7,944 research outputs found
International perspectives on validity in action research: introduction to the special issue
This special issue has its roots in a series of meetings at the annual EGOS conferences held between 2001 and 2007. The Action Research sub-theme at these annual meetings has attracted almost 200 papers from authors on every continent. A particular focus of the group has been the socio-economic approach to action research developed by Henri Savall and the ISEOR team which discusses what Savall describes as "Generic Contingencies” and a “qualimetrics research methodology” (2003). The meetings have drawn together a truly international grouping of researchers who share a common interest in working closely with the world of practice to “make a difference.
False‑positive technetium‑99m methylene diphosphonate bone scan activity in the orbit in a patient with a history of breast carcinoma
Metastasis of breast carcinoma to the orbit is an uncommon entity and carries a poor prognosis. This case report presents false-positive technetium-99m methylene diphosphonate activity in the right orbit of a patient with a history of a primary breast neoplasm. Orbital computed tomography imaging was obtained to further characterize the radiotracer uptake identified on the bone scan and demonstrated diffuse right globe intraocular calcifications secondary to degenerative intraocular changes. A brief literature review of orbital metastasis from breast carcinoma and causes of intraocular calcification in the context of chronic vision loss are provided
Next 50 years of space research
Forecasting the next 50 years of space research is a dangerous game and a somewhat irresponsible action. Fortunately, the past 50 years have evidenced what remains in the realm of realism and of the feasible and what definitely belongs to the realm of utopia. Nevertheless those who, like me today, take the risk of forecasting such a relatively long time trend are sure of one thing: to be wrong
Infrared Exponents and the Running Coupling of Landau gauge QCD and their Relation to Confinement
The infrared behaviour of the gluon and ghost propagators in Landau gauge QCD
is reviewed. The Kugo-Ojima confinement criterion and the Gribov-Zwanziger
horizon condition result from quite general properties of the ghost
Dyson-Schwinger equation. The numerical solutions for the gluon and ghost
propagators obtained from a truncated set of Dyson-Schwinger equations provide
an explicit example for the anticipated infrared behaviour. The results are in
good agreement with corresponding lattice data obtained recently. The resulting
running coupling approaches a fix point in the infrared, . Two different fits for the scale dependence of the running coupling
are given and discussed.Comment: 3 pages, 3 figures; talk given by R.A. at the conference Quark
Nuclear Physics 200
Kugo-Ojima confinement and QCD Green's functions in covariant gauges
In Landau gauge QCD the Kugo-Ojima confinement criterion and its relation to
the infrared behaviour of the gluon and ghost propagators are reviewed. It is
demonstrated that the realization of this confinement criterion (which is
closely related to the Gribov-Zwanziger horizon condition) results from quite
general properties of the ghost Dyson-Schwinger equation. The numerical
solutions for the gluon and ghost propagators obtained from a truncated set of
Dyson--Schwinger equations provide an explicit example for the anticipated
infrared behaviour. The results are in good agreement, also quantitatively,
with corresponding lattice data obtained recently. The resulting running
coupling approaches a fixed point in the infrared, .
Solutions for the coupled system of Dyson--Schwinger equations for the quark,
gluon and ghost propagators are presented. Dynamical generation of quark masses
and thus spontaneous breaking of chiral symmetry takes place. In the quenched
approximation the quark propagator functions agree well with those of
corresponding lattice calculations. For a small number of light flavours the
quark, gluon and ghost propagators deviate only slightly from the ones in
quenched approximation. While the positivity violation of the gluon spectral
function is manifest in the gluon propagator, there are no clear indications of
analogous positivity violations for quarks so far.Comment: 10 pages, 5 figures; Talk given by R.A. at the International School
on Nuclear Physics ``Quarks in Hadrons and Nuclei'' in Erice (Italy),
September 16 - 24, 200
Break-up fragments excitation and the freeze-out volume
We investigate, in microcanonical multifragmentation models, the influence of
the amount of energy dissipated in break-up fragments excitation on freeze-out
volume determination. Assuming a limiting temperature decreasing with nuclear
mass, we obtain for the Xe+Sn at 32 MeV/nucleon reaction [J. D. Frankland et
al., Nucl. Phys. A689, 905 (2001); A689, 940 (2001)] a freeze-out volume almost
half the one deduced using a constant limiting temperature.Comment: 11 pages, 6 figure
Direct observation of a hydrophobic bond in loop-closure of a capped (-OCH2CH2-)n oligomer in water
The small r variation of the probability density P(r) for end-to-end
separations of a -CH2CH3 capped (-OCH2CH2-)n oligomer in water is computed to
be closely similar to the CH4 ... CH4 potential of mean force under the same
circumstances. Since the aqueous solution CH4 ... CH4 potential of mean force
is the natural physical definition of a primitive hydrophobic bond, the present
result identifies an experimentally accessible circumstance for direct
observation of a hydrophobic bond which has not been observed previously
because of the low solubility of CH4 in water. The physical picture is that the
soluble chain molecule carries the capping groups into aqueous solution, and
permits them to find one another with reasonable frequency. Comparison with the
corresponding results without the solvent shows that hydration of the solute
oxygen atoms swells the chain molecule globule. This supports the view that the
chain molecule globule might have a secondary effect on the hydrophobic
interaction which is of first interest here. The volume of the chain molecule
globule is important for comparing the probabilities with and without solvent
because it characterizes the local concentration of capping groups. Study of
other capping groups to enable X-ray and neutron diffraction measurements of
P(r) is discussed.Comment: 4 pages, 3 figure
Improved Smoothing Algorithms for Lattice Gauge Theory
The relative smoothing rates of various gauge field smoothing algorithms are
investigated on -improved \suthree Yang--Mills gauge field
configurations. In particular, an -improved version of APE
smearing is motivated by considerations of smeared link projection and cooling.
The extent to which the established benefits of improved cooling carry over to
improved smearing is critically examined. We consider representative gauge
field configurations generated with an -improved gauge field
action on \1 lattices at and \2 lattices at
having lattice spacings of 0.165(2) fm and 0.077(1) fm respectively. While the
merits of improved algorithms are clearly displayed for the coarse lattice
spacing, the fine lattice results put the various algorithms on a more equal
footing and allow a quantitative calibration of the smoothing rates for the
various algorithms. We find the relative rate of variation in the action may be
succinctly described in terms of simple calibration formulae which accurately
describe the relative smoothness of the gauge field configurations at a
microscopic level
Scaling behavior of the overlap quark propagator in Landau gauge
The properties of the momentum space quark propagator in Landau gauge are
examined for the overlap quark action in quenched lattice QCD. Numerical
calculations are done on three lattices with different lattice spacings and
similar physical volumes to explore the approach of the quark propagator toward
the continuum limit. We have calculated the nonperturbative momentum-dependent
wave function renormalization function Z(p) and the nonperturbative mass
function M(p) for a variety of bare quark masses and perform an extrapolation
to the chiral limit. We find the behavior of Z(p) and M(p) are in reasonable
agreement between the two finer lattices in the chiral limit, however the data
suggest that an even finer lattice is desirable. The large momentum behavior is
examined to determine the quark condensate.Comment: 9 pages, 5 figures, Revtex 4. Streamlined presentation, additional
data. Final versio
Infrared Exponents and Running Coupling of SU(N) Yang-Mills Theories
We present approximate solutions for the gluon and ghost propagators as well
as the running coupling in Landau gauge Yang-Mills theories. We solve the
corresponding Dyson-Schwinger equations in flat Euclidean space-time without
any angular approximation. This supplements recently obtained results employing
a four-torus, i.e. a compact space-time manifold, as infrared regulator. We
confirm previous findings deduced from an extrapolation with tori of different
volumes: the gluon propagator is weakly vanishing in the infrared and the ghost
propagator is highly singular. For non-vanishing momenta our propagators are in
remarkable agreement with recent lattice calculations.Comment: 11 pages, 4 figure
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