1,144 research outputs found
Towards an improved understanding of eta --> gamma^* gamma^*
We argue that high-quality data on the reaction
will allow one to determine the double off-shell form factor in a model-independent way with controlled accuracy. This is
an important step towards a reliable evaluation of the hadronic light-by-light
scattering contribution to the anomalous magnetic moment of the muon. When
analyzing the existing data for in the range of
total energies , we demonstrate that the
double off-shell form factor is
consistent with the commonly employed factorization ansatz at least for
, if the effect of the meson is taken into account.
However, better data are needed to draw firm conclusions.Comment: 7 pages, 3 figure
Addition of Synthetic Feeding Attractant Increases Catches of Rhagoletis batava Hering and Carpomyia schineri Loew. in Fluorescent Yellow Sticky Traps
The addition of the synthetic Rhagoletis feeding attractant (consisting of ammonium carbonate and ammonium acetate, developed previously for Rhagoletis cerasi L.) to both fluorescent yellow or transparent sticky traps significantly increased catches of the fruit flies Rhagoletis batava Hering (pest of sea buckthorn) and Carpomyia schineri Loew. (pest of rose hips). Traps with lures were detecting the occurrence of both species 1–2 weeks before as compared to traps without lure, and quantitative aspects of the flight could be followed in more detail in traps with lure. Thus in detection and monitoring surveys, where sensitivity of the trap is highly important, the use of traps with synthetic lure added is strongly recommended
Automated analysis of digital fundus autofluorescence images of geographic atrophy in advanced age-related macular degeneration using confocal scanning laser ophthalmoscopy (cSLO)
BACKGROUND: Fundus autofluorescence (AF) imaging using confocal scanning laser ophthalmoscopy (cSLO) provides an accurate delineation of areas of geographic atrophy (GA). Automated computer-assisted methods for detecting and removing interfering vessels are needed to support the GA quantification process in longitudinal studies and in reading centres. METHODS: A test tool was implemented that uses region-growing techniques to segment GA areas. An algorithm for illuminating shadows can be used to process low-quality images. Agreement between observers and between three different methods was evaluated by two independent readers in a pilot study. Agreement and objectivity were assessed using the Bland-Altman approach. RESULTS: The new method (C) identifies vascular structures that interfere with the delineation of GA. Results are comparable to those of two commonly used procedures (A, B), with a mean difference between C and A of -0.67 mm(2 )(95% CI [-0.99, -0.36]), between B and A of -0.81 mm(2), (95% CI [-1.08, -0.53]), and between C and B of 0.15 mm(2 )(95% CI [-0.12, 0.41]). Objectivity of a method is quantified by the mean difference between observers: A 0.30 mm(2 )(95% CI [0.02, 0.57]), B -0.11 mm(2 )(95% CI [-0.28, 0.10]), and C 0.12 mm(2 )(95% CI [0.02, 0.22]). CONCLUSION: The novel procedure is comparable with regard to objectivity and inter-reader agreement to established methods of quantifying GA. It considerably speeds up the lengthy measurement process in AF with well defined GA zones
Safety in numbers: Gravitational Lensing Degradation of the Luminosity Distance-Redshift Relation
Observation of the expansion history of the Universe allows exploration of
the physical properties and energy density of the Universe's various
constituents. Standardizable candles such as Type Ia supernovae remain one of
the most promising and robust tools in this endeavor, by allowing for a direct
measure of the luminosity distance-redshift curve, and thereby producing
detailed studies of the dark energy responsible for the Universe's currently
accelerating expansion. As such observations are pushed to higher redshifts,
the observed flux is increasingly affected by gravitational lensing
magnification due to intervening structure along the line-of-sight. We simulate
and analyze the non-Gaussian probability distribution function of
de/amplification due to lensing of standard candles, quantify the effect of a
convolution over many independent sources (which acts to restore the intrinsic
average (unlensed) luminosity due to flux conservation), and compute the
additional uncertainty due to lensing on derived cosmological parameters. For
example, the ``degradation factor'' due to lensing is a factor of three
reduction in the effective number of usable supernovae at z=1.5 (for sources
with intrinsic flux dispersion of 10%). We also derive a useful expression for
the effective increased dispersion in standard candles due to lensing, as a
function of redshift.Comment: 11 pages, 10 figure
Addition of synthetic feeding attractant increases catches of Rhagoletis batava Hering and Carpomyia schineri Loew. in fluorescent yellow sticky traps
The addition of the synthetic
Rhagoletis
feeding attractant (consisting of ammonium carbonate and
ammonium acetate, developed previously for
Rhagoletis cerasi
L.) to both fluorescent yellow or transparent
sticky traps significantly increased catches of the fruit flies
Rhagoletis batava
Hering (pest of sea buckthorn)
and
Carpomyia schineri
Loew. (pest of rose hips). Traps with lures were detecting the occurrence of both
species 1–2 weeks before as compared to traps without lure, and quantitative aspects of the flight could be fol-
lowed in more detail in traps with lure. Thus in detection and monitoring surveys, where sensitivity of the trap
is highly important, the use of traps with synthetic lure added is strongly recommended
Gravitational Wave Sirens as a Triple Probe of Dark Energy
Gravitational wave standard sirens have been considered as precision distance
indicators to high redshift; however, at high redshift standard sirens or
standard candles such as supernovae suffer from lensing noise. We investigate
lensing noise as a signal instead and show how measurements of the maximum
demagnification (minimum convergence) probe cosmology in a highly complementary
manner to the distance itself. Revisiting the original form for minimum
convergence we quantify the bias arising from the commonly used approximation.
Furthermore, after presenting a new lensing probability function we discuss how
the width of the lensed standard siren amplitude distribution also probes
growth of structure. Thus standard sirens and candles can serve as triple
probes of dark energy, measuring both the cosmic expansion history and growth
history.Comment: 7 pages, 5 figures; v2 minor changes matching published versio
Short GRB and binary black hole standard sirens as a probe of dark energy
Observations of the gravitational radiation from well-localized, inspiraling
compact object binaries can measure absolute source distances with high
accuracy. When coupled with an independent determination of redshift through an
electromagnetic counterpart, these standard sirens can provide an excellent
probe of the expansion history of the Universe and the dark energy. Short
gamma-ray bursts, if produced by merging neutron star binaries, would be
standard sirens with known redshifts detectable by ground-based GW networks
such as LIGO-II, Virgo, and AIGO. Depending upon the collimation of these GRBs,
a single year of observation of their gravitational waves can measure the
Hubble constant to about 2%. When combined with measurement of the absolute
distance to the last scattering surface of the cosmic microwave background,
this determines the dark energy equation of state parameter w to 9%. Similarly,
supermassive binary black hole inspirals will be standard sirens detectable by
LISA. Depending upon the precise redshift distribution, 100 sources could
measure w at the 4% level.Comment: 8 pages, submitted to PR
Can the Acceleration of Our Universe Be Explained by the Effects of Inhomogeneities?
No. It is simply not plausible that cosmic acceleration could arise within
the context of general relativity from a back-reaction effect of
inhomogeneities in our universe, without the presence of a cosmological
constant or ``dark energy.'' We point out that our universe appears to be
described very accurately on all scales by a Newtonianly perturbed FLRW metric.
(This assertion is entirely consistent with the fact that we commonly encounter
.) If the universe is accurately described by a
Newtonianly perturbed FLRW metric, then the back-reaction of inhomogeneities on
the dynamics of the universe is negligible. If not, then it is the burden of an
alternative model to account for the observed properties of our universe. We
emphasize with concrete examples that it is {\it not} adequate to attempt to
justify a model by merely showing that some spatially averaged quantities
behave the same way as in FLRW models with acceleration. A quantity
representing the ``scale factor'' may ``accelerate'' without there being any
physically observable consequences of this acceleration. It also is {\it not}
adequate to calculate the second-order stress energy tensor and show that it
has a form similar to that of a cosmological constant of the appropriate
magnitude. The second-order stress energy tensor is gauge dependent, and if it
were large, contributions of higher perturbative order could not be neglected.
We attempt to clear up the apparent confusion between the second-order stress
energy tensor arising in perturbation theory and the ``effective stress energy
tensor'' arising in the ``shortwave approximation.''Comment: 20 pages, 1 figure, several footnotes and references added, version
accepted for publication in CQG;some clarifying comments adde
Recommended from our members
MACUSTAR: Development and Clinical Validation of Functional, Structural, and Patient-Reported Endpoints in Intermediate Age-Related Macular Degeneration
Purpose: Currently, no outcome measures are clinically validated and accepted as clinical endpoints by regulatory agencies for drug development in intermediate age-related macular degeneration (iAMD). The MACUSTAR Consortium, a public-private research group funded by the European Innovative Medicines Initiative intends to close this gap.
Procedures: Development of study protocol and statistical analysis plan including predictive modelling of multimodal endpoints based on a review of the literature and expert consensus.
Results: This observational study consists of a cross-sectional and a longitudinal part. Functional outcome measures assessed under low contrast and low luminance have the potential to detect progression of visual deficit within iAMD and to late AMD. Structural outcome measures will be multimodal and investigate topographical relationships with function. Current patient-reported outcome measures (PROMs) are not acceptable to regulators and may not capture the functional deficit specific to iAMD with needed precision, justifying development of novel PROMs for iAMD. The total sample size will be n = 750, consisting mainly of subjects with iAMD (n = 600).
Conclusions: As clinical endpoints currently accepted by regulators cannot detect functional loss or patient-relevant impact in iAMD, we will clinically validate novel candidate endpoints for iAMD
Non-Baryonic Dark Matter - Observational Evidence and Detection Methods
The evidence for the existence of dark matter in the universe is reviewed. A
general picture emerges, where both baryonic and non-baryonic dark matter is
needed to explain current observations. In particular, a wealth of
observational information points to the existence of a non-baryonic component,
contributing between around 20 and 40 percent of the critical mass density
needed to make the universe geometrically flat on large scales. In addition, an
even larger contribution from vacuum energy (or cosmological constant) is
indicated by recent observations. To the theoretically favoured particle
candidates for non-baryonic dark matter belong axions, supersymmetric
particles, and of less importance, massive neutrinos. The theoretical
foundation and experimental situation for each of these is reviewed. Direct and
indirect methods for detection of supersymmetric dark matter are described in
some detail. Present experiments are just reaching the required sensitivity to
discover or rule out some of these candidates, and major improvements are
planned over the coming years.Comment: Submitted to Reports on Progress in Physics, 59 pages, LaTeX, iopart
macro, 14 embedded postscript figure
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