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Now showing items 129 - 136 of 136

  • WAVY LEAF1, an Ortholog of Arabidopsis HEN1, Regulates Shoot Development by Maintaining MicroRNA and Trans-Acting Small Interfering RNA Accumulation in Rice RID A-6040-2010

    Abe, Masashi   Yoshikawa, Takanori   Nosaka, Misuzu   Sakakibara, Hitoshi   Sato, Yutaka   Nagato, Yasuo   Itoh, Jun-ichi  

    In rice (Oryza sativa), trans-acting small interfering RNA (ta-siRNA) is essential for shoot development, including shoot apical meristem (SAM) formation and leaf morphogenesis. The rice wavy leaf1 (waf1) mutant has been identified as an embryonic mutant resembling shoot organization1 (sho1) and sho2, homologs of a loss-of-function mutant of DICER-LIKE4 and a hypomorphic mutant of ARGONAUTE7, respectively, which both act in the ta-siRNA production pathway. About half of the waf1 mutants showed seedling lethality due to defects in SAM maintenance, but the rest survived to the reproductive phase and exhibited pleiotropic phenotypes in leaf morphology and floral development. Map-based cloning of WAF1 revealed that it encodes an RNA methyltransferase, a homolog of Arabidopsis (Arabidopsis thaliana) HUA ENHANCER1. The reduced accumulation of small RNAs in waf1 indicated that the stability of the small RNA was decreased. Despite the greatly reduced level of microRNAs and ta-siRNA, microarray and reverse transcription-polymerase chain reaction experiments revealed that the expression levels of their target genes were not always enhanced. A double mutant between sho and waf1 showed an enhanced SAM defect, suggesting that the amount and/or quality of ta-siRNA is crucial for SAM maintenance. Our results indicate that stabilization of small RNAs by WAF1 is indispensable for rice development, especially for SAM maintenance and leaf morphogenesis governed by the ta-siRNA pathway. In addition, the inconsistent relationship between the amount of small RNAs and the level of the target mRNA in waf1 suggest that there is a complex regulatory mechanism that modifies the effects of microRNA/ta-siRNA on the expression of the target gene.
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  • Square wave operation for a single-phase PFC three-phase motor drive system without a reactor

    Ohtani, Nobuhiro   Itoh, Jun-ichi  

    This paper proposes a square wave control strategy for a new boost-up converter which uses the leakage inductance of a motor instead of a boost up reactor. Since the power supply is connected to the neutral point of the motor; the current distortion in the power supply occurs when the inverter outputs square waveforms. First; this paper describes the characteristic of the proposed circuit and the problems in the square wave operation. Next; a current control method for the square waveform is proposed to suppress the current distortion. Finally; the validity of the proposed converter and its control strategy are demonstrated by experimental results.
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  • Reduction of a boost inductance using a switched capacitor DC-DC converter

    Itoh, Jun-ichi   Matsuura, Koichi   Orikawa, Koji  

    The loss analysis of a switched capacitor converter (SCC) with a boost reactor is discussed in this paper. The proposed SCC can deliver an output voltage independent from the circuit structure comparing to other voltage control methods. The main feature of this circuit is that most of the energy for the boost up function is transferred from a flying capacitor which results the inductance of the input reactor can be reduced. The reactor size of the proposed SCC is smaller than that of the conventional boost converters. A 1000 W 3-level SCC prototype has been built and tested. The efficiency of 97.8%is achieved at 1000 W when the boost up ratio is three times. Moreover; the loss analysis shows the main loss of the proposed SCC is the diode conduction loss.
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  • A Novel Control Strategy for Matrix Converters in Over-modulation Range.

    Tamai, Yasuhiro   Ohguchi, Hideki   Sato, Ikuya   Odaka, Akihiro   Mine, Hironori   Itoh, Jun-ichi  

    This paper proposes a control strategy for matrix converters to reduce the torque ripple in the overmodulation range. In the over-modulation range; motor drive performance of matrix converters is deteriorated because of the output voltage saturation. Especially; the torque ripple which has lower frequency components than the input voltage frequency is remarkable. In this paper; the theoretical analysis about the causes of the torque ripple and the effect of the proposed control strategy are shown. Experimental results verify the validity of the theoretical analysis and confirm the effectiveness of the proposed control strategy. Furthermore; the harmonic distortion of the output current is also reduced compared with another control strategy.
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  • Behavior of a matrix converter with a feed back control in an input side

    Itoh, Jun-ichi   Haruna, Junnosuke  

    This paper discusses about characteristics of a matrix converter where a current feedback is applied to the input side. When the impedance of the power grid is high; such as a generator; the control stability of the matrix converter will be deteriorated. One of the solutions to this problem is to apply an input current stability control that is proposed. However; the efficiency of the generator will decrease at light load and heavy load. In this paper; the behavior of the input current control is analyzed; then the vector control is applied to the input side in order to obtain a stable operation and the maximum efficiency according to the pole position of the generator. This study confirms the validity of the vector control for the matrix converter input side with experimental results. The input current THD 2.8%is obtained under a RL load.
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  • Investigation of a two-stage boost converter using the neutral point of a motor

    Ikarashi, Daisuke   Itoh, Jun-ichi  

    This paper discusses about a six-step operation strategy for a proposed two-stage boost converter using the neutral point of a motor. The proposed converter consists of a small boost chopper and a three-phase inverter; which has a boost up function from the use of the leakage inductance of a motor instead of a boost-up reactor; for a DC to AC conversion. When the inverter part outputs a square waveform of 180 degree; the input current has distortion because the neutral point voltage of the motor is fluctuated at three times of the output frequency. The input current distortion because of the voltage fluctuation is reduced to 1/8 smaller by applying a feed forward control. Additionally; in this proposed circuit; the DC current is imposed into the phase current of the motor. Therefore; the influence of the imposed DC current is investigated in a FEM by simulating a 1.5-kW IPM motor.
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  • Input current stabilization control of a matrix converter with boost-up functionality

    Kato, Koji   Koiwa, Kazuhiro   Itoh, Jun-ichi  

    This paper proposes a circuit topology of a matrix converter that adding a boost up function in the input side. The proposed circuit combines the matrix converter with a V-connection AC chopper. A conventional control method can be applied in this matrix converter; so called the virtual indirect method. In order to suppress the input filter resonance; this paper discusses about the input filter design with a damping resistor. In addition; this paper also proposed a stabilization control for the input current that is using a V-connection chopper. The basic operation and validity of the proposed method is confirmed by the simulation and experimental results. The total loss of the proposed circuit is 20%less than that the loss of the conventional back to back system.
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  • A control strategy for a matrix converter under a large impedance power supply

    Haruna, Junnosuke   Itoh, Jun-Ichi  

    This paper proposes a control strategy for a matrix converter with an input power supply such as generator. Currently, applications for grid connection have been considered such as micro-gas turbines, wind power systems, engine generators and so on. However, very large impedance power supply such as the generator has not been sufficiently examined. Especially the PM generator which is used in various applications has large synchronous reactance. Terminal voltage of the generator is not stable due to resonant phenomena between synchronous reactance and an input capacitor. Therefore, the induced electromotive force (e.m.f) in the generator is estimated using a band pass filter (BPF). In addition, stabilization control on a rotating frame is also proposed for the input terminal voltage. In addition, this paper suggests an optimum input power factor control because the output voltage is smaller than the output voltage command when a conventional power factor control is used. By using the stabilization control, the input current THD of 4.2% is obtained through experimental results. Moreover, the validly of the optimum input power factor control is also confirmed by the experimental results.
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