The least‐squares meshfree method

A new efficient meshfree method is presented in which the first‐order least‐squares method is employed instead of the Galerkin's method. In the meshfree methods based on the Galerkin formulation, the source of many difficulties is in the numerical integration. The current method, in this respect, has different characteristics and is expected to remove some of the integration‐related problems. It is demonstrated through numerical examples that the present formulation is highly robust to integration errors. Therefore, numerical integration can be performed with great ease and effectiveness using very simple algorithms. Copyright © 2001 John Wiley & Sons, Ltd.     

Infrared conductivity and carrier mobility of large scale graphene on various substrates

It is known that low-field mobility of graphene depends largely on the substrate material on which it is transferred. We measured Drude optical conductivity of graphene on various substrates and determined the carrier density and carrier scattering rate. The carrier density varies widely depending on the substrate material. However the scattering rate is almost constant, approximately 100 cm(-1), for 5 different substrates. We calculate carrier mobility of graphene using the two quantities, i.e., carrier density and scattering rate, to find that it agrees with the mobility measured from dc transport experiment. We conclude that substrate-depent mobility of graphene originates from different carrier density but not from the scattering rate.     

On-line dead-time compensation method using disturbance observer

A new on-line dead-time compensation method for a permanent magnet (PM) synchronous motor drive is proposed. Using a simple disturbance observer without any additional circuit and off-line experimental measurement, disturbance voltages in the rotor reference dq frame caused by the dead time and nonideal switching characteristics of power devices are estimated in an on-line manner and fed to voltage references in order to compensate the dead-time effects. The proposed method is applied to a PM synchronous motor drive system and implemented by using software of a digital signal processor (DSP) TMS320C31. Simulations and experiments are carried out for this system and the results well demonstrate the effectiveness of the proposed method.     

Phase-shifted parallel-input/series-output dual converter forhigh-power step-up applications

A new phase-shifted parallel-input/series-output dual converter is proposed. It features a low-output voltage ripple, a low rms current in the output capacitor, and a greatly reduced constant switch turn-off stress, whereby the efficiency is significantly improved. This converter is considered to be well suited to high-power step-up applications     

High-performance optical pick-up actuator with singlet objective lens for BD/DVD/CD compatible drive

For perfect compatibility of BD/DVD/CD, a heavy objective lens assembly is inevitable. However, BD format needs very high transfer rate to edit the contents of HD media, without delay. And performance of an optical pick-up actuator is one of several keys to make it possible. To secure high sensitivity, we introduce a magnetic circuit composed of two 3-pole magnets. As a result of it, despite heavy weight of lens assembly, we achieved high performance enough to operate the disc drive as BD CLV 4X.     

A discretized current control technique with delayed input voltagefeedback for a voltage-fed PWM inverter

A current control technique for a voltage-fed PWM inverter is presented. The discretized state equation of an inverter and a load independent of operating conditions with the delayed input voltage feedback has been derived using the averaging concept. The discretized current controller is proposed to reduce the current error as fast as possible using the deadbeat control strategy and to stabilize the closed loop system asymptotically when the variations of load parameters are given in the predetermined stabilized region. This proposed control scheme is realized by the symmetrical uniform sampling method and is easily implemented using a microprocessor-based system. Computer simulation for the proposed controller has been carried out and the results show good static and dynamic performances     

On multistage interconnection networks with small clock cycles

In packet switching using multistage interconnection networks (MIN's), it is generally assumed that the packet movements successively propagate from the last stage to the first stage in one network cycle. Ding and Bhuyan (1994), however, have shown that the network performance can be significantly improved if the packet movements are confined within each pair of adjacent stages using small clock cycles. In this short note, we present a model for estimating the performance of multibuffered MIN's employing the approach. Using the model, the relative effectiveness of the approach is identified compared to the traditional design