The nuclear magnetic resonance spectra of porphyrins—XI : Self-aggregation of zinc(II) meso-trifluoroacetoxyoctaethylporphyrin

Complex formation in zinc(II) meso-trifluoroacetoxyoctacthylporphyrin (1) and the corresponding acetate (3) has been studied by ¹H and ¹³C NMR spectroscopy. The large concentration dependence of the ¹H chemical shifts of 1 has been analysed in terms of a monomer-dimer equilibrium to give K ～ 3.01 mole^?1 and monomer-dimer shifts of up to 4.2 ppm (for the γ-meso proton). The dimers are immediately dissociated upon addition of methanol. In complete contrast, 3 shows no concentration dependence nor any change upon addition of methanol.The conformations of the model compounds phenyl acetate (4) and phenyl trifluoroacetate (5) were studied by CNDO and solvation calculations and, for 4, by a LIS experiment. Compound 4 exists as the endo conformer in non-polar media, but the exo conformer is preferentially solvated and is also formed when 4 complexes with Eu(fod)₃. In compound 5, the exo-endo energy difference is smaller and is not so affected by solvation; 5 shows no LIS.The large complex shifts found for compound 1 are best explained on the basis of a dimer structure in which the O·CO·CF₃ groups play no part in the association, which is presumably due to a novel metal to porphyrin interaction.     

Evaluation of models for flame stretch due to curvature in the thin reaction zones regime

Direct numerical simulation (DNS) was used to study modelling assumptions for the curvature-propagation component of flame stretch in the thin reaction zones regime of turbulent premixed combustion, a regime in which small eddies can penetrate the preheat zone but not the thinner fuel breakdown zone. Simulations of lean hydrogen–air and methane–air flames were conducted, and statistics of flame stretch due to curvature, henceforth referred to simply as stretch, were extracted from a species mass fraction iso-surface taken to represent the flame. The study focussed on investigating the modelling assumptions of Peters [J. Fluid Mech. 384 (1999) 107]. It was found that the mean stretch is dominated by stretch due to correlations of flame speed with curvature, and specifically the effects of tangential diffusion. The modelling suggestions of Peters were found to provide an improvement over the assumptions of a constant flame speed or a flame speed governed by the linear relationship with stretch at small and steady stretch. However for the conditions considered here, diffusive-thermal effects remain well into the thin reaction zones regime, and the suggestions of Peters generally over-predict the mean compressive stretch. An effective diffusivity for flame stretch was suggested and evaluated for the methane simulations. It was found that the effective diffusivity was comparable to the mass diffusivity for flames with a high ratio of flame time to eddy turnover time. The length scales contributing to stretch were investigated, and it was found that while most flame area has a radius of curvature greater than the laminar flame thickness, most stretch occurs in more tightly curved flame elements.     

Poloidal rotation dynamics, radial electric field, and neoclassical theory in the jet internal-transport-barrier region

Results from the first measurements of a core plasma poloidal rotation velocity (upsilontheta) across internal transport barriers (ITB) on JET are presented. The spatial and temporal evolution of the ITB can be followed along with the upsilontheta radial profiles, providing a very clear link between the location of the steepest region of the ion temperature gradient and localized spin-up of upsilontheta. The upsilontheta measurements are an order of magnitude higher than the neoclassical predictions for thermal particles in the ITB region, contrary to the close agreement found between the determined and predicted particle and heat transport coefficients [K.-D. Zastrow, Plasma Phys. Controlled Fusion 46, B255 (2004)]. These results have significant implications for the understanding of transport barrier dynamics due to their large impact on the measured radial electric field profile.     

Observation of a broad structure in the pi+ pi- J/psi mass spectrum around 4.26 GeV/c2

We study initial-state radiation events, e+ e- --> gammaISR pi+ pi- J/psi, with data collected with the BABAR detector. We observe an accumulation of events near 4.26 GeV/c2 in the invariant-mass spectrum of pi+ pi- J/psi. Fits to the mass spectrum indicate that a broad resonance with a mass of about 4.26 GeV/c2 is required to describe the observed structure. The presence of additional narrow resonances cannot be excluded. The fitted width of the broad resonance is 50 to 90 MeV/c2, depending on the fit hypothesis.     

Search for factorization-suppressed B-->chi(c)K(*) decays

We search for the factorization-suppressed decays B-->chi(c0)K(*) and B-->chi(c2)K(*), with chi(c0) and chi(c2) decaying into J/psi gamma, using a sample of 124 x 10(6) BB events collected with the BABAR detector at the PEP-II storage ring of the Stanford Linear Accelerator Center. We find no significant signal and set upper bounds for the branching fractions.