Examination of the Thermal Equilibrium Assumption in the Microscopic Parabolic Heat Conduction Model Under the Effect of Two Types of Heating Sources

Abstract

The validity of using the microscopic parabolic heat conduction model under the effect of two types of volumetric heating sources is investigated analytically. The considered volumetric heating sources are a fluctuating periodic source and a unit step source of short duration. Also, the role of the electron gas thermal capacity term is investigated. Criteria are derived to show the necessity of using the microscopic parabolic heat conduction model. Other criteria are derived to show a justification for neglecting the electron gas thermal capacity term from the microscopic parabolic heat conduction model.     

DNA Sequencing and Analysis of 130 kb from Yeast Chromosome XV

We have determined the nucleotide sequence of 129 524 bases of yeast (Saccharomyces cerevisiae) chromosome XV. Sequence analysis revealed the presence of 59 non-overlapping open reading frames (ORFs) of length >300 bp, three tRNA genes, four delta elements and one Ty-element. Among the 21 previously known yeast genes (36% of all ORFs in this fragment) were nucleoporin (NUP1), ras protein (RAS1), RNA polymerase III (RPC1) and elongation factor 2 (EF2). Further, 31 ORFs (53% of the total) were found to be homologous to known protein or DNA sequences, or sequence patterns. For seven ORFs (11% of the total) no homology was found. Among the most interesting protein identifications in this DNA fragment are an inositol polyphosphatase, the second gene of this type found in yeast (homologous to the human OCRL gene involved in Lowe's syndrome), a new ADP ribosylation factor of the arf6 subfamily, the first protein containing three C2 domains, and an ORF similar to a Bacillus subtilis cell-cycle related protein. For each ORF detailed sequence analysis was carried out, with a full consideration of its biological function and pointing out key regions of interest for further functional analysis. The sequence has been submitted to the EMBL data library under Accession Number X94335.© 1997 John Wiley & Sons, Ltd.     

BEAM STIFFNESS MATRIX BASED ON THE ELASTICITY EQUATIONS

A new general beam stiffness matrix which accounts for bending, torsion and shear deformation is derived from an elasticity solution of the beam. The influence of shear and torsion is considered using a 3×3 matrix of deformation coefficients. Numerical examples are presented to demonstrate the behaviour of the deformation coefficients and of the beam stiffness matrix. © 1997 by John Wiley & Sons, Ltd.     

Computer-based informatization of manufacturing engineering activities

The paper deals with the problem of optimization of a quality inspection process structure. The problem is identified with designing an optimal arrangement of inspection operations in a production process (linkages of the quality inspection process with manufacturing and accessory processes). Three mathematical models for the cases of specialized and versatile inspection stations are formulated. It is shown that the problem can be treated as a particular case of a standard assignment problem. An optimization procedure, grounded on Balas' algorithm, is proposed. A numerical example, based on real data, is given.     

Practical significance of relative assimilable nitrogen requirements of yeast: a preliminary study of fermentation performance and liberation of H2S

Saccharomyces cerevisiae wine yeast strains AWRI 796 and AWRI 835, representing a high and a low nitrogen-requiring strain respectively, were cultured in media of varying nitrogen (ammonium) content. Ammonium utilisation, biomass yield, fermentation progress and the liberation of hydrogen sulfide were monitored. Findings from this study support the original classification of these strains in terms of their relative requirement for nitrogen. Accordingly, when compared with AWRI 835 grown under the same conditions, the high nitrogen-requiring strain, AWRI 796, removed c. 8% more nitrogen from the medium, produced c. 7 to 13% more biomass, failed to complete fermentation in the time frame of the experiment and liberated hydrogen sulfide in greater amounts and/or over longer periods. These findings confirm that measures of relative nitrogen requirement form an extremely useful parameter by which to select strains that are better suited to the problem-free fermentation of musts of low nitrogen content.     

Lyapunov function candidates for semi-state systems

This paper deals with the preliminary selection of Lyapunov function candidates (LFC) for semi-state systems (SSS). The problems that appear in the process of the evaluation of the total time derivative of an LFC along the motions of SSS are discussed. As a result some convenient classes of the LFC are determined. Some concrete hints on the methodology of the construction of LFC are given. Also, the well-known formula of Yoshizawa (1966) for the calculation of the upper right-hand Dini derivative of non-differentiable LFC is extended and generalized to cover the problems of SSS. The results are illustrated through the analysis of general linear RLCMT unforced electrical networks and a non-linear feedback system.     

Reactivity,Stored Energy,and Dislocations in Solid-Solid Reacting Systems

Strong neutron bombardment of graphite can displace many atoms from their lattice positions; many of the dislocated atoms do not anneal during the irradiation process and the net result is an increase of internal energy of the graphite. This increase is usually referred to as stored energy, or in the older literature this phenomenon is sometimes called the total Wigner energy. In addition to irradiation, mechanical milling, decomposition, precipitation, reduction of chemical compounds, and condensation of metal vapors can also produce stored energy in powders. The stored energy associated with defects in solids is an important aspect of the nature of the defects and the processes that produce them. It has been shown experimentally that stored energy results in a large increase of reactivity of the solid materials, and the spontaneous release of the energy in an inert atmosphere can lead to a large temperature rise. This short communication reports on several typical features of stored energy and illustrates the problem with a few experimental examples. Since stored energy substantially increases the reaction rate we can carry out many reactions at much lower temperatures. Consequently, in technical applications for specific reactions high-temperature furnaces can be replaced by high-performance mills operating at room temperatures or by cheap low-temperature furnaces.

Non-catalytic reactions, in spite of their importance, have not received as much attention as catalysis in the past. Major developments and working plants erected at the end of the last century without participation of the chemical engineering community, as, for example, cement manufacturing, steel production, and ore processing, did not encourage chemical engineers to study the governing phenomena in a systematic way. Consequently, modeling and experimental studies have been relatively few, and applied physics or metallurgy propelled development in the field.

Reactions, that take place in gaseous or liquid systems can usually be well reproduced if the external conditions of the experiment are identical and the experiment is carried out with precursors of identical concentration. The situation is rather different in systems where solid precursors participate in the reaction scheme. In this short note we will report on some phenomena, that are not well known in the realm of chemical reaction engineering and that might play a very important role in experimental investigation and optimization of a particular solid reaction system.     

Differential utilisation of sulfur compounds for H2S liberation by nitrogen-starved wine yeasts

Hydrogen sulfide (H₂S) liberation by Saccharomyces cerevisiae wine yeast was studied as a function of different inorganic sulfurous precursors using a model winemaking system. In a medium analogous to grape juice, and following nitrogen starvation of the yeast culture, a combination of 5 mM sulfate and 300 μM sulfite was more potent than 5 mM sulfate alone as a substrate for H₂S liberation. Sulfate plus sulfite allowed H₂S liberation in greater amounts, at higher rates and over a longer period than sulfate alone, by most of the five yeast strains examined. Nevertheless, a sulfate-only medium still supported the liberation of between 11 and 86% of the H₂S observed in the sulfate plus sulfite medium. After nitrogen depletion of the medium, sulfate uptake by yeast cells was stable for at least 7 h and even increased in a cycloheximide-sensitive manner by ca 35%. The relatively limited formation of H₂S from sulfate is therefore not attributable to losses of sulfate transport by the culture as might occur through elevated permease turnover. Similarly, an inhibition of sulfate transport could not account for the lesser formation of H₂S from sulfate because cultures starved of nitrogen in the presence of sulfate continued to accumulate sulfate in excess of the rates of H₂S liberation. Instead, sulfate deprivation/supplementation experiments implied that limited utilisation of sulfate was due to an inhibition of sulfate reduction to sulfide. Experiments also highlighted a contribution by intracellular sulfur pools of between 35 and 70% to the total H₂S liberated from sulfate by nitrogen starved yeasts. As a component of this pool, glutathione was a precursor for 40% of the H₂S liberated from sulfate-containing medium.     

Equilibrium in the System CaSO4.2H2O-CaSO4.½H2O-H2O

Using a simple geometric model, the conditions of equilibrium for topotactical dehydration of gypsum to the hemihydrate in liquid H₂O were determined. The calculated equilibrium temperature agrees with the experimentally determined temperature at which the rate of topotactical dehydration of gypsum single crystals approaches zero.     

A survey of lactic acid bacteria for enzymes of interest to oenology

Isolates from wine-associated genera of lactic acid bacteria (LAB), including Lactobacillus , Oenococcus and Pediococcus , were examined for enzymatic properties that could be of value in the production and processing of wine. Up to 438 combinations of bacterial isolates and substrates were examined. Across the 50 isolates investigated, all were found to hydrolyse esters, with the greatest activity being seen amongst the oenococci followed by the lactobacilli and pediococci. Lipase activity was restricted to three Lactobacillus isolates, while all tested isolates displayed tannase activity. Cellulase, β-glucanase and lichenase activities were observed for almost all Pediococcus and Lactobacillus isolates, while such activities were seen for only a minority of oenococci. No degradation of the xylan substrate was detected. Once confirmed under winelike conditions, our findings will help define potentially interesting genera of LAB for winemaking.