Yamamoto D.,RIKEN |
Ozaki T.,Tokyo University of Science, Suwa |
Sa De Melo C.A.R.,Georgia Institute of Technology |
Danshita I.,Kyoto University |
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013
We study the first-order quantum phase transitions of Bose gases in optical lattices. A special emphasis is placed on an anomalous hysteresis behavior, in which the phase transition occurs in a unidirectional way and a hysteresis loop does not form. We first revisit the hardcore Bose-Hubbard model with dipole-dipole interactions on a triangular lattice to analyze accurately the ground-state phase diagram and the hysteresis using the cluster mean-field theory combined with cluster-size scaling. Details of the anomalous hysteresis are presented. We next consider the two-component and spin-1 Bose-Hubbard models on a hypercubic lattice and show that the anomalous hysteresis can emerge in these systems as well. In particular, for the former model, we discuss the experimental feasibility of the first-order transitions and the associated hysteresis. We also explain an underlying mechanism of the anomalous hysteresis by means of the Ginzburg-Landau theory. From the given cases, we conclude that the anomalous hysteresis is a ubiquitous phenomenon of systems with a phase region of lobe shape that is surrounded by the first-order boundary. © 2013 American Physical Society.
Ooshima M.,Tokyo University of Science, Suwa |
Takeuchi C.,OGIHARA.MFG. Co.
IEEE Transactions on Industry Applications | Year: 2011
This paper presents the experiment results from the testing of a magnetic suspension system in a bearingless brushless dc motor. This machine is suitable for use in small liquid pumps. The bearingless motor structure, the principle of the suspension force generation, and the magnetic suspension control strategy are proposed by the author. A prototype bearingless brushless dc motor is designed using computed results from a finite-element method simulation of the system. The simulation is experimentally verified using a prototype machine where the rotor is successfully suspended without mechanical contact when it drives a liquid pump at the maximum rotational speed of 2200 r/min and the maximum fluid flow of 8.2 L/min. This result shows that the proposed bearingless brushless dc motor is suitable as the drive for small liquid pumps. © 2011 IEEE.
Minami S.,University of Tokyo |
Kawai H.,Tokyo University of Science, Suwa |
Yoshimura S.,University of Tokyo
Computational Mechanics | Year: 2012
Parallel BDD-based monolithic algorithms for acoustic fluid-structure interaction problems are developed. In a previous study, two schemes, NN-I + CGC-FULL and NN-I + CGC-DIAG, have been proven to be efficient among several BDD-type schemes for one processor. Thus, the parallelization of these schemes is discussed in the present study. These BDD-type schemes consist of the operations of the Schur complement matrix-vector (Sv) product, Neumann-Neumann (NN) preconditioning, and the coarse problem. In the present study, the Sv product and NN preconditioning are parallelized for both schemes, and the parallel implementation of the solid and fluid parts of the coarse problem is considered for NN-I + CGC-DIAG. The results of numerical experiments indicate that both schemes exhibit performances that are almost as good as those of single solid and fluid analyses in the Sv product and NN preconditioning. Moreover, NN-I + CGC-DIAG appears to become more efficient as the problem size becomes large due to the parallel calculation of the coarse problem. © 2012 Springer-Verlag.
Aihara S.I.,Tokyo University of Science, Suwa |
Bagchi A.,University of Twente
International Journal of Innovative Computing, Information and Control | Year: 2010
We consider a slight perturbation of the Hull-White short rate model and result in modified forward rate equation as studied in . We develop the general frame-work of the Kalman filter for the stochastic hyperbolic system for the factor process of bonds. The noise covariance parameters included in the systems are estimated by calcu-lating the quadratic variation of observation data. The market price of risk parameters are then identified with the aid of the maximum likelihood method. © 2010 ISSN.
Aihara S.,Tokyo University of Science, Suwa |
Bagchi A.,University of Twente
International Journal of Innovative Computing, Information and Control | Year: 2012
We consider the adaptive filtering problem for estimating the randomly changing risk premium and its system parameters for zero-coupon bond models. The term structure model for a zero-coupon bond is formulated including the stochastic risk-premium factor. We specify our observation data from the yield curve and bond data which are used to hedge some option claims. For the fixed system parameters, the Kalman filter for the risk-premium and the factor process is constructed first. Secondly, by using the parallel filtering technique and resampling technique commonly used in particle filters, the on-line estimation algorithm for model parameters is constructed. Some simulation studies are finally presented. © 2012 ISSN 1349-4198.
Ooshima M.,Tokyo University of Science, Suwa
2010 International Power Electronics Conference - ECCE Asia -, IPEC 2010 | Year: 2010
This paper presents a new decoupling method of the radial forces in a dual rotor-type magnetic suspension motor. The dual rotor-type magnetic suspension motor has been proposed by the author, and the motor structure and the principle of the suspension force generation have been introduced. However, it is possible that the mutual interference between the radial suspension forces in two perpendicular axes occurs, which causes the unstable levitation of the rotor. In this paper, the new decoupling method of the radial suspension forces is proposed to stably levitate the rotor. It is confirmed by the simulation using Finite Element Method (FEM) that the suspension forces are successfully decoupled between the perpendicular axes. The proposed decoupling method is found effective to decrease the vibration of the suspension force and stably support the rotor without mechanical contact. © 2010 IEEE.
Nara M.,Tokyo University of Science, Suwa
Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B | Year: 2012
We researched concerning the new energy technology of producing the hydrogen gases with the organic refuse by using sunlight and phototropic bacteria. Electricity can be generated by supplying the produced hydrogen gases to the fuel cell. Hydrogen production efficiency enough to put it to practical use has not been obtained in the past though a full-scale experiment for the hydrogen production that uses algae and the microorganism that does the photosynthesis has been conducted. That is, the cost performance for practical use is not obtained. We did an experimental research that used the wavelength conversion material of sunlight and the optical reflection material of the aluminum foil as a method for the efficiency gain of the hydrogen production. As a result, the design parameter of the system to produce hydrogen with the waste fluid by using the purple non-sulfur bacteria that carried out photosynthesis was able to be decided. Substrate (The sugar manufacture waste fluid: [Molasses]) dosage in which the highest incidence of hydrogen was obtained was 0.4mg/100kcells * day for the pure culture system. Moreover, the improvement of the hydrogen production efficiency of about 15% was obtained in the maximum with a light wave length conversion net. A design parameter of the biomass hydrogen energy production system and basic data concerning the efficiency gain of the system were able to be obtained from the above-mentioned results. © 2012 The Japan Society of Mechanical Engineers.
Ooshima M.,Tokyo University of Science, Suwa |
2011 IEEE International Electric Machines and Drives Conference, IEMDC 2011 | Year: 2011
This paper presents magnetic suspension performance of a bearingless brushless dc motor. The new motor structure, the winding distribution in the stator, the principle of suspension force generation and the magnetic suspension control strategy for the bearingless brushless dc motor have been proposed. The rotational torque and suspension force have been analyzed by Finite Element Method (FEM) using machine model. A prototype bearingless brushless dc motor was designed on the basis of the analyzed results by FEM. In this paper, the prototype machine is built and the rotor levitation tests are carried out to confirm the validity of the proposed magnetic suspension control method and experimentally measure the magnetic suspension performance. From the experimental results, it is confirmed that the rotor shaft is stably suspended without the mechanical contacts. The proposed control method is found suitable to realize the stable levitation of the rotor in the bearingless brushless dc motor. © 2011 IEEE.
Itabashi M.,Tokyo University of Science, Suwa
Applied Mechanics and Materials | Year: 2014
In the one bar method, one of the standardized high velocity tensile testing techniques for thin steel plate, sometimes it shows an apparent effect of transverse vibration of an output bar on dynamic behavior of the plate. Suppressing the lateral vibration of the loading end of the bar is the most important factor to decrease the apparent effect, as pointed by Yoshida, Kuriyama, Uenishi and Takahashi in 2002, and the present author in 2011. He proposed an output-bar supporting technique with a polytetrafluoroethylene (PTFE) collar. In the former work, the lateral vibration was not fully suppressed, because the collar had some clearance to the output bar. He convinced that, in order to eliminate the clearance, it was worthy to give some transverse pre-load on the bar from the outer surface of the collar. However, the output bar is a load-sensing elastic body with strain gages adhered on it. The axial strain signal is a source of load detection. If such transverse compression is applied to the output bar, the axial skin strain of it is reduced to some extent. The key factor is the collar material, PTFE. This solid polymer possesses the lowest coefficient of friction in the situation of PTFE on steel, typically 0.05-0.10. The present author has modified an output-bar supporting stand to apply the lateral compressive load to the output bar with the divided PTFE collars which allow the smooth axial movement of the bar. The transverse compressive load is varied as 0, 70, 200 and 420 N. Obtained dynamic stress-strain curves at the strain rate of 500 s-1 are compared each other to indicate the effect of the lateral compression on the bar. As a result, the lateral compression of 200 N is found as the most suitable condition. © (2014) Trans Tech Publications, Switzerland.
Itabashi M.,Tokyo University of Science, Suwa
Key Engineering Materials | Year: 2016
In 2012, a novel production line was developed to produce electric arc furnace steel sheet for automotive structure, as a national project in Japan. From the viewpoint of crashworthiness, the evaluation of joint strength under dynamic loading is essential. In this study, single-lap spot-welded joint specimens are prepared with the variation of welding current. The specimen sheet is 980-MPa grade electric arc furnace steel and 1.0 mm in thickness, which is supplied by Tokyo Steel Co., Ltd. Nugget diameter d is recommended by a well-known empirical equation, d = 5√t′, where t′ is sheet thickness. The nugget diameter can be adjusted mainly by welding current. In order to find the optimum nugget diameter under dynamic tensile-shear, five values of welding current, 6.1, 6.4, 6.7, 7.0 and 7.3 kA are tried. The values are set for the recommended nugget diameter 5.00 mm, and ±5% and ±10% of the recommended diameter. Experimental results of quasi-static (loading velocity: 2.0 mm/min = 3.3×10-5 m/s) and dynamic (initial loading velocity: 7 m/s) tensile-shear tests shows that, despite of loading velocity and welding current (equivalent to nugget diameter), tensile-shear strengths are almost constant. Absorbed energies up to the strength give complicated tendencies. At the recommended welding current (equivalent to d = 5.00 mm), the most stable strengths and energies are obtained. © 2016 Trans Tech Publications, Switzerland.