Multiple Oscillation Modes Research Articles

A New Mutation at thePeriodLocus ofDrosophila MelanogasterWith Some Novel Effects on Circadian Rhythms

A new period mutation has been induced and characterized in D. melanogaster. It causes flies to be apparently arrhythmic in tests of locomotor activity and thus is superficially similar to the original per01 mutant. Yet, the new "zero" allele, per04, has some novel properties and effects: Behaviorally, per04 adults often exhibit weak, long-period rhythms of locomotor activity in constant darkness; this low-frequency rhythmicity usually was not obvious in the analog behavioral records but was readily revealed by spectral analyses. These treatments of the data also extracted hidden high-frequency (ultradian) rhythms in many of the behavioral records, of the type associated with per01 and other per-nulls. The wide range of periodicities exhibited by different per04-expressing flies implies the expression of multiple oscillatory modes by this mutant. The new mutation also leads to a tendency for flies to be hyperactive during activity monitoring and is thus dissimilar to the other arrhythmic variants in the per gene but similar to the effects of a deletion of the locus. During light:dark cycling, per04 adults once more behave differently from other per0's and in fact tend to resemble wild-type flies in these conditions. The new mutation is not caused by the same nucleotide substitution that created a stop codon in the original arrhythmic per mutant and, as it turns out, per02 and per03 as well. per04 is also not a null variant at the transcriptional level; but it leads to an anomalous form of per mRNA, which is smaller than the normal 4.5 kb species encoded by this clock gene.

Applying Power System Stabilizers Part II: Performance Objectives and Tuning Concepts

This part of a three-part paper deals first with the performance objectives of power system stabilizers in terms of the type of oscillations for which they are intended to provide damping, the operating conditions for which the requirement for stabilization is greatest, the need to accommodate multiple modes of oscillation, and the significance of interplant modes of oscillation. It next treats stabilizer tuning. General tuning guidelines are developed as well as variations required for different input signals. The operating conditions under which each type of stabilizer should be tuned are identified. The relationship between phase compensation tuning and root locus analysis is presented. Finally, the relative performance characteristics of the three types of stabilizers are examined for both small perturbations and large disturbances.