1,720,957 research outputs found
Spectrophotometric and Calorimetric Studies of Np(V) Complexation with Acetate at Various Temperatures from T=283 to 343 K
No full textSpectrophotometric titrations were performed to identify the Np(V)/acetate complex and determine the equilibrium constants at various temperatures (T=283 to 343 K) and at the ionic strength 1.05 mola <...kg(-1). The enthalpies of complexation at the corresponding temperatures were determined by microcalorimetric titrations. Results show that the complexation of Np(V) with acetate is weak but strengthens as the temperature increases. The complexation reaction is endothermic and entropy driven. The enhancement of complexation at higher temperatures is primarily due to the increasingly larger entropy gain when the solvent molecules are released from the highly-ordered solvation spheres of NpO(2)(+) and acetate to the bulk solvent where the degree of disorder is higher at higher temperatures
Complexation of uranium(VI) and samarium(III) with oxydiacetic acid: Temperature effect and coordination modes
No full texthe complexation of uranium(VI) and samarium(III) with oxydiacetate (ODA) in 1.05 mol kg(-1) NaClO4 is studied at variable temperatures (25-70 degreesC). Three U(VI)/ODA complexes (UO2L, UO2L22-, and UO2HL2-) and three Sm(III)/ ODA complexes (SmLj(3-2j)+ with j = 1, 2, 3) are identified in this temperature range. The formation constants and the molar enthalpies of complexation are determined by potentiometry and calorimetry. The complexation of uranium(VI) and samarium(111) with oxydiacetate becomes more endothermic at higher temperatures. However, the complexes become stronger due to increasingly more positive entropy of complexation at higher temperatures that exceeds the increase in the enthalpy of complexation. The values of the heat capacity of complexation (DeltaC(p)degrees in J K-1 mol(-1)) are 95 +/- 6, 297 +/- 14, and 162 +/- 19 for UO2L, UO2L22-, and UO2HL2-, and 142 +/- 6, 198 +/- 14, and 157 +/- 19 for SmL+, SmL2-, and SmL33-, respectively. The thermodynamic parameters, in conjunction with the structural information from spectroscopy, help to identify the coordination modes in the uranium oxydiacetate complexes. The effect of temperature on the thermodynamics of the complexation is discussed in terms of the electrostatic model and the change in the solvent structure
Protonation of D-Gluconate and its Complexation with Np(V) in Acidic to Nearly Neutral Solutions
No full textThermodynamic properties of the protonation of D-gluconic acid (HGH(4)(aq)) and its complexation with Np(V) have been studied in acidic to nearly neutral solutions at t = 25 degrees C and I = 1 M NaClO4 by potentiometry, spectrophotometry and calorimetry. The protonation constant (log K-H) and enthalpy (Delta H-H) of the carboxylate group are determined to be (3.30 +/- 0.10) and -(4.03 +/- 0.07) kJ mol(-1), respectively. Gluconate forms two Np(V) complexes in nearly neutral solutions. The formation constants and enthalpies of complexation are: log beta(1) = (1.48 +/- 0.03) and Delta H-1 = - (7.42 +/- 0.13) kJ mol(-1) for NpO2 (GH(4)) (aq), log beta(2) = (2.14 +/- 0.09) and Delta H-2 = - (12.08 +/- 0.45) kJ mol(-1) for NpO2 (GH(4))(2)(-). The thermodynamic parameters indicate that gluconic acid, like isosaccharinic acid and other alpha-hydroxycarboxylic acids, is a slightly stronger acid and forms stronger complexes with Np(V) than simple monocarboxylic acid
Thermodynamics of the complexation of uranium(VI) with oxalate in aqueous solution at 10-70 degrees C
No full textThe protonation reactions of oxalate (ox) and the complex formation of uranium(VI) with oxalate in 1.05 mol kg(-1) NaClO(4) were studied at variable temperatures (10-70 degrees C). Three U(VI)/ox complexes (UO(2)ox(j)((2-2j)+) with j = 1, 2, 3) were identified in this temperature range. The formation constants and the molar enthalpies of complexation were determined by spectrophotometry and calorimetry. The complexation of uranium(VI) with oxalate ion is exothermic at lower temperatures (10-40 degrees C) and becomes endothermic at higher temperatures (55-70 degrees C). In spite of this, the free energy of complexation becomes more negative at higher temperatures due to increasingly more positive entropy of complexation that exceeds the increase of the enthalpy of complexation. The thermodynamic parameters at different temperatures, in conjunction with the literature data for other dicarboxylic acids, provide insight into the relative strength of U(VI) complexes with a series of dicarboxylic acids (oxalic, malonic and oxydiacetic) and rationalization for the highest stability of U(VI)/oxalate complexes in the series. The data reported in this study are of importance in predicting the migration of uranium(VI) in geological environments in the case of failure of the engineering barriers, which protect waste repositories
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
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