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Practical Realization (practical + realization)

Distribution by Scientific Domains
Polymers and Materials Science40%
Engineering40%

Selected Abstracts

Comparison of methods to model the gravitational gradients from topographic data bases

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006
Christopher Jekeli
SUMMARY A number of methods have been developed over the last few decades to model the gravitational gradients using digital elevation data. All methods are based on second-order derivatives of the Newtonian mass integral for the gravitational potential. Foremost are algorithms that divide the topographic masses into prisms or more general polyhedra and sum the corresponding gradient contributions. Other methods are designed for computational speed and make use of the fast Fourier transform (FFT), require a regular rectangular grid of data, and yield gradients on the entire grid, but only at constant altitude. We add to these the ordinary numerical integration (in horizontal coordinates) of the gradient integrals. In total we compare two prism, two FFT and two ordinary numerical integration methods using 1, elevation data in two topographic regimes (rough and moderate terrain). Prism methods depend on the type of finite elements that are generated with the elevation data; in particular, alternative triangulations can yield significant differences in the gradients (up to tens of Eötvös). The FFT methods depend on a series development of the topographic heights, requiring terms up to 14th order in rough terrain; and, one popular method has significant bias errors (e.g. 13 Eötvös in the vertical,vertical gradient) embedded in its practical realization. The straightforward numerical integrations, whether on a rectangular or triangulated grid, yield sub-Eötvös differences in the gradients when compared to the other methods (except near the edges of the integration area) and they are as efficient computationally as the finite element methods. [source]

Nanocomposite Hybrid Molecular Materials for Application in Solid-State Electrochemical Supercapacitors,

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005
K. Cuentas-Gallegos
Abstract Molecular hybrid materials formed from polyoxometalates dispersed in conducting polymers represent an innovative concept in energy storage. This work reports in detail the first practical realization of electrodes based on these materials for energy storage in electrochemical supercapacitors. The molecular hybrids PAni/H4SiW12O40, PAni/H3PW12O40, and PAni/H3PMo12O40 (PAni: polyaniline) have been prepared electrochemically on platinum or carbon substrates, with PAni/H3PMo12O40 being the prototypical example presenting the best energy-storage performance in the series. This hybrid displays the combined activity of its organic and inorganic components to store and release charge in solid-state electrochemical capacitor cells, leading to a promising value of 120,F,g,1 and good cyclability beyond 1000,cycles. [source]

Modification of Electronic Structures of a Carbon Nanotube by Hydrogen Functionalization

ADVANCED MATERIALS, Issue 24 2002
K.S. Kim
A rigorous method to engineer the electronic structure of carbon nanotubes from metallic to semiconducting is reported (see inside front cover). An intramolecular junction in carbon nanotube is fabricated, where half of the nanotube is masked by a silicon oxide thin film. Functionalization of the nanotube by atomic hydrogen leads to the formation of an intramolecular junction, resulting in clear rectifying behavior at room temperature. This represents an important step towards the practical realization of nanotube-based nanotransistors. [source]

Exhaustive approach to the coupling matrix synthesis problem and application to the design of high degree asymmetric filters

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2007
Richard J. Cameron
Abstract In this paper a new approach to the synthesis of coupling matrices for microwave filters is presented. The new approach represents an advance on existing direct and optimization methods for coupling matrix synthesis, in that it will exhaustively discover all possible coupling matrix solutions for a network if more than one exists. This enables a selection to be made of the set of coupling values, resonator frequency offsets, parasitic coupling tolerance, etc. that will be best suited to the technology it is intended to realize the microwave filter with. To demonstrate the use of the method, the case of the recently introduced "extended box" coupling matrix configuration is taken. The extended box is a new class of filter configuration adapted to the synthesis of asymmetric filtering characteristics of any degree. For this configuration the number of solutions to the coupling matrix synthesis problem appears to be high and offers therefore some flexibility that can be used during the design phase. We illustrate this by carrying out the synthesis process of two asymmetric filters of 8th and 10th degree. In the first example a ranking criterion is defined in anticipation of a dual mode realization and allows the selection of a "best" coupling matrix out of 16 possible ones. For the 10th degree filter a new technique of approximate synthesis is presented, yielding some simplifications of the practical realization of the filter as well as of its computer aided tuning phase. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [source]

Quantitative evaluation of shunts in solar cells by lock-in thermography

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2003
O. Breitenstein
Abstract Infrared lock-in thermography allows to image shunts very sensitively in all kinds of solar cells and also to measure dark currents flowing in certain regions of the cell quantitatively. After a summary of the physical basis of lock-in thermography and its practical realization, four types of quantitative measurements are described: local I,V characteristics measured thermally up to a constant factor (LIVT); the quantitative measurement of the current through a local shunt; the evaluation of the influence of shunts on the efficiency of a cell as a function of the illumination intensity; and the mapping of the ideality factor n and the saturation current density J0 over the whole cell. The investigation of a typical multicrystalline solar cell shows that the shunts are predominantly responsible for deterioration of the low-light-level performance of the cell, and that variations of the injection current density related to crystal defects are predominantly determined by variation of J0 rather than of n. Copyright © 2003 John Wiley & Sons, Ltd. [source]