2,176 research outputs found
Comparative analysis of different preparation methods of chalcogenide glasses: Molecular dynamics structure simulations
Two different preparation methods (liquid-quenching and evaporation) of
chalcogenide glasses have been investigated by molecular dynamics simulations.
Our particular aim was to determine how the structural changes occur due to the
different preparation methods. We applied a classical empirical three-body
potential of selenium to describe the interactions between atoms.
Our simulation shows that a significant difference can be observed in the
homogeneities
Negative frequency tuning of a carbon nanotube nano-electromechanical resonator
A suspended, doubly clamped single wall carbon nanotube is characterized as
driven nano-electromechanical resonator at cryogenic temperatures.
Electronically, the carbon nanotube displays small bandgap behaviour with
Coulomb blockade oscillations in electron conduction and transparent contacts
in hole conduction. We observe the driven mechanical resonance in dc-transport,
including multiple higher harmonic responses. The data shows a distinct
negative frequency tuning at finite applied gate voltage, enabling us to
electrostatically decrease the resonance frequency to 75% of its maximum value.
This is consistently explained via electrostatic softening of the mechanical
mode.Comment: 4 pages, 4 figures; submitted for the IWEPNM 2013 conference
proceeding
Electronic structure of multiquantum giant vortex states in mesoscopic superconducting disks
We report self-consistent calculations of the microscopic electronic
structure of the so-called giant vortex states. These novel multiquantum vortex
states, detected by recent magnetization measurements on submicron disks, are
qualitatively different from the Abrikosov vortices in the bulk. We find that,
in addition to multiple branches of bound states in the core region, the local
tunneling density of states exhibits Tomasch oscillations due to the
single-particle interference arising from quantum confinement. These features
should be directly observable by scanning tunneling spectroscopy.Comment: 5 pages, 4 figure
Baryons and baryonic matter in the large Nc and heavy quark limits
This paper explores properties of baryons and finite density baryonic matter
in an artificial world in which Nc, the number of colors, is large and the
quarks of all species are degenerate and much larger than {\Lambda}_QCD. It has
long been known that in large Nc QCD, baryons composed entirely of heavy quarks
are accurately described in the mean-field approximation. However, the detailed
properties of baryons in the combined large Nc and heavy quark limits have not
been fully explored. Here some basic properties of baryons are computed using a
variational approach. At leading order in both the large Nc and heavy quark
expansions the baryon mass is computed explicitly as is the baryon form factor.
Baryonic matter, the analog of nuclear matter in this artificial world, should
also be well described in the mean-field approximation. In the special case
where all baryons have an identical spin flavor structure, it is shown that in
the formal heavy quark and large Nc limit interactions between baryons are
strictly repulsive at low densities. The energy per baryon is computed in this
limit and found to be exponentially small. It is shown that when the
restriction to baryons with an identical spin-flavor structure is dropped, a
phase of baryonic matter exists with a density of 2Nf times that for the
restricted case but with the same energy (where Nf is the number of degenerate
flavors). It is shown that this phase is at least metastable.Comment: 19 page
AIOps for a Cloud Object Storage Service
With the growing reliance on the ubiquitous availability of IT systems and
services, these systems become more global, scaled, and complex to operate. To
maintain business viability, IT service providers must put in place reliable
and cost efficient operations support. Artificial Intelligence for IT
Operations (AIOps) is a promising technology for alleviating operational
complexity of IT systems and services. AIOps platforms utilize big data,
machine learning and other advanced analytics technologies to enhance IT
operations with proactive actionable dynamic insight.
In this paper we share our experience applying the AIOps approach to a
production cloud object storage service to get actionable insights into
system's behavior and health. We describe a real-life production cloud scale
service and its operational data, present the AIOps platform we have created,
and show how it has helped us resolving operational pain points.Comment: 5 page
Photo-induced volume changes in selenium. Tight-binding molecular dynamics study
Tight-binding molecular dynamics simulations of photo-excitations in small Se
clusters (isolated Se ring and helical Se chain) and glassy Se networks
(containing 162 atoms) were carried out in order to analyse the photo induced
instability inside the amorphous selenium. In the cluster systems after taking
an electron from the highest occupied molecular orbital to the lowest
unoccupied molecular orbital a bond breaking occurs. In the glassy networks
photoinduced volume expansion was observed and at the same time the number of
coordination defects changed significantly due to illumination
In vitro activity of BAY 12-8039, a novel 8-methoxyquinolone, compared to activities of six fluoroquinolones against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis
The in vitro activity of a novel 8-methoxyquinolone, BAY 12-8039, against recent clinical isolates of Streptococcus pneumoniae (n = 404), Haemophilus influenzae (n = 330), and Moraxella catarrhalis (n = 250) was evaluated. Activity was compared to those of six other fluoroquinolones: ciprofloxacin, clinafloxacin, levofloxacin, ofloxacin, sparfloxacin and trovafloxacin. BAY 12-8039 and clinafloxacin had the highest levels of activity against S. pneumoniae, both with a MIC at which 90% of the isolates were inhibited (MIC90) of 0.06 microg/ml. Trovafloxacin and sparfloxacin were the next most active agents versus S. pneumoniae (MIC90s = 0.12 microg/ml). No differences in activity against penicillin-susceptible, -intermediate, or -resistant strains of S. pneumoniae were noted for any of the fluoroquinolones tested. MIC90s for the seven fluoroquinolones ranged from 0.008 to 0.06 microg/ml versus H. influenzae and from 0.008 to 0.12 microg/ml for M. catarrhalis. The MICs for two strains of S. pneumoniae and one strain of H. influenzae were noted to be higher than those for the general population of organisms for all of the fluoroquinolones tested. Finally, the activity of BAY 12-8039 versus S. pneumoniae was found to be diminished when MIC determinations were performed with incubation of agar dilution plates or broth microdilution trays in 5 to 7% CO2 versus ambient air
Band structure of helimagnons in MnSi resolved by inelastic neutron scattering
A magnetic helix realizes a one-dimensional magnetic crystal with a period
given by the pitch length . Its spin-wave excitations -- the
helimagnons -- experience Bragg scattering off this periodicity leading to gaps
in the spectrum that inhibit their propagation along the pitch direction. Using
high-resolution inelastic neutron scattering the resulting band structure of
helimagnons was resolved by preparing a single crystal of MnSi in a single
magnetic-helix domain. At least five helimagnon bands could be identified that
cover the crossover from flat bands at low energies with helimagnons basically
localized along the pitch direction to dispersing bands at higher energies. In
the low-energy limit, we find the helimagnon spectrum to be determined by a
universal, parameter-free theory. Taking into account corrections to this
low-energy theory, quantitative agreement is obtained in the entire energy
range studied with the help of a single fitting parameter.Comment: 5 pages, 3 figures; (v2) slight modifications, published versio
Spin dynamics in p-doped semiconductor nanostructures subject to a magnetic field tilted from the Voigt geometry
We develop a theoretical description of the spin dynamics of resident holes
in a p-doped semiconductor quantum well (QW) subject to a magnetic field tilted
from the Voigt geometry. We find the expressions for the signals measured in
time-resolved Faraday rotation (TRFR) and resonant spin amplification (RSA)
experiments and study their behavior for a range of system parameters. We find
that an inversion of the RSA peaks can occur for long hole spin dephasing times
and tilted magnetic fields. We verify the validity of our theoretical findings
by performing a series of TRFR and RSA experiments on a p-modulation doped
GaAs/Al_{0.3}Ga_{0.7}As single QW and showing that our model can reproduce
experimentally observed signals.Comment: 9 pages, 3 figures; corrected typo
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