A Stochastic Representation of the Local Structure of Turbulence

Based on the mechanics of the Euler equation at short time, we show that a Recent Fluid Deformation (RFD) closure for the vorticity field, neglecting the early stage of advection of fluid particles, allows to build a 3D incompressible velocity field that shares many properties with empirical turbulence, such as the teardrop shape of the R-Q plane. Unfortunately, non gaussianity is weak (i.e. no intermittency) and vorticity gets preferentially aligned with the wrong eigenvector of the deformation. We then show that slightly modifying the former vectorial field in order to impose the long range correlated nature of turbulence allows to reproduce the main properties of stationary flows. Doing so, we end up with a realistic incompressible, skewed and intermittent velocity field that reproduces the main characteristics of 3D turbulence in the inertial range, including correct vorticity alignment properties.Comment: 6 pages, 3 figures, final version, published

Long range predictability of atmospheric flows

International audienceIn the light of recent advances in 2D turbulence, we investigate the long range predictability problem of atmospheric flows. Using 2D Euler equations, we show that the full nonlinearity acting on a large number of degrees of freedom can, paradoxically, improve the predictability of the large scale motion, giving a picture opposite to the one largely popularized by Lorenz: a small local perturbation of the atmosphere will progressively gain larger and larger scales by nonlinear interaction and will finally cause large scale change in the atmospheric flow

A self‐consistent theory of nonequilibrium excitation transport in energetically disordered systems

The migration of incoherent excitations in energetically disordered systems is studied theoretically using a self‐consistent diagrammatic approximation. Spatial diffusion and energy relaxation observables are related to the solutions of a nonlinear integral equation. Extensive numerical illustrations are given for two‐component and multicomponent systems. In the latter, spatial transport is found to be highly dispersive (nondiffusive) over an extremely wide range of timescales, in accordance with results from simulations and experiments. The dependence of spatial and spectral transport properties upon the spatial range and the energy dependence of the intermolecular hopping rates is examined. Several measures of energy relaxation, including detailed probability distributions in energy space, relaxation‐time spectra, and the nonequilibrium entropy are calculated and compared. The intimate relationship between spatial transport and energy relaxation is discussed in detail.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70474/2/JCPSA6-82-8-3692-1.pd

Understanding forest users' participation in participatory forest management (PFM): Insights from Mt. Elgon forest ecosystem, Kenya

Participation of local communities in forest management decision-making has been promoted as a mechanism of improving livelihoods and forest conditions, yet the level of participation in many programs remains low. Using data from a cross-sectional survey of 924 forest-dependent households in Western Kenya, we examine the factors that support or constrain forest dependent people's participation in a Participatory Forest Management (PFM) program. We run a probit model to assess households' choice to join PFM and then compute a Participation Index (PI) for forest users' participation across different stages of the PFM program – planning, implementation and Monitoring and Evaluation (M&E). The determinants of participation are then analyzed using the fractional regression approach. Results show that over half (52%) of the respondents participated in PFM. While vulnerability to shocks, being in a farmers' group, a household's access to the forest within the previous 12 months and access to extension were associated with the likelihood of participating in PFM, the influence of the household head's age and education, access to credit and food insecurity had a negative influence. Our results reveal PIs of 41%, 49%, and 42% at the planning, implementation, and M&E stages respectively, indicating a moderate participation level. The fractional regression model shows that transaction costs associated with access to markets, gender (being male), household expenditure and expected forest benefits positively influence household participation in PFM, while the opportunity costs associated with off-farm income, distance to the forest and lack of extension have a negative influence on participation. These results point to the need to take the household context (gender, education, household expenditure and vulnerability) into consideration during planning and implementation of the forestry programs. The implication is that forest authorities should identify and implement mechanisms to enhance benefits from forests but also reduce costs of participation, especially for women

From Convergence to Connectivism: Teaching Journalism 2.0

Media Convergence leads to fundamental changes in the journalistic field. This is a challenge not only for the news industry but also for teaching journalism at universities. Improved skills and competences are needed in multi-modal editorial planning and cross-channel develop-ment of news stories. This paper describes the main drivers of change in the news industry, discusses consequences for journalism and teaching, and offers an innovative didactical ap-proach, which combines an interdisciplinary perspective with the concept of connectivism and cognitive apprenticeship. The consequences of convergence that affect journalism educa-tion are inspected under three sub-topics: the changes in the curricula, the changes in the courses syllabi, and the changes in the technological infrastructures of the academic institu-tions. It is pointed out, that recognizing connections and patterns to develop novel ideas and concepts is the core skill for individuals today. The paper shows, how that approach could be realized in an international 10-day-intensive program