Facultad de Ciencias Exactas y Naturales

URI permanente para esta comunidadhttp://10.0.96.45:4000/handle/11056/14053

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32. Catalogo 2.0. de recursos para la alfabetización en competencias digitales del profesorado de la Escuela de Bibliotecología y Ciencias de la Información
(2016) Calvo Guillén, Ginnette
Proyecto de investigación cuyo fin es desarrollar un catálogo 2.0 de recursos para la alfabetización digital en competencias digitales del profesorado de la Escuela de Bibliotecología y Ciencias de la Información (EBCI). En la Universidad de Costa Rica (UCR), aunque existen acciones encaminadas al desarrollo de las competencias digitales del profesorado, aún no se cuenta con un perfil en la materia. Además, los cursos y capacitaciones brindados por las diferentes instancias, se encuentran dispersos y desarticulados; incluso, muchos de estos esfuerzos no toman en consideración las necesidades específicas del profesorado que les posibilite regular por sí mismos su proceso de actualización y adecuarlo según sus posibilidades, es decir de forma autónoma. A su vez, hay muchos recursos en línea que pueden ser aprovechados por los profesores. El desarrollo del catálogo contempla la definición del perfil de competencias digitales del profesorado, su estado actual con respecto al perfil, la identificación de las necesidades puntuales de capacitación, el diseño del catálogo mediante la arquitectura de información y su implementación con el software libre Koha. Se trabaja desde la investigación-acción y el enfoque cualitativo, para la recolección de la información se utilizó la técnica de grupos focales y entre los instrumentos destacan la guía de entrevista y el formulario de cotejo. Se concluye sobre la importancia de contar con un perfil que oriente acerca de cuáles son las áreas prioritarias por ser abordadas, la necesidad de trabajar las competencias digitales integralmente, así como de integrar en las capacitaciones el componente curricular y didáctico de la mano con la tecnología. Se motiva al profesorado a capacitarse desde la óptica de mejoramiento y el aprendizaje continuo; y a poner en práctica constantemente los conocimientos adquiridos en las capacitaciones. Para finalizar, se insta a las diferentes instancias de la Universidad a tomar la investigación como un referente para ofertar capacitaciones.
33. Comunidades de aprendientes en entornos virtuales: una alternativa de educación sin distancias en el marco del Paradigma Emergente
(2016) Morado, Florencia
La presente investigación cumple con el objetivo de exponer una alternativa de construcción de entornos virtuales de aprendizaje (EVA) bajo los lineamientos del Paradigma Emergente. A partir de un proceso de investigación acción participativa en conjunto con el profesorado de la Universidad De La Salle, se analizan los lineamientos básicos del Paradigma Emergente y se busca determinar de qué manera se debe desarrollar un entorno de aprendizaje en la plataforma Moodle, que responda al paradigma propuesto, incorporando también herramientas de la Web 2.0. Se exponen alternativas para la presentación de los contenidos, con el fin de incentivar diferentes estilos de aprendizaje. Además, se analizan qué propuestas de participación, interacción y trabajo colaborativo propician la mediación pedagógica de los aprendizajes del estudiantado. Se propone un modelo de “educación sin distancias”, caracterizado por la creación de un vínculo entre los participantes que constituyen una comunidad de aprendientes en línea a partir de las conversaciones que generan.
50 metros al este del antiguo Higuerón: formas culturales de abordar la localización espacial con potencialidades etnomatemáticas
(Bolema: Boletim de Educação Matemática, 2021) Gavarrete Villaverde, María Elena; Albanese, Veronica
Desde la Etnomatemática se plantea la importancia de tener en consideración aspectos propios de la cultura de los estudiantes, para acercarlos al aprendizaje de conceptos matemáticos que están en uso durante las prácticas cotidianas. Para ello es necesario, primero, analizar en profundidad tales elementos de la cultura para identificar relaciones con la matemática escolar y después formar adecuadamente a los docentes. Presentamos entonces, aquí, el análisis etnomatemático del signo cultural costarricense de las direcciones a la tica como un signo idiosincrático para la localización espacial de las direcciones postales o de las indicaciones para determinar un lugar. Utilizamos las perspectivas teóricas ética local, émica global, y dialógica glocal como principales herramientas teóricas y metodológicas para realizar el análisis. Finalmente, problematizamos este signo cultural para la acción pedagógica describiendo algunas actividades que se han llevado a cabo para la formación de docentes en Costa Rica.
A new species and three hybrids in the ferns from Cocos Island, Puntarenas, Costa Rica
(Universidad Nacional (Costa Rica), 2017-12) Rojas Alvarado, Alexander
Una nueva especie y tres híbridos en helechos para la Isla del Coco, Puntarenas, Costa Rica. Una especie nueva y tres híbridos de helechos para la Isla del Coco (Costa Rica) son descritos e ilustrados aquí: Nephrolepis cocosensis A. Rojas, Cyathea × robusta A. Rojas, Elaphoglossum × intermedium A. Rojas y Tectaria × epilithica A. Rojas. La nueva especie difiere de Nephrolepis rivularis (Vahl) Mett. ex Krug por su hábitat terrestre, frondas más pequeñas, pinnas más pequeñas and estas perpendicular al raquis, pinnas marginalmente lobuladas a bilobuladas distalmente, escamas del raquis pardo pálido con el punto de inserción pardo oscuro, escamas de la lámina 0.2–0.4 mm en diámetro, algunas veces reducidas a puntos resinosos, soros submarginales, muchas veces en los lóbulos internos de cada segmento, indusios cordiformes and basalmente adheridos, estos pardo pálidos con el punto de inserción pardo oscuro. El primer híbrido es intermedio entre Cyathea alfonsiana L.D. Gómez y C. notabilis Domin, en tamaño del tronco, tamaño y forma de las escamas del rizoma y base del estípite, tamaño de las frondas, pares de venas por segmento and grado de división de estas and y tamaño de los parafisos, pero tiene frondas más grandes que ambos progenitores, por esta razón el nombre del epíteto. Elaphoglossum x intermedium es un híbrido entre E. alvaradoanumA. Rojas y E. crinitum (L.) Christ, el cual es caracterizado por escamas del estípite y lámina pardos, lámina con base cuneada and ápice obtuso, y venas parcial e irregularmente anastomosadas. Tectaria x epilithica tiene caracteres intermedios entre T. incisa Cav. y T. mexicana (Fée) C.V. Morton, y es fácil de reconocer porque tiene lámina 1-pinnado-pinnatífida y tamaño intermedio entre las escamas del rizoma.
A checklist of the amphibians and reptiles of Río Macho Biological Station, Provincia de Cartago, Costa Rica
(Check List vo.11 no.6 article 1784 1-10 2015, 2015-11-02) Acosta-Chaves, Victor; Chaves, Gerardo; Abarca, Juan G.; García-Rodríguez, Adrián; Bolaños, Federico
We provide a checklist of the amphibians and reptiles of Río Macho Biological Station (RMBS), Costa Rica. During a period of a year (2012–2013) we conducted visual and acoustic surveys in a natural mature forest plot (>50 years old) (MF), secondary forest plot (~17 years old) (SF), in open areas and riparian forest at RMBS. We found a total of 11 species of amphibians and 15 species of reptiles belonging to 11 taxonomic families. We also compared the diversity of the MF against the SF. The MF contained 10 species (five amphibians and five reptiles) and the SF seven (three amphibians and four reptiles), with similar dominance between sites. Unfortunately, some forest and riparian species have vanished at this elevation after an enigmatic decline, according to historical literature pristine areas should contain higher species richness. Perhaps, the secondary forest will provide an available habitat for an important percentage of the remaining forest species.
A combined experimental and theoretical study of gas sorption on nanoporous silver triazolato metal-organic frameworks
(2014-01-01) Yang, Guang; Santana, Juan A; Rivera Ramos, Milton E.; García - Ricard, Omar; Saavedra-Arias, José; Ishikawa, Yasuyuki; Hernandez-Maldonado, Arturo; Raptis, Raphael G.
A new silver-triazolate metal-organic framework (MOF), {Ag 3[Ag5(μ3-3,5-tBu 2tz)6](BF4)2}n (2), has been prepared and structurally characterized. The CO2 sorption properties of this new MOF and previously reported isostructural analog {Ag 3[Ag5(μ3-3,5-Ph2tz) 6](NO3)2}n (1), were determined experimentally and probed theoretically by a density functional (DF) method. The structures of 1 and 2 are based on flexible Ag5tz 6-structural building units (SBUs), which allow the expansion/contraction of the structure, depending on either the steric requirements of the pendant groups - tBu, or Ph - of the SBUs, or the pressure of the gaseous sorbate. Both silver-triazolate MOFs sorb CO 2 preferentially to N2, O2, CH4 and H2. DF calculations show CO2 to be bound by van der Waals forces to the organic moieties of the porous framework. This work shows that van der Waals interactions of CO2 and the aromatic and aliphatic hydrocarbons of silver-triazolate MOFs are sufficient to achieve preferential sorption of CO2.
A combined first-principles computational/experimental study on LiNi 0.66Co 0.17Mn 0.17O 2 as a potential layered cathode material
(Elsevier, 2012-08-01) Saavedra-Arias, José; Venkateswara Rao, Chitturi; Shojan, Jifi; Manivannan, Ayyakkannu; Torres, Lorraine; Ishikawa, Yasuyuki; Katiyar, Ram
First-principles calculations are used to analyze the phase stability, formation energy, and Li intercalation potential for a series of layered cathode materials. The calculations show LiNi 0.66Co 0.17Mn 0.17O 2 as a promising cathode for lithium-ion batteries. The layer-structured LiNi 0.66Co 0.17Mn 0.17O 2 is prepared via wet chemical route, followed by annealing at 1123 K and characterized using powder X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The characterization techniques reveal single-phase LiNi 0.66Co 0.17Mn 0.17O 2 with highly ordered structure. Galvanostatic charge-discharge curves recorded at 1C show the discharge capacity of ca. 167 mAh g -1 and good cyclic performance for 25 cycles.
A dynamic simulation model for the blooming of Oscillatoria agardhii in a monomictic lake
(Elsevier, 1995-01-15) Jiménez, Ricardo; Verreth, Johan; Steenbergen, Kees; Moed, Jan; Machiels, Marcel
The occurrence of phytoplankton blooms is a common problem in water bodies. The quantitative description of the algal population growth is of primary importance to understand the mechanisms which lead to these phytoplankton blooms, hence also for the development of a successful water-quality management. Due to the high degree of complexity of phytoplankton blooms, dynamic simulation models may be a powerful tool to study and elucidate the mechanisms leading to these blooms. In the present study, a simulation model for the blooming of a natural population of Oscillatoria agardhii in Lake Vechten (lat. 52°04′N, long. 5°05′E, the Netherlands) using measured temperature, filament length and nutrient concentrations as external drives, is presented. The lake was sampled weekly from January to the middle of May, 1992. Temperature, nutrient concentration (nitrate and phosphate in the water) and filament length were recorded. Because cell size was constant, filament length could be converted to number of cells per litre to estimate algal biomass. To implement the model additional information, e.g. some algal growth parameters, was obtained from the literature. The model simulated well the growth of the Oscillatoria agardhii population in the lake during the research period. According to the model, temperature was the most important rate-limitating factor for growth at the beginning of the year. Nutrient limitation became increasingly important while the importance of temperature limitation decreased during the season. During the whole period, light was strongly limiting and became the most important rate-limiting factor in the second week of April. Via sensitivity analysis, the model showed to be highly affected by temperature-related factors, and it was useful in the identification of research needs.
A first estimation of Tsunami Hazard of the Caribbean Coast of Costa Rica from Local and Distant Seismogenic Sources
(IV Assembly of the Latin American and Caribbean Seismological Commission, LACSC 2022, 2022-10-04) Chacon-Barrantes, Silvia; Murillo Gutiérrez, Anthony; Rivera, Fabio
Costa Rica has experienced 41 tsunamis since 1746, 36 of them at the Pacific coast and only 5 at the Caribbean coast. However, the oldest record belongs to the Caribbean coast, as well as the only tsunami that has caused deaths in Costa Rica: the 1991 Limón tsunami.
A first estimation of tsunami hazard of the Pacific coast of Costa Rica from local and distant seismogenic sources
(Springer, 2021-06-04) Chacon-Barrantes, Silvia; Arozarena-Llopis, Isabel
Costa Rica has been affected by several local and distant tsunamis in the past, but the historical information is scarce and incomplete. Its Pacific coast stretches for over a thousand kilometers, and tsunami hazard has never been evaluated for its full extent. Numerical modeling of tsunami propagation and inundation is a useful tool to assess tsunami hazard, particularly in cases with limited historical information available. Here, we perform a first estimation of tsunami hazard for the Pacific coast of Costa Rica from seismogenic sources, by numerical propagation of 57 local and distant tsunamis to a depth of 20 m. The results of our study identified tsunami sources that are particularly threatening for Costa Rica and determined locations with higher tsunami hazard. For the analysis, the Pacific coast of Costa Rica was divided into segments and subsegments based on differences in continental slope morphology. Subsegments with higher tsunami heights were Southwest Nicoya Peninsula and West Osa Peninsula, and in a lesser extent North Guanacaste, North Nicoya Peninsula, and Central Pacific. Regions with long and gentle slopes and narrow continental shelf were affected by higher tsunami waves, due to more efficient tsunami energy transmission to the shelf and reduced energy loss while traveling through a narrow shelf. On the opposite, steeper continental slopes reflected most of the tsunami energy, causing smaller tsunami heights nearshore, regardless of the shelf width. Nevertheless, other effects played a major role, like curved coastlines that focused tsunami energy, wave refraction, interference, and trapped edge waves. Distant tsunamis dominated the threat, with tsunamis coming from the Tonga-Kermadec and the Colombia-Ecuador Trenches causing the greatest heights due to directivity, and arrival times of about 15 h and 75 min, respectively. Local tsunamis had short arrival times but a localized impact, mainly at the shoreline in front of the generation region but were also affected by tsunami focusing, wave refraction, and edge waves. Outer rise and Osa sources caused the lowest impact within local sources. These results provide a guide for emergency planners to prioritize coastal locations and tsunami sources for tsunami preparedness actions and warning protocols.
A lightweight environment for 2D visual applications
(EasyChair, 2019) Arce-Orozco, Armando; Gonzalez-Torres, Antonio; Mata-Montero, Erick
People and organizations constantly use a wide variety of devices and formats to produce large volumes of data. This involves a series of challenges related to processing and transforming data into valuable knowledge to carry out informed decisions. This research work departs from the fact that information visualization is a critical element in the process of data analysis that takes advantage of the visual and cognitive abilities of people to explore, discover, interpret, and understand patterns in data with the use of visual representations and human-computer interaction techniques. This research proposes Di¨ok¨ol, a programming environment developed with Lua and OpenVG to facilitate the learning process of programmers with little experience in the implementation of visualizations. The environment was designed after the careful study of similar tools and the most popular visualization libraries. Its design takes into account their weaknesses and strengths to propose a set of features that can make it an efficient alternative to learning about and program visualizations. In addition to typical functionality provided by several visualization tools and libraries, Di¨ok¨ol is a lightweight environment that provides a simple and effective event manager, is scalable, small, portable and contributes an environment with a simple and easy to understand graphical interface and functionality, similar to the ones provided by Processing.
A management plan for the sport fishery of Parachromis dovii (Pisces: Cichlidae) in Hule lake, Costa Rica
(Universidad de Costa Rica, 2000-06) Tabash, Farid; Guadamuz, Emilier
A first attempt to regulate the fishing activity while preserving the species and its habitats is presented for Hule lake. We intensively sampled the "guapote" between March 1996 and April 1997 using monofilament gill nets and a floating line, collecting 421 individuals. P. dovii biomass was relatively low; this species had a long life cycle (8-10 years) and the growth oscillation was low (C=0.3). Maximum life expectation was estimated at 12 years and the point of minimum growth coincided with the spawning that takes place between November and December. After spawning, P. dovii take around seven months to reach recruitment size (54.6 mm). The length for sexual maturity was 134 mm Lt, which indicates that this species is viable for reproduction soon after leaving the protection zones around the lagoon. "Guapote" sport fishing in the Hule lake is in equilibrium, the renewal rate is 80%. An increment in the actual fishery effort is not recommended, since it could seriously affect the natural renewal capacity of the stock.
A methane sink in the Central American high elevation páramo: Topographic, soil moisture and vegetation effects
(Elsevier B.V., 2020-03-15) Chai, Leanne L.; Hernández Ramirez, Guillermo; Hik, David S; Barrio, Isabel C.; Frost, Carol M.; Chinchilla Soto, Isabel Cristina; Esquivel-Hernández, Germain
Methane (CH4) is a strong greenhouse gas with a global warming potential 23 times larger than that of carbon dioxide. Characterizing ecosystems as either sources or sinks for methane and their magnitudes informs on biosphere contributions to the global CH4 budget and to warming of the atmosphere. We quantified methane fluxes for the first time in a neotropical alpine páramo (Valle de Los Conejos, Chirripó Massif, Costa Rica) and examined the relationships of these fluxes with topography, soil moisture and vegetation, during the transition from dry to rainy season. Using closed chambers and laser spectroscopy, we measured soil CH4 and CO2 fluxes across a field site encompassing: a grassy plain as well as a plain, a gentle slope and a plateau dominated by a dwarf bamboo (Chusquea subtessellata Hitchcock). We found that the páramo landscape acts as a sink for CH4 [−53.1 ± 29.6 (mean ± SE) µg C m−2 hr−1]. Of the four field areas, the grassy plain was on average the strongest CH4 sink, likely because this soil profile had no drainage restrictions and was well aerated. By contrast, in the slope and plateau, a heavily-consolidated subsurface layer was shown to perch water, increasing surface soil moisture and limiting CH4 uptake. Conversely, in certain parts of the plain, where Chusquea grew vigorously in discrete, tall patches, we found intense CH4 uptake beneath these patches. Within the Chusquea plain, these hot spots of CH4 uptake localized under the tall Chusquea had double the uptake rates than outside these patches, with even greater uptake than the average in the grassy plain. Our results show that CH4 uptake in the páramo is driven by moisture interacting with impeding soil layers, vegetation and topography.
A Microscopic Model for a One Parameter Class of Fractional Laplacians with Dirichlet Boundary Conditions
(Springer Science and Business Media Deutschland GmbH, 2021) Bernardin, Cèdric; Gonçalves, Patrícia; Jiménez-Oviedo, Byron
We prove the hydrodynamic limit for the symmetric exclusion process with long jumps given by a mean zero probability transition rate with infinite variance and in contact with infinitely many reservoirs with density α at the left of the system and β at the right of the system. The strength of the reservoirs is ruled by κN−θ > 0. Here N is the size of the system, κ > 0 and θ ∈ R. Our results are valid for θ ≤ 0. For θ = 0, we obtain a collection of fractional reaction–diffusion equations indexed by the parameter κ and with Dirichlet boundary conditions. Their solutions also depend on κ. For θ < 0, the hydrodynamic equation corresponds to a reaction equation with Dirichlet boundary conditions. The case θ > 0 is still open. For that reason we also analyze the convergence of the unique weak solution of the equation in the case θ = 0 when we send the parameter κ to zero. Indeed, we conjecture that the limiting profile when κ → 0 is the one that we should obtain when taking small values of θ > 0
A mixed virtual element method for a pseudostress-based formulation of linear elasticity
(Elsevier B.V., 2019) Cáceres, Ernesto; Gatica, Gabriel N.; Sequeira, Filander
In this paper we introduce and analyze a mixed virtual element method (mixed-VEM) for a pseudostress-displacement formulation of the linear elasticity problem with non homogeneous Dirichlet boundary conditions. We follow a previous work by some of the authors, and employ a mixed formulation that does not require symmetric tensor spaces in the finite element discretization. More precisely, the main unknowns here are given by the pseudostress and the displacement, whereas other physical quantities such as the stress, the strain tensor of small deformations, and the rotation, are computed through simple postprocessing formulae in terms of the pseudostress variable. We first recall the corresponding variational formulation, and then summarize the main mixed-VEM ingredients that are required for our discrete analysis. In particular, we utilize a well known local projector onto a suitable polynomial subspace to define a calculable version of our discrete bilinear form, whose continuous version requires information of the variables on the interior of each element. Next, we show that the global discrete bilinear form satisfies the hypotheses required by the Babuška–Brezzi theory. In this way, we conclude the well-posedness of our mixed-VEM scheme and derive the associated a priori error estimates for the virtual solutions as well as for the fully computable projections of them. Furthermore, we also introduce a second element-by-element postprocessing formula for the pseudostress, which yields an optimally convergent approximation of this unknown with respect to the broken H(div)-norm. In addition, this postprocessing formula can also be applied to the postprocessed stress tensor. Finally, several numerical results illustrating the good performance of the method and confirming the theoretical rates of convergence are presented.
A mixed virtual element method for quasi-Newtonian stokes flows
(SIAM, 2018) CACERES, ERNESTO; Gatica, Gabriel; Sequeira, Filander
In this paper we introduce and analyze a virtual element method (VEM) for an augmented mixed variational formulation of a class of nonlinear Stokes models arising in quasi-Newtonian fluids. While the original unknowns are given by the pseudostress, the velocity, and the pressure, the latter is eliminated by using the incompressibility condition, and in order to handle the nonlinearity involved, the velocity gradient is set as an auxiliary one. In this way, and adding a redundant term arising from the constitutive equation relating the psdeudostress and the velocity, an augmented formulation showing a saddle point structure is obtained, whose well-posedness has been established previously by using known results from nonlinear functional analysis. Then, following the basic principles and ideas of the mixed- VEM approach, we introduce a Galerkin scheme employing generic virtual element subspaces and projectors satisfying suitable abstract conditions and derive the corresponding solvability analysis, along with the associated a priori error estimates for the virtual element solution as well as for the fully computable projection of it. Next, we provide two specific choices of subspaces and local projectors verifying the required hypotheses, one of them yielding an optimally convergent mixed- VEM for the fully nonlinear problem studied here, and the other one providing a new approach for the linear version of it, that is, for the Stokes problem. In addition, we are able to apply a second element-by-element postprocessing formula for the pseudostress, which yields an optimally convergent approximation of it with respect to the broken H(div)-norm. Finally, several numerical results illustrating the good performance of the method and confirming the theoretical rates of convergence are reported. © 2018 Society for Industrial and Applied Mathematics.
A mixed virtual element method for the boussinesq problem on polygonal meshes
(Global Science Press, 2021) Gatica, Gabriel; Munar Benitez, Edgar Mauricio; Sequeira, Filander
In this work we introduce and analyze a mixed virtual element method (mixed-VEM) for the two-dimensional stationary Boussinesq problem. The continuous formulation is based on the introduction of a pseudostress tensor depending nonlinearly on the velocity, which allows to obtain an equivalent model in which the main unknowns are given by the aforementioned pseudostress tensor, the velocity and the temperature, whereas the pressure is computed via a postprocessing formula. In addition, an augmented approach together with a fixed point strategy is used to analyze the well-posedness of the resulting continuous formulation. Regarding the discrete problem, we follow the approach employed in a previous work dealing with the Navier-Stokes equations, and couple it with a VEM for the convection-diffiusion equation modelling the temperature. More precisely, we use a mixed-VEM for the scheme associated with the uid equations in such a way that the pseudostress and the velocity are approximated on virtual element subspaces of H(div) and H1, respectively, whereas a VEM is proposed to approximate the temperature on a virtual element subspace of H1. In this way, we make use of the L2-orthogonal projectors onto suitable polynomial spaces, which allows the explicit integration of the terms that appear in the bilinear and trilinear forms involved in the scheme for the uid equations. On the other hand, in order to manipulate the bilinear form associated to the heat equations, we define a suitable projector onto a space of polynomials to deal with the fact that the diffiusion tensor, which represents the thermal conductivity, is variable. Next, the corresponding solvability analysis is performed using again appropriate fixed-point arguments. Further, Strang-type estimates are applied to derive the a priori error estimates for the components of the virtual element solution as well as for the fully computable projections of them and the postprocessed pressure. The corresponding rates of convergence are also established. Finally, several numerical examples illustrating the performance of the mixed-VEM scheme and confirming these theoretical rates are presented.
A mixed virtual element method for the Brinkman problem
(Mathematical Models and Methods in Applied Sciences vol.27 no.4 707-743 2017, 2017) Cáceres, Ernesto; Gatica, G.N.; Sequeira, Filander
In this paper, we introduce and analyze a mixed virtual element method (mixed-VEM) for the two-dimensional Brinkman model of porous media flow with non-homogeneous Dirichlet boundary conditions. More precisely, we employ a dual-mixed formulation in which the only unknown is given by the pseudostress, whereas the velocity and pressure are computed via postprocessing formulae. We first recall the corresponding variational formulation, and then summarize the main mixed-VEM ingredients that are required for our discrete analysis. In particular, in order to define a calculable discrete bilinear form, whose continuous version involves deviatoric tensors, we propose two well-known alternatives for the local projector onto a suitable polynomial subspace, which allows the explicit integration of these terms. Next, we show that the global discrete bilinear form satisfies the hypotheses required by the Lax–Milgram lemma. In this way, we conclude the well-posedness of our mixed-VEM scheme and derive the associated a priori error estimates for the virtual solution as well as for the fully computable projection of it. Furthermore, we also introduce a second element-by-element postprocessing formula for the pseudostress, which yields an optimally convergent approximation of this unknown with respect to the broken ℍ(div)-norm. Finally, several numerical results illustrating the good performance of the method and confirming the theoretical rates of convergence are presented.
A Monte Carlo Study of the Photon Spectrum due to the Different Materials Used in the Construction of Flattening Filters of LINAC
(Hindawi, 2017-07-10) Estepa Jiménez, Juan Sebastián; Díaz Lagos, Mercedes; Martínez Ovalle, Segundo Agustín
Different types the spectrum of photons were studied; they were emitted from the flattening filter of a LINAC Varian 2100 C/D that operates at 15 MV. The simplified geometry of the LINAC head was calculated using the MCNPX code based on the studies of the materials of the flattening filter, namely, SST, W, Pb, Fe, Ta, Al, and Cu. These materials were replaced in the flattening filter to calculate the photon spectra at the output of this device to obtain the spectrum that makes an impact with the patient. The different spectra obtained were analyzed and compared to the emission from the original spectra configuration of the LINAC, which uses material W. In the study, different combinations of materials were considered in order to establish differences between the use of different materials and the original material, with the objective of establishing advantages and disadvantages from a clinical standpoint.
A multidisciplinary approach using hydrogeochemistry, δ15NNO3 isotopes, land use, and statistical tools in evaluating nitrate pollution sources and biochemical processes in Costa Rican volcanic aquifers
(Elsevier B. V., 2024) Madrigal-Solís, Helga; Vadillo Pérez, Iñaki; Jiménez Gavilán, Pablo; Fonseca Sánchez, Alicia; Calderón Sánchez, Hazel; Gómez - Cruz, Alicia; Herrera-Murillo, Jorge; Pérez-Salazar, Roy
Nitrate pollution threatens the Barva and Colima multi-aquifer system, the primary drinking water source in the Greater Metropolitan Area of Costa Rica. In addressing nitrate contamination dynamics, this study proposes an integrated approach by combining multivariate statistical analyses, hydrochemical parameters, sewage discharge, and regional land-use and land-cover patterns to assess the extent and degree of contamination, dominant biogeochemical processes, and refine the interpretation of nitrate sources previously derived solely from δ15NNO3 information. Over seven years (2015-2022), 714 groundwater samples from 43 sites were analyzed for nitrate and major ions, including two sampling campaigns for dissolved organic and inorganic carbon, nitrite, ammonium, FeTotal, MnTotal, and δ15NNO3 analyses. The findings presented elevated nitrate concentrations in urban and agricultural/urban areas, surpassing the Maximum Concentration Levels on several occasions, and oxidizing conditions favoring mineralization and nitrification processes in unconfined Barva and locally confined Upper Colima/Lower Colima aquifers. Similar nitrate contents and spatial patterns in agricultural and urban zones in the shallow Barva aquifer suggest comparable contributions from nitrogen fertilizers and urban wastewaters despite the gradual increase in urban land cover and the reduction of agricultural areas. Isotopic analyses and dissolved organic carbon (DOC) indicate a shift in nitrate sources from agricultural to urban areas in both Barva and Colima aquifers. Principal Component and Hierarchical Cluster Analyses link land use, nitrate sources, and water quality. Three distinct sample clusters aligned with forest/grassland, agricultural/urban, and urban land use, emphasizing the impact of anthropogenic activities on groundwater quality, even in the deeper Colima aquifers. The study challenges nitrate isotope mixing models, enhancing accuracy in identifying pollution sources and assessing the spatial extent of contamination by incorporating DOC and other hydrochemical parameters. Similar outcomes, with and without the use of nitrate isotopes, reinforce the usefulness of the integrated approach, providing a practical and cost-effective alternative.

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