Representing temporal knowledge in conceptual graphs

This study was motivated by some difficulties encountered by the authors when trying to express temporal knowledge using Sowa's conceptual graph (CG) approach. An overview of Sowa's approach is given and the difficulties encountered when trying to model temporal knowledge are outlined: the disparity of notations allowed by CG theory for expressing temporal information; the ambiguity and incompleteness of tense sspecification; the difficulty of harmonizing tenses and intergraph temporal relations. Various approaches suggested for representing time both in artificial intelligence and linguistics are presented, and an extension to Sowa's approach is proposed in which temporal and nontemporal knowledge are differentiated. In this model points in time are represented as well as time intervals. A semantic interpretation of verbs is provided based on an extension of Reichenbach's model of temporal markers. The authors show how their approach enables the representation of tenses as well as the aspectual properties of natural language sentences.     

Cramer-Rao bounds for parametric shape estimation in inverse problems

We address the problem of computing fundamental performance bounds for estimation of object boundaries from noisy measurements in inverse problems, when the boundaries are parameterized by a finite number of unknown variables. Our model applies to multiple unknown objects, each with its own unknown gray level, or color, and boundary parameterization, on an arbitrary known background. While such fundamental bounds on the performance of shape estimation algorithms can in principle be derived from the Cramer-Rao lower bounds, very few results have been reported due to the difficulty of computing the derivatives of a functional with respect to shape deformation. We provide a general formula for computing Cramer-Rao lower bounds in inverse problems where the observations are related to the object by a general linear transform, followed by a possibly nonlinear and noisy measurement system. As an illustration, we derive explicit formulas for computed tomography, Fourier imaging, and deconvolution problems. The bounds reveal that highly accurate parametric reconstructions are possible in these examples, using severely limited and noisy data.     

The influence of surface melting by CW-CO2 laser on the structure,composition and stress of the (1 0 0) surface of the Fe-17Cr-13Ni alloy

During the laser surface treatment, oxidation can take place even with the protection of helium gas. The CW-CO₂ laser melting of the surface does not induce a large distortion of the crystallographic orientation which remains (1 0 0). A misorientation of 3–4 degrees between the melted zone and the unaffected base alloy was measured by Laue diffraction and ion channelling studies. Surface chemical analysis was carried out by X-ray photoelectron and Auger electron spectroscopies in order to obtain information on surface segregation during either the laser cooling, or after annealing up to 850 °C, in PO₂=5 × 10^–9 Torr. The latter causes segregation of sulphur and/or nitrogen to the surface. This segregation of sulphur and nitrogen is modified between the untreated zone and the treated surfaces (thermal affected zone and melted zone). For instance, on the contrary of nitrogen, the diffusion of sulphur is increased on the melted surface and the activation energy for this diffusion is very dependent upon the defect nature. A difference of nearly 65–70 kJ mol^–1 is calculated for the enthalpy for the surface segregation of sulphur H ^seg, between the treated and untreated surface. This difference is only 37 kJ mol^–1 for nitrogen. In both cases the absolute H ^seg values are smaller for the treated zone than for the base alloy. A structural study by low electron diffraction (LEED) which gives information on the structure of the surface when clean and in the presence of sulphur and/or nitrogen, shows also the formation of edges, terraces and steps on the treated surfaces. These results are mainly associated with the difference in the content and nature of the defects between the different zones, as observed by scanning electron microscopy analysis or channelling study. Finally a comparison between the mechanical properties of the different zones is made on account of the observation of a linear change of the microhardness on the thermally affected surface. In the thin outer surface zone which is treated by the laser, the stresses associated with the cooling or the isothermal annealing are calculated using formula which associate the stress and the radius of curvature of the sample (from the misorientation which was analysed by ion channelling between the different surface domains). The influence of such an isothermal stress is believed to increase the percentage of vacancies in the melted zone and therefore to modify the activation energy for the diffusion of a substitutional element, such as sulphur. The influence of the elastic energy which is kept during cooling, for example according to the analysis of Evans and Lobb [12], is also discussed.Part of this work was done in the Laboratoire de Physicochimie des Surfaces, associe au CNRS, ENSCP, Université P et M Curie, 11 rue P et M Curie, 75005 Paris, France.     

Analytical study of surface and bulk oxidation of Astroloy

Nickel-base alloys, such as Astroloy, used for aeronautical turbine disks, are sensitive to time-dependent cracking in environments containing oxygen. The mosaic structure of the alloy consisting islands (200 nm average size) surrounded by the -phase (100 nm thick) induces complex oxidation phenomena. Various analytical approaches allow the delineation of all the steps from segregation to oxidation occurring on the surface of such a duplex structure. The protection of Astroloy by its outer oxide layer against oxygen penetration was studied also, using alternative ¹⁶O₂ then ¹⁸O₂ oxidation. In association with STEM studies, it is shown that the outer oxide scale is not a real barrier against oxygen penetration and that inner precipitation of chronium (+ aluminium and titanium)-enriched oxides, takes place especially in the structure.     

Relation between impurities and oxide-scale growth mechanisms on Ni-34Cr and Ni-20Cr alloys. II. Influence of sulphur

The oxidation of presulphidized Ni-Cr alloys has been studied by taking into account the influence of the two distinct oxidation mechanisms described in part I of this article. Sulphur enters the Cr₂O₃ scale (in Ni-34Cr alloys) mainly as S^2– species, which at high temperatures increases the V_Cr content, and hence the oxidation kinetics. Sulphur is randomly distributed in the scale, except at the inner oxide-alloy interface, where intergranular microsulphides are analyzed in the oxide-scale zone. In the case of NiO, NiCr₂O₄, Cr₂O₃ oxide multilayers (in a Ni-20Cr alloy), sulphur in the S^2– state is distributed in the oxide layers or at Si-precipitate interfaces. Such a distribution leads to crack formation, especially during cooling.     

Copper planar microcoils applied to magnetic actuation

Recent advances in microtechnology allow realization of planar microcoils. These components are integrated in MEMS as magnetic sensor or actuator. In the latter case, it is necessary to maximize the effective magnetic field which is proportional to the current passing through the copper track and depends on the distance to the generation microcoil. The aim of this work was to determine the optimal microcoil design configuration for magnetic field generation. The results were applied to magnetic actuation, taking into account technological constraints. In particular, we have considered different realistic configurations that involve a magnetically actuated device coupled to a microcoil. Calculations by a semi-analytical method using Matlab software were validated by experimental measurements. The copper planar microcoils are fabricated by UV micromoulding on different substrates: flexible polymer (Kapton^®) and silicate on silicon. They are constituted by a spiral-like continuous track. Their total surface is about 1 mm².     

A taxonomy of argumentation models used for knowledge representation

Understanding argumentation and its role in human reasoning has been a continuous subject of investigation for scholars from the ancient Greek philosophers to current researchers in philosophy, logic and artificial intelligence. In recent years, argumentation models have been used in different areas such as knowledge representation, explanation, proof elaboration, commonsense reasoning, logic programming, legal reasoning, decision making, and negotiation. However, these models address quite specific needs and there is need for a conceptual framework that would organize and compare existing argumentation-based models and methods. Such a framework would be very useful especially for researchers and practitioners who want to select appropriate argumentation models or techniques to be incorporated in new software systems with argumentation capabilities. In this paper, we propose such a conceptual framework, based on taxonomy of the most important argumentation models, approaches and systems found in the literature. This framework highlights the similarities and differences between these argumentation models. As an illustration of the practical use of this framework, we present a case study which shows how we used this framework to select and enrich an argumentation model in a knowledge acquisition project which aimed at representing argumentative knowledge contained in texts critiquing military courses of action.     

A modelling framework to support farmers in designing agricultural production systems

Given the new challenges confronting world agriculture, innovative production systems need to be designed at the farm level. As experiments are not easy to conduct at this level, modelling is required to evaluate ex-ante the multiple impacts of proposed innovations. A conceptual framework based on three sub-systems (biophysical, technical, and decisional) interacting within the farm is proposed to guide this process. The advantages and limitations of the framework are illustrated with three examples. The first describes a conceptual, rule-based model representing management decisions for the cultivation of salad in southern France. The second uses a computerized model of the three sub-systems to study irrigation management strategies on farms producing hay in southern France. The third presents a spreadsheet model designed to assist dairy farms in Morocco to define new livestock and forage system strategies. The lessons learned concern the modelling process, the fit between the type of model and its use, and the advantage of involving stakeholders in the design process of tools and innovations.