高校学生网络评教影响因素研究

抽取4个院系、12个专业,约37 724个原始数据,经过异常值处理后,获得34 022个有效个案。在信度和效度检验的基础上,采取均值相等性的稳健性检验和Tamhane方法进行方差不相等情况下的多重比较,探索了学生网上评教影响因素。研究结果表明,学生年级、学生成绩、教学班级数、教师年龄、授课门数、课程性质等非教学因素显著影响教师教学综合评价。     

基于动态双门限和D-S证据理论的合作频谱感知算法

针对传统能量检测算法门限设置单一且不适应感知信道环境差异的问题,为了提高合作频谱感知结果的可靠性,减小网络开销和融合中心计算的负担,提出了将动态双门限能量检测和D-S证据理论相结合的合作频谱感知算法.在进行本地感知时,该算法可以让认知用户通过双门限能量检测方法直接得到本地判决结果,同时根据信道环境的变化自适应调整双门限值,并在双门限内使用D-S证据理论,感知双门限内未判决结果的信任度函数,将其发往融合中心,这样可以减少融合中心的计算量以及传输带来的网络开销.仿真结果表明,双门限D-S证据理论的融合结果要优于D-S证据理论和OR准则.     

Hydrostatic-pressure-induced depolarization of (Pb1-1.5xLax)(Zr0.80Ti0.20)O3 ferroelectric ceramics

Pulse power energy conversion materials with ultrafast discharge processes and ultrahigh power densities have been widely used in the defense, energy, medical, and mining fields. The pressure-driven depolarization in ferroelectric materials is significant and accounts for the discharge processes. In this study, we focus on pressure-induced depolarization in (Pb_1-1.5xLa_x)(Zr_0.80Ti_0.20)O₃ (PLZT) (x = 0-0.07) ceramics, and their corresponding phase structure, dielectric properties, ferroelectric properties, and thermal depolarization performances. Although a satisfactory pulse power energy conversion performance has been achieved in Pb(Zr_0.95Ti_0.05)O₃ materials, poor temperature stability negatively influences their application. The static charge densities of PLZT (x = 0.04, 0.06) decreased from 29.11 μC/cm² and 31.53 μC/cm² to 19.76 μC/cm² and 6.56 μC/cm² under 400 MPa hydrostatic pressure, respectively, which is attributed to a pressure-driven ferroelectric-antiferroelectric phase structural transition. In particular, the temperature stability of PLZT (x = 0.06) materials is up to 87°C. This study may guide the further development pulse power energy conversion devices.     

The effect of washing process on the cracking of ZrO2 microspheres by internal gelation

ZrO₂ microspheres are widely used as a simulant of UO₂ in the development of nuclear fuel. However, the cracking of ZrO₂ microspheres prepared by internal gelation is still a challenge during drying and sintering processes. To address this issue, we designed and optimized the washing process for obtaining crack-free ZrO₂ microspheres. Through thermogravimetric, infrared, Raman, BET, and SEM analysis, it is shown that the cracking of the microspheres is mainly related to the pores in microspheres. The washing solvent with low surface tension is used to reduce the effect of capillary force on pore shrinkage. Therefore, the optimal washing process was designed as trichloroethylene (TCE)—0.5 M NH₃.H₂O—Propylene glycol methyl ether (PM) and gel microspheres with a high specific surface area of 315.3 m²/g and pore volume of 0.4125 cm³/g were obtained. The characterizations also further showed that when the microspheres were dried and sintered, the water vapor and the decomposition gas of organic matter were completely released from the pores in the microspheres. Our new washing process could be directly extended for preparing crack-free ceramic microspheres by internal gelation.     

High extinction-ratio microstructure fiber based on chalcogenide glasses

Extinction ratio (ER) is one of the important parameters to characterize the polarization-maintaining (PM) performance of the fiber. In this paper, we report the preparation and properties of a novel chalcogenide microstructure fiber with a high ER. We fabricate a preform using a peeled-off extrusion method. The core and cladding material of the fiber are Ge₉As₂₃Se₆₈ and Ge₁₀As₂₂Se₆₈. The preform was drawn into a fiber with an average ER of −17.08 dB. The loss of the fiber is less than 2 dB over 5.20–8.55 μm, and the minimum loss of the fiber is 0.57 dB/m at 6.2 μm. Moreover, a flat mid-infrared supercontinuum spectrum spanning from 1.53 to 12.50 μm is generated by pumping an 18-cm-long PM fiber for the first time.     

热扰动冲击下的高温超导电缆失超恢复特性

高温超导(HTS)电缆在运行过程中,不可避免会遇到热扰动冲击,当热扰动能量足够大时会引起高温超导电缆的局部失超,并沿着电缆轴向传播.该文通过建立等效电路模型和一维传热模型,实现电场和温度场的耦合求解,得到高温超导电缆在热扰动冲击下的失超恢复特性,并考虑热流脉冲和液氮流速对电缆失超恢复过程的影响.结果表明:当热扰动能量低于临界恢复能量时,高温超导电缆在液氮冷却下逐渐恢复至超导态;否则,电缆的失超段将沿着轴向传播,导致电缆整体失超.随着努塞尔数的增大,临界恢复能量呈指数增大.电缆恢复时间与液氮流速呈幂律关系.该文计算结果对高温超导电缆的正常运行具有指导意义.     

120°相带环形绕组圆筒型永磁直线发电机定位力降低的优化设计

圆筒型永磁直线发电机(TPMLG)采用120°相带环型绕组可以提高其功率密度,然而,TPLMG具有较大的定位力,这会引起发电机的振荡甚至使系统不稳定.为了解决这一问题,该文对120°相带环形绕组(120°-TPMLG)的圆筒型永磁直线发电机进行优化设计.首先利用有限元方法研究不同结构参数(定子铁心长度、极弧系数、槽肩宽度、定子齿宽和气隙长度)对定位力的影响.根据分析结果,结合田口方法对发电机进行优化设计,在不损失输出功率的情况下使定位力最小,得到120°-TPMLG的最优结构参数.为了验证优化设计过程的有效性,将优化后的120°-TPMLG与初始发电机的性能进行比较.结果表明,优化后的120°-TPMLG的定位力得到了极大的减小,输出功率也略有增加.因此,该文采用的优化方法对减小120°-TPMLG的定位力是有效的.     

基于IGBT行为模型的有源中点钳位五电平变换器损耗特性分析

有源中点钳位五电平拓扑(5L-ANPC)通常用于中压大容量电能变换领域,同时由于其拓扑结构复杂和各器件有效开关频率不同,使得损耗分析较为困难,并且对计算精度要求较高.该文分析基于载波移相脉宽调制(PS-PWM)的损耗计算方法,根据电压电流关系,详细分析所有器件的导通规律,推导导通损耗计算方法.针对传统的开关损耗计算方法在中压大容量条件下误差较大的问题,详细分析IGBT的开关瞬态过程,提出一种基于行为模型的开关暂态损耗计算方法,并将其运用于5L-ANPC拓扑开关损耗分析.对5L-ANPC拓扑损耗特性进行分析,为散热系统设计奠定了坚实的基础.实验结果表明,该文所提方法提高了损耗计算精度,最大误差为10.4％,最小误差为8.4％,验证了所提损耗计算方法的有效性.     

在工业中采用钛合金的微弧氧化

采用硬度测试，金相显微观察和透射电镜分析等方法，研究了微量稀土Er对高纯铝再结晶行为的影响，结果表明，弥散分布的细小Al3Er质点对位错和亚晶界具有钉扎作用，可以有效抑制再结晶，将高纯铝的再结晶温度提高50左右，同时还能显著细化再结晶晶粒，再结晶形核机制是亚晶聚合和亚昌长大双重机制。     

烷基磺酸钠型砂的质量控制

介绍了控制烷基磺酸钠型砂的混砂工艺、配制要点及保存使用等控制要点，并就实际生产中可能出现的一些问题作了探讨，提出了解决的办法。