Anaerobic fermentation of xylose by pichia stipitis: The effect of forced cycling of ph

Xylose fermentation by Pichia stipitis was examined using a two-stage batch process. The cells were first grown aerobically on D-xylose (5 g/L), whereafter additional xylose (10 g/L) was added and fermented during anaerobic conditions (T=30°C). The optimum pH value for a fermentation with constant pH was found to be 4.5 (maximum specific ethanol production rate 0.21 g/(g h). Forced square wave cycling of the pH between 4 and 5, and 3.5 and 5.5 (cycle time 30 min) during the fermentation stage resulted in a fermentation rate lower than the maximum rate, but with unchanged ethanol yields.     

Comments on "Compression of the ECG by Prediction or Interpolation and Entropy Encoding"

A recent paper1 discusses prediction and interpolation for data compression of ECG. This communication points out that both methods can be viewed as linear filtering. They are therefore equivalent and give the same result in terms of the amount of data compression achieved.     

Age-related changes in the metabolism of cholesterol in rat liver microsomes

The effects of aging on the hepatic metabolism of cholesterol were studied in 1-, 6- and 24-month-old male Sprague-Dawley rats. Microsomal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity, which regulates cholesterol biosynthesis, decreased from 835±144 (SEM) pmol/min/mg protein in the youngest group to 219±34 and 205±53 pmol/min/mg protein (p<0.001) in the 6- and 24-month-old groups, respectively. Cholesterol 7α-hydroxylase activity, which governs bile acid synthesis, was gradually reduced from 70±14 pmol/min/mg protein in the 1-month-old group to 32±7 and 16±3 pmol/min/mg protein (p<0.05) in the 6- and 24-month-old groups, respectively. Acyl coenzyme A:cholesterol acyltransferase activity, which catalyzes the esterification of cholesterol, averaged 431±47 and 452 ±48 pmol/min/mg protein in the 1- and 6-month-old groups, respectively, and was increased to 585±55 pmol/min/mg protein (p<0.05) in the 24-month-old group. The level of total cholesterol showed an age-related increase from 1.56±0.16 mg/g liver in the 1-month-old group to 1.70±0.15 and 2.20±0.19 mg/g liver (p<0.05) in the 6- and 24-month-old groups, respectively. The increase was mainly caused by an accumulation of esterified cholesterol. We conclude that a marked decrease in HMG-CoA reductase occurs between 1 and 6 months of age; thereafter the enzyme activity stays unchanged. The activity of cholesterol 7α-hydroxylase decreases progressively and drastically with age, whereas the capacity for esterifying cholesterol increases slightly. We speculate that the reduced conversion of cholesterol to bile acids may be one explanation of the age-related increase of plasma cholesterol seen in rats.     

Electromagnetic scattering by a thin resistive wire

A theoretical investigation concerning scattering of a plane electromagnetic wave by a straight resistive wire of finite length in an isotropic homogeneous medium is reported. The work is based on the travelling-wave solution obtained by repeated use of the Wiener-Hopf method. Some numerical data for backscattering cross-section at broadside incidence are given.     

Computer-assisted instruction in communication engineering

This paper gives an account of a pedagogical project using the computer in teaching an electrical engineering subject. The aim was not to let the computer replace the teacher but, rather, to introduce it, in combination with other activities, as one element in an active educational process. This has led to a small-group instructional approach where the computer is used in various ways in courses on different levels.The various teaching activities constituting the instructional model are presented, followed by an evaluation in terms of experiences gained from several different courses (given at the Electrical Engineering Department, University of Lund). The project has provided insight into what the computer can be used for in this type of education—and what it should not be used for, Important in this context are the relationships between the computer and other educational activities and between the students and the computer.     

A PC-controlled module system for automatic sample preparation and analysis

A simple automatic analytical system, consisting of separate modules, for liquid chromatography has been constructed. The different parts of the automatic machine are an auto sampler, an auto dispenser, a selector valve with eight channels, a heater/cooler, a mixing chamber and a pressure air driven injector valve. The process was controlled by a PC from an easily changeable run protocol. The system was applied to analysis of primary amines. The analysis was performed as a pre-column derivatization reaction of the amines and separation by isocratic reversed-phase HPLC with fluorescent detection. Reproducibility and analytical precision have been studied. Comparison between automatically and manually made derivatization reaction and injection was also made. The automatic system was easy to handle, cost-effective and gave good reproducibility.     

Opportunities for direct use of geoheat in central america and other tropical countries

While present efforts are primarily aimed at electric power generation, direct use of geoheat are important means of saving petroleum. In Iceland for instance geoheat has primarily been used for non-power purposes such as house heating and in industries. Its use has been increasing by about 10% annually for more than 15 yr.Technical, economic and institutional aspects of geoheat utilization are discussed.It is found that prolific opportunities exist for use of geoheat in agro-industrial processing in the tropical countries like Central America, and a number of potential applications are mentioned. The cane sugar industry for instance seems to offer important possibilities, since the introduction of geoheat could release the bagasse as raw material for byproduct industries of great economic importance. Geoheat could also provide pulp and paper industries based on fast growing species of pulpwood with heat energy at great savings.Potential geoheat applications in Central America could be equivalent to millions of barrels of petroleum in terms of energy.     

Remark on algorithm 24, regarding a very common violation of the Fortran standard

According to the Fortran standard, variables in a subprogram will become undefined at the execution of the RETURN statement, if they are not contained in the list of dummy arguments or in a common block.