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Attosecond charge migration in organic molecules: Initiating and probing localized electron holes
No full textWhen forced out of equilibrium, electrons in molecules can respond exceedingly fast, on time scales approaching the attosecond (10−18 s). At this time scale, the dynamics are inherently quantum and the response is driven by intricate multi-electron correlations in what is commonly referred to as charge migration (CM). In this chapter, we provide an overview of what we have learned from a decade of investigations in our group on attosecond CM in organic molecules. First, we briefly review the history of CM, from early experiments and theory to current development. Then, we discuss practical aspects of CM simulations, including how to initiate, analyze, and visualize migration dynamics using time-dependent density-functional theory. Finally, we dive into the attochemistry of CM with a special focus on the migration dynamics of localized electron holes, the physical/chemical mechanisms that make them possible, and strategies for probing them. We conclude the chapter with outlooks for measuring CM and the interplay between CM and the molecular environment. This chapter aims to provide a road map for understanding and predicting CM dynamics in organic molecules, together with experimentally relevant avenues for initiating and probing them
Recent synthetic methodology advancements towards all-carbon quaternary center formation and applications
No full textThe synthesis of organic molecules through regioselective and enantioselective processes represents a significant challenge in organic chemistry, but constructing molecules with all-carbon quaternary centers poses even greater complexity. The importance of synthetic organic chemistry in daily life cannot be overstated, as organic molecules are fundamental to human existence - from the nutrients that sustain us to the pharmaceutical products that maintain our health. Fundamental knowledge on chemical reactivity, particularly that of carbon-carbon bond formation in sterically hindered substrates, is of great interest in developing and studying new chemical matter. Increases in precision medicine have also highlighted the importance of molecular selectivity towards biological targets and the need to access complex molecular scaffolds with unique stereochemistry features such as quaternary carbon centers. The scarcity of molecules containing all-carbon quaternary centers has constrained our ability to fully explore their properties. This report examines recent methodological advances since 2019 in their synthesis, focusing on three key synthetic approaches: single electron transfer (SET) mediated reactions, reactions mediated by chemical phenomena associated with charge separation (electrochemistry), Lewis acid and transition metal mediated cyclization/rearrangement reactions. These innovative synthetic strategies open new pathways for creating complex chemical structures, advancing our ability to develop both novel therapeutic candidates and new materials. The enhanced efficiency of these approaches enables the exploration of increasingly sophisticated molecular architectures, expanding opportunities for discovering compounds with unique biological activities and material properties
Cuerpos anormales. Metabolismo y alimentación en el México posrevolucionario by Joel Vargas Domínguez (review)
No full textCorn and Soybean Responses to Phosphorus and Potassium Application Timings and Methods and Fertilizer Sources
Get PDFThis research was driven by concerns over phosphorus (P) and potassium (K) losses from fall-applied fertilizers and the increasing marketing popularity of liquid-P and K fertilizers over traditional granular-dry forms. We evaluated corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yield and tissue nutrient concentration responses to fertilizer-P and K application timings, methods, and sources across 9-13 site-years on silt-loam soils in Louisiana from 2020-2024. For timing and method study, five treatments were evaluated: a no fertilizer-P and/or K check, fall broadcast followed by rehipping the seedbed, spring broadcast without rehipping, spring broadcast with rehipping, and spring top-of-bed application. In P- and K-deficient soils, no significant differences in yield or leaf nutrient concentrations were measured among fertilizer-P timings and methods for corn, or fertilizer-K timings and methods for soybean. Spring broadcast-K with rehipping increased corn yield by 7.6% over fall broadcast-K with rehipping. When fertilizer-P and K were applied together in suboptimal-P and K soils, no significant yield or nutrient concentration differences were found across timings and methods for either crop. The fertilizer source study included five treatments: a no-fertilizer check, and half- and full-recommended rates of both dry and liquid fertilizers. Triple superphosphate (0-46-0) and muriate of potash (0-0-60) were used as dry-P and K sources and ammonium polyphosphate (11-37-0) and Nachurs K-fuel (0-0-24) as liquid sources. In P- and K-deficient soils, corn yield did not differ between dry and liquid sources, but full-rate applications produced 5-13%, depending on nutrients, greater corn yield than half-rate. For soybean, no significant yield differences were noted between sources or rates for either P or K. However, when both nutrients were applied together, full-rate treatments produced 9-10% greater soybean yield than half-rate. These yield differences did not consistently correlate with leaf nutrient concentrations for either crop. Overall, results suggest that fertilizer-P can be applied in either fall or spring, but fertilizer-K should be applied in spring, at or before planting, especially in coarse-textured, low cation exchange capacity (CEC) soils. Additionally, liquid-P and K sources offer no significant advantage over traditional granular-dry fertilizers, and the nutrient rates should follow soil-test-based rate recommendations
Experimental study on tsunami-driven debris damming loads on columns of an elevated coastal structure
No full textThis study presents experimental findings on debris damming loads on columns of an elevated coastal structure under tsunami-like wave conditions. A total of 183 cases (140 with and 43 without debris) were tested at a 1:20 scale to understand the impact of various factors on debris-driven damming loads, including wave characteristics, structure configurations, and debris shapes. The debris impact and damming processes were observed and quantified from optical measurements, and corresponding loads were measured on the entire structure using a force balance plate and on an individual column in the front row using a multi-axial load cell. The experimental results indicated the horizontal debris damming load on the entire column structure increased by up to 3.2 times compared to conditions without debris, while the load on the individual column increased by up to 11.0 times. The total damming loads for the whole structure increased, but the load for the individual column decreased at a reduced opening ratio. The smaller debris sizes relative to column spacing showed significantly lower chances of debris damming across different column configurations. Overall, the load on the whole structure showed stronger correlations between debris damming loads and hydro-kinematic variables such as flow depth, velocity, momentum flux, and Froude number compared to the loads on the individual column. Among these variables, momentum flux emerged as the most consistently influential across all categories
Examining infrared thermography based approaches to rapid fatigue characterization of additively manufactured compression molded short fiber thermoplastic composites
No full textA novel additive manufacturing (AM) methodology combined with a compression molding (CM) process has been previously developed to optimize the microstructure of short fiber thermoplastic (SFTs) composites with higher fiber alignment and lower porosity, yielding superior stiffness, strength, and structural integrity. The current work examines the efficacy of the ‘passive’ infrared thermography (IRT) techniques for rapid fatigue characterization of SFTs that use the surface temperature evolution during cyclic loading due to self-heating as a fatigue indicator. A comparison of fatigue limits obtained from traditional stress-life (SN) (≈53.1%σuts) and IRT (≈54.1%σuts) shows a close match. However, the SN curve required 18 specimens and two weeks of continuous cyclic testing, while IRT used three specimens with 5 h of testing. Thus, the IRT approach provides an accelerated testing framework for rapidly estimating the fatigue limit. Additionally, existing phenomenological approaches to IRT fatigue characterization have been examined
Understanding leaf development under high salinity in the extremophyte model, Schrenkiella parvula and leaf shape variation in multiple brassicaceae using multi-omics approach
No full textSchrenkiella parvula, a wild relative of Arabidopsis thaliana from Brassicaceae family, is an extremophyte plant whose natural habitat is the shore of saline lakes in the Irano-Turanian region. It is known for its resilience to thrive in diverse ion-rich environments including Na+ and K+. In my research, I explored the molecular genetics underlying high Na+ tolerance in plants studying S. parvula at different developmental stages and compared the leaf shape variation with closely related two other species, Arabidopsis thaliana and Sisymbrium irio integrating physiological, ionomic, transcriptomic, and metabolomic methodologies.
In my first project, I used integrated omics approach to explore the cellular and molecular processes impacted under longer salt treatment duration at two developmental stages of leaves in S. parvula. My result indicated that the mature leaves preferentially accumulated excess Na compared to young leaves and serves as a sink to protect young and growing leaves. I observed reprogramming of salt transporters specifically in young leaf samples to protect them from accumulating excess salt.
In my second project, I utilized multi-omics approach to understand how S. parvula leaf develops upon high salinity condition starting at early seedling establishment phase to unset of reproductive stage using single leaf (5th leaves) developed after salt treatment. I identified that S. parvula increased leaf mass per unit area upon salt treatment in 5th developmental stages with both medium (150 mM NaCl) and high (250 mM NaCl) salt treatment while accumulating significantly higher amounts of Na under both medium and high salt treatment. I observed increased abundance of sugar, amino acids, and fatty acids in the 5th developmental stage compared to 4th developmental stage upon salt treatment suggesting those might be playing a role to mitigate osmotic and oxidative stress amidst salt accumulation. Transcriptionally, I observed induced expression of genes related to salt extrusion and vacuolar compartmentalization while suppressed expression of key potassium transport related genes.
In my third project, I explored leaf shape variation within closely related Brassicaceae species. I identified gene expression modules specific to each species suggesting role of those genes in leaf shape variation and adaptation to the extreme environment
Rainbow Road To Prismatic Playwriting: Black Women\u27s Dramatic Praxis in Practice
Get PDFThis dissertation explores the lived experiences of Black women in academia, uplifting those interested in non-traditional or creative scholarship. Underrepresentation and attrition due to exclusionary academic practices is a systemic problem. What can Black feminist playwriting as research do for Black women in academia hoping to resist and connect to themselves and their community? What can playwriting as a Black woman doctoral student elucidate about the utility of playwriting as research, culturally informed epistemologies, and African American women\u27s drama? By merging African American women\u27s drama, Black feminist epistemologies, Practice as Research, and playwriting as research, I developed an onto-epistemological method called Prismatic Playwriting. Prismatic playwrights analyze Black women\u27s creative and scholarly work and place them in dialogue with their lived experiences through playwriting as a research method. Prismatic Playwriting will provide an approach to scholarship for Black women that allows them to examine their lived experiences, engage with their community, and utilize creativity as a force for resistance and wellness. This dissertation will also demonstrate a model of culturally informed artistic scholarship for stakeholders in academia and provide insight into the immense need and desire for its acceptance
Strong electrostatic adsorption sequence of Ni and Co affects low temperature dry reforming performance over NiCo/MgAlOx/ZrO2
No full textIn bimetallic catalysts, the synergistic interactions between the metals and the support are crucial for catalytic performance, especially when supported on low-dimensional materials like metal oxide rafts. This study investigates the effect of the impregnation sequence of Ni and Co on the formation of bimetallic NiCo alloy catalysts and their impact on the dry reforming of methane (DRM) activity. We show that on reducible supports, the process of metal adsorption is governed by the metal-support interactions (MSI) and the synthesis sequence, which in turn affects low-temperature DRM catalysis. Using a MgAlOx/ZrO2 hierarchical support, we observed dramatic changes in DRM activity, achieving a minimum at 534 °C and 240 Lgcat⁻¹h⁻¹, compared to 696 °C and 48 Lgcat⁻¹h⁻¹ in the control. The study employs XANES/XAFS, XPS, HAADF-STEM-EDS, and H2-TPR to reveal that NiCo alloy nanoparticle formation and Ni/Co molar ratio depend on impregnation order, correlating changes in catalyst properties with performance and MSI levels
Ghost Fishing Due to Derelict Crab Traps in Louisiana’s Barataria Basin
Get PDFGhost fishing, the unintentional entrapment of sea life by derelict fishing gear, is an ecologic and socioeconomic concern in Louisiana\u27s crabbing industry (blue crab, Callinectes sapidus). These ghost fishing traps cause unknown and unaccounted for mortality in blue crab and bycatch species. I aimed to track changes to derelict crab trap catch and trap deterioration over seasons and between habitats. I set and monitored 33 simulated derelict crab traps over 367 soak days in three varying habitats along Barataria Bay, Louisiana. Traps were checked once every two weeks and an additional daily check for five days per season. Blue crabs and Gulf stone crabs (Menippe adina) were tagged to determine longevity in the traps. Deterioration of trap condition was recorded over time as well as DO, salinity, temperature, and depth to address seasonal changes. Known human interactions were also recorded. Results found the highest average number of new crabs caught per trap at the Golden Meadow site (lowest salinity, 1.02 ± 0.80 crabs per trap per sampling trip for the biweekly sampling regime). The average length of blue crabs across sites was 13.4 ± 3.4 cm. The highest average number of bycatch individuals came from Port Fourchon (highest salinity), and the bycatch species of highest abundance was the Gulf stone crab. Traps in Grand Isle and Port Fourchon accumulated a higher level of biofouling than Golden Meadow by the end of the study. These results further our understanding of ghost fishing in Louisiana crab traps