604 research outputs found
Direct Neutron Capture for Magic-Shell Nuclei
In neutron capture for magic--shell nuclei the direct reaction mechanism can
be important and may even dominate. As an example we investigated the reaction
Ca(n,Ca for projectile energies below 250\,keV in a direct
capture model using the folding procedure for optical and bound state
potentials. The obtained theoretical cross sections are in agreement with the
experimental data showing the dominance of the direct reaction mechanism in
this case. The above method was also used to calculate the cross section for
Ca(n,Ca.Comment: REVTeX, 7 pages plus 3 uuencoded figures, the complete uuencoded
postscript file is available at ftp://is1.kph.tuwien.ac.at/pub/ohu/calcium.u
Inter-vendor harmonization of Computed Tomography (CT) reconstruction kernels using unpaired image translation
The reconstruction kernel in computed tomography (CT) generation determines
the texture of the image. Consistency in reconstruction kernels is important as
the underlying CT texture can impact measurements during quantitative image
analysis. Harmonization (i.e., kernel conversion) minimizes differences in
measurements due to inconsistent reconstruction kernels. Existing methods
investigate harmonization of CT scans in single or multiple manufacturers.
However, these methods require paired scans of hard and soft reconstruction
kernels that are spatially and anatomically aligned. Additionally, a large
number of models need to be trained across different kernel pairs within
manufacturers. In this study, we adopt an unpaired image translation approach
to investigate harmonization between and across reconstruction kernels from
different manufacturers by constructing a multipath cycle generative
adversarial network (GAN). We use hard and soft reconstruction kernels from the
Siemens and GE vendors from the National Lung Screening Trial dataset. We use
50 scans from each reconstruction kernel and train a multipath cycle GAN. To
evaluate the effect of harmonization on the reconstruction kernels, we
harmonize 50 scans each from Siemens hard kernel, GE soft kernel and GE hard
kernel to a reference Siemens soft kernel (B30f) and evaluate percent
emphysema. We fit a linear model by considering the age, smoking status, sex
and vendor and perform an analysis of variance (ANOVA) on the emphysema scores.
Our approach minimizes differences in emphysema measurement and highlights the
impact of age, sex, smoking status and vendor on emphysema quantification.Comment: 9 pages, 6 figures, 1 table, Submitted to SPIE Medical Imaging :
Image Processing. San Diego, CA. February 202
Measurement of neutron capture on Ca at thermal and thermonuclear energies
At the Karlsruhe pulsed 3.75\,MV Van de Graaff accelerator the thermonuclear
Ca(n,)Ca(8.72\,min) cross section was measured by the
fast cyclic activation technique via the 3084.5\,keV -ray line of the
Ca-decay. Samples of CaCO enriched in Ca by 77.87\,\% were
irradiated between two gold foils which served as capture standards. The
capture cross-section was measured at the neutron energies 25, 151, 176, and
218\,keV, respectively. Additionally, the thermal capture cross-section was
measured at the reactor BR1 in Mol, Belgium, via the prompt and decay
-ray lines using the same target material. The
Ca(n,)Ca cross-section in the thermonuclear and thermal
energy range has been calculated using the direct-capture model combined with
folding potentials. The potential strengths are adjusted to the scattering
length and the binding energies of the final states in Ca. The small
coherent elastic cross section of Ca+n is explained through the nuclear
Ramsauer effect. Spectroscopic factors of Ca have been extracted from
the thermal capture cross-section with better accuracy than from a recent (d,p)
experiment. Within the uncertainties both results are in agreement. The
non-resonant thermal and thermonuclear experimental data for this reaction can
be reproduced using the direct-capture model. A possible interference with a
resonant contribution is discussed. The neutron spectroscopic factors of
Ca determined from shell-model calculations are compared with the values
extracted from the experimental cross sections for Ca(d,p)Ca and
Ca(n,)Ca.Comment: 15 pages (uses Revtex), 7 postscript figures (uses psfig), accepted
for publication in PRC, uuencoded tex-files and postscript-files also
available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Ca.u
Longitudinal Multimodal Transformer Integrating Imaging and Latent Clinical Signatures From Routine EHRs for Pulmonary Nodule Classification
The accuracy of predictive models for solitary pulmonary nodule (SPN)
diagnosis can be greatly increased by incorporating repeat imaging and medical
context, such as electronic health records (EHRs). However, clinically routine
modalities such as imaging and diagnostic codes can be asynchronous and
irregularly sampled over different time scales which are obstacles to
longitudinal multimodal learning. In this work, we propose a transformer-based
multimodal strategy to integrate repeat imaging with longitudinal clinical
signatures from routinely collected EHRs for SPN classification. We perform
unsupervised disentanglement of latent clinical signatures and leverage
time-distance scaled self-attention to jointly learn from clinical signatures
expressions and chest computed tomography (CT) scans. Our classifier is
pretrained on 2,668 scans from a public dataset and 1,149 subjects with
longitudinal chest CTs, billing codes, medications, and laboratory tests from
EHRs of our home institution. Evaluation on 227 subjects with challenging SPNs
revealed a significant AUC improvement over a longitudinal multimodal baseline
(0.824 vs 0.752 AUC), as well as improvements over a single cross-section
multimodal scenario (0.809 AUC) and a longitudinal imaging-only scenario (0.741
AUC). This work demonstrates significant advantages with a novel approach for
co-learning longitudinal imaging and non-imaging phenotypes with transformers
Factors Associated With Shorter Colonoscopy Surveillance Intervals for Patients With Low-Risk Colorectal Adenomas and Effects on Outcome
BACKGROUND & AIMS: Endoscopists do not routinely follow guidelines to survey individuals with low-risk adenomas (LRAs; 1-2 small tubular adenomas, < 1 cm) every 5-10 years for colorectal cancer; many recommend shorter surveillance intervals for these individuals. We aimed to identify the reasons that endoscopists recommend shorter surveillance intervals for some individuals with LRAs and determine whether timing affects outcomes at follow-up examinations.
METHODS: We collected data from 1560 individuals (45-75 years old) who participated in a prospective chemoprevention trial (of vitamin D and calcium) from 2004 through 2008. Participants in the trial had at least 1 adenoma, detected at their index colonoscopy, and were recommended to receive follow-up colonoscopy examinations at 3 or 5 years after adenoma identification, as recommended by the endoscopist. For this analysis we collected data from only participants with LRAs. These data included characteristics of participants and endoscopists and findings from index and follow-up colonoscopies. Primary endpoints were frequency of recommending shorter (3-year) vs longer (5-year) surveillance intervals, factors associated with these recommendations, and effect on outcome, determined at the follow-up colonoscopy.
RESULTS: A 3-year surveillance interval was recommended for 594 of the subjects (38.1%). Factors most significantly associated with recommendation of 3-year vs a 5-year surveillance interval included African American race (relative risk [RR] to white, 1.41; 95% confidence interval [CI], 1.14-1.75), Asian/Pacific Islander ethnicity (RR to white, 1.7; 95% CI, 1.22-2.43), detection of 2 adenomas at the index examination (RR vs 1 adenoma, 1.47; 95% CI, 1.27-1.71), more than 3 serrated polyps at the index examination (RR=2.16, 95% CI, 1.59-2.93), or index examination with fair or poor quality bowel preparation (RR vs excellent quality, 2.16; 95% CI, 1.66-2.83). Other factors that had a significant association with recommendation for a 3-year surveillance interval included family history of colorectal cancer and detection of 1-2 serrated polyps at the index examination. In comparisons of outcomes, we found no significant differences between the 3-year vs 5-year recommendation groups in proportions of subjects found to have 1 or more adenomas (38.8% vs 41.7% respectively; PÂ =Â .27), advanced adenomas (7.7% vs 8.2%; PÂ =Â .73) or clinically significant serrated polyps (10.0% vs 10.3%; PÂ = .82) at the follow-up colonoscopy.
CONCLUSIONS: Possibly influenced by patients' family history, race, quality of bowel preparation, or number or size of polyps, endoscopists frequently recommend 3-year surveillance intervals instead of guideline-recommended intervals of 5 years or longer for individuals with LRAs. However, at the follow-up colonoscopy, similar proportions of participants have 1 or more adenomas, advanced adenomas, or serrated polyps. These findings support the current guideline recommendations of performing follow-up examinations of individuals with LRAs at least 5 years after the index colonoscopy
Probing Mechanical Properties of Graphene with Raman Spectroscopy
The use of Raman scattering techniques to study the mechanical properties of
graphene films is reviewed here. The determination of Gruneisen parameters of
suspended graphene sheets under uni- and bi-axial strain is discussed and the
values are compared to theoretical predictions. The effects of the
graphene-substrate interaction on strain and to the temperature evolution of
the graphene Raman spectra are discussed. Finally, the relation between
mechanical and thermal properties is presented along with the characterization
of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc
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