412 research outputs found
Preliminary investigations of Monte Carlo Simulations of neutron energy and LET spectra for fast neutron therapy facilities
No fast neutron therapy facility has been built with optimized beam quality
based on a thorough understanding of the neutron spectrum and its resulting
biological effectiveness. A study has been initiated to provide the information
necessary for such an optimization. Monte Carlo studies will be used to
simulate neutron energy spectra and LET spectra. These studies will be
bench-marked with data taken at existing fast neutron therapy facilities.
Results will also be compared with radiobiological studies to further support
beam quality optimization. These simulations, anchored by this data, will then
be used to determine what parameters might be optimized to take full advantage
of the unique LET properties of fast neutron beams. This paper will present
preliminary work in generating energy and LET spectra for the Fermilab fast
neutron therapy facility.Comment: 9 pp. 11th Neutron and Ion Dosimetry Symposium (NEUDOS 11). 12-16 Oct
2009. Cape Town, South Afric
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Monte Carlo Simulations Demonstrating Physics of Equivalency of Gamma, Electronbeam, and X-ray for Radiation Sterilization
The sterilization of medical devices using the gamma rays from the decay of
cobalt-60 has accumulated decades of experience of the performance of the
materials and devices that are irradiated. The use of radiation using electron
beams and x-rays has much less experience and this leads to questions of
equivalency between these three technologies. Computer simulations were
conducted to model the relevant physical processes of the interactions of each
of the three forms of radiation in order to compare the spectra of electron
energies at energies below 500 keV. It is predominantly the electrons below
this threshold that produce the sterilization dose. No difference in energy
spectra was seen between the three types of initial radiation. It is concluded
that there is no energy dependent difference between gamma, e-beam, and x-ray
for radiation sterilization
Inference in particle tracking experiments by passing messages between images
Methods to extract information from the tracking of mobile objects/particles
have broad interest in biological and physical sciences. Techniques based on
simple criteria of proximity in time-consecutive snapshots are useful to
identify the trajectories of the particles. However, they become problematic as
the motility and/or the density of the particles increases due to uncertainties
on the trajectories that particles followed during the images' acquisition
time. Here, we report an efficient method for learning parameters of the
dynamics of the particles from their positions in time-consecutive images. Our
algorithm belongs to the class of message-passing algorithms, known in computer
science, information theory and statistical physics as Belief Propagation (BP).
The algorithm is distributed, thus allowing parallel implementation suitable
for computations on multiple machines without significant inter-machine
overhead. We test our method on the model example of particle tracking in
turbulent flows, which is particularly challenging due to the strong transport
that those flows produce. Our numerical experiments show that the BP algorithm
compares in quality with exact Markov Chain Monte-Carlo algorithms, yet BP is
far superior in speed. We also suggest and analyze a random-distance model that
provides theoretical justification for BP accuracy. Methods developed here
systematically formulate the problem of particle tracking and provide fast and
reliable tools for its extensive range of applications.Comment: 18 pages, 9 figure
Calibration of Measurements
Traditional notions of measurement error typically rely on a strong mean-zero assumption on the expectation of the errors conditional on an unobservable “true score” (classical measurement error) or on the data themselves (Berkson measurement error). Weakly calibrated measurements for an unobservable true quantity are defined based on a weaker mean-zero assumption, giving rise to a measurement model of differential error. Applications show it retains many attractive features of estimation and inference when performing a naive data analysis (i.e. when performing an analysis on the error-prone measurements themselves), and other interesting properties not present in the classical or Berkson cases. Applied researchers concerned with measurement error should consider weakly calibrated errors and rely on the stronger formulations only when both a stronger model\u27s assumptions are justifiable and would result in appreciable inferential gains
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