595 research outputs found
The Continuing Search for a Meaningful Model of Judicial Rankings and Why It (Unfortunately) Matters
Two Dimensional Ir-Cluster Lattices on Moir\'e of Graphene with Ir(111)
Lattices of Ir clusters have been grown by vapor phase deposition on graphene
moir\'{e}s on Ir(111). The clusters are highly ordered, spatially and thermally
stable below 500K. Their narrow size distribution is tunable from 4 to about
130 atoms. A model for cluster binding to the graphene is presented based on
scanning tunneling microscopy and density functional theory. The proposed
binding mechanism suggests that similar cluster lattices might be grown of
materials other than Ir.Comment: Submitted to PRL on 27Apr0
Diffusion of Pt dimers on Pt(111)
We report the results of a density-functional study of the diffusion of Pt
dimers on the (111) surface of Pt. The calculated activation energy of 0.37 eV
is in {\em exact} agreement with the recent experiment of Kyuno {\em et al.}
\protect{[}Surf. Sci. {\bf 397}, 191 (1998)\protect{]}. Our calculations
establish that the dimers are mobile at temperatures of interest for adatom
diffusion, and thus contribute to mass transport. They also indicate that the
diffusion path for dimers consists of a sequence of one-atom and (concerted)
two-atom jumps.Comment: Pour pages postscript formatted, including one figure; submitted to
Physical Review B; other papers of interest can be found at url
http://www.centrcn.umontreal.ca/~lewi
Adlayer core-level shifts of random metal overlayers on transition-metal substrates
We calculate the difference of the ionization energies of a core-electron of
a surface alloy, i.e., a B-atom in a A_(1-x) B_x overlayer on a
fcc-B(001)-substrate, and a core-electron of the clean fcc-B(001) surface using
density-functional-theory. We analyze the initial-state contributions and the
screening effects induced by the core hole, and study the influence of the
alloy composition for a number of noble metal-transition metal systems. Data
are presented for Cu_(1-x)Pd_x/Pd(001), Ag_(1-x) Pd_x/Pd(001), Pd_(1-x)
Cu_x/Cu(001), and Pd_(1-x) Ag_x/Ag(001), changing x from 0 to 100 %. Our
analysis clearly indicates the importance of final-state screening effects for
the interpretation of measured core-level shifts. Calculated deviations from
the initial-state trends are explained in terms of the change of inter- and
intra-atomic screening upon alloying. A possible role of alloying on the
chemical reactivity of metal surfaces is discussed.Comment: 4 pages, 2 figures, Phys. Rev. Letters, to appear in Feb. 199
International ultraviolet explorer spectral atlas of planetary nebulae, central stars, and related objects
The International Ultraviolet Explorer (IUE) archives contain a wealth of information on high quality ultraviolet spectra of approximately 180 planetary nebulae, their central stars, and related objects. Selected are representative low-dispersion IUE spectra in the range 1200 to 3200 A for 177 objects arranged by Right Ascension (RA) for this atlas. For most entries, the combined short wavelength (SWP) (1200to 1900) and long wavelength (LWR) (or LWP, 1900 to 3200 A) regions are shown on 30 cm by 10 cm Calcomp plots on a uniform scale to facilitate intercomparison of the spectra. Each calibrated spectrum is also shown on an expanded vertical scale to bring out some of the weaker features
A Full-Potential-Linearized-Augmented-Plane-Wave Electronic Structure Study of delta-Plutonium and the (001) Surface
The electronic and geometric properties of bulk fcc delta-plutonium and the
quantum size effects in the surface energies and the work functions of the
(001) ultra thin films (UTF) up to 7 layers have been investigated with
periodic density functional theory calculations within the full-potential
linearized augmented-plane wave (FP-LAPW) approach as implemented in the WIEN2k
package. Our calculated equilibrium atomic volume of 178.3 a.u.^3 and bulk
modulus of 24.9 GPa at the fully relativistic level of theory, i.e.
spin-polarization and spin-orbit coupling included, are in good agreement with
the experimental values of 168.2 a.u.^3 and 25 GPa (593 K), respectively. The
calculated equilibrium lattice constants at different levels of approximation
are used in the surface properties calculations for the thin films. The surface
energy is found to be rapidly converged with the semi-infinite surface energy
predicted to be 0.692eV at the fully-relativistic level.Comment: 27 pages,8 figure
On the O II ground configuration energy levels
The most accurate way to measure the energy levels for the O II 2p^3 ground
configuration has been from the forbidden lines in planetary nebulae. We
present an analysis of modern planetary nebula data that nicely constrain the
splitting within the ^2D term and the separation of this term from the ground
^4S_{3/2} level. We extend this method to H II regions using high-resolution
spectroscopy of the Orion nebula, covering all six visible transitions within
the ground configuration. These data confirm the splitting of the ^2D term
while additionally constraining the splitting of the ^2P term. The energies of
the ^2P and ^2D terms relative to the ground (^4S) term are constrained by
requiring that all six lines give the same radial velocity, consistent with
independent limits placed on the motion of the O+ gas and the planetary nebula
data.Comment: 20 pages, 3 figures. To be published in Ap
Surface relaxation and ferromagnetism of Rh(001)
The significant discrepancy between first-principles calculations and
experimental analyses for the relaxation of the (001) surface of rhodium has
been a puzzle for some years. In this paper we present density functional
theory calculations using the local-density approximation and the generalized
gradient approximation of the exchange-correlation functional. We investigate
the thermal expansion of the surface and the possibility of surface magnetism.
The results throw light on several, hitherto overlooked, aspects of metal
surfaces. We find, that, when the free energy is considered, density-functional
theory provides results in good agreement with experiments.Comment: 6 pages, 4 figures, submitted to Phys. Rev. Lett. (April 28, 1996
Damping of differential rotation in neutron stars
We derive the transport relaxation times for quasiparticle-vortex scattering
processes via nuclear force, relevant for the damping of differential rotation
of superfluids in the quantum liquid core of a neutron star. The proton
scattering off the neutron vortices provides the dominant resistive force on
the vortex lattice at all relevant temperatures in the phase where neutrons
only are in the paired state. If protons are superconducting, a small fraction
of hyperons and resonances in the normal state would be the dominant source of
friction on neutron and proton vortex lattices at the core temperatures K.Comment: 5 pages, Revtex, Phys. Rev. D 58, Rapid Communication, in pres
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