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  • 1
    Electronic Resource
    Electronic Resource
    The existence of quasi-two-dimensional glass-like structures at strongly interacting polymer-solid interfaces (1991)
    s.l. : American Chemical Society
    Macromolecules 24 (1991), S. 5226-5229 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00018a033
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  • 2
    Electronic Resource
    Electronic Resource
    Monte Carlo Simulations of Random Copolymers near Solid Surfaces (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 7447-7453 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00126a025
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamics of poly(methyl methacrylate) chains adsorbed on aluminum surfaces (1993)
    s.l. : American Chemical Society
    Macromolecules 26 (1993), S. 1120-1136 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00057a036
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  • 4
    Electronic Resource
    Electronic Resource
    Computer Simulation of Homopolymer and Copolymer Adsorption Dynamics (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 2987-2995 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00089a014
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamics of excited-state proton transfer systems via time-resolved photoelectron spectroscopy (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2519-2522 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the applicability of time-resolved photoelectron spectroscopy to excited state intramolecular proton transfer (ESIPT) and internal conversion dynamics in the model system o-hydroxybenzaldehyde (OHBA) and related compounds. Photoelectron spectra of both the excited state enol and keto tautomers were obtained as a function of pump laser wavelength and pump-probe time delay. The ESIPT was found to occur in less than 50 fs over the whole absorption range of the S1(ππ*) state for both OHBA and its monodeuterated analog, suggestive of a small or nonexistent barrier. The subsequent keto internal conversion rate in OHBA varies from 0.63 to 0.17 ps−1 over the S1(ππ*) absorption band and the OD-deuterated analog shows no significant isotope effect. Based upon ab initio calculations and comparison with the two-ring analog, 1-hydroxy-2-acetonaphthone (HAN), we suggest that the internal conversion dynamics in OHBA is influenced by interactions with a close-lying nπ* state. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345876
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  • 6
    Electronic Resource
    Electronic Resource
    Electronic continua in time-resolved photoelectron spectroscopy. II. Corresponding ionization correlations (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1206-1213 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate further the role of ion electronic continua in time-resolved photoelectron spectroscopic measurements of ultrafast nonadiabatic coupling. In the preceding paper [Blanchet, Zgierski, and Stolow, J. Chem. Phys. 114, 1194 (2000)], the limiting case of complementary ionization correlations permitted a disentangling of electronic from vibrational dynamics. Here we examine the other limiting case in which the nonadiabatically coupled sates (e.g., S2 and S1) correlations correspond to the same ionic continua, presumably an unfavorable case. We use ultrafast internal conversion in the polyaromatic hydrocarbons phenanthrene and naphthalene as examples. In this situation, the geometry changes (displacements) upon nonadiabatic crossing and upon ionization will strongly affect the ability to disentangle electronic from vibrational dynamics. Particularly, phenanthrene and naphthalene are both very rigid molecules and have small displacements upon internal conversion and ionization, still allowing for direct monitoring of the S2 state internal conversion rate. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331637
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of chain topology on polymer dynamics: Configurational relaxation in polymer melts (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 761-772 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report computer simulations of chain dynamics in monodisperse, linear polymer melts using a model which allows the dynamical effects of chain topology to be isolated from the individual effects of excluded volume and chain connectivity. The chain topology is controlled by either allowing or forbidding chain crossing events while maintaining the chain connectivity and excluded volume interactions between monomers. This chain crossing condition does not significantly alter the polymer structure or even the local, segment-level dynamics. For each topological condition, "crossing'' and "noncrossing,'' we decompose the polymer dynamics into a set of relaxation modes, calculate the autocorrelation functions for each mode, and obtain the complete distribution of internal relaxation times {τp}, where p labels the mode index. Several regimes of relaxation behavior are present, depending on the chain length N, the wavelength of the mode (N/p), and the chain topology. Noncrossing chains below a critical chain length, Nc, exhibit relaxation dynamics that are consistent with Rouse chains in the melt. Above Nc, noncrossing chains still exhibit Rouse-type dynamics in the short wavelength relaxation modes. For the modes of intermediate wavelength, however, the internal relaxation times scale with the mode wavelength according to τp∼(N/p)3 and the autocorrelation functions are strongly nonexponential. Relaxation behavior that is roughly consistent with the reptation model is finally seen for the first few relaxation modes of the noncrossing chains above Nc. In contrast to the noncrossing chains, the chains which are allowed to cross (in the presence of excluded volume and chain connectivity) exhibit Rouse-type relaxation dynamics for all long wavelength modes, even modes with characteristic wavelengths beyond the effective entanglement spacing of the noncrossing chains. Since we have controlled all factors other than chain topology which may in principle affect polymer dynamics, the results illustrate the role of chain topology in the transition from Rouse-type to reptationlike relaxation behavior in polymer melts. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470108
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of chain topology on polymer dynamics: Bulk melts (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4205-4213 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce a new lattice-based Monte Carlo model of polymer dynamics in which the polymer chain topology can be altered without perturbing any static properties or the local segment mobility. Chain entanglements can then simply be switched "on'' and "off,'' and their effects on global dynamics can be clearly isolated. Two sets of simulations have been conducted for bulk polymer melts. In the first set chain crossing is rigorously forbidden, but in the second set the polymer chains are allowed to cross through each other. When the chains are not allowed to cross, the self-diffusion coefficient exhibits the classic signature of the crossover from unentangled to entangled dynamics. For short chains, D∼N−1, while for long chains, D∼N−2, where D is the diffusion coefficient and N is the number of polymer segments. Furthermore, the longest noncrossing chains show a clear preference for anisotropic motion along their own contours—they appear to move by reptation. When the chains are allowed to cross, however, D∼N−1 at all chain lengths, characteristic of unentangled dynamics. No crossover is indicated in this case, and no signs of reptation are present. Since the structure and local mobility are nearly identical in the two cases, the dynamical differences are due only to the chain topology through the crossing condition. We discuss how the results illustrate the role of entanglements in bulk polymers and how the model may be used in the future as a tool to examine entanglement effects in adsorbed layers and confined polymer fluids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467470
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  • 9
    Electronic Resource
    Electronic Resource
    The nature of the interactions of poly(methyl methacrylate) oligomers with an aluminum surface (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8616-8630 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polymer–metal interfaces are of increasing technological importance in a variety of applications. These interfaces are characterized by specific interactions between functional groups of the organic polymer and the metallic substrate. In order to study the structure of these interfaces at the molecular level, the energetics of the segment–surface interactions must be well characterized. We have used density functional theory to investigate the interactions of poly(methyl methacrylate) (PMMA) oligomers with aluminum surfaces. The aluminum surface is represented by the simple jellium model. The energetics of the interactions between the organic molecules and the aluminum surface are calculated as a function of the orientation with respect to the surface of the organic molecule and various internal degrees of freedom. The computed energy hypersurfaces exhibit a rich structure characterized by several energy minima and barriers. Implications of such an energy hypersurface for the architecture of long chain molecules at the interface are discussed. The energy hypersurfaces also show that the rotational conformational statistics of PMMA interacting with an aluminum surface should be quite different from that of bulk PMMA. The reported energy hypersurfaces have been used to construct an empirical force-field for future molecular simulations of long chains subject to the proper potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461240
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  • 10
    Electronic Resource
    Electronic Resource
    Harvest frequency effects on forage yield and quality of rapes and rape hybrids (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Grass and forage science 43 (1988), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Spring-seeded rape requires approximately two-thirds of the growing season in the north-cast USA, to reach physiological maturity. Harvest frequency studies were conducted with rapes and rape hybrids in Pennsylvania to determine whether forage yields and/or quality can be improved with multiple harvests, and whether cultivars respond similarly to harvest management. Nitrogen was applied at 75 kg ha−1 at seeding and 75 kg ha−1 70 d after seeding. Additional fertilizer was applied according to soil test results. A split-split-block design was used. Harvest frequencies of 180, 90, 60, or 30 d were randomly assigned to blocks. Cultivars were randomized within each harvest frequency, with four replicates. Amount of regrowth of all cultivars after mid-August was highly variable, depending on weather. Foliar diseases and aphids lowered yields in different years. Cultivars differed in susceptibility to diseases and aphids as well as in morphology. Forage yields and crude protein yields of rape generally were highest with the 90-d harvest frequency, whereas crude protein concentration was highest with the 30-d frequency. Mean in vitro dry matter digestibility (IVDMD) values were high regardless of harvest frequency, cuttivar, or sampling date. Yield differences between cultivars generally were greatest with one harvest at 180 d; mean yield was highest for forage rapes, intermediate for winter oil rapes, and lowest for rape x Chinese cabbage hybrids. Under frequent harvesting, BLE rape and the rape x Chinese cabbage hybrid performances were exceptional as regards forage yield and quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2494.1988.tb01895.x
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