Článek shrnuje různé teoretické úvahy i empirické pokusy o dosažení laserové akce na mezipásových elektronových přechodech v polovodičích s nepřímým zakázaným pásem (germanium a křemík), počínaje zrodem "laserové epochy" na začátku šedesátých let minulého století. Zatímco v germaniu bylo laserování za pokojové teploty a při elektrickém čerpání nedávno konečně experimentálně demonstrováno, v křemíku zůstává tento cíl stále ještě iluzorní. Pro tento případ článek zdůrazňuje nutnost použít poněkud jiný přístup než u germania. V tomto smyslu jsou diskutovány nejnovější výsledky získané s použitím luminiscenčních křemíkových kvantových teček (nanokrystalů)., Various theoretical, as well as empirical considerations, about how to achieve lasing between the conduction and valence bands in indirect band gap semiconductors (germanium and silicon) are reviewed, starting from the dawn of the laser epoch in the beginning of the sixties. Whilst room-temperature lasing under electrical pumping has recently been achieved for Ge, this objective for Si still remains illusory. The necessity of applying a slightly different approach in Si as opposed to Ge is stressed. Recent advances in the field are discussed, based in particular, on light-emitting Si quantum dots., Ivan Pelant, Kateřina Kůsová., and Obsahuje bibliografické odkazy
The present work investigates the effect of the flow profile induced by an inlet condition on the roll-wave evolution in turbulent clear-water flows. The study employs theoretical and numerical analyses. Firstly, the influence of the inlet condition on the spatial evolution of a single perturbation in a hypercritical flow is examined through the expansion near a wavefront analysis. The results show that an accelerated unperturbed profile reduces the disturbance spatial growth. A decelerated profile causes an increase. The effect of the flow profile on the spatial evolution of rollwave trains is then numerically investigated solving the Saint Venant equations with a second-order Runge-Kutta Total Variation Diminishing (TVD) Finite Volume scheme. The numerical simulations comply with the analytical results for the initial and transition phases of the roll-wave development. The unperturbed profile influences even the roll-waves statistical characteristics in the final stage, with a more evident effect in case of accelerated profiles. The influence of the flow profile should be therefore accounted for in the formulation of predictive criteria for roll-waves appearance based on the estimation of the disturbance spatial growth rate.
A structural look at the employment of women with young children shows that this group is marginalized in the labour market when it is unable or only with difficulty is able to find employment in the labour market, as the current labour market revolves around the principle of independent, fully flexible individuals unencumbered by any obligations outside work. What significance in their lives do these women ascribe to being mothers and what significance do they assign to work? How does the perception of the relationship between work and family influence how they define for themselves the combination of these two spheres of life? How does this group of women see their opportunities for finding work in the labour market? Answers to these questions were sought from an analysis of 29 semi-structured interviews carried out in 2006 with women on parental leave or women just returning to work from leave, who had taken a requalification course. Their view is the view from “below”, which is a legitimate one, but given that it mainly relates to their own experiences or the experiences of others in their social surroundings there may be limitations to it. The potential limitations in this view are pointed out in the article’s conclusion., Hana Maříková., and Obsahuje bibliografii
The detection of the Kautsky effect, i.e. the chlorophyll (Chl) fluorescence índuction kínetics induced in the dark-adapted leaves because of a sudden irradiation, by Hans Kautsky and his students is reviewed here on the occasíon of the 60* anniversary of this CW fluorescence transient discovery and oftBě 100* birth anniversary of Hans Kautsky in 1991.