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31.
First-principles calculations were performed to investigate magnetic phenomena in surface reactions involving O(2). We present two magnetized surface cases: (1) oxidation of paramagnetic Ag, and magnetic properties of the high coverage oxide phase, which correspond to a magnetic impurity superlattice on paramagnetic surfaces and (2) oxidation of ferromagnetic Pt, represented by the Pt layer on M (M = Fe and Co) relevant to the oxidation reduction reaction (ORR) on Pt, in relation to both fundamental and application interests. In the first case, we found that the dissociative adsorption of O(2), resulting in oxide phases in Ag(111), reveals interesting magnetic interactions. We note that the magnetic states are induced by the ferromagnetic superexchange interactions and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Specifically, the superlattice structures with short O-O distances have an effective ferromagnetic superexchange and RKKY interaction. In the second case, we found that a magnetic moment is induced on the Pt layer by the M substrate. The spin polarization of Pt-d states is due to hybridization with M-d states. The d-band center (ε(d)) of Pt (on M), is shifted downwards with respect to pure Pt. However, because of the spin polarization, the otherwise filled spin-down d(zz) orbital in paramagnetic pure Pt is shifted towards the Fermi level. This promotes π(z↑)-d(zz↓) interactions, which influences the O(2)-Pt interaction at O(2) far from the surface. Details and mechanisms of these two magnetic phenomena are discussed. 相似文献
32.
33.
Kota Kasai Yoshihiro Tonegawa 《Calculus of Variations and Partial Differential Equations》2014,50(1-2):1-68
We give a new proof of Brakke’s partial regularity theorem up to $C^{1,\varsigma }$ for weak varifold solutions of mean curvature flow by utilizing parabolic monotonicity formula, parabolic Lipschitz approximation and blow-up technique. The new proof extends to a general flow whose velocity is the sum of the mean curvature and any given background flow field in a dimensionally sharp integrability class. It is a natural parabolic generalization of Allard’s regularity theorem in the sense that the special time-independent case reduces to Allard’s theorem. 相似文献
34.
35.
D. N. Son N. ArboledaJr W. A. Dino H. Kasai 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):27-35
We consider a two-terminal Aharonov-Bohm (AB) interferometer with a quantum dot inserted in one path of the AB ring.
We investigate the transport properties of this system in and out of the Kondo regime. We utilize perturbation theory to
calculate the electron self-energy of the quantum dot with respect to the intradot Coulomb interaction. We show the expression
of the Kondo temperature as a function of the AB phase together with its dependence on other characteristics such as the
linewidth of the ring and the finite Coulomb interaction and the energy levels of the quantum dot. The current oscillates
periodically as a function
of the AB phase. The amplitude of the current oscillation decreases with increasing Coulomb interaction. For a given temperature,
the electron transport through the AB interferometer
can be selected to be in or out of the Kondo regime by changing the magnetic flux threading perpendicular to the AB ring of
the system. 相似文献
36.
The rotational-state-selected CH (v = 0, J, F(i)) beam has been prepared by using an electric hexapole and applied to the crossed beam reaction of CH (v = 0, J, F(i)) + O(2) → OH (A) + CO at different O(2) beam conditions. The rotational state selected reactive cross sections of CH (RSSRCS-CH) turn out to depend remarkably on the rotational state distribution of O(2) molecules at a collision energy of ~?0.19 eV. The reactivity of CH molecules in the N = 1 rotational states (namely ∣J = 1∕2, F(2)> and ∣J = 3∕2, F(1)> states, N designates the angular momentum excluding spin) becomes strongly enhanced upon a lowering of the rotational temperature of the O(2) beam. The RSSRCS-CH in these two rotational states correlate linearly with the population of O(2) molecule in the specific K(O(2)) frame rotation number states: CH(|J = 1/2,F(2)>) with O(2)(|K(O(2)) = 1>);CH(|J = 3/2,F(1)>) with O(2)(|K(O(2)) = 3>). These linear correlations mean that the rotational-state-selected CH molecules are selectively reactive upon the incoming O(2) molecules in a specific rotational state; here, we use the term "rotationally correlated reactivity" to such specific reactivity depending on the combination of the rotational states between two molecular reactants. In addition, the steric asymmetry in the oriented CH (∣J = 1∕2,?F(2),?M = 1∕2>) + O(2) (|K(O(2)) = 1>) reaction turns out to be negligible (< ±1%). This observation supports the reaction mechanism as theoretically predicted by Huang et al. [J. Phys. Chem. A 106, 5490 (2002)] that the first step is an intermediate formation with no energy barrier in which C-atom of CH molecule attacks on one O-atom of O(2) molecule at a sideways configuration. 相似文献
37.
Tsai PY Che DC Nakamura M Lin KC Kasai T 《Physical chemistry chemical physics : PCCP》2011,13(4):1419-1423
The orientation dependence of Br-atom formation in the reaction of the oriented OH radical with the HBr molecule using the hexapole electrostatic field was studied. Experimental results for the orientation dependence in the reaction were analyzed using a Legendre polynomial fit. The results show two reactive sites. It was found that O-end attack is most favored for this reaction, and that H-end attack also shows a pronounced reactivity. The reactivity of the side-ways attack was found to be small. By comparing the results of the orientation dependence in the reaction with studies of inelastic collisions and theoretical calculations, two reaction pathways are proposed. Reaction by O-end attack is followed by a direct abstraction of the H-atom from the HBr molecule. The mechanism for H-end attack may have H-atom migration from HBr to form the water molecule. 相似文献
38.
W. Brenig S. Küchenhoff H. Kasai 《Applied Physics A: Materials Science & Processing》1990,51(2):115-120
A quantum mechanical coupled channels approach to associative or recombinative desorption and scattering of diatomic molecules is described. The formulation is based on the concept of a reaction path and allows prediction of the vibrational excitation of desorbing molecules. We first consider very light molecules such as H2 and D2 desorbing via a Langmuir-Hinshelwood reaction. In a simple model neglecting rotations and substrate vibrations, the dependence of molecular vibrational excitation on incident energy, the curvature of the reaction path and the position and height of the saddle point are discussed. Various experimental results can be described with reasonable parameters. Vibrational excitation in Eley-Rideal reactions and rotational excitations in general are discussed only in a semiquantitative way. For heavier molecules the coupling to substrate vibrations in principle will become more important. Arguments will be presented that for the problem of vibrational excitation in desorption and scattering this coupling may still be neglected approximately. Results for vibrational excitations of CuF desorbing from Cu are in support of this simple point of view. 相似文献
39.
The order-disorder transition of chemisorbed H on Ni (111) has been analyzed by Kittler and Bennemann in terms of the lattice gas model. The main purpose of this paper is to refine the above calculation. The expression with regard to adlayer domains is given for the half-order LEED spot intensity, from which the dependence of the transition temperature and of the LEED spot intensity on H-coverages is calculated. In particular, the H-coverage dependence of the transition-temperature Tc and the LEED intensity I for θ? 0.25 is restudied. We present results obtained by using only pair interactions between the H-atoms and no 3H-interactions. It is shown that the observed asymmetric phase diagram with respect to H-coverages can result from the two kinds of pair interactions between chemisorbed H atoms. 相似文献
40.
Masuhiro Tsukada Giuliano Freddi Yoko Gotoh Nobutami Kasai 《Journal of Polymer Science.Polymer Physics》1994,32(8):1407-1412
Physical and chemical structure, as well as thermal behavior of solution-cast regenerated films, prepared from tussah (Antheraea pernyi) silk fibroin, were compared with those of solution-cast native films, in order to ascertain whether treatment (degumming, dissolution) used for preparation affected their properties. Regenerated fibroin films exhibited a higher thermal stability than native ones, as shown by differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical behavior. Glass transition temperature and other relevant thermal transitions of the regenerated silk specimen shifted to higher temperatures compared with those of native specimen. Molecular conformation and crystalline structure did not show significant differences between the two kinds of silk films. Amino acid composition and molecular weight, however, distribution changed markedly after dissolving tussah silk fibroin fiber in concentrated LiSCN in polypeptide size was the main features for the regenerated silk fibroin. © 1994 John Wiley & Sons, Inc. 相似文献