306 research outputs found
Regulation of plant development and defense response by fireman, a new small endogenous peptide
A homogenization study of the effects of cycling on the electronic conductivity of commercial lithium-ion battery cathodes
State-of-the-art image acquisition,
image analysis, and modern homogenization theory are used to study
the effects of cycling on commercial lithium-ion battery cathodesâ
ability to conduct electronic current. This framework allows for a
rigorous computation of an effective, or macroscale, electronic conductivity
given an arbitrarily complicated three-dimensional microstructure
comprised of three different material phases, i.e., active material,
binder (polymer mixed with conductive carbon black), and electrolyte.
The approach explicitly takes into account the geometry and is thus
a vast improvement over the commonly used Bruggeman approximation.
We apply our framework to two different types of lithium-ion battery
cathodes before and after cycling. This leads us to predict an appreciable
decrease in the effective electronic conductivity as a direct result
of cycling. In addition, we present an ad-hoc âneighbor countingâ
methodology which meaningfully quantifies the effect of binder detaching
from the surface of the active material due to the internal mechanical
stresses experienced under operating conditions, thereby supporting
the results of the homogenization calculations
Optical Confinement of a Bose-Einstein Condensate
Bose-Einstein condensates of sodium atoms have been confined in an optical
dipole trap using a single focused infrared laser beam. This eliminates the
restrictions of magnetic traps for further studies of atom lasers and
Bose-Einstein condensates. More than five million condensed atoms were
transferred into the optical trap. Densities of up to of Bose condensed atoms were obtained, allowing for a measurement of
the three-body decay rate constant for sodium condensates as . At lower densities, the observed 1/e
lifetime was more than 10 sec. Simultaneous confinement of Bose-Einstein
condensates in several hyperfine states was demonstrated.Comment: 5 pages, 4 figure
Discovery of a New WZ Sagittae Type Cataclysmic Variable in the Kepler/K2 Data
We identify a new, bright transient in the Kepler/K2 Campaign 11 field. Its
light curve rises over seven magnitudes in a day and then declines three
magnitudes over a month before quickly fading another two magnitudes. The
transient was still detectable at the end of the campaign. The light curve is
consistent with a WZ~Sge type dwarf nova outburst. Early superhumps with a
period of 82 minutes are seen in the first 10 days and suggest that this is the
orbital period of the binary which is typical for the WZ~Sge class. Strong
superhump oscillations develop ten days after peak brightness with periods
ranging between 83 and 84 minutes. At 25 days after the peak brightness a bump
in the light curve appears to signal a subtle rebrightening phase implying that
this was an unusual type-A outburst. This is the only WZ~Sge type system
observed by Kepler/K2 during an outburst. The early rise of this outburst is
well-fit with a broken power law. In first 10 hours the system brightened
linearly and then transitioned to a steep rise with a power law index of 4.8.
Looking at archival Kepler/K2 data and new TESS observations, a linear rise in
the first several hours at the initiation of a superoutburst appears to be
common in SU~UMa stars.Comment: 11 pages, 14 figures, 2 tables, accepted to appear in the Monthly
Notices of the Royal Astronomical Societ
The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses
We present spatially and spectrally resolved Atacama Large
Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the
pre-main sequence hierarchical triple star system GW Ori. A forward-modeling of
the CO and CO =2-1 transitions permits a measurement of
the total stellar mass in this system, , and the
circum-triple disk inclination, . Optical spectra spanning
a 35 year period were used to derive new radial velocities and, coupled with a
spectroscopic disentangling technique, revealed that the A and B components of
GW Ori form a double-lined spectroscopic binary with a day
period; a tertiary companion orbits that inner pair with a day
period. Combining the results from the ALMA data and the optical spectra with
three epochs of astrometry in the literature, we constrain the individual
stellar masses in the system (,
, ) and
find strong evidence that at least one (and likely both) stellar orbital planes
are misaligned with the disk plane by as much as . A -band light
curve spanning 30 years reveals several new 30 day eclipse events
0.1-0.7~mag in depth and a 0.2 mag sinusoidal oscillation that is clearly
phased with the AB-C orbital period. Taken together, these features suggest
that the A-B pair may be partially obscured by material in the inner disk as
the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude
that stellar evolutionary models are consistent with our measurements of the
masses and basic photospheric properties if the GW Ori system is 1 Myr
old.Comment: 26 pages, 15 figures, accepted to Ap
Spin states of asteroids in the Eos collisional family
Eos family was created during a catastrophic impact about 1.3 Gyr ago.
Rotation states of individual family members contain information about the
history of the whole population. We aim to increase the number of asteroid
shape models and rotation states within the Eos collision family, as well as to
revise previously published shape models from the literature. Such results can
be used to constrain theoretical collisional and evolution models of the
family, or to estimate other physical parameters by a thermophysical modeling
of the thermal infrared data. We use all available disk-integrated optical data
(i.e., classical dense-in-time photometry obtained from public databases and
through a large collaboration network as well as sparse-in-time individual
measurements from a few sky surveys) as input for the convex inversion method,
and derive 3D shape models of asteroids together with their rotation periods
and orientations of rotation axes. We present updated shape models for 15
asteroids and new shape model determinations for 16 asteroids. Together with
the already published models from the publicly available DAMIT database, we
compiled a sample of 56 Eos family members with known shape models that we used
in our analysis of physical properties within the family. Rotation states of
asteroids smaller than ~20 km are heavily influenced by the YORP effect, whilst
the large objects more or less retained their rotation state properties since
the family creation. Moreover, we also present a shape model and bulk density
of asteroid (423) Diotima, an interloper in the Eos family, based on the
disk-resolved data obtained by the Near InfraRed Camera (Nirc2) mounted on the
W.M. Keck II telescope.Comment: Accepted for publication in ICARUS Special Issue - Asteroids: Origin,
Evolution & Characterizatio
Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed
to locate quasars during the epoch of reionization. In this paper we present
the discovery of the first four CFHQS quasars at redshift greater than 6,
including the most distant known quasar, CFHQS J2329-0301 at z=6.43. We
describe the observational method used to identify the quasars and present
optical, infrared, and millimeter photometry and optical and near-infrared
spectroscopy. We investigate the dust properties of these quasars finding an
unusual dust extinction curve for one quasar and a high far-infrared luminosity
due to dust emission for another. The mean millimeter continuum flux for CFHQS
quasars is substantially lower than that for SDSS quasars at the same redshift,
likely due to a correlation with quasar UV luminosity. For two quasars with
sufficiently high signal-to-noise optical spectra, we use the spectra to
investigate the ionization state of hydrogen at z>5. For CFHQS J1509-1749 at
z=6.12, we find significant evolution (beyond a simple extrapolation of lower
redshift data) in the Gunn-Peterson optical depth at z>5.4. The line-of-sight
to this quasar has one of the highest known optical depths at z~5.8. An
analysis of the sizes of the highly-ionized near-zones in the spectra of two
quasars at z=6.12 and z=6.43 suggest the IGM surrounding these quasars was
substantially ionized before these quasars turned on. Together, these
observations point towards an extended reionization process, but we caution
that cosmic variance is still a major limitation in z>6 quasar observations.Comment: 15 pages, 9 figures, AJ, in press, minor changes to previous versio
Porphyromonas gingivalis peptidylarginine deiminase, a key contributor in the pathogenesis of experimental periodontal disease and experimental arthritis
OBJECTIVES: To investigate the suggested role of Porphyromonas gingivalis peptidylarginine deiminase (PAD) in the relationship between the aetiology of periodontal disease and experimentally induced arthritis and the possible association between these two conditions. METHODS: A genetically modified PAD-deficient strain of P. gingivalis W50 was produced. The effect of this strain, compared to the wild type, in an established murine model for experimental periodontitis and experimental arthritis was assessed. Experimental periodontitis was induced following oral inoculation with the PAD-deficient and wild type strains of P. gingivalis. Experimental arthritis was induced via the collagen antibody induction process and was monitored by assessment of paw swelling and micro-CT analysis of the radio-carpal joints. Experimental periodontitis was monitored by micro CT scans of the mandible and histological assessment of the periodontal tissues around the mandibular molars. Serum levels of anti-citrullinated protein antibodies (ACPA) and P. gingivalis were assessed by ELISA. RESULTS: The development of experimental periodontitis was significantly reduced in the presence of the PAD-deficient P. gingivalis strain. When experimental arthritis was induced in the presence of the PAD-deficient strain there was less paw swelling, less erosive bone damage to the joints and reduced serum ACPA levels when compared to the wild type P. gingivalis inoculated group. CONCLUSION: This study has demonstrated that a PAD-deficient strain of P. gingivalis was associated with significantly reduced periodontal inflammation. In addition the extent of experimental arthritis was significantly reduced in animals exposed to prior induction of periodontal disease through oral inoculation of the PAD-deficient strain versus the wild type. This adds further evidence to the potential role for P. gingivalis and its PAD in the pathogenesis of periodontitis and exacerbation of arthritis. Further studies are now needed to elucidate the mechanisms which drive these processes.Neville Gully, Richard Bright, Victor Marino, Ceilidh Marchant, Melissa Cantley, David Haynes, Catherine Butler, Stuart Dashper, Eric Reynolds, Mark Bartol
On dynamic network entropy in cancer
The cellular phenotype is described by a complex network of molecular
interactions. Elucidating network properties that distinguish disease from the
healthy cellular state is therefore of critical importance for gaining
systems-level insights into disease mechanisms and ultimately for developing
improved therapies. By integrating gene expression data with a protein
interaction network to induce a stochastic dynamics on the network, we here
demonstrate that cancer cells are characterised by an increase in the dynamic
network entropy, compared to cells of normal physiology. Using a fundamental
relation between the macroscopic resilience of a dynamical system and the
uncertainty (entropy) in the underlying microscopic processes, we argue that
cancer cells will be more robust to random gene perturbations. In addition, we
formally demonstrate that gene expression differences between normal and cancer
tissue are anticorrelated with local dynamic entropy changes, thus providing a
systemic link between gene expression changes at the nodes and their local
network dynamics. In particular, we also find that genes which drive
cell-proliferation in cancer cells and which often encode oncogenes are
associated with reductions in the dynamic network entropy. In summary, our
results support the view that the observed increased robustness of cancer cells
to perturbation and therapy may be due to an increase in the dynamic network
entropy that allows cells to adapt to the new cellular stresses. Conversely,
genes that exhibit local flux entropy decreases in cancer may render cancer
cells more susceptible to targeted intervention and may therefore represent
promising drug targets.Comment: 10 pages, 3 figures, 4 tables. Submitte
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