1,580 research outputs found
Ground-state structure of the hydrogen double vacancy on Pd(111)
We determine the ground-state structure of a double vacancy in a hydrogen
monolayer on the Pd(111) surface. We represent the double vacancy as a triple
vacancy containing one additional hydrogen atom. The potential-energy surface
for a hydrogen atom moving in the triple vacancy is obtained by
density-functional theory, and the wave function of the fully quantum hydrogen
atom is obtained by solving the Schr\"odinger equation. We find that an H atom
in a divacancy defect experiences significant quantum effects, and that the
ground-state wave function is centered at the hcp site rather than the fcc site
normally occupied by H atoms on Pd(111). Our results agree well with scanning
tunneling microscopy images.Comment: 5 pages, 3 figure
Structure of AlSb(001) and GaSb(001) Surfaces Under Extreme Sb-rich Conditions
We use density-functional theory to study the structure of AlSb(001) and
GaSb(001) surfaces. Based on a variety of reconstruction models, we construct
surface stability diagrams for AlSb and GaSb under different growth conditions.
For AlSb(001), the predictions are in excellent agreement with experimentally
observed reconstructions. For GaSb(001), we show that previously proposed model
accounts for the experimentally observed reconstructions under Ga-rich growth
conditions, but fails to explain the experimental observations under Sb-rich
conditions. We propose a new model that has a substantially lower surface
energy than all (nx5)-like reconstructions proposed previously and that, in
addition, leads to a simulated STM image in better agreement with experiment
than existing models. However, this new model has higher surface energy than
some of (4x3)-like reconstructions, models with periodicity that has not been
observed. Hence we conclude that the experimentally observed (1x5) and (2x5)
structures on GaSb(001) are kinetically limited rather than at the ground
state.Comment: 6 pages, 6 figure
Keepin’ it Real: From the Bronx to Cape Town, an Analysis of Hip-Hop in South Africa
Honors (Bachelor's)HistoryUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/98923/1/erwinkim.pd
Two-Dimensional Magnetohydrodynamic Simulations of Barred Galaxies
Barred galaxies are known to possess magnetic fields that may affect the
properties of bar substructures such as dust lanes and nuclear rings. We use
two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to
investigate the effects of magnetic fields on the formation and evolution of
such substructures as well as on the mass inflow rates to the galaxy center.
The gaseous medium is assumed to be infinitesimally-thin, isothermal,
non-self-gravitating, and threaded by initially uniform, azimuthal magnetic
fields. We find that there exists an outermost x1-orbit relative to which
gaseous responses to an imposed stellar bar potential are completely different
between inside and outside. Inside this orbit, gas is shocked into dust lanes
and infalls to form a nuclear ring. Magnetic fields are compressed in dust
lanes, reducing their peak density. Magnetic stress removes further angular
momentum of the gas at the shocks, temporarily causing the dust lanes to bend
into an 'L' shape and eventually leading to a smaller and more centrally
distributed ring than in unmagnetized models. The mass inflow rates in
magnetized models correspondingly become larger, by more than two orders of
magnitude when the initial fields have an equipartition value with thermal
energy, than in the unmagnetized counterparts. Outside the outermost x1-orbit,
on the other hand, an MHD dynamo due to the combined action of the bar
potential and background shear operates near the corotation and bar-end
regions, efficiently amplifying magnetic fields. The amplified fields shape
into trailing magnetic arms with strong fields and low density. The base of the
magnetic arms has a thin layer in which magnetic fields with opposite polarity
reconnect via a tearing-mode instability. This produces numerous magnetic
islands with large density which propagate along the arms to turn the outer
disk into a highly chaotic state.Comment: 22 pages, 19 figures, 3 tables; Accepted for publication in the ApJ;
Version with full-resolution figures available at
http://mirzam.snu.ac.kr/~wkim/Bar/mhdbar.pd
Cloudbus Toolkit for Market-Oriented Cloud Computing
This keynote paper: (1) presents the 21st century vision of computing and
identifies various IT paradigms promising to deliver computing as a utility;
(2) defines the architecture for creating market-oriented Clouds and computing
atmosphere by leveraging technologies such as virtual machines; (3) provides
thoughts on market-based resource management strategies that encompass both
customer-driven service management and computational risk management to sustain
SLA-oriented resource allocation; (4) presents the work carried out as part of
our new Cloud Computing initiative, called Cloudbus: (i) Aneka, a Platform as a
Service software system containing SDK (Software Development Kit) for
construction of Cloud applications and deployment on private or public Clouds,
in addition to supporting market-oriented resource management; (ii)
internetworking of Clouds for dynamic creation of federated computing
environments for scaling of elastic applications; (iii) creation of 3rd party
Cloud brokering services for building content delivery networks and e-Science
applications and their deployment on capabilities of IaaS providers such as
Amazon along with Grid mashups; (iv) CloudSim supporting modelling and
simulation of Clouds for performance studies; (v) Energy Efficient Resource
Allocation Mechanisms and Techniques for creation and management of Green
Clouds; and (vi) pathways for future research.Comment: 21 pages, 6 figures, 2 tables, Conference pape
The Black Hole Mass-Bulge Luminosity Relationship for Active Galactic Nuclei from Reverberation Mapping and Hubble Space Telescope Imaging
We investigate the relationship between black hole mass and bulge luminosity
for AGNs with reverberation-based black hole mass measurements and bulge
luminosities from two-dimensional decompositions of Hubble Space Telescope host
galaxy images. We find that the slope of the relationship for AGNs is 0.76-0.85
with an uncertainty of ~0.1, somewhat shallower than the M_BH \propto
L^{1.0+/-0.1} relationship that has been fit to nearby quiescent galaxies with
dynamical black hole mass measurements. This is somewhat perplexing, as the AGN
black hole masses include an overall scaling factor that brings the AGN
M_BH-sigma relationship into agreement with that of quiescent galaxies. We
discuss biases that may be inherent to the AGN and quiescent galaxy samples and
could cause the apparent inconsistency in the forms of their M_BH-L_bulge
relationships.Comment: 5 pages, 3 figures and 2 tables, submitted to ApJ Letter
Polarization tomography of metallic nanohole arrays
We report polarization tomography experiments on metallic nanohole arrays
with square and hexagonal symmetry. As a main result, we find that a fully
polarized input beam is partly depolarized after transmission through a
nanohole array. This loss of polarization coherence is found to be anisotropic,
i.e. it depends on the polarization state of the input beam. The depolarization
is ascribed to a combination of two factors: i) the nonlocal response of the
array due to surface plasmon propagation, ii) the non-plane wave nature of a
practical input beam.Comment: 4 pages, 3 figures, 1 table, submitted to PR
Understanding visual map formation through vortex dynamics of spin Hamiltonian models
The pattern formation in orientation and ocular dominance columns is one of
the most investigated problems in the brain. From a known cortical structure,
we build spin-like Hamiltonian models with long-range interactions of the
Mexican hat type. These Hamiltonian models allow a coherent interpretation of
the diverse phenomena in the visual map formation with the help of relaxation
dynamics of spin systems. In particular, we explain various phenomena of
self-organization in orientation and ocular dominance map formation including
the pinwheel annihilation and its dependency on the columnar wave vector and
boundary conditions.Comment: 4 pages, 15 figure
In vitro antimicrobial and in vivo antioomycete activities of the novel antibiotic thiobutacin
BACKGROUND: A number of synthetic fungicides are not effective when confronted by oomycete pathogens because many fungicide targets are absent from oomycetes. Moreover, resistance to fungicides has already arisen in oomycete species, and thus development of new, effective and safe compounds for use in oomycete disease control is necessary. RESULTS: Zoospore lysis began at 10 µg mL −1 of thiobutacin, and most of the zoospores were collapsed at 50 µg mL −1 . Thiobutacin also revealed inhibitory activity against the cyst germination and hyphal growth of Phytophthora capsici at 50 µg mL −1 . Treatment with thiobutacin exhibited protective activity against development of Phytophthora disease on pepper plants. CONCLUSION: The authors verified in vitro antioomycete activity of thiobutacin against P. capsici and its control efficacy against Phytophthora blight in vivo . This is the first report to demonstrate in vivo antioomycete activity of the novel antibiotic thiobutacin against P. capsici infection. Copyright © 2007 Society of Chemical IndustryPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57925/1/1494_ftp.pd
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