扁锭横裂纹的形成原因

1989年韶关特殊钢公司为优化产品结构,提高效益,决定生产扁锭加工成板材。但由于经验不足和条件不具备等原因,扁锭表面出现了裂纹,出现率严重时占生产支数的     

Surveys on the intelligent surface: an innovative technology forwireless networks beyond 5G

With the rapid development of wireless communication technology and the explosive growth of mobile data traffic,more and more users are eager to get faster and better internet access. In order to meet the needs of users, energyand spectrum utilization are becoming more and more important as new challenges in wireless communicationnetworks. In recent years, reconfigurable intelligent surface ( RIS ) technology has been proposed in aprogrammable intelligent way to improve the performance and quality of wireless communication systems. Inaddition, the RIS performs better in terms of energy efficiency than other technologies. Therefore, the RIS hasbecome research hotspot rapidly because of its unique wireless communication ability. This paper aims to review theRIS, including channel model, design for transmitter and receiver, information theory, and the latest developmentof RIS-assisted multiple-input multiple-output (MIMO) systems. The applications of RISs in physical layersecurity, device to device (D2D) and cell coverage extension are also introduced in detail. In addition, we discussmajor research challenges related to the RIS. Finally, the potential research directions are proposed.