Unbiased sampling of globular lattice proteins in three dimensions

We present a Monte Carlo method that allows efficient and unbiased sampling of Hamiltonian walks on a cubic lattice. Such walks are self-avoiding and visit each lattice site exactly once. They are often used as simple models of globular proteins, upon adding suitable local interactions. Our algorithm can easily be equipped with such interactions, but we study here mainly the flexible homopolymer case where each conformation is generated with uniform probability. We argue that the algorithm is ergodic and has dynamical exponent z=0. We then use it to study polymers of size up to 64^3 = 262144 monomers. Results are presented for the effective interaction between end points, and the interaction with the boundaries of the system

The Use of Downside Risk Measures in Portfolio Construction and Evaluation

One of the challenges of using downside risk measures as an alternative constructor of portfolios and diagnostic devise is in their computational intensity. This paper outlines how to use downside risk measures to construct efficient portfolios and to evaluate portfolio performance in light of investor loss aversiondownside risk, portfolios, performance measure

Prosper. An evaluation of tourism's contribution to regional economies

Prosper has delivered a three part model for assessing and enhancing the value of tourism in regional areas. The first part of the model uses simple indicators to provide an assessment of the economic, social, and environmental value attached to tourism. An indicators approach was adopted following extensive review of the application of more complex approaches to regional economic analysis. The review found that complex approaches are unlikely to produce results of sufficient validity and applicability to warrant their high resource costs (time, money, and skills). Complex models are also more difficult to maintain. The economic value is represented through quantitative indicators relating to employment and the number of businesses in tourism related sectors. These are all relative indicators (for example, proportion of all businesses which are businesses in the tourism sector or proportion of change in employment that can be attributed to change in tourism related employment). These indicators are drawn from national data sets which provide information for statistical local areas and/or postcode areas. This offers the opportunity to develop and deliver consistent national profiles through a vehicle such as Decipher. National standard data sets are supplemented in the model by more qualitative assessments of tourism’s contribution to the local economy made by business operators through interviews or surveys. Again, tracking the change in these assessments over time is the key to the model. Social and environmental values are substantially more difficult to assess. The Prosper case studies have included qualitative assessments derived from business and community meetings, local government and other administrative documents, media and a simplified network analysis identifying the extent to which community based organisations interact with the delivery of tourism services. Data sets have been identified which would allow a quantitative analysis of the extent to which tourism activity (visitor movements, business activity, business construction) encroaches on environmentally sensitive areas or is responsible for redevelopment or preservation of built environments. The case studies have not been able to implement this quantitative analysis. The second part of the model conducts a ‘diagnostic’ assessment of the capacity in the region to harness the value of tourism through innovation. Innovation is seen as a very important mechanism for both identifying regional issues and developing responses to those issues. Innovation is widely accepted in the literature as a driver of economic growth, and concepts such as ‘systems of innovation’ and ‘regional systems of innovation’ have become common in understanding how that innovation can be encouraged and placed within technical or geographical contexts. The diagnostic element of the Prosper model uses a series of techniques (including historical document analysis, interviews, and network analysis) to investigate the characteristics of region’s human tourism resources in relation to their ‘innovation potential’. Innovation potential is influenced by: • Economic competence – the extent to which those resources include capacity to manage projects and implement new ideas; • Clustering of resources – the spatial relationships between tourism attractions and amenities and nontourism amenities and resources which may be critical in the delivery of tourism product; • Networks – the social and professional relationships between tourism attractions and amenities and nontourism amenities and resources which may be critical in the delivery of tourism product; • Development blocks – the existence of sufficient new resources or new ways of looking at existing resources to provide opportunities for innovation. Development blocks need also to be a source of tension or disequilibrium so that their use is contested and therefore options more likely to be scrutinized as to their viability; • Entrepreneurship – the capacity for human resources to engage in new tasks and drive activity; • Critical mass – the relationship between the capacity to supply tourism product, and the capacity to access sufficient and appropriate markets (including resident markets) to support ongoing supply; • Local government – the extent to which local government considers tourism an important issue and is willing to engage in the innovation process • Production and distribution of knowledge – the extent to which the history and current status of tourism is understood and communicated, and the degree to which stakeholders can access and apply new information for identifying the potential or need for change, assessing the viability of projects, and evaluating activities; • Social, political and cultural capital – the strength of the social, political and cultural environments, and the degree to which those environments can be effectively harnessed to support tourism innovation. The third part of the model uses ‘visioning’ techniques (drawing in part on experiences from Sustainable Tourism CRC projects on ‘Gold Coast Visioning’ led by Professor Bill Faulkner at Griffith University, and research by Walker, Lee, Goddard, Kelly & Pedersen, 2005) to engage stakeholders in developing strategies for identifying tourism value issues (based on the community awareness of the value of tourism, aspirations for enhancing value, and strategies for addressing deficiencies in innovation potential). A number of processes are available for applying visioning techniques. Our case studies typically involved community leaders accepting ownership of the results of the application of the first components of the model and, in a facilitated or nonfacilitated way, delivering these results broadly through the community. In some cases, strategies emerged entirely from within the region, while in others, the research team was further engaged to collate strategy suggestions and summarise the arguments attached to these suggestions. In most cases, the final case study write-up included reference to suggestions which appeared likely to be carried forward. The Prosper model was tested in thirteen case studies, not simply to establish whether the relationships hypothesized between innovation potential and harnessing the value of tourism could be observed, but also to establish to extent to which participating regions viewed the application of the model as important and worthwhile in their attempts to move forward. The case studies were a mix of five new studies conducted using the Prosper model in a direct way and meta-analysis of eight previous case studies. The short time frame for the research (2 and ½ years) and the relatively long term nature of change made it impossible to design the research to evaluate the success of the strategies developed or any specific innovations in new case studies, so the metaanalysis studies were significant in this respect. The case studies strongly supported the second part of the model in particular, and the research served as an influential tool for many of the case study communities who were able to implement programs of value monitoring (through quantitative or qualitative means), identify ways in which their systems of innovation could be strengthened, and develop context specific mechanisms for identifying and assessing the feasibility of tourism development proposals. The research has delivered a number of outputs which may be used in dissemination and commercialisation of the intellectual property. A stand-alone publication reviewing the applicability of various economic value assessment techniques to regional tourism has been produced. A quick guide to the Prosper model and assessing whether application of the model would assist a particular region has been drafted, and is slated for development in collaboration with Sustainable Tourism CRC. A detailed methodology specification has been prepared, and may be used as the basis of consulting services or the conduct of further case studies. The quantitative data sets (Census, Sensis, TTF employment analysis, labour force statistics etc.) may be made available through Decipher and included in a structured Decipher product which facilitates analysis and interpretation. A book containing research results of the thirteen case studies and an overview of the relationship between those case studies and the Prosper model has been edited by Dean Carson and Dr Jim Macbeth and has been submitted to the Sustainable Tourism CRC editorial team led by Professor Chris Cooper at the University of Queensland

The traveling salesman problem, conformal invariance, and dense polymers

We propose that the statistics of the optimal tour in the planar random Euclidean traveling salesman problem is conformally invariant on large scales. This is exhibited in power-law behavior of the probabilities for the tour to zigzag repeatedly between two regions, and in subleading corrections to the length of the tour. The universality class should be the same as for dense polymers and minimal spanning trees. The conjectures for the length of the tour on a cylinder are tested numerically.Comment: 4 pages. v2: small revisions, improved argument about dimensions d>2. v3: Final version, with a correction to the form of the tour length in a domain, and a new referenc

Selfduality for coupled Potts models on the triangular lattice

We present selfdual manifolds for coupled Potts models on the triangular lattice. We exploit two different techniques: duality followed by decimation, and mapping to a related loop model. The latter technique is found to be superior, and it allows to include three-spin couplings. Starting from three coupled models, such couplings are necessary for generating selfdual solutions. A numerical study of the case of two coupled models leads to the identification of novel critical points

On the universality of compact polymers

Fully packed loop models on the square and the honeycomb lattice constitute new classes of critical behaviour, distinct from those of the low-temperature O(n) model. A simple symmetry argument suggests that such compact phases are only possible when the underlying lattice is bipartite. Motivated by the hope of identifying further compact universality classes we therefore study the fully packed loop model on the square-octagon lattice. Surprisingly, this model is only critical for loop weights n < 1.88, and its scaling limit coincides with the dense phase of the O(n) model. For n=2 it is exactly equivalent to the selfdual 9-state Potts model. These analytical predictions are confirmed by numerical transfer matrix results. Our conclusions extend to a large class of bipartite decorated lattices.Comment: 13 pages including 4 figure

Marriage, Specialization, and the Gender Division of Labor

A customary gender division of labor is one in which women and men are directed towards certain tasks and/or explicitly prohibited from performing others. We offer an explanation as to why the gender division of labor is so often enforced by custom, and why customary gender divisions of labor generally involve both direction and prohibition. Our model builds on the literature on the marital hold-up problem, and considers both problems in choice of specialty and human capital acquisition in a framework in which agents learn a variety of skills and must search for a marriage partner on the marriage market. We show that wasteful behavior may emerge due to strategic incentives in career choice and human capital acquisition, and that both problems may be mitigated through the customary gender division of labor. We find, however, that a gender division of labor is not Pareto-improving; one gender is made worse off. Both the distributional effects and welfare gains to a customary gender division of labor decrease as opportunities to exchange in markets increase.

Evaluation of a Wake Vortex Upset Model Based on Simultaneous Measurements of Wake Velocities and Probe-Aircraft Accelerations

Simultaneous measurements were made of the upset responses experienced and the wake velocities encountered by an instrumented Learjet probe aircraft behind a Boeing 747 vortex-generating aircraft. The vortex-induced angular accelerations experienced could be predicted within 30% by a mathematical upset response model when the characteristics of the wake were well represented by the vortex model. The vortex model used in the present study adequately represented the wake flow field when the vortices dissipated symmetrically and only one vortex pair existed in the wake