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In this paper, an experimental study aimed at achieving better control of the deposition patterns of carbon nanotubes (CNTs) is presented. CNTs were grown on a long of reactor by the catalytic chemical vapor deposition (CVD) of a benzene/ferrocene solution at 1073 K. The deposition patterns on the substrate were controlled for process times and carrier gas flow rates. In order to investigate the reaction mechanism and production rate for the growth of CNTs in catalyst CVD, computational fluid dynamics (CFD) model was developed in this study. Then the computational model was integrated with the dynamic model to optimize the process parameters formulating a correlation between turbulence, deposition rate for the growth of carbon nanotubes and parameters as process time and carrier gas flow rate. Scanning electron microscopes (SEM) are used to characterize carbon nanotubes products.
Presently, rotational isomeric state (RIS) theory directly addresses polymer chain conformation as it relates to mechanical response trends. The primary goal of this work is to explore the adaptation of this methodology to the prediction of material stiffness. This multiscale modeling approach relies on ionomer chain conformation and polymer morphology and thus has potential as both a predictive modeling tool and a synthesis guide. The Mark–Curro Monte Carlo methodology is applied to generate a statistically valid number of end-to-end chain lengths via RIS theory for four solvated Nafion® cases. For each case, a probability density function for chain length is estimated using various statistical techniques, including the classically applied cubic spline approach. It is found that the stiffness prediction is sensitive to the fitting strategy. The significance of various fitting strategies, as they relate to the physical structure of the polymer, are explored so that a method suitable for stiffness prediction may be identified.
Titanium oxide and titanates based on Ba, Sr and Ca were prepared from commercial solutions of TiCl4 and HNO3. The main preparation steps for the sols consisted of elimination of chloride anions by distillation with nitric acid and addition of metal hydroxides for the titanates. Resulting sols were gelled and used to (1) prepare irregularly shaped powders by evaporation; (2) produce by a dipping technique thin films on glass, Ag, or Ti substrates; and (3) produce spherical powders (diameters <100 μm) by solvent extraction. Results of thermal and X-ray-diffraction analyses indicated that the temperatures required to form the various compounds were lower than those necessary to form the compounds by conventional solid-state reactions and comparable to those required with use of organometallic based sol-gel methods. Temperatures of formation could be further reduced by addition of ascorbic acid to the sols.
Most of the H2 in our Galaxy resides in the cold interiors of molecular clouds. The most reliable way to trace the H2 content of a molecular cloud is, in principle, to measure the distribution of dust through it. In this contribution we present a new observational approach that uses infrared dust extinction of starlight to construct high resolution maps of the distribution of dust (H2) inside molecular clouds over unprecedented ranges of cloud depth: 1 < Av < 40 magnitudes. We also present a comparison of our results with conventional molecular-line column density tracer C18O and conclude that for cloud depths of Av > 10 magnitudes this species is a very poor tracer of H2.
Molecular clouds are the reservoirs of H2 in the Galaxy. They contain about half of the mass of the Interstellar Medium and hence an important fraction of the mass of the Galaxy. By far the most important characteristic of molecular clouds is that they are the nurseries out of which stars like our Sun were born. This creation process not only determines the origins of stars and planetary systems in our Galaxy but also regulates the structure and evolution of galaxies on the large scale. To understand star and planet formation is to understand how cold H2 clouds evolve.
With the exception of the activities associated with the XXIII IAU General Assembly in Kyoto, Japan, in August 1997, the report period (July 1, 1996 through June 30, 1999) has been a relatively quiet one for Commission 37. Commission activities have been restricted primarily to the consideration of proposals for IAU Symposia and Colloquia together with some activity related to cluster nomenclature issues. At the General Assembly the commission was involved in either supporting or co-supporting four Joint Discussion sessions and one of the accompanying Symposia. Eighteen new members were added to the commission, increasing membership by just under 10%.
Thermal conversion of acetate-derived gels to YBa2Cu3Ox (Y–123), Bi2Sr2CaCu2Ox (Bi–2212), and (Bi, Pb)2Sr2Ca2Cu3Ox (Bi-2223) has been studied by thermal analysis, x-ray diffraction, and infrared spectroscopy. Carbonates formed above 200 °C during thermal treatment of all gels. Decomposition of the carbonates proved to be more difficult for Y-123 than for Bi-2212 or Bi-2223. However, all of the gels that were heated contained significant amounts of carbon after calcination. Complete decarbonization of materials was attained by treating the intermediate phases (e.g., those formed after calcination at 600 °C) with nitric acid and then subjecting them to a final thermal treatment. Removal of carbonates from the intermediate phases strongly accelerated formation of the superconducting compounds.
Various kinds of active alumina supports were obtained in the following
steps: (1) preparation of alumina sols by extraction of nitrates with
Primene JMT from aluminium nitrate solution, (2) gelation to spherical
particles (with diameter < 100 μm) by extraction of water from sol
emulsion in 2-ethyl -1-hexanol, (3) sometimes conversion of NO3− stabilized gel to OH− form by reaction with ammonia,
(4) calcination of gels to γ-Al2O3 with specific
surface area >100 m2/g at 500°C . The powders were then
impregnated with chloroplatinic acid and recalcined at 500°C. Catalysts were
also prepared by direct gelation of alumina sol containing hydroplatinic
acid followed by steps (3) and (4). Pt/Al2O3 catalysts
were used for reduction of 1M UO2(NO3-0.5M HCOOH
solution with hydrogen at atmospheric pressure. The course of the reduction
was controlled analytically and by measuring the U(VI)/U(IV) redox
potential. It was concluded that the catalysts obtained by impregnation of
supports prepared from nitrate stabilized gels exhibit the best activity and