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  • 1
    Electronic Resource
    Electronic Resource
    Interaction of molecular rotation with large-amplitude internal motions: a rigid twister model of hydrogen peroxide (1988)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 92 (1988), S. 7193-7204 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100337a009
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  • 2
    Electronic Resource
    Electronic Resource
    Unimolecular decay lifetimes and intramolecular energy redistribution in hydrogen peroxide: sensitivity to potential energy surface (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 3877-3880 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100347a001
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  • 3
    Electronic Resource
    Electronic Resource
    Neural network predictions of energy transfer in macromolecules (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 2761-2767 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100185a066
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  • 4
    Electronic Resource
    Electronic Resource
    Computational studies of submicron probing of polymer surfaces. I (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7072-7085 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The atomistic details of the interaction of an atomic force microscopic (AFM) probe with a polymer surface are examined by using the molecular-dynamics method. It is found that the perturbation of the AFM probe can produce a deformation of the local structure of the polymer surface. The dynamics study reveals how the structural changes evolve during the surface probing experiment, and whether the deformations result in permanent or reversible structural damage upon removing the probe. The effects of probe features (radius of curvature) and load force on the surface deformation(s) and image resolution are investigated in both a constant-force and constant-height AFM mode. Load forces between 10−8 and 10−11 N were determined to be an optimum working range for nondestructive AFM probing of polymer surfaces, and consequently for well-resolved surface image production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462539
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  • 5
    Electronic Resource
    Electronic Resource
    Computer experiments on the internal dynamics of crystalline polyethylene: Mechanistic details of conformational disorder (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6875-6889 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The atomistic details of the internal dynamics of a polyethylene-like crystal are studied using molecular dynamics. Crystals with up to 6100 chain atoms have been studied for up to 30 ps. A microscopic description of the atomic motion has been examined and a link to available experimental data on the macroscopic and microscopic motion is provided. The results show that the onset of a significant population of rotational isomers is strongly altered by the intermolecular forces. Typical rates for the formation of isomers are 1010 to 1012 s−1 at 350 K (depending on the size of the simulated crystal, which changes the overall nature of the intermolecular forces) and increase exponentially with temperature. The large number of created defects causes a continuous decrease in the end-to-end distance. Specific defects, however, have extremely limited lifetime (i.e., those suggested by molecular mechanics calculations). These results suggest that at the temperatures where annealing or deformation of metastable crystals is possible, only randomly generated defects cause the macroscopically observed changes. The defects should move under the free enthalpy gradient set up within the crystal toward a more stable location. The activation energy required for motion which ultimately results in mass transport or lamellar thickening can be shown to be temperature and chain-length dependent. The highly uncorrelated behavior of the creation and annealing of defects reveals the underlying chaotic nature of the "transition'' from an ordered crystal to a conformationally disordered crystal (CONDIS crystal). In the simulated case, the transition to the conformationally disordered state occurs gradually, involving little or no cooperative motion. This continuous transition to the condis state was suggested earlier on the basis of experimental evidence and is expected to occur in many other polymers in addition to and at lower temperature than possible additional first-order transitions to the condis state. Thermodynamic and kinetic parameters of the simulations have been determined and compared to the available experimental data with good agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458921
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  • 6
    Electronic Resource
    Electronic Resource
    A neural network approach to the study of internal energy flow in molecular systems (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 293-306 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Neural networks are used to develop a new technique for efficient analysis of data obtained from molecular-dynamics calculations and is applied to the study of mode energy flow in molecular systems. The methodology is based on teaching an appropriate neural network the relationship between phase-space points along a classical trajectory and mode energies for stretch, bend, and torsion vibrations. Results are discussed for reactive and nonreactive classical trajectories of hydrogen peroxide (H2O2) on a semiempirical potential-energy surface. The neural-network approach is shown to produce reasonably accurate values for the mode energies, with average errors between 1% and 12%, and is applicable to any region within the 24-dimensional phase space of H2O2. In addition, the generic knowledge learned by the neural network allows calculations to be made for other molecular systems. Results are discussed for a series of tetratomic molecules: H2X2, X=C, N, O, Si, S, or Se, and preliminary results are given for energy flow predictions in macromolecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463628
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  • 7
    Electronic Resource
    Electronic Resource
    Infrared laser-induced chaos and conformational disorder in a model polymer crystal: Melting vs ablation (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6081-6091 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics-based computer simulations are presented for the interaction of one and two infrared (IR) laser beams with a model polymer surface. When a single laser beam system is studied over a wide range of intensities, only melting of the polymer, or melting followed by bond dissociation, is observed for up to 100 picoseconds. In contrast, the two-laser simulation results exhibit a marked difference in the energy absorption behavior of the irradiated polymer which, in turn, results in multiple bond dissociations. The results for the one- and two-laser cases studied can be divided into four different classes of physical behavior: (a) the polymer remains in the solid state; (b) the polymer crystal melts; (c) the polymer ablates, but with significant melting (charring); or (d) the polymer ablates with minimal melting. Damage to the model polymer crystal from absorption of energy from either one or two lasers occurs through a mechanism that involves the competition between the absorption of energy and internal energy redistribution. The rate of energy loss from the absorption site(s) relative to the rate of absorption of energy from the radiation field determines rather the polymer melts or ablates (low absorption rates lead to melting or no change and high rates lead to ablation). A sufficiently large rate of energy absorption is only obtainable through the use of two lasers. Two lasers also significantly decrease the total laser intensity required to cause polymer crystal melting. The differences between the one- and two-laser cases are studied by adapting novel signal/subspace techniques to analyze the dynamical changes in the mode spectrum of the polymer as it melts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459496
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  • 8
    Electronic Resource
    Electronic Resource
    Neural Network-Graph Theory Approach to the Prediction of the Physical Properties of Organic Compounds (1994)
    s.l. : American Chemical Society
    Journal of chemical information and modeling 34 (1994), S. 832-839 
    Details
    ISSN: 1520-5142
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ci00020a017
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  • 9
    Electronic Resource
    Electronic Resource
    Symplectic integrators for large scale molecular dynamics simulations: A comparison of several explicit methods (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4062-4072 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We test the suitability of a variety of explicit symplectic integrators for molecular dynamics calculations on Hamiltonian systems. These integrators are extremely simple algorithms with low memory requirements, and appear to be well suited for large scale simulations. We first apply all the methods to a simple test case using the ideas of Berendsen and van Gunsteren. We then use the integrators to generate long time trajectories of a 1000 unit polyethylene chain. Calculations are also performed with two popular but nonsymplectic integrators. The most efficient integrators of the set investigated are deduced. We also discuss certain variations on the basic symplectic integration technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467523
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  • 10
    Electronic Resource
    Electronic Resource
    The onset of instability in nanostructures: The role of nonlinear resonance (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6619-6622 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical trajectory methods are used to examine the vibrational dynamics of carbon nanotubes. The results clearly demonstrate an integral relationship between the diameter and length of a nanotube and its positional stability: tubes having diameters smaller than 0.7 nm undergo large-amplitude motion. The origin of this motion is due to strong coupling(s) between the longitudinal (vibration along the length) and a ring breathing mode (vibration about the axis of the cylinder). It is shown that the vibrational frequency of these modes follow a simple scaling law: ωc∝1/C, ωL∝1/L, where C is the contour length around the end of the tube and L is the length of the tube along its axis. This law should be applicable to any isotropic material with a cylindrical shape and provides an analytical equation for predicting mechanical stability: When the frequencies have small integer ratios with one another, in particular a 1:2 ratio, instability will occur on a short time scale (this phenomena represents a nonlinear resonance controlled by the geometry of the system). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469378
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