On the mutual effect of ion temperature gradient instabilities and impurity peaking in the reversed field pinch

The presence of impurities is considered in gyrokinetic calculations of ion temperature gradient (ITG) instabilities and turbulence in the reversed field pinch device RFX-mod. This device usually exhibits hollow Carbon/Oxygen profiles, peaked in the outer core region. We describe the role of the impurities in ITG mode destabilization, and analyze whether ITG turbulence is compatible with their experimental gradients.Comment: 19 pages, 9 figures, accepted for publication in Plasma Phys. Control. Fusio

Crack propagation in concrete at very early ages

Surface defects and cracks in early-age concrete slabs have been observed to propagate under adverse conditions, impairing the performance and service life of these structures. However, the underlying mechanism of this form of crack propagation has remained largely unexplained, with very limited literature available. In this paper, simple yet sufficiently rigorous theoretical analyses of crack propagation in early-age concrete slabs, based on combined geotechnical engineering and fracture mechanics models, are presented. The results obtained clearly show how surface cracks can become unstable and propagate further, and either become stable again or develop through the full depth of the slab. They also convincingly demonstrate the roles of surface cracks and defects, pore moisture suctions and exposure conditions in this process. Importantly, the critical role of good construction practices in minimising this form of cracking is highlighted. These include proper compaction and effective curing as well as timely and adequate saw-cutting

Plastic cracking of concrete: The roles of osmotic and matric suctions

Plastic cracking of concrete is primarily attributable to desiccation by evaporation from unprotected surfaces. This causes high matric suctions to develop in the pore water in the voids adjacent to these surfaces. Dissolved salts in the pore water generate osmotic suctions. However, the effects of these suctions on the strength of plastic concrete are imperfectly understood. In this paper, equations describing total (matric plus osmotic) and osmotic suctions and the shear strength of desiccated particulate materials are discussed briefly. The development of suctions in desiccating fly ash and their effect on its shear strength are illustrated by experimental data. These show that matric suctions do but osmotic suctions do not affect the shear strength of fly ash and hence of comparable materials, including plastic concrete