Image sequence processing to supervise fish passes

This paper presents an automatic system of fish identification and counting using image sequences taken in fish passes. At first, real time is not considered and, so, images have to be stored. We present the electronic system designed to code and store them in real time, on optical disks in files of sequences. Then, we describe the tracking process implemented to count the fish when they cross the pass from down-river to up-river, the recognition process and the overlap problem. A result file can be edited by a human operator. Obtained results are satisfactory with regard to static recognition and are improved by the temporal redundancy generated by the tracking process. The processing time is, on average, lower than the storage time and thus there is no data accumulation

In-Situ Bulk Polymerization of Dilute Particle/MMA Dispersions

Composites of poly(methyl methacrylate) and various nanoscale inorganic particles (zinc oxide, titanium dioxide, zirconium dioxide, silicon dioxide, and aluminum nitride) were prepared by in-situ bulk polymerization using 2,2‘-azobis(isobutyronitrile) as initiator. The particles of ZnO, TiO2, and ZrO2 were surface-modified by alkylphosphonic acids to render them dispersible in the monomer. The effect of these nanoparticles on the free radical polymerization was investigated. Regardless of chemical nature and size, the particles suppress the autoacceleration which would otherwise occur in the bulk free-radical polymerization of methyl methacrylate (MMA). A degenerative chain transfer is proposed to take place between surface-adsorbed water on the particles and propagating chain radicals. This reaction competes with normal termination. Formation of vinylidene chains ends originating from disproportionation is suppressed. In consequence, thermal stability of PMMA produced in the presence of particles is improved. Aggregation of individual particles upon polymerization has been observed and presumably is due to interparticle depletion attraction, even though the particles are individually dispersed in the monomer. Formation of particle clusters is suppressed when a difunctional monomer (e.g., ethylene glycol dimethacrylate) is used as comonomer. The cross-linked medium slows down the diffusion of the particles and therefore interferes with particle aggregation via a depletion mechanism

Sequential catalytic growth of carbon nanotubes

Nanofilaments made of repeated units of multiwall carbon nanotubes (MWCNT) with a metal particle encapsulated at one end were synthesized by thermal chemical vapor deposition (CVD) of methane on Ni-Fe catalysts. The nanofilaments were characterized using scanning electron microscopy (SEM), low- and high-resolution transmission electron microscopy (TEM). A mechanism based on a sequential growth is here proposed to explain the structure. Using the structural information from the TEM micrographs, we demonstrate the existence of two different growth regimes depending on the size of the catalyst particle and estimate the critical carbon concentration in the catalyst particle to initiate the growth. (C) 2002 Elsevier Science B.V. All rights reserved

Sequentially grown carbon nanotubes

Nanofibers consisting of repeated units of multiwall carbon nanotubes (MWCNT) with a metal particle encapsulated at one end were synthesized by thermal chemical vapor deposition (CVD) of methane/hydrogen on Ni-Fe catalysts. The grown structures were studied by scanning electron microscopy (SEM), low and high-resolution transmission electron microscopy (TEM). Sequential growth is proposed to explain the periodicity of the nanofibers. The nanofibers are broken by sonication into single elementary units open at one end

Reducing the Degree of Branching in Polyacrylates via Midchain Radical Patching: A Quantitative Melt-State NMR Study

Degrees of branching were measured with 13C melt-state NMR in poly(n-butyl acrylates) synthesized in both the presence and absence of 1-octanethiol at various temperatures, and their precision calculated based on the signal-to-noise ratio of the quaternary carbon at the branching point. Nitrogen gas was used for all pneumatics. Samples synthesized with thiol were measured in 7 mm rotors at MAS rotational frequencies of 1.8 to 4.5 kHz, while samples synthesized without thiol were measured in 4 mm rotors at 9 kHz MAS. The relative standard deviation SD of DB was calculated from the signal-to-noise ratio of the quaternary carbon SNR. The accuracy of measured degrees of branching was ensured by full relaxation of the relevant signals between pulses. A significant decrease of branching was observed in the presence of a thiol during the polymerization process, experimentally confirming the patching effect of midchain tertiary radicals by the thiol

Determination of propagation rate coefficients for methyl and 2-ethylhexyl acrylate via high frequency PLP-SEC under consideration of the impact of chain branching

The radical propagation rate coefficients, kp, of methyl acrylate (MA) and 2-ethylhexyl acrylate (EHA) have been determined in bulk via high frequency (500 Hz) pulsed laser polymerization coupled to size exclusion chromatography (PLP-SEC) up to elevated temperatures (20 ≤ T/°C ≤ 80). Prior to the analysis of the generated polymeric material, an investigation into the branching behavior of the generated polymers has been undertaken, employing the concept of local dispersity, D(Ve). In addition, the Mark-Houwkink-Kuhn-Sakurada parameters for both poly(MA) and polyEHA were determined at each studied reaction temperature. The temperature averaged values read (K = 10.2 × 10-5 dL g-1; α = 0.741) and (K = 9.85 × 10-5 dL g-1; α = 0.719) for poly(MA) and polyEHA, respectively. The local dispersity data indicate that branching in polyEHA may be considerably more prevalent than in poly(MA), as with increasing temperature polymer microinhomogeneities are observed. Consequently, the Arrhenius parameters for kp of EHA are beset with a larger error than those of MA. The activation parameters in the temperature range between 20 and 80 °C read: EA MA = 18.5 (+0.8 to -0.9) kJ•mol-1 and AMA = 2.5 (+1.2 to -0.6) × 107 L•mol-1•s-1; EA EHA = 15.8 (+1.6 to -1.4) kJ•mol-1 and A EHA = 9.1 (+10.1 to -2.9) × 106 L•mol -1•s-1. © 2010 American Chemical Society