An efficient length- and rate-preserving concatenation of polar and repetition codes

We improve the method in \cite{Seidl:10} for increasing the finite-lengh performance of polar codes by protecting specific, less reliable symbols with simple outer repetition codes. Decoding of the scheme integrates easily in the known successive decoding algorithms for polar codes. Overall rate and block length remain unchanged, the decoding complexity is at most doubled. A comparison to related methods for performance improvement of polar codes is drawn.Comment: to be presented at International Zurich Seminar (IZS) 201

Teolenn: an efficient and customizable workflow to design high-quality probes for microarray experiments

Despite the development of new high-throughput sequencing techniques, microarrays are still attractive tools to study small genome organisms, thanks to sample multiplexing and high-feature densities. However, the oligonucleotide design remains a delicate step for most users. A vast array of software is available to deal with this problem, but each program is developed with its own strategy, which makes the choice of the best solution difficult. Here we describe Teolenn, a universal probe design workflow developed with a flexible and customizable module organization allowing fixed or variable length oligonucleotide generation. In addition, our software is able to supply quality scores for each of the designed probes. In order to assess the relevance of these scores, we performed a real hybridization using a tiling array designed against the Trichoderma reesei fungus genome. We show that our scoring pipeline correlates with signal quality for 97.2% of all the designed probes, allowing for a posteriori comparisons between quality scores and signal intensities. This result is useful in discarding any bad scoring probes during the design step in order to get high-quality microarrays. Teolenn is available at http://transcriptome.ens.fr/teolenn/

Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating

We model the photoelectric emission from and charging of interstellar dust and obtain photoelectric gas heating efficiencies as a function of grain size and the relevant ambient conditions. Using realistic grain size distributions, we evaluate the net gas heating rate for various interstellar environments, and find less heating for dense regions characterized by R_V=5.5 than for diffuse regions with R_V=3.1. We provide fitting functions which reproduce our numerical results for photoelectric heating and recombination cooling for a wide range of interstellar conditions. In a separate paper we will examine the implications of these results for the thermal structure of the interstellar medium. Finally, we investigate the potential importance of photoelectric heating in H II regions, including the warm ionized medium. We find that photoelectric heating could be comparable to or exceed heating due to photoionization of H for high ratios of the radiation intensity to the gas density. We also find that photoelectric heating by dust can account for the observed variation of temperature with distance from the galactic midplane in the warm ionized medium.Comment: 50 pages, including 18 figures; corrected title and abstract field

A comprehensive set of simulations of high-velocity collisions between main sequence stars

We report on a very large set of simulations of collisions between two main sequence (MS) stars. These computations were done with the ``Smoothed Particle Hydrodynamics'' method. Realistic stellar structure models for evolved MS stars were used. In order to sample an extended domain of initial parameters space (masses of the stars, relative velocity and impact parameter), more than 15000 simulations were carried out. We considered stellar masses ranging between 0.1 and 75 Msun and relative velocities up to a few thousands km/s. To limit the computational burden, a resolution of 2000-30000 particles per star was used. The primary goal of this study was to build a complete database from which the result of any collision can be interpolated. This allows us to incorporate the effects of stellar collisions with an unprecedented level of realism into dynamical simulations of galactic nuclei and other dense stellar clusters. We make the data describing the initial condition and outcome (mass and energy loss, angle of deflection) of all our simulations freely available on the Internet. We find that the outcome of collisions depends sensitively on the stellar structure and that, in most cases, using polytropic models is inappropriate. Published fitting formulas for the collision outcomes, established from a limited set of collisions, prove of limited use because they do not allow robust extrapolation to other stellar structures or relative velocities.Comment: 45 pages, 44 figures. Modified to reflect the changes in the published version (MNRAS). PDF version with high-res figures at http://obswww.unige.ch/~freitag/papers/article_collisions.pdf, simulation data at http://obswww.unige.ch/~freitag/MODEST_WG4/FB_Collision_Data/, movies at http://obswww.unige.ch/~freitag/collisions/animations/index.htm

Aspekte von Polar Coding mit endlichen Blocklängen

Polar coding, introduced in 2008 by E. Arikan, is known as the first explicit error correction coding construction that is able to approach the capacity of symmmetric memoryless channels arbitrarily close (with increasing block length) while using a low-complexity successive decoding algorithm of order N log(N). Since then, the asymptotic properties of polar coding at large block lengths have been subject of much scientific research. In this thesis, we have put the focus on polar coding at finite block lengths instead. We explore the potential of polar coding as a practical channel coding scheme, draw comparisons to competing coding approaches and present methods for improving its performance. Moreover, we introduce an efficient coded-modulation approach for increased bandwidth efficiency that extends the concept of binary polar coding to higher-order modulation schemes.In dieser Dissertation wird ein erstmalig 2008 unter dem Namen Polar Coding vorgestelltes, neuartiges Verfahren zur blockbasierten Kanalcodierung untersucht. Im Unterschied zu etlichen Arbeiten über Polar Coding, die die asymptotischen Eigenschaften dieser Codierungsmethode für sehr große Blocklängen zum Gegenstand haben, legen wir hier den Schwerpunkt auf den praxisrelevanten Fall von Codes mit endlichen Blocklängen. Wir diskutieren verbesserte Ansätze zur Decodierung und untersuchen verschiedene Möglichkeiten der Verkettung von Polar Codes mit anderen codierungstheoretischen Konstruktionen. In diesem Zusammenhang vergleichen wir die Eigenschaften und die Leistungsfähigkeit von Polar Codes mit diversen in heutigen Kommunikationsstandards implementierten Methoden der Kanalcodierung. Des weiteren entwickeln wir ein effizientes Verfahren zur Verwendung von binären Polar Codes in Verbindung mit mehrstufigen Modulationsverfahren für erhöhte Bandbreiteneffizienz, das auf dem Konzept der codierten Modulation basiert