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Local Field (local + field)

Distribution by Scientific Domains

Chemistry	37%

Terms modified by Local Field

local field potential

Selected Abstracts

Imaging the Electric-Field Distribution in Organic Devices by Confocal Electroreflectance Microscopy

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2009
Michele Celebrano
Abstract Space resolved Stark spectroscopy is introduced as a non invasive optical technique for imaging electric field distribution in organic semiconductors. Stark spectroscopy relies on the electric field induced change in the absorption/reflection. It is shown that local monitoring of Stark shift with confocal spatial resolution provides quantitative information on the strength of the local field as well as charge distribution within the transport channel. [source]

The Kneser relation and the Hilbert pairing in multidimensional local field

MATHEMATISCHE NACHRICHTEN, Issue 16 2007
K. F. Lai
Abstract We generalize the Kneser relation to multidimensional local fields and use it to obtain an explicit formula for the Hilbert pairing of multidimensional local fields directly from the definition of the pairing. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The pair-functional method for direct solution of molecular structures.

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2001

The pair-functional principle shows how to construct a unique statistical ensemble of strongly interacting atoms that corresponds to any feasible measured set of X-ray intensities. The ensemble and all its distribution functions are strictly periodic in the crystal lattice, so that each unit cell has exactly the same arrangement of atoms at all times. The mean particle density in the cell is uniform because the ensemble has undefined phases and the origin is not fixed. The atoms in this maximum-entropy ensemble interact through pairwise additive periodic statistical forces within the unit cell. The ensemble average pair-correlation function is matched to the observed originless Patterson function of the crystal. The derived pairing force then becomes approximately proportional to the Ornstein,Zernicke direct correlation function of the ensemble. The atoms have a many-body Boltzmann distribution and the logarithm of the likelihood of any particular conformation is related to its total pairing potential. The pairing potential of a group of atoms acts like a local field in the cell. This property is used in the pair-functional method. Molecular structures can be solved by a direct search in real space for clusters of atoms with high pair potentials. During a successful search, the atoms move from their original random positions to form larger and larger clusters of correctly formed fragments. Finally, every atom belongs to a single cluster, which is the correct solution. [source]

Polymer Matrix Effects on the Nonlinear Optical Response of Incorporated Chromophore: New Analytical Models

CHEMPHYSCHEM, Issue 10 2006
Marina Yu.
Abstract A new approach aimed at the modeling of the nonlinear optical (NLO) response of a dipole chromophore incorporated into a locally anisotropic, deformable, polarizable polymer matrix is suggested. The general continuum methodology is used with a specific cavity ansatz being employed; the cavity is chosen to be conformal to the characteristic ellipsoid of the generalized permittivity tensor of the polymer medium. The suggested ansatz allows the electrostatic boundary value problem to be solved analytically, and the local field experienced by the chromophore in the polymer electret to be found. Four analytically solvable models, which correspond to two singular and two nonsingular models, are considered; in two of them the chromophore is characterized by singular dipole and quadrupole moments; the other two use the approximation of the electric moment of the chromophore with that of the polarized ellipsoid. The relation between the macroscopic polymer properties and the microscopic characteristics of the NLO chromophore is established. The compliance of the obtained formulas for the local field with those of the classical Onsager approach is analyzed, and their specific features are considered. [source]

TROSY effects in MAS solid-state NMR

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2008
Veniamin Chevelkov
Abstract Use of transverse relaxation-optimized spectroscopy (TROSY) type techniques had a dramatic impact on the study of large proteins with a molecular weight >30kDa for solution-state NMR. In the solid-state, such an effect would not be expected a prior, as the investigated molecules are immobilized. However, local motions induce fluctuations of the local fields experienced by the nuclear spins and, this way, are effective for relaxation. We demonstrate that protein dynamics can significantly influence the resonance line width in ultra high resolution MAS (magic angle spinning) solid-state NMR experiments. Averaging of the 15NH,/, multiplet components as a consequence of 1H decoupling induces effective broadening of the 15N resonance. Application of TROSY type techniques that select only the narrow component of the multiplet pattern results in an increased resolution and, thus, will be of benefit for MAS solid-state NMR spectroscopy. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 143,156, 2008. [source]

An accelerated FFT algorithm for thermoelastic and non-linear composites

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2008
V. Vinogradov
Abstract A fast numerical algorithm to compute the local and overall responses of non-linear composite materials is developed. This alternative formulation allows us to improve the convergence of the existing method of Moulinec and Suquet (e.g. Comput. Meth. Appl. Mech. Eng. 1998; 157(1,2):69,94). In the present method, a non-linear elastic (or conducting) material is replaced by infinitely many locally linear thermoelastic materials with moduli that depend on the values of the local fields. This makes it possible to use the advantages of an algorithm developed by Eyre and Milton (Eur. Phys. J. Appl. Phys. 1999; 6(1):41,47), which has faster convergence. The method is applied to compute the local fields as well as the effective response of non-linear conducting and elastic periodic composites. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Time-dependent density functional theory calculations of X-ray absorption

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2003
J. J. Rehr
Abstract There has been dramatic progress in recent years both in calculations and in the interpretation of X-ray absorption spectra (XAS). Often an independent-electron approximation with final state potentials is adequate. However, for soft X-rays (i.e., energies less than about 1 keV) local field effects can be important. Such local fields arise from the dynamic screening of both the external X-ray field and the coupling to the core hole created in the absorption process. These effects require a theory that goes beyond the independent-electron approximation. We developed an efficient approach for treating such effects in molecules and solids based on a generalization of time-dependent density functional theory (TDDFT), with a local approximation for the screening response. The approach has been implemented in our self-consistent, real-space Green's function code FEFF8 in terms of screened dipole transition matrix elements. Typical results are discussed for the XAS of the N4,5 edges of solid Xe and for the L2,3 edges of 3d transition metals. Our approach accounts for the deviations of the L3/L2 intensity branching ratio from the 2:1 value of the independent electron approximation. For the N4,5 edges of Xe, the approach also accounts for the observed fine structure. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [source]