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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Subplane collision probabilities method applied to control rod cusping in 2D/1D

The MPACT code is being jointly developed by the University of Michigan and Oak Ridge National Laboratory. It uses the 2D/1D method to solve neutron transport problems for reactors. The 2D/1D method decomposes the problem into a stack of 2D planes, and uses a high fidelity transport method to resolve all heterogeneity in each plane. These planes are then coupled axially using a lower order solver. Using this scheme, 3D solutions to the transport equation can be obtained at a much lower cost.One assumption made by the 2D/1D method is that the materials are axially homogeneous for each 2D plane. Violation of this assumption requires homogenization, which can significantly reduce the accuracy of the calculation. This paper presents two new subgrid methods to address this issue. The first method is polynomial decusping, a simple correction used to address control rods partially inserted into a 2D plane. The second is the subplane collision probabilities method, which is a more accurate, more robust subgrid method that can be applied to other axial heterogeneities.Each method was applied to a variety of problems. Results were compared to fine mesh solutions which had no axial heterogeneity and to Monte Carlo reference solutions generated using KENO-VI. It was shown that the polynomial decusping method was effective in many cases, but it had some limitations, with 3D pin power errors as high as 25% compared to KENO-VI. In conclusion, the subplane collision probabilities method performed much better, lowering the maximum pin power error to less than 5% in every calculation.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

Observer POD for radiographic testing

The radiographic testing (RT) is a non-destructive testing (NDT) method capable of finding volumetric and open planar defects depending on their orientation. The radiographic contrast is higher for larger penetrated length of the defect in a component. Even though, the detectability of defects does not only depend on the contrast, but also on the noise, the defect area and the geometry of the defect. The currently applied Probability of Detection (POD) approach uses a detection threshold that is only based on a constant noise level or on a constant contrast threshold. This does not reflect accurately the results of evaluations by human observers. A new approach is introduced, using the widely applied POD evaluation and additionally a detection threshold depending on the lateral area and shape of the indication. This work shows the process of calculating the POD curves with simulated data by the modeling software aRTist and with artificial reference data of different defect types, such as ASTM E 476 EPS plates, flat bottom holes and notches. Additional experiments with different operators confirm that the depth of a defect, the lateral area and shape of its indication contribute with different weight to the detectability of the defect if evaluated by human operators on monitors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Environmental assessment in The Netherlands: Effectively governing environmental protection? A discourse analysis

Environmental assessment (EA) aims to enhance environmental awareness and to ensure that environmental values are fully considered in decision-making. In the EA arena, different discourses exist on what EA should aim for and how it functions. We hypothesise that these discourses influence its application in practice as well as its effectiveness in terms of achieving the above goals. For instance, actors who consider EA as a hindrance to fast implementation of their projects will probably apply it as a mandatory checklist, whereas actors who believe that EA can help to develop more environmentally sound decisions will use EIA as a tool to design their initiatives. In this paper we explore discourses on EA in The Netherlands and elaborate on their implications for EA effectiveness. Based on an innovative research design comprising an online survey with 443 respondents and 20 supplementary semi-structured interviews we conclude that the dominant discourse is that EA is mainly a legal requirement; EAs are conducted because they have to be conducted, not because actors choose to do so. EA effectiveness however seems reasonably high, as a majority of respondents perceive that it enhances environmental awareness and contributes to environmental protection. However, the 'legal requirement' discourse also results in decision-makers seldom going beyond what is prescribed by EA and environmental law. Despite its mandatory character, the predominant attitude towards EA is quite positive. For most respondents, EA is instrumental in providing transparency of decision-making and in minimising the legal risks of not complying with environmental laws. Differences in discourses seldom reflect extreme opposites. The 'common ground' regarding EA provides a good basis for working with EA in terms of meeting legal requirements but at the same time does not stimulate creativity in decision-making or optimisation of environmental values. In countries characterised by less consensual political cultures we may expect more extreme discourses on EA, the consequences of which are reflected upon in this paper. - Highlights: Black-Right-Pointing-Pointer The effectiveness of environmental assessment (EA) depends in part on meanings associated with EA (i.e., discourse). Black-Right-Pointing-Pointer Our results suggest that the general discourse in The Netherlands is that EA is a legal requirement, nothing more. Black-Right-Pointing-Pointer This discourse makes EA effective in protecting the environment, but not in the optimisation of environmental values. Black-Right-Pointing-Pointer EA has a limited contribution to the development of policy alternatives or innovative solutions to environmental problems. Black-Right-Pointing-Pointer There is a high consensus among EA professionals, providing a common ground for working with EA.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Sub-10 second fly-scan nano-tomography using machine learning

Abstract X-ray computed tomography is a versatile technique for 3D structure characterization. However, conventional reconstruction algorithms require that the sample not change throughout the scan, and the timescale of sample dynamics must be longer than the data acquisition time to fulfill the stable sample requirement. Meanwhile, concerns about X-ray-induced parasite reaction and sample damage have driven research efforts to reduce beam dosage. Here, we report a machine-learning-based image processing method that can significantly reduce data acquisition time and X-ray dose, outperforming conventional approaches like Filtered-Back Projection, maximum-likelihood, and model-based maximum-a-posteriori probability. Applying machine learning, we achieve ultrafast nano-tomography with sub-10 second data acquisition time and sub-50 nm pixel resolution in a transmission X-ray microscope. We apply our algorithm to study dynamic morphology changes in a lithium-ion battery cathode under a heating rate of 50 o C min −1 , revealing crack self-healing during thermal annealing. The proposed method can be applied to various tomography modalities.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Isotopic effects in sub-barrier fusion of Si + Si systems

Recent measurements of fusion cross sections for the 28 Si + 28 Si system revealed a rather unsystematic behavior; i.e., they drop faster near the barrier than at lower energies. This was tentatively attributed to the large oblate deformation of 28 Si because coupled-channels (CC) calculations largely underestimate the 28 Si + 28 Si cross sections at low energies, unless a weak imaginary potential is applied, probably simulating the deformation. 30 Si has no permanent deformation and its low-energy excitations are of a vibrational nature. Here, previous measurements of this system reached only 4 mb, which is not sufficient to obtain information on effects that should show up at lower energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Translating macroecological models to predict microbial establishment probability in an agricultural inoculant introduction

The use of potentially beneficial microorganisms in agriculture (microbial inoculants) has rapidly accelerated in recent years. For microbial inoculants to be effective as agricultural tools, these organisms must be able to survive and persist in novel environments while not destabilizing the resident community or spilling over into adjacent natural ecosystems. Despite the importance of propagule pressure to species introductions, few tools exist in microbial ecology to predict the outcomes of agricultural microbial introductions. Here, we adapt a macroecological propagule pressure model to a microbial scale and present an experimental approach for testing the role of propagule pressure in microbial inoculant introductions. We experimentally determined the risk-release relationship for an IAA-expressing Pseudomonas simiae inoculant in a model monocot system. We then used this relationship to simulate establishment outcomes under a range of application frequencies (propagule number) and inoculant concentrations (propagule size). Our simulations show that repeated inoculant applications may increase establishment, even when increased inoculant concentration does not alter establishment probabilities. Applying ecological modeling approaches like those presented here to microbial inoculants may aid their sustainable use and provide a monitoring tool for microbial inoculants.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Magnetic tunnel junction random number generators applied to dynamically tuned probability trees driven by spin orbit torque

Abstract Perpendicular magnetic tunnel junction (pMTJ)-based true-random number generators (RNGs) can consume orders of magnitude less energy per bit than CMOS pseudo-RNGs. Here, we numerically investigate with a macrospin Landau–Lifshitz-Gilbert equation solver the use of pMTJs driven by spin–orbit torque to directly sample numbers from arbitrary probability distributions with the help of a tunable probability tree. The tree operates by dynamically biasing sequences of pMTJ relaxation events, called ‘coinflips’, via an additional applied spin-transfer-torque current. Specifically, using a single, ideal pMTJ device we successfully draw integer samples on the interval [0, 255] from an exponential distribution based on p -value distribution analysis. In order to investigate device-to-device variations, the thermal stability of the pMTJs are varied based on manufactured device data. It is found that while repeatedly using a varied device inhibits ability to recover the probability distribution, the device variations average out when considering the entire set of devices as a ‘bucket’ to agnostically draw random numbers from. Further, it is noted that the device variations most significantly impact the highest level of the probability tree, with diminishing errors at lower levels. The devices are then used to draw both uniformly and exponentially distributed numbers for the Monte Carlo computation of a problem from particle transport, showing excellent data fit with the analytical solution. Finally, the devices are benchmarked against CMOS and memristor RNGs, showing faster bit generation and significantly lower energy use.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Sensitivity analysis applied to SiC failure probability in TRISO modeled with BISON

Here, a sensitivity analysis on the failure probability of the Silicon Carbide (SiC) layer in tristructural isotropic (TRISO) nuclear fuel during transient conditions predicted by the BISON fuel performance code is performed. The principal goal of the analysis is to understand the most important parameters dictating SiC failure behavior in BISON during Reactivity Initiated Accidents (RIAs). SiC brittle fracture probability is modeled using Weibull statistics. A total of seven inputs related to SiC failure has been selected for the analysis, including the Weibull statistics parameters, elastic moduli for SiC and Pyrolitic Carbon (PyC) and SiC stress-free temperature. A 1D TRISO BISON model has been established for various reactivity insertions performed at the Nuclear Safety Research Reactor (NSRR). The principal advantage associated with the 1D TRISO model developed in this work is its computational efficiency. The Sobol variance decomposition method is used, and the sensitivity indices are presented for eight different values of the energy deposition. The results show that the two most important parameters impacting the predicted SiC failure probability are the Weibull modulus and the characteristic stress, and a co-variance amongst these parameters is obtained for low reactivity insertions. An additional new finding of this work is that the relative importance of Weibull parameters depends on the energy deposition, and thus reactivity, regime. For low energy depositions, two parameters are of influence on SiC failure probability, while for high energy depositions only one parameter impacts failure probability results. Moreover, optimization of the Weibull modulus and characteristic stress is performed by minimizing the RMSE between BISON failure probability predictions and experimental failure fractions for each energy deposition. This work also demonstrates the validity of the NSRR tests BISON simulations and of the respective sensitivity analysis results as conservative, yet indicative for slower transients characterized by lower deposited energies. Such verification is achieved through the partial extension of the analysis to a group Control Rod Withdrawal reproduced from a previous study. Another novel result of this analysis is that no single set of Weibull parameters can reproduce all reactivity insertion experimental failure results, which is related to the intrinsic nature of SiC failure properties, and a new range for the parameters is proposed to produce a failure probability envelope that encompasses the experimental fractions. Additionaly, this work proposes a new approach for future failure analysis with BISON, consisting in the use of Weibull parameters ranges, rather than fixed sets, along with failure envelopes generation.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Reliability comparisons between additively manufactured and conventional SiC–Si ceramic composites

Abstract An additively manufactured reaction‐bonded silicon carbide ceramic composite is fabricated using a bimodal powder feedstock and the binder‐jetting printing technique. On fabricating, the ceramic is investigated to report its composition, mechanical, and thermal properties at room temperature and high temperatures (up to 750). The ceramic has a density of 2.76 g/cc, and shows a hardness of 21.74 GPa, and a flexure strength of 207.5 MPa at room temperature. The mechanical property of flexure strength is used to estimate its failure probability under applied stress, using a Weibull distribution. The mechanical properties and failure probabilities are compared with those of conventionally fabricated reaction‐bonded silicon carbide ceramics reported in the literature. These ceramics were fabricated using methods such as slip‐casting, compacting, and tape‐casting. The comparison is used to elucidate the advantages and areas of improvement of the present additive manufacturing technique for reaction‐bonded ceramics.

14 SOLAR ENERGY↗
DOE OSTI2015

Learn-as-you-go acceleration of cosmological parameter estimates

Cosmological analyses can be accelerated by approximating slow calculations using a training set, which is either precomputed or generated dynamically. However, this approach is only safe if the approximations are well understood and controlled. This paper surveys issues associated with the use of machine-learning based emulation strategies for accelerating cosmological parameter estimation. We describe a learn-as-you-go algorithm that is implemented in the Cosmo++ code and (1) trains the emulator while simultaneously estimating posterior probabilities; (2) identifies unreliable estimates, computing the exact numerical likelihoods if necessary; and (3) progressively learns and updates the error model as the calculation progresses. We explicitly describe and model the emulation error and show how this can be propagated into the posterior probabilities. We apply these techniques to the Planck likelihood and the calculation of ΛCDM posterior probabilities. The computation is significantly accelerated without a pre-defined training set and uncertainties in the posterior probabilities are subdominant to statistical fluctuations. We have obtained a speedup factor of 6.5 for Metropolis-Hastings and 3.5 for nested sampling. Finally, we discuss the general requirements for a credible error model and show how to update them on-the-fly.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CYCLIC TRANSIT PROBABILITIES OF LONG-PERIOD ECCENTRIC PLANETS DUE TO PERIASTRON PRECESSION

The observed properties of transiting exoplanets are an exceptionally rich source of information that allows us to understand and characterize their physical properties. Unfortunately, only a relatively small fraction of the known exoplanets discovered using the radial velocity technique are known to transit their host due to the stringent orbital geometry requirements. For each target, the transit probability and predicted transit time can be calculated to great accuracy with refinement of the orbital parameters. However, the transit probability of short period and eccentric orbits can have a reasonable time dependence due to the effects of apsidal and nodal precession, thus altering their transit potential and predicted transit time. Here we investigate the magnitude of these precession effects on transit probabilities and apply this to the known radial velocity exoplanets. We assess the refinement of orbital parameters as a path to measuring these precessions and cyclic transit probabilities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Distributed resonance self-shielding using the equivalence principle

This paper presents an extension of the equivalence principle to allow distributed resonance self-shielding in a multi-region fuel configuration. Rational expansion of fuel-to-fuel collision probability is applied in order to establish equivalence between the actual fuel configuration and a homogeneous mixture of hydrogen and resonant absorber, which is a commonly used model to calculate library tables of resonance integrals. The main steps in derivation are given along with the basic physics assumptions on which the presented approach relies. The method has been implemented in the lattice code WIMS-AECL and routinely used for calculation of CANDU-type reactor lattices. Its capabilities are illustrated by comparison of WIMS-AECL and MCNP results of {sup 238}U resonance capture in a CANDU lattice cell. In order to determine optimal rational expansion of fuel-to-fuel collision probability, the calculations were carried out by varying the number of rational terms from 1 to 6. The results show that 4 terms are sufficient. The further increase of the number of terms affects the computing time, while the impact on accuracy is negligible. To illustrate the convergence of the results, the fuel subdivision is gradually refined varying the number of fuel pin subdivisions from 1 to 32 equal-area annuli. The results show very good agreement with the reference MCNP calculation. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2014

Estimating the epidemic threshold on networks by deterministic connections

For many epidemic networks some connections between nodes are treated as deterministic, while the remainder are random and have different connection probabilities. By applying spectral analysis to several constructed models, we find that one can estimate the epidemic thresholds of these networks by investigating information from only the deterministic connections. Nonetheless, in these models, generic nonuniform stochastic connections and heterogeneous community structure are also considered. The estimation of epidemic thresholds is achieved via inequalities with upper and lower bounds, which are found to be in very good agreement with numerical simulations. Since these deterministic connections are easier to detect than those stochastic connections, this work provides a feasible and effective method to estimate the epidemic thresholds in real epidemic networks.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

An Empirical Quantile Estimation Approach for Chance-Constrained Nonlinear Optimization Problems

We investigate an empirical quantile estimation approach to solve chance-constrained nonlinear optimization problems. Our approach is based on the reformulation of the chance constraint as an equivalent quantile constraint to provide stronger signals on the gradient. In this approach, the value of the quantile function is estimated empirically from samples drawn from the random parameters, and the gradient of the quantile function is estimated via a finite-difference approximation on top of the quantile-function-value estimation. We establish a convergence theory of this approach within the framework of an augmented Lagrangian method for solving general nonlinear constrained optimization problems. The foundation of the convergence analysis is a concentration property of the empirical quantile process, and the analysis is divided based on whether or not the quantile function is differentiable. In contrast to the sampling-and-smoothing approach used in the literature, the method developed in this paper does not involve any smoothing function and hence the quantile-function gradient approximation is easier to implement and there are less accuracy-control parameters to tune. Furthermore, we demonstrate the effectiveness of this approach and compare it with a smoothing method for the quantile-gradient estimation. Numerical investigation shows that the two approaches are competitive for certain problem instances.

Applied Probability↗
DOE OSTI2013

Synthesis of TiO{sub 2} core/RuO{sub 2} shell particles using multistep ultrasonic spray pyrolysis

Graphical abstract: - Highlights: • TiO{sub 2} core/RuO{sub 2} shell submicron-particles were prepared via a sequential spray pyrolysis. • Spherical particles have the mean particle diameters between 200 and 400 nm. • This method is promising for synthesis of core–shell and core–multishell materials. - Abstract: Spherical submicron-particles with TiO{sub 2} core–RuO{sub 2} shell structure have been synthesized by employing sequential ultrasonic spray pyrolysis. The particles have been investigated by X-ray powder diffraction, scanning electron microscopy and different transmission electron microscopy techniques. The quality of the core–shell structure of the particles has been confirmed by comparison of the experimental data with those generated on the basis of a hard sphere core–shell model. It has been found that the mixing of the Ru-containing aerosol with the TiO{sub 2} particle stream has a significant impact on the core–shell formation. The method introduced in this study can probably be applied for preparation of core–shell and core–multishell materials that are difficult to synthesize in a single step spray pyrolysis process.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Analysis of Solids Flow Rate through Nonmechanical L-Valve in an Industrial-Scale Circulating Fluidized Bed Using Group B Particles

A series of statistically designed experiments were conducted using two different Geldart Group B particles in a 0.3 m diameter circulating fluidized bed (CFB) cold model to evaluate the nonmechanical L-valve for controlling the solids flow rate. The objective of this study was to investigate the effects of standpipe aeration, L-valve aeration, solids inventory, and superficial gas velocity through the riser on the solids flow rate. A stochastic correlation was developed for calculating the solid flow rate as a function of these variables. It was found that the solid flow rate increased directly proportional to each of these variables. Dimensional analysis was used to generate an expression for the solids turnover ratio. The model developed in the present study is intended to simulate flow in the present CFB loop. In conclusion, it is not intended for scale-up and will probably not apply for alternative CFB loops with different geometries/pressure balance conditions.

42 ENGINEERING↗
DOE OSTI2014

Critique of information geometry

As applied to probability, information geometry fails because probability distributions do not form a metric space. Probability theory rests on a compelling foundation of elementary symmetries, which also support information (aka minus entropy, Kullback-Leibler) H(p;q) as the unique measure of divergence from source probability distribution q to destination p. Because the only compatible connective H is from≠to asymmetric, H(p;q)≠H(q;p), there can be no compatible geometrical distance (which would necessarily be from=to symmetric). Hence there is no distance relationship compatible with the structure of probability theory. Metrics g and densities sqrt(det(g)) interpreted as prior probabilities follow from the definition of distance, and must fail likewise. Various metrics and corresponding priors have been proposed, Fisher's being the most popular, but all must behave unacceptably. This is illustrated with simple counter-examples.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Observational diagnostics of self-gravitating MHD turbulence in giant molecular clouds

We study the observable signatures of self-gravitating magnetohydrodynamics (MHD) turbulence by applying the probability density functions (PDFs) and the spatial density power spectrum to synthetic column density maps. We find that there exists three characterizable stages of the evolution of the collapsing cloud which we term “early,” “intermediate,” and “advanced.” At early times, i.e., t<0.15t{sub ff}, the column density has a power spectral slope similar to nongravitating supersonic turbulence and a lognormal distribution. At an intermediate stage, i.e., 0.15t{sub ff} 0.35t{sub ff}, the power spectral slope is positive valued, and a dramatic increase is observed in the PDF moments and the Tsallis incremental PDF parameters, which gives rise to deviations between PDF-sonic Mach number relations. Finally, we show that the imprint of gravity on the density power spectrum can be replicated in non-gravitating turbulence by introducing a delta-function with amplitude equivalent to the maximum valued point in a given self-gravitating map. We find that the turbulence power spectrum restored through spatial filtering of the high density material.

79 ASTRONOMY AND ASTROPHYSICS↗