矿物掺合料对混凝土氯离子扩散行为的时间依赖性的影响

通过自然扩散法,研究了掺加矿物掺合料的混凝土在高浓度环境溶液中的氯离子扩散行为,探讨了暴露时间对混凝土表观氯离子扩散系数的影响.结果表明,混凝土的表观氯离子扩散系数均随着暴露时间的延长而降低,其时间依赖性与矿物掺合料掺量有关.当粉煤灰掺量和硅灰掺量分别达到30％和15％时,粉煤灰混凝土和硅灰混凝土的表现氯扩散系数随时间的降低速度最快.因此,粉煤灰混凝土和硅灰混凝土具有比普通混凝土更好的长期抵抗氯侵蚀能力.     

SiO_2气凝胶材料的制备、性能及其低温保温隔热应用

由于SiO2气凝胶独特的纳米多孔结构,使其具有诸多其他材料所不能比拟的优异性能,比如极高的孔隙率和比表面积、极低的热导率及密度等特性。这些优异的性能使得SiO2气凝胶在高效保温隔热、隔声等领域具有极大的应用潜力。本文阐述了SiO2气凝胶的溶胶-凝胶制备过程及其机理,分别对SiO2气凝胶的热学、力学、光学和疏水性能的研究进展进行了概述,同时分析了气凝胶的微观结构与上述性能之间的关系,并介绍了SiO2气凝胶在低温保温隔热领域的应用现状和前景。     

高硅氧玻璃纤维布增强聚四氟乙烯(PTFE)复合材料介电性能研究

对高硅氧玻璃纤维布增强聚四氟乙烯（ＰＴＦＥ）复合材料的含胶量、成型压力、烧结温度及环境湿度等多种因素对其介电性能的影响进行了较为系统的实验研究。结果表明,高硅氧玻璃纤维布增强聚;上氟乙烯复合材料在上述因素影响下,其介电常数在２．９０￣３．３０的范围内变化,其中环境湿度是主要的影响因素。     

大型铝合金航空精密铸件硅溶胶型壳

针对航空大型铝合金精密铸件的成形特点，研制出强度高、重量轻的硅溶胶型壳，并成功地应用于航空机载电子设备箱体的铸造．介绍了其制壳工艺．     

SiO2—Si3N4天线窗材料的热学性能和抗热震性能研究

研究了ＳｉＯ２－Ｓｉ３Ｎ４天线窗材料的热学性能和抗热震性能。结果表明，复合材料的热膨胀系数、导温系数、导热系数随Ｓｉ３Ｎ４含量的增加而增大，对于同一Ｓｉ３Ｎ４含量的复合材料，三者均随温度的升高而增大，复合材料保持了ＳｉＯ２基体材料的良好抗热震性。     

溶剂对RTM石英／酚醛复合材料溶液浸润过程影响研究

研究了不同溶剂对于RTM石英/酚醛复合材料溶液浸润过程的影响.采用X光电子能谱(XPS)和原位电子顺磁共振(EPR)研究了石英纤维表面硅烷偶联剂和不同酚醛树脂溶液组分间的界面化学反应.采用TGA和层间剪切强度(ILSS)测试方法研究了溶剂对酚醛树脂分布和材料界面结合强度的影响.结果表明,溶剂能够与酚醛树脂在石英纤维表面形成竞争性吸附,从而影响树脂在RTM模具内部不同位置的分布和复合材料的力学性能.随着溶剂形成氢键能力的增强,其影响程度依次为四氢呋喃＜丙酮＜乙醇.     

抛光参量对抛光光学元件亚表层的影响

研究了抛光粉的种类、抛光速度的大小以及抛光玻璃的性质等抛光参量对光学元件亚表层特征的影响,并结合抛光机理进行了分析。     

GNSS geodetic techniques for time and frequency transfer applications

We performed an initial analysis of the pseudorange data of the GIOVE-B satellite, one of the two experimental Galileo satellites currently in operation, for time transfer.¹ For this specific aim, software was developed to process the GIOVE-B raw pseudoranges and broadcast navigation messages collected by the Galileo Experimental Sensor Stations (GESS) tracking network, yielding station clock phase errors with respect to the Experimental Galileo System Time (EGST). The software also allows processing the Global Positioning System (GPS) P1 and P2 pseudorange data with broadcast navigation message collected at the same stations to obtain the station clock phase errors with respect to the GPS system time (GPST). Differencing these solutions between stations provides two independent means of GNSS time transfer. We compared these time transfer results with Precise Point Positioning (PPP) method applied to GPS data in combined carrier-phase and pseudorange mode as well as in pseudorange-only mode to show their relative merits. The PPP solutions in combined carrier-phase and pseudorange mode showed the least instability of the methods tested herein at all scales, at few parts in 10¹⁵ at 1 day for the stations processed, following a tau^−½ interval dependency. Conversely, the PPP solutions in pseudorange-only mode are an order of magnitude worst (few parts in 10¹⁴ at 1 day for the stations processed) following a tau⁻¹ power-law, but slightly better than the single-satellite raw GPS time transfer solutions obtained using the developed software, since the PPP least-squares solution effectively averages the pseudorange noise. The pseudorange noise levels estimated from PPP pseudorange residuals and from clock solution comparisons are largely consistent, providing a validation of our software operation. The raw GIOVE-B time transfer, as implemented in this work, proves to be slightly better than single-satellite raw GPS satellite time transfer, at least in the medium term. However, one of the processed stations shows a combined GPS P1 and P2 pseudorange noise level at 2 m, a factor 2 worst than usually seen for geodetic receivers, so the GPS time transfer results may not be at their best for the cases processed. Over the short term, the GPS single-satellite time transfer instability outperforms the GIOVE-B by an order of magnitude at 1 s interval, which would be due to the different characteristics of the tracking loop filters for GPS P1 and P2 on one hand and the GIOVE-B signals on the other. Even at this preliminary stage and using an experimental satellite system, results show that the GIOVE-B (and hence Galileo) signals offer interesting perspectives for high precision time transfer between metrological laboratories.     

湍流等离子体尾迹雷达散射截面的计算及其影响因素分析

针对一阶畸变波Born近似模型,深入分析了湍流内外尺度和电子数密度脉动值对雷达散射截面的影响,并且给出了关于湍流外尺度的一个经验的,能被工程上较好使用的公式.在以上分析的基础上,计算了几种高程条件下再入小钝头锥体等离子尾迹的雷达散射截面,与已有实验结果进行了对比分析.分析和计算结果表明,湍流的外尺度和局部电子数密度值对雷达散射截面值影响较大;湍流内尺度变化的影响不大.     

石英玻璃的机械振动能量损耗特性

为研究石英玻璃的机械振动能量损耗特性，以石英半球谐振子为实验对象，考察了铣磨、抛光、刻蚀和退火对石英玻璃机械振动能量损耗大小的影响，并分析其作用机理。研究结果表明：对于机械加工成型的石英玻璃，表面损耗占主导作用，亚表面损伤是造成表面损耗的主要原因；退火可以消除机械应力，降低石英玻璃的“假想温度”，改善石英玻璃的结构稳定性，减小本征损耗。