921 research outputs found
Improved drought tolerance in wheat is required to unlock the production potential of the Brazilian Cerrado.
ABSTRACT Improving rainfed wheat cultivation in central Brazil, where the Cerrado biome (Brazilian savanna) is predominant, remains a bottleneck for future increases in domestic wheat production. In the Cerrado, the limited water availability during the wheat-growing season is an obstacle to increase wheat yield. To address this issue, the physiological and molecular drought response of wheat and the environmental conditions of this region must be better understood. In this review, we characterized the impact of drought on rainfed wheat production in the Cerrado. Based on the peculiarities of this environment, we suggest that certain traits should be prioritized in selection. These traits and their molecular basis are important to raise wheat yields in the Cerrado and also to improve food security in Brazil, one of the top wheat-importing countries in the world
Passive galaxies as tracers of cluster environments at z~2
Even 10 billion years ago, the cores of the first galaxy clusters are often
found to host a characteristic population of massive galaxies with already
suppressed star formation. Here we search for distant cluster candidates at z~2
using massive passive galaxies as tracers. With a sample of ~40
spectroscopically confirmed passive galaxies at 1.3<z<2.1, we tune photometric
redshifts of several thousands passive sources in the full 2 sq.deg. COSMOS
field. This allows us to map their density in redshift slices, probing the
large scale structure in the COSMOS field as traced by passive sources. We
report here on the three strongest passive galaxy overdensities that we
identify in the redshift range 1.5<z<2.5. While the actual nature of these
concentrations is still to be confirmed, we discuss their identification
procedure, and the arguments supporting them as candidate galaxy clusters
(likely mid-10^13 M_sun range). Although this search approach is likely biased
towards more evolved structures, it has the potential to select still rare,
cluster-like environments close to their epoch of first appearance, enabling
new investigations of the evolution of galaxies in the context of structure
growth.Comment: 5 pages, 5 figures; A&A Letters, in pres
Restrictions on the lifetime of sterile neutrinos from primordial nucleosynthesis
We analyze the influence of decaying sterile neutrinos with the masses in the
range 1-140 MeV on the primordial Helium-4 abundance, explicitly solving the
Boltzmann equations for all particle species, taking into account neutrino
flavour oscillations, and paying special attention to systematic uncertainties.
We show that the Helium abundance depends only on the sterile neutrino lifetime
and not on the way the active-sterile mixing is distributed between flavours,
and derive an upper bound on the lifetime. We also demonstrate that the recent
results of Izotov & Thuan [arXiv:1001.4440], who find 2sigma higher than
predicted by the standard primordial nucleosynthesis value of Helium-4
abundance, are consistent with the presence in the plasma of sterile neutrinos
with the lifetime 0.01-2 seconds. The decay of these particles perturbs the
spectra of (decoupled) neutrinos and heats photons, changing the ratio of
neutrino to photon energy density, that can be interpreted as extra neutrino
species at the recombination epoch.Comment: 17 pp. + Appendices. Analysis of deuterium bounds and more accurate
account of CMB bounds on Helium-4 is added. Final version to appear in JCA
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