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Quadratic Dependence (quadratic + dependence)

Distribution by Scientific Domains

Polymers and Materials Science	33%

Selected Abstracts

Studies of thioguanine-resistant lymphocytes induced by in vivo irradiation of mice

ENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 5 2008
Irene M. Jones
Abstract The frequency of Hprt -deficient lymphocytes in mice after in vivo , irradiation, has been found to vary as a function of time elapsed after exposure and irradiation dose. The frequency of mutant lymphocytes in spleen was determined using an in vitro, clonogenic assay for thioguanine-resistant T-lymphocytes. Mice were exposed to single doses of 0,400 cGy from cesium-137 or to eight daily doses of 50 cGy. The time to maximum-induced mutant frequency was 3 weeks. The dose response was strikingly curvilinear at 3,5 weeks after irradiation, but less precisely defined for 10,53 weeks after exposure, being fit by either linear or quadratic dependence. Three weeks after eight daily 50 cGy exposures, mutant frequency was elevated above controls and mice exposed to 50 cGy (which were not distinct from the nonirradiated controls), but only 17% in that of mice given a single 400 cGy fraction. This fractionation effect and the curvilinearity of the early dose,response curve suggested that saturation of repair increased the yield of mutations at higher acute doses. The decline of spleen mutant frequency in mice observed between 5 and 10 weeks after irradiation may reflect selection against some mutants. The marked variation of mutant frequency, as a function of time after irradiation and of dose rate, emphasize the need to evaluate these variables carefully and consistently in future studies. Environ. Mol. Mutagen., 2008. © 2008 Wiley-Liss, Inc. [source]

Kinetic and Equilibrium Studies of Reactions of N-Heterocycles with Dimeric and Monomeric Oxorhenium(V) Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003
James H. Espenson
Abstract Equilibrium constants have been evaluated for the reaction {MeReO(edt)}2 + 2 L , 2 MeReO(edt)L, where edt is 1,2-ethanedithiolate and L is any of 13 N-donor heterocyclic ligands. The values of K range from 1.37(27)×10,2 for pyrimidine to 1.95(6)×106 for imidazole at 25 °C in chloroform. A successful correlation of logK with log (Ka) of HL+ was realized except in the case of the 2-substituted ligands 2-picoline and quinoline, where steric effects make K smaller than expected from the proton basicity of L. The kinetics of the same reactions were studied; the rate law for the reaction in the forward direction is given by ,d[{MeReO(edt)}2]/dt = {ka + kb[L]}[L] × [{MeReO(edt)}2]. Except for 2-picoline and quinoline, the major pathway is provided by the term that shows the quadratic dependence on [L]. Values of log (kb) also correlate with log K, and therefore necessarily with log (Ka). [source]

Combined Optical and MR Bioimaging Using Rare Earth Ion Doped NaYF4 Nanocrystals

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2009
Rajiv Kumar
Abstract Here, novel nanoprobes for combined optical and magnetic resonance (MR) bioimaging are reported. Fluoride (NaYF4) nanocrystals (20,30,nm size) co-doped with the rare earth ions Gd3+ and Er3+/Yb3+/Eu3+ are synthesized and dispersed in water. An efficient up- and downconverted photoluminescence from the rare-earth ions (Er3+ and Yb3+ or Eu3+) doped into fluoride nanomatrix allows optical imaging modality for the nanoprobes. Upconversion nanophosphors (UCNPs) show nearly quadratic dependence of the photoluminescence intensity on the excitation light power, confirming a two-photon induced process and allowing two-photon imaging with UCNPs with low power continuous wave laser diodes due to the sequential nature of the two-photon process. Furthermore, both UCNPs and downconversion nanophosphors (DCNPs) are modified with biorecognition biomolecules such as anti-claudin-4 and anti-mesothelin, and show in vitro targeted delivery to cancer cells using confocal microscopy. The possibility of using nanoprobes for optical imaging in vivo is also demonstrated. It is also shown that Gd3+ co-doped within the nanophosphors imparts strong T1 (Spin-lattice relaxation time) and T2 (spin-spin relaxation time) for high contrast MR imaging. Thus, nanoprobes based on fluoride nanophosphors doped with rare earth ions are shown to provide the dual modality of optical and magnetic resonance imaging. [source]

Phase Behavior, 3-D Structure, and Rheology of Colloidal Microsphere,Nanoparticle Suspensions

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006
Summer K. Rhodes
A new route for tailoring the behavior of colloidal suspensions through nanoparticle additions is reviewed. Specifically, the interparticle interactions, phase behavior, 3-D structure, and rheological properties of microsphere,nanoparticle mixtures that possess both high charge and size asymmetry are described. Negligibly charged microspheres, which flocculate when suspended alone, undergo a remarkable stabilizing transition upon the addition of highly charged nanoparticles. The formation of a dynamic nanoparticle halo around each colloid induces an effective repulsion between the microspheres that promotes their stability. With increasing nanoparticle concentration, the colloids again undergo flocculation because of the emergence of an effective microsphere attraction, whose magnitude exhibits a quadratic dependence on nanoparticle volume fraction. The broader impact of these observations on colloidal stabilization and assembly of advanced ceramics is highlighted. [source]

Influence of quadratic contributions in magnetization-induced second harmonic generation studies of magnetization reversal

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005
V. K. Valev
Abstract Magnetization-induced optical Second Harmonic Generation (MSHG) from an exchange-biased CoO/Fe multilayer produces an asymmetrical hysteresis loop that indicates different magnetization reversal behaviour between the interface and the bulk ferromagnet. A more careful analysis of the data demonstrates that this asymmetry is in fact due to a quadratic dependence on the magnetization of the MSHG intensity. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Reactive ion etching of dielectrics and silicon for photovoltaic applications

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2006
Prakash N. K. Deenapanray
Abstract This paper investigates the reactive ion etching of SiO2, Si3N4, and Si using CHF3/O2 plasma. In particular, we have characterized the time and rf power dependence of the carrier lifetimes in n- and p-type FZ Si. The time dependence of reactive ion etching (RIE) at different rf powers provide insight into the two competing processes of damage accumulation and damage removal in the near-surface region of the Si during plasma etching. The carrier lifetime, measured using the quasi-steady-state photoconductance (QSSPC) technique, has a quadratic dependence on the rf power, which can be related to changes in the dc self-bias generated by the plasma at different rf powers. The change in carrier lifetime is similar in both n- and p-type Si of the same doping concentration. Using this fact, together with the electronic properties of defects obtained by deep level transient spectroscopy (DLTS), we have modeled the injection-dependence of the measured carrier lifetimes using the Shockley,Read,Hall model. The isochronal annealing behavior of plasma etched Si has also been studied. Copyright © 2006 John Wiley & Sons, Ltd. [source]