Electrical Conductivity of o-, m-, and p-Terphenyls

Many investigations have been carried out on the electrical properties of p-terphenyl1-9, and, as far as we know, only one on m-terphenyl10. In the present work, the d. c. electrical conductivities of the three isomeric terphenyls are compared to establish the influence of the molecular structure on the electrical properties and to explain the mechanism of the energy transport in organic molecules

Abundance Patterns in the Draco, Sextans and Ursa Minor Dwarf Spheroidal Galaxies

The Keck I telescope has been used to obtain HIRES spectra for red giants belonging to the Draco, Sextans and Ursa Minor dwarf spheroidal (dSph) galaxies. An analysis of these spectra is presented, along with abundance ratios for more than 20 elements. The resulting database of element abundances for 17 stars is the most extensive yet assembled for stars in dSph environments. Our main findings are summarized as follows: (1) There is unambiguous evidence for a large internal spread in metallicity in all three galaxies: our program stars span a range of [Fe/H] = 1.53, 1.40 and 0.73 dex in Draco, Sextans and Ursa Minor, respectively. (2) The abundance patterns among the dSph stars are remarkably uniform, suggesting that all three galaxies have similar nucleosynthetic histories. (3) A comparison of the measured abundance ratios for our sample of dSph stars with published values for Galactic halo and disk field stars suggests that the dSph galaxies have 0.02 < [alpha/Fe] < 0.13 dex, whereas the halo field star sample has [alpha/Fe] ~ 0.28 dex over the same range in metallicity. (4) The most metal-rich dSph stars in our sample have [Y/Fe] abundances which are significantly lower than those measured for halo field stars of similar metallicity, while the measured [Ba/Eu] ratios for the dSph stars suggest that the early chemical evolution of these galaxies was dominated by the r-process. Taken together, these results suggest that the Galactic halo is unlikely to have assembled, in its entirety, through the disruption of dwarf galaxies similar to the low-luminosity dSphs studied here. (ABRIDGED).Comment: 24 pages, 8 postscript figures (including 6 color figures). Accepted for publication in the Astrophysical Journa

New data on OZI rule violation in bar{p}p annihilation at rest

The results of a measurement of the ratio R = Y(phi pi+ pi-) / Y(omega pi+ pi-) for antiproton annihilation at rest in a gaseous and in a liquid hydrogen target are presented. It was found that the value of this ratio increases with the decreasing of the dipion mass, which demonstrates the difference in the phi and omega production mechanisms. An indication on the momentum transfer dependence of the apparent OZI rule violation for phi production from the 3S1 initial state was found.Comment: 11 pages, 3 PostScript figures, submitted to Physics Letter

Synthesis and polymerization of a new thiophene functionalized with both NLO-active chromophore and an alkylic self-plastifying chain

This paper describes a new easy and straight-forward synthetic pathway leading to a thiophenic monomer functionalized with a second-order NLO chromophore and with an alkylic plastifying chain, namely the 3-{6-[4-(40- nitrophenylazo)-N-ethyl-N-phenylamino]hexyl}-4-hexylthiophene. The corresponding polymers obtained by direct oxidative polymerization and by post-polymerization functionalization of a polymeric precursor are soluble in common organic solvents even if their chromophore content is 100%. The final materials have been characterized by using 1Hand 13C-NMR spectrometry, FT-IR spectroscopy, SEC, DSC analysis and conductivity measurements. The thermal characteristics and the electrical behaviour of the \u2018\u2018self-plastifying\u2019\u2019 polymers are comparable to those of the alkylthiophene/ chromophorized-alkylthiophene copolymers, but the presence of the highest content in NLO chromophoric substituent in the new synthesized homopolymers makes them particularly interesting for optoelectronic applications

Poli[3-esil-4-(6-bromoesil)tiofene]: un intermedio-chiave per la sintesi di politiofeni multifunzionali autoplastificanti

none3Autore/i del volume: AIM (ASSOCIAZIONE ITALIANA DI SCIENZA E TECNOLOGIA DELLE MACROMOLECOLE)mixedL. Paganin; M. Lanzi; P. Costa BizzarriL. Paganin; M. Lanzi; P. Costa Bizzarr

Electrical Conductivity of o-, m-, and p-Terphenyls

Many investigations have been carried out on the electrical properties of p-terphenyl1-9, and, as far as we know, only one on m-terphenyl10. In the present work, the d. c. electrical conductivities of the three isomeric terphenyls are compared to establish the influence of the molecular structure on the electrical properties and to explain the mechanism of the energy transport in organic molecules

Solvatochromic properties of poly [3-(6-methoxyhexyl)-2,5-thienylene] in different solvent mixtures

Two samples of poly [3-(6-methoxyhexyl)-2,5-thienylene] with a slight difference in regioregularity and a greater difference in molecular weights were obtained by chemical oxidation with FeCl3. The solvatochromism of the two polymers was investigated in mixtures of various solvents (dioxane, dimethylpropyleneurea, methylene chloride, tetrahydrofuran, chloroform and toluene) with different non-solvent (methanol) molar fractions, at constant polymer concentration and temperature. Some solvent/non-solvent couples were able to distinguish between the two samples, giving a different solvatochromic effect. This can be considered a very useful tool to characterize polymers with configurational and molecular weight differences. © 1997 Elsevier Science S.A