Prediction of power system generator self-excitation using patternrecognition

Power-system generators may experience self-excitation overvoltages due to certain contingencies. In an attempt to derive a novel self-excitation (SE) preventive scheme, the authors describe a prediction system based on pattern-recognition techniques. Several design approaches are explained. A hyperplane discriminant is used to define the predictor surface. An algorithm is developed to reduce the number of telemetered channels required and hence the complexity of the prediction system structure. Moreover, a fast corrective algorithm designed to provide security improvement action is explained. The system studied is the Manitoba Hydro northern AC collector system where SE is the operating problem of concern. The results obtained prove the effectiveness of the proposed prediction scheme     

Airborne detection of oceanic turbidity cell structure using depth-resolved laser-induced water Raman backscatter

Airborne depth-resolved laser-induced sea-water Raman-backscatter waveforms have been obtained along a flight line extending westward from a point approximately 30 km seaward of Assateague Island to a point where the beach was intersected at latitude 38.1 degrees N and longitude 75.2 degrees W. Pulses from a 337.1-nm nitrogen laser were repetitively transmitted vertically downward into the water column. The laser-induced water Raman backscatter pulse at 381-nm wavelength was depth (or time) resolved into forty bins having widths of -25 cm each. When converted to along-track profiles, the waveforms reveal cells of decreased Raman backscatter superimposed on an overall trend of monotonically decreasing water column optical transmission. This airborne lidar technique shows potential for (1) rapid, quantitative, synoptic study of the homogeneity of the oceanic water column and (2) measurement of the horizontal spatial distribution of the optical transmission of the upper mixed layer of the ocean. A multiple convolution model of a Gaussian transmitted pulse, Gaussian sea surface height, and slope probability density, together with an exponential-decay water-column impulse response, is shown to qualitatively account for the observed pulse shape.     

The electrolytic reduction of chalcopyrite in acid solution

Chalcopyrite electrodes of both natural and synthetic material were cathodically reduced in several acid electrolytes. At current densities below 10mA cm^–2 chalcocite was formed and at higher currents the solid product contained elemental copper. The other reduction products were H₂S and Fe⁺⁺. The current efficiency, measured in terms of the Fe⁺⁺ produced, generally fell with the amount of charge passed, the extent of the decrease depending on current density and the composition and temperature of the electrolyte. The decrease was attributed to evolution of hydrogen on the increasing surface area of the porous solid product as a consequence of inhibition of the chalcopyrite reduction process by ferrous salt precipitated in the pores. At sufficiently low current densities and short periods of electrolysis, chalcopyrite reduction was found to be activation controlled over a three order of magnitude range of currents, with a Tafel slope consistent with a one electron rate-determining step.Presented in part at the 102nd Annual Meeting, AIME, Chicago, 1973.     

Rice bran oil. V. The stability and processing characteristics of some rice bran oils

1. The extraction, processing, characteristics, and stability properties of nine batches of hexane-extracted rice bran oil were investigated. The oils were refined, bleached, and deodorized and their color and stability determined. Samples of the bleached oils were hydrogenated to approximately shortening consistency, deodorized, and the stability of the hydrogenated products determined.
2. Pilot plant extractions of five batches of rice bran yielded crude oils equivalent to 91% of the hexane-soluble portions of the bran.
3. The nine crude oils whose content of free fatty acids ranged from 2.0 to 6.3% were refined by the cup method with losses ranging from 12.0 to 23.5% although the neutral oil content of six crude rice bran oils ranged from 89.9 to 92.6%.
4. The Lovibond color of the nine refined oils ranged from 35 yellow and 4.5 red to 70 yellow and 9.5 red, and the color of the bleached oils ranged from 15 yellow and 1.5 red to 35 yellow and 3.2 red.
5. Steam-refining, employed in conjunction with alkali-refining, proved effective as a means of reducing the losses in refining rice bran oil.
6. The nine batches of refined, bleached, and deodorized rice bran oils had iodine values ranging from 101.3 to 105.7 and stabilities averaging 24 hours.
7. Nine bleached oils hydrogenated to approximate shortening consistency had iodine values averaging approximately 66 and stabilities averaging 370 hours.
8. Refined, bleached, and deodorized rice bran oil is bland but has some tendency toward flavor reversion.
9. The most outstanding characteristics of rice bran oil is its exceptional stability after hydrogenation.

     

Gamma-tocopherol as a precursor of a red quinoid substance developed in cottonseed oil during oxidation

Summary On the basis of spectrophotometric data on the characteristic spectral absorptions observed in oxidizing substrates with and without added γ-tocopherol, it has been shown that the red color which develops on accelerated oxidation of fat substrates containing this tocopherol results from its conversion to chroman-5,6-quinone. The chroman-5,6-quinone thus produced possesses relatively little antioxidant activity. Presented before the American Oil Chemists’ Meeting, New Orleans, Louisiana, May 10 to 12, 1944. National Cottonseed Products Association Fellow. This is one of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

THE MEASUREMENTS OF HUMAN INHALABILITY OF ULTRALARGE AEROSOLS IN CALM AIR USING MANNIKINS

An idea was first introduced during the 1970s that particles cannot produce adverse health effect unless they are inhaled into the human respiratory tract. Since then several studies have been carried out to investigate the inhalable fraction of ambient aerosols. However, the previous studies were confined to the conditions of external convective flow and particle aerodynamic diameter smaller than 100 μm. This paper reports the results from an inhalability study for particle aerodynamic diameter for a range of diameters which include diameters greater than 100 μm under a condition of no external convective flow. The concept of mass balance was used in this study to derive an equation for determining the ambient particle concentration from which inhalability was calculated. The results suggested that difference in ventilation demands between adults and children does not affect inhalability, however, the inhaled dose was significantly higher in adults than children because of higher ventilation demand of adults. In terms of the breathing mode, the inhalabilities of oronasal breathing for people at heavy exercise are much higher than those of nasal breathing which simulates breath at rest and moderate exercise. The inhalability curve derived from this study indicated that a cutoff diameter for zero inhalability exists, which should be considered in the future revision of ACGIH inhalable aerosols criteria.     

Recent developments in techniques and methodologies for improving thickener performance

Research projects directed towards ‘Improving Thickener Technology’ have been conducted by the AJ Parker Cooperative Research Centre for Hydrometallurgy since 1988 through the Australian Mineral Industries Research Association with support from 25 Australian and international mineral processing companies. These projects have resulted in the development of a range of research tools and techniques to address flocculation and thickening issues. Laboratory and plant studies have focused on how key factors, such as mixing intensity, mixing duration and solids concentration, affect flocculation efficiency and, hence, thickener performance. A comprehensive computational fluid dynamics (CFD) model has been developed to predict likely full-scale performance under various process conditions, based upon a knowledge of thickener design, plant flows and laboratory assessment of the flocculation behaviour of the feed slurry. Application of this CFD model to problems within specific mineral processing operations has resulted in significant benefits, in one case leading to doubling of a thickener’s throughput. This paper presents an overview of the work conducted during these projects, focusing on the research tools, the nature of the information that has been gained and the implications for thickener performance. Brief details will be presented on research issues currently being investigated.     

Performance Pathologies in Hardware Transactional Memory

Transactional memory is a promising approach to ease parallel programming. Hardware transactional memory system designs reflect choices along three key design dimensions: conflict detection, version management, and conflict resolution. The authors identify a set of performance pathologies that could degrade performance in proposed HTM designs. Improving conflict resolution could eliminate these pathologies so designers can build robust HTM systems.