空间红外大口径折射式低温镜头设计与验证

针对目标探测类空间红外相机大范围成像、高灵敏度探测、高精度定位等应用需求,文中提出采用像方远心光路和低温光学技术结合的解决方案,设计了物方视场角8°×8°、入瞳口径265 mm、工作温度200 K的像方远心折射式光学系统。镜头最大口径280 mm,采用多级分散的弹性支撑设计,解决大口径低温透镜装框、透镜组件支撑和镜头整体安装各环节的热应力卸载问题。在保证高刚度和低漏热的情况下,使低温下透镜的热应力对镜头能量集中度的影响降低到可接受范围内。镜头完成装调及室温下像质确认后,进行了力学振动试验,并将其制冷到200 K水平测试像质,测试结果表明,镜头能量集中度达到轴上75%,边缘视场72%。     

电视民生新闻现状及发展趋势探析

自2002年起,我国开始出现电视民生新闻,并得到观众的广泛喜爱,但在整个发展过程当中电视新闻存在一些问题有待解决,探讨电视民生新闻的现状及发展趋势,对其中存在的问题提出解决方案。     

Local community detection for multi-layer mobile network based on the trust relation

Wireless Networks - With the fast development of mobile Internet, people’s social exchange media has transformed from the traditional social network to mobile network. With the explosion of...     

Data broadcasting strategies for cognitive radio based AMI networks

Wireless Networks - Communication systems play an important role in smart grid (SG). Advanced Metering Infrastructure (AMI) is hybrid architecture in smart grid comprising of smart meters and...     

Simulating study on RHCRP protocol in utility tunnel WSN

Wireless Networks - Utility tunnel is one of the important infrastructures for the planning and building of smart city. It is of great significance to improve the efficiency of maintenance and...     

Microstructural evolution and defect formation in a powder metallurgy nickel-based superalloy processed by selective laser melting

In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart.Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point(γ+γ')eutectic played a vital role in their formation mechanism.Columnar grains oriented along building direction were ubiquitous,corresponding to strong<001>fiber texture.Solidification cell structures and melt pools are pervasive and noγ'precipitates were detected at about 10 nm scale before heat treatment.After supersolvus solution and two-step aging treatments,high volume fractionγ'precipitates emerged and their sizes and morphologies were comparable to those in PM alloy.<001>texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events.Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization.Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology.     

Empirical Analysis of Agricultural Cultural Resources Value Evaluation under DEA Model

Agricultural culture is a productive activity about education and management. It aims at high efficiency and high quality, uses technology as its means, and takes nature as its carrier. Agricultural cultural resources are the product of the rapid development of modern economy. It promotes the development of the national economy and profoundly affects people's production and life. DEA model, also known as data envelope analysis method, is an algorithm that uses multiple data decision units for input and output training to obtain the final model. This article explains the concept and basic characteristics of agricultural culture. Through questionnaire surveys and expert interviews, we collected development data, screened human, material, and financial data, and calculated information on economic and social resources. On this basis, this paper establishes the evaluation index of agricultural culture based on DEA model. Then, through empirical analysis from a specific perspective, it can be concluded that increasing human, material and financial input can achieve economic and social benefits. Generally speaking, cultural investment can promote the development of the industry. The research results of this paper laid a theoretical foundation for the development of agricultural culture, and put forward a development model focusing on technology development, improving investment efficiency, and investing in material resources.     

MOOC Learner’s Final Grade Prediction Based on an Improved Random Forests Method

Massive Open Online Course (MOOC) has become a popular way of online learning used across the world by millions of people. Meanwhile, a vast amount of information has been collected from the MOOC learners and institutions. Based on the educational data, a lot of researches have been investigated for the prediction of the MOOC learner’s final grade. However, there are still two problems in this research field. The first problem is how to select the most proper features to improve the prediction accuracy, and the second problem is how to use or modify the data mining algorithms for a better analysis of the MOOC data. In order to solve these two problems, an improved random forests method is proposed in this paper. First, a hybrid indicator is defined to measure the importance of the features, and a rule is further established for the feature selection; then, a Clustering-Synthetic Minority Over-sampling Technique (SMOTE) is embedded into the traditional random forests algorithm to solve the class imbalance problem. In experiment part, we verify the performance of the proposed method by using the Canvas Network Person-Course (CNPC) dataset. Furthermore, four well-known prediction methods have been applied for comparison, where the superiority of our method has been proved.