四川退耕农户自我发展模式及启示

四川退耕还林工程自1999年启动以来,取得了显著的生态效益和社会经济效益。文章通过对四川退耕还林典型地区的调查,总结出两类主要的退耕农户自我发展模式,并对其优点和存在的问题进行了分析,最后从寻找适合农户自我发展模式,保障农户长远发展和巩固退耕还林成果的角度,总结了许多有益的经验和启示。     

浅析二项分布、泊松分布和正态分布之间的关系

二项分布、泊松分布和正态分布一直是学习和研究概率统计的基础。在一定条件下,这三个分布之间存在着密切关系。文章通过求极限分布,研究了二项分布与泊松分布、二项分布与正态分布之间的关系,并利用特征函数和分布函数相互唯一确定这一性质,分析了泊松分布和正态分布之间的关系。     

Olive oil production and soil conservation in southern Spain, in relation to EU subsidy policies

The European Union spent about two billion ECU per year on subsidies for the olive oil sector, of which Spain received about 35%. For the rainfed areas in southern Spain the olive oil sector is crucial, and so are these subsidies. The European Commission has formulated two options to change the subsidy system, but these do not take the production systems and environmental aspects into account. Many olive plantations are affected by soil erosion. This paper analyses the olive tree production systems in southern Spain, the subsidy systems and the soil erosion problems. It then raises the question whether the subsidies could not be provided in a different way, in order to make olive tree cultivation more sustainable by reducing soil erosion and flood hazard.     

黑龙江省垂直绿化攀缘树种的筛选

在分析垂直绿化植物生长主要限制因子--土壤干旱与贫瘠的基础上,从黑龙江省山地植被中引种栽培19种攀援树种,对其生物学特性、生活习性、抗旱性等关键因素进行了试验研究。根据试验及露地栽培观察结果,采用"百分法"综合评价出17种适宜立体绿化的攀援树种,为立体绿化与植被恢复提供了更多可供参考的植物种类,以满足绿化中对景观多样性、植物多样性的要求。     

Achieving smooth asymptotics for the prices of European options in binomial trees

A new binomial approximation to the Black–Scholes model is introduced. It is shown that, for digital options and vanilla European call and put options, a complete asymptotic expansion of the error in powers of n ^?1 exists. This is the first binomial tree for which an asymptotic expansion has been shown to exist.     

A safe speed guidance model for highways

ABSTRACT

This paper presents a fuzzy logic model to support decisions for the suggested speed limit for sections of highways as they become affected by adverse road conditions, environmental factors and differing traffic levels. The definition of the main factors, and their weight, that reduce safety on highways was conducted by the Delphi method, consulting traffic engineering experts. The survey served as a basis for structuring indicators and indexes in a soft decision tree, structured by a fuzzy logic system. The system can be used to support the decisions of those that manage the roads, indicating to drivers’ speeds, by visual, audible or combined systems.     

湿陷性黄土地区城市绿化与地基变形的关系研究

湿陷性黄土地区绿化带需灌溉,如果灌溉水量过大将会导致湿陷性土层的含水量增大,当含水量增大至湿陷起始含水量时,湿陷性土层开始产生湿陷现象。为了防止湿陷性黄土地区因大量灌溉水进入土中,导致湿陷,本文根据湿陷性土层的湿陷机理及湿陷性黄土的本构关系,提出湿陷性土层上绿化区域防止湿陷的具体方法。     

邯郸市主城区主要行道树的多样性调查分析

本项研究采用抽样调查方法对邯郸市主城区20条主要道路的行道树进行的详细调查,分析邯郸市主城区行道树的物种组成、胸径,探讨多样性指数和行道树绿化发展趋势。结果表明:①邯郸市主城区行道树共有18科25属28种,其中乔木20种,隶属19属14科;行道树种类最多的科是蔷薇科,悬铃木(Platanus hispanica)、国槐(Sophora japonica linn)、紫薇(Lagerstroemia indica)、毛白杨(Populus tomentosa Carr)、栾树(Koelreuteria paniclata Laxm)、银杏(Ginkgo biloba)、臭椿(Ailanthus altissima)、美国白蜡(Fraxinus americana)是邯郸市主城区行道树的骨干树种。②针对邯郸市行道树多样性的不足,提出了邯郸市行道树绿化的发展趋势。     

A hybrid clustering and classification approach for predicting crash injury severity on rural roads

As a threat for transportation system, traffic crashes have a wide range of social consequences for governments. Traffic crashes are increasing in developing countries and Iran as a developing country is not immune from this risk. There are several researches in the literature to predict traffic crash severity based on artificial neural networks (ANNs), support vector machines and decision trees. This paper attempts to investigate the crash injury severity of rural roads by using a hybrid clustering and classification approach to compare the performance of classification algorithms before and after applying the clustering. In this paper, a novel rule-based genetic algorithm (GA) is proposed to predict crash injury severity, which is evaluated by performance criteria in comparison with classification algorithms like ANN. The results obtained from analysis of 13,673 crashes (5600 property damage, 778 fatal crashes, 4690 slight injuries and 2605 severe injuries) on rural roads in Tehran Province of Iran during 2011–2013 revealed that the proposed GA method outperforms other classification algorithms based on classification metrics like precision (86%), recall (88%) and accuracy (87%). Moreover, the proposed GA method has the highest level of interpretation, is easy to understand and provides feedback to analysts.     

Introducing a general class of species diversification models for phylogenetic trees

Phylogenetic trees are types of networks that describe the temporal relationship between individuals, species, or other units that are subject to evolutionary diversification. Many phylogenetic trees are constructed from molecular data that is often only available for extant species, and hence they lack all or some of the branches that did not make it into the present. This feature makes inference on the diversification process challenging. For relatively simple diversification models, analytical or numerical methods to compute the likelihood exist, but these do not work for more realistic models in which the likelihood depends on properties of the missing lineages. In this article, we study a general class of species diversification models, and we provide an expectation-maximization framework in combination with a uniform sampling scheme to perform maximum likelihood estimation of the parameters of the diversification process.