Mixed-initiative control of intelligent systems

Mixed-initiative user interfaces provide a means by which a human operator and an intelligent system may collectively share the task of deciding what to do next. Such interfaces are important to the effective utilization of real-time expert systems as assistants in the execution of critical tasks. Presented here is the Incremental Inference algorithm, a symbolic reasoning mechanism based on propositional logic and suited to the construction of mixed-initiative interfaces. The algorithm is similar in some respects to the Truth Maintenance System, but replaces the notion of 'justifications' with a notion of recency, allowing newer values to override older values yet permitting various interested parties to refresh these values as they become older and thus more vulnerable to change. A simple example is given of the use of the Incremental Inference algorithm plus an overview of the integration of this mechanism within the SPECTRUM expert system for geological interpretation of imaging spectrometer data

STAR (Simple Tool for Automated Reasoning): Tutorial guide and reference manual

STAR is an interactive, interpreted programming language for the development and operation of Artificial Intelligence application systems. The language is intended for use primarily in the development of software application systems which rely on a combination of symbolic processing, central to the vast majority of AI algorithms, with routines and data structures defined in compiled languages such as C, FORTRAN and PASCAL. References to routines and data structures defined in compiled languages are intermixed with symbolic structures in STAR, resulting in a hybrid operating environment in which symbolic and non-symbolic processing and organization of data may interact to a high degree within the execution of particular application systems. The STAR language was developed in the course of a project involving AI techniques in the interpretation of imaging spectrometer data and is derived in part from a previous language called CLIP. The interpreter for STAR is implemented as a program defined in the language C and has been made available for distribution in source code form through NASA's Computer Software Management and Information Center (COSMIC). Contained within this report are the STAR Tutorial Guide, which introduces the language in a step-by-step manner, and the STAR Reference Manual, which provides a detailed summary of the features of STAR

Impact of titanium doping on Al self-diffusion in alumina

α-Al2O3 is an important refractory material which has numerous technical applications: as an in situ growing self-healing oxide scale, as a massive material and as reinforcement fibres in composites. For modelling diffusion controlled processes (creep, sintering, alpha-alumina scale growth on aluminium bearing Fe or Ni base alloys) it is necessary to study self-diffusion of the constituent elements

Relationship between Intracellular Concentration of S-Adenosylhomocysteine and Inhibition of Vaccinia Virus Replication and Inhibition of Murine L-929 Cell Growth

9-(trans-2',trans-3'-Dihydroxycyclopent-4'-enyl)-adenine (compound 1) and -3-deazaadenine (compound 2), which are specific inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase, were reported earlier by our laboratory (M. Hasobe, J. G. McKee, D. R. Borcherding, and R. T. Borchardt, Antimicrob. Agents Chemother. 31:1849-1851, 1987) to have anti-vaccinia virus activity with reduced murine L-929 cell toxicity compared with the prototype compound neplanocin A. In this study, we showed that the antiviral and cytotoxic effects of compounds 1 and 2 can be related to intracellular concentrations of AdoHey, which are elevated in cells treated with these inhibitors of AdoHcy hydrolase. For example, concentrations of analogs 1 and 2 that produce 50% inhibition of vaccinia virus replication caused only slight elevations in intracellular levels of AdoHcy (from 50 [controls] to 100 to 125 [drug-treated cells] pmol/mg of protein) and elevations in the ratios of AdoHcy/S-adenosylmethionine (from 0.05 to 0.1 [controls] to 0.15 to 0.19 [drug-treated cells]). In contrast to the extreme susceptibility of virus replication to slight elevations in intracellular AdoHcy, cell viability was quite tolerant to higher levels of this metabolite. For example, concentrations of analogs 1 and 2 that produced 50% inhibition of L-929 cell replication caused significant increases in intracellular levels of AdoHcy (to 825 to 950 pmol/mg of protein) and elevations in AdoHcy/S-adenosylmethionine ratios (approximately 1.3). These data make it possible to assign a therapeutic index of 7 to 8 to these compounds on the basis of the comparison of intracellular levels of AdoHcy that caused 50% inhibition of vaccinia virus replication with those that caused 50% inhibition of L-929 cell replication.This work was supported by a Public Health Service grant from the National Institutes of Health (GM-29332) and a grant from Glaxo, Inc

9-(trans-2',trans-3'-Dihydroxycyclopent-4'-Enyl)-Adenine and -3-Deazaadenine: Analogs of Neplanocin A Which Retain Potent Antiviral Activity but Exhibit Reduced Cytotoxicity

Two synthetic analogs of neplanocin A, which were shown in a separate study to be inhibitors of S-adenosylhomocysteine hydrolase and devoid of substrate activity with adenosine kinase, were found in this study to inhibit vaccinia virus replication in murine L929 cells but to have reduced cytotoxicity compared with that of the parent compound. These results confirm that S-adenosylhomocysteine hydrolase is the molecular target which mediates the antiviral effects of neplanocin A and that transformation by cellular adenosine kinase mediates its cytotoxic properties.This work was supported by Public Health Service research grant GM-29332 from the National Institutes of Health

Juxtaposition of Spin Freezing and Long Range Order in a Series of Geometrically Frustrated Antiferromagnetic Gadolinium Garnets

Specific heat measurements in zero magnetic field are presented on a homologous series of geometrically frustrated, antiferromagnetic, Heisenberg garnet systems. Measurements of Gd3Ga5O12, grown with isotopically pure Gd, agree well with previous results on samples with naturally abundant Gd, showing no ordering features. In contrast, samples of Gd3Te2Li3O12 and Gd3Al5O12 are found to exhibit clear ordering transitions at 243 mK and 175 mK respectively. The effects of low level disorder are studied through dilution of Gd3+ with non-magnetic Y3+ in Gd3Te2Li3O12. A thorough structural characterization, using X-ray diffraction, is performed on all of the samples studied. We discuss possible explanations for such diverse behavior in very similar systems.Comment: Accepted for publication in Physical Review

On Measuring Non-Recursive Trade-Offs

We investigate the phenomenon of non-recursive trade-offs between descriptional systems in an abstract fashion. We aim at categorizing non-recursive trade-offs by bounds on their growth rate, and show how to deduce such bounds in general. We also identify criteria which, in the spirit of abstract language theory, allow us to deduce non-recursive tradeoffs from effective closure properties of language families on the one hand, and differences in the decidability status of basic decision problems on the other. We develop a qualitative classification of non-recursive trade-offs in order to obtain a better understanding of this very fundamental behaviour of descriptional systems

Evolution of porosity in carbide-derived carbon aerogels

Carbide-derived carbon (CDC) aerogel monoliths with very high porosity are synthesized starting from polymeric precursors. Cross-linking by platinum-catalyzed hydrosilylation of polycarbosilanes followed by supercritical drying yields preceramic aerogels. After ceramic conversion and silicon extraction in hot chlorine gas, hierarchically porous carbon materials with specific surface areas as high as 2122 m² g⁻¹ and outstanding total pore volumes close to 9 cm³ g⁻¹ are obtained. Their pore structure is controllable by the applied synthesis temperature as shown by combined nitrogen (-196 °C) and carbon dioxide (0 °C) measurements coupled with electron microscopic methods. The combination of large micropore volumes and the aerogel-type pore system leads to advanced adsorption properties due to a combination of large storage capacities and effective materials transport in comparison with purely microporous reference materials as shown by thermal response measurements