We show that the hexagonal cross-section of germanium nanowires grown in the 〈110〉 direction by physical vapor deposition is a consequence of minimization of surface energy of the collector droplet. If the droplet is lost or solidified, two {001} sidewall facets are quickly overgrown and the nanowire exhibits a rhomboidal cross-section. This process can be controlled by switching between the liquid and solid state of the droplet, enabling the growth of nanowires with segments having different cross-sections. These experiments are supported by in-situ microscopic observations and theoretical model.

Present methods for determination of kinetic and stoichiometric parameters are mostly based on simple and rapid batch cultivation. An alternative technique of mathematical simulation and a batch cultivation was proposed for estimation of maximum specific growth rates of heterotrophic and autotrophic microorganisms in activated sludge. Estimation of heterotrophic and autotrophic fractions in the biomass is based on mathematical model calibration of continuously operated system. Maximum growth rates are then calculated from the maximum OUR measured in batch tests. The proposed method was compared with a batch test cultivation based on an exponential growth of microorganisms when a proportion of filtered wastewater is mixed together with a small proportion of biomass and aerated in time. Comparing both methods, a disproportion between obtained results was found (μH,max = 4 d−1 from the proposed, and μH,max = 10 d−1 from the batch test method). An explanation of this observation was based on a hypothesis that under batch test conditions (higher S0/X0 ratio) faster-growing microorganisms can be favoured in their growth. This phenomenon was mathematically simulated with a simplified model and confirmed. Therefore, it is recommended that some constants for mathematical modelling obtained from batch tests should be applied on continuously operated systems only with care.

Study of the effect of gas pressure and catalyst droplets number density on silicon nanowires growth, tapering, and gold coverage

Nitrification is the rate-limiting process in the design of activated sludge process. It is especially unstable during the winter season (when the temperature of activated sludge mixed liquor drops below 13 degrees C). It is therefore difficult to meet the ammonia effluent standards in winter. The common way to compensate for low nitrification rates at low temperatures is to increase sludge retention time (SRT). However, the increase of SRT is accompanied by negative factors such as elevated sludge concentration, higher sludge loading of secondary clarifiers, formation of unsettleable microflocs, etc. The low performance of nitrification at low temperatures can also be compensated for by enhancing the nitrification population in activated sludge. This paper describes such a method called bioaugmentation of nitrification in situ. This procedure takes place in a so-called regeneration tank, which is situated in the return activated sludge stream. The results of the operation of two wastewater treatment plants with regeneration zones are described in this paper, together with some economic evaluation of the bioaugmentation method.

No abstract