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Controle da dinâmica caótica do oscilador de morse forçado
No full textIn this work, the dissociation dynamics of heteronuclear diatomic molecules is investigated by means of the classical driven Morse oscillator. The interaction of the molecule and the laser field is represented through the product of the molecule dipole function and the electric field of the laser. This interaction may lead to the breaking of the chemical bound, that is, to the dissociation of the molecule. The work was developed in two parts. In the first part, we studied the dissociation as a function of the range of the permanent dipole. In the second part, we maximized the dissociation probability manipulating the parameters of the external field. We have observed that the dissociation can be controlled by means of variations of parameters associated with the range of the permanent dipoleNeste trabalho, a dinâmica de dissociação de moléculas diatômicas heteronucleares é investigada através do oscilador de Morse forçado clássico. A interação da molécula com um laser é representada através do produto da função momento de dipolo da molécula com o campo elétrico do laser. Essa interação pode levar a quebra da ligação química, ou seja, à dissociação molecular. O trabalho foi realizado em duas etapas. Na primeira etapa, estudamos a dissociação em função do alcance do momento de dipolo permanente. Na segunda etapa, maximizamos a probabilidade de dissociação através do controle dos parâmetros do campo externo. Observamos que a dissociação pode ser controlada por meio de variações dos parâmetros associados ao alcance do dipolo permanent
Controle da dinâmica caótica do oscilador de morse forçado
No full textIn this work, the dissociation dynamics of heteronuclear diatomic molecules is investigated by means of the classical driven Morse oscillator. The interaction of the molecule and the laser field is represented through the product of the molecule dipole function and the electric field of the laser. This interaction may lead to the breaking of the chemical bound, that is, to the dissociation of the molecule. The work was developed in two parts. In the first part, we studied the dissociation as a function of the range of the permanent dipole. In the second part, we maximized the dissociation probability manipulating the parameters of the external field. We have observed that the dissociation can be controlled by means of variations of parameters associated with the range of the permanent dipoleNeste trabalho, a dinâmica de dissociação de moléculas diatômicas heteronucleares é investigada através do oscilador de Morse forçado clássico. A interação da molécula com um laser é representada através do produto da função momento de dipolo da molécula com o campo elétrico do laser. Essa interação pode levar a quebra da ligação química, ou seja, à dissociação molecular. O trabalho foi realizado em duas etapas. Na primeira etapa, estudamos a dissociação em função do alcance do momento de dipolo permanente. Na segunda etapa, maximizamos a probabilidade de dissociação através do controle dos parâmetros do campo externo. Observamos que a dissociação pode ser controlada por meio de variações dos parâmetros associados ao alcance do dipolo permanent
Controle da dinâmica caótica do oscilador de morse forçado
No full textIn this work, the dissociation dynamics of heteronuclear diatomic molecules is investigated by means of the classical driven Morse oscillator. The interaction of the molecule and the laser field is represented through the product of the molecule dipole function and the electric field of the laser. This interaction may lead to the breaking of the chemical bound, that is, to the dissociation of the molecule. The work was developed in two parts. In the first part, we studied the dissociation as a function of the range of the permanent dipole. In the second part, we maximized the dissociation probability manipulating the parameters of the external field. We have observed that the dissociation can be controlled by means of variations of parameters associated with the range of the permanent dipoleNeste trabalho, a dinâmica de dissociação de moléculas diatômicas heteronucleares é investigada através do oscilador de Morse forçado clássico. A interação da molécula com um laser é representada através do produto da função momento de dipolo da molécula com o campo elétrico do laser. Essa interação pode levar a quebra da ligação química, ou seja, à dissociação molecular. O trabalho foi realizado em duas etapas. Na primeira etapa, estudamos a dissociação em função do alcance do momento de dipolo permanente. Na segunda etapa, maximizamos a probabilidade de dissociação através do controle dos parâmetros do campo externo. Observamos que a dissociação pode ser controlada por meio de variações dos parâmetros associados ao alcance do dipolo permanent
Two-Photon Absorption Spectroscopy in Organic Molecules Including Solvent Effects
Full text linkAs propriedades eletrônicas relacionadas com o processo de absorção de dois fótons (A2F) em moléculas orgânicas isoladas e em meio líquido foram estudadas buscando caracterizar as transições eletrônicas, modular a intensidade da A2F e propor uma forma de atribuir o valor ao parâmetro de alargamento espectral, incluindo os efeitos de solventes. Os efeitos de solventes foram incluídos utilizando solvatação explícita com Born-Oppenheimer Molecular Dynamics, Dinâmica Molecular Clássica e amostragem de Monte Carlo Metropolis além da solvatação implícita com Polarizable Continuum Model. Utilizando a metodologia Sequential-Quantum Mechanics / Molecular Mechanics avaliamos diferentes procedimentos para convoluir o espectro de A2F e obter a respectiva seção de choque de A2F. Considerando a contribuição das configurações extraídas das simulações moleculares propomos um ajuste da largura total da banda de A2F. Deste ajuste resultou as melhores descrições do valor máximo e da intensidade relativa da seção de choque de A2F da molécula para-Nitroanilina em ambientes líquidos. Uma estratégia utilizando campos eletrostáticos externos para modular a A2F também foi explorada em duas betainas. A presença do campo eletrostático realçou a intensidade da seção de choque de A2F ao mesmo tempo que reduziu a probabilidade de absorção de um fóton (A1F), evidenciando potencial utilização para evitar efeitos espúrios provenientes da A1F em aplicações do processo de A2F. Mostramos para sistemas moleculares grandes que a utilização de métodos semi-empíricos, os quais apresentam baixo custo computacional, pode fornecer descrições mais precisas para as intensidades de A2F, em particular quando excitações duplas são incluídas. Por fim, utilizando simulações moleculares de complexos neutros constituídos por pares iônicos mostramos que a resposta Electric Field-Induced Second Harmonic Generation é modulada pela posição relativa do ânion. Esta dependência ocorre principalmente devido às variações do momento de dipolo e não devido às variações das componentes da primeira hiperpolarizabilidade.The electronic properties related with the two-photon absorption process (TPA) in isolated or solvated organic molecules were studied aiming at characterizing the electronic transitions, tune the TPA intensity and to suggest a way to assign the value of the spectral broadening parameter, including solvent effects. The solvent effects were included using explicit solvation with Born-Oppenheimer Molecular Dynamics, Classical Molecular Dynamics and Monte Carlo Metropolis sampling as well the implicit solvation with Polarizable Continuum Model. Employing the Sequential-Quantum Mechanics / Molecular Mechanics we evaluate different procedures to convolute the TPA spectrum and to obtain the respective TPA cross-section. Considering the contributions of sampled configurations from molecular simulations we suggest a fit of the full width at half maximum of the TPA band. This fit resulted in better description of the maximum value and the relative intensity of the TPA cross-section of the para-Nitroaniline in liquid environments. A strategy using external electrostatic fields enhanced the TPA cross-section was also explored for two betaines. The presence of the field reduced the transition probability of the one-photon absorption (OPA), highlighting the potential use to avoid spurious effects from OPA in the TPA process applications. We showed for large molecular systems that using semi empirical methods, which are computationally cheap, can provide more accurate descriptions for the TPA intensities, especially when the double excitations are included in the calculations. Using molecular simulations of ion pairs as neutral complexes we showed that the Electric Field-Induced Second Harmonic Generation response is tuned by the anion relative position. This dependence become of the anion ability to change the dipole moment and it is not related with changing the first-hyperpolarizability tensor components
Solvent Effects on Absorption and Emission Spectra of Dimethoxy Curcumin
No full textA Curcumin há muito tempo é utilizada como condimento, colorífico e na medicina tradicional asiática. Conhecida como açafrão-da-índia, recentemente tem chamado a atenção devido ao grande potencial medicinal. Surgiram trabalhos principalmente sobre seus supostos efeitos benignos no tratamento de câncer e Alzheimer porém não limitados a estas enfermidades. Na tentativa de otimizar as propriedades medicinais surgiu a Dimethoxy Curcumin, um composto sintético que apresenta maior citotoxicidade e estabilidade biológica que a Curcumin. A maioria das reações químicas e biológicas ocorrem em soluções e os efeitos dos solventes são de extrema importância e complexidade. Neste trabalho nós estudamos os efeitos dos solventes ciclohexano e acetonitrila nos espectros de absorção e emissão da Dimethoxy Curcumin. Consideramos a contribuição de diferentes isômeros e estados excitados usando a Teoria do Funcional Densidade Dependente do Tempo (TD-DFT) utilizando a aproximação Modelo Contínuo Polarizável para o solvente. Nós observamos que as energias de emissão dos estados singletos sofrem um deslocamento para o vermelho enquanto que os estados tripletos sofrem um deslocamento para o azul. Respondemos estas questões analisando a variação do momento de dipolo durante a transição. Neste trabalho encontramos boa concordância com os valores experimentais dos espectros de absorção, emissão, deslocamento espectral e deslocamento Stokes.The Curcumin has long been used as a condiment, pigment and in the traditional Asian medicine. Known as turmeric, recently has attracted attention because of the large medical potential. Several studies were made mainly about the supposed benign effects in the treatment of cancer and Alzheimer but not limited to these diseases. Attempt to optimize their medicinal properties there appeared the Dimethoxy Curcumin, a synthetic compound that has a higher cytotoxicity and biological stability than Curcumin. Most of the chemical and biological reactions occur in solutions and the solvent effects are of great importance and complexity. In the present work, we study the effects of the solvents cyclohexane and acetonitrile in the absorption and emission spectra of Dimethoxy Curcumin. We consider the contribution of various isomers and excited states using the Time Dependent Density Functional Theory (TD-DFT) with the Polarizable Continuum Model (PCM) approximation for the solvent. We observe that the emission energy of the singlet states are red shifted while the triplet states are blue shifted. We address this by analyzing the dipole moment variation after the transition. We find good agreement with the experimental values for the absorption, emission, spectral shift and Stokes shif
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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