2,297 research outputs found
Attentional demand estimation with attentive driving models
The task of driving can sometimes require the processing of large amounts of visual information; such situations can overload the perceptual systems of human drivers
leading to ‘inattentional blindness’, where potentially critical visual information is overlooked. This phenomenon of ‘looking but failing to see’ is the third largest contributor
to traffic accidents in the UK. In this work we develop a method to identify these particularly demanding driving scenes using an end-to-end driving architecture, imbued with
a spatial attention mechanism and trained to mimic ground-truth driving controls from
video input. At test time, the network’s attention distribution is segmented to identify
relevant items in the driving scene which are used to estimate the attentional demand on
the driver according to an established model in cognitive neuroscience. Without collecting any ground-truth attentional demand data - instead using readily available odometry
data in a novel way - our approach is shown to outperform several baselines on a new
dataset of 1200 driving scenes labelled for attentional demand in driving
Structural characterization of the closed conformation of mouse guanylate kinase
Guanylate kinase (GMPK) is a nucleoside monophosphate kinase that catalyzes the reversible phosphoryl transfer from ATP to GMP to yield ADP and GDP. In addition to phosphorylating GMP, antiviral prodrugs such as acyclovir, ganciclovir, and carbovir and anticancer prodrugs such as the thiopurines are dependent on GMPK for their activation. Hence, structural information on mammalian GMPK could play a role in the design of improved antiviral and antineoplastic agents. Here we present the structure of the mouse enzyme in an abortive complex with the nucleotides ADP and GMP, refined at 2.1 Angstrom resolution with a final crystallographic R factor of 0.19 (R-free = 0.23). Guanylate kinase is a member of the nucleoside monophosphate (NMP) kinase family, a family of enzymes that despite having a low primary structure identity share a similar fold, which consists of three structurally distinct regions termed the CORE, LID, and NMP-binding regions. Previous studies on the yeast enzyme have shown that these parts move as rigid bodies upon substrate binding. It has been proposed that consecutive binding of substrates leads to "closing" of the active site bringing the NMP-binding and LID regions closer to each other and to the CORE region. Our structure, which is the first of any guanylate kinase with both substrates bound, supports this hypothesis. It also reveals the binding site of ATP and implicates arginines 44, 137, and 148 (in addition to the invariant P-loop lysine) as candidates for catalyzing the chemical step of the phosphoryl transfer
HELIOS-Retrieval: An Open-source, Nested Sampling Atmospheric Retrieval Code, Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation
We present an open-source retrieval code named HELIOS-Retrieval (hereafter
HELIOS-R), designed to obtain chemical abundances and temperature-pressure
profiles from inverting the measured spectra of exoplanetary atmospheres. In
the current implementation, we use an exact solution of the radiative transfer
equation, in the pure absorption limit, in our forward model, which allows us
to analytically integrate over all of the outgoing rays (instead of performing
Gaussian quadrature). Two chemistry models are considered: unconstrained
chemistry (where the mixing ratios are treated as free parameters) and
equilibrium chemistry (enforced via analytical formulae, where only the
elemental abundances are free parameters). The nested sampling algorithm allows
us to formally implement Occam's Razor based on a comparison of the Bayesian
evidence between models. We perform a retrieval analysis on the measured
spectra of the HR 8799b, c, d and e directly imaged exoplanets. Chemical
equilibrium is disfavored by the Bayesian evidence for HR 8799b, c and d. We
find supersolar C/O, C/H and O/H values for the outer HR 8799b and c
exoplanets, while the inner HR 8799d and e exoplanets have substellar C/O,
substellar C/H and superstellar O/H values. If these retrieved properties are
representative of the bulk compositions of the exoplanets, then they are
inconsistent with formation via gravitational instability (without late-time
accretion) and consistent with a core accretion scenario in which late-time
accretion of ices occurred differently for the inner and outer exoplanets. For
HR 8799e, we find that spectroscopy in the K band is crucial for constraining
C/O and C/H. HELIOS-R is publicly available as part of the Exoclimes Simulation
Platform (ESP; www.exoclime.org).Comment: 27 pages, 21 figures, 3 tables, published in A
Predicting the Perceptual Demands of Urban Driving with Video Regression
To drive safely requires perceiving vast amounts of rapidly changing visual information. This can exhaust our limited perceptual capacity and lead to cases of 'looking but failing to see', reportedly the third largest contributing factor to road traffic accidents. In the present work we use a 3D convolutional neural network to model the perceptual demand of varied driving situations. To validate the method we introduce a new labelled dataset of approximately 2300 videos of driving in Brussels and California
Early response to adalimumab predicts long-term remission through 5 years of treatment in patients with ankylosing spondylitis
Pathophysiology and treatment of rheumatic disease
A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b
Context: KELT-9 b exemplifies a newly emerging class of short-period gaseous
exoplanets that tend to orbit hot, early type stars - termed ultra-hot
Jupiters. The severe stellar irradiation heats their atmospheres to
temperatures of K, similar to the photospheres of dwarf stars. Due
to the absence of aerosols and complex molecular chemistry at such
temperatures, these planets offer the potential of detailed chemical
characterisation through transit and day-side spectroscopy. Studies of their
chemical inventories may provide crucial constraints on their formation process
and evolution history.
Aims: To search the optical transmission spectrum of KELT-9 b for absorption
lines by metals using the cross-correlation technique.
Methods: We analyse 2 transits observed with the HARPS-N spectrograph. We use
an isothermal equilibrium chemistry model to predict the transmission spectrum
for each of the neutral and singly-ionized atoms with atomic numbers between 3
and 78. Of these, we identify the elements that are expected to have spectral
lines in the visible wavelength range and use those as cross-correlation
templates.
Results: We detect absorption of Na I, Cr II, Sc II and Y II, and confirm
previous detections of Mg I, Fe I, Fe II and Ti II. In addition, we find
evidence of Ca I, Cr I, Co I, and Sr II that will require further observations
to verify. The detected absorption lines are significantly deeper than model
predictions, suggesting that material is transported to higher altitudes where
the density is enhanced compared to a hydrostatic profile. There appears to be
no significant blue-shift of the absorption spectrum due to a net day-to-night
side wind. In particular, the strong Fe II feature is shifted by km~s, consistent with zero. Using the orbital velocity of the
planet we revise the steller and planetary masses and radii.Comment: Submitted to Astronomy and Astrophysics on January 18, 2019. Accepted
on May 3, 2019. 26 pages, 11 figure
Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) I. Detection of hot neutral sodium at high altitudes on WASP-49b
High-resolution optical spectroscopy during the transit of HD 189733b, a
prototypical hot Jupiter, allowed the resolution of the Na I D sodium lines in
the planet, giving access to the extreme conditions of the planet upper
atmosphere. We have undertaken HEARTS, a spectroscopic survey of exoplanet
upper atmospheres, to perform a comparative study of hot gas giants and
determine how stellar irradiation affect them. Here, we report on the first
HEARTS observations of the hot Saturn-mass planet WASP-49b. We observed the
planet with the HARPS high-resolution spectrograph at ESO 3.6m telescope. We
collected 126 spectra of WASP-49, covering three transits of WASP-49b. We
analyzed and modeled the planet transit spectrum, while paying particular
attention to the treatment of potentially spurious signals of stellar origin.
We spectrally resolve the Na I D lines in the planet atmosphere and show that
these signatures are unlikely to arise from stellar contamination. The large
contrasts of (D) and (D) require the
presence of hot neutral sodium ( K) at high altitudes
(1.5 planet radius or 45,000 km). From estimating the cloudiness
index of WASP-49b, we determine its atmosphere to be cloud free at the
altitudes probed by the sodium lines. WASP-49b is close to the border of the
evaporation desert and exhibits an enhanced thermospheric signature with
respect to a farther-away planet such as HD 189733b.Comment: Accepted for publication in A&A. 14 page
Wind of Change: retrieving exoplanet atmospheric winds from high-resolution spectroscopy
Context. The atmosphere of exoplanets has been studied extensively in recent
years, using numerical models to retrieve chemical composition, dynamical
circulation or temperature from data. One of the best observational probes in
transmission is the sodium doublet, due to its large cross section. However,
modelling the shape of the planetary sodium lines has proven to be challenging.
Models with different assumptions regarding the atmosphere have been employed
to fit the lines in the literature, yet statistically sound direct comparisons
of different models are needed to paint a clear picture. Aims. We will compare
different wind and temperature patterns and provide a tool to distinguish them
driven by their best fit for the sodium transmission spectrum of the hot
Jupiter HD 189733b. We parametrise different possible wind patterns already
tested in literature and introduce the new option of an upwards driven vertical
wind. Methods. We construct a forward model where the wind speed, wind geometry
and temperature are injected into the calculation of the transmission spectrum.
We embed this forward model in a nested sampling retrieval code to rank the
models via their Bayesian evidence. Results. We retrieve a best-fit to the HD
189733b data for vertical upward winds
km/s at altitudes above
bar. With the current data from HARPS, we cannot distinguish wind
patterns for higher pressure atmospheric layers. Conclusions. We show that
vertical upwards winds in the upper atmosphere are a possible explanation for
the broad sodium signature in hot Jupiters. We highlight other influences on
the width of the doublet and explore strong magnetic fields acting on the lower
atmosphere as one possible origin of the retrieved wind speed.Comment: 17 pages, 30 figures, accepted for publication in Astronomy &
Astrophysics (04.12.2019
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