Orientational anisotropic studies by field rotation technique: near zero-field pulsed EPR experiments of pentacene doped in p-terphenyl

We report a new technique to map the orientational anisotropy of paramagnetic systems without physically changing the crystal orientations in near zero-field (NZF) pulsed EPR experiments. By implementing three sets of orthogonal coils around the sample, we are ble to create a magnetic vector up to 2 mT in any three-dimensional orientation in space. In NZF region, the hyperfine tensor elements are comparable to the electronic Zeeman interaction energy, thus very rich spectral patterns can be obtained by "dialing" in a magnetic field vector without moving the sample. The technique further allows us to examine the site symmetry of organic crystals and powdered solids doped with chromophores which can be photo-excited to the triplet state by laser light. The technique is exemplified in the study of pentacene in p-terphenyl crystals.     

Quinoline formation via a modified Combes reaction: examination of kinetics,substituent effects,and mechanistic pathways

This is the first reported investigation of the Combes condensation employing 19F NMR spectroscopy to monitor intermediate consumption and product formation rates. The reaction was found to be first order in both the diketone and aniline. Product regioselectivity and reaction rates were found to be influenced by substituents on the diketones and anilines with rates varying as much as five fold. The consumption rate of key imine and enamine intermediates mirrored quinoline formation rates, in accord with rate determining annulation. A ρ of ?0.32 was determined for this cyclization. While the sign of the reaction constant is consistent with rate limiting electrophilic aromatic substitution (EAS), the magnitude is likely a composite value, resulting from opposing substituent effects in the nucleophilic addition and EAS steps. Mechanistic details and reaction pathways supporting these findings are proposed. Copyright © 2008 John Wiley & Sons, Ltd.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.     

Vectorial Approach to Fast Correlation Attacks

A new, vectorial approach to fast correlation attacks on binary memoryless combiners is proposed. Instead of individual input sequences or their linear combinations, the new attack is targeting subsets of input sequences as a whole thus exploiting the full correlation between the chosen subset and the output sequence. In particular, the set of all the input sequences can be chosen as the target. The attack is based on a novel iterative probabilistic algorithm which is also applicable to general memoryless combiners over finite fields or finite rings. To illustrate the effectiveness of the introduced approach, experimental results obtained for random balanced combining functions are presentedMost of this work was done while he was with Rome CryptoDesign Center, Gemplus, Italy     

On the Motion of a Dynamic System with Minimal Dissipation

The motion of a holonomic scleronomic non-conservative mechanicalsystem with minimal dissipation is considered. As applicationsof the theory several problems are studied in detail.     

Keto-enol and enol-enol tautomerism in trifluoromethyl-β-diketones

The keto-enol (K?E) and enol-enol (E?E) equilibria of a variety of trifluoromethyl-β-diketones were investigated using ¹H, ¹³C, ¹⁹F NMR spectroscopy, infrared spectroscopy and ultraviolet-visible spectrophotometry in nonpolar solvents. In general, NMR, IR and UV spectral evidence indicates that trifluoromethyl-β-diketones exist as mixtures of two chelated cis-enol forms in nonpolar media. Infrared spectroscopy and ultraviolet spectrophotometry show the E?E equilibrium lies in the direction of the enol form which maximizes conjugation in most cases. Exceptions are noted and discussed.