Quasicrystals, model sets, and automatic sequences

We survey mathematical properties of quasicrystals, first from the point of view of harmonic analysis, then from the point of view of morphic and automatic sequences. Nous proposons un tour d'horizon de propri\'et\'es math\'ematiques des quasicristaux, d'abord du point de vue de l'analyse harmonique, ensuite du point de vue des suites morphiques et automatiques

Compresión de datos y restauración de imágenes con ruido según David Donoho

Las ondículas ofrecen interesantes posibilidades en el tratamiento eliminación del ruido de señales e imágenes y forman una base incondicional universal apta para todos los espacios de Besov, los cuales prevén una descripción detallada y precisa de ciertas clases de señales e imágenes permitiendo evaluar la calidad de la imagen reconstruida tras la compresión no lineal. Los algoritmos de compresión óptima están en el corazón de los problemas de eliminación de ruido no lineal. Se presenta una descripción de los descubrimientos de Donoho sobre imágenes de tipo geométrico. El reto consiste en encontrar una base ortonormal privilegiada del espacio de señales de energía finit

Crystalline measures in two dimensions

Some crystalline measures supported by a Delone set Λ ⊂ R2 are constructed in this note. This gives a new proof of a remarkable theorem by Pavel Kurasov and Peter Sarnak

From Salomon Bochner to Dan Shechtman

Any locally finite set Λ ⊂ R n which satisfies Bochner's property is a coherent set of frequencies. The proof of this result is based on the properties of the harmonic coherence score of a locally finite set Λ

Bees, farmers, tourists and hunters: conflict dynamics around Western Tanzania protected areas

Following important donor funding in Tanzania since the 1990s to support community based natural resource management, several cooperation agencies have implemented projects aiming at developing innovative conservation strategies combining protected and sustainable use areas. Based on data gathered in the Katavi Rukwa Lukwati and Ugalla core areas of Western Tanzania, this paper compares and analyses how projects developed their strategy and objectives to address conflicts between local population and conservation agents, and how this led to changes in conservation practices. The projects managed to achieve their objectives in conservation and poverty reduction at various degrees. Enhanced conflict resolution capacity involving private stakeholders, conservation agents and local communities, as well as improved collaboration between projects, helped to solve part of the conflicts. This was the case with the negotiation of rights of access for beekeepers to Rukwa game reserve. However, enduring sector based approaches continue to hinder opportunities for developing multiple use approaches. Contrasted results of the projects can be explained by factors inherent to projects' planning and management, but also by factors that are beyond projects' influence such as the historical and contemporary context in terms of governance of natural resources and more globally, of power relationships between the state, private organisations and the communitie

Purification and characterization of a three-component salicylate 1-hydroxylase from Sphingomonas CHY-1

International audienceIn the bacterial degradation of polycyclic aromatic hydrocarbons (PAHs), salicylate hydroxylases catalyze essential reactions at the junction between the so-called upper and lower catabolic pathways. Unlike the salicylate 1-hydroxylase from pseudomonads, which is a well-characterized flavoprotein, the enzyme found in sphingomonads appears to be a three-component Fe-S protein complex, which has not so far been characterized. Here, the salicylate 1-hydroxylase from Sphingomonas CHY-1 has been purified and characterized with respect to its biochemical and catalytic properties. The oxygenase component called PhnII, exhibited an α3β3 heterohexameric structure and contained one Rieske-type [2Fe-2S] cluster and one mononuclear iron per α subunit. In the presence of purified reductase (PhnA4) and ferredoxin (PhnA3) components, PhnII catalyzed the hydroxylation of salicylate to catechol with a maximal specific activity of 0.89 U/mg and showed an apparent Km for salicylate of 1.1 ± 0.2 µM. The hydroxylase exhibited similar activity levels with methylsalicylates and low activity with salicylate analogues bearing additional hydroxyl or electron-withdrawing substituents. PhnII converted anthranilate to 2-aminophenol and exhibited a relatively low affinity for this substrate (Km = 28 ± 6 µM). 1-Hydroxy-2-naphthoate, which is an intermediate in phenanthrene degradation, was not hydroxylated by PhnII, but induced a high rate of uncoupled oxidation of NADH. It also exerted a strong competitive inhibition of salicylate hydroxylation, with a Ki of 0.68 µM. The properties of this three-component hydroxylase are compared with those of analogous bacterial hydroxylases and discussed in the light of our current knowledge of PAH degradation by sphingomonads

Dihydroxylation of four- and five-ring aromatic hydrocarbons by the naphthalene dioxygenase from Sphingomonas CHY-1

International audienceThe naphthalene dioxygenase from Sphingomonas CHY-1 exhibits extremely broad substrate specificity toward polycyclic aromatic hydrocarbons (PAHs). In a previous study, the catalytic rates of oxidation of 9 PAHs were determined using the purified dioxygenase, but the oxidation products formed from 4- to 5-ring hydrocarbons were incompletely characterized. Here, we reexamined PAH oxygenation reactions using Escherichia coli recombinant cells overproducing strain CHY-1 dioxygenase. Hydroxylated products generated by the dioxygenase were purified, and characterized by means of GC-MS, UV absorbance as well as 1H and 13C-NMR spectroscopy. Fluoranthene was converted to 3 dihydrodiols, the most abundant of which was identified as cis-7,8-dihydroxy-7,8-dihydrofluoranthene. This diol turned out to be highly unstable, converting to 8-hydroxyfluoranthene by spontaneous dehydration. The dioxygenase also catalyzed dihydroxylations on the C2-C3, and presumably the C1-C2 positions, although at much lower rates. Benz[a]anthracene was converted into three dihydrodiols, hydroxylated in positions C1-C2, C8-C9 and C10-C11, and one bis-cis-dihydrodiol. The latter compound was identified as cis,cis-1,2,10,11-tetrahydroxy-1,2,10,11-tetrahydrobenz[a]anthracene, which resulted from the subsequent dioxygenation of the 1,2- or 10,11-dihydrodiols. Chrysene dioxygenation yielded a single diol identified as cis-3,4-dihydroxy-3,4-dihydrochrysene, which underwent further oxidation to give cis,cis-3,4,9,10 chrysene tetraol. Pyrene was a poor substrate for the CHY-1 dioxygenase and gave a single dihydrodiol hydroxylated on C4 and C5, whereas benzo[a}pyrene was converted to two dihydrodiols, one of which was identified as cis-9,10-dihydrodiol. The selectivity of the dioxygenase is discussed in the light of the known 3D structure of its catalytic component, and compared to that of the few enzymes able to attack 4- and 5-ring PAHs