NASA Research Park

Abstract Winter body condition is an important driver of survival, reproductive output, and overall population health in waterfowl. Diving duck species use distinct habitats, exploit unique resources, and can collectively provide an integrated index of winter habitat quality. The San Francisco Bay (SFB) is the largest estuary on the west coast of North America, serving as critical wintering habitat for diving ducks in the Pacific Flyway. To evaluate the body condition of diving ducks after multiple decades of tidal habitat restoration in SFB, we compared structurally corrected measurements (annual and decadal) of total carcass lipid among canvasback ( Aythya valisineria ), greater scaup ( Aythya marila ), lesser scaup ( Aythya affinis ), and ruddy duck ( Oxyura jamaicensis ). We found greater and lesser scaup gained lipid reserves within the estuary prior to spring migration; however, canvasback and ruddy duck lipid levels declined throughout the winter and into the spring. Lipid loss over the wintering period could indicate a reduction in foraging resource availability, dietary shifts, or metabolic changes. These deficiencies could have negative cross‐seasonal implications, as these species must accumulate resources outside of their wintering areas to fuel migration and reproduction. Lipid levels were elevated in lesser scaup collected in 2017‐2019 compared to 1998‐2000, while we found no decadal differences in lipid levels for canvasback or greater scaup. Our findings suggest tidal restoration in SFB, among other factors, may benefit some diving duck species.

ABSTRACT Synchrotron radiation from the reverse- and forward-shock regions typically describes the evolution of temporal and spectral features given by the closure relations (CRs) during the late and long-/short-lasting emission in the afterglow phase of gamma-ray bursts (GRBs). Although synchrotron photons are restricted to keV and a few MeV energies, the synchrotron self-Compton (SSC) mechanism can disperse them above hundreds of MeV energies. We present the CRs of the SSC process radiated from the reverse-shock region for the case of a thick and thin shell, considering that the reverse shock lies in the adiabatic regime and evolves in an environment with a homogeneous and stratified medium. We analyse these CRs with the spectral and temporal characteristics of the bursts described in the second Fermi-LAT GRB catalogue (2FLGC) and found that (i) the thin shell case is preferred over a thick shell and a constant-density medium over a stellar-wind environment, (ii) bursts with an atypical and hard spectral index could be successfully described by this scenario in different cooling conditions, (iii) the early optical flash and GeV emission exhibited in GRB 160625B and 180720B were generated from the same accelerated region and electron population, concluding that LAT emission originated during the early afterglow, and (iv) the maximum synchrotron energy radiated from the reverse-shock scenario could explain only a few photons with the exception of a pair of bursts, so that scattered photons by the SSC process must be required.

Abstract We present an augmentation to long-standing evidence from observations and MHD modeling that (1) every solar emerging bipolar magnetic region (BMR) is made by an emerging Ω-loop flux rope, and (2) a twist in the flux-rope field makes the emerged field sigmoidal. Using cotemporal full-disk coronal EUV images, magnetograms, and continuum images from the Solar Dynamics Observatory (SDO), we found and tracked the emergence of 42 emerging single-BMR sigmoidal active regions (ARs) that have sunspots in both polarity domains. Throughout each AR’s emergence, we quantified the emerging BMR’s tilt angle to the east–west direction (the x-direction in SDO images) by measuring in the continuum images the tilt angle of the line through the (visually located) two centroids of the BMR’s opposite-polarity sunspot clusters. As each AR emerges, it becomes either S-shaped (shows net right-handed magnetic twist) or Z-shaped (shows net left-handed magnetic twist) in the coronal EUV images. Nineteen of the ARs become S-shaped, and 23 become Z-shaped. For all 42 ARs, in agreement with published MHD simulations of the emergence of a single-BMR sigmoidal AR from a subsurface twisted flux rope, if the AR becomes S-shaped, the emerging BMR pivots counterclockwise, and if the AR becomes Z-shaped, the emerging BMR pivots clockwise. For our 42 ARs, the pivot amount roughly ranges from 10° to 90° and averages about 35°. Thus, at the onset of the emergence of our average emerging Ω-loop flux rope, the magnetic field’s twist pitch angle at the flux rope’s top edge is plausibly about 35°.

Keto-enol tautomerism plays a very important role in pyruvate chemistry and metabolic transformations. The enol form of pyruvate is thermodynamically much less stable, and its tautomerization to the keto form is one of the strongly favored energetic single rearrangements, endowing phosphoenolpyruvate as one of the most potent phosphate donors in biology. In this work, we report the keto-enol rearrangement of pyruvate and pyruvate-derived compounds, such as zymomate, using high-quality density functional theory for the gas phase and molecular dynamics methods for the aqueous phase. Our results indicate a preference for the keto tautomer of pyruvic acid and pyruvate both in the gas as well as in the aqueous phase. Zymonic acid prefers to be in the enol form in gas as well as in an aqueous medium. Tautomerization contributes approximately 42% of the energetic driving force in the hydrolysis of phosphenol pyruvate. Keto tautomer of zymonate, however, is lower in energy in the gas phase, while the enol tautomer, due to its strong solvation free energy, is lower in energy in the aqueous phase. The results of our work are also discussed in the context of astrobiology, where we explore how fundamental carbonyl chemistry such as keto-enol tautomerization reactions may have influenced the selection of phosphoenolpyruvate. We propose a scenario for how the emergence of PEP might have taken place through a process of chemical evolution originating from a wider variety of possible enol phosphates operating within a proto-metabolism.

Abstract Functional Hazard Assessment (FHA) is a key early-stage engineering process that supports the incorporation of safety in design by identifying the high-level functional hazards the system may encounter. Functional Hazard Assessment is often supported by models of system functionality that abstract system behavior at a functional level. However, diagramming languages and conventions used to create these abstractions are limited in what types of behavior they can coherently represent--often leaving out or misrepresenting the key behavioral interactions that cause hazardous conditions to propagate from one function to another. To resolve these limitations, this paper introduces the Functional Reasoning Design Language (FRDL), a formal modelling language for describing the functional elements of a system and their behavioral interactions. To demonstrate the use of FRDL, an autonomous rover system is analyzed using FRDL along with a traditional Failure/Fault Analyses Procedure to show how FRDL can improve understanding of hazardous behavior. The results of this demonstration highlight the potential for FRDL's more rigorous representation of system function to improve the hazard analysis process.

ABSTRACTDetermining strength to hardness correlation coefficients on nano and microscale in correspondence to microstructure and composition leads the way to inexpensive, non‐destructive ways to predict tensile strength of bulk materials, which is important for developing preventive maintenance procedures in a variety of industries. Nanohardness and microhardness tests were performed on an in‐house prepared eutectic SnBi alloy. Elemental composition and eutectic morphology were verified by scanning electron microscopy and energy dispersive spectroscopy. The linear correlation coefficient, C1 = HIT/Hv, between nanoindentation hardness and Vickers microhardness was determined based on experimental measurements. A value of C1 > 1.25 was obtained, exceeding the expected value for polycrystalline alloys C1 = 1.25. The Tabor factor, k = Hv/σ at 8% strain, is well known to be about 3 for polycrystalline alloys. However, for the eutectic alloy, the estimated Tabor factor was consistently greater than 3. The stronger correlation in both cases suggests the presence of an unaccounted factor contributing to both C1 and k. Comparison to coefficients estimated from data available for other alloy systems is discussed.

The middle and upper atmosphere plays a critical role in linking the lower atmosphere forcing with ionospheric variability, especially during strong atmospheric activities. This study examines the dynamical response in the altitude range from ~20-80 km to a major Sudden Stratospheric Warming (SSW) event peaking on February 11, 2018. We compare the reanalysis product of the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) from the Goddard Earth Observing System (GEOS) to the satellite observations by Thermosphere Ionosphere and Mesosphere Electric Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry TIMED/SABER that are not assimilated in MERRA-2. Our study shows that the zonal mean wind and temperature and planetary wave 1 and 2 variations are generally consistent between the reanalysis and observations. We also identify a strong ~6-day wave propagating both westward and eastward with zonal wavenumber-1 with the westward propagating component likely generated by baroclinic/barotropic instability. However, important disagreements arise specifically above ~60 km, where the wind and temperature are not well represented in MERRA-2, causing differences in the day-to-day development of 6-day wave. This study highlights the need for additional assimilation of mesospheric data and development of high-altitude vertically extended GEOS model.

Magnetic reconnection on the dayside magnetopause is considered the primary mechanism for transporting mass, momentum, and energy from the solar wind into the terrestrial magnetosphere. Several studies have demonstrated that the spatiotemporal dynamics of the dayside magnetic reconnection can be inferred remotely from the analysis of the time-energy dispersion of ions in the Earth’s cusps. Despite the immense number of in-situ cusp measurements acquired by numerous space-based instruments, it is still challenging to determine the overall cusp behavior owing to the intermittency of the measurement acquisition. To overcome this issue, this work implements a regression model of the three-dimensional (3-D) ion flux in the Earth’s Northern cusp based on deep learning techniques and numerous measurements of the cusp under varying solar wind conditions. For the training process, we have used solar wind parameters obtained from NASA's OMNI database as input and in-situ ion flux measurements acquired by the CIS/HIA instruments on board ESA’s multi-spacecraft Cluster mission during the period from 2001 to 2010 for supervised output. The model allows the reconstruction of the time-dependent, 3-D ion flux distribution within the cusp region, which serves to determine the boundaries of the high-altitude cusp, analyze its structural response to time-dependent solar wind conditions, and investigate the relationship between the cusp and dayside magnetic reconnection. The experiments under controlled input parameters show that our model is capable of reproducing  expected ion dispersion signatures as a response to variable solar wind conditions.