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Notes: We present a theoretical investigation of the electronic structure of tetraphenyldithiapyranylidene (DIPSΦ4) using the nonempirical valence effective Hamiltonian (VEH) method. Molecular geometries are optimized at the semiempirical PM3 level which predicts an alternating nonaromatic structure for the dithiapyranylidene (DIPS) framework. The VEH one-electron energy level distribution calculated for DIPSΦ4 is presented as a theoretical XPS simulation and is analyzed by comparison to the electronic structure of its molecular components DIPS and benzene. The theoretical VEH spectrum is found to be fully consistent with the experimental solid-state x-ray photoelectron spectroscopy (XPS) spectrum and an excellent quantitative agreement between theory and experiment is achieved when comparing the energies of the main peaks. A detailed interpretation of all the experimental photoemission bands is reported in the light of the VEH results.

Notes: We present a theoretical investigation of the electronic structure of oligorylenes (from perylene to heptarylene, including also the naphthalene molecule) and their corresponding polymer poly(peri-naphthalene) (PPN) using the nonempirical valence effective (VEH) method. The geometry of the unit cell used to generate the polymer is extrapolated from the PM3-optimized molecular geometries of the longest oligorylenes. That geometry shows some bond alternation along the perimeter carbon chains and a bond length of ≈1.46 A(ring) is calculated for the peri bonds connecting the naphthalene units. The VEH one-electron energy level distributions calculated for oligorylenes are used to interpret the experimental trends reported for the first ionization potentials, redox potentials, and lowest energy optical transitions. An excellent agreement is found between theoretical estimates and experimental values. The VEH band structure calculated for an isolated chain of PPN is interpreted in terms of the molecular orbitals of naphthalene. The ionization potential, electron affinity, and bandwidths obtained for PPN suggest a large capacity to form conducting p- or n-type materials. The small band gap of 0.56 eV predicted for PPN from VEH band structure calculations is in good agreement with theoretical and experimental estimates calculated by extrapolating the data reported for the oligomers.

Notes: An automated system for determinations of transport current–voltage (I–V) characteristics as a function of temperature (25–125 K), magnetic field (0–1.6 T), and magnetic field orientation (−125 to +145°) is described. Currents of up to 100 A are applied either as a continuous ramp or as pulses of 2–100 ms duration. A closed-cycle helium refrigerator provides a rapid (∼45 min), convenient, cost effective, cooldown from 300 to 25 K. Control of current, temperature, magnetic field, and field orientation is fully automated and requires no user interaction. The characterization of performance of a ceramic superconductor typically involves several temperatures, fields, and orientations and requires 8–30 h to complete. © 1996 American Institute of Physics.

Notes: Perennial ryegrass and meadow fescue were grown alone and in association in field plots, to gain an idea of the nature and importance of the competitive interactions between them, and their relative contributions to the yield of the newly-established sward.Experiments over 10 weeks and 9 months both showed that the contribution by fescue to the overall dry-matter yield was severely restricted by perennial ryegrass. There were no deaths of fescue plants during the experimental period (which included an overwintered treatment). The depression in yield was rather a result of a marked decrease in size and weight of the individual plants, brought about by competition for light and nutrients from the faster-growing ryegrass.

Notes: In the course of investigating synthesis routes, stability information was developed for YBa2Cu3O7−x, Y2Ba4Cu7O15−x, and YBa2Cu4O8. The results were obtained between ∼900 and 1040 °C and involve oxygen pressures between 10 and 145 atm. The observations show that the PO2-T ranges for stability of the three phases overlap and that some stable mixtures of the phases can be synthesized. The results are compared to the results of other experimental studies and to calculations based on calorimetric data.

Notes: Seebeck, electrical, and thermal conductivity data are reported on CoSb3, and doped and undoped alloys of Co1−xIrxSb3−yAsy from 20 to 700 K. n-type semiconductors were obtained by doping with Ni, Te, or Pd, and the hole concentration in p-type samples was increased by substitution of Fe, Ru, Os, and Ge. An estimated maximum value for ZT of 0.6 (Z is the figure of merit) was found for a Te-doped (n-type) alloy at 700 K. For p-type alloys, the maximum value of ZT was found to be 0.3 at 550 K. Electrical and thermal transport data also are reported for CoAs3, RhSb3, and IrSb3. Most of the samples investigated were polycrystalline, but a few measurements on CoSb3 single crystals also are discussed. © 1995 American Institute of Physics.

Notes: A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high-temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 105 A/cm2 at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high-Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures. © 1996 American Institute of Physics.

Notes: Capacitance measurements are used to investigate a series of single-barrier n-i-n GaAs/AlAs/GaAs heterostructures incorporating a layer of self-assembled InAs quantum dots into the AlAs barrier. They reveal a low-density, excess positive charge in the AlAs barrier which we attribute to defects associated with quantum dot formation. The quantity of positive charge is proportional to the amount of AlAs deposited on top of the dots. © 2000 American Institute of Physics.

Notes: Eupatorium adenophorum is a weed of coastal areas of eastern Australia. An account of the history of its introduction and spread is given and its distribution is described. Experiments showed that the seeds have a low percentage viability which may be related to their development by apomixis. The viable seeds have a germination requirement for light which, together with their small size, restricts the invasive power of the species. Seedlings display a degree of tolerance to shading to 10% daylight which is regarded as a useful attribute in competition with other colonizing plants. The period of maximum vegetative growth of established plants occurs when competition from summer pastures is declining in late summer and autumn.The necessity for mechanical control procedures to uproot crowns to prevent regrowth is demonstrated in a regeneration experiment. It is concluded that the species does not represent a threat to densely covered pastures and that the establishment of improved pastures is the main remaining limitation to E. adenophorum control. L'autécologie d'Eupatorium adenophorum (Spreng) en AustralieL'Eupatorium adenophorum est une plante du littoral de l'Australie orientale. Les auteurs donnent un aperçu de l'histoire de son introduction; sa dissimination est indiquée et sa distribution décrite. Les expériences ont montré que les semences n'avaient qu'un faible pourcentage de viabilité qui peut être en relation avec leur développement par apoximis. Les semences viables ont des besoins en lumière qui, avec leur petite taille, restreignent le pouvoir d'invasion des espèces. Les plantules manifestent un degréde tolérance à l'ombrage à 10% de la lumière du jour, ce qui est considéré comme une propriété favorable à la compétition avec d'autres plantes colonisantes. La période de la croissance végétative maximale des plantes établies se situe lorsque la compétition des prairies d'été est en décroissance, à la fin de l'rété et en automne.La nécessité d'utiliser des moyens mécaniques pour prévenir la repousse des couronnes de racines est démontrée dans une experience de régénération. II en est conclu que les espèces ne représentent pas une menace pour les pâtures à couverture dense et que l'établissement des prairies artificielles reste la principale limitation à la lutte contre Eupatorium adenophorum.Ein Beitrag zur Ökologie von Eupatorium adenophorum Spreng. in Australien Eupatorium adenophorum kommt als Unkraut in den Küsten-regionen Ost-Australiens vor. Die Geschichte der Einsch-leppung und Ausbrietung wird dargestellt und das Vorkommen beschrieben. Versuche zeigten, dass nur ein geringer Prozentsatz der Samen lebensfähig ist, was mit ihrer apomiktischen Entstehung zusammenhängen dürfte. Die lebens-fähigen Samen brauchen Licht zur Keimung, was zusammen mit ihrer geringen Grösse die Verbreitung der Art behindert. Keimlinge hatten eine Schattenverträglichkeit bis 10% des vollen [Tageslichtes, was als nützliche Eigenschaft für die Konkurrenz mit andered angesiedelten Pflanzen angesehen wird. Das starkste vegetative Wachstum der vorhandenen Pflanzen tritt ein, wenn die Konkurrenz der Weidepflanzen im Spätsommer und Herbst abnimmt.In einem Austriebsversuch konnte gezeigt weden, dasses bei mechanischen Bekämpfungsverfahren notwendig ist, die Schösslinge zu entwurseln (auszureissen), um den Wieder-austrieb zu verhindern. Es wird gefolgert, dass die Art für dicht Weidebestände keine Gefahr darstellt und die Verbes-serung der Weiden die vielversprechendste Massnahme zur Bekämpfung von Eupatorium adenophorum ist.

Notes: YBa2Cu3O7−δ (YBCO) films were fabricated via a fluorine-free metal organic deposition (MOD) method followed by high-temperature, low oxygen partial pressure annealing. Trimethyl acetate salts of copper, yttrium, and barium hydroxide were used as the precursors, which were dissolved in proponic acid- and amine-based solvents. After spin-coating and burnout, samples were annealed at 740°C in 180 ppm oxygen partial pressure and exposed to humid atmosphere for different times. A critical transition temperature, Tc(R=0) of 90.2 K and a transport critical current density (Jc) of 0.55 MA/cm2 (77 K and self-field) were obtained for 0.2 μm YBCO films on CeO2-buffered yttria-stabilized zirconia (YSZ) substrates. X-ray studies shows that the YBCO films have sharp in-plane and out-of-plane texture for all samples; however, the porosity of the YBCO film varies with the time of exposure to the humid atmosphere. A reaction between YBCO and CeO2 during the high-temperature anneals and formation of the reaction product BaCeO3 was confirmed by X-ray diffraction (XRD) studies. The XRD and transmission electron microscopy analysis indicated that the epitaxial relations in the film were YBCO (00l)//CeO2 (00l)//YSZ (00l) and YBCO [100]//CeO2 [110]//YSZ [110].