Temperature control and stabilization in the cryodielectrometer for temperatures 0.5 – 300 K
To meet requirements, which arise while design of equipment for research the dielectric parameters of low-loss materials in the millimeter waveband, the necessity of high-precision temperature stabilization and measurement appear. Despite the fact that a lot of attention [1,2] is devoted to this task already, it reminds still actual, due to a plenty of specific features, which each given measuring complex possess.Thermometers intended to measure low and very low temperatures, as a rule use the temperature dependence of certain physical properties of basis substances. There is known quite large amount of temperature controllers [3-6], which are able to operate in a wide temperature range. However, some of them operate in direct current DC-mode [4], and others, which are used AC-mode, intended for operation in too narrow temperature range ≈ 1 K [3, 6]. Besides, they are able to use only one type of sensor and possess, in our opinion, too complicated feedback scheme for the temperature stabilization [5]. In this paper we consider the scheme of the temperature regulator-stabilizer with two temperature sensors having both positive and negative temperature coefficients of resistance (TCR). It designed for low temperature measurements on the cryodielectrometer “TORNADO” in the temperature range 0.5-300 K. As well results of the low-temperature radiospectroscopy experiment using the device designed are given.
Low-Temperature Thermocouple Thermometry
Precision temperature measurements are becoming increasingly Important in industrial and military cryogenic engineering. Of the many ways of measuring cryogenic temperatures, thermocouples are among the simplest and most useful. Four general considerations are of importance in designing and determining the feasibility of thermocouple systems. First, the selection of the best thermocouple pair depends on the temperature range since both the sensitivity and reliability of a junction change markedly with temperature and are quite different for different systems. Second, a calibration curve must be obtained for each junction pair since the thermoelectric potential differences are not primary temperature scales, Third, estimates must be made of the effects of inhomogeneities and other sources of error that will affect the reliability of the temperature readings. And fourth, for high accuracy at the lowest temperatures the electrical circuitry and measuring apparatus must be carefully designed. The last item is one of instrumentation and will not be discussed here. The other three considerations are discussed for gold-cobalt and constantan versus copper or “normal” silver, chromel versus aiumel, and iron versus constantan.
l-Phenylalanine dehydrogenase from Brevibacterium sp. for production of l-phenylalanine by reductive amination of phenylpyruvate
SummaryFor production of l-phenylalanine the reductive amination of phenylpyruvate, catalyzed by phenylalanine-dehydrogenase was examined. To reach high levels and a sufficient stability of the inducible intracellular enzyme, growth conditions of Brevibacterium sp. are optimized. For continuous production of l-phenylalanine in an enzyme membrane reactor, the kinetic parameters of the partially purified enzyme are determined.In continuous production a space time yield of 37.4 g l-Phe l-1 d-1 can be reached.By means of the measured kinetic parameters and simultaneous calculation of the mass balances of all reaction components the behaviour of the reactor can be simulated. For certain conditions the multi-enzyme-system shows multiple steady-states.