2,682 research outputs found
Erasure Coding for Real-Time Streaming
We consider a real-time streaming system where messages are created
sequentially at the source, and are encoded for transmission to the receiver
over a packet erasure link. Each message must subsequently be decoded at the
receiver within a given delay from its creation time. The goal is to construct
an erasure correction code that achieves the maximum message size when all
messages must be decoded by their respective deadlines under a specified set of
erasure patterns (erasure model). We present an explicit intrasession code
construction that is asymptotically optimal under erasure models containing a
limited number of erasures per coding window, per sliding window, and
containing erasure bursts of a limited length.Comment: Extended version of a conference paper in the IEEE International
Symposium on Information Theory (ISIT), July 2012. 12 pages, 3 figure
Mass Predictions of Open-Flavour Hybrid Mesons from QCD Sum Rules
Within QCD, colourless states may be constructed corresponding to exotic
matter outside of the traditional quark model. Experiments have recently
observed tetraquark and pentaquark states, but no definitive hybrid meson
signals have been observed. With the construction of the PANDA experiment at
FAIR, and with full commissioning of the GlueX experiment at JLab expected to
be completed this year, the opportunity for the observation of hybrid mesons
has greatly increased. However, theoretical calculations are necessary to
ascertain the identity of any experimental resonances that may be observed. We
present selected QCD sum rule results from a full range of quantum numbers for
open-flavour hybrid mesons with heavy valence quark content, including
non-perturbative condensate contributions up to six-dimensions.Comment: Formatted from poster presented at 38th International Conference on
High Energy Physics, 3-10 August 2016, Chicago, USA. 4 pages, 1 table and 2
figures. Submitted for publication in Proceedings of Science as
PoS(ICHEP2016)849. Original poster attache
Symmetric Allocations for Distributed Storage
We consider the problem of optimally allocating a given total storage budget
in a distributed storage system. A source has a data object which it can code
and store over a set of storage nodes; it is allowed to store any amount of
coded data in each node, as long as the total amount of storage used does not
exceed the given budget. A data collector subsequently attempts to recover the
original data object by accessing each of the nodes independently with some
constant probability. By using an appropriate code, successful recovery occurs
when the total amount of data in the accessed nodes is at least the size of the
original data object. The goal is to find an optimal storage allocation that
maximizes the probability of successful recovery. This optimization problem is
challenging because of its discrete nature and nonconvexity, despite its simple
formulation. Symmetric allocations (in which all nonempty nodes store the same
amount of data), though intuitive, may be suboptimal; the problem is nontrivial
even if we optimize over only symmetric allocations. Our main result shows that
the symmetric allocation that spreads the budget maximally over all nodes is
asymptotically optimal in a regime of interest. Specifically, we derive an
upper bound for the suboptimality of this allocation and show that the
performance gap vanishes asymptotically in the specified regime. Further, we
explicitly find the optimal symmetric allocation for a variety of cases. Our
results can be applied to distributed storage systems and other problems
dealing with reliability under uncertainty, including delay tolerant networks
(DTNs) and content delivery networks (CDNs).Comment: 7 pages, 3 figures, extended version of an IEEE GLOBECOM 2010 pape
Aspects of Floquet Bands and Topological Phase Transitions in a Continuously Driven Superlattice
Recently the creation of novel topological states of matter by a periodic
driving field has attracted great attention. To motivate further experimental
and theoretical studies, we investigate interesting aspects of Floquet bands
and topological phase transitions in a continuously driven Harper model. In
such a continuously driven system with an odd number of Floquet bands, the
bands are found to have nonzero Chern numbers in general and topological phase
transitions take place as we tune various system parameters, such as the
amplitude or the period of the driving field. The nontrivial Floquet band
topology results in a quantized transport of Wannier states in the lattice
space. For certain parameter choices, very flat yet topologically nontrivial
Floquet bands may also emerge, a feature that is potentially useful for the
simulation of physics of strongly correlated systems. Some cases with an even
number of Floquet bands may also have intriguing Dirac cones in the spectrum.
Under open boundary conditions, anomalous counter-propagating chiral edge modes
and degenerate zero modes are also found as the system parameters are tuned.
These results should be of experimental interest because a continuously driven
system is easier to realize than a periodically kicked system.Comment: 29 pages, 9 figures. Comments are welcom
Optimal content delivery with network coding
We present a unified linear program formulation for optimal content delivery in content delivery networks (CDNs), taking into account various costs and constraints associated with content dissemination from the origin server to storage nodes, data storage, and the eventual fetching of content from storage nodes by end users. Our formulation can be used to achieve a variety of performance goals and system behavior, including the bounding of fetch delay, load balancing, and robustness against node and arc failures. Simulation results suggest that our formulation performs significantly better than the traditional minimum k-median formulation for the delivery of multiple content, even under modest circumstances (small network, few objects, low storage budget, low dissemination costs)
Quantized Adiabatic Transport in Momentum Space
Though topological aspects of energy bands are known to play a key role in
quantum transport in solid-state systems, the implications of Floquet band
topology for transport in momentum space (i.e., acceleration) are not explored
so far. Using a ratchet accelerator model inspired by existing cold-atom
experiments, here we characterize a class of extended Floquet bands of
one-dimensional driven quantum systems by Chern numbers, reveal topological
phase transitions therein, and theoretically predict the quantization of
adiabatic transport in momentum space. Numerical results confirm our theory and
indicate the feasibility of experimental studies.Comment: Main text of 11 pages plus Appendix of 13 pages. To appear in Phys.
Rev. Let
Distributed Storage Allocation Problems
We investigate the problem of using
several storage nodes to store a data object, subject
to an aggregate storage budget or redundancy constraint.
It is challenging to find the optimal allocation
that maximizes the probability of successful recovery
by the data collector because of the large space of possible
symmetric and nonsymmetric allocations, and
the nonconvexity of the problem. For the special case
of probability-l recovery, we show that the optimal
allocation that minimizes the required budget is symmetric.
We further explore several storage allocation
and access models, and determine the optimal symmetric
allocation in the high-probability regime for a
case of interest. Based on our experimental investigation,
we make a general conjecture about a phase
transition on the optimal allocation
- …