Nonlinear diffusion model for Rayleigh-Taylor mixing

The complex evolution of turbulent mixing in Rayleigh-Taylor convection is studied in terms of eddy diffusiviy models for the mean temperature profile. It is found that a non-linear model, derived within the general framework of Prandtl mixing theory, reproduces accurately the evolution of turbulent profiles obtained from numerical simulations. Our model allows to give very precise predictions for the turbulent heat flux and for the Nusselt number in the ultimate state regime of thermal convection.Comment: 4 pages, 4 figure, PRL in pres

Dynamics and stability of vortex-antivortex fronts in type II superconductors

The dynamics of vortices in type II superconductors exhibit a variety of patterns whose origin is poorly understood. This is partly due to the nonlinearity of the vortex mobility which gives rise to singular behavior in the vortex densities. Such singular behavior complicates the application of standard linear stability analysis. In this paper, as a first step towards dealing with these dynamical phenomena, we analyze the dynamical stability of a front between vortices and antivortices. In particular we focus on the question of whether an instability of the vortex front can occur in the absence of a coupling to the temperature. Borrowing ideas developed for singular bacterial growth fronts, we perform an explicit linear stability analysis which shows that, for sufficiently large front velocities and in the absence of coupling to the temperature, such vortex fronts are stable even in the presence of in-plane anisotropy. This result differs from previous conclusions drawn on the basis of approximate calculations for stationary fronts. As our method extends to more complicated models, which could include coupling to the temperature or to other fields, it provides the basis for a more systematic stability analysis of nonlinear vortex front dynamics.Comment: 13 pages, 8 figure

Statistics of precursors to fingering processes

We present an analysis of the statistical properties of hydrodynamic field fluctuations which reveal the existence of precursors to fingering processes. These precursors are found to exhibit power law distributions, and these power laws are shown to follow from spatial $q$-Gaussian structures which are solutions to the generalized non-linear diffusion equation.Comment: 7 pages incl. 5 figs; tp appear in Europhysics Letter

Adaptación transcultural y validación del contenido del Delaware School Climate Survey-Student (DSCS-S) en Brasil

El clima escolar evalúa las dimensiones: social, emocional, ética, académica y ambiental de la vida escolar, tales como normas, metas, valores, relaciones interpersonales, prácticas de enseñanza y aprendizaje y estructuras institucionales. El presente artículo pretende presentar el proceso de traducción, adaptación cultural y de investigación de la validación del contenido del instrumento de clima escolar del Delaware School Climate Survey-Student (DSCS-S) en Brasil, especialmente la investigación de la validad del contenido del instrumento a través del coeficiente de validad de contenido (CVC). El proceso consistió en etapas de traducción y retraducción, estudio piloto con público albo, evaluaciones con especialistas y minuciosos ajustes en el instrumento. El análisis apunta a la importancia de seguir un riguroso método de adaptación transcultural de instrumentos para garantizar la validez del contenido, así como la existencia de evidencias de validez de contenido (CVC > 0,8 para todas las escalas del instrumento) del DSCS-S para la lengua portuguesa de Brasil. Este instrumento puede ayudar a las escuelas brasileñas a evaluar el clima escolar y desarrollar estrategias, programas y políticas escolares más eficacesSchool climate assessments aim to evaluate the social, emotional, ethical, academic and environmental aspects of school life, such as rules, goals, values, interpersonal relationships, teaching and learning practices as well as institutional structures. This paper presents the process of cross-cultural adaptation and content validity investigation of the Delaware School Climate Survey Student (DSCS-S) in Brazil. A content validity research was conducted through the content validity coefficient (CVC). The process consisted in translations and back-translation steps, pilot study with the target population, evaluations by an expert committee and rigorous revisions of the instrument. The analysis suggest the importance of a thorough method of cross-cultural adaptation to ensure its content validity, and the existence of content validity evidence (CVC > 0.8 for all instrument's scales) of the DSCS-S in Brazil. This instrument can support Brazilian schools to assess its climate in order to develop more effective school strategies, programs and policies

Cattle Temporal and Spatial Distribution in Midwestern Pastures Using Global Positioning (Three-year Progress Report)

Previous research has shown that grazing cattle tend to congregate in streamside zones of pastures to obtain water and shade for thermoregulation. However, problems associated with thermoregulation may be increased because of the presence of endophyte-infected tall fescue in pastures. Defining relationships between cattle distribution, such pasture characteristics as size, shape, shade distribution, botanical composition, and climatic factors related to heat stress, will provide the basis for the development and implementation of management practices that minimize nonpoint source pollution possibly associated with grazing cattle

Cattle Temporal & Spatial Distribution in Midwestern Pastures Using Global Positioning (A Three-Year Progress Report)

Eight pastures on five southern Iowa cow-calf farms were used to evaluate the effects of pasture characteristics and microclimatic conditions on cattle grazing cool-season grass pastures with streams and/or ponds. Pastures ranged from 19 to 309 acres and contained varying proportions of cool-season grasses, legumes, sedge, broadleaf weeds, brush, and bare ground. The percentages of pasture area that were shaded ranged from 19 to 73%. Cows were Angus and Angus-Cross on seven of the pastures, and Mexican Corriente on the remaining pasture. In spring, summer, and fall of 2007, 2008, and 2009, 2 to 3 cows per pasture were fitted with Global Positioning System (GPS) collars to record position at 10 minute intervals for periods of 5 to 14 days. Ambient temperature, black globe temperature, dew point, relative humidity, and wind speed and direction were collected with HOBO data loggers at ten minute intervals over the 2007, 2008, and 2009 grazing seasons on each farm. Streams, ponds, and fence lines were referenced on a geospatial map and used to establish zones in the pastures. Designated zones were: in the stream or pond, within 100 feet, or greater than 100 ft (uplands) from the stream or pond (water source). One hundred thirty-nine data sets were obtained throughout the three-year project. Mean proportions of observations when cattle were in the water source differed (P\u3c0.0001) between farms, but not between seasons (P=0.5824). Mean proportions of time cattle spent within 100, or greater 100 ft of the water source differed (P\u3c0.0001) among farms. The proportion of time cattle were within the streamside zone (defined as being in the water source or within 100 feet of the water source) increased with increasing ambient temperature, increasing the proportion of streamside zone within a pasture, increasing the proportion of total pasture shade within the streamside zone, and decreasing pasture size. Therefore, implementation of grazing management practices for the protection of pasture streams are more likely to be effective on small and/or narrow pastures in which cattle have less opportunity to locate in upland locations

Designing nutrition-based interventional trials for the future: addressing the known knowns

Abstract The consistent decline in critical illness mortality has a significant effect on trial design, whereby either an improbable effect sizes or large number of patients are required. The signal-to-noise ratio is of particular interest for the critically ill. When considering the potential signal, interventions need to match outcomes in regard to biological plausibility. Provision of nutrition is a complex decision with many underappreciated aspects of noise. However, a fundamental interaction is often not accounted for time. Working as a community to evolve trial design will be our challenge for nutrition interventions in the critically ill for the future