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991.
Limin Dong David J. T. Hill James H. O'Donnell Peter J. Pomery Koichi Hatada 《应用聚合物科学杂志》1996,59(4):589-597
The γ irradiation of poly(methacrylate)s with various ester groups at room temperature was investigated by gel permeation chromatography and NMR techniques. The G values for scission and crosslinking for each of the polymers were estimated from the changes in the molecular weights and molecular weight distributions. The new structures formed during γ irradiation were examined by 1H-NMR spectroscopy. All of the investigated poly(alkanemethacrylate)s were found to produce the alkane formates during γ irradiation, and for poly(2-methyl heptyl methacrylate) G(S) was less than 4G(X), indicating gel formation in this polymer. In the investigation of poly(benzyl methacrylate), no formate ester was found, but some small molecule compounds formed from the benzyl radical were detected. The benzyl group was also found to stabilize the polymer against radiation damage. © 1996 John Wiley & Sons, Inc. 相似文献
992.
Dense films of poly[(4-ethylphenoxy)(phenoxy)phosphazene] (PEPP), a potentially attractive ion-exchange membrane material, were crosslinked to varying degrees using UV light and a photoinitiator. This polymer contained two kinds of substituents: phenoxy groups to be used for possible functionalization (e.g., sulfonation) and ethylphenoxy side-chains for photocrosslinking, where hydrogens at the benzylic carbons could be abstracted by a photoinitiator-leaving macroradicals that after recombination formed covalent bonds. The polyphosphazene polymer was synthesized, mixed with a photoinitiator, shaped into a thin film by solvent casting, and irradiated with UV light for a specified period of time. Benzophenone (BP), was selected as the photoinitiator because it was miscible with poly-phosphazene, had the highest rate of hydrogen abstraction, and absorbed UV light of 365 nm wavelength. The half-life of benzophenone in 50 μm-thick irradiated films was determined to be 20 min. When the BP–PEPP molar ratio was increased from 0 to 0.5, the glass transition temperature increased after irradiation from −8.8 to 53.5°C. At the same time, the equilibrium swelling in dimethylacetamide, at 25°C, decreased from infinity to 0.31. Tensile strength tests of the crosslinked films revealed a nonlinear dependence on BP–PEPP molar ratio. © 1996 John Wiley & Sons, Inc. 相似文献
993.
The effect of ozone gas treatment on the adhesion between low-density polyethylene (LDPE) and cellulose was investigated. The ozone treatment of LDPE resulted in a significant increase in the interfacial shear strength as measured by the single fiber fragmentation test, whereas the ozone treatment of cellulose was not successful in improving the adhesion. An extensive surface characterization was performed to elucidate the adhesion mechanism using ESCA, ATR-FTIR, contact angle measurements and iodometry. Among the species formed during the ozone treatment were several different carbonylic compounds, as well as hydroperoxides. The polar component of the surface energy increased for the ozone-treated materials as a result of the oxidation. Extraction of LDPE laminated with a re-generated cellulose film showed that strong bonding as achieved between the ozone-treated LDPE and cellulose during the lamination procedure. The suggestion proposed here for the adhesion mechanism is based on interactions between oxygen-containing species in both materials and the formation of covalent bonds originating from the decomposition of hydroperoxides. © 1996 John Wiley & Sons, Inc. 相似文献
994.
Ewen R Brierley Peter J Wilde Akiko Onishi Paul S Hughes William J Simpson David C Clark 《Journal of the science of food and agriculture》1996,70(4):531-537
The effect of ethanol on the foaming properties of beer protein fractions was studied using a microconductivity method and nitrogen gas to generate the foam. Increasing the ethanol concentration resulted in a decrease in foam stability. Interfacial studies including thin film drainage and dilational elasticity measurements indicated that ethanol reduced the rigidity of the adsorbed protein layer resulting in accelerated drainage from the foam lamellae and increased probability of film rupture. These results conflict with data from the Rudin method (using nitrogen gas to generate the foam) which indicate that, at low concentration, ethanol improves foam stability. These apparently conflicting results may be explained by the foam positive effects of a decline in bubble size and increase in bulk viscosity observed for the Rudin method, contrasted with the negative influence of a reduction in surface viscosity observed for the microconductivity foam assessment method. 相似文献
995.
The nucleotide sequence of a 26·7 kb DNA segment from the left arm of Saccharomyces cerevisiae chromosome IV is presented. An analysis of this segment revealed 11 open reading frames (ORFs) longer than 300 bp and one split gene. These ORFs include the genes encoding the large subunit of RNA polymerase II, the biotin apo-protein ligase, an ADP-ribosylation factor (ARF 2), the ‘L35’-ribosomal protein, a rho GDP dissociation factor, and the sequence encoding the protein phosphatase 2A. Further sequence analysis revealed a short ORF encoding the ribosomal protein YL41B, an intron in a 5′ untranslated region and an extended homology with another cosmid (X83276) located on the same chromosome. The potential biological relevance of these findings is discussed. The sequence was submitted to the EMBL database under Accession Number X96876. 相似文献
996.
Richard A. Pethrick Elisabeth A. Hollins Lain McEwan A. Pollock David Hayward Peter Johncock 《Polymer International》1996,39(4):275-288
Dielectric and rheological measurements are reported on the effect of cure temperature on the water absorption of tris[(2,3-epoxypropoxy)phenyl] methane cured with a 1 : 1 stoichiometric ratio of 4,4′-diaminodiphenylsulphone. Analysis of the water absorption characteristics of these materials using a combination of dielectric and gravimetric measurements has indicated that water molecules can be found in two distinctly different types of environments. There are water molecules which are strongly interacting with polar groups and water molecules clustered together into sub-micro-scale cavities within the matrix structure. Changes in the final cure temperature have the effect of changing both the extent and distribution of the types of water molecules present in the matrix. Validation of the diffusion coefficients obtained from the dielectric analysis is based on a comparison with gravimetric data and the implications are discussed. Differences observed between these two different types of measurement are related to peculiarity in the dielectric method and its extreme sensitivity to interfacial phenomena. 相似文献
997.
David W. Niles Xiaonan Li David Albin Doug Rose Timothy Gessert Peter Sheldon 《Progress in Photovoltaics: Research and Applications》1996,4(3):225-229
A commonly used process for forming low-resistance contacts to thin-film p-type CdTe involves the formation of a Te layer by etching the CdTe film in a concentrated mixture of nitric and phosphoric acids. The authors compare evaporated Te back contacts with ‘control’ back contacts formed by the usual etching process, and demonstrate that evaporating Te onto a CdTe thin film is a viable process for forming a low-resistance contact. The best efficiency achieved for a CdTe solar cell made with an evaporated Te back contact is 12.1%, whereas the efficiency of the device made with the control back contact was 11.9%. The evaporation process offers numerous advantages over acid etching, most notably vacuum compatibility amenable to large-scale production of CdTe solar cell modules. 相似文献
998.
Littoral habitats in large rivers are influenced to varying degrees by changes in discharge. Irrigation abstractions can increase the amount of habitat that would naturally be dewatered during low flow periods and therefore it is important to have some knowledge of the potential impact this may have on riverine macroinvertebrates. The macroinvertebrate assemblages of common littoral habitats in riffles, pools and runs in two reaches each of the Macquarie and Mersey Rivers, northern Tasmania, Australia were compared from samples collected during the low flow and irrigation season, between December 1991 and April 1992. The area under water of these habitats, riffle substrata, macrophyte beds and coarse woody debris, responded differently to changes in discharge. Within a reach, the same taxonomic groups often dominated the total number of macroinvertebrates for all habitats, but there were differences in the proportions contributed by these taxa to the different habitats. In general, taxa characteristic of slow-flowing or lentic habitats, such as ostracods and amphipods, were dominant in macrophyte beds in pools and runs, whereas taxa such as larval elmid beetles and hydropsychid caddisflies were dominant in riffles. A substantial component of the fauna from each habitat within a reach was unique to that habitat, but there was always a similar number of taxa common to all habitats. Classification and ordination grouped samples from both rivers firstly by habitat and secondly by month and reach. Total density and family richness of invertebrates differed by reach, habitat and month in both rivers, except for richness in the Mersey River where habitat was not significant. Differences in densities and numbers of invertebrate families among habitats were not consistent between reaches for each river. This study has highlighted the differences in macroinvertebrate assemblages of several littoral habitats in two lowland rivers in Tasmania. Differences in taxonomic composition, density and richness among habitats within reaches strongly imply the uniqueness of these habitats in terms of the invertebrate faunas that occupy them. We suggest that if maintenance of biotic diversity is an aim of instream flow management, water allocations that address low flows should place a high priority on the maintenance of a diversity of habitats. 相似文献
999.
Peter Zipper Andrs Jnosi Wolfgang Geymayer Elisabeth Ingolic Ernst Fleischmann 《Polymer Engineering and Science》1996,36(4):467-482
Rectangular plates were injection molded from two grades of commercial polypropylene (PP) differing in the molar mass distribution. The mold was mechanically sealed when a desired pressure pi,max (up to 1560 bar) was reached. Samples were taken from each plate at different distances from the gate and were investigated by applying various methods. In spatially resolved wide-angle X-ray studies, the cross section of the sample was scanned with a fine X-ray beam (collimated by a Kratky small-angle camera) and the intensity of scattering was registered by a linear detector as a function of position in the cross section. The evaluation of the scattering data delivered profiles of several parameters, describing the distribution of crystallite modification β-PP and γ-PP, the degree of orientation, the size of crystallites, and interplanar spacing, depending on the distance from surface. These results and those from measurements of birefringence and elongation at break, and from polarization microscopy and transmission electron microscopy, provided details of the layered structures in the plates, at different flow lengths, and allowed far-reaching statements about the influence of molecular properties and processing conditions on the development of texture in the plates. 相似文献
1000.
Peter Meyer Zarlink Semiconductor 《电子产品世界》2006,(14):80-81
随着VoIP网关能够在POTS线或T1/E1中继器与IP网络之间进行业务的互操作,传真、MODEM和电话业务正越来越多地依靠VoIP技术,取代了传统的TDM设备.在部署VoIP网关时,发送和接收时序同步的机理经常被忽视.因而需要改进包同步以提高业务的可靠性和质量,这一点在传统的电路交换设备中是能够实现的. 相似文献