220 research outputs found
Local-Ansatz Approach with Momentum Dependent Variational Parameters to Correlated Electron Systems
A new wavefunction which improves the Gutzwiller-type local ansatz method has
been proposed to describe the correlated electron system. The ground-state
energy, double occupation number, momentum distribution function, and
quasiparticle weight have been calculated for the half-filled band Hubbard
model in infinite dimensions. It is shown that the new wavefunction improves
the local-ansatz approach (LA) proposed by Stollhoff and Fulde. Especially,
calculated momentum distribution functions show a reasonable momentum
dependence. The result qualitatively differs from those obtained by the LA and
the Gutzwiller wavefunction. Furthermore, the present approach combined with
the projection operator method CPA is shown to describe quantitatively the
excitation spectra in the insulator regime as well as the critical Coulomb
interactions for a gap formation in infinite dimensions.Comment: To be published in Phys. Soc. Jpn. 77 No.11 (2008
Kink Structure in the Quasiparticle Band of Doped Hubbard Systems
By making use of the self-consistent projection operator method with
high-momentum and high-energy resolutions, we find a kink structure in the
quasiparticle excitation spectrum of the two-dimensional Hubbard model in the
underdoped regime. The kink is caused by a mixing between the quasiparticle
state and excitations with short-range antiferromagnetic order. We suggest that
this might be the origin of the strong concentration dependence of the 'kink'
found in La_{2-x}Sr_{x}CuO_{4} (x=0.03-0.07).Comment: 3 pages, 4 figures. to be published in J. Phys. Soc. Jpn., Vol. 74,
No. 9, September 15, 200
Theory of Magnetic Short--Range Order for High-T_c Superconductors
A theory of magnetic short--range order for high-- cuprates is presented
on the basis of the one--band ----Hubbard model combining the
four--field slave--boson functional integral technique with the Bethe cluster
method. The ground--state phase diagram evaluated self--consistently at the
saddle--point and pair--approximation levels shows the experimentally observed
suppression of magnetic long--range order in the favour of a paraphase with
antiferromagnetic short--range order. In this phase the uniform static spin
susceptibility consists of interrelated itinerant and local parts and increases
upon doping up to the transition to the Pauli paraphase. Using realistic values
of the Hubbard interaction we obtain the cusp position and the doping
dependence of the zero--temperature susceptibility in reasonable agreement with
experiments on .Comment: 3 pages, 2 Postscript figure, Proc. Int. Conf. SCES Zuerich
Switzerland Aug. 96, to appear in Physica
First-Principles Dynamical Coherent-Potential Approximation Approach to the Ferromagnetism of Fe, Co, and Ni
Magnetic properties of Fe, Co, and Ni at finite temperatures have been
investigated on the basis of the first-principles dynamical CPA (Coherent
Potential Approximation) combined with the LDA (Local Density Approximation) +
Hamiltonian in the Tight-Binding Linear Muffintin Orbital (TB-LMTO)
representation. The Hamiltonian includes the transverse spin fluctuation terms.
Numerical calculations have been performed within the harmonic approximation
with 4th-order dynamical corrections. Calculated single-particle densities of
states in the ferromagnetic state indicate that the dynamical effects reduce
the exchange splitting, suppress the band width of the quasi-particle state,
and causes incoherent excitations corresponding the 6 eV satellites. Results of
the magnetization vs temperature curves, paramagnetic spin susceptibilities,
and the amplitudes of local moments are presented. Calculated Curie
temperatures () are reported to be 1930K for Fe, 2550K for Co, and
620K for Ni; for Fe and Co are overestimated by a factor of 1.8,
while in Ni agrees with the experimental result. Effective Bohr
magneton numbers calculated from the inverse susceptibilities are 3.0 (Fe), 3.0 (Co), and 1.6 (Ni), being in
agreement with the experimental ones. Overestimate of in Fe and Co
is attributed to the neglects of the higher-order dynamical effects as well as
the magnetic short range order.Comment: 10 pages, 13 figure
Evaluation of the Subchronic Toxicity of Dietary Administered Equisetum arvense in F344 Rats
Equisetum arvense, commonly known as the field horsetail, has
potential as a new functional food ingredient. However, little information is
available on its side effects, and the general toxicity of Equisetum
arvense has yet to be examined in detail. In the present study, we
evaluated the influence of administration in diet at doses of 0, 0.3, 1 and 3%
for 13 weeks in male and female F344 rats. No toxicity was detected with
reference to clinical signs, body weight, urinalysis, hematology and serum
biochemistry data and organ weights. Microscopic examination revealed no
histopathological lesions associated with treatment. In conclusion, the
no-observed-adverse-effect level (NOAEL) for Equisetum arvense
was determined to be greater than 3% in both sexes of F344 rat (males and
females: >1.79 g/kg BW/day and >1.85 g/kg BW/day, respectively) under the
conditions of the present study
Evidence of Strong Electron Correlations in Gamma-Iron
Single-particle excitation spectra of gamma-Fe in the paramagnetic state have
been investigated by means of the first-principles dynamical coherent potential
approximation theory which has recently been developed. It is found that the
central peak in the density of states consisting of the t2g bands is destroyed
by electron correlations, and the Mott-Hubbard type correlated bands appear.
The results indicate that the gamma-Fe can behave as correlated electrons at
high temperatures.Comment: 7 pages, 3 figures, to be published in J. Phys. Soc. Jpn. Vol.78,
No.9 (2009
Dynamical coherent-potential approximation approach to excitation spectra in 3d transition metals
First-principles dynamical CPA (Coherent-Potential Approximation) for
electron correlations has been developed further by taking into account
higher-order dynamical corrections with use of the asymptotic approximation.
The theory is applied to the investigations of a systematic change of
excitation spectra in transition metals from Sc to Cu at finite
temperatures. It is shown that the dynamical effects damp main peaks in the
densities of states (DOS) obtained by the local density approximation to the
density functional theory, reduce the band broadening due to thermal spin
fluctuations, create the Mott-Hubbard type bands in the case of fcc Mn and fcc
Fe, and create a small hump corresponding to the `6 eV' satellite in the case
of Co, Ni, and Cu. Calculated DOS explain the X-ray photoelectron spectroscopy
data as well as the bremsstrahlung isochromat spectroscopy data. Moreover, it
is found that screening effects on the exchange energy parameters are
significant for understanding the spectra in magnetic transition metals.Comment: To be published in Phys. Rev.
Reduction in eddy current loss for a power coupler in an electrodeless discharged lamp
We investigated reduction in an eddy current loss for a power coupler in an electrodeless discharged lamp with our previously proposed analysis method for plasma in the lamp. We confirmed that a large eddy current flow was observed at the top of an Al stage in the power coupler and the loss was reduced by a decrease in the height of the Al stage. This result suggests that a decrease in the height is effective to reduce wasted power losses and implies the possibility of an improvement in the lamp efficiency. We also confirmed that upward-moving and moderate-elongation of the ferrite core in the power coupler is effective to reduce the wasted loss. In order to verify the result, we evaluated the lamp efficiency of a lamp with a modified power coupler. Resultantly, the lamp efficiency was increased by approximately 3 lm/W (lumen per Watt). Therefore, we can conclude that reducing the eddy current loss in the power coupler is one of the important factors to obtain high lamp efficiency
Magnetic design for an electrodeless discharged lamp
We proposed an analysis method for plasma in an electrodeless discharged lamp light-emitting by inductively-coupled plasma, and a design of a power coupler was investigated by focusing on the electric power from the exciting coil to the plasma. We found that the power of the plasma was increased and of an Al stage was decreased with moving the core upward. This result suggests that the moving of the core upward is effective to reduce wasted power loss by eddy current and improves the lamp efficiency. In order to verify the result, we changed the position of the power coupler in the commercial lamp. Resultantly, the luminous flux of the lamp was increased by approximately 150 lm (lumen), when the power coupler was moved upward by 25 mm compared with the position of a commercial lamp. Therefore, we can conclude that our proposed method is applicable to the design of the lamp and suitable design is important to obtain high lamp efficiency
Geography-dependent horizontal gene transfer from vertebrate predators to their prey
Horizontal transfer (HT) of genes between multicellular animals, once thought to be extremely rare, is being more commonly detected, but its global geographic trend and transfer mechanism have not been investigated. We discovered a unique HT pattern of Bovine-B (BovB) LINE retrotransposons in vertebrates, with a bizarre transfer direction from predators (snakes) to their prey (frogs). At least 54 instances of BovB HT were detected, which we estimate to have occurred across time between 85 and 1.3 Ma. Using comprehensive transcontinental sampling, our study demonstrates that BovB HT is highly prevalent in one geographical region, Madagascar, suggesting important regional differences in the occurrence of HTs. We discovered parasite vectors that may plausibly transmit BovB and found that the proportion of BovB-positive parasites is also high in Madagascar where BovB thus might be physically transported by parasites to diverse vertebrates, potentially including humans. Remarkably, in two frog lineages, BovB HT occurred after migration from a non-HT area (Africa) to the HT hotspot (Madagascar). These results provide a novel perspective on how the prevalence of parasites influences the occurrence of HT in a region, similar to pathogens and their vectors in some endemic diseases
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