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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Searching for Turbulent Spectra in Mutliple Spacecraft Observations

The subject of magnetohydrodynamic simulations in the 1980's, magnetic turbulence has reemerged as a favored explanation for the production of fast magnetic reconnection. Recent three-dimensional simulations reveal the formation of secondary islands that serve to shorten the current sheet and increase the accelerating electric field, while both simulations and observations witness electron holes whose collapse energizes electrons. However, little work has been done to investigate the presence of turbulent magnetic and electric field spectra in association with in situ reconnection observations in space. In this study we address this deficiency by analyzing the wavelength spectra of two reconnection events established by multiple spacecraft observations in previous publications. We apply a k-filtering analysis to determine the wave vectors. To optimize the quality of the k-filtering analysis and minimize aliasing, we select multi-spacecraft observations having optimal spacecraft tetrahedral geometry and dimensions that resolve wavelengths within the ion diffusion region. We have chosen one dayside and one nightside reconnection event each observed by the Cluster spacecraft. Spatial correlation between the reconnecting current sheet and a turbulent magnetic spectrum supports an association between turbulence and reconnection in space. The k-filtering method, a wavelet time-frequency spectrum, and a polarization analysis serve to identify wave modes associated with the turbulence. A calculation of the reconnection electric field based on the normal component of the reconnecting magnetic field provides an estimate of the reconnection rate.

Wendel, Deirdre E.↗
NASA NTRS1995

Prediction of the interplanetary magnetic field strength

A new model of the coronal and interplanetary magnetic field can predict both the interplanetary magnetic field strength and its polarity from measurements of the photospheric magnetic field. The model includes the effects of the large-scale horizontal electric currents flowing in the inner corona, of the warped heliospheric current sheet in the upper corona, and of volume currents flowing in the region where the solar wind plasma totally controls the magnetic field. The model matches the MHD solution for a simple dipole test case better than earlier source surface and current sheet models. The strength and polarity of the radial interplanetary magnetic field component predicted for quiet time samples in each year from 1977 to 1986 agree with observations made near the Earth's orbit better than the hybrid MHD-source surface model (Wang and Sheeley, 1988). The results raise the question of whether coronal holes are the only solar source of the interplantary magnetic field in the solar wind. If some interplanetary flux originates outside coronal holes, the model can match the observed field using the accepted 1.8 saturation correction factor for lambda 5250 A magnetograph observations. Requiring open flux to come exclusively from coronal holes requires and additional factor of two.

Zhao, Xuepu↗
DOE OSTI2023

Domain-wall magnetoelectric coupling in multiferroic hexagonal YbFeO 3 films

Electrical modulation of magnetic states in single-phase multiferroic materials, using domain-wall magnetoelectric (ME) coupling, can be enhanced substantially by controlling the population density of the ferroelectric (FE) domain walls during polarization switching. In this work, we investigate the domain-wall ME coupling in multiferroic h-YbFeO 3 thin films, in which the FE domain walls induce clamped antiferromagnetic (AFM) domain walls with reduced magnetization magnitude. Simulation according to the phenomenological theory indicates that the domain-wall ME effect is dramatically enhanced when the separation between the FE domain walls shrinks below the characteristic width of the clamped AFM domain walls during the ferroelectric switching. Experimentally, we show that while the magnetization magnitude remains same for both the positive and the negative saturation polarization states, there is evidence of magnetization reduction at the coercive voltages. These results suggest that the domain-wall ME effect is viable for electrical control of magnetization.

42 ENGINEERING↗
NASA NTRS2011

GEM-CEDAR Challenge: Comparing Ionospheric Models with Poynting Flux from DMSP Observations

As part to the GEM-CEDAR challenge we are extending the model-data comparisons to electrodynamic in-situ measurements in low-Earth orbit. We use DMSP observations of electric and magnetic fields to compute Poynting Flux values along the satellite track in high latitudes including the auroral zones and the polar cap. Models of the ionosphere that include electrodynamic parameters have been run for five events selected for the GEM-CEDAR modeling challenge for which DMSP data are available for comparison. Combined with a magnetic field model we use the modeled electric fields to compute Poynting Flux and Joule Dissipation values from outputs of CTIPe, TIE-GCM, the ionospheric electrodynamics solvers of the SWMF, LFM and OpenGGCM magnetosphere-ionosphere coupled models, and the Weimer electric field model. The online metrics analysis tool at the Community Coordinated Modeling Center (CCMC) has been updated to handle the analysis of separate short segments of available data (high-latitude sections of the satellite orbit) with model outputs to analyze how well auroral patterns are being reproduced by the models. We present initial results from the new analysis tool in terms of model yields (ratio of the difference between maximum and minimum values of model results to the observation), timing/location errors of local maxima in the inbound and outbound auroral crossings as well as cross-correlations for individual passes. We collect the information for many DMSP passes and present an analysis for model performance during quiet and geomagnetically disturbed time periods using half-orbit integrated values as well.

Rastaetter, Lutz↗
NASA NTRS2000

Solar Sail Trajectories for Solar Polar and Heliopause Missions

Over the last several years, interest in a more vigorous space exploration program has renewed interest in the use of solar sails for the more demanding space missions. Solar sail is eminently suited for some of the higher energy missions since no fuel is consumed and the only criteria is that of the total time required to perform a particular mission. Although solar sail missions to planets and small bodies have been examined previously, and reported in the literature' classes of space missions with no well defined target body have received little attention. These Space Physics missions include some with extremely high energy requirements. Not only are these missions difficult, if not impractical, to accomplish with conventional chemical propulsion spacecraft, but they are also difficult to perform in the near future using projected electric-propulsion systems. Solar sail trajectories for two of the high energy Space Physics missions, a Solar Polar mission and a Heliopause mission, are examined in this paper. The object of the Solar Polar mission is to place 'a payload into a short period orbit around the Sun at a 90 degree inclination to either the ecliptic plane or the equatorial plane of the sun. A forerunner for this type of mission was the Ulysses spacecraft which used a gravity assist of Jupiter to place the spacecraft into a 90 degree inclination orbit around the Sun with a perihelion distance of around .55 AU. The orbital period for the Ulysses mission was around 5 years however, and future Solar Polar missions require many observational passes over the pole of the Sun each year thus implying a significantly shorter orbit period than that for Ulysses.

Sauer, Carl G., Jr.↗
NASA NTRS2017

Synergistic Use of Nighttime Satellite Data, Electric Utility Infrastructure, and Ambient Population to Improve Power Outage Detections in Urban Areas

Natural and anthropogenic hazards are frequently responsible for disaster events, leading to damaged physical infrastructure, which can result in loss of electrical power for affected locations. Remotely-sensed, nighttime satellite imagery from the Suomi National Polar-orbiting Partnership (Suomi-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) can monitor power outages in disaster-affected areas through the identification of missing city lights. When combined with locally-relevant geospatial information, these observations can be used to estimate power outages, defined as geographic locations requiring manual intervention to restore power. In this study, we produced a power outage product based on Suomi-NPP VIIRS DNB observations to estimate power outages following Hurricane Sandy in 2012. This product, combined with known power outage data and ambient population estimates, was then used to predict power outages in a layered, feedforward neural network model. We believe this is the first attempt to synergistically combine such data sources to quantitatively estimate power outages. The VIIRS DNB power outage product was able to identify initial loss of light following Hurricane Sandy, as well as the gradual restoration of electrical power. The neural network model predicted power outages with reasonable spatial accuracy, achieving Pearson coefficients (r) between 0.48 and 0.58 across all folds. Our results show promise for producing a continental United States (CONUS)- or global-scale power outage monitoring network using satellite imagery and locally-relevant geospatial data.

da/night band↗
NASA NTRS1981

Investigation from Japanese MAGSAT Team. Part A. Crustal structure near Japan and in Antarctic station. Part B. Electric currents and hydromagnetic waves in the ionosphere and the magnetosphere

Preliminary results of MAGSAT data analysis are described. Regional anomaly maps (deviations from the MGST model field) for X,Y,Z, and F in the area of 115 to 155 deg E and 20 to 60 deg N were obtained. A similar map for the geomagnetic total force anomaly in the vicinity of Japan showed that the observed anomaly can be explained by the difference in crustal magnetization between the Japan Sea and the Japan Island, which reflects a difference of 25 km in the thickness of the magnetized layer. The MAGSAT record of a sudden commencement of a magnetic storm above the South Atlantic Ocean showed a reverse impulse particularly in the D-component. Results relating to toroidal currents in the ionosphere, transverse and parallel perturbations over the polar regions, the relationship between field aligned currents and precipitating electrons, and the calculation of the subsatellite electric field are also discussed.

Fukushima, N.↗
NASA NTRS2008

On Alfvenic Waves and Stochastic Ion Heating with 1Re Observations of Strong Field-aligned Currents, Electric Fields, and O+ ions

The role that the cleft/cusp has in ionosphere/magnetosphere coupling makes it a very dynamic region having similar fundamental processes to those within the auroral regions. With Polar passing through the cusp at 1 Re in the Spring of 1996, we observe a strong correlation between ion heating and broadband ELF (BBELF) emissions. This commonly observed relationship led to the study of the coupling of large field-aligned currents, burst electric fields, and the thermal O+ ions. We demonstrate the role of these measurements to Alfvenic waves and stochastic ion heating. Finally we will show the properties of the resulting density cavities.

Coffey, Victoria↗
NASA NTRS2011

Forced ion migration for chalcogenide phase change memory device

Non-volatile memory devices with two stacked layers of chalcogenide materials comprising the active memory device have been investigated for their potential as phase change memories. The devices tested included GeTe/SnTe, Ge.sub.2Se.sub.3/SnTe, and Ge.sub.2Se.sub.3/SnSe stacks. All devices exhibited resistance switching behavior. The polarity of the applied voltage with respect to the SnTe or SnSe layer was critical to the memory switching properties, due to the electric field induced movement of either Sn or Te into the Ge-chalcogenide layer. One embodiment of the invention is a device comprising a stack of chalcogenide-containing layers which exhibit phase change switching only after a reverse polarity voltage potential is applied across the stack causing ion movement into an adjacent layer and thus "activating" the device to act as a phase change random access memory device or a reconfigurable electronics device when the applied voltage potential is returned to the normal polarity. Another embodiment of the invention is a device that is capable of exhibiting more that two data states.

Campbell, Kristy A.↗
DOE OSTI2025

Physics of wurtzite ferroelectrics

Ferroelectricity was long considered incompatible with the wurtzite structure, but the recent discovery of switchable polarization in wurtzite alloys has renewed interest in these materials for integrated electronic and memory applications. The development of wurtzite ferroelectrics faces significant technological challenges, which can be addressed through a fundamental physical understanding of their dielectric and ferroelectric properties. This article focuses on the physics that govern the polarization switching behavior, emphasizing the atomic- and meso-scale (domain) mechanisms involved in the transition between polarization states. A distinguishing feature of this article is a deep dive into the role of intrinsic and extrinsic defects—an area that has received limited attention in prior reviews, but is increasingly recognized as central to polarization switching, coercive fields, leakage, and fatigue. We highlight how defect behavior evolves during processing and electrical cycling, often contributing to long-term degradation. We also introduce powerful first-principles defect calculations, common in semiconductors but not yet widespread in ferroelectrics, as tools to understand and design materials. By integrating recent theoretical and experimental insights, we aim to provide a framework for advancing wurtzite ferroelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Carrier-Envelope Phase Control in Terahertz Pulse Generation Using InAs Ribbon Metasurfaces

Generation of broadband terahertz (THz) pulses with variable polarization and carrier-envelope phase can enable the tailoring of THz beam wavefronts for advanced applications in THz imaging and spectroscopy and for strong THz field optics. While metasurfaces composed of deeply subwavelength THz emitters have recently been demonstrated to define the polarization and spatial profile of the generated THz fields, precise phase control or synthesis of THz pulse waveforms remains a challenging problem. Here, we propose and demonstrate metasurfaces composed of indium arsenide (InAs) nanoscale ribbon arrays capable of generating THz pulses with variable carrier-envelope phase. We show that different THz generation mechanisms, each contributing distinct phases, can be activated in the ribbons, enabling carrier-envelope phase control spanning a range of π over a wide band of frequencies (∼1–3 THz). This is achieved solely through the ribbon array geometry using linearly polarized optical excitation of the ribbons. The arrays enable precise control of the THz phase and amplitude, opening the door to advanced structured THz wavefront synthesis using ultrathin dielectric metasurfaces.

carrier-envelope phase↗
DOE OSTI2022

Stabilized Synthesis of 2D Verbeekite: Monoclinic PdSe 2 Crystals with High Mobility and In-Plane Optical and Electrical Anisotropy

PdSe 2 has a layered structure with an unusual, puckered Cairo pentagonal tiling. Its atomic bond configuration features planar 4-fold-coordinated Pd atoms and intralayer Se–Se bonds that enable polymorphic phases with distinct electronic and quantum properties, especially when atomically thin. PdSe 2 is conventionally orthorhombic, and direct synthesis of its metastable polymorphic phases is still a challenge. Here, we report an ambient-pressure chemical vapor deposition approach to synthesize metastable monoclinic PdSe 2 . Monoclinic PdSe 2 is shown to be synthesized selectively under Se-deficient conditions that induce Se vacancies. These defects are shown by first-principles density functional theory calculations to reduce the free energy of the metastable monoclinic phase, thereby stabilizing it during synthesis. Further, the structure and composition of the monoclinic PdSe 2 crystals are identified and characterized by scanning transmission electron microscopy imaging, convergent beam electron diffraction, and electron energy loss spectroscopy. Polarized Raman spectroscopy of the monoclinic PdSe 2 flakes reveals their strong in-plane optical anisotropy. Electrical transport measurements show that the monoclinic PdSe 2 exhibits n-type charge carrier conduction with electron mobilities up to ~298 cm 2 V –1 s –1 and a strong in-plane electron mobility anisotropy of ~1.9. The defect-mediated growth pathway identified in this work is promising for phase-selective direct synthesis of other 2D transition metal dichalcogenides.

2D material↗
NASA NTRS1994

Polar cap potential distributions during periods of positive IMF B(sub y) and B(sub z)

We compare the DE-2 electric field measurements used by HEPPNER and MAYNARD (1987) to illustrate strongly distorted, BC convection patterns for interplanetary magnetic field (IMF) B(sub z) greater than 0 and large absolute value of B(sub y), with simultaneous detections of particle spectra, plasma drifts and magnetic perturbations. Measured potentials greater than 50 keV, driven by the solar wind speeds exceeding 500 km/s, are greater than published correlation analysis predictions by up to 27%. The potential distributions show only two extrema and thus support the basic conclusion that under these conditions the solar wind/IMF drives two-rather than four-cell convection patterns. However, several aspects of the distorted two-cell convection pattern must be revised. In addition to the strong east-west convection in the vicinity of the cusp, indicated by Heppner and Maynard, we also detect comparable components of sunward (equatorward) plasma flow. Combined equipotential and particle precipitation distributions indicate the presence of a lobe cell embedded within the larger, afternoon reconnection cell. Both types rotate in the same sense, with the lobe cell carrying 20-40% of the total afternoon cell potential. We detected no lobe cell within morning convection cell.

Burke, William J.↗
NASA NTRS2012

Forced ion migration for chalcogenide phase change memory device

Non-volatile memory devices with two stacked layers of chalcogenide materials comprising the active memory device have been investigated for their potential as phase-change memories. The devices tested included GeTe/SnTe, Ge.sub.2Se.sub.3/SnTe, and Ge.sub.2Se.sub.3/SnSe stacks. All devices exhibited resistance switching behavior. The polarity of the applied voltage with respect to the SnTe or SnSe layer was critical to the memory switching properties, due to the electric field induced movement of either Sn or Te into the Ge-chalcogenide layer. One embodiment of the invention is a device comprising a stack of chalcogenide-containing layers which exhibit phase-change switching only after a reverse polarity voltage potential is applied across the stack causing ion movement into an adjacent layer and thus "activating" the device to act as a phase-change random access memory device or a reconfigurable electronics device when the applied voltage potential is returned to the normal polarity. Another embodiment of the invention is a device that is capable of exhibiting more than two data states.

Campbell, Kristy A.↗
NASA NTRS2013

Forced Ion Migration for Chalcogenide Phase Change Memory Device

Non-volatile memory devices with two stacked layers of chalcogenide materials comprising the active memory device have been investigated for their potential as phase-change memories. The devices tested included GeTe/SnTe, Ge2Se3/SnTe, and Ge2Se3/SnSe stacks. All devices exhibited resistance switching behavior. The polarity of the applied voltage with respect to the SnTe or SnSe layer was critical to the memory switching properties, due to the electric field induced movement of either Sn or Te into the Ge-chalcogenide layer. One embodiment of the invention is a device comprising a stack of chalcogenide-containing layers which exhibit phase-change switching only after a reverse polarity voltage potential is applied across the stack causing ion movement into an adjacent layer and thus "activating" the device to act as a phase-change random access memory device or a reconfigurable electronics device when the applied voltage potential is returned to the normal polarity. Another embodiment of the invention is a device that is capable of exhibiting more than two data states.

Campbell, Kristy A↗
DOE OSTI2020

Chirality-Dependent Second Harmonic Generation of MoS 2 Nanoscroll with Enhanced Efficiency

Materials with high second harmonic generation (SHG) efficiency and reduced dimensions are favorable for integrated photonics and nonlinear optical applications. Here, we fabricate MoS 2 nanoscrolls with different chiralities and study their SHG performances. As a 1D material, MoS 2 nanoscroll shows reduced symmetry and strong chirality dependency in the polarization-resolved SHG characterizations. This SHG performance can be well explained by the superposition theory of second harmonic field of the nanoscroll walls. MoS 2 nanoscrolls with certain chiralities and diameters in our experiment can have SHG intensity up to 95 times stronger than that of monolayer MoS 2 , and the full potential can still be further exploited. The same chirality-dependent SHG can be expected for nanoscrolls or nanotubes composed of other noncentrosymmetric 2D materials, such as WS 2 , WSe 2 , and hBN. Here, the characterization and analysis results presented here can also be exploited as a nondestructive technique to determine the chiralities of these nanoscrolls and nanotubes.

42 ENGINEERING↗
NASA NTRS1998

Electro-Optic Lightning Detector

Electric field measurements are fundamental to the study of thunderstorm electrification, thundercloud charge structure, and the determination of the locations and magnitudes of charges deposited by lightning. Continuous field observations can also be used to warn of impending electrical hazards. For example, the USAF Eastern Range (ER) and NASA Kennedy Space Center (KSC) in Florida currently operate a ground-based network of electric field mill sensors to warn against lightning hazards to space vehicle operations/launches. The sensors provide continuous recordings of the ambient field. Others investigators have employed flat-plate electric field antennas to detect changes In the ambient field due to lightning. In each approach, electronic circuitry is used to directly detect and amplify the effects of the ambient field on an exposed metal conductor (antenna plate); in the case of continuous field recordings, the antenna plate is alternately shielded and unshielded by a grounded conductor. In this work effort, an alternate optical method for detecting lightning-caused electric field changes is Introduced. The primary component in the detector is an anisotropic electro-optic crystal of potassium di-hydrogen phosphate (chemically written as KH2PO4 (KDP)). When a voltage Is placed across the electro-optic crystal, the refractive Indices of the crystal change. This change alters the polarization state of a laser light beam that is passed down the crystal optic axis. With suitable application of vertical and horizontal polarizers, a light transmission measurement is related to the applied crystal voltage (which in turn Is related to the lightning caused electric field change). During the past two years, all critical optical components were procured, assembled, and aligned. An optical housing, calibration set-up, and data acquisition system was integrated for breadboard testing. The sensor was deployed at NASA Marshall Space Flight Center (MSFC) in the summer of 1998 to collect storm data. Because solid-state technology is used, future designs of the sensor will be significantly scaled down In physical dimension and weight compared to the present optical breadboard prototype. The use of fiber optics would also provide significant practical improvements.

Koshak, William J.↗
NASA NTRS1993

Computer code for scattering from impedance bodies of revolution. Part 3: Surface impedance with s and phi variation. Analytical and numerical results

The third phase of the development of the computer codes for scattering by coated bodies that has been part of an ongoing effort in the Electromagnetics Laboratory of the Electrical Engineering and Computer Science Department at the University of Illinois at Chicago is described. The work reported discusses the analytical and numerical results for the scattering of an obliquely incident plane wave by impedance bodies of revolution with phi variation of the surface impedance. Integral equation formulation of the problem is considered. All three types of integral equations, electric field, magnetic field, and combined field, are considered. These equations are solved numerically via the method of moments with parametric elements. Both TE and TM polarization of the incident plane wave are considered. The surface impedance is allowed to vary along both the profile of the scatterer and in the phi direction. Computer code developed for this purpose determines the electric surface current as well as the bistatic radar cross section. The results obtained with this code were validated by comparing the results with available results for specific scatterers such as the perfectly conducting sphere. Results for the cone-sphere and cone-cylinder-sphere for the case of an axially incident plane were validated by comparing the results with the results with those obtained in the first phase of this project. Results for body of revolution scatterers with an abrupt change in the surface impedance along both the profile of the scatterer and the phi direction are presented.

Uslenghi, Piergiorgio L. E.↗