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Digitale Medien

Structure and Electrical Properties of Ni-substituted Lanthanum Gallate Perovskites (1999)

Long, N.J. ; 'Lecarpentier, F. ; Tuller, H.L.

Springer

Journal of electroceramics 3 (1999), S. 399-407

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ISSN: 1573-8663

Schlagwort(e): lanthanum gallate ; mixed conductor ; fuel cell cathode ; blocking cell

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau

Notizen: Abstract Crystal structure, electrical conductivity and thermal expansion of materials in the system La0.9Sr0.1Ga1–yNiyO3 (LSGN) with 0 〈 y ≤ 0.5 have been studied as a function of Ni content, temperature and Po 2. The materials have an orthorhombic structure at low dopant content and a hexagonal structure for higher Ni content. The σ(Po 2, T) results show increasing electronic conductivity at high Po 2 with increasing Ni content. At low Po 2 the conductivity fits a model for predominant ionic conductivity. AC impedance spectroscopy on an electron blocking cell of the form M/LSG/LSGN/LSG/M was used to isolate the ionic conductivity in the y=0.1 and 0.2 materials. The materials were found to have appreciable ionic conductivity in air with a similar magnitude and activation energy to the electrolyte materials. An analysis of the low frequency impedance of the blocking cell provided values for D at 800°C of the order of 9 × 10−5 cm2/s. An evaluation of the so called chemical capacitance enabled determination of the electron density and mobility. The calculated electronic mobility of 3.8 × 10−3 cm2/Vs and activation energy of 0.14 eV for the y = 0.2 material are in excellent agreement with expectations of an electronic transport model involving electron hopping within the Ni impurity band. The thermal expansion coefficients of the Ni doped materials were determined as a function of temperature and dopant level. The presence of mixed conductivity suggests that this material may be useful as an electrode for a lanthanum gallate based fuel cell or other electrochemical device.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1009974116458

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Digitale Medien

A New Bit Rate Control of MPEG with Predictive and Adaptive Perceptual Quantization (1997)

Lin, Yig-Shyang ; Liu, Tsann-Shyong ; Chang, Long-Wen

Springer

Multidimensional systems and signal processing 8 (1997), S. 295-313

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ISSN: 1573-0824

Schlagwort(e): rate control ; MPEG adaptive quantization ; video coding ; motion compensation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: Abstract Bit rate control has been proved to be an important technique used to transmit the variable rate bit stream over a fixed rate channel in MPEG coding. In this paper, a hybrid algorithm is proposed to achieve the rate control and obtain a good picture quality. In the picture layer, the algorithm estimates numbers of bits required for different type of frames. In the macroblock layer, it utilizes the predictive and adaptive perceptual techniques in the regulation of the quantization scale to allocate the target bits. In the upper and left boundary of the picture, the macroblocks are quantized with the perceptual basis to adjust the quantization scale and in the other part of the picture a predictive method is used to update the quantization scale. By using the proposed scheme, the distortion of coding is uniformly distributed in the picture layer as well as in the macroblock layer and better bit rate control is achieved.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1008261712258

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Digitale Medien

ERROR ESTIMATES AND ADAPTIVE REMESHING TECHNIQUES IN ELASTO-PLASTICITY (1997)

LI, LONG-YUAN ; BETTESS, PETER

Chichester : Wiley-Blackwell

Communications in Numerical Methods in Engineering 13 (1997), S. 285-299

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ISSN: 1069-8299

Schlagwort(e): error estimates ; remeshing strategies ; finite elements ; adaptive analysis ; elasto-plastic analysis ; Engineering ; Numerical Methods and Modeling

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Mathematik , Technik allgemein

Notizen: The major difficulty in applying the finite element method to practical problems is the design of a suitable mesh and the assessment of discretization errors. To overcome this difficulty considerable effort has been made in developing adaptive finite element methods, but most of the work has been limited to linear problems. In this paper, fundamental concepts related to error estimates and mesh refinement strategies for non-linear problems are addressed. A simple, but reliable, path-dependent error estimator is proposed. Based on the errors estimated by the present method, a mesh refinement strategy is also suggested. Numerical examples of two ideal plasticity plane stress problems are shown. The non-linear plasticity model is based on an incremental theory using the von Mises yield criterion. © 1997 by John Wiley & Sons, Ltd.

Zusätzliches Material: 11 Ill.

Materialart: Digitale Medien

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