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651.
Although associations between myrmecophytes and their plant ants are recognized as a particularly effective form of protective
mutualism, their functioning remains incompletely understood. This field study examined the ant-plant Hirtella physophora and its obligate ant associate Allomerus decemarticulatus. We formulated two hypotheses on the highly specific nature of this association: (1) Ant presence should be correlated with
a marked reduction in the amount of herbivory on the plant foliage; (2) ant activity should be consistent with the "optimal
defense" theory predicting that the most vulnerable and valuable parts of the plant are the best defended. We validated the
first hypothesis by demonstrating that for ant-excluded plants, expanding leaves, but also newly matured ones in the long
term, suffered significantly more herbivore damage than ant-inhabited plants. We showed that A. decemarticulatus workers represent both constitutive and inducible defenses for their host, by patrolling its foliage and rapidly recruiting
nestmates to foliar wounds. On examining how these activities change according to the leaves’ developmental stage, we found
that the number of patrolling ants dramatically decreased as the leaves matured, while leaf wounds induced ant recruitment
regardless of the leaf’s age. The resulting level of these indirect defenses was roughly proportional to leaf vulnerability
and value during its development, thus validating our second hypothesis predicting optimal protection. This led us to discuss
the factors influencing ant activity on the plant’s surface. Our study emphasizes the importance of studying both the constitutive
and inducible components of indirect defense when evaluating its efficacy and optimality. 相似文献
652.
PROBLEM: In today's economic environment, enterprises may not be able to fund every new project aimed at promoting health and safety in the workplace. Company level economic evaluation of interventions can provide guidance in sound business decision-making. The Economic Evaluation of Occupational Health and Safety Interventions at the Company Level Meeting brought together members of the global occupational safety and health community interested in encouraging the use of economic knowledge and tools to evaluate economic gains from occupational health and safety interventions. DISCUSSION: Discussions of the six models presented explored similarities, reliability, and potential use by corporate enterprises, small and medium enterprises, developing and transitioning nations, and economic theorists. Each group provided specific projects that could be pursued to advance knowledge in the area of economic evaluation at the company level. CONCLUSION: This conference established pathway to incorporate economic evaluation of health and safety interventions or programs at the workplace. 相似文献
653.
采空区场流安全理论及其研究的新进展 总被引:8,自引:2,他引:6
李宗翔 《中国安全科学学报》2005,15(12):85-88
提出采空区场流安全理论的概念,并对采空区场流流态、瓦斯涌出和自燃“三带”理论及自燃温度等数值模拟计算的发展历程进行概要总结;分析了当前采空区场流安全理论研究的最新进展和发展趋势。指出目前的现代通风安全理论研究正处在前所未有的历史变革时期,即从网络流通风安全理论到场流安全理论的过渡与统一。采空区问题(瓦斯涌出和自燃)应综合考虑特定开采条件下的采场漏风与供氧系统的背景环境。其理论研究的主流方向应是基于场流方法的灾害与各因素影响关系的分析,重点是灾害机理和多灾害间耦合等一般规律;技术手段是多孔介质渗流力学、多相气体扩散、综合传热理论和有限元数值模拟方法,关键是模型求解的收敛稳定性和流场分布解问题。 相似文献
654.
《组织行为杂志》2017,38(8):1183-1195
Using conservation of resources theory, we challenge traditional unity of command models of leadership and propose that a dual‐leadership framework can serve as a potential solution to the inherent challenges of innovation. Leading for innovation demands are depicted as uniquely disparate from other forms of leadership, resulting in several types of conflict and resource depletion for individual leaders. We contend that this exploration–exploitation role conflict and the resulting need to manage incongruent role identities produce stress, strain, and resource depletion that in turn hamper innovative goal achievement for both a single leader directly and via subordinates more indirectly. We propose, however, that as an extension of the resource investment tenet of the conservation of resources theory, a dual‐leadership approach may alleviate many of these challenges for innovation. Specifically, the addition of a second leader can add resources to innovation and in turn decrease the role conflict inherent in managing the generation and implementation of creative ideas. Limitations and areas for future research are offered. 相似文献
655.
656.
苯作为垃圾中普遍存在的成分是形成多氯二苯并对二噁英/呋喃(PCDD/Fs)的重要前驱物之一.应用密度泛函理论(DFT)在B3LYP/6-311+G (d,p)水平上研究了苯生成PCDD/Fs的两阶段气相反应机理,获得相关基元反应的势垒与反应热.采用隧道效应校正的变分过渡态理论(VTST)对300~1300K的各基元反应进行速率常数计算.结果表明:苯的氯化过程在合成PCDD/Fs各基元反应中势垒最高,是整个过程的控速步骤;氯酚更有可能被HO·进攻氯苯发生亲核反应后经分子内脱氢形成;邻位Cl能提高芳香烃H的抽取势垒,降低分子反应活性;苯氧自由基经碳碳或碳氧耦合二聚化过程形成不同PCDD/Fs存在竞争机制.相关计算结果可以用于在总二噁英产量基础上评估由苯产生的PCDD/Fs贡献率. 相似文献
657.
Ian Christoplos 《Disasters》1998,22(1):1-20
The role of local service institutions is not a major focus of current discourse on humanitarianism and complex emergencies. These institutions, in the few places where they are mentioned, are usually presented as either the seed of civil society and future democracy, or as pawns and components of the predatory economic, political and military élites. Few would deny that examples can be found which conform to both of these stereotypes. This simplistic representation of local institutions ignores the perspectives of the actors themselves — the nurses, extension agents, school teachers and others who actually staff most NGO-supported projects. The debate has focused on what ‘we’ should do; the moral dilemmas of aid agencies and their expatriate staff, inevitably leading to the question of whether or not humanitarian workers should stay or leave situations in which aid may be causing more harm than good. Without denying the fundamental importance of these issues, it is important to consider also how the discourse has unfortunately moved away from those humanitarian workers who have no such choice, since they live there. Current concerns about keeping humanitarian aid from feeding local political and military struggles may inadvertently and paradoxically serve to constrain room for man?uvre in the field, particularly among those individuals with the greatest tacit understanding of the predatory environment. There is a need to understand how actors in local service institutions make sense of their own situations, including the factors which frame their moral dilemmas and their day-to-day choices. By analysing the organisational processes within local service institutions, this study is intended to provoke consideration of how these individuals and their institutions may be effectively supported in complex emergencies through a focus on how they themselves deal with danger and complexity. It is suggested that there is a value in considering the lessons learnt in recent years about how service organisations in the North function in turbulent environments. This experience points to the importance of allowing workers the discretion to develop a relationship with their clients, and in so doing make sense of a confusing and ambivalent environment. 相似文献
658.
The 1994 Northridge, California earthquake has proven to be one of the most costly disasters in United States history. Federal and state assistance programmes received some 681,000 applications from victims for various forms of relief. In spite of the flow of US$11 billion in federal assistance into Los Angeles and Ventura counties, many victims have failed to obtain adequate relief. These unmet needs relate to the vulnerability of particular class and ethnic groups. In response to unmet needs, a number of non-governmental organisations (NGOs) have become involved in the recovery process. This paper, based on evidence collected from hundreds of in-depth interviews with the people involved, examines the activities of several community-based organisations (CBOs) and other NGOs as they have attempted to assist vulnerable people with unmet post-disaster needs. We discuss two small ethnically diverse communities in Ventura County, on the periphery of the Los Angeles metropolitan region. The earthquake and resultant disaster declaration provided an opportunity for local government and NGOs to acquire federal resources not normally available for economic development. At the same time the earthquake created political openings in which longer-term issues of community development could be addressed by various local stakeholders. A key issue in recovery has been the availability of affordable housing for those on low incomes, particularly Latinos, the elderly and farm workers. We discuss the successes and limitations of CBOs and NGOs as mechanisms for dealing with vulnerable populations, unmet needs and recovery issues in the two communities. 相似文献
659.
660.
以松嫩平原西部为例,在构建生态环境胁迫评价指标体系的基础上,运用分形理论对生态环境胁迫进行量化研究.结果表明,1989-2004年15 a间,除松原市和扶余县以外,其他县市生态环境胁迫系数都呈增大趋势,特别是大安市、长岭县、乾安县等地胁迫系数较大.采用相对指标法,运用GIS-EIS集成技术,对松嫩平原西部生态环境胁迫度进行分级.最后,分析了影响生态环境胁迫变化的驱动因子,并提出减缓生态环境胁迫的措施. 相似文献