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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Laboratory Automation of a Quadrupole Mass Spectrometer

Efforts directed toward interfacing an LSI II bus of a PDP 11/23 desktop computer with a quadrupole mass spectrometer for the purpose of providing a convenient system whereby mass spectral data, of the products of thermal decomposition, may be rapidly acquired and processed under programmed conditions are described. The versatility and operations of the quadrupole mass spectrometer are discussed as well as the procedure for configurating the LSI II bus of the PDP 11/23 desktop computer for interfacing with the quadrupole mass spectrometer system. Data from the mass filter and other units of the spectrometer are digitally transferred to the computer whereupon mass spectral data and related data are generated.

Thompson, J. M.↗
NASA NTRS1984

Coronal mass ejection recurrence studies indicating global activity and local suppression

The distribution of time intervals between successive coronal mass ejection events observed from the SMM and Skylab coronagraphs has been analyzed. Histograms of such recurrence times show that mass ejections tend to cluster in periods of activity. Evidence is found for simultaneous activity on a global scale. A second result is that, statistically, limb regions within + or - 59 deg position angle of a mass ejection show a marked absence of subsequent observable ejections for approximately 10 h. Flares of importance greater than or equal to 1 show no such deficit; however, large disparitons brusques tend similarly to be suppressed, for 24 h. This result, together with the closer association of mass ejection with eruptive prominences rather than with flares and the realization that eruptive prominences are rarely if ever seen without an accompanying mass ejection, obviates suggestions that magnetohydrodynamic conditions in the outflow following the earlier mass ejection hide subsequent coronal events.

Wagner, W. J.↗
NASA NTRS1984

Mass loss from red giants - A simple evolutionary model for NGC 7027

NGC 7027 is a young planetary nebula with the remnants of a red giant circumstellar envelope surrounding the central, ionized region. By comparing the outer molecular envelope with the inner ionized material, it is argued that the mass loss rate has decreased by at least a factor of 3, and more probably by about a factor of 10, during the past 1000 years. From this result, it is argued that the luminosity of the central star has also decreased substantially during the same time, consistent with models for the rapid evolution of stars just after they evolve off the asymptotic giant branch. In this picture, the distance to NGC 7027 is less than 1300 pc. NGC 7027 was the last (and best) example of a star where apparently the momentum in the outflowing mass /M(dot)v/ is considerably greater than the momentum in the radiation field (L/c). With the above description of this object, the evidence is now strong that quite often the mass lost from late-type giants is ultimately driven to infinity by radiation pressure on grains. If M(dot)v is as large as L/c for asymptotic branch stars, then it is expected that the total amount of mass lost during this stage of evolution is of the same magnitude as the initial mass of the star, and therefore this mass loss can profoundly affect the star's ultimate fate.

Jura, M.↗
NASA NTRS1984

Measurement of mass distribution of chemical species in aerosol particles

Aerosols may be generated through the nebulizing of solutions and the evaporation of their solvent, leaving the dry solute particles. Attention is presently given to a method for the direct determination of the masses of chemical species in individual aerosol particles on a continuous, real-time basis, using mass spectrometry. After the aerosol particles are introduced into the ion source of a quadrupole mass spectrometer, the particles impinge on a hot rhenium filament in the mass spectrometer's ion source. The resulting vapor plume is ionized by electron bombardment, and a pulse of ions is generated by each particle. The intensities of different masses in the ion pulses can then be measured by the mass spectrometer.

Sinha, M. P.↗
NASA NTRS1984

Iterative and function-continuation Fourier deconvolution methods for enhancing mass spectrometer resolution

Mass spectrometer data in the form of ion current versus mass-to-charge ratio often include overlapping mass peaks, especially in low- and medium-resolution instruments. Numerical deconvolution of such data effectively enhances the resolution by decreasing the overlap of mass peaks. In this paper two approaches to deconvolution are presented: a function-domain iterative technique and a Fourier transform method which uses transform-domain function-continuation. Both techniques include data smoothing to reduce the sensitivity of the deconvolution to noise. The efficacy of these methods is demonstrated through application to representative mass spectrometer data and the deconvolved results are discussed and compared to data obtained from a spectrometer with sufficient resolution to achieve separation of the mass peaks studied. A case for which the deconvolution is seriously affected by Gibbs oscillations is analyzed.

Ioup, J. W.↗
NASA NTRS1985

Skeletal mass change as a function of gravitational loading

The hypothesis that increased loading on an animal by chronic centrifugation results in an increase in skeletal mass was tested, using metabolically mature hamsters, rats, guinea pigs, Dutch rabbits and New Zealand rabbits representing a body mass range from 0.15 to 3.8 kg. Groups of 12 male animals of each species were subjeted to 2.0 g for 6 weeks on a 2.74 radius centrifuge with one degree of freedom. Subsequently, six of the animals were killed to measure whole body composition, while the rest comprised the control group, recovering for four weeks at 1.0 g prior to composition analysis. Results show a significant increase in bone mineral mass at 2.0 g. These centrifuge experiment results were then compared with the results of the USSR Cosmos Biosatellite experiment, whereby five rats experienced osteoporosis after 18.5 days of weightlessness. The opposing nature of effects that occurred at 0 g and 2.0 g is indicated schematically of particular interest is the fact that the bone mineral mass of the Cosmos 1129 flight rats was 17 pct less than that of the 1.0 g controls; whereas the bone mineral mass of the centrifuge rats was 18 pct greater than that of their 1.0 g controls. It is concluded that the bone mineral mass of the rat is directly proportional to gravitational loading over the range of 0 g to 2.0 g.

Pace, N.↗
NASA NTRS1986

Concentrated mass effects on the flutter of a composite advanced turboprop model

The effects on bending-torsion flutter due to the addition of a concentrated mass to an advanced turboprop model blade with rigid hub are studied. Specifically the effects of the magnitude and location of added mass on the natural frequencies, mode shapes, critical interblade phase angle, and flutter Mach number are analytically investigated. The flutter of a propfan model is shown to be sensitive to the change in mass distribution. Static unbalance effects, like those for fixed wings, were shown to occur as the concentrated mass was moved from the leading edge to the trailing edge with the exception of one mass location. Mass balancing is also inferred to be a feasible method for increasing the flutter speed.

Ramsey, J. K.↗
NASA NTRS1986

Are the virial masses of clusters smaller than we think?

The constraints that the available X-ray spectral and imaging data place on the mass distribution and mass to light ratio of rich clusters are considered. It was found for the best determined cases that the mass to light ratio is less than 125 h sub 50 at radii exceeding 1 h sub 50 Mpc. The mass to light ratio is approximately constant at radii exceeding 1 h sub 50 Mpc but may rise to values of roughly 200 h sub 50 in the central regions. The fraction of the total mass that is in baryons, primarily the hot X-ray emitting gas, is roughly 30% thus setting the mass to light ratio of the dark material to roughly 70. The model that fits the X-ray data for Coma is in good agreement with the observed optical velocity dispersion vs. radius data.

Cowie, L. L.↗
NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overalll system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1880 kg/cu m.

Juhasz, Albert J.↗
NASA NTRS1986

Self-regulated cooling flows in elliptical galaxies and in cluster cores - Is exclusively low mass star formation really necessary?

A self-consistent treatment of the heating by supernovae associated with star formation in a spherically symmetric cooling flow in a cluster core or elliptical galaxy is presented. An initial stellar mass function similar to that in the solar neighborhood is adopted. Inferred star-formation rates, within the cooling region - typically the inner 100 kpc around dominant galaxies at the centers of cooling flows in XD clusters - are reduced by about a factor of 2, relative to rates inferred when the heat input from star formation is ignored. Truncated initial mass functions (IMFs) are also considered, in which massive star formation is suppressed in accordance with previous treatments, and colors are predicted for star formation in cooling flows associated with central dominant elliptical galaxies and with isolated elliptical galaxies surrounded by gaseous coronae. The low inferred cooling-flow rates around isolated elliptical galaxies are found to be insensitive to the upper mass cutoff in the IMF, provided that the upper mass cutoff exceeds 2 M solar mass. Comparison with observed colors favors a cutoff in the IMF above 1 M solar mass in at least two well-studied cluster cooling flows, but a normal IMF cannot be excluded definitively. Models for NGC 1275 support a young (less than about 3 Gyr) cooling flow. As for the isolated elliptical galaxies, the spread in colors is consistent with a normal IMF. A definitive test of the IMF arising via star formation in cooling flows requires either UV spectral data or supernova searches in the cooling-flow-centered galaxies.

Silk, J.↗
NASA NTRS1987

Mass-losing red giants in open clusters

Mass-losing stars in open clusters with main-sequence turn-offs at intermediate mass have been searched for by using the IRAS data base. The absence of many strong 60 micron sources in open clusters implies that intermediate-mass stars lose much of their mass during an intense wind phase of rather short duration. For stars of about seven solar masses, this phase, if it exists at all, lasts for not much more than 100,000 yr. For stars of about four solar masses, the intense wind phase appears to last considerably less than 10 million yr; it may well last for less than a million yr.

Jura, M.↗
NASA NTRS1987

Are the virial masses of clusters smaller than we think?

The constraints that the available X-ray spectral and imaging data place on the mass distribution and mass to light ratio of rich clusters are considered. It was found for the best determined cases that the mass to light ratio is less than 125 h sub 50 at radii exceeding 1 h sub 50 Mpc. The mass to light ratio is approximately constant at radii exceeding 1 h sub 50 Mpc but may rise to values of roughly 200 h sub 50 in the central regions. The fraction of the total mass that is in baryons, primarily the hot X-ray emitting gas, is roughly 30 percent thus setting the mass to light ratio of the dark material to roughly 70. The model that fits the X-ray data for Coma is in good agreement with the observed optical velocity dispersion vs. radius data.

Cowie, L. L.↗
NASA NTRS1987

Mass loss

Observational evidence for mass loss from cool stars is reviewed. Spectra line profiles are used for the derivation of mass-loss rates with the aid of the equation of continuity. This equation implies steady mass loss with spherical symmetry. Data from binary stars, Mira variables, and red giants in globular clusters are examined. Silicate emission is discussed as a useful indicator of mass loss in the middle infrared spectra. The use of thermal millimeter-wave radiation, Very Large Array (VLA) measurement of radio emission, and OH/IR masers are discussed as a tool for mass loss measurement. Evidence for nonsteady mass loss is also reviewed.

Goldberg, Leo↗
NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overall system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1800 kg/cu m).

Juhasz, Albert J.↗
NASA NTRS1988

4U 1626-67 - The binary with the smallest known mass function

The pulsing X-ray source 4U 1626-67 is an accreting neutron star in a binary system with a very low mass companion. The source was observed by Exosat continuously for 23 hr on March 30-31, 1986 UT. It is found that, if the orbital inclination angle equals 90 deg, the optical companion star has a mass of less than about 0.002 solar mass; however, it is found that a companion star mass of greater than about 0.06 solar mass is required if gravitational radiation is responsible for driving the mass transfer in this system. Also presented are results on flaring activity in the system on time scales of about 1000 s, the energy-dependent pulse profiles, and the pulse period history over the past decade.

Levine, A.↗
NASA NTRS1988

X-ray induced stellar mass loss near active galactic nuclei

The effects of UV and X-ray radiation on stars in active galactic nuclei (AGN) are critically evaluated. Mass loss rates in X-ray-induced winds are evaluated for realistic red giant models, and the effects of the ablation of stellar envelopes by radiation pressure are considered. The importance of X-ray-induced mass loss in the standard quasar model is evaluated and whether it can provide a source of accretion fuel or emission-line clouds is discussed. It is concluded that thermal winds driven by X-ray heating are a minor total supply of mass to AGN, but that thermal plus line-driven winds and stellar ablation may increase the mass loss and improve the chances for supplying a fraction of the necessary mass supply to the central object. It is speculated that when steady winds are inefficient, complex time-dependent processes due to X-ray energy injection deep into a stellar atmosphere could still release significant mass from stars.

Voit, G. Mark↗
NASA NTRS1988

Determination of the area and mass distribution of orbital debris fragments

An important factor in modeling the orbital debris environment is the loss rate of debris due to atmospheric drag and lunisolar perturbations. An accurate knowledge of the area-to-mass ratio of debris fragments is required to calculate the effects of atmospheric drag. It is shown here that the orbital elements as a function of time can be used to invert any propagation algorithm to yield the area-to-mass ratio of an orbiting object. From these calculations and the observed radar cross-section of the object, the mass can be calculated to an accuracy of about 30 percent. It is shown that the mass is related to the effective cross-section area by a power-law relation, but for a given area the mass distribution is very broad. An expression is given for the cumulative mass distribution.

Badhwar, G. D.↗
NASA NTRS1988

The effects of excitation waveforms and shaker moving mass on the measured modal characteristics of a 2- by 5-foot aluminum plate

Ground vibration tests were conducted to compare and to investigate the effects of five excitation waveforms and the shaker moving mass (equipment and armature used to attach the shaker to the structure) on the experimental modal characteristics of a 2- by 5-ft aluminum plate using fast Fourier transform techniques. The five types of excitation waveforms studied were sine dwell, random, impact, sine sweep, and impulsive sine. The results showed that the experimental modal frequencies for all types of excitation were within 3 percent, while the modal damping data exhibited greater scatter. The sets of mode shapes obtained by the five types of excitation were consistent. The results of the shaker moving mass investigation on the 2- by 5-ft aluminum plate showed that modal frequency decreases and modal damping remains relatively constant with an increase in shaker moving mass. The generalized mass of the structure appears to decrease with an increase in shaker moving mass. In addition, it was seen that having a shaker near a node line can reduce some of the effects of the added shaker moving mass on the frequencies and the damping.

Voracek, David F.↗