FO-PINNs: A First-Order formulation for Physics Informed Neural Networks

We present FO-PINNs, physics-informed neural networks that are trained using the first-order formulation of the Partial Differential Equation (PDE) losses. We show that FO-PINNs offer significantly higher accuracy in solving parameterized systems compared to traditional PINNs, and reduce time-per-iteration by removing the extra backpropagations needed to compute the second or higher-order derivatives. Additionally, unlike standard PINNs, FO-PINNs can be used with exact imposition of boundary conditions using approximate distance functions, and can be trained using Automatic Mixed Precision (AMP) to further speed up the training. Through two Helmholtz and Navier-Stokes examples, we demonstrate the advantages of FO-PINNs over traditional PINNs in terms of accuracy and training speedup.Comment: 6 pages, 3 figures, Selected for ML4PS workshop at NeurIPS 202

Three-dimensional phase-field simulation of micropore formation during solidification: Morphological analysis and pinching effect

A three-dimensional (3-D) multiphase-field model has been developed in order to study the formation of a micropore constrained to grow in a solid network (i.e. pinching effect). The model accounts for the pressure difference due to capillarity between liquid and gas, the equilibrium condition at triple (solid-liquid-pore) lines, and the partitioning and diffusion of dissolved gases such as hydrogen. From the predicted 3-D morphology of the pore, entities such as the interfacial shape distribution are plotted and analyzed. It is shown that the mean curvature of the pore-liquid surface, and thus also the pressure inside the pore, is uniform. The results are then compared with analytical pinching models. While predicting a similar trend, analytical models tend to underestimate the pore curvature at high solid fractions. Despite the complex morphology of pores reconstructed using high-resolution X-ray tomography, the present phase-field results suggest that a simple pinching model based on a spherical tip growing in between remaining liquid channels is a fairly good approximation. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Data Trends and Variability in Quality Control for Performance and Pay for Performance Specifications: Statistical Analysis

Quality assurance programs for hot-mix asphalt (HMA) have evolved from method specifications to quality assurance specifications that distribute responsibilities and risks between contractors and owners. The Illinois Department of Transportation (IDOT) developed two acceptance specifications, quality control for performance (QCP) and pay for performance (PFP), integrating contractor pay incentives and/or disincentives associated with air voids (AV), voids in mineral aggregate (VMA), and in-place density limits. A major factor that could compromise contractors’ pay in both specifications is the variability of test results due to mix production, construction, sampling, and/or inherent testing variability. Therefore, the objective of this project was to understand the distribution and variability of the test results observed under QCP and PFP specifications, as well as the potential causes of variability. The assessment approach included statistical analysis of the test results obtained for the 2015–2017 construction seasons and on-site field observations of 11 projects visited during the 2018 construction season. The pay factors of the 2015–2017 construction seasons showed contractors earned pay incentives under the PFP specification but received disincentives under QCP and PFP specifications. Contractors appeared to have more experience working with QCP projects than PFP projects. The statistical analysis identified that more than 80% of the test results between the contractor and the district were not significantly different. In those cases, it is likely that issues with mix production or construction were the reasons that led to a disincentive. However, there are possible testing issues that need to be addressed by the district and contractor such as reheating consistency and test weight control. Density was a major factor driving contractor disincentives in both specifications, followed by AV. Finally, the site visit identified mix production and construction issues that can lead to possible causes of pay disincentives, including mix switching, dust control, and aggregate contamination.IDOT-R27-189Ope

Disposable Platform Provides Visual and Color-Based Point-of-Care Anemia Self-Testing

Anemia, or low blood hemoglobin (Hgb) levels, afflicts 2 billion people worldwide. Currently, Hgb levels are typically measured from blood samples using hematology analyzers, which are housed in hospitals, clinics, or commercial laboratories and require skilled technicians to operate. A reliable, inexpensive point-of-care (POC) Hgb test would enable cost-effective anemia screening and chronically anemic patients to self-monitor their disease. We present a rapid, standalone, and disposable POC anemia test that, via a single drop of blood, outputs color-based visual results that correlate with Hgb levels. METHODS. We tested blood from 238 pediatric and adult patients with anemia of varying degrees and etiologies and compared hematology analyzer Hgb levels with POC Hgb levels, which were estimated via visual interpretation using a color scale and an optional smartphone app for automated analysis. RESULTS. POC Hgb levels correlated with hematology analyzer Hgb levels (r = 0.864 and r = 0.856 for visual interpretation and smartphone app, respectively), and both POC test methods yielded comparable sensitivity and specificity for detecting any anemia (n = 178) (/dl) (sensitivity: 90.2% and 91.1%, specificity: 83.7% and 79.2%, respectively) and severe anemia (n = 10) (/dl) (sensitivity: 90.0% and 100%, specificity: 94.6% and 93.9%, respectively). CONCLUSIONS. These results demonstrate the feasibility of this POC color-based diagnostic test for self-screening/self-monitoring of anemia. TRIAL REGISTRATION. Not applicable. FUNDING. This work was funded by the FDA-funded Atlantic Pediatric Device Consortium, the Georgia Research Alliance, Children\u27s Healthcare of Atlanta, the Georgia Center of Innovation for Manufacturing, and the InVenture Prize and Ideas to Serve competitions at the Georgia Institute of Technology

Phase-field simulation of micropores constrained by a solid network

A 2D phase-field model has been developed in order to describe the morphology of a pore forming within interdendritic liquid channels and the geometrical effect of mechanical contacts with neighboring solid. The distribution of the solid, liquid and gas phases is calculated with a multiphase-field approach which accounts for the pressure difference between the liquid and gas phases, as well as diffusion of dissolved gases in the liquid. The model incorporates the perfect gas and Sievert’s laws to describe the concentration and partitioning of gas molecules or atoms at the pore/liquid interface. The results show that the presence of solid can substantially influence the volume and pressure of the pore. A pore constrained to grow in narrow liquid channels exhibits a substantially higher mean curvature, a larger pressure and a smaller volume as compared with a pore grown under unconstrained conditions