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  • Chemical Engineering  (1,289)
  • ASTRONOMY  (831)
  • COMMUNICATIONS AND RADAR
  • 1980-1984  (1,201)
  • 1975-1979  (1,564)
  • 1950-1954
  • 1984  (1,201)
  • 1977  (786)
  • 1976  (778)
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  • 1980-1984  (1,201)
  • 1975-1979  (1,564)
  • 1950-1954
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  • 1
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    Toward diffraction-limited seeing of dim astronomical objects from the Earth's surface using LIDAR (1977)
    In:  CASI
    Details
    Publication Date: 2005-02-28
    Keywords: ASTRONOMY
    Type: Res. in the Space Sci., Vol. 2, No. 1; 12 p
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  • 2
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    Infrared astronomy and high energy astrophysics (1977)
    In:  CASI
    Details
    Publication Date: 2006-08-09
    Description: Observations of the diffuse far-infrared flux from the galactic plane, as well as far-infrared measurements of the properties of dense molecular clouds, when combined with recent high-energy gamma-ray measurements and radio observations of carbon monoxide, yield information about the total mass of molecular clouds, the large-scale structure of the inner galaxy, and the density of cosmic rays.
    Keywords: ASTRONOMY
    Type: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 203-214
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  • 3
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    Radar backscatter modelling (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-06
    Description: The terrain analysis software package was restructured and documentation was added. A program was written to test Johnson Space Center's four band scatterometer data for spurious signals data. A catalog of terrain roughness statistics and calibrated four frequency multipolarization scatterometer data is being published to support the maintenance of Death Valley as a radar backscatter calibration test site for all future airborne and spacecraft missions. Test pits were dug through sand covered terrains in the Eastern Sahara to define the depth and character of subsurface interfaces responsible for either backscatter or specular response in SIR-A imagery. Blocky sandstone bedrock surfaces at about 1 m depth were responsible for the brightest SIR-A returns. Irregular very dense CaCO3 cemented sand interfaces were responsible for intermediate grey tones. Ancient river valleys had the weakest response. Reexamination of SEASAT l-band imagery of U.S. deserts continues.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Washington Rept. of Planetary Geology Program, 1983; p 268-269
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  • 4
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    Design optimization of the 34-meter DSN-NCP antennas (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The new NASA Deep Space Network (DSN) 34-m-diameter azimuth-elevation (Az-El) antenna structure is an example of an essentially computer-automated design. In addition to pivotal comptuer Lagrange multiplier design optimization software, much of the associated pre- and post-processing was also performed by computer. The construction of one of these antennas at Goldstone, California, is well advanced and will be completed this summer. A second installation is in progress in Australia. Both atennas will be used primarily for spacecraft tracking and will operate in the 8.5-GHz, 3.5-cm (1.4-in.) wavelength microwave frequency.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Recent Experiences in Multidisciplinary Analysis and Optimization, Part 2; 16 p
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  • 5
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    Speech communications in noise (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The physical characteristics of speech, the methods of speech masking measurement, and the effects of noise on speech communication are investigated. Topics include the speech signal and intelligibility, the effects of noise on intelligibility, the articulation index, and various devices for evaluating speech systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Physiol., Psychol., and Social Effects of Noise; p 57-110
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  • 6
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    The PDS-VAX intelligent plate scanning system of Trieste Astronomical Observatory (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: An intelligent subsystem for interfacing a PDS1010A digital microdensitometer to a DEC DR11W DMA 16 bit UNIBUS port in DEC VAX VMS environment was tested. The subsystem employs two MOTOROLA M68000 microprocessors with 128 KB data memory. The PDS primitives and the user defined high level scanning functions and preprocessing modules are loaded from the host computer into two 8 KB RAM memories in the microprocessors using a dedicated PDS control language. The subsystem is planned to employ a nonstandard photomultiplier electronics. Two design schemes were tested: (1) based on three amplifiers of gain 10 cascaded and multiplexed to a 12 bit AD converter, and (2) based on a single amplifier of gain 100 and two 14 bit AD converters.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center Astron. Microdensitometry Conf.; p 175-187
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  • 7
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    A study of the cosmic sources of hard X-rays (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: An actively-shielded, high-energy X-ray telescope was launched onboard OSO-8 on 21 June 1975. The primary objectives of this experiment are the measurements of the energy spectrum of discrete cosmic X-ray sources in the range 20 keV to 3 MeV and of the temporal variations in the intensity of each source detected with a time resolution of 0.3 msec. This detector provides the highest duty factor and the finest time resolution of any of its kind for observations over a period of up to 10 days. The background spectrum of this detector in orbit was monitored continuously since shortly after launch. The minimum detectable source strength is estimated to be between 10,000 and 100,000 photons/sq-cm-sec keV, limited primary by the effects of induced radioactivity. From 16 July through 18 July 1975, the X-ray binary, Cen X-3, was observed with the hard X-ray telescope.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 739-746
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  • 8
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    Simultaneous X-ray and optical observations of X Persei (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Photoelectric photometry of X Persei was obtained on five out of seven consective nights in January 1975, from the Lick and Leuschner Observatories. The observations yield B = 6.848 + or - 0.002, B-V = 0.139 + or - 0.001, with no strong evidence for variability during the observing run. These are the faintest and bluest photoelectric magnitudes and colors ever reported for X Per; this change apparently occured relatively uniformly during 1973-74 and is reminiscent of behavior last observed in approximately 1900. The suggested association of X Persei with the weak X-ray source 3U 0352+30 raises the possibility of detection of X-ray/optical covariability. On January 21, 1975, 7 hours of data were obtained from both observatories simulataneous with OAO Copernicus X-ray observations of 3U 0352+30. The X-ray data varied during this period by a factor of two, but there is no obviously correspondent optical activity, to a level of 0.02 mag. The optical data are also used to limit to 0.01 mag variations coincident with the X-ray periodicity.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 719-726
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  • 9
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    OSO-8 GSFC results on Cen X-3 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Spectra of Cen X-3 during eclipse, in transition out of eclipse, and during several later phases of the binary orbit were obtained from quick look data of the July 16-25, 1975 observation by the Goddard X-ray spectroscopy experiment on OSO-8. In the high state there was no absorption turn over. Pulsations were present at least to 23 keV. The spectrum at the pulse minimum was flatter above 7 keV than that of the pulse peak. In transition out of eclipse Cen X-3 emerged above a small low energy flux seen during eclipse. The observations appear to indicate absorption by cold and ionized matter and the presence of iron in the companion's atmosphere. Decreased intensities were observed at late phases of some binary orbits in some cases corresponding to dips. Absorption appears although the low energy component remains. Variable features may be interpretable as absorption and emission by iron and possibly other trace elements.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 207-218
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  • 10
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    X-ray spectroscopy with the ANS satellite (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Preliminary results from the Bragg crystal spectrometer on the ANS satellite are given. No significant Si XIII and Si XIV narrow line emission has been detected from Cygnus X-1, -2, or -3.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 49-52
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  • 11
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    OSO-8 observations of Hercules X-1 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The X-ray binary Her X-1 was observed by the GSFC cosmic X-ray detectors aboard OSO-8 between August 26 and September 3, 1975. The results reported are based on quick look tapes which contain less than 10% of the total time spent on source. Spectra were observed during different phases of the binary period including the anomalous low state (dip) in X-ray intensity. The normal high spectra is well represented by a power law with a short cutoff above approximately 25 keV. A significant and varying enhancement in the intensity around 6.7 keV was observed, suggesting the presence of an iron line. Absorption was seen in the spectrum immediately following eclipse. The dip spectrum is found to be considerably flattened. Also spectra are presented for different phases of the pulse period.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 161-168
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  • 12
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    Some features of the X-ray source Cyg X-3 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Data from the Copernicus satellite are presented which show that the 4.8 hour light curve of Cyg X-3 has been relatively stable in period, shape, and amplitude since the observation of the first giant radio outburst in September 1972. A pulse height spectrum of the source obtained by the Ariel 5 satellite in the 1.5 to 26 kev energy band shows convincing evidence for line emission at about 6.5 keV. The strength of this feature varies in phase with the 4.8 hour continuum modulation, but there is no simple long term relation with the mean continuum intensity per 4.8 hour cycle. Evidence is presented which indicates that the average 2-6 kev intensity of Cyg X-3 has been higher by a factor of 3 since the onset of the radio flares.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 255-265
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  • 13
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    OSO-8 observing schedule for X-ray binaries (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Six different instruments on OSO-8 have observed several binary X-ray sources between energies of 0.13 keV and 1 MeV at various times since 21 June 1975. The schedule for these observations is given, as well as the present plan for such future observations through July 1976. Included is the OSO-8 observing schedule for the transient X-ray source A0620-00.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 729-738
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  • 14
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    X-ray observation of 3U 1700-37 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: X-ray observations with Copernicus reveal three categories of flux variability in 3U 1700-37. High amplitude hourly variations are energy independent in the 3-11 keV range while a change in the low energy absorbing column causes variations in flux level on an orbital time scale. This absorption is most severe prior to eclipse ingress, suggesting that the distribution of absorbing material around the X-ray source is asymmetrical with respect to the line of centers of the binary system. The absorbing material may be identical with a high density region inferred from optical observations of HD 153919. In the third category, the maximum source intensity per binary cycle is variable by at least a factor of two between observations. Measurement of the eclipse duration on three occasions indicate that it is significantly less than when observed by Uhuru.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 559-567
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  • 15
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    A review of 3U 1700-37 = HD 153919 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: X-ray, spectroscopic, and photometric data for the source are reviewed briefly. Some points of controversy and difficulty are discussed. The X-ray source 3U 1700-37 is moderately strong (approximately 100 Uhuru counts) and shows a long eclipse, with a period of 3.412 days. The X-rays are attenuated near 0.5 phase, and show a very wide gradual decrease on either side of the total eclipse. The low-energy cutoff is the strongest of all the X-ray binaries. These characteristics are all qualitatively compatible with the optical star's, which represent an extreme in several ways: (1) the primary is an extreme star with large mass outflow through a spherically symmetric stellar wind; (2) it is the hottest of all X-ray binary primaries (with possible exception of Cen X-3); and (3) the mass ratio is very high and the relative separation of the stars is low.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 531-535
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  • 16
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    The nature of the X-ray nova A0620-00 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: A model is presented for the X-ray nova A0620-00. Identification with a nova can be ruled out on two counts. A binary consisting of a late-type subgiant near the Roche lobe, irradiated by an accreting compact companion is shown, however, to be in agreement with all known observations. Photometry of the optical object should be pursued since variability on an approximately eight hour period is expected.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 361-367
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  • 17
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    New results from long-term observations of Cyg X-1 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Observations of Cyg X-1 between October 1974 and July 1975 reveal a persistent 5.6 day modulation of the 3-6 keV X-ray intensity, having a minimum in phase with superior conjunction of the HDE 226868 binary system. The modulation is found to be most pronounced just prior to the April-May 1975 increase of Cyg X-1, after which both the modulation and intensity are at their lowest values for the entire duration of the observations. These data imply that the X-ray emission from Cyg X-1 arises from the compact member of HDE 226868, and that the increase of April-May 1975 may have represented the depletion of accreting material which had not yet been mixed into a cylindrically symmetric accretion disk about the compact member.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 391-405
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  • 18
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    The interpretation of optical light variations of Centaurus X-3 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The interpretation of optical light variations of X-ray binaries is discussed for the case of negligible reflection effect. The limiting cases of synchronous rotation of the visible star (Roche configuration) and of no rotation (pure tidal deformation) are considered. The theoretical results are compared with the available light curves of Cen X-3. X-ray data of the Copernicus satellite are used to get an impression of the atmospheric structure of the outer layers of the visible component. It is shown, that the X-ray eclipse duration is in good agreement with the mass ration derived from the optical variations. The X-ray eclipse duration is discussed with respect to the extended low states, and a possible correlation of the extended lows with the appearance of the optical light curves is considered.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 179-185
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  • 19
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    The observation program for the GSFC cosmic X-ray spectroscopy experiment (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The cosmic X-ray spectroscopy experiment on OSO-8 will observe seven X-ray binary sources in its first six months of operation. If possible, each of these sources will be observed for one or more binary orbits so that the X-ray spectrum of each object can be observed through all phases of its orbit. For the two pulsing binaries, Her X-1 and Cen X-3, spectral variations over the pulse period will be studied. Simultaneous radio observations of Cyg X-1 and Cyg X-3 will search for any correlation between radio and X-ray emission. During the first year of operation, the detectors will observe over 50% of the known X-ray sources.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 737-738
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  • 20
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    Spectrophotometry of the unusual optical candidate for 3U 1728-24 (=GX 2+5 = GX 1+4) a recurrent nova? (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The spectrum of the object suggested as a possible optical counterpart of GX 2+5, was studied, using the image tube scanner attached to the 3-m telescope of Lick Observatory. An improved X-ray error box obtained with Copernicus strongly supports this proposed identification. The candidate displays all the characteristics of the symbiotic stars and the related recurrent novae. The spectrum reveals the presence of an M star together with a blue component and a large number of emission lines displaying a wide range of ionization. There is evidence of variability of both the continuum and the line intensities. This object provides strong support for the often proposed association of some X-ray sources with nova-like systems.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 691-701
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  • 21
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    Long term X-ray studies of Sco X-1 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: No modulation of the 3-6 keV X-ray intensity of Sco X-1 at a level of excess of 1% is observed at the optical period of .787313d. Evidence is found for shot-noise character in a large fraction or the X-ray emission. Almost all of the Sco X-1 emission can be synthesized in terms of approximately 200 shots per day, each with a duration of approximately 1/3 day.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 703-716
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  • 22
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    The X-ray binary HD 77581 + 3U 0900-40 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The properties of the binary system in the different regions of the electromagnetic spectrum are presented from X-rays to the radio. Physical parameters and a model for the system are derived.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 575-614
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  • 23
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    The Skylab S019 ultraviolet spectra of HD 153919 (=3U 1700-37) and HDE 226868 (=Cyg X-1) (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Ultraviolet spectra of HD153919 (=3U1700-37) and HDE226868 (=Cyg X-1) were obtained with the ultraviolet objective-prism spectrograph of Skylab Experiment S019. The data consist of unwidened spectra which extend to 1,600A for HD153919 and to 2,400A for HDE226868. The wavelength resolution is about 2A to 1,400A and 12A at 2,000A. For HD153919, an unwidened spectrum of fair quality and extending to a wavelength of 1,600A was obtained at 22 sup h 08 sup m on 1 September 1973. The energy distribution in this spectrum generally resembles that of other reddened O stars. A break in continuum intensity seems to occur at a wavelength of about 1,720A. There is a suggestion of an emission line on the longward edge of the break but this could be either a chance clumping of grains or else a photographic edge-effect caused by the break.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 551-553
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  • 24
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    High resolution measurements of Cyg X-1 from rockets (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Cyg X-1 was observed on two occasions (Oct. 4, 1973 and Oct. 3, 1974) by the Goddard X-ray rocket payload. This payload consisted of two gas proportional counters (xenon-methane with 710 sq cm and argon-methane with 610 sq cm using the same 128 channel pulse height analyzer and having 320 micro sec temporal resolution on the 1973 flight and 160 micro sec resolution on the 1974 flight. During both flights, bursts of 1 ms duration were observed with very high statistical certainty. To date all 13 of these bursts were analyzed for spectral and temporal character, and the results of this analysis are presented. The spectra of overall X-ray emission from both flights is also presented. In a source known for its variability, it is remarkable that the spectra taken one year apart are virtually identical.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 443-451
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  • 25
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    The early light curve of A0620-00 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The Ariel-5 All-Sky Monitor measured the 3-6 keV X-ray intensity of 0620-00 for two days shortly after peak emission in August 1975, and continuously throughout September 1975. The effective exposure each day for this source (and every other source in the 80% of the celestial sphere covered by the monitor) is approximately 250 sq cm sec. The light curve obtained through October 1 (when the spin axis was again pointed to A0620-00) is shown. The intensity difference at maximum is obviously a manifestation of the very soft spectrum of the source. Clearly, A0620-00 was approximately four times as bright as Sco X-1 at maximum in the band 3-6 keV. The decay is quite smooth, but cannot be fit with a single e-folding time. The interval between the early All-Sky Monitor points and the onset of continuous coverage has an inferred e-folding time of 22 days, but it is continually increasing throughout September. A0620-00 is apparently similar in its X-ray character to the very strong, long-lasting transient X-ray sources which presently number six. In contrast, only three can be sensibly reconciled with the lower-intensity, shorter-duration hard-spectrum transients which have been found to pulse on a time scale of minutes.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 311-316
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  • 26
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    Absence of iron line emission in Cyg X-3 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: An observation of Cygnus X-3 was made with soft X-ray detectors launched on an Aerobee rocket. The iron line emission observed one month later and in May 1975 was not found. A 3 sigma upper limit for this feature is 0.006 ph/2 cm/s.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 285-292
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  • 27
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    The radio sources associated with Cyg X-3 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Some of the conclusions derived from the data on the radio flaring of Cyg X-3 are summarized. In addition, recent data showing that Cyg X-3 has both active and quiet radio behavior are presented.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 233-244
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  • 28
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    Recent Uhuru results on Centaurus X-3 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The current status of the analysis of Cen X-3 data from Uhuru concerning pulsations, orbital period and eccentricity, and extended lows, are reviewed. The pulse period decreases irregularly. The pulsed fraction (2-7 keV) is 70%-90% for single pulses but significantly less for superpositions of pulses, due to variability in shape. The pulses are narrower at higher energies with a correlated increase in fraction pulsed. The orbital period is found to both decrease and increase with p/p on the order of a few times 0.00001/year. A three sigma upper limit on the eccentricity of 0.003 is obtained; if no significant periastron motion is allowed over two years, the upper limit becomes 0.0016. The orbital period is found to be detectable during some extended lows but with a significantly decreased ratio of eclipsed to non-eclipsed intensity. Two transitions between normal high states and extended lows are studied, and a consistent model is obtained in which extended lows are caused by both burying the source in an increased stellar wind from the companion, and starving the source by decreasing the stellar wind. Changes in fraction pulsed during transitions and systematic differences in the harmonic content of the pulses are also found.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 197-206
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  • 29
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    Optical observations of HDE 226868 = Cygnus X-1: A review (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The present state of knowledge of the binary system HDE226868 = Cygnus X-1 is summarized, including system dimensions, nature of the secondary X-ray source, and mass transfer properties. Some deficiencies in the optical observations are pointed out; these deficiencies make interpretation of the system difficult, but can be corrected.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 465-484
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  • 30
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    Intensity and spectral variations of Cyg X-1 observed from balloons (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Observations of Cyg X-1 with a 20 to 200 keV balloon carried X-ray telescope in 1969, 1970, and 1972 are presented. These results reveal the following characteristics of Cyg X-1: The steep spectrum observed at E 10 keV during the radio quiet phase can extend to 200 keV. This phase may have lasted 21 months (July 1969 to March 1971). The low flux values are factors of 3 and 8 below the normal values at 30 and 100 keV respectively, are rarely observed, and may be associated with the early phase of the 1971 April X-ray transition. During some one hour periods, the intensity remained constant to approximately 20% and during other periods it varied a factor 2 in 5 minutes and a factor 10 in 1 hour. Complex spectral variations accompanied the intensity changes.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 407-424
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    Introduction to Cyg X-1 X-ray panel (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The status of X-ray observations is summarized in tabular form along with general aspects of X-ray emission. Specific questions that arise when the observed phenomena are pieced together into a coherent picture are presented. Spectral states, transitions, periodic behavior, fluctuations, and bursts are among the topics discussed.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 369-372
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    The transient X-ray source A0620-00 (Nova Monocerotis 1975) (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: A0620-00 is the first of the so-called X-ray novae to be identified with an optical object. Emission in the ultraviolet, infrared, and radio wavelength regions was observed from this source. From the observed properties of the optical radiation, it is suggested that the source is a recurrent nova.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 293-309
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  • 33
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    Pulsed X-ray observations of Cen X-3 from Ariel-5 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The 4.8 second X-ray pulsations from Centaurus X-3 were monitored by the MSSL collimated proportional counter on board Ariel-5 between 18-27 January 1975. Analysis of the source Doppler effect shows that the pulsation period of Cen X-3 decreased by 3.70 + or - 0.04 milliseconds during the preceding 2.3 years. The Doppler analysis also yields updated values for the binary phase and period of Cen X-3. Phase zero occurred at JD 2442438.628 + or - 0.003, and the average heliocentric binary period between October 1972 and January 1975 was 2.087129 + or - 0.000007 days. Light curves of the 4.8 second pulsations in the 3-9 keV band are characterized by two pronounced peaks, in contrast with the single peak profiles observed by Uhuru.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 219-231
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    The interstellar matter column density to Cen X-3 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The usual gas-to-dust ratio is shown to hold quite precisely for a sample of supernova remnants with available X-ray spectra and interstellar reddening observations. Supernova remnants are extended objects, tenuous enough to be optically thin in the X-ray range; it is shown that the X-ray observations can readily be interpreted in terms of a main source component and of an interstellar perturbation affecting the lower part of the spectrum. Cen X-3 is associated with an OB supergiant. The effect of the column density is easily detectable in the X-ray range. The spectrum exhibits a low energy cut-off, which is parameterized by a column of cold matter, NX. The cut-off is definitely observed to be variable. There is a suggestion that sometimes NX NH. It is concluded that on those occasions a spurious soft X-ray component is present in the source, bearing close similarity with Cyg X-1.
    Keywords: ASTRONOMY
    Type: X-ray Binaries; p 189-195
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    Flight test of a synthetic aperture radar antenna using STEP (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-03
    Description: To establish confidence in its overall performance, credible information on the synthetic aperture radar antenna's mechanical properties in orbit must be obtained. However, the antenna's size, design, and operating environment make it difficult to simulate operating conditions under 1-g Earth conditions. The Space Technology Experiments Platform (STEP) offers a timely opportunity to mechanically qualify and characterize the antenna design in a representative environment. The proposed experimental configuration would employ a half-system of the full-scale RADARSAT antenna which would be mounted on the STEP platform in the orbiter cargo bay such that it could be deployed and retracted in orbit (as shown in this figure). The antenna would be subjected to typical environmental exposures while an array of targets and sensors on the antenna support structure and reflecting surface are observed and monitored. In particular, the typical environments would include deployment and retraction, dynamic response to vehicle thruster or base exciter inputs, and thermal soak and transient effects upon entering or exiting Earth eclipse. The proposed experiment would also provide generic information on the properties of large space structures in space and on techniques to obtain the desired information.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center STEP Expt. Requirements; p 339-354
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    A comparison of lightning and nuclear electromagnetic pulse response of tactical shelters (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The internal response (electromagnetic fields and cable responses) of tactical shelters is addressed. Tactical shelters are usually well-shielded systems. Apart from penetrations by signal and power lines, the main leakage paths to the interior are via seams and the environment control unit (ECU) honeycomb filter. The time domain in three-dimensional finite-difference technique is employed to determine the external and internal coupling to a shelter excited by nuclear electromagnetic pulses (NEMP) and attached lightning. The responses of interest are the internal electromagnetic fields and the voltage, current, power, and energy coupled to internal cables. Leakage through the seams and ECU filter is accomplished by their transfer impedances which relate internal electric fields to external current densities. Transfer impedances which were experimentally measured are used in the analysis. The internal numerical results are favorably compared to actual shelter test data under simulated NEMP illumination.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Intern. Aerospace and Ground Conf. on Lightning and Static Elec.; 12 p
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    Upset susceptibility study employing circuit analysis and digital simulation (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: An approach to predict the susceptibility of digital systems to signal disturbances is described. Electrical disturbances on a digital system's input and output lines can be induced by activities and conditions including static electricity, lightning discharge, electromagnetic interference (EMI), and electromagnetic pulsation (EMP). The electrical signal disturbances employed for the susceptibility study were limited to nondestructive levels, i.e., the system does not sustain partial or total physical damage and reset and/or reload brings the system to an operational status. The front-end transition from the electrical disturbances to the equivalent digital signals was accomplished by computer-aided circuit analysis. The super-sceptre (system for circuit evaluation of transient radiation effects) programs was used. Gate models were developed according to manufacturers' performance specifications and parameters resulting from construction processes characteristic of the technology. Digital simulation at the gate and functional level was employed to determine the impact of the abnormal signals on system performance and to study the propagation characteristics of these signals through the system architecture. Example results are included for an Intel 8080 processor configuration.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Aerospace and Ground Conf. on Lightning and Static Elec.; 14 p
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    A comparison of lightning and nuclear electromagnetic pulse response of a helicopter (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A numerical modeling technique is utilized to investigate the response of a UH-60A helicopter to both lightning and nuclear electromagnetic pulses (NEMP). The analytical approach involves the three-dimensional time domain finite-difference solutions of Maxwell's equations. Both the external currents and charges as well as the internal electromagnetic fields and cable responses are computed. Results of the analysis indicate that, in general, the short circuit current on internal cables is larger for lightning, whereas the open-circuit voltages are slightly higher for NEMP. The lightning response is highly dependent upon the rise time of the injected current as was expected. The analysis shows that a coupling levels to cables in a helicopter are 20 to 30 dB larger than those observed in fixed-wing aircraft.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Intern. Aerospace and Ground Conf. on Lightning and Static Elec.; 7 p
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  • 39
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    Data and results of a laboratory investigation of microprocessor upset caused by simulated lightning-induced analog transients (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Advanced composite aircraft designs include fault-tolerant computer-based digital control systems with thigh reliability requirements for adverse as well as optimum operating environments. Since aircraft penetrate intense electromagnetic fields during thunderstorms, onboard computer systems maya be subjected to field-induced transient voltages and currents resulting in functional error modes which are collectively referred to as digital system upset. A methodology was developed for assessing the upset susceptibility of a computer system onboard an aircraft flying through a lightning environment. Upset error modes in a general-purpose microprocessor were studied via tests which involved the random input of analog transients which model lightning-induced signals onto interface lines of an 8080-based microcomputer from which upset error data were recorded. The application of Markov modeling to upset susceptibility estimation is discussed and a stochastic model development.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Aerospace and Ground Conf. on Lightning and Static Elec.; 12 p
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  • 40
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    Radiation mechanisms and magnetospheric structure of pulsars (1976)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: A model of pulsars is outlined. Key early considerations were those which led to the identification of pulsars with neutron stars, the Goldreich-Julian model of pulsar magnetospheres, and the recognition that, in a pulsar magnetosphere, a high energy gamma ray may annihilate to produce an electron-positron pair. Arguments that suggest that pulsar magnetospheres may contain large masses of plasma, a suggestion which has important implications concerning the structure of the magnetosphere, are considered along with observational data which support a magnetosphere model based on that idea rather than the Goldreich-Julian model.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 108-117
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    Galactic distribution of pulsars (1976)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: The density distributions of pulsars in luminosity, period, Z-distance, and galactocentric distance were derived using a uniform sample of pulsars detected during a 408 MHz pulsar survey at Jodrell Bank. There are indications of a fine scale structure in the spatial distribution and evidence that there is a general correlation with other galactic populations and the overall spiral structure. The electron layer in the galaxy is shown to be wider than the pulsar layer and uniform on a large scale. The number of pulsars in the galaxy was estimated and used to derive the pulsar birthrate.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 299-319
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  • 42
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    Gamma ray pulsars (1976)
    In:  CASI
    Details
    Publication Date: 2006-01-12
    Description: Recent data from the high energy gamma ray experiment have revealed the existence of four pulsars emitting photons above 35 MeV. An attempt is made to explain the gamma ray emission from these pulsars in terms of an electron-photon cascade that develops in the magnetosphere of the pulsar. Although there is very little material above the surface of the pulsar, the very intense magnetic fields correspond to many radiation lengths which cause electrons to emit photons via magnetic bremsstrahlung and these photons to pair produce. The cascade develops until the mean photon energy drops below the pair production threshold which happens to be in the gamma ray range; at this stage the photons break out from the source.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 118-127
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    Real-time synthetic aperture radar processing (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-09
    Description: Real-time acousto-optic SAR processors are described and experimentally demonstrated. SAR imaging is performed in one of the architectures by applying the signal to an acousto-optic device and correlating it with chirp signals recorded on an optical transparency by time integration on a CCD detector. In a different implementation, the imaging is preformed by interfering the light beams diffracted from two separate acousto-optic devices, one modulated the radar signal and the second by the reference chirp waveform.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Opt. Inform. Process. for Aerospace Appl. 2; p 199-213
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    Microwave reflector characterization using simple instruments in EVA (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-03
    Description: An antenna with rigid panels which can be measured under ground conditions, carried to space in a packaged condition, deployed into a form similar to the Earth-measured one, measured under space conditions, restowed, and brought back to Earth so that the original measurements can be verified is the type being proposed for this experiment. The antenna chosen will be measured under ground conditions, carried aloft, deployed into its antenna shape, lifted by the remote manipulator system to a position where it can be sighted by two astronauts at the two theodolites, and held there until the surface characterization can be completed. An alternate method would be to use photogrammetry and take pictures of the surface from the payload handling station. After the surface characterization is completed, the antenna will be folded and restowed into the Shuttle bay for return to Earth. The surface characterization will be repeated on Earth after its return for verification both of the original measurement taken on Earth and the measurement taken in space.
    Keywords: COMMUNICATIONS AND RADAR
    Type: STEP Expt. Requirements; p 333-338
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  • 45
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    Adaptive microwave reflector (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-03
    Description: As an interim step in going to the 100-meter reflector that was evaluated, a 5-meter reflector is proposed to test the electrostatic concept under space conditions. Some of the issues which require the space environment for evaluation are the following questions: Can deployment of a box ring structure with a thin film reflector attached be manually deployed? In the absence of humidity, can a 0.3-mil aluminized Kapton film reflector be formed by the electrostatic process suitable for antenna applications? Can the photogrammetric process be used to evaluate the reflector surface with pictures taken from the payload handling station? Can the space charging effect be evaluated with the 5-meter reflector attached to the Shuttle? Does the outgassing of moisture from 0.3-mil Kapton film affect its reflector capability? A box ring truss support structure and an automatic sequence deployment system are discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: STEP Expt. Requirements; p 325-331
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    STEP flight experiments Large Deployable Reflector (LDR) telescope (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-03
    Description: Flight testing plans for a large deployable infrared reflector telescope to be tested on a space platform are discussed. Subsystem parts, subassemblies, and whole assemblies are discussed. Assurance of operational deployability, rigidization, alignment, and serviceability will be sought.
    Keywords: ASTRONOMY
    Type: NASA. Langley Research Center STEP Expt. Requirements; p 257-278
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  • 47
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    Effect of space environment on space-based radar phased-array antenna (A0133) (1984)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Kapton polyimide film was selected as the baseline material for the Grumman spce based radar (SBR) concept. To gain the requisite confidence for long-term service durability, it is desirable to subject material specimens as well as a portion of the SBR antenna directly to the combined space environment and compare property degradation to that caused by laboratory simulation. The overall objective of this program is to evauate the effect of the space environment on polymeric materials currently being considered for the Grumman SBR Phased-Array Antenna. Degradation mechanisms caused by thermal cycling, ultraviolet and charged-particle irradiation, applied load, and high-voltage plasma interaction will be evaluated. The experiment occupies a 6-in.-deep end corner tray located on the space end of the Long Duration Exposure Facility and consists of both passive and active parts. The passive part addresses the effect of environment and stress on the dimensional stability spliced and continuous Kapton, both plain and reinforced. The active part will study the interaction of high voltage and low-Earth-orbit plasma.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Long Duration Exposure Facility (LDEF); p 21-23
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  • 48
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    Optical observation of WRA 977 (3U 1233-62?) (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: UBV photometry of WRA 977 on 36 nights between January and July of 1974 shows that this object is active on a time scale of days at the 0.1 mag level, but that it remains quite constant during monitoring intervals lasting up to 1 hour. Periodogram analysis reveals no significant periodic variation in the brightness of this object.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 677-682
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  • 49
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    He II lambda 4686 photometry of HD 153919 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The optical component of the binary X-ray source 3U1700-37/HD 153919 was observed with the interference filter centered on the He II lambda 4686 emission. This photometry does not reveal any dependence of lambda 4686 emission on the orbital phase thereby confirming earlier spectroscopic result that the region of formation of the ionized helium emission is confined to the envelope of the 06f primary.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 555-557
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    Blue band photometry of Cygnus X-1 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Results of blue band photometry of HDE 226868 in the years 1972-3-4 and provisional results for 1975 are presented. A mean light curve is obtained from the first three years observations which is based on 192 nights observations. Intercomparison of the results from the different years shows that the light curve is not constant.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 521-527
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    A0620-00 as a recurrent nova (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Evidence for and against the star associated with A0620-00 being a nova is presented. The conclusion is that this star closely resembles other recurrent novae with the only unusual characteristic being the apparent high temperature at maximum brightness.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 335-341
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  • 52
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    Optical identification of A0620-00 (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Identification of the optical counterpart to the transient X-ray source A0620-00 was made using image tube photography. Spectra taken subsequent to the identification showed no stellar absorption or emission features. Photometric data gave a V magnitude of 11.2 + or - .1. This is about 8 magnitudes brighter than the object appears on the Palomar Sky Survey.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 327-333
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    Observations of Cygnus X-3 by ANS (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The hard X-ray experiment (1 - 28 keV) on ANS observed Cygnus X-3 in November 1974, and in May 1975. The average flux intensities for these time periods were found to be 22.4 + or - 0.5 cts/sec and 12.8 + or - 0.3 cts/sec (1.3 - 7.1 keV), the former being the highest average value ever observed. The spectrum studies show an excess in the flux above the fitted continuum which can be interpreted as a line emission of FeXXIV and/or FeXXV, at approximately 6.5 keV. The strength of this feature varied in phase with the 4.8 hr X-ray modulation, and remained at a constant relative intensity. The period of the X-ray modulation is refined to 0.1996813 + or - 0.0000006 day and obtained at a 2 sigma upper limit to a continuous change in the period of 50 to the minus 13th power/sec. This new limit places serious constraints on several models for this object.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 267-275
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    Copernicus observations of a number of galactic X-ray sources (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The Copernicus satellite was launched on 21 August 1972. The main experiment on board is the University of Princeton UV telescope. In addition a cosmic X-ray package of somewhat modest aperture was provided by the Mullard Space Science Laboratory (MSSL) of University College London. Following a brief description of the instrument, a list of galactic sources observed during the year is presented. Although the X-ray detection aperture is small, the ability to point the satellite for long periods of time with high accuracy makes Copernicus an ideal vehicle for the study of variable sources.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 1-25
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  • 55
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    Centaurus X-3: The observational picture (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Observations of Centaurus X-3 are briefly reviewed. The composition of the neutron star, optical light curves, and X-ray pulsations are among the topics discussed.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 173-176
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    Periodic flickering in the optical spectrum of HZ Herculis (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: Photometric observations of HZ Herculis in the ultraviolet with a time resolution of 5 seconds are discussed. The existence of periodic flickering with a time scale of 115 to 130 seconds is observed. The amplitude modulation is about 3 to 6 percent, larger than that associated with the erratic white flickering. The flickering, either erratic or periodic, occurs, but not always, near orbital phase 0.5, irrespective of the on and off parts of the X-ray cycle.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 101-111
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  • 57
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    ANS results on X-ray binaries (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: A short description is given of the Astronomical Netherlands Satellite (ANS) and the X-ray instruments of the Space Research Laboratory in Utrecht. The ANS observed in February 1975 a soft (1/4 keV) X-ray flux in Her X-1 during the 'off'-state with an intensity of a factor 10 lower than observed in the 'on'-state. The ANS observations on Cyg X-1 are summarized. During the May 1975 flaring state a very high intensity at 0.5 keV is measured consistent with a power-law photon-spectrum with index 3.5 and an interstellar absorption of 7.10 to the 21st power atoms/sq cm, but not consistent with spectra that show an additional cut-off below 1 KeV and an absorption of 7.10 to the 21st power atoms/sq cm. Intensity changes on a time scale of minutes, as observed in Cyg X-1 low state, are not observed during the flaring state.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 27-47
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    Tropospheric calibration in radio interferometry (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A new tropospheric mapping function is derived which is more accurate than previous mapping functions above elevations of 4 deg. The error due to the given analytic aproximation is estimated to be less than 0.2 percent for elevation angles larger than 6 deg (less than 0.4 cm at 6 deg). The mathematical expansion used in the derivation is valid for any laterally homogeneous atmospheric model of refractivity. The new mapping function, computer-generated ray tracing tables, and other mapping functions are compared.
    Keywords: COMMUNICATIONS AND RADAR
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    The NASA-NMSU automated meteor observatory (1976)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: A new observatory for meteor research which provides data for study of meteor heights, velocities, orbits, and meteoroid abundances is described. The observing equipment is automated to take advantage of the long periods of favorable observing weather common to the region. Four K-24 cameras, electrically operated, provide the triangulation observations, and four Maksutov f/1.3 cameras with blazed transmission grating provide spectral coverage. The patrol cameras have operated for a year and a half, and approximately 6,000 frames have been exposed by 9 March 1975. Meteor trails appear on 260 of these frames. Sixty-eight trails are of meteors photographed from two locations and thus allow trajectory and orbit determinations for 34 meteors. Photoelectric sensors initiate the 2-second spectrograph exposures, and electrical controls open and close the observatory at present times.
    Keywords: ASTRONOMY
    Type: N. Mex. State Univ. Contrib. of the Observatory of N. Mex. State Univ., Vol 1, No. 4; p 166-173
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    Photometry of R Coronae Borealis (1976)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Visual and photoelectric observations of R Coronae Borealis are presented, including a number of observations surrounding the 1974 minimum. The recent visual history of the variable is examined and the discrete cloud obscuration model is considered.
    Keywords: ASTRONOMY
    Type: Contrib. of the Observatory of N. Mex. State Univ., Vol. 1, No. 4; p 134-139
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    Intermediate-band photometry of faint standard stars (1976)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: The David Dunlap Observatory system uses six intermediate-band filters whose central wavelengths were chosen to cover important features in the spectrum of a late-type star. Calibrations of the color indices with physical parameters, allow one to estimate T sub eff, log g, Fe/H, M sub v and reddening directly from the photometry. Although a number of standards lists exist, only a small fraction of the stars is fainter than V=6. It is desirable to add to the numbers of faint standards. Results are presented of photometry of sixteen stars obtained during a program of variable-star photometry at Blue Mesa Observatory.
    Keywords: ASTRONOMY
    Type: Contrib. of the Observatory of N. Mex. State Univ., Vol. 1, No. 4; p 140-142
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  • 62
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    Stabilization of Kepler's problem (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A regularization of Kepler's problem due to Moser (1970) is used to stabilize the equations of motion. In other words, a particular solution of Kepler's problem is imbedded in a Liapunov stable system. Perturbations can be introduced into the stabilized equations.
    Keywords: ASTRONOMY
    Type: Celestial Mechanics; 16; Sept
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  • 63
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    Aperture averaging effects in stellar scintillation (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Stellar scintillation has been measured for apertures as low as 0.012 m by using photoncounting techniques. The scintillation measurements have been made for various aperture sizes in quick succession in order to determine experimentally the effects of aperture averaging. The results of the experiment are compared with the predictions of a model proposed earlier in the literature to quantify the phenomenon.
    Keywords: ASTRONOMY
    Type: Optics Communications; 22; Sept
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  • 64
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    Infrared mapping of galaxian centers: Star forming regions with kiloparsec scale sizes (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A 1 to 20 micron mapping of the centers of galaxies encompassing the regions that extend out to several kiloparsecs from the nuclei is reviewed. Power emerging at or = 5 microns is a direct measure of the number of young stars present. This conclusion is strongly supported by the large-scale association of the infrared-emitting regions with visual continuum and line emission indicative of young stars, and by the similarity of the energy distributions to those of Galactic HII region/molecular cloud complexes. Much of the young-star activity is completely hidden from view. At shorter wavelengths, a variety of processes, including bremsstrahlung, are evident.
    Keywords: ASTRONOMY
    Type: Royal Observatory Star Formation Workshop; p 183-198
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  • 65
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    The Gamma-Ray Observatory mission objectives and its significance for gamma-ray astronomy (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Gamma Ray Observatory (GRO) is an approved NASA mission, programmed for launch in 1988. Its complement of four detectors has established goals: (1) to study the nature of compact gamma-ray sources such as neutron stars and black holes, or objects whose nature is yet to be understood; (2) to search for evidence of nucleosynthesis especially in the regions of supernovae; (3) to study structural features and dynamical properties of the Galaxy; (4) to explore other galaxies, especially the extraordinary types such as radio, Seyferts, and quasars; and (5) to study cosmological effects by examining the diffuse radiation in detail. This paper discusses the design, objectives, and expected scientific results of each of the GRO instruments in view of the GRO mission goals.
    Keywords: ASTRONOMY
    Type: Advances in Space Research (ISSN 0273-1177); 3; 10-12
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  • 66
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    The S201 far-ultraviolet imaging survey. II - A field in Cygnus (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Far-ultraviolet imagery of a region in Cygnus, a 20 deg diameter field centered near (1950) R. A. 21 h 31.2 m decl. +37 deg 25 arcmin, was obtained by the S201 far-ultraviolet camera during the Apollo 16 mission. In a 10 minute exposure covering the 1250-1600 A wavelength range (effective wavelength 1400 A), 730 star images can be detected, corresponding to a limiting ultraviolet magnitude of about m (1400) = 10. Assuming nominal interstellar extinction values in this region near the galactic plane, this result corresponds to the detection of A0 V stars to a distance of 300 pc and of B0 V stars to 1500 pc. Uncertainties in spectral classification and interstellar extinction for individual objects are probably more significant than calibration or measurement errors. Most of the objects detected are identified with stars in the Smithsonian Astrophysical Observatory Star Catalog (1966), or the Catalog of Stellar Identifications (1979) or both, but 87 objects remain unidentified (or are identified with late-type stars).
    Keywords: ASTRONOMY
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 54; 271-290
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  • 67
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    Determining asteroid masses from perturbations on Mars (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The orbit of Mars is perturbed more than 5 m, a value compatible with the accuracy of the Viking Lander ranging data, by about three dozen asteroids. In addition to larger asteroids throughout the belt, significant perturbations of long period are generated by smaller objects near commensurabilities with Mars. The largest periodic terms induced by 1 Ceres and 2 Pallas have amplitudes of 0.8 and 0.2 km, respectively, both with 10-year periods. Due to a near commensurability, 4 Vesta causes a 5-km, 52-year term. While the Viking ranges will yield significant mass determinations for the largest three asteroids, and some of the smaller bodies should be detectable, it will be difficult to separate the smaller bodies with useful accuracies. Accurate discrimination must await range data from future missions to Mars or other bodies in the neighborhood of the asteroid belt. The Viking ranges can also yield improved masses for the outer planets (except Pluto), an application which is being exploited by groups analyzing these data. Uncertainties in the asteroid masses limit the ultimate accuracy of the Viking determinations of both the long time scale motion of the system of the inner four planets with respect to an inertial frame and the rate of change of the gravitational constant.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 57; 1-13
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    A search for the 10-micron silicate feature in periodic Comet Grigg-Skjellerup (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A 10-micron spectrum of periodic Comet Grigg-Skjellerup was obtained on 22 June 1982 with the UCL array spectrometer at the United Kingdom Infrared Telescope, Mauna Kea. No emission feature is obvious in the spectrum. The observed spectrum can be fit equally well by a model of small hot absorbing grains or by a composite model with less than or equal to 30 percent (3sigma) warm, 'dirty' silicate grains. The latter model is consistent with the silicate abundance in Comet Kohoutek, which did display an emission feature at 10 microns.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 89; 170
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  • 69
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    Broad band X-ray astronomical spectroscopy (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Broad Band X-Ray Telescope (BBXRT) experiment has been designed for high sensitivity, moderate resolution spectrophotometry of cosmic sources in the range 0.5 to 12 keV. Principal elements are two co-aligned imaging telescopes with cooled Si(Li) detectors at each focus. The mirror design uses an approximate geometry of tightly nested, conical, foil reflectors that allow a large filling factor (high throughput) at small grazing angles (high energy response). Each detector consists of a cluster of five elements defined with grooves on a single crystal. This arrangement affords some spatial resolution as well as a means of substantial background reduction. Shuttle borne measurements will typically be of 2000 s duration for sources with a flux of 10 to the -12 erg/sq cm-s.
    Keywords: ASTRONOMY
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); NS-31; 786-790
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  • 70
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    Ultraviolet spectra of planetary nebulae. X - Physical conditions in the compact planetary nebula Sw St 1 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Photoelectric visual and ultraviolet observations of the compact planetary nebula Sw St 1 are analyzed. The electron density, determined from the C III 1907/1909 A line ratio, is N(e) = (1.1 + or - 0.1) x 10 to the 5th/cu cm, consistent with the high emission measure and high critical frequency determined from observations of the thermal radio emission. The C/O abundance ratio in the nebula is found to be N(C)/N(O) = 0.72 + or - 0.1, i.e. the envelope is oxygen-rich, as suggested by the identification of the silicate feature in the 8-13 micron infrared spectrum. Difficulties remain in accurately determining the reddening constant to the nebula and its electron temperature.
    Keywords: ASTRONOMY
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 206; 293-304
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    Differential detection of Gaussian MSK in a mobile radio environment (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Minimum shift keying with Gaussian shaped transmit pulses is a strong candidate for a modulation technique that satisfies the stringent out-of-band radiated power requirements of the mobil radio application. Numerous studies and field experiments have been conducted by the Japanese on urban and suburban mobile radio channels with systems employing Gaussian minimum-shift keying (GMSK) transmission and differentially coherent reception. A comprehensive analytical treatment is presented of the performance of such systems emphasizing the important trade-offs among the various system design parameters such as transmit and receiver filter bandwidths and detection threshold level. It is shown that two-bit differential detection of GMSK is capable of offering far superior performance to the more conventional one-bit detection method both in the presence of an additive Gaussian noise background and Rician fading.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Vehicular Technology (ISSN 0018-9545); VT-33; 307-320
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  • 72
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    Radioastronomical observations of comets IRAS-Araki-Alcock (1983d) and Sugano-Saigusa-Fujikawa (1983e) (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Continuum and spectral-line radio observations of the comets IRAS-Araki-Alcock and Sugano-Saigusa-Fujikawa obtained at a number of observatories during May and June, 1983, are compiled in tables and briefly characterized. The species NH3, H2O, CO, and HCN are considered in detail; visible-range observations of CN are compared; and the implications of the results and the experience gained in performing and coordinating the observations for the detection of important species in other comets, especially Halley's Comet, are explored.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 60; 215-220
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  • 73
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    Performance of OOK and low-order PPM modulations in optical communications when using APD-based receivers (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The paper computes direct detection laser communications receiver performance when using avalanche photodiode (APD) detectors. The performances are compared in terms of bit error probability vs average signal required per bit when the transmitter uses either on-off keying (OOK) or low-order PPM formats. It is shown that QPPM requires 3 dB less signal than OOK, while BPPM requires the same or slightly more than OOK for the same performance. Optimum APD gain values range from 200 to 400. When using QPPM, k(eff) = 0.006, and optimum gain, 60 signal counts/bit are required at 500 Mbits/s for a 0.000001 bit error probability. It is concluded that QPPM may be an attractive signaling format for some fiber or free space laser communication applications.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-32; 1140-114
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    A search at the millijansky level for milli-arcsecond cores in a complete sample of radio galaxies (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A complete sample of 26 extended radio galaxies was observed at 2.29 GHz with the Mark III VLBI system. The fringe spacing was about 3 milli-arcsec, and the detection limit was about 2 millijanskys. Half of the galaxies were found to possess milli-arcsec radio cores. In all but three sources, the nuclear flux density was less than 0.04 of the total flux density. Galaxies with high optical luminosity (less than -21.2) were more likely than less luminous galaxies to contain a detectable milliparcsec radio core (69 percent vs. 20 percent). For objects with arcsec cores, 80 percent were found to have a milli-arcsec core, even though the milli-arcsec object did not always contribute the greater part of the arcsec flux density.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 284; 519-522
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  • 75
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    The radar cross section of dielectric disks (1984)
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    Publication Date: 2011-08-18
    Description: A solution is presented for the backscatter (monostatic) radar cross section of dielectric disks of arbitrary shape, thickness, and dielectric constant. The result is obtained by employing a Kirchhoff-type approximation to obtain the fields inside the disk. The internal fields induce polarization and conduction currents from which the scattered fields and the radar cross section can be computed. The solution for the radar cross section obtained in this manner will be shown to agree with known results in the special cases of normal incidence, thin disks, and perfect conductivity. It will also be shown that the solution can be written as a product of the reflection coefficient of an identically oriented slab times the physical optics solution for the backscatter cross section of a perfectly conducting disk of the same shape. This result follows directly from the Kirchhoff-type approximation without additional assumptions.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-32; 6-12
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    New infrared observations of IRS1, IRS3, and the adjacent nebula in the OMC-2 cluster (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations of the infrared cluster of low luminosity protostars in Orion Molecular Cloud 2 (OMC2) are reported. Results show that the asymmetric distribution of the extended emission seen about IRS1 is another infrared reflection nebula. Energy distributions show that the spectral shape is fairly constant throughout the nebula which indicates there is little internal extinction within this region. Integrated surface brightness values show that the nebula is 5 times brighter than IRS1 at K. Energy distributions show that IRS1 has a more pronounced ice band absorption feature at 3.1 micron; suggesting that there is more extinction along the direct line of sight to IRS1 than along a line from IRS1 to the scattering grains and then to the observer. The distribution of the extended emission around IRS1 is similar to the reflection nebula seen in NGC 7538 (Werner et al. 1979). The asymmetric shapes of the two nebulae are similar and in each case there is excess extinction along line of sight to the illuminating source.
    Keywords: ASTRONOMY
    Type: Royal Observatory Lab. and Observational Infrared Spectra of Interstellar Dust; p 162-166
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  • 77
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    Transient dips of Cygnus X-1 observed from Tenma (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The transient intensity dips of the binary system Cyg X-1 have been observed, using the gas scintillation proportional counter (GSPC) array onboard the Tenma X-ray astronomy satellite. The duration of the dips was in the range from several seconds to 10 minutes, with several dips occurring as much as 15 h before the superior conjunction. Within the dips, complex structures were observed with time scales of several seconds, and, in at least one case, shorter than two seconds. For a dip lasting longer than 10 minutes, a high-quality spectrum was obtained which reveals the K-absorption edge of iron at 7.18 + or - 0.18 keV. On the basis of the observed absorption, it is suggested that the dips are caused by absorption due to relatively cool matter (less than about 30,000 k); the low-energy excess observed during the dips is due either to an extended soft X-ray emitting corona or to partial obscuration of the X-ray source by multiple blobs. From the time structure of the dip, a blob size of the order of 10 to the 9th cm is derived.
    Keywords: ASTRONOMY
    Type: Astronomical Society of Japan, Publications (ISSN 0004-6264); 36; 4, 19
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  • 78
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    Optimum cyclic redundancy codes for noisy channels (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Binary cyclic redundancy codes for feedback communication over noisy digital links are considered. The standard 16 bit American Data and Computer Communication Protocol (ADCCP) polynomial is designed for digital links which already have a low input bit error probability. For file transfer between personal computers over telephone circuits, the quality of resulting digital circuit may be much lower. The 3 byte (24 bit) and 4 byte (32 bit) polynomials are considered. Generator polynomials of a certain class have minimum weight and yet achieve the bound on minimum distance for arbitrary codes. Particular choices for 24 bit and 32 bit redundancies are exhibited: of weight and distance 6 in the 24-bit case; and weight 10 and distance 8 in the 32-bit case.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Information Theory (ISSN 0018-9448); IT-30; 865-867
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  • 79
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    Performance analysis of an adaptive multiple access scheme for the message service of a land mobile satellite experiment (MSAT-X) (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes an Adaptive Mobile Access Protocol (AMAP) for the message service of MSAT-X., a proposed experimental mobile satellite communication network. Message lengths generated by the mobiles are assumed to be uniformly distributed. The mobiles are dispersed over a wide geographical area and the channel data rate is limited. AMAP is a reservation based multiple access scheme. The available bandwidth is divided into subchannels, which are divided into reservation and message channels. The ALOHA multiple access scheme is employed in the reservation channels, while the message channels are demand assigned. AMAP adaptively reallocates the reservation and message channels to optimize the total average message delay.
    Keywords: COMMUNICATIONS AND RADAR
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    IUE observations of the 'Butterfly' Nebula M2-9 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: IUE observations of the peculiar 'Butterfy' nebula M2-9 indicate that it is not a normal planetary nebula. The ultraviolet spectrum is characterized by few emission lines and a weak continuum. Mg II 2800 A is the strongest emission line present and may be indicative of a binary nucleus. Lines of N v, Q I, N III, N IV, Si III, and C III are seen, but C IV and O III are conspicuous by their absence. T(e) = 10,250 + or - 400 K was determined for the core. Nitrogen in the core is found to be overabundant by about a factor of 5 over the solar value. M2-9 may be an object in the early stages of becoming a planetary nebula.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 287; 353-358
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  • 81
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    Cometary showers and unseen solar companions (1984)
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    Publication Date: 2011-08-19
    Description: The possibility that an invisible solar companion passing through the Oort cloud every 28 Myr precipitates a sufficiently high rate of cometary collisions with the earth to account for periodic mass species extinctions recorded in the fossil record is discussed. A Monte Carlo simulation shows that any hypothesized 'death star' with a 28 Myr orbit would experience an average 10 percent change in period per orbit. Production of an 18-fold increase in cometary impacts would be associated with a 0.055 probability that a 10 km nucleus would hit the earth in a shower once every 510 Myr, longer than the proposed extinction periodicity. However, if the death star orbit has a 0.6 eccentricity and the Oort cloud is sufficiently densely populated, a 2 billion comet shower may be possible. A survey of large terrestrial impact craters indicates that 6-12 craters with diameters over 10 km originated in periodic showers. The extinctions in any case occur at 26 Myr periods and cannot be correlated with the 33 Myr period of recrossing the galactic plane, or with any other known phenomena.
    Keywords: ASTRONOMY
    Type: Nature (ISSN 0028-0836); 312; 380; Rep
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  • 82
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    Evidence for material between Saturn's A and F rings from the Voyager 2 photopolarimeter experiment (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The region in the Saturn system between the F ring and the outer edge of the A ring is an area that appears, in images from the imaging experiment, to be virtually devoid of material except for three small satellites. Near the orbit of 1980S28, Atlas - the innermost satellite - the Voyager Photopolarimeter Stellar Occultation data show a discontinuity in count rate which marks a boundary between the tenuous material near the outer edge of the A ring and the orbit of Atlas. The data pertaining to this region have been examined with the aid of statistics and models generated from other similar ring structures. It is concluded that the discontinuity is real, implying the existence of tenuous material of normal optical depth of 0.01 to 0.006 in this region.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 60; 409-415
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  • 83
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    1984 AB - A unique Mars-crossing asteroid (1984)
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    Publication Date: 2011-08-19
    Description: Asteroid 1984 AB, discovered in January 1984, proved to be a unique object with a close dynamical relationship to Mars. A brief history of the discovery and subsequent 'evolution' of the orbit as it was refined is presented. The preliminary orbit of 1984 AB indicated that it might be a Mars Trojan, and an extended discussion of this interesting possibility is presented, but this hypothesis had to be dismissed after further observations had refined the orbit. The semimajor axis and orbital eccentricity are very similar to that of Mars. No other known Mars-crossing asteroid exists with an orbit as closely associated to Mars.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 60; 404-408
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  • 84
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    An integrated voice and data multiple-access scheme for a land-mobile satellite system (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analytical study is performed of the satellite requirements for a land mobile satellite system (LMSS). The spacecraft (MSAT-X) would be in GEO and would be compatible with multiple access by mobile radios and antennas and fixed stations. The FCC has received a petition from NASA to reserve the 821-825 and 866-870 MHz frequencies for the LMSS, while communications with fixed earth stations would be in the Ku band. MSAT-X transponders would alter the frequencies of signal and do no processing in the original configuration considered. Channel use would be governed by an integrated demand-assigned, multiple access protocol, which would divide channels into reservation and information channels, governed by a network management center. Further analyses will cover tradeoffs between data and voice users, probability of blocking, and the performance impacts of on-board switching and variable bandwidth assignment. Initial calculations indicate that a large traffic volume can be handled with acceptable delays and voice blocking probabilities.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE, Proceedings (ISSN 0018-9219); 72; 1611-161
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  • 85
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    A radar study of Comet IRAS-Araki-Alcock 1983d (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Radar echoes from Comet IRAS-Araki-Alcock at wavelengths 3.54 and 12.9 cm indicate that the comet's nucleus is very rough on a scale larger than the radar wavelengths; however, the low polarization ratio (25 percent at 3.54 cm) indicates that the scattering is not dominated by multiple reflections, internal reflections, or large abundances of sharp edges, cracks, and pits. The shape of the nucleus probably departs greatly from a sphere with average radii near 3-4 km. The nucleus does not appear to look significantly different from a number of Apollo and Amor asteroids except that: (1) there is a suggestion that minor structure moves rapidly across the spectra, and (2) the debris not gravitationally bound to the comet was detected, and contributes 25 percent of the total radar cross section at the 12.9-cm wavelength. Other considerations suggest that the pole was at least 45 deg away from the line of sight on two days of observation, and that the rotation period is approximately 1-2 days.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 89; 1745-175
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  • 86
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    A solar spectral line list between 10 and 200 A modified for application to high spectral resolution X-ray astronomy (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A spectral line list for the 10-200 A range is developed from existing solar spectra for application to high spectral resolution measurements of astrophysical plasmas. The solar spectral line lists are merged into a single comprehensive list. The effect of the solar emission measure distribution is removed from the line intensities, which results in a set of emission rates for the lines that can be applied to many optically thin, low density high temperature plasmas in ionization equilibrium. In addition to the measured solar lines, 250 theoretical lines are added to this list. These lines fall in wavelength regions where the existing solar lists have few lines because of limitations in instrumental sensitivity. Also, some lines have been added because the sun has very little plasma at temperatures of about one million K, and consequently these lines are weak or absent in solar spectra. The entire list contains about 600 lines. Finally, predicted spectra of the two RS CVn stars, alpha Aur (Capella) and UX Ari, are presented at 1 and 0.25 A spectral resolution. Also, the solar spectrum is shown at 1 A resolution, and the emission rate spectrum (spectrum not modified by an emission measure distribution) is shown at very high spectral resolution. The predicted spectra for Capella and UX Ari are based on results obtained from the Einstein and International Ultraviolet Explorer (IUE) spacecraft.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 56; 67-89
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  • 87
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    Far-infrared scans of the Galactic plane (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Results are reported for balloon-borne scans of the Galactic plane between longitudes of 348 and 32.5 deg, which were made in two broad spectral bands from 60 to 300 microns and from 150 to 300 microns. These results indicate that there are many bright H II regions embedded in a diffuse underlying band of emission in the examined longitude range, that the color temperatures range from 30 to 90 K, and that the width of the plane is at least 2 deg of arc in both spectral bands. A lower-limit IR luminosity of the order of 1 billion suns is computed for both the bright complex of sources at the nucleus and the underlying diffuse emission out to about + or -15 deg of arc from the nucleus. The strong relationship between far-IR emission and radio continuum expected for discrete sources is illustrated, and the results are compared with those of previous studies. It is concluded that the total far-IR luminosity of the central part of the Galaxy is understandable solely in terms of known distributions of stars and dust.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 214
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  • 88
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    A radio lens in the ionosphere (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Using a modified version of the classical Cornu spiral, fading patterns in agreement with observations of radio signals on 140 and 360 MHz from the geostationary satellite ATS6, have been obtained. The particular fading patterns chosen show modulated quasi-periodic fading before and after a deep central minimum. It is shown that a cylindrical lens in the ionosphere required to produce this is only about 100 m across (an order of magnitude smaller than the size of the pattern on the ground) and if it were circular in cross-section would have a maximum plasma frequency of over 40 MHz. This suggests the reason why calculations based on a transparent phase screen did not give the observed fading pattern for 40 MHz signals. It was not possible to deduce the height of the lens above the ground, though we would incline to an E-region origin.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Journal of Atmospheric and Terrestrial Physics; 39; Mar. 197
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  • 89
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    90-GHz flux-density measurements of variable radio sources (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Results are presented for measurements of the flux densities of 10 variable extragalactic sources at 85.2 or 90 GHz, which were made over a period of almost seven years with the NRAO 36-ft millimeter-wave antenna. The primary flux-density calibration standards used include Jupiter, Saturn, Mars, and the small-diameter Galactic source DR 21. Measured flux densities are given as a function of time (in years) for the sources 3C 84, NRAO 150, 3C 120, OJ 287, 4C 39.25, 3C 273, 3C 279, 3C 345, BL Lac, and 3C 454.3. No statistically meaningful flux-density changes during an observing interval (1 to 3 days) are detected for any source, and a high degree of correlation between flux-density variations at 85.2 or 90 GHz and those observed at lower frequencies is found in all 10 sources. Some variations observed at different frequencies in several individual sources are briefly discussed.
    Keywords: ASTRONOMY
    Type: Astronomical Journal; 82; Apr. 197
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  • 90
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    Linearization of dynamical systems using integrals of the motion (1976)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A method is presented which transforms certain nonlinear differential equations of dynamics into linear equations by introducing an independent variable and utilizing the integrals of motion. As examples of special interest, the linearizations of unperturbed and perturbed Keplerian motions are discussed.
    Keywords: ASTRONOMY
    Type: Celestial Mechanics; 14; Dec. 197
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  • 91
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    On the stability of the solutions of the general problem of three bodies (1976)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The extent through which the initial conditions of a given three-body system may be varied without completely changing the qualitative nature of the subsequent system evolution is investigated. It is assumed that the three masses are equal, all initial velocities are zero, the first two bodies initially lie on the x-axis, and the position of the third body is confined to a specific region of space. Analysis of the system evolution for different initial positions of the third body shows that there is a whole area or 'island' in the x-y plane throughout which the initial position of the third body may be moved in a continuous fashion to produce an evolution which also changes in a continuous manner. A Monte Carlo approach is adopted to determine the full extent of this island in the general problem. It is concluded that the stability of a full solution may be directly related to the size of its island in phase space.
    Keywords: ASTRONOMY
    Type: Celestial Mechanics; 14; Dec. 197
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  • 92
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    Limitations on oceanographic use of beam-limited target-referenced radars (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A general development is undertaken to determine the limitations on the use of beam-limited target-referenced radars in the measurement of ocean wave height. This class of radars is concerned only with the range extent of the target, not the range to the target. The nonzero range extent of a flat waveless sea and the compounding effect of pointing errors due to radar platform instability cause difficulty in measuring low wave heights and impose a maximum operating altitude on such systems. It is seen that it is impractical to obtain accurate measurements for wave heights of interest at altitudes above those used by commercial aircraft (10,000 m). Additionally, the typical ratio of dominant wavelength to significant wave height (SWH) of 30 for wind-driven gravity waves imposes an upper limit on the SWH measurable for a given altitude and beamwidth.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation; AP-25; May 1977
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  • 93
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    Tracking performance of symbol synchronizers for Manchester coded data (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The implementation and tracking performance of symbol synchronizers for Manchester coded data is presented with motivation provided by maximum a posteriori (MAP) estimation theory. Certain physically relizable closed-loop structures, readily implemented in practice, are suggested by the theory for uncoded data symbols with arbitrary data transition probabilities. The tracking performance of these loops is optimized and comparisons are made among the various configurations over a wide range of system parameters. Although not the major intent of the paper, the acquisition problem is briefly addressed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-25; Apr. 197
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  • 94
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    Copernicus observations of the Ap star Epsilon Ursae Majoris (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Spectral scans of the Ap star Epsilon UMa made with the Copernicus satellite show strong line blanketing from profuse Cr II and Fe II lines. In the spectral region covering 1900 to 3000 A, about 500 lines are present which suppress the apparent continuum by at least 15-30%. An accurate line-identification list is compiled showing Eu II present in addition to Mn II and Ni II. The identification of Eu II, however, rests on very stringent identification limits for Fe II. If these are relaxed, the existence of Eu II is dubious. There are no broad features in this spectral region which would suggest strong photoionization discontinuities by metals, but one feature near 2137 A might contain the photoionization edge due to Cr I 5S lying 0.94 eV above the ground level. However, a significant correlation between the line-blanketing strength and the amplitude of the OAO-2 ultraviolet light curves was found such that both monotonically increase in the same proportion toward shorter wavelengths. This gives additional strength to the suggestion that variations in the metal line-blanketing cause the observed photometric variations.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal Supplement Series; 33; Jan. 197
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  • 95
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    An antenna for limited scan in one plane - Design criteria and numerical simulation (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Aperture illumination is synthesized through the use of overlapping subarrays with independently controlled excitations. Detailed analysis and design criteria are provided for a specific limited-scan antenna configuration scanning in one plane. The number of phase shifts is the theoretical minimum corresponding to specified aperture size and field of view. Beam pointing and width are approximately constant for moderate frequency variation, and ultralow sidelobes outside the field of view can be produced at the cost of a slight loss of illumination efficiency. Accurate aperture illumination control makes for excellent independently specified sum and difference patterns in beamforming.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation; AP-25; Mar. 197
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  • 96
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    5 GHz observations of galactic supernova remnants (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Brightness and polarization distributions over several galactic supernova remnants have been observed at a wavelength of 6 cm. These observations have confirmed the nonthermal nature of most of the observed sources. It is suggested, however, that the objects G33.1-0.1 (KES 78), G35.6-0.0, G37.6-0.1, G37.7+0.1, and G37.9-0.4 are thermal. The results of these observations are presented in the form of total intensity contour maps with superimposed polarization vectors.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics; 55; 1, Fe; Feb. 197
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  • 97
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    Far-ultraviolet imagery of the Barnard Loop Nebula (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: An electrographic Schmidt camera carried on a sounding rocket has yielded far-ultraviolet (1050-2000 A and 1230-2000 A) images of the Barnard Loop Nebula and of the general background in the Orion region due to scattering of ultraviolet starlight by interstellar dust particles. The total intensity in the Barnard Loop region agrees well with OAO-2 measurements, but the discrete Loop structure contributes only some 15% of the total. The measurements are consistent with a relatively high albedo for the dust grains in the far-ultraviolet.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 212
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  • 98
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    Optimum performance of suppressed carrier receivers with Costas loop tracking (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The performance of suppressed carrier receivers with Costas loop tracking is optimized by proper choice of loop arm filter bandwidth. In particular, it is shown that for a variety of passive arm filter types, there exists, for a given data rate and data signal-to-noise ratio, an optimum filter bandwidth in the sense of minimizing the loop's squaring loss. For the linear theory case, this is equivalent to minimizing the loop's tracking jitter. When symbol synchronization is known, it is shown that by replacing the passive arm filters with active filters, i.e., integrate-and-dump circuits, one can achieve an improvement in carrier-to-noise ratio of as much as 4 to 6 dB depending on the passive arm filter type used for comparison and the value of data signal-to-noise ratio.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-25; Feb. 197
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  • 99
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    Apollo-16 far-ultraviolet spectra in the Large Magellanic Cloud (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Spectra in the wavelength ranges from 900 to 1600 A and 1050 to 1600 A of some OB associations in the Large Magellanic Cloud were obtained from the lunar surface by the Apollo-16 far-ultraviolet camera/spectrograph on April 22, 1972. The observed spectral distributions appear consistent with a stellar model having an effective temperature of 30,000 K, reddened by E(B-V) = 0.3, and characterized by the average far-ultraviolet extinction curve of Bless and Savage (1972). However, the absolute intensity of the far-ultraviolet spectrum of the associations NGC 2050 and 2055 seems somewhat too bright in comparison with ground-based photometry.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 211
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  • 100
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    Far infrared observations of IRC + 10216 (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Results are reported for measurements of IRC + 10216 at 100 microns made with the 91-cm telescope of NASA's Kuiper Airborne Infrared Observatory. The IR photometer employed consisted of a gallium-doped germanium photoconductive detector with a MOSFET preamplifier and load resistor. Signals obtained from the source at modulation frequencies of 30 and 100 Hz are plotted, and the 100-micron flux measurements are shown to be in agreement with previous bolometric measurements. It is noted that the sensitivity of the photoconductive detection system is comparable to that of the conventional bolometers that have been used in airborne IR observations.
    Keywords: ASTRONOMY
    Type: Nature; 265; Feb. 10
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