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451.
邻-邻位亚甲基桥是酚醛树脂主体结构单元之间的主要链接方式之一。采用Gaussian 09中的密度泛函理论B3LYP/6-311G(d,p)方法,对邻-邻位亚甲基桥型模型化合物邻位双羟苯基甲烷(2BHM)的热解反应机理进行了量子化学理论研究。设计了5种热解反应途径,对每种反应途径的反应物、产物和过渡态的结构进行了能量梯度全优化,并对过渡态进行了IRC验证。计算了各反应途径的标准动力学参数,最后进行了相关实验验证。计算结果表明Path3为2BHM的最优热解路径,对应的产物为苯酚和邻甲酚,所有路径的终产物中均有苯酚,且CO_2要比CO更容易生成。热解实验结果显示热解产物中苯酚含量最高,而CO并未出现。这说明计算结果与实验结果基本一致,同时也表明应用量子化学计算理论研究酚醛树脂的热解机理是一种有效的研究方法。 相似文献
452.
为提高C/C复合材料的抗氧化性能,采用包埋法和低压化学气相法制备了SiC/SiO2涂层.借助XRD、SEM和EDS等测试手段分析了复合涂层的微观结构,并研究了其在l273、1773 K静态空气中的抗氧化性能.结果表明,包埋法制备的SiC涂层具有一定的浓度梯度.低压化学气相法制备的非晶Si02外涂层则有效地封堵了SiC内涂层的的裂纹和孔洞,并解决了SiC涂层在中温区(1073~1473 K)无法形成完整SiO2膜的问题.在l 273、1 773 K静态空气中经10h氧化后,涂层试样的质量损失率分别仅有4.97和0.36 mg/cm2,表现出良好的抗氧化性能. 相似文献
453.
原始喷涂粉末经过喷雾干燥法造粒,采用等离子喷涂工艺在普通载玻片上制备了纳米TiO2涂层,并对涂层在300℃,400℃,500℃进行热处理.采用X射线衍射(XRD)方法对TiO2涂层进行了相结构分析;用扫描电子显微镜(SEM)、透射电子显微镜(TEM)观察涂层的微观形貌;用压汞方法测量涂层的孔隙率.结果表明,喷涂后锐钛矿型TiO2含量大约在30%~50%,粒径10~30nm,孔隙率小于6%,热处理后涂层更致密,孔隙率降低.喷涂电流为400A且未经过热处理的TiO2涂层具有最佳光催化效果. 相似文献
454.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1657-1669
The Global Navigation Satellite System (GNSS) receivers equipped on the Haiyang-2D (HY-2D) satellite is capable of tracking the signals of both the third generation of BeiDou satellite navigation System (BDS-3) and the Global Positioning System (GPS), which make it feasible to assess the performance of real-time orbit determination (RTOD) for the HY-2D using onboard GNSS observations. In this study, the achievable accuracy and convergence time of RTOD for the HY-2D using onboard BDS-3 and GPS observations are analyzed. Benefiting from the binary-offset-carrier (BOC) modulation, the BDS-3 C1X signal includes less noise than the GPS C1C signal, which has the same signal frequency and chipping rate. The root mean squares (RMS) of the noises of C1X and C1C code measurements are 0.579 m and 1.636 m, respectively. Thanks to a ten-times higher chipping rate, the code measurements of BDS-3 C5P, GPS C1W and C2W are less noisy. The RMS of code noises of BDS-3 C5P, GPS C1W, and C2W are 0.044 m, 0.386 m, and 0.272 m, respectively. For the HY-2D orbit, the three-dimensional (3D) and radial accuracies can reach 31.8 cm and 7.5 cm with only BDS-3 observations, around 50 % better than the corresponding accuracies with GPS. Better performance of the BDS-3 in RTOD for the HY-2D is attributed to the high quality of its broadcast ephemeris. When random parameters are used to absorb ephemeris errors, substantial improvement is seen in the accuracy of HY-2D orbit with either BDS-3 or GPS. The 3D RMS of HY-2D orbit errors with BDS-3 and GPS are enhanced to 23.1 cm and 33.6 cm, and the RMS of the radial components are improved to 6.1 cm and 13.3 cm, respectively. The convergence time is 41.6 and 75.5 min for the RTOD with BDS-3 and GPS, while it is reduced to 39.2 and 27.4 min after the broadcast ephemeris errors are absorbed by random parameters. Overall, the achievable accuracy of RTOD with BDS-3 reaches decimeter level, which is even better than that with GPS, making real-time navigation using onboard BDS-3 observations a feasible choice for future remote sensing missions. 相似文献
455.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(5):2370-2383
Intra-system biases (ISBs) between BDS-2 and BDS-3 are of critical importance when combining observations from the BDS-2 and BDS-3 systems, which is meaningful to fully take advantage of the BDS positioning capability. Meanwhile, ISBs should also be considered in the estimation of BDS uncalibrated phase delays (UPDs). In this research, we present a BDS-2/BDS-3 joint-processing scheme, as well as a method for estimating BDS UPDs. The characteristics of ISBs and the quality of BDS UPDs are analyzed based on 30-day data from 130 multi-GNSS experimental (MGEX) stations. Our results indicate that the ISBs are related to the type and version of the receiver. The ISBs can be regarded as constant across the course of a given day, and the mean standard deviation (STD) values of ISBs over one month for different types of receivers are generally within 0.2 m. Moreover, to assess the quality of UPD products, the residuals of the estimated UPDs and the utilization rates of the observation data are computed. The results show that the quality of BDS UPDs can be improved by correcting the satellite-induced pseudo-range variations, and by estimating the wide-lane (WL) UPD difference between BDS-2 and BDS-3. The average RMS values of the estimated residuals of WL UPD and narrow-lane (NL) UPD are 0.07 and 0.09 cycles, respectively; moreover, the utilization rate of the observation data of WL UPD and NL UPD can reach above 90 %. The performance of BDS precise point positioning (PPP) and PPP ambiguity resolution (PPP-AR) is analyzed in terms of positioning accuracy and convergence performance in both the static and kinematic modes. Compared with PPP ambiguity-float solutions, the positioning accuracy of PPP-AR is significantly improved, especially in the east direction. The impact of ISBs on PPP and PPP-AR is also analyzed, and the results indicate that ISBs can improve the convergence speed of float PPP, but can be disregarded in PPP-AR. 相似文献
456.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(5):2318-2331
Global Navigation Satellite System’s (GNSS) positioning calculation is prone to ionospheric errors. Single frequency GNSS users receive ionospheric corrections through broadcast ionospheric models. Therefore, the accuracy of ionospheric models must be validated based on various geographic and geomagnetic conditions. In this work, an attempt is made to validate NeQuick2 electron density (Ne) using multiple sources of space-based and ground-based data at the Arabian Peninsula and for low solar activity conditions. These sources include space-based data from Swarm, DMSP and COSMIC-2 satellite constellations and ground-based data from GNSS receiver and the ionosonde. The period of this study is 1 year from October 2019 to September 2020. Analysis shows that the agreement between NeQuick2 and experimental Ne close to the peak density height depends on seasons and time of the day with the largest errors found in Autumn and during the daytime. NeQuick2 generally overestimates Ne during the daytime. During the early morning and evening hours, Ne estimates seem to be fairly accurate with slight underestimation in Winter and Spring. Estimation of slab thickness by NeQuick2 is found to be close to the values calculated using collocated ionosonde and GNSS receiver. 相似文献
457.
任仁良 《中国民航学院学报》1995,(3)
本文介绍了利用8031单片机实现三相异步电动机经济运行参数测试的基本原理,说明了硬件、软件结构和主要数学模型。讨论了对钳式电流互感器进行非线性频率补偿问题、并分析了实现自动量程转换及由E2PROM构成定标系统的方法。最后给出研制结果。 相似文献
458.
459.
NASICON固体电解质SO2传感器的特性研究 总被引:4,自引:0,他引:4
采用溶胶-凝胶法合成NASICON固体电解质材料,并以其为基体材料制作管式SO2传感器,敏感电极采用Na2SO3-30?SO4或者Na2SO4-30?SO4(摩尔比)复合硫酸盐.SO2浓度在(10~100)×10-6体积分数范围内,两种器件的灵敏度分别为81.1和60.6mV/decade.敏感电极为Na2SO3-30?SO4的元件响应和恢复时间分别为28.2 s和57.7 s;敏感电极为Na2SO4-30?SO4的元件响应和恢复时间分别为39.8 s和67.4 s. 相似文献
460.