Stability analysis of nonlinear control systems with characteristics equations having complex coefficients

In this paper, the stability equation method is applied to the analysis of nonlinear systems with characteristics equations having complex coefficients. Three types of systems are studied: those with unstable open-loop poles, unstable characteristics roots or an equal number of open-loop poles and zeros.     

Das Pädagogische Konzept Maria Montessoris: Die Permanente Diskussion

This article emphasises the internal consistency of Maria Montessori's work by identifying her main educational ideas and clarifying the interrelationships between the individual experimental schools and her writings. An elucidation of the vital part played by the anthropological basis of Maria Montessori's work shows that her entire efforts were directed towards illuminating childhood as the foundation of human development. Within this framework her relationship to Rousseau on the one hand, and to educational reform trends on the other is brought out. It is in this connection that her relations with the World Education Fellowship in general and with Decroly in particular find their significance.     

Essential gyrators and reciprocity in junction structures

This paper proposes an extended definition of reciprocity for a multiport junction structure based on the concept of essential gyrator coupling. Two theorems are given for junction structures containing gyrators and an algorithm is presented for identifying essential gyrators. The results are useful both theoretically and for designing efficient computation procedures for junction structures.     

Fact and fantasy in chemical analysis

Chemical analysis is now so precise and sophisticated a science that it is difficult to appreciate that scarcely a century ago its deficiencies were a cause for public scandal. This article reviews some of the main causes for complaint and how they were remedied.     

Developmental priority of identity conservation: acceleration of identity and equivalence in normal and moderately retarded children

In an attempt to clarify the chronological relationship between identity and equivalence conservation, normal preschool-aged children (experiment 1) were exposed to brief videotape demonstrations of a model conserving identity and equivalence, identity only, equivalence only, or neither. Subsequent performances indicate that identity was easier to accelerate than equivalence, and training in both identity and equivalence appeared to be most effective in accelerating conservation. Trainable mentally retarded (TMR) children were then exposed to either the identity-equivalence-conserving or control model (experiment 2). This population, which some have argued remains at a preoperational level of functioning, was more likely to conserve identity than equivalence. In addition, conservation in the training group increased following training, though these gains were not maintained over a 3-week retention interval.