Justifications and Blocking Sets in a Rule-Based Answer Set Computation

Notions of justifications for logic programs under answer set semantics have been recently studied for atom-based approaches or argumentation approaches. The paper addresses the question in a rule-based answer set computation: the search algorithm does not guess on the truth or falsity of an atom but on the application or non application of a non monotonic rule. In this view, justifications are sets of ground rules with particular properties. Properties of these justifications are established; in particular the notion of blocking set (a reason incompatible with an answer set) is defined, that permits to explain computation failures. Backjumping, learning, debugging and explanations are possible applications

Local and global properties of solutions of quasilinear Hamilton-Jacobi equations

We study some properties of the solutions of (E) \;-\Gd_p u+|\nabla u|^q=0 in a domain \Gw \sbs \BBR^N, mostly when $p\geq q>p-1$. We give a universal priori estimate of the gradient of the solutions with respect to the distance to the boundary. We give a full classification of the isolated singularities of the positive solutions of (E), a partial classification of isolated singularities of the negative solutions. We prove a general removability result in expressed in terms of some Bessel capacity of the removable set. We extend our estimates to equations on complete non compact manifolds satisfying a lower bound estimate on the Ricci curvature, and derive some Liouville type theorems.Comment: to appear J. Funct. Ana

Toughening and hardening in double-walled carbon nanotube/nanostructured magnesia composites

Dense double-walled carbon nanotube (DWCNT)/nanostructured MgO composites were prepared using an in situ route obviating any milling step for the synthesis of powders and consolidation by spark-plasma-sintering. An unambiguous increase in both toughness and microhardness is reported. The mechanisms of crack-bridging on an unprecedented scale, crack-deflection and DWCNT pullout have been evidenced. The very long DWCNTs, which appear to be mostly undamaged, are very homogeneously dispersed at the grain boundaries of the matrix, greatly inhibiting the grain growth during sintering. These results arise because the unique microstructure (low content of long DWCNTs, nanometric matrix grains and grain boundary cohesion) provides the appropriate scale of the reinforcement to make the material tough

Possibilistic Stable Models

We present the main lines of a new framework that we have defined in order to improve the knowledge representation power of Answer Set Programming paradigm. Our proposal is to use notions from possibility theory to extend the stable model semantics by taking into account a certainty level, expressed in terms of necessity measure, on each rule of a normal logic program. First of all, we introduce possibilistic definite logic programs and show how to compute the conclusions of such programs both in syntactic and semantic ways. The syntactic handling is done by help of a fix-point operator, the semantic part relies on a possibility distribution on all sets of atoms and the two approaches are shown to be equivalent. In a second part, we define what is a possibilistic stable model for a normal logic program, with default negation. Again, we define a possibility distribution allowing to determine the stable models. We end our presentation by showing how we can use our framework to adressing inconsistency in Answer Set Programming

Spark-plasma-sintering of double-walled carbon nanotube–magnesia nanocomposites

A double-walled carbon nanotube–MgO powder is prepared without any mixing. The applied pressure is the main parameter acting on densification. Increasing the maximum temperature and holding time is marginally beneficial. The nanotubes are blocking the matrix grain growth. The nanocomposite prepared using the most severe spark plasma sintering conditions (1700 °C, 150 MPa) shows mostly undamaged nanotubes and a higher microhardness than the other materials, reflecting a better bonding between nanotubes and matrix. The electrical conductivity of all nanocomposites is over 12 S/cm

Synthesis of Fe-ZrO2 nanocomposite powders by reduction in H2 of a nanocrystalline (Zr, Fe)O2 solid solution

The formation of Fe-ZrO2 nanocomposite powders by reduction in hydrogen of a nanocrystalline totally stabilized Zr0.9Fe0.1O1.95 solid solution was investigated by X-ray diffraction (XRD), field-emission-gun scanning electron microscopy (FEG-SEM) and Mössbauer spectroscopy. The reduction of the stabilized Zr0.9Fe0.1O1.95 solid solution and the formation of metallic particles precedes the transformation of zirconia into the monoclinic phase, which becomes the major zirconia phase upon reduction at 950 °C. α-Fe particles with a size distribution slightly increasing from 10–50 to 20–70 nm upon the increase in reduction temperature are observed and a second population of smaller (<5 nm) γ-Fe nanoparticles is also noticed when the reduction is performed at 1000 °C. Another metallic phase with a hyperfine field of not, vert, similar200 kOe at RT (not, vert, similar250 kOe at 80 K) is detected, which could account for an Fe/Zr phase. It could be formed by the reduction on an Fe2+-rich transient phase incorporating a small fraction of the Zr4+ ions, formed by a phase partitioning process superimposed to the reduciton processes

Iron-stabilized nanocrystalline ZrO2 solid solutions: Synthesis by combustion and thermal stability

The synthesis of Fe3+-stabilized zirconia by the nitrate/urea combustion route was investigated. Using several characterization techniques, including X-ray diffraction, field-emission-gun scanning electron microscopy and notably Mo¨ ssbauer spectroscopy, it was possible to determine the appropriate amount of urea that allows to obtain a totally stabilized Zr0.9Fe0.1O1.95 solid solution. The nanocrystalline zirconia solid solution is mostly tetragonal, but the presence of the cubic phase could not be ruled out. An indepth study of the thermal stability in air showed that the Fe3+ solubility in the stabilized solid solution starts to decrease at about 875 8C which results in the formation of hematite (possibly containing some Zr4+) at the surface of the zirconia grains and further provokes the progressive transformation into the monoclinic zirconia phase

Tetragonal-(Zr,Co)O2 solid solution: Combustion synthesis, thermal stability in air and reduction in H2, H2–CH4 and H2–C2H4 atmospheres

The synthesis of Co2+-stabilized zirconia by the nitrate/urea combustion route is investigated. Using seven times the so-called stoichiometric urea proportion allows to obtain for the first time the Zr0.9Co0.1O1.9 solid solution fully stabilized in tetragonal form. The thermal stability in air and the reduction in H2, H2–CH4 and H2–C2H4 atmospheres are studied. The carbon forms obtained upon reduction are investigated. Reduction in H2–CH4 produces many carbon species including short carbon nanofibers, nanoribbons, hollow particles often forming bamboo structures, carbon-encapsulated Co particles and carbon nanotubes. Reduction in H2–C2H4 produces 15–30 nm nanofibers