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  • Articles  (113)
  • 1995-1999  (113)
  • 1970-1974
  • 1997  (54)
  • 1996  (59)
  • Chemistry and Pharmacology  (106)
  • Mathematics  (7)
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  • Articles  (113)
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  • 1995-1999  (113)
  • 1970-1974
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  • 1
    Electronic Resource
    Electronic Resource
    Full configuration–interaction and state of the art correlation calculations on water in a valence double-zeta basis with polarization functions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8007-8015 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a valence double-zeta polarization basis, full configuration–interaction (FCI) calculations are carried out on water at its equilibrium geometry and at geometries where the OH bond lengths are stretched until dissociation. At the same geometries and with the same basis set configuration interaction calculations at excitation levels up to hextuples, multireference singles doubles configuration interaction calculations, coupled cluster calculations at excitation levels up to quadruples, Møller–Plesset perturbation theory calculations through order fifteen, and complete active space second-order perturbation theory calculations are also carried out. The static correlation contribution increase with increasing bond length. The calculations show that the coupled cluster approach has a remarkable ability to describe even relatively large static correlation contributions. The single reference perturbation expansion breaks down for larger OH bond length, while the multireference approach preserves the accuracy for the whole potential curve. At the equilibrium geometry, FCI calculations have also been carried out for the lowest state of 2A1, 2B1, and 2B2 symmetry of H2O+, and the results compared with state of the art correlation results for total energies and ionization potentials (IP's). Differential energies (IP's) are obtained more accurately than absolute (total) energies in the size extensive coupled cluster and perturbation approaches. For the nonsize extensive configuration interaction method errors are obtained of the same size for differential and absolute energies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471518
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  • 2
    Electronic Resource
    Electronic Resource
    Direct subsurface absorption of hydrogen on Pd(111) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4330-4336 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We summarize and discuss some of the available experimental and theoretical data important for understanding the role played by subsurface sites in dissociative chemisorption calculations for the H2/Pd(111) system. Then we use a semi-empirical potential energy surface (PES) to model the interaction of a H2 molecule impinging on a Pd(111) surface. The London–Eyring–Polanyi–Sato (LEPS) construction has been extended to make direct subsurface absorption possible. A two-dimensional wave packet calculation is used to find qualitative trends in the direct subsurface absorption and to reveal the time scales involved. We suggest that a partial in-plane relaxation occurs for the slowest incoming particles, thus resulting in a higher direct subsurface absorption probability for low energies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471541
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  • 3
    Electronic Resource
    Electronic Resource
    Quasiperiodicity in a detailed model of the peroxidase–oxidase reaction (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 10849-10859 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quasiperiodicity in models of the peroxidase–oxidase reaction has previously been reported in "abstract'' or phenomenological models which sacrifice chemical realism for tractability. In the present paper, we discuss how such behavior can arise in a detailed model (BFSO) of the reaction which has previously been shown to be consistent with experimental findings. We distinguish two types of quasiperiodic behavior. Regions of what we here refer to as "primary'' quasiperiodicity are delimited by supercritical secondary Hopf bifurcations at one end of the relevant range of parameter values and by heteroclinic transitions at the other. Regions of so-called "secondary quasiperiodicity'' are delimited by supercritical Hopf bifurcations at both ends of the parameter range. The existence of a quasiperiodic route to chaos in a modified version of BFSO is also described. This paper emphasizes the experimental circumstances under which quasiperiodic dynamics may be detected in the lab and offers specific prescriptions for its observation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472927
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  • 4
    Electronic Resource
    Electronic Resource
    Surprising cases of divergent behavior in Møller–Plesset perturbation theory (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5082-5090 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-order Møller–Plesset perturbation calculations have been carried out for several small molecules and compared to full configuration interaction (FCI) results. The convergence of the Møller–Plesset series is found to depend crucially on the one-electron basis sets. Addition of diffuse basis functions leads in some cases to divergent behavior of the Møller–Plesset series, even for highly single reference dominated systems as Ne and HF. The results thus questions the usefulness of higher-order perturbation calculations as a vehicle for obtaining arbitrary accuracy of quantum chemical calculations and raises the fundamental theoretical question: When does Møller–Plesset perturbation theory converge for many-electron systems in extended basis sets? © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472352
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  • 5
    Electronic Resource
    Electronic Resource
    Direct subsurface absorption of hydrogen on Pd(111): Quantum mechanical calculations on a new two-dimensional potential energy surface (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 9286-9296 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have calculated a two-dimensional (2D) potential energy surface (PES) for H2 interacting with a Pd(111) surface. The geometry considered is for H2 approaching a bridge site and dissociating into neighboring hollow sites and the subsurface sites directly below these. Density functional calculations were performed using both the local density approximation (LDA) and the generalized gradient approximation (GGA). The LDA PES gives the usual overbinding and shows no barrier (relative to the bottom of the H2 potential) to subsurface absorption, while the GGA PES agrees with the experimental adsorption energies and has a large barrier. We have performed quantum mechanical wave packet calculations on the GGA PES to obtain the direct subsurface absorption probability. We have also calculated the barrier height's dependence on a coordinate that can be associated with a local surface vibrational mode and the results suggest that this degree of freedom should be taken into account in the dynamical calculations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474040
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  • 6
    Electronic Resource
    Electronic Resource
    The influence of surface motion on the direct subsurface absorption of H2 on Pd(111) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10652-10661 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Based on density functional theory (DFT) within the generalized gradient approximation (GGA) we have calculated a three-dimensional (3D) potential energy surface (PES) for H2+Pd(111), depending on two hydrogen molecular degrees of freedom and one palladium surface degree of freedom. The PES is then used in 3D quantum mechanical wave packet calculations to investigate the effect of the surface motion on the direct subsurface absorption. We also compare the full 3D calculations to calculations where the surface motion is included through the sudden approximation. The calculations show a large downward shift of the onset energy for direct subsurface absorption upon inclusion of palladium surface motion (from 0.74 eV to 0.40 eV for H2). The use of the sudden approximation works well at collision energies greater than 1.3 eV (for H2), but leads to a significant underestimation of the direct subsurface absorption probability at lower energies. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474181
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  • 7
    Electronic Resource
    Electronic Resource
    A Triassic Lagerstätte from eastern North America (1996)
    [s.l.] : Nature Publishing Group
    Nature 380 (1996), S. 615-619 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A series of markedly cyclical lacustrine sediments of the Carnian Cow Branch Formation are exposed at the Solite Quarry, Cascade, Virginia, USA2 (Fig. 1), and these are fossiliferous throughout. The cycles are thought to represent periodic changes in lake depth under the control of known variations ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/380615a0
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  • 8
    Electronic Resource
    Electronic Resource
    Structure of a Bovine Thrombin–Hirudin51−65 Complex Determined by a Combination of Molecular Replacement and Graphics. Incorporation of Known Structural Information in Molecular Replacement (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 453-464 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Crystals of the bovine thrombin-hirudins51–65 complex have space group P6122 with cell constants a = 116.4, and c = 200.6 Å and two thrombin molecules in the asymmetric unit. Only one thrombin molecule could be located by generalized molecular replacement; the second was fit visually as a rigid body to an improved electron-density difference map. The structure was refined to R = 0.192 with two B values per residue (main chain and side chain) at 3.2 Å. The polar interactions of the peptides with the exosite of thrombin show differences consistent with the known flexibility in the interactions of the C-terminal peptide of hirudin with thrombin. The hirudin peptide in complex 2 has a higher temperature factor as compared with peptide 1 which may be correlated partly with a larger number of short-range electrostatic interactions between peptide 1 and thrombin and partly with the fact that thrombin 2 is ε-thrombin which is cleaved at Thr149A near the peptide binding site. Later, using this structure as a test case, it was shown that the position for the second thrombin could also be determined by a novel modification of the molecular-replacement method in which the contribution of the known molecule is subtracted from the structure factors. This approach is facile and applicable to any crystal containing two or more macromolecules in the asymmetric unit in which some but not all of the molecules can be determined by molecular replacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444996000364
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  • 9
    Electronic Resource
    Electronic Resource
    A mathematical model for fibro-proliferative wound healing disorders (1996)
    Springer
    Bulletin of mathematical biology 58 (1996), S. 787-808 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The normal process of dermal wound healing fails in some cases, due to fibro-proliferative disorders such as keloid and hypertrophic scars. These types of abnormal healing may be regarded as pathologically excessive responses to wounding in terms of fibroblastic cell profiles and their inflammatory growth-factor mediators. Biologically, these conditions are poorly understood and current medical treatments are thus unreliable. In this paper, the authors apply an existing deterministic mathematical model for fibroplasia and wound contraction in adult mammalian dermis (Olsenet al., J. theor. Biol. 177, 113–128, 1995) to investigate key clinical problems concerning these healing disorders. A caricature model is proposed which retains the fundamental cellular and chemical components of the full model, in order to analyse the spatiotemporal dynamics of the initiation, progression, cessation and regression of fibro-contractive diseases in relation to normal healing. This model accounts for fibroblastic cell migration, proliferation and death and growth-factor diffusion, production by cells and tissue removal/decay. Explicit results are obtained in terms of the model processes and parameters. The rate of cellular production of the chemical is shown to be critical to the development of a stable pathological state. Further, cessation and/or regression of the disease depend on appropriate spatiotemporally varying forms for this production rate, which can be understood in terms of the bistability of the normal dermal and pathological steady states—a central property of the model, which is evident from stability and bifurcation analyses. The work predicts novel, biologically realistic and testable pathogenic and control mechanisms, the understanding of which will lead toward more effective strategies for clinical therapy of fibro-proliferative disorders.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02459482
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  • 10
    Electronic Resource
    Electronic Resource
    Book reviews (1997)
    Springer
    Bulletin of mathematical biology 59 (1997), S. 197-204 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02459475
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