The extended finite element method for three-dimensional reinforced composites.

Conference (2011, November 16)

This paper deals with the use of eXtended Finite Element Method (XFEM) to perform local effects in three-dimensional reinforced composites. This method was first introduced to model cracks. It is based on ... [more ▼]

This paper deals with the use of eXtended Finite Element Method (XFEM) to perform local effects in three-dimensional reinforced composites. This method was first introduced to model cracks. It is based on the partition of unity concept and the description of discontinuities like the location of holes and material interfaces is often realized by the level-set method. The approach considered allows (i) to easily model the real geometry of reinforcing fibers (not idealized), (ii) to impose arbitrary Dirichlet and Neumann boundary conditions on the implicit defined boundaries and (iii) to introduce models of degradation. Numerical applications are presented on some academic tests. [less ▲]

Phalangeal osteosonogrammetry study: age-related changes, diagnostic sensitivity, and discrimination power. The Phalangeal Osteosonogrammetry Study Group.

in Journal of Bone and Mineral Research (2000), 15(8), 1603-14

Phalangeal osteosonogrammetry was introduced as a method for bone tissue investigation in 1992. It is based on the measure of the velocity of ultrasound (amplitude-dependent speed of sound [AD-SoS]) and ... [more ▼]

Phalangeal osteosonogrammetry was introduced as a method for bone tissue investigation in 1992. It is based on the measure of the velocity of ultrasound (amplitude-dependent speed of sound [AD-SoS]) and on the interpretation of the characteristics of the ultrasound signal. In this study we have collected a database of 10,115 subjects to evaluate the performance of AD-SoS and to develop a parameter that is able to quantify the signal characteristics: ultrasound bone profile index (UBPI). The database only includes females of which 4.5% had documented vertebral osteoporotic fractures, 16% lumbar spine dual X-ray absorptiometry (DXA), and 6% hip DXA. The analysis of the ultrasound signal has shown that with aging the UBPI, first wave amplitude (FWA), and signal dynamics (SDy) follow a trend that is different from the one observed for AD-SoS; that is, there is no increase during childhood. In the whole population, the risk of fracture per SD decrease for AD-SOS was odds ratio (OR) 1.71 (CI, 1.58-1.84). The AD-SoS in fractured subjects was significantly lower than in a group of age-matched nonfractured subjects (p < 0.0001). In a small cohort of hip-fractured patients UBPI proved to be lower than in a control age-matched group (p < 0.0001). When the World Health Organization (WHO) working group criteria were applied to this population to identify the T score value for osteoporosis, for AD-SoS we found a T score of -3.2 and for UBPI we found a T score of -3.14. Sixty-six percent of vertebral fractures were below the AD-SoS -3.2 T score and 62% were below UBPI -3.14. We observed the highest incidence of fractures (63.6%) among subjects with AD-SoS who had both DXA T score values below the threshold. We conclude from this study that ultrasound investigation at the hand phalanges is a valid methodology for osteoporosis assessment. It has been possible to quantify signal changes by means of UBPI, a parameter that will improve the possibility of investigating bone structure. [less ▲]