Desenvolvimento de um compósito de espuma rígida de poliuretana de mamona e fibras de sisal para isolação térmica

The search for sustainable technologies that can contribute to reduce energy consumption is a great challenge in the field of insulation materials. In this context, composites manufactured from vegetal sources are an alternative technology. The principal objectives of this work are the development and characterization of a composite composed by the rigid polyurethane foam derived from castor oil (commercially available as RESPAN D40) and sisal fibers. The manufacture of the composite was done with expansion controlled inside a closed mold. The sisal fibers where used in the form of needlepunched nonwoven with a mean density of 1150 g/m2 and 1350 g/m2. The composite characterization was performed through the following tests: thermal conductivity, thermal behavior, thermo gravimetric analysis (TG/DTG), mechanical strength in compression and flexural, apparent density, water absorption in percentile, and the samples morphology was analyzed in a MEV. The density and humidity percentage of the sisal fiber were also determined. The thermal conductivity of the composites was higher than the pure polyurethane foam, the addition of nonwoven sisal fibers will become in a higher level of compact foam, reducing empty spaces (cells) of polyurethane, inducing an increase in k value. The apparent density of the composites was higher than pure polyurethane foam. In the results of water absorption tests, was seen a higher absorption percent of the composites, what is related to the presence of sisal fibers which are hygroscopic. From TG/DTG results, with the addition of sisal fibers reduced the strength to thermal degradation of the composites, a higher loss of mass was observed in the temperature band between 200 and 340 °C, related to urethane bonds decomposition and cellulose degradation and its derivatives. About mechanical behavior in compression and flexural, composites presented a better mechanical behavior than the rigid polyurethane foam. An increase in the amount of sisal fibers induces a higher rigidity of the composites. At the thermal behavior tests, the composites were more mechanically and thermally resistant than some materials commonly used for thermal insulation, they present the same or better results. The density of nonwoven sisal fiber had influence over the insulation grade; this means that, an increaser in sisal fiber density helped to retain the heat

Metalização mecânica de ZrO2 com Ti para brasagem ZrO2/Aço com ligas de adição sem metal ativo

Metal/ceramic interfaces using zirconia have dominated the industrial applications in the last decade, due to the high mechanical strength and fracture toughness of zirconia, especially at temperatures below 300 ºC. Also noteworthy is the good ionic conductivity in high temperatures of this component. In this work joining between ZrO2 Y-TZP and ZrO2 Mg-PSZ with austenitic stainless steel was studied. These joints were brazed at high-vacuum after mechanical metallization with Ti using filler alloys composed by Ag-Cu and Ag-Cu-Ni. The influence of the metallization, and the affinity between the different groups (ceramic / filler alloys) was evaluated, in order to achieve strong metal/ceramic joints. Evaluation of joints and interfaces, also the characterization of base materials was implemented using various techniques, such as: x-ray diffraction, leak test, three-point flexural test and scanning electron microscopy with chemical analysis. The microstructural analysis revealed physical and chemical bonds in the metal/ceramic interfaces, providing superior leak proof joints and stress cracking, in order to a good joint in all brazed samples. Precipitation zones and reaction layers with eutetic characteristics were observed between the steel and the filler metal

Multiplicando veredas entre guimarães rosa e oswaldo lamartine

Universidade Federal do Rio Grande do Norte

Aplicações da teoria da percolação à modelagem e simulação de reservatórios de petróleo

In this thesis we study some problems related to petroleum reservoirs using methods and concepts of Statistical Physics. The thesis could be divided percolation problem in random multifractal support motivated by its potential application in modelling oil reservoirs. We develped an heterogeneous and anisotropic grid that followin two parts. The first one introduce a study of the percolations a random multifractal distribution of its sites. After, we determine the percolation threshold for this grid, the fractal dimension of the percolating cluster and the critical exponents ß and v. In the second part, we propose an alternative systematic of modelling and simulating oil reservoirs. We introduce a statistical model based in a stochastic formulation do Darcy Law. In this model, the distribution of permeabilities is localy equivalent to the basic model of bond percolation

Fases e criticalidade no modelo ashkin - teller de três cores

The usual Ashkin-Teller (AT) model is obtained as a superposition of two Ising models coupled through a four-spin interaction term. In two dimension the AT model displays a line of fixed points along which the exponents vary continuously. On this line the model becomes soluble via a mapping onto the Baxter model. Such richness of multicritical behavior led Grest and Widom to introduce the N-color Ashkin-Teller model (N-AT). Those authors made an extensive analysis of the model thus introduced both in the isotropic as well as in the anisotropic cases by several analytical and computational methods. In the present work we define a more general version of the 3-color Ashkin-Teller model by introducing a 6-spin interaction term. We investigate the corresponding symmetry structure presented by our model in conjunction with an analysis of possible phase diagrams obtained by real space renormalization group techniques. The phase diagram are obtained at finite temperature in the region where the ferromagnetic behavior is predominant. Through the use of the transmissivities concepts we obtain the recursion relations in some periodical as well as aperiodic hierarchical lattices. In a first analysis we initially consider the two-color Ashkin-Teller model in order to obtain some results with could be used as a guide to our main purpose. In the anisotropic case the model was previously studied on the Wheatstone bridge by Claudionor Bezerra in his Master Degree dissertation. By using more appropriated computational resources we obtained isomorphic critical surfaces described in Bezerra's work but not properly identified. Besides, we also analyzed the isotropic version in an aperiodic hierarchical lattice, and we showed how the geometric fluctuations are affected by such aperiodicity and its consequences in the corresponding critical behavior. Those analysis were carried out by the use of appropriated definitions of transmissivities. Finally, we considered the modified 3-AT model with a 6-spin couplings. With the inclusion of such term the model becomes more attractive from the symmetry point of view. For some hierarchical lattices we derived general recursion relations in the anisotropic version of the model (3-AAT), from which case we can obtain the corresponding equations for the isotropic version (3-IAT). The 3-IAT was studied extensively in the whole region where the ferromagnetic couplings are dominant. The fixed points and the respective critical exponents were determined. By analyzing the attraction basins of such fixed points we were able to find the three-parameter phase diagram (temperature £ 4-spin coupling £ 6-spin coupling). We could identify fixed points corresponding to the universality class of Ising and 4- and 8-state Potts model. We also obtained a fixed point which seems to be a sort of reminiscence of a 6-state Potts fixed point as well as a possible indication of the existence of a Baxter line. Some unstable fixed points which do not belong to any aforementioned q-state Potts universality class was also found

Estudo de sistemas complexos com interações de longo alcance : percolação, redes e tráfego

In this thesis we investigate physical problems which present a high degree of complexity using tools and models of Statistical Mechanics. We give a special attention to systems with long-range interactions, such as one-dimensional long-range bondpercolation, complex networks without metric and vehicular traffic. The flux in linear chain (percolation) with bond between first neighbor only happens if pc = 1, but when we consider long-range interactions , the situation is completely different, i.e., the transitions between the percolating phase and non-percolating phase happens for pc < 1. This kind of transition happens even when the system is diluted ( dilution of sites ). Some of these effects are investigated in this work, for example, the extensivity of the system, the relation between critical properties and the dilution, etc. In particular we show that the dilution does not change the universality of the system. In another work, we analyze the implications of using a power law quality distribution for vertices in the growth dynamics of a network studied by Bianconi and Barabási. It incorporates in the preferential attachment the different ability (fitness) of the nodes to compete for links. Finally, we study the vehicular traffic on road networks when it is submitted to an increasing flux of cars. In this way, we develop two models which enable the analysis of the total flux on each road as well as the flux leaving the system and the behavior of the total number of congested roads

Estudo de propriedades críticas em sistemas complexos: método de procura automática em sistemas tipo Ising e percolação de longo alcance

The new technique for automatic search of the order parameters and critical properties is applied to several well-know physical systems, testing the efficiency of such a procedure, in order to apply it for complex systems in general. The automatic-search method is combined with Monte Carlo simulations, which makes use of a given dynamical rule for the time evolution of the system. In the problems inves¬tigated, the Metropolis and Glauber dynamics produced essentially equivalent results. We present a brief introduction to critical phenomena and phase transitions. We describe the automatic-search method and discuss some previous works, where the method has been applied successfully. We apply the method for the ferromagnetic fsing model, computing the critical fron¬tiers and the magnetization exponent (3 for several geometric lattices. We also apply the method for the site-diluted ferromagnetic Ising model on a square lattice, computing its critical frontier, as well as the magnetization exponent f3 and the susceptibility exponent 7. We verify that the universality class of the system remains unchanged when the site dilution is introduced. We study the problem of long-range bond percolation in a diluted linear chain and discuss the non-extensivity questions inherent to long-range-interaction systems. Finally we present our conclusions and possible extensions of this work

Análises estatísticas em redes complexas: propriedades topológicas, críticas e dinâmicas

In this thesis, we address two issues of broad conceptual and practical relevance in the study of complex networks. The first is associated with the topological characterization of networks while the second relates to dynamical processes that occur on top of them. Regarding the first line of study, we initially designed a model for networks growth where preferential attachment includes: (i) connectivity and (ii) homophily (links between sites with similar characteristics are more likely). From this, we observe that the competition between these two aspects leads to a heterogeneous pattern of connections with the topological properties of the network showing quite interesting results. In particular, we emphasize that there is a region where the characteristics of sites play an important role not only for the rate at which they get links, but also for the number of connections which occur between sites with similar and dissimilar characteristics. Finally, we investigate the spread of epidemics on the network topology developed, whereas its dissemination follows the rules of the contact process. Using Monte Carlo simulations, we show that the competition between states (infected/healthy) sites, induces a transition between an active phase (presence of sick) and an inactive (no sick). In this context, we estimate the critical point of the transition phase through the cumulant Binder and ratio between moments of the order parameter. Then, using finite size scaling analysis, we determine the critical exponents associated with this transition

Propriedades críticas de sistemas fora do equilíbrio via simulação Monte Carlo

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Sistemas Nanoestruturados: Heteroestruturas Quasi-Periódicas de Nitretos e Cálculos Ab initio em Polimorfos CaCO3

The physical properties and the excitations spectrum in oxides and semiconductors materials are presented in this work, whose the first part presents a study on the confinement of optical phonons in artificial systems based on III-V nitrides, grown in periodic and quasiperiodic forms. The second part of this work describes the Ab initio calculations which were carried out to obtain the optoeletronic properties of Calcium Oxide (CaO) and Calcium Carbonate (CaCO3) crystals. For periodic and quasi-periodic superlattices, we present some dynamical properties related to confined optical phonons (bulk and surface), obtained through simple theories, such as the dielectric continuous model, and using techniques such as the transfer-matrix method. The localization character of confined optical phonon modes, the magnitude of the bands in the spectrum and the power laws of these structures are presented as functions of the generation number of sequence. The ab initio calculations have been carried out using the CASTEP software (Cambridge Total Sequential Energy Package), and they were based on ultrasoft-like pseudopotentials and Density Functional Theory (DFT). Two di®erent geometry optimizations have been e®ectuated for CaO crystals and CaCO3 polymorphs, according to LDA (local density approximation) and GGA (generalized gradient approximation) approaches, determining several properties, e. g. lattice parameters, bond length, electrons density, energy band structures, electrons density of states, e®ective masses and optical properties, such as dielectric constant, absorption, re°ectivity, conductivity and refractive index. Those results were employed to investigate the confinement of excitons in spherical Si@CaCO3 and CaCO3@SiO2 quantum dots and in calcium carbonate nanoparticles, and were also employed in investigations of the photoluminescence spectra of CaCO3 crystal

Contribuições ao estudo das redes complexas: modelo de qualidade

In this work we analyse the implications of using a power law distribution of vertice's quality in the growth dynamics of a network studied by Bianconi anel Barabási. In particular, we start studying the random networks which characterize or are related to some real situations, for instance the tide movement. In this context of complex networks, we investigate several real networks, as well as we define some important concepts in the network studies. Furthermore, we present the first scale-free network model, which was proposed by Barabási et al., and a modified model studied by Bianconi and Barabási, where now the preferential attachment incorporates the different ability (fitness) of the nodes to compete for links. At the end, our results, discussions and conclusions are presented

A festa da urbe e o nascimento da cidade: A Cidade Antiga como prelúdio da modernidade

This work is a result of an research that aims to understand in which way the work The Ancient City of the French historian Fustel de Coulanges built a moral model for the institutions and for the construction of the French territory in the century XIX understood like The Modern City . Our intention is to present a study on the way like the ancient city it was built, when nationalist of century XIX is taking into account his connections with the space reforms and the discussion in France. In this sense, we go besides the works of the historiography of the century XIX on this subject and of the articles and tests of the beginning of the century XX, when urbanity planner tied the narrative Scientifics of Fustel with the discussion in France of this period and his contribution, through this connection between history and space, with the national education of the individuals and the formation of the French identity. In this way, we understand which History, Nation and Space were the bases of sustenance of the theory of Coulanges about The Ancient City and of the formation of the French territory. Besides, the discussion historiography between Frenchmen and Germans on the origins of his respective nations influenced Coulanges the perspective of narrating a history of the Antiquity, taking into account the cultural approach of the past and the modern Institutions

Encontros entre dança, subjetivação e saúde mental

Taking from starting point the contact with the experience of a dancing body language group at Centro de Atenção Psicossocial (CAPS) II in Fortaleza-CE, aiming to investigate the relationship between what we denominate dancing-dispositive and the process of de-institutionalization of insanity. Based in the philosophy of difference and in the cartographic perspective, we used the concept of dispositive in order to make visible the lines that compose it and the way they tangle in the production of different ways of subjectivation through another form of expression using the body. We followed two fortnight groups of body language recording the conversations that took place in the beginning and in the end of the activities. We also recorded our informal talks with the workshopper, with the psychiatrist responsible for the course of formation of artists of CAPS and the choreographer who was part of the artistic formation of the workshopper aiming to elucidate the body, dance and art conceptions which guided such work. Finally, we interviewed some technicians and we participated of a meeting of the team aiming to understand how that activity was perceived. We observed that the use of certain conception of dance in the field of mental health is in consonance with the the Phychiatric Reform, since it provides another way of dealing with the body, different from that produced by the contention and by the discipline. Nevertheless, we understood that there is a risk that, in some moments, the group being more a place of normalization than one of experimenting other ways of relating with yourself and with the others. We also noted that the dancing-dispositive appears as an important analyzer of the connections established at CAPS, indicating a need of the service to be more opened to the production of new care and harboring strategies, breaking the mental health facility logic of incarceration of life which still persists in the quotidian of that institution

Estudo do comportamento térmico e da luminescência de filmes de quitosana com os íons Eu3+ e Tb3+

Films of chitosan with trivalent lanthanides ions Eu3+ and Tb3+ were respectively prepared in the ratio of 3:1 m/m (chitosan: lanthanide) and 6:1 m/m (chitosan: lanthanide). There were no formations of films in a ratio of 1:1 m/m (chitosan: lanthanides). The films of chitosan with the Tb3+ ion have the same transparent appearance than the pure chitosan films. The film of chitosan with Eu3+ ion has a muddy appearance. These films present good resistance to tear. The appearance of the compounds prepared in ratio 1:1m/m is a white powder. The films and compounds of chitosan were characterized by Elementary Analysis (CHN), Thermal Analysis (TG/DTG) and Spectroscopy of Luminescence. The CHN analysis was made only for compounds prepared in ratio 1:1m/m, suggesting that these compounds possess the formula QUILn.6H2O, where QUI = Chitosan and Ln = Lanthanide. The results of the curves TG/DTG indicated that there are strong interactions between Eu3+ or Tb3+ and chitosan, causing a lesser lost of mass in the films. The luminescence analysis showed that the films of chitosan with the ions Eu3+ and Tb3+ present emissions in the region of the visible one, with bands of the chitosan and of the Eu3+ ion. The luminescence analysis of the compounds of chitosan with the Eu3+ and Tb3+ ions suggest that the chitosan does not transfer into energy to the ions lanthanides, however the chemical neighborhood around of the ion lanthanides breaks the selection rules and, conseqüently the 4f-4f transitions of the lanthanide ions are observed

Estudo dos principais fatores que influenciam na solubilização dos hpas em águas

Polycyclic aromatic hydrocarbons (PAHs) constitute a family of compounds characterized by having two or more condensed aromatic rings and for being a class of substances that are widely distributed in the environment as a complex mixture, being very persistent in the environment due to its low solubility in water. The application of chemometric methods to analytical chemistry has provided excellent results in studying the solubility of PAHs in aqueous media in order to understand the mechanisms involved in environmental contamination. The method consists in analyzing the solubilization of PAHs from diesel oil in water varying parameters such as stirring time, volume of oil added and pH, using a full factorial design of two levels and three factors. PAHs were extracted with n-hexane and analyzed by fluorescence spectroscopy because they have molecular characteristics fluorescent due to the large number of condensed rings and links, and gas chromatography coupled to a mass spectrometer (GC-MS). The results of fluorescence analysis showed that only the stirring time and pH influenced the solubility of PAHs in diesel fuel. How is a non-selective technique for the study of fluorescence was performed on form and semi-quantitative. And for the chromatographic analysis the results showed that the solubility of the different PAHs is influenced differently so that you can classify them into groups by the results of the effects