Effect of electrical stimulation of the cranial tibial muscle after end-to-side neurorrhaphy of the peroneal nerve in rats

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

Vortex lattice of a long superconducting wire with a columnar defect

In the present work we study a long superconducting wire with a columnar defect in the presence of an applied magnetic field. The cross section of the cylinder is assumed to be circular. The field is taken uniform and parallel to the cylinder axis. We use the London theory to investigate the vortex lattice inside the wire. Although this theory is valid in the limit of low vortex density, that is, when the nearest neighbor vortex distance is much larger than the coherence length, we can obtain a reasonable qualitative description of lattice properties. We calculate: (1) the vortex lattice structure using the simulated annealing technique; (2) the magnetization curve as a function of the applied field.

Water at interfaces and its influence on the electrical properties of adsorbed films

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

Electrical and microstructural properties of microwave sintered SnO2-based varistors

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Grain size effect on the electrical response of SnO2 thin and thick film gas sensors

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

EFFECT OF CR2O3 ON THE ELECTRICAL-PROPERTIES OF MULTICOMPONENT ZNO VARISTORS AT THE PREBREAKDOWN REGION

The effect of Cr2O3 on the electrical properties of the multicomponent ZnO varistors was investigated using voltage-current curves and impedance spectroscopy. The structure and morphological modifications were analysed by X-ray diffraction and scanning electron microscopy, respectively. It was observed in samples with addition 0.1 mol% Cr2O3 that there was an improvement in the electrical properties of the varistors, but the increase in concentration had a deleterious effect on the potential barrier at the grain boundary. The excess Cr2O3 segregates at the grain-boundary region and increases the donor concentration, leading to a higher leakage current.

Nonlinear electrical behaviour of the Cr2O3, ZnO, CoO and Ta2O5-doped SnO2 varistors

The effects of Cr2O3 on the properties of (Zn, Co, Ta)-doped SnO2 varistors were investigated in this study. The samples with different Cr2O3 concentrations were sintered at 1400 degrees C for 2 h. The properties of (Zn, Co, Ta, Cr)-doped SnO2 varistors were evaluated by XRD. dilatornetry, SEM, I-V and impedance spectroscopy. DC electrical characterization showed a dramatic increase ill the breakdown electrical field and in the nonlinear coefficient with the increase in Cr2O3 concentration. The grain size was found to decrease from 13 to 5 mu m with increasing the Cr2O3 content. The impedance data, represented by means of Nyquist diagrams, show two time constants, one at low frequencies and the other at high frequencies. (c) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Preparation and characterization of LiNi0.8Co0.2O2/PANI microcomposite electrode materials under assisted ultrasonic irradiation

A preparation method for a new electrode material based on the LiNi0.8Co0.2O2/polyaniline (PANI) composite is reported. This material is prepared by in situ polymerization of aniline in the presence of LiNi0.8Co0.2O2 assisted by ultrasonic irradiation. The materials are characterized by XRD, TG-DTA, FTIR, XPS, SEM-EDX, AFM, nitrogen adsorption (BET surface area) and electrical conductivity measurements. PANI in the emeraldine salt form interacts with metal-oxide particles to assure good connectivity. The dc electrical conductivity measurements at room temperature indicate that conductivity values are one order of magnitude higher in the composite than in the oxide alone. This behavior determines better reversibility for Li-insertion in charge-discharge cycles compared to the pristine mixed oxide when used as electrode of lithium batteries. (c) 2005 Elsevier B.V. All rights reserved.

Study of the thermomechanical and electrical properties of conducting composites containing natural rubber and carbon black

This work describes the preparation and characterization of composite materials obtained by the combination of natural rubber (NR) and carbon black (CB) in different percentages, aiming to improve their mechanical properties, processability, and electrical conductivity, aiming future applications as transducer in pressure sensors. The composites NR/CB were characterized through optical microscopy (OM), DC conductivity, thermal analysis using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), thermogravimetry (TGA), and stress-strain test. The electrical conductivity varied between 10(-9) and 10 S m(-1), depending on the percentage of CB in the composite. Furthermore, a linear (and reversible) dependence of the conductivity on the applied pressure between 0 and 1.6 MPa was observed for the sample with containing 80 wt % of NR and 20% of CB. (C) 2007 Wiley Periodicals, Inc.

Dependence of La2O3 content on the nonlinear electrical behaviour of ZnO, CoO and Ta2O5 doped SnO2 varistors

The effects of La2O3 on the properties of (Zn, Co, Ta) doped SnO2 varistors were investigated in this study. The samples with different La2O3 concentrations were sintered at 1400 degrees C for 2 h and their properties were characterized by XRD, SEM, I-V and impedance spectroscopy. The grain size was found to decrease from 13 pm to 9 gm with increasing La2O3 content. The addition of rare earth element leads to increase the nonlinear coefficient and the breakdown voltage. The enhancement was expected to arise from the possible segregation of lanthanide ion due to its larger ionic radius to the grain boundaries, thereby modifying its electrical characteristics. Furthermore, the dopants such as La may help in the adsorption of O' to O '' at the grain boundaries characteristics. (c) 2006 Elsevier B.V. All rights reserved.

Effect of In concentration in the starting solution on the structural and electrical properties of ZnO films prepared by the pyrosol process at 450 degrees C

Undoped and indium-doped Zinc oxide (ZnO) solid films were deposited by the pyrosol process at 450 degrees C on glass substrates From solutions where In/Zn ratio was 2, 5, and 10 at.%. Electrical measurements performed at room temperature show that the addition of indium changes the resistance of the films. The resistivities of doped films are less than non-doped ZnO films by one to two orders of magnitude depending on the dopant concentration in the solution. Preferential orientation of the films with the c-axis perpendicular to the substrate was detected by X-ray diffraction and polarized extended X-ray absorption fine structures measurements at the Zn K edge. This orientation depends on the indium concentration in the starting solution. The most textured films were obtained for solutions where In/Zn ratio was 2 and 5 at.%. When In/Zn = 10 at.%, the films had a nearly random orientation of crystallites. Evidence of the incorporation of indium in the ZnO lattice was obtained from extended X-ray absorption fine structures at the In and Zn K edges. The structural analysis of the least resistive film (Zn/In = 5 at.%) shows that In substitutes Zn in the wurtzite structure. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Effect of La2O3 doping on the microstructure and electrical properties of a SnO2-based varistor

The effect of La2O3 addition on the densification and electrical properties of the (0.9895 - x) SnO2 + 0.01 CoO + 0.0005 Nb2O5 + x La2O5 system, where x = 0.0005 or 0.00075, was considered in this study. The samples were sintered at 1300 degreesC for 2 and 4 h and a single SnO2 phase was identified by X-ray diffraction. Microstructure analysis by scanning electron microscopy showed that the affect of La2O3 addition is to decrease the SnO2 grain size. J versus E curves indicated that the system exhibits a varistor behavior and the effect of La2O3 is to increase both the non-linear coefficient (alpha) and the breakdown voltage (E-2). Considering the Schottky thermionic emission model the potential height and the width were estimated. The addition of small amounts of La2O3 to the basic system increases the potential barrier height and decreases both grain size and potential barrier width. (C) 2001 Kluwer Academic Publishers.

Effect of oxidizing and reducing atmospheres on the electrical properties of dense SnO2-based varistors

The SnO2 based varistor systems recently presented in the literature appear to have a promising potential in commercial applications. Experimental evidence shows that there is a dependence of nonlinear constant values with thermal treatment under different atmospheres. Thermal treatments in oxygen and nitrogen rich atmospheres at 900 degreesC prove this dependence, indicating that the nonlinear constant values are significantly lower when the material is submitted to a nitrogen atmosphere. Moreover, electrical properties can be restored when the varistor is subjected to thermal treatment at the same temperature in an oxygen atmosphere, indicating that the mechanism seems to be reversible. This paper discusses this behavior focusing in the grain boundary region. Ta2O5 mol% concentrations are also analyzed and the results indicate an optimum Ta2O5 concentration of 0.05 mol% for the electrical properties (alpha = 44 and E-B = 6150 V cm(-1)). (C) 2001 Elsevier B.V. Ltd. All rights reserved.