A bidirectional AC-DC power converter with power factor correction

This paper presents new operation and performance of a thyristor-based AC-DC current-controlled boost-type converter that allows bidirectional power handling capability and provides input power factor correction and a near-sinusoidal input current waveform. The new converter can reduce harmonic pollution and disturbance on the supply mains. The feature of bidirectional power flow allows the stored energy in loads, such as motors, to regenerate back to the supply source, leading to an increase in overall energy efficiency and possibly a reduction in the size of the DC link capacitor. The operation is confirmed with the successful implementation of an experimental prototype     

Effect of combining boron nitride with fluoroelastomer on the melt fracture of HDPE in extrusion blow molding

Boron nitride (BN) is a new polymer processing aid which not only eliminates surface melt fracture in the extrusion of molten polymers, but also postpones the critical shear rate for the onset of gross melt fracture to significantly higher values that depend on resin type and additive concentration. In this work, the influence of BN as a polymer processing additive is first examined in the extrusion blow molding of high‐density polyethylene (HDPE) resins in order to evaluate its usefulness and performance in operations other than continuous extrusion. The equipment used includes both a Battenfeld/Fisher 50‐mm extrusion blow molding machine and a parallel‐plate rheometer. Two types of HDPE, which are blended with boron nitride at various concentration levels, are tested accordingly. It is found that the degree of BN dispersion, characteristics of the HDPE resins, extrusion temperature, and induction time play an important role in eliminating melt fracture. Finally, the influence of combining BN with fluoroelastomer, as an enhanced and potentially better processing aid on the melt fracture of a third HDPE is examined. It is found that such a combination is a superior processing aid that allows extrusion blow molding at very high shear rates.     

A Fast Computational Algorithm for the Discrete Sine Transform

A sparse-matrix factorization is developed for the discrete sine transform (DST). This factorization has a recursive structure and leads directly to an efficient algorithm for implementing the DST, a feature most desirable and very similar ot that of the DCT. This algorithm requires fewer arithmetic operations compared to that for the discrete cosine transform (DCT).     

Life prediction of stainless steels by cyclic and stable hysteresis curves

Abstract

This study develops an analytical expression to describe the cyclic stress‐strain curve obtained from a series of fully‐reversed fatigue tests. A set of stress‐strain relationships is proposed to simulate the tensile branch of the stable hysteresis loop. The complete shape of the stable hysteresis loop is then constructed and the associated theoretical plastic work calculated by integrating the area within the enclosed curve. The theoretical plastic work is employed to predict the fatigue lives of the investigated materials on the basis of their respective stable plastic work per cyclelife curves. In this paper, the current mathematical derivations are based upon the endochronic theory of plasticity. The accuracy of the proposed set of stress‐strain relationships is verified by conducting fully‐reversed constant strain amplitude fatigue tests on AISI 316 and AISI 304 stainless steels. The experimental and simulation results are found to be in good agreement, hence confirming the accuracy of the proposed analytical stress‐strain relationships. Again, comparing the obverted and predicted fatigue lives, a good agreement is found between the two sets of results.     

Kinetic Monte Carlo approach to modeling dislocation mobility

We describe a kinetic Monte Carlo (kMC) approach to modeling dislocation motion, directly linking the energetics of dislocation kink nucleation and migration on the atomistic scale with the experimental data on the microscale. A study of planar glide of screw dislocation in Si, an ideal test-bed for our method is first discussed, followed by preliminary results for a more complicated problem, three-dimensional motion of screw dislocation in BCC metals. We find that accuracy of the model predictions, even in the favorable case of Si, cannot claim to be quantitative because of uncertainties in the atomistic results for kink energetics. On the other hand, the kMC method is useful for qualitatively probing the mechanisms controlling dislocation motion, and it is capable of providing plausible explanation of some puzzling features of the experimental data.     

In Search of Molecular Markers for Cerebellar Neurons

The cerebellum, the region of the brain primarily responsible for motor coordination and balance, also contributes to non-motor functions, such as cognition, speech, and language comprehension. Maldevelopment and dysfunction of the cerebellum lead to cerebellar ataxia and may even be associated with autism, depression, and cognitive deficits. Hence, normal development of the cerebellum and its neuronal circuitry is critical for the cerebellum to function properly. Although nine major types of cerebellar neurons have been identified in the cerebellar cortex to date, the exact functions of each type are not fully understood due to a lack of cell-specific markers in neurons that renders cell-specific labeling and functional study by genetic manipulation unfeasible. The availability of cell-specific markers is thus vital for understanding the role of each neuronal type in the cerebellum and for elucidating the interactions between cell types within both the developing and mature cerebellum. This review discusses various technical approaches and recent progress in the search for cell-specific markers for cerebellar neurons.     

Puffer fish poisoning

Seven Vietnamese boat-people in Tai A Chau Detention Centre in Hong Kong caught, barbecued and ate a puffer fish. After 2 h, two of them developed severe symptoms of numbness and vomiting, while the remaining five subjects developed symptoms about 18 h later. They were all transferred to Queen Elizabeth Hospital. One patient died, and the others made an uneventful recovery.