225,595 research outputs found
Density Criteria for the Identification of Linear Time-Varying Systems
This paper addresses the problem of identifying a linear time-varying (LTV)
system characterized by a (possibly infinite) discrete set of delays and
Doppler shifts. We prove that stable identifiability is possible if the upper
uniform Beurling density of the delay-Doppler support set is strictly smaller
than 1/2 and stable identifiability is impossible for densities strictly larger
than 1/2. The proof of this density theorem reveals an interesting relation
between LTV system identification and interpolation in the Bargmann-Fock space.
Finally, we introduce a subspace method for solving the system identification
problem at hand.Comment: IEEE International Symposium on Information Theory (ISIT), Hong Kong,
China, June 201
Towards Real-Time Detection and Tracking of Spatio-Temporal Features: Blob-Filaments in Fusion Plasma
A novel algorithm and implementation of real-time identification and tracking
of blob-filaments in fusion reactor data is presented. Similar spatio-temporal
features are important in many other applications, for example, ignition
kernels in combustion and tumor cells in a medical image. This work presents an
approach for extracting these features by dividing the overall task into three
steps: local identification of feature cells, grouping feature cells into
extended feature, and tracking movement of feature through overlapping in
space. Through our extensive work in parallelization, we demonstrate that this
approach can effectively make use of a large number of compute nodes to detect
and track blob-filaments in real time in fusion plasma. On a set of 30GB fusion
simulation data, we observed linear speedup on 1024 processes and completed
blob detection in less than three milliseconds using Edison, a Cray XC30 system
at NERSC.Comment: 14 pages, 40 figure
Paradoxical Interpretations of Urban Scaling Laws
Scaling laws are powerful summaries of the variations of urban attributes
with city size. However, the validity of their universal meaning for cities is
hampered by the observation that different scaling regimes can be encountered
for the same territory, time and attribute, depending on the criteria used to
delineate cities. The aim of this paper is to present new insights concerning
this variation, coupled with a sensitivity analysis of urban scaling in France,
for several socio-economic and infrastructural attributes from data collected
exhaustively at the local level. The sensitivity analysis considers different
aggregations of local units for which data are given by the Population Census.
We produce a large variety of definitions of cities (approximatively 5000) by
aggregating local Census units corresponding to the systematic combination of
three definitional criteria: density, commuting flows and population cutoffs.
We then measure the magnitude of scaling estimations and their sensitivity to
city definitions for several urban indicators, showing for example that simple
population cutoffs impact dramatically on the results obtained for a given
system and attribute. Variations are interpreted with respect to the meaning of
the attributes (socio-economic descriptors as well as infrastructure) and the
urban definitions used (understood as the combination of the three criteria).
Because of the Modifiable Areal Unit Problem and of the heterogeneous
morphologies and social landscapes in the cities internal space, scaling
estimations are subject to large variations, distorting many of the conclusions
on which generative models are based. We conclude that examining scaling
variations might be an opportunity to understand better the inner composition
of cities with regard to their size, i.e. to link the scales of the city-system
with the system of cities
Mathematical control of complex systems
Copyright © 2013 ZidongWang et al.This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
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