12,991 research outputs found
Atomic helium scattering and diffraction from solid surfaces
It is shown that whether or not diffractive scattering is observed from solid surfaces depends not only on the elastic scattering cross section, i.e. the normalized Debye-Waller factor, but also on the surface structure or local surface potential of the particular solid
Nitric oxide adsorption on Ru(001) at 78 and 120 K: Temperature dependence on the bonding geometry
The influence of surface temperature on NO adsorption on
Ru(001) between 78 and 120 K has been investigated by
high-resolution electron energy-loss spectroscopy (EELS)
and thermal desorption mass spectrometry. Metastable NO
adsorption states were isolated at 78 K and were identified
by EELS. In all cases, heating of the NO overlayer from 78 to 120 K resulted in an irreversible conversion between adsites. All the measurements were performed in an UHV system that has been described in detail previously. Experimental techniques were employed that have also been documented thoroughly
Effective theory of excitations in a Feshbach resonant superfluid
A strongly interacting Fermi gas, such as that of cold atoms operative near a
Feshbach resonance, is difficult to study by perturbative many-body theory to
go beyond mean field approximation. Here I develop an effective field theory
for the resonant superfluid based on broken symmetry. The theory retains both
fermionic quasiparticles and superfluid phonons, the interaction between them
being derived non-perturbatively. The theory converges and can be improved
order by order, in a manner governed by a low energy expansion rather than by
coupling constant. I apply the effective theory to calculate the specific heat
and propose a mechanism of understanding the empirical power law of energy
versus temperature recently measured in a heat capacity experiment.Comment: 4+ pages, 1 figure; Added references, corrected and clarified minor
statements (v.2
Chemisorption on a model bcc metal
The system considered here is that of a single atom with one energy level chemisorbed on the (001) surface of a model bcc metal. We present the change in the density of electronic states În (E) due to chemisorption for two cases: one when the adatom is bound to a single substrate atom in the "onâsite" configuration and the other when it is bound to four substrate atoms in the "centered fourfold site." In principle, this change in the density of states În can be related to the results of photoemission measurements
Points of General Relativisitic Shock Wave Interaction are "Regularity Singularities" where Spacetime is Not Locally Flat
We show that the regularity of the gravitational metric tensor in spherically
symmetric spacetimes cannot be lifted from to within the
class of coordinate transformations in a neighborhood of a point of
shock wave interaction in General Relativity, without forcing the determinant
of the metric tensor to vanish at the point of interaction. This is in contrast
to Israel's Theorem which states that such coordinate transformations always
exist in a neighborhood of a point on a smooth single shock surface. The
results thus imply that points of shock wave interaction represent a new kind
of singularity for perfect fluids evolving in spacetime, singularities that
make perfectly good sense physically, that can form from the evolution of
smooth initial data, but at which the spacetime is not locally Minkowskian
under any coordinate transformation. In particular, at such singularities,
delta function sources in the second derivatives of the gravitational metric
tensor exist in all coordinate systems of the atlas, but due to
cancelation, the curvature tensor remains uniformly bounded.Comment: This article has been withdrawn since the main result is wrong due to
an computational error. See arXiv:1506.04081 and arXiv:1409.5060 for a
correction of this error and a proof of the opposite statemen
Kinetics of dissociative chemisorption of methane and ethane on Pt(110)-(1X2)
The initial probability of dissociative chemisorption Pr of methane and ethane on the highly corrugated, reconstructed Pt(110)â(1Ă2) surface has been measured in a microreactor by counting the number of carbon atoms on the surface following the reaction of methane and ethane on the surface which was held at various constant temperatures between 450 and 900 K during the reaction. Methane dissociatively chemisorbs on the Pt(110)â(1Ă2) surface with an apparent activation energy of 14.4 kcal/mol and an apparent preexponential factor of 0.6. Ethane chemisorbs dissociatively with an apparent activation energy of 2.8 kcal/mol and an apparent preexponential factor of 4.7Ă10^(â3). Kinetic isotope effects were observed for both reactions. The fact that P_r is a strong function of surface temperature implies that the dissociation reactions proceed via a trappingâmediated mechanism. A model based on a trappingâmediated mechanism is used to explain the observed kinetic behavior. Kinetic parameters for CâH bond dissociation of the thermally accommodated methane and ethane are extracted from the model
The fate of cannibalized fundamental-plane ellipticals
Evolution and disruption of galaxies orbiting in the gravitational field of a
larger cluster galaxy are driven by three coupled mechanisms: 1) the heating
due to its time dependent motion in the primary; 2) mass loss due to the tidal
strain field; and 3) orbital decay. Previous work demonstrated that tidal
heating is effective well inside the impulse approximation limit. Not only does
the overall energy increase over previous predictions, but the work is done
deep inside the secondary galaxy, e.g. at or inside the half mass radius in
most cases. Here, these ideas applied to cannibalization of elliptical galaxies
with fundamental-plane parameters. In summary, satellites which can fall to the
center of a cluster giant by dynamical friction are evaporated by internal
heating by the time they reach the center. This suggests that true
merger-produced multiple nuclei giants should be rare. Specifically,
secondaries with mass ratios as small as 1\% on any initial orbit evaporate and
those on eccentric orbits with mass ratios as small as 0.1\% evolve
significantly and nearly evaporate in a galaxian age. Captured satellites with
mass ratios smaller than roughly 1\% have insufficient time to decay to the
center. After many accretion events, the model predicts that the merged system
has a profile similar to that of the original primary with a weak increase in
concentration.Comment: 19 pages, 10 Postscript figures, uses aaspp4.sty. Submitted to
Astrophysical Journa
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