3,704 research outputs found
Physics Prospects at the HL-LHC with ATLAS
The High-Luminosity LHC aims to provide a total integrated luminosity of 3000 fb−1
from
proton-proton collisions at √
s = 14 TeV over the course of ∼ 10 years, reaching instantaneous
luminosities of up to L = 7.5 × 1034cm−2
s
−1
, corresponding to an average of 200 inelastic pp
collisions per bunch crossing (µ = 200) . The upgraded ATLAS detector and trigger system
must be able to cope well with increased occupancies and data rates. The performance of the
upgrade has been estimated in full simulation studies, assuming expected HL-LHC conditions
and a detector configuration intended to maximise physics performance and discovery potential
at the HL-LHC, and is expected to be similar to current performance. Fast simulation studies have
been carried out to evaluate the prospects of various benchmark physics analyses to be performed
using the upgraded ATLAS detector with the full HL-LHC dataset
On the dependence of X-ray burst rate on accretion and spin rate
Nuclear burning and its dependence on the mass accretion rate are fundamental
ingredients for describing the complicated observational phenomenology of
neutron stars in binary systems. Motivated by high quality burst rate data
emerging from large statistical studies, we report general calculations
relating bursting rate to mass accretion rate and neutron star rotation
frequency. In this first work we neglect general relativistic effects and
accretion topology, though we discuss where their inclusion should play a role.
The relations we derive are suitable for different burning regimes and provide
a direct link between parameters predicted by theory and what is to be expected
in observations. We illustrate this for analytical relations of different
unstable burning regimes that operate on the surface of an accreting neutron
star. We also use the observed behaviour of burst rate to suggest new
constraints on burning parameters. We are able to provide an explanation for
the long standing problem of the observed decrease of burst rate with
increasing mass accretion that follows naturally from these calculations: when
accretion rate crosses a certain threshold, ignition moves away from its
initially preferential site and this can cause a net reduction of the burst
rate due to the effects of local conditions that set local differences in both
burst rate and stabilization criteria. We show under which conditions this can
happen even if locally the burst rate keeps increasing with accretion.Comment: Accepted for publication on Ap
The Heterotaxy Candidate Gene, Tmem195, Regulates Nuclear Localization Of Beta-Catenin
Congenital heart disease (CHD) affects 1 in every 130 newborns and is the leading cause of infant mortality (2). Heterotaxy (Htx), a disorder of left-right (LR) development, commonly leads to CHD. Despite aggressive surgical management, patients with Htx have poor survival rates and severe morbidity due to their complex CHD. Many of the genetic causes of Htx remain undefined, however, a recent genetic analysis of Htx patients identified a single mutant allele in the novel candidate gene, TMEM195 (3). TMEM195 is an alkylglyercol monooxygenase that cleaves ether lipids, but neither its molecular target nor its role in development has been described (4).
The aim of this project is to identify the molecular mechanism by which TMEM195 alters LR cardiac development. I examined the role of TMEM195 using morpholino (MO) knockdown and mRNA overexpression in Xenopus tropicalis. At a low dose of MO, the patient\u27s Htx phenotype was recapitulated in Xenopus. At a higher dose of MO, a significant gastrulation defect occurs. Experimental data suggest that the gastrulation defect is secondary to changes in the Wnt signaling pathway. Analysis of TMEM195 knockdown shows a significant decrease in beta-catenin expression and nuclear localization during gastrulation. Nuclear localization of beta-catenin cannot be rescued by stabilizing beta-catenin, but is rescued by adding a nuclear-localization signal (NLS). These results suggest for the first time that TMEM195 plays a role in the nuclear import of beta-catenin.
TMEM195\u27s role in nuclear localization many not only be specific to Wnt, but may also affect TGF-beta signaling. Smad2 is an important transcription factor for TGF-beta signaling and must be phosphorylated prior to entering the nucleus. TMEM195 depletion leads to an increase in phosphorylated but not total Smad2. In contrast, Smad1 is unaffected. Significantly, both Smad2 and beta-catenin lack NLS signals, while Smad1 has one (5). These results suggest a potentially broader role of TMEM195 in nuclear localization of non-NLS tagged proteins.
Defining the role of TMEM195 will permit a better understanding of the relationship between nuclear localization, gastrulation errors and defects in LR axis development. Importantly, it may also inform our understanding of the currently unknown mechanisms regulating nuclear import of several key signaling factors including beta-catenin and Smad2 and thus pave the way for the development of novel clinical treatments. Both Wnt and TGF-beta signaling are important for a myriad of different disease processes including congenital and vascular malformations, stem cells and cancer
Optimized perturbation method for the propagation in the anharmonic oscillator potential
The application of the optimized expansion for the quantum-mechanical
propagation in the anharmonic potential is discussed for real and
imaginary time. The first order results in the imaginary time formalism provide
approximations to the free energy and particle density which agree well with
the exact results in the whole range of temperatures.Comment: 13 pages, plain LATEX, 3 compressed and uuencoded Postscript figures,
submitted to Phys.Lett.
4D sequential actuation:Combining ionoprinting and redox chemistry in hydrogels
The programmable sequential actuation of two-dimensional hydrogel membranes into three-dimensional folded architectures has been achieved by combining ionoprinting and redox chemistry; this methodology permits the programmed evolution of complex architectures triggered through localized out-of-plane deformations. In our study we describe a soft actuator which utilizes ionoprinting of iron and vanadium, with the selective reduction of iron through a mild reducing agent, to achieve chemically controlled sequential folding. Through the optimization of solvent polarity and ionoprinting variables (voltage, duration and anode composition), we have shown how the actuation pathways, rate-of-movement and magnitude of angular rotation can be controlled for the design of a 4D sequential actuator
The stellar, molecular gas and dust content of the host galaxies of two z~2.8 dust obscured quasars
We present optical through radio observations of the host galaxies of two
dust obscured, luminous quasars selected in the mid-infrared, at z=2.62 and
z=2.99, including a search for CO emission. Our limits on the CO luminosities
are consistent with these objects having masses of molecular gas <~10^10 solar
masses, several times less than those of luminous submillimeter-detected
galaxies (SMGs) at comparable redshifts. Their near-infrared spectral energy
distributions, however, imply that these galaxies have high stellar masses
(~10^11-12 solar masses). The relatively small reservoirs of molecular gas and
low dust masses are consistent with them being relatively mature systems at
high-z.Comment: AJ, in pres
On the Stellar Kinematics and Mass of the Virgo Ultra-Diffuse Galaxy VCC 1287
Here, we present a kinematical analysis of the Virgo cluster ultra-diffuse
galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager
(KCWI). We confirm VCC 1287's association both with the Virgo cluster and its
globular cluster (GC) system, measuring a recessional velocity of $1116 \pm 2\
\mathrm{km\ s^{-1}}19 \pm 6\
\mathrm{km\ s^{-1}}1.11^{+0.81}_{-0.81}
\times 10^{9} \ \mathrm{M_{\odot}}13^{+11}_{-11}$)
within the half light radius (4.4 kpc). This places VCC 1287 slightly above the
well established relation for normal galaxies, with a higher mass to light
ratio for its dynamical mass than normal galaxies. We use our dynamical mass,
and an estimate of GC system richness, to place VCC 1287 on the GC number --
dynamical mass relation, finding good agreement with a sample of normal
galaxies. Based on a total halo mass derived from GC counts, we then infer that
VCC 1287 likely resides in a cored or low concentration dark matter halo. Based
on the comparison of our measurements to predictions from simulations, we find
that strong stellar feedback and/or tidal effects are plausibly the dominant
mechanisms in the formation of VCC 1287. Finally, we compare our measurement of
the dynamical mass with those for other UDGs. These dynamical mass estimates
suggest relatively massive halos and a failed galaxy origin for at least some
UDGs.Comment: 13 pages, 10 figures with an additional 5 pages and 5 figures in
appendices. Accepted for publication in MNRAS. v2: with small updates from
publication formatting and a minor plotting fix for Fig. 1
Viscoelastic properties of human and bovine articular cartilage : a comparison of frequency-dependent trends
Acknowledgments The authors would like to thank Spencer C. Barnes and Hamid Sadeghi for assistance during experimentation. We would also like to thank patients donating tissue and the surgeons collecting these. Funding The equipment used in this study was funded by Arthritis Research UK (Grant number H0671). We are grateful to Arthritis Research UK for the award of a PhD studentship to Anna A. Cederlund (Grant number 19971). Arthritis Research UK had no role in the design of the study and collection, analysis and interpretation of data and in writing the manuscript.Peer reviewedPublisher PD
An Application of Multi-band Forced Photometry to One Square Degree of SERVS: Accurate Photometric Redshifts and Implications for Future Science
We apply The Tractor image modeling code to improve upon existing multi-band
photometry for the Spitzer Extragalactic Representative Volume Survey (SERVS).
SERVS consists of post-cryogenic Spitzer observations at 3.6 and 4.5 micron
over five well-studied deep fields spanning 18 square degrees. In concert with
data from ground-based near-infrared (NIR) and optical surveys, SERVS aims to
provide a census of the properties of massive galaxies out to z ~ 5. To
accomplish this, we are using The Tractor to perform "forced photometry." This
technique employs prior measurements of source positions and surface brightness
profiles from a high-resolution fiducial band from the VISTA Deep Extragalactic
Observations (VIDEO) survey to model and fit the fluxes at lower-resolution
bands. We discuss our implementation of The Tractor over a square degree test
region within the XMM-LSS field with deep imaging in 12 NIR/optical bands. Our
new multi-band source catalogs offer a number of advantages over traditional
position-matched catalogs, including 1) consistent source cross-identification
between bands, 2) de-blending of sources that are clearly resolved in the
fiducial band but blended in the lower-resolution SERVS data, 3) a higher
source detection fraction in each band, 4) a larger number of candidate
galaxies in the redshift range 5 < z < 6, and 5) a statistically significant
improvement in the photometric redshift accuracy as evidenced by the
significant decrease in the fraction of outliers compared to spectroscopic
redshifts. Thus, forced photometry using The Tractor offers a means of
improving the accuracy of multi-band extragalactic surveys designed for galaxy
evolution studies. We will extend our application of this technique to the full
SERVS footprint in the future.Comment: accepted to ApJ, 22 pages, 12 figure
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