In Vivo GABA Detection by Single Pulse Editing with One Shot

Over the past two decades, magnetic resonance spectroscopy with two-shot difference editing has been widely employed to characterize altered levels of GABA, the primary inhibitory neurotransmitter in the brain, in various neuropsychiatric disorders. This conventional technique detects the GABA H4 resonance, making it unsuitable for investigating GABA metabolism. It also suffers from subtraction artifacts, signal loss, and significant contamination by macromolecules. Here, we introduce a single-shot method for detecting GABA H2, effectively overcoming these difficulties. Since GABA turnover initiates at its protonated C2 and unprotonated C1 positions, we demonstrate, for the first time, noninvasive real-time monitoring of GABA metabolism in the human brain, utilizing GABA H2 as a highly sensitive reporter for GABA C2. This new method not only enhances the quantitative measurement of GABA levels but also opens up a new avenue to probe the metabolic processes underlying alterations in GABA levels in patients

The impact of product variety on consumer demand and firm performance

This dissertation work is an empirical examination of the inter-related decisions made by manufacturers, retailers and consumers with respect to product variety in competitive market contexts. The first chapter investigates grocers' assortment of goods from multiple product categories in a common retail space. Within such "target" space, shoppers are exposed to a selection of product categories that are not necessarily correlated in consumption *a priori*. Using a model of multicategory purchase incidence, I show that consumers are less likely to purchase from a category of a given assortment when it is presented with another independent category assortment of greater variety. Results from analyzing IRI field data and an online experiment provide strong evidence that this effect is driven by the display proximity. Further, results from an eye-tracking study point to the consumers' allocation of limited attention to category assortments as an explanation for the finding. The second chapter documents a multi-product firm's use of product variety in its strategic interactions with potential entrant firms in a context of the post-deregulation Korean soju market. This market, previously composed of independent geographic markets, each with a protected incumbent producer, became open to nation-wide competition as a result of market deregulation in the early 1990's. I build an econometric model that accounts for causal structures surrounding the incumbent firms' product variety and the number of firms in the market and find that product proliferation and dominant market leadership of the incumbent firm served as significant barriers to entry. The third chapter presents descriptive evidence of the effect of commodity taxation on product variety and market structure. By studying the Korean alcoholic beverage market which was affected by a tax reform, I show a negative relationship between the tax rate and product variety offered by individual firms. Simple regressions also reveal that a tax hike could result in higher market concentration. The results are consistent with theoretical predictions

Magnetic Field Dependence of Spectral Correlations between 31P-Containing Metabolites in Brain

Spectral correlations between metabolites in 31P magnetic resonance spectroscopy (MRS) spectra of human brain were compared at 3 and 7 Tesla, the two commonly used magnetic field strengths for clinical research. It was found that at both field strengths, there are significant correlations between 31P-containing metabolites arising from spectral overlap, and their downfield correlations are markedly altered by the background spectral baseline. Overall, the spectral correlations between 31P-containing metabolites are markedly reduced at 7 Tesla with the increased chemical shift dispersion and the decreased membrane phospholipid signal. The findings provide the quantitative landscape of pre-existing correlations in 31P MRS spectra due to overlapping signals. Detailed procedures for quantifying the pre-existing correlations between 31P-containing metabolites are presented to facilitate incorporation of spectral correlations into statistical modeling in clinical correlation studies

Reach up, fit in, or stand out? The evaluation of academic quality and fit in college choices

Understanding students’ college enrollment decisions is critical because the admission outcome can affect the school’s quality and its reputation. In this paper, we study how students consider their relative academic ability compared to their potential peers. Drawing from social comparison theory, we posit that there are asymmetric effects due to deviation from peers’ ability, depending on the deviations’ direction. Using a rich data set of college applicants, we find that while the applicants negatively evaluate their deviations below their potential peers, they value positively those above their peers (the ‘big fish, little pond’ effect). Moreover, students who applied to many universities are more susceptible to these psychological effects. Further analysis points to the level of the individual student’s self-confidence as a possible explanation. Finally, we derive suggestions for college administrators to improve the yield of admitted students

The impact of commodity taxation on product variety: a multi-category investigation

Excise taxes are one of the primary tools used to discourage consumption of socially undesirable or unhealthy products. When considering implementation of such taxes, the current policy and academic discussions have focused on potential outcomes due to price changes. In this paper, we document that price changes are only the immediate response to tax policy changes, and in the long run tax changes can impact product offerings. Using exogenous changes in tax rates from multiple empirical contexts; (1) the Korean soju market and (2) the U.S. cigarette market, we show that a tax increase is followed by a significant drop in number and variety of product offerings. In addition, the change in product assortments post-tax hinges critically on the nature of tax imposed. We find that specific taxes, as opposed to ad valorem taxes, lead to the exit of products with larger pack size. We conduct a simulation experiment and estimate that studies which do not consider assortment changes can result in a 9% upward bias in consumer welfare for large tax increases. Our findings have important policy implications for research examining the impact of taxes on market outcomes

The perils of category management: the effect of product assortment on multicategory purchase incidence

Retailers determine the assortment for a mix of product categories in a particular space (e.g., the checkout aisle, endcaps, freezer space). Within such a “target” space, shoppers are exposed to a selection of product categories that are not necessarily correlated in consumption. In this article, the authors examine whether the assortment of one category affects consumers’ purchase incidence decision in another, independent category that shares a common display space (e.g., frozen meals and ice cream). They use a multivariate probit model of purchase incidence and incorporate assortment variety captured by an entropy measure. Results from analyses of IRI data and an online experiment provide strong evidence that consumers are less likely to purchase from a category of a given assortment when it is presented with another category assortment of greater variety and that this effect is driven by the display proximity. Furthermore, results from an eye-tracking study indicate consumers’ allocation of limited attention to category assortments as an explanation for the finding. This work serves as one of the first studies to document the impact of product assortment beyond a focal category, and the results highlight a limitation of individual category management when grocery retailers make product assortment decisions

Ethanol-based green-solution processing of alpha-formamidinium lead triiodide perovskite layers

Manufacturing of perovskite solar cells would benefit from the avoidance of hazardous solvents and multistep processing. Now, Yun et al. report an ethanol-based perovskite precursor solution that does not need an antisolvent step, enabling devices with 25% efficiency. The use of non-toxic or less-toxic solvents in the mass production of solution-processed perovskite solar cells is essential. However, halide perovskites are generally not completely soluble in most non-toxic solvents. Here we report the deposition of dense and uniform alpha-formamidinium lead triiodide (alpha-FAPbI(3)) films using perovskite precursor solutions dissolved in ethanol-based solvent. The process does not require an antisolvent dripping step. The combination of a Lewis base, such as dimethylacetamide (or dimethylsulfoxide), and an alkylammonium chloride (RNH3Cl) in ethanol results in the stable solvation of FAPbI(3). The RNH3Cl added to the FAPbI(3) precursor solution is removed during spin-coating and high-temperature annealing via iodoplumbate complexes, such as PbI2 center dot RNH2 and PbI2 center dot HCl, coordinated with dimethylacetamide (or dimethylsulfoxide). It is possible to form very dense and uniform alpha-FAPbI(3) perovskite films with high crystallinity by combining several types of RNH3Cl. We obtain power conversion efficiencies of 24.3% using a TiO2 electrode, and of 25.1% with a SnO2 electrode

Efficient perovskite solar mini-modules fabricated via bar-coating using 2-methoxyethanol-based formamidinium lead tri-iodide precursor solution

In small-area perovskite solar cells, efficiencies of >25% have been achieved using an antisolvent dripping technique; however, it is not applicable for coatings on an industrial scale. Currently, largearea devices based on scalable perovskite coatings still show a very large gap with small- area devices. This means that a uniform perovskite coating and defect control on large-area devices are not as secure as they are on small devices. Here, we report the deposition of dense and uniform perovskite films using an air-knife-assisted bar-coating employing a perovskite [(FAPbI(3))(0.95)(MAPbBr(3))(0.05)] precursor solution dissolved in 2- methoxyethanol. A pinhole-free and homogeneous surface morphology was achieved by adding n-cyclohexyl-2-pyrrolidone to ensure a balance between rapid nucleation and slowed crystal growth in the precursor solution. By applying surface passivation with acetylcholine bromide and laser etching to thin layers, mini-modules with an aperture area of 31 cm(2) were fabricated, attaining an efficiency of >20% (17.53% in the efficiency certified by a quasi-steady-state protocol)