824 research outputs found
Relativistic state reduction dynamics
A mechanism describing state reduction dynamics in relativistic quantum field
theory is outlined. The mechanism involves nonlinear stochastic modifications
to the standard description of unitary state evolution and the introduction of
a relativistic field in which a quantized degree of freedom is associated to
each point in spacetime. The purpose of this field is to mediate in the
interaction between classical stochastic influences and conventional quantum
fields. The equations of motion are Lorentz covariant, frame independent, and
do not result in divergent behavior. It is shown that the mathematical
framework permits the specification of unambiguous local properties providing a
connection between the model and evidence of real world phenomena. The collapse
process is demonstrated for an idealized example.Comment: 20 pages, 2 figures, replacement with minor correction
Semi-naive dimensional renormalization
We propose a treatment of in dimensional regularization which is
based on an algebraically consistent extension of the Breitenlohner-Maison-'t
Hooft-Veltman (BMHV) scheme; we define the corresponding minimal
renormalization scheme and show its equivalence with a non-minimal BMHV scheme.
The restoration of the chiral Ward identities requires the introduction of
considerably fewer finite counterterms than in the BMHV scheme. This scheme is
the same as the minimal naive dimensional renormalization in the case of
diagrams not involving fermionic traces with an odd number of , but
unlike the latter it is a consistent scheme. As a simple example we apply our
minimal subtraction scheme to the Yukawa model at two loops in presence of
external gauge fields.Comment: 28 pages, 3 figure
Joint Image Reconstruction and Nonrigid Motion Estimation with a Simple Penalty That Encourages Local Invertibility
Motion artifacts are a significant issue in medical image reconstruction. There are many methods for incorporating motion
information into image reconstruction. However, there are fewer studies that focus on deformation regularization in motioncompensated
image reconstruction. The usual choice for deformation regularization has been penalty functions based on
the assumption that tissues are elastic. In the image registration field, there have been some methods proposed that impose
deformation invertibility using constraints or regularization, assuming that organ motions are invertible transformations.
However, most of these methods require very high memory or computation complexity, making them poorly suited for
dealing with multiple images simultaneously in motion-compensated image reconstruction. Recently we proposed an
image registration method that uses a simple penalty function based on a sufficient condition for the local invertibility of
deformations.1 That approach encourages local invertibility in a fast and memory-efficient way. This paper investigates
the use of that regularization method for the more challenging problem of joint image reconstruction and nonrigid motion
estimation. A 2D PET simulation (based on realistic motion from real patient CT data) demonstrates the benefits of such
motion regularization for joint image reconstruction/registration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85929/1/Fessler237.pd
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