Resonant Raman spectroscopy of ethylene-acetylene copolymers doped with iodine

The relative contents of short and long conjugated chains in ethylene-acetylene copolymers (EAC) are determined by varying the lasing wavelength, as was done earlier for pure poly(acetylene). The Raman spectra of the copolymer samples doped with iodine contain the bands attributed to the iodine polyions I ₃ ^? and I ₅ ^? Unlike poly(acetylene), the ethylene-acetylene copolymer is characterized by the Raman spectra in which the intensities of the bands assigned to the I ₅ ^? polyions are higher than those of the I ₃ ^? polyions even at low degrees of doping. The structural features responsible for this difference are discussed.     

On the transferred hyperfine interaction in substituted yig

NMR of⁵⁷Fe is studied in a number of (M_xY_3–x) Fe₅O₁₂ garnets for small concentrations of M (M is either trivalent RE ion –Ho 3+, Gd 3+, Nd3+, Pr 3+, La 3+ or Bi 3+ ion). Beside the main resonance lines, the satellites were observed, which correspond to those Fe, in vicinity of which the impurity M is located. After correcting for the dipolar field, the field corresponding to the change of the transferred hyperfine interaction in M³⁺–O^2–-Fe³⁺ vs. Y³⁺–O^2–-Fe³⁺ triad was deduced from the satellites splitting. The analysis of the results indicates that the observed change in the transferred hyperfine field is mainly connected with the transfer of electrons between M³⁺ and Fe³⁺ ions and not with the local deformation around the impurity.     

Finite-size effects in single chain magnets: an experimental and theoretical study

The problem of finite-size effects in s=1/2 Ising systems showing slow dynamics of the magnetization is investigated introducing diamagnetic impurities in a Co2+-radical chain. The static magnetic properties have been measured and analyzed considering the peculiarities induced by the ferrimagnetic character of the compound. The dynamic susceptibility shows that an Arrhenius law is observed with the same energy barrier for the pure and the doped compounds while the prefactor decreases, as theoretically predicted. Multiple spin reversal has also been investigated.     

Measurement of 2+ 1 level lifetimes in 162Yb and 162Er by fast electronic scintillation timing

Lifetime measurements for the 2⁺ ₁ levels of ¹⁶²Er and ¹⁶²Yb were obtained in β⁺/ɛ decay at the Yale Moving Tape Collector by fast electronic scintillation timing of β⁺γ coincidences. Received: 2 September 2002 / Accepted: 1 October 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: mark.caprio@yale.edu Communicated by J. ?yst?     

Hemicellulose bioconversion to polyanionic heteropolysaccharides

Applied Biochemistry and Biotechnology - Anionic polysaccharides, traditionally obtained from plant or algal sources, have a variety of commercial uses. Such gums from microorganisms have received...     

Molecular destruction of polymers at the apex of a major crack

We employed infrared spectroscopy and infrared spectroscopy of deflected total internal reflection to study the rupture of polymer macromolecular chains (polyethylene and polypropylene) at the apex of a growing crack. It was shown that the break concentration at the crack surface is of the same order of magnitude as the total concentration of chemical bonds in the polymer; molecular rupture occurs not only at the apex itself but also at some distance from it. The dependence of the break concentration on the distance from the crack apex was measured. The observed patterns were related to the experimentally determined external-load distribution function for individual chemical bonds near the crack apex.I. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 621–625, July–August, 1972.     

Comparative spectral attenuation measurements on optical fibres: final report by members of COST 208

Comparative spectral attenuation measurements on a graded-index fibre have been perfomed by nine participants, covering the range 700–1800 nm. Details of measurement equipment and techniques are being reported. Since the attenuation of a graded-index fibre depends on the energy distribution launched into the fibre, only careful control of this parameter leads to comparable results. A method was developed to check the energy distribution in the fibre over a broad spectral range. By this method agreement of attenuation values to within ± 5% from 800 to 1500 nm has been achieved. This is about half of the deviation found in other comparison measurements which are usually restricted to one or two wavelengths.