Effect of chain-end free volume on the diffusion of oligomers

We have used the pulsed-gradient spin-echo technique to measure self-diffusion in low-molecular-weight polymers in the melt and dissolved in identical polymers of high molecular weight. Specimens used were cis-polyisoprenes and polydimethylsiloxane. We find that, except for substantial free-volume corrections, self-diffusion in unentangled polyisoprene melts scales inversely with molecular weight. The results include sensitive determinations of chain-end free volume.     

Equation-of-state measurement of dense plasmas heated with fast protons

Using an ultrafast pulse of mega-electron-volt energy protons accelerated from a laser-irradiated foil, we have heated solid density aluminum plasmas to temperatures in excess of 15 eV. By measuring the temperature and the expansion rate of the heated Al plasma simultaneously and with picosecond time resolution we have found the predictions of the SESAME Livermore equation-of-state (LEOS) tables to be accurate to within 18%, in this dense plasma regime, where there have been few previous experimental measurements.     

Mass spectrometry—III: Further studies of the unimolecular decomposition of acetophenone azine in the gas phase induced by electron-impact

Mass spectra of acetophenone azine-d₁₀ (II) and acetophenone azine-d₆ (III) were obtained to ascertain the validity of the proposed mass spectral fragmentation mechanisms proposed for acetophenone azine (I). Data from II and III reveal that the [M –1] ion in the spectrum of I is formed via loss of ring hydrogen. Within experimental uncertainty the major fragmentation reactions of the molecular ion of I, the [M –1] ion, and the [M –15] ion occur without loss of structural identity of the phenyl and methyl moieties. Ionization of I occurs with a high degree of structural integrity.     

Apparent spin polarization decay in Cu-dusted Co/Al2O3/Co tunnel junctions

Co/Al2O3/Co magnetic tunnel junctions with an interfacial Cu layer have been investigated with in situ growth characterization and ex situ magnetotransport measurements. Cu interlayers grown on Co give an approximately exponential decay of the tunneling magnetoresistance with xi approximately 0.26 nm while those grown on Al2O3 have a decay length of 0.70 nm. The difference in decay lengths can be explained by different growth morphologies, and in this way clarifies a present disagreement in the literature. For monolayer coverage of Cu, we show that the tunneling spin polarization is suppressed by at least a factor of 2 compared to Co and beyond approximately 5 ML it becomes vanishingly small.