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In certain polymer-penetrant systems, nonlinear viscoelasticeffects dominate those of Ficlcian diffusion. By introducinga dependence of the chemical potential on concentration history,this behaviour can be modelled by a memory integral. The mathematicalframework presented is a moving boundary-value problem wherethe boundary separates the polymer into two distinct states:glassy and rubbery. In each region, a different operator holdsat leading order. The problem which results is not solvableby similarity solutions, but can be solved by perturbation andintegral equation techniques. By introducing a new model wherethe diffusion coefficient changes with phase, asymptotic solutionsare obtained where sharp fronts initially move like t3/2. Thissuper-Case II behaviour is found in various non-Fickianpolymer-penetrant systems. 相似文献
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Abstract— –Chemiluminescence is reported from two types of reactions; those involving the reduction of amine cations yield fluorescence amines: RN H2+m+ reductant → RN H2+hv and those involving reduction of transition metal chelates where the reduced form of the chelate is fluorescent: MLx+(n+1)+ reductant →MLx+n+hv The results reported here are for reduction of the cation radical of 1,6-diaminopyrene and ruthenium (III) chelates where chelate ligands are substituted 1,10-phenanthrolines or 2,2'-bipyridine. Reducing agents for 1,6-diaminopyrene were hydrazine or the naphthalene radical anion; for the ruthenium chelates either hydroxyl ion or hydrazine in acid solution. A detailed study is reported for the kinetics of the ruthenium (III)-hydrazine reaction, using a computer kinetic modeling program. A quantitative fit of the experimental data to computer-generated curves can be accomplished at low hydrazine concentrations. At higher hydrazine concentrations the correct qualitative shapes of curves can be generated but the quantitative fit is not exact. 相似文献
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CONOR P. McGOWAN DAVID R. SMITH JOHN A SWEKA JULIEN MARTIN JAMES D NICHOLS RICHARD WONG JAMES E LYONS LAWRENCE J NILES KEVIN KALASZ JEFFREY BRUST MICHELLE KLOPFER BRADDOCK SPEAR 《Natural Resource Modeling》2011,24(1):117-156
Abstract Adaptive management requires that predictive models be explicit and transparent to improve decisions by comparing management actions, directing further research and monitoring, and facilitating learning. The rufa subspecies of red knots (Calidris canutus rufa), which has recently exhibited steep population declines, relies on horseshoe crab (Limulus polyphemus) eggs as their primary food source during stopover in Delaware Bay during spring migration. We present a model with two different parameterizations for use in the adaptive management of horseshoe crab harvests in the Delaware Bay that links red knot mass gain, annual survival, and fecundity to horseshoe crab dynamics. The models reflect prevailing hypotheses regarding ecological links between these two species. When reported crab harvest from 1998 to 2008 was applied, projections corresponded to the observed red knot population abundances depending on strengths of the demographic relationship between these species. We compared different simulated horseshoe crab harvest strategies to evaluate whether, given this model, horseshoe crab harvest management can affect red knot conservation and found that restricting harvest can benefit red knot populations. Our model is the first to explicitly and quantitatively link these two species and will be used within an adaptive management framework to manage the Delaware Bay system and learn more about the specific nature of the linkage between the two species. 相似文献
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MARY E. NEUBERT DAVID G. ABDALLAH Jr. SANDRA S. KEAST JULIE M. KIM SOONNAM LEE RYAN M. STAYSHICH 《Liquid crystals》2013,40(6):711-731
New diphenyldiacetylenes of the type with A, B = H and/or F; m = 0, 1; n = 1–4; and X = C n H2n+1, F, CF3 or CN were synthesized and their mesomorphic properties determined by hot stage polarizing microscopy and DSC. When m = 0, all of these compounds showed only a nematic phase except when X = CF3 when both nematic and smectic A phases were seen. Both clearing and melting temperatures were higher than those reported for substitution with the corresponding alkyl chains but the much larger increase in clearing temperatures produced considerably wider nematic phases. Eutectic mixtures of a few of these olefins yielded nematic materials also having much wider temperature ranges and higher clearing temperatures than the eutectic mixtures of the alkyl compounds, while retaining their high birefringence and low viscosities. Such materials are of interest for beam-steering devices. Four of the diacetylenes with m = 1 (A, B = H) were also prepared (X = C6H13, F, n= 2, 3). When X was C6H13 (n=2), the nematic range was smaller in the 2- than in the 1-olefin but wider than in the alkyl series. When X=F, either no nematic phase or a monotropic one was observed, whereas the 1-olefins gave a much wider nematic phase. Both transition temperatures were lower than those for the corresponding 1-olefin and alkyl analogues. The compound with X=C6H13 and n=2 had a melting temperature below room temperature. 相似文献