The effect of rare-earth oxide CeO2 on the electromagnetic properties of ferrite-ceramic composite materials
In this work, we present the influence of rare-earth element additions on this new composite material. A great improvement of the electromagnetic properties was obtained. The constituent chemicals were mixed in the stoichiometric composition, calcined at 850degC for 2 h and blended with PVA to press into steroidal or disc shaped specimens. These specimens were sintered at 900degC for 2.5 h in air. The complex permeability, capacity and impedance were measured with HP4291B and 4291A instruments, respectively, in the frequency range from 1MHz to 2GHz.
Electromagnetic properties of a new ferrite-ceramic low-temperature cocalcined (LTCC) composite materials
A new ferrite-ceramic composite material with inductive, capacitive, and impedance properties was fabricated by a solid-state reaction. The composite materials were prepared with ferromagnetic NiCuZn ferrites and ferroelectric BaTiO/sub 3/ perovskite. Co/sup 2+/, Bi/sup 3+/, Y/sup 3+/, Dy/sup 3+/, and Ca/sup 2+/ ions are selected to improve the electromagnetic properties. We found that this new material has excellent frequency dependence of magnetic and dielectric properties, which can be used not only as inductor and resistor materials but also as capacitor materials in the wide range of 1 KHz to 4 GHz. At 1 MHz, the dielectric constant /spl epsiv/' of the composite material is 60-120, and the initial permeability /spl mu/' is 5.6-13.
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.