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  • 1
    Publication Date: 2019-01-25
    Description: A low-power cathodoluminescence (CL) mosaic of a 1x2 cm section of the Murchison CM chondrite contains chondrules of two types: one contains olivines with red CL and is thought to be the equivalent of group A chondrules of Sears et.; and one without observable CL, which is probably equivalent to their group B chondrules. Both types of chondrule contain dust mantles with a characteristic uniform red CL due to very fine-grained forsterites, but the mantles of group A chondrules have a complex internal structure and are much thicker than the relatively thin rims on the group B chondrules. The variety of internal textures and the progressive integration of the objects with the surrounding matrix suggests to us that these features are large group A chondrules in the process of being destroyed by aqueous alteration. Prior to aqueous alteration, group A chondrules in CM chondrites were larger than group B chondrules, which is contrary to the situation in ordinary chondrites and were apparently destroyed more rapidly than group B chondrules by aqueous alteration.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z; p 1269-1270
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  • 2
    Publication Date: 2013-08-31
    Description: Initial results from the measurement conducted by the dust particle experiment on the lunar orbiting satellite Lunar Explorer 35 (LE 35) were reported with the data interpreted as indicating that the moon is a significant source of micrometeroids. Primary sporadic and stream meteoroids impacting the surface of the moon at hypervelocity was proposed as the source of micron and submicron particles that leave the lunar craters with velocities sufficient to escape the moon's gravitational sphere of influence. No enhanced flux of lunar ejecta with masses greater than a nanogram was detected by LE 35 or the Lunar Orbiters. Hypervelocity meteoroid simulation experiments concentrating on ejecta production combined with extensive analyses of the orbital dynamics of micron and submicron lunar ejecta in selenocentric, cislunar, and geocentric space have shown that a pulse of these lunar ejecta, with a time correlation relative to the position of the moon relative to the earth, intercepts the earth's magnetopause surface (EMPs). As shown, a strong reason exists for expecting a significant enhancement of submicron dust particles in the region of the magnetosphere between L values of 1.2 and 3.0. This is the basis for the proposal of a series of experiments to investigate the enhancement or even trapping of submicron lunar ejecta in this region. The subsequent interaction of this mass with the upper-lower atmosphere of the earth and possible geophysical effects can then be studied.
    Keywords: ASTROPHYSICS
    Type: NASA, Lyndon B. Johnson Space Center, Experiments in Planetary and Related Sciences and the Space Station; 9 p
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  • 3
    Publication Date: 2016-06-07
    Description: Particulate matter possessing lunar escape velocity sufficient to enhance the cislunar meteroid flux was investigated. While the interplanetary flux was extensively studied, lunar ejecta created by the impact of this material on the lunar surface is only now being studied. Two recently reported flux models are employed to calculate the total mass impacting the lunar surface due to sporadic meteor flux. There is ample evidence to support the contention that the sporadic interplanetary meteoroid flux enhances the meteroid flux of cislunar space through the creation of micron and submicron lunar ejecta with lunar escape velocity.
    Keywords: ASTROPHYSICS
    Type: NASA. Lyndon B. Johnson Space Center Space Station Planetology Experiments (SSPEX); 3 p
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  • 4
    Publication Date: 2016-06-07
    Description: Extensive studies were conducted concerning the indivdual mass, temporal and positional distribution of micron and submicron lunar ejecta existing in the Earth-Moon gravitational sphere of influence. Initial results show a direct correlation between the position of the Moon, relative to the Earth, and the percentage of lunar ejecta leaving the Moon and intercepting the magnetosphere of the Earth at the magnetopause surface. It is seen that the Lorentz Force dominates all other forces, thus suggesting that submicron dust particles might possibly be magnetically trapped in the well known radiation zones.
    Keywords: ASTROPHYSICS
    Type: NASA. Lyndon B. Johnson Space Center Space Station Planetology Experiments (SSPEX); 3 p
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  • 5
    Publication Date: 2016-06-07
    Description: The level of natural thermoluminescence (TL) in meteorites is the result of competition between build-up, due to exposure to cosmic radiation, and thermal decay. Antarctic meteorites tend to have lower natural TL than non-Antarctic meteorites because of their generally larger terrestrial ages. However, since a few observed falls have low TL due to a recent heating event, such as passage within approximately 0.7 astronomical units of the Sun, this could also be the case for some Antarctic meteorites. Dose rate variations due to shielding, heating during atmospheric passage, and anomalous fading also cause natural TL variations, but the effects are either relatively small, occur infrequently, or can be experimentally circumvented. The TL sensitivity of meteorites reflects the abundance and nature of the feldspar. Thus intense shock, which destroys feldspar, causes the TL sensitivity to decrease by 1 to 2 orders of magnitude, while metamorphism, which generates feldspar through the devitrification of glass, causes TL sensitivity to increase by a factor of approximately 10000. The TL-metamorphism relationship is particularly strong for the lowest levels of metamorphism. The order-disorder transformation in feldspar also affect the TL emission characteristics and thus TL provides a means of paleothermometry.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst. International Workshop on Antarctic Meteorites; p 83-100
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  • 6
    Publication Date: 2011-08-16
    Description: Low-resolution ultraviolet spectra were obtained for six early-type stars in 1972 December, using an Ebert spectrometer mounted in the service module of the Apollo 17 spacecraft. The spectrometer scanned from 1180 A to 1680 A, with a speed that varied with wavelength according to a program chosen for lunar studies. Spectral resolution was 11 A. The ultraviolet absolute calibration of the instrument was determined by comparison with National Bureau of Standards calibrated photodiodes, and is believed known to plus or minus 10 percent. The absolute intensities are in good general agreement with the observations of other stars and with the predictions of stellar model-atmosphere calculations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 201; Nov. 1
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  • 7
    Publication Date: 2011-08-18
    Description: The formulation of generalized models tracing the geometry and intensity of the synchrotron emission from precessing, twin, relativistic jets as projected on the plane of the sky is presented. It is shown that neither the shape of the image nor its relative intensities are altered by including the effects of a cosmological redshift and a relative velocity between the source and observer. The models are fitted to the available data for several quasars and radio galaxies and demonstrate the plausibility of the phenomenon. Probable selection effects are considered and diagnostics given for recognizing objects showing this behavior. In the radio galaxies considered, velocities up to about 0.2c and precession periods of 1,000,000 yr are deduced. In the QSOs investigated, velocities of 0.7c and greater are found and periods of order 10,000 yr. In some cases precession cone angles increase with time. Consequences in terms of lifetimes of QSO behavior and binary supermassive objects are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 262
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  • 8
    Publication Date: 2011-08-18
    Description: The Apollo 17 wide-field far-ultraviolet spectrometer was used to scan six large bands of the sky during trans-earth coast. After accounting for internal scattered light and the light expected from stars in the field of view, no significant residual flux remains. This imposes important constraints on the scattering properties of the interstellar dust grains: either the grains are extremely strongly forward scattering, or the albedo of the grains is low. The absence of a scattered light signal from dusty, moderate galactic latitude regions of the sky indicates that the high galactic latitude flux reported by Henry et al. (1977) and by Anderson et al. (1979) does not represent starlight backscattered by dust.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 259
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  • 9
    Publication Date: 2011-08-18
    Description: An area of 7.5 sq deg of the galactic plane at 70 microns have been surveyed with a 1-arcmin beam. The region lies between lII equals 10 deg and lII equals 16 deg and includes the M17 and W33 complexes. The weakest of the 42 sources detected had a flux density of 350 Jy at 70 microns. Detailed far-infrared, (C-12)O, (C-13)O, and radio continuum observations of the sources are presented. The derivation of the important physical parameters of the sources and their surrounding molecular clouds are discussed. The properties of the individual regions are also discussed and maps of selected sources are presented.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series; 48; Jan. 198
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  • 10
    Publication Date: 2011-08-17
    Description: The first direct observation of the ultraviolet spectrum of a quasi-stellar object (QSO) has been made with a rocket-borne telescope. The emission line spectrum of 3C273 is similar to the spectra of high-redshift QSOs, but no absorption is observed. The results provide important new constraints on theoretical models of QSOs, place a severe limit on the density of neutral hydrogen in the intergalactic medium, and suggest a cosmological origin for much of the absorption seen in high-redshift QSOs. Comparison of the ultraviolet spectrophotometry of low- and high-redshift QSOs suggests that the universe is closed, with a deceleration parameter of about 1.
    Keywords: ASTROPHYSICS
    Type: Nature; 269; Sept. 15
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