Mechanical behavior and properties of fiber reinforced ceramic matrix composites for high temperature use

Ceramics can keep their mechanical characteristics up to 2 000℃ or higher.In this paper,A model to predict ultimate strength of continuous fiber-reinforced brittle matrix composites is developed.A statistical theory for the strength of a uni-axially fiber-reinforced brittle matrix composite is presented.Also a semi-empirical frictional heating method for estimating in-situ interfacial shear in fiber-reinforced ceramic matrix composites was improved.Local uneven fiber packing variation as well as uneven micro-damage during fatigue can be expected to have effects on the composites:generation of frictional heating,thermal gradients,and residual stresses around local fiber breaks.This study examined those engineering interests by the finite element method.      

Flight Flutter Modal Parameters Identification with Atmospheric Turbulence Excitation Based on Wavelet Transformation

针对基于大气紊流激励的飞机颤振试验数据具有信噪比低以及测量数据以加速度响应形式给出等特点,将小波变换与随机减量法相结合对飞机颤振模态参数进行识别,首先利用随机减量法获得结构在非零初始加速度条件下的自由衰减响应,然后对该自由衰减响应进行Morlet连续小波变换,为使变换简单,本文采用了Parseval定理和留数定理,利用Morlet的带通滤波特性,通过搜索小波变换系数在不同的尺度区域内的极大值,再根据小波变换系数的极大值、相角与固有振动频率及阻尼系数间的关系,即可识别出各模态参数。并对利用小波变换识别颤振模态参数时,实现模态解耦应满足的条件进行了分析研究。通过仿真和飞机颤振试验数据分析,验证了该识别方法不仅简单、有效和可行,而且具有较强的抗噪性。     

GEO卫星热控涂层αS退化空间综合环境模拟试验

文章用综合低能辐照试验模拟15年地球同步轨道环境对热控材料S781白漆、SR107-ZK白漆、镀银FEP、OSR片的太阳吸收率退化趋势。有机白漆有严重退化,而OSR和 镀银FEP材料退化较少。通过与飞行试验结果比较,证明了本次模拟试验的有效性。通过利用退化趋势的试验数据,应用最小二乘法获得退化数学模型。二次指数退化模型与4种材料退化曲线符合较好。更长试验时间结果可以通过数学模型外推的方法获得。经试验验证,用8年试验数据外推15年数据误差不超过1%。     

Latitudinal variation of the topside electron temperature at different levels of solar activity

A database of electron temperature (T_e) measurements comprising of most of the available satellite measurements in the topside ionosphere is used for studying the solar activity variations of the electron temperature T_e at different latitudes, altitudes, local times and seasons. The T_e data are grouped into three levels of solar activity (low, medium, high) at four altitude ranges, for day and night, and for equinox and solstices. We find that in general T_e changes with solar activity are small and comparable in magnitude with seasonal changes but much smaller than the changes with altitude, latitude, and from day to night. In all cases, except at low altitude during daytime, T_e increases with increasing solar activity. But this increase is not linear as assumed in most empirical T_e models but requires at least a parabolic approximation. At 550 km during daytime negative as well as positive correlation is found with solar activity. Our global data base allows to quantify the latitude range and seasonal conditions for which these correlations occur. A negative correlation with solar activity is found in the invdip latitude range from 20 to 55 degrees during equinox and from 20 degrees onward during winter. In the low latitude (20 to −20 degrees invdip) F-region there is almost no change with solar activity during solstice and a positive correlation during equinox. A positive correlation is also observed during summer from 30 degrees onward.     

火星磁层顶形成和变化的理论研究

考虑太阳风动压与行星电离层中的带电粒子热压及磁压之和平衡,建立了有大气（电离层）的行星磁层顶形成的理论模型,结合卫星对火星的观测数据,对子午面内向日侧火星磁层顶位形进行了数值计算和分析,研究了火星磁层顶位形及其与太阳风动压之间的变化关系．结果认为,火星磁层顶位形与地球磁层顶相似．太阳风动压越大,火星磁层顶越靠近火星;太阳风动压越弱,火星磁层顶越远离火星．根据火星内秉磁矩从古到今逐渐减小的观点,探索了大尺度磁场（内禀磁矩）对火星磁层顶的贡献作用,结果认为大尺度磁场越强,火星磁层顶越远离行星．这对于进一步研究火星磁层的长期演化以及其他行星磁层的位形变化都具有重要的意义．     

The Crab pulsar seen with AquEYE at Asiago Cima Ekar observatory

We are developing fast photon-counter instruments to study the rapid variability of astrophysical sources by time tagging photon arrival times with unprecedented accuracy, making use of a Rubidium clock and GPS receiver. The first realization of such optical photon-counters, dubbed AquEYE (the Asiago Quantum Eye), was mounted in 2008 at the 182 cm Copernicus Observatory in Asiago. AquEYE observed the Crab pulsar several times and collected data of extraordinary quality that allowed us to perform accurate optical timing of the Crab pulsar and to study the pulse shape stability on a timescale from days to years with an excellent definition. Our results reinforce the evidence for decadal stability of the inclination angle between the spin and magnetic axis of the Crab pulsar. Future realizations of our instrument will make use of the Galileo Global Navigation Satellite System (GNSS) time signal.     

An attempt to study long-term variation of sporadic E layers using neural networks

Strong positive correlation between sporadic E layers and the solar activity and the long-term declining trend of Es were found in this paper. Then the feed-forward back propagation neural networks (NNs) were used to simulate the long-term variation of Es at four stations and predict foEs yearly average values. The inputs used for NNs are the yearly mean values of foEs in the daytime of the past ten years and the yearly averaged data of solar 10.7 cm radio flux (F107) of the present year, and the output is the present yearly mean value of daytime foEs. The outputs of trained NNs have high correlation with the desired values and the foEs yearly mean values predicted by NNs have good agreement with the observed data. The results indicate that NNs can make full use of the observed data to simulate the long variation rule of Es. Also, the results confirm the effect of solar activity on Es.     

Statistical characterisation of spread F over South Africa

The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes in 1996 and 2000 at Grahamstown (33.32 °S, 26.50 °E) and Madimbo (22.38 °S, 30.88 °E) respectively. This study is intended to quantify the probability of occurrence of F region disturbances associated with SF over South Africa. A study was conducted using data for 8 years (2001–2008) over Madimbo (with a time resolution of 30 min) and Grahamstown (with a variable time resolution of 15 and 30 min). In this study, SF has been classified into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The SF events were identified by manually identifying ionograms showing SF and tabulating them according to type for further statistical analysis. The results show that the diurnal pattern of SF peaks strongly between 01:00 and 02:00 local time, LT (LT = UT + 2 h), where UT is the universal time. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown in 2001 and 2005, except for RSF which had peaks during autumn and spring in 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing solar activity, with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study, SF was evident in ∼0.03% and ∼0.06% of the available ionograms at Madimbo and Grahamstown respectively during the 8 years.     

浅议我国个人所得税实施中存在的问题及解决对策

个人所得税在调节个人收入、增加财政收入、维护国家权益等方面发挥了积极作用,但是随着我国经济的发展,在实施个人所得税中也逐渐暴露出一些问题.本文针对这些问题,进行了深刻的分析,并提出了解决的对策.     

基于混合卡尔曼滤波器组故障传感器定位方法

为了在发动机性能蜕化与传感器故障并存的情况下实现故障传感器的定位与部件蜕化情况的估计,并实现故障诊断基准数据的修正,构建了1种包含了机载模型与线性卡尔曼滤波器的组合结构混合卡尔曼滤波器组。该卡尔曼滤波器组能够在之前所描述的故障/蜕化耦合情况下定位故障传感器,并得到较为准确的部件蜕化估计结果。为了验证了混合卡尔曼滤波器组的有效性,进行了相关仿真。仿真结果表明:混合卡尔曼滤波器组能够在发动机动态过程中遭遇传感器故障与部件蜕化并存的情况下完成故障定位与蜕化估计。