Threshold Boundaries Research Articles

An expert system for transformer fault diagnosis using dissolved gas analysis

A prototype expert system based on the dissolved gas analysis (DGA) technique for diagnosis of suspected transformer faults and their maintenance actions is developed. A synthetic method is proposed to assist the gas ratio method. The uncertainties of key gas analysis, norms threshold, and gas ratio boundaries, are managed by using a fuzzy set concept. The expert system is implemented on a PC-AT using KES with rule-based knowledge representation. The system has been tested to show its effectiveness in transformer diagnosis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A simple physical principle for determining mode boundaries in superconducting loop circuits

A new physical principle is presented that immediately yields the auxiliary equation needed for the calculation of threshold or mode boundaries in superconducting loop circuits. We call this principle the loop inductance law, or L3 for short. The principle states that the determinant of the differential loop inductance matrix vanishes at threshold. L3 is equivalent to the resultant equation obtained by the method of Lagrange multipliers devised by Tsang and Van Duzer [J. Appl. Phys. 46, 4573 (1975)], but in contrast to that method, the auxiliary equation is much more quickly apparent. A number of examples are explicitly demonstrated.

INTERREGIONAL COMPARISON OF ALLUVIAL STREAM CHANNEL MORPHOLOGY: GREAT PLAINS VERSUS CENTRAL LOWLANDS1

ABSTRACT: Stream channel development is a complicated process involving many factors. A major goal of research in fluvial geomorphology is to develop an understanding of the relations between channel form, water discharge, and sediment discharge characteristics. The concept of thresholds has been introduced as an element in fluvial processes, with the implication that the factors involved in a process might change in some way as threshold boundaries are passed. This study is focused on the extent to which a particular regional boundary represents a threshold in the process of stream channel development. Twenty‐four alluvial stream channels from the Great Plains region and 24 from the Central Lowlands region are compared with regard to the distributional form, central tendency and dispersion characteristics, and correlation structure of ten variables, including indicators of discharge, channel sediment, and channel morphology. The results suggest that these aspects of the data are very similar between the regions, except for certain differences in central tendency characteristics, which are assumed to reflect underlying differences between the regions in geology and climate. In general, the results support the idea that this regional boundary is not an effective threshold with respect to the stream channel development process, and that, therefore, stream channels develop in these environmentally distinct regions by way of a similar process.

High Speed Digital Directional Comparison Relaying

ABSTRACT A high speed directional comparison relay based on the evaluation of the locally measured deviations of the voltage and current from their prefault values is described in this paper. Signal processing techniques are used to damp out the exponentially decaying dc component and high frequency transient components so that the operation of the relay depends on the power frequency components of the voltage and current deviation signals. The direction to a fault is determined by detecting the first transgression of the fault trajectories across threshold boundaries in the deviation plane. Studies on a three phase power system model show that the direction to a fault is determined within a first few milliseconds following the inception of a fault.

Boundaries of two-tone rate suppression of cochlear-nerve activity.

Two-tone rate suppression was examined in the responses of single cochlear-nerve fibers in Mongolian gerbils. The iso-rate tracking algorithm developed by Kiang and Moxon (Kiang, N.Y.-S. and Moxon, E.C. (1974): J. Acoust Soc. Am. 55, 620-630) for obtaining tuning curves was modified to track iso-rate suppression boundaries as a function of frequency with the excitor tone fixed at the characteristic frequency (CF) of the fiber. Lower threshold boundaries of the areas of suppression flanking the tuning curve above and below CF were outlined for fibers over a large CF range. It was found that the boundaries of rate suppression obtained below CF were very stable in their absolute positions on the intensity-frequency plane. This stability was evident both as a function of fiber CF (0.6-15 kHz) and as a function of the shape of the tuning curve at a given CF. In other words, the suppression boundary obtained below CF was largely independent of the tuning curve. In a second series of experiments tuning curves were taken in the presence of a fixed tone placed in the suppression area located above the fiber CF. The fixed tone by itself was not excitatory. These tuning curves were compared to tuning curves obtained with a single tone. It was found that frequencies around the fiber CF were most affected (suppressed) by the presence of the second tone, and that the low-frequency tail of the tuning curve tended to shift toward the boundary of the suppression area below CF. Because this suppression boundary lies below the threshold of the normal tail of the tuning curve for many mid- and high-CF fibers, these fibers often became hypersensitive at low frequencies in the presence of the second tone above CF.