1,721,073 research outputs found
El ADN como un conjunto de osciladores armónicos acoplados
No full textSe modela el ADN como una cadena lineal de osciladores armónicos acoplados, encontrando el espectro vibracional para cadenas ordenadas y desordenadas. En particular se calcula la relación de dispersión para sistemas ordenados y la densidad de estados para ambas situaciones. En el caso desordenado se encuentran resultados sugiriendo un comportamiento tipo molécula biatómica.Fil: Gómez Carrillo, Sandra Carolina. 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: Rey González, R. R.. Universidad Nacional de Colombia; Colombi
Adsorption of atoms on surfaces and study of electronic properties low dimensional systems
No full textFil: Gómez Carrillo, Sandra Carolina. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina.Fil: Gómez Carrillo, Sandra Carolina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentina.This thesis is focused in two important aspects of surface physics and nanoscopic systems:
the calculation of electronic properties low dimensional systems, used in electronic transport through of nanostructures; and the adsorption of atoms on metallic surfaces. In the electric transport through atomic or molecular junction is very important to know the contact forms and the crystalline orientation, since they can define channels of conduction. In this sense, we examine different geometries of contacts of palladium, pyramidal lead grown following (001) and (111) directions, and the surfaces Pd(001) and Pd(111). In the adsorption of atoms on metallic surfaces, we choose study theoreticaly the case of sulfur adsorbed on Au(111). This complex represents an active research area in which, depending on the coverage and the temperature, a very rich variety of superficial sulfur structures and adsorption properties are reported. The calculations have been done in the frame of the LDA for the exchange-correlation functional to the DFT applied to systems with or without translational periodicity. We use the FIREBALL code. This program, is a realization of a tight-binding DFT approach complemented with a molecular dynamic allowing calculations at temperatures different to cero. Complementary, we have improved the use and application to the own developed Bond-Pair model. Based in a Anderson’s model Hamiltonian (solved here whithin a Hartree-Fock approximation), the terms of the Hamiltonian are calculated from the atomic functions of each interacting agents, adsorbate-surface. In this case, the studying system was the adsorption of atoms to hydrogen on surfaces Al (111) and Al(001).Este trabajo de tesis esta focalizado en dos aspectos centrales: el calculo de propiedades electrónicas de sistemas de baja dimensionalidad utilizados en transporte electrónico a través de nanoestructuras y el otro refiere a problemas de adsorción de átomos en superficies metálicas. En el caso de transporte electrónico a través de junturas atómicas o moleculares es importante conocer la forma y orientación cristalina de los contactos lo que define posibles canales de conducción. En este sentido hemos estudiado las geometrías: puntas piramidales crecidas en las direcciones Pd(001) y Pd(111) y las superficies Pd(001) y Pd(111). En el caso de la adsorción de átomos sobre superficies metálicas, elegimos estudiar teoricamente el caso de S/Au(111) dado que presenta un rico escenario experimental de situaciones de adsorción conforme cambia la temperatura de la muestra y su recubrimiento. La herramienta principal que hemos utilizado es un código de cálculo ab-initio (FIREBALL), basado en DFT, en el cual hemos utilizado la aproximación LDA para la parte de correlación e intercambio. Este programa además realiza dinámica molecular a temperaturas diferentes de cero. Complementariamente hemos profundizado el uso y aplicación del modelo de enlaces de a pares, el cual esta basado en un hamiltoniano tipo Anderson con aproximación Hartree-Fock y donde los términos de dicho hamiltoniano son calculados a partir de las funciones atómicas de cada uno de los agentes interactuantes, superficie - adsorbato. En este caso el sistema estudiado fue el de adsorción de átomos de hidrógeno sobre superficies de Al(111) y Al(001).Consejo Nacional de Investigaciones Científicas y Técnica
Adsorption of atoms on surfaces and study of electronic properties low dimensional systems
No full textFil: Gómez Carrillo, Sandra Carolina. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina.Fil: Gómez Carrillo, Sandra Carolina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentina.This thesis is focused in two important aspects of surface physics and nanoscopic systems:
the calculation of electronic properties low dimensional systems, used in electronic transport through of nanostructures; and the adsorption of atoms on metallic surfaces. In the electric transport through atomic or molecular junction is very important to know the contact forms and the crystalline orientation, since they can define channels of conduction. In this sense, we examine different geometries of contacts of palladium, pyramidal lead grown following (001) and (111) directions, and the surfaces Pd(001) and Pd(111). In the adsorption of atoms on metallic surfaces, we choose study theoreticaly the case of sulfur adsorbed on Au(111). This complex represents an active research area in which, depending on the coverage and the temperature, a very rich variety of superficial sulfur structures and adsorption properties are reported. The calculations have been done in the frame of the LDA for the exchange-correlation functional to the DFT applied to systems with or without translational periodicity. We use the FIREBALL code. This program, is a realization of a tight-binding DFT approach complemented with a molecular dynamic allowing calculations at temperatures different to cero. Complementary, we have improved the use and application to the own developed Bond-Pair model. Based in a Anderson’s model Hamiltonian (solved here whithin a Hartree-Fock approximation), the terms of the Hamiltonian are calculated from the atomic functions of each interacting agents, adsorbate-surface. In this case, the studying system was the adsorption of atoms to hydrogen on surfaces Al (111) and Al(001).Este trabajo de tesis esta focalizado en dos aspectos centrales: el calculo de propiedades electrónicas de sistemas de baja dimensionalidad utilizados en transporte electrónico a través de nanoestructuras y el otro refiere a problemas de adsorción de átomos en superficies metálicas. En el caso de transporte electrónico a través de junturas atómicas o moleculares es importante conocer la forma y orientación cristalina de los contactos lo que define posibles canales de conducción. En este sentido hemos estudiado las geometrías: puntas piramidales crecidas en las direcciones Pd(001) y Pd(111) y las superficies Pd(001) y Pd(111). En el caso de la adsorción de átomos sobre superficies metálicas, elegimos estudiar teoricamente el caso de S/Au(111) dado que presenta un rico escenario experimental de situaciones de adsorción conforme cambia la temperatura de la muestra y su recubrimiento. La herramienta principal que hemos utilizado es un código de cálculo ab-initio (FIREBALL), basado en DFT, en el cual hemos utilizado la aproximación LDA para la parte de correlación e intercambio. Este programa además realiza dinámica molecular a temperaturas diferentes de cero. Complementariamente hemos profundizado el uso y aplicación del modelo de enlaces de a pares, el cual esta basado en un hamiltoniano tipo Anderson con aproximación Hartree-Fock y donde los términos de dicho hamiltoniano son calculados a partir de las funciones atómicas de cada uno de los agentes interactuantes, superficie - adsorbato. En este caso el sistema estudiado fue el de adsorción de átomos de hidrógeno sobre superficies de Al(111) y Al(001).Consejo Nacional de Investigaciones Científicas y Técnica
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Exploring the T–Θ phase diagram of S adsorbed on Au(111) substrate on the Θ = 0.5 ML line
Get PDFTheoretical results for the adsorption of half of a monolayer of S on Au(111) are presented. The simulations were made using a density functional theory (DFT) tight binding approach combined with classical molecular dynamics at 800, 500, 300, 150 and 1 K. By considering a minimal unit cell, two stable adsorbed phases are found: a dimeric one and another forming a rhomboidal structure depending on the preparation of the sample at high temperatures. Optimized calculations at T = 0 K indicate that the stability of the dimeric phase is due to the increase of the binding energies between sulfur atoms. Enforcing previous results (Gómez-Carrillo et al 2011 Phys. Chem. Chem. Phys. 13 461) it is verified that at high temperatures (T > 300 K) sulfur atoms have a high mobility which allows migration among different adsorption sites. The mobility decreases with the temperature and, as in the previous work, a thermal barrier of 25–30 meV is found. On enlarging the unit cell new agglomerates are found, in good agreement with experimental data.Fil: Gómez Carrillo, Sandra Carolina. Universidad Nacional del Litoral. Facultad de Ingenieria Quimica. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe; ArgentinaFil: Bolcatto, Pablo Guillermo. Universidad Nacional del Litoral. Facultad de Ingenieria Quimica. Departamento de Fisica; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe; Argentin
Sulfur adsorbed (Q = 1=2) on gold (111) substrate
Get PDFThe adsorption of Q = 1=2 monolayer (ML) of S on Au(111) is calculated. The evolution of the positions of adatoms for 800 K, 500 K, 300 K, 150 K and 1 K is evaluated by using a density functional theory (DFT)-tight binding approach combined with classical molecular dynamics. For this coverage there is a controversy about the existence of superficial composite AuS or molecular aggregates. We find a configuration in which sulfur atoms form quasi-S2 superficial molecules with total energy very close to the monoatomic phase suggesting the coexistence of both configurations at room temperature. We find that the stability of the dimeric phase is due to the increase of the binding energies between sulfurs. In the other phase, the stabilization occur due to a formation of AuS dimers. At high temperatures (T> 300 K) sulfurs have high mobility which allows the migration among different adsorption sites. At low temperatures the mobility decreases and a thermal activation barrier of 25 30 meV can be estimated.Fil: Bolcatto, Pablo Guillermo. Universidad Nacional del Litoral. Facultad de Ingenieria Quimica. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe; ArgentinaFil: Gómez Carrillo, Sandra Carolina. Universidad Nacional del Litoral. Facultad de Ingenieria Quimica. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe; Argentin
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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