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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Impact of Newly Measured 𝛽-Delayed Neutron Emitters around 78 Ni on Light Element Nucleosynthesis in the Neutrino Wind Following a Neutron Star Merger

Neutron emission probabilities and half-lives of 37 𝛽-delayed neutron emitters from 75 Ni to 92 Br were measured at the RIKEN Nishina Center in Japan, including 11 one-neutron and 13 two-neutron emission probabilities and six half-lives for the first time that supersede theoretical estimates. These nuclei lie in the path of the weak 𝑟 process occurring in neutrino-driven winds from the accretion disk formed after the merger of two neutron stars synthesizing elements in the 𝐴∼80 abundance peak. The presence of such elements dominates the accompanying kilonova emission over the first few days and have been identified in the AT2017gfo event, associated to the gravitational wave detection GW170817. Abundance calculations based on over 17,000 simulated trajectories describing the evolution of matter properties in the merger outflows show that the new data lead to an increase of 50%–70% in the abundance of Y, Zr, Nb, and Mo. This enhancement is large compared to the scatter of relative abundances observed in old very metal poor stars and thus is significant in the comparison with other possible astrophysical processes contributing to the light-element production. These results underline the importance of including experimental decay data for very neutron-rich 𝛽 -delayed neutron emitters into 𝑟 -process models.

59 ≤ A ≤ 89↗
DOE OSTI2021

Brought to Light. I. Quantification of Disk Substructure in Dwarf Early-type Galaxies

Dwarf early-type galaxies (ETGs) display a rich diversity in their photometric, structural, and dynamical properties. In this work, we address their structural complexity by studying with deep imaging a sample of nine dwarf ETGs from the Virgo galaxy cluster, characterized by having faint disk features such as bars and spiral arms, that lie mostly hidden within the bright diffuse light of the galaxies. We present a new, robust method that aims to identify and extract the disk substructure embedded in these dwarf ETGs. The method consists in an iterative procedure that gradually separates a galaxy image into two components: the bright, dominant, diffuse component, and the much fainter, underlying disk component. By applying it to the dwarf ETG sample, we quantify their disk substructure and find that its relative contribution to the total galaxy light ranges between 2.2% and 6.4% within two effective radii. We test the reliability of the method, and prove that it is accurate in recovering the disk substructure we introduce in mock galaxy images, even at low disk-to-total light fractions of a few percent. As a potential application of the method, we perform a Fourier analysis on the extracted disk substructures and measure the orientation, length, and strength of the bars, as well as the pitch angle and strength of the spiral arms. We also briefly discuss a scenario based on the numerical simulations presented in our companion paper, Brought to Light II: Smith et al., in which we investigate the origins of the substructure in such dwarf systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Position-dependent Voronoi probability distribution functions for matter and halos

Here, we measure the Voronoi density probability distribution function (PDF) for both dark matter and halos in N-body simulations. For the dark matter, Voronoi densities represent the matter density field smoothed on a uniform mass scale, which approximates the Lagrangian density field. For halos, the Voronoi densities contain information about the local environment of each halo. We measure the halo virial masses, the total amount of dark matter within each halo Voronoi cell, and the halo Voronoi cell volumes, and we show how halo abundances depend on these three quantities. We then study the position-dependent Voronoi density PDF, measured within finite subregions of the Universe, using separate universe simulations. We demonstrate that the spatial variation of the position-dependent PDF is due to large-scale density fluctuations, indicating that the position-dependent PDF is a biased tracer of large-scale structure. We measure this bias for the dark matter, and interpret it as the bias of regions of the Lagrangian density field that are selected based on density. For the halos, this bias can be interpreted as a form of assembly bias. We present the mapping from late-time to early-time Voronoi density for each simulation dark matter particle, which is highly stochastic. We compare the median of this stochastic map with spherical collapse calculations and discuss challenges involved in modeling the evolution of the density field on these scales.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Large scale structure reconstruction with short-wavelength modes

Large scale density modes are difficult to measure because they are sensitive to systematic observational errors in galaxy surveys, but we can study them indirectly by observing their impact on small scale perturbations. Cosmological perturbation theory predicts that second-order density inhomogeneities are a convolution of a short- and a long-wavelength mode. This arises physically because small scale structures grow at different rates depending on the large scale environment in which they reside. This induces an off-diagonal term in the two-point statistics in Fourier space that we use as the basis for a quadratic estimator for the large scale field. Here, we demonstrate that this quadratic estimator works well on an N-body simulation of size (2.5 h -1 Gpc) 3 . In particular, the quadratic estimator successfully reconstructs the long-wavelength modes using only small-scale information. This opens up novel opportunities to study structure on the largest observable scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Beware of fake ν ’s: The effect of massive neutrinos on the nonlinear evolution of cosmic structure

Massive neutrinos suppress the growth of cosmic structure on small, nonlinear scales. It is thus often proposed that using statistics beyond the power spectrum can tighten constraints on the neutrino mass by extracting additional information from these nonlinear scales. We study the information content regarding neutrino mass at the field level, quantifying how much of this information arises from the difference in nonlinear evolution between a cosmology with one fluid [cold dark matter (CDM)] and two fluids ( CDM + neutrinos ). We do so by running two N -body simulations, one with and one without massive neutrinos, both with the same phases, and matching their linear power spectrum at a given low redshift. This effectively isolates the information encoded in the linear initial conditions from the nonlinear cosmic evolution. We demonstrate that, for k ≲ 1 h / Mpc , and for a single redshift, there is negligible difference in the real-space CDM field between the two simulations. This suggests that all the information regarding neutrino mass is in the linear power spectrum set by the initial conditions. Thus, any probe based on the CDM field alone will have negligible constraining power beyond that which exists at the linear level over the same range of scales. Consequently, any probe based on the halo field will contain little information beyond the linear power. We find similar results for the matter field responsible for weak lensing. We also demonstrate that there may be much information beyond the power spectrum in the 3D matter field; however, this is not observable in modern surveys via dark matter halos or weak lensing. Finally, we show that there is additional information to be found in redshift space.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Machine learning opportunities for nucleosynthesis studies

Nuclear astrophysics is an interdisciplinary field focused on exploring the impact of nuclear physics on the evolution and explosions of stars and the cosmic creation of the elements. While researchers in astrophysics and in nuclear physics are separately using machine learning approaches to advance studies in their fields, there is currently little use of machine learning in nuclear astrophysics. We briefly describe the most common types of machine learning algorithms, and then detail their numerous possible uses to advance nuclear astrophysics, with a focus on simulation-based nucleosynthesis studies. We show that machine learning offers novel, complementary, creative approaches to address many important nucleosynthesis puzzles, with the potential to initiate a new frontier in nuclear astrophysics research.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Quantifying the Influence of Jupiter on the Earth’s Orbital Cycles

A wealth of Earth-sized exoplanets will be discovered in the coming years, providing a large pool of candidates from which the targets for the search for life beyond the solar system will be chosen. The target selection process will require the leveraging of all available information in order to maximize the robustness of the target list and make the most productive use of follow-up resources. Here, we present the results of a suite of n-body simulations that demonstrate the degree to which the orbital architecture of the solar system impacts the variability of Earth’s orbital elements. By varying the orbit of Jupiter and keeping the initial orbits of the other planets constant, we demonstrate how subtle changes in solar system architecture could alter the Earth’s orbital evolution—a key factor in the Milankovitch cycles that alter the amount and distribution of solar insolation, thereby driving periodic climate change on our planet. The amplitudes and frequencies of Earth’s modern orbital cycles fall in the middle of the range seen in our runs for all parameters considered—neither unusually fast nor slow, neither large nor small. This finding runs counter to the “Rare Earth” hypothesis, which suggests that conditions on Earth are so unusual that life elsewhere is essentially impossible. Our results highlight how dynamical simulations of newly discovered exoplanetary systems could be used as an additional means to assess the potential targets of biosignature searches, and thereby help focus the search for life to the most promising targets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Dynamical Avenues for Mercury’s Origin. I. The Lone Survivor of a Primordial Generation of Short-period Protoplanets

The absence of planets interior to Mercury continues to puzzle terrestrial-planet formation models, particularly when contrasted with the relatively high derived occurrence rates of short-period planets around Sun-like stars. Recent work proposed that the majority of systems hosting hot super-Earths attain their orbital architectures through an epoch of dynamical instability after forming in quasi-stable, tightly packed configurations. Isotopic evidence seems to suggest that the formation of objects in the super-Earth-mass regime is unlikely to have occurred in the solar system as the terrestrial-forming disk is thought to have been significantly mass deprived starting around 2 Myr after the formation of calcium-aluminum-rich inclusions—a consequence of either Jupiter’s growth or an intrinsic disk feature. Nevertheless, terrestrial-planet formation models and high-resolution investigations of planetesimal dynamics in the gas-disk phase occasionally find that quasi-stable protoplanets with mass comparable to that of Mars emerge in the vicinity of Mercury’s modern orbit. In this paper, we investigate whether it is possible for a primordial configuration of such objects to be cataclysmically destroyed in a manner that leaves Mercury behind as the sole survivor without disturbing the other terrestrial worlds. We use numerical simulations to show that this scenario is plausible. In many cases, the surviving Mercury analog experiences a series of erosive impacts, thereby boosting its Fe/Si ratio. A caveat of our proposed genesis scenario for Mercury is that Venus typically experiences at least one late giant impact.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Supernova Shock Breakout/Emergence Detection Predictions for a Wide-field X-Ray Survey

There are currently many large-field surveys that are operational and are being planned including the powerful Vera C. Rubin Observatory Legacy Survey of Space and Time. These surveys will increase the number and diversity of transients dramatically. However, for some transients, like supernovae (SNe), we can gain more understanding by directed observations (e.g., shock breakout and γ-ray detections) than by simply increasing the sample size. For example, the initial emission from these transients can be a powerful probe of these explosions. Upcoming ground-based detectors are not ideally suited to observing the initial emission (shock emergence) of these transients. These observations require a large field-of-view X-ray mission with a UV follow-up within the first hour of shock breakout. The emission in the first 1 hr to even 1 day provides strong constraints on the stellar radius and asymmetries in the outer layers of stars, the properties of the circumstellar medium (e.g., inhomogeneities in the wind for core-collapse SNe and accreting companions in thermonuclear SNe), and the transition region between these two areas. This paper describes a simulation for the number of SNe that could be seen by a large field-of-view lobster-eye X-ray and UV observatory.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Nonplanar effects in simulations of laser-driven ejecta microjet experiments

Recent experiments of laser-driven ejecta microjets performed at OMEGA 60 reveal tortuous jets whereby the jets appear to deviate from their initial trajectory as they travel in vacuum. To understand these data, we perform two dimensional numerical simulations, considering different target thicknesses, pressures, and models of the drive conditions. In particular, modeling the finite laser spot size appears essential in reproducing qualitatively the non-planar shock observed in the experiment. Simulations capture jet deflection by accounting for a slight misalignment of the laser pointing with respect to the groove axis along with spatial variation of the laser pulse intensity. The principal physical mechanism appears to be that lateral momentum is imparted by release waves arising from the non-planar drive. The induced off-axis velocity is small in comparison to the jet axial velocity but integrates into a pronounced deflection over the course of the experiment. The analysis of jet axial and lateral mass distributions is found to be reproduced reasonably by the simulations. Simulated radiographs are in qualitative agreement with the experiments, though their differences point to potential shortcomings in modeling strictly three-dimensional experiments using two-dimensional hydrodynamic simulations. The simple analysis is able to explain part of the observed discrepancy in simulated vs experimental jet masses.

42 ENGINEERING↗
DOE OSTI2021

On the Estimation of Circumbinary Orbital Properties

We describe a fast, approximate method to characterize the orbits of satellites around a central binary in numerical simulations. A goal is to distinguish the free eccentricity—the random motion of a satellite relative to a dynamically cool orbit—from oscillatory modes driven by the central binary’s time-varying gravitational potential. We assess the performance of the method using the Kepler-16, Kepler-47, and Pluto–Charon systems. We then apply the method to a simulation of orbital damping in a circumbinary environment, resolving relative speeds between small bodies that are slow enough to promote mergers and growth. These results illustrate how dynamical cooling can set the stage for the formation of Tatooine-like planets around stellar binaries and the small moons around the Pluto–Charon binary planet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Hi-COLA: fast, approximate simulations of structure formation in Horndeski gravity

We introduce Hi-COLA, a code designed to run fast, approximate N-body simulations of non-linear structure formation in reduced Horndeski gravity. Given an input Lagrangian, Hi-COLA dynamically constructs the appropriate field equations and consistently solves for the cosmological background, linear growth, and screened fifth force of that theory. Hence Hi-COLA is a general, adaptable, and useful tool that allows the mildly non-linear regime of many Horndeski theories to be investigated for the first time, at low computational cost. In this work, we first describe the screening approximations and simulation setup of Hi-COLA for theories with Vainshtein screening. We validate the code against traditional N-body simulations for cubic Galileon gravity, finding 2.5% agreement up to k max = 1.2 h/Mpc. To demonstrate the flexibility of Hi-COLA, we additionally run the first simulations of an extended shift-symmetric gravity theory. We use the consistency and modularity of Hi-COLA to dissect how the modified background, linear growth, and screened fifth force all contribute to departures from ΛCDM in the non-linear matter power spectrum. Hi-COLA can be found at https://github.com/Hi-COLACode/Hi-COLA.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Evaluation of cosmogenic production of 39 Ar and 42 Ar for rare-event physics using underground argon

Underground argon (UAr) with lower cosmogenic activities of 39 Ar and 42 Ar has been planned as a detector in detecting scintillation light and charge collection using time projection chambers for dark matter searches and as a veto detector in suppressing backgrounds for neutrinoless double beta decay (0$vββ$ ) experiments. Long-lived radioactive isotopes, 39 Ar and 42 Ar, can also be produced on the surface when UAr is pumped out from a deep well. Understanding the production of long-lived isotopes in Ar is important for utilizing UAr for dark matter and 0$vββ$ experiments in terms of its production, transportation, and storage. Ar exposure to cosmic rays at sea-level is simulated using Geant4 for a given cosmic ray muon, neutron, and proton energy spectrum. Here we report the simulated cosmogenic production rates of 39 Ar, 42 Ar, and other long-lived isotopes at sea-level from fast neutrons, high energy muons, and high energy protons. Total production rates of 938.53/kg Ar day and 5.81 × 10 -3 /kg Ar day for 39 Ar and 42 Ar are found from our simulation. Utilizing these production rates, we set a time limit of 954 days constrained by the production of 39 Ar for UAr to be on the surface before it compromises the sensitivity for a dark matter experiment. Similarly, a time limit of 1702 days constrained by the production of 42 Ar is found for a 0$vββ$ experiment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Fast radio burst dispersion measure distribution as a probe of helium reionization

Fast radio burst (FRB) discoveries are occurring rapidly, with thousands expected from upcoming surveys. The dispersion measures (DM) observed for FRB include important information on cosmological distances and the ionization state of the universe from the redshift of emission until today. Rather than considering the DM–redshift relation, we investigate the statistical ensemble of the distribution of dispersion measures. Here, we explore the use of this abundance information, with and without redshift information, to probe helium reionization through simulated data to redshift z = 6. Carrying out Monte Carlo simulations of FRB survey samples, we examine the effect of different source redshift distributions, host galaxy models, sudden vs gradual reionization, and covariance with cosmological parameters on determination of helium reionization properties. We find that a fluence limited survey with 10 4 FRBs can discriminate different helium reionization histories at ~6σ using the DM-distribution of bursts, without redshift information (and ~10σ with redshifts).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Moving lens effect: Simulations, forecasts, and foreground mitigation

The peculiar motion of massive objects across the line of sight imprints a dipolar temperature anisotropy pattern on the cosmic microwave background known as the moving lens effect. This effect provides a unique probe of the transverse components of the peculiar velocity field, but has not yet been detected due to its small size. We implement and validate a stacking estimator for the moving lens signal using a galaxy catalog as a tracer of massive haloes combined with reconstructed velocities from the galaxy number density field. Using simulations, we forecast detection prospects for the moving lens signal from current and upcoming microwave background and galaxy surveys. Here, we demonstrate a new foreground mitigation strategy likely sufficient for current datasets, and discuss various sources of systematic error and noise. Upcoming galaxy surveys will provide high-significance statistical detections of the moving lens effect.

Astrophysical & cosmological simulations↗
DOE OSTI2025

Impact of neutrino flavor conversions on neutron star merger dynamics, ejecta, nucleosynthesis, and multimessenger signals

We present numerical relativity simulations of binary neutron star mergers incorporating neutrino flavor transformations triggered by fast flavor instability, quantum many-body effects, or potential beyond standard model physics. In both long-lived and short-lived remnant scenarios, neutrino flavor conversions modify species-dependent neutrino luminosities and mean energies, and drive the matter towards more neutron rich conditions. They produce up to more neutron rich ejecta and significantly boost the r-process yields, especially in low-density, near-equatorial outflows. We identify regions unstable to fast flavor instabilities and find that these instabilities persist despite flavor conversions. We further test the sensitivity to the equilibration timescale of the flavor conversions, finding that slower flavor conversions can interact with thermodynamic equilibration, and increase the neutron richness of the ejecta. Flavor conversions may also contribute to stronger gravitational wave and neutrino emissions, pointing to a correlation between neutrino transport and merger dynamics. Furthermore, these results highlight the potential impact of flavor conversions while motivating future work to improve on theoretical understanding of flavor instabilities in global simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Evolution of Main-sequence-like Surviving Companions in Type Ia Supernova Remnants

Recent theoretical and numerical studies of Type Ia supernovae (SNe Ia) explosions within the single-degenerate scenario suggest that the nondegenerate companions could survive during the supernova impact and could be detectable in nearby supernova remnants. However, observational efforts show less promising evidence of the existence of surviving companions from the standard single-degenerate channels. The spin-up/spin-down models are possible mechanisms to explain the nondetection of surviving companions. In these models, the spin-up phase could increase the critical mass for explosion, leading to a super-Chandrasekhar-mass explosion, and the spin-down phase could lead to extra mass loss and angular momentum redistribution. Since the spin-down timescale for the delayed explosion of a rotating white dwarf is unclear, in this paper we explore a vast parameter space of main-sequence-like surviving companions via two-dimensional hydrodynamic simulations of supernova impact and the subsequent stellar evolution of surviving companions. Tight universal relations to describe the mass-stripping effect, supernova kick, and depth of supernova heating are provided. Our results suggest that the not-yet-detected surviving companions from observations of nearby SN Ia remnants might favor low-mass companions, short binary separation, or stronger supernova explosion energies than the standard single-degenerate channels.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Exploring Plasma Heating in the Current Sheet Region in a Three-dimensional Coronal Mass Ejection Simulation

We simulate a coronal mass ejection using a three-dimensional magnetohydrodynamic code that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The magnetic flux distribution at 1 Rs is produced by a localized subsurface dipole superimposed on a global dipole field, mimicking the presence of an active region within the global corona. Transverse electric fields are applied near the polarity inversion line to introduce a transverse magnetic field, followed by the imposition of a converging flow to form and destabilize a flux rope, producing an eruption. We examine the quantities responsible for plasma heating and cooling during the eruption, including thermal conduction, radiation, adiabatic effects, coronal heating, and ohmic heating. We find that ohmic heating is an important contributor to hot temperatures in the current sheet region early in the eruption, but in the late phase, adiabatic compression plays an important role in heating the plasma there. Thermal conduction also plays an important role in the transport of thermal energy away from the current sheet region throughout the reconnection process, producing a “thermal halo” and widening the region of high temperatures. We simulate emission from solar telescopes for this eruption and find that there is evidence for emission from heated plasma above the flare loops late in the eruption, when the adiabatic heating is the dominant heating term. These results provide an explanation for hot supra-arcade plasma sheets that are often observed in X-rays and extreme ultraviolet wavelengths during the decay phase of large flares.

79 ASTRONOMY AND ASTROPHYSICS↗