Surface acoustic devices have been shown to be suitable not only for signal processing but also for sensor applications. In this paper high temperature surface acoustic wave devices based on gallium orthophosphate have been fabricated, using a lift-off technique and tested for high frequency applications at temperatures up to 600• C. The measured S-parameter (S 11 ) has been used to study the mass loading effect of the platinum electrodes and turnover temperature of GaPO 4 with a 5• cut. The analysis of these results shows that the mass loading effect can be used to predict the desired resonant frequency of the SAW devices. Also two different adhesion layers for Pt metallisation were studied. Our results show that Zirconium is a more suitable under layer than Titanium.
Two poly(amino acid) systems were studied: (a) poly[N5‐(2‐hydroxyethyl)‐L‐glutamine] (PHEG) derivatives prepared by NCA polymerization; (b) poly‐α,β‐[N‐(2‐hydroxyethyl)‐DL‐aspartamide] (PHEA) derivatives prepared by thermal polycondensation of aspartic acid to racemic polysuccinimide followed by chemical modification reactions. The degradation of polymers by isolated enzymes and homogenate of kidney tissue was studied in vitro and the effect of polymer structure on the rate of degradation and the size of degradation products was evaluated. A PHEA derivative (modified by tyramine residues in 9.6 % of side chains) was accumulated in the lysosomes of kidney cells of rats and the molecular‐weight distribution of the polymer retained inside the lysosomes of living cells and that of the polymer excreted into urine was analysed by a high‐sensitivity size‐exclusion chromatography using the fluorescence and radioactive labelling. While PHEG derivatives were degraded by isolated mammalian enzymes and a tissue homogenate, no significant degradation of PHEA and derivatives was observed, either in vitro, with isolated enzymes and homogenate or in vivo, under a long‐term exposure to the lysosomal enzymes in living cells.
SynopsisStatistical copolymers were prepared from N-carboxyanhydrides of L-valine and y-benzyl-L-glutamate in dioxan with triethylamine as an initiator. The copolymerization conversion was determined by ir spectroscopy, the copolymer composition by amino acid analysis, and the molecular weights by light scattering. The monomer reactivity ratios were found to be rvd = 0.14 and rG'olu(oBrl) = 6.4. High-molecular-weight copolymers are formed even at low conversions. The content of 8-structure in the copolymers was estimated from the ir spectra in copolymerization mixtures. The sequencelength distribution of L-valine and y-benzyl-L-glutamate copolymers was calculated and its dependence on copolymerization conversion is discussed. Relations between the sequence-length distribution and the content of 8-structure were studied. It was found that the content of /?-structure in samples with the same composition is different for low-and high-conversion copolymers. The formation of &structure in copolymers in the copolymerization mixture requires a certain minimal sequence length, which has been found to be about 6 valine units. INTRODUCTIONStatistical copolymers prepared by the copolymerization of two monomers to medium and high conversions are always chemically heterogeneous (i.e., the contents .of different monomer units in the individual macromolecules are different), and at the same time, are sequentially heterogeneous (i.e., the lengths of sequences of monomeric units differ in individual copolymer chains). In the case of binary statistical copolymers, according to classical copolymerization theory, the chemical composition of the arising copolymer and the ordering of monomeric units in its chains are determined, of all the kinetic parameters, only by reactivity ratios of both monomers; they also depend, of course, on the initial composition of the monomer mixture and on copolymerization conversion. Hence, the chemical heterogeneity and the sequence heterogeneity are interdependent, with their mutual relation determined just by the monomer reactivity ratio values.Further discussion is limited to the conversion heterogeneity, which reflects the change of the monomer mixture composition during copolymerization and, subsequently, results in the change in the composition of the forming c o p *To whom all correspondence should be a d d r d . This study extends the analysis of the heterogeneity of copolymers of Glu(OBz1) and Biopolymer~We also reexamine existing procedures used in the analysis of secondary structure by ir spectroscopy. Secondary structure of the copolymers must be investigated and quantitatively characterized directly in the copolymerization mixture. In the present study we try to correlate the sequence-length distribution of Val and Glu(OBz1) constitutional units calculated from the known initial composition of the mixture of monomers and conversion with the content of the secondary structure of various copolymers. THEORETICAL Sequence-Length Distribution in a Chemically Heterogeneous Statistical CopolymerL...
Research into surface acoustic wave (SAW) devices began in the early 1970s and led to the development of high performance, small size, and high reproducibility devices. Much research has now been done on the application of such devices to consumer electronics, process monitoring, and communication systems. The use of novel materials, such as gallium phosphate (GaPO4), extends the operating temperature of the elements. SAW devices based on this material operating at 434 MHz and up 800 C, can be used for passive wireless sensor applications. Interdigital transducer (IDT) devices with platinum/zirconium metallization and 1.4 m finger-gap ratio of 1:1 have been fabricated using direct write e-beam lithography and a lift-off process. The performance and long-term stability of these devices has been studied, and the results are reported in this paper.
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