3,506 research outputs found
Linear Programming Decoding of Spatially Coupled Codes
For a given family of spatially coupled codes, we prove that the LP threshold
on the BSC of the graph cover ensemble is the same as the LP threshold on the
BSC of the derived spatially coupled ensemble. This result is in contrast with
the fact that the BP threshold of the derived spatially coupled ensemble is
believed to be larger than the BP threshold of the graph cover ensemble as
noted by the work of Kudekar et al. (2011, 2012). To prove this, we establish
some properties related to the dual witness for LP decoding which was
introduced by Feldman et al. (2007) and simplified by Daskalakis et al. (2008).
More precisely, we prove that the existence of a dual witness which was
previously known to be sufficient for LP decoding success is also necessary and
is equivalent to the existence of certain acyclic hyperflows. We also derive a
sublinear (in the block length) upper bound on the weight of any edge in such
hyperflows, both for regular LPDC codes and for spatially coupled codes and we
prove that the bound is asymptotically tight for regular LDPC codes. Moreover,
we show how to trade crossover probability for "LP excess" on all the variable
nodes, for any binary linear code.Comment: 37 pages; Added tightness construction, expanded abstrac
On a new algorithm for time step integration of nonlinear systems
A new implicit algorithm for time step integration of finite element structural dynamic equations is presented. Convergence, stability and numerical damping properties are discussed. Due to the way nonlinear structural behavior is taken into account, the algorithm is expected to compare favorably with existing ones. Some simple numerical results are presented. A related explicit algorithm is also derived and shortly discussed
Calculations of nuclear quasi-bound states based on chiral meson-baryon amplitudes
In-medium scattering amplitudes developed within a new chirally
motivated coupled-channel model due to Cieply and Smejkal that fits the recent
SIDDHARTA kaonic hydrogen 1s level shift and width are used to construct
nuclear potentials for calculations of nuclear quasi-bound states. The
strong energy and density dependence of scattering amplitudes at and near
threshold leads to potential depths MeV.
Self-consistent calculations of all nuclear quasi-bound states, including
excited states, are reported. Model dependence, polarization effects, the role
of p-wave interactions, and two-nucleon absorption modes
are discussed. The absorption widths are comparable or even
larger than the corresponding binding energies for all nuclear
quasi-bound states, exceeding considerably the level spacing. This discourages
search for nuclear quasi-bound states in any but lightest nuclear
systems.Comment: 12 pages, 11 figure
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