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  • Organic Chemistry  (68,964)
  • Life and Medical Sciences  (30,791)
  • Analytical Chemistry and Spectroscopy  (25,033)
  • GEOPHYSICS  (21,936)
  • ASTROPHYSICS  (16,581)
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  • 1
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    Frontiers in Chemistry: Rising Stars (2021)
    Frontiers Media SA
    Details
    Publication Date: 2024-04-04
    Description: The Frontiers in Chemistry Editorial Office team are delighted to present the inaugural “Frontiers in Chemistry: Rising Stars” article collection, showcasing the high-quality work of internationally recognized researchers in the early stages of their independent careers. All Rising Star researchers featured within this collection were individually nominated by the Journal’s Chief Editors in recognition of their potential to influence the future directions in their respective fields. The work presented here highlights the diversity of research performed across the entire breadth of the chemical sciences, and presents advances in theory, experiment and methodology with applications to compelling problems. This Editorial features the corresponding author(s) of each paper published within this important collection, ordered by section alphabetically, highlighting them as the great researchers of the future. The Frontiers in Chemistry Editorial Office team would like to thank each researcher who contributed their work to this collection. We would also like to personally thank our Chief Editors for their exemplary leadership of this article collection; their strong support and passion for this important, community-driven collection has ensured its success and global impact.
    Keywords: Green and Sustainable Chemistry ; Analytical Chemistry ; Theoretical and Computational Chemistry ; Polymer Chemistry ; Medicinal and Pharmaceutical Chemistry ; Organic Chemistry ; Nanoscience ; Catalysis and Photocatalysis ; Supramolecular Chemistry ; Electrochemistry ; Inorganic Chemistry ; Chemical Biology ; thema EDItEUR::P Mathematics and Science::PD Science: general issues
    Language: English
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    E-BOOK
  • 2
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    [Editors' Choice] Carboxylating stubborn alkyl chlorides (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-07-08
    Description: Author: Phil Szuromi
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
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    [This Week in Science] Olefins enlisted to attack ketones (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-07-08
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
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    [This Week in Science] A radical route to ophiobolin rings (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-05-27
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
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    [This Week in Science] A light approach to C-N bond formation (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-07-15
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    [Editors' Choice] Iron takes alcohols to carboxylic acids (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-07-22
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
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    [This Week in Science] Catalysis gets all tied up in knots (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-06-24
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    [This Week in Science] Adding two fluorines to just one carbon (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-07-01
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    [Perspective] Three catalysts for activating carbon-hydrogen bonds (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-06-10
    Description: Transition metal–catalyzed arylation of C–H bonds has been intensively studied for forming C–C bonds in complex-molecule synthesis (1). An acidic C–H bond (for example, one near a double bond or an O atom) is cleaved to form a carbon–metal bond, which then couples to arene. Many of these organometallic species can be generated catalytically. Much less research has dealt with unreactive nonacidic sp3 C–H bond functionalization (3). On page 1304 of this issue, Shaw et al. (3) report an efficient and general method that focuses on arylation of sp3 C–H bonds at carbon atoms adjacent to amines and to cyclic ethers by combining nickel, visible-light photoredox, and hydrogen-atom transfer (HAT) catalysis. Author: Corinne Fruit
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    [This Week in Science] A tip of the HAT to C-C bond formation (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-06-10
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 11
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    [This Week in Science] A rhodium route from C-H to C-N bonds (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-09-09
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 12
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    [This Week in Science] Copper-catalyzed radical relay (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-09-07
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 13
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    [In Depth] A modular route to new antibiotics (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-05-20
    Description: Antibiotics have been taking it on the chin lately. Not only has resistance to the anti-infective medications been growing, but drug companies have been dropping antibiotic research programs, because the drugs are difficult and expensive to make. Now, new help is on the way. Researchers report this week that they've found a way to churn out new members of one of the most widely used classes of antibiotics. These drugs, called macrolides, were first developed in the 1950s and now represent a major bulwark against infections. A bevy of possible new drugs in this class could lead to new weapons against antibiotic-resistant infections, and possibly save millions of lives. Author: Robert F. Service
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 14
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    [This Week in Science] Copper adds alkyls asymmetrically (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-04-22
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 15
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    [This Week in Science] EZ catalyst control in olefin metathesis (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-04-29
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 16
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    [This Week in Science] Carbon links without helpful neighbors (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-05-13
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 17
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    [Perspective] Rethinking the SN2 reaction (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-04-01
    Description: The SN2 nucleophilic substitution reaction, X− + RY → XR + Y−, is a paradigm reaction in organic chemistry (1). The modern understanding of the SN2 reaction mechanism is based on work of Hughes and Ingold (2), who proposed that the nucleophile (X−) approaches the carbon atom that bears the leaving group (Y−). As a result, the bond between the carbon atom and the leaving group becomes weakened. As this bond breaks and a new bond forms between the nucleophile and the carbon atom, the configuration of the carbon atom is inverted. Analyses of gas-phase reaction rates led to the suggestion of a potential energy surface (PES) with two wells connected by a central barrier transition state (3). Electronic structure calculations have confirmed this picture for some SN2 reactions (4), but recent studies have shown that the actual reaction dynamics may be considerably more complex (see the figure) (5–8). Authors: Jing Xie, William L. Hase
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 18
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    [This Week in Science] Beyond textbook SN2 chemistry (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-04-01
    Description: Author: Julia Fahrenkamp-Uppenbrink
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 19
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    [This Week in Science] CO takes the lead to make β-lactam rings (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-11-18
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 20
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    [This Week in Science] Pluses and minuses of BTX behavior (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-11-18
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 21
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    [Editors' Choice] Lighting the way to fluorine placement (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-03-03
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 22
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    [This Week in Science] Catching a break in polyphenol synthesis (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-12-09
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 23
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    [This Week in Science] How to turn olefins into nucleophiles (2016)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2016-10-21
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 24
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    [This Week in Science] Stitching a belt out of carbon rings (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-14
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 25
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    [Perspective] Allotropy by design—Carbon nanohoops (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-14
    Description: The allotropes formed by carbon reflect differences in its bonding: single bonds in diamond, double bonds in graphite and graphene, and triple bonds in polyynes. Fashioning graphene sheets into bowls, monkey saddles, balls, and tubes has led to a number of molecular allotropes of carbon or carbon-rich quasi-allotropes with novel topologies and shapes. A simple ring of carbon can be reduced to practice in various forms (1): a cyclic array of carbon atoms, a “pearl necklace” of benzene rings, or a cylindrical hoop of flank-fused benzenes, just to name a few. On page 172 of this issue, Povie et al. (2) report on the synthesis of an angular-fused hoop structure, which has been a long-standing target. Author: Jay S. Siegel
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 26
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    [This Week in Science] Stitching one alkyl group to another (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-14
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 27
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    [This Week in Science] Boron choreographs a double reaction (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-03-03
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 28
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    [This Week in Science] Turning benzene into a C–H bond cleaver (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-01
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 29
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    [This Week in Science] A cyclic catalyst to pair up sugars (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-01-13
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 30
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    Evaluation of thermal radiation at high temperatures (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Emittance measuring apparatus for temperatures up to 4000-deg f
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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    NASA TECHNICAL REPORTS
  • 31
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    A very rapid 3000 deg f technique for measuring emittance of opaque solid materials (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Total normal emittance measurement technique for opaque solid materials over 1000- to 3000-deg f range
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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    NASA TECHNICAL REPORTS
  • 32
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    Pitfalls in thermal emission studies (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Pitfalls in thermal emission studies - terminology, experimental procedure, and physical standards
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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    NASA TECHNICAL REPORTS
  • 33
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    ICE navigation support (1986)
    In:  CASI
    Details
    Publication Date: 2009-11-17
    Description: The International Cometary Explorer (ICE) encounter with Comet Giacobini-Zinner took place 7 years after the spacecraft's original launch on 12 August 1978 as the International Sun Earth Explorer 3 (ISEE-3), part of a three-spacecraft project to study the interaction between the solar wind and the Earth's magnetosphere. Transfer to an interplanetary trajectory was performed via a 119-km-altitute, gravity-assist, lunar swingby on December 1983. Navigation support during interplanetary cruise and comet encounter was provided by orbit determination utilizing radio metric data from the DSN 64-meter antennas in Goldstone, California and Madrid, Spain. Orbit solutions yielding predictions of 50-km geocentric delivery accuracy in the target aim plane were achieved during interplanetary cruise and at comet encounter using 6-to-12-week data arcs between periodic attitude-change maneuvers. One-sigma two-way range and range rate residuals were consistently 40 meters and 0.2 mm/s or better, respectively. Non-gravitational forces affected the comet's motion during late August and early September 1985 and caused a 2300-km shift in the orbit of the comet relative to the spacecraft. This necessitated a final ICE orbit trim maneuver 3 days prior to encounter. Near-real-time assessment of two-way 2-GHz (S-band) Doppler pseudo-residuals during the June and July 1985 trajectory change maneuvers aided in calibration of the spacecraft's thrusters in preparation for this final critical maneuver. Post-flight analysis indicates tail centerline passage was achieved within 10 seconds of the predicted time and geocentric position uncertainty at encounter was less than 40 km.
    Keywords: ASTROPHYSICS
    Type: The Telecommunications and Data Acquisition Report (date]; p 268 - 283
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    NASA TECHNICAL REPORTS
  • 34
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    Periodic heat flow in a hollow cylinder rotating in a furnace with a viewing port (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Rotating-specimen furnace for use in determining spectral & total emittance of materials from measurement of radiant flux from specimen surface
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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    NASA TECHNICAL REPORTS
  • 35
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    The total hemispherical emittance of platinum, columbium-1 percent zirconium, and polished and oxidized inor-8 in the range 100 deg to 1200 deg c (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Temperature dependence of hemispherical emittance of metal and alloy strips in 100- to 1200-deg c range using blackbody vacuum chamber
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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    NASA TECHNICAL REPORTS
  • 36
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    Measurement of spectral normal emittance of materials under simulated spacecraft powerplant operating conditions (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Spectral normal emittance of materials under simulated space environment
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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    NASA TECHNICAL REPORTS
  • 37
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    Heated cavity reflectometer modifications (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Heated cavity reflectometer for thermal reflectance measurements of opaque surface
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 38
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    Inspection tool for measurement of the radiation properties of satellite temperature control surfaces (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Apparatus for measuring emittance and absorptivity of satellite temperature control surfaces
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 39
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    An apparatus for measuring total hemispherical emittance between ambient and liquid nitrogen temperatures (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Apparatus for measuring hemispherical emittance of solids in ambient & liquid nitrogen temperature range, with copper & aluminum foil data
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 40
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    Thermocouple and radiation thermometry above 900 deg k (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Thermocouple and radiation thermometry above 900 deg k
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 41
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    Measurement of total hemispherical emittance of structural materials and coatings under simulated spacecraft conditions (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Hemispherical emittance of structural materials & coatings under simulated spacecraft conditions over wide temperature range
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 42
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    The measurement of total normal emittance of three nuclear reactor materials (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Measurement of total normal emittance of nuclear reactor materials - carbon steel, boron steel, & borated graphite
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 43
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    Radiative property measurements of thermal control coatings for spacecraft (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Solar absorptance, emittance, & transmittance of thermal control coating for spacecraft
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 44
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    Spectral emittance measurements from 40 deg c to 200 deg c (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Spectral emittance of opaque and transparent materials from 40- to 200-deg c
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 45
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    Hemispheric spectral reflectance of solids (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Hemispheric spectral reflectance of opaque solids
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 46
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    Calorimetric determination of infrared emittance and the absorptance/emission ratio (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Calorimetric device for determination of solar absorption & infrared emittance ratio of materials at room temperature
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 47
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    Thermal radiation properties of solids at low temperatures (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: Thermal radiation properties of solids at cryogenic temperatures
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 48
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    Temperature measurements below 1000 deg k 〈an abstract〈 (1963)
    In:  CASI
    Details
    Publication Date: 2009-12-28
    Description: International practical temperature scale for temperature measurements below 1000-deg k using platinum resistance thermometers
    Keywords: GEOPHYSICS
    Type: Measurement of Thermal Radiation Properties of Solids; NASA-SP-31
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  • 49
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    Global and local current sheet thickness estimates during the late growth phase (1992)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The thinning and intensification of the cross tail current sheet during the substorm growth phase are analyzed during the CDAW 6 substorm (22 Mar. 1979) using two complementary methods. The magnetic field and current sheet development are determined using data from two spacecraft and a global magnetic field model with several free parameters. These results are compared with the local calculation of the current sheet location and structure previously done by McPherron et al. Both methods lead to the conclusion that an extremely thin current sheet existed prior to the substorm onset, and the thicknesses estimated by the two methods at substorm onset agree relatively well. The plasma data from the ISEE 1 spacecraft at 13 R(sub E) show an anisotropy in the low energy electrons during the growth phase which disappears just before the substorm onset. The global magnetic model results suggest that the field is sufficiently stretched to scatter such low energy electrons. The strong stretching may improve the conditions for the growth of the ion tearing instability in the near Earth tail at substorm onset.
    Keywords: GEOPHYSICS
    Type: ESA, Substorms 1; p 131-135
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  • 50
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    Magnetic cloud passage at Earth and associated substorm activity (1992)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: An approach to the study of the solar wind-magnetosphere interaction by signal type, that is, by examining the effect in the magnetosphere of well defined interplanetary structures, is presented. Focus is on the response of the magnetosphere to interplanetary magnetic clouds. Among their properties are: the slow and smooth variation of the magnetic field vector, with fluctuation level well below common interplanetary values; the similarly well behaved bulk flow; the wide range of field and flow parameters; and the longevity of passage (1 to 2 days). If the magnetic cloud is oriented such that a long period of uninterruptedly northward pointing field is followed by a long interval of continuously southward pointing field, then the transition of the magnetosphere from a quiescent state (the 'ground state') to a very active state can be studied, the latter being sustained by continued forcing from the magnetic cloud. A synopsis of the main findings of a recent study in such an interaction is given, concentrating on the substorm activity attending the second part of cloud passage.
    Keywords: GEOPHYSICS
    Type: ESA, Substorms 1; p 371-376
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  • 51
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    An ensemble pulsar time (1993)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Millisecond pulsars are galactic objects that exhibit a very stable spinning period. Several tens of these celestial clocks have now been discovered, which opens the possibility that an average time scale may be deduced through a long-term stability algorithm. Such an ensemble average makes it possible to reduce the level of the instabilities originating from the pulsars or from other sources of noise, which are unknown but independent. The basis for such an algorithm is presented and applied to real pulsar data. It is shown that pulsar time could shortly become more stable than the present atomic time, for averaging times of a few years. Pulsar time can also be used as a flywheel to maintain the accuracy of atomic time in case of temporary failure of the primary standards, or to transfer the improved accuracy of future standards back to the present.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center, The 24th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; p 73-86
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  • 52
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    Magnetotail instability (1992)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The stability of the geomagnetic tail is investigated on the basis of three dimensional resistive magnetohydrodynamic simulations, using different dynamic constraints and different initial equilibria. Different forms of the energy equation for isotropic pressure are found to have no significant effect on the dynamic growth of a resistive tearing instability, which is responsible for near Earth reconnection, plasmoid formation and ejection, and the generation of fast plasma flows. The constraints of a modified double adiabatic approach, however, can quench the tearing instability through the development of large, mirror type, anisotropies in the boundary regions of the plasma sheet, unless isotropization occurs on fast, nearly Alfvenic, time scales. The presence of a net cross tail magnetic field component B(sub yN) can reduce the growth of the instability without complete stabilization. An increase of B(sub z) from midnight toward the tail flanks, however, by more than a factor of about 3, apparently completely stabilizes the tearing mode. Stabilization and destabilization thus may depend on properties and constraints (and their release) in regions other than the neutral sheet where reconnection is initiated.
    Keywords: GEOPHYSICS
    Type: ESA, Substorms 1; p 225-230
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  • 53
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    Driven and unloading aspects of magnetospheric substorms (1992)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Issues concerning the 'driven' versus 'unloading' nature of substorms are presented. The original concepts attendant to this debate are presented and substorms are concluded to inextricably combine aspects that are driven with aspects that represent a loading-unloading system. For isolated substorms, the magnetosphere-ionosphere system is shown to exhibit a bimodal response to solar wind changes. A 20 min response characteristic is associated with the driven aspect of substorms, while a 1 hr response time is associated with unloading. It is found that for strong solar wind input conditions, the magnetospheric response becomes more nearly unimodal. This is interpreted in terms of a nonlinear dynamical evolution of the system. Simple analog models are described which capture the essence of the nonlinear magnetospheric behavior. These models exhibit chaotic transitions for strong driving conditions: this may explain the observed behavior of the magnetosphere during strong geomagnetic activity.
    Keywords: GEOPHYSICS
    Type: ESA, Substorms 1; p 185-191
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  • 54
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    Characteristics of pseudobreakups (1992)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A pseudobreakup is a phenomenon similar to the substorm expansive phase onset, including an activation of an auroral arc, a burst of Pi2 micropulsations, and enhancement of the westward electrojet. However, these effects are weak and a pseudobreak is generally assumed to be very localized. The pseudobreakups are discussed based on simultaneous observations made in space and on the ground during the substorm growth phase. In the events studied the main features listed above are found, but the significance of the localization is unclear. The optical pseudobreakup, with associated magnetic perturbations, is highly localized, but simultaneously a wide local time sector of the auroral oval may be activated. The major differences between pseudobreakups and substorm expansive phase onsets are concluded to be the intensity and the development that follows. Careful study of pseudobreakups may help to determine phase initiation, and the role of the ionosphere-magnetosphere coupling in the substorm process.
    Keywords: GEOPHYSICS
    Type: ESA, Substorms 1; p 111-116
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  • 55
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    Potential applications of GSC-2 for GAIA operations (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The second guide star catalog (GSC-2) is a project that aims to create a complete catalog of stars and galaxies to about the 18th magnitude, and would contain colors, magnitudes, positions and proper motions. The catalog would provide an object list for the construction of an input catalog for possible future astrometric satellites, such as the global astrometric interferometer for astrophysics (GAIA) satellite. With a schedule that is compatible with the projected timeframe of GAIA, the GSC-2 could be available in time to support the preparatory astrophysical observations for an input catalog. The availability of the digitalized images for the preparation of finding charts would improve the efficiency of this task.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 137-141
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  • 56
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    Time delay in the Einstein ring PKS 1830-211 (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We present radio observations of the gravitational lens PKS 1830-211 at 8.4 and 15 GHz acquired using the Very Large Array. The observations were made over a 13 month period. Significant flux density changes over this period provide strong constraints on the time delay between the two lensed images and suffest a value of 44 +/- 9 days. This offers new direct evidence that this source is indeed a gravitational lens. The lens distance is dependent upon the model chosen, but reasonable limits on the mass of the lensing galaxy suggest that it is unlikely to be at a redshift less than a few tenths, and may well be significantly more distant.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 2; p. 561-566
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  • 57
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    Calculations of the outflow velocity of envelopes of cool giants (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We study the transfer of momentum from photons to dust grains to (molecular) gas in the outflow around cool giants (carbon-stars, Mira variables and OH/IR stars) beyond the radius where the dust grains condense. The problem is circular: radiation pressure determines the outflow velocity of the dust and thus also the dust density; on the other hand the dust density determines, via radiative transfer effects, the spectrum of the photons and thus the effective radiation pressure. This circular problem is solved by a rapidly converging iterative procedure. We compare our predictions with observed properties of a large sample of OH/IR stars and of Miras and find a good qualitative and quantitative agreement. We confirm a conclusion by Wood et al. (1993) that very luminous OH/IR stars in the Large Magellanic Cloud (LMC) owe their low outflow velocity to the low dust-to-gas ratio, a consequence of the low metallicity of the LMC. Similarly we consider a sample of about 100 OH/IR stars within 200 pc from the galactic center that has an average asymptotic giant branch (AGB) luminosity and an uncommonly high value of v(sub out); we conclude that these stars are probably very metal rich, perhaps even more than the stars in the Baade window studied by Rich (1990).
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 286; 2; p. 523-534
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    An intercomparison of plasma turbulence at three comets: Grigg-Skjellerup, Giacobini-Zinner, and Halley (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The power laws are approximately f(exp -1.9), f(exp -1.9), and f(exp -2.1) respectively for the Grigg-Shjellerup (GS), Giacobini-Zinner (GZ), and Halley (H) comets. Other than similarities in the power spectra, the magnetic field turbulence is considerably different at the three comets. Phase steepening is demonstrated to occur at the trailing edges of the GS waves. This is probably due to nonlinear steepening plus dispersion of the left-hand mode components, i.e., the turbulence is whistler-mode. This too can be explained by nonlinear steepening plus dispersion of the magnetosonic waves. At the level of GS and GZ turbulence development when the spacecraft measurements were made, classical three-wave processes, such as the decay or modulation instabilities do not appear to play important roles. It is most likely that the nonlinear steepening and dispersive time scales are more rapid than three-wave processes, and the latter had not had time to develop for the relatively new turbulence. The wave turbulence at Halley is linearly polarized. The exact nature of this turbulence is still not well understood. Several possibilities are suggested, based on a preliminary analyses.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 9; p. 1149-1152
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    Evolution of the Pinatubo volcanic cloud over Hampton, Virginia (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The eruption of Mt. Pinatubo in June 1991 produced the largest enhancement of stratospheric aerosol loading ever observed by lidar over Hampton, Virginia. Low altitude layers (less than 20 km) were the first to arrive over Hampton in early August, the result of transport associated with a tropospheric anticyclonic cell over North America. The maximum peak scattering ratio, 34 at 22.4 km, and the maximum stratospheric integrated backscatter of 0.0053 sr(exp -1), both at 694 nm, observed since the eruption were measured on February 20, 1992. After decreasing during the spring and summer of 1992, the aerosol burden increased significantly during the winter of 1992-93, evidence of a poleward winter transport from the equatorial reservoir. Over the period from February 1992 to February 1994, the stratospheric aerosol loading decreased with an average 1/e decay time of 10.1 months. The vertical distribution, intensity, and transport of Pinatubo aerosols over this site are described and compared with similar measurements after El Chichon.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 9; p. 1101-1104
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  • 60
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    Nonsphericity of dust-like tropospheric aerosols: Implications for aerosol remote sensing and climate modeling (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: T-matrix computations of light scattering by polydispersions of randomly oriented nonspherical aerosols and Mie computations for equivalent spheres are compared. Findings show that even moderate nonsphericity results in suubstantial errors in the retrieved aerosol optical thickness if satellite reflectance measurements are analyzed using Mie theory. On the other hand, the use of Mie theory for nonspherical aerosols produces negligible errors in the computation of albedo and flux related quantities, provided that the aerosol size distribution and optical thickness are known beforehand. The first result can be explained by large nonspherical-spherical differences in scattering phase function, while the second result follows from small nonspherical-spherical differences in single-scattering albedo and asymmetry parameter. No cancellation of errors occurs if one consistently uses Mie theory in the retrieval algorithm and then in computing the albedo for the retrieved aerosol optical thickness.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 9; p. 1077-1080
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    Atmospheric gradients from very long baseline interferometry observations (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Azimuthal asymmetries in the atmospheric refractive index can lead to errors in estimated vertical and horizontal station coordinates. Daily average gradient effects can be as large as 50 mm of delay at a 7 deg elevation. To model gradients, the constrained estimation of gradient paramters was added to the standard VLBI solution procedure. Here the analysis of two sets of data is summarized: the set of all geodetic VLBI experiments from 1990-1993 and a series of 12 state-of-the-art R&D experiments run on consecutive days in January 1994. In both cases, when the gradient parameters are estimated, the overall fit of the geodetic solution is improved at greater than the 99% confidence level. Repeatabilities of baseline lengths ranging up to 11,000 km are improved by 1 to 8 mm in a root-sum-square sense. This varies from about 20% to 40% of the total baseline length scatter without gradient modeling for the 1990-1993 series and 40% to 50% for the January series. Gradients estimated independently for each day as a piecewise linear function are mostly continuous from day to day within their formal uncertainties.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 9; p. 1041-1044
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  • 62
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    Observations of Pc5 micropulsation-related electric field oscillations in equatorial ionosphere (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5 deg N, 77 deg E, 0.5 deg N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (A(sub p) = 161). Simultaneous 100-n T-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6 deg N gm) and at Narsarsuaq, Greenland (70.6 deg N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730-1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV/m and it increases with height, while it is about 1.0 mV/m in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brofelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the assoicated ionospheric electric field penetrating from high latitudes to the magnetic equator.
    Keywords: GEOPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 12; 6; p. 565-573
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    Centrifugal trapping in the magnetotail (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Particles leving the neutral sheet in the distant magnetotail at times display adiabatic trajectory sequences characterized by an inflection toward the equator and subsequent mirroring in its vicinity. We demonstrate that this low-latitude mirroring results primarily from a centrifugal deceleration due to the fast direction-changing E x B drift. This effect which we refer to as 'centrifugal trapping' appears both in guiding centre and full particle treatments. It thus does not directly relate to nonadiabatic motion. However, pitch angle scattering due to nonadiabatic neutral sheet interaction does play a role in reducing the parallel speed of the particles. We show that centrifugal trapping is an important mechanism for the confinement of the slowest (typically below the equatorial E x B drift speed) plasma sheet populations to the midplane vicinity.
    Keywords: GEOPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 13; 3; p. 242-246
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  • 64
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    Topographic form of the Coast Ranges of the Cascadia Margin in relation ot coastal uplift rates and plate subduction (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Coast Ranges of the Cascadia margin are overriding the subducted Juan de Fuca/Gorda plate. We investigate the extent to which the latitudinal change in attributes related to the subduction process. These attributes include the varibale age of the subducted slab that underlies the Coast Ranges and average vertical crustal velocities of the western margin of the Coast Rnages for two markedly different time periods, the last 45 years and the last 100 kyr. These vertical crustal velocities are computed from the resurveying of highway bech marks and from the present elevation of shore platforms that have been uplifted in the late Quaternary, respectively. Topogarphy of the Coast Ranges is in part a function of the age and bouyancy of the underlying subducted plate. This is evident in the fact that the two highest topographic elements of the Coast Rnages, the Klamath Mountains and the Olympic Mountains, are underlain by youngest subducted oceanic crust. The subducted Blanco Fracture Zone in southernmost Oregon is responsible for an age discontinuity of subducted crust under the Klamath Mountains. The norhtern terminus of hte topographically higher Klamaths is offset to the north relative to the position of the underlying Blanco Fracture Zone, teh offset being in the direction of migration of the farcture zone, as dictated by relative plate motions. Vertical crustal velocities at the coast, derived from becnh mark surveys, are as much as an order of magnitude greater than vertical crustal velocities derived from uplifted shore platforms. This uplift rate discrepancy indicates that strain is accumulating on the plate margin, to be released during the next interplate earthquake. In a latitudinal sense, average Coast Rnage topography is relatively high where bench mark-derived, short-term vertical crustal velocities are highest. Becuase the shore platform vertical crustal velocities reflect longer-term, premanent uplift, we infer that a small percentage of the interseismic strain that accumulates as rapid short-term uplift is not recovered by subduction earthquakes but rather contributes to rock uplift of the Coast Ranges. The conjecture that permanent rock uplift is related to interseismic uplift is consistent with the observation that those segments of the subduction zone subject to greater interseismic uplift rates are at approximately the same latitudes as those segments of the Coast Ranges that have higher magnitudes of rock uplift over the long term.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; B6; p. 12,245-12,255
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    A study of coronal X-ray emission from short-period Algol binaries (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A study of X-ray emission from five short-period Algol-type binaries based on observations with Advanced Satellite for Cosmology and Astrophysics (ASCA) and ROSAT is presented. We have observed RZ Cas with both satellites, and beta Per, U Cep, delta Lib, and TW Dra with ROSAT. Significant intensity variations are seen in the X-ray emission from RZ Cas, U Cep, TW Dra, and delta Lib. These variations seem unrelated to the eclipsing behavior of these systems and are probably due to either rotational modulation of compact active regions on the surfaces of the chromospherically active secondary components or to flaring activity in the systems. The spectra of all but one of the systems require the presence of at least two discrete plasma components with different temperatures (0.6 - 0.7 keV, and approximately 2 keV) and the abundances of the medium-Z elements 20% - 50% of the solar photospheric values. The high resolving power and signal-to-noise ratio of the ASCA spectra allow us to individually constrain the coronal abundances of O, Ne, Mg, Si, S, and Fe in RZ Cas. We demonstrate that, if we use the elemental abundances and temperatures obtained from the analysis of their ASCA spectra as (fixed) inputs, to fit the ROSAT PSPC spectra well requires the presence of a third component (kT approximately 0.2 - 0.3 keV) in RZ Cas and beta Per. A continuous emission measure model of the power-law type (EM(T) variesas (T/T(sub max)(sup alpha)) generally gives a poor fit to the ASCA and ROSAT data on most sources. Circumstellar or circumbinary absorbing matter seems to be present in some of these systems, as indicated by the variable total column density needed to fit their X-ray spectra.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 840-854
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    The relationship between the magnetic field in the Martian magnetotail and upstream solar wind parameters (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Magnetic field data measured by the MAGMA instrument in the Martian magnetotail lobes are compared with the ram pressure of the upstream solar wind observed by the TAUS instrument in the circular orbits of the Phobos 2 spacecraft. High correlation was found between the magnetic field intensity in the Martian magnetotail lobes and the solar wind ram pressure. From this relationship the average flaring angle of the Martian magnetotail was determined as approximately 13 deg, and the average magnetosonic Mach number was estimated as approximately 5. The observed relationship between the Martian magnetotail magnetic field intensity and the solar wind magnetic field reflects the correlation of the solar wind magnetic field to the ram pressure providing a value of approximately 7 for the average Alfvenic Mach number. The flaring angle obtained for the Martian magnetotail was found to be an intermediate value between the flaring angle of the magnetotail of the Earth and that of Venus at comparable distances.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A9; p. 17,199-17,204
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    The art of mapping the magnetosphere (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A comprehensive review is presented of the mathematical models used to represent magnetic fields in the Earth's magnetosphere, of the way existing data-based models use these methods and of the associated problems and concepts. The magnetic field has five main components: the internal field, the magnetopause, the ring current, the tail and Birkeland currents. Methods of representing separately each of these are discussed, as is the deformation of magnetic fields; Appendix B traces the connection between deformations and the Cauchy integral. A summary section lists the uses of data-based models and their likely future evolution, and Appendix A supplements the text with a set of problems.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A9; p. 17,169-17,198
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  • 68
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    On the derivation of coseismic displacement fields using differential radar interferometry: The Landers earthquake (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present a map of the coseimic displacement field resulting from the Landers, California, June 28, 1992, earthquake derived using data acquired from an orbiting high-resolution radar system. We achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques. Data from the ERS 1 synthetic aperture radar instrument acquired in April, July, and August 1992 are used to generate a high-resolution, wide area map of the displacements. The data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30-m resolution element in a 113 km by 90 km image. Our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake. Fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing. Comparison of these data with Global Positioning System and electronic distance measurement survey data yield a correlation of 0.96; thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format. The technique we use is (1) more automatic, (2) more precise, and (3) better validated than previous similar applications of differential radar interferometry. Since we require only remotely sensed satellite data with no additioanl requirements for ancillary information. the technique is well suited for global seismic monitoring and analysis.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; B10; p. 19,617-19,635
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  • 69
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    A tentative detection of the 183-GHz water vapor line in the martian atmosphere: Constraints upon the H2O abundance and vertical distribution (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The 183-GHz water vapor line was tentatively detected on Mars in January 1991, with the IRAM 30-m millimeter antenna, under extremely dry atmospheric conditions. The measurement refers to the whole disk. The spectral line, although marginally detected, can be fit with a constant H2O mixing ratio of 1.0 x 10(exp -5), which corresponds to a water abundance of 1 pr-microns; in any case, an upper limit of 3 pr-microns is inferred. This value is comparable to the very small abundances measured by Clancy (1992) 5 weeks before our observation and seems to imply both seasonal and long-term variations in the martian water cycle.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 110-118
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  • 70
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    Tidal dissipation in oceans on Titan (1995)
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    Publication Date: 2011-08-24
    Description: Titan's large free eccentricity results in significant tidal dissipation. This can be used to constrain the existence and depth of hydrocarbon oceans. A hydrodynamical-numerical 2 deg ocean tide model has been constructed to investigate this connection. The model allows some simple land configurations. The results indicate that existence of such an ocean over the age of the solar system is hard to explain, as is the existence of the large eccentricity itself. If such an ocean exists, it is likely to be more than 500 m deep, ignoring the influence of land masses.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 39-56
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  • 71
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    Birkeland currents in the plasma sheet (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A search was conducted for the signatures of Birkeland currents in the Earth's magnetic tail, using observed values of B(sub x) and B(sub y) from large sets of spacecraft data. The data were binned by x and y for -10 greater than x(sub GSM) greater than -35 and absolute value of y(sub GSM) less than or equal to 20 R(sub E) (less than or equal to 30 R(sub E) for x(sub GSM) less than or equal to -25 R(sub E)) and in each bin their distribution in the (B(sub x), B(sub y)) plane was fitted by least squares to a piecewise linear function. That gave average x-y distributions of the flaring angle between B(sub xy) and the x direction, as well as that angle's variation across the thickness of the plasma sheet. Angles obtained in the central plasma sheet differed from those derived near the lobe boundary. That is the expected signature if earthward or tailward Birkeland current sheets are embedded in the plasma sheet, and from this dfiference we derived the dawn-dusk profiles of the tail Birkeland currents for several x(sub GSM) intervals. It was found that (1) the Birkeland currents have the sense of region 1 currents, when mapped to the ionosphere; (2) both the linear current density (kiloamperes/R(sub E)) and the net magnitude of the field-aligned currents decrease rapidly down the tail; (3) the total Birkeland current at x approximately equals -10 R(sub E) equals approximately equals 500-700 kA, which is approx. 30% of the net region 1 current observed at ionospheric altitudes, in agreement with model mapping results; and (4) the B(sub z) and B(sub y) components of the interplanetary magnetic field influence the distribution of Birkeland currents in the tail.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A11; p. 19,455-19,464
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    Precession and nutation from joint analysis of radio interferometric and lunar laser ranging observations (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: 24 years of Lunar Laser Ranging (LLR) observations and 16 years of Very Long Baseline Interferometry (VLBI) observations are combined in a global analysis to yield improved estimates of the Earth's precession and nutation. The correction to the International Astronomical Union (IAU) (1976) precession constant inferred from this joint VLBI/LLR analysis is -3.00 +/- 0.20 milliarcsec/yr (mas/yr). A significant obliquity rate correction of -0.20 +/- 0.08 mas/yr is also found. In all, 32 forced nutation coefficients are estimated. These coefficients confirm that the IAU (1980) nutation theory is in error by several mas. The estimated nutation coeficients are found to vary by as much as several tenths of mas, depending on the a priori nutation model used to analyze the VLBI and LLR data. Forced circular nutations derived from this analysis agree with the ZMOA-1990-2 nutation theory at the 0.2 mas level for the 18.6 yr terms, and at the 0.05 mas level for the other terms (periods less than or = 1 yr). A retrograde free core nutation with an amplitude of 0.20 mas is also detected. Its phase is found to be very sensitive to the precise value of the free core nutation period used in the solution. Separate analyses of four independent subsets of the LVBI data indicate no significant variations of the free core nutation since 1988. The pre-1988 estimates of the free core nutation are consistent with the post-1988 estimates but are not accurate enough to rule out possible variations of the free core nutation at these earlier epochs.
    Keywords: ASTROPHYSICS
    Type: The Astronomical Journal (ISSN 0004-6256); 109; 1669; p. 418-427
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    Three-dimensional magnetic reconnection and the magnetic topology of coronal mass ejection events (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Measurements of superthermal electron fluxes in the solar wind indicate that field lines within coronal mass ejections, CMEs, near and beyond 1 AU are normally connected to the Sun at both ends. However, on occasion some field lines embedded deep within CMEs appear to be connected to the Sun at only one end. Here we propose an explanation for how such field lines arise in terms of 3-dimensional reconnection close to the Sun. Such reconnection also provides a natural explanation for the flux rope topology characteristic of many CMEs as well as the coronal loops formed during long-duration, solar X-ray events. Our consideration of the field topologies resulting from 3-dimensional reconnection indicates that field lines within and near CMEs may on occasion be connected to the outer heliosphere at both ends.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 8; p. 869-872
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  • 74
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    Focused interplanetary transport of approximately 1 MeV solar energetic protons through self-generated Alfven waves (1994)
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    Publication Date: 2011-08-24
    Description: We present a model of the focused transport of approximately 1 MeV solar energetic protons through interplanetary Alfven waves that the protons themselves amplify or damp. It is based on the quasi-linear theory but with a phenomenological pitch angle diffusion coefficient in the 'resonance gap.' For initial Alfven wave distributions that give mean free paths greater than approximately 0.5 AU for approximately 1 MeV protons in the inner heliosphere, the model predicts greater than roughly an order of magnitude amplification (damping) in the outward (inward) propagating resonant Alfven waves at less than or approximately equal to o.3 AU heliocentric distance. As the strength of proton source is increased, the peak differential proton intensity at approximately 1 MeV at 1 AU increases to a maximum of approximately 250 particles (/(sq cm)(s)(sr)(MeV)) and then decreases slowly. It may be attenuated by a factor of 5 or more relative to the case without wave evolution, provided that the proton source is sufficiently intense that the resulting peak differential intensity of approximately 1 MeV protons at 1 AU exceeds approximately 200 particles (/(sq cm)(s)(sr)(MeV)). Therefore, in large solar proton events, (1) one may have to take into account self-amplified waves in studying solar particle propagation, (2) the number of accelerated protons escaping from a flare or interplanetary shock may have been underestimated in past studies by a significant factor, and (3) accelerated protons escaping from a traveling interplanetary shock at r less than or approximately equal to 0.3 AU should amplify the ambient hydromagnetic waves siginificantly to make the shock an efficient accelerator, even if initially the mean free path is greater than or approximately equal to 1 AU.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 424; 2; p. 1032-1048
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    One-photon annihilation of thermal positrons with bound atomic electrons (1994)
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    Publication Date: 2011-08-24
    Description: Direct one-photon annihilation rate of positrons with a bound atomic electron is evaluated in the nonrelativistic limit. The K- and L-shell contributions are estimated including the screening and effective Coulomb repulsion effects. The annihilation rate of thermal positrons is calculated for various temperatures. The total number of one-photon annihilation events in the interstellar medium is discussed. These results provide the directional and structural information for cosmic gamma-ray sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 424; 2; p. 988-990
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    Ulysses magnetic field observations of fluctuations within polar coronal flows (1995)
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    Publication Date: 2011-08-24
    Description: The Ulysses spacecraft has gathered data from within flows from the Sun's southern polar coronal hole, the first in situ measurement of this region. We present a brief analysis of the heliospheric magnetic field data from this region, using a fractal method. As is the case near the ecliptic, estimated spectral exponents are near 5/3 on spacecraft scales of seconds to minutes. On longer time scales, however, there appears to be a significantly different population in polar flows, which is similar to that found by the Helios spacecraft in fast solar wind flows at 0.3 AU.
    Keywords: ASTROPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 13; 1; p. 105-107
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    The efficiency of 'viscous interaction' between the solar wind and the magnetosphere during intense northward IMF events (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We examined 11 cases when the interplanetary magnetic field (IMF) was intensely northward (greater than 10 nT) for long durations of time (greater than 3 hours), to quantitatively determine an uppler limit on the efficiency of solar wind energy injection into the magnetosphere. We have specifically selected these large B(sub N) events to minimize the effects of magnetic reconnection. Many of these cases occurred during intervals of high-speed streams associated with coronal mass ejections when viscous interaction effects might be at a maximum. It is found that the typical efficiency of solar wind energy injection into the magnetosphere is 1.0 x 10(exp -3) to 4.0 x 10(exp -3), 100 to 30 times less efficient than during periods of intense southward IMFs. Other energy sinks not included in these numbers are discussed. Estimates of their magnitudes are provided.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 6; p. 663-666
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    The neutral oxygen spectrum. 2: Pumping by hydrogen Lyman-beta under the optically thin condition: A first application to the classical novae (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A calculation, employing a detailed model of neutral oxygen, is carried out to give fluorescent line intensities expected in a long-proposed photoexcitation by accidental resonance (PAR) process in which hydrogen Lyman-beta photoexcites the oxygen spectrum. The results pertain to the optically thin case but provide an upper limit to the fluorescent intensities which can be attained. They are applied to analyze line ratios involving the strong 8446 A line observed in classical novae during the diffusion-enhanced and Orion phases. Operation of the PAR process in the novae is verified. It is found that photoexcitation rates in the ejecta reach values greater than 0.1/sec, corresponding to hydrogen Lyman-beta radiation field intensities greater than 1250 ergs/cm/sec/sr.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 1; p. 346-356
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    Physical properties of the OMC-2 and OMC-3 cores from CS and C(18)O observations (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have investigated the properties of the OMC-2 and OMC-3 cores in the Orion giant molecular cloud using high spatial spectral resolution observations of several transitions of the (13)CO, C(18)O, C(S-32) and C(S-34) molecules taken with the SEST telescope. The OMC-2 core consists of one clump (22 solar mass) with a radius of 0.11 pc surrounded by a cluster of 11 discrete infrared sources. The H2 column density and volume density in the center of this clump are 2 x 10(exp 22)/sq cm and 9 x 10(exp 5)/cu cm respectively. From a comparison between physical parameters derived from C(18)O and C(S-32) observations we conclude that the molecular envelope around the core has been completely removed by these sources and that only the very dense gas is left. OMC-3 shows a more complex elongated structure in C(18)O and CS than OMC-2. The C(S-32) and C(S-34) maps show that the denser region can be separated into at least sub-cores of roughly equal sizes (radius approximately equals 0.13 pc), with n(H2) = 6 x 10(exp 5)/cu cm, and a mass of 10 solar mass (from C(S-32)). The very different masses obtained for the central core from C(18)O and C(S-32) (55 and 12 solar mass respectively) indicate that a massive envelope is still present around the very dense sub-cores. We report the first detection of several molecular outflows in OMC-3. The presence of an IRAS source and the first detection of these outflows confirm that star formation is going on in OMC-3. Based on the different physical properties of these regions compared with OMC-1, OMC-2 appears to be in an intermediate evolutionary stage between OMC-1 and OMC-3.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 294; 3; p. 835-854
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    Origin of tektites (1994)
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    Publication Date: 2011-08-24
    Description: The origin of tektites has been obscure because of the following dilemma. The application of physical principles to the data available on tektites points strongly to origin from one or more lunar volcanoes; but few glasses of tektite composition have hitherto been reported from the lunar samples. Instead, the lunar silicic glasses consist chiefly of a material very rich in K2O and poor in MgO. The ratio of K2O/MgO is higher in these glasses than in any tektites reported. The solution of the dilemma seems to come from the study of some recently discovered terrestrial deposits of tektite glass with high values of K2O/MgO at the Cretaceous Tertiary boundary. These glasses are found to be very vulnerable to crystallization into sandine or to alteration to smectite. These end products are known and are more abundant than any terrestrial deposits of tektite glass. It seems possible that, in fact, the moon produces tektite glass, mostly of the high K2O-low MgO type; but on Earth these deposits are destroyed. The much less abundant deposits with lower K and higher Mg are observed because they survive. Other objections to the lunar origin hypothesis appear to be answerable.
    Keywords: ASTROPHYSICS
    Type: Meteoritics (ISSN 0026-1114); 29; 1; p. 73-78
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    Radiative shock overstability of finite-sized objects (1994)
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    Publication Date: 2011-08-24
    Description: We investigate the radiative shock overstability for finite-sized objects. We follow the analysis of Chevalier & Imamura (1982), but we take into account the transverse flow of material out of the potshock region. The mass loss from the postshock region stabilizes the flow. As a rough estimate, the shock radiative instability takes place when the shock wave position with no radiative cooling (only mass loss present) is larger than the shock position with no mass loss (only radiative cooling present). For typical conditions of planetary nebulae we find that in order for the shock radiative overstability to occur, the nebular radius should be R approximately less than 10(exp 19) n(sub a)(exp -1) cm, where n(sub alpha) is the total number density of the interstellar medium (in units of cm(exp -3). We give several examples of interacting planetary nebulae in light of this condition.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 434; 1; p. 262-267
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    High resolution studies of heacy NO(y) molecules in atmospheric spectra (1994)
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    Publication Date: 2011-08-24
    Description: New line parameters for two heavy odd nitrogen molecules HNO3 in the nu(sub 5)/2nu(sub 9) region, and ClONO2 in the nu(sub 4) region are incorporated in the analysis of high resolution i.r. atmospheric spectra. The line parameters are tested and renormalized vs laboratory spectra, and then applied to retrievals from balloon-borne and ground-based solar absorption spectra.
    Keywords: GEOPHYSICS
    Type: Journal of Quantitative Spectroscopy & Radiative Transfer (ISSN 0022-4073); 52; 3-4; p. 367-377
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    The Earth's magnetosphere is 165 R(sub E) long: Self-consistent currents, convection, magnetospheric structure, and processes for northward interplanetary magnetic field (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The subject of this paper is a self-consistent, magnetohydrodynamic numerical realization for the Earth's magnetosphere which is in a quasi-steady dynamic equilibrium for a due northward interplanetary magnetic field (IMF). Although a few hours of steady northward IMF are required for this asymptotic state to be set up, it should still be of considerable theoretical interest because it constitutes a 'ground state' for the solar wind-magnetosphere interaction. Moreover, particular features of this ground state magnetosphere should be observable even under less extreme solar wind conditions. Certain characteristics of this magnetosphere, namely, NBZ Birkeland currents, four-cell ionospheric convection, a relatively weak cross-polar potential, and a prominent flow boundary layer, are widely expected. Other characteristics, such as no open tail lobes, no Earth-connected magnetic flux beyond 155 R(sub E) downstream, magnetic merging in a closed topology at the cusps, and a 'tadpole' shaped magnetospheric boundary, might not be expected. In this paper, we will present the evidence for this unusual but interesting magnetospheric equilibrium. We will also discuss our present understanding of this singular state.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3623-3635
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    Localized tearing modes in the magnetotail driven by curvature effects (1995)
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    Publication Date: 2011-08-24
    Description: The stability of collisionless tearing modes is examined in the presence of curvature drift resonances and the trapped particle effects. A kinetic description for both electrons and ions is employed to investigate the stability of a two-dimensional equilibrium model. The main features of the study are to treat the ion dynamics properly by incorporating effects associated with particle trajectories in the tail fields and to include the linear coupling of trapped particle modes. Generalized dispersion relations are derived in several parameter regimes by considering two important sublayers of the reconnecting region. For a typical choice of parameters appropriate to the current sheet region, we demonstrate that localized tearing modes driven by ion curvature drift resonance effects are excited in the current sheet region with growth time of the order of a few seconds. Also, we examine nonlocal characteristics of tearing modes driven by curvature effects and show that modes growing in a fraction of a second arise when mode widths are larger than the current sheet width. Further, we show that trapped particle effects, in an interesting frequency regime, significantly enhance the growth rate of the tearing mode. The relevance of this theory for substorm onset phase and other features of the substorms is briefly discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3563-3572
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    Identification of the HNO3 3 nu(sub 9) - nu(sub 9) band Q branch in stratospheric solar occultation spectra (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The spectroscopic identification for the HNO3 3 nu(sub 9) - nu(sub 9) band Q branch at 830.4/cm is reported based on 0.01/cm resolution solar occultation spectra of the lower stratosphere recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer and a recent analysis of this band. Least-squares fits to 0.0025/cm resolution laboratory spectra in the Q branch region indicate an integrated intensity of 0.529 x 10(exp -18)/cm/mol/sq cm at 296 K for this weak band. Stratospheric HNO3 retrievals derived from the ATMOS data are consistent with this value within its estimated uncertainty of about +/- 30%. A set of spectroscopic line parameters suitable for atmospheric studies has been generated.
    Keywords: GEOPHYSICS
    Type: Journal of Quantitative Spectroscopy & Radiative Transfer (ISSN 0022-4073); 52; 3-4; p. 319-322
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    Infrared spectroscopic measurements of the ethane (C2H6) total column abundance above Mauna Loa, Hawaii -- seasonal variations (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: About 200 i.r. solar spectra recorded at 0.01/cm resolution on 71 days between November 1991 and July 1993 at the Network for the Detection of Stratospheric Change (NDSC) station at Mauna Loa, Hawaii (latitude 19.53 deg N, longitude 155.58 deg W, elevation 3.459 km) have been analyzed with a nonlinear least-squares spectral fitting technique to study temporal variations in the total column of atmospheric ethane (C2H6) above the site. The results were derived from the analysis of the unresolved nu(sub 7) band (P)Q(sub 3) subbranch at 2976.8/cm. A distinct seasonal cycle is observed with a factor of 2 variation, a maximum total column of 1.16 x 10(exp 16) mol/sq cm at the end of winter, and a minimum total column of 0.53 x 10(exp 16) mol/sq cm at the end of summer. Our measurements are compared with previous observations and model predictions.
    Keywords: GEOPHYSICS
    Type: Journal of Quantitative Spectroscopy & Radiative Transfer (ISSN 0022-4073); 52; 3-4; p. 273-279
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    Mid-infrared extinction by sulfate aerosols from the Mt. Pinatubo eruption (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Quantitative measurements of the wavelength dependence of aerosol extinction in the 750-3400/cm spectral region have been derived from 0.01/cm resolution stratospheric solar occultation spectra recorded by the ATMOS (Atmospheric Trace Molecule Spectroscopy) Fourier transform spectrometer about 9 1/2 months after the Mt Pinatubo volcanic eruption. Strong, broad aerosol features have been identified near 900, 1060, 1190, 1720, and 2900/cm below a tangent height of approximately 30 km. Aerosol extinction measurements derived from approximately 0.05/cm wide microwindows nearly free of telluric line absorption in the ATMOS spectra are compared with transmission calculations derived from aerosol size distribution profiles retrieved from correlative SAGE (Stratospheric Aerosol and Gas Experiment) II visible and near i.r. extinction measurements, seasonal and zonally averaged H2SO4 aerosol weight percentage profiles, and published sulfuric acid optical constants derived from room temperature laboratory measurements. The calculated shapes and positions of the aerosol features are generally consistent with the observations, thereby confirming that the aerosols are predominantly concentrated H2SO4-H2O droplets, but there are significant differences between the measured and calculated wavelength dependences of the aerosol extinction. We attribute these differences as primarily the result of errors in the calculated low temperature H2SO4-H2O optical constants. Errors in both the published room temperature optical constants and the limitations of the Lorentz-Lorenz relation are likely to be important.
    Keywords: GEOPHYSICS
    Type: Journal of Quantitative Spectroscopy & Radiative Transfer (ISSN 0022-4073); 52; 3-4; p. 241-252
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  • 88
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    Mass loading and velocity diffusion models for heavy pickup ions at comet Grigg-Skjellerup (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We compare model predictions of cometary water group ion densities and the solar wind slow down with measurements made by the Giotto Johnstone plasma analyzer implanted ion sensor at the encounter with comet Grigg-Skjellerup (G-S) on July 10, 1992. The observed slope of the ion density profile on approach to the comet is unexpectedly steep. Possible explanations for this are discussed. We present also a preliminary investigation of the quasilinear velocity-space diffusion of the implanted heavy ion population at G-S using a transport equation including souce, convection, adiabatic compression, and velocity diffusion terms. Resulting distributions are anisotropic, in agreement with observations. We consider theoretically the waves that may be generated by the diffusion process for the observed solar wind conditions. At initial ion injections, waves are generated at omega approximately Omega(sub i) the ion gyrofrequency, and lower frequencies are predicted for diffusion toward a bispherical shell.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A12; p. 20,995-21,002
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  • 89
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    Mirror modes and fast magnetoacoustic waves near the magnetic pileup boundary of comet P/Halley (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Large-amplitude ultralow-frequency wave structure observed on both sides of the magnetic pileup boundary of comet P/Halley during the flyby of the Giotto spacecraft have been analyzed using suprathermal electron density and magnetic field observations. Upstream of the boundary, electron density and magnetic field magnitude variations are anticorrelated, while in the pileup region these quantities are clearly correlated. Both in front of and behind the pileup boundary the observed waves are quasi-perpendicular wave structures as a minimum variance analysis shows. A detailed comparison of our observations in the prepileup region with theoretical and numerical results shows that the mirror mode mode waves may have been generated by a mirror instability driven by the pressure anisotropy of the ring-type distributions of the heavy (water group) pickup cometary ions.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A12; p. 20,955-20,964
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  • 90
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    Latitude variations of stratospheric trace gases (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present vertical column abundances of H2O, N2O, HNO3, NO2, O3, HF, HCl, and ClNO3, determined from solar absorption spectra measured by the JPL MkIV interferometer from the NASA DC-8 aircraft. These observations, taken in 1987 and 1992, covered latitudes ranging from 85 deg S to 85 deg N. Although most gases display latitude symmetry, large asymmetries in H2O, HNO3, and O3 are apparent, which can be ascribed to processes enhanced by the colder Antarctic winter temperatures.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 23; p. 2599-2602
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  • 91
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    In situ measurements of the NO2/NO ratio for testing atmospheric photochemical models (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Simultaneous in situ measurements of NO2, NO, O3, ClO, pressure and temperature have been made for the first time, presenting a unique opportunity to test our current understanding of the photochemistry of the lower stratospere. Data were collected from several flights of the ER-2 aircraft at mid-latitudes in May 1993 during NASA's Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE). The daytime ratio of NO2/NO remains fairly constant at 19 km with a typical value of 0.68 and standard deviation of +/- 17. The ratio observations are compared with simple steady-state calculations based on laboratory-measured reaction rates and modeled NO2 photolysis rates. At each measurement point the daytime NO2/NO with its measurements uncertainty overlap the results of steady-state caculations and associated uncertainty. Possible sources of error are examined in both model and measurements. It is shown that more accurate laboratory determinations of the NO + 03 reaction rate and of the NO2 cross-sections in the 200-220 K temperature range characteristic of the lower stratosphere would allow for a more robust test of our knowledge of NO(X) phtochemistry by reducing significant sources if uncertainties in the interpretation of statospheric measurements.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 23; p. 2555-2558
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  • 92
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    The short-term prediction of universal time and length of day using atmospheric angular momentum (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The ability to predict short-term variations in the Earth's rotation has gained importance in recent years owing to more precise spacecraft tracking requirements. Universal time (UT1), that component of the Earth's orientation corresponding to the rotation angle, can be measured by number of high-precision space geodetic techniques. A Kalman filter developed at the Jet Propulsion Laboratory (JPL) optimally combines these different data sets and generates a smoothed times series and a set of predictions for UT1, as well as for additional Earth orientation components. These UT1 predictions utilize an empirically derived random walk stochastic model for the length of the day (LOD) and require frequent and up-to-date measurements of either UT1 or LOD to keep errors from quickly accumulating. Recent studies have shown that LOD variations are correlated with changes in the Earth's axial atmospheric angular momentum (AAM) over timescales of several years down to as little as 8 days. AAM estimates and forecasts out to 10 days are routinely available from meteorological analysis centers; these data can supplement geodetic measurements to improve the short-term prediction of LOD and have therefore been incorporated as independent data types in the JPL Kalman filter. We find that AAM and, to a lesser extent, AAM forecast data are extremely helpful in generating accurate near-real-time estimates of UT1 and LOD and in improving short-term predictions of these quantities out to about 10 days.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; B4; p. 6981-6996
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  • 93
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    Grains in ionized nebulae: Spectral line diagnostics (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the ((Ca II) lambda lambda 291, 7324 doublet and the detection of Al II) lambda lambda 2660, 2669 in the ultraviolet, we determine the extent of aluminum and calcium depletion onto grains in NGC 7027 and the Orion Nebula. Our results show a approximately 0.3 dex depletion for Al, but a depletion of more than two and a half orders of magnitude for Ca. A similar calculation based on Mg II lambda 2798 yields roughly a 0.8 dex depletion for Mg. This reaffirms the discrepancy between depletion determined from high and low ionization Mg lines. We also find evidence for a 'depletion gradient' in Ca in NGC 7027, since the calcium depletion we infer for the outer, more neutral regions using (Ca II) is somewhat higher than that inferred for the inner high-ionization region, using (Ca v). This gradient can test current models of the survival of grains within hot ionized gas.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 793-799
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  • 94
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    Spectral study of GX 339-4 in the low-intensity state observed with Ginga (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The energy spectra of the black-hole candidate GX 339-4 in the low-intensity state were observed on four occasions through 1989 to 1991 with the Large Area Counter on board the Ginga satellite. The spectra showed significant deviations from a power-law, with an iron K(sub alpha) emission line at approximetaly 6.4 keV and a broad iron K-edge structure above approximately 7 keV. The enrgy spectra above approximately 4 keV were successfully explained with a reflection model, in which part of the incident X-rays with a power-law spectrum is Compton reflected by optically thick matter, resulting in a harder continuum component with iron K-edge absorption and an iron flourescent line. The line equivalent width with respect to the reflection component decreases as the source flux increases. This is consistent with an increase in the ionization state of the material, so that resonant absorption followed by Auger ionization depletes the line. The photon-index of the power-law component was clearly variable, and it correlated with the relative amount of the reflection component. Such a correlation may be explained in the context of the anisotropic Comptonization models of Haardt et al. (1993), or by a variation of the relative geometry of the source and disk.
    Keywords: ASTROPHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 46; 1; p. 107-115
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  • 95
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    Possible radio wave precursors associated with the comet Shoemaker-Levy 9/Jupiter impacts (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We suggest that prior to its impact with Jupiter, comet Shoemaker-Levy 9 will behave as an electrical generator in the Jovian magnetosphere, converting planetary rotational energy to electrical energy via a dust/plasma interaction. This electrical energy will then be deposited in the dayside auroral region where it may drive various auroral phenomena including cyclotron radio emission. Such emission could be detected by spacecraft like Ulysses and Galileo many hours prior to the actual comet impact with the upper atmosphere. We apply the theory originally developed to explain the spokes in Saturn's rings. This theory allows us to quantify the driving potential associated with the comet and, consequently, to determine the radio power created in the auroral region. We conclude that if enough fine dust is present in the cometary system, comet-induced auroral radio emissions will reach detectable levels. This emission should be observable in the dayside hemisphere about 12-24 hours prior to each fragment impact.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 11; p. 1067-1070
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  • 96
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    Cosmic microwave background dipole spectrum measured by the COBE FIRAS instrument (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Far-Infrared Absolute Spectrophotometer (FIRAS) instrument on the Cosmic Background Explorer (COBE) has determined the dipole spectrum of the cosmic microwave background radiation (CMBR) from 2 to 20/cm. For each frequency the signal is decomposed by fitting to a monopole, a dipole, and a Galactic template for approximately 60% of the sky. The overall dipole spectrum fits the derivative of a Planck function with an amplitude of 3.343 +/- 0.016 mK (95% confidence level), a temperature of 2.714 +/- 0.022 K (95% confidence level), and an rms deviation of 6 x 10(exp -9) ergs/sq cm/s/sr cm limited by a detector and cosmic-ray noise. The monopole temperature is consistent with that determined by direct measurement in the accompanying article by Mather et al.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 420; 2; p. 445-449
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  • 97
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    Relative emission-line strengths for the 146 and 63 micron transitions in O I and a comparison with far-infrared observations of photodissociation regions (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Theoretical O I density-sensitive emission-line ratios R = I(2s(sup 2))(2p(sup 4))((sup 3)P(sub 0))-((2s(sup 2))(2p(sup 4))((sup 3)P(sub 1)))/I((2s(sup 2))(2p(sup 4))((sup 3)P(sub 1))-(2s(sup 2))(2p(sup 4))((sup 3)P(sub 2))) = I(146 micrometers)/I(63 micrometers) are presented for a range of temperatures (T = 100-10,000 K), neutral hydrogen densities (N(sub H) = 10(exp -2) to 10(exp 7)/cu cm) and radiation fields (G(sub 0) = 1-10(exp 6)) applicable to both photodissociation regions (PDRs) and H II regions and the diffuse ionized medium (DIM). The observed values of R for several PDRs, measured from far-infrared spectra obtained with the Kuiper Airborne Observatory (KAO), imply hydrogen densities which are in good agreement with those determined using other methods. This provides observational support for the validity of the theoretical O I line ratios, and hence the atomic data used in their derivation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 434; 2; p. 811-815
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  • 98
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    Detection of the overtone of the 3.3 micron emission feature in IRAS 21282+5050 (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The 1.6-1.8 micron spectrum of the planetary nebula, IRAS 21282+5050, a strong emitter of the unidentified interstellar bands, contains a 0.02 micron wide eimission feature centered at 1.680 micron, which is well matched by laboratory spectra of the 0-2 CH stretching mode in polycyclic aromatic hydrocarbons (PAHs). We identify the new feature as the overtone of the well-known 3.3 micron band. In view of the high excitation required for emission in this band, the identification indicates that the emission is by free molecules rather than molecular moieties in solid dust grains. Modeling of the intensity ratio of the 2-0 to 1-0 band implied that the PAHs emitting in these bands contain about 60 carbon atoms. It is inferred that the nu = 2-1 hot band of the CH stretching mode occurs at about 3.43 micron and contributes to the long-wavelength shoulder of the 3.40 micron feature. The main 3.40 micron feature probably is due to aliphatic sidegroups on PAH molecules.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 434; 1; p. L15-L18
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  • 99
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    Nonlinear stability of Halley comethosheath with transverse plasma motion (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Weakly nonlinear Magneto Hydrodynamic (MHD) stability of the Halley cometosheath determined by the balance between the outward ion-neutral drag force and the inward Lorentz force is investigated including the transverse plasma motion as observed in the flanks with the help of the method of multiple scales. The eigenvalues and the eigenfunctions are obtained for the linear problem and the time evolution of the amplitude is obtained using the solvability condition for the solution of the second order problem. The diamagnetic cavity boundary and the adjacent layer of about 100 km thickness is found unstable for the travelling waves of certain wave numbers. Halley ionopause has been observed to have strong ripples with a wavelength of several hundred kilometers. It is found that nonlinear effects have stabilizing effect.
    Keywords: ASTROPHYSICS
    Type: Astrophysics and Space Science (ISSN 0004-640X); 222; 1-2; p. 113-125
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  • 100
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    Molecular rotational line profiles from oxygen-rich red giant winds (1994)
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    Publication Date: 2011-08-24
    Description: We have developed a radiative transfer model of the dust and gas envelopes around late-type stars. The gas kinetic temperature for each star is calculated by solving equations of motion and the energy balance simultaneously. The main processes include viscous heating and adiabatic and radiative cooling. Heating is dominated by viscosity as the grains stream outward through the gas, with some contribution in oxygen-rich stars by near-IR pumping of H2O followed by collisional de-excitation in the inner envelope. For O-rich stars, rotational H2O cooling is a dominant mechanism in the middle part of the envelope, with CO cooling being less significant. We have applied our model to three well-studied oxygen-rich red giant stars. The three stars cover a wide range of mass-loss rates, and hence they have different temperature structures. The derived temperature structures are used in calculating CO line profiles for these objects. Comparison of the dust and gas mass-loss rates suggests that mass-loss rates are not constant during the asymptotic giant branch phase. In particular, the results show that the low CO 1-0 antenna temperatures of OH/IR stars reflect an earlier phase of much lower mass-loss rate.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 435; 2; p. 852-863
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