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Organic vapour sensing and thermoelectric properties of carbon nanotubes/ethylene-octene copolymer composites combined in a thermopile
Slobodian, P. ; Říha, Pavel ; Olejník, R. ; Benlikaya, R.
A novel self-powered thermoelectric vapor sensor, whose thermogenerated voltage was modulated by chemical vapors is presented. The sensor was made of composites of oxidized multi-walled carbon nanotubes within\nethylene-octene copolymer. The multi-walled carbon nanotubes within ethylene-octene copolymer showed that the oxidation with KMnO4 enhanced its p-type electrical conductivity and that the thermoelectric power increase was proportional to the formation of new oxygen-containing\nfunctional groups on the surface of carbon nanotubes. When this composite was subjected to a saturated vapor of either heptane (aliphatic hydrocarbon), toluene (aromatic hydrocarbon) or ethanol (alcohol), its respective relative resistance increased in average by 3.6, 1.1 and 0.05.
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Saltation of sand in vicinity of cylindrical column
Kharlamova, Irina ; Kharlamov, Alexander ; Vlasák, Pavel
The paper presents a model of sand sediment transport in water stre am in vicinity of a high cylindrical col umn. It is assumed that an averaged turbulent flow is horizontally layered in vicinity of the cylinder. In ea ch layer the flow around the cylinder is modelled as a potential flow generated by a vertical dipole line. Flow in viscous sub-layer on the surface of the cylinder is neglected. The presented flow model is approximate; however it is simple for use. Trajectories of saltating particles near the cylinder were calculated. Further investigation of such flow will allow a determination of zones where solid particles will collide with the column. That might be useful for prevention of its damage or destruction
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Sedimentation of dilute suspension in intermediate region
Vlasák, Pavel ; Chára, Zdeněk
The present paper describes the results of experimental investigation of the continuous sedimentation of a dilute model of fine-grained suspension in the intermediate region of settlement. The effects of particle size (glass beads of average diameter 150–850 μm), concentration, and inclination of the vessel axis on particle fall velocity were evaluated. It was confirmed that the local relative particle-liquid velocity has a practically constant value across the vessel cross-section. The settling pattern is strongly affected even by a very gentle slope of the vessel axis, which causes an asymmetrical absolute velocity profile and significant increase of the local concentration and absolute fall velocity of particles near the upward-facing wall of the vessel.
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Dependence of saltation parameters on bed roughness and bed porosity
Kharlamova, Irina ; Vlasák, Pavel
In numerical models of bed load transport a bed structure of channel could be described by two parameters, a size of bed particles and a standard deviation of normal distribution of bed particles in the vertical direction. The present paper deals with the effect of bed parameters on average length and height of one jump of saltating particle. A new formula was proposed for bed roughness based on size and standard deviation of the normal distribution of the bed particles. The dependences of length and height of the jump on the diameter of the saltating and bed particles were determined for different variation of vertical distribution of the bed particles.
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Vztah chemismu povrchových vod a horninového prostředí v lesním povodí LIZ na Šumavě
Škoda, S. ; Váchal, J. ; Dumbrovský, M. ; Tesař, Miroslav ; Váchalová, R.
V katastru obce Zdíkov na Šumavě je již přes 20 let sledován v lesním povodí LIZ v rámci projektu GEOMON chemismus povrchových vod. Velmi významným faktem pro stanovení vstupu a výstupu látek do/z povodí je znalost složení a chemismu horninového prostředí. To je zde budováno migmatitizovanými biotitickými a sillimanit-biotitickými pararulami šumavského moldanubika. Půdy, zastoupené oligotrofními až oligomezotrofními kambizeměmi, jsou silně kyselé, sorpčně nenasycené. Jejich silikátový pufrační systém výrazně přispívá k poklesu vyplavování vápníku, manganu, chlóru i celkového hliníku, a tím i ke snižování intenzity zvětrávání hornin.
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Multi-wall carbon nanotube networks prepared from pure MWCNT and their oxidised forms effect of compressive strain on electric resistence
Olejník, R. ; Slobodian, P. ; Říha, Pavel ; Kimmer, D. ; Sáha, P.
Multi-wall carbon nanotube networks were prepared by filtration of CNT aqueous dispersions. CNT dispersions were prepared with the help of surfactant system (sodium dodecyl sulfate with amylalcohol) by ultrasonication. Three types of MWCNT tubes were used. The first were pure CNT delivered by supplier. The others were oxidized CNT oxidized (1. acid solution of KMnO4; 2. the mixture of acids H2SO4 + HNO3). It was found that oxidization significantly changes properties of prepared carbon nanotube networks. There were observed differences in porous structures networks analyzed by SEM microscopy. Moreover, the apparent density of prepared MWCNT networks also changes according to the used CNT. The network electrical resistance is also affected by process of MWCNT oxidation as well as by compressive strain. It was found that the network resistance is sensitive to compressive strain both in the course of strain growth and when loading/unloading cycles are imposed.
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