Models for the two-phase flow of concentrated suspensions

A new two-phase model for concentrated suspensions is derived that incorporates a constitutive law combining the rheology for non-Brownian suspension and granular flow. The resulting model exhibits a yield-stress behavior for the solid phase depending on the collision pressure. This property is investigated for the simple geometry of plane Poiseuille flow, where an unyielded or jammed zone of finite width arises in the center of the channel. For the steady states of this problem, the governing equations are reduced to a boundary value problem for a system of ordinary differential equations and the conditions for existence of solutions with jammed regions are investigated using phase-space methods. For the general time-dependent case a new drift-flux model is derived using matched asymptotic expansions that takes into account the boundary layers at the walls and the interface between the yielded and unyielded region. The drift-flux model is used to numerically study the dynamic behavior of the suspension flow including the appearance and evolution of an unyielded or jammed region

Localized Instabilities and Spinodal Decomposition in Driven Systems in the Presence of Elasticity

We study numerically and analytically the instabilities associated with phase separation in a solid layer on which an external material ux is imposed. The first instability is localized within a boundary layer at the exposed free surface by a process akin to spinodal decomposition. In the limiting static case, when there is no material ux, the coherent spinodal decomposition is recovered. In the present problem stability analysis of the time-dependent and non-uniform base states as well as numerical simulations of the full governing equations are used to establish the dependence of the wavelength and onset of the instability on parameter settings and its transient nature as the patterns eventually coarsen into a at moving front. The second instability is related to the Mullins- Sekerka instability in the presence of elasticity and arises at the moving front between the two phases when the ux is reversed. Stability analyses of the full model and the corresponding sharp-interface model are carried out and compared. Our results demonstrate how interface and bulk instabilities can be analysed within the same framework which allows to identify and distinguish each of them clearly. The relevance for a detailed understanding of both instabilities and their interconnections in a realistic setting are demonstrated for a system of equations modelling the lithiation/delithiation processes within the context of Lithium ion batteries.Comment: 8 figures, 19 page

Thin film models for active gels

In this study we present a free-boundary problem for an active liquid crystal based on the Beris-Edwards theory that uses a tensorial order parameter and includes active contributions to the stress tensor to analyse the rich defect structure observed in applications such as the Adenosinetriphosphate (ATP) driven motion of a thin film of an actin filament network. The small aspect ratio of the film geometry allows for an asymptotic approximation of the free-boundary problem in the limit of weak elasticity of the network and strong active terms. The new thin film model captures the defect dynamcs in the bulk as well as wall defects and thus presents a significant extension of previous models based on the Lesli-Erickson-Parodi theory. Analytic expression are derived that reveal the interplay of anchoring conditions, film thickness and active terms and their control of transitions of flow structure.Comment: 33 pages, 3 figure

Preferências dos consumidores de carne bovina: uma abordagem referente às cidades de Florianópolis – SC e Botucatu – SP

TCC (graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Agrárias. Curso de Zootecnia.Objetiva-se avaliar as preferências do consumidor em relação à carne bovina, através de um questionário sobre questões relacionadas à compra, como onde prefere e onde compra a carne bovina. Questionar sobre questões relacionadas ao consumo, como o tipo de refeição que faz com a carne bovina (churrasco, refeição dia-a-dia ou especial). Além de indagar sobre a idade, sexo e renda mensal, a fim de relacionar esses resultados, para verificar a possibilidade de introdução de uma boutique de carnes, na cidade de Florianópolis, Santa Catarina. Este questionário foi aplicado em clientes de mercados, açougues e boutiques de carne em Botucatu, estado de São Paulo, e também em açougues e mercados, na região do bairro Santa Mônica, na cidade de Florianópolis, estado de Santa Catarina, para detecção de fatores comuns aos consumidores desses locais. O resultado encontrado nesse estudo foi que existe diferença entre os cortes preferidos e os comprados, assim como quanto ao local preferido e o local onde se compra a carne bovina. Também foi encontrada diferença entre a renda com os cortes de preferência e com oos cortes comprados, assim como com o local de preferência e com o local onde se compra a carne, mas em relação à idade, somente houve diferença alguns cortes comprados. Não existiu divergência para nenhum dos fatores analisados quando relacionado ao sexo. A renda interferiu no tipo de refeição que o consumidor costuma fazer com a carne bovina, assim como nos critérios de compra destes. Concluiu-se que as cidades são semelhantes quanto ao sexo, idade e renda, assim como nos hábitos de compra e consumo, tendo espaço para um local com produtos diferenciados em Florianópolis, Santa Catarina, após estudo mais detalhados sobre o mercado local

Second kind similarity solutions of the modified porous medium equation

We consider the problem of a spreading ground water mound of liquid in a porous medium, situated on an impermeable horizontal solid layer. The mathematical formulation for this problem is given by the modified porous medium equation. We derive a global condition in form of an energy integral, describing the loss of liquid in the porous medium. This yields the necessary condition that determines the similarity exponents for the similarity solution of second kind, describing the long time behavior of the mound. We further apply our method to the problem when instead of an energy integral another conservation law, such as the first moment integral, obeyed by a family of antisymmetric solutions, is violated. Here, we consider as an application the problem of the impact of a flood infiltrating a porous medium. In all cases we will also solve and compare our analytical results with our numerical solution, and, if available, with examples existing in the literature

Variations in the Invertebrate Communities of Wild Cape Cod Cranberry Bogs

As a species domesticated only in the last century, agricultural cranberry plants (Vaccinium macrocarpon) remain little removed from their wild relatives. Thus, it is a potential model species for studies of the earliest stages of domestication; however, there is little available quantitative information on its wild population biology and ecology. As such information is vital to studies of the ecological changes occurring during domestication, the purpose of this study was to consolidate the relevant knowledge available and conduct a preliminary search for patterns in the invertebrate communities of wild bogs. The alpha diversity was found to be greater than the overall (gamma diversity), which is likely a result of the metric used and the fact that there was minimal overlap in rare species between bogs. In addition, alpha diversity was found to be significantly negatively correlated with bog age. Two pairs of species were found to be correlated with each other, Blunt-nosed (Limotettix vaccinia (Van Duzee)) and Sharp-nosed leafhopper (Scaphytopius sp.), along with fleabeetle (Sysena frontalis (F.)) and firebeetle (Cryptocephalus incertus (Oliv.). In addition, it was found that spiders are significantly more common in western bogs, while firebeetle is significantly more common in eastern bogs. However, this may be indicative of a correlation with bog age rather than a true correlation with geographic location. More work is needed to determine the true dynamics driving these findings, so that the information could eventually be used to improve the efficacy and decrease the environmental impact of pest management on agricultural bogs

Effect of weathering product assemblages on Pb bioaccessibility in mine waste: implications for risk management

General assessments of orebody types and associated mine wastes with regards to their environmental signature and human health hazards are needed to help managing present and historical mine waste facilities. Bioaccessibility tests and mineralogical analysis were carried out on mine waste from a systematic sampling of mine sites from the Central Wales orefield, UK. The bioaccessible Pb widely ranged from 270 to 20300 mg/kg (mean 7250 mg/kg; median 4890 mg/kg) and the bioaccessible fraction from 4.53 % to >100 % (mean 33.2 %; median 32.2 %), with significant (p=0.001) differences among the mine sites. This implies sensitivity of bioaccessibility to site-specific conditions and suggests caution in the use of models to assess human health impacts generalised on the basis of the mineral deposit type. Mineralogical similarities of the oxidation products of primary galena provided a better control over the observed Pb bioaccessibility range. The higher Pb bioaccessibility (%) was related to samples containing cerussite, irrespective of the presence of other Pb minerals in the mineral assemblage; lower Pb bioaccessibility resulted where anglesite was the main Pb mineral phase and cerussite was absent. A solubility diagram for the various Pb minerals in the waste was derived using PHREEQC model and the experimental Pb concentration measured in the simulated gastric solution compared with the equilibrium modelling results. For samples containing cerussite, the model well predicted the soluble Pb concentrations measured in the experimental simulated gastric solution, indicative of the carbonate mineral phase control on the Pb in solution for these samples and little kinetic control on the dissolution of cerussite. On the contrary, most mine waste samples containing dominant anglesite and or plumbojarosite (no cerussite) had lower solution Pb values, falling at or below the anglesite and plumbojarosite solubility equilibrium concentrations, implying kinetic or textural factors hindering the dissolution

Impact of energy dissipation on interface shapes and on rates for dewetting from liquid substrates

We revisit the fundamental problem of liquid-liquid dewetting and perform a detailed comparison of theoretical predictions based on thin-film models with experimental measurements obtained by atomic force microscopy (AFM). Specifically, we consider the dewetting of a liquid polystyrene (PS) layer from a liquid polymethyl methacrylate (PMMA) layer, where the thicknesses and the viscosities of PS and PMMA layers are similar. The excellent agreement of experiment and theory reveals that dewetting rates for such systems follow no universal power law, in contrast to dewetting scenarios on solid substrates. Our new energetic approach allows to assess the physical importance of different contributions to the energy-dissipation mechanism, for which we analyze the local flow fields and the local dissipation rates.Comment: 15 pages, 5 figure