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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Using X-ray absorption lines to determine the distances to clusters of galaxies

The stronger resonant X-ray lines from the intracluster gas should be observable as absorption lines in the spectrum of an X-ray emitting background quasar. The equivalent widths of the strongest absorption lines in a set of model clusters with typical parameters are calculated, and the strongest lines are found to have equivalent widths of several eV. By comparing the equivalent width of such a line and the flux from the same line seen in emission, the distance to the cluster can be directly determined, independent of the standard extragalactic distance scale. A method of analyzing the X-ray absorption and emission measurements is presented, and the effects of resonant scattering on the distances are discussed.

Sarazin, Craig L.↗
NASA NTRS1991

Gamma-ray bursts from colliding strange stars

The rate of collisions between the neutron stars is about 0.0001/yr in the galaxy and about 0.00001/yr within the Hubble distance. The collisions are the final phases of binary orbit decay driven by gravitational radiation and may produce gamma-ray bursts detectable at extragalactic distances. If strange stars exist then their collisions must release about 10 to the 50th ergs in gamma rays over 0.2 s. Such events should be detectable out to 1 Gpc with the current instruments. The distance to the majority of gamma-ray bursts is not known at this time. The Burst and Transient Source Experiment (BATSE) on Gamma Ray Observatory should determine the distance scale by determining the angular distribution of very weak bursts. If the majority of gamma-ray bursts turn out to be extragalactic, and if their distances are about 1 Gpc, then the collisions between strange stars may be the least speculative events that might account for so energetic bursts.

Haensel, P.↗
NASA NTRS1996

The Compatibility of Friedmann Cosmological Models with Observed Properties of Gamma-Ray Bursts and a Large Hubble Constant

The distance scale to cosmic gamma-ray bursts (GRB's) is still uncertain by many orders of magnitude; however, one viable scenario places GRB's at cosmological distances, thereby permitting them to be used as tracers of the cosmological expansion over a significant range of redshifts zeta. Also, several recent measurements of the Hubble constant H(sub 0) appearing in the referred literature report values of 70-80 km/s /Mpc. Although there is significant debate regarding these measurements, we proceed here under the assumption that they are evidence of a large value for H(sub 0). This is done in order to investigate the additional constraints on cosmological models that can be obtained under this hypothesis when combined with the age of the universe and the brightness distribution of cosmological gamma-ray bursts. We show that the range of cosmological models that can be consistent with the GRB brightness distribution, a Hubble constant of 70-80 km/s/Mpc, and a minimum age of the universe of 13-15 Gyr is constrained significantly, largely independent of a wide range of assumptions regarding the evolutionary nature of the burst population. Low-density, Lambda greater than 0 cosmological models with deceleration parameter in the range -1 less than q(sub 0) less than 0 and density parameter sigma(sub 0) in the range approximately equals 0.10-0.25(Omega(sub 0) approximately equals 0.2-0.5) are strongly favored.

Horack, John M.↗
NASA NTRS1981

On the detectability of icy grains in the comae of comets

While there is no direct evidence for the presence of icy grains in cometary comae, they are assumed in order to explain observed phenomena. The evaporation of icy grains over the distance scale of the visible cometary coma sets specific limits on their temperature. Unless the grains are pure water ice, maximum icy grain halo size will be limited to a few hundred km at heliocentric distances not greater than about 2.5 AU. While it is unlikely that the 1.5- or 2.0-micron ice band could be detected in the scattering by icy grains, detection of the 3.0-micron ice band may be possible in comets displaying a coma at large heliocentric distances.

Hanner, M. S.↗
NASA NTRS1985

Gamma-ray burst statistics - Guidance or deception?

An evaluation is made of efforts to statistically ascertain the distance scale of gamma-ray bursts. The Venera 11 and 12 KONUS experiment peak count flux P sampling is noted to be incomplete for the longest and shortest bursts. This may be due to the effect being either a real physical limit to the burst population, or an artifact. Current data favor the latter explanation. Where N is the annual rate of bursts with a fluence exceeding S ergs/sq cm, it is shown that an unbounded, isotropic, homogeneous burst source distribution must have d log N/d log P of less than -3/2, for all P independent of any intrinsic P distribution or the existence and relative distance of any separate burst classes. The KONUS data are consistent with earlier conclusions that bursts are distributed on a large galactic scale.

Jennings, M. C.↗
NASA NTRS2002

The Velocity Distribution of Isolated Radio Pulsars

We infer the velocity distribution of radio pulsars based on large-scale 0.4 GHz pulsar surveys. We do so by modelling evolution of the locations, velocities, spins, and radio luminosities of pulsars; calculating pulsed flux according to a beaming model and random orientation angles of spin and beam; applying selection effects of pulsar surveys; and comparing model distributions of measurable pulsar properties with survey data using a likelihood function. The surveys analyzed have well-defined characteristics and cover approx. 95% of the sky. We maximize the likelihood in a 6-dimensional space of observables P, dot-P, DM, absolute value of b, mu, F (period, period derivative, dispersion measure, Galactic latitude, proper motion, and flux density). The models we test are described by 12 parameters that characterize a population's birth rate, luminosity, shutoff of radio emission, birth locations, and birth velocities. We infer that the radio beam luminosity (i) is comparable to the energy flux of relativistic particles in models for spin-driven magnetospheres, signifying that radio emission losses reach nearly 100% for the oldest pulsars; and (ii) scales approximately as E(exp 1/2) which, in magnetosphere models, is proportional to the voltage drop available for acceleration of particles. We find that a two-component velocity distribution with characteristic velocities of 90 km/ s and 500 km/ s is greatly preferred to any one-component distribution; this preference is largely immune to variations in other population parameters, such as the luminosity or distance scale, or the assumed spin-down law. We explore some consequences of the preferred birth velocity distribution: (1) roughly 50% of pulsars in the solar neighborhood will escape the Galaxy, while approx. 15% have velocities greater than 1000 km/ s (2) observational bias against high velocity pulsars is relatively unimportant for surveys that reach high Galactic absolute value of z distances, but is severe for spatially bounded surveys; (3) an important low-velocity population exists that increases the fraction of neutron stars retained by globular clusters and is consistent with the number of old objects that accrete from the interstellar medium; (4) under standard assumptions for supernova remnant expansion and pulsar spin-down, approx. 10% of pulsars younger than 20 kyr will appear to lie outside of their host remnants. Finally, we comment on the ramifications of our birth velocity distribution for binary survival and the population of inspiraling binary neutron stars relevant to some GRB models and potential sources for LIGO.

Arzoumanian, Z.↗
NASA NTRS1999

Multi-Spacecraft Observations of Interplanetary Shocks

Using multi-spacecraft observations primarily from ACE and WIND, and from IMP 8 and Geotail when available, the 3-dimensional structure of interplanetary shocks on the hundred Earth radii scale will be discussed. The complete magnetic field, and solar wind ion and electron data sets were used to fit the shocks with a full non-linear least squares fit "Rankine-Hugoniot" technique yielding the local shock surface normals and speeds with associated uncertainties. Multi-spacecraft results reveal that on the distance scale of ACE's L1 halo orbit the shocks deviate significantly from a simple planar geometry. This result has important consequences for the prediction of the exact arrival times of interplanetary shocks at the Earth's magnetosphere, and hence, on the reliability of space weather predictions. It also has implications on the coherence scale of solar wind structures and their evolution from the Sun to Earth.

Szabo, A.↗
NASA NTRS1999

Multi-Spacecraft Observations of Interplanetary Shocks

Using multi-spacecraft observations primarily from ACE and WIND and from IMP 8 and Geotail when available, the 3-dimensional structure of interplanetary shocks on the hundred Earth radii scale will be discussed. The complete magnetic field, and solar wind ion and electron data sets were used to fit the shocks with a full non-linear least squares fitting "Rankine-Hugoniot" technique yielding the local shock surface normals and speeds with associated uncertainties. Multi-spacecraft results reveal that on the distance scale of ACE's L1 halo orbit the shocks deviate from a simple planar geometry. This result has important consequences for the prediction of the exact arrival times of interplanetary shocks at the Earth's magnetosphere, and hence, on the reliability of space weather predictions. It also has implications on the coherence scale of solar wind structures and their evolution from the Sun to Earth.

Smith, C. W.↗
NASA NTRS2012

Carnegie Hubble Program: A Mid-Infrared Calibration of the Hubble Constant

Using a mid-infrared calibration of the Cepheid distance scale based on recent observations at 3.6 micrometers with the Spitzer Space Telescope, we have obtained a new, high-accuracy calibration of the Hubble constant. We have established the mid-IR zero point of the Leavitt law (the Cepheid period-luminosity relation) using time-averaged 3.6 micrometers data for 10 high-metallicity, MilkyWay Cepheids having independently measured trigonometric parallaxes. We have adopted the slope of the PL relation using time-averaged 3.6micrometers data for 80 long-period Large Magellanic Cloud (LMC) Cepheids falling in the period range 0.8 < log(P) < 1.8.We find a new reddening-corrected distance to the LMC of 18.477 +/- 0.033 (systematic) mag. We re-examine the systematic uncertainties in H(sub 0), also taking into account new data over the past decade. In combination with the new Spitzer calibration, the systematic uncertainty in H(sub 0) over that obtained by the Hubble Space Telescope Key Project has decreased by over a factor of three. Applying the Spitzer calibration to the Key Project sample, we find a value of H(sub 0) = 74.3 with a systematic uncertainty of +/-2.1 (systematic) kilometers per second Mpc(sup −1), corresponding to a 2.8% systematic uncertainty in the Hubble constant. This result, in combination with WMAP7measurements of the cosmic microwave background anisotropies and assuming a flat universe, yields a value of the equation of state for dark energy, w(sub 0) = −1.09 +/- 0.10. Alternatively, relaxing the constraints on flatness and the numbers of relativistic species, and combining our results with those of WMAP7, Type Ia supernovae and baryon acoustic oscillations yield w(sub 0) = −1.08 +/- 0.10 and a value of N(sub eff) = 4.13 +/- 0.67, mildly consistent with the existence of a fourth neutrino species.

Program↗
NASA NTRS2019

Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray Bursts

The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Our pursuit of more than a century to uncover the origins and fate of these cosmic energetic particles has given rise to some of the most interesting and challenging questions in astrophysics. Within our own galaxy, we have seen that energetic particles engage in a complex interplay with the galactic environment and even drive many of its key characteristics (for more information, see the first white paper in this series). On cosmological scales, the energetic particles supplied by the jets of active galactic nuclei (AGN) are an important source of energy for the intracluster and intergalactic media, providing a mechanism for regulating star formation and black hole growth and cultivating galaxy evolution (AGN feedback). Gamma-ray burst (GRB) afterglows encode information about their circumburst environment, which has implications for massive stellar winds during previous epochs over the stellar lifecycle. As such, GRB afterglows provide a means for studying very high-redshift galaxies since GRBs can be detected even if their host galaxy cannot. It has even been suggest that GRB could be used to measure cosmological distance scales if they could be shown to be standard candles. Though they play a key role in cultivating the cosmological environment and/or enabling our studies of it, there is still much we do not know about AGNs and GRBs, particularly the avenue in which and through which they supply radiation and energetic particles, namely their jets. Despite the enormous progress in particle-in-cell and magnetohydrodynamic simulations, we have yet to pinpoint the processes involved in jet formation and collimation and the conditions under which they can occur. For that matter, we have yet to identify the mechanism(s) through which the jet accelerates energetic particles – is it the commonly invoked diffusive shock acceleration process or is another mechanism, such as magnetic reconnection, required? Do AGNs and GRBs accelerate hadrons, and if so, do they accelerate them to ultra-high energies and are there high-energy neutrinos associated with them? MeV gamma-ray astronomy, enabled by technological advances that will be realized in the coming decade, will provide a unique and indispensable perspective on the persistent mysteries of the energetic universe. This White Paper is the second of a two-part series highlighting the most well-known high-energy cosmic accelerators and contributions that MeV gamma-ray astronomy will bring to understanding their energetic particle phenomena. Specifically, MeV astronomy will: 1. Determine whether AGNs accelerate CRs to ultra-high energies; 2. Provide the missing pieces for the physics of the GRB prompt emission; 3. Measure magnetization in cosmic accelerators and search for acceleration via reconnection.

Venters, Tonia M.↗
NASA NTRS2001

Cool Flame Quenching

Cool flame quenching distances are generally presumed to be larger than those associated with hot flames, because the quenching distance scales with the inverse of the flame propagation speed, and cool flame propagation speeds are often times slower than those associated with hot flames. To date, this presumption has never been put to a rigorous test, because unstirred, non-isothermal cool flame studies on Earth are complicated by natural convection. Moreover, the critical Peclet number (Pe) for quenching of cool flames has never been established and may not be the same as that associated with wall quenching due to conduction heat loss in hot flames, Pe approx. = 40-60. The objectives of this ground-based study are to: (1) better understand the role of conduction heat loss and species diffusion on cool flame quenching (i.e., Lewis number effects), (2) determine cool flame quenching distances (i.e, critical Peclet number, Pe) for different experimental parameters and vessel surface pretreatments, and (3) understand the mechanisms that govern the quenching distances in premixtures that support cool flames as well as hot flames induced by spark-ignition. Objective (3) poses a unique fire safety hazard if conditions exist where cool flame quenching distances are smaller than those associated with hot flames. For example, a significant, yet unexplored risk, can occur if a multi-stage ignition (a cool flame that transitions to a hot flame) occurs in a vessel size that is smaller than that associated with the hot quenching distance. To accomplish the above objectives, a variety of hydrocarbon-air mixtures will be tested in a static reactor at elevated temperature in the laboratory (1g). In addition, reactions with chemical induction times that are sufficiently short will be tested aboard NASA's KC-135 microgravity (mu-g) aircraft. The mu-g results will be compared to a numerical model that includes species diffusion, heat conduction, and a skeletal kinetic mechanism, following the work on diffusion-controlled cool flames by Fairlie et,al., 2000.

Pearlman, Howard↗
NASA NTRS1992

Extragalactic scenarios for gamma-ray bursts

The cosmological distance scale to gamma-ray bursts is indicated by the observed distribution of the bursts in angle and intensity. The redshifts of the weakest and the strongest bursts detected by the BATSE experiment are estimated to be z = 1.5 and z = 0.2, respectively, while the strongest bursts detected by the PVO in its 11 years of operation were at z = 0.05. The bursts' rate is about 10 exp -6 per year in a galaxy like ours, and a typical energy release is about 10 exp 51 ergs, assuming isotropic emission. The rate of the neutron star and black hole collisions in close binaries is somewhat higher, and those collisions release 10 exp 53 - 10 exp 54 ergs in a burstlike form, making them the primary candidates for the observed gamma-ray events. Contrary to the common belief, no observations available to date are in conflict with the cosmological distance to the bursters. A detection of gravitational lensing of some bursts, the redshift of the weakest events, and the absorption of soft X-rays by the interstellar matter in the plane of our galaxy, are the specific predictions of the cosmological scenario.

Paczynski, Bohdan↗
NASA NTRS1972

Spectral energy distributions of nuclei of peculiar galaxies.

Consideration of galaxies of the types described by Seyfert, Zwicky, Markarian and others. Quasars are discussed in terms of their similarities to the nuclei of peculiar galaxies. The data discussed were obtained almost exclusively with photoelectric spectrometers. Peculiar galaxies have a wide range of properties insofar as their spectra are concerned. Many have very strong emission lines. Sources of continuous radiation, and distance scale problems and selection effects are discussed. Data are presented which are representative of spectrophotometric observational results for 12 Markarian galaxies, 14 Zwicky compact objects, and 16 radio galaxies. The general properties of spectral energy distributions of peculiar galaxies and quasars are discussed.

Oke, J. B.↗
NASA NTRS1974

Sonic boom measurements from accelerating supersonic tracked sleds

Supersonic sled tests on the Sandia 1524-m (5000-ft) track generate sonic booms of sufficient intensity to allow some airblast measurements at distance scales not obtained from wind tunnel or flight tests. During acceleration, an emitted curved boom wave propagates to a caustic, or focus. Detailed measurements around these caustics may help to clarify the overpressure magnification which can occur from real aircraft operations. Six fixed pressure gages have been operated to document the general noise field, and a mobile array of twelve gages.

Reed, J. W.↗
NASA NTRS1974

Lift-induced wing-tip vortex attenuation

It has been shown by a new static airflow visualization method that a drogue device properly positioned downstream of the wing tip causes vortex breakdown. This same result has been obtained by mounting a jet engine simulator at the wing tip and directing the high-energy jet blast downstream into the vortex. These configurations, among others, are now under intensive investigation in the new Langley Vortex Research Facility. In this facility a balance mounted vortex generating model is propelled along the 1800-foot track while a second model trailed at 160 feet (scale distance of 1 mile) measures the far-field rolling moment induced by the vortex of the generating model.

Patterson, J. C., Jr.↗
NASA NTRS1977

Elastic wave propagation in a highly scattering medium - A diffusion approach

The propagation of elastic waves in the moon, where the first seismograms were characterized by the presence of a long coda attributed to strongly scattered waves, is modeled with the aid of the time-dependent equation of radiative transfer. The average energy density as a function of time and space is described by the diffusion equation with linear dissipation on the assumption that all the energy present has been scattered many times and the time and distance scales of the problem are long compared to the scales of the scattering process. Ultrasonic experiments in the laboratory confirm the applicability of the formalism.

Dainty, A. M.↗
NASA NTRS1978

Measured wake-vortex characteristics of aircraft in ground effect

In support of the NASA wake vortex alleviation program, measurements were made of the influences of a ground plane on vortex trajectories and velocity profiles within lift-generated wakes. The wakes were generated by towing 0.61-m (2-ft) span models of two jumbo jets under water in a ship model basin. The models were configured with landing flaps and flight spoilers to investigate the wake characteristics of these aircraft in ground effect at simulated full-scale distances of 19 m (62 ft) to 116 m (380 ft) above the ground. The ground plane caused modifications in the vortex trajectories but did not alter vortex interactions and merging patterns in these multiple vortex wakes. Some distortions in vortex vertical (tangential) velocity profiles were recorded as a result of vortex lateral motions and vortex interactions with the viscous boundary layer on the ground plane; however, maximum tangential velocities remained unchanged.

Ciffone, D. L.↗