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Symbiotic nitrogen fixation in the fungus gardens of leaf-cutter ants
(SCIENCE, 2009-11-20) Pinto Tomás, Adrián Alberto; Anderson, Mark A.; Suen, Garret; Stevenson, David M.; Chu, Fiona S. T.; Cleland, Wallace W.; Weimer, Paul J.; Currie, Cameron R.
Bacteria-mediated acquisition of atmospheric N2 serves as a critical source of nitrogen in terrestrial ecosystems. Here we reveal that symbiotic nitrogen fixation facilitates the cultivation of specialized fungal crops by leaf-cutter ants. By using acetylene reduction and stable isotope experiments, we demonstrated that N2 fixation occurred in the fungus gardens of eight leaf-cutter ant species and, further, that this fixed nitrogen was incorporated into ant biomass. Symbiotic N2-fixing bacteria were consistently isolated from the fungus gardens of 80 leaf-cutter ant colonies collected in Argentina, Costa Rica, and Panama. The discovery of N2 fixation within the leaf-cutter ant−microbe symbiosis reveals a previously unrecognized nitrogen source in neotropical ecosystems.
Octocorals in the Galapagos Islands
(Galapagos Research, 2009-06-01) Breedy Shadid, Odalisca; Hickman, Cleveland, P.; Williams, Gary C.
The Galapagos octocorals were almost unknown until recent years. Of the three orders within the subclass Octocorallia (Anthozoa, Cnidaria), the Pennatulacea (sea pens) and Alcyonacea (soft corals and gorgonians) occur in the Galapagos. Recent collections and research bring the total known octocorallian fauna to three sea pens (Virgularia galapagensis, Ptilosarcus undulatus and Cavernulina darwini) and 15 gorgonians. Of the 13 gorgonians that we have collected, several are new species. Pacifigorgia is widely distributed in the archipelago, with four named species (P. dampieri, P. symbiotica, P. rubripunctata, and P. darwinii), three of them recently described, and two others yet to be described. The genus Muricea contains three widely distributed undescribed species, one of which appears in three chromotypes, and one deepwater species that has not been collected recently. Two species of Heterogorgia occur in the central archipelago, H. verrucosa and the recently described and widely distributed H. hickmani. The remaining gorgonians are Eugorgia daniana, Leptogorgi alba and Adelogorgia telones.
La filosofía y los hallazgos de las ciencias cognitivas sobre los procesos de pensamiento humano: exigencia de una revisión a fondo de la ética y la filosofía política
(2025) Richards Palaoro, Edgardo; Solis Umaña, Mario
Durante siglos las reflexiones sobre los procesos de pensamiento humano fueron principalmente especulativas, pero durante la segunda mitad del siglo XX se desarrollaron nuevas herramientas científicas para estudiarlos. Para la filosofía es crucial determinar lo que significan los hallazgos de la psicología cognitiva, porque de lo contrario la reflexión filosófica sobre el pensamiento humano estaría prescindiendo de fundamentos empíricos. La pregunta que guió mi investigación fue: ¿Qué consecuencias tienen los hallazgos de las ciencias cognitivas para la ética y la filosofía política? Como conclusión de mi trabajo de investigación planteo que los hallazgos que vienen produciendo las ciencias cognitivas causan grandes vacíos en el pensamiento filosófico y en concepciones sobre la condición humana, debido a que destacan la subordinación del pensamiento humano a las emociones y porque exponen la profunda complejidad y el carácter fundamentalmente biológico y orgánico de la experiencia humana. Ante el escepticismo al que pueden conducir los hallazgos de las ciencias cognitivas, planteo que la homeostasis puede haber condicionado la división sexual del trabajo, dando lugar al ejercicio de un poder desproporcionado, construyéndose así un patriarcado que premió estrategias a veces despiadadas de dominación del Otro. Las manifestaciones concretas de la razón, entonces, se habrían desarrollado como instrumento de la homeostasis patriarcal, en condiciones privilegiadas por el ocio y la reflexión, alentando y normalizando la superioridad de valores como la fuerza y el poder despótico. Planteo la necesidad de desarrollar una Nueva Razón, que no se sustentaría en los procesos reflexivos sino en las expresiones de una ética y una política de la protección, y que tomaría como punto de partida la esperanza que surge de constatar el compromiso y la pasión de lo femenino por el Otro y la vida.
Mamografía contrastada para la detección del cáncer de mama: una revisión sistemática
(2025-08) Hernández Blanco, Aracelly; Fonseca Alvarado, Jose Andrés
La mamografía con contraste ha emergido como una herramienta complementaria y eficaz en la evaluación diagnóstica del cáncer de mama, especialmente en mujeres con tejido mamario denso. Numerosos estudios han demostrado que ofrece una sensibilidad comparable a la resonancia magnética para la detección de cáncer de mama, con ventajas adicionales como menor costo, mayor accesibilidad, menor tiempo de adquisición y menor tasa de falsos positivos. También ha mostrado utilidad en la caracterización de microcalcificaciones, evaluación de lesiones palpables, respuesta al tratamiento neoadyuvante, y como técnica de detección secundaria en casos indeterminados o de alto riesgo. A pesar de implicar una dosis de radiación ligeramente mayor que la mamografía digital convencional y el riesgo inherente al uso de contraste yodado, los eventos adversos graves son poco frecuentes. Su implementación es factible en la mayoría de los centros que ya cuentan con equipos de mamografía actualizados, lo cual la convierte en una opción rentable para el diagnóstico y tamizaje en poblaciones seleccionadas.
Design and performance of frames with intentionally eccentric braces
(2020-09) González Ureña, Andrés; Tremblay, Robert; Rogers, Colin A.
Concentrically Braced Frames (CBFs) with Hollow Structural Sections (HSSs) as the bracing members present significant shortcomings that pose limits to their convenience. Due to their inherently stiff nature, CBFs are usually constrained to low fundamental periods of vibration and, thus, high acceleration and force demands, which, in conjunction with the intrinsic overstrength that derives from the compression resistance controlling the dimensioning of the bracing members, results in high design forces for the capacity-protected components of the structure and its foundations. Furthermore, their ductility and energy dissipation capacity are hindered by the susceptibility of HSSs to low-cycle fatigue induced premature fracturing at the plastic hinge region after the onset of local buckling. To address these shortcomings of Conventional Concentric Braces (CCBs), researchers from Japan recently proposed the use of Braces with Intentional Eccentricity (BIEs). Being subject to both flexural and axial deformations under axial loading, BIEs are inherently less stiff than CCBs. Moreover, their axial stiffness can be adjusted by varying the eccentricity to obtain the desired frame response. Also, initiation of local buckling occurs at larger axial displacements because the strain demand is more evenly distributed over the brace length. However, BIEs are not well suited for standard force-based design procedures given that the force they develop varies continuously with their axial deformation, and that they attain their maximum capacity at large deformation values that depend on the eccentricity. For this reason, the use of BIEs compels the use of an alternative design approach that handles explicitly their particular response to loading. This article presents a Direct Displacement-Based Design (DDBD) procedure for the seismic design of Frames with Intentionally Eccentric Braces (FIEBs). The proposed procedure includes provisions aiming to control the performance of the structure when subjected to design level earthquakes and to minimize its damage under frequent earthquakes. The method is applied to prototype buildings of 4, 8 and 12 storeys, with square HSS bracing members, and considering two levels of target drift ratio. The structures are designed for a region of high seismic hazard and for a region of moderate seismic hazard, both within Canada. The performance of the so designed buildings is then evaluated through Non-Linear Response-History Analysis (NLRHA). The results show that the seismic performance of FIEBs is satisfactory and on par with the performance objectives incorporated in the procedure and those of the National Building Code of Canada. Furthermore, the resulting tonnage of the FIEB buildings is compared to that of traditional Moderately Ductile and Limited Ductility CBFs designed for identical conditions, showing that FIEBs may constitute an economically advantageous alternative to conventional CBFs, specially in the case of moderately tall buildings located in regions of high seismic hazard.