Characteristic Loci Research Articles

Dyadic expansion, characteristic loci and multivariable-control-systems design

Recent results in the dyadic representation of system interactions are used to derive a systematic approach to the manipulation and compensation of the characteristic loci of a system described by the N × N transfer-function matrix G(s), using rational-transfer-function approximations to the characteristic loci. The approach is thought to strengthen the link between single-input and multivariable control-system design techniques by releasing well known classical compensation techniques for application to multivariable systems.

Application of Frequency Response Methods to Nuclear Power Station Once-Through Boiler Control

In recent years frequency response methods have been extended to the multi-input multi-output case and control system design techniques developed. In this paper a design approach based on a combination of two of the methods, the Inverse Nyquist Array method and the Characteristic Locus method, is applied to the design of the control scheme for the once-through boiler of a nuclear power station.

Human chromosome banding by Feulgen stain aids in localizing classes of chromatin.

The band patterns of human chromosomes displayed by the Feulgen stain are similar to but not identical with those of the conventional quinacrine and Giemsa preparations. The parallelism among the three is principally that of prominent negative bands that appear consistently at characteristic loci throughout a wide range of chromosome compaction. The correlation of those bands with regions of low optical density in nonbanded Fuelgen-stained chromosomes suggests that they are loci of DNA that is inherently difluse or readily labile. The instances of disparity among the patterns of the three modes of banding occur at the telomeres and at known regions of heterochromatin, and are interpreted here as reflecting the heterogeneity of the protein moieties in their reactivity to the cytochemical treatments.

The characteristic locus design method

The classical work of Nyquist and Bode on the frequency-response analysis of scalar feedback systems leads to flexible and useful design procedures because it enables the conflicting requirements of stability and accuracy to be handled simultaneously via a single form of system representation—the open-loop frequency response function of a complex variable. State-space methods derive their elegance and power from the systematic exploitation of the algebraic and geometric properties of linear vector spaces. The basic idea underlying the Characteristic Locus Method developed here is the combination of the essence of these two approaches by exploiting the properties of linear vector spaces defined over base fields of functions of a complex variable. What then emerges is a general vector feedback theory in which the classical Bode-Nyquist technique is a special case, and from which a frequency-response based design technique called the Characteristic Locus Method is developed.

A survey of some recent results in linear multivariable feedback theory

By adopting the viewpoint that the classical frequency-response methods originally introduced by Bode, Nyquist and Wiener, when suitably generalised, form the natural approach to the design problem for multivariable feedback systems, a coherent and unified treatment of the subject is given. The treatment is largely based on work recently carried out at U.M.I.S.T., but an attempt has been made to deal with most of the currently available approaches to the problem. Although a significant fraction of the available literature is cited, this is mostly confined to work available in English and which is directly relevant to the viewpoint adopted here. After a treatment of the algebraic theory of feedback systems represented by signal-flow graphs, a vector generalisation is given of Nyquist's stability theorem and Bode's sensitivity work. The survey then continues with a sketch of the theory underlying all the main available techniques for the design of feedback systems. It concludes with a review of multivariable feedback system design techniques from the frequency-response viewpoint, including a comparison of the advantages and disadvantages of each type of design method, including Non-Interacting Control, Modal Control, Optimal Control, Commutative Control, The Inverse Nyquist Array and The Characteristic Locus.

Multicategory Classification of Patterns Represented by High-Order Vectors of Multilevel Measurements

A method is introduced for deciding the class of a pattern described by a vector of measured features. Memory requirements and the time required for classifying a pattern are not excessive, even when there are many classes and many multilevel feature measurements. Two initial steps use univariate distributions of the measurements to select, for a pattern in question, a small subset of neighboring classes. If the pattern is one used in deriving the distributions, its true class is certain to be in the selected subset. The final step distinguishes among the members, if there are more than one, of the subset by using discriminants derivable by classic methods. The technique is tested experimentally on a set of about 26 000 alphabetic characters of nine type fonts. The characters range widely in quality. One third are taken as training patterns from which histograms for the first two steps and discriminants for the third step are derived. The rest are used to test the method. The features used are the characteristic loci.

Characteristic loci techniques in multivariable-control-system design

A design technique is developed which is based on the frequency-response loci associated with a set of characteristic transfer functions for a multivariable feedback system. This leads to a simple technique, suitable for use with a computer-aided-design facility, which permits a designer to achieve his objectives in a step-by-step fashion. The method encompasses all aspects of feedback-system behaviour, including integrity against transducer- and actuator-failure conditions.

Experiments with "Characteristic Loci" for Recognition of Handprinted Characters

Recognition experiments have been performed on handprinted characters using a set of features which has not been applied previously to handprinting. Glucksman's "characteristic loci" were utilized in experiments with the well-known Highleyman data, as well as samples generated at Stanford Research Institute and Honeywell. Two recognition algorithms were tested. Results on numeric samples compare favorably with those of other investigators despite the small dimensionality of the feature vector. On the constrained Honeywell samples, recognition rates exceeding 98 percent were achieved using the simpler algorithm. With alphabetic samples, some problems remain in resolving persistent ambiguities, and methods for attacking these problems are considered.

Characteristic Locus in Magneto-Fluid Dynamics

First Page

The histochemical localization of triphosphopyridine nucleotide diaphorase.

A histochemical method is described for the localization of triphosphopyridine nucleotide diaphorase using a recently synthesized tetrazolium salt (Nitro-BT). By virtue of the favorable histochemical properties of this reagent, it has been possible to demonstrate that whereas DPN diaphorase is usually restricted to the mitochondria, the TPN diaphorase activity of corresponding cells was distributed throughout the cytoplasm in granules too fine to be considered mitochondria. Furthermore, although the diaphorase alone is responsible for the passage of electrons from TPNH to the tetrazole, it has been found that sites of activity of different TPN-linked dehydrogenases can be visualized in tissue sections, and characteristic loci for each enzyme may be observed. For example, whereas TPN diaphorase and isocitric dehydrogenase have an extensive distribution in the kidney cortex, 6-phosphogluconic dehydrogenase is limited to the cells of the macula densa.