IF - Instituto de Física

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http://200.137.215.59//handle/ri/841

O IF - Instituto de Física, da Universidade Federal de Goiás, oferece Graduação em: Bacharelado em Física; Licenciatura em Física; Física Médica; e, Engenharia Física.

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Agora exibindo 1 - 20 de 386

Cyclotron resonance of interface polarons in sernicomductor heterostructures
(1994) Osorio, Francisco Aparecido Pinto; Degani, Marcos Henrique; Hipólito, Oscar
Solução da equação de Schrodinger independente do tempo para um poço de potencial quadrado assimétrico
(1997-03) Machado, Paulo César Miranda; Osorio, Francisco Aparecido Pinto; Borges, Antonio Newton
Using a common theme in Quantum Mechanics, we reached an interesting result which is not usually developed in the traditional literature. This theme is the calculation of the electron energy eigenvalue in assymmetric nite square potential wells. We will show that the electron energy eigenvalue in assymmetric nite square potential wells may be obtained from rst and second classes solutions of symmetric nite square potential wells, which are found in Quantum Mechanics books.
Vanadium characterization in BTO: V sillenite crystals
(1999) Carvalho, Jesiel Freitas; Franco, Roberto Weider de Assis; Magon, Claudio José; Nunes, Luiz Antonio de Oliveira; Pelegrini, Fernando; Hernandes, Antonio Carlos
Visible and Infrared Optical Absorption and Electron Paramagnetic Resonance (EPR) techniques have been used to characterize the intrinsic defects in sillenite type crystals: nominally pure Bi12TiO20 (BTO) and doped with vanadium (BTO:V). Optical quality crystals, with the composition Bi12.04±0.08Ti0.76±0.07V0.16±0.02O20, have been grown. Results obtained by these different techniques have shown unambiguously the 5+ valence state of the vanadium ion in BTO:V crystals. In pure BTO samples, the EPR and optical spectra show strong evidence of the presence of the intrinsic defect BiM 3+ + ho +, which consists of a hole h+, mainly located on the oxygen neighbors of the tetrahedrally coordinated Bi3+ ion. After doping with vanadium, results have shown that the characteristic bands, associated to this hole defect center, disappear, suggesting its transformation in single Bi3+. Anisotropy of the EPR spectra , at 20 K, is related to Fe3+ impurities.
Cyclotron mass of electrons in gaas-algan heterostructures
(1999-12) Oliveira, Solemar Silva; Souza, Márcio Adriano Rodrigues; Borges, Antonio Newton; Osorio, Francisco Aparecido Pinto
The quasi-two-dimensional electron cyclotron mass in GaN-AlxGa1􀀀xN heterostructures is theoret- ically calculated. The shifting in Landau Levels due to the electron Longitudinal Optical phonon interaction is calculated through the Second Order Improved Wigner Brillouin Perturbation Theory (IWBPT). Experimental results recently obtained for GaN heterojunction are well described by the theory. We have also investigated the e ects of the electronic density on the Cyclotron Resonance frequency.
Non-classical properties of even circular states
(2000) Pereira, Regiane Aparecida Ragi; Baseia, Basílio; Mizrahi, Salomon Sylvain
Here we investigate some general properties of the so-called even circular state (ECS) produced in a cavity, consisting of a superposition of N coherent states |αk (k = 1, 2, . . . , N) with the same |αk |. Several special states may emerge from this kind of superposition: in particular, when 1 (e|αk |2/N)N 4N a Fock state with N quanta is produced, whereas when (e|αk |2/N)N 1 one gets a vacuum state. We analyse the atomic scattering the ECSs produce when two-level atoms go through the cavity and also the non-classical depth of these states.
Synthesis, crystal growth and characterization of γ-Phase bismuth titanium oxide with gallium
(2000) Lobato, Arilson Reges; Lanfredi, Silvania; Carvalho, Jesiel Freitas; Hernandes, Antonio Carlos
Gallium solubility in the Bi12TiO20 (BTO) matrix was investigated by solid state reaction synthesis and Bi12Ti(1-x)GaxO20 (BTGaO) single crystals were grown by Top Seeded Solution Growth (TSSG). We determined that it is possible to obtain a continuous solid solution from (x)Bi12TiO20:(1-x)Bi12[Ga0.7Bi0.3]O20andthatGareplacesTiintheBTOmatrixgivingBi12Ti(1-x)Ga(x)O20 up to x < 0.2. BTGaO single crystals grown with an excess of Bi2O3 were transparent, a bleaching effect was observed due to the presence of gallium in the crystalline sillenite structure and their lattice parameter was higher than for pure BTO. The results for BTGaO single crystals showed an increase in the optical activity from ρ0 = 6.4° ± 0.3°/mm, for BTO, to ρ0 = 9.7° ± 0.3°/mm, for BTGaO grown with x = 0.30 in the melt. The BTGaO crystal presented an activation energy value of 0.48 ± 0.02 eV for 100 °C ≤ T ≤ 300 °C.
Interpolation from number states to chaotic states of the electromagnetic field
(2001) Baseia, Basílio; Duarte, Sérgio José Barbosa; Malbouisson, Jorge Mário Carvalho
We introduce new two-parameter states of the quantized radiation field interpolating from number states to chaotic states. Instead of dealing with pure states, we consider truncated mixtures of number states—number-chaotic states (NCS)—which reduce to number and chaotic (thermal) states in two well-defined limits. We study the statistical and squeezing properties of such states and show that there is a value of the chaoticity parameter ¯n at which a transition from sub- to super-Poissonian characteristics occurs. Analysing the atomic population inversion in the Jaynes–Cummings model for these NCSs, we demonstrate the appearance of collapses and revivals as ¯n is increased. Their phase space representations are studied emphasizing the changes as the parameters are varied and we discuss the nonclassical depth.
Zeeman effect in CdMnTe parabolic and half parabolic quantum wells
(2002) Cunha, Jalles Franco Ribeiro da; Osorio, Francisco Aparecido Pinto; Borges, Antonio Newton; Souza, Márcio Adriano Rodrigues
We have investigated the electronic structure of Cd1􀀀xMnxTe parabolic quantum wells and half- parabolic quantum wells heterostructures in the envelope function approximation using the k p method. We have considered an external magnetic eld applied in two di erent con gurations: in the plane of the layer and in the growth direction. The con ned states have been calculated taking into account the e ective mass dependence of the Mn concentration and the strain e ects. In this work we analyze the giant Zeeman splitting due to applied magnetic elds and we have compared the energies of the excitonic transitions hh (lh) ! el for the magnetic eld in the two considered con gurations. Comparison of our results for the half-parabolic quantum wells with available experimental data is made.
Construção de uma fonte de corrente e de uma sonda para medida de condutividade pelo método da sonda de quatro pontas
(2003) Araújo, Olacir Alves de; Botter Júnior, Wilson; Carvalho, Jesiel Freitas; Verde, Ediron Lima
This paper describes the construction of an eletrical current source and of a probe to be used in the measurement of eletrical conductivity through a four-point probe method. These pieces of equipments can be obtained at the low price of US$ 50.00 and are adequate for eletrical conductivity measurements in the semiconductor range, that is from 10-1 to 10-6 S cm-1.
Study of the RPA pair correlation function in GaAs-AlGaAs parabolic quantum well wires
(2004-06) Cunha, J. B. B. da; Cunha, Jalles Franco Ribeiro da; Machado, Paulo César Miranda; Osorio, Francisco Aparecido Pinto; Borges, Antonio Newton
The ground state intrasubband pair-correlation function for a quasi-one-dimensional electron gas confined in a GaAs-AlxGa1¡xAs parabolic quantum well wire within the Random-Phase Approximation (RPA) is calculated. We have considered two wires with subband energies separation ~ = 2:0 meV and ~ = 2:5 meV. The dependence of the pair-correlation function on the electronic density was studied and the regions where the RPA approach cannot be used were precisely determined.
Sculpturing coherent states to get highly excited fock states for stationary and travelling fields
(2004-06) Maia, Luciano Paula de Araújo; Baseia, Basílio; Avelar, Ardiley Torres; Malbouisson, Jorge Mário Carvalho
An adapted sequential application of dispersive atom–field interaction is used to engineer a field in a highly excited Fock state. A few atoms are used to group into a number component all photons inside a microwave cavity which initially contains a coherent state. The scheme differs from those adding photons to an empty cavity via successive passage of resonant atoms. A conveniently equipped sequence of Mach–Zehnder interferometers is found to be the complementary scheme, extending the result for (optical) travelling waves.
Generation of superposed phase states via raman interaction
(2004-08) Avelar, Ardiley Torres; Souza, Leomar Alves de; Rocha Filho, Tarcísio Marciano da; Baseia, Basílio
A recent proposal producing superpositions of two truncated phase states in a high-Q microwave cavity has been presented. The scheme was based on dispersive interactions of two-level Rydberg atoms with a single mode field inside a cavity. Here we consider a simplified scheme doing the same, via Raman interaction of the field with degenerate three-level atoms. The extension to 2K phase states components (K > 1) is discussed.
Complementary coherent state for measuring the Q-function: generation and properties
(2004-10) Avelar, Ardiley Torres; Baseia, Basílio; Almeida, Norton Gomes de
In a previous paper a proposal for measuring the Husimi Q-function based on the projection synthesis method (Barnett and Pegg 1996 Phys. Rev. Lett. 76 4148) was presented. The scheme required the presence of an unavailable state, named the complementary coherent state. This paper shows how to generate this state in travelling waves and studies its properties.
Preparing highly excited fock states of a cavity field using driven atoms
(2005-05) Avelar, Ardiley Torres; Baseia, Basílio
Inspired by a previous work (Zheng and Guo 1998 Phys. Lett. A 244 512) we propose a scheme for creating Fock states |2N of the quantized radiation field using atoms driven by a classical field. This scheme is an alternative to another published one (Maia et al 2004 J. Opt. B: Quantum Semiclass. Opt. 6 351). Comparisons between them and others are discussed.
Magnetopolaron effects on the intradonor 1s-2p+ transition energies in a GaAs-AlGaAs double quantum well
(2006) Osorio, Francisco Aparecido Pinto; Machado, Paulo César Miranda; Borges, Antonio Newton
In this work we present a calculation of the intradonor 1s-2p+ transition energies for an impurity donor present in a GaAs-AlGaAs Double Quantum Well structure as a function of an applied external magnetic field. In our calculation the impurity energy levels were obtained from a variational method by choosing a Gaussian trial wave function, and the energy corrections due to the polaronic effect were included by second order perturbation theory IWBPT as modified by Cohn, Larsen and Lax. We have considered only the GaAs bulk LO phonon in the electron-phonon coupling. A very good agreement between the theoretical and experimental results for a DQW consisting of two 100 °A well widths separated by a 100 °A potential barrier width was obtained.
Wang-landau monte carlo simulation of the blume-capel model
(2006) Silva, Cláudio José da; Caparica, Álvaro de Almeida; Plascak, João Antônio
We carry out a study of the two-dimensional Blume-Capel model using the Wang-Landau Monte Carlo method which estimates the density of states g E directly. This work validates the applicability of this method to multiparametric systems, since only one computer run is needed for all range of macroscopic parameters temperature, anisotropy, etc. . The location of the tricritical point is determined as kBTt /J=0.609 3 , Dt /J =1.966 2 and is in excellent agreement with previous estimates. The free energy and the entropy, which are not directly accessible by conventional Monte Carlo simulations, are obtained simply using g E .
The effects of the plasmon LO phonon interaction on the critical densities of RPA approach in quasi-one-dimensional system
(2006-06) Machado, Paulo César Miranda; Osorio, Francisco Aparecido Pinto; Borges, Antonio Newton
In this work we have studied the electron LO phonon interaction on the pair-correlation function g(x) and its dependence on the electronic density for a GaAs-AlGaAs rectangular quantum wire within the random-phase approximation (RPA). We assumed two different values of the wire width. As negative non-physical results are found for lower electronic densities and small interparticle separations in the RPA approach, we have delimited the regions where the RPA approach cannot be used for the calculation of the Q1D electron gas collective excitation.
O isocronismo dos triângulos retângulos
(2007) Caparica, Álvaro de Almeida
We show that plates having the shape of right triangles with equal hypotenuses which are free to swing about a perpendicular axis passing through the vertex of the right angle exhibit an isochronism similar to that of the simple pendulum, where the period depends on a single geometric parameter, namely the length of the string. In this case the parameter is the half-length of the hypotenuse and we show in addition that the center of oscillation is located exactly at the center of the opposite edge.
Role of surfactant molecules in magnetic fluid: comparison of monte carlo simulation and electron magnetic resonance
(2008) Castro, Leonardo Luiz e; Gonçalves, Gil Renato Ribeiro; Skeff Neto, Kalil; Morais, Paulo César de; Bakuziz, Andris Figueiroa; Miotto, Ronei
We investigate a magnetic fluid composed of magnetite nanoparticles surfacted with dodecanoic acid molecules and stably dispersed in a hydrocarbon solvent. A comparison between Monte Carlo simulation and different experimental techniques allows us to validate our methodology and investigate the behavior of the surfactant molecules. Our analysis, based on the Langmuir model, suggests that the surfactant grafting number on isolate nanoparticles increases with the nanoparticle concentration, while the grafting on agglomerated nanoparticles presents a more complicated behavior. Our results suggests that, if properly coated and at a certain concentration range, colloids can become stable even in the presence of agglomerates. The role of the Hamaker constant, which controls the van derWaals interaction intensity, was also investigated.We have found that the ratio between grafting and Hamaker constant governs the level of nanoparticle agglomeration.
Improving wang-landau sampling with adaptive windows
(2008) Cunha Netto, Antônio Gonçalves da; Caparica, Álvaro de Almeida; Tsai, Shan-Ho; Dickman, Ronald; Landau, David Paul
Wang-Landau sampling WLS of large systems requires dividing the energy range into “windows” and joining the results of simulations in each window. The resulting density of states and associated thermodynamic functions is shown to suffer from boundary effects in simulations of lattice polymers and the five-state Potts model. Here, we implement WLS using adaptive windows. Instead of defining fixed energy windows or windows in the energy-magnetization plane for the Potts model , the boundary positions depend on the set of energy values on which the histogram is flat at a given stage of the simulation. Shifting the windows each time the modification factor f is reduced, we eliminate border effects that arise in simulations using fixed windows. Adaptive windows extend significantly the range of system sizes that may be studied reliably using WLS.

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