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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 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Calculation of the weighting functions for the reconstruction of absorbing inhomogeneities in tissue by time-resolved optical projections

We report a new method for determining the weighting functions to reconstruct absorbing inhomogeneities in tissue by perturbation time-domain diffuse optical tomography using the transmission geometry of a flat layer. The method is based on an analytical approach to the calculation of the weighting functions for a semi-infinite scattering medium and on the use of the original method of an equivalent inverse source in order to obtain weight distributions for the flat layer geometry. The correctness of the proposed method of the weighting function calculation is evaluated by a numerical experiment on the reconstruction of absorbing inhomogeneities. It is shown that the perturbation reconstruction model based on the proposed weighting function calculation method allows the inhomogeneities smaller than 0.3 cm and ∼0.4 cm, located respectively in the transverse and longitudinal directions to the probe light direction, to be resolved in the centre of an 8-cm-thick object. (laser biophotonics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

de Gennes narrowing describes the relative motion of protein domains

The relative motion of structural domains is essential for the biological function of many proteins. Here, by analyzing neutron scattering data and performing molecular dynamics simulations, we find that interdomain motion in several proteins obeys the principle of de Gennes narrowing, in which the wave vector dependence of the interdomain diffusion coefficient is inversely proportional to the interdomain structure factor. Furthermore, the rate of interdomain motion is inversely proportional to the probability distribution of the spatial configurations of domains.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

ULTRAVIOLET HALOS AROUND SPIRAL GALAXIES. I. MORPHOLOGY

We examine ultraviolet halos around a sample of highly inclined galaxies within 25 Mpc to measure their morphology and luminosity. Despite contamination from galactic light scattered into the wings of the point-spread function, we find that ultraviolet (UV) halos occur around each galaxy in our sample. Around most galaxies the halos form a thick, diffuse disk-like structure, but starburst galaxies with galactic superwinds have qualitatively different halos that are more extensive and have filamentary structure. The spatial coincidence of the UV halos above star-forming regions, the lack of consistent association with outflows or extraplanar ionized gas, and the strong correlation between the halo and galaxy UV luminosity suggest that the UV light is an extragalactic reflection nebula. UV halos may thus represent 10{sup 6}–10{sup 7} M {sub ⊙} of dust within 2–10 kpc of the disk, whose properties may change with height in starburst galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Electron scattering by magnetosonic waves in the inner magnetosphere

Here, we investigate the importance of electron scattering by magnetosonic waves in the Earth’s inner magnetosphere. A statistical survey of the magnetosonic wave amplitude and wave frequency spectrum, as a function of geomagnetic activity, is performed using the Van Allen Probes wave measurements and is found to be generally consistent with the wave distribution obtained from previous spacecraft missions. Outside the plasmapause the statistical frequency distribution of magnetosonic waves follows the variation of the lower hybrid resonance frequency, but this trend is not observed inside the plasmasphere. Drift and bounce averaged electron diffusion rates due to magnetosonic waves are calculated using a recently developed analytical formula. The resulting timescale of electron energization during disturbed conditions (when AE* > 300 nT) is more than 10 days. We perform a 2-D simulation of the electron phase space density evolution due to magnetosonic wave scattering during disturbed conditions. Outside the plasmapause, the waves accelerate electrons with pitch angles between 50° and 70° and form butterfly pitch angle distributions at energies from ~100 keV to a few MeV over a timescale of several days; whereas inside the plasmapause, the electron acceleration is very weak. Our study suggests that intense magnetosonic waves may cause the butterfly distribution of radiation belt electrons especially outside the plasmapause, but electron acceleration due to magnetosonic waves is generally not as effective as chorus wave acceleration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

Au/Ag bimetallic dendrites were synthesized successfully from the corresponding aqueous solution via the AC electrodeposition method. Both of the morphologies and compositions could be tuned by the electrolyte concentration and AC frequency. The prepared bimetallic dendrites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and UV–vis spectroscopy. The underlying dendrite growth mechanism was then proposed in the context of the Directed Electrochemical Nanowires Assembly (DENA) models. Owing to the unscreened voltage dropping in the electrolyte bulk, electromigration dominates the species flux process, and cations tend to accumulate in areas with strong electric field intensity, such as electrode edges. Moreover, Faradaic AC-electro-osmosis (ACEO) flow could increase the effective diffusion layer thickness in these areas during the electrochemical reaction, and leads to dendrite growth. Further Micro-Raman observations illustrated that the Au/Ag bimetallic dendrites exhibited pronounced surface-enhanced Raman scattering (SERS) activity, using 4-mercaptopyridine (4-MP) as model molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Method for estimating optimal spectral and energy parameters of laser irradiation in photodynamic therapy of biological tissue

We have solved the problem of layer-by-layer laser-light dosimetry in biological tissues and of selecting an individual therapeutic dose in laser therapy. A method is proposed for real-time monitoring of the radiation density in tissue layers in vivo, concentrations of its endogenous (natural) and exogenous (specially administered) chromophores, as well as in-depth distributions of the spectrum of light action on these chromophores. As the background information use is made of the spectrum of diffuse light reflected from a patient's tissue, measured by a fibre-optic spectrophotometer. The measured spectrum is quantitatively analysed by the method of approximating functions for fluxes of light multiply scattered in tissue and by a semi-analytical method for calculating the in-depth distribution of the light flux in a multi-layered medium. We have shown the possibility of employing the developed method for monitoring photosensitizer and oxyhaemoglobin concentrations in tissue, light power absorbed by chromophores in tissue layers at different depths and laser-induced changes in the tissue morphology (vascular volume content and ratios of various forms of haemoglobin) during photodynamic therapy. (biophotonics)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Floating dark matter in celestial bodies

Dark matter (DM) can be captured in celestial bodies after scattering and losing sufficient energy to become gravitationally bound. We derive a general framework that describes the current DM distribution inside celestial objects, which self-consistently includes the effects of concentration diffusion, thermal diffusion, gravity, and capture accumulation. For DM with sufficient interactions, we show that a significant DM population can thermalize and sit towards the celestial-body surface. This surface-enhanced DM distribution allows for new phenomenology for DM searches in a wide range of celestial bodies, including the Sun, Earth, Jupiter, Brown Dwarfs, and Exoplanets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Nonlinear diffusion acceleration for the multigroup transport equation discretized with S{sub N} and continuous FEM with rattlesnake

Nonlinear diffusion acceleration (NDA) can improve the performance of a neutron transport solver significantly especially for the multigroup eigenvalue problems. The high-order transport equation and the transport-corrected low-order diffusion equation form a nonlinear system in NDA, which can be solved via a Picard iteration. The consistency of the correction of the low-order equation is important to ensure the stabilization and effectiveness of the iteration. It also makes the low-order equation preserve the scalar flux of the high-order equation. In this paper, the consistent correction for a particular discretization scheme, self-adjoint angular flux (SAAF) formulation with discrete ordinates method (S{sub N}) and continuous finite element method (CFEM) is proposed for the multigroup neutron transport equation. Equations with the anisotropic scatterings and a void treatment are included. The Picard iteration with this scheme has been implemented and tested with RattleS{sub N}ake, a MOOSE-based application at INL. Convergence results are presented. (authors)

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

INTERPLANETARY PROPAGATION OF SOLAR ENERGETIC PARTICLE HEAVY IONS OBSERVED AT 1 AU AND THE ROLE OF ENERGY SCALING

We have studied {approx}0.3 to >100 MeV nucleon{sup -1} H, He, O, and Fe in 17 large western hemisphere solar energetic particle events (SEP) to examine whether the often observed decrease of Fe/O during the rise phase is due to mixing of separate SEP particle populations, or is an interplanetary transport effect. Our earlier study showed that the decrease in Fe/O nearly disappeared if Fe and O were compared at energies where the two species interplanetary diffusion coefficient were equal, and therefore their kinetic energy nucleon{sup -1} was different by typically a factor {approx}2 ({sup e}nergy scaling{sup )}. Using an interplanetary transport model that includes effects of focusing, convection, adiabatic deceleration, and pitch angle scattering we have fit the particle spectral forms and intensity profiles over a broad range of conditions where the 1 AU intensities were reasonably well connected to the source and not obviously dominated by local shock effects. The transport parameters we derive are similar to earlier studies. Our model follows individual particles with a Monte Carlo calculation, making it possible to determine many properties and effects of the transport. We find that the energy scaling feature is preserved, and that the model is reasonably successful at fitting the magnitude and duration of the Fe/O ratio decrease. This along with successfully fitting the observed decrease of the O/He ratio leads us to conclude that this feature is best understood as a transport effect. Although the effects of transport, in particular adiabatic deceleration, are very significant below a few MeV nucleon{sup -1}, the spectral break observed in these events at 1 AU is only somewhat modified by transport, and so the commonly observed spectral breaks must be present at injection. For scattering mean free paths of the order of 0.1 AU adiabatic deceleration is so large below {approx}200 keV nucleon{sup -1} that ions starting with such energies at injection are cooled sufficiently as to be unobservable at 1 AU. Because of the complicating factors of different spectral break energies for different elements, it appears that SEP abundances determined below the break are least susceptible to systematic distortions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Diffusive excitonic bands from frustrated triangular sublattice in a singlet-ground-state system

Magnetic order in most materials occurs when magnetic ions with finite moments arrange in a particular pattern below the ordering temperature. Intriguingly, if the crystal electric field (CEF) effect results in a spin-singlet ground state, a magnetic order can still occur due to the exchange interactions between neighboring ions admixing the excited CEF levels. The magnetic excitations in such a state are spin excitons generally dispersionless in reciprocal space. Here we use neutron scattering to study stoichiometric Ni 2 Mo 3 O 8 , where Ni 2+ ions form a bipartite honeycomb lattice comprised of two triangular lattices, with ions subject to the tetrahedral and octahedral crystalline environment, respectively. We find that in both types of ions, the CEF excitations have nonmagnetic singlet ground states, yet the material has magnetic order. Furthermore, CEF spin excitons from the tetrahedral sites form a dispersive diffusive pattern around the Brillouin zone boundary, likely due to spin entanglement and geometric frustrations.

36 MATERIALS SCIENCE↗
DOE OSTI2013

MONTE CARLO SIMULATIONS OF NONLINEAR PARTICLE ACCELERATION IN PARALLEL TRANS-RELATIVISTIC SHOCKS

We present results from a Monte Carlo simulation of a parallel collisionless shock undergoing particle acceleration. Our simulation, which contains parameterized scattering and a particular thermal leakage injection model, calculates the feedback between accelerated particles ahead of the shock, which influence the shock precursor and 'smooth' the shock, and thermal particle injection. We show that there is a transition between nonrelativistic shocks, where the acceleration efficiency can be extremely high and the nonlinear compression ratio can be substantially greater than the Rankine-Hugoniot value, and fully relativistic shocks, where diffusive shock acceleration is less efficient and the compression ratio remains at the Rankine-Hugoniot value. This transition occurs in the trans-relativistic regime and, for the particular parameters we use, occurs around a shock Lorentz factor γ{sub 0} = 1.5. We also find that nonlinear shock smoothing dramatically reduces the acceleration efficiency presumed to occur with large-angle scattering in ultra-relativistic shocks. Our ability to seamlessly treat the transition from ultra-relativistic to trans-relativistic to nonrelativistic shocks may be important for evolving relativistic systems, such as gamma-ray bursts and Type Ibc supernovae. We expect a substantial evolution of shock accelerated spectra during this transition from soft early on to much harder when the blast-wave shock becomes nonrelativistic.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Electron mobility enhancement in (100) oxygen-inserted silicon channel

High performance improvement (+88% in peak G{sub m} and >30% in linear and saturation region drain currents) was observed for N-MOSFETs with Oxygen-Inserted (OI) Si channel. From TCAD analysis of the C-V measurement data, the improvement was confirmed to be due to electron mobility enhancement of the OI Si channel (+75% at N{sub inv} = 4.0 × 10{sup 12} cm{sup −2} and +25% at N{sub inv} = 8.0 × 10{sup 12} cm{sup −2}). Raman and high-resolution Rutherford backscattering measurements confirmed that negligible strain is induced in the OI Si layer, and hence, it cannot be used to explain the origin of mobility improvement. Poisson-Schrödinger based quantum mechanical simulation was performed, taking into account phonon, surface roughness and Coulomb scatterings. The OI layer was modeled as a “quasi barrier” region with reference to the Si conduction band edge to confine inversion electrons. Simulation explains the measured electron mobility enhancement as the confinement effect of inversion electrons while the formation of an super-steep retrograde well doping profile in the channel (as a result of dopant diffusion blocking effect accompanied by introduction of the OI layer) also contributes 50%–60% of the mobility improvement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Year-end report on FY13 activities for J8A6

The Russian-3 (R3) HANE, a 60 km high-latitude burst with yield estimated at 300 kt, was chosen for the demonstration. This test was selected because it allowed LLNL to leverage existing funding, which was directed at extending LLNL’s capability to simulate HANEs at atmospheric altitudes (<100 km). David Larsen (LLNL) developed a new particle-tracing code that tracks monoenergetic electrons of various energies from a point source as they interact with the atmosphere, losing energy and ‘pitch-angle scattering’ as they are transported. A relatively large fraction of the initial electrons are able to escape the atmosphere and were handed off to LANL for further processing to calculate the effect on space based assets. LANL binned the electrons into a phase-space density as a function of energy and equatorial pitch-angle and showed that all of the electrons would travel along field lines to the conjugate point in the Southern hemisphere, where they would likely be absorbed, because their equatorial pitch-angles were too field-aligned to permit them to ‘mirror’ above the atmosphere and be ‘trapped’. Thus, the initial LLNL output did not produce any trapped electrons to input into LANL’s diffusion code and so no study of the long-term evolution of the trapped population and its effect on space-based assets could be performed. It was recognized that LLNL’s calculation did not properly model the low-probability, large-angle scattering associated with a single Coulomb interaction between a beta-decay electron and the nucleus of the neutral particles in the high atmosphere, which would be the dominant interaction above some altitude (>100 km) and might allow the electrons to be pitch-angle scattered sufficiently to become trapped. A second LLNL calculation that properly included this single interaction probability was conducted and the output processed by LANL. It was shown that a small fraction of the initial population (~0.01%) would be ‘locally trapped’; however, even this small population would likely be absorbed within a few minutes as the electrons drifted around earth and eventually ended up on field lines where they would be absorbed in the atmosphere. The output of the second LLNL calculation was found to produce about 4x fewer backscattered electrons than previous work (Selesnick et al 2012), and so the remainder of the FY13 LANL effort on the project was aimed at trying to resolve this discrepancy. LANL implemented a stochastic differential equation to simulate the backscatter process so that the results could be compared to Larsen and Selesnick. Initial results from this capability have been obtained, but no quantitative comparison to Larsen or Selesnick has been done yet.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons

In this paper we show that the kinetic instabilities associated with runaway electron beams play an essential role for the production of high-level non-thermal electron–cyclotron-emission (ECE) radiation. Most of the non-thermal ECE comes from runaway electrons in the low-energy regime with large pitch angle, which are strongly scattered by the excited whistler waves. The power of ECE from runaway electrons is obtained using a synthetic diagnostic model based on the reciprocity method. The electron distribution function is calculated using a kinetic simulation model including the whistler wave instabilities and the quasilinear diffusion effects. Simulations based on DIII-D low-density discharge reproduces the rapid growth of the ECE signals observed in DIII-D experiments. Unlike the thermal ECE where radiation for a certain frequency is strongly localized inside the resonance region, the non-thermal ECE radiation from runaway electrons is nonlocal, and the emission-absorption ratio is higher than that of thermal electrons. The runaway electron tail is more significant for ECE with higher frequencies, and the ECE spectrum becomes flatter as RE population grows. The nonlinear behavior of the kinetic instabilities is illustrated in the oscillations of the ECE waves. In conclusion, the good agreement with the DIII-D experimental observations after including the kinetic instabilities clearly illustrate the significance of the scattering effects from wave-particle interactions, which can also be important for runaway electrons produced in disruptions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Healing X-ray scattering images

X-ray scattering images contain numerous gaps and defects arising from detector limitations and experimental configuration. Here, we present a method to heal X-ray scattering images, filling gaps in the data and removing defects in a physically meaningful manner. Unlike generic inpainting methods, this method is closely tuned to the expected structure of reciprocal-space data. In particular, we exploit statistical tests and symmetry analysis to identify the structure of an image; we then copy, average and interpolate measured data into gaps in a way that respects the identified structure and symmetry. Importantly, the underlying analysis methods provide useful characterization of structures present in the image, including the identification of diffuse versus sharp features, anisotropy and symmetry. The presented method leverages known characteristics of reciprocal space, enabling physically reasonable reconstruction even with large image gaps. The method will correspondingly fail for images that violate these underlying assumptions. The method assumes point symmetry and is thus applicable to small-angle X-ray scattering (SAXS) data, but only to a subset of wide-angle data. Our method succeeds in filling gaps and healing defects in experimental images, including extending data beyond the original detector borders.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Incorporation of Melittin Enhances Interfacial Fluidity of Bicontinuous Microemulsions

The effect of an antimicrobial peptide, melittin, on the long-range collective and local undulation motions of bicontinuous microemulsions (BμEs) was evaluated using dynamic light scattering (DLS) and neutron spin echo (NSE) spectroscopy. Small-angle neutron scattering (SANS) was also used to study the effect of melittin on the structure and the correlation length of BμEs. BμEs were isolated from Winsor-III systems formed by mixing aqueous melittin solutions containing sodium dodecyl sulfate with dodecane/1-pentanol mixtures at optimal salinity. An increase of melittin concentration linearly increased the diffusivity of the microemulsions (D DLS ) and decreased the bending rigidity (κ NSE ) up to an aqueous melittin concentration of 2 g/L, thus indicating an increase of interfacial fluidity. Further increase of melittin concentration above 2 g/L did not change D DLS and slightly increased κ NSE . The changes reflect differences of interaction between melittin and BμE surfactant monolayers at different melittin concentrations. At low concentrations, melittin is highly associated with the surfactant monolayers, likely ion-paired to the sulfate surfactant head groups and perhaps partially penetrating into the surfactant tail region. Above 2 g/L, an apparent saturation concentration, added melittin is less strongly associated with the monolayers. In contrast, the bare bending constant derived from SANS data (κ bare ) underwent only a minor decrease. Noting that κ bare reflects contributions from both the elasticity and saddle-splay moduli, this suggests that κ bare is not an effective indicator of dynamics for the BμEs investigated. Our study demonstrates that amphiphilic solubilizates can have a complex impact on dynamics of surfactant monolayers in microemulsions, with implications for transmembrane diffusion and the kinetics of release from the microemulsion phase, which are important characteristics for the use of BμEs as delivery vehicles and host systems for (bio)chemical reactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Feasibility Study of Making Metallic Hybrid Materials Using Additive Manufacturing

In this paper, a metallic hybrid structure, consisting of an Inconel-718 matrix and a Co-Cr internal structure, was successfully manufactured using laser direct energy deposition process. Characterizations were performed using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), neutron-computed tomography (nCT), and electron back-scatter diffraction (EBSD) to verify the interfaces between Co-rich and Ni-rich phases. nCT revealed the internal structures to be continuous without cracking or significant intermixing due to inter-diffusion of Co and Ni (i.e., dissolved boundaries between the two structures). Minor porosity was detected. EBSD confirmed a good bond at the granular level. No precipitate phases were detected with XRD. Finally, EDS revealed dilution/intermixing between the Co and Ni interfaces presumably due to melt-pool overlay between the matrix and the internal structures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mesoscale shock structure in particulate composites

Multiscale experiments in heterogeneous materials and the knowledge of their physics under shock compression are limited. Here, this study examines the multiscale shock response of particulate composites comprised of soda-lime glass particles in a PMMA matrix using full-field high speed digital image correlation (DIC) for the first time. Normal plate impact experiments, and complementary numerical simulations, are conducted at stresses ranging from 1.1 - 3.1 GPa to elucidate the mesoscale mechanisms responsible for the distinct shock structure observed in particulate composites. The particle velocity from the macroscopic measurement at continuum scale shows a relatively smooth velocity profile, with shock thickness decreasing with an increase in shock stress, and the composite exhibits strain rate scaling as the second power of the shock stress. In contrast, the mesoscopic response was highly heterogeneous, which led to a rough shock front and the formation of a train of weak shocks traveling at different velocities. Additionally, the normal shock was seen to diffuse the momentum in the transverse direction, affecting the shock rise and the rounding-off observed at the continuum scale measurements. The numerical simulations indicate that the reflections at the interfaces, wave scattering, and interference of these reflected waves are the primary mechanisms for the observed rough shock fronts.

36 MATERIALS SCIENCE↗