1,583 research outputs found
Spin, charge, and orbital correlations in the one-dimensional t2g-orbital Hubbard model
We present the zero-temperature phase diagram of the one-dimensional
t2g-orbital Hubbard model, obtained using the density-matrix renormalization
group and Lanczos techniques. Emphasis is given to the case for the electron
density n=5 corresponding to five electrons per site, of relevance for some
Co-based compounds. However, several other cases for electron densities between
n=3 and 6 are also studied. At n=5, our results indicate a first-order
transition between a paramagnetic (PM) insulator phase and a fully-polarized
ferromagnetic (FM) state by tuning the Hund's coupling. The results also
suggest a transition from the n=5 PM insulator phase to a metallic regime by
changing the electron density, either via hole or electron doping. The behavior
of the spin, charge, and orbital correlation functions in the FM and PM states
are also described in the text and discussed. The robustness of these two
states varying parameters suggests that they may be of relevance in more
realistic higher dimensional systems as well.Comment: 9 pages, 8 figure
Antiferro-quadrupole state of orbital-degenerate Kondo lattice model with f^2 configuration
To clarify a key role of orbitals in the emergence of
antiferro-quadrupole structure in PrPb, we investigate the ground-state
property of an orbital-degenerate Kondo lattice model by numerical
diagonalization techniques. In PrPb, Pr has a
configuration and the crystalline-electric-field ground state is a non-Kramers
doublet . In a - coupling scheme, the state is
described by two local singlets, each of which consists of two electrons
with one in and another in orbitals. Since in a cubic
structure, has localized nature, while orbitals are
rather itinerant, we propose the orbital-degenerate Kondo lattice model for an
effective Hamiltonian of PrPb. We show that an antiferro-orbital state is
favored by the so-called double-exchange mechanism which is characteristic of
multi-orbital systems.Comment: 3 pages, 3 figures, Proceedings of Skutterudite2007 (September 26-30,
2007, Kobe
Structure and apparent topography of TiO2 (110) surfaces
We present self-consistent ab-initio total-energy and electronic-structure
calculations on stoichiometric and non-stoichiometric TiO2 (110) surfaces.
Scanning tunneling microscopy (STM) topographs are simulated by calculating the
local electronic density of states over an energy window appropriate for the
experimental positive-bias conditions. We find that under these conditions the
STM tends to image the undercoordinated Ti atoms, in spite of the physical
protrusion of the O atoms, giving an apparent reversal of topographic contrast
on the stoichiometric 1x1 or missing-row 2x1 surface. We also show that both
the interpretation of STM images and the direct comparison of surface energies
favor an added-row structure over the missing-row structure for the
oxygen-deficient 2x1 surface.Comment: 6 pages, two-column style with 5 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#ng_tio
The Dynamical State fo the Starless Dense Core FeSt 1-457: A Pulsating Globule?
High resolution molecular line observations of CS, HCO+, C18O and N2H+ were
obtained toward the starless globule FeSt 1-457 in order to investigate its
kinematics and chemistry. The HCO+ and CS spectra show clear self-reversed and
asymmetric profiles across the face of the globule. The sense of the observed
asymmetry is indicative of the global presence of expansion motions in the
outer layers of the globule. These motions appear to be subsonic and
significantly below the escape velocity of the globule. Comparison of our
observations with near-infrared extinction data indicate that the globule is
gravitationally bound. Taken together these considerations lead us to suggest
that the observed expansion has its origin in an oscillatory motion of the
outer layers of the globule which itself is likely in a quasi-stable state near
hydrostatic equilibrium. Analysis of the observed linewidths of CO and N2H+
confirm that thermal pressure is the dominant component of the cloud's internal
support. A simple calculation suggests that the dominant mode of pulsation
would be an l = 2 mode with a period of 0.3 Myr. Deformation of the globule due
to the large amplitude l = 2 oscillation may be responsible for the
double-peaked structure of the core detected in high resolution extinction
maps. Detailed comparison of the molecular-line observations and extinction
data provides evidence for significant depletion of C18O and perhaps HCO+ while
N2H+ may be undepleted to a cloud depth of about 40 magnitudes of visual
extinction.Comment: to appear in ApJ vol 665 20 August 2007
Multipole correlations of -orbital Hubbard model with spin-orbit coupling
We investigate the ground-state properties of a one-dimensional -orbital Hubbard model including an atomic spin-orbit coupling by using
numerical methods, such as Lanczos diagonalization and density-matrix
renormalization group. As the spin-orbit coupling increases, we find a
ground-state transition from a paramegnetic state to a ferromagnetic state. In
the ferromagnetic state, since the spin-orbit coupling mixes spin and orbital
states with complex number coefficients, an antiferro-orbital state with
complex orbitals appears. According to the appearance of the complex orbital
state, we observe an enhancement of octupole correlations.Comment: 3 pages, 3 figures, To appear in J. Phys. Soc. Jpn. Suppl.,
Proceedings of ICHE2010 (September 17-20, 2010, Hachioji, Japan
Effective Crystalline Electric Field Potential in a j-j Coupling Scheme
We propose an effective model on the basis of a - coupling scheme to
describe local -electron states for realistic values of Coulomb interaction
and spin-orbit coupling , for future development of microscopic
theory of magnetism and superconductivity in -electron systems, where
is the number of local electrons. The effective model is systematically
constructed by including the effect of a crystalline electric field (CEF)
potential in the perturbation expansion in terms of . In this paper,
we collect all the terms up to the first order of . Solving the
effective model, we show the results of the CEF states for each case of
=25 with symmetry in comparison with those of the Stevens
Hamiltonian for the weak CEF. In particular, we carefully discuss the CEF
energy levels in an intermediate coupling region with in the order
of 0.1 corresponding to actual -electron materials between the and
- coupling schemes. Note that the relevant energy scale of is the
Hund's rule interaction. It is found that the CEF energy levels in the
intermediate coupling region can be quantitatively reproduced by our modified
- coupling scheme, when we correctly take into account the corrections in
the order of in addition to the CEF terms and Coulomb interactions
which remain in the limit of =. As an application of the
modified - coupling scheme, we discuss the CEF energy levels of filled
skutterudites with symmetry.Comment: 12 pages, 7 figures. Typeset with jpsj2.cl
On the disappearance of a cold molecular torus around the low-luminosity active galactic nucleus of NGC 1097
We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map the
CO(3-2) and the underlying continuum emissions around the type 1 low-luminosity
active galactic nucleus (LLAGN; bolometric luminosity
erg~s) of NGC 1097 at pc resolution. These observations
revealed a detailed cold gas distribution within a pc of this LLAGN.
In contrast to the luminous Seyfert galaxy NGC 1068, where a pc cold
molecular torus was recently revealed, a distinctively dense and compact torus
is missing in our CO(3-2) integrated intensity map of NGC 1097. Based on the
CO(3-2) flux, the gas mass of the torus of NGC 1097 would be a factor of
less than that found for NGC 1068 by using the same CO-to-H
conversion factor, which implies less active nuclear star formation and/or
inflows in NGC 1097. Our dynamical modeling of the CO(3-2) velocity field
implies that the cold molecular gas is concentrated in a thin layer as compared
to the hot gas traced by the 2.12 m H emission in and around the
torus. Furthermore, we suggest that NGC 1097 hosts a geometrically thinner
torus than NGC 1068. Although the physical origin of the torus thickness
remains unclear, our observations support a theoretical prediction that
geometrically thick tori with high opacity will become deficient as AGNs evolve
from luminous Seyferts to LLAGNs.Comment: 9 pages, 5 figures. Accepted for publication in ApJ
Local magnetic structure due to inhomogeneity of interaction in S=1/2 antiferromagnetic chain
We study the magnetic properties of antiferromagnetic Heisenberg
chains with inhomogeneity of interaction. Using a quantum Monte Carlo method
and an exact diagonalization method, we study bond-impurity effect in the
uniform chain and also in the bond-alternating chain. Here `bond
impurity' means a bond with strength different from those in the bulk or a
defect in the alternating order. Local magnetic structures induced by bond
impurities are investigated both in the ground state and at finite
temperatures, calculating the local magnetization, the local susceptibility and
the local field susceptibility. We also investigate the force acting between
bond impurities and find the force generally attractive.Comment: 15pages, 34figure
Bridging the Two Plans in the Semantics for Relevant Logic
Part of the Synthese Library book series (SYLI, volume 418)This paper considers how the two plans in the semantics for relevant logic are related to each other. The so-called American plan, classical-style four-valued semantics, is intuitive, but weak. The so-called Australian plan, two-valued frame semantics, is very powerful, but the semantic devices employed need some explanation. Examining R. Routleyâs 1984 paper âAmerican plan completed, â this paper argues that the American plan provides an explanatory and ontological basis for the Australian plan, and that the latter is just a developed form of the former
Zero-Liquid Discharge Desalination of Hypersaline Shale Gas Wastewater: Challenges and Future Directions
EMCEI 2017 - Euro-Mediterranean Conference for Environmental IntegrationUnconventional natural gas extraction from tight shale reservoirs, or shale gas, has recently emerged as an attractive energy resource to face the rising worldwide demand. Over the past decade, advanced technologies of horizontal drilling and hydraulic fracturing (âfrackingâ) have allowed the economic viability of shale gas exploration from rather unattainable deposits. Apart from optimistic growth projections, shale gas production is also responsible for worrying environmental and social implications, which are related, among others, to elevated freshwater consumption and hazardous wastewater generation. Within this framework, the ability of zero-liquid discharge desalination to promote water reuse and/or water recycling is critical for shale gas industry. Hence, application of effective desalination processes is mandatory to treat the large amounts of polluting hypersaline wastewater, alleviating environmental and public health impacts and enhancing overall shale gas process sustainability. This work outlines the challenges and future directions for ZLD desalination of shale gas wastewater.This project has received funding from the European Unionâs Horizon 2020 Research and Innovation Programme under grant agreement No. 640979
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