			Home About us Contact

Dispersive Effects (dispersive + effects)

Distribution by Scientific Domains

Physics and Astronomy	40%

Selected Abstracts

Dispersive Effects in Chemomechanical Reactions with Polyallylamine-Derived Hydrogels

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2008
Kazuaki Kato
Abstract Volume changes of polyallylamine-derived hydrogels crosslinked with glutaraldehyde are determined with a large variety of effector compounds. Monocarboxylic effectors lead to smaller contractions, in contrast to dicarboxylate structures, which allow more effective non-covalent crosslinking between the positively charged nitrogen centers of the polymer backbone. Electroneutral compounds lead to negligible changes, whereas effectors with either a large p -moiety like in naphthoic acid or phenyl derivatives with polarizable substituents induce large contractions. This finding is in line with significant contributions of van der Waals interactions between the effectors within the hydrogel. Chemomechanical differences between regioisomeric effectors such as p - and o -nitrobenzoic acid are in agreement with independent results of dispersive interactions in related complexes. The volume decrease corresponds almost entirely to the gravimetrically determined water content of the gels. The acidity profile shows a strong contraction above pH 10, which is consistent with the known pK value of such polyamines. NMR spectra of the gels indicate strong binding of the effectors by line broadening, which is significant only for the chemomechanically active compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Solution of non-linear dispersive wave problems using a moving finite element method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 4 2007
Abigail Wacher
Abstract The solution of the fully non-linear time-dependent two-dimensional shallow water equations is considered. Dispersive effects due to the Coriolis forces are taken into account. Such effects are of major importance in geophysical fluid dynamics applications. The recently proposed string gradient weighted moving finite element method is extended for this class of problems. This method simultaneously determines, at each time step, the solution of the governing partial differential equations and an optimal location of the finite element nodes. It has previously been applied to non-dispersive wave problems; here its performance under the demanding conditions of large Coriolis forces, inducing large mesh and field rotation, is studied. Optimal rates of convergence are obtained. Results for some example problems of water hump release are presented. Non-linear and linearized solutions are compared. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Reexamining the quantification of perfusion MRI data in the presence of bolus dispersion,

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2007
Linda Ko BSc
Abstract Purpose To determine the true impact of dispersion upon cerebral blood flow (CBF) quantification by removing an algorithm implementation-induced systematic error. Materials and Methods The impact of dispersion on the arterial input function (AIF) between measurement and entry into the tissue of interest on CBF estimates was simulated assuming: 1) contralateral circulation flow that introduces a true arterial tissue delay (ATD)-related dispersive component; and 2) the presence of an arterial stenosis that disperses and shifts the AIF peak entering the tissue; increasing the apparent ATD relative to the original AIF. Results Previously reported CBF estimates for the stenosis dispersion model were found to be a mixture of true dispersive effects and an algorithm implementation-induced systematic error. The true CBFMEASURED/CBFNO-DISPERSION ratios for short mean transit times (MTT) (normal) and long MTT (infarcted) tissue were similar for both dispersion models evaluated; this was an unanticipated result. The CBF quantification inaccuracies induced through the dispersion model truly related to ATD were lower than for the local stenosis-based dispersion for small ATD values. Conclusion Correcting the systematic error present in a previous deconvolution study removes the reported ATD-related impact on CBF quantification. The impact of dispersion was smaller than half that reported in previous simulation studies. J. Magn. Reson. Imaging 2007;25:639,643. © 2007 Wiley-Liss, Inc. [source]

Ultra-large effective-area, higher-order mode fibers: a new strategy for high-power lasers

LASER & PHOTONICS REVIEWS, Issue 6 2008
S. Ramachandran
Abstract This paper describes the physics and properties of a novel optical fiber that would be attractive for building high-power fiber lasers and amplifiers. Instead of propagating light in the fundamental, Gaussian-shaped mode, we describe a fiber in which the signal is forced to travel in a single, desired higher order mode (HOM). This provides for several advantages over the conventional approach, ranging from significantly higher ability to scale mode areas (and hence laser powers) to managing dispersion for ultra-short pulses , a capability that is practically nonexistent in conventional fibers. Particularly interesting is the fact that this approach challenges conventional wisdom, and demonstrates that for applications requiring meter-length fibers (as in high-power lasers), signal stability actually increases with mode order. Using this approach, we demonstrate mode areas exceeding 3200 ,m2, and propagate signals with negligible mode distortions over up to 50-meter lengths. We describe several pulse propagation experiments in which we test the nonlinear response of this fiber platform, ranging from managing dispersive effects in femtosecond pulse systems, to reducing Brillouin scattering impairments in systems operating with the nanosecond pulses. [source]

Non-linear bending waves in Keplerian accretion discs

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
G. I. Ogilvie
ABSTRACT The non-linear dynamics of a warped accretion disc is investigated in the important case of a thin Keplerian disc with negligible viscosity and self-gravity. A one-dimensional evolutionary equation is formally derived that describes the primary non-linear and dispersive effects on propagating bending waves other than parametric instabilities. It has the form of a derivative non-linear Schrödinger (DNLS) equation with coefficients that are obtained explicitly for a particular model of a disc. The properties of this equation are analysed in some detail and illustrative numerical solutions are presented. The non-linear and dispersive effects both depend on the compressibility of the gas through its adiabatic index ,. In the physically realistic case , < 3, non-linearity does not lead to the steepening of bending waves but instead enhances their linear dispersion. In the opposite case , > 3, non-linearity leads to wave steepening and solitary waves are supported. The effects of a small effective viscosity, which may suppress parametric instabilities, are also considered. This analysis may provide a useful point of comparison between theory and numerical simulations of warped accretion discs. [source]