Electron-stimulated reactions in thin (<3 monolayer, ML) water films adsorbed on TiO2(110) are investigated. For electron fluences less than ∼1 × 1016 e-/cm2, irradiation with 100 eV electrons results in electron-stimulated desorption (ESD) of atomic hydrogen and small amounts of molecular hydrogen but no measurable O2. The ESD results in oxygen enrichment (“oxidation”) of the remaining film and oxidation of the oxygen vacancies originally present on the TiO2(110) surface. The postirradiation temperature-programmed desorption (TPD) spectra of the remaining water change in characteristic ways. The species remaining on the TiO2(110) after irradiation of adsorbed water films are similar to those produced by codosing water and O2 without irradiation. Annealing above ∼600 K reduces the oxidized surface, and water TPD spectra characteristic of a reduced (i.e., ion-sputtered and vacuum annealed) TiO2(110) surface are recovered. The rate of electron-stimulated “oxidation” of the water films is proportional to the coverage of water in the first layer for coverages less than 1 ML. However, higher coverages suppress this reaction. When thin water films are irradiated, the rate of electron-stimulated oxidation is independent of the initial oxygen vacancy concentration, as is the final state achieved at high electron fluences. To explain the results, we propose that electron excitation of water molecules adsorbed on Ti4+ sites leads to dissociation and desorption of hydrogen atoms while leaving OHs adsorbed at those sites. If hydroxyls are present in the bridging oxygen rows, these react with the OHs on the Ti4+ sites to re-form water and heal the oxygen vacancy associated with the bridging OH. Once the bridging hydroxyls have been eliminated, further irradiation increases the concentration of OHs in the Ti4+ rows leading to the creation of species which block sites in the Ti4+ rows, perhaps H2O2 and/or HO2. The results show that electron-stimulated oxidation of the adsorbed water films via H atom ESD is considerably more efficient than electron-stimulated reduction of the TiO2 substrate due to O+ and O ESD:  the ratio of the dissociation cross section of adsorbed water to the cross section for ESD of substrate oxygen is estimated to be ∼18:1 for 100 eV electrons.

SummaryThe ONCOCIN Interviewer program provides a graphical interface between physicians and an expert system that is designed to assist with therapy selection for patients receiving experimental cancer therapy. A principal goal has been to increase acceptance of advanced computer tools in a clinical setting. The interface has been developed for high-performance Lisp workstations and is tailored to the existing paper forms and practices of the outpatient clinic. To be flexible, the program makes use of a document formatting language to control a raster graphics display of medical forms, traditional paper versions of which have been used to track patient progress. The program utilizes a mouse input device coupled with a software-defined data entry approach that may be customized to the specific environment. The work described suggests ways in which high density graphics interfaces, with pointing devices rather than an emphasis on keyboards, may make decision support tools more useful to physicians and more acceptable to them.

Electron-stimulated reactions in thin [<3 ML (monolayer)] water films adsorbed on TiO(2)(110) are investigated. Irradiation with 100 eV electrons results in electron-stimulated dissociation and electron-stimulated desorption (ESD) of adsorbed water molecules. The molecular water ESD yield increases linearly with water coverage theta for 0< or =theta< or =1 ML and 11 ML, the water ESD yield per additional water molecule adsorbed (i.e., the slope of the ESD yield versus coverage) is 3.5 times larger than for theta<1 ML. In contrast, the number of water molecules dissociated per incident electron increases linearly for theta< or =2 ML without changing slope at theta=1 ML. The total electron-stimulated sputtering rate, as measured by postirradiation temperature programmed desorption of the remaining water, is larger for theta>1 ML due to the increased water ESD for those coverages. The water ESD yields versus electron energy (for 5-50 eV) are qualitatively similar for 1, 2, and 40 ML water films. In each case, the observed ESD threshold is at approximately 10 eV and the yield increases monotonically with increasing electron energy. The results indicate that excitations in the adsorbed water layer are primarily responsible for the ESD in thin water films on TiO(2)(110). Experiments on "isotopically layered" films with D(2)O adsorbed on the Ti(4+) sites (D(2)O(Ti)) and H(2)O adsorbed on the bridging oxygen atoms (H(2)O(BBO)) demonstrate that increasing the water coverage above 1 ML rapidly suppresses the electron-stimulated desorption of D(2)O(Ti) and D atoms, despite the fact that the total water ESD and atomic hydrogen ESD yields increase with increasing coverage. The coverage dependence of the electron-stimulated reactions is probably related to the different bonding geometries for H(2)O(Ti) and H(2)O(BBO) and its influence on the desorption probability of the reaction products.

SummaryKnowledge acquisition for expert systems typically is a tedious, iterative process involving long hours of consultation between the domain experts and the computer scientists who serve as knowledge engineers. For well-understood domains, however, it may be possible to facilitate the knowledge acquisition process by allowing domain experts to develop and edit a knowledge base directly. Administration of protocol-directed cancer chemotherapy is such a well-understood application area, and a knowledge acquisition system, called OPAL, has been developed for eliciting chemotherapy-protocol knowledge directly from expert oncologists. OPAL’s knowledge acquisition approach is based on the interactive graphics environment available on current generation workstations. The use of graphics improves the interface by reducing typing, avoiding natural language interpretations, and allowing flexibility in entry sequence. The knowledge in OPAL is displayed using an arrangement of hierarchically related, graphical forms. The position of a particular form in the hierarchy defines the context of the knowledge contained in the form. Intelligent editing programs such as OPAL can streamline the knowledge engineering process for highly structured domains requiring repetitive knowledge entry.