Substructure Discovery Using Minimum Description Length and Background Knowledge

The ability to identify interesting and repetitive substructures is an essential component to discovering knowledge in structural data. We describe a new version of our SUBDUE substructure discovery system based on the minimum description length principle. The SUBDUE system discovers substructures that compress the original data and represent structural concepts in the data. By replacing previously-discovered substructures in the data, multiple passes of SUBDUE produce a hierarchical description of the structural regularities in the data. SUBDUE uses a computationally-bounded inexact graph match that identifies similar, but not identical, instances of a substructure and finds an approximate measure of closeness of two substructures when under computational constraints. In addition to the minimum description length principle, other background knowledge can be used by SUBDUE to guide the search towards more appropriate substructures. Experiments in a variety of domains demonstrate SUBDUE's ability to find substructures capable of compressing the original data and to discover structural concepts important to the domain. Description of Online Appendix: This is a compressed tar file containing the SUBDUE discovery system, written in C. The program accepts as input databases represented in graph form, and will output discovered substructures with their corresponding value.Comment: See http://www.jair.org/ for an online appendix and other files accompanying this articl

The experiences of accession 8 migrants in England : motivations, work and agency

Drawing on a recently completed qualitative study in a northern English city, this paper explores motivations and experiences of Accession 8 (A8) migrants who have entered the United Kingdom following the expansion of the European Union in 2004. The paper considers commonalities and differences among the group of migrants routinely referred to as A8 migrant workers/labourers. Diversity is apparent in three particular respects: first, the motivations and forms of movement undertaken; second, their experiences of work within the UK paid labour market; and third, the extent to which the act and experience of migration offers new individual and collective opportunities and potentially opens up spaces for people to negotiate structural constraints and reconfigure aspects of their identity

‘Good relations’ among neighbours and workmates? The everyday encounters of Accession 8 migrants and established communities in urban England

Drawing on data generated in a recently completed qualitative study in a northern, English city, this paper explores the everyday social encounters of Accession 8 (A8) migrants who entered the UK following the expansion of the European Union in 2004. A number of options from permanent residence in another Member State on the one hand, to more fleeting circulatory and multiple short-term moves on the other, now exist for these new European citizens. The relatively short-term and temporary residence of some A8 migrants calls into question the focus of much UK government policy, which emphasises the need for migrants to integrate into diverse yet cohesive communities. Against this backdrop, the aim of this paper is two-fold. First, it considers the somewhat different character of A8 migration (encompassing a spectrum from permanency to temporariness) and what this means for routine experiences of mixing between new migrants and established host communities. Second, the paper explores such interactions in terms of ‘everyday encounters’ in both neighbourhood and work spaces and asks whether such spatio-temporal practices and experiences enhance or inhibit the building of ‘good relations’ in a multicultural city

Interplay between finite resources and local defect in an asymmetric simple exclusion process

When particle flux is regulated by multiple factors such as particle supply and varying transport rate, it is important to identify the respective dominant regimes. We extend the well-studied totally asymmetric simple exclusion model to investigate the interplay between a controlled entrance and a local defect site. The model mimics cellular transport phenomena where there is typically a finite particle pool and non-uniform moving rates due to biochemical kinetics. Our simulations reveal regions where, despite an increasing particle supply, the current remains constant while particles redistribute in the system. Exploiting a domain wall approach with mean-field approximation, we provide a theoretical ground for our findings. The results in steady state current and density profiles provide quantitative insights into the regulation of the transcription and translation process in bacterial protein synthesis. We investigate the totally asymmetric simple exclusion model with controlled entrance and a defect site in the bulk to mimic the finite particle pool and non-uniform moving rates in particle transport processes.Comment: 9 pages, 12 figures; v2: minor format changes; v3: major revision, additional references; v4: minor format change to figures, additional reference

Lessons from Community Entrepreneurship: The Concept of Spawning

Capital-constrained cooperatives are being challenged by producer-members to provide vertical integration opportunities. We find evidence producer groups are utilizing an investment strategy described as spawning. Producer-investors familiar with a particular organizational form and who have developed joint investment networks were more apt to invest in newly spawned ventures.Spawning, Collective Entrepreneurship, Cooperative Development, Community/Rural/Urban Development,

A Primer On Collective Entrepreneurship: A Preliminary Taxonomy

We document an increasing prevalence of the term ―collective entrepreneurship‖ in scholarly research. By examining the context in which the term is utilized, we present a framework through which to understand motivations for research in collective entrepreneurship and the variety of entrepreneurial endeavors described as collective entrepreneurship. We identify five primary motivations for research: advancement of theory, intra-organizational efficiency, inter-organizational gains, economic growth and development, and socio-political change. We find preliminary evidence collective entrepreneurs may be able to generate rents inaccessible to the sole entrepreneur. In addition, we propose mechanisms which foster entrepreneurship may differ for sole and collective entrepreneurs.International Relations/Trade,

Testing a Simplified Version of Einstein's Equations for Numerical Relativity

Solving dynamical problems in general relativity requires the full machinery of numerical relativity. Wilson has proposed a simpler but approximate scheme for systems near equilibrium, like binary neutron stars. We test the scheme on isolated, rapidly rotating, relativistic stars. Since these objects are in equilibrium, it is crucial that the approximation work well if we are to believe its predictions for more complicated systems like binaries. Our results are very encouraging.Comment: 9 pages (RevTeX 3.0 with 6 uuencoded figures), CRSR-107

Optimizing evacuation flow in a two-channel exclusion process

We use a basic setup of two coupled exclusion processes to model a stylised situation in evacuation dynamics, in which evacuees have to choose between two escape routes. The coupling between the two processes occurs through one common point at which particles are injected, the process can be controlled by directing incoming individuals into either of the two escape routes. Based on a mean-field approach we determine the phase behaviour of the model, and analytically compute optimal control strategies, maximising the total current through the system. Results are confirmed by numerical simulations. We also show that dynamic intervention, exploiting fluctuations about the mean-field stationary state, can lead to a further increase in total current.Comment: 16 pages, 6 figure