Homogeneous vs. catalytic combustion of lean methane—air mixtures in reverse-flow reactors

To carry out a comparative assessment of a recently proposed idea of using thermal flow-reversal reactors (TFRR) for mine ventilation air, the results for the catalytic flow-reversal reactor (CFRR) investigated within the European Project (2003) are briefly presented. Next, experimental investigations of thermal combustion are presented in this paper. These consisted of the kinetic study of homogeneous combustion in the pelletized bed and in the monolith. Kinetic equations for the two cases are derived and discussed. Experimental autothermal reverse-flow operation in a laboratory setup was performed. Due to the high heat capacity of the wall and insulation of the pelletized bed reactor, with considerable heat losses to the surroundings, autothermal operation was successful only in the monolithic reactor. It is finally concluded that the thermal combustion can be competitive compared with the catalytic oxidation.     

Phase Equilibria in the Nd ― Re ― B System

XRD has been applied to component interaction in the Nd ― Re ― B system. Isothermal sections have been constructed for the phase diagram at 600°C (a region >33 at.% boron) and 800°C (>33 at.% boron). It is confirmed that it contains the previously known borides Nd₂Re₃B₆ (Pr₂Re₃B₆ structure type) and Nd₈Re_{13 − x} B₁₂ (Pr₈Re_{13 − x} B₁₂ structure type). Two new ternary compounds are reported: ∼NdRe₄B₄ considered to have a tetragonal incommensurate structure and ∼Nd₅Re₂B₆, whose structure is unknown.

     

Development of transparent, conducting composites by surface infiltration of nanotubes into commercial polymer films

Here we present a novel technique for the preparation of thin, transparent and conducting, nanotube containing layers at the surface of commercially available polyethylene films. This is achieved by the swelling of the polyethylene in nanotube/tetrahydrofuran dispersions, followed by nanotube infiltration. These layers, typically 250 nm thick, display conductivities of up to 66 S/m, depending on the nanotube content. This results in sheet resistances of as low as 50 kΩ/□ at optical transparencies of 80%.     

Optical vortices in twisted elliptical optical fibers with torsional stress

In the present paper we have derived the analytical expressions for the modes of twisted elliptical fibers with torsional mechanical stress at various relationships of the fiber parameters. It was shown that circularly polarized optical vortices with the topological charges ±1 can propagate in elliptical fibers as generic modes if ellipticity and the twist-induced circular birefringence suppress the spin-orbit interaction. A comparison of the obtained results with the corresponding results for spun elliptical fibers is made.     

ASTER and field observations of the 24 December 2006 eruption of Bezymianny Volcano, Russia

An explosive eruption occurred at Bezymianny Volcano (Kamchatka Peninsula, Russia) on 24 December 2006 at 09:17 (UTC). Seismicity increased three weeks prior to the large eruption, which produced a 12–15 km above sea level (ASL) ash column. We present field observations from 27 December 2006 and 2 March 2007, combined with satellite data collected from 8 October 2006 to 11 April 2007 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), as part of the instrument's rapid-response program to volcanic eruptions. Pixel-integrated brightness temperatures were calculated from both ASTER 90 m/pixel thermal infrared (TIR) data as well as 30 m/pixel short-wave infrared (SWIR) data. Four days prior to the eruption, the maximum TIR temperature was 45 °C above the average background temperature (− 33 °C) at the dome, which we interpret was a precursory signal, and had dropped to 8 °C above background by 18 March 2007. On 20 December 2006, there was also a clear thermal signal in the SWIR data of 128 °C using ASTER Band 7 (2.26 μm). The maximum SWIR temperature was 181 °C on the lava dome on 4 January 2007, decreasing below the detection limit of the SWIR data by 11 April 2007. On 4 January 2007 a hot linear feature was observed at the dome in the SWIR data, which produced a maximum temperature of 700 °C for the hot fraction of the pixel using the dual band technique. This suggests that magmatic temperatures were present at the dome at this time, consistent with the emplacement of a new lava lobe following the eruption. The eruption also produced a large, 6.5 km long by up to 425 m wide pyroclastic flow (PF) deposit that was channelled into a valley to the south–southeast. The PF deposit cooled over the following three months but remained elevated above the average background temperature. A second field investigation in March 2007 revealed a still-warm PF deposit that contained fumaroles. It was also observed that the upper dome morphology had changed in the past year, with a new lava lobe having in-filled the crater that formed following the 9 May 2006 eruption. These data provide further information on effusive and explosive activity at Bezymianny using quantitative remote sensing data and reinforced by field observations to assist in pre-eruption detection as well as post-eruption monitoring.     

Kinetics and Mechanism of Thermal Decomposition of Dinitramide

Kinetics of the thermal decomposition of dinitramide (HDN) in aqueous solutions and of NH₄N(NO₂)₂ (ADN) and KN(NO₂)₂ (KDN) in sulfuric acid, nitric acid and anhydrous acetic acid solutions was studied. The species N(NO₂)₋₂, HN(NO₂)₂ and H₂N(NO₂) were established to take part in the decomposition over a wide range of the medium acidity. Kinetic regularities of their thermal decomposition were determined. The role of the decomposition of dinitramide at the initial and self-acceleration stages of the decomposition of ADN was determined. The most likely mechanism of the decomposition of dinitramide, N(NO₂)₋₂ and H₂N(NO₂)₊₂ was proposed.     

Some Phenomenological Aspects of Heterogeneous Combustion of Condensed Systems

The combustion process of heterogeneous condensed systems (HCS) is a complex phenomenon characterized by some peculiarities: Phase transitions in the combustion wave, time and space inhomogeneity of the temperature and burning rate, agglomeration and dispersion of the condensed phase, concentration limits, etc. The order and completeness of chemical reactions in a HCS combustion wave depend not only on the energetic parameters but on the composite structure as well (porosity, component particle size and shape, etc.). Some phenomenological aspects of the HCS combustion process are analyzed. Peculiarities of metal particle agglomeration and its influence on the metal oxide size are discussed. The high‐temperature kinetics of Al+Al₂O₃ interaction are shown. The complexity of the analyzed phenomenon calls for a non‐traditional approach and technique.     

Synthesis,transport, and sorption properties and free volume of polystyrene derivatives containing Si and F

Gas permeation, sorption, and free volume was studied in a series of glassy vinylic type Si‐containing polymers. They included p‐substituted derivatives of polystyrene, which were compared with polystyrene, and poly(vinylphenyldimethyl silane). The strongest increase in permeability and diffusion coefficients were observed for the polymer containing the Si(CH₃)₃ group directly attached to phenylene ring. An introduction of spacers between phenylene ring and Si(CH₃)₃ group results in much lower gas permeability. Positron annihilation study of free volume in these polymers showed that lifetime spectra are composed of four components. It implies that size distribution of free volume in these polymers, which are characterized by a modest level of gas permeability, is bimodal, a feature previously observed only for extra large free volume and permeability materials such as poly(trimethylsilyl propyne). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1612–1620, 2000     

Multifunctional Magnetic-fluorescent Nanocomposites for Biomedical Applications

Nanotechnology is a fast-growing area, involving the fabrication and use of nano-sized materials and devices. Various nanocomposite materials play a number of important roles in modern science and technology. Magnetic and fluorescent inorganic nanoparticles are of particular importance due to their broad range of potential applications. It is expected that the combination of magnetic and fluorescent properties in one nanocomposite would enable the engineering of unique multifunctional nanoscale devices, which could be manipulated using external magnetic fields. The aim of this review is to present an overview of bimodal “two-in-one” magnetic-fluorescent nanocomposite materials which combine both magnetic and fluorescent properties in one entity, in particular those with potential applications in biotechnology and nanomedicine. There is a great necessity for the development of these multifunctional nanocomposites, but there are some difficulties and challenges to overcome in their fabrication such as quenching of the fluorescent entity by the magnetic core. Fluorescent-magnetic nanocomposites include a variety of materials including silica-based, dye-functionalised magnetic nanoparticles and quantum dots-magnetic nanoparticle composites. The classification and main synthesis strategies, along with approaches for the fabrication of fluorescent-magnetic nanocomposites, are considered. The current and potential biomedical uses, including biological imaging, cell tracking, magnetic bioseparation, nanomedicine and bio- and chemo-sensoring, of magnetic-fluorescent nanocomposites are also discussed.