Browsing by Author "Martinez, Francisco"

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    First approach of fractals nickel-copper dendrites on stainless steel electrodes for ammonia oxidation to nitrogen monitored in operando by differential electrochemical mass spectroscopy
    (2024) Matamala-Troncoso, Felipe; Diaz-Coello, Sergio; Martinez, Francisco; Barrientos, Herna; Lisoni, Judit; Armijo, Francisco; Lozano, David; Pizarro, Jaime; Arevalo, Maria del Carmen; Pastor, Elena; Aguirre, Maria Jesus
    Fractal nickel-copper dendrites were synthesized by electrochemical deposition (ECD) on a stainless steel electrode (SS/NiCu). The electrode surface was characterized using Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The Ni-Cu molar ratio and the time applied in the ECD method were studied, revealing that both are critical factors in modifying and controlling the surface morphology. The SS/NiCu electrodes show a higher density current response when exposed to ammonium hydroxide, reaching a limiting current density at concentrations above 0.050 M NH4OH. 4 OH. Ammonia oxidation reaction (AOR) was monitored in operando using differential electrochemical mass spectroscopy (DEMS). When a bias potential over +1.50 V (vs. RHE) was applied, the evolution of oxygen and NO was observed. However, N2 2 was the only oxidation product at a constant potential below +1.50 V (vs. RHE). Oxygen (O2) 2 ) evolution was the main competitive reaction during the AOR. The results show that products are strongly dependent on the electrochemical perturbation applied. The study demonstrated that the SS/NiCu electrodes are suitable for AOR to N2 2 in high alkaline conditions.
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    Occurrence, residency, and habitat characterization of leopard seals in Chile
    (2024) Borras-Chavez, Renato; Soteres, Rodrigo L.; Gomez-Gonzalez, Gabriela; Martinez, Francisco; Fernandez-Ferrada, Nicolas; Castillo-Aguilar, Matias; Moreno Azua, Fredy; Dougnac, Catherine; Arredondo, Cristobal; Brown, Nicholi; Sperou, Emily S.; Bonin, Carolina A.; Goebel, Michael E.; Guerrero, Alicia I.; Donke, Marcelo; Kienle, Sarah S.
    Leopard seals have traditionally been considered Antarctic predators with a Southern Ocean distribution. Historically, sightings north of the Antarctic Polar Front were considered extralimital. However, recent studies suggest a significant presence of leopard seals in subantarctic regions. Here, we assess the spatial occurrence, residency status, and temporal trends of leopard seals in Chile using historical records, stranding reports, standardized monitoring data, photo-identification (photo ID) catalogs, and sightings from four research expeditions. We also characterize glaciers where sightings are concentrated, identifying glaciological and geomorphic attributes that prolong iceberg residency time, which is linked to high leopard seal concentrations. Based on these attributes, we evaluated other potential suitable glacial habitats in Patagonia. We obtained 438 sighting records of leopard seals from 1927 to 2023. Over the last 15 years, we documented a 4-18% annual increase in stranding events reported to national authorities. Most sightings (75%) were concentrated in two hotspots: National Park San Rafael Lagoon, located in Northern Patagonia, and Parry Fjord in Tierra del Fuego. Using photo ID catalogs, we identified 19 resident leopard seals, including 16 multi-year residents observed between 2010-2023 (10 in San Rafael, 6 in Tierra del Fuego) and 3 potential residents (observed multiple months in the same year in Tierra del Fuego). San Rafael monitoring data showed no inter-annual trend, but seasonal trends were observed. We also provide evidence of breeding in Chile, with records of at least 14 pups born and at least two females giving birth in multiple years. Our habitat characterization suggests that calving flux, fjord sinuosity, and fjord width variation are crucial for prolonging iceberg residency in hotspot areas. Based on these attributes, we identified 13 additional fjords in Patagonia as "very likely" suitable for leopard seals. Our study confirms that Patagonia is part of the species' breeding distribution, shifting the paradigm that leopard seals are merely visitors north of the Antarctic Polar Front. Given the limited number of suitable glaciers in Chile and the potential impacts of climate change, our assessment highlights glacial retreat as a major threat for the ecosystem of this pagophilic marine apex predator in South America.
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    Optimizing location and size of rural schools in Chile
    (WILEY-BLACKWELL, 2012) Araya, Fernando; Dell, Robert; Donoso, Pedro; Marianov, Vladimir; Martinez, Francisco; Weintraub, Andres
    The Chilean Ministry of Education oversees preschool, primary, and secondary education in both urban and rural areas. Many parts of Chile are sparsely populated and there are currently over 4,000 rural schools (almost 38% of all schools in Chile) educating 9.5% of the students in the country. Many of the rural schools are small with only one teacher responsible for instruction of all local students (multigrade schools). The geographical distribution of the rural schools has not been coordinated and this has resulted in unequal utilization of existing schools and some unreasonably long travel distances by students. Good management of the rural schools is fundamental to meeting Chile's goal of providing quality education to its citizens. Seeking to improve the situation, the Ministry of Education ordered a study of the optimal location and size of rural schools with the general goals of reducing the number of lesser quality multigrade schools and reducing student travel distances while maintaining reasonable costs. This paper presents results of this study obtained using an integer linear program that has been embedded in a geographical information system. We present computational results for the entire country. Recommendations include where to open new rural schools as well as where to expand, reduce, close, or leave unchanged existing schools. We show how recommendations are sensitive to key parameters such as the cost of transportation.
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    Reduced Graphene Oxide Overlayer on Copper Nanocube Electrodes Steers the Selectivity Towards Ethanol in Electrochemical Reduction of Carbon Dioxide
    (2022) Mardones-Herrera, Elias; Castro-Castillo, Carmen; Nanda, Kamala Kanta; Veloso, Nicolas; Leyton, Felipe; Martinez, Francisco; Saez-Pizarro, Natalia; Ruiz-Leon, Domingo; Jesus Aguirre, Maria; Armijo, Francisco; Isaacs, Mauricio
    Developing copper-based electrocatalysts that favor high-value multi-carbon oxygenates is desired, given their use as platform chemicals and as a direct fuel for transportation. Combining a CO-selective catalyst with copper shifts the selectivity of CO2 electroreduction toward C-2 products. Herein, we developed a reduced graphene oxide (rGO)-modified copper nanocube electrocatalyst that could shift the selectivity of CO2 electroreduction towards ethanol (Faradaic efficiency 76. 84 % at -0.9 V vs. reversible hydrogen electrode (RHE)). Spectroelectrochemical Raman analysis reveals a higher population of *C2HxOy intermediates at -0.9 V vs. RHE on the rGO-modified copper nanocube electrocatalyst surface, which coincides with the highest faradaic efficiency of ethanol upon CO2 electroreduction at the same potential. Our results demonstrate that the rGO modification can enhance ethanol selectivity through a probable tandem electrocatalysis mechanism and provide insights into controlling electrocatalytic activity and product selectivity in the CO2 electroreduction reaction.
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    Solubilization of Phenol Derivatives in Polymer Micelles Formed by Cationic Block Copolymer
    (HINDAWI LTD, 2017) Fuentes, Irma; Silva, Patricio; Martinez, Francisco; Olea, Andres F.
    The aggregation of cationic block copolymers formed by polystyrene (PS) and poly(ethyl-4-vinylpyridine) (PS-b-PE4VP) was studied in aqueous solution. Diblock copolymers of PS and poly(4-vinylpyridine) were synthesized by sequential anionic polymerization using BuLi as initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PS-b-PE4VP block copolymers with different quaternization degree. The self-aggregation of cationic block copolymers was studied by fluorescence probing, whereas the morphology and size of polymer micelles were determined by transmission electronic microscopy. Results indicate that spherical micelles with sizes lower than 100 nm were formed, whereas their micropolarity decreases with increasing quaternization degree. The partition of phenols between the micellar and aqueous phase was studied by using the pseudo-phase model, and the results show that the partition coefficients increase with increasing length of the side alkyl chain and are larger for star micelles. These results are discussed in terms of three-region model.