3,275 research outputs found
The nature and origins of sub-Neptune size planets
Planets intermediate in size between the Earth and Neptune, and orbiting closer to their host stars than Mercury does the Sun, are the most common type of planet revealed by exoplanet surveys over the last quarter century. Results from NASA's Kepler mission have revealed a bimodality in the radius distribution of these objects, with a relative underabundance of planets between 1.5 and 2.0 urn:x-wiley:21699097:media:jgre21507:jgre21507-math-0001. This bimodality suggests that subâNeptunes are mostly rocky planets that were born with primary atmospheres a few percent by mass accreted from the protoplanetary nebula. Planets above the radius gap were able to retain their atmospheres (âgasârich superâEarthsâ), while planets below the radius gap lost their atmospheres and are stripped cores (âtrue superâEarthsâ). The mechanism that drives atmospheric loss for these planets remains an outstanding question, with photoevaporation and coreâpowered mass loss being the prime candidates. As with the massâloss mechanism, there are two contenders for the origins of the solids in subâNeptune planets: the migration model involves the growth and migration of embryos from beyond the ice line, while the drift model involves inwardâdrifting pebbles that coagulate to form planets closeâin. Atmospheric studies have the potential to break degeneracies in interior structure models and place additional constraints on the origins of these planets. However, most atmospheric characterization efforts have been confounded by aerosols. Observations with upcoming facilities are expected to finally reveal the atmospheric compositions of these worlds, which are arguably the first fundamentally new type of planetary object identified from the study of exoplanets
The Teleost Retina as a Model for Developmental and Regeneration Biology
Retinal development in teleosts can broadly be divided into three epochs. The first is the specification of cellular domains in the larval forebrain that give rise to the retinal primordia and undergo early morphogenetic movements. The second is the neurogenic events within the retina properâproliferation, cell fate determination, and pattern formationâthat establish neuronal identities and form retinal laminae and cellular mosaics. The third, which is unique to teleosts and occurs in the functioning eye, is stretching of the retina and persistent neurogenesis that allows the growth of the retina to keep pace with the growth of the eye and other tissues. The first two events are rapid, complete by about 3 days postfertilization in the zebrafish embryo. The third is life-long and accounts for the bulk of retinal growth and the vast majority of adult retinal neurons. In addition, but clearly related to the retina's developmental history, lesions that kill retinal neurons elicit robust neuronal regeneration that originates from cells intrinsic to the retina. This paper reviews recent studies of retinal development in teleosts, focusing on those that shed light on the genetic and molecular regulation of retinal specification and morphogenesis in the embryo, retinal neurogenesis in larvae and adults, and injury-induced neuronal regeneration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63365/1/zeb.2004.1.257.pd
Ubiquitin-dependent proteasomal degradation of AMPK gamma subunit by Cereblon inhibits AMPK activity
Cereblon (CRBN), a substrate receptor for Cullin-ring E3 ubiquitin ligase (CRL), is a major target protein of immunomodulatory drugs. An earlier study demonstrated that CRBN directly interacts with the catalytic α subunit of AMP-activated protein kinase (AMPK), a master regulator of energy homeostasis, down-regulating the enzymatic activity of AMPK. However, it is not clear how CRBN modulates AMPK activity. To investigate the mechanism of CRBN-dependent AMPK inhibition, we measured protein levels of each AMPK subunit in brains, livers, lungs, hearts, spleens, skeletal muscles, testes, kidneys, and embryonic fibroblasts from wild-type and Crbn^(â/â) mice. Protein levels and stability of the regulatory AMPKÎł subunit were increased in Crbn^(â/â) mice. Increased stability of AMPKÎł in Crbn^(â/â) MEFs was dramatically reduced by exogenous expression of Crbn. In wild-type MEFs, the proteasomal inhibitor MG132 blocked degradation of AMPKÎł. We also found that CRL4^(CRBN) directly ubiquitinated AMPKÎł. Taken together, these findings suggest that CRL4^(CRBN) regulates AMPK through ubiquitin-dependent proteasomal degradation of AMPKÎł
Ten Simple Rules for Getting Help from Online Scientific Communities
The increasing complexity of research requires scientists to work at the intersection of multiple fields and to face problems for which their formal education has not prepared them. For example, biologists with no or little background in programming are now often using complex scripts to handle the results from their experiments; vice versa, programmers wishing to enter the world of bioinformatics must know about biochemistry, genetics, and other fields.
In this context, communication tools such as mailing lists, web forums, and online communities acquire increasing importance. These tools permit scientists to quickly contact people skilled in a specialized field. A question posed properly to the right online scientific community can help in solving difficult problems, often faster than screening literature or writing to publication authors. The growth of active online scientific communities, such as those listed in Table S1, demonstrates how these tools are becoming an important source of support for an increasing number of researchers.
Nevertheless, making proper use of these resources is not easy. Adhering to the social norms of World Wide Web communicationâloosely termed ânetiquetteââis both important and non-trivial.
In this article, we take inspiration from our experience on Internet-shared scientific knowledge, and from similar documents such as âAsking the Questions the Smart Wayâ and âGetting Answersâ, to provide guidelines and suggestions on how to use online communities to solve scientific problems
The magnetic nature of disk accretion onto black holes
Although disk accretion onto compact objects - white dwarfs, neutron stars,
and black holes - is central to much of high energy astrophysics, the
mechanisms which enable this process have remained observationally elusive.
Accretion disks must transfer angular momentum for matter to travel radially
inward onto the compact object. Internal viscosity from magnetic processes and
disk winds can in principle both transfer angular momentum, but hitherto we
lacked evidence that either occurs. Here we report that an X-ray-absorbing wind
discovered in an observation of the stellar-mass black hole binary GRO J1655-40
must be powered by a magnetic process that can also drive accretion through the
disk. Detailed spectral analysis and modeling of the wind shows that it can
only be powered by pressure generated by magnetic viscosity internal to the
disk or magnetocentrifugal forces. This result demonstrates that disk accretion
onto black holes is a fundamentally magnetic process.Comment: 15 pages, 2 color figures, accepted for publication in Nature.
Supplemental materials may be obtained by clicking
http://www.astro.lsa.umich.edu/~jonmm/nature1655.p
Temporal perception deficits in schizophrenia: integration is the problem, not deployment of attentions
Patients with schizophrenia are known to have impairments in sensory processing. In order
to understand the specific temporal perception deficits of schizophrenia, we investigated and determined to what extent impairments in temporal integration can be dissociated from attention deployment using Attentional Blink (AB). Our findings showed that there was no evident deficit in the deployment of attention in patients with schizophrenia. However, patients showed an increased temporal integration deficit within a hundred-millisecond timescale. The degree of such integration dysfunction was correlated with the clinical manifestations of schizophrenia. There was no difference between individuals with/without schizotypal personality disorder in temporal integration. Differently from previous studies using the AB, we did not find a significant impairment in deployment of attention in schizophrenia. Instead, we used both theoretical and empirical approaches to show
that previous findings (using the suppression ratio to correct for the baseline difference) produced a systematic exaggeration of the attention deficits. Instead, we modulated the perceptual difficulty of the task to bring the baseline levels of target detection between the groups into closer alignment. We found that the integration dysfunction rather than deployment of attention is clinically relevant, and thus should be an additional focus of research in schizophrenia
SPECULOOS exoplanet search and its prototype on TRAPPIST
One of the most significant goals of modern science is establishing whether
life exists around other suns. The most direct path towards its achievement is
the detection and atmospheric characterization of terrestrial exoplanets with
potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs),
i.e. very-low-mass stars and brown dwarfs with effective temperatures lower
than 2700 K, represent a unique opportunity to reach this goal within the next
decade. The potential of the transit method for detecting potentially habitable
Earth-sized planets around these objects is drastically increased compared to
Earth-Sun analogs. Furthermore, only a terrestrial planet transiting a nearby
UCD would be amenable for a thorough atmospheric characterization, including
the search for possible biosignatures, with near-future facilities such as the
James Webb Space Telescope. In this chapter, we first describe the physical
properties of UCDs as well as the unique potential they offer for the detection
of potentially habitable Earth-sized planets suitable for atmospheric
characterization. Then, we present the SPECULOOS ground-based transit survey,
that will search for Earth-sized planets transiting the nearest UCDs, as well
as its prototype survey on the TRAPPIST telescopes. We conclude by discussing
the prospects offered by the recent detection by this prototype survey of a
system of seven temperate Earth-sized planets transiting a nearby UCD,
TRAPPIST-1.Comment: Submitted as a chapter in the "Handbook of Exoplanets" (editors: H.
Deeg & J.A. Belmonte; Section Editor: N. Narita). 16 pages, 4 figure
Dutch translation and cross-cultural validation of the Adult Social Care Outcomes Toolkit (ASCOT)
Background: The Adult Social Care Outcomes Toolkit was developed to measure outcomes of social care in England. In this study, we translated the four level self-completion version (SCT-4) of the ASCOT for use in the Netherlands and performed a cross-cultural validation.
Methods: The ASCOT SCT-4 was translated into Dutch following international guidelines, including two forward and back translations. The resulting version was pilot tested among frail older adults using think-aloud interviews. Furthermore, using a subsample of the Dutch ACT-study, we investigated test-retest reliability and construct validity and compared response distributions with data from a comparable English study.
Results: The pilot tests showed that translated items were in general understood as intended, that most items were reliable, and that the response distributions of the Dutch translation and associations with other measures were comparable to the original English version. Based on the results of the pilot tests, some small modifications and a revision of the Dignity items were proposed for the final translation, which were approved by the ASCOT development team. The complete original English version and the final Dutch translation can be obtained after registration on the ASCOT website (http://www.pssru.ac.uk/ascot).
Conclusions: This study provides preliminary evidence that the Dutch translation of the ASCOT is valid, reliable and comparable to the original English version. We recommend further research to confirm the validity of the modified Dutch ASCOT translation
Planetary Dynamics and Habitable Planet Formation In Binary Star Systems
Whether binaries can harbor potentially habitable planets depends on several
factors including the physical properties and the orbital characteristics of
the binary system. While the former determines the location of the habitable
zone (HZ), the latter affects the dynamics of the material from which
terrestrial planets are formed (i.e., planetesimals and planetary embryos), and
drives the final architecture of the planets assembly. In order for a habitable
planet to form in a binary star system, these two factors have to work in
harmony. That is, the orbital dynamics of the two stars and their interactions
with the planet-forming material have to allow terrestrial planet formation in
the habitable zone, and ensure that the orbit of a potentially habitable planet
will be stable for long times. We have organized this chapter with the same
order in mind. We begin by presenting a general discussion on the motion of
planets in binary stars and their stability. We then discuss the stability of
terrestrial planets, and the formation of potentially habitable planets in a
binary-planetary system.Comment: 56 pages, 29 figures, chapter to appear in the book: Planets in
Binary Star Systems (Ed. N. Haghighipour, Springer publishing company
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