RCAAP Repository

In this work, we investigate in parallel physical and mathematical aspects inherent to the problem of confinement of massless Dirac fermions in graphene nanostructures. In a low energy approach, we propose models to describe confining systems in graphene and study how the choice of boundary conditions of the problem - or, equivalently, of domains of the Dirac operator - affects the physical properties of such systems. In this scenario, we concentrate essentially on the study of the physical behavior of graphene nanorings and nanoribbons in response to aspects such as topology, edge and interface geometry and interactions with external fields. At the same time, a rigorous investigation concerning formal aspects of the problem and the way that they manifest themselves physically is also performed. In light of the theory of linear operators on Hilbert spaces, we analyze the role played by the notion of self-adjointness in the problem and establish sets of boundary conditions physically acceptable in graphene, which mathematically corresponds to the definition of self-adjoint extensions of the Dirac Hamiltonian from the continuum description. Sets proposed in the treatment of some studied configurations are approached in this context. In addition, we present a particular study in which we examine the influence of topological defects on the physics of massive fermions in graphene in the presence of Coulomb and uniform magnetic fields.

Investigating the stability and electronic structure of nanomaterials is essential for their application in electronic devices. In this thesis were analysed two types of nanostructures, a derivative of h-BN and the other of graphene. This analysis was performed using first-principles calculations by Density Functional Theory (DFT), implemented by the SIESTA code. First we investigated two kinds of stacks of h-BN bilayer with impurities and by means of the calculation of interaction and formation energies was identified the most stable bilayers, both due to the nature of the stack and to the type impurity introduced. We also note that the combination of these two effects cause considerable variations in the gaps of energy and impurity. We also use an electric field perpendicular to the plane of the bilayer and observe different changes in the electronic structure related to the permanent electric dipole moment of each nanostructure. The second nanomaterial investigated in this work, the Carbon bicones have been proposed based on the experimental observation of nanocones. The possibility of bicones are experimentally obtained was analyzed by comparing the stability of these nanostructures with existing cones. It was found that some of them are as stable as the cones, which, at least theoretically, enables the synthesis of these nanomaterials. The effect of the electric field and impurities on the electronic structure of bicones were also analyzed, resulting in significant changes in the state density, evidenced by the emergence of new states near the Fermi level

The objective of this research is to evaluate the productive characteristics of yam, the percentage of tubers with symptoms of nematode attack on tubers and foliar N as a function of subdivision nitrogen. The experimental delineation that we used was randomized blocks with fifteen treatments with four repetitions. The treatments were represented by the following portions of nitrogen (100% on the plantation; 100% at 60 days after the plantation (DAP); 100% at 90 (DAP); 100% at 120 DAP; 50% on the plantation; and 50% at 60 DAP; 50% on the plantation and 50% at 90 DAP; 50% on the plantation and 50% at 120 DAP; 33% on the plantation and 33% at 60 and 33% at 90 DAP; 33% on the plantation, 33% at 90 and 33% at 120 DAP; 33% at 60, 33% at 90 and 33% at 120 DAP; 50% at 60 and 50% at 90 DAP; 50% at 90 and 50% at 120 DAP; 33% at 60, 33% at 90 and 33% at 120 DAP; 50% at 60 and 50% at 120 DAP; and 33% on the plantation, 33% at 60 and 33% at 120 DAP). Each subdivision there were 40 plants, and they were 1.2 x 0.6 m away, one from each other, and all of them were considered useful. The supplying of nitrogen of 100% at 90 DAP showed the greatest length of tubers that measured 25.33 cm, following the subdivisions of 50% on the plantation and 50% at 120 DAP (25.10 cm). The average mass of commercial tubers was superior only on the subdivision of nitrogen of 33% on the plantation, 33% at 60 DAP and 33% at 90 DAP reaching the maximum value of 2.23 kg. The subdivision of nitrogen of 50% at 60 DAP and 50% at 90 DAP provided the highest total productivity and commercial of tubers, 21.7 and 18.9 t ha-1, respectively. The maximum percentage of tubers with attack symptoms of nematodes (dried bark and thick bark) they were 53% and 94%, respectively, obtained when the nitrogen was applied 100% at 60 DAP and 100% on the plantation. When the nitrogen was divided in 33% at 60 DAP, 33% at 90 DAP and 33% at 120 DAP; and 50% on the plantation and 50% at 90 DAP, we did not observed any tubers with the attack symptoms of nematodes. For the content of N in the leaves, we did not see any difference among the treatments.

Papaya crop (Carica papaya L.) presents high expenses with agricultural supplies and pesticides showing the necessity of the use of alternative products such as bovine biofertilizers aiming to reduce costs and environmental damages. Therefore, an essay was done during May/2004 to April/2006, in the city of Remígio, State of Paraíba, to evaluate the bovine biofertilizer effects when applied on soil as a liquid and in combination with mineral fertilization with NPK, on the growth, yield, post-harvest quality of fruits, mineral nutrition of papaya and soil fertility. The experimental design was randomized blocks, with three repetitions and four plants per parcel, using 5x2+2 factorial arrangement referring to doses 0.0; 0.8; 1.6; 2.4 and 3.2 L plant-1 of bovine biofertilizer, with and without mineral fertilization with NPK and additional treatments referring to soil without biofertilizer, without limestone and with biofertilizer on medium dose and without limestone. The biofertilizer was applied 30 days before the transplanting and every 60 days until the end of cropping. According to the results, the growths in height and stem diameter were appropriate, showing superiority on soil with bovine biofertilizer and mineral fertilization. Productivity was low, but significantly higher on treatments with organic matter and NPK. Fruits from treatments with biofertilizer and without NPK had highest pulp contend, highest levels of soluble solids, highest firmness and lowest peel mass. Plants in the beginning of fructification were nutritionally balanced in nitrogen, phosphorus, potassium, magnesium, boron and zinc but had deficiency in calcium, copper, iron and manganese. The biofertilizer without NPK, promoted higher increases of pH, organic matter and calcium and accented and greater reductions of aluminum and hydrogen contents on soil, when compared to treatments that received application of mineral fertilization.

Castor bean (Ricinus communis L. - Euphorbiaceae) is an oilseed metabolism of C3, rustic, resistant to drought, probably originated in Ethiopia, cultivated in a wide latitude because it has good adaptative capacity. The commercial application of culture is broad in agriculture and industry, being the oil and intake its main products. Given the environmental changes underway, aggravated by increased consumption of fossil fuels, many biochemical and physiological impacts may affect the productivity of important crops, such as castor bean. So, the main goal of this project was to evaluate biochemical and physiological impacts on castor bean in response to high temperature and increased CO2. The experiment was conducted in Phytotron located at Embrapa Algodão, in 2010. We adopted a experiment completely randomized experimental design with four treatments in a factorial combination of two temperatures (30 and 37ºC) and two levels of CO2 (400 and 800 ppm), with four replicates, obtained in five surveys over the cycle, comprising 80 sample units. The growth analysis proceeded as well as the quantification of photosynthetic rate, transpiration, stomatal conductance, electrolyte leakage, accumulation of solutes in symplasm, photosynthetic pigments and soluble carbohydrates. The increase concentration of atmospheric CO2 and temperature elevation benefited to cultivate in the early stages of growth, however, as the phenological cycle progressed both factors, independently of the majority of variables, they acted negatively on the biochemistry and physiology of the castor bean, which showed a reduction in growth rate, decrease in net photosynthesis, transpiration, stomatal conductance and levels of chlorophyll a, b, and total; accumulation of solutes in simplasma, reducing the osmotic potential, and soluble carbohydrates in the roots.

The aim of this study was to evaluate the behavior of peanut (Arachis hypogaea L.) variety BR-1 under different periods of application of organic sources. The experiment was conducted in a greenhouse without temperature control, at the headquarters of EMBRAPA /CNPA, Campina Grande, from October 2009 to March 2010. The treatments were distributed in 4 x 3 factorial arrangement, consisting of four periods of manure application (0, 15, 30 and 45 days before sowing) and three organic sources (manure cattle, goat and poultry) with four replications in completely randomized design. Peanuts have a significant effect on age assessment in main stem length, leaf area and number of branches, was also significant in interaction between age assessment with organic sources applied to the last variable. Regarding of the peg not reach the ground, number of pods produced and root dry matter were influenced significantly by the organic sources applied, while the number of normal pods and shoot dry matter showed a significant effect for treatments, both in times of application and organic sources. The use of poultry manure as organic source provided higher biomass of peanut. The peanut has benefited from fertilization with poultry manure to produce more normal pods and, consequently, increased production of pods. The peanut production was negatively influenced by the use of poultry manure, goat manure and cattle manure before sowing.

In this Dissertation we’ll consider a scalar field theory where the breaking of Lorentz symmetry is present. Basically we will adopt the Ho˘rava-Lifshtz theory. We’ll study the modifications that an anisotropy in space-time produces in the Casimir effect. Let’s deal with a massless real scalar field in two distinct situations: between parallel plates and inside a two-dimensional rectangular box. In both cases we will adopt specific boundary conditions on the field. As we shall see, the Casimir energy and force strongly depends on the parameter associated with the breaking of Lorentz symmetry.

Here we present a systematic analysis of the dynamics in the frequency of semiconductor lasers in systems under orthogonal optical feedback or external injection, with and without frequency discriminator. We measure the parameter of proportionality between the change of frequency and the power level of the orthogonally polarized light injected into the cavity. We perform an application of this injection technique for frequency sweep that allows varying the frequency in a range of tens of GHz and apply it in an experience of spectroscopy. This technique allows frequency sweep without changing the main laser power, which is fed by another, control laser, whose wavelength is di erent from the principal. We have analyzed the dynamics of the semiconductor laser frequency subject to orthogonal optical feedback and injection in a con guration where a di raction grating works as a spectral lter. Using a di raction grating as frequency discriminator in these systems, we observe a dynamical behavior in the laser emission frequency.

We developed a general formalism for models described by one real scalar led, in two dimensional space-time, perturbed by a function which modi es the standard dynamics also deforming the potential. We consider starting models which has stable static solutions. Our formalism makes possible to obtain perturbed static solutions, its energy density and energy, and to examine the corresponding linear stability. We work with three distinct forms of perturbation: one modifying the dynamics, other deforming the potential, and another as a product acting in both ways. Particularly, if we have only the potential perturbation, we show that the perturbed static solutions is always stable. Otherwise, we can stabilize the perturbed solution choosing the sign of the parameter , adequately. We consider some speci c forms of the perturbation function, and illustrated with several examples.

We investigate some non-relativistic quantum phenomena, such topological phases and Landau quantization, in a non-commutative quantum mechanics context and in a Lorentzsymmetry violation regime. We present these e ects considering the quantum mechanics of neutral particles systems submitted to electromagnetic elds. In this sense we use the term \analog of e ect". Under certain conditions to the elds con guration, we can nd quantized energy levels to a system of neutral particles coupled to a electromagnetic eld. Another analog e ects may be obtained if we consider duality transformations, such the Heaviside duality transformations. In the Lorentz-symmetry violation context, we nd some e ects related to the background that controls the breaking of vacuum isotropy. Thus we obtain interesting contributions to the Anandan phase. In the same context, we realize the Landau quantization to neutral particles in a Lorentz-invariance breaking framework. As another way of Lorentz-symmetry violation, we study topological phases for neutral particles systems taking account the non-commutativity of the coordinates of space and phase space. Also we investigate a analog of Landau quantization to neutral particles in the non-commutativity context. Since we have found the wave functions related to the Landau levels, we construct a analog of the quantum Hall e ect to neutral particles submitted to electromagnetic elds. We also consider a analog of quantum Hall e ect in a neutral particle system submitted to Lorentz-symmetry breaking background.

This dissertation is the result of the project for the development and automation of highprecision refractometers, which is to obtain the refractive index of liquids with an accuracy of one part in 106. Some interferometric measurement techniques, methods of measurement and movement control were studied during the development of this project. Deionized water was used as object of study. There are more bibliographic source with measurements in distilled water than deionized water but both are considered pure, and properties are quite similar, although they have different specific applications. The thermo-optical analysis of pure water with high accuracy allows the observation of anomalous behavior in the refractive index curve at temperatures above 36 C above, and such behavior can be observed with few measurements using equipment described here.

This dissertation deals with localized solutions in several dimensions. Initially, we review some topics in classical theory of fields by using scalar fields both in flat and curved spacetime. Here they are: kinks, lumps, vortices, monopoles, dyons, cosmology with scalar fields and branes modeled by scalar fields. After this, we present some original results. Firstly, by introducing a real or integer parameter in the models, we study a way to go from kinks to compactons in models with standard dynamics and show how the procedure works in the braneworld scenario. Finally, by using the deformation method, we present new models that support compact structures and then study their linear stability.

The fact that the universe is expanding with acceleration and that only 5% of its content of matter is baryonic suggests, in principle, the possibility of new alternatives to Einstein’s theory of gravity, as proposed throught the last years. Among them, the so called f(R) theories received a great deal of attention. In this dissertation, we will present these theories in two main formulations and study some solutions, specially, the spherical and axially symmetrical ones. Our aim is to show that such f(R) theories do not satisfy the observational constraints related to the solar system, and as a consequence of this, are not good candidates to substitute Einstein’s theory of gravity. Their results, however, are important to increase our knowledge related to alternative gravitational theories. We will also consider a solution which corresponds to a global monopole in f(R), and apply a method due to Newman and Janis to construct the corresponding solution, with rotation.

The Standard Model of elementary particles has been verified by all experimental tests up to the present moment. However, theoretical and experimental evidences guarantee us that this model is not the final one that describes the fundamentals interactions. In this way, the aim of this work is to develop model based on the gauge group (3)⊗(3)⊗ () (331 model), a simple extension of the gauge group of the Standard Model, which solves some problems not covered by this model. There are many versions of 331 model well-founded, one of these is the minimal version, which leptonic content is identical to the Standard Model. In the minimal 331 model, the scalar sector is formed by three triplets and one sextet of scalars, which leads to large amount of interactions, so this proposal complicates the phenomenology of the scalar sector. In my work, we shall show that the structure of the minimal 331 model can be constructed with only two triplets. In relation to the later model, our model presents some advantages, like making the phenomenology of the scalar sector more tractable.

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The castor bean plant (Ricinus communis L.) is a diploid specie that have chromosomes in number of 2n=2x=20. The castor bean plantlets are hard to be in vitro regenerated because its recalcitrance requires a good in vitro regeneration protocol. The aim of this work was to develop an in vitro and ex vitro polyploidy induction protocol for castor bean (Ricinus communis). Experiments were conducted in Tissue Culture Laboratory of Agricultural Sciences Center from Universidade Federal da Paraíba, Campus II, Areia – PB. Castor bean seeds of variety E1P17 A/B were utilized. In the 1 experiment, the explants had been inoculated along eight different nutritive mediums of Margara (N5Ca, N30Ca, N30K, N15K, N15Ca, N45K, N5K, N30NH4), in the 2 experiment, in médium N5Ca with 6 sucrose concentrations (0, 1,0, 2,0, 3,0, 4,0 e 5,0%,), in the 3 experiment, the plantlets had being added in Trifluralin solutions with 0, 5, 10, 15, 20, 25 μM concentrations for 16 hours, and in the 4 experiment was applied a Trifluralin solution (10 M), which treatments were T0 (no application), T1 (only one application), T2 (two applications) e T3 (three applications) over the apical meristem of the plantlets. Therefore, based on these experiments results, the conclusion is that it is possible to propagate in vitro castor bean plant utilizing N5Ca medium of Margara and sucrose by 3% had shown the best morphogenetic result. For in vitro induction of the castor bean polyploidy, might be tested less than 10 M concentrations or reduce exposition time for 16 hours; and morphological variations are important at polyploidy plants identification in castor bean plants.

A coordinate system has the function to locate the space-time events with respect to a reference system. The construction of the coordinate system depends crucially on the notion of simultaneity associated with the reference. However, there is no natural way, or privileged, set concurrency for non-inertial reference frames, even in Minkowski spacetime. Each procedure leads to different coordinate systems. In this paper, we discuss some methods well known in the literature. We studied the coordinates Rindler, Fermi-Walker radar coordinates and emission coordinates (or GPS). The Rindler coordinate system is one of the prominent systems because it allows to simulate some properties of the geometry of the black hole in a flat space-time. The Rindler coordinates are associated with a family of uniformly accelerated observers who obey the relationship a = (1 / ρ), where is the actual acceleration of the observer and ρ its initial position with respect to some inertial reference system. In this paper, we propose a method for constructing coordinate systems suitable for observers whose acceleration depends on the initial position of the general form a = a (ρ) using this physical principle of locality. The Rindler coordinate system appears as a feature of our generalization. Other particular cases allow us to discuss the relationship between the non-Euclidean geometry of space sections and accelerated reference frames, as was originally proposed by Einstein. Moreover, with the generalization can simulate the behavior of static observers both near the horizon of a black hole, which are subject to a kind of acceleration field (ρ) = 1 / ρ, as in remote areas, for which the (ρ) = 1 / ρ2. In the latter two cases, ρ is from the accelerated observer to the event horizon. With the intention of analyzing the effects of instantaneous acceleration of the rate of atomic clocks, we consider a free massive particle in a box of infinite walls, which is drawn by observers of Rindler. We assume that the particle obeys the Klein-Gordon equation and so we found the frequencies of the stationary states of the system. The transitions between the stationary states are used to set a default frequency for our atomic clock toy. Comparing the accelerated system power spectrum with the energy spectrum of a similar system in an inertial frame, we determined the influence of instantaneous acceleration of the rate of atomic clocks.

Native palm trees belong to Arecaceae family and are among the most useful plant resources for the Amazon man. Despite the great diversity and utilities, few species can be considered economically important, being necessary to perform more comprehensive studies on quality for species not yet explored. This study aimed to evaluate the quality, bioactive compounds and functional potential of native fruit and palm oils derived from Amapá. We evaluated bacaba, buriti inajá, pupunha and tucumã fruits and oils. Initially, there was characterized both physical and physicochemical of fruit, then evaluated bioactive compounds and total antioxidant activity by ORAC methods, DPPH and β-carotene / linoleic acid. Subsequently, the oils were extracted by Soxhlet and held a full characterization of their major and minor components by gas chromatography and high performance liquid chromatography, were also evaluated their physicochemical characteristics, oxidative stability in Rancimat equipment, unsaponifiable matter and polar compounds. Among the physical characteristics of the fruits, the pupunha palm stands out for its high yield (76,38 %). In physicochemical tests, were observed, among others, high levels of starch in pupunha and inajá (24,89 and 14,49 %, respectively) and total pectin (overall mean 0,81 %). The fruits of palm trees stood out by the high content of PET, especially bacaba and tucumã (941,56 and 158,98 mg of galic acid.100g-1, respectively), total carotenoids in tucumã and buriti (7,24 and 4,67 mg 100g-1, respectively) and anthocyanins in bacaba (80,76 mg 100g-1). As for the antioxidant capacity, bacaba had the highest total antioxidant activity by ORAC method (194,67 μM Trolox.g-1), DPPH (47,46 g-1 pulp.g DPPH) and β-carotene / linoleic acid (92,17 % I.O). Bacaba, inajá, buriti, tucumã and pupunha oils, presented percentages of fatty matter about 38, 35, 28, 26 and 17 %, respectively. Buriti, bacaba and tucumã oils presented a high content of unsaturated fatty acids with more than 73, 70 and 67 %, respectively, for triglycerides, in general, there is a predominance of species with 50, 52 and 54 carbon atoms identified as (POP, POO and OOO). In referring to the minor compounds, sterols are present in significant amounts in all samples, particularly in pupunha and tucumã oils (4456 and 2708 mg.kg-1), the tocopherols have been found in larger quantities in buriti and tucumã oils (1567 and 483 mg.kg-1), for the carotenoids, the β-carotene group showed 90% higher concentrations of oil, and the tucumã has the highest concentrations (1222,33 mg.kg-1) followed by buriti, pupunha and inajá. By physicochemical characteristics obtained, as low levels of acidity (<2,4 %) and peroxide (<12,0 meq O2.kg-1), unsaponifiable matter values below 2,0 %, great stability toward oxidation and polar compounds between 3,3 and 5,2 %, oils studied here showed little change. Both fruits and oils exhibited excellent quality characteristics, as well as proved nutritional potential.

In this thesis, we investigate by the first time the impact of non-inertial effects associated with the rotation of the reference system on charged and neutral particles confined by a quantum ring, which is described by the potential of Tan-Inkson. The contribution of the rotation is introduced by its coupling with angular momentum of the system. We show that the rotation is introduced via a non-minimum coupling to the kinetic part of the Hamiltonian describing the quantum dynamics of systems studied here. Thus, we show that non-inertial effects of the rotation induce on the quantum properties of the particles similar effects generated by a magnetic field. We also investigated the contribution of a screw dislocation on the physical properties of the particles. The topological defect contributes as a torsion source, presenting a contribution similar to the Aharonov-Bohm flux. Besides charged particles (electrons and holes), we also study the effects of rotation on neutral particles in three different scenarios: a neutral particle with a permanent magnetic dipole moment coupled by the Aharanov-Casher interaction; a neutral particle with a permanent electric dipole moment coupled by the interaction proposed by He-McKellar-Wilkens and a neutral particle with an electric dipole moment induced by the field configuration proposed by Wei-Han-Wei. In all three cases it is shown the similarity between the neutral and charged particles. We analyze the non-relativistic quantum dynamics of these particles by solving the Schrödinger equation. In addition to the energy spectrum and wave functions, we calculate the persistent current and the magnetization for the four systems studied here, and we also analyzed, from the expression for the persistent current for quantum rings, the limit case for quantum dots.

The difficulty of implementing no tillage in the Northeast region of Brazil occurs due to low rainfall, which limits the plant growth and high rates of decomposition. In the Brejo Paraibano microregion, beyond this aspect, another problem is related to changes in the use of soil, without considering their potentialities and limitations, which provided serious damage to conservation. In order to select cover crops for no tillage and understand the soil degradation due to changes in use, was implanted two experiments completely randomized. The experiment of cultural residues was conducted in the Chã of Jardim farm, of Center of Agrarian Sciences of UFPB, and the treatments consisted of three residues of grass species (Brachiaria decumbens), corn (Zea mays) and sorghum (Sorghum bicolor) and three legumes species: pigeon pea (Canavalia ensiformis), guandu (Cajanus cajan) and leucena (Leucaena leucocephala). The residues were placed in litter bags and placed in the experimental field under the litter, in the presence and absence of nitrogen. The experiment about use of soil was conduced in three systems: native secondary forest, cultivation of sabiá (Mimosa caesalpiniaefolia) and pasture (Brachiaria decumbens). In each area, soil samples were collected at four depths for physical and chemical analisys, fractionation of organic matter and root density. The physical analisys consisted of the separation of aggregates size, grain size, density and total porosity of soil. The chemical ones consisted of determining the pH and concentration of calcium, magnesium, phosphorus, potassium, sodium, aluminum and C. The organic matter was fractionated into fulvic acid fraction (FAF), humic acid fraction (HAF) and humin (HUM). They were quantified deposition and accumulation of litter and its rate of decomposition in areas of woodland and thrush. In the pasture, one evaluated the production of forage. In the case of crop residues, it was observed that the rate of decomposition of the grass is slower than that of legumes, however, this rate is equivalent in the last months of the evaluated year. The grasses showed no differences, but the guandu showed slower rate of decomposition amongst the legumes. Nitrogen fertilization did not affect the waste decomposition rate. In the case of the changes in the use of the soil, the amount of clay, DMPAs, DMPAu and the relationship DMPAu / DMPAs and porosity showed higher values in the area under forest. The soil density was lower in the area under forest. The development of roots was higher in areas under forest and pasture. The waste disposal was greater in the area under sabiá and the N, P and K were higher in these residues, which shows the sabiá capacity in nutrient cycling. The accumulation of litter in the soil was higher in the area under forest. The decomposition rate of the waste was 48% in area under sabiá and 40% in that one under forest. The percentage of C, H + Al, Al, and CTC potential and aluminum saturation (m) are higher in the soil in the area under forest. The soil pH, the base saturation (V) and the concentrations of Na and K are similar in areas under pasture and under sabiá and larger than that under forest. The percentages of Ca, Mg and available P and SB and effective CTC did not differ among the studied areas. The C of the soil is best preserved in the area under forest in function of higher levels in HAF and HUM fractions and the lowest ratio EA / HUM. In turn, the replacement from the grass for sabiá begins to recover the levels of C lost in the area under pasture, with intermediate fraction values of HAF and HUM, demonstrating the sabiá ability to recover soil quality.