Performance analysis of large-scale MIMO system for wireless backhaul network

In this paper, we present a performance analysis of large-scale multi-input multi-output (MIMO) systems for wireless backhaul networks. We focus on fully connected N nodes in a wireless meshed and multi-hop network topology. We also consider a large number of antennas at both the receiver and transmitter. We investigate the transmission schemes to support fully connected N nodes for half-duplex and full-duplex transmission, analyze the achievable ergodic sum rate among N nodes, and propose a closed-form expression of the achievable ergodic sum rate for each scheme. Furthermore, we present numerical evaluation results and compare the resuts with closed-form expressions.     

Assessing students' conceptual understanding using an online three‐tier diagnostic test

When solving a mathematical problem, students who do not have sufficient conceptual understanding may perform poorly and exhibit misconceptions. This study was aimed to examine students' conceptual understanding and significant misconceptions when solving number sense‐related problems. An online three‐tier diagnostic test was administered to 125 fifth‐grade students with varied socio‐economic backgrounds in Hong Kong. Only 14.40% of the students exhibited high performance with high confidence, indicating that these students had a profound conceptual understanding of number sense. In addition, the majority of the students (66.40%) did not demonstrate number sense; these students exhibited several significant misconceptions and could solve the questions only by using a rule‐based method or guessing. Accordingly, most students performed unsatisfactorily on number sense‐related problems. This study is imperative in identifying early predictors and provides information for further compatible interventions in the teaching and learning of number sense in Hong Kong in particular and worldwide in general.     

Regelwerke für die Werkstoffauswahl und Dauerhaftigkeit von nichtrostenden Stählen für Stahlbauten – Entwicklung und aktueller Stand

Technical regulations for the selection of materials and dura bility for steel structures – Development and current status. One of the most important changes of the revised DIN EN 1993‐1‐4 released in October 2015 can be found in the annex section A ”Selection of materials and durability“. Contrary to the previous version this annex is now normative. By means of a point system considering different key variables that influence the selection of stainless steel alloys and combines values for each to give a total corrosion resistance factor suitable alloys can be selected. The annex aims to provide a methodology for use by designers with no specialist knowledge of either corrosion or stainless steels. The paper also discusses differences and similarities with the previous valid German national technical approval Z‐30.3.6.     

The double coupled microwave resonance probes and application for diagnosing atmospheric pressure plasma jet

The double-coupled microwave resonance probe(DMRP) based on the hairpin probe is proposed for diagnosing atmospheric plasma jet(n_e10~(17) m~(-3)). In this work, the resonance characteristics of DMRP are investigated by numerical simulation. It shows that two resonance peaks on the reflectance spectrum can be observed, and influenced significantly by some parameters, such as the probe separation, the distance to the handheld radio frequency atmospheric pressure glow discharge plasma jet(RF-APGDPJ) and the plasma electron density less than 1017 m~(-3). Based on two resonance modes of DMRP, the electron densities in the afterglow of RF-APGDPJ at the different rf powers and helium flow rates are diagnosed experimentally by matching the change of FWHM(Df_1-Df_(1,air)and Df_2-Df_(2,air)) measured by vector network analyzer with the simulated relation between the FWHM changes and the plasma density.     

Computational study on influence of RF shielding box on inductance of coil

Despite the fact that a radio frequency (RF) shielding box affects a coil inductance used in matching network, RF engineers have used a coil inductance measured in open space on designing matching networks since it is difficult to precisely measure the coil inductance within the RF shielding box. In this work, we investigate the influences of the RF shielding box on the coil inductance via a 3D full electromagnetic wave simulation. Simulation results shows that the coil inductance decreases from -6.0% to -11.9% compared with its ideal inductance depending on coil positions within the RF shielding box. Both inductive and capacitive coupling between the coil and surfaces of the RF shielding box contribute to the reduction of the coil inductance. We expect that these results would be useful for those who design RF matching networks.     

钢纤维混凝土早期水化热温度的试验研究

本文通过三种不同钢纤维掺量的钢纤维混凝土早期水化热温度和变形实测,得到了不同掺量钢纤维混凝土的水化热温度及温度变形的时程线.试验结果表明:钢纤维混凝土的最高温升随掺量增加而有所增大;水化反应结束后,掺量大的温度曲线最接近外界气温,降温速率也明显增加.应变曲线总体上能反映钢纤维混凝土抗应变能力强于普通混凝土.根据热传导理论,给出了钢纤维掺量与混凝土导温系数的关系,得出钢纤维混凝土有较好的导热性,该特性对水工混凝土结构防止表面裂缝起到良好的作用.     

长输油气管道的钢管设计选用

介绍了长输油气管道用钢管的选用程序和原则.在此基础上,根据管输介质、管径、设计压力、自然条件等因素,结合几种常用钢管的优缺点,确定管型;在进行钢级的选择时,应考虑钢管可焊性、焊接工艺、壁厚圆整和最小壁厚等问题.     

钽粉氧含量对其钽阳极漏电流的影响

在多年实践经验基础上，用氧含量Ｘ１（质量分数）０．２０％～０．３８％的四种钽粉，控制钽阳极中残余氧含量Ｘ２（质量分数）在０．０８％～０．２０％间，采用正交设计实验研究了对其漏电流的影响，并建立了漏电流峰值ＩＬ和Ｘ１、Ｘ２间的预示方程，描述了漏电流和钽粉氧含量（Ｘ１）、残余氧含量（Ｘ２）间的关系。随后，用预示方程讨论了钽中氧和钽阳极中残余氧对其漏电流的影响。     

椭圆孔六角点阵聚合物光子晶体光纤的偏振特性研究

基于全矢量平面波方法,以聚甲基丙烯酸甲酯为基材,设计了一种高双折射光子晶体光纤,并对其传输性质和偏振特性进行了数值模拟。结果表明,椭圆孔六角点阵聚合物光子晶体光纤的双折射是由于包层的不对称性引起的全局双折射,通过调节椭圆率,发现该光纤可以以单模方式在一合适波段运行,该波段与聚合物光纤的低损耗通信窗口一致。并且在 时,其双折射最高可达 。该研究结果为高双折射聚合物光子晶体保偏光纤的制备提供了理论依据。