867 research outputs found
Influence of viscosity and the adiabatic index on planetary migration
The strength and direction of migration of low mass embedded planets depends
on the disk's thermodynamic state, where the internal dissipation is balanced
by radiative transport, and the migration can be directed outwards, a process
which extends the lifetime of growing embryos. Very important parameters
determining the structure of disks, and hence the direction of migration, are
the viscosity and the adiabatic index. In this paper we investigate the
influence of different viscosity prescriptions (alpha-type and constant) and
adiabatic indices on disk structures and how this affects the migration rate of
planets embedded in such disks. We perform 3D numerical simulations of
accretion disks with embedded planets. We use the explicit/implicit
hydrodynamical code NIRVANA that includes full tensor viscosity and radiation
transport in the flux-limited diffusion approximation, as well as a proper
equation of state for molecular hydrogen. The migration of embedded 20Earthmass
planets is studied. Low-viscosity disks have cooler temperatures and the
migration rates of embedded planets tend toward the isothermal limit. In these
disks, planets migrate inwards even in the fully radiative case. The effect of
outward migration can only be sustained if the viscosity in the disk is large.
Overall, the differences between the treatments for the equation of state seem
to play a more important role in disks with higher viscosity. A change in the
adiabatic index and in the viscosity changes the zero-torque radius that
separates inward from outward migration. For larger viscosities, temperatures
in the disk become higher and the zero-torque radius moves to larger radii,
allowing outward migration of a 20 Earth-mass planet to persist over an
extended radial range. In combination with large disk masses, this may allow
for an extended period of the outward migration of growing protoplanetary
cores
Genomics of a Metamorphic Timing QTL: Met1 Maps to a Unique Genomic Position and Regulates Morph and Species-Specific Patterns of Brain Transcription
Very little is known about genetic factors that regulate life history transitions during ontogeny. Closely related tiger salamanders (Ambystoma species complex) show extreme variation in metamorphic timing, with some species foregoing metamorphosis altogether, an adaptive trait called paedomorphosis. Previous studies identified a major effect quantitative trait locus (met1) for metamorphic timing and expression of paedomorphosis in hybrid crosses between the biphasic Eastern tiger salamander (Ambystoma tigrinum tigrinum) and the paedomorphic Mexican axolotl (Ambystoma mexicanum). We used existing hybrid mapping panels and a newly created hybrid cross to map the met1 genomic region and determine the effect of met1 on larval growth, metamorphic timing, and gene expression in the brain. We show that met1 maps to the position of a urodele-specific chromosome rearrangement on linkage group 2 that uniquely brought functionally associated genes into linkage. Furthermore, we found that more than 200 genes were differentially expressed during larval development as a function of met1 genotype. This list of differentially expressed genes is enriched for proteins that function in the mitochondria, providing evidence of a link between met1, thyroid hormone signaling, and mitochondrial energetics associated with metamorphosis. Finally, we found that met1 significantly affected metamorphic timing in hybrids, but not early larval growth rate. Collectively, our results show that met1 regulates species and morph-specific patterns of brain transcription and life history variation
Genomics of a metamorphic timing QTL: \u3ci\u3emet1\u3c/i\u3e maps to a unique genomic position and regulates morph and species-specific patterns of brain transcription
Very little is known about genetic factors that regulate life history transitions during ontogeny. Closely related tiger salamanders (Ambystoma species complex) show extreme variation in metamorphic timing, with some species foregoing metamorphosis altogether, an adaptive trait called paedomorphosis. Previous studies identified a major effect QTL (met1) for metamorphic timing and expression of paedomorphosis in hybrid crosses between the biphasic Eastern tiger salamander (Ambystoma tigrinum tigrinum) and the paedomorphic Mexican axolotl (Ambystoma mexicanum). We used existing hybrid mapping panels and a newly created hybrid cross to map the met1 genomic region and determine the effect of met1 on larval growth, metamorphic timing, and gene expression in the brain. We show that met1 maps to the position of a urodele specific chromosome rearrangement on linkage group 2 that uniquely brought functionally-associated genes into linkage. Further, we found that \u3e 200 genes were differentially expressed during larval development as a function of met1 genotype. This list of differentially expressed genes is enriched for proteins that function in the mitochondria, providing evidence of a link between met1, thyroid hormone signaling, and mitochondrial energetics associated with metamorphosis. Finally, we found that met1 significantly affected metamorphic timing in hybrids, but not early larval growth rate. Collectively, our results show that met1 regulates species and morph-specific patterns of brain transcription and life history variation
Recommended from our members
Pro-tobacco marketing and anti-tobacco campaigns aimed at vulnerable populations: A review of the literature.
INTRODUCTION:We reviewed research literature on pro-tobacco marketing and anti-tobacco campaigns targeting eight vulnerable populations to determine key findings and research gaps. Results can inform tobacco policy and control efforts and the design of public education campaigns for these groups. METHODS:Five journal databases in medicine, communication, and science, were used to identify 8875 peer-reviewed, original articles in English, published in the period 2004-2018. There were 144 articles that met inclusion criteria on pro-tobacco marketing or anti-tobacco campaigns aimed at eight US groups: women of reproductive age, racial/ethnic minority groups (African American, Hispanic/Latino, Asian/Pacific Islander and American Indian/Alaska Native), Lesbian/Gay/Bisexual/Transgender (LGBT) populations, groups with low socioeconomic status, rural/inner city residents, military/veterans, and people with mental health or medical co-morbidities. We summarized the number of articles for each population, type of tobacco, and pro-tobacco or anti-tobacco focus. Narrative summaries were organized by population and by pro-tobacco or anti-tobacco focus, with key strategies and gaps by group. RESULTS:There were more studies on pro-tobacco marketing rather than anti-tobacco campaigns, and on cigarettes rather than other tobacco products. Major gaps included studies on Asian Americans, American Indian/Alaska Natives, pregnant women, LGBT populations, and those with mental health or medical co-morbidities. Gaps related to tobacco products were found for hookah, snus, and pipe/roll-your-own tobacco in the pro-tobacco studies, and for all products except cigarettes in anti-tobacco studies. Common tobacco industry methods used were tailoring of product and package design and messages that were used to reach and appeal to different sociodemographic groups. Studies varied by research design making it difficult to compare results. CONCLUSIONS:We found major research gaps for specific groups and tobacco products. Public education campaigns need a stronger foundation in empirical studies focused on these populations. Research and practice would benefit from studies that permit comparisons across studies
The VLTI/MIDI survey of massive young stellar objects - Sounding the inner regions around intermediate- and high-mass young stars using mid-infrared interferometry
We aim to characterize the distribution and composition of circumstellar
material around young massive stars, and to investigate exactly which physical
structures in these objects are probed by long-baseline mid-infrared
interferometric observations. We used the two-telescope interferometric
instrument MIDI of the Very Large Telescope Interferometer of the European
Southern Observatory to observe a sample of 24 intermediate- and high-mass
young stellar objects in the N band (8-13 micron). We had successful fringe
detections for 20 objects, and present spectrally-resolved correlated fluxes
and visibility levels for projected baselines of up to 128 m. We fit the
visibilities with geometric models to derive the sizes of the emitting regions,
as well as the orientation and elongation of the circumstellar material.
Fourteen objects in the sample show the 10 micron silicate feature in
absorption in the total and correlated flux spectra. For 13 of these objects,
we were able to fit the correlated flux spectra with a simple absorption model,
allowing us to constrain the composition and absorptive properties of the
circumstellar material. Nearly all of the massive young stellar objects
observed show significant deviations from spherical symmetry at mid-infrared
wavelengths. In general, the mid-infrared emission can trace both disks and
outflows, and in many cases it may be difficult to disentangle these components
on the basis of interferometric data alone, because of the sparse spatial
frequency coverage normally provided by current long-baseline interferometers.
For the majority of the objects in this sample, the absorption occurs on
spatial scales larger than those probed by MIDI. Finally, the physical extent
of the mid-infrared emission around these sources is correlated with the total
luminosity, albeit with significant scatter.Comment: 36 pages, 22 figures. Accepted to Astronomy and Astrophysic
Hydraulic/Shock-Jumps in Protoplanetary Disks
In this paper, we describe the nonlinear outcome of spiral shocks in
protoplanetary disks. Spiral shocks, for most protoplanetary disk conditions,
create a loss of vertical force balance in the post-shock region and result in
rapid expansion of the gas perpendicular to the disk midplane. This expansion
has characteristics similar to hydraulic jumps, which occur in incompressible
fluids. We present a theory to describe the behavior of these hybrids between
shocks and hydraulic jumps (shock bores) and then compare the theory to
three-dimensional hydrodynamics simulations. We discuss the fully
three-dimensional shock structures that shock bores produce and discuss
possible consequences for disk mixing, turbulence, and evolution of solids.Comment: 39 pages, 18 figures, 1 table. Edited to match as closely as possible
the ApJ proofs, which resulted in the correction of several typos. In
addition, section 5.3 was slightly altered because an error in an analysis
tool was discovered; the differences between the entropy gradient method and
the Schwarzschild criterion method are minor. Figure 18 now only includes
what was Figure18
- …