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  • 1
    Electronic Resource
    Electronic Resource
    Dynamic behavior of continuous vinyl chloride bulk and suspension polymerization reactors. A simple model analysis (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 291-302 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Based on previous works, a simple model is built to simulate the vinyl chloride monomer (VCM) polymerization in continuous suspension and bulk reactors. The branches of steady-state solutions are computed and their dynamic behavior is analyzed. It is observed that these systems present multiple steady-state solutions for some ranges of parameter values and that non-adiabatic reactors can also present ISOLAs. These reactors can also experience self-sustained oscillations in a very wide region of operation conditions.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760300506
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamic behavior of continuous vinyl chloride suspension polymerization reactors: Effects of segregation (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 925-930 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Assumed is that there is no mass transfer among the droplets of reacting organic phase in a continuous vinyl chloride (VCM) suspension polymerization reactor. A mathematical model is thus developed to allow the calculation of steady states and the analysis of their dynamic stability. The results obtained are compared with those obtained with the hypothesis of perfect micromixing. It Is shown that both assumptions lead to similar dynamic structures, which confirms the complex behavior of these reactors. There are major differences, however, that can be exploited in future experimental work.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760301507
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The kinetics of photo-oxidation of low-density polyethylene films (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 567-572 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The kinetics of the accelerated photo-oxidation of low-density polyethylene (LDPE) films has been studied within a range of temperatures, using an ultraviolet radiation enclosure. A simple, lumped parameter, kinetic model was developed to interpret the results of measurements of carbonyl and hydroperoxide absorbances as functions of time; the model predicts, with reasonable accuracy, the general experimental behavior and also that both the formation of hydroperoxides and carbonyl Norrish-I reactions are important initiation steps. Slightly more complex models may thus have the potential of interpreting other fine details of the degradation behavior, namely the generation of other chemical species and the chain scission and cross-linking processes, which are directly related to changes in the mechanical properties.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760320808
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The kinetics and mechanism of polyethylene photo-oxidationPaper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 113-133 
    Details
    ISSN: 0003-3146
    Keywords: polyethylene ; photo-oxidation ; weathering ; mechanism ; kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the natural and accelerated photo-oxidation of low-denisty polyethylene (LDPE) films have been studied; different geographical locations have been selected for the natural tests, and a range of temperatures used in the accelerated experiments in a specially built temperature-controlled ultraviolet radiation enclosure. A meaningful correlation between natural and accelerated weathering results was established, by means of an adequate superposition of the effects of UV radiation exposure and temperature. Reasonably detailed and accurate, lumped-parameter, kinetic models of the photo-oxidation process have also been developed, to interpret and predict the results of measurements of carbonyl, hydroperoxide and vinyl absorbances as functions of time and temperature; the models predict the general experimental behaviour, and also that both the formation of hydroperoxides and carbonyl Norrish-I reactions are important initiation steps. More complex models have the potential of interpreting other fine details of the degradation behaviour, namely the generation of other chemical species, and the chain scission and cross-linking process which are directly related to changes in the mechanical properties.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052160108
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  • 5
    Electronic Resource
    Electronic Resource
    Refractive index of solutions containing poly(vinyl acetate) and poly(methyl methacrylate) (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 2795-2809 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Refractive index measurements can be used successfully for on-line evaluation of extent of reaction in solution polymerization reactors. For this reason, the refractive index of solutions containing tert-butanol (TBOH), methyl methacrylate (MMA), vinyl acetate (VA), poly(methyl methacrylate) (PMMA), and poly(vinyl acetate) (PVA) were measured and a mathematical correlation was developed to fit the experimental data. The correlation can be extended to fit published data obtained with different solvents.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1991.070421018
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Vinyl chloride suspension polymerization with constant rate. A numerical study of batch reactors (1990)
    Brookfield, Conn. : Wiley-Blackwell
    Journal of Vinyl and Additive Technology 12 (1990), S. 7-12 
    Details
    ISSN: 0193-7197
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Based on the analysis of a simple mathematical model, different temperature profiles are generated in order to provide vinyl chloride (VCM) suspension polymerization with constant reaction rates in batch reactors. In order to reproduce these temperature profiles in industrial-scale reactors, some process variables, such as coolant temperature, initiator concentration, and rate of water and monomer condensation, have to be manipulated. It is shown that those temperature practices can almost never be applied to large-scale reactors if the jacket temperature is the only variable that can be manipulated. It is also shown that developing an initiator feed procedure or using a reflux condenser may be advantageous.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/vnl.730120104
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  • 7
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    Intercomparison of Field Measurements of Nitrous Acid (HONO) during the SHARP Campaign (2014)
    Wiley-Blackwell
    Details
    Publication Date: 2014-04-11
    Description: Because of the importance of HONO as a radical reservoir, consistent and accurate measurements of its concentration are needed. As part of SHARP (Study of Houston Atmospheric Radical Precursors), time series of HONO were obtained by six different measurement techniques on the roof of the Moody Tower (MT) at the University of Houston. Techniques used were long path differential optical absorption spectroscopy (DOAS), stripping coil- visible absorption photometry (SC-AP), long-path absorption photometry (LOPAP®), mist chamber/ ion chromatography (MC-IC), quantum cascade-tunable infrared laser differential absorption spectroscopy (QC-TILDAS) and ion drift -chemical ionization mass spectrometry (ID-CIMS). Various combinations of techniques were in operation from 15 April through 31 May 2009. All instruments recorded a similar diurnal pattern of HONO concentrations with higher median and mean values during the night than during the day. Highest values were observed in the final two weeks of the campaign. Inlets for the MC-IC, SC-AP, and QC-TILDAS were collocated and agreed most closely with each other based on several measures. Largest differences between pairs of measurements were evident during the day for concentrations 〈 ~100 ppt. Above ~ 200 ppt, concentrations from the SC-AP, MC-IC and QC-TILDAS converged to within about 20%, with slightly larger discrepancies when DOAS was considered. During the first two weeks, HONO measured by ID-CIMS agreed with these techniques, but ID-CIMS reported higher values during the afternoon and evening of the final four weeks, possibly from interference from unknown sources. A number of factors, including building related sources, likely affected measured concentrations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 8
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    Spatial distribution of the eddy diffusion coefficients in the plasma sheet during quiet time and substorms from THEMIS satellite data (2011)
    Wiley-Blackwell
    Details
    Publication Date: 2011-01-27
    Description: During the last decade, a number of studies have shown that turbulent processes in the plasma sheet are very important for the analysis of the formation of quasi-stable plasma sheet configurations. The existence of this turbulence provides a self-consistent approach to study the dynamics of the Earth's magnetosphere, including the plasma sheet stability. The turbulence can also be very important for an understanding of the location of an isolated substorm expansion phase onset. In this study the level of turbulence has been evaluated by calculating the eddy diffusion coefficients using the Time History of Events and Macroscale Interactions during Substorms satellite data. It was found that the value of the eddy diffusion coefficients may vary by at least 3 orders of magnitude, generally ranging from 103 to 106 km2/s, increasing with the distance from the Earth. The area of low eddy diffusion coefficients, less than 104 km2/s, is situated at distances below 12 RE in the tail where we found the transition region between the dipole and the tail-like geomagnetic field configuration. This region is consistent with the location of isolated substorms, as indicated by the first auroral arc brightening situated at the equatorial edge of the auroral oval.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 9
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    Distinct mechanisms eliminate mother and daughter centrioles in meiosis of starfish oocytes (2016)
    Rockefeller University Press
    Details
    Publication Date: 2016-03-29
    Description: Centriole elimination is an essential process that occurs in female meiosis of metazoa to reset centriole number in the zygote at fertilization. How centrioles are eliminated remains poorly understood. Here we visualize the entire elimination process live in starfish oocytes. Using specific fluorescent markers, we demonstrate that the two older, mother centrioles are selectively removed from the oocyte by extrusion into polar bodies. We show that this requires specific positioning of the second meiotic spindle, achieved by dynein-driven transport, and anchorage of the mother centriole to the plasma membrane via mother-specific appendages. In contrast, the single daughter centriole remaining in the egg is eliminated before the first embryonic cleavage. We demonstrate that these distinct elimination mechanisms are necessary because if mother centrioles are artificially retained, they cannot be inactivated, resulting in multipolar zygotic spindles. Thus, our findings reveal a dual mechanism to eliminate centrioles: mothers are physically removed, whereas daughters are eliminated in the cytoplasm, preparing the egg for fertilization.
    Electronic ISSN: 1540-8140
    Topics: Biology
    Published by Rockefeller University Press
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