Scholarworks

ScholarWorks is an open access repository for the capture of the intellectual work of Montana State University (MSU) in support of its teaching, research and service missions. MSU ScholarWorks is a central point of discovery for accessing, collecting, sharing, preserving, and distributing knowledge to the Montana State University community and the world.

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Positioning theory as a framework for understanding student engagement in mathematical modeling competencies
(Montana State University - Bozeman, College of Letters & Science, 2025) Greene, Mary Philomena; Chairperson, Graduate Committee: Mary Alice Carlson
While mathematical modeling is more prominent in secondary grades, research has demonstrated that elementary learners are also capable of mathematical modeling - the process of translating open-ended, real-world situations into mathematical representations, developing models, generating solutions, and interpreting solutions within the context. Student facility with modeling can be viewed through their engagement in mathematical modeling competencies, the set of skills students use to carry out the modeling process. Although research on mathematical modeling in the elementary grades is still in its infancy, scholars increasingly advocate for providing these learners with greater access to modeling experiences. Elementary students are both capable of and benefit from experiences with mathematical modeling. Situated within the theoretical framework of positioning theory, this study investigated how fourth-grade students engaged in mathematical modeling competencies during group-work conversations. Positioning theory illuminates how students' social interactions shape the positions they enact and, in turn, influence their engagement in modeling competencies. Using two groups of three and four students, this qualitative case study examined how students' use of the task context and their enacted positions influenced their engagement in modeling competencies during group conversations. Findings indicate that student attention to the context of the situation supported their access to and engagement in modeling competencies, particularly when developing mathematical models and generating solutions. Additionally, student positions were linked to differing levels of positional authority that influenced their access to and engagement in modeling competencies. These findings contribute to the limited literature on elementary students' modeling work by illustrating how engagement in modeling competencies is interactionally produced and mediated through positioning and contextual engagement. The study offers implications for theory, practice, and research by extending positioning theory into modeling conversations, supporting teacher facilitation of modeling tasks, and suggesting directions for future research on learning and assessment in elementary mathematical modeling.
Development and characterization of salt hydrate and nanocellulose composites for thermal energy storage
(Montana State University - Bozeman, College of Letters & Science, 2025) Blake, Daniel C.; Chairperson, Graduate Committee: Dilpreet S. Bajwa; This is a manuscript style paper that includes co-authored chapters.
Salt hydrates have demonstrated thermal energy storage capabilities via reversible bonding of water molecules. Materials exhibit an energy density of 400-870 kWh/m 3, operate at low temperatures (<150°C), are generally low-cost, but are prone to degradation. Previous efforts to improve stability have primarily focused on impregnating a porous host matrix with salt. However, salt expansion during hydration leads to degradation of the host matrix and salt leakage. Cellulose nanocrystals (CNCs) have shown promise in strengthening the structural frameworks of composites across numerous applications. CNCs have generated significant interest due to their high mechanical strength, high aspect ratio, high surface area, liquid-crystalline nature, and hydrophilicity, which support interaction between salt and water. CaCl 2, MgSO 4, and SrCl 2 were employed in the study, as well as several blends of species (MgSO 4:SrCl 2; SrCl2:CaCl 2; MgSO 4:CaCl 2). Salts and CNCs are combined to produce composites with varying mass ratios (60:40, 80:20, 90:10). Material performance is evaluated using simultaneous thermal analysis. SrCl 2:CNC and SrCl 2:CaCl 2:CNC (SrCl 2:CaCl 2-90:10) are the most promising materials that were developed based on energy density and uniformity. SrCl 2-based formulations possess high energy storage capabilities exceeding 600 J/g and demonstrate unique interactions with CNC through water molecules. CNCs were produced from waste sugar beet pulp (SBP) to develop a more sustainable and cost-effective process. SBPCNC-containing formulations exhibit lower energy density than those using control CNC, attributed to reduced purity, zeta potential magnitude, crystallinity, and a larger aspect ratio. FTIR results indicate that the salt:CNC chemical interaction is mediated by electrostatic forces between CNC and the water molecules of the salt hydrate. The interpretations are supported by Raman spectroscopy, which also indicates unique salt:CNC lattice vibrations and/or CNC effects on water vibrations--the hydrophilic properties of CNC increase drying resistance by binding free water and water molecules in salt hydrates. The composite materials form through mechanical and electrostatic interactions, with strong chemical affinity between the components, which supports material stability.
Maternal environment and embryo origin effects on placental function, offspring vigor, growth, and reproductive parameters
(Montana State University - Bozeman, College of Agriculture, 2025) Brenner, Makayla Anne; Chairperson, Graduate Committee: Sarah R. McCoski; This is a manuscript style paper that includes co-authored chapters.
Maternal nutrition and the use of assisted reproductive technologies have previously been reported to impact placental function, nutrient transfer, calf growth and vigor, and offspring reproductive parameters. It is important to describe these effects as they may uncover new targets for improving embryonic and fetal development and pregnancy retention in livestock species. The overreaching goal of this work was to determine how maternal nutrition and embryo origin affects offspring growth through weaning, neonate vigor, and reproductive parameters. For study 1) we hypothesized that maternal injectable mineral administration during mid and late gestation will improve calf growth through weaning and offspring reproductive parameters. Lastly, in study 2) we hypothesized that embryo origin would alter placental hormone production consequently impacting placental morphology, calf vigor and growth through weaning. Study 1) A total of 278 cows were enrolled in the study, blocked by body weight, parity, and day of gestation, and then randomly assigned to one of two groups: 1) a group that received an injectable mineral (MM = 138) or control group (CON = 138) which did not receive injectable mineral. Adjusted birth weight and weaning weights were recorded. Calves whose dams received the mineral injection were heavier at birth compared to the control (P = 0.05). Study 2) Cows carrying an artificial insemination derived pregnancy (AI = 23), natural service derived pregnancy (NS = 23), or in- vitro produced embryo (IVP = 23) were randomly selected for placental collection and calf vigor and growth assessments. A group by calf sex interaction was observed for calf birth weight, time between birth and nursing (minutes), and time between standing and nursing (minutes; P < or = 0.05). Overall, the method by which embryo was produced, or the intrauterine environment can positively, negatively, or have no impact on the postnatal growth and development of the offspring.
Investigation into the influence of surface & microstructural characteristics on the corrosion of metallic materials through advanced materials characterizations
(Montana State University - Bozeman, College of Engineering, 2025) Acharjee, Amit; Chairperson, Graduate Committee: Roberta Amendola; This is a manuscript style paper that includes co-authored chapters.
Corrosion of metallic materials is a persistent issue that causes industries worldwide to suffer immense financial losses, yet the underlying principles of corrosion are still not fully understood. As a result, predicting and preventing it remains a challenge. This dissertation focuses on how key material properties such as microstructural features, surface topography and surface work function affect the degradation behavior of metallic materials during both abiotic and microbial corrosion. It also aims to develop streamlined strategies to mitigate corrosion by modifying these properties. Three complementary studies were conducted in this regard. The first study examined the effects of varying surface roughness of copper on microbiologically influenced corrosion (MIC) by a model sulfate-reducing bacterium, Oleisdevibrio alaskensis G20, under anaerobic conditions using microscopic, spectroscopic, and surface characterization techniques. The second study focused on modifying the microstructure of copper to increase the fraction of special low- energy Sigma3 grain boundaries by optimizing heat-treatment parameters and investigating their influence on corrosion behavior. The third study employed a novel characterization method to identify corrosion-susceptible regions on metallic surfaces by mapping work function variations using a state-of-the-art scanning auger nanoprobe. The studies revealed that a reduction of up to 75% in MIC rate was achieved by modifying the surface roughness of pure copper coupons during anaerobic biotic exposure. Also, microstructural modification by increasing the special grain boundary fraction through annealing reduced the corrosion rate of copper by 32% compared to as-received copper and showed a more stable electrochemical behavior as well as developed a comparatively uniform and protective oxide film. The work function mapping using scanning auger nanoprobe was successfully employed to predict regions of preferential corrosion initiation in both multiphase 1018 carbon steel and single- phase pure copper coupons. By integrating microstructural optimization and surface characteristics, this dissertation provides a framework for corrosion mitigation strategies in metallic materials, spanning both fundamental research and applied materials design.
Mechanistic and spectroscopic investigations of radical generation and epimerization pathways in radical SAM enzymes
(Montana State University - Bozeman, College of Letters & Science, 2025) Gleason, Andrew Buckley; Chairperson, Graduate Committee: Joan B. Broderick
Metalloproteins are ubiquitous biocatalysts that mediate diverse chemical transformations by exploiting the redox flexibility of metal cofactors. Among these, iron-sulfur (FeS) clusters are exceptionally versatile, enabling electron transfer, radical generation, and complex bond-forming reactions. The radical S-adenosyl-L-methionine (rSAM) superfamily represents one of the largest and most functionally diverse groups of enzymes that rely on [4Fe-4S] clusters to catalyze chemically challenging reactions via radical intermediates. In these enzymes, SAM coordinates to the unique iron of the [4Fe-4S] cluster, undergoing reductive cleavage to generate the potent 5'-deoxyadenosyl radical (5'-dAdo*). The work described in this chapter first examines the electronic basis of SAM activation, highlighting the substantial thermodynamic barrier between SAM reduction and cluster redox potentials, and presents evidence implicating the Jahn-Teller effect in determining the regioselectivity of S-C bond cleavage. The latter section focuses on the biochemical and spectroscopic characterization of OpgD, a newly identified radical SAM epimerase belonging to the origamin family. EPR analysis of OpgD reveals an auxiliary [4Fe-4S] cluster (AuxI) that may participate in electron transfer or radical quenching during catalysis. Together, these studies advance our understanding of sulfonium activation and the functional diversity of auxiliary clusters in radical SAM enzymes.