穿越型扩张式封隔器的研制与试验

渤海油田采用大段防砂完井,防砂段内小层多,地层非均质严重,层间矛盾突出,注水开发效果难以进一步提高。为了实现细分层系开发,除了防砂管柱外层与层封隔,还需要在防砂管柱内相应位置配合形成管内封隔。为了适应不同分层采油注水工艺措施,研制穿越型扩张式封隔器,介绍该封隔器的应用环境、结构、工作原理等,并对该封隔器进行了室内试验和现场试验。结果表明：穿越型扩张式封隔器能顺利实现外径 6.35 mm的管线穿越,无遇阻,所设置的保护功能可有效保护管线,能按要求顺利坐封、解封,中心打压16 MPa,上下环空承压均可达15 MPa,最大可满足 157.1 mm内径密封要求,满足现场不同应用环境的需求。     

Methods for approximate reliability analysis

Approximate solutions are developed for reliability problems involving constant-in-time and time-dependent random parameters. They are based on estimates of the distribution of scalar control variables obtained from approximations of the safety condition (control variable approach) or on a transformation of the input space of parameters into a space in which the safety condition is nearly linear (linearization approach). The distribution of the control variable or of the random parameters in the transformed space can be estimated from moments of these variables. The control variable approach is most effective when the random parameters are constant in time while the linearization approach is useful for time-dependent reliability studies since it permits application of various rules (e.g., Turkstra's rule) for approximate load combination analysis.     

输电跨越塔设计回顾与展望

本文介绍国外跨越塔建设的历史和现状,回顾了我国跨越塔的建设和发展情况,对跨越塔结构型式、材料强度、冲击韧性、高强度螺栓、节点设计等要点分别作了论述,展望了跨越塔的设计前景。     

交叉变轮距底盘机械式可变特性转向系统研究

分析了变轮距车辆的转向要求及常用转向方法;介绍了一种利用双对角线几何原理实现轮距可变特性的交叉变轮距车辆底盘技术;针对目前国内的机械式转向系统一般不能满足变轮距车辆的转向要求的现状,提出了一种利用基于阿克曼梯形转向机构的可变特性转向单元实现交叉变轮距底盘机械式转向的技术方案。分析结果表明,该方案不仅可以较好地实现交叉变轮距底盘的前轮转向和四轮转向,而且降低了转向机构及其控制程序的复杂程度,提高了转向精度和可靠性,具有较高的理论研究和推广应用价值。     

Illegal road crossing behavior of pedestrians at overpass locations: Factors affecting gap acceptance,crossing times and overpass use

The aim of designing overpasses is to provide safe road crossings for pedestrians by helping them to avoid conflicts with motor vehicles. However, the number of pedestrians who do not use overpasses to cross the road is very high. An observational survey of illegal road crossings was conducted at four overpass locations in Izmir, Turkey to determine the crossing time, crossing speed of the pedestrians and their distance and time gap perception for safe road-crossing within 25 m of the overpasses in both directions. Crossing time is the time needed for a pedestrian to cross a particular road. Time gap is strongly related with safety margin. If a pedestrian chooses a larger time gap, then the arrival time of the oncoming vehicle to the crossing point of the pedestrian increases thus, the possibility of a collision decreases. Each overpass was observed on weekdays during peak afternoon (12.30–13.30) and evening hours (17.00–18.00). At all overpass locations 454 illegal crossings were observed. ANOVA results revealed that age had a significant effect both on safety margin and crossing time. During the observations a survey was conducted among pedestrians who completed their crossings either using the overpass or at street level within 25 m of the overpass (n = 231). Factors affecting the crossing choice of pedestrians were specified in the surveys. The major part of the respondents (71.7%) indicated that time saving was the main reason for crossing at street level. Pedestrians’ crossing speeds were extracted from the video recordings to observe the effect of speed limit on pedestrian behavior. As a result, at locations where the speed limit was 70 km/h, pedestrians’ average crossing speed was found to be 1.60 m/s and 1.73 m/s while at locations where the speed limit was 50 km/h, pedestrians’ average crossing speed was found to be 1.04 m/s and 0.97 m/s. This shows that pedestrians feel safer while crossing when the vehicle speed is low.     

建筑外延

文章将建筑师从事建筑学领域以外的活动分类梳理为四个方向——生活体验、艺术创作、空间运营、媒体传播,发现外延活动的共性所在,并期待其对建筑学本身的影响可以成为值得研究的课题。     

Lay discourse about hydrogen energy and the environment: Discussion by young people and adults following a first visit to a Hydrogen Research and Demonstration Centre

This paper explores the public's understanding of 'sustainable energy', focusing upon hydrogen, which for most is unfamiliar. We report reactions to a first tour of the recently established 'Hydrogen Research and Demonstration Centre' in the Valleys of South Wales, which was guided by its scientists and engineers. The visitors lived within 50 miles and fell into three age-categories: 14-year old Baccalaureate students; 18–19 year old students at Tertiary College; and adult- members of a Citizens' Panel. They took part in six focus groups which were facilitated, recorded and then analysed thematically by independent sociologists. The paper examines themes on which the groups agreed or disagreed, and how clear or ambiguous their discourse was. While broad consensus was reached on benefits, costs and safety of hydrogen, there were differences in how groups imagined incorporating it into their lives. In conclusion, we draw lessons for securing wider public commitment to sustainable energy.     

The influence of pedestrian countdown signals on children’s crossing behavior at school intersections

Previous studies have shown that pedestrian countdown signals had different influences on pedestrian crossing behavior. The purpose of this study was to examine the effects of the installation of countdown signals at school intersections on children’s crossing behavior. A comparison analysis was carried out on the basis of observations at two different school intersections with or without pedestrian countdown signals in the city of Jinan, China. Four types of children’s crossing behavior and child pedestrian-vehicle conflicts were analyzed in detail. The analysis results showed that using pedestrian countdown timers during the Red Man phase led to more children’s violation and running behavior. Theses violators created more conflicts with vehicles. However, pedestrian countdown signals were effective at helping child pedestrian to complete crossing before the red light onset, avoid getting caught in the middle of crosswalk. No significant difference was found in children who started crossing during Flashing Green Man phase between the two types of pedestrian signals. Moreover, analysis results indicated that children who crossed the road alone had more violation and adventure crossing behavior than those had companions. Boys were found more likely to run crossing than girls, but there was no significant gender difference in other crossing behavior. Finally, it’s recommended to remove countdown at the end of the Red Man phase to improve children’s crossing behavior and reduce the conflicts with vehicles. Meanwhile other measures are proposed to improve children safety at school intersections.     

Unfolding the frequency spectrum for undersampled wideband data

In this letter, we discuss the problem of unfolding the frequency spectrum for undersampled wideband data. The problem is of relevance to state-of-the-art radio frequency measurement systems, which capture repetitive waveform based on a sampling rate that violates the Nyquist constraint. The problem is presented in a compact form by the inclusion of a complex operator called the CN operator. The ease-of-use problem formulation eliminates the ambiguity caused by folded frequency spectra, in particular those with lines standing on multiples of the Nyquist frequency that are captured with erroneous amplitude and phase values.