3,201 research outputs found

    Active particle dynamics beyond the jamming density

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    Many biological systems form colonies at high density. Passive granular systems will be jammed at such densities, yet for the survival of biological systems it is crucial that they are dynamic. We construct a phase diagram for a system of active particles interacting via Vicsek alignment, and vary the density, self-propulsion force, and orientational noise. We find that the system exhibits four different phases, characterized by transitions in the effective diffusion constant and in the orientational order parameter. Our simulations show that there exists an optimal noise such that particles require a minimal force to unjam, allowing for rearrangements.Comment: 7 pages, 8 figure

    Introduction: Peasants, Pastoralists and Proletarians: Joining the Debates on Trajectories of Agrarian Change, Livelihoods and Land Use

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    Recent changes in the agrarian studies and geography literatures present differing views on the pace and trajectory of change in rural developing areas. In this special section of Human Geography, we contrast the theoretical and practice implications of these differing approaches, namely depeasantization, accumulation by dispossession and deproletarianization. Depeasantization refers to change in livelihood activities out of agriculture, long theorized as necessary for an area’s transition into capitalism. Accumulation by dispossession is a process of on-going capital accumulation where a give resource is privatized, seized, or in some other manner alienated from common ownership in order to provide a basis for continued capital accumulation. Deproletarianization occurs when workers are no longer able to freely commodify and recommodify their only commodity, their own labour. In this section, we explore these three theses with case studies that draw upon empirical data. The papers in this collection all speak to one aspect or another of these debates. We do not intend to try to determine a “best approach”, rather we explore strengths and weaknesses of each argument. The production of nature, change in the mode of production and the political economy of nature are discussed in the first article by Brent McCusker. Phil O’Keefe and Geoff O’Brien examine the evolution of worked landscape under pre-capitalist modes of production in riverine ecologies. Through further case studies, Paul O’Keefe explores links between livelihoods and climate change in Mt. Kilimanjaro, Tanzania, while Franklin Graham explores the persistence of pastoralism in the Sahel. Finally, Naomi Shanguhyia and Brent McCusker examine the process of governance in dry land Kenya through the study of chronic food shortages

    Mindfulness in social work education and practice

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    Learning through architecture and successful capital projects in the post-capitalist economy of Northern England

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    Through the lens of architecture and empirical research, this paper demonstrates how successful, award-winning capital projects are not the preserve of the economically privileged in a post-capitalist UK. Considering a background of professional and academic theory it links the 2011 Localism Act with a growing Social & Solidarity Economy and draws on the author’s historic research on the architectural heritage of the co-operative movement and how co-operative societies have approached this in the past. The discussion reflects on the author’s direct experience of working on three architectural co-operative projects (Unicorn Grocery, Bamford Community Society’s Public House, and Stretford Public Hall) with themes of community asset transfer, funding, co-operative business models, implementation of the 6th co-operative principle; sustainable capital projects, evolution of a business plan, and the potential role of the architect as an educator within that to inform decisions on such projects including responsible specification and recycling of waste materials from site

    Cryptographic key distribution in wireless sensor networks: a hardware perspective

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    In this work the suitability of different methods of symmetric key distribution for application in wireless sensor networks are discussed. Each method is considered in terms of its security implications for the network. It is concluded that an asymmetric scheme is the optimum choice for key distribution. In particular, Identity-Based Cryptography (IBC) is proposed as the most suitable of the various asymmetric approaches. A protocol for key distribution using identity based Non-Interactive Key Distribution Scheme (NIKDS) and Identity-Based Signature (IBS) scheme is presented. The protocol is analysed on the ARM920T processor and measurements were taken for the run time and energy of its components parts. It was found that the Tate pairing component of the NIKDS consumes significants amounts of energy, and so it should be ported to hardware. An accelerator was implemented in 65nm Complementary Metal Oxide Silicon (CMOS) technology and area, timing and energy figures have been obtained for the design. Initial results indicate that a hardware implementation of IBC would meet the strict energy constraint of a wireless sensor network node

    Trusty URIs: Verifiable, Immutable, and Permanent Digital Artifacts for Linked Data

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    To make digital resources on the web verifiable, immutable, and permanent, we propose a technique to include cryptographic hash values in URIs. We call them trusty URIs and we show how they can be used for approaches like nanopublications to make not only specific resources but their entire reference trees verifiable. Digital artifacts can be identified not only on the byte level but on more abstract levels such as RDF graphs, which means that resources keep their hash values even when presented in a different format. Our approach sticks to the core principles of the web, namely openness and decentralized architecture, is fully compatible with existing standards and protocols, and can therefore be used right away. Evaluation of our reference implementations shows that these desired properties are indeed accomplished by our approach, and that it remains practical even for very large files.Comment: Small error corrected in the text (table data was correct) on page 13: "All average values are below 0.8s (0.03s for batch mode). Using Java in batch mode even requires only 1ms per file.
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