REACTIVITY OF PHOTOCHEMICALLY-GENERATED LIPID HYDROPEROXIDES IN CELL MEMBRANES WITH GLUTATHIONE PEROXIDASE

The ability of glutathione peroxidase (Gpx) to catalyze the reductive inactivation of photochemically-generated lipid hydroperoxides (LOOHs) was investigated, using hematoporphyrin derivative (HPD) as a photosensitizing agent and erythrocyte ghosts as membrane targets. Glutathione peroxidase was reactive toward photoperoxidized membranes only after their exposure to phospholipase A2 (PLA2). Iodometrically-determined LOOH values were typically 30-40% greater than values measured by enzymatic assay using Gpx and glutathione reductase. A consistent result was obtained when photooxidized membranes were treated with PLA2 and GSH/Gpx followed by iodometric assay, viz. persistence of approximately 40% of the starting LOOH. Whereas photooxidized egg phosphatidylcholine liposomes underwent total LOOH loss when incubated with PLA2 and GSH/Gpx, no net loss was observed with photooxidized cholesterol/dimyristoyl-phosphatidylcholine liposomes. The results suggest that cholesterol hydroperoxides in ghost membranes account for the Gpx-resistant fraction of LOOHs.     

THE MAXIMUM EFFICIENCY OF PHOTOSYNTHESIS *

Within the ideal assumptions: (1) two Photosystems for photosynthetic fixation of CO₂, (2) all solar photons with Λ≥ 700 nm are absorbed, (3) the photon requirement is 8 for each CO₂ molecule fixed and O₂ molecule evolved and (4) the principal stable product of photosynthesis is d-glucose, the theoretical maximum efficiency of conversion of light to stored chemical energy in green-plant type (oxygen-evolving) photosynthesis in bright sunlight is calculated to be 13.0%. Thermodynamic arguments are presented which indicate that a photosynthetic system with one Photosystem would be highly unlikely to be able to drive each electron from water to evolve O₂ and reduce CO₂. The practical maximum efficiency of photosynthesis under optimum conditions is estimated to be 8–9%.     

A new theory of electric conductivity

This theory proposes that electric conductivity, metallic or otherwise, ohmic or superconducting, is simply the result of electron density moving through atomic and molecular orbital overlaps in material bodies. The theory argues that electron density moves without resistance (is superconducting) while it is contained within extended quantum mechanical (QM) states which are constructed so that the electron wave function does not experience reflections at any interface. The theory states that ohmic conduction results when the electron wave function does experience reflections at QM interfaces, and requires the continuous external application of electromotive force (EMF) to overcome those reflections and maintain an electric current.     

Weighted Uniform Sampling -- a Monte Carlo Technique for Reducing Variance

A new Monte Carlo technique for reducing variance is presentedand analysed. It obtains gains in accuracy comparable to thoserealized by importance sampling (Hammersley & Handscomb,1964), without requiring the use of non-uniform probabilitydistributions. Some numerical examples illustrate the theory.     

Multiple groups in the symmetry classification of adiabatic electronic wavefunctions

It was originally shown by Longuet-Higgins and colleagues that when the electronic Schrödinger equation is solved as a function of the nuclear coordinates the adiabatic electronic wavefunction can undergo a change of sign after completing a closed circuit. This geometric phase occurs for a circuit around a conical intersection, and in particular around a conical intersection corresponding to a linear Jahn—Teller effect. The adiabatic wavefunctions are classified here under a group called the adiabatic multiple group, which is a generalization of the ‘vibronic double group’ of C _3v introduced by Hougen, and is distinct from the familiar electron-spin double group. Although the real electronic wavefunctions can be only double-valued, the groups can have higher multiplicity because of the possibility of different circuits. For a number of symmetric- and spherical-top point groups, the adiabatic multiple group is shown to be the direct product of the point group with a phase group. The adiabatic multiple group can be applied to individual adiabatic orbitals, and so to configurations built from these orbitals. This leads to the rule that the linear Jahn—Teller effect vanishes in the single-configuration approximation for configurations containing non-degenerate electrons plus an even number of e electrons. There does not appear to be any cancellation effect for electron configurations of cubic molecules containing f electrons.     

On the Convergence of the Variable Metric Algorithm

The variable metric algorithm is a frequently used method forcalculating the least value of a function of several variables.However it has been proved only that the method is successfulif the objective function is quadratic, although in practiceit treats many types of objective functions successfully. Thispaper extends the theory, for it proves that successful convergenceis obtained provided that the objective function has a strictlypositive definite second derivative matrix for all values ofits variables. Moreover it is shown that the rate of convergenceis super-linear.     

Spurious Behaviour of Numerically Computed Fluid Flow

We investigate the stability to aliasing errors of numericalschemes for hydrodynamics, taking the viscous Burgers' equationas a model for systems with a term that is quadratic in thevelocity. Considering wavelengths equal to three times the mesh-spacing,and arbitrary mean flow, we are able to demonstrate explicitlyfor common schemes (a) a sufficient criterion for stabilityand (b) blow-up of solutions in a finite time when (a) is violated.Singular behaviour is shown to persist at all wavelengths: studiesof wavelengths up to thirty times mesh-spacing make it clearthat a profile with a single region of strong convergent flowis most conducive to instability. In contrast, spectral (Galerkin)and upwind schemes are shown to be stable for all flows andperiods.     

A NOVEL METHOD OF FITTING SPATIO‐TEMPORAL MODELS TO DATA,WITH APPLICATIONS TO THE DYNAMICS OF MOUNTAIN PINE BEETLES

Abstract We develop a modular landscape model for the mountain pine beetle (Dendroctonus ponderosae Hopkins) infestation of a stage‐structured forest of lodgepole pine (Pinus contorta Douglas). Beetle attack dynamics are modeled using response functions and beetle movement using dispersal kernels. This modeling technique yields four model candidates. These models allow discrimination between four broad possibilities at the landscape scale: whether or not beetles are subject to an Allee effect at the landscape scale and whether or not host selection is random or directed. We fit the models with aerial damage survey data to the Sawtooth National Recreation Area using estimating functions, which allows for more rapid and complete parameter determination. We then introduce a novel model selection procedure based on facial recognition technology to compliment traditional nonspatial selection metrics. Together with these we are able to select a best model and draw inferences regarding the behavior of the beetle in outbreak conditions.