A new method of excitation control based on fuzzy set theory

The synthesis of the structure of the power system stabiliser (PSS) and its parametrization are based entirely on methods of linear system theory. Thus the desired effect of the PSS is limited to a bounded area around one system operating point. The use of a controller based on fuzzy set theory introduces an event controlled excitation of the synchronous machine taking into account the power system operation. The desired response of the fuzzy controller is given by a set of rules which are obtained from the limits of the voltage regulator and the undesired performance of the conventional excitation control. A fuzzy controller has been developed for which simulation results are provided. These results support the concept of a fuzzy controller for the purpose of excitation control. They show that a well designed fuzzy controller is superior to a fast excitation control with an additional PSS     

A theoretical and photoelastic contact stress analysis relevant to orthopaedic knee prostheses

This study is based on a theoretical and photoelastic static contact stress analysis, relevant to the design of the plastic tibial plateau in an orthopaedic knee prosthesis. It involves the review of existing theoretical analyses concerned with the contact mechanics of layered elastic systems and, where possible, the validation of any relevant findings using two dimensional photoelasticity. Significant findings include the identification of a general minimum recommendable design thickness for the plastic tibial plateau, the endorsement of using the Hertzian contact theory to predict contact stress levels in the tibial plateau of certain knee implants and the slight improvement in contact conditions in the plastic when the plateau is perfectly bonded to its supporting metal tray.     

IEA joint trials: New lessons from old plantations

Two international trials of potential biomass species families and clones planted in 1985 have been analyzed to determine changing patterns in growth, diseases, and insects. In the Swedish trial, with close spacing and short rotations, Salix viminalis clones gave the best average yield of 17.4 Mg/Ha/yr on the first coppice rotation. In the Minnesota, USA trial, with wider spacings and a longer rotation Populus alba hybrid clones gave the best average yields of 5.5 Mg/Ha/yr. The most important disease and insect problems encountered were Septoria musiva stem cankers on some Populus clones; frost die back in some Salix clones; and the leaf blotch miner, Fenusa dohrnii, on most Alnus families. Recommendations for future international cooperation in field trials are presented.     

Specimen size effect during tensile testing of an unreinforced polymer

Various specimen sizes of an unreinforced polymer, Hercules 3501 -6 thermosetting epoxy, were subjected to a tensile test. The general specimen geometry was a rectangular dog-bone shape with constant gauge length, but with each specimen size having a different crosssectional area. These cross-sectional areas were obtained by varying the thickness of the epoxy during casting, and the gauge section width during grinding. The resulting failure surfaces of the specimens were observed and photographed using scanning electron microscopy. The results indicate that failure stress, dimensions of the critical flaw which caused failure, and a quantity which is proportional to the fracture toughness, are all correlated with specimen size.     

Investigation of solar selective and microstructural properties of molybdenum black immersion coatings on cobalt substrates

Molybdenum black solar selective coatings have been produced on cobalt by immersion in a solution of ammonium paramolybdate and nickel sulphate. The cobalt was electroplated on nickel-plated copper prior to immersion in the paramolybdate solution. The maximum solar absorptance of the resulting molybdenum black coating was about 0.91. The minimum emittance was about 0.1 for coatings on cobalt deposited with an addition agent and about 0.23 for coatings on cobalt deposited without addition agent in the 60 °C plating solution. These differences have been related to the coating morphology determined by scanning electron microscopy. The emittance of coatings on cobalt deposited without addition agent decreases (or remains unchanged) during short-term heat treatment while that of coatings deposited on cobalt plated with addition agent increases somewhat. Reduction of the cobalt plating bath temperature to 45 °C can also lead to good initial coating properties but without the requirement for an addition agent in the cobalt plating bath. XPS studies show that the oxidation state of molybdenum in the coatings is approximately + 5 corresponding to Mo₄O₁₁. This reduces to + 4 after argon ion bombardment. Some cobalt may be present in the coatings in the form of CoO.     

Differential effects of aging on directional and absolute errors in visuospatial memory.

Studied memory for visuospatial arrays in 28 male and 34 female healthy dextral adults (aged 20–90 yrs). 10 abstract figures were presented in each hemispace over a series of learning trials, and then delayed free recall of figure placement was obtained. Figures were misplaced significantly downward and leftward in both hemispaces. Both vertical and horizontal absolute error increased significanty with age, but no age effects on directional errors were observed. The increase in absolute error over age is consistent with decreased anterograde memory and visuospatial skills in the elderly. The directional errors are believed to result from an attentional shift toward proximal peripersonal space, in combination with attentional shifts from differential left vs right cerebral activation. Gender effects were also observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prolonged poststrike elevation in tongue-flicking rate with rapid onset in gila monster,Heloderma suspectum: Relation to diet and foraging and implications for evolution of chemosensory searching

Experimental tests showed that poststrike elevation in tongue-flicking rate (PETF) and strike-induced chemosensory searching (SICS) in the gila monster last longer than reported for any other lizard. Based on analysis of numbers of tongue-flicks emitted in 5-min intervals, significant PETF was detected in all intervals up to and including minutes 41–45. Using 10-min intervals, PETF lasted though minutes 46–55. Two of eight individuals continued tongue-flicking throughout the 60 min after biting prey, whereas all individuals ceased tongue-flicking in a control condition after minute 35. The apparent presence of PETF lasting at least an hour in some individuals suggests that there may be important individual differences in duration of PETF. PETF and/or SICS are present in all families of autarchoglossan lizards studied except Cordylidae, the only family lacking linguallly mediated prey chemical discrimination. However, its duration is known to be greater than 2-min only in Helodermatidae and Varanidae, the living representatives of Varanoidea. That prolonged PETF and SICS are typical of snakes provides another character supporting a possible a varanoid ancestry for Serpentes. Analysis of 1-min intervals showed that PETF occurred in the first minute. A review of the literature suggests that a pause in tongue-flicking and delay of searching movements are absent in lizards and the few nonvenomous colubrid snakes tested. The delayed onset of SICS may be a specific adaptation of some viperid snakes to allow potentially dangerous prey to be rendered harmless by venom following voluntary release after envenomation and preceding further physical contact with the prey.     

Phase effects in a semiconductor laser with diffraction extraction of radiation

Phase effects arising in a semiconductor laser with diffraction extraction of radiation and a distributed Bragg reflector on the substrate side are taken into account exactly quantitatively and the possibilities of using these effects in lasers is analyzed. It is shown that the phase effects studied can be used to increase the laser efficiency substantially. Pis’ma Zh. Tekh. Fiz. 23, 7–11 (September 26, 1997)     

Richard Lester Solomon (1918–1995): Obituary.

Memorializes Richard Solomon, one of the major learning theorists of the 2nd half of the 20th century. Solomon was named the 1st James M. Skinner University Professor of Science in 1975, was elected to the National Academy of Sciences, and was awarded, among other honors, the Warren Medal for research by the Society of Experimental Psychologists, the American Psychological Association Distinguished Scientific Contribution Award, and the American Psychological Foundation's Award for Distinguished Teaching in Experimental Psychology. He conducted research on a broad array of topics such as word frequency and perceptual defense, children's estimation of the size of tokens, hoarding behaviors in rats, and personality ratings and sociometric patterns. His work made a major contribution to the exploration of Pavlovian conditioning. Other topics of research focused on in Solomon's laboratories included avoidance learning, learned helplessness, punishment, and the opponent-process theory of acquired motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)