The univoltine leaf miner Chromatomyia fuscula (Zetterstedt) (Diptera: Agromyzidae) is a regular cereal pest in Scandinavia. The fly and its most important parasitoids were studied in a 15.5 ha organically-grown field in southern Norway. Each year (1992-1997), one Malaise trap was placed in the spring barley part (2.5 ha) of the field, and (except for 1994) another along the nearest wooded boundary for the whole season. Because of crop rotation, the traps changed position every year. C. fuscula and 15 parasitoid species previously reared from C. fuscula were sorted from the catches.
Few C. fuscula were trapped in the boundary, suggesting that at least the lower vegetation strata were unimportant for the overwintering fly (C. fuscula overwinters as an adult). The parasitoid complex was remarkably stable over years, and 13-15 of the species were: found each year (habitats combined); 0-6 of the species were not found in both habitats each year. Only 4 species attained fractions higher than 10% of the total annual catches in both habitats during the 6 years: the larval parasitoids Diglyphus begini (Ashmead) and Hemiptarsenus unguicellus (Zetterstedt), and the pupal parasitoids Cyrtogaster vulgaris Walker and Chrysocharis pubicornis (Zetterstedt). In the boundary, C. vulgaris dominated every year (43-83%). In the crop, this species alternated with D. begini (1992, 1994) or H. unguicellus (1997) as the dominant species.
In most years, the catches of both the leaf miner and its parasitoids were larger in the crop than in the boundary, but the species number and composition were fairly similar in the two habitats. The parasitoid diversity (Shannon-Wiener H') tended to be higher in the crop (0.8-2.0) than in the boundary (0.8-1.8). Correspondingly, the evenness (both Shannon-Wiener J' and species rank on In abundance) was higher, and the dominance (Berger-Parker) lower, in the crop than in the boundary. Every year, overwintered C. fuscula invaded the crop, but only in 1993 and 1997 did the trapping reveal a distinct next generation, suggesting a very high pre-adult mortality the other years. In 1993 and 1997, C. vulgaris and D. begini had rather similar abundances in the crop, and the lowest combined fractions (less than 60%) of the years, leading to the highest diversity and the lowest dominance through the 6 years (in both habitats).
Our results indicate that the boundary was part of the parasitoids' foraging/overwintering area, and that the boundary was more important to the parasitoids than to their leaf miner host. Boundaries therefore seem to be important for the control of C. fuscula.
The control problem consists of stabilizing a control system while minimizing the norm of its transfer function. Several solutions to this problem are available. For systems in form, an optimal regulator can be obtained by solving two algebraic Riccati equations. For systems described by , either Wiener-Hopf optimization or projection results can be applied. The optimal regulator is then obtained using operations with proper stable rational matrices: inner-outer factorizations and stable projections. The aim of this paper is to compare the two approaches. It is well understood that the inner-outer factorization is equivalent to solving an algebraic Riccati equation. However, why are the stable projections not needed in the state-space approach? The difference between the two approaches derives from a different construction of doubly coprime, proper stable matrix fractions used to represent the plant. The transfer-function approach takes any doubly coprime fractions, while the state-space approach parameterizes such representations and those selected then obviate the need for stable projections.
This informal essay, written on the occasion of 60th anniversary of Wienerian cybernetics, presents a series of themes and ideas that has emerged during last several decades and which have direct or indirect relationships to the principal concepts of cybernetics. Moreover, they share with original cybernetics the same transdisciplinary character.
This year coincides with the 60-year anniversary of the publication of Norbert Wiener's seminal book: , in which he introduced, under the name "cybernetic", a host of radically new ideas and views regarding science, engineering, and other areas of human affairs that emerged shortly after World War II. It is thus appropriate for a journal whose title is , the Czech name for cybernetics, to use this anniversary for reflecting on the evolution of cybernetics during the last 60 years. In this essay, which I was invited to write for on this occasion, I intend to express my personal opinion about what I consider the most important ideas of cybernetics from among those suggested and discussed by Wiener in his book. In addition, I intend to trace the evolution of these principal ideas, especially in the United States, since the publication of Wiener's book.
The interdisciplinary workshops, focused on methodological and philosophical aspects, have helped - and still undoubtedly are helping - in forging links among different members of the academic community or research teams, which are today described as "intellectual networks" or "invisible colleges". Their focus of interest is known to transcend the boundaries of the traditionally divided scientific disciplines or research areas. That is also why the network that was instrumental in shaping the genesis of cybernetics includes, to this day, the names of C.Shannon, the pioneer of the mathematical theory of information, J.von Neumann, the founder of the theory of games and decision-making, linguist R.Jakobson, the above-mentioned specialists in the medicine- and biology-oriented branches, and many other scholars. Similar conceptions and aspirations connected therewith also proved to be conducive to the emergence and expansion of the works and studies devoted to the role of the sign, its creation, significance and function in communication, i.e. semantics and semiotics. Efforts were made to uncover more profound links and subsequently to outline paths leading to a unification of different scientific domains, particularly by integrating the language of science. There was a mounting interest in methodological and epistemological problems and - generally speaking - in finding ways and means of attaining more profound and thorough learning. All these and similar tendencies had and still have one common trait: they kept enhancing respect, weight and significance attached to mathematics, to mathematical methods of expressing and depicting problems, and to mathematical thinking in general.