409 research outputs found
Preliminary Study of H₂O Adsorption on Cr₂O₃ and Al₂O₃ Surfaces by Ab Initio Cluster Calculations
Adsorption and desorption of water over Cr-oxide and alumina are of great concern with the contamination of stainless steel and gas chromatographic isotope separation. However,the mechanisms of those phenomena have not been fully clarified. A preliminary ab inito study on the behavior of water molecules on the (001) surfaces of α-Cr₂O₃ and α-Al₂O₃ was carried out for small clusters of Me4O4 (Me=Cr or Al) by use of the Gaussian 03 package. It was found that water molecules can be adsorbed molecularly and dissociatively on these surfaces. Molecular adsorption of a H₂O molecule takes place on a metal atom of the cluster as Me-OH₂, with the bond length of about 2.0 Å. Dissociative adsorption occurs by forming Me-OH (on-top site) or Me2-OH (bridge site) and O-H bonds. There appeared a feature that the bond length of Me2-OH is greater than that of Me-OH. Calculated adsorption energies were examined by comparing with the values estimated from the thermal desorption spectra of water for α-Cr₂O₃ and γ-alumina. The ab initio calculations coincided quite well with the observed thermal desorption spectrum for α-Cr₂O₃, whereas they did not for γ-alumina. Further studies are required to clarify the structures of adsorbed species, adsorptiron energies and kinetic processes
Summary of Working Group 3: Assessment of the Wire Lens Scheme at LHC from the Current Pulsed Power Technology Point of View
Anomalous thermal conductivity and local temperature distribution on harmonic Fibonacci chains
The harmonic Fibonacci chain, which is one of a quasiperiodic chain
constructed with a recursion relation, has a singular continuous
frequency-spectrum and critical eigenstates. The validity of the Fourier law is
examined for the harmonic Fibonacci chain with stochastic heat baths at both
ends by investigating the system size N dependence of the heat current J and
the local temperature distribution. It is shown that J asymptotically behaves
as (ln N)^{-1} and the local temperature strongly oscillates along the chain.
These results indicate that the Fourier law does not hold on the harmonic
Fibonacci chain. Furthermore the local temperature exhibits two different
distribution according to the generation of the Fibonacci chain, i.e., the
local temperature distribution does not have a definite form in the
thermodynamic limit. The relations between N-dependence of J and the
frequency-spectrum, and between the local temperature and critical eigenstates
are discussed.Comment: 10 pages, 4 figures, submitted to J. Phys.: Cond. Ma
Universalities in One-electron Properties of Limit Quasi-periodic Lattices
We investigate one-electron properties of one-dimensional self-similar
structures called limit quasi-periodic lattices. The trace map of such a
lattice is nonconservative in contrast to the quasi-periodic case, and we can
determine the structure of its attractor. It allows us to obtain the three new
features of the present system: 1) The multi-fractal characters of the energy
spectra are {\it universal}. 2) The supports of the -spectra extend
over the whole unit interval, . 3) There exist marginal critical
states.Comment: 4 pages, 2figure
Equation of State for Parallel Rigid Spherocylinders
The pair distribution function of monodisperse rigid spherocylinders is
calculated by Shinomoto's method, which was originally proposed for hard
spheres. The equation of state is derived by two different routes: Shinomoto's
original route, in which a hard wall is introduced to estimate the pressure
exerted on it, and the virial route. The pressure from Shinomoto's original
route is valid only when the length-to-width ratio is less than or equal to
0.25 (i.e., when the spherocylinders are nearly spherical). The virial equation
of state is shown to agree very well with the results of numerical simulations
of spherocylinders with length-to-width ratio greater than or equal to 2
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