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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Constraining the magnitude of the carbon isotope excursion during the Paleocene-Eocene thermal maximum using larger benthic foraminifera

The Paleocene-Eocene thermal maximum (PETM) was an extraordinary pulse of global warming approximately 56 Ma. This warmingevent is associated with an addition of large amounts of 13C-depleted carbon into the atmosphere-ocean system, but the magnitude of the negative carbon isotope excursion (CIE)signaling the PETMand often used to estimate mass of the released carbonis still debated. Here we gauge the CIE magnitude usingsecondary ion mass spectrometry (SIMS) to perform in situ δ 13 C measurements within individual larger benthic foraminifera preserved in a tropical shallow marine limestone section in south Tibet. This SIMS-based δ 13 C record yields a negative CIE (Δ~7‰) comparable in magnitude to that registered by terrestrial records but larger than the ~4‰CIE returned by surface-dwelling planktonic foraminiferain deep-sea records. We therefore posit that the CIE magnitude was~7‰ in the surface ocean, and that theprevious~4‰ estimates for the CIE areattenuated by incomplete preservation and diagenetic overprinting. The large CIE magnitude in the surface ocean (~7‰) and the evidently smaller CIE magnitude registeredby deep-sea benthic foraminifera(~2-3.5‰) arelikely a function of rateand duration of carbon release as well as ocean stratification during the PETM.

58 GEOSCIENCES↗
DOE OSTI2019

Automated Vehicles in Hazardous Merging Traffic: A Chance-Constrained Approach

To realize the energy efficiency and productivity benefits of automated driving, control algorithms must function safely among conventional vehicles. Prototype tests on public roads have revealed a trend of human-driven vehicles rear-ending automated ones. A popular belief holds that unusually conservative control algorithms play a role in such collisions. In August 2018, an automated vehicle was rear-ended while waiting to merge. Inspired by that incident, this paper examines a resemblant scenario in simulation using model predictive control for the automated vehicle. Constraint setup alternatives to avoid collisions with inattentive following vehicles are proposed and assessed in this simulation environment. In one variant, imminent rear-end collisions are detected and constraints are modified to promote more aggressive merging during such an event. Results show that higher-performing chance constraint designs can reduce collision probability, but may have other adverse effects depending on the particular algorithm.

Dollar, R. Austin↗
DOE OSTI2019

Options for low-global-warming-potential and natural refrigerants part I: Constrains of the shape of the P–T and T–S saturation phase boundaries

Current research focus is migrating toward low-global-warming-potential (GWP) and natural refrigerants to address the human impact on climate change. In this paper, we examine 13 refrigerants from the perspective of the characteristic shape of their respective temperature–entropy (T–S) and the logarithm of the pressure versus inverse absolute temperature (log P vs. T –1 ) saturated phase boundary. Such analyses explain why certain refrigerants possess a re-entrant characteristic while others do not. The re-entrant region is due to skewness of the saturation boundary. The cause of skewness is investigated for its importance in heat pump performance, design, and configuration. Re-entrant behavior contributes to premature mechanical wear of compressor components. Knowledge of the properties of the phase boundary on either side of the critical point, is useful for a better perspective on discriminating refrigerants, as hydrochlorofluorocarbons are phased out and replacement refrigerants must be found. Here, we conclude by identifying a candidate low-GWP refrigerant for heat pumps. In Part II, we evaluate all 13 refrigerants in thermodynamic cycles based on exergy analysis to identify sources of irreversibility, the root cause of systemic inefficiency.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2017

Nation-Scale Adoption of Shorter Breast Radiation Therapy Schedules Can Increase Survival in Resource Constrained Economies: Results From a Markov Chain Analysis

Purpose: Hypofractionated whole breast irradiation and accelerated partial breast irradiation (APBI) offer women options for shorter courses of breast radiation therapy. The impact of these shorter schedules on the breast cancer populations of emerging economies with limited radiation therapy resources is unknown. We hypothesized that adoption of these schedules would improve throughput in the system and, by allowing more women access to life-saving treatments, improve patient survival within the system. Methods and Materials: We designed a Markov chain model to simulate the different health states that a postlumpectomy or postmastectomy patient could enter over the course of a 20-year follow-up period. Transition rates between health states were adapted from published data on recurrence rates. We used primary data from a tertiary care hospital in Lahore, Pakistan, to populate the model with proportional use of mastectomy versus breast conservation and to estimate the proportion of patients suitable for APBI. Sensitivity analyses on the use of APBI and relative efficacy of APBI were conducted to study the impact on the population. Results: The shorter schedule resulted in more women alive and more women remaining without evidence of disease (NED) compared with the conventional schedule, with an absolute difference of about 4% and 7% at 15 years, respectively. Among women who had lumpectomies, the chance of remaining alive and with an intact breast was 62% in the hypofractionation model and 54% in the conventional fractionation model. Conclusions: Increasing throughput in the system can result in improved survival, improved chances of remaining without evidence of disease, and improved chances of remaining alive with a breast. These findings are significant and suggest that adoption of hypofractionation in emerging economies is not simply a question of efficiency and cost but one of access to care and patient survivorship.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Robust constrained tension control for high-precision roll-to-roll processes

Tension control is critical for maintaining good product quality in most roll-to-roll (R2R) production systems. Previous work has primarily focused on improving the disturbance rejection performance of tension controllers. Here, a robust linear parameter-varying model predictive control (LPV-MPC) scheme is designed to enhance the tension tracking performance of a pilot R2R system for deposition of materials used in flexible thin film applications. The performance of a tension controller may degrade due to disturbances associated with model uncertainties and the slowly-changing dynamics in R2R systems. We introduce a method that separately treats these two sources of disturbance. The controller utilizes an incremental model to eliminate the errors caused by the mismatch between the nominal model and the actual system. A tube-based MPC formulation combined with scheduled parameters adequately updates models and corrects for the time-varying dynamics. Constraints on the rated motor torque are incorporated in the MPC to maintain the controller reliability and avoid machine failures. We illustrate the operation of our control algorithm through simulation of an actual R2R system. The controller outperforms the benchmarks in terms of fast transient response and offset-free tension tracking. Furthermore, it also demonstrates immunity from variations due to parametric uncertainties.

42 ENGINEERING↗
DOE OSTI2018

Constrained optimization framework for interface-aware sub-scale dynamics models for voids closure in Lagrangian hydrodynamics

In hydrocodes, voids are used to represent vacuum and model free boundaries between vacuum and real materials. We give a systematic description of a new treatment of void closure in the framework of the multimaterial arbitrary Lagrangian–Eulerian (ALE) methods. This includes a new formulation of the interface-aware sub-scale-dynamics (IA-SSD) closure model for multimaterial cells with voids, which is used in the Lagrangian stage of our indirect ALE scheme. The results of the comprehensive testing of the new model are presented for one- and two-dimensional multimaterial calculations in the presence of voids. Finally, we also present a sneak peek of a realistic shaped charge calculation in the presence of voids and solids.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Space-time discretizations using constrained first-order system least squares (CFOSLS)

This work studies finite element discretizations for three types of time-dependent PDEs, namely heat equation, scalar conservation law and wave equation, which we reformulate as first order systems in a least-squares setting, subject to a space-time conservation constraint (coming from the original PDE). Available piecewise polynomial finite element spaces in (n + 1)-dimensions for functional spaces from the (n + 1)-dimensional de Rham sequence for n = 2, 3 are used for the implementation of the method. Computational results illustrating the error behavior, iteration counts and performance of block-diagonal and monolithic geometric multigrid preconditioners are presented for the discrete CFOSLS system. The results are obtained from a parallel implementation of the methods for which we report reasonable scalability.

4D de Rham sequence↗
DOE OSTI2022

Physics constrained learning for data-driven inverse modeling from sparse observations

Deep neural networks (DNN) have been used to model nonlinear relations between physical quantities. Those DNNs are embedded in physical systems described by partial differential equations (PDE) and trained by minimizing a loss function that measures the discrepancy between predictions and observations in some chosen norm. This loss function often includes the PDE constraints as a penalty term when only sparse observations are available. As a result, the PDE is only satisfied approximately by the solution. However, the penalty term typically slows down the convergence of the optimizer for stiff problems. We present a new approach that trains the embedded DNNs while numerically satisfying the PDE constraints. We develop an algorithm that enables differentiating both explicit and implicit numerical solvers in reverse-mode automatic differentiation. This allows the gradients of the DNNs and the PDE solvers to be computed in a unified framework. We demonstrate that our approach enjoys faster convergence and better stability in relatively stiff problems compared to the penalty method. Furthermore, our approach allows for the potential to solve and accelerate a wide range of data-driven inverse modeling, where the physical constraints are described by PDEs and need to be satisfied accurately.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

On magnetic structure of CuFe 2 Ge 2 : Constrains from the 57 Fe Mössbauer spectroscopy

57 Fe Mössbauer spectroscopy measurements were performed on a powdered CuFe 2 Ge 2 sample that orders antiferromagnetically at ~175 K. Whereas a paramagnetic doublet was observed above the Néel temperature, a superposition of paramagnetic doublet and magnetic sextet (in approximately 0.5:0.5 ratio) was observed in the magnetically ordered state, suggesting a magnetic structure similar to a double-Q spin density wave with half of the Fe paramagnetic and another half bearing static moment of ~0.5–1μ B . Lastly, these results call for a re-evaluation of the recent neutron scattering data and band structure calculations, as well as for deeper examination of details of sample preparation techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Experimental methodology and theoretical framework in describing constrained plastic flow of FCC microscale tensile specimens

Small scale mechanical testing (SSMT) allows for the quantification of the mechanical responses for microscale and nanoscale material volumes. It has significant potential in improving our fundamental understanding of plastic deformation and in providing an engineering solution for testing complex and/or critical materials. Importantly, previous studies have revealed that plastic intermittency, manifested as strain bursts, are characteristic of the plastic flow behavior at the small length scale. In this work, interfacial constraint has been utilized to suppress strain bursts in order to stabilize plasticity. A new parameter, blocked volume ratio (BVR), is introduced to quantify the degree of constraint for a microscale specimen due to an interface. Here, we showed that the plastic flow behavior in FCC Ni-based metals is highly dependent on the BVR of the specimen.

36 MATERIALS SCIENCE↗