6,211 research outputs found
The effect of Fe atoms on the adsorption of a W atom on W(100) surface
We report a first-principles calculation that models the effect of iron (Fe)
atoms on the adsorption of a tungsten (W) atom on W(100) surfaces. The
adsorption of a W atom on a clean W(100) surface is compared with that of a W
atom on a W(100) surface covered with a monolayer of Fe atoms. The total energy
of the system is computed as the function of the height of the W adatom. Our
result shows that the W atom first adsorbs on top of the Fe monolayer. Then the
W atom can replace one of the Fe atoms through a path with a moderate energy
barrier and reduce its energy further. This intermediate site makes the
adsorption (and desorption) of W atoms a two-step process in the presence of Fe
atoms and lowers the overall adsorption energy by nearly 2.4 eV. The Fe atoms
also provide a surface for W atoms to adsorb facilitating the diffusion of W
atoms. The combination of these two effects result in a much more efficient
desorption and diffusion of W atoms in the presence of Fe atoms. Our result
provides a fundamental mechanism that can explain the activated sintering of
tungsten by Fe atoms.Comment: 9 pages, 2 figure
Kaluza-Klein masses of bulk fields with general boundary conditions in AdS
Recently bulk Randall-Sundrum theories with the gauge group have drawn a lot of interest as an alternative to
electroweak symmetry breaking mechanism. These models are in better agreement
with electroweak precision data since custodial isospin symmetry on the IR
brane is protected by the extended bulk gauge symmetry. We comprehensively
study, in the S^1/\ZZ orbifold, the bulk gauge and fermion fields with the
general boundary conditions as well as the bulk and localized mass terms.
Master equations to determine the Kaluza-Klein (KK) mass spectra are derived
without any approximation, which is an important basic step for various
phenomenologies at high energy colliders. The correspondence between orbifold
boundary conditions and localized mass terms is demonstrated not only in the
gauge sector but also in the fermion sector. As the localized mass increases,
the first KK fermion mass is shown to decrease while the first KK gauge boson
mass to increase. The degree of gauge coupling universality violation is
computed to be small in most parameter space, and its correlation with the mass
difference between the top quark and light quark KK mode is also studied.Comment: 25 pages with 10 figures, Final version accepted by PR
Some Grüss' Type Inequalities in 2-Inner Product Spaces and Applications for Determinantal Integral Inequalities
Some new Grüss type inequalities in 2-inner product spaces are given. Using this framework, some determinantal integral inequalities for synchronous functions are also derived
Charge-Focusing Readout of Time Projection Chambers
Time projection chambers (TPCs) have found a wide range of applications in
particle physics, nuclear physics, and homeland security. For TPCs with
high-resolution readout, the readout electronics often dominate the price of
the final detector. We have developed a novel method which could be used to
build large-scale detectors while limiting the necessary readout area. By
focusing the drift charge with static electric fields, we would allow a small
area of electronics to be sensitive to particle detection for a much larger
detector volume. The resulting cost reduction could be important in areas of
research which demand large-scale detectors, including dark matter searches and
detection of special nuclear material. We present simulations made using the
software package Garfield of a focusing structure to be used with a prototype
TPC with pixel readout. This design should enable significant focusing while
retaining directional sensitivity to incoming particles. We also present first
experimental results and compare them with simulation.Comment: 5 pages, 17 figures, Presented at IEEE Nuclear Science Symposium 201
Searching for rotating galaxy clusters in SDSS and 2dFGRS
We present a result of searching for galaxy clusters that show an indication
of global rotation using a spectroscopic sample of galaxies in SDSS and 2dFGRS.
We have determined the member galaxies of 899 Abell clusters covered in SDSS
and 2dFGRS using the redshift and the positional data of galaxies, and have
estimated the ratio of the cluster rotation amplitude to the cluster velocity
dispersion and the velocity gradient across the cluster. We have found 12
tentative rotating clusters that have large ratios of rotation amplitude to
dispersion and large velocity gradients. We have determined the morphological
parameters for 12 tentative rotating clusters using the positional information
of the member galaxies: the ellipticity of the dispersion ellipse is in the
range of 0.080.57, and the position angle of major or minor axis does not
appear to be related to the position angle of rotation axis. We have
investigated the substructures in the sample of tentative rotating clusters,
finding from the Dressler-Shectman plots that the majority (9 out of 12) of
clusters show an evidence of substructure due to the spatially correlated
velocities of galaxies. We have selected six probable rotating clusters (A0954,
A1139, A1399, A2162, A2169, and A2366) that show a single number density peak
around the cluster center with a spatial segregation of the high and low
velocity galaxies. We have found no strong evidences of a recent merging for
the probable rotating clusters: the probable rotating clusters do not deviate
significantly from the relation of the X-ray luminosity and the velocity
dispersion or the virial mass of the clusters, and two probable rotating
clusters (A0954 and A1399) have small values of the peculiar velocities and the
clustercentric distances of the brightest cluster galaxies.Comment: 33 pages, 9 figures. To appear in Ap
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