Gas permeability and n‐butane solubility of poly(1‐trimethylgermyl‐1‐propyne)

The gas permeability and n‐butane solubility in glassy poly(1‐trimethylgermyl‐1‐propyne) (PTMGP) are reported. As synthesized, the PTMGP product contains two fractions: (1) one that is insoluble in toluene and soluble only in carbon disulfide (the toluene‐insoluble polymer) and (2) one that is soluble in both toluene and carbon disulfide (the toluene‐soluble polymer). In as‐cast films, the gas permeability and n‐butane solubility are higher in films prepared from the toluene‐soluble polymer (particularly in those films cast from toluene) than in films prepared from the toluene‐insoluble polymer and increase to a maximum in both fractions after methanol conditioning. For example, in as‐cast films prepared from carbon disulfide, the oxygen permeability at 35 °C is 330 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐soluble polymer and 73 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐insoluble polymer. After these films are conditioned in methanol, the oxygen permeability increases to 5200 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐soluble polymer and 6200 × 10^?10 cm³ (STP) cm/(cm² s cmHg) for the toluene‐insoluble polymer. The rankings of the fractional free volume and nonequilibrium excess free volume in the various PTMGP films are consistent with the measured gas permeability and n‐butane solubility values. Methanol conditioning increases gas permeability and n‐butane solubility of as‐cast PTMGP films, regardless of the polymer fraction type and casting solvent used, and minimizes the permeability and solubility differences between the various films (i.e., the permeability and solubility values of all conditioned PTMGP films are similar). © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2228–2236, 2002     

Neutron-spin resonance in the optimally electron-doped superconductor Nd1.85Ce0.15CuO4-delta

We use inelastic neutron scattering to probe magnetic excitations of an optimally electron-doped superconductor Nd1.85Ce0.15CuO4-delta above and below its superconducting transition temperature Tc=25 K. In addition to gradually opening a spin pseudogap at the antiferromagnetic ordering wave vector Q=(1/2,1/2,0), the effect of superconductivity is to form a resonance centered also at Q=(1/2,1/2,0) but at energies above the spin pseudogap. The intensity of the resonance develops like a superconducting order parameter, similar to those for hole-doped superconductors and electron-doped Pr0.88LaCe0.12CuO4. The resonance is therefore a general phenomenon of cuprate superconductors, and must be fundamental to the mechanism of high-Tc superconductivity.     

Hybridization Gap and Dresselhaus Spin Splitting in EuIr4In2Ge4

EuIr₄In₂Ge₄ is a new intermetallic semiconductor that adopts a non‐centrosymmetric structure in the tetragonal ${I\bar 42m}$ space group with unit cell parameters a=6.9016(5) Å and c=8.7153(9) Å. The compound features an indirect optical band gap E_g=0.26(2) eV, and electronic‐structure calculations show that the energy gap originates primarily from hybridization of the Ir 5d orbitals, with small contributions from the Ge 4p and In 5p orbitals. The strong spin–orbit coupling arising from the Ir atoms, and the lack of inversion symmetry leads to significant spin splitting, which is described by the Dresselhaus term, at both the conduction‐ and valence‐band edges. The magnetic Eu²⁺ ions present in the structure, which do not play a role in gap formation, order antiferromagnetically at 2.5 K.     

Determination of the relative signs of proton spin coupling constants by double irradiation

The method of Evans [1] for determining relative signs of nuclear spin coupling constants by double irradiation experiments has been extended to the case where the three coupled nuclei are all protons. It is thus possible to demonstrate from the high resolution proton magnetic resonance spectrum of the ring protons of 2-Furoic acid that the three spin coupling constants are all of like sign.     

Continuous production of acetaldehyde by immobilized yeast within situ product trapping

Applied Biochemistry and Biotechnology - Two alternative enzymatic routes to continuous biological acetaldehyde production from ethanol by immobilized yeast were compared: ADH ofCandida utilis and...     

Self-assembled monolayers for liquid crystal alignment: simple preparation on glass using alkyltrialkoxysilanes

A simple procedure for the preparation of octadecylsiloxane self-assembled monolayers (SAMs) on float glass substrates is described. The method utilizes commercial octadecyltriethoxysilane, OTE: n-C₁₈H₃₇Si(OCH₂CH₃)₃, as the SAM precursor, with deposition accomplished in toluene solution using n-butylamine as catalyst. This synthetic approach obviates the use of the problematic trichlorosilanes typically required for the preparation of high quality SAMs, and is characterized by a wide 'process window,' utilizing off-the-shelf reagents without special handling.     

The fine structure of submicron iron particles

Summary High resolution electron micrographs are shown of samples of colloidal alpha iron. According to the conditions of manufacture the samples occur as (1) large, well-formed dendrites, (2) shorter, more fragile dendrites, (3) serrated rods, (4) needles and (5) cubic particulates. The central stem is a line-up of single cubic crystals. Representative dimensions are given for the various measurable units. A fine laminar structure in the cubic particulates, and some of the side branches and main stems is noted. The same laminar structure is observed in some of the background platelet material from the mother liquor. Stereoscopic studies show that the dendrites are three dimensional with their branches and main stem not in the same plane. X-ray diffraction detects alpha iron plus some form of Fe₂O₃ in most samples.

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Zusammenfassung Es werden elektronenmikroskopische Aufnahmen mit hohem Aufl?sungsverm?gen von kolloiden α-Eisenteilchen gezeigt. Entsprechend den Herstellungsbedingungen fallen die Teilchen als gro\e, gut ausgebildete Dendriten, als kürzere schw?chere Dendriten, als gezackte Stangen, als Nadeln und als kubische Partikeln an. Der zentrale Stamm ist eine lineare Anordnung aus einzelnen kubischen Kristallen. Repr?sentative Dimensionen sind für die verschiedenen me\baren Einheiten eingezeichnet. Eine fein laminierte Struktur der kubischen Teilchen und von einigen Seiten?sten und Hauptachsen ist zu erkennen. Dieselbe Laminarstruktur wird teilweise an dem pl?ttchenartigen Material, das als Untergrund aus der Mutterflüssigkeit dazwischen liegt, beobachtet. Stereoskopische Aufnahmen zeigen, da\ die Dendriten dreidimensional sind und da\ Seitenzweige und Hauptachsen nicht in der gleichen Ebene liegen. R?ntgeninterferenzen lassen aufα-Eisen, sowie eine Form von Fe₂O₃ in den meisten Proben schlie\en.

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The U.S. Navy Department, Bureau of Aeronautics, Industrial Planning Division, is credited with the development and sponsoring of the process for producing these fine powdered irons under contract No a (S) 52–792 C and NO a (S) 54–5190.

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Presented in part before the Conference and Exhibit on Magnetism and Magnetic Materials held at Pittsburgh, Pennsylvania, June 14, 15 and 16, 1955 and before the annual meeting of the Electron Microscope Society of America, held at State College, Pennsylvania, October 1955; abstract, J. App. Phys.26, 1391 (1955).     

Strong resonant behaviour of the 12C + 14C reaction

Strong correlated resonances have been found in the inelastic and transfer channels of ¹²C + ¹⁴C at energies above the Coulomb barrier. It is argued that the system may be sufficiently transparent to the grazing partial waves to enable predicted resonant effects to be observed.