6,780 research outputs found
The QCD trace anomaly
In this brief report we compare the predictions of a recent
next-to-next-to-leading order hard-thermal-loop perturbation theory (HTLpt)
calculation of the QCD trace anomaly to available lattice data. We focus on the
trace anomaly scaled by T^2 in two cases: N_f=0 and N_f=3. When using the
canonical value of mu = 2 pi T for the renormalization scale, we find that for
Yang-Mills theory (N_f=0) agreement between HTLpt and lattice data for the
T^2-scaled trace anomaly begins at temperatures on the order of 8 T_c while
when including quarks (N_f=3) agreement begins already at temperatures above 2
T_c. In both cases we find that at very high temperatures the T^2-scaled trace
anomaly increases with temperature in accordance with the predictions of HTLpt.Comment: 12 pages, 4 figures; v3 published versio
Hard-thermal-loop QCD Thermodynamics
Naively resummed perturbative approximations to the thermodynamic functions
of QCD do not converge at phenomenologically relevant temperatures. Here we
review recent results of a three-loop hard-thermal-loop perturbation theory
calculation of the thermodynamic functions of a quark-gluon plasma for general
N_c and N_f. We show comparisons of our recent results with lattice data from
both the hotQCD and Wuppertal-Budapest groups. We demonstrate that the
three-loop hard-thermal-loop perturbation result for QCD thermodynamics agrees
with lattice data down to temperatures T ~ 2 T_c.Comment: 8 pages, 2 figures; Talk given at the Symposium on "High Energy
Strong Interactions", Aug. 9-13, 2010, Yukawa Institute for Theoretical
Physics, Kyoto, Japan; submitted to Prog. Theor. Phys. Supp
A Cosmology-Independent Calibration of Gamma-Ray Burst Luminosity Relations and the Hubble Diagram
An important concern in the application of gamma-ray bursts (GRBs) to
cosmology is that the calibration of GRB luminosity/energy relations depends on
the cosmological model, due to the lack of a sufficient low-redshift GRB
sample. In this paper, we present a new method to calibrate GRB relations in a
cosmology-independent way. Since objects at the same redshift should have the
same luminosity distance and since the distance moduli of Type Ia supernovae
(SNe Ia) obtained directly from observations are completely cosmology
independent, we obtain the distance modulus of a GRB at a given redshift by
interpolating from the Hubble diagram of SNe Ia. Then we calibrate seven GRB
relations without assuming a particular cosmological model and construct a GRB
Hubble diagram to constrain cosmological parameters. From the 42 GRBs at
, we obtain ,
for the flat CDM model, and
for the dark energy model with a constant equation of state
, which is consistent with the concordance model in
a 1- confidence region.Comment: 7 pages, 3 figures, 1 table, now matches the editorially revised
version; accepted for publication in ApJ (vol 685)
Gluon Thermodynamics at Intermediate Coupling
We calculate the thermodynamic functions of Yang-Mills theory to three-loop
order using the hard-thermal-loop perturbation theory reorganization of finite
temperature quantum field theory. We show that at three-loop order
hard-thermal-loop perturbation theory is compatible with lattice results for
the pressure, energy density, and entropy down to temperatures T ~ 2 - 3 T_c.Comment: 4 pages, 3 figures; v2 - published version
Automated Lensing Learner: Automated Strong Lensing Identification with a Computer Vision Technique
Forthcoming surveys such as the Large Synoptic Survey Telescope (LSST) and
Euclid necessitate automatic and efficient identification methods of strong
lensing systems. We present a strong lensing identification approach that
utilizes a feature extraction method from computer vision, the Histogram of
Oriented Gradients (HOG), to capture edge patterns of arcs. We train a
supervised classifier model on the HOG of mock strong galaxy-galaxy lens images
similar to observations from the Hubble Space Telescope (HST) and LSST. We
assess model performance with the area under the curve (AUC) of a Receiver
Operating Characteristic (ROC) curve. Models trained on 10,000 lens and
non-lens containing images images exhibit an AUC of 0.975 for an HST-like
sample, 0.625 for one exposure of LSST, and 0.809 for 10-year mock LSST
observations. Performance appears to continually improve with the training set
size. Models trained on fewer images perform better in absence of the lens
galaxy light. However, with larger training data sets, information from the
lens galaxy actually improves model performance, indicating that HOG captures
much of the morphological complexity of the arc finding problem. We test our
classifier on data from the Sloan Lens ACS Survey and find that small scale
image features reduces the efficiency of our trained model. However, these
preliminary tests indicate that some parameterizations of HOG can compensate
for differences between observed mock data. One example best-case
parameterization results in an AUC of 0.6 in the F814 filter image with other
parameterization results equivalent to random performance.Comment: 18 pages, 14 figures, summarizing results in figure
A coupled mitral valve - left ventricle model with fluid-structure interaction
Understanding the interaction between the valves and walls of the heart is important in assessing and subsequently treating heart dysfunction. This study presents an integrated model of the mitral valve (MV) coupled to the left ventricle (LV), with the geometry derived from in vivo clinical magnetic resonance images. Numerical simulations using this coupled MV–LV model are developed using an immersed boundary/finite element method. The model incorporates detailed valvular features, left ventricular contraction, nonlinear soft tissue mechanics, and fluid-mediated interactions between the MV and LV wall. We use the model to simulate cardiac function from diastole to systole. Numerically predicted LV pump function agrees well with in vivo data of the imaged healthy volunteer, including the peak aortic flow rate, the systolic ejection duration, and the LV ejection fraction. In vivo MV dynamics are qualitatively captured. We further demonstrate that the diastolic filling pressure increases significantly with impaired myocardial active relaxation to maintain a normal cardiac output. This is consistent with clinical observations. The coupled model has the potential to advance our fundamental knowledge of mechanisms underlying MV–LV interaction, and help in risk stratification and optimisation of therapies for heart diseases
Workplace Violence in Chinese Hospitals: The Effects of Healthcare Disturbance on the Psychological Well-Being of Chinese Healthcare Workers
Healthcare disturbance is a form of workplace violence against healthcare workers perpetrated by patients, their relatives, and gangs hired by them. It is a prevalent phenomenon in China, where evidence suggests that it impacts on the job satisfaction of healthcare workers. This study aims to examine the relationship between healthcare disturbance, surface acting as a response to emotional labour, and depressive symptoms in Chinese healthcare workers. The study adopted a cross-sectional design and used an online survey methodology. Data were collected from 418 doctors and nurses from one hospital in China. The results showed that frequency of healthcare disturbance was positively related to surface acting and depressive symptoms, respectively; surface acting was also positively related to depression, while deep acting showed no effect on symptoms of depression. Furthermore, surface acting in response to emotional labour mediated the relationship between healthcare disturbance and depressive symptoms. The results highlight the importance of preventing healthcare disturbance and of training healthcare staff in strategies for managing emotional demands in reducing depressive symptoms in Chinese healthcare staff
Next-to-leading-order corrections to exclusive processes in factorization
We calculate next-to-leading-order (NLO) corrections to exclusive processes
in factorization theorem, taking as an example.
Partons off-shell by are considered in both the quark diagrams from
full QCD and the effective diagrams for the pion wave function. The gauge
dependences in the above two sets of diagrams cancel, when deriving the
-dependent hard kernel as their difference. The gauge invariance of the
hard kernel is then proven to all orders by induction. The light-cone
singularities in the -dependent pion wave function are regularized by
rotating the Wilson lines away from the light cone. This regularization
introduces a factorization-scheme dependence into the hard kernel, which can be
minimized in the standard way. Both the large double logarithms and
, being a parton momentum fraction, arise from the loop correction
to the virtual photon vertex, the former being absorbed into the pion wave
function and organized by the resummation, and the latter absorbed into a
jet function and organized by the threshold resummation. The NLO corrections
are found to be only few-percent for , if setting the
factorization scale to the momentum transfer from the virtual photon.Comment: 13 pages; version to appear in Physical Review
Dilaton Black Holes in de Sitter or Anti-de Sitter Universe
Poletti and Wiltshire have shown that, with the exception of a pure
cosmological constant, the solution of a dilaton black hole in the background
of de Sitter or anti-de Sitter universe, does not exist in the presence of one
Liouville-type dilaton potential. Here with the combination of three
Liouville-type dilaton potentials, we obtain the dilaton black hole solutions
in the background of de Sitter or anti-de Sitter universe.Comment: 13 pages,to appear in Phys. Rev.
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