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All sources NASA NTRS DOE OSTI

DOE OSTI2016

Complex fracture nucleation and evolution with nonlocal elastodynamics

In this study, a mechanical model is introduced for predicting the initiation and evolution of complex fracture patterns without the need for damage variable or law. The model, a continuum variant of Newton's second law, uses integral rather than partial differential operators where the region of integration is over finite domain. The force interaction is derived from a novel nonconvex strain energy density function, resulting in a nonmonotomic material model. The resulting equation of motion is proved to be mathematically well-posed. The model has the capacity to simulate nucleation and growth of multiple, mutually interacting dynamic fractures. In the limit of zero region of integration, the model reproduces the classic Griffith model of brittle fracture. The simplicity of the formulation avoids the need for supplemental kinetic relations that dictate crack growth or the need for an explicit damage evolution law.

36 MATERIALS SCIENCE↗

DOE OSTI2016

MODELING THE SOLAR WIND AT THE ULYSSES , VOYAGER , AND NEW HORIZONS SPACECRAFT

The outer heliosphere is a dynamic region shaped largely by the interaction between the solar wind and the interstellar medium. While interplanetary magnetic field and plasma observations by the Voyager spacecraft have significantly improved our understanding of this vast region, modeling the outer heliosphere still remains a challenge. We simulate the three-dimensional, time-dependent solar wind flow from 1 to 80 astronomical units (au), where the solar wind is assumed to be supersonic, using a two-fluid model in which protons and interstellar neutral hydrogen atoms are treated as separate fluids. We use 1 day averages of the solar wind parameters from the OMNI data set as inner boundary conditions to reproduce time-dependent effects in a simplified manner which involves interpolation in both space and time. Our model generally agrees with Ulysses data in the inner heliosphere and Voyager data in the outer heliosphere. Ultimately, we present the model solar wind parameters extracted along the trajectory of the New Horizons spacecraft. We compare our results with in situ plasma data taken between 11 and 33 au and at the closest approach to Pluto on 2015 July 14.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1971

Some experimental observations on circulating currents in a crossed field plasma accelerator

Experiments on a thermally ionized argon plasma suggest that applying a Lorentz force by means of orthogonal electric and magnetic fields to an electrically conducting fluid flow imposes necessary but not sufficient conditions for acceleration. There are, in fact, many combinations of current and magnetic field which cause decelerations of the fluid. The deceleration arises from a retarding force which may be larger than the applied Lorentz force. The retarding force causing the deceleration is a consequence of currents circulating completely within the fluid. These currents arise from differences in velocity between the central and wall regions of the duct which interact with the imposed magnetic field to produce differences in induced voltages. The observed physical effects of the circulating currents cause a loss in velocity in the central region of the duct, an increase in thermal energy in the sidewall region, and little change in thermal energy near the electrode wall region. For similar velocity profiles, the adverse effects appear to be related to the product of electrical conductivity and velocity, and performance as an accelerator appears to be controlled by the Hoffman loading parameter (i.e., the ratio of the applied to the induced currents).

Jedlicka, J.↗

DOE OSTI2016

OBSERVATIONS OF THE GROWTH OF AN ACTIVE REGION FILAMENT

We present observations of the growth of an active region filament caused by magnetic interactions among the filament and its adjacent superpenumbral filament (SF) and dark thread-like structures (T). Multistep reconnections are identified during the whole growing process. Magnetic flux convergence and cancellation occurring at the positive footpoint region of the filament is the first step reconnection, which resulted in the filament bifurcating into two sets of intertwined threads. One set anchored in situ, while the other set moved toward and interacted with the SF and part of T. This indicates the second step reconnection, which gave rise to the disappearance of the SF and the formation of a long thread-like structure that connects the far ends of the filament and T. The long thread-like structure further interacted with the T and then separated into two parts, representing the third step reconnection. Finally, another similar long thread-like structure, which intertwined with the fixed filament threads, appeared. H {sub α} observations show that this twisted structure is a longer sinistral filament. Based on the observed photospheric vector magnetograms, we performed a non-linear force-free field extrapolation to reconstruct the magnetic fields above the photosphere and found that the coronal magnetic field lines associated with the filament consists of two twisted flux ropes winding around each other. These results suggest that magnetic interactions among filaments and their adjacent SFs and T could lead to the growth of the filaments, and the filament is probably supported in a flux rope.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Strongly-coupled quantum critical point in an all-in-all-out antiferromagnet

Dimensionality and symmetry play deterministic roles in the laws of Nature. They are important tools to characterize and understand quantum phase transitions, especially in the limit of strong correlations between spin, orbit, charge, and structural degrees of freedom. Using newly-developed, high-pressure resonant x-ray magnetic and charge diffraction techniques, we have discovered a quantum critical point in Cd 2 Os 2 O 7 as the all-in-all-out antiferromagnetic order is continuously suppressed to zero temperature and, concomitantly, the cubic lattice structure continuously changes from space group Fd-3m to F-43m. Surrounded by three phases of different time reversal and spatial inversion symmetries, the quantum critical region anchors two phase lines of opposite curvature, with striking departures from a mean-field form at high pressure. As spin fluctuations, lattice breathing modes, and quasiparticle excitations interact in the quantum critical region, we argue that they present the necessary components for strongly-coupled quantum criticality in this three-dimensional compound.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Local hybrid functionals with orbital-free mixing functions and balanced elimination of self-interaction error

The recently introduced density overlap regions indicator (DORI) [P. de Silva and C. Corminboeuf, J. Chem. Theory Comput. 10(9), 3745–3756 (2014)] is a density-dependent scalar field revealing regions of high density overlap between shells, atoms, and molecules. In this work, we exploit its properties to construct local hybrid exchange-correlation functionals aiming at balanced reduction of the self-interaction error. We show that DORI can successfully replace the ratio of the von Weizsäcker and exact positive-definite kinetic energy densities, which is commonly used in mixing functions of local hybrids. Additionally, we introduce several semi-empirical parameters to control the local and global admixture of exact exchange. The most promising of our local hybrids clearly outperforms the underlying semi-local functionals as well as their global hybrids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

A combined theoretical-experimental study of interactions between vanadium ions and Nafion membrane in all-vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) are a promising solution for large-scale energy storage, but a number of problems still impede the deployment of long-lifetime VRFBs. One important aspect of efficient operation of VRFBs is understanding interactions between vanadium species and the membrane. Herein, we investigate the interactions between all four vanadium cations and Nafion membrane by a combination of infrared (IR) spectroscopy and density-functional-theory (DFT)-based static and molecular dynamics simulations. It is observed that vanadium species primarily lead to changes in the IR spectrum of Nafion in the SO 3 - spectral region which is attributed to the interaction between vanadium species and the SO 3 - exchange sites. DFT calculations of vanadium - Nafion complexes in the gas phase show that it is thermodynamically favorable for all vanadium cations to bind to SO 3 - via a contact pair mechanism. Car-Parrinello molecular dynamics-based metadynamics simulations of cation-Nafion systems in aqueous solution suggest that and species coordinate spontaneously to SO 3 - , which is not the case for VO 2+ and VO 2 + . The interaction behavior of the uncycled membrane determined in this study is used to explain the experimentally observed changes in the vibrational spectra, and is discussed in light of previous results on device-cycled membranes.

00-01↗

DOE OSTI2023

Structural insights into the unique recognition module between α-synuclein peptide and nanobody

Nanobodies are single-domain fragments of antibodies with comparable specificity and affinity to antibodies. They are emerging as versatile tools in biology due to their relatively small size. Here, we report the crystal structure of a specific nanobody Nbα-syn01, bound to a 14 amino acid long peptide of α-synuclein (αSyn), a 140-residue protein whose aggregation is associated with Parkinson's disease. The complex structure exhibits a unique binding pattern where the αSyn peptide replaces the N-terminal region of nanobody. Recognition is mediated principally by extended main chain interaction of the αSyn peptide and specificity of the interaction lies in the central 48–52 region of αSyn peptide. Structure-guided truncation of Nbα-syn01 shows tighter binding to αSyn peptide and improved inhibition of α-synuclein aggregation. The structure of the truncated complex was subsequently determined and was indistinguishable to full length complex as the full-length form had no visible electron density for the N-terminal end. These findings reveal the molecular basis for a previously unobserved binding mode for nanobody recognition of α-synuclein, providing an explanation for the enhanced binding, and potential for an alternate framework for structure-based protein engineering of nanobodies to develop better diagnostic and therapeutic tools.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2015

SEMICIRCULAR-LIKE SECONDARY FLARE RIBBONS ASSOCIATED WITH A FAILED ERUPTION

Flare ribbons (FRs) are one of the most apparent signatures of solar flares and have been treated as an indicator of magnetic reconnection. Drawing upon the observations from the Solar Dynamics Observatory, we present semicircular-like secondary FRs (SFRs) of a C2.3 flare on 2013 June 19. Before the flare eruption, two bipoles in this core region subsequently emerged. Due to the interaction between the two bipoles, a tether-cutting eruption took place in the core region. The SFRs, surrounding the core region nearly simultaneously with the flare onset, were much weaker than the two normal FRs. Two ends of the SFRs experienced a separation and extension movement, but the middle part of the SFRs hardly expanded outward. We find SFRs are closely associated with the footpoint brightenings of some small loops around the core region. The eruption was confined by transequatorial loops (TLs), which resulted in the plasma material falling in the north end of the TLs and remote brightenings showing up in the south end of the TLs. The disappearance of the faint (filament) material during the emergence of the SFRs could indicate another eruption. We conclude that two or more magnetic reconnections are involved in this event and propose that SFRs consisting of a small part of true FRs resulted from the second magnetic reconnection and bright footpoints of loop clusters likely heated by the main flare.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1985

Size distributions of air showers accompanied with high energy gamma ray bundles observed at Mt. Chacaltaya

Size distributions of air showers accompanied with bundle of high energy gamma rays and/or large size bursts under emulsion chambers, to study the composition of primary cosmic rays and also characteristics of high energy nuclear interaction. Air showers initiated by particles with a large cross section of interaction may develop from narrow region of the atmosphere near the top. Starting levels of air showers by particles with smaller cross section fluctuate in wider region of the atmosphere. Air showers of extremely small size accompanied with bundle of gamma rays may be ones initiated by protons at lower level after penetrating deep atmosphere without interaction. It is determined that the relative size distribution according to the total energy of bundle of gamma rays and the total burst size observed under 15 cm lead absorber.

Matano, T.↗

DOE OSTI2015

In situ optical diagnostic for monitoring or control of sodium diffusion in photovoltaics manufacturing

A method of fabricating a photovoltaic device 100, includes the steps of providing a glass substrate 102, depositing a molybdenum layer 104 on a surface of the glass substrate, directing light through the glass substrate to the near-substrate region of the molybdenum layer 206, detecting an optical property of the near-substrate region of the molybdenum layer after interaction with the incident light 208 and determining a density of the near-substrate region of the molybdenum layer from the detected optical property 210. A molybdenum deposition parameter may be controlled based upon the determined density of the near-substrate region of the molybdenum layer 218. A non-contact method measures a density of the near-substrate region of a molybdenum layer and a deposition chamber 300.

14 SOLAR ENERGY↗

DOE OSTI2026

Southern Ocean Sulfate Aerosol Sources Quantified From Sulfur Isotopes in Antarctic Ice Cores

The Southern Ocean has emerged as a key region for constraining aerosol-climate interactions due to its relatively low anthropogenic influence. Sulfate is an important aerosol over the Southern Ocean, and models suggest dimethyl sulfide (DMS) is the largest source of sulfate during summer. However, sulfur isotopes of sulfate (δ 34 S(SO 4 2− )) in Antarctic ice cores suggest a significant contribution from a previously unexplained non-DMS source. Here we show that the fractional contribution from passive volcanic degassing (f volc ) explains observed δ 34 S(SO 4 2− ), and that a global chemical transport model underestimates f volc across Antarctica. Underestimated f volc implies that the model mischaracterizes sulfate sources in this important region. The discrepancy between observed and modeled sulfate sources can be reconciled by increasing passive volcanic sulfur degassing emissions and decreasing DMS emissions. Our results imply that current biases in emissions inventories could bias assessments of aerosol-cloud interactions in the Southern Ocean region and globally.

Jongebloed, Ursula A. [Univ. of Washington, Seattl↗

DOE OSTI2023

Glutamine-rich regions of the disordered CREB transactivation domain mediate dynamic intra- and intermolecular interactions

The cyclic AMP response element (CRE) binding protein (CREB) is a transcription factor that contains a 280-residue N-terminal transactivation domain and a basic leucine zipper that mediates interaction with DNA. The transactivation domain comprises three subdomains, the glutamine-rich domains Q1 and Q2 and the kinase inducible activation domain (KID). NMR chemical shifts show that the isolated subdomains are intrinsically disordered but have a propensity to populate local elements of secondary structure. The Q1 and Q2 domains exhibit a propensity for formation of short β-hairpin motifs that function as binding sites for glutamine-rich sequences. These motifs mediate intramolecular interactions between the CREB Q1 and Q2 domains as well as intermolecular interactions with the glutamine-rich Q1 domain of the TATA-box binding protein associated factor 4 (TAF4) subunit of transcription factor IID (TFIID). Using small-angle X-ray scattering, NMR, and single-molecule Förster resonance energy transfer, we show that the Q1, Q2, and KID regions remain dynamically disordered in a full-length CREB transactivation domain (CREB TAD ) construct. The CREB TAD polypeptide chain is largely extended although some compaction is evident in the KID and Q2 domains. Paramagnetic relaxation enhancement reveals transient long-range contacts both within and between the Q1 and Q2 domains while the intervening KID domain is largely devoid of intramolecular interactions. Phosphorylation results in expansion of the KID domain, presumably making it more accessible for binding the CBP/p300 transcriptional coactivators. In conclusion, our study reveals the complex nature of the interactions within the intrinsically disordered transactivation domain of CREB and provides molecular-level insights into dynamic and transient interactions mediated by the glutamine-rich domains.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2016

Effect of Pressure Gradients on the Initiation of PBX-9502 via Irregular (Mach) Reflection of Low Pressure Curved Shock Waves

In the instance of multiple fragment impact on cased explosive, isolated curved shocks are generated in the explosive. These curved shocks propagate and may interact and form irregular or Mach reflections along the interaction loci, thereby producing a single shock that may be sufficient to initiate PBX-9501. However, the incident shocks are divergent and their intensity generally decreases as they expand, and the regions behind the Mach stem interaction loci are generally unsupported and allow release waves to rapidly affect the flow. The effects of release waves and divergent shocks may be considered theoretically through a “Shock Change Equation”.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗

DOE OSTI2022

On the new universality class in structurally disordered n -vector model with long-range interactions

We study a stability boundary of a region where nontrivial critical behavior of an n-vector model with long-range power-law decaying interactions is induced by the presence of a structural disorder (e.g., weak quenched dilution). This boundary is given by the marginal dimension of the order parameter nc dependent on space dimension, d, and a control parameter of the interaction decay, σ, below which the model belongs to the new dilution-induced universality class. Exploiting the Harris criterion and recent field theoretical renormalization group results for the pure model with long-range interactions, we get nc as a three loop ɛ = 2σ – d-expansion. We provide numerical values for nc applying series resummation methods. Our results show that not only the Ising systems (n = 1) can belong to the new disorder-induced long-range universality class at d = 2 and 3.

Physics↗

DOE OSTI2013

The Regional Nature of Global Challenges. A Need and Strategy for Integrated Regional Modeling

In this paper, we explore the regional nature of global environmental challenges. We take a broad approach by examining the scientific foundation that is needed to support policy and decision making and identifying some of the most important barriers to progress that are truly scale-dependent. In so doing, we hope to show that understanding global environmental changes requires understanding a number of intrinsically regional phenomena, and that successful decision making likewise requires an integrated approach that accounts for a variety of regional Earth system processes—which we define to include both human activities and environmental systems that operate or interact primarily at sub-continental scales. Understanding regional processes and phenomena, including regional decision-making processes and information needs, should thus be an integral part of the global change research agenda. To address some of the key issues and challenges, we propose an integrated regional modeling approach that accounts for the dynamic interactions among physical, ecological, biogeochemical, and human processes and provides relevant information to regional decision makers and stakeholders.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1990

Modelling of E-region auroral winds

A numerical code, describing the interactions between chemistry and dynamics in the coupled thermosphere and ionosphere systems, has been used to investigate the morphology of wind systems of the auroral E-region and, in particular, their response to geomagnetic forcing. The structure and dynamics of both the thermosphere and the ionosphere show very strong interactions at all levels of geomagnetic disturbance. By comparison, other perturbations, particularly those resulting from tidal and gravity wave sources within the lower atmosphere, which are important and easily identified during quiet periods, are always overwhelmed by the magnitude of the effects of large geomagnetic disturbances above about 110 km altitude. The model simulations will be used to characterize the geomagnetic response of the E-region neutral wind, temperature, and composition in different parts of the polar cap and the auroral oval, and the major changes resulting from seasonal variations.

Rees, David↗

NASA NTRS2023

Analysis of VFR Traffic Uncertainty and its Impact on Uncrewed Aircraft Operational Capacity at Regional Airports

This paper proposes a method to characterize Visual Flight Rules traffic around a regional airport. The applicability of the method is discussed in the context of Uncrewed Aircraft operations at a regional airport. The relation between traffic interaction uncertainty and operational capacity at the runway is also investigated. The spatio-temporal distribution of traffic operating under Visual Flight Rules is analyzed from historical track data and visualized as heat maps generated at different altitudes. These are used to characterize the spatio-temporal uncertainty associated with traffic density, around a given airport, down to the runway. The traffic patterns at the runway are used to compute the runway capacity as a function of the probability of interaction with traffic operating under visual flight rules. Fort Worth Alliance is used as a representative regional airport for the study. Applications of the traffic characterization methods developed in this paper are also discussed.

VFR traffic, uncertainty, air mobility↗