417 research outputs found
Dimers and cluster integrable systems
We show that the dimer model on a bipartite graph on a torus gives rise to a
quantum integrable system of special type - a cluster integrable system. The
phase space of the classical system contains, as an open dense subset, the
moduli space of line bundles with connections on the graph. The sum of
Hamiltonians is essentially the partition function of the dimer model. Any
graph on a torus gives rise to a bipartite graph on the torus. We show that the
phase space of the latter has a Lagrangian subvariety. We identify it with the
space parametrizing resistor networks on the original graph.We construct
several discrete quantum integrable systems.Comment: This is an updated version, 75 pages, which will appear in Ann. Sci.
EN
Semiclassical analysis of Wigner -symbol
We analyze the asymptotics of the Wigner -symbol as a matrix element
connecting eigenfunctions of a pair of integrable systems, obtained by lifting
the problem of the addition of angular momenta into the space of Schwinger's
oscillators. A novel element is the appearance of compact Lagrangian manifolds
that are not tori, due to the fact that the observables defining the quantum
states are noncommuting. These manifolds can be quantized by generalized
Bohr-Sommerfeld rules and yield all the correct quantum numbers. The geometry
of the classical angular momentum vectors emerges in a clear manner. Efficient
methods for computing amplitude determinants in terms of Poisson brackets are
developed and illustrated.Comment: 7 figure file
Source Coding Optimization for Distributed Average Consensus
Consensus is a common method for computing a function of the data distributed
among the nodes of a network. Of particular interest is distributed average
consensus, whereby the nodes iteratively compute the sample average of the data
stored at all the nodes of the network using only near-neighbor communications.
In real-world scenarios, these communications must undergo quantization, which
introduces distortion to the internode messages. In this thesis, a model for
the evolution of the network state statistics at each iteration is developed
under the assumptions of Gaussian data and additive quantization error. It is
shown that minimization of the communication load in terms of aggregate source
coding rate can be posed as a generalized geometric program, for which an
equivalent convex optimization can efficiently solve for the global minimum.
Optimization procedures are developed for rate-distortion-optimal vector
quantization, uniform entropy-coded scalar quantization, and fixed-rate uniform
quantization. Numerical results demonstrate the performance of these
approaches. For small numbers of iterations, the fixed-rate optimizations are
verified using exhaustive search. Comparison to the prior art suggests
competitive performance under certain circumstances but strongly motivates the
incorporation of more sophisticated coding strategies, such as differential,
predictive, or Wyner-Ziv coding.Comment: Master's Thesis, Electrical Engineering, North Carolina State
Universit
Journal Maps, Interactive Overlays, and the Measurement of Interdisciplinarity on the Basis of Scopus Data (1996-2012)
Using Scopus data, we construct a global map of science based on aggregated
journal-journal citations from 1996-2012 (N of journals = 20,554). This base
map enables users to overlay downloads from Scopus interactively. Using a
single year (e.g., 2012), results can be compared with mappings based on the
Journal Citation Reports at the Web-of-Science (N = 10,936). The Scopus maps
are more detailed at both the local and global levels because of their greater
coverage, including, for example, the arts and humanities. The base maps can be
interactively overlaid with journal distributions in sets downloaded from
Scopus, for example, for the purpose of portfolio analysis. Rao-Stirling
diversity can be used as a measure of interdisciplinarity in the sets under
study. Maps at the global and the local level, however, can be very different
because of the different levels of aggregation involved. Two journals, for
example, can both belong to the humanities in the global map, but participate
in different specialty structures locally. The base map and interactive tools
are available online (with instructions) at
http://www.leydesdorff.net/scopus_ovl.Comment: accepted for publication in the Journal of the Association for
Information Science and Technology (JASIST
Cooperative high-performance computing with FPGAs - matrix multiply case-study
In high-performance computing, there is great opportunity for systems
that use FPGAs to handle communication while also performing
computation on data in transit in an ``altruistic'' manner--that is,
using resources for computation that might otherwise be used for
communication, and in a way that improves overall system performance
and efficiency. We provide a specific definition of \textbf{Computing
in the Network} that captures this opportunity. We then outline some
overall requirements and guidelines for cooperative computing that
include this ability, and make suggestions for specific computing
capabilities to be added to the networking hardware in a system. We
then explore some algorithms running on a network so equipped
for a few specific computing tasks: dense matrix multiplication,
sparse matrix transposition and sparse matrix multiplication. In the
first instance we give limits of problem size and estimates of
performance that should be attainable with present-day FPGA hardware
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