Bubbles dynamics in microchannels: inertial and capillary migration forces

This work focuses on the dynamics of a train of unconfined bubbles flowing in microchan- nels. We investigate the transverse position of a train of bubbles, its velocity and the associated pressure drop when flowing in a microchannel depending on the internal forces due to viscosity, inertia and capillarity. Despite the small scales of the system, inertia, referred to as inertial migration force, play a crucial role in determining the transverse equilibrium position of the bubbles. Beside inertia and viscosity, other effects may also affect the transverse migration of bubbles such as the Marangoni surface stresses and the surface deformability. We look at the influence of surfactants in the limit of infinite Marangoni effect which yields rigid bubble interface. The resulting migration force may balance external body forces if present such as buoyancy, Dean or magnetic ones. This balance not only determines the transverse position of the bubbles but, consequently, the surrounding flow structure, which can be determinant for any mass/heat transfer process involved. Finally, we look at the influence of the bubble deformation on the equilibrium position and compare it to the inertial migration force at the centred position, explaining the stable or unstable character of this position accordingly. A systematic study of the influence of the parameters - such as the bubble size, uniform body force, Reynolds and capillary numbers - has been carried out using numerical simulations based on the Finite Element Method, solving the full steady Navier-Stokes equations and its asymptotic counterpart for the limits of small Reynolds and/or capillary numbers.Comment: Submitted to JF

On the Credibility of the Irish Pound in the EMS

This paper assesses the degree of credibility of the Irish Pound in the European Monetary System between 1983 and 1997. Different credibility indicators proposed in the literature are used to measure agents’ perceptions of the credibility of the ERM commitment in an attempt to distinguish between events stemming from problems in the ERM itself and those that appear to have been exclusive to Ireland.

Bubbles dissolution in cylindrical microchannels

This work focuses on the dissolution of a train of unconfined bubbles in cylindrical microchannels. We investigate how the mass transfer is affected by the channel and bubble sizes, distance between bubbles, diffusivity, superficial velocity, deformation of the bubble, the presence of surfactants in the limit of rigid interface and off-centred positions of the bubbles. We analyse the influence of the dimensionless numbers and especially the distance between bubbles and the P\'eclet number, Pe, which we vary among eight decades and identify five different dissolution regimes. We show different concentration patterns and the dependence of the Sherwood numbers, Sh. These regimes can be classified by either the importance of the streamline diffusion or by the interaction between bubbles. For small Pe the streamline diffusion is not negligible as compared to convection whereas for large Pe, convection dominates in the streamline direction and, thus, crosswind diffusion becomes crucial in governing the dissolution through boundary layers or of the remaining wake behind the bubbles. Bubbles interaction takes place for very small Pe for which the dissolution is purely diffusive or for very large Pe numbers in which case long wakes eventually reach the following bubble. We also observe that the bubble deformability mainly affects the Sh in the regime for very large Pe in which bubbles interaction matters, and also that the rigid interface effect affects the boundary layer and the remaining wake. The effect of off-centred position of the bubble, determined by the transverse force balance, is also limited to large Pe. The boundary layers in rigid bubble surfaces are thicker as compared to those on stress-free bubble surface and, thus, the dissolution is smaller. For centred bubbles, the influence of inertia on the dissolution is negligible. Finally, we discuss underlying hypothesis of the model.Comment: Submitted to JF

Proposta para melhoria da adesão ao tratamento em hipertensos em uma Unidade de Saúde da Família no município de Craíbas - AL

A hipertensão arterial apresenta elevada prevalência na população brasileira. Craíbas é um município brasileiro do estado de Alagoas e atende a população pertencente à PSF Rosa Mística. A principal causa de morbidade e mortalidade no município está relacionada às complicações da hipertensão arterial devido a não adesão ao tratamento. Este trabalho justifica-se pela alta prevalência de hipertensão arterial essencial provocado por fatores de risco presentes na população, assim como a baixa adesão ao tratamento medicamentoso e não medicamentoso, provocando complicações e sequelas graves que limita a qualidade de vida. No presente trabalho objetiva-se aumentar a adesão de pacientes adultos hipertensos ao tratamento medicamentoso e não medicamentoso da hipertensão arterial na unidade de saúde Rosa Mística. Trata-se de um projeto de intervenção utilizando o método do Planejamento Estratégico Situacional, onde serão realizadas as seguintes ações visando alcançar o objetivo proposto: serão identificados todos os indivíduos com 18 anos ou mais que sofrem a doença, garantir realização de consulta médica, captar após fazer pesquisa de dados os pacientes hipertensos não aderentes ao tratamento. Utilizaremos como procedimentos sessões de educação em saúde por meio de círculo de cultura, palestras e rodas de conversas. Para uma melhor compreensão do tema foi realizada uma revisão de literatura. O material bibliográfico foi coletado na Biblioteca Virtual em Saúde (BVS), nas bases de dados da literatura Latino-Americana e do Caribe em Ciências da Saúde (LILACS) e no Scientific Eletronic Library Online (SciELO), bem como nos módulos do Curso de Especialização em Atenção Básica em Saúde da Família da Universidade Federal de Minas Gerais (UFMG).Com o trabalho em equipe pretende-se melhorar o nível de conhecimento sobre a doença e suas complicações e obter uma melhora da qualidade de vida com melhor controle e maior aceitação da doença, reduzindo assim o número das complicaçõe

Context-aware Services for Mobile Devices: From Architecture Design to Empirical Inference

Currently, mobile devices are aware of user position, which can be provided to mobile apps for the development of tailored services known as Location-Based Services. Further advances on current Location-based Services (LBS), i.e. using any other information from the user such as gender, music preferences etc, may lead to transition from a Location-Based environment to a fully developed ContextAware environment.The current trend towards Context-aware Services (CAS) is reflected in academic research since more than twenty years as well as in the progress in Software Development Kits (SDKs) of the main mobile operating systems, where CAS frameworks are currently being used. However, there is no community agreement for modelling context CAS and little is known about the architecture of these context management frameworks of the mobile operating systems.Based on previous research in the area of CAS, I establish and analyse a reasoning architecture, the Context Engine (CE), that enables the main steps of designing and implementing context-aware services. The chief utility of CAS is their ability to formulate and encapsulate information, obtain user context through context acquisition tools and distribute it to third-party applications that build personalised services based on the provided information. The CE has the responsibility of selecting the optimal context acquisition tool to solve a concrete problem which is discussed in this dissertation.Furthermore, this thesis contributes to the development of context inference tools by studying two particular cases. The first case aims at inferring user (semantic) location information based on mobile phone usage data. This first case has been carried out in collaboration with Microsoft Finland, which provides a similar context inference solution to mobile developers through their Software Development Kit (SDK). The second case aims at inferring user information based on social network information, i.e. infer user information based on his or her connections. Both studies yield positive results and have the potential to be extended to obtain better context acquisition tools and, therefore, better user context

A new Approach to Segmentation of Remote Sensing Images with Hidden Markov Models

In this work, we present a new segmentation algorithm for remote sensing images based on two-dimensional Hidden Markov Models (2D-HMM). In contrast to most 2D-HMM approaches, we do not use Viterbi Training, instead we propose to propagate the state probabilities through the image. Therefore, we denote our algorithm Complete Enumeration Propagation (CEP). To evaluate the performance of CEP, we compare it to the standard 2D-HMM approach called Path Constrained Viterbi Training (PCVT). As both algorithms are not restricted to a certain emission probability, we evaluate the performance of seven probability functions, namely Gamma, Generalized Extreme Value, inverse Gaussian, Logistic, Nakagami, Normal and Weibull. The experimental results show that our approach outperforms PCVT and other benchmark algorithms. Furthermore, we show that the choice of the probability distribution is crucial for many segmentation tasks.http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6868456Fil: Baumgartner, Josef. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Laboratorio de Investigación Matemática Aplicada a Control; Argentina.Fil: Scavuzzo, Marcelo. Comision Nacional de Actividades Espaciales; Argentina.Fil: Rodriguez Rivero, Cristian. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Laboratorio de Investigación Matemática Aplicada a Control; Argentina.Fil: Pucheta, Julián. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Laboratorio de Investigación Matemática Aplicada a Control; Argentina.Sistemas de Automatización y Contro

The presence of striped dolphins, Stenella coeruleoalba (Meyen,1833), in the Argentine sea

El conocimiento del género Stenella en el Atlántico Sudoccidental ha sido muy limitado. A pesar que el holotipo fuera capturado por Meyen (1833) en el estuario del Río de la Plata, sólo unos pocos especímenes se registraron en el sector durante las últimas décadas. El presente estudio analiza la distribución y ocurrencia de delfines listados en el Mar Argentino, y sintetiza el conocimiento sobre su presencia en el Atlántico Sudoccidental. Stenella coeruleoalba se registra entre los 70 y 420 S, aunque la mayoría de los ejemplares se hallaron entre los 300 y 400 S. Cerca del 70% de los ejemplares hallados correspondieron a varamientos solitarios y, en todos los casos en que pudo determinarse el sexo, correspondieron a machos subadultos o adultos (205-242 cm). Un total de 10 cráneos se encuentran depositados actualmente en museos de Brasil, Uruguay y Argentina (LCB 402-471 mm). Los avistajes predominaron entre fines de primavera y verano (octubre-febrero), comprendiendo grupos reducidos (1-4 delfines) en aguas relativamente poco profundas (30 -100 m). Un único ejemplar de esta especie fue capturado incidentalmente en operaciones de pesca de anchoíta en el norte de Patagonia y asociado con delfines comunes. Los patrones de coloración observados fueron el gris azulado en ejemplares varados y pardusco en ejemplares avistados, con la combinación característica de bandas laterales y la mancha dorsal. La corriente cálida del Brasil podría estar influenciando la presencia de delfines listados en Uruguay y Argentina durante el verano, a pesar que algunos de los ejemplares fueron registrados en aguas de temperaturas inferiores a los 200 C, las cuales están influenciadas por la Corriente de Malvinas. Las investigaciones futuras deberían focalizarse en la relación entre las condiciones ambientales y la distribución del género Stenella en el Atlántico Sudoccidental.The knowledge about the presence of striped dolphins (Stenella coeruleoalba) in the South Western Atlantic Ocean (SWAO) is very limited. Although the holotype was captured by Meyen (1833) in the La Plata River Estuary, only a few museum specimens and isolated strandings were recorded in the area. This study presents the distribution and occurrence of striped dolphins in the Argentine Sea and reviews its presence in the SWAO. S.coeruleoalba is found from 70 to 420 S, although most of the sixteen records were found between 300 and 400 S. Seventy percent of the dolphins were single stranded animals, and in the cases that sex was determined, all of them were juvenile to adult males (205-242 cm). A total amount of 10 skulls are deposited in museum collections of Brazil, Uruguay and Argentina (CBL 402-471 mm). The sightings were concentrated in late spring and summer (OctoberFebruary), comprising small groups (1-4 dolphins) in relatively shallow water (30-100 m). Only a single incidental catch was recorded, being a dolphin associated with common dolphins feeding on anchovies in northern Patagonia. The colour pattern found was bluish grey in stranded animals and brownish in live dolphins, with the characteristic combination of lateral stripes and spinal blaze. The southbound warm Brazil Current may influence in the presence of striped dolphins in Uruguay and Argentina during austral summer, even though some animals were found during winter in waters of temperatures below 200 C clearly associated with the northbound cold Malvinas-Falkland Current. Future research should focus on the relationship between the environmental conditions and the distribution of the genus Stenella in the South Western Atlantic.Fil: Bastida, Ricardo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Marinas; ArgentinaFil: Rodriguez, Diego Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Marinas; ArgentinaFil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rivero, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Marinas; Argentin

Raydrop : a universal droplet generator based on a non-embedded co-flow-focusing

Most commercial microfluidic droplet generators rely on the planar flow-focusing configuration implemented in polymer or glass chips. The planar geometry, however, suffers from many limitations and drawbacks, such as the need of specific coatings or the use of dedicated surfactants, depending on the fluids in play. On the contrary, and thanks to their axisymmetric geometry, glass capillary-based droplet generators are a priori not fluid-dependent. Nevertheless, they have never reached the market because their assembly requires art-dependent and not scalable fabrication techniques. Here we present a new device, called Raydrop, based on the alignment of two capillaries immersed in a pressurized chamber containing the continuous phase. The dispersed phase exits one of the capillaries through a 3D-printed nozzle, placed in front of the extraction capillary for collecting the droplets. This non-embedded implementation of an axisymmetric flow-focusing is referred to {\it co-flow-focusing}. Experimental results demonstrate the universality of the device in terms of the variety of fluids that can be emulsified, as well as the range of droplet radii that can be obtained, without neither the need of surfactant nor coating. Additionally, numerical computations of the Navier-Stokes equations based on the quasi-steadiness assumption are shown to correctly predict the droplet radius in the dripping regime and the dripping-jetting transition when varying the geometrical and fluid parameters. The monodispersity ensured by the dripping regime, the robustness of the fabrication technique, the optimization capabilities from the numerical modeling and the universality of the configuration confer to the Raydrop technology a very high potential in the race towards high-throughput droplet generation processes