11,986 research outputs found
Extended Variational Cluster Approximation
The variational cluster approximation (VCA) proposed by M. Potthoff {\it et
al.} [Phys. Rev. Lett. {\bf 91}, 206402 (2003)] is extended to electron or spin
systems with nonlocal interactions. By introducing more than one source field
in the action and employing the Legendre transformation, we derive a
generalized self-energy functional with stationary properties. Applying this
functional to a proper reference system, we construct the extended VCA (EVCA).
In the limit of continuous degrees of freedom for the reference system, EVCA
can recover the cluster extension of the extended dynamical mean-field theory
(EDMFT). For a system with correlated hopping, the EVCA recovers the cluster
extension of the dynamical mean-field theory for correlated hopping. Using a
discrete reference system composed of decoupled three-site single impurities,
we test the theory for the extended Hubbard model. Quantitatively good results
as compared with EDMFT are obtained. We also propose VCA (EVCA) based on
clusters with periodic boundary conditions. It has the (extended) dynamical
cluster approximation as the continuous limit. A number of related issues are
discussed.Comment: 23 pages, 5 figures, statements about DCA corrected; published
versio
Superconductivity Near a Quantum Critical Point in Ba(Fe,Co)2As2
We will examine the possible link between spin fluctuations and the
superconducting mechanism in the iron-based high temperature superconductor
Ba(Fe,Co)2As2 based on NMR and high pressure transport measurements.Comment: Invited paper to m2s-IX (2009
Adjusted Empirical Likelihood for Long-memory Time Series Models
Empirical likelihood method has been applied to short-memory time series
models by Monti (1997) through the Whittle's estimation method. Yau (2012)
extended this idea to long-memory time series models. Asymptotic distributions
of the empirical likelihood ratio statistic for short and long-memory time
series have been derived to construct confidence regions for the corresponding
model parameters. However, computing profile empirical likelihood function
involving constrained maximization does not always have a solution which leads
to several drawbacks. In this paper, we propose an adjusted empirical
likelihood procedure to modify the one proposed by Yau (2012) for
autoregressive fractionally integrated moving average (ARFIMA) model. It
guarantees the existence of a solution to the required maximization problem as
well as maintains same asymptotic properties obtained by Yau (2012).
Simulations have been carried out to illustrate that the adjusted empirical
likelihood method for different long-time series models provides better
confidence regions and coverage probabilities than the unadjusted ones,
especially for small sample sizes
Equivalence of glass transition and colloidal glass transition in the hard-sphere limit
We show that the slowing of the dynamics in simulations of several model
glass-forming liquids is equivalent to the hard-sphere glass transition in the
low-pressure limit. In this limit, we find universal behavior of the relaxation
time by collapsing molecular-dynamics data for all systems studied onto a
single curve as a function of , the ratio of the temperature to the
pressure. At higher pressures, there are deviations from this universal
behavior that depend on the inter-particle potential, implying that additional
physical processes must enter into the dynamics of glass-formation.Comment: 4 pages, 4 figure
NETWORK CONNECTIVITY QUALITY - USER INTERFACE ICONS AND REPORTS
A computing device (e.g. mobile phone, smartphone, tablet computer, etc.) with multiple network connectivities may be configured to display a user interface with an indication of network quality to a user. For example, the displayed user interface may include an icon indicating the network quality (e.g., data transmission speeds, of a selected network connection) in a status bar. The computing device may also generate a network report detailing various performance metrics (e.g. an amount of data used, network speed, network reliability) of a selected network connection for a user-specified or pre-defined time period. The computing device may also provide a user with network usage suggestions based on the user’s network connection patterns. The computing device may also monitor changes in the network connection report and suggest a user take actions to correct, improve, or otherwise change network connectivity quality
- …