Dependence of the Properties of Moving Striations in the Plasma of the Positive Column on Some External and Internal Parameters
Dependence of the Properties of Moving Striations in the Plasma of the Positive Column on Some External and Internal Parameters
OSCILLATIONS IN IONIZED GASES
A simple theory of electronic and ionic oscillations in an ionized gas has been developed. The electronic oscillations are so rapid (ca. 10 9 cycles) that the heavier positive ions are unaffected. They have a natural frequency v e = ( ne 2 /πm ) 1/2 and, except for secondary factors, do not transmit energy. The ionic oscillations are so slow that the electron density has its equilibrium value at all times. They vary in type according to their wave-length. The oscillations of shorter wave-length are similar to the electron vibrations, approaching the natural frequency v p = v e ( m e /m p ) 1/2 as upper limit. The oscillations of longer wave-length are similar to sound waves, the velocity approaching the value v = (kTe/m p ) 1/2 . The transition occurs roughly (i.e. to 5% of limiting values) within a 10-fold wave-length range centering around 2(2) 1/2 π λ D , λ D being the “Debye distance.” While the theory offers no explanation of the cause of the observed oscillations, the frequency range of the most rapid oscillations, namely from 300 to 1000 megacycles agrees with that predicted for the oscillations of the ultimate electrons. Another observed frequency of 50 to 60 megacycles may correspond to oscillations of the beam electrons. Frequencies from 1.5 megacycles down can be attributed to positive ion oscillations. The correlation between theory and observed oscillations is to be considered tentative until simpler experimental conditions can be attained.
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.