Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “II&C”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

The Solar Chromosphere/Corona Interface. I. Far-Ultraviolet to Extreme-Ultraviolet Observations and Modeling of Unresolved Coronal Funnels

A coronal funnel model, developed by D. Rabin, was tested against a calibrated spectroheliogram recorded in the 170-1 75 A bandpass. This image was recorded on board a sounding-rocket experiment flown on 1994 November 3, called the Multi-Spectral Solar Telescope Array II (MSSTA II). MSSTA, a joint project of Stanford University, the NASA Marshall Space Flight Center, and the Lawrence Livermore National Laboratory' is an observing platform composed of a set of normal-incidence, multilayer-coated optics designed to obtain narrow-bandpass, high-resolution images (1 sec.- 3 sec.) at selected far-ultraviolet (FUV), extreme-ultraviolet (EUV), and soft X-ray wavelengths (44-1550 A). Using full disk images centered at 1550 A (C IV) and 173 A (Fe IX/X), the funnel model, which is based on coronal back-heating, was tested against the data incorporating observed constraints on global coverage and measured flux. Found was a class of funnel models that could account for the quiescent, globally diffuse and unresolved emission seen in the 171-175 A bandpass, where the funnels are assumed to be rooted in the C IV supergranular network. These models, when incorporated with the CHIANTI spectral code, suggest that this emission is mostly of upper transition region origin and primarily composed of Fe IX plasma. The funnels are found to have constrictions, Gamma approx. 6-20, which is in good agreement with the observations. Further, the fitted models simultaneously satisfy global areal constraints seen in both images; namely,that a global network of funnels must cover approx. 700 - 95% of the total solar surface area seen in the 171-175 A image, and a 5% of the disk area seen in the 1550 A bandpass. These findings support the configuration of the EUV magnetic network as suggested by Reeves et al. and put forth in more detail by Gabriel. Furthermore, the models are in good agreement with differential emission measure estimates made of the transition region by J. C. Raymond & J. G. Doyle for temperatures 250,000 K less than or = T less than or = 650,000 K, based on full-disk observations made on board Skylab.

Martinez-Galarce, Dennis S.↗
NASA NTRS1994

Satellite emission features in two Seyfert galaxies: New evidence that radio-quiet AGN possess subrelativistic winds

Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) spectra are presented for three bright Seyfert galaxies including one (PG 1351+64) which possesses blue-displaced absorption features in C IV, Si IV, N V, and Ly-alpha (but not in Mg II) similar to those seen at high redshift in the broad-absorption-line (BAL) quasi-stellar objects (QSOs). Several features of the absorptions in PG 1351+64, including variability seen in archival International Ultraviolet Explorer (IUE) data, confirm their similarity to the BAL clouds rather than to the 'associated absorber' phenomenon which they superficially resemble. In PG 1351+64 'satellite' emission lines (called herein E1 and E2) have been detected nearly symmetrically placed at +/- 4000 km/s around the Mg II emission line; this velocity is just larger than the most blue-displaced of the BALs, suggesting that these two phenomena are related. The satellite line luminosity, L(E1) approximately = (3 x 10(exp 41) erg/s)/sq. h(sub 75), requires a cloud emission measure n(sub e)(exp 2)V(sub c) approximately = (1 x 10(exp 64)/cc)/sq. h(sub 75) at T approximately = 30,000 K. We believe the Mg II lines are produced by 50-90 km/s shocks driven into dense (approximately 10(exp 6)/cc, pre-shock) clouds by the ram pressure of a 0.1 solar mass/yr wind leaving the nucleus at velocity 4000 km/s. The detection of satellite lines in Mg II, the detection of the blue-shifted cloud in H-alpha and H-beta and the nondetection of this cloud in C IV restricts the cloud shocks to velocities v(sub c) less than or = 90 km/s and requires a cloud/wind density contrast greater than or = 10(exp 3). In this model, the emitting clouds are located at distances of R(sub eff) approximately = 10(exp 18-19) cm from the nucleus and are entrained and shock-accelerated to approximately 4000 km/s. The possible detection of similar 'satellite' emission features in the non-BAL Seyfert, Ton 951, suggests that the subrelativistic wind that accelerates BAL clouds is a physical feature of many radio-quiet active galactic nuclei (AGN).

Stocke, John T.↗
NASA NTRS1988

The anomalous C 4 intensity ratio in symbiotic stars

The C IV lambda lambda 1548.2,1550.8 resonance doublet in a symbiotic stars was shown to exhibit anomalous line intensity ratios in which I (lambda 1548.2)/I(lambda 1550.8) less than 1, or less than the optically-thick limit of unity. The R Aquarii-central HII region and RX Puppis exhibit this phenomena. The I(lambda 1548.2)/I(lambda 1550.8) ratio in RX Puppis is found to vary inversely with the total C IV line intensity, and with the FES-visual light, as the object declined over a 5 yr period following a brightening in UV and optical emission which peaked in 1982. This doublet intensity behavior could be explained by a wind which has a narrow velocity range of 600 approx. less than sup v wind approx. less than 1000 km/sec, or by the pumping of the Fe II (mul. 45.01) transition a sup 4 F sub 9/2 - y sup 4 H(o) sub 11/2 by C IV lambda 1548.2, which effectively scatters C IV photons into the Fe II spectrum in these objects.

Michalitsianos, A. G.↗
NASA NTRS1994

A search for ultraviolet circumstellar gas absorption features in alpha Piscis Austrinus (Fomalhaut), a possible Beta Pictoris-like system

Archival high-dispersion International Ultraviolet Explorer (IUE) spectra have been used to search for circumstellar gas absorption features in alpha PsA (A3 V), a nearby (6.7 pc) proto-planetary system candidate. Recent sub-millimeter mapping observations around the region of alpha PsA indicate a spatially resolved dust disk like the one seen around Beta Pic. To determine how closely this putative disk resembles that of Beta Pic, we have searched for signatures of circumstellar gaseous absorption in all the available IUE high-dispersion data of alpha PsA. Examination of co-added IUE spectra shows weak circumstellar absorptions from excited levels in the resonance multiplet of Fe II near 2600 A. We also conclude that the sharp C I feature near 1657 A, previously identified as interstellar absorption toward alpha PsA, likely has a circumstellar origin. However, because the weakness of these absorption features, we will consider the presence of circumstellar gas as tentative and should be verified by using the Goddard High-Resolution Spectrograph aboard the Hubble Space Telescope. No corresponding circumstellar absorption is detected in higher ionization Fe III and Al III. Since the collisionally ionized nonphotospheric Al III resonance absorption seen in Beta Pic is likely formed close to the stellar surface, its absence in the UV spectra of alpha PsA could imply that, in contrast with Beta Pic, there is no active gaseous disk infall onto the central star. In the alpha PsA gaseous disk, if we assume a solar abundance for iron and all the iron is in the form of Fe II, plus a disk temperature of 5000 K, the Fe II UV1 absorption at 2611.8743 A infers a total hydrogen column density along the line of sight through the circumstellar disk of N(H) approximately equals 3.8 x 10(exp 17)/cm.

Cheng, K.-P.↗
NASA NTRS2009

X-48B Flight Research Progress Overview

Program Objectives; I. Assess stability & control characteristics of a BWB class vehicle in free-flight conditions: a) Assess dynamic interaction of control surfaces; b) Assess control requirements to accommodate asymmetric thrust; c) Assess stability and controllability about each axis at a range of flight conditions II. Assess flight control algorithms designed to provide desired flight characteristics: a) Assess control surface allocation and blending; b) Assess edge of envelope protection schemes; c) Assess takeoff and landing characteristics; d) Test experimental control laws and control design methods. III. Evaluate prediction and test methods for BWB class vehicles: a) Correlate flight measurements with ground-based predictions and measurements.

Risch, Tim↗
NASA NTRS2009

X-48B Flight Research - Test Progress and Instrumentation Needs for the Future

Program Objectives: I. Assess stability & control characteristics of a BWB class vehicle in free-flight conditions: a) Assess dynamic interaction of control surfaces; b) Assess control requirements to accommodate asymmetric thrust; and c) Assess stability and controllability about each axis at a range of flight conditions. II. Assess flight control algorithms designed to provide desired flight characteristics: a) Assess control surface allocation and blending; b) Assess edge of envelope protection schemes; c) Assess takeoff and landing characteristics; and d) Test experimental control laws and control design methods III. Evaluate prediction and test methods for BWB class vehicles: a) Correlate flight measurements with ground-based predictions and measurements.

Risch, Tim↗
NASA NTRS1975

Spectroscopic studies of very old hot stars. I - NGC 246 and its exciting star

The planetary nebula NGC 246 and its exciting stars were studied, using an image-tube spectrograph at the Cassegrain focus of a 36-inch telescope. Observations of the central star indicate that it has one of the most highly excited spectra known to optical astronomers. The only lines definitely present in the spectrum are lines of C IV and O VI, although lines of He II are probably present. Since nitrogen lines (in any ionization state) are absent, the stellar spectrum suggests that the star has experienced the triple-alpha process. Nebular observations were used to estimate the atmospheric properties of the exciting star by the Zanstra method. The results are found to correlate well with the spectral appearance of the star. Comparison of the properties of the star and surrounding nebula with Paczynski's evolutionary tracks for planetary nuclei suggests that the star is very near the point of exhaustion of its nuclear fuels.

Heap, S. R.↗
NASA NTRS1976

Local and large scale galactic gamma-ray emission

A study of the gas-to-dust ratio suggests that interstellar reddening may provide an accurate way of assessing column densities in various directions in the Galaxy. A gamma ray intensity of 7.25 x 10 to the -5th E sub B-V photon/sq cm/s/sterad is predicted for regions of the Galaxy where the medium cosmic ray density is equal to that observed close to the sun. It is found that in the longitude range of about 0-180 degrees, the large scale cosmic ray distribution producing the gamma rays follows that of extreme population I stars put in evidence by giant H II regions, and that of molecular hydrogen traced by carbon monoxide emission. The gamma-ray production exhibits a maximum at R roughly equal to 5 kpc, and practically vanishes at R not less than 11 kpc, beyond the location of the outermost H II regions.

Puget, J. L.↗
NASA NTRS1981

Statistical equilibrium in cometary C2. III - Triplet-singlet, Phillips, Ballik-Ramsay, and Mulliken bands

A new series of vibrational bands is predicted which arises from transitions between the lowest electron states of the triplet and singlet states of homonuclear C2. The predictions are useful for C2 identifications and for disentangling congested low resolution spectra that characterize new observations. Predictions are also made for Mulliken, Phillips, and Ballik-Ramsay band sequences, and all calculations are made with the assumed molecular constants and computational methods of KSO-II.

Swamy, K. S. K.↗
NASA NTRS1991

Mach 6.5 air induction system design for the Beta II Two-Stage-to-Orbit booster vehicle

A preliminary, two-dimensional, mixed compression air induction system is designed for the Beta II Two-Stage-to-Orbit booster vehicle to minimize installation losses and efficiently deliver the required airflow. Design concepts, such as an external isentropic compression ramp and a bypass system, are developed and evaluated for performance benefits. The design is optimized by maximizing installed propulsion/vehicle system performance, and the resulting system design operating characteristics and performance are presented. The air induction system design has significantly lower transonic drag than similar designs, and only requires approximately 1/3 of the bleed extraction. In addition, the design efficiently provides the integrated system required airflow, while maintaining adequate levels of total pressure recovery. The excellent performance of this highly integrated air induction system is essential for the successful completion of the Beta II booster vehicle mission.

Midea, Anthony C.↗
NASA NTRS1991

Mach 6.5 air induction system design for the Beta 2 two-stage-to-orbit booster vehicle

A preliminary, two-dimensional, mixed compression air induction system is designed for the Beta II Two Stage to Orbit booster vehicle to minimize installation losses and efficiently deliver the required airflow. Design concepts, such as an external isentropic compression ramp and a bypass system were developed and evaluated for performance benefits. The design was optimized by maximizing installed propulsion/vehicle system performance. The resulting system design operating characteristics and performance are presented. The air induction system design has significantly lower transonic drag than similar designs and only requires about 1/3 of the bleed extraction. In addition, the design efficiently provides the integrated system required airflow, while maintaining adequate levels of total pressure recovery. The excellent performance of this highly integrated air induction system is essential for the successful completion of the Beta II booster vehicle mission.

Midea, Anthony C.↗
NASA NTRS1995

Infrared observations of an outburst of small dust grains from the nucleus of Comet P/Halley 1986 III at perihelion

A close examination of the 0.7- to 23-micron infrared data base acquired by Gehrz and Ney (1992), suggests that the nucleus of Comet P/Halley 1986 III emitted a burst of small dust grains during a 3-day period commencing within hours of perihelion passage on 1986 February 9.46 UT. The outburst was characterized by significant increases in the coma's grain color temperature T(sub obs), temperature excess (superheat: S = T(sub obs)/T(sub BB)), infrared luminosity, albedo, and 10-micron silicate emission feature strength. These changes are all consistent with the sudden ejection from the nucleus of a cloud of grains with radii of approximately 0.5 micron. This outburst may have produced the dust that was responsible for some of the tail streamers photographed on 1986 February 22 UT. The peak of the dust outburst occurred about 3 days before a pronounced increase in the water production rate measured by the Pioneer Venus Orbiter Ultraviolet Spectrometer. We suggest that jets that release large quantities of small particles may be largely responsible for some of the variable infrared behavior that has been reported for P/Halley and other comets during the past two decades. Such jets may also account for some of the differences IR Type I and IR Type II comets.

Gehrz, R. D.↗
NASA NTRS2007

Polarization Measurements on SUMI's TVLS Gratings

We present measurements of toroidal variable-line-space (TVLS) gratings for the Solar Ultraviolet Magnetograph Investigation (SUMI), currently being developed an the National Space Science and Technology Center (NSSTC). SUMI zs a spectro-polarimeter designed no measure magnetic fields in the solar chromosphere by observing two UV emission lines sensitive to magnetic fields, the C-IV line at 155nm and the Mg-II line at 280nm. The instrument uses a pair of TVLS gratings, to observe both linear polarizations simultaneously. Efficiency measurements were done on bare aluminum gratings and MgF2 coated gratings, at both linear polarizations.

Kobayashi, K.↗
NASA NTRS1988

IUE spectroscopy of U Cephei during the mass flow outburst of 1986 June

The interacting Algol-type binary U Cep underwent another of its irregularly occurring transient high-mass flow events during June 1986. For the first time, high-resolution ultraviolet spectroscopy of U Cep during such an event was possible. High-resolution spectra in the far-ultraviolet and near-ultraviolet were obtained with IUE. These spectra show that the ultraviolet continuum decreased by factors of 1.2 to 3.0 during the greatest activity. In addition, one or more narrow absorption components with radial velocities as high as -500 km/s appeared in association with a number of C, Si, Al, Fe, Zn, and Mg lines. The Mg II doublet developed a flat-bottomed appearance with a residual intensity of about 0.31 and a width of at least 800 km/s. These phenomena are interpreted in terms of high-velocity gas streams, mass loss from the system, and the formation of an optically thick equatorial bulge around the B star.

Mccluskey, George E., Jr.↗
NASA NTRS1982

The gaseous galactic halo as inferred from the line spectra of the galaxies Markarian 509 and Fairall 9

Narrow interstellar absorption lines of S II 1259.52, Si II 1260.42, and Fe II 1608.46 due to gas in the disk and the halo of the Galaxy have been detected in the spectrum of the Seyfert galaxy Mrk 509 with the International Ultraviolet Explorer. This gas is also seen at higher resolution in the Ca II and Na I absorption lines in two components at LSR velocities of +6 and +62 km/s. In addition, narrow Ly-alpha and C IV absorption near the Seyfert redshift seem to be present in the spectrum. Si II 1260.42 absorption from the galactic disk and from the Magellanic Stream or the halo of the SMC have been detected with the IUE in the spectrum of Fairall 9. The observations of these two objects when combined with existing results are shown to be consistent with a corotating galactic halo having a height of less than 10 kpc at the sun.

York, D. G.↗