Portfolio Optimization and the Random Magnet Problem

Diversification of an investment into independently fluctuating assets reduces its risk. In reality, movement of assets are are mutually correlated and therefore knowledge of cross--correlations among asset price movements are of great importance. Our results support the possibility that the problem of finding an investment in stocks which exposes invested funds to a minimum level of risk is analogous to the problem of finding the magnetization of a random magnet. The interactions for this ``random magnet problem'' are given by the cross-correlation matrix {\bf \sf C} of stock returns. We find that random matrix theory allows us to make an estimate for {\bf \sf C} which outperforms the standard estimate in terms of constructing an investment which carries a minimum level of risk.Comment: 12 pages, 4 figures, revte

Visual engagement with urban street edges: insights using mobile eye-tracking

This study provides empirical insight into the extent to which pedestrians visually engage with urban street edges and how social and spatial factors impact such engagement. This was achieved using mobile eye-tracking. The gaze distribution of 24 study participants was systematically recorded as they carried out everyday tasks on differing streets. The findings demonstrated that street edges are the most visually engaged component of streets; that street edge visual engagement is impacted by everyday social tasks as well as the spatial and physical materiality of edges on differing streets; and that street edges, which attract a lot of visual engagement while undertaking optional tasks, also attract greater amounts of visual engagement while undertaking necessary tasks. These findings offer new insight into urban street edge engagement from the direct perspective of street inhabitants and in doing so provide greater understanding of how street edges are experienced

Places as Intersecting Flows: Mapping Urban Morphologies, Functional Constellations and Pedestrian Activity Rhythms

Starting from an open and dynamic conception of place as a socio-spatial and temporal assemblage, this paper explores high density urban areas as dynamic environments of social interaction. While Lefebvre's call for a rhythmanalysis of the city significantly influenced contemporary urban discourse, such understanding still lacks empirical depth. This paper seeks to advance the empirical grounding of rhythmanalysis through a comparative study of nine selected street intersections in London, New York and Melbourne. It explores the links between the observed, filmed and measured daily and weekly rhythms of pedestrian flows on the one hand and density, permeability, grain size and functional mix, the four preconditions of urban vitality according to Jacobs, on the other hand. Further, mapping is used as a means of revealing the forces underlying each place. It is shown that the overlay of regular patterns of everyday habits and routines, rhythms of social interactions and mechanical micro-rhythms of transportation systems, all mediated by urban form, lead to place specific polyrhythms. Place is thus conceived as emerging from the intersection of rhythmic flows, mediated by urban morphology and functional constellations

Streetlife Rhythms

Lefebvre's call for a 'rhythmanalysis' of the city has long inspired urban thinking, but like most texts on space it lacks any specific spatiality. This chapter is an empirical approach to urban rhythms through a comparative study of nine selected street intersections in London, New York and Melbourne. It explores the links between the daily and weekly rhythms of pedestrian flows and the detailed morphology and functional mix of the urban context. Such mapping is a means of revealing the synergies between morphology and streetlife that produce emergent and place specific polyrhythms

Urban block enclosure and labyrinthineness: measuring morphological attributes that matter

This paper proposes two new urban morphological measures: Block Enclosure Ratio (BER) and Block Labyrinthineness Ratio (BLR). BER captures the built-up ratio of the block perimeter, linked to the sense of enclosure. BLR is the ratio between the shortest route around a block and its total perimeter, capturing how labyrinthine its shape is. The analytical value of these metrics is demonstrated based on the case study of Paris. Results indicate that these measures combined with diagramming and mapping are effective tools to analyse urban form attributes, and can bridge some of the gap between morphological studies and statistical analysis

Walkability: From Spatial Analytics to Urban Coding and Actual Walking

Walkability has become a key focus of urban research, linked to the aims of reversing car‐dependence and re‐enabling walking as a healthy, environmentally sustainable and sociable mode of mobility. This thematic issue presents a collection of articles using cutting‐edge research methods ranging from walk‐along interviews to statistical analysis of historic photography, topological and morphological analysis of street networks, and analysis of the spatio‐temporality of various aspects of streetlife. The articles included here provide new insights in understanding morphologies of walkability in cities across the globe. This concise selection of non‐reductionist walkability research reveals the exceptional breadth of research tools, inspiring further methodological innovation, and supporting future urban design and planning practice