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  • 1
    Publikationsdatum: 2011-08-24
    Beschreibung: The composition of the Earth's early atmosphere is a subject of continuing debate. In particular, it has been suggested that elevated concentrations of atmospheric carbon dioxide would have been necessary to maintain normal surface temperatures in the face of lower solar luminosity in early Earth history. Fossil weathering profiles, known as palaeosols, have provided semi-quantitative constraints on atmospheric oxygen partial pressure (pO2) before 2.2 Gyr ago. Here we use the same well studied palaeosols to constrain atmospheric pCO2 between 2.75 and 2.2 Gyr ago. The observation that iron lost from the tops of these profiles was reprecipitated lower down as iron silicate minerals, rather than as iron carbonate, indicates that atmospheric pCO2 must have been less than 10(-1.4) atm--about 100 times today's level of 360 p.p.m., and at least five times lower than that required in one-dimensional climate models to compensate for lower solar luminosity at 2.75 Gyr. Our results suggest that either the Earth's early climate was much more sensitive to increases in pCO2 than has been thought, or that one or more greenhouse gases other than CO2 contributed significantly to the atmosphere's radiative balance during the late Archaean and early Proterozoic eons.
    Schlagwort(e): Meteorology and Climatology
    Materialart: Nature (ISSN 0028-0836); Volume 378; 6557; 603-5
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2004-12-03
    Beschreibung: The development of a microcooler for operations below 80 K, for low temperature electronic devices requiring small cooling powers of the order of 10 mW is described. A sorption compressor combined with Joule-Thomson (JT) expansion was selected for miniaturization. The advantage of the system is considered to be its absence of moving parts, with the exception of the check valves. This facilitates the scaling down of the system, minimizes interferences and contributes to a long lifetime. The requirements for small scale cooling of low temperature electronics are listed. The sorption compressor and the JT expansion are described. A parameter study is reviewed together with the scaling of the sorption compressor.
    Schlagwort(e): Engineering (General)
    Materialart: Proceedings of the 6th European Symposium on Space Environmental Control Systems, volume 2; Volume 2; 489-496; ESA-SP-400-Vol-2
    Format: text
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  • 3
    Publikationsdatum: 2011-08-12
    Beschreibung: Gravitational and magnetic torque effect on rotational motion of triaxial rigid body in regressing orbit about oblate primary mass
    Schlagwort(e): SPACE SCIENCES
    Materialart: ; ERA, TP NO. 661, (
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2011-08-19
    Beschreibung: Surface plasmons on opposite sides of a thin metal film can cross couple in the presence of a surface corrugation, or grating. The observation of this cross-coupling phenomenon as a radiative-decay mechanism for molecules near a corrugated thin metal film is reported.
    Schlagwort(e): ATOMIC AND MOLECULAR PHYSICS
    Materialart: Physical Review Letters (ISSN 0031-9007); 56; 2838-284
    Format: text
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  • 5
    Publikationsdatum: 2016-06-07
    Beschreibung: The purpose of this presentation is to discuss the developmental approach to the Environmental Impact Statement regarding the X-33 vehicle.
    Schlagwort(e): Environment Pollution
    Materialart: Third Aerospace Environmental Technology Conference; 43-53; NASA/CP-1999-209258
    Format: application/pdf
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  • 6
    Publikationsdatum: 2018-06-08
    Beschreibung: We report the detection of Cepheid Variable stars in the barred spiral galaxy NGC925, using the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC2). Twelve V (F555W), four I (F814W) and three B (F439W) epochs of cosmic ray split observations were obtained. Eighty Cepheids were discovered, with periods from 6 to +-80 days. Light curves of the Cepheids are presented, and their corresponding period-luminosity diagrams are discussed.
    Schlagwort(e): Astronomy
    Format: text
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  • 7
    Publikationsdatum: 2019-06-28
    Beschreibung: As part of a co-operative agreement with General Electric Aircraft Engines (GEAE), NASA LeRC is modifying and validating the Ceramic Analysis and Reliability Evaluation of Structures algorithm for use in design of components made of high strength NiAl based intermetallic materials. NiAl single crystal alloys are being actively investigated by GEAE as a replacement for Ni-based single crystal superalloys for use in high pressure turbine blades and vanes. The driving force for this research lies in the numerous property advantages offered by NiAl alloys over their superalloy counterparts. These include a reduction of density by as much as a third without significantly sacrificing strength, higher melting point, greater thermal conductivity, better oxidation resistance, and a better response to thermal barrier coatings. The current drawback to high strength NiAl single crystals is their limited ductility. Consequently, significant efforts including the work agreement with GEAE are underway to develop testing and design methodologies for these materials. The approach to validation and component analysis involves the following steps: determination of the statistical nature and source of fracture in a high strength, NiAl single crystal turbine blade material; measurement of the failure strength envelope of the material; coding of statistically based reliability models; verification of the code and model; and modeling of turbine blades and vanes for rig testing.
    Schlagwort(e): METALLIC MATERIALS
    Materialart: NASA-TM-111138 , NAS 1.15:111138 , NIPS-95-06099
    Format: application/pdf
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  • 8
    Publikationsdatum: 2019-06-28
    Beschreibung: The two estimation methods, individual data and arithmetic mean methods, were used to determine the slow crack growth (SCG) parameters (n and D) of advanced ceramics and glass from a large number of room- and elevated-temperature constant stress-rate ('dynamic fatigue') test data. For ceramic materials with Weibull modulus greater than 10, the difference in the SCG parameters between the two estimation methods was negligible; whereas, for glass specimens exhibiting Weibull modulus of about 3, the difference was amplified, resulting in a maximum difference of 16 and 13 %, respectively, in n and D. Of the two SCG parameters, the parameter n was more sensitive to the estimation method than the other. The coefficient of variation in n was found to be somewhat greater in the individual data method than in the arithmetic mean method.
    Schlagwort(e): Nonmetallic Materials
    Materialart: NASA-TM-107369 , NAS 1.15:107369 , E-10537
    Format: application/pdf
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  • 9
    Publikationsdatum: 2019-06-28
    Beschreibung: We report finding charts and accurate positions for 432 compact H-alpha emitting regions in the Local Group galaxy M 33 (NGC 598), in an effort to isolate candidates for an SS433-like stellar system. The objects were extracted from narrow band images, centered in the rest-frame H-alpha (lambda 6563 A) and in the red continuum at 6100 A. The atlas is complete down to V approximately equal to 20 and includes 279 compact HII regions and 153 line emitting point-like sources. The point-like sources undoubtedly include a variety of objects: very small HII regions, early type stars with intense stellar winds, and Wolf-Rayet stars, but should also contain objects with the characteristics of SS433. This extensive survey of compact H-alpha regions in M 33 is a first step towards the identification of peculiar stellar systems like SS433 in external galaxies.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-CR-200004 , NAS 1.26:200004 , NIPS-96-07149
    Format: application/pdf
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  • 10
    Publikationsdatum: 2019-06-28
    Beschreibung: The present work documents the experimental database of a combined computational and experimental parametric study of the internal aerodynamics of a generic three-dimensional sidewall compression scramjet inlet configuration at Mach 10. A total of 356 channels of pressure data, including static pressure orifices, pitot pressures, and exit flow rakes, along with oil flow and infrared thermography, provided a detailed experimental description of the flow. Mach 10 tests were performed for three geometric contraction ratios (3, 5, and 9), three Reynolds numbers (0.55 x 10(exp 6) per foot, 1.14 x 10(exp 6) per foot, and 2.15 x 10(exp 6) per foot), and three cowl positions (at the throat and two forward positions). For the higher contraction ratios, a large forward separation of the inflow boundary layer was observed, making the high contraction ratio configurations unsuitable for flight operation. A decrease in the freestream unit Reynolds number (Re) of only a factor of 2 led to a similar upstream separation. Although the presence of such large-scale separations leads to the question of whether the inlet is started, the presence of internal oblique swept shock interactions on the sidewalls seems to indicate that at least in the classical sense, the inlet is not unstarted. The laminar inflow boundary layer therefore appears to be very sensitive to increases in contraction ratio (CR) or decreases in Reynolds number; only the CR = 3 configuration with 0.25, and 50 percent cowl at Re = 2.15 x 10(exp 6) per foot operated 'on design'.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-4648 , L-17349 , NAS 1.15:4648
    Format: application/pdf
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