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Initial velocities of free-settling spherical particle
Chára, Zdeněk ; Kysela, Bohuš
The paper deals with experimental research of the initial phase of free-settling spherical particle which density is close to the density of water. The experiments were carried out with a smooth particle as well as with a particle with a rough surface. The obtained results show that in the initial phase of sedimentation, there is a formation of vortex structures, which are reflected in the increase of resistance in coefficient values.
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Sphagnum mosses – Ecosystem engineers of bogs
Hájek, Tomáš
I evaluated production and decomposition characteristics of six dominant Sphagnum species in their natural microhabitats distributed along the gradient of water table in an open ombrotrophic bog. The growth in length was much higher in pools and hollows than in hummocks but the resulting annual production was roughly similar between the microhabitats due to a greater shoot and bulk density in hummocks. Although hummocks provided much higher potential for decomposition than hollows, the Sphagnum litter decomposed more slowly in hummocks due to much lower litter quality of the hummock sphagna. Thus the hummock Sphagnum species possess both principal mechanisms participating in maintaining hummocks above hollows – a sufficient production rate and limited decomposition rate. These mechanisms emphasize the role of Sphagnum mosses as autogenic ecosystem engineers controlling also the microhabitat diversification in patterned mires.
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Účinek elektronového svazku na poly[fenyl(methyl)silylen]
Horák, Petr ; Schauer, Petr
The study of Poly[Methyl(Phenyl)Silylene] properties using cathodoluminescent method is complicated by the material degradation. The speed of degradation depends on the irradiation time as well as on the current density of the excitation beam. CL investigation of PMPSi proved creating of metastable states in the material. The degradation is a reversible process in this case.
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Šíření znečišťujících látek v idealizované městské zástavbě
Šeděnková, Hana ; Jaňour, Zbyněk
The essence of the problem consists in the way of pollutant diffusion in the urban build-area. The measurement of the concentration field the emission from the point (chimney) and line (street) source in the model of the idealized urban build-up area was done in the boundary layer wind tunnel. Dependence on the location of the source against the model and also dependence on the geometric setting of the model (both density of buildings and location of street canyons) was found.
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Pollutant diffusion in the idealized build-up area
Šeděnková, Hana ; Jaňour, Zbyněk ; Leitl, B.
The essence of the problem consist in the way of pollutant diffusion in the urban build-up area. The measurement of the concentration field of the emission from the point (chimney) and line (street) source in the model of the idealized urban build-up area was done in the boundary layer wind tunnel. Dependence on the location of this source against model and also dependence on the geometric setting of the model (both density of buildings and location of street canyons) was found.
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Kultivace mikrořas v trubicovém fotobioreaktoru založeném na solárních koncentrátorech: distribuce světla
Sergejevová, M. ; Zaťková, I. ; Červený, J. ; Zrotalová, Kateřina ; Masojídek, Jiří
The cultivation system consists of two types of irradiance modules – vertical, lower-irradiance unit (close to ambient conditions) and roof, higher-irradiance unit (up to 3.5-times higher than ambient intensity) which are used to compare the growth and behaviour of microalgal cultures of various density at high light intensities. The aim of these experiments has been to monitor a diel course of irradiance intensity and spectral composition concentrated by Linear Fresnel lenses and the light distribution on the surface and inside cultivation tubes. As a model organism, we have used the cyanobacterium Spirulina platensis M2. Three concentration of biomass (about 0.5, 1 and 2 g L-1) have been tested. In higher-irradiance modules we also follow the induction of carotenoids synthesis
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Metastability of poly[methyl(phenyl)silylene]
Horák, Petr
Metastability of the poly[methyl(phenyl)silylene] (PMPhSi) specimen was studied using the cathodoluminescent (CL) method. The process of the CL emission recovery, depending on the irradiation time as well as on the current density of the excitation beam, was observed. The process of the CL recovery is the strongest at the smallest current densities. Knowledge of the time dependence of the PMPhSi degradation will be used for the CL spectra measurement.
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Polymer surface tension and properties of state
Jůza, Josef
This contribution presents transformation of some well-known equations expressing surface tension using state properties and other parameters to express the ratio of the surface tension to the drop density, which is more reliable and available even if density is unknown.
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Experimentální výzkum odporu rotačně se pohybující kulové částice
Lukerchenko, Nikolay ; Kvurt, Y. ; Chára, Zdeněk ; Vlasák, Pavel
Saltatory solid particles conveyed by fluid impact a channel bed from time to time. As a result of the collision the particles receive angular velocity, which gradually decreases with time. For numerical simulation of saltation it is necessary to know values of the drag rotation coefficient. In this paper experimental results of the rotating spherical particles moving in water are described. The rubber spherical balls with density near that of water were used; each of them was speeded up in a special chute that ensured that the particle rotated in a given plane. Values of the drag coefficient of the rotating spherical particle were determined in a dependence on rotation particle Reynolds number
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