29,657 research outputs found
A miniature surgical drill using ultrasonic/sonic frequency vibration
A study is presented of a miniature ultrasonic surgical drill designed for bone biopsy, based on an ultrasonic/sonic drill which converts high frequency to low frequency vibrations through a freely vibrating mass between an ultrasonic transducer-horn and a drill bit. For conventional surgical drilling using a rotary drill or an ultrasonic drill, considerable power is required to penetrate into bone and the efficiency is low. However, for ultrasonic/sonic drilling, sufficient acoustic energy is accumulated and then released through each impact to achieve precise drilling with a lower power requirement. The ultrasonic/sonic drill was originally invented for rock drilling in low gravity environments. In this study it is incorporated in a miniature ultrasonic surgical drill and the effective impulse delivered to the bone is used to evaluate the drilling performance. To develop a miniature surgical device based on maximising the effective impulse, optimisation of the ultrasonic horn and free-mass is first demonstrated. The shape and dimensions of the ultrasonic horn and free-mass are determined through FEA, which focuses on maximising the post-collision velocity of the free-mass. Then, the entire dynamic stack constituting the surgical drill device is modelled as a mass-spring-damper system to analyse the dynamic behaviour. The numerical model is validated through experiments, using a prototype drill, which record the velocity of the free-mass and the drilling force. The results of the numerical models and experiments indicate this miniature ultrasonic surgical drill can deliver sufficient impulse to penetrate bone and form the basis of an ultrasonically activated bone biopsy device
Diffusive optical tomography in the Bayesian framework
Many naturally-occuring models in the sciences are well-approximated by
simplified models, using multiscale techniques. In such settings it is natural
to ask about the relationship between inverse problems defined by the original
problem and by the multiscale approximation. We develop an approach to this
problem and exemplify it in the context of optical tomographic imaging.
Optical tomographic imaging is a technique for infering the properties of
biological tissue via measurements of the incoming and outgoing light
intensity; it may be used as a medical imaging methodology. Mathematically,
light propagation is modeled by the radiative transfer equation (RTE), and
optical tomography amounts to reconstructing the scattering and the absorption
coefficients in the RTE from boundary measurements. We study this problem in
the Bayesian framework, focussing on the strong scattering regime. In this
regime the forward RTE is close to the diffusion equation (DE). We study the
RTE in the asymptotic regime where the forward problem approaches the DE, and
prove convergence of the inverse RTE to the inverse DE in both nonlinear and
linear settings. Convergence is proved by studying the distance between the two
posterior distributions using the Hellinger metric, and using Kullback-Leibler
divergence
Isospin Diffusion in Heavy-Ion Collisions and the Neutron Skin Thickness of Lead
The correlation between the thickness of the neutron skin in Pb-208, and the
degree of isospin diffusion in heavy-ion collisions is examined. The same
equation of state is used to compute the degree of isospin diffusion in an
isospin-depedent transport model and the neutron skin thickness in the
Hartree-Fock approximation. We find that skin thicknesses less than 0.15 fm are
excluded by the isospin diffusion data.Comment: 5 pages, 4 figures; few minor corrections and updates; version to
appear in PR
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