Designing field experiments which are subject to representation bias

The term 'representation bias' is used to describe the disparities that exist between treatment effects estimated from field experiments, and those effects that would be seen if treatments were used in the field. In this paper we are specifically concerned with representation bias caused by disease inoculum travelling between plots, or out of the experimental area altogether. The scope for such bias is maximized in the case of airborne spread diseases. This paper extends the work of Deardon et al. (2004), using simulation methods to explore the relationship between design and representation bias. In doing so, we illustrate the importance of plot size and spacing, as well as treatment-to-plot allocation. We examine a novel class of designs, incomplete column designs, to develop an understanding of the mechanisms behind representation bias. We also introduce general methods of designing field trials, which can be used to limit representation bias by carefully controlling treatment to block allocation in both incomplete column and incomplete randomized block designs. Finally, we show how the commonly used practice of sampling from the centres of plots, rather than entire plots, can also help to control representation bias.     

浅议居住区的绿化问题

针对当前城镇建设中较为活跃的居住区建设在规划、设计、施工中较重视硬质景观,而真正对居住环境起着改善作用的绿化,因其受建成速度的限制而得不到重视的问题,提出了居住环境应以绿化为主,应服从生态原则,从设计思想等各个环节予以保证实施的理念.     

决策树算法在反洗钱领域中的应用研究

简要介绍了决策树算法的基本原理,并对这一算法的实际应用进行举例,然后针对洗钱活动的特征,寻找出在反洗钱领域中应用决策树算法的各个属性,最后通过给出一个具体的训练集学习,详细计算了面向账户的反洗钱决策树的生成过程并对其结构进行了优化。     

"人类纪"新地质时期理论研析之三——"自然选择进化论"还是"生存斗争进化论"

生命的历史是漫长攸久的演替过程表征着植物群落演替进化的周期性特征,即“演替-分化-灭绝-突变-进化”的过程。历经变异多样化、物种形成、适应性族群演替进化、种群散布、转化传递和演替进化。就是通过这一过程,最终导致了现代人类社会的产生。在这一地球历史过程中,生物的进化经历着严峻状态的地球环境,从单细胞生物开始直至高等动物产生,一路历经为生存而艰难挣扎斗争,在斗争中求生存,在生存中力图挣扎前进。为笔者曾提出的“生存斗争进化论”[1]提供了进一步的佐证。     

绍兴地区电池厂周围环境中铅的含量及其评价

对绍兴地区电池厂周围土壤、水和植物中的重金属铅含量采用火焰原子吸收光谱法进行了测定 .结果表明 ,土壤、水和植物中铅污染都较严重 .土壤中铅的含量是清洁对照区的 2 .2～ 5 .8倍 ,水体中铅的含量是清洁对照区的 2 0 .8～ 5 19倍 ,植物根、茎、叶和果实中铅的含量分别是清洁对照区的 3.0～ 6 .8倍、12 .1～ 17.4倍、14 .5～ 17.1倍和 2 .5～ 8.9倍 .     

Analyses of spatial patterns and population processes of clonal plants

The nonrandom spatial structure of terrestrial plants is formed by ecological interactions and reproduction with a limited dispersal range, and in turn this may strongly affect population dynamics and population genetics. The traditional method of modelling in population ecology is either to neglect spatial pattern (e.g. in transition matrix models) or to do straightforward computer simulation. We review here three analytical mothods to deal with plant populations in a lattice-structured habitat, which propagate both by seeds that scatter over the whole habitat and by vegetative reproduction (producing runners, rhizomes, etc.) to neighboring vacant sites. [1]Dynamics of global and local densities: Dynamical equations of population density considering nearest-neighbor correlation (spatial clumping) are developed as the joint dynamics of global average density and local density (comparable to mean crowding) based onpair approximation. If there is a linear trade-off between seed production and vegetative reproduction, the equilibrium abundance of the population may be maximized by engaging both means of reproduction. This result is accurately predicted by the pair approximation method, but not by mean-field approximation (neglect of spatial structure). [2]Cluster size distributions: Using global and local densities obtained by pair approximation, we predicted cluster size distribution, i.e. the number of clusters of occupied sites of various sizes. [3]Clonal identity probability decreasing with distance: Multi-locus measurement of allozymes or other neutral molecular markers tells us whether or not a given pair of individuals belong to the same clone. From the pattern of clonal identity probability decreasing with the distance between ramets, we can estimate the relative importance of two modes of reproduction: vegetative propagation and sexual seed production.     

吉林西部水生植物资源的调查

自2003年至2005年,笔者对吉林西部的水生植物进行了调查,初步查明,吉林西部有水生植物30科,32属,72种,其中可食用的6种,药用的27种,观赏的5种,饲用的44种,编织用的9种,部分植物兼具多种用途。     

重要经济植物——罗布麻

本文对罗布麻的形态特征、自然分布、在纺织、做保健品、药用成份及应用、做蜜源植物等方面进行了综述。     

风险和不确定下的供应商数量优化问题研究

考虑企业所面临的不确定性环境和各种风险,以效用值和概率为变量,建立基于风险和不确定环境下供应商数量优化方法的决策树模型;从效用值和风险均衡的角度出发,讨论多供应商策略优于单供应商策略的条件和模型参数,并通过具体数值的计算分析采购方应选择的最优供应商数量随各参数变化的规律。     

由全局到局部的树木建模方法

基于全局到局部的树木计算机建模方法,生成大型场景构造中的树木模型,由用户设定树冠形状来确定枝条的生长范围,采用最短距离和分形方法控制枝条的生成。