Explanation-based learning: its role in problem solving

Abstract

‘Explanation-based’ learning is a semantically-driven. knowledge-intensive paradigm for machine learning which contrasts sharply with syntactic or ‘similarity-based’ approaches. This paper redevelops the foundations of EBL from the perspective of problem-solving. Viewed in this light, the technique is revealed as a simple modification to an inference engine which gives it the ability to generalize the conditions under which the solution to a particular problem holds. We show how to embed generalization invisibly within the problem solver, so that it is accomplished as inference proceeds rather than as a separate step. The approach is also extended to the more complex domain of planning to illustrate that it is applicable to a variety of logic-based problem-solvers and is by no means restricted to only simple ones. We argue against the current trend to isolate learning from other activity and study it separately, preferred instead to integrate it into the very heart of problem solving.     

The influence of pH on particle packing in YSZ coatings electrophoretically deposited from a non-aqueous suspension

Yttria stabilized zirconia (YSZ) coatings were produced from a YSZ suspension in acetylacetone (ACAC) using electrophoretic deposition (EPD) and then sintered with substrate constraint at 1200 and 1300 °C. Before EPD, the operational pH of the suspension was adjusted by addition of acetic acid or triethanolamine (TEA) base. The effect of suspension pH on the deposition of EPD coatings was studied with respect to the suspension stability, coating density and microstructure. Results showed that the zeta potential had a high positive value on both sides of the iso-electric point (IEP). This probably resulted from the adsorption of TEA, detected by Fourier transform infrared spectroscopy. Three alkalies with different molecular structures were compared and the effect of their molecule length on the interparticle repulsion was discussed. Based on this, particle interactions were estimated for different pH suspensions. The reduced particle coagulation increased the packing density of the EPD coatings from 38% at pH 7.4 to 53% at pH 8.4. Therefore, subsequent sintering of coatings was promoted. The sinterability was evaluated by micro-hardness and microstructure. After sintering at 1200 °C, coatings made in pH 8.4 suspensions obtained a hardness of 786 MPa and had fewer big pores than coatings fabricated in pH 7.4 suspensions that had a hardness of 457 MPa.     

Calculations and measurements on the flow in unconfined detonation

Abstract

In this work a comparison is made between measured and calculated flows in axisymmetric detonations based on the axial density profile in the detonation, the shockfront radius of curvature of the detonation, and the reaction zone length. Measurements were made using flash radiography, optical photography, and electromagnetic particle velocity gauging in a commercial air-sensitised emulsion explosive at two voidages, each at two charge diameters. Calculations were performed using the alternative approaches of slightly divergent flow theory and a finite element Lagrangian hydrocode. Chemical reaction rate models in the calculations were parameterised against the measured unconfined detonation velocity charge diameter effect. The result of the study was that both modelling techniques gave good agreement with available experimental data, though the slightly divergent flow model was more accurate in the region close to the shock. It has also been demonstrated that providing the two approaches had been carefully calibrated, the agreement between them was not sensitive to the form of the models used.     

Landscape design: signposts to a postmodern future?

The authors of Landscape Design: An International Survey, a wide‐ranging review of contemporary practice, are forced to conclude that they can find little solid evidence of substantial design theory underlying the schemes selected. This paper asks whether this is so, and uses insights provided by Lodewijk Baljon's technique of comparative design analysis (developed in his study of the entries for the Pare de la Villette competition) to examine the state of contemporary landscape architecture as it approaches the millenium.     

A New Strategy toward “Simple” Water‐Soluble AIE Probes for Hypoxia Detection

Hypoxia‐responsive fluorescent probes have emerged as a novel scaffold for tumor diagnosis. However, dilemma often exists between simple synthesis and high water solubility in traditional probes. Owing to the intrinsic property of N‐oxides, herein, a new strategy is proposed to design and synthesize probes for in vitro hypoxia imaging. Equipped with tetraphenylethene (TPE), the N‐oxides exhibit aggregation‐induced emission characteristics and emit no light in aqueous solutions. Interestingly, the N‐oxides can be reduced by ferrous ions in different rates. The aggregation of the resulting hydrophobic TPE residues restricts the intramolecular motions of the molecules, which “turns‐on” their fluorescence. The N? O covalent bond of one molecule can be specifically cleaved by cellular reductase overexpressed under hypoxic conditions, and thus turn‐on hypoxia imaging in vitro is achieved. The new strategy to design hypoxia imaging probes is extremely valuable and has great potential for application in tumor diagnosis.