281 research outputs found
Representation of the three-body Coulomb Green's function in parabolic coordinates: paths of integration
The possibility is discussed of using straight-line paths of integration in
computing the integral representation of the three-body Coulomb Green's
function. In our numerical examples two different integration contours are
considered. It is demonstrated that only one of these straight-line paths
provides that the integral representation is valid
Semiclassical Quantization by Pade Approximant to Periodic Orbit Sums
Periodic orbit quantization requires an analytic continuation of
non-convergent semiclassical trace formulae. We propose a method for
semiclassical quantization based upon the Pade approximant to the periodic
orbit sums. The Pade approximant allows the re-summation of the typically
exponentially divergent periodic orbit terms. The technique does not depend on
the existence of a symbolic dynamics and can be applied to both bound and open
systems. Numerical results are presented for two different systems with chaotic
and regular classical dynamics, viz. the three-disk scattering system and the
circle billiard.Comment: 7 pages, 3 figures, submitted to Europhys. Let
Segmentation of brain tumors in MRI images using three-dimensional active contour without edge
Brain tumor segmentation in magnetic resonance imaging (MRI) is considered a complex procedure because of the variability of tumor shapes and the complexity of determining the tumor location, size, and texture. Manual tumor segmentation is a time-consuming task highly prone to
human error. Hence, this study proposes an automated method that can identify tumor slices and segment the tumor across all image slices in volumetric MRI brain scans. First, a set of algorithms in the pre-processing stage is used to clean and standardize the collected data. A modified gray-level co-occurrence matrix and Analysis of Variance (ANOVA) are employed for feature extraction and
feature selection, respectively. A multi-layer perceptron neural network is adopted as a classifier, and
a bounding 3D-box-based genetic algorithm is used to identify the location of pathological tissues in
the MRI slices. Finally, the 3D active contour without edge is applied to segment the brain tumors in
volumetric MRI scans. The experimental dataset consists of 165 patient images collected from the
MRI Unit of Al-Kadhimiya Teaching Hospital in Iraq. Results of the tumor segmentation achieved an
accuracy of 89% +/- 4.7% compared with manual processes
The parabolic Sturmian-function basis representation of the six-dimensional Coulomb Green's function
The square integrable basis set representation of the resolvent of the
asymptotic three-body Coulomb wave operator in parabolic coordinates is
obtained. The resulting six-dimensional Green's function matrix is expressed as
a convolution integral over separation constants.Comment: 14 pages, 2 figure
Factors Affecting the Designation of Cerebrovascular Diseases as Work-Related in Administrative Litigation
The purpose of this study was to identify factors that could be used as standardized criteria for evaluating occupational diseases in initial assessments or requests for examination. Using 100 administrative litigation cases on the work-relatedness of cerebrovascular diseases (CVDs) by the Seoul Branch of the Korea Labor Welfare Corporation (KLWC) from 1997 to 2002, we estimated the relationship between the investigated variables and designation of the work-relatedness of the CVD. As for the age, the odds ratio of the acceptance rate of a case as work-related in subjects over 60 yr of age was 0.08 (95% CI, 0.01-0.75), which was compared to subjects under 30 yr of age. Regarding working hours, the odds ratio of the acceptance rate of a case as work-related in CVDs in those over 56 hr was 9.50 (95% CI, 1.92-47.10) when compared to those less than 56 hr. As for the benefit type, the odds ratio of the acceptance rate of a case as work-related in medical benefits was 5.74 (95% CI, 1.29-25.54), compared to survivor benefits. As for the criteria for defining situations as work overload, the odds ratio of the acceptance rate of a case as work-related in injured workers was 12.06 (95% CI, 3.12-46.62), compared to that in non-injured workers. Our findings show that the criteria for defining situations of work overload played an important role in assessing the work-relatedness of CVDs in administrative litigation, and it is necessary to make the scientific evidence on judgement of work-relatedness on overwork
Decimation and Harmonic Inversion of Periodic Orbit Signals
We present and compare three generically applicable signal processing methods
for periodic orbit quantization via harmonic inversion of semiclassical
recurrence functions. In a first step of each method, a band-limited decimated
periodic orbit signal is obtained by analytical frequency windowing of the
periodic orbit sum. In a second step, the frequencies and amplitudes of the
decimated signal are determined by either Decimated Linear Predictor, Decimated
Pade Approximant, or Decimated Signal Diagonalization. These techniques, which
would have been numerically unstable without the windowing, provide numerically
more accurate semiclassical spectra than does the filter-diagonalization
method.Comment: 22 pages, 3 figures, submitted to J. Phys.
Computational aspects and applications of a new transform for solving the complex exponentials approximation problem
Many real life problems can be reduced to the solution of a complex
exponentials approximation problem which is usually ill posed. Recently a new
transform for solving this problem, formulated as a specific moments problem in
the plane, has been proposed in a theoretical framework. In this work some
computational issues are addressed to make this new tool useful in practice. An
algorithm is developed and used to solve a Nuclear Magnetic Resonance
spectrometry problem, two time series interpolation and extrapolation problems
and a shape from moments problem.Comment: 28 pages, 20 figure
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