Influence of technological conditions on mechanical stresses inside diamond-like carbon films

In this paper the influences of the technological conditions, i.e. the influences of the hydrogen flow rate and deposition time, on the values of the intrinsic mechanical stresses inside the diamond-like carbon (DLC) thin films prepared by plasma enhanced chemical vapor deposition onto silicon substrates are studied. These stresses are measured by two-beam interferometry and optical profilometry based on chromatic aberration through the measurements of deformations of the silicon substrates originating in consequence of the film stresses. It is shown that the influence of the deposition time (i.e. film thickness) on the film stress is relatively slight in contrast to the influence of the hydrogen flow rate on this quantity. It is namely shown that the film stresses are influenced by the hydrogen flow rate values in a pronounced way within the interval of interest, i.e. within the interval 1–7 sccm. Moreover, it is shown that the method of optical profilometry used can be competitive to the method of two-beam interferometry from the practical point of view.     

The use of upflow anaerobic filter and AnSBR for wastewater treatment at ambient temperature

This research was carried out in order to study the effect of the temperature and hydraulic retention time (HRT) on the start-up and steady-state performance of upflow anaerobic filter (UAF) and anaerobic sequencing batch reactor (AnSBR). A mixture of synthetic substrate (glucose and sodium acetate) and real municipal wastewater was used as a laboratory substrate. The temperature (in the range 9-23 degrees C) and HRT (in the range 6-46 h) were selected as the most decisive technological parameters for a practical application. Average removal efficiency of COD found for tested anaerobic reactors were 56-88% (AnSBR) and 46-92% (UAF) depending on used temperature and HRTs. Based on the observed results, the use of AnSBR and UAF in practice seems to be a potential technology for (pre)-treatment of wastewater produced by small communities.     

Numerical simulation of interaction between turbulent flow and a vibrating airfoil

The subject of this paper is the numerical simulation of the interaction of two-dimensional incompressible viscous flow and a vibrating airfoil. A solid elastically supported airfoil with two degrees of freedom, which can rotate around the elastic axis and oscillate in the vertical direction, is considered. The numerical simulation consists of the stabilized finite element treatment of the Reynolds averaged Navier–Stokes (RANS) approach, the use of turbulence models and the solution of the system of ordinary differential equations describing the airfoil motion. The time dependent computational domain and a moving grid are taken into account with the aid of the Arbitrary Lagrangian–Eulerian (ALE) formulation of the Navier–Stokes equations. High Reynolds numbers up to 10⁶ require to use a suitable stabilization of the finite element discretization and the application of a turbulence model. We apply the algebraic turbulence model, which was designed by Baldwin and Lomax and modified by Rostand. The developed technique was tested by the simulation of flow past a flat rigid plate and the computation of pressure distribution around a rotating airfoil with prescribed motion. Finally, the method was applied to the simulation of flow induced airfoil vibrations. This research was supported under the Grant No. IAA200760613 of the Grant Agency of Academy of Sciences of the Czech Republic. The research of M. Feistauer was partly supported by the research project MSM 0021620839 financed by the Ministry of Education of the Czech Republic and the research of L. Dubcová was partly supported by the grant No. 48607 of the Grant Agency of the Charles University. The authors acknowledge the support of these institutions.     

Extraction fractionation of segmented polyurethanes according to composition

Extraction of solid polyester-based segmented polyurethanes by chloroform and its mixtures with an increasing amount of N,N-dimethylformamide is described. Unlike the precipitation in a solvent-nonsolvent system, where fractionation according to the molecular weight dominates, the extraction can resolve the copolymer into fractions differing in the content of diisocyanate units. © 1995 John Wiley & Sons, Inc.     

Effects of freezing and frozen storage on the microstructure and texture of ewe's milk cheese

Semi-hard ewe's milk cheeses, frozen immediately after manufacture either slowly at –35 °C or rapidly at –80 °C and stored at –20 °C for 4 months were studied for microstructural and textural characteristics during subsequent ripening. Two control groups were used to establish the effect of freezing: the fresh unfrozen cheese and cheese thawed immediately after freezing. Freezing proper did not result in any marked changes in the textural parameters of the cheeses, but considerable changes were found in slowly frozen cheeses after 4 months of frozen storage. Shear strength values were lower in all frozen and stored cheeses, particularly in cheese samples frozen slowly compared to those in the unfrozen control batch. This parameter and firmness values were significantly lower in both slowly and rapidly frozen cheeses at the completion of ripening. Ripening tended to offset differences in elasticity, noticeable in the cheeses during the first 30 days of ripening. Light microscopy and electron microscopy revealed small cracks and ruptures in the cheeses which could not be observed by the naked eye. More extensive damage to the cheese microstructure was found in slowly frozen cheese samples stored frozen for 4 months.     

Effects of monomer impurities on the emulsion polymerization of chloroprene and properties of polychloroprene. I. Effect of methyl vinyl ketone

The influences of small amounts (up to 2%) of methyl vinyl ketone in chloroprene on properties of polychloroprene and kinetics of the emulsion polymerization of chloroprene with mercaptans as regulators has been studied. Methyl vinyl ketone causes a substantial increase in molecular weight of polymer, which results in increased viscosity, gel formation, lowered plasticity of polymer, deterioration of processability, decreased tensile strength, and high modulus of vulcanizates. Methyl vinyl ketone interferes with the regulation of molecular weight by both primary and tertiary dodecylmercaptan; some differences are due to lower reactivity of tertiary dodecylmercaptan. In the presence of diisopropyl xanthogene disulfide as a molecular weight regulator the polychloroprene properties are not affected by methyl vinyl ketone. All changes in polymer properties have been proved to be caused by the addition reaction of dodecylmercaptan on methyl vinyl ketone, yielding 1-dodecylthiobutan-3-one. This compound itself has no influence on the polymerization of chloroprene. Methyl vinyl ketone has a marked promoting effect on polymerization rates, which accounts for its high reactivity and solubility in the water phase. A fast polymerization of methyl vinyl ketone takes place in the water phase of emulsion polymerization system simultaneously with the reaction of methyl vinyl ketone with dodecylmercaptan.     

Human sources of landscape stewardship: the re‐emergence of private farming in the Czech Republic

Historically, an important role informing the Czech cultural landscape was played by the strong middle class of farmers. The period of collectivization which occurred progressively between 1950 and 1989 meant liquidation of the rural community. Whereas in 1950 there were 1,404,225 private farmers, this number had decreased to only 2,000 in 1988. This paper focuses on the problems of stewardship and responsibility towards landscape associated with this social group, which recently has started a new period of growth. The research uses a variety of qualitative and quantitative methods. Dialogues with interviewees have enabled us to interpret stewardship and responsibility into a coherent story about the relationship between people and landscape. Similarities and differences have been related to variables such as farmer's age and length of time in farming. The results show that patterns of stewardship and responsibility are not related to economic variables, but rather to common features of ‘timeless’ rural culture.