Laser weld: microstructure and corrosion study of Ag-Pd-Au-Cu alloy of the dental application

The laser Welding process was introduced into dentistry by the end of the 1980s, resulting on a great impulse to that area with the development of cheaper and smaller equipment, using simpler technique. This allowed greater use of that process on the confection of prostheses compared to the brazing process since the heat source for that process is a concentrated light beam of high power, which minimizes distortion problems on the prosthetic pieces. Ag-Pd-Au-Cu alloy used on the confection of dental implant prostheses was observed before and after subjection to the laser welding process. The microstructure was analyzed with the. use of optic microscopy and the corrosion resistance was studied by the traditional electrochemical techniques and by electrochemical impedance, under environmental conditions simulating the aggressiveness found in the mouth cavity. A structural change was detected on the weld area, which presented a refined microstructure deriving from the high-speed cooling. The base metal out of the weld area presented a fusion coarse microstructure. The electrochemical essays showed differences on the potentiodynamic polarization behavior in both weld and metal base areas, indicating superior corrosion resistance in the weld area. The impedance spectra were characterized by capacitive distorted components, presenting linear impedance in the low frequencies area. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Comments on spin operators and spin-polarization states of 2+1 fermions

In this brief article we discuss spin-polarization operators and spin-polarization states of 2 + 1 massive Dirac fermions and find a convenient representation by the help of 4-spinors for their description. We stress that in particular the use of such a representation allows us to introduce the conserved covariant spin operator in the 2 + 1 field theory. Another advantage of this representation is related to the pseudoclassical limit of the theory. Indeed, quantization of the pseudoclassical model of a spinning particle in 2 + 1 dimensions leads to the 4-spinor representation as the adequate realization of the operator algebra, where the corresponding operator of a first-class constraint, which cannot be gauged out by imposing the gauge condition, is just the covariant operator previously introduced in the quantum theory.

Surface modifications on Teflon FEP and Mylar C induced by a low energy electron beam: a Raman and FTIR spectroscopic study

The surface modifications induced on Teflon FEP and Mylar C polymer films by a low energy electron beam are probed using Raman and FTIR spectroscopy. The electron beam, which does not affect the Mylar C, surface, may break the copolymer chain into its monomers degrading the Teflon FEP surface. For Mylar C the electron beam decreases the roughness of the polymer surface. This difference in behavior may explain recent results in which the surface modifications investigated by measuring the second crossover energy shift in the electronic emission curve differed for the two polymers (Chinaglia et al [1]). In addition, the Raman data showed no evidence of carbon formation for either polymer samples, which is explained by the fact that only a low energy electron beam is used.

Transient current effects on poly(o-methoxyaniline) films irradiated by pulsed electron beam

Fast transient current decay was recorded on POMA samples during current pulses (in the order of milliseconds) provided by a low energy electron beam under an applied field. The characteristic time decay depends on the electron beam energy and on the bias polarity. The results were explained taking into account the effect of space charge, the intrinsic conductivity of the non-irradiated region of the sample and the radiation-induced conductivity of the thin irradiated region. Fitting parameters may provide the value of both intrinsic and radiation-induced conductivities and the average electron range.

VACUUM POLARIZATION TENSOR IN 3-DIMENSIONAL QUANTUM ELECTRODYNAMICS

We evaluate the one-loop vacuum polarization tensor for three-dimensional quantum electrodynamics (QED), using an analytic regularization technique, implemented in a gauge-invariant way. We show thus that a gauge boson mass is generated at this level of radiative correction to the photon propagator. We also point out in our conclusions that the generalization for the non Abelian case is straightforward.

Effects of ion beam on nanoindentation characteristics of glassy polymeric carbon surface

Glassy polymeric carbon (GPC) is a useful material for medical applications due to its chemical inertness and biocompatible characteristics. Mitral and aortic and hydrocephalic valves are examples of GPC prosthetic devices that have been fabricated and commercialized in Brazil. In this work, ion beam was used to improve the mechanical characteristics of GPC surface and therefore to avoid the propagation of microcracks where the cardiac valves are more fragile. A control group of phenolic resin samples heat-treated at 300, 400, 700, 1000, 1500, and 2500 degrees C was characterized by measuring their hardness and Young's reduced elastic modulus with the depth of indentation. The control group was compared to results obtained with samples heat-treated at 700, 1000, and 1500 degrees C and bombarded with energetic ions of silicon, carbon, oxygen, and gold at energies of 5, 6, 8, and 10 MeV, respectively, with fluences between 10x10(13) and 10x10(16) ions/cm(2). GPC nonbombarded samples showed that hardness depends on the heat treatment temperature (HTT), with a maximum hardness for heat treatment at 1000 degrees C. The comparison between the control group and bombarded group also showed that hardness, after bombardment, had a greater increase for samples prepared at 700 degrees C than for samples prepared at higher temperatures. The Young's elastic modulus presents an exponential relationship with depth. The parameters obtained by fitting depend on the HTT and on the ion used in the bombardment more than on energy and fluence. The hardness results show clearly that bombardment can promote carbonization, increase the linkage between the chains of the polymeric material, and promote recombination of broken bonds in lateral groups that are more numerous for samples heat-treated at 700 degrees C. (c) 2004 Elsevier B.V. All rights reserved.

Effect of temperature on the optical properties of GaAsSbN/GaAs single quantum wells grown by molecular-beam epitaxy

GaAsSbN/GaAs strained-layer single quantum wells grown on a GaAs substrate by molecular-beam epitaxy with different N concentrations were studied using the photoluminescence (PL) technique in the temperature range from 9 to 296 K. A strong redshift in optical transition energies induced by a small increase in N concentration has been observed in the PL spectra. This effect can be explained by the interaction between a narrow resonant band formed by the N-localized states and the conduction band of the host semiconductor. Excitonic transitions in the quantum wells show a successive red/blue/redshift with increasing temperature in the 2-100 K range. The activation energies of nonradiative channels responsible for a strong thermal quenching are deduced from an Arrhenius plot of the integrated PL intensity. (C) 2003 American Institute of Physics.

Importance of cone beam computed tomography for diagnosis of calcifying cystic odontogenic tumor associated to odontoma. Report of a case

The calcifying cystic odontogenic tumour (CCOT) is a rare benign cystic neoplasm not infrequently associated with odontoma. This report documents a case of CCOT associated with compound odontoma arising in the anterior maxilla in a 25-year-old woman. Conventional radiographs showed a large calcified mass with poorly visualized radiolucent margins. The extent and condition of the internal structure of the CCOT associated with odontoma was able to be determined based on radiographic findings from cone beam computed tomography. This advanced image technique proved to be extremely useful in the radiographic assessment of this particular neoplasm of the jawbones.

A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Crystal structure of a novel myotoxic Arg49 phospholipase A(2) homolog (zhaoermiatoxin) from Zhaoermia mangshanensis snake venom: Insights into Arg49 coordination and the role of Lys122 in the polarization of the C-terminus

The venom of Zhaoermia mangshanensis, encountered solely in Mt Mang in China's Hunan Province, exhibits coagulant, phosphodiesterase, L-amino acid oxidase, kallikrein, phospholipase A(2) and myotoxic activities. The catalytically inactive PLA(2) homolog referred to as zhaoermiatoxin is highly myotoxic and displays high myonecrotic and edema activities. Zhaoermiatoxin possesses a molecular weight of 13,972 Da, consists of 121 amino-acid residues crosslinked by seven disulfide bridges and shares high sequence homology with Lys49-PLA(2)s from the distantly related Asian pitvipers. However, zhaoermiatoxin possesses an arginine residue at position 49 instead of a lysine, thereby suggesting a secondary Lys49 -> Arg substitution which results in a catalytically inactive protein. We have determined the first crystal structure of zhaoermiatoxin, an Arg49-PLA(2), from Zhaoermia mangshanensis venom at 2.05 A resolution, which represents a novel member of phospholipase A(2) family. In this structure, unlike the Lys49 PLA(2)s, the C-terminus is well ordered and an unexpected non-polarized state of the putative calcium-binding loop due to the flip of Lys122 towards the bulk solvent is observed. The orientation of the Arg-49 side chain results in a similar binding mode to that observed in the Lys49 PLA(2)s; however, the guadinidium group is tri-coordinated by carbonyl oxygen atoms of the putative calcium-binding loop, whereas the N zeta atom of lysine is tetra-coordinated as a result of the different conformation adopted by the putative calcium-binding loop. (c) 2008 Elsevier Ltd. All rights reserved.

Contribution of an extrinsic mechanism for the electrical polarization in BiMn2O5 ceramics

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

Mandibular cortical bone evaluation on cone beam computed tomography images of patients with bisphosphonate-related osteonecrosis of the jaw

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Kinetics of the polarization reversal process in a non-constant applied electric field and the generalized superposition principle

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Discriminating new physics scenarios at the Next Linear Collider: The role of polarization

We explore the potential of the Next Linear Collider, operating in the e γ mode, to disentangle new physics scenarios in single W production. We study the effects related to the exchange of composite fermions in the reaction e γ→Wνe, and compare them with those arising from trilinear gauge boson anomalous couplings. We stress the role played by the initial state polarization to increase the reach of this machine and to discriminate the possible origin of the new phenomena.