单纤维过滤介质表面尘粒捕集的随机模拟

基于控制面概念和粒子运动轨迹计算,建立单纤维过滤介质表面尘粒捕集的三维随机计算模型,采用Ku-wabara流场表征单纤维表面的气流绕流特征。计算分析了St数、无量纲粒径及单纤维过滤模型填充密度对沉积物形态结构和积尘状态下单纤维捕集效率的影响。结果指出,St数对沉积物形态结构具有显著作用,随St数减小,沉积物由紧密的堆积结构演变为分叉显著的树枝状结构。模拟结果还发现,无论过滤条件如何变化,无量纲单纤维捕集效率随捕集粒子数呈近似线性增加关系。     

How the redox state of tobacco 'Bel-W3' is modified in response to ozone and other environmental factors in a sub-tropical area?

This study intended to determine whether the redox state in plants of Nicotiana tabacum ‘Bel-W3’ fluctuates in response to the environmental factors in a sub-tropical area contaminated by ozone (São Paulo, SE - Brazil) and which environmental factors are related to this fluctuation, discussing their biomonitoring efficiency. We comparatively evaluated the indicators of redox state (ascorbic acid, glutathione, superoxide dismutase, ascorbate peroxidase, and glutathione reductase) and leaf injury in 17 field experiments performed in 2008. The redox state was explained by the combined effects of chronic levels of O₃ and meteorological variables 4-6 days prior to the plant sampling. Moderate leaf injury was observed in most cases. The redox state of tobacco decreases few days after their placement in the sub-tropical environment, causing them to become susceptible to oxidative stress imposed by chronic doses of O₃. Its bioindicator efficiency would not be diminished in such levels of atmospheric contamination.     

Living at the Edge: Local versus Positional Factors in the Long‐Term Population Dynamics of an Endangered Orchid

Abstract: Populations at the margin of geographic ranges of distribution have been considered more vulnerable than central ones, but recent reviews have caste doubt on this generalization. We examined the reproductive and demographic performance of a rare Euroasiatic orchid (Cypripedium calceolus) at its southwesterly range limit and compared our findings with those of previous studies of nine central populations at the center of the orchid's range. We sought to test the central‐marginal model and to evaluate factors involved in long‐term performance of forest Eurosiberian species with peripheral populations in southern European mountains. We characterized (structure, temporal fluctuations, herbivory, reproductive success, and recruitment at different habitats) four Pyrenean populations of C. calceolus of different sizes (5–3500 ramets) and monitored three of them for up to 13 years. Two quantitative stochastic models (count data and matrix models) were used to assess population trends and viability and the effect of herbivory. Contrary to expectations, and despite the negative effect of sporadic events of herbivory, the peripheral populations we studied (except the smallest one) performed similarly or better than populations occurring in central part of the species’ range in terms of reproductive success and population growth rates. Landscape changes over the last 50 years suggest that natural reforestation could be involved in the success of this plant at its southern limit. Forest expansion in the mountain regions of southern Europe may provide new opportunities for plants with geographic distributions centered mainly at higher latitudes and give some hope for their recovery in future scenarios dominated by biodiversity loss.     

基于随机Petri网的平交道口建模及事故率分析

基于公路道口使用者的违规进入及违规人数比例是道口发生事故的主要原因为背景,分析道口使用者违规进入道口前的平均等待时间及违规比例,列车在各个区段的时间特性与道口事故率之间的定量关系。采用随机Petri网基于道口公路使用者、道口铁路列车的经过道口过程、道口安全防护系统功能及三者之间的相关性进行建模及事故率分析。根据模型的仿真表明:当列车由道口传感器区进入接近区的时间和由接近区进入道口的时间由随机值变为固定值时,道口事故率大大降低;公路使用者在违规进入道口前,等待某个时间后进入道口发生事故的风险最大。当列车由接近区进入道口的时间为随机值时,公路使用者的违规比例增加会明显加大事故率。     

Integrating intraseasonal grassland dynamics in cross-scale distribution modeling to support waterbird recovery plans

Despite much discussion about the utility of remote sensing for effective conservation, the inclusion of these technologies in species recovery plans remains largely anecdotal. We developed a modeling approach for the integration of local, spatially measured ecosystem functional dynamics into a species distribution modeling (SDM) framework in which other ecologically relevant factors are modeled separately at broad scales. To illustrate the approach, we incorporated intraseasonal water-vegetation dynamics into a cross-scale SDM for the Common Snipe (Gallinago gallinago), which is highly dependent on water and vegetation dynamics. The Common Snipe is an Iberian grassland waterbird characteristic of European agricultural meadows and a member of one of the most threatened bird guilds. The intraseasonal dynamics of water content of vegetation were measured using the standard deviation of the normalized difference water index time series computed from bimonthly images of the Sentinel-2 satellite. The recovery plan for the Common Snipe in Galicia (northwestern Iberian Peninsula) provided an opportunity to apply our modeling framework. Model accuracy in predicting the species’ distribution at a regional scale (resulting from integration of downscaled climate projections with regional habitat–topographic suitability models) was very high (area under the curve [AUC] of 0.981 and Boyce's index of 0.971). Local water-vegetation dynamic models, based exclusively on Sentinel-2 imagery, were good predictors (AUC of 0.849 and Boyce's index of 0.976). The predictive power improved (AUC of 0.92 and Boyce's index of 0.98) when local model predictions were restricted to areas identified by the continental and regional models as priorities for conservation. Our models also performed well (AUC of 0.90 and Boyce's index of 0.93) when projected to updated water-vegetation conditions. Our modeling framework enabled incorporation of key ecosystem processes closely related to water and carbon cycles while accounting for other factors ecologically relevant to endangered grassland waterbirds across different scales, allowed identification of priority areas for conservation, and provided an opportunity for cost-effective recovery planning by monitoring management effectiveness from space.     

HYDROLOGIC DESIGN CONSIDERATIONS OF CONSTRUCTED WETLANDS FOR URBAN STORMWATER RUNOFF1

ABSTRACT: The successful design of constructed wetlands requires a continuous supply of water or vegetation that can withstand drought conditions. Having a constant water source is the best alternative to insure species diversity throughout the season. Consequently, detention structure designs should be based on times between events as well as on hydrologic return periods, since between events is when most evaporation and infiltration losses are likely to occur. In arid or semi-arid environments, this is a difficult process because of long interevent times and seasonal changes in precipitation patterns. This discussion is predicated on the assumption that phytoplankton, epiphytic algae, and emergent vegetation require moist conditions to be effective at removing nutrients, metals and other pollutants. There are drought tolerant species of vegetation that can be used in constructed wetlands but it may take several days to re-establish the attached bacteria communities necessary for optimum pollutant removal. This paper examines a stochastic framework to examine the probability of extended dry periods based on historic rainfall data. The number of consecutive dry days is selected for a specified level of assurance. By multiplying this value by the sum of daily system losses, an overall pond volume can be determined that ensures a minimum depth of water. To illustrate the utility of the approach, the method is applied to a site in Spokane, Washington.     

基于竞争失效的导弹机电产品可靠性评估

目的 解决导弹机电产品退化-突发竞争失效模式下的可靠性评估问题。方法 对导弹典型机电产品电机进行贮存失效分析,同时考虑双参数退化失效和突发失效对电机贮存可靠性的影响。首先,以具有随机效应的非线性Wiener过程描述电机贮存退化失效过程中的非线性、随机性和样本差异性。然后,采用Weibull分布描述突发失效过程规律,并考虑退化程度对突发失效的影响。最后,利用Copula函数刻画退化性能参数之间的相互作用关系,建立双参数退化-突发竞争失效模型,并给出基于两步极大似然估计的参数估计方法。结果 以仿真导弹电机退化突发失效数据为例进行分析,实现了基于双参数退化-突发竞争失效模型的系统可靠性评估,得到电机贮存5 a时的可靠度估计值为0.465。结论 所构建的双参数随机退化与突发失效相关的竞争失效模型有效,为导弹机电产品可靠性验证评估及寿命预测提供了相应的理论依据。     

环境评价Petri网理论可移植性的方法学研究

从复杂系统、开放式巨系统仿真的角度分析,环境影响评价工程分析项目的系统属性为离散事件动态系统,而污染物的产生、排放过程属于随机过程,所以,需要采用复杂系统分析的方法对现有的环评工程分析理论进行改进。Petri网理论是分析离散事件动态系统的方法之一,其特点也非常适合对现今的环评工程分析方法进行改进。将Petri网的基础理论与环评理论相融合,使Petri网理论拥有了系统的环评学释义,进而为将Petri网理论引入环评科学开辟了道路。     

The impact of privatization approaches on the productivity growth of the water industry: A case study of Chile

The water industry faces the challenge of implementing privatization reforms. This process mainly adopts the following two approaches: the privatization of public water and sewerage services (WSS) and the privatization of water companies’ ownership. This paper investigates the impact of both privatization approaches on changes in productivity in the water industry. In doing so, the Luenberger productivity indicator (LPI) was computed for a sample of Chilean water and sewerage companies (WaSCs) for the period 1997–2013. Unlike the most commonly applied index (Malmquist productivity index), the LPI simultaneously takes into account output expansion and input contraction. The results evidenced that productivity in the Chilean water industry decreased after its privatization. However, in the sub-periods in which the ownership of WaSCs was privatized, the productivity of the water industry increased due to technical improvements. On the other hand, the concession of WWS to private WaSCs involved a regression in productivity. From a policy perspective, regulators and managers of WaSCs at the international level can learn important lessons from the Chilean case to improve the productivity of the water industries in their countries.     

Zero-inflated models with application to spatial count data

Count data arises in many contexts. Here our concern is with spatial count data which exhibit an excessive number of zeros. Using the class of zero-inflated count models provides a flexible way to address this problem. Available covariate information suggests formulation of such modeling within a regression framework. We employ zero-inflated Poisson regression models. Spatial association is introduced through suitable random effects yielding a hierarchical model. We propose fitting this model within a Bayesian framework considering issues of posterior propriety, informative prior specification and well-behaved simulation based model fitting. Finally, we illustrate the model fitting with a data set involving counts of isopod nest burrows for 1649 pixels over a portion of the Negev desert in Israel.