278 research outputs found
Proton Capture on ^{17}O and its astrophysical implications
The reaction OF influences hydrogen-burning
nucleosynthesis in several stellar sites, such as red giants, asymptotic giant
branch (AGB) stars, massive stars and classical novae. In the relevant
temperature range for these environments (E_{r}=65.1E_{r}=557E_{c.m.}=345\theta_{lab}=0^{\circ},45^{\circ},90^{\circ},135^{\circ}\gammaR^{18}^{17}(p,\gamma)^{18}$F at low
energies from cross section data taken at higher energies. No significant
changes in the nucleosynthesis are expected from the newly calculated reaction
rate.Comment: Accepted in Physical Review
Direct measurements of hydrophobic slippage using double-focus fluorescence cross-correlation
We report results of direct measurements of velocity profiles in a
microchannel with hydrophobic and hydrophilic walls, using a new high precision
method of double-focus spacial fluorescence cross-correlation under a confocal
microscope. In the vicinity of both walls the measured velocity profiles do not
turn to zero by giving a plateau of constant velocity. This apparent slip is
proven to be due to a Taylor dispersion, an augmented by shear diffusion of
nanotracers in the direction of flow. Comparing the velocity profiles near the
hydrophobic and hydrophilic walls for various conditions shows that there is a
true slip length due to hydrophobicity. This length, of the order of several
tens of nanometers, is independent on electrolyte concentration and shear rate
Masses of excited baryons from chirally improved quenched lattice QCD
Whereas ground state spectroscopy for quenched QCD is well understood, it is
still a challenge to obtain results for excited hadron states. In our study we
present results from a new approach for determining spatially optimized
operators for lattice spectroscopy of excited hadrons. In order to be able to
approach physical quark masses we work with the chirally improved Dirac
operator, i.e., approximate Ginsparg-Wilson fermions. Since these are
computationally expensive we restrict ourselves to a few quark sources. We use
Jacobi smeared quark sources with different widths and combine them to
construct hadron operators with different spatial wave functions. This allows
us to identify the Roper state and other excited baryons, also in the strange
sector.Comment: Contribution to BARYONS 2004, Palaiseau, France, October 25 - 29,
2004; 4 pages, 1 figure, Style espcrc
Excited hadrons from improved interpolating fields
The calculation of quark propagators for Ginsparg-Wilson-type Dirac operators
is costly and thus limited to a few different sources. We present a new
approach for determining spatially optimized operators for lattice spectroscopy
of excited hadrons. Jacobi smeared quark sources with different widths are
combined to construct hadron operators with different spatial wave functions.
We study the Roper state and excited rho and pion mesons.Comment: Lattice2004(spectrum), 3 pages, 1 figure, (LaTeX style file
espcrc2.sty and AMS style files
A microscopic semiclassical confining field equation for lattice gauge theory in 2+1 dimensions
We present a semiclassical nonlinear field equation for the confining field
in 2+1--dimensional lattice gauge theory (compact QED). The equation is
derived directly from the underlying microscopic quantum Hamiltonian by means
of truncation. Its nonlinearities express the dynamic creation of magnetic
monopole currents leading to the confinement of the electric field between two
static electric charges. We solve the equation numerically and show that it can
be interpreted as a London relation in a dual superconductor.Comment: 21 pages, epsf postscript figures included, full postscript available
at ftp://ftp.th.physik.uni-frankfurt.de/pub/cbest/micro.ps.Z or
http://www.th.physik.uni-frankfurt.de/~cbest/pub.htm
Quenched QCD with fixed-point and chirally improved fermion
In this contribution we present results from quenched QCD simulations with
the parameterized fixed-point (FP) and the chirally improved (CI) Dirac
operator. Both these operators are approximate solutions of the Ginsparg-Wilson
equation and have good chiral properties. We focus our discussion on
observables sensitive to chirality. In particular we explore pion masses down
to 210 MeV in light hadron spectroscopy, quenched chiral logs, the pion decay
constant and the pion scattering length. We discuss finite volume effects,
scaling properties of the FP and CI operators and performance issues in their
numerical implementation.Comment: Lattice2002(chiral), 17 pages, 21 figures, (LaTeX style file
espcrc2.sty and AMS style files
Direct Evidence for Termination of Obscured Star Formation by Radiatively Driven Outflows in Reddened QSOs
We present optical to far-infrared photometry of 31 reddened QSOs that show
evidence for radiatively driven outflows originating from AGN in their
rest-frame UV spectra. We use these data to study the relationships between the
AGN-driven outflows, and the AGN and starburst infrared luminosities. We find
that FeLoBAL QSOs are invariably IR-luminous, with IR luminosities exceeding
10^{12} Solar luminosities in all cases. The AGN supplies 76% of the total IR
emission, on average, but with a range from 20% to 100%. We find no evidence
that the absolute luminosity of obscured star formation is affected by the
AGN-driven outflows. Conversely, we find an anticorrelation between the
strength of AGN-driven outflows, as measured from the range of outflow
velocities over which absorption exceeds a minimal threshold, and the
contribution from star formation to the total IR luminosity, with a much higher
chance of seeing a starburst contribution in excess of 25% in systems with weak
outflows than in systems with strong outflows. Moreover, we find no convincing
evidence that this effect is driven by the IR luminosity of the AGN. We
conclude that radiatively driven outflows from AGN can have a dramatic,
negative impact on luminous star formation in their host galaxies. We find that
such outflows act to curtail star formation such that star formation
contributes less than ~25% of the total IR luminosity. We also propose that the
degree to which termination of star formation takes place is not deducible from
the IR luminosity of the AGN.Comment: Accepted for publication in Ap
Quenched spectroscopy with fixed-point and chirally improved fermions
We present results from quenched spectroscopy calculations with the
parametrized fixed-point and the chirally improved Dirac operators. Both these
operators are approximate solutions of the Ginsparg-Wilson equation and have
good chiral properties. This allows us to work at small quark masses and we
explore pseudoscalar-mass to vector-mass ratios down to 0.28. We discuss meson
and baryon masses, their scaling properties, finite volume effects and compare
our results with recent large scale simulations. We find that the size of
quenching artifacts of the masses is strongly correlated with their
experimentally observed widths and that the gauge and hadronic scales are
consistent.Comment: 66 pages, 33 figures. Published version: minor modifications in the
text, references adde
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