Contrôle artistique par édition de la propagation des rayons en photon mapping

National audiencePhysically based rendering with global illumination effects, has become a standard technique for high quality computer generated imagery. Nonetheless, being able to control the resulting picture so that it corresponds to the artist vision is still a tedious trial and error process. We introduce a path selection and edition metaphor, to give the artist a precise control over the final rendering without modifying the scene parameters. Starting from the identification of a lighting feature and its transcription in a path space regular expression, the proposed approach consists in selecting the corresponding light transport paths in 3D space and transforms them according to user defined operations.These operations affect both the geometry and the color spectrum of the paths.We demonstrate the wide range of control it permits on various lighting features, from low frequency color bleeding to high frequency caustics as well as view-dependent reflections.e rendu produisant des effets d'éclairement global est devenu un standard pour la synthèse d'image de haute qualité.Néanmoins, les graphistes ne peuvent éditer les images générées informatiquement qu'au prix d'un travail long et fastidieux sur la définition des sources de lumières et des matériaux de la scène 3D.Nous proposons une approche d'édition qui donne un contrôle précis sur le rendu final, sans modifier les paramètres de la scène 3D.À partir de l'identification d'un effet lumineux définie par une syntaxe d'interaction, l'approche consiste à sélectionner des chemins de transport lumineux et de les transformer suivant des opérations définies par le graphiste.Ces opérations sont des transformations sur la géométrie du transport lumineux ainsi que sur les spectres transportés par les chemins.Nous montrons la large gamme d'éditions que notre approche permet sur divers effets lumineux, allant des variations basses fréquences de diffusion indirecte de couleur, jusqu'aux variations hautes fréquences typiques des caustiques

Author Q and A with editor Phil Crockett Thomas and contributors on abolition science fiction

In this author Q&A, Rémy-Paulin Twahirwa speaks to editor Phil Crockett Thomas and contributors about their recent collection, Abolition Science Fiction, a collection of short science fiction stories written by activists and scholars involved in prison abolition and transformative justice in the UK

Taming denumerable Markov decision processes with decisiveness

Decisiveness has proven to be an elegant concept for denumerable Markov chains: it is general enough to encompass several natural classes of denumerable Markov chains, and is a sufficient condition for simple qualitative and approximate quantitative model checking algorithms to exist. In this paper, we explore how to extend the notion of decisiveness to Markov decision processes. Compared to Markov chains, the extra non-determinism can be resolved in an adversarial or cooperative way, yielding two natural notions of decisiveness. We then explore whether these notions yield model checking procedures concerning the infimum and supremum probabilities of reachability properties

Nonlinear evolution of the step meandering instability of a growing crystal surface

The growth of crystal surfaces, under non-equilibrium conditions, involves the displacement of mono-atomic steps by atom diffusion and atom incorporations into steps. The time-evolution of the growing crystal surface is thus governed by a free boundary value problem [known as the Burton--Cabrera--Franck model]. In the presence of an asymmetry of the kinetic coefficients [Erlich--Schwoebel barriers], ruling the rates of incorporation of atoms at each step, it has been shown that a train of straight steps is unstable to two dimensional transverse perturbations. This instability is now known as the Bales-Zangwill instability (meandering instability). We study the non-linear evolution of the step meandering instability that occurs on a crystalline vicinal surface under growth, in the absence of evaporation, in the limit of a weak asymmetry of atom incorporation at the steps. We derive a nonlinear amplitude equation displaying spatiotemporal coarsening. We characterize the self-similar solutions of this equation.Comment: 6 pages, submitted to Physica D, 200

Streptococcus halichoeri : Comparative Genomics of an Emerging Pathogen

Streptococcus halichoeri is an emerging pathogen with a variety of host species and zoonotic potential. It has been isolated from grey seals and other marine mammals as well as from human infections. Beginning in 2010, two concurrent epidemics were identified in Finland, in fur animals and domestic dogs, respectively. The fur animals suffered from a new disease fur animal epidemic necrotic pyoderma (FENP) and the dogs presented with ear infections with poor treatment response. S. halichoeri was isolated in both studies, albeit among other pathogens, indicating a possible role in the disease etiologies. The aim was to find a possible common origin of the fur animal and dog isolates and study the virulence factors to assess pathogenic potential. Isolates from seal, human, dogs, and fur animals were obtained for comparison. The whole genomes were sequenced from 20 different strains using the Illumina MiSeq platform and annotated using an automatic annotation pipeline RAST. The core and pangenomes were formed by comparing the genomes against each other in an all-against-all comparison. A phylogenetic tree was constructed using the genes of the core genome. Virulence factors were assessed using the Virulence Factor Database (VFDB) concentrating on the previously confirmed streptococcal factors. A core genome was formed which encompassed approximately half of the genes in Streptococcus halichoeri. The resulting core was nearly saturated and would not change significantly by adding more genomes. The remaining genes formed the pangenome which was highly variable and would still evolve after additional genomes. The results highlight the great adaptability of this bacterium possibly explaining the ease at which it switches hosts and environments. Virulence factors were also analyzed and were found primarily in the core genome. They represented many classes and functions, but the largest single category was adhesins which again supports the marine origin of this species.Peer reviewe

Differential ATAC-seq and ChIP-seq peak detection using ROTS

Changes in cellular chromatin states fine-tune transcriptional output and ultimately lead to phenotypic changes. Here we propose a novel application of our reproducibility-optimized test statistics (ROTS) to detect differential chromatin states (ATAC-seq) or differential chromatin modification states (ChIP-seq) between conditions. We compare the performance of ROTS to existing and widely used methods for ATAC-seq and ChIP-seq data using both synthetic and real datasets. Our results show that ROTS outperformed other commonly used methods when analyzing ATAC-seq data. ROTS also displayed the most accurate detection of small differences when modeling with synthetic data. We observed that two-step methods that require the use of a separate peak caller often more accurately called enrichment borders, whereas one-step methods without a separate peak calling step were more versatile in calling sub-peaks. The top ranked differential regions detected by the methods had marked correlation with transcriptional differences of the closest genes. Overall, our study provides evidence that ROTS is a useful addition to the available differential peak detection methods to study chromatin and performs especially well when applied to study differential chromatin states in ATAC-seq data. </p

The impact of high spatial frequency atmospheric distortions on weak lensing measurements

High precision cosmology with weak gravitational lensing requires a precise measure of the Point Spread Function across the imaging data where the accuracy to which high spatial frequency variation can be modelled is limited by the stellar number density across the field. We analyse dense stellar fields imaged at the Canada-France-Hawaii Telescope to quantify the degree of high spatial frequency variation in ground-based imaging Point Spread Functions and compare our results to models of atmospheric turbulence. The data shows an anisotropic turbulence pattern with an orientation independent of the wind direction and wind speed. We find the amplitude of the high spatial frequencies to decrease with increasing exposure time as $t^{-1/2}$, and find a negligibly small atmospheric contribution to the Point Spread Function ellipticity variation for exposure times $t>180$ seconds. For future surveys analysing shorter exposure data, this anisotropic turbulence will need to be taken into account as the amplitude of the correlated atmospheric distortions becomes comparable to a cosmological lensing signal on scales less than $\sim 10$ arcminutes. This effect could be mitigated, however, by correlating galaxy shear measured on exposures imaged with a time separation greater than 50 seconds, for which we find the spatial turbulence patterns to be uncorrelated.Comment: 9 pages, 7 figures, version accepted by MNRA

Gene expression and metabolite profiling of Populus euphratica growing in the Negev desert

BACKGROUND: Plants growing in their natural habitat represent a valuable resource for elucidating mechanisms of acclimation to environmental constraints. Populus euphratica is a salt-tolerant tree species growing in saline semi-arid areas. To identify genes involved in abiotic stress responses under natural conditions we constructed several normalized and subtracted cDNA libraries from control, stress-exposed and desert-grown P. euphratica trees. In addition, we identified several metabolites in desert-grown P. euphratica trees. RESULTS: About 14,000 expressed sequence tag (EST) sequences were obtained with a good representation of genes putatively involved in resistance and tolerance to salt and other abiotic stresses. A P. euphratica DNA microarray with a uni-gene set of ESTs representing approximately 6,340 different genes was constructed. The microarray was used to study gene expression in adult P. euphratica trees growing in the desert canyon of Ein Avdat in Israel. In parallel, 22 selected metabolites were profiled in the same trees. CONCLUSION: Of the obtained ESTs, 98% were found in the sequenced P. trichocarpa genome and 74% in other Populus EST collections. This implies that the P. euphratica genome does not contain different genes per se, but that regulation of gene expression might be different and that P. euphratica expresses a different set of genes that contribute to adaptation to saline growth conditions. Also, all of the five measured amino acids show increased levels in trees growing in the more saline soil