2,832 research outputs found
Complete factorization of equations of motion for generalized scalar field theories
We demonstrate that the complete factorization of equations of motion into
first-order differential equations can be obtained for real and complex scalar
field theories with non-canonical dynamics.Comment: 5 pages; version published in EP
Slow light in molecular aggregates nanofilms
We study slow light performance of molecular aggregates arranged in nanofilms
by means of coherent population oscillations (CPO). The molecular cooperative
behavior inside the aggregate enhances the delay of input signals in the GHz
range in comparison with other CPO-based devices. Moreover, the problem of
residual absorption present in CPO processes, is removed. We also propose an
optical switch between different delays by exploiting the optical bistability
of these aggregates.Comment: 4 pages, 4 figure
Electronic structure of Fe and magnetism in the double perovskites CaFeReO and BaFeReO
The Fe electronic structure and magnetism in (i) monoclinic CaFeReO
with a metal-insulator transition at K and (ii) quasi-cubic
half-metallic BaFeReO ceramic double perovskites are probed by soft
x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD).
These materials show distinct Fe XAS and XMCD spectra, which are
primarily associated with their different average Fe oxidation states (close to
Fe for CaFeReO and intermediate between Fe and Fe
for BaFeReO) despite being related by an isoelectronic
(Ca/Ba) substitution. For CaFeReO, the powder-averaged Fe
spin moment along the field direction ( T), as probed by the XMCD
experiment, is strongly reduced in comparison with the spontaneous Fe moment
previously obtained by neutron diffraction, consistent with a scenario where
the magnetic moments are constrained to remain within an easy plane. For
T, the unsaturated XMCD signal is reduced below consistent with a
magnetic transition to an easy-axis state that further reduces the
powder-averaged magnetization in the field direction. For BaFeReO, the
field-aligned Fe spins are larger than for CaFeReO ( T) and the
temperature dependence of the Fe magnetic moment is consistent with the
magnetic ordering transition at K. Our results illustrate the
dramatic influence of the specific spin-orbital configuration of Re
electrons on the Fe local magnetism of these Fe/Re double perovskites.Comment: 7 pages, 3 figure
Investigation of element-specific and bulk magnetism, electronic and crystal structures of La{0.70}Ca{0.30}Mn{1-x}Cr{x}O{3}
The magnetic interactions in La{0.70}Ca{0.30}Mn{1-x}Cr{x}O{3} (x = 0.15, 0.50
and 0.70) are investigated by x-ray absorption spectroscopy (XAS), x-ray
magnetic circular dichroism (XMCD), high-resolution x-ray powder diffraction,
and bulk magnetization measurements. XAS in the Mn and Cr L{2,3} edges support
stable single valent Cr{3+} ions and a varying Mn valence state with x, while
the O K edge XAS spectrum reveals local maxima in the O 2p density of states
close to the Fermi level due to mixing with Mn and Cr 3d states. A robust
antiferromagnetic state is found for x=0.70 below TN = 258 K. For x=0.15,
combined XMCD and bulk magnetization measurements indicate a fully polarized
ferrimagnetic state for the Mn and Cr spins below Tc=224 K. For x=0.50, a
reduced ferrimagnetic component dominated by Mn spins is present below Tc=154
K. No evidence of lattice anomalies due to cooperative charge and orbital
orderings is found by x-ray diffraction for all samples. The magnetic
properties of this system are rationalized in terms of a competition of
ferromagnetic Mn-Mn double exchange and antiferromagnetic Cr-Cr and Cr-Mn
superexchange interactions.Comment: 25 pages, 9 figure
Orbital order-disorder transition in La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) and La(1-x-y)Nd(yx)Sr(y)MnO(3) (x = 0.1; y = 0.05,0.1)
The nature of orbital order-disorder transition has been studied in the
La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) series which covers the entire range between
two end points - LaMnO(3) and NdMnO(3) - as well as in
La(0.85)Nd(0.1)Sr(0.05)MnO(3) and La(0.8)Nd(0.1)Sr(0.1)MnO(3). It has been
observed that the first-order nature of the transition gives way to higher
order with the increase in "x" in the case of pure manganites. The latent heat
(L) associated with the transition, first, drops with a steeper slope within x
= 0.0-0.3 and, then, gradually over a range 0.3<x<0.9. This drop could,
possibly, be due to evolution of finer orbital domain structure with "x". In
the case of Sr-doped samples, the transition appears to be of higher-order
nature even for a doping level 5 at%. In both cases, of course, the transition
temperature T(JT) rises systematically with the drop in average A-site radius
or rise in average Mn-O-Mn bond bending angle while no
apparent correlation could be observed with doping induced disorder sigma^2.
The cooperative nature of the orbital order, therefore, appears to be robust.Comment: 15 pages including 4 figures; pdf onl
Genotyping strategies for maximizing genomic information in evaluations of the Latxa dairy sheep breed
Genomic selection has been implemented over the years in several livestock species, due to the achievable higher genetic progress. The use of genomic information in evaluations provides better prediction accuracy than do pedigree-based evaluations, and the makeup of the genotyped population is a decisive point. The aim of this work is to compare the effect of different genotyping strategies (number and type of animals) on the prediction accuracy for dairy sheep Latxa breeds. A simulation study was designed based on the real data structure of each population, and the phenotypic and genotypic data obtained were used in genetic (BLUP) and genomic (single-step genomic BLUP) evaluations of different genotyping strategies. The genotyping of males was beneficial when they were genetically connected individuals and if they had daughters with phenotypic records. Genotyping females with their own lactation records increased prediction accuracy, and the connection level has less relevance. The differences in genotyping females were independent of their estimated breeding value. The combined genotyping of males and females provided intermediate accuracy results regardless of the female selection strategy. Therefore, assuming that genotyping rams is interesting, the incorporation of genotyped females would be beneficial and worthwhile. The benefits of genotyping individuals from various generations were highlighted, although it was also possible to gain prediction accuracy when historic individuals were not considered. Greater genotyped population sizes resulted in more accuracy, even if the increase seems to reach a plateau
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