Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “LINING”

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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Solar flare gamma-ray line shapes

A computer code has been developed which is used to calculate ab initio the laboratory shapes and energy shifts of gamma-ray lines from (C-12)(p, gamma/4.438/)p-prime(C-12) and (O-16)(p, gamma/6.129/)p-prime(O-16) reactions and to calculate the expected shapes of these lines from solar flares. The sensitivity of observable solar flare gamma-ray line shapes to the directionality of the incident particles is investigated for several projectile angular distributions. Shapes of the carbon and oxygen lines are calculated assuming realistic proton energy spectra for particles in circular orbits at the mirror points of magnetic loops, for particle beams directed downward into the photosphere, and for isotropic particle distributions. Line shapes for flare sites near the center of the sun and on the limb are shown for both thin-target and thick-target interaction models.

Werntz, C.↗
NASA NTRS1990

Improved line parameters for ozone bands in the 10-micron spectral region

A complete update of spectroscopic line parameters for the 10-micron bands of ozone is reported. The listing contains calculated positions, intensities, lower state energies, and air- and self-broadened halfwidths of more than 53,000 lines. The results have been generated using improved spectroscopic parameters obtained in a number of recent high resolution laboratory studies. A total of eighteen bands of (O-16)3 (sixteen hot bands plus the nu(1) and nu(3) fundamentals) are included along with the nu(1) and nu(3) fundamentals of both (O-16)(O-16)(O-18) and (O-16)(O-18)(O-16). As shown by comparisons of line-by-line simulations with 0.003/cm resolution balloon-borne stratospheric solar spectra, the new parameters greatly improve the accuracy of atmospheric calculations in the 10-micron region, especially for the isotopic (O-16)(O-16)(O-18) and (O-16)(O-18)(O-16) lines.

Flaud, Jean-Marie↗
NASA NTRS1990

H2 line emission in three Seyfert nuclei: Evidence against UV-excitation

Line emission from vibrationally excited molecular hydrogen has been detected in a considerable number of active galactic nuclei (AGNs), including those generally believed to contain compact and luminous central engines (e.g., Seyfert nuclei) and those in which the luminosity is believed to arise from massive bursts of star formation (starburst nuclei). In most of these AGNs, only the bright 1-0 S(1) line (rest wavelength 2.12 microns) has been searched for and detected to date. Line-emitting H2 can be excited directly either by energetic collisions created by shock waves or by absorption of UV radiation. Each of these excitation mechanisms has been clearly identified in galactic and extragalactic regions. In active galactic nuclei strong sources of UV and (in some case) x rays are present. If the nuclear molecular matter is quiescent (i.e., isolated from the active nucleus and not set into motion by episodes of star formation) the H2 line emission will be dominated by fluorescence, or possibly by thermal emission due to heating by x rays (Krolik, this conference). However, it is expected or indeed observed that a significant fraction of the interstellar medium in and near these nuclei is undergoing rapid motions; either generated by the central engine or by a nuclear starburst, which are capable of producing strong shock phenomena in nearby molecular gas. Thus, a priori it is not obvious which mechanism is responsible for the H2 line emission from the nucleus of an active galaxy.

Geballe, T. R.↗
NASA NTRS1990

The effect of coupling line loss in microstrip to dielectric resonator coupling

The interaction between a dielectric resonator and a microstrip transmission line is fundamentally a field phenomenon. However, the model of Figure 1b widely is used to represent the arrangement in Figure 1a, and predicts the behavior encountered in practice. The microstrip line of length l = n(lambda)/4 between the input and coupling planes and the lambda/4 open-circuit stub usually is assumed to be lossless. This paper considers the effect of coupling line loss on the unloaded-Q and coupling coefficient beta of the combination. It shows that transmission line loss can cause the decrease in unloaded-Q that has been observed to occur with tight coupling, and limits the coupling coefficient to a much lower value than would be obtained with a lossless coupling line.

Hearn, C. P.↗
NASA NTRS1990

Optical coronal emission lines from equilibrium and cooling plasmas

A calculation has been made of the emission from gas at temperature of about 10 to the 6th K due to optical coronal lines that result from fine structure transitions within the ground states of highly ionized atoms. These lines include the Forbidden Fe X 6374-A line, the Forbidden Fe XIV 5303-A line, and many other lines from stages of ionization of S, Ca, Fe, and Ni. The calculations are valid in the limit of very low density, and apply to the diffuse gas found in supernova remnants, the interstellar medium in galaxies, and intergalactic gas. It is found that the amount of optical coronal emission produced by a given amount of cooling gas is largely unaffected by changes in element abundances (provided the proportions of heavy elements remain the same).

Graney, Christopher M.↗
NASA NTRS1990

Study of electron impact excitation of argon in the extreme ultraviolet - Emission cross section of resonance lines of Ar I, Ar II

In a crossed-beam experiment under optically thin conditions the EUV spectrum of argon produced by electron impact excitation is studied. The cross sections of the resonance lines of Ar I and II are measured. The resonance lines of Ar I at 104.8 nm and 106.7 nm, and of Ar II at 91.96 nm and 93.21 nm are the most prominent features of the EUV spectrum between 40 and 110 nm. The relative-flow technique is used to measure the absolute cross sections of these lines at 200 eV. The measurements are compared with previous estimates. The measured emission cross section values at 200 eV for the Ar I lines at 104.8 nm and 106.7 nm, when compared to the electron energy loss estimates of the direct excitation cross sections, establish that cascading is larger for the Ar I resonance lines than previous emission experiments have indicated. In addition, all the emission cross sections for the Ar I and II Rydberg series in the EUV are measured at 0.5 nm resolution. The FUV spectrum is also surveyed and found to consist of Ar II multiplets from simultaneous ionization-excitation.

Ajello, Joseph M.↗
NASA NTRS1991

A line identification study of the IUE SWP high dispersion spectrum of the UV-bright star Barnard 29 of Messier 13

A line identification study was performed of the coaddition of three SWP high dispersion IUE exposures of the UV-bright star Barnard 29 of Messier 13. One of these images took two IUE shifts. The previous study by de Boer and Savage (1983) was extended and stellar lines of C I, C II, C III, C IV, N I, N III, O I, O III, O IV,Al III, Si II, Si III, Si IV, P III, S II, and S III and interstellar lines of C I, C II, C IV, N I, N III, N IV, N V, O I, Al II, Al III, Si II, Si IV, S II, and Fe II were found. These lines are the strongest expected lines in a hot Population II star. Apparent intensity minima corresponding to interstellar features are noted, especially those matching a high velocity cloud found by de Boer and Savage.

Adelman, S. J.↗
NASA NTRS1991

The analysis of apparent optical depth profiles for interstellar absorption lines

Attention is given to the apparent optical depth method, a procedure for analyzing interstellar absorption lines. Observed absorption-line profiles are converted into profiles of apparent optical depth, and apparent column density per unit velocity. By comparing the latter for a given interstellar species having two or more absorption lines which differ in the product, the presence or absence of unresolved saturated structure in the profiles can be directly inferred. The method is illustrated using absorption-line data from the IUE satellite for the highly ionized gas toward HD 64760. Additional illustrations and a study of the method's accuracy are provided through a series of numerical simulations of multicomponent interstellar absorption situations. The method is compared to the standard growth curve method for deriving interstellar column densities. The principal value of the apparent optical depth method is that the absorption-line data are directly converted into a form that provides for direct scientific interpretations of the physical conditions in the interstellar absorbing medium as a function of velocity.

Savage, Blair D.↗
NASA NTRS1992

Improved Stacking Of Vent Lines Of A Parachute

New arrangement provides nearly uniform distribution of load among vent lines and points of attachment of vent lines to vent band. New method eliminates large stack height between first and last lines and, just as important, maintains constant stack height between any two adjacent vent lines around entire vent. Distributes loads at vent band more nearly evenly among lines. Adverse concentrations of loads in vent band reduced.

Hengel, John E.↗
NASA NTRS1992

Dynamic modeling of fluid transmission lines of the DSN 70-meter antennas by using a lumped parameter model

Fluid transmission lines and fittings were found to significantly affect the dynamic and steady state operation of the engineering system in which they are incorporated. Therefore, a better understanding of the operation of a system can be obtained by including the performance of the transmission lines and fittings within the system model. The most accurate model of a transmission line or fitting is obtained by using a distributed parameter model. However, a distributed parameter model tends to be very complex. This complexity can be avoided without significant loss of model accuracy by using a lumped parameter model when the length of the fluid path through the transmission line or fitting is short. This article develops a lumped parameter model for short fluid transmission lines and fittings, describes the conditions under which the model is valid, and presents the model parameters associated with the servo hydraulic system of the Deep Space Network (DSN) 70-meter antennas.

Bartos, R. D.↗
NASA NTRS1991

First identification of pure rotation lines of NH in the infrared solar spectrum

Pure rotation lines of NH of the v = 0 level and v = 1 level are detected in high-resolution solar spectra obtained from the Atmospheric Trace Molecule Spectroscopy (ATMOS) experimental observations. It is pointed out that the identification of the lines is favored by the typical appearance of the triplet lines of nearly equal intensities. The observed equivalent widths of these triplet lines are compared with predicted intensities, and it is observed that these widths are systematically larger than the predicted values. It is noted that because these very faint lines are observed in a region where the signal is very low, a systematic error in the measurements of the equivalent widths cannot be ruled out; therefore, the disagreement between the observed and predicted intensities is not considered to be real.

Geller, M.↗
NASA NTRS1992

Winds from T Tauri stars. II - Balmer line profiles for inner disk winds

Results are presented of calculations of Balmer emission line profiles using escape probability methods for T Tauri wind models with nonspherically symmetric geometry. The wind is assumed to originate in the inner regions of an accretion disk surrounding the T Tauri star, and flows outward in a 'cone' geometry. Two types of wind models are considered, both with monotonically increasing expansion velocities as a function of radial distance. For flows with large turbulent velocities, such as the HF Alfven wave-driven wind models, the effect of cone geometry is to increase the blue wing emission, and to move the absorption reversal close to line center. Line profiles for a wind model rotating with the same angular velocity as the inner disk are also calculated. The Balmer lines of this model are significantly broader than observed in most objects, suggesting that the observed emission lines do not arise in a region rotating at Keplerian velocity.

Calvet, Nuria↗
NASA NTRS1992

Stratospheric HNO3 measurements from 0.002/cm resolution solar occultation spectra and improved spectroscopic line parameters in the 5.8-micron region

Very-high-resolution FWHM solar-occultation spectra are investigated with a balloon-borne interferometer using revised spectroscopic line parameters for HNO3, O3, and H2O. The O3 and H2O data are evaluated to determine their capacity for interference in the HNO3 line which is studied in the nu sub 2 band at 5.8 microns. The line parameters developed with the stratospheric data are compared to data based on a HITRAN compilation as well as laboratory spectra with a 0.002/cm resolution. The line list is calculated and shown to include J and Ka transitions which improve the line parameters for HNO3 by accounting for the weaker absorption features in the stratospheric spectra. The stratospheric HNO3 profile developed analytically is compared to those based on reported measurements, and the one developed with the stratospheric solar spectra is found to be consistent with the measurements and confirm inherent measurement biases.

Goldman, A.↗
NASA NTRS1992

Variability of near-infrared emission lines in NGC 4151 - Implications for nuclear star formation

Multiaperture infrared spectra of the circumnuclear region of the Seyfert galaxy NGC 4151 taken over a 10 year period show that the N = 7-4 B-gamma hydrogen recombination line is variable. The H2 quadrupole line emission shows no sign of variability. It is shown that there is a substantial contribution to the nuclear B-gamma flux from the active nucleus, making it impossible to determine star formation rates from infrared hydrogen recombination lines in active galaxies. The lack of variability in the H2 line fluxes indicates that ionizing photons from the active nucleus is not important in exciting the molecular line emission.

Prestwich, Andrea H.↗
NASA NTRS1992

The evolution of line-tied coronal arcades including a converging footpoint motion

It has been demonstrated in the past that single, 2D coronal arcades are very unlikely driven unstable by a simple shear of the photospheric footpoints of the magnetic field lines. By means of 2D, time-dependent MHD simulations, evidence is presented that a resistive instability can result if in addition to the footpoint shear a slow motion of the footpoints toward the photospheric neutral line is included. The photospheric footpoint velocity in this model is nonsingular and the shear dominates everywhere. Starting from a planar potential field geometry for the arcade, it is found that after some time a current sheet is formed which is unstable with respect to the tearing instability. The time of its onset scales with the logarithm of the magnetic diffusivity assumed in the calculation. In its nonlinear phase, a quasi-stationary situation arises in the vicinity of the x-line with an almost constant reconnection rate. The height of the x-line above the photosphere and the distance of the separatrix footpoints remain almost constant in this phase, while the helical flux tube, formed above the neutral line, continuously grows in size.

Inhester, B.↗
NASA NTRS1991

Measurements of gamma-ray line profiles from SN1987A and the structure of the ejecta

A few balloon-borne-instrument measurements of SN1987A's gamma-ray line profiles furnish the most direct indication of the distribution of freshly synthesized Co-56 radioactive material in the SN ejecta. Most of these profiles exhibit line shapes inconsistent with the standard, spherically symmetric and homogeneously mixed models, and are very similar to line profiles for IR lines of Fe observed prior to day 500 of the SN. The consistency of the line profile from IR to gamma-ray energies may reflect the distribution of freshly synthesized material in the expanding SN shell.

Tueller, J.↗
NASA NTRS1992

Energetic ions as remote probes of X type neutral lines in the geomagnetic tail

The study presents a summary of particle orbit signatures of a neutral line in the geomagnetic tail current sheet (CS) as a function of spatial position along the CS boundary layer, as well as within the CS. Six types of CS particle orbits are reviewed: transient B sub z, transient X line, quasi-trapped, trapped, noncrossing X line, and limiting (singular) cases. It is found that for single particle dynamics in a current sheet with neutral line, the phase space ridge is predicted to be found throughout the current sheet if it is not destroyed by collective behavior. An initially tailward flowing distribution causes asymmetries in distributions earthward vs tailward of the neutral line. It is suggested that the chaotic pitch angle scattering may be a dominant mechanism to produce nightside proton isotropy in the auroral zones.

Speiser, T. W.↗
NASA NTRS1992

Gas temperature measurements using the dual-line detection Rayleigh scattering technique

A new laser-induced Rayleigh scattering method is presented for the improved temperature diagnostics of gas flows. In the present technique, the two lines of a copper vapor laser are used to obtain the time and space resolved temperature. A single set of optics is used to form the optical probe and to collect the signal simultaneously from both the 510 nm and the 578 nm lines. The dual-line detection allows for the determination and removal of surface-scattered laser light from a Rayleigh signal thereby improving the applicability of Rayleigh scattering to near wall flows with a high degree of glare. An optical system using the dual-line detection technique is built, calibrated and tested in a hot air jet under various levels of background contamination. The results indicate that highly accurate temperature measurements are possible even when the laser-line background intensity, captured by the collecting optics, is five times that of the Rayleigh signal.

Otugen, M. Volkan↗