Mechanism of magnetism in stacked nanographite: Theoretical study

Nanographite systems, where graphene sheets of the orders of the nanometer size are stacked, show novel magnetic properties, such as, spin-glass like behaviors and the change of ESR line widths in the course of gas adsorptions. We theoretically investigate stacking effects in the zigzag nanographite sheets by using a tight binding model with the Hubbard-like onsite interactions. We find a remarkable difference in the magnetic properties between the simple A-A and A-B type stackings. For the simple stacking, there are not magnetic solutions. For the A-B stacking, we find antiferromagnetic solutions for strong onsite repulsions. The local magnetic moments tend to exist at the edge sites in each layer due to the large amplitude of wavefunctions at these sites. Relations with experiments are discussed.Comment: PACS numbers: 75.30.-m, 75.70.Cn, 75.10.Lp, 75.40.Mg; E-mail: [email protected]; http://www.etl.go.jp/~harigaya/welcome_E.htm

Calculations of Electric Capacitance in Carbon and BN Nanotubes, and Zigzag Nanographite (BN, BCN) Ribbons

Electronic states in nanographite ribbons with zigzag edges are studied using the extended Hubbard model with nearest neighbor Coulomb interactions. The electronic states with the opposite electric charges separated along both edges are analogous as nanocondensers. Therefore, electric capacitance, defined using a relation of polarizability, is calculated to examine nano-functionalities. We find that the behavior of the capacitance is widely different depending on whether the system is in the magnetic or charge polarized phases. In the magnetic phase, the capacitance is dominated by the presence of the edge states while the ribbon width is small. As the ribbon becomes wider, the capacitance remains with large magnitudes as the system develops into metallic zigzag nanotubes. It is proportional to the inverse of the width, when the system corresponds to the semiconducting nanotubes and the system is in the charge polarized phase also. The latter behavior could be understood by the presence of an energy gap for charge excitations. In the BN (BCN) nanotubes and ribbons, the electronic structure is always like of semiconductors. The calculated capacitance is inversely proportional to the distance between the positive and negative electrodes.Comment: 4 pages; 6 figures; related: http://staff.aist.go.jp/k.harigaya

Optimal Design Methodology of Common Components for a Class of

ABSTRACT This paper discusses the optimal design of common components used for a class of products. While simultaneously designing multiple products has become an important concept in manufacturing in these days, alliances involved in such activities are extended from the traditional form. This means the existence of a chance that an integrator designs a set of components apart from particular products or a supplier commonalizes components independently from integrators. That is, any methodology for simultaneously designing a set of components becomes necessary behind ones for simultaneously designing a set of products. This paper formulates the design problem of common components as an optimization problem, investigates the condition of optimal design through the tradeoff among the level of system-level performance, the number of different components, etc. Then a computational procedure is configured for optimizing the commonalization of components apart from designing a particular set of products by using multivariate analysis, an optimization code based on mini-max operation and a genetic algorithm for constrained nonlinear mathematical programming. Finally the proposed optimization procedure is preliminarily applied to a design problem of liftgate dumpers for passenger cars for demonstrating the meaning of the levels of optimal design and tradeoff structure