Mathematics achievement in the secondary high school context of STEM and non‐STEM schools

The purpose of this study is to compare students’ mathematics achievement growth rate in Texas science, technology, engineering, and mathematics (T‐STEM) academies to students’ mathematics achievement growth rate in traditional public high schools. Forty‐six schools, 23 of which were T‐STEM academies and 23 of which were matched non‐STEM schools, were included in this study. A hierarchical linear modeling method was conducted. The result of the present study revealed that there was no difference in students’ mathematics achievement growth rate in T‐STEM academies compared to students’ mathematics achievement growth rate in comparison schools. However, in terms of ethnicity, the results indicated that African American and Hispanic students in T‐STEM academies outperformed African American and Hispanic students in comparison schools on their mathematics growth rate.     

A semi-abelian extension of a theorem by Takeuchi

We prove that the category of cocommutative Hopf algebras over a field is a semi-abelian category. This result extends a previous special case of it, based on the Milnor–Moore theorem, where the field was assumed to have zero characteristic. Takeuchi's theorem asserting that the category of commutative and cocommutative Hopf algebras over a field is abelian immediately follows from this new observation. We also prove that the category of cocommutative Hopf algebras over a field is action representable. We make some new observations concerning the categorical commutator of normal Hopf subalgebras, and this leads to the proof that two definitions of crossed modules of cocommutative Hopf algebras are equivalent in this context.     

Möbius disjointness for topological models of ergodic measure-preserving systems with quasi-discrete spectrum

By using a decomposition result for ergodic measure-preserving system with quasi-discrete spectrum, we prove that a generic point of an ergodic quasi-discrete spectrum measure in a topological dynamical system satisfies the required disjointness condition in Sarnak's Möbius Disjointness Conjecture. As a direct application, we have that Sarnak's Möbius Disjointness Conjecture holds for any topological model of an ergodic measure-preserving system with quasi-discrete spectrum.     

某C波段收发子阵系统设计

本文以有源相控阵雷达为应用背景,介绍了一种利用MMIC技术和MCM工艺技术实现小型化、高可靠的C波段T/R组件的具体实现方法,进而实现收发子阵系统的一体化设计。采用变频形式的收发子阵系统设计,大大简化馈电网络,有效提高阵面的集成度和可靠性。通过实验验证,设计取得良好的效果,为高密集度、集成化的收发子阵系统设计积累了经验。     

一种IGBT全桥逆变驱动电路的设计

简单阐述了2SC0435T模块的特点和IGBT的H桥互锁电路的特点。以2SC0435T为核心,给出了直接模式下的外围电路,以驱动IGBT全桥逆变电路。设计了栅极电阻的接法及其阻值的大小以及IGBT的栅极过压保护电路,给出了驱动信号波形,同时验证了此驱动器具有良好的保护功能和驱动功能。     

某气密封毫米波收发组件的故障统计与分析

毫米波组件作为毫米波电子系统的重要组成部分,其可靠性和故障率在很大程度上决定了整个毫米波系统的工作状态。目前,关于毫米波组件在批量使用过程中的可靠性情况和故障数据还鲜有研究。收集了某批量生产的毫米波收发组件在交付和使用中所出现的故障,并对故障进行了统计和分析,最后根据统计结果给出了技术和管理方面的改进建议。     

CFE条件下基于循环维纳滤波的单通道分离算法

在航天测控数传（C＆T）信号中,频谱混叠的现象非常普遍,因此对频谱严重混叠的信号进行单通道盲分离成为信号处理领域中研究的热点和难点。基于线性-共轭-线性频移（LCL-FRESH）滤波的基本概念,考虑到在实际非合作通信应用中基于循环平稳的LCL-FRESH滤波依赖于较高的循环频率精度,然而循环频率误差（CFE）总是无可避免,提出了一种改进的CFE校正算法,简单分析了误差条件下滤波器性能下降的原因。仿真表明,所研究的算法可以有效分离存在CFE下时频重叠的数传通信信号。     

宽带双喇叭单脉冲馈源设计

本文阐述了宽带双喇叭单脉冲馈源的工作原理和设计方法,设计了一种结构紧凑、性能优良的宽带单脉冲馈源馈电网络,通过仿真,该网络在相对带宽19%的频率范围内达到了较好的电性能指标。     

技术成熟度及其在核高基重大专项实施中的应用探讨

技术成熟度评价已在国外科技研发项目和武器装备采办管理中得到大量应用。本文列举了多个组织给出的技术成熟度定义,分析了技术成熟度含义,简要介绍了技术成熟度评价在"核高基"重大专项实施管理中的应用试验。     

0.34 THz无线通信收发前端

描述了一种基于肖特基二极管技术的0.34 THz无线通信收发前端。该前端采用超外差结构,由0.34 THz谐波混频器、0.17 THz本振8倍频链和偏置电路组成。0.34 THz谐波混频器基于反向并联肖特基二极管,可以实现信号的上变频发射和下变频低噪声检测。0.17 THz本振8倍频链由三级二倍频及驱动放大链路组成,可将20~22.5 GHz信号倍频至0.16~0.18 THz,为混频器提供5~10 dBm左右的本振信号。实验测试结果表明：该前端用于信号发射时,在0.34 THz频点的饱和输出功率为-14.58 dBm;用于信号检测时,最低单边带(SSB)变频损耗为10.0 dB,3 dB中频带宽约30 GHz。限于测试条件,未能测试前端接收噪声温度,仿真得到的双边带噪声温度数值低于1000 K。在该前端基础上,完成了首次基于16QAM 数字调制体制的0.34 THz无线通信实验,传输速率达3 Gb/s。