Liquid-Metal-Enabled Synthesis of Aluminum-Containing III-Nitrides by Plasma-Assisted Molecular Beam Epitaxy

Nitride films are promising for advanced optoelectronic and electronic device applications. However, some challenges continue to impede development of high aluminum-containing devices. The two major difficulties are growth of high crystalline quality films with aluminum-rich compositions, and efficiently doping such films p-type. These problems have severely limited use of aluminum-rich nitride films grown by molecular beam epitaxy. A way around these problems is through use of a liquid-metal-enabled approach to molecular beam epitaxy. Although the presence of a liquid metal layer at the growth front is reminiscent of conventional liquid phase epitaxy, this approach is different in its details. Conventional liquid epitaxy is a near-thermodynamic equilibrium process which liquid-metal assisted molecular beam epitaxy is not. Growth of aluminum-rich nitrides is primarily driven by the kinetics of the molecular vapor fluxes, and the surface diffusion of adatoms through a liquid metal layer before incorporation. This paper reports on growth of high crystalline quality and highly doped aluminum-containing nitride films. Measured optical and electrical characterization data show that the approach is viable for growth of atomically smooth aluminum-containing nitride heterostructures. Extremely high p-type doping of up to $6 \times 10$$^{17}$ cm$^{-3}$ and n-type doping of up to $1 \times 10$$^{20}$ cm$^{-3}$ in Al$_{0.7}$Ga$_{0.3}$N films was achieved. Use of these metal-rich conditions is expected to have a significant impact on high efficiency and high power optoelectronic and electronic devices that require both high crystalline quality and highly doped (Al,Ga)N films

Nuhschedule: A Web Application For Automated Course Scheduling

College students take on a large amount of coursework, and require much time and physical energy to be able to successfully complete their tasks. Students would like to develop course schedules that save them time spent on campus, and physical energy walking between halls on campus. These are somehow overlooked among the different schedule possibilities. In this thesis, we present a web application, named NuhSchedule, that is designed to automate the development of course schedules for students at Appalachian State University. Based on user preferences, like course sections, and break times, the application generates and presents a set of schedules that tries to optimize based on schedule conciseness (opting for minimum time on campus) and minimum walking time between halls on campus. These objectives allow students to save valuable time that could otherwise be spent on other activities, and physical energy by walking less between classrooms. A small-sampled beta-testing was performed with the help of actual students. Our schedules were found to be comparable to the manual ones created by them

Evaluating the effects and interaction of item set size and instructional time on student fluency growth rates with multiplication facts

The present study evaluated the effects and interaction of item set size and instructional time on students' fluency growth rates with multiplication facts over time when using an Explicit Timing intervention. The first goal was to determine an interaction between set size and instructional time across time that would influence the fluency growth rate on multiplication facts. A second goal was to determine an optimal combination of set size and instructional time to promote highest fluency growth rate. A third goal was to determine an optimal combination of set size and instructional time to enhance generalization of multiplication facts. A fourth goal was to determine an optimal combination of set size and instructional time to enhance maintenance of multiplication facts over time. A total of 11 fluency measures were taken among 204 fourth grade students from 10 general education classrooms among two public schools in central Oklahoma, who were randomly assigned to one of nine condition groups. Condition groups represented a combination among three levels of set size, defined as the number of multiplication problems, and three levels of instructional time, defined as minutes of instruction per session. Intervention and assessments were given in a class-wide group format. Teachers administered the intervention daily by playing a video, which contained instructions and four 2-minute built-in intervention timed intervals. The total number of digits answered correctly per minute determined fluency performance on each dependent measure (i.e., pre-test, progress monitoring, post-test). Data were analyzed using a 3 x 3 x 8 mixed ANOVA. The between-subjects factors were set size and instructional time, each containing three levels: 9-problems, 18-problems and 36-problems for set size and 2-minutes, 4-minutes and 8-minutes for instructional time. The within- subjects factor was time with eight levels, in the form of progress monitoring assessments (PM1-PM8). Results of the final analysis indicated the absence of a significant three-way interaction between set size, instructional time and time. However, within-subjects effects indicated a significant interaction between time and set size as well as between time and instructional time, indicating that all levels of set size and instructional time performed differently across time

Lead coprecipitation with iron oxyhydroxide nano-particles

Pb2+ and Fe3+ coprecipitation was studied with sorption edge measurements, desorption experiments, sorbent aging, High Resolution Transmission and Analytical Electron Microscopy (HR TEM–AEM), and geochemical modeling. Companion adsorption experiments were also conducted for comparison. The macroscopic chemical and near atomic scale HRTEM data supplemented our molecule scale analysis with EXAFS (Kelly et al., 2008). Coprecipitation of Pb2+ with ferric oxyhydroxides occurred at pH 4 and is more efficient than adsorption in removing Pb2+ from aqueous solutions at similar sorbate/sorbent ratios and pH. X-ray Diffraction (XRD) shows peaks of lepidocrocite and two additional broad peaks similar to fine particles of 2-line ferrihydrite (2LFh). HRTEM of the Pb–Fe coprecipitates shows a mixture of 2–6 nm diameter spheres and 8–20 by 200–300 nm needles, both uniformly distributed with Pb2+. Geochemical modeling shows that surface complexation models fit the experimental data of low Pb:Fe ratios when a high site density is used. Desorption experiments show that more Pb2+ was released from loaded sorbents collected from adsorption experiments than from Pb to Fe coprecipitates at dilute EDTA concentrations. Desorbed Pb2+ versus dissolved Fe3+ data show a linear relationship for coprecipitation (CPT) desorption experiments but a parabolic relationship for adsorption (ADS) experiments. Based on these results, we hypothesize that Pb2+ was first adsorbed onto the nanometer-sized, metastable, iron oxyhydrox- ide polymers of 2LFh with domain size of 2–3 nm. As these nano-particles assembled into larger particles, some Pb2+ was trapped in the iron oxyhydroxide structure and re-arranged to form solid solutions. Therefore, the CPT contact method pro- duced more efficient removal of Pb2+ than the adsorption contact method, and Pb2+ bound in CPT solids represent a more stable sequestration of Pb2+ in the environment than Pb2+ adsorbed on iron oxyhydroxide surfaces

The (mis)use of performance quartiles in metacognition and face perception: A comment on Zhou and Jenkins (2020) and Estudillo and Wong (2021)

A common measurement convention within the field of metacognition is to divide participants into quartiles based on task performance, and then compare self-estimated and actual scores within these sub-groups. This analysis strategy created the famous Dunning-Kruger effect, which asserts that the poorest performers tend to grossly overestimate their abilities. A study by Zhou and Jenkins (2020) has recently replicated this effect within the domain of face matching. However, it can be shown that the analysis strategy induces numerical artefacts prone to misinterpretation, and that randomly generated data lead to the same pattern of results. Estudillo and Wong (2021) used a different quartiles-based approach to argue that only the lowest and highest performers on a task of face recognition showed some insight into their performance. Again, a numerical artefact can explain their result, with the restricted range of the second and third quartiles causing reduced observed correlations between actual and self-estimated abilities. These studies highlight the need for methodological caution when exploring metacognitive questions, and we outline some avenues that may aid future investigation

Phase, grain structure, stress, and resistivity of sputter-deposited tungsten films

Sputter-deposited W films with nominal thicknesses between 5 and 180 nm were prepared by varying the base pressure prior to film deposition and by including or not including sputtered SiO(2) encapsulation layers. X-ray and electron diffraction studies showed that single phase, polycrystalline alpha-W could be achieved in as-deposited films as thin as 5 nm. The stress state in the as-deposited films was found to be inhomogeneous. Annealing resulted in stress relaxation and reduction of resistivity for all films, except the thinnest, unencapsulated film, which agglomerated. In-plane film grain sizes measured for a subset of the annealed films with thicknesses between 5 and 180 nm surprisingly showed a near constant value (101-116 nm), independent of film thickness. Thick-film ( \u3e = 120 nm) resistivity values as low as 8.6 mu Omega cm at 301 K were obtained after annealing at 850 degrees C for 2 h. Film resistivities were found to increase with decreasing film thicknesses below 120 nm, even for films which are fully A2 alpha-W with no metastable, A15 beta-W evident

Phase, grain structure, stress, and resistivity of sputter-deposited tungsten films

Sputter-deposited W films with nominal thicknesses between 5 and 180 nm were prepared by varying the base pressure prior to film deposition and by including or not including sputtered SiO(2) encapsulation layers. X-ray and electron diffraction studies showed that single phase, polycrystalline alpha-W could be achieved in as-deposited films as thin as 5 nm. The stress state in the as-deposited films was found to be inhomogeneous. Annealing resulted in stress relaxation and reduction of resistivity for all films, except the thinnest, unencapsulated film, which agglomerated. In-plane film grain sizes measured for a subset of the annealed films with thicknesses between 5 and 180 nm surprisingly showed a near constant value (101-116 nm), independent of film thickness. Thick-film ( \u3e = 120 nm) resistivity values as low as 8.6 mu Omega cm at 301 K were obtained after annealing at 850 degrees C for 2 h. Film resistivities were found to increase with decreasing film thicknesses below 120 nm, even for films which are fully A2 alpha-W with no metastable, A15 beta-W evident

Self-Directed Learning

This book on self-directed learning (SDL) is devoted to original academic scholarship within the field of education, and is the 6th volume in the North-West University (NWU) SDL book series. In this book the authors explore how self-directed learning can be considered an imperative for education in a complex modern society. Although each chapter represents independent research in the field of self-directed learning, the chapters form a coherent contribution concerning the scholarship of self-directed learning, and specifically the effect of environmental and praxis contexts on the enhancement of self-directed learning in a complex society. The publication as a whole provides diverse perspectives on the importance of self-directed learning in varied contexts. Scholars working in a wide range of fields are drawn together in this scholarly work to present a comprehensive dialogue regarding self-directed learning and how this concept functions in a complex and dynamic higher education context. This book presents a combination of theory and practice, which reflects selected conceptual dimensions of self-directed learning in society, as well as research-based findings pertaining to current topical issues relating to implementing self-directed learning in the modern world. The varied methodologies provide the reader with different and balanced perspectives, as well as varied and innovative ideas on how to conduct research in the field of self-directed learning