Explaining obesity with urban form: a cautionary tale

In recent years, there has been a dramatic increase in studies exploring associations between the built environment and obesity. Many studies have found that built environment characteristics, such as high-density land developments, mixed-land uses, and connected street networks, are associated with lower rates of obesity. However, depending on the research field and the researcher, how one specifies the experimental model and how sociodemographic characteristics of the population are defined and included in the model has led to different policy conclusions and implications. This is not a surprising observation; however, it is one that does seem to have been lost in current discussions. This article highlights several data-processing, model-specification, and model-estimation factors that should be comprehensively considered in studies of the built environment and obesity. Empirical results based on data from Atlanta, GA, USA, illustrate that the association between the built environment and obesity is sensitive to how age, income, and educational attainment are included in the model. Also, a detailed examination of land-use-mix measures shows that it is difficult to create this measure and that results are sensitive to the treatment of missing values. Models that distinguish between overweight and obese individuals are shown to provide richer insights into the associations among obesity, built environment, and sociodemographic characteristics for the Atlanta area. The article concludes by offering modeling recommendations for future studies.

Design and Combustion Characteristic Analysis of Free Piston Stirling Engine External Combustion System

The free piston Stirling engine external combustion system was simulated to investigate the diesel-air combustion characteristics in order to demonstrate its feasibility by computational fluid dynamics (CFD). The different effects on combustion were distinguished by analyzing the combustion burner, the injection position of diesel oil, the front tube arrangement of Stirling heater head and the back fin. The results show that the tilted front tube arrangement of the heater head with the back fin is the best practicable technology while the distance between the diesel nozzle position and the swirler top is 0. Its total heat flux is 15.6 kW, and the average heat transfer coefficients of the front and back tubes are 127W/(m² · K) and 192W/(m² · K), respectively. The heat transfer is mainly through convection, and the proportion of radiative heat transfer is only 16.9%. The best combustion efficiency of the free piston Stirling engine external combustion system is 86%.     

高速道岔尖轨点云的复合拼接及数据处理优化

为实现高速铁路尖轨磨耗的高效检测,结合高速尖轨的检测需求及其几何特征,提出了基于距离编码器的复合拼接方法.该方法将距离信息融合到点云拼接中,提高了检测系统的自动化程度.在计算点特征直方图（point feature histograms,PFH）的过程中,引入OpenCL（open computing language）异构加速模型调整点云的数据结构,发挥GPU的并行处理优势获得了更快的数据处理速度.利用实际尖轨开展磨耗检测实验,证明了针对高速尖轨的结构光检测系统有效可行.经过点云拼接和点云扫描数据处理的优化,系统的整体检测效率获得了70%左右的提升.      

梯形动铁式交流焊机优化设计研究

对梯形动铁式交流焊机的优化目标进行了探讨,在此基础上建立了动铁式交流焊机优化设计的数学模型,编制了计算机优化设计软件,利用该软件对焊机进行了优化设计,结果表明:利用该软件所设计的交流焊机具有较低的制造成本和较高的综合性能     

EDFS40对深低温保存兔颈总动脉结构和舒缩功能的影响

目的 评价玻璃化溶液EDFS40对深低温保存兔颈总动脉形态结构和舒缩功能的影响.方法 无菌条件下取兔颈总动脉,分别以EDFS40和1.5 mol/L二甲亚砜为低温保护剂,经玻璃化法和慢速冷冻法深低温保存14 d.复温后和新鲜动脉进行大体和显微形态的观察,器官浴槽内进行非内皮依赖性舒缩功能的测定.结果 EDFS40组动脉的大体、组织学及超微结构与新鲜动脉相似,对氯化钾的收缩力和慢速冷冻组动脉无明显差别(P>0.05),对去甲肾上腺素和硝普钠的收缩或舒张张力优于后者(P<0.05),但均低于新鲜动脉(P<0.05).结论 EDFS40能较好保持兔颈总动脉的形态结构及功能,可用于血管的玻璃化保存.     

大鼠肝脏干细胞的胰十二指肠同源盒基因表达系的构建与初步鉴定

目的 建立大鼠肝脏干细胞的Pdx-1基因表达系.方法 逆行穿刺SD大鼠乳鼠肝脏门静脉,经胶原酶Ⅳ消化并分离肝脏干细胞;免疫组织化学鉴定大鼠肝脏干细胞标志物细胞角蛋白18/19、甲胎蛋白的表达;构建pEGFP-Pdx-1表达载体并酶切鉴定,用脂质体2000介导表达载体转染大鼠肝脏干细胞后,荧光显微镜观察GFP表达,免疫组织化学鉴定Pdx-1的表达.结果 肝脏门静脉逆行穿刺分离培养大鼠肝脏干细胞具有分裂增殖能力、角蛋白18/19、甲胎蛋白表达阳性;pEGFP-Pdx-1表达载体转染后的肝脏干细胞可表达绿色荧光蛋白报告基因和Pdx-1蛋白.结论 成功建立了大鼠肝脏干细胞Pdx-1表达系.     

半月神经节射频热凝温控术治疗原发性三叉神经痛

目的 观察和分析射频热凝术治疗原发性三叉神经痛的临床疗效及并发症.方法 在DSA或C型臂引导下,采用Hartel前入路法,穿刺三叉神经半月节后以温控射频热凝对靶点毁损,温度控制在76～80 ℃,持续时间1～2 min,共3～4次.结果 本组56例中,53例术后疼痛完全消失,为Ⅰ级,视为临床治愈,治愈率为94.6%;1例达Ⅱ级明显缓解;1例达Ⅲ级;1例为Ⅳ级无效.治疗优良率为96.4%,总有效率为98.2%.无严重并发症.结论 射频热凝术是治疗原发性三叉神经痛安全可靠及有效的一种微创治疗技术.     

灌砂法在路基压实度检测中的应用

结合工程实践,浅谈灌砂法在路基压实度检测中的应用.     

北京地铁9号线“W”型折返线列车救援分析

北京西站"W"型折返线为北京地铁9号线列车故障救援困难点。结合北京西站"W"型折返线的信号系统和线路特点,分析其行车组织方式和折返能力,并在保证最大限度地维持区段运营的情况下,提出列车故障情况下的列车救援方案和行车组织方案。     

青春期与育龄期多囊卵巢综合征患者的临床对照研究

目的 通过对青春期多囊卵巢综合征(polycystic ovarian syndrome, PCOS)与育龄期PCOS患者的临床资料的对照研究,分析两组患者的临床特点以及PCOS对女性健康和血管内皮功能的影响.方法 选择在我院妇产科门诊就诊的PCOS患者68例,其中青春期33例,育龄期35例.所有患者记录基线资料,采用ELISA法检测内皮素-1(ET-1)浓度,免疫浊度法检测C-反应蛋白(CRP)浓度,放射免疫法测定女性激素.结果 ①基线资料的比较:青春期组F-G评分及痤疮评分较育龄期组显著升高(P<0.05),而其余指标无显著性差异.②临床特点的比较:青春期患者月经失调、多毛、痤疮发生率较育龄期显著升高(P<0.05).③女性激素的比较:青春期组睾酮(T)、黄体生成素(LH)、LH/卵泡刺激素(FSH)显著高于育龄期组(P<0.05),而FSH、催乳素(PRL)、孕酮(P)和雌二醇(E2)无显著性差异(P>0.05);④ET-1浓度的测定结果:育龄期组较青春期组显著升高(P<0.05);育龄期肥胖组及胰岛素抵抗(IR)组血清ET-1浓度分别较非肥胖组及非IR组显著升高(P<0.05),而青春期组无此改变.⑤两组CRP浓度无显著性差异.结论 PCOS在女性青春期与育龄期的临床特点不同,育龄期尤其是伴有IR和(或)肥胖者血管内皮功能紊乱较明显.