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  • 1
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    Globular cluster systems as clues to galaxy evolution (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We investigate the properties of systems of globular clusters in light of the hypothesis that galaxy mergers play a major role in galaxy evolution. In a previous paper, we presented a model in which the formation of globular clusters occurs during galaxy interactions and mergers. We discussed several predictions of the model, including the existence of young globular clusters in currently merging galaxies and the presence of two or more metallicity peaks in the globular clusters systems of normal elliptical galaxies. Here, we present recent observational evidence which supports both of these predictions and suggests that mergers may have a significant influence on the formation and evolution of galaxies and their globular clusters.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 48-49
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  • 2
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    On the design and development of a miniature ceramic gimbal bearing (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A review is made of a program to develop ceramic gimbal bearings for a miniaturized missile guidance system requiring nonmagnetic properties and higher load capacity than possible with conventional AISI 440C stainless steel bearings. A new gimbal design concept is described which utilizes the compressive strength and nonmagnetic properties of silicon nitride (Si3N4) ceramics for the gimbal bearing. Considerable manufacturing development has occurred in the last 5 years making ceramic bearings a viable option in the gimbal design phase. A preliminary study into the feasibility of the proposed design is summarized. Finite element analysis of the brittle ceramic bearing components under thermal stress and high acceleration loading were conducted to ensure the components will not fail catastrophically in service. Finite element analysis was also used to optimize the adhesive joint design. Bearing torque tests run at various axial loads indicate that the average running torque of ceramic bearings varies with load similarly to that of conventional steel bearings.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA, John F. Kennedy Space Center, The 24th Aerospace Mechanisms Symposium; p 289-300
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  • 3
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    Cockpit avionics integration and automation (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Information on cockpit avionics integration and automation is given in viewgraph form, with a number of photographs. The benefits of cockpit integration are listed. The MD-11 flight guidance/flight deck system is illustrated.
    Keywords: AIRCRAFT INSTRUMENTATION
    Type: NASA, Langley Research Center, Aviation Safety(Automation Program Conference; p 27-44
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  • 4
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    Performance of the PRAXyS X-Ray Polarimeter (2016)
    In:  Other Sources
    Details
    Publication Date: 2017-04-29
    Description: The performance of the Time Projection Chamber (TPC) polarimeter for the Polarimeter for Relativistic Astrophysical X-ray Sources (PRAXyS) Small Explorer was evaluated using polarized and unpolarized X-ray sources. The PRAXyS mission will enable exploration of the universe through X-ray polarimetry in the 2-10 keV energy band. We carried out performance tests of the polarimeter at the Brookhaven National Laboratory, National Synchrotron Light Source (BNL-NSLS) and at NASA's Goddard Space Flight Center. The polarimeter was tested with linearly polarized, monochromatic X-rays at 11 different energies between 2.5 and 8.0 keV. At maximum sensitivity, the measured modulation factors at 2.7, 4.5 and 8.0 keV are 27%, 43% and 59%, respectively and the measured angle of polarization is consistent with the expected value at all energies. Measurements with a broadband, unpolarized X-ray source placed a limit of less than 1% on false polarization in the PRAXyS polarimeter.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN41158 , Nuclear Instruments and Methods in Physics Research A (ISSN 0168-9002); Volume 838; 89-95
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  • 5
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    Performance Evaluation and Life Testing of the SPT-100 (1993)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: A cyclic endurance test of the Russian 1.35 kW Stationary Plasma Thruster SPT-100 is described.
    Keywords: Spacecraft Propulsion and Power
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  • 6
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    Does the Blazar Gamma-ray Spectrum Harden with Increasing Flux? - Analysis of Nine Years of EGRET Data (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) discovered gamma-ray emission from more than 67 blazars during its nine-year lifetime. We conducted an exhaustive search of the EGRET archives and selected all the blazars that were observed multiple times and were bright enough to enable a spectral analysis using standard powerlaw models. The sample consists of 18 flat-spectrum radio quasars (FSRQs), 6 low-frequency-peaked BL Lacs (LBLs) and 2 high-frequency-peaked BL Lacs (HBLs). We do not detect any clear pattern in'the variation of spectral index with flux. Some of the blazars do not show any statistical evidence for spectral variability. The spectrum hardens with increasing flux in a few cases. There is also evidence for a flux-hardness anticorrelation at lo\v fluxes in five blazars. The well observed blazars (3C 279,3C 273, PKS 0528-i-134, PKS 1622-297, PKS 0208- 512) do not show any overall trend in the long-term spectral dependence on flux, but the sample shows a mixture of hard and soft states. We observed spectral hysteresis at weekly timescales in all the three FSRQs for which data from flares lasting for 3 approx. 4 weeks were available. All three sources show a counterclockwise rotation despite the widely different flux profiles. Hysteresis in the spectral index vs. flux space has never been observed in FSRQs in gamma-rays at weekly timescales. itre analyze the observed spectral behavior in the context of various inverse-Compton mechanisms believed to be responsible for emission in the EGRET energy range. Our analysis uses the EGRET skymaps that were regenerated to include the changes in performance during the mission.
    Keywords: Astronomy
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  • 7
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    An Intriguing Convex Break in the EGRET SED of Mrk 421 (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Based upon analysis of the entire EGRET data from Mrk 421, it is found that the time-averaged spectra are inconsistent with the predictions of current theoretical models that have had success in describing simultaneous X-ray/TeV observations, and suggest additional components in the GeV band, as well as complex time variability. Current theoretical pictures explain the GeV emission as comptonization of the synchrotron photons in the jet, and predict hard spectra that should join smoothly with the TeV emission. Our analysis shows that the situation is more complex. The spectrum ranges from hard to soft during individual epochs, and shows a convext break in the aggregated data. We also present the mission-averaged EGRET spectrum for PKS 2155-304, which shows a similar (but not as pronounced) convex curvature. We discuss a series of possible explanations for the 10(exp 22) - 10(exp 23) HZ declining part of the EGRET nu F(sub nu), spectrum for Mrk 421, and suggest that it is synchrotron emission from the high energy tail of the electron population that produces the X-rays during the highest X-ray states. Such multi-MeV photons are produced by electrons accelerated close to the limit of diffusive shock acceleration. Simultaneous GLAST and X-ray observations of high X-ray states will address the issue of the convex curvature in the future.
    Keywords: Astrophysics
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  • 8
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    A full field, 3-D velocimeter for microgravity crystallization experiments (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The programming and algorithms needed for implementing a full-field, 3-D velocimeter for laminar flow systems and the appropriate hardware to fully implement this ultimate system are discussed. It appears that imaging using a synched pair of video cameras and digitizer boards with synched rails for camera motion will provide a viable solution to the laminar tracking problem. The algorithms given here are simple, which should speed processing. On a heavily loaded VAXstation 3100 the particle identification can take 15 to 30 seconds, with the tracking taking less than one second. It seeems reasonable to assume that four image pairs can thus be acquired and analyzed in under one minute.
    Keywords: MATERIALS PROCESSING
    Type: NASA-CR-188147 , NAS 1.26:188147
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  • 9
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    Circuit design tool. User's manual, revision 2 (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The CAM chip design was produced in a UNIX software environment using a design tool that supports definition of digital electronic modules, composition of these modules into higher level circuits, and event-driven simulation of these circuits. Our design tool provides an interface whose goals include straightforward but flexible primitive module definition and circuit composition, efficient simulation, and a debugging environment that facilitates design verification and alteration. The tool provides a set of primitive modules which can be composed into higher level circuits. Each module is a C-language subroutine that uses a set of interface protocols understood by the design tool. Primitives can be altered simply by recoding their C-code image; in addition new primitives can be added allowing higher level circuits to be described in C-code rather than as a composition of primitive modules--this feature can greatly enhance the speed of simulation.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-191361 , NAS 1.26:191361 , LCSR-TR-191-REV-2
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  • 10
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    NASA's nuclear thermal propulsion technology project (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The nonnuclear subsystem technologies required for incorporating nuclear thermal propulsion (NTP) into space-exploration missions are discussed. Of particular interest to planned missions are such technologies as materials, instrumentation and controls, turbomachinery, CFD modeling, nozzle extension designs and models, and analyses of exhaust plumes. NASA studies are described and/or proposed for refractory metals and alloys, robotic NTP controls, and turbopump materials candidates. Alternative nozzle concepts such as aerospikes and truncated plugs are proposed, and numerical simulations are set forth for studying heavy molecules and the backstreaming of highly reactive free-radical hydrogen in the exhaust plume. The critical technologies described in the paper are central to the development of NTP, and NTP has the potential to facilitate a range of space exploration activities.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 92-3581
    Format: text
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