A damping of rotor natural vibration in three‐phase hybrid stepping motors

This paper proposes a damping method of rotor natural vibration in three‐phase hybrid stepping motors, in which optimal commutation signals are calculated from the period of the natural vibration measured by detecting the motor voltages. Moreover, an acceleration and deceleration pattern is derived from a simple model of the rotor vibration, to suppress undesirable transient oscillation in acceleration, deceleration, and positioning operations. An experimental drive system has been implemented and tested to confirm the effectiveness and versatility of the proposed method. Some experimental results show that the experimental system can damp the rotor natural vibration even if the rotor inertia varies. Compared with the conventional pattern, it is confirmed that the proposed pattern makes a great contribution to damping the undesirable transient oscillations. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 69–77, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10153     

A Factor Analysis Model for a Mixture of Various Types of Variables

A factor analysis model is proposed for the case of a mixture of various types of discrete and continuous manifest variables. It is indicated that the likelihood of parameters can be described for a mixture of different types of distributions by assuming local independence. For estimation of the parameters of interest, the method of marginal maximum likelihood is used, where scores of latent factors are integrated out from the likelihood. A kind of the EM algorithm is utilized for optimization. As an example, the case of a mixture of normal, binomial and Poisson distributions is provided.

     

The use of scanning laser ophthalmoscope microperimetry to detect visual impairment caused by macular photocoagulation

The use of Tamoxifen as treatment for breast cancer is well established and its use experimentally as prophylaxis is promising, but little has been written about mammographically detected changes in breast parenchyma as a result of Tamoxifen therapy. We report two cases of spontaneous regression of breast cysts after Tamoxifen therapy for premenopausal breast cancer in the contralateral breast.     

Efficient gene transfer into cardiac myocytes using adeno-associated virus (AAV) vectors

Adeno-associated virus (AAV) vectors, derived from a non-pathogenic parvovirus, are considered to be an appropriate gene transfer vehicle for both dividing and non-dividing cells. In the present study, we investigated whether the rat heart could be efficiently transduced with AAV vectors. Rat cardiac myocytes (CM) were infected with AAV-lacZ vector containing beta-galactosidase (beta-gal) gene in vitro, and the expression of beta-gal in CM was evaluated by X-gal staining and beta-gal ELISA. With increasing multiplicities of infection (MOI), more than 60% of CM were stained positively with X-gal, and the beta-gal expression increased to 31.1 +/- 4.6 ng/mg protein in a MOI-dependent manner (MOI: 10(4) to 10(6) particles/cell). The beta-gal expression was also increased in an incubation period-dependent manner (1-24 h). beta-gal expression was maximal at day 3 and then gradually decreased with time. However, beta-gal expression at day 14 was almost the same level as that at day 1 (45.5 +/- 5.9 v 55.2 +/- 6.2 ng/mg protein). Excised rat right ventricular papillary muscles were also infected with AAV-lacZ ex vivo. When the beta-gal expression was evaluated by X-gal staining, more than 80% of CM in the papillary muscles were stained positively, indicating efficient gene transfer into CM using AAV vectors. These findings suggest that AAV vectors are promising for cardiac gene therapy.     

Performance of automatic gain adjustment in a shunt active filter intended for installation on power distribution systems

This paper discusses automatic gain adjustment in a fully‐digital‐controlled shunt active filter intended for installation on power distribution systems. This is the first step in cooperative control of multiple shunt active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, an optimal control gain is equal to the characteristic impedance of a distribution line. However, it is difficult to know the circuit parameters of a real distribution line, which depend strongly on feeder connections, shunt capacitors, and loads. Therefore, the main purpose of the gain adjustment is to help the active filter to damp out harmonic propagation without considering the circuit parameters. Moreover, the gain adjustment can reduce the compensating current and losses in the active filter. The active filter having the function of automatic gain adjustment is experimentally compared to that with a constant gain. Experiment results verify the effectiveness of the active filter having the function of automatic gain adjustment. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 56–65, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10094     

The crack tip opening angle (CTOA) of the plane stress moving crack

Recently, Crack Tip Opening Angle (CTOA) was proposed by C.F. Shih et al. to describe the instability criterion of ductile crack propagation during plane strain (flat crack) conditions, and was derived by J. R. Rice analytically by means of the slip line field theory and the incremental theory of plasticity. CTOA appears to be applicable in (some or most) cases, but does not accurately describe the plane stress growing crack (slant crack).Unstable ductile crack propagation of the plane stress crack is widely studied for the safe design of highly pressurized gas pipelines. The impact absorption energy of the Charpy test is well correlated to the fracture arresting properties of the structures, but the mechanics of the fracture are not yet well established.In this paper, CTOA of the plane stress growing crack is derived from the plane stress plasticity of perfectly plastic materials by Sokolovsky's approach. Our proposed modification of CTOA expressed as follows: $\text{CTOA}\text{= (α/δ}{}_0\text{)(}\text{d}\text{J/}\text{d}\text{l) + β(δ}{}_0\text{/E)}\text{ln}\text{(eR/r)}$ where $\text{β = 1.40}$ under the plane stress conditions.CTOA in the Dugdale model is also defined and compared with the results of laboratory test. The results show that $\text{α = 0.5}$, and $\text{β = 1.27}$ for plane stress crack growth. These analyses give similar results to those obtained by Rice et al. for CTOA under plane strain conditions, that is, $\text{α = 0.65}$ from the experimental results and $\text{β = 5.08}$ from the slip line theory.The CTOA obtained for plane stress ductile crack growth is applied to the wide plate tensile crack growth test. The results of the present analysis coincide well with those of the plane stress finite element method (FEM) computed by T. Kanazawa et al. The phenomena of plane stress ductile crack propagation are also explained by the CTOA criterion under plane stress conditions.     

A low loss NbTi multifilamentary composite conductor for A.C. use

Investigations of a.c. losses and stability of a mixed-matrix NbTi multifilamentary conductor are presented. Fine filament size of 1.0 μm and a tight twist of 5.5 times the wire diameter 0.2 mm result in a time constant of the eddy current of 0.024 msec at 1.0 T. If this conductor is used in superconducting armature windings of rotating machines or in a.c. magnets, generating a maximum field of 1.0 T, economical benefits are expected at operation frequencies below 20 Hz.     

Two-stage equilibrium model for a coal gasifier to predict the accurate carbon conversion in hydrogen production

The performance of the Texaco gasifier in hydrogen production was studied numerically. To estimate the accurate carbon conversion, a two-stage equilibrium model was proposed. In the proposed model, the two reactions which determined the carbon conversion were separated from other vapor–vapor reactions. The governing equations of the proposed model were derived and a self-consistent method was developed to solve the governing equations. The %AAD of the calculated carbon conversions from the measured values was 2.89 and that of the calculated gas production rate was 0.64. Calculated gas compositions showed a fairly good agreement with the experimental ones for commercial scale plants. It was found that the chemical reactions that occurred in the Texaco gasifier possess a mechanism for keeping the carbon conversion close to unity against a wide variation in the H₂O to coal ratios.     

Evaluation of the implant type tissue-engineered cartilage by scanning acoustic microscopy

The tissue-engineered cartilages after implantation were nonuniform tissues which were mingling with biodegradable polymers, regeneration cartilage and others. It is a hard task to evaluate the biodegradation of polymers or the maturation of regenerated tissues in the transplants by the conventional examination. Otherwise, scanning acoustic microscopy (SAM) system specially developed to measure the tissue acoustic properties at a microscopic level. In this study, we examined acoustic properties of the tissue-engineered cartilage using SAM, and discuss the usefulness of this devise in the field of tissue engineering. We administered chondrocytes/atelocollagen mixture into the scaffolds of various polymers, and transplanted the constructs in the subcutaneous areas of nude mice for 2 months. We harvested them and examined the sound speed and the attenuation in the section of each construct by the SAM. As the results, images mapping the sound speed exhibited homogenous patterns mainly colored in blue, in all the tissue-engineered cartilage constructs. Contrarily, the images of the attenuation by SAM showed the variation of color ranged between blue and red. The low attenuation area colored in red, which meant hard materials, were corresponding to the polymer remnant in the toluidine blue images. The localizations of blue were almost similar with the metachromatic areas in the histology. In conclusion, the SAM is regarded as a useful tool to provide the information on acoustic properties and their localizations in the transplants that consist of heterogeneous tissues with various components.