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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 NTRS1986

Optical model calculations of heavy-ion target fragmentation

The fragmentation of target nuclei by relativistic protons and heavy ions is described within the context of a simple abrasion-ablation-final-state interaction model. Abrasion is described by a quantum mechanical formalism utilizing an optical model potential approximation. Nuclear charge distributions of the excited prefragments are calculated by both a hypergeometric distribution and a method based upon the zero-point oscillations of the giant dipole resonance. Excitation energies are estimated from the excess surface energy resulting from the abrasion process and the additional energy deposited by frictional spectator interactions of the abraded nucleons. The ablation probabilities are obtained from the EVA-3 computer program. Isotope production cross sections for the spallation of copper targets by relativistic protons and for the fragmenting of carbon targets by relativistic carbon, neon, and iron projectiles are calculated and compared with available experimental data.

Townsend, L. W.↗
NASA NTRS1989

On the effects of Cosmions upon the structure and evolution of very low mass stars

A number of recent studies have suggested that cosmions, or WIMPS, may play an important role in the energetics of the solar interior; in particular, it has been argued that these hypothetical particles may transport sufficient energy within the nuclear-burning solar core so as to depress the solar core temperature to the point of resolving the solar neutrino problem. Solutions to the solar neutrino problem have proven themselves to be quite nonunique, so that it is of some interest whether the cosmion solution can be tested in some independent manner. It is argued that if cosmions solve the solar neutrino problem, then they must also play an important role in the evolution of low mass main sequence stars; and, second, that if they do so, then a simple (long mean free path) model for the interaction of cosmions with baryons leads to changes in the structure of the nuclear-burning core which may be in principal observable. Such changes include suppression of a fully-convective core in very low mass main sequence stars; and a possible thermal runaway in the core of the nuclear burning region. Some of these changes may be directly observable, and hence may provide independent constraints on the properties of the cosmions required to solve the solar neutrino problem, perhaps even ruling them out.

Deluca, E. E.↗
NASA NTRS2000

CLUST - EVAP Monte Carlo Simulation Applications for Determining Effective Energy Deposition in Silicon by High Energy Protons

The CLUST-EVAP is a Monte Carlo simulation of the interaction of high energy (25 - 400 MeV) protons with silicon nuclei. The initial nuclear cascade stage is modeled using the CLUST model developed by Indiana University over 30 years ago. The second stage, in which the excited nucleus evaporates particles in random directions, is modeled according to the evaporation algorithm provided by H. H. K. Tang of IBM. Using the CLUST-EVAP code to model fragment produ6tion and the Vavilov-Landau theory to model fluctuations in direct ionization in thin silicon layers, we have predicted energy deposition in silicon components for various geometrical configurations. We have compared actual measurements with model predictions for geometry's such as single, thin silicon particle detectors, telescopic particle detectors flown in space to measure the environment, and thin sensitive volumes of modern micro-electronic components. We have recently compared the model predictions with actual measurements made by the DOSTEL spectrometer flown in the Shuttle payload bay on STS-84. The model faithfully reproduces the features and aids in interpretation of flight results of this instrument. We have also applied the CLUST-EVAP model to determine energy deposition in the thin sensitive volumes of modern micro-electronic components. We have accessed the ability of high energy (200 MeV) protons to induce latch-up in certain devices that are known to latch up in heavy ion environments. However, some devices are not nearly as susceptible to proton induced latch-up as expected according to their measured heavy ion latch-up cross sections. The discrepancy is believed to be caused by the limited range of the proton-silicon interaction fragments. The CLUST-EV AP model was used to determine a distribution of these fragments and their range and this is compared to knowledge of the ranges required based on the known device structure. This information is especially useful in accessing the risk to on-orbit perfonnance in a heavy ion environment based on testing performed with only protons.

ONeill, Pat M.↗
NASA NTRS1996

Identification of the cAMP response element that controls transcriptional activation of the insulin-like growth factor-I gene by prostaglandin E2 in osteoblasts

Insulin-like growth factor-I (IGF-I), a multifunctional growth factor, plays a key role in skeletal growth and can enhance bone cell replication and differentiation. We previously showed that prostaglandin E2 (PGE2) and other agents that increase cAMP activated IGF-I gene transcription in primary rat osteoblast cultures through promoter 1 (P1), the major IGF-I promoter, and found that transcriptional induction was mediated by protein kinase A. We now have identified a short segment of P1 that is essential for full hormonal regulation and have characterized inducible DNA-protein interactions involving this site. Transient transfections of IGF-I P1 reporter genes into primary rat osteoblasts showed that the 328-base pair untranslated region of exon 1 was required for a full 5.3-fold response to PGE2; mutation in a previously footprinted site, HS3D (base pairs +193 to +215), reduced induction by 65%. PGE2 stimulated nuclear protein binding to HS3D. Binding, as determined by gel mobility shift assay, was not seen in nuclear extracts from untreated osteoblast cultures, was detected within 2 h of PGE2 treatment, and was maximal by 4 h. This DNA-protein interaction was not observed in cytoplasmic extracts from PGE2-treated cultures, indicating nuclear localization of the protein kinase A-activated factor(s). Activation of this factor was not blocked by cycloheximide (Chx), and Chx did not impair stimulation of IGF-I gene expression by PGE2. In contrast, binding to a consensus cAMP response element (CRE; 5'-TGACGTCA-3') from the rat somatostatin gene was not modulated by PGE2 or Chx. Competition gel mobility shift analysis using mutated DNA probes identified 5'-CGCAATCG-3' as the minimal sequence needed for inducible binding. All modified IGF-I P1 promoterreporter genes with mutations within this CRE sequence also showed a diminished functional response to PGE2. These results identify the CRE within the 5'-untranslated region of IGF-I exon 1 that is required for hormonal activation of IGF-I gene transcription by cAMP in osteoblasts.

NASA Discipline Musculoskeletal↗
NASA NTRS1975

Frontiers in propulsion research: Laser, matter-antimatter, excited helium, energy exchange thermonuclear fusion

Concepts are described that presently appear to have the potential for propulsion applications in the post-1990 era of space technology. The studies are still in progress, and only the current status of investigation is presented. The topics for possible propulsion application are lasers, nuclear fusion, matter-antimatter annihilation, electronically excited helium, energy exchange through the interaction of various fields, laser propagation, and thermonuclear fusion technology.

Papailiou, D. D.↗
NASA NTRS1992

Dosimetric mapping inside biorack (7-IML-1)

This experiment documents the radiation environment inside Biorack and compares it to theoretical predictions. Other experiments inside Biorack need this information to determine whether changes to samples are caused by radiation or microgravity. Dosimetric stacks, each with 20 to 100 sheets of plastic detector foils (cellulose nitrate, Lexan, and CR39) and nuclear emulsions of different radiation sensitivity are packed together with Thermoluminescence dosimeters (TLD) inside Type 1 containers. Crew members place two stacks in the 37 C incubator and four in the 36 C incubator, two of which are placed on the 1 g centrifuge. Two stacks are located in a stowage position at ambient temperature. After the mission, the plastic detectors are etched and the nuclear emulsions are developed similar to photographic emulsions. The traces resulting from the interaction of heavy ions with matter can then be evaluated under the microscope. The number, charge, and energy of the particles will be determined. From the TLD readings, the absorbed dose of the low LET components will be received.

Reitz, G.↗
NASA NTRS1993

Star trapping and metallicity enrichment in quasars and active galactic nuclei

Recent observational evidence suggests that the metallicity in quasars within a wide range of redshifts, in particular in gas flowing out of the nuclear regions, may be approximately redshift-independent and comparable with or larger than solar. It is plausible that the nuclear metallicity can be internally generated and maintained at approximately time-stationary values in quasars. We identify and estimate efficiency of a mechanism for rapid metallicity enrichment of quasar nuclear gas (in general, in active galactic nuclei) based on star-gas interactions and equivalent to an unusual mode of massive star formation. The mechanism involves capture of low-mass stars from the host galaxy's nucleus by the assemblages of clouds or by accretion disks orbiting the central massive objects (e.g., black holes). Trapping of stars within gaseous disks/clouds occurs through resonant density and bending wave excitation, as well as by hydrodynamical drag. The time scale for trapping stars with total mass equal to that of disk fragment/cloud is of order Hubble time and is remarkably model-independent. Our results show that the described mechanism can produce features suggested by observations, for example, the (super) solar gas metallicity in the nucleus. Thus the observed metallicities in high-redshift quasars do not necessarily imply that global star formation and efficient chemical changes have occurred in their host galaxies at very early cosmological epochs.

Artymowicz, Pawel↗
NASA NTRS1993

Discovery of orbital decay in SMC X-1

Three observations of the binary X-ray pulsar SMC X-1 with the Ginga satellite, conducted on 3 days in 1987 May, 8.4 days in 1988 August-September, and 4 days in 1989 July-August, are reported. Based on the three observation epochs, the rate of change in the orbital period is estimated at (-3.36 +/- 0.02) x 10 exp -6/yr. An interpretation of the orbital decay is made in the context of tidal evolution with allowance for the effect of the increasing moment of inertia of the companion star due to its nuclear evolution. While the orbital decay is thought to be driven by tidal interactions, it is suggested that the asynchronism between the orbit and the rotation of the companion star is most likely maintained by the evolutionary expansion of the companion star (Sk 160) rather than via the Darwin instability.

Levine, A.↗
NASA NTRS1998

Inclusive dielectron cross sections in p + p and p + d interactions at beam energies from 1.04 to 4.88 GeV

Measurements of dielectron production in p + p and p + d collisions with beamkinetic energies from 1.04 to 4.88 GeV are presented. The differential cross section is presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the mass spectra and their evolution with beam energy provide information about the relative importance of the various dielectron production mechanisms in this energy regime. The p + d to p + p ratio of the dielectron yield is also presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the transverse momentum and rapidity spectra from the p + d and p + p systems are found to be similar to one another for each of the beam energies studied. The beam energy dependence of the integrated cross sections is also presented.

NASA Discipline Radiation Health↗
NASA NTRS1998

Ground-based simulations of cosmic ray heavy ion interactions in spacecraft and planetary habitat shielding materials

This paper surveys some recent accelerator-based measurements of the nuclear fragmentation of high energy nuclei in shielding and tissue-equivalent materials. These data are needed to make accurate predictions of the radiation field produced at depth in spacecraft and planetary habitat shielding materials and in the human body by heavy charged particles in the galactic cosmic radiation. Projectile-target combinations include 1 GeV/nucleon 56Fe incident on aluminum and graphite and 600 MeV/nucleon 56Fe and 290 MeV/nucleon 12C on polyethylene. We present examples of the dependence of fragmentation on material type and thickness, of a comparison between data and a fragmentation model, and of multiple fragments produced along the beam axis.

NASA Discipline Radiation Health↗
NASA NTRS1988

Luminous extranuclear star formation in the interacting galaxy Arp 118 - NGC 1143/44

The interacting system Arp 118 (NGC 1143/44) has been observed at infrared and radio wavelengths. The interaction has produced a pair of distorted loops and several luminous radio and infrared sources in NGC 1144 which emit a total power of 2.5 x 10 to the 11th lunar masses, 80 percent of which is reradiated in the thermal infrared. Remarkably, the present observations reveal that much of the midinfrared emission originates in an extra-nuclear star-forming region. Arp 118 has many of the same characteristics as the well-studied interacting system Arp 299 (NGC 3690), including luminous extranuclear activity; the main difference between the two systems is that the nuclei of NGC 1143/44 are much less luminous at 10 microns than their counterparts in NGC 3690.

Joy, Marshall↗
NASA NTRS1972

Human visual response to nuclear particle exposures

Experiments with accelerated helium ions were performed in an effort to localize the site of initial radiation interactions in the eye that lead to light flash observations by astronauts during spaceflight. The character and efficiency of helium ion induction of visual sensations depended on the state of dark adaptation of the retina; also, the same events were seen with different efficiencies and details when particle flux density changed. It was concluded that fast particles cause interactions in the retina, particularly in the receptor layer, and thus give rise to the sensations of light flashes, streaks, and supernovae.

Tobias, C. A.↗
NASA NTRS1987

The physics of charge separation preceding lightning strokes in thunderclouds

The physics of charge separation preceding lightning strokes in thunderclouds is presented by three types of arguments: An explanation is given for the aggregation of electrical charges of like sign overcoming Coulomb repulsion by attraction due to exchange interaction. The latter is well known in quantum mechanics from the theories of the nuclear bond and the covalent bond. A classical electrostatic model of charge balls of segregated positive and negative charges in the thundercloud is presented. These charge balls can only be maintained in temporarily stable locations by a containing vortex. Because they will be of different sizes and masses, they will stabilize at different altitudes when drag forces are included with the given electrostatic force. The question of how the charges become concentrated again after lightning discharges is approached by means of the collisional Boltzmann transport equation to explain quasi-periodic recharging. It is shown that solutions cannot be separable in both position and time if they are to represent aggregation.

Kyrala, Ali↗
NASA NTRS1993

Discovery of Orbital Decay in SMC X-1

We report on the results of three observations of the binary X-ray pulsar SMC X-1 with the Ginga satellite. Timing analyses of the 0.71 s X-ray pulsations yield Doppler delay curves which, in turn, enable the most accurate determination of the SMC X-1 orbital parameters available to date. Epochs of phase zero for the 3.9 day orbit were determined for 1987 May, 1988 August, and 1989 August with accuracies of 13, 0.6, and 3 s, respectively. These epochs are combined with two previous determinations of the orbital epoch to yield the rate of change in the orbital period dot-P(orb)/P(orb) = ( 3.36 +/- 0.02) x 10(exp -6) yr(exp -1). An interpretation of the orbital decay is made in the context of tidal evolution, with consideration of the influence of the increasing moment of inertia of the companion star due to its nuclear evolution. We find that, while the orbital decay is probably driven by tidal interactions, the asynchronism between the orbit and the rotation of the companion star is most likely maintained by the evolutionary expansion of the companion star (Sk 160) rather than via the Darwin instability. In this case Sk 160 is likely to be in the hydrogen shell burning phase of its evolution. Finally, a discussion is presented of the relation among the time scales for stellar evolution (less than 10(exp 7) yr), orbital decay (3 x 10(exp 5) yr), and neutron-star spin-up in the SMC X-1 system (2000 yr). In particular, we present the result of a self-consistent calculation for the histories of the spin of the neutron star and the mass transfer in this system. A plausible case can be made for the spin-up time scale being directly related to the lifetime of the luminous X-ray phase which will end in a common-envelope phase within a time of less than approx. 10(exp 4) yr.

Levine, A.↗
NASA NTRS2003

Large-Eddy Simulation of Conductive Flows at Low Magnetic Reynolds Number

In this paper we study the LES method with dynamic procedure in the context of conductive flows subject to an applied external magnetic field at low magnetic Reynolds number R(sub m). These kind of flows are encountered in many industrial applications. For example, in the steel industry, applied magnetic fields can be used to damp turbulence in the casting process. In nuclear fusion devices (Tokamaks), liquid-lithium flows are used as coolant blankets and interact with the surrounding magnetic field that drives and confines the fusion plasma. Also, in experimental facilities investigating the dynamo effect, the flow consists of liquid-sodium for which the Prandtl number and, as a consequence, the magnetic Reynolds number is low. Our attention is focused here on the case of homogeneous (initially isotropic) decaying turbulence. The numerical simulations performed mimic the thought experiment described in Moffatt in which an initially homogeneous isotropic conductive flow is suddenly subjected to an applied magnetic field and freely decays without any forcing. Note that this flow was first studied numerically by Schumann. It is well known that in that case, extra damping of turbulence occurs due to the Joule effect and that the flow tends to become progressively independent of the coordinate along the direction of the magnetic field. Our comparison of filtered direct numerical simulation (DNS) predictions and LES predictions show that the dynamic Smagorinsky model enables one to capture successfully the flow with LES, and that it automatically incorporates the effect of the magnetic field on the turbulence. Our paper is organized as follows. In the next section we summarize the LES approach in the case of MHD turbulence at low R(sub m) and recall the definition of the dynamic Smagorinsky model. In Sec. 3 we describe the parameters of the numerical experiments performed and the code used. Section 4 is devoted to the comparison of filtered DNS results and LES results. Conclusions are presented in Sec. 5.

Knaepen, B.↗
NASA NTRS1993

The line-emitting gas in active galaxies - A probe of the nuclear engine

This paper reviews some of the basic questions regarding the structure of the engine powering active galactic nuclei (AGN), the nature of the interaction between the AGN and the host galaxy, and the origin and evolution of AGN. The study of the dynamics and physical characteristics of the line-emitting gas in these objects has proven fruitful in addressing many of these issues. Recent advances in optical and infrared detector technology combined with the development of superior ground-based instruments have produced efficient new tools for the study of the line-emitting gas on nuclear and Galactic scales. Programs which take advantage of two of these new techniques, Fabry-Perot imaging spectroscopy and infrared spectroscopy, are described in this paper. The origin of nuclear activity in galaxies is also addressed in a third project which aims at determining the nature of luminous infrared galaxies.

Veilleux, Sylvain↗