1,134 research outputs found
A self-consistent first-principles calculation scheme for correlated electron systems
A self-consistent calculation scheme for correlated electron systems is
created based on the density-functional theory (DFT). Our scheme is a
multi-reference DFT (MR-DFT) calculation in which the electron charge density
is reproduced by an auxiliary interacting Fermion system. A short-range
Hubbard-type interaction is introduced by a rigorous manner with a residual
term for the exchange-correlation energy. The Hubbard term is determined
uniquely by referencing the density fluctuation at a selected localized
orbital. This strategy to obtain an extension of the Kohn-Sham scheme provides
a self-consistent electronic structure calculation for the materials design.
Introducing an approximation for the residual exchange-correlation energy
functional, we have the LDA+U energy functional. Practical self-consistent
calculations are exemplified by simulations of Hydrogen systems, i.e. a
molecule and a periodic one-dimensional array, which is a proof of existence of
the interaction strength U as a continuous function of the local fluctuation
and structural parameters of the system.Comment: 23 pages, 8 figures, to appear in J. Phys. Condens. Matte
A Simultaneous Solution to the ^6Li and ^7Li Big Bang Nucleosynthesis Problems from a Long-Lived Negatively-Charged Leptonic Particle
The Li abundance observed in metal poor halo stars exhibits a plateau
similar to that for Li suggesting a primordial origin. However, the
observed abundance of Li is a factor of larger and that of Li is
a factor of 3 lower than the abundances predicted in the standard big bang when
the baryon-to-photon ratio is fixed by WMAP. Here we show that both of these
abundance anomalies can be explained by the existence of a long-lived massive,
negatively-charged leptonic particle during nucleosynthesis. Such particles
would capture onto the synthesized nuclei thereby reducing the reaction Coulomb
barriers and opening new transfer reaction possibilities, and catalyzing a
second round of big bang nucleosynthesis. This novel solution to both of the Li
problems can be achieved with or without the additional effects of stellar
destruction.Comment: 6 pages, 2 figures, to be published in Physical Review
Redox functionality mediated by adsorbed oxygen on a Pd-oxide film over a Pd(100) thin structure: A first-principles study
Stable oxygen sites on a PdO film over a Pd(100) thin structures with a
(sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the
first-principles electronic structure calculations with the generalized
gradient approximation. The adsorbed monatomic oxygen goes to a site bridging
two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd
atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO
oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by
oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen atom
between the two stable sites is evaluated using the nudged elastic band method,
where an energy barrier for a translational motion of the adsorbed oxygen may
become sim 0.45 eV, which is low enough to allow fluxionality of the surface
oxygen at high temperatures. The oxygen fluxionality is allowed by existence of
2-fold-coordinated Pd atoms on the PdO film, whose local structure has
similarity to that of Pd catalysts for the Suzuki-Miyaura cross coupling.
Although NO_x (including NO_2 and NO) reduction is not always catalyzed only by
the PdO film, we conclude that there may happen continual redox reactions
mediated by oxygen-adsorbed PdO films over a Pd surface structure, when the
influx of NO_x and CO continues, and when the reaction cycle is kept on a
well-designed oxygen surface.Comment: 15 pages, 6 figures, submitted to J. Phys. Condens. Matte
Spin-twist driven persistent current in a strongly correlated two-dimensional electron system: a manifestation of the gauge field
A persistent current, coupled with the spin state, of purely many-body origin
is shown to exist in Nagaoka's ferromagnetic state in two dimensions (2D). This
we regard as a manifestation of a gauge field, which comes from the surrounding
spin configuration and acts on the hole motion, being coupled to the
Aharonov-Bohm flux. This provides an example where the electron-electron
interaction exerts a profound effect involving the spins in clean
two-dimensional lattice systems in sharp contrast to continuum or spinless
fermion systems.Comment: 11 pages, typeset using Revtex 3.0, Phys. Rev. B in press, 2 figures
available upon request at [email protected]
JHKs time-series observations of a few ultracool dwarfs
The M8.5 object SSSPM J0109â5101 has recently been shown to be both a periodic and a
flaring variable, based on optical observations in the extreme red. More than 16 h of monitoring
in the near-infrared (NIR) reported here failed to show any variability. Similarly, no NIR
variability could be detected in intensive monitoring of three other suspected optical variables.
This paper also reports on photometry of half a dozen targets monitored over a few weeks, and
on the comparison of intensive monitoring at different epochs. In only one case, that of the
T dwarf binary Indi Bab, is there good evidence for variability. Our results allow stringent
limits to be placed on the NIR variability levels in a large sample of ultracool dwarfs.Web of Scienc
Transforming aquatic agricultural systems towards gender equality: a five country review
Aquatic agricultural systems (AAS) are systems in which the annual production dynamics of freshwater and/or coastal ecosystems contribute significantly to total household income. Improving the livelihood security and wellbeing of the estimated 250 million poor people dependent on AAS in Bangladesh, Cambodia, the Philippines, the Solomon Islands and Zambia is the goal of the Worldfish Center-led Consortium Research Program (CRP), âHarnessing the development potential of aquatic agricultural systems for development.â One component expected to contribute to sustainably achieving this goal is enhancing the gender and wider social equity of the social, economic and political systems within which the AAS function. The CRPâs focus on social equity, and particularly gender equity, responds to the limited progress to date in enhancing the inclusiveness of development outcomes through interventions that offer improved availability of resources and technologies without addressing the wider social constraints that marginalized populations face in making use of them. The CRP aims to both offer improved availability and address the wider social constraints in order to determine whether a multi-level approach that engages with individuals, households and communities, as well as the wider social, economic and political contexts in which they function, is more successful in extending developmentâs benefits to women and other excluded groups. Designing the research in development initiatives to test this hypothesis requires a solid understanding of each CRP countryâs social, cultural and economic contexts and of the variations across them. This paper provides an initial input into developing this knowledge, based on a review of literature on agriculture, aquaculture and gender relations within the five focal countries. Before delving into the findings of the literature review, the paper first justifies the expectation that successfully achieving lasting wellbeing improvements for poor women and men dependent on AAS rests in part on advances in gender equity, and in light of this justification, presents the AAS CRPâs conceptual frame
V1647 Orionis (IRAS 05436-0007) : A New Look at McNeil's Nebula
We present a study of the newly discovered McNeil's nebula in Orion using the
JHKs-band simultaneous observations with the near-infrared (NIR) camera SIRIUS
on the IRSF 1.4m telescope. The cometary infrared nebula is clearly seen
extending toward north and south from the NIR source (V1647 Orionis) that
illuminates McNeil's nebula. The compact nebula has an apparent diameter of
about 70 arcsec. The nebula is blue (bright in J) and has a cavity structure
with two rims extending toward north-east and north-west. The north-east rim is
brighter and sharp, while the north-west rim is diffuse. The north-east rim can
be traced out to ~ 40 arcsec from the location of the NIR source. In contrast,
no cavity structure is seen toward the south, although diffuse nebula is
extended out to ~ 20 arcsec. New NIR photometric data show a significant
variation in the magnitudes (> 0.15 mag) of the source of McNeil's nebula
within a period of one week, that is possibly under the phase of eruptive
variables like FUors or EXors.Comment: 13 pages, 5 figures in JPEG format. Accepted for the publication in
PASJ Letter
Finite-size scaling of string order parameters characterizing the Haldane phase
We have developed a numerical procedure to clarify the critical behavior near
a quantum phase transition by analyzing a multi-point correlation function
characterizing the ground state. This work presents a successful application of
this procedure to the string order parameter of the S = 1 XXZ chain with
uniaxial single-ion anisotropy. The finite-size string correlation function is
estimated by the density matrix renormalization group method. We focus on the
gradient of the inversedsystem- size dependence of the correlation function on
a logarithmic plot. This quantity shows that the finite-size scaling
sensitively changes at the critical point. The behavior of the gradient with
increasing system size is divergent, stable at a finite value, or rapidly
decreases to zero when the system is in the disordered phase, at the critical
point, or in the ordered phase, respectively. The analysis of the finite-size
string correlation functions allows precise determination of the boundary of
the Haldane phase and estimation of the critical exponent of the correlation
length. Our estimates of the transition point and the critical exponents, which
are determined only by the ground-state quantities, are consistent with results
obtained from the analysis of the energy-level structure. Our analysis requires
only the correlation functions of several finite sizes under the same condition
as a candidate for the long-range order. The quantity is treated in the same
manner irrespective of the kind of elements which destroy the order concerned.
This work will assist in the development of a method to directly observe
quantum phase transitions.Comment: 15pages, 13figures, accepted to Phys. Rev.
Flat-Bands on Partial Line Graphs -- Systematic Method for Generating Flat-Band Lattice Structures
We introduce a systematic method for constructing a class of lattice
structures that we call ``partial line graphs''.In tight-binding models on
partial line graphs, energy bands with flat energy dispersions emerge.This
method can be applied to two- and three-dimensional systems. We show examples
of partial line graphs of square and cubic lattices. The method is useful in
providing a guideline for synthesizing materials with flat energy bands, since
the tight-binding models on the partial line graphs provide us a large room for
modification, maintaining the flat energy dispersions.Comment: 9 pages, 4 figure
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