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Graphical Markov models determined by acyclic digraphs (ADGs), also called directed acyclic graphs (DAOs), are widely studied in statistics, computer science (as Bayesian networks), operations research (as influence diagrams), and many related fields. Because different ADOs may determine the same Markov equivalence class, it long has been of interest to… (More)

- Steven B. Gillispie, Michael D. Perlman
- Artif. Intell.
- 2002

Bayesian networks, equivalently graphical Markov models determined by acyclic digraphs or ADGs (also called directed acyclic graphs or dags), have proved to be both effective and efficient for representing complex multivariate dependence structures in terms of local relations. However, model search and selection is potentially complicated by the many-to-one… (More)

- Robert L Harrison, Steven B Gillispie, Thomas K Lewellen
- IEEE Nuclear Science Symposium conference record…
- 2006

SimSET (a Simulation System for Emission Tomography) is being modified to more accurately simulate typical PET block detector tomographs. A new detector module that models the detector system as a collection of rectangular boxes is being added to the software. The new model is sufficiently general to allow many more imaginative or speculative detector… (More)

By adding a second parameter, Conway and Maxwell created a new distribution for situations where data deviate from the standard Poisson distribution. This new distribution contains a normalization constant expressed as an infinite sum whose summation has no known closed-form expression. Shmueli et al. produced an approximation for this sum but proved only… (More)

- Steven B. Gillispie, Branko Grünbaum
- Electr. J. Comb.
- 2009

Isogonal polyhedra are those polyhedra having the property of being vertex-transitive. By this we mean that every vertex can be mapped to any other vertex via a symmetry of the whole polyhedron; in a sense, every vertex looks exactly like any other. The Platonic solids are examples, but these are bounded polyhedra and our focus here is on infinite… (More)

We consider the problem of a consumer wishing to evaluate bundles of options from a list of N independently selectable binary options. The consumer's goal is to find the t best bundles out of the 2 N possible bundle subsets, when ranked according to supplied utility and cost functions. Although 2 N is very large (e.g., for N = 100, 2 N ≈ 10 30), we show how… (More)

- William C J Hunter, Robert L Harrison, Steven B Gillispie, Lawrence R Macdonald, Thomas K Lewellen
- IEEE Nuclear Science Symposium conference record…
- 2009

We are conducting a two-phase study, which aims to select design parameters of a long-axis positron emission tomography (PET) scanner that are a compromise between detection performance and cost. In this first phase, we examine the effects of axial length, detector thickness and collimator geometry on the noise equivalent count rate per axial length (λNEC)… (More)

- R E Schmitz, S B Gillispie, R L Harrison, L R Macdonald, P E Kinahan, T K Lewellen
- IEEE Nuclear Science Symposium conference record…
- 2007

We present a study that introduces two approaches to implementing block detectors into SimSET and compares their performance. SimSET is a photon tracking simulation package, which currently incorporates only detectors made of a solid annulus of scinitillator material. A pseudo-block approximation has been imposed on the solid annulus of conventional SimSET… (More)

- Robert Harrison, Steven Gillispie, Ruth Schmitz, Thomas Lewellen
- Journal of nuclear medicine : official…
- 2008

OBJECTIVES: We have added a block detector model to the Simulation System for Emission Tomography (SimSET) software version 2.9. METHODS: The new model simulates the detector system as a collection of right rectangular boxes and allows for very flexible positioning of these boxes. This model allows users to simulate typical block-based cylindrical… (More)

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