Tohoku University

About: Tohoku University is a education organization based out in Sendai, Japan. It is known for research contribution in the topics: Magnetization & Population. The organization has 72116 authors who have published 170791 publications receiving 3941714 citations. The organization is also known as: Tōhoku daigaku.

Chelyabinsk airburst, damage assessment, meteorite recovery, and characterization

Abstract: The asteroid impact near the Russian city of Chelyabinsk on 15 February 2013 was the largest airburst on Earth since the 1908 Tunguska event, causing a natural disaster in an area with a population exceeding one million. Because it occurred in an era with modern consumer electronics, field sensors, and laboratory techniques, unprecedented measurements were made of the impact event and the meteoroid that caused it. Here, we document the account of what happened, as understood now, using comprehensive data obtained from astronomy, planetary science, geophysics, meteorology, meteoritics, and cosmochemistry and from social science surveys. A good understanding of the Chelyabinsk incident provides an opportunity to calibrate the event, with implications for the study of near-Earth objects and developing hazard mitigation strategies for planetary protection.

A Novel Preparation Method of Organic Microcrystals

Abstract: Organic microcrystals ranging from several tens nm to µm in size of several chromophores were successfully prepared by simply dispersing ethanol solutions of compounds into stirred water, i.e. by a reprecipitation method. The size of microcrystals was found to depend on concentration of ethanol solutions, dispersing conditions, temperature and so on.

Optical properties due to electronic transitions in two-dimensional semiconductors (CnH2n+1NH3)2PbI4.

Abstract: Optical spectra in the visible and uv regions are investigated in layer-type perovskite compounds (${\mathrm{C}}_{\mathit{n}}$${\mathrm{H}}_{2\mathit{n}+1}$${\mathrm{NH}}_{3}$)${\mathrm{PbI}}_{4}$ with n=4, 6, 8, 9, 10, and 12. The spacing between the ${\mathrm{PbI}}_{4}$ layers changes from 15.17 \AA{} for n=4 to 24.51 \AA{} for n=12. In spite of these different spacings, the optical spectra are almost the same for these compounds, which means that the interaction between the layers is weak. The lowest exciton is located at 2.56 eV at 1.6 K, and its oscillator strength and binding energy are 0.7 per formula unit and 320 meV, respectively. These values are very large compared with those in a three-dimensional analog ${\mathrm{PbI}}_{2}$. The large oscillator strength and binding energy can be explained by the small dielectric constant of the alkylammonium ``barrier layer,'' which strengthens the Coulomb interaction between an electron and a hole.

Topological node-line semimetal in three-dimensional graphene networks

Abstract: Graphene, a two-dimensional (2D) carbon sheet, acquires many of its amazing properties from the Dirac point nature of its electronic structures with negligible spin-orbit coupling. Extending to 3D space, graphene networks with negative curvature, called Mackay-Terrones crystals (MTCs), have been proposed and experimentally explored, yet their topological properties have yet to be discovered. Based on the first-principle calculations, we report an all-carbon MTC with topologically nontrivial electronic states by exhibiting node lines in bulk. When the node lines are projected onto surfaces to form circles, ``drumhead''-like flat surface bands nestled inside of the circles are formed. The bulk node line can evolve into a 3D Dirac point in the absence of inversion symmetry, the existence of which has been shown to be plausible in recent experiments.