No abstract

A numerical study of the plasma presheath has been performed, extending earlier work to include the effects of general source functions, and allowing for collisions in the presheath. Analytic results for a collisionless presheath with particular source functions have been confirmed, and comparisons with a numerical study of a weakly collisional presheath have been made. The extrapolation of these calculations to high collision frequency, where they are compared to a simple analytic model, and the effects of the choice of source functions are presented.

In his 2018 Stockholm prize winner lecture, Goldstein highlighted the need for problem-oriented policing (POP) to be not only effective but also fair. Contributing to the development of POP, this study examines how a wider perspective on problem-solving generally, and scoping in particular, can be adopted to address some of the growing challenges in 21st century policing. We demonstrate that the concept of ‘problem’ was too narrowly defined and that, as a result, many problem-solving models found in criminology are ill-structured to minimize the negative side-effects of interventions and deliver broader benefits. Problem-solving concepts and models are compared across disciplines and recommendations are made to improve POP, drawing on examples in architecture, conservation science, industrial ecology and ethics.

Resilience defined as the capacity of a system to manage impacts, keep its efficiency and continue its development has been scrutinized by researchers from different points of view over the past decades. Due to the prominence of resilience in urban planning, this paper intends to find out how the spatial structure of cities deals with disturbances, and if geographical phenomena such as rivers affect the resilience in cities. Using the space syntax methods syntactically analyze the resilience in cities, we innovatively introduce two measures; similarity and sameness. These measures are in relation with the syntactical properties of cities and compare the degree of resilience between different groups. Similarity measures the degree to which each city retains the relative magnitude of its foreground network after a disturbance and sameness is the degree to which each city retains the same segments as its foreground network after a disturbance. Likewise to network resilience studies, we apply different disturbances on cities and explore the reaction of cities to disturbances in terms of size of the foreground network and which segments are parts thereof. We then compare different groups based on these measurements as a method to analyze sameness and similarity. The results show that the resilience, in the way we define it, is different in different cities depending on in which view and based on which parameters we are discussing the resilience. Additionally morphological phenomena such as rivers have a great impact on the structure of cities and in turn on their resilience.

During the COVID-19 pandemic, physical distancing, mobility restrictions and self-isolation measures were implemented around the world as the primary intervention to prevent the virus from spreading. Urban life has undergone sweeping changes, with people using spaces in new ways. Stockholm is a particularly relevant case of this phenomenon since most facilities, such as day care centres and schools, have remained open, in contrast to cities with a broader lockdown. In this study, we use Twitter data and an online map survey to study how COVID-19 restrictions have impacted the use of different locations, services and amenities in Stockholm. First, we compare the spatial distribution of 87,000 geolocated tweets pre-COVID-19 and during the COVID-19 pandemic. Second, we analyse 895 survey responses asking people to identify places they ‘still visit’, ‘use more’, ‘avoid’ and self-report reasons for using locations. The survey provides a nuanced understanding of whether and how restrictions have affected people. Service and seclusion were found to be important; therefore, the accessibility of such amenities was analysed, demonstrating how changes in urban habits are related to conditions of the local environment. We find how different parts of the city show different capacities to accommodate new habits and mitigate the effects of restrictions on people’s use of urban spaces. In addition to the immediate relevance to COVID-19, this paper thus contributes to understanding how restrictions on movement and gathering, in any situation, expose more profound urban challenges related to segregation and social inequality.

In light of the urgent threats presented by climate change and rapid urbanisation, interest in ‘smart city systems’ is mounting. In contrast to scholarship that poses ‘smartness’ as something that needs to be added to cities, recent developments in spatial morphology research pursue a view of the built fabric of cities as an extension of the cognitive human apparatus, as well as a material formulation of social, cultural and economic relations and processes. The built fabric of cities needs to be understood as a highly intelligent artefact in itself, rather than simple, dead matter. The current focus on high-tech systems risks concealing the fact that the machine is already there. In contrast to the technological ‘implements’ of smart city systems, this article looks at cities as ‘facilities’ – that is, as technologies that slow down, store and maintain energy as a resource for a variety of purposes. The article builds on space syntax research in order to give precision to the understanding of the affordances the cities offer their various processes and the ways in which cities operate as information storage and retrieval devices for individuals and for society. The city must be considered, we argue, in terms of a range of tangled, interdependent systems, reaching from individual buildings to the whole city, an understanding anchored in notions of ‘diversity’ and ‘density’ (recently gathered under the concept of ‘spatial capital’) and in research addressing how the distribution of space and artefacts serve as means of knowledge communication (specifically, in complex buildings such as libraries and department stores). In conclusion, we argue that existing discussions on ‘smart city systems’ would benefit acknowledgement of the role of cities as facilities.

Background: As dynamic systems rivers and cities have been in interaction under changing relations over time, and the morphology of many cities has risen through a long and steady struggle between the city functions and the river system flowing inside. This makes river cities an interesting case to study how the presence of geographical features interacts with spatial morphology in the formation of cities. Methods:The basis of this research is enabled by utilizing a novel model for cross-city comparison presented by Hillier in his Santiago keynote in 2012 called a "star model". This is done on large samples of cities investigating concurrent configurations, as well as how the properties in this star model react to specific forms of disturbance. Results:Results illustrate that the foreground network as identified through maximum choice values in cities are more vital to the structure of cities than the bridges. The overall syntactic structure tends to retain its character (degree of distributedness) and the location of its foreground network (which street segments constitute the foreground network) even when bridges are targeted. Furthermore, counter to the initial hypothesis, river cities tend to change less than non-river cities after targeted disturbance of the systems. Finally, the results show that while there is a statistical morphological difference between river cities and non-river cities, this difference is not directly explained through the bridges. Conclusion:Integrating space syntax with statistical and geospatial analysis can throw light on the way in which the properties of city networks and urban structure reflect the relative effect of rivers on the morphology of river cities. The paper, finally, contributes through offering one piece of a better perception of the structure of river-cities that can support strategies of river-cities interaction as well as enhance our knowledge on the constraints and limits to that interaction.

Recent empirical research has confirmed the importance of green infrastructure and outdoor recreation to urban people’s well-being during the COVID-19 pandemic. However, only a few studies provide cross-city analyses. We analyse outdoor recreation behaviour across four Nordic cities ranging from metropolitan areas to a middle-sized city. We collected map-based survey data from residents (n = 469–4992) in spring 2020 and spatially analyse green infrastructure near mapped outdoor recreation sites and respondents’ places of residence. Our statistical examination reveals how the interplay among access to green infrastructure across cities and at respondents’ residential location, together with respondents’ socio-demographic profiles and lockdown policies or pandemic restrictions, affects outdoor recreation behaviour. The results highlight that for pandemic resilience, the history of Nordic spatial planning is important. To support well-being in exceptional situations as well as in the long term, green infrastructure planning should prioritise nature wedges in and close to cities and support small-scale green infrastructure.