Artículos científicos

URI permanente para esta colecciónhttp://10.0.96.45:4000/handle/11056/14610

Examinar

Mostrando 1 - 20 de 132

Interacción Océano-Atmósfera: Surgencia y Generación de Anillos en la Región de Papagayo
(Universidad Nacional (Costa Rica), 2002) Vargas, José Mauro
Resumen. Haciendo uso de datos de AVHRR, de datos de viento del QuikScat y de una estación meteorológica en la zona de Cuajiniquil en Costa Rica, se ha encontrado una clara relación entre la velocidad de los vientos y el fenómeno de surgencia en Papagayo entre el 14 de diciembre de 2001 y el 5 de abril de 2002. Se observa también un corrimiento notable hacia el norte de los vórtices anticiclónicos formados en Papagayo para finales de febrero de 2002 con respecto a los anillos investigados por Ballestero y Coen en el experimento llevado a cabo en 1996 (Ballestero y Coen, 2004).
Hydrographic variability in the Gulf of Papagayo, Costa Rica during 2017-2019
(Universidad de Costa Rica (Costa Rica), 2021-10) Cambronero-Solano, Sergio; Tisseaux-Navarro, Alexandre; Vargas-Hernández, José Mauro; Salazar-Ceciliano, Juan P.; Benavides-Morera, Rosario; Quesada Ávila, Isabel; Brenes-Rodríguez, Carlos
Abstract: Introduction: The Gulf of Papagayo (GP) is a site of socioeconomic importance located in the North Pacific of Costa Rica. The ecosystem services of this site represent a benefit in local communities, and its dynamics are influenced by a coastal upwelling system that affects fishing and commercial activity. Objective: The objective of this study was to characterize the spatio-temporal variability of the main hydrographic parameters through measurements in situ during the period 2017-2019. Methods: Eight measurement campaigns were carried out, where a CTD probe was deployed to perform vertical profiles in 23 stations distributed throughout the GP, to characterize the variations in temperature, salinity, dissolved oxygen and chlorophyll concentration. Results: A minimum in surface and bottom temperature associated with upwelling caused by the wind was found in the first period of the year. The increase in salinity was associated with the decrease in temperature, being its highest value in the first period of the year, decreasing until reaching a minimum in November. The maximum chlorophyll concentration coincided with the lowest surface temperatures and the minimum oxygen values were associated with the minimum bottom temperatures, both occurring during the upwelling season. The parameter distribution was similar on dry and rainy seasons in stations located inside Bahía Culebra, likely attributed to the bathymetry effect. Conclusions: Bathymetry determines a south-north asymmetry for salinity and temperature. Subsurface cooling events coincide with strong wind periods. Upwelling influences the surface and bottom hydrographic dynamic in GP and determines the seasonal variability. The negative ENSO phase of 2018 corresponded with the strongest upwelling period, possibly promoting the interaction of upwelled coastal waters and the Costa Rica Thermal Dome.
Upwelling-induced inflow pulses in a tropical bay during mid-summer drought
(Elsevier (Países Bajos), 2024) Tisseaux-Navarro, Alexandre; Juárez, Braulio; Vargas-Hernández, J. Mauro; Cambronero-Solano, Sergio; Espinoza, Mario; Ruiz de Alegría-Arzaburu, Amaia; Salazar-Ceciliano, Juan Pablo
Abstract. Bahía Santa Elena is a tropical bay located in the northern Pacific region of Costa Rica. This region experiences a period of reduced precipitation from July to August, known as mid-summer drought, induced by the intensification of northeastern winds from the Caribbean Low-Level Jet. Intensification of upwelling-favorable winds can cool surface waters adjacent to the bay, leading to a reduction in water temperatures within the bay, that alters the biological dynamics of coastal habitats. This study aims to analyze upwelling-induced inflow pulses in Bahía Santa Elena during mid-summer drought, focusing on the cooling effect of intensified upwelling-favorable winds and the subsequent warm water inflows following wind relaxation. We conducted two measuring campaigns from June to July in 2021 and in 2022. The first campaign consisted of a single acoustic Doppler current profiler (ADCP) moored inside the bay. The second campaign consisted of two mooring deployments: an ADCP with a thermistor chain inside the bay and an ADCP installed at the inlet. Each campaign presented five distinct events of upwelled water inflows into the bay promoted by an offshore Ekman transport. Upwelling-favorable wind peaks were followed by a decrease in temperature of the water column. When the upwelling-favorable wind relaxed, a warm water pulse entered the bay. These events are expected to play an important role in biological processes within tropical bays adjacent to upwelling zones during mid-summer drought.
Diurnal and semidiurnal movements of two commercially important fish in a tropical bay
(Springer Nature (Alemania), 2024) Tisseaux-Navarro, Alexandre; Juárez, Braulio; Vargas-Hernández, José Mauro; Salazar-Ceciliano, Juan Pablo; Cambronero-Solano, Sergio; Ruiz de Alegría-Arzaburu, Amaia; Vargas-Araya, Lucía; Matley, Jordan; Fisk, Aaron T.; Espinoza, Mario
Abstract. Biological data collection often overlooks short-term environmental variations, potentially leading to under- or over-estimation of species abundance and ineffective conservation actions. This study investigated the complex relationship between oceanic and meteorological processes and the short-term abundance patterns of two economically important fish species in Bahía Santa Elena, a tropical bay on the north Pacific coast of Costa Rica. Using two months of continuous acoustic telemetry data from 14 Colorado (Lutjanus colorado) and 16 Pacific dog (Lutjanus novemfasciatus) snappers, we investigated temporal and spatial changes in their relative abundance patterns. A wavelet analysis revealed dominant diurnal and semidiurnal frequencies in both species. The observed semi-diurnal and diurnal periodicity in fish abundance was correlated with water level and sunlight, particularly near the mangrove in the inner bay, suggesting that both species may be using these habitats for food and shelter during periods of high tide and at night. Understanding how oceanic and meteorological conditions influence the dynamics of marine organisms in coastal environments, particularly those that are often exploited by fisheries is crucial for developing effective management and conservation approaches.
Plasma-Surface Interactions Within Helicon Plasma Sources
(Frontiers Media (Suiza), 2022) Del Valle, Juan I.; Chang Diaz, Franklin R.; Granados, Víctor H.
Abstract. Helicon plasma sources do not require electrodes or grids directly immersed in the plasma, and also present an axial magnetic field confining the plasma discharge. These factors are believed to provide them with long operational lifetimes because of the reduced potential for surface etching. The physics of helicon waves, cylindrical magnetized plasmas, sheaths, and plasma-surface interactions are discussed in the context of this claim. Practical implementation aspects are also reviewed, along with relevant experimental results. It is shown that understanding the distribution of ion density within the source, the presence of induced potentials in its surfaces, and the physics of low-energy sputtering reactions is essential to properly model erosion phenomena within helicons, and consequently predict their performance in practical applications.
Estimation of erosion phenomena within helicon plasma sources through a steady-state explicit analytical model
(Frontiers Media (Suiza), 2022-08) Del Valle, Juan I.; Granados, Víctor H.; Chang Díaz, Franklin R.
Abstract. Helicon plasma sources produce high-density discharges without the need of electrodes in direct contact with the plasma, which is thought to provide them with long operational lifetimes. An explicit steady-state analytical model is described with the capability of depicting the 2D plasma density distribution, the sheath potentials and the estimated sputtering and etch rates along the plasma-facing components of the source. The individual constituting submodels are fitted against available experimental data, and the model is used to predict erosion rates within the VX-CR research helicon plasma source. Erosion within these components is dependent on the value of plasma density along the boundaries, the electron temperature and the particular ion-target material combination. The highest erosion rates are found along the upstream system boundary, followed by the regions near the helicon antenna straps where a capacitive RF sheath is formed. The assumptions and limitations of the model are discussed, and future improvements are proposed.
Thermal Stability of Highly Filled Cellulosic Biocomposites Based on Ethylene–Vinyl Acetate Copolymer
(Multidisciplinary Digital Publishing Institute (MDPI) (Suiza), 2024) Shelenkov, Pavel Gennadievich; Pantyukhov, Petr; Aleshinskaya, Svetlana Vladimirovna; Maltsev, Alexander Andreevich; Abushakhmanova, Zubarzhat Rafisovna; Popov, Anatoly; Saavedra-Arias, José; Poletto, Matheus
Abstract. The effect of plant-based fillers on thermal resistance in highly filled biocomposites based on ethylene–vinyl acetate copolymer (EVA) was studied. Wood flour and microcrystalline cellulose were used as fillers. It was shown that the introduction of microcrystalline cellulose into EVA did not affect the thermal stability of the polymer matrix. In contrast, the introduction of wood flour into EVA led to a significant increase in the thermal stability of the entire biocomposite. Oxidation induction time increased from 0 (pure EVA) to 73 min (EVA + wood flour biocomposites). The low-molecular weight phenolic compounds contained in wood flour are likely able to diffuse into the polymer matrix, exerting a stabilizing effect. The discovered stabilizing effect is a positive development for expanding the possibilities of technological processing of biocomposites, including multiple processing.
Characterization of Extracellular Vesicles Secreted by a Clinical Isolate of Naegleria fowleri and Identification of Immunogenic Components within Their Protein Cargo
(Multidisciplinary Digital Publishing Institute (MDPI) (Suiza), 2022) Retana Moreira, Lissette; Steller Espinoza, María Fernanda; Chacón Camacho, Natalia; Cornet-Gomez, Alberto; Sáenz-Arce, Giovanni; Osuna, Antonio; Lomonte, Bruno; Abrahams Sandí, Elizabeth
Abstract. Extracellular vesicles (EVs) are small lipid vesicles released by both prokaryotic and eukaryotic cells, involved in intercellular communication, immunomodulation and pathogenesis. In this study, we performed a characterization of the EVs produced by trophozoites of a clinical isolate of the free-living amoeba Naegleria fowleri (N. fowleri). Size distribution, zeta potential, protein profile and protease activity were analyzed. Under our incubation conditions, EVs of different sizes were observed, with a predominant population ranging from 206 to 227 nm. SDS-PAGE revealed protein bands of 25 to 260 KDa. The presence of antigenic proteins was confirmed by Western blot, which evidenced strongest recognition by rat polyclonal antibodies raised against N. fowleri in the region close to 80 KDa and included peptidases, as revealed by zymography. Proteins in selected immunorecognized bands were further identified using nano-ESI-MS/MS. A preliminary proteomic profile of the EVs identified at least 184 proteins as part of the vesicles’ cargo. Protease activity assays, in combination with the use of inhibitors, revealed the predominance of serine proteases. The present characterization uncovers the complexity of EVs produced by N. fowleri, suggesting their potential relevance in the release of virulence factors involved in pathogenicity. Owing to their cargo’s diversity, further research on EVs could reveal new therapeutic targets or biomarkers for developing rapid and accurate diagnostic tools for lethal infections such as the one caused by this amoeba.
Evaluating the Effect of Iron(III) in the Preparation of a Conductive Porous Composite Using a Biomass Waste-Based Starch Template
(Multidisciplinary Digital Publishing Institute (MDPI) (Suiza), 2023) Rodríguez-Quesada, Laria; Ramírez-Sánchez, Karla; León-Carvajal, Sebastián; Sáenz-Arce, Giovanni; Vásquez-Sancho, Fabián; Avendaño-Soto, Esteban; Montero-Rodríguez, Juan José; Starbird-Perez, Ricardo
Abstract. In this work, the effect of iron(III) in the preparation of a conductive porous composite using a biomass waste-based starch template was evaluated. Biopolymers are obtained from natural sources, for instance, starch from potato waste, and its conversion into value-added products is highly significant in a circular economy. The biomass starch-based conductive cryogel was polymerized via chemical oxidation of 3,4-ethylenedioxythiophene (EDOT) using iron(III) p-toluenesulfonate as a strategy to functionalize porous biopolymers. Thermal, spectrophotometric, physical, and chemical properties of the starch template, starch/iron(III), and the conductive polymer composites were evaluated. The impedance data of the conductive polymer deposited onto the starch template confirmed that at a longer soaking time, the electrical performance of the composite was improved, slightly modifying its microstructure. The functionalization of porous cryogels and aerogels using polysaccharides as raw materials is of great interest for applications in electronic, environmental, and biological fields.
Chemical and structural heterogeneity of olive leaves and their trichomes
(Springer (Alemania), 2024) Fernández, Victoria; Almonte, Lisa; Bahamonde, Héctor Alejandro; Galindo-Bernabeu, Ana; Sáenz-Arce, Giovanni; Colchero, Jaime
Abstract. Many biological surfaces have hairs, known as trichomes in plants. Here, the wettability and macro- and micro-scale features of olive leaves are analyzed. The upper leaf side has few trichomes, while the lower side has a high trichome density. By combining different techniques including electron and atomic force microscopy, trichome surfaces are found to be chemically (hydrophilic-hydrophobic) heterogeneous at the nano-scale. Both olive leaf surfaces are wettable by water, having a high water contact angle hysteresis and great drop adhesion. The ultra-structural pattern observed for epidermal pavement cells differs from the reticulate cuticle structure of trichomes which shows that leaf surface areas may be substantially different despite being located nearby. Our study provides evidence for the nano-scale chemical heterogeneity of a trichome which may influence the functional properties of biological surfaces, such as water and solute permeability or water capture as discussed here for plants.
Costa Rican fungi as potential biomaterials
(Tecnológico de Costa Rica (TEC) (Costa Rica), 2024-08) Fallas-Méndez, Adriana; Solano-Campos, Frank; Mau Inchaustegui, Silvia; Sáenz-Arce, Giovanni; Solano-González, Stefany
Abstract. Fungal biomaterials are gaining relevance due to their intrinsic ability of self-repair, higher sensitivity to external conditions and faster growth respective to synthetic materials. This project consists of evaluating and characterizing the physical properties of fungal strains isolated from a Pacific Coast Mangrove in Costa Rica. We identified environmental strains by recording their morphological features and complemented this by ITS-based DNA barcoding, and subsequently, classified three strains based on morphological features and seven strains by molecular analyses. Ongoing work is being done to measure electrical responses of these fungi upon light stimulation; in addition, a protocol for studying their piezoelectric properties is being developed to identify potential candidates to be used in the field of electronics. To the extent of our knowledge, our project is the first one to report piezoelectric properties from microscopic fungi in Costa Rica as means to determine its potential as biomaterials.
Evaluation of Conductive Porous Biobased Composites with Tunable Mechanical Properties for Potential Biological Applications
(ACS Publications (Estados Unidos), 2024) Rodríguez-Quesada, Laria; Ramírez-Sánchez, Karla; Formosa-Dague, Cécile; Dague, Etienne; Sáenz-Arce, Giovanni; García-González, Carlos A.; Vásquez-Sancho, Fabián; Avendaño-Soto, Esteban; Starbird-Pérez, Ricardo
Abstract. In this work, starch-based porous cryogels with controlled mechanical and electrical properties were prepared for tissue engineering applications. The starch cryogels were formulated using κ-carrageenan, poly(vinyl alcohol) (PVA), and styrylpyridinium-substituted PVA (SbQ) into the composite. A conductive cryogel was polymerized by chemical oxidation of 3,4-ethylenedioxythiophene (EDOT) using iron(III) p-toluenesulfonate as a strategy to control the electrical properties. The physical, thermal, and mechanical properties were evaluated for the obtained composites. Macro- and nanoscale results confirmed the capability of tuning the mechanical properties of the material by the addition of biopolymers in different contents. The presence of κ-carrageenan significantly increased the storage modulus and decreased the damping effect in the formulations. The presence of PVA showed a plasticizing effect in the formulations, confirmed by the buffering effect and an increase in storage modulus. PVA-SBQ improved the mechanical properties by cross-linking. The addition of PEDOT increased the mechanical and electrical properties of the obtained materials.
Cambio Climático y Recursos Marino-Costeros
(Universidad Nacional (Costa Rica), 2008-06) Gutiérrez, Alejandro; Chacón, Silvia
Resumen. El cambio climático y sus efectos en la biosfera preocupan actualmente incluso a aquellos científicos y tomadores de decisiones que tiempo atrás se negaron a reconocerlos en su gravedad. Y entre ellos están destacadamente interesados los del mundo desarrollado, que temen que su calidad de vida, y la de la humanidad en general, se vea seriamente dañada en el futuro. En este artículo, que es el resultado de una indagación sobre el impacto del cambio climático en los recursos marino-costeros en Costa Rica, se procura poner en claro tal impacto a partir de la información científica disponible.
Evaluación realizada desde la perspectiva de un grupo universitario de docentes sobre los cursos de Física General de la Universidad Nacional de Costa Rica durante el 2014 y el 2019
(Universidad Nacional (Costa Rica), 2022) Márquez-Artavia, Xiomara; Delgado-Orozco, Luis; Saavedra-Arias, José
Resumen. Objetivo. Evaluar los cursos de Física General (teoría y laboratorio) de la carrera de Enseñanza de las Ciencias a través del personal docente universitario, en el periodo comprendido entre el 2014 al 2019, con el fin de identificar las fortalezas y debilidades en la metodología y replantear nuevas estrategias educativas. Metodología. La investigación mixta (cuantitativa y cualitativa) se realizó mediante una encuesta virtual con el programa LimeSurvey al profesorado que ha impartido los cursos de Física para la carrera de Enseñanza de las Ciencias en los últimos cinco años. Esta se aplicó a la población total de 20 docentes de la cual solo 12 participaron. El instrumento fue diseñado por el personal docente que trabaja en el proyecto de mejoramiento de las guías de laboratorio y su análisis se realizó con la ayuda de una hoja de cálculo de Excel, suministrada por el programa LimeSurvey. El instrumento se validó por personal del IDESPO de la Universidad Nacional en cuanto a la pertinencia del contenido de los enunciados, la claridad de las preguntas y la coherencia con el objetivo de este estudio. Resultados. La estructura y organización de los cursos de Física General tiene una valoración positiva por parte del profesorado, que también mostró una preferencia por la clase magistral; pero, aun así, mostró disposición a capacitarse y aprender nuevas estrategias didácticas. Conclusiones. Además, se determinó que el personal docente está anuente al cambio tecnológico y a trabajar en los retos que han propuesto las políticas del gobierno.
Rossby waves impact on persistent oxic and suboxic chlorophyll maxima in the Eastern Tropical North Pacific
(PAGEPress (Italy), 2024) Márquez-Artavia, Amaru; Márquez-Artavia, Xiomara; Salazar-Ceciliano, Juan P.; Sánchez-Velasco, Laura; Beier, Emilio; Paulmier, Aurélien
Abstract. This study aims to describe the response of two persistent chlorophyll-a maxima to physical processes that affect the po- sition of the thermocline/nitracline in the Eastern Tropical North Pacific (ETNP). We focused on Long Rossby Waves (LRWs) due to their relevance to the ETNP circulation and their potential role in introducing nutrients into the euphotic zone. We found that the shallower chlorophyll-a maximum in oxygenated waters became more intense when denser waters (containing more nu- trients) moved toward the surface. This suggests that changes in isopycnals and nitracline displacements modify nutrient supply in the euphotic zone, leading to changes in phytoplankton growth. The suboxic and deeper chlorophyll-a maximum showed a strong association with the 26 kg m-3 isopycnal, which was only mechanically displaced, and its chlorophyll-a content did not seem to covary with irradiance or nutrients. The decor- related responses of the chlorophyll-a maxima could be ex- plained if different phytoplankton groups are associated with them. LRWs can affect the position of the thermocline/nitracline and isopycnals in an annual cycle, but it seems to be a “back- ground” signal modulated by higher frequency processes such as mesoscale eddies and other Rossby waves. The co-occurrence of processes can control the nitracline depth, and thus the input of nutrients into the euphotic zone, leading to sporadic enhance- ments in chlorophyll-a concentration in one maximum.
Desarrollo de un escáner láser con aplicaciones en dosimetría de gel polimérico
(Asociación Física Argentina (Argentina), 2020) Chacón, D.; Romero, M.; Mattea, F.; Valente, M.
Resumen. Los avances en las aplicaciones de radiación ionizante en la medicina, y en particular el tratamiento contra el cáncer, se encuentran en continuo desarrollo y evolución. Es por ello, que las capacidades para demostrar que estas aplicaciones son seguras requieren de sistemas dosimétricos innovadores, que proporcionen información tridimensional para la verificación dosimétrica. Los dosímetros de gel polimérico son parte de estos sistemas dosimétricos notables, ya que pueden registrar cuantitativamente la dosis absorbida y obtener distribuciones de dosis en 3D con alta resolución manteniendo propiedades tejido-equivalentes. Los métodos utilizados para interpretar la señal registrada por estos sistemas a valores de dosis incluyen complejos y costosos instrumentos, tales como resonadores magnéticos y tomógrafos de rayos-X. Sin embargo, existen alternativas de menor costo como métodos de lectura ópticos que pueden optimizarse y diseñarse para el estudio de dosimetría polimérica. El objetivo de este trabajo es presentar el diseño, construcción y caracterización de un escáner láser de bajo costo, con capacidad 2D, apropiado para el análisis de los dosímetros de gel polimérico. Con este equipo, se realizaron pruebas de caracterización y optimización, contrastando los resultados con los obtenidos por instrumentos comerciales ó validados, obteniendo resultados comparables demostrando la capacidad del escáner láser como herramienta de lectura para dosimetría de gel polimérico.
Hatching Success Rather Than Temperature-Dependent Sex Determination as the Main Driver of Olive Ridley (Lepidochelys olivacea) Nesting Activity in the Pacific Coast of Central America
(MDPI, 2021-11-05) Morales Mérida, Berta Alejandra; Helier, Aude; Cortés-Gómez, Adriana A.; Girondot, Marc
En las tortugas marinas, el sexo se determina durante un periodo preciso durante la incubación: los machos se producen a temperaturas más bajas y las hembras a temperaturas más altas, un fenómeno denominado determinación del sexo dependiente de la temperatura. La temperatura del nido depende de muchos factores, entre ellos la radiación solar. El albedo es la medida de la proporción de radiación solar reflejada, y en términos de color de la arena, la arena negra absorbe la mayor parte de la energía, mientras que la arena blanca refleja más radiación solar. Basándose en esta observación, las playas de arena más oscura con temperaturas más altas deberían producir más hembras. Dado que las tortugas marinas muestran un alto grado de filopatría, incluido el regreso al hogar natal, las playas oscuras también deberían producir más crías hembras que regresen al nido cuando maduren. Cuando el color de la arena es heterogéneo en una región, nuestra hipótesis es que las playas más oscuras tendrían el mayor número de nidos. No obstante, la elevada temperatura de incubación en las playas con un albedo bajo puede dar lugar a un bajo éxito de eclosión. Utilizando imágenes de Google Earth y la base de datos SWOT de tortugas lora (Lepidochelys olivacea) nidificantes en la costa del Pacífico de México y América Central, modelamos el color de la arena y la actividad de nidificación para probar la hipótesis de que las playas más oscuras albergan mayores concentraciones de hembras debido a la feminización en las playas más oscuras y a la filopatría femenina. Encontramos el resultado opuesto: el menor éxito de eclosión en playas con un albedo más bajo podría ser el principal impulsor de la heterogeneidad de la actividad de nidificación para las tortugas lora en América Central.

Examinar

Envíos recientes