33,982 research outputs found
Heavy Quark diffusion from lattice QCD spectral functions
We analyze the low frequency part of charmonium spectral functions on large
lattices close to the continuum limit in the temperature region as well as for . We present evidence for the
existence of a transport peak above and its absence below . The
heavy quark diffusion constant is then estimated using the Kubo formula. As
part of the calculation we also determine the temperature dependence of the
signature for the charmonium bound state in the spectral function and discuss
the fate of charmonium states in the hot medium.Comment: 4 pages, Proceedings for Quark Matter 2011 Conference, May 23-28,
2011, Annecy, Franc
Superconducting gap symmetry of Ba0.6K0.4Fe2As2 studied by angle-resolved photoemission spectroscopy
We have performed high-resolution angle-resolved photoemission spectroscopy
on the optimally-doped BaKFeAs compound and determined
the accurate momentum dependence of the superconducting (SC) gap in four
Fermi-surface sheets including a newly discovered outer electron pocket at the
M point. The SC gap on this pocket is nearly isotropic and its magnitude is
comparable ( 11 meV) to that of the inner electron and hole
pockets (12 meV), although it is substantially larger than that of the
outer hole pocket (6 meV). The Fermi-surface dependence of the SC gap
value is basically consistent with () = coscos
formula expected for the extended s-wave symmetry. The observed finite
deviation from the simple formula suggests the importance of multi-orbital
effects.Comment: 4 pages, 3 figures, 1 tabl
Charge and spin Hall effect in graphene with magnetic impurities
We point out the existence of finite charge and spin Hall conductivities of
graphene in the presence of a spin orbit interaction (SOI) and localized
magnetic impurities. The SOI in graphene results in different transverse forces
on the two spin channels yielding the spin Hall current. The magnetic
scatterers act as spin-dependent barriers, and in combination with the SOI
effect lead to a charge imbalance at the boundaries. As indicated here, the
charge and spin Hall effects should be observable in graphene by changing the
chemical potential close to the gap.Comment: 7 page
A blind deconvolution approach to recover effective connectivity brain networks from resting state fMRI data
A great improvement to the insight on brain function that we can get from
fMRI data can come from effective connectivity analysis, in which the flow of
information between even remote brain regions is inferred by the parameters of
a predictive dynamical model. As opposed to biologically inspired models, some
techniques as Granger causality (GC) are purely data-driven and rely on
statistical prediction and temporal precedence. While powerful and widely
applicable, this approach could suffer from two main limitations when applied
to BOLD fMRI data: confounding effect of hemodynamic response function (HRF)
and conditioning to a large number of variables in presence of short time
series. For task-related fMRI, neural population dynamics can be captured by
modeling signal dynamics with explicit exogenous inputs; for resting-state fMRI
on the other hand, the absence of explicit inputs makes this task more
difficult, unless relying on some specific prior physiological hypothesis. In
order to overcome these issues and to allow a more general approach, here we
present a simple and novel blind-deconvolution technique for BOLD-fMRI signal.
Coming to the second limitation, a fully multivariate conditioning with short
and noisy data leads to computational problems due to overfitting. Furthermore,
conceptual issues arise in presence of redundancy. We thus apply partial
conditioning to a limited subset of variables in the framework of information
theory, as recently proposed. Mixing these two improvements we compare the
differences between BOLD and deconvolved BOLD level effective networks and draw
some conclusions
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