51 research outputs found

    Surface effects in nucleation and growth of smectic B crystals in thin samples

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    We present an experimental study of the surface effects (interactions with the container walls) during the nucleation and growth of smectic B crystals from the nematic in free growth and directional solidification of a mesogenic molecule (C4H9(C6H10)2CNC_4H_9-(C_6H_{10})_2CN) called CCH4 in thin (of thickness in the 10 μ\mum range) samples. We follow the dynamics of the system in real time with a polarizing microscope. The inner surfaces of the glass-plate samples are coated with polymeric films, either rubbed polyimid (PI) films or monooriented poly(tetrafluoroethylene) (PTFE) films deposited by friction at high temperature. The orientation of the nematic and the smectic B is planar. In PI-coated samples, the orientation effect of SmB crystals is mediated by the nematic, whereas, in PTFE-coated samples, it results from a homoepitaxy phenomenon occurring for two degenerate orientations. A recrystallization phenomenon partly destroys the initial distribution of crystal orientations. In directional solidification of polycrystals in PTFE-coated samples, a particular dynamics of faceted grain boundary grooves is at the origin of a dynamical mechanism of grain selection. Surface effects also are responsible for the nucleation of misoriented terraces on facets and the generation of lattice defects in the solid.Comment: 15 pages, 24 figures, submitted to PR

    The Physics of the B Factories

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    Thermochemical treatment for algal fermentation

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    The purpose of this study was to determine the influence of the thermochemical pretreatment process of algal fermentation on the efficiency with which algal energy is converted microbiologically to the energy in methane. The variables studies were pretreatment temperature, duration, concentration, and dosage of sodium hydroxide (NaOH). In order to optimize the thermochemical pretreatment of algae, an independent variables study was selected. The results indicate that pretreatment best efficiency was attained with a temperature of 100 degrees C for 8 h at a concentration 3.7% solids and without NaOH. Compared with untreated algae, pretreatment improved the efficiency of methane fermentation a maximum at 33%. An orthogonal square design was selected to determine the mathematical model to describe the effects of algal thermochemical pretreatment and to determine the relative significance among the pretreatment parameters. (C) 1998 Elsevier Science Ltd
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