The measurement of velocity gradients in laminar flow by homodyne light-scattering spectroscopy

A technique for measuring velocity gradients in laminar flows by homodyne light scattering is presented. A theory which describes the light-scattering spectrum is derived that includes the effects of different types of linear flow fields, particle diffusion and the intensity profile in the scattering volume. The conditions which must be satisfied in order that the theory describe the experimental situation are outlined and complementary experiments are performed which both verify the theory and apply the technique. Verification is provided using the flow in a Couette device, and the flow due to single rotating cylinder in a large bath of fluid. The technique is then applied to measure the spatial variation of the shear rate in a four-roll mill

The scenario of two-dimensional instabilities of the cylinder wake under EHD forcing: A linear stability analysis

We propose to study the stability properties of an air flow wake forced by a dielectric barrier discharge (DBD) actuator, which is a type of electrohydrodynamic (EHD) actuator. These actuators add momentum to the flow around a cylinder in regions close to the wall and, in our case, are symmetrically disposed near the boundary layer separation point. Since the forcing frequencies, typical of DBD, are much higher than the natural shedding frequency of the flow, we will be considering the forcing actuation as stationary. In the first part, the flow around a circular cylinder modified by EHD actuators will be experimentally studied by means of particle image velocimetry (PIV). In the second part, the EHD actuators have been numerically implemented as a boundary condition on the cylinder surface. Using this boundary condition, the computationally obtained base flow is then compared with the experimental one in order to relate the control parameters from both methodologies. After validating the obtained agreement, we study the Hopf bifurcation that appears once the flow starts the vortex shedding through experimental and computational approaches. For the base flow derived from experimentally obtained snapshots, we monitor the evolution of the velocity amplitude oscillations. As to the computationally obtained base flow, its stability is analyzed by solving a global eigenvalue problem obtained from the linearized Navier–Stokes equations. Finally, the critical parameters obtained from both approaches are compared

Ferida da moda: epidemiologia, diagnóstico, tratamento e experiência com eqüinos infectados no Pantanal.

A pitiose é uma doença granulomatosa que atinge eqüinos, caninos, bovinos, felinos e humanos e ocorre em áreas tropicais, subtropicais ou temperadas (Meireles et al., 1993; Mendoza et al., 1996), causada pelo omiceto Pythium insidiosum (De Cock et al., 1987). A espécie eqüina é a mais atingida, principalmente nas formas cutânea e subcutânea, seguida dos caninos (Mendoza et al., 1996). A enfermidade em eqüinos caracteriza-se pela formação de granulomas eosinofílicos, com a presença de massas necróticas chamadas de kunkers (Mendoza e Alfaro, 1986; Meireles et al., 1993). Em humanos, a doença é mais comum no sudeste asiático, caracterizando-se por formas sistêmicas com arterites e também formas oftálmicas e subcutâneas, sendo as duas últimas associadas a a e b-talassemias (Imwidthaya, 1994; Imwidthaya, 1995). Vários tratamentos têm sido utilizados, principalmente em eqüinos, incluindo tratamento químico (antifúngicos), cirúrgico e imunoterápico. A imunoterapia, proposta inicialmente por Miller (1981), surgiu como uma alternativa concreta para o controle da doença e tem apresentado resultados promissores (Monteiro, 1999). Pythium insidiosum; Epidemiologia; Pitiose nos eqüinos; Imunoterapia; Diagnóstico; Tratamento; Experiência no Pantanal; Pitiose em bovinos; Pitiose experimental; Perspecivas para o controle da pitiose.bitstream/item/79509/1/COT34.pd

Orientation dynamics of weakly Brownian particles in periodic viscous flows

Evolution equations for the orientation distribution of axisymmetric particles in periodic flows are derived in the regime of small but non-zero Brownian rotations. The equations are based on a multiple time scale approach that allows fast computation of the relaxation processes leading to statistical equilibrium. The approach has been applied to the calculation of the effective viscosity of a thin disk suspension in gravity waves.Comment: 16 pages, 7 eps figures include

Ultra Low-Power Analog Median Filters

The design and implementation of three analog median filter topologies, whose transistors operate in the deep weak-inversion region, is described. The first topology is a differential pairs array, in which drain currents are driven into two nodes in a differential fashion, while the second topology is based on a wide range OTA, which is used to maximize the dynamic range. Finally, the third topology uses three range-extended OTAs. The proposed weak-inversion filters were designed and fabricated in ON Semiconductor 0.5 micrometer technology through MOSIS. Experimental results of three-input fabricated prototypes for all three topologies are show, where power consumptions of 90nW in the first case, and 270nW in the other two cases can be noticed. A dual power supply +/-1.5 Volts were used

Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) off the Surface of Helium Nanodroplets

We present a combined ion imaging and density functional theory study of the dynamics of the desorption process of rubidium and cesium atoms off the surface of helium nanodroplets upon excitation of the perturbed $6s$ and $7s$ states, respectively. Both experimental and theoretical results are well represented by the pseudodiatomic model for effective masses of the helium droplet in the desorption reaction of m_eff/m_He~10 (Rb) and 13 (Cs). Deviations from this model are found for Rb excited to the 6p state. Photoelectron spectra indicate that the dopant-droplet interaction induces relaxation into low-lying electronic states of the desorbed atoms in the course of the ejection process.Comment: in press, J. Phys. Chem. A (2014

Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses

Experiments by several groups during the past decade have shown that a molten polymer nanofilm subject to a large transverse thermal gradient undergoes spontaneous formation of periodic nanopillar arrays. The prevailing explanation is that coherent reflections of acoustic phonons within the film cause a periodic modulation of the radiation pressure which enhances pillar growth. By exploring a deformational instability of particular relevance to nanofilms, we demonstrate that thermocapillary forces play a crucial role in the formation process. Analytic and numerical predictions show good agreement with the pillar spacings obtained in experiment. Simulations of the interface equation further determine the rate of pillar growth of importance to technological applications.Comment: 5 pages, 4 figure

Interacting Particles and Strings in Path and Surface Representations

Non-relativistic charged particles and strings coupled with abelian gauge fields are quantized in a geometric representation that generalizes the Loop Representation. We consider three models: the string in self-interaction through a Kalb-Ramond field in four dimensions, the topological interaction of two particles due to a BF term in 2+1 dimensions, and the string-particle interaction mediated by a BF term in 3+1 dimensions. In the first case one finds that a consistent "surface-representation" can be built provided that the coupling constant is quantized. The geometrical setting that arises corresponds to a generalized version of the Faraday's lines picture: quantum states are labeled by the shape of the string, from which emanate "Faraday`s surfaces". In the other models, the topological interaction can also be described by geometrical means. It is shown that the open-path (or open-surface) dependence carried by the wave functional in these models can be eliminated through an unitary transformation, except by a remaining dependence on the boundary of the path (or surface). These feature is closely related to the presence of anomalous statistics in the 2+1 model, and to a generalized "anyonic behavior" of the string in the other case.Comment: RevTeX 4, 28 page

Aproveitamento das vagens de faveira como suplemento a silagem de sorgo na alimentação de bovinos.

Avaliou-se a variação de peso de bovinos alimentados com silagem de sorgo (Sorghum bicolor (L.) Moench) e suplementados com vagens de faveira (Parkia playtycephala Benth) inteiras e moidas. Foram utilizados 3 grupos de 5 bezeros, mestiços de zebu x holandês, com idade de 10 a 14 meses e peso vivo medio inicial de 175+-31 kg/animal. Os animais foram confinados em baias individuais, distribuidos ao acaso, tendo a disposição os alimentos, água e sal mineral. O primeiro grupo de animais recebeu somente silagem; o segundo, silagem mais vagens inteiras;e o terceiro, silagem mais vagens moidas. A duração do trabalho foi de 106 dias, sendo o periodo inicial de 22 dias, considerados de adaptação, e os 84 dias seguintes como de coleta de dados. Os animais foram pesados inicialmente e a cada 28 dias, após um jejum de 16 horas. Os ganhos medios diarios por bezerro foram de 210 g. para os animais suplementados com vagens moidas, l99 g, para os animais suplementados com vagens inteiras, e não houve variação de peso dos animais alimentados somente com silagem. A análise estatistica destes resultados apresentou diferença significativa (P 0,05), sendo o tratamento silagem mais vagens moidas superior aos tratamento com somente silagem. O ganho de peso do grupo de animais suplementado com vagens moidas foi 76,3% superior ao suplementado com vagens inteiras, mas esta diferença não foi estatisticamente significativa ao nivel de 5% de probabilidade.bitstream/item/98425/1/BOL70001.pd