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

The unusual case of plastic deformation and high dislocation densities with the cold sintering of the piezoelectric ceramic K0.5Na0.5NbO3

K0.5Na0.5NbO3 (KNN) can be readily densified using the cold sintering process, but despite observing high relative permittivity, the ferroelectric hysteresis is strongly suppressed along with a major suppression in the all-important piezoelectric properties. In this study, KNN is fabricated using a NaOH+KOH transient flux under a uniaxial pressure of 400 MPa and heating to 300 °C for 2 h to drive densification to 93% theoretical. It is only after a secondary heat treatment that we observe improvements of the ferroelectric hysteresis and piezoelectric properties. From a detailed structural-property-processing study using analytical transmission electron microscopy (TEM), X-ray line broadening and high field dielectric characterization methodologies we conclude that there is an unusual in-situ plastic deformation process that takes place in addition to the densification under the cold sintering process. High densities of dislocations within grains were observed that lead to multiple pinning sites that impact both the intrinsic and extrinsic contributions to the high field dielectric and piezoelectric properties. Annealing significantly reduced the dislocation density in the highly defective crystallites, observed directly from the TEM and from the sharpening of the X-ray diffraction peaks, resulting in piezoelectric and ferroelectric properties that approached those of conventionally sintered KNN

Robust Vehicle Detection under Various Environments to Realize Road Traffic Flow Surveillance Using an Infrared Thermal Camera

To realize road traffic flow surveillance under various environments which contain poor visibility conditions, we have already proposed two vehicle detection methods using thermal images taken with an infrared thermal camera. The first method uses pattern recognition for the windshields and their surroundings to detect vehicles. However, the first method decreases the vehicle detection accuracy in winter season. To maintain high vehicle detection accuracy in all seasons, we developed the second method. The second method uses tires’ thermal energy reflection areas on a road as the detection targets. The second method did not achieve high detection accuracy for vehicles on left-hand and right-hand lanes except for two center-lanes. Therefore, we have developed a new method based on the second method to increase the vehicle detection accuracy. This paper proposes the new method and shows that the detection accuracy for vehicles on all lanes is 92.1%. Therefore, by combining the first method and the new method, high vehicle detection accuracies are maintained under various environments, and road traffic flow surveillance can be realized

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

MYCL promotes iPSC-like colony formation via MYC Box 0 and 2 domains

iPS細胞作製過程における初期化因子MYCLのタンパク質ドメインの機能解析. 京都大学プレスリリース. 2021-12-20.Protein domain structures affect the quality of stem cells. 京都大学プレスリリース. 2021-12-20.Human induced pluripotent stem cells (hiPSCs) can differentiate into cells of the three germ layers and are promising cell sources for regenerative medicine therapies. However, current protocols generate hiPSCs with low efficiency, and the generated iPSCs have variable differentiation capacity among different clones. Our previous study reported that MYC proteins (c-MYC and MYCL) are essential for reprogramming and germline transmission but that MYCL can generate hiPSC colonies more efficiently than c-MYC. The molecular underpinnings for the different reprogramming efficiencies between c-MYC and MYCL, however, are unknown. In this study, we found that MYC Box 0 (MB0) and MB2, two functional domains conserved in the MYC protein family, contribute to the phenotypic differences and promote hiPSC generation in MYCL-induced reprogramming. Proteome analyses suggested that in MYCL-induced reprogramming, cell adhesion-related cytoskeletal proteins are regulated by the MB0 domain, while the MB2 domain regulates RNA processes. These findings provide a molecular explanation for why MYCL has higher reprogramming efficiency than c-MYC