Programa de Pós-graduação em Física

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Análise comparativa da eficiência fotodinâmica de fotossensibilizadores em sua forma base livre e formando complexados com zinco
(Universidade Federal de Goiás, 2014-04-09) Alonso, Lais; Gonçalves, Pablo José; http://lattes.cnpq.br/0515343409614452; Gonçalves, Pablo José; Borissevitch, Iouri; Bakuzis, Andris Figueiroa
Photodynamic therapy (PDT) is a technique that has been increasingly used in cancer treatment. It consists in introduce a photosensitizer (PS) in cancerous tissue and irradiate it with light in the visible range. Targeting a more effective treatment of PDT, currently there are several studies on the efficacy of these PS. In this work, we studied the photodynamic efficiency seven PS: meso-tetrametilpiridil, meso-tetrasulfonatofenil and carboxiftalocianinas with their base free or metallated with zinc atom in its center ring and protoporphyrin IX. Erythrocytes suspended in 2 to 10% hematocrit were treated with or without 25 μM of PS were exposed to light from a halogen lamp, and measured the time required to obtain 50 % hemolysis (T1/2). To examine whether the photodynamic efficiency is related to the affinity of PS by membrane, we performed measurements of the octanol/water partition coefficient (PO/W) of each PS. Our results indicated that the PS studied were very hydrophilic and showed a trend for greater photodynamic efficiency the PS with higher Log PO/W. To better understand the mechanism of action of the studied PS the degree of lipid peroxidation in erythrocyte membranes irradiated with PS was assessed by measuring the formation of malondialdehyde (MDA) and a correlation between the rate of peroxidation and hemolytic potential was found. The ability of PS to degrade proteins was assessed using bovine serum albumin (BSA), monitoring the fluorescent signal of this protein into solution and under irradiation in the presence of PS.
Análise estrutural cristalográfica de protótipos de fármacos derivados de N-fenilpiperazina e de N-acilidrazona
(Universidade Federal de Goiás, 2012-03-26) Castro, Rosane de Paula; Sabino, José Ricardo; Sabino, José Ricardo; Aparício, Ricardo; Marques, Ivo de Almeida
In this work will be done initially, a review of the fundamentals of crystallography, besides the description of Direct Methods, commonly used in structural determination of small molecules, and the process of refinement of the obtained structure. The techniques for crystal growth will be presented and also a discussion about the process of data collection in the CAD4 diffractometer. Next, the process of obtaining single crystals and the crystallographic analysis of five novel compounds, which were synthesized by the Laborat´orio de Avaliac¸ ˜ao e S´ıntese de Substˆancias Bioativas (LASSBio) of Universidade Federal do Rio de Janeiro (UFRJ), are presented. These compounds are analogues of drugs, derivatives of N-phenylpiperazine and N-acylhydrazones, fragments that have important biological activities. The crystallographic structures of the following derivatives of N-phenylpiperazine were elucidated : LASSBio-1597, very active as anti-inflammatory, and an inclusion complex of the antipsychotic prototype, LASSBio-579, a dopamine receptor agonist, in β- cyclodextrin. The other compounds elucidated by X-ray crystallography are the N-acylhydrazones derivatives LASSBio-1606 analogue of Piroxicam, and compounds LASSBio-1586 polymorph I and LASSBio-1586 polymorph II , combretastatin-A4 analogue having potent anti-cancer activity, whose crystallographic analysis aimed to verify the existence of polymorphism suggested by DSC analysis (Differential scanning calorimetry).
Anisotropia magnética em filmes epitaxiais Fe/Mn, Fe/Mn/Fe e Fe/Mn/Co
(Universidade Federal de Goiás, 2013-06-07) Pessoa, Márcio Solino; Pelegrini, Fernando; http://lattes.cnpq.br/0159280600583768; Pelegrini, Fernando; Silva, Edson Corrêa da; Saitovitch, Elisa Maria Baggio; Franco Júnior, Adolfo; Rabelo, José Nicodemos Teixeira
This work reports the study of magnetic anisotropy of Fe/Mn bilayers, and Fe/Mn/Fe and Fe/Mn/Co trilayers, grown by molecular beam epitaxy onto monocrystalline MgO(001) substrates. Samples were produced with the Fe layer grown at a temperature of 175 ° C, with a thickness of 5 or 10 nm, the Co layer grown at 50 ° C, with a thickness of 2 or 5 nm, and the Mn layer grown at temperatures of 50 ° C, 150 ° C or 175 ° C, with thicknesses in the range from 0.80 to 2.20 nm. The angular variations of the in-plane absorption field, at Q-band (33.9 Ghz) microwave frequency, reveal the presence of a large four-fold magnetic anisotropy in all studied films. In samples with thicker Mn layers, two uniform resonance modes of bcc-Fe and bcc-Co layers are excited by the microwave field. The angular variations of the in-plane absorption field reveal for both layers the presence of fourth order cubic magnetic anisotropy. Films with the Mn layer thickness exceeding 1.16 nm exhibits, however, only a single absorption mode due to the overlapping of Fe-bcc and Co-bcc uniform resonance modes. Experiments at X-band (9.4 GHz) microwave frequency reveal the excitation of non-aligned and non-resonant modes, suggesting, for samples with the Mn layer grown at low temperature, a non-collinear coupling between the magnetic layers in the presence of low-intensity magnetic fields. Four-fold magnetic anisotropy constants in the range from 3.0 x 105 to 4.8 x 105 erg/cm3 for the Fe layer, and from 2.0 x 105 to 6.4 x 105 erg/cm3, for the Co layer, are given by the experiments. The magnetic parameters deduced from the in-plane measurements at Q-band microwave frequency are used to fit the in-plane and out-of-plane angular variations of resonance fields at X-band frequency.
Anisotropia magnética em tricamadas epitaxiais Fe/Mn/Fe
(Universidade Federal de Goiás, 2010-04-08) Pessoa, Marcio Solino; Pelegrini, Fernando; http://lattes.cnpq.br/0159280600583768; Pelegrini, Fernando; Nascimento, Valberto Pedruzzi; Avelar, Ardiley Torres
The ferromagnetic resonance (FMR) technique at the microwave frequencies of X-band (9.79 GHz) and Q-band (34 Ghz) was used to study, at room temperature, the magnetic anisotropy of Fe/Mn/Fe trilayers. The samples studied were grown by molecular beam epitaxy onto MgO substrates at the temperatures of 50 ° C, 150 ° C and 175 ° C, at the pressure of 4 x 10-11 Torr. The thicknesses of the distinct layers were 5 or 10 nm for the bottom Fe layer grown onto the MgO substrate, varied from 0.8 to 1.35 nm, for the Mn spacer layer, and was kept constant and equal to 5 nm, for the top Fe layer. The FMR spectra of the symmetrical trilayer at X and Q-band microwave frequencies show only the uniform resonance mode. Asymmetrical trilayers also show non resonant and/or non aligned modes at X-band frequency, but only the uniform mode at Q-band frequency. For some samples this result gives evidence of a non-collinear coupling between the Fe layers in the presence of low intensity magnetic fields. The out-of-plane angular dependence of the absorption fields show that the magnetization for all trilayers studied is in the plane of the sample. The magnetic anisotropy was deduced from the in-plane angular dependence of the uniform resonance mode at Q-band frequency, taking the free energy of the magnetic system as the result of contributions from Zeeman, demagnetizing, and in-plane cubic magnetocrystalline anisotropy energies. Fourfold in-plane anisotropy fields of 600 Oe and effective magnetizations above 16000 G were observed. The set of results obtained shows the high sensitivity and versatility of the FMR technique to study the magnetic properties of epitaxially grown monocrystalline nanometric structures.
Aplicação do método de Rietveld `a determinação da distribuição de cátions em ferritas de cobalto e de magnésio
(Universidade Federal de Goiás, 2010) Nunes, Rafael Silva; Sabino, José Ricardo; http://lattes.cnpq.br/9101677399031185
We present cobalt ferrites (CoxFe3−xO4) and magnesium ferrites (MgxFe3−xO4) nanoparticles synthesized by combustion reaction and coprecipitation. The study by powder diffraction, with CuK (λ =1,5406 °A) radiation, allowed us a phase qualitative analysis, determine the lattice parameter and the crystallites average size. How Co and Fe scattering factor are close to this radiation, we also used synchrotron radiation with energies 7.038 KeV, 7.112 KeV, 7.122 KeV and 7.718 KeV. With Rietveld refinement we made a phase quantitative analysis, we found Fe2O3, MgO and MgO2 as additional phases for MgxFe3−xO4 and we found CoO and Co3O4 as additional phases for Co1,2Fe1,8O4, all obtained by combustion method. The distribution determined for all ferrites nanoparticles characterized a cubic spinel type mixed, i.e. divalent ions were found in both sites. With experiments on a vibrating sample magnetometer (VSM) we compare the saturation magnetization of our samples with the magnetization of the unit cell calculated from the distribution determined experimentally.
Aspectos de modelos eletrônicos bidimensionais fortemente correlacionados: aplicações em cupratos supercondutores
(Universidade Federal de Goiás, 2016-06-06) Carvalho, Vanuildo Silva de; SIlva, Hermann Freire Ferreira Lima e; http://lattes.cnpq.br/7198902316435183; Silva, Hermann Freire Ferreira Lima e; Oliveira, Luiz Nunes de; Miranda, Eduardo; Rabelo, Jose Nicodemos Teixeira; Braghin, Fabio Luis
We investigate here the low-energy properties of two strongly correlated electronic models in two spatial dimensions. The first one consists in a version of the Hubbard model in which are considered just the degrees of freedom of the system in the neighborhood of the so-called hot spots, which are defined as the intersection of the Fermi surface of the model with the antiferromagnetic zone. Initially, we set our theory up by linearizing the dispersion model in hot spots and consider all the interacting processes between these regions that conserve momentum within a reciprocal-lattice wave vector. In order to access the physics of the model, we then turn to the renormalization group method of quantum field theory and derive the flow equations for the couplings in the two-loop approximation. As a result, we obtain that the Fermi surface is strongly renormalized in hot spots as the renormalized couplings flow to a non-trivial fixed point in the low-energy limit. Then we suggest that this system can be viewed as an example of a non-Fermi liquid in two spatial dimensions, due to the lack of well defined quasiparticle fermionic excitations in the region close to hot spots. Moreover, we solve the Callan-Symanzik equation for the oneparticle Green function up to two-loop order, calculate the density of states in the hot spots, and derive the renormalization group equations for the order parameters of the potential instabilities which may eventually occur in the system at lower energies. We verify that the system can be characterized, in this regime, in terms of an emergent pseudospin symmetry [SU(2)]4, which leads to the appearance of entangled orders in the region close to the non-trivial fixed point of the model. We also show that the fermionic excitations in the adjacent regions to the hot spots get a gap in both charge a spin excitation spectra. Because of this, we argue that the Fermi surface of the model can be reconstructed, leading therefore to the formation of either Fermi arcs or electronic pockets. The second model analyzed in this thesis was the three-band Emery model, which describes all the interacting processes between fermionic excitations localized in both copper (Cu) and oxygen (O) orbitals in the CuO2 unit cell. By making use of a Hubbard-Stratonovich transformation, we introduce two order parameters in the system: one for the so-called ΘII-loop-current order, which violates Z2 time-reversal symmetry, and another one for the entangled phase with dx 2 -y 2 symmetry involving the singlet superconducting instability and the quadrupole density wave order, whose wave vector points in the direction of the Brillouin zone diagonal. Minimizing the free energy of the model, we derive the self-consistent mean-field equations for these order parameters. The solution of these equations for the zero temperature regime shows that the two phases compete with themselves for the same region of the phase space and, consequently, the system tends not to display coexistence between them. We argue that this effect could be the main reason for the fact that the quadrupole density wave order has never been observed in experiments performed on the cuprate superconductors. Next, we analyze the competition between the ΘII-loop-current order, which is experimentally observed, and charge order with dx 2 -y 2 symmetry and wave vectors in the direction of the main axes of the Brillouin zone. As a result, we obtain that the system only exhibits coexistence between the ΘII-loop-current phase and the bidirectional charge order. Due to the existence of a pseudospin symmetry in this model, we also confirm that the ΘII-loop-current phase coexists with the bidirectional pair density wave order. Finally, we discuss the implications of these results for the pseudogap phase of the cuprate superconductors, which appears in the underdoped regime in these systems.
Avaliação da dependência com a pressão de propriedades estruturais de compostos orgânicos de interesse farmacêutico
(Universidade Federal de Goiás, 2018-05-07) Castro, Rosane de Paula; Sabino, José Ricardo; http://lattes.cnpq.br/9101677399031185; Pinheiro, Carlos Basílio; Santos Júnior, Sauli dos; Bufaiçal, Leandro Félix de Sousa; Fonseca, Tertius Lima da
This thesis presents the structure determination using single crystal x-ray crystallography of four drug candidates under ambient conditions of temperature and pressure, as well as submitted to high pressure. The crystallographic analysis of this type of compound allows to obtain the three-dimensional structure in an unambiguous way. This information is useful for the development process of new drugs in order to achieve the planned properties, such as the study of combinations of the drug with the excipients to be used to guarantee the rate of expected release of the drug in the human body and the optimization of interaction between the drug and the target. Furthermore during the process of drug manufacturing in the pharmaceutical industry polymorphic phases may arise due to the application of pressure, which occurs during grinding and in the preparation of tablets, which may alter the bioavailability, solubility and stability of the medicament. Thus, identifying the conditions under which such modifications may occur guarantees the reliability of the final product. In this sense, the crystallization and crystallographic analysis of drug candidates developed by the Laboratório de Avaliação e Síntese de Substâncias Bioativas (LASSBio) of the Universidade Federal do Rio de Janeiro (UFRJ) was carried out. The compounds analyzed were: LASSBio-1773 and LASSBio-1774, which have hypoglycemic activity, LASSBio-1606, with anti-inflammatory properties, and LASSBio-1735, which has been shown to be active against several types of cancer. For the compounds LASSBio-1774 and LASSBio-1606 X-ray diffraction at high pressures was also performed with Diamond Anvil Cell (DAC), determining their unit cells and analyzing the effects of pressure on the crystalline arrangement. In both compounds reversible phase transitions were observed. The analysis of the structural changes for LASSBio-1774 due to pressure was performed with the aid of strain tensors.
Avaliação dos efeitos das hipertermias magnética e fototérmica na síntese de heteroestruturas à base de nanopartículas de MnFe2O4 e Au
(Universidade Federal de Goiás, 2015-12-14) Sousa Júnior, Ailton Antônio de; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Lima, Emília Celma de Oliveira; Castro, Marcos Antônio de; Mendanha Neto, Sebastião Antônio
The purpose of this project is to synthesize and characterize heterostructures composed by manganese ferrite nanoparticles (MnFe2O4 NPs) and gold nanoparticles (Au NPs) able to: 1) respond to external alternating magnetic fields, what would enable their use in cancer diagnostic as contrast agentes for magnetic resonance imaging, as well as in cancer treatment via magnetic hyperthermia; 2) respond to eletromagnetic radiation, what would enable their use in cancer diagnostic as contrast agents for X-ray computed tomography (CT), as well as in cancer treatment via photothermal hyperthermia. We evaluate four MnFe2O4-Au heterostructures synthesis protocols. On Protocol 1, we use part of the energy of a laser beam (808 nm, 800 mW) to promote the nucleation of Au NPs at the surface of previously synthesized MnFe2O4 NPs covered by DMSA (dimercaptosuccinic acid). On Protocol 2, we use part of the energy of an alternating magnetic field (333,8 kHz, 17 mT) to promote this nucleation. We also perform an analysis of the influence of MnFe2O4 NPs covering layer, by comparing the ionic surfactants DMSA and sodium citrate. On Protocols 3 and 4, both the magnetic cores (MnFe2O4 NPs) and the metalic cores (Au NPs) are previously synthesized. Therefore, three Au NPs synthesis methods are evaluated. On Protocol 3, we promote the coupling between Au NPs and MnFe2O4-DMSA NPs using part of the energy from the same laser beam used on Protocol 1. On Protocol 4, we promote the coupling between cysteine-covered Au NPs and lysine-covered MnFe2O4 NPs via peptidic reaction between these two aminoacids. Finally, we conduct a comparative analysis between magnetic and photothermal hyperthermia, proposing a method for the determination of the optical SLP (Specific Loss Power). Moreover, we submit some of our samples to CT imaging. Protocol 1 is the best one in terms of covering the magnetic core by Au NPs. Protocol 2 allows the nucleation of Au NPs with diameters greater than the ones obtained via Protocol 1. Protocols 3 and 4 offer nanostructures with better potential with respect to their use as contrast agents in CT. However, the final yield of all four protocols is very low. Comparing magnetic and photothermal hyperthermia, we verify that the optical SLP is two to three orders of magnitude greater than the magnetic SLP under the assessed conditions, what suggests that protocols using laser beams have more energy available for the nucleation/coupling of Au NPs at the surface of MnFe2O4 NPs than those using alternating magnetic fields or simple heating on hot plate.
Avaliação experimental e teórica da hipertermia magnética de magnetolipossomos para tratamento oncológico
(Universidade Federal de Goiás, 2016-08-17) Silva, Anderson Costa da; Bakuzis, Andris Fisgueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Miotto, Ronei; Silva, Sebastião William da; Bufaiçal, Leandro Felix; Pelegrini, Fernando
In this work we investigated the magnetothermal efficacy of two nanocarriers, magnetic fluids (MF) and magnetoliposomes (ML), with potential for oncology therapy. Ferrofluids based on manganese ferrite nanoparticles, surface coated with citric acid, were synthesized. Magnetoliposomes, vesicles containing magnetic nanoparticles inside, were prepared by the extrusion method. X-ray diffraction corfimed the spinel structure, while transmission electron microscopy revealed spherical nanoparticles with a lognormal size distribution and mean diameter of (11,1 ± 3,5) nm. Magnetization curves, at quasi-static conditions revealed particles at the superparamagnetic regime. A reduction in the saturation magnetization in comparison with bulk samples were explained by a nonmagnetic shell with thickness of 1.1 nm. The concentration and particle size distribution of the liposomes (mean diameter of 180 nm) were obtained from the nanoparticle tracking analysis (NTA). The combination of magnetometry and NTA data revealed an encapsulation particle volume fraction in the range of 0.26 to 0.83% for the samples. Magnetic birefringence data showed a higher fraction of aggregates in ML in comparison to MF. Magnetic hyperthermia experiments were perfomed at distinct frequencies (111 -632 kHz) and field amplitudes (up to 250 Oe) for distinct ML and MF samples. In general, we found a reduction of magnetothermal efficacy for magnetoliposomes when compared to MF. although the effect is less evident at lower frequencies (<170 kHz). The explanation was obtained through a new theoretical model that, not only takes into account the effect of dipolar interaction in the magnetic anisotropy, but also the reduction of susceptibility due to blocked nanoparticles. This contribution was shown to be strongly dependent upon field frequency, amplitude and aggregates in the suspension.
Cálculo da condutividade térmica do Argônio sólido puro e com defeito pontual
(Universidade Federal de Goiás, 2008-03-14) Trindade, Ranyere Deyler; Silva, Ladir Cândido da; http://lattes.cnpq.br/7442411485710574
In this work, using the Green-Kubo method combined with Molecular Dynamic (DM), we calculate the thermal conductivity of a solid Argon "free of defects"and with point defect present, for temperatures varying from 10 up to 60 K at density 22,3 ml/mol. The obtained results are in good agreement with the available theoretical and experimental results in the limites of low and high temperatures, but with some discrepances in about 15 % for intermediate values of temperatures. The purpose to include point defects with the objective of correction of the simulational results to compare with experimental measuremments for intermediate temperatues had not the expected e?ect. However, we believe that it should be due to the fact that the density used in the simulation for the point defect is high based on the experimental estimates of point defect density in this system. Our results suggest that the Green-Kubo method combined with Molecular Dynamics is a powerful tool to calculate the thermal conductivity of solids at high temperatures. With the construction of accurate and reliable interatomic potentials to describe more complex materials, such as high temperature ceramic and minerals at extreme condiction of pressure and temperature, this method could soon become very useful to calculate thermal conductivity in materials where the access to experimental data is hard.
Cálculo da energia de correlação de pequenos clusters de lítio via teoria da informação
(Universidade Federal de Goiás, 2015-07-24) Mello, Victor Giovanni Pina de; Silva, Ladir Cândido da; http://lattes.cnpq.br/7442411485710574; Silva, Ladir Cândido da; Prataviera, Gilberto Aparecido; Almeida, Norton Gomes de
In this dissertation, we use the information theory to obtain the correlation energy of small lithium clusters. Unlike conventional methods for calculation of the correlation energy, the method used here requires only a single calculation in a Hartree-Fock level. With this calculation we obtain a total information energy of the clusters, through the addition of information energy of each atom of the cluster. The correlation energy is a bilinear function of the information energy and number of electrons in the cluster. In order to obtain a general equation for the correlation energy, we use the correlation energy expression that has been obtained through the information theory to t the exact energy of the system using a Monte Carlo quantum simulation of clusters ranging from 1 to 8 lithium atoms. The e ciency of the general equation for the correlation energy has been veri ed through the calculation of the binding energy for clusters of up to 9 and 10 atoms which have not been used in the obtained t. The obtained values for the binding energies are in good agreement with the experimental measurements using photoelectron spectroscopy.
Cálculos de (hiper)polarizabilidades dinâmicas das moléculas de ozônio, dióxido de enxofre, óxido nitroso e dióxido de carbono incluindo correções vibracionais e efeitos de correlação eletrônica
(Universidade Federal de Goiás, 2013-11-08) Naves, Emílio Santiago; Castro, Marcos Antônio de; http://lattes.cnpq.br/3500875789893244; Fileti, Thaciana Valentina Malaspina Fileti; http://lattes.cnpq.br/2600060786895700; Silva Filho, Demétrio Antônio da; http://lattes.cnpq.br/8032106763743620; Georg, Herbert de Castro; http://lattes.cnpq.br/8026419467214372; Braghin, Fabio Luis; http://lattes.cnpq.br/9375085677737347
This work presents results for the dynamic (hyper)polarizabilities of ozone, sulfur dioxide, nitrous oxide and carbon dioxide molecules, with inclusion of vibrational corrections. The electronic contributions for the properties of interest were computed analytically at the single and double coupled cluster level through response theory. Ozone and sulfur dioxide were studied separately. For both systems, contributions of connected triple excitations were also estimated by the multiplicative correction scheme. The vibrational corrections were calculated by the perturbation theoretical method (PT). The zero-point vibrational average correction, calculated only for ozone and sulfur dioxide, proved to be small. Results also show that the pure vibrational correction is relevant for the following nonlinear optical processes: dc-Pockels effect, intensity dependent refractive index, and dc-Kerr effect. For the ozone molecule the dc-second harmonic generation effect also had a significant pure vibrational correction. In addition, pure vibrational correction was calculated according to a variational methodology proposed by our research group (VAR) for the four systems, and the results were compared with the corresponding PT results. A comparison between PT and VAR results shows that ozone is the system most sensitive to the method, while sulfur dioxide and carbon dioxide are the most well behaved.
Cálculos de propriedades elétricas da metanol incluindo correções vibracionais e correlação eletrônica
(Universidade Federal de Goiás, 2009) Dutra, Adriano da Silva; Castro, Marcos Antônio de; http://lattes.cnpq.br/3500875789893244
In this work we report results for the polarizability, and first and second hyperpolariz- abilities of the methanol molecule including vibrational corrections and electron correlation effects. The Vibrational corrections were computed using the perturbation theoretic approach of Bishop and Kirtman and the electron correlation effects were taken into account through the CCSD(T) method implemented in the GAUSSIAN 03 program. The electronic contributions to the electric properties were calculated using the finite-field scheme. Comparisons of our CCSD(T) values with previous TDHF result show that the electron correlation effects, are in general, important. An analysis of the importance of the vibrational corrections shows that the zpva correction is not negligible, specially for the hyperpolarizabilities. The pv correction is, in general, important and the double-harmonic approximation is suitable to the calculation of this correction for most of the nonlinear optical processes studied.
Campos escalares aplicados em cosmologia
(Universidade Federal de Goiás, 2018-07-13) Vieira, Lucas Elias; Avelar, Ardiley Torres; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4766756E0; Avelar, Ardiley Torres; Cardoso, Wesley Bueno; Brito, Francisco de Assis de
In this work, we study topological defects in classical field theory aiming applications in cosmology. Topological and non-topological solutions were investigated in two dimensions, where we also analyzed the stability of some of these. We consider models of one and two real scalar fields, whose solutions were obtained via quadrature, BPS and orbit methods. The stability of these solutions also were investigated in some cases. In order to apply scalar field theory in cosmology, we revisit some topics of general relativity, such that the principle of equivalence, Einstein's field equations and Schwarzschild's solution for Einstein's equation. We also present some topics in cosmology, relevant to the present work, such that the cosmological principle, Hubble's law and cosmological inflation. We discuss the solutions of the Einstein's equations in the FRW metric in the so-called Hot Big Bang model-the universe composed of matter and radiation. In order to solve some problems of initial conditions of the universe, we introduce the inflationary theory, which supposes that the primordial universe was underwent an accelerated expansion guided by a scalar field. In sequence, we introduce the standard cosmological model, which states that the universe is in accelerated expansion driving by a cosmological constant, named dark energy, which constitutes about seventy percent of the universe energy. Finally, we present a first order formalism for cosmology and discuss two model describing the standard and tachyonics dynamics for scalar field that represent the dark energy.
Caracterização estrutural e investigação do efeito exchange bias espontâneo na perovskita dupla La1,5Sr0,5CoMn0,5Fe0,5O6
(Universidade Federal de Goiás, 2021-02-26) Silva, Arthur Garcia; Bufaiçal, Leandro Felix de Sousa; http://lattes.cnpq.br/1392206843733548; Bufaiçal, Leandro Felix de Sousa; Bittar, Eduardo Matzenbacher; Santana, Ricardo Costa de
In this work we describe the synthesis and characterization of the structural, eletronic and magnetic properties of La1.5Sr0.5CoMn0.5Fe0.5O6 compound. Our main focus was on the investigation of 50% of Mn to Fe substitution in La1.5Sr0.5CoMnO6, with a particular interest in the spontaneous exchange bias effect, a phenomena characterized by the shift in the magnetic hysteresis curves taken after the system bein cooled in zero magnetic field. The polycrystalline sample here investigated was syntesized by conventional solid state reaction technique and investigated by means of X-ray powder diffraction, magnetization as a function of temperature [M(T)] and magnetization as a function of magnetic field [M(H)]. The La1.5Sr0.5CoMn0.5Fe0.5O6 crystal forms in rhombohedral symmetry, space group, in agreement with results observed for similar compounds. The M(T) measurements have revealed a ferromagnetic-like transition at TC ≈ 150 K, and also indicated the presence of competing magnetic phases, which leads to the formation of ferromagnetics clusters embedded in a paramagnetic matrix at high temperature. This is a hallmark of the Griffiths Phase, here occurring in the 150 K < T < 205 K range. The M(H) curves carried after cooling the system in zero field have showed that La1.5Sr0.5CoMn0.5Fe0.5O6 exhibits the spontaneous Exchange Bias effect at low temperatures, while for the measurements carried after cooling the system in the presence of a external magnetic field it is observed a significant enhancement of the shift in the M(H) curve.
Caracterização estrutural e magnética do compósito cerâmico ZnO – CoFe2O4
(Universidade Federal de Goiás, 2015-08-12) Oliveira Neto, Francisco de; Franco Júnior, Adolfo; http://lattes.cnpq.br/0187547195548392; Franco Júnior, Adolfo; Araújo, Olacir Alves; Bufaiçal, Leandro Felix de Sousa
Multiferroic materials that simultaneously exhibit two or more physical properties have increasingly raised the interest of the scientific and technological community to develop new multifunctional materials. The discuss all stages of manufacturing, morphological, structural and magnetic characterization of a multifunctional composite containing zinc oxide and cobalt ferrite. Thus, studies of ZnO, and the CoFe2O4 composite (0,80ZnO+0,20 CoFe2O4) initiated by the synthesis of nanosized powders by combustion reaction phases were performed. The compounds studied were sintered at different temperatures (1100 to 1250°C) to obtain relative density near to 90% of the theoretical density. Analysis by scanning electron microscopy, spectroscopy energy dispersive, vibrating sample magnometry and diffraction ray-X were made. Measurements of magnetic properties were conducted at room temperature (22°C) and high temperature (22°C to 700°C). In the samples, formation of ceramic structures was verified, the stoichiometry of the proposed chemical compounds was maintained and possibly the formation of a mixed zinc and cobalt ferrite to composite samples. In the sample of the composite sintered at 1250°C there was the formation of cubic zinc oxide. The magnetic behavior and magnetic anisotropy of the samples were similar, however, significant differences were observed in the values of the Curie temperature, coercive field, can assume different origins for the magnetic CoFe2O4 and the composite (0,80ZnO+0,20CoFe2O4) due, perhaps to the formation of a mixed ferrite.
Caracterizações óptica e elétrica de cristais de Bi2TeO5 crescidos por um método de duplo cadinho
(Universidade Federal de Goiás, 2015-01-22) Fabris, Zanine Vargas; Carvalho, Jesiel Freitas; http://lattes.cnpq.br/5841291496427516; Carvalho, Jesiel Freitas; Baldochi, Sonia Licia; Santo, Ana Maria do Espírito; Lariucci, Carlito; Gonçalves, Pablo José
Bismuth tellurite, Bi2TeO5, here labeled BTeO has a lot of properties like improper ferroelectricity, photochromic, photorefractive, with two optical axes large optical window and another interesting optical and electrical properties, as recently we discovered, photovoltaic effect. BTeO single crystal growth and processing has two inherent difficulties, high vapor pressure of tellurium oxide close to bismuth tellurite melting point and BTeO cleavage plane parallel to (100) plane. So, BTeO factory good sample for material characterization require singular precautions and depends on researcher experience invariably. Present work is dedicated to detailed study of BTeO single crystals growth parameters in a modified Czochralski method with unpublished concept double crucible system. In our case, we used oxides mix on external crucible with volatile oxide bigger quantity related to internal crucible to create a supersaturated atmosphere used to control crystal growth liquid phase stoichiometry reducing tellurium oxide evaporation. We also highlighted important details about good quality samples production, like crystal cut and polish enclosed in acrylic resin to avoid cleavages during this processes. Finally, we characterized BTeO by optical spectroscopy (optical absorption, Raman scattering and luminescence) and electrical properties (conductivity, photoconductivity and impedance spectroscopy). We measured BTeO photorefractive properties with 633 nm wavelength for the first time and results suggested that material could be photovoltaic, hypothesis tested and confirmed in the present work.
Cerâmicas multifuncionais de oxido de zinco dopadas com cobalto: propriedades ópticas, dielétricas e magnéticas
(Universidade Federal de Goiás, 2019-10-23) Silva, Hermínia Veridiana dos Santos Pessoni e; Franco Júnior, Adolfo; http://lattes.cnpq.br/0187547195548392; Franco Júnior, Adolfo; Machado, Fernando Luis de Araujo; Silva, Sebastião Willian da; Bufaiçal, Leandro Felix de Sousa; Rosa, Andreia Luisa da
In this work, Zinc oxide Cobalt-doped ceramics (Zn1−xCoxO) were produced with 0,00≤x≤0,05 molar concentrations to obtain multifunctional materials. The Solid State Reaction with slow pressing step and maximum sintering temperature of T=1150ºC was used. Structural characterization by Apparent Density (ρap), Energy Dispersion Spectroscopy (EDS), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) indicated formation of typical ZnO hexagonal wurtizite phase for all samples (space group - P63mc (C6v)), without formation of spurious phases and good stoichiometric measured coherence. The results also indicated good densification for the ceramics (ρrel=97−91%). The optical characterizations performed by Infrared (FTIR), UV-Vis and Raman allowed the observation of the characteristic vibrational modes of ZnO and the confirmation of the total introduction of Co ions in the tetrahedral sites in the lattice, it also allows the study of evolution in the defects’ amount of VO and Zni type and systematic reduction of optical bandgap Eg due to doping. Electrical characterizations performed by Dielectric Permittivity Spectroscopy (EPD) and Impedance revealed Colossal Dielectric Permittivity (PDC) behavior in all samples (ϵ’~105) and, doping intensifies the effect. The overall dielectric behavior of ceramics is consistent with the Maxwell-Wagner (MW) dielectric relaxation model, which was also used to explain the PDC phenomenon. Magnetic characterizations performed using Magnetic Hysteresis, Zero Field / Field Cooling (ZFC / FC) and Electronic Paramagnetic Resonance (EPR) measurements indicated diamagnetic ordering (DM) in the pure sample and predominant paramagnetic (PM) ordering in the doped samples, as well antiferromagnetic ordering (AFM) in doped samples due to the approximation of Co ions in the lattice (sample x=0,05 - 62%PM×38%AFM). Weak Co-ion spin-orbit coupling has been identified in the presence of the ZnO crystalline field. Non-occurrence of ferromagnetism (FM) was discussed in terms of the defects’ placement in ZnO samples.
Condutância em nanofios magnéticos diluídos
(Universidade Federal de Goiás, 2010) Mendes, Udson Cabra; Leão, Salvino de Araújo; Avelar, Ardiley Torres; http://lattes.cnpq.br/5732286631137637
We investigate core-shell nanowires of diluted magnetic semiconductors (DMS) with remote n-type modulation doping. The incorporation of Mn2 ions acting as spin 5/2 impurities in the core region of the wire gives rise to a strong s-d exchange coupling between electrons in the wire and those of the d levels of the Mn2 ions. Applying an external magnetic eld along the axis of the wire, within the mean eld approximation, the s-d exchange generates a spin-dependent core potential. A gate voltage is applied radially to wire, to obtain some control over the density of the wire. Electronic strucutre of the wire was calculated within the e?ective mass approximation, in both approximations Hartree and spin density functional theory. We calculated the conductance of wire using the Landauer-B?uttiker formulation in the linear response regime, which generally results in a total conductance with well-de ned plateaus in GT = 2; 6; 10G0 (G0 = e2=h is the quanta of conductance), which occurred because in the system investigated the rst level is twofold degenerated (spin degenerescence) and the others are fourfold degenerated (spin degenerescence and orbital angular momentum). In the absence of a magnetic eld we observe that when we take into account the e?ects of exchange and correlation, the states with eigenvalues of Lz nonzero will be polarized while those with l = 0 isn't polarized. This unpolarized level with eigenvalue of Lz null suggests that, perhaps, the 0.7 anomaly (the emergence of two plateau at G = 0:7G0 and the other in G = G0) quantum wires on existing geometry of split-gate is related to the geometry of the wire. The results for total energy show that there are a competition between the ferromagnetic and paramagnetic states.
Construção, caracterização e otimização da magnetohipertermia de nanocarreadores multifuncionais fluorescentes: a importância da relaxação coletiva na geração de calor
(Universidade Federal de Goiás, 2018-02-22) Zufelato, Nícholas; Bakuzis, Andris Figueiroa; http://lattes.cnpq.br/3477269475651042; Bakuzis, Andris Figueiroa; Nunes, Wallace de Castro; Silva, Sebastião William da; Pelegrini, Fernando; Bufaiçal, Leandro Felix de Sousa
In this work, we developed a multifunctional nanocarrier that has diagnostics and therapeutic applications in oncology, and evaluated the magnetothermal efficiency (SLP) properties in a comparative manner with respect to magnetic fluids. The nanocarrier consists of Mn-ferrite magnetic nanoparticles, a near-infrared fluorescent molecule IR-780, that are surface-coated with albumin proteins (BSA). The samples were characterized by dynamic light scattering (DLS), electron microscopy (TEM and MEV-FEG), vibrating sample magnetometer (VSM), fluorescence molecular tomography (FMT). FMT data proved the coupling of IR-780 to the protein allowing the fabrication of a magnetofluorescent nanostructure. Magnetic hyperthermia data as function of field amplitude (60-200 Oe) and frequency (170-990 kHz) were obtained for all samples containing the same magnetic particle volume fraction in the liquid carrier, but with distinct agregate sizes. The sizes were controlled by tuning the ionic force, and monitored experimentally using DLS. Magnetization curves revealed a (quasi-static) superparamagneticlike behavior, and was used to extract the particle concentration. The hyperthermia efficiency SLP of the magnetic fluids decreased increasing the hidrodynamic diameter. On the contrary, the nanocarrier showed a maximum of SLP, that can be optimized for hyperthermia and is more efficient than the ferrofluid. SLP data as function of frequency revealed a relaxation time of the order of 10-7 s and an equilibrium susceptibility lower than the Langevin value. A theoretical analysis of SLP at the linear responde regime was developed taking into account the dipolar interaction of nanoparticles organized in distinct arrangements. In magnetic fluids we considered a linear chain using the longitudinal configuration (anisotropy axis aligned), while for the nanocarriers we considered spherical agregates where the anisotropy axis of the nanoparticles are arranged randomly. The theoretical analysis indicate that the relaxation time cannot be explained by brownian relaxation or the Néel relaxation of single particle (even considering the dipolar effect). But instead, a mechanism of collective relaxation, mediated by dipolar interaction, is responsible for heat generation. It also indicates that only a fraction of agregates in the colloid is responsible for heating. In addition, the theoretical model revealed the existence of a transition from single particle relaxation to collective relaxation only if the dipolar interaction for the aggregate is higher than a critical value, which depends on material parameters, as for instance anisotropy field and saturation magnetization. Indeed, the model indicates that collective states are more easily achieved on soft magnets, and therefore suggests enhanced magnetothermal properties for this kind of materials.

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