Estudio del flujo sanguíneo para diferentes técnicas de implantación de stents en bifurcaciones coronarias

Las enfermedades arteriales vienen presididas por la aterosclerosis, que es un proceso crónico de degeneración, que evoluciona hacia la obstrucción de la luz arterial. La pared de la arteria se engrosa debido al depósito de elementos grasos tales como el colesterol. Los stents intraluminales son diminutas estructuras tubulares autoexpandibles de malla de metal, que se colocan dentro de la arteria coronaria después de una angioplastia con balón para prevenir el cierre de dicha arteria. A pesar de estar diseñados para ser compatibles con el tejido humano, a menudo se da una reacción en cadena de consecuencias indeseables. La reestenosis intra-stent es un problema creciente debido al importante incremento que se ha producido en la utilización del stent intracoronario como forma de revascularización percutánea. Se habla de una incidencia global del 28%, siendo la causa principal de su aparición la proliferación neointimal a través de una compleja cascada de sucesos que pueden tardar meses en desarrollarse. Una de las reacciones más importantes es la trombosis o la formación de una fina capa de coágulo como respuesta a la presencia de un material extraño. Este proceso es multifactorial, y en él intervienen la regresión de la pared como consecuencia del estiramiento previo, la denudación endotelial, lo que permite la agregación plaquetaria, la proliferación neointimal, lo que facilita a los receptores de membrana desencadenar un proceso de agregación posterior y, por último, el remodelado negativo inadecuado de la pared, lo que produce pérdida de luz arterial. Se ha observado frecuentemente que el depósito de ateroma en la pared arterial está relacionado con el valor de los esfuerzos cortantes en la misma. Hay mayores probabilidades de engrosamiento de la pared en las zonas donde son bajos los esfuerzos cortantes, quizá por el mayor tiempo de residencia de las partículas circulantes por el torrente sanguíneo. Si nos centramos en la afirmación anterior, el siguiente paso sería buscar las zonas susceptibles de presentar un valor bajo de dichos esfuerzos. Las zonas potencialmente peligrosas son los codos y bifurcaciones, entre otras. Nos hemos centrado en una bifurcación coronaria, ya que los patrones de flujo que se suelen presentar, tales como recirculación y desprendimiento de vórtices están íntimamente relacionados con las técnicas de implantación de stents en esta zona. Proyectamos nuestros esfuerzos en el estudio de dos técnicas de implante, utilizando un único stent y una tercera a través de una configuración de culotte con el uso de dos stents. El primer caso trata de una bifurcación con un único stent en la rama principal cuyos struts cierran el orificio lateral que da salida a la rama secundaria de la bifurcación, es decir sería un stent sin orificio. El segundo consiste en un único stent también, pero con la diferencia de que éste presenta un orificio de comunicación con la rama lateral. Todas estas técnicas se aplicaron a bifurcaciones de 45º y de 90º. Introdujimos las geometrías -una vez confeccionadas con el código comercial Gambit- en el programa Ansys-Fluent contemplando régimen estacionario. Los resultados obtenidos fueron cotejados con los experimentales, que se realizaron paralelamente, con el fin de corroborarlos. Una vez validados, el estudio computacional ya contó con la fiabilidad suficiente como para abordar el régimen no estacionario, tanto en la versión de reposo como en la de ejercicio –hiperemia- El comportamiento reológico de la sangre para régimen no estacionario en estado de reposo es otra de las tareas abordadas, realizando una comparativa de los modelos Newtoniano, Carreau y Ley de Potencias. Finalmente, en una última etapa, debido a la reciente incursión de los stents diseñados específicamente frente a los convencionales, se aborda el comportamiento hemodinámico de los mismos. Concretamente, se comparó el patrón de flujo en un modelo de bifurcación coronaria con los nuevos stents (Stentys) y los convencionales. Se estudiaron cuatro modelos, a saber, stent simple en la rama principal, stent simple en la rama secundaria, culotte desplegando el primer stent en la rama principal y culotte desplegando el primer stent en la rama secundaria. La bifurcación estudiada presenta un ángulo de apertura de 45º y la relación de diámetros de las ramas hija se ajustaron de acuerdo a la ley de Finet. Se recogieron resultados experimentales en el laboratorio y se corrieron simulaciones numéricas con Ansys Fluent paralelamente. Las magnitudes que se tuvieron en cuenta con el fin de ubicar las regiones potencialmente ateroscleróticas fueron los esfuerzos cortantes, vorticidad y caída de presión. ABSTRACT Nowadays, restenosis after percutaneous dilation is the major drawback of coronary angioplasty. It represents a special form of atherosclerosis due to the healing process secondary to extensive vessel trauma induced after intracoronary balloon inflation. The use of coronary stents may decrease the incidence of this phenomenon. Unfortunately, intra-stent restenosis still occurs in 20-30% of the cases following the stent implantation. Most experiments suggest a correlation between low wall shear stress and wall thickness. The preferential locations for the atherosclerotic plaque are bifurcations. The objective of this work is to analyze the local hemodynamic changes caused in a coronary bifurcation by three different stenting techniques: simple stenting of the main vessel, simple stenting of the main vessel with kissing balloon in the side branch and culotte. To carry out this study an idealized geometry of a coronary bifurcation is used, and two bifurcation angles, 45º and 90º, are chosen as representative of the wide variety of real configurations. Both numerical simulations and experimental measurements are performed. First, steady simulations are carried out with the commercial code Ansys-Fluent, then, experimental measurements with PIV (Particle Image Velocimetry), obtained in the laboratory, are used to validate the numerical simulations. The steady computational simulations show a good overall agreement with the experimental data. Then, pulsatile flow is considered to take into account the transient effects. The time averaged wall shear stress, oscillatory shear index and pressure drop obtained numerically are used to compare the behavior of the stenting techniques. In a second step, the rheologic behavior of blood was considered comparing Newtonian, Carreau and Power Law models. Finally, as a result of previous investigations with conventional stents and after the recent emergence of several devices specifically designed for coronary bifurcations angioplasty, the hemodynamic performance of these new devices (Stentys) was compared to conventional ones and techniques in a coronary bifurcation model. Four different stenting techniques: simple stenting of the main vessel, simple stenting of the side vessel, culotte deploying the first stent in the main vessel and culotte deploying the first stent in the side vessel have been considered. To carry out this study an idealized geometry of a coronary bifurcation is used. A 45 degrees bifurcation angle is considered and the daughter branches diameters are obtained according to the Finet law. Both experiments in the laboratory and numerical simulations were used , focusing on important factors for the atherosclerosis development, like the wall shear stress, the oscillation shear index, the pressure loss and the vorticity.

Caracterización teórica y experimental de un reactor de lecho fluidizado para operaciones de termoquímica solar

El objetivo del presente trabajo es la caracterización, tanto teórica como experimental, de un reactor de lecho fluidizado para operaciones de termoquímica solar. En el apartado experimental se emplea un reactor de lecho fluidizado cedido por el CIEMAT. Para la parte numérica, se realiza un análisis óptico-energético y un estudio termofluidodinámico (dinámica de fluidos computacional, DFC). Se llevan a cabo ensayos en frío y en caliente para la parte experimental. Los ensayos en frío tienen el objetivo de demostrar la teoría establecida de fluidización, usando partículas de alúmina y ferritas de níquel. Los ensayos en caliente se realizan para observar el comportamiento de un reactor de lecho fluidizado irradiado. Se emplean partículas de carburo de silicio (SiC) y ferritas de níquel. El análisis óptico-energético se realiza usando el software de trazado de rayos TracePro. La simulación se hace con partículas de α-SiC. Las propiedades del material se obtienen con un software adicional. Por otra parte, el estudio DFC se realiza con una licencia académica de Ansys Fluent. Se hacen 2 simulaciones de un modelo euleriano de 2 fases, sin condiciones de calor y con 2 paredes con una temperatura fijada.

Personal Reflections on Providing Psychotherapy in a Third Language

This paper reflects upon the increasing diversity of the United States and the subsequent necessity for mental health providers who can provide psychotherapy services in more than one language. Review of the current literature of clinicians who provide bilingual services highlight the challenges and rewards of working in a second language. The literature focuses on the experiences of those bilingual clinicians who are bilingual in English and Spanish. However, there is little to no research concerning clinicians who can provide psychotherapy in three languages. This writer speaks of her experience growing up in a bilingual Vietnamese-English household in Southern California and her journey of becoming fluent in Spanish. Lastly, she provides recommendations to training programs on how to support trainees who aim to provide psychotherapy services in multiple languages.

Teaching College Writing in a High School Setting: The Impact of Concurrent Enrollment on Teacher Learning and Practice

Thesis (Ph.D.)--University of Washington, 2016-06

Theory-of-mind development in oral deaf children with cochlear implants or conventional hearing aids

Background: In the context of the established finding that theory-of-mind (ToM) growth is seriously delayed in late-signing deaf children, and some evidence of equivalent delays in those learning speech with conventional hearing aids, this study's novel contribution was to explore ToM development in deaf children with cochlear implants. Implants can substantially boost auditory acuity and rates of language growth. Despite the implant, there are often problems socialising with hearing peers and some language difficulties, lending special theoretical interest to the present comparative design. Methods: A total of 52 children aged 4 to 12 years took a battery of false belief tests of ToM. There were 26 oral deaf children, half with implants and half with hearing aids, evenly divided between oral-only versus sign-plus-oral schools. Comparison groups of age-matched high-functioning children with autism and younger hearing children were also included. Results: No significant ToM differences emerged between deaf children with implants and those with hearing aids, nor between those in oral-only versus sign-plus-oral schools. Nor did the deaf children perform any better on the ToM tasks than their age peers with autism. Hearing preschoolers scored significantly higher than all other groups. For the deaf and the autistic children, as well as the preschoolers, rate of language development and verbal maturity significantly predicted variability in ToM, over and above chronological age. Conclusions: The finding that deaf children with cochlear implants are as delayed in ToM development as children with autism and their deaf peers with hearing aids or late sign language highlights the likely significance of peer interaction and early fluent communication with peers and family, whether in sign or in speech, in order to optimally facilitate the growth of social cognition and language.

Eulogizing a language: The Ngarnka experience

In 1996, I worked with what appear to have been the last fluent speakers of Ngarnka, a language of central northern Australia. To the best of my knowledge, the last fluent speaker passed away in 1997 or 1998. In 2000, I began to collect all available information on the language. This article describes some of the challenges that have arisen in working with a language during and after the final stages of its death, and examines some of the possible reasons for, and impact of, this kind of work.

Numerical simulation of magnetite segregation in a dense medium cyclone

Numerical simulations of turbulent driven flow in a dense medium cyclone with magnetite medium have been conducted using Fluent. The predicted air core shape and diameter were found to be close to the experimental results measured by gamma ray tomography. It is possible that the Large eddy simulation (LES) turbulence model with Mixture multi-phase model can be used to predict the air/slurry interface accurately although the LES may need a finer grid. Multi-phase simulations (air/water/medium) are showing appropriate medium segregation effects but are over-predicting the level of segregation compared to that measured by gamma-ray tomography in particular with over prediction of medium concentrations near the wall. Further, investigated the accurate prediction of axial segregation of magnetite using the LES turbulence model together with the multi-phase mixture model and viscosity corrections according to the feed particle loading factor. Addition of lift forces and viscosity correction improved the predictions especially near the wall. Predicted density profiles are very close to gamma ray tomography data showing a clear density drop near the wall. The effect of size distribution of the magnetite has been fully studied. It is interesting to note that the ultra-fine magnetite sizes (i.e. 2 and 7 mu m) are distributed uniformly throughout the cyclone. As the size of magnetite increases, more segregation of magnetite occurs close to the wall. The cut-density (d(50)) of the magnetite segregation is 32 gm, which is expected with superfine magnetite feed size distribution. At higher feed densities the agreement between the [Dungilson, 1999; Wood, J.C., 1990. A performance model for coal-washing dense medium cyclones, Ph.D. Thesis, JKMRC, University of Queensland] correlations and the CFD are reasonably good, but the overflow density is lower than the model predictions. It is believed that the excessive underflow volumetric flow rates are responsible for under prediction of the overflow density. (c) 2006 Elsevier Ltd. All rights reserved.

CFD simulations of hydrocyclones with an air core - Comparison between large eddy simulations and a second moment closure

CFD simulations of the 75 mm, hydrocyclone of Hsieh (1988) have been conducted using Fluent TM. The simulations used 3-dimensional body fitted grids. The simulations were two phase simulations where the air core was resolved using the mixture (Manninen et al., 1996) and VOF (Hirt and Nichols, 1981) models. Velocity predictions from large eddy simulations (LES), using the Smagorinsky-Lilly sub grid scale model (Smagorinsky, 1963; Lilly, 1966) and RANS simulations using the differential Reynolds stress turbulence model (Launder et al., 1975) were compared with Hsieh's experimental velocity data. The LES simulations gave very good agreement with Hsieh's data but required very fine grids to predict the velocities correctly in the bottom of the apex. The DRSM/RANS simulations under predicted tangential velocities, and there was little difference between the velocity predictions using the linear (Launder, 1989) and quadratic (Speziale et al., 1991) pressure strain models. Velocity predictions using the DRSM turbulence model and the linear pressure strain model could be improved by adjusting the pressure strain model constants.

Testing the protracted lexical restructuring hypothesis: The effects of position and acoustic-phonetic clarity on sensitivity to mispronunciations in children and adults

Although developmental increases in the size of the position effect within a mispronunciation detection task have been interpreted as consistent with a view of the lexical restructuring process as protracted, the position effect itself might not be reliable. The current research examined the effects of position and clarity of acoustic-phonetic information on sensitivity to mispronounced onsets in 5- and 6-year-olds and adults. Both children and adults showed a position effect only when mispronunciations also differed in the amount of relevant acoustic-phonetic information. Adults' sensitivity to mispronounced second-syllable onsets also reflected the availability of acoustic-phonetic information. The implications of these findings are discussed in relation to the lexical restructuring hypothesis. (c) 2006 Elsevier Inc. All rights reserved.

Patterns of phonological errors as a function of a phonological versus an articulatory locus of impairment

WWe present the case of two aphasic patients: one with fluent speech, MM, and one with dysfluent speech, DB. Both patients make similar proportions of phonological errors in speech production and the errors have similar characteristics. A closer analysis, however, shows a number of differences. DB's phonological errors involve, for the most part, simplifications of syllabic structure; they affect consonants more than vowels; and, among vowels, they show effects of sonority/complexity. This error pattern may reflect articulatory difficulties. MM's errors, instead, show little effect of syllable structure, affect vowels at least as much as consonants and, and affect all different vowels to a similar extent. This pattern is consistent with a more central impairment involving the selection of the right phoneme among competing alternatives. We propose that, at this level, vowel selection may be more difficult than consonant selection because vowels belong to a smaller set of repeatedly activated units.

CFD modelling of the fast pyrolysis of biomass in fluidised bed reactors. Part B: Heat, momentum and mass transport in bubbling fluidised beds

The fluid–particle interaction inside a 150 g/h fluidised bed reactor is modelled. The biomass particle is injected into the fluidised bed and the heat, momentum and mass transport from the fluidising gas and fluidised sand is modelled. The Eulerian approach is used to model the bubbling behaviour of the sand, which is treated as a continuum. Heat transfer from the bubbling bed to the discrete biomass particle, as well as biomass reaction kinetics are modelled according to the literature. The particle motion inside the reactor is computed using drag laws, dependent on the local volume fraction of each phase. FLUENT 6.2 has been used as the modelling framework of the simulations with the whole pyrolysis model incorporated in the form of user-defined function (UDF). The study completes the fast pyrolysis modelling in bubbling fluidised bed reactors.

CFD modelling of the fast pyrolysis of biomass in fluidised bed reactors, Part A: Eulerian computation of momentum transport in bubbling fluidised beds

The fluid–particle interaction inside a 150 g/h fluidised bed reactor is modelled. The biomass particle is injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. The Eulerian approach is used to model the bubbling behaviour of the sand, which is treated as a continuum. The particle motion inside the reactor is computed using drag laws, dependent on the local volume fraction of each phase, according to the literature. FLUENT 6.2 has been used as the modelling framework of the simulations with a completely revised drag model, in the form of user defined function (UDF), to calculate the forces exerted on the particle as well as its velocity components. 2-D and 3-D simulations are tested and compared. The study is the first part of a complete pyrolysis model in fluidised bed reactors.

CFD modelling of the fast pyrolysis of biomass in fluidised bed reactors: modelling the impact of biomass shrinkage

The fluid–particle interaction and the impact of shrinkage on pyrolysis of biomass inside a 150 g/h fluidised bed reactor is modelled. Two 500 View the MathML sourcem in diameter biomass particles are injected into the fluidised bed with different shrinkage conditions. The two different conditions consist of (1) shrinkage equal to the volume left by the solid devolatilization, and (2) shrinkage parameters equal to approximately half of particle volume. The effect of shrinkage is analysed in terms of heat and momentum transfer as well as product yields, pyrolysis time and particle size considering spherical geometries. The Eulerian approach is used to model the bubbling behaviour of the sand, which is treated as a continuum. Heat transfer from the bubbling bed to the discrete biomass particle, as well as biomass reaction kinetics are modelled according to the literature. The particle motion inside the reactor is computed using drag laws, dependent on the local volume fraction of each phase. FLUENT 6.2 has been used as the modelling framework of the simulations with the whole pyrolysis model incorporated in the form of user defined function (UDF).

A CFD approach on the effect of particle size on char entrainment in bubbling fluidised bed reactors

The fluid – particle interaction inside a 41.7 mg s-1 fluidised bed reactor is modelled. Three char particles of sizes 500 µm, 250 µm, and 100 µm are injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. Due to the fluidising conditions and reactor design the char particles will either be entrained from the reactor or remain inside the bubbling bed. The particle size is the factor that differentiates the particle motion inside the reactor and their efficient entrainment out of it. A 3-Dimensional simulation has been performed with a completele revised momentum transport model for bubble three-phase flow according to the literature as an extension to the commercial finite volume code FLUENT 6.2.

Computational modelling of the impact of particle size to the heat transfer coefficient between biomass particles and a fluidised bed

The fluid–particle interaction and the impact of different heat transfer conditions on pyrolysis of biomass inside a 150 g/h fluidised bed reactor are modelled. Two different size biomass particles (350 µm and 550 µm in diameter) are injected into the fluidised bed. The different biomass particle sizes result in different heat transfer conditions. This is due to the fact that the 350 µm diameter particle is smaller than the sand particles of the reactor (440 µm), while the 550 µm one is larger. The bed-to-particle heat transfer for both cases is calculated according to the literature. Conductive heat transfer is assumed for the larger biomass particle (550 µm) inside the bed, while biomass–sand contacts for the smaller biomass particle (350 µm) were considered unimportant. The Eulerian approach is used to model the bubbling behaviour of the sand, which is treated as a continuum. Biomass reaction kinetics is modelled according to the literature using a two-stage, semi-global model which takes into account secondary reactions. The particle motion inside the reactor is computed using drag laws, dependent on the local volume fraction of each phase. FLUENT 6.2 has been used as the modelling framework of the simulations with the whole pyrolysis model incorporated in the form of User Defined Function (UDF).