16,037 research outputs found
Emergent Nesting of the Fermi Surface from Local-Moment Description of Iron-Pnictide High-Tc Superconductors
We uncover the low-energy spectrum of a t-J model for electrons on a square
lattice of spin-1 iron atoms with 3dxz and 3dyz orbital character by applying
Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of
one hole roaming over a 4 x 4 x 2 lattice. Hopping matrix elements are set to
produce hole bands centered at zero two-dimensional (2D) momentum in the
free-electron limit. Holes can propagate coherently in the t-J model below a
threshold Hund coupling when long-range antiferromagnetic order across the d+ =
3d(x+iy)z and d- = 3d(x-iy)z orbitals is established by magnetic frustration
that is off-diagonal in the orbital indices. This leads to two hole-pocket
Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate
spin-density wave (cSDW) that exists above the threshold Hund coupling results
in emergent Fermi surface pockets about cSDW momenta at a quantum critical
point (QCP). This motivates the introduction of a new Gutzwiller wavefunction
for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta
indicates that the dispersion of the nested band of one-particle states that
emerges is electron-type. Increasing Hund coupling past the QCP can push the
hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy
level, in agreement with recent determinations of the electronic structure of
mono-layer iron-selenide superconductors.Comment: 41 pages, 12 figures, published versio
Early Aspects at ICSE 2007: Workshop on Aspect-Oriented Requirements Engineering and Architecture Design
The “Early Aspects @ ICSE’07” is the 11th workshop in the series of Early Aspects workshops [1] which focuses on aspect identification during the requirements engineering and architecture derivation activities. The specific aim of the present workshop is twofold: (a) to initiate creation of an Early Aspects application demonstration and comparisons benchmark; and (b) to solicit submission of new
research
Fundraising and vote distribution: a non-equilibrium statistical approach
The number of votes correlates strongly with the money spent in a campaign,
but the relation between the two is not straightforward. Among other factors,
the output of a ballot depends on the number of candidates, voters, and
available resources. Here, we develop a conceptual framework based on Shannon
entropy maximization and Superstatistics to establish a relation between the
distributions of money spent by candidates and their votes. By establishing
such a relation, we provide a tool to predict the outcome of a ballot and to
alert for possible misconduct either in the report of fundraising and spending
of campaigns or on vote counting. As an example, we consider real data from a
proportional election with candidates, where a detailed data
verification is virtually impossible, and show that the number of potential
misconducting candidates to audit can be reduced to only nine
The Efroimsky formalism adapted to high-frequency perturbations
The Efroimsky perturbation scheme for consistent treatment of gravitational
waves and their influence on the background is summarized and compared with
classical Isaacson's high-frequency approach. We demonstrate that the Efroimsky
method in its present form is not compatible with the Isaacson limit of
high-frequency gravitational waves, and we propose its natural generalization
to resolve this drawback.Comment: 7 pages, to appear in Class. Quantum Gra
Hubbard-model description of the high-energy spin-spectral-weight distribution in La(2)CuO(4)
The spectral-weight distribution in recent neutron scattering experiments on
the parent compound LaCuO (LCO), which are limited in energy range to
about 450\,meV, is studied in the framework of the Hubbard model on the square
lattice with effective nearest-neighbor transfer integral and on-site
repulsion . Our study combines a number of numerical and theoretical
approaches, including, in addition to standard treatments, density matrix
renormalization group calculations for Hubbard cylinders and a suitable spinon
approach for the spin excitations. Our results confirm that the
magnitude suitable to LCO corresponds to intermediate values smaller than
the bandwidth , which we estimate to be eV for
. This confirms the unsuitability of the conventional linear
spin-wave theory. Our theoretical studies provide evidence for the occurrence
of ground-state d-wave spinon pairing in the half-filled Hubbard model on the
square lattice. This pairing applies only to the rotated-electron spin degrees
of freedom, but it could play a role in a possible electron d-wave pairing
formation upon hole doping. We find that the higher-energy spin spectral weight
extends to about 566 meV and is located at and near the momentum .
The continuum weight energy-integrated intensity vanishes or is extremely small
at momentum . This behavior of this intensity is consistent with that
of the spin waves observed in recent high-energy neutron scattering
experiments, which are damped at the momentum . We suggest that future
LCO neutron scattering experiments scan the energies between 450 meV and 566
meV and momenta around .Comment: 23 pages, 5 figure
VCube-PS: A Causal Broadcast Topic-based Publish/Subscribe System
In this work we present VCube-PS, a topic-based Publish/Subscribe system
built on the top of a virtual hypercube-like topology. Membership information
and published messages are broadcast to subscribers (members) of a topic group
over dynamically built spanning trees rooted at the publisher. For a given
topic, the delivery of published messages respects the causal order. VCube-PS
was implemented on the PeerSim simulator, and experiments are reported
including a comparison with the traditional Publish/Subscribe approach that
employs a single rooted static spanning-tree for message distribution. Results
confirm the efficiency of VCube-PS in terms of scalability, latency, number and
size of messages.Comment: Improved text and performance evaluation. Added proof for the
algorithms (Section 3.4
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