3,381 research outputs found

    Is practice aligned with the principles? Implementing New Urbanism in Perth, Western Australia

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    New Urbanism is a recent American reform approach to urban development, which attempts to reduce car dependence through traditional design qualities such as connected streets with paths, higher density and mix with local centres. The Western Australian State Government has developed ‘Liveable Neighbourhoods’, which is a context-specific design code based on new Urbanist principles. This design code has been applied in the development of several dozen new neighbourhoods in Perth over the last decade. This paper shows that these developments do create more local walking but are no different to conventional suburban development in their regional car dependence. The causes of this are pursued in terms of a gap between principles and practice

    Clustering Phase Transitions and Hysteresis: Pitfalls in Constructing Network Ensembles

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    Ensembles of networks are used as null models in many applications. However, simple null models often show much less clustering than their real-world counterparts. In this paper, we study a model where clustering is enhanced by means of a fugacity term as in the Strauss (or "triangle") model, but where the degree sequence is strictly preserved -- thus maintaining the quenched heterogeneity of nodes found in the original degree sequence. Similar models had been proposed previously in [R. Milo et al., Science 298, 824 (2002)]. We find that our model exhibits phase transitions as the fugacity is changed. For regular graphs (identical degrees for all nodes) with degree k > 2 we find a single first order transition. For all non-regular networks that we studied (including Erdos - Renyi and scale-free networks) we find multiple jumps resembling first order transitions, together with strong hysteresis. The latter transitions are driven by the sudden emergence of "cluster cores": groups of highly interconnected nodes with higher than average degrees. To study these cluster cores visually, we introduce q-clique adjacency plots. We find that these cluster cores constitute distinct communities which emerge spontaneously from the triangle generating process. Finally, we point out that cluster cores produce pitfalls when using the present (and similar) models as null models for strongly clustered networks, due to the very strong hysteresis which effectively leads to broken ergodicity on realistic time scales.Comment: 13 pages, 11 figure

    The Density Profiles of Massive, Relaxed Galaxy Clusters. II. Separating Luminous and Dark Matter in Cluster Cores

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    We present stellar and dark matter (DM) density profiles for a sample of seven massive, relaxed galaxy clusters derived from strong and weak gravitational lensing and resolved stellar kinematic observations within the centrally-located brightest cluster galaxies (BCGs). In Paper I of the series, we demonstrated that the total density profile derived from these data, which span 3 decades in radius, is consistent with numerical DM-only simulations at radii >~ 5-10 kpc, despite the significant contribution of stellar material in the core. Here we decompose the inner mass profiles of these clusters into stellar and dark components. Parametrizing the DM density profile as a power law rho_DM ~ r^{-\beta} on small scales, we find a mean slope = 0.50 +- 0.10 (random) +0.14-0.13 (systematic). Alternatively, cored Navarro-Frenk-White (NFW) profiles with = 1.14 +- 0.13 (random) +0.14-0.22 (systematic) provide an equally good description. These density profiles are significantly shallower than canonical NFW models at radii <~ 30 kpc, comparable to the effective radii of the BCGs. The inner DM profile is correlated with the distribution of stars in the BCG, suggesting a connection between the inner halo and the assembly of stars in the central galaxy. The stellar mass-to-light ratio inferred from lensing and stellar dynamics is consistent with that inferred using stellar population synthesis models if a Salpeter initial mass function is adopted. We compare these results to theories describing the interaction between baryons and DM in cluster cores, including adiabatic contraction models and the possible effects of galaxy mergers and active galactic nucleus feedback, and evaluate possible signatures of alternative DM candidates.Comment: Updated to matched the published version in Ap

    Changes in recreational behaviors of outdoor enthusiasts during the COVID-19 pandemic: analysis across urban and rural communities

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    The COVID-19 pandemic presents not only a global health crisis but has also disrupted the daily lives of people around the world. From a leisure perspective, urban outdoor enthusiasts are one group particularly impacted by the pandemic and the subsequent institutional response. Stay-at-home orders and physical distancing recommendations serve as potential inhibitors to outdoor recreation activities central to the lifestyles and wellbeing of outdoor enthusiasts. In urban areas, where these orders and recommendations are most restrictive, the potential impacts on recreation behavior are most consequential. This study provides an empirical analysis of the COVID-19 pandemic’s impact on the recreational behaviors of outdoor enthusiasts across urban and rural communities. Results suggest that the frequency of outdoor recreation participation, distance travelled to participate in outdoor recreation and distance travelled beyond roads during outdoor recreation have declined significantly more among outdoor enthusiasts residing in urban areas than urban clusters or rural areas

    A revised Cepheid distance to NGC 4258 and a test of the distance scale

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    In a previous paper (Maoz et al. 1999), we reported a Hubble Space Telescope (HST) Cepheid distance to the galaxy NGC 4258 obtained using the calibrations and methods then standard for the Key Project on the Extragalactic Distance Scale. Here, we reevaluate the Cepheid distance using the revised Key Project procedures described in Freedman et al. (2001). These revisions alter the zero points and slopes of the Cepheid Period-Luminosity (P-L) relations derived at the Large Magellanic Cloud (LMC), the calibration of the HST WFPC2 camera, and the treatment of metallicity differences. We also provide herein full information on the Cepheids described in Maoz et al. 1999. Using the refined Key Project techniques and calibrations, we determine the distance modulus of NGC 4258 to be 29.47 +/- 0.09 mag (unique to this determination) +/- 0.15 mag (systematic uncertainties in Key Project distances), corresponding to a metric distance of 7.8 +/- 0.3 +/- 0.5 Mpc and 1.2 sigma from the maser distance of 7.2 +/- 0.5 Mpc. We also test the alternative Cepheid P-L relations of Feast (1999), which yield more discrepant results. Additionally, we place weak limits upon the distance to the LMC and upon the effect of metallicity in Cepheid distance determinations.Comment: 26 pages in emulateapj5 format, including 6 figures and 5 tables. Accepted for publication in the Astrophysical Journa
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