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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Multipolar Raman Scattering vs Interfacial Nanochemistry: Case of 4-Mercaptopyridine on Gold

Caution needs to be exercised in associating changes in plasmon-enhanced Raman spectra with chemical transformations. This is demonstrated through a detailed analysis of tip-enhanced Raman (TER) scattering from 4-mercaptopyridine (MPY) on gold. The substrate used consists of gold nanoplates atop a gold surface featuring heterogeneous grooves, all coated with a monolayer of MPY. The brightest spectra across the substrate exhibit features that can only be recovered by considering the generalized polarizability of oriented MPY molecules. Finally, the complex TER spectra we observe do not mark interfacial chemistry, but rather, multipolar TER scattering driven by local field gradients.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Mars Aeronomy Observer: Report of the Science Working Team

The Mars Aeronomy Observer (MAO) is a candidate follow-on mission to Mars Observer (MO) in the Planetary Observer Program. The four Mariner and two Viking spacecraft sent to Mars between 1965 and 1976 have provided a wealth of information concerning Martian planetology. The Mars Observer, to be launched in 1990, will build on their results by further examining the elemental and mineralogical composition of the surface, the strength and multipolar composition of the planetary magnetic field, the gravitational field and topography, and the circulation of the lower atmosphere. The Mars Aeronomy Observer is intended to address the last major aspects of Martian environment which have yet to be investigated: the upper atmosphere, the ionsphere, and the solar wind interaction region.

Hunten, Donald M.↗
DOE OSTI2014

Dispersion potential between three-bodies with arbitrary electric multipole polarizabilities: Molecular QED theory

Molecular quantum electrodynamics is used to obtain an expression for the retarded dispersion energy shift between three arbitrarily electrically polarizable atoms or molecules. A generalized Craig-Power Hamiltonian that depends quadratically on the electric displacement field is employed together with third-order diagrammatic perturbation theory. This approach simplifies the calculation relative to the use of the usual multipolar coupling Hamiltonian that is linear in the displacement field. Specific higher multipole non-additive contributions are then extracted. These include dipole-dipole-quadrupole, dipole-quadrupole-quadrupole, and dipole-dipole-octupole potentials valid for oriented and isotropic species with arbitrary separation distances between particles, extending recent work in which these energy shifts were given for equilateral triangle and collinear geometries. Near-zone limiting forms are found to agree with earlier works in which static inter-particle couplings were used.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Local properties of the large-scale peaks of the CMB temperature

In the present work, we study the largest structures of the CMB temperature measured by Planck in terms of the most prominent peaks on the sky, which, in particular, are located in the southern galactic hemisphere. Besides these large-scale features, the well-known Cold Spot anomaly is included in the analysis. All these peaks would contribute significantly to some of the CMB large-scale anomalies, as the parity and hemispherical asymmetries, the dipole modulation, the alignment between the quadrupole and the octopole, or in the case of the Cold Spot, to the non-Gaussianity of the field. The analysis of the peaks is performed by using their multipolar profiles, which characterize the local shape of the peaks in terms of the discrete Fourier transform of the azimuthal angle. In order to quantify the local anisotropy of the peaks, the distribution of the phases of the multipolar profiles is studied by using the Rayleigh random walk methodology. Finally, a direct analysis of the 2-dimensional field around the peaks is performed in order to take into account the effect of the galactic mask. The results of the analysis conclude that, once the peak amplitude and its first and second order derivatives at the centre are conditioned, the rest of the field is compatible with the standard model. In particular, it is observed that the Cold Spot anomaly is caused by the large value of curvature at the centre.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Electrostatic force distribution on an electrodynamic screen

The enormous potential of solar energy harvesting plants to provide clean energy is severely limited by dust accumulation on their optical surfaces. In lieu of the most commonly-practiced manual cleaning method of using high-pressure water jets, electrodynamic screen (EDS) technology offers an attractive solution for removing dust particles from optical surfaces using electrostatic forces. In this paper, the impacts of different EDS design parameters in the electric field distribution on an EDS have been studied. Furthermore, based on electric field expressions, closed-form solutions for multipolar dielectrophoretic (DEP) forces in the EDS application are provided. Detailed evaluation of the EDS performance necessi- tates investigation of different forces involved in the dust removal process. Different comparisons are made between repelling and attracting forces exerted on dust particles deposited on an EDS surface. These comparisons elucidate EDS performance in the removal of a given size range of dust particles. The significant detrimental impact of relative humidity upon the dust removal process is quantitatively addressed. As a result, it is shown how just a 10 percent increase in relative humidity can make the repelling force ineffective in the dust removal process.

14 SOLAR ENERGY↗
NASA NTRS1996

On the Accurate Calibration of the SeaWinds Radar Antenna: A Cylindrical Near-Field Measurement Approach

The radar antenna for the SeaWinds scatterometer will be of the multipolarized, multi- incidence angle, conical scanning design. It will measure echos from the sea surface to derive both the speed and direction of winds. To calibrate this radar, measurement error models are used to define the effects of near-field measurement bias errors on antenna gain and far-field radiation patterns.

SeaWinds↗
DOE OSTI2017

Indirect measurements of slow modes in the Hermean magnetosphere

The aim of this study is to simulate slow mode structures in the Hermean magnetosphere. We use the single fluid MHD code PLUTO and a multipolar expansion of the Northward displaced Hermean magnetic field, to perform simulations mimicking the solar wind and interplanetary magnetic field conditions during 08/09/2011 MESSERGER orbit, susceptible to cross a slow mode structure [F. Pantellini et al, PSS, 112, 1 (2015) and J. Varela et al, PSS, 125, 80 (2016)]. The simulation shows the presence of a slow mode structure nearby the North pole. The satellite trajectory crosses the slow mode compressional front, although the region with the largest pressure and magnetic field lines bending is located Northernmost. The comparison with the MESSENGER data shows a decrease of the magnetic field module in the trajectory region where the slow mode structure is predicted by the simulation. Further analysis of the plasma density measurements by MESSENGER Fast Imaging Plasma Spectrometer are required to confirm the presence of the slow mode structure.

Filippo, Pantellini↗
DOE OSTI2020

A quantum liquid of magnetic octupoles on the pyrochlore lattice

Spin liquids are highly correlated yet disordered states formed by the entanglement of magnetic dipoles. Theories define such states using gauge fields and deconfined quasiparticle excitations that emerge from a local constraint governing the ground state of a frustrated magnet. For example, the ‘2-in–2-out’ ice rule for dipole moments on a tetrahedron can lead to a quantum spin ice in rare-earth pyrochlores. However, $f$-electron ions often carry multipole degrees of freedom of higher rank than dipoles, leading to intriguing behaviours and ‘hidden’ orders. In this paper we show that the correlated ground state of a Ce 3+ -based pyrochlore, Ce 2 Sn 2 O 7 , is a quantum liquid of magnetic octupoles. Our neutron scattering results are consistent with a fluid-like state where degrees of freedom have a more complex magnetization density than that of magnetic dipoles. The nature and strength of the octupole–octupole couplings, together with the existence of a continuum of excitations attributed to spinons, provides further evidence for a quantum ice of octupoles governed by a ‘2-plus–2-minus’ rule. Our work identifies Ce 2 Sn 2 O 7 as a unique example of frustrated multipoles forming a ‘hidden’ topological order, thus generalizing observations on quantum spin liquids to multipolar phases that can support novel types of emergent fields and excitations.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tip-Enhanced Multipolar Raman Scattering

We record nanoscale chemical images of thiobenzonitrile (TBN)-functionalized plasmonic gold nanocubes via tip-enhanced Raman spectroscopy (TERS). The spatially averaged optical response is dominated by conventional (dipolar) TERS scattering from TBN but also contains weaker spectral signatures in the 1225-1500 cm-1 region. The weak optical signatures dominate some of the recorded single pixel spectra. We can uniquely assign these Raman forbidden transitions to multipolar Raman scattering, which implicates spatially varying enhanced electric field gradients at plasmonic tip-sample nanojunctions. Specifically, we can assign observations of tip-enhanced electric dipole-magnetic dipole as well as electric dipole-electric quadrupole driven transitions. These signals need to be understood and accounted for in the interpretation of TERS spectral images, particularly in on-going quests aimed at chemical reaction mapping via TERS.

Wang, Chih-Feng↗
DOE OSTI2016

Generalized theoretical method for the interaction between arbitrary nonuniform electric field and molecular vibrations: Toward near-field infrared spectroscopy and microscopy

A theoretical method to compute infrared absorption spectra when a molecule is interacting with an arbitrary nonuniform electric field such as near-fields is developed and numerically applied to simple model systems. The method is based on the multipolar Hamiltonian where the light-matter interaction is described by a spatial integral of the inner product of the molecular polarization and applied electric field. The computation scheme is developed under the harmonic approximation for the molecular vibrations and the framework of modern electronic structure calculations such as the density functional theory. Infrared reflection absorption and near-field infrared absorption are considered as model systems. The obtained IR spectra successfully reflect the spatial structure of the applied electric field and corresponding vibrational modes, demonstrating applicability of the present method to analyze modern nanovibrational spectroscopy using near-fields. The present method can use arbitral electric fields and thus can integrate two fields such as computational chemistry and electromagnetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Application of high-quality SiO2 grown by multipolar ECR source to Si/SiGe MISFET

A 5 nm-thick SiO2 gate was grown on an Si(p+)/Si(0.8)Ge(0.2) modulation-doped heterostructure at 26 C with an oxygen plasma generated by a multipolar electron cyclotron resonance source. The ultrathin oxide has breakdown field above 12 MV/cm and fixed charge density about 3 x 10 exp 10/sq cm. Leakage current as low as 1/micro-A was obtained with the gate biased at 4 V. The MISFET with 0.25 x 25 sq m gate shows maximum drain current of 41.6 mA/mm and peak transconductance of 21 mS/mm.

Sung, K. T.↗
DOE OSTI2015

NUMERICAL STUDY ON THE EMERGENCE OF KINKED FLUX TUBE FOR UNDERSTANDING OF POSSIBLE ORIGIN OF δ-SPOT REGIONS

We carried out an magnetohydrodynamic simulation where a subsurface twisted kink-unstable flux tube emerges from the solar interior to the corona. Unlike the previous expectations based on the bodily emergence of a knotted tube, we found that the kinked tube can spontaneously form a complex quadrupole structure at the photosphere. Due to the development of the kink instability before the emergence, the magnetic twist at the kinked apex of the tube is greatly reduced, although the other parts of the tube are still strongly twisted. This leads to the formation of a complex quadrupole structure: a pair of the coherent, strongly twisted spots and a narrow complex bipolar pair between it. The quadrupole is formed by the submergence of a portion of emerged magnetic fields. This result is relevant for understanding the origin of the complex multipolar δ-spot regions that have a strong magnetic shear and emerge with polarity orientations not following Hale-Nicholson and Joy Laws.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

BREAKOUT RECONNECTION OBSERVED BY THE TESIS EUV TELESCOPE

We present experimental evidence of the coronal mass ejection (CME) breakout reconnection, observed by the TESIS EUV telescope. The telescope could observe solar corona up to 2 R{sub ⊙} from the Sun center in the Fe 171 Å line. Starting from 2009 April 8, TESIS observed an active region (AR) that had a quadrupolar structure with an X-point 0.5 R{sub ⊙} above photosphere. A magnetic field reconstructed from the Michelson Doppler Imager data also has a multipolar structure with an X-point above the AR. At 21:45 UT on April 9, the loops near the X-point started to move away from each other with a velocity of ≈7 km s{sup −1}. At 01:15 UT on April 10, a bright stripe appeared between the loops, and the flux in the GOES 0.5–4 Å channel increased. We interpret the loops’ sideways motion and the bright stripe as evidence of the breakout reconnection. At 01:45 UT, the loops below the X-point started to slowly move up. At 15:10 UT, the CME started to accelerate impulsively, while at the same time a flare arcade formed below the CME. After 15:50 UT, the CME moved with constant velocity. The CME evolution precisely followed the breakout model scenario.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Remote sensing of forest ecosystem dynamics: Measurements and modeling

The development of an integrated approach to the modeling of forest dynamics encompassing submodels of forest growth and succession, soil processes and radiation interactions, is reported. Remote sensing technology is a key element of this study in that it provides data for developing, initializing, updating, and validating the models. The objectives are reviewed, the data collected and models in use are discussed, and a framework for studying interactions between the forest growth, soil process and energy interaction components, is described. Remote sensing technology used in the study includes optical and microwave field, aircraft and satellite borne instruments. The types of data collected during intensive field and aircraft campaigns included bidirectional reflectance, thermal emittance and multifrequency, multipolarization synthetic aperture radar backscatter. Synthetic imagery of derived products such as forest biomass and NDVI (Normalized Difference Vegetative Index), and collections of ground data are being assembled in a georeferenced data base. These data are used to drive or test multidiscipline simulations of forested ecosystems. Enhancements to the modeling environment permit considerable flexibility in configuring simulations and selecting results for reporting and graphical display.

Williams, Darrel L.↗
NASA NTRS2008

Topological Evolution of a Fast Magnetic Breakout CME in 3-Dimensions

W present the extension of the magnetic breakout model for CME initiation to a fully 3-dimensional, spherical geometry. Given the increased complexity of the dynamic magnetic field interactions in 3-dimensions, we first present a summary of the well known axisymmetric breakout scenario in terms of the topological evolution associated with the various phases of the eruptive process. In this context, we discuss the completely analogous topological evolution during the magnetic breakout CME initiation process in the simplest 3-dimensional multipolar system. We show that an extended bipolar active region embedded in an oppositely directed background dipole field has all the necessary topological features required for magnetic breakout, i.e. a fan separatrix surface between the two distinct flux systems, a pair of spine fieldlines, and a true 3-dimensional coronal null point at their intersection. We then present the results of a numerical MHD simulation of this 3-dimensional system where boundary shearing flows introduce free magnetic energy, eventually leading to a fast magnetic breakout CME. The eruptive flare reconnection facilitates the rapid conversion of this stored free magnetic energy into kinetic energy and the associated acceleration causes the erupting field and plasma structure to reach an asymptotic eruption velocity of greater than or approx. equal to 1100 km/s over an approx.15 minute time period. The simulation results are discussed using the topological insight developed to interpret the various phases of the eruption and the complex, dynamic, and interacting magnetic field structures.

Lynch, B. J.↗
DOE OSTI2012

DIPOLE COLLAPSE AND DYNAMO WAVES IN GLOBAL DIRECT NUMERICAL SIMULATIONS

Magnetic fields of low-mass stars and planets are thought to originate from self-excited dynamo action in their convective interiors. Observations reveal a variety of field topologies ranging from large-scale, axial dipoles to more structured magnetic fields. In this article, we investigate more than 70 three-dimensional, self-consistent dynamo models in the Boussinesq approximation obtained by direct numerical simulations. The control parameters, the aspect ratio, and the mechanical boundary conditions have been varied to build up this sample of models. Both strongly dipolar and multipolar models have been obtained. We show that these dynamo regimes in general can be distinguished by the ratio of a typical convective length scale to the Rossby radius. Models with a predominantly dipolar magnetic field were obtained, if the convective length scale is at least an order of magnitude larger than the Rossby radius. Moreover, we highlight the role of the strong shear associated with the geostrophic zonal flow for models with stress-free boundary conditions. In this case the above transition disappears and is replaced by a region of bistability for which dipolar and multipolar dynamos coexist. We interpret our results in terms of dynamo eigenmodes using the so-called test-field method. We can thus show that models in the dipolar regime are characterized by an isolated 'single mode'. Competing overtones become significant as the boundary to multipolar dynamos is approached. We discuss how these findings relate to previous models and to observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Pre-planetary nebulae: a context for principles, progress, and questions on how binaries and magnetic fields produce jets

Astrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of CE for close binaries (PPN-C). Furthermore, the physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally.

(ISM:) planetary nebulae: general↗