Relaxation dynamics of excited states of Tm3+ ions in TeO2-ZnO-Na2O-Y2O3 glasses

Tellurite glasses with the composition of xTm_2O_3-(6-x)Y_2O_3-3Na_2O-25ZnO-66TeO_2(where 0≤x≤6)were obtained by the melt-quenching technique.Absorption(300 K),excitation(300 K) and fluorescence spectra(300 K) as well as fluorescence decay curves of Tm~(3+)-doped title glasses are presented and discussed in details.The Judd-Ofelt analysis based on the room temperature absorption spectrum was applied for determination of fundamental fluorescence properties such as radiative transition probabilities(A_T),branching ratios(β_R),radiative lifetimes(τ_R) of the emitting levels of the Tm~(3+) ion and stimulated emission cross-sections(σ_(em)).Fluorescence spectra were recorded and analysed in the visible and near-infrared spectral range.The emission and effective cross-section were calculated for the ~3F_4→~3H_6 transition,showing that the investigated glasses are promising laser host materials,operating at 1.8 μm.The observed concentration quenching and non-exponential decay curves from the ~1 G_4 and ~3H_4 states indicate nonradiative energy transfer between Tm~(3+) ions.The analysis of non-exponential fluorescence decay curves from the ~1 G_4 and ~3H_4 levels was carried out in framework of the InokutiHirayama and Yokota-Tanimoto models and energy transfer microparameters were determined.The self-quenching model was proposed for describing relaxation of the first excited state of the Tm~(3+) ion.     

Chemical composition of the cell wall of probiotic and brewer’s yeast in response to cultivation medium with glycerol as a carbon source

The structure of cell wall of yeasts (genus Saccharomyces) is one of the factors that determine their health-promoting properties connected to the presence of β-glucans and mannoprotein. The aim of the study was to determine the influence of glycerol as a carbon source on structural polymers of cell wall (β-glucan and mannoprotein) of probiotic yeasts Saccharomyces cerevisiae var. boulardii and brewer’s yeasts S. cerevisiae R9. Significant increase of the percentage of polysaccharide content in the cell wall dry weight of S. cerevisiae R9 brewer’s yeasts was noted (in the range of 10–20 %) after cultivation in medium containing glycerol at a concentration of 2–5 % and pH 4.0. The highest content of carbohydrates in probiotic yeasts’ cell wall (58 %) was observed after cultivation in medium containing 3 % of glycerol and pH 5.0. The cell wall of probiotic yeasts was characterized by higher content of mannoprotein comparing with cell wall preparation of brewer’s yeasts S. cerevisiae R9 composed mainly of β-glucans. After cultivation in mediums with 2 and 3 % of glycerol, the cell of brewer’s yeasts contained the highest amount of β(1,3/1,6)-glucan in dry weight of the cell wall (about 36 %). Glycerol at a concentration of 3 and 5 % also intensified mannoprotein biosynthesis in cell wall of S. cerevisiae R9, approximating their content to those noted in the cells of probiotic yeasts (about 29 % (w/w) of dry weight of the cell wall) after cultivation in a medium of pH 5.0 containing 3 % of glycerol.     

Long-term storage stability of selected potato starch – Non-starchy hydrocolloid binary gels

All 3, 4 and 5% potato starch gels containing either κ-carrageenan, guar gum or xanthan gum were prepared and their stability in terms of rheological and textural properties was checked on 30 day storage. It was shown that rheology of these binary potato starch – non-starchy hydrocolloid mixtures could be controlled by anionic character of the admixed hydrocolloid. Depending on the hydrocolloid added, gels made of the tuber starch can either retain their pattern typical for tuber starches or turn into that typical for gels of cereal starches. Hydrocolloids added plasticity to the binary gels but it was lost to a significant extent within the first day of storage. Resulting gels with dominating elastic character are rheologically and texturally fairly stable for subsequent 30 days of storage. Generally, hydrocolloids stabilized potato starch gel on long-time storage to the extent dependent on the gel concentration.     

Optimized carry lookahead adders with direct feeding

This paper describes improvements to the parallel prefix adder designs and optimization algorithms of Chan, Oklobdzija, Schlag, Thomborson and Wei. Our “direct feeding” (DF) adder design avoids large signal fanouts along critical adder paths. Our “random pruning” heuristic limits the time and space required to find near-optimal DF adders, so that the search process runs in a few minutes on a Sun-4 workstation. Our improved carry lookahead adders are well suited for static CMOS implementation; our improvements may be applied to other parallel prefix CMOS circuits. Simulations with Mentor Graphics' Lsim indicate that our best DIP adders are 12% to 20% faster than the carry lookahead adders presented by Chan et al.     

Synergistic Roll‐to‐Roll Transfer and Doping of CVD‐Graphene Using Parylene for Ambient‐Stable and Ultra‐Lightweight Photovoltaics

A roll‐to‐roll (R2R) transfer technique is employed to improve the electrical properties of transferred graphene on flexible substrates using parylene as an interfacial layer. A layer of parylene is deposited on graphene/copper (Cu) foils grown by chemical vapor deposition and are laminated onto ethylene vinyl acetate (EVA)/poly(ethylene terephthalate). Then, the samples are delaminated from the Cu using an electrochemical transfer process, resulting in flexible and conductive substrates with sheet resistances of below 300 Ω sq^?1, which is significantly better (fourfold) than the sample transferred by R2R without parylene (1200 Ω sq^?1). The characterization results indicate that parylene C and D dope graphene due to the presence of chlorine atoms in their structure, resulting in higher carrier density and thus lower sheet resistance. Density functional theory calculations reveal that the binding energy between parylene and graphene is stronger than that of EVA and graphene, which may lead to less tear in graphene during the R2R transfer. Finally, organic solar cells are fabricated on the ultrathin and flexible parylene/graphene substrates and an ultra‐lightweight device is achieved with a power conversion efficiency of 5.86%. Additionally, the device shows a high power per weight of 6.46 W g^?1 with superior air stability.     

The Effect of Implanted Al and/or Y on the Scale Formation on Low-Al Fe20Cr2Al Alloy

The very early stages of the oxidation of an Fe20Cr2Al alloy, unmodified and ion-implanted by aluminium, yttrium and a combination of both elements, Al and Y, were studied at 1100 °C in oxygen using two-stage-oxidation exposures with ¹⁸O₂ as a tracer and subsequent characterisation of the scales using SIMS analyses of distribution of oxygen isotopes and oxide-related negative ion clusters, SEM observations of the surface morphology and photoluminescence spectroscopy analysis of the phase composition. The scales formed in all cases, except for the Al-implanted alloy, exhibited layered structures, with the outer part comprising Fe- and Cr-rich oxide, and the inner part being Al₂O₃, which grew due to a mixed outward–inward mechanism . The alumina sub-layers contained the transient oxides and α-Al₂O₃. Implanted Al significantly affected the mechanism of the scale growth, providing that the scale consisted essentially of α-Al₂O₃, and grew via a mixed inward-outward mechanism typical for scales on alumina formers.     

Technological aspects of sunflower biomass and brown coal co-firing

The technological problems occurring in the co-firing of biomass and brown coal (lignite) prompted this research project. During the fuel preparation, accidental self-ignition and explosions were several times reported by power plants operators. The aim of this study was to evaluate brown coal, sunflower husks and sunflower husk pellets as fuels for co-firing in energetic boilers. Sunflower husk had a lower ash content and calorific value than the pellets. The range of the combustion temperatures of the biomass (200–300 °C) was narrower than that of brown coal (200–800 °C). The formation of highly alkaline ash from the biomass resulted in the formation in boiler of agglomerates of ash. The elemental composition, thermogravimetric and biological analyses suggested that the pellets contained synthetic additives difficult to identify. The biological method was proposed for evaluating biomass additives. The use of additional agents in the pelletizing process may influence on the combustion parameters. Mixing biomass with brown coal may occasionally result in self-ignition in the logistic chain. Plastic additives and biological activity may contribute to self-ignition.     

Energy recovery and economy aspects of steam-explosion pretreatment in waste phytomass management

Steam-explosion pretreatment allows lowering of the natural resistance of plant material to subsequent biodegrading processes, such as anaerobic fermentation. This is achieved by a complex of cavitation forces that disintegrate rigid lignocellulose structures and liberate labile organic matter during a quick release of phytomass from a steam-pressurized reactor back to the atmospheric pressure. Hydrolyzing reactants or catalysts may increase the effect; however, the management of chemicals raises financial and environmental concerns. The current state of knowledge was reviewed to identify promising designs and reengineering that would enable subsequent transfer into the commercial scale in order to reverse the current trend of phytomass waste management – landfilling. In an effort to achieve profitability, it has been concluded that further development should focus on a deeper interconnection of the apparatus with associated technology units, reuse of waste heat from the subsequent biogas combustion, widening the range of processing parameters, reuse of nutrients, and utilization of the ballast organic matter.