High individual variation in pheromone production by tree-killing bark beetles (Coleoptera: Curculionidae: Scolytinae)

Aggregation via pheromone signalling is essential for tree-killing bark beetles to overcome tree defenses and reproduce within hosts. Pheromone production is a trait that is linked to fitness, so high individual variation is paradoxical. One explanation is that the technique of measuring static pheromone pools overestimates true variation among individuals. An alternative hypothesis is that aggregation behaviour dilutes the contribution of individuals to the trait under selection and reduces the efficacy of natural selection on pheromone production by individuals. We compared pheromone measurements from traditional hindgut extractions of female southern pine beetles with those obtained by aerating individuals till they died. Aerations showed greater total pheromone production than hindgut extractions, but coefficients of variation (CV) remained high (60-182%) regardless of collection technique. This leaves the puzzle of high variation unresolved. A novel but simple explanation emerges from considering bark beetle aggregation behaviour. The phenotype visible to natural selection is the collective pheromone plume from hundreds of colonisers. The influence of a single beetle on this plume is enhanced by high variation among individuals but constrained by large group sizes. We estimated the average contribution of an individual to the pheromone plume across a range of aggregation sizes and showed that large aggregation sizes typical in mass attacks limit the potential of natural selection because each individual has so little effect on the overall plume. Genetic variation in pheromone production could accumulate via mutation and recombination, despite strong effects of the pheromone plume on the fitness of individuals within the aggregation. Thus, aggregation behaviour, by limiting the efficacy of natural selection, can allow the persistence of extreme phenotypes in nature.     

事故类型因子对人群聚集风险影响的综合度量

公共场所事故以人群聚集为条件,人群风险的控制和减缓不同于一般工业危险源风险,不确定性和随机性大,风险触发因子较多,难以控制.将人群聚集风险影响因子归结为心理扰动因素和物理扰动因素两大类,并用综合扰动强度表示两者之和.通过对公共场所内火灾、爆炸、中毒、结构失效以及人群拥挤踩踏5类事故统计资料的分析表明,5个影响因子满足林德伯格条件,依据中心极限定理,综合扰动强度可以近似用1个正态分布加以描述.以火灾事故发生的研究作为基础,推广到其余4个因子,通过李雅普诺夫定理得出公共场所中综合扰动强度的概率密度函数,并通过傅立叶级数将其表征为多个余弦函数的线性组合,并根据统计资料进行了实例分析.最终该方法可以通过某一类型公共场所的事故发生次数,得到统计平均意义下,该场所周边环境存在的各种扰动因素对聚集人群影响的大小.     

地震作用下滑坡永久位移预测

在地震区滑坡防治结构的抗震设计中,滑坡体自身的稳定安全性可利用其地震作用下产生的永久位移直接判断,可见对其地震永久变形的预测至关重要。因此,以极限分析上限定理为基础,分别针对平移式和旋转式两种滑坡滑移形式,推导出这两种滑移形式下滑坡体产生永久位移的临界加速度,考虑地震输入能量及结构能量耗散之间的平衡关系并建立预测地震作用下滑坡永久位移的计算方法。最后,通过算例表明其合理性。     

Rao-Blackwell versions of the Horvitz-Thompson and Hansen-Hurwitz in adaptive cluster sampling

Thompson (1990) introduced the adaptive cluster sampling design and developed two unbiased estimators, the modified Horvitz-Thompson (HT) and Hansen-Hurwitz (HH) estimators, for this sampling design and noticed that these estimators are not a function of the minimal sufficient statistics. He applied the Rao-Blackwell theorem to improve them. Despite having smaller variances, these latter estimators have not received attention because a suitable method or algorithm for computing them was not available. In this paper we obtain closed forms of the Rao-Blackwell versions which can easily be computed. We also show that the variance reduction for the HH estimator is greater than that for the HT estimator using Rao-Blackwell versions. When the condition for extra samples is 0$$ " align="middle" border="0"> , one can expect some Rao-Blackwell improvement in the HH estimator but not in the HT estimator. Two examples are given.     

安全的本质、规律和定理

揭示安全的本质和规律,确认安全、安全规律和安全定理的概念,指导人们从本质上超前有效预防事故发生,这不仅对安全的认识是一次理性飞跃,而且对如何预防事故发生和达到征服事故的目的也是一次重大突破。     

影子价格与企业管理决策

影子价格实际上是在最优决策下对一种资源效用价值的估价,它真实反映了资源在经济结构中对目标函数值的影响和贡献大小,资源的影子价格越高,表明该种资源对总目标的贡献越大.影子价格有利于资源的优化配置,并为调整产品结构、优化产业结构、增加经济效益提供了一个十分重要和有价值的数量依据.     

基于最小路集求可靠度函数的系统Bayes置信限评估

阐述了复杂系统的Bayes置信限评估原理,并将其与最小路集求可靠度函数的方法相结合,对已知系统可靠性框图或可靠度函数的复杂系统进行可靠度置信限评估.该方法便于工程应用,对于大型复杂系统可靠性评定,具有重要的参考价值.     

‘Enclosing country park land and the conservation of military heritage:’ an Ostromian interpretation of the fools’ paradise

British colonial military heritage structures in Hong Kong are in a state of ruin and government neglect. Urgent attention is required in the form of active management to avoid the loss of valuable heritage resources and the negative impact on the landscape and environment. This paper explores two possible alternatives – user participation and social entrepreneur participation – to achieve innovative solutions to rent dissipation of these structures situated in isolated areas within protected-area boundaries, with a focus on a specific case. Emphasis is placed on fostering public participation, involving the allocation of some property rights. Elinor Ostrom's diagnostic approach to common-pool resource problems is applied to both solutions to determine the conditions necessary to achieve the objectives. The discussions are informed by social entrepreneurship principles and a version of the Coase Theorem, the latter coinciding with Ostrom's view regarding the role of property rights in achieving sustainable outcomes.     

我国排污权交易制度的相关问题探析

随着经济的快速发展,工业生产中排放的废弃物越来越多,由此造成的环境压力也越来越大,随着可持续发展概念的不断提出,排污权交易制度也被逐渐确定下来,该制度在我国的施行不但具有可行性,更加具有必要性。本文对我国当前排污权制度实施的不足之处进行了详细分析,并提出了我国排污权制度未来的完善路径。     

流域生态用水分配的协调性评价研究

流域生态用水分配的合理性来源于生态需水的自身满意度和流域子系统生态用水的协调性，因而评价流域生态用水分配的协调性非常必要。本文应用整体分析法，基于最大概率乘积定理和“木桶法则”，构造了流域生态用水分配系统的协调性评价模型，分析了各子系统生态用水分配的合理度，完善了流域生态用水分配合理性的评价内容和方法。以黄淮海流域为例，得到黄淮海流域生态用水分配协调度分别为O．9307．0．9603．0．8099．均小于协调度为0．996的一般标准，故其协调度都比较低，而流域之间的差异源于子系统生态需水自身满意度的差异程度不同。考虑这种用水协调性。流域生态用水系统的合理性程度在生态需水自身满意度的基础上各有不同程度的降低。利用该模型还可以对未来生态用水分配合理性进行评价．获得最佳分配方案，以获得最大的生态经济效益。