Thermal stability of NO 2 ⋅ and NO⋅ radicals formed in an Al23 catalyst during its preparation from a nitrate precursor

During the preparation of alumina as a catalyst support from aluminium nitrates by precipitation with a NH₄OH base, NO ₂ ^⋅ radicals have been formed in the catalyst after calcination under air in the solid at different temperatures. These radicals remained stable until a calcination temperature of 800°C. When the calcined catalyst was degassed under vacuum above 300 °C, the NO ₂ ^⋅ was reduced to give NO^⋅ and O^- species which were both tightly trapped in the solid. These latter species remained stable until vacuum treatment at 800 °C. This revised version was published online in July 2006 with corrections to the Cover Date.     

CEVCLUS: evidential clustering with instance-level constraints for relational data

Recent advances in clustering consider incorporating background knowledge in the partitioning algorithm, using, e.g., pairwise constraints between objects. As a matter of fact, prior information, when available, often makes it possible to better retrieve meaningful clusters in data. Here, this approach is investigated in the framework of belief functions, which allows us to handle the imprecision and the uncertainty of the clustering process. In this context, the EVCLUS algorithm was proposed for partitioning objects described by a dissimilarity matrix. It is extended here so as to take pairwise constraints into account, by adding a term to its objective function. This term corresponds to a penalty term that expresses pairwise constraints in the belief function framework. Various synthetic and real datasets are considered to demonstrate the interest of the proposed method, called CEVCLUS, and two applications are presented. The performances of CEVCLUS are also compared to those of other constrained clustering algorithms.     

Enthalpy recovery of gases issued from H2 production processes: Activity and stability of oxide and noble metal catalysts in oxidation reaction under highly severe conditions

Oxidation activity and stability under reaction was investigated for a series of mixed oxide catalysts, doped or not by a precious metal (Pd, Pt). The reaction feedstock, containing CO, H₂, CH₄, CO₂ and H₂O, simulated gases issued from H₂ production processes for fuel cells. Contrarily to conventional noble metal catalysts, mixed oxide samples present generally good stability under reaction at high temperature. The activities measured for the perovskite and hexaaluminate catalysts, are however largely lower than that of the reference Pd/Al₂O₃ catalyst. High activities were obtained after impregnation of 1.1 wt.% Pd or 0.8 wt.% Pt on the hexaaluminates samples. Even if Pd/Al₂O₃ was found to present a high activity, this sample suffered from drastic deactivation at 700 °C. Better stability were obtained on perovskite. Furthermore, doping hexaaluminate by Pt led to samples with good activities and high stability. Even if better activities were obtained by doping the hexaaluminate samples by Pd, the Pd/BaAl₁₂O₁₉ strongly deactivated, as it was previously observed for the reference catalyst. Interestingly, this Pd deactivation was not observed when Pd was impregnated on the Mn substituted hexaaluminate, leading to a stable and active catalyst. This suggests that it is possible to stabilize the palladium in its oxidized form at high temperature (700 °C) on the surface of some supports.     

How the risk of failure in lifetime of tempered glass depends on the size of NiS inclusions and heat soak test duration

The probability of breakage in service lifetime of heat-tempered glass panes contaminated by nickel sulfide inclusions is estimated with a multiscale micromechanically motivated statistical theory, which considers the effects of the heat soak test (HST). Short and long HSTs differently affect the phase transformation of NiS of diverse chemical composition, whose increase in volume can break the glass. The main hypothesis, corroborated by experiments, is that there is a lower limit for the size of NiS stones below which no crack can be initiated from the volumetric expansion. The catastrophic propagation of nucleated fractures in the long term is modeled through a rescaled critical stress intensity factor, which accounts for the subcritical crack propagation and the slow phase transformation of NiS. A parametric analysis evidences how the failure probability is strongly affected by these parameters, depending on the holding time in the HST. Tailored experimental activity is suggested for the proper calibration of the model.     

Robustness of ISS systems to inputs with limited moving average: Application to spacecraft formations

We provide a theoretical framework that fits realistic challenges related to spacecraft formation with disturbances. We show that the input‐to‐state stability of such systems guarantees some robustness with respect to a class of signals with bounded average‐energy, which encompasses the typical disturbances acting on spacecraft formations. Solutions are shown to converge to the desired formation, up to an offset, which is somewhat proportional to the considered moving average of disturbances. In the presence of fast peaking perturbations, the approach provides a tighter evaluation of the disturbances' influence, which allows for the use of more parsimonious control gains. Copyright © 2015 John Wiley & Sons, Ltd.     

On the composition of ISO 25964 hierarchical relations (BTG,BTP, BTI)

Knowledge organization systems (KOS) can use different types of hierarchical relations: broader generic (BTG), broader partitive (BTP), and broader instantial (BTI). The latest ISO standard on thesauri (ISO 25964) has formalized these relations in a corresponding OWL ontology (De Smedt et al., ISO 25964 part 1: thesauri for information retrieval: RDF/OWL vocabulary, extension of SKOS and SKOS-XL. http://purl.org/iso25964/skos-thes, 2013) and expressed them as properties: broaderGeneric, broaderPartitive, and broaderInstantial, respectively. These relations are used in actual thesaurus data. The compositionality of these types of hierarchical relations has not been investigated systematically yet. They all contribute to the general broader (BT) thesaurus relation and its transitive generalization broader transitive defined in the SKOS model for representing KOS. But specialized relationship types cannot be arbitrarily combined to produce new statements that have the same semantic precision, leading to cases where inference of broader transitive relationships may be misleading. We define Extended properties (BTGE, BTPE, BTIE) and analyze which compositions of the original “one-step” properties and the Extended properties are appropriate. This enables providing the new properties with valuable semantics usable, e.g., for fine-grained information retrieval purposes. In addition, we relax some of the constraints assigned to the ISO properties, namely the fact that hierarchical relationships apply to SKOS concepts only. This allows us to apply them to the Getty Art and Architecture Thesaurus (AAT), where they are also used for non-concepts (facets, hierarchy names, guide terms). In this paper, we present extensive examples derived from the recent publication of AAT as linked open data.     

A framework for dynamic implicit curve approximation by an irregular discrete approach

The approximation of implicit planar curves by line segments is a very classical problem. Many algorithms use interval analysis to approximate this curve, and to handle the topology of the final reconstruction. In this article, we use discrete geometry tools to build an original geometrical and topological representation of the implicit curve. The polygonal approximation contains few segments, and the Reeb graph permits to sum up efficiently the shape and the topology of the curve. Furthermore, we propose two algorithms to process local cells refinement and local cells grouping schemes. We illustrate these schemes with a global system that efficiently handles manual or automatic fast updates on the global reconstruction, by considering topological or geometrical constraints. We also compare the speed and the quality of our approach with two classical methods.     

Workload assignment for global real-time scheduling on unrelated clustered platforms

Real-Time Systems - Heterogeneous MPSoCs are being used more and more, from cellphones to critical embedded systems. Most of those systems offer heterogeneous sets of identical cores. In this...