激光通道传输热特性对远场光束质量的影响

 通过仿真计算分析了激光在光束控制系统通道内传输所产生的热效应及其对远场光束质量的影响。激光传播由近轴波方程描述，用快速傅里叶变换技术求解；激光热效应引起的流场密度变化采用完全Navier-Stokes方程计算。计算给出了不同波长、不同吸收系数条件下的远场光斑情况。计算结果表明，在典型的工作条件和状态下，较高能量激光在光束控制系统通道内产生的热效应影响不容忽视，它会明显降低远场目标处的能量集中度，增大光斑的发散。     

Simultaneous determination of eight components in Angelica sinensis based on UHPLC‐ESI‐MS/MS method for quality evaluation

A method employing ultra‐high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) for determination of eight components including ferulic acid, senkyunolide A, butylphthalide, ligustilide, butylidenephalide, senkyunolide I, senkyunolide H and levistolide A in Angelica sinensis was established. The separation was carried out using a Waters ACQUITY UHPLC BEH C₁₈ column with gradient elution with 0.1% formic acid aqueous and acetonitrile at a flow rate of 0.4 mL/min. Good linearity was attained with R² of 0.9983–0.9998 in wide concentration ranges. The method had limit of detection (LOD) and quantitation (LOQ) in the range of 0.42–6.98 ng/mL and 1.39–23.28 ng/mL, respectively. Intra‐ and inter‐day precisions varied with relative standard deviations (RSDs) from 0.33% to 0.88% and 0.37% to 1.04%, respectively. Moreover, the average recoveries were in a satisfactory range of 92.7%–102.1% with RSDs of less than 3.60%. Finally, the method was successfully applied to analyze 19 batches of A. sinensis samples grown in Min County, Gansu province, China, as well as that collected in other regions. The findings indicated that the established method is reliable and may thus be applied as a powerful tool for qualitative and quantitative analysis of components in A. sinensis, which has its implications in quality control of A. sinensis.     

大同市居民对室内空气质量认知程度的调查

为了解大同市居民对室内空气质量的认知情况，并分析认知程度与教育的关系，于2016年3月至5月，在大同市城区的9个社区随机对居民进行问卷调查。问卷内容包括居民对室内空气质量安全知识的了解，检测室内空气质量的意愿和治理意愿3个方面。将居民所处地域、居民的年龄与学历对室内空气质量安全认知程度的影响分别进行统计学分析。结果表明，大同市居民室内空气质量安全认知程度总体得分15.8，得分率为52.7%；新城区的居民对室内空气质量安全认知水平高于老城区居民（p<0.05）；学历越高且越年轻的居民对室内空气质量安全的认知水平越高，寻求有关机构进行室内空气检测和治理的意愿更强烈，且对检测和治理的费用承受度较高。大同市居民对室内空气质量安全认知程度总体不高，还应加强对市民的室内空气质量安全方面的教育。     

Influence of staff number and internal constellation on surgical site infection in an operating room

Prediction of bacteria-carrying particle (BCP) dispersion and particle distribution released from staff members in an operating room (OR) is very important for creating and sustaining a safe indoor environment. Postoperative wound infections cause significant morbidity and mortality, and contribute to increased hospitalization time. Increasing the number of personnel within the OR disrupts the ventilation airflow pattern and causes enhanced contamination risk in the area of an open wound. Whether the amount of staff within the OR influences the BCP distribution in the surgical zone has rarely been investigated. This study was conducted to explore the influence of the number of personnel in the OR on the airflow field and the BCP distribution. This was performed by applying a numerical calculation to map the airflow field and Lagrangian particle tracking (LPT) for the BCP phase. The results are reported both for active sampling and passive monitoring approaches. Not surprisingly, a growing trend in the BCP concentration (cfu/m³) was observed as the amount of staff in the OR increased. Passive sampling shows unpredictable results due to the sedimentation rate, especially for small particles (5–10 μm). Risk factors for surgical site infections (SSIs) must be well understood to develop more effective prevention programs.     

哈佛大学有效提升物理教学质量的举措分析

深入探讨了哈佛大学提升物理课程教学质量的举措,诸如卓越的教学方法、全面的教师培养、科学的教学指导、高效的教学评价等.哈佛大学的这些全面、细致、具体、实用的举措对我国大学物理教学质量的提升具有一定的借鉴意义.     

Adaptive multimedia streaming using a simulation test bed

The major purpose of this paper is to transmit an existing video above a complete simulated video streaming architecture based on Network Simulator (NS2). Thanks to our architecture, the visual quality evaluation of the distributed streaming platform under various conditions is simplified. Indeed, the received video can be easily visualized using a classic video client or be compared using the Peak Signal-Noise Ratio (PSNR) value and the Structural SIMilarity (SSIM) value. In the case study, we compare adaptive video congestion strategies using a transcoder, Datagram Congestion Control Protocol (DCCP) and TCP-Friendly Rate Control (TFRC).     

JEM-2100PLUS透射电子显微镜操作方法与技巧及常见故障排除

以JEM-2100PLUS透射电子显微镜为例，介绍了电镜的基本结构、操作面板和成像原理。使用透射电子显微镜的最终目的就是要得到高质量的照片，结合透射电镜的操作步骤，总结了如何拍摄高质量的照片以及常见故障排除方法。     

高速公路PPP项目股权结构、质量水平与VFM的关系研究

高速公路PPP项目属于具有经营收益的准经营性项目,政府制定有效的激励措施,可以鼓励项目公司发挥专业的建设和运营能力,提高项目质量和收益水平。本文以VFM作为政府绩效评价指标,通过构建完全信息静态博弈模型,研究了PPP项目股权结构、质量水平与VFM之间的关系,结果发现:虽然社会资本较多持有项目公司股份有助于提高VFM水平,但随着社会资本方股权比例的增加,项目质量水平在不断降低,所以政府应该将社会资本方的持股比例控制在一定范围内,在保证项目质量的同时达到VFM最大化,从而降低政府方风险,提高社会效益。在高速公路PPP项目中,政府应优化股权决策,激励项目公司改善项目质量和水平,为公私双方带来良好的绩效水平。     

Electrochemical sensors for environmental gas analysis

The application of electrochemical sensors for measurement of concentration of pollutant gases in air in the part-per-billion (10⁹) range is reviewed. Performance-limiting factors, particularly the effects of extremes and of relatively rapid changes in ambient temperature and humidity, are noted. Variations in composition of the electrolyte in the meniscus at the electrode–gas interface and instability of the solid–liquid–gas contact line, causing important variations in current due to background electrode reactions, are deduced and suggested as the reason for the performance limitations. Suggestions are made for mitigation through instrument design.