10,979 research outputs found
MSPlayer: Multi-Source and multi-Path LeverAged YoutubER
Online video streaming through mobile devices has become extremely popular
nowadays. YouTube, for example, reported that the percentage of its traffic
streaming to mobile devices has soared from 6% to more than 40% over the past
two years. Moreover, people are constantly seeking to stream high quality video
for better experience while often suffering from limited bandwidth. Thanks to
the rapid deployment of content delivery networks (CDNs), popular videos are
now replicated at different sites, and users can stream videos from close-by
locations with low latencies. As mobile devices nowadays are equipped with
multiple wireless interfaces (e.g., WiFi and 3G/4G), aggregating bandwidth for
high definition video streaming has become possible.
We propose a client-based video streaming solution, MSPlayer, that takes
advantage of multiple video sources as well as multiple network paths through
different interfaces. MSPlayer reduces start-up latency and provides high
quality video streaming and robust data transport in mobile scenarios. We
experimentally demonstrate our solution on a testbed and through the YouTube
video service.Comment: accepted to ACM CoNEXT'1
Graphene Spin Transistor
Graphitic nanostructures, e.g. carbon nanotubes (CNT) and graphene, have been
proposed as ideal materials for spin conduction[1-7]; they have long electronic
mean free paths[8] and small spin-orbit coupling[9], hence are expected to have
very long spin-scattering times. In addition, spin injection and detection in
graphene opens new opportunities to study exotic electronic states such as the
quantum Hall[10,11] and quantum spin Hall[9] states, and spin-polarized edge
states[12] in graphene ribbons. Here we perform the first non-local four-probe
experiments[13] on graphene contacted by ferromagnetic Permalloy electrodes. We
observe sharp switching and often sign-reversal of the non-local resistance at
the coercive field of the electrodes, indicating definitively the presence of a
spin current between injector and detector. The non-local resistance changes
magnitude and sign quasi-periodically with back-gate voltage, and
Fabry-Perot-like oscillations[6,14,15] are observed, consistent with
quantum-coherent transport. The non-local resistance signal can be observed up
to at least T = 300 K
Quantum phase transitions in attractive extended Bose-Hubbard Model with three-body constraint
The effect of nearest-neighbor repulsion on the ground-state phase diagrams
of three-body constrained attractive Bose lattice gases is explored
numerically. When the repulsion is turned on, in addition to the uniform Mott
insulating state and two superfluid phases (the atomic and the dimer
superfluids), a dimer checkerboard solid state appears at unit filling, where
boson pairs form a solid with checkerboard structure. We find also that the
first-order transitions between the uniform Mott insulating state and the
atomic superfluid state can be turned into the continuous ones as the repulsion
is increased. Moreover, the stability regions of the dimer superfluid phase can
be extended to modest values of the hopping parameter by tuning the strength of
the repulsion. Our conclusions hence shed light on the search of the dimer
superfluid phase in real ultracold Bose gases in optical lattices.Comment: 4 + epsilon pages, 5 figures. Rewritten to emphasize the effect of
nonzero nearest-neighbor repulsion. Conclusions unchanged. Accepted for
publication in Phys. Rev.
Optimal 1->M universal quantum cloning via spin networks
We present a scheme that transform 1 qubit to M identical copies with optimal
fidedelity via free dynamical evolution of spin star networks. We show that the
Heisenberg XXZ coupling can fulfill the challenge. The initial state of the
copying machine and the parameters of the spin Hamiltonian are discussed in
detail. Furthermore we have proposed a feasible method to prepare the initial
state of the copying machine.Comment: 4 pages, 2 figure
Supersolid phases in the extended boson hubbard model
We present a comprehensive numerical study on the ground state phase diagram
of the two-dimensional hardcore boson extended Hubbard model with nearest
() and next nearest neighbor () repulsions. In addition to the
quantum solid and superfluid phases, we report the existence of striped
supersolid and three-quarter (quarter) filled supersolid at commensurate
density (0.25) due to the interplay of and
interactions. The nature of three-quarter filled supersolid and the associated
quantum solid will be discussed. Quantum phase transition between the two
supersolids of different symmetries is observed and is clearly of first order.Comment: 4 pages, 6 figure
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