R/S法的土石坝施工期沉降规律及预警标准研究

为提高施工期土石坝沉降安全性,研究其具有复杂非线性特征的施工期沉降规律和相应的预警标准。基于国内某在建高土石坝的沉降数据,采用R/S法分析坝体不同高程测点、同高程测点和同测点不同时期沉降数据的Hurst指数及分形维数,提出评价坝体施工期沉降安全性的预警标准。结果表明:各测点的Hurst指数最小值为0.763,坝内各处沉降仍处于快速增长阶段;坝体下部比上部、中部比下游堆石区沉降能更快趋于稳定,且坝体下部的沉降速率已经渐趋平缓。     

Motorcyclist perception response time in stopping sight distance situations

One of the most effective engineering measures is the provision of an exclusive motorcycle lane that separates motorcycles from other mixed traffic to reduce traffic congestion and motorcycle crashes. Even though the existing exclusive motorcycle lanes in Malaysia reduced the incidents of motorcycle crashes with other vehicles, the design of this special motorcycle lane was based on a cross reference between a bicycle track and a highway. Thus, a suitable design guide is yet to be developed for the geometrical design of a proper and safer exclusive motorcycle lane. Safe stopping sight distance (SSD) has been recognized as a criterion for road design and should be taken into account. Motorcyclist perception response time (PRT) is the time from detection object until the rider reduces motorcycle speed in braking action is an essential component of motorcycle SSD. Two road experiments were conducted to obtain empirical values of motorcycle PRT to expected and unexpected objects. In the expected condition, 89 motorcyclists applied brake as quickly as possible following activation of a light beside the road. In the unexpected condition, 16 riders responded by braking in response to an obstacle that appeared suddenly in their lane. The mean PRT to expected and unexpected object is 0.71 s and 1.25 s respectively. The 85th percentile PRT to unexpected object is 2.12 s. This study found that most riders are capable of responding to an unexpected object along the roadway in 2.5 s or less. Therefore, PRT of 2.5 s is an appropriate value for motorcycle lane geometric design.     

基于雷电监测预警的加油站防雷预案执行研究

基于雷电监测预警技术,提出了一种新型的加油站防雷预案执行方案,解决了现有的应急预案无准确执行依据的问题。方案引入近几年成熟的电场监测和雷电定位技术,对加油站周边地区的电场和雷击情况进行实时监测,并基于监测数据和加油站业务特点建立数学模型,结合先进的物联网和云计算技术,在雷电发生前获得高精度的短时雷电预警信息,在此基础上设计了加油站防雷预案执行方案,最后对方案的应用效果进行了分析。     

街道峡谷内不同车道污染物扩散的数值模拟

为掌握不同位置车道污染物的扩散规律,提出降低街道峡谷内居民与行人交通源暴露水平的可能途径,采用二维k-ε两方程模型和组分输运方程对典型结构双车道街谷内的流场与不同车道污染物的扩散进行模拟,模拟结果与风洞试验结果相符合. 研究发现:迎风车道的污染物更易于向街道峡谷外部扩散;不同位置车道的污染物均在背风侧堆积,可使两侧人行道暴露水平相差5倍. 街道峡谷底部污染物分布对车道位置较敏感,车道位置向街道峡谷中部靠拢,将使得背风建筑物底部及人行道的污染物浓度明显降低;迎风侧污染物浓度对车道位置不敏感,但当车道位置处于迎风侧次级旋涡内时,将导致迎风建筑物底部及人行道的污染物浓度近乎成倍增长. 将车道位于街道峡谷中部,优先采用道路两侧绿化,是增加行人舒适度和减少行人交通源暴露水平,并改善大楼低层住宅及底部出入口、临街商铺等人群活动区空气质量的可行途径之一.      

Allometric scaling of resource acquisition by ruminants in dynamic and heterogeneous environments

We present a mechanistic formulation of the intake response of ruminants to vegetation biomass based solely on physiological and morphological parameters that scale allometrically with the animal's body mass. The model is applied to describe herbivore-vegetation interactions in dynamic and heterogeneous landscapes with low quality but abundant “tall grass” and high quality but sparsely available “short grass”, under two conditions: “uncoupled” (such that the effect of food intake on vegetation biomass can be neglected), or “coupled” (such that the vegetation biomass is determined by herbivore feeding). The results show that under uncoupled conditions, the minimum acceptance (proportion of vegetation consumed by the herbivore) at which the herbivore can leave its current patch without reducing its intake rate is when it has depleted the current patch by the energetic cost required to travel to another patch. The maximum acceptance at which the herbivore should leave its patch is when it has depleted the current patch by the cumulative energetic cost of traveling, handling, cropping, and digesting. Under coupled conditions, the optimal acceptance equals half the relative growth rate of the vegetation. Analytical solutions are obtained for equilibrium values for utilization of the vegetation, and for the densities of vegetation and ruminants, expressed in physiological and morphological herbivore parameters.     

长江,黄淮流域近期特大洪水预警和防洪形势

根据太阳黑子活动和长江，黄淮流域１８４０￣１９９４年历史和实测的洪水资料，推断在１９９７年及其前后，长江，黄淮流域很有可能出现一次特大的洪水。同时指出，目前长江、淮河、黄河的防洪形势不容乐观，必须及早采取对策，确保人民生命和财产的安全。     

Does nutritional surveillance have a role to play in early warning of food crisis and in the management of relief operations?*

A major area of investment in data collection in developing countries has been that of nutritional surveillance and monitoring. From recent debate it is clear that there is currently no consensus on the potential role of nutritional status as an early warning indicator. The author presents a synthesis of the broad spectrum of views on the role nutritional surveillance could or should have in early warning. Conceptual problems and technical difficulties are reviewed in the light of recent experiences in Africa and Asia. The author raises a number of issues for future discussion in this ongoing debate.     

CFD方法对突发性化学事故中危险物质泄漏范围的确定

简要分析了目前国内主要用于预测易燃易爆(有毒)物质发生泄漏事故后浓度扩散范围的计算方法。并介绍了国际上比较成熟的计算流体力学相关软件的数学模型及特点和边界条件的设置。针对液氨发生泄漏后氨气在一定大气环境条件下扩散的过程和特征,建立了相应的数学模型并设置了边界条件,通过数值计算得到氨气在水平方向风速环境下在三维空间内浓度分布规律。通过分析氨气扩散后爆炸浓度下限范围,探讨了如何设置警戒区的方法。最后分析了将计算流体力学方法应用于确定易燃易爆(有毒)物质泄漏后浓度范围的前景与不足。     

Predictors for people's response to a tornado warning: Arkansas, 1 March 1997

On 1 March 1997, powerful tornadoes touched down in Arkansas (USA) on a Saturday afternoon. Twenty-six fatalities and 400 non-fatal injuries were reported. We performed a population-based cross-sectional study to determine factors associated with appropriate responses to tornado warnings. Of 146 survey participants, 140 (96 per cent) knew the difference between 'tornado watch' and 'tornado warning' and were aware of when the warning was announced. Of those 140 participants, 64 (45.7 per cent) responded to the warning by seeking shelter, and 58 (90.6 per cent) of those 64 acted within five minutes of hearing the warning. Four factors were positively associated with those seeking shelter: having graduated from high school (OR = 4.2, 95 per cent CI = 1.1-15.5); having a basement in one's house (OR = 3.8, 95 per cent exact CI = 1.1-17.1); hearing a siren (OR = 4.4, 95 per cent CI = 1.3-18.9); and having prepared a household plan of response when tornadoes occur (OR = 2.6, 95 per cent CI = 1.1-6.3). On the basis of these findings, we recommend: first, that people who live in tornadoprone areas have a personal plan of action to help them respond immediately to warnings; second, public-health education officials in areas with frequent tornadic activity should do more to educate the public about what they can do to protect themselves from a tornado; and third, that emergency-management officials planning protection measures for vulnerable communities should consider that most people have limited time (our study documented five minutes) in which to respond to a tornado warning. Thus, shelters in tornado-prone areas should be quickly accessible by residents.     

Flood information systems: Needs and improvements in Eastern India

Flood warning systems offer a large potential for reducing human losses and property damage in flood-prone regions. This article illustrates why official organized systems should not be relied on completely in either developing or developed societies. It then discusses an indigenous flood warning system in a rural area of Eastern India, its value, and its importance in providing an alternative means of detecting, interpreting, and relaying flood warning information to the ultimate users of this information, i.e., those populations most at risk from floods.The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research and is sponsored by the National Science Foundation.