4,382 research outputs found
Asymmetrical Reactive Power Capability of Modular Multilevel Cascade Converter Based STATCOMs for Offshore Wind Farm
Structure and photo-induced volume changes of obliquely deposited amorphous selenium
Atomic scale computer simulations on structures and photo induced volume
changes of flatly and obliquely deposited amorphous selenium films have been
carried out in order to understand how the properties of chalcogenide glasses
are influenced by their preparation method. Obliquely deposited a-Se thin films
contain more coordination defects, larger voids than the flatly deposited ones.
To model the photo induced volume changes the electron excitation and hole
creation were treated independently within the framework of tight-binding
formalism. Covalent and interchain bond breakings and formations were found.
The obliquely deposited samples containing voids showed a wide spectrum of
photo induced structural changes in microscopic and volume changes in
macroscopic levels.Comment: 14 page
Stress-induced Biomarkers in Liver with Non-alcohol Fatty Liver Diseases and Non-alcohol Steatohepatitis
Direct entropy determination and application to artificial spin ice
From thermodynamic origins, the concept of entropy has expanded to a range of
statistical measures of uncertainty, which may still be thermodynamically
significant. However, laboratory measurements of entropy continue to rely on
direct measurements of heat. New technologies that can map out myriads of
microscopic degrees of freedom suggest direct determination of configurational
entropy by counting in systems where it is thermodynamically inaccessible, such
as granular and colloidal materials, proteins and lithographically fabricated
nanometre-scale arrays. Here, we demonstrate a conditional-probability
technique to calculate entropy densities of translation-invariant states on
lattices using limited configuration data on small clusters, and apply it to
arrays of interacting nanometre-scale magnetic islands (artificial spin ice).
Models for statistically disordered systems can be assessed by applying the
method to relative entropy densities. For artificial spin ice, this analysis
shows that nearest-neighbour correlations drive longer-range ones.Comment: 10 page
The Importance of Disk Structure in Stalling Type I Migration
As planets form they tidally interact with their natal disks. Though the
tidal perturbation induced by Earth and super-Earth mass planets is generally
too weak to significantly modify the structure of the disk, the interaction is
potentially strong enough to cause the planets to undergo rapid type I
migration. This physical process may provide a source of short-period
super-Earths, though it may also pose a challenge to the emergence and
retention of cores on long-period orbits with sufficient mass to evolve into
gas giants. Previous numerical simulations have shown that the type I migration
rate sensitively depends upon the circumstellar disk's properties, particularly
the temperature and surface density gradients. Here, we derive these structure
parameters for 1) a self-consistent viscous-disk model based on a constant
\alpha-prescription, 2) an irradiated disk model that takes into account
heating due to the absorption of stellar photons, and 3) a layered-accretion
disk model with variable \alpha-parameter. We show that in the inner
viscously-heated regions of typical protostellar disks, the horseshoe and
corotation torques of super-Earths can exceed their differential Lindblad
torque and cause them to undergo outward migration. However, the temperature
profile due to passive stellar irradiation causes type I migration to be
inwards throughout much of the disk. For disks in which there is outwards
migration, we show that location and the mass range of the "planet traps"
depends on some uncertain assumptions adopted for these disk models. Competing
physical effects may lead to dispersion in super-Earths' mass-period
distribution.Comment: 12 pages, Submitted to Ap
Prevalence of Avian-Pathogenic Escherichia coli Strain O1 Genomic Islands among Extraintestinal and Commensal E. coli Isolates
Escherichia coli strains that cause disease outside the intestine are known as extraintestinal pathogenic E. coli (ExPEC) and include pathogens of humans and animals. Previously, the genome of avian-pathogenic E. coli (APEC) O1:K1:H7 strain O1, from ST95, was sequenced and compared to those of several other E. coli strains, identifying 43 genomic islands. Here, the genomic islands of APEC O1 were compared to those of other sequenced E. coli strains, and the distribution of 81 genes belonging to 12 APEC O1 genomic islands among 828 human and avian ExPEC and commensal E. coli isolates was determined. Multiple islands were highly prevalent among isolates belonging to the O1 and O18 serogroups within phylogenetic group B2, which are implicated in human neonatal meningitis. Because of the extensive genomic similarities between APEC O1 and other human ExPEC strains belonging to the ST95 phylogenetic lineage, its ability to cause disease in a rat model of sepsis and meningitis was assessed. Unlike other ST95 lineage strains, APEC O1 was unable to cause bacteremia or meningitis in the neonatal rat model and was significantly less virulent than uropathogenic E. coli (UPEC) CFT073 in a mouse sepsis model, despite carrying multiple neonatal meningitis E. coli (NMEC) virulence factors and belonging to the ST95 phylogenetic lineage. These results suggest that host adaptation or genome modifications have occurred either in APEC O1 or in highly virulent ExPEC isolates, resulting in differences in pathogenicity. Overall, the genomic islands examined provide targets for further discrimination of the different ExPEC subpathotypes, serogroups, phylogenetic types, and sequence types
The fermi arc and fermi pocket in cuprates in a short-range diagonal stripe phase
In this paper we studied the fermi arc and the fermi pocket in cuprates in a
short-range diagonal stripe phase with wave vectors , which
reproduce with a high accuracy the positions and sizes of the fermi arc and
fermi pocket and the superstructure in cuprates observed by Meng et
al\cite{Meng}. The low-energy spectral function indicates that the fermi pocket
results from the main band and the shadow band at the fermi energy. Above the
fermi energy the shadow band gradually departs away from the main band, leaving
a fermi arc. Thus we conclude that the fermi arc and fermi pocket can be fully
attributed to the stripe phase but has nothing to do with pairing.
Incorporating a d-wave pairing potential in the stripe phase the spectral
weight in the antinodal region is removed, leaving a clean fermi pocket in the
nodal region.Comment: 5 pages, 6 figure
Perimembrane Aurora-A Expression is a Significant Prognostic Factor in Correlation with Proliferative Activity in Non-Small-Cell Lung Cancer (NSCLC)
An extrasolar planetary system with three Neptune-mass planets
Over the past two years, the search for low-mass extrasolar planets has led
to the detection of seven so-called 'hot Neptunes' or 'super-Earths' around
Sun-like stars. These planets have masses 5-20 times larger than the Earth and
are mainly found on close-in orbits with periods of 2-15 days. Here we report a
system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days,
orbiting the nearby star HD 69830. This star was already known to show an
infrared excess possibly caused by an asteroid belt within 1 AU (the Sun-Earth
distance). Simulations show that the system is in a dynamically stable
configuration. Theoretical calculations favour a mainly rocky composition for
both inner planets, while the outer planet probably has a significant gaseous
envelope surrounding its rocky/icy core; the outer planet orbits within the
habitable zone of this star.Comment: 17 pages, 3 figures, preprint of the paper published in Nature on May
18, 200
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