A PULSE RADIOLYSIS STUDY OF THE ONE-ELECTRON OXIDATION AND REDUCTION OF 5, 10-METHENYLTETRAHYDROFOLATE

Abstract— The one-electron reduction and oxidation of 5,10-methenyltetrahydrofolate has been studied in aqueous solution in the acidity range H₀= -1 to pH = 7 using the reducing species CO^-₂ and (CH₃)₂-COH and oxidising species Br^-₂, and H₂SeO+₃. The spectral and other properties of the radicals so formed were found to be indcpendent of the reductant/oxidant used. Two protolytic forms of both the oxidised and reduced radicals were observed with approximate p K , values of 0.5 ± 0.3 being determined. Both the bridged form (5.10-methenyltetrahydrofolate) and the unbridged form (5- formyltetrahydrofolate) were found to be easily oxidised, whereas only the former could be reduced.     

The Phase Transition between Chiral Nematic and Smectic A* Liquid Crystals

 In this paper we study the Landau-de Gennes free energy used to describe the transition between chiral nematic and smectic A liquid crystal phases. We consider the phenomenology of the transition and discuss the behavior of the material constants. Within the present mathematical framework, the physically observed growth behavior of the twist and bend Frank constants, K ² and K ³ respectively, plays a major role in determining the transition regime. We show existence of minimizers in a large class of admissible fields. Then, under the hypothesis that K ² and K ³ are large, we establish estimates for the transition regime separating the two phases. The work emphasizes the interplay between two competing effects: the layer formation of the smectic A phase and the twist tendency of the chiral nematic phase. Our discussion also illustrates the analogies as well as the discrepancies in modeling and behavior between smectic A^* liquid crystals and superconducting materials described by the Ginzburg-Landau theory. (Accepted May 7, 2002) Published online November 5, 2002     

FLAVINS IN LIPOSOMES-ANOMALOUS PHOTOCHEMICAL EFFECTS AT HIGH PIGMENT CONCENTRATIONS

Abstract Laser flash photolysis of riboflavin tetrabutyrate incorporated in lecithin liposomes has been studied as a function of the number of flavins per liposome, ^NRFTB.
Both the flavin triplet decay rate and its susceptibility to quenching by oxygen and glycyl-tyrosine depend markedly on the value of ^NRFTB. The results are interpreted on the basis of the existence of two distinct locations for the flavin chromophore within the liposome structure.     

Singular Matched Eigenfunction Expansions for Stokes Flow around a Corner

A singular matched eigenfunction expansion method is describedfor solving Stokes flow around a corner. The flow region isdecomposed into a number of simpler rectangular subregions;this enables the stream function to be represented by meansof an expansion of Papkovich-Fadle eigenfunctions in each ofthese subregions. The coefficients in these expansions are obtainedby matching them across common interfaces in a weak sense. Theresulting solution is used in a post-processing technique todetermine the coefficients in the known locally convergent expansionof the stream function at reentrant and salient corners. A smallnumber of terms in this expansion is necessary to produce accurateapproximations.     

Forbidden Shapes in the Finite Element Method

In two dimensional finite element analysis, increased accuracyis obtained by the addition of a number of nodal points alongthe sides of the elements. Curvilinear coordinates (p, q) wereintroduced to enable the interpolating functions to be obtainedin these complicated situations. Unfortunately as was pointedout by Jordan (1970) and is further outlined here, many usefulelement shapes with side nodes are "forbidden" by this proceduredue to the vanishing of the Jacobian of the transformation fromthe (p, q) system to the fixed (x, y) system. A new technique is introduced in the present paper, based ongeometrical considerations, whereby interpolating functionsare obtained directly in terms of x and y for the triangle andquadrilateral with arbitrarily placed side points. These localfunctions can be used to construct piecewise smooth global interpolatingfunctions with C^° continuity over regions possessing curvedboundaries and composed of elements which are triangles andparallelograms with arbitrarily positioned side points.     

On the Legendre Coefficients of a General-Order Derivative of an Infinitely Differentiable Function

An expression relating the Legendre coefficients of a generalderivative of an infinitely differentiable function in termsof the Legendre coefficients of the function is proved.     

HABITAT PATCH OCCUPANCY DYNAMICS OF GLAUCOUS‐WINGED GULLS (LARUS GLAUCESCENS) I: A DISCRETE‐TIME MODEL

ABSTRACT. Diurnal habitat occupancy dynamics of Glaucous‐winged Gulls were evaluated in a system of six habitats on and around Protection Island, Washington. Data were collected on the rates of gull movement between habitat patches, and from these data the probabilities of transitions between habitats were estimated as functions of tide height and time of day. A discrete‐time matrix model based on the transition probabilities was used to generate habitat occupancy predictions, which were then compared to hourly census data. All model parameters were estimated directly from data rather than through model fitting. The model made reasonable predictions for two of the six habitats and explained 45% of the variability in the data from 2003. The construction and testing of mathematical models that predict occupancies in multiple habitats may play increasingly important roles in the understanding and management of animal populations within complex environments.