1,720,975 research outputs found
Second-order magnetic critical points at finite magnetic fields: Revisiting Arrott plots
Full text linkThe so-called Arrott plot, which consists in plotting H/M against M2, with H the applied magnetic field and M the magnetization, is used to extract valuable information in second-order magnetic phase transitions. Besides, it is widely accepted that a negative slope in the Arrott plot is indicative of a first-order magnetic transition. This is known as the Banerjee criterion. In consequence, the zero-field transition temperature T∗ is reported as the characteristic first-order transition temperature. By carefully analyzing the mean-field Landau model used for studying first-order magnetic transitions, we show in this work that T∗ corresponds in fact to a triple point where three first-order lines meet. More importantly, this analysis reveals the existence of two symmetricalsecond-order critical points at finite magnetic field (Tc,±Hc). We then show that a modified Arrott plot can be used to obtain information about these second-order critical points. To support this idea we analyze experimentaldata on La2/3Ca1/3MnO3 and discuss an estimate for the location of the triple point and the second-order critical pointsFil: Bustingorry, Sebastián. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pomiro, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Aurelio, Gabriela. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Curiale, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin
Surface chemical reactions induced on pyrite by ion bombardment
Full text linkThrough X-ray photoemission spectroscopy (XPS), we studied the chemical changes induced in a natural crystal of pyrite (FeS2) upon exposure to 4.5 keV He+ beam. We found an important reducing effect induced by ion bombardment leading to the production of iron embedded in the pyrite matrix. Through a combination of the usual Doniach–Sunjic treatment and Factor Analysis of XPS yields, we were able of analyzing the full Fe 2p XPS signal. We could in this way distinguish Fe compounds with the same binding energy for the Fe 2p3/2 yield. Our results show that He+ bombardment disrupts the ionic environment producing S2−2 and S0, Fe2+ and Fe3+ ions, and the reduction to metallic iron. The remaining pyrite matrix does not passivate the embedded iron structures, which are readily oxidized under air exposure. The oxide formed resembled that of magnetite from the XPS point of view. Further He+ bombardment proved to be efficient to reduce the iron oxide back to iron again.Fil: Ruano Sandoval, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Pomiro, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Ferron, Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin
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
Nuevos materiales con potenciales propiedades magnetoeléctricas : influencia de los cationes de los bloques d y f
Full text linkTesis (Doctor en Ciencias Químicas) - - Universidad Nacional de Córdoba. Facultad de Ciencias Químicas, 2016Un material multiferroico es aquel que presenta simultáneamente ferroelectricidad y ferromagnetismo. El objetivo general de esta tesis consiste en diseñar, sintetizar y caracterizar por diversos métodos nuevos materiales con potenciales propiedades ferroeléctricas, magnéticas y magnetoeléctricas (o multiferroicas) que, en un futuro, puedan ser aplicados en algún dispositivo tecnológico. Para ello se utilizaron diferentes métodos sintéticos para la obtención de óxidos inorgánicos, entre los que se incluyen el método de sol-gel, el método de co-precipitación y de descomposición térmica de complejos inorgánicos, tratamientos a altas temperaturas y altas presiones de oxígenos, entre otros. Se logró la síntesis exitosa de un gran número de nuevos compuestos, no informados previamente, los cuales fueron agrupados en cuatro familias estructurales: RCrMnO5 (R=Sm, Gd, Eu, Tb, Ho y Er), YFe1xCoxO3 (0x1), RFe0;5Cr0;5O3 (R= Lu, Yb, Tm, Er, Ho, Dy y Tb) y RFe0;5Co0;5O3 (R= Lu, Yb, Tm, Er, Ho, Dy y Tb). Todos los compuestos sintetizados fueron exhaustivamente estudiados en lo que respecta a su estructura cristalina y magnética y a sus propiedades magnéticas y eléctricas utilizando una gran diversidad de técnicas experimentales, entre las que se destacan la difracción de rayos X y de neutrones de polvos, mediciones de magnetización vs. temperatura (y campo magnético), mediciones de permitividad dieléctrica vs. temperatura (y campo magnético) y espectroscopia Mössbauer. Entre los resultados más relevantes obtenidos en esta tesis se pueden resaltar el evidente acople magneto-dieléctrico observado en la muestra TbFe0;5Cr0;5O3 por debajo de la temperatura de reorientación de espín y la aparición de ferroelectricidad a la temperatura de orden magnético en el compuesto TmFe0;5Co0;5O3. Además, en los compuestos RFe0;5Cr0;5O3 y RFe0;5Co0;5O3 se encontró una muy buena correlación entre las estructuras magnéticas obtenidas y las curvas de magnetización vs. temperatura, caracterizando de una manera muy precisa las transiciones de reorientación de espín observadas en estos compuestos.Pomiro, Fernando. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas; Argentina.Carbonio, Raul Ernesto. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba; Argentina.Sánchez, Rodolfo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina.Pérez, Manuel Alejo. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba; Argentina.Rossi, Laura Isabel. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Fisicoquímica de Córdoba; Argentina.Serquis, Adriana Cristina. Universidad Nacional de Río Negro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
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
Chlorination of Pr2O3 and Pr6O11. Crystal structure, magnetic and spectroscopic properties of praseodymium oxychloride
No full textThe reactions of Pr2O3 and Pr6O11 with Cl2(g) were studied thermodynamically and experimentally, and proposed in the systems Pr2O3/Cl2(g) and Pr6O11/Cl2(g). A kinetic analysis was performed on Pr6O11 chlorination, which differs from with other light rare earth oxide chlorinations. The praseodymium oxychlorides obtained by full chlorination of Pr6O11 at 425 C and 800 C are different, being well characterized by X-ray diffraction, scanning electron microscopy, magnetic susceptibility measurements and X-ray photoelectron spectroscopy. The crystal structures of the oxychlorides were refined with theRietveld method. The comparison between the theoretical magnetic moment of Pr3þ and the estimated magnetic moment in the praseodymium oxychloride obtained at 425 C revealed the presence of Pr3þ and Pr4þ, whereas no significant difference was observed between the theoretical and the experimental values of Pr3þ obtained for the praseodymium oxychloride prepared at 800 C. These observations are consistent with the analyses in the X-ray photoelectron spectra for both oxychlorides. Finally, a general formula of PrO1þxCl is proposed for the oxychlorides synthesized at T < 800 C.Fil: Pomiro, Fernando. Comisión Nacional de Energía Atómica. Gerencia Complejo Tecnológico Pilcaniyeu; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gaviría, Juan Pablo. Comisión Nacional de Energía Atómica. Gerencia Complejo Tecnológico Pilcaniyeu; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fouga, Gastón Galo. Comisión Nacional de Energía Atómica. Gerencia Complejo Tecnológico Pilcaniyeu; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vega, Leonardo Daniel. Comisión Nacional de Energía Atómica. Gerencia Complejo Tecnológico Pilcaniyeu; ArgentinaFil: Bohe, Ana Ester. Comisión Nacional de Energía Atómica. Gerencia Complejo Tecnológico Pilcaniyeu; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
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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