11,723 research outputs found
Circular dichroism induced by Fano resonances in planar chiral oligomers
We present a general theory of circular dichroism in planar chiral
nanostructures with rotational symmetry. It is demonstrated, analytically, that
the handedness of the incident field's polarization can control whether a
nanostructure induces either absorption or scattering losses, even when the
total optical loss (extinction) is polarization-independent. We show that this
effect is a consequence of modal interference so that strong circular dichroism
in absorption and scattering can be engineered by combining Fano resonances
with planar chiral nanoparticle clusters.Comment: 12 pages, 5 figure
Electropolishing the rare-earth metals
This paper describes a method whereby the rare-earth metals can be consistently electropolished and chemically etched. The method involves cooling an alcohol-perchloric electrolyte to -76° C before electropolishing. The metals are chemically polished in the same solution
Novel 16S rRNA methyltransferase RmtE3 in acinetobacter baumannii ST79.
Introduction. The 16S rRNA methyltransferase (16S RMTase) gene armA is the most common mechanism conferring high-level aminoglycoside resistance in Acinetobacter baumannii, although rmtA, rmtB, rmtC, rmtD and rmtE have also been reported.Hypothesis/Gap statement. The occurrence of 16S RMTase genes in A. baumannii in the UK and Republic of Ireland is currently unknown.Aim. To identify the occurrence of 16S RMTase genes in A. baumannii isolates from the UK and the Republic of Ireland between 2004 and 2015.Methodology. Five hundred and fifty pan-aminoglycoside-resistant A. baumannii isolates isolated from the UK and the Republic of Ireland between 2004 and 2015 were screened by PCR to detect known 16S RMTase genes, and then whole-genome sequencing was conducted to screen for novel 16S RMTase genes.Results. A total of 96.5 % (531/550) of isolates were positive for 16S RMTase genes, with all but 1 harbouring armA (99.8 %, 530/531). The remaining isolates harboured rmtE3, a new rmtE variant. Most (89.2 %, 473/530) armA-positive isolates belonged to international clone II (ST2), and the rmtE3-positive isolate belonged to ST79. rmtE3 shared a similar genetic environment to rmtE2 but lacked an ISCR20 element found upstream of rmtE2.Conclusion. This is the first report of rmtE in A. baumannii in Europe; the potential for transmission of rmtE3 to other bacterial species requires further research
Strongly Time-Variable Ultra-Violet Metal Line Emission from the Circum-Galactic Medium of High-Redshift Galaxies
We use cosmological simulations from the Feedback In Realistic Environments
(FIRE) project, which implement a comprehensive set of stellar feedback
processes, to study ultra-violet (UV) metal line emission from the
circum-galactic medium of high-redshift (z=2-4) galaxies. Our simulations cover
the halo mass range Mh ~ 2x10^11 - 8.5x10^12 Msun at z=2, representative of
Lyman break galaxies. Of the transitions we analyze, the low-ionization C III
(977 A) and Si III (1207 A) emission lines are the most luminous, with C IV
(1548 A) and Si IV (1394 A) also showing interesting spatially-extended
structures. The more massive halos are on average more UV-luminous. The UV
metal line emission from galactic halos in our simulations arises primarily
from collisionally ionized gas and is strongly time variable, with
peak-to-trough variations of up to ~2 dex. The peaks of UV metal line
luminosity correspond closely to massive and energetic mass outflow events,
which follow bursts of star formation and inject sufficient energy into
galactic halos to power the metal line emission. The strong time variability
implies that even some relatively low-mass halos may be detectable. Conversely,
flux-limited samples will be biased toward halos whose central galaxy has
recently experienced a strong burst of star formation. Spatially-extended UV
metal line emission around high-redshift galaxies should be detectable by
current and upcoming integral field spectrographs such as the Multi Unit
Spectroscopic Explorer (MUSE) on the Very Large Telescope and Keck Cosmic Web
Imager (KCWI).Comment: 16 pages, 8 figures, accepted for publication in MNRA
The Experimental Observation of a Superfluid Gyroscope in a dilute Bose Condensed Gas
We have observed a superfluid gyroscope effect in a dilute gas Bose-Einstein
condensate. A condensate with a vortex possesses a single quantum of angular
momentum and this causes the plane of oscillation of the scissors mode to
precess around the vortex line. We have measured the precession rate of the
scissors oscillation. From this we deduced the angular momentum associated with
the vortex line and found a value close to per particle, as predicted
for a superfluid.Comment: 4 pages 5 fig
How Much Mass do Supermassive Black Holes Eat in their Old Age?
We consider the distribution of local supermassive black hole Eddington
ratios and accretion rates, accounting for the dependence of radiative
efficiency and bolometric corrections on the accretion rate. We find that black
hole mass growth, both of the integrated mass density and the masses of most
individual objects, must be dominated by an earlier, radiatively efficient,
high accretion rate stage, and not by the radiatively inefficient low accretion
rate phase in which most local supermassive black holes are currently observed.
This conclusion is particularly true of supermassive black holes in elliptical
host galaxies, as expected if they have undergone merger activity in the past
which would fuel quasar activity and rapid growth. We discuss models of the
time evolution of accretion rates and show that they all predict significant
mass growth in a prior radiatively efficient state. The only way to avoid this
conclusion is through careful fine-tuning of the accretion/quasar timescale to
a value that is inconsistent with observations. Our results agree with a wide
range of observational inferences drawn from the quasar luminosity function and
X-ray background synthesis models, but our approach has the virtue of being
independent of the modeling of source populations. Models in which black holes
spend the great majority of their time in low accretion rate phases are thus
completely consistent both with observations implying mass gain in relatively
short, high accretion rate phases and with the local distribution of accretion
rates.Comment: 11 pages, 4 figures, matches version accepted to Ap
Discovery of TUG-770: a highly potent free fatty acid receptor 1 (FFA1/GPR40) agonist for treatment of type 2 diabetes
Free fatty acid receptor 1 (FFA1 or GPR40) enhances glucose-stimulated insulin secretion from pancreatic β-cells and currently attracts high interest as a new target for the treatment of type 2 diabetes. We here report the discovery of a highly potent FFA1 agonist with favorable physicochemical and pharmacokinetic properties. The compound efficiently normalizes glucose tolerance in diet-induced obese mice, an effect that is fully sustained after 29 days of chronic dosing
Testing Convolutional Neural Networks for finding strong gravitational lenses in KiDS
Convolutional Neural Networks (ConvNets) are one of the most promising
methods for identifying strong gravitational lens candidates in survey data. We
present two ConvNet lens-finders which we have trained with a dataset composed
of real galaxies from the Kilo Degree Survey (KiDS) and simulated lensed
sources. One ConvNet is trained with single \textit{r}-band galaxy images,
hence basing the classification mostly on the morphology. While the other
ConvNet is trained on \textit{g-r-i} composite images, relying mostly on
colours and morphology. We have tested the ConvNet lens-finders on a sample of
21789 Luminous Red Galaxies (LRGs) selected from KiDS and we have analyzed and
compared the results with our previous ConvNet lens-finder on the same sample.
The new lens-finders achieve a higher accuracy and completeness in identifying
gravitational lens candidates, especially the single-band ConvNet. Our analysis
indicates that this is mainly due to improved simulations of the lensed
sources. In particular, the single-band ConvNet can select a sample of lens
candidates with purity, retrieving 3 out of 4 of the confirmed
gravitational lenses in the LRG sample. With this particular setup and limited
human intervention, it will be possible to retrieve, in future surveys such as
Euclid, a sample of lenses exceeding in size the total number of currently
known gravitational lenses.Comment: 16 pages, 10 figures. Accepted for publication in MNRA
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