9,095 research outputs found
Interactive computation of radiation view factors
The development of a pair of computer programs to calculate the radiation exchange view factors is described. The surface generation program is based upon current graphics capabilities and includes special provisions which are unique to the radiation problem. The calculational program uses a combination of contour and double area integration to permit consideration of radiation with obstruction surfaces. Examples of the surface generation and the calculation are given
Effects of Umklapp Scattering on Electronic States in One Dimension
The effects of Umklapp scattering on electronic states are studied in one
spatial dimension at absolute zero. The model is basically the Hubbard model,
where parameters characterizing the normal () and Umklapp () scattering
are treated independently. The density of states is calculated in the t-matrix
approximation by taking only the forward and Umklapp scattering into account.
It is found that the Umklapp scattering causes the global splitting of the
density of states. In the presence of sufficiently strong Umklapp scattering, a
pole in the t-matrix appears in the upper half plane, signalling an instability
towards the 'pairing' ordered state ( is the reciprocal lattice
vector), whose consequences are studied in the mean field approximation. It
turns out that this ordered state coexists with spin-density-wave state and
also brings about Cooper-pairs. A phase diagram is determined in the plane of
and electron filling .Comment: 22 pages, LaTeX, 17 figures included, uses jpsj.st
Study of the ionic Peierls-Hubbard model using density matrix renormalization group methods
Density matrix renormalization group methods are used to investigate the
quantum phase diagram of a one-dimensional half-filled ionic Hubbard model with
bond-charge attraction, which can be mapped from the Su-Schrieffer-Heeger-type
electron-phonon coupling at the antiadiabatic limit. A bond order wave
(dimerized) phase which separates the band insulator from the Mott insulator
always exists as long as electron-phonon coupling is present. This is
qualitatively different from that at the adiabatic limit. Our results indicate
that electron-electron interaction, ionic potential and quantum phonon
fluctuations combine in the formation of the bond-order wave phase
Pressure-induced enhancement of superconductivity and superconducting-superconducting transition in CaC
We measured the electrical resistivity, , of superconducting
CaC at ambient and high pressure up to 16 GPa. For 8 GPa, we found
a large increase of with pressure from 11.5 up to 15.1 K. At 8 GPa,
drops and levels off at 5 K above 10 GPa. Correspondingly, the residual
increases by 200 times and the behavior
becomes flat. The recovery of the pristine behavior after depressurization is
suggestive of a phase transition at 8 GPa between two superconducting phases
with good and bad metallic properties, the latter with a lower and more
static disorder
A note on density correlations in the half-filled Hubbard model
We consider density-density correlations in the one-dimensional Hubbard model
at half filling. On intuitive grounds one might expect them to exhibit an
exponential decay. However, as has been noted recently, this is not obvious
from the Bethe Ansatz/conformal field theory (BA/CFT) approach. We show that by
supplementing the BA/CFT analysis with simple symmetry arguments one can easily
prove that correlations of the lattice density operators decay exponentially.Comment: 3 pages, RevTe
Static versus dynamic fluctuations in the one-dimensional extended Hubbard model
The extended Hubbard Hamiltonian is a widely accepted model for uncovering
the effects of strong correlations on the phase diagram of low-dimensional
systems, and a variety of theoretical techniques have been applied to it. In
this paper the world-line quantum Monte Carlo method is used to study spin,
charge, and bond order correlations of the one-dimensional extended Hubbard
model in the presence of coupling to the lattice. A static alternating lattice
distortion (the ionic Hubbard model) leads to enhanced charge density wave
correlations at the expense of antiferromagnetic order. When the lattice
degrees of freedom are dynamic (the Hubbard-Holstein model), we show that a
similar effect occurs even though the charge asymmetry must arise
spontaneously. Although the evolution of the total energy with lattice coupling
is smooth, the individual components exhibit sharp crossovers at the phase
boundaries. Finally, we observe a tendency for bond order in the region between
the charge and spin density wave phases.Comment: Corrected typos. (10 pages, 9 figures
Superconductivity of a Metallic Stripe Embedded in an Antiferromagnet
We study a simple model for the metallic stripes found in
: two chain Hubbard ladder embedded in a static
antiferromagnetic environments. We consider two cases: a ``topological
stripe'', for which the phase of the Neel order parameter shifts by
across the ladder, and a ``non-topological stripe'', for which there is no
phase shift across the ladder. We perform one-loop renormalization group
calculations to determine the low energy properties. We compare the results
with those of the isolated ladder and show that for small doping
superconductivity is enhanced in the topological stripe, and suppressed in the
non-topological one. In the topological stripe, the superconducting order
parameter is a mixture of a spin singlet component with zero momentum and a
spin triplet component with momentum . We argue that this mixture is
generic, and is due to the presence of a new term in the quantum
Ginzburg-Landau action. Some consequences of this mixing are discussed.Comment: 6 pages, 3 eps figure
Phase Separation of the Two-Dimensional t-J model
The boundary of phase separation of the two-dimensional t-J model is
investigated by the power-Lanczos method and Maxwell construction. The method
is similar to a variational approach and it determines the lower bound of the
phase separation boundary with in the limit . In
the physical interesting regime of high T_c superconductors where
there is no phase separation.Comment: LaTex 5 pages, 4 figure
An introduction to the EULAR–OMERACT rheumatoid arthritis MRI reference image atlas
This article gives a short overview of the development and characteristics of the OMERACT rheumatoid arthritis MRI scoring system (RAMRIS), followed by an introduction to the use of the EULAR–OMERACT rheumatoid arthritis MRI reference image atlas. With this atlas, MRIs of wrist and metacarpophalangeal joints of patients with rheumatoid arthritis can be scored for synovitis, bone oedema, and bone erosion, guided by standard reference images
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