11,305 research outputs found
Yield instability of winter oilseed rape modulated by early winter temperature
Yield stability is a major problem in oilseed rape with inter-annual variation accounting for between 30–50% of the crop value among the major global rapeseed producers. The United Kingdom has persistent problems with yield instability, but the underlying causes remain unclear. We tested whether temperature plays a role in UK winter oilseed rape (WOSR) yield variation through analysis of aggregated country-wide on-farm yield data and in annual Recommended List variety trial data run by the UK Agriculture and Horticulture Development Board (AHDB). Our analyses of the two independent datasets both show that mean temperature in early winter is strongly and uniquely linked to variation in WOSR yield, with a rise in mean temperature of 1 °C associated with an average reduction of 113 (+−21) kg ha−1 in yield. We propose that understanding the mechanism by which early winter chilling affects WOSR yield will enable the breeding of varieties with a more stable and resilient yield in Western Europe as climatic variation increases
Accurate exchange-correlation energies for the warm dense electron gas
Density matrix quantum Monte Carlo (DMQMC) is used to sample exact-on-average
-body density matrices for uniform electron gas systems of up to 10
matrix elements via a stochastic solution of the Bloch equation. The results of
these calculations resolve a current debate over the accuracy of the data used
to parametrize finite-temperature density functionals. Exchange-correlation
energies calculated using the real-space restricted path-integral formalism and
the -space configuration path-integral formalism disagree by up to
\% at certain reduced temperatures and densities . Our calculations confirm the accuracy of the configuration
path-integral Monte Carlo results available at high density and bridge the gap
to lower densities, providing trustworthy data in the regime typical of
planetary interiors and solids subject to laser irradiation. We demonstrate
that DMQMC can calculate free energies directly and present exact free energies
for and .Comment: Accepted version: added free energy data and restructured text. Now
includes supplementary materia
Verification: The Key to Arms Control in the 1990s and Naval Arms Control: A Strategic Assessment
Positivity of Entropy in the Semi-Classical Theory of Black Holes and Radiation
Quantum stress-energy tensors of fields renormalized on a Schwarzschild
background violate the classical energy conditions near the black hole.
Nevertheless, the associated equilibrium thermodynamical entropy by
which such fields augment the usual black hole entropy is found to be positive.
More precisely, the derivative of with respect to radius, at fixed
black hole mass, is found to vanish at the horizon for {\it all} regular
renormalized stress-energy quantum tensors. For the cases of conformal scalar
fields and U(1) gauge fields, the corresponding second derivative is positive,
indicating that has a local minimum there. Explicit calculation
shows that indeed increases monotonically for increasing radius and
is positive. (The same conclusions hold for a massless spin 1/2 field, but the
accuracy of the stress-energy tensor we employ has not been confirmed, in
contrast to the scalar and vector cases). None of these results would hold if
the back-reaction of the radiation on the spacetime geometry were ignored;
consequently, one must regard as arising from both the radiation
fields and their effects on the gravitational field. The back-reaction, no
matter how "small",Comment: 19 pages, RevTe
Photon Rates for Heavy-Ion Collisions from Hidden Local Symmetry
We study photon production from the hidden local symmetry approach that
includes pions, rho and a1 mesons and compute the corresponding photon emission
rates from a hadronic gas in thermal equilibrium. Together with experimental
radiative decay widths of the background, these rates are used in a
relativistic transport model to calculate single photon spectra in heavy-ion
collisions at SPS energies. We then employ this effective theory to test three
scenarios for the chiral phase transition in high-temperature nuclear matter
including decreasing vector meson masses. Although all calculations respect the
upper bound set by the WA80 Collaboration, we find the scenarios could be
distinguished with more detailed data.Comment: 12 pages, 12 Postscript figures; discussion of thermal equilibrium
rates expanded, minor corrections to text and graph
The Swift-UVOT ultraviolet and visible grism calibration
We present the calibration of the Swift UVOT grisms, of which there are two,
providing low-resolution field spectroscopy in the ultraviolet and optical
bands respectively. The UV grism covers the range 1700-5000 Angstrom with a
spectral resolution of 75 at 2600 Angstrom for source magnitudes of u=10-16
mag, while the visible grism covers the range 2850-6600 Angstrom with a
spectral resolution of 100 at 4000 Angstrom for source magnitudes of b=12-17
mag. This calibration extends over all detector positions, for all modes used
during operations. The wavelength accuracy (1-sigma) is 9 Angstrom in the UV
grism clocked mode, 17 Angstrom in the UV grism nominal mode and 22 Angstrom in
the visible grism. The range below 2740 Angstrom in the UV grism and 5200
Angstrom in the visible grism never suffers from overlapping by higher spectral
orders. The flux calibration of the grisms includes a correction we developed
for coincidence loss in the detector. The error in the coincidence loss
correction is less than 20%. The position of the spectrum on the detector only
affects the effective area (sensitivity) by a few percent in the nominal modes,
but varies substantially in the clocked modes. The error in the effective area
is from 9% in the UV grism clocked mode to 15% in the visible grism clocked
mode .Comment: 27 pages, 31 figures; MNRAS accepted 23 February 201
New Constraints on the Lyman Continuum Escape Fraction at z~1.3
We examine deep far-ultraviolet (1600 Angstrom) imaging of the Hubble Deep
Field-North (HDFN) and the Hubble Ultra Deep Field (HUDF) to search for leaking
Lyman continuum radiation from starburst galaxies at z~1.3. There are 21
(primarily sub-L*) galaxies with spectroscopic redshifts between 1.1<z<1.5 and
none are detected in the far-UV. We fit stellar population templates to the
galaxies' optical/near-infrared SEDs to determine the starburst age and level
of dust attenuation, giving an accurate estimate of the intrinsic Lyman
continuum ratio, f_1500/f_700, and allowing a conversion from f_700 limits to
relative escape fractions. We show that previous high-redshift studies may have
underestimated the amplitude of the Lyman Break, and thus the relative escape
fraction, by a factor of ~2. Once the starburst age and intergalactic HI
absorption are accounted for, 18 galaxies in our sample have limits to the
relative escape fraction, f_esc,rel < 1.0 with some limits as low as f_esc,rel
< 0.10 and a stacked limit of f_esc,rel < 0.08. This demonstrates, for the
first time, that most sub-L* galaxies at high redshift do not have large escape
fractions. When combined with a similar study of more luminous galaxies at the
same redshift we show that, if all star-forming galaxies at z~1 have similar
relative escape fractions, the value must be less than 0.14 (3 sigma). We also
show that less than 20% (3 sigma) of star-forming galaxies at z~1 have relative
escape fractions near unity. These limits contrast with the large escape
fractions found at z~3 and suggest that the average escape fraction has
decreased between z~3 and z~1. (Abridged)Comment: Accepted for publication in ApJ. aastex format. 39 pages, 11 figure
- …