基于PLECS的三相两电平变流器仿真实验设计

利用仿真软件PLECS的损耗和热分析功能,设计了三相两电平变流器仿真实验,建立了变流器损耗数学模型。采用周期平均模块获得通态损耗,通过脉冲平均模块获得开关损耗,连接散热器模块进行温升分析。在不同调制度、开关频率和电流幅值条件下,对比仿真实验和计算结果的误差。实践表明,该仿真实验可使学生更加直观、形象地认识实际工程应用中的变流器损耗和发热问题,有效提高教学效果和质量。     

一类带有饱和与竞争函数项的捕食模型解的稳定性

讨论一类边界条件为Neumann边界、带有饱和与竞争项的捕食模型解的损耗性和持久性,应用抛物方程比较原理和上下解方法获得解的损耗性和持久性的条件,和非负常稳态解的稳定性.     

自我损耗的后效述评

自我损耗会消耗人们有限的自我控制资源,使其在日常生活中无法进行有效的自我控制。因此,研究自我损耗的后效对于社会适应不良的预防和干预有着重要的理论和实践价值。从心理学的分析框架看,自我损耗的后效作用往往涉及两个方面:一方面,个体的基本认知能力和社会性认知,个体对情绪的知觉和调节,以及个体的意志力、选择决策、亲社会性和攻击性等行为,都会受自我损耗的直接影响;另一方面,自我损耗还会通过个体差异产生间接影响,即在自我损耗条件下,人格对某些行为表现的预测力可能会被放大或被削弱。在由自我损耗导致的诸多后效中,有些是短暂并可逆的,有些则会是长期和稳定的,其影响的持续时间往往由自我损耗的强度所决定。     

LD泵浦Nd:GdVO4三能级激光跃迁研究

目的研究实现LD泵浦Nd：GdVO4三能级激光跃迁的相关条件.方法实验探测分析.结果得到在不同腔损耗情况下的能级跃迁光谱.结论由于发射截面大的四能级跃迁对激光上能级粒子数损耗严重,很难形成高效的三能级激光振荡,抑制四能级跃迁是获得这些三能级激光振荡的前提条件.随着腔镜对这些三能级跃迁损耗的增加,激光发射和泵浦吸收的平衡过程将导致激光发射波长蓝移.     

四分之一波片补偿热退偏损耗实验研究

对四分之一波片补偿腔内退热偏损耗进行了实验研究.在泵浦电流为20 A条件下,带有四分之一波片补偿作用的侧泵Nd:YAG激光谐振腔输出2.67 W 1 064 nm激光输出,其腔内光束退偏率远小于没有腔内补偿的退片率.研究结果证明腔内四分之一波片补偿作用对于降低腔内光束退偏损耗、提升激光功率具有较好的效果.     

功率变换器中磁元件损耗测量方法的综述

磁元件损耗在功率变换器总损耗中占据了较大的比例,其损耗的准确评估对功率变换器的效率至关重要。测量技术是一切研究磁元件损耗的基础,也是评估磁元件损耗的最直接和有效的手段。总结现有磁元件损耗的测量技术,对比分析各种热量测量法,电气测量法的工作原理、特点及应用场合,展望磁元件损耗测量技术的发展趋势和研究方向。     

高压电气设备介质损耗测量方法分析

电力系统中检测高压设备的运行可靠性和发现电气绝缘方面缺陷,介质损耗测量是必不可少的项目。本文对多种介质损耗测量方法进行分析比较。分析了传统介质损耗测量方法特点,阐述了应用微机实现介质损耗测量方法的基本原理、特点,并指出了有应用前景的测量方法。     

浅谈建筑电气节能设计

变压器损耗,线路损耗,照明用电是建筑物中无谓电能源消耗的三大部分,电气设计方案及电气设备选择直接影响建筑能耗的大小.本文着重分析了电能损耗产生的原因,进而提出减小电能损耗的具体措施.     

无取向电工钢损耗浅析

结合铁芯损耗研究的历史,对无取向电工钢损耗(10Hz~1kHz)进行了测量,并应用两种物理模型对总损耗进行了分离。Brailsford模型对总损耗的拟合比较准确,在整个频率范围内存在-1.2%~2.5%的偏差。另一种常规的三段式损耗分离中,工频下磁滞损耗占71.1%,涡流损耗占21.1%,且随频率增加分别呈衰减和升高趋势,反常涡流损耗占总损耗的百分比先是随频率缓慢升高,在200Hz以后几乎不随频率而改变。     

双作用叶片泵轴向间隙优化分析

通过分析油液经过双作用叶片泵而引起泄漏损耗及粘性摩擦损耗 ,找出了总的功率损耗与轴向间隙的关系 ,通过微分分析法 ,求出了轴向间隙最优值的近似表达方法     

具非局部源多孔介质方程的爆破

考虑带有齐次Dirichlet边界条件且具有非局部源项的多孔介质方程正解的爆破性质.在适当条件下,建立了该问题解的局部存在性,证明解在有限时刻爆破,并得到了该问题解的一致爆破模式.     

利用折射表征盐水浓度

光从一种介质进入到另外一种介质,光的传播方向会发生改变。每一种物质都有其自身的光学特性,其物质本身特性决定了光从另外一种介质进入介质本身的折射情况,对于不同浓度的食盐水对应了相应不同的密度,同时也就对应了相应不同的折射率。本文所设计的装置可直接读出食盐水浓度。     

社会合力下的网络原创视频生产传播机制

2005年以来网络原创视频发展迅速,影响力从网络蔓延至各传统媒体,受到人们极大的关注.作为一种新的媒介文本,原创视频从表达主题到表达方式都与传统媒介文本不同.本文从生产及传播两个角度探讨原创视频的特殊机制,通过对媒介性质、主体需求、文化背景及社会条件等外部影响力的分析,研究作用于这种机制背后的社会合力及网络创作力量的精...     

介质中两态叠加多模叠加态光场的和压缩特性研究

利用多模压缩态理论,对介质中两态叠加多模叠加态光场｜ψ^（α）〉q的不等幂次Nj次方和压缩特性进行了详细的研究．结果发现当各模压缩幂次数之和为偶数时,介质中多模叠加态光场｜ψ^（α）〉q恒处于不等幂次Nj最不测不准态;而当各模压缩幂次数之和为奇数时,多模叠加态光场｜ψ^（α）〉q在一定条件下呈现出周期性变化的Nj次方和压缩效应．     

负折射介质的物理特性

负折射介质具有许多独特的物理性质,即反常折射现象、自聚焦效应、逆Dopp ler频移和反常Cerenkov辐射等,这些性质为人们提供了控制光的全新手段,具有良好的应用前景。先回顾了负折射介质的研究历史,然后对负折射介质主要物理性质的物理机制进行了详细的解释,最后简单介绍了光子晶体负折射效应。     

Analytical layer-element solutions for a multi-layered transversely isotropic elastic medium subjected to axisymmetric loading

This paper presents an analytical layer-element method used to analyze the displacement of a multi-layered transversely isotropic elastic medium of arbitrary depth subjected to axisymmetric loading. Based on the basic constitutive equations and the HU Hai-chang’s solutions for transversely isotropic elastic media, the state vectors of a multi-layered transversely isotropic medium were deduced. From the state vectors, an analytical layer element for a single layer (i.e., a symmetric and exact stiffness matrix) was acquired in the Hankel transformed domain, which not only simplified the calculation but also improved the numerical efficiency and stability due to the absence of positive exponential functions. The global stiffness matrix was obtained by assembling the interrelated layer elements based on the principle of the finite layer method. By solving the algebraic equations of the global stiffness matrix which satisfy the boundary conditions, the solutions for multi-layered transversely isotropic media in the Hankel transformed domain were obtained. The actual solutions of this problem in the physical domain were acquired by inverting the Hankel transform. This paper presents numerical examples to verify the proposed solutions and investigate the influence of the properties of the multi-layered medium on the load-displacement response.     

Targeted yield concept and a framework of fertilizer recommendation in irrigated rice domains of subtropical India

Soil test crop response （STCR） correlation studies were carried out in Vindhyan alluvial plain during 2001 to 2004 taking IR-36 as test crop to quantify rice production in the context of the variability of soil properties and use of balanced fertilizers based on targeted yield concept. The soils were developed on gently sloping alluvial plain with different physiographic settings and notable variation in drainage condition. Soil properties show moderate variation in texture （loamy to clay）, organic carbon content （4.4 to 9.8 g/kg）, cation exchange capacity （10,2 to 22.4 cmol （p＋）/kg） and pH （5.3 to 6,4）, Soil fertility status for N is low to medium （224 to 348 kg/ha）, P is medium to high （87 to 320 kg/ha） and K ranges from medium to high （158 to 678 kg/ha）. Database regarding nutrient requirement in kg/t of grain produce （NR）, the percent contribution from the soil available nutrients [CS （%）] and the percent contribution from the applied fertilizer nutrients [CF （%）] were computed for calibrating and fbrmulating fertilizer recommendations. Validity of the yield target for 7 and 8 t/ha was tested in farmers＇ fields and yields targets varied at less than 10%. The percent achievement of targets aimed at different level was more than 90%, indicating soil test based fertilizer recommendation approach was economically viable within the agro-ecological zone with relatively uniform cropping practices and socio-economic conditions.     

Storage and Subsequent Reactivation of Phosphate-Accumulating Aerobic Granules

Phosphate-accumulating aerobic granules cultivated in a sequencing batch reactor were composed of inner rod-shaped bacteria aggregates and outer twining filamentous bacteria. The influence of two-month storage under different conditions on the storage and subsequent reactivation performance of aerobic granules was investigated. After two-month storage the granules sealed at 4 ℃ in distilled water or normal saline (named granules A and granules B, respectively) could maintain their characteristics as before, while the granules idled in the reactor at room temperature (named granules C) exhibited decreased properties. During reactivation, granules A and granules B presented almost identical recovery performance, faster than granules C, in terms of phosphorus removal efficiency, mixed liquor suspended solids (MLSS), phosphate release and accumulating ability. The results suggest that hermetical storage at low temperature promoted the maintenance of the granular properties and the reviving behaviors of phosphateaccumulating aerobic granules, and storage medium had little influence on the storage and recovery performance.     

英国古代赡养习俗

在英国古代流行着这样的赡养习俗：当儿子继承家庭的土地等财产的时候,要与退出生产领域的父母订立一份＂赡养协议＂,说明赡养的各项细节及维护协议的措施方法。当父母没有得到适当照顾时,他们可以依据协议维护自己的权益。在以协议作为保障的同时,社区邻里也起着监督作用。赡养责任的承担与财产转移密切相关,以财产转移为赡养介质,谁继承谁赡养,谁赡养谁继承,无论继承人是谁。这种赡养方式,虽不尽合于我国的国情和传统,但对于我国老人权益的保障和家庭赡养关系的法治化却具有现实的借鉴意义。     

关于电磁场边界条件的讨论

对由相同和不同介质所组成的电磁场场域的边界条件进行了整理和讨论.并用积分形式的麦克斯韦方程组对两种介质分界面上的电磁场边值关系进行了简洁推导,以这种普遍的边值关系为基础导出了理想导体表面上的边界条件,并对该边界条件作了详细的说明.