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At least 235 records · Page 13

Blind Validation Study of PRICE TruePlanning and SEER-H

Two of the primary parametric costing tools used to estimate the development and production cost of future spacecraft hardware are PRICE TruePlanning by PRICE Systems, and System Estimation and Evaluation of Resources-Hardware (SEER-H) by Galorath. These are standard tools used by NASA and industry to estimate the cost of new aerospace hardware. This study is an independent verification of the accuracy of these tools and was originally published in 2018. The purpose of this presentation is to circulate the findings of that study among the NASA cost community. Both PRICE Systems and Galorath have completed internal validation studies of their parametric cost estimating tools; however, they only provided the results of the studies and did not detail the exact methods used to perform the validation. In the present study, cost estimators used PRICE TruePlanning and SEER-H to estimate the cost of twelve different past NASA science missions. The estimators were prevented from knowing the actual cost of the missions in an effort to minimize cognitive biases. In the present study, SEER-H had an average error of 23%, median error of -0.3%, with a standard deviation of 43%. PRICE had an average error of 52%, median error of 50%, and standard deviation of 45%. Nine of the twelve mission's actual costs fell within the 80% confidence interval of SEER's probabilistic estimates; however, none of the missions fell within PRICE’s confidence intervals. There were several factors independent of PRICE and SEER-H which may have affected the accuracy of the results in the present study including: uncertainty in the technical data used for the estimates, the methods used to estimate uncertainty in spacecraft component mass and numbers of prototypes, and the experience of the estimators.

SEER↗

D autoionization states of He and ionic H

Positions of the lowest 1,3De autoionization states of He and H(-) below the n = 2 level of the He(+) and H were calculated variationally, using Feshbach's Q-operator formalism. The trial wave function is of the Hylleraas-type with appropriate angular momentum factors. The widths and the shifts of the states have also been calculated. The shifts are found to be positive for all the states calculated here. The results with 112 terms for most states are lower than any previously calculated. The calculated lowest autoionization states of the He and H(-) (relative to the ground states of He and H respectively) are 59.902 eV and 10.1185 eV, in good agreement with the observed values of 59.9 eV and 10.13 + or 0.015 eV.

Bhatia, A. K.↗

D autoionization states of He and H/-/.

Burke (1967) observed a number of resonances in He and H(-) below the threshold of H(+) and H. Bhatia et al. (1969, 1967) showed that Feshbach's Q-operator formalism can be used to calculate the positions and widths of the S and P autoionization states. These calculations are extended to the D autoionization states in He and H(-) observed below the n = 2 threshold of the respective targets. The shifts of the states are found to be positive for all the states computed.

Bhatia, A. K.↗

Spatial relationship between 5303-A and H alpha components of a loop prominence system.

There are remarkable similarities in the structure of loop prominences when observed in H alpha and coronal lines, although the lines arise from extremely different excitation conditions. This leads to the consideration of a multicomponent model, where different emission lines come from different elements of the structure. The late phases of a large west limb loop prominence system followed by a surge were recorded at Haleakala Observatory on March 6, 1970. Simultaneous filtergrams in H alpha and 5303-A were obtained, together with spectra at three heights in the prominence over the range from 3850 to 5950 A. The positions of bright knots of emission as seen in the green line are compared with associated H alpha knots. With these relative positions determined, the filtergrams are superimposed to demonstrate the two-dimensional spatial relationship between H alpha and 5303-A structures. The results support a model of cool loops within a closely associated hot-loop system.

Mccabe, M. K.↗

Isolated Stroemgren spheres as a source of galactic H alpha emission

The isolated H alpha emission features reported by Reynolds et al. are identified with Stroemgren spheres surrounding observed O stars; the root mean square electron densities and Stroemgren radii are calculated from the observed emission measure and stellar type. The density has an average value of 2 per cu cm but increases to 3.3 per cu cm for stars within 200 pc of the galactic plane. An analysis of the Catalogue of Galactic O Stars shows that enhanced H alpha emission is observed around all known O stars. The diffuse component of H alpha emission is what one would expect from the line-of-sight overlapping of isolated Stroemgren spheres surrounding B stars and appears to correlate with features on extinction maps, as derived. There is no compelling reason to suggest any large-scale intercloud ionization from H alpha data alone.

Elmergreen, B. G.↗

The low energy cosmic ray H-2 and He-3 spectra and the anomalous He-4 component

Measurements of the 1974 low-energy spectra of H-2, He-3, and He-4 with the IMP-8 satellite reveal the continued presence of the anomalous flat He-4 spectrum first reported in 1972 for roughly below 50 MeV/nucleon. Measurements of the isotope quartet H-1, H-2, He-3, He-4 are reported and compared, for 1974 quiet time, and are compared to 1965 observations at near solar minimum. Comparison of H-3 and He-3 data with accepted models of interstellar propagation and solar modulation supports a galactic origin for these isotopes down to about 10 MeV/nucleon. No evidence is found for a low-energy breakdown or other anomalous behavior of galactic propagation or solar modulation models capable of accounting for the anomalous He-4 component.

Garcia-Munoz, M.↗

A search for optical pulsations from GX 1+4 at H-alpha

H-alpha observations of the binary-star candidate for the slowly pulsating hard X-ray source GX 1+4 are reported which were undertaken to search for pulsations in the H-alpha flux that are synchronous with the X-ray period of about 2 min. No significant periodic variation of the candidate star was detected in the frequency band searched. Three-sigma upper limits of 1.7% (sinusoidal pulse shape) and 0.7% (X-ray pulse shape) are set for the pulsed fraction of the H-alpha flux. It is noted that because of possible diffusion from a cloud that is optically thick to Balmer radiation, the observed lack of pulsations in the H-alpha flux need not compromise the identification of GX 1+4 with the candidate star.

Krzeminski, W.↗

Far-infrared observations of the Carina I and II H II regions

Far-infrared (35-175 microns) mapping and photometry are presented of the Carina I and II H II regions in the Carina Nebula (NGC 3372). The far-infrared source associated with Carina I has a half-power width of 2.7 arcmin and has no compact high-surface-brightness condensations, unlike many northern H II regions such as W51 or W49. The peak emission region is offset from the radio continuum peak in the direction of a dust lane to the west. It is proposed that the H II regions and far-IR source are both powered by the O-star cluster Tr 14 about 4 arcmin to the east. The H II region then represents an ionization front at the boundary of the dense cloud west of Tr 14, and the far-infrared emission is due to thermal radiation from the heated dust in the dark cloud. A similar model may also be applicable to the Carina II region.

Harvey, P. M.↗

Solar wind latitudinal variations deduced from Mariner 10 interplanetary H /1216 A/ observations

The Mariner 10 H (1216-A) interplanetary observations are examined by using models that consider anisotropies in the solar fluxes. It is verified that the dominant contribution to asymmetric structure in the Mariner 10 H (1216-A) data is a latitudinal variation of the solar-wind flux and of the solar wind velocity, leading to a hydrogen atom lifetime that is latitude dependent. The average lifetime at 1 AU is found to increase from the solar equator to the solar poles by about 25%. This allows interstellar hydrogen to penetrate closer to the solar poles than to the equator. A general analytic model is constructed for evaluating the neutral hydrogen density distribution in interplanetary space. This model takes into account the latitude-dependent ionization rate. When this model is applied to the Mariner 10 H (1216-A) data, it is shown to be capable of matching the observations with a statistical accuracy of 5%. The effect of this latitudinal variation on H (1216-A) sky background maps is to produce a latitudinal shift in the maximum toward the north ecliptic pole.

Witt, N.↗

Spectrophotometry of H II regions and the nucleus of NGC 1566

The paper presents spectrophotometric observations of the nucleus and nine H II regions in the spiral arms of the Sbc galaxy NGC 1566. The emission line spectra of the H II regions are characterized by a low grade of ionization, and most of the line intensities do not show radial gradients; the N II/O II forbidden line ratio appears to increase toward the nucleus, and the forbidden O III/H-beta ratio may decrease in the same direction. This is explained by the increase of the oxygen abundance and decrease of the electron temperature toward the nucleus; the spectra confirm the presence of the weak, broad emission wings at H-alpha, and the nuclear spectrum of NGC 1566 resembles that of a giant H II region rather than that of a Seyfert galaxy.

Hawley, S. A.↗

X-ray and H-alpha observations of a filament-disappearance flare - An empirical analysis of the magnetic field configuration

On August, 29, 1973, a flare event occurred that involved the disappearance of a filament near central meridian. The event, well-observed in X-rays on Skylab and in H-alpha, was a four-ribbon flare involving both new and old magnetic inversion lines which were roughly parallel. The H-alpha, X-ray, and magnetic field data are used to deduce the magnetic polarities of the H-alpha brightening at the footpoints of the brightest X-ray loops. It is suggested that the event involved a reconnection of magnetic field lines rather than a brightening in place of preexisting loops. The simultaneity of the H-alpha brightening onsets in the four ribbons and the apparent lack of an eruption of the filament are consistent with this interpretation.

Kahler, S. W.↗

The thermal fatigue resistance of H-13 Die Steel for aluminum die casting dies

The effects of welding, five selected surface coatings, and stress relieving on the thermal fatigue resistance of H-13 Die Steel for aluminum die casting dies were studied using eleven thermal fatigue specimens. Stress relieving was conducted after each 5,000 cycle interval at 1050 F for three hours. Four thermal fatigue specimens were welded with H-13 or maraging steel welding rods at ambient and elevated temperatures and subsequently, subjected to different post-weld heat treatments. Crack patterns were examined at 5,000, 10,000, and 15,000 cycles. The thermal fatigue resistance is expressed by two crack parameters which are the average maximum crack and the average cracked area. The results indicate that a significant improvement in thermal fatigue resistance over the control was obtained from the stress-relieving treatment. Small improvements were obtained from the H-13 welded specimens and from a salt bath nitrogen and carbon-surface treatment. The other surface treatments and welded specimens either did not affect or had a detrimental influence on the thermal fatigue properties of the H-13 die steel.

Source record↗

An H-alpha velocity study of S252

The H II region S252 (NGC 2175) was studied by means of H-alpha radial velocities and line widths. The velocity structure appears to be dominated by the western ionization front, abutting a dense neutral cloud which is a CO source, and by symmetry abut the ionizing star. This data, together with other studies of CO, H167-alpha, and the H II radio continuum, allow construction of a model of S252. The H II model is basically a double blister formed by a luminous hot star being located between two orthogonal, elongated neutral clouds.

Fountain, W. F.↗

Dynamics of a surge observed in the C IV and H alpha lines

Time sequences of a surge have been obtained in Active Region 2701 during a coordinated SMY program, on October 2nd, 1980, while the MSDP spectrograph operated in H-alpha at the Meudon Solar Tower and the UVSP spectrometer on SMM observed in the 1548 A C IV resonance line. The cold (H-alpha) and hot (C IV) material follow the same channel, and the event lasts about 10 min in both lines. A good correlation is found between H-alpha and C IV velocities; radial velocities along the surge are in the range 40-60 km/s in both cases. The observations are consistent with the hypothesis that a pressure gradient drives the surge. The H-alpha data seem to indicate the presence of a shock wave in the chromosphere, while the C IV quantities (velocities, accelerations) vary on a very short time scale. Their maxima occur at some locations which could be interpreted as 'pinched' zones.

Schmieder, B.↗

A measurement of the energy spectra and relative abundance of the cosmic-ray H and He isotopes over a broad energy range

The measurements reported of these isotopes were made using two sets of detectors during the same minimum modulation period in 1977. One measurement was made with a balloon-borne telescope, the other with telescopes on the Voyager spacecraft. It is noted that together they provide the widest energy range yet available for studying these isotopes: 14-150 MeV per nucleon for H2 and 10-290 MeV per nucleon for He-3. The simultaneous helium isotope observations are used to give a mutually consistent picture of galactic propagation and solar modulation. The data define the form of the interstellar H-1 and He-4 spectra, an interstellar matter path length for both H-1 and He-4, and a total residual modulation for He-4. The H-2 observations suggest a picture that is very similar for the galactic propagation of H-1 and He-4.

Webber, W. R.↗

The gravity dependence of the H-alpha width in late-type stars

A theoretical gravity-scaling law for the H-alpha absorption width in late-type stars is developed. The derivation is based upon (1) the hydrostatic thickening of stellar chromospheres with decreasing surface gravity, and (2) a dependence of the H-alpha width upon opacity and Doppler width in a region subject to a chromospheric temperature rise. The scaling relation is approximately consistent with the mean gravity dependence deduced from the empirical correlation between H-alpha and Ca II K Wilson-Bappu widths. The calculations suggest that gravity variations in chromospheric-mass column density may, in addition to Doppler velocity enhancements, control the width-luminosity broadening of the H-alpha profile in late-type stars.

Zarro, D. M.↗

Observations of the 157.7 micron (C II) emission from the galactic H II regions W3 and W51

The 157.7 micron ground-state fine-structure transition of singly ionized carbon was detected from three positions, each in galactic H II region W3 and W51. These findings show that this emission goes beyond the H II regions and the carbon recombination region in each source. In addition these observations establish a lower limit to the luminosity in the 157.7 micron (C II) line of 360 solar luminosity from W3 and 41 solar luminosity from W51. Mechanisms for 157.7 micron-line excitation are discussed, and it is noted that a substantial part of the observed emission originates in the thin carbon recombination line-emitting region which borders on the H II regions and the warm atomic and molecular gas at the surface of neighboring molecular clouds. It is proposed that excitation by electrons present in the diffuse gas surrounding W51 contributes to the extended 157.7 micron (C II) line emission from this region. It was found that the (C II)FIR continuum ratios for W3 and W51 are in agreement with those of other galactic H II regions.

Melnick, G.↗

H and K maps of two star-forming regions: S 140 and CEP A OB3

The molecular clouds near S 140 and Cep A OB3 both contain regions that emit strongly in the infrared but which have relatively little or no emission in radio wavelengths. The lack of radio emission is usually interpreted to mean that little ionization has taken place, and that the IR emission comes from dust heated by a central pre-main sequence object. We have made high resolution maps of these two areas with H and K broadband filters with the 2.3m telescope of the Wyoming Infrared Observatory (WIRO). Our observations were made with an InSb detector using the standard WIRO mapping technique of multiple scanning to construct a series of 64x64 pictures. Our scanning was made in one arcsec steps with a 7 inch aperture to produce a resolution of about 6 sec FWHM. Observations of S 140 by Blair et al (1978) with moderate resolution in J, H, and K, revealed a prominent IR source that they called S 140IR. We have scanned an area surrounding their S 140IR region and have obtained total IR fluxes which are in close agreement with Blair et al. Additional detail corresponds to that seen by Dinerstein et al (1979) at 0.9 microns and Campbell (1986) at 1.0 microns. The large (H-K) values for all components of S 140IR indicates that they are probably embedded in the parent molecular cloud with A(v) = 25 mag and A(K) = 2.2 mag. Recent radio studies of Cep A by Hughes and Wouterloot (1984) and FIR studies by Evans et al (1981) have shown the similarity of Cep A to S 140. There is, however, some emission detected from ionized regions by the radio observations, indicating a slightly more advanced stage of evolution for Cep A. We observed an area around the strongest source in Cep A in both H and K, and the K map is presented. We have identified three sources separate from the main source.

Graadalen, G. L.↗