A generalization of bounds for cyclic codes, including the HT and BS bounds

We use the algebraic structure of cyclic codes and some properties of the discrete Fourier transform to give a reformulation of several classical bounds for the distance of cyclic codes, by extending techniques of linear algebra. We propose a bound, whose computational complexity is polynomial bounded, which is a generalization of the Hartmann-Tzeng bound and the Betti-Sala bound. In the majority of computed cases, our bound is the tightest among all known polynomial-time bounds, including the Roos bound

Formation of offshore tidal sandbanks triggered by a gasmined bed subsidence

Offshore gasmining is an example of a human intervention with a morphological impact. On land, it is usually attended with a dish-like bed depression. We show that, if located at sea, such a bed depression can become morphodynamically active by triggering mechanisms related to tidal sand bank formation. To that end, a simple morphological model is considered which describes an erodible bed subject to a tidal wave in a shallow sea. The continuous subsidence is modelled by a sink term in the sediment balance. Then, a linear approximation is carried out to describe the bed evolution after the onset of subsidence. The results, presented in physical space, show that the subsidence triggers the formation of a sand bank pattern that gradually spreads around the centre of subsidence, at a rate that may go up to 160 m year¿1, depending on the tidal transport rate and the tidal eccentricity. The dimension of the depression does not affect the spreading rate nor the orientation of the sand banks, but it does influence their spacing. The main conclusion is that the horizontal extent of the area influenced by the bed depression by far exceeds that of the direct subsidence, thus showing that bed depressions on land and at sea indeed behave in fundamentally different ways. The results suggest that nonlinear effects are worthwhile to be investigated in order to describe finite amplitude development of sand banks as well as the interaction between subsidence and bed forms