A comprehensive introduction to the boundary state approach to Dirichlet branes is given. Various examples of BPS and non-BPS Dirichlet branes are discussed. In particular, the non-BPS states in the duality of type IIA on K3 and the heterotic string on T 4 are analysed in detail.PACS numbers: 1125, 1125H, 1125S * Lectures given at the TMR network school on 'Quantum aspects of gauge theories, supersymmetry and quantum
In this study, we investigated the sintering atmosphere dependence of the electric properties of Sn-doped (Ba0.82Ca0.13)TiO3 ceramics to clarify the effect of Sn2+ ions. The temperature of the dielectric constant peak for Sn-doped (Ba0.82Ca0.13)TiO3 ceramics sintered in a low P(O2) (1×10-11 MPa) atmosphere is higher than that for the sample sintered in a high P(O2) (2×10-2 MPa) atmosphere. The remanent polarization and coercive field for the Sn-doped (Ba0.82Ca0.13)TiO3 ceramics sintered at low P(O2) (1×10-11 MPa) also increased compared with those of the sample sintered at high P(O2) (2×10-2 MPa) at room temperature. The low P(O2) sintering atmosphere for Sn-doped (Ba0.82Ca0.13)TiO3 ceramics leads to a high tetragonality and the existence of Sn2+ ions. In addition, by X-ray absorption spectroscopy, it was verified that Sn2+ ions occupy Ba2+ sites in the (Ba0.82Ca0.13)TiO3 ceramics. Consequently, it is concluded that the high ferroelectric-to-paraelectric phase transition temperature and the high remanent polarization on the ceramics originate from Sn2+ ions substituted for Ba2+ sites in Sn-doped (Ba0.82Ca0.13)TiO3 ceramics.
Articles you may be interested inSeparation of bulk and interface contributions to electroforming and resistive switching behavior of epitaxial Fedoped SrTiO 3
The positive temperature coefficient (PTC) of resistivity characteristics of donor-doped BaTiO 3 fired at 1350 C in a reducing atmosphere of 1 Â 10 À7 MPa at the partial pressure of oxygen is investigated. The result reveals that BaTiO 3 ceramics fired in such a reducing atmosphere usually exhibit low PTC characteristics, whereas La-doped BaTiO 3 with compositions in the range of ðBa þ LaÞ=Ti = 1:02 exhibit pronounced PTC characteristics. A La content of less than 0.4 mol % is suitable for the PTC characteristics, while samples doped with more than 0.8 mol % La do not show the PTC characteristics. The PTC characteristics of semiconducting BaTiO 3 fired in a reducing atmosphere are enhanced with a decrease in the ion radius of a donor ion in the order La < Nd < Sm, therefore, semiconducting BaTiO 3 doped with Sm shows pronounced PTC characteristics with a resistivity increase of more than 6 orders of magnitude. However, the resistivity of BaTiO 3 ceramics doped with Y, whose ion radius is less than that of Sm, is extremely high resistivity that decreases with increasing temperature, thereby indicating only a negative temperature coefficient (NTC) characteristics.
The ball balancer has been used as a vibration suppression device in rotor systems. It has a superior characteristic that the vibration amplitude is reduced to zero theoretically at a rotational speed range higher than the critical speed. However, the ball balancer causes a self-excited vibration near the critical speed when the balls rotate in the balancer. This self-excited vibration may occur in the wide rotational speed range with a large amplitude vibration, and in such a case, escaping from it becomes difficult. In this paper, the occurrence region and the vibration characteristics of the self-excited vibration caused by the ball balancer are investigated. The nonlinear theoretical analysis is performed and a set of the fundamental equations governing the self-excited vibration is obtained. The influences of the parameters of the ball balancer, such as, the damping of the ball’s motion, the ball’s mass, and radius of the balls’ path, are explained and they are also validated experimentally.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.