Home About us Contact
|
Home About us Contact | ||
|
|
||
Electric Dipoles (electric + dipole)
Selected AbstractsAn interpolated spatial images method for the analysis of multilayered shielded microwave circuitsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2008J. S. Gómez-Díaz Abstract In this article, an efficient interpolation method is presented to compute the Green's function associated with electrical sources, when they are placed inside cylindrical cavities. The interpolation scheme is formulated in the frame of the spatial images technique recently developed. The original idea was to calculate, for every location of a point electric source, the complex values of the electric dipole and charge images, placed outside the cavity, to impose the appropriate boundary conditions for the potentials. To considerably reduce the computational cost of the original technique, a simple interpolation method is proposed to obtain the complex values of the images for any source location. To do that, a rectangular spatial subdivision inside the cavity is proposed. Each new subregion is controlled by means of the exact image values obtained when the source is placed at the four corners of the region. The key idea is to use a bilinear interpolation to obtain the image complex values when the source is located anywhere inside this subregion. The interpolated images provide the Green's functions of the new source positions fast, and with high accuracy. This new approach can be directly applied to analyze printed planar filters. Two examples with CPU time comparisons are provided, showing the high accuracy and computational gain achieved with the technique just derived. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2294,2300, 2008; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.23683 [source] Combination of electric and magnetic dipoles with single-element feeding for broadband applicationsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2006Karlo Q. da Costa Abstract This work presents four types of broadband compound antennas. The antennas are a combination of an electric dipole and small square or circular loops. The feeding of the electric dipole only is realized. The input impedance, reflection coefficient, and gain of the antennas with different geometries are analyzed numerically using the method of moments (MoM). It is shown that for the level of the reflection coefficient |,| < ,10 dB, 80% to 90% bandwidth can theoretically be achieved for the proposed antennas. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 8,12, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21248 [source] Theoretical Determination of the Vibrational Raman Optical Activity Signatures of Helical Polypropylene ChainsCHEMPHYSCHEM, Issue 11 2006Ewa Lamparska Abstract Raman and vibrational Raman optical activity (VROA) spectra of helical conformers of polypropylene chains are simulated using ab initio methods to unravel the relationships between the vibrational signatures and the primary and secondary structures of the chains. For a polypropylene chain containing three units, conformational effects are shown to lead to more acute signatures for VROA than for Raman spectra. In addition to regular polypropylene chains, which can display right and left helicities with the same probability, chirality and therefore helicity are enforced by substituting one chain end with a phenyl group. The simulations predict that the threefold helical structures, which correspond to (TG)N conformations of the backbone, have a specific VROA backward signature in the form of an intense couplet around 1100 cm,1. This couplet is associated with collective wagging and twisting motions, while most of its intensity comes from the anisotropic invariants combining normal coordinate derivatives of the electric dipole,electric dipole polarizability and of the electric dipole,magnetic dipole polarizability. A similar signature has already been found in model helical polyethylene chains, whereas it is very weak in forward VROA. [source] Giant Room,Temperature Magnetodielectric Response in the Electronic Ferroelectric LuFe2O4ADVANCED MATERIALS, Issue 13 2006A. Subramanian A very large drop in dielectric constant upon application of small magnetic fields is observed at room temperature for LuFe2O4 (see figure). Such behavior is unprecedented and indicates a strong coupling of spins and electric dipoles at room temperature. This behavior of LuFe2O4 is apparently related to its ferroelectricity, which occurs through the highly unusual mechanism of Fe2+ and Fe3+ ordering. [source] New energy terms for reduced protein models implemented in an off-lattice force fieldJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2001Tommi Hassinen Abstract Parameterization and test calculations of a reduced protein model with new energy terms are presented. The new energy terms retain the steric properties and the most significant degrees of freedom of protein side chains in an efficient way using only one to three virtual atoms per amino acid residue. The energy terms are implemented in a force field containing predefined secondary structure elements as constraints, electrostatic interaction terms, and a solvent-accessible surface area term to include the effect of solvation. In the force field the main-chain peptide units are modeled as electric dipoles, which have constant directions in ,-helices and ,-sheets and variable conformation-dependent directions in loops. Protein secondary structures can be readily modeled using these dipole terms. Parameters of the force field were derived using a large set of experimental protein structures and refined by minimizing RMS errors between the experimental structures and structures generated using molecular dynamics simulations. The final average RMS error was 3.7 Å for the main-chain virtual atoms (C, atoms) and 4.2 Å for all virtual atoms for a test set of 10 proteins with 58,294 amino acid residues. The force field was further tested with a substantially larger test set of 608 proteins yielding somewhat lower accuracy. The fold recognition capabilities of the force field were also evaluated using a set of 27,814 misfolded decoy structures. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1229,1242, 2001 [source] Local solutions to a model of piezoelectric materialsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 14 2004Kamel Hamdache Abstract A local existence theorem is proved for a non-linear coupled system modelling the electromechanical motion of a one-dimensional piezoelectric body with domain switching. The system is composed by a heat equation describing the behaviour of the number of electric dipoles and by a wave equation governing the dynamic of the electric displacement. The main coupling in the system appears in the time-dependent velocity of the waves depending on the number of electric dipoles. The proof of the result relies on a time decay estimate satisfied by the number of electric dipoles and an uniform estimate of the solution of the regularized wave equation. Copyright © 2004 John Wiley & Sons, Ltd. [source] Optimization of integrated circuits placement for electric field reduction inside telecommunications equipment using Monte Carlo simulation and parallel recombinative simulated annealingMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2007Sotirios K. Goudos Abstract This article presents a novel approach to the modeling and reduction of electromagnetic interference (EMI) caused by radiated emissions of integrated circuits (ICs) inside rectangular metallic enclosures of telecommunications devices. This type of analysis applies for several types of modern telecommunications equipment found in high-speed networks as well as in mobile communications. A generic model of such a device is created. The ICs are modeled as small electric dipoles and their interaction with the enclosure walls is studied by using the dyadic Green's functions. The electric field on the enclosure walls is computed and its reduction is studied as optimization problem using evolutionary algorithms. Two algorithms are employed: Genetic algorithms (GAs) and parallel recombinative simulated annealing (PRSA). PRSA is a hybrid evolutionary strategy that inherits properties from both GAs and simulated annealing. Monte Carlo simulation is subsequently applied to the optimization results to derive the electric field on the metallic walls and also to perform a worst-case analysis. The applications of the above approach in early PCB design process are discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3049,3055, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22893 [source] Reverse piezoelectric behavior of carbon fiber thermoplastic-matrix compositePOLYMER COMPOSITES, Issue 5 2002Zhen Mei The reverse piezoelectric effect was observed in the through-thickness direction of a continuous carbon fiber nylon-6 matrix composite. The piezoelectric coupling coefficient was 2.2 × 10,6 m/V, as determined up to an electric field of 261 V/m. The effect was largely reversible upon turning off the field and was unaffected by field reversal. It is attributed to the electric dipoles in the nylon-6 matrix. [source] | |||||||||||||