Mass transfer in aerated fermentation broths in a stirred tank reactor

The volumetric mass transfer coefficients, k_La, measured in a pilot plant (0.1 m³) and an industrial (67.5 m³) fermentor during an actual fermentation process are presented. Problems related to the estimation of the phsyical properties as well as to the correlation of experimental data and to scale up procedures are discussed. Although the scale up factor was rather high, both sets of data could be represented by single correlation. Comparison of the experimental data with several available correlations demonstrated the need for pilot plant experiments and scale up procedures, since it is almost impossible to take into account all relevant system properties.     

Water Sorption and Diffusion in (Reduced) Graphene Oxide‐Alginate Biopolymer Nanocomposites

The water sorption and diffusion in (reduced) graphene oxide‐alginate composites of various compositions is analyzed. Water sorption of sodium alginate can be significantly reduced by the inclusion of graphene oxide sheets due to the formation of an extensive hydrogen bonding network between oxygenated groups. Crosslinking alginate with divalent metal ions and the presence of reduced graphene oxide can further improve the swelling resistance due to the strong interactions between metal ions, alginate, and filler sheets. Depending on conditions and composition, the overall water barrier properties of alginate composites improve upon (reduced) graphene oxide filling, making them attractive for moisture barrier coating applications. Water sorption kinetics in all alginate composites indicate a non‐Fickian diffusion process that can be accurately described by the Variable Surface Concentration model. In addition, the water barrier properties of sodium alginate‐graphene oxide composites can be adequately predicted using a simple model that takes the orientational order of filler sheets and their effective aspect ratio into account.

     

BEM simulation of compressible fluid flow in an enclosure induced by thermoacoustic waves

The problem of unsteady compressible fluid flow in an enclosure induced by thermoacoustic waves is studied numerically. Full compressible set of Navier–Stokes equations are considered and numerically solved by boundary-domain integral equations approach coupled with wavelet compression and domain decomposition to achieve numerical efficiency. The thermal energy equation is written in its most general form including the Rayleigh and reversible expansion rate terms. Both, the classical Fourier heat flux model and wave heat conduction model are investigated.The velocity–vorticity formulation of the governing Navier–Stokes equations is employed, while the pressure field is evaluated from the corresponding pressure Poisson equation. Material properties are taken to be for the perfect gas, and assumed to be pressure and temperature dependent.     

The features of sustainable Solar Hydroelectric Power Plant

This work presents the main features of the new power plant that comprises the modified reversible hydroelectric (HE) power plant operating together with the photovoltaic (PV) power plant. Such Solar Hydroelectric Power Plant (SHE) uses solar energy as the only input for production of solar and hydro energy. Thereat, water reservoir serves for daily and seasonal energy storage, thus basically solving the problem of energy storage, which is the biggest problem of wider use of solar energy. The most expensive part of SHE is the PV generator, whose optimal sizing is essential for providing energetic independence of a settlement or isolated consumer. A systematic approach that includes all relevant elements of this system has been implemented for optimal sizing of the PV power plant. The developed model was used in analysis of certain parameters of the SHE system. The results of the analysis show the system characteristics and that the proposed model describes the operation of the power plant very well. The feasibility and characteristics of the power plant were tested on electric energy supply of the island of Vis in Croatia. It has been established that the system is real, feasible and can be very successfully applied on different locations, for different consumers and can vary in size. The prerequisite for realization of such system is the construction of a modified reversible HE power plant. The presented SHE represents a permanently sustainable energy source that can continuously provide power supply to a consumer, using exclusively natural and renewable energy sources, without causing harmful effects on the environment.     

Determination of the mechanical thermostat electrical contacts switching quality with sound and vibration analysis

A mechanical thermostat is a device that switches heating or cooling appliances on or off based on temperature. For this kind of use, electronic or mechanical switching concepts are applied. During the production of electrical contacts, several irregularities can occur leading to improper switching events of the thermostat electrical contacts. This paper presents a non-obstructive method based on the fact that when the switching event occurs it can be heard and felt by human senses. We performed several laboratory tests with two different methods. The first method includes thermostat switch sound signal analysis during the switching event. The second method is based on sampling of the accelerometer signal during the switching event. The results show that the sound analysis approach has great potential. The approach enables an accurate determination of the switching event even if the sampled signal carries also the switching event of the neighbour thermostat.     

YOUTH AND NATIONAL URBAN POLICY: The Florida Experience

ABSTRACT: Throughout the 1980s conditions worsened for children and youth in urban areas throughout the US. Lacking a national youth policy, formulation and implementation of youth policy has been left to the states and localities. One of the most innovative youth policy responses was enacted in Florida where the state authorized the creation of children's services councils at the county level. This paper traces the efforts of Florida's urban counties to develop programs, strategies, and the use of special tax districts that target unmet needs and children's issues. The Florida legislation and the experience of local governments offer one approach for other states and localities, as well as a model for national youth policy.     

Trace element concentrations in higher fungi

The concentrations of ten trace elements, As. Br, Cd, Cu, Hg I, Mn, Se, Zn and V, have been determined in up to 27 species of higher fungi from several sites in Slovenia, Yugoslavia. Analyses were based on destructive neutron activation techniques. Data are presented and compared with the concentrations found in soils. Previously values were non-existent or scanty for these elements, so that the data represent typical levels for basidiomycetes. In addition to confirming high levels of mercury in many species, the survey also found that cadmium is accumulated to a surprising extent by most fungi, the average value being 5 ppm. Among other accumulations found was bromine by the genus Amanita, and selenium by the edible Boletus. Correlation analysis between all pairs of trace elements gave values for r of from 0.75 to 0.43 for 7 pairs (Cu and Hg, 0.75; Se and As, 0.69). As well as these features of biochemical interest, the values found and the pattern of accumulation suggest potential uses of fungi in environmental studies.     

Distinct roles for the mammalian A-type cyclins during oogenesis

There are two A-type cyclins in higher vertebrates, cyclin A1 and A2. Targeted mutagenesis has shown that cyclin A2 is essential for early embryonic development while cyclin A1 is required only for male meiosis. The embryonic lethality of cyclin A2 knockout mice has obviated understanding its role in other aspects of mammalian development, including the germ line. We reported previously that cyclin A2 expression in the male germ line is consistent with a role in both mitotic and meiotic cell cycles. Using in situ hybridization and immunohistochemistry, we now observe high levels of cyclin A2 in granulosa cells and less-abundant but readily detectable expression in ovarian and ovulated oocytes. A decrease in cyclin A2 protein was observed in oocytes from embryonic stages to post-natal and adult ovaries. Interestingly, cyclin A2 protein was nuclear in oocytes from embryonic day 13.5 to 15.5, changing to largely cytoplasmic in oocytes from embryonic day 16.5 to post-natal and adults. Readily detectable expression of the cyclin-dependent kinases Cdk1 and Cdk2, two common partners for the A-type cyclins, was observed in granulosa cells and oocytes at all stages of folliculogenesis. Cdk1 was predominantly cytoplasmic, whereas Cdk2 was both cytoplasmic and nuclear in oocytes. No cyclin A1 expression, at either the mRNA level or the protein level was detected in either embryonic or adult ovaries, consistent with the full fertility observed in female cyclin A1-deficient mice. These results suggest that in the female germ line, cyclin A2 but not cyclin A1 has distinct roles in both mitosis and meiosis.