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排序方式: 共有131条查询结果,搜索用时 46 毫秒
1.
S Whitman L Lacey D Ansell EH Chen J Dell CW Phillips 《Canadian Metallurgical Quarterly》1993,22(3):393-397
Magnetic resonance imaging allows a noninvasive assessment of myelination during normal brain maturation as well as the detection of genetically determined and acquired diseases that affect the synthesis and maintenance of myelin. If this high sensitivity of magnetic resonance imaging for white matter changes is completed by adequate clinical and biochemical information, a unique diagnostic tool is available to gain new insights in the formation of myelin and pathogenesis of myelin disorders. 相似文献
2.
Molecularly imprinted polymer-magnetic iron oxide composite materials which exhibit recognition properties and can be withdrawn from solution by application of a magnetic field were prepared for the first time. Magnetic iron oxide was incorporated using a suspension polymerisation methodology with a perfluorocarbon liquid as the dispersing phase for the preparation of methacrylic acid-1,1,1-trimethylolpropane trimethacrylate copolymer beads molecularly imprinted with the beta-blocker (S)-propranolol. The resulting superparamagnetic imprinted polymer beads were capable of binding [3H]-(S)-propranolol more strongly than a non-imprinted, otherwise identical, polymer. In a competitive radioligand binding assay using a magnet to separate polymer from solution, (R)-propranolol and (R,S)-metoprolol exhibited cross-reactivities of 19 and 0.7%, respectively, compared with (S)-propranolol. 相似文献
3.
Plant fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of surface impurities and the large amount of hydroxyl groups make plant fibers less attractive for reinforcement of polymeric materials. Hemp, sisal, jute, and kapok fibers were subjected to alkalization by using sodium hydroxide. The thermal characteristics, crystallinity index, reactivity, and surface morphology of untreated and chemically modified fibers have been studied using differential scanning calorimetry (DSC), X‐ray diffraction (WAXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. Following alkalization the DSC showed a rapid degradation of the cellulose between 0.8 and 8% NaOH, beyond which degradation was found to be marginal. There was a marginal drop in the crystallinity index of hemp fiber while sisal, jute, and kapok fibers showed a slight increase in crystallinity at caustic soda concentration of 0.8–30%. FTIR showed that kapok fiber was found to be the most reactive followed by jute, sisal, and then hemp fiber. SEM showed a relatively smooth surface for all the untreated fibers; however, after alkalization, all the fibers showed uneven surfaces. These results show that alkalization modifies plant fibers promoting the development of fiber–resin adhesion, which then will result in increased interfacial energy and, hence, improvement in the mechanical and thermal stability of the composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2222–2234, 2002 相似文献
4.
The application of cryogenics in manufacturing has previously received significant attention in supporting manufacturing processes. This paper explores the continued application of cryogenic manufacturing for producing personalised products. This paper presents the novel concept of cryogenic CNC machining of elastomers and the development of a process control system for cryogenic CNC machining. The control process is illustrated alongside material dependent machining data and example soft elastomer machined parts. An enhancement to the process is also detailed within a closed loop thermally monitored cryogenic CNC machining facility. 相似文献
5.
In this study a thorough analysis of physical and fine structure of hemp fibre bundles, namely surface topography, diameter,
cellulose content and crystallinity index, have been presented. The fibre bundles have been alkalised and physical and mechanical
properties analysed. Alkalisation was found to change the surface topography of fibre bundles and the diameter decreased with
increased concentration of caustic soda. Cellulose content increase slightly at lower NaOH concentrations and decrease at
higher NaOH concentrations. The crystallinity index decrease with increase in caustic soda concentration up to 0.24% NaOH
beyond which, it decreases with increase in NaOH concentration. It was also found that the tensile strength and stiffness
increases with increase in the concentration of NaOH up to a limit. Tensile strength and Young’s modulus increase with decrease
in cellulose content, while crystalline cellulose decreases slightly but with improved crystalline packing order resulting
in increased mechanical properties. Similar observations are elucidated by the crystallinity index. Alkalised hemp fibre bundles
were found to exhibit a similar specific stiffness to steel, E-glass and Kevlar 29 fibres. The results also show that crystallinity
index obtained following alkalisation has a reverse correlation to the mechanical properties. Stiffer alkalised hemp fibre
bundles are suitable candidates as reinforcements to replace synthetic fibres. The improvement in mechanical properties of
alkali treated hemp fibre bundles confirms their use as reinforcement materials. 相似文献
6.
Bio‐composites for structural applications: Poly‐l‐lactide reinforced with long sisal fiber bundles
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Fully bio‐based and biodegradable composites were compression molded from unidirectionally aligned sisal fiber bundles and a polylactide polymer matrix (PLLA). Caustic soda treatment was employed to modify the strength of sisal fibers and to improve fiber to matrix adhesion. Mechanical properties of PLLA/sisal fiber composites improved with caustic soda treatment: the mean flexural strength and modulus increased from 279 MPa and 19.4 GPa respectively to 286 MPa and 22 GPa at a fiber volume fraction of Vf = 0.6. The glass transition temperature decreased with increasing fiber content in composites reinforced with untreated sisal fibers due to interfacial friction. The damping at the caustic soda‐treated fibers‐PLLA interface was reduced due to the presence of transcrystalline morphology at the fiber to matrix interface. It was demonstrated that high strength, high modulus sisal‐PLLA composites can be produced with effective stress transfer at well‐bonded fiber to matrix interfaces. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40999. 相似文献
7.
Presents a short story to illustrate how developmental themes of therapists' own lives are inextricably tied to their therapeutic styles, and to the client issues that rivet attention. The story tells about an aging man who sits in his office and looks at his paintings and imagines that his paintings are looking back at him. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
A series of Ni-15 Cr-Al-Ti-Mo alloys with varying γy-γ’ mismatch, Ti/Al atomic ratio, and weight fraction of γ’ were tension tested at ambient temperature after aging to peak yield
strength at 760°C. After subtracting the alloy yield stress in the solution treated condition, σss, the increment in yield
stress due to precipitation of γ’, Δσy, was found to be principally influenced by the weight fraction of γ’ and the measured
γ-γ’ mismatch. Only a small contribution of APBE to alloy strength was observed between two compositions of similar mismatch and
differing measured APBE. The work hardening behavior of the alloys was similarly influenced by weight fraction of γ’ and γy-γ’ mismatch. Alloys with low mismatch exhibited sheared γ’ precipitates following tensile deformation. A model for shear of
ordered γ’ precipitates by residual dislocation loops in low γ-γ’ mismatch alloys is proposed to account for the low work hardening rates observed. 相似文献
9.
R. . Ansell 《Journal of Materials Science》1986,21(2):365-379
The factors which influence the stability of sodium ion conducting beta-alumina ceramics are reviewed from the standpoint of their major application, the sodium-sulphur battery. Significant progress towards understanding the degradation of the ceramic has been made in recent years. 相似文献
10.