Exergy Optimization of a Moving Bed Heat Exchanger

The MBHE proposed can be analyzed as a crossflow heat exchanger where one of the phases is a moving granular medium. In the present work the exergy analysis of the MBHE is carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the stationary problem and a simplified analysis. The numerical simulation is carried over the two steady state energy equations (fluid and solid), involving (for the fluid) the convection heat transfer to the solid and the diffusion term in the flow direction, and (for the solid) only the convection heat transfer to the fluid. The simplified analysis followed the well-known e-NTU method, taking the equipment as a crossflow heat exchanger with both fluids unmixed.Publicad

Hegemony and alternatives in education policies for children in Colombia : subjects, discourses and practices (1982 - 2015)

Páginas 197-222.Desde una historia interpretativa, indagamos por el significado, el sentido, las transformaciones y los alcances de la política educativa para la infancia. Se develó cómo las reformas educativas promovidas desde la Constitución Política de 1991, la Ley General de Educación (115/94) y el Código de Infancia (1098 /2006), son discursos que se han ido configurando por las tensiones entre las propuestas hegemónicas y las construcciones alternativas lideradas por diferentes grupos sociales y políticos. Estas tensiones en clave de tiempo, muestran que las transformaciones educativas hunden sus raíces en propuestas alternativas que interpelan tanto los planteamientos hegemónicos como la realidad educativa del país. El estudio se inscribe en una visión histórica que recupera diferentes aspectos de la humanidad como la cultura, las significaciones, los sujetos, los saberes, las prácticas y los discursos, elementos que se resignifican y cobran sentido en la medida que pueden ser asumidos como fuente de información. La investigación se desarrolló desde la metodología cualitativa documental que centra la mirada en la producción discursiva de la política educativa, la pedagogía y la educación en unos periodos establecidos. Discursos que se constituyeron en el archivo documental desde los cuales fue posible develar las intenciones, los sentidos y las significaciones de quienes los produjeron, dando cuenta de las transformaciones y contribuciones alcanzadas en materia de la educación para la infancia en este período de tiempo.ABASTRACT: It was studied from the interpretive history, the meaning; sense; transformations and scope of education policy for children. This paper reveals how the education reforms promoted since the enactment of the Political Constitution of 1991, the General Education Law (115/94) and the Children's Code (1098/2006) constitute discourses shaped by tensions between the hegemonic proposals and alternative constructions led by different social and political groups. These tensions, over time, show that the educational transformations sink their roots in alternative proposals that address both the hegemonic approaches and the educational reality of the country. The study is part of a historical vision that recovers different aspects of humanity such as culture, meanings, subjects, knowledge, practices and discourses; all these, elements that can be resignified and become meaningful to the extent that they can be assumed as a source of information.This research used the qualitative documentary methodology focused on the discursive production of education policy, pedagogy, and education in established periods. These discourses made up the documentary archive where it was possible to unveil the intentions, senses and meanings of those who produced them. Transformations and contributions achieved in the field of children's education, during this period, are explained.Bibliografía: páginas 221-222.Artículo revisado por pares

Revisión bibliográfica, médica y odontológica de covid-19

El 8 de enero de 2020, el Centro Chino de Control y Prevención de Enfermedades anunció oficialmente la presencia de un nuevo coronavirus como patógeno causante del COVID-19, este es un agente infeccioso que varía desde un estado asintomático hasta provocar un brote de neumonía viral, insuficiencia respiratoria e incluso la muerte. Los primeros casos de esta enfermedad fueron en el mes de diciembre del 2019 en Wuhan-China, en el presente existen una suma extremadamente alta a nivel mundial declarando en estado de emergencia por su rápida propagación. Así mismo está causando problemas de salud pública, al punto de colapsarse en ciertos países. Este virus recién descubierto provoca enfermedades respiratorias agudas graves y está relacionado con el coronavirus del síndrome respiratorio agudo severo (SARS) y el coronavirus del síndrome respiratorio del Medio Oriente (MERS), pero es distinto de cada uno de estos. El objetivo de este trabajo es, mediante la recopilación de información de diferentes artículos poder indicar información básica y detallada tanto médica como odontológica acerca de esta nueva enfermedad debido a la alta posibilidad de contagio intrahospitalario de los profesionales de la salud

First Detection of the Molecular Cloud Population in the Extended Ultraviolet (XUV) Disk of M83

We report a CO(3-2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with ALMA. The observed 1kpc^2 region is at about 1.24 times the optical radius (R25) of the disk, where CO(2-1) was previously not detected. The detection and non-detection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A -- with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The cloud and clump masses, estimated from CO(3-2), range from 8.2x10^2 to 2.3x10^4 Msun and from 2.7x10^2 to 7.5x10^3 Msun, respectively. The most massive clouds appear similar to Orion A in star formation activity as well as in mass, as expected if the cloud mass structure is universal. The overall low SF activity in the XUV disk could be due to the relative shortage of gas in the molecular phase. The clouds are distributed like chains up to 600 pc (or longer) in length, suggesting that the trigger of cloud formation is on large scales. The universal cloud mass structure also justifies the use of high-J CO transitions to trace the total gas mass of clouds, or galaxies, even in the high-z universe. This study is the first demonstration that CO(3-2) is an efficient tracer of molecular clouds even in low-metallicity environments.Comment: Accepted for AAS Journal

Carbon monoxide in clouds at low metallicity in the dwarf irregular galaxy WLM

Carbon monoxide (CO) is the primary tracer for interstellar clouds where stars form, but it has never been detected in galaxies in which the oxygen abundance relative to hydrogen is less than 20 per cent of that of the Sun, even though such ‘low-metallicity’ galaxies often form stars. This raises the question of whether stars can form in dense gas without molecules, cooling to the required near-zero temperatures by atomic transitions and dust radiation rather than by molecular line emission; and it highlights uncertainties about star formation in the early Universe, when the metallicity was generally low. Here we report the detection of CO in two regions of a local dwarf irregular galaxy, WLM, where the metallicity is 13 per cent of the solar value. We use new submillimetre observations and archival far-infrared observations to estimate the cloud masses, which are both slightly greater than 100,000 solar masses. The clouds have produced stars at a rate per molecule equal to 10 per cent of that in the local Orion nebula cloud. The CO fraction of the molecular gas is also low, about 3 per cent of the Milky Way value. These results suggest that in small galaxies both star-forming cores and CO molecules become increasingly rare in molecular hydrogen clouds as the metallicity decreases

Objeto Virtuales de aprendizaje en Cefalometría como estrategia para el aprendizaje de la Ortodoncia

Este artículo presenta una guía para el diseño de objetos virtuales de aprendizaje (OVA), también conocidos como intermediarios pedagógicos, utilizan las tecnologías de la información y la comunicación (TIC), diseñados para un propósito en general, orientar a los docentes en mejorar el proceso de enseñanza- aprendizaje, son herramientas que permiten implementar nuevas e innovadoras estrategias didácticas. El objetivo es describir el desarrollo de un OVA sobre Cefalometría, que brinde conocimiento de una manera didáctica a los estudiantes de Odontología. Metodología: estudio metodológico del desarrollo del sitio web, el diseño de la aplicación se realizó a través de dos fases, la primera recopiló información teórica, se elaboró material educativo y la otra donde se llevó a cabo la elaboración de la aplicación utilizando el modelo de diseño instruccional (análisis, diseño, desarrollo e implementación), tomando en consideración los requerimientos. Resultados: el objeto virtual, disponible en formato SCORM que aporta material textual, visual, y auditivo, su desarrollo se logró a través de la utilización de herramientas Exelearning y la plataforma Moodle, cuenta con un cuestionario donde se pone a prueba los conocimientos adquiridos. Conclusión: la metodología utilizada permitió el desarrollo del OVA, puede ser utilizado como herramienta para guiar y permitir una mayor retención del conocimiento, permitiendo que el proceso de enseñanza –aprendizaje se facilite tanto a los estudiantes como al profesor, es necesario la elaboración de nuevos OVAS en las distintas cátedras de la odontologí

First Results from the HerschelHerschel and ALMA Spectroscopic Surveys of the SMC: The Relationship Between [CII]-bright Gas and CO-bright Gas at Low Metallicity

The Small Magellanic Cloud (SMC) provides the only laboratory to study the structure of molecular gas at high resolution and low metallicity. We present results from the Herschel Spectroscopic Survey of the SMC (HS$^{3}$), which mapped the key far-IR cooling lines [CII], [OI], [NII], and [OIII] in five star-forming regions, and new ALMA 7m-array maps of $^{12}$CO and $^{13}$CO $(2-1)$ with coverage overlapping four of the five HS$^{3}$ regions. We detect [CII] and [OI] throughout all of the regions mapped. The data allow us to compare the structure of the molecular clouds and surrounding photodissociation regions using $^{13}$CO, CO, [CII], and [OI] emission at $<10$" ($<3$ pc) scales. We estimate Av using far-IR thermal continuum emission from dust and find the CO/[CII] ratios reach the Milky Way value at high A$_{V}$ in the centers of the clouds and fall to $\sim{1/5-1/10}\times$ the Milky Way value in the outskirts, indicating the presence of translucent molecular gas not traced by bright CO emission. We estimate the amount of molecular gas traced by bright [CII] emission at low A$_{V}$ and bright CO emission at high A$_{V}$. We find that most of the molecular gas is at low A$_{V}$ and traced by bright [CII] emission, but that faint CO emission appears to extend to where we estimate the H$_{2}$-to-HI transition occurs. By converting our H$_{2}$ gas estimates to a CO-to-H$_{2}$ conversion factor ($X_{CO}$), we show that $X_{CO}$ is primarily a function of A$_{V}$, consistent with simulations and models of low metallicity molecular clouds.Comment: Accepted for publication in Ap

Formation des étoiles dans les environnements de basse densité de gaz et de basse métallicité

In nearby galaxies, an empirical relation has been established between star formation and gas surface densities, the Kennicutt-Schmidt (KS). The relation is nearly linear when molecular gas (H2) is considered, while is less tight with atomic hydrogen (HI). These low gas density regions are of a key importance in the field of star formation, since the are also low metallicity environments, resembling the conditions of a younger universe. This thesis summarizes the observational work done with the IRAM 30MT telescope in two kinds of such regions : disk galaxies with extended ultra-violet emission (XUV), and the interstellar medium going into the hot intra-cluster medium (ICM) under ram-pressure stripping in the Virgo cluster. The galex telescope has unveiled in far ultra-violet (FUV) star formation in the outer parts of some disk galaxies that was not traced by HA. To determine the presence of H2 and analyse the K-S relation in these regions, CO observations where done in the outskirts of several XUV disk galaxies, finding both detections and upper limits. These K-S relations showed a broken power law at low gas densities, below the HI-H2 threshold. In the Virgo cluster, similar CO observations were done along the HI tidal arm connecting NGC4388 and M86, where no H2 is expected. Two detections were found, showing very low star formation efficiencies (depleting less than 0,1 % of the gas reservoir per 10 [exposant] 8 yr), and showing again a disconuity of the K-S relation at low gas densities, probing that the process of a gas consumption into stars well known at high densities cannot be extrapolated to lower densities, and that H2 can survive a certain time in the hostile ICM.Dans les galaxies proches, la relation empirique de Kennicutt-Schmidt (KS) a été établie entre la densité surfacique de formation d’étoiles et la densité surfacique de gaz. Elle est forte et presque linéaire quand on considère le gaz moléculaire (H2) mais devient moins valable lorsque l’hydrogène n’est qu’atomique (HI). Ces régions de densité de gaz faible sont d’une importance cruciale dans le domaine de la formation d’étoiles, car elles possèdent les mêmes conditions que dans les galaxies de l’univers jeune, de faible métallicité. Cette thèse compile les données observationnelles obtenues au télescope de 30 m. de l’IRAM sur deux types de régions distinctes : les galaxies à disque ayant une émission ultra-violet étendue (XUV), et le milieu interstellaire déplacé dans le milieu intra-amas (ICM) chaud sous l’effet du balayage de la pression dynamique dans l’amas de la Vierge. Pour déterminer la présence des molécules H2 et afin d’étudier la relation KS dans ces régions, des observations de CO ont été faites dans les parties externes des galaxies XUV, et nous avons à la fois des détections et des limites supérieures. Les relations KS ont montré une loi de puissance discontinue pour des densités de gaz faibles, en dessous du seuil de la transition de phase HI-H2. Dans l’amas de la Vierge, des observations similaires de Co ont été faites le long des bras marée qui relient NGC4388 et M86, où aucune présence de H2 n’est attendue. Nous avons effectué des détections, montrant une efficacité de formation d’étoiles très faible, et montrant de nouveau une discontinuité de la relation KS pour des densités de gaz faibles, prouvant que les processus bien connus de consommation du gaz à forte densité ne peuvent être généralisés aux densités plus faibles. D’autre part, nos résultats montrent que le gaz H2 peut survivre un temps long que prévu dans l’ICM hostile

Ram Pressure Stripping in the Virgo Cluster

Gas can be violently stripped from their galaxy disks in rich clusters, and be dispersed over 100kpc-scale tails or plumes. Young stars have been observed in these tails, suggesting they are formed in situ. This will contribute to the intracluster light, in addition to tidal stripping of old stars. We want to quantify the efficiency of intracluster star formation. We present CO(1--0) and CO(2--1) observations, made with the IRAM-30m telescope, towards the ram-pressure stripped tail northeast of NGC4388 in Virgo. HII regions found all along the tails, together with dust patches have been targeted. We detect molecular gas in 4 positions along the tail, with masses between 7x10$^5$ to 2x10$^6$ M$_\odot$. Given the large distance from the NGC 4388 galaxy, the molecular clouds must have formed in situ, from the HI gas plume. We compute the relation between surface densities of star formation and molecular gas in these regions, and find that the star formation has very low efficiency. The corresponding depletion time of the molecular gas can be up to 500 Gyr and more. Since this value exceeds a by far Hubble time, this gas will not be converted into stars, and will stay in a gaseous phase to join the intracluster medium

ALMA CO(2-1) observations in the XUV disk of M83

International audienceThe extended ultraviolet (XUV) disk galaxies are some of the most interesting objects studied in the last few years. The UV emission, revealed by GALEX, extends well beyond the optical disk after the drop in Hα emission, the usual tracer of star formation. This shows that sporadic star formation can occur in a large fraction of the HI disk at radii up to 3 or 4 times the optical radius. In most galaxies, these regions are poor in stars and are dominated by under-recycled gas; they therefore bear some similarity to the early stages of spiral galaxies and high-redshift galaxies. One remarkable example is M83, a nearby galaxy with an extended UV disk reaching 2 times the optical radius. It offers the opportunity to search for molecular gas and to characterize the star formation in outer disk regions, traced by the UV emission. We obtained CO(2-1) observations with ALMA of a small region in a 1.5′ × 3′ rectangle located at rgal = 7.85′ over a bright UV region of M83. There is no CO detection, in spite of the abundance of HI gas, and the presence of young stars traced by their HII regions. Our spatial resolution (17 pc × 13 pc) was perfectly fitted to detect giant molecular clouds (GMC), but none were detected. The corresponding upper limits occur in a region of the Kennicutt–Schmidt diagram where dense molecular clouds are expected. Stacking our data over HI-rich regions, using the observed HI velocity, we obtain a tentative detection corresponding to a H2-to-HI mass ratio of < 3 × 10−2. A possible explanation is that the expected molecular clouds are CO-dark because of the strong UV radiation field. This field preferentially dissociates CO with respect to H2, due to the small size of the star-forming clumps in the outer regions of galaxies