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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2862-2871 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio molecular orbital calculations were performed toward the determination of the potential energy surface for the unimolecular ground-state dissociation of vinylcyanide. Reaction pathways for the three- and four-center elimination reactions of HCN and H2, as well as migration and radical elimination channels of H and CN, were examined. MP2 gradient geometry optimizations and QCISD(T) single point energy calculations were performed for all the relevant product species and transition states. The results are compared to the analogous unimolecular dissociation of vinylchloride which has been theoretically investigated by Morokuma and co-workers [J. Chem. Phys. 100, 8976 (1994)]. The unimolecular rates for all reaction channels have been calculated using Rice–Ramsperger–Kassel–Marcus (RRKM) theory employing ab initio transition state energies and MP2 vibrational frequencies. Our calculations indicate that the elimination of H2 and HCN preferentially proceed via three-center transition states. We also find that H-migration reactions are rapid, suggesting that substantial H-atom scrambling precedes dissociation. This result is important for the interpretation of several isotopic substitution measurements which are all consistent with exclusive three-center elimination of H2 and HCN. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
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    Unknown
    Berlin : Periodicals Archive Online (PAO)
    Fabula. 9:1/3 (1967) 169 
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 129 (1990), S. 313-324 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract On 22 October, 1980, near the solar central meridian in the western vicinity of a large spot group, a subflare of the two-ribbon type was observed. Three surges were associated with this flare. Their starting points were situated close to the principal flare patches on both sides of a short filament that was visible for only a few hours. True flow velocities and decelerations along the arch-shaped surge trajectories have been determined for two of the surges. The highest velocities were found at the onset of the surges. The event was studied from a series of Hα on- and off-band flltergrams taken with the Debrecen coronagraph of 53 cm aperture.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 151 (1994), S. 385-388 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is shown that sunspots as tracers can give the same results for the differential rotation of the solar photosphere as the Doppler-shift measurements, if the sunspots used have only insignificant motion relative to their immediate photospheric surroundings.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Series of white light heliograms and oft- and on-band Hα filtergrams have been obtained, with an average spatial resolution of 1″, to study the flare active McMath region 15403 on 11 July, 1978. A great number of accurate heliographic positions were determined for the umbrae, the white light flare patches and several bright Hα flare knots, as well as along the principal zero filament and an arch prominence. Using the measured heliographic coordinates of these objects their motions could be analyzed in some detail. The velocities of several different objects could be deduced from the coordinates. Since the heliocentric angle of the region was about 45°, the variation in apparent heliographic coordinates also enabled some variations in heights to be determined. It is pointed out that the flare when fully developed, consisted almost entirely of loops. The zero filament which was activated prior to the flare ran between two umbrae of common penumbra and opposite polarity, one belonging to an old, the other to a new spot group. The white light flare developed on both sides of the filament where it passed between these two umbrae; it was also the place where the flare started. Observational evidence appears to indicate that the erupted filament re-formed from below. An indication has been found that there was a link between the motion of some umbrae and the major flare occurrence.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 58 (1996), S. 193-202 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe enhancements to the method of partial retention of diatomic differential overlap (PRDDO). The new method, denoted PRDDO/M, employs a basis set of not quite orthogonal atomic orbitals (NQOAOS) and utilizes sparse matrix techniques to greatly increase the computational efficiency for large molecules. Other modifications, including a complete reparametrization of the method against ab initio STO-3G calculations and implementation of integral screening/damping algorithms, are described. The method is an order of magnitude or more faster than are STO 3G single-point calculations using modern ab initio codes, with little loss in accuracy. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 67-76 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variation of the frozen-core potential (FCP) method is developed and implemented within the modified version of the method of partial retention of diatomic differential overlap (PRDDO/M). The explicit treatment of core electrons is replaced with a potential based on the actual core-valence integrals rather than upon an arbitrary model potential. The core-valence orthogonality requirement is replaced by an energy shift operator. PRDDO/M/FCP calculations exhibit good agreement with ab initio calculations with the same basis set, while reducing the computational cost significantly. © 1997 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 403-423 
    ISSN: 0271-2091
    Keywords: Velocity correction method ; Bilinear interpolation functions ; Pressure boundary conditions ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper a finite element solution for two-dimensional incompressible viscous flow is considered. The velocity correction method (explicit forward Euler) is applied for time integration. Discretization in space is carried out by the Galerkin weighted residual method. The solution is in terms of primitive variables, which are approximated by piecewise bilinear basis functions defined on isoparametric rectangular elements. The second step of the obtained algorithm is the solution of the Poisson equation derived for pressure. Emphasis is placed on the prescription of the proper boundary conditions for pressure in order to achieve the correct solution. The scheme is completed by the introduction of the balancing tensor viscosity; this makes this method stable (for the advection-dominated case) and permits us to employ a larger time increment. Two types of example are presented in order to demonstrate the performance of the developed scheme. In the first case all normal velocity components on the boundary are specified (e.g. lid-driven cavity flow). In the second type of example the normal derivative of velocity is applied over a portion of the boundary (e.g. flow through sudden expansion). The application of the described method to non-isothermal flows (forced convection) is also included.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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