Response of a stream in disequilibrium to timber harvest

Timber was harvested on South Fork of Thomas Creek, White Mountains of Arizona, USA, for the first time in 1978–1979. This caused significant increases in annual flow volumes and annual instantaneous peak flows. North Fork remained untouched, but both streams were in disequilibrium before harvest time. Due to wetter years during the postharvest period, North Fork also experienced some flow increases, but the difference was not significant. Flow increases cause increased erosion in disequilibrium channels. While in South Fork channel cross sections enlarged by 10% since preharvest time, those in North Fork enlarged by only 2.5%. The number of knickpoints tripled in South Fork, which was about double that in North Fork. Knickpoint development resulted in destruction of the natural control structures (log steps and transverse gravel bars) in South Fork (47%), while in North Fork they increased by 23%. Knickpoints are scarps on the channel bed that have the appearance of gully headcuts. The tripling of the number of knickpoints signifies that adjustment processes of the bed profile are intensified drastically in South Fork. The geomorphic changes signify that due to increases in discharge, the extent of disequilibrium is exacerbated in South Fork. Yet, volumes of erosion are relatively small, as will be sediment volumes leaving the watershed at a given time, because of the stepwise sediment transport occurring in this ephemeral stream.     

When is overfishing underfishing?

The term overfishing is being used with increasing frequency to designate an undesirable level of fisheries exploitation. All too often, however, the term is taken as being self-evident. This article demonstrates that many definitions of overfishing are possible, depending essentially on what objective is being pursued for the fishery. Various possible biological and economic objectives are considered, both in a static and dynamic model of the fishery. Consideration is given to the best utilization of the fish stock from the viewpoint of the individual fishermen as well as that of society. It is shown that overfishing by one definition may be underfishing by another, and it is concluded therefore that anyone using the term overfishing ought, as a matter of course, to define it.     

地震活动趋势的多层递阶预报

多层递阶预报是动态系统的新型统计预报理论,由于它把动态系统看成是一个时变参数系统,因而与客观实际较为符合,预报误差也相对较小,利用它来预报一个地区未来的地震活动趋势,具有一定的实用价值。     

The time-varying factors influencing the recycling rate of products

In Europe targets have been laid down by EU legislation for the recycling rate of end-of-life vehicles to be achieved within the nearby future. It is illustrated in this paper that the definition of the recycling rate and the realisation of the imposed targets are very much dependent on different parameters such as the changing lifetime of the product and product design. It may seem obvious that the recycling rate is determined by various time-varying factors, however, this paper endeavours to describe and quantify the role of these factors on the recycling rate over time by the use of a dynamic systems model. This model permits the prediction of the recycling rate as a function of the numerous presented parameters, changing design scenarios etc. In addition, different definitions of the recycling rate will be presented and discussed. This will lead to a better understanding of the parameters affecting the recycling system and a more precise understanding of the recycling targets and their realisation as imposed by EU legislation. This paper focuses on cars, but the discussion and the definitions derived are equally valid for any end-of-life product.     

关于防灾工程的投资决策问题

本文对研究防灾工程动态投资决策理论和方法的意义进行了阐述;对灾害的定义、灾害的共性、灾害的分类和开展一般性防灾投资决策理论和方法研究的可行性进行了讨论;阐明了防灾工程动态投资决策的概念和特点;提出了防灾工程的抗力、灾损度、灾害的灾害势等概念;提出了防灾工程动态投资决策准则。     

基于ADAMS/Rail的直线电机轨道交通安全性研究

阐述了直线电机轨道交通的技术特点,并就其安全评价体系做了介绍,应用ADAMS/Rail软件分别建立了轮对、构架、悬挂系统、止挡、自导向径向转向架、直线电机以及车体的模型,并考虑轮轨关系组合为直线电机轨道交通的车辆-轨道耦合动力学整体模型,进行了大量的计算仿真。笔者主要以脱轨系数为例进行了动力响应分析,给出考虑了径向转向架和直线电机后的安全评判指标,比较了与径向转向架和未安装直线电机的区别,验证了模型的正确性和有效性。为后续研究直线电机轨道交通车辆-轨道耦合动力学模型提供了理论基础,从而可以进一步从安全性角度研究线路设计参数。为我国今后直线电机轨道交通建设就线路参数对车辆运行安全性的影响研究方面起到理论指导作用。     

Combining HAZOP with dynamic simulation—Applications for safety education

A quantitative variation of the hazard and operability analysis (HAZOP) procedure is demonstrated. The process is divided into sections and dynamic models of the separate sections are prepared. Those models are used in the framework of the HAZOP procedure to determine the magnitude of the deviations from normal operation conditions that may lead to serious accidents and to test design modification to improve the safety characteristic of the process. A process involving an exothermic reaction conducted in a semi-batch reactor is used to demonstrate the advantages of the proposed procedure and its application for safety education and operator training. The programs used for simulating the reactor are available at: ftp://ftp.bgu.ac.il/shacham/OctanoneProd/.

It is shown that the use of those programs can enhance considerably the safety education by providing tools for systematic screening of process deviation associated with possible hazardous events, determining the threshold values that may lead to such events and enabling the examination of a particular design for the adequate safe range of operation.     

大庆市土地利用动态变化分析与预测

本文主要以土地利用类型的时空变化为研究重点,通过数学建模,来研究大庆市土地利用的时空演变,尤其重点研究大庆市土地利用动态变化的预测。     

Hydrological Responses to Climate and Land‐Use Changes along the North American East Coast: A 110‐Year Historical Reconstruction

The North American east coast (NAEC) region experienced significant climate and land‐use changes in the past century. To explore how these changes have affected land water cycling, the Dynamic Land Ecosystem Model (DLEM 2.0) was used to investigate the spatial and temporal variability of runoff and river discharge during 1901‐2010 in the study area. Annual runoff over the NAEC was 420 ± 61 mm/yr (average ± standard deviation). Runoff increased in parts of the northern NAEC but decreased in some areas of the southern NAEC. Annual freshwater discharge from the study area was 378 ± 61 km³/yr (average ± standard deviation). Factorial simulation experiments suggested that climate change and variability explained 97.5% of the interannual variability of runoff and also resulted in the opposite changes in runoff in northern and southern regions of the NAEC. Land‐use change reduced runoff by 5‐22 mm/yr from 1931 to 2010, but the impacts were divergent over the Piedmont region and Coastal Plain areas of the southern NAEC. Land‐use change impacts were more significant at local and watershed spatial scales rather than at regional scales. Different responses of runoff to changing climate and land‐use should be noted in future water resource management. Hydrological impacts of afforestation and deforestation as well as urbanization should also be noted by land‐use policy makers.     

Modeling of the venting of an untempered system under runaway conditions

The prediction of the consequences of a runaway reaction in terms of temperature and pressure evolution in a reactor requires the knowledge of the reaction kinetics, thermodynamics and fluid dynamics inside the vessel during venting. Such phenomena and their interaction are complex and yet to be fully understood, especially reactions where the pressure generation is totally or partially due to the production of permanent gases (gassy or hybrid systems). Moreover, these phenomena cannot be easily determined by laboratory scale experiments. In this paper, a dynamic model developed to simulate the behavior of an untempered reacting mixture during venting is presented. The model provides the temperature, pressure and mass inventory profiles before and during venting. A sensitivity study of the model was performed. This modeling work provides some insight regarding the interpretation of the data obtained from untempered system venting experiments. The outcome of this work contribute to improving the design of emergency relief systems for hybrid and gassy systems, where significant progress is still to be made in the experimental and modeling areas.