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At least 163 records · Page 9

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NASA NTRS1998

Global MHD Simulations of the Substorm Current Wedge and Dipolarization

This paper presents results from global MHD simulations showing the evolution of the plasma and field in the near-Earth tail during the substorm phases. The late growth phase is characterized by pronounced thinning of the plasma sheet and stretching of the field in the region between approximately -6 R(sub E) to -30 R(sub E). A pre-existing X-line moves tailward to beyond -50 R(sub E). Close to onset, a new X-line forms near -18 R(sub E) in the midnight sector. Earthward flows emanating from this X-line dipolarize the near-Earth field, leading to a reduction of the cross-tail current in the midnight sector, but not elsewhere. The magnetic shear between the dipolarized field near midnight and the stretched field elsewhere is equivalent to currents flowing through the ionosphere in a region I sense, and so forming the current wedge. Later in the expansion phase, the dipolarization spreads in local time at a rate of about 0.3 hours MLT per minute. A strong electric field and a rapid increase of the plasma pressure is associated with the dipolarization. Near midnight the dipolarization appears to occur at all distances between 6.6 and 13 R(sub E) at the same time within the resolution (+/- 2 min) of our model. However, the model results indicate that dipolarization starts before ground onset in the pre-midnight sector and propagates both earthward and eastward.THus, dipolarization may be much more complex than simple earthward/tailward and/or azimuthal expansion.

Raeder, J.↗

DOE OSTI2024

Stochastic modal velocity field in rough-wall turbulence

Stochastically generated instantaneous velocity profiles are used to reproduce the outer region of rough-wall turbulent boundary layers in a range of Reynolds numbers extending from the wind tunnel to field conditions. Each profile consists in a sequence of steps, defined by the modal velocities and representing uniform momentum zones (UMZs), separated by velocity jumps representing the internal shear layers. Height-dependent UMZ is described by a minimal set of attributes: thickness, mid-height elevation, and streamwise (modal) and vertical velocities. These are informed by experimental observations and reproducing the statistical behaviour of rough-wall turbulence and attached eddy scaling, consistent with the corresponding experimental datasets. Sets of independently generated profiles are reorganized in the streamwise direction to form a spatially consistent modal velocity field, starting from any randomly selected profile. The operation allows one to stretch or compress the velocity field in space, increases the size of the domain and adjusts the size of the largest emerging structures to the Reynolds number of the simulated flow. By imposing the autocorrelation function of the modal velocity field to be anchored on the experimental measurements, we obtain a physically based spatial resolution, which is employed in the computation of the velocity spectrum, and second-order structure functions. The results reproduce the Kolmogorov inertial range extending from the UMZ and their attached-eddy vertical organization to the very-large-scale motions (VLSMs) introduced with the reordering process. The dynamic role of VLSM is confirmed in the –u'w' co-spectra and in their vertical derivative, representing a scale-dependent pressure gradient contribution.

42 ENGINEERING↗

DOE OSTI2022

Mapping periplasmic binding protein oligosaccharide recognition with neutron crystallography

Numerous studies have shown how periplasmic binding proteins (PBPs) bind substrates with exquisite specificity, even distinguishing between sugar epimers and anomers, or structurally similar ions. Yet, marked substrate promiscuity is also a feature encoded in some PBPs. Except for three sub-Ångström crystal structures, there are no reports of hydrogen atom positions in the remaining (> 1000) PBP structures. The previous X-ray crystal structure of the maltodextrin periplasmic-binding protein from Thermotoga maritima (tmMBP) complexed with oligosaccharide showed a large network of interconnected water molecules stretching from one end of the substrate binding pocket to the other. These water molecules are positioned to form multiple hydrogen bonds, as well as forming interactions between the protein and substrate. Here we present the neutron crystal structure of tmMBP to a resolution of 2.1 Å. This is the first neutron crystal structure from the PBP superfamily and here we unambiguously identify the nature and orientation of the hydrogen bonding and water-mediated interactions involved in stabilizing a tetrasaccharide in the binding site. More broadly, these results demonstrate the conserved intricate mechanisms that underlie substrate-specificity and affinity in PBPs.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

Vibrational Spectroscopic Monitoring of the Gelation Transition in Nafion Ionomer Dispersions

Infrared and Raman spectroscopy techniques were applied to investigate the drying and aggregation behavior of Nafion ionomer particles dispersed in aqueous solution. Gravimetric measurements aided the identification of gel-phase development within a series of time-resolved spectra that tracked transformations of a dispersion sample during solvent evaporation. A spectral band characteristic of ionomer sidechain end group vibration provided a quantitative probe of the dispersion-to-gel change. For sets of attenuated total reflection Fourier transform infrared (ATR FT-IR) spectra, adherence to Beer's law was attributed to the relatively constant refractive index in the frequency region of hydrated –SO$^{–}_{3}$ group vibrations as fluorocarbon-rich ionomer regions aggregate in forming the structural framework of membranes and thin films. Although vibrational bands associated with ionomer backbone CF 2 stretching vibrations were affected by distortion characteristic of wavelength-dependent refractive index change within a sample, the onset of band distortion signaled gel formation and coincided with ionomer mass % values just below the critical gelation point for Nafion aqueous dispersions. Similar temporal behavior was observed in confocal Raman microscopy experiments that monitored the formation of a thin ionomer film from an individual dispersion droplet. For the ATR FT-IR spectroscopy and confocal Raman microscopy techniques, intensity in the water H–O–H bending vibrational band dropped sharply at the ionomer critical gelation point and displayed a time dependence consistent with changes in water content derived from gravimetric measurements. The reported studies lay groundwork for examining the impact of dispersing solvents and above-ambient temperatures on fluorinated ionomer transformations that influence structural properties of dispersion-cast membranes and thin films.

36 MATERIALS SCIENCE↗

NASA NTRS1991

On the state of the emitter of the 3.3 micron unidentified infrared band - Absorption spectroscopy of polycyclic aromatic hydrocarbon species

Results of absorption measurements indicate that the PAH species responsible for the UIR (unidentified infrared) emission probably exist in a condensed form rather than as isolated molecules. It is shown that the peak absorption of the C-H stretch feature of vapor-phase PAHs occurs at a higher frequency than that of the condensed-phase PAHs and does not match the 3.289-micron interstellar feature. The vapor-phase experiments duplicate the phenomenon of the 3.3-micron profile simplification of PAH in KBr at elevated temperature. This confirms that the change of the profile with temperature is an intrinsic molecular effect, and is not a consequence of matrix (KBr) or condensed state interactions.

Flickinger, Gregory C.↗

NASA NTRS1993

Cellulose triacetate, thin film dielectric capacitor

Very thin films of cellulose triacetate are cast from a solution containing a small amount of high boiling temperature, non-solvent which evaporates last and lifts the film from the casting surface. Stretched, oriented, crystallized films have high electrical breakdown properties. Metallized films less than about 2 microns in thickness form self-healing electrodes for high energy density, pulsed power capacitors. Thicker films can be utilized as a dielectric for a capacitor.

Yen, Shiao-Ping S.↗

NASA NTRS1995

Cellulose triacetate, thin film dielectric capacitor

Yen, Shiao-Ping S.↗

NASA NTRS2003

The Conductance of Nanotubes Deformed by the AFM Tip

The conductance drop under AFM-tip deformation can be explained by stretching of the tube length. NT sensors can be built utilizing uniform stretching. Single sp3 bond cross section cannot block electrons, because another conducting path may exist. AFM tip which forms sp3 bonds with the tube will decrease conductance. In the "table experiment" a conductance drop of 2 orders of magnitude happened only after some bonds were broken.

Svizhenko, Alexei↗

NASA NTRS2015

Cauchy Drag Estimation For Low Earth Orbiters

Recent work on minimum variances estimators based on Cauchy distributions appear relevant to orbital drag estimation. Samples form Cauchy distributions which are part of a class of heavy-tailed distributions, are characterized by long stretches of fairly small variation, punctuated by large variations that are many times larger than could be expected from a Gaussian. Such behavior can occur when solar storms perturb the atmosphere. In this context, the present work describes an embedding of the scalar Idan-Speyer Cauchy Estimator to estimate density corrections, within an Extended Kalman Filter that estimates the state of a low Earth orbiter. In contrast to the baseline Kalman approach, the larger formal errors of the present approach fully and conservatively bound the predictive error distribution, even in the face of unanticipated density disturbances of hundreds of percent.

Low Earth↗

DOE OSTI2021

Establishment of FXS-A9 panel with a single human X chromosome from fragile X syndrome-associated individual

Highlights: • We established mouse A9 cells with human X chromosome from FXS carrier and patient. • FXS-associated CGG repeats were stably maintained in established rodent cells. • Epigenetic status of CGG repeat region were maintained in established rodent cells. • Human FMR1 expression in these cells was according to each CGG repeat length. Fragile X syndrome (FXS) is the most common inheritable form of intellectual disability. FMR1, the gene responsible for FXS, is located on human chromosome Xq27.3 and contains a stretch of CGG trinucleotide repeats in its 5′ untranslated region. FXS is caused by CGG repeats that expand beyond 200, resulting in FMR1 silencing via promoter hypermethylation. The molecular mechanism underlying CGG repeat expansion, a fundamental cause of FXS, remains poorly understood, partly due to a lack of experimental systems. Accumulated evidence indicates that the large chromosomal region flanking a CGG repeat is critical for repeat dynamics. In the present study, we isolated and introduced whole human X chromosomes from healthy, FXS premutation carriers, or FXS patients who carried disease condition-associated CGG repeat lengths, into mouse A9 cells via microcell-mediated chromosome transfer. The CGG repeat length-associated methylation status and human FMR1 expression in these monochromosomal hybrid cells mimicked those in humans. Thus, this set of A9 cells containing CGG repeats from three different origins (FXS-A9 panel) may provide a valuable resource for investigating a series of genetic and epigenetic CGG repeat dynamics during FXS pathogenesis.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1990

Three-dimensional driven reconnection in magnetic loops

A numerical study of reconnection in a three-dimensional axially bounded magnetic flux tube is presented. An axial magnetic field is embedded in a conducting fluid, between conducting end plates. An applied flow in the end plates causes distortion and stretching of the magnetic field in the flux tube, and the creation of current sheets. After the current sheets form, the reconnection rate is fast; with a merging rate M of about 1. The reconnection mechanism resembles flux pileup in two dimensions. It is also similar to the nonlinear behavior of a subcritically excited current-driven MHD mode. The numerical model is relevant to a mechanism thought to be important for heating the solar corona, as well as producing solar flares.

Strauss, H. R.↗

DOE OSTI2026

Identification of Carbonyl Species on Palladium Supported on Ceria in Complex Microenvironments

Herein, we present a systematic comparison between Pd carbonyl (Pd-CO) species, specifically over Pd/CeO 2 based catalysts, observed during isothermal adsorption and in several prototypical catalytic reactions to identify and understand CO adsorption on palladium-ceria based catalysts. Pd-CO is observed via DRIFTS to probe the gas-solid conditions, while ATR-IR is used to probe the affinity of Pd-CO under more complex solvated gas-solid-liquid conditions to discern the influence of the microenvironments for carbonyl adsorption. Here, we explore the presence of Pd-CO under several reactive environments, including CO adsorption, CO 2 + H 2 , CO + H 2 , CH 4 + CO 2 and CO under gas-solid-liquid media, highlighting reactions with notable Pd-CO formation. The differences between palladium carbonyls and carbonate species show that carbonyl species are much more affected via a shifting of the peak position than carbonates, which remain static irrespective of the immediate chemical environment. By following the rate of CO accumulation via K-M mode DRIFTS, we observe migration from linear, 2095 cm -1 , to bridge site, 1978 cm -1 , as a function of time under a static CO atmosphere. With the use of DFT, we discerned changes in Pd-carbonyl stretches due to both coverage effects of CO under simulated reaction conditions and temperature effects. Regardless of whether CO is formed as an intermediate or a reactant, the competitive adsorption of *H and *CO affects the binding strength of *CO at all temperatures, with low temperature favoring atop binding and high temperature favoring the more stable FCC Pd-CO site.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Spectroscopic Identification of Carbamate Formation and Synergistic Binding in Amide–CO$^{–}_{2}$ Complexes

Carbamate formation is an elementary step that governs nitrogencentered nucleophilic CO 2 capture across diverse environments, yet a direct, structure-specific understanding has been lacking. Here, we report the first gas-phase characterization of closed-shell carbamate formation by deprotonated amides, using cryogenic ion trap vibrational spectroscopy combined with quantum chemical calculations. Reactions of deprotonated benzamide and isophthalamide anions with CO 2 form carbamate species, with the amide nitrogen serving as the nucleophilic site. Diagnostic, strongly red-shifted antisymmetric CO 2 stretching vibrational bands, supported by a bonding analysis, establish chemisorption with substantial charge transfer. In the multiamide system, an intramolecular N−H···O hydrogen bond provides synergistic stabilization, correlating with larger red shifts and more exothermic binding. These structure-assigned benchmarks provide molecular-level insights into the binding motif, charge redistribution, and hydrogen bond-mediated stabilization of amide carbamates, which aid the characterization of carbamate formation in condensed phase.

Amides↗

NASA NTRS1991

Structure and properties during aging of an Al-Cu-Li-Ag-Mg alloy, Weldalite (tm) 049

An Al-Cu-Li-Ag-Mg alloy, Weldalite (trademark) 049, was recently introduced as an ultra-high strength alloy (7000 MPa yield strength in artificially aged tempers) with good weldability. In addition, the alloy exhibits an extraordinary natural aging response (440 MPa yield strength (YS) in the unstretch condition) and a high ductility reversion condition which may be useful as a cold-forming temper. In contrast to other Al-Li alloys, these properties can essentially be obtained with or without a stretch or other coldworking operation prior to aging. Preliminary studies have revealed that the T4 temper (no stretch, natural age) is strengthened by a combination of GP zones and delta prime (Al3Li). The T6 temper (no stretch, aged at 180 C to peak strength) was reported to be strengthened primarily by T(sub 1) phase (Al2CuLi) with a minor presence of a theta prime like (Al2Cu) phase. On the other hand, a similar but lower solute containing alloy was reported to contain omega, (stoichiometry unknown), theta prime, and S prime in the peak strength condition. The purpose of this study is to further elucidate the strengthening phases in Weldalite (trademark) 049 in the unstretched tempers, and to follow the development of the microstructure from the T4 temper through reversion (180 C for 5 to 45 minutes) to the T6 temper.

Gayle, Frank W.↗

DOE OSTI2026

Dynamic Interfacial Design in Adaptive Hybrid Materials Enables Reversible and Tunable Mechano-Optic Smart Responses

Next-generation polymeric materials are shifting toward adaptive and interactive behaviors of living systems; however, designing materials that can reversibly modulate optical properties under mechanical deformation while maintaining mechanical robustness remains a key challenge. Here, we report a mechanically robust vitrimer-based adaptive hybrid material (AHM) that exhibits a stretch-induced reversible transparency-to-opacity transition, enabled by the integration of dynamic interactions at the polymer–silica nanoparticle interface and controlled nanoparticle self-assembly. The AHM combines boronic ester–functionalized polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (S-Bpin) with diol-functionalized silica nanoparticles (diol-SiNPs) to form a hybrid network hosting both dynamic boronic ester and hydrogen-bonding interactions. These reversible linkages facilitate controlled nanoparticle self-assembly and enable strain-induced nanoparticle alignment/aggregation. Upon stretching, SiNP-rich domains align and aggregate within the polymer matrix, while local modulus mismatch between stiff aggregated SiNP/borylated-styrene-rich regions and the softer elastomeric midblock induces surface microwrinkle formation. These internal aggregates and surface wrinkles cooperatively enhance light scattering, producing the opaque state under strain. Furthermore, the tailored AHM exhibits high toughness, thermomechanical stability, reprocessability, and programmable shape-memory behavior. This work presents a dynamic interfacial design strategy for mechanically robust, optically reconfigurable, and reusable soft materials for adaptive optics, smart windows, sensing, soft robotics, and circular smart-material platforms.

adaptive hybrid materials↗

NASA NTRS1990

Non-solar UV produced ions observed optically from the 'Crit I' critical velocity ionization experiment

A critical velocity ionization experiment was carried out with a heavily instrumented rocket launched from Wallops Island on May 13, 1986. Two neutral barium beams were created by explosive shaped charges released from the rocket and detonated at 48 deg to B at altitudes near 400 km and below the solar UV cutoff. Critical velocity ionization was expected to form a detectable ion jet along the release field line, but, instead, an ion cloud of fairly uniform intensity was observed stretching from the release field line across to where the neutral barium jet reached sunlight. The process creating these ions must have been present from the time of the release; the efficiency is estimated to be equivalent to an ionization time constant of 1800 sec. This ionization is most likely from collisions between the neutral barium jet and the ambient atmospheric oxygen, and, if so, the cross section for collisional ionization is 9 x 10 to the -18th sq cm.

Stenbaek-Nielsen, H. C.↗

NASA NTRS2002

Detection of HCN and C2H2 in ISO Spectra of Oxygen-Rich AGB Stars

Cool oxygen-rich AGB stars were not expected to have organic molecules like HCN in either their photospheres or circumstellar envelopes (CSEs). The discovery of HCN and CS microwave emission from the shallowest CSE layers of these stars was a considerable surprise and much theoretical effort has been expended in explaining the presence of such organics. To further explore this problem, we have undertaken a systematic search of oxygen-rich AGB stellar spectra in the Infrared Space Observatory (ISO) data archive. Our purposes are to find evidence regarding critical molecular species that could be of value in choosing among the proposed theoretical models, to locate spectral features which might give clues to conditions deeper in the CSEs, and to lay the groundwork for future SIRTF (Space Infrared Telescope Facility) and SOFIA (Stratospheric Observatory for Infrared Astronomy) observations. Using carefully reduced observations, we have detected weak absorption features arising from HCN and possibly C2H2 in a small number of oxygen-rich AGB stars. The most compelling case is NML Cyg which shows both HCN (14 microns) and CO2 (15 microns). VY CMa, a similar star, shows evidence for HCN, but not CO2. Two S-type stars show evidence for the C-H bending transitions: W Aql at 14 microns (HCN) and both W Aql and S Cas at 13.7 microns (C2H2). Both W Aql and S Cas as well as S Lyr, a SC-type star, show 3 micron absorption which may arise from the C-H stretch of HCN and C2H2. In the case of NML Cyg, we show that the HCN and CO2 spectral features are formed in the CSE at temperatures well above those of the outermost CSE layers and derive approximate column densities. In the case of the S-stars, we discuss the evidence for the organic features and their photospheric origin.

Carbon, Duane F.↗

DOE OSTI2022

Stretchable form of single crystal silicon for high performance electronics on rubber substrates

The present invention provides stretchable, and optionally printable, semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed or otherwise deformed. Stretchable semiconductors and electronic circuits of the present invention preferred for some applications are flexible, in addition to being stretchable, and thus are capable of significant elongation, flexing, bending or other deformation along one or more axes. Further, stretchable semiconductors and electronic circuits of the present invention may be adapted to a wide range of device configurations to provide fully flexible electronic and optoelectronic devices.

Rogers, John A.↗