592 research outputs found
Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs. :III. Stellar masses, star formation rates, and metallicities at z > 1
Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs. :III. Stellar masses, star formation rates, and metallicities at z > 1
(Abridged) Long gamma-ray bursts (LGRB) have been suggested as promising
tracers of star formation owing to their association with the core-collapse of
massive stars. The goal of this work is to characterise the population of host
galaxies of LGRBs at 1 < z < 2, investigate the conditions in which LGRBs form
at these redshifts and assess their use as tracers of star formation. We
perform a spectro-photometric analysis to determine the stellar mass, star
formation rate, specific star formation rate and metallicity of the complete,
unbiased host galaxy sample of the Swift/BAT6 LGRB sample at 1 < z < 2. We
compare the distribution of these properties to the ones of typical
star-forming galaxies from the MOSDEF and COSMOS2015 Ultra Deep surveys, within
the same redshift range. We find that, similarly to z < 1, LGRBs do not
directly trace star formation at 1 < z < 2, and they tend to avoid high-mass,
high-metallicity host galaxies. We also find evidence for an enhanced fraction
of starbursts among the LGRB host sample with respect to the star-forming
population of galaxies. Nonetheless we demonstrate that the driving factor
ruling the LGRB efficiency is metallicity. The LGRB host distributions can be
reconciled with the ones expected from galaxy surveys by imposing a metallicity
upper limit of 12+logOH ~ 8.55. Metallicity rules the LGRB production
efficiency, which is stifled at Z > 0.7 Zsun. Under this hypothesis we can
expect LGRBs to trace star formation at z > 3, once the bulk of the star
forming galaxy population are characterised by metallicities below this limit.
The moderately high metallicity threshold found is in agreement with the
conditions necessary to rapidly produce a fast-rotating Wolf-Rayet star a in
close binary system, and could be accommodated by single star models under
chemically homogeneous mixing with very rapid rotation and weak magnetic
coupling.Comment: 19 pages, 17 figures, accepted for publication in Astronomy &
Astrophysic
Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors
We present results from new experiments to study the dynamics of radiative
shocks, reverse shocks and radiative precursors. Laser ablation of a solid
piston by the Orion high-power laser at AWE Aldermaston UK was used to drive
radiative shocks into a gas cell initially pressurised between and $1.0 \
bar with different noble gases. Shocks propagated at {80 \pm 10 \ km/s} and
experienced strong radiative cooling resulting in post-shock compressions of {
\times 25 \pm 2}. A combination of X-ray backlighting, optical self-emission
streak imaging and interferometry (multi-frame and streak imaging) were used to
simultaneously study both the shock front and the radiative precursor. These
experiments present a new configuration to produce counter-propagating
radiative shocks, allowing for the study of reverse shocks and providing a
unique platform for numerical validation. In addition, the radiative shocks
were able to expand freely into a large gas volume without being confined by
the walls of the gas cell. This allows for 3-D effects of the shocks to be
studied which, in principle, could lead to a more direct comparison to
astrophysical phenomena. By maintaining a constant mass density between
different gas fills the shocks evolved with similar hydrodynamics but the
radiative precursor was found to extend significantly further in higher atomic
number gases (\sim4$ times further in xenon than neon). Finally, 1-D and 2-D
radiative-hydrodynamic simulations are presented showing good agreement with
the experimental data.Comment: HEDLA 2016 conference proceeding
Transiting Exoplanets with JWST
The era of exoplanet characterization is upon us. For a subset of exoplanets
-- the transiting planets -- physical properties can be measured, including
mass, radius, and atmosphere characteristics. Indeed, measuring the atmospheres
of a further subset of transiting planets, the hot Jupiters, is now routine
with the Spitzer Space Telescope. The James Webb Space Telescope (JWST) will
continue Spitzer's legacy with its large mirror size and precise thermal
stability. JWST is poised for the significant achievement of identifying
habitable planets around bright M through G stars--rocky planets lacking
extensive gas envelopes, with water vapor and signs of chemical disequilibrium
in their atmospheres. Favorable transiting planet systems, are, however,
anticipated to be rare and their atmosphere observations will require tens to
hundreds of hours of JWST time per planet. We review what is known about the
physical characteristics of transiting planets, summarize lessons learned from
Spitzer high-contrast exoplanet measurements, and give several examples of
potential JWST observations.Comment: 22 pages, 11 figures. In press in "Astrophysics in the Next Decade:
JWST and Concurrent Facilities, Astrophysics & Space Science Library,
Thronson, H. A., Tielens, A., Stiavelli, M., eds., Springer: Dordrecht
(2008)." The original publication will be available at
http://www.springerlink.co
Neural model of dopaminergic control of arm movements in Parkinson’s disease bradykinesia
Patients suffering from Parkinson’s disease display a number of
symptoms such a resting tremor, bradykinesia, etc. Bradykinesia is the hallmark
and most disabling symptom of Parkinson’s disease (PD). Herein, a basal
ganglia-cortico-spinal circuit for the control of voluntary arm movements in PD
bradykinesia is extended by incorporating DAergic innervation of cells in the
cortical and spinal components of the circuit. The resultant model simulates
successfully several of the main reported effects of DA depletion on neuronal,
electromyographic and movement parameters of PD bradykinesia
Optimal estimation of qubit states with continuous time measurements
We propose an adaptive, two steps strategy, for the estimation of mixed qubit
states. We show that the strategy is optimal in a local minimax sense for the
trace norm distance as well as other locally quadratic figures of merit. Local
minimax optimality means that given identical qubits, there exists no
estimator which can perform better than the proposed estimator on a
neighborhood of size of an arbitrary state. In particular, it is
asymptotically Bayesian optimal for a large class of prior distributions.
We present a physical implementation of the optimal estimation strategy based
on continuous time measurements in a field that couples with the qubits.
The crucial ingredient of the result is the concept of local asymptotic
normality (or LAN) for qubits. This means that, for large , the statistical
model described by identically prepared qubits is locally equivalent to a
model with only a classical Gaussian distribution and a Gaussian state of a
quantum harmonic oscillator.
The term `local' refers to a shrinking neighborhood around a fixed state
. An essential result is that the neighborhood radius can be chosen
arbitrarily close to . This allows us to use a two steps procedure by
which we first localize the state within a smaller neighborhood of radius
, and then use LAN to perform optimal estimation.Comment: 32 pages, 3 figures, to appear in Commun. Math. Phy
Quantum optics in the phase space - A tutorial on Gaussian states
In this tutorial, we introduce the basic concepts and mathematical tools
needed for phase-space description of a very common class of states, whose
phase properties are described by Gaussian Wigner functions: the Gaussian
states. In particular, we address their manipulation, evolution and
characterization in view of their application to quantum information.Comment: Tutorial. 23 pages, 1 figure. Updated version accepted for
publication in EPJ - ST devoted to the memory of Federico Casagrand
Faithful Squashed Entanglement
Squashed entanglement is a measure for the entanglement of bipartite quantum
states. In this paper we present a lower bound for squashed entanglement in
terms of a distance to the set of separable states. This implies that squashed
entanglement is faithful, that is, strictly positive if and only if the state
is entangled. We derive the bound on squashed entanglement from a bound on
quantum conditional mutual information, which is used to define squashed
entanglement and corresponds to the amount by which strong subadditivity of von
Neumann entropy fails to be saturated. Our result therefore sheds light on the
structure of states that almost satisfy strong subadditivity with equality. The
proof is based on two recent results from quantum information theory: the
operational interpretation of the quantum mutual information as the optimal
rate for state redistribution and the interpretation of the regularised
relative entropy of entanglement as an error exponent in hypothesis testing.
The distance to the set of separable states is measured by the one-way LOCC
norm, an operationally-motivated norm giving the optimal probability of
distinguishing two bipartite quantum states, each shared by two parties, using
any protocol formed by local quantum operations and one-directional classical
communication between the parties. A similar result for the Frobenius or
Euclidean norm follows immediately. The result has two applications in
complexity theory. The first is a quasipolynomial-time algorithm solving the
weak membership problem for the set of separable states in one-way LOCC or
Euclidean norm. The second concerns quantum Merlin-Arthur games. Here we show
that multiple provers are not more powerful than a single prover when the
verifier is restricted to one-way LOCC operations thereby providing a new
characterisation of the complexity class QMA.Comment: 24 pages, 1 figure, 1 table. Due to an error in the published
version, claims have been weakened from the LOCC norm to the one-way LOCC
nor
Extended Human Papillomavirus Genotyping to Predict Progression to High-Grade Cervical Precancer: A Prospective Cohort Study in the Southeastern United States
Background: High-risk human papillomavirus (hrHPV) testing (HPV16; else HPV18/45; else HPV31/33/35/52/58; else HPV39/ is utilized in primary cervical cancer screening, generally along with 51/56/59/68). cytology, to triage abnormalities to colposcopy. Most screening-Results: At enrollment, median participant age was 30.1 years; based hrHPV testing involves pooled detection of any hrHPV or of most (63%) were hrHPV-positive. Over follow-up, 24 participants HPV16/18. Cervical neoplasia progression risks based on extended progressed to CIN2þ (7.0%). CIN2þ IR among hrHPV-positive hrHPV genotyping—particularly non-16/18 hrHPV types—are not participants was 3.4/1,000 person-months. CIN2þ IRs were highest well characterized. HPV genotype-specific incidence of high-grade for HPV16 (8.3), HPV33 (7.8), and HPV58 (4.9). Five-year CIN2þ cervical intraepithelial neoplasia or more severe (CIN2þ) following risk was higher for HPV16 (0.34) compared with HPV18/45 (0.12), an abnormal screening result was examined. HPV31/33/35/52/58 (0.12), and HPV39/51/56/59/68 (0.16) (P ¼ 0.05). Methods: We assessed a US-based prospective, multiracial, Conclusions: Non-16/18 hrHPV types are associated with difclinical cohort of 343 colposcopy patients with normal histology ferential CIN2þ progression rates. HPV16, 33, and 58 exhibited the (n ¼ 226) or CIN1 (n ¼ 117). Baseline cervical samples underwent highest rates over 5 years. HPV risk groups warrant further invesHPV DNA genotyping, and participants were followed up to 5 years. tigation in diverse US populations. Genotype-specific CIN2þ incidence rates (IR) were estimated with Impact: These novel data assessing extended HPV genotyping in accelerated failure time models. Five-year CIN2þ risks were estia diverse clinical cohort can inform future directions to improve mated nonparametrically for hierarchical hrHPV risk groups screening practices in the general population
Global Search for New Physics with 2.0/fb at CDF
Data collected in Run II of the Fermilab Tevatron are searched for
indications of new electroweak-scale physics. Rather than focusing on
particular new physics scenarios, CDF data are analyzed for discrepancies with
the standard model prediction. A model-independent approach (Vista) considers
gross features of the data, and is sensitive to new large cross-section
physics. Further sensitivity to new physics is provided by two additional
algorithms: a Bump Hunter searches invariant mass distributions for "bumps"
that could indicate resonant production of new particles; and the Sleuth
procedure scans for data excesses at large summed transverse momentum. This
combined global search for new physics in 2.0/fb of ppbar collisions at
sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D
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