454 research outputs found
Exoplanet Biosignatures: Observational Prospects
Exoplanet hunting efforts have revealed the prevalence of exotic worlds with
diverse properties, including Earth-sized bodies, which has fueled our endeavor
to search for life beyond the Solar System. Accumulating experiences in
astrophysical, chemical, and climatological characterization of uninhabitable
planets are paving the way to characterization of potentially habitable
planets. In this paper, we review our possibilities and limitations in
characterizing temperate terrestrial planets with future observational
capabilities through 2030s and beyond, as a basis of a broad range of
discussions on how to advance "astrobiology" with exoplanets. We discuss the
observability of not only the proposed biosignature candidates themselves, but
also of more general planetary properties that provide circumstantial evidence,
since the evaluation of any biosignature candidate relies on their context.
Characterization of temperate Earth-size planets in the coming years will focus
on those around nearby late-type stars. JWST and later 30 meter-class
ground-based telescopes will empower their chemical investigations.
Spectroscopic studies of potentially habitable planets around solar-type stars
will likely require a designated spacecraft mission for direct imaging,
leveraging technologies that are already being developed and tested as part of
the WFIRST mission. Successful initial characterization of a few nearby targets
will be an important touchstone toward a more detailed scrutiny and a larger
survey that are envisioned beyond 2030. The broad outlook this paper presents
may help develop new observational techniques to detect relevant features as
well as frameworks to diagnose planets based on the observables.Comment: part of a series of 5 review manuscripts of the NExSS Exoplanet
Biosgnatures Worksho
Reliability and Validity of the Child and Adolescent Functioning Impairment Scale in Children with Attention-Deficit/Hyperactivity Disorder
Prediction of equilibrium Li isotope fractionation between minerals and aqueous solutions at high P and T: an efficient ab initio approach
The mass-dependent equilibrium stable isotope fractionation between different
materials is an important geochemical process. Here we present an efficient
method to compute the isotope fractionation between complex minerals and fluids
at high pressure, P, and temperature, T, representative for the Earth's crust
and mantle. The method is tested by computation of the equilibrium
fractionation of lithium isotopes between aqueous fluids and various Li bearing
minerals such as staurolite, spodumene and mica. We are able to correctly
predict the direction of the isotope fractionation as observed in the
experiments. On the quantitative level the computed fractionation factors agree
within 1.0 permil with the experimental values indicating predictive power of
ab initio methods. We show that with ab initio methods we are able to
investigate the underlying mechanisms driving the equilibrium isotope
fractionation process, such as coordination of the fractionating elements,
their bond strengths to the neighboring atoms, compression of fluids and
thermal expansion of solids. This gives valuable insight into the processes
governing the isotope fractionation mechanisms on the atomic scale. The method
is applicable to any state and does not require different treatment of crystals
and fluids.Comment: 14 pages, 10 figures, accepted for publication in Geochimica et
Cosmochimica Act
Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment
Here we review how environmental context can be used to interpret whether O2
is a biosignature in extrasolar planetary observations. This paper builds on
the overview of current biosignature research discussed in Schwieterman et al.
(2017), and provides an in-depth, interdisciplinary example of biosignature
identification and observation that serves as a basis for the development of
the general framework for biosignature assessment described in Catling et al.,
(2017). O2 is a potentially strong biosignature that was originally thought to
be an unambiguous indicator for life at high-abundance. We describe the
coevolution of life with the early Earth's environment, and how the interplay
of sources and sinks in the planetary environment may have resulted in
suppression of O2 release into the atmosphere for several billion years, a
false negative for biologically generated O2. False positives may also be
possible, with recent research showing potential mechanisms in exoplanet
environments that may generate relatively high abundances of atmospheric O2
without a biosphere being present. These studies suggest that planetary
characteristics that may enhance false negatives should be considered when
selecting targets for biosignature searches. Similarly our ability to interpret
O2 observed in an exoplanetary atmosphere is also crucially dependent on
environmental context to rule out false positive mechanisms. We describe future
photometric, spectroscopic and time-dependent observations of O2 and the
planetary environment that could increase our confidence that any observed O2
is a biosignature, and help discriminate it from potential false positives. By
observing and understanding O2 in its planetary context we can increase our
confidence in the remote detection of life, and provide a model for
biosignature development for other proposed biosignatures.Comment: 55 pages. The paper is the second in a series of 5 review manuscripts
of the NExSS Exoplanet Biosignatures Workshop. Community commenting is
solicited at https://nexss.info/groups/ebww
Ventricular pacing or dual-chamber pacing for sinus-node dysfunction
BACKGROUND
Dual-chamber (atrioventricular) and single-chamber (ventricular) pacing are alternative treatment approaches for sinus-node dysfunction that causes clinically significant bradycardia. However, it is unknown which type of pacing results in the better outcome. METHODS
We randomly assigned a total of 2010 patients with sinus-node dysfunction to dual-chamber pacing (1014 patients) or ventricular pacing (996 patients) and followed them for a median of 33.1 months. The primary end point was death from any cause or nonfatal stroke. Secondary end points included the composite of death, stroke, or hospitalization for heart failure; atrial fibrillation; heart-failure score; the pacemaker syndrome; and the quality of life. RESULTS
The incidence of the primary end point did not differ significantly between the dual-chamber group (21.5 percent) and the ventricular-paced group (23.0 percent, P=0.48). In patients assigned to dual-chamber pacing, the risk of atrial fibrillation was lower (hazard ratio, 0.79; 95 percent confidence interval, 0.66 to 0.94; P=0.008), and heart-failure scores were better (P CONCLUSIONS
In sinus-node dysfunction, dual-chamber pacing does not improve stroke-free survival, as compared with ventricular pacing. However, dual-chamber pacing reduces the risk of atrial fibrillation, reduces signs and symptoms of heart failure, and slightly improves the quality of life. Overall, dual-chamber pacing offers significant improvement as compared with ventricular pacing
The cytolinker plectin regulates nuclear mechanotransduction in keratinocytes.
The transmission of mechanical forces to the nucleus is important for intracellular positioning, mitosis and cell motility, yet the contribution of specific components of the cytoskeleton to nuclear mechanotransduction remains unclear. In this study, we examine how crosstalk between the cytolinker plectin and F-actin controls keratin network organisation and the 3D nuclear morphology of keratinocytes. Using micro-patterned surfaces to precisely manipulate cell shape, we find that cell adhesion and spreading regulate the size and shape of the nucleus. Disruption of the keratin cytoskeleton through loss of plectin facilitated greater nuclear deformation, which depended on acto-myosin contractility. Nuclear morphology did not depend on direct linkage of the keratin cytoskeleton with the nuclear membrane, rather loss of plectin reduced keratin filament density around the nucleus. We further demonstrate that keratinocytes have abnormal nuclear morphologies in the epidermis of plectin-deficient, epidermolysis bullosa simplex patients. Taken together, our data demonstrate that plectin is an essential regulator of nuclear morphology in vitro and in vivo and protects the nucleus from mechanical deformation.This work was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) [grant number BB/J000914/1]; and by the Barts and the London Charity [grant number 442/1032]
Hyperbrain features of team mental models within a juggling paradigm: a proof of concept
Background
Research on cooperative behavior and the social brain exists, but little research has focused on real-time motor cooperative behavior and its neural correlates. In this proof of concept study, we explored the conceptual notion of shared and complementary mental models through EEG mapping of two brains performing a real-world interactive motor task of increasing difficulty. We used the recently introduced participative “juggling paradigm,” and collected neuro-physiological and psycho-social data. We were interested in analyzing the between-brains coupling during a dyadic juggling task, and in exploring the relationship between the motor task execution, the jugglers’skill level and the task difficulty. We also investigated how this relationship could be mirrored in the coupled functional organization of the interacting brains.
Methods
To capture the neural schemas underlying the notion of shared and complementary mental models, we examined the functional connectivity patterns and hyperbrain features of a juggling dyad involved in cooperative motor tasks of increasing difficulty. Jugglers’ cortical activity was measured using two synchronized 32-channel EEG systems during dyadic juggling performed with 3, 4, 5 and 6 balls. Individual and hyperbrain functional connections were quantified through coherence maps calculated across all electrode pairs in the theta and alpha bands (4–8 and 8–12 Hz). Graph metrics were used to typify the global topology and efficiency of the functional networks for the four difficulty levels in the theta and alpha bands.
Results
Results indicated that, as task difficulty increased, the cortical functional organization of the more skilled juggler became progressively more segregated in both frequency bands, with a small-world organization in the theta band during easier tasks, indicative of a flow-like state in line with the neural efficiency hypothesis. Conversely, more integrated functional patterns were observed for the less skilled juggler in both frequency bands, possibly related to cognitive overload due to the difficulty of the task at hand (reinvestment hypothesis). At the hyperbrain level, a segregated functional organization involving areas of the visuo-attentional networks of both jugglers was observed in both frequency bands and for the easier task only.
Discussion
These results suggest that cooperative juggling is supported by integrated activity of specialized cortical areas from both brains only during easier tasks, whereas it relies on individual skills, mirrored in uncorrelated individual brain activations, during more difficult tasks. These findings suggest that task difficulty and jugglers’ personal skills may influence the features of the hyperbrain network in its shared/integrative and complementary/segregative tendencies
The twilight of the Liberal Social Contract? On the Reception of Rawlsian Political Liberalism
This chapter discusses the Rawlsian project of public reason, or public justification-based 'political' liberalism, and its reception. After a brief philosophical rather than philological reconstruction of the project, the chapter revolves around a distinction between idealist and realist responses to it. Focusing on political liberalism’s critical reception illuminates an overarching question: was Rawls’s revival of a contractualist approach to liberal legitimacy a fruitful move for liberalism and/or the social contract tradition? The last section contains a largely negative answer to that question. Nonetheless the chapter's conclusion shows that the research programme of political liberalism provided and continues to provide illuminating insights into the limitations of liberal contractualism, especially under conditions of persistent and radical diversity. The programme is, however, less receptive to challenges to do with the relative decline of the power of modern states
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