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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The effect of plasma background on the instability of two non-parallel quantum plasma shells in whole K space

In this paper, quantum fluid equations together with Maxwell's equations are used to study the stability problem of non-parallel and non-relativistic plasma shells colliding over a “background plasma” at arbitrary angle, as a first step towards a microscopic understanding of the collision shocks. The calculations have been performed for all magnitude and directions of wave vectors. The colliding plasma shells in the vacuum region have been investigated in the previous works as a counter-streaming model. While, in the presence of background plasma (more realistic system), the colliding shells are mainly non-paralleled. The obtained results show that the presence of background plasma often suppresses the maximum growth rate of instabilities (in particular case, this behavior is contrary). It is also found that the largest maximum growth rate occurs for the two-stream instability of the configuration consisting of counter-streaming currents in a very dilute plasma background. The results derived in this study can be used to analyze the systems of three colliding plasma slabs, provided that the used coordinate system is stationary relative to the one of the particle slabs. The present analytical investigations can be applied to describe the quantum violent astrophysical phenomena such as white dwarf stars collision with other dense astrophysical bodies or supernova remnants. Moreover, at the limit of ℏ→0, the obtained results described the classical (sufficiently dilute) events of colliding plasma shells such as gamma-ray bursts and flares in the solar winds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

KEPLER ECLIPSING BINARIES WITH DELTA SCUTI/GAMMA DORADUS PULSATING COMPONENTS. I. KIC 9851944

KIC 9851944 is a short-period ( P = 2.16 days) eclipsing binary in the Kepler field of view. By combining the analysis of Kepler photometry and phase-resolved spectra from Kitt Peak National Observatory and Lowell Observatory, we determine the atmospheric and physical parameters of both stars. The two components have very different radii (2.27 R {sub ⊙}, 3.19 R {sub ⊙}) but close masses (1.76 M {sub ⊙}, 1.79 M {sub ⊙}) and effective temperatures (7026, 6902 K), indicating different evolutionary stages. The hotter primary is still on the main sequence (MS), while the cooler and larger secondary star has evolved to the post-MS, burning hydrogen in a shell. A comparison with coeval evolutionary models shows that it requires solar metallicity and a higher mass ratio to fit the radii and temperatures of both stars simultaneously. Both components show δ Scuti-type pulsations, which we interpret as p -modes and p and g mixed modes. After a close examination of the evolution of δ Scuti pulsational frequencies, we make a comparison of the observed frequencies with those calculated from MESA/GYRE.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Sensitivity Study of Mini-Batch Size on a Long Short-Term Memory Network for In-situ Sensing of Core-to-shell Ratio of Microencapsulated Phase Change Materials

Microencapsulated phase change materials are being studied for applications for thermal energy storage in concentrated solar fields. During fabrication, the thickness of the encapsulation cannot be readily measured for real-time control. Therefore, a machine learning network, specifically a Long Short-Term Memory network, is being developed to estimate the ratio of the shell radius to core radius based on a one second temperature history. The mini-batch size determines how often the algorithm weights are updated during network training, and shuffle indicates whether the training data is shuffled during training. A general factorial design is used to analyze the effects of varying mini-batch size and shuffle, along with the core-to-shell ratio, on the RMSE of the response from the Long Short-Term Memory network. It was found that the network performed better for smaller core to shell ratios (less than 0.6) and had the lowest RMSE when the minibatch size was 128. The minimum RMSE found was 0.00501.

Shannon, Rebecca↗
DOE OSTI2012

Astrophysical models of r-process nucleosynthesis: An update

An update on astrophysical models for nucleosynthesis via rapid neutron capture, the r process, is given. A neutrino-induced r process in supernova helium shells may have operated up to metallicities of {approx} 10{sup -3} times the solar value. Another r-process source, possibly neutron star mergers, is required for higher metallicities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

PICK-UP ION DISTRIBUTIONS AND THEIR INFLUENCE ON ENERGETIC NEUTRAL ATOM SPECTRAL CURVATURE

This paper focuses on the analysis and significance of the spectral curvature of energetic neutral atoms (ENAs) detected by the Interstellar Boundary Explorer. The flux versus energy spectrum is analytically expressed in terms of the source proton distributions, namely: (1) the solar wind kappa distribution of protons and (2) the coexisting filled spherical shell distribution of pick-up ions (PUIs). The influence of PUIs on the spectral index and curvature is modeled and investigated in detail. It is analytically shown that (1) the PUI speed upper limit is restricted by the Earthward PUI velocity vector, (2) the PUI distribution causes a positive spectral curvature, and (3) the exact expressions of the spectral index and curvature can be used to extract information about the governing parameters of the parent proton distributions. The sky maps of the spectral curvature reveal a possible band-like configuration of positive spectral curvature that is missing in the original flux sky maps. This band can be roughly separated into the north/south polar regions and two ecliptic meridional 'columns' located around the ecliptic longitudes {approx}5 Degree-Sign and {approx}150 Degree-Sign . The geometric locus between the two cones with noseward axis, and apertures {approx}60 Degree-Sign and {approx}120 Degree-Sign , configures the band-like region of (1) the positive curvature and (2) the maximum values of PUI distribution. Indeed, the observed curvature band is highly correlated with PUI distributions, and is possibly caused by the influence of PUIs on bending the spectrum from linear (log-log scale) to concave upward, thus increasing its spectral curvature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Side-by-Side Field Evaluation of Highly Insulating Windows in the PNNL Lab Homes

To examine the energy, air leakage, and thermal performance of highly insulating windows, a field evaluation was undertaken in a matched pair of all-electric, factory-built “Lab Homes” located on the Pacific Northwest National Laboratory (PNNL) campus in Richland, Washington. The “baseline” Lab Home B was retrofitted with “standard” double-pane clear aluminum-frame slider windows and patio doors, while the “experimental” Lab Home A was retrofitted with Jeld-Wen® triple-pane vinyl-frame slider windows and patio doors with a U-factor of 0.2 and solar heat gain coefficient of 0.19. To assess the window, the building shell air leakage, energy use, and interior temperatures of each home were compared during the 2012 winter heating and summer cooling seasons. The measured energy savings in Lab Home B averaged 5,821 watt-hours per day (Wh/day) during the heating season and 6,518 Wh/day during the cooling season. The overall whole-house energy savings of Lab Home B compared to Lab Home A are 11.6% ± 1.53% for the heating season and 18.4 ± 2.06% for the cooling season for identical occupancy conditions with no window coverings deployed. Extrapolating these energy savings numbers based on typical average heating degree days and cooling degree days per year yields an estimated annual energy savings of 12.2%, or 1,784 kWh/yr. The data suggest that highly insulating windows are an effective energy-saving measure that should be considered for high-performance new homes and in existing retrofits. However, the cost effectiveness of the measure, as determined by the simple payback period, suggests that highly insulating window costs continue to make windows difficult to justify on a cost basis alone. Additional reductions in costs via improvements in manufacturing and/or market penetration that continue to drive down costs will make highly insulating windows much more viable as a cost-effective energy efficiency measure. This study also illustrates that highly insulating windows have important impacts on peak load, occupant comfort, and condensation potential, which are not captured in the energy savings calculation. More consistent and uniform interior temperature distributions suggest that highly insulated windows, as part of a high performance building envelope, may enable more centralized duct design and downsized HVAC systems. Shorter, more centralized duct systems and smaller HVAC systems to yield additional cost savings, making highly insulating windows more cost effective as part of a package of new construction or retrofit measures which achieve significant reductions in home energy use.

PNNL Lab Homes↗
DOE OSTI2014

Control and diagnosis of temperature, density, and uniformity in x-ray heated iron/magnesium samples for opacity measurements

Experimental tests are in progress to evaluate the accuracy of the modeled iron opacity at solar interior conditions, in particular to better constrain the solar abundance problem [S. Basu and H. M. Antia, Phys. Rep. 457, 217 (2008)]. Here, we describe measurements addressing three of the key requirements for reliable opacity experiments: control of sample conditions, independent sample condition diagnostics, and verification of sample condition uniformity. The opacity samples consist of iron/magnesium layers tamped by plastic. By changing the plastic thicknesses, we have controlled the iron plasma conditions to reach (1) T{sub e} = 167 ± 3 eV and n{sub e} = (7.1 ± 1.5)× 10{sup 21} cm{sup −3}, (2) T{sub e} = 170 ± 2 eV and n{sub e} = (2.0 ± 0.2) × 10{sup 22} cm{sup −3}, and (3) T{sub e} = 196 ± 6 eV and n{sub e} = (3.8 ± 0.8) × 10{sup 22} cm{sup −3}, which were measured by magnesium tracer K-shell spectroscopy. The opacity sample non-uniformity was directly measured by a separate experiment where Al is mixed into the side of the sample facing the radiation source and Mg into the other side. The iron condition was confirmed to be uniform within their measurement uncertainties by Al and Mg K-shell spectroscopy. The conditions are suitable for testing opacity calculations needed for modeling the solar interior, other stars, and high energy density plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

GLOBAL DYNAMICS OF SUBSURFACE SOLAR ACTIVE REGIONS

We present three-dimensional numerical simulations of a magnetic loop evolving in either a convectively stable or unstable rotating shell. The magnetic loop is introduced into the shell in such a way that it is buoyant only in a certain portion in longitude, thus creating an {Omega}-loop. Due to the action of magnetic buoyancy, the loop rises and develops asymmetries between its leading and following legs, creating emerging bipolar regions whose characteristics are similar to those of observed spots at the solar surface. In particular, we self-consistently reproduce the creation of tongues around the spot polarities, which can be strongly affected by convection. We further emphasize the presence of ring-shaped magnetic structures around our simulated emerging regions, which we call 'magnetic necklace' and which were seen in a number of observations without being reported as of today. We show that those necklaces are markers of vorticity generation at the periphery and below the rising magnetic loop. We also find that the asymmetry between the two legs of the loop is crucially dependent on the initial magnetic field strength. The tilt angle of the emerging regions is also studied in the stable and unstable cases and seems to be affected both by the convective motions and the presence of a differential rotation in the convective cases.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Upconverting core-shell nanocrystals with high quantum yield under low irradiance: On the role of isotropic and thick shells

Colloidal upconverter nanocrystals (UCNCs) that convert near-infrared photons to higher energies are promising for applications ranging from life sciences to solar energy harvesting. However, practical applications of UCNCs are hindered by their low upconversion quantum yield (UCQY) and the high irradiances necessary to produce relevant upconversion luminescence. Achieving high UCQY under practically relevant irradiance remains a major challenge. The UCQY is severely limited due to non-radiative surface quenching processes. We present a rate equation model for migration of the excitation energy to show that surface quenching does not only affect the lanthanide ions directly at the surface but also many other lanthanide ions quite far away from the surface. The average migration path length is on the order of several nanometers and depends on the doping as well as the irradiance of the excitation. Using Er{sup 3+}-doped β-NaYF{sub 4} UCNCs, we show that very isotropic and thick (∼10 nm) β-NaLuF{sub 4} inert shells dramatically reduce the surface-related quenching processes, resulting in much brighter upconversion luminescence at simultaneously considerably lower irradiances. For these UCNCs embedded in poly(methyl methacrylate), we determined an internal UCQY of 2.0% ± 0.2% using an irradiance of only 0.43 ± 0.03 W/cm{sup 2} at 1523 nm. Normalized to the irradiance, this UCQY is 120× higher than the highest values of comparable nanomaterials in the literature. Our findings demonstrate the important role of isotropic and thick shells in achieving high UCQY at low irradiances from UCNCs. Additionally, we measured the additional short-circuit current due to upconversion in silicon solar cell devices as a proof of concept and to support our findings determined using optical measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Simultaneous Observations of Electromagnetic Ion Cyclotron (EMIC) Waves and Pitch Angle Scattering During a Van Allen Probes Conjunction

On 22 December 2015, the two Van Allen Probes observed two sets of electromagnetic ion cyclotron (EMIC) wave bursts during a close conjunction when both Probe A and Probe B were separated by 0.57 to 0.68 R E . Here, the EMIC waves occurred during an active period in the recovery phase of a coronal mass ejection-driven geomagnetic storm. Both spacecraft observed EMIC wave bursts that had similar spatial structure within a 1–2 min time delay. The EMIC waves occurred outside the plasmasphere, within ΔL ≈ 1–2 of the plasmapause and within a few degrees in magnetic latitude of the equatorial plane. The spatial structure of the EMIC wave bursts may have been related to the proton drift paths outside the plasmasphere and influenced by total magnetic field strength variations associated with solar wind pressure enhancements. The EMIC waves were observed in a narrow L shell region from L ≈ 4.55–5.32 between 10 and 11 magnetic local time (MLT) on the outbound halves of the spacecraft orbits and from L ≈ 4.82–5.51 between 13 and 14 MLT on the inbound halves of the spacecraft orbits. However, Pc1 pulsations were observed on the ground over a broad range of local times. The anisotropy of the proton pitch angle distributions was enhanced when the EMIC waves were observed. Although the overall radiation belt response during this storm was dominated by acceleration and transport processes, the EMIC waves produced local pitch angle scattering of 13–15 keV protons and 2.1–2.6 MeV electrons, consistent with calculations of the expected resonant energies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

PRESSURE OF THE PROTON PLASMA IN THE INNER HELIOSHEATH

We develop a physical model to study the pressure of the source proton plasma in the inner heliosheath based on the IBEX Energetic Neutral Atom (ENA) spectra. A multiple linear regression technique is used to parameterize the proton distribution function, by connecting the observed ENA flux spectrum from IBEX-Hi with the power-law of the model proton distribution. We calculate the partial pressure over the measured energy range, using (1) a non-parametric method by integrating the observed ENA flux, and (2) a parametric method by integrating the modeled distribution of protons in the inner heliosheath. The two sky maps of the parametric and non-parametric partial pressures are nearly identical, owing to their power-law distributions at high energies; the kappa distribution is such a function that can be reduced to a power-law in the IBEX-Hi energy range. The slight differences between the two partial pressures may indicate protons that are not described by the kappa distribution, and instead, involve newer or 'immature' (spherical shell) pick-up proton distributions. Ultimately, however, these become incorporated with the solar wind into one single proton population described by a kappa distribution. Moreover, we derive analytically (1) the ENA flux spectra, which suggests that this flux maximizes at {approx}30 eV, and (2) the differential pressure, which provides estimates of the partial pressures outside of those measured by IBEX-Hi. Under the assumptions of the modeled ENA spectra, the Ribbon emissions appear to be primarily limited to the energy ranges of IBEX-Lo and IBEX-Hi.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Photo-physical properties enhancement of bare and core-shell quantum dots

Semiconductor nanocrystals (NCs) (also known as quantum dots, QDs) have attracted immense attention for their size-tunable optical properties that makes them impressive candidates for solar cells, light emitting devices, lasers, as well as biomedical imaging. However monodispersity, high and consistent photoluminescence, photostability, and biocompatibility are still major challenges. This work focuses on optimizing the photophysical properties and biocompatibility of QDs by forming core-shell nanostructures and their encapsulation by a carrier. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm sizes were synthesized using a facile approach based on pyrolysis of the single molecule precursors. After capping the CdS QDs with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction. This encapsulation enhanced the quantum yield and photostability compared to the bare QDs by providing much stronger resistance to oxidation and Oswald ripening of QDs. Encapsulation also improved biocompatibility of QDs that was evaluated with human umbilical vein endothelial cell lines (HUVEC)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO

ZnO nanoparticles (NPs) have great potential for their use in, e.g., thin film solar cells due to their electro-optical properties adjustable on the nanoscale. Therefore, the production of well-defined NPs is of major interest. For a targeted production process, the knowledge of the stabilization layer of the NPs during and after their formation is of particular importance. For the study of the stabilizer layer of ZnO NPs prepared in a wet chemical synthesis from zinc acetate, only ex situ studies have been performed so far. An acetate layer bound to the surface of the dried NPs was found; however, an in situ study which addresses the stabilizing layer surrounding the NPs in a native dispersion was missing. By the combination of small angle scattering with neutrons and X-rays (SANS and SAXS) for the same sample, we are now able to observe the acetate shell in situ for the first time. In addition, the changes of this shell could be followed during the ripening process for different temperatures. With increasing size of the ZnO core (d core ) the surrounding shell (d shell ) becomes larger, and the acetate concentration within the shell is reduced. For all samples, the shell thickness was found to be larger than the maximum extension of an acetate molecule with acetate concentrations within the shell below 50 vol %. Furthermore, there is not a monolayer of acetate molecules that covers the NPs but rather a swollen shell of acetate ions. This shell is assumed to hinder the growth of the NPs to larger macrostructures. In addition, we found that the partition coefficient μ between acetate in the shell surrounding the NPs and the total amount of acetate in the solution is about 10% which is in good agreement with ex situ data determined by thermogravimetric analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

PROTON HEATING BY PICK-UP ION DRIVEN CYCLOTRON WAVES IN THE OUTER HELIOSPHERE: HYBRID EXPANDING BOX SIMULATIONS

Using a one-dimensional hybrid expanding box model, we investigate properties of the solar wind in the outer heliosphere. We assume a proton–electron plasma with a strictly transverse ambient magnetic field and, aside from the expansion, we take into account the influence of a continuous injection of cold pick-up protons through the charge-exchange process between the solar wind protons and hydrogen of interstellar origin. The injected cold pick-up protons form a ring distribution function, which rapidly becomes unstable, and generate Alfvén cyclotron waves. The Alfvén cyclotron waves scatter pick-up protons to a spherical shell distribution function that thickens over that time owing to the expansion-driven cooling. The Alfvén cyclotron waves heat solar wind protons in the perpendicular direction (with respect to the ambient magnetic field) through cyclotron resonance. At later times, the Alfvén cyclotron waves become parametrically unstable and the generated ion-acoustic waves heat protons in the parallel direction through Landau resonance. The resulting heating of the solar wind protons is efficient on the expansion timescale.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Evidence for Reduced, Carbon-rich Regions in the Solar Nebula from an Unusual Cometary Dust Particle

Geochemical indicators in meteorites imply that most formed under relatively oxidizing conditions. However, some planetary materials, such as the enstatite chondrites, aubrite achondrites, and Mercury, were produced in reduced nebular environments. Because of large-scale radial nebular mixing, comets and other Kuiper Belt objects likely contain some primitive material related to these reduced planetary bodies. Here, we describe an unusual assemblage in a dust particle from comet 81P/Wild 2 captured in silica aerogel by the NASA Stardust spacecraft. The bulk of this ∼20 μ m particle is comprised of an aggregate of nanoparticulate Cr-rich magnetite, containing opaque sub-domains composed of poorly graphitized carbon (PGC). The PGC forms conformal shells around tiny 5–15 nm core grains of Fe carbide. The C, N, and O isotopic compositions of these components are identical within errors to terrestrial standards, indicating a formation inside the solar system. Magnetite compositions are consistent with oxidation of reduced metal, similar to that seen in enstatite chondrites. Similarly, the core–shell structure of the carbide + PGC inclusions suggests a formation via FTT reactions on the surface of metal or carbide grains in warm, reduced regions of the solar nebula. Together, the nanoscale assemblage in the cometary particle is most consistent with the alteration of primary solids condensed from a C-rich, reduced nebular gas. The nanoparticulate components in the cometary particle provide the first direct evidence from comets of reduced, carbon-rich regions that were present in the solar nebula.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Investigation of iron opacity experiment plasma gradients with synthetic data analyses

Experiments have been performed at Sandia National Laboratories Z-facility to validate iron opacity models relevant to the solar convection/radiation zone boundary. Sample conditions were measured by mixing Mg with the Fe and using Mg K-shell line transmission spectra, assuming that the plasma was uniform. We develop a spectral model that accounts for hypothetical gradients, and compute synthetic spectra to quantitatively evaluate the plasma gradient size that can be diagnosed. Two sample designs are investigated, assuming linear temperature and density gradients. First, Mg uniformly mixed with Fe enables temperature gradients greater than 10% to be detected. The second design uses Mg mixed into one side and Al mixed into the other side of the sample in an attempt to more accurately infer the sample gradient. Both temperature and density gradients as small as a few percent can be detected with this design. Experiments have successfully recorded spectra with the second design. In future research, the spectral model will be used to place bounds on gradients that exist in Z opacity experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Design and Fabrication of a Precious Metal‐Free Tandem Core–Shell p + n Si/W‐Doped BiVO 4 Photoanode for Unassisted Water Splitting

Abstract Tandem photoelectrochemical water splitting cells utilizing crystalline Si and metal oxide photoabsorbers are promising for low‐cost solar hydrogen production. This study presents a device design and a scalable fabrication scheme for a tandem heterostructure photoanode: p + n black silicon (Si)/SnO 2 interface/W‐doped bismuth vanadate (BiVO 4 )/cobalt phosphate (CoPi) catalyst. The black‐Si not only provides a substantial photovoltage of 550 mV, but it also serves as a conductive scaffold to decrease charge transport pathlengths within the W‐doped BiVO 4 shell. When coupled with cobalt phosphide (CoP) nanoparticles as hydrogen evolution catalysts, the device demonstrates spontaneous water splitting without employing any precious metals, achieving an average solar‐to‐hydrogen efficiency of 0.45% over the course of an hour at pH 7. This fabrication scheme offers the modularity to optimize individual cell components, e.g., Si nanowire dimensions and metal oxide film thickness, involving steps that are compatible with fabricating monolithic devices. This design is general in nature and can be readily adapted to novel, higher performance semiconducting materials beyond BiVO 4 as they become available, which will accelerate the process of device realization.

Chakthranont, Pongkarn↗
DOE OSTI2021

Pyroelectricity of Lead Sulfide (PbS) Quantum Dot Films Induced by Janus-Ligand Shells

Asymmetry is an essential property to control. To do that in nanocrystalline systems we have developed methods to produce Janus-ligand shells on otherwise symmetric PbS quantum dots (QDs). In this work, we demonstrate that control by constructing a system that exhibits pyroelectricity built from spherical PbS QDs. We observed a pyroelectric current in two different configurations. In one configuration, the QDs are self-assembled into close-packed arrays while in the second configuration, the QDs are dispersed into an electro-inactive polymer, polydimethylsiloxane. Both exhibit a pyroelectric response. In the first configuration we estimate a lower limit of the pyroelectric coefficient to be 1.97 × 10 -7 C/m 2 K, which is likely limited by the degree of QD alignment during film formation but is already on par with common pyroelectric systems. Compared with inorganic ceramic-like and polymeric pyroelectric materials, pyroelectric films self-assembled from polar QDs are easier to prepare, responsive to light with different energies based on QD exciton energy, and the polarization of each QD could be easily tuned by constructing different Janus-ligand shells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗