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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Sub-cloud moist entropy curvature as a predictor for changes in the seasonal cycle of tropical precipitation

Convective Quasi-Equilibrium (CQE) may be a useful framework for understanding the precipitation minus evaporation (P-E) response to CO2-induced warming. To explore this proposition, a suite of aquaplanet simulations with a slab ocean from TRACMIP (the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project) is analyzed. A linear relationship between P-E and the curvature of sub-cloud moist entropy, a marker for the spatial distribution of sub-cloud moist energy and onset of a tropical direct overturning circulation under CQE conditions, is shown to exist across many of the TRACMIP simulations. Furthermore, this linear relationship is a skillful predictor of changes in P-E in response to CO2-induced warming. The curvature metric also shows improvement in predicting P-E changes compared to the simpler method of relating P-E directly to the sub-cloud moist entropy field or a simple ‘wet-get-wetter’ type null hypothesis, especially on seasonal and shorter timescales. Using fixed relative humidity in the curvature metric and sub-cloud moist entropy degrades their ability to predict P-E changes, implying that both temperature and relative humidity changes in the boundary layer are important for characterizing future precipitation changes. To understand why the curvature metric is a skillful predictor of hydrological changes, a moist static energy (MSE) budget analysis is performed, which shows that MSE divergence on sub-daily timescales is well parameterized as a downgradient diffusive process. Additionally, this transient MSE divergence has a similar structure to the curvature term. Assuming that the transient MSE divergence is related to convective activity, these findings suggest that the theoretical underpinning of the linear relationship between the curvature term and P-E resides in cloud processes that both remove spatial gradients of sub-cloud moist entropy and generate precipitation at sub-seasonal and shorter timescales.

aquaplanet simulations↗
DOE OSTI2016

A CHEMICAL KINETICS NETWORK FOR LIGHTNING AND LIFE IN PLANETARY ATMOSPHERES

There are many open questions about prebiotic chemistry in both planetary and exoplanetary environments. The increasing number of known exoplanets and other ultra-cool, substellar objects has propelled the desire to detect life and prebiotic chemistry outside the solar system. We present an ion–neutral chemical network constructed from scratch, Stand2015, that treats hydrogen, nitrogen, carbon, and oxygen chemistry accurately within a temperature range between 100 and 30,000 K. Formation pathways for glycine and other organic molecules are included. The network is complete up to H6C2N2O3. Stand2015 is successfully tested against atmospheric chemistry models for HD 209458b, Jupiter, and the present-day Earth using a simple one-dimensional photochemistry/diffusion code. Our results for the early Earth agree with those of Kasting for CO{sub 2}, H{sub 2}, CO, and O{sub 2}, but do not agree for water and atomic oxygen. We use the network to simulate an experiment where varied chemical initial conditions are irradiated by UV light. The result from our simulation is that more glycine is produced when more ammonia and methane is present. Very little glycine is produced in the absence of any molecular nitrogen and oxygen. This suggests that the production of glycine is inhibited if a gas is too strongly reducing. Possible applications and limitations of the chemical kinetics network are also discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Resonance broadened quasi-linear (RBQ) model for fast ion distribution relaxation due to Alfvénic eigenmodes

The burning plasma performance is limited by the confinement of the super-alfvénic fusion products such as alpha particles and the auxiliary heating ions capable of exciting the Alfvénic eigenmodes (AEs) (Gorelenkov et al 2014 Nucl. Fusion 54 125001). Here in this work the effect of AEs on fast ions is formulated within the quasi-linear (QL) theory generalized for this problem recently (Duarte 2017 PhD Thesis University of São Paulo, Brazil). The generalization involves the resonance line broadened interaction of energetic particles (EP) with AEs supplemented by the diffusion coefficients depending on EP position in the velocity space. A new resonance broadened QL code (or RBQ1D) based on this formulation allowing for EP diffusion in radial direction is built and presented in details. In RBQ1D applications we reduce the wave particle interaction (WPI) dynamics to 1D case when the particle kinetic energy is nearly constant. The diffusion equation for EP distribution evolution is then solved simultaneously for all particles along the angular momentum direction. We make initial applications of the RBQ1D to a DIII-D plasma with elevated q-profile where the beam ions show stiff transport properties (Collins et al (The DIII-D Team) 2016 Phys. Rev. Lett. 116 095001). In conclusion, AE driven fast ion profile relaxation is studied for validations of the QL approach in realistic conditions of beam ion driven instabilities in DIII-D.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Polarization diagnostics for cool core cluster emission lines

The nature of the interaction between low-excitation gas filaments at ∼10{sup 4} K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ∼10{sup 7} K in the centers of galaxy clusters remains a puzzle. The presence of a strong, empirical correlation between the two gas phases is indicative of a fundamental relationship between them, though as yet of undetermined cause. The cooler filaments, originally thought to have condensed from the hot gas, could also arise from a merger or the disturbance of cool circumnuclear gas by nuclear activity. Here, we have searched for intrinsic line emission polarization in cool core galaxy clusters as a diagnostic of fundamental transport processes. Drawing on developments in solar astrophysics, direct energetic particle impact induced polarization holds the promise to definitively determine the role of collisional processes such as thermal conduction in the ISM physics of galaxy clusters, while providing insight into other highly anisotropic excitation mechanisms such as shocks, intense radiation fields, and suprathermal particles. Under certain physical conditions, theoretical calculations predict of the order of 10% polarization. Our observations of the filaments in four nearby cool core clusters place stringent upper limits (≲ 0.1%) on the presence of emission line polarization, requiring that if thermal conduction is operative, the thermal gradients are not in the saturated regime. This limit is consistent with theoretical models of the thermal structure of filament interfaces.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Model Package Report: Composite Analysis Solid Waste Release Model (CASWR Model)

This document describes the implementation of a solid waste form release model in GoldSim for the Hanford Site Composite Analysis (CA) Update. This Composite Analysis Solid Waste Release model (CASWR model) was designed to generate deterministic radionuclide release rates for Hanford’s Central Plateau solid waste disposal sites using single realizations of release model coefficients. Five generalized waste form types are used for the conceptual model of waste release: surplus reactor block, cement, soil-debris, grouted residual waste, and ancillary equipment. The surplus reactor block waste form consists of radionuclide leaching from surplus production graphite reactor core blocks via unspecified processes (White et al., 1984 as cited in PNNL-15965). The cement waste form represents solidified wastes whose permeability is much lower than that of the surrounding soil. The soil-debris waste form type is defined as unconsolidated waste mixed with soil material. Tanks and canyon complexes comprise the grouted residual waste form such that their solid waste will be grouted and capped with a surface barrier at the completion of their cleanup. Finally, the ancillary equipment waste form constitutes contaminant releases from ancillary and auxiliary waste form residues associated with tank farms at closure. Individual sub-models are implemented to numerically represent a respective waste form within the CASWR Model: Surplus Reactor Block Sub-model, Cement Sub-model, SoilDebris Sub-model, Grouted Residual Waste Sub-model, and Ancillary Equipment Submodel. Advection is assumed to be the primary transport process governing the release of radionuclides in the Ancillary Equipment and Soil-Debris Sub-models. Diffusion is assumed to be the primary release process in the Grouted Residual Waste and Cement Sub-models. An unspecified zero-order release process is considered in the Surplus Reactor Block Sub-model due to the lack of information regarding actual processes involved in irradiated graphite leaching. The Surplus Reactor Block, Cement, and SoilDebris Sub-models were compared against analytical solutions (PNNL-11800, Composite Analysis for Low-Level Waste Disposal in the 200 Area Plateau of the Hanford Site). The agreement between results of these analytical solutions and the corresponding waste form models verified their correct implementation in GoldSim. A 1-D modeling abstraction approach for the Grouted Residual Waste and Ancillary Equipment Sub-models was adopted from existing Performance Assessment (PA) models. Despite the simplifications made in these sub-models, they were found to be appropriate representations of the waste forms, similar to what was used in the Waste Management Area C PA model (RPP-ENV-58782, Performance Assessment of Waste Management Area C, Hanford Site, Washington, Rev. 0). A sensitivity analysis was conducted to identify the most influential parameters in each waste form sub-model. Suggestions for considering pH-dependent and redox-dependent release mechanisms are formulated through the development of a conditional constant approach in GoldSim.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Microstructural impacts on ionic conductivity of oxide solid electrolytes from a combined atomistic-mesoscale approach

Abstract Although multiple oxide-based solid electrolyte materials with intrinsically high ionic conductivities have emerged, practical processing and synthesis routes introduce grain boundaries and other interfaces that can perturb primary conduction channels. To directly probe these effects, we demonstrate an efficient and general mesoscopic computational method capable of predicting effective ionic conductivity through a complex polycrystalline oxide-based solid electrolyte microstructure without relying on simplified equivalent circuit description. We parameterize the framework for Li 7- x La 3 Zr 2 O 12 (LLZO) garnet solid electrolyte by combining synthetic microstructures from phase-field simulations with diffusivities from molecular dynamics simulations of ordered and disordered systems. Systematically designed simulations reveal an interdependence between atomistic and mesoscopic microstructural impacts on the effective ionic conductivity of polycrystalline LLZO, quantified by newly defined metrics that characterize the complex ionic transport mechanism. Our results provide fundamental understanding of the physical origins of the reported variability in ionic conductivities based on an extensive analysis of literature data, while simultaneously outlining practical design guidance for achieving desired ionic transport properties based on conditions for which sensitivity to microstructural features is highest. Additional implications of our results are discussed, including a possible connection between ion conduction behavior and dendrite formation.

25 ENERGY STORAGE↗
DOE OSTI2018

An adaptive local reduced basis method for solving PDEs with uncertain inputs and evaluating risk

Many physical systems are modeled using partial differential equations (PDEs) with uncertain or random inputs. For such systems, naively propagating a fixed number of samples of the input probability law (or an approximation thereof) through the PDE is often inadequate to accurately quantify the "risk" associated with critical system responses. In this paper, we develop a goal-oriented, adaptive sampling and local reduced basis approximation for PDEs with random inputs. Our method determines a set of samples and an associated (implicit) Voronoi partition of the parameter domain on which we build local reduced basis approximations of the PDE solution. The samples are selected in an adaptive manner using an a posteriori error indicator. A notable advantage of the proposed approach is that the computational cost of the approximation during the adaptive process remains constant. We provide theoretical error bounds for our approximation and numerically demonstrate the performance of our method when compared to widely used adaptive sparse grid techniques. In addition, we tailor our approach to accurately quantify the risk of quantities of interest that depend on the PDE solution. We demonstrate our method on an advection-diffusion example and a Helmholtz example. Keywords: stochastic partial differential equation, adaptive sampling, reduced basis, a posteriori error estimation, coherent risk measure, conditional value-at-risk.

42 ENGINEERING↗
DOE OSTI2015

Micro-/mesoporous carbons for controlled release of antipyrine and indomethacin

Here, we have demonstrated the potential of meso- and microporous carbons in controlled release applications and targeted oral drug delivery. We have employed two mesoporous and two microporous carbons for the sustained release of one water-soluble drug (antipyrine) and one water-insoluble drug (indomethacin), using these as models to examine the controlled release characteristics. The micro-/mesoporous carbons were characterized as having a BET surface area of 372–2251 m 2 g –1 and pore volume 0.63–1.03 cm 3 g –1 . The toxicity studies with E. coli bacterial cells did not reveal significant toxicity, which is in accordance with our previous studies on human cells with similar materials. Mucin adsorption tests with type III pork mucin demonstrated 20–30% mucin adsorption by the carbon samples and higher mucin adsorption could be attributed to higher surface area and more oxygen functionalities. Antipyrine and indomethacin loading was 6–78% in these micro-/mesoporous carbons. The signatures in thermogravimetric studies revealed the presence of drug molecules within the porous moieties of the carbon. The partial shifting of the decomposition peak of the drug adsorbed within the carbon pores was caused by the confinement of drug molecules within the narrow pore space of the carbon. The release profiles of both drugs were examined in simulated gastric fluid (pH = 1.2) and in three other release media with respective pH values of 4.5, 6.8 and 7.4, along with varying residence times to simulate the physiological conditions of the stomach, duodenum, small intestine and colon, respectively. All the release profiles manifested diffusion controlled sustained release that corroborates the effective role of micro-/mesoporous carbons as potential drug carriers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

ON THE IMPORTANCE OF THE EQUATION OF STATE FOR THE NEUTRINO-DRIVEN SUPERNOVA EXPLOSION MECHANISM

By implementing the widely used equations of state (EOS) from Lattimer and Swesty (LS) and H. Shen et al. (SHEN) in core-collapse supernova simulations, we explore possible impacts of these EOS on the post-bounce dynamics prior to the onset of neutrino-driven explosions. Our spherically symmetric (1D) and axially symmetric (2D) models are based on neutrino radiation hydrodynamics including spectral transport, which is solved by the isotropic diffusion source approximation. We confirm that in 1D simulations neutrino-driven explosions cannot be obtained for any of the employed EOS. Impacts of the EOS on the post-bounce hydrodynamics are more clearly visible in 2D simulations. In 2D models of a 15 M {sub Sun} progenitor using the LS EOS, the stalled bounce shock expands to increasingly larger radii, which is not the case when using the SHEN EOS. Keeping in mind that the omission of the energy drain by heavy-lepton neutrinos in the present scheme could facilitate explosions, we find that 2D models of an 11.2 M {sub Sun} progenitor produce neutrino-driven explosions for all the EOS under investigation. Models using the LS EOS are slightly more energetic compared with those with the SHEN EOS. The more efficient neutrino heating in the LS models coincides with a higher electron antineutrino luminosity and a larger mass that is enclosed within the gain region. The models based on the LS EOS also show a more vigorous and aspherical downflow of accreting matter to the surface of the protoneutron star (PNS). The accretion pattern is essential for the production and strength of outgoing pressure waves, which can push in turn the shock to larger radii and provide more favorable conditions for the explosion. Based on our models, we investigate several diagnostic indicators of the explosion that have been suggested in the literature, e.g., the amplitude of the standing accretion shock instability mode, the mass-weighted average entropy in the gain region, the PNS radius, the antesonic condition, the ratio of advection and heating timescales, the neutrino heating efficiency, and the growth parameter of convection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Atmosphere-Biosphere Interaction Study (Field Campaign Report)

The objective of this campaign was to collect hyperspectral reflectance measurements and complementary optical and infrared data of land surface (i.e., vegetation and soil) throughout the growing season (i.e., from March to September) at high temporal frequency (e.g., < 30 minutes). To collect the measurements, the EcoSpec system, a tower-based sensor system housing seven optical and infrared sensors that was developed at Argonne National Laboratory, was deployed to the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility Southern Great Plains (SGP) atmospheric observatory (within the crop, south of the eddy correlation flux measurement system [ECOR] tower). The EcoSpec system consists of a spectroradiometer having 2,151 channels (350–2,500 nm), red-greenblue (RGB) camera, diffuse radiometer, thermal infrared (TIR) sensors, albedometers, Photochemical Reflectance Index (PRI) sensors, Normalized Difference Vegetation Index (NDVI) sensors, and wetness sensor. The system is designed to collect an array of land surface measurements, including hyperspectral reflectance of plants and soils, RGB photos capturing contextual information of land surface, radiant temperature of sky and land surface, incoming and reflected shortwave radiation, and incoming radiation components (direct and diffuse) as frequent as every minute from up to 12 discrete positions around the tower. This would allow us to capture inherent heterogeneity of the terrestrial ecosystem and to obtain representative spectral signatures of the plant and soil surfaces via averaging those measurements. The SGP site provides advanced atmospheric and other physical measurements that are essential for our investigation of ecosystem functions using hyperspectral reflectance measurements of land surfaces. Located in the mid-latitudes, the SGP site exhibits dynamic seasonality and a wide range of meteorological variability and flux properties that make it ideal for studying interactions between near-surface atmosphere and biosphere across a range of environmental conditions. The atmosphere, plants, and soil control terrestrial carbon and water cycles. To make more accurate climate forecasts, researchers need to understand ecosystem dynamics at the biosphere–atmosphere interface. Even though our ability to forecast ecosystem dynamics and climate at both the regional and global scales has advanced significantly, we still do not know how local phenomena affecting water and carbon fluxes—such as diurnal variations—interrelate with large-scale atmospheric/climate phenomena, and vice versa. The lack of a more thorough understanding of ecosystem dynamics and climate interactions is a key knowledge gap for the improvement of earth system models (ESMs).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Verification of the pin power reconstruction method in NESTLE

NESTLE is a 3D nodal core simulator that solves the few group neutron diffusion equation using the nodal expansion method (NEM) for the steady state (eigenvalue or fixed-source), adjoint (eigenvalue), and transient (eigenvalue or fixed-source) problems. NESTLE has been in use for over 25 years and has been continuously improved and developed. NESTLE can be used to model either Cartesian geometries (for use with typical PWR, BWR fuel assemblies) or hexagonal geometries (for use with VVER and other triangularly pitched fuel assemblies). As part of NESTLE's ongoing verification and validation process, several computational comparisons have been made to quantify the discrepancies in NESTLE's hexagonal pin power reconstruction method. In this paper, we present the results of these code-to-code comparisons and find that the root mean squared (RMS) error in pin power is comparable to other nodal codes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2012

Using in situ X-ray absorption spectroscopy to study the local structure and oxygen ion conduction mechanism in (La{sub 0.6}Sr{sub 0.4})(Co{sub 0.2}Fe{sub 0.8})O{sub 3-{delta}}

To study the local structure and oxygen ion conduction mechanism in (La{sub 0.6}Sr{sub 0.4})(Co{sub 0.2}Fe{sub 0.8})O{sub 3-{delta}} (LSCF) as a function of the oxygen partial pressure (P(O{sub 2})), in situ the Co and Fe K-edge X-ray absorption spectroscopy (XAS) was measured at elevated temperatures of 900 and 1000 K. The reduction of the Co and Fe valence, i.e., the oxygen content (3-{delta}) in LSCF, followed the change of P(O{sub 2}) from 1 to 10{sup -4} atm during{approx}4000 s. The quantitative analysis of the X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) indicated that the Fe valence was higher than the Co valence at oxidative condition ({delta} Almost-Equal-To 0) in LSCF. Whereas the Co valence decreased more than the Fe valence after reduction of P(O{sub 2}) at both 900 and 1000 K. From the relaxation plots of the valence and the oxygen content (3-{delta}) for Co and Fe after changing P(O{sub 2}), we successfully determined D{sub chem} and E{sub a} of an oxygen ion migration around Co and Fe in LSCF. A structural model with and without oxygen vacancies and an oxygen ion conduction mechanism for LSCF are proposed based on these results. - Graphical abstract: A structural model with and without oxygen vacancies, and the oxygen ion conduction mechanism of LSCF were speculated. In other words, oxygen vacancies would form more preferentially around Co than Fe from the results of in situ XAS analysis during reduction, and oxygen ions needs to pass through at the vicinity of Fe from the results of D{sub chem} and E{sub a}. Highlights: Black-Right-Pointing-Pointer Study of the oxygen ion conduction mechanism in (La{sub 0.6}Sr{sub 0.4})(Co{sub 0.2}Fe{sub 0.8})O{sub 3-{delta}} (LSCF). Black-Right-Pointing-Pointer Using in situ X-ray absorption for study of valence and oxygen diffusion coefficient. Black-Right-Pointing-Pointer The oxygen vacancies should be preferentially localized around Co in LSCF. Black-Right-Pointing-Pointer The values of the dynamics parameters for Co and Fe are close to each other.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Fast redox switches lead to rapid transformation of goethite in humid tropical soils: A Mössbauer spectroscopy study

Abstract Humid tropical forest soils experience frequent rainfall, which limits oxygen diffusion and creates redox heterogeneity in upland soils. In this study we gauged the effect of short‐term anoxic conditions on Fe mineralogy of relatively Fe‐ and C‐rich surface soils (C/Fe mole ratio ∼5) from a humid tropical forest in Puerto Rico. Soils subjected to 4‐d oxic/anoxic oscillation were characterized by selective chemical extractions, Mössbauer spectroscopy (MBS), and X‐ray diffraction. Chemical extraction data suggested that rapidly switching redox conditions had subtle effects on bulk Fe mineralogy. Mössbauer, on the other hand, indicated that (a) the soil Fe is a mixture of goethites of varying characteristics with minor contributions from ferrihydrite (<5%) and Fe(III)‐organic matter (OM) phases (∼10%), and (b) anoxic conditions rapidly transformed all forms of goethite to relatively stable Fe oxides. Such fast changes in goethite features could be due to rapid depletion and sorption of bio‐released structural Al or sorbed OM onto residual soil components. The rapid temporal changes in MBS parameters and corresponding pore water nominal oxidation state of C values suggest that Fe‐C transformations in these upland tropical soils are complex and intricately coupled. A comprehensive understanding of the fate of Fe, Al, and OM (Fe‐organic moieties) during redox switches and concurrent changes in pore water chemistry is critical for development of robust transport models in humid tropical soils, which are subject to episodic low‐redox events.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Multi-scale modelling to relate beryllium surface temperature, deuterium concentration and erosion in fusion reactor environment

Beryllium (Be) has been chosen as the plasma-facing material for the main wall of ITER, the next generation fusion reactor. Identifying the key parameters that determine Be erosion under reactor relevant conditions is vital to predict the ITER plasma-facing component lifetime and viability. To date, a certain prediction of Be erosion, focusing on the effect of two such parameters, surface temperature and D surface content, has not been achieved. In this paper, we develop the first multi-scale KMC-MD modeling approach for Be to provide a more accurate database for its erosion, as well as investigating parameters that affect erosion. First, we calculate the complex relationship between surface temperature and D concentration precisely by simulating the time evolution of the system using an object kinetic Monte Carlo (OKMC) technique. These simulations provide a D surface concentration profile for any surface temperature and incoming D energy. We then describe how this profile can be implemented as a starting configuration in molecular dynamics (MD) simulations. We finally use MD simulations to investigate the effect of temperature (300–800 K) and impact energy (10–200 eV) on the erosion of Be due to D plasma irradiations. The results reveal a strong dependency of the D surface content on temperature. Increasing the surface temperature leads to a lower D concentration at the surface, because of the tendency of D atoms to avoid being accommodated in a vacancy, and de-trapping from impurity sites diffuse fast toward bulk. At the next step, total and molecular Be erosion yields due to D irradiations are analyzed using MD simulations. The results show a strong dependency of erosion yields on surface temperature and incoming ion energy. The total Be erosion yield increases with temperature for impact energies up to 100 eV. However, increasing temperature and impact energy results in a lower fraction of Be atoms being sputtered as BeD molecules due to the lower D surface concentrations at higher temperatures. Finally, these findings correlate well with different experiments performed at JET and PISCES-B devices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Modeling Peste des Petits Ruminants (PPR) Disease Propagation and Control Strategies Using Memoryless State Transitions

Peste des Petits Ruminants (PPR) is an infectious disease affecting goats and sheep. PPR has a mortality rate of 80% and a morbidity rate of 100% in naïve herds. This disease is currently of concern to Afghani goat and sheep herders as conditions in Afghanistan are conducive to the disease becoming an epidemic. PPR is similar to Rinderpest, but is not as well studied. There is a lack of empirical data on how the disease spreads or effective large-scale mitigation strategies. We developed a herd-level, event-driven model of PPR, using memoryless state transitions, to study how the virus propagates through a herd, and to identify effective control strategies for disparate herd configurations and environments. This model allows us to perform Sensitivity Analyses (SA) on environmental and disease parameters for which we do not have empirical data and to simulate the effectiveness of various control strategies. We find that reducing the amount of time from the identification of PPR in a herd to the vaccination of the herd will radically reduce the number of deaths that result from PPR. The goal of this model is to give policy makers a tool to develop effective containment strategies for managing outbreaks of PPR.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Learning in Modal Space: Solving Time-Dependent Stochastic PDEs Using Physics-Informed Neural Networks

One of the open problems in scientific computing is the long-time integration of nonlinear stochastic partial differential equations (SPDEs), especially with arbitrary initial data. We address this problem by taking advantage of recent advances in scientific machine learning and the spectral dynamically orthogonal (DO) and borthogonal (BO) methods for representing stochastic processes. The recently introduced DO/BO methods reduce the SPDE to solving a system of deterministic PDEs and a system of stochastic ordinary differential equations. Specifically, we propose two new physics-informed neural networks (PINNs) for solving time-dependent SPDEs, namely the neural network (NN)-DO/BO methods. The proposed methods incorporate the DO/BO constraints into the loss function (along with the modal decomposition of the SPDE) with an implicit form instead of generating explicit expressions for the temporal derivatives of the DO/BO modes. Hence, the NN-DO/BO methods can overcome some of the drawbacks of the original DO/BO methods. For example, we do not need the assumption that the covariance matrix of the random coefficients is invertible as in the original DO method, and we can remove the assumption of no eigenvalue crossing as in the original BO method. Moreover, the NN-DO/BO methods can be used to solve time-dependent stochastic inverse problems with the same formulation and same computational complexity as for forward problems. Furthermore, we demonstrate the capability of the proposed methods via several numerical examples, namely: (1) A linear stochastic advection equation with deterministic initial condition: we obtain good results with the proposed methods, while the original DO/BO methods cannot be applied directly in this case. (2) Long-time integration of the stochastic Burgers' equation: we show the good performance of NN-DO/BO methods, especially the effectiveness of the NN-BO approach for such problems with many eigenvalue crossings during the whole time evolution, while the original BO method fails. (3) Nonlinear reaction diffusion equation: we consider both the forward problem and the inverse problems, including very noisy initial point values, to investigate the flexibility of the NN-DO/BO methods in handling inverse and mixed type problems. Taken together, these simulation results demonstrate that the NN-DO/BO methods can be employed to effectively quantify uncertainty propagation in a wide range of physical problems, but future work should address the efficiency issue of PINNs for forward problems.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

A unique but flexible space–time could challenge multiverse theories

Highlights: The growing law of a billiard multiverse is independent of the discretization scale E. The time for any final state to be accessible from any initial one is around 3E shocks. The paths of billiard balls can change without changing initial or final states. Space-time flexibility can be achieved through paths commutations and entanglement. -- Abstract: In a previous paper (Guillemant et al., 2018), we have shown using a 2D billiard toy model that the propagation of uncertainties resulting from space–time discretization leads to a classical multiverse. In this one we estimate the growing law of the number of its branches, thanks to an original shock indexation method that permits a very fast comparison of trajectories. For different involved parameters we use random sets of infinitesimally perturbed initial conditions. From each set, we compute a collection up to hundred millions of different billiard histories. Our main result is the calculation of a Brownian saturation time when the number of branches begins to exceed the total number of billiard states. We discuss the possibility suggested by this result to change locally the paths of objects without changing their past and future histories and then subverting their global system. We conclude that a unique but flexible space–time could compete with the current many-worlds interpretation claiming that each branch is a different universe.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Restoring ZSM-5 performance for catalytic fast pyrolysis of biomass: Effect of regeneration temperature

Zeolite catalysts used for biomass catalytic fast pyrolysis (CFP) deactivate rapidly, similar to a fluidized catalytic cracking (FCC) catalyst used in refining. To operate effectively when there is rapid deactivation, biomass CFP can take place in a riser FCC-style reactor in which the catalyst has a short contact time (seconds) with reactants before it is regenerated. The regeneration, therefore, has two major needs for effective operation: 1) heat balance, since the heat required for the CFP reactions is brought into the reactor by the hot catalyst and 2) relatively short (minutes) regeneration to restore the catalyst activity to be near its initial state. In order to understand effective conditions to regenerate zeolites used for CFP, a series of experiments were performed to determine the effect of regeneration temperature on the activity of ZSM-5 (SiO 2 /Al 2 O 3 = 30). After use for pine pyrolysis vapor upgrading, the catalyst was oxidized in 4% O 2 at temperatures between 500-700 °C and reevaluated for the upgrading of pine pyrolysis vapors to assess the extent of regeneration. Additional testing was performed using ethylene aromatization as a surrogate reaction to probe regeneration efficiency. Regeneration experiments were performed for either a fixed length of time (20 min) or until there was no further CO 2 measured in the effluent gas. Results from the ethylene aromatization reactions were shown to serve as an excellent surrogate for CFP reactivity and indicated that the use of model compound studies can effectively be used to understand reaction and regeneration processes from biomass CFP. Both sets of results indicate that a spent ZSM-5 used for biomass CFP could be fully regenerated at 650 degrees C and 700 °C within 20 min, whereas regeneration temperatures of 550 °C and 600 °C required longer regeneration temperatures and in the case of regeneration at 500 °C, there may be coke species that are not removed and the catalyst activity may never be fully restored. Characterization by pyridine diffuse reflectance infrared spectroscopy, thermogravimetric analysis coupled with infrared spectroscopy, and N 2 physisorption showed that higher regeneration temperatures are more effective for restoring Bronsted acid sites and catalyst mesoporosity by rapidly removing aromatic coke deposits. In conclusion, regeneration at 650 °C and 700 °C led to a slightly higher total porosity as compared to the pristine catalyst, which was attributed to the formation of additional mesoporosity from catalyst steaming.

09 BIOMASS FUELS↗