Weaknesses of Margulis and Ramanujan-Margulis low-density parity-check codes

We report weaknesses in two algebraic constructions of low-density parity-check codes based on expander graphs. The Margulis construction gives a code with near-codewords, which cause problems for the sum-product decoder; The Ramanujan-Margulis construction gives a code with low-weight codewords, which produce an error-floor. © 2004 Elsevier B.V.

Performance of low density parity check codes as a function of actual and assumed noise levels

We investigate how sensitive Gallager's codes are, when decoded by the sum-product algorithm, to the assumed noise level. We have found a remarkably simple function that fits the empirical results as a function of the actual noise level at both high and low noise levels. © 2004 Elsevier B.V.

Performance of low density parity check codes as a function of actual and assumed noise levels

We investigate how sensitive Gallager's codes are, when decoded by the sum-product algorithm, to the assumed noise level. We have found a remarkably simple function that fits the empirical results as a function of the actual noise level at both high and low noise levels. ©2003 Published by Elsevier Science B. V.

Weaknesses of margulis and ramanujan-margulis low-density parity-check codes

We report weaknesses in two algebraic constructions of low-density parity-check codes based on expander graphs. The Margulis construction gives a code with near-codewords, which cause problems for the sum-product decoder; The Ramanujan-Margulis construction gives a code with low-weight codewords, which produce an error-floor. ©2003 Published by Elsevier Science B. V.

Impact response of polyethylene nanocomposites

The quasi-static and dynamic behaviour of Linear Low Density Polyethylene (LLDPE) and two LLDPE nanocomposites were studied. Nanocomposites consisting of LLDPE filled with 1% carbon black and 0.5% nanoclay fillers, by weight, were considered. Under quasi-static tensile loading, an improvement in the energy absorbing capability was achieved by adding 1% carbon black fillers. However, during quasi-static puncture and dynamic impact loading, the advantage provided by the fillers was lost. Thermal softening due to adiabatic heating under high strain rate deformation and difference s in the state of stress are considered as reasons for this reduction. © 2011 Published by Elsevier Ltd.