Fernando Moraes

Landau levels in the presence of disclinations

Abstract This work is an investigation of the influence of a disclination on the spectrum of an electron or hole in a magnetic field in the framework of the theory of defects/three-dimensional gravity of Katanaev and Volovich. The presence of the defect reduces the degeneracy of the Landau levels to a finite value, except for very particular deficit angles. Inclusion of the self-interaction in the study further breaks the degeneracy. Exact wavefunctions and energy eigenvalues are found for special values of the magnetic field.

Surgery for endomyocardial fibrosis revisited

OBJECTIVE To identify life expectancy after surgery for endomyocardial fibrosis (EMF) and the events that influence it. METHODS Eighty-three patients with EMF underwent endocardial decortication and atrioventricular valve replacement or repair, between December 1977 and December 1997. There were 66 (79.6%) female and 17 (20.4%) male patients, ranging in age from 4 to 59 years (mean, 31). Thirty-seven (44.5%) had biventricular disease, 34 (41.0%) had disease of the right ventricle alone and 12 (14.5%) had EMF confined to the left ventricle. All were in functional class III or IV (New York Heart Association classification). RESULTS Sixty-eight (81.9%) patients survived the operation and were followed up for periods ranging from 2 months to 17 years. The total follow-up time was 6290 patient/months (mean, 92 months). There were 15 late deaths, but in six, the cause was not related to the underlying disease. Four (5.8%) patients presented recurrence of the fibrosis and were reoperated on and in six (8.8%), EMF appeared in the other ventricle. Five (7.3%) patients were reoperated on to replace either a valve prosthesis or a native valve which had been preserved during the first procedure. Only 24 (45%) of the 53 surviving patients are in functional class I or II. The actuarial probability of survival at 17 years, including operative mortality, was 55%. CONCLUSION Surgical treatment of EMF should be considered a palliative procedure because surgery does not alter the progressive nature of the disease. However, surgical therapy is recommended for patients with EMF and heart failure as it is their only hope of survival.

On the binding of electrons and holes to disclinations

Abstract In this work we study the bound states of electrons and holes to disclinations in the framework of the theory of defects/three- dimensional gravity of Katanaev and Volovich. We find that positive disclinations repel both electrons and holes while negative disclinations act as attractors to both, giving rise to bound states. We compute the wavefunctions and the eigenvalues for these bound states.

Quantum scattering by a magnetic flux screw dislocation

Abstract We investigate the quantum scattering of one electron by a screw dislocation with an internal magnetic flux. The Aharonov–Bohm effect for bound states is analyzed and we demonstrate that the wave function and the energy spectra associated with the particle depend on the Burgers vectors of dislocation and the magnetic flux. We also calculate Berrys phase associated to the dynamics of the electrons in this background. For some specific values of the magnetic flux there is a matching of the effects produced by the flux and by the dislocation in such a way that there is neither scattering nor Berrys phase.

Condensed Matter Physics as a laboratory for gravitation and Cosmology

The geometric language of General Relativity is not normally related to Condensed Matter (CM) Physics since it is the electromagnetic and not the gravitational interaction that dominates the physics of CM systems. What points in common would then CMP have with Cosmology and the dynamics of objects in a gravitational field? There is at least one that is very important: topological defects formed in symmetry breaking phase transitions. To explore the similarities and differences here has been a very fruitful experience for both sides. On one hand, topological defects in solids started to be described by a gravity-like theory including torsion and, on the other hand, experiments have been proposed and performed in CM systems with the purpose of testing cosmological theories. Some examples are: 1) Landau levels and the Aharonov-Bohm effect of electrons moving in a crystal containing a screw dislocation can be described in a simple way in a geometric formalism; 2) closed timelike curves have been proposed in the vicinity of vortices in superfluid Helium; 3) Kibble mechanism, for the generation of topological defects, has been experimentally verified in liquid crystals. In summary, Condensed Matter Physics with its rich diversity of systems and phenomena and of relatively easy access to experiments, appears as a laboratory for testing hypotheses of gravitational theory and cosmology involving topological defects. In this work I summarize recent results in this interface area focusing mainly in the results obtained by our research group.

Geometric phases in graphitic cones

Abstract In this Letter we use a geometric approach to study geometric phases in graphitic cones. The spinor that describes the low energy states near the Fermi energy acquires a phase when transported around the apex of the cone, as found by a holonomy transformation. This topological result can be viewed as an analogue of the Aharonov–Bohm effect. The topological analysis is extended to a system with n cones, whose resulting configuration is described by an effective defect.

Harmonic oscillator interacting with conical singularities

We study the quantum dynamics of a particle interacting harmonically with conical singularities that physically correspond to either a cosmic string, a global monopole, a magnetic flux string or a screw dislocation, by solving the corresponding Schrodinger equations. Exact expressions for the energy eigenfunctions and eigenvalues are found.

Avaliação do EuroSCORE como preditor de mortalidade em cirurgia de revascularização miocárdica no Instituto do Coração de Pernambuco

OBJECTIVE: To assess the applicability of the European Risk System in Cardiac Operations (EuroSCORE) in patients undergoing myocardial revascularization at the Heart Institute of Pernambuco. METHOD: During 2003 and 2004, 759 patients underwent myocardial revascularization. Of these, seven were excluded owing to the lack of information on one aspect or another involved in obtaining a EuroSCORE. In order to assess the applicability of the EuroSCORE, an adjustment was made using a logistic regression model of operative mortality (response variable) on the EuroSCORE (explanatory variable). The calibration of the model was measured by comparing the morbidity observed with that expected, using the Hosmer-Lemeshow Test of Goodness of Fit. The accuracy of the model was evaluated by means of Statistic-c. RESULTS: The accuracy of the model, estimated at 69.9%, and the calibration (Hosmer-Lemeshow test, p=0.663) were satisfactory. The total predicted mortality was practically identical to that observed - 1.7%. The low-risk group (EuroSCORE: 0-2) comprised 231 patients and two (0.87%) deaths occurred. The medium-risk group (EuroSCORE: 3-5) comprised 268 patients and one (0.37%) death occurred. The high-risk group (EuroSCORE: > 6) comprised 253 patients and ten (3.95%) deaths occurred. The discrepancies between the percentages of deaths observed in these groups and those predicted by the model were not statistically significant on the basis of the result of the chi-square test (p=0.624). CONCLUSION: The EuroSCORE, a simple and objective index, proved to be a satisfactory predictor of operative mortality in patients submitted to myocardial revascularization in the Heart Institute of Pernambuco.

Lensing effects in a nematic liquid crystal with topological defects

Abstract.Light traveling through a liquid crystal with disclinations perceives a geometrical background which causes lensing effects similar to the ones predicted for cosmic objects like global monopoles and cosmic strings. In this paper we explore the effective geometry as perceived by light in such media. The comparison between both systems suggests that experiments can be done in the laboratory to simulate optical properties, like gravitational lensing, of cosmic objects.

Topological Aharonov-Bohm effect around a disclination

Abstract In this work we study the changes introduced by a disclination on the energy spectrum of a free particle confined to move between two concentrical cylindrical shells. It is seen that the change in topology caused by the defect produces an analogue of the bound-state Aharonov-Bohm effect in condensed matter.