Scanning tunneling microscope operating as a spin diode

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Analysis of failed commercially pure titanium dental implants: A scanning electron microscopy and energy-dispersive spectrometer X-ray study

Background: the failure of osseointegration in oral rehabilitation has gained importance in current literature and in clinical practice. The integration of titanium dental implants in alveolar bone has been partly ascribed to the biocompatibility of the implant surface oxide layer. The aim of this investigation was to analyze the surface topography and composition of failed titanium dental implants in order to determine possible causes of failure.Methods: Twenty-one commercially pure titanium (cpTi) implants were retrieved from 16 patients (mean age of 50.33 +/- 11.81 years). Fourteen implants were retrieved before loading (early failures), six after loading (late failures), and one because of mandibular canal damage. The failure criterion was lack of osseointegration characterized as dental implant mobility. Two unused implants were used as a control group. All implant surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive spectrometer x-ray (EDS) to element analysis. Evaluations were performed on several locations of the same implant.Results: SEM showed that the surface of all retrieved implants consisted of different degrees of organic residues, appearing mainly as dark stains. The surface topography presented as grooves and ridges along the machined surface similar to control group. Overall, foreign elements such as carbon, oxygen, sodium, calcium, silicon, and aluminum were detected in failed implants. The implants from control group presented no macroscopic contamination and clear signs of titanium.Conclusion: These preliminary results do not suggest any material-related cause for implant failures, although different element composition was assessed between failed implants and control implants.

Filmes finos de SrBi2Ta2O9 processados em forno microondas

Filmes finos de SrBi2Ta2O9 foram depositados em substratos de Pt/Ti/SiO2/Si e, pela primeira vez, sinterizados em forno microondas doméstico. Os padrões de difração de raios X mostraram que os filmes são policristalinos. O processamento por microondas permite utilizar baixa temperatura na síntese e obter filmes com boas propriedades elétricas. Ensaios de microscopia eletrônica de varredura (MEV) e de Força Atômica (MFA) revelam boa aderência entre filme e substrato, com microestrutura de superfície apresentando grãos finos e esféricos e rugosidade de 4,7 nm. A constante dielétrica e o fator de dissipação, para freqüência de 100 KHz, à temperatura ambiente, foram de 77 e 0,04, respectivamente. A polarização remanescente (2Pr) e o campo coercitivo (Ec) foram 1,04 miC/cm² e 33 kV/cm. O comportamento da densidade de corrente de fuga revela três mecanismos de condução: linear, ôhmico e outro mecanismo que pode ser atribuído à corrente de Schottky. Dos padrões de DRX, análises das imagens por MEV e topografia de superfície por MFA observa-se que 10 min de tratamento térmico a 550 ºC, em forno microondas, é tempo suficiente para se obter a cristalização do filme.

Synthesis of SnO2 by chemical routes and its use in varistors production

Tin oxide, SnO2. is a very used compound in industry and one of its uses is as varistor. For the current requirements of the technology is necessary a strict control of the chemical purity and the particle size of the raw material; for that reason the great interest that exists at the moment to develop synthesis methods that allow to get these requirements. In this work, ceramic powders of the Sn-Co-Nb-Ti-Al system using the controlled precipitation and polymeric precursor (Pechini) methods were synthesized. The raw material obtained was characterized using X-ray diffraction (XRD), thermal analysis (DTA/FG) and scanning electron microscopy (SEM). The sintering samples shown a good varistor behavior with non-linear coefficient (alpha) values similar to 22, and Er 2083 V/cm(2). (c) 2007 Elsevier Ltd. All rights reserved.

Ferroelectric properties and leakage current characteristics of Bi3.25La0.75Ti3O12 thin films prepared by the polymeric precursor method

The ferroelectric properties and leakage current mechanisms of preferred oriented Bi3.25La0.75Ti3O12 (BLT) thin films deposited on La0.5Sr0.5CoO3 by the polymeric precursor method were investigated. These films showed excellent ferroelectric properties in terms of large remnant polarization (2P(r)) of 47.6 mu C/cm(2) and (2E(c)) of 55 kV/cm, fatigue-free characteristics up to 10(10) switching cycles, and a current density of 0.7 mu A/cm(2) at 10 kV/cm. X-ray diffraction and scanning electron microscope investigations indicate that the deposited films exhibit a dense, well-crystallized microstructure having random orientations and with a rather smooth surface morphology. The improved ferroelectric and leakage current characteristics can be ascribed to the platelike grains of the BLT films, which make the domain walls easier to be switched under external field.

The influence of the synthesis route on the final properties of SnO2-based varistors

A comparative study of two customary routes of ceramics processing applied to the synthesis of SnO2-based varistors is reported in this paper. Devices of equivalent composition were prepared through the Pechini method and through directly mixing the oxides without the addition of anti-agglomerants or binders. The microstructures of the sintered samples were characterised with X-ray diffraction and scanning and transmission electron microscopies. The electrical behaviour of the devices was studied on the basis of the current density versus electric field (J-E) characteristics and impedance spectroscopy measurements. The Pechini method ensures the homogeneity in the distribution of the additives in the tin oxide matrix but the formation of secondary phases seems to be independent of the synthesis route. Devices with similar non-linear coefficients of 18 and 21 were obtained through the mixed oxides route and the Pechini method, respectively. (C) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Structure, ferroelectric/magnetoelectric properties and leakage current density of (Bi0.85Nd0.15)FeO3 thin films

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

Inverter-fed linear asynchronous machine

The behaviors of an arc-shaped stator induction machine (the sector-motor) and a disc-secondary linear induction motor are analyzed in this work for different values of the frequency. Variable frequency is produced by a voltage source controlled-current inverter which keeps constant the r.m.s. value of the phase current, also assuring a sinusoidal waveform. For the simulations of the machine developed thrust, an equivalent circuit is used. It is obtained through the application of the one-dimensional theory to the modeling. The circuit parameters take into account the end effects, always present is these kind of machines. The phase current waveforms are analyzed for their harmonic contents. Experimental measurements were carried out in laboratory and are presented with the simulations, for comparison.

A low-voltage triode-MOSFET four-quadrant multiplier with optimized current-efficiency

A low-voltage, low-power four-quadrant analog multiplier with optimized current-efficiency is presented. Its core corresponds to a pseudodifferential cascode, gain-boosting triode-transconductor. According to a low-voltage 1.2μm CMOS n-well process, operand differential-amplitudes are 1.0Vpp and 0.32Vpp for a 1.3V-supply. Common-mode voltages are properly chosen to maximize current-efficiency to 58%. Total quiescent dissipation is 260μW. A range of PSPICE simulation supports theoretical analysis. Excellent linearity is observed on dc characteristic. Assuming a ±0.5% mismatch on (W/L) and VTH THD at full-scale is 0.93% and 1.42%, for output frequencies of 1MHz and 10MHz, respectively.

Effect of powder milling and dopant addition on the current-voltage characteristics of SnO2-based ceramics

Non-linear electrical properties of SnO2-based ceramics were investigated as a function of powder agglomeration condition and as a function of dopant addition. All doped powders presented a single phase, cassiterite, as evidenced by X-ray diffraction analysis. The effect of milling was quite evident, with non-milled powder showing higher agglomerated particle size than milled powder. Cr addition seemed to increase the non-linear coefficient. Cu and Mn rendered dense ceramics, but α values for systems with Mn were higher than for systems with Cu.

On non-ideal and non-linear portal frame dynamics analysis using Bogoliubov averaging method

We apply the Bogoliubov Averaging Method to the study of the vibrations of an elastic foundation, forced by a Non-ideal energy source. The considered model consists of a portal plane frame with quadratic nonlinearities, with internal resonance 1:2, supporting a direct current motor with limited power. The non-ideal excitation is in primary resonance in the order of one-half with the second mode frequency. The results of the averaging method, plotted in time evolution curve and phase diagrams are compared to those obtained by numerically integrating of the original differential equations. The presence of the saturation phenomenon is verified by analytical procedures.

Critical evaluation of FBD, pq and CPT current decompositions for four-wire circuits

This paper investigates the major similarities and discrepancies of three important current decompositions proposed for the interpretation of unbalanced and/or non linear three-phase four-wire circuits. The considered approaches were the so-called FBD Theory, the pq-Theory and the CPT. Although the methods are based on different concepts, the results obtained under ideal conditions (sinusoidal and balanced signals) are very similar. The main differences appear in the presence of unbalanced and non linear load conditions. It will be demonstrated and discussed how the choice of the voltage referential and the return conductor impedance can influence in the resulting current components, as well as, the way of interpreting a power circuit with return conductor. Under linear unbalanced conditions, both FBD and pq-Theory suggest that the some current components contain a third-order harmonic. Besides, neither pq-Theory nor FBD method are able to provide accurate information for reactive current under unbalanced and distorted conditions, what seems to be done by means of the CPT. © 2009 IEEE.

A comparative analysis of FBD, PQ and CPT current decompositions - Part II: Three-phase four-wire systems

This paper investigates the major similarities and discrepancies among three important current decompositions proposed for the interpretation of unbalanced and/or non linear three-phase four-wire power circuits. The considered approaches were the so-called FBD Theory, the pq-Theory and the CPT. Although the methods are based on different concepts, the results obtained under ideal conditions (sinusoidal and balanced signals) are very similar. The main differences appear in the presence of unbalanced and non linear load conditions. It will be demonstrated and discussed how the choice of the voltage referential and the return conductor impedance can influence in the resulting current components, as well as, the way of interpreting a power circuit with return conductor. Under linear unbalanced conditions, both FBD and pq-Theory suggest that the some current components contain a third-order harmonic. Besides, neither pq-Theory nor FBD method are able to provide accurate information for reactive current under unbalanced and distorted conditions, what can be done by means of the CPT. © 2009 IEEE.

H ∞ state feedback control of discrete-time Markov jump linear systems through linear matrix inequalities

This paper addresses the H ∞ state-feedback control design problem of discretetime Markov jump linear systems. First, under the assumption that the Markov parameter is measured, the main contribution is on the LMI characterization of all linear feedback controllers such that the closed loop output remains bounded by a given norm level. This results allows the robust controller design to deal with convex bounded parameter uncertainty, probability uncertainty and cluster availability of the Markov mode. For partly unknown transition probabilities, the proposed design problem is proved to be less conservative than one available in the current literature. An example is solved for illustration and comparisons. © 2011 IFAC.

A mixed-integer linear programming approach for optimal type, size and allocation of distributed generation in radial distribution systems

This paper presents a mixed-integer linear programming approach to solving the problem of optimal type, size and allocation of distributed generators (DGs) in radial distribution systems. In the proposed formulation, (a) the steady-state operation of the radial distribution system, considering different load levels, is modeled through linear expressions; (b) different types of DGs are represented by their capability curves; (c) the short-circuit current capacity of the circuits is modeled through linear expressions; and (d) different topologies of the radial distribution system are considered. The objective function minimizes the annualized investment and operation costs. The use of a mixed-integer linear formulation guarantees convergence to optimality using existing optimization software. The results of one test system are presented in order to show the accuracy as well as the efficiency of the proposed solution technique.© 2012 Elsevier B.V. All rights reserved.