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  • Chemistry  (9,496)
  • Polymer and Materials Science  (3,965)
  • LUNAR AND PLANETARY EXPLORATION  (613)
  • STRUCTURAL MECHANICS  (443)
  • 1990-1994  (10,552)
  • 1980-1984
  • 1945-1949
  • 1925-1929
  • 1990  (10,552)
Collection
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  • 1990-1994  (10,552)
  • 1980-1984
  • 1945-1949
  • 1925-1929
Year
  • 1
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    A base dispute (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-08-03
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Waldrop, M M -- New York, N.Y. -- Science. 1990 Aug 3;249(4968):472-3.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2382127" target="_blank"〉PubMed〈/a〉
    Keywords: Chemical Phenomena ; Chemistry ; *Information Systems ; Jurisprudence ; Societies, Scientific ; United States
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Direct measurement of forces between linear polysaccharides xanthan and schizophyllan (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-09-14
    Description: Direct osmotic stress measurements have been made of forces between helices of xanthan, an industrially important charged polysaccharide. Exponentially decaying hydration forces, much like those already measured between lipid bilayer membranes or DNA double helices, dominate the interactions at close separation. Interactions between uncharged schizophyllans also show the same kind of hydration force seen between xanthans. In addition to the practical possibilities for modifying solution and suspension properties through recognition and control of molecular forces, there is now finally the opportunity for theorists to relate macroscopic properties of a polymer solution to the microscopic properties that underlie them.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Rau, D C -- Parsegian, V A -- New York, N.Y. -- Science. 1990 Sep 14;249(4974):1278-81.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory of Biochemistry and Metabolism, National Institute of Diabetes and Digestive and Kidney Diseases, National Institues of Health, Bethesda, MD 20892.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2144663" target="_blank"〉PubMed〈/a〉
    Keywords: Carbohydrate Sequence ; Chemical Phenomena ; Chemistry ; Gels ; *Glycosaminoglycans ; Macromolecular Substances ; Molecular Sequence Data ; Osmosis ; *Polysaccharides, Bacterial ; *Sizofiran ; Solutions ; Viscosity
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
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    Common features of protein unfolding and dissolution of hydrophobic compounds (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-02-02
    Description: Protein unfolding and the dissolution of hydrophobic compounds (including solids, liquids, and gases) in water are characterized by a linear relation between entropy change and heat capacity change. The same slope is found for various classes of compounds, whereas the intercept depends on the particular class. The feature common to these processes is exposure of hydrophobic groups to water. These observations make possible the assignment of the heat capacity change to hydrophobic solvation and lead to the description of protein stability in terms of a hydrophobic and a nonhydrophobic contribution. A general representation of protein stability is given by the heat capacity change and the temperature.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Murphy, K P -- Privalov, P L -- Gill, S J -- New York, N.Y. -- Science. 1990 Feb 2;247(4942):559-61.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2300815" target="_blank"〉PubMed〈/a〉
    Keywords: Chemical Phenomena ; Chemistry ; *Protein Denaturation ; *Proteins ; Thermodynamics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
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    Interparticle collisions driven by ultrasound (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-03-02
    Description: Ultrasound has become an important synthetic tool in liquid-solid chemical reactions, but the origins of the observed enhancements remained unknown. The effects of high-intensity ultrasound on solid-liquid slurries were examined. Turbulent flow and shock waves produced by acoustic cavitation were found to drive metal particles together at sufficiently high velocities to induce melting upon collision. A series of transition-metal powders were used to probe the maximum temperatures and speeds reached during such interparticle collisions. Metal particles that were irradiated in hydrocarbon liquids with ultrasound underwent collisions at roughly half the speed of sound and generated localized effective temperatures between 2600 degrees C and 3400 degrees C at the point of impact for particles with an average diameter of approximately 10 microns.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Doktycz, S J -- Suslick, K S -- New York, N.Y. -- Science. 1990 Mar 2;247(4946):1067-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Chemical Sciences, University of Illinois, Urbana 61801.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2309118" target="_blank"〉PubMed〈/a〉
    Keywords: Chemical Phenomena ; Chemistry ; *Metals ; Microscopy, Electron, Scanning ; Microspheres ; *Ultrasonics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
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    Changes in mean concentration, phase shifts, and dissipation in a forced oscillatory reaction (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-01-12
    Description: Experiments are presented that confirm earlier predictions that the mode of supply of reactants to a nonlinear (bio)chemical reaction determines or controls concentrations at steady states far from equilibrium. The oxidation of nicotinamide adenine dinucleotide (NADH) catalyzed by the enzyme horseradish peroxidase with continuous input of oxygen was studied; NAD+ is continuously recycled to NADH through a glucose-6-phosphate dehydrogenase system. A comparison of steady-state concentrations is made with an oscillatory oxygen input and a constant input at the same average oxygen input for both modes. By varying the frequency and amplitude of the perturbation (O2 influx), the following may be changed: the average concentration of NADH; the Gibbs free energy difference delta G of the reactants and products at steady state; the average rate of the reaction; the phase relation between the oscillatory rate and delta G; and the dissipation. These results confirm the possibility of an "alternating current chemistry," of control and optimization of thermodynamic efficiency and dissipation by means of external variation of constraints in classes of nonlinear reactions and biological pumps, and of improvements of the yield in such reactions (heterogeneous catalysis, for example).〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lazar, J G -- Ross, J -- New York, N.Y. -- Science. 1990 Jan 12;247(4939):189-92.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, Stanford University, CA 94305.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2294601" target="_blank"〉PubMed〈/a〉
    Keywords: Adenosine Triphosphate/metabolism ; Chemical Phenomena ; Chemistry ; Glucosephosphate Dehydrogenase/*metabolism ; Horseradish Peroxidase/*metabolism ; Kinetics ; NAD/*metabolism ; Oxidation-Reduction ; Oxygen/metabolism ; Peroxidases/*metabolism ; Thermodynamics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    An antibody binding site on cytochrome c defined by hydrogen exchange and two-dimensional NMR (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-08-17
    Description: The interaction of a protein antigen, horse cytochrome c (cyt c), with a monoclonal antibody has been studied by hydrogen-deuterium (H-D) exchange labeling and two-dimensional nuclear magnetic resonance (2D NMR) methods. The H-exchange rate of residues in three discontiguous regions of the cyt c polypeptide backbone was slowed by factors up to 340-fold in the antibody-antigen complex compared with free cyt c. The protected residues, 36 to 38, 59, 60, 64 to 67, 100, and 101, and their hydrogen-bond acceptors, are brought together in the three-dimensional structure to form a contiguous, largely exposed protein surface with an area of about 750 square angstroms. The interaction site determined in this way is consistent with prior epitope mapping studies and includes several residues that were not previously identified. The hydrogen exchange labeling approach can be used to map binding sites on small proteins in antibody-antigen complexes and may be applicable to protein-protein and protein-ligand interactions in general.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3432411/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3432411/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Paterson, Y -- Englander, S W -- Roder, H -- GM 31847/GM/NIGMS NIH HHS/ -- GM 35926/GM/NIGMS NIH HHS/ -- R01 GM031847/GM/NIGMS NIH HHS/ -- S07-RR-05415-28/RR/NCRR NIH HHS/ -- New York, N.Y. -- Science. 1990 Aug 17;249(4970):755-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Microbiology, University of Pennsylvania, Philadelphia 19104.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1697101" target="_blank"〉PubMed〈/a〉
    Keywords: Antibodies, Monoclonal/immunology/metabolism ; Antigen-Antibody Complex ; *Binding Sites, Antibody ; Chemical Phenomena ; Chemistry ; Cytochrome c Group/*immunology ; Deuterium ; Epitopes/immunology ; Hydrogen/*metabolism ; Hydrogen Bonding ; Kinetics ; *Magnetic Resonance Spectroscopy ; Molecular Structure ; Protein Conformation
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
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    Studies of unusual simple molecules by neutralization-reionization mass spectrometry (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-02-23
    Description: Reactive or unstable molecules are key intermediates in many important reactions, but can be difficult to prepare for experimental studies. Species with missing (:CH-OH) or extra (H3) substituents can often be formed conveniently in the gas phase by neutralizing a beam of a more stable ionic counterpart (CH = O+H, H3+). Reionization of the neutral after approximately 10(-6) seconds tests its stability, whereas its unimolecular chemistry can be probed by preparing it with different amounts of internal energy. The resulting neutral products are reionized and mass analyzed. Isomers are then characterized by ion dissociation and a third mass-analysis step. Many unusual molecules have been characterized with this technique, which can also be used to probe complex unimolecular chemistry, such as that of cyclobutadiene and ethylene oxide.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McLafferty, F W -- GM-16609/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 1990 Feb 23;247(4945):925-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Cornell University, Baker Laboratory, Ithaca, NY 14853-1301.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2305261" target="_blank"〉PubMed〈/a〉
    Keywords: Butadienes ; Chemical Phenomena ; Chemistry ; Ethylene Oxide ; Free Radicals ; Hydrocarbons ; *Ions ; *Mass Spectrometry ; Methane/analogs & derivatives ; Molecular Structure ; Thermodynamics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    Inhibition of FKBP rotamase activity by immunosuppressant FK506: twisted amide surrogate (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-05-18
    Description: The immunosuppressive agents cyclosporin A and FK506 inhibit the transcription of early T cell activation genes. The binding proteins for cyclosporin A and FK506, cyclophilin and FKBP, respectively, are peptidyl-prolyl-cis-trans isomerases, or rotamases. One proposed mechanism for rotamase catalysis by cyclophilin involves a tetrahedral adduct of an amide carbonyl and an enzyme-bound nucleophile. The potent FKBP rotamase inhibitor FK506 has a highly electrophilic carbonyl that is adjacent to an acyl-pipicolinyl (homoprolyl) amide bond. Such a functional group would be expected to form a stabilized, enzyme-bound tetrahedral adduct. Spectroscopic and chemical evidence reveals that the drug interacts noncovalently with its receptor, suggesting that the alpha-keto amid of FK506 serves as a surrogate for the twisted amide of a bound peptide substrate.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Rosen, M K -- Standaert, R F -- Galat, A -- Nakatsuka, M -- Schreiber, S L -- GM-38627/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 1990 May 18;248(4957):863-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, Harvard University, Cambridge, MA 02138.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1693013" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Isomerases/*antagonists & inhibitors ; Anti-Bacterial Agents/metabolism/*pharmacology ; Binding Sites ; Carrier Proteins/antagonists & inhibitors/metabolism ; Chemical Phenomena ; Chemistry ; Cloning, Molecular ; Cyclosporins/metabolism/pharmacology ; Escherichia coli/genetics ; Gene Expression ; *Immunosuppressive Agents ; Lymphocyte Activation ; Magnetic Resonance Spectroscopy ; Molecular Structure ; Peptidylprolyl Isomerase ; Recombinant Proteins ; T-Lymphocytes/immunology ; Tacrolimus
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Uranus - The planet, rings and satellites (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The present overview of available data regarding Uranus and its planetary structures encompasses ground- and space-based observations of the planet with specific attention given to the interpretation of Voyager 2 data. A brief examination of historical observations is given which includes its discovery, position determination, and the related discoveries of Uranus' five large satellites and rings. The observational data preceding the Voyager 2 mission are reviewed in terms of the planetary interior, atmosphere, and magnetosphere. The Voyager 2 mission is given detailed treatment with descriptions of NASA's development and deployment of the spacecraft as well as detailed data from the Uranus encounter. Reference is given to structure and composition of Uranus' atmosphere, valid models of the interior, and wave-particle interactions in the magnetosphere. The structures of the rings and satellites are examined with reference to specific observational requirements from future missions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 10
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    Postbuckling of long thick plates in compression including higher order transverse shearing effects (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Aluminum plates of various length/width ratios loaded in compression are examined analytically in terms of buckling and postbuckling for comparison with classical theory. The plates are considered to be subjected to longitudinal compressive displacement with no edge stress and are assumed to be simply supported at the side edges. The average longitudinal direct stresses are computed to plot characteristic curves by means of the following theories: 3D flexibility, higher-order shear deformation, first-order shear deformation, and classical von Karman. The 3D flexibility approach yields the lowest results with more unknowns than the higher-order shear-deformation method. The 3D flexibility approach is considered to be the most accurate, and it is shown that the calculated resultants and displacements tend to vary when consideration is given to the effects of transverse shear.
    Keywords: STRUCTURAL MECHANICS
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  • 11
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    Thermal stress analysis of the NASA Dryden hypersonic wing test structure (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Present interest in hypersonic vehicles has resulted in a renewed interest in thermal stress analysis of airframe structures. While there are numerous texts and papers on thermal stress analysis, practical examples and experience on light gage aircraft structures are fairly limited. A research program has been undertaken at General Dynamics to demonstrate the present state of the art, verify methods of analysis, gain experience in their use, and develop engineering judgement in thermal stress analysis. The approach for this project has been to conduct a series of analyses of this sample problem and compare analysis results with test data. This comparison will give an idea of how to use our present methods of thermal stress analysis, and how accurate we can expect them to be.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 303-311
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  • 12
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    Optimum seismic structural design based on random vibration and fuzzy graded damages (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: This paper presents the fuzzy dynamical reliability and failure probability as well as the basic principles and the analytical method of loss assessment for nonlinear seismic steel structures. Also presented is the optimization formulation and a numerical example for double objectives, initial construction cost and expected failure loss, and dynamical reliability constraints. The earthquake ground motion is based on a stationary filtered non-white noise and the fuzzy damage grade is described by damage index.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 162-170
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  • 13
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    Efficient eigensolution reanalysis of nonclassically damped structures (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Effective methods of approximate eigensolution reanalysis of modified nonclassically damped structures are developed. For structures with passive or active discrete damping devices or with damping treatment, the system becomes nonproportionally damped and the computation of its dynamic responses may require the use of complex modes. For larger systems, the computation of complex modes is very expensive. Thus it is desirable to have approximate reanalysis techniques for the efficient evaluation of the effect of design changes. In recent years, the assumed mode reanalysis method was successfully applied to minimum weight design of undamped structures with natural frequency constraints. The accuracy of the assumed mode reanalysis method can be improved dramatically if the global approximation function includes the normal modes of the original system and their derivatives. This approach was demonstrated to be effective even for a system with shape changes. The approach used by Noor et al. for eigensolution reanalysis of undamped structures is extended to treat a nonclassically damped system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 105-114
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  • 14
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    A unified approach to the analysis and design of elasto-plastic structures with mechanical contact (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: With structural design in mind, a new unified variational model has been developed which represents the mechanics of deformation elasto-plasticity with unilateral contact conditions. For a design problem formulated as maximization of the load carrying capacity of a structure under certain constraints, the unified model allows for a simultaneous analysis and design synthesis for a whole range of mechanical behavior.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 340-346
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  • 15
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    Parallel structural optimization with different parallel analysis interfaces (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: The real benefit of structural optimization techniques is in the application of these techniques to large structures such as full vehicles or full aircraft. For these structures, however, the sequential computer's time and memory requirements prohibit the solutions. With the rapid development of parallel computers, parallel processing of large scale structural optimization problems is achievable. In this paper we discuss the parallel processing of structural optimization problems with parallel structural analysis. Two different types of interface between the optimization and analysis routines are developed and tested.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 398-403
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  • 16
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    Improved approximations of displacements for structural optimization (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: In most structural optimization problems the implicit behavior constraints are evaluated for successive modifications in the design. For each trial design, the analysis equations must be solved and the multiple repeated analyses usually involve extensive computational effort. This difficulty motivated several studies on explicit approximations of the structural behavior in terms of the design variables. The latter approach can considerably reduce the amount of computations, but the quality of the approximations might not be sufficient. Many of the approximate behavior models proposed in the past are valid only for relatively small changes in the design variables. The accuracy of the results is often insufficient for large changes in the design. The object of this study is to present efficient and high quality approximations of the structural behavior. It will be shown that the quality of the approximations can greatly be improved by combining scaling of the initial design, using intervening variables, and scaling a set of fictitious loads. Integrating these means, a powerful solution procedure can be introduced. In addition, the errors in satisfying the analysis equations can readily be evaluated. A numerical example illustrates the solution methodology and the effectiveness of the proposed approach.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 393-397
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  • 17
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    A stiffness tailored wing cover concept for structural efficiency and postbuckling application (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: The weight savings due to usage of composite materials in aircraft structural applications is well known. Significant weight and cost benefits are achievable by developing structurally tailored concepts and efficiently integrating them with suitable material and manufacturing technologies. The proposed paper will describe such an efficient concept for application to primary aircraft structures.
    Keywords: STRUCTURAL MECHANICS
    Type: The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 353-356
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  • 18
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    Application and assessment of structural optimization and active control for seismic structures (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: This paper first presents a brief review on the application of optimization and active control of seismic structures along with some of the author's recent work. It then assesses the practicality and future development of seismic structural optimization, and some practical problems associated with active control.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 171-177
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  • 19
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    Implementation of efficient sensitivity analysis for optimization of large structures (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: The paper presents the theoretical bases and implementation techniques of sensitivity analyses for efficient structural optimization of large structures, based on finite element static and dynamic analysis methods. The sensitivity analyses have been implemented in conjunction with two methods for optimization, namely, the Mathematical Programming and Optimality Criteria methods. The paper discusses the implementation of the sensitivity analysis method into our in-house software package, AutoDesign.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 587-592
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  • 20
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    Simplified detection and correction of critical data for ill-conditioned systems (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Ill-conditioned systems arising in analysis and optimization can display a high sensitivity to numerical precision for changes and errors in data input. Such data may be in the form of system parameter input or desired system response. The ill-conditioning referred to generally arises from the lack of sufficient independent data to define a complex system or the weak sensitivity of response to source input parameters. It is shown how small errors in data and assumed fixed and known parameters can lead to highly erroneous results in ill-conditioned linear algebraic equations. A simplified detection and correction of critical input data arising in the coefficient matrix and desired response (i.e., right hand side) is proposed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 71-76
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  • 21
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    Sensitivity analysis of the optimal solution obtained from the structural damage indentification process (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: An identification procedure proposed by Shen and Taylor to determine the crack characteristics (location and size of the crack) from dynamic measurements is tested. This procedure was based on minimization of either the 'mean-square' measure of difference between measurement data (natural frequencies and mode shapes) and the corresponding predictions obtained from the computational model. The procedure is tested for simulated damage in the form of symmetric cracks in a simply-supported Bernoulli-Euler beam. The sensitivity of the solution of damage identification problems to the values of parameters that characterize damage is discussed. A sensitivity formula is derived.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 65-70
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    New evidence favoring multilevel decomposition and optimization (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: The issue of the utility of multilevel decomposition and optimization remains controversial. To date, only the structural optimization community has actively developed and promoted multilevel optimization techniques. However, even this community acknowledges that multilevel optimization is ideally suited for a rather limited set of problems. It is warned that decomposition typically requires eliminating local variables by using global variables and that this in turn causes ill-conditioning of the multilevel optimization by adding equality constraints. The purpose is to suggest a new multilevel optimization technique. This technique uses behavior variables, in addition to design variables and constraints, to decompose the problem. The new technique removes the need for equality constraints, simplifies the decomposition of the design problem, simplifies the programming task, and improves the convergence speed of multilevel optimization compared to conventional optimization.
    Keywords: STRUCTURAL MECHANICS
    Type: The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 30-35
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    Direct handling of equality constraints in multilevel optimization (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: In recent years there have been several hierarchic multilevel optimization algorithms proposed and implemented in design studies. Equality constraints are often imposed between levels in these multilevel optimizations to maintain system and subsystem variable continuity. Equality constraints of this nature will be referred to as coupling equality constraints. In many implementation studies these coupling equality constraints have been handled indirectly. This indirect handling has been accomplished using the coupling equality constraints' explicit functional relations to eliminate design variables (generally at the subsystem level), with the resulting optimization taking place in a reduced design space. In one multilevel optimization study where the coupling equality constraints were handled directly, the researchers encountered numerical difficulties which prevented their multilevel optimization from reaching the same minimum found in conventional single level solutions. The researchers did not explain the exact nature of the numerical difficulties other than to associate them with the direct handling of the coupling equality constraints. The coupling equality constraints are handled directly, by employing the Generalized Reduced Gradient (GRG) method as the optimizer within a multilevel linear decomposition scheme based on the Sobieski hierarchic algorithm. Two engineering design examples are solved using this approach. The results show that the direct handling of coupling equality constraints in a multilevel optimization does not introduce any problems when the GRG method is employed as the internal optimizer. The optimums achieved are comparable to those achieved in single level solutions and in multilevel studies where the equality constraints have been handled indirectly.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 36-43
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    Reliability of degrading dynamic systems subject to dynamic random loads (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Reliability was determined for two degrading dynamic systems subject to random load processes. Damage is caused by loss of components for Daniels systems and crack extension for plates with cracks. The analysis accounted for the coupling between response and current damage state of the system. It is based on mean crossing rates of conditional processes and properties of diffusion models. Simple systems are used to illustrate proposed methods for estimating reliability.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 16-21
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    Structural damping optimization via non-obstructive particle damping technique (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: A passive vibration damping technique that is referred to as 'Non-Obstructive Particle Damping (NOPD)' is presented. The NOPD technique consists of making small diameter holes (or cavities) at appropriate locations inside vibrating structures and filling these holes to appropriate levels with particles which yield the maximum damping effectiveness for the desired mode (or modes). Powders, spherical shaped, metallic, non-metallic or liquid particles (or mixtures) with different densities, viscosities and adhesive or cohesive characteristics can be used.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 7-15
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    Thickness and orientational design for a maximum stiff membrane (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Recent results from sensitivity analysis for strain energy with anisotropic elasticity are applied to thickness and orientational design of laminated membranes. Primarily, the first order gradients of the total elastic energy are used in an optimality criteria based method. This traditional method is shown to give slow convergence with respect to design parameters, although the convergence of strain energy is very good. To get a deeper insight into this rather general characteristic, second order derivatives are included and it is shown how they can be obtained by first order sensitivity analysis. Examples of only thickness design, only orientational design, and combined thickness--orientational design are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 607-612
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    Computer simulation of multigrid body dynamics and control (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: The objective is to set up and analyze benchmark problems on multibody dynamics and to verify the predictions of two multibody computer simulation codes. TREETOPS and DISCOS have been used to run three example problems - one degree-of-freedom spring mass dashpot system, an inverted pendulum system, and a triple pendulum. To study the dynamics and control interaction, an inverted planar pendulum with an external body force and a torsional control spring was modeled as a hinge connected two-rigid body system. TREETOPS and DISCOS affected the time history simulation of this problem. System state space variables and their time derivatives from two simulation codes were compared.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 22-29
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  • 28
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    Employment of CB models for non-linear dynamic analysis (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: The non-linear dynamic analysis of large structures is always very time, effort and CPU consuming. Whenever possible the reduction of the size of the mathematical model involved is of main importance to speed up the computational procedures. Such reduction can be performed for the part of the structure which perform linearly. Most of the time, the classical Guyan reduction process is used. For non-linear dynamic process where the non-linearity is present at interfaces between different structures, Craig-Bampton models can provide a very rich information, and allow easy selection of the relevant modes with respect to the phenomenon driving the non-linearity. The paper presents the employment of Craig-Bampton models combined with Newmark direct integration for solving non-linear friction problems appearing at the interface between the Hubble Space Telescope and its solar arrays during in-orbit maneuvers. Theory, implementation in the FEM code ASKA, and practical results are shown.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 266-275
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    Structural optimization with constraints from dynamics in Lagrange (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: Structural optimization problems are mostly solved under constraints from statics, such as stresses, strains, or displacements under static loads. But in the design process, dynamic quantities like eigenfrequencies or accelerations under dynamic loads become more and more important. Therefore, it is obvious that constraints from dynamics must be considered in structural optimization packages. This paper addresses the dynamics branch in MBB-LAGRANGE. It will concentrate on two topics, namely on the different formulations for eigenfrequency constraints and on frequency response constraints. For the latter the necessity of a system reduction is emphasized. The methods implemented in LAGRANGE are presented and examples are given.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 129-134
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    Weight minimization of a support structure (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: This paper addresses the weight minimization of a circular plate-like structure which resulted in a 26 percent weight reduction. The optimization was performed numerically with the COPES/ADS program using the modified method of feasible directions. Design parameters were the inner thickness and outer thickness of the plate with constraints on maximum yield stress and maximum transverse displacement. Also, constraints were specified for the upper and lower bounds of the fundamental frequency and plate thicknesses. The MSC/NASTRAN finite element program was used for the evaluation of response variables. Original and final designs of the plate were tested using an Instron tension-compression machine to compare finite element results to measured strain data. The difference between finite element strain components and measured strain data was within engineering accuracy.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 312-317
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    Shape optimization for maximum stability and dynamic stiffness (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: Any optimization of structures for maximum stability or for maximum dynamic stiffness deals with an eigenvalue problem. The goal of this optimization is to raise the lowest eigenvalue (or eigenvalues) of the problem to its highest (optimal) level at a constant volume of the structure. Likely the lowest eigenvalue may be either inherently multi-modal or it can become multi-modal as a result of the optimization process. The multimodeness introduces some ambiguity to the eigenvalue problem and make the optimization difficult to handle. Thus far, only the simplest cases of multi-modal structures have been effectively optimized using rather elaborate analytical methods. Numerous publications report design of a minimum volume structure with different eigenvalues constraints, in which, however, the modality of the problem is assumed a priori. The method presented here utilizes a multi-modal optimality criteria and allows for inclusion of an arbitrary number of buckling or vibrations modes which might influence the optimization process. The real multi-modality of the problem, that is the number of modes participating in the final optimal design is determined iteratively. Because of a natural use of the FEM technique the method is easy to program and might be helpful in design of large flexible space structures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 297-302
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    Optimization of structure-control systems with efficiency constraint (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: The structure-control system optimization problem is formulated with constraints on the closed-loop eigenvalues and the efficiency of the reduced order system. The feasibility of the approach is illustrated by designing the ACOSS-FOUR structure with a reduced order system and improving the efficiency characteristics of the structures-control system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 495-500
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    Improving stability and strength characteristics of framed structures with nonlinear behavior (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: In this paper an optimal design procedure is introduced to improve the overall performance of nonlinear framed structures. The design methodology presented here is a multiple-objective optimization procedure whose objective functions involve the buckling eigenvalues and eigenvectors of the structure. A constant volume with bounds on the design variables is used in conjunction with an optimality criterion approach. The method provides a general tool for solving complex design problems and generally leads to structures with better limit strength and stability. Many algorithms have been developed to improve the limit strength of structures. In most applications geometrically linear analysis is employed with the consequence that overall strength of the design is overestimated. Directly optimizing the limit load of the structure would require a full nonlinear analysis at each iteration which would be prohibitively expensive. The objective of this paper is to develop an algorithm that can improve the limit-load of geometrically nonlinear framed structures while avoiding the nonlinear analysis. One of the novelties of the new design methodology is its ability to efficiently model and design structures under multiple loading conditions. These loading conditions can be different factored loads or any kind of loads that can be applied to the structure simultaneously or independently. Attention is focused on optimal design of space framed structures. Three-dimensional design problems are more complicated to carry out, but they yield insight into real behavior of the structure and can help avoiding some of the problems that might appear in planar design procedure such as the need for out-of-plane buckling constraint. Although researchers in the field of structural engineering generally agree that optimum design of three-dimension building frames especially in the seismic regions would be beneficial, methods have been slow to emerge. Most of the research in this area has dealt with the optimization of truss and plane frame structures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 347-352
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    Configuration design sensitivity analysis of built-up structures (1990)
    In:  CASI
    Details
    Publication Date: 2009-11-16
    Description: In the design of complex built-up structures that are made of truss, beam, membrane, shell, and solid, there are five different kinds of design variables: material property, sizing, shape, configuration, and topological variables. Previous research has shown that the improvement in performances obtained by altering the configuration of structural components can be much more significant than those obtained when the geometry is assumed to be fixed. Using the variational approach, a unified design sensitivity was developed for the first three kinds of design variables, and was further extended recently in many structural analysis problems such as nonlinear, structural dynamics, and frequency response analysis. A continuum design sensitivity analysis method is developed for the configuration design variable of built-up structures.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 44-49
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    Mars Observer's global mapping mission (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The objectives of the Mars Observer global mapping mission are to determine the global elemental and mineralogical character of the Martian surface material, define globally the topography and gravitational field of Mars, establish the nature of Mars's magnetic field, determine the time and space distribution, abundance, sources, and sinks of volatile Martian material and dust over a seasonal cycle, and explore the structure and aspects of the circulation of the Martian atmosphere. The experiments and instruments to be used in this mission are described, and the operations and data analysis are briefly considered.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: EOS (ISSN 0096-3941); 71; 1099
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    Small-scale plasma, magnetic, and neutral density fluctuations in the nightside Venus atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The evolution of the Venus small-scale waves as they propagate into the nightsite is examined, and the small-scale structures are compared with the waves in the three components of the magnetic field, magnetic dip angle, and neutral density. It is demonstrated that the small-scale fluctuations evolve between the transterminator and antisolar regions. It is shown that atmospheric gravity waves may also be producing some of the fluctuations observed at longer wavelengths. The electron temperature and density are shown to be approximately 180 deg out of phase and exhibiting the highest correlation of any pair of variables. Waves in the electron and neutral densities are found to be correlated moderately on most orbits, while the average electron temperature is higher when the average magnetic field is more horizontal.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 4085-410
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    Constructing second-order structural models with specified mass submatrix condition numbers (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents a simple new algorithm for constructing second-order models for any given flexible structure, with these models satisfying the constraint that each leading principal submatrix of the mass matrix must have a specified condition number. Now, the effects of rounding errors in practical computation generally increase with increasing condition number, i.e. as the matrix considered approaches singularity. Thus, the new models should prove useful for the systematic testing of the numerical properties of many algorithms in the dynamics and control of flexible structures.
    Keywords: STRUCTURAL MECHANICS
    Type: Communications in Applied Numerical Methods (ISSN 0748-8025); 6; 77-81
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    Comment on 'Update on terrestrial ages of Antarctic meteorites' by K. Nishiizumi, D. Elmore and P. W. Kubik (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 99; 4, Se; 380-382;
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    An improved fully stressed design algorithm for plate/shell structures (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The stress-ratio algorithm associated with fully stressed design philosophy has been used as a convenient tool to achieve minimum weight design of strength-limited structures. The algorithm is effective and converges quickly for many cases. However, it presents extremely slow oscillatory iteration histories for plate-thickness design problems that involve transverse bending loads. Modification of the basic algorithm presented in this paper provides an effective remedy to this problem when both membrane and bending loads are present. The modified resizing algorithm requires numerical solutions of a fourth-order algebraic equation. No additional data, beyond the ordinary static analysis results, are required.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Optimization (ISSN 0934-4373); 2; 233-237
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    Geochemistry and genesis of the angrites (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The major and trace elements were analyzed in samples of LEW86010, LEW87051, and Angra dos Reis angrites were analyzed using INAA and fused-bead EMP techniques. Results suggest that all three angrites originated on a volatile-depleted (Na-poor) but oxidized parent body or on several bodies. The combination of low Na and high FeO/MnO found in these samples suggests that the extreme Na depletion was caused by parent-body outgassing during differentiation, rather than by nebular processes. It was also found that the refractory-element abundances observed in LEW86010 and LEW87051 are related via olivine control; it is suggested that LEW86010 may be a residual melt from a LEW87051-like precursor or that LEW87051 formed from a LEW86010-like precursor via olivine accumulation. On the other hand, the Angra dos Reis displayed an unusual refractory element pattern suggesting that either the angrite parent body was heterogeneous or that Angra dos Reis was formed on a parent body different from that of the other two angrites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 3209-321
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    Zonal motion and structure in Jupiter's upper troposphere from Voyager infrared and imaging observations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Global digital maps of Jupiter's upper-tropospheric temperature have been generated at the 270- and 150-mb pressure levels, together with IR cloud optical depths at 5 and 45 microns and the ammonia abundance near the 680-mb pressure level, on the basis of Voyager IRIS north-south mapping sequences. Attention is given to the 270-mb and 45 micron data; global digital maps are presented for violet and orange reflectivities. The dominant upper tropospheric thermal structures move at a rate far different from that of the cloud indicators, and are noted to remain stationary relative to the planet's bulk rotation. Strong stationary features are found at a zonal wavenumber of 9 near 15 deg N latitude and of 11 near 20 deg latitude.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 88; 39-72
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    Tidal disruption of solid bodies (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The problem of stress, strain, and breakup in solid satellites and stray bodies subject to tidal perturbations is presently addressed in view of three novel considerations. After presenting a new analytic solution for the stress tensor in a homogeneous and compressible elastic sphere, where the inclusion of compressibility alters stresses by several percent, realistic failure criteria are noted to demonstrate the general failure of such ductile bodies as iron meteoroids by plastic shear, while brittle ice bodies fail by either tensile or shear fracture. A reexamination of crack propagation after initial failure allows the diverse breakup criteria to be reconciled.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 88; 24-38
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    Global/local stress analysis of composite panels (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A method for performing a global/local stress analysis is described and its capabilities are demonstrated. The method employs spline interpolation functions which satisfy the linear plate bending equation to determine displacements and rotations from a global model which are used as 'boundary conditions' for the local model. Then, the local model is analyzed independently of the global model of the structure. This approach can be used to determine local, detailed stress states for specific structural regions using independent, refined local models which exploit information from less-refined global models. The method presented is not restricted to having a priori knowledge of the location of the regions requiring local detailed stress analysis. This approach also reduces the computational effort necessary to obtain the detailed stress state. Criteria for applying the method are developed. The effectiveness of the method is demonstrated using a classical stress concentration problem and a graphite-epoxy blade-stiffened panel with a discontinuous stiffener.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 37; 4, 19
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    An analytical investigation of delamination front curvature in double cantilever beam specimens (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analytical investigation is conducted to determine the shape of a growing delamination and the distribution of the energy release rate along the delamination front in a laminated composite double cantilever beam specimen. Distributions of the energy release rate for specimens with straight delamination fronts and delamination front contours for delaminations whose growth is governed by the fracture criterion that G = Gc at all points are predicted as a function of material properties and delamination length. The predicted delamination front contours are utilized to ascertain the effect of the changing shape of the delamination front on the value of the critical strain energy release rate as computed from double cantilever beam fracture toughness test data.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 24; 1124-113
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    Transient thermal-structural analysis using adaptive unstructured remeshing and mesh movement (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An adaptive unstructured remeshing technique is applied to transient thermal-structural analysis. The effectiveness of the technique, together with the finite element method and an error estimation technique, is evaluated by two applications which have exact solutions: (1) the steady-state thermal analysis of a plate subjected to a highly localized surface heating, and (2) the transient thermal-structural analysis of a simulated convectively cooled leading edge subjected to a translating heat source. These applications demonstrate that the remeshing technique significantly reduces the problem size as well as the analysis solution error as compared to the results produced using standard structured meshes.
    Keywords: STRUCTURAL MECHANICS
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    Probabilistic simulation of uncertainties in thermal structures (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Development of probabilistic structural analysis methods for hot structures is a major activity at NASA-Lewis, and consists of five program elements: (1) probabilistic loads, (2) probabilistic finite element analysis, (3) probabilistic material behavior, (4) assessment of reliability and risk, and (5) probabilistic structural performance evaluation. Attention is given to quantification of the effects of uncertainties for several variables on High Pressure Fuel Turbopump blade temperature, pressure, and torque of the Space Shuttle Main Engine; the evaluation of the cumulative distribution function for various structural response variables based on assumed uncertainties in primitive structural variables; evaluation of the failure probability; reliability and risk-cost assessment; and an outline of an emerging approach for eventual hot structures certification. Collectively, the results demonstrate that the structural durability/reliability of hot structural components can be effectively evaluated in a formal probabilistic framework. In addition, the approach can be readily extended to computationally simulate certification of hot structures for aerospace environments.
    Keywords: STRUCTURAL MECHANICS
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    Buckling analysis and test correlation of high temperature structural panels (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper focuses on the design, analysis, and test of a high temperature structural panel, constructed of Ti-6-4, subjected to a variety of thermal and mechanical load conditions. A follow-on panel, constructed of TMC, is also discussed in less detail. The design constraints and test set-up are discussed, as well as the test methods that were used: the grid shadow moire method and a single gage force stiffness method. The agreement between the test data and analysis for this test program provides confidence in the methods that are currently being used to design structures for hypersonic vehicles. The agreement also suggests that postbuckled strength may potentially be used to reduce the vehicle weight.
    Keywords: STRUCTURAL MECHANICS
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    Finite-element thermo-viscoplastic analysis of aerospace structures (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The time-dependent thermo-viscoplastic response of aerospace structures subjected to intense aerothermal loads is predicted using the finite-element method. The finite-element analysis uses the Bodner-Partom unified viscoplastic constitutive relations to determine rate-dependent nonlinear material behavior. The methodology is verified by comparison with experimental data and other numerical results for a uniaxially-loaded bar. The method is then used (1) to predict the structural response of a rectangular plate subjected to line heating along a centerline, and (2) to predict the thermal-structural response of a convectively-cooled engine cowl leading edge subjected to aerodynamic shock-shock interference heating. Compared to linear elastic analysis, the viscoplastic analysis results in lower peak stresses and regions of plastic deformations.
    Keywords: STRUCTURAL MECHANICS
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    Cloud-tracked winds from Pioneer Venus OCPP images (1990)
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    Publication Date: 2011-08-19
    Description: Results are presented on the analysis of the Pioneer Venus Orbiter Cloud Photopolarimeter (OCPP) UV images, covering 80-day periods from 1979 to 1985. The analysis provides a method for determining wind speeds at the cloud level, from the motions of cloud UV features. Data used for tracking the cloud feature motions are described along with the analysis method. The results identified four wave modes: a diurnal solar tide, a semidiurnal solar tide, a '4-day equatorial' wave, and a '5-day midlatitude' wave. The features of these wave modes are described.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 47; 2053-208
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    (Ar-39)-(Ar-40) dating of mesosiderites - Evidence for major parent body disruption less than 4 Ga ago (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The (Ar-39) (Ar-40) chronologies were determined for 14 different mesosiderites representing the full range of classification according to recrystallization, and these chronologies were compared with analogous data for other meteorite types and for lunar highland rocks. Results of Ar-Ar chronologies indicate the history of a degassing of Ar due to a major thermal event that occurred less than 3.9 Ga ago; this event is not the metal-silicate mixing event, which is known to have occurred earlier than 4.4 Ga ago. It is suggested that a major collisional disruption-reassembly event less than 3.9 Ga ago took place, leaving the metal-silicate breccias buried under tens of kilometers of rubble, where they cooled slowly through the Ar closure temperatures.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2549-256
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    Inter- and intra-group compositional variations in Apollo 15 pyroclastic green glass - An electron- and ion-microprobe study (1990)
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    Publication Date: 2011-08-19
    Description: Results are presented on major- and trace-element abundance analyses of Apollo 15 pyroclastic green glasses from groups A, B, C, D, and E, carried out using electron- and ion-microprobe techniques. The diagrams depicting Sr, Zr, Ba, and Nd vs Co variations indicate the presence of a high-Co trend in groups A and D and a low-Co trend in groups B and C. Group-E glasses were found to be significantly enriched in Sr, relative to the other four glass groups. Chemical data of this study were integrated with previous data to evaluate various magmatic processes that have been proposed in the past to explain chemical variations in the lunar green glass. Results of calculations using a source mixing model suggest that the Apollo 15 green glasses represent multiple eruptive events from three chemically distinct but compositionally variable source regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2565-257
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    General purpose program to generate compatibility matrix for the integrated force method (1990)
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    Publication Date: 2011-08-19
    Description: An efficient procedure for obtaining the compatibility conditions of finite-element models involves the generation of both field and compatibility conditions from deformation-displacement relations, using (1) the compatibility bandwidth, and (2) the node-determinacy concept. A computer program thus structured will generate sparse and banded compatibility conditions for a structure that is idealized by the finite elements.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 28; 1838-184
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    Energy sources for Triton's geyser-like plumes (1990)
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    Publication Date: 2011-08-19
    Description: Four geyser-like plumes were discovered near Triton's south pole in areas now in permanent sunlight. Because Triton's southern hemisphere is nearing a maximum summer solstice, insolation as a driver or a trigger for Triton's geyser-like plumes is an attractive hypothesis. Trapping of solar radiation in a translucent, low-conductivity surface layer (in a solid-state greenhouse), which is subsequently released in the form of latent heat of sublimation, could provide the required energy. Both the classical solid-state greenhouse consisting of exponentially absorbed insolation in a gray, translucent layer of solid nitrogen, and the 'super' greenhouse consisting of a relatively transparent solid-nitrogen layer over an opaque, absorbing layer are plausible candidates. Geothermal heat may also play a part if assisted by the added energy input of seasonal cycles of insolation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 431-435
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    Temperature and thermal emissivity of the surface of Neptune's satellite Triton (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Analysis of the preliminary results from the Voyager mission to the Neptune system has provided the scientific community with several methods by which the temperature of Neptune's satellite Triton may be determined. If the 37.5 K surface temperature reported by several Voyager investigations is correct, then the photometry reported by the imaging experiment on Voyager requires that Triton's surface have a remarkably low emissivity. Such a low emissivity is not required in order to explain the photometry from the photopolarimeter experiment on Voyager. A low emissivity would be inconsistent with Triton having a rough surface at the about 100-micron scale as might be expected given the active renewal processes which appear to dominate Triton's surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 429-431
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    Subsurface energy storage and transport for solar-powered geysers on Triton (1990)
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    Publication Date: 2011-08-19
    Description: The location of active geyser-like eruptions and related features close to the current subsolar latitude on Triton suggests a solar energy source for these phenomena. Solid-state greenhouse calculations have shown that sunlight can generate substantially elevated subsurface temperatures. A variety of models for the storage of solar energy in a subgreenhouse layer and for the supply of gas and energy to a geyser are examined. 'Leaky greenhouse' models with only vertical gas transport are inconsistent with the observed upper limit on geyser radius of about 1.5 km. However, lateral transport of energy by gas flow in a porous N2 layer with a block size on the order of a meter can supply the required amount of gas to a source region about 1 km in radius. The decline of gas output to steady state may occur over a period comparable with the inferred active geyser lifetime of 5 earth years. The required subsurface permeability may be maintained by thermal fracturing of the residual N2 polar cap. A lower limit on geyser source radius of about 50 to 100 m predicted by a theory of negatively buoyant jets is not readily attained.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 424-429
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    Triton's geyser-like plumes - Discovery and basic characterization (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: One model for the mechanism driving the plumes of the four active geyser-like eruptions observed by Voyager 2 on Triton is a heating up of nitrogen ice in a subsurface greenhouse environment, where nitrogen gas pressurized by solar heating explosively vents to the surface carrying clouds of ice and dark particles into the atmosphere. A temperature increase of less than 4 K above the ambient surface value of 38 + or - 3 K suffices to drive the plumes to 8-km altitude. Each eruption may last a year or more, over the course of which 0.1 cu km of ice is sublimed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 410-415
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    Magellan orbits Venus (1990)
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    Publication Date: 2011-08-19
    Description: Various events surrounding Magellan's orbit of Venus are recounted. Significant events include the successful firing of a solid rocket motor while the spacecraft was behind Venus to transfer it from a solar-centered trajectory to an orbit around the planet. The spacecraft orbits Venus every 3.26 hours at a maximum altitude of 8500 km and minimum altitude of 291 km in an elliptical orbit. The successful August 16 test of the synthetic-aperture radar system is discussed, noting that it produced two strips, each about 20 km x 16,000 km, revealing details as small as 120 m. Two anomalies causing a delay in the start of mapping operations and subsequent breaks in the communication link with earth for 14.5 hours and 17.7 hours are discussed. Protective measures directed from the spacecraft's ROM during breach of contact are listed, and possible causes of the anomalies are suggested, such as solar activity or hardware or software elements, although the actual cause is not yet known.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Spaceflight (ISSN 0038-6340); 32; 334-337
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    Comparative dynamics of the ionospheres of Venus and Mars at large solar zenith angles (1990)
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    Publication Date: 2011-08-19
    Description: Simple three-ion spectral models of the dynamics and ion chemistry in the upper ionospheres of Venus and Mars have been constructed by including two minor ions, H(+) and O2(+) for Venus and O(+) and CO2(+) for Mars, along with the major ion, O(+) for Venus and O2(+) for Mars. Horizontal flow velocities and ion densities have been calculated in each case and compared with available measured data. For Venus, the present calculations yield results in agreement with earlier finite-difference model studies and with experimental observations. Calculations for Mars are in agreement with the limited observational data obtained by the Viking landers.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Indian Journal of Radio and Space Physics (ISSN 0367-8393); 19; 88-102
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    Albedo and color maps of the Saturnian satellites (1990)
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    Publication Date: 2011-08-19
    Description: The paper discusses the production of maps of the albedos and colors of Mimas, Enceladus, Tethys, Dione, and Rhea over the full range of their imaged surfaces. Voyager images were used to prepare maps of the normal reflectances and color ratios (0.58/0.41 micron) of these satelites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 87; 339-357
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  • 60
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    Cosmogenic nuclides in extraterrestrial materials (1990)
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    Publication Date: 2011-08-19
    Description: Research on cosmogenic nuclides in extraterrestrial materials is summarized. Methods for determining average production rates in meteorites are considered as well as the composition dependence of production rates. Also discussed are lunar meteorites, solar-gas-rich meteorites, presolar grains, and solar cosmic rays.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Reviews of Geophysics (ISSN 8755-1209); 28; 253-275
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    A robust self-starting explicit computational methodology for structural dynamic applications - Architecture and representations (1990)
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    Publication Date: 2011-08-19
    Description: A robust self-starting explicit architecture for computational structural dynamics is described. The proposed methodology involves expressing the governing equations of motion in conservation form and temporal discretization is accomplished in the spirit of the Lax-Wendroff type formulations. The development of the basic methodology is shown. Discretization in space is accomplished by introducing stress-based representations and employing the classical Galerkin scheme. Numerical test model results are presented which validate the architecture.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 29; 1441-145
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    A model of Saturn's magnetic field based on all available data (1990)
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    Publication Date: 2011-08-19
    Description: A model of Saturn's magnetic field, called Saturn Pioneer Voyager (SPV), is developed on the basis of an analysis of three sets of data: those from the Pioneer 11, the Voyager 1, and the Voyager 2 magnetometers. It is shown that the SPV model fits the data observed between 1.3 and 8.0 Saturn radii from the planet's center with a 1.13 percent weighted rms average of the percent differences between the observed and modeled fields, which is substantially better than the fits yielded by any of the previous models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 15257-15
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  • 63
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    Backscattering from frost on icy satellites in the outer solar system (1990)
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    Publication Date: 2011-08-19
    Description: Two extreme models are presented of how frost and ice might be intermixed on a typical satellite surface: areal and intimate mixing. Applying such models to selected representative satellite data, it is found that the frost component of the surfaces of these outer satellites must itself be backscattering, unlike its terrestrial counterpart. The difference may arise because frost particles can have much more complex internal textures under the low-temperature and low-gravity conditions of the outer satellites than is the case on earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 347; 162-164
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    Ubiquitous interstellar diamond and SiC in primitive chondrites - Abundances reflect metamorphism (1990)
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    Publication Date: 2011-08-19
    Description: It is shown here that interstellar diamond and SiC were incorporated into all groups of chondrite meteorites. Abundances rapidly go to zero with increasing metamorphic grade, suggesting that metamorphic destruction is responsible for the apparent absence of these grains in most chondrites. In unmetamorphosed chondrites, abundances normalized to matrix content are similar for different classes. Diamond samples from chondrites of different classes have remarkably similar noble-gas constants and isotropic compositions, although constituent diamonds may have come from many sources. SiC seems to be more diverse, partly because grains are large enough to measure individually, but average characteristics seem to be similar from meteorite to meteorite. These observations suggest that various classes of chondritic meteorites sample the same solar system-wide reservoir of interstellar grains.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 347; 159-162
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    Vertical distribution of water in the atmosphere of Venus - A simple thermochemical explanation (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Several lines of evidence concerning the vertical abundance profile of water in the atmosphere of Venus lead to strikingly unusual distributions (the water vapor abundance decreases sharply in the immediate vicinity of the surface) or to serious conflicts in the profiles (different IR bands suggest water abundances that are discrepant by a factor of 2.5 to 10). These data sets can be reconciled if (1) water molecules associate with carbon dioxide and sulfur trioxide to make gaseous carbonic acid and sulfuric acid in the lower atmosphere, and (2) the discrepant 0.94-micrometer water measurements are due to gaseous sulfuric acid, requiring it to be a somewhat stronger absorber than water vapor in this wavelength region. A mean total water abundance of 50 + or - 20 parts/million and a near-surface free water vapor abundance of 10 + or - 4 parts/million are derived.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 249; 1273-127
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    Variations of Mars gravitational field and rotation due to seasonal CO2 exchange (1990)
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    Publication Date: 2011-08-19
    Description: About a quarter of the Martian atmospheric mass is exchanged between the atmosphere and the polar caps in the course of a Martian year: CO2 condenses to form (or add to) the polar caps in winter and sublimes into the atmosphere in summer. This paper studies the effect of this CO2 mass redistribution on Martian rotation and gravitational field. Two mechanisms are examined: (1) the waxing and waning of solid CO2 in the polar caps and (2) the geographical distribution of gaseous CO2 in the atmosphere. In particular, the net peak-to-peak changes in J2 and J3 over a Martian year are both found to be as much as about 6 x 10 to the -9th. A simulation suggests that these changes may be detected by the upcoming Mars Observer under favorable but realistic conditions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14755-14
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    Atmospheric measurements at Mars via gamma ray spectroscopy (1990)
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    Publication Date: 2011-08-19
    Description: This paper describes three methods for measuring the Martian atmosphere using gamma ray spectroscopy. One method determines atmospheric thickness based on the energy-dependent differential attenuation of gamma-ray line pairs from a common element. Another makes a direct determination based on measurements of the line flux generated in the atmosphere, requires knowledge of the concentration of the component being used. The third, which makes use of a single line emitted from the surface where its flux can be established. The effects of stratigraphy on the differential attenuation method are studied, and calculations are reported which show that the measurement of atmospheric argon will be a sensitive indicator of the atmospheric fractionation accompanying CO2 precipitation in south polar regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14695-14
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    Infrared radiative transfer in the dust-free Martian atmosphere (1990)
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    Publication Date: 2011-08-19
    Description: Two theoretical radiative transfer methods are used here to derive synthetic spectra of dust-free Martian atmospheres. One is a versatile, accurate, line-by-line model which completely resolves individual absorption lines to produce high-resolution spectra within gas absorption bands. The other is a fast Voigt quasi-random model which produces accurate results for spectral regions as narrow as 1/cm and is fast enough for routine use in broadband transmission calculations. Synthetic transmission and radiance spectra from these models for dust-free conditions in the Martian atmosphere are used to illustrate the radiative effects of each important absorbing gas and to provide a baseline for comparisons with dust atmosphere spectra.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14577-14
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    Thermal emission spectra of Mars (5.4-10.5 microns) - Evidence for sulfates, carbonates, and hydrates (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Spectra of the Martian thermal emission in the 5.4-10.5 micron region are reported. Emission features at 7.8 and 9.7 microns are attributed to surface silicates, and an emission feature at 6.1 micron is attributed to a molecular water component of the surface material. An absorption band at 8.7 micron and a possible one at 9.8 microns is attributed to sulfate or bisulfate anions probably located at a distorted crystalline site, and an absorption band at 6.7 microns is attributed to carbonate or bicarbonate anions located in a distorted crystalline site. Spectral simulations indicate that the sulfate- and carbonate-bearing minerals are contained in the same particles of airborne dust as the dominant silicate minerals, that the dust optical depth is about 0.6 at a reference wavelength of 0.3 micron over the area of the observed spots, and that sulfates and carbonates constitute 10-15 percent and 1-3 percent by volume of the airborne dust, respectively.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14595-14
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    Origins of Marslike spectral and magnetic properties of a Hawaiian palagonitic soil (1990)
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    Publication Date: 2011-08-19
    Description: Results are presented on spectral, Moessbauer, static magnetic, petrographic, and compositional data for a Hawaiian palagonitic soil from Mauna Kea (HWMK1). It was found that reflectivity spectra of size separates smaller than 20 microns resemble spectra for Martian bright regions, while spectra of larger size separates show characteristics in common with spectra for Martian dark regions. Data on the HWMK1 soil are consistent with the partitioning of iron among the following minerals: olivine, titanomagnetite, hematite, and a superparamagnetic colored ferric oxide. These mineralogies are heterogeneously distributed within the soil with respect to both particle type and soil-particle diameter. The strongly magnetic titanomagnetite is associated with black particles and is responsible for the magnetic nature of the soil, while the colored weakly magnetic superparamagnetic ferric oxide and minor hematite are associated with orange particles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14427-14
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    Emplacement of lava flow fields - Application of terrestrial studies to Alba Patera, Mars (1990)
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    Publication Date: 2011-08-19
    Description: The relationships obtained by Kilburn and Lopes (1988, 1990) for their models of lava flow fields were used to calculate the duration of the emplacement, the average discharge rates, and the average velocities of lavas for the Martian volcano Alba Patera, on which two distinct planimetric types of lava flow field were identified. The validity of using terrestrial analogues for investigating the emplacement conditions of the Alba Patera flow fields is examined. It is concluded that, at least for basaltic-basaltic andesitic compositions, the essential conditions of eruption from Alba Patera may have been similar to those currently observed on earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14383-14
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    Fault propagation folds induced by gravitational failure and slumping of the Central Costa Rica volcanic range - Implications for large terrestrial and Martian volcanic edifices (1990)
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    Publication Date: 2011-08-19
    Description: Maps are presented that describe the compressional tectonic structures found at the base of the Central Costa Rica volcanic range (CCRVR), which comprise thrust faults and related fault propagation folds, only partly covered by syntectonic and posttectonic volcanoclastic deposits. Evidence is presented that these structures formed by gravitational failure and lumping of the flanks of the volcanic range. It is suggested that similar structures may be found at the toe of the southern flank of Kilauea volcano, Hawaii, and along the perimeter scarp of the Olympus Mons volcano on Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14357-14
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    Flank tectonics of Martian volcanoes (1990)
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    Publication Date: 2011-08-19
    Description: The origin of the numerous terraces on the flanks of the Olympus Mons volcano on Mars, seen on space images to be arranged in a roughly concentric pattern, is investigated. The images of the volcano show that the base of each terrace is marked by a modest but abrupt change in slope, suggesting that these terraces could be thrust faults caused by a compressional failure of the cone. The mechanism of faulting and the possible effect of the interior structure of Olympus Mons was investigated using a numerical model for elastic stresses within a Martian volcano, constructed for that purpose. Results of the analysis supports the view that the terraces on Olympus Mons, as well as on other three Martian volcanoes, including Ascraeus Mons, Arsia Mons, and Pavonis Mons are indeed thrust faults.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14345-14
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    The shallow structure of the Martian lithosphere in the vicinity of the ridged plains (1990)
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    Publication Date: 2011-08-19
    Description: On Mars, the most prominent assemblage of regularly spaced plain ridges occurs in the plains of the Coprates and Lunae Planum regions. In this paper, a number of tectonic models is developed and quantitatively evaluated, that relate the regular spacing of these ridges to the shallow internal structure of Mars. It is shown that models with both rigid and deformable megaregolith-basement interface conditions can provide solutions which can explain the ridge spacing within the constraint provided by the estimated thickness of the smooth plains materials. Implications of the models for the structure and state of stress in the Tharsis region at the time of ridge formation are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14215-14
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    Speculations on the origin and evolution of the Utopia-Elysium lowlands of Mars (1990)
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    Publication Date: 2011-08-19
    Description: This paper proposes a qualitative model for the origin of the Utopia-Elysium northern lowlands on eastern Mars in terms of the long-term evolution of two large overlapping impact basins. The model, which is consistent with both the observed geologic constraints and more quantitative results obtained by numerical modeling of smaller (Orientale-size) impact basins, is shown to qualitatively account for the major topographic variation seen in the Utopia-Elysium region, including the overall 'lowness' of the area and localized depressions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14203-14
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    Discontinuities in the shallow Martian crust at Lunae, Syria, and Sinai Plana (1990)
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    Publication Date: 2011-08-19
    Description: Detailed photoclinometric data are presented for a variety of surface features (pits, troughs, wall valleys, and grabens) within three study areas in the western equatorial regions of Mars (Lunae, Syria, and Sinai Plana) that provide evidence for mechanical discontinuities within the shallow Martian crust in these regions. The data's relation to some of the previously proposed mechanical discontinuities within the Martian crust is discussed, and the geologic significance of these features is speculated upon.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14231-14
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    A new survey of multiring impact basins on Mars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Literature data on Martian multiring impact basins with diameters greater than 500 km are summarized, and evidence is found for eight new such basins. The pattern of changes of basin morphology with increasing basin size suggests three subclasses of multiring basins: (1) multiring basins with diameters up to about 1850 km, which are characterized by the Orientale type concentric structure and cumulative frequency power law slope of -0.75; (2) the Argyre-type basins (with diameters between 1850 and 3600 km, defined by rugged concentric annnuli and a power law slope of nearly -2.0; and (3) the Chryse-type basins (with diameters greater than 3600 km), which exhibit multiple concentric rings and very shallow topographic profiles. Multiring basins are found in all parts of Mars, including the northern lowlands, Tharsis, and surrounding highlands, and are associated with much of the subsequent resurfacing of cratered terrain.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14175-14
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    Mars gravity field error analysis from simulated radio tracking of Mars Observer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on the analysis of the recovery of the Martian gravity field from tracking data in the presence of unmodeled error effects associated with different orbit orientations. The analysis was based on the mission plan for the Mars Observer (MO) radio tracking data from the Deep Space Network. From the analysis, a conservative estimate of the gravitational accuracy for the entire mission could be obtained. The results suggest that, because the atmospheric drag is the dominant error source, the spacecraft orbit could possibly be raised in altitude without a significant loss of gravitational signal. A change in altitude will also alleviate the large effects seen in the spectrum the satellite resonant orders.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14155-14
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  • 79
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    Martian impact craters - Correlations of ejecta and interior morphologies with diameter, latitude, and terrain (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An effort is made to establish the ability of a correlation between crater morphology and latitude, diameter, and terrain, to discriminate among the effects of impact energy, atmosphere, and subsurface volatiles in 3819 larger-than-8 km diameter craters distributed over the Martian surface. It is noted that changes in ejecta and interior morphology correlate with increases in crater diameter, and that while many of the interior structures exhibit distributions interpretable as terrain-dependent, central peak and peak ring interior morphologies exhibit minimal relationships with planetary properties.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 87; 156-179
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  • 80
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    A goal and strategy for human exploration of the moon and Mars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Eventual settlement of the solar system, beginning with the moon and Mars, is proposed, and a strategy for the exploration of and initial settlement of the moon and Mars, based on the model of European settlement of the Americas, is discussed. Strategies suggest an allocation of functions between humans and telerobots to conduct the exploration and initial settlement.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Policy (ISSN 0265-9646); 6; 195-208
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    Large-scale patterns of eolian sediment transport on Venus - Predictions for Magellan (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The atmosphere of Venus is likely to exert a major influence on the surface. Arecibo and Venera 15/16 observations of the population of impact craters with bright halos give direct evidence of surface modification, on the scale of centimeters, to smooth the surface on time scales of 50 - 250 my. Both chemical and mechanical modifications probably occur. Diurnal winds in the planetary boundary layer can transport particles. Using boundary layer theory, including the effects of topography, surface stresses and resulting transport and deposition of sand-size particles are calculated. Regional slopes are sites of largest surface stresses. Sand will be generally transported downhill, although there is a preferential net transport from east to west, in the same direction as the atmospheric superrotation. It is predicted here that streaks may be seen in the Magellan radar images which will indicate directions of net eolian transport on the surface of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1365-136
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  • 82
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    Small domes on Venus - Probable analogs of Icelandic lava shields (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: On the basis of observed shapes and volumetric estimates, small, dome-like features on radar images of Venus are interpreted to be analogs of Icelandic lava-shield volcanoes. Morphometric data for Venusian domes in Aubele and Slyuta as well as measurements of representative dome volumes and areas from Tethus Regio are used to demonstrate that the characteristic aspect ratios and flank slopes of these features are consistent with a subclass of low Icelandic lava-shield volcanoes (LILS).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1381-138
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  • 83
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    Geologic evidence of hotspot activity of Venus - Predictions for Magellan (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A number of distinctive types of geologic features have been identified on Venus that are interpreted to be related to thermal plumes including domal rises, coronae, and major composite shield volcanoes. The basic characteristics of these features as well as their distribution are documented. The three types of features have related morphologies and are interpreted to represent a continuum of features formed by mantle plumes at scales from 100s to over 1000 km. The Artemis structure, located in Aphrodite Terra, is proposed to be a large corona. If crustal spreading processes are operating on Venus, hotspot features should form chains on the surface as seen in terrestrial ocean basins. On the basis of current data on hotspot-related feature distribution on Venus, no clear evidence exists for hotspot chains. The complete distribution of hotspot features in Magellan data will be used to understand better the relationship between interior processes and surface features, as well as to provide a test for the crustal spreading hypothesis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1377-138
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  • 84
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    Radar characteristics of the equatorial plains of Venus from Goldstone observations - Implications for interpretation of Magellan data (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Based on analyses of recent high resolution observations of the approximately 1000 km diameter Heng-O ring structure by the Goldstone Solar System Radar, it is predicted that the structure is a large corona. Calibrated values of radar backscatter coefficient indicate lateral variations of a factor of 4 in Fresnel reflectivity in the vicinity of Heng-O, as well as in other areas of the plains, at scales of tens of km. It is predicted that areas with very low reflectivity values, which occur in a variety of geological settings, are soil-dominated, with bulk densities as low as 1.5 g/cu cm.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1357-136
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    Projection and assembly method for multibody component model reduction (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The problem addressed is that of obtaining reduced-order component models for use in simulating the dynamics of a multibody system. In certain cases, nonlinear system models may be constructed using linear dynamic models for each component, but allowing large angle motion between components. Without some form of model reduction, system models constructed in this manner may be too large for use in control system design and simulation trades. This paper analyzes one method of component model reduction that allows systems level requirements (e.g., capturing the effect of body 1 reaction wheel noise on body 2 camera pointing) to aid in the selection of the reduced-order component models. Briefly stated, important modes are selected at the system level and projected onto the components, and reduced-order components are then assembled into a reduced-order system model that retains the projected modes.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 13; 905-912
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  • 86
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    Titan and other icy satellites - Dielectric properties of constituent materials and implications for radar sounding (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Radar sounding observations of Titan and the other outer solar system icy satellites have been conducted in order to ascertain the materials present, their dielectric properties, and the degree of radar signal penetration. Deep penetration is possible at long wavelengths, while strong reflections may occur due to pockets or layers of H2O-NH3 solution. Attention is given to the case of Titan, using models to calculate radar reflection S/N ratios; the models involve H2O ice covered by a 100-m thick layer of organic sediments that are overlain by an ocean of liquid CH4-C2H6-N2. At 13.6-cm wavelength, a greater-than-10 dB S/N is computed from the ocean-sediment and sediment-ice interfaces, suggesting that the geology of Titan may be investigated by such a sounding mode despite deep ocean coverage of the satellite.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 86; 336-354
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  • 87
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    The deep atmosphere of Venus revealed by high-resolution nightside spectra (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The first high-resolution spectroscopic observations of the night side of Venus obtained in two narrow spectral windows centered at 1.74 and 2.3 microns, where the nightside is anomalously bright, are reported. Absorption features from CO2, CO, H2O, HDO, HCl, HF, and COS are detected, and there are a number of unidentified features. A preliminary analysis indicates that the observed radiation is thermal emission from atmospheric layers in the eight-bar pressure region for the 2.3 micron window and even deeper at 1.7 micron. The derived CO and H2O abundances agree with in situ Pioneer measurements in the deep troposphere and are consistent with the high deuterium enrichment inferred from Pioneer data. The first measurements of HCl and HF below the clouds are reported along with the first firm detection of COS.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 345; 508-511
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  • 88
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    Application of optimization methods to helicopter rotor blade design (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A procedure for the minimum weight design of helicopter rotor blades with constraints on multiple coupled flap-lag natural frequencies, autorotational inertia, and centrifugal stress is presented. Optimum designs are obtained for blades with both rectangular and tapered planforms and are compared within a reference blade. The effects of higher-frequency constraints and stress constraints on the optimum blade designs are assessed. The results indicate that there is an increase in blade weight and a significant change in the design variable distributions with an increase in the number of frequency constraints. The inclusion of stress constraints has different effects on the wall thickness distributions of rectangular and tapered blades, but tends to increase the magnitude of the nonstructural segment weight distributions for both blade types.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Optimization (ISSN 0934-4373); 2; 1, 19
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  • 89
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    Mars ionopause during solar minimum - A lesson from Venus (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ion densities measured by the Viking landers (Hanson et al., 1977) do not show an abrupt falloff with height, giving the false impression that Mars has no ionopause. On the basis of knowledge gained from the solar wind interaction at Venus during solar minimum, it is demonstrated that the observed O2 profile above about 160 km on Mars is a distributed photodynamical ionosphere and can produce an ionopause at around 325 km, similar to that observed on Venus during solar minimum. It is concluded that the solar wind interacts directly with the Mars ionosphere, suggesting that the planet does not have an intrinsic magnetic field of any consequence.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 8265-826
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  • 90
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    A method for estimating eruption rates of planetary lava flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The eruption rates of single-lobed planetary lava flows are presently accounted for by a model for radiative losses from a partially crusted hotter core, assuming thermal characteristics similar to terrestrial flows. Eruption rates are within this framework expressible as functions of (1) exposed core area fraction, (2) initial core temperature, (3) core temperature upon cessation of flow, (3) crust thickness, and (4) the lava's density and heat capacity.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 512-515
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    CH4 nonlocal thermodynamic equilibrium in the atmospheres of the giant planets (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present consideration of methane's vibrational relaxation in the Giant Planets' upper stratospheres employs a model for the thermalization of solar energy absorbed under non-LTE conditions, at the 1.7, 2.3. and 3.3 micron-centered CH4 band groups. On this basis, a range of model atmospheres was produced, reflecting current uncertainties concerning CH4 collisional excitation rates. At 0.1 mbar, all of the non-LTE models are within 2 K of the LTE reference models; the extreme non-LTE models steadily depart from reference LTE ones, however, and reach about + or - 20 K at 0,1 mbar.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 355-379
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  • 92
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    Titan's stratospheric temperatures - A case for dynamical inertia? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Voyager IRIS spectral radiances in the nu4-band of CH4 for the Titan atmosphere exhibit a hemispheric asymmetry. While asymmetry in the meridional distribution of opacity about the equator cannot be discounted, attention is given to the need for angular momentum transport concurrent with seasonally varying temperatures in the Titan stratosphere, which would maintain the cyclostrophic thermal wind relation between zonal winds and temperatures. The adiabatic heating and cooling associated with these motions can produce the observed temperature asymmetry.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 346-354
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    The extraordinary radar echoes from Europa, Ganymede, and Callisto - A geological perspective (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Electromagnetic echo-scattering models, empirical and theoretical considerations on regolith formation, and ice physics, are presently invoked in a geologic treatment of the anomalous radar properties of the icy Galilean satellites. These are held to arise because of the electrical differences between ice and silicates, and the absence of icy regoliths' ice-density structures in silicate regoliths. Icy regoliths may uniquely smooth out discontinuities between solid ejecta fragments and more porous surroundings, forming refraction-scattering 'lenses'; high-order multiple scatterings will thereby become more likely responsible for the echoes than low-order scattering.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 335-345
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    On the effect of X rays on the color of elemental sulfur - Implications for Jupiter's satellite Io (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Absorption features arose at 0.42 and 0.52 microns when spectral reflectance measurements were conducted for elemental sulfur allotrope mixtures produced by the exposure of the cyclooctal S(8) allotrope of sulfur to X-rays; while these features due to the presence of short-chain molecules are stable at low temperatures, they fade upon warming of the sample. The hypothesis that X-rays in the Jovian environment would cause other allotropic forms of sulfur to revert to S(8) is contradicted by the fact that these features are not present in S(8) at the same temperature that had not been exposed to X-rays.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 326-334
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    Internal structure of Io and the global distribution of its topography (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A global topography is presently calculated for two multilayer Io models in which dissipation occurs in a viscous asthenosphere and a solid mantle: (1) a 'thermal swell' model, in which topography and heat flow are positively correlated, and (2) a 'differentiated lithosphere' model, in which topography and heat flow are negatively correlated. Both the polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model are better matched with observations than the thermal swell model. The shift of the equatorial basin-swell pattern indicates a recent zonal rotation of about 25 deg for Io's lithosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 309-325
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    TV observations of Phobos - First results (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: From February to March, 1989, Phobos-2 acquired 37 TV images of Phobos at distances from 200 to 1100 km. These images will be used to update the figure model and topographic and geological maps of Phobos, its spectral characteristics and scattering law, the surface composition and texture, and the parameters of the orbital motion and forced libration.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Pis'ma v Astronomicheskii Zhurnal (ISSN 0320-0108); 16; 378-388
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  • 97
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    Adaptive structures (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Current research in the field of advanced adaptive structures for space applications is reviewed. A classification of adaptive structures is proposed whereby such structures are subdivided into adaptive, sensory, controlled, active, and intelligent structures. The definition and properties of each type of adaptive structures are presented, and methods of structure control are discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Intelligent Material Systems and Structures (ISSN 1045-389X); 1; 157-174
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    Simultaneous active control of flexural and extensional waves in beams (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The simultaneous active control of flexural and extensional vibrations in elastic beams is experimentally investigated. The results demonstrate that using pairs of piezoceramic transducers, whose elements are symmetrically located and independently controlled by a multichannel adaptive controller, enables the high attenuation of both flexural and extensional response. This capability is due to the nature of the piezoceramic element, which when bonded to the surface of the structure and electrically excited, exerts a surface strain on the structure. This strain enables input of both shear forces and moments into the structural system. The results are applicable to many situations where extensional vibrations couple to large flexural vibrations and subsequently radiate significant sound levels.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Intelligent Material Systems and Structures (ISSN 1045-389X); 1; 235-247
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  • 99
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    Charge-coupled device spectra of asteroids. I - Near-earth and 3:1 resonance asteroids (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Main-belt asteroids and cometary nuclei are both frequently suggested sources of the relatively short-lived near-earth asteroids (NEAs). The asteroidal origin hypothesis is studied by obtaining new high-quality reflectivity spectra of 19 NEAs and 23 asteroids near the 3:1 resonance, and by performing a systematic comparison of these two groups of spectra. Nonparametric statistical tests are used to check for consistency between the color distributions of the two populations. The tests indicate that the difference between the two distributions is generally not significant at the 3 sigma level. However, this conclusion is dependent on the (unknown) size distribution of the NEAs. The observations are compatible with the hypothesis that the NEAs are derived from the 3:1 resonance region, but do not imply that this is the only possible source region.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 99; 1985-201
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  • 100
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    Mars - Change in axial tilt due to climate? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The average tilt of Mars' equator with respect to its orbital plane may have increased significantly over the age of the solar system. Obliquity oscillations might have induced changes in the climate, which altered the mass distribution and hence the solar torque on the planet. Viscous deformation attributable to loading by the large polar caps expected at low obliquity may have induced secular changes in the axial tilt. Earth-like effective viscosities can account for virtually the entire present obliquity of 24.4 degrees. Thus the present average tilt of Mars may not be primordial.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 248; 720
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