922 research outputs found
Orbitally-driven Peierls state in spinels
We consider the superstructures, which can be formed in spinels containing on
B-sites the transition-metal ions with partially filled t2g levels. We show
that, when such systems are close to itinerant state (e.g. have an
insulator-metal transition), there may appear in them an orbitally-driven
Peierls state. We explain by this mechanism the very unusual superstructures
observed in CuIr2S4 (octamers) and MgTi2O4 (chiral superstructures) and suggest
that similar phenomenon should be observed in NaTiO2 and possibly in some other
systems.Comment: 4 pages, 3 figure
Proximal business intelligence on the semantic web
This is the post-print version of this article. The official version can be accessed from the link below - Copyright @ 2010 Springer.Ubiquitous information systems (UBIS) extend current Information System thinking to explicitly differentiate technology between devices and software components with relation to people and process. Adapting business data and management information to support specific user actions in context is an ongoing topic of research. Approaches typically focus on providing mechanisms to
improve specific information access and transcoding but not on how the information
can be accessed in a mobile, dynamic and ad-hoc manner. Although web ontology has been used to facilitate the loading of data warehouses, less research has been carried out on ontology based mobile reporting. This paper explores how business data can be modeled and accessed using the web ontology
language and then re-used to provide the invisibility of pervasive access; uncovering
more effective architectural models for adaptive information system strategies of this type. This exploratory work is guided in part by a vision of business intelligence that is highly distributed, mobile and fluid, adapting to sensory understanding of the underlying environment in which it operates. A proof-of concept mobile and ambient data access architecture is developed in order to further test the viability of such an approach. The paper concludes with an ontology engineering framework for systems of this type – named UBIS-ONTO
Charge and orbital order in Fe_3O_4
Charge and orbital ordering in the low-temperature monoclinic structure of
magnetite (Fe_3O_4) is investigated using LSDA+U. While the difference between
t_{2g} minority occupancies of Fe^{2+}_B and Fe^{3+}_B cations is large and
gives direct evidence for charge ordering, the screening is so effective that
the total 3d charge disproportion is rather small. The charge order has a
pronounced [001] modulation, which is incompatible with the Anderson criterion.
The orbital order agrees with the Kugel-Khomskii theory.Comment: 4 pages, 2 figure
On the sigma-model structure of type IIA supergravity action in doubled field approach
In this letter we describe how to string together the doubled field approach
by Cremmer, Julia, Lu and Pope with Pasti-Sorokin-Tonin technique to construct
the sigma-model-like action for type IIA supergravity. The relation of the
results with that of obtained in the context of searching for
Superstring/M-theory hidden symmetry group is discussed.Comment: 9 pp, LATEX; published in JETP Let
Free boson formulation of boundary states in W_3 minimal models and the critical Potts model
We develop a Coulomb gas formalism for boundary conformal field theory having
a symmetry and illustrate its operation using the three state Potts model.
We find that there are free-field representations for six conserving
boundary states, which yield the fixed and mixed physical boundary conditions,
and two violating boundary states which yield the free and new boundary
conditions. Other violating boundary states can be constructed but they
decouple from the rest of the theory. Thus we have a complete free-field
realization of the known boundary states of the three state Potts model. We
then use the formalism to calculate boundary correlation functions in various
cases. We find that the conformal blocks arising when the two point function of
is calculated in the presence of free and new boundary conditions
are indeed the last two solutions of the sixth order differential equation
generated by the singular vector.Comment: 25 page
Penrose limits and Green-Schwarz strings
We discuss the Green-Schwarz action for type IIB strings in general
plane-wave backgrounds obtained as Penrose limits from any IIB supergravity
solutions with vanishing background fermions. Using the normal-coordinate
expansion in superspace, we prove that the light-cone action is necessarily
quadratic in the fermionic coordinates. This proof is valid for more general
pp-wave backgrounds under certain conditions. We also write down the complete
quadratic action for general bosonic on-shell backgrounds in a form in which
its geometrical meaning is manifest both in the Einstein and string frames.
When the dilaton and 1-form field strength are vanishing, and the other field
strengths are constant, our string-frame action reduces, up to conventions, to
the one which has been written down using the supercovariant derivative.Comment: 18 pages, latex, no figures; (v2) relation to ref.14 clarified; (v3)
typos corrected, minor change
Homogeneous heterotic supergravity solutions with linear dilaton
I construct solutions to the heterotic supergravity BPS-equations on products
of Minkowski space with a non-symmetric coset. All of the bosonic fields are
homogeneous and non-vanishing, the dilaton being a linear function on the
non-compact part of spacetime.Comment: 36 pages; v2 conclusion updated and references adde
On the possible space-time fractality of the emitting source
Using simple space-time implementation of the random cascade model we
investigate numerically a conjecture made some time ago which was joining the
intermittent behaviour of spectra of emitted particles with the possible
fractal structure of the emitting source. We demonstrate that such details are
seen, as expected, in the Bose-Einstein correlations between identical
particles. \\Comment: Thoroughly rewritten and modify version, to be published in Phys.
Rev.
Diagrammar and metamorphosis of coset symmetries in dimensionally reduced type IIB supergravity
Studying the reduction of type IIB supergravity from ten to three space-time
dimensions we describe the metamorphosis of Dynkin diagram for gravity line
"caterpillar" into a type IIB supergravity "dragonfly" that is triggered by
inclusion of scalars and antisymmetric tensor fields. The final diagram
corresponds to type IIB string theory E8 global symmetry group which is the
subgroup of the conjectured E11 hidden symmetry group. Application of the
results for getting the type IIA/IIB T-duality rules and for searching for type
IIB vacua solutions is considered.Comment: 9 pp, 7 figs, LATEX; to be published in JETP Let
Complex-Orbital Order in Fe_3O_4 and Mechanism of the Verwey Transition
Electronic state and the Verwey transition in magnetite (Fe_3O_4) are studied
using a spinless three-band Hubbard model for 3d electrons on the B sites with
the Hartree-Fock approximation and the exact diagonalisation method.
Complex-orbital, e.g., 1/sqrt(2)[|zx> + i |yz>], ordered (COO) states having
noncollinear orbital moments ~ 0.4 mu_B on the B sites are obtained with the
cubic lattice structure of the high-temperature phase. The COO state is a novel
form of magnetic ordering within the orbital degree of freedom. It arises from
the formation of Hund's second rule states of spinless pseudo-d molecular
orbitals in the Fe_4 tetrahedral units of the B sites and ferromagnetic
alignment of their fictitious orbital moments. A COO state with longer
periodicity is obtained with pseudo-orthorhombic Pmca and Pmc2_1 structures for
the low-temperature phase. The state spontaneously lowers the crystal symmetry
to the monoclinic and explains experimentally observed rhombohedral cell
deformation and Jahn-Teller like distortion. From these findings, we consider
that at the Verwey transition temperature, the COO state remaining to be
short-range order impeded by dynamical lattice distortion in high temperature
is developed into that with long-range order coupled with the monoclinic
lattice distortion.Comment: 16 pages, 13 figures, 6 tables, accepted for publication in J. Phys.
Soc. Jp
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