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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 OSTI2020

Effect of Many Modes on Self-Polarization and Photochemical Suppression in Cavities

The standard description of cavity-modified molecular reactions typically involves a single (resonant) mode, while in reality the quantum cavity supports a range of photon modes. In this work we demonstrate that as more photon modes are accounted for, physico-chemical phenomena can dramatically change, as illustrated by the cavity-induced suppression of the important and ubiquitous process of proton-coupled electron-transfer. Using a multi-trajectory Ehrenfest treatment for the photonmodes, we find that self-polarization effects become essential, and we introduce the concept of selfpolarization- modified Born-Oppenheimer surfaces as a new construct to analyze dynamics. As the number of cavity photon modes increases, the increasing deviation of these surfaces from the cavityfree Born-Oppenheimer surfaces, together with the interplay between photon emission and absorption inside the widening bands of these surfaces, leads to enhanced suppression. The present findings are general and will have implications for the description and control of cavity-driven physical processes of molecules, nanostructures and solids embedded in cavities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1996

Modification of Einstein A Coefficient in Dissipative Gas Medium

Spontaneous radiation in dissipative gas medium such as plasmas is investigated by Langevin equations and the modified Weisskopf-Wigner approximation. Since the refractive index of gas medium is expected to be nearly unity, we shall first neglect the medium polarization effect. We show that absorption in plasmas may in certain case modify the Einstein A coefficient significantly and cause a pit in the A coefficient-density curves for relatively low temperature plasmas and also a pit in the A coefficient-temperature curves. In the next, the effect of medium polarization is taken into account in addition. To our surprise, its effect in certain case is quite significant. The dispersive curves show different behaviors in different region of parameters.

Cao, Chang-Qi↗
NASA NTRS2004

Relativistic Effects and Polarization in Three High-Energy Pulsar Models

We present the influence of the special relativistic effects of aberration and light travel time delay on pulsar high-energy lightcurves and polarization characteristics predicted by three models: the two-pole caustic model, the outer gap model, and the polar cap model. Position angle curves and degree of polarization are calculated for the models and compared with the optical data on the Crab pulsar. The relative positions of peaks in gamma-ray and radio lightcurves are discussed in detail for the models. We find that the two-pole caustic model can reproduce qualitatively the optical polarization characteristics of the Crab pulsar - fast swings of the position angle and minima in polarization degree associated with both peaks. The anticorrelation between the observed flux and the polarization degree (observed in the optical band also for B0656+14) naturally results from the caustic nature of the peaks which are produced in the model due to the superposition of radiation from many different altitudes, ie. polarized at different angles. The two-pole caustic model also provides an acceptable interpretation of the main features in the Crab's radio profile. Neither the outer gap model nor the polar cap model are able to reproduce the optical polarization data on the Crab. Although the outer gap model is very successful in reproducing the relative positions of gamma-ray and radio peaks in pulse profiles, it can reproduce the high-energy lightcurves only when photon emission from regions very close to the light cylinder is included.

Dyks, J.↗
NASA NTRS1993

The effect of polar caps on obliquity

Rubincam has shown that the Martian obliquity is dependent on the seasonal polar caps. In particular, Rubincam analytically derived this dependence and showed that the change in obliquity is directly proportional to the seasonal polar cap mass. Rubincam concludes that seasonal friction does not appear to have changed Mars' climate significantly. Using a computer model for the evolution of the Martian atmosphere, Haberle et al. have made a convincing case for the possibility of huge polar caps, about 10 times the mass of the current polar caps, that exist for a significant fraction of the planet's history. Since Rubincam showed that the effect of seasonal friction on obliquity is directly proportional to polar cap mass, a scenario with a ten-fold increase in polar cap mass over a significant fraction of the planet's history would result in a secular increase in Mars' obliquity of perhaps 10 degrees. Hence, the Rubincam conclusion of an insignificant contribution to Mars' climate by seasonal friction may be incorrect. Furthermore, if seasonal friction is an important consideration in the obliquity of Mars, this would significantly alter the predictions of past obliquity.

Lindner, B. L.↗
NASA NTRS1985

Effect of polarized radiative transfer on the Hanle magnetic field determination in prominences: Analysis of hydrogen H alpha line observations at Pic-du-Midi

The linear polarization of the Hydrogen H alpha line of prominences has been computed, taking into account the effect of a magnetic field (Hanle effect), of the radiative transfer in the prominence, and of the depolarization due to collisions with the surrounding electrons and protons. The corresponding formalisms are developed in a forthcoming series of papers. In this paper, the main features of the computation method are summarized. The results of computation have been used for interpretation in terms of magnetic field vector measurements from H alpha polarimetric observations in prominences performed at Pic-du-Midi coronagraph-polarimeter. Simultaneous observations in one optically thin line (He I D(3)) and one optically thick line (H alpha) give an opportunity for solving the ambiguity on the field vector determination.

Bommier, V.↗
NASA NTRS2016

Effects of Polar Stratospheric Clouds in the Nimbus 7 LIMS Version 6 Data Set

The historic Limb Infrared Monitor of the Stratosphere (LIMS) measurements of 1978-1979 from the Nimbus 7 satellite were re-processed with Version 6 (V6) algorithms and archived in 2002. The V6 data set employs updated radiance registration methods, improved spectroscopic line parameters, and a common vertical resolution for all retrieved parameters. Retrieved profiles are spaced about every 1.6 of latitude along orbits and include the additional parameter of geopotential height. Profiles of O3 are sensitive to perturbations from emissions of polar stratospheric clouds (PSCs). This work presents results of implementing a first-order screening for effects of PSCs using simple algorithms based on vertical gradients of the O3 mixing ratio. Their occurrences are compared with the co-located, retrieved temperatures and related to the temperature thresholds needed for saturation of H2O and/or HNO3 vapor onto PSC particles. Observed daily locations where the major PSC screening criteria are satisfied are validated against PSCs observed with the Stratospheric Aerosol Monitor (SAM) II experiment also on Nimbus 7. Remnants of emissions from PSCs are characterized for O3 and HNO3 following the screening. PSCs may also impart a warm bias in the co-located LIMS temperatures, but by no more than 1-2K at the altitudes of where effects of PSCs are a maximum in the ozone; thus, no PSC screening was applied to the V6 temperatures. Minimum temperatures vary between 187 and 194K and often occur 1 to 2 km above where PSC effects are first identified in the ozone (most often between about 21 and 28 hPa). Those temperature-pressure values are consistent with conditions for the existence of nitric acid trihydrate (NAT) mixtures and to a lesser extent of super-cooled ternary solution (STS) droplets. A local, temporary uptake of HNO3 vapor of order 1-3 ppbv is indicated during mid-January for the 550K surface. Seven-month time series of the distributions of LIMS O3 and HNO3 are shown based on their gridded Level 3 data following the PSC screening. Zonal coefficients of both species are essentially free of effects from PSCs on the 550K surface, based on their average values along PV contours and in terms of equivalent latitude. Remnants of PSCs are still present in O3 on the 450K surface during mid- January. It is judged that the LIMS Level 3 data are of good quality for analyzing the larger-scale, stratospheric chemistry and transport processes during the Arctic winter of 1978- 1979.

Remsberg, Ellis↗
NASA NTRS1993

Comment on 'The semiannual variation of great geomagnetic storms and the postshock Russell-McPherron effect preceding coronal mass ejecta' by N. U. Crooker, E. W. Cliver and B. T. Tsurutani

It is proposed by Crooker et al. (1992) that for a subgroup of great geomagnetic storms, for which the associated strong southward IMF (B(S)) fields reside in the postshock plasma, preceding the driver gas of coronal mass ejections, such strong B(S) fields result from a 'major increase in the Russell-McPherron polarity effect, through a systematic pattern of compression and draping' of the Archimedean field in the x-y plane. The critics test the scenario proposed by Crooker et al., namely, that the Russell-McPherron polarity effect is a major contribution to the semiannual variable of intense geomagnetic storms. It is found by the critics that in the cases studied there is little difference between the B(S) values as measured in geocentric solar ecliptic and geocentric solar magnetospheric coordinates, and it is concluded that the Russell-McPherron mechanism cannot explain by itself the seasonal dependence of intense storms, for which the variation is the largest. Crooker et al. present arguments to show that the combined preshock and postshock Russell-McPherron effect remains the sole cause of the semiannual variation of great storm occurrence.

Gonzalez, W. D.↗
NASA NTRS1990

Polarization analysis of the Advanced X-ray Astrophysical Facility telescope assembly

The Advanced X-ray Astrophysical Facility (AXAF) telescope consists of six concentric paraboloid-hyperboloid pairs of mirrors operating near grazing incidence. Because of the substantial polarization effects at large angles of incidence, there is concern about the feasibility of polarimetry near the focal plane. The primary mirror acts as a tangentially directed half-wave linear retarder and nearly completely depolarizes the linearly polarized component of the light. The secondary mirror introduces an additional half wave of linear retardance. The tangentially directed one-wave linear retarder leaves the transmitted beam in the incident polarization state. The net instrumental polarization effects are small, and polarimetry is feasible with the AXAF.

Brown, Daniel M.↗
DOE OSTI2026

High-throughput computation of electric polarization in solids via Berry flux diagonalization

Electric polarization in the absence of an externally applied electric field is a key property of polar materials, but the standard interpolation-based ab initio approach to compute polarization differences within the modern theory of polarization presents challenges for automated high-throughput calculations. Berry flux diagonalization [J. Bonini et al., Phys. Rev. B 102, 045141 (2020)] has been proposed as an efficient and reliable alternative, though it has yet to be widely deployed. Here, we assess Berry flux diagonalization using ab initio calculations of a large set of materials, introducing and validating heuristics that ensure branch alignment with a minimal number of intermediate interpolated structures. Our automated implementation of Berry flux diagonalization succeeds in cases where prior interpolation-based workflows fail due to band-gap closures or branch ambiguities. Benchmarking with ab initio calculations of 176 candidate ferroelectrics, we demonstrate the efficacy of the approach on a broad range of insulating materials and obtain accurate effective polarization values with fewer interpolated structures than prior automated interpolation-based workflows. Our real-space heuristics that can predict gauge stability a priori from ionic displacements enable a general automated framework for reliable polarization calculations and efficient high-throughput screening of chemically and structurally diverse polar insulators. These results establish Berry flux diagonalization as a robust and efficient method to compute the effective polarization of solids and to accelerate the data-driven discovery of functional polar materials.

Poteshman, Abigail N. [University of Chicago, IL (↗
NASA NTRS1992

Polarization aberration analysis of the Advanced X-ray Astrophysics Facility Telescope assembly

The Advanced X-ray Astrophysics Facility (AXAF) Telescope consists of six concentric paraboloid-hyperboloid pairs of mirrors that operate near grazing incidence. Because of the substantial polarization effects at large angles of incidence there has been concern regarding the feasibility of doing polarimetry near the telescope focal plane. The primary mirror is here shown to act as a tangentially directed half-wave linear retarder and almost completely to depolarize the linearly polarized component of the light. The secondary mirror introduces and additional half-wave of linear retardance. The two-mirror telescope assembly acts as a tangentially directed one-wave linear retarder. Each mirror depolarizes alone but together the two-mirror assembly preserves the polarization state. The net instrumental polarization effects are small and polarimetry is feasible with AXAF.

Chipman, Russell A.↗
NASA NTRS1996

Ocean observations with EOS/MODIS: Algorithm development and post launch studies

An investigation of the influence of stratospheric aerosol on the performance of the atmospheric correction algorithm is nearly complete. The results indicate how the performance of the algorithm is degraded if the stratospheric aerosol is ignored. Use of the MODIS 1380 nm band to effect a correction for stratospheric aerosols was also studied. Simple algorithms such as subtracting the reflectance at 1380 nm from the visible and near infrared bands can significantly reduce the error; however, only if the diffuse transmittance of the aerosol layer is taken into account. The atmospheric correction code has been modified for use with absorbing aerosols. Tests of the code showed that, in contrast to non absorbing aerosols, the retrievals were strongly influenced by the vertical structure of the aerosol, even when the candidate aerosol set was restricted to a set appropriate to the absorbing aerosol. This will further complicate the problem of atmospheric correction in an atmosphere with strongly absorbing aerosols. Our whitecap radiometer system and solar aureole camera were both tested at sea and performed well. Investigation of a technique to remove the effects of residual instrument polarization sensitivity were initiated and applied to an instrument possessing (approx.) 3-4 times the polarization sensitivity expected for MODIS. Preliminary results suggest that for such an instrument, elimination of the polarization effect is possible at the required level of accuracy by estimating the polarization of the top-of-atmosphere radiance to be that expected for a pure Rayleigh scattering atmosphere. This may be of significance for design of a follow-on MODIS instrument. W.M. Balch participated on two month-long cruises to the Arabian sea, measuring coccolithophore abundance, production, and optical properties. A thorough understanding of the relationship between calcite abundance and light scatter, in situ, will provide the basis for a generic suspended calcite algorithm.

Gordon, Howard R.↗
NASA NTRS1972

Effect of polarity of electric current on friction behavior of two gallium-lubricated tantalum slipring assemblies

Computer-processed data from low-speed (10 rpm) slipring experiments with two similar (but of opposite polarity) gallium-lubricated tantalum slipring assemblies (hemisphere against disk) carrying 50 amperes dc in vacuum (10 to the minus 9th power torr) showed that the slipring assembly with the anodic hemisphere had significantly lower peak-to-peak values and standard deviations of coefficient-of-friction samples (a measure of smoothness of operation) than the slipring assembly with the cathodic hemisphere. Similar data from an experiment with the same slipring assemblies running currentless showed more random differences in the frictional behavior between the two assemblies.

Przybyszewski, J.↗
NASA NTRS1971

A polarization-color effect in the K-corona.

An observation of the corona during the 7 March, 1970 eclipse through a Wollaston prism-red and blue filter combination was carried out for the purpose of confirming the prediction that the component of the K-corona with electric vector radial to the Sun is redder than the tangential component. An analysis of a portion of the resulting data seems to confirm this prediction, and also indicates that the method is useful for determining the three-dimensional configuration of the very inner corona. A three-dimensional configuration is suggested for a portion of the NE quadrant of the Sun, including the large NE streamer and an adjacent low-lying loop.

Billings, D. E.↗
NASA NTRS1976

Recent decametric and hectometric observations of Jupiter

Observational results on Jupiter's high-frequency radiation, for the range 1-35 MHz (10 to 100 m), obtained over the past six years with the aid of orbited telescopes, are surveyed. Spectral distributions, periodic effects, burst waveforms and dynamic spectra of storms, polarization effects, high-resolution interferometry, and possible correlations with solar activity are discussed. Related spacecraft experiments are described. Close attention is given to long-term accumulation of occurrence probability data as functions of time and frequency (synoptic monitoring) on Jovian HF emission, and to dominating effects of the Jovian satellite Io, as well as modulation of periodicities by the 11.9-year orbital motion period of Jupiter. Possible effects of the other four Jovian satellites immersed in the Jovian magnetosphere are also taken into consideration. Absence of a Jovian Faraday effect and polarization of fine burst structure are discussed.

Carr, T. D.↗
NASA NTRS1978

The effects of polar stratwarms on the winds at the mesopause level in mid latitudes

The continuous measurement of the wind profile over the 80 to 100 km region by means of radio reflections from meteor trails provides data which can be correlated with stratospheric temperature changes inferred from satellite radiance data. The very preliminary results presented show a tendency for stratospheric warming events to produce dramatic changes in the circulation in the neighborhood of the mesopause at 34 deg N. The mean zonal wind over the height range 80 to 100 km above Atlanta for the period November, 1974 through February, 1975 is presented in a graph.

Roper, R. G.↗