Estudo das características magnéticas e absorvedoras das ferritas de nizn, niznmn, mnzn, nimg, nicuzn e nicuznmg obtidas via método do citrato precursor

Were synthesized systems Ni0,5Zn0,5Fe2O4, i0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 and Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350°C/3h. The evolution of the phases formed after calcinations at 350, 500, 900 and 1100ºC/3h was accompanied by X-ray diffraction using the Rietveld refinement to better identify the structures formed. The materials were also analyzed by scanning electron microscopy, magnetic measurements and analysis of the reflectivity of the material. The samples calcined at different temperatures showed an increase of crystallinity with increasing calcination temperature, verifying that for some compositions at temperatures above 500°C precipitates of second phase such as hematite and CuO. The compositions of manganese present in the structure diffusion processes slower due to the ionic radius of manganese is greater than for other ions substitutes, a fact that delays the stabilization of spinel structure and promotes the precipitation of second phase. The compositions presented with copper precipitation CuO phase at a temperature of 900 and 1100ºC/3h This occurs according to the literature because the concentration of copper in the structure is greater than 0.25 mol%. The magnetic measurements revealed features of a soft ferrimagnetic material, resulting in better magnetic properties for the NiZn ferrite and NiCuZnMg at high temperatures. The reflectivity measurements showed greater absorption of electromagnetic radiation in the microwave band for the samples calcined at 1100ºC/3h, which has higher crystallite size and consequently the formation of multi-domain, increasing the magnetization of the material. The results of absorption agreed with the magnetic measurements, indicating among the ferrites studied, those of NiZn and NiCuZnMg as better absorbing the incident radiation.

Síntese, caracterização de ferritas espinélio com propriedades magnéticas e absorvedoras de microondas

Were synthesized spinel-type ferrites with general formula Ni0,8Mg0.2-xMxFe2O4, where M represents the doping Mn, Co or Mn + Co simultaneously, x ranges for the values 0.02, 0.05 and 0.1. The value of x was divided by 2 in cases where M equals Mn and Co conjugates. We used the citrate precursor method and heat treatment to obtain the phases at 1100°C. The materials were characterized by XRD, TGA/ DTGA, SEM, MAV and reflectivity measurements by the method of waveguide. Powders to 350°C/3.5 h were crystalline and nanosized. According to the results this temperature all powders have a percentage of ferrite phase over 90%. The composition had the addition of Mn and Co simultaneously showed a higher percentage of secondary phase NiO, 5.8%. The TGA/DTGA curves indicate that this sample reached phase (s) crystalline (s) at lowest temperatures. The X-ray diffractograms of the samples calcined at 350°C and 1100°C were treated with the Rietveld refinament technique. The powders calcined at 1100 °C/3h in air show to be 100% except spinel phase composition with 0.02 doping. The micrographs show clusters of particles with sizes smaller than 1 μm in calcination temperature of 1100°C which agreed with the result of Rietveld refinement. In the compositions doped with Mn were higher values of magnetization (45.90 and 53.20 Am2/kg), which did not cause high microwave absorption. The theoretical calculation of magnetization (MT) was consistent with the results, considering that there was agreement between the increase of magnetization experimental and theoretical. It was observed that there was the interrelation of the final effect of absorption with the thickness of MARE, the composition of ferrimagnetic materials and in particular the specific values of frequency. The analysis shows that the reflectivity increases in the concentration of cobalt increased the frequency range and also for absorption 10.17 GHz and 84%, respectively. The best result of chemical homogeneity and the value of 2.96 x 10-2 tesla coercive field were crucial for high performance ferrite absorber with 0.1 cobalt. The Cobalt has high magnetocrystalline anisotropy, it is associated with an increased coercive field, Hc. Therefore, this property improves the results of reflectivity of spinel ferrites

Seleção de clones de figueira cv. roxo de Valinhos formados por gemas irradiadas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Avaliação de seleções mutantes de figueira cv. Roxo-de-Valinhos

A figueira (Ficus carica L.), pertencente à família das Moráceas, constitui-se numa das mais importantes frutíferas cultivadas, elevando o Brasil à condição de décimo maior produtor e exportador de figos do mundo. Porém, a ficicultura apresenta alguns problemas fitossanitários, além de, no Brasil, estar toda implantada com uma única cultivar, a Roxo-de-Valinhos, que produz frutos sem sementes, inviabilizando o melhoramento convencional. Nesse sentido, o melhoramento genético, com o uso de mutagênicos, passa a ser uma linha de pesquisa altamente importante, podendo contribuir enormemente para o desenvolvimento da cultura. Diante disto, o objetivo do presente trabalho foi avaliar seleções mutantes de figueira originadas de plantas formadas por estacas provenientes de gemas irradiadas com raio gama, bem como compará-las com as principais cultivares da cultura em plantio comercial. Utilizou-se de plantas originadas de estacas de 5 cultivares tradicionais de figueira e de cinco seleções de figueiras mutantes (formadas por estacas originadas de gemas da cultivar Roxo-de-Valinhos irradiadas com raio gama, na dose de 30 Gy), cultivadas em espaçamento de 2,5 x 1,5 m. O delineamento experimental utilizado foi o de blocos inteiramente casualizados, contendo 10 tratamentos, com 3 repetições e 5 plantas por parcela. As avaliações foram realizadas a partir do desenvolvimento vegetativo das plantas, bem como as características dos frutos. da análise dos dados, conclui-se que há variabilidade entre as seleções mutantes e destas com as cultivares tradicionais, e que o tratamento PI-189 foi superior à cultivar-padrão Roxo-de-Valinhos em características de grande importância comercial, como número de frutos por planta, massa média por fruto e produtividade, igualando-se nas demais características, mostrando-se, assim, com enorme potencial para posteriores estudos.

Análise da toxicidade no açude Riacho da Cachoeira, Lajes Pintadas (RN): um desafio interdisciplinar

Contamination by complex mixtures of various origins has been explored and studied for decades. Radon is a naturally occurring environmental contaminant that causes carcinogenic effects. These emissions can cause mutations in the lung tissue, which can initiate a carcinogenic process. Thus the dam Creek Falls, located in the municipality of Lajes Pintadas, was chosen for the development of this study, since cancer rates in the region reach 9% of the population annually, with this, the main objective of this study was evaluate the mutagenicity and toxicity of Riacho da Cachoeira damunder the influence of radon. The methodology ecotoxicological tests were performed with Ceriodaphinia dubia, as well as tests with Tradescantia pallida genotoxicologicos and Oreochromis niloticus. To understand how the population of Pintadas Slabs realizes the environment, we performed a study of environmental perception. The test results indicated that the reservoir water is toxic to test organimos exposed, found heavy metals, chloride, total and fecal coliforms as well as radon levels above the maximum allowed under Brazilian law. These results can be justified because it is so complex samples composed of different compounds that interact only with each other or causing synergistic effects. It was concluded that the dam Creek Waterfall, is contaminated with radon, as well as heavy metals, coliforms and chloride, causing toxic effects to the natural community. Thus, further studies should be performed with the human population of the region, to verify that the high rates of cancer in the population of the municipality may be linked to the presence of natural radiation. Thus, it is expected that the competent bodies that administer the municipality of Lajes Pintadas take reasonable steps to minimize risks and ensure the health of the community that still makes use of the weir

Uma nova proposta de antena planar multibanda para comunicações móveis

The great interest observed in wireless communication systems has required the development of new configurations of microstrip antennas, because they are easily built and integrated to other microwave circuit components, which is suitable for the construction and development of planar antenna arrays and microwave integrated circuits. This work presents a new configuration of tapered microstrip antenna, which is obtained by impressing U-slots on the conducting patch combined with a transmission line matching circuit that uses an inset length. It is shown that the use of U-slots in the microstrip antenna conducting patch excites new resonating modes, that gives a multiband characteristic for the slotted microstrip antenna, that is suitable for applications in communication systems that operates several frequencies simultaneously. Up to this date, the works reported in the literature deals with the use of Uslotted microstrip rectangular antennas fed by a coaxial probe. The properties of a linear array of microstrip patch tapered antennas are also investigated. The main parameters of the U slotted tapered microstrip antennas are investigated for different sizes and locations of the slots impressed on the conducting patch. The analysis of the proposed antenna is performed by using the resonant cavity and equivalent transmission line methods, in combination with a parametric study, that is conducted by the use of the Ansoft Designer, a commercial computer aided microwave software well known by its accuracy and efficiency. The mentioned methods are used to evaluate the effect in the antennas parameters, like resonant frequency and return loss, produced by variations of the antenna structural parameters, accomplished separately or simultaneously. An experimental investigation is also developed, that consists of the design, construction and measurement of several U slotted microstrip antenna prototypes. Finally, theoretical and simulated results are presented that are in agreement with the measured ones. These results are related to the resonating modes identification and to the determination of the main characteristics of the investigated antennas, such as resonant frequency, return loss, and radiation pattern

Teorias f(R) de gravidade na formulação de Palatini

In this dissertation, after a brief review on the Einstein s General Relativity Theory and its application to the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological models, we present and discuss the alternative theories of gravity dubbed f(R) gravity. These theories come about when one substitute in the Einstein-Hilbert action the Ricci curvature R by some well behaved nonlinear function f(R). They provide an alternative way to explain the current cosmic acceleration with no need of invoking neither a dark energy component, nor the existence of extra spatial dimensions. In dealing with f(R) gravity, two different variational approaches may be followed, namely the metric and the Palatini formalisms, which lead to very different equations of motion. We briefly describe the metric formalism and then concentrate on the Palatini variational approach to the gravity action. We make a systematic and detailed derivation of the field equations for Palatini f(R) gravity, which generalize the Einsteins equations of General Relativity, and obtain also the generalized Friedmann equations, which can be used for cosmological tests. As an example, using recent compilations of type Ia Supernovae observations, we show how the f(R) = R − fi/Rn class of gravity theories explain the recent observed acceleration of the universe by placing reasonable constraints on the free parameters fi and n. We also examine the question as to whether Palatini f(R) gravity theories permit space-times in which causality, a fundamental issue in any physical theory [22], is violated. As is well known, in General Relativity there are solutions to the viii field equations that have causal anomalies in the form of closed time-like curves, the renowned Gödel model being the best known example of such a solution. Here we show that every perfect-fluid Gödel-type solution of Palatini f(R) gravity with density and pressure p that satisfy the weak energy condition + p 0 is necessarily isometric to the Gödel geometry, demonstrating, therefore, that these theories present causal anomalies in the form of closed time-like curves. This result extends a theorem on Gödel-type models to the framework of Palatini f(R) gravity theory. We derive an expression for a critical radius rc (beyond which causality is violated) for an arbitrary Palatini f(R) theory. The expression makes apparent that the violation of causality depends on the form of f(R) and on the matter content components. We concretely examine the Gödel-type perfect-fluid solutions in the f(R) = R−fi/Rn class of Palatini gravity theories, and show that for positive matter density and for fi and n in the range permitted by the observations, these theories do not admit the Gödel geometry as a perfect-fluid solution of its field equations. In this sense, f(R) gravity theory remedies the causal pathology in the form of closed timelike curves which is allowed in General Relativity. We also examine the violation of causality of Gödel-type by considering a single scalar field as the matter content. For this source, we show that Palatini f(R) gravity gives rise to a unique Gödeltype solution with no violation of causality. Finally, we show that by combining a perfect fluid plus a scalar field as sources of Gödel-type geometries, we obtain both solutions in the form of closed time-like curves, as well as solutions with no violation of causality

Actinic keratosis: a clinical and epidemiological revision

Queratoses actínicas são neoplasias benignas intraepiteliais formadas por proliferações atípicas de queratinócitos com potencial de transformação em carcinoma espinocelular. Desenvolvem-se em áreas fotoexpostas da pele, são induzidas principalmente pela radiação ultravioleta e constituem marcadores de exposição solar crônica. Acometem indivíduos adultos e idosos, de fototipos claros, representando o quarto diagnóstico dermatológico mais comum no Brasil. Danos nas vias de apoptose do epitélio fotoexposto favorecem a proliferação celular e manutenção das lesões. Nesta revisão os autores reúnem os principais dados epidemiológicos sobre a doença e defendem que estratégias de identificação de fenótipos de risco, diagnóstico precoce, tratamento adequado, seguimento clínico, incentivo ao autoexame da pele, fotoeducação e fotoproteção devem ser promovidas, a fim de evitar a evolução das lesões, e também prevenir e diagnosticar neoplasias concomitantes também induzidas pela radiação solar.

Termodinâmica de um gás de fótons no contexto de eletrodinâmicas não-lineares

The objective of this dissertation is the development of a general formalism to analyze the thermodynamical properties of a photon gas under the context of nonlinear electrodynamics (NLED). To this end it is obtained, through the systematic analysis of Maxwell s electromagnetism (EM) properties, the general dependence of the Lagrangian that describes this kind of theories. From this Lagrangian and in the background of classical field theory, we derive the general dispersion relation that photons must obey in terms of a background field and the NLED properties. It is important to note that, in order to achieve this result, an aproximation has been made in order to allow the separation of the total electromagnetic field into a strong background electromagnetic field and a perturbation. Once the dispersion relation is in hand, the usual Bose-Einstein statistical procedure is followed through which the thermodynamical properties, energy density and pressure relations are obtained. An important result of this work is the fact that equation of state remains identical to the one obtained under EM. Then, two examples are made where the thermodynamic properties are explicitly derived in the context of two NLED, Born-Infelds and a quadratic approximation. The choice of the first one is due to the vast appearance in literature and, the second one, because it is a first order approximation of a large class of NLED. Ultimately, both are chosen because of their simplicity. Finally, the results are compared to EM and interpreted, suggesting possible tests to verify the internal consistency of NLED and motivating further developement into the formalism s quantum case

Espectros fractais em sistemas nanoestruturados e cristais fotônicos

The study of the elementary excitations such as photons, phonons, plasmons, polaritons, polarons, excitons and magnons, in crystalline solids and nanostructures systems are nowdays important active field for research works in solid state physics as well as in statistical physics. With this aim in mind, this work has two distinct parts. In the first one, we investigate the propagation of excitons polaritons in nanostructured periodic and quasiperiodic multilayers, from the description of the behavior for bulk and surface modes in their individual constituents. Through analytical, as well as computational numerical calculation, we obtain the spectra for both surface and bulk exciton-polaritons modes in the superstructures. Besides, we investigate also how the quasiperiodicity modifies the band structure related to the periodic case, stressing their amazing self-similar behavior leaving to their fractal/multifractal aspects. Afterwards, we present our results related to the so-called photonic crystals, the eletromagnetic analogue of the electronic crystalline structure. We consider periodic and quasiperiodic structures, in which one of their component presents a negative refractive index. This unusual optic characteristic is obtained when the electric permissivity and the magnetic permeability µ are both negatives for the same range of angular frequency ω of the incident wave. The given curves show how the transmission of the photon waves is modified, with a striking self-similar profile. Moreover, we analyze the modification of the usual Planck´s thermal spectrum when we use a quasiperiodic fotonic superlattice as a filter.