Flow of low viscosity Boger fluids through a microfluidic hyperbolic contraction

In this work we focus on the development of low viscosity Boger fluids and assess their elasticity analyzing the flow through a microfluidic hyperbolic contraction. Rheological tests in shear and extensional flows were carried out in order to evaluate the effect of the addition of a salt (NaCl) to dilute aqueous solutions of polyacrylamide at 400, 250, 125 and 50 ppm (w/w). The rheological data showed that when 1% (w/w) of NaCl was added, a significant decrease of the shear viscosity curve was observed, and a nearly constant shear viscosity was found for a wide range of shear rates, indicating Boger fluid behavior. The relaxation times, measured using a capillary break-up extensional rheometer (CaBER), decreased for lower polymer concentrations, and with the addition of NaCl. Visualizations of these Boger fluids flowing through a planar microfluidic geometry containing a hyperbolic contraction, which promotes a nearly uniform extension rate at the centerline of the geometry, was important to corroborate their degree of elasticity. Additionally, the quantification of the vortex growth upstream of the hyperbolic contraction was used with good accuracy and reproducibility to assess the relaxation time for the less concentrated Boger fluids, for which CaBER measurements are difficult to perform

Nanogel formation of polymer solutions flowing through porous media

A gelation process was seen to occur when Boger fluids made from aqueous solutions of polyacrylamide (PAA) and NaCl flowed through porous media with certain characteristics. As these viscoelastic fluids flow through a porous medium, the pressure drop across the bed varies linearly with the flow rate, as also happens with Newtonian fluids. Above a critical flow rate, elastic effects set in and the pressure drop grows above the low-flow-rate linear regime. Increasing further the flow rate, a more dramatic increase in the slope of the pressure drop curve can be observed as a consequence of nanogel formation. In this work, we discuss the reasons for this gelation process based on our measurements using porous media of different sizes, porosity and chemical composition. Additionally, the rheological properties of the fluids were investigated for shear and extensional flows. The fluids were also tested as they flowed through different microfluidic analogues of the porous media. The results indicate that the nanogel inception occurs with the adsorption of PAA molecules on the surface of the porous media particles that contain silica on their surfaces. Subsequently, if the interparticle space is small enough a jamming process occurs leading to flow-induced gel formation

Optimised cross-slot microdevices for homogeneous extension

Microfluidic cross-slot devices can generate wide regions of vorticity-free strong extensional flow near the stagnation point, resulting in large extensional deformation and orientation of the microstructure of complex fluids, with possible applications in extensional rheometry and hydrodynamic stretching of single cells or molecules. Standard cross-slot devices, with sharp or rounded corners, generate a flow field with a non-homogeneous extension rate that peaks at the stagnation point, but decays significantly with distance from the stagnation point. To circumvent this limitation, an optimized shape cross-slot extensional rheometer (OSCER) was designed numerically and shown to generate constant extension rate over a wide region of the in- and out-flowing symmetry planes [Haward et al., Phys. Rev. Lett., 2012, 109, 128301]. Since the OSCER device was based on a 2D flow approximation, the practical implementation requires a large aspect ratio, which cannot be reproduced by standard soft-lithography techniques. Here, we propose a set of new designs for optimized cross-slot geometries, considering aspect ratios of order 1 and different lengths of the homogeneous inlet/outlet-flow regions. Micro-particle image velocimetry experiments were carried out in order to validate the flow kinematics, and the velocity profiles were found to be linear along the in- and outflow centrelines in good quantitative agreement with the numerical predictions

Comparative environmental and economic analysis of south european building constructive systems

The choice between different materials and constructive systems can influence significantly the environmental impact and economic cost of construction. In this context, four constructive systems used in South European were studied: one conventional - composed by hollow brick walls and steel reinforced post and beam concrete structure; and three non-conventional - light steel framing (LSF); wood frame (WF); and insulation concrete form (ICF). Using a case study based on a contemporary Portuguese typology of a single family dwelling, some environmental impact indicators, as well as the weight and the economic cost of these solutions were evaluated.(undefined

a systematic review and meta-analysis

OKThere is significant evidence linking a 'reward deficiency syndrome' (RDS), comprising decreased availability of striatal dopamine D2-like receptors (DD2lR) and addiction-like behaviors underlying substance use disorders and obesity. Regarding obesity, a systematic review of the literature with a meta-analysis of such data is lacking. Following a systematic review of the literature, we performed random-effects meta-analyses to determine group differences in case-control studies comparing DD2lR between individuals with obesity and non-obese controls and prospective studies of pre- to post-bariatric surgery DD2lR changes. Cohen's d was used to measure effect size. Additionally, we explored factors potentially associated with group differences in DD2lR availability, such as obesity severity, using univariate meta-regression. In a meta-analysis including positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies, striatal DD2lR availability did not significantly differ between obesity and controls. However, in studies comprising patients with class III obesity or higher, group differences were significant, favoring lower DD2lR availability in the obesity group. This effect of obesity severity was corroborated by meta-regressions showing inverse associations between the body mass index (BMI) of the obesity group and DD2lR availability. Post-bariatric changes in DD2lR availability were not found, although a limited number of studies were included in this meta-analysis. These results support lower DD2lR in higher classes of obesity which is a more targeted population to explore unanswered questions regarding the RDS.publishersversionpublishe

Parasitóides dos Açores : possível utilização no controlo da mosca da fruta Ceratitis capitata (W.).

I Congresso de Fruticultura e Viticultura, Angra de Heroísmo, 17 a 19 de Abril de 2008.Desde Setembro de 2005 tem vindo a ser efectuado o levantamento dos parasitóides de Ceratitis capitata com o objectivo da sua possível utilização no controlo da mosca da fruta nos Açores, evitando assim a introdução de espécies exóticas. Halticoptera patellana, Toxeumorpha nigricola e Spalangia endius foram recolhidas no campo parasilando pupas de C. capitata, enquanto Tachinaephagus zealandicus, Pachycrepoideus vindemmiae e Asobara rufescens parasitaram larvas ou pupas da mosca em condições laboratoriais. As duas primeiras espécies encontram-se as várias gerações, em cultura laboratorial tendo como hospedeiro C. capitata. Um novo registo de hospedeiro foi assinalado para H. patellana, T. nigricola, T. zealandicus, e A. rufescens, uma vez que nenhuma referência foi encontrada indicando C. capitata como hospedeiro destas espécies. Com este trabalho as espécies H. patellana, T. nigricola, T. zealandicus, S. endius, P. vindemmiae e A. rufescens são citadas pela primeira vez para os Açores, enquanto T. zealandicus, anteriormente referenciado para as ilhas do Pico e Terceira, foi observado pela primeira vez em São Miguel.ABSTRACT: Since September 2005 a survey for parasitoids of Ceratitis capitata was performed to evaluate their possible use in the Medfly control in Azores to avoid the introduction of exotic species. Halticoptera patellana, Toxeumorpha nigricola and Spalangia endius were collected in fruit crop parasitizing pupae of C. capitata. Field-collected Tachinaephagus zealandicus, Pachycrepoideus vindemmiae and Asobara rufescens parasitized larvae or pupae of the Medfly under laboratory conditions. The first two species were successfully reared for consecutive generations in laboratory using larvae of C. capitata as hosts. With this study a new record for host is given for H. patellana, T. nigricola, T. zealandicus and A. rufescens since no previous references indicate C. capitata as host. Also, the presence of H. patellana, T. nigricola, T. zealandicus, S. endius, P. vindemmiae and A. rufescens are first cited for Azores Islands, while T. zealandicus previously referred to the islands of Pico and Terceira, was first noticed in São Miguel

IDENTIFICA??O E CLASSIFICA??O DE SINALIZA??O HORIZONTAL EM AUTOVIAS UTILIZANDO OPENCV

Acidentes de tr?nsito podem ser fatais, causando a morte ou invalidez de motoristas e pedestres. Desta forma, muitos pesquisadores est?o desenvolvendo meios para deixar os ve?culos mais seguros, atrav?s do uso de sistemas de apoio ? condu??o que auxiliem os motoristas nas mais diversas situa??es no tr?nsito. O objetivo deste trabalho ? propor um sistema para detec??o e classifica??o de linhas de sinaliza??o horizontais em autovias. Sistemas deste tipo podem ajudar a diminuir a quantidade de acidentes de tr?nsito, auxiliando o condutor do ve?culo a permanecer em sua faixa e realizar ultrapassagens apenas em locais permitidos. As imagens das autovias, capturadas por uma c?mera fixada ao para-brisa no interior do ve?culo, s?o analisadas quadro a quadro em tempo real. O sistema proposto foi desenvolvido na linguagem de programa??o C++, utilizando a biblioteca OpenCV, de c?digo aberto, amplamente empregada em vis?o computacional. Dentre outras t?cnicas, utilizou-se o detector de bordas de Canny e a Transformada Probabil?stica de Hough para identifica??o de segmentos de reta. Adicionalmente, foram desenvolvidos m?todos geom?tricos para otimiza??o e elimina??o de segmentos desnecess?rios e um algoritmo para estima??o do ponto de fuga, o qual auxilia na identifica??o dos segmentos mais relevantes para o sistema. Foram realizados sete experimentos apresentando diferentes n?veis de dificuldade. Acur?cias na faixa de valores de 86,58% a 100% foram alcan?adas. Em m?dia, os experimentos obtiveram uma acur?cia de 94,56% na classifica??o dos diferentes tipos de sinaliza??es horizontais

Thermal and structural analysis of 4,5,6-trimethoxyisatin

4,5,6-Trimethoxyisatin was crystallized from water to give dark red needles that were characterized by NMR and IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), single-crystal X-ray diffraction (XRD) and hot-stage microscopy.Fundação para a Ciência e a Tecnologia (FCT) - POCTISFA-3-686Fundo Europeu de Desenvolvimento Regional (FEDER

Homoclinic chaos in the dynamics of a general Bianchi IX model

The dynamics of a general Bianchi IX model with three scale factors is examined. The matter content of the model is assumed to be comoving dust plus a positive cosmological constant. The model presents a critical point of saddle-center-center type in the finite region of phase space. This critical point engenders in the phase space dynamics the topology of stable and unstable four dimensional tubes $R \times S^3$, where $R$ is a saddle direction and $S^3$ is the manifold of unstable periodic orbits in the center-center sector. A general characteristic of the dynamical flow is an oscillatory mode about orbits of an invariant plane of the dynamics which contains the critical point and a Friedmann-Robertson-Walker (FRW) singularity. We show that a pair of tubes (one stable, one unstable) emerging from the neighborhood of the critical point towards the FRW singularity have homoclinic transversal crossings. The homoclinic intersection manifold has topology $R \times S^2$ and is constituted of homoclinic orbits which are bi-asymptotic to the $S^3$ center-center manifold. This is an invariant signature of chaos in the model, and produces chaotic sets in phase space. The model also presents an asymptotic DeSitter attractor at infinity and initial conditions sets are shown to have fractal basin boundaries connected to the escape into the DeSitter configuration (escape into inflation), characterizing the critical point as a chaotic scatterer.Comment: 11 pages, 6 ps figures. Accepted for publication in Phys. Rev.

Chaos in Anisotropic Pre-Inflationary Universes

We study the dynamics of anisotropic Bianchi type-IX models with matter and cosmological constant. The models can be thought as describing the role of anisotropy in the early stages of inflation. The concurrence of the cosmological constant and anisotropy are sufficient to produce a chaotic dynamics in the gravitational degrees of freedom, connected to the presence of a critical point of saddle-center type in the phase space of the system. The invariant character of chaos is guaranteed by the topology of the cylinders emanating from unstable periodic orbits in the neighborhood of the saddle-center. We discuss a possible mechanism for amplification of specific wavelengths of inhomogeneous fluctuations in the models. A geometrical interpretation is given for Wald's inequality in terms of invariant tori and their destruction by increasing values of the cosmological constant.Comment: 14 pages, figures available under request. submitted to Physical Review