15,712 research outputs found
Frijol silvestre en el Valle Central de Costa Rica: distribución ecológica y caracterización molecular.
No full textThis work offers an update on thedistribution of wild common bean in Costa Rica, its ecologyand molecular characterization. To date 22 populations havebeen discovered in four watersheds around the Central Valley,usually in man-made habitats (often sides of coffeeplantations), under varying conservation status (from protectedto threatened). Molecular characterization indicates that thewild common bean belong to the Mesoamerican gene pool.Different markers indicate an increased genetic diversity insome wild populations, and allow to hypothesize the presenceof gene flow and introgression from cultivated materials.Estetrabajo presenta una actualización sobre la distribución de lasformas silvestres de fríjol común en Costa Rica, su ecología ysu caracterización molecular. Ala fecha 22 poblaciones fueronencontradas en cuatro cuencas alrededor del Valle Central, generalmenteen vegetaciones ruderales (frecuentemente bordesde cafetales), con estatuto de conservación variable (desdeprotegido a amenazado). Su caracterización molecular indicasu pertenencia al acervo genético mesoamericano. Varios marcadoresindican una variabilidad aumentada en las formas silvestresy permiten inferir la presencia de un fenómeno de flujogenético e introgresión desde materiales cultivados
ESTADO INMUNOLÓGICO DE TERNERAS Y TERNEROS DE LECHERÍA EN LA REGIÓN HUETAR NORTE DE COSTA RICA. AÑO II
Get PDFEl objetivo del presente estudio fue realizar por segundo año consecutivo una caracterización del estado inmunológico de terneras y terneros de lechería en la región Huetar Norte de Costa Rica. Los datos corresponden a medidas de proteína sérica total (PST) obtenidas durante el periodo comprendido entre agosto y noviembre del 2011 en 33 fincas lecheras. Las razas de las vacas se clasificaron en Holstein, Jersey, cruce HolsteinxJersey y otras. Para fines del presente estudio, se consideró una falla en la adquisición de inmunidad pasiva cuando la concentración de PST fue menor a 5,5 g/dl. La concentración varió entre 2,0 y 10,0 g/dl, con un contenido promedio general de 5,7 g/dl. De los animales evaluados un 43,7% presentaron niveles inadecuados de inmunidad. Cuando se consideró el sexo de la cría, el 44,1% de las hembras y el 38,3% de los machos obtuvieron niveles inade- cuados de inmunidad y la concentración de PST no presentó diferencias para hembras y machos (6,0 y 6,1 g/dl). Los animales provenientes del cruce HolsteinxJersey obtuvieron una concentración de PST significativamente mayor a los de las demás razas. Las crías nacidas de novillas de primer parto presentaron concentraciones de 6,3 g/dl y la menor proporción de crías con niveles inadecuados de inmunidad. Estos datos sugieren que es necesario establecer prácticas de manejo del calostro que permitan minimizar el riesgo de ter- neros con una transferencia de inmunidad pasiva inadecuada en hatos lecheros de la región Huetar Norte de Costa Rica
Two-stage dispersal of <i>Guarea glabra</i> and <i>G. kunthiana</i> (Meliaceae) in Monteverde, Costa Rica
No full textSeed dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica was studied to determine how seed predation and secondary dispersal affect the distribution of seeds available for recruitment. The arillate seeds are consumed mainly by birds that regurgitate or defecate the seeds intact. After dispersal, 45.6% of G. glabra and 26.6% of G. kunthiana seeds were buried 1–3 cm in the soil, presumably by scatterhoarding rodents such as agoutis (Dasyprocta punctata). G. glabra seeds that were not cached were eaten mostly by beetles, and 33.7% of the seeds remained cached after 12 wk. The cached G. glabra seeds did not germinate, however, perhaps as a result of experimental procedures used to mark the seeds. In greenhouse experiments, G. glabra seeds buried to mimic scatterhoarding had higher germination success than seeds on the soil surface. G. kunthiana seeds not cached were eaten by peccaries (Tayassu tajacu) and other seed predators (60%) or were inviable (10%). Only nine (7.5%) viable G. kunthiana seeds remained in caches after 12 wk. Secondary dispersal resulted in a rearrangement of the seed shadow. G. glabra seeds were moved to sites with less leaf litter and lower vegetation density, while G. kunthiana seeds were moved farther from conspecific trees and closer to fallen logs during secondary dispersal. Considering the high rates of seed predation in the field for both species, the germination advantages for G. glabra in the greenhouse, and the shifts in microhabitat during scatterhoarding, it is likely that secondary dispersal by scatterhoarding rodents is an important stage in Guarea recruitment.RESUMEN. Dispersión de semillas de Guarea glabra y G. kunthiana (Meliaceae) en Monteverde, Costa Rica fureon examinadas para determinar como la predación de semillas y dispersión secundaria afectan la distribución de semillas disponibles para recrutamiento. Las semillas ariladas son consumidas principalmente por aves que regurgitan o defecan la semilla intacta. Luego de dispersión, 30–45% de las semillas fueron enterradas 1–3 cm en el suelo, posiblemente por roedores que disperan y acumulan como al agouti (Dasyprocta puncaata). Semillas de G. kunthiana que no fueron escondidas fueron comidas por pécaris (Tayassu tajacu) y otros predadores de semillas (60%) o no fueron viables (10%). Solo neuve (7.5%) semillas viables de G. kunthiana permanecieron en los escondites luego de 12 semanas. En contraste, semillas de G. glabra que no fueron escondidas fueron comidas mayormente por escarabajos que por pécaris, y 33.7% de las semillas permanecieron escondidas luego de 12 semanas. Las semillas esconditas de G. glabra enterradas para imitar dispersión y acumulión tuvieron una germinación mayor que semillas en la superficie del suelo. Dispersión secundaria resulto en un rearreglo de la sombra de semillas. Las dos especies experimentaron un leve aumento neto en la distancia promedio de conspecificos en frutos luego de dispersión y acumulación. Semillas de G. kunthiana fueron movidas cerca de troncos caidos durante dispersión secundaria, mientras semillas de G. glabra fueron movidas a lugares con menos lecho de hojas y baja densidad de vegetación. Considerando la alta proporción de predación de semillas en el campo para ambas especies, la ventaja de germinación de G. glabra en el invernáculo, y el cambio en micrambiente durante dispersión y acumulación, es posible que dispersión secundaria por roedores que dispersan y acumulan es importante in etapas de recrutamiento en Guarea.</jats:p
FIGURE 1. Beilschmiedia osacola. A. Fertile branch. B. Fruit. C. Partial inflorescence. D. Flower. E. Anther representing whorl. I. F. Staminode representing whorl III. G in Beilschmiedia osacola (Lauraceae) a new species from the Osa Peninsula, Costa Rica
No full textFIGURE 1. Beilschmiedia osacola. A. Fertile branch. B. Fruit. C. Partial inflorescence. D. Flower. E. Anther representing whorl. I. F. Staminode representing whorl III. G. Ovary. Drawn by Pedro Juárez, from R. Aguilar & D. Santamaría 11554 (A, C–G); B from digital image R. Aguilar 15358, available in https://www.flickr.com/photos/plantaspeninsulaosa/Published as part of Santamaría-Aguilar, Daniel, Fernández, Reinaldo Aguilar & Werff, Henk Van Der, 2021, Beilschmiedia osacola (Lauraceae) a new species from the Osa Peninsula, Costa Rica, pp. 197-204 in Phytotaxa 498 (3) on page 198, DOI: 10.11646/phytotaxa.498.3.5, http://zenodo.org/record/542424
Discourses on violence in Costa Rica, El Salvador and Nicaragua: Social Perceptions in Everyday Life
Get PDFHuhn S. Discourses on violence in Costa Rica, El Salvador and Nicaragua: Social Perceptions in Everyday Life. GIGA Working Papers. Vol 81. Hamburg: GIGA; 2008.Central America has the reputation of being a violent region with high crime rates, youth
gangs, drug traffic, and ubiquitous insecurity. Politicians, the media, and social scientists
in and outside the region often claim that the societies are in complete agreement with
their judgment of the situation and that all society members are calling for law and order
and social segregation. Focusing on Costa Rica, El Salvador, and Nicaragua, the paper analyzes
the social perception of violence and crime. On the basis of essays written by secondary
school students and interviews with citizens from all walks of life in the three countries,
the paper points out how elite arguments on violence and crime are translated into
everyday life, and what society members suggest be done to deal with these problems.
The sources prove that there are noticeable hegemonic discourses on violence and crime in
Costa Rica, El Salvador, and Nicaragua. Simultaneously, a majority of the respondents call
for social and integrative solutions rather than the so-called “iron fist.” The repressive
trend in Central American policies therefore does not necessarily receive the presumed affirmation
asserted by many authorities on and in the region
Efecto de niveles crecientes de nitrógeno en el rendimiento y calidad post cosecha de dos cultivares promisorios de papa (Solanum tuberosum L.) Zarcero, Alajuela, Costa Rica
Get PDFProyecto de Graduación (Licenciatura en Ingeniería en Agronomía) Instituto Tecnológico de Costa Rica. Escuela de Ingeniería en Agronomía, 2020.El trabajo se realizó en la localidad de Tapezco (1960 msnm) de Zarcero, Alajuela Costa Rica, entre los meses de mayo y setiembre del 2019. El propósito fue evaluar el efecto de niveles crecientes de nitrógeno (N) en el comportamiento agronómico de dos cultivares promisorios de papa (Solanum tuberosum L.), CIP396009,240 y CIP398017,53, los que se compararon con la variedad comercial Granola. Se determinó rendimiento, clasificación de tubérculos en categorías según el peso, porcentaje de materia seca, incidencia de corazón vacío y porcentaje de afectación a los agentes causales de la enfermedad roña y Rhizoctonia sp. Los tratamientos consistieron en cuatro dosis diferentes de nitrógeno, 80, 120, 160 y 200 Kg N por hectárea. Los otros nutrientes fueron suplidos en cantidades iguales en todos los tratamientos.
Se encontró diferencias entre las dosis utilizadas y entre cultivares. Los cultivares promisorios evaluados presentaron un rendimiento promedio de 30 t/ha, cerca de un 70% de los tubérculos correspondieron a las categorías comerciales. Además, acumularon mayor cantidad de materia seca y fueron más tolerantes a los agentes causales de la enfermedad roña y Rhizoctonia sp. Sin embargo, tienden a producir tubérculos con peso superior a los 300 g que los hace susceptibles al defecto fisiológico de corazón vacío. Se concluyó que los cultivares evaluados tienen demandas diferentes de N por lo que se debe de diseñar el manejo nutricional específico para cada uno. Los cultivares promisorios tienen potencial de beneficiar a los productores paperos del país ya que se mejorarían los rendimientos por hectárea con tubérculos que se pueden comercializar como producto fresco o en agroindustria incidiendo positivamente en la economía de los agricultores.The work was carried out in the town of Tapezco (1960 m.a.s.l.) of Zarcero, Alajuela Costa Rica, between the months of May and September of 2019. The purpose was evaluating the effect of increasing levels of nitrogen (N) on the agronomic behavior of two promising potato crops (Solanum tuberosum L.), CIP396009,240 and CIP398017,53, which were compared with the commercial variety Granola. The performance, classification of tubers into categories according to weight, percentage of dry matter, incidence of empty heart and percentage of involvement to the causative agents of the disease “Roña” and Rhizoctonia sp. were determinate. The treatments consisted of four different doses of nitrogen, 80, 120, 160 and 200 Kg N/ha. The other nutrients were supplied in equal amounts in all treatments.
Differences were found between the doses used and between cultivars. The promising cultivars evaluated showed an average yield of 30 t/ha, about 70% of the tubers corresponded to the commercial categories. In addition, they accumulated more dry matter and were more tolerant to the causative agents of the disease “Roña” and Rhizoctonia sp. However, they tend to produce tubers with weight greater than 300 g that make them susceptible to the physiological defect of a hollow heart. It was concluded that the cultivars evaluated have different demands of N, so the specific nutritional management for each one must be designed. Promising cultivars have the potential to benefit the country's potato producers as yields per hectare would be improved with tubers that can be marketed as fresh product or in agribusiness, positively impacting the farmers' economy
Preliminary Study of Optimized Metasurface Matching Layer in Near Field
No full textElectromagnetic devices often require the maximization of the transmitted field, especially for biomedical applications. The employment of a matching layer can reduce the reflections at the air/skin interface, but it is often realized without design guidelines and it may result bulky. On the other hand, introducing a metasurface can improve user's comfort. A rigorous procedure to find the parameters of the matching layer, also comprising the metasurface, can help in its design. Here, we extend the analytical optimization procedure of our previous works by considering a real patch antenna instead of a short dipole. An experimental setup for retrieving the electric field inside a tissue-mimicking phantom is also presented. Three cases are considered: no matching layer, dielectric-only matching layer and metasurface matching layer. The preliminary results show a good agreements with the theoretical ones
Analytical Approach for Metasurface Matching Layer Design for Electric Field Maximization in Biological Tissues
No full textThe application of an electromagnetic field inside biological tissues can be advantageous in several applications, from physiological parameters monitoring to microwave imaging. In those cases, the maximization of the transmitted signal is desired. Therefore, designing a matching layer able to reduce unwanted reflections at the air/skin interface is a relevant issue. The employment of a metasurface can be useful since it may reduce the thickness of the matching layer. Here we propose an analytical method for the design of matching layers to maximize the electric field inside the muscle tissue. Two cases are considered: when the matching layer consists of solely a dielectric, and when a metasurface is placed upon a dielectric substrate
Analytical Approach to Matching Layer Design for Electric Field Maximization in Biological Tissues
No full textThe electromagnetic waves transmission inside biological tissues can be useful in several biomedical applications, such as rehabilitation and microwave imaging. In this context, an important point is to design a matching layer to enhance the penetration of the electric field into a target tissue. Here we present an analytical method to design a matching layer under the near-field regime, i.e. when the electromagnetic source, as for instance a short dipole antenna, lies in the proximity of the body. In particular, two cases are examined: when the matching layer only consists of a dielectric slab, and when it is composed by a metasurface printed on a dielectric substrate. The proposed approach is based on the wave-transmission chain matrix and on the Schelkunoff's definition of wave impedance to consider the source. The body is modeled as a multilayered planar medium. An optimization procedure based on a stochastic algorithm is applied to determine the parameters of the matching layer which could realize the maximum electric field transmission inside the muscle. These parameters are then used to simulate the overall system with a numerical software. The results show that the matching layer comprising the metasurface is the most effective solution in terms of electric field maximization and dimensions of the substrate
Matching Layer Design for Far-Field and Near-Field Penetration Into a Multilayered Lossy Media
No full textThe remarkable spreading of medical devices relying on electromagnetic (EM) fields stimulates a deeper analysis of their interactions with the human body. The electric field generated by a radio-frequency (RF) source, such as an antenna, can be transmitted inside biological tissues and used in disease treatment, rehabilitation, and noninvasive imaging. In this context, it is important to facilitate the penetration of the electric field inside tissues. Matching layers (MLs) consisting of dielectric media or impedance surfaces provide an approach to maximize the field penetration. However, the presence of a source in close proximity to the body complicates the EM analysis and the design of such a structure. Here, we analyze an analytical method based on the wave-transmission-chain matrix and the wave-impedance concept, as defined by Schelkunoff for near-field sources. Examples of the usefulness of this approach in designing an ML that could improve the penetration of the electric field inside tissues are presented. The results obtained analytically are finally compared with those of a full-wave solver, showing good agreement
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