Onsager's Wien Effect on a Lattice

The Second Wien Effect describes the non-linear, non-equilibrium response of a weak electrolyte in moderate to high electric fields. Onsager's 1934 electrodiffusion theory along with various extensions has been invoked for systems and phenomena as diverse as solar cells, surfactant solutions, water splitting reactions, dielectric liquids, electrohydrodynamic flow, water and ice physics, electrical double layers, non-Ohmic conduction in semiconductors and oxide glasses, biochemical nerve response and magnetic monopoles in spin ice. In view of this technological importance and the experimental ubiquity of such phenomena, it is surprising that Onsager's Wien effect has never been studied by numerical simulation. Here we present simulations of a lattice Coulomb gas, treating the widely applicable case of a double equilibrium for free charge generation. We obtain detailed characterisation of the Wien effect and confirm the accuracy of the analytical theories as regards the field evolution of the free charge density and correlations. We also demonstrate that simulations can uncover further corrections, such as how the field-dependent conductivity may be influenced by details of microscopic dynamics. We conclude that lattice simulation offers a powerful means by which to investigate system-specific corrections to the Onsager theory, and thus constitutes a valuable tool for detailed theoretical studies of the numerous practical applications of the Second Wien Effect.Comment: Main: 12 pages, 4 figures. Supplementary Information: 7 page

Origin of the approximate universality of distributions in equilibrium correlated systems

We propose an interpretation of previous experimental and numerical experiments, showing that for a large class of systems, distributions of global quantities are similar to a distribution originally obtained for the magnetization in the 2D-XY model . This approach, developed for the Ising model, is based on previous numerical observations. We obtain an effective action using a perturbative method, which successfully describes the order parameter fluctuations near the phase transition. This leads to a direct link between the D-dimensional Ising model and the XY model in the same dimension, which appears to be a generic feature of many equilibrium critical systems and which is at the heart of the above observations.Comment: To appear in Europhysics Letter

On modeling player fitness in training for team sports with application to professional rugby

It is increasingly important for professional sports teams to monitor player fitness in order to optimize performance. Models have been put forward linking fitness in training to performance in competition but rely on regular measurements of player fitness. As formal tests for measuring player fitness are typically time-consuming and inconvenient, measurements are taken infrequently. As such, it may be challenging to accurately predict performance in competition as player fitness is unknown.Alternatively, other data, such as how the players are feeling, may be measured more regularly. This data, however, may be biased as players may answer the questions differently and these differences may dominate the data. Linear Mixed Methods and Support Vector Machines were used to estimate player fitness from available covariates at times when explicit measures of fitness are unavailable. Using data provided by Glasgow Warriors Rugby Club, a case study was used to illustrate the application and value of these models. Both models performed well with R2 values ranging from 60% to 85%, demonstrating that the models largely captured the biases introduced by individual players

Magnetic Monopole Dynamics in Spin Ice

One of the most remarkable examples of emergent quasi-particles, is that of the "fractionalization" of magnetic dipoles in the low energy configurations of materials known as "spin ice", into free and unconfined magnetic monopoles interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45 (2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges really does exist at low temperature in these materials and this discovery provides a new perspective on otherwise largely inaccessible phenomenology. In this paper, after a review of the different spin ice models, we present detailed results describing the diffusive dynamics of monopole particles starting both from the dipolar spin ice model and directly from a Coulomb gas within the grand canonical ensemble. The diffusive quasi-particle dynamics of real spin ice materials within "quantum tunneling" regime is modeled with Metropolis dynamics, with the particles constrained to move along an underlying network of oriented paths, which are classical analogues of the Dirac strings connecting pairs of Dirac monopoles.Comment: 26 pages, 12 figure

Exploiting changes in the tumour microenvironment with sequential cytokine and matrix metalloprotease inhibitor treatment in a murine breast cancer model

The study of treatment-induced changes in the tumour microenvironment might lead to effective combinations of biological therapy. IL-12 induced tumour regression and cure of an experimental murine breast cancer, HTH-K, but only after long-term treatment that was associated with chronic toxicity. During IL-12 therapy, tumour levels of the matrix metalloprotease MMP-9 declined and its inhibitor TIMP-1 was strongly induced. We therefore administered alternate cycles of IL-12 and the MMP inhibitor Batimastat (BB94) to mice. Therapeutic efficacy was increased compared with short-term IL-12 therapy but without the chronic toxicity associated with long-term IL-12 treatment. Image analysis of treated tumours revealed that BB94 prevented regeneration of tumour and stromal compartments that normally occurred after short-term IL-12 therapy. © 2000 Cancer Research Campaign http://www.bjcancer.co

Relevance of soft modes for order parameter fluctuations in the Two-Dimensional XY model

We analyse the spin wave approximation for the 2D-XY model, directly in reciprocal space. In this limit the model is diagonal and the normal modes are statistically independent. Despite this simplicity non-trivial critical properties are observed and exploited. We confirm that the observed asymmetry for the probability density function for order parameter fluctuations comes from the divergence of the mode amplitudes across the Brillouin zone. We show that the asymmetry is a many body effect despite the importance played by the zone centre. The precise form of the function is dependent on the details of the Gibbs measure, giving weight to the idea that an effective Gibbs measure should exist in non-equilibrium systems, if a similar distribution is observed.Comment: 12 pages, 9 figure

Mixed couples in France. Statistical facts, definitions, and social reality

Mixed couples are usually defined as combining national, cultural, racial or religious dif­ferences, but these definitions are generally elaborated only empirically. More recently, researchers have proposed the concept of "mixedness" which goes beyond those descriptive factors of difference. The French national Migration, Tradition and Citizenship Act also helps to show why it is not easy to reach a single definition.A detailed look at statistical realities illustrates how complex it is to count mixed cou­ples. The figures differ if we consider mixed marriages as flows (new marriages each year) or as stock (how many people live in a mixed family). They also vary depending on what differences —cultural belonging or nationality— are taken into account. Many French-foreign marriages bring together people who have the same cultural identities. From the sociological point of view, mixed marriage should be defined as combining perceived differences and existing social order and norms. Studies on mixedness look at how socially constructed differences in contact, e.g. in private life, influence social relations and modify social realities. Mixed couples experience specific social constraints due to the migration situation of at least one of the partners, and therefore these couples need time to learn to manage the cultural and social differences in their relationship. Differences between the partners due to their cultural and social affiliations or gender roles are not equal and also influence the transcultural hybridisation process, sometimes even hindering it considerably.Una pareja mixta se define generalmente como la combinación de las diferencias nacio­nales, culturales, raciales o religiosas. Pero estas definiciones generalmente se elaboran sólo empíricamente. Más recientemente, los investigadores han propuesto el concepto de «mestizaje», que va más allá de los factores descriptivos de la diferencia. La tradición de migración nacional francesa y la Ley de ciudadanía también ayudan a entender por qué no es fácil llegar a una definición única. Una mirada pormenorizada a la realidad estadística ilustra lo complejo que es contar el número de parejas mixtas. Las cifras difieren si se considera el matrimonio mixto como un flujo (los matrimonios nuevos cada año) o como población (número de personas que viven en una familia mixta). También varían en función de qué diferencias se tienen en cuenta —la pertenencia cultural o la nacionalidad. Muchos matrimonios entre franceses y extranjeros unen a personas que tienen la misma identidad cultural. Desde el punto de vista sociológico, el matrimonio mixto debería definirse como la combinación de las diferencias percibidas y el orden social existente y las normas. Los estu­dios sobre el mestizaje tratan de cómo las diferencias sociales en contacto -por ejemplo en la vida privada- influyen en las relaciones sociales y modifican la realidad social. Las parejas mixtas están involucradas en determinadas limitaciones sociales debido a la situación de migrante de por lo menos uno de los cónyuges. Por lo tanto, estas parejas necesitan tiempo para aprender a gestionar las diferencias culturales y sociales en su relación. Las diferencias entre los cónyuges, debidas a sus filiaciones sociales y culturales y a los roles de género, no están en pie de igualdad y también influyen en el proceso de hibridación transcultural, a veces incluso obstaculizándolo considerablemente

Universal Magnetic Fluctuations with a Field Induced Length Scale

We calculate the probability density function for the order parameter fluctuations in the low temperature phase of the 2D-XY model of magnetism near the line of critical points. A finite correlation length, \xi, is introduced with a small magnetic field, h, and an accurate expression for \xi(h) is developed by treating non-linear contributions to the field energy using a Hartree approximation. We find analytically a series of universal non-Gaussian distributions with a finite size scaling form and present a Gumbel-like function that gives the PDF to an excellent approximation. We propose the Gumbel exponent, a(h), as an indirect measure of the length scale of correlations in a wide range of complex systems.Comment: 7 pages, 4 figures, 1 table. To appear in Phys. Rev.

Implementation of healthy food environment policies to prevent nutrition-related non-communicable diseases in Ghana : national experts’ assessment of Government action

Nutrition-related non-communicable diseases (NR-NCDs) are a global health problem, increasingly recognised as driven by unhealthy food environments. Yet little is known about government action to implement food environment-relevant policies, particularly in low-and lower-middle income countries. This study assessed government action, implementation gaps, and priorities to improve the food environment in Ghana. Using the Healthy Food-Environment Policy Index (Food-EPI), a panel comprising government and independent experts (n = 19) rated government action to improve the healthiness of food environment in Ghana against international best practices and according to steps within a policy cycle. Forty-three good practice indicators of food environment policy and infrastructure support were used, with ratings informed by systematically collected evidence of action validated by government officials. Following the rating exercise, the expert panel proposed and prioritized actions for government implementation. Three-quarters of all good practice indicators were rated at ‘low’/‘very little’ implementation. Restricting the marketing of breast milk substitutes was the only indicator rated “very high”. Of ten policy actions prioritized for implementation, restricting unhealthy food marketing in children’s settings and in the media were ranked the highest priority. Providing sufficient funds for nationally-relevant research on nutrition and NCDs was the highest priority infrastructure-support action. Other priority infrastructure-support actions related to leadership, monitoring and evaluation. This study identified gaps in Ghana’s implementation of internationally-recommended policies to promote healthy food environments. National stakeholders recommended actions, which will require legislation and leadership. The findings provide a baseline for measuring government progress towards implementing effective policies to prevent NR-NCDs