Variable redundancy product coders

Variable redundancy error detection code

On Linear Product Codes and Their Duals Scientific Report No. 4

Tensor products of linear codes, and product codes with dual cyclic component code

Dense blocks of energetic ions driven by multi-petawatt lasers

Laser-driven ion accelerators have the advantages of compact size, high density, and short bunch duration over conventional accelerators. Nevertheless, it is still challenging to simultaneously enhance the yield and quality of laser-driven ion beams for practical applications. Here we propose a scheme to address this challenge via the use of emerging multi-petawatt lasers and a density-modulated target. The density-modulated target permits its ions to be uniformly accelerated as a dense block by laser radiation pressure. In addition, the beam quality of the accelerated ions is remarkably improved by embedding the target in a thick enough substrate, which suppresses hot electron refluxing and thus alleviates plasma heating. Particle-in-cell simulations demonstrate that almost all ions in a solid-density plasma of a few microns can be uniformly accelerated to about 25% of the speed of light by a laser pulse at an intensity around 1022 W/cm2. The resulting dense block of energetic ions may drive fusion ignition and more generally create matter with unprecedented high energy density.Comment: 18 pages, 4 figure

Frozen light in photonic crystals with degenerate band edge

Consider a plane monochromatic wave incident on a semi-infinite periodic structure. What happens if the normal component of the transmitted wave group velocity vanishes? At first sight, zero normal component of the transmitted wave group velocity simply implies total reflection of the incident wave. But we demonstrate that total reflection is not the only possible outcome. Instead, the transmitted wave can appear in the form of a frozen mode with very large diverging amplitude and either zero, or purely tangential energy flux. The field amplitude in the transmitted wave can exceed that of the incident wave by several orders of magnitude. There are two qualitatively different kinds of frozen mode regime. The first one is associated with a stationary inflection point of electromagnetic dispersion relation. This phenomenon has been analyzed in our previous publications. Now, our focus is on the frozen mode regime related to a degenerate photonic band edge. An advantage of this new phenomenon is that it can occur in much simpler periodic structures. This spectacular effect is extremely sensitive to the frequency and direction of propagation of the incident plane wave. These features can be very attractive in a variety practical applications, such as higher harmonic generation and wave mixing, light amplification and lasing, highly efficient superprizms, etc

Slow wave resonance in periodic stacks of anisotropic layers

We consider transmission band edge resonance in periodic layered structures involving birefringent layers. Previously we have shown that the presence of birefringent layers with misaligned in-plane anisotropy can dramatically enhance the performance of the photonic-crystal Fabry-Perot resonator. It allows to reduce its size by an order of magnitude without compromising on its performance. The key characteristic of the enhanced photonic-crystal cavity is that its Bloch dispersion relation displays a degenerate photonic band edge, rather than only regular ones. This can be realized in specially arranged stacks of misaligned anisotropic layers. On the down side, the presence of birefringent layers results in the Fabry-Perot resonance being coupled only with one (elliptic) polarization component of the incident wave, while the other polarization component is reflected back to space. In this paper we show how a small modification of the periodic layered array can solve the above fundamental problem and provide a perfect impedance match regardless of the incident wave polarization, while preserving the giant transmission resonance, characteristic of a degenerate photonic band edge. Both features are of critical importance for a variety of practical applications, including antennas, light amplification, optical and microwave filters, etc.Comment: To be submitted to Phys. Rev.

Nitrogen dynamics in the shallow groundwater of a riparian wetland zone of the Garonne, SW France: nitrate inputs, bacterial densities, organic matter supply and denitrification measurements

This study highlights the role of interactions between surface and sub-surface water of the riparian zone of a large river (the Garonne, SW France). Information is given about the role of surface water in supplying Dissolved Organic Carbon (DOC ) to the riparian zone for nitrate removal processes. The densities of bacteria (up to 3.3106 cell m L-1) in groundwater are strongly conditioned by the water moving during flood events. Total bacterial densities in groundwater were related to surface water bacterial densities. In sediment, total bacteria are attached mainly to fine particles (90 % in the fraction < 1 mm). Spatial variations in organic carbon and nitrate content in groundwater at the site studied are correlated with exchanges between the groundwater and the river, from the upstream to the downstream part of the meander. Total bacterial densities, nitrate and decressing organic carbon concentrations follow the same pattern. These results suggest that, in this kind of riparian wetland, nitrate from alluvial groundwater influenced by agricultural practices may be denitrified by bacteria in the presence of organic carbon from river surface water