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Obara S.,Kitami Institute of Technology | Kawai M.,Hakodate National College of Technology | Kawae O.,Technology Innovation Center | Morizane Y.,Kitami Institute of Technology
Applied Energy | Year: 2013

The development of local energy systems is important to curtailing global warming and improving public safety. Therefore, in this work, the basic performance of an independent microgrid consisting of tidal power generators, photovoltaics, fuel cells, and heat pumps to locally produce energy for local consumption was analyzed. Fast tidal currents near inlets that join lakes to the sea were converted into electrical energy via a three-phase synchronized generator connected to Darius water turbines. On the basis of the results of an oceanographic survey, the production of electricity and the CO2 emissions of each generator were calculated using balanced equations for electricity and heat. The calculations indicated that 33% of the CO2 emissions were associated with the energy supplied through conventional methods during the summer season. Although the frequency and waveform of the electricity of the microgrid were high quality, improvement in the voltage regulation was still required. © 2012 Elsevier Ltd.

Kotobuki M.,Tokyo Metroplitan University | Kotobuki M.,Hakodate National College of Technology | Kanamura K.,Tokyo Metroplitan University
Ceramics International | Year: 2013

The chemical and electrochemical properties of Li5La 3Ta2O12 (LLTa) solid electrolyte were extensively investigated to determine its compatibility with an all-solid-state battery. A well-sintered LLTa pellet with a garnet-like structure was obtained after sintering at 1200 °C for 24 h. Li ion conductivity of the LLTa pellet was estimated to be 1.3×10-4 S cm-1. The LLTa pellet was stable when in contact with lithium metal. This indicates that Li metal anode, which is the best anode material, can be applied with the LLTa system. A full cell composed of LiCoO2/LLTa/Li configuration was constructed, and its electrochemical properties were tested. In the resulting cyclic voltammogram, a clear redox couple of LiCoO2 was observed, implying that the all-solid-state battery with the Li metal anode was successfully operated at room temperature. The redox peaks of the battery were still observed even after one year of storage in an Ar-filled glove-box. It can be concluded that the LLTa electrolyte is a promising candidate for the all-solid-state battery because of its relatively high Li ion conductivity and good stability when in contact with Li metal anode and LiCoO2 cathode. © 2013 Elsevier Ltd and Techna Group S.r.l.

Kawajiri S.,Kobe University | Shibuya S.,Kobe University | Kato S.,Kobe University | Kawaguchi T.,Hakodate National College of Technology
Unsaturated Soils - Proceedings of the 5th International Conference on Unsaturated Soils | Year: 2011

An oedometer type apparatus has been newly developed for measuring variations of the elastic shear modulus, G of unsaturated soil under constant matric suction, which is equipped with a ceramic disk and a pair of bender elements (BE). Three kinds of soil sample were used to prepare specimens. After consolidation process, specified pore air pressure was applied to desaturate the specimen in step by step. Then the elastic shear modulus of unsaturated soils under each step were measured with the BE method to examine the effects of matric suction. It was found that the normalized shear modulus, G/f(e) for three sample were arranged uniquely against a confining pressure, (2/3σ v,net + s). This result means that the matric suction has influence in more wide suction range on small-strain behaviors of unsaturated soil as a component of the confining pressure. © 2011 Taylor & Francis Group, London.

Mufundirwa A.,Hokkaido University | Fujii Y.,Hokkaido University | Kodama N.,Hakodate National College of Technology | Kodama J.-I.,Hokkaido University
Cold Regions Science and Technology | Year: 2011

In this paper, natural rock slope deformation across fractures predominantly in a chert rock mass was monitored using six surface fracture displacement sensors, and the deformations arising from thermal stresses were predicted using (5. m × 5. m) two-dimensional (2D) finite element (FE) plane strain analysis coupled with a model for rock mass expansion due to freezing of pore water. A new and simple method to minimize displacement proportional to temperature (due to thermal response of chert rock mass and sensor) was proposed. By applying the method, the corrected displacement, u', can be well recognized. Under u', clear rock mass movement, which could be related to fracture growth, was observed. In addition, progressive fracture opening and closure were noted. Results from this study indicate insignificant influences of weather conditions on fracture/rock mass movement. Furthermore, under numerical analysis (FE), in the rock mass model (with 1-m deep fracture), tensile stresses that were large enough to induce fracture growth appeared at the fracture tip when temperature lowered. And in the rock slope model (with 1-m deep fracture), small tensile stresses, which were sufficient to cause fracture growth along the planes of weakness, were observed. This research suggests that freezing effects on deformation of chert rock mass are insignificant, and we tentatively suggest that thermal fatigue predominantly caused the permanent fracture deformations. © 2010 Elsevier B.V.

Kimura A.,Hakodate National College of Technology
Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) | Year: 2011

In inverter-converter driving systems for AC electric cars, the DC input voltage of an inverter contains a ripple component with a frequency that is twice the line voltage frequency, due to the use of a single-phase converter. The ripple component of the inverter input voltage causes pulsations in the torque and current of driving motors. To decrease the pulsations, a beatless control method, which modifies the slip frequency depending on the ripple component, is applied to the inverter control. In the present paper, the beatless control method is analyzed in the frequency domain. In the first step of the analysis, transfer functions which revealed the relationship among the ripple component of the inverter input voltage, the slip frequency, the motor torque pulsation, and the current pulsation were derived with a synchronous rotating model of induction motors. An analytical model of the beatless control method was then constructed using the transfer functions. The optimal setting of the control method was obtained according to the analytical model. The transfer functions and the analytical model were verified by simulations. © 2010 Wiley Periodicals, Inc.

Kotobuki M.,Hakodate National College of Technology
Advanced Materials Research | Year: 2013

Lithium ion battery prefers an electrode consist of small particles so as to allow giving short Li+ diffusion pathway. In order to obtain small particles of LiCoO2, which has been commonly used as cathode for lithium battery, the ball-milling is applied to LiCoO2 prepared through a sol-gel method. By the ball-milling, the particle size of LiCoO2 can be reduced from 400 to 250 nm. The discharge capacity of milled LiCoO2 under high current density of 5C is about 100 mA h g-1, that is much higher than non-milled LiCoO2 (60 mA h g-1). It is concluded that the small LiCoO2 prepared by the ball-milling possess superior performance due to short Li+ diffusion length. © (2013) Trans Tech Publications, Switzerland.

Kotobuki M.,Hakodate National College of Technology | Koishi M.,Hakodate National College of Technology
Ceramics International | Year: 2014

In this research, Li7La3Zr2O12 (LLZ), which has been recognized as a promising solid electrolyte for next-generation Li-ion batteries, is prepared by a sol-gel method to lower the calcination temperature. A precursor sol is prepared from lithium acetate, lanthanum acetate and zirconium tetrabutoxide. After gelation, the gel is heated at 700 C, and a white powder, which consisted mainly of La2Zr 2O7, is obtained. Sintered pellets are prepared by calcination at 1000 C or 1100 C. The tetragonal-phase LLZ with low Li-ion conductivity is contained in the pellet calcined at 1000 C. After the calcination at 1100 C, the tetragonal LLZ transforms into a cubic phase which possesses high Li-ion conductivity. With the sol-gel method, the cubic-phase LLZ can be obtained after calcination at 1100 C, which is 130 C lower than the temperature in conventional solid-state reaction. The Li-ion conductivity of the prepared cubic LLZ is 1.5×10-4 S cm-1, which is comparable with the previously reported values. It is concluded that the cubic LLZ with high Li-ion conductivity can be successfully prepared at low temperature using the sol-gel method. © 2013 Elsevier Ltd and Techna Group S.r.l.

Kotobuki M.,Hakodate National College of Technology | Koishi M.,Hakodate National College of Technology
Ceramics International | Year: 2013

Li1.5Al0.5Ti1.5(PO4) 3 (LATP) has received much attention as a solid electrolyte for lithium ion batteries due to its high Li ion conductivity. In this study, the LATP is prepared by a sol-gel process using water-soluble Al(NO 3)3 and water-insoluble Al(C3H 7O)3 as Al sources to examine the influence of the Al source on the properties of the produced LATP. The LATP is successfully produced in both cases; however, a small amount of AlPO4 impurity is formed in the Al(NO3)3 sample due to insufficient mixing of the water-insoluble Ti(C3H7O)4 with the water-soluble Al(NO3)3. In contrast, the AlPO4 formation is not observed in the Al(C3H7O)3 sample. The Li ion conductivity of the Al(C3H7O) 3 sample is higher than that of the Al(NO3)3 sample, implying that the AlPO4 impurity acts as a resistance layer. The performance of LATP prepared by the sol-gel method is strongly affected by the Al sources, and the water-insoluble Al source is suitable for water-insoluble Ti(C3H7O)4, which has been the most widely used Ti source to date. © 2012 Elsevier Ltd and Techna Group S.r.l.

Kotobuki M.,Hakodate National College of Technology | Koishi M.,Hakodate National College of Technology | Kato Y.,Hakodate National College of Technology
Ionics | Year: 2013

The co-precipitation method can make the materials react uniformly at molecular level and has the advantages of lower polycrystalline synthesized temperature and shorter sintering time. Therefore, it is expected that the mass production of Li1.5Al0.5Ti1.5(PO4)3 (LATP) solid electrolyte would be possible by application of the co-precipitation method for LATP preparation. In this study, an application of the co-precipitation method for a preparation of LATP solid electrolyte is attempted. Crystallized LATP powder is obtained by heating precipitant containing Li, Al, Ti, and PO4 at 800 °C for 30 min. The LATP bulk sintered pellet is successfully prepared using the crystallized LATP powder by calcinating at 1,050 °C. The cross-sectional SEM images show that many crystal grains exist, and the grains are in good contact with each other, i.e., there is no void space. All diffraction peaks of the pellet are attributed to LATP in XRD pattern. The sintered pellet is obtained by calcinating at 1,050 °C, which is more than 150 °C lower than that of conventional method. The LATP solid electrolyte shows a good conductivity which is 1.4 × 10-3 S cm-1 for bulk and 1.5 × 10-4 S cm-1 for total conductivities, respectively. © 2013 Springer-Verlag Berlin Heidelberg.

Kotobuki M.,Hakodate National College of Technology
International Journal of Energy and Environmental Engineering | Year: 2013

LiCoPO4 has been recognized as a promising cathode material for lithium batteries due to its high stability and high operation voltage. However, poor electronic conductivity of LiCoPO4 prohibits its practical use. A carbon coating can improve electronic conductivity of LiCoPO4. A hydrothermal synthesis is a very convenient method because it allows us easy preparation of small particles of carbon-coated LiCoPO4; however, an effect of precursor for LiCoPO4 preparation on the performance of the synthesized LiCoPO4 has yet to be cleared. In this paper, the effect of Co source for carbon-coated LiCoPO4 (LiCoPO4/C) preparation on performance as a cathode material for Li-ion battery is investigated. The Co source strongly affects the pH value in the starting solution and final products. The single-phase LiCoPO4 is obtained only when CoSO4 or CoCl2 are used as the Co sources. A quality of carbon layer on the LiCoPO4 is also affected by the Co source. The carbon layer on the LiCoPO4 synthesized from CoSO4 contains graphite carbon with high concentration which provides high electronic conductivity compared with that from CoCl2. Accordingly, the LiCoPO4/C synthesized from CoSO4 shows a superior performance than that from CoCl2 due to high-quality carbon layer. © 2013 Kotobuki.

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