DSpace Collection: Publicaciones de artículos de investigadores en revistasPublicaciones de artículos de investigadores en revistashttp://hdl.handle.net/123456789/7432024-03-19T04:08:33Z2024-03-19T04:08:33ZMulti-scale analysis of environmental constraints on macrophyte distribution, floristic groups and plant diversity in the Lower Paraná River floodplainMorandeira, Natalia SoledadKandus, Patriciahttp://hdl.handle.net/123456789/10122023-03-27T21:19:05Z2015-05-01T00:00:00ZTitle: Multi-scale analysis of environmental constraints on macrophyte distribution, floristic groups and plant diversity in the Lower Paraná River floodplain
Authors: Morandeira, Natalia Soledad; Kandus, Patricia
Abstract: The Paraná River floodplain comprises one of the largest wetland systems of South America. In a sector of the Lower Paraná River floodplain (100km length, 3650km2), floristic composition and species diversity was characterized in 88 sites surveyed during summers 2010-11 and 2011-12. Hierarchical and fuzzy classifications were used to construct 26 floristic groups and 8 associations of floristic groups, and their indicator species were identified. A number of 124 species was distributed with a zonation pattern conforming marshes, salt marshes, wet prairies, bunchgrasses, grasslands and scrublands. We assessed how vegetation is affected by four nested levels of environmental constraints, representing a gradient from a landscape to a local scale, and including hydrological, geomorphological, topographic and edaphic variables. Species richness differed within categories of broad-scale landscape units (level 1) and within topographic positions (level 3). Also, 30 plant species, six floristic groups and five associations of groups responded to levels 1-3. The first two axes of a constrained Outlying Mean Index ordination accounted for 60% of the marginality of 61 common species as a function of soil features and flood frequency (level 4). Thus, the distribution of seven species showed significant marginality in association to soil electrical conductivity, soil silt percent and soil total nitrogen concentration. Multi-scale environmental constraints determined vegetation zones, and emerging floristic and diversity patterns. The multi-scale approach significantly improves the understanding of floristic patterns and plant biodiversity in the study area, and may be extended to other floodplain wetlands.2015-05-01T00:00:00ZFacile synthesis of cobalt ferrite nanotubes using bacterial nanocellulose as templateMenchaca Nal, SandraLondoño Calderon, Cesar LeandroCerrutti, PatriciaForesti, María LauraPampillo, Laura GabrielaBilovol, VitaliyCandal, Roberto JorgeMartinez Garcia, Ricardohttp://hdl.handle.net/123456789/10112023-03-27T21:16:11Z2016-02-01T00:00:00ZTitle: Facile synthesis of cobalt ferrite nanotubes using bacterial nanocellulose as template
Authors: Menchaca Nal, Sandra; Londoño Calderon, Cesar Leandro; Cerrutti, Patricia; Foresti, María Laura; Pampillo, Laura Gabriela; Bilovol, Vitaliy; Candal, Roberto Jorge; Martinez Garcia, Ricardo
Abstract: A facile method for the preparation of cobalt ferrite nanotubes by use of bacterial cellulose nanoribbons as a template is described. The proposed method relays on a simple coprecipitation operation, which is a technique extensively used for the synthesis of nanoparticles (either isolated or as aggregates) but not for the synthesis of nanotubes. The precursors employed in the synthesis are chlorides, and the procedure is carried out at low temperature (90 °C). By the method proposed a homogeneous distribution of cobalt ferrite nanotubes with an average diameter of 217 nm in the bacterial nanocellulose (BC) aerogel (3%) was obtained. The obtained nanotubes are formed by 26-102 nm cobalt ferrite clusters of cobalt ferrite nanoparticles with diameters in the 9-13 nm interval. The nanoparticles that form the nanotubes showed to have a certain crystalline disorder, which could be attributed in a greater extent to the small crystallite size, and, in a lesser extent, to microstrains existing in the crystalline lattice. The BC-templated-CoFe2O4 nanotubes exhibited magnetic behavior at room temperature. The magnetic properties showed to be influenced by a fraction of nanoparticles in superparamagnetic state.2016-02-01T00:00:00ZChemical, structural and hyperfine characterization of goethites with simultaneous incorporation of manganese, cobalt and aluminum ionsAlvarez, MarianaTufo, Ana ElisabethZenobi, Maria CristinaRamos, Cinthia PaulaSileo, Elsa Esterhttp://hdl.handle.net/123456789/10102023-03-27T21:10:23Z2015-10-01T00:00:00ZTitle: Chemical, structural and hyperfine characterization of goethites with simultaneous incorporation of manganese, cobalt and aluminum ions
Authors: Alvarez, Mariana; Tufo, Ana Elisabeth; Zenobi, Maria Cristina; Ramos, Cinthia Paula; Sileo, Elsa Ester
Abstract: To elucidate the influence of bi-substitution on the structural and hyperfine properties of goetites, two series of (Al,Co)- and (Mn,Co)-substituted goethites were synthesized in alkaline media by aging several ferrihydrites with different Al/Co and Mn/Co ratios. The samples were fully characterized by chemical analyses, X-ray diffraction (XRD) and Mössbauer spectroscopy; scanning electron microscopy (SEM), zeta potential and BET surface area measurements were also performed. All the solids presented only an α-FeOOH-like structure, with the exception of two preparations with high Co concentrations that developed two phases, goethite and small amounts of the Co-ferrite (CoFe2O4). The cell parameters in the Co-substituted goethites were markedly smaller than that of the pure sample indicating a oxidation of Co(II) to Co(III) before the incorporation step. In the Co+Mn series the metal substitution followed the trend Co~Mn, and in the Co+Al series the trend was Al>Co, and in both cases the incorporation of Co decreased the crystallite size of the samples. The metal-for-Fe incorporation changed the specific surface areas and the morphology of the acicular formed particles. Cobalt containing samples had the highest SSA, while Mn-containing samples had the lowest SSA. The IEP values of the bi-substituted samples were similar to that of pure α-FeOOH, but mono-substitution by Mn and Al diminished the isoelectric points. The low IEP values detected in Mn-goethite (5.8) and Al-goethite (5.2) could be respectively ascribed to an inhomogeneous distribution of Mn(III), and to the different basicity properties of the surface Fe-OH and Al-OH groups. The hyperfine magnetic field Bhf, increased quasi linearly with the incorporation of Co in both series. In the Co-Mn series the effect was attributed to variations in particle size distribution, in contrast the marked increase observed in the Co-Al series can be attributed to the decrease in the content of diamagnetic ion Al(III). The results indicate that simultaneous substitutions produce substantial changes in the structural, surface and hyperfine properties of goethites. As the characteristics of the dissolution and adsorption processes of the goethites greatly depend on particle size, BET areas and surface charge of the solids, the reported results will allow us to predict changes in the chemical reactivity and adsorption of the multi-substituted goethites. Also the data on hyperfine properties will help to elucidate the probable substitution in natural samples. The fact that Co-incorporation in bi-substituted samples greatly decreased the particle size increasing the specific surface area is an important parameter for technological applications in adsorption removal processes.2015-10-01T00:00:00ZSelf-Organizing Maps for Imputation of Missing Data in Incomplete Data MatricesFolguera, LauraZupan, JureCicerone, DanielMagallanes, Jorgehttp://hdl.handle.net/123456789/10092023-03-27T21:04:50Z2015-03-01T00:00:00ZTitle: Self-Organizing Maps for Imputation of Missing Data in Incomplete Data Matrices
Authors: Folguera, Laura; Zupan, Jure; Cicerone, Daniel; Magallanes, Jorge
Abstract: The problem of incomplete data matrices is repeatedly found in large databases; posing a significant obstacle for an effective treatment of data. This paper examines a self-organizing-map (SOM) based method of data imputation under the concept of distance object per one weight; to predict physicochemical parameters of water samples in a data set where concentrations of different analytes were missed. The method was evaluated according to two different possibilities: (a) including vectors of samples with and without missing data in the training data set and (b) pre-training a SOM for a data set with no missing values and then making imputations for a second data set (prediction set) of samples with missing values. Evaluations were made using a surface water data set of 270 samples from Reconquista River; in Buenos Aires Province; Argentina; by artificially setting a range of 17% to 39% of the data to missing. Results were compared to imputations made through professional criteria. SOMs gave reasonable estimates; with no statistically significant differences from estimates made through professional criteria; proving thus to be a suitable time-saving imputation method.2015-03-01T00:00:00Z