1,693 research outputs found
Shifting the scaling relations of single-atom catalysts for facile methane activation by tuning the coordination number
No full textWe investigate oxidative methane activation on a wide range of single transition metal atom catalysts embedded on N-doped graphene derivatives using density functional theory calculations. An inverse scaling relationship between *O formation and its hydrogen affinity is observed, consistent with a previous report. However, we find that the latter scaling line can be shifted towards a more reactive region by tuning the coordination number (CN) of the active metal sites. Specifically, we find that lowering the CN plays an important role in increasing the reactivity for methane activation via a radical-like transition state by moving the scaling lines. Thus, in the new design strategy suggested here, different from the conventional efforts focusing mainly on breaking the scaling relations, one maintains the scaling relations but moves them towards more reactive regions by controlling the coordination number of the active sites. With this design principle, we suggest several single atom catalysts with lower C-H activation barriers than some of the most active methane activation catalysts in the literature such as Cu-based zeolites.
Measurement of ignition delay time of jet fuels in shock tube for the development of the chemical kinetic mechanism
No full textReliable yet tractable kinetic mechanisms for real aviation fuels are essential for predictive simulations of advanced combustors, and this thesis develops an F-24–specific HyChem mechanism by combining new experiments in a high-pressure shock tube with regularization-constrained, data-driven optimization of lumped reaction rates. GC×GC compositional analysis, together with prior work on F-24 and Jet-A, is used to justify Jet-A HyChem as the base mechanism and to highlight the distinct character of alternative fuels such as ATJ and CycloSAF. The UIUC shock tube is re-instrumented with a tailored driver and an endwall pressure transducer, enabling robust measurement of both overall and first-stage ignition delays for F-24 at 5–20 bar down to ~650–700 K and providing comparative data for a cycloalkane-rich CycloSAF. A Covariance Matrix Adaptation Evolution Strategy (CMA-ES) is then employed to optimize selected Arrhenius parameters of the 16 lumped HyChem reactions using a multi-objective function that combines ignition-delay RMSE and L1/L2-type regularization, with tight parameter bounds to preserve physical plausibility. The optimized mechanisms correct the baseline underprediction of F-24 ignition delays in the negative-temperature-coefficient and low-temperature regimes while maintaining high-temperature performance, and identify a small subset of high- and low-temperature reactions that dominate the required adjustments. First-stage ignition delays are shown to be critical for constraining low-temperature QOOH-cycle reactions, and a staged strategy that first optimizes overall ignition delays and then refines only low-temperature reactions against first-stage data is demonstrated to reproduce fully coupled multi-objective results at reduced computational cost. Validation against independent laminar flame speed measurements and shock-tube species profiles confirms that the regularized mechanisms retain balanced fidelity across ignition, flame propagation, and intermediate chemistry, while revealing specific larger unsaturated and aromatic species that require new kinetic pathways, thereby establishing a practical framework for constructing robust, fuel-specific HyChem mechanisms for current and emerging aviation fuels.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2027-12-01The student, Sungho Yoon, accepted the attached license on 2025-12-07 at 15:08.The student, Sungho Yoon, submitted this Thesis for approval on 2025-12-09 at 08:04.This Thesis was approved for publication on 2025-12-09 at 08:43.DSpace SAF Submission Ingestion Package generated from Vireo submission #23094 on 2026-02-19 at 18:46:5
Effect of general health checks on the treatment of chronic diseases: accounting for self-selection in the retrospective cohort study using Korea National Health Insurance data
No full textObjective This study examines the effect of general health checks on the detection and treatment of diabetes and hypertension with controlling for the self-selection problem of undergoing general health checks.Design Retrospective observational cohort study.Setting Sample Research Database offered by Korean National Health Insurance Service, between 2002 and 2013.Participants Two datasets, focusing on diabetes and hypertensions one by one, are constructed. The number of participants for the datasets is 133 329 (diabetes) and 101 738 (hypertension), respectively.Methods A bivariate probit model with selection was adopted to investigate the impact of general health checks on the diagnosis of critical chronic diseases. The dependent variable was an indicator variable denoting whether a participant has been treated for diabetes (or hypertension) or not for the first time during the sample period. An indicator variable that indicates whether that participant is eligible for free general health checks or not in the focal year (year of the first treatment or last year in the sample) was used as instrument variables to control for the self-selection problem of undergoing general health checks.Results We found that there exists substantial self-selection between undergoing general health checks and diagnosis for chronic diseases. The correlations between the unobserved factors influencing the decisions to obtain general health checks and those determining the detection of chronic diseases are highly significant and positive (ie, 0.188 (p<0.001) in diabetes and 0.220 (p<0.001) in hypertension). We confirmed that these positive, significant correlations generate upward bias in the estimated effect of general health checks on the detection and treatment of diabetes (0.312 (p<0.001) when self-selection ignored but 0.099 (p<0.001) when self-selection considered) and hypertension (0.293 (p<0.001) when self-selection ignored but insignificant when self-selection considered). The effect of general health checks and people’s self-selection behaviour may differ by socio-economic characteristics of individuals. The general health check is effective in detecting chronic diseases among low-income individuals rather than high-income individuals, implying that general health checks are contributing to helping medically underprivileged low-income people detect and treat their chronic diseases. High-income individuals showed stronger self-selection behaviour than low-income individuals and this may overstate the effect of general health checks if the self-selection is overlooked, particularly among high-income individuals.Conclusion Self-selection due to unobserved factors between undergoing general health checks and diagnosis of chronic diseases are substantial. After accounting for this, the effect of general health checks on the detection and treatment of diabetes and hypertension is insignificant or marginal. The increases in the treatments of the two diseases following general health checks are 1% and insignificant in diabetes and hypertension, respectively
In situ-prepared composite materials of PEDOT: PSS buffer layer-metal nanoparticles and their application to organic solar cells
No full textWe report an enhancement in the efficiency of organic solar cells via the incorporation of gold (Au) or silver (Ag) nanoparticles (NPs) in the hole-transporting buffer layer of poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which was formed on an indium tin oxide (ITO) surface by the spin-coating of PEDOT:PSS-Au or Ag NPs composite solution. The composite solution was synthesized by a simple in situ preparation method which involved the reduction of chloroauric acid (HAuCl4) or silver nitrate (AgNO3) with sodium borohydride (NaBH4) solution in the presence of aqueous PEDOT:PSS media. The NPs were well dispersed in the PEDOT:PSS media and showed a characteristic absorption peak due to the surface plasmon resonance effect. Organic solar cells with the structure of ITO/PEDOT:PSS-Au, Ag NPs/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM)/LiF/Al exhibited an 8% improvement in their power conversion efficiency mainly due to the enlarged surface roughness of the PEDOT:PSS, which lead to an improvement in the charge collection and ultimately improvements in the short-circuit current density and fill factor. © 2012 Woo et al.1
Molecular Rh(III) and Ir(III) Catalysts Immobilized on Bipyridine-Based Covalent Triazine Frameworks for the Hydrogenation of CO2 to Formate
No full textThe catalytic reactivity of molecular Rh(III)/Ir(III) catalysts immobilized on two- and three-dimensional Bipyridine-based Covalent Triazine Frameworks (bpy-CTF) for the hydrogenation of CO2 to formate has been described. The heterogenized Ir complex demonstrated superior catalytic efficiency over its Rh counterpart. The Ir catalyst immobilized on two-dimensional bpy-CTF showed an improved turnover frequency and turnover number compared to its three-dimensional counterpart. The two-dimensional Ir catalyst produced a maximum formate concentration of 1.8 M and maintained its catalytic efficiency over five consecutive runs with an average of 92% in each cycle. The reduced activity after recycling was studied by density functional theory calculations, and a plausible leaching pathway along with a rational catalyst design guidance have been proposed
Role of an unclassified Lachnospiraceae in the pathogenesis of type 2 diabetes: a longitudinal study of the urine microbiome and metabolites
No full textRecent investigations have revealed that the human microbiome plays an essential role in the occurrence of type 2 diabetes (T2D). However, despite the importance of understanding the involvement of the microbiota throughout the body in T2D, most studies have focused specifically on the intestinal microbiota. Extracellular vesicles (EVs) have been recently found to provide important evidence regarding the mechanisms of T2D pathogenesis, as they act as key messengers between intestinal microorganisms and the host. Herein, we explored microorganisms potentially associated with T2D by tracking changes in microbiota-derived EVs from patient urine samples collected three times over four years. Mendelian randomization analysis was conducted to evaluate the causal relationships among microbial organisms, metabolites, and clinical measurements to provide a comprehensive view of how microbiota can influence T2D. We also analyzed EV-derived metagenomic (N = 393), clinical (N = 5032), genomic (N = 8842), and metabolite (N = 574) data from a prospective longitudinal Korean community-based cohort. Our data revealed that GU174097_g, an unclassified Lachnospiraceae, was associated with T2D (beta = -189.13; p = 0.00006), and it was associated with the ketone bodies acetoacetate and 3-hydroxybutyrate (r = -0.0938 and -0.0829, respectively; p = 0.0022 and 0.0069, respectively). Furthermore, a causal relationship was identified between acetoacetate and HbA1c levels (beta = 0.0002; p = 0.0154). GU174097_g reduced ketone body levels, thus decreasing HbA1c levels and the risk of T2D. Taken together, our findings indicate that GU174097_g may lower the risk of T2D by reducing ketone body levels. Diabetes: a little help from the microbiome A microbe that may help protect against type II diabetes has been detected by examining extracellular vesicles (EVs), tiny membrane-wrapped packages secreted by human cells and by the bacteria making up the microbiome. Examining EVs allows researchers to sample microbial populations other than the intensively studied intestinal microbiome. Sungho Won, Seoul National University, and Geum-Sook Hwang, Korea Basic Science Institute, Seoul, and coworkers studied the microbial EVs in urine samples collected from South Korean subjects over four years. They identified a previously unclassified bacterial species in the family Lachnospiraceae that was associated with lower risk of developing type II diabetes. Further investigation showed that these bacteria may break down ketone bodies, metabolic byproducts that signal disrupted sugar metabolism leading to diabetes. These results contribute to understanding how the microbiome contributes to metabolic health and disease.N
Study of high transverse momentum charged particle suppression in heavy ion collisions at LHC
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references.The charged particle spectrum at large transverse momentum (PT), dominated by hadrons originating from parton fragmentation, is an important observable for studying the properties of the hot, dense medium produced in high-energy heavy-ion collisions. The study of the modifications of the PT spectrum in PbPb compared to pp collisions at the same collision energy can shed light on the detailed mechanism by which hard partons lose energy traversing the medium. In this thesis, the transverse momentum spectra of charged particles in pp and PbPb collisions at [square root of]Snn = 2.76 TeV measured up to PT = 100 GeV/c with the CMS experiment at the Large Hadron Collider (LHC) are presented. In the transverse momentum range PT = 5-10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 7 compared to the pp yield scaled by the number of incoherent nucleon-nucleon collisions. At higher PT, this suppression is significantly reduced, approaching roughly a factor of 2 for particles with PT in the range PT = 40-100 GeV/c. A simple modeling of the parton energy loss applied to the PYTHIA Monte-Carlo (MC) reveals that the charged particle spectrum with the pQCD-motivated fractional parton energy loss can describes the shape of the measured suppression well in the range PT = 5-100 GeV/c.by Andre Sungho Yoon.Ph.D
Trametinib activates endogenous neurogenesis and recovers neuropathology in a model of Alzheimer’s disease
No full textAbstract Enhancing adult neurogenesis in the brain has been suggested as a potential therapeutic strategy for AD. We developed a screening platform, ATRIVIEW®, for molecules that activate neuronal differentiation of adult mouse NSCs. The most potent hit from an FDA-approved drug library was SNR1611 (trametinib), a selective MEK1/2 inhibitor. We found that trametinib increases the levels of P15INK4b and Neurog2, suggesting a mechanism by which MEK1/2 inhibition induces neuronal differentiation. Oral administration of trametinib increased adult neurogenesis in the dentate gyrus and subventricular zone of the 5XFAD AD mouse model. Surprisingly, we also found that trametinib enhanced adult neurogenesis in the cortex. Consequently, trametinib rescued AD pathologies such as neuronal loss and cognitive impairment in 5XFAD mice. Finally, trametinib induced neurogenic differentiation of NSCs derived from AD patient iPSCs, which suggests its potential therapeutic application. Altogether, we suggest that restoration of endogenous adult neurogenesis by trametinib may be a promising therapeutic approach to AD
Decentralized Approximate Bayesian Inference for Distributed Sensor Network
No full textBayesian models provide a framework for probabilistic modelling of complex datasets. Many such models are computationally demanding, especially in the presence of large datasets. In sensor network applications, statistical (Bayesian) parameter estimation usually relies on decentralized algorithms, in which both data and computation are distributed across the nodes of the network. In this paper we propose a framework for decentralized Bayesian learning using Bregman Alternating Direction Method of Multipliers (B-ADMM).We demonstrate the utility of our framework, with Mean Field Variational Bayes (MFVB) as the primitive for distributed affine structure from motion (SfM).Peer reviewe
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