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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 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

SU-E-T-747: The Use of the EQD2 Formalism and Repair Estimates in the Re-Irradiation Setting and Correlation with Patient Follow-Up Data

Purpose: Medical advances have resulted in cancer patients living longer as evidenced by the number of patients seen for possible re-irradiation. Original normal tissue dose volume constraints remain in the re-irradiation setting to minimize normal tissue toxicity. This work correlates estimates of equivalent dose and repair with sequelae. Methods: CNS and GI tract re-irradiation patient follow-up records (including imaging studies) were reviewed with side effects correlated with the calculated EQD2 and repair estimates. Results: Follow-up records for 16 re-irradiation patients with potential overlap to the spinal cord were analyzed. The mean time interval between 1st and last courses was 76.6 months. Three patients underwent a 3rd course of radiotherapy with a mean time interval between 2nd and final courses of 19.7 months. The mean values for assumed repair were 18.8% and 8.3%, respectively. The calculated total EQD2 doses were 48.09Gy and 50.98Gy with and without repair. At a mean follow-up time of 5.0 months, 6 patients were deceased and no records indicate radiation related neurological deficits. The records for 11 patients with potential overlap to the bowel were also analyzed. The mean time interval between 1st and last courses was 105.9 months. The mean value for assumed repair was 15.9%. The calculated total EQD2 doses were 64.96Gy and 70.80Gy with and without repair. At a mean follow-up time of 4.9 months, 6 patients were deceased, one having a potential enteric fistulization of the bladder. Clinical review of the case determined that the fistula was caused by tumor progression and not a side effect of radiotherapy treatments. Conclusion: Application of the EQD2 method in the re-irradiation setting using conservative estimates of repair is presented. Adhering to accepted dose volume limits following this application is demonstrated to be safe through empirical records as limited by this small patient cohort and short follow-up.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Cherenkov Radiation Generated by an Electron Bunch in a Rectangular Dielectric Waveguide Filled with a Transversely Isotropic Medium

Dielectric waveguides are being intensively studied as accelerating structures excited by an electron bunch. Rectangular dielectric structures are used both to test the principles of new accelerating schemes and to study the electric properties of filling materials. Several dielectric materials used as fillers of waveguides have anisotropic properties (sapphire, ceramic films). Anisotropy can have a significant effect on the wakefields generated by an electron bunch in a structure. The paper presents an analytical calculation of Vavilov–Cherenkov radiation generated by a relativistic electron bunch in a rectangular waveguide filled with a transversely inhomogeneous transversely isotropic dielectric. A method for constructing an orthogonal basis of the transverse operator with its subsequent use to find the wakefield is presented. A dispersion relation for the structure and expressions for the wakefield created by a point electron bunch in a transversely isotropic rectangular dielectric structure are obtained. Based on the formalism presented, parameters of an accelerating structure based on sapphire, allowing the generation of fields above 100 MV/m, are calculated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1982

Dipole-field sums and Lorentz factors for orthorhombic lattices, and implications for polarizable molecules

A method for computing the Lorentz tensor components in single crystals via rapidly convergent sums of Bessels functions is developed using the relationship between dipole-field sums and the tensor components. The Lorentz factors for simple, body-centered, and base-centered orthorhombic lattices are computed using this method, and the derivative Lorentz factors for simple orthorhombic lattices are also determined. Both the Lorentz factors and their derivatives are shown to be very sensitive to a lattice structure. The equivalent of the Clausius-Mossotti relation for general orthorhombic lattices is derived using the Lorentz-factor formalism, and the permanent molecular dipole moment is related to crystal polarization for the case of a ferroelectric of polarizable point dipoles. It is concluded that the polarization enhancement due to self-polarization familiar from classical theory may actually be a reduction in consequences of negative Lorentz factors in one or two lattice directions for noncubic crystals.

Purvis, C. K.↗
NASA NTRS1990

Viscosity and mass transport in nonuniform Keplerian disks

A quantitative formalism for Keplerian particulate disk dynamics having its basis in a heuristic description of viscous transport is presently applied to the case of a ring with optical thickness radial gradient. A steady-state velocity distribution solution directly yields both the radial mass transport and the viscosity. The analytical method employed involves the solution of a novel form of the Krook equation through the separation of the phase-space collisional-products distribution into a symmetrical component and a delta function-approachable remainder. While this model is simplified for the case treated, its general approach may be extended to less artificially restricted cases.

Ojakangas, G. W.↗
NASA NTRS2004

Software for Fault-Tolerant Matrix Multiplication

Formal Linear Algebra Recovery Environment is a computer program for high-performance, fault-tolerant matrix multiplication. The program is based on an extension of the prior theory and practice of fault-tolerant matrix matrix multiplication of the form C = AB. This extension provides low-overhead methods for detecting errors, not only in C, but also in A and/or B. These methods enable the detection of all errors as long as, in a given case, only one entry in A, B, or C is corrupted. The program also provides for following a low-overhead rollback approach to correct errors once detected. Results of computational experiments have demonstrated that the methods implemented in this program work well in practice while imposing an acceptably low level of overhead, relative to high-performance matrix-multiplication methods that do not afford fault tolerance.

Katz, Daniel↗
NASA NTRS2015

Technology Alignment and Portfolio Prioritization (TAPP): Advanced Methods in Strategic Analysis, Technology Forecasting and Long Term Planning for Human Exploration and Operations, Advanced Exploration Systems and Advanced Concepts

The Advanced Concepts Office (ACO) at NASA, Marshall Space Flight Center is expanding its current technology assessment methodologies. ACO is developing a framework called TAPP that uses a variety of methods, such as association mining and rule learning from data mining, structure development using a Technological Innovation System (TIS), and social network modeling to measure structural relationships. The role of ACO is to 1) produce a broad spectrum of ideas and alternatives for a variety of NASA's missions, 2) determine mission architecture feasibility and appropriateness to NASA's strategic plans, and 3) define a project in enough detail to establish an initial baseline capable of meeting mission objectives ACO's role supports the decision­-making process associated with the maturation of concepts for traveling through, living in, and understanding space. ACO performs concept studies and technology assessments to determine the degree of alignment between mission objectives and new technologies. The first step in technology assessment is to identify the current technology maturity in terms of a technology readiness level (TRL). The second step is to determine the difficulty associated with advancing a technology from one state to the next state. NASA has used TRLs since 1970 and ACO formalized them in 1995. The DoD, ESA, Oil & Gas, and DoE have adopted TRLs as a means to assess technology maturity. However, "with the emergence of more complex systems and system of systems, it has been increasingly recognized that TRL assessments have limitations, especially when considering [the] integration of complex systems." When performing the second step in a technology assessment, NASA requires that an Advancement Degree of Difficulty (AD2) method be utilized. NASA has used and developed or used a variety of methods to perform this step: Expert Opinion or Delphi Approach, Value Engineering or Value Stream, Analytical Hierarchy Process (AHP), Technique for the Order of Prioritization by Similarity to Ideal Solution (TOPSIS), and other multi­‐criteria decision-making methods. These methods can be labor-intensive, often contain cognitive or parochial bias, and do not consider the competing prioritization between mission architectures. Strategic Decision-Making (SDM) processes cannot be properly understood unless the context of the technology is understood. This makes assessing technological change particularly challenging due to the relationships "between incumbent technology and the incumbent (innovation) system in relation to the emerging technology and the emerging innovation system." The central idea in technology dynamics is to consider all activities that contribute to the development, diffusion, and use of innovations as system functions. Bergek defines system functions within a TIS to address what is actually happening and has a direct influence on the ultimate performance of the system and technology development. ACO uses similar metrics and is expanding these metrics to account for the structure and context of the technology. At NASA technology and strategy is strongly interrelated. NASA's Strategic Space Technology Investment Plan (SSTIP) prioritizes those technologies essential to the pursuit of NASA's missions and national interests. The SSTIP is strongly coupled with NASA's Technology Roadmaps to provide investment guidance during the next four years, within a twenty-year horizon. This paper discusses the methods ACO is currently developing to better perform technology assessments while taking into consideration Strategic Alignment, Technology Forecasting, and Long Term Planning.

Funaro, Gregory V.↗
DOE OSTI2020

Boundary-consistent B-spline filtering schemes and application to high-fidelity simulations of turbulence

A filtering operation, based on B-spline discretizations, is introduced to target weakly growing mesh-scale oscillations that can arise in high-fidelity turbulence simulations. This is a spectral regularization that can be described using the singular values of a banded matrix operator, with the filtering strength set by a scalar- or vector-valued penalty parameter. The penalty parameter can be specified though it can also be advantageously selected to minimize the generalized cross validation (GCV) measure of distance between the pre- and post-filtered solutions. Efficient algorithms are developed to compute both the scalar and vector penalty parameters. The B-spline filter has a sharper localization to high-wavenumber than compact or explicit filters of the same stencil width and is demonstrated for solutions of the Burgers' equation, decaying Burgers' turbulence, and compressible Navier–Stokes turbulent channel flow. Furthermore, these simulations confirm the scheme's numerical stability and ability to narrowly target the high wavenumber components of numerical solutions. An advantage over finite-difference filters is that these B-spline filters are stable on bounded domains and even preserve formal order of accuracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Shadow Distillation: Quantum Error Mitigation with Classical Shadows for Near-Term Quantum Processors

Mitigating errors in quantum information processing devices is especially important in the absence of fault tolerance. An effective method in suppressing state-preparation errors is using multiple copies to distill the ideal component from a noisy quantum state. Here, we use classical shadows and randomized measurements to circumvent the need for coherent access to multiple copies at an exponential cost. We study the scaling of resources using numerical simulations and find that the overhead is still favorable compared to full state tomography. We optimize measurement resources under realistic experimental constraints and apply our method to an experiment preparing a Greenberger-Horne-Zeilinger state with trapped ions. In addition to improving stabilizer measurements, the analysis of the improved results reveals the nature of errors affecting the experiment. Hence, our results provide a directly applicable method for mitigating errors in near-term quantum computers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1992

Renormalization group methods for the Reynolds stress transport equations

The Yakhot-Orszag renormalization group is used to analyze the pressure gradient-velocity correlation and return to isotropy terms in the Reynolds stress transport equations. The perturbation series for the relevant correlations, evaluated to lowest order in the epsilon-expansion of the Yakhot-Orszag theory, are infinite series in tensor product powers of the mean velocity gradient and its transpose. Formal lowest order Pade approximations to the sums of these series produce a rapid pressure strain model of the form proposed by Launder, Reece, and Rodi, and a return to isotropy model of the form proposed by Rotta. In both cases, the model constants are computed theoretically. The predicted Reynolds stress ratios in simple shear flows are evaluated and compared with experimental data. The possibility is discussed of deriving higher order nonlinear models by approximating the sums more accurately. The Yakhot-Orszag renormalization group provides a systematic procedure for deriving turbulence models. Typical applications have included theoretical derivation of the universal constants of isotropic turbulence theory, such as the Kolmogorov constant, and derivation of two equation models, again with theoretically computed constants and low Reynolds number forms of the equations. Recent work has applied this formalism to Reynolds stress modeling, previously in the form of a nonlinear eddy viscosity representation of the Reynolds stresses, which can be used to model the simplest normal stress effects. The present work attempts to apply the Yakhot-Orszag formalism to Reynolds stress transport modeling.

Rubinstein, R.↗
DOE OSTI2024

tLaSDI: Thermodynamics-informed latent space dynamics identification

Here we propose a latent space dynamics identification method, namely tLaSDI, that embeds the first and second principles of thermodynamics. The latent variables are learned through an autoencoder as a nonlinear dimension reduction model. The latent dynamics are constructed by a neural network-based model that precisely preserves certain structures for the thermodynamic laws through the GENERIC formalism. An abstract error estimate is established, which provides a new loss formulation involving the Jacobian computation of autoencoder. The autoencoder and the latent dynamics are simultaneously trained to minimize the new loss. Computational examples demonstrate the effectiveness of tLaSDI, which exhibits robust generalization ability, even in extrapolation. In addition, an intriguing correlation is empirically observed between a quantity from tLaSDI in the latent space and the behaviors of the full-state solution.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Utilization of MCNP ® 6 implicit-capture simulations for quantification of systematic uncertainties from experimental environments

In this study, the high statistical precision that can be achieved using modern data collection techniques implies that systematic uncertainties that were ignored or not considered for past experiments must now be explored. The folding of Monte Carlo simulations into experimental data analysis, which is becoming common practice, requires an estimate of the systematic uncertainty present in the experimental result from uncertainties in the library of cross sections used during the simulation, but this source of uncertainty is typically not quantified. Here we describe a method to estimate this systematic uncertainty by varying the cross sections used during simulation runtime. As opposed carrying out hundreds of sequential analog Monte Carlo simulations, this task was accomplished through a post-processing calculation of output from a single simulation that was run using the implicit-capture formalism available with MCNP ® 6.2 and the PTRAC output format.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Stabilization of [(N 5 ) 2 BX] 2– and [(N 5 ) 2 B 2 X 2 ] 2– (X = H, F, Cl, Br) by Conjugation and Hyperconjugation Effects

The isolation of nucleophilic boron bases has led to a paradigm shift in boron chemistry. Previous studies of the bis(carbene) borylene complexes revealed that these compounds possess strong donor abilities, and their reaction inertness is due to the large steric hindrance between boron reagents and reactant. In the present study, we have theoretically studied the [(N 5 ) 2 BX] 2– and [(N 5 ) 2 B 2 X 2 ] 2– compounds (X = H, F, Cl, Br). Their electronic structures and properties are discussed by using the NBO, LOL, and ELF methods. We found that both π-conjugation and hyperconjugation effects can effectively stabilize the substituted nucleophilic anionic boron compounds [(N 5 ) 2 BX] 2– and [(N 5 ) 2 B 2 X 2 ] 2– . Substituents, especially X = H, stabilize the boron center through highly delocalized π-bonding, involving the formally “empty” in-plane p orbitals of the boron atom. While the halogen substituents have high electron withdrawal ability, leading to systems being less stable, we suggest the borinium anions [(N 5 ) 2 BH] 2– and [(N 5 ) 2 B 2 H 2 ] 2– as possible synthetic targets of novel environmentally friendly catalysts.

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

Partially polaron-transformed quantum master equation for exciton and charge transport dynamics

Polaron-transformed quantum master equation (PQME) offers a unified framework to describe the dynamics of quantum systems in both limits of weak and strong couplings to environmental degrees of freedom. Thus, the PQME serves as an efficient method to describe charge and exciton transfer/transport dynamics for a broad range of parameters in condensed or complex environments. However, in some cases, the polaron transformation (PT) being employed in the formulation invokes an over-relaxation of slow modes and results in premature suppression of important coherence terms. A formal framework to address this issue is developed in the present work by employing a partial PT that has smaller weights for low frequency bath modes. In this work, it is shown that a closed form expression of a second order time-local PQME including all the inhomogeneous terms can be derived for a general form of partial PT, although more complicated than that for the full PT. All the expressions needed for numerical calculation are derived in detail. Applications to a model of a two-level system coupled to a bath of harmonic oscillators, with test calculations focused on those due to homogeneous relaxation terms, demonstrate the feasibility and the utility of the present approach.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Photoluminescence line shapes of nanocrystals: Contributions from first- and second-order vibronic couplings

Here, we present a microscopic, parameter-free approach for computing the photoluminescence spectra of a single semiconductor nanocrystal. The method derives exciton–phonon coupling directly from the semi-empirical pseudopotential framework and systematically incorporates both diagonal and off-diagonal exciton-phonon interactions, expanded to second-order in the phonon coordinates. The dipole–dipole correlation function was calculated using a Dyson expansion within the Kubo–Toyozawa formalism, enabling a consistent description of the role of pure dephasing and population transfer on the photoluminescence spectral features. Applied to CdSe/CdS core–shell nanocrystals, the approach quantitatively reproduces experimental photoluminescence spectra over a wide temperature range, revealing that quadratic phonon couplings account for nearly half of the homogeneous linewidth above ≈ 100−150 K, while off-diagonal couplings leading to exciton thermalization play only a minor role and only as T → 300 K.

Dephasing Rate↗
DOE OSTI2025

A Parallel Alternative for Energy-Efficient Neural Network Training and Inferencing

Energy efficiency of training and inferencing with large neural network models is a critical challenge facing the future of sustainable large-scale machine learning workloads. This paper introduces an alternative strategy, called phantom parallelism, to minimize the net energy consumption of traditional tensor (model) parallelism, the most energy-inefficient component of large neural network training. The approach is presented in the context of feed-forward network architectures as a preliminary, but comprehensive, proof-of-principle study of the proposed methodology. We derive new forward and backward propagation operators for phantom parallelism, implement them as custom autograd operations within an end-to-end phantom parallel training pipeline and compare its parallel performance and energy-efficiency against those of conventional tensor parallel training pipelines. Formal analyses that predict lower bandwidth and FLOP counts are presented with supporting empirical results on up to 256 GPUs that corroborate these gains. Experiments are shown to deliver ∼50% reduction in the energy consumed to train FFNs using the proposed phantom parallel approach when compared with conventional tensor parallel methods. Additionally, the proposed approach is shown to train smaller phantom models to the same model loss on smaller GPU counts as larger tensor parallel models on larger GPU counts offering the possibility for even greater energy savings.

Seal, Sudip [ORNL] (ORCID:0000000332330656)↗
DOE OSTI2015

SU-E-T-364: Estimating the Minimum Number of Patients Required to Estimate the Required Planning Target Volume Margins for Prostate Glands

Purpose: To establish a minimum number of patients required to obtain statistically accurate Planning Target Volume (PTV) margins for prostate Intensity Modulated Radiation Therapy (IMRT). Methods: A total of 320 prostate patients, consisting of a total number of 9311 daily setups, were analyzed. These patients had gone under IMRT treatments. Daily localization was done using the skin marks and the proper shifts were determined by the CBCT to match the prostate gland. The Van Herk formalism is used to obtain the margins using the systematic and random setup variations. The total patient population was divided into different grouping sizes varying from 1 group of 320 patients to 64 groups of 5 patients. Each grouping was used to determine the average PTV margin and its associated standard deviation. Results: Analyzing all 320 patients lead to an average Superior-Inferior margin of 1.15 cm. The grouping with 10 patients per group (32 groups) resulted to an average PTV margin between 0.6–1.7 cm with the mean value of 1.09 cm and a standard deviation (STD) of 0.30 cm. As the number of patients in groups increases the mean value of average margin between groups tends to converge to the true average PTV of 1.15 cm and STD decreases. For groups of 20, 64, and 160 patients a Superior-Inferior margin of 1.12, 1.14, and 1.16 cm with STD of 0.22, 0.11, and 0.01 cm were found, respectively. Similar tendency was observed for Left-Right and Anterior-Posterior margins. Conclusion: The estimation of the required margin for PTV strongly depends on the number of patients studied. According to this study at least ∼60 patients are needed to calculate a statistically acceptable PTV margin for a criterion of STD < 0.1 cm. Numbers greater than ∼60 patients do little to increase the accuracy of the PTV margin estimation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Thermodynamics-informed latent space dynamics identification

This software showcases a latent space dynamics identification method, namely tLaSDI, that embeds the first and second principles of thermodynamics. The latent variables are learned through an autoencoder as a nonlinear dimension reduction model. The latent dynamics are constructed by a neural network-based model that precisely preserves certain structures for the thermodynamic laws through the GENERIC formalism. An abstract error estimate is established, which provides a new loss formulation involving the Jacobian computation of autoencoder. The autoencoder and the latent dynamics are simultaneously trained to minimize the new loss. Computational examples demonstrate the effectiveness of tLaSDI, which exhibits robust generalization ability, even in extrapolation. In addition, an intriguing correlation is empirically observed between a quantity from tLaSDI in the latent space and the behaviors of the full-state solution.

Cheung, Siu Wun↗
NASA NTRS1986

Heat and mass transfer in flames

Heat- and mass-transfer processes in turbulent diffusion flames are discussed, considering turbulent mixing and the structure of single-phase flames, drop processes in spray flames, and nonluminous and luminous flame radiation. Interactions between turbulence and other phenomena are emphasized, concentrating on past work of the author and his associates. The conserved-scalar formalism, along with the laminar-flamelet approximation, is shown to provide reasonable estimates of the structure of gas flames, with modest levels of empiricism. Extending this approach to spray flames has highlighted the importance of drop/turbulence interactions; e.g., turbulent dispersion of drops, modification of turbulence by drops, etc. Stochastic methods being developed to treat these phenomena are yielding encouraging results.

Faeth, G. M.↗