Estudio y diseño numérico de un evaporador de doble tubo con flujo bifásico utilizando mapas de flujo

El presente proyecto se centra en la simulación numérica de un intercambiador de doble tubo equicorriente que evapora agua con el fin de recuperar el calor residual de una instalación que utiliza gas-oil como combustible. El fenómeno de la ebullición es uno de los procesos de transferencia de calor con cambio de fase más complejo. Normalmente para su estudio se realizan una serie de hipótesis que facilitan la labor, como pueda ser suponer el flujo de calor aportado constante o temperatura de pared constante, las cuales este proyecto evita realizar. La ebullición en flujo implica además la circulación de una mezcla bifásica de composición no constante, ya que el líquido se evapora continuamente. Primeramente se presentan las ecuaciones gobernantes para el flujo bifásico. A continuación, con el objetivo de un correcto análisis del proceso de transferencia de calor, se efectúa un estudio detallado de los diferentes regímenes de flujo y su transición, a través del desarrollo de un mapa de flujo (flow-pattern). En la región de flujo bifásico es necesario determinar el coeficiente de convección para un óptimo diseño del intercambiador. Más adelante se muestran algunas ecuaciones de coeficientes promedios, desarrolladas experimentalmente por sus autores, y se propone un modelo actual para la obtención de un coeficiente basado en el mapa de flujo. De este modo se desarrolla un programa basado en la discretización del sistema, con la finalidad de abordar una simulación térmica de todo el cambiador y desarrollar un algoritmo que controle en cada punto de la geometría el estado del fluido a evaporar. El conocimiento de dicho estado gracias al diseño del mapa de flujo, la correcta aplicación de un coeficiente que se adapte al correspondiente régimen y el hecho de prescindir de hipótesis determinantes, establecen que la simulación realizada se adecue lo máximo a la realidad del proceso

New cell wall-affecting antifungal antibiotics

Capítulo 9.Fungi have emerged worldwide as increasingly frequent causes of healthcare-associated infections. Invasive fungal infections can be life-threatening. However, the number of antifungal agents available and their use in therapy is very limited. Recently, a new family of specific fungal cell wall synthesis inhibitors has emerged as an alternative antifungal therapy and is gaining increasing relevance yearly. The cell wall is a multilayer dynamic structure, essential to the integrity and shape of the fungal cell, whose function is to counteract the osmotic forces that could otherwise produce fungal cell lysis. The cell wall is absent in nonfungal cells, therefore representing a useful target in discovering selective drugs for the treatment of fungal infections without causing toxicity in the host. Although fungi exhibit a considerable diversity in their cell wall structure, all present β(1,3)-, β(1,6)- and α(1,3)-glucans, chitin, and mannoproteins as their major cell wall components. Three different cell wall synthesis inhibitors of the lipopeptide family of echinocandins, named caspofungin, micafungin, and anidulafungin, are commercially available and new classes of cell wall synthesis inhibitors are emerging. This review provides an overview of what is so far known about the different classes of cell wall-affecting antifungal agents and their mechanism of action, offering new alternatives with clinical potential.Peer reviewe

The effect of magnetic activity on low-mass stars in eclipsing binaries

In recent years, analyses of eclipsing binary systems have unveiled differences between the observed fundamental properties of low-mass stars and those predicted by stellar structure models. Particularly, radius and effective temperatures computed from models are ~ 5-10% lower and ~ 3-5% higher than observed, respectively. These discrepancies have been attributed to different factors, notably to the high levels of magnetic activity present on these stars. In this paper, we test the effect of magnetic activity both on models and on the observational analysis of eclipsing binaries using a sample of such systems with accurate fundamental properties. Regarding stellar models, we have found that unrealistically high spot coverages need to be assumed to reproduce the observations. Tests considering metallicity effects and missing opacities on models indicate that these are not able to explain the radius discrepancies observed. With respect to the observations, we have tested the effect of several spot distributions on the light curve analysis. Our results show that spots cause systematic deviations on the stellar radii derived from light curve analysis when distributed mainly over the stellar poles. Assuming the existence of polar spots, overall agreement between models and observations is reached when ~ 35% spot coverage is considered on stellar models. Such spot coverage induces a systematic deviation in the radius determination from the light curve analysis of ~ 3% and is also compatible with the modulations observed on the light curves of these systems. Finally, we have found that the effect of activity or rotation on convective transport in partially radiative stars may also contribute to explain the differences seen in some of the systems with shorter orbital periods.Comment: 12 pages, 9 figures, accepted for publication in Ap

Numerical modeling of wave soldering in PCB

Manufacturing of electronic boards (commonly referred as PCB) is a highly automated process that requires an accurate control of the various processing variables. Amongst the soldering processes, wave soldering is one of the most often used. In this, the various electronic components are provisionally inserted onto the PCB, and a low velocity jet of melted solder is directed to the moving board. Due to capillarity effects the solder adheres to the component/board interface and the process is completed. This methodology is most often used for small components. The adjusting of the operating parameters (solder nozzle orientation and velocity) is often carried out on a trial and error basis resulting in a time consuming process that is at odds with the increasing demand for smaller production series that the electronics industry is faced with. In addition the number of defects (mostly from missing components that are washed away by the impacting jet) is more likely to occur when thinner substrates are used in the PCB manufacturing. The present paper describes the application of a Computational Fluid Dynamics model to describe the interaction of the solder jet with the PCB and the integrated circuits. The model includes the conservation equations for mass, momentum and energy in a transient time frame. The jet and surrounding ambient atmosphere are modeled as two separate fluids and the interface is tracked by a VOF model. By adjusting the computational mesh refinement the interface is captured with accuracy. The drag forces occurring in the various components are computed from the pressure data field. The model allows the optimization of the wave operating parameters as a function of the component type of and its layout in the PCB

Machine learning in critical care: state-of-the-art and a sepsis case study

Background: Like other scientific fields, such as cosmology, high-energy physics, or even the life sciences, medicine and healthcare face the challenge of an extremely quick transformation into data-driven sciences. This challenge entails the daunting task of extracting usable knowledge from these data using algorithmic methods. In the medical context this may for instance realized through the design of medical decision support systems for diagnosis, prognosis and patient management. The intensive care unit (ICU), and by extension the whole area of critical care, is becoming one of the most data-driven clinical environments. Results: The increasing availability of complex and heterogeneous data at the point of patient attention in critical care environments makes the development of fresh approaches to data analysis almost compulsory. Computational Intelligence (CI) and Machine Learning (ML) methods can provide such approaches and have already shown their usefulness in addressing problems in this context. The current study has a dual goal: it is first a review of the state-of-the-art on the use and application of such methods in the field of critical care. Such review is presented from the viewpoint of the different subfields of critical care, but also from the viewpoint of the different available ML and CI techniques. The second goal is presenting a collection of results that illustrate the breath of possibilities opened by ML and CI methods using a single problem, the investigation of septic shock at the ICU. Conclusion: We have presented a structured state-of-the-art that illustrates the broad-ranging ways in which ML and CI methods can make a difference in problems affecting the manifold areas of critical care. The potential of ML and CI has been illustrated in detail through an example concerning the sepsis pathology. The new definitions of sepsis and the relevance of using the systemic inflammatory response syndrome (SIRS) in its diagnosis have been considered. Conditional independence models have been used to address this problem, showing that SIRS depends on both organ dysfunction measured through the Sequential Organ Failure (SOFA) score and the ICU outcome, thus concluding that SIRS should still be considered in the study of the pathophysiology of Sepsis. Current assessment of the risk of dead at the ICU lacks specificity. ML and CI techniques are shown to improve the assessment using both indicators already in place and other clinical variables that are routinely measured. Kernel methods in particular are shown to provide the best performance balance while being amenable to representation through graphical models, which increases their interpretability and, with it, their likelihood to be accepted in medical practice.Peer ReviewedPostprint (published version

The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams

This is the accepted version of the following article: [Cladera, A., Marí, A., Bairán, J. M., Ribas, C., Oller, E. and Duarte, N. (2016), The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams. Structural Concrete, 17: 1017–1032. doi:10.1002/suco.201500214], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/suco.201500214/fullA simplified mechanical model is presented for the shear strength prediction of reinforced and prestressed concrete members with and without transverse reinforcement, with I, T or rectangular cross-section. The model, derived with further simplifications from a previous one developed by the authors, incorporates the contributions of the concrete compression chord, the cracked web, the dowel action and the shear reinforcement in a compact formulation. The mechanical character of the model provides valuable information about the physics of the problem and incorporates the most relevant parameters governing the shear strength of structural concrete members. The predictions of the model fit very well the experimental results collected in the ACI-DAfStb databases of shear tests on slender reinforced and prestressed concrete beams with and without stirrups. Due to this fact and the simplicity of the derived equations it may become a very useful tool for structural design and assessment in engineering practice.Peer ReviewedPostprint (author's final draft

Simple sugar intake and hepatocellular carcinoma: epidemiological and mechanistic insight

Sugar intake has dramatically increased during the last few decades. Specifically, there has been a clear trend towards higher consumption of fructose and high fructose corn syrup, which are the most common added sugars in processed food, soft drinks and other sweetened beverages. Although still controversial, this rising trend in simple sugar consumption has been positively associated with weight gain and obesity, insulin resistance and type 2 diabetes mellitus and non-alcoholic fatty liver disease. Interestingly, all of these metabolic alterations have also been related to the development of hepatocellular carcinoma. The purpose of this review is to discuss the evidence coming from epidemiological studies and data from animal models relating the consumption of simple sugars, and specifically fructose, with an increased risk of hepatocellular carcinoma and to gain insight into the putative molecular mechanisms involved

The addition of liguid fructose to a Western-type diet in LDL-R-/- mice induces liver inflammation and fibrogenesis markers without disrupting insulin receptor signalling after an insulin challenge

A high consumption of fat and simple sugars, especially fructose, has been related to the development of insulin resistance, but the mechanisms involved in the effects of these nutrients are not fully understood. This study investigates the effects of a Western-type diet and liquid fructose supplementation, alone and combined, on insulin signalling and inflammation in low-density lipoprotein (LDL) receptor-deficient mice (LDL-R−/−). LDL-R−/− mice were fed chow or Western diet ±15% fructose solution for 12 weeks. Plasma glucose and insulin, and the expression of genes related to inflammation in the liver and visceral white adipose tissue (vWAT), were analysed. V-akt murine thymoma viral oncogene homolog-2 (Akt) activation was measured in the liver of the mice after a single injection of saline or insulin. None of the dietary interventions caused inflammation in vWAT, whereas the Western diet induced hepatic inflammation, which was further enhanced by liquid fructose, leading also to a significant increase in fibrogenesis markers. However, there was no change in plasma glucose or insulin, or insulin-induced Akt phosphorylation. In conclusion, hepatic inflammation and fibrogenesis markers induced by a Western diet supplemented with liquid fructose in LDL-R−/− mice are not associated with a significant impairment of hepatic insulin signalling

Un modelo unificado de resistencia a flexión y cortante de vigas esbeltas de hormigón armado bajo caras puntuales y repartidas

Se presenta un modelo mecánico para la predicción de la resistencia a cortante-flexión de vigas esbeltas de hormigón armado sometidas a cargas puntuales y/o repartidas. El modelo incorpora las contribuciones a la resistencia a cortante de la cabeza comprimida, del alma fisurada y de las armaduras longitudinales y transversales. Se considera que la rotura tiene lugar en la cabeza comprimida no fisurada de hormigón, sometida a un estado biaxial de tensiones, cuando se alcanza la envolvente de Kupfer, habiendo plastificado las armaduras transversales. Basándose en consideraciones de equilibrio y en una distribución de tensiones en ELU para la cabeza comprimida, se proponen ecuaciones sencillas y directas para dimensionamiento y comprobación. Las predicciones del modelo se han comparado con más de 1300 ensayos a cortante de vigas, obteniéndose muy buenos resultados. El modelo proporciona una explicación física del comportamiento a cortante, lo que junto a su sencillez y precisión, le convierte en una herramienta muy útil para el proyecto basado en prestaciones.Peer ReviewedPostprint (author's final draft

Absolute properties of the low-mass eclipsing binary CM Draconis

Spectroscopic and eclipsing binary systems offer the best means for determining accurate physical properties of stars, including their masses and radii. The data available for low-mass stars have yielded firm evidence that stellar structure models predict smaller radii and higher effective temperatures than observed, but the number of systems with detailed analyses is still small. In this paper we present a complete reanalysis of one of such eclipsing systems, CM Dra, composed of two dM4.5 stars. New and existing light curves as well as a radial velocity curve are modeled to measure the physical properties of both components. The masses and radii determined for the components of CM Dra are M1=0.2310+/-0.0009 Msun, M2=0.2141+/-0.0010 Msun, R1=0.2534+/-0.0019 Rsun, and R2=0.2396+/-0.0015 Rsun. With relative uncertainties well below the 1% level, these values constitute the most accurate properties to date for fully convective stars. This makes CM Dra a valuable benchmark for testing theoretical models. In comparing our measurements with theory, we confirm the discrepancies reported previously for other low-mass eclipsing binaries. These discrepancies seem likely to be due to the effects of magnetic activity. We find that the orbit of this system is slightly eccentric, and we have made use of eclipse timings spanning three decades to infer the apsidal motion and other related properties.Comment: 19 pages, 9 figures. Accepted for publication in Ap