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  • 1
    Electronic Resource
    Electronic Resource
    Dehydrogenation induced phase transitions of p-aminobenzoic acid on Cu(110) (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 460-470 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Temperature and coverage dependent studies of p-aminobenzoic acid on a Cu(110) single crystal surface show a novel sequence of periodic structures linked to successive removal of hydrogen from the adsorbed species, as shown by LEED, STM, HREELS, and TPD. At room temperature, flat-lying molecules with a primitive unit cell of (3×4) periodicity with glide plane along the 〈001〉 direction are observed. Annealing this surface to 464 K causes partial desorption of H2 and a variation of the intensity in HREELS of various bands and formation of a (5 −22 4) periodicity. STM images suggest the formation of dimers, as a result of the dehydrogenation. On annealing to higher temperatures (510 K), further dehydrogenation forms (6 −51 2) structure. Finally, at 540 K, a (4 −31 2) periodicity is revealed in which all species correspond to dehydrogenated dimers. Through this sequence, all species retain a flat-lying orientation on the surface. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1426379
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of trailing jet instability on vortex ring formation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 589-596 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical simulations of an impulsively started jet were performed in order to investigate the effects of trailing jet instability on axisymmetric vortex ring formation. The predictions were compared to experimental results reported in the literature and to recently published numerical results. The total and vortex ring circulations were found to be in good agreement with both the experimental and the numerical results. The presence of a universal formation time scale was confirmed. The results also highlighted an important interaction between an instability which develops in the trailing jet for large discharge times and the dynamics of the head vortex ring. This interaction accelerates the process by which the vortex ring detaches from the trailing jet and has a significant effect on the vortex ring circulation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870264
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  • 3
    Electronic Resource
    Electronic Resource
    Numerical simulations of sound radiated from an axisymmetric premixed reacting jet (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 2671-2681 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sound radiated by an axisymmetric (two-dimensional) premixed reacting free jet was studied using direct numerical simulation. The jet was injected into cold combustion products. A narrow (in radial extent) high temperature pulse was specified at the jet inlet to stabilize the reacting jet. The computational domain included both the near-field flow and far-field acoustic regions. Both reacting and nonreacting cases were considered. The heat release associated with the reacting jet had a significant effect on the vortical structure, as well as the sound radiation level and pattern, within the jet. The sound radiation pattern and the source terms in Lighthill's equation were used to identify apparent sound source locations. Within the context of the assumptions of the present simulations, the results showed that the effect of heat release was to: (1) Stabilize the jet, (2) enhance sound radiation levels due to an increase in the entropy source, and (3) shift the frequency of the most unstable mode to lower values, resulting in a broader sound spectrum. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1386940
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  • 4
    Electronic Resource
    Electronic Resource
    Lévy flights: Exact results and asymptotics beyond all orders (2002)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 43 (2002), S. 2670-2689 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A comprehensive study of the symmetric Lévy stable probability density function is presented. This is performed for orders both less than 2, and greater than 2. The latter class of functions are traditionally neglected because of a failure to satisfy non-negativity. The complete asymptotic expansions of the symmetric Lévy stable densities of order greater than 2 are constructed, and shown to exhibit intricate series of transcendentally small terms—asymptotics beyond all orders. It is demonstrated that the symmetric Lévy stable densities of any arbitrary rational order can be written in terms of generalized hypergeometric functions, and a number of new special cases are given representations in terms of special functions. A link is shown between the symmetric Lévy stable density of order 4, and Pearcey's integral, which is used widely in problems of optical diffraction and wave propagation. This suggests the existence of applications for the symmetric Lévy stable densities of order greater than 2, despite their failure to define a probability density function. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1467095
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  • 5
    Electronic Resource
    Electronic Resource
    Complete asymptotic expansions of the Fermi–Dirac integrals Fp(η)=1/Γ(p+1)∫0∞[εp/(1+eε−η)]dε (2001)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 42 (2001), S. 1860-1868 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The complete asymptotic expansions, that is to say expansions which include any exponentially small terms lying beyond all orders of the asymptotic power series, are calculated for the Fermi–Dirac integrals. We present two methods to accomplish this, the first in the complex plane utilizing Mellin transforms and Hankel's representation of the gamma function, and the second on the real line using the known asymptotic expansions of the confluent hypergeometric functions. The complete expansions of Fp(η) are then used to investigate the effect that these traditionally neglected exponentially small terms have on physical systems. It is shown that for a 2 dimensional nonrelativistic ideal Fermi gas, the subdominant exponentially small series becomes dominant. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1350634
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