2,209 research outputs found
Influence of environmental factors during seed development and after full-ripeness on pre-harvest sprouting in wheat
Results on environmental and genotypic factors influencing preharvest sprouting of wheat are summarized. Other possible areas where additional research is needed is suggested
Ten microsatellite loci for the strawberry poison frog (Oophaga pumilio)
We describe primers and PCR conditions to amplify nine new tetranucleotide loci and one new dinucleotide locus isolated from the strawberry poison frog (Oophaga pumilio). In 21 individuals from Costa Rica, the number of alleles ranged from 4 to 16, observed heterozygosities from 40 to 100%, and polymorphic information content ranged from 0.60 to 0.90 per locus. Evidence for linkage disequilibrium was found only between two loci, but this pattern was not found in other populations tested. All primer pairs cross-amplified in Oophaga vicentei from Panama
Solutions to Maxwell's Equations using Spheroidal Coordinates
Analytical solutions to the wave equation in spheroidal coordinates in the
short wavelength limit are considered. The asymptotic solutions for the radial
function are significantly simplified, allowing scalar spheroidal wave
functions to be defined in a form which is directly reminiscent of the
Laguerre-Gaussian solutions to the paraxial wave equation in optics.
Expressions for the Cartesian derivatives of the scalar spheroidal wave
functions are derived, leading to a new set of vector solutions to Maxwell's
equations. The results are an ideal starting point for calculations of
corrections to the paraxial approximation
Improved seasonal prediction of European summer temperatures with new five-layer soil-hydrology scheme
We evaluate the impact of a new 5-layer soil-hydrology scheme on seasonal hindcast skill of 2-meter temperatures over Europe obtained with the Max Planck Institute Earth System Model (MPI-ESM). Assimilation experiments from 1981 to 2010 and 10-member seasonal hindcasts initialized on 1 May each year are performed with MPI-ESM in two soil configurations, one using a bucket scheme and one a new 5-layer soil-hydrology scheme. We find the seasonal hindcast skill for European summer temperatures to improve with the 5-layer scheme compared to the bucket scheme, and investigate possible causes for these improvements. First, improved indirect soil moisture assimilation allows for enhanced soil moisture-temperature feedbacks in the hindcasts. Additionally, this leads to improved prediction of anomalies in the 500 hPa geopotential height surface, reflecting more realistic atmospheric circulation patterns over Europe
Density matrix calculation of optical constants from optical to x-ray frequencies
We present a theory of linear optical constants based on a single-particle
density matrix and implemented in an extension of the real-space multiple
scattering code FEFF. This approach avoids the need to compute wave-functions
explicitly, and yields efficient calculations for frequencies ranging from the
IR to hard x-rays, and applicable to arbitrary aperiodic systems. Our approach
is illustrated with calculations of optical properties and applications for
several materials
Field induced transitions in a kagome antiferromagnet
The thermal order by disorder effect in magnetic field is studied for a
classical Heisenberg antiferromagnet on the kagome lattice. Using analytical
arguments we predict a unique H-T phase diagram for this strongly frustrated
magnet: states with a coplanar and a uniaxial triatic order parameters
respectively at low and high magnetic fields and an incompressible collinear
spin-liquid state at a one-third of the saturation field. We also present the
Monte Carlo data which confirm existence of these phases.Comment: 4 pages, 2 figures, accepted versio
Frustration driven lattice distortion; an NMR investigation of Y2Mo2O7
We have investigated the 89Y NMR spectrum and spin lattice relaxation, T1, in
the magnetically frustrated pyrochlore Y2Mo2O7. We find that upon cooling the
spectrum shifts, and broadens asymmetrically. A detailed examination of the low
T spectrum reveals that it is constructed from multiple peaks, each shifted by
a different amount. We argue that this spectrum is due to discrete lattice
distortions, and speculate that these distortions relieve the frustration and
reduce the system's energy.Comment: To be published in Phys. Rev. Let
Ocean circulation and Tropical Variability in the Coupled Model ECHAM5/MPI-OM
This paper describes the mean ocean circulation and the tropical variability simulated by the Max Planck Institute for Meteorology (MPI-M) coupled atmosphere–ocean general circulation model (AOGCM). Results are presented from a version of the coupled model that served as a prototype for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) simulations. The model does not require flux adjustment to maintain a stable climate. A control simulation with present-day greenhouse gases is analyzed, and the simulation of key oceanic features, such as sea surface temperatures (SSTs), large-scale circulation, meridional heat and freshwater transports, and sea ice are compared with observations.
A parameterization that accounts for the effect of ocean currents on surface wind stress is implemented in the model. The largest impact of this parameterization is in the tropical Pacific, where the mean state is significantly improved: the strength of the trade winds and the associated equatorial upwelling weaken, and there is a reduction of the model’s equatorial cold SST bias by more than 1 K. Equatorial SST variability also becomes more realistic. The strength of the variability is reduced by about 30% in the eastern equatorial Pacific and the extension of SST variability into the warm pool is significantly reduced. The dominant El Niño–Southern Oscillation (ENSO) period shifts from 3 to 4 yr. Without the parameterization an unrealistically strong westward propagation of SST anomalies is simulated. The reasons for the changes in variability are linked to changes in both the mean state and to a reduction in atmospheric sensitivity to SST changes and oceanic sensitivity to wind anomalies
Effects of site dilution on the magnetic properties of geometrically frustrated antiferromagnets
The effect of site dilution by non magnetic impurities on the susceptibility
of geometrically frustrated antiferromagnets (kagome and pyrochlore lattices)
is discussed in the framework of the Generalized Constant Coupling model, for
both classical and quantum Heisenberg spins. For the classical diluted
pyrochlore lattice, excellent agreement is found when compared with Monte Carlo
data. Results for the quantum case are also presented and discussed.Comment: 5 pages, 3 figure
Slow Relaxation of Spin Structure in Exotic Ferromagnetic Phase of Ising-like Heisenberg Kagome Antiferromagnets
In the corner-sharing lattice, magnetic frustration causes macroscopic
degeneracy in the ground state, which prevents systems from ordering. However,
if the ensemble of the degenerate configuration has some global structure, the
system can have a symmetry breaking phenomenon and thus posses a finite
temperature phase transition. As a typical example of such cases, the magnetic
phase transition of the Ising-like Heisenberg antiferromagnetic model on the
kagome lattice has been studied. There, a phase transition of the
two-dimensional ferromagnetic Ising universality class occurs accompanying with
the uniform spontaneous magnetization. Because of the macroscopic degeneracy in
the ordered phase, the system is found to show an entropy-driven ordering
process, which is quantitatively characterized by the number of ``weathervane
loop''. We investigate this novel type of slow relaxation in regularly
frustrated system.Comment: 4 pages, 6 figure
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