Theory and characteristics of novel variable reluctance 1X resolver

Although brushless resolvers have been used widely as angular position transducers, they are expensive due to their intricate construction, involving a rotary transformer to supply the exciting coils wound on the rotor poles with the current. It is shown theoretically in this paper that the resolver without rotary transformer or brushes can be realized by simple construction, which consists of the stator core with both 4-poles exciting windings and 2-poles output ones and the rotor core carrying no windings. In this resolver the rotor core has minimum gap at one side and a maximum gap at another side of the diameter. It is characterized by an outer surface form that makes the fluctuation part of gap permeance very in proportion to cos θ, where θ represents the angular position of a point in the air gap with respect to the origin on the rotor, the point of minimum air gap. The method determining the rotor form to embody the aforementioned gap permeance variation is also shown. It has been confirmed not only by simulation but also experiment that the 2-phase output voltages of a model designed based on the theory have sinusoidal waveforms with very small harmonic contents. Moreover, the rotor position detected by processing the output voltages through the conventional resolver/digital converter was within acceptable engineering accuracy.     

An abnormally shortened fatigue life of steels caused by anelasticity

Some abnormal fatigue life shortenings dependent upon load frequency for several steels are discussed. A possible relation between anelasticity caused by interstitial atoms and the abnormal fatigue life drop is presented. Normally, interstitial atoms are in a position which minimizes the energy around a dislocation, the Snoek ordering sites. We consider the Snoek effect as a typical example of anelasticity, and the possibility on atoms moving from attractive sites to repulsive ones when repeated stresses are applied and discuss a theory to explain the reduction of the fatigue life using Snoek ordered atoms moving out by fatigue stress at the frequency of Snoek effect. Bending fatigue tests were conducted to obtain the relationship between fatigue life and load frequency at two different temperatures (298 K and 333 K) for an iron nitrided steel. A sharp fatigue life drop was observed at a load frequency corresponding to the resonant frequency of the Snoek effect for nitrogen atoms. The frequency was about 3 Hz and 298 K and shifted to a higher frequency — about 6 Hz — at 333 K. Results reveal that the possible explanation to those abnormal phenomena may be anelasticity.Work partially conducted at Laboratorio E and Departamento de Ciencias de Materiales, Universidad Simón Bolívar, Venezuela.     

Effect of Grain Boundaries on Thermal Conductivity of Silicon Carbide Ceramic at 5 to 1300 K

The thermal conductivity of a SiC ceramic was measured as 270 W·m⁻¹·K⁻¹ at room temperature. At low temperatures ( T < 25 K), the decrease in the conductivity was proportional to T ³ on a logarithmic scale, which indicated that the conductivity was controlled by boundaries. The calculated phonon mean free path in the ceramic increased with decreased temperature, but was limited to ∼4 μm, a length almost equal to the grain size, at temperatures below 30 K. We concluded that the thermal conductivity of the ceramic below 30 K was influenced significantly by grain boundaries and grain junctions.     

A superconducting filter to separate an oxygen and argon mixture

Hot isostatic pressing in an oxygen atmosphere, known as O₂-HIP method, has been used successfully to synthesize oxide materials, as well as to produce porous materials. In this paper a porous superconducting oxide is synthesized by this method and its application as a gas filter is described. Porous superconductors can be used to separate a mixture of paramagnetic and diamagnetic gases, such as oxygen and argon. Separation occurs after a magnetic field is applied and is based on the Meissner effect. Experimental results showed that the oxygen content of an oxygen/argon mixture increased after passing through a filter with large pore size (about 10 m).     

Frequency characteristics of stiffness and damping effect of ferro fluid bearing

Damping characteristics and frequency characteristics of ferro fluid bearing (FFB) spindles were measured using a high-frequency vibration base driven by a piezo actuator. Using the high-frequency vibration base, high-frequency excitation was added to ferro fluid bearing spindles mounted on the vibration base, and it was proved that ferro fluid bearing spindles have effective damping. And the damping effect became larger with higher spindle rotational speed. Also we have measured spindle runout of a ferro fluid bearing spindle using a lock-in amplifier to increase S/N ratio and succeeded to measure nano meter order displacements.     

Synchronized fresh cell bioreactor system for continuous L-(+)-lactic acid production using Lactococcus lactis IO-1 in hydrolysed sago starch

An efficient bioreactor, termed a 'synchronized fresh cell bioreactor', was developed and consisted of a pH-dependent substrate feed system coupled with cross flow filtration and turbidity control. The effect of high dilution rate and high cell density coupled with high cell viability on the production of l-lactic acid in continuous culture by Lactococcus lactis IO-1 in enzyme-hydrolysed sago starch medium was investigated. For all changes in dilution rate, cells responded in a synchronized way to the addition of glucose by increasing the rate of biomass formation. Consequently, a glucose-free feed solution was required to maintain the cell concentration at a particular pre-set value. This set-up facilitated the maintenance of the cells in a permanent log phase. At a cell concentration of 15 gl(-1) and a feed glucose concentration of 53 gl(-1), volumetric LA productivities of 8.2, 19.3 and 33.1 gl(-1)h(-1) were obtained at dilution rates of 0.21, 0.50 and 1.1 h(-1), respectively. The respective residual glucose concentrations in the spent medium were 1.90, 0.24 and 3.80 gl(-1). By increasing the cell density, the volumetric productivity increased proportionally. At high cell density, higher dilution rates resulted in lower lactate concentrations in the culture medium resulting in higher productivity. This reactor facilitated efficient operation with high cell viability by maintaining the cells in continuous growth phase for long-term fermentation. Therefore, the growth rate (mu) was calculated according to the Monod equation. Using this system, high specific productivities can be obtained which guarantees high commercial productivity at economical cost with only a small investment for setting up the sago industry.     

Human buprenorphine N-dealkylation is catalyzed by cytochrome P450 3A4

Buprenorphine (BN) is a thebaine derivative with analgesic properties. To identify and characterize the cytochrome P450 (CYP) enzyme(s) involved in BN N-dealkylation, in vitro studies using human liver microsomes and recombinant human CYP enzymes were performed. Norbuprenorphine formation from BN was measured by a simple HPLC-UV assay method, without extraction. The BN N-dealkylation activities in 10 human liver microsomal preparations were strongly correlated with microsomal CYP3A-specific metabolic reactions, i.e. triazolam 1'-hydroxylation (r = 0.954), midazolam 1'-hydroxylation (r = 0.928), and testosterone 6beta-hydroxylation (r = 0.897). Among the eight recombinant CYP enzymes studied (CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4), only CYP3A4 could catalyze BN N-dealkylation. The apparent KM value for recombinant CYP3A4 was similar to that for human liver microsomes (23.7 vs. 39.3 +/- 9.2 microM). The demonstration of BN N-dealkylation by recombinant CYP3A4 and the agreement in the affinities (apparent KM values) of human liver microsomes and recombinant CYP3A4 provide the most supportive evidence for BN N-dealkylation being catalyzed by CYP3A4.