Energetics of BAMO

3,3-Bis(azidomethyl)oxetane (BAMO) is a typical energetic azide polymer containing two N₃, bonds in the molecular structure. Since BAMO is a solidified polymer at room temperature, a liquid BAMO copolymer with tetrahydrofuran (THF) was synthesized in order to gain energetic binders for solid propellants. Various types of experiments were carried out to elucidate the decomposition and combustion processes of BAMO polymer, BAMO/THF copolymer, and crosslinked BAMO/THF copolymer. The heat produced by the decomposition is caused by the bond breakage of -N₃ to produce N₂, gas. The burning rate characteristics of crosslinked BAMO/THF copolymer depend largely on the mole fraction ratio of BAMO and THF.     

Reduction and Sintering of a Nickel–Dispersed-Alumina Composite and Its Properties

High-density nickel–dispersed-alumina (Al₂O₃/nickel) composites with superior mechanical properties were obtained by the hydrogen reduction and the hot pressing of alumina–nickel oxide (Al₂O₃/NiO) mixed powders. The mixtures were prepared by using NiO or nickel nitrate (Ni(NO₃)₂· n H₂O) as a dispersion source of nickel metal. Microstructural investigations of the composite fabricated using nitrate powder revealed that fine nickel particles, } 100 nm in diameter, dispersed homogeneously at the matrix grain boundaries, forming the intergranular nanocomposite. High strength (.1 GPa) and high-temperature hardness were registered for the composite that contained a small amount of nickel dispersion. The ferromagnetic properties of nickel, such as high coercive force, were observed, because of the fine magnetic dispersions, which indicates a functional value of structural composites.     

Computational fluid dynamics simulation and statistical procedure for estimating wide-area distributions of airborne sea salt considering local ground conditions

Steel corrosion under atmospheric conditions is a critical issue in the maintenance of structures such as electric transmission towers and bridges during their long-term operation, which are generally located at many places over a wide area. Since a major factor causing corrosion is airborne salt particles coming from the sea, wide-area distributions of the long-term cumulative amount of sea salt deposited on surfaces are needed. Moreover, since the amount of airborne sea salt varies locally with the topography, it is also important to consider the effects of topography. In this paper, a method combining a computational fluid dynamics model and a statistical procedure is proposed to efficiently estimate wide-area distributions of the cumulative amount of airborne sea salt by considering the local topography. The predicted amount of airborne sea salt decreases with increasing distance from the coast and varies with the topography and the offshore wind. A comparison between predicted and observed amounts revealed that: (1) this method appropriately estimates topographical effects on sea-salt transport and enables the estimation of deposited sea salt on structure surfaces, and (2) consideration of the trapping efficiency of sea-salt particles on structure surfaces improves the prediction accuracy.     

Oxidation kinetics for <Emphasis Type="Italic">cis</Emphasis>-9,<Emphasis Type="Italic">trans</Emphasis>-11 and <Emphasis Type="Italic">trans</Emphasis>-10,<Emphasis Type="Italic">cis</Emphasis>-12 isomers of CLA

The autoxidation processes of the cis-9,trans-11 (c9,t11) and trans-10,cis-12 (t10,c12) isomers of CLA were separately observed at ca. 0% RH and different temperatures. The t10,c12 CLA oxidized faster than the c9,t11 isomer at all tested temperatures. The first half of the oxidation process of t10,c12 CLA obeyed an autocatalytic-type rate expression, but the latter half followed first-order kinetics. On the other hand, the entire oxidation process of c9,t11 CLA could be expressed by the autocatalytic-type rate expression. The apparent activation energies and frequency factors for the autoxidation of the isomers were estimated from the rate constants obtained at various temperatures based on the Arrhenius equation. The apparent activation energies for the CLA isomers were greater than those for the nonconjugated n−6 and n−3 PUFA or their esters. However, the enthalpyentropy compensation held during the autoxidation of both the CLA and PUFA. This suggested that the autoxidation mechanisms for the CLA and PUFA were essentially the same.     

The influence of drawing,twisting, heat setting and untwisting on the structure and mechanical properties of melt spun polypropylene filament

The changes in structure and mechanical properties of melt spun polypropylene filaments were determined as the filaments were successively (i) drawn, (ii) twisted, (iii) annealed, and (iv) untwisted. Filaments spun to two different melt draw down levels were studied. The effects of draw temperature and draw ratio, extent of twist, annealing temperature, and the extent of untwisting were examined. Melt spun and twisted filaments (draw ratio of 1) were also considered. Structural characterization techniques used in this study include wide angle (WAXS) and small angle (SAXS) diffraction, scanning electron microscopy (SEM), birefringence and density measurement. Drawing increased crystalline orientation and at low temperatures disrupted the monoclinic unit. cell existing in the melt spun fibers. The drawing produced considerable fibrillation under all conditions even when carried out at 120°C. The fibrillation quid void formation due to low temperature drawing was more pronounced. The variation of WAXS patterns and mechanical properties of twisted drawn filaments was interpreted by presuming that the fibrils act in a manner analogous to that of the filaments in a continuous filament twisted yarn. In the case of incompletely drawn filaments the effect of additional drawing occurring during twistin must be considered. Twisted fibers annealed at 150°C sowed a drastic reduction in tensile properties, while those annealed at 125°C did not set the twist and caused the fibers to tend to untwist. Annealing at 140°C appeared to give satisfactory heat setting. Annealing of cold drawn and cold drawn and twisted fibers increased the density, removed many defects and reformed a well defined monoclinic crystal structure and a lamellar morphology. Untwisting of heat set filaments tended to give back the properties of hot drawn fibers. In some cases, however, the opening of cracks was noted.     

Stereocomplex formation between enantiomeric poly(lactic acid). VIII. Complex fibers spun from mixed solution of poly(D-lactic acid) and poly(L-lactic acid)

To obtain poly(lactic acid) (PLA) complex fibers, spinning was performed by wet and dry methods from 5–10 g/dL chloroform solutions of poly(D-lactic acid) (PDLA) and poly(L-lactic), both with a viscosity-average molecular weight of 3 × 10⁵. The dope was extruded from a monohole nozzle into coagulation baths from ethanol and chloroform for wet spinning and into a drying column kept at 60°C for dry spinning. Scanning electron microscopic observation of the as-spun fibers showed that the surface of the wet-spun fiber had large basins with diameters of 50–100 μm and many pores with diameters from sub μm to 10 μm, whereas the surface of dry-spun fiber had a microporous structure with the pore diameter of 1–3 μm. The tensile strength of the wet-spun complex fiber was very low and could not be drawn at high temperatures, in contrast to the dry-spun fiber. The tensile strength of dry-spun complex fiber increased upon hot drawing and showed the tensile strength of 94 kg/mm² by drawing at 160°C to the draw ratio of 13. Differential scanning calorimetry revealed that the complex fibers contained both the stereocomplex crystallites (racemic crystallites) and the crystallites of the single polymers, PDLA and PLLA, regardless of the spinning methods. The ratio of the racemic crystallites to the single-polymer crystallites increased with the draw ratio of the complex fiber. © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of polyacetylenes carrying N-phenylcarbazole and triphenylamine moieties

Novel acetylene monomers containing N-phenyl-substituted carbazole (Cz) and triphenylamine (TPA) groups, namely, 3-ethynyl-9-phenylcarbazole (1) and p-(N,N-diphenylamino)phenylacetylene (2) were synthesized, and polymerized with several Rh-, W-, and Mo-based catalysts. Poly(1) and poly(2) with high number-average molecular weights (15?500-974?000) were obtained in good yields (77-97%), when [(nbd)RhCl]₂-Et₃N (nbd = norbornadiene) was used as a catalyst. The polymers exhibited UV-vis absorption peaks derived from the Cz and TPA moieties at 250-350 nm and polyacetylene backbone above 350 nm. The UV-vis absorption band edge wavelengths of the polymers were longer than those of the corresponding monomers. Poly(2) exhibited a UV-vis absorption peak at a longer wavelength than poly(1) did, which indicates that poly(2) has main chain conjugation longer than that of poly(1). The molecular weights and photoluminescence quantum yields of the polymers obtained by the polymerization using [(nbd)RhCl]₂-Et₃N were larger than those of the Rh⁺(nbd)[η⁶-C₆H₅B⁻(C₆H₅)₃]-based counterparts. The cyclic voltammograms of the polymers indicated that they had clear electrochemical properties; the onset oxidation voltage of poly(1) was higher than those of N-alkyl-substituted Cz derivatives. The polymers showed electrochromism and changed the color from pale yellow to blue by application of voltage, presumably caused by the formation of charged polaron at the Cz and TPA moieties. The temperatures for 5% weight loss of the polymers were around 350-420 °C under air, indicating the high thermal stability.     

Study of crater formation and sputtering process with large gas cluster impact by molecular dynamics simulations

Molecular dynamics (MD) simulations of large argon clusters impacting on silicon solid targets were performed in order to study the transient process of crater formation and sputtering. The MD simulations demonstrate that the initial momentum of incident cluster is transferred to target surface atoms through multiple collision mechanism, where the initial momentum, which is along to the surface normal before impact, is deflected to lateral direction. This momentum transfer process was analyzed by the calculation of the velocity at the crater edge (the interface between cluster and target). In the case of Ar₁₀₀₀ cluster impact on Si(1 0 0) target at low energy per atom less than 40 eV/atom, the maximum value of lateral velocity of the crater edge increases in proportional to the velocity of incident cluster atoms. On the other hand, the crater edge velocity saturates over 40 eV/atom of incident energy per atom. In this case, the whole of constituent cluster atoms are implanted into the target and expand in both lateral and reflective directions at the subsurface region of the target. These MD simulations demonstrated that this collisional process result in the high yield sputtering of the target atoms.     

Overview of wireless personal communications

This article presents an overview of the current state of wireless communications, including relevant ongoing activities in technology development, standards, and spectrum allocation. The authors discuss cellular radio, cordless telephony, and wireless data systems. Ongoing and planned future developments are summarized. The presentation is oriented toward broad coverage rather than technical depth. However, brief discussions of the air interfaces for existing digital cellular and digital cordless systems are provided, because the air interface bears heavily on system capacity and the environments in which the system can be used, as well as on the cost and complexity of the equipment     

Mixture distribution measurement using laser induced breakdown spectroscopy in hydrogen direct injection stratified charge

Reduction in cooling loss due to the heat transfer from burning gas to the combustion chamber wall is very important for improving the thermal efficiency in hydrogen engines. The previous research has shown that the direct injection stratified charge can be a technique to reduce the cooling loss and improve thermal efficiency in hydrogen combustion. For effective reductions in cooling loss by the stratified charge, it is very important to know the relation between the fuel injection conditions and mixture distribution. The current research employs the laser induced breakdown spectroscopy as a method to measure the hydrogen concentration distribution in the direct injection stratified charge. Measurement of instantaneous local equivalence ratio by the method clears the characteristics of mixture formation in hydrogen direct injection stratified charge. This research also tries to actively control the mixture distribution using a split fuel injection.