Modelling the reworking effects of bioturbation on the incorporation of radionuclides into the sediment column: implications for the fate of particle-reactive radionuclides in Irish Sea sediments

A microcosm laboratory experiment was conducted to determine the impact of biological reworking by the ragworm Nereis diversicolor on the redistribution of particle-bound radionuclides deposited at the sediment-water interface. Over the course of the 40-day experiment, as much as 35% of a ¹³⁷Cs-labelled particulate tracer deposited on the sediment surface was redistributed to depths of up to 11 cm by the polychaete. Three different reworking models were employed to model the profiles and quantify the biodiffusion and biotransport coefficients: a gallery-diffuser model, a continuous sub-surface egestion model and a biodiffusion model. Although the biodiffusion coefficients obtained for each model were quite similar, the continuous sub-surface egestion model provided the best fit to the data. The average biodiffusion coefficient, at 1.8 ± 0.9 cm² y⁻¹, is in good agreement with the values quoted by other workers on the bioturbation effects of this polychaete species. The corresponding value for the biotransport coefficient was found to be 0.9 ± 0.4 cm y⁻¹. The effects of non-local mixing were incorporated in a model to describe the temporal evolution of measured ⁹⁹Tc and ⁶⁰Co radionuclide sediment profiles in the eastern Irish Sea, influenced by radioactive waste discharged from the Sellafield reprocessing plant. Reworking conditions in the sediment column were simulated by considering an upper mixed layer, an exponentially decreasing diffusion coefficient, and appropriate biotransport coefficients to account for non-local mixing. The diffusion coefficients calculated from the ⁹⁹Tc and ⁶⁰Co cores were in the range 2-14 cm² y⁻¹, which are consistent with the values found by other workers in the same marine area, while the biotransport coefficients were similar to those obtained for a variety of macrobenthic organisms in controlled laboratories and field studies.     

基于需求分析的应急资源结构框架研究

应急资源结构是指在应对公共突发事件中所利用的应急资源的内部联系和一定秩序,构建应急资源结构框架是进行应急资源体系建设的重要基础。本文以2008雪灾和"5.12"汶川大地震的应急管理为案例,分析了在两次自然灾害应急管理中的应急资源需求,对应急资源进行了归类。在此基础上,充分考虑国民经济与社会发展指标体系的现状,构建了层次递阶的应急资源结构框架:第一个层次为应急资源类别,包括应急救援资源、基础设施与服务、专业处置资源和支撑保障资源四大类别;第二个层次为应急资源子类,在每个资源类别下划分若干个应急资源子类;第三个层次为应急资源细目,在每个子类下设计若干应急资源细目。从而形成了以应急救援资源为核心、以基础设施与服务为基础、以专业处置资源为依托、兼顾支撑保障资源的应急资源结构框架。     

Representing general theoretical concepts in structural equation models: the role of composite variables

Structural equation modeling (SEM) holds the promise of providing natural scientists the capacity to evaluate complex multivariate hypotheses about ecological systems. Building on its predecessors, path analysis and factor analysis, SEM allows for the incorporation of both observed and unobserved (latent) variables into theoretically-based probabilistic models. In this paper we discuss the interface between theory and data in SEM and the use of an additional variable type, the composite. In simple terms, composite variables specify the influences of collections of other variables and can be helpful in modeling heterogeneous concepts of the sort commonly of interest to ecologists. While long recognized as a potentially important element of SEM, composite variables have received very limited use, in part because of a lack of theoretical consideration, but also because of difficulties that arise in parameter estimation when using conventional solution procedures. In this paper we present a framework for discussing composites and demonstrate how the use of partially-reduced-form models can help to overcome some of the parameter estimation and evaluation problems associated with models containing composites. Diagnostic procedures for evaluating the most appropriate and effective use of composites are illustrated with an example from the ecological literature. It is argued that an ability to incorporate composite variables into structural equation models may be particularly valuable in the study of natural systems, where concepts are frequently multifaceted and the influence of suites of variables are often of interest.     

Farmer models of socio-ecologic systems: Application of causal mapping across multiple locations

Modelling ecological or environmental problems has potential to provide understanding of the causes of such problems and to indicate how to better manage them. Özesmi and Özesmi (2004) showed that cognitive or causal mapping can be used to develop maps of socio-ecological systems but these maps were based on stakeholders concerned with one ecosystem. This article shows how maps from a number of different dairy farmers in different locations, but each considering his or her own farm, can be used in meta analysis to make maps that represent how farmers think their farm ecosystem works. It also shows that the combination of causal mapping with the additional technique of Q method provides a useful solution to the practical problem of selecting from a sufficiently broad range of factors with potential to use in a map. Causal mapping in single or multiple locations contributes to the goal of using peoples’ knowledge of ecosystems to improve our understanding of socio-ecological systems.     

Ecological Trap for Desert Lizards Caused by Anthropogenic Changes in Habitat Structure that Favor Predator Activity

Abstract: Anthropogenic habitat perturbation is a major cause of population decline. A standard practice managers use to protect populations is to leave portions of natural habitat intact. We describe a case study in which, despite the use of this practice, the critically endangered lizard Acanthodactylus beershebensis was locally extirpated from both manipulated and natural patches within a mosaic landscape of an afforestation project. We hypothesized that increased structural complexity in planted patches favors avian predator activity and makes these patches less suitable for lizards due to a heightened risk of predation. Spatial rarity of natural perches (e.g., trees) in arid scrublands may hinder the ability of desert lizards to associate perches with low‐quality habitat, turning planted patches into ecological traps for such species. We erected artificial trees in a structurally simple arid habitat (similar to the way trees were planted in the afforestation project) and compared lizard population dynamics in plots with these structures and without. Survival of lizards in the plots with artificial trees was lower than survival in plots without artificial trees. Hatchlings dispersed into plots with artificial trees in a manner that indicated they perceived the quality of these plots as similar to the surrounding, unmanipulated landscape. Our results showed that local anthropogenic changes in habitat structure that seem relatively harmless may have a considerable negative effect beyond the immediate area of the perturbation because the disturbed habitat may become an ecological trap.     

Modelling and analysis of sustainable manufacturing system using a digraph-based approach

Abstract

Sustainable manufacturing practices have many benefits like cleaner production, resource efficiency along with economic benefits. Sustainable manufacturing practices focuses on four dimensions environment, economy, business and society. The effective deployment of sustainable concepts mostly depends on interaction of these sustainable dimensions. In this study, an attempt on assessment through modelling has been presented. Mostly two factors determine the sustainable performance of organisation: the performance of the criteria is identified under four dimensions (inheritance) and their interaction (interdependency) among each other. Thus, graph theory-based modelling has been done considering both inheritance and interdependency for computing Overall Organisation Sustainability (OOS) score. Finally, permanent scores for matrices obtained from experts’ team have been computed. OOS score for the organisation has been computed and is compared with the scores of hypothetical scenarios. Through the comparison with hypothetically generated practical best and worst-case scenario, insights have been derived.     

Application of TISM and MICMAC for analysis of influential factors of sustainable development of tablet devices: a case study

Abstract

With the advancements in technology and increase in demand for eco-efficient products, manufacturers are focusing on sustainable development of products. Enticing a huge demand over the recent years, sustainable development of Information and Communication Technology (ICT) products are a subject of interest for most practitioners and academicians. A number of factors are found to influence the sustainable development of ICT products. It is necessary to identify the most important factors and determine the dependencies of factors among themselves. In this regard, a case study has been conducted in the context of sustainable development of tablet devices. The most influential factors have been identified from literature and with experts input. The factor dependencies are established using Total Interpretive Structural Modelling (TISM) methodology. MICMAC analysis is used to classify the factors based on their ability to influence other factors. The output of TISM forms the input for MICMAC analysis. From the study, it was found that the factors, ‘Customer pressure’, ‘Government regulations’, ‘Competitiveness’, ‘Organization initiative’ and ‘Technological advancements’ are the most driving factors. Factors ‘Environmental impact’, ‘Energy efficiency’ and ‘Opportunities to upgrade’ were found to be dependent.     

某三基发射药老化性能退化规律及失效模式探究

目的 获得某三基发射药老化后性能的退化规律,确定其失效模式,预估贮存及使用寿命.方法 根据某三基发射药实际使用环境及方式,采用温度-湿度双应力加速老化试验,模拟装药条件,获得老化样品.以安定剂含量、抗压强度、燃烧性能和机械感度为监测指标,对老化后样品进行测试,探究其性能变化规律,明确失效模式.通过Berthelot方程...     

Mathematical Modelling of Muscle Effect on the Kinematics of the Head-Neck Complex in a Frontal Car Collision: A Parameter Study

A 2-dimensional multibody model of the head-neck complex with muscle elements was developed to estimate the influence of muscles on the kinematics of the head-neck complex in a frontal car collision. With this model the authors evaluated how strongly the calculated influence of muscles depends on 3 important factors: (a) impact severity, (b) reflex time, and (c) parameters that determine characteristics of different components of the muscle model. When muscles were triggered at the beginning of impact, the maximum angle of the head flexion was decreased by the muscles by 40% in a frontal collision with an acceleration of 15g. The influence of muscles was significant for reflex times lower than 60 (80) ms. The calculated influence of muscles was not sensitive to most parameters of the muscle model.     

跨国工程项目安全绩效与安全文化关系模型研究

为探讨跨国工程项目的安全文化构成及其影响绩效的机制,以巴基斯坦工程项目为调查对象,基于扎根理论提出包含管理层观念文化、作业层观念文化、制度文化、物质文化、安全行为及安全结果等6个结构变量的12个假设。运用AMOS软件,构建并验证了国外项目安全文化影响安全绩效的结构方程模型(SEM)。结果显示,管理层观念文化是影响安全绩效的最重要因素,安全制度文化也是相对重要的因素,而受到宗教文化影响的作业层观念文化则是改善安全绩效的难点。最后提出有利于我国跨国施工企业安全文化建设的建议。