Transport Processes on Homogeneous Planar Graphs with Scale-Free Loops

We consider the role of network geometry in two types of diffusion processes: transport of constant-density information packets with queuing on nodes, and constant voltage-driven tunneling of electrons. The underlying network is a homogeneous graph with scale-free distribution of loops, which is constrained to a planar geometry and fixed node connectivity $k=3$. We determine properties of noise, flow and return-times statistics for both processes on this graph and relate the observed differences to the microscopic process details. Our main findings are: (i) Through the local interaction between packets queuing at the same node, long-range correlations build up in traffic streams, which are practically absent in the case of electron transport; (ii) Noise fluctuations in the number of packets and in the number of tunnelings recorded at each node appear to obey the scaling laws in two distinct universality classes; (iii) The topological inhomogeneity of betweenness plays the key role in the occurrence of broad distributions of return times and in the dynamic flow. The maximum-flow spanning trees are characteristic for each process type.Comment: 14 pages, 5 figure

Transition-metal interactions in aluminum-rich intermetallics

The extension of the first-principles generalized pseudopotential theory (GPT) to transition-metal (TM) aluminides produces pair and many-body interactions that allow efficient calculations of total energies. In aluminum-rich systems treated at the pair-potential level, one practical limitation is a transition-metal over-binding that creates an unrealistic TM-TM attraction at short separations in the absence of balancing many-body contributions. Even with this limitation, the GPT pair potentials have been used effectively in total-energy calculations for Al-TM systems with TM atoms at separations greater than 4 AA. An additional potential term may be added for systems with shorter TM atom separations, formally folding repulsive contributions of the three- and higher-body interactions into the pair potentials, resulting in structure-dependent TM-TM potentials. Towards this end, we have performed numerical ab-initio total-energy calculations using VASP (Vienna Ab Initio Simulation Package) for an Al-Co-Ni compound in a particular quasicrystalline approximant structure. The results allow us to fit a short-ranged, many-body correction of the form a(r_0/r)^{b} to the GPT pair potentials for Co-Co, Co-Ni, and Ni-Ni interactions.Comment: 18 pages, 5 figures, submitted to PR

Assessing the State of Demersal Fish to Address Formal Ecosystem Based Management Needs: Making Fisheries Independent Trawl Survey Data ‘Fit for Purpose’

In Europe, introduction of the Marine Strategy Framework Directive (MSFD) represents formal, legally-binding, adoption of ecosystem-based management (EBM) across most European waters. Member States of the European Union have invariably nominated their groundfish surveys as part of the marine monitoring programs required under the MSFD. Groundfish surveys were originally intended to provide fisheries independent abundance indices for commercially valuable species to support fisheries stock assessments and fisheries management. However, early studies, primarily intended to make the case for the need for EBM, exposed these data to a broader range of uses and highlighted various data quality issues. Individual scientists, pursuing personal research agendas, addressed these as each thought best. This informal approach to assuring data quality is not sufficient to support formal assessments of fish species status and fish community status required under legally-mandated EBM, such as the MSFD, because quality audit, formal logging of issues identified, and remedial measures taken, is often lacking. Groundfish survey data, needed to implement legally-mandated EBM, should be subjected to a formal Quality Assurance–Quality Audit (QAQA) process to ensure that they are properly fit for purpose. This paper describes a QAQA process applied European groundfish survey data to ensure their adequacy to support MSFD needs and considers how this process might be taken forward in the future

A Solvable Two-Dimensional Degenerate Singular Stochastic Control Problem with Nonconvex Costs

In this paper we provide a complete theoretical analysis of a two-dimensional degenerate nonconvex singular stochastic control problem. The optimisation is motivated by a storage-consumption model in an electricity market, and features a stochastic real-valued spot price modelled by Brownian motion. We find analytical expressions for the value function, the optimal control, and the boundaries of the action and inaction regions. The optimal policy is characterised in terms of two monotone and discontinuous repelling free boundaries, although part of one boundary is constant and the smooth fit condition holds there

Climbing the water ladder: multiple-use water services for poverty reduction

Multiple use / Models / Water productivity / Research projects / Water supply / Domestic water / Irrigation water / Water governance / Poverty / Gender / Rural areas / Wells / Water harvesting / Runoff / Water storage / Water purification / Appropriate technology / Costs / Local government / Non governmental organizations / Case studies / Ehiopia / Nepal / Zimbabwe / Bolivia / India / Colombia / Thailand / South Africa

Musical pathways: An exploratory study of young people in the criminal justice system, engaged with a creative music programme

There is growing evidence from across the arts and health field that suggests that participatory arts programmes can contribute to health improvement, emotional resilience and social reintegration, among vulnerable and excluded groups including criminal justice populations. This report presents a three-year research project funded by the BIG Lottery Fund that completed in 2013. The project was a collaboration between Superact Community Interest Company and the University of the West of England, Bristol. It used mixed methods to investigate a participatory music programme delivered to young people in justice settings by Superact.The research was conducted within a range of custody and community based youth justice settings. These included Young Offender Institutions, Juvenile Secure Units and Prisons, Secure Children’s Homes and Youth Offending Teams. Ethnographic research explored responses and perceptions of Superact’s music programme, focusing on links between music and health, wellbeing, behaviour and social inclusion. Data collection included participant observation, semi-structured interviews and focus groups across eight sites and fifteen programes. As well as examining in depth the responses and views of young people who took part, the research explored the perceptions of stakeholders including prison staff and musicians. A key objective of the research was to pilot conventional validated health, wellbeing and social inclusion questionnaires with this population, partly to establish baseline scores and also to explore the feasibility of measuring these indicators with a transient and ‘hard-to-reach’ population.The research has yielded valuable insight into the perspectives and attitudes of young people in justice settings, in relation to music and their identification with it, and participatory music programming. The research reveals the effects of group dynamics, institutional systems, behavioural factors and population transience on delivery of programmes across these settings. Perhaps inevitably, the high degree of transience of the population impacted on programme attendance and participation, limiting what could be drawn from the quantitative data. However, while the baseline questionnaire data reveal no significant findings with respect to health, wellbeing and social inclusion indicators, the qualitative findings reveal a myriad of themes that underlie the process of programme delivery and the value of music to individuals. These data reveal significant affordances offered by music making for young people and illustrate programme and contextual factors necessary for these affordances to be realised. Essentially, creative music making has the potential to engage even ‘hard to reach’ young people, delivering positive learning experiences and enabling them to forge new identities. Active engagement in arts programmes of this kind can deliver life-changing benefits for some individuals; certainly, for the majority of participants in this study, the programme was valuable in helping them cope with difficult circumstances, including custody, and to consider how music could help them look positively towards the future. Team-building, group dynamics and creativity were key factors underlining successful programme delivery and effective engagement of young people.In conclusion, we argue that participatory music programmes provide opportunities to young people to engage alternative skills and competencies that are not routinely afforded them via conventional education and training programmes. Moreover, music provides a medium that enables young people to engage their life experiences in creative ways, to identify positively with music, to draw on knowledge and experiences, and to engage with their peer group. An important feature of programmes delivered by professional musicians is that they have the skills and experience to garner respect from young people, particularly groups that are difficult to engage and present with challenging attitudes and behaviours. We believe that music programmes that take this approach are a major asset to youth justice organisations, especially since they are located outside the system and therefore command respect and credibility from young people

A Nonconvex Singular Stochastic Control Problem and its Related Optimal Stopping Boundaries

Abstract. Equivalences are known between problems of singular stochastic control (SSC) with convex performance criteria and related questions of optimal stopping; see, for example, Karatzas and Shreve [SIAM J. Control Optim., 22 (1984), pp. 856–877]. The aim of this paper is to inves-tigate how far connections of this type generalize to a nonconvex problem of purchasing electricity. Where the classical equivalence breaks down we provide alternative connections to optimal stopping problems. We consider a nonconvex infinite time horizon SSC problem whose state consists of an un-controlled diffusion representing a real-valued commodity price, and a controlled increasing bounded process representing an inventory. We analyze the geometry of the action and inaction regions by characterizing their (optimal) boundaries. Unlike the case of convex SSC problems we find that the optimal boundaries may be both reflecting and repelling and it is natural to interpret the problem as one of SSC with discretionary stopping

On the calculation of normals in free-surface flow problems

The use of boundary-conforming finite element methods is considered for the solution of surface-tension-dominated free-surface flow problems in three dimensions. This class of method is based upon the use of a moving mesh whose velocity is driven by the motion of the free surface, which is in turn determined via a kinematic boundary condition for the normal velocity. The significance of the method used to compute the normal direction at the finite element node points for a C0 piecewise-polynomial free surface is investigated. In particular, it is demonstrated that the concept of mass-consistent normals on an isoparametric quadratic tetrahedral mesh is flawed. In this case an alternative, purely geometric, normal is shown to lead to a far more robust numerical algorithm

Monte Carlo Hamiltonian - From Statistical Physics to Quantum Theory

Monte Carlo techniques have been widely employed in statistical physics as well as in quantum theory in the Lagrangian formulation. However, in some areas of application to quantum theories computational progress has been slow. Here we present a recently developed approach: the Monte Carlo Hamiltonian method, designed to overcome the difficulties of the conventional approach.Comment: StatPhys-Taiwan-1999, 6 pages, LaTeX using elsart.cl