R-CURVE MODEL OF CERTAIN CERAMIC COMPOSITES

Abstract— The influence of crack-bridging on the R -curve for certain types of ceramic composites is modeled. Small scale bridging conditions are assumed. A recurrence procedure is used to solve the governing coupled integral equations, resulting in R -curves (stress intensity factor versus crack growth) that depend on well defined microstructural parameters. In addition, the bridging stresses and the crack opening diplacements were computed for all stages of the R -curve development. The numerical scheme is quite general and can be used for a variety of bridging laws. The convergence of the solution method is uniform, and the accuracy is a priori controlled. The results are normalized so that they can be applied for a large variety of composites with different micromechanical parameters. R -curves were computed for different bridiging laws, and were found to be sensitive to the specific bridging law used each time. Some strength-toughness relations are also discussed. The results are particularly suitable for slow crack growth analysis.     

Stereo vision for robotic applications in the presence of non-ideal lighting conditions

Many robotic and machine-vision applications rely on the accurate results of stereo correspondence algorithms. However, difficult environmental conditions, such as differentiations in illumination depending on the viewpoint, heavily affect the stereo algorithms’ performance. This work proposes a new illumination-invariant dissimilarity measure in order to substitute the established intensity-based ones. The proposed measure can be adopted by almost any of the existing stereo algorithms, enhancing it with its robust features. The performance of the dissimilarity measure is validated through experimentation with a new adaptive support weight (ASW) stereo correspondence algorithm. Experimental results for a variety of lighting conditions are gathered and compared to those of intensity-based algorithms. The algorithm using the proposed dissimilarity measure outperforms all the other examined algorithms, exhibiting tolerance to illumination differentiations and robust behavior.     

Durability of particleboards made from wood particles chemically modified with propionic anhydride: results after six years in ground stake-test

Propionylated particleboard stakes with 12.2% propionyl content were tested in ground contact in Western Greece. The stakes showed severe attack after five years of testing and total decay after six years, whereas the unmodified boards showed total decay during the fourth year of testing.     

An investigation of the suitability of some Greek wood species in wood-cement composites manufacture

Eight Greek wood species were examined as potential raw materials for wood-cement composites. Hydration tests were carried out to determine the inhibitory index in order to classify wood-cement compatibility. The mixture with the highest compatibility (low inhibition) was that of poplar and cement with an inhibition index of 7.44.     

Combined effect of light salting,modified atmosphere packaging and oregano essential oil on the shelf-life of sea bream (Sparus aurata): Biochemical and sensory attributes

The combined effect of modified atmosphere packaging (MAP: 40% CO₂/30% O₂/30% N₂) and oregano essential oil, on the shelf-life of lightly salted cultured sea bream (Sparus aurata) fillets stored under refrigeration was studied. Quality assessment was based on sensory analysis and biochemical indices determination. Total volatile basic nitrogen (TVBN) and trimethylamine nitrogen (TMAN) values were higher in sea bream fillets stored in air followed by salted fillets stored in air. For salted sea bream fillets stored under MAP the inhibition in the TVBN and TMAN values was evident in the order MAP < MAP/0.4% (v/w) oregano oil < MAP/0.8% (v/w) oregano oil indicating the preservative effect of oregano oil. Salting had a noticeable preservative effect but produced an increase in the 2-thiobarbituric acid (TBA) values while oregano oil had a strong antioxidant activity giving the lowest TBA values. All raw sea bream fillet samples received acceptable sensory scores during the first 15–16 days of storage. The salted samples remained acceptable up to ca. 20–21 days while the MAP salted samples up to ca. 27–28 days of storage. The oregano oil addition in MAP salted samples yielded a distinct but pleasant flavor and contributed to a considerable slower process of fish spoilage given that the fillets treated with 0.8% (v/w) oregano oil were still sensory acceptable after 33 days of storage. The preservative effect was greater as the oregano oil concentration was greater.     

An axiomatization of graphs

The magmoid of hypergraphs labelled over a finite doubly ranked alphabet, is characterized as the quotient of the free magmoid generated by this alphabet divided by a finite set of equations. Thus a relevant open problem, posed by Engelfriet and Vereijken, is being solved.Received: 27 April 2004, Published online: 14 October 2004     

Materials Selection for Semisolid Processing

The mechanical behavior of alloys in the semisolid state is very sensitive to the volume fraction of solid. In this paper, a simple criterion for processability in the semisolid range is introduced, based on the sensitivity of the volume fraction of solid with respect to minor temperature variations. In addition it is proposed that the processability in the semisolid state can be enhanced using microsegregated material.     

Physical characterization of thermally induced networks of lupin protein isolates prepared by isoelectric precipitation and dialysis

Summary Protein isolates of Lupinus albus were obtained from full fat and defatted lupin flour using isoelectric precipitation or dialysis. Calorimetric tests demonstrated that the main protein fractions of the isolates denature well below 100 °C. Mechanical spectra of isolate dispersions obtained at 80 °C indicated the formation of a 'pseudogel' whose cohesion increased during cooling to 10 °C. Subsequent heating to 90 °C encouraged extensive formation of disulphide bonds as it produced gels that were insoluble in sodium dodecyl sulphate and urea solutions. Dialysis produced isolates of lower gelling concentrations, which also formed networks of a stronger relative elastic character. The presence of NaCl at concentrations up to 0.5 m had a reinforcing effect on networks. Protein over-aggregation caused the opposite effect at higher salt levels. Finally, a comparison with results in the literature on soybean protein gelation suggested similar denaturation temperatures and a common pattern of structure formation for the two legume proteins.     

Spatiotemporal salient points for visual recognition of human actions.

This paper addresses the problem of human-action recognition by introducing a sparse representation of image sequences as a collection of spatiotemporal events that are localized at points that are salient both in space and time. The spatiotemporal salient points are detected by measuring the variations in the information content of pixel neighborhoods not only in space but also in time. An appropriate distance metric between two collections of spatiotemporal salient points is introduced, which is based on the chamfer distance and an iterative linear time-warping technique that deals with time expansion or time-compression issues. A classification scheme that is based on relevance vector machines and on the proposed distance measure is proposed. Results on real image sequences from a small database depicting people performing 19 aerobic exercises are presented.