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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Case studies of the time-dependent potential energy surface for dynamics in cavities

Here, the exact time-dependent potential energy surface driving the nuclear dynamics was recently shown to be a useful tool to understand and interpret the coupling of nuclei, electrons, and photons in cavity settings. Here, we provide a detailed analysis of its structure for exactly solvable systems that model two phenomena: cavity-induced suppression of proton-coupled electron-transfer and its dependence on the initial state, and cavity-induced electronic excitation. We demonstrate the inadequacy of simply using a weighted average of polaritonic surfaces to determine the dynamics. Such a weighted average misses a crucial term that redistributes energy between the nuclear and the polaritonic systems, and this term can in fact become a predominant term in determining the nuclear dynamics when several polaritonic surfaces are involved. Evolving an ensemble of classical trajectories on the exact potential energy surface reproduces the nuclear wavepacket quite accurately, while evolving on the weighted polaritonic surface fails after a short period of time. The implications and prospects for application of mixed quantum-classical methods based on this surface are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1990

Stress versus temperature dependent activation energies in creep

The activation energy for creep at low stresses and elevated temperatures is lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from that of dislocation climb to one of obstacle-controlled dislocation glide. Along with this change, there occurs a change in the activation energy. It is shown that a temperature-dependent Gibbs free energy does a good job of correlating steady-state creep data, while a stress-dependent Gibbs free energy does a less desirable job of correlating the same data. Applications are made to copper and a LiF-22 mol. percent CaF2 hypereutectic salt.

Freed, A. D.↗
DOE OSTI2024

Assessment of the polygeneration approach in wastewater treatment plants for enhanced energy efficiency and green hydrogen/ammonia production

Wastewater treatment plants (WWTPs) offer opportunities to optimize resource utilization and enhance energy efficiency. Here, this study provides a comprehensive analysis of using the polygeneration approach in WWTPs to reduce grid energy dependence, optimize energy distribution, and utilize surplus energy for hydrogen (H 2 ) and ammonia (NH 3 ) production. Several models were employed, including photovoltaic (PV) cells, parabolic trough collectors (PTCs), steam methane reforming, and polymer electrolyte membranes, to assess the feasibility of this approach. Three scenarios were evaluated and compared: Scenario 1 (Baseline) represents the current situation, Scenario 2 maximizes the Net Present Value (NPV), and Scenario 3 minimizes NH 3 production costs. Real data from As-Samra WWTP in Jordan was used to accurately assess the feasibility of each scenario. The results show that Scenario 2 offers the highest profitability and efficiency, with a NPV of 87.48 million USD and an annual NH 3 production of 15,417 tons, reducing both grid dependency and biogas fuel consumption. Both Scenarios 2 and 3 demonstrate the ability to meet thermal demands efficiently while generating significant revenue from NH 3 production. Scenario 3, in particular, achieves competitive H 2 and NH 3 production costs. Environmentally, Scenario 2 significantly reduces annual greenhouse gas emissions by 12.66 kilotons of CO 2eq , with near-zero carbon intensity for thermal energy due to solar reliance. In conclusion, the polygeneration approach offers a promising pathway for WWTPs to achieve greater sustainability, economic gains, and reduced environmental impact, providing valuable insights for decision-makers.

42 ENGINEERING↗
DOE OSTI2022

Evidence of Mass Ordering of Charm and Bottom Quark Energy Loss in Au+Au Collisions at RHIC

Abstract Partons traversing the strongly interacting medium produced in heavy-ion collisions are expected to lose energy depending on their color charge and mass. We measure the nuclear modification factors for charm- and bottom-decay electrons, defined as the ratio of yields, divided by the number of binary nucleon–nucleon collisions, in $$\sqrt{s_{\textrm{NN}}}=200$$ s NN = 200 GeV Au+Au collisions to p + p collisions ( $$R_{\textrm{AA}}$$ R AA ), or in central to peripheral Au+Au collisions ( $$R_{\textrm{CP}}$$ R CP ). We find the bottom-decay electron $$R_{\textrm{AA}}$$ R AA and $$R_{\textrm{CP}}$$ R CP to be significantly higher than those of charm-decay electrons. Model calculations including mass-dependent parton energy loss in a strongly coupled medium are consistent with the measured data. These observations provide evidence of mass ordering of charm and bottom quark energy loss when traversing through the strongly coupled medium created in heavy-ion collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1979

The search for, and study of black holes in the galaxy

The study of the short-term (less than 10 s) time variability of Cygnus X-1 is reviewed, with attention given to measurements of the autocorrelation function and of the cross-correlation between different energy bandwidths, as well as to a simple shot noise model for describing all such short-term variations. Observational questions with regard to Cygnus X-1 are discussed, relating to the average shape of the randomly occurring flares, energy dependence in the cross-correlation and the dependence on energy of the X-ray polarization. Concerning the study of the Cyg X-1-like aperiodic X-ray sources, an estimate is made of what can be accomplished at the limits of sensitivity where Poisson fluctuations are at least as important as the intrinsic variability of the source, considering the third moment due to the source fluctuations.

Weisskopf, M. C.↗
NASA NTRS1982

Gamma-ray and optical observations of the 1979 November 8 solar flare

The solar flare on 1979 November 8 11h 21m 28s UT was observed by the Tel Aviv telescope of the Big Bear Solar Observatory and the High Resolution Gamma-Ray Spectrometer on the High Energy Astronomy Observatory HEAO 3. Photographs in alpha hydrogen show the development of the flare and a subsequent Moreton wave. Although the flare was not detected with the high spectral resolution germanium detectors, the HEAO C-1 CsI shield detected a statistically significant signal above 80 keV, from 420 to 585 keV, and above 3.8 MeV. The temporal structure of microwave, optical, X-ray, and gamma-ray emission is consistent to within about 1 s with a simultaneous flare response at all energies. There is no evidence for either second-stage acceleration of charged particles (Bai and Ramaty, 1979) or a delay between gamma-ray and X-ray continuum emission due to energy-dependent electron energy loss times (Bai and Ramaty).

Riegler, G. R.↗
NASA NTRS1999

The Near-Earth Asteroid Rendezvous (NEAR) Mission, the Mars Surveyor 2001 (MS01) Mission, and the Planetary Instrument Definition and Development Program (PIDDP)

The NEAR Mission was launched on February 17, 1996 for a three year cruise to the asteroid 433 Eros. During October, November, and December 1998 cruise measurements with the gamma-ray spectrometer were made at three different escape-window-width settings. These were done in order to understand how the count rate and peak width change as the window width settings change. Analysis of these spectra was completed using the latest version of the spectral analysis program, RobWin. Results as a function of energy were combined with the results from the Schlumberger-Doll Research experiments (described below). Laboratory measurements were needed to confirm efficiency calculations above 6 MeV and to understand the relationship between the full energy peak areas and the areas of the first and second escape peaks as a function of the escape peak widths. A week of measurements was made at Schlumberger-Doll Research using their 14-MeV pulsed neutron generator and large soil samples. Data were collected after adding iron and nickel to the sample to increase the emission of high-energy lines. Approximately 24 hours of data were accumulated at each of three escape peak window widths. These data were analyzed with RobWin. Combining results from the cruise measurements and the laboratory measurements indicated that both data sets had similar energy dependence and that this energy dependence was different from that obtained using standard Monte Carlo calculations. Alternate methods of simulating the response of the detector to changes in the escape window widths are being investigated.

Source record↗
NASA NTRS2005

Evolution of the Electron Yield Curves of Insulators as a Function of Impinging Electron Fluence and Energy

Electron emission and concomitant change accumulation near the surface of insulators in central to understanding spacecraft charging. We present a study of changes in electron emission yields as a result of internal charge build up due to electron dose. Evolution of total, backscattered and secondary yield results over a broad range of incident energies are presented for two representative insulators, Kapton(trademark) and Al2O3. Reliable yield curves for uncharged insulators are measured and quantifiable changes in yield are observed due to < 100 fC/sq mm fluences. We find excellent agreement with a phenomenological argument based on insulator charging predicted by the yield curve; this includes a decrease in the rate of change of the yield as incident energies approach the crossover energies and as accumulated internal charge reduces the landing energy to asymptotically approach a steady state surface charge and unity yield. We also find that the exponential decay of yield curves with fluence exhibit an energy dependent decay constant, alpha(E). Finally, we discuss physics based models for this energy dependence. To understand fluence and energy dependence of these charging processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators.

Sim, Alec↗
NASA NTRS1987

Cosmic-ray propagation in the Galaxy and in the heliosphere - The path-length distribution at low energy

The energy dependence of the path-length distribution of cosmic rays at low energies, below relativistic velocities, is studied, and its implications for models of cosmic-ray confinement and propagation in the Galaxy and Galactic halo, including the effects of a possible Galactic wind, are studied. It is found that the mean free path in Galactic propagation must be fully energy-dependent, with the mean of an exponential path-length distribution increasing with increasing energy below 1 GeV per nucleon and decreasing with increasing energy above 1 GeV per nucleon. This indicates that, at low energies, diffusion is not the controlling process. The path-length distribution is not purely exponential but is depleted in short path lengths at low energies. This depletion is energy-dependent, being largest at low energies and decreasing with increasing energy.

Garcia-Munoz, M.↗
DOE OSTI2024

Gray two-moment neutrino transport: Comprehensive tests and improvements for supernova simulations

Aims. In this work we extended an energy-integrated neutrino transport method to facilitate efficient, yet precise, modeling of compact astrophysical objects. We particularly focus on core-collapse supernovae. Methods. We implemented a gray neutrino-transport framework from the literature into FLASH and performed a detailed evaluation of its accuracy in core-collapse supernova simulations. Based on comparisons with results from simulations using energy-dependent neutrino transport, we incorporated several improvements to the original scheme. Results. Our analysis shows that our gray neutrino transport method successfully reproduces key aspects from more complex energy-dependent transport across a variety of progenitors and equations of state. We find both qualitative and reasonable quantitative agreement with multi-group M1 transport simulations. However, the gray scheme tends to slightly favor shock revival. In terms of gravitational wave and neutrino signals, there is a good alignment with the energy-dependent transport, although we find 15–30% discrepancies in the average energy and luminosity of heavy-lepton neutrinos. Simulations using the gray transport are around four times faster than those using energy-dependent transport.

Astronomy & Astrophysics↗
DOE OSTI2024

Evaluation of neutron dosimetry capabilities with the MC-15 portable multiplicity counter

This work proposes a preliminary neutron dose rate estimation method for a neutron multiplicity detector through measurement- and simulation-based analyses. Uncharacterized neutron-emitting sources may be encountered in situations such as nuclear emergency response, safeguards, and treaty verification. These circumstances may present irradiation risk to personnel conducting field assay, search, and characterization measurements. It is therefore of interest to provide a field neutron dosimetry capability with the existing neutron multiplicity counting (NMC) capabilities. To date, no commercially-available neutron detection systems are capable of both accurate NMC and real-time neutron dosimetry. This work will focus on estimating dose rate using input from a single fielded NMC called the MC-15. The energy-dependent neutron detection efficiency response of the MC-15 was quantified in monoenergetic neutron simulations and evaluated in response to two neutron-emitting sources and to a polyethylene-moderated source. The results were compared to existing neutron dosimeters and established the proof of concept for further investigation of the MC-15 for dose estimation. Measurement results were also replicated in simulations; additional simulations were then conducted to expand upon the limited empirical data. The initial empirical results provided a conversion factor appropriate for use when measuring 252 Cf neutrons that is independent of polyethylene shielding presence and thickness. The simulated data sets were then used to evaluate a fit equation allowing estimation of the neutron dose rate for less restricted geometric configurations and dependent only on the distance between the source and the detector. Additionally, the energy dependence of the efficiency response indicates that further empirical evaluations could provide energy-dependent conversion factors for broader neutron dosimetry capabilities with a wider range of neutron-emitting sources.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Delving into the depths of NGC 3783 with XRISM II. Cross-calibration of X-ray instruments used in the large, multi-mission observational campaign

Context. Accurate X-ray spectroscopic measurements are fundamental for deriving basic physical parameters of the most abundant baryon components in the Universe. The plethora of X-ray observatories currently operational enables a panchromatic view of the high-energy emission of celestial sources. However, uncertainties in the energy-dependent calibration of the instrument transfer functions (e.g. the effective area, energy redistribution, or gain) can limit - and historically, did limit - the accuracy of X-ray spectroscopic measurements. Aims. We revised the status of the cross-calibration among the scientific payload on board four operation missions: Chandra, NuSTAR, XMM-Newton, and the recently launched XRISM. XRISM carries the micro-calorimeter Resolve, which yields the best energy resolution at energies ≥2 keV. For this purpose, we used the data from a 10-day-long observational campaign targeting the nearby active galactic nucleus NGC 3783, carried out in July 2024. Methods. We present a novel model-independent method for assessing the cross-calibration status that is based on a multi-node spline of the spectra with the highest-resolving power (XRISM/Resolve in our campaign). We also estimated the impact of the intrinsic variability of NGC 3783 on the cross-calibration status due to the different time coverages of participating observatories and performed an empirical reassessment of the Resolve throughput at low energies. Results. Based on this analysis, we derived a set of energy-dependent correction factors of the observed responses, enabling a statistically robust analysis of the whole spectral dataset. They will be employed in subsequent papers describing the astrophysical results of the campaign. Aims. We revised the status of the cross-calibration among the scientific payload on board four operation missions: Chandra, NuSTAR, XMM-Newton, and the recently launched XRISM. XRISM carries the micro-calorimeter Resolve, which yields the best energy resolution at energies ≥2 keV. For this purpose, we used the data from a 10-day-long observational campaign targeting the nearby active galactic nucleus NGC 3783, carried out in July 2024. Methods. We present a novel model-independent method for assessing the cross-calibration status that is based on a multi-node spline of the spectra with the highest-resolving power (XRISM/Resolve in our campaign). We also estimated the impact of the intrinsic variability of NGC 3783 on the cross-calibration status due to the different time coverages of participating observatories and performed an empirical reassessment of the Resolve throughput at low energies. Results. Based on this analysis, we derived a set of energy-dependent correction factors of the observed responses, enabling a statistically robust analysis of the whole spectral dataset. They will be employed in subsequent papers describing the astrophysical results of the campaign.

Active Galactic Nuclei, individual: NGC 3783↗
DOE OSTI2020

Toward monochromated sub-nanometer UEM and femtosecond UED

A preliminary design of a mega-electron-volt (MeV) monochromator with 10 –5 energy spread for ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) is presented. Such a narrow energy spread is advantageous in both the single shot mode, where the momentum resolution in diffraction is improved, and the accumulation mode, where shot-to-shot energy jitter is reduced. In the single-shot mode, we numerically optimized the monochromator efficiency up to 13% achieving 1.3 million electrons per pulse. In the accumulation mode, to mitigate the efficiency degradation caused by the shot-to-shot energy jitter, an optimized gun phase yields only a mild reduction of the single-shot efficiency, therefore the number of accumulated electrons nearly proportional to the repetition rate. Inspired by the recent work of Qi et al. (Phys Rev Lett 124:134803, 2020), a novel concept of applying reverse bending magnets to adjust the energy-dependent path length difference has been successfully realized in designing a MeV monochromator to achieve the minimum energy-dependent path length difference between cathode and sample. Thanks to the achromat design, the pulse length of the electron bunches and the energy-dependent timing jitter can be greatly reduced to the 10 fs level. The introduction of such a monochromator provides a major step forward, towards constructing a UEM with sub-nm resolution and a UED with ten-femtosecond temporal resolution. The one-to-one mapping between the electron beam parameter and the diffraction peak broadening enables a real-time nondestructive diagnosis of the beam energy spread and divergence. The tunable electric–magnetic monochromator allows the scanning of the electron beam energy with a 10 –5 precision, enabling online energy matching for the UEM, on-momentum flux maximizing for the UED and real-time energy measuring for energy-loss spectroscopy. A combination of the monochromator and a downstream chicane enables “two-color” double pulses with femtosecond duration and the tunable delay in the range of 10 to 160 fs, which can potentially provide an unprecedented femtosecond time resolution for time resolved UED.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Extension of the discrete generalized multigroup method using SPH factors

The discrete generalized multigroup (DGM) method provides a way to treat the energy dependence of neutron transport similarly to the standard multigroup approximation. However, DGM uses an orthogonal basis to retain the energy dependence in higher-order terms. Using correction factors similar to traditional Superhomogénéisation (SPH) factors, the DGM method may be extended to produce cross sections that are homogenized over both space and energy. Additionally, since some fine-group energy dependence is retained, the resulting homogenized cross sections are more problem-independent than cross sections homogenized by SPH factors alone. In particular, a 44-group set of cross sections is collapsed to approximately a 1% error in the pincell fission densities for a test problem using three DOF per coarse energy group.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1998

Cosmic Ray Energy Determination by the Reduced-Opening Angle Method

Accurate measurement of the primary galactic cosmic ray species energy dependence in the regime beyond approx. 500 GeV/a is difficult due to the low flux and the limitations of energy measurement techniques. However, such observations are essential to resolve several questions of current interest such as: Is the enrichment of heavy species (Z greater that or equal to 6) cosmic rays first reported at higher energies by the proton satellite' and then later at lower energies real? The results from a previous deployment of the reduced opening angle technique are inconclusive but the authors do point to limitations in the previous techniques. Another intriguing puzzle is the energy dependence of silicon cosmic rays. Two independent experiments using different experimental techniques indicate that silicon is under-abundant. At present the observation is limited by statistics; it could still be a three sigma fluctuation. However, if confirmed the current models of acceleration and propagation which are species independent are seriously inadequate. To progress further the species and energy dependence must be accurately measured in a manner that is free from systematic uncertainty. In this report we show that the reduced opening angle method offers a simple and relatively inexpensive method to answer these questions. First we present the physics of the reduced opening angle and indicate the expected energy and charge resolution. The proposed detector design is then presented followed by the expected performance. Where ever possible simple phenomenological expressions that allow 'back of the envelope' estimates are given. More details are presented in the appendices. The limit of the energy resolution and the expected event rates for iron cosmic rays are calculated. Salient points are summarized in the conclusions.

Smith, Arthur E.↗
NASA NTRS1976

Secondary cosmic-ray electrons and positrons from 1 to 100 GeV in the upper atmosphere and interstellar space, and interpretation of a recent positron flux measurement

Secondary electron and positron fluxes generated in interstellar space and in the atmosphere from the decays of pions and kaons in inelastic nuclear interactions are calculated by Monte Carlo techniques for lepton energies in the range from 1 to 100 GeV and an assumed thickness of 10 g/sq cm or less for the interstellar or atmospheric material. A simple and accurate analytical model which summarizes the Monte Carlo results and identifies the essential parameters involved is developed and used to interpret a previous positron measurement. It is found that the thickness of interstellar and source material is about 4.3 g/sq cm for cosmic-ray positrons with energies exceeding 4 GeV, a result that is difficult to reconcile with recently proposed two-containment-volume propagation models which predict a thickness of 1.8 g/sq cm for the same energies on the basis of the energy dependence of the measured (Li+Be+B)/(C+O) ratio. It is shown that single-containment-volume (galactic) models invoking an energy-dependent leakage lifetime are compatible with the positron data, but lack a mechanism to explain the energy dependence.

Orth, C. D.↗
NASA NTRS2012

On the Nature of QPO Phase Lags in Black Hole Candidates

Observations of quasi-periodic oscillations (QPOs) in X-ray binaries hold a key to understanding many aspects of these enigmatic systems. Complex appearance of the Fourier phase lags related to QPOs is one of the most puzzling observational effects in accreting black holes. In this Letter we show that QPO properties, including phase lags, can be explained in a framework of a simple scenario, where the oscillating media provides a feedback on the emerging spectrum. We demonstrate that the QPO waveform is presented by the product of a perturbation and a time delayed response factors, where the response is energy dependent. The essential property of this effect is its non-linear and multiplicative nature. Our multiplicative reverberation model successfully describes the QPO components in energy dependent power spectra as well as the appearance of the phase lags between signal in different energy bands. We apply our model to QPOs observed by Rossi X-ray Timing Explorer in BH candidate XTE J1550-564. We briefly discuss the implications of the observed energy dependence of the QPO reverberation times and amplitudes to the nature of the power law spectral component and its variability.

Shaposhnikov, Nikolai↗