Nakagawa T.,Tohoku Institute of Technology
Journal of Geophysical Research: Space Physics | Year: 2013
The ion entry into the wake behind an obstacle in the solar wind is studied using two-dimensional, electromagnetic full-particle simulations. A significant difference is found between the number of ions and electrons in the near wake, mainly due to the negative electric charge on the nightside surface of the obstacle. The ion acceleration toward the void is observed far from the position of the rarefaction wave expected in the self-similar solution. The velocity profile of the ions in the wake approaches the self-similar solution with finite ion temperature asymptotically until they reach the distance where the ions from both sides of the wake meet. The ions that entered from both sides are accelerated in the opposite directions. They raise the ion temperature and the pressure in the center of the wake, although each component remains cool when treated separately. The electron temperature appears nearly constant, except for the edge of the complete void of electrons. The large-scale obstacle and a slow solar wind are favorable conditions for a detection of well-accelerated ions near the nightside surface of the obstacle, because they have enough time to accelerate. The direction of the electric field in the wake seems consistent with the gradient of the electron pressure. Key PointsIon entry into the wake is faster than the self-similar solutionSurface charging that accelerates ions is important for ion entry into the wakeIons enter the void deeper behind a large obstacle in the solw solar wind ©2013. American Geophysical Union. All Rights Reserved.
Hashimoto K.,Tohoku Institute of Technology
Applied Surface Science | Year: 2011
Amorphous alloys have many attractive characteristics including extremely high corrosion resistance if the sufficient amounts of corrosion-resistant elements are added. The superiority of amorphous alloys is based on the homogeneous single phase nature without any chemical and physical heterogeneities. Although there are processing limitations to avoid the formation of heterogeneous crystalline structure in addition to no welding technology without crystallization, the application of corrosion-resistant amorphous alloys is expected particularly to the very aggressive environments, where any conventional crystalline metallic materials cannot be used. Some amorphous bulk alloys showed zero corrosion mass loss due to spontaneous passivation even in 12 M HCl. Production of amorphous bulk alloys became possible for selected compositions. The homogeneous single phase nature is also effective to form useful catalysts with unique composition and structure. An example of catalysts is for carbon dioxide methanation useful for supply of renewable energy in the form of methane. © 2011 Elsevier B.V. All rights reserved.
Anazawa M.,Tohoku Institute of Technology
Theoretical Population Biology | Year: 2012
This paper provides first-principles derivations of population models for competition involving multiple resources with different competition types, based on resource partitioning between individuals. The following two cases are investigated. The first is the case in which the resource competed for and its competition type change depending on life stages from scramble to contest competition, or from contest to scramble competition. The second is the case in which individuals compete for two resources simultaneously with scramble and contest types, respectively. In both cases, population models are derived analytically, and in particular, the Hassell model is derived in the second case. The nature of reproduction curves and the stability properties of three population models derived are compared with each other. These models provide three representative models for competition involving both scramble and contest types. © 2011 Elsevier Inc.
Saito T.,Tohoku Institute of Technology
Metrologia | Year: 2012
Among possible losses in the efficiency of semiconductor photodiodes and solar cells, optical losses are dominant in many cases and, therefore, are important. The optical losses, mainly consisting of reflection from the surface and absorption in a dead layer, are evaluated based on a theoretical model whose validity was confirmed by experiments. The effect of the surface layer on the optical properties of the whole system is analysed, using a complex plane representation of reflectance and transmittance, to be quite important, and is sensitive to its layer thickness and the angle of incidence. The results are presented as a function of wavelength, surface film thickness and angle of incidence. The results show that the optical properties of the layered system are completely different from those of a single boundary system and change steeply in the UV range due to the change in optical indices of both the surface layer and the substrate. © 2012 BIPM & IOP Publishing Ltd.
Mihashi H.,Tohoku Institute of Technology |
Nishiwaki T.,Tohoku University
Journal of Advanced Concrete Technology | Year: 2012
Challenging studies of engineered self-healing and self-repairing functions in concrete structures are briefly reviewed. While self-healing of concrete has been studied for a long time, it was only recently noticed that some engineered technologies are useful to stimulate the potential of concrete to be self-healed. For example, fiber reinforced cementitious composites (FRCC) have a much higher potential of self-healing than ordinary concrete because of their capability to keep cracks thinner and also because of the bridging network system in cracks; a specific bio-chemical approach, i.e. the application of mineral-precipitating bacteria, is now available; and various mineral admixtures are useful for practical application. Furthermore, the new concept of self-repairing concrete, which is based on the design concept of intelligent materials, is reported. Self-repairing concrete is concrete that incorporates devices for achieving the three key functions of an intelligent material, (1) sensing, (2) processing, and (3) actuating. This paper is a state-of-the-art report on the recent development of engineered self-healing and self-repairing concrete. © 2012 Japan Concrete Institute.