Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract: Oxidation behavior of two ferrite/martensite(F/M) steels, namely a novel 9%-12% Cr modified F/M steel (SIMP steel) and a commercial T91 steel were comparatively studied in air at 800oC. The oxide scales formed on the two steels were characterized by XRD, SEM and EPMA. The results show that the oxide scale formed on SIMP steel is single-layer composed of Cr2O3 and Mn1.5Cr1.5O4 spinel particles, and Si was enriched at the interface between the chromia scale and matrix; while the oxide scale formed on T91 steel has a double layered structure with an outer hematite Fe2O3 layer and an inner Fe-Cr spinel layer. The SIMP steel has better high temperature oxidation resistance than T91 steel, which may be due to the higher content of Cr and Si beneficial to the formation of the compact oxide scale on the SIMP steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract: Oxide dispersion strengthened (ODS) steels are being developed as a promising structural material for next-generation nuclear energy systems, due to its excellent resistance to both irradiation damage and high-temperature creep. In this work, the mechanical alloying (MA) and hot isostatic pressing (HIP) technologies were used to prepare a ODS low-activation steel, based on the China low activation martensitic (CLAM) steel. SEM, XRD analysis and EPMA were used to examine the particle size, alloying element distribution and lattice distortion of the ball-milled powders. In order to obtain uniform powders, CLAM powders with 0.3%Y2O3 particles should be milled with hard steel balls of 6 mm in diameter for 50 h in Ar protective atmosphere, and the ball- to- powder weight ratio at 10∶1. The microstructure of well-prepared ODS-CLAM steel was stable till 1200 ℃ for 1 h, with grain size of 50~60 mm and martensitic lath width of 200 nm, meanwhile, the Y2O3 particles could still be found in the steel matrix.
Subjects: Astronomy >> Astrophysical processes submitted time 2022-11-17 Cooperative journals: 《天文研究与技术》
Abstract: Shadowing effects is one of the main consideration factors in designing complex system with multiple antennas. There will be 373 sets of antennas in Mingantu Station, after completing the construction of the program Meridian II equipment of National Major Science and Technology Infrastructure. Limited by test site, model complexity and computation, shadowing effect is usually hard to measure and to predict especially for electrically large-size structures. The observed solar radio data on S/C/X bands between 2017 and 2020 by MST (Mingantu Solar Radio Telescope), present the shadowing effect with the 20m antenna and remote hills as obstacles. The observed data with shadowing effect can be divided into antenna area, atmosphere area and hills area with different shadowing characteristics. Based on the prediction method of single knife-edge diffraction loss recommended by ITU-R P.526-15, a model of 20m antenna reflector is built, the shadowing effects on S/C/X-bands are simulated, and the results show agreement with those of observation. From simulation and observing results, shadowing effects are related with wavelength, obstacle character, distance and angle among obstacle, source and receiving antenna, the receiving antenna’s beam, and dynamic range of receiving system, etc.
Subjects: Astronomy >> Astrophysical processes submitted time 2022-04-14 Cooperative journals: 《天文研究与技术》
Abstract:卫星导航星基增强系统(SBAS)由不同国家建设,所增强卫星星座和参考时间系统不尽相同,因此SBAS时间基准之间的兼容互操作一直是国际民航组织(ICAO)SBAS标准研究中的重要技术问题。本文介绍了SBAS网络时间(SNT)概念和研究现状,结合ICAO SBAS标准与建议措施(SAPRs)制定,对SNT兼容互操作问题进行了分析和研究,并给出了目前最新的联合解决方案。在此基础上,对北斗星基增强系统(BDSBAS)地面状态进行了升级,并开展了服务性能初步测试。结果表明,BDSBAS单频(SF)SNT和双频多星座(DFMC)SNT与参考GNSS时间基准之间的最大偏差分别为37 ns、0.17 s,满足ICAO标准要求;服务性能基本符合APV-I等级要求,证明了BDSBAS时间基准互操作的可行性和可靠性。
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2019-01-28 Cooperative journals: 《计算机应用研究》
Abstract: Aiming at the problem that lightweight deep neural network MobileNet can reduce classification accuracy, this paper proposed an D-MobileNet (dilated convolution MobileNet) model based on local receptive field expansion by introducing dilated convolution kernel into a convolution layer of MobileNet model. The models consisted of three structures according to the location of the dilated convolution kernel. Without increasing the number of parameters, it could expand the local receptive field of the layer convolution kernel and improve the classification accuracy. This paper carried out the experiments on Caltech-101 database, Caltech-256 database and Uebingen animals with attributes database. The results show that the D-MobileNet model can achieve better classification accuracy than that of MobileNet, and can improve the classification accuracy by up to 2%.
Subjects: Astronomy submitted time 2018-12-04 Cooperative journals: 《天文研究与技术》
Abstract:射电干涉阵列宽视场成像网格化处理过程中必须考虑w项的影响。w-projection和w-stacking是两个重要的宽视场成像网格化处理算法, w-plane参数是算法中影响计算速度和成图质量的一个重要因素。本文研究了w-projection和w-stacking两种网格化算法,利用SKA1低频阵台站数据和ASKAP软件包进行模拟观测,对两种算法在不同w-plane参数取值情况下的成图速度和成图质量进行了定量分析对比。结果进一步表明w-plane是性能改善的重要参数,针对w-projection算法来说,w-plane取值应比一般给定的经验值要大才能较好的得到成像效果。w-stacking算法虽然有很大的速度优势,但算法实现中w-plane的影响更为显著,论文给出了推荐的w-plane取值。本文工作是大视场成像算法的基础研究工作,对未来SKA科学数据处理中的管线设计有较好的参考价值。
Subjects: Astronomy >> Astrophysical processes submitted time 2017-10-20 Cooperative journals: 《天文研究与技术》
Abstract:中国明安图超宽频谱射电日像仪(Mingantu Ultrawide Spectral Radioheliograph ,MUSER)进入实际观测后,每3 ms产生一帧100 kB左右的数据,每天的原始观测数据约3. 5 TB。由于射电日像仪的原始数据采用自定义格式,为了后续数据分析和共享的需要,有必要根据数据存储需求把这些原始数据转换成天文常用的文件格式。在前期工作中已经实现了原始数据格式到UVFITS文件的转换,在此基拙上研究了基于MPI的集群并行环境下UVFITS合成系统性能优化。通过实验验证,在改进后的并行环境下,UVFITS合成系统的性能达到了需求的2. 5倍,可以有效处理当前及未来一定时间内射电日像仪的海量观测数据。同时,改进后的系统具有良好的横向扩展能力,能够为相关项目的数据处理提供借鉴和参考。
Subjects: Astronomy >> Astrophysical processes submitted time 2017-10-20 Cooperative journals: 《天文研究与技术》
Abstract:介绍了明安图射电频谱日像仪高频阵模拟接收机总体设计方案和研制情况,详细说明所采用的光传输、温控、滤波、LTCC等技术以及针对射电日像仪阵列特别采取的可靠性保证措施。经过全面的系统指标测试和幅、相稳定性温度环境测试,结果表明模拟接收机系统的性能、功能和稳定性等指标满足总系统的设计要求。
Subjects: Astronomy >> Astrophysical processes submitted time 2017-10-11 Cooperative journals: 《天文研究与技术》
Abstract:明安图射电频谱日像仪(Mingantu Ultrawide SpEctral Radioheliograph, MUSER)是新一代具有高时间、高空间、高频率分辨率的太阳专用射电望远镜,采用综合孔径原理成像,所以幅度和相位是决定最后成图质量的关键因素。天线的相位方向图会影响日像仪输出的幅度和相位,根据日像仪的馈源设计和综合孔径原理,针对明安图射电频谱日像仪天线数目多,且为户外环境,根据天文观测须经常测试天线性能的特点,给出了基于相关结果测量日像仪天线相位方向图的方法,该方法可以直接通过日像仪的相关输出结果高效准确地得到天线的相位方向图。对MUSER-I天线的相位方向图进行了测量和分析,同时分析了天线相位方向图对日像仪成像的影响,为得到高质量的太阳图像提供了参考和保障。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract:本文采用高分辨透射电镜(HRTEM)和原子探针层析技术(APT)等分析手段研究了一种多相强化型马氏体时效不锈钢时效过程中的元素偏聚特征及其与材料力学/耐蚀性能的关系。结果表明,实验钢在时效过程中析出三种强化相,即富Mo的R′相、Ni3Ti金属间化合物η相和富Cr的α′相,其中R′相与η相一起形成核壳状结构,α′相则单独弥散分布于基体中。时效时间延长至40h后,主要强化相η相的成分、数量密度和等效半径基本稳定,同时实验钢的强度不再发生明显的变化,这种优异的抗过时效能力得益于主要强化相形成的核壳状结构。腐蚀试验结果表明,由于富Cr的α′相的析出,导致了贫Cr区的形成,进而降低了实验钢的耐蚀性能。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract:加速器驱动次临界ADS(Accelerator Driven Subcritical system)系统由加速器、散裂靶、反应堆三部分组成,被认为是安全处理核废料最具前景的技术方案。其中,散裂靶用结构材料需要同时具有耐高温、抗辐照、抗液态金属腐蚀等性能。针对这一挑战研发了新型核用马氏体耐热钢-SIMP钢。通过制衡9-12Cr%马氏体耐热钢中C、Cr、Si等重要元素含量对耐高温、抗辐照、抗液态金属腐蚀性能的影响,获得了SIMP钢优化的化学成分,极好地平衡了SIMP钢耐高温、抗辐照、抗液态金属腐蚀三方面性能。以1吨级和5吨级SIMP钢为实验材料的各项性能测试结果表明,SIMP钢是ADS系统中散裂靶的首选结构材料。