Variable Sampling Period Research Articles

Periodic behaviour in nonlinear biscrete-time systems and its application to a digital control system

In this paper, the behaviour of a two-dimensional nonlinear discrete-time model is considered with a view to understanding the effects of a varying sampling period in digital control systems. The analysis is carried out in the neighbourhood of a critical point which, on the unit circle, corresponds to a pair of complex-conjugate points with non-zero imaginary parts. It is demonstrated that, as the sampling period is varied from a critical sampling value, the branches of root-locus may cross the unit circle and secondary solutions bifurcate under certain conditions. The analysis here is facilitated by adapting the intrinsic method of harmonic balancing (a multi-parameter perturbation technique) to discrete-time systems

Overcoming Biases of Precipitation Measurement: A History of the USSR Experience

Abstract Documenting the instrumentally observed precipitation climate record presents many challenges because scientists must rely on data from stations that undergo many changes in the course of their operation. Detecting changes from such networks is essential for adequate understanding of climate and global change. As an illustrative example, we review the history of the instrumentally observed precipitation in the USSR. In the USSR, similar to other countries, numerous problems must be addressed before reliable estimates of precipitation can be made. The types of problems range from inadequate and changing exposures of raingages to varying sampling periods used to measure precipitation. Using information about measurement procedures, instrument intercomparisons, and field studies, various methods have been devised to overcome biases in the measurements.

Identification of a Glass Tube Drawing Bench

Abstract In this paper we present a comprehensive application of identification methods for the modelling of a glass tube drawing process which is multivariable. A preliminary structure determination is carried out through a correlation analysis. Parametric models are then obtained, using a prediction error method, for different tube sizes. This identification study leads to the following non-standard conclusion : it appears to be more suitable to use different sampling periods (ranging from 1 to 5 sec.) for the different input-output relations of the multivariable model but to adopt a unique global model structure for different tube sizes provided time varying sampling periods (depending on the drawing speed) are used.

The Development of a Green Peach Aphid 1 Natural Enemy Sampling Procedure 2

The relative diurnal and weekly abundance of the most common natural enemies of the green peach aphid, Myzus persicae (Sulzer, was determined in a potato field in 1977. Two sampling methods were also compared for use in sampling the natural enemies. Groundcloth samples were taken 4 times a day, twice weekly, for 7 wk during the growing season. A natural enemy sampling scheme was developed from the informatlon collected. Coleomegilla maculata (DeGeed adults (Coleoptera: Coccinellidae) and coccinellid larvae were the most abundant green peach aphid natural enemies collected. Linear models significantly explained the relationship between counts for C. maculata adults and degree days, and between counts for coccinellid larvae and degree days. The 0900–1115 period was the least variable sampling period tested for sampling C. maculata adults according to the results of a chi-square analysis on the ranks of the diurnal means. The groundcloth sampling technique was chosen for use in future studies because it is an absolute and non-destructive sampling method, and because it more accurately estimated the size of the larval coccinellid population peak than the other method tested. The between samples variance was the largest component of the variation in the experiment according to a variance component analysis. Coccinellid larvae were aggregated on a stem on 3 of 4 sample dates near the larval population peak according to a chi-square analysis on the variance:mean ratios. C. maculata adults were aggregated on a stem on only the last sample date, when many mating pairs were observed.