278 research outputs found
Gas flow around a planet embedded in a protoplanetary disc: the dependence on the planetary mass
The three-dimensional structure of the gas flow around a planet is thought to
influence the accretion of both gas and solid materials. In particular, the
outflow in the mid-plane region may prevent the accretion of the solid
materials and delay the formation of super-Earths' cores. However, it is not
yet understood how the nature of the flow field and outflow speed change as a
function of the planetary mass. In this study, we investigate the dependence of
gas flow around a planet embedded in a protoplanetary disc on the planetary
mass. Assuming an isothermal, inviscid gas disc, we perform three-dimensional
hydrodynamical simulations on the spherical polar grid, which has a planet
located at its centre. We find that gas enters the Bondi or Hill sphere at high
latitudes and exits through the mid-plane region of the disc regardless of the
assumed dimensionless planetary mass , where
and are the Bondi radius of the planet and disc scale height, respectively.
The altitude from where gas predominantly enters the envelope varies with the
planetary mass. The outflow speed can be expressed as or (),
where is the isothermal sound speed and is the Hill
radius. The outflow around a planet may reduce the accretion of dust and
pebbles onto the planet when , where St is the Stokes
number. Our results suggest that the flow around proto-cores of super-Earths
may delay their growth and, consequently, help them to avoid runaway gas
accretion within the lifetime of the gas disc.Comment: 16 pages, 14 figures, Accepted for publication in Astronomy and
Astrophysics (A&A
Transcriptional regulation of the Drosophila moira and osa genes by the DREF pathway
The DNA replication-related element binding factor (DREF) plays an important role in regulation of cell proliferation in Drosophila, binding to DRE and activating transcription of genes carrying this element in their promoter regions. Overexpression of DREF in eye imaginal discs induces a rough eye phenotype in adults, which can be suppressed by half dose reduction of the osa or moira (mor) genes encoding subunits of the BRM complex. This ATP-dependent chromatin remodeling complex is known to control gene expression and the cell cycle. In the 5ā² flanking regions of the osa and mor genes, DRE and DRE-like sequences exist which contribute to their promoter activities. Expression levels and promoter activities of osa and mor are decreased in DREF knockdown cells and our results in vitro and in cultured cells indicate that transcription of osa and mor is regulated by the DRE/DREF regulatory pathway. In addition, mRNA levels of other BRM complex subunits and a target gene, string/cdc25, were found to be decreased by knockdown of DREF. These results indicate that DREF is involved in regulation of the BRM complex and thereby the cell cycle
Dust ring and gap formation by gas flow induced by low-mass planets embedded in protoplanetary disks . Steady-state model
Recent high-spatial-resolution observations have revealed dust substructures
in protoplanetary disks such as rings and gaps, which do not always correlate
with gas. Because radial gas flow induced by low-mass, non-gas-gap-opening
planets could affect the radial drift of dust, it potentially forms these dust
substructures in disks. We investigate the potential of gas flow induced by
low-mass planets to sculpt the rings and gaps in the dust profiles. We first
perform three-dimensional hydrodynamical simulations, which resolve the local
gas flow past a planet. We then calculate the trajectories of dust influenced
by the planet-induced gas flow. Finally, we compute the steady-state dust
surface density by incorporating the influences of the planet-induced gas flow
into a one-dimensional dust advection-diffusion model. The outflow of the gas
toward the outside of the planetary orbit inhibits the radial drift of dust,
leading to dust accumulation (the dust ring). The outflow toward the inside of
the planetary orbit enhances the inward drift of dust, causing dust depletion
around the planetary orbit (the dust gap). Under weak turbulence (, where is the turbulence strength
parameter), the gas flow induced by the planet with
(Earth mass) generates the dust ring and gap in the distribution of small dust
grains ( cm) with the radial extent of times gas
scale height around the planetary orbit without creating a gas gap and pressure
bump. The gas flow induced by low-mass, non-gas-gap-opening planets can be
considered a possible origin of the observed dust substructures in disks. Our
results may be helpful to explain the disks whose dust substructures were found
not to correlate with those of the gas.Comment: 25 pages, 20 figures, Accepted for publication in Astronomy and
Astrophysics (A&A
Spin of protoplanets generated by pebble accretion: Influences of protoplanet-induced gas flow
We investigate the spin state of a protoplanet during the pebble accretion
influenced by the gas flow in the gravitational potential of the protoplanet
and how it depends on the planetary mass, the headwind speed, the distance from
the host star, and the pebble size. We perform nonisothermal three-dimensional
hydrodynamical simulations in a local frame to obtain the gas flow around the
planet. We then numerically integrate three-dimensional orbits of pebbles under
the obtained gas flow. Finally, assuming uniform spatial distribution of
incoming pebbles, we calculate net spin by summing up specific angular momentum
that individual pebbles transfer to the protoplanet at impacts. We find that a
protoplanet with the envelope acquires prograde net spin rotation regardless of
the planetary mass, the pebble size, and the headwind speed of the gas. This is
because accreting pebbles are dragged by the envelope that commonly has
prograde rotation. As the planetary mass or orbital radius increases, the
envelope is thicker and the prograde rotation is faster, resulting in faster
net prograde spin. When the dimensionless thermal mass of the planet, , where and are the Bondi
radius and the disk gas scale height, is larger than a certain critical mass
( at or at ), the spin rotation exceeds the breakup one. The predicted spin
frequency reaches the breakup one at the planetary mass (where is the orbital radius),
suggesting that the protoplanet cannot grow beyond . It
is consistent with the Earth's current mass and could help the formation of the
Moon by a giant impact on fast-spinning proto-Earth.Comment: 14 pages, 10 figures, Accepted for publication in Astronomy and
Astrophysics (A&A
Evaluation of Esophageal Varices by Multidetector-row CT: Correlation with Endoscopic āRed Color Signā
<P>To evaluate the ability of multidetector-row CT (MDCT) to predict a risk of hemorrhage in patients with esophageal varices, a total of 40 MDCT scans were performed in 29 patients who had been diagnosed with esophageal varices by conventional upper gastrointestinal tract endoscopy. In 11 patients, MDCT was performed both before and after endoscopic injection sclerotherapy (EIS). Endoscopically, the red color sign (RC sign) was present in 28 scans. Of the 11 patients who underwent EIS, the RC sign disappeared after EIS in 9. The MDCT scans were obtained in the arterial, portal, and equilibrial phases, and the portal phase images were used in this study. Subsequently, the extent of esophageal varices was categorized into four MDCT scores. The variceal score, the maximum short axis of the varices, and the presence of palisade vein dilatation obtained from MDCT had significant correlation with endoscopic variceal forms, and the presence and severity of RC sign, respectively (p<0.01). All cases with a maximum minor axis of more than 4 mm showed positive RC sign. MDCT was useful in the evaluation of esophageal varices for predicting a risk of hemorrhage
The somatic mutations in Interferon-Ī³ signal molecules in human uterine leiomyosarcoma
Human uterine leiomyosarcoma (U-LMS) is neoplastic malignancy that typically arises in tissues of mesenchymal origin. The identification of novel molecular mechanism leading to human U-LMS formation and the establishment of new therapies has been hampered by several critical points. We earlier reported that mice with a homozygous deficiency for proteasome beta subunit 9 (Psmb9)/Ī²1i, an interferon (IFN)-Ī³ inducible factor, spontaneously develop U-LMS. The use of research findings of the experiment with mouse model has been successful in increasing our knowledge and understanding of how alterations, in relevant oncogenic, tumour suppressive, and signaling pathways directly impact sarcomagenesis. The IFN-Ī³ pathway is important for control of tumour growth and invasion and has been implicated in several malignant tumours. In this study, experiments with human tissues revealed a defective expression of PSMB9/Ī²1i in human U-LMS that was traced to the IFN-Ī³ pathway and the specific effect of somatic mutations of JANUS KINASE (JAK) 1 molecule or promoter region on the locus cording PSMB9/Ī²1i gene. Understanding the molecular mechanisms of human U-LMS may lead to identification of new diagnostic candidates or therapeutic targets against human U-LMS
Ex Vivo Gene Therapy Treats Bone Complications of Mucopolysaccharidosis Type II Mouse Models through Bone Remodeling Reactivation
Mucopolysaccharidosis type II is a disease caused by organ accumulation of glycosaminoglycans due to iduronate 2-sulfatase deficiency. This study investigated the pathophysiology of the bone complications associated with mucopolysaccharidosis II and the effect of lentivirus-mediated gene therapy of hematopoietic stem cells on bone lesions of mucopolysaccharidosis type II mouse models in comparison with enzyme replacement therapy. Bone volume, density, strength, and trabecular number were significantly higher in the untreated mucopolysaccharidosis type II mice than in wild-type mice. Accumulation of glycosaminoglycans caused reduced bone metabolism. Specifically, persistent high serum iduronate 2-sulfatase levels and release of glycosaminoglycans from osteoblasts and osteoclasts in mucopolysaccharidosis type II mice that had undergone gene therapy reactivated bone lineage remodeling, subsequently reducing bone mineral density, strength, and trabecular number to a similar degree as that observed in wild-type mice. Bone formation, resorption parameters, and mineral density in the diaphysis edge did not appear to have been affected by the irradiation administered as a pre-treatment for gene therapy. Hence, the therapeutic effect of gene therapy on the bone complications of mucopolysaccharidosis type II mice possibly outweighed that of enzyme replacement therapy in many aspects.Wada M., Shimada Y., Iizuka S., et al. Ex Vivo Gene Therapy Treats Bone Complications of Mucopolysaccharidosis Type II Mouse Models through Bone Remodeling Reactivation. Molecular Therapy - Methods and Clinical Development, 19, 261. https://doi.org/10.1016/j.omtm.2020.09.012
Characterization of isotope effect on ion internal transport barrier and its parameter dependence in the Large Helical Device
In this paper, the background physics of the isotope effects in the ion internal transport barrier (ITB) are discussed in detail. An heuristic criterion for the ITB strength is defined based on the nonlinear dependence of the ion thermal diffusivity on the local ion temperature in the L-mode phase. Comparing deuterium plasmas and hydrogen plasmas, two isotope effects on the ion ITB are clarified: stronger ITBs formed in the deuterium plasmas and an ITB concomitant edge confinement degradation in the hydrogen plasmas. Principal component analysis reveals that the ion ITB becomes strong when a high input power normalized by the line averaged electron density is applied and electron density profile is peaked. A gyrokinetic simulation suggests that the ITB profile is determined by the ion temperature gradient driven turbulence, while the way the profile saturates in L-mode plasmas is unknown. In the electron density turbulence behavior, a branch transition is observed, where the increasing trend in turbulence amplitude against the ITB strength is flipped to a decreasing trend across the ITB formation. The radial electric field structure is measured by the charge exchange recombination spectroscopy system. It is found that the radial electric field shear plays a minor role in determining the ITB strength
Bulk gravitational field and dark radiation on the brane in dilatonic brane world
We discuss the connection between the dark radiation on the brane and the
bulk gravitational field in a dilatonic brane world model proposed by Koyama
and Takahashi where the exact solutions for the five dimensional cosmological
perturbations can be obtained analytically. It is shown that the dark radiation
perturbation is related to the non-normalizable Kaluza-Klein (KK) mode of the
bulk perturbations. For the de Sitter brane in the anti-de Sitter bulk, the
squared mass of this KK mode is where is the Hubble parameter on
the brane. This mode is shown to be connected to the excitation of small black
hole in the bulk in the long wavelength limit. The exact solution for an
anisotropic stress on the brane induced by this KK mode is found, which plays
an important role in the calculation of cosmic microwave background radiation
anisotropies in the brane world.Comment: 11 page
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