Elimination of Chaos in Multimode, Intracavity-doubled Lasers in the Presence of Spatial Hole-burning

In this paper possibilities of a stabilization of large amplitude fluctuations in an intracavity-doubled solid-state laser are studied. The modification of the cross-saturation coefficient by the effect of spatial hole-burning is taken into account. The stabilization of the laser radiation by an increase of the number of modes, as proposed by James et al. (1990) and Magni et al. (1993), is analyzed. It is found that when the cross-saturation coefficient is modulated by the spatial hole-burning the stabilization is not always possible. We propose a new way of obtaining a stable steady-state configuration based on an increase of the strength of nonlinearity, which leads to a strong cancellation of modes, so that during the evolution all of the modes, but a single one, are canceled. Such a steady-state solution is found to be stable with respect to small perturbations.Comment: 18 pages, 6 figures, LaTeX, psfig.sty, to be published in J. Bif. Chao

Electronic magnification for astronomical camera tubes

Definitions, test schemes, and analyses used to provide variable magnification in the image section of the television sensor for large space telescopes are outlined. Experimental results show a definite form of magnetic field distribution is necessary to achieve magnification in the range 3X to 4X. Coil systems to establish the required field shapes were built, and both image intensifiers and camera tubes were operated at high magnification. The experiments confirm that such operation is practical and can provide satisfactory image quality. The main problem with such a system was identified as heating of the photocathode due to concentration of coil power dissipation in that vicinity. Suggestions for overcoming this disadvantage are included

Swimming efficiency in a shear-thinning fluid

Micro-organisms expend energy moving through complex media. While propulsion speed is an important property of locomotion, efficiency is another factor that may determine the swimming gait adopted by a micro-organism in order to locomote in an energetically favorable manner. The efficiency of swimming in a Newtonian fluid is well characterized for different biological and artificial swimmers. However, these swimmers often encounter biological fluids displaying shear-thinning viscosities. Little is known about how this nonlinear rheology influences the efficiency of locomotion. Does the shear-thinning rheology render swimming more efficient or less? How does the swimming efficiency depend on the propulsion mechanism of a swimmer and rheological properties of the surrounding shear-thinning fluid? In this work, we address these fundamental questions on the efficiency of locomotion in a shear-thinning fluid by considering the squirmer model as a general locomotion model to represent different types of swimmers. Our analysis reveals how the choice of surface velocity distribution on a squirmer may reduce or enhance the swimming efficiency. We determine optimal shear rates at which the swimming efficiency can be substantially enhanced com- pared with the Newtonian case. The non-trivial variations of swimming efficiency prompt questions on how micro-organisms may tune their swimming gaits to exploit the shear-thinning rheology. The findings also provide insights into how artificial swimmers should be designed to move through complex media efficiently

Civic and institutional dimensions of democratization in Ukraine : the role of civic unity

The theoretical analysis presented in this article links the social and institutional conditions of democratization by looking at two rarely associated concepts, civic unity and the rule of law. It attempts to bring a novel approach to the study of democratization in a divided society such as Ukraine, building on a selection of the existing literature on the subject and focusing on the civic dimension of the process. It follows the approach of those political scientists who have challenged the “no precondition’ line in democratization research by looking precisely at context specific conditions that may sustain democracy. It is argued that the common sense of citizenship and belonging to a political community, supported by legal and institutional mechanisms and conscious effort of political elites, would contribute to the development of civil society and perhaps even democratic consolidation in the long run. Thus the civic and institutional dimensions of democratization should not be separated, especially in case of some post-communist societies such as Ukraine. The relationship between these two dimensions, however, is problematic at least from a methodological point of view and requires careful examinatio

Lernanforderungen von Arbeitsaufgaben und Kompetenzentwicklung

Veränderungen in der Arbeitswelt begründen, dass Lernen ein wesentlicher Bestandteil von Berufsarbeit ist. Die in der Berufsarbeit erforderliche Qualität des Lernens wird in jüngerer Zeit mit Kompetenzentwicklung bezeichnet. Unter Kompetenz wird die Befähigung zu selbst organisiertem Lernen verstanden. Kompetenzentwicklung findet zum großen Teil im Prozess der Arbeit durch die Auseinandersetzung mit Aufgaben statt. Eine Stichprobe Erwerbstätiger mit einer Qualifikation auf technischem Gebiet wird in Personen mit stabilen, qualifikationsgerechten Berufsbiografien und in Berufsbiografien mit Brüchen klassifiziert. Deutliche Effektunterschiede im Selbstkonzept beruflicher Kompetenz können mit dem Umfang an Lernanforderungen in den Arbeitsaufgaben in Zusammenhang gebracht werden. Mit linearen und hierarchischen Regressionsanalysen wird geprüft, in welchem Umfang eine Varianzaufklärung im Selbstkonzept beruflicher Kompetenz durch die Lernanforderungen in der Arbeit gelingt.Changes in the area of work give reasons to believe that learning is a substantial component of professional work. Lately, the quality of learning, which is necessary for professional work, is described as development of competence. Competence can be understood as the ability of self-organized learning. Development of competence largely takes place in the process of work by dealing with tasks. A sample of employees with a technological qualification is classified into persons with qualification related jobs and in persons with non-qualification related jobs. Differences in criteria of the self concept of competence exist between these groups. Multiple and hierarchical regression analyses show learning demands at work as a predictor of the self concept of professional competence