250 research outputs found
The Formation and Destruction of Molecular Clouds and Galactic Star Formation
We describe an overall picture of galactic-scale star formation. Recent
high-resolution magneto-hydrodynamical simulations of two-fluid dynamics with
cooling/heating and thermal conduction have shown that the formation of
molecular clouds requires multiple episodes of supersonic compression. This
finding enables us to create a scenario in which molecular clouds form in
interacting shells or bubbles on a galactic scale. First we estimate the
ensemble-averaged growth rate of molecular clouds over a timescale larger than
a million years. Next we perform radiation hydrodynamics simulations to
evaluate the destruction rate of magnetized molecular clouds by the stellar FUV
radiation. We also investigate the resultant star formation efficiency within a
cloud which amounts to a low value (a few percent) if we adopt the power-law
exponent -2.5 for the mass distribution of stars in the cloud. We finally
describe the time evolution of the mass function of molecular clouds over a
long timescale (>1Myr) and discuss the steady state exponent of the power-law
slope in various environments.Comment: 7 pages, 3 figures. Accepted for publication in Astronomy and
Astrophysic
Sarcopenia and the Modified Glasgow Prognostic Score are Significant Predictors of Survival Among Patients with Metastatic Renal Cell Carcinoma Who are Receiving First-Line Sunitinib Treatment.
Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages
The formation of molecular clouds out of HI gas is the first step toward star
formation. Its metallicity dependence plays a key role to determine star
formation through the cosmic history. Previous theoretical studies with
detailed chemical networks calculate thermal equilibrium states and/or thermal
evolution under one-zone collapsing background. The molecular cloud formation
in reality, however, involves supersonic flows, and thus resolving the cloud
internal turbulence/density structure in three dimension is still essential. We
here perform magnetohydrodynamics simulations of 20 km s^-1 converging flows of
Warm Neutral Medium (WNM) with 1 uG mean magnetic field in the metallicity
range from the Solar (1.0 Zsun) to 0.2 Zsun environment. The Cold Neutral
Medium (CNM) clumps form faster with higher metallicity due to more efficient
cooling. Meanwhile, their mass functions commonly follow dn/dm proportional to
m^-1.7 at three cooling times regardless of the metallicity. Their total
turbulence power also commonly shows the Kolmogorov spectrum with its 80
percent in the solenoidal mode, while the CNM volume alone indicates the
transition towards the Larson's law. These similarities measured at the same
time in the unit of the cooling time suggest that the molecular cloud formation
directly from the WNM alone requires a longer physical time in a lower
metallicity environment in the 1.0-0.2 Zsun range. To explain the rapid
formation of molecular clouds and subsequent massive star formation possibly
within 10 Myr as observed in the Large/Small Magellanic Clouds (LMC/SMC), the
HI gas already contains CNM volume instead of pure WNM.Comment: 23 pages, 11 figures. Accepted for publication in Ap
Evaluation of renal function change during first-line tyrosine kinase inhibitor therapy for metastatic renal cell carcinoma
Late recurrence of a malignant hypoglycemia‑inducing pelvic solitary fibrous tumor secreting high‑molecular‑weight insulin‑like growth factor‑II: A case report with protein analysis
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