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Teachers use digital activities for student collaboration; however, it is not known what digital collaboration strategies teachers implement, nor how they perceive students' ability to apply collaboration skills in a digital environment. It is necessary to understand strategies needed by students to be able to collaborate in a digital environment. The purpose of this basic qualitative study was to explore secondary teachers' experiences involving implementing digital collaboration strategies and their perceptions of students' development of digital collaboration skills. Vygotsky's social learning theory and Siemens' connectivism theory were used to guide research questions for this study. Taken together, these theories hold that learning is social in nature and can be technologically enhanced. The criteria for participant selection, via purposeful and snowball sampling, included teaching in a rural mid-Atlantic Title I secondary school that had digital learning initiatives where each student had their own device. Data from 13 semistructured interviews were analyzed using open coding to generate themes. Findings indicated that teachers could use communication, leadership, critical thinking, and problem-solving skills in their secondary classrooms to help students develop digital collaborative skills. This study contributes to social change by providing deeper understanding into the phenomenon. This, in turn, promotes needed skills, including digital collaboration and critical thinking, that can help students become more successful in the classroom. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Bismuth-containing semiconducting materials were used as visible light absorbing heterogeneous photocatalysts for selective chemical transformations. The work demonstrates the importance of kinetic control in achieving selectivity; either through photocatalyst inhibition or through the presence of reagents capable of fast reactions with known intermediates. Bismuth oxide (β-Bi2O3), bismuth ferrite (BiFeO3), bismuth tungstate microflowers (Bi2WO6) and bismuth vanadate nanoparticles (nan-BiVO4) were synthesised and characterised by PXRD, SEM, DRUVS and BET. The bismuth-containing oxides were compared as photocatalysts for the aerobic oxidation of benzyl alcohol. The highest benzyl alcohol conversion (88%) and benzaldehyde selectivity (95%) was achieved with the use of nan-BiVO4. Further modifications to nan-BiVO4 resulted in materials that were less active for selective benzyl alcohol oxidation than unmodified nan-BiVO4. Further study of nan-BiVO4 as a heterogeneous photocatalysts for the selective oxidation of para-substituted benzyl alcohols was carried out. It was found that alcohol conversions and aldehyde selectivities were affected by by-product inhibition. The addition of 1 mol% 4-methoxybenzoic acid significantly reduced 4-methoxybenzyl alcohol conversion (to 49%). Isotopically labelled benzyl alcohols were used to show that α C-H bond cleavage was not rate limiting. However, changes in charge carrier lifetimes observed using TRPLS suggested that the charge carriers associated to the lifetimes observed were relevant to benzyl alcohol oxidation. Bismuth-containing semiconductors were also investigated as trifluoromethylation heterogeneous photocatalysts. Nan-BiVO4 was capable of oxytrifluoromethylation of styrene via the reduction of Umemoto’s reagents. The highly selective reaction produced the corresponding trifluoromethylated ketone in an 88% yield. Platinised bismuth tungstate (0.15-Pt-Bi2WO6) was found to give high conversions and product selectivities for the formation of Photo-Giese products (phenylacetic acid conversion = 99%, Photo-Giese product selectivity = 94%). Several coupling products were synthesised from different carboxylic acids and electron deficient alkenes. Competitive adsorption from by-products inhibition had an impact on acid conversions and Photo-Giese product selectivities.

This thesis explores the nature of river dunes in unsteady conditions. River dune research has two main philosophical approaches that are necessitated by the nature of dunes; they are individually dynamic features emergent from the interaction between flow and sediment transport, whilst this dynamism is restricted by a mixture of instantaneous and historical flow and sediment boundary conditions. This thesis has applied both philosophical approaches to the investigation of river dunes in unsteady conditions and highlights key areas where flow and sediment processes at the laboratory scale overlap that of the larger scale river, such as in the suspension of sediment, and importance of velocity profile shape on dune shape. Normalising the downstream velocity with shear velocity was repeatedly found to simplify and explain the fluid processes over dunes across a range of conditions and indicates that the dominant processes controlling dune shape and sediment mobility are hydraulically smooth, despite hydraulically rough grain sizes. The existence of a turbulent wave over dunes reduces the magnitude of flow velocity that reaches the bed and effectively changes the grain Reynolds number. This turbulent flow structure was extensively measured in this thesis, with detailed instantaneous flow velocity measurements, across a range of flow conditions over fixed bedforms with the use of Particle Imaging Velocimetry. This also revealed that the well-known equilibrium turbulent flow structure over dunes is dramatically altered when in transient flow-morphology conditions. It was found that the wake and stacked wake, changes location and intensity with flow depth and discharge, and that reattachment length is strongly related to U/u* as measured at the dune crest. This research provides descriptions of the causal mechanisms behind many bedform adaptions to flow unsteadiness, such as the formation of humpback dunes in high shear stress conditions. A second set of laboratory experiments explored the mean scaling of dunes with a mobile bed in a recirculating flume. The mean velocity profile shape was adjusted to move the point of maximum downstream velocity toward the bed, whilst keeping depth and depth averaged velocity- two variables used in almost all bedform stability diagrams, the same. It was found that dune height scaled with bed shear stress in a parabola, whilst dune wavelength scaled linearly. This indicates that dune height is primarily controlled via flow separation and dune wavelength scales most well is shear velocity and grain size (i.e. sediment transport lengths). Lastly, dunes were measured in the field during the falling leg of the monsoonal wet season floods on a section of the Mekong River in Cambodia. The river bed consisted of large dunes with superimposed bedforms. The geometry of the large dunes showed no relationship with the hydraulic conditions present; however the secondary dunes size responded to the variations in flow depth. All large dunes migrated at a constant rate, despite variation in height, and it was hypothesised that the superimposed bedforms provided any excess sediment for the host dune migration. Large dune height was half that predicted from empirical equations using flow depth. Variations in suspended sediment did not match those predicted via the Rouse number, instead, plotting U/u*, across variations in discharge and depth showed a good relationship with suspended sediment concentration. This relationship between flow structure and suspended sediment, with the concurrent variation secondary dune size indicated that the large dunes were depth limited. This is despite the consistent presence of secondary dunes at the crest of the host bedform or strong free surface interaction and suggests that dune height in rivers with superimposed bedforms is controlled by the existence of superimposed bedforms.