Silk fabric reinforced epoxy composites (SFRPs) were prepared by simple hot-press and vacuum treatment, to achieve a maximum reinforcement fraction of 70vol.%-silk. Mechanical behaviour, specifically tensile, flexural, interlaminar shear, impact, dynamic and thermal properties of the SFRPs, was investigated. It was shown that reinforcement by silk fabric can greatly enhance the mechanical performance of SFRPs. In particular, the tensile modulus and breaking energy of 70vol.%-silk SFRP were 145% and 467% higher than the pristine epoxy resin. Moreover, the flexural modulus, ultimate strength and breaking energy were also markedly increased for SFRPs. The flexural strength increased linearly with increasing silk volume fraction from 30 to 60vol.% but diminished slightly at 70vol.%. Additionally, interlaminar shear results showed that the silk and the matrix epoxy resin had better adhesion properties than plain woven flax fibre. Of most significance is that the impact strength reached a maximum of ~71kJ m−2 for the 60vol.%-silk SFRP, which demonstrates the potential of silk reinforcements in impact-resistant composites for applications such as wind turbine blades. Our study may shed light on improving the strength and toughness of engineering composites by incorporating high volume fractions of natural fibres.
The concept of a natural tiling for a periodic net is introduced and used to derive a transitivity associated with the structure. It is accordingly shown that the transitivity provides a useful method of classifying polyhedra and nets. For design of materials to serve as targets for synthesis, structures with one kind of edge (edge transitive) are particularly important. Edge-transitive polyhedra, layers and 3-periodic nets are then described. Some other nets of special importance in crystal chemistry are also identified.
Throughout the 1990s health care providers were interested in developing organized delivery systems. However, industry observers have increasingly questioned the sense of these efforts. Using an established taxonomy of health networks and systems, we examined whether there was a nationwide trend away from the vertical and horizontal arrangements that serve as the backbone to organized delivery systems. Studying 1994-1998, we found that both health networks and systems became less centralized in their hospital services, physician arrangements, and insurance product development. We did not find a general pathway to disintegration but instead found considerable experimentation in organizational form.
ABSTRACT The thiosulfate reductase gene ( phsABC ) from Salmonella enterica serovar Typhimurium was expressed in Escherichia coli to overproduce hydrogen sulfide from thiosulfate for heavy metal removal (or precipitation). A 5.1-kb DNA fragment containing phsABC was inserted into the pMB1-based, high-copy, isopropyl-β- d -thiogalactopyranoside-inducible expression vector pTrc99A and the RK2-based, medium-copy, m -toluate-inducible expression vector pJB866, resulting in plasmids pSB74 and pSB77. A 3.7-kb DNA fragment, excluding putative promoter and regulatory regions, was inserted into the same vectors, making plasmids pSB103 and pSB107. E. coli DH5α strains harboring the phsABC constructs showed higher thiosulfate reductase activity and produced significantly more sulfide than the control strains under both aerobic and anaerobic conditions. Among the four phsABC constructs, E. coli DH5α (pSB74) produced thiosulfate reductase at the highest level and removed the most cadmium from solution under anaerobic conditions: 98% of all concentrations up to 150 μM and 91% of 200 μM. In contrast, a negative control did not produce any measurable sulfide and removed very little cadmium from solution. Energy-dispersive X-ray spectroscopy revealed that the metal removed from solution precipitated as a complex of cadmium and sulfur, most likely cadmium sulfide.
No abstract is provided for this article.
A bstract : Some discussion of the development of affect regulation in relation to two papers by Drs. Kalin and Leibenluft is provided. The goals are to frame the broader issues, including the conceptualization and definitions of affect regulation, to address questions about the development of affect regulation, and to consider ways to bridge between basic and clinical approaches to understanding disorders of affect regulation emerging in childhood and adolescence. The conceptual framework for affect regulation presented here focuses on interactions between cognitive systems and affective systems. It also appears that this area of research is at a very early point in its development—one rich with opportunities to bridge between basic research in affective neuroscience, developmental psychology, and developmental psychopathology, and holds great promise to advance understanding regarding the earliest roots of these disorders.
