Solid-state optical properties of linear polyconjugated molecules: pi-stack contra herringbone

The intermolecular arrangement in the solid state and the consequences on the optical and photophysical properties are studied on different derivatives of oligophenylenevinylenes by UV/VIS absorption and angular-resolved polarized fluorescence spectroscopy. Unsubstituted distyrylbenzene (DSB) organizes in a herringbone manner, with the long axes of the molecules oriented in parallel, but the short axes almost perpendicular to each other. Fluorinated distyrylbenzene (F(12)DSB) as well as the DSB:F(12)DSB cocrystals prefer cofacial pi-stacking in the solid state. For all structures, the consequence of the parallel alignment of the transition moments is a strongly blueshifted H-type absorption spectrum and a low radiative rate constant k(F). Significant differences are observed for the emission spectra: the perpendicular arrangement of the short axes in DSB crystals leads to only very weak intermolecular vibronic coupling. Hence the emission spectrum is well structured, very similar to the one in solution. For F(12)DSB and DSB:F(12)DSB, the cofacial arrangement of the adjacent molecules enables strong intermolecular vibronic coupling of adjacent molecules. Thus, an unstructured and strongly redshifted excimerlike emission spectrum is observed. The differences in the electronic nature of the excited states are highlighted by quantum-chemical calculations, revealing the contribution of interchain excitations to the electronic transitions.     

Scale-free brain functional networks

Functional magnetic resonance imaging is used to extract functional networks connecting correlated human brain sites. Analysis of the resulting networks in different tasks shows that (a) the distribution of functional connections, and the probability of finding a link versus distance are both scale-free, (b) the characteristic path length is small and comparable with those of equivalent random networks, and (c) the clustering coefficient is orders of magnitude larger than those of equivalent random networks. All these properties, typical of scale-free small-world networks, reflect important functional information about brain states.     

A comparative study of the ability of different techniques to extract menthol from Mentha piperita

Supercritical fluid extraction, direct thermal desorption, hydroalcoholic extraction, and atomization are used to extract menthol from leaf plants of Mentha piperita. The investigated methods are comparatively evaluated on the basis of their reliability to determine the enantiomeric distribution of menthol. The enantioselectivity required for the gas chromatographic analysis is achieved using Octakis (2,6-di-O-n-pentyl-3-O-butyryl)-gamma-cyclodextrin as the stationary phase. From the obtained results, it is established that there is a significant effect of the combination of pressure and temperature to achieve the effective isolation and fractionation of the less and most volatile compounds using supercritical fluids.     

Dihydropyridines in MCRs. Tandem processes leading to modular tetrahydroquinoline systems with up to 6 diversity elements

An efficient, modular method for the synthesis of highly substituted tetrahydroquinoline systems is described. The Lewis acid catalyzed interaction of dihydropyridines with glyoxalate and anilines affords the heterocyclic parent systems in good yields. Tandem one-pot processes allow the incorporation of additional components: a preliminary nucleophilic attack on pyridinium salts generates the reactive dihydropyridine in situ, and subsequent electrophilic reactions on the secondary amine complete the assembly of the final targets, which have up to 6 diversity points.     

A simple “market value” bargaining model for weighted voting games: characterization and limit theorems

We offer a bargaining model for weighted voting games that is a close relative of the nucleolus and the kernel. We look for a set of weights that preserves winning coalitions that has the property of minimizing the difference between the weight of the smallest and the weight of the largest Minimum Winning Coalition. We claim that such a set of weights provides an a priori measure of a weighted voter’s bribeworthiness or market value. After introducing our model, we provide a characterization result for this model and show its links to other bargaining model approaches in the literature. Then we offer some limit results showing that, with certain reasonable conditions on the distributions of weights, as the size of the voting body increases, the values of bribeworthiness we calculate will approach both the weights themselves and the Banzhaf scores for the weighted voting game. We also show that, even for relatively small groups using weighted voting, such as the membership of the European Council of Ministers (and its predecessors) 1958–2003, similarities among the usual a priori power scores, bribeworthiness/market value, and the weights themselves, will be quite strong.     

A generalized Riemann problem for quasi-one-dimensional gas flows

A generalization of the Riemann problem for gas dynamical flows influenced by curved geometry, such as flows in a variable-area duct, is solved. For this generalized Riemann problem the initial data consist of a pair of steady-state solutions separated by a jump discontinuity. The solution of the generalized Riemann problem is used as a basis for a random choice method in which steady-state solutions are used as an Ansatz to approximate the spatial variation of the solution between grid points. For nearly steady flow in a Laval nozzle, where this Ansatz is appropriate, this generalized random choice method gives greatly improved results.     

The formate anion: the harmonic and anharmonic force fields

Harmonic and anharmonic symmetry force constant matrices have been obtained for six isotopically substituted species of the formate anion. The valence force fields derived from the above matrices were used to recalculate the vibrational frequencies. These force fields are compared with others previously reported and obtained via other methods.