hwloc: a Generic Framework for Managing Hardware Affinities in HPC Applications

International audienceThe increasing numbers of cores, shared caches and memory nodes within machines introduces a complex hardware topology. High-performance computing applications now have to carefully adapt their placement and behavior according to the underlying hierarchy of hardware resources and their software affinities. We introduce the Hardware Locality (hwloc) software which gathers hardware information about processors, caches, memory nodes and more, and exposes it to applications and runtime systems in a abstracted and portable hierarchical manner. hwloc may significantly help performance by having runtime systems place their tasks or adapt their communication strategies depending on hardware affinities. We show that hwloc can already be used by popular high-performance OpenMP or MPI software. Indeed, scheduling OpenMP threads according to their affinities or placing MPI processes according to their communication patterns shows interesting performance improvement thanks to hwloc. An optimized MPI communication strategy may also be dynamically chosen according to the location of the communicating processes in the machine and its hardware characteristics

Toward an Understanding of the Microstructure and Interfacial Properties of PIMs/ZIF-8 Mixed Matrix Membranes

A study integrating advanced experimental and modeling tools was undertaken to characterize the microstructural and interfacial properties of mixed matrix membranes (MMMs) composed of the zeolitic imidazolate framework ZIF-8 nanoparticles (NPs) and two polymers of intrinsic microporosity (PIM-1 and PIM-EA-TB). Analysis probed both the initial ZIF-8/PIM-1 colloidal suspensions and the final hybrid membranes. By combination of dynamic light scattering (DLS) and transmission electron microscopy (TEM) analytical and imaging techniques with small-angle X-ray scattering (SAXS), the colloidal suspensions were shown to consist mainly of two distinct kinds of particles, namely, polymer aggregates of about 200 nm in diameter and densely packed ZIF-8-NP aggregates of a few 100 nm in diameter with a 3 nm thick polymer top-layer. Such aggregates are likely to impart the granular texture of ZIF-8/PIMs MMMs as shown by SEM-XEDS analysis. At the molecular scale, modeling studies showed that the surface coverage of ZIF-8 NPs by both polymers appears not to be optimal with the presence of microvoids at the interfaces that indicates only a moderate compatibility between the polymer and ZIF-8. This study shows that the microstructure of MMMs results from a complex interplay between the ZIF-8/PIM compatibility, solvent, surface chemistry of the ZIF-8 NPs, and the physicochemical properties of the polymers such as molecular structure and rigidity

Raman spectroscopy for materials and catalysts analysis

SéminaireInternational audienc

Discriminating molybdate and tungstate layered materials by operando Raman spectroscopy at the solid-liquid interface

International audienceIn order to perform the characterization of liquid phase reactions catalysed by solid materials, several methodologies were developed using Raman spectroscopy. By following both the liquid and the solid-liquid interface, several layered materials could be discriminated. Indeed, molybdates or tungstates layered mixed oxides (with Nb or Ta oxides) show acidic properties that can catalyse several reactions including the conversion of polyalcohols. Therefore, these catalysts were extensively characterized not only initially to highlight their acidity and their capacity to favour molecular intercalation within their interlayers, but also to evaluate and monitor the catalysts under operando conditions. Layered molybdates, and HNbMoO6 in particular, proved to outperform the equivalent tungstates in hexanediol cyclodehydration, while tantalates were very similar to niobates. Our results show that while the moderate acidity of the molybdates is sufficient to perform this reaction, the overall catalytic activity is rather directly influenced by the accessibility of the reactant to the active sites in the interlayer

A comparison of layered materials used as catalysts for diols conversion

International audienc

Simultaneous monitoring of acidity and intercalation for layered transition metal oxides in liquid media

International audienceLayered transition metal oxides have a potential as catalysts for biomass conversions or as adsorbents. A better understanding of their properties is thus necessary, notably in liquid phase, where these materials have the specificity to intercalate molecules within their interlayers. To discriminate between potential catalysts or adsorbents, it is desirable to study the surface properties in the conditions of intercalation. The intercalation behaviour and acidity of four different acidic layered materials: pure tungstate phases H2W2O7, H2WO4 and mixed oxides HNbWO6 and HNbMoO6 have thus been investigated directly in liquid phase. Besides Powder X-ray diffraction, Raman spectroscopy provided valuable informations first during the preliminary protonation step and second by monitoring both the intercalation of liquid organic bases and the accessible acidity. N-alkylamines such as butylamine and octylamine were found unsuitable to discriminate the layered solids while pyridine was more selective. Pyridine did not intercalate in H2W2O7, highlighting also the lower acidity of this solid, but gave rise to new Raman features for H2WO4, HNbMoO6 and HNbWO6. Lewis and Brønsted acid sites could be discriminated from the perturbation of the inorganic layers and related to surface sites. Therefore, the characterization by Raman spectroscopy in conditions of liquid intercalation proves to efficiently evaluate layered materials

Quantitative IR characterization of the acidity of various oxide catalysts

International audienceThe integrated molar absorption coefficients of the infrared bands characteristic of adsorbed lutidine (2,6-dimethylpyridine) were determined for the purpose of quantifying the acid sites of solid catalysts. The integrated molar absorption coefficients were measured for lutidine adsorbed through H-bonding, coordination to Lewis sites and protonation on Brønsted acid sites. The solids were chosen to present all possible bondings with lutidine and to cover a wide range of common types of catalysts or supports: silica, phosphated silica, HY zeolite, alumina, zirconia, WOx supported on zirconia and NbOx supported on zirconi

A comparison of layered materials used as catalysts for diols conversion

International audienc

Caractérisation des catalyseurs hétérogènes par réactions modèles

International audienc

Caractérisation des catalyseurs hétérogènes par réactions modèles

International audienc