1,469 research outputs found
The Effects of Elevated CO2 Levels on Broad Bean, Vicia faba, Growth/Defense Tradeoffs
Atmospheric changes, associated with global climate change, are increasing at an unprecedented rate. Plants generally display higher rates of growth in response to elevated CO2 levels, but this response varies among species. In addition, very little is known about how plant growth/defense tradeoffs will be altered by increasing CO2 levels. By raising Broad bean, Vicia faba L., plants under ambient (400 ppm) and elevated (900 ppm) levels of CO2, it was shown that atmospheric composition directly altered plant growth/defense tradeoffs. Plants grown under elevated CO2 had lighter stem weights but greater numbers of extrafloral nectaries and higher rates of extrafloral nectar secretion. Thus, plants grown under elevated CO2 invested more in defense (extrafloral nectaries and extrafloral nectar production) than growth (biomass). These results indicate that CO2 may act as a stressor for Broad bean plants
Short-range force detection using optically-cooled levitated microspheres
We propose an experiment using optically trapped and cooled dielectric
microspheres for the detection of short-range forces. The center-of-mass motion
of a microsphere trapped in vacuum can experience extremely low dissipation and
quality factors of , leading to yoctonewton force sensitivity.
Trapping the sphere in an optical field enables positioning at less than 1
m from a surface, a regime where exotic new forces may exist. We expect
that the proposed system could advance the search for non-Newtonian gravity
forces via an enhanced sensitivity of over current experiments at
the 1 m length scale. Moreover, our system may be useful for
characterizing other short-range physics such as Casimir forces.Comment: 4 pages, 3 figures, minor changes, Figs. 1 and 2 replace
Cosmological Systematics Beyond Nuisance Parameters : Form Filling Functions
In the absence of any compelling physical model, cosmological systematics are
often misrepresented as statistical effects and the approach of marginalising
over extra nuisance systematic parameters is used to gauge the effect of the
systematic. In this article we argue that such an approach is risky at best
since the key choice of function can have a large effect on the resultant
cosmological errors. As an alternative we present a functional form filling
technique in which an unknown, residual, systematic is treated as such. Since
the underlying function is unknown we evaluate the effect of every functional
form allowed by the information available (either a hard boundary or some
data). Using a simple toy model we introduce the formalism of functional form
filling. We show that parameter errors can be dramatically affected by the
choice of function in the case of marginalising over a systematic, but that in
contrast the functional form filling approach is independent of the choice of
basis set. We then apply the technique to cosmic shear shape measurement
systematics and show that a shear calibration bias of |m(z)|< 0.001(1+z)^0.7 is
required for a future all-sky photometric survey to yield unbiased cosmological
parameter constraints to percent accuracy. A module associated with the work in
this paper is available through the open source iCosmo code available at
http://www.icosmo.org .Comment: 24 pages, 18 figures, accepted to MNRA
Second-Generation Curvelets on the Sphere
Curvelets are efficient to represent highly anisotropic signal content, such as a local linear and curvilinear structure. First-generation curvelets on the sphere, however, suffered from blocking artefacts. We present a new second-generation curvelet transform, where scale-discretized curvelets are constructed directly on the sphere. Scale-discretized curvelets exhibit a parabolic scaling relation, are well localized in both spatial and harmonic domains, support the exact analysis and synthesis of both scalar and spin signals, and are free of blocking artefacts. We present fast algorithms to compute the exact curvelet transform, reducing computational complexity from O(L5) to O(L3 log2 L) for signals band limited at L. The implementation of these algorithms is made publicly available. Finally, we present an illustrative application demonstrating the effectiveness of curvelets for representing directional curve-like features in natural spherical images
Size magnification as a complement to Cosmic Shear
We investigate the extent to which cosmic size magnification may be used to
com- plement cosmic shear in weak gravitational lensing surveys, with a view to
obtaining high-precision estimates of cosmological parameters. Using simulated
galaxy images, we find that size estimation can be an excellent complement,
finding that unbiased estimation of the convergence field is possible with
galaxies with angular sizes larger than the point-spread function (PSF) and
signal-to-noise ratio in excess of 10. The statistical power is similar to, but
not quite as good as, cosmic shear, and it is subject to different systematic
effects. Application to ground-based data will be challeng- ing, with
relatively large empirical corrections required to account for with biases for
galaxies which are smaller than the PSF, but for space-based data with 0.1
arcsecond resolution, the size distribution of galaxies brighter than i=24 is
ideal for accurate estimation of cosmic size magnification.Comment: 11 pages, 11 figures, accepted by MNRA
Cosmological systematics beyond nuisance parameters: form-filling functions
In the absence of any compelling physical model, cosmological systematics are often misrepresented as statistical effects and the approach of marginalizing over extra nuisance systematic parameters is used to gauge the effect of the systematic. In this article, we argue that such an approach is risky at best since the key choice of function can have a large effect on the resultant cosmological errors. As an alternative we present a functional form-filling technique in which an unknown, residual, systematic is treated as such. Since the underlying function is unknown, we evaluate the effect of every functional form allowed by the information available (either a hard boundary or some data). Using a simple toy model, we introduce the formalism of functional form filling. We show that parameter errors can be dramatically affected by the choice of function in the case of marginalizing over a systematic, but that in contrast the functional form-filling approach is independent of the choice of basis set. We then apply the technique to cosmic shear shape measurement systematics and show that a shear calibration bias of |m(z)| ≲ 10−3 (1 +z)0.7 is required for a future all-sky photometric survey to yield unbiased cosmological parameter constraints to per cent accuracy. A module associated with the work in this paper is available through the open source icosmo code available at http://www.icosmo.or
Weak gravitational lensing with the Square Kilometre Array
We investigate the capabilities of various stages of the SKA to perform
world-leading weak gravitational lensing surveys. We outline a way forward to
develop the tools needed for pursuing weak lensing in the radio band. We
identify the key analysis challenges and the key pathfinder experiments that
will allow us to address them in the run up to the SKA. We identify and
summarize the unique and potentially very powerful aspects of radio weak
lensing surveys, facilitated by the SKA, that can solve major challenges in the
field of weak lensing. These include the use of polarization and rotational
velocity information to control intrinsic alignments, and the new area of weak
lensing using intensity mapping experiments. We show how the SKA lensing
surveys will both complement and enhance corresponding efforts in the optical
wavebands through cross-correlation techniques and by way of extending the
reach of weak lensing to high redshift.Comment: 19 pages, 6 figures. Cosmology Chapter, Advancing Astrophysics with
the SKA (AASKA14) Conference, Giardini Naxos (Italy), June 9th-13th 201
Mapping dark matter on the celestial sphere with weak gravitational lensing
Convergence maps of the integrated matter distribution are a key science result from weak gravitational lensing surveys. To date, recovering convergence maps has been performed using a planar approximation of the celestial sphere. However, with the increasing area of sky covered by dark energy experiments, such as Euclid, the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST), and the Nancy Grace Roman Space Telescope, this assumption will no longer be valid. We recover convergence fields on the celestial sphere using an extension of the Kaiser–Squires estimator to the spherical setting. Through simulations, we study the error introduced by planar approximations. Moreover, we examine how best to recover convergence maps in the planar setting, considering a variety of different projections and defining the local rotations that are required when projecting spin fields such as cosmic shear. For the sky coverages typical of future surveys, errors introduced by projection effects can be of the order of tens of percent, exceeding 50 per cent in some cases. The stereographic projection, which is conformal and so preserves local angles, is the most effective planar projection. In any case, these errors can be avoided entirely by recovering convergence fields directly on the celestial sphere. We apply the spherical Kaiser–Squires mass-mapping method presented to the public Dark Energy Survey science verification data to recover convergence maps directly on the celestial sphere
Direct Kerr-frequency-comb atomic spectroscopy
Microresonator-based soliton frequency combs - microcombs - have recently
emerged to offer low-noise, photonic-chip sources for optical measurements.
Owing to nonlinear-optical physics, microcombs can be built with various
materials and tuned or stabilized with a consistent framework. Some
applications require phase stabilization, including optical-frequency synthesis
and measurements, optical-frequency division, and optical clocks. Partially
stabilized microcombs can also benefit applications, such as oscillators,
ranging, dual-comb spectroscopy, wavelength calibration, and optical
communications. Broad optical bandwidth, brightness, coherence, and frequency
stability have made frequency-comb sources important for studying comb-matter
interactions with atoms and molecules. Here, we explore direct microcomb atomic
spectroscopy, utilizing a cascaded, two-photon 1529-nm atomic transition of
rubidium. Both the microcomb and the atomic vapor are implemented with planar
fabrication techniques to support integration. By fine and simultaneous control
of the repetition rate and carrier-envelope-offset frequency of the soliton
microcomb, we obtain direct sub-Doppler and hyperfine spectroscopy of the
manifold. Moreover, the entire set of microcomb modes are
stabilized to this atomic transition, yielding absolute optical-frequency
fluctuations of the microcomb at the kilohertz-level over a few seconds and < 1
MHz day-to-day accuracy. Our work demonstrates atomic spectroscopy with
microcombs and provides a rubidium-stabilized microcomb laser source, operating
across the 1550 nm band for sensing, dimensional metrology, and communication.Comment: 5 pages, 3 figure
Relativistic eikonal description of A(p,pN) reactions
The authors present a relativistic and cross-section factorized framework for
computing quasielastic A(p,pN) observables at intermediate and high energies.
The model is based on the eikonal approximation and can accomodate both optical
potentials and the Glauber method for dealing with the initial- and final-state
interactions (IFSI). At lower nucleon energies, the optical-potential
philosophy is preferred, whereas at higher energies the Glauber method is more
natural. This versatility in dealing with the IFSI allows one to describe
A(p,pN) reactions in a wide energy range. Most results presented here use
optical potentials as this approach is argued to be the optimum choice for the
kinematics of the experiments considered in the present paper. The properties
of the IFSI factor, a function wherein the entire effect of the IFSI is
contained, are studied in detail. The predictions of the presented framework
are compared with two kinematically different experiments. First, differential
cross sections for quasielastic proton scattering at 1 GeV off 12C, 16O, and
40Ca target nuclei are computed and compared to data from PNPI. Second, the
formalism is applied to the analysis of a 4He(p,2p) experiment at 250 MeV. The
optical-potential calculations are found to be in good agreement with the data
from both experiments, showing the reliability of the adopted model in a wide
energy range.Comment: 34 pages, 14 figures, accepted for publication in Phys. Rev.
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