The non-integer cyclovoltammetric electron-exchange numbers of reversible redox reactions of adsorbates: theoretical considerations

Two types of non-integer electron-exchange numbers from uniform and reversible surface-redox reactions without side reactions have been distinguished. The first being the apparent number, n _app, of the apparent faradaic charge corresponding to cyclovoltammetric peak areas above the interpolated baseline, and the second the thermodynamically defined surface-redox valency, n', of Nernstian slopes of cyclovoltammetric peak potentials depending on different solution pH. An analytical expression has been derived for n _app based on a simplified capacitive equivalent circuit and for n' using the potential-dependent free adsorption energies of the reactants involved. It should be pointed out that the different experimental values of n _app and n' refer to the same integer number of electrons per molecule oxidized or reduced. Electronic Publication     

Computational Approach to the Receptor-Bound Conformation of Cyclosporin A

The conversion of the conformation of cyclosporin A (CsA) observed in CHCl₃ to the receptor-bound state is investigated by two molecular-mechanics methods, template forcing and dynamic forcing. The conformations of CsA in CHCl₃ and complexed with LiCl in THF as determined by NMR are used as starting structures. The transition starting from the CsA/CHCl₃-derived conformation is hindered by steric interactions of two side chains (MeBmt¹ and Val⁵). While starting with the CsA/LiCl-derived conformation, the conversion is facile. It is illustrated that these calculations, which are of artificial character, using only the starting and final structures of the observed conformational transition during the receptor-binding event, allow an insight into the interactions between the substrates and receptor in terms of an induced fit.     

Risk minimization and optimal derivative design in a principal agent game

We consider the problem of Adverse Selection and optimal derivative design within a Principal–Agent framework. The principal’s income is exposed to non-hedgeable risk factors arising, for instance, from weather or climate phenomena. She evaluates her risk using a coherent and law invariant risk measure and tries minimize her exposure by selling derivative securities on her income to individual agents. The agents have mean–variance preferences with heterogeneous risk aversion coefficients. An agent’s degree of risk aversion is private information and hidden from the principal who only knows the overall distribution. We show that the principal’s risk minimization problem has a solution and illustrate the effects of risk transfer on her income by means of two specific examples. Our model extends earlier work of Barrieu and El Karoui (in Financ Stochast 9, 269–298, 2005) and Carlier et al. (in Math Financ Econ 1, 57–80, 2007). We thank Guillaume Carlier, Pierre-Andre Chiappori, Ivar Ekeland, Andreas Putz and seminar participants at various institutions for valuable comments and suggestions. Financial support through an NSERC individual discovery grant is gratefully acknowledged.     

Influence of the Ca:Pb ratio on the superconducting properties of Bi-based ceramics of type 2223

From a study of the influence of the Ca: Pb ratio on the superconducting properties of Bibased ceramics of 2223 type it follows that as a second parameter the employed gas atmosphere must be taken into consideration. In case of air preparation good intragrain and intergrain properties are obtained for Ca rich samples (e.g. Bi_1.8Pb_0.2Sr_1.9Ca_2.1 Cu₃O_z); whereas for Pb rich materials (e.g. Bi_1.7Pb_0.5Sr_1.9Ca_1.9 Cu₃O_z) improved conditions are encountered by employment of an Ar/O₂ (8%) atmosphere during synthesis. Independently, the transition temperature is situated near 108 K.     

Screening of collective cyclotron resonance in inversion layers on InSb

Cyclotron Resonance (CR) of inversion electrons on InSb is studied in parallel magnetic fields with normally incident light. Whereas in this Voigt configuration collective CR is observed in thin bulk samples, we observe single particle CR in the case of inversion layers. The apparent screening of the collective mode is explained by the inhomogeneity of the inversion electron gas in crossed electric and magnetic fields.