复杂陶瓷件烧结过程温度场数值模拟及仿真

随着陶瓷应用领域的不断扩展,对其品质要求也越来越高.而传统的设计工艺与制造过程是相分离的,到最终生产工艺的定型需要大量的反复修改.为解决传统陶瓷设计工艺只能依靠经验的现状,节约成本,缩短生产周期,故开发了复杂陶瓷零构件烧结过程计算机仿真软件.首先借助传热学原理来建立温度场模型,其次借助有限差分法处理温度场模型,编写出此仿真模拟软件的核心计算代码,从而实现了复杂陶瓷零件和组合构件烧结过程中温度场的模拟仿真.      

阳极氧化铝模板法制备CoPt纳米管

采用电化学直流沉积,首次在氧化铝模板中成功制备出直径为50 nm的CoPt纳米管高度有序阵列。利用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)以及振动样品磁强计(VSM)对样品的结构和磁学特性进行测试。分析表明,CoPt纳米管是以面心立方(fcc)结构存在。当外加磁场与纳米线平行时,CoPt合金纳米管的矫顽力达450 Oe,这种大面积制备的CoPt纳米管希望在超高密度信息磁存储上得到应用。     

激波管中测量JP-10点火延时的吸附问题研究

在JP-10点火延时的激波管实验中,JP-10在激波管壁的吸附导致气相浓度的不确定是测量结果分散的主要原因之一.利用精确测定的吸附曲线确定了实验时JP-10真实的气相浓度,解决了高碳数碳氢燃料点火延时激波管实验时管壁吸附影响燃料气相浓度确定的困难.实验显示JP-10的吸附符合Langmuir吸附等温关系.     

子孔径拼接检测方法的目标函数优化

子孔径拼接检测技术是一种利用小口径干涉仪实现对大口径光学系统检测的有效方法.在子孔径拼接算法中,需要对子孔径重叠区域的采样数据进行最小二乘拟合,得到各孔径的相对误差,从而将它们统一到同一参考面上,完成拼接.最小二乘拟合目标函数的优劣将直接影响拼接精度的高低.文章利用光学仿真软件,提取对误差敏感的Zernike多项式的项,并推导得到具有较高精度的目标函数,通过仿真计算验证了该目标函数能满足高精度子孔径拼接的要求.     

一种测量航空发动机T_4温度的新方法

采用热电偶信号放大集成电路AD595结合镍铬─镍铝热电偶温度传感器 ,设计了航空发动机T 4 温度热电偶测温电路 ,实现了冷端自动补偿、热电偶断线报警信号输出功能。实测数据分析表明 :输出幅值大 ,误差小 ,重复性好。测量电路简单 ,具有较强的实用性。     

基于树模型机器学习方法的GNSS-R海面风速反演

GNSS-R是基于GNSS卫星反射信号的一种新技术.GNSS-R技术可以运用到海面风场反演中,传统的GNSS-R技术反演海面风场主要有波形匹配和经验函数两种方法,风速反演精度约为2m·s^-1.波形匹配方法耗时多,计算量大;经验函数方法通常只使用少量物理观测量,会造成信息浪费,损失一定的反演精度.为了提高海面风速的反演精度,引入机器学习领域常用的树模型算法决策树、随机森林、GBDT等对海面风速进行预测.利用GNSS-R与ECMWF数据构成训练集和验证集,训练集用于模型学习,验证集用于检验模型的反演效果.实验结果显示,决策树和随机森林预测误差约为0.6m·s^-1,GBDT等算法的预测误差约为2m·s^-1,满足风速反演要求.与GNSS-R传统反演方法相比,机器学习树模型算法效果更好,在验证集上表现稳定且误差较小.因此,可以将机器学习树模型算法运用到海面风速反演中.     

China's Future Missions for Deep Space Exploration and Exoplanet Space Survey by 2030

Four future missions for deep space exploration and future space-based exoplanet surveys on habitable planets by 2030 are scheduled to be launched. Two Mars exploration missions are designed to investigate geological structure, the material on Martian surface, and retrieve returned samples. The asteroids and main belt comet exploration is expected to explore two objects within 10 years. The small-body mission will aim to land on the asteroid and get samples return to Earth. The basic physical characteristics of the two objects will be obtained through the mission. The exploration of Jupiter system will characterize the environment of Jupiter and the four largest Moons and understand the atmosphere of Jupiter. In addition, we further introduce two space-based exoplanet survey by 2030, Miyin Program and Closeby Habitable Exoplanet Survey (CHES Mission). Miyin program aims to detect habitable exoplanets using interferometry, while CHES mission expects to discover habitable exoplanets orbiting FGK stars within 10 pc through astrometry. The above-mentioned missions are positively to achieve breakthroughs in the field of planetary science.     

Load balancing strategy and its lookup-table enhancement in deterministic space delay/disruption tolerant networks

Space networks, in which connectivity is deterministic and intermittent, can be modeled by delay/disruption tolerant networks. In space delay/disruption tolerant networks, a packet is usually transmitted from the source node to the destination node indirectly via a series of relay nodes. If anyone of the nodes in the path becomes congested, the packet will be dropped due to buffer overflow. One of the main reasons behind congestion is the unbalanced network traffic distribution. We propose a load balancing strategy which takes the congestion status of both the local node and relay nodes into account. The congestion status, together with the end-to-end delay, is used in the routing selection. A lookup-table enhancement is also proposed. The off-line computation and the on-line adjustment are combined together to make a more precise estimate of the end-to-end delay while at the same time reducing the onboard computation. Simulation results show that the proposed strategy helps to distribute network traffic more evenly and therefore reduces the packet drop ratio. In addition, the average delay is also decreased in most cases. The lookup-table enhancement provides a compromise between the need for better communication performance and the desire for less onboard computation.     

Assessing ecohydrological factors variations and their relationships at different spatio-temporal scales in semiarid area,northwestern China

As a typical semiarid farming-pastoral ecotone sensitive to the environmennt, the Plain of West Liaohe Basin (WLBP) is currently experiencing drastic environmental changes. To identify how environmental change affect vegetation in the WLBP, we analysed spatiotemporal variation characteristics of Ecological environment factors based on monthly and annual air temperature (T), precipitation (P) and Normalized Difference Vegetation Index (NDVI) from 1982 to 2015. And the correlations between them were investigated by correlation analysis (Simple correlation, partial correlation and complex correlation) at temporal and spatial scale. The results showed that: (1) the vegetation growth of the WLBP showed ameliorated trend, with a change rate of 0.004/yr.; (2) P was more sensitive to NDVI than T; (3) and the influence of hydrothermal changes on vegetation growth was more significant than that of the change of single climate factors at time scales; (4) the effects of anthropogenic factors on vegetation change were 75.07% (1982–1993) and 98.08% (1994–2015), respectively. At the temp-special scales, P&T and land use type change (LUCC) were the main climatic and anthropogenic factors that affect vegetation changes, respectively.     

Post-midnight equatorial irregularity distributions and vertical drift velocity variations during solstices

Longitudinal distributions of post-midnight equatorial ionospheric irregularity occurrences observed by ROCSAT-1 (1st satellite of the Republic of China) during moderate to high solar activity years in two solstices are studied with respect to the vertical drift velocity and density variations. The post-midnight irregularity distributions are found to be similar to the well-documented pre-midnight ones, but are different from some published distributions taken during solar minimum years. Even though the post-midnight ionosphere is sinking in general, longitudes of frequent positive vertical drift and high density seems to coincide with the longitudes of high irregularity occurrences. Large scatters found in the vertical drift velocity and density around the dip equator in different ROCSAT-1 orbits indicate the existence of large and frequent variations in the vertical drift velocity and density that seem to be able to provide sufficient perturbations for the Rayleigh-Taylor (RT) instability to cause the irregularity occurrences. The need of seeding agents such as gravity waves from atmospheric convective clouds to initiate the Rayleigh-Taylor instability may not be necessary.