Numerical study of bio-fluids and mass transfer processes through membranes

La reologia de la sang (hemoreología) exerceix un ppel important en la perforació de teixits i l'alteració de les seves condicions fisiològiques és gairebé sempre la principal causa de patologies cardiovasculars. Per tant, l'estudi dels perfils de velocitat i l'esforç de tall de la sang al llarg de micro-venes és important en la investigació de malalties cardiovasculars. Recents avenços en organs-on-a-chip remarquen la possibilitat d'usar lung-on-a-xips el qual ha estat desenvolupat per reemplaçar les funcions respiratòries de l'home en assajos farmaceuticos. S'ha avançat en l'estudi de processos de micro-separació a través de membranes micro-poroses desenvolupant una eina numèrica per modelar el comportaments dels micro-dispositius usant la geometria dels lung-on-a-chip en dues i tres dimensions, on una membrana artificial separa dos canals amb dos diferents fluids i així dos diferents règims de flux. A causa de que és un problema de múltiples escales, el nou codi consisteix d'un model híbrid LBM-FD (Lattice Boltzmann - diferències finites) sobre una malla no uniforme que modela processos de transferència de massa en fluxos no newtonians. El model híbrid LBM-FD va ser usat per estudiar el transport de massa a través d'una membrana hidrofòbica i microporosa ocalizada entre un flux co-corrent passant a través de canals rectangulars, similar als microdispositius usats en el projecte lung-on-a- xip. Estecódigo ha estat usat per fer un estudi paramètric en la recerca de la correlació entre el nombre de Peclet al canal permeat i els processos de transferència de massa a través de la membrana (Sherwood number mitjana ). Les correlacions al microdispositiu bidimensional reprodueix correctament la relació lineal de amb el nombre de porus. Les correlacions mostren un valor de l'exponencial en la llei de potències de 1/3 (el que caracteritza el problema de Graetz-Leveque) de pel que fa a Pe. S'han trobat les correlacions en dues i tres dimensions. En el cas tridimensional es comparen els resultats obtinguts usant el flux del model de la llei de pontencias truncat amb un grau de pseudo-plasticitat de n = 0.7 pel que fa als resultats obtinguts per flux newtonià n = 1. El cas no-newtonià mostra un increment del 5% en la transferència de massa () respecte al cas newtonià.La reología de la sangre (hemoreología) desempeña un papel importante en la perforación de tejidos y la alteración de sus condiciones fisiológicas es casi siempre la principal causa de patologías cardiovasculares. Por lo tanto, el estudio de los perfiles de velocidad y el esfuerzo de corte de la sangre a lo largo de micro-venas es importante en la investigación de enfermedades cardiovasculares. Recientes avances remarcan la posibilidad de usar micro-dispositivos como lung-on-a-chip, el cual ha sido desarrollado para reemplazar las funciones respiratorias del hombre en ensayos farmaceuticos. Se ha avanzado en el estudio de procesos de micro-separación a través de membranas micro-porosas desarrollando una herramienta numérica para modelar el comportamientos de los micro-dispositivos usando la geometría de los lung-on-a-chip en dos y tres dimensiones. Debido a que es un problema de múltiples escalas, el nuevo código consiste de un modelo híbrido LBM-FD (Lattice Boltzmann - Diferencias finitas) sobre una malla no uniforme que modela procesos de transferencia de masa en flujos no Newtonianos. El modelo híbrido LBM-FD fue usado para estudiar el transporte de masa a través de una membrana hidrofóbica y microporosa localizada entre un flujo co-corriente pasando a través de canales rectangulares, similar a los microdispositivos usados en el proyecto lung-on-a-chip. Con este código, un estudio paramétrico en la busqueda de la correlación entre el Peclet en el canal permeado y el Sherwood promedio ha sido realizado. Las correlaciones en el microdispositivo bi-dimensional reproduce correctamente la relación lineal de con el número de poros. Las correlaciones muestran un valor del exponencial en la ley de potencias de 1/3 ( lo que caracteriza el problema de Graetz-Leveque) de con respecto a Pe. Se han hallado las correlaciones en dos y tres dimensiones. En el caso tri-dimensional se comparan los resultados obtenidos usando el flujo del modelo del modelo de la ley de pontencias truncado con un grado de pseudo-plasticidad de n=0.7 con respecto a los resultados obtenidos para flujo Newtoniano n=1. El caso no-Newtoniano muestra un incremento del 5% en la transferencia de masa () con respecto al caso Newtoniano.Blood rheology (haemorheology) plays a key role in tissue perfusion and its alteration from physiological conditions is often the main cause of cardiovascular pathologies. Therefore, the study of blood velocity profiles and wall shear stress distribution along micro-vessels is important in the field of cardiovascular diseases research. Recent advances in organ-on-a-chip highlighted the possibility of using artificial lung-on-chips which have been developed to replace the respiratory functions of the human lungs in pharmaceutical tests. We have expanded the study of micro-separation processes through micro-porous membranes by developing a numerical tool able to model the behavior of lung-on-a-chip micro-devices in both two and three dimensional geometries. As this is a multiscale problem, the new code consists in a hybrid LBM-FD (Lattice Boltzmann - finite difference) model on a non-uniform material grid, that models mass transfer processes in non-Newtonian flows. A part from the validation of the code, results obtained include the correlations of the non-dimensional numbers involved in mass transfer processes and the dependence on porosity, and the study of concentration profiles under steady (pipe flow) and the beginning of the study in non-steady (Womersley flow) conditions. The LBM-FD hybrid model was used to study the mass transport through a hydrophobic micro-porous membrane located in-between a co-current flow passing through rectangular channels, which is similar to the micro-device used in Lung-On-a-Chip research. This code has been used to perform a parametric study to find the empirical correlation between Peclet number in the permeate channel and the mass transfer processes across the membrane which is quantified by mean of Sherwood number. The correlations in the two-dimensional micro-device reproduce correctly the linear scaling law of with the number of pores. The correlations give a power value equal to 1/3 (which characteristic of the Graetz-Leveque problem) for the scaling exponent of the average Sherwood number with Pe. This has been done in 2D and 3D models. In the three-dimensional case, we compared the results obtained using the power-law flow with a shear-thinning degree of n=0.7 against the results obtained using the Newtonian hypothesis (n=1). The non-Newtonian case

Exploring AGN and star formation activity of massive galaxies at cosmic noon

We investigate the relation between AGN and star formation (SF) activity at 0.5 10⁴⁴ erg s⁻¹) and a large comparison sample of ~ 320,000 galaxies without X-ray luminous AGN. Our samples are selected from a large (11.8 deg²) area in Stripe 82 that has multi-wavelength (X-ray to far-IR) data. The enormous comoving volume (~ 0.3 Gpc³) at 0.5 10¹¹ \ [solar mass]) and X-ray luminous AGN. While many galaxy studies discard AGN hosts, we fit the SED of galaxies with and without X-ray luminous AGN with Code Investigating GALaxy Emission (CIGALE) and include AGN emission templates. We find that without this inclusion, stellar masses and star formation rates (SFRs) in AGN host galaxies can be overestimated, on average, by factors of up to ~ 5 and ~ 10, respectively. The average SFR of galaxies with X-ray luminous AGN is higher by a factor of ~ 3 to 10 compared to galaxies without X-ray luminous AGN at fixed stellar mass and redshift, suggesting that high SFRs and high AGN X-ray luminosities may be fueled by common mechanisms. The vast majority (> 95%) of galaxies with X-ray luminous AGN at z = 0.5 - 3 do not show quenched SF: this suggests that if AGN feedback quenches SF, the associated quenching process takes a significant time to act and the quenched phase sets in after the highly luminous phases of AGN activity.Astronom

Exploring the interplay between star formation and active galactic nuclei and the role of environment in galaxy evolution

One of the central goals of extragalactic astronomy is to understand how galaxies grow their stellar mass and central black holes, the connection between star formation and active galactic nuclei (AGN), and the impact of environment on this growth. In this thesis, I utilize multiwavelength surveys that are both deep and wide, advanced computational codes that model the spectral energy distributions of galaxies with and without AGN, as well as state-of-the-art simulations of galaxy evolution in order to explore how galaxy properties are impacted by their surrounding environment and AGN activity. These studies explore galaxies over a redshift range of 0.015 10¹¹ M☉) and extremely luminous AGN (with X-ray luminosity L [subscript X] > 10⁴⁴ erg s⁻¹) out to z ~ 3, thereby limiting the effects of cosmic variance and Poisson statistics. I analyze the observed stellar masses and star formation rates of galaxies as a function of environment and AGN activity, compare the empirical results to theoretical models of galaxy evolution, and discuss the implications of such comparisons. This work will provide significant guidance and constraints to the future development of theoretical models of galaxy growth. In Chapter 2 (Florez et al. 2021, ApJ, 906, 97) I measure the environmental dependence, where environment is defined by the distance to the third nearest neighbor, of multiple galaxy properties inside the Environmental COntext (ECO) catalog. I focus primarily on void galaxies at redshifts z = 0.015 - 0.023, which I define as the 10% of galaxies having the lowest local density. I compare the properties of void and non-void galaxies: baryonic mass, color, fractional stellar mass growth rate (FSMGR), morphology, and gas-to-stellar-mass ratio. The void galaxies typically have lower baryonic masses than galaxies in denser environments, and they display the properties expected of a lower mass population: they have more late-types, are bluer, have higher FSMGR, and are more gas rich. I also control for baryonic mass and investigate the extent to which void galaxies are different at fixed mass. I find that void galaxies are bluer, more gas-rich, and more star forming at fixed mass than non-void galaxies, which is a possible signature of galaxy assembly bias and other environmental processes. Furthermore, I show that these trends persist even at fixed mass and morphology, and I find that voids host a distinct population of early-types that are bluer and more star-forming than the typical red and quenched early-types. In addition to these empirical observational results, I also present theoretical results from mock catalogs with built-in galaxy assembly bias. I show that a simple matching of galaxy properties to (sub)halo properties, such as mass and age, can recover the observed environmental trends in the local galaxy population. In Chapter 3 (Florez et al. 2020, MNRAS, 497, 3273) I investigate the relation between AGN and star formation activity at 0.5 10⁴⁴ erg s⁻¹) and a large comparison sample of ~ 320,000 galaxies without such AGN. My samples are selected from a large (11.8 deg²) area in Stripe 82 that has multi-wavelength (X-ray to far-IR) data. The enormous comoving volume (~ 0.3 Gpc³) at 0.5 10¹¹ M☉) and high X-ray luminosity AGN. While it is typical for studies of galaxy evolution to discard AGN host galaxies, I fit the SED of galaxies with and without high X-ray luminosity AGN with Code Investigating GALaxy Emission (CIGALE) and include AGN emission templates. I find that without this inclusion, stellar masses and star formation rates in AGN host galaxies can be overestimated, on average, by factors of up to ~ 5 and ~ 10, respectively. The average star formation rate of galaxies with X-ray luminous AGN is higher by a factor of ~ 3 to 10 compared to galaxies without X-ray luminous AGN at fixed stellar mass and redshift, suggesting that high star formation rates and high AGN X-ray luminosities may be fueled by common mechanisms. The vast majority (> 95%) of galaxies with X-ray luminous AGN at z = 0.5 - 3 do not show quenched star formation: this suggests that if AGN feedback quenches star formation, the associated quenching process takes a significant time to act and the quenched phase sets in after the highly luminous phases of AGN activity. In numerical simulations and theoretical models of galaxy evolution, AGN and star formation activity are closely linked and AGN feedback is invoked to regulate galaxy growth. However, few empirical tests exist on how well the models and simulations implement the growth and interplay between AGN and star formation. To address this issue, in Chapter 4 (Florez et al. submitted) I compare the hydrodynamical simulations IllustrisTNG and SIMBA, and the semi-analytical model SAG to the empirical results on AGN and star formation at cosmic noon reported in Chapter 3. The main results of my comparisons are: (i) SAG and IllustrisTNG both qualitatively reproduce the empirical result that galaxies with high X-ray luminosity AGN have higher mean star formation rates, at a given stellar mass, than galaxies without such AGN. SAG, however, strongly over-produces the number density of high X-ray luminosity AGN by a factor of 10 to 100, while IllustrisTNG shows a lack of high X-ray luminosity AGN at high stellar mass (M [subscript *] > 10¹¹ M☉) at z ~ 2. (ii) In SIMBA, the mean star formation rate of galaxies with high X-ray luminosity AGN is lower than the star formation rate of galaxies without such AGN. Contrary to the data, many high X-ray luminosity AGN in SIMBA have quenched star formation, suggesting that AGN feedback, or other feedback modes in galaxies with such AGN, might be too efficient in SIMBA. I discuss the implications of these results for our understanding of the evolution of galaxies and the growth of their stellar masses and black holes across cosmic time.Astronom

Simulación de los patrones de profundidad, velocidad y salinidad del agua de la Ciénaga Grande de Santa Marta por el método Lattice Boltzmann

La Ciénaga Grande de Santa Marta (CGSM), es la laguna costera más grande de Colombia, y una de las más estratégicas para el Caribe colombiano [30], pero la adecuación de las tierras aledañas para la ganadería extensiva ha disminuido sustancialmente la entrada de agua fresca a la laguna principal, generando una extrema hipersalinización de sus suelos que ha sido la causa principal de la mortandad masiva del manglar y de su fauna asociada [19, 16]. La evaluación de alternativas de intervención sobre la Ciénaga ha motivado la construcción y calibración de modelos numéricos de su hidrodinámica, por ejemplo con la técnica de diferencias finitas [24, 17, 37], pero existen técnicas alternativas por explorar. Una de éstas la constituyen los modelos de Lattice-Boltzmann, que desde su aparición hace veinte años han constituido una alternativa valiosa para las simulaciones hidrodinámicas [27, 42, 3]. El objetivo del presente trabajo es acoplar dos modelos de lattice-Boltzmann: un modelo generalizado (MRT-LBE) para aguas someras, y un modelo de advección-difusión para el transporte de solutos, construidos desde cero en un lenguaje de programación de alto nivel (C++), cada uno de los modelos y el modelo acoplado, fue probado reproduciendo correctamente algunos problemas típicos de la ingeniería hidráulica explorando las capacidades del método para simular flujos en diferentes condiciones. Como situación final, se construyó un modelo acoplado de lattice-Boltzmann de la Ciénaga Grande de Santa Marta y se exploró la capacidad para reproducir los patrones de nivel de superficie libre, velocidad y salinidad obtenidos en campo por Camacho [17]. Para su calibración se utilizaron algunos de los datos de campo obtenidos por Camacho [17]. El modelo as__ construido es capaz de reproducir aproximadamente los valores medios de velocidad horizontal, profundidad y salinidad medidos en campo, con una precisión algo mayor que la de los trabajos anteriores en diferencias finitas. Igualmente, el modelo estima de manera coherente el efecto de la apertura de un caño en la parte occidental de la Ciénaga, una intervención que en efecto se realizó en fecha posterior a la toma de datos. Este trabajo reporta el primer modelo de lattice-Boltzmann para la simulación de aguas someras que se compara con datos de campo y permite apreciar en una primera instancia la capacidad que puede llegar a tener el método para la modelación de lagunas costeras.Abstract. The Ciénaga Grande de Santa Marta (CGSM) is the largest coastal lagoon in Colombia, and one of the most strategic for the Colombian Caribbean. However, the adjustment of the surrounding lands for extensive livestock has decreased substantially fresh water input to the main lagoon, which as outcome creates an extreme hypersalinization of its soil which has been the main cause of the mass mortality of mangroves and associated fauna . The evaluation of alternatives of intervention on the CGSM has led to the construction and calibration of numerical models based on their hydrodynamic characteristics, for example with the technique of finite differences, although there are alternative techniques to explore. One of these is the Lattice-Boltzmann model, which since its origin twenty years ago, has been a valuable alternative to the hydrodynamic simulations. The goal of this research is to couple two lattice-Boltzmann models: a generalized model (MRT-LBE) for shallow water and an advection-diffusion model for solute transport. These models were built from zero, by using a high level (C + +) programming language. Each model and the coupled model was tested and it successfully reproduced some typical problems of hydraulic engineering, and at the same time the capabilities of the method to simulate flows under different conditions were explored. Finally, a coupled model of lattice-Boltzmann for the CGSM was constructed and its ability to reproduce the field data patterns of free surface level, velocity and salinity obtained by Camacho was explored. The model calibration used some of the field data obtained by Camacho. The constructed model is able to reproduce approximately the mean horizontal velocity, depth and salinity measured in the field, with an greater accuracy than in previous studies that used finite differences. Also, the model consistently estimates the effect of the opening of a pipe in the western part of the CGSM, an intervention that actually took place posteriorly to data collection. This study present the first lattice- Boltzmann model for the shallow water simulation compared with field data, which also allow us to appreciate the method capacity at lagoon modeling.Maestrí

Formic acid oxidation over hierarchical porous carbon containing PtPd catalysts

The use of high surface monolithic carbon as support for catalysts offers important advantage, such as elimination of the ohmic drop originated in the interparticle contact and improved mass transport by ad-hoc pore design. Moreover, the approach discussed here has the advantage that it allows the synthesis of materials having a multimodal porous size distribution, with each pore size contributing to the desired properties. On the other hand, the monolithic nature of the porous support also imposes new challenges for metal loading. In this work, the use of Hierarchical Porous Carbon (HPC) as support for PtPd nanoparticles was explored. Three hierarchical porous carbon samples (denoted as HPC-300, HPC-400 and HPC-500) with main pore size around 300, 400 and 500 nm respectively, are used as porous support. PtPd nanoparticles were loaded by impregnation and subsequent chemical reduction with NaBH4. The resulting material was characterized by EDX, XRD and conventional electrochemical techniques. The catalytic activity toward formic acid and methanol electrooxidation was evaluated by electrochemical methods, and the results compared with commercial carbon supported PtPd. The Hierarchical Porous Carbon support discussed here seems to be promising for use in DFAFC anodes.Fil: Baena Moncada, Angélica María. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Morales, Gustavo Marcelo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Barbero, César Alfredo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Planes, Gabriel Angel. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Florez Montano, Jonathan. Universidad de la Laguna; EspañaFil: Pastor, Elena. Universidad de la Laguna; Españ

Linking Recent Discrimination-Related Experiences and Wellbeing via Social Cohesion and Resilience

The current study examined the relationship between recent experiences of discrimination and wellbeing and the mediating effects that social cohesion and resilience had on this relationship. Using online sampling, participants (N =255) from a South London community rated the levels of discrimination related experiences in the past 6 months, alongside measures of social cohesion, resilience, and wellbeing (happiness and depressive symptoms). Results revealed a negative relationship between recent experiences of discrimination and wellbeing which was explained by a serial mediation relationship between social cohesion and resilience, and singly by resilience alone. The study highlights how recent experiences of discrimination can lead to a depletion of personal resources and social resources (which in turn also lead to reduced personal resources) and in turn, to lower levels of wellbeing

Strain Effects on the Oxidation of CO and HCOOH at Au-Pd Core-Shell Nanoparticles

The mechanism of CO and HCOOH electrooxidation in an acidic solution on carbon-supported Au–Pd core–shell nanoparticles was investigated by differential electrochemical mass spectrometry and in situ Fourier transform infrared (FTIR) spectroscopy. Analysis performed in nanostructures with 1.3 ± 0.1 nm (CS1) and 9.9 ± 1.1 nm (CS10) Pd shells provides compelling evidence that the mechanism of adsorbed CO (COads) oxidation is affected by structural and electronic effects introduced by the Au cores. In the case of CS10, a band associated with adsorbed OH species (OHads) is observed in the potential range of CO oxidation. This feature is not detected in the case of CS1, suggesting that the reaction follows an alternative mechanism involving COOHads species. The faradaic charge associated with COads oxidation as well as the Stark slope measured from FTIR indicates that the overall affinity and orbital coupling of CO to Pd are weaker for CS1 shells. FTIR spectroscopy also revealed the presence of HCOOads intermediate species only in the case of CS1. This observation allowed us to conclude that the higher activity of CS10 toward this reaction is due to a fast HCOOads oxidation step, probably involving OHads, to generate CO2. Density functional theory calculations are used to estimate the contributions of the so-called ligand and strain effects on the local density of states of the Pd d-band. The calculations strongly suggest that the key parameter contributing to the change in mechanism is the effective lattice strain