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DOE OSTI2020

Step-patterned survivorship curves: Mortality and loss of equilibrium responses to high temperature and food restriction in juvenile rainbow trout ( Oncorhynchus mykiss )

While survivorship curves typically exhibit smooth declines over time, step-patterned curves can occur with multiple stressors within a life stage. To explore this process, we examined the effects of heat (24°C) and food restriction on juvenile rainbow trout (Oncorhynchus mykiss Walbaum) in challenge experiments. We observed step-patterned survivorship curves determined by mortality and loss of equilibrium (LOE) endpoints. To examine the cause of heterogeneity in the stress responses from early to late mortality and LOE, we measured indices of energetic reserves. The step transition in the survivorship curves, the peak mortality rates, and start of when individuals reached a critical energetic threshold (14% dry mass; 4.0 kJ∙g -1 energy) all occurred at around days 10–15 of the challenge. The coherence in these temporal patterns suggest heterogeneity in the cohort stress responses, in which an early subgroup died from heat stress and a late subgroup died from starvation. Thus, their endpoint sensitivities resulted in step-patterned survivorship curves. We discuss the implications of the study for understanding effects of multiple stressors on population heterogeneity and note the possible significance of stress response selection under climate change in which heat stress and food limitations occur in concert.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2006

Maximizing the Scientific Return of the Sentinels Mission Using Global MHD Models

The Sentinels mission promises to provide a unique view of the acceleration and transport processes of energetic particles as well as the initiation and evolution of coronal mass ejections (CMEs). A crucial component in understanding the physics associated with these processes lies in the large-scale structure of the corona and heliosphere, particularly during the eruption and propagation of fast CMEs. In this talk we review the current status of our MHD modeling efforts, focusing on Sentinels-specific science, and project forward to envisage what capabilities we may have developed by the time that the Sentinels launch (2012). In conjunction with Solar Orbiter, the farside and near-Earth Sentinels spacecraft will provide simultaneous photospheric magnetograph measurements at multiple longitudes, which will lead to major improvements in our ability to prescribe accurate, time-dependent global boundary conditions. Data returned from the inner heliospheric Sentinels will be used to validate these results. The model results can be used in a variety of ways to interpret the observations. For example, products from the model, such as the properties of CME-driven shocks and CME-associated reconnection sites can be used to interpret complex energetic particle profiles. Also, by tracing along magnetic field lines, the inferred sites of the energetic particles can be connected directly with the in situ measurements at each spacecraft. Perhaps more so than any previous mission, sophisticated models will be required to unravel the broad and disparate measurements returned by the suite of Sentinels spacecraft.

Riley, P.↗

DOE OSTI2025

Effect of a Fine-Scale Layered Structure of the Atmosphere on Infrasound Signals from Fragmenting Meteoroids

We investigate the influence of a fine-scale (FS) layered structure in the atmosphere on the propagation of infrasound signals generated by fragmenting meteoroids. Using a pseudo-differential parabolic equation (PPE) approach, we model broadband acoustic signals from point sources at altitudes of 35–100 km. The presence of FS fluctuations in the stratosphere (37–45 km) and the lower thermosphere (100–120 km) modifies ray trajectories, causing multiple arrivals and prolonged signal durations at ground stations. In particular, meteoroids fragmenting at 80–100 km can produce two distinct thermospheric arrivals beyond 150 km range, while meteoroids descending to 50 km or below yield weak, long-lived arrivals within the acoustic shadow zone via antiguiding propagation and diffraction. Comparison with observed infrasound data confirms that FS-layered inhomogeneities can account for multi-arrival “N-waves,” broadening potential interpretations of meteoroid signals. The results also apply to other atmospheric-entry objects, such as sample return capsules, emphasizing how FS structure impacts shock wave propagation. In conclusion, our findings advance understanding of wavefield evolution in a layered atmosphere and have broad relevance for global infrasound monitoring of diverse phenomena (e.g., re-entry capsules, rocket launches, and large-scale explosions).

Aeroacoustics↗

DOE OSTI2018

Additively Manufactured Shock Absorbing Engineered Materials

This study investigates the static and dynamic mechanical performance of conformal negative stiffness honeycomb structures. Negative stiffness honeycombs are capable of elastically absorbing a static or dynamic mechanical load at a predefined force threshold and returning to their initial configuration after the load is released. Most negative stiffness honeycombs rely on mechanical loading that is orthogonal to the base of the structure. In this study, a more three-dimensional design is presented that allows the honeycomb to conform to complex surfaces and protect against impacts from multiple directions. The conformal designs are additively manufactured in nylon and stainless steel and subjected to quasi-static mechanical loading and dynamic mechanical impact tests that demonstrate their impact protection capabilities.

36 MATERIALS SCIENCE↗

DOE OSTI2015

EVIDENCE OF MAGNETIC FIELD SWITCH-OFF IN COLLISIONLESS MAGNETIC RECONNECTION

The long-term evolution of large domain particle-in-cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: toward a Petschek-like configuration or toward multiple X points. In the present simulation, a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminiscent of Petschek’s switch-off then ensues. Switch-off is obtained through a slow shock/rotational discontinuity compound structure. Two external slow shocks (SS) located at the separatrices reduce the in-plane tangential component of the magnetic field, but not to zero. Two transitions reminiscent of rotational discontinuities (RD) in the internal part of the exhaust then perform the final switch-off. Both the SS and the RD are characterized through analysis of their Rankine–Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Solar Energetic Particle Acceleration at a Spherical Shock with the Shock Normal Angle $θ$ $B_n$ Evolving in Space and Time

We present a 2D kinematic model to study the acceleration of solar energetic particles (SEPs) at a shock driven by a coronal mass ejection. The shock is assumed to be spherical about an origin that is offset from the center of the Sun. This leads to a spatial and temporal evolution of the angle between the magnetic field and the shock-normal direction (θ Bn ) as it propagates through the Parker spiral magnetic field from the lower corona to 1 au. We find that the high-energy SEP intensity varies significantly along the shock front due to the evolution of θ Bn . Generally, the west flank of the shock preferentially accelerates particles to high energies compared to the east flank and shock nose. This can be understood in terms of the rate of acceleration, which is higher at the west flank. Double power-law energy spectra are reproduced in our model as a consequence of the local acceleration and transport effects. These results will help us to better understand the evolution of SEP acceleration and provide new insights into large SEP events observed by multiple spacecraft, especially those close to the Sun, such as Parker Solar Probe and Solar Orbiter.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1991

Low-frequency radio emissions in the outer heliosphere

Progress is reported toward a model for the 2 and 3 kHz radio waves observed by Voyagers 1 and 2 during the 1983-1987 interval at radial distances from the sun of 17 and 13 AU, respectively. The brightness temperature and range of the volume emissivity for the radiation are calculated, and the results are compared with the characteristics of known radiation at multiples of the plasma frequency. The derived brightness temperatures are used to constrain the source of the Langmuir waves required to generate the observed emission and to rule out certain emission mechanisms. Minimum values of 3-30 micro-V/m are derived for the Langmuir wave electric field intensity and are found to be in reasonable agreement with observed values at planetary bow shocks. Path lengths required for the radiation to reach the observed levels are derived and discussed. The relevance of these ideas to possible direct observations of heliospheric boundaries is addressed.

Macek, W. M.↗

DOE OSTI2019

Core Collapse Supernovae and Multi-Messenger Astronomy

Multi-messenger diagnostics for core-collapse supernovae (CCSN) have been used for over half a century when astronomers began using dust grains to probe the yields from supernovae. But the concurrent neutrino and electromagnetic observations of SN 1987A, a core-collapse supernova in the Large Magellanic Cloud, cemented the importance of multi-messenger diagnostics for these transients. Although rare in the Milky Way where supernovae can be probed by multiple messengers, the science enabled in each event is enormous.Most of the gravitational energy released during collapse is emitted in MeV neutrinos that should be detectable within a few Mpc with next generation (NG) neutrino experiments. They may also be detected by future gravitational wave (GW) interferometers. Including dust grains (and other nucleosynthetic yield probes), cosmic rays and high-energy neutrinos that probe shocks, and abroad range of thermal and non-thermal photon emission, these messengers probe nearly all aspects of the supernova physics and its progenitor evolution. Here, the multitude of diagnostics from a nearby supernova will allow us to tightly constrain our theories to maximize what we can learn about the universe from more distant, but less-well diagnosed, supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

A monolithic mass tracking formulation for bubbles in incompressible flow

We devise a novel method for treating bubbles in incompressible flow that relies on the conservative advection of bubble mass and an associated equation of state in order to determine pressure boundary conditions inside each bubble. We show that executing this algorithm in a traditional manner leads to stability issues similar to those seen for partitioned methods for solid–fluid coupling. Therefore, we reformulate the problem monolithically. This is accomplished by first proposing a new fully monolithic approach to coupling incompressible flow to fully nonlinear compressible flow including the effects of shocks and rarefactions, and then subsequently making a number of simplifying assumptions on the air flow removing not only the nonlinearities but also the spatial variations of both the density and the pressure. The resulting algorithm is quite robust, has been shown to converge to known solutions for test problems, and has been shown to be quite effective on more realistic problems including those with multiple bubbles, merging and pinching, etc. Notably, this approach departs from a standard two-phase incompressible flow model where the air flow preserves its volume despite potentially large forces and pressure differentials in the surrounding incompressible fluid that should change its volume. Our bubbles readily change volume according to an isothermal equation of state.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2012

COSMIC ORIGINS SPECTROGRAPH OBSERVATIONS OF WARM INTERVENING GAS AT z {approx} 0.325 TOWARD 3C 263

We present HST/COS high-S/N observations of the z = 0.32566 multiphase absorber toward 3C 263. The Cosmic Origins Spectrograph (COS) data show absorption from H I (Ly{alpha} to Ly{theta}), O VI, C III, N III, Si III, and C II. The Ne VIII in this absorber is detected in the FUSE spectrum along with O III, O IV, and N IV. The low and intermediate ions are kinematically aligned with each other and H I and display narrow line widths of b {approx} 6-8 km s{sup -1}. The O VI {lambda}{lambda}1031, 1037 lines are kinematically offset by {Delta}v {approx} 12 km s{sup -1} from the low ions and are a factor of {approx}4 broader. All metal ions except O VI and Ne VIII are consistent with an origin in gas photoionized by the extragalactic background radiation. The bulk of the observed H I is also traced by this photoionized medium. The metallicity in this gas phase is Z {approx}> 0.15 Z{sub Sun} with carbon having near-solar abundances. The O VI and Ne VIII favor an origin in collisionally ionized gas at T = 5.2 Multiplication-Sign 10{sup 5} K. The H I absorption associated with this warm absorber is a broad-Ly{alpha} absorber (BLA) marginally detected in the COS spectrum. This warm gas phase has a metallicity of [X/H] {approx}-0.12 dex, and a total hydrogen column density of N( H) {approx} 3 Multiplication-Sign 10{sup 19} cm{sup -2}, which is {approx}2 dex higher than what is traced by the photoionized gas. Simultaneous detection of O VI, Ne VIII, and BLAs in an absorber can be a strong diagnostic of gas with T {approx} 10{sup 5}-10{sup 6} K corresponding to the warm phase of the warm-hot intergalactic medium or shock-heated gas in the extended halos of galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1973

Improved multiple-shot gun for use as a combustion stability rating device

A program was conducted to develop and experimentally evaluate an improved version of a modified machine gun for use as a device for rating the relative combustion stability of various rocket combustors. Following the results of a previous study involving a caliber .30 machine gun, a caliber .50 machine gun was modified in order to extend the charge-size range of the device. Nitrocellulose charge sizes ranging from 1.004 to 9.720 grams were fired at rates up to four shots per second. Shock pressures up to 25,512 kN/sq m were measured near the end of a shortened gun barrel. A minimal resistance type of check valve permitted the gun to fire into pressurized regions; back pressures up to 3448 kN/sq m abs were tested. The final modified assembly was evaluated during combustion stability tests on rocket combustors burning a FLOX-methane propellant combination.

Sokolowski, D. E.↗

DOE OSTI2014

Observation of early shell-dopant mix in OMEGA direct-drive implosions and comparisons with radiation-hydrodynamic simulations

Temporally, spatially, and spectrally resolved x-ray image data from direct-drive implosions on OMEGA were interpreted with the aid of radiation-hydrodynamic simulations. Neither clean calculations nor those using a turbulent mix model can explain fully the observed migration of shell-dopant material (titanium) into the core. Shell-dopant migration was observed via time-dependent, spatially integrated spectra, and spatially and spectrally resolved x-ray images of capsule implosions and resultant dopant emissions. The titanium emission was centrally peaked in narrowband x-ray images. In post-processed clean simulations, the peak titanium emission forms in a ring in self-emission images as the capsule implodes. Post-processed simulations with mix reproduce trends in time-dependent, spatially integrated spectra, as well having centrally peaked Ti emission in synthetic multiple monochromatic imager. However, mix simulations still do not transport Ti to the core as is observed in the experiment. This suggests that phenomena in addition to the turbulent mix must be responsible for the transport of Ti. Simple diffusion estimates are unable to explain the early Ti mix into the core. Mechanisms suggested for further study are capsule surface roughness, illumination non-uniformity, and shock entrainment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1993

Research program on the Manson impact structure, Iowa

At or near the end of the Cretaceous, at least two large impact events occurred in the western hemisphere. One impact formed the 180-km diameter Chicxulub crater on the northern tip of the Yucatan peninsula. Another formed the 35-km diameter Manson structure in western Iowa. Several lines of evidence, including the chemical and isotopic composition of glass found in the K/T boundary layer at sites in the Gulf of Mexico and Caribbean region, the regional variation in thickness and the size of spherules in the K/T boundary layer, and indications at and near the boundary of disturbance and deposition of beds by giant waves in the Gulf of Mexico, point to Chicxulub as a major source of K/T boundary material, including a lower layer of clay at K/T boundary sites in western North America. The size, abundance, and mineral and lithic composition of shocked grains from an upper K/T boundary layer found at western North American sites, on the other hand, point to Manson as a possible source crater. More than one impact seems to be indicated by the K/T boundary stratigraphy in western North America, and present constraints on the age of the Manson structure suggest that it, as well as Chicxulub, may be a K/T boundary crater. Multiple craters produced over a relatively short interval of time are much more likely to have been formed by impact of comets rather than by impact of asteroids. Among likely mechanisms that could have produced multiple craters at or near the time of the K/T boundary are as follows: (1) splitting of a comet shortly before impact with Earth (impacts may have been spaced over about an hour), (2) fragmentation of a very large, Sun-grazing, periodic comet to form a compact stream of comets that intercepted the Earth's orbit (impacts may have been spread over about a century), and (3) perturbation of the Oort comet cloud by a passing massive object to form a comet shower in the inner solar system (impacts may have been spread over about a million years). Only in the first two cases are the impacts likely to have been close enough in time to contribute to the observed K/T boundary layers. All mechanisms could have produced many more than two craters.

Shoemaker, E. M.↗

NASA NTRS1993

Numerical study of the SSME nozzle flow fields during transient operations: A comparison of the animated results with test

A computational fluid dynamics (CFD) model has been applied to study the transient flow phenomena of the nozzle and exhaust plume of the Space Shuttle Main Engine (SSME), fired at sea level. The CFD model is a time accurate, pressure based, reactive flow solver. A six-species hydrogen/oxygen equilibrium chemistry is used to describe the chemical-thermodynamics. An adaptive upwinding scheme is employed for the spatial discretization, and a predictor, multiple corrector method is used for the temporal solution. Both engine start-up and shut-down processes were simulated. The elapse time is approximately five seconds for both cases. The computed results were animated and compared with the test. The images for the animation were created with PLOT3D and FAST and then animated with ABEKAS. The hysteresis effects, and the issues of free-shock separation, restricted-shock separation and the end-effects were addressed.

Wang, Ten-See↗

NASA NTRSDate not supplied

New Developments In NASA’s Entry Systems Modeling Project

This paper describes recent developments for modeling entry, descent, and landing (EDL)of spacecraft in support of NASA’s exploration missions. Mission-specific research and model development for entry systems occurs across the Agency (e.g., within flight programs like Artemis/Orion and Mars Sample Return), however the aim of this paper is to discuss the research conducted by NASA’s Entry Systems Modeling (ESM) Project, which serves as the Agency’s only effort dedicated to advancing modeling capabilities that cross-cut multiple technical disciplines, missions and destinations. The ESM portfolio is developed to address the specific needs expressed by a cross-section of NASA stakeholders, including flight and research projects, technical leadership, and subject matter experts. Technology development in ESM is organized and prioritized from a system-level perspective, resulting in four broad technical areas of investment: (1) Thermal Protection System (TPS) material modeling, (2) Shock layer kinetics and radiation, (3) Aerosciences, and (4) Guidance, navigation, and control. In addition to the core technical areas, special topics are rolled into the project portfolio as specific demands arise. Current special topics include TPS Certification by Analysis, improving understanding of woven TPS material performance; Hypersonic Wake Flows, assessing and improving predictions of base flows; and the MEDLI2 Deep Dive, furthering analysis of data obtained during Mars2020 mission’s entry and descent at Mars. Key results from each of these areas are presented in this paper, along with associated references to serve as a roadmap for other EDL researchers to access NASA’s publications.

Aaron M Brandis↗

NASA NTRS1989

Flux-vector splitting for unsteady calculations on dynamic meshes

The method of flux vector splitting used is that of Van Leer. The fluxes split in this manner have the advantage of being continuously differentiable at eigenvalue sign changes and this allows normal shocks to be captured with at most two interior zones, although in practice only one zone is usually observed. The fluxes as originally derived, however did not include the necessary terms appropriate for calculations on a dynamic mesh. The extension of the splitting to include these terms while retaining the advantages of the original splitting is the main purpose of this investigation. In addition, the use of multiple grids to reduce the computer time is investigated. A subiterative procedure to eliminate factorization and linearization error so that larger time steps can be used is also investigated.

Anderson, W. Kyle↗

NASA NTRS2013

Composite Aerogel Multifoil Protective Shielding

New technologies are needed to survive the temperatures, radiation, and hypervelocity particles that exploration spacecraft encounter. Multilayer insulations (MLIs) have been used on many spacecraft as thermal insulation. Other materials and composites have been used as micrometeorite shielding or radiation shielding. However, no material composite has been developed and employed as a combined thermal insulation, micrometeorite, and radiation shielding. By replacing the scrims that have been used to separate the foil layers in MLIs with various aerogels, and by using a variety of different metal foils, the overall protective performance of MLIs can be greatly expanded to act as thermal insulation, radiation shielding, and hypervelocity particle shielding. Aerogels are highly porous, low-density solids that are produced by the gelation of metal alkoxides and supercritical drying. Aerogels have been flown in NASA missions as a hypervelocity particle capture medium (Stardust) and as thermal insulation (2003 MER). Composite aerogel multifoil protective shielding would be used to provide thermal insulation, while also shielding spacecraft or components from radiation and hypervelocity particle impacts. Multiple layers of foil separated by aerogel would act as a thermal barrier by preventing the transport of heat energy through the composite. The silica aerogel would act as a convective and conductive thermal barrier, while the titania powder and metal foils would absorb and reflect the radiative heat. It would also capture small hypervelocity particles, such as micrometeorites, since it would be a stuffed, multi-shock Whipple shield. The metal foil layers would slow and break up the impacting particles, while the aerogel layers would convert the kinetic energy of the particles to thermal and mechanical energy and stop the particles.

Jones, Steven M.↗

NASA NTRS2016

On-orbit RNA Purification and qRT-PCR Capabilities of the WetLab-2 System

NASA Ames Research Center’s WetLab-2 system brings new capabilities to the ISS for researchers. The system can lyse cells and extract RNA on-orbit from different sample types ranging from microbial cultures to animal tissues. Our purification method has the advantage of using non-toxic chemicals and does not require alcohols or other organics. The purified RNA can then either be stabilized for return to Earth or can be used to conduct on-orbit quantitative Reverse Transcriptase PCR (qRT-PCR) analysis without the need for sample return. qRT-PCR reactions are performed by dispensing the RNA into reaction tubes that contain all lyophilized reagents needed to perform the analysis. The system uses a Cepheid® SmartCycler that allows for multiplexing of assays, this can be used to normalize for RNA concentration and integrity and to study multiple genes of interest in each tube. There are a total of 16 independent PCR modules each capable of detecting up to four fluorescent channels. The WetLab- 2 system can downlink data from the ISS to the ground after a completed run and uplink new thermal cycling programs. The ability to purify and stabilize RNA on-orbit can eliminate the confounding effects of reentry stresses and shock acting on live cells and organisms or the concern of RNA degradation of some samples. It also has the benefit of minimizing the needed downmass. Conducting qRT-PCR and generating results on-orbit is also an important step towards utilizing the ISS as a National Laboratory facility. Specifically, the ability to get on-orbit data will provide investigators with the opportunity to adjust experimental parameters in real time without the need for sample return and re-flight. On orbit gene expression analysis can also provide benchmarking prior to sample return. The system can also be used for analysis of air, surface, water, and clinical samples to monitor environmental pathogens and crew health. The validation flight of the WetLab-2 system using E. coli bacteria and mouse liver is scheduled to launch on SpaceX-8 this spring. Pending operations, the preliminary results from the validation flight will be presented. To support the needs of future researchers, we are adapting our system to purify RNA from two additional sample types: fibrous tissue such as muscle and mammalian adherent cells grown on alginate beads. Progress of this work will also be presented. The WetLab-2 Project is supported by the Research Integration Office in the ISS Program.

Parra, Macarena↗