Analytical approach to viscous fingering in a cylindrical Hele-Shaw cell

We report analytical results for the development of the viscous fingering instability in a cylindrical Hele-Shaw cell of radius a and thickness b. We derive a generalized version of Darcy's law in such cylindrical background, and find it recovers the usual Darcy's law for flow in flat, rectangular cells, with corrections of higher order in b/a. We focus our interest on the influence of cell's radius of curvature on the instability characteristics. Linear and slightly nonlinear flow regimes are studied through a mode-coupling analysis. Our analytical results reveal that linear growth rates and finger competition are inhibited for increasingly larger radius of curvature. The absence of tip-splitting events in cylindrical cells is also discussed.Comment: 14 pages, 3 ps figures, Revte

Fractal measures of video-recorded trajectories can classify motor subtypes in Parkinson’s disease

[Abstract] Parkinson’s Disease is one of the most prevalent neurodegenerative diseases in the world and affects millions of individuals worldwide. The clinical criteria for classification of motor subtypes in Parkinson’s Disease are subjective and may be misleading when symptoms are not clearly identifiable. A video recording protocol was used to measure hand tremor of 14 individuals with Parkinson’s Disease and 7 healthy subjects. A method for motor subtype classification was proposed based on the spectral distribution of the movement and compared with the existing clinical criteria. Box-counting dimension and Hurst Exponent calculated from the trajectories were used as the relevant measures for the statistical tests. The classification based on the power-spectrum is shown to be well suited to separate patients with and without tremor from healthy subjects and could provide clinicians with a tool to aid in the diagnosis of patients in an early stage of the disease.Brasil. Conselho Nacional de Desenvolvimento Científico e Tecnológico; 306571/2011-0Brasil. Conselho Nacional de Desenvolvimento Científico e Tecnológico; 481414/2012-

Estimation of the friction velocity in stably stratified boundary-layer flows over hills

A method is suggested for the calculation of the friction velocity for stable turbulent boundary-layer flow over hills. The method is tested using a continuous upstream mean velocity profile compatible with the propagation of gravity waves, and is incorporated into the linear model of Hunt, Leibovich and Richards with the modification proposed by Hunt, Richards and Brighton to include the effects of stability, and the reformulated solution of Weng for the near-surface region. Those theoretical results are compared with results from simulations using a non-hydrostatic microscale-mesoscale two-dimensional numerical model, and with field observations for different values of stability. These comparisons show a considerable improvement in the behaviour of the theoretical model when the friction velocity is calculated using the method proposed here, leading to a consistent variation of the boundary-layer structure with stability, and better agreement with observational and numerical data

Application of satellite images to locate and inventory vineyards in the designation of origin "Bierzo" in Spain

P. 277-290With a view to contributing to the improvement of the current vineyard registers, this study presents a methodology for vineyard mapping based on satellite remote sensing systems. The procedure was validated for the Designation of origin "Bierzo" in Spain. Different supervised classifications were performed besed on two Landsat images acquired in the same year. The objetives of the present study were to determine which classification yielded the best results and to quantify the influence of different factors that affected the overall classification accuracy, such as the resampling method, the use of georeferenced mosaics, or the combination of the two imagesS

Rapid detection and identification of strains carrying carbapenemases directly from positive blood cultures using MALDI-TOF MS

MALDI-TOF MS has been evaluated to detect carbapenemases activity and pathogen identification directly from positive blood cultures. 21 non-carbapenemase producers and 19 carbapenemase producers Enterobacteriaceae and Pseudomonas aeruginosa strains were included in the study. This technique is simple and detects carbapenemases in 4.5h with high sensitivity and specificity

The influence of processing parameters on morphology and granulometry of a wet-milled sol-gel glass powder

A quaternary bioactive sol-gel glass of high silica content was heat treated at different temperatures, and then wet ball milled under different balls-to-powder ratios. A total of sixteen experiments were performed to study in detail the effects of both experimental variables on the structure, morphology, particle size distributions and nitrogen adsorption isotherms. The balls–to–powder ratio exerts a tremendous influence on the final particle size distribution of the powders, while its effects on the pore volume and morphology are minimal. These structural features are mostly governed by the changes in calcination temperature. Therefore, understanding the specific roles of each experimental parameter is of paramount importance towards achieving optimum powders with the desired properties. This work sheds light on the importance of using a suitable combination of these two parameters for tuning the morphology and the granulometry of the sol-gel derived bioactive glass powders.publishe

The shock of reality: I went to sleep an accountant and woke up a professor

O presente estudo tem o objetivo de identificar os principais problemas enfrentados pelos docentes da área contábil nos seus três primeiros anos de carreira. Para alcançar esse objetivo, foram consultados estudos sobre as fases de vida dos professores e os problemas que esses enfrentaram (Gonçalves, 1995, 2009; Huberman, 1989, 2000; Veenman, 1984). Foram aplicados questionários, com questões abertas e fechadas, a 84 professores brasileiros ingressantes na carreira em Ciências Contábeis. Por meio de uma análise quantitativa e qualitativa, os resultados indicaram que a falta de formação para o exercício da docência pode levar os docentes da área contábil ao fenômeno "choque com a realidade". Os achados também evidenciam que os principais problemas que afligem os docentes são: desmotivação dos discentes, heterogeneidade das classes, salas lotadas, falta de tempo, dificuldade para determinar nível de aprendizado, e quantidade de atividades administrativasThis study aims to identify the main problems faced by teachers of accounting in the first three years of their career. For this purpose, references were consulted on the career phases of professors and the problems they face (Gonçalves, 1995, 2009; Huberman, 1989, 2000; Veenman, 1984). Questionnaires, with open and closed questions, were given to 84 recently hired Brazilian professors of accounting. By means of a quantitative and qualitative analysis, the results indicate that the lack of teacher training can cause these professors to suffer a “shock of reality”. The findings also evidence that the main problems that afflict these teachers are: unmotivated students, heterogeneous class makeup, crowded classrooms, lack of time, difficulty to determine the level of learning, and burdensome administrative dutie

How bias-correction can improve air quality forecast over Portugal

Currently three air quality modelling systems operate routinely with high-resolution over mainland Portugal for forecasting purposes, namely MM5-CHIMERE, MM5-EURAD, and CALIOPE. They each operate daily using different horizontal resolutions (10 km × 10 km, 5 km × 5 km, and 4 km × 4 km, respectively), specific physical and chemical parameterizations, and their own emission pre-processors (with a common EMEP emission database source but different spatial disaggregation methodologies). The operational BSC-DREAM8b model is coupled offline within the aforementioned air quality systems to provide the Saharan dust contribution to particulate matter. Bias-correction studies have demonstrated the benefit of using past observational data to reduce systematic model forecast errors. The present contribution aims to evaluate the application of two bias-correction techniques, the multiplicative ratio and the Kalman filter, in order to improve air quality forecasts for Portugal. Both techniques are applied to the three modelling systems over the full year of 2010. Raw and unbiased model results for the main atmospheric pollutants (O3, NO2, SO2, PM10, and PM2.5) are analysed and compared with data from 18 monitoring stations distributed within inland Portugal on an hourly basis. Statistical analysis shows that both bias-correction techniques improve the raw forecast skills (for all the modelling systems and pollutants). In the case of O3 max-8 h, correlation coefficients improve by 19-45%, from 0.56-0.81 (raw models) to 0.78-0.86 (corrected models). PM2.5 also presents significant improvements, for example correlation coefficients increase by more than 50% (with both techniques), reaching values between 0.50 and 0.64. The corrected primary pollutants NO2 and SO2 demonstrate significant relative improvements compared to O3, mostly because the original modelling system skills are lower for those species. Although the applied techniques have different mathematical formulations and complexity levels, there are comparable answers for all of the forecasting systems. Analysis performed over specific situations such as air quality episodes and cases of unvalidated or missing data reveals different behaviours of the bias-correction techniques under study. The results confirm the advantage of the application of bias-correction techniques for air quality forecasts. Both techniques can be applied routinely in operational forecast systems and they will be useful to provide accurate alerts about exceedances to the population

The Saffman-Taylor problem on a sphere

The Saffman-Taylor problem addresses the morphological instability of an interface separating two immiscible, viscous fluids when they move in a narrow gap between two flat parallel plates (Hele-Shaw cell). In this work, we extend the classic Saffman-Taylor situation, by considering the flow between two curved, closely spaced, concentric spheres (spherical Hele-Shaw cell). We derive the mode-coupling differential equation for the interface perturbation amplitudes and study both linear and nonlinear flow regimes. The effect of the spherical cell (positive) spatial curvature on the shape of the interfacial patterns is investigated. We show that stability properties of the fluid-fluid interface are sensitive to the curvature of the surface. In particular, it is found that positive spatial curvature inhibits finger tip-splitting. Hele-Shaw flow on weakly negative, curved surfaces is briefly discussed.Comment: 26 pages, 4 figures, RevTex, accepted for publication in Phys. Rev.

Rotating Hele-Shaw cells with ferrofluids

We investigate the flow of two immiscible, viscous fluids in a rotating Hele-Shaw cell, when one of the fluids is a ferrofluid and an external magnetic field is applied. The interplay between centrifugal and magnetic forces in determining the instability of the fluid-fluid interface is analyzed. The linear stability analysis of the problem shows that a non-uniform, azimuthal magnetic field, applied tangential to the cell, tends to stabilize the interface. We verify that maximum growth rate selection of initial patterns is influenced by the applied field, which tends to decrease the number of interface ripples. We contrast these results with the situation in which a uniform magnetic field is applied normally to the plane defined by the rotating Hele-Shaw cell.Comment: 12 pages, 3 ps figures, RevTe