Browsing by Author "Valenzuela, Matias"

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    Development of the Historical Analysis of the Seismic Parameters for Retroffiting Measures in Chilean Bridges
    (2023) Calderon, Enrique; Valenzuela, Matias; Minatogawa, Vinicius; Pinto, Hernan
    Chile is exposed to the occurrence of medium- and large-magnitude earthquakes. As a result, national and international design codes have been developed, whose objectives are to grant an ideal behavior to the structures. However, in Chile, many of these structures do not comply with the design and construction standards of current regulations. Therefore, we propose to carry out a historical compilation that allows establishing the components that present the seismic vulnerability in bridges built from 1920 to 2010. We explored information gathered from the Government of Chile. We analyzed 553 bridges out of a total of 6835, considering superstructure and infrastructure components and seismic design evolution. The analysis emphasizes the elements that help improve the seismic performance of a bridge when natural or induced dynamic forces act on it, such as the length support, elastomeric bearing, seismic hold-down bars, transverse girders, seismic stoppers, bracing, and expansion joints. We identified that the most significant problems in bridges are the lack of seismic stoppers, both interior and exterior; lack of development length in the support tables; use of deficient expansion joints; and the inefficient construction of cross girders and baring support; in addition to the presence of differential settlements in elements of the infrastructure.
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    Hydrophobic eutectic solvents for the selective solvent extraction of molybdenum (VI) and rhenium (VII) from a synthetic pregnant leach solution
    (2023) Olea, Felipe; Valenzuela, Matias; Zurob, Elsie; Parraguez, Benjamin; Abejon, Ricardo; Cabezas, Rene; Merlet, Gaston; Tapia, Ricardo; Romero, Julio; Quijada-Maldonado, Esteban
    In this work, a study on the selective solvent extraction (SX) of molybdenum (Mo) and rhenium (Re) from a synthetic pregnant leach solution (PLS) has been carried out using nine different hydrophobic eutectic solvents (HES). Experiments were carried out using pure HES to evaluate the selective extraction and the subsequent stripping of these metal ions; then, the best HES was dissolved in kerosene to study the SX stoichiometry. Results indicated that only TOPO-based and N8881-Cl-based HES did not form emulsions, third phases or precipitates. These HES achieved a selective extraction because these obtained almost a 100% extraction towards Mo and Re from the PLS and very low extractions for Copper (Cu) and Iron (Fe) in one equilibrium stage. The stripping experiments showed that 95% of Mo and 22% of Re were stripped out from the loaded TOPO-based HDES, respectively, opening the possibility for the selective stripping of the metal species for further purification. Finally, the extraction stoichiometry was proposed based on an experimental slope analysis and the measurement of cations and anions transferred into the aqueous phase in which HES acts as a neutral extractant in the complexation of the Mo and Re salts. These promising results suggest that HES could be attractive for more sustainable mining industry.
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    The extinct Notiomastodon platensis (proboscidea, Gomphoteriidae) inhabited mediterranean ecosystems during the Late Pleistocene in north-central Chile (31°S-36°S)
    (2024) Gonzalez-Guarda, Erwin; Segovia, Ricardo A.; Valenzuela, Matias; Asevedo, Lidiane; Villavicencio, Natalia; Tornero, Carlos; Ramirez-Pedraza, Ivan; Ortega, Sebastian; Capriles, Jose; Labarca, Rafael; Latorre, Claudio
    Limited pollen and limnogeological evidence show that central Chile (31 degrees S-36 degrees S) had a more temperate climate during the Late Pleistocene. Questions remain, however, regarding the extent of the mediterranean sclerophyllous forest currently found in this region and its postglacial dynamics. The extinct Notiomastodon platensis was the only proboscidean species that inhabited central Chile and ranged across a broad latitudinal range (31 degrees S-42 degrees S) during the Pleistocene. Although this species was a mixed-feeder, we reconstructed past ecosystems when these animals were alive using stable isotope evidence from dental root collagen (delta C-13 and delta N-15) of N. platensis specimens collected from present-day semi-arid and mediterranean ecosystems in central Chile (31 degrees S-36 degrees S). Compared to modern vegetation isotope baselines, we expected the isotopic value of the Estimated Consumed Diet (ECD) (the probable diet of N. platensis) to be similar to the isotopic signal (low values) from vegetation adapted to temperate rainforests. However, elevated delta N-15(ECD) values indicate a paleo-vegetation more similar to a xerophyte scrub influenced by a semi-arid paleoclimate. delta C-13(ECD) values reflect a wooded/forested environment but adapted to more arid conditions. Although high delta N-15 values could be influenced by other non-climatic factors (e.g., grazing effect), our combined evidence suggests that these gomphotheres roamed through ecosystem very similar to those found today in central Chile. Our results show the need for multiproxy reconstructions of past environmental change in Mediterranean regions where the abundance of entomophilous species can lead to biased pollen reconstructions.