Friction behavior of laser cladding magnesium alloy against AISI 52100 steel

The use of magnesium alloys in engineering applications is becoming increasingly important as a relatively low density allows savings in energy consumption and therefore reduction in air pollution. An associated reduction in inertia makes these alloys potential candidates for friction components, but they suffer from poor wear resistance. Laser surface alloying with appropriate powder mixture is an innovative technique to improve surface properties of metallic alloys. In this study, the effect of laser surface alloying using Al12%Si powder on wear resistance of a magnesium alloy ZE41 is investigated. Hardness and wear resistance of the alloy are significantly enhanced after treatment

Dynamics of seston constituants in the Ariège and Garonne rivers (France)

Water contents of suspended matter, algal pigments, particulate organic carbon and particulate phosphorus were measured in the rivers Garonne (2 sites) and Ariege (1 site) throughout an annual cycle. The general trend of the parameters was similar at the three sites. Depending on the sites, the period of algal growth (chlorophyll a + phaeopigments > 25 µg l-1), lasted from two to six weeks in August-September. The algal peaks reached 50 to 90 µg l-1 of total pigments. High contents of particulate organic carbon (> 2 mg l-1) occurred at the end of summer (coinciding with algal growth), and during the November and May floods. In summer 50-75 % of the suspended matter was organic, in spring this was 10 times less. The high linear correlation between particulate organic carbon and pigment contents (r = 0.87; P = 0.0001) suggested an algal origin of at least part of the particulate carbon. Algal carbon was minor in the annual fluxes of particulate carbon (25 to 39% depending on the sites), but relatively high in comparison with other rivers. The mean particulate phosphorus content calculated over the year was 24 µg l-1; it varied from 15 µg l-1 during the high water period to 28 µg l-1 during the low water period. Likewise the percentage of particulate phosphorus in the suspended matter varied from 0.17 to 0.40. A negative linear correlation existed between particulate phosphorus content and specific discharge (r = - 0.46; P = 0.0001). The very marked seasonal trend of the parameters and the interactions led us to differentiate two modes of the rivers' functioning: a 'hydrologic' phase and a 'biological' phase. The hydrologic phase (high water) was dominated by the processes of erosion and transfer over the whole catchment area and the floodplain, while the biological phase was characterized by a high primary production in the river bed

Friction behavior of laser cladding magnesium alloy against AISI 52100 steel

The use of magnesium alloys in engineering applications is becoming increasingly important as a relatively low density allows savings in energy consumption and therefore reduction in air pollution. An associated reduction in inertia makes these alloys potential candidates for friction components, but they suffer from poor wear resistance. Laser surface alloying with appropriate powder mixture is an innovative technique to improve surface properties of metallic alloys. In this study, the effect of laser surface alloying using Al12%Si powder on wear resistance of a magnesium alloy ZE41 is investigated. Hardness and wear resistance of the alloy are significantly enhanced after treatment

On the construction of pullbacks for safe Petri nets

The product of safe Petri nets is a well known operation: it generalizes to concurrent systems the usual synchronous product of automata. In this short note, we consider the definition of pullbacks of safe PNs, another categorical construction. Pullbacks generalize the product to nets which interact both by synchronized transitions and by a shared sub-net. \\ Le produit de réseaux de Petri saufs (éventuellement à labels) est une opération bien connue~: on peut la voir comme une généralisation du produit synchrone d'automates à des systèmes concurrents. Dans cette note, on s'intéresse à la construction de pullbacks de réseaux saufs, une autre construction catégorique. Les pullbacks généralisent le produit de réseaux en permettant une interaction non seulement par la synchronisation de transitions, mais aussi par partage de places et de transitions

Classification Among Hidden Markov Models

An important task in AI is one of classifying an observation as belonging to one class among several (e.g. image classification). We revisit this problem in a verification context: given k partially observable systems modeled as Hidden Markov Models (also called labeled Markov chains), and an execution of one of them, can we eventually classify which system performed this execution, just by looking at its observations? Interestingly, this problem generalizes several problems in verification and control, such as fault diagnosis and opacity. Also, classification has strong connections with different notions of distances between stochastic models. In this paper, we study a general and practical notion of classifiers, namely limit-sure classifiers, which allow misclassification, i.e. errors in classification, as long as the probability of misclassification tends to 0 as the length of the observation grows. To study the complexity of several notions of classification, we develop techniques based on a simple but powerful notion of stationary distributions for HMMs. We prove that one cannot classify among HMMs iff there is a finite separating word from their stationary distributions. This provides a direct proof that classifiability can be checked in PTIME, as an alternative to existing proofs using separating events (i.e. sets of infinite separating words) for the total variation distance. Our approach also allows us to introduce and tackle new notions of classifiability which are applicable in a security context

Afforestation with Eucalyptus globulus and leaf litter decomposition in streams of northern Spain

To test the hypothesis that decomposition of leaf species in streams is influenced by afforestation with Eucalyptus globulus, we compared decay rates, nutrient levels, fungal biomass and macroinvertebrate assemblages on alder and eucalyptus leaf litter in three streams (two headwaters under different forests, and a mid reach) of the Agüera catchment (northern Spain). Whatever the reach, alder always decomposed significantly faster than eucalyptus. Litter contents in nitrogen and phosphorus rose during breakdown at the mid reach, but not at the headwaters. No differences in fungal biomass were found between alder and eucalyptus leaves at the headwater reaches; however, at the mid reach, eucalyptus showed the highest values. Alder litter, a high quality substratum, was readily colonized by shredders, and decayed rapidly at all sites. Eucalyptus, a low quality species, had lower nutrient contents and was less favoured by shredders. Under high nutrient levels (particularly phosphorus), however, it was readily colonized by fungi, thus shifting from medium to high breakdown rates. The potentially negative impact of afforestation with eucalyptus on streams can thus be reduced in situations of high concentrations of dissolved nutrients