Learning Decision Rules from Sets of Decision Trees

This paper is devoted to the study of the problems of learning inner and general decision rules that are true for the maximum number of decision trees from a given set. Inner rules correspond to paths in decision trees from the root to terminal nodes. General rules are arbitrary rules that use attributes from the considered decision trees. We propose a polynomial time algorithm for the optimization of inner rules, show that the problem of optimization of general rules is NP-hard, and describe a heuristic for this problem. We compare the considered algorithm and heuristic experimentally on artificially generated datasets and induced from them decision trees with Gini index as a splitting criterion

Potbelly and Potato Bug

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Microstructural evolution/durability of magnesium phosphate cement paste over time in neutral and basic environments

International audienceThis study investigates the evolutions of the mineralogy, pore solution and porosity of magnesium potassium phosphate cement pastes (MKPC) over time in neutral and basic environments, media that MKPC pastes might encounter when used as patch repair materials or as stabilization materials for hazardous wastes. Mineralogy evolutions were characterized by X-ray diffraction/Rietveld (XRD) and thermogravimetric analyses (TGA) and completed with scanning electron microscopy (SEM/EDX) microanalyses. Pore solution compositions (ICP-OES, IC) and the porosity of the materials were also analyzed. The results showed an amorphization of MKPC pastes over time that might be related to structural changes for the K-struvite phase. Achieving chemical equilibrium between the cementitious waters and the MKPC pore solution can result in porosity evolutions within the materials. Transport and mechanical changes might be expected, especially for MKPC pastes kept in basic media, since K-struvite [MgKPO4·6H2O], could be partially dissolved, leading to a higher total pore volume

Investigation of the percentage and the compacting pressure effect on the structural, optical and thermal properties of alumina-zeolite mixture

This paper presents a detailed investigation of the correlation between micro-structural, optical and thermal properties of a mixture constituted of NaA zeolite and Al2O3 alumina with different portions at various compacting pressures. A comprehensive study was made by using SEM, EDX, XRD, PL and PTD analysis. Through this full characterization, it was demonstrated that a mixture of grain size ranging from 50 nm to 85 nm can be used as a red emitter of mean wave length λ=650μm in optical devices. This mixture also proved to be used as a thermoinsultor or a thermocondensor material; with a thermal conductivity of about 0.22–1.33 W·m−1·K−1 and a thermal diffusivity of about 0.070–0.174 cm2·s−1. Keywords: NaA zeolite, Alumina, Photoluminescence, Thermal propertie

Alkaline activation of metakaolinite-silica mixtures: role of dissolved silica concentration on the formation of geopolymers

The alkali activation of metakaolinite permits the preparation of new amorphous cementitious materials denoted as “geopolymers”. The formation of these aluminosilicates depends on the thermal activation of kaolinites and the amount of silica in the activating solutions. In this work, the influence of Si:Al ratios on the geopolymer's formation is investigated for short reaction times. Structural and morphological transformations were followed with the XRD, SEM, IR and MAS NMR (Si, Al, Na and H) techniques. For kaolinites (SiAl =1) heated at 550 °C, geopolymers with tectosilicate networks easily formed; however, in kaolinites heated at 800 °C, the formation of geopolymers was delayed as a consequence of silica segregation. The addition of silica (Si:Al= 3) favoured the formation of geopolymers particles surrounded by sodium-silicates with tubular morphology. In this association, kinetic and thermodynamic parameters play an important role. For prolonged alkaline activations, zeolites formed from the geopolymers. The quantitative analysis of the NMR spectra made possible the study of the formation of zeolites from amorphous geopolymers.The authors would like to thank the Tunisian Ministry of Education for two short training grants covering the collaboration established between the Spain and Tunisia groups