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Numerical simulation of a possible origin of the positive radial metallicity gradient of the thick disk

Research in Astronomy and Astrophysics 2014年第11期14卷 1406-1414页

作者： Awat Rahimi Kenneth Carrell daisuke kawata National Astronomical Observatories Chinese Academy of Sciences Mullard Space Science Laboratory University College London Holmbury St.Mary DorkingSurrey RH5 6NT UK

We analyze the radial and vertical metallicity and [α/Fe] gradients of the disk stars of a disk galaxy simulated in a fully cosmological setting with the chemo- dynamical galaxy evolution code GCD＋. We study how the radial abundance gradients vary as a function of height above the plane and find that the metallicity （[α/Fe]） gra- dient becomes more positive （negative） with increasing height, changing sign around 1.5 kpc above the plane. At the largest vertical height （2 〈丨z丨〈 3 kpc）, our simulated galaxy shows a positive radial metallicity gradient. We find that the positive metallicity gradient is caused by the age-metallicity and age-velocity dispersion relation, where younger stars have higher metallicity and lower velocity dispersion. Due to the age- velocity dispersion relation, a greater fraction of younger stars reaches 丨z丨〉 2 kpc at the outer region, because of the lower gravitational restoring force of the disk, i.e. flaring. As a result, the fraction of younger stars with higher metallicity due to the age-metallicity relation becomes higher at the outer radii, which makes the median metallicity higher at the outer radii. Combining this result with the recently observed age-metallicity and age-velocity dispersion relation for the Milky Way thick disk stars suggested by Haywood et al., we argue that the observed （small） positive radial metal- licity gradient at large heights of the Milky Way disk stars can be explained by flaring of the younger thick and/or thin disk stars.

关键词： Galaxy disk -- Galaxy kinematics and dynamics -- galaxies interac-tions- galaxies formation- galaxies evolution- galaxies abundances

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Controllability of intense-laser ion acceleration

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High Power Laser Science and Engineering 2014年第1期2卷 18-28页

作者： Shigeo kawata Toshihiro Nagashima Masahiro Takano Takeshi Izumiyama Daiki Kamiyama daisuke Barada Qing Kong Yan Jun Gu Ping Xiao Wang Yan Yun Ma Wei Ming Wang Wu Zhang Jiang Xie Huiran Zhang Dongbo Dai Department of Advanced Interdisciplinary Sciences Utsunomiya University CORE (Center for Optical Research and Education) Utsunomiya University School of Computer Engineering and Sciences Shanghai University Institute of Modern Physics Fudan University Department of Physics National University of Defense Technology Institute of Physics Chinese Academy of Sciences

An ion beam has the unique feature of being able to deposit its main energy inside a human body to kill cancer cells or inside material. However, conventional ion accelerators tend to be huge in size and cost. In this paper, a future intenselaser ion accelerator is discussed to make the laser-based ion accelerator compact and controllable. The issues in the laser ion accelerator include the energy efficiency from the laser to the ions, the ion beam collimation, the ion energy spectrum control, the ion beam bunching, and the ion particle energy control. In the study, each component is designed to control the ion beam quality by particle simulations. The energy efficiency from the laser to ions is improved by using a solid target with a fine sub-wavelength structure or a near-critical-density gas plasma. The ion beam collimation is performed by holes behind the solid target or a multi-layered solid target. The control of the ion energy spectrum and the ion particle energy, and the ion beam bunching are successfully realized by a multi-stage laser–target interaction.

关键词： Intense short-pulse laser laser ion acceleration laser ion cancer therapy laser–plasma interaction

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