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Comprehensive Exploration of Graphically Defined Reaction Spaces
Get PDFExisting reaction transition state (TS) databases are comparatively small and lack chemical diversity. Here, this data gap has been addressed using the concept of a graphically-defined model reaction to comprehensively characterize a reaction space associated with C, H, O, and N containing molecules with up to 10 heavy (non-hydrogen) atoms. The resulting dataset is composed of 176,992 organic reactions possessing at least one validated TS, activation energy, heat of reaction, reactant and product geometries, frequencies, and atom-mapping. For 33,032 reactions, more than one TS was discovered by conformational sampling, allowing conformational errors in TS prediction to be assessed. Data is supplied at the GFN2-xTB and B3LYP-D3/TZVP levels of theory. A subset of reactions were recalculated at the CCSD(T)-F12/cc-pVDZ-F12 and ωB97X-D2/def2-TZVP levels to establish relative errors. The resulting collection of reactions and properties are called the Reaction Graph Depth 1 (RGD1) dataset. RGD1 represents the largest and most chemically diverse TS dataset published to date and should find immediate use in developing novel machine learning models for predicting reaction properties
Gradient Nanostructured Steel With Superior Tensile Plasticity
Get PDFNanostructured metallic materials with abundant high-angle grain boundaries exhibit high strength and good radiation resistance. While the nanoscale grains induce high strength, they also degrade tensile ductility. We show that a gradient nanostructured ferritic steel exhibits simultaneous improvement in yield strength by 36% and uniform elongation by 50% compared to the homogenously structured counterpart. In situ tension studies coupled with electron backscattered diffraction analyses reveal intricate coordinated deformation mechanisms in the gradient structures. The outermost nanolaminate grains sustain a substantial plastic strain via a profound deformation mechanism involving prominent grain reorientation. This synergistic plastic co-deformation process alters the rupture mode in the post-necking regime, thus delaying the onset of fracture. The present discovery highlights the intrinsic plasticity of nanolaminate grains and their significance in simultaneous improvement of strength and tensile ductility of structural metallic materials
Critical Nematic Correlations Throughout The Superconducting Doping Range in Bi2−zPbzSr2−yLayCuO6+x
Get PDFCharge modulations have been widely observed in cuprates, suggesting their centrality for understanding the high-Tc superconductivity in these materials. However, the dimensionality of these modulations remains controversial, including whether their wavevector is unidirectional or bidirectional, and also whether they extend seamlessly from the surface of the material into the bulk. Material disorder presents severe challenges to understanding the charge modulations through bulk scattering techniques. We use a local technique, scanning tunneling microscopy, to image the static charge modulations on Bi2−zPbzSr2−yLayCuO6+x. The ratio of the phase correlation length ξCDW to the orientation correlation length ξorient points to unidirectional charge modulations. By computing new critical exponents at free surfaces including that of the pair connectivity correlation function, we show that these locally 1D charge modulations are actually a bulk effect resulting from classical 3D criticality of the random field Ising model throughout the entire superconducting doping range
A Novel Method for Alleviating Numerical Stiffness in Li-ion Thermal Abuse Models
Get PDFNumerical modeling of thermal runaway in Lithium-ion batteries has become a critical tool for designing safer battery systems. Significant progress has been made in developing kinetic mechanisms for decomposition reactions and including additional physics such as venting and combustion. However, the governing heat conduction equation and decomposition reaction equations become numerically stiff during thermal runaway, which limits the utility of thermal abuse models to low-dimensional formulations. The present work introduces a new solution strategy, which switches from the full, 3D transient heat conduction formulation to an adiabatic, 0D lumped body formulation only during the stiff portion of the simulation, i.e., only during thermal runaway. To test the new solver, a 3D thermal abuse model was configured to simulate an oven test of an 18650-format cell. The new solver was exercised for scenarios of varying degrees of stiffness, and the results were compared with a baseline solver using typical integration methods. For an extremely stiff scenario, computation speed was increased by a factor of 183x relative to the baseline solver, with little impact on solution accuracy, thus effectively alleviating the numerical stiffness issue. The new solution strategy addresses the poor scalability of high-dimensional models, such as 3D-CFD-based thermal abuse models, and improves their practicality for industrial use
Use them or lose them: Are manipulatives needed to assess numeracy and geometry performance in preschool?
Get PDFIn two studies, we investigated whether using three-dimensional (3D) manipulatives during assessment aided performance on a variety of preschool mathematics tasks compared to pictorial representations. On measures of children\u27s understanding of counting and cardinality (n = 103), there was no difference in performance between manipulatives and pictures, with Bayes factors suggesting moderate evidence in favor of the null hypothesis. On a measure of children\u27s shape identification (n = 93), there was no difference in performance between objects and pictures, with Bayes factors suggesting moderate evidence in favor of the null hypothesis. These results suggest flexibility in the materials that can be used during assessment. Pictures, or 2D renderings of 3D objects, which can be easily printed and reproduced, may be sufficient for assessing counting and shape knowledge without the need for more cumbersome concrete manipulatives
Forecasting Shifts in Hoosiers’ Travel Demand and Behavior
Get PDFThe changing landscape of transportation technology and traveler behavior, accelerated by recent events like COVID-19, has led to significant shifts in travel demand and vehicle miles traveled in Indiana. This study seeks to understand the long-term implications of these changes and their potential impact on passenger, freight, and micro-mobility movements across the state. To achieve this objective, this project focused on forecasting future transportation demand conditions and carrying out long-range scenario planning by accomplishing four tasks: forecasting travel demand shifts based on location-based data, evaluating medium-term inter- and intra-urban transportation demand shifts, forecasting county-level industry shifts using scenario-based growth models, and providing recommendations and guidance to the Indiana Department of Transportation (INDOT) based on the study results. Results offer improved planning for infrastructure investments and operations, the incorporation of emerging technologies into transportation planning processes, and an enhanced understanding of passenger and freight movements at the statewide and regional levels. Deliverables from this study include valuable tools and models that can help INDOT navigate potential transportation system changes and accommodate the evolving needs of the future
Inaugural Defense and Security Research Symposium of the Purdue Military Research Institute
Get PDFThis document is the full conference proceedings from June 26-27, 2023
Keynote: Notions of Writing Center Community and Some Challenges to Them
Get PDFIt is crucial for writing center professionals who discuss community to ask ourselves what we mean by the term as applied to writing centers. In this keynote, I explore various notions of community that are influenced by writing center growth, expansion, and complexity, especially in relation to Iowa’s writing center. After relating a personal story about our new tutors’ traditional notion of community and an account of our own center’s expansion and growing complexity over the decades, which challenges their traditional notion, I discuss other obstacles to community, bringing in the critiques of writing center scholars. Finally, I synthesize what I consider to be the most important bases on which to build writing center community today, focusing on the special I-Thou relationships writing center tutors form with students
Large-Eddy Simulation of Rotationally- And Externally-Induced Ingress in an Axial Rim Seal of a Stator-Rotor Configuration
No full textIn gas turbines, the hot gas exiting the combustor can be as high as 2000 oC, and some of this hot gas enter into the space between the stator and rotor disks (wheelspace). Since the hot gas entering with its high temperatures could damage the disks, hot-gas ingestion must be minimized. This is done by using rim seals and by introducing a flow of cooler air from the compressor (sealing flow) into the wheelspaceIngress and egress into rim seals are driven by the stator vanes, the rotor and its rotation, and the rotor blades. This study focuses on the first-stage turbine, where ingress could cause the most damage and has two parts. The first part focuses on understanding ingress and egress driven by the rotor and its rotation, known as rotationally-induced ingress, by studying ingress about an axial seal in a stator-rotor configuration without vanes and without blades. The second part focuses on understanding ingress and egress driven by stator vanes, known as externally-induced ingress, by studying a stator-rotor configuration with vanes but no blades, where the ratio of the external Reynolds number to the rotational Reynolds number is 0.538. For both parts, solutions were generated by wall-resolved large-eddy simulation (LES) based on the WALE subgrid model and by Reynolds-averaged Navier-Stokes (RANS) based on the SST model. For both stator-rotor configurations, the grid-independent solutions obtained were compared with available experimental data.Results obtained for the configuration without vanes and blades show Kelvin-Helmholtz instability (KHI) to form even without swirl from the hot-gas flow and to create a wavy shear layer on the rotor. Also, Vortex shedding (VS) occurs on the backward-facing side of the seal and impinges on the rotor side of the seal. The KHI and VS produce alternating regions of high and low pressures about the rotor-side of the axial seal, which cause ingress to start on the rotor side of the seal. Results obtained for the configuration with vanes but no blades show both LES and RANS to correctly predict the coefficient of pressure, Cp, upstream of the axial seal. However, only LES was able to correctly predict the sealing effectiveness. This shows Cp by itself maybe is inadequate in quantifying externally-induced ingress. One reason why RANS was unable to predict sealing effectiveness is significantly under predicting the pressure drop on the rotor surface, which affected the pressure variation along the hot-gas path and hence the pressure difference across the axial seal, which ultimately drives ingress