The Dust Mantle of Comet 9P/Tempel 1: Dynamical Constraints on Physical Properties

The trajectories of dust particles ejected from a comet are affected by solar radiation pressure as a function of their ratios of radiation pressure cross section to mass. Therefore, a study on the orbital evolution of the particles caused by the radiation pressure reveals the physical properties of dust on the surface of the comet nucleus. In the course of NASA's Deep Impact mission, the ejecta plume evolved under the influence of the radiation pressure. From the evolution and shape of the plume, we have succeeded in obtaining $\beta \approx 0.4$, where $\beta$ is the ratio of the radiation pressure to the solar gravity. Taking into account $\beta \approx 0.4$ as well as the observational constraints of a high color temperature and a small silicate-feature strength, dust particles ejected from the surface of comet 9P/Tempel 1 are likely compact dust aggregates of sizes $\approx 20\,\mu$m (mass $\sim 10^{-8}$\,g). This is comparable to the major dust on the surface of comet 1P/Halley ($\sim 10\mu$m) inferred from in-situ measurements and theoretical considerations. Since such dust aggregates with $\beta \approx 0.4$ must have survived on the surface against jets due to ice sublimation, the temperature of ice in the nucleus must be kept below 145\,K, which is much lower than equilibrium temperature determined by solar irradiation and thermal emission. These facts indicate that 9P/Tempel 1 has a dust mantle composed of $20\,\mu$m-sized dust aggregates with low thermal conductivities $\sim 1 \, {\rm erg\, cm}^{-1} \, {\rm K}^{-1}\,{\rm s}^{-1}$.Comment: 4 pages, 3 figures, accepted for publication in Astronomy and Astrophysic

Formation of \eta'(958)-mesic nuclei and axial U_A(1) anomaly at finite density

We discuss the possibility to produce the bound states of the $\eta'(958)$ meson in nuclei theoretically. We calculate the formation cross sections of the $\eta'$ bound states with the Green function method for ($\gamma$,p) reaction and discuss the experimental feasibility at photon facilities like SPring-8. We conclude that we can expect to observe resonance peaks in ($\gamma$,p) spectra for the formation of $\eta'$ bound states and we can deduce new information on $\eta'$ properties at finite density. These observations are believed to be essential to know the possible mass shift of $\eta'$ and deduce new information of the effective restoration of the chiral $U_A(1)$ anomaly in the nuclear medium.Comment: 4 pages, 3 figure

Skyrmion and vortex crystals in the Hubbard model

A mutual interplay between the charge and spin degrees of freedom in itinerant magnets leads to a plethora of topological spin textures, such as magnetic skyrmion and vortex crystals, in both centrosymmetric and noncentrosymmetric hosts. Meanwhile, their stabilization has been extensively studied in the system including the classical localized spins. We here study a realization of the skyrmion crystal in the centrosymmetric triangular-lattice Hubbard model, where the itinerant nature of electrons plays a more significant role. By performing the self-consistent mean-field calculations, we find that two types of skyrmion crystals with spatially nonuniform charge modulations appear in the ground state at a zero magnetic field. Moreover, we obtain another noncoplanar vortex crystal phase without a net scalar chirality in the vicinity of the skyrmion crystal phase. We show that the latter vortex crystal exhibits the topological phase transition to a different skyrmion phase in an applied magnetic field. Our results provide a possibility of the skyrmion and vortex crystals in itinerant magnets without the localized moments.Comment: 6 pages, 5 figure

Effect of pressure on the magnetic, transport, and thermal-transport properties of the electron-doped manganite CaMn1−x_{1-x}Sbx_{x}O3_{3}

We have demonstrated the effect of hydrostatic pressure on magnetic and transport properties, and thermal transport properties in electron-doped manganites CaMn$_{1-x}$Sb$_{x}$O$_{3}$. The substitution of Sb$^{5+}$ ion for Mn $^{4+}$site of the parent matrix causes one-electron doping with the chemical formula CaMn$^{4+}_{1-2x}$Mn$^{3+}_{x}$Sb$^{5+}_{x}$O$_{3}$ accompanied by a monotonous increase in unit cell volume as a function of $x$. Upon increasing the doping level of Sb, the magnitudes of both electrical resistivity and negative Seebeck coefficient are suppressed at high temperatures, indicating the electron doping. Anomalous diamagnetic behaviors at $x=0.05$ and 0.08 are clearly observed in field cooled dc magnetization. The effect of hydrostatic pressure on dc magnetization is in contrast to the chemical pressure effect due to Sb doping. The dynamical effect of ac magnetic susceptibility measurement points to the formation of the magnetically frustrated clusters such as FM clusters embedded in canted AFM matrix.Comment: 12 pages,11 figures, 3 table

Effect of pressure on the magnetic, transport, and thermal-transport properties of the electron-doped manganite CaMn1−x_{1-x}Sbx_{x}O3_{3}

We have demonstrated the effect of hydrostatic pressure on magnetic and transport properties, and thermal transport properties in electron-doped manganites CaMn$_{1-x}$Sb$_{x}$O$_{3}$. The substitution of Sb$^{5+}$ ion for Mn $^{4+}$site of the parent matrix causes one-electron doping with the chemical formula CaMn$^{4+}_{1-2x}$Mn$^{3+}_{x}$Sb$^{5+}_{x}$O$_{3}$ accompanied by a monotonous increase in unit cell volume as a function of $x$. Upon increasing the doping level of Sb, the magnitudes of both electrical resistivity and negative Seebeck coefficient are suppressed at high temperatures, indicating the electron doping. Anomalous diamagnetic behaviors at $x=0.05$ and 0.08 are clearly observed in field cooled dc magnetization. The effect of hydrostatic pressure on dc magnetization is in contrast to the chemical pressure effect due to Sb doping. The dynamical effect of ac magnetic susceptibility measurement points to the formation of the magnetically frustrated clusters such as FM clusters embedded in canted AFM matrix.Comment: 12 pages,11 figures, 3 table

Function and Characteristics of PINK1 in Mitochondria

Mutations in phosphatase and tensin homologue-induced kinase 1 (PINK1) cause recessively inherited Parkinson’s disease, a neurodegenerative disorder linked to mitochondrial dysfunction. Studies support the notion of neuroprotective roles for the PINK1, as it protects cells from damage-mediated mitochondrial dysfunction, oxidative stress, and cell apoptosis. PARL is a mitochondrial resident rhomboid serine protease, and it has been reported to mediate the cleavage of the PINK1. Interestingly, impaired mitophagy, an important autophagic quality control mechanism that clears the cells of damaged mitochondria, may also be an underlying mechanism of disease pathogenesis in patients for Parkinson’s disease with the PARL mutations. Functional studies have revealed that PINK1 recruits Parkin to mitochondria to initiate the mitophagy. PINK1 is posttranslationally processed, whose level is definitely regulated in healthy steady state of mitochondria. As a consequence, PINK1 plays a pivotal role in mitochondrial healthy homeostasis