Collineation groups of translation planes admitting hyperbolic Buekenhout or parabolic Buekenhout-Metz unitals

It is shown that for every semifield spread in PG(3,q) and for every parabolic Buekenhout-Metz unital, there is a collineation group of the associated translation plane that acts transitively and regularly on the affine points of the parabolic unital. Conversely, any spread admitting such a group is shown to be a semifield spread. For hyperbolic Buekenhout unitals, various collineation groups of translation planes admitting such unitals and the associated planes are determined.     

Fixed-Point Methods for a Certain Class of Operators

We introduce in this paper a new class of nonlinear operators, which contains, among others, the class of operators with semimonotone additive inverse and also the class of nonexpansive mappings. We study this class and discuss some of its properties. Then we present iterative procedures for computing fixed points of operators in this class, which allow for inexact solutions of the subproblems and relative error criteria. We prove weak convergence of the generated sequences in the context of Hilbert spaces. Strong convergence is also discussed.     

Recursive adaptive control of Markov decision processes with the average reward criterion

We are concerned with Markov decision processes with Borel state and action spaces; the transition law and the reward function depend on anunknown parameter. In this framework, we study therecursive adaptive nonstationary value iteration policy, which is proved to be optimal under thesame conditions usually imposed to obtain the optimality of other well-knownnonrecursive adaptive policies. The results are illustrated by showing the existence of optimal adaptive policies for a class of additive-noise systems with unknown noise distribution.This research was supported in part by the Consejo Nacional de Ciencia y Tecnología under Grants PCEXCNA-050156 and A128CCOEO550, and in part by the Third World Academy of Sciences under Grant TWAS RG MP 898-152.     

Recent results on conditions for the existence of average optimal stationary policies

This paper concerns countable state space Markov decision processes endowed with a (long-run expected)average reward criterion. For these models we summarize and, in some cases,extend some recent results on sufficient conditions to establish the existence of optimal stationary policies. The topics considered are the following: (i) the new assumptions introduced by Sennott in [20–23], (ii)necessary and sufficient conditions for the existence of a bounded solution to the optimality equation, and (iii) equivalence of average optimality criteria. Some problems are posed.This research was partially supported by the Third World Academy of Sciences (TWAS) under Grant No. TWAS RG MP 898-152.     

Scanning Near-Field Optical Microscopy and Microspectroscopy of Green Fluorescent Protein in Intact Escherichia coli Bacteria

Scanning near-field optical microscopy (SNOM) yields high-resolution topographic and optical information and constitutes an important new technique for visualizing biological systems. By coupling a spectrograph to a near-field microscope, we have been able to perform microspectroscopic measurements with a spatial resolution greatly exceeding that of the conventional optical microscope. Here we present SNOM images of Escherichia coli bacteria expressing a mutant green fluorescent protein (GFP), an important reporter molecule in cell, developmental, and molecular biology. Near-field emission spectra confirm that the fluorescence detected by SNOM arises from bacterially expressed GFP molecules.     

Structure and stability of (CuNO) isomers

Quantum-mechanical calculations have been performed on various isomers of the (CuNO)⁺ system. A ²Π ground state is found for the linear CuNO⁺ and CuON⁺ isomers and a ²A′ state for the bent CuNO⁺ and CuON⁺ isomers. Energy calculations indicate that the linear CuNO⁺ structure is the most stable, the bent CuNO⁺ and CuON⁺ and the linear CuON⁺ structures are at 0.86 eV, 0.99 eV and 1.04 eV above this respectively. In the CuNO⁺ → CuON⁺ interconversion between the linear isomers, three transition states are involved, whereas the bent CuNO⁺ isomer is found to be an intermediate species. The isomerization barriers, dissociation energies, equilibrium geometries and vibration frequencies are given for all isomers in their ground and first excited states.     

Electrochemical properties of monolayer-protected Au and Pd nanoparticles extracted from within dendrimer templates

The electrochemical properties of Au and Pd monolayer-protected clusters (MPCs), prepared by dendrimer-templating and subsequent extraction, are described. Differential pulse voltammetry was used to estimate the size of the MPCs, and the results were compared to microscopic data and calculated values. Purification of the extracted Au and Pd nanoparticles was not required to obtain well-defined differential pulse voltammetry peaks arising from quantized double-layer charging. The calculated sizes of the nanoparticles were essentially identical to those determined from the electrochemical data. The capacitance of the particles was independent of the composition of core metal. Transmission electron microscopy data overestimated the size of the smallest Pd nanoparticles because of inadequate point-to-point resolution.     

Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes: Part IV. Carbon Tetrachloride electroreduction in the presence of Cl−, Br−, SCN−, and N3−

The rate constant for CCl₄ electroreduction on mercury, once corrected for diffuselayer effects according to Frumkin, still depends on the charge density q_i due to specifically abdsorbed supporting ions. Thus, in the presence of the adsorbed anions Cl^?, Br^?, SCN^? and N₃^?, the logarithm Φ of the rate constant corrected for diffuse-layer effects decreases linearly with |q_i|. The slopes of the various Φ vs. q_i plots are in fairly good agreement with the theoretical treatment of ref. 9, which accounts for the electrostatic interactions between the activated complex for the electrode reaction and the neighbouring adsorbed electroinactive ions within the compact layer. An analogous behaviour is observed in the reduction of CBr₄.