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Item Hexavalent chromium reduction by Cellulomonas sp. strain ES6: the influence of carbon source, iron minerals, and electron shuttling compounds(Springer Science and Business Media LLC, 2012-11) Erin K. Field; Robin Gerlach; Sridhar Viamajala; Laura K. Jennings; Brent M. PeytonThe reduction of hexavalent chromium, Cr(VI), to trivalent chromium, Cr(III), can be an important aspect of remediation processes at contaminated sites. Cellulomonas species are found at several Cr(VI) contaminated and uncontaminated locations at the Department of Energy site in Hanford, Washington. Members of this genus have demonstrated the ability to effectively reduce Cr(VI) to Cr(III) fermentatively and therefore play a potential role in Cr(VI) remediation at this site. Batch studies were conducted with Cellulomonas sp. strain ES6 to assess the influence of various carbon sources, iron minerals, and electron shuttling compounds on Cr(VI) reduction rates as these chemical species are likely to be present in, or added to, the environment during in situ bioremediation. Results indicated that the type of carbon source as well as the type of electron shuttle present influenced Cr(VI) reduction rates. Molasses stimulated Cr(VI) reduction more effectively than pure sucrose, presumably due to presence of more easily utilizable sugars, electron shuttling compounds or compounds with direct Cr(VI) reduction capabilities. Cr(VI) reduction rates increased with increasing concentration of anthraquinone-2,6-disulfonate (AQDS) regardless of the carbon source. The presence of iron minerals and their concentrations did not significantly influence Cr(VI) reduction rates. However, strain ES6 or AQDS could directly reduce surface-associated Fe(III) to Fe(II), which was capable of reducing Cr(VI) at a near instantaneous rate. These results suggest the rate limiting step in these systems was the transfer of electrons from strain ES6 to the intermediate or terminal electron acceptor whether that was Cr(VI), Fe(III), or AQDS.Item Dynamics of a plant–pollinator network: extending the Bianconi–Barabási model(Springer Science and Business Media LLC, 2024-06) Castillo, William J.; Burkle, Laura A.; Dormann, Carsten F.We study the dynamical assembly of weighted bipartite networks to understand the hidden mechanisms of pollination, expanding the Bianconi–Barabási model where nodes have intrinsic properties. Allowing for a non-linear interaction rate, which represents the seasonality of flowers and pollinators, our analysis reveals similarity of this extended Bianconi–Barabási model with field observations. While our current approach may not fully account for the diverse range of interaction accretion slopes observed in the real world, we regard it as an important step towards enriching theoretical models with biological realism.Item The effectiveness of traditional tests versus science lab reports as summative assessments(Montana State University - Bozeman, College of Letters & Science, 2022) Smith, Caleb Glaeser; Chairperson, Graduate Committee: C. John GravesThere are a number of different ways students can be assessed over a unit. The most common way is through traditional tests. This study was conducted to determine if scientific lab reports are more effective assessments to gauge what a student knows. To analyze this topic, students took traditional tests and wrote science lab reports, and the scores were compared. The results of the study found that students can express more of what they know in lab reports than in traditional tests.Item The effects of incorporating visual representation daily into the high school science classroom(Montana State University - Bozeman, College of Letters & Science, 2022) Finkbohner, Sydney Aaron; Chairperson, Graduate Committee: C. John GravesThe purpose of this study was to determine if student understanding and output on assessments would increase if visual representation, both teacher provided and student created, was used on a regular basis. A sub purpose of this study was to see if student attitudes and interest in the class increased when visual representation was used during the lessons. The same group of students went through a nontreatment unit and two treatment units in a conceptual chemistry course. The nontreatment unit, dimensional analysis, was taught in a more teacher centered way, using more lectures and traditional labs and little to no visual representation, while the treatment units, stoichiometry and solution: Molarity, were taught with daily visual representation, included demonstrations, manipulatives, hands on exploration labs, flow charts, and infographics. Pretest and post test scores for each unit were compared through normalized gains to see if there was an increase from the nontreatment unit to the two treatment units. Statistical testing indicated that students learned chemistry concepts better when visual representation were used during the learning process. The students had higher normalized gains on both treatment units compared to the non-treatment unit. Using visual representations on a regular basis also increased student interest and attitudes towards the content being taught. Students were more curious about the topics as well as had better attitudes about the class and what they were learning when they could see it visually and explore it though hands on explorations.Item The 5E model of learning in a chemistry classroom(Montana State University - Bozeman, College of Letters & Science, 2022) Lippert, Mercedes; Chairperson, Graduate Committee: C. John GravesThe 5E model of learning includes five stages: engage, explore, explain, evaluate, and elaborate. The focus of my action research was to study the effect of the 5E model of learning on student learning and retention in chemistry. The study also investigated its effect on students' attitudes towards science and inquiry. During the duration of the study, two chemistry units were taught to two high school chemistry classes consisting of a total of 35 students. One class was taught one unit with the 5E model while the other class was taught using traditional methods, and then the classes were swapped for the next unit. Average test scores among treatment and non-treatment groups were not very different. However, lower-level students largely benefitted from following the 5E model. Students' attitudes towards science and inquiry improved after treatment. I'm looking forward to further incorporating the 5E model in a chemistry classroom throughout the school year.Item Using case studies to help chemistry students understand science concepts(Montana State University - Bozeman, College of Letters & Science, 2021) Ronquillo, Elizabeth Roxanne; Chairperson, Graduate Committee: Greg FrancisThe purpose of this project was to study the effects of problem solving case studies on student understanding of high school concepts. Students were exposed to a case study that related chemistry content to real world applications. The project began with a non-treatment group studying periodic trends where students engaged in traditional chemistry learning activities which included reading, lecture, video, and virtual labs. The treatment group also had students engaged in traditional chemistry learning activities with the addition of including a real-world case study with class discussion. Data were collected using student pre-unit and post-unit assessments, surveys and interviews as a measure of student content understand, higher-level thinking, student attitude and motivation. Teacher data were also collected using student observations and teacher reflections to gain understanding of student attitudes and motivation. The data showed no difference between the two groups regarding post-assessment scores. The data showed some of the students' attitudes about science improved when applied to real world scenarios using case studies.Item The effects of incorporating organization in notebooks to synthesize knowledge in a high school chemistry class(Montana State University - Bozeman, College of Letters & Science, 2021) Herrington, Kendia Clara-Emma; Chairperson, Graduate Committee: Greg FrancisThe lack of organization in a science notebook makes it difficult for students to put multiple science concepts together in a chemistry class. This research study looked at how incorporating organization in notebooks through reflections on activities, group conversations, class discourse, summaries of labs, and creating a graphical organizer will impact their class conversation, self-regulation, and assessment scores. Three classes were studied over a full unit on bonding in a suburban chemistry class. Two classes were given a treatment of daily organizational support towards making a graphical organizer while the comparison group was given the same time without the guided questions or organizational support. A weekly survey of students' feelings on their understanding was given. The survey showed that overall students felt the graphical organizer was helpful. The comparison group found it overwhelming to complete without the guidance that the treatment received. The time each group took showed a significant difference in their ability to answer beginning of class questions. The treatment group showed a significant growth in their ability to make a graphical organizer. The students showed self-regulation by not completing different class assignments and assessments. The class discourse was very limited by both groups due to the class being online on Zoom. The treatment group showed a positive gain in supporting students in organizing a reflection notebook in their chemistry class because it forced them to do discourse.Item Goal setting in high school chemistry(Montana State University - Bozeman, College of Letters & Science, 2021) Cordon, Ryan Walter; Chairperson, Graduate Committee: Greg FrancisIn high school chemistry classes, it was evident that many students were not reaching their full academic potential. Most students would demonstrate their abilities but struggled to be consistent. These students often appeared to lack a sense of academic purpose. To help students find this purpose, research into the benefits of teaching goal setting to high school chemistry students was conducted. Students were taught how to set specific, measurable, achievable, relevant, and time-bound (SMART) goals. In each treatment unit, students took time in class to check-in on their goals and reflect on any potentially needed adjustments. The data showed that treatment helped many students and at least slightly helped most students find an academic purpose. Check-in data pertaining to students' goals showed that most students knew what to do, but a large portion lacked the motivation to actualize their intentions. While the data obtained herein demonstrated general success with regards to the methods of implementation, the treatment remains in need of further refinement. Findings show a larger emphasis is needed on identifying the rationale behind achieving each student's stated goals. Such a focus would enable students to find the motivation needed to take the acknowledged steps towards their goal.Item Influence of lithogenic energy on subglacial microbial community composition(Montana State University - Bozeman, College of Agriculture, 2021) Dunham, Eric Corwin; Chairperson, Graduate Committee: Eric Boyd; John E. Dore, Mark L. Skidmore, Eric E. Roden and Eric S. Boyd were co-authors of the article, 'Lithogenic hydrogen supports microbial primary production in subglacial and proglacial environments' in the journal 'Proceedings of the National Academy of Sciences of the United States of America' which is contained within this dissertation.; K. Rebecca Mitchell, Mark L. Skidmore and Eric S. Boyd were co-authors of the article, 'Influence of ferric iron on community composition in a basaltic glacial catchment' which is contained within this dissertation.Chemosynthesis, the generation of biomass using chemical energy, supported life on early Earth and continues to sustain contemporary light-independent ecosystems. The mechanisms of nutrient release from the geosphere are critical to understanding the present and historical distribution and diversity of life. Glaciers release such nutrients through comminution of bedrock, continuously resurfacing reactive minerals that can be colonized and exploited by chemosynthetic microorganisms. Bedrock mineralogy influences the nutrients available in these environments, but little is known about which nutrients are most important or how they affect microbial community composition, particularly in catchments overlying igneous bedrock like basalt. Iron and silicate minerals, common in basalt, readily generate both reductants such as H 2 and oxidants such as Fe(III) through interactions with water. Abundant H 2 in meltwaters of the basalt-based Icelandic glacier Kotlujokull (KJ) were found to support sediment microbial communities better adapted to use H 2 in chemosynthetic metabolism than those found beneath the carbonate-based Robertson Glacier (RG), Canada. KJ communities exhibited shorter lag-times and faster rates of net H 2 oxidation and dark carbon dioxide (CO 2) fixation than those from RG. A KJ sediment enrichment culture provided with H 2, CO 2, and Fe(III) produced a chemolithoautotrophic population related to Rhodoferax ferrireducens, which was also detected using molecular techniques in sediments from Kaldalonsjokull (Kal), another basalt-based Icelandic glacier. The abundance and composition of microbial communities that colonized defined minerals incubated for 12 months in Kal meltwater streams were examined by extracting DNA and sequencing PCR-amplifiable 16S rRNA genes. DNA quantities and the composition of 16S rRNA genes recovered from Kal sediments were most similar to those recovered from incubated Fe(III)-bearing minerals hematite and magnetite, with putative Fe(III) reducers dominating all three communities. These findings point to the importance of bedrock mineral composition in influencing the supplies of nutrients like H 2 and Fe(III) that, in turn, influence the diversity, abundance, and activity of microbial communities in subglacial environments. They further indicate the potential for subglacial habitats to serve as refugia for microbial communities in the absence of sunlight, such as during Snowball Earth episodes, or on icy planets without photosynthetic life.Item The effects of atomic oxygen on silicon-carbon systems in extreme environments(Montana State University - Bozeman, College of Letters & Science, 2021) Chen, David Zuyu; Chairperson, Graduate Committee: Timothy Minton; Chenbiao Xu, Vanessa J. Murray and Timothy K. Minton were co-authors of the article, 'Oxidation of silicon carbide through the passive-to-active transition' submitted to the journal 'The journal of chemical physics' which is contained within this dissertation.; Chenbiao Xu and Timothy K. Minton were co-authors of the article, 'Effect of atomic oxygen on CV-1144-0 and RTV-560 silicones' submitted to the journal 'Acta astronautica' which is contained within this dissertation.; Chenbiao Xu and Timothy K. Minton were co-authors of the article, 'Effect of silicone coating on atomic oxygen reactivity with fiberform and phenolic impregnated carbon ablator' submitted to the journal 'Journal of spacecraft and rockets' which is contained within this dissertation.Vehicles traveling at hypersonic speeds require thermal protection systems (TPSs) that can withstand the extreme temperatures and reactive atomic oxygen species present in these environments. Ultra-high temperature ceramics are candidate TPSs, and many of them contain silicon carbide, allowing them to resist chemical attack by forming a protective oxide-containing layer, called passive oxidation. At very high temperatures, however, the layer will decompose, subjecting the material to ablation from reaction with O-atoms, called active oxidation, through a process called the passive-to-active oxidation transition (PAT). We have conducted molecular beam-surface scattering experiments to investigate the interactions of O-atoms with SiC at high temperatures, which revealed that with a lower fluence of O-atoms above the PAT, the SiC surface undergoes graphitization, while a sufficiently higher fluence of O-atoms promotes active oxidation. Analysis of the oxide layer decomposition revealed a decomposition process that initiated at the oxide-SiC interface. These insights will be useful for the development of more accurate predictive models, but they also aided understanding of the ablation of silicone-coated heat shields for atmospheric entry applications. For these applications, phenolic impregnated carbon ablator (PICA), a material composed of a carbon fiber network (FiberForm) and a resole phenolic resin stable against high heat convection and conduction, is used. Silicone is sprayed onto PICA to reduce dust, but the silicone can also form an oxide layer, which, like on SiC, will resist O-atom attack until it decomposes at very high temperatures, exposing the underlying material to reactive O-atoms. We conducted additional experiments in which a beam of atomic oxygen was directed at silicone-coated and uncoated samples of PICA as well as FiberForm, which revealed high nonreactive O-atom product scattering when the oxide layer was present, while with the decomposition of the oxide, product scattering resembled O-atom scattering from the underlying substrate. Additional studies probed the oxidation layer that is formed on pure silicone during O-atom bombardment, which revealed a three orders of magnitude reduction in erosion yield compared to that of Kapton H, a polyimide. This new data on PICA and FiberForm has been provided to NASA Ames for their development of an ablation model.