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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Kinetic Simulations of Magnetic Reconnection in Partially Ionized Plasmas

Fast magnetic reconnection occurs in nearly all natural and laboratory plasmas and rapidly releases stored magnetic energy. Although commonly studied in fully ionized plasmas, if and when fast reconnection can occur in partially ionized plasmas, such as the interstellar medium or solar chromosphere, is not well understood. Here, this Letter presents the first fully kinetic particle-in-cell simulations of partially ionized reconnection and demonstrates that fast reconnection can occur in partially ionized systems. In the simulations, the transition to fast reconnection occurs when the current sheet width thins below the ion-inertial length in contrast to previous analytic predictions. The peak reconnection rate is ≥ 0.08 when normalized to the bulk Alfvén speed (including both ion and neutral mass), consistent with previous experimental results. However, when the bulk Alfvén speed falls below the neutral sound speed, the rate becomes system size dependent. The normalized inflow velocity is ionization fraction dependent, which is shown to be a result of neutral momentum transport. A model for the inflow is developed which agrees well with the simulation results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Properties of Cosmic Lithium Isotopes Measured by the Alpha Magnetic Spectrometer

We present the first measurement of cosmic-ray fluxes of 6 Li and 7 Li isotopes in the rigidity range from 1.9 to 25 GV. The measurements are based on 9.7 × 10 5 6 Li and 1.04 × 10 6 7 Li nuclei collected by the Alpha Magnetic Spectrometer on the International Space Station from May 2011 to October 2023. We observe that over the entire rigidity range the 6 Li and 7 Li fluxes exhibit nearly identical time variations and, above ∼4 GV, the time variations of 6 Li , 7 Li , He, Be, B, C, N, and O fluxes are identical. Above ∼7 GV, we find an identical rigidity dependence of the 6 Li and 7 Li fluxes. This shows that they are both produced by collisions of heavier cosmic-ray nuclei with the interstellar medium and, in particular, excludes the existence of a sizable primary component in the 7 Li flux.

cosmic ray acceleration↗
DOE OSTI2021

A Tunable Unidirectional Source for GUSTO's Local Oscillator at 4.74 THz

The Galactic/Extra Ultra long Duration Balloon Spectroscopic-Stratospheric Terahertz Observatory (GUSTO), is a NASA balloon-borne project and is scheduled for launch in late 2022. The balloon will carry a spectroscopic telescope that will detect three brightest emission lines from interstellar medium. GUSTO measurements will shed light on the life-cycle of the gases in the Milky Way and Large Magellanic Cloud (LMC). In this study, we will discuss the details of a quantum cascade laser used in the local oscillator for detecting the oxygen line at 4.74 THz.

42 ENGINEERING↗
DOE OSTI2024

Ultrafast studies of elusive chemical reactions in the gas phase

The chemical composition of the interstellar medium and planetary atmospheres is constantly in flux as atoms and molecules collide and interact with high-energy particles such as electrons, protons, and photons. These transformative processes ultimately lead to the coalescence of molecules and eventually the birth of stars. Our understanding of these chemical ecosystems relies on models that synthesize data from gas-phase experiments, providing insights into reaction cross sections. This Review examines efforts to delve into the fundamental bond-forming and bond-breaking dynamics that occur during bimolecular and electron-initiated reactions. Furthermore, these experiments involve clever approaches to establish a time reference and the collision geometry necessary for tracking atomic motion with femtosecond time resolution. Findings from these efforts enhance present models and improve predictions for molecule-molecule and electron-molecule collisions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

The methodology of the search for a correlated signal from a supernova explosion using the data of gravitational wave detectors and neutrino observatories

The proposed methodology developed in cooperation of the LIGO, VIRGO, Borexino, LVD, and IceCube collaborations is based on a joint analysis of data from neutrino and gravitational wave detectors which record corresponding radiations, almost undistorted by the interstellar medium and propagating with similar speeds. This approach allows to increase the reliability of observations, detect the so-called Silent supernovae and explore the properties and generation mechanisms of gravitational waves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

On propagators of nonlocal relativistic diffusion of galactic cosmic rays

This report discusses a new model of cosmic ray propagation in the Galaxy. In contrast to the known models based on the principles of Brownian motion, the proposed model agrees with the relativistic principle of speed limitation and takes into account the large-scale turbulence of the interstellar medium, justifying introduction of fractional differential operators.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Measurement of antiproton production from antihyperon decays in ${p} \textrm{He}$ collisions at $\sqrt{s_{\scriptscriptstyle \mathrm NN}} =110$ GeV

The interpretation of cosmic antiproton flux measurements from space-borne experiments is currently limited by the knowledge of the antiproton production cross-section in collisions between primary cosmic rays and the interstellar medium. Using collisions of protons with an energy of 6.5 TeV incident on helium nuclei at rest in the proximity of the interaction region of the LHCb experiment, the ratio of antiprotons originating from antihyperon decays to prompt production is measured for antiproton momenta between 12 and 110 GeV/c. The dominant antihyperon contribution, namely ${\overline{\varLambda }} \rightarrow {\overline{{p}}} {{\pi } ^+}$ decays from promptly produced $\overline{\varLambda }$ particles, is also exclusively measured. The results complement the measurement of prompt antiproton production obtained from the same data sample. At the energy scale of this measurement, the antihyperon contributions to antiproton production are observed to be significantly larger than predictions of commonly used hadronic production models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Program Repository for Tools for Heliophysics Science (Theseus)

This software is being developed to support data analysis and simulation for the growing field of outer heliosphere physics. In particular, this software will allow data analysis, inference, and simulation of physical mechanisms describing how energetic neutral atoms behave that originate from the solar system's boundary with the interstellar medium.

Weaver, Brian↗
DOE OSTI2023

Software for Heliospheric Science

This software is being developed to support data analysis, modeling, and simulation for the growing field of heliosphere physics. In particular, this software will implement data analysis, modeling, inference, and simulation of physical mechanisms describing how energetic neutral atoms behave within the Earth’s heliosphere and in the interstellar medium beyond.

VanDervort, Lauren↗
DOE OSTI2017

Exposing Hierarchical Parallelism in the FLASH Code for Supernova Simulation on Summit and Other Architectures

Since roughly 100 million years after the big bang, the primordial elements hydrogen (H), helium (He), and lithium (Li) have been synthesized into heavier elements by thermonuclear reactions inside of the stars. The change in stellar composition resulting from these reactions causes stars to evolve over the course of their lives. Although most stars burn through their nuclear fuel and end their lives quietly as inert, compact objects, whereas others end in explosive deaths. These stellar explosions are called supernovae and are among the most energetic events known to occur in our universe. Supernovae themselves further process the matter of their progenitor stars and distribute this material into the interstellar medium of their host galaxies. In the process, they generate ~1051 ergs of kinetic energy by sending shock waves into their surroundings, thereby contributing to galactic dynamics as well.

Papatheodore, Thomas L.↗
DOE OSTI2019

Catching Element Formation In The Act - The Case for a New MeV Gamma-Ray Mission: Radionuclide Astronomy in the 2020s

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV γ-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nu-clear de-excitation, and positron annihilation. The substantial information carried byγ-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted atγ-ray energies, and radioactivity provides a natural physical clock that adds unique information.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Dependence of Dust Formation on the Supernova Explosion and nuDust

Dust is ubiquitous in the interstellar medium, serving as both a source of information and headaches to astronomers, depending on who you ask. The out-flows of core collapse supernovae (CCSNe) serve as a factory for dust nucleation and are one of a few known sources of dust in the universe. From observations of local CCSNe such as 1987A and Cassiopeia A, we know that dust is abundant in CCSN ejecta prior to interacting with the ISM. Furthermore, the explosion energy, explosive engine, metallicity, and progenitor mass of the CCSN will all impact the subsequent dust formation history and composition. Observations of the supernova ejecta probe the detailed composition of the ejecta which, in turn, can be used probe the properties of the progenitor star and the process of the explosion

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Nuclear Astrophysics through simulations of neutron star mergers using Monte‐Carlo neutrino radiation transport (DE-SC0020435 Final Technical Report)

Neutron star mergers are an important source of information for nuclear physics. Except for black holes, neutron stars are the densest macroscopic objects known to exist in the Universe. They provide us with a remarkable laboratory to study the poorly understood high-density states of matter, complementing the study of heavy nuclei performed by nuclear physics experiments on Earth. Collisions of neutron stars are of particular interest. They are among the most energetic events observable in the Universe, powering a broad range of signals across the electromagnetic spectrum as well as gravitational wave signals. These signals contain important information about the properties of extremely dense matter. Colliding neutron stars additionally eject large amounts of neutron-rich material into the surrounding interstellar medium -- material that then undergoes rapid neutron-capture (r-process) nucleosynthesis, the mechanism thought to be responsible for the production of about half of the heavy nuclei. In order to understand current and future observations of neutron star mergers, we need reliable models for the signals that they power. An important component in the construction of such models are numerical simulations of colliding neutron stars. These simulations are costly, running for multiple months on supercomputers, and require the inclusion of complex physics (general relativity, magnetohydrodynamics, neutrino physics, nuclear reactions). In this document, we describe the development of new methods for the treatment of neutrinos in merger simulations, as well as the first simulations capable of evolving the equations of neutrino radiation transport directly and their impact on our understanding of neutron star mergers and more broadly in nuclear astrophysics. We also discuss additional work performed in the study of nucleosynthesis and neutrino physics in neutron star mergers as part of Early Career Award DE-SC0020435.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Final Technical Report: Testing the robustness of CMB-S4 inflation measurements to foreground models

This report summarizes the research activities for DOE award SC0024462, which focused on enhancing the robustness of CMB-S4 inflation measurements by characterizing and mitigating Galactic foreground interference. The project grounded foreground models in the physical processes of the Interstellar Medium with MHD and semi-analytic filament models, and developed analysis pipelines, such as Needlet Internal Linear Combination (NILC) techniques, to isolate faint cosmological signals.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

First Galactic Survey of Energy-Dependent Diffusion by HAWC

HAWC’s wide field-of-view enables unbiased observations of much of the galaxy, allowing for analysis of many candidate sources in the HAWC dataset. Recent work has allowed HAWC to start investigating electron diffusion around pulsars at TeV energies. Surveying electron diffusion at TeV energies along the galactic plane is a unique capability of HAWC that allows us to examine the sources of electrons in our galaxy and constrain the energy dependence of the diffusion mechanism. HAWC has already applied this model to the Geminga and Monogem pulsars. This work will expand the study to include multiple sources associated with pulsars in the latest HAWC dataset. Unlike older pulsars, lepton transport around young pulsars is likely to be dominated by advective processes. Using simple assumptions, both advective and diffusive processes predict that the size of the emission region follows a power law dependence on energy. This study has important consequences for the positron excess reported by space-based instruments; if electron diffusion is suppressed for tens of parsecs around pulsars relative to diffusion in the interstellar medium (a "two-zone" model), they may be able to explain at least part of the observed increase in the positron fraction above 10 GeV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy

We report on the use of extreme ultraviolet (XUV, 30.3 nm) radiation from the Free-electron LASer in Hamburg (FLASH) and visible (Vis, 405 nm) photons from an optical laser to investigate the relaxation and fragmentation dynamics of fluorene ions. The ultrashort laser pulses allow to resolve the molecular processes occurring on the femtosecond timescales. Fluorene is a prototypical small polycyclic aromatic hydrocarbon (PAH). Through their infrared emission signature, PAHs have been shown to be ubiquitous in the universe, and they are assumed to play an important role in the chemistry of the interstellar medium. Our experiments track the ionization and dissociative ionization products of fluorene through time-of-flight mass spectrometry and velocity-map imaging. Multiple processes involved in the formation of each of the fragment ions are disentangled through analysis of the ion images. The relaxation lifetimes of the excited fluorene monocation and dication obtained through the fragment formation channels are reported to be in the range of a few tens of femtoseconds to a few picoseconds.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Simultaneous observations of giant pulses from pulsar PSR B0950+08 at 42 and 74 MHz

We report the detection of giant pulse (GP) emission from PSR B0950+08 in 12 hr of observations made simultaneously at 42 and 74 MHz, using the first station of the Long Wavelength Array. We detected 275 GPs (in 0.16% of the pulse periods) and 465 GPs (0.27%) at 42 and 74 MHz, respectively. The pulsar is weaker and produces less frequent GPs than at 100 MHz. Here, GPs are taken as having ⩾ 10 times the flux density of an average pulse (AP); their cumulative distribution of pulse strength follows a power law, with an index of −4.1 at 42 MHz and −5.1 at 74 MHz, which is much less steep than would be expected if we were observing the tail of a Gaussian distribution of normal pulses. We detected no other transient pulses in a wide dispersion measure range from 1 to 5000 pc cm{sup −3}. There were 128 GPs detected within the same periods from both 42 and 74 MHz, which means more than half of them are not generated in a wide band. The CLEAN-based algorithm was used to deconvolve the the effect of scattering broadening and we have concluded that the scattering effect from the interstellar medium at 42 and 74 MHz is weak and cannot be distinguished from the pulse profiles. We calculated the altitude r of the emission region using the dipolar magnetic field model. We found r(42 MHz) = 29.27 km (0.242% of R{sub LC}) and r(74 MHz) = 29.01 km (0.240% of R{sub LC}) for the AP, while for GPs, r(42 MHz) = 29.10 km (0.241% of R{sub LC}) and r(74 MHz) = 28.95 km (0.240% of R{sub LC}). GPs, which have a double-peak structure, have a smaller mean peak-to-peak separation compared to the AP.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

GLOBAL PROPERTIES OF NEUTRAL HYDROGEN IN COMPACT GROUPS

Compact groups of galaxies provide a unique environment to study the evolution of galaxies amid frequent gravitational encounters. These nearby groups have conditions similar to those in the earlier universe when galaxies were assembled and give us the opportunity to witness hierarchical formation in progress. To understand how the compact group environment affects galaxy evolution, we examine the gas and dust in these groups. We present new single-dish GBT neutral hydrogen (H i) observations of 30 compact groups and define a new way to quantify the group H i content as the H i-to-stellar mass ratio of the group as a whole. We compare the H i content with mid-IR indicators of star formation and optical [g − r] color to search for correlations between group gas content and star formation activity of individual group members. Quiescent galaxies tend to live in H i-poor groups, and galaxies with active star formation are more commonly found in H i-rich groups. Intriguingly, we also find “rogue” galaxies whose star formation does not correlate with group H i content. In particular, we identify three galaxies (NGC 2968 in RSCG 34, KUG 1131+202A in RSCG 42, and NGC 4613 in RSCG 64) whose mid-IR activity is discrepant with the H i. We speculate that this mismatch between mid-IR activity and H i content is a consequence of strong interactions in this environment that can strip H i from galaxies and abruptly affect star formation. Ultimately, characterizing how and on what timescales the gas is processed in compact groups will help us understand the interstellar medium in complex, dense environments similar to the earlier universe.

79 ASTRONOMY AND ASTROPHYSICS↗