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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

A rapid change of the Hercules X-1 pulse profile and high-state duration

Her X-1 has been observed in the 13-180 keV energy range by the HEAO 1 A-4 Low-Energy Detectors during selected phases of the 35 d on-off cycle. During a pointing observation in September 1978, the pulse profile was observed to change continuously from its normal shape to an anomalous double-pulsed form. Moreover, at this time the main-on state, normally of the duration 10 d, was seen to terminate after only 7 d. Since such an anomalous pulse profile has also been reported by Truemper et al. in 1986 during a short-on state, three short-on states in the HEAO 1 data were also investigated. One short-on observation had the sensitivity to detect pulsing, and the observed profile also had an anomalous double-pulsed form. Current models for the 35 d cycle of Her X-1 have been examined, and a model with a neutron star undergoing free precession could not explain the sudden change of pulse profile within 20 hr at the end of a main-on state.

Soong, Yang↗
NASA NTRS1989

Characterization of hollow cathode, ring cusp discharge chambers

An experimental study into the effects of changes in such physical design parameters as hollow cathode position, anode position and ring cusp magnetic field configuration and strength on discharge chamber performance, is described. The results are presented in terms of comparative plasma ion energy cost, extracted ion fraction and ion beam profile data. Such comparisons are used to demonstrate specific means by which changes in these design parameters induce changes in performance, i.e., through changes in the loss rates of primary electrons to the anode, of ions to discharge chamber walls or of ions to cathode and anode surfaces. Results show: (1) the rate of primary electron loss to the anode decreases as the anode is moved downstream of the ring cusp toward the screen grid, (2) the loss rate of ions to hollow cathode surfaces are excessive if the cathode is located upstream of a point of peak magnetic flux density on the discharge chamber centerline, and (3) the fraction of the ions produced that are lost to discharge chamber walls and ring magnet surfaces is reduced by positioning the magnet rings so the plasma density is uniform over the grid surface and so there are no steep magnetic flux density gradients near the walls through which ions can be lost by Bohm diffusion. The uniformity of the plasma density at the grids can also be improved by moving the point of primary electron injection into the discharge chamber off of the chamber centerline. Other results show the discharge chamber losses decrease when a filament cathode is substituted for a hollow cathode to the extent of the hollow cathode operating power. When plasma ion energy cost is determined in such a way that the cost of operating the hollow cathode is subtracted out, the performance using either electron source is similar.

Vaughn, Jason A.↗
NASA NTRS2017

Realistic Modeling of Interaction of Quiet-Sun Magnetic Fields with the Chromosphere

High­‐resolution observations and 3D MHD simulations reveal intense interaction between the convection zone dynamics and the solar atmosphere on subarcsecond scales. To investigate processes of the dynamical coupling and energy exchange between the subsurface layers and the chromosphere we perform 3D radiative MHD modeling for a computational domain that includes the upper convection zone and the chromosphere, and investigate the structure and dynamics for different intensity of the photospheric magnetic flux. For comparison with observations, the simulation models have been used to calculate synthetic Stokes profiles of various spectral lines. The results show intense energy exchange through small­‐scale magnetized vortex tubes rooted below the photosphere, which provide extra heating of the chromosphere, initiate shock waves, and small­‐scale eruptions.

quiet-sun↗
NASA NTRS2022

Mitigation Strategies for the Impact of Low Energy Laser Pulses in CALIOP Calibration and Level 2 Retrievals

Since mid-2016, the frequency of low energy laser pulses emitted by the CALIPSO lidar has been slowly increasing due to pressure losses in the canister housing the laser. While originally confined primarily to the South Atlantic Anomaly (SAA) region, these low energy pulses now occur intermittently around the globe. Low energy pulses can cause calibration biases and degrade the science quality of level 2 retrievals. We describe a new low energy mitigation (LEM) algorithm that will be implemented incrementally in future versions of the CALIOP data processing to identify and reject affected profiles during calibration and feature detection. The LEM algorithm effectively eliminates low energy calibration biases, improves level 2 retrievals, and minimizes level 2 data loss.

Jason Tackett↗
NASA NTRS1994

The early ultraviolet, optical, and radio evolution of the soft X-ray transient GRO J0422+32

We have monitored the evolution of the transient X-ray source GRO J0422+32 from approximately 2 weeks postdiscovery into its early decline phase at ultraviolet, optical, and radio wavelengths. Optical and ultraviolet spectra exhibit numerous, but relatively weak, high-excitation emission lines such as those arising from He II, N III, N V, and C IV superposed on an intrinsically blue continuum. High-resolution optical spectroscopy reveals line profiles which are double peaked, and in the case of the higher order Balmer lines, superposed on a broad absorption profile. The early outburst optical-ultraviolet continuum energy distribution is well represented by a two power-law fit with a break at approximately equal 4000 A. Radio observations with the Very Large Array (VLA) reveal a flat-spectrum source, slowly increasing in intensity at the earliest epochs observed, followed by an approximate power-law decay light curve with an index of -1. Light curves for each wavelength domain are presented and discussed. Notable are the multiple secondary outbursts seen in the optical more than 1 year postdiscovery, and spectral changes associated with secondary rises seen in the radio and UV. We find that the ultraviolet and optical characteristics of GRO J0422+32 as well as its radio evolution, are similar to other recent well-observed soft X-ray transients (also called X-ray novae) such as Cen X-4, A0620-00 (V616 Mon), and Nova Muscae 1991 (GS 1124-683), suggesting that GRO J0422+32 is also a member of that subclass of low-mass X-ray binaries. We present definitive astrometric determination of the source position, and place an upper limit of R approximately equals 20 from our analysis of the Palomar Observatory Sky Survey (POSS). Additionally, we derive distinct values for color excess from analysis of the optical (E(B-V) = 0.23) and ultraviolet (E(B-V) = 0.4) data, suggesting an intrinsic magnitude of 19-19.5 for the progenitor if it is mid-K dwarf. This leads to a likely range of 2.4-3.0 kpc for the source distance, which is consistent with our separate estimate of 2.4 +/- 0.4 kpc based on measurement of the NaD interstellar line profile. Adopting 2.4 kpc and E(B-V) = 0.23, the outburst absolute magnitude was M approximately equals 0.0, which is a typical value for this class of objects.

Shrader, C. R.↗
NASA NTRS1977

A heavy ion beam probe system for investigation of a modified Penning discharge

An ion beam probe diagnostic system can measure time- and space-resolved profiles of plasma space potential and electron density. In combination with a computer iterative technique, the ion beam probe can determine both the space potential profile in plasmas containing strong electric fields and potentials comparable in magnitude to the energy of the probing ion beam. During ion beam probing of a modified Penning discharge, several groups of secondary ions were observed coming from the plasma with a fixed primary beam energy and momentum. The energies of these ions were within 10 percent of the values predicted by a computer-generated model of the potential profile in the plasma. The mechanical and electronic components of the system are described, with particular emphasis on those features required to probe plasma potentials comparable in magnitude to the ion beam energy.

Kambic, G. X.↗
NASA NTRS1995

Laboratory studies of 3.3 micron emission from naphthalene induced by 193 and 248 nanometer excitation

Laboratory studies of infrared emission from gas-phase naphthalene in the 3.3 micrometer region following ultraviolet laser excitation are used to interpret the unidentified infrared bands observed in many astronomical objects. A time-resolved Fourier transform infrared emission technique acquires the time and spectrally resolved data. Two excitation wavelengths are employed: 193 nm and 248 nm. The infrared emission features are strongly dependent on the initial excitation energy. Wavelength-resolved spectra recorded 6.8 microseconds after the laser pulse show a 45/cm redshift from the gas-phase absorption spectra for 193 nm excitation and 25/cm for 248 nm excitation. We hypothesize that a series of sequence bands originating from the highly vibrationally excited ensemble of molecules is responsible for the observed shift. As collisional and radiative deactivation removes energy from the highly vibrationally excited molecules, the maximum in the emission profile gradually approaches the customary absorption maximum. This indicates that the amount of redshift is strongly dependent on the amount of internal vibrational energy in the molecule at the time of the vibrational transition.

Williams, Richard M.↗
NASA NTRS2011

Base Heating Sensitivity Study for a 4-Cluster Rocket Motor Configuration in Supersonic Freestream

In support of launch vehicle base heating and pressure prediction efforts using the Loci-CHEM Navier-Stokes computational fluid dynamics solver, 35 numerical simulations of the NASA TND-1093 wind tunnel test have been modeled and analyzed. This test article is composed of four JP-4/LOX 500 lbf rocket motors exhausting into a Mach 2 - 3.5 wind tunnel at various ambient pressure conditions. These water-cooled motors are attached to a base plate of a standard missile forebody. We explore the base heating profiles for fully coupled finite-rate chemistry simulations, one-way coupled RAMP (Reacting And Multiphase Program using Method of Characteristics)-BLIMPJ (Boundary Layer Integral Matrix Program - Jet Version) derived solutions and variable and constant specific heat ratio frozen flow simulations. Variations in turbulence models, temperature boundary conditions and thermodynamic properties of the plume have been investigated at two ambient pressure conditions: 255 lb/sq ft (simulated low altitude) and 35 lb/sq ft (simulated high altitude). It is observed that the convective base heat flux and base temperature are most sensitive to the nozzle inner wall thermal boundary layer profile which is dependent on the wall temperature, boundary layer s specific energy and chemical reactions. Recovery shock dynamics and afterburning significantly influences convective base heating. Turbulence models and external nozzle wall thermal boundary layer profiles show less sensitivity to base heating characteristics. Base heating rates are validated for the highest fidelity solutions which show an agreement within +/-10% with respect to test data.

Mehta, Manish↗
NASA NTRS1968

Nighttime cooling of the protonosphere.

Protonosphere nighttime cooling, calculating time dependent electron temperature and density profiles along geomagnetic field lines and electron and energy fluxes

Bauer, P.↗
NASA NTRS1976

Similarity theory of the buoyantly interactive planetary boundary layer with entrainment

A similarity model is developed for the vertical profiles of turbulent flow variables in an entraining turbulent boundary layer of arbitrary buoyant stability. In the general formulation the vertical profiles, internal rotation of the velocity vector, discontinuities or jumps at a capping inversion and bulk aerodynamic coefficients of the boundary layer are given by solutions to a system of ordinary differential equations in the similarity variable. To close the system, a formulation for buoyantly interactive eddy diffusivity in the boundary layer is introduced which recovers Monin-Obukhov similarity near the surface and incorporates a hypothesis accounting for the observed variation of mixing length throughout the boundary layer. The model is tested in simplified versions which depend only on roughness, surface buoyancy, and Coriolis effects by comparison with planetary-boundary-layer wind- and temperature-profile observations, measurements of flat-plate boundary layers in a thermally stratified wind tunnel and observations of profiles of terms in the turbulent kinetic-energy budget of convective planetary boundary layers. On balance, the simplified model reproduced the trend of these various observations and experiments reasonably well, suggesting that the full similarity formulation be pursued further.

Hoffert, M. I.↗
NASA NTRS1981

IUE observations of Seyfert galaxies

The L alpha/H beta ratio and line profiles for several galaxies are presented. The continuous energy distribution of NGC 4151 and MKN 509 are presented from the X-ray region to the infrared.

Wu, C. C.↗
NASA NTRS1981

Steady-state observations of geomagnetically trapped energetic heavy ions and their implications for theory

Data from the Heavy Ion Telescope on board Explorer 45 and the heavy ion channels on the ATS-6 spacecraft are used to describe the equatorial radial profiles of protons and He ions in the energy range of 0.1-1 MeV/nucleon. Measurements during a quiet period in June 1972 revealed that: fluxes of energetic protons and heavy ions inside L equals 4.5 are stable, with no observed decay; He ions of a given level are confined to the equatorial plane in a narrow L-range centered at Lmax; the equatorial differential flux ratio, compared on the basis of equal energy/ion, can exceed unity, indicating that He ion fluxes can be greater than equivalent energy proton fluxes; radial diffusion driven by variations of the magnetic field adequately models processes occurring in the inner magnetosphere for ion energies over 200 keV. The ATS-6 data from GEO found energetic heavy ions always present at L equals 6.6 and enhanced during magnetospheric substorms.

Fritz, T. A.↗
NASA NTRS1984

Vibrational and rotational excitation of CO in comets. Part 1: Non-equilibrium calculations. Part 2: Results of the calculation for standard bright comet, comet Iras-Araki-Alcock and comet Halley

The vibrational and rotational excitation of the CO molecule in cometary comae were investigated using a model which includes IR vibrational pumping by the solar flux, vibrational and rotational radiative decay, and collisional coupling among rotational states. Steady state was not assumed in solving the rate equations. The evolution of a shell of CO gas was monitored as it expanded from the nucleus into the outer coma. Collisional effects were treated using a kinetic temperature profile derived from theoretical work on the coma energy balance. The kinetic temperature was assumed to be extremely cold in the inner coma; this has significant consequences for the CO excitation. If optical depth effects are ignored, only low J transitions will be significantly excited in comets observed at high spatial resolution. Ground-based observations of CO co-vibrational and rotational transitions will be extremely difficult due to lack of sensitivity and/or terrestrial absorption. However, CO should be detectable from a large comet with favorable observing geometry if the CO is a parent molecule present at the 10% level (or greater) relative to H2O. Observations using cooled, spaceborne instruments should be capable of detecting CO emission from even moderately bright comets.

Chin, G.↗
NASA NTRS1985

An analysis of the bright white dwarf CD - 38 deg 10980

The bright DA white dwarf CD - 38 deg 10980 is comprehensively analyzed using all available data. Detailed comparisons of the overall energy distribution and Lyman-alpha and Balmer profiles are made with theoretical predictions based on a homogeneous grid of model atmospheres. These comparisons yield a consistent, well-defined effective temperature and surface gravity for this star of 24,700 + or - 250 K and log g = 7.95 + or - 0.15, respectively. A new gravitational redshift of 28.4 + or - 4.8 km/s is derived from an IUE high-dispersion spectrum. Conclusions regarding the mass and radius of CD - 38 deg 10980 are also presented.

Holberg, J. B.↗
NASA NTRS1990

Atmospheric radiative flux divergence from Clouds and Earth Radiant Energy System (CERES)

A major objective of the Clouds and Earth Radiant Energy System (CERES) is the computation of vertical profiles through the atmosphere of the divergence of radiation flux, with global coverage. This paper discusses the need for radiation divergence and presents some options for its inference from CERES measurements and other data from the Earth Observating System.

Smith, Louis G.↗
NASA NTRS1991

Outflows driven by cosmic-ray pressure in broad absorption line QSOs

It is shown how the escape of ultrarelativistic neutrons from the central engine of an AGN can lead to the production of a strong fast wind with most of the acceleration occurring outside the broad emission line region. This feature is required in order to explain observations of broad absorption line (BAL) QSOs, in which the blue wings of the broad emission lines are often absorbed. The dynamical and thermal structure of the wind is determined, and the formation of BALs in such an outflow is modeled, deriving line profiles and constraining the rate at which the energy or relativistic protons has be be converted to thermal energy in order to provide pressure confinement for the BAL clouds. The problem of acceleration and survival of the clouds is discussed.

Begelman, Mitchell↗
NASA NTRS1997

JPL Experience with the Mars Pathfinder, Mission Simulation Battery

A summary of the Mars Pathfinder Battery is given. The battery survived 47 days at 25 deg. C; it survived a 7 month stand at 10 to -5 deg. C; it met and exceeded 40 ampere-hour capacity for EDL; it met the 30 cycle minimum for Mars surface operation; and the project power profile for MArs surface operation does not yield energy balance.

Perrone, Dave↗
NASA NTRS2000

Lidar Remote Sensing for Industry and Environment Monitoring

Contents include the following: 1. Keynote paper: Overview of lidar technology for industrial and environmental monitoring in Japan. 2. lidar technology I: NASA's future active remote sensing mission for earth science. Geometrical detector consideration s in laser sensing application (invited paper). 3. Lidar technology II: High-power femtosecond light strings as novel atmospheric probes (invited paper). Design of a compact high-sensitivity aerosol profiling lidar. 4. Lasers for lidars: High-energy 2 microns laser for multiple lidar applications. New submount requirement of conductively cooled laser diodes for lidar applications. 5. Tropospheric aerosols and clouds I: Lidar monitoring of clouds and aerosols at the facility for atmospheric remote sensing (invited paper). Measurement of asian dust by using multiwavelength lidar. Global monitoring of clouds and aerosols using a network of micropulse lidar systems. 6. Troposphere aerosols and clouds II: Scanning lidar measurements of marine aerosol fields at a coastal site in Hawaii. 7. Tropospheric aerosols and clouds III: Formation of ice cloud from asian dust particles in the upper troposphere. Atmospheric boundary layer observation by ground-based lidar at KMITL, Thailand (13 deg N, 100 deg. E). 8. Boundary layer, urban pollution: Studies of the spatial correlation between urban aerosols and local traffic congestion using a slant angle scanning on the research vessel Mirai. 9. Middle atmosphere: Lidar-observed arctic PSC's over Svalbard (invited paper). Sodium temperature lidar measurements of the mesopause region over Syowa Station. 10. Differential absorption lidar (dIAL) and DOAS: Airborne UV DIAL measurements of ozone and aerosols (invited paper). Measurement of water vapor, surface ozone, and ethylene using differential absorption lidar. 12. Space lidar I: Lightweight lidar telescopes for space applications (invited paper). Coherent lidar development for Doppler wind measurement from the International Space Station. 13. Space lidar II: Using coherent Doppler lidar to estimate river discharge. 14. Poster session: Lidar technology, optics for lidar. Laser for lidar. Middle atmosphere observations. Tropospheric observations (aerosols, clouds). Boundary layer, urban pollution. Differential absorption lidar. Doppler lidar. and Space lidar.

Singh, Upendra N.↗