Long-term variations of turbulent transport coefficients in a solar-like convective dynamo simulation

The Sun, aside from its eleven year sunspot cycle is additionally subject to long term variation in its activity. In this work we analyse a solar-like convective dynamo simulation, containing approximately 60 magnetic cycles, exhibiting equatorward propagation of the magnetic field, multiple frequencies, and irregular variability, including a missed cycle and complex parity transitions between dipolar and quadrupolar modes. We compute the turbulent transport coefficients, describing the effects of the turbulent velocity field on the mean magnetic field, using the test-field method. The test-field analysis provides a plausible explanation of the missing cycle in terms of the reduction of $\alpha_{\phi\phi}$ in advance of the reduced surface activity, and enhanced downward turbulent pumping during the event to confine some of the magnetic field at the bottom of the convection zone, where local maximum of magnetic energy is observed during the event. At the same time, however, a quenching of the turbulent magnetic diffusivities is observed, albeit differently distributed in depth compared to the other transport coefficients. Therefore, dedicated mean-field modelling is required for verification.Comment: 11 pages, 12 figures, accepted by AN for 14th Potsdam Thinksho

Allocation in Practice

How do we allocate scarcere sources? How do we fairly allocate costs? These are two pressing challenges facing society today. I discuss two recent projects at NICTA concerning resource and cost allocation. In the first, we have been working with FoodBank Local, a social startup working in collaboration with food bank charities around the world to optimise the logistics of collecting and distributing donated food. Before we can distribute this food, we must decide how to allocate it to different charities and food kitchens. This gives rise to a fair division problem with several new dimensions, rarely considered in the literature. In the second, we have been looking at cost allocation within the distribution network of a large multinational company. This also has several new dimensions rarely considered in the literature.Comment: To appear in Proc. of 37th edition of the German Conference on Artificial Intelligence (KI 2014), Springer LNC

On-campus service projects: an experiment in education for liberation

This article describes an approach to service-learning based on Paulo Freire’s model of education for liberation. On-campus Service Projects (OCSPs) differ markedly from typical service-learning assignments in two ways: (1) they take place in the students’ own college setting rather than out in the community; and (2) in my version, they challenge students to engage in critical thinking and acting (praxis) to transform ‘‘oppressive’’ situations within their institution. The article reviews Freire’s pedagogical approach and details how it is implemented in OCSPs. Like all service-learning, the OCSP experience enables students to practice course-related skills (e.g., team building, project planning). More importantly, it gives students insights into the political reality of organizations, and makes them aware of their ability, collectively, to change that reality

Electricity in Central America: paradigms, reforms and the energy trilemma

A new global energy era is emerging, one driven by the confluence of energy security, climate politics and energy equity issues. This ‘energy trilemma’ is shaping the global political economy of energy, which in turn influences how decisions are made about how energy is provided—referred to as global energy governance. This article analyzes historical and contemporary developments in Central America’s power sectors. This is a region that has long been an implementation space for global policy priorities, but has been overlooked by those engaging with the challenges of the energy trilemma. During the 1990s and 2000s, the statist model of energy governance gave way to a market-led model in the Central American isthmus. This led to the privatization of state-owned utilities and the promotion of a regional electricity market. During this period, the dominance of largely hydro-based renewable electricity generation diminished to be replaced by imported fossil fuel-based generation. Oil price increases during the early 2000s highlighted the region’s dependence on imports, with some countries turning to energy rationing. Increasingly interventionist state policies, which now seek to reduce oil dependence, improve energy efficiency and expand access to electricity, are being pursued in the region. This interventionist turn reflects the pressures of the energy trilemma, although energy security, particularly the need to reduce dependence on imported oil, remains the most important driver

The supernova-regulated ISM. II. The mean magnetic field

The origin and structure of the magnetic fields in the interstellar medium of spiral galaxies is investigated with 3D, non-ideal, compressible MHD simulations, including stratification in the galactic gravity field, differential rotation and radiative cooling. A rectangular domain, 1x1x2 kpc^{3} in size, spans both sides of the galactic mid-plane. Supernova explosions drive transonic turbulence. A seed magnetic field grows exponentially to reach a statistically steady state within 1.6 Gyr. Following Germano (1992) we use volume averaging with a Gaussian kernel to separate magnetic field into a mean field and fluctuations. Such averaging does not satisfy all Reynolds rules, yet allows a formulation of mean-field theory. The mean field thus obtained varies in both space and time. Growth rates differ for the mean-field and fluctuating field and there is clear scale separation between the two elements, whose integral scales are about 0.7 kpc and 0.3 kpc, respectively.Comment: 5 pages, 10 figures, submitted to Monthly Notices Letter

The supernova-regulated ISM. I. The multi-phase structure

We simulate the multi-phase interstellar medium randomly heated and stirred by supernovae, with gravity, differential rotation and other parameters of the solar neighbourhood. Here we describe in detail both numerical and physical aspects of the model, including injection of thermal and kinetic energy by SN explosions, radiative cooling, photoelectric heating and various transport processes. With 3D domain extending 1 kpc^2 horizontally and 2 kpc vertically, the model routinely spans gas number densities 10^-5 - 10^2 cm^-3, temperatures 10-10^8 K, local velocities up to 10^3 km s^-1 (with Mach number up to 25). The thermal structure of the modelled ISM is classified by inspection of the joint probability density of the gas number density and temperature. We confirm that most of the complexity can be captured in terms of just three phases, separated by temperature borderlines at about 10^3 K and 5x10^5 K. The probability distribution of gas density within each phase is approximately lognormal. We clarify the connection between the fractional volume of a phase and its various proxies, and derive an exact relation between the fractional volume and the filling factors defined in terms of the volume and probabilistic averages. These results are discussed in both observational and computational contexts. The correlation scale of the random flows is calculated from the velocity autocorrelation function; it is of order 100 pc and tends to grow with distance from the mid-plane. We use two distinct parameterizations of radiative cooling to show that the multi-phase structure of the gas is robust, as it does not depend significantly on this choice.Comment: 28 pages, 22 figures and 8 table

Directions for national mastitis control programs: experiences from The Netherlands

The general aim of mastitis control programs is to improve udder health on dairy farms. Over the last five years an intensive national mastitis program was executed in the Netherlands with the goal to improve udder health at a national level. Different groups of farmers have different motivations and should be approached differently, and their behaviour is influenced by different advisors. Therefore, as many different groups of advisors as possible should be involved in the program. Most of the veterinary practices in the Netherlands participated as did, in later years, other farm advisors. We experienced that for a successful program it is crucial to have knowledge on motivating factors of dairy farmers. Many advisors are convinced that the only way to change farmers’ behavior is through economics. We found that economics are important, but that other factors are as important in influencing farmers’ behaviour. To have a successful national mastitis program it is advisable to involve professionals on communication in designing the program. Although the technical knowledge on which the program is built should be optimal, that generally is not the bottle-neck in being successful. There often is more to gain in presenting knowledge in such a way that it is actually used, than in increasing the amount of existing knowledge

Chromoionophores in optical ion sensors

The feasibility of surface plasmon resonance (SPR) for ion sensing has been investigated. Emphasis is laid on a simulation-based optimization of the SP carrying structure, as well as the applicability of a specific chemo—optical interface we have developed. A preliminary result is presented