2,377 research outputs found
SCORPIO-II: Spectral indices of weak Galactic radio sources
In the next few years the classification of radio sources observed by the
large surveys will be a challenging problem, and spectral index is a powerful
tool for addressing it. Here we present an algorithm to estimate the spectral
index of sources from multiwavelength radio images. We have applied our
algorithm to SCORPIO (Umana et al. 2015), a Galactic Plane survey centred
around 2.1 GHz carried out with ATCA, and found we can measure reliable
spectral indices only for sources stronger than 40 times the rms noise. Above a
threshold of 1 mJy, the source density in SCORPIO is 20 percent greater than in
a typical extra-galactic field, like ATLAS (Norris et al. 2006), because of the
presence of Galactic sources. Among this excess population, 16 sources per
square degree have a spectral index of about zero, suggesting optically thin
thermal emission such as Hii regions and planetary nebulae, while 12 per square
degree present a rising spectrum, suggesting optically thick thermal emission
such as stars and UCHii regions.Comment: 12 pages, 11 figures, accepted by MNRA
Preparation of distilled and purified continuous variable entangled states
The distribution of entangled states of light over long distances is a major
challenge in the field of quantum information. Optical losses, phase diffusion
and mixing with thermal states lead to decoherence and destroy the
non-classical states after some finite transmission-line length. Quantum
repeater protocols, which combine quantum memory, entanglement distillation and
entanglement swapping, were proposed to overcome this problem. Here we report
on the experimental demonstration of entanglement distillation in the
continuous-variable regime. Entangled states were first disturbed by random
phase fluctuations and then distilled and purified using interference on beam
splitters and homodyne detection. Measurements of covariance matrices clearly
indicate a regained strength of entanglement and purity of the distilled
states. In contrast to previous demonstrations of entanglement distillation in
the complementary discrete-variable regime, our scheme achieved the actual
preparation of the distilled states, which might therefore be used to improve
the quality of downstream applications such as quantum teleportation
Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology
The best European locality for complete Eocene mammal skeletons is Grube Messel, near Darmstadt, Germany. Although the site was surrounded by a para-tropical rain forest in the Eocene, primates are remarkably rare there, and only eight fragmentary specimens were known until now. Messel has now yielded a full primate skeleton. The specimen has an unusual history: it was privately collected and sold in two parts, with only the lesser part previously known. The second part, which has just come to light, shows the skeleton to be the most complete primate known in the fossil record.We describe the morphology and investigate the paleobiology of the skeleton. The specimen is described as Darwinius masillae n.gen. n.sp. belonging to the Cercamoniinae. Because the skeleton is lightly crushed and bones cannot be handled individually, imaging studies are of particular importance. Skull radiography shows a host of teeth developing within the juvenile face. Investigation of growth and proportion suggest that the individual was a weaned and independent-feeding female that died in her first year of life, and might have attained a body weight of 650-900 g had she lived to adulthood. She was an agile, nail-bearing, generalized arboreal quadruped living above the floor of the Messel rain forest.Darwinius masillae represents the most complete fossil primate ever found, including both skeleton, soft body outline and contents of the digestive tract. Study of all these features allows a fairly complete reconstruction of life history, locomotion, and diet. Any future study of Eocene-Oligocene primates should benefit from information preserved in the Darwinius holotype. Of particular importance to phylogenetic studies, the absence of a toilet claw and a toothcomb demonstrates that Darwinius masillae is not simply a fossil lemur, but part of a larger group of primates, Adapoidea, representative of the early haplorhine diversification
Supersymmetric completion of M-theory 4D-gauge algebra from twisted tori and fluxes
We present the supersymmetric completion of the M-theory free differential
algebra resulting from a compactification to four dimensions on a twisted
seven-torus with 4-form and 7-form fluxes turned on. The super--curvatures are
given and the local supersymmetry transformations derived. Dual formulations of
the theory are discussed in connection with classes of gaugings corresponding
to diverse choices of vacua. This also includes seven dimensional
compactifications on more general spaces not described by group manifolds.Comment: 19 pages, LaTeX, typos corrected, references adde
Follow-up observations at 16 and 33 GHz of extragalactic sources from WMAP 3-year data: I - Spectral properties
We present follow-up observations of 97 point sources from the Wilkinson
Microwave Anisotropy Probe (WMAP) 3-year data, contained within the New
Extragalactic WMAP Point Source (NEWPS) catalogue between declinations of -4
and +60 degrees; the sources form a flux-density-limited sample complete to 1.1
Jy (approximately 5 sigma) at 33 GHz. Our observations were made at 16 GHz
using the Arcminute Microkelvin Imager (AMI) and at 33 GHz with the Very Small
Array (VSA). 94 of the sources have reliable, simultaneous -- typically a few
minutes apart -- observations with both telescopes. The spectra between 13.9
and 33.75 GHz are very different from those of bright sources at low frequency:
44 per cent have rising spectra (alpha < 0.0), where flux density is
proportional to frequency^-alpha, and 93 per cent have spectra with alpha <
0.5; the median spectral index is 0.04. For the brighter sources, the agreement
between VSA and WMAP 33-GHz flux densities averaged over sources is very good.
However, for the fainter sources, the VSA tends to measure lower values for the
flux densities than WMAP. We suggest that the main cause of this effect is
Eddington bias arising from variability.Comment: 12 pages, 13 figures, submitted to MNRA
Cold gas outflows from the Small Magellanic Cloud traced with ASKAP
Feedback from massive stars plays a critical role in the evolution of the
Universe by driving powerful outflows from galaxies that enrich the
intergalactic medium and regulate star formation. An important source of
outflows may be the most numerous galaxies in the Universe: dwarf galaxies.
With small gravitational potential wells, these galaxies easily lose their
star-forming material in the presence of intense stellar feedback. Here, we
show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic
hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming
bar of the galaxy. The outflows are cold, , and may have formed
during a period of active star formation million years (Myr) ago. The
total mass of atomic gas in the outflow is solar masses, , or % of the total atomic gas of the galaxy. The inferred
mass flux in atomic gas alone, , is up to an order of magnitude greater than the star
formation rate. We suggest that most of the observed outflow will be stripped
from the SMC through its interaction with its companion, the Large Magellanic
Cloud (LMC), and the Milky Way, feeding the Magellanic Stream of hydrogen
encircling the Milky Way.Comment: Published in Nature Astronomy, 29 October 2018,
http://dx.doi.org/10.1038/s41550-018-0608-
Experimental entanglement distillation of mesoscopic quantum states
The distribution of entangled states between distant parties in an optical
network is crucial for the successful implementation of various quantum
communication protocols such as quantum cryptography, teleportation and dense
coding [1-3]. However, owing to the unavoidable loss in any real optical
channel, the distribution of loss-intolerant entangled states is inevitably
inflicted by decoherence, which causes a degradation of the transmitted
entanglement. To combat the decoherence, entanglement distillation, which is
the process of extracting a small set of highly entangled states from a large
set of less entangled states, can be used [4-14]. Here we report on the
mesoscopic distillation of deterministically prepared entangled light pulses
that have undergone non-Gaussian noise. The entangled light pulses [15-17] are
sent through a lossy channel, where the transmission is varying in time
similarly to light propagation in the atmosphere. By employing linear optical
components and global classical communication, the entanglement is
probabilistically increased.Comment: 13 pages, 4 figures. It's the first submitted version to the Nature
Physics. The final version is already published on Nature Physics vol.4,
No.12, 919 - 923 (2008
A systematic review investigating fatigue, psychological and cognitive impairment following TIA and minor stroke:protocol paper
Approximately 20,000 people have a transient ischemic attack (TIA) and 23,375 have a minor stroke in England each year. Fatigue, psychological and cognitive impairments are well documented post-stroke. Evidence suggests that TIA and minor stroke patients also experience these impairments; however, they are not routinely offered relevant treatment. This systematic review aims to: (1) establish the prevalence of fatigue, anxiety, depression, post-traumatic stress disorder (PTSD) and cognitive impairment following TIA and minor stroke and to investigate the temporal course of these impairments; (2) explore impact on quality of life (QoL), change in emotions and return to work; (3) identify where further research is required and to potentially inform an intervention study
A blind detection of a large, complex, Sunyaev--Zel'dovich structure
We present an interesting Sunyaev-Zel'dovich (SZ) detection in the first of
the Arcminute Microkelvin Imager (AMI) 'blind', degree-square fields to have
been observed down to our target sensitivity of 100{\mu}Jy/beam. In follow-up
deep pointed observations the SZ effect is detected with a maximum peak
decrement greater than 8 \times the thermal noise. No corresponding emission is
visible in the ROSAT all-sky X-ray survey and no cluster is evident in the
Palomar all-sky optical survey. Compared with existing SZ images of distant
clusters, the extent is large (\approx 10') and complex; our analysis favours a
model containing two clusters rather than a single cluster. Our Bayesian
analysis is currently limited to modelling each cluster with an ellipsoidal or
spherical beta-model, which do not do justice to this decrement. Fitting an
ellipsoid to the deeper candidate we find the following. (a) Assuming that the
Evrard et al. (2002) approximation to Press & Schechter (1974) correctly gives
the number density of clusters as a function of mass and redshift, then, in the
search area, the formal Bayesian probability ratio of the AMI detection of this
cluster is 7.9 \times 10^4:1; alternatively assuming Jenkins et al. (2001) as
the true prior, the formal Bayesian probability ratio of detection is 2.1
\times 10^5:1. (b) The cluster mass is MT,200 = 5.5+1.2\times 10^14h-1M\odot.
(c) Abandoning a physical model with num- -1.3 70 ber density prior and instead
simply modelling the SZ decrement using a phenomenological {\beta}-model of
temperature decrement as a function of angular distance, we find a central SZ
temperature decrement of -295+36 {\mu}K - this allows for CMB primary
anisotropies, receiver -15 noise and radio sources. We are unsure if the
cluster system we observe is a merging system or two separate clusters.Comment: accepted MNRAS. 12 pages, 9 figure
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