College of Letters & Science
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The College of Letters and Science, the largest center for learning, teaching and research at Montana State University, offers students an excellent liberal arts and sciences education in nearly 50 majors, 25 minors and over 25 graduate degrees within the four areas of the humanities, natural sciences, mathematics and social sciences.
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Item A Photovoltaic Self-Powered Volatile Organic Compounds Sensor Based on Asymmetric Geometry 2D MoS2 Diodes(The Electrochemical Society, 2024-09) Fawzy, Mirette; Reza Mohammadzadeh, Mohammad; Abnavi, Amin; De Silva, Thushani; Ahmadi, Ribwar; Ghanbari, Hamidreza; Kabir, Fahmid; Kavanagh, Karen L.; Hasani, Amirhossein; Adachi, Michael M.Transition metal dichalcogenides have gained considerable interest for vapour sensing applications due to their large surface-to-volume ratio and high sensitivity. Herein, we demonstrate a new self-powered volatile organic compounds (VOC) sensor based on asymmetric geometry multi-layer molybdenum disulfide (MoS2) diode. The asymmetric contact geometry of the MoS2 diode induces an internal built-in electric field resulting in self-powering via a photovoltaic response. While illuminated by UV-light, the sensor exhibited a high responsivity of ∼60% with a relatively fast response time of ∼10 sec to 200 ppm of acetone, without an external bias voltage. The MoS2 VOC diode sensor is a promising candidate for self-powered, fast, portable, and highly sensitive VOC sensor applications.Item 2D MoSe2 Geometrically Asymmetric Schottky Photodiodes(Wiley, 2024-09) Ghanbari, Hamidreza; Abnavi, Amin; Ahmadi, Ribwar; Reza Mohammadzadeh, Mohammad; Fawzy, Mirette; Hasani, Amirhossein; Adachi, Michael M.Optoelectronic devices based on geometrically asymmetric architecture have recently attracted attention due to their high performance as photodetectors and simple fabrication process. Herein, a p-type 2D MoSe2 photodetector based on geometrically asymmetric contacts is reported for the first time. The device exhibits a high current rectification ratio of ≈104 and a large self-powered photovoltage responsivity of ≈4.38 × 107 V W−1, as well as a maximum photocurrent responsivity of ≈430 mA W−1 along with a response time of ≈2.3 ms under 470 nm wavelength at 3 V bias voltage. The photocurrent responsivity is further enhanced to an ultrahigh responsivity of ≈1615 mA W−1 by applying a gate bias voltage due to the electrostatic modulation of carrier concentration in the MoSe2 channel. The simple fabrication process of the geometrically asymmetric MoSe2 diodes along with their high photodetection and diode rectifying performance make them excellent candidates for electronic and optoelectronic applications.Item The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya(GeoScienceWorld, 2024-10) Giri, Bibek; Hubbard, Mary; McDonald, Christopher S.; Seifert, Neil; KC, BishalThe Benkar Fault Zone (BFZ) is a recently recognized, NNE-striking, brittle to ductile, cross fault that cuts across the dominant metamorphic fabric of the Greater Himalayan Sequence (GHS) and the Lesser Himalayan Sequence (LHS) in eastern Nepal. 40Ar/39Ar-muscovite cooling ages along a transect across the BFZ in the GHS indicate movement younger than 12 Ma. To understand the mode of genesis, and seismo-tectonic implications of the BFZ, we mapped this fault from the Everest region in the upper Khumbu valley toward the south, across the Main Central Thrust, into the LHS and the Greater Himalayan Nappe. We recognize a series of cross faults segments, which we interpret the BFZ system. The currently mapped section of the BFZ is >100 km long, and its width is up to 4 km in the LHS. The BFZ is semi-ductile in the GHS region but is brittle in the south, where it is expressed as gouge zones, tectonically brecciated zones, sharp fault planes, and segments of nonpenetrative brittle deformation zones. From petrographic and kinematic analysis, we interpret largely a right-lateral, extensional sense of shear. Our work did not continue into the Sub-Himalaya, but the BFZ may continue through this zone into the foreland as documented in other Himalayan cross faults. While several genetic models have been proposed for cross faults in the Himalaya and other convergent orogens, we suggest that the BFZ may be related to extensional structures in Tibet. Understanding cross faults is not only important for the tectonic history of the Himalaya but due to the co-location of cross faults and seismogenic boundaries, there may be a causal relationship. Cross faults also follow many of the north-south river segments of the Himalaya and weakened fault rocks on the valley walls may enhance the landslide hazard in these areas.Item Increased Formation of Trions and Charged Biexcitons by Above-Gap Excitation in Single-layer WSe2(American Chemical Society, 2024-11) Strasbourg, Matthew; Yanev, Emanuil; Parvez, Sheikh; Afrin, Sajia; Johns, Cory; Noble, Zoe; Darlington, Thomas; Grumstrup, Erik M.; Hone, James; Schuck, P. James; Borys, Nicholas J.Two-dimensional semiconductors exhibit pronounced many-body effects and intense optical responses due to strong Coulombic interactions. Consequently, subtle differences in photoexcitation conditions can strongly influence how the material dissipates energy during thermalization. Here, using multiple excitation spectroscopies, we show that a distinct thermalization pathway emerges at elevated excitation energies, enhancing the formation of trions and charged biexcitons in single-layer WSe2 by up to 2× and 5× , respectively. Power- and temperature-dependent measurements lend insights into the origin of the enhancement. These observations underscore the complexity of excited state relaxation in monolayer semiconductors, provide insights for the continued development of carrier thermalization models, and highlight the potential to precisely control excitonic yields and probe nonequilibrium dynamics in 2D semiconductors.Item Width-dependent continuous growth of atomically thin quantum nanoribbons from nanoalloy seeds in chalcogen vapor(Springer Science and Business Media LLC, 2024-11) Li, Xufan; Wyss, Samuel; Yanev, Emanuil; Li, Qing-Jie; Wu, Shuang; Sun, Yongwen; Unocic, Raymond R.; Stage, Joseph; Strasbourg, Matthew; Sassi, Lucas M.; Zhu, Yingxin; Li, Ju; Yang, Yang; Hone, James; Borys, Nicholas; Schuck, P. James; Harutyunyan, Avetik R.Nanoribbons (NRs) of atomic layer transition metal dichalcogenides (TMDs) can boost the rapidly emerging field of quantum materials owing to their width-dependent phases and electronic properties. However, the controllable downscaling of width by direct growth and the underlying mechanism remain elusive. Here, we demonstrate the vapor-liquid-solid growth of single crystal of single layer NRs of a series of TMDs (MeX2: Me = Mo, W; X = S, Se) under chalcogen vapor atmosphere, seeded by pre-deposited and respective transition metal-alloyed nanoparticles that also control the NR width. We find linear dependence of growth rate on supersaturation, known as a criterion for continues growth mechanism, which decreases with decreasing of NR width driven by the Gibbs-Thomson effect. The NRs show width-dependent photoluminescence and strain-induced quantum emission signatures with up to ≈ 90% purity of single photons. We propose the path and underlying mechanism for width-controllable growth of TMD NRs for applications in quantum optoelectronics.Item Multistability and predominant hybrid phenotypes in a four node mutually repressive network of Th1/Th2/Th17/Treg differentiation(Springer Science and Business Media LLC, 2024-10) Srinivas Duddu, Atchuta; Andreas, Elizabeth; BV, Harshavardhan; Grover, Kaushal; Raj Singh, Vivek; Hari, Kishore; Jhunjhunwala, Siddharth; Cummins, Breschine; Gedeon, Tomas; Kumar Jolly, MohitElucidating the emergent dynamics of cellular differentiation networks is crucial to understanding cell-fate decisions. Toggle switch – a network of mutually repressive lineage-specific transcription factors A and B – enables two phenotypes from a common progenitor: (high A, low B) and (low A, high B). However, the dynamics of networks enabling differentiation of more than two phenotypes from a progenitor cell has not been well-studied. Here, we investigate the dynamics of a four-node network A, B, C, and D inhibiting each other, forming a toggle tetrahedron. Our simulations show that this network is multistable and predominantly allows for the co-existence of six hybrid phenotypes where two of the nodes are expressed relatively high as compared to the remaining two, for instance (high A, high B, low C, low D). Finally, we apply our results to understand naïve CD4+ T cell differentiation into Th1, Th2, Th17 and Treg subsets, suggesting Th1/Th2/Th17/Treg decision-making to be a two-step process.Item Melt embayments record multi-stage magma decompression histories(Elsevier BV, 2024-10) Hosseini, Behnaz; Myers, MadisonOver the last decade, the melt embayment has proven its merit as a robust petrological tool capable of recording magma decompression rates for explosive eruptions. However, the models developed and applied to extract this information from embayments have not accounted for the complexity and nonlinearity of magma flow in the conduit. We present Embayment Decompression in Two Stages (EDiTS): a numerical model for extracting magma decompression rates from measured volatile diffusion profiles preserved in crystal-hosted embayments, approximating magma acceleration using two constant-rate decompression paths. This model solves for three unknown parameters: initial (deeper) and final (shallower) decompression rates, as well as the pressure where a transition occurs. We successfully benchmark EDiTS against existing numerical diffusion models, and use controlled multi-stage decompression experiments on natural quartz-hosted embayments to test the ability of our model to recover known decompression paths. We find that EDiTS is able to closely approximate the known two-stage path in the mixed-volatile (H2O + CO2) experiment, while a constant-rate modeling approach is unable to simultaneously fit H2O and CO2 gradients. However, in the H2O-saturated experiment, there is no unique solution to the resulting gradient, with both constant-rate and two-stage models reproducing the measured profile, and EDiTS notably overestimating the known total ascent time by several hours. Using decompression experiments, we show that constant-rate models can provide misleadingly good fits to embayment H2O gradients produced by more complex decompression histories, and thus the measurement and modeling of multiple diffusing species, when available, can provide crucial constraints. We then apply EDiTS to re-evaluate mixed-volatile embayment datasets from explosive silicic arc and caldera-forming eruptions from five volcanic centers (Yellowstone, WY, USA; Valles, NM, USA; Long Valley, CA, USA; Taupo, NZ; Mount St. Helens, WA, USA). In contrast to the minutes to hours of total ascent time extracted from embayment volatile profiles using constant-rate models, our two-stage model resolves slower initial ascent times that span 3.5–11 h. Final ascent rates are 1–2 orders of magnitude faster than the initial extracted rates, in agreement with theoretical conduit flow model predictions. Reassessment of embayments from the May 18th, 1980 eruption of Mount St. Helens results in an initial stage of ascent consistent with the timing of magma arrival at the surface from the seismically-inferred storage region (7–9 km) ∼3.5 h after the initial blast, and a final stage of ascent (<1–5 min) in close agreement with time-integrated bubble number densities. Our combined numerical and experimental results, and reevaluation of natural datasets, suggest that, with the application of advanced models, the melt embayment can provide a more nuanced picture of magma decompression timescales from the deep conduit to the surface.Item Evaluation of nature-based climate solutions for agricultural landscapes in the Galapagos Islands(Elsevier BV, 2024-10) Alomia, Ilia; Molina, Armando; Montes, Tessenia; Dixon, J. L.; Vanacker, VeerleThe Galápagos Islands are highly vulnerable to climate and environmental change, and nature-based solutions can help local communities adapt local agricultural systems. Through a comparative analysis, we evaluated the effects of three land management strategies on soil temperature, soil water availability and storage, and carbon stocks in Santa Cruz Island (Galápagos Archipelago). We installed six monitoring sites that consisted of two replicates per pathway: (i) the avoided loss of tropical forest, (ii) the conservation of scattered trees and living fences in at-risk agroforestry system, and (iii) the increase in biomass after a reduction of the grazing intensity. The monitoring sites were equipped with a dense network of rain gauges, air temperature and relative humidity sensors, and capacitance/frequency probes that registered volumetric water content and soil temperature. After pedological characterization of the soil profiles, the soil physico-chemical and hydrophysical properties were determined in laboratory. Over a period of 30 months (July 2019 to December 2021), hydrometeorological and soil environmental data were collected. We assessed differences in soil temperature, moisture availability and soil organic carbon content between native forests, sites under traditional agroforestry and under passive restoration. Forest soils were 12 % cooler;, and soil moisture under forest was 20 % higher than in parcels with silvopastural management. Forest soils had a lower dry bulk density, lower saturated hydraulic conductivity and higher water retention capacity in comparison with the other two management types. In silvopastural systems, a decrease of grazing intensity had a positive effect on soil carbon stocks, that were about 50 % higher than in soils under traditional management. This study shows that avoided loss of tropical forest within an agricultural landscape is a promising strategy to mitigate increasing soil temperatures, agricultural drought, and decline in soil organic carbon content. Continued monitoring of the experimental sites is necessary to corroborate the findings of this investigation at longer temporal scales.Item Hurricane‐induced changes in mayfly assemblage structure, production and emergence in a tropical island stream(Wiley, 2024-10) Ramírez, Alonso; Meza-Salazar, Ana María; Gómez, Jesús E.; Gutiérrez‐Fonseca, Pablo E.; Sánchez-Ruíz, Jose A.Hurricanes are major disturbances with important consequences to stream ecosystems as they create major floods and remove riparian vegetation. Understanding their impacts is a priority, as hurricane intensity is expected to increase due to global climate change. Mayfly assemblages in streams fill a diversity of ecological roles and functions. They are important consumers of algae by scraping benthic biofilms and detritivores associated with fine particles and leaf litter. Other taxa are filterers and even predators. Mayflies are also important prey items in aquatic and terrestrial food webs. Here, we assessed the effects of two consecutive hurricanes that impacted Puerto Rico in 2017 to understand how hurricane-induced changes in the environment alter mayfly composition, secondary production and emergence. The study was conducted in the Luquillo Experimental Forest, Puerto Rico. Mayflies were sampled as nymphs and emerging adults for 6 months before and 17 months after hurricanes Irma and María hit the island in September 2017. Leaf litter inputs, canopy cover and chlorophyll a concentrations were monitored along with mayflies. Mayfly assemblages were dominated by two genera of Leptophlebiidae before the hurricane, Neohagenulus (two species: N. julio Traver, 1938, N. luteolus Traver, 1938) and Borinquena (one species: B. carmencita Traver, 1938). Both genera decreased in density after the hurricanes and were replaced with the Baetidae Cloeodes maculipes Traver, 1938 as the dominant taxon. This pattern was observed in both nymph and emerging adult densities. The secondary production of Leptophlebiidae species was highest before hurricane disturbance, with the Baetidae C. maculipes showing the opposite pattern. Neohagenulus had an annual production of 445 mg m−2 year−1, C. maculipes of 153 mg m−2 year−1 and B. carmencita of 68 mg m−2 year−1. Overall, the mayfly assemblages in our studied stream are vulnerable to hurricane disturbances. Expected increases in hurricane impacts might result in assemblage shifts that could change assemblage composition and alter energy flows within the ecosystem.Item Sleeping on the Edge: Adolescents Living at Moderate Altitude Report Greater Sleep Need(Elsevier BV, 2024-10) Montenegro, Alexandria; Alvarado, Giovanni; Hilton, Ashleigh; Palmer, Cara A.Purpose. Research in adults suggests that altitude impacts the restorative properties of sleep and increases risk for mental health concerns. The aim of this study was to extend this research to an adolescent sample to examine how living at altitude may be associated with greater sleep need and mental health symptoms during a period of the life-span when risk for insufficient sleep and mental health difficulties is high. Methods. Data were collected from 105 adolescents aged 10–17 years residing at moderate-high altitudes. Parents reported on sociodemographics and adolescent depressive and anxiety symptoms, and adolescents reported on their subjective sleep need and sleep duration. Altitude was calculated using U.S. Geological Survey data. Results. Adjusting for age, sex, socioeconomic status, rurality, and sleep duration, living at higher altitude was associated with reports of greater sleep need. Altitude was unrelated to mental health symptoms. Discussion. The majority of adolescents do not obtain the recommended amount of sleep. These findings suggest that adolescents living at moderate-high altitudes may be at further risk due increased sleep need at higher elevations.