850 research outputs found
An Electronic Model for layer based systems: Chiral RVB metal and Superconductivity
Takada et al. have reported superconductivity in layered Na__x CoO_2.yH_2O
() and more recently Wen et al. in ()(\tc). We model a reference neutral \cob layer as an
orbitally non-degenerate spin-\half antiferromagnetic Mott insulator on a
triangular lattice and Na__x CoO_2.yH_2O and as electron
doped Mott insulators described by a t-J model. It is suggested that at optimal
doping chiral spin fluctuations enhanced by the dopant dynamics leads to a
d-wave superconducting state. A chiral RVB metal, a PT violating state with
condensed RVB gauge fields, with a possible weak ferromagnetism and low
temperature p-wave superconductivity are also suggested at higher dopings.Comment: 4 pages of LaTex file, 6 figures in eps files. Typos and minor
corrections mad
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High post-anthesis temperature effects on 3 bread wheat (Triticum aestivum L.) grain 4 transcriptome during early grain-filling
Background: High post-anthesis (p.a) temperatures reduce mature grain weights in wheat and other cereals.
However, the causes of this reduction are not entirely known. Control of grain expansion by the maternally derived pericarp of the grain has previously been suggested, although this interaction has not been investigated under high p.a. temperatures. Down-regulation of pericarp localised genes that regulate cell wall expansion under high p.a. temperatures may limit expansion of the encapsulated endosperm due to a loss of plasticity in the pericarp,reducing mature grain weight. Here the effect of high p.a. temperatures on the transcriptome of the pericarp and endosperm of the wheat grain during early grain-filling was investigated via RNA-Seq and is discussed alongside grain moisture dynamics during early grain development and mature grain weight.
Results: High p.a. temperatures applied from 6-days after anthesis (daa) and until 18daa reduced the grain’s ability to accumulate water, with total grain moisture and percentage grain moisture content being significantly reduced from 14daa onwards. Mature grain weight was also significantly reduced by the same high p.a. temperatures
applied from 6daa for 4-days or more, in a separate experiment. Comparison of our RNA-Seq data from whole
grains, with existing data sets from isolated pericarp and endosperm tissues enabled the identification of subsets of genes whose expression was significantly affected by high p.a. temperature and predominantly expressed in either tissue. Hierarchical clustering and gene ontology analysis resulted in the identification of a number of genes implicated in the regulation of cell wall expansion, predominantly expressed in the pericarp and significantly down26 regulated under high p.a. temperatures, including endoglucanase, xyloglucan endotransglycosylases and a β27 expansin. An over-representation of genes involved in the ‘cuticle development’ functional pathway that were
expressed in the pericarp and affected by high p.a. temperatures was also observed.
Conclusions: High p.a. temperature induced down-regulation of genes involved in regulating pericarp cell wall expansion. This concomitant down-regulation with a reduction in total grain moisture content and grain weight following the same treatment period, adds support to the theory that high p.a. temperatures may cause a
reduction in mature grain weight as result of decreased pericarp cell wall expansion
Calculation of resonances in the Coulomb three-body system with two disintegration channels in the adiabatic hyperspherical approach
The method of calculation of the resonance characteristics is developed for
the metastable states of the Coulomb three-body (CTB) system with two
disintegration channels. The energy dependence of K-matrix in the resonance
region is calculated with the use of the stabilization method. Resonance
position and partial widths are obtained by fitting the numerically calculated
K(E)-matrix with the help of the generalized Breit-Wigner formula.Comment: Latex, 11 pages with 5 figures and 2 table
Charge Ordering in Organic ET Compounds
The charge ordering phenomena in quasi two-dimensional 1/4-filled organic
compounds (ET)_2X (ET=BEDT-TTF) are investigated theoretically for the
and -type structures, based on the Hartree approximation for the
extended Hubbard models with both on-site and intersite Coulomb interactions.
It is found that charge ordered states of stripe-type are stabilized for the
relevant values of Coulomb energies, while the spatial pattern of the stripes
sensitively depends on the anisotropy of the models. By comparing the results
of calculations with the experimental facts, where the effects of quantum
fluctuation is incorporated by mapping the stripe-type charge ordered states to
the S=1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating
phases of -(ET)_2MM'(SCN)_4 and -(ET)_2I_3 are deduced.
Furthermore, to obtain a unified view among the , and
-(ET)_2X families, the stability of the charge ordered state in
competition with the dimeric antiferromagnetic state viewed as the Mott
insulating state, which is typically realized in -type compounds, and
with the paramagnetic metallic state, is also pursued by extracting essential
parameters.Comment: 35 pages, 27 figures, submitted to J. Phys. Soc. Jp
The Heisenberg antiferromagnet on an anisotropic triangular lattice: linear spin-wave theory
We consider the effect of quantum spin fluctuations on the ground state
properties of the Heisenberg antiferromagnet on an anisotropic triangular
lattice using linear spin-wave theory. This model should describe the magnetic
properties of the insulating phase of the kappa-(BEDT-TTF)_2 X family of
superconducting molecular crystals. The ground state energy, the staggered
magnetization, magnon excitation spectra and spin-wave velocities are computed
as a function of the ratio between the second and first neighbours, J2/J1. We
find that near J2/J1 = 0.5, i.e., in the region where the classical spin
configuration changes from a Neel ordered phase to a spiral phase, the
staggered magnetization vanishes, suggesting the possibility of a quantum
disordered state. In this region, the quantum correction to the magnetization
is large but finite. This is in contrast to the frustrated Heisenberg model on
a square lattice, for which the quantum correction diverges logarithmically at
the transition from the Neel to the collinear phase. For large J2/J1, the model
becomes a set of chains with frustrated interchain coupling. For J2 > 4 J1, the
quantum correction to the magnetization, within LSW, becomes comparable to the
classical magnetization, suggesting the possibility of a quantum disordered
state. We show that, in this regime, quantum fluctuations are much larger than
for a set of weakly coupled chains with non-frustated interchain coupling.Comment: 10 pages, RevTeX + epsf, 5 figures Replaced with published version.
Comparison to series expansions energies include
Antiferromagnetic Heisenberg model on anisotropic triangular lattice in the presence of magnetic field
We use Schwinger boson mean field theory to study the antiferromagnetic
spin-1/2 Heisenberg model on an anisotropic triangular lattice in the presence
of a uniform external magnetic field. We calculate the field dependence of the
spin incommensurability in the ordered spin spiral phase, and compare the
results to the recent experiments in CsCuCl by Coldea et al. (Phys.
Rev. Lett. 86, 1335 (2001)).Comment: 4 pages with 4 figures include
Re-examination of half-metallic ferromagnetism for doped LaMnO3 in quasiparticle self-consistent method
We apply the quasiparicle self-consistent (\qsgw) method to a cubic
virtual-crystal alloy LaBaMnO %(LBMO) as a theoretical
representative for colossal magnetoresistive perovskite manganites. The \qsgw\
predicts it as a fully-polarized half-metallic ferromagnet for a wide range of
and lattice constant. Calculated density of states and dielectric functions
are consistent with experiments. In contrast, the energies of calculated spin
wave are very low in comparison with experiments. This is affected neither by
rhombohedral deformation nor the intrinsic deficiency in the \qsgw method. Thus
we ends up with a conjecture that phonons related to the Jahn-Teller distortion
should hybridize with spin waves more strongly than people thought until now
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