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  • ASTRONOMY  (161)
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  • METEOROLOGY AND CLIMATOLOGY  (88)
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  • 11
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    African Homo erectus: old radiometric ages and young Oldowan assemblages in the Middle Awash Valley, Ethiopia (1994)
    American Association for the Advancement of Science (AAAS)
    Details
    Publikationsdatum: 1994-06-24
    Beschreibung: Fossils and artifacts recovered from the middle Awash Valley of Ethiopia's Afar depression sample the Middle Pleistocene transition from Homo erectus to Homo sapiens. Ar/Ar ages, biostratigraphy, and tephrachronology from this area indicate that the Pleistocene Bodo hominid cranium and newer specimens are approximately 0.6 million years old. Only Oldowan chopper and flake assemblages are present in the lower stratigraphic units, but Acheulean bifacial artifacts are consistently prevalent and widespread in directly overlying deposits. This technological transition is related to a shift in sedimentary regime, supporting the hypothesis that Middle Pleistocene Oldowan assemblages represent a behavioral facies of the Acheulean industrial complex.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Clark, J D -- de Heinzelin, J -- Schick, K D -- Hart, W K -- White, T D -- WoldeGabriel, G -- Walter, R C -- Suwa, G -- Asfaw, B -- Vrba, E -- New York, N.Y. -- Science. 1994 Jun 24;264(5167):1907-10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Anthropology, University of California, Berkeley 94720.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8009220" target="_blank"〉PubMed〈/a〉
    Schlagwort(e): Animals ; Ethiopia ; *Fossils ; Geology/history ; History, Ancient ; Hominidae/*anatomy & histology ; Humans ; Skull/anatomy & histology
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 12
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    Results of international Dobson spectrophotometer calibrations at Arosa, Switzerland, 1990 (1994)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: An international comparison of Dobson ozone spectrophotometers, organized and partially funded by the World Meteorological Organization (WMO), was held at the Lichtklimatisches Observatorium (LKO) in Arosa, Switzerland, July-August 1990. Countries participating with a total of 18 Dobson instruments were Belgium, Czechoslovakia, Denmark, Germany, Greece, Hungary, Iceland, Norway, Poland, Portugal, Rumania, Spain, Switzerland, the United Kingdom, the United States, and the United Soviet Socialist Republics. The reference standard instrument for the comparison was U.S.A. Secondary Standard Dobson Spectrophotometer 65 maintained by the NOAA Climate and Monitoring and Diagnostics Laboratory, Boulder, Colorado. The mean difference in ozone obtained with the Dobson instruments relative to Dobson instrument 65, calculated from ADDSGQP observations in the air mass range 1.15-3.2, was minus 1.0 plus or minus 1.2 (1 sigma) percent. The WMO Standard Brewer Spectrometer 39 also participated. In the mean, the Brewer instrument measured 0.6 plus or minus 0.2 (1 sigma) percent more ozone than did Dobson instrument 65. Results are presented, also, of ozone vertical profile measurements made with the Dobson instruments, two Brewer spectrometers, a LIDAR, a balloon ozonesonde flown from Hohenpeissenberg, Germany, and balloon ozonesondes flown from Payerne, Switzerland.
    Schlagwort(e): METEOROLOGY AND CLIMATOLOGY
    Materialart: NASA. Goddard Space Flight Center, Ozone in the Troposphere and Stratosphere, Part 1; p 266-270
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  • 13
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    Total ozone trends over the USA during 1979-1991 from Dobson spectrophotometer observations (1994)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Ozone trends for 1979-1991, determined from Dobson spectrophotometer observations made at eight stations in the United States, are augmented with trend data from four foreign cooperative stations operated by NOAA/CMDL. Results are based on provisional data archived routinely throughout the years at the World Ozone Data Center in Toronto, Canada, with calibration corrections applied to some of the data. Trends through 1990 exhibit values of minus 0.3 percent to minus 0.5 percent yr(exp -1) at mid-to-high latitudes in the northern hemisphere. With the addition of 1991 data, however, the trends become less negative, indicating that ozone increased in many parts of the world during 1991. Stations located within the plus or minus 20 deg N-S latitude band exhibit no ozone trends. Early 1992 data show decreased ozone values at some of the stations. At South Pole, Antarctica, October ozone values have remained low during the past 3 years.
    Schlagwort(e): METEOROLOGY AND CLIMATOLOGY
    Materialart: NASA. Goddard Space Flight Center, Ozone in the Troposphere and Stratosphere, Part 1; p 195-198
    Format: application/pdf
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  • 14
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    Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. 8: An intensive HST, IUE, and ground-based study of NGC 5548 (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: We present the data and initial results from a combined HST/IUE/ground-based spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-89. IUE spectra were obtained once every two days for a period of 74 days beginning on 14 March 1993. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations (both CCD imaging and aperture photometry), are reported for the period 1992 October to 1993 September, although much of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution, we describe the acquisition and reduction of all of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies. During the HST portion of the monitoring campaign, the 1350 A continuum flux is found to have varied by nearly a factor of two. In other wavebands, the continuum shows nearly identical behavior, except that the amplitude of variability is larger at shorter wavelengths, and the continuum light curves appear to show more short time-scale variability at shorter wavelengths. The broad emission lines also vary in flux, with amplitudes that are slightly smaller than the UV continuum variations and with a small time delay relative to the UV continuum. On the basis of simple time-series analysis of the UV and optical continuum and emission line light curves, we find (1) that the ultraviolet and optical continuum variations are virtually simultaneous, with any lag between the 1350 A continuum and the 5100 A continuum amounting to less than about one day; (2) that the variations in the highest ionization lines observed, He II lambda 1640 and N V lambda 1240, lag behind the continuum variations by somewhat less than 2 days, and (3) that the velocity field of the C IV-emitting region is not dominated by radial motion. The results on the C IV velocity field are preliminary and quite uncertain, but there are some weak indications that the emission-line (wings absolute value of Delta upsilon is greater than or equal to 3000 km/s) respond to continuum variations slightly more rapidly than does the core. The optical observations show that the variations in the broad H beta line flux follow the continuum variations with a time lag of around two weeks, about twice the lag for Ly alpha and C IV, as in our previous monitoring campaign on this same galaxy. However, the lags measured for Ly alpha, C IV, and H Beta are each slightly smaller than previously determined. We confirm two trends reported earlier, namely (1) that the UV/optical continuum becomes 'harder' as it gets brighter, and (2) that the highest ionization emission lines have the shortest lags, thus indicating radial ionization stratificatin of a broad-line region that spans over an order of magnitude range in radius.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-CR-199341 , NAS 1.26:199341
    Format: application/pdf
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  • 15
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    EGRET observations of the Vela pulsar PSR 0833-45 (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: During the all sky survey (May 1991 - Nov. 1992) of the Compton Gamma Ray Observatory the Vela pulsar PSR0833-45 was in the field of view of the Energetic Gamma Ray Experiment Telescope (EGRET) in ten separate viewing periods. The pulsar was detected in each one. The average intensity from 100 MeV to 2 GeV was (7.8 +/- 1.0) x 10 (exp -6) photons cm(exp -2) s(exp -1), which indicates that the pulsar in the years 1991/92 was in a state comparable to the low fluxes observed in 1977-1980. No significant changes in intensity were detected during the EGRET observations. The total spectrum of PSR0833-45 measured by EGRET can be described by a power law with index -(1.70 +/- 0.02) over the range 30 MeV to 2 GeV. The extrapolation of this spectrum into the 3 to 30 MeV range agrees with the observations by COMPTEL. Above 2 to 4 GeV EGRET detects a strong spectral break. The lightcurves obtained show a familar structure in the phase histogram: two peaks separated by 0.424 +/- 0.002 in phase with considerable emission in the phase interval between the peaks. The first gamma ray peak maximum trails the single radio peak maximum by 10.54 +/- 0.09 ms (= 0.118 +/- 0.001 in phase). The widths of the emission peaks (FWHM) are 2.7 ms for the first peak (0.03 phase) and 4.1 ms for the second peak (0.05 phase). The widths are approximately constant below a GeV, but show a tendency to become narrower at higher energies. On Jul. 20 1991 a glitch of the Vela period was registered in monitor radio observations. No significant differences between the pre- and post-glitch gamma ray lightcurves were found. The statistics available for the Vela observations allow for a division of the lightcurve into eight phase intervals. The emission peak cores (central FWHM) with leading and trailing wings and two interval regions were defined and spectra were derived for all parts of the lightcurve. The energy spectra for the eight phase intervals show significant differences: the first peak (approximately E(exp -1.81 +/- 0.04)) is somewhat softer than the second peak (approximately E(exp -1.71 +/- 0.03)); the wings attached to each peak show softer spectra than the code of the peaks; the interval emission has the hardest spectrum (approximately E(exp -1.52 +/- 0.03)).
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-CR-197959 , NAS 1.26:197959 , MPE-PREPRINT-289
    Format: text
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  • 16
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    A programmable heater control circuit for spacecraft (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Spacecraft thermal control is accomplished for many components through use of multilayer insulation systems, electrical heaters, and radiator systems. The heaters are commanded to maintain component temperatures within design specifications. The programmable heater control circuit (PHCC) was designed to obtain an effective and efficient means of spacecraft thermal control. The hybrid circuit provides use of control instrumentation as temperature data, available to the spacecraft central data system, reprogramming capability of the local microprocessor during the spacecraft's mission, and the elimination of significant spacecraft wiring. The hybrid integrated circuit has a temperature sensing and conditioning circuit, a microprocessor, and a heater power and control circuit. The device is miniature and housed in a volume which allows physical integration with the component to be controlled. Applications might include alternate battery-powered logic-circuit configurations. A prototype unit with appropriate physical and functional interfaces was procured for testing. The physical functionality and the feasibility of fabrication of the hybrid integrated circuit were successfully verified. The remaining work to develop a flight-qualified device includes fabrication and testing of a Mil-certified part. An option for completing the PHCC flight qualification testing is to enter into a joint venture with industry.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-108459 , NAS 1.15:108459
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  • 17
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    The multifrequency spectral evolution of blazar 3C 345 (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The blazar 3C 345 underwent a 2.5 mag optical outburst between 1990 November and 1991 May. We have obtained 10 nearly simultaneous multifrequency spectra during the course of the outburst in order to study the multifrequency spectral variations of 3C 345 as a function of time. Although our observations were not sampled frequently enough to completely resolve the variations in every frequency band, the general rise and decline of the outburst were seen in the UV through radio with differing rise times. Simulations of an electron distribution injected into a tangled magnetic field show a relationship between frequency and characteristic timescale that was also observed in the radio variations of 3C 345. The two X-ray observations made during the monitoring period showed no evidence of variability. The multifrequency spectrum was modeled with two major components: a relativistic jet and a relativistic thermal accretion disk. Models calculated for each spectrum indicate that the outburst can be explained in terms of these models by varying the high-energy cutoff of the injected electron distribution in the jet model, while also varying the mass accretion rate in the disk model. There is marginal evidence that the inferred accretion rate varies with the jet luminosity.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 422; 2; p. 570-585
    Format: text
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  • 18
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    The temporal evolution of the 4-14 micron spectrum of V1974 Cygni (Nova Cygni 1992) (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: We present 4-14 micron spectra of the ONeMg nova V1974 Cygni (Nova Cygni 1992) obtained during 1992 May on the NASA Kuiper Airborne Observatory (KAO) and from the NASA 1.52 m infrared telescope at Mount Lemmon, Arizona in 1992 October/November with the HIFOGS mid-infrared spectrometer. The spectra at both epochs showed continuum emission from thermal bremstrahlung (free-free radiation) with emission lines from hydrogen and (Ne II), (Ar III), and Ne VI). During May, approximately = 80 days after outburst, the dominant emission lines in the mid-infrared spectra were a blend of three lines (Pf-alpha, Hu-beta, H11-7) near 7.5 microns and (Ne II) at 12.8 microns. By October (approximately 160 days later), the hydrogen emission had virtually disappeared, the (Ne II) 12.8 micron line had weakened considerably, and a pronounced (Ne VI) emission line had appeared at 7.6 microns. This behavior confirms that V1974 Cyg is similar to the prototypical slow ONeMg 'neon nova', Nova QU Vulpeculae (1984 No. 2). The remarkable evolution of the spectrum suggests that the ionization conditions changed drastically between 1992 May and 1992 October. We find that the ejecta of V1974 Cyg were overabundant in neon with respect to silicon by a factor of approximately 10 relative to the solar photosphere. We present new model calculations of infrared sodium forbidden line emission from (Na III) 7.319 microns (Na IV) 9.039 microns, and (Na IV) 21.29 microns that can be compared with recent model predictions of sodium synthesis in ONeMg nova outbursts. We conclude that sodium abundances in ONeMg novae can be determined by observations of infrared coronal lines of sodium that are accssible to the Infrared Space Observatory (ISO) and instruments at the NASA Infrared Telescope Facility (IRTF).
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 421; 2; p. 762-770
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  • 19
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    EGRET observations of the Vela pulsar, PSR0833-45 (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: During the all sky survey (May 1991 to November 1992) of the Compton Gamma Ray Observatory, the Vela pulsar PSR0833-45 was in the field of view of the Energetic Gamma Ray Experiment Telescope (EGRET) in ten separate viewing periods. The pulsar was detected in each one. The average intensity from 100 MeV to 2GeV was (7.8 +/- 1.0) x 10(exp -6) photons /sq cm/s, which indicates that the pulsar in the years 1991/92 was in a state comparable to the low fluxes observed in 1977-1980. No significant changes in intensity were detected during the EGRET observations. The total spectrum of PSR0833-45 measured by EGRET can be described by a power-law with index -1.70 +/- 0.02 over the range 30 MeV to 2 GeV. The extrapolation of this spectrum into the 3-30 MeV range agrees with the observations by COMPTEL. Above 2-4 GeV EGRET detects a strong spectral break. The lightcurves obtained show a familiar structure in the phase histogram: two peaks separated by 0.424 +/- 0.002 in phase with considerable emission in the phase interval between the peaks. The first gamma ray peak maximum trails the single radio peak maximum by 10.54 +/- 0.09 ms (= 0.118 +/- 0.001 in phase). The widths of the emission peaks (FWHM) are 2.7 ms for the first peak (0.03 phase) and 4.1 ms for the second peak (0.05 phase). The widths are approximately constant below a GeV, but show a tendency to become narrower at higher energies. The statistics available for the Vela observations allow for a division of the lightcurve into eight phase intervals. The emission peak cores (central FWHM) with leading and trailing wings and two interval regions were defined and spectra were derived for all parts of the lightcurve. The energy spectra for the eight phase intervals show significant differences: the first peak (approximately E(exp -1.81 +/- 0.04)) is somewhat softer than the second peak (approximately E(exp -1.71 +/- 0.03)); the wings attached to each peak show softer spectra than the core of the peaks; the interval emission has the hardest spectrum (approximately E(exp -1.52 +/- 0.03)).
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 289; 3; p. 855-867
    Format: text
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  • 20
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    Search of the energetic gamma-ray experiment telescope (EGRET) data for high-energy gamma-ray microsecond bursts (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: Hawking (1974) and Page & Hawking (1976) investigated theoretically the possibility of detecting high-energy gamma rays produced by the quantum-mechanical decay of a small black hole created in the early universe. They concluded that, at the very end of the life of the small black hole, it would radiate a burst of gamma rays peaked near 250 MeV with a total energy of about 10(exp 34) ergs in the order of a microsecond or less. The characteristics of a black hole are determined by laws of physics beyond the range of current particle accelerators; hence, the search for these short bursts of high-energy gamma rays provides at least the possibility of being the first test of this region of physics. The Compton Observatory Energetic Gamma-Ray Experiment Telescope (EGRET) has the capability of detecting directly the gamma rays from such bursts at a much fainter level than SAS 2, and a search of the EGRET data has led to an upper limit of 5 x 10(exp -2) black hole decays per cu pc per yr, placing constraints on this and other theories predicting microsecond high-energy gamma-ray bursts.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 434; 2; p. 557-559
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