Thermal decomposition of allantoin as probed by matrix isolation FTIR spectroscopy

The optimized geometries, energies of the possible conformers of allantoin (2,5-dioxo-4-imidazolidinyl urea, the diureide of glyoxylic acid) as well as the barriers for conformational interconversion have been calculated using the density functional theory [DFT(B3LYP)/6-311++G(d,p)] method. The calculations predicted the existence of four conformers (gC, tT, g′C, and g′T; where the first and second symbols in the name of the conformers designate the conformation around the exocyclic NHC–NHCO and CNH–CO axes, respectively), with the gC form contributing to more than 98% of the population in gas phase at room temperature. This conformer is different from that corresponding to the monomeric unit found in crystalline RS-allantoin (g′C; Mootz, D. Acta Crystallogr.1965, 19, 726), stressing the importance of intermolecular H-bonding in determining the structure of the crystal. Upon sublimation under vacuum (10−6 mbar), the compound was found to undergo extensive decomposition to urea, isocyanic acid, NH3, and carbon. The identification of the decomposition products was made by using matrix isolation infrared spectroscopy. In consonance with the theoretical predictions, the allantoin molecules surviving thermal decomposition were found to undergo conformational isomerization and be present in the cryogenic argon matrix in both the gC and g′C conformations. The solid state room temperature infrared spectrum of allantoin was also investigated and assigned

Managerial delegation in a dynamic renewable resource oligopoly

I propose a differential oligopoly game of resource extraction under (quasi-static) open-loop and nonlinear feedback strategies, where firms are managerial and two alternative types of delegation contract are considered. Under open-loop information, delegation expands the residual steady state resource stock. Conversely, under nonlinear feedback information the outcome depends on the structure of managerial incentives. If sales are used, once again delegation favours resource preservation. On the contrary, if market shares are included in the delegation contract, this combines with an underlying voracity effect in shrinking the steady state volume of the resource

Les Discamphiceratinae (Psiloceratidae), une nouvelle sous-famille d'ammonites (Cephalopoda) du Jurassique inférieur

The main reason for using visual languages is that they are often far more convenientto the user than traditional textual languages. Therefore, visual languages intended for use by both computers and humans ought to be designed and analyzed not only from the perspective of computational resource requirements, but equally importantly, also from the perspectiveof languages that are cognitively usable and useful. Theoretical and practical research on visual languages need to takeinto account the full context of a coupled human-computer system in which the visual language facilitates interactions between the computational and the cognitive parts. This implies that theoretical analyses ought to address issues of comprehension, reasoning and interaction in the cognitive realm as well as issues of visual program parsing, execution and feedback in the computational realm. The human aspect is crucial to visual languages, and therefore weadvocate a correspondingly broadened scope of in..