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51.
Damage due to thermal shock in cross-ply Nicalon/calcium aluminosilicate ceramic matrix composites has been investigated.
Heated specimens of two simple [(0°/90°)s and (90°/0°)s] and two multi-layer [(0°/90°)3s and (90°/0°)3s] materials were quenched into water at room temperature. Crack morphologies were assessed by reflected light microscopy and
scanning electron microscopy. The use of image assembling software allowed the generation of reflected light microscopy images
of all of the thermally-shocked surfaces onto which the crack patterns were then superimposed. This allowed clear identification
of damage mechanisms and accurate quantification of damage accumulation with increasing severity of thermal shock. Damage
was first detected in the central plies of each composite. Composites with 0° central plies exhibited slightly higher resistance
to thermal shock than their counterparts with 90° central plies. Although damage extended to the outer plies as the severity
of the shock increased, crack density was found to vary with position at every shock: it was highest in the central plies
and gradually reduced towards the outer plies. Multiple matrix cracking perpendicular to the fibre direction was the damage
mode identified in 0° plies, while 90° plies contained cracks that ran along the ply length. At more severe shocks the morphology
of these crack patterns was affected in significantly different ways. In addition, the thinner, simple cross-ply composites
exhibited much higher resistance to thermal shock than their multi-layer counterparts. 相似文献
52.
Denniston C Marenduzzo D Orlandini E Yeomans JM 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2004,362(1821):1745-1754
We describe a lattice Boltzmann algorithm to simulate liquid-crystal hydrodynamics in three dimensions. The equations of motion are written in terms of a tensor order parameter. This allows both the isotropic and the nematic phases to be considered. Backflow effects and the hydrodynamics of topological defects are naturally included in the simulations, as are viscoelastic effects such as shear-thinning and shear-banding. We describe the implementation of velocity boundary conditions and show that the algorithm can be used to describe optical bounce in twisted nematic devices and secondary flow in sheared nematics with an imposed twist. 相似文献
53.
54.
Blow ML Yeomans JM 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2011,369(1945):2519-2527
We present and interpret lattice Boltzmann simulations of thick films spreading on surfaces patterned with polygonal posts. We show that the mechanism of pinning and depinning differs with the direction of advance, and demonstrate that this leads to anisotropic spreading within a certain range of material contact angles. 相似文献
55.
Highly selective inhibitors of cyclooxygenase-2 (COX-2i) were introduced to minimize peptic ulcers and their complications caused by dual COX inhibitors (COXi). Co-prescribing a (generally cheap) dual COXi with a gastroprotectant is an alternative strategy, proven to reduce the incidence of NSAID-associated endoscopic ulcers. This review compares the efficacies of these two strategies and makes some estimates of their relative cost-effectiveness. In standard risk patients, endoscopic ulcers are reduced to about the same extent (around 70-80%) by either co-prescribing omeprazole or lansoprazole with a dual COXi or preferring a COX-2i alone. COX-2i reduced ulcer complications by a weighted mean of around 60% in comparative studies with dual COXi. There is little information about the influence of PPI on this endpoint, although one study using H. pylori treatment as a possible surrogate for placebo intervention found 77% protection against recurrent upper gastrointestinal bleeding by co-administered omeprazole. One direct comparison of the two strategies in high-risk patients (recent ulcer bleed) found quite high rates of re-presentation with bleeding ulcer using either strategy, and the differences between them were not significant. Drug costs in four Western countries were compared for each strategy. In one, the costs were similar, but in the others the combination of a cheap dual COXi with omeprazole was usually more expensive than using a COX-2i. The safest strategy in highest risk patients may be to co-prescribe a gastroprotectant with a COX-2i, with resulting higher drug costs but possibly offset by savings in other health costs. The efficacy and cost-benefit of this alternative approach warrants investigation. 相似文献
56.
Xudong SUNJ.A. Yeomans 《材料科学技术学报》1996,12(1):29-34
The main Iimitation to the toughening of the α-Al2O3/Ni composite is the poor bonding atthe interface. which causes the nickel particles to be pulled-out during crack propagation with-out obvious plastic deformation. A proper control of oxygen content at the Al2O3-Ni interfacecan promote wetting at the intedece, and produce a mechanically interlocked and chemically strengthened intedece, causing most of the nickel particles to be stretched to failure and to expe-rience severe plastic deformation during crack propagation in the composite. Fracture toughnesstesting using a modified double cantilever beam method with in situ observation of crack prop-agation in a scanning electron microscope shows that the composite with the strengthenedinterface has a more desirable R-curve behaviour and a higher fracture toughness value than thenormal composite. 相似文献
57.
The problem of determining the maximum matching in a convex bipartite graph, G = (V1, V2, E), is considered. It is shown that by using the appropriate data structures, the maximum matching problem can be efficiently transformed into an off-line minimum problem. Since the off-line minimum problem has been shown to be linear, the maximum matching in a convex bipartite graph can be determined in O(|V1|) time. 相似文献
58.
The behaviour of two Nicalon/calcium aluminosilicate ceramic composite laminates (a (±45°)3s and a plain-weave woven) under conditions of thermal shock has been studied. Test specimens heated at various temperatures
were quenched into room-temperature water. This was followed by detailed damage characterisation. In addition, post-shock
mechanical properties were assessed by tensile tests (for the woven laminate) and flexural tests (for both laminates). Both
materials were found to have comparable thermal shock resistance. Crack morphologies comprised matrix cracks of various orientations
that exhibited similar characteristics to those described for thermally shocked cross-ply laminates with the same constituents,
but cracking was found to be less widespread in the woven laminate. Fibre breaks were also detected on the woven material
when high-temperature degradation of the fibre–matrix interface was present. A gradual reduction in properties (stiffness,
proportional limit stress, fracture strength) of thermally shocked specimens was identified, which began at larger shocks
than those at which thermal shock damage initiated. This was attributed to the extension of some matrix cracks into the bulk
of material. 相似文献
59.
Yeomans Martin R.; Mobini Sirous; Elliman Toby D.; Walker Helen C.; Stevenson Richard J. 《Canadian Metallurgical Quarterly》2006,32(3):215
Animals readily acquire positive odor-taste hedonic associations, but evidence for this in humans remains weak and was explored further. Retronasal pairing of odors with sucrose or salty stimuli (Experiment 1) increased the rated sweetness of sucrose-paired odors without altering liking, although changes in odor pleasantness correlated with sucrose liking. Experience of odors with sucrose or quinine by sweet likers (Experiment 2) found increased pleasantness and sweetness for sucrose-paired odors, whereas quinine-paired odors became less liked and more bitter. Odor-sucrose pairings in sweet likers and dislikers (Experiment 3) found increased sweetness in both groups but increased odor liking only in likers. These data suggest that evaluative and sensory learning are dissociable and that evaluative changes are sensitive to individual differences in sweet liking. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
60.
Stafford Lorenzo D.; Wright Claire; Yeomans Martin R. 《Canadian Metallurgical Quarterly》2010,24(2):274
Research has demonstrated that high, but not low caffeine users exhibit an attentional bias to caffeine related stimuli. Separately, the Implicit Association Test (IAT; Greenwald, McGhee, & Schwartz, 1998) has been used to investigate the valence of implicit cognitions to drugs with some contradictory findings, though no work has addressed this issue with respect to caffeine. Here, we examined whether attentional bias would be found in high and moderate caffeine users using a pictorial version of the dot-probe task. A second aim was to explore differences in implicit cognitions between users and non-users. Fifteen high, moderate and non-caffeine users completed a picture dot-probe, IAT, and mood questionnaire following overnight caffeine deprivation. In the IAT, results demonstrated positive associations to caffeine related words for high but not moderate or non-users. Lower ratings for calmness were evident in both groups of caffeine compared to non-users. Dot-probe findings revealed an attentional bias among moderate caffeine users and non-users but not heavy users. The observed positive implicit associations to caffeine suggest that drug acceptability is the key in such perceptions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献