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GREIT: towards a consensus EIT algorithm for lung images,
Get PDFRecently, electrical impedance tomogra-
phy (EIT) has begun to see a signi¯cant clinical in-
terest for monitoring of ventilated patients. The key
capability of EIT is to provide real-time images of
the distribution of ventilation in the patient's lungs.
However, most clinical and physiological research in
lung EIT is done using older and proprietary algo-
rithms; this is an obstacle to interpretation of EIT
results because the reconstructed images are not well
characterized. To address this issue, we are devel-
oping a consensus linear reconstruction algorithm for
lung EIT, called GREIT (Graz consensus Reconstruc-
tion algorithm for EIT). This algorithm is being de-
veloped in three phases: 1) selection of the "ingre-
dients" and evaluation methodology (this paper), 2)
evaluation and experience with GREIT variants, and
3) consensus and definition of the GREIT algorithm.
Algorithms evaluation criteria are identified to be: a)
quantitative output for all positions, b) reconstructed
position error (low and uniform), c) resolution (small
PSF, uniform, few artefacts), d) good noise perfor-
mance, e) low sensitivity to electrode and boundary
movement, f) good performance on clinical and exper-
imental data. This approach represents the consensus
of a large and representative group of experts in EIT
algorithm and clinical applications. All software and
data to implement and test GREIT will be made avail-
able under an open source license which allows free
research and commercial use
Simple FEMs aren’t as good as we thought: experiences developing EIDORS v3.3
Get PDFIn this paper, we 1: announce EIDORS
version 3.3, and clarify the new features and changes
to the software. Brie
y, the new version includes: a)
interfaces to FEM generation (distmesh, netgen) and
dual model solvers, b) new algorithms (total varia-
tion, electrode movement solver, temporal solvers),
c) a data repository with in vivo and simulated data
and models, d) faster algorithms with better caching,
and e) improved graphics and extensive tutorials.
2: we review the use of dual models in EIT, and
the architecture to support their use in EIDORS. 3:
we discuss accuracy limitations to the single-order
tetrahedral nite element models that are used in
much EIT research. We recommend that models
be used of at least 104 elements (for 2D FEMs) and
106 elements (for 3D FEMs). FEM accuracy may
be partially addressed using dual model solvers, for
which EIDORS v3.3 provides support
Reconstruction algorithm for the polarization tomography problem with incomplete data.
Get PDFIn this paper we discuss some issues in polarization tomography. Specifically we describes a slice-by-slice reconstruction algorithm for the truncated transverse ray transform using data from rays normal to only a small number of directions. Specifically an unstable reconstruction procedure is given for three directions and a stable
reconstruction procedure for six directions. It is expected that these methods will prove useful in photoelastic tomography
Pure-injectivity and model theory for G-sets
Get PDFIn the model theory of modules the Ziegler spectrum,
the space of indecomposable pure-injective modules, has played a key
role. We investigate the possibility of defining a similar space in
the context of -sets where is a group
A Note on Priest’s Finite Inconsistent Arithmetics
Get PDFWe give a complete characterization of Priest’s Finite Inconsistent Arithmetics observing that his original putative characterization included arithmetics which cannot in fact be realized
An Improved Arc Algorithm for Detecting Definite Hermitian Pairs
Get PDFA 25-year old and somewhat neglected algorithm of Crawford and Moon
attempts to determine
whether a given Hermitian matrix pair is definite by exploring the
range of the function
,
which is a subset of the unit circle.
We revisit the algorithm and show that
with suitable modifications and careful attention to implementation
details it provides a reliable and efficient means of testing definiteness.
A clearer derivation of the basic algorithm is given
that emphasizes an arc expansion viewpoint
and makes no assumptions about the definiteness of the pair.
Convergence of the algorithm is proved for all ), definite or not.
It is shown that proper handling of three details of the algorithm is
crucial to the efficiency and reliability:
how the midpoint of an arc is computed,
whether shrinkage of an arc is permitted,
and how directions of negative curvature are computed.
For the latter, several variants of
Cholesky factorization with complete pivoting are explored and the benefits of
pivoting demonstrated.
The overall cost of our improved algorithm is typically just a few Cholesky
factorizations.
Applications of the algorithm are described to testing the hyperbolicity of a
Hermitian quadratic matrix polynomial,
constructing conjugate gradient methods for sparse linear systems in saddle point form,
and computing the Crawford number of the pair via a quasiconvex univariate
minimization problem
Cholesky Factorization
Get PDFThis article, aimed at a general audience of computational scientists, surveys the Cholesky factorization for symmetric positive definite matrices, covering algorithms for computing it, the numerical stability of the algorithms, and updating and downdating of the factorization. Cholesky factorization with pivoting for semidefinite matrices is also treated
Perfect generalized characters inducing the Alperin-McKay conjecture
Get PDFIt is well known that the perfect isometries predicted in
Broue's conjecture do not always exist when the defect groups are non-abelian, even when the blocks have equivalent Brauer categories. We consider perfect generalized characters which induce bijections between the sets of irreducible characters of height zero of a block and of its Brauer correspondent in the normalizer of a defect group. In this way the perfect isometries
predicted in Broue's conjecture for blocks with abelian defect groups are generalized. Whilst such generalized characters do not exist in general, we show that they do exist when the defect groups are non-abelian trivial intersection subgroups of order , as well as for for a power of two and for all . Further, we show that these blocks satisfy
a generalized version of an isotypy
Detecting Juvenile Wood in Southern Pine Logs with Brush Electrodes
Get PDFLog scanning to determine internal characteristics to maximize lumber value has been a long-term goal of the sawmilling industry. Juvenile wood is wood formed in southern pine trees during the first 10 years of growth. Juvenile wood is characterized by wood with high moisture content and that undergoes a high degree of longitudinal shrinkage during kiln drying. This shrinkage results in large amounts of warp that produce lumber degrade and very high value loss. Detection of juvenile wood prior to sawing logs will allow application of sawing patterns and drying procedures that result in reduced influence on the final lumber value. Our research tested EIT scanning with brush electrodes to determine the potential for detecting juvenile wood in green southern pine logs. EIT and computed tomography (CT) images were compared to determine that juvenile wood could be detected with acceptable