NMR and conductivity study of the protonic conductor HPb2Nb3O10 center dot nH(2)O

Electrical conductivity and H-1 Nuclear Magnetic Resonance (NMR) techniques were used to investigate the ion-exchanged layered lead-niobate perovskite HPb2Nb3O10. nH(2)O, over the temperature range 90-350 K. Compounds were synthesized by the sol-gel method and calcinated at 650 degreesC. Analysis of the NMR data gives activation energies for the proton motion in the range 0.14-0.40 eV, which are dependent on the water content. The frequency and temperature dependencies of the proton spin-lattice relaxation times show that the character of the motion of the: water molecules is essentially two-dimensional, reflecting the layered structure of the material. The H-1 line-narrowing transition and the single spin-lattice relaxation rate maximum, observed in the hydrated compounds, are consistent with a Grotthuss-like mechanism for the proton diffusion. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Effect of maltodextrin on the freezing point and thermal conductivity of uvaia pulp (Eugenia piriformis Cambess)

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

Influence of fluid concentration on freezing point depression and thermal conductivity of frozen orange juice

The freezing point depression (FPD) of orange juice at different concentrations was measured by using a simple apparatus. Results showed that the initial freezing point decreased approximately 90% with the increase of juice concentration between 46degrees and 66degrees Brix (water content respectively between 52.8 and 32.8% w/w). The thermal conductivity of orange juice as a function of fluid concentration was also investigated by using a coaxial dual-cylinder apparatus. Below the freezing point, the thermal conductivity was strongly affected by both the orange juice concentration and temperature. Simple equations in terms of water content and temperature could be adjusted to experimental data of FPD and thermal conductivity.

Modeling thermal conductivity, specific heat, and density of milk: A neural network approach

The accurate determination of thermophysical properties of milk is very important for design, simulation, optimization, and control of food processing such as evaporation, heat exchanging, spray drying, and so forth. Generally, polynomial methods are used for prediction of these properties based on empirical correlation to experimental data. Artificial neural networks are better Suited for processing noisy and extensive knowledge indexing. This article proposed the application of neural networks for prediction of specific heat, thermal conductivity, and density of milk with temperature ranged from 2.0 to 71.0degreesC, 72.0 to 92.0% of water content (w/w), and 1.350 to 7.822% of fat content (w/w). Artificial neural networks presented a better prediction capability of specific heat, thermal conductivity, and density of milk than polynomial modeling. It showed a reasonable alternative to empirical modeling for thermophysical properties of foods.

Field-dependent conductivity at low electric fields in pressed pellets of doped poly (3-methylthiophene): evidence of charge-density wave depinning

Field-dependent conductivity at low electric fields was observed from low to room temperature in pressed pellets of doped poly(3-methylthiophene). The room temperature data showed good agreement with Bardeen's theory of charge-density wave depinning and the values of the parameters obtained are consistent with a strong electron-phonon interaction as expected for quasi-one dimensional systems. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Density, heat capacity and thermal conductivity of liquid egg products

Density, heat capacity and thermal conductivity of liquid egg products, such as egg white, egg yolk, whole egg and various white and yolk blends, were determined as affected by temperature and water content ranging from 273 to 311 K and 51.8 to 88.2% (mass), respectively. Polynomial models fitted the experimental data very well, showing a linear relationship both for temperature and water content. (c) 2005 Published by Elsevier Ltd.

Decay of photo-excited conductivity of Er-doped SnO2 thin films

Er-doped SnO2 thin films, obtained by sol-gel-dip-coating technique, were submitted to excitation with the 4th harmonic of a Nd:YAG laser (266 nm), at low temperature, and a conductivity decay is observed when the illumination is removed. This decay is modeled by considering a thermally activated cross section of an Er-related trapping center. Besides, grain boundary scattering is considered as dominant for electronic mobility. X-ray diffraction data show a characteristic profile of nanoscopic crystallite material (grain average size approximate to 5 nm) in agreement with this model. Temperature dependent and concentration dependent decays are measured and the capture barrier is evaluated from the model, yielding 100 meV for SnO2:0.1% Er and 148 meV for SnO2:4% Er.

Investigation of temperature influence on photo-induced conductivity in n-type AlxGa1-xAs

We present conductance as function of temperature (G×T) under influence of monochromatic light in the range 0.5-1.5 μm for direct as well as indirect bandgap n-type AlxGa1-xAs. Results obtained below 60 K in indirect bandgap sample show the presence of another level of trapping, besides the DX centre, probably a X-valley effective mass state. In direct bandgap samples, these G×T curves show that above bandgap light increases conductivity to higher values than at room temperature and below bandgap light is not enough to avoid trapping. Photoconductivity spectra in indirect bandgap AlxGa1-xAs show that above ≅120 K, the absence of persistent photoconductivity contributes for a very clean spectrum. The mobility of AlxGa1-xAs is modelled considering dipole scattering. Data of transient decay of persistent photoconductivity is simulated using this approach.

Freezing point and thermal conductivity of tropical fruit pulps: Mango and papaya

The freezing point depression of mango and papaya pulps was measured by using a simple apparatus, consisting of two major sections: a freezing vessel and a data acquisition system. The thermal conductivity of both pulps as a function of frozen water fraction and temperature was also investigated by using a coaxial dual-cylinder apparatus. Thermal conductivity above the initial freezing point was well fitted by polynomial equations. Below the freezing point, the thermal conductivity was strongly affected by both the frozen water fraction and temperature. Simple equations in terms of frozen water fraction and temperature could be fitted to the experimental data of freezing point depression and thermal conductivity.

Properties of individual YBCO layers in a two-layered design for energy-efficient digital data cables

We are developing two-layered Yttrium Barium Copper Oxide (YBCO) thin film structures for energy efficient data links for superconducting electronics and present the results of their property measurements. High temperature superconductors (HTS) are advantageous for the implementation of energy-efficient cables interconnecting low temperature superconductor-based circuits and other cryogenic electronics circuits at higher temperature stages. The advantages of the HTS cables come from their low loss and low dispersion properties, allowing ballistic transfer of low power signals with very high bandwidth, low heat conduction and negligible inter-line crosstalk. The microstrip line cable geometry for typical materials is a two-layered film, in which the two superconducting layers are separated by an insulation layer with a minimized permittivity. We have made a proof of concept design of two YBCO films grown by pulsed laser deposition and then assembled into a sandwich with uniform insulating interlayer of tens of micrometers thick. We report on results obtained from such systems assembled in different ways. Structural and electromagnetic properties have been examined on individual films and on the corresponding sandwich composite. © 2013 IEEE.

Density, Refractive Index, Apparent Specific Volume, and Electrical Conductivity of Aqueous Solutions of Poly(ethylene glycol) 1500 at Different Temperatures

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Non ohmic gigahertz conductivity in pressed pellets of ClO4 doped poly(3-methylthiophene)

ESR measurements In pressed pellets of doped Poly(3-Methylthiophene)(P3MT) were performed at 10 K and 50 K after cooling the system slowly from room temperature to 110 K, quenching to 77 K and then to 10 K. ESR line asymmetry (A/B) as a function of microwave power was observed and 9.4 GHz conductivity was obtained from Dyson's theory. The data is discussed in terms of Charge-Density Wave (CDW) depinning. At 50 K the threshold electric field is estimated to be less than 1 V/cm. At 10 K a subtle pinning of the CDW was observed around 15 mW.

Automated system of seedling image analysis (SVIS) and electrical conductivity to assess sun hemp seed vigor

The development of new procedures for quickly obtaining accurate information on the physiological potential of seed lots is essential for developing quality control programs for the seed industry. In this study, the effectiveness of an automated system of seedling image analysis (Seed Vigor Imaging System - SVIS) in determining the physiological potential of sun hemp seeds and its relationship with electrical conductivity tests, were evaluated. SVIS evaluations were performed three and four days after sowing and data on the vigor index and the length and uniformity of seedling growth were collected. The electrical conductivity test was made on 50 seed replicates placed in containers with 75 mL of deionised water at 25 ºC and readings were taken after 1, 2, 4, 8 and 16 hours of imbibition. Electrical conductivity measurements at 4 or 8 hours and the use of the SVIS on 3-day old seedlings can effectively detect differences in vigor between different sun hemp seed lots.

A Model to Predict Percolation Threshold and Effective Conductivity of Infiltrated Electrodes for Solid Oxide Fuel Cells

We present a mechanistic modeling methodology to predict both the percolation threshold and effective conductivity of infiltrated Solid Oxide Fuel Cell (SOFC) electrodes. The model has been developed to mirror each step of the experimental fabrication process. The primary model output is the infiltrated electrode effective conductivity which provides results over a range of infiltrate loadings that are independent of the chosen electronically conducting material. The percolation threshold is utilized as a valuable output data point directly related to the effective conductivity to compare a wide range of input value choices. The predictive capability of the model is demonstrated by favorable comparison to two separate published experimental studies, one using strontium molybdate and one using La0.8Sr0.2FeO3-δ as infiltrate materials. Effective conductivities and percolation thresholds are shown for varied infiltrate particle size, pore size, and porosity with the infiltrate particle size having the largest impact on the results.

A Model to Predict Percolation Threshold and Effective Conductivity of Infiltrated Electrodes for Solid Oxide Fuel Cells

We present a mechanistic modeling methodology to predict both the percolation threshold and effective conductivity of infiltrated Solid Oxide Fuel Cell (SOFC) electrodes. The model has been developed to mirror each step of the experimental fabrication process. The primary model output is the infiltrated electrode effective conductivity which provides results over a range of infiltrate loadings that are independent of the chosen electronically conducting material. The percolation threshold is utilized as a valuable output data point directly related to the effective conductivity to compare a wide range of input value choices. The predictive capability of the model is demonstrated by favorable comparison to two separate published experimental studies, one using strontium molybdate and one using La0.8Sr0.2FeO3-delta as infiltrate materials. Effective conductivities and percolation thresholds are shown for varied infiltrate particle size, pore size, and porosity with the infiltrate particle size having the largest impact on the results. (C) 2013 The Electrochemical Society. All rights reserved.