711 research outputs found
Critical core mass for enriched envelopes: the role of H2O condensation
Context. Within the core accretion scenario of planetary formation, most
simulations performed so far always assume the accreting envelope to have a
solar composition. From the study of meteorite showers on Earth and numerical
simulations, we know that planetesimals must undergo thermal ablation and
disruption when crossing a protoplanetary envelope. Once the protoplanet has
acquired an atmosphere, the primordial envelope gets enriched in volatiles and
silicates from the planetesimals. This change of envelope composition during
the formation can have a significant effect in the final atmospheric
composition and on the formation timescale of giant planets.
Aims. To investigate the physical implications of considering the envelope
enrichment of protoplanets due to the disruption of icy planetesimals during
their way to the core. Particular focus is placed on the effect on the critical
core mass for envelopes where condensation of water can occur.
Methods. Internal structure models are numerically solved with the
implementation of updated opacities for all ranges of metallicities and the
software CEA to compute the equation of state. CEA computes the chemical
equilibrium for an arbitrary mixture of gases and allows the condensation of
some species, including water. This means that the latent heat of phase
transitions is consistently incorporated in the total energy budget.
Results. The critical core mass is found to decrease significantly when an
enriched envelope composition is considered in the internal structure
equations. A particular strong reduction of the critical core mass is obtained
for planets whose envelope metallicity is larger than Z=0.45 when the outer
boundary conditions are suitable for condensation of water to occur in the top
layers of the atmosphere. We show that this effect is qualitatively preserved
when the atmosphere is out of chemical equilibrium.Comment: Accepted for publication in A&
Orbital Evolution of Planets around Intermediate-Mass Giants
Around low- and intermediate-mass (1.5-3 M_sun) red giants, no planets have
been found inside 0.6 AU. Such a paucity is not seen in the case of 1 M_sun
main sequence stars. In this study, we examine the possibility that
short-period planets were engulfed by their host star evolving off the main
sequence. To do so, we have simulated the orbital evolution of planets,
including the effects of stellar tide and mass loss, to determine the critical
semimajor axis, a_crit, beyond which planets survive the RGB expansion of their
host star. We have found that a_crit changes drastically around 2 M_sun: In the
lower-mass range, a_crit is more than 1 AU, while a_crit is as small as about
0.2 AU in the higher-mass range. Comparison with measured semimajor axes of
known planets suggests that there is a lack of planets that only planet
engulfment never accounts for in the higher-mass range. Whether the lack is
real affects our understanding of planet formation. Therefore, increasing the
number of planet samples around evolved intermediate-mass stars is quite
meaningful to confirm robustness of the lack of planets.Comment: 4 pages, 3 figures, Part of PlanetsbeyondMS/2010 proceedings
http://arxiv.org/html/1011.660
Ductal-cutaneous fistula secondary to recurrent Bartholinās cysts: a case report
Background: Disorders of the Bartholinās duct and gland, including cyst and abscess formation, account for 2% of gynecologic visits annually. An uncommon complication of a Bartholinās duct or gland abscess is fistula formation. Literature has described cases of recto-Bartholinās and recto-vaginal fistulas. Case: We present a case of fistula development between the perineum and the Bartholinās duct and gland. The patient was successfully managed with fistulectomy and Bartholinās gland excision. Conclusion: Though fistula formation is a rare complication of Bartholinās duct and gland pathology, investigation is warranted. A ductal-cutaneous fistula is possible in the setting of recurrent cysts located beyond the vaginal introitus. The best method of prevention is appropriate execution of a marsupialization. Complete removal of the fistulous tract and Bartholinās duct and/or gland can result in resolution of symptoms
The naked planet Earth: Most essential pre-requisite for the origin and evolution of life
AbstractOur blue planet Earth has long been regarded to carry full of nutrients for hosting life since the birth of the planet. Here we speculate the processes that led to the birth of early life on Earth and its aftermath, finally leading to the evolution of metazoans. We evaluate: (1) the source of nutrients, (2) the chemistry of primordial ocean, (3) the initial mass of ocean, and (4) the size of planet. Among the life-building nutrients, phosphorus and potassium play a key role. Only three types of rocks can serve as an adequate source of nutrients: (a) continent-forming TTG (granite), enabling the evolution of primitive life to metazoans; (b) primordial continents carrying anorthosite with KREEP (Potassium, Rare Earth Elements, and Phosphorus) basalts, which is a key to bear life; (c) carbonatite magma, enriched in radiogenic elements such as U and Th, which can cause mutation to speed up evolution and promote the birth of new species in continental rift settings. The second important factor is ocean chemistry. The primordial ocean was extremely acidic (pHĀ =Ā 1ā2) and enriched in halogens (Cl, F and others), S, N and metallic elements (Cd, Cu, Zn, and others), inhibiting the birth of life. Plate tectonics cleaned up these elements which interfered with RNA. Blue ocean finally appeared in the Phanerozoic with pHĀ =Ā 7 through extensive interaction with surface continental crust by weathering, erosion and transportation into ocean. The initial ocean mass was also important. The birth of life and aftermath of evolution was possible in the habitable zone with 3ā5 km deep ocean which was able to supply sufficient nutrients. Without a huge landmass, nutrients cannot be supplied into the ocean only by ridge-hydrothermal circulation in the Hadean. Finally, the size of the planet plays a crucial role. Cooling of massive planets is less efficient than smaller ones, so that return-flow of seawater into mantle does not occur until central stars finish their main sequence. Due to the suitable size of Earth, the dawn of Phanerozoic witnessed the initiation of return-flow of seawater into the mantle, leading to the emergence of huge landmass above sea-level, and the distribution of nutrients on a global scale. Oxygen pump also played a critical role to keep high-PO2 in atmosphere since then, leading to the emergence of ozone layer and enabling animals and plants to invade the land.To satisfy the tight conditions to make the Earth habitable, the formation mechanism of primordial Earth is an important factor. At first, a ādry Earthā must be made through giant impact, followed by magma ocean to float nutrient-enriched primordial continents (anorthosite + KREEP). Late bombardment from asteroid belt supplied water to make 3ā5 km thick ocean, and not from icy meteorites from Kuiper belt beyond cool Jupiter. It was essential to meet the above conditions that enabled the Earth as a habitable planet with evolved life forms. The tight constraints that we evaluate for birth and evolution of life on Earth would provide important guidelines for planetary scientists hunting for life in the exo-solar planets
Comparison of Reliable Change Indices of CNS Vital Signs for Different Ranges of Baseline Scores
Computerized neurocognitive tests are widely used in the management of sport-related concussion. Many of these assessments use reliable change confidence intervalsācomputed as baseline score Ā± reliable change index (RCI)āto classify an individual as impaired or unimpaired at a follow-up test point. If an individualās retest score falls outside of the reliable change confidence interval on a given domain, he or she is classified as impaired on that domain. The purpose of this study was to compare RCIs for three different ranges of CNS Vital Signs baseline scores: the lowest quintile (0-20th percentile), middle quintile (40-60th percentile), and highest quintile (80-100th percentile). One-hundred seven Division I student-athletes completed baseline and follow-up computerized neurocognitive testing on CNS Vital Signs and were divided into quintile groups based on their baseline score for each clinical domain. RCIs were computed for the lowest, middle, and highest quintiles for each domain. Overall group RCIs were also computed. The RCIs varied considerably across the quintile groups, with average and high baseline performers tending to have smaller RCIs than low baseline performers and the full group in each domain. In addition, significant interaction effects of time and quintile group were found for several domains as well as for Neurocognition Index. These results suggest that it is important for clinicians to consider an individualās baseline performance level when interpreting CNS Vital Signs neurocognitive test results using a baseline/post-injury comparison model.Bachelor of Scienc
Detectability of Rocky-Vapour atmospheres on super-Earths with Ariel
Ariel will mark the dawn of a new era as the first large-scale survey characterising exoplanetary atmospheres with science objectives to address fundamental questions about planetary composition, evolution and formation. In this study, we explore the detectability of atmospheres vaporised from magma oceans on dry, rocky Super-Earths orbiting very close to their host stars. The detection of such atmospheres would provide a definitive piece of evidence for rocky planets but are challenging measurements with currently available instruments due to their small spectral signatures. However, some of the hottest planets are believed to have atmospheres composed of vaporised rock, such as Na and SiO, with spectral signatures bright enough to be detected through eclipse observations with planned space-based telescopes. In this study, we find that rocky super-Earths with a irradiation temperature of 3000 K and a distance from Earth of up to 20 pc, as well as planets hotter than 3500 K and closer than 50 pc, have SiO features which are potentially detectable in eclipse spectra observed with Ariel
Formation of giant planets around stars with various masses
We examine the predictions of the core accretion - gas capture model
concerning the efficiency of planet formation around stars with various masses.
First, we follow the evolution of gas and solids from the moment when all
solids are in the form of small grains to the stage when most of them are in
the form of planetesimals. We show that the surface density of the planetesimal
swarm tends to be higher around less massive stars. Then, we derive the minimum
surface density of the planetesimal swarm required for the formation of a giant
planet both in a numerical and in an approximate analytical approach. We
combine these results by calculating a set of representative disk models
characterized by different masses, sizes, and metallicities, and by estimating
their capability of forming giant planets. Our results show that the set of
protoplanetary disks capable of giant planet formation is larger for less
massive stars. Provided that the distribution of initial disk parameters does
not depend too strongly on the mass of the central star, we predict that the
percentage of stars with giant planets should increase with decreasing stellar
mass. Furthermore, we identify the radial redistribution of solids during the
formation of planetesimal swarms as the key element in explaining these
effects.Comment: Accepted for publication in A&A. 9 pages, 9 figure
TRPV1-expressing primary afferents generate behavioral responses to pruritogens via multiple mechanisms
The mechanisms that generate itch are poorly understood at both the molecular and cellular levels despite its clinical importance. To explore the peripheral neuronal mechanisms underlying itch, we assessed the behavioral responses (scratching) produced by s.c. injection of various pruritogens in PLCĪ²3- or TRPV1-deficient mice. We provide evidence that at least 3 different molecular pathways contribute to the transduction of itch responses to different pruritogens: 1) histamine requires the function of both PLCĪ²3 and the TRPV1 channel; 2) serotonin, or a selective agonist, Ī±-methyl-serotonin (Ī±-Me-5-HT), requires the presence of PLCĪ²3 but not TRPV1, and 3) endothelin-1 (ET-1) does not require either PLCĪ²3 or TRPV1. To determine whether the activity of these molecules is represented in a particular subpopulation of sensory neurons, we examined the behavioral consequences of selectively eliminating 2 nonoverlapping subsets of nociceptors. The genetic ablation of MrgprD^+ neurons that represent ā90% of cutaneous nonpeptidergic neurons did not affect the scratching responses to a number of pruritogens. In contrast, chemical ablation of the central branch of TRPV1+ nociceptors led to a significant behavioral deficit for pruritogens, including Ī±-Me-5-HT and ET-1, that is, the TRPV1-expressing nociceptor was required, whether or not TRPV1 itself was essential. Thus, TRPV1 neurons are equipped with multiple signaling mechanisms that respond to different pruritogens. Some of these require TRPV1 function; others use alternate signal transduction pathways
Migration then assembly: Formation of Neptune mass planets inside 1 AU
We demonstrate that the observed distribution of `Hot Neptune'/`Super-Earth'
systems is well reproduced by a model in which planet assembly occurs in situ,
with no significant migration post-assembly. This is achieved only if the
amount of mass in rocky material is -- interior to 1
AU. Such a reservoir of material implies that significant radial migration of
solid material takes place, and that it occur before the stage of final planet
assembly.
The model not only reproduces the general distribution of mass versus period,
but also the detailed statistics of multiple planet systems in the sample.
We furthermore demonstrate that cores of this size are also likely to meet
the criterion to gravitationally capture gas from the nebula, although
accretion is rapidly limited by the opening of gaps in the gas disk. If the
mass growth is limited by this tidal truncation, then the scenario sketched
here naturally produces Neptune-mass objects with substantial components of
both rock and gas, as is observed.
The quantitative expectations of this scenario are that most planets in the
`Hot Neptune/Super-Earth' class inhabit multiple-planet systems, with
characteristic orbital spacings. The model also provides a natural division
into gas-rich (Hot Neptune) and gas-poor (Super-Earth) classes at fixed period.
The dividing mass ranges from at 10 day orbital periods to
at 100 day orbital periods. For orbital periods
days, the division is less clear because a gas atmosphere may be significantly
eroded by stellar radiation.Comment: 41 pages in preprint style, 15 figures, final version accepted to Ap
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