1,720,963 research outputs found
Agroecological Innovations for Resilience and Sustainability of Alpine Livestock Farming Systems (INVERSION)
No full textDifferences between metal-ligand speciation results of electrospray ionization mass spectrometry (ESI-MS) and those of traditional techniques
No full textElectrospray ionization mass spectrometry (ESI-MS) is being increasingly applied to study the solution equilibria of metal-ligand systems,[1] together with or in alternative to the techniques traditionally employed to this aim, e.g. potentiometry, UV-Vis, NMR. ESI-MS results are usually different from those obtained by traditional techniques, both in the qualitative (number and stoichiometry of the species observed in solution) and quantitative data (relative concentrations of all species at equilibrium). To our knowledge, a systematic investigation of the nature of these differences and of their causes is lacking in the literature.
In this work, selected aluminium(III)-ligand systems were examined by ESI-MS. The ligands considered were 3-hydroxy-2(1H)-pyridinone, 3,4-dihydroxybenzoic acid, citric acid, and ethylenediaminetetramethylenephosphonic acid. Spectra (in positive and/or in negative ion mode) were obtained at various metal-to-ligand ratios and pH values, and results were compared with those obtained previously [2-5] by traditional techniques.
For the qualitative results, the main differences between ESI-MS and traditional techniques regard the acidic proton content of the metal-ligand species, and the presence of clusters at ES conditions. The former difference is observed when the complexes in solution have acid-base properties and a high charge (> ± 1), and it is due to the easy of the proton displacement at ES conditions. The formation of clusters is an ES artifact which regards polycarboxylic and polyphosphonic ligands, but it can be minimized by strictly optimizing the instrumental parameters. Other minor ES artifacts are the formation of solvent and cation (or anion) adducts, which usually don’t impair the qualitative analysis.
For the quantitative results, the differences between ESI-MS and traditional techniques are more evident for the systems which also show significant qualitative differences, and they are due to different solvents and ionic strengths of the solutions analysed, to a different pH definition, and to the presence of ion response factors in ESI-MS.
References
(1) Di Marco V.B.; Bombi G.G. Mass Spectrometry Reviews 2005, submitted for publication
(2) Di Marco V.B.; Bombi G.G; Tapparo A.; Powell A.K.; Anson C.E. J. Chem. Soc. Dalton Trans. 1999, 2427
(3) Kiss T.; Atkári K.; Jezowska-Bojczuk M.; Decock P. J. Coord. Chem. 1993, 29, 81
(4) Harris W.R.; Wang Z.P.; Hamada Y.Z. Inorg. Chem. 2003, 42, 3262
(5) Di Marco V.; Kilyen M.; Jakusch T.; Forgó P.; Dombi G.; Kiss T. Eur. J. Inorg. Chem. 2004, 252
Surface-activated chemical ionization versus electrospray ionization in the study of selected aluminium(III)/ligand solution equilibria
No full textSACI-MS and ESI-MS are compared in the study of the solution chemistry of aluminioum(III)+2,3-dihydroxypyridine aqueous-methanol solutions. SACI-MS and ESI-MS gave comparable spectra, but the latter technique appears more convenient for solution chemistry studie
Landslide susceptibility assessment in the southern sector of the Tammaro River basin (Italy)
No full textNumerous methods have been proposed in literature for the landslide susceptibility assessment at basin scale using Geographical Information Systems (GIS). Among them, statistical methods have became increasingly popular in recent years. In particular, the Homogeneous Territorial Unit (HTU) method [DE VITA et al., 1994; GUIDA et al., 1996; CALCATERRA et al., 2010] has been applied in this work, which is well suited to problems of slope stability in structurally complex formations [ESU, 1977]. HTU method was applied to the southern sector of the Tammaro River basin, which corresponds to the municipalities of Paduli and Pietrelcina, in the southern part of the Apennines fold-and-thrust belt (Campania Region, Italy). From a geological point of view, this area consists of argillitic-marly-calcareous and argillitic-marly formations, known as "Varicoloured Clays", a structurally complex formation [ESU, 1977], well-known in literature for its susceptibility to landslides. The area of interest includes about 73 km2 of hilly territory, where 303 landslides, divided in 127 earthflows, 87 rotational/translational slides and 89 earth slides-earthflows, have been mapped, at 1:5.000 scale, by means of field survey and stored in a GIS-database. Moreover, geolithological and geomorphological maps (at 1:10.000 scale), as GIS-layers, were used to implement the homogeneous domains for the statistical analysis. Such domains represent specific mapping units, called HTUs, which define the classification of each slope-instability factor into four classes, stored into a single map, or layer. By means of the overlay of the HTU map and the landslide-inventory map, the susceptibility assessment is then extended to non-landslide areas by applying a statistical method
Functional diversity of cover crop mixtures enhances biomass yield and weed suppression in a Mediterranean agroecosystem
Full text link
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
