795 research outputs found
Pion Loop Contribution to the Electromagnetic Pion Charge Radius
A phenomenological Dyson-Schwinger equation approach to QCD, formalised in
terms of a QCD based model field theory, is used to calculate the
electromagnetic charge radius of the pion. The contributions from the quark
core and pion loop, as defined in this approach, are identified and compared.
It is shown explicitly that the divergence of the charge radius in the chiral
limit is due to the pion loop and that, at the physical value of the pion mass,
this loop contributes less than 15\% to ; i.e. the
quark core is the dominant determining characteristic for the pion. This
suggests that quark based models which fail to reproduce the
divergence of may nevertheless incorporate the
dominant characteristic of the pion: its quark core.Comment: 22 Pages, 5 figures uuencoded and appended to this file, REVTEX 3.0.
ANL-PHY-7663-TH-93, UNITUE-THEP-13/199
Deconfinement and Hadron Properties at Extremes of Temperature and Density
After introducing essential, qualitative concepts and results, we discuss the
application of Dyson-Schwinger equations to QCD at finite T and mu. We
summarise the calculation of the critical exponents of two-light-flavour QCD
using the chiral and thermal susceptibilities; and an algebraic model that
elucidates the origin of an anticorrelation between the mu- and T-dependence of
a range of meson properties. That model also provides an algebraic
understanding of why the finite-T behaviour of bulk thermodynamic properties is
mirrored in their mu-dependence, and why meson masses decrease with mu even
though f_pi and - increase. The possibility of diquark condensation is
canvassed. Its realisation is uncertain because it is contingent upon an
assumption about the quark-quark scattering kernel that is demonstrably false
in some applications; e.g., it predicts the existence of coloured diquarks in
the strong interaction spectrum, which are not observed.Comment: Summary of presentations at the Workshop on QCD at Finite Baryon
Density, Bielefeld, Germany, 27-30/April/1998, 13 pages, 9 figures,
espcrc1.sty, epsfig.sty. Correcting typsetting problem
Infrared Behaviour of Propagators and Vertices
We elucidate constraints imposed by confinement and dynamical chiral symmetry
breaking on the infrared behaviour of the dressed-quark and -gluon propagators,
and dressed-quark-gluon vertex. In covariant gauges the dressing of the gluon
propagator is completely specified by P(k^2):= 1/[1+Pi(k^2)], where Pi(k^2) is
the vacuum polarisation. In the absence of particle-like singularities in the
dressed-quark-gluon vertex, extant proposals for the dressed-gluon propagator
that manifest P(k^2=0)=0 and Max[P(k^2)]~10 neither confine quarks nor break
chiral symmetry dynamically. This class includes all existing estimates of
P(k^2) via numerical simulations.Comment: 10 pages, 2 figure
Quantum Electrodynamics near a Huttner-Barnett dielectric
We build up a consistent theory of quantum electrodynamics in the presence of
macroscopic polarizable media. We use the Huttner-Barnett model of a dispersive
and absorbing dielectric medium and formulate the theory in terms of
interacting quantum fields. We integrate out the damped polaritons by using
diagrammatic techniques and find an exact expression for the displacement field
(photon) propagator in the presence of a dispersive and absorbing dielectric
half-space. This opens a new route to traceable perturbative calculations of
the same kind as in free-space quantum electrodynamics. As a worked-through
example we consider the interaction of a neutral atom with a dispersive and
absorbing dielectric half-space. For that we use the multipolar coupling
of the atomic dipole moment to the
electromagnetic displacement field. We apply the newly developed formalism to
calculate the one-loop correction to the atomic electron propagator and find
the energy-level shift and changes in the spontaneous decay rates for a neutral
atom close to an absorptive dielectric mirror.Comment: 25 pages, 4 figure
SBS 0335-052W - an Extremely Low Metallicity Dwarf Galaxy
We present Multiple Mirror Telescope (MMT) and Keck II telescope
spectrophotometry and 3.5m Calar Alto telescope R, I photometry of the western
component of the extremely low-metallicity blue compact galaxy SBS 0335-052.
The components, separated by 22 kpc, appear to be members of a unique,
physically connected system. It is shown that SBS 0335-052W consists of at
least three stellar clusters and has the same redshift as SBS 0335-052. The
oxygen abundance in its two brightest knots is extremely low, 12+log(O/H)=
7.22+/-0.03 and 7.13+/-0.08, respectively. These values are lower than in SBS
0335-052 and are nearly the same as those in I Zw 18. The (R-I) color profiles
are very blue in both galaxies due to the combined effects of ionized gas and a
young stellar population emission. We argue that SBS 0335-052W is likely to be
a nearby, young dwarf galaxy.Comment: 18 pages, 4 EPS figures, to appear in ApJ, 1 July 199
The Lantern Vol. 32, No. 2, January 1966
⢠Mission 63 ⢠The Kiss ⢠The Dream ⢠Silence is Golden ⢠Self-Pity ⢠The Excuse ⢠Car Eighteen ⢠Clothes Make the Man ⢠The Place of a Just Man ⢠Golden Gods ⢠The Journey ⢠Third Prize Picture ⢠Gone Now ⢠In Vain ⢠Deep Dying ⢠Marnie ⢠Ruthttps://digitalcommons.ursinus.edu/lantern/1088/thumbnail.jp
A pilot study evaluating concordance between blood-based and patient-matched tumor molecular testing within pancreatic cancer patients participating in the Know Your Tumor (KYT) initiative
Recent improvements in next-generation sequencing (NGS) technology have enabled detection of biomarkers in cell-free DNA in blood and may ultimately replace invasive tissue biopsies. However, a better understanding of the performance of blood-based NGS assays is needed prior to routine clinical use. As part of an IRBapproved molecular profiling registry trial of pancreatic ductal adenocarcinoma (PDA) patients, we facilitated blood-based NGS testing of 34 patients from multiple community-based and high-volume academic oncology practices. 23 of these patients also underwent traditional tumor tissue-based NGS testing. cfDNA was not detected in 9/34 (26%) patients. Overall concordance between blood and tumor tissue NGS assays was low, with only 25% sensitivity of blood-based NGS for tumor tissue NGS. Mutations in KRAS, the major PDA oncogene, were only detected in 10/34 (29%) blood samples, compared to 20/23 (87%) tumor tissue biopsies. The presence of mutations in circulating DNA was associated with reduced overall survival (54% in mutation-positive versus 90% in mutation-negative). Our results suggest that in the setting of previously treated, advanced PDA, liquid biopsies are not yet an adequate substitute for tissue biopsies. Further refinement in defining the optimal patient population and timing of blood sampling may improve the value of a blood-based test. Š Pishvaian et al
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