On the relationship between the electronic density of states and the superconducting critical temperature of disordered V3Si

The available data on the effect of neutron and α-particle irradiation on the superconducting properties and the low-temperature specific heat capacity of single- and polycrystalline V₃Si were analyzed in a unified manner. It was found that the electron-phonon renormalization parameter λ does not vary simply proportionally to the bare density of electron states at the Fermi level as had been earlier conjectured by Dynes and Varma, nor does it vary in exactly the same manner as found by Fradin and Williamson to hold for a variety of vanadium-based A15 structure compounds and pseudobinary alloys. When the behavior of V₃Si is compared with that of Nb₃Sn, Nb₃Al, and Nb₃Ge, it is seen that the response to disorder of parameters of importance in the superconductivity of these compounds does not follow any simple, universal behavior.     

10 × 10 Gb/s DWDM Transmission Through 2.2-km Multimode Fiber Using Adaptive Optics

Transmitter-based adaptive optics and receiver-based single-mode filtering are combined to compensate modal dispersion in multimode fiber (MMF). A liquid-crystal spatial light modulator controls the launched field pattern for ten 10-Gb/s nonreturn-to-zero channels, wavelength-division multiplexed on a 200-GHz grid in the C-band. Error-free transmission through 2.2 km of 50-mum graded-index MMF is achieved for launch offsets up to 10 mum and for worst-case launched polarization. A ten-channel transceiver based on parallel integration of electronics and photonics is employed.     

Performance characteristics of high power CW, 1 cm wide monolithic AlGaAs laser diode arrays with a 2 mm total aperture width

One cm wide monolithic laser diode arrays emitting around 810 nm with a 2 mm total aperture width have been characterised under CW conditions. CW operation up to 16 W has been achieved at a heatsink temperature of 70 degrees C. Several arrays have been lifetested at 10 W CW at a 20 degrees C heatsink temperature for a few thousand hours and have projected lifetimes of between 5000 and 17000 hours. The temperature dependence of the degradation rate was characterised, from which data an activation energy of 0.2 eV was obtained.<>     

Single-lobe `Y? coupled laser diode arrays

`Y? Coupled laser arrays have been fabricated with flared waveguides at the output facet to expand the near-field spot and increase the near-field fill factor to greater than 80%. The far-field radiation pattern is predominantly single-lobe, and power outputs of 150mW CW have been obtained with threshold currents as low as 130mA.     

Studies of the Structure and Reactivity of Soot

Vibrational spectroscopy, supplemented with other techniques, is providing a comprehensive picture of the structure and reactivity of soot. Reactions such as soot-NO₂/N₂O₄, soot-O₃, and soot-SO₂, at atmospheric and subatmospheric pressures and at different temperatures, have been studied. Determination of the kinetics and mechanisms of the formation of CO and CO₂ during the soot-O₃ reaction, and the effect of temperatures and the concentrations of soot and ozone on this reaction, have led to further insights about the soot structure. Examination of the identity and role of linkages bonding carbon layers together is underway. Application of the Elovich equation to determine initial rates for the formation of surface species in these reactions indicates that the soot-O₃ reaction is faster than the rapid soot-NO₂/ N₂O₄ reaction which, in turn, is faster than that of soot-SO₂. Oxidation of SO₂ to ionic sulfate, confirmed by isotopic substitution, occurs in the presence of soot, water vapor, and oxygen. The presence of simulated solar radiation results in the formation of both ionic and covalent sulfate species. The substrate, whether it is carbon black, cab-o-sil, or the glass walls of the reaction vessel, seems to play a role in the nonphotochemical oxidation of SO₂ to sulfate. The miscibilities of the reaction products of soot-O₃, soot-NO₂/N₂O₄, soot-SO₂, with water vary greatly and have implications for the depletion of tropospheric ozone in the presence of soot-containing particulates.     

Characterization of nicotinamide mononucleotide adenylyltransferase from thermophilic archaea

The enzyme nicotinamide mononucleotide (NMN) adenylyltransferase (EC 2.7.7.1) catalyzes the synthesis of NAD+ and nicotinic acid adenine dinucleotide. It has been purified to homogeneity from cellular extracts of the thermophilic archaeon Sulfolobus solfataricus. Through a database search, a highly significant match was found between its N-terminal sequence and a hypothetical protein coded by the thermophilic archaeon Methanococcus jannaschii MJ0541 open reading frame (GenBank accession no. U67503). The MJ0541 gene was isolated, cloned into a T7-based vector, and expressed in Escherichia coli cells, yielding a high level of thermophilic NMN adenylyltransferase activity. The expressed protein was purified to homogeneity by a single-step chromatographic procedure. Both the subunit molecular mass and the N-terminal sequence of the pure recombinant protein were as expected from the deduced amino acid sequence of the MJ0541 open reading frame-encoded protein. Molecular and kinetic properties of the enzymes from both archaea are reported and compared with those already known for the mesophilic eukaryotic NMN adenylyltransferase.