Este trabalho apresenta uma análise das superfícies e das regiões interfaciais da estrutura nanométrica de TiN sobre o substrato de aço AISI M2 nitretado a plasma com uso de camada intermediária de Ti. O objetivo da investigação foi identificar os principais componentes químicos formados nesta estrutura e como estes estão distribuídos na região de interface filme-substrato. O efeito da pré-nitretação do substrato nas ligações interfaciais foi o foco principal. A nitretação a plasma do substrato foi do tipo brilhante (bright nitriding), ou seja, baixa temperatura (400oC) e mistura pobre em nitrogênio (5% de N2 em balanço com H2) para evitar a formação de camada de compostos. Depois de calibradas as taxas de deposição do TiN e do Ti em substratos de silício, filmes ultrafinos de TiN e Ti (menores que 10 nm), a temperatura ambiente, foram depositados por sputtering reativo nas amostras de aço rápido. A taxa de deposição e a estequiometria foram obtidas por espectrometria de retroespalhamento Rutherford (RBS) e por análises por reações nucleares (NRA). Também foi analisado o perfil de Ti por espalhamento de íons de média energia (MEIS). A caracterização química das superfícies e interfaces das amostras de aço e do sistema composto TiN/Ti/Aço foi realizada por espectroscopia de fotoelétrons excitados por raios X (XPS). As interfaces e os perfis de concentração do Ti e do N, foram analisada por espalhamento de íons de média energia (MEIS) e pelo uso de ressonâncias estreitas na curva de seção de choque (NRP). Os resultados mostraram a formação de nitretos de ferro e de cromo na camada de difusão da superfície nitretada e uma menor quantidade relativa de óxidos e hidróxidos metálicos nesta superfície. No sistema TiN/Ti/Aço, a nitretação do substrato induziu a formação de uma maior quantidade de nitretos de Ti, Fe e Cr nesta estrutura. As análises dos perfis de concentração mostraram que a interdifusão nas interfaces (TiN/Ti e Ti/Aço) foi significativamente intensificada na amostra com substrato de aço nitretado. O efeito da desoxidação promovido pela nitretação a plasma e o incremento da interdifusão interfacial vão ao encontro de uma transição de propriedades mais suave e de uma maior adesão do revestimento duro ao substrato de aço. / This research presents a study about compound formation and interfacial mixing in TiN/Ti nanolayers on plasma nitrided AISI M2 tool steel. The investigation goal was to identify the main components formed by this structure and the effects in the chemical bonding and in the interfacial regions caused by the use of nitriding plasma on the substrate and on the Ti interlayer. The substrate used was bright plasma nitriding to avoid a compound layer formation. Low temperature (400oC) and low-nitrogen mixture (5% of N2, balance H2) were used. After the TiN and Ti deposition rate on silicon substrates were calibrated, thin TiN and Ti films (smaller than 10 nm), were deposited on the steel samples by reactive sputtering at room temperature. The deposition rate and stoichiometry of films were determined Rutherford Backscattering Spectrometry (RBS) and through Nuclear Reaction Analysis (NRA). The profile of Ti was analyzed through Medium Energy Ion Scattering as well. The chemistry characterization of steel surfaces and interfaces samples of TiN/Ti/Steel structure was made through X-Ray Photoelectron Spectroscopy (XPS). Ti e N interfaces and concentration profile were analyzed through Medium Energy Ion Scattering (MEIS) and through the use of Narrow Nuclear Reaction Profiling (NRP). Results showed the formation of Fe and Cr nitrides in the nitrited steel diffusion layer and a smaller quantity, related to metal oxides and hydroxides, on this surface. In the TiN/Ti/Steel system, the nitriding inducted the formation of a larger amount of Ti, Fe and Cr nitrates on this structure. Concentration profile analyses showed interface interdiffusion (TiN/Ti and Ti/Steel) was significantly intensified in the sample with nitrited steel substrate. The effect of the desoxidation promoted by plasma nitriding and the increasing in the interfacial interdiffusion indicate a smoother property transition and a larger hard coating adhesion on substrate.

Factor H (FH) is a 155-kDa plasma protein that regulates the alternative pathway of the complement system. Its 20 CCP modules, of 51-62 amino acid residues each, are linked by short stretches (“linkers’) of three to eight residues. We set out to test the hypothesis that long linkers towards the middle of FH play a role in ensuring that its architecture allows binding sites near its N- and C-termini to engage cooperatively with the main target, C3b, which is the key complement pathway-triggering product of C3 cleavage. In initial work, site-directed mutagenesis was used to test whether two mutations, R53H and R78G, located within CCP 1 and linked to the kidney disease atypical hemolytic uremic syndrome, are functionally deficient. Mutant versions and a native-sequence version of CCPs 1-4 of FH (i.e. FH 1-4) were tested for their ability to act as a cofactor for the FI-mediated cleavage of C3b, and accelerate the decay of the C3 convertase. It was shown that FH 1-4 R53H binds normally to C3b but has no regulatory activity while FH 1-4 R78G binds very poorly and is also deficient in cofactor and decay-accelerating activities. In subsequent work, mutagenesis was used to make the eight-residue CCPs 12-13 linker shorter (SL), or more flexible through introduction of glycine residues (3xGLY), within recombinant (r) module pair FH 12-13, and in rFH 10-15 and rFH 8-15 as well as full-length rFH. NMR showed CCPs 12 and 13 remain intact following mutation of the linker but (in FH 12-13) are more flexibly mutually disposed, as expected. SAXS indicated that both FH 10-15 SL and FH 10-15 3xGLY nonetheless have similar compact structures to native sequence (WT) FH 10-15. On the other hand, FH linker mutants interact with C3b (according to surface plasmon resonance) somewhat less well than WT FH and in the case of FH SL, affinity is similar to that of FH 19-20, i.e. there is no evidence that both C3b-binding sites in this mutant bind to the target simultaneously. Nonetheless, the bacterial protein PspCN boosts binding of linker mutants to C3b by a similar factor (three-to-fivefold) to that observed for FH WT. Thus, while interactions between non-sequential CCPs are important for FH architecture, a bend at the 12-13 linker is needed for full-length FH to adopt a fully biological activity confirmation. The use of EPR for structural studies of rFH and its mutants was explored. Free cysteines were engineered in so they could have spin labels site-specifically attached. Alternatively, a recognition site for transglutaminase was introduced so a spin label could be incorporated. These strategies were applied to rFH 12-13 and rFH 10-15 as a prelude to studies of full-length FH. Several suitably engineered proteins were prepared but only one paramagnetically labeled sample (of FH 12-13) made it for EPR; this yielded results commensurate with the NMR-derived structure. Taken together, these promising data lay the groundwork for a future, potentially very insightful, combined mutagenesis and EPR study of FH architecture and its role in complement activation.

The determination of magnetohydrostatic equilibria usually requires that two of the equilibrium functions be given. as there is usually no a priori basis for specifying the form of these two functions, the functions and the equilibria they determine may be considered random.;In this dissertation, the author reviews a recent statistical method for determining the equilibrium of an axially symmetric cylindrical plasma which is most probable (in the maximum entropy sense) given four global constraints (i.e., energy, magnetic helicity, longitudinal magnetic flux, and longitudinal current flux). Previous results from this model have been limited to non-negative random equilibrium functions (B(,z), J(,z), where B is the magnetic field and J is the current density), and to analytically derived solutions of the determining equations in which one constraint (magnetic helicity) has been relaxed.;The present work extends these results to the fully constrained problem by presenting numerically computed solutions of the governing equations. Some of these solutions are specialized to values of the constraints appropriate to tokamaks. States which are approximately force-free (B = J x const.) are shown to exist as solutions to the most probable state equations.;A further extension of the model is attempted in order to alleviate the restriction to non-negative random equilibrium functions. The extended model is applied to the problem of finding most probable equilibria with reversed magnetic fields. An examination of solutions constrained to different values of energy and magnetic helicity shows a tendency toward low pressure equilibria when the energy-to-helicity ratio is lowered. This result is consistent with the Bessel function model of reverse-field equilibria in which dynamical relaxation of the energy with respect to a fixed magnetic helicity results in pressureless, Bellel function equilibria.;A study is made of the influence of the pinch ratio, an experimental parameter, on the degree of magnetic field reversal in the most probable state model. The dependence of solutions on this parameter is found to be consistent qualitatively with experiments.

For a plasma in the collisionless regime, test-particle modelling can lend some insight into the macroscopic behavior of the plasma, e.g conductivity and heating. A common example for which this technique is used is a system with electric and magnetic fields given by B = {dollar}\delta y{dollar}cx x + xcx y + {dollar}\gamma{dollar}cx z and E = {dollar}\epsilon{dollar}cx z, where {dollar}\delta{dollar}, {dollar}\gamma{dollar}, and {dollar}\epsilon{dollar} are constant parameters. This model can be used to model plasma behavior near neutral lines, ({dollar}\gamma{dollar} = 0), as well as current sheets ({dollar}\gamma{dollar} = 0, {dollar}\delta{dollar} = 0). The integrability properties of the particle motion in such fields might affect the plasma's macroscopic behavior, and we have asked the question "For what values of {dollar}\delta{dollar}, {dollar}\gamma{dollar}, and {dollar}\epsilon{dollar} is the system integrable?" to answer this question, we have employed Painleve singularity analysis, which is an examination of the singularity properties of a test particle's equations of motion in the complex time plane. This analysis has identified two field geometries for which the system's particle dynamics are integrable in terms of the second Painleve transcendent: the circular O-line case and the case of the neutral sheet configuration. These geometries yield particle dynamics that are integrable in the Liouville sense (i.e. there exist the proper number of integrals in involution) in an extended phase space which includes the time as a canonical coordinate, and this property is also true for nonzero {dollar}\gamma{dollar}. The singularity property tests also identified a large, dense set of X-line and O-line field geometries that yield dynamics that may possess the weak Painleve property. In the case of the X-line geometries, this result shows little relevance to the physical nature of the system, but the existence of a dense set of elliptical O-line geometries with this property may be related to the fact that for {dollar}\epsilon{dollar} positive, one can construct asymptotic solutions in the limit {dollar}t \to \infty{dollar}.

No description available.

The goal of nuclear fusion research is to confine a deuterium-tritium plasma at a sufficiently high temperature (15 keV) and density (3 $\times$ 10$\sp{20}$ m$\sp{-3}$) for a sufficient length of time (1 sec) to produce net fusion power. One means to attain the required plasma confinement is to embed the plasma within a magnetic field. The global structure of this magnetic field determines the variation of magnetic field strength within the surfaces of constant plasma pressure. This field strength variation in turn determines many of the stability and confinement properties of the plasma. This dissertation gives the first detailed exposition of the spectrum of possible forms for magnetic field strength corresponding to toroidal plasma equilibria, both within any three-dimensional volume and within any two-dimensional surface of constant plasma pressure. Constraints due to the toroidicity of the configuration and the divergence-free property of the magnetic field are found to limit the form of the field strength. Three-dimensional stellarator equilibria corresponding to a particular form of the magnetic field strength are especially interesting. These "quasi-helically symmetric" equilibria are non-axisymmetric, toroidal configurations in which the magnetic field strength depends on only one angular coordinate, instead of two, within the constant plasma pressure surfaces. Unlike conventional stellarator equilibria, these quasi-helically symmetric equilibria exhibit the favorable confinement properties of axisymmetric tokamak equilibria. We show that stellarators with exact quasi-helical symmetry do not to exist, but that good approximations can be found.

A Monte Carlo code has been developed which very efficiently calculates plasma parameters, such as currents, potentials and transport coefficients for a fully three dimensional magnetic field configuration. The code computes the deviation, f, of the exact distribution function, f, from the Maxwellian, {dollar}F\sb{lcub}M{rcub},{dollar} with {dollar}\psi{dollar} the toroidal magnetic flux enclosed by a pressure surface and H the Hamiltonian. The particles in the simulation are followed with a traditional Monte Carlo scheme consisting of an orbit step in which new values for the positions and momenta are obtained and a collision step in which a Monte Carlo equivalent of the Lorentz operator is applied to change the pitch of each particle. Since the {dollar}\delta f{dollar} code calculates only the deviations from the Maxwellian rather than the full distribution function, it is about 10{dollar}\sp4{dollar} times as efficient as other Monte Carlo techniques used to calculate currents in plasmas.;The {dollar}\delta f{dollar} code was used to study the aspect ratio and collisionality dependence of the bootstrap current and two Fourier components of the Pfirsch-Schluter current. It was also used to calculate electric potentials within magnetic surfaces due to the explicit enforcement of the quasi-neutrality condition. The code also calculated transport coefficients for the ions and electrons under various conditions. The agreement between the values predicted by the code for the plasma currents and analytic theory is excellent. The transport parameters calculated for the ions and electrons are in qualitative agreement with values predicted from neoclassical transport theory, including transport induced by a toroidal ripple. The in-surface electric potentials induced by explicitly enforcing the quasi-neutrality condition are too small to significantly enhance transport across the magnetic surfaces.

Orientador: Carlos Renato Zacharias / Banca: Ernesto Vieira Neto / Banca: Alvaro Jose Damião / Resumo: Este trabalho trata da simulação da ótica do olho humano, em especial a determinação do perfil de índices de refração do cristalino. Mostramos que a hipótese de índice de refração constante, para os meios óticos, não é adequada quando o objetivo é minimizar aberrações e se fazer um estudo da imagem formada na retina. Desenvolvemos um código computacional que utiliza a técnica do Traçado de Raio (ray tracing) acoplada a um processo de busca e otimização (recozimento simulado), visando determinar o perfil de variação dos índices de refração do cristalino, com a condição de minimização das aberrações. A parametrização do modelo foi baseada em resultados da Literatura e utilizamos faces asféricas (parabólicas). Para validar nosso modelo, comparamos nossos resultados com outros modelos existentes, e verificamos a qualidade da imagem formada na retina / Abstract: This work deals with the human eye optics simulation, focusing in the lens refraction index profile. We show that the hypothesis of constant refraction index, for the lens, is not adequate when the objective is minimize aberrations and to study the image formed in the retina. We developed a computational code that uses the ray tracing technique coupled to a search and optimization algorithm (simulated annealing), seeking to determine the profile of the refraction index for the crystalline lens that minimize the aberrations. The model's parametrization was based on Literature results and we implemented aspherical faces for the lenses. In order to validate our results, we compare with those in the Literature, and verify the image quality formed on the retina / Mestre

An experimental study was carried out on Rayleigh-Benard convection in Couette flow in a horizontal annulus of water. Measurements of heat and momentum fluxes and observations of plan form were made in the low Rayleigh number (Ra) range from 5 $\times$ 10$\sp3$ to 8 $\times$ 10$\sp4$, and in the Reynolds number (Re) range of 10 to 90 to study the effect of shear on plan form and fluxes. Measurements of heat and momentum fluxes were made in the turbulent range of Rayleigh number from 2 $\times$ 10$\sp5$ to 5 $\times$ 10$\sp7$, and for Reynolds numbers in the range of 40 to 350 to study the effect of shear on momentum flux at high Rayleigh numbers. / In the low Rayleigh number range, with Reynolds numbers in the range from 35 to 86, longitudinal rolls are observed at low Rayleigh numbers and they become unstable as the Rayleigh number is increased. A previously unknown result is that the wave number of these longitudinal rolls increases as the Reynolds number is increased. Instabilities of longitudinal rolls are found to be both wavy and cross-roll. Wavy rolls with cross-roll disturbances are found to be stable in most of the parameter space for $Ra > 4\times 10\sp4$. Discrete slope increases in both the heat and momentum flux curves are observed at the transitions where the longitudinal rolls become unstable. / At high Rayleigh and Reynolds numbers, the Nusselt number (Nu) is observed to depend on Rayleigh number to the 0.33 $\pm$ 0.04 power. Curves of Nu vs Ra at high Re lie slightly below corresponding curves at lower Re. The dimensionless momentum flux (Mo) is observed to have different linear dependence upon Nusselt number in different parts within the parameter space. Curves of Mo vs Nu at high Re are well below curves at lower Re. Slopes of these curves decrease with increased Nusselt number and at the highest range of Rayleigh and Reynolds number, the slope becomes negative. / Source: Dissertation Abstracts International, Volume: 52-10, Section: B, page: 5170. / Major Professor: Ruby Krishnamurti. / Thesis (Ph.D.)--The Florida State University, 1991.

No description available.