加工小模数渐开线齿廓谐波齿轮用插齿刀设计

模数小于等于1mm的渐开线齿廓小模数谐波齿轮被广泛应用于航天、航空等领域。通常情况下,谐波齿轮变位采用正变位,变位系数非常大,导致内齿圈钢轮小径大于分度圆直径。此时已无法用传统方法设计出加工此类齿轮的插齿刀,需采用变模数与变压力角的方法来进行插齿刀的设计。     

Migration and occupational careers: The static and dynamic urban wage premium by education and city size

Using matched employer-employee full population data on regional migrants in Sweden, this paper addresses the question whether the urban wage premium, and ‘thick’ labour market matching effects, are to be found across all educational groups, and whether the population threshold for these types of effects varies by educational category. Estimating initial wages, average wage level and wage growth 2001-2009, we find similar wage premiums for all workers in the three largest metropolitan areas, but that there are distinct population thresholds for these type of effects, regardless of educational background. However, job search behaviour as explaining dynamic effects over time seems to pertain mostly to those with higher education.     

Co-Production as a Driver of Urban Governance Transformation? The Case of the Oplan LIKAS Programme in Metro Manila,Philippines

Social movement-initiated co-production has been increasingly described as an approach that enables urban poor communities in the South to gain wider access to urban governance. However, with a predominant focus on project-level interventions, the case studies in which movements truly affect governance matters in a metro scale are rare. One of the examples involving such an achievement is the activism of civil society organisations and urban poor groups in Metro Manila, Philippines, which have succeeded to have a major impact on the housing and resettlement programme; the Oplan LIKAS. This article analyses how the civil society was able to gain such a position and the way it utilised it. The documentation of the challenges experienced by the civil society reflects the nature of co-productive engagement in the South and shows that it may easily reach its limits in an exclusionary governance setting.     

A dynamic programming approach for economic optimisation of lifetime-extending maintenance,renovation, and replacement of public infrastructure assets under differential inflation

In the next decades, many public infrastructure assets will reach the end of their life that they were originally designed for. Replacement costs are high, and therefore increasing effort is put into lifetime-extending maintenance, including major overhauls and renovations. A key question is whether the investments in lifetime-extending maintenance justify the postponement of a full replacement. This question becomes more complicated when future life cycle cash flows are non-repeatable. Differential inflation and technological change, including multiple intervention strategies to maintain a desired functionality, cause such non-repeatability. In this case, classic replacement analysis techniques will not suffice in answering this question. Literature demonstrates that case-specific modelling with dynamic or linear programming techniques is required to find economic optimisation. However, such literature primarily addresses replacement interval optimisation of new investments within relative short time horizons, whereas the current research develops a nested dynamic programming (DP) approach for typical ageing infrastructure assets over long service life periods. The model can deal with multiple and various successive intervention strategies and addresses differential inflation and age-related cost increases. Finally, it is shown in an infrastructure case study that this DP approach leads to a better decision in comparison to the application of classical replacement techniques.     

基于生产性景观的城市节地生态补偿策略研究

通过对以往紧凑高密度、立体化以及地下空间开发等城市节地策略进行梳理与剖析,结合当前生产性景观的发展趋势,提出城市节地的3项新策略:农业、新能源和复合型生产性景观的生态补偿,其实施方法包括填空、置换、叠加和重构。以城市屋顶为例,对3项新策略的节地与生产潜力进行估算,初步验证其有效性。基于城市生产性景观的生态补偿节地策略兼具经济、生态和社会价值,是未来景观与城市可持续发展领域的新课题。     

罗尔斯公平观视角下的美国城市更新策略研究——以亚特兰大环线再开发为例

近年来,美国一些以城市更新为导向的大型景观项目因其巨大的规模和尺度、多元的利益相关方以及所产生的积极社会效应而受到广泛关注,如纽约高线公园、亚特兰大环线。这些景观项目除关注空间设计品质外,相较传统更新实践更加重视利益分配、社会参与以及景观服务可达性等社会公平议题。基于罗尔斯公平理论的视角,系统分析了以亚特兰大环线项目为代表的美国城市更新策略,重点探讨了程序正义、重叠共识、结果正义的实现方法和形式,以期对中国当下的城市更新提供参考与借鉴。     

Using the past to indicate the possible presence of relics in the present-day landscape: the Western Front of the Great War in Belgium

The First World War (WWI) had a notable influence on the landscape at the former Western Front in Belgium. Research on a landscape scale is necessary to understand the destructive and constructive impact of the war and its consequences for the post-war landscape in a holistic manner. This paper focuses on the trajectory and impact analysis of three study areas with contrasting landscape types and aims to indicate possible preserved military relics today. Therefore, landscape changes are studied using historical aerial photographs (WWI and WWII) and contemporary orthophotos. A military landscape characterisation is made based on land use/land cover and linear structures that were mapped throughout time. Specific landscape trajectories could be designated as areas with a possible preservation of WWI heritage, with a related impact degree. The results are useful for sustainable heritage management and for further interdisciplinary research on WWI-heritage, by providing a broad knowledge of the area.     

Lake extent changes in Basotu,Tanzania: a mixed-methods approach to understanding the impacts of anthropogenic influence and climate variability

Incompatible land use is a major contributor to ecosystem degradation, and is often exacerbated by climate change impacts. We investigate Lake Basotu, Tanzania as a case study where natural lake variability has been affected by agricultural land use. Comparisons between a satellite-derived history of lake surface area, local precipitation records, and corresponding anthropogenic activity show the impacts of agricultural and historical practices. We argue that insufficient consideration to the wider ecological impacts of large agricultural projects has lasting implications. This is particularly true in semi-arid environments where food production demands need to be continuously met. In the future, major conservation strategies should be investigated to maintain the environmental integrity and sustainability of freshwater resources.