1,777 research outputs found
Information gap for classical and quantum communication in a Schwarzschild spacetime
Communication between a free-falling observer and an observer hovering above
the Schwarzschild horizon of a black hole suffers from Unruh-Hawking noise,
which degrades communication channels. Ignoring time dilation, which affects
all channels equally, we show that for bosonic communication using single and
dual rail encoding the classical channel capacity reaches a finite value and
the quantum coherent information tends to zero. We conclude that classical
correlations still exist at infinite acceleration, whereas the quantum
coherence is fully removed.Comment: 5 pages, 4 figure
Exoplanet atmospheres with GIANO. I. Water in the transmission spectrum of HD 189733b
High-resolution spectroscopy (R 20,000) at near-infrared wavelengths
can be used to investigate the composition, structure, and circulation patterns
of exoplanet atmospheres. However, up to now it has been the exclusive dominion
of the biggest telescope facilities on the ground, due to the large amount of
photons necessary to measure a signal in high-dispersion spectra. Here we show
that spectrographs with a novel design - in particular a large spectral range -
can open exoplanet characterisation to smaller telescope facilities too. We aim
to demonstrate the concept on a series of spectra of the exoplanet HD 189733 b
taken at the Telescopio Nazionale Galileo with the near-infrared spectrograph
GIANO during two transits of the planet. In contrast to absorption in the
Earth's atmosphere (telluric absorption), the planet transmission spectrum
shifts in radial velocity during transit due to the changing orbital motion of
the planet. This allows us to remove the telluric spectrum while preserving the
signal of the exoplanet. The latter is then extracted by cross-correlating the
residual spectra with template models of the planet atmosphere computed through
line-by-line radiative transfer calculations, and containing molecular
absorption lines from water and methane. By combining the signal of many
thousands of planet molecular lines, we confirm the presence of water vapour in
the atmosphere of HD 189733 b at the 5.5- level. This signal was
measured only in the first of the two observing nights. By injecting and
retrieving artificial signals, we show that the non-detection on the second
night is likely due to an inferior quality of the data. The measured strength
of the planet transmission spectrum is fully consistent with past CRIRES
observations at the VLT, excluding a strong variability in the depth of
molecular absorption lines.Comment: 10 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. v2 includes language editin
Titan's atmosphere as observed by Cassini/VIMS solar occultations: CH, CO and evidence for CH absorption
We present an analysis of the VIMS solar occultations dataset, which allows
us to extract vertically resolved information on the characteristics of Titan's
atmosphere between 100-700 km with a characteristic vertical resolution of 10
km. After a series of data treatment procedures, 4 occultations out of 10 are
retained. This sample covers different seasons and latitudes of Titan. The
transmittances show clearly the evolution of the haze and detect the detached
layer at 310 km in Sept. 2011 at mid-northern latitudes. Through the inversion
of the transmission spectra with a line-by-line radiative transfer code we
retrieve the vertical distribution of CH and CO mixing ratio. The two
methane bands at 1.4 and 1.7 {\mu}m are always in good agreement and yield an
average stratospheric abundance of %. This is significantly less
than the value of 1.48% obtained by the GCMS/Huygens instrument. The analysis
of the residual spectra after the inversion shows that there are additional
absorptions which affect a great part of the VIMS wavelength range. We
attribute many of these additional bands to gaseous ethane, whose near-infrared
spectrum is not well modeled yet. Ethane contributes significantly to the
strong absorption between 3.2-3.5 {\mu}m that was previously attributed only to
C-H stretching bands from aerosols. Ethane bands may affect the surface windows
too, especially at 2.7 {\mu}m. Other residual bands are generated by stretching
modes of C-H, C-C and C-N bonds. In addition to the C-H stretch from aliphatic
hydrocarbons at 3.4 {\mu}m, we detect a strong and narrow absorption at 3.28
{\mu}m which we tentatively attribute to the presence of PAHs in the
stratosphere. C-C and C-N stretching bands are possibly present between 4.3-4.5
{\mu}m. Finally, we obtain the CO mixing ratio between 70-170 km. The average
result of ppm is in good agreement with previous studies.Comment: 51 pages, 28 figure
Stubborn Predictions in Primary Visual Cortex
Perceivers can use past experiences to make sense of ambiguous sensory signals. However, this may be inappropriate when the world changes and past experiences no longer predict what the future holds. Optimal learning models propose that observers decide whether to stick with or update their predictions by tracking the uncertainty or "precision" of their expectations. However, contrasting theories of prediction have argued that we are prone to misestimate uncertainty-leading to stubborn predictions that are difficult to dislodge. To compare these possibilities, we had participants learn novel perceptual predictions before using fMRI to record visual brain activity when predictive contingencies were disrupted-meaning that previously "expected" events become objectively improbable. Multivariate pattern analyses revealed that expected events continued to be decoded with greater fidelity from primary visual cortex, despite marked changes in the statistical structure of the environment, which rendered these expectations no longer valid. These results suggest that our perceptual systems do indeed form stubborn predictions even from short periods of learning-and more generally suggest that top-down expectations have the potential to help or hinder perceptual inference in bounded minds like ours
Optical to near-infrared transit observations of super-Earth GJ1214b: water-world or mini-Neptune?
GJ1214b is thought to be either a mini-Neptune with a thick, hydrogen-rich
atmosphere, or a planet with a composition dominated by water. In the case of a
hydrogen-rich atmosphere, molecular absorption and scattering processes may
result in detectable radius variations as a function of wavelength. The aim of
this paper is to measure these variations. We have obtained observations of the
transit of GJ1214b in the r- and I-band with the INT, in the g, r, i and z
bands with the 2.2 meter MPI/ESO telescope, in the Ks-band with the NOT, and in
the Kc-band with the WHT. By comparing the transit depth between the the
different bands, which is a measure for the planet-to-star size ratio, the
atmosphere is investigated. We do not detect clearly significant variations in
the planet-to-star size ratio as function of wavelength. Although the ratio at
the shortest measured wavelength, in g-band, is 2sigma larger than in the other
bands. The uncertainties in the Ks and Kc bands are large, due to systematic
features in the light curves. The tentative increase in the planet-to-star size
ratio at the shortest wavelength could be a sign of an increase in the
effective planet-size due to Rayleigh scattering, which would require GJ1214b
to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have
both clouds, to suppress planet-size variations at red optical wavelengths, as
well as a sub-solar metallicity, to suppress strong molecular features in the
near- and mid-infrared. However, star spots, which are known to be present on
the hoststar's surface, can (partly) cancel out the expected variations in
planet-to-star size ratio, due to the lower surface temperature of the spots .
A hypothetical spot-fraction of 10% would be able to raise the infrared points
sufficiently with respect to the optical measurements to be inconsistent with a
water-dominated atmosphere. [abridged]Comment: 13 pages, 8 figures. Accepted for publication in A&
Polar Smectic Films
We report on a new experimental procedure for forming and studying polar
smectic liquid crystal films. A free standing smectic film is put in contact
with a liquid drop, so that the film has one liquid crystal/liquid interface
and one liquid crystal/air interface. This polar environment results in changes
in the textures observed in the film, including a boojum texture and a
previously unobserved spiral texture in which the winding direction of the
spiral reverses at a finite radius from its center. Some aspects of these
textures are explained by the presence of a Ksb term in the bulk elastic free
energy density that favors a combination of splay and bend deformations.Comment: 4 pages, REVTeX, 3 figures, submitted to PR
HCN ice in Titan's high-altitude southern polar cloud
Titan's middle atmosphere is currently experiencing a rapid change of season
after northern spring arrived in 2009. A large cloud was observed for the first
time above Titan's southern pole in May 2012, at an altitude of 300 km. This
altitude previously showed a temperature maximum and condensation was not
expected for any of Titan's atmospheric gases. Here we show that this cloud is
composed of micron-sized hydrogen cyanide (HCN) ice particles. The presence of
HCN particles at this altitude, together with new temperature determinations
from mid-infrared observations, indicate a very dramatic cooling of Titan's
atmosphere inside the winter polar vortex in early 2012. Such a cooling is
completely contrary to previously measured high-altitude warming in the polar
vortex, and temperatures are a hundred degrees colder than predicted by
circulation models. Besides elucidating the nature of Titan's mysterious polar
cloud, these results thus show that post-equinox cooling at the winter pole is
much more efficient than previously thought.Comment: Published in Nature on 2 October 2014. This is the author version,
before final editing by Natur
Effect of intraperitoneal chemotherapy concentration on morbidity and survival
Contains fulltext :
218098.pdf (publisher's version ) (Open Access)BACKGROUND: Selected patients with colorectal peritoneal metastases are treated with cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). The concentration of intraperitoneal chemotherapy reflects the administered dose and perfusate volume. The aim of this study was to calculate intraperitoneal chemotherapy concentration during HIPEC and see whether this was related to clinical outcomes. METHODS: An observational multicentre study included consecutive patients with colorectal peritoneal metastases who were treated with CRS-HIPEC between 2010 and 2018 at three Dutch centres. Data were retrieved from prospectively developed databases. Chemotherapy dose and total circulating volumes of carrier solution were used to calculate chemotherapy concentrations. Postoperative complications, disease-free and overall survival were correlated with intraoperative chemotherapy concentrations. Univariable and multivariable logistic regression, Cox regression and survival analyses were performed. RESULTS: Of 320 patients, 220 received intraperitoneal mitomycin C (MMC) and 100 received oxaliplatin. Median perfusate volume for HIPEC was 5.0 (range 0.7-10.0) litres. Median intraperitoneal chemotherapy concentration was 13.3 (range 7.0-76.0) mg/l for MMC and 156.0 (91.9-377.6) mg/l in patients treated with oxaliplatin. Grade III or higher complications occurred in 75 patients (23.4 per cent). Median overall survival was 36.9 (i.q.r. 19.5-62.9) months. Intraperitoneal chemotherapy concentrations were not associated with postoperative complications or survival. CONCLUSION: CRS-HIPEC was performed with a wide variation in intraperitoneal chemotherapy concentrations that were not associated with complications or survival
Experimental Mapping of the Canine KCNJ2 and KCNJ12 Gene Structures and Functional Analysis of the Canine KIR2.2 ion Channel
For many model organisms traditionally in use for cardiac electrophysiological studies, characterization of ion channel genes is lacking. We focused here on two genes encoding the inward rectifier current, KCNJ2 and KCNJ12, in the dog heart. A combination of RT-PCR, 5′-RACE, and 3′-RACE demonstrated the status of KCNJ2 as a two exon gene. The complete open reading frame (ORF) was located on the second exon. One transcription initiation site was mapped. Four differential transcription termination sites were found downstream of two consensus polyadenylation signals. The canine KCNJ12 gene was found to consist of three exons, with its ORF located on the third exon. One transcription initiation and one termination site were found. No alternative splicing was observed in right ventricle or brain cortex. The gene structure of canine KCNJ2 and KCNJ12 was conserved amongst other vertebrates, while current GenBank gene annotation was determined as incomplete. In silico translation of KCN12 revealed a non-conserved glycine rich stretch located near the carboxy-terminus of the KIR2.2 protein. However, no differences were observed when comparing dog with human KIR2.2 protein upon ectopic expression in COS-7 or HEK293 cells with respect to subcellular localization or electrophysiological properties
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