1,721,007 research outputs found
Wheeler–DeWitt universe wave function in the presence of stiff matter
No full textWe study the Wheeler–DeWitt (WDW) equation close to the Big Bang. We argue that an interaction-dominated fluid (speed of sound equal to the speed of light), if present, would dominate during such an early phase. Such a fluid with p = ρ ∝ 1/a6 generates a term in the potential of the wave function of the WDW equation proportional to −1/a2. This very peculiar potential, which embodies a spontaneous breaking of dilatation invariance, has some very remarkable consequences for the wave function of the Universe: Ψ(a) vanishes at the Big Bang: Ψ(0) = 0; the wave function Ψ(a) is always real; a superselection rule assures that the system is confined to a ≥ 0 without the need of imposing any additional artificial barrier for unphysical negative a. These results are valid for a continuous class of choices of the operator ordering of the WDW equation
Video-densitometric analysis of bone remodelling in retrospective follow-up of patients with prostheses
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FEM analysis of bone-implant system by using videodensitometric measurements
No full textFinite element method is the best means to obtain meaningful results in bone implant system biomechanics. Since mechanical characteristics of bone change from person to person and, in the same person, they vary over the time, we have chosen to construct individual models, in terms of geometrical and mechanical characteristics, by means of X-ray images analysis. Our aim is to improve surgery planning and to evaluate patient follow-up. The application of the proposed procedure is illustrated throug the construction of a bidimensional FEM model concerning a patient who underwent surgery for the implant of a total hip prosthesis with a six years follow-up. The paper shows that even a bidimensional individual model can give reliable clinical indication
Analisi per imaging del rimodellamento: parte II - Applicazione a casi di artroprotesi d'anca
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