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Strain-engineering is a powerful means to tune the polar, structural, and electronic instabilities of incipient ferroelectrics. KTaO3 is near a polar instability and shows anisotropic superconductivity in electron-doped samples. Here, we demonstrate growth of high quality KTaO3 thin films by molecular-beam epitaxy. Tantalum was provided by both a suboxide source emanating a TaO2 flux from Ta2O5 contained in a conventional effusion cell as well as an electron-beam-heated tantalum source. Excess potassium and a combination of ozone and oxygen (10 \% O3 + 90 \% O2) were simultaneously supplied with the TaO$_2$ (or tantalum) molecular beams to grow the KTaO$_3$ films. Laue fringes suggest that the films are smooth with an abrupt film/substrate interface. Cross-sectional scanning transmission electron microscopy does not show any extended defects and confirms that the films have an atomically abrupt interface with the substrate. Atomic force microscopy reveals atomic steps at the surface of the grown films. Reciprocal space mapping demonstrates that the films, when sufficiently thin, are coherently strained to the SrTiO$_3$ (001) and GdScO$_3$ (110) substrates.

We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow $\beta$-Ga$_2$O$_3$ at a growth rate of ~1 ${\mu}$m/h with control of the silicon doping concentration from 5x10$^{16}$ to 10$^{19}$ cm$^{-3}$. In S-MBE, pre-oxidized gallium in the form of a molecular beam that is 99.98\% Ga$_2$O, i.e., gallium suboxide, is supplied. Directly supplying Ga2O to the growth surface bypasses the rate-limiting first step of the two-step reaction mechanism involved in the growth of $\beta$-Ga$_2$O$_3$ by conventional MBE. As a result, a growth rate of ~1 ${\mu}$m/h is readily achieved at a relatively low growth temperature (T$_{sub}$ = 525 $^\circ$C), resulting in films with high structural perfection and smooth surfaces (rms roughness of < 2 nm on ~1 ${\mu}$m thick films). Silicon-containing oxide sources (SiO and SiO$_2$) producing an SiO suboxide molecular beam are used to dope the $\beta$-Ga$_2$O$_3$ layers. Temperature-dependent Hall effect measurements on a 1 ${\mu}$m thick film with a mobile carrier concentration of 2.7x10$^{17}$ cm$^{-3}$ reveal a room-temperature mobility of 124 cm$^2$ V$^{-1}$ s$^{-1}$ that increases to 627 cm$^2$ V$^{-1}$ s$^{-1}$ at 76 K; the silicon dopants are found to exhibit an activation energy of 27 meV. We also demonstrate working MESFETs made from these silicon-doped $\beta$-Ga$_2$O$_3$ films grown by S-MBE at growth rates of ~1 ${\mu}$m/h., Comment: 19 pages, 7 figures, 2 tables, 2 pages supplementary materials

We describe an ongoing variable star search program and present the first reduced results of a search in a 19 square degree (4.4\circle x 4.4\circle) field centered on J2000 {\alpha} = 22:03:24, {\delta} = +18:54:32. The search was carried out with the Baker-Nunn Patrol Camera located at the Rothney Astrophysical Observatory in the foothills of the Canadian Rockies. A total of 26,271 stars were detected in the field, over a range of about 11-15 (instrumental) magnitudes. Our image processing made use of the IRAF version of the DAOPHOT aperture photometry routine and we used the ANOVA method to search for periodic variations in the light curves. We formally detected periodic variability in 35 stars, that we tentatively classify according to light curve characteristics: 6 EA (Algol), 5 EB ({\beta} Lyrae), 19 EW (W UMa), and 5 RR (RR Lyrae) stars. Eleven of the detected variable stars have been reported previously in the literature. The eclipsing binary light curves have been analyzed with a package of light curve modeling programs and 25 have yielded converged solutions. Nine of these systems are detached, 3 semi0detached, 10 over-contact, and 2 appear to be in marginal contact. We discuss these results as well as the advantages and disadvantages of the instrument and of the program., Comment: 62 pages, 21 figures, 5 tables

The effectiveness of providing a specific kind of motivational feedback was investigated in a computer-based instruction (CBI) environment for different kinds of students and different levels of instructional control. Feedback was intended to affect students' temporal perceptions of the causes of learning successes and failures, their attributions of performance outcomes. Subjects from nine high school economics classes (64 males and 78 females) studied a computer lesson in economics and completed pretests and posttests or an attributional style questionnaire. The study used a randomized block factorial design with attributional feedback and source of control as treatment factors and the multiple-choice posttest and the recall posttest as dependent variables. Six attributional style variables were used as blocking factors. There were no overall advantages for any version of the main experimental treatments. Versions of source of control (program and learner) and attributional feedback (with and without) were not found to differ in their effects on both types of posttest. Results support the fact that learner control is differentially successful for learners with different motivation levels. Learner control can help some students with dysfunctional motivation patterns improve their learning. Findings also support the inclusion of attributions as a variable from which to adapt instruction. Five tables and seven figures present study findings. (Contains 66 references.) (SLD)

Some specific computer-based tools for collecting and examining audit trails, i.e., data that describe a learner's path through a computer-based instruction (CBI) lesson, are detailed. Data analysis and measurement issues related to audit trails are also discussed. A particular set of embedded computer-based tools currently being used at San Diego State University (California) is described. These tools assess the what, where, and when of learner actions. The examples are developed in HyperCard. Researchers may attempt to interpret student responses by looking at the audit trail output file, but are probably better served by replaying the lesson to experience CBI as the learner did. Data from large numbers of learners may be aggregated for analysis. Issues of measurement error and concerns in dealing with aggregated data are reviewed. Audit trails can provide a great deal of understanding of how students experience CBI. Three figures illustrate the discussion. An appendix presents some scripts for audit trail handlers in HyperCard. (SLD)

This paper reviews findings from over 70 published studies investigating various facets of learner-control in computer-based instruction (CBI). General conclusions about the relative effectiveness of learner-control versus program-control are equivocal. Across these studies, however, are strong suggestions that individual learner differences can greatly contribute to both the choices students make and to the effectiveness of those choices. Some researchers examine those differences on a global level, interacting with such broad instructional variables as learner-control versus program-control, following an aptitude-treatment interaction paradigm. Other investigators, however, look for interactions occurring on a moment-by-moment basis under micro-instructional conditions, that is the task-specific situation encountered during the course of the lesson delivery. Other paradigms are also discussed. The review extends the previous surveys of Carrier (1984), Hannafin (1984), Milheim and Martin (1981), and Steinberg (1977, 1989), paying particular attention to the role of learner individual differences in the effectiveness of learner-controlled CBI. Specifically, the impact on learner-control effectiveness of both rational-cognitive processes and emotional-motivational states of the learner are highlighted. Useful instructional prescriptions are proposed which take into account these variables. Recommendations for future research are offered. (Contains 188 references.) (Author/KRN)