Use Of Enrichment Techniques Research Articles

Energy consistent framework for continuously evolving 3D crack propagation

This paper presents an enhanced theoretical formulation and associated computational framework for brittle fracture in elastic solids within the context of configurational mechanics, building on the authors’ previous paper, Kaczmarczyk et al. (2014). The local form of the first law of thermodynamics provides an equilibrium condition for the crack front, expressed in terms of the configurational forces. Applying the principle of maximal energy dissipation, it is shown that the direction of the crack propagation is given by the direction of the configurational forces. In combination with a fracture criterion, these are utilised to determine the position of the continuously evolving crack front. This exploitation of the crack front equilibrium condition leads to a completely new, implicit, crack propagation formulation. A monolithic solution strategy is adopted, solving simultaneously for both the material displacements (i.e. crack extension) and the spatial displacements. The resulting crack path is resolved as a discrete displacement discontinuity, where the material displacements of the nodes on the crack front change continuously, without the need for mesh splitting or the use of enrichment techniques. In order to trace the dissipative loading path, an arc-length procedure is adopted that controls the incremental crack area growth. In order to maintain mesh quality, smoothing of the mesh is undertaken as a continuous process, together with face flipping, node merging and edge splitting where necessary. Hierarchical basis functions of arbitrary polynomial order are adopted to increase the order of approximation without the need to change the finite element mesh. Performance of the formulation is demonstrated by means of three representative numerical simulations, demonstrating both accuracy and robustness.

Multicentre epidemiological survey on the incidence of Streptococcus agalactiae in pregnancy

ß-hemolytic streptococci group B (GBS) cause infections of the urinary tract, endometrium, amnion, and superinfection of wounds, with complications in 2% -4% of cases in pregnant woman.The infection transmitted to newborns is a cause of sepsis and meningitis with high incidence of mortality.A recent report on a multicentric study of the ISS, showed that detection of S. agalactiae in pregnant women in different realities of healthcare, ranging from 3.9% to 19.4%. This survey covers a sample of 29607 women screened in a total of 36852 childbirths, with a positivity of 4183 subjects equal to 14.1%. Thanks to the GBS Study Group of Piemonte and Valle d’Aosta microbiology laboratories, with the support of 42 study centres have been involved. Collection techniques, types of medium, environmental of incubation of the culture, possible enrichment in broth, of the swabs of 28491 women during 2006/2007 have been considered. 24.36% were vaginal swab while 75.64% vagino/rectal. According to data collected at 31 centers with eligible data (22,175 pregnant) GBS positivity was 12.7% (CI [Confidence Interval] + / -95%: 13.1% -12.2%) with wide variability between individual centers (2% -22.6%). The enrichment broth is used by 6 out of 9 centers with positivity> 15% (M: 20.05%), from 6 to 14 with positivity between 10-15% (M: 12.61%), from none to 8 centers with less than 10% positivity (M: 4.95%).This multicentre survey underlined the preference for vagino/rectal swab, as recommended by the literature. The frequency of GBS positivity of pregnant women on the whole samples is similar to that found in other national surveys, even if with large differences between the different centers.The sensitivity tends to increase with the use of enrichment techniques, whose use is uneven between the centers, perhaps indicating the need for greater uniformity of protocols based on the results of microbiological analysis EBM (Evidence Based Medicine).