4,462 research outputs found
Atmospheric Characterization of the Hot Jupiter Kepler-13Ab
Kepler-13Ab (= KOI-13.01) is a unique transiting hot Jupiter. It is one of
very few known short-period planets orbiting a hot A-type star, making it one
of the hottest planets currently known. The availability of Kepler data allows
us to measure the planet's occultation (secondary eclipse) and phase curve in
the optical, which we combine with occultations observed by warm Spitzer at 4.5
mic and 3.6 mic and a ground-based occultation observation in the Ks band (2.1
mic). We derive a day-side hemisphere temperature of 2,750 +- 160 K as the
effective temperature of a black body showing the same occultation depths.
Comparing the occultation depths with one-dimensional planetary atmosphere
models suggests the presence of an atmospheric temperature inversion. Our
analysis shows evidence for a relatively high geometric albedo, Ag= 0.33 +0.04
-0.06. While measured with a simplistic method, a high Ag is supported also by
the fact that the one-dimensional atmosphere models underestimate the
occultation depth in the optical. We use stellar spectra to determine the
dilution, in the four wide bands where occultation was measured, due to the
visual stellar binary companion 1.15 +- 0.05" away. The revised stellar
parameters measured using these spectra are combined with other measurements
leading to revised planetary mass and radius estimates of Mp = 4.94 - 8.09 Mjup
and Rp = 1.406 +- 0.038 Rjup. Finally, we measure a Kepler mid-occultation time
that is 34.0 +- 6.9 s earlier than expected based on the mid-transit time and
the delay due to light travel time, and discuss possible scenarios.Comment: V2: Accepted to ApJ on 2014 April 11. Spitzer photometry and model
fitting Matlab pipeline code is publicly available at:
http://gps.caltech.edu/~shporer/spitzerphot
Think, Collaborate, Decide, Teach: A Guide for Success
Through recent and documented observations, interviews, and assessments, it has been determined that many educational institutions are in need of intervention in regards to four specific areas, particularly as related to its school leadership team and instructional staff. Proper interventions are needed for institutions to reach their fullest potential and ultimately provide students with the most effective and engaging school experience possible. There are specific challenges related to the ability to effectively make sound decisions, particularly when encountering stressful circumstances that often exist within a complex school environment. This lack of effective decision-making has contributed to shortcomings in the way in which school faculty and staff are working together. This guidebook will present educational institutions with pragmatic ways in which teams can work together to foster collaboration and promote synergy. It will also outline strategies whereby communication may be enhanced to improve student achievement and outcomes. Ultimately, leaders are concerned with the development of critical thinking in the classroom for educators, which will result in behavior issues being solved before administrative intervention. Furthermore, this can reduce or eliminate the pressure on administrators if the situations can be diffused on the classroom level. Therefore, this is the ultimate guide for success: Think, Collaborate, Decide,
There are specific challenges related to the ability to effectively make sound decisions, particularly when encountering stressful circumstances that often exist within a complex school environment. This lack of effective decision-making has contributed to shortcomings in the way in which school faculty and staff are working together. This guidebook will present educational institutions with pragmatic ways in which teams can work together to foster collaboration and promote synergy. It will also outline strategies whereby communication may be enhanced to improve student achievement and outcomes. Ultimately, leaders are concerned with the development of critical thinking in the classroom for educators, which will result in behavior issues being solved before administrative intervention. Furthermore, this can reduce or eliminate the pressure on administrators if the situations can be diffused on the classroom level. Therefore, this is the ultimate guide for success: Think, Collaborate, Decide, Teach
The Factory and the Beehive III: PTFEB132.707+19.810, a Low-Mass Eclipsing Binary in Praesepe Observed by PTF and K2
Theoretical models of stars constitute a fundamental bedrock upon which much
of astrophysics is built, but large swaths of model parameter space remain
uncalibrated by observations. The best calibrators are eclipsing binaries in
clusters, allowing measurement of masses, radii, luminosities, and
temperatures, for stars of known metallicity and age. We present the discovery
and detailed characterization of PTFEB132.707+19.810, a P=6.0 day eclipsing
binary in the Praesepe cluster (~600--800 Myr; [Fe/H]=0.140.04). The
system contains two late-type stars (SpT=M3.50.2;
SpT=M4.30.7) with precise masses (~;
~) and radii (~;
~). Neither star meets the predictions of stellar
evolutionary models. The primary has the expected radius, but is cooler and
less luminous, while the secondary has the expected luminosity, but is cooler
and substantially larger (by 20%). The system is not tidally locked or
circularized. Exploiting a fortuitous 4:5 commensurability between
and , we demonstrate that fitting errors from the unknown spot
configuration only change the inferred radii by <1--2%. We also analyze subsets
of data to test the robustness of radius measurements; the radius sum is more
robust to systematic errors and preferable for model comparisons. We also test
plausible changes in limb darkening, and find corresponding uncertainties of
~1%. Finally, we validate our pipeline using extant data for GU Boo, finding
that our independent results match previous radii to within the mutual
uncertainties (2--3%). We therefore suggest that the substantial discrepancies
are astrophysical; since they are larger than for old field stars, they may be
tied to the intermediate age of PTFEB132.707+19.810.Comment: Accepted to ApJ; 36 pages, 19 figures, 8 tables in two-column AASTEX6
forma
Walks of molecular motors in two and three dimensions
Molecular motors interacting with cytoskeletal filaments undergo peculiar
random walks consisting of alternating sequences of directed movements along
the filaments and diffusive motion in the surrounding solution. An ensemble of
motors is studied which interacts with a single filament in two and three
dimensions. The time evolution of the probability distribution for the bound
and unbound motors is determined analytically. The diffusion of the motors is
strongly enhanced parallel to the filament. The analytical expressions are in
excellent agreement with the results of Monte Carlo simulations.Comment: 7 pages, 2 figures, to be published in Europhys. Let
Transcription-translation coupling: direct interactions of RNA polymerase with ribosomes and ribosomal subunits.
In prokaryotes, RNA polymerase and ribosomes can bind concurrently to the same RNA transcript, leading to the functional coupling of transcription and translation. The interactions between RNA polymerase and ribosomes are crucial for the coordination of transcription with translation. Here, we report that RNA polymerase directly binds ribosomes and isolated large and small ribosomal subunits. RNA polymerase and ribosomes form a one-to-one complex with a micromolar dissociation constant. The formation of the complex is modulated by the conformational and functional states of RNA polymerase and the ribosome. The binding interface on the large ribosomal subunit is buried by the small subunit during protein synthesis, whereas that on the small subunit remains solvent-accessible. The RNA polymerase binding site on the ribosome includes that of the isolated small ribosomal subunit. This direct interaction between RNA polymerase and ribosomes may contribute to the coupling of transcription to translation
The importance of sustained attention in early Alzheimer\u27s disease
Introduction: There is conflicting evidence regarding impairment of sustained attention in early Alzheimer\u27s disease (AD). We examine whether sustained attention is impaired and predicts deficits in other cognitive domains in early AD. Methods: Fifty-one patients with early AD (MMSE \u3e 18) and 15 healthy elderly controls were recruited. The sustained attention to response task (SART) was used to assess sustained attention. A subset of 25 patients also performed tasks assessing general cognitive function (ADAS-Cog), episodic memory (Logical memory scale, Paired Associates Learning), executive function (verbal fluency, grammatical reasoning) and working memory (digit and spatial span). Results: AD patients were significantly impaired on the SART compared to healthy controls (total error β = 19.75, p = 0.027). SART errors significantly correlated with MMSE score (Spearman\u27s rho = −0.338, p = 0.015) and significantly predicted deficits in ADAS-Cog (β = 0.14, p = 0.004). Discussions: Patients with early AD have significant deficits in sustained attention, as measured using the SART. This may impair performance on general cognitive testing, and therefore should be taken into account during clinical assessment, and everyday management of individuals with early AD. Copyright © 2016 John Wiley & Sons, Ltd
Predicting recovery following stroke: deep learning, multimodal data and feature selection using explainable AI
Machine learning offers great potential for automated prediction of
post-stroke symptoms and their response to rehabilitation. Major challenges for
this endeavour include the very high dimensionality of neuroimaging data, the
relatively small size of the datasets available for learning, and how to
effectively combine neuroimaging and tabular data (e.g. demographic information
and clinical characteristics). This paper evaluates several solutions based on
two strategies. The first is to use 2D images that summarise MRI scans. The
second is to select key features that improve classification accuracy.
Additionally, we introduce the novel approach of training a convolutional
neural network (CNN) on images that combine regions-of-interest extracted from
MRIs, with symbolic representations of tabular data. We evaluate a series of
CNN architectures (both 2D and a 3D) that are trained on different
representations of MRI and tabular data, to predict whether a composite measure
of post-stroke spoken picture description ability is in the aphasic or
non-aphasic range. MRI and tabular data were acquired from 758 English speaking
stroke survivors who participated in the PLORAS study. The classification
accuracy for a baseline logistic regression was 0.678 for lesion size alone,
rising to 0.757 and 0.813 when initial symptom severity and recovery time were
successively added. The highest classification accuracy 0.854 was observed when
8 regions-of-interest was extracted from each MRI scan and combined with lesion
size, initial severity and recovery time in a 2D Residual Neural Network.Our
findings demonstrate how imaging and tabular data can be combined for high
post-stroke classification accuracy, even when the dataset is small in machine
learning terms. We conclude by proposing how the current models could be
improved to achieve even higher levels of accuracy using images from hospital
scanners
Spitzer Secondary Eclipse Observations of Five Cool Gas Giant Planets and Empirical Trends in Cool Planet Emission Spectra
In this work we present Spitzer 3.6 and 4.5 micron secondary eclipse
observations of five new cool (<1200 K) transiting gas giant planets:
HAT-P-19b, WASP-6b, WASP-10b, WASP-39b, and WASP-67b. We compare our measured
eclipse depths to the predictions of a suite of atmosphere models and to
eclipse depths for planets with previously published observations in order to
constrain the temperature- and mass-dependent properties of gas giant planet
atmospheres. We find that the dayside emission spectra of planets less massive
than Jupiter require models with efficient circulation of energy to the night
side and/or increased albedos, while those with masses greater than that of
Jupiter are consistently best-matched by models with inefficient circulation
and low albedos. At these relatively low temperatures we expect the atmospheric
methane to CO ratio to vary as a function of metallicity, and we therefore use
our observations of these planets to constrain their atmospheric metallicities.
We find that the most massive planets have dayside emission spectra that are
best-matched by solar metallicity atmosphere models, but we are not able to
place strong constraints on metallicities of the smaller planets in our sample.
Interestingly, we find that the ratio of the 3.6 and 4.5 micron brightness
temperatures for these cool transiting planets is independent of planet
temperature, and instead exhibits a tentative correlation with planet mass. If
this trend can be confirmed, it would suggest that the shape of these planets'
emission spectra depends primarily on their masses, consistent with the
hypothesis that lower-mass planets are more likely to have metal-rich
atmospheres.Comment: 16 pages, 14 figures, accepted for publication in Ap
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