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  • 1
    Electronic Resource
    Electronic Resource
    Development of simple fitness landscapes for peptides by artificial neural filter systems (1995)
    Springer
    Biological cybernetics 73 (1995), S. 245-254 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The applicability of artificial neural filter systems as fitness functions for sequence-oriented peptide design was evaluated. Two example applications were selected: classification of dipeptides according to their hydrophobicity and classification of proteolytic cleavage-sites of protein precursor sequences according to their mean hydrophobicities and mean side-chain volumes. The cleavage-sites covered 12 residues. In the dipeptide experiments the objective was to separate a selected set of molecules from all other possible dipeptide sequences. Perceptrons, feedforward networks with one hidden layer, and a hybrid network were applied. The filters were trained by a (1,λ) evolution strategy. Two types of network units employing either a sigmoidal or a unimodal transfer function were used in the feedforward filters, and their influence on classification was investigated. The two-layer hybrid network employed gaussian activation functions. To analyze classification of the different filter systems, their output was plotted in the two-dimensional sequence space. The diagrams were interpreted as fitness landscapes qualifying the markedness of a characteristic peptide feature which can be used as a guide through sequence space for rational peptide design. It is demonstrated that the applicability of neural filter systems as a heuristic method for sequence optimization depends on both the appropriate network architecture and selection of representative sequence data. The networks with unimodal activation functions and the hybrid networks both led to a number of local optima. However, the hybrid networks produced the best prediction results. In contrast, the filters with sigmoidal activation produced good reclassification results leading to fitness landscapes lacking unreasonable local optima. Similar results were obtained for classification of both dipeptides and cleavage-site sequences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201426
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  • 2
    Electronic Resource
    Electronic Resource
    Development of simple fitness landscapes for peptides by artificial neural filter systems (1995)
    Springer
    Biological cybernetics 73 (1995), S. 245-254 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. The applicability of artificial neural filter systems as fitness functions for sequence-oriented peptide design was evaluated. Two example applications were selected: classification of dipeptides according to their hydrophobicity and classification of proteolytic cleavagesites of protein precursor sequences according to their mean hydrophobicities and mean side-chain volumes. The cleavage-sites covered 12 residues. In the dipeptide experiments the objective was to separate a selected set of molecules from all other possible dipeptide sequences. Perceptrons, feedforward networks with one hidden layer, and a hybrid network were applied. The filters were trained by a (1, λ) evolution strategy. Two types of network units employing either a sigmoidal or a unimodal transfer function were used in the feedforward filters, and their influence on classification was investigated. The two-layer hybrid network employed gaussian activation functions. To analyze classification of the different filter systems, their output was plotted in the two-dimensional sequence space. The diagrams were interpreted as fitness landscapes qualifying the markedness of a characteristic peptide feature which can be used as a guide through sequence space for rational peptide design. It is demonstrated that the applicability of neural filter systems as a heuristic method for sequence optimization depends on both the appropriate network architecture and selection of representative sequence data. The networks with unimodal activation functions and the hybrid networks both led to a number of local optima. However, the hybrid networks produced the best prediction results. In contrast, the filters with sigmoidal activation produced good reclassification results leading to fitness landscapes lacking unreasonable local optima. Similar results were obtained for classification of both dipeptides and cleavage-site sequences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004220050180
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental determination of quantum state resolved differential cross sections for the hydrogen exchange reaction H+D2→HD+D (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 6175-6195 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have carried out a systematic crossed molecular beam study of the hydrogen exchange reaction in the H+D2→HD+D isotopic form at two collision energies: 0.53 and 1.28 eV. The Rydberg atom time-of-flight method was used to measure the D-atom product angle-velocity distribution. For the first time ro-vibrational quantum state resolved differential cross sections for the title reaction were measured, which can directly be compared to theoretical predictions at this detailed level. Experimental results are compared to theoretical predictions from both quasi classical and quantum mechanical calculations on different potential energy surfaces as well as to earlier experiments. A general good agreement is found for the converged quantum mechanical calculations with indications that the Boothroyd-Keogh-Martin-Peterson potential energy surface is better suited to describe the dynamics of the reaction. For the higher collision energy the quasi classical trajectory calculations reproduce the experimental data quite well, whereas they fail to describe the situation at the lower collision energy especially with respect to angular resolved differential cross sections. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474283
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  • 4
    Electronic Resource
    Electronic Resource
    Dissociation dynamics of acetylene Rydberg states as a function of excited state lifetime (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5231-5246 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state selective photodissociation of acetylene, C2H2/C2D2, was studied in the wavelength range 121.2–132.2 nm by high resolution Rydberg atom time-of-flight measurements on the atomic fragment, H/D. In the wavelength region studied members of all four Rydberg series and the highly excited E˜ valence state were state selectively excited using tunable vacuum-ultraviolet laser radiation. The lifetime of the excited states which were studied varied from 58 fs to more than 2 ps. Formation of the ethynyl radical in its X˜ electronic ground state and its first electronically excited A˜ state is observed with practically no indication of B˜ state fragments. Two decay channels with different dissociation dynamics were also observed. In both channels the observed decay dynamics depended strongly on the excited state of the parent molecule. Further there are major differences between these two dissociation pathways with respect to the measured internal energy and angular distributions. In one channel the dissociation is dominated by dynamical effects and the C2H fragments are formed with a high degree of vibrational excitation. In contrast to this in the second channel a smooth internal energy distribution is observed indicating that the fragment quantum state distribution is spread over a considerable range of the available phase space. Moreover, this second channel can be fit with a phase space model constrained only by conservation of energy and angular momentum. This is further evidence for the randomization of internal energy during the dissociation process. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477140
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  • 5
    Electronic Resource
    Electronic Resource
    On the appearance of resonances in reactive scattering: An experimental study of the H+D2→HD+D reaction at collision energies near 1.29 eV (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 786-790 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hydrogen exchange reaction H+D2(v=0,j=0)→HD(v′,j′)+D was investigated at collision energies between 1.27 and 1.30 eV in a high resolution crossed beam experiment. The angle-velocity distribution of nascent D-atoms was measured using the technique of Rydberg atom time-of-flight spectroscopy. The resolution of this technique allows the identification of individual ro-vibrational states of the associated HD product molecule. Calculations done on the Liu–Siegbahn–Truhlar–Horowitz (LSTH) potential energy surface (PES) explicitly including the Geometric Phase effect predict a resonance in reactive scattering for collision energies close to 1.29 eV. The experimental data do not show signatures of this resonance in the energy range investigated. Instead of this a general good agreement between experiment and theory even on the basis of state-to-state differential cross sections is already found for calculations on the LSTH PES at a collision energy of 1.30 eV not including the Geometric Phase indicating that this effect does not play an important role at these collision energies. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474378
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  • 6
    Electronic Resource
    Electronic Resource
    The dynamics of the hydrogen exchange reaction at 2.20 eV collision energy: Comparison of experimental and theoretical differential cross sections (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9971-9981 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The H+D2(v=0,j=0)→HD(v′,j′)+D isotopic variant of the hydrogen atom exchange reaction has been studied in a crossed molecular beam experiment at a collision energy of 2.20 eV. Kinetic energy spectra of the nascent D atoms were obtained by using the Rydberg atom time-of-flight technique. The extensive set of spectra collected has permitted the derivation of rovibrationally state-resolved differential cross sections in the center-of-mass frame for most of the internal states of the HD product molecules, allowing a direct comparison with theoretical predictions. Accurate 3D quantum mechanical calculations have been carried out on the refined version of the latest Boothroyd–Keogh–Martin–Peterson potential energy surface, yielding an excellent agreement with the experimentally determined differential cross sections. The comparison of the results from quasi-classical trajectory calculations on the same potential surface reveals some discrepancies with the measured data, but shows a good global accordance. The theoretical calculations demonstrate that, at this energy, reactive encounters are predominantly noncollinear and that collinear collisions lead mostly to nonreactive recrossing. The experimental results are satisfactorily accounted for by theoretical calculations without consideration of Geometric Phase effects. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478870
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  • 7
    Electronic Resource
    Electronic Resource
    The H+D2 reaction in the vicinity of the conical intersection (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 7862-7864 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Scattering measurements performed at an energy slightly higher than that of the lowest crossing between the ground and the first electronically excited state of the H3 system are reported. The essentials of the reactive dynamics are describable in terms of a classical motion of the nuclei on the lowest adiabatic electronic potential.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473745
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  • 8
    Electronic Resource
    Electronic Resource
    Evolutionary optimization in multimodal search space (1996)
    Springer
    Biological cybernetics 74 (1996), S. 203-207 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract.  Optimization by a simple evolution strategy based on a mutation and selection scheme without recombination was tested for its efficiency in multimodal search space. A modified Rastrigin function served as an objective function providing fitness landscapes with many local optima. It turned out that the evolutionary algorithm including adaptive stepsize control is well-suited for optimization. The process is able to efficiently surmount local energy barriers and converge to the global optimum. The relation between the optimization time available and the optimal number of offspring was investigated and a simple rule proposed. Several numbers of offspring are nearly equally suited in a smooth search space, whereas in rough fitness landscapes an optimum is observed. In either case both very large and very small numbers of offspring turned out to be unfavourable for optimization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652221
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  • 9
    Electronic Resource
    Electronic Resource
    Evolutionary optimization in multimodal search space (1996)
    Springer
    Biological cybernetics 74 (1996), S. 203-207 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Optimization by a simple evolution strategy based on a mutation and selection scheme without recombination was tested for its efficiency in multimodal search space. A modified Rastrigin function served as an objective function providing fitness landscapes with many local optima. It turned out that the evolutionary algorithm including adaptive stepsize control is wellsuited for optimization. The process is able to efficiently surmount local energy barriers and converge to the global optimum. The relation between the optimization time available and the optimal number of offspring was investigated and a simple rule proposed. Several numbers of offspring are nearly equally suited in a smooth search space, whereas in rough fitness landscapes an optimum is observed. In either case both very large and very small numbers of offspring turned out to be unfavourable for optimization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652221
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  • 10
    Electronic Resource
    Electronic Resource
    Tragedy of the Fiscal Common?: Fiscal Stock Externalities in a Leviathan Model of Federalism (1999)
    Springer
    Public choice 101 (1999), S. 177-193 
    Details
    ISSN: 1573-7101
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract The paper deals with vertical tax competition between self-interested governments in a dynamic environment. In a federation, competition between the federal and the state governments arises when tax sources are not separated but pooled. Since dynamic inefficiencies will be stressed, the focus is on fiscal stock externalities rather than on flow externalities. The paper shows that the Leviathans in a federation tax the fiscal common resource more extensively than the single Leviathan in a unitary state. Furthermore, the positive impact of political stability on public consumption of the fiscal common will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018322225197
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