Underpinning and benchmarking multi-scale models with micro- and nanoscale experiments

Predictive models of materials behavior depend on: accurate databases of constitutive material properties, identification of underlying deformation mechanisms, and the availability of experimentally measured benchmarks with which to compare. Micro- and nano-scale experiments can be used to facilitate collection of salient mechanical properties of individual phases at appropriate temperatures, chemistries and microstructural states. Coupling with TEM observations allows one to identify underlying deformation mechanisms and to imbibe models with the requisite fundamental physics and materials science. Simulations must be benchmarked with experiments, conducted at scale with relevant material volumes and identifiable microstructures. This presentation will outline efforts to characterize the constitutive behavior of materials, to identify deformation mechanisms, and to benchmark crystal plasticity simulations at appropriate length scales. Micro-scale experiments designed and conducted to complement crystal plasticity modeling of two different microstructural variants of Ni-base superalloys, polycrystalline Rene 88 and directionally solidified GTE 444, will be presented. If size-scale effect can be avoided, constitutive (single-crystalline) data may be obtained with micro-tensile tests at various orientations and temperatures. Moreover, preparing and testing specimens with reduced volumes and a finite number of grains allows for direct comparison with crystal plasticity simulations of stress-strain behavior as well as strain localization. With regard to the latter, digital image correlation (DIC) of spatially resolved surface displacements produces strain maps that provide a much more rigorous benchmark for crystal plasticity predictions than stress-strain curves. Using directionally solidified specimens allows for 2.5D microstructures (grains that extend through the thickness of the specimen) and greatly simplifies such comparisons. Moving beyond uniaxial tension, micro-bending resonance fatigue experiments provide an opportunity to measure the number of cycles, location, and microstructural features associated with slip, intragranular crack formation, and eventual transgranular crack growth. These experimental measures can in turn be used to inform and benchmark multi-scale fatigue simulations. Similarly, strain-controlled fracture experiments involving 2.5D unidirectional polymer matrix composites (PMC) have been developed and are being used to identify the microstructural features and fracture paths that govern delamination and fracture. The availability of orientation mapping techniques (EBSD, PACOM, TKD) now allows for nano-scale characterization of underlying deformation mechanisms and their relation to crystallographic microstructures and surrounding neighborhoods. Studies investigating the role of grain growth, twinning and dislocation plasticity will be presented. Special attention will be placed on attempts to measure intragranular strains that can be related to the accumulation of geometrically necessary dislocations (GNDs) and compared with crystal plasticity simulations. Support for these projects has been provided through the AFOSR and AFRL funded Center of Excellence on Integrated Materials Modeling and the DOE office of Basic Energy Sciences

Combined coagulation and inflammation markers as predictors of venous thrombo-embolism and death in COVID-19

BackgroundThe COVID-19 pandemic related to SARS-CoV-2 virus was responsible for global pandemic. The severe form of the disease was linked to excessive activation of immune pathways together with a systemic cytokine storm response and thrombotic venous or arterial complications. Factors predicting severe outcomes including venous and/or pulmonary thrombosis (VT) and death were identified, but the prognostic role of their combination was not addressed extensively.ObjectivesWe investigated the role of prognostic factors from the coagulation or inflammatory pathways to better understand the outcome of the disease.MethodsFor this, we prospectively studied 167 SARS-CoV-2-positive patients from admission in intensive care units (ICU) or emergency departments from four academic hospitals over a 14-month period. Besides standard biology, we assessed serum concentrations of inflammatory markers, coagulation factors and peripheral blood cells immunophenotyping.ResultsThirty-nine patients (23.3%) developed VT and 30 patients (18%) died. By univariate analysis, C-reactive protein (CRP) level > 150 mg/L, interleukin-6 (IL-6) ≥ 20 pg/mL, D-dimers > 1,500 μg/L, ADAMTS13 activity ≤ 50%, VonConclusionA combination of coagulation and inflammatory markers can refine the prognostication of severe outcome in COVID-19, and could be useful for the initial evaluation of other types of viral infection

Ultraviolet Spectroscopy of Comet 9P/Tempel 1 with Alice/Rosetta during the Deep Impact Encounter

We report on spectroscopic observations of periodic comet 9P/Tempel 1 by the Alice ultraviolet spectrograph on the Rosetta spacecraft in conjunction with NASA's Deep Impact mission. Our objectives were to measure an increase in atomic and molecular emissions produced by the excavation of volatile sub-surface material. We unambiguously detected atomic oxygen emission from the quiescent coma but no enhancement at the 10% (1-sigma) level following the impact. We derive a quiescent water production rate of 9 x 10^27 molecules per second with an estimated uncertainty of 30%. Our upper limits to the volatiles produced by the impact are consistent with other estimates.Comment: 11 pages, 4 postscript figures. Accepted for publication in Icarus special issue on Deep Impac

Metastable lifetimes in a kinetic Ising model: Dependence on field and system size

The lifetimes of metastable states in kinetic Ising ferromagnets are studied by droplet theory and Monte Carlo simulation, in order to determine their dependences on applied field and system size. For a wide range of fields, the dominant field dependence is universal for local dynamics and has the form of an exponential in the inverse field, modified by universal and nonuniversal power-law prefactors. Quantitative droplet-theory predictions are numerically verified, and small deviations are shown to depend nonuniversally on the details of the dynamics. We identify four distinct field intervals in which the field dependence and statistical properties of the lifetimes are different. The field marking the crossover between the weak-field regime, in which the decay is dominated by a single droplet, and the intermediate-field regime, in which it is dominated by a finite droplet density, vanishes logarithmically with system size. As a consequence the slow decay characteristic of the former regime may be observable in systems that are macroscopic as far as their equilibrium properties are concerned.Comment: 18 pages single spaced. RevTex Version 3. FSU-SCRI-94-1