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  • 1
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    Measurements by the plasma diagnostics package on STS-3 (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: A comprehensive set of measurements about the orbiter environment are provided by the plasma diagnostics package (PDP). Ion and electron particle densities, energies, and spatial distribution functions; ion mass for identification of particular molecular ion species; and magnetic fields, electric fields and electromagnetic waves over a broad frequency range are studied. Shuttle environmental measurements will be made both on the pallet and, by use of the remote manipulator system (RMS), the PDP will be maneuvered in and external to the bay area to continue environmental measurements and to carry on a joint plasma experiment with the Utah State University fast-pulsed electron generator. Results of orbiter environment EMI measurements and S-band field strengths as well as preliminary results from wake search operations indicating wake boundary identifiers are reported.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 8 p
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  • 2
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    Design and development of the ERBE data management system (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: The Earth radiation budget experiment (ERBE) software development approach is described. An iterative development approach was adopted which provides for three releases or versions of the processing system, each of increasing levels of complexity and solidity. The final release of the system will be used to process the flight data. The major phases for each iterative release consist of specifications developed in concert with the science team, preliminary design, subsystem reviews, coding, subsystem code walkthroughs, system testing, system documentation, and project status review.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 15 p
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  • 3
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    Outgassing: Its effects on spacecraft. Vibration damping materials (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: The correlation of outgassing to the stability of the damping properties of polymer materials to be used in spacecraft structures is discussed. A test series was devised to obtain basic information from off-the-shelf damping materials. The test results could be considered as a guideline toward the application of these materials. Eight materials were selected to form a representative cross section of those polymers having both ready availability as commercial damping materials and desirable properties. A table indicates the temperatures at which peak damping occurs at 1 Hz and the type of beam specimen used in the vacuum exposure tests. These materials as a group cover the temperature range of -85 C to 38 C.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 25 p
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  • 4
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    A facility for the simulation of low orbit atmospheric oxygen bombardment (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: A molecular beam facility to simulate the space environment of a spacecraft at low orbit was designed with the intent of studying the effect on the properties of optical elements of oxygen atoms impacting at orbital velocity. The four-stage differentially pumped molecular beam facility includes a variety of oxygen atom beam sources which cover a wide range of velocities (1 km/sec to approximately 8 km/sec), in addition to the ultra-clean experimental environmental of an ultra-high vacuum chamber and an optical diagnostic set-up. The primary oxygen atom beam source used to obtain the 8 km/sec O atoms is an arc heated source. It consists of a modified commercially available plasma torch. The modifications include attachments which provide for a nozzle which is used to expand the atomic beam into the vacuum system, and exhaust channels to dispose of excess torch gas. The torch operates in the 'nontransferred' mode of operation, that is the electric arc is confined within the torch. A plasma is formed in helium by a dc arc. A small amount of O2 is injected downstream from the arc where it is thermally dissociated by the hot He into oxygen atoms. The high temperature and isentropic expansion give the oxygen atoms their velocity. Using seeded beam techniques, oxygen atom beams of approximately 3.5 and approximately 1.5 km/sec, respectively, are obtained.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 1 p
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  • 5
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    Space Shuttle preliminary. Contamination assessment from STS-1 and STS-2 (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: A preliminary assessment of the space shuttle contamination environment was made using data from the first two orbital flight tests, STS-1 and STS-2. Data sources consisted of crew observations during flight, postflight vehicle inspection, and the induced environment contamination monitor which was used on STS-2 and consists of 10 instruments. These instruments are used to measure gas phase contaminants, particle population, humidity, and molecular deposition in the orbiter payload bay during ascent and descent and particle population, molecular deposition, and gas cloud during orbital flight. Results of the measurements described are presented in summary form and indicate low molecular deposition rates for both pressurized and orbital flight.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 21 p
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  • 6
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    Environmental test facilities used in Europe for ESA satellite programmes (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: The structure of the European Space Agency (ESA) is described. The major test facilities used for ESA programs are described. Facility characteristics and special test methods are described.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 28 p
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  • 7
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    Education and training of personnel in space simulation (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: The training program and procedures developed and implemented at the space simulation laboratory at Martin Marietta Aerospace in Denver are discussed. The training of technicians and professionals as well as preparation for instructors is covered. Training manuals and their compilation are reported as applicable to the specific needs of the laboratory. The development of a space simulation course as part of the Martin Marietta Continuing Education Night School approaching space simulation from an academic viewpoint is presented. Finally, public relations tours of the facility as an informational/educational tool are discussed.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 5 p
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  • 8
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    Cryopump for large pulses of hydrogen (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: A test involving a flow of hot hydrazine decomposition products at a rate of 13.6 g/s (0.03 lb/s) established the requirement to maintain pressure in an 11.9-m-(39 ft) diameter space chamber below 200 microns. The flow, 2/3 hydrogen and 1/3 nitrogen by volume, continued for several periods ranging from 3 to 15 min. The pressure requirement was necessary to minimize thermal effects of the gas on the test vehicle but was well beyond the capability of the existing facility pumps. Various methods of obtaining additional temporary jump capacity were considered. From these, the slugged-charcoal approach was selected as the quickest and least expensive method to implement.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 23 p
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  • 9
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    Spacecraft thermal balance testing using infrared sources (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: A thermal balance test (controlled flux intensity) on a simple black dummy spacecraft using IR lamps was performed and evaluated, the latter being aimed specifically at thermal mathematical model (TMM) verification. For reference purposes the model was also subjected to a solar simulation test (SST). The results show that the temperature distributions measured during IR testing for two different model attitudes under steady state conditions are reproducible with a TMM. The TMM test data correlation is not as accurate for IRT as for SST. Using the standard deviation of the temperature difference distribution (analysis minus test) the SST data correlation is better by a factor of 1.8 to 2.5. The lower figure applies to the measured and the higher to the computer-generated IR flux intensity distribution. Techniques of lamp power control are presented. A continuing work program is described which is aimed at quantifying the differences between solar simulation and infrared techniques for a model representing the thermal radiating surfaces of a large communications spacecraft.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 26 p
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  • 10
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    Optical characterization of solar concentrator mirrors using the solar beam of the JPL 25-foot space simulator (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: The Jet Propulsion Laboratory 25-foot space simulator with its 5.8-m (19-ft) diameter simulated solar beam provides an excellent facility for measuring the optical characteristics of parabolic solar concentrator panels and gores. The virtual source position and size were determined by using a single lamp of the 37 xenon 30-kW source array with only the center lens in the 19-channel optical mixer. This data was used to define the optical test geometry, and it allowed accurate measurement of focal length and surface deviations of the mirror under test. A flux distribution of a typical solar concentrator placed directly on the solar beam gives measurements of performance at the focal point of the parabolic surface.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 19 p
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  • 11
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    Fuel optimal maneuvers for spacecraft with fixed thrusters (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: Several mathematical models, including a minimum integral square criterion problem, were used for the qualitative investigation of fuel optimal maneuvers for spacecraft with fixed thrusters. The solutions consist of intervals of "full thrust" and "coast" indicating that thrusters do not need to be designed as "throttleable" for fuel optimal performance. For the primary model considered, singular solutions occur only if the optimal solution is "pure translation". "Time optimal" singular solutions can be found which consist of intervals of "coast" and "full thrust". The shape of the optimal fuel consumption curve as a function of flight time was found to depend on whether or not the initial state is in the region admitting singular solutions. Comparisons of fuel optimal maneuvers in deep space with those relative to a point in circular orbit indicate that qualitative differences in the solutions can occur. Computation of fuel consumption for certain "pure translation" cases indicates that considerable savings in fuel can result from the fuel optimal maneuvers.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 21 p
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  • 12
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    Kinetic theory in astrophysics and cosmology (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: Results associated with exact solution of the Einstein-Boltzmann and Einstein-Maxwell-Boltzmann equations are presented. The generalization of Ehler's killing vector approach for the distribution function to charged particles is considered.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 21 p
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  • 13
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    Attitude control of the space construction base: A modular approach (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: A planar model of a space base and one module is considered. For this simplified system, a feedback controller which is compatible with the modular construction method is described. The systems dynamics are decomposed into two parts corresponding to base and module. The information structure of the problem is non-classical in that not all system information is supplied to each controller. The base controller is designed to accommodate structural changes that occur as the module is added and the module controller is designed to regulate its own states and follow commands from the base. Overall stability of the system is checked by Liapunov analysis and controller effectiveness is verified by computer simulation.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 35 p
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  • 14
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    Automating a residual gas analyzer (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: A residual gas analyzer (RGA), a device for measuring the amounts and species of various gases present in a vacuum system is discussed. In a recent update of the RGA, it was shown that the use of microprocessors could revolutionize data acquisition and data reduction. This revolution is exemplified by the Inficon 1Q200 RGA which was selected to meet the needs of this update. The Inficon RGA and the Zilog microcomputer were interfaced in order the receive and format the digital data from the RGA. This automated approach is discussed in detail.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 16 p
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  • 15
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    Remote sensing of tornadic storms from space (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: By using infrared images obtained from GOES satellite, the digital count values of pixels representing blackbody temperatures of the cloud top, convective storms are observed throughout their life cycles. Clouds associated with a tornadic storm are compared with those without a tornadic storm to illustrate how the infrared and visible observations from a geosynchronous satellite can be used to study the differences in their life cycles.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 11 p
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  • 16
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    Environmental noise assessment STS-1 Columbia launch (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: An environmental noise assessement of the initial launch of the Space Transportation System, STS-1 Columbia was conducted. The principal objective of the environmental noise assessment was to measure the noise generated during the initial launch of the space shuttle to ascertain the validity of the levels predicted in the 1979 environmental impact statement. In the 1979 study information obtained for expendable launch vehicles, Titan, Saturn and Atlas was used to predict the noise levels that would be generated by the simultaneous firing of the two solid rocket boosters and the three space shuttle main engines. Fifteen monitoring sites were established in accessable areas located from 4,953 to 23,640 meters from the launch pad. Precision sound level meters were used to capture the peak level during the launch. Data obtained was compared to the predicted levels and were also compared to the identified levels, standards and criteria established by the federal agencies with noise abatement and control responsibilities.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 16 p
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  • 17
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    Improved multilayer insulation applications (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: Multilayer insulation blankets used for the attenuation of radiant heat transfer in spacecraft are addressed. Typically, blanket effectiveness is degraded by heat leaks in the joints between adjacent blankets and by heat leaks caused by the blanket fastener system. An approach to blanket design based upon modular sub-blankets with distributed seams and upon an associated fastener system that practically eliminates the through-the-blanket conductive path is described. Test results are discussed providing confirmation of the approach. The specific case of the thermal control system for the optical assembly of the Space Telescope is examined.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Goddard Space Flight Center 12th Space Simulation Conf.; 8 p
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  • 18
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    Durability of spacecraft materials (1982)
    In:  CASI
    Details
    Publikationsdatum: 2006-04-12
    Beschreibung: Research efforts are reviewed on the space durability of materials, including radiation effects on polymer matrix composites and films, dimensional stability of polymer matrix composites and tension-stabilized cables, and thermal control coatings. Research to date has concentrated on establishing a fundamental understanding of space environmental effects on current graphite-reinforced composites and polymer systems, and development of analytical models to explain observed changes in mechanical, physical, and optical properties. As a result of these research efforts, new experimental facilities have been developed to simulate the space environment and measure the observed property changes. Chemical and microstructural analyses have also been performed to establish damage mechanisms and the limits for accelerated testing. The implications of these results on material selection and system performance are discussed and additional research needs and opportunities in the area of tougher resin/matrix and metal/matrix composites are identified.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Advan. Mater. Technol.; p 357-380
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  • 19
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    X-ray spectra of young supernova remnants (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: Einstein solid-state-spectrometer (SSS) spectra are presented for the Crab Nebula, Cas A, SN 1006, the Tycho SNR, and the Kepler SNR. The history of X-ray observations of SNRs is reviewed; the SSS instrument is briefly characterized; a reduction technique which accounts for all background sources in the 0.5-4.5-keV band is applied; and the physical models of SNRs constructed to reproduce the refined spectra are discussed. The limitations of the modeling methods and the need for further observations, especially of localized regions, are indicated.
    Schlagwort(e): ASTROPHYSICS
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  • 20
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    Magnetic topology and the heating of extended chromospheres (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: New data indicate that red giants are surrounded by geometrically thick chromospheres of several stellar radii extent. Such chromospheres occur among stars which apparently lack coronae. Maintenance of this extended warm region may require non-compressional wave heating of a magnetic character, and this may provide a crucial clue to the mechanism of rapid mass loss from red giant stars.
    Schlagwort(e): ASTROPHYSICS
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  • 21
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    A note on the oxygen gradient in NGC 628 (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: The Kitt Peak 2.1-m telescope and Intensified Image Dissector Scanner have been used to gather spectrophotometric data in the 3600-5200 A spectral region for five H II regions in the spiral galaxy NGC 628. The Pagel et al (1979) technique was then applied to determine the relative number abundances of O to H in each of the H II regions. An examination of the abundance values obtained as a function of the radial coordinate yields an O gradient of -0.05 + or - 0.03 dex/kpc.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 95; 986-988
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  • 22
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    HZE particle shielding using confined magnetic fields (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The great rigidities characteristic of high energy heavy ion (HZE) particles are judged to preclude near term use of confined magnetic fields of reasonable dimensions and strengths for small spacecraft shielding on long duration manned missions. It is noted that a Mars mission-class shield, although effective against solar protons, would be useless for HZE particles unless the mass and size of the shield are increased by several orders of magnitude (to yield a shield comparable to those contemplated for permanent space stations).
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 20; 629
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  • 23
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    Testing for a cosmological influence on local physics using atomic and gravitational clocks (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The existence of a possible influence of the large-scale structure of the universe on local physics is discussed. A particular realization of such an influence is discussed in terms of the behavior in time of atomic and gravitational clocks. Two natural categories of metric theories embodying a cosmic infuence exist. The first category has geodesic equations of motion in atomic units, while the second category has geodesic equations of motion in gravitational units. Equations of motion for test bodies are derived for both categories of theories in the appropriate parametrized post-Newtonian limit and are applied to the Solar System. Ranging data to the Viking lander on Mars are of sufficient precision to reveal (1) if such a cosmological influence exists at the level of Hubble's constant, and (2) which category of theories is appropriate for a descripton of the phenomenon.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 28; 1822-182
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  • 24
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    Observations of NGC 7027 from 5.2 to 7.5 microns - The detection of Ni II and additional dust features (1983)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: NGC 7027 was observed with a multichannel grating spectrometer from 5.2 to 7.5 microns at a spectral resolving power of 120-200. Two new dust emission features are resolved at 5.62 and 6.95 microns, and for the first time the Ni II fine-structure line at 6.64 microns is detected. It is shown that a single molecular dust constituent might account for six of the nine observed dust features between 2 and 14 microns. The strength of the Ni II line indicates either that Ni is not depleted in the neutral gas, or that the line is formed at high density.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 666-670
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  • 25
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    A new calibration of the extragalactic distance scale using Cepheids and RR Lyrae stars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Visual absolute magnitudes of classical Cepheids, metal-poor RR Lyrae stars and short-period type II Cepheids have been determined with very high precision by combining a large number of old and new astrophysical data. Five independent methods (four observational and one theoretical) have been successfully used: (1) secular and statistical parallaxes; (2) moving-group parallaxes; (3) cluster main-sequence fitting; (4) the Baade-Wesselink method and its modifications; and (5) light-curve and velocity-curve fitting (the theoretical method). With these five adopted methods, the zero point of the galactic and extragalactic distance scale can be set on a relatively firm and self-consistent basis. Classical Cepheids and RR Lyrae stars now provide essentially identical distances to nearby galaxies: the distance modulus to the Large Magellanic Cloud is 18.5 and to the Small Magellanic Cloud is 18.8, both with an uncertainty of 0.1. The distance to the center of our Galaxy is 8.6 plus or minus 0.5 kiloparsecs. The major uncertainty in these values lies in the correction for interstellar extinction.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 20-30
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  • 26
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    On the line profile coefficient for stimulated emission (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is pointed out that the line profile coefficients for spontaneous and stimulated emission are identical in low-intensity radiation fields. In more intense radiation fields, however, the stimulated emission profiles in the radiative transfer equation and in the rate equations for the atomic level populations may differ from each other, owing to their different physical nature. A seeming discrepancy between the stimulated emission profiles of the usual semi-classical aproach and a recent quantum mechanical approach by Cooper et al. (1982), which should also be valid for intense 'broadband' fields, is discussed and shown to have negligible consequences for low-intensity radiation fields.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 127; 1, Oc; 224-226
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  • 27
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    Observational tests of baryon symmetric cosmology (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observational evidence for Baryon symmetric (matter/antimatter) cosmology and future observational tests are reviewed. The most significant consequences of Baryon symmetric cosmology lie in the prediction of an observable cosmic background of gamma radiation from the decay of Pi(O)-mesons produced in nucleon-antinucleon annihilations. Equations for the prediction of the gamma ray background spectrum for the case of high redshifts are presented. The theoretical and observational plots of the background spectrum are shown to be in good agreement. Measurements of cosmic ray antiprotons and the use of high energy neutrino astronomy to look for antimatter elsewhere in the universe are also addressed. Previously announced in STAR as N83-10996
    Schlagwort(e): ASTROPHYSICS
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  • 28
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    Interacting binary stars - Freaks or rosetta stones (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Attention is given to semidetached binaries of the Algol type and to related interacting systems, such as Beta Lyrae and the W Serpentis stars. A brief description is given of observational problems. The basic properties of the Algol variables are satisfactorily explained by means of evolutionary models that assume considerable mass transfer between the components. It is pointed out that ultraviolet spectra obtained with the IUE satellite corroborate the view that the present subgiant secondary component was initially the more massive star and that it has been stripped of a large fraction of its mass so that the deep layers affected by CNO processing are now denuded. It is believed that the present-day 'classical' Algols must have undergone a phase of rapid mass transfer in the past and that Beta Lyrae and the W Serpentis stars are probably closer to that stage than ordinary Algols. Around the accreting star a complex structure is formed, and an induced stellar wind may blow a large part of the transferred matter out of the system.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society of Canada, Journal (ISSN 0035-872X); 77; 283-304
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  • 29
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    What causes the buoyancy reversal in compressible convection? (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The problem posed by the existence of a negative buoyancy work region at the top of cellular type convection in a deeply stratified superadiabatic layer (Massaguer and Zahn, 1980) is addressed. It is approached by studying two-dimensional cellular compressible convection with different physical parameters. The results suggest that a large viscosity, together with density stratification, is responsible for the buoyancy reversal. The numerical results obtained are analyzed. It is pointed out, however, that in an astrophysical situation a fluid involved in convection will generally have very small viscosity. It is therefore thought unlikely that buoyancy reversal occurs in this way.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 2, Se; 453-457
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  • 30
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    On a vibronic origin for the diffuse band spectrum (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Duley (1982) has proposed that many of the diffuse interstellar bands in the wavelength interval 542-677 nm arise from vibronic transitions of Cr (3+) ions in MgO grains. No explanation has been offered for the fact that as many as 85 of the possible 108 transitions of this system have not been observed in the interstellar medium. Moreover, the relative intensities of the diffuse bands which are observed appear to be inconsistent with their assignment. It is therefore concluded that this model is not consistent with the observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 1, Se
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  • 31
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    A note on the composition and structure of interstellar grains (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The plausibility of relatively pure diatomic oxide crystals forming in the expanding atmospheres of cool stars is commented on, and the likelihood of SiO grains condensing is discussed on the basis of laboratory nucleation experiments. Results of annealing experiments are used to consider the further evolution of silicon oxide and silicate grains. The evidence shows that SiO solids form only when SiO condenses directly onto surfaces, and that the probability of pure crystalline SiO grains forming is rather small.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 1, Se
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  • 32
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    Planetary nebulae and stellar evolution (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Newly defined characteristics of planetary nebulae (PN) derived from analysis of a photometric survey of 57 PN are reported. The data were combined with measurements of 27 other PN made since 1918 and were found to indicate core masses ranging from 0.55-1.0 solar mass. N/O elemental abundance ratios observed were correlated with the planetary nuclei masses, and were in direct proportion. IUE data on PN that overlapped a large part of the survey indicated that the PN in the galactic disk are more massive than PN in the halo. It is suggested that PN evolve into white dwarfs, a hypothesis supported by astrometric solutions for three nearby visual binaries featuring white dwarfs with well-determined masses. It is noted, however, that PN with masses exceeding one solar mass have been sighted in the Magellanic Clouds.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 305; 670
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  • 33
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    Two new possible planetary nebulae (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Two new possible planetary nebulae have been identified using the Parker, Gull, and Kirshner (1979) emission-line survey of the galactic plane. Both objects exhibit very strong forbidden O III lambda 5007 line emission, a symmetrical morphology, and a faint blue central star.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 95; 614-618
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  • 34
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    Ultraviolet observations of M1-2 (= VV 8) (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: First IUE spectrograms of the peculiar emission-line object M1-2 (= VV 8) are presented. In the wavelength region 1150-3200 A this object is characterized by emission lines superposed on a moderately strong continuum. Some ultraviolet and optical properties of M1-2 are discussed in the context of symbiotic stars and protoplanetary and planetary nebulae. An E(B-V) extinction of 0.37 mag is obtained from the ratio of the He II flux at 1640 and 4686 A and is compared with values derived from other parameters. The ultraviolet observations suggest that M1-2 is a young, high-density planetary nebula of excitation class 5 or 6 with characteristics similar to IC 4997.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 275; 628-635
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  • 35
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    The origin of the Gum nebula (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Obsrvations and theoretical investigations of the Gum nebula (GN) since about 1971 are reviewed. Direct observations of the GN, the Vela X supernova remnant (SNR), the Vela pulsar, and other stars in or near the GN are discussed with those of related phenomena such as the radio loops and known SNRs; the emphasis is on studies of the interstellar absorption lines, the evidence for hot gas in the GN, and the extended diffuse emission. The four basic models proposed for the GN are considered: a fossil Stromgren sphere, an old SNR, an H II region, or a superbubble. The GN physical parameters predicted by each model are listed in a table and compared. A minimum explanation which attributes the 36 x 36-deg filamentary structure and the 125-pc radius structure to the action of the stellar winds from Zeta Pup and Gamma-2 Vel (and perhaps the effect of a Vel X supernova explosion 20,000 years ago) is found most appropriate, at least until the questions of the net expansion rate of the GN (about 20 km/sec or about zero?) and the existence of the diffuse emission beyond the filamentary structure are resolved by observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Comments on Modern Physics, Part C - Comments on Astrophysics (ISSN 0146-2970); 10; 1-14
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  • 36
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    Electron velocity distributions near interplantary shocks (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Previous work on electron heating mechanisms operating at the supercritical earth's bow shock is extended to the generally lower Mach number interplanetary shocks. This is done by studying electron velocity distributions observed both upstream and downstream of interplanetary shocks observed by ISEE 3 between August 1978 and December 1979. It is found that perpendicular heating accompanied by little or no parallel heating occurs at the weaker shocks but that parallel heating is dominant for the stronger shocks. When perpendicular heating is dominant, downstream velocity distributions are for the most part Gaussian at low energies (core) and Lorentzian at high energies (halo). When parallel heating is dominant, however, these distributions are flat-topped at low energies, having power law extensions to higher energies. At the weaker shocks, the observations are consistent with electron heating resulting from conservation of the magnetic moment, whereas at the stronger shocks the heating is quite similar to that observed at the earth's bow shock.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 9949-995
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  • 37
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    Sharp shortward-shifted features in the spectra of O subdwarfs (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Preliminary inspection of archival high-dispersion ultraviolet spectra obtained by the International Ultraviolet Explorer reveal sharp shortward-shifted features in the spectra of O subdwarfs. In three examples presented here, BD + 75.325 deg, HD 128220 B, and BD + 28.4211 deg, stable, multiple, discrete shortward-shifted components of the N V, C IV, and Si IV resonance doublets are seen. The available data suggest that some of these features are persistent, being relatively stable in velocity and intensity over at least 9 months. It is tentatively suggested that the mechanism, or mechanisms, producing these discrete features operates universally in hot stars, from luminous O and B stars down through the O subdwarfs to include the hot white dwarfs. If true, this has important ramifications for current knowledge of mass loss in hot stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L87-L91
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  • 38
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    Images in the rocket ultraviolet - The starburst in the nucleus of M83 (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Ultraviolet images of the SAB(s)c I-II galaxy M83 (NGC 5236) obtained with a rocketborne telescope in broad bandpasses centered at 1540 A and 2360 A show a bright resolved nuclear source which accounts for approximately 20 percent of the flux of the galaxy in both bandpasses. Low-resolution International Ultraviolet Explorer spectra of this source reveal an energy distribution similar to that of the starburst nucleus of NGC 7714. Strong blueshifted absorption lines can be interpreted as evidence for a nuclear wind powered by supernovae. Observations from UV, X-ray, optical, and far-infrared bandpasses are consistent with a starburst approximately one-sixth as strong as that in M82. A scaling of the M82 models of Rieke et al. (1980) predicts that the nucleus of M83 contains 10 to the 6th - 3 x 10 to the 7th solar masses in young stars and has a supernova rate of approximately 0.01 per yr.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L53-L56
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  • 39
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    X-ray observations of LMC X-3 with the monitor proportional counter aboard the HEAO 2 Einstein observatory - A comparison with Cygnus X-1 (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A comparison is presented of the black hole candidates LMC X-3 and Cygnus X-1 based on Einstein observations of LMC X-3 with the monitor proportional counter. A spectral analysis shows LMC X-3 to be more like the typical bright galactic X-ray source than Cygnus X-1. A search for periodic pulsations over a period range from 0.2 ms to over 1000 s set upper limits at the 90 percent confidence level of the order of 10 percent. An analysis of the aperiodic variability of LMC X-3 shows none of the shot noise behavior characteristic of Cygnus X-1. The absence of distinctive X-ray properties common to both sources suggests that the identification of black hole candidates on the basis of X-ray properties similar to Cygnus X-1 (or LMC X-3) is not reliable.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L65-L69
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  • 40
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    Stellar evolution in N-body simulations of disk galaxies. I (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Kalnajs (1972, 1976) Omega models of global mass and velocity distributions are employed in the present two-dimensional N-body simulation, which allows for a spectrum of particle masses, stellar explosions, explosion remnant interactions with an interstellar medium, and the creation of new stars from the gas. Two sequences of runs using the Omega values of 0.8 and 0.9 examine the separate and combined effects of particle mass distribution, the gravitational influence of an interstellar gas distribution on the N-body particles, and stellar evolution, allowing for stellar explosions and star formation from the gas. It is found that both Omega values' nonequilibrium results dramatically change when evolution is allowed to occur. These results call for more realistic coupled N-body and evolution simulations in order to improve the understanding of disk galaxy evolution.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 595-610
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  • 41
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    The (an)isotropy of the X-ray sky (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: An assessment is made of the extent to which the study of the isotropy of the X-ray sky has contributed to the present understanding of the structure of the universe at moderate redshifts. It is, of course, the anisotropic character of the sky flux that is valuable in this context. Although it is not currently possible to undertake measurements with the precision and small solid angles that are typically achieved in the microwave range, the comparatively crude limits from the X-ray fluctuations place limits on the largest scale structure of the universe. After indicating the nature of measurements made, with the HEAO 1 A-2 experiment, of the X-ray sky and its anisotropies, it is shown how these place limits on the origin of the X-ray sky and on any large scale structure of the universe.
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  • 42
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    Comments concerning magnetic fields as a possible cause of rapid, irregular variability of early-type stars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is noted that it is helpful to divide the atmosphere of an early-type star into two parts: a photosphere and a mantle. The photosphere can be modeled satisfactorily by normal model-atmosphere procedures. When modeling the mantle, one must take account of the deposition of nonradiative heat and momentum and one should recognize that the mantles of hot stars do not appear to be uniform or spherically symmetric. Five areas of discrepancy between classical theory and observation are noted and a possible way of modeling the mantles of early-type stars is outlined. The model consists of arcades of magnetic loops which form helmet-type structures in the equatorial band of the star, and of coronal-hole-type structures emmanating from weak unipolar regions which are chiefly distributed at polar latitudes.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Hvar Observatory, Bulletin (ISSN 0351-2651); 7; 1, 19
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  • 43
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    Observational knowledge about the physical properties of O stars (1983)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Information about the effective temperatures, radii, and masses of O-type stars is presented. It is argued that rapid variations in the amount of light from O stars and the spectral distribution are a result chiefly of changes which occur in the envelope of the star. The stability of the photospheric layers of O stars against convection is reviewed and it is noted that late O stars and early B stars have a convection zone in the deeper parts of the photosphere. This convection zone is due to the second ionization of helium. Evidence is reviewed that most of the line-profile changes seen for O stars are generated by changes in the physical state of the mantle of the star, that is of the outer atmosphere where the deposition of non-radiative energy and momentum controls the physical state of the atmosphere. The physical state of the mantle may change in response to changes in the upper envelope of a star with a different time constant than the photosphere does.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Hvar Observatory, Bulletin (ISSN 0351-2651); 7; 1, 19; 1-15; Di
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  • 44
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    The Crab Nebula's progenitor (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The initial mass of the Crab Nebula's progenitor star is estimated by comparing the observed nebular chemical abundances with detailed evolutionary calculations for 2.4- and 2.6-solar-mass helium cores of stars with masses of 8 to 10 solar masses. The results indicate that the mass of the Crab's progenitor was between the upper limit of about 8 solar masses for carbon deflagration and the lower limit of about 9.5 solar masses set by the dredge-up of the helium layer before the development of the helium-burning convective region. A scenario is outlined for the evolution of the progenitor star. It is suggested that the Crab Nebula was probably the product of an electron-capture supernova.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 299; Oct. 28
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  • 45
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    Cosmic turbulence and the angular momenta of astronomical systems (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is suggested that gravitationally bound astronomical systems ranging from asteroids to galaxy superclusters may derive their rotation from a hierarchy of cosmic turbulence, thus explaining the empirical specific angular momentum-mass relationship (j approximately equal to M to the 3/4 power) exhibited by these systems. It is shown that many of the properties of these systems, e.g., the random orientation of their spin vectors, can be accounted for if astronomical objects form in a turbulent environment.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 261
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  • 46
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    Relativistic kinematics for motions faster than light (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-20197)
    Schlagwort(e): ASTROPHYSICS
    Materialart: vol. 35; Nov. 198
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  • 47
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    On vibration control of tethered satellite systems (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The general dynamics of a shuttle supported tethered subsatellite system taking into account the longitudinal and three dimensional transverse vibrations is considered. It is noted that control of inherently unstable dynamics during retrieval of the subsatellite can be carried out by letting the rate of change length depend on the state variables in an appropriate manner. Control laws using linear feedback of inplane state variables and nonlinear feedback of out-of-plane state variables are proposed.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 317-327
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  • 48
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    A design procedure for active control of beam vibrations (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The transverse vibrations of beams is discussed and a methodology for the design of an active damping device is given. The Bernoulli-Euler equation is used to derive a transcendental transfer function, which relates a torque applied at one end of the beam to the rotational position and velocity at that point. The active damping device consists of a wire, a linear actuator and a short torque arm attached to one end of the beam. The action of the actuator varies a tension in the wire and creates a torque which opposes the rotation of the beam and thus damps vibration. A design procedure for such an active damper is given. This procedure shows the relationships and trade-offs between the actuator stroke, power required, stress levels in the wire and beam and the geometry of the beam and wire. It is shown that by consideration of the frequency response at the beam natural frequencies, the aforementioned relationships can be greatly simplified. Similarly, a simple way of estimating the effective damping ratios and eigenvalue locations of actively controlled beams is presented.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 305-316
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  • 49
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    Orbiting chains and rings (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Two very different, highly flexible, space structures proposed during the last decade which involve analytical solution of certain partial differential equations are discussed. The first structure is an array, or hanging chain of aluminum beads which would serve as a convenient communicator if, under the influence of the Earth's gravity gradient, it assumes a local vertical orientation as it circles the Earth. Two passive schemes have been proposed for damping the rigid modes: twist the wire at the ends to provide non-zero moment of inertia about the vertical, thereby inducing relative motion of the two tips during rigid pitch or roll, and thus exercising a damper; and introduce weak lossy springs between the end sections and the main section; thereby providing linear coupling between the springs and all the in-plane (pitch) modes. The second structure is a complete ring of satellites cabled together at synchronous altitude. By a slight increase in altitude, the cable is in tension. This configuration is, however, unstable, and an active feedback control scheme is required to stabilize it. A possible scheme involves local cable length adjustment based on measurement of local altitude and shape variations and their rates.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 329-336
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  • 50
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    Number and placement of control system sensors considering possible failures (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A methodology has been presented which is intended to assist the designer of a control system for a large space structure to decide how many sensors should be incorporated in the system and where they should be placed on the structure. This approach is intended to be especially useful in the early stages of the evolution of the system, before a complete control system concept has been defined. This methodology is based on a quantitative measure of the observability of the system for a given set of sensors. The effect of possible component failures during the mission period was incorporated in the measure. The question of sensor placement is then resolved by finding the locations which maximize the performance measure. The number of components to use cannot be determined by optimizing the measure because the observability always improves with increased number of sensors if they are optimally located. However, the improvement in the measure with component number can be determined, and this information can be used along with data on cost, power required, etc., to decide how many sensors to use.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 253-268
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    Active Control of Space Structures (ACOSS) model 2 (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A complete description of the active control of space structures model #2 which is a simple but realistic evaluation model is given. The design of this system was driven by the desire to incorporate certain attributes into the overall system characteristics. The desired features were structural design based on realistic sizes and weights; a simple unclassified optical system with associated performance measures and tolerance; and a set of disturbances typical of equipment vibration and attitude control (slew). The resulting model is described in detail along with the resulting mode shapes and natural frequencies of the system. A description of the line-of-sight performance measure including theory and implementation is given.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 195-210
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  • 52
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    Introduction and survey on continuum models for repetitive lattice structures (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A brief introduction and survey to aid and familiarize researchers interested in the use of continuum modeling procedures applied towards large space structure technology are presented. The use of such structural models for the distributed control of large flexible lattice structures offers a significant advantage over a numerical approach.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 63-70
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  • 53
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    Control of flexible structures: A systematic overview of the problem (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A way of designing a control system using a finite model that accounts for the distributed nature of the control problem in a systematic way is described. This is accomplished by using a mode description of the system and from that description determining the number of modes that must be retained based on the performance and the disturbance descriptions. The design then uses a full order model that includes all of the dynamics: sensor, actuator, disturbance and flexible motion. The designs that result are simple, robust, perform well and have the added distinction of being easy to implement.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 49-61
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    Minimum information modelling of structural systems with uncertain parameters (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Work is reviewed wherein the design of active structural control is formulated as the mean-square optimal control of a linear mechanical system with stochastic parameters. In practice, a complete probabilistic description of model parameters can never be provided by empirical determinations, and a suitable design approach must accept very limited a priori data on parameter statistics. In consequence, the mean-square optimization problem is formulated using a complete probability assignment which is made to be consistent with available data but maximally unconstrained otherwise through use of a maximum entropy principle. The ramifications of this approach for both robustness and large dimensionality are illustrated by consideration of the full-state feedback regulation problem.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 71-88
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    On the analytical modeling of the nonlinear vibrations of pretensioned space structures (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Pretensioned structures are receiving considerable attention as candidate large space structures. A typical example is a hoop-column antenna. The large number of preloaded members requires efficient analytical methods for concept validation and design. Validation through analyses is especially important since ground testing may be limited due to gravity effects and structural size. The present investigation has the objective to present an examination of the analytical modeling of pretensioned members undergoing nonlinear vibrations. Two approximate nonlinear analysis are developed to model general structural arrangements which include beam-columns and pretensioned cables attached to a common nucleus, such as may occur at a joint of a pretensioned structure. Attention is given to structures undergoing nonlinear steady-state oscillations due to sinusoidal excitation forces. Three analyses, linear, quasi-linear, and nonlinear are conducted and applied to study the response of a relatively simple cable stiffened structure.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
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  • 56
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    Water as a probe of star-forming regions (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Preliminary calculations employing statistical equilibrium techniques were carried out to determine brightness temperatures of water transitions occurring in the submillimeter band. The interesting candidates appear to be the 325 GHz, 380 GHz, and 448 GHz transitions, they are compared with the 183 GHz and 380 GHz transitions observed in the Orion Kleinmann-Low nebula and the combined results seem to be consistent with H2 densities of 100,000 -1 million cm-3 and a water column density of approximately 10 to 18th power. This implies a relative abundance of approximately 0.00001 which means that water may be about one twentieth of CO. In addition, it was found that for the conditions of the Orion plateau source, the 448 GHz line is expected to be a mild maser.
    Schlagwort(e): ASTROPHYSICS
    Materialart: ESA The Sci. Importance of Submillimetre Observations; p 129-130
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    Radiation from the accretion column of magnetized neutron stars (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Some developments in radiative transfer for magnetized neutron star conditions, and their application in models of the structure and properties of self-consistent polar cap emission regions are reviewed. Several of the assumptions and uncertainties involved are discussed, and present problems are indicated.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Max-Planck Inst. Phys. and Astrophys. Accreting Neutron Stars; p 253-274
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    Advanced rocket propulsion technology assessment for future space transportation (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Single-stage and two-stage launch vehicles were evaluated for various levels of propulsion technology and payloads. The evaluation included tradeoffs between ascent flight performance and vehicle sizing that were driven by engine mass, specific impulse, and propellant requirements. Numerous mission, flight, and vehicle-related requirements and constraints were satisfied in the design process. The results showed that advanced technology had a large effect on reducing both single- and two-stage vehicle size. High-pressure hydrocarbon-fueled engines that were burned in parallel with two-position nozzle hydrogen-fueled engines reduced dry mass by 23% for the two-stage vehicle and 28% for the single-stage vehicle as compared to an all-hydrogen-fueled system. The dual-expander engine reduced single-stage vehicle dry mass by 41%. Using advanced technology, the single-stage vehicle became comparable in size and sensitivity to that of the two-stage vehicle for small payloads.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Journal of Spacecraft and Rockets; 19; July-Aug
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  • 59
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    Spectral evolution of active galactic nuclei - A unified description of the X-ray and gamma-ray backgrounds (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-22137)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 260
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  • 60
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    On OMC-1 temperatures determined from methyl cyanide observations (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: An analysis is performed on the J(k) = 12(k)-11(k) and 13(k)-12(k) transitions of methyl cyanide detected by other investigators in the direction of OMC-1. The original interpretation of those observations argues for the presence of two distinct temperature regions or possibly a temperature gradient within the cloud. The analysis presented here demonstrates that the observations of these particular molecular transitions are consistent with a single methyl cyanide emission region with a source kinetic temperature of 121.2 + or - 8.2 K and a molecular rotational temperature of 16.6 + or - 1.8 K.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 260
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  • 61
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    A large scale height galactic component of the diffuse 2-60 keV background (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The diffuse 2-60 keV X-ray background has a galactic component clearly detectable by its strong variation with both galactic latitude and longitude. This galactic component is typically 10 percent of the extragalactic background toward the galactic center, half that strong toward the anticenter, and extrapolated to a few percent of the extragalactic background toward the galactic poles. It is acceptably modeled by a finite radius emission disk with a scale height of several kiloparsecs. The averaged galactic spectrum is best fitted by a thermal spectrum of kT about 9 keV, a spectrum much softer than the about 40 keV spectrum of the extragalactic component. The most likely source of this emission is low luminosity stars with large scale heights such as subdwarfs. Inverse Compton emission from GeV electrons on the microwave background contributes only a fraction of the galactic component unless the local cosmic ray electron spectrum and intensity are atypical.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 260
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  • 62
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    BL Herculis stars - Theoretical models for field variables (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Type II Cepheids with periods between 1 and 3 days, commonly designated as Bl Herculis stars, have been modeled here with the aim of interpreting the wide variety of light curves observed among the field variables. Previously modeled globular cluster members are used as standard calibration objects. The major finding is that only a small range of luminosities is capable of generating a large variety of light curve types at a given period. For a mass of approximately 0.60 solar mass, the models are able to reproduce the observed mean luminosities, dispersion of mean luminosities, periods, light amplitudes, light asymmetries, and phases of secondary features in the light curves of known BL Her stars. It is possible that the metal-rich variables (which are found only in the field) have luminosities lower than those of most metal-poor variables. The present revised mass for BL Her, a metal-rich object, is not significantly different from the mean mass of the metal-poor variables.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 259
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    A heuristic criterion for instability to fragmentation in rotating, interstellar clouds (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A heuristic criterion, based on linear perturbation analysis, is applied to the initial growth of density perturbations in isothermal or adiabatic gas clouds, with initially uniform density and uniform rotation. The heuristic criterion is shown to be consistent with the available results from numerical calculations of cloud collapse. The criterion predicts that perturbations varying as cos(m-phi) will be most likely to grow when m is small, unless the cloud is nearly pressureless.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 259
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    High energy X-ray observations of Cyg X-3 from OSO-8 - Further evidence of a 34.1 day period (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-18085)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Letters; 22; 4, 19; 1982
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    Neutron star collisions and the r-process (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that a natural consequence of the binary pulsar's evolution is a neutron star collision. Such a collision is expected to eject neutron-rich matter of an r-process character. Taking reasonable estimates for the number of such events over the history of the galaxy, it may be that they account for all of the r-process nuclei.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Letters; 22; 4, 19; 1982
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  • 66
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    The peculiar variable star R Aquarii and its jet (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observations of the variable star R Aquarii from 1928 to the present are examined to conclude that the star is a binary system with a jet. The orbital period of the objects is estimated at 22 yr, and a supercritical mass transfer that occurs once every 44 yr is suggested as a mechanism to explain deep minima observed on two occasions that many years apart. Calculations presented for the critical accretion rate of the two Miras indicated that one of the objects possesses a substantially stronger gravitational field than the other and features a large accretion disk. Oriental astronomical records from 930 AD are cited as evidence that a nova occurred in the vicinity of R Aquarii at that time. The system is noted to be the closest jet thus far observed, and the accretion disk may be visible with the Space Telescope.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 298; Aug. 5
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    The photospheric velocity field of Procyon (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Balloon-borne Ultraviolet Stellar Spectrometer observations of the profiles of two well observed spectral lines in the ultraviolet spectrum of Alpha CMI (Procyon; F5IV-V) are analyzed with a Fourier transform method in order to determine values of various parameters of the velocity field of the upper photosphere. A microturbulent line-of-sight velocity component of 0.9 + or - 0.4 km/s, a macroturbulent velocity component of 5.3 + or - 0.2 km/s, and a rotational velocity component of 10.0 + or - 1.2 km/s were determined. In these calculations a single-moded sinusoidal isotropic macroturbulent velocity function was assumed. The result appears to be sensitive to the assumed shape of the macroturbulence function.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science; 84; 2, Ju; June 198
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    On the structure of the outer layers of cool carbon stars (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Exposures on the spectra of four late C-type stars have been made with the IUE satellite in the wavelength range of the LWR camera (1900-3200 A). Two Mira variables near maximum light and two semiregular variables were observed. Although the exposure times used, which range up to 240 min in the low-resolution mode, were more than sufficient to record the continuum and emission lines of Mg II, Fe II, and Al II in normal M stars of similar magnitude and temperature, no light was recorded. It is concluded that the far-ultraviolet continuum is strongly depressed in these cool carbon stars. The absence of UV emission lines implies either that the chromospheric lines observed in M stars require an ultraviolet flux for their excitation, or that cool carbon stars have no chromosphere at all or that the opacity source is located above even the emission-line-forming region. This opacity source, which is probably some carbon condensate since it is weak or absent in M stars while absorbing strongly in C stars, is discussed both in terms of the chromospheric interpretation of the emission lines and in terms of their shock-wave interpretation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 111; 1, Ju; July 198
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    A precessing relativistic jet model for 3C 449 (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that the radio structure of 3C 449 can be matched with a model in which the jets are precessing and have relativistic (beta greater-than or equal to 0.4) velocities. The best-fit model implies a precession period of about 100,000 yr and a cone angle which increases with time. A similar model may be relevant for the radio structure of 3C 31. A brief discussion of the implications for 3C 449 is given.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 258
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  • 70
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    Collapse of accreting, rotating, isothermal, interstellar clouds (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The evolutions of the envelopes of collapsing, accreting, isothermal clouds have been numerically calculated for both spherically symmetric and rotating (axisymmetric) clouds. The results provide a cohesive picture of isothermal collapse, and their relationship to previous numerical calculations and similarity solutions is discussed. Even with a large initial rotation rate, the majority of the cloud envelope is accreted, in one case leaving behind a large-scale circulation current. The calculations are performed for both initially uniform density and centrally condensed clouds. Density and velocity profiles for a wide variety of observed systems are compared with those obtained in this study, providing a preliminary assessment of the stage of evolution and initial structure for the observed systems.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 258
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    Laboratory measurements of amorphous silicate smokes and the infrared spectra of oxygen-rich stars (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The infrared spectra of smokes condensed from SiO-H2 and Mg-SiO-H2 vapors and of smoke samples annealed for various times at 1000 K and 1250 K are presented. The spectra of these materials show features in the 8-25 micron interval in addition to the well-known bands near 10 and 20 microns. It is suggested that these features may correspond to weak structures that can be seen in the infrared spectra of oxygen-rich stars. Observations are needed to determine the reality and characteristics of such weak features.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 257
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    The distribution of free electrons in the inner Galaxy from pulsar dispersion measures (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-18096)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 257
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    Star formation - The influence of velocity fields and turbulence (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is shown that the Jeans mass for gravitational collapse can be very much reduced by the influence velocity fields, even when allowance is made for non-isothermal gas behavior. We examine the role of turbulence in establishing the initial stellar mass function and show that the flattening and/or turnover at the low mass end may be a signature of interstellar turbulence. We consider also the implications of primordial turbulence for the formation of stars in the early universe.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 256
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  • 74
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    Effect of storable propellants on single-stage earth-to-orbit vehicles (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A comparison is made between the storable-propellant engine and an equivalent dual-expander engine using oxygen, propane, and hydrogen propellants. The propane and hydrogen dual-expander engine is then compared with previous results with separate propane and hydrocarbon engines. It is shown that the dual-expander reduces vehicle dry mass from 94 to 89 Mg, or 5%. The hydrogen-only thrust of the dual-expander is 0.4 MN, while the separate hydrogen engines have a thrust of 2.3 MN. The low thrust level increases the difficulty of cooling the dual-expander engine, and additional hydrogen flow is added for transpirational cooling. This additional hydrogen flow leads to an increase in the hydrogen tank size. It is also shown that storable propellants increase the dry mass of single-stage earth-to-orbit vehicles by about 20% and the gross mass by about 54%. It is concluded that dual-expander engines should be studied with several thrust splits and thrust levels.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Journal of Spacecraft and Rockets; 19; May-June
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    A model of a comet coma with interstellar molecules in the nucleus (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The coma of a comet is modeled assuming the icy nucleus contains interstellar molecules. This composition overcomes discrepancies between observation and earlier model predictions for CN, C2, C3, and NH2 abundances. It is found that the abundances of CN, C2, and C3-bearing compounds in the nucleus must be constrained to trace amounts in order to account for the observed column densities. NH3 also cannot be abundant by more than about 1%. The model gives good agreement with observed relative ranges of neutral species in the coma as well as with their observed relative intensity dependence on heliocentric distance. The size of the nucleus and the heliocentric ranges considered are relevant to comet Halley.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 108; 2, Ap; Apr. 198
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    Radial evolution of power spectra of interplanetary Alfvenic turbulence (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-18097)
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research; 87; May 1
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    Infrared emission line studies of the structure and excitation of H II regions (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Maps of five H II regions in one or more of the infrared fine-structure lines of Ne II (12.8 microns), Ar III (9.0 microns), and S IV (10.5 microns) have been obtained with angular resolutions ranging from 4 to 7 arcsec. The observations are used to discuss the morphology and excitation of these nebulae. Considerable diversity is found in the structures of the nebulae, probably resulting from differences in their ages and the circumstances of their formation. In all cases, more ionizing luminosity than would be provided by a single dominant ionizing star appears to be required, although uncertainties in the model nebulae make this conclusion uncertain.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 255
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    Evidence for extended X-ray emission from globular clusters (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Deep exposures with the Einstein Observatory show evidence for diffuse X-ray emission from three globular clusters. One possible interpretation of these observations is that the interaction between a cluster wind and a hot gaseous galactic halo is being observed. The one cluster for which the proper motion has been measured is consistent with this interpretation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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    A different type of maser star (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A systematic survey of short-period, semiregular variable stars has been made resulting in the detection of six new water masers. Of the 14 short-period maser stars now known, nine are classified as SRb variables. All are very late spectral type SRb's, typically M7, while the overwhelming majority of normal SRb stars is M4 to M6. Their 2.2-11 micron color indices are among the lowest of any known maser stars. They are presumably less dusty as well. Four of the SRb stars and two of the remainder do not obey the correlation between period and velocity spread of the emission features that is found for the Mira and long-period, semiregular variables. Finally, high galactic latitudes dominate; 13 of the 14 are in excess of 13 deg, and nine of these are greater than 25 deg. These facts suggest that the short-period semiregular variables - particularly in SRb stars - may be a very different type of maser star than the Mira and long-period semiregular variables.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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    The discovery of 50 minute periodic absorption events from 4U 1915-05 (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: An analysis of X-ray observations shows that the steady flux from 4U 1915-05 undergoes periodic absorption dips with a period of 50 minutes. This period most probably represents the underlying orbital period of the system, and variations in the depth and duration of these events suggest that they are caused by a bulge on the edge of the accretion disk at the point where the gas stream impacts the disk. The mass-losing star in this system is probably a low-mass white dwarf, and the spectrum of the dips indicates that the metallicity of the absorbing material is at least a factor of 17 below solar values. The discovery of the 50-minute binary period supports earlier suggestions that X-ray burst sources are in binary systems.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 253
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    Search for interstellar superheavy hydrogen (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Models for fundamental physical interactions allow for the existence of stable or nearly stable elementary particles much heavier than the proton. Stellar spectra were searched for a positively charged superheavy particle, X(+), which, with a bound electron, should appear as apparently superheavy neutral hydrogen in the interstellar medium. An upper limit for the abundance of X relative to normal hydrogen in the line of sight toward the bright star gamma Cassiopeiae is 2 x 10 to the -8th.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Science; 216; Apr. 2
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    Resonant electrodynamic heating of stellar coronal loops - An LRC circuit analog (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The problem of electrodynamic coupling of stellar coronal loops where beta is less than 1 to underlying velocity fields where beta is greater than approximately 1 is treated. A rigorous analysis reveals that the physics can be represented by a simple yet equivalent LRC circuit analog. This derived analog suggests the existence of global structure oscillations which resonantly excite internal field line oscillations at a spatial resonance within the coronal loop. Even though the width of this spatial resonance, as well as the induced currents and coronal velocity field, within the resonance region explicitly depends on viscosity and resistivity, the resonant form of the generalized electrodynamic heating functions is virtually independent of irreversibilities. This is a classic feature of high-quality resonators that are driven externally by a broad-band source of spectral power.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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    Observations of interstellar zinc (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: IUE observations toward 10 stars have shown that zinc is not depleted in the interstellar medium by more than a factor of two, suggesting that its abundance may serve as a tracer of the true metallicity in the gas. A result pertinent to the history of nucleosynthesis in the solar neighborhood is that the local interstellar medium has abundances that appear to be homogeneous to within a factor of two, when integrated over paths of about 500 pc.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 254
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  • 84
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    Electromagnetic cascades in pulsars (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The development of pair-photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters, and follows the curvature radiation emitted by the primary, the conversion of this radiation to e(+)e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma-ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma-ray spectrum above 25 MeV, and that the final gamma-ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 252
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  • 85
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    Model atmospheres, predicted spectra, and colors (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Theoretical models of stellar atmospheres and the process of forming a spectrum are reviewed with particular reference to the spectra of B stars. In the case of classical models the stellar atmosphere is though to consist of plane parallel layers of gas in which radiative and hydrostatic equilibrium exists. No radiative energy is lost or gained in the model atmosphere, but the detailed shape of the spectrum is changed as a result of the interactions with the ionized gas. Predicted line spectra using statistical equilibrium local thermodynamic equilibrium (LTE), and non-LTE physics are compared and the determination of abundances is discussed. The limitations of classical modeling are examined. Models developed to demonstrate what motions in the upper atmosphere will do to the spectrum and to explore the effects of using geometries different from plane parallel layer are reviewed. In particular the problem of radiative transfer is addressed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: B stars With and Without Emission Lines, Parts 1 and 2; p 165-197
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  • 86
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    Isolated grain condensation behavior: Computation methods and first results (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A set of efficient programs for calculation of condensation behavior in a system with either solar or carbon-rich elemental composition was developed to treat the course of condensation at very low pressures. These programs were applied to the problem of condensation at very low pressures. The minerals produced in the stellar and nova-related processes under study, including carriers of important volatile elements such as carbon and nitrogen, are candidates for accretion into meteorite parent bodies and planets, and may still be discernible in the enstatite chondrites.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Planetary Atmospheres Program; p 36-47
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  • 87
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    Numerical models for cometary dust environments (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The development of a numerical model for the dust environment near a comet is described. The major components of the model are a simple treatment of the acceleration of the dust by the gas outflow from an isothermal icy nucleus, a detailed treatment of the dust particle trajectories controlled by solar gravity and radiation pressure, including the formation of the dust envelope and tail, and a simple treatment of the radiation from the dust in the visible and thermal infrared. The results of recent comet observations are used to estimate parameter values for the model, including dust-to-gas ratios by light and by mass, the distribution of dust and gas emission on the nuclear surface, the distributions of dust particle size, density, mass, and radiative properties, and other quantities. Gas and dust production rates as functions of time are derived from observed light curves using the simple photometric theory. Sample results are presented for the dust concentration, flux and fluence along the trajectory of a spacecraft which flies by Comet P/Halley in 1986.
    Schlagwort(e): ASTROPHYSICS
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  • 88
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    An outer ion coma model in two dimension (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A simple cometary outer ion coma model is constructed by adopting published results from numerical MHD computations. The ion composition and density distributions so derived are used to highlight some of the basic features of cometary plasma flows and the need for cometary ion observations with absolute brightness calibration.
    Schlagwort(e): ASTROPHYSICS
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  • 89
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    Search for hydrogen atoms and the noble gas abundances in the head of Comet Schwassmann - Wachmann 1 (1974 II) from Voyager 2 UVS spectra (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): ASTROPHYSICS
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  • 90
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    The nature of cometary dust from remote sensing (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observational data on the thermal emission from cometary dust grains and theoretical models constructed to explain them are reviewed. Consideration is given to grain temperature, the size distribution of the grains, thermal-emission models, the silicate component, dust-grain albedo, and icy grains; model predictions and observations are compared in graphs. It is pointed out that no unambiguous detection of icy grains has been achieved, probably because these grains are vaporized within a few hundred km of the nucleus when the comet is within 2.5 AU of the sun.
    Schlagwort(e): ASTROPHYSICS
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  • 91
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    Electromagnetically-tracked free-mass gravitational wave antennas (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The response to a gravitational wave of two free masses whose relative motion is monitored with an electromagnetic tracking signal is derived. The results indicate a two-feature signature in one-way data and a three-feature signature in two-way data. The effect is applied to gravitational wave experiments using laser interferometers, spacecraft Doppler tracking, planetary ranging, and pulsar timing analysis. Actual results are presented from spacecraft Doppler experiments and from pulsar timing data analysis, with new upper limits being set on a possible cosmic gravitational wave background via the pulsar data.
    Schlagwort(e): ASTROPHYSICS
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  • 92
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    Infrared properties of extragalactic H II complexes (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Infrared observations of relatively isolated giant H II complexes in the LMC and the spiral arms of M33 and M101 are discussed, and complexes which extend over several kiloparsecs near the galactic centers are examined. The 30 Doradus nebula is emphasized, showing the variation of the 50-100 micron color temperature with position in that object. Ten-micron scans through the nucleus of NGC 1097 are compared to a visual photograph, showing the enhanced infrared emission which occurs at the nucleus and at the ring of H II regions about 1 kpc from the nucleus.
    Schlagwort(e): ASTROPHYSICS
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  • 93
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    Control structure interactions in large space structures Analysis using energy approach (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A simple energy approach to study the problem of control structure interactions in large space structures is presented. For the illustrative cases of free-free beam and free rectangular plate, the vibrational energy imparted during operation of constant and pulsed thrusters is found in a nondimensional form. Then based on a parametric study, suggestions are made on the choice of the thruster location and parameters to minimize the control structure interactions.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Aeronautical Society of India, Journal (ISSN 0001-9267); 35; 59-67
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  • 94
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    Theory of electron-positron showers in double radio sources (1982)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A black hole of mass of about 300 million solar masses is assumed to be present in the nucleus of an active galaxy or quasar. With an axial magnetic field near 1000 gauss, a potential drop 10 to the 19th volts is generated by the unipolar induction of a rotating accretion disk surrounding the black hole. The possibility that the acceleration of electrons or positrons in the unipolar fields initiates an electromagnetic cascade shower at distances at least 10 to the 16th cm from the black hole is investigated. The scattering medium for the shower is considered to be the spectrum of low energy photons originating from the inner region of the disk. It is found that at completion of the cascade, power-law energy spectra of relativistic electrons and positrons and of gamma-rays emerge under appropriate conditions. If the cascade-initiating particles are collimated, the electrons and positrons emerge in a collimated beam. Such beams may power extragalactic double radio sources.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 262
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  • 95
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    Approximation in control of flexible structures, theory and application (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The sense in which the feedback control law based on an approximate finite dimensional model of a continuous structure approximates a control law which is optimal for the distributed, or infinite dimensional, model of the structure is studied. From the analysis of the various control and stability issues associated with this basis question, useful information for designing finite dimensional compensators which produce near-optimal performance in infinite dimensional systems is gained. Some of the important predictions that can be made about large-order finite dimensional control laws, using the theory of infinite dimensional Riccati equations are indicated.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 383-389
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  • 96
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    Analysis of structural perturbations in systems via cost decomposition methods (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: It has long been common practice to analyze linear dynamic systems by decomposing the total response in terms of individual contributions which are easier to analyze. Examples of this philosophy include the expansion of transfer functions using: (1) the superposition principle, (2) residue theory and partial fraction expansions, (3) Markov parameters, Hankel matrices, and (4) regular and singular perturbations. This paper summarizes a new and different kind of expansion designed to decompose the norm of the response vector rather than the response vector itself. This is referred to as "cost-decomposition' of the system. The notable advantages of this type of decomposition are: (a) easy application to multi-input, multi-output systems, (b) natural compatibility with Linear Quadratic Gaussian Theory, (c) applicability to the analysis of more general types of structural perturbations involving inputs, outputs, states, parameters. Property (c) makes the method suitable for problems in model reduction, measurement/actuator selections, and sensitivity analysis.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 465-475
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  • 97
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    Fixed-order dynamic compensation through optimal projection (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: This paper reviews a formulation for the design of fixed-order dynamic compensation for flexible mechanical systems which is based upon explicit optimality conditions derived under the minimum data/maximum entropy stochastic modelling approach. The optimality conditions give rise to the novel concept of "optimal projection' which provides significant insight with regard to the compensator structure and permits earlier, more restricted and/or ad hoc design schemes to be seen as special cases of the present formulation.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 409-425
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  • 98
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    Hardware verification of distributed/adaptive control (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Adaptive control techniques are studied for their future application to the control of large space structures, where uncertain or changing parameters may destabilize standard control system designs. The approach used is to examine an extended Kalman filter estimator, in which the state vector is augmented with the unknown parameters. The associated Riccatti equation is linearized about the case of exact knowledge of the parameters. By assuming that parameter variations occur slowly, the filter complexity is reduced further yet. Simulations on a two degree-of-freedom oscillator demonstrate the parameter-tracking capability of the filter, and an implementation on the JPL Flexible Beam Facility using an incorrect model shows the adaptive filter/optimal control to be stable where a standard Kalman filter/optimal control design is unstable.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 337-350
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    The TOYSAT structural control experiment (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Lockheed TOYSAT experiment is described. The experiment was designed to test hypothesis concerning the application of optimal control theory to flexible spacecraft. The theory is presented, and results described.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 269-285
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    The WC6 star HD76536 compact companion (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The variability of HD76536 was observed by IUE. Photometric variability is confirmed by measurements with the IUE fine error sensor. Profile changes in the ultraviolet emission lines and stellar wind absorptions were studied. Data favor a binary model with a low luminosity (perhaps compact) secondary.
    Schlagwort(e): ASTROPHYSICS
    Materialart: ESA 3rd European IUE Conf.; p 269-271
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