158 research outputs found
Resonance estimates of O(p^6) low-energy constants and QCD short-distance constraints
Starting from the study of the low-energy and high-energy behaviours of the
QCD three-point functions , and , several O(p^6) low-energy
constants of the chiral Lagrangian are evaluated within the framework of the
lowest meson dominance (LMD) approximation to the large-N_C limit of QCD. In
certain cases, values that differ substantially from estimates based on a
resonance Lagrangian are obtained. It is pointed out that the differences arise
through the fact that QCD short-distance constraints are in general not
correctly taken into account in the approaches using resonance Lagrangians. We
discuss the implications of our results for the O(p^6) counterterm
contributions to the vector form factor of the pion and to the decay \pi -> e
\nu_e \gamma, and for the pion-photon-photon transition form factor.Comment: 39 pages, Latex. v2: some typos corrected, references updated,
version to appear in Eur. Phys. J.
Performance analysis of vertically mounted bifacial PV modules on green roof system
A combination of PV and green roof is an ideal fusion in terms of ecology. The green roof improves the water retention in the city, whereas the PV system produces electric power at the place where it is consumed. Flat tilted modules in south or east west direction on green roofs generally require intensive maintenance to prevent them from being shaded by plants and often cover the roof area to a large extent. Because of the space requirement conflict between PV on the roof and green roofs, it is essential to combine these two systems in a smart way. Vertically mounted bifacial modules can be an option to combine PV and green roof and to also allow a cost-effective maintenance.
In this paper we report about the layout and the performance of a corresponding system, subdivided into two groups with differing albedo. Custom made bifacial modules with 20 cells were produced to reduce the wind load and to improve the general appearance. This 9.09 kWp bifacial plant achieved a specific yield of 942 kWh/kWp in one year (11.08.2017 to 10.08.2018). High quality DC power measurement systems are installed to monitor two modules in each bifacial test field and a reference south-facing module. This allows an energy yield comparison between the vertical bifacial test system with east-west orientation and the monofacial south-facing reference over four months of outdoor measurements. The use of plants with good reflective properties, which are also well suited two the ambient conditions on flat roofs, resulted in a yield increase of 17 % compared to a standard green roof planting. The vertically installed bifacial modules obtained an almost identical specific yield (-1.4 %) compared to a stand-alone monofacial southfacing reference module. Due to the increased yield in the mornings and afternoons, the vertical bifacial modules can achieve higher self-consumption depending on the load profile
Charge-state distribution of Li ions from the decay of laser-trapped He atoms
Background: The accurate determination of atomic final states following
nuclear decay plays an important role in many experiments. In
particular, the charge state distributions of ions following nuclear
decay are important for determinations of the angular correlation
with improved precision. Purpose: Our measurement aims at providing benchmarks
to test theoretical calculations. Method: The kinematics of Li ions
produced following the decay of within an electric field
were measured using atoms in the metastable and
in the states confined by a magneto-optical trap. The
electron shake-off probabilities were deduced including their dependence on ion
energy. Results: We find significant discrepancies on the fractions of Li ions
in the different charge states with respect to a recent calculation and discuss
a plausible explanation. We also point out that there is no explanation for a
large discrepancy between the same calculation and a previous measurement of
the Li-ion energy dependence of the charge distribution from decays of the
electronic ground state
The Hadronic Contribution to the Muon Anomalous Magnetic Moment and to the Running Electromagnetic Fine Structure Constant at MZ - Overview and Latest Results
Quantum loops induce an anomaly, a_mu, in the magnetic moment of the muon
that can be accurately measured. Its Standard Model prediction is limited in
precision by contributions from hadronic vacuum polarisation of the photon. The
dominant lowest-order hadronic term can be calculated with a combination of
experimental cross section data, involving e+e- annihilation to hadrons, and
perturbative QCD. These are used to evaluate an energy-squared dispersion
integral that strongly emphasises low photon virtualities. The dominant
contribution to the integral stems from the two-pion channel that can be
measured both in e+e- annihilation and in tau decays. The corresponding e+e-
and tau-based predictions of a_mu exhibit deviations by, respectively, 3.6
sigma and 2.4 sigma from experiment, leaving room for a possible interpretation
in terms of new physics. This talk reviews the status of the Standard Model
prediction with emphasis on the lowest-order hadronic contribution. Also given
is the latest result for the running electromagnetic fine structure constant at
the Z-mass pole, whose precision is limited by hadronic vacuum polarisation
contributions, determined in a way similar to those of the magnetic anomaly.Comment: Proceedings of talk at Tau2010 Workshop, Manchester, UK, 13-17 Sep,
2010; 10 pages, 8 figure
Hadronic light-by-light corrections to the muon g-2: the pion-pole contribution
The correction to the muon anomalous magnetic moment from the pion-pole
contribution to the hadronic light-by-light scattering is considered using a
description of the pi0 - gamma* - gamma* transition form factor based on the
large-Nc and short-distance properties of QCD. The resulting two-loop integrals
are treated by first performing the angular integration analytically, using the
method of Gegenbauer polynomials, followed by a numerical evaluation of the
remaining two-dimensional integration over the moduli of the Euclidean loop
momenta. The value obtained, a_{mu}(LbyL;pi0) = +5.8 (1.0) x 10^{-10},
disagrees with other recent calculations. In the case of the vector meson
dominance form factor, the result obtained by following the same procedure
reads a_{mu}(LbyL;pi0)_{VMD} = +5.6 x 10^{-10}, and differs only by its overall
sign from the value obtained by previous authors. Inclusion of the eta and
eta-prime poles gives a total value a_{mu}(LbyL;PS) = +8.3 (1.2) x 10^{-10} for
the three pseudoscalar states. This result substantially reduces the difference
between the experimental value of a_{mu} and its theoretical counterpart in the
standard model.Comment: 27 pages, Latex, 3 figures. v2: version to be published in Phys. Rev.
D, Note added and references updated (don't worry, sign has not changed
Improved X-ray detection and particle identification with avalanche photodiodes
Avalanche photodiodes are commonly used as detectors for low energy x-rays.
In this work we report on a fitting technique used to account for different
detector responses resulting from photo absorption in the various APD layers.
The use of this technique results in an improvement of the energy resolution at
8.2 keV by up to a factor of 2, and corrects the timing information by up to 25
ns to account for space dependent electron drift time. In addition, this
waveform analysis is used for particle identification, e.g. to distinguish
between x-rays and MeV electrons in our experiment.Comment: 6 pages, 6 figure
The Rainbow Cohort: saquinavir/r is effective and well tolerated in antiretroviral therapy (ART)-naïve patients – 48-week results from Germany
Poster presentation: Purpose of the study The aim of the Rainbow Cohort is to assess the tolerability and efficacy of initiating treatment with, or switching treatment to saquinavir (SQV) 500 mg film-coated tablet formulation. We present the final 48-week subgroup analysis of antiretroviral therapy (ART)-naïve patients. ..
Towards Precision Muonic X-Ray Measurements of Charge Radii of Light Nuclei
Precision studies of the properties of nuclei are essential both for
understanding nuclear physics at low energy, and for confronting experiment and
theory in simple atomic systems. Such comparisons advance our understanding of
bound-state quantum electrodynamics and are useful for searching for new
physics beyond the Standard Model. The energy levels of muonic atoms are highly
susceptible to nuclear structure, especially to the RMS charge radius. The
radii of the lightest nuclei () have been determined with high accuracy
via laser spectroscopy in muonic atoms, while those of medium mass and above,
from X-ray spectroscopy with semiconductor detectors. In this communication we
present a new experiment aiming at precision measurements of the radii of light
nuclei via single-photon energy measurements with cryogenic
microcalorimeters; a quantum sensing technology capable of high efficiency and
outstanding resolution for low-energy X-rays
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