Kerr-Newman solution as a Dirac particle

For m(2) < a(2) + q(2), with m, a, and q respectively the source mass, angular momentum per unit mass, and electric charge, the Kerr-Newman (KN) solution of Einstein's equation reduces to a naked singularity of circular shape, enclosing a disk across which the metric components fail to be smooth. By considering the Hawking and Ellis extended interpretation of the KN spacetime, it is shown that, similarly to the electron-positron system, this solution presents four inequivalent classical states. Making use of Wheeler's idea of charge without charge, the topological structure of the extended KN spatial section is found to be highly non-trivial, leading thus to the existence of gravitational states with half-integral angular momentum. This property is corroborated by the fact that, under a rotation of the space coordinates, those inequivalent states transform into themselves only after a 4π rotation. As a consequence, it becomes possible to naturally represent them in a Lorentz spinor basis. The state vector representing the whole KN solution is then constructed, and its evolution is shown to be governed by the Dirac equation. The KN solution can thus be consistently interpreted as a model for the electron-positron system, in which the concepts of mass, charge and spin become connected with the spacetime geometry. Some phenomenological consequences of the model are explored.

Evolution of magnetic field and spin period in accreting neutron stars

Based on the accretion-induced magnetic field decay model, in which a frozen field and an incompressible fluid are assumed, we obtain the following results: (1) an analytic relation between the magnetic field and spin period, if the fastness parameter of the accretion disk is neglected (The evolutionary tracks of accreting neutron stars in the P-B diagram in our model are different from the equilibrium period lines when the influence of the fastness parameter is taken into account.); (2) the theoretical minimum spin period of an accreting neutron star is max(1.1ms (DeltaM/M(circle dot))(-1)R(6)(-5/14) I(45)(M/M(circle dot))(-1/2),1.1ms (M/M(circle dot))(-1/2) R(6)(17/14)), independent of the accretion rate (X-ray luminosity) but dependent on the total accretion mass, DeltaM; however, the minimum magnetic field depends on the accretion rate; (3) the magnetic field strength decreases faster with time than does the period.

On the HBO mechanism of X-ray neutron star

We ascribe the 15-60 Hz Quasi Periodic Oscillation (QPO) to the periastron precession frequency of the orbiting accreted matter at the boundary of magnetosphere-disk of Xray neutron star (NS). Considering the relativistic motion mechanism for the kHz QPO, that the radii of the inner disk and magnetosphere-disk of NS are correlated with each other by a factor is assumed. The obtained conclusions include: all QPO frequencies increase with increasing the accretion rate. The theoretical relations between 15-60 Hz QPO (HBO) frequency and the twin kHz QPOs are similar to the measured empirical formula. Further, the better fitted NS mass by the proposed model is about 1.9 solar masses for the detected LMXBs.

Anisotropic sound and shock waves in dipolar Bose-Einstein condensate

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

Numerical and variational solutions of the dipolar Gross-Pitaevskii equation in reduced dimensions

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

Dimensional reduction of a binary Bose-Einstein condensate in mixed dimensions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Dipolar Bose-Einstein condensates with large scattering length

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

Mixing, demixing, and structure formation in a binary dipolar Bose-Einstein condensate

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

High-velocity oxyfuel Cr3C2-NiCr replacing hard chromium coatings

Comparative wear and corrosion properties of Cr3C2-NiCr (CC-TS) (a high-velocity oxyfuel [HVOF]) and hard chromium (HC) coating's obtained on a steel substrate have been studied. The structural characterization was done before and after measurements by optical microscopy, scanning electron microscopy, and scanning white light interferometry. Wear and corrosion properties were evaluated by ball on disk (ASTM G99-90), rubber wheel (ASTM G65-91), and electrochemical measurements of open circuit and polarization curves. The best corrosion and wear resistance was for the CC-TS obtained by HVOF. The open-circuit potential values measured for both samples after 18 h of immersion we're: -0.240 and -0.550 V, respectively, for CC-TS and HC, versus Ag/AgCl,KClsat. Three orders of magnitude lower volume loss were found for CC-TS (HVOF) after friction tests compared with HC.

Influence of HVOF parameters on the corrosion and wear resistance of WC-Co coatings sprayed on AA7050 T7

Thermal spray WC-based coatings are widely used in the aircraft industry mainly for their resistance to wear, reworking and rebuilding operations and repair of worn components on landing gear, hydraulic cylinders, actuators, propeller hub assemblies, gas turbine engines, and so on. The aircraft industry is also trying to use thermal spray technology to replace electroplating coatings such as hard chromium. In the present work, WC-Co coatings were built up on an AA 7050 aluminum alloy using high velocity oxygen fuel (HVOF) technology and a liquid nitrogen cooling prototype system. The influence of the spray parameters (standard conditions, W19S, increasing the oxygen flux, W19H, and also increasing the carrier gas flux, W19F) on corrosion, friction, and abrasive wear resistance were also studied. The coatings were characterized using optical (OM) and scanning electron (SEM) microscopy, and X-ray diffraction (XRD). The friction and abrasive wear resistance of the coatings were studied using Rubber Wheel and Ball on Disk tests. The electrochemical studies were conducted using open-circuit potential (E(oc)) measurements and electrochemical impedance spectroscopy (EIS). Differences among coated samples were mainly related to the variation of the thermal spray parameters used during the spray process. No significant differences were observed in the wear resistance for the coatings studied, and all of them showed a wear rate around 10 times lower than that of the aluminum alloy. The results of mass loss and wear rate were interpreted considering different mechanisms. Comparing the different spray parameters, the oxygen flux (higher flame temperature) produced the sample which showed the highest corrosion resistance in aerated and unstirred 3.5% NaCl solution. Aluminum ions were detected on the surface almost immediately after the immersion of samples W19S and W19F in chloride solution, showing that the electrolyte reached the substrate and galvanic corrosion probably occurred. For sample W19H, aluminum ions were not detected even after 120 min of immersion in NaCl solution. (C) 2008 Elsevier B.V. All rights reserved.

The Oxidation of Hydroxylamine on Gold Electrodes in Mildly Acidic Aqueous Electrolytes: Electrochemical and In Situ Differential Reflectance Studies

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Well-Alloyed PtFe/C Nanocatalysts of Controlled Composition and Same Particle Size: Oxygen Reduction and Methanol Tolerance

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

Corrosion and Wear Studies of Cr3C2NiCr-HVOF Coatings Sprayed on AA7050 T7 Under Cooling

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

Erbium and ytterbium co-doped SiO2 : GeO2 planar waveguide prepared by the sol-gel route using an alternative precursor

The sol-gel method combined with a spin-coating technique has been successfully applied for the preparation of rare-earth doped silica:germania films used for the fabrication of erbium-doped waveguide amplifiers (EDWA), presenting several advantages over other methods for the preparation of thin films. As with other methods, the sol-gel route also shows some drawbacks, such as cracks related to the thickness of silica films and high hydrolysis rate of certain precursors such as germanium alkoxides. This article describes the preparation and optical characterization of erbium and ytterbium co-doped SiO2:GeO2 crack-free thick films prepared by the sol-gel route combined with a spin-coating technique using a chemically stable non-aqueous germanium oxide solution as an alternative precursor. The non-crystalline films obtained are planar waveguides exhibiting a single mode at 1,550 nm with an average thickness of 3.9 mu m presenting low percentages of porosity evaluated by the Lorentz-Lorenz Effective Medium Approximation, and low stress, according to the refractive index values measured in both transversal electric and magnetic polarizations. Weakly confining core layers (0.3% < Delta n < 0.75%) were obtained according to the refractive index difference between the core and buffer layers, suggesting that low-loss coupling EDWA may be obtained. The life time of the erbium I-4(13/2) metastable state was measured as a function of erbium concentration in different systems and based on these values it is possible to infer that the hydroxyl group was reduced and the formation of rare-earth clusters was avoided.

Produtividade do arroz de terras altas em função do manejo do solo e da época de aplicação de nitrogênio

O manejo adequado do solo e a identificação da época de aplicação de N podem aumentar, significativamente, a produtividade do arroz de terras altas. Neste contexto, objetivou-se, com este trabalho, avaliar a interação do manejo do solo com a época de aplicação de nitrogênio, no desenvolvimento e produtividade da cultura. O delineamento experimental utilizado foi o de blocos ao acaso, em esquema fatorial 5x2, sendo 5 tipos de manejo do solo (arado de aiveca e grade niveladora; grade aradora e grade niveladora; escarificador tipo matabroto; SPD; e Aeromix - equipamento de escarificação superficial) e duas épocas de aplicação de nitrogênio (todo N na base, sendo 45 kg ha-1 de nitrogênio aplicados com adubadora de tração mecânica, 1 dia antes da semeadura do arroz, + 45 kg ha-1 de nitrogênio aplicados no ato da semeadura; e 45 kg ha-1 de nitrogênio aplicados no ato da semeadura + 45 kg ha-1 aplicados no início do perfilhamento das plantas), com 4 repetições. Não houve interação dos fatores, para a variável estande final de plantas. Nos tratamentos onde houve revolvimento de solo com arado de aiveca e grade, observou-se maior produtividade quando o nitrogênio foi parcelado. Quando o nitrogênio foi aplicado todo no plantio, o tratamento com escarificador tipo matabroto apresentou a maior produtividade, diferindo de todos os outros tratamentos. O plantio convencional (aiveca ou grade) apresentou produtividade semelhante ao SPD, quando se aplicou o N todo no plantio.