9,538 research outputs found
Bragg spectroscopy of trapped one dimensional strongly interacting bosons in optical lattices: Probing the cake-structure
We study Bragg spectroscopy of strongly interacting one dimensional bosons
loaded in an optical lattice plus an additional parabolic potential. We
calculate the dynamic structure factor by using Monte Carlo simulations for the
Bose-Hubbard Hamiltonian, exact diagonalizations and the results of a recently
introduced effective fermionization (EF) model. We find that, due to the
system's inhomogeneity, the excitation spectrum exhibits a multi-branched
structure, whose origin is related to the presence of superfluid regions with
different densities in the atomic distribution. We thus suggest that Bragg
spectroscopy in the linear regime can be used as an experimental tool to unveil
the shell structure of alternating Mott insulator and superfluid phases
characteristic of trapped bosons.Comment: 7 pages, 4 figure
On Fundamental Trade-offs of Device-to-Device Communications in Large Wireless Networks
This paper studies the gains, in terms of served requests, attainable through
out-of-band device-to-device (D2D) video exchanges in large cellular networks.
A stochastic framework, in which users are clustered to exchange videos, is
introduced, considering several aspects of this problem: the video-caching
policy, user matching for exchanges, aspects regarding scheduling and
transmissions. A family of \emph{admissible protocols} is introduced: in each
protocol the users are clustered by means of a hard-core point process and,
within the clusters, video exchanges take place. Two metrics, quantifying the
"local" and "global" fraction of video requests served through D2D are defined,
and relevant trade-off regions involving these metrics, as well as
quality-of-service constraints, are identified. A simple communication strategy
is proposed and analyzed, to obtain inner bounds to the trade-off regions, and
draw conclusions on the performance attainable through D2D. To this end, an
analysis of the time-varying interference that the nodes experience, and tight
approximations of its Laplace transform are derived.Comment: 33 pages, 9 figures. Updated version, to appear in IEEE Transactions
on Wireless Communication
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