Métodos geofísicos aplicados a prospecção mineral na região do Igarapé Chega Tudo, Maranhão - Brasil

O presente trabalho de prospecção geofísica abrange o levantamento de uma faixa de direção NW-SE, desde o local denomina do Chatão, à margem direita do rio Gurupi, até 5 km além de Chega Tudo, no estado de Maranhão. Esse levantamento foi feito em travessas perpendiculares àquela faixa, a qual constitui uma extensa zona de falha. Os trabalhos de geofísica de campo, envolvendo os métodos magnético (campo total), cintilómétrico, eletro-resistivo (Schlumberger, Wenner e Half-Schlumberger) e E.M. (Slingram), foram realizados em duas etapas: a) levantamento de reconhecimento em uma área de 22 km², onde foram aplicados magnetometria e cintilometria e b) levantamento de detalhe em uma área de 3,50 km², onde foram aplicados eletro-resistividade e E.M. Os objetivos principais deste trabalho foram determinar e localizar as principais feições estruturais e geo-elétricas associadas às zonas mineralizadas, e selecionar, entre os métodos geofísicos empregados, qual o de melhor poder resolutivo na indicação de veios de quartzo em sub-superfície, possivelmente associados à mineração de ouro. O método magnético indicou uma anomalia principal no lado NE da área de reconhecimento, enquanto que o cintilométrico apresentou somente o valor do "background" da região. Por isso o método cintilométrico não será discutido nesse trabalho. Com os métodos eletro-resistivo e E.M. foram observadas várias anomalias ao longo de toda a área de detalhe. A interpretação dos dados de magnetometria e de eletro-resistividade foi realizada com técnicas computacionais, enquanto que para a dos dados eletromagnéticos foram empregados diagramas de fase. Os resultados apresentam uma estreita correlação das anomalias magnéticas e eletro-resistivas com a zona mineralizada. O método E.M. não apresentou nenhum poder resolutivo, uma vez que detectou anomalias semelhantes dentro e fora das áreas mais promissoras. Todas as anomalias foram confirmadas com furos de sondagem. Considerando-se que a área prospectada apresenta, devido ao difícil acesso, o mesmo grau de dificuldade para realização da pesquisa por métodos diretos (perfuração, poços ou trincheiras), como qualquer outra área similar na região amazônica, os resultados aqui apresentados confirmaram que os métodos magnético e eletro-resistivo podem ser utilizados com sucesso como ferramenta indireta na localização de zonas promissoras à exploração de ouro dentro da zona de falha de Chega Tudo ou em outros ambientes geológicos de semelhantes características.

Estudo de corrosão das fases componentes de amálgamas dentários

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

Desenvolvimento e caracterização físico-química e biofarmacêutica de nano e microemulsões lipídicas de uso intravenoso contendo metildiidrojasmonato

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Microstructural and electrochemical characterization of friction stir welded duplex stainless steels

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Demixing and symmetry breaking in binary dipolar Bose-Einstein-condensate solitons

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

Statics and dynamics of a binary dipolar Bose-Einstein condensate soliton

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

Effect of temperature on salt-salt aqueous biphasic systems: manifestations of upper critical solution temperature

Water-miscible ionic liquids (ILs) may be salted out using kosmotropic salts such as potassium phosphate (K3PO4) to form salt-salt aqueous biphasic systems (ABS). The effect of temperature on these systems has been studied using phase diagrams and it is observed that the degree of binodal shift decreases (requiring lower IL and kosmotropic salt concentrations) with the increase of temperature following the trend [C(4)mim]Cl > [C(4)py]Cl > [C(4)mmim] Cl > [N-4444]Cl. This trend can be correlated with the decreasing hydrogen bonding abilities of each salt. The phase behavior was also interpreted on the basis of critical solution temperature behavior of pure aqueous ionic liquid solutions. Additionally, the distribution of alcohols in these systems was studied as a function of temperature and it was found that the distribution ratios did not change with changes in temperature. The Gibbs energy of transfer of a methylene group in these systems and correlation to tie-line length was also determined. It was concluded that while the miscibility of alcohols increases in the ILs with increasing temperature, phase divergence in the aqueous biphasic system decreases, and thus these competing forces tend to cancel each other out for small polar molecules. A comparison is provided for the response to temperature in the currently studied salt-salt systems and analogous ABS formed by the addition of hydrophilic polymers to kosmotropic salts (polymer-salt) or other polymers (polymer-polymer).

Complementary study on the electrical and structural properties of poly(3-alkylthiophene) and its copolymers synthesized on ITO by electrochemical impedance and Raman spectroscopy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A Monte Carlo study of the anisotropic N=3 Ashkin-Teller model

The phase diagram of an asymmetric N = 3 Ashkin-Teller model is obtained by a numerical analysis which combines Monte Carlo renormalization group and reweighting techniques. Present results reveal several differences with those obtained by mean-field calculations and a Hamiltonian approach. In particular, we found Ising critical exponents along a line where Goldschmidt has located the Kosterlitz-Thouless multicritical point. On the other hand, we did find nonuniversal exponents along another transition line. Symmetry breaking in this case is very similar to the N = 2 case, since the symmetries associated to only two of the Ising variables are broken. However, for large values of the coupling constant ratio XW = W/K, when the only broken symmetry is of a hidden variable, we detected first-order phase transitions giving evidence supporting the existence of a multicritical point, as suggested by Goldschmidt, but in a different region of the phase diagram. © 2002 Elsevier Science B.V. All rights reserved.

Ordered phases in the extended Hubbard model

A novel method to probe the diverse phases for the extended Hubbard model (EHM), including the correlated hopping term, is presented. We extend an effective medium approach [1] to a bipartite lattice, allowing for charge- and/or spin-ordered phases. We calculate the necessary correlation functions to build the EHM phase diagram.

Aeroelastic behavior of a wing with a magnetorheological hysteretic model to the damping

This paper shows the application of a hysteretic model for the Magnetorheological Damper (MRD) placed in the plunge degree-of-freedom of aeroelastic model of a wing. This hysteretic MRD model was developed by the researchers of the French Aerospace Lab. (ONERA) and describe, with a very good precision, the hysteretic behavior of the MRD. The aeroelastic model used in this paper do not have structural nonlinearities, the only nonlinearities showed in the model, are in the unsteady flow equations and are the same proposed by Theodorsen and Wagner in their unsteady aerodynamics theory; and the nonlinearity introduced by the hysteretic model used. The main objective of this paper is show the mathematical modeling of the problem and the equations that describes the aeroelastic response of our problem; and the gain obtained with the introduction of this hysteretic model in the equations with respect to other models that do not show the this behavior, through of pictures that represents the time response and Phase diagrams. These pictures are obtained using flow velocities before and after the flutter velocity. Finally, an open-loop control was made to show the effect of the MRD in the aeroelastic behavior.

Dissipation effects in random transverse-field Ising chains

We study the effects of Ohmic, super-Ohmic, and sub-Ohmic dissipation on the zero-temperature quantum phase transition in the random transverse-field Ising chain by means of an (asymptotically exact) analytical strong-disorder renormalization-group approach. We find that Ohmic damping destabilizes the infinite-randomness critical point and the associated quantum Griffiths singularities of the dissipationless system. The quantum dynamics of large magnetic clusters freezes completely, which destroys the sharp phase transition by smearing. The effects of sub-Ohmic dissipation are similar and also lead to a smeared transition. In contrast, super-Ohmic damping is an irrelevant perturbation; the critical behavior is thus identical to that of the dissipationless system. We discuss the resulting phase diagrams, the behavior of various observables, and the implications to higher dimensions and experiments.

Microstructural characterization of as-cast hf-b alloys

An accurate knowledge of several metal-boron phase diagrams is important to evaluation of higher order systems such as metal-silicon-boron ternaries. The refinement and reassessment of phase diagram data is a continuous work, thus the reevaluation of metal-boron systems provides the possibility to confirm previous data from an investigation using higher purity materials and better analytical techniques. This work presents results of rigorous microstructural characterization of as-cast hafnium-boron alloys which are significant to assess the liquid composition associated to most of the invariant reactions of this system. Alloys were prepared by arc melting high purity hafnium (minimum 99.8%) and boron (minimum 99.5%) slices under argon atmosphere in water-cooled copper crucible with non consumable tungsten electrode and titanium getter. The phases were identified by scanning electron microscopy, using back-scattered electron image mode and X-ray diffraction. In general, a good agreement was found between our data and those from the currently accepted Hafnium-Boron phase diagram. The phases identified are αHfSS and B-RhomSS, the intermediate compounds HfB and HfB2 and the liquide L. The reactions are the eutectic L ⇔ αHfSS + HfB and L ⇔ HfB2 + B-Rhom, the peritectic L + HfB2 ⇔ HfB and the congruent formation of HfB2.

On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

Recently, a new ternary phase was discovered in the Ti-Si-B system, located near the Ti6Si2B composition. The present study concerns the preparation of titanium alloys that contain such phase mixed with α-titanium and other intermetallic phases. High-purity powders were initially processed in a planetary ball-mill under argon atmosphere with Ti-18Si-6B and Ti-7.5Si-22.5B at. (%) initial compositions. Variation of parameters such as rotary speed, time, and ball diameters were adopted. The as-milled powders were pressureless sintered and hot pressed. Both the as-milled and sintered materials were characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometry. Sintered samples have presented equilibrium structures formed mainly by the α-Ti+Ti6Si2B+Ti5Si3+TiB phases. Silicon and boron peaks disappear throughout the milling processes, as observed in the powder diffraction data. Furthermore, an iron contamination of up to 10 at. (%) is measured by X-ray spectroscopy analysis on some regions of the sintered samples. Density, hardness and tribological results for these two compositions are also presented here.

Annealed Ising model on hierarchical structures: a transfer matrix approach.

Spin systems in the presence of disorder are described by two sets of degrees of freedom, associated with orientational (spin) and disorder variables, which may be characterized by two distinct relaxation times. Disordered spin models have been mostly investigated in the quenched regime, which is the usual situation in solid state physics, and in which the relaxation time of the disorder variables is much larger than the typical measurement times. In this quenched regime, disorder variables are fixed, and only the orientational variables are duly thermalized. Recent studies in the context of lattice statistical models for the phase diagrams of nematic liquid-crystalline systems have stimulated the interest of going beyond the quenched regime. The phase diagrams predicted by these calculations for a simple Maier-Saupe model turn out to be qualitative different from the quenched case if the two sets of degrees of freedom are allowed to reach thermal equilibrium during the experimental time, which is known as the fully annealed regime. In this work, we develop a transfer matrix formalism to investigate annealed disordered Ising models on two hierarchical structures, the diamond hierarchical lattice (DHL) and the Apollonian network (AN). The calculations follow the same steps used for the analysis of simple uniform systems, which amounts to deriving proper recurrence maps for the thermodynamic and magnetic variables in terms of the generations of the construction of the hierarchical structures. In this context, we may consider different kinds of disorder, and different types of ferromagnetic and anti-ferromagnetic interactions. In the present work, we analyze the effects of dilution, which are produced by the removal of some magnetic ions. The system is treated in a “grand canonical" ensemble. The introduction of two extra fields, related to the concentration of two different types of particles, leads to higher-rank transfer matrices as compared with the formalism for the usual uniform models. Preliminary calculations on a DHL indicate that there is a phase transition for a wide range of dilution concentrations. Ising spin systems on the AN are known to be ferromagnetically ordered at all temperatures; in the presence of dilution, however, there are indications of a disordered (paramagnetic) phase at low concentrations of magnetic ions.