度上相差约17.29%,历经SAA时间上缩短约31.7%。