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Item 1D and 2D Fourier-based approaches to numeric curvature estimation and their comparative performance assessment.(2003) Estrozi, Leandro Farias; Rios Filho, Luiz Gonzaga; Bianchi, Andrea Gomes Campos; César Júnior, Roberto Marcondes; Costa, Luciano da FontouraA careful comparison of three numeric techniques for estimation of the curvature along spatially quantized contours is reported. Two of the considered techniques are based on the Fourier transform (operating over 1D and 2D signals) and Gaussian regularization required to attenuate the spatial quantization noise. While the 1D approach has been reported before and used in a series of applications, the 2D Fourier transform-based method is reported in this article for the first time. The third approach, based on splines, represents a more traditional alternative. Three classes of parametric curves are investigated: analytical, B-splines, and synthesized in the Fourier domain. Four quantization schemes are considered: grid intersect quantization, square box quantization, a table scanner, and a video camera. The performances of the methods are evaluated in terms of their execution speed, curvature error, and sensitivity to the involved parameters. The third approach resulted the fastest, but implied larger errors; the Fourier methods allowed higher accuracy and were robust to parameter configurations. The 2D Fourier method provides the curvature values along the whole image, but exhibits interference in some situations. Such results are important not only for characterizing the relative performance of the considered methods, but also for providing practical guidelines for those interested in applying those techniques to real problems.Item Ab initio molecular dynamics simulation of methanol and acetonitrile : the effect of van der Waals interactions.(2019) Resende, Rafael Fanni Dias; Costa, Cleidinéia Cavalcante da; Manhabosco, Taíse Matte; Oliveira, Alan Barros de; Matos, Matheus Josué de Souza; Soares, Jaqueline dos Santos; Batista, Ronaldo Junio CamposWe employed PBE and BLYP semi-local functionals and the van der Waals density functional of Dion et al. (2004) (vdW-DF) to investigate structural properties of liquid acetonitrile and methanol. Among those functionals the vdW-DF is the only one that correctly predicts energy minima in inter-molecular interactions between acetonitrile molecules. We found that van der Waals interactions have a negligible effect on H-bonds in methanol chains. However, it significantly increases chain packing resulting in a more dense liquid in comparison to the other two functionals. The overall trend is that the vdW-DF tends to overestimate density and bulk modulus, meanwhile the semi-local functionals tend to underestimate density. Thus, van der Waals interactions play an important role in the properties of liquids in which much stronger dipole-dipole interactions are present.Item About the oxygen diffusion mechanism in ZnO.(2004) Sabioni, Antônio Claret SoaresThe more recent works dealing with the study of oxygen self-diffusion in ZnO have shown that the oxygen diffusion takes place by means of doubly negatively ionized interstitial oxygen. This oxygen diffusion mechanism in zinc oxide is reviewed and based on experimental data of oxygen self-diffusion and electrical conductivity; for Al-doped and undoped ZnO, it is suggested that oxygen selfdiffusion in ZnO takes place by means of an interstitial mechanism, but with the interstitial oxygen having a null or a single negative effective charge.Item About the role of chromium and oxygen ion diffusion on the growth mechanism of oxidation films of the AISI 304 austenitic stainless steel.(2012) Sabioni, Antônio Claret Soares; Ramos, Roberto Paulo Barbosa; Ji, Vincent; Jomard, François; Macedo, Waldemar Augusto de Almeida; Gastelois, Pedro Lana; Trindade, Vicente BrazTo study the role of ion diffusion on the oxidation process of the AISI 304 austenitic stainless steel, chromium diffusion coefficients were determined in oxide films grown on this steel at 750, 800 and 850 C, in air. The isotope 54Cr was used as a chromium tracer and the diffusion profiles were established by SIMS. The bulk diffusion coefficients are five orders of magnitude smaller than the grain boundary diffusion coefficients. It was found that the values of the chromium diffusivities are lower than the corresponding oxygen diffusivities obtained in previous work. Parabolic oxidation constants calculated as a function of the chrome and oxygen diffusivities, using Wagner0 s theory, are close to those determined experimentally, which shows that the growth rate of chromia is controlled by ion diffusion, but inward oxygen diffusion plays the main role on the growth kinetics of chromia formed by the oxidation of the AISI 304 steel.Item Absence of ferromagnetic order in high quality bulk Co-doped ZnO samples.(2010) Carvalho, Hugo Bonette de; Godoy, Marcio Peron Franco de; Pais, Rafael Witter Dias; Mir, Mirta; Zevallos, Ângela Maria Ortiz de; Iikawa, Fernando; Brasil, Maria José Santos Pompeu; Chitta, Valmir Antônio; Ferraz, Wilmar Barbosa; Boselli, Marco Aurélio; Sabioni, Antônio Claret SoaresBulk Zn1−xCoxO samples were synthesized via standard solid-state reaction route with different Co molar concentrations up to 21%. A detailed microstructural analysis was carried out to investigate alternative sources of ferromagnetism, such as secondary phases and nanocrystals embedded in the bulk material. Conjugating different techniques we confirmed the Zn replacement by Co ions in the wurtzite ZnO structure, which retains, however, a high crystalline quality. No segregated secondary phases neither Co-rich nanocrystals were detected. Superconducting quantum interference device magnetometry demonstrates a paramagnetic Curie–Weiss behavior with antiferromagnetic interactions. We discuss the observed room temperature paramagnetism of our samples considering the current models for the magnetic properties of diluted magnetic semiconductors.Item Accurate calculation of near-critical heat capacities CP and CV of argon using molecular dynamics.(2017) Nichele, Jakler; Oliveira, Alan Barros de; Alves, Leonardo Santos de Brito; Borges Júnior, ItamarMolecular dynamics (MD) employing the Lennard-Jones (LJ) interaction potentialwas used to compute the heat capacities of argon at constant volume CV and constant pressure CP near the critical point very close to the asymptotic region. The accurateMD calculation of critical divergenceswas shown to be related to a careful choice of the cutoff radius rc and the inclusion of long-range corrections in the LJ potential. The computed CP and CV values have very good agreement as compared to available NIST data. Furthermore, values of CV in a range of temperatures for which NIST data is not available could be computed. In the investigated range of temperatures, both CP and CVMD results were fitted to a simple mathematical expression based on an empirical model that describes the critical effectswhen the asymptotic models are not appropriate. The present approach is of general applicability and robust to compute thermophysical properties of fluids in the near-critical region.Item Aerosol-printed MoS2 ink as a high sensitivity humidity sensor.(2022) Pereira, Neuma das Mercês; Rezende, Natália Pereira; Cunha, Thiago Henrique Rodrigues da; Barboza, Ana Paula Moreira; Silva, Glaura Goulart; Lippross, Daniel; Neves, Bernardo Ruegger Almeida; Chacham, Helio; Ferlauto, Andre Santarosa; Lacerda, Rodrigo GribelMolybdenum disulfide (MoS2) is attractive for use in nextgeneration nanoelectronic devices and exhibits great potential for humidity sensing applications. Herein, MoS2 ink was successfully prepared via a simple exfoliation method by sonication. The structural and surface morphology of a deposited ink film was analyzed by scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). The aerosol-printed MoS2 ink sensor has high sensitivity, with a conductivity increase by 6 orders of magnitude upon relative humidity increase from 10 to 95% at room temperature. The sensor also has fast response/recovery times and excellent repeatability. Possible mechanisms for the water-induced conductivity increase are discussed. An analytical model that encompasses two ionic conduction regimes, with a percolation transition to an insulating state below a low humidity threshold, describes the sensor response successfully. In conclusion, our work provides a low-cost and straightforward strategy for fabricating a highperformance humidity sensor and fundamental insights into the sensing mechanism.Item Ajuste do limite de detecção elétrica de compósitos condutivos para melhorar o desempenho de sensores híbridos.(2019) Calheiro, Daniel Silva; Bianchi, Rodrigo Fernando; Gil, Laurent Frédéric; Bianchi, Rodrigo Fernando; Faria, Roberto MendonçaAs pesquisas em eletrônica híbrida têm proporcionado importantes avanços em novos materiais, dispositivos e formas de composição e estruturas desses sistemas. Contudo, controvérsias ainda existem sobre a limitação da eficiência elétrica de materiais híbridos e seus dispositivos, tais como as relações entre a estrutura, o processamento, o design e suas propriedades. Este trabalho descreve uma abordagem prática para melhorar o desempenho elétrico de um sensor de gás de amônia cujo princípio de operação baseia-se nas mudanças de condutividade elétrica, no baixo regime de percolação e na limitação de corrente elétrica utilizando, para tanto, um sistema composto de polímero semicondutor e óxido metálico. O dispositivo foi fabricado a partir de filmes finos totalmente impressos de polianilina / nanopartículas óxido de estanho e índio - PAni100xITOx [0 x 50% (wt/wt)] depositados sobre substrato de polietileno de alta densidade. Foi verificado que a corrente elétrica do dispositivo diminui e tende a se estabilizar à medida que a concentração de gás aumenta, e o valor desse limite de corrente elétrica (IL) depende de x, ou seja, quanto maior x, menor IL. Quando a corrente que flui através do dispositivo eletrônico é dominada pelas nanopartículas de ITO preenchidas com PAni, ocorre o aumento da concentração de portadores de salto que contribui para a resposta elétrica desejada de um sensor de gás heterogêneo. Neste regime, foi encontrada uma boa dependência linear de x na concentração de amônia na faixa de 0 a 35 ppm, com limite de detecção de até 0,5 ppm e resposta rápida (< 1 min). Estas descobertas sugerem direções para futuras pesquisas sobre o desenvolvimento de sistemas heterogêneos nos quais uma variação de corrente elétrica é desejada para melhorar a sensibilidade e a estabilidade da produção escalável de sensores híbridos funcionais.Item Ammonia gas sensor based on the frequency-dependent impedancecharacteristics of ultrathin polyaniline films.(2016) Santos, Mirela de Castro; Ushizima, Daniela Mayumi; Bianchi, Andrea Gomes Campos; Pavinatto, Felippe J.; Bianchi, Rodrigo FernandoThis paper describes a variety of experiments that reveal the potential application of impedance spec-troscopy (IS) measurements to enhance performance of ultrathin polyaniline (PANI)-based films onflexible substrate to control ammonia gas exposure in the 0–20 ppm range. Further, the device is mechan-ically robust for making electrical contact without lithography. We have employed the IS technique toproper adjust the optimal operation frequency of an easy-to-process, inexpensive and user-friendly PANI-based resistometric detectors in which drift current and delay problems related to electrode effects anddielectric absorption of PANI are insignificant. These requirements place emphasis upon the material anddevice configuration, and the range of frequencies from 10 to 100 Hz corresponds to the ideal workingregion to operate the device to unify sensibility inside 5%, reproducibility, linearity, stability and lowresponse time (<1 min). These results are as efficient as those obtained using a more expensive commer-cial apparatus and can rival the affordability of traditional sensors. Linear Discriminant Analysis (LDA)and K-Means clustering confirmed that the device has the capacity to recognize ammonia concentrationaround 20 ppm with total accuracy of 95%. Our study provides evidence of a new way to improve theperformance of PANI-based sensors that can potentially be employed to monitor the environment oflivestock buildings, for example.Item An alternative order parameter for the 4-state Potts model.(2006) Fernandes, Henrique Almeida; Arashiro, Everaldo; Felício, José Roberto Drugowich de; Caparica, Álvaro de AlmeidaWe have investigated the dynamic critical behavior of the two-dimensional 4-state Potts model using an alternative order parameter first used by Vanderzande [J. Phys. A 20 (1987) L549] in the study of the Z(5) model. We have estimated the global persistence exponent θg by following the time evolution of the probability P(t) that the considered order parameter does not change its sign up to time t. We have also obtained the critical exponents θ, z, ν, and β using this alternative definition of the order parameter and our results are in complete agreement with available values found in literature.Item An explicit Schrodinger picture for Aharonov’s modular-variable concept.(2021) Lobo, Augusto César; Ribeiro, Clyffe de AssisWe propose to address in a natural manner the modular-variable concept explicitly in a Schr ̈odinger picture. The idea of modular variables was introduced in 1969 by Aharonov, Pendleton, and Petersen to explain certain nonlocal properties of quantum mechanics. Our approach to this subject is based on Schwinger’s finite quantum kinematics and its continuous limit.Item Uma análise crítica sobre a implementação do SCALE-UP no Instituto de Física da Universidade de São Paulo.(2022) Guimarães, Michele Hidemi Ueno; Muramatsu, Mikiya; Passos, Marinez MeneghelloEste artigo apresenta o resultado de uma análise sobre a implementação do SCALE-UP como metodologia de ensino no Instituto de Física da Universidade de São Paulo (IFUSP). Esse método tem sido aplicado neste instituto desde o ano de 2015, nos cursos de Física I e Física II. O interesse na aplicação de uma forma alternativa de ensino surgiu a partir das experiências dos autores, como professores do Ensino Superior, em Universidades brasileiras públicas e privadas, ao identificar as dificuldades de aprendizado dos estudantes, no que diz respeito às formas como a Física experimental tem sido ensinada, na disciplina de laboratório de Física. Partindo de um roteiro semiestruturado, foram feitas entrevistas com alguns professores e alunos, que nos permitiram ter uma percepção teórica, do ponto de vista dos professores, e as principais impressões sobre o processo, do ponto de vista dos alunos. Foi realizada, considerando as transcrições das entrevistas, uma análise sobre a implementação do método, bem como destaques às divergências relatadas no que diz respeito às vantagens e desvantagens apontadas pelos depoentes. Neste artigo consideramos que: os professores que ministram as aulas básicas de Física não são necessariamente professores com formação em licenciatura ou desenvolver pesquisas relacionadas ao Ensino de Física, fato que pode ter como consequência alguns equívocos com relação à forma de implementação da metodologia e à concepção de aprendizagem dos alunos. Os resultados que aqui trazemos caracterizam esta situação.Item Análise da composição química em variedades de berilo, por Ativação Neutrônica Instrumental (INAA).(2006) Polli, Gabriel de Oliveira; Oliveira, Elisângela Fátima de; Sabioni, Antônio Claret Soares; Ferreira, Ana Claudia Mousinho; Roeser, Hubert Mathias PeterAnálises químicas de elementos maiores, menores e traço foram realizadas utilizando Análise por Ativação Neutrônica Instrumental (INAA) em vinte e quatro amostras das seguintes variedades de berilo brasileiras: água-marinha azul e verde, goshenita, heliodoro e morganita. O objetivo é utilizar a caracterização química como ferramenta auxiliar para compreender aspectos relativos às cores dos minerais do grupo do berilo. Trinta elementos químicos foram investigados, mas somente Na, Rb, Cs, Sc, La, Sm, Eu, Tb, U, Hf, Ta, Mo, W, Fe, Co, Ni, Au, Zn, Sb e Br foram detectados. Interferências ocasionadas pelas elevadas concentrações de Cs não permitiram as determinações de Sr, Ba, Ce, Nd, Yb, Th, Zr, Cr, Ag e As. Os resultados indicam correlações entre os teores de Cs, Na e Rb e as cores das variedades de berilo. Os teores de Cs e Na são expressivos na maioria das amostras, destacando-se nas amostras de morganita, goshenita e água-marinha azul e verde, o que justifica classificá-las como ricas em Cs e Na. Os teores de Cs estão vinculados às variedades de berilo. O teor médio de Na diminui gradativamente na seguinte seqüência: morganita, goshenita, água-marinha azul e verde e heliodoro. O teor médio de Rb na goshenita supera o da morganita, água-marinha azul, águamarinha verde e heliodoro. Os resultados confirmam a influência do teor de Fe nas cores das variedades água-marinha azul e verde e do heliodoro, e sugerem que não é a quantidade de Fe que define a saturação da cor, mas o estado de oxidação e o número de coordenação deste elemento.Item Análise numérica bidimensional da morfologia dendrítica do níquel e do ferro utilizando o método de campo de fase.(2009) Furtado, Henrique Silva; Bernardes, Américo Tristão; Machado, Romuel Figueiredo; Silva, Carlos Antônio daNesse trabalho, são apresentados os resultados de simulações bidimensionais da formação de dendritas durante a solidificação do níquel e do ferro puros, utilizando um modelo de campo de fase. A morfologia obtida mostrou-se qualitativamente semelhante à forma dendrítica, com braços primários e secundários bem desenvolvidos. Além disso, as velocidades de crescimento em regime permanente, calculadas no presente trabalho, apresenta ram boa conformidade com os dados experimentais em uma grande faixa de super-resfriamentos. Foi observado que a espessura da interface apresenta um forte efeito sobre a morfologia e a velocidade de solidificação. Interfaces espessas reduzem o tempo computacional; entretanto podem gerar resultados inconsistentes. A espessura que apresentou os melhores resultados sem aumento acentuado do tempo de processamento foi 4x10-8 m.Item Analogia eletrônica no ensino de Física.(2005) Rocha, Ronilson; Martins Filho, Luiz de Siqueira; Machado, Romuel FigueiredoEste artigo introduz um procedimento para o projeto de circuitos eletrônicos analógicos simples que emulam o comportamento dinâmico de sistemas físicos e matemáticos. Tais circuitos podem ser utilizados como uma aproximação experimental para desenvolvimento de atividades experimentais de ensino, sendo facilmente aplicáveis em qualquer laboratório. Como exemplo, as versões eletrônicas dos sistemas caóticos de Duffing e Rossler são projetadas e implementadas, resultando em protótipos simples, baratos, robustos, versáteis e funcionais.Item Analysis of chaotic behaviour in the population dynamics.(2001) Silva, Alcides Volpato Carneiro de Castro e; Bernardes, Américo TristãoRecently, we have shown that the Penna bitstring model for population senescence can be used to model cyclic or chaotic behaviours in population dynamics. In this paper, we analyse the attractor of the dynamics, through the calculation of the Lyapunov exponents. We obtained that the dynamics is characterized by the existence of some small exponents, which we relate to the existence of homeochaos, needed for the generation of stability and diversity in living systems.Item Angle-tunable intersubband photoabsorption and enhanced photobleaching in twisted bilayer graphene.(2021) Pogna, Eva A. A.; Miao, Xianchong; Dreifus, Driele Von; Souza, Thonimar Vieira de Alencar; Moutinho, Marcus Vinicius de Oliveira; Venezuela, Pedro Paulo de Mello; Manzoni, Cristian; Ji, Minbiao; Cerullo, Giulio; Paula, Ana Maria deVan der Waals heterostructures obtained by artificially stacking two-dimensional crystals represent the frontier of material engineering, demonstrating properties superior to those of the starting materials. Fine control of the interlayer twist angle has opened new possibilities for tailoring the optoelectronic properties of these heterostructures. Twisted bilayer graphene with a strong interlayer coupling is a prototype of twisted heterostructure inheriting the intriguing electronic properties of graphene. Understanding the effects of the twist angle on its out-of-equilibrium optical properties is crucial for devising optoelectronic applications. With this aim, we here combine excitation-resolved hot photoluminescence with femtosecond transient absorption microscopy. The hot charge carrier distribution induced by photo-excitation results in peaked absorption bleaching and photo-induced absorption bands, both with pronounced twist angle dependence. Theoretical simulations of the electronic band structure and of the joint density of states enable to assign these bands to the blocking of interband transitions at the van Hove singularities and to photo-activated intersubband transitions. The tens of picoseconds relaxation dynamics of the observed bands is attributed to the angle-dependence of electron and phonon heat capacities of twisted bilayer graphene.Item Anisotropic electron mobility in fluorene-PPV and fluorene-MEH-PPV.(2017) Magalhães, Carlos Eduardo Tavares de; Silva, Marcio M. da; Savedra, Ranylson Marcello Leal; Savedra, Melissa Fabíola SiqueiraPolyfluorene copolymers are attractive semiconductor materials, in particular for applications in the organic electronics field. They are versatile to be chemically modified and allow a tuning of the emission to cover the entire visible spectrum. A better understanding of the fundamental aspects of the nature of electronic structure and charge transport properties contribute to the improvement of optoelectronic properties of polymeric materials. Here, we provide a structure–property relationship for models of fluorene-PPV and fluorene-MEH-PPV copolymers, using molecular quantummechanics modelling. The anisotropy is discussed revisitingMulliken’s transitionmomenttheory. Accordingly, our results show that electron mobility occurs preferentially intrachain for both copolymers. Moreover, the interchain electron mobility has the most propensity to occur via π-stacking interactions.Item Anomalous coalescence from a nonlinear Schroedinger equation with a quintic term: interpretation through Thompson’s approach.(2003) Cruz, Cláudio Nassif da; Silva, P. R.Inspired by models for A+A→A(0) reactions with non-Brownian diffusion, we suggest a possible analytical explanation for the phenomena of anomalous coalescence of bubbles found in one-dimension (1d) by Josserand and Rica through numerical work [Phys. Rev. Letters 78 (1997) 1215]. The explanation firstly requires an exponent γ, which is sometimes used to describe anomalous diffusion. Here it displays an explicit dependence on the dimensionality (γ=γ(d)=4/d for d⩽2). So we have dc=2, coinciding with the upper critical dimension of A+A→A(0) reactions (Mod. Phys. Lett. B 13 (1999) 829; Mod. Phys. Lett. B 15(26) (2001) 1205) with Brownian diffusion condition (γ=2). Thus anomalous coalescence emerges, only below the critical dimension (d<2). We show that the typical size of the structures (bubbles) grows as R(t)∼t1/4 in 1d. An alternative explanation could also be thought as a diffusion constant D which depends on the average concentration (〈n〉), namely D=D0〈n〉α. It is introduced into an effective action for A+A→A(0) reactions. Therefore we are also able to reproduce the anomalous behavior for n(t) and R(t) in 1d, being α=0 for d⩾2 (mean field behavior) and α=2(2−d)/d2 for d⩽2.Item Anomalous coalescence phenomena under stationary regime condition through Thompson’s method.(2004) Cruz, Cláudio Nassif daIn this work, anomalous coalescence phenomena of type A+A→A(0) are considered in the case of stationary regime, namely the case of an external homogeneous source (h) of single particles A, in the limit of zero external field rate. The main purpose here is to pick up new critical exponents in the stationary regime for the phenomenon of anomalous coalescence of bubbles found in one-dimension by Josserand and Rica (JR) (Phys. Rev. Lett. 78 (1997) 1215). The critical exponents of statical concentration (δ), relaxation time (Δ′) and the exponent for concentration decay (ξ) are evaluated in the limit h→0 (zero field rate). We show that such critical exponents depend on the parameter γ (Physica A 334 (2004) 335), which characterizes the anomalous diffusion condition. In order to explain the anomalous coalescence of JR's work as already made before by the present author (Physica A 334 (2004) 335), the parameter γ must display an explicit dependence on the dimensionality . We use such a result [γ(d)] in order to pick up new critical exponents for the special case of anomalous coalescence found by JR (we find δ=5, and in 1-d). We also verify that the known scaling relations among such critical indexes (Phys. Rev. A 32(2) (1985) 1129) are obeyed, so that in the special case of γ=2 (brownian diffusion condition given to mean field regime), we naturally recover those results previously obtained by Rácz (Phys. Rev. A 32(2) (1985) 1129). We go further to give a better explanation for such new results, taking into account another exponent α (Physica A 334 (2004) 335) to explain the behavior of diffusion constant, which depends on concentration (D=D0〈n〉α), that is to say, we obtain analytically new critical indexes which controll the diffusion behavior (D) for long-time regime, in the presence of an external homogeneous source.