1,761 research outputs found
Kovalenko's Full-Rank Limit and Overhead as Lower Bounds for Error-Performances of LDPC and LT Codes over Binary Erasure Channels
We present Kovalenko's full-rank limit as a tight lower bound for decoding
error probability of LDPC codes and LT codes over BEC. From the limit, we
derive a full-rank overhead as a lower bound for stable overheads for
successful maximum-likelihood decoding of the codes.Comment: A short version of this paper was presented at ISITA 2008, Auckland
NZ. The first draft was submitted to IEEE Transactions on Information Theory,
2008/0
Anomalous response in the vicinity of spontaneous symmetry breaking
We propose a mechanism to induce negative AC permittivity in the vicinity of
a ferroelectric phase transition involved with spontaneous symmetry breaking.
This mechanism makes use of responses at low frequency, yielding a high gain
and a large phase delay, when the system jumps over the free-energy barrier
with the aid of external fields. We illustrate the mechanism by analytically
studying spin models with the Glauber-typed dynamics under periodic
perturbations. Then, we show that the scenario is supported by numerical
simulations of mean-field as well as two-dimensional spin systems.Comment: 6 pages, 5 figure
Generalized gravity model for human migration
The gravity model (GM) analogous to Newton's law of universal gravitation has
successfully described the flow between different spatial regions, such as
human migration, traffic flows, international economic trades, etc. This simple
but powerful approach relies only on the 'mass' factor represented by the scale
of the regions and the 'geometrical' factor represented by the geographical
distance. However, when the population has a subpopulation structure
distinguished by different attributes, the estimation of the flow solely from
the coarse-grained geographical factors in the GM causes the loss of
differential geographical information for each attribute. To exploit the full
information contained in the geographical information of subpopulation
structure, we generalize the GM for population flow by explicitly harnessing
the subpopulation properties characterized by both attributes and geography. As
a concrete example, we examine the marriage patterns between the bride and the
groom clans of Korea in the past. By exploiting more refined geographical and
clan information, our generalized GM properly describes the real data, a part
of which could not be explained by the conventional GM. Therefore, we would
like to emphasize the necessity of using our generalized version of the GM,
when the information on such nongeographical subpopulation structures is
available.Comment: 14 pages, 6 figures, 2 table
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