基于航空器高度保持性能的风险碰撞模型优化*

为提高Reich风险碰撞模型在“缩小垂直间隔”(Reduced Vertical Separation Minimum,RVSM)标准实施后的适用性。基于同一机型航空器的测高系统误差（Altimetry System Error,ASE）数据在超高空各高度层中并不服从相同分布且具有显著的统计学差异,针对现有的Reich模型对同一机型仍使用整个航空空域的ASE数值进行经验分布拟合的现状,对模型中ASE混合累积经验分布参数部分进行改进,添加高度层相关的参数,使原有仅根据机型进行累积的ASE经验分布细化为根据机型和高度层2部分进行累积。结果表明:改进后模型可准确体现ASE数据在不同高度层的差异性;采用改进的风险模型进行仿真计算,得到更加精确的结果;验证改进后模型的合理性和其在应用中的有效性。     

Social foraging in stingless bees: how colonies of Melipona fasciata choose among nectar sources

In an experimental set-up, a colony of the stingless bee Melipona fasciata demonstrated its ability to choose the better of two nectar sources. This colony pattern was a result of the following individual behavioural decisions: continue foraging, abandon the feeder, restart foraging and initiate foraging. Only very rarely did individuals switch from one feeder to the other. With the first combination of a rich (2.7 M) and a poor (0.8 M) feeder M. fasciata behaved differently from Apis mellifera. Recruitment occurred to both feeders and the poor feeder was not abandoned completely. When the poor feeder was set to 0.4 M, M. fasciata abandoned the poor feeder rapidly and allocated more foragers to the rich feeder. These patterns were similar to those reported for A. mellifera with the first combination of feeders. Over a sequence of 4 days, experienced bees increasingly determined the colony patterns, and the major function of communication between workers became the reactivation of experienced foragers. The foragers modulated their behaviour not only according to the profitability of the feeder, but also according to previous experience with profitability switches. Thus, experience and communication together regulated colony foraging behaviour. These findings and the results of studies with honeybees suggest that M. fasciata and honeybees use similar decision-making mechanisms and only partly different tools. Received: 21 December 1998 / Accepted: 5 January 1999     

基于VaR的我国煤炭行业金融安全影响因素分析

从金融科学、安全科学角度,提出煤炭行业金融安全的定义,认为煤炭企业融资和投资过程中的金融安全管理是我国能源安全的重要保证。可以从宏观经济状况、融资状况和投资条件3个方面分析影响煤炭行业金融安全的因素。采用金融安全管理中的VaR风险估价方法将煤炭行业金融安全影响指标进行定量化描述,运用Eviews软件构建误差修正模型分析各个影响指标与煤炭行业金融安全之间的长期、短期经济关系,明确二者之间的影响机制。CPI、资金成本率和借款率对煤炭行业金融安全的短期波动有影响;从长期来看,GDP、资金成本率和借款率指标与煤炭金融安全有着正相关关系,CPI、资产负债率和汇率与煤炭金融安全有着负相关关系。     

Inverse modeling to estimate LNAPL plume release timing

Methodologies are presented for dating releases of light nonaqueous phase liquids (LNAPLs) using an inverse modeling approach with simple analytical models. Models for LNAPL plume migration are presented to predict LNAPL plume velocity in the unsaturated and saturated zones as a function of basic soil and fluid properties. A relative mobility factor is introduced for LNAPL movement at the water table that depends primarily on the van Genuchten n parameter (related to the breadth of the soil pore size distribution) and the magnitude of water table fluctuations. Estimated LNAPL plume velocities compare reasonably with more rigorous numerical models, which may be used in cases where data availability warrant the greater effort entailed.Two methods of estimating release timing and its uncertainty are investigated. A direct estimation method is described that determines travel time for a single observed travel distance based on estimated soil and fluid properties. Release date uncertainty may be determined using the first order (FO) or Monte Carlo (MC) methods. The second method for estimating release date involves nonlinear parameter estimation utilizing distance vs. time measurements and other data.A case study is presented for a field site where independent estimates of release timing were obtained from a numerical modeling analysis. Release timing estimates based on direct inversion of the analytical timing model agree well with the numerical analysis. Results for a second field site indicate that release date confidence limits estimated by the FO method, assuming log-normally distributed travel times, are close to values determined by the MC method, which makes no assumption regarding the form of the travel time probability distribution.Results for a hypothetical problem indicate that LNAPL velocity and travel time may be accurately estimated if sufficient data on travel distance vs. time are available. Incorporating prior information on relevant soil and fluid properties into the objective function reduces the uncertainty in release date if prior estimates are accurate. However, biased prior estimates may lead to over- or underestimation of release date uncertainty. Simultaneous estimation of soil and fluid properties and release date is possible if prior information is available to condition the parameter estimates.     

河流污染物通量估算方法分析(Ⅰ)——时段通量估算方法比较分析

通过对河流时段通量所采用的估算方法的误差比较分析,说明了实测河流断面时段通量中时间平均离散通量的贡献;并讨论了污染源的点源、非点源类型的差别对选择年通量估算方法的影响.通过实例探讨了河流长时间通量估算方法的使用范围,对估算方法的取舍原则进行了分析.      

人因失误的机理及其可靠性研究

随着科技的发展 ,在系统安全中 ,机器设备可靠性越来越高 ,由于人本身的复杂性 ,人因失误变得愈来愈严重。本文基于人行为的原理 ,对人因失误的机理、影响人失误的因素、人行为的模型和失误模型及其可靠性的量化进行了分析 ,建立了计算人可靠性的威布尔分布模型 ,并对其参数进行了讨论 ,可用此来评价人的可靠性。     

用马尔可夫模型分析基于通信的列车控制系统(CBTC)的安全性

基于通信的列车控制系统 (CBTC)极有可能成为未来铁路的发展方向 ,只是目前人们对它的安全性还抱有疑虑。笔者给出一种利用马尔可夫模型分析 CBTC安全性的方法。利用系统分解和模型压缩的方法解决状态空间的激增问题。将 CBTC设备分为故障—降级型和故障—安全型两类 ,分别建立子模型 ,分析人员因素及设备故障覆盖率对系统安全性的影响。根据子模型间的独立性 ,将各子模型的事故率相加获得系统的事故率     

APPLICATION OF GREY MODEL TOWARD RUNOFF FORECASTING1

ABSTRACT: A reliable forecasting model is essential in real‐time flood forecasting for reducing natural damage. Efforts to develop a real‐time forecasting model over the past two decades have been numerous. This work applies the Grey model to forecast rainfall and runoff owing to the model's relative ability to predict the future using a small amount of historical data. Such a model significantly differs from the stochastic and deterministic models developed previously. Ten historical storm events from two catchment areas in northern Taiwan are selected to calibrate and verify the model. Results in this study demonstrate that the proposed models can reasonably forecast runoff one to four hours ahead, if the Grey error prediction method is further used to update the output of the model.     

农业科技资源与农业经济发展关系实证

农业科技资源是实现农业发展方式转变和农业可持续发展的重要因素,发展现代农业也迫切需要将农业科技资源转化为现实生产力.为了分析农业科技资源与农业经济发展之间的动态关系,作者选取中国1990-2008年的统计数据,运用协整分析和格兰杰因果关系检验,考察了农业研究与开发机构科技活动经费支出、农业技术人员及农业机械总动力与农业经济增长的内在关系.实证结果表明:农业科技资源与农业经济发展之间存在协整关系,即长期稳定的均衡关系,但在短期内会偏离长期均衡.当偏离均衡时,长期对短期偏离均衡的调整力度为59.8%;存在从农业研究与开发机构科技活动经费支出、农业技术人员到农业经济发展的单向格兰杰因果关系,而反向关系得不到实证支持.但农业机械总动力与农业经济发展之间存在显著的双向格兰杰因果关系.因此,增加农业科技活动经费支出、培养农业技术人才、提高农业机械利用效率是促进农业经济发展的重要路径选择.     

对低浓度环境样品监测的质量控制

通过环境监测中对低浓度环境样品监测所经过的每个步骤可能引入的误差进行分析,找出产生误差的原因,并提出相应的减小或消除误差的措施。