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  • 1
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8474-8485 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a model describing the dynamics of a flexible linear polymer in a monodisperse melt. The polymer is represented by a freely jointed chain that moves by two coupled dynamical processes. The first is a kink–jump motion that may be blocked by obstacles, and the second is a slithering motion that mimics reptation. The obstacles relax with a distribution of time scales. This distribution is determined self-consistently by the requirement that it be identical to a distribution of time scales associated with the relaxation of the slowest internal modes of the chain. The calculation of observables is shown to be equivalent to the solution of a random walk problem with dynamical disorder. We determine this solution by applying the dynamical effective medium approximation. Within the resulting theory, the mean squared displacement of a polymer bead on any time scale may be determined by solving a fifth order algebraic equation and inverting a Laplace transform. We present calculations of the self-diffusion coefficient in a melt and of the tracer diffusion coefficient of a chain of a given molecular weight at infinite dilution in a melt of another molecular weight. For the self-diffusion coefficient, the theory predicts results consistent with the Rouse model for short chains and behavior consistent with the reptation picture for long chains. The crossover between these limiting behaviors is described. Comparison is made to measurements of tracer and self-diffusion in polystyrene melts.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3710-3721 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a theory of the dynamics of flexible linear polymers in a melt composed of macromolecules of two molecular weights and of the same chemical species. A polymer is represented by a freely jointed chain that moves by two dynamical processes. The first is a local jump motion that may be blocked by obstacles, and the second is a slithering mode that mimics reptation. The dynamics of the obstacles are determined self-consistently by an ansatz that associates their relaxation with the dynamics of the slowest mode of conformational relaxation of a chain. The calculations of the autocorrelation function of the end-to-end vector and of the mean squared displacement of the center of mass are related exactly to the solution of a random walk problem with dynamical disorder. We calculate the necessary random walk propagator by applying the dynamical effective medium approximation. Calculations of the dependence of the self-diffusion coefficient of both components on blend composition and on molecular weights are presented. The theory is shown to provide a unified description of diffusion in the unentangled and entangled regimes.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7150-7168 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We calculate the dependence on time and on molecular weight of the mean-squared displacement of a polymer segment in a dense fluid of linear chain molecules. Time scales are considered that range from times sufficiently short that a segment behaves as a free Brownian particle to times over which terminal diffusion occurs. We employ a stochastic model that has formed the basis of our earlier studies of the self-diffusion coefficient in monodisperse and polydisperse melts. A macromolecule is represented by a freely jointed chain that moves through space by two mechanisms—a local conformational change and a cooperative slithering motion. The local motions are blocked by dynamical obstacles, whose relaxation rate is determined self-consistently from the dynamics of the chain. Calculations of polymer properties are exactly mapped onto the solution of random walk problems with dynamical disorder, which are treated within the dynamical effective medium approximation. Our results are shown to share common features with recent molecular dynamics and dynamical Monte Carlo simulations of polymer melts. A procedure is suggested for assigning values to our model parameters in order to mimic specific experimental systems or other theoretical models.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1641-1649 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present calculations of the single-chain dynamic structure factor for a polymer melt composed of linear molecules of the same chemical identity but of two different chain lengths. The fluid is treated within a dynamical mean-field approach, in which each molecule is represented as a freely jointed chain moving among stochastic obstacles. The obstacles are of two types, each representing the obstruction of local conformational changes by one of the species present. The obstacle dynamics are determined self-consistently by equating the relaxation rate of an obstacle of a given type to the smallest conformational relaxation rate of the species that it represents. Calculation of the dynamic structure factor is mapped onto the solution of a random walk with dynamical disorder, in which a walker moves on a one-dimensional lattice with hopping rates that randomly fluctuate among three states. The relevant random walk problem is solved within the effective medium approximation, and the results are employed to examine the dependence of the dynamic structure factor on time, wave vector, chain lengths, and fluid composition. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 328 (1987), S. 585-585 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] CLAYS and clay minerals occur in geo-logical environments as diverse as soils, sediments and hydrothermally altered rocks and are utilized for a remarkable variety of purposes, particularly in the ceramic, paper, chemical and oil indus-tries. These materials therefore occupy an important niche at ...
    Type of Medium: Electronic Resource
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  • 7
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    In:  Geological Society Special Publication 343: 161-173.
    Publication Date: 2010-10-06
    Description: The history of dinosaur collecting in central India (former Central Provinces and Central India Agency) began in 1828 when W. H. Sleeman discovered isolated sauropod caudal vertebrae in the Lameta Formation near Jabalpur. Subsequently, the area became a focal point for fossil collection, leading to a series of further discoveries that continues today. The earliest discoveries were made by numerous collectors for whom palaeontology was a secondary pursuit, and who were employed in the armed forces (W. H. Sleeman and W. T. Nicolls), medicine (G. G. Spilsbury) or as geologists (T. Oldham, H. B. Medlicott, T. W. H. Hughes and C. A. Matley). Most of their finds were concentrated around Jabalpur or farther south near Pisdura and often consisted of isolated, surface-collected bones. Charles Matley undertook the two most extensive collecting efforts, in 1917-1919 and 1932-1933 (Percy Sladen Trust Expedition). As a result he discovered significant deposits of dinosaurs on Bara Simla and Chhota Simla, revisited Pisdura, and mapped the Lameta Formation. Many new dinosaur taxa resulted from Matley's studies, which still represent most of the known Lameta Formation dinosaur fauna. Current scientific understanding places these fossils among the Sauropoda (as titanosaurians) and Theropoda (as abelisaurids and noasaurids). Early reports of armoured ornithischians were erroneous; these materials also pertain to sauropods and theropods. Supplementary materialA list of the archival documents in the Natural History Museum, London that were used for this study is available at http://www.geolsoc.org.uk/SUP18418.
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  • 8
  • 9
    Publication Date: 2020-04-02
    Print ISSN: 0944-1344
    Electronic ISSN: 1614-7499
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Springer
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  • 10
    Publication Date: 2020-07-09
    Description: Amidst a contemporary culture of climate awareness, unprecedented levels of transparency and visibility are forcing industrial organizations to broaden their value chains and deepen the impacts of Corporate Social Responsibility (CSR) initiatives. While it may be common knowledge that the 2030 agenda cannot be achieved on a business-as-usual trajectory, this study seeks to determine to what ends the United Nations Sustainable Development Goals (SDGs) have impacted CSR research. Highlighting linkages and interdependencies between the SDGs and evolution of CSR practice, this paper analyzes a final sample of 56 relevant journal articles from the period 2015–2020. With the intent of bridging policy and practice, thematic coding analysis has supported the identification and interpretation of key emergent research themes. Using three descriptive categorical classifications (i.e., single-dimension, bi-combination of dimensions, sustainability dimension), the results of this paper provide an in-depth discussion into strategic community, company, consumer, investor, and employee foci. Furthermore, the analysis provides a timely and descriptive overview of how CSR research has approached the SDGs and which ones are being prioritized. By deepening the understanding of potential synergies between business strategy, global climate agendas and the common good, this paper contributes to an increased comprehension of how CSR and financial performance can be improved over the long-term.
    Electronic ISSN: 2071-1050
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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