関屋 大雄

String-topology multi-hop network is often selected as an analysis object because it is one of the fundamental network topologies. The purpose of this paper is to establish expression for end-to-end delay for IEEE 802.11 string-topology multi-hop networks. For obtaining the analytical expression, the effects of frame collisions and carrier-sensing effect from other nodes under the non-saturated condition are obtained for each node in the network. For expressing the properties in non-saturated condition, a new parameter, which is frame-existence probability, is defined. The end-to-end delay of a string-topology multi-hop network can be derived as the sum of the transmission delays in the network flow. The analytical predictions agree with simulation results well, which show validity of the obtained analytical expressions.

To make power devices with lower losses and higher power capabilities, superjunctions (SJs), based on GaN, GaAs, and related materials, are attractive. It is because they have higher breakdown fields than Si and allow the use of heterostructures, where highly conductive layers of 2-D electrons and holes can be formed. As a step toward such SJ devices, we have fabricated AlGaAs/GaAs four-terminal devices in which a pair of electron/hole channels is embedded. Transport properties of electrons and holes are studied by operating the devices as FETs in which the conductance of one channel is controlled by using the other as a gate. Current-voltage and capacitance-voltage characteristics between the two channels are evaluated by operating the devices as p-n diodes. Measured characteristics are examined by comparing them with device simulations with a focus on the carrier depletion process in each channel.

This paper presents analytical expressions of network throughput for wireless 2-hop networks with tethering function at any offered load. Network throughputs can be obtained analytically by expressing collision probabilities and frame existence probabilities with respect to each node. The validities of the analytical expressions are confirmed from quantitative agreements between analytical and simulation results.

This paper presents a RIC-WPT system with class-E inverter and class-DE rectifier along with its analytical design procedure. By using the class-E inverter as a transmitter and the class-DE rectifier as a receiver, the designed WPT system can achieve a high power-delivery efficiency because of the class-E ZVS /ZDS conditions in both the inverter and the rectifier. In the experimental results, the system achieved 73.0% overall efficiency at 9.87 W (50 Omega) output power, coil distance 10 cm, and 1 MHz operating frequency. The experimental results showed good agreement with the design specifications, which indicates the validity of the design procedure.

This paper proposes analytical expressions of end-to-end throughput for IEEE 802.11e Enhanced Distributed Channel Access (EDCA) wireless string-topology multi-hop networks. For obtaining the IEEE 802.11e EDCA performance, internal collisions between Access Categories (ACs) in a node, frame collisions with external nodes, and frame-existence probabilities of buffers at each AC are expressed as functions of EDCA access parameters. Therefore, it is possible to obtain the effects of the EDCA access parameters to Quality of Service (QoS) support in the EDCA. It is possible to obtain the end-to-end throughput at any offered load with respect to each AC because the buffer states can be expressed according to ACs. The obtained analytical expressions are verified by showing the quantitative agreements with simulation results.

本研究では、分散型発電機と従来の発電機を含む最新の電力システムにおけるCO2排出コストを考慮した最適潮流計算を行っている。CO2排出コスト以外に発電コスト、電圧偏差、電力損失を目的関数とした最適化を行っている。

A new family of Class I) resonant inverters is proposed in this paper. Multiple identical series resonant inverters are paralleled using intercell transformers to form phase-controlled multiphase resonant inverter with a common resonant circuit. Inverters can operate at constant frequency utilizing phase-shift control to regulate output. A frequency-domain analysis of the proposed family is performed. An experimental prototype of a three-phase resonant inverter with common resonant circuit was built and extensively tested at an output power of 550 W and switching frequency of 167 kHz.

This paper presents a resonant inductive coupling wireless power transfer (RIC-WPT) system with a class-E2 dc-dc converter along with its analytical design procedure. By using the class-E inverter as a transmitter and the class-E rectifier as a receiver, the designed WPT system can achieve a high power-conversion efficiency because of the class-E ZVS/ZDS conditions satisfied in both the inverter and the rectifier. In the simulation results, the system achieved 65.9 % overall efficiency at 5 W (50 ω) output power, coil distance 30 cm, and 5 MHz operating frequency. Additionally, the simulation results showed good agreement with the design specifications, which indicates the validity of the design procedure. © 2014 IEEE.

Gold-nickel bimetallic catalysts were prepared from Au/NiO and Au(OH) 3-Ni(OH)2-NiCO3 coprecipitates by treatment with hydrogen. Gold promoted the reduction of Ni(II) to Ni(0) at relatively low temperatures in the range of 100-150 C, which was confirmed by H2-TPR and in situ XAFS measurements, whereas NiO without Au was not fully reduced even at 300 C. The obtained catalysts were characterized by XRD, HAADF-STEM, XAFS, and 197Au Mössbauer, and these analyses revealed the formation of Au-Ni alloy components in the obtained catalysts. Au existed as Au nanoparticles together with Au-Ni alloy components in Au-Ni-1 prepared from Au/NiO by H2 treatment. When Au(OH)3-Ni(OH) 2-NiCO3 was treated in a flow of H2 to produce Au-Ni-2, the formation of Au NPs was not clearly observed, thereby meaning that Au atoms were highly dispersed as a single atom and/or small clusters in the obtained catalysts. Moreover, most of the Au atoms were alloyed with Ni atoms for Au-Ni-2. The obtained Au-Ni-1 and Au-Ni-2 exhibited superior catalytic activities for the selective hydrogenolysis of benzylic alcohols into alkylbenzene derivatives in terms of reaction rates normalized by catalyst surface area. Accordingly, Au-Ni-1 and Au-Ni-2 recorded the reaction rates of 4.79 and 9.79 mmol L-1 h-1 m-2, respectively. These values were greater than that obtained for Raney Ni (0.14 mmol L -1 h-1 m-2). In addition, Au-Ni-2, which contains higher Au-Ni alloy content, showed greater reaction rates when compared to Au-Ni-1. Since Au/TiO2 showed poor catalytic activity for the hydrogenolysis, Au-Ni alloy enhanced the catalytic activities of Ni(0). © 2013 Elsevier Inc. All rights reserved.

This paper presents analytical expressions of the MOSFET-parasitic-capacitance effects on the output envelope of the EER transmitter, taking into account the MOSFET linear gate-to-drain and nonlinear drain-to-source parasitic capacitances in the class-E amplifier. The analysis is useful to predict the behavior of the EER transmitter using the class-E amplifier. It is shown that the envelope of the output voltage is not in proportion to the dc-supply voltage due to the MOSFET-parasitic-capacitance effects. Additionally, the driving voltage waveform affects the output-voltage amplitude and phase shift between the driving voltage and the output voltage.

We herein propose a MAC protocol for the smart antenna network, which applies pulse/tone exchange prior to the RTS/CTS handshake process. RTS frame collisions are drastically reduced with little additional overhead due to pulse/tone exchange in the proposed protocol. In addition, the number of exposed nodes is reduced by using smart antennas. Furthermore, since the occurrence of the deafness problem can be identified by pulse/tone exchange failure, retransmission is conducted using a fixed contention window value. Therefore, the wastage of wireless resources due to the deafness problem is reduced. As a result, the network throughput can be effectively improved compared with that for previous protocols. Simulation results demonstrate the validity and effectiveness of the proposed protocol.

This letter presents a bifurcation analysis of the class-E inverter for switching-pattern derivations. The transition conditions of switching patterns are the same as the bifurcation condition of the border-collision bifurcation or the grazing bifurcation. Therefore, the switching-pattern distribution maps for wide parameter region can be obtained by applying the analytical algorithm of bifurcation-curve derivations.

The class-E amplifier is one of the switching amplifiers, which satisfies the class-E switching conditions. It is, however, difficult to determine the values of the passive elements included in the circuit for achieving the class-E switching conditions. The particle swarm optimization algorithm for designing the class-E amplifier is presented in this paper. To reduce the computational cost and consider the nonlinear effects of MOSFET in the amplifier, a circuit simulator which finds the steady-state solution is introduced. Moreover, OpenMP, which is an API for multi-platform shared-memory parallel programming, is used in the developed program to accelerate the proposed procedure. In a design example, the class-E amplifier, the element values of which were obtained by the particle swarm optimization, showed a good performance.

In IEEE 802.11 wireless multi-hop networks, each node works individually and their individual operations generate entire network dynamics. It is important to clarify the network dynamics in wireless multi-hop networks for designing and constructing multi-hop communication networks. This paper presents the network-dynamics investigations for three-hop string-topology wireless network in detail. From the investigations, a “backoff-stage synchronization” phenomenon, which is mutuality between hidden nodes, is found. The mechanism of the backoff-stage synchronization is expressed and the sufficient conditions for the synchronization occurrence are given. This phenomenon gives some impacts on the IEEE 802.11 multi-hop-network communications.

This paper gives analytical expressions for the output power and the power conversion efficiency of the class-E power amplifier outside the class-E ZVS/ZDS switching conditions. The analytical predictions agreed with the experimental results quantitatively, which indicates the validity of the analytical expressions. Moreover, a design example applying the analytical expressions for the power conversion efficiency is given. By using the analytical expressions, it is possible to design the class-E amplifier, which improves the power conversion efficiency compared with that of the class-E amplifier satisfying the class-E ZVS/ZDS conditions.

本稿では並列接続されているＤ級増幅器が互いに違う周波数で動作している場合について研究を行う。本研究では２つの増幅器は並列接続されているため互いに出力電力に影響があることがシミュレーションにより確認された。本論文では、これらを減らすためにより高い周波数の増幅器の出力に分離フィルタを挿入することを提案する。提案された分離フィルタにより正常に増幅器間のカップリングが改善されることが示される。

In this paper, equations for waveforms and design relationships are derived for class DE amplifiers with nonlinear shunt capacitances. Using the analytical waveform equations, it is shown that the nonlinearity of the shunt capacitances affects the waveforms only during the dead-time intervals. Additionally, the waveforms with nonlinear and linear shunt capacitances are not very different if class E zero-voltage switching/zero-derivative switching conditions are satisfied. The operation of a class DE amplifier has two dead-time intervals in one period. The switch-voltage waveforms for both dead-time intervals exhibit symmetry. Therefore, the nonlinearity does not have any effect on the series-resonant-circuit elements. As a result, analytical design equations indicate that the series-resonant-circuit elements are independent of the nonlinearity of the shunt capacitances when the supply voltage and the output power are given as design specifications, which is an important result of this paper. The validity of our analysis is confirmed by PSpice simulations and the circuit experiment.

This paper presents novel design procedures for class E switching circuits allowing implicit circuit equations. Because of the allowance, circuit simulators can be used in the proposed design procedures. Moreover, the proposed design procedures also allow any conditions considered until now., The proposed design algorithms are implemented by using PSpice and OPTIMUS. This paper shows the design examples of two kinds of class E switching circuits. In particular, the design example of the class E oscillator shows the benefit of the proposed design procedure eminently, i.e., it is unnecessary to make an equivalent model of the semiconductor devices for the design. These design examples show the validity and effectiveness of the proposed design procedures.

Reverse transcription-PCR targeting the VP0 gene of human parechoviruses (HPeVs) was used to identify two isolates from two Japanese children's stool specimens. Molecular analysis revealed that these isolates belonged to HPeV type 4, and their nucleotide identity in the P1 region was 85.0%. Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The authors point out that the rate of fatalities for occupants of sedans is higher than that for occupants of sports-utility vehicles (SUVs) for collisions between vehicles of equal weight from the analysis of traffic accident data in Japan. Precise 1:10 scale model vehicles are used for crash test experiments. In the case of a collision with a flat barrier, the compartment force of the sedan is mainly supported by lower structures. Conversely, for collisions with an SUV-type barrier, the compartment force of the sedan is supported by the door-beltline structures. New diagrams are proposed to indicate these differences in compartment force. It can be concluded that the results of the above-mentioned traffic accident data are attributed to the input force transferred the path along the door-beltline in the passenger compartment. © 2008 Taylor &amp Francis.

This paper investigates the design curves of the class DE amplifier with nonlinear shunt capacitances for any output Q and any grading coefficient m of the diode junction in MOSFET. The design curves are derived by the numerical calculation. It is clarified that the nonlinearities of shunt capacitances affect the VD design curves of the class DE amplifier, especially, for low output Q. The waveforms from Spice denote the validity of the design curves.

This paper presents an interleaved class E(2) dc/dc converter. In the proposed converter, N class E(2) dc/dc converters are connected in parallel at the class E rectifier. The proposed converter is suitable to the low-voltage/high-current applications. Since less current flows through the each converter, the amount of the power losses on the parasitic resistances are also reduced. In addition, the output filter of the rectifier is downsized because of higher frequency of the interleaved current. By carrying out the circuit experiments, we show that the experimental results agree with the numerical ones quantitatively. The laboratory measurement achieves the over 90% power conversion efficiency under 3.2W and 1MHz operation.

A design of phase-controlled class E inverter with asymmetric circuit configuration is presented. By using the presented design method, it is possible to derive the design values, which let the inverters achieve zero-voltage switching continuously in the control range, are derived. By carrying out circuit experiments, it is verified that the experimental results agree with numerical predictions quantitatively, and the validity of the presented design procedure is denoted.

This paper presents a new control scheme for a Class DE inverter, that is, frequency modulation/pulsewidth modulation (FM/PWM) control. Further, the FM/PWM controlled Class DE inverter is analyzed and we clarify performance characteristics. Since the FM/PWM controlled inverter has two control parameters, namely, the switching frequency and the switch-on duty ratio, it has one more degree of freedom for the control than the inverter with the conventional control scheme. The increased degree of freedom is used to minimize the switching losses. Therefore, it is possible to control the output power with high power-conversion efficiency for wide-range control. Carrying out the circuit experiments, we confirm that the experimental results agree well with the theoretical predictions quantitatively. For example, the proposed controlled inverter can control the output voltage from 56% to 191% of the optimum one, which is designed for 1.8 W at 1.0 MHz, with maintaining over 90% power-conversion efficiency.

In order to reduce the angle component of measurement noise (cross-range errors), we propose multisensor tracking system with the airborne and stationary sensor. The airborne sensor is a phased array sensor witch an aircraft carries. In the proposed system the airborne sensor moves in order to keep the pencil beams from the airborne and stationary sensors to be orthogonal. Therefore the proposed system minimizes cross-range errors and high tracking quality could be obtained. Simulation results are given for a comparison of tracking performance of our proposed system with that of conventional systems.

The Class DE inverter offers high-efficiency power conversion under high operating frequency (megahertz order) with low switching noises and low switch voltage stress. It has been applied to dc/dc converters as high-density power sources. Conventional converters with the Class DE inverter are controlled by varying the operating frequency, the switch duty ratio or the phase difference with two inverters. However, in general, frequency-modulated control requires a complex control unit. Changing the switching duty ratio puts the switch-voltage waveforms out of shape, and the phase shift control needs the double space of inverters, which is not suitable for the low output power circuit. As a remedy to these problems, we propose to combine the Class DE inverter with the Class E rectifier using the thinned-out method (deleting some of the pulses to the rectifier). The dc/dc converter's output power is controlled in the rectifier by eliminating its diode-voltage pulse at a desirable rate. The operating frequency is fixed and the waveforms keep the characteristics of Class DE. An experimental circuit was designed at 1-MHz operating frequency and in the optimum operation, the measured dc/dc power conversion efficiency was over 80% with 2.2-W output power at 1 MHz. Characteristics of the converter for the line and load variations are given by circuit experiments. It is shown that the proposed circuit has good characteristics with high power conversion efficiency in a wide range of these variations.