1,843 research outputs found
The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape
It has been proposed that supermassive black holes (SMBHs) are originated
from direct-collapse black holes (DCBHs) that are formed at z gtrsim 10 in the
primordial gas in the case that H2 cooling is suppressed by strong external
radiation. In this work, we study the critical specific intensity J^crit
required for DCBH formation for various radiation spectral shapes by a series
of one-zone calculations of a collapsing primordial- gas cloud. We calculate
the critical specific intensity at the Lyman-Werner (LW) bands J^crit_LW,21 (in
units of 10^-21 erg s^-1 Hz^-1 sr^-1 cm^-2) for realistic spectra of metal-poor
galaxies. We find J^crit is not sensitive to the age or metallicity for the
constant star formation galaxies with J^crit_LW,21 = 1300-1400, while J^crit
decreases as galaxies become older or more metal-enriched for the instantaneous
starburst galaxies. However, such dependence for the instantaneous starburst
galaxies is weak for the young or extremely metal-poor galaxies: J^crit_LW,21 =
1000-1400 for the young galaxies and J^crit_LW,21 approx 1400 for the extremely
metal-poor galaxies. The typical value of J^crit for the realistic spectra is
higher than those expected in the literature, which affects the estimated DCBH
number density n_DCBH. By extrapolating the result of Dijkstra, Ferrara and
Mesinger, we obtain n_DCBH sim 10^-10 cMpc^-3 at z = 10, although there is
still large uncertainty in this estimation.Comment: 11 pages, 6 figures, submitted to MNRA
Robustness of force and stress inference in an epithelial tissue
During morphogenesis, the shape of a tissue emerges from collective cellular
behaviors, which are in part regulated by mechanical and biochemical
interactions between cells. Quantification of force and stress is therefore
necessary to analyze the mechanisms controlling tissue morphogenesis. Recently,
a mechanical measurement method based on force inference from cell shapes and
connectivity has been developed. It is non-invasive, and can provide space-time
maps of force and stress within an epithelial tissue, up to prefactors. We
previously performed a comparative study of three force-inference methods,
which differ in their approach of treating indefiniteness in an inverse problem
between cell shapes and forces. In the present study, to further validate and
compare the three force inference methods, we tested their robustness by
measuring temporal fluctuation of estimated forces. Quantitative data of
cell-level dynamics in a developing tissue suggests that variation of forces
and stress will remain small within a short period of time (minutes).
Here, we showed that cell-junction tensions and global stress inferred by the
Bayesian force inference method varied less with time than those inferred by
the method that estimates only tension. In contrast, the amplitude of temporal
fluctuations of estimated cell pressures differs less between different
methods. Altogether, the present study strengthens the validity and robustness
of the Bayesian force-inference method.Comment: 4 pages, 4 figure
Non-Gaussian bubbles in the sky
We point out a possible generation mechanism of non-Gaussian bubbles in the
sky due to bubble nucleation in the early universe. We consider a curvaton
scenario for inflation and assume that the curvaton field phi, whose energy
density is subdominant during inflation but which is responsible for the
curvature perturbation of the universe, is coupled to another field sigma which
undergoes false vacuum decay through quantum tunneling. For this model, we
compute the skewness of the curvaton fluctuations due to its interaction with
sigma during tunneling, that is, on the background of an instanton solution
that describes false vacuum decay. We find that the resulting skewness of the
curvaton can become large in the spacetime region inside the bubble. We then
compute the corresponding skewness in the statistical distribution of the
cosmic microwave background (CMB) temperature fluctuations. We find a
non-vanishing skewness in a bubble-shaped region in the sky. It can be large
enough to be detected in the near future, and if detected it will bring us
invaluable information about the physics in the early universe.Comment: 6 pages, 6 figure
Multi-field open inflation model and multi-field dynamics in tunneling
We consider a multi-field open inflation model, in which one of the fields
dominates quantum tunneling from a false vacuum while the other field governs
slow-roll inflation within the bubble nucleated from false vacuum decay. We
call the former the tunneling field and the latter the inflaton field. In the
limit of a negligible interaction between the two fields, the false vacuum
decay is described by a Coleman-De Luccia instanton. Here we take into account
the coupling between the two fields and construct explicitly a multi-field
instanton for a simple quartic potential model. We also solve the evolution of
the scalar fields within the bubble. We find our model realizes open inflation
successfully. This is the first concrete, viable model of open inflation
realized with a simple potential. We then study the effect of the multi-field
dynamics on the false vacuum decay, specifically on the tunneling rate. We find
the tunneling rate increases in general in comparison with the single field
case, though the increase is small unless the inflaton affects the instanton
solution substantially.Comment: 13 pages, 4 figure
ZEB2 and MEIS1 independently contribute to hematopoiesis via early hematopoietic enhancer activation
血球細胞分化に必要な新たな因子を同定. 京都大学プレスリリース. 2023-09-29.Delineating the dynamic transcriptional and epigenetic landscape regulating hematopoiesis. 京都大学プレスリリース. 2023-10-17.Cell differentiation is achieved by acquiring a cell type-specific transcriptional program and epigenetic landscape. While the cell type-specific patterning of enhancers has been shown to precede cell fate decisions, it remains unclear how regulators of these enhancers are induced to initiate cell specification and how they appropriately restrict cells that differentiate. Here, using embryonic stem cell–derived hematopoietic cell differentiation cultures, we show the activation of some hematopoietic enhancers during arterialization of hemogenic endothelium, a prerequisite for hematopoiesis. We further reveal that ZEB2, a factor involved in the transcriptional regulation of arterial endothelial cells, and a hematopoietic regulator MEIS1 are independently required for activating these enhancers. Concomitantly, ZEB2 or MEIS1 deficiency impaired hematopoietic cell development. These results suggest that multiple regulators expressed from an earlier developmental stage non-redundantly contribute to the establishment of hematopoietic enhancer landscape, thereby restricting cell differentiation despite the unrestricted expression of these regulators to hematopoietic cells
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