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  • 1
    Electronic Resource
    Electronic Resource
    Fluorine atom abstraction by Si(100). I. Experimental (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3679-3695 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the interaction of low energy F2 with Si(100) at 250 K, a dissociative chemisorption mechanism called atom abstraction is identified in which only one of the F atoms is adsorbed while the other F atom is scattered into the gas phase. The dynamics of atom abstraction are characterized via time-of-flight measurements of the scattered F atoms. The F atoms are translationally hyperthermal but only carry a small fraction (∼3%) of the tremendous exothermicity of the reaction. The angular distribution of F atoms is unusually broad for the product of an exothermic reaction. These results suggest an "attractive" interaction potential between F2 and the Si dangling bond with a transition state that is not constrained geometrically. These results are in disagreement with the results of theoretical investigations implying that the available potential energy surfaces are inadequate to describe the dynamics of this gas–surface interaction. In addition to single atom abstraction, two atom adsorption, a mechanism analogous to classic dissociative chemisorption in which both F atoms are adsorbed onto the surface, is also observed. The absolute probability of the three scattering channels (single atom abstraction, two atom adsorption, and unreactive scattering) for an incident F2 are determined as a function of F2 exposure. The fluorine coverage is determined by integrating the reaction probabilities over F2 exposure, and the reaction probabilities are recast as a function of fluorine coverage. Two atom adsorption is the dominant channel [P2=0.83±0.03(95%, N=9)] in the limit of zero coverage and decays monotonically to zero. Single atom abstraction is the minor channel (P1=0.13±0.03) at low coverage but increases to a maximum (P1=0.35±0.08) at about 0.5 monolayer (ML) coverage before decaying to zero. The reaction ceases at 0.94±0.11(95%, N=9) ML. Thermal desorption and helium diffraction confirm that the dangling bonds are the abstraction and adsorption sites. No Si lattice bonds are broken, in contrast to speculation by other investigators that the reaction exothermicity causes lattice disorder. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479677
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of the SSAP Method for the Numerical Valuation of High-Dimensional Multivariate American Securities (1999)
    Springer
    Algorithmica 25 (1999), S. 75-98 
    Details
    ISSN: 1432-0541
    Keywords: Key words. American options, American pricing, Monte Carlo simulation, Optimal control, Finite-difference, Itô process.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We consider a new numerical method developed by Barraquand and Martineau for the pricing of American securities where the payoff depends on several sources of uncertainty. This method utilizes Monte Carlo simulation and is referred to as Stratified State Aggregation along the Payoff (SSAP). Since there are no other methods that so effectively reduce the dimensionality of high-dimensional problems, the SSAP method has generated significant interest. Numerical results are presented showing that, if a sufficiently large number of time steps are used, in the cases of the two-dimensional maximum and minimum options, SSAP typically prices to within 6 cents of the true price. However, we show that if the security depends on two or more sources of uncertainty, then the price obtained by the SSAP method will not, in general, converge to the correct theoretical price, due in large part to incorrect exercise decisions being made. We analyze the exercise regions in the cases of the two-dimensional maximum and minimum options and show how SSAP makes incorrect exercise decisions. Suggestions for improving SSAP pricing accuracy by choosing a partition other than the payoff are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009284
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  • 3
    Electronic Resource
    Electronic Resource
    $\Lambda, \bar{\Lambda}$ polarization and spin transfer in lepton deep-inelastic scattering (2000)
    Springer
    The European physical journal 16 (2000), S. 657-664 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The flavor and helicity distributions of the $\Lambda$ and $\bar{\Lambda}$ hyperons for both valence and sea quarks are calculated in a perturbative QCD (pQCD) based model. We relate these quark distributions to the fragmentation functions of $\Lambda$ and $\bar{\Lambda}$ , and calculate the z-dependence of the longitudinal spin transfer to $\Lambda$ and $\bar{\Lambda}$ in lepton deep-inelastic scattering (DIS). It is shown that the spin transfer to the $\Lambda$ is compatible with the first HERMES results at DESY, and further tests are suggested. We also make predictions for the z-dependence of the $\Lambda$ and $\bar{\Lambda}$ longitudinal polarizations in neutrino (antineutrino) DIS processes. We investigate the sea contribution to the fragmentation functions, and we test a possible scenario where the sea quarks in $\Lambda$ (or the sea antiquarks in $\bar{\Lambda}$ ) are negatively polarized, whereas the sea antiquarks in the $\Lambda$ (or the sea quarks in $\bar{\Lambda}$ ) are positively polarized. The asymmetry of the polarized fragmentation functions of the sea quarks and antiquarks to $\Lambda$ and $\bar{\Lambda}$ provides a way to understand the different behavior between the $\Lambda$ and $\bar{\Lambda}$ spin transfers observed in the recent E665 experiment at FNAL.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520000447
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  • 4
    Electronic Resource
    Electronic Resource
    Nuclear effects on the extraction of neutron structure functions (2001)
    Springer
    The European physical journal 20 (2001), S. 63-70 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Nuclear effects due to the presence of spin-1 isosinglet 6-quark clusters in the deuteron on the extraction of both spin-independent and spin-dependent neutron structure functions are investigated. The x-dependences of the 6-quark cluster structure functions are estimated by using a perturbative QCD (pQCD) dimensional counting rules. Within this framework, the ratio of the deuteron structure function to the free nucleon structure function can be well described. We find that the nuclear effect on the extracted spin-dependent neutron structure function is very different from that on the spin-independent neutron structure function. The effect enhances the Bjorken sum by about 10%, whereas it decreases the Gottfried sum by about 7%. The formalism for calculating nuclear effects is further used to evaluate the spin-dependent structure function of the $^3$ He nucleus and a good self-consistent check is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100520100647
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