An improved approach to application-specific power electronicseducation. Curriculum development

This paper presents an innovative power electronics curriculum spanning the undergraduate and graduate programs. The curriculum develops the basic concepts of the field and applies them to modern industrial challenges to solve practical problems. It is based on three fundamental disciplines: switching devices, circuits and topologies and control and drives. The curriculum, which will facilitate the development of optimal systems, bridges the gap between power semiconductor devices and circuit design. An underlying principle of the curriculum is the development of optimal application-specific power electronics systems, achieved primarily through optimization of power semiconductor devices. The curriculum is described in detail with an emphasis on the courses pertaining to power semiconductor device physics and converter circuit design. The role of advanced computer-aided design tools is also identified and shown to facilitate an application-specific device design and optimization methodology. To further illustrate the effectiveness of this approach, two industry-relevant course projects performed in the curriculum are presented in detail     

Heptaldehyde and undecylenic acid from castor oil

Castor Oil was pyrolyzed in a vertical stainless steel tubular reactor packed with 12.5-mm diameter mild steel balls in presence of 0.5% benzoyl peroxide. The operating parameters were optimized to obtain high yields of heptaldehyde and undecylenic acid. Heating at 550 C under reduced pressure of 45 mm (Hg) yielded 24.8% heptaldehyde and 36.0% undecylenic acid.     

The development of solidification microstructures in the presence of lateral constraints

The effect of a sudden change in cross section on the microstructural development has been investigated by the directional solidification technique. Experiments have been carried out in a transparent model system of succinonitrile-acetone so that the dynamical changes in the interface shapes can be monitoredin situ as the interface travels from a region of uniform cross section to a region of sharply reduced cross section. Different experimental conditions which give rise to initial steady-state planar, cellular, and dendritic interfaces have been investigated. Significant changes in microstructures have been observed as the interface approaches a sharply reduced cross section. The planar interface undergoes transitions to cellular and dendritic morphologies as the cross section is reduced, and reverse transitions are observed as the cross section is then increased gradually to its original value. An initial cellular interface is found to become dendritic as the cross section is reduced, and again it becomes cellular as the cross section is increased. When the experimental conditions are designed to give initial dendritic structures, the change in microstructure is found to occur only when the reduced cross section is of the order of primary dendrite spacing. When the reduced cross section is more than about 5 times the primary spacing, no appreciable change is observed in the dendritic array which travels across the cross-sectional change. The dynamical changes in the interface shape and the microstructural transitions that occur with the change in cross section have been examined quantitatively and discussed. Formerly with Ames Laboratory     

Differential behavior of (25R)-5,6-epoxyspirostan-22 alpha-O-3 beta-ol and (25R)-5,6-epoxyspirostan-22 alpha-O-3 beta, 4 beta-diol toward Dowex

The acid-catalyzed hydrolytic cleavage of the 5,6-epoxyspirostane derivatives by the cation exchange resin Dowex 50W X8 has been exploited with the goal of developing synthetic protocols toward 3,4,5,6-polyhydroxyspirostane analogs that can serve as intermediates to potential biologically active compounds. Whereas the diastereomers (25R)-5 alpha, 6 alpha-epoxyspirostan-22 alpha-O-3 beta-ol and (25R)-5 beta, 6 beta-epoxyspirostan-22 alpha-O-3 beta-ol yield two products, (25R)-6 beta-methoxyspirostan-22 alpha-O-3 beta, 5 alpha-diol and (25R)-spirostan-22 alpha-O-3 beta, 5 alpha, 6 beta-triol on Dowex treatment in water-methanol, the alpha- and beta-diastereomers of the 5,6-epoxy derivative of 3 beta, 4 beta-diol provide a single product, (25R)-3 beta, 6 beta-dihydroxy-5 alpha-spirostan-4-one, in good yields. The structures of these products have been confirmed using 1H NMR, 13C NMR, and 1H-1H J-correlated spectroscopies. Multifunctional product formation suggests tremendous utility of Dowex in steroid synthesis. The product formation has been rationalized on the basis of differential conformational constraints of the A/B rings of the different epoxides in directing the reaction course. The reaction shows an interesting example of stereoelectronic effect of a single hydroxy group in discriminating solvent participation.     

Recent advances in modeling response-time distributions in real-time systems

Real-time systems are an important class of process control systems that need to respond to events under time constraints, or deadlines. Such systems may also be required to deliver service in spite of hardware or software faults in their components. This fault-tolerant characteristic is especially critical in systems whose failure can cause economic disaster and/or loss of lives. This paper reports recent research in the area of analytical modeling of the three major characteristics of real-time systems: timeliness, dependability, and external environmental dependencies. The paper starts with a brief introduction to analytical modeling frameworks such as Markov models and stochastic petri nets. This is followed by an examination of advances in modeling response-time distributions, reliability, distributed messaging services, and software fault-tolerance in real-time systems.     

Pulmonary sequestration: the setting sun sign

Acquired immune deficiency syndrome (AIDS) has become a topic of increasing public concern. Several conditions have been described in patients who are afraid that they have acquired AIDS, including depression, somatization disorders, hypochondriasis, adjustment disorders and various psychoses. This paper presents a case study of a young man with persistent fear of having AIDS. In spite of negative HIV test results, the patient still insisted that he suffered from AIDS. The psychiatric diagnosis was major depressive disorder with delusion of having AIDS. The patient was treated with fluoxetine 40 mg qd and sulpiride 400 mg qn. After two weeks on medication, his fear of AIDS subsided and he improved remarkably. The most important intervention in patients with delusion of having AIDS is to identify and treat the underlying psychopathology. The following case is representative of our experience.     

Comment/correction: dependability modeling using Petri nets

Two arcs are missing in a figure of Malhotra & Trivedi (see ibid., vol. 44, p. 428-40, 1995); these arcs are necessary for the proper functioning of the generalized stochastic Petri net (GSPN). Also, priorities of immediate transitions in that figure must be clearer. This note presents a correctly drawn GSPN and describes the priority assignment to immediate transitions in this GSPN     

Korrosion von Aluminium in Salzgemischen und Korrosionseinfluß von Kupferionen

Corrosion of aluminium in mixtures of salts and effect of copper ions Corrosion of aluminium has been studied in stagnant condition, in mixtures of salts, NaCl + NaHCO₃, Na₂CO₃ + NaHCO₃ and NaCl + Na₂CO₃; effect of addition of copper ions has also been studied. It has been found that (shallow) pits are formed only when both chloride and bicarbonate are present. Addition of copper ions occasionally increases the numbers of pits but may some times decrease corrosion.