11,394 research outputs found
High-temperature QCD and the classical Boltzmann equation in curved spacetime
It has been shown that the high-temperature limit of perturbative thermal QCD
is easily obtained from the Boltzmann transport equation for `classical'
coloured particles. We generalize this treatment to curved space-time. We are
thus able to construct the effective stress-energy tensor. We give a
construction for an effective action. As an example of the convenience of the
Boltzmann method, we derive the high-temperature 3-graviton function. We
discuss the static case.Comment: uuencoded gz-compressed .dvi fil
The long wavelength limit of hard thermal loop effective actions
We derive a closed form expression for the long wavelength limit of the
effective action for hard thermal loops in an external gravitational field. It
is a function of the metric, independent of time derivatives. It is compared
and contrasted with the static limit, and with the corresponding limits in an
external Yang-Mills field.Comment: 5 page
The energy of the high-temperature quark-gluon plasma
For the quark-gluon plasma, an energy-momentum tensor is found corresponding
to the high-temperature Braaten-Pisarski effective action. The tensor is found
by considering the interaction of the plasma with a weak gravitational field
and the positivity of the energy is studied. In addition, the complete
effective action in curved spacetime is written down.Comment: 13 pages, one figure, plain TeX forma
Energy and momentum density of thermal gluon oscillations
In the exact propagator for finite temperature gluons the location of the
transverse and longitudinal poles in the gluon propagator are unknown functions
of wave vector: and . The residues of the poles,
also unknown, fix the normalization of the one gluon vector potential and thus
of the field strength. The naive energy density
\pol{E}\cdot\pol{D}+\pol{B}\cdot\pol{H} is not correct because of dispersion.
By keeping the modulations due to the source currents the energy density is
shown to be and regardless of the functional form
of and . The momentum density is . The
resulting energy-momentum tensor is not symmetric.Comment: 16 pages, RevTex, no figure
A Simultaneous Stacking and Deblending Algorithm for Astronomical Images
Stacking analysis is a means of detecting faint sources using a priori
position information to estimate an aggregate signal from individually
undetected objects. Confusion severely limits the effectiveness of stacking in
deep surveys with limited angular resolution, particularly at far infrared to
submillimeter wavelengths, and causes a bias in stacking results. Deblending
corrects measured fluxes for confusion from adjacent sources; however, we find
that standard deblending methods only reduce the bias by roughly a factor of
two while tripling the variance. We present an improved algorithm for
simultaneous stacking and deblending that greatly reduces bias in the flux
estimate with nearly minimum variance. When confusion from neighboring sources
is the dominant error, our method improves upon RMS error by at least a factor
of three and as much as an order of magnitude compared to other algorithms.
This improvement will be useful for Herschel and other telescopes working in a
source confused, low signal to noise regime.Comment: accepted to The Astronomical Journal. 18 pages, 6 figure
Renormalization of Wilson Operators in Minkowski space
We make some comments on the renormalization of Wilson operators (not just
vacuum -expectation values of Wilson operators), and the features which arise
in Minkowski space. If the Wilson loop contains a straight light-like segment,
charge renormalization does not work in a simple graph-by-graph way; but does
work when certain graphs are added together. We also verify that, in a simple
example of a smooth loop in Minkowski space, the existence of pairs of points
which are light-like separated does not cause any extra divergences.Comment: plain tex, 8 pages, 5 figures not include
Semi-supervised clinical text classification with Laplacian SVMs: An application to cancer case management
AbstractObjectiveTo compare linear and Laplacian SVMs on a clinical text classification task; to evaluate the effect of unlabeled training data on Laplacian SVM performance.BackgroundThe development of machine-learning based clinical text classifiers requires the creation of labeled training data, obtained via manual review by clinicians. Due to the effort and expense involved in labeling data, training data sets in the clinical domain are of limited size. In contrast, electronic medical record (EMR) systems contain hundreds of thousands of unlabeled notes that are not used by supervised machine learning approaches. Semi-supervised learning algorithms use both labeled and unlabeled data to train classifiers, and can outperform their supervised counterparts.MethodsWe trained support vector machines (SVMs) and Laplacian SVMs on a training reference standard of 820 abdominal CT, MRI, and ultrasound reports labeled for the presence of potentially malignant liver lesions that require follow up (positive class prevalence 77%). The Laplacian SVM used 19,845 randomly sampled unlabeled notes in addition to the training reference standard. We evaluated SVMs and Laplacian SVMs on a test set of 520 labeled reports.ResultsThe Laplacian SVM trained on labeled and unlabeled radiology reports significantly outperformed supervised SVMs (Macro-F1 0.773 vs. 0.741, Sensitivity 0.943 vs. 0.911, Positive Predictive value 0.877 vs. 0.883). Performance improved with the number of labeled and unlabeled notes used to train the Laplacian SVM (pearson’s ρ=0.529 for correlation between number of unlabeled notes and macro-F1 score). These results suggest that practical semi-supervised methods such as the Laplacian SVM can leverage the large, unlabeled corpora that reside within EMRs to improve clinical text classification
Distribution functions for hard thermal particles in QCD
We find a closed-form for the distribution function (defined in terms of a
Wigner operator) for hot coloured particles in a background gluon field, in the
hard thermal loop approximation. We verify that the current is the same as that
derived from the known effective action.Comment: 12 page
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