Variable-speed control of brushless half-speed synchronous motor byvoltage source inverter

The variable-speed control of a voltage source inverter-fed cylindrical rotor type of brushless half-speed synchronous motor with feedback of the rotor position is described. On the basis of an approximate analysis of the steady state, an expression for torque is derived, and two methods of speed control are discussed. The step response of speed in the drive system is almost the same as that in a speed control method based on a slip frequency control in an induction motor drive, and a relatively high torque is obtained even in a low speed region. The motor has the capability of line start and change over from an induction motor (Gorges phenomenon) to a self-controlled half-speed synchronous motor by using a simple position sensor     

New GTO Current Source Inverter with Pulsewidth Modulation Control Techniques

A new GTO current source inverter in which two auxiliary GTO's are added to the basic inverter circuit, which consists of six GTO's and three capacitors, is presented. One of the auxiliary GTO's is connected between the positive line of the inverter and the neutral of three Y-connected capacitors; another is connected between the negative line and the neutral. In the proposed inverter, the charges of three capacitors are controlled at the same time by means of pulsewidth modulation (PWM) to main GTO's and auxiliary GTO's. This inverter can supply both the sinusoidal current and voltage to the motor. The PWM control technique, the operating principle, and the experimental results for 2.2-kW induction motor drives are described. The output current waveform of this inverter is closely sinusoidal, as opposed to trapezoidal in the basic inverter circuit. The steady-state characteristics of the GTO-CSI induction motor drive system are analyzed by the state-variable methods, and a close agreement between the analyzed and the experimental results is obtained. Smooth and noiseless drive of induction motor over a wide range of speed is observed.     

Low-Speed Drive of PWM-VSI-Fed Brushless Self-Excited Synchronous Motor

The brushless self-excited synchronous motor with halfwave rectified field circuits has been invented already by Nonaka. For the low-speed drive of the motor a new method of the voltage supply which superimposes a higher-order harmonic component on sinusoidal low-frequency voltage by a pulsewidth modulated (PWM) GTO inverter is presented. The amplitude and frequency of the fundamental component and those of the harmonic component are controlled independently by a microcomputer-based PWM strategy. It is confirmed from the experimental results that controllable brushless self-excitation and smooth low-speed operation without torque pulsation are achieved by the proposed scheme.     

A firm as a dialectical being: towards a dynamic theory of a firm

Today, firms are facing many contradictions: efficiency versuscreativity; exploitation versus exploration; speed versus time-consumingresource building. This paper argues that a firm's capabilityto synthesize such contradictions is the key to understandingwhy a firm can be more efficient at producing knowledge thanmarket. A firm can create new knowledge and capability thatgo beyond the balancing point in the existing frontier withits synthesizing capability, which is embedded in its knowledgevision, its ba, its creative routines, its incentive systemsand its distributed leadership.     

Motional coherency in chain dynamics of polybutadiene studied by molecular dynamics simulations

Molecular dynamics simulations of 1,4-polybutadiene in bulk amorphous state were performed. Results were compared with the recent neutron spin-echo measurements. To investigate motional coherency the relaxation rates for the collective and self-motions, the collective and self-relaxation rates, were evaluated for the short and long time regimes of the normalized intermediate scattering functions. The scattering vector dependence of the collective relaxation rates estimated for both fast and slow processes indicated a minimum at scattering vector q = 1.5 Å⁻¹, corresponding to the position of a peak in the static structure factor. The self-relaxation rates increased monotonously with q. A phenomenon known as de Gennes narrowing was reproduced well in the simulation and found to be originated from the inter-molecular correlation. The collective relaxation rate evaluated for fast process appeared to modulate around a peak of q = 2.9 Å⁻¹, corresponding to the intra-molecular correlation.     

Phase and magnetic properties of iron oxide clusters in 20CaO·20SiO2·7Fe2O3·6FeO glasses

The annealing of 20CaO·20SiO₂·7Fe₂O₃·6FeO glasses at 973K in vacuo produced clusters of iron oxide, the shape of which was nearly spherical and the diameter distributed in the narrow range 25–115Å. The phase of clusters was identified to be Fe³⁺(Fe³⁺ _{poststagger|1.30}Fe²⁺ _{poststagger|0.55}V_0.15)·O₄ in the inverse spinel structure based upon the Mössbauer spectra and x-ray diffraction profiles. The clusters exhibited superparamagnetism and their effective anisotropy energy constant was inversely proportional to the cluster diameter. The magnetization of the glasses measured by a vibrating sample magnetometer was 7.2 × 10^-6 Wbmkg^-1 at 10 kOe at room temperature and smaller than the value calculated assuming that the whole clusters have superparamagnetism. These results suggest the pinning of spins near the cluster surface.     

Cloning and heterologous expression of a beta-fructofuranosidase gene from Arthrobacter globiformis IFO 3062, and site-directed mutagenesis of the essential aspartic acid and glutamic acid of the active site

We have cloned the gene encoding a beta-fructofuranosidase from Arthrobacter globiformis IFO 3062, and subsequently, the gene was heterologously expressed in Escherichia coli. This beta-fructofuranosidase gene encodes a protein of 548 amino acid residues with a calculated molecular mass of 60,519 Da. We have examined the roles of three residues of A. globiformis IFO 3062 beta-fructofuranosidase by site-directed mutagenesis, and found that aspartic acid 130 and glutamic acid 392, which are two of the apparent catalytic residues, are essential for hydrolase activity. This study provides the first experimental evidence showing that these two amino acid residues of beta-fructofuranosidase play a critical role in hydrolyzing sucrose.     

Fluorogenic derivatization reagents suitable for isolation and identification of cysteine-containing proteins utilizing high-performance liquid chromatography-tandem mass spectrometry

The fluorogenic derivatization reagents with a positive charge, 4-(dimethylaminoethylaminosulfonyl)-7-chloro-2,1,3-benzoxadiazole (DAABD-Cl) and 7-chloro-2,1,3-benzoxadiazole-4-sulfonylaminoethyltrimethylammonium chloride (TAABD-Cl), are proposed for use in proteomics studies. Following derivatization of protein mixtures with these reagents, a series of standard processes of isolation, digestion, and identification of the proteins were performed utilizing high-performance liquid chromatography-fluorescence detection and tandem mass spectrometry with the probability-based protein identification algorithm. Both DAABD and TAABD derivatives were detected fluorometrically at the femtomole level and showed more than 100-fold improvement in sensitivity compared to the underivatized original compounds with an electrospray ionization ion trap mass spectrometer analysis. The modification of the MASCOT database search system memorized with the fragment information of a DAABD-attached Cys residue allowed the identification of the proteolytic peptide fragments of the derivatized bovine serum albumin (BSA) with an estimated 38% sequence coverage of BSA. Utilizing DAABD-Cl as a derivatization reagent, identification of several proteins was also possible in a soluble extract of Caenorhabditis elegans (10 microg of protein). Consequently, for identification of proteins in the complex matrixes of proteins, DAABD-Cl could be a more appropriate reagent than ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate as reported previously.