基于载波相移系统的二倍频光电振荡器

为了扩展光电振荡器(OEO)的频率范围,设计了 一种基于载波相移系统的二倍频OEO(FD-OEO)。 系统采用相位调制器(PM)和Mach-Zehnder调制器(MZM)并联,构成载波相移系统,利用载 波相移双边带(CPS-DSB) 调制的方法产生二次谐波分量;同时利用啁啾光纤布拉格光栅(CFBG)色散特性实现边带分 量与CPS补偿,维持 OEO环路中基频信号的振荡。实验结果显示,在OEO环路系统基频信号为2.23GHz情况下,产生了4.30 GHz的FD信号,且通过边模抑制性能、稳定性及相位噪声对系统性能进行了验证。     

基于MSP430的空气环境质量监测系统设计

为了实现城市环境参数的分布式检测和集中统计管理,设计了一个空气环境质量监测系统。该系统分为上位机监控中心和下位机检测与传输终端两部分,下位机采用MSP430F149单片机作为控制核心,以温湿度传感器SHT11和PM2.5传感器进行数据采集。下位机有液晶显示,可以实时显示测量数据,并可手动设置报警值,检测数据同时通过Sim900无线模块传至监控中心。监控中心完成空气环境质量数据的统计管理,生成报表,便于管理部门做出决策。该系统已经在大学校园环境下进行了测试、应用,效果良好。     

PM2．5与城市规划要素的空间对应——以沈阳为例

快速工业化和城市化进程引发了巨大的环境危机。如何有效地调节城市规模和城市结构的关系是减少城市污染的一条既经济又切实可行的方案。本文以传统老工业基地——沈阳为研究区．对比城市PM2．5与城市规划要素的空间效应,直面其空间性。并为优化城市规划布局、建设美丽中国提供一定的数据支撑。结论表明：市政基础设施——电源厂是沈阳PM2．5浓度最高区域：绿地对PM2．5具有净化作用,其分布范围内PM2．5浓度最低;工业用地的PM2．5浓度偏高,而且影响其周边空气质量．适合“小集中、大分散”的布局;而约有1／6居住用地PM2．5浓度偏高。     

Numerical study on PM10 collection efficiency in a wire-cylinder electrostatic precipitator under multi-field coupling

The PM10 collection efficiency of a wire-cylinder electrostatic precipitator (ESP) was studied by means of a developed mathematical model, including the multi-field coupling between the gas flow field, the particle dynamic field and the electric field, and applying the Deutsch–Anderson Equation. The diffusion charging mechanism was considered due to the diameter range of PM10. The investigated variables were the applied potential, the gas velocity and the particle distribution. Numerical results indicate that the diffusion charging has significant influence on PM10 removal performance and the effect is more obvious with the decreasing diameter, and that the PM10 collection efficiency increases with the increasing applied potential and the increment of collection efficiency is more significant at lower voltage. Moreover, as the gas velocity at inlet decreases, collection efficiency of PM10 will increase. Finally, the overall efficiency increases with increasing the mean diameter of particle distribution. The research results can provide theoretical and technical references for the design of novel ESP aiming at economy and environment protection.     

Urban development and particulate air pollution in Coimbatore city,India

Haphazard urbanization and unprecedented vehicular growth that exacerbate air quality are prevalent features in India. Coimbatore, an important industrial city ranking 15th in terms of principal urban agglomerations of India, was classified as a moderately polluted area in National Ambient Air Quality Monitoring survey in 1997. The current study (March 1999–February 2001) was undertaken to assess suspended particulate matter (SPM) in urban and suburban Coimbatore. It was found that in the Coimbatore atmosphere SPM with a diameter of less than 10 µm (respirable fraction, RSPM or PM₁₀) and those with a diameter above 10 µm, the non‐respirable (NRSPM) fraction, ranged between 30–149 µg/m³ and 24.4–460 µg/m³ respectively. The study infers that urban areas, especially those with frequent vehicular traffic and traffic congestion, had comparatively high RSPM exceeding the Indian prescribed standards (60 µg/m³). Emission inventory estimated for current vehicle strength showed that about 840 000 kg of particulate matter was emitted during 2001. Wind speed negatively correlated with RSPM, while it was positively correlated with NRSPM. Temperature had a negative correlation with RSPM values.     

Predicting chaotic time series of PM10 concentration using artificial neural network

Respirable particulate matter (PM10) concentration at one residential site in Delhi, India was predicted using the neural network approach. The concepts of chaotic systems theory were utilized to build the neural network model. The embedding dimension was estimated to provide the inputs to the neural network. The model evaluation results indicated the importance of noise reduction before selecting the embedding dimension of the time series. The selection of a proper embedding dimension is considered to be essential for obtaining reliable predictions. The model’s performance shows the capability of neural networks in modelling the chaotic time series.     

A randomized double‐blind crossover study of indoor air filtration and acute changes in cardiorespiratory health in a First Nations community

Few studies have examined indoor air quality in First Nations communities and its impact on cardiorespiratory health. To address this need, we conducted a crossover study on a First Nations reserve in Manitoba, Canada, including 37 residents in 20 homes. Each home received an electrostatic air filter and a placebo filter for 1 week in random order, and lung function, blood pressure, and endothelial function measures were collected at the beginning and end of each week. Indoor air pollutants were monitored throughout the study period. Indoor PM_2.5 decreased substantially during air filter weeks relative to placebo (mean difference: 37 μg/m³, 95% CI: 10, 64) but remained approximately five times greater than outdoor concentrations owing to a high prevalence of indoor smoking. On average, air filter use was associated with a 217‐ml (95% CI: 23, 410) increase in forced expiratory volume in 1 s, a 7.9‐mm Hg (95% CI: ?17, 0.82) decrease in systolic blood pressure, and a 4.5‐mm Hg (95% CI: ?11, 2.4) decrease in diastolic blood pressure. Consistent inverse associations were also observed between indoor PM_2.5 and lung function. In general, our findings suggest that reducing indoor PM_2.5 may contribute to improved lung function in First Nations communities.     

西安市某办公建筑室内外颗粒物浓度变化特征分析

本文通过建立质量平衡方程对西安市某办公建筑室内颗粒物浓度进行了理论分析,并对该建筑室内外PM10和PM2.5的质量浓度进行了实时监测。结合线性回归方程、室内外监测浓度线性拟合曲线及室内浓度随时间的指数拟合曲线,对该普通办公房间室内颗粒排放源及室内颗粒浓度变化特征进行了研究。结果表明,该建筑室内PM10的平均发尘为7.93～12.48 mg/h,室内PM2.5的平均发尘为2.89～4.08 mg/h;室内PM10和PM2.5呈现指数变化且随时间呈下降趋势。     

永磁无刷单相电机场路耦合有限元仿真与实验研究

针对永磁无刷单相电机在异步起动时必须借助起动副绕组而需进行电容切换,导致电机结构复杂和可靠性降低的问题,首先从电机的电磁设计入手,提出了一种电机磁路不对称、具有自起动能力的永磁无刷单相电机结构,然后采用V/f控制的变频控制方法,实现了电机带额定负载的平滑自起动和稳定运行。并利用Maxwell软件建立了电机的场路耦合有限元仿真模型,对电机及其控制系统进行了仿真分析。最后利用样机及其控制器的实验平台对样机系统的各种运行状态进行了实验测试,并将实验结果与有限元仿真结果进行了对比分析,两者达到了很好的一致性。研究结果表明,气隙不对称永磁无刷单相电机系统具有自起动迅速、运动平稳、效率较高的特性,在空调等家用电器领域具有很好的应用前景。     

常化温度对2.5%Si无取向硅钢第二相析出行为的影响

采用扫描电镜、透射电镜和双束扫描电镜对不同常化温度2.5%Si无取向硅钢中不同类型第二相析出物的析出行为和演化规律进行了研究。结果表明,常化温度从850℃升高至1100℃,微米级大尺度第二相粒子呈一次长大-析出-二次长大-回溶的变化规律;当常化温度<920℃时,析出相以AlN+MnS复合长大为主;随后小尺寸的MnS、AlN及其复合析出物数量迅速增多,并在950℃时达到峰值;随着常化温度的进一步升高,第二相粒子析出数量快速减少,然后缓慢增长至趋于平衡,大尺寸析出物出现部分回溶。纳米级析出物则以Cu₂S和Cu₂S+MnS复合析出为主。并且950℃常化时,2.5%Si无取向硅钢的铁损最低。