Search NASA⌕ Search

SEARCH · Search NASA

Results for “lines”

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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Application of helium line intensity ratio spectroscopy to xenon plasma in E × B Penning discharge

Here, we propose the application of helium line intensity ratio spectroscopy in a low-pressure (0.3 mTorr) xenon E × B discharge with an electron temperature of ~2 eV and a density of 10 10 –10 11 cm –3 . We successfully identified the helium atom line emissions at 388.9, 447.1, 501.6, 504.8, and 706.5 nm with helium pressures of up to ~20 mTorr. The measured electron temperature, density, and I–V characteristics of the discharge remained almost constant in all helium pressures in the present experiment, indicating the suitability of the helium gas as a diagnostic gas. The results of helium line intensity ratio spectroscopy using the line emissions at 388.9, 447.1, and 504.8 nm showed fair agreement with the Langmuir probe measurement. Considering the trade-off relationship between the disturbance introduced by the helium gas and the signal-to-noise ratio, we conclude that a helium pressure of approximately 4 mTorr (approximately 13 times the partial pressure of xenon) represents the optimal pressure range for the application of the helium line emission intensity ratio method to this xenon plasma. It is found that the use of the line emissions at 501.6 and 706.5 nm result in a significant disturbance in the helium line intensity ratio method due to the radiation trapping effect.

helium line intensity ratio spectroscopy↗
NASA NTRS2016

Ames S-32 O-16 O-18 Line List for High-Resolution Experimental IR Analysis

By comparing to the most recent experimental data and spectra of the SO2 628 ν1/ν3 bands (see Ulenikov et al., JQSRT 168 (2016) 29-39), this study illustrates the reliability and accuracy of the Ames-296K SO2 line list, which is accurate enough to facilitate such high-resolution spectroscopic analysis. The SO2 628 IR line list is computed on a recently improved potential energy surface (PES) refinement, denoted Ames-Pre2, and the published purely ab initio CCSD(T)/aug-cc-pVQZ dipole moment surface. Progress has been made in both energy level convergence and rovibrational quantum number assignments agreeing with laboratory analysis models. The accuracy of the computed 628 energy levels and line list is similar to what has been achieved and reported for SO2 626 and 646, i.e. 0.01-0.03 cm(exp −1) for bands up to 5500 cm(exp −1). During the comparison, we found some discrepancies in addition to overall good agreements. The three-IR-list based feature-by-feature analysis in a 0.25 cm(exp −1) spectral window clearly demonstrates the power of the current Ames line lists with new assignments, correction of some errors, and intensity contributions from varied sources including other isotopologues. We are inclined to attribute part of detected discrepancies to an incomplete experimental analysis and missing intensity in the model. With complete line position, intensity, and rovibrational quantum numbers determined at 296 K, spectroscopic analysis is significantly facilitated especially for a spectral range exhibiting such an unusually high density of lines. The computed 628 rovibrational levels and line list are accurate enough to provide alternatives for the missing bands or suspicious assignments, as well as helpful to identify these isotopologues in various celestial environments. The next step will be to revisit the SO2 828 and 646 spectral analyses.

Sulfur dioxide↗
DOE OSTI2025

Determining the Minimum Phase‐to‐Phase Gap Distance for Unconventional Transmission Lines Using Numerical Method

With the increasing demand for power transmission, compact, high surge impedance loading (HSIL) high-voltage transmission lines have emerged as a viable solution due to their reduced land acquisition costs and higher power delivery capability. The compactness of a transmission line depends on effective insulation coordination, particularly in determining the phase-to-phase clearance, which is governed by the critical flashover voltage under switching and lightning overvoltage conditions. Traditional methods for phase-to-phase clearance rely on empirical formulas derived from experimental data, which are convenient for conventional high-voltage lines. However, unconventional HSIL lines require a faster and more adaptable evaluation method, as they involve optimized conductor positioning to reduce right-of-way requirements while enhancing natural power loadability. This study presents a simplified numerical approach to determine the minimum phase-to-phase gap, utilizing arc propagation viability curves, and offers an efficient alternative to conventional empirical methods. The proposed method was successfully applied to a 500 kV conventional line as well as 500 and 735 kV unconventional line designs, demonstrating its capability in accurately assessing insulation requirements. Results reveal that the method can support reduced gap clearances while still maintaining reliability, thereby validating its usefulness in optimizing compact transmission line configurations.

Arafat, Easir [The University of Texas at Dallas, ↗
NASA NTRS1972

Space and time variations of the solar Na D line profiles.

Preliminary results are presented of observations of the solar Na D lines obtained with high space and time resolution. The line profiles vary strongly with space and time implying that time averaging over a long period and large area will not produce the 'true' profile. The centre-limb increase in apparent Doppler width in the D lines is intrinsic. It is not due to space or time averaging. The amplitude of the 300-sec oscillation may range up to 1.5 km/sec in the region of formation of the D lines. The variation of the D line profile caused by the 300-sec oscillation may be described as follows: (1) the core is raised and lowered without change of shape, and (2) the wings broaden as the central intensity rises and narrow as it falls. Doppler width values derived from pairs of D line profiles are strongly correlated with the motion of the element observed. Indications of running waves have been found in the time variation of the core line bisectors.

Slaughter, C. D.↗
NASA NTRS1972

Shapes and widths of ammonia lines collision-broadened by hydrogen.

Measurement of half-widths and shapes of several rotational lines in nu sub 2 bands of ammonia, collision-broadened by hydrogen. The measurements were made at room temperature with a spectral resolution of 0.15 per cm. Line intensities and self-broadened half-widths were also measured. From the line-intensity data, an estimate of S sub band = 600 plus or minus 30 per sq cm per atm has been derived for the absolute intensity of the pair of bands. Hydrogen-broadened half-widths of all the lines have been found to be equal to 0.075 plus or minus 0.004 per cm per atm. For all the lines measured, shapes of the lines in NH3-H2 collisions seem to conform to the super-Lorenz line shape proposed by Varanasi et al. (1972) for dipole quadrupole collisions.

Varanasi, P.↗
NASA NTRS1974

Gamma ray lines from solar flares

The strongest line, both predicted theoretically and detected observationally at 2.2 MeV, is due to neutron capture by protons in the photosphere. The neutrons are produced in nuclear reactions of flare accelerated particles which also positrons and prompt nuclear gamma rays. From the comparison of the observed and calculated intensities of the lines at 4.4 or 6.1 MeV to that of the 2.2 MeV line, it is possible to deduce the spectrum of accelerated nuclei in the flare region; and from the absolute intensities of these lines, it is possible to obtain the total number of accelerated nuclei at the sun. The study of the 2.2 MeV line also gives information on the amount of He-3 in the photosphere. The study of the line at 0.51 MeV resulting from positron annihilation complements the data obtained from the other lines; in addition it gives information on the temperature and density in the annihilation region.

Ramaty, R.↗
NASA NTRS1974

Ultraviolet photometry from the orbiting astronomical observatory. XVI - The stellar Lyman-alpha absorption line

The stellar Lyman-alpha line at 1216 A was observed in 29 lightly reddened stars of spectral type B2.5 to B9 by a far-UV spectrophotometer on OAO-2. The equivalent widths obtained range from 15 A at type B2.5 to 65 A at type B8; in the late-B stars, the L-alpha line removes 2 to 3% of the total stellar flux. In this sampling, the strength of the L-alpha line correlates well with measures of the Balmer discontinuity and Balmer line strengths; luminosity classification does not seem to affect the line strength. The observed line widths also agree with the predictions of Mihala's grid of non-LTE model atmospheres. In some cases, the L-alpha line influences the interstellar column densities reported in the interstellar OAO-2 L-alpha survey. Hence, these data toward lightly reddened B2 and B1.5 stars should be regarded as upper limits only.

Savage, B. D.↗
NASA NTRS1975

Observations and theory of Mg II lines in early type stars. II - Theory and predicted profiles. III - The observations and a comparison with the predictions

Profiles of the UV Mg II lines in the spectra of early type stars are computed in a grid of model atmospheres with effective temperatures between 8000 and 35,000 K and log g values of 2.5 to 4.0 using the LTE and non-LTE theories of line formation. The theoretical results indicate that the line cores are strengthened by non-LTE effects over the entire temperature range, resonance-line wings are weaker in the cooler models than in the LTE case, and very large deviations from LTE occur in the hot low-gravity models. These predictions are compared with the equivalent widths of the UV Mg II lines in 106 stars and of the visual lines in 48 stars (spectral types O4 to A3). The observed equivalent widths of normal stars in luminosity classes II through V are found to agree with the predictions over the entire range from O8 to A2 if a certain Mg/H abundance is adopted. The line intensities observed in supergiants, Be, Bp, and Ap stars are discussed.

Snijders, M. A. J.↗
NASA NTRS1975

The intensities and profiles of XUV transition zone lines in a quiet sun region compared to a polar coronal hole

The intensities of XUV transition-zone lines from limb spectra of a quiet-sun region and a polar coronal hole are compared. The spectra were obtained with a slit spectrograph on Skylab and cover a region from -12 sec within the limb to 20 sec above it. The lines selected for comparison are formed at temperatures that range from 36,000 to 220,000 K. Lines of the higher-temperature ions, e.g. O v, are significantly less intense in the coronal hole, and lines of lower-temperature ions show little change. Profiles of selected optically thin transition-zone lines from the quiet-sun and coronal-hole spectra are also shown. The lines are broader than expected in ionization equilibrium, and bulk-motion velocities are deduced from the widths of the lines. There appears to be little, if any, statistically significant difference in the velocities obtained from the quiet-sun region and the coronal hole.

Feldman, U.↗
NASA NTRS1976

The emission-line spectrum of a sunspot in the far-ultraviolet

The emission-line spectrum between 1200 and 1817 A from a sunspot in McMath region 12510 near the solar center is discussed. The spectrum was obtained by the normal-incidence spectrograph on Skylab. The principal results are: (1) the widths of emission lines originating in the chromosphere and lower transition region over the sunspot are much narrower than those previously reported for a polar coronal hole observed above the limb and a quiet chromospheric network observed near the solar center, indicating that the mass motions in the sunspot are less than in these other regions; (2) the sunspot spectrum, aside from the narrow widths of emission lines, is similar to spectra from the chromospheric network boundary. The intensities of lines in the sunspot are much enhanced relative to the network interior. From the full-width at half-maximum of the 1207-A Si III line, an optical depth at line center of 3.6 is deduced. Comparison with Parker's (1974) theory of sunspots shows that, if the enhancement of emission lines is due to enhanced transport of hydromagnetic waves generated in the sunspot convective zone, the mode of the waves is predominately Alfvenic.

Cheng, C.-C.↗
NASA NTRS1977

Facular line profiles and facular models

Profiles for lines near 5250 A have been calculated from facular models and compared with observed profiles. The observations are from photographic and photoelectric spectra. The atomic parameters are determined by comparison of calculated profiles with those observed for the quiet sun. The effects of finite spatial resolution and a magnetic field are required to obtain agreement with observed facular line profiles. The empirical magnetic field deduced by matching observed and calculated profiles is reasonably consistent with that in the facular models. The main purpose of this paper is to show that by including the effects of scattered photospheric light and a strong magnetic field, reasonable agreement can be achieved between observed and calculated facular line profiles. Results are also presented for the wing of the Ca II K line, showing line profiles and effective filtergram contrasts for several facular models. It is concluded that observations made with weak Fraunhofer lines are not very useful for discrimination among facular models, particularly without simultaneous magnetic-field measurements. The K line may offer a better discriminator. The facular model presently favored has a magnetic field strength of about 1500 gauss at the surface of the photosphere.

Chapman, G. A.↗
NASA NTRS1978

The role of O-type neutral lines in magnetic merging during substorms and solar flares

An analytical model of O-type configurations was derived, for visualizing the geometry and for numerical treatment of plasma flows. It was found that at a certain distance from the neutral line the mean particle motion became decoupled from that of magnetic field lines (which obey the MHD condition). The decoupling distance depended on initial conditions in momentum space, suggesting that the MHD approximation which averages out such conditions may not suffice for describing plasma dynamics near the neutral line. It was also found that after inflowing particles are decoupled from the field line motion, they go over to a mode of runaway acceleration along the neutral line. It is concluded that if merging occurs at an X-O pair, two particle populations may be expected - low energy particles accelerated adiabatically by earthward convection past the X-type line and high-energy particles convected towards the O-type line. The second acceleration process depends critically on the rapidity of merging and is therefore expected to vary considerably from event to event.

Stern, D. P.↗
NASA NTRS1978

Observations of the 51.8 micron (O III) emission line in Orion

The 51.8 micron fine structure transition P2:3P2 3P1 for doubly ionized oxygen was observed in the Orion nebula. The observed line strength is of 5 plus or minus 3 times 10 to the minus 15th power watt/sq cm is in good agreement with theoretical predictions. Observations are consistent with the newly predicted 51.8 micron line position. The line lies close to an atmospheric water vapor feature at 51.7 micron, but is sufficiently distant so that corrections for this feature are straightforward. Observations of the 51.8 (O III) line are particularly important since the previously discovered 88 micron line from the same ion also is strong. This pair of lines should, therefore, yield new data about densities in observed H II regions; or else, if density data already are available from radio or other observations, the lines can be used to determine the differential dust absorption between 52 and 88 micron in front of heavily obscured regions.

Melnick, G.↗
NASA NTRS1978

Gamma-ray lines from neutron stars as probes of fundamental physics

The detection of gamma-ray lines produced at the surface of neutron stars will serve to test both the strong and gravitational interactions under conditions unavailable in terrestrial laboratories. Observation of a single redshifted gamma-ray line, combined with an estimate of the mass of the star will serve as a strong constraint on allowable equations of state of matter at supernuclear densities. Detection of two redshifted lines arising from different physical processes at the neutron star surface can provide a test of the strong principle of equivalence. Expected fluxes of nuclear gamma-ray lines from accreting neutron stars were calculated, including threshold, radiative transfer and redshift effects. The most promising probes of neutron star structure are the deuterium formation line and the positron annihilation line. Detection of sharp redshifted gamma-ray lines from X-ray sources such as Cyg X-1 would argue strongly in favor of a neutron star rather than black hole identification for the object.

Brecher, K.↗
NASA NTRS1978

Line shifts due to blending

The reported investigation is concerned with the case in which the measured position of a strong line of the spectrum is blended with a weaker one, taking into account the traditional solution proposed by Hartmann (1901) concerning the mean of the solar lines. An arbitrary element regarding the use of the centroid is related to the decision at which separation the components pass from being 'blended' to being 'resolved'. At this separation, the adopted wavelength suddenly jumps from the centroid of the blend to the position of the stronger line alone. It is pointed out that this discontinuous behavior is physically implausible. Attention is given to a solution involving a gradual diminution of the effect of the weaker line with increasing separation. Thus the weight of each component should depend on its position as well as its intensity. When partially blended lines cannot be decomposed into their components, and an effective line-position for the hole blend is needed, the line peak is the criterion least affected by blending. A method is presented for calculating such peak positions.

Young, A. T.↗
NASA NTRS1978

Observations of the 51.8 micron forbidden O III emission line in Orion

This letter reports observations of the 51.8-micron fine-structure transition p2: 3P(2) - 3P(1) for doubly ionized oxygen. The observed line strength in the Orion Nebula is (5 + or - 3) by 10 to the -15th power W/sq cm, in good agreement with the theoretical predictions of Simpson (1975). The observations are also consistent with the predicted line position, 51.8 microns. The line lies close to an atmospheric water-vapor feature at 51.7 microns but is sufficiently distant so that corrections for this feature are straightforward. Observations of the 51.8-micron forbidden O III line are particularly important, since the previously discovered 88-micron line from the same ion also is strong. This pair of lines should therefore yield new data about densities in observed H II regions; or else, if density data already are available from radio or other observations, the lines can be used to determine the differential dust absorption between 52 and 88 microns in front of heavily obscured regions.

Melnick, G.↗
NASA NTRS1978

Emission lines of H2 in the extreme-ultraviolet solar spectrum

A sunspot EUV spectrum covering the wavelength range from 1175 to 1714 A with high spatial and spectral resolution is examined which contains about 200 lines not previously reported in solar spectra. Many of the lines are identified as transitions in the Lyman bands of H2. It is shown that the H2 lines are photoexcited not only by H L-alpha, as reported previously, but also by the strong transition-region lines of C II, Si IV, and O IV. The line intensities are analyzed as far as is possible at present, and differences between the quiet chromosphere and the sunspot chromosphere are deduced. The polarization of the observed lines is briefly discussed, the importance of the H L-alpha fluorescence mechanism for the excitation of the H2 Lyman bands is demonstrated, and it is concluded that the H2 lines could also be observable in stars of spectral type later than the sun.

Jordan, C.↗
NASA NTRS1979

The emission-line spectrum of 3C 48

The spectrum and absolute energy distribution of the quasar 3C 48 are analyzed, yielding the following results. The forbidden lines are blueshifted with respect to the permitted lines by 600 km/s. The Balmer lines can be decomposed into a narrow and a broad component, with the narrow component having the redshift of the forbidden lines. The Mg II profile fits well the broad components of H-beta and H-gamma along with the Fe II profiles, and the forbidden O II profile fits well the profiles of forbidden O III and higher-ionization forbidden lines. The spatial coverage in the broad-line region is large, ranging from 0.1 to 0.4, and the optical depth at the Lyman limit is much greater than unity; the electron density is greater than 10 million per cu cm. The forbidden-line region has a lower density (less than 1 million per cu cm) and is subdivided into a low-excitation (forbidden O II) and high-excitation (forbidden O III) zone. The helium abundance appears to be normal.

Thuan, T. X.↗