Browsing by Author "Rojas, Carlos"

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    Ex situ prepared nafion-coated antimony film electrode for adsorptive stripping voltammetry of model metal ions in the presence of pyrogallol red
    (2013) Arancibia, Veronica; Nagles, Edgar; Rojas, Carlos; Gomez, Marisol
    A nafion-coated antimony film electrode (NSbFE) was prepared ex situ and applied to the model metal ions Pb(II) and Cd(II) by adsorptive stripping voltammetry in the presence of pyrogallol red (PGR). To enhance the electroanalytical performance of the NSbFE, we optimized several operational parameters, including antimony concentration, deposition potential and time used in the preparation of the electrode, and effect of pH, ligand concentration (C-PGR), adsorptive potential, and time (E-ads, t(ads)). The NSbFE exhibited well developed signals for the reduction of the adsorbed complexes at -0.63 and -0.92 V for Pb-PGR and Cd-PGR, respectively, with higher current compared to unmodified electrodes. The optimum parameters for NSbFE preparation consisting of 100 mg L-1 Sb(III), 0.5 mol L-1 HCl at -1.5 V (150 s) and for the determination of Pb(II) and Cd(II) were pH = 4.5 (acetate buffer); C-PGR = 2.8 mu mol L-1; E-ads = -0.40 V and t(ads) = 100 s. The electrode presents good linear behavior in the examined concentration range from 0.9 to 12.0 mu g L-1 for both metal ions, with a limit of detection (3 sigma) of 0.4 and 0.9 mu g L-1 for Pb(II) and 0.5 and 1.0 mu g L-1 for Cd(II) using 2-mm and 3-mm diameter glassy carbon electrodes, respectively. The relative standard deviation for a Pb(II) a Cd(II) solution (9.8 mu g L-1) was 2.0% for six successive assays. The method was validated using certified reference water for trace elements (TMDA-61) with satisfactory results. Finally, the method was applied to the determination of Pb(II) and Cd(II) in tap and mineral water. (C) 2013 Elsevier B.V. All rights reserved.
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    Impact of Delirium on Short-Term Mortality in Elderly Inpatients: A Prospective Cohort Study
    (ELSEVIER SCIENCE INC, 2009) Gonzalez, Matias; Martinez, Gabriel; Calderon, Jorge; Villarroel, Luis; Yuri, Francisca; Rojas, Carlos; Jeria, Alvaro; Valdivia, Gonzalo; Marin, Pedro Paulo; Carrasco, Marcela
    Background: Delirium is an important problem especially in older medical inpatients. Objective: The authors asked whether delirium and its duration are associated with higher mortality in a 3-month follow-up period. Method: In this prospective cohort study, inpatients age 65 and older were assessed every 48 hours with the Confusion Assessment Method. Results: Of 542 patients enrolled, 192 (35.4%) developed delirium. After 3 months, mortality in the delirium cohort was 25.9%, and in the nondelirium cohort was 5.8%. Delirium was independently associated with mortality, and increased by 11% for every 48 hours of delirium. Conclusion: Delirium and increased delirium durations are significantly associated with higher mortality. (Psychosomatics 2009; 50: 234-238)
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    MillenniumDB: An Open-Source Graph Database System
    (2023) Vrgoc, Domagoj; Rojas, Carlos; Angles, Renzo; Arenas, Marcelo; Arroyuelo, Diego; Buil-Aranda, Carlos; Hogan, Aidan; Navarro, Gonzalo; Riveros, Cristian; Romero, Juan
    In this systems paper, we present MillenniumDB: a novel graph database engine that is modular, persistent, and open source. MillenniumDB is based on a graph data model, which we call domain graphs, that provides a simple abstraction upon which a variety of popular graph models can be supported, thus providing a flexible data management engine for diverse types of knowledge graph. The engine itself is founded on a combination of tried and tested techniques from relational data management, state-of-the-art algorithms for worst-case-optimal joins, as well as graph-specific algorithms for evaluating path queries. In this paper, we present the main design principles underlying MillenniumDB, describing the abstract graph model and query semantics supported, the concrete data model and query syntax implemented, as well as the storage, indexing, query planning and query evaluation techniques used. We evaluate MillenniumDB over real-world data and queries from the Wikidata knowledge graph, where we find that it outperforms other popular persistent graph database engines (including both enterprise and open source alternatives) that support similar query features.
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    Nafion-mercury coated film electrode for the adsorptive stripping voltammetric determination of lead and cadmium in the presence of pyrogallol red
    (2012) Nagles, Edgar; Arancibia, Veronica; Rojas, Carlos; Segura, Rodrigo
    An adsorptive stripping voltammetric (AdSV) method is presented for the simultaneous determination of Pb(II) and Cd(II) at trace levels in natural waters, based on metal complexation with pyrogallol red (PR) and subsequent adsorptive deposition on a Nation-mercury coated glassy carbon electrode (NHgFE). Pyrogallol red forms complexes with a metal:ligand stoichiometry of 1:1 with Pb(II) and of 1:2 with Cd(II). Optimal analytical conditions were pH 4.0 (acetate buffer); C-PR = 2.8 mu mol L-1; E-ads = -0.40 V vs. Ag/AgCl; t(ads) = 100 s. The linear calibration curves ranged from 1.0 mu g L-1 to 16.0 mu g L-1 for Pb(II) and from 1.0 mu g L-1 to 13.0 mg L-1 for Cd(II). The detection limits (S/N=3) were 0.05 mu g L-1 for Pb(II) and 0.01 mg L-1 for Cd(II). The relative standard deviation was 1.0% and 2.0% (n = 7), respectively, for a solution containing 5.0 mu g L-1 Pb(II) and Cd(II). The method was validated by determining Pb(II) and Cd(II) in certified reference waste water (SPS-WW1). Finally, the method was applied to the determination of Pb(II) and Cd(II) in commercial mineral water samples after UV digestion. (C) 2012 Elsevier B.V. All rights reserved.
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    Representing Paths in Graph Database Pattern Matching
    (2023) Martens, Wim; Niewerth, Matthias; Popp, Tina; Rojas, Carlos; Vansummeren, Stijn; Vrgoc, Domagoj
    Modern graph database query languages such as GQL, SQL/PGQ, and their academic predecessor G-Core promote paths to first-class citizens in the sense that their pattern matching facility can return paths, as opposed to only nodes and edges. This is challenging for database engines, since graphs can have a large number of paths between a given node pair, which can cause huge intermediate results in query evaluation., We introduce the concept of path multiset representations (PMRs), which can represent multisets of paths exponentially succinctly and therefore bring significant advantages for representing intermediate results. We give a detailed theoretical analysis that shows that they are especially well-suited for representing results of regular path queries and extensions thereof involving counting, random sampling, and unions. Our experiments show that they drastically improve scalability for regular path query evaluation, with speedups of several orders of magnitude.
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    Simultaneous Determination of Antimony(III) and Molybdenum(VI) by Adsorptive Stripping Voltammetry Using Quercetin as Complexing Agent
    (2013) Rojas, Carlos; Arancibia, Veronica; Gomez, Marisol; Nagles, Edgar
    A sensitive and selective voltammetric method for simultaneous determination of Sb(III) and Mo(VI) using Quercetin (Q) as complexing agent is described. Optimal conditions were found to be: pH3.7, CQ=6.0 mu molL1 and Eacc=0.10V. The LOD (3 sigma) for Sb(III) are 0.076 and 0.040 mu gL1, whereas for Mo(VI) are 0.086 and 0.048 mu gL1 with tacc of 60 and 120s, respectively. The method was validated using synthetic sea water (ASTM D665) and was applied to the determination of Sb(III) and Mo(VI) in natural waters with satisfactory results.
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    TelarKG: a knowledge graph of Chile's constitutional process
    (2024) Angles, Renzo; Calisto, Vicente; Díaz, Javiera; Ferrada, Sebastián; Hogan, Aidan; Pinto, Alexander; Reutter de la Maza, Juan Lorenzo; Rojas, Carlos; Rosales-Méndez, Henry; Sarmiento, Hernán; Toussaint, Etienne; Vrgoc Domagoj
    In this paper we present TelarKG, a knowledge graph (KG) that consolidates multiple sources of information regarding the Chilean Constitutional process, particularly about the work of the members of the Constitutional Convention. TelarKG contains a wide range of public data, such as the materials from the commissions and information about the members' interventions and votes. In addition, the KG has been enriched with online user-generated content including posts from social networks related to the constitutional process, and transcriptions from the YouTube videos of the plenary sessions. Among other features, TelarKG leverages the semantic similarity search capabilities of the MillenniumDB endpoint to compute text similarity among convention members' Twitter messages. Additionally, we employ Entity Linking techniques to identify references to members of the Convention and Parties within these messages. TelarKG constitutes one of the most comprehensive historical archives on a political event, enabling users to query and navigate through diverse aspects of Chile's constitutional process.