We study Type I migration of a planet in a radiatively efficient disc using global twodimensional hydrodynamic simulations. The large positive corotation torque is exerted on a planet by an adiabatic disc at early times when the disc has the steep negative entropy gradient. The gas on the horseshoe orbit of the planet is compressed adiabatically during the change of the orbit from the slow orbit to the fast orbit, increasing its density and exerting the positive torque on the planet. The planet would migrate outward in the adiabatic disc before saturation sets in. We further study the effect of energy dissipation by radiation on Type I migration of the planet. The corotation torque decreases when the energy dissipates effectively because the density of the gas on the horseshoe orbit does not increase by the compression compared with the gas of the adiabatic disc. The total torque is mainly determined by the negative Lindblad torque and becomes negative. The planet migrates inwards towards the central star in the radiatively efficient disc. The migration velocity is dependent on the radiative efficiency and is greatly reduced if the radiative cooling works inefficiently.

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We study the torque acting on a planet embedded in an optically thick accretion disc, using global two-dimensional hydrodynamic simulations. The temperature of an optically thick accretion disc is determined by the energy balance between the viscous heating and the radiative cooling. The radiative cooling rate depends on the opacity of the disc. The opacity is expressed as a function of the temperature. We find the disc is divided into three regions that have different temperature distributions. The slope of the entropy distribution becomes steep in the inner region of the disc with the high temperature and the outer region of the disc with the low temperature, while it becomes shallow in the middle region with the intermediate temperature. Planets in the inner and outer regions move outward owing to the large positive corotation torque exerted on the planet by an adiabatic disc, on the other hand, a planet in the middle region moves inward toward the central star. Planets are expected to accumulate at the boundary between the inner and middle regions of the adiabatic disc. The positive corotation torque decreases with an increase in the viscosity of the disc. We find that the positive corotation torque acting on the planet in the inner region becomes too small to cancel the negative Lindblad torque when we include the large viscosity, which destroys the enhancement of the density in the horseshoe orbit of the planet. This leads to the inward migration of the planet in the inner region of the disc. A planet with 5 Earth masses in the inner region can move outward in a disc with the surface density of 100 g/cm^2 at 1 AU when the accretion rate of a disc is smaller than 2x10^{-8} solar mass/yr.Comment: 17 pages, 15 figure

A GaAs/GaAsP strain-compensated superlattice (SL) is a highly promising spin-polarized electron source. To realize higher quantum efficiency, it is necessary to consider spin relaxation mechanisms. We have investigated the electron spin relaxation time in a Zn-doped GaAs/GaAsP strain-compensated SL by time-resolved spin-dependent pump and probe reflection measurements. The long spin relaxation time of 104 ps was observed at room temperature (RT), which is about three times longer than that of conventional undoped GaAs multiple quantum wells. Even when the excitation power increases from 30 to 110 mW, the change in the spin relaxation time at RT was small. This relationship implies that the intensity of the electron beam can be increased without affecting the spin relaxation time. These results indicate that a Zn-doped GaAs/GaAsP strain-compensated SL has the great advantage for use as a spin-polarized electron source.

This paper studies the news coverage of the 2014 Mt. Ontake eruption disaster from 2015 to 2019, and the public response to the fifth anniversary coverage. Information on the issues regarding the risk of low-frequency disaster events such as volcanic eruption is brought into the public largely through the media. Unless there is a volcano nearby, there are few opportunities to discuss volcanic disaster prevention, and enhance volcanic risk perception. Therefore, the media agendas on volcanic risk are an indicator of what people know about volcanic disaster preparedness. This study quantitatively analyzed the 2014 Mt. Ontake eruption reports of national, regional, and local newspapers to reveal their topic distributions. In addition, the anniversary gained intense public attention due to the large amount of media coverage. It was a significant opportunity for society to discuss volcanic risk. By observing people’s online responses to the anniversary coverage, a trend could be identified. We found a significant difference in media attention among the three newspaper types. The local newspaper covered four topics relating to volcanic risk in a well-balanced way, but the national and regional newspapers paid greater attention to one or two topics. Many online comments presented the view that a mountaineering should be done at individuals’ own risk, and volcano shelters would be ineffective for averting volcanic disasters. The anniversary coverage unintentionally contributes to stigmatizing or scapegoating a certain group, rather than promoting risk communication in the public sphere on the Web. With the onset of the information and communication information technology era, an online dialogue regarding disaster awareness and prevention is important. A volcano disaster risk communication strategy on the Web should be developed.