Oxygen mobility and structural phase transformation in Bi2Sr2CaCu2O8+delta measured by anelastic spectroscopy

One of the most studied ceramic superconductors for application has been, undoubtedly, Bi2Sr2CaCu2O8+delta. Although being a multiphasic material, it has proved to have great advantages compared to other ceramic systems. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature call distinguish among different atomic jumps that occur inside the various phases or at different local ordering. In this paper, mechanical loss spectra of Bi2Sr2CaCu2O8+delta bar shaped samples, made by a conventional method, have been measured between 80 and 600 K, using a torsion pendulum operating in frequencies below 50 Hz, for samples annealed in vacuum up to 600 K. Possible relaxation mechanisms are proposed to explain the origin of the mechanical-loss peaks observed 300 and 500 K. (C) 2004 Elsevier B.V. All rights reserved.

Effect of tannin levels in sorghum silage and concentrate supplementation on apparent digestibility and methane emission in beef cattle

This study evaluated the effect of diets containing sorghum silages with higher (HT) and lower-tannin (LT) concentrations supplemented with concentrate or urea on intake, digestibility, ruminal digestibility, methane emission and rumen parameters in beef cattle. Four treatments were distributed according to a 2 x 2 factorial arrangement in a duplicate 4 x 4 Latin square: LT sorghum silage + urea, LT sorghum silage + concentrate, HT sorghum silage + urea, and HT sorghum silage + concentrate. Total digestibility of the organic matter was higher when concentrate was included in the diet (0.749 and 0.753 in the LT and HT treatments, respectively). It was observed lower ruminal apparent digested matter of neutral detergent fiber in HT diets. There was no effect of tannin levels on digestibility and methane emission. The supplementation with concentrate in the LT diet decreased gas losses as a function of gross energy intake in comparison to the supplementation of the diet with urea. These results suggest the potential of concentrate supplementation to minimize energy loss as methane emission by ruminants and increase the efficiency of energy utilization. (c) 2006 Elsevier B.V. All rights reserved.

Relaxation and tunnelling of structural units within the LTO phase of La2CuO4

The anelastic relaxation (elastic energy loss and Young modulus) of nearly stoichiometric La2CuO4+delta with LTO structure was measured. Extraordinarily intense effects are present below room temperature in the elastic dynamic susceptibility, indicating relaxational dynamics of a relevant fraction of the lattice. The involved degrees of freedom are identified as rotations of the CuO6 octahedra. Two distinct processes are found at frequencies around 1 kKz: one is observed around 150 K and is characterized by a mean activation energy of 2800 K; the second one occurs below 30 K and is governed by atomic tunnelling. Two explanations are proposed for the faster process: i) formation of fluctuating LTT domains on a scale of few atomic cells; ii) the LTO phase is a dynamical Jahn-Teller phase with all the octahedra tunneling between two LTT-like tilts. In both cases there would be important implications regarding the mechanisms giving rise to charge nanophase separation and strong electron-phonon coupling.

Electro-precipitation of Fe(3)O(4) nanoparticles in ethanol

The preparation of superparamagnetic magnetite (Fe(3)O(4)) nanoparticles by electro-precipitation in ethanol is proposed. Particle average size can be set from 4.4 to 9 nm with a standard deviation around 20%. Combination of wide-angle X-ray scattering (WAXS), Electron energy loss spectroscopy (EELS) and Mossbauer spectroscopy characterizations clearly identifies the particles as magnetite single-crystals (Fe(3)O(4)). (C) 2008 Elsevier B.V. All rights reserved.

Anelastic spectroscopy in TiO2

Titanium dioxide (rutile) has a lot of interesting and useful features and hence is widely utilized for application. It has been used as white pigment, photocatalyst, biocompatible material and semiconductor material used in solar battery. In semiconducting TiO2 oxygen vacancies are said to play an important role in the electrical conduction. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occur in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in TiO2 samples using a torsion pendulum operating in frequencies around 40Hz, in the temperature range between -173°C to 330°C with heating rate of 1°C/min. The results shown a reduction in the elasticity modulus with the increase in the corn starch content used for this consolidation.

Anelastic spectroscopy in Al2O3

Engineering ceramics have found use in many applications, such as engine parts, ball bearings, artificial bone and hip replacements and gyroscopes, because of their good chemical inertness, hardness, high temperature stability and excellent wear resistance. Oxide ceramic may meet these demands. Alumina (Al2O3) ceramics offer a high potential for many engineering applications, such as wear- and/or corrosion-resistant components, and as material for substrates or housings in microelectronic devices. Alumina is used among other things for seal ring, draw-cones, guides, water mixing tapes, bearing parts, medical prostheses and cutting tools. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occurs in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in Al2O3 samples using commercial starch. These measurements were carried out in a torsion pendulum operating in frequencies around 40 Hz. The results shown strongly influence of the type of forming in the elastic modulus obtained by anelastic relaxation measurements.

Measurement of the muon stopping power in lead tungstate

A large sample of cosmic ray events collected by the CMS detector is exploited to measure the specific energy loss of muons in the lead tungstate (PbWO4) of the electromagnetic calorimeter. The measurement spans a momentum range from 5 GeV/c to 1 TeV/c. The results are consistent with the expectations over the entire range. The calorimeter energy scale, set with 120 GeV/c electrons, is validated down to the sub-GeV region using energy deposits, of order 100 MeV, associated with low-momentum muons. The muon critical energy in PbWO4 is measured to be 160+5 -68 GeV, in agreement with expectations. This is the first experimental determination of muon critical energy. © 2010 IOP Publishing Ltd and SISSA.

Nanoscale effects and polaronic relaxation in CaCu3Ti 4O12 compounds

In the present communication, by using dielectric spectroscopy measurement, the correlations between Nanosized Barrier Layer Capacitance (NBLC) (Bueno et al. (2009) [7]) and the high frequency polaronic near-Debye dipolar relaxation found in CaCu3Ti4O12 compounds was discussed. The polaronic process was confirmed to be closely associated with the ultrahigh dielectric features of CaCu3Ti4O12 materials and its concomitant dielectric loss. Herein, the shift in relaxation frequency as a function of temperature was used for calculating the activation energy for hopping electronic conduction. The value obtained was 33 meV, an energy whose magnitude is compatible and confirmed the hypothesis of polaronic features for this high frequency dipolar relaxation process. Furthermore, it is shown that the nanosized barrier inferred from the NBLC model has a polaronic feature with dielectric permittivity exiting orthogonally to dielectric loss, a phenomenological pattern that contradicts the normally observed behavior for traditional dielectrics but explain the dielectric and conductivity feature of CaCu3Ti4O12 compounds. © 2010 Elsevier Ltd. All rights reserved.

Studies of jet quenching using isolated-photon+jet correlations in PbPb and pp collisions at sNN=2.76TeV

Results from the first study of isolated-photon+jet correlations in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a centre-of-mass energy of 2.76TeV per nucleon pair corresponding to an integrated luminosity of 150μb-1 recorded by the CMS experiment at the LHC. For events containing an isolated photon with transverse momentum pTγ>60GeV/c and an associated jet with pTJet>30GeV/c, the photon+jet pT imbalance is studied as a function of collision centrality and compared to pp data and pythia calculations at the same collision energy. Using the pTγ of the isolated photon as an estimate of the momentum of the associated parton at production, this measurement allows an unbiased characterisation of the in-medium parton energy loss. For more central PbPb collisions, a significant decrease in the ratio pTJet/pTγ relative to that in the pythia reference is observed. Furthermore, significantly more pTγ>60GeV/c photons in PbPb are observed not to have an associated pTJet>30GeV/c jet, compared to the reference. However, no significant broadening of the photon+jet azimuthal correlation is observed. © 2012 CERN.

Determinação da eficiência de um coletor solar plano com aletas de vidro

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Avaliação das propriedades mecânicas de fios de Níquel-Titânio após incorporação de dobras e/ou tratamento elétrico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo das características física do filme diamante CVD para utilização em coletores solares

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Study of the production of charged pions, kaons, and protons in pPb collisions at root SNN=5.02 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Vanadium-doped TiO2 anatase nanostructures: the role of V in solid solution formation and its effect on the optical properties

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

Effect of lipid sources with different fatty acid profiles on the intake, performance, and methane emissions of feedlot Nellore steers

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