Screening effects in flow through rough channels

A surprising similarity is found between the distribution of hydrodynamic stress on the wall of an irregular channel and the distribution of flux from a purely Laplacian field on the same geometry. This finding is a direct outcome from numerical simulations of the Navier-Stokes equations for flow at low Reynolds numbers in two-dimensional channels with rough walls presenting either deterministic or random self-similar geometries. For high Reynolds numbers, when inertial effects become relevant, the distribution of wall stresses on deterministic and random fractal rough channels becomes substantially dependent on the microscopic details of the walls geometry. In addition, we find that, while the permeability of the random channel follows the usual decrease with Reynolds, our results indicate an unexpected permeability increase for the deterministic case, i.e., ``the rougher the better''. We show that this complex behavior is closely related with the presence and relative intensity of recirculation zones in the reentrant regions of the rough channel.Comment: 4 pages, 5 figure

Avaliação da atividade inseticida de óleos essenciais de plantas da flora nordestina contra a mosca-branca (Bemisia argentifolii).

E conhecido que muitas plantas encerram micromoleculas oriundas do metabolismo secundario, tais como alcaloides, flavonoides, triterpenos, limnnoides, dentre outras, as quais apresentam funcao de protecao contra fitopatogenos e insetos fitofagos. Dos varios exemplos, podemos citar os glicoalcaloides em Solanaceace, os limonoides em Rutaceae, Meliaceae e Simarubaceae. Algumas dessas substancias sao conhecidas por suas propriedade inseticidas, dentre as quais podemos citar: rotenoides obtidos das especies de Lonchocarpus; nicotina de Nicotiana tabacum; precocenos de Ageratrum conyzoides e piretrinas de Crysanthemum cineraefolium (Craveiro e Machado, 1986).bitstream/CNPAT-2010/5858/1/Pa-080.pd

Numerical and experimental investigation of the stability of a drop in a single-axis acoustic levitator

Acoustic levitation can be employed to hold liquid drops in midair, enabling novel applications in X-ray scattering of proteins, amorphous crystallization of solutions, or contactless mixing. Multiple studies have characterized the physical behavior of a levitated drop inside an acoustic field. Here, we present a numerical and experimental study on the acoustic levitation of water drops in a single-Axis acoustic levitator consisting of an ultrasonic transducer and an opposing reflector. Instead of modeling an abstract incident acoustic field, our model considers the shape of the drop as well as the real geometry of the levitator. We also use a high-speed camera to observe the disintegration and the undesired oscillations of the drops. Our results show that the insertion of a drop in the levitator provokes a shift in its resonant frequency that depends on the shape of the drop. Second, the levitation behavior depends on whether the levitator operates slightly below or above the resonance. Third, if the levitator is driven above the resonant frequency, it is possible to levitate with more strength and avoid disintegration of the drop. This research provides an insight on how to achieve more stable experiments that avoid the bursting and undesired oscillations of the levitated sample. We hope that it will facilitate numerous experiments involving acoustically levitated liquid drops.This work was supported by the São Paulo Research Foundation—FAPESP (Grant No. 2017/27078-0)

High Order Correction Terms for The Peak-Peak Correlation Function in Nearly-Gaussian Models

One possible way to investigate the nature of the primordial power spectrum fluctuations is by investigating the statistical properties of the local maximum in the density fluctuation fields. In this work we present a study of the mean correlation function, $\xi_r$, and the correlation function for high amplitude fluctuations (the peak-peak correlation) in a slighlty non-Gaussian context. From the definition of the correlation excess, we compute the Gaussian two-point correlation function and, using an expansion in Generalized Hermite polynomials, we estimate the correlation of high density peaks in a non-Gaussian field with generic distribution and power spectrum. We also apply the results obtained to a scale-mixed distribution model, which correspond to a nearly Gaussian model. The results reveal that, even for a small deviation from Gaussianity, we can expect high density peaks to be much more correlated than in a Gaussian field with the same power spectrum. In addition, the calculations reveal how the amplitude of the peaks in the fluctuations field is related to the existing correlations. Our results may be used as an additional tool to investigate the behavior of the N-point correlation function, to understand how non-Gaussian correlations affect the peak-peak statistics and extract more information about the statistics of the density field.Comment: Accepted for publication in A&

Polyphenolic and chromatic characterization of tropical red wines produced in the São Francisco river Valley (Northeast Brazil).

Young varietal and experimental wines from Vitis vinifera - Petit Verdot,Tempranillo and Syrah - cultivated in a tropical semiarid region (Northeast Brazil) were evaluated with regard to their phenolic composition and chromatic characteristics during a storage period of 12-month. The wine was stored in bottles and evaluated using spectrophotometry and high efficiency liquid chromatography to determine color, total polyphenols, anthocyanins, flavanols and flavonols. The Petit Verdot had a less color variation when compared to wines from temperate climates. Although the wines followed the traditional pattem of decreasing polyphenol concentration during storage, the concentrations of these compounds remained higher than those reported in literature, such as for the anthocyanins in Petit Verdot wines and transresveratrolin Syrah, showing possible beneficial health effects even after storag

The Cauchy convergence of T and P-approximant templates for test-mass Kerr binary systems

In this work we examine the Cauchy convergence of both post-Newtonian (T-approximant) and re-summed post-Newtonian (P-approximant) templates for the case of a test-mass orbiting a Kerr black hole along a circular equatorial orbit. The Cauchy criterion demands that the inner product between the $n$ and $n+1$ order approximation approaches unity, as we increase the order of approximation. In previous works, it has been shown that we achieve greater fitting factors and better parameter estimation using the P-approximant templates for both Schwarzschild and Kerr black holes. In this work, we show that the P-approximant templates also display a faster Cauchy convergence making them a superior template to the standard post-Newtonian templates.Comment: 5 pages, Replaced with shortened published versio