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  • Books  (8)
  • Other Sources  (30,359)
  • LUNAR AND PLANETARY EXPLORATION  (14,409)
  • STRUCTURAL MECHANICS  (10,233)
  • SOLAR PHYSICS  (5,716)
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  • Inorganic Chemistry
  • 1
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    Calgary (2022)
    University of Calgary Press
    Details
    Publication Date: 2022-07-19
    Description: How have our interactions with animals shaped Calgary? What can we do to ensure that humans and animals in the city continue to co-exist, and even flourish together? This wide-ranging book explores the ways that animals inhabit our city, our lives and our imaginations. Essays from animal historians, wildlife specialists, artists and writers address key issues such as human-wildlife interactions, livestock in the city, and animal performers at the Calgary Stampede. Contributions from some of Calgary's iconic arts institutions, including One Yellow Rabbit Performance Theatre, Decidedly Jazz Danceworks, and the Glenbow Museum, demonstrate how animals continue to be a source of inspiration and exploration for fashion, art, dance, and theatre. The full-colour volume is beautifully illustrated throughout with archival images, wildlife photography, documentary and production stills, and original artwork. Calgary: City of Animals is published in co-operation with the Calgary Institute for the Humanities.
    Keywords: Nature ; Animals ; bic Book Industry Communication::J Society & social sciences::JF Society & culture: general::JFF Social issues & processes::JFFZ Animals & society
    Language: English
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  • 2
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    Animal Metropolis (2022)
    University of Calgary Press
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    Publication Date: 2022-07-19
    Description: Animal Metropolis brings a Canadian perspective to the growing field of animal history, ranging across species and cities, from the beavers who engineered Stanley Park to the carthorses who shaped the city of Montreal. Some essays consider animals as spectacle: orca captivity in Vancouver, polar bear tourism in Churchill, Manitoba, fish on display in the Dominion Fisheries Museum, and the racialized memory of Jumbo the elephant in St. Thomas, Ontario. Others examine the bodily intimacies of shared urban spaces: the regulation of rabid dogs in Banff, the maternal politics of pure milk in Hamilton and the circulation of tetanus bacilli from horse to human in Toronto. Another considers the marginalization of women in Canada’s animal welfare movement. The authors collectively push forward from a historiography that features nonhuman animals as objects within human-centered inquiries to a historiography that considers the eclectic contacts, exchanges, and cohabitation of human and nonhuman animals. With contributions by: Kristoffer Archibald, Jason Colby, George Colpitts, Joanna Dean, Carla Hustak, Darcy Ingram, Sean Kheraj, William Knight, Sherry Olson, Rachel Poliquin, and Christabelle Sethna
    Keywords: Animals ; Anthropology ; Environmental Science ; History ; bic Book Industry Communication::J Society & social sciences::JH Sociology & anthropology::JHM Anthropology ; bic Book Industry Communication::H Humanities::HB History ; bic Book Industry Communication::K Economics, finance, business & management::KC Economics::KCN Environmental economics ; bic Book Industry Communication::J Society & social sciences::JF Society & culture: general::JFF Social issues & processes::JFFZ Animals & society
    Language: English
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  • 3
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    Sentient Ecologies (2022)
    Berghahn Books | Berghahn Books
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    Publication Date: 2023-02-02
    Description: Employing methodological perspectives from the fields of political geography, environmental studies, anthropology, and their cognate disciplines, this volume explores alternative logics of sentient landscapes as racist, xenophobic, and right-wing. While the field of sentient landscapes has gained critical attention, the literature rarely seems to question the intentionality of sentient landscapes, which are often romanticized as pure, good, and just, and perceived as protectors of those who are powerless, indigenous, and colonized. The book takes a new stance on sentient landscapes with the intention of dispelling the denial of “coevalness” represented by their scholarly romanticization.
    Keywords: Social Science ; Sociology ; Rural ; Nature ; Animals ; Social Science ; Anthropology ; Cultural & Social ; bic Book Industry Communication::J Society & social sciences::JF Society & culture: general::JFS Social groups::JFSF Rural communities ; bic Book Industry Communication::W Lifestyle, sport & leisure::WN Natural history::WNC Wildlife: general interest ; bic Book Industry Communication::J Society & social sciences::JH Sociology & anthropology::JHM Anthropology::JHMC Social & cultural anthropology, ethnography
    Language: English
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  • 4
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    Frontiers in Chemistry: Rising Stars (2021)
    Frontiers Media SA
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    Publication Date: 2024-04-04
    Description: The Frontiers in Chemistry Editorial Office team are delighted to present the inaugural “Frontiers in Chemistry: Rising Stars” article collection, showcasing the high-quality work of internationally recognized researchers in the early stages of their independent careers. All Rising Star researchers featured within this collection were individually nominated by the Journal’s Chief Editors in recognition of their potential to influence the future directions in their respective fields. The work presented here highlights the diversity of research performed across the entire breadth of the chemical sciences, and presents advances in theory, experiment and methodology with applications to compelling problems. This Editorial features the corresponding author(s) of each paper published within this important collection, ordered by section alphabetically, highlighting them as the great researchers of the future. The Frontiers in Chemistry Editorial Office team would like to thank each researcher who contributed their work to this collection. We would also like to personally thank our Chief Editors for their exemplary leadership of this article collection; their strong support and passion for this important, community-driven collection has ensured its success and global impact.
    Keywords: Green and Sustainable Chemistry ; Analytical Chemistry ; Theoretical and Computational Chemistry ; Polymer Chemistry ; Medicinal and Pharmaceutical Chemistry ; Organic Chemistry ; Nanoscience ; Catalysis and Photocatalysis ; Supramolecular Chemistry ; Electrochemistry ; Inorganic Chemistry ; Chemical Biology ; thema EDItEUR::P Mathematics and Science::PD Science: general issues
    Language: English
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  • 5
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    Multispezies-Ethnographie (2021)
    transcript Verlag | transcript Verlag
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    Publication Date: 2024-03-28
    Description: Wie werden Natur und Tiere durch die Multispezies-Ethnographie inklusiv in Forschungsprojekte integriert? Katharina Ameli fokussiert die inter- und multidisziplinäre Zusammenarbeit. Aus einer Untersuchung der Schnittstellen zwischen gesellschafts- und naturwissenschaftlich orientierten Fachdisziplinen ergibt sich eine komplexe Betrachtung von Natur, Mensch und Tier. Die Einblicke in Interdependenzen unterschiedlicher Fachdisziplinen verdeutlichen den Bedarf an einer Multispezies-Ethnographie zur Analyse von MenschenTiereNaturenKulturen.
    Keywords: Natur ; Mensch ; Tiere ; Naturverständnis ; Interdisziplinarität ; Qualitative Forschung ; Kultur ; Ethnographie ; Umwelt ; Tier ; Human-animal Studies ; Umweltsoziologie ; Kulturanthropologie ; Kultursoziologie ; Kulturwissenschaft ; Nature ; Human ; Animals ; Understanding of Nature ; Interdisciplinarity ; Qualitative Research ; Culture ; Ethnography ; Environment ; Animal ; Environmental Sociology ; Cultural Anthropology ; Sociology of Culture ; Cultural Studies ; thema EDItEUR::J Society and Social Sciences::JB Society and culture: general::JBF Social and ethical issues::JBFU Animals and society ; thema EDItEUR::R Earth Sciences, Geography, Environment, Planning::RN The environment::RNT Social impact of environmental issues ; thema EDItEUR::J Society and Social Sciences::JH Sociology and anthropology::JHM Anthropology::JHMC Social and cultural anthropology
    Language: German
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  • 6
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    Animals and Inequality in the Ancient World (2021)
    University Press of Colorado | University Press of Colorado
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    Publication Date: 2024-04-02
    Description: Animals and Inequality in the Ancient World explores the current trends in the social archaeology of human-animal relationships, focusing on the ways in which animals are used to structure, create, support, and even deconstruct social inequalities. The authors provide a global range of case studies from both New and Old World archaeology—royal Aztec dog burial, the monumental horse tombs of Central Asia, and the ceremonial macaw cages of ancient Mexico among them. They explore the complex relationships between people and animals in social, economic, political, and ritual contexts, incorporating animal remains from archaeological sites with artifacts, texts, and iconography to develop their interpretations. Animals and Inequality in the Ancient World presents new data and interpretations that reveal the role of animals, their products, and their symbolism in structuring social inequalities in the ancient world. The volume will be of interest to archaeologists, especially zooarchaeologists, and classical scholars of pre-modern civilizations and societies.  Contributors: Alejandra Aguirre Molina, Benjamin S. Arbuckle, Levent Atici, Douglas V. Campana, Roderick Campbell, Ximena Chá­vez Balderas, Pam J. Crabtree, Susan D. deFrance, Kitty F. Emery, Abigail Holeman, H. Edwin Jackson, Leonardo López Lujá­n, Michael MacKinnon, Arkadiusz Marciniak, Sue Ann McCarty, Neil L. Norman, Gilberto Perez, Bernardo Rodriguez, William A. Saturno, Ashley E. Sharpe, Nawa Sugiyama, Charlotte K. Sunseri, Naomi Sykes, Fabiola Torres, Raul Valadez, Norma Valentin Maldonado, Adam S. Watson, Joshua Wright, Belem Zuniga-Arelleno
    Keywords: History ; Ancient ; Social Science ; Archaeology ; Nature ; Animals ; thema EDItEUR::N History and Archaeology::NH History::NHC Ancient history ; thema EDItEUR::N History and Archaeology::NK Archaeology ; thema EDItEUR::W Lifestyle, Hobbies and Leisure::WN Nature and the natural world: general interest::WNC Wildlife: general interest
    Language: English
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  • 7
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    Human and Animal Models for Translational Research on Neurodegeneration: Challenges and Opportunities From South America (2021)
    Frontiers Media SA
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    Publication Date: 2024-04-05
    Description: Neurodegenerative diseases are the most frequent cause of dementia, representing a burden for public health systems (especially in middle and middle-high income countries). Although most research on this issue is concentrated in first-world centers, growing efforts in South America are affording important breakthroughs. This emerging agenda poses new challenges for the region but also new opportunities for the field. This book aims to integrate the community of experts across the globe and the region, and to establish new challenges and developments for future investigation. We present research focused on neurodegenerative research in South America. We introduce studies assessing the interplay among genetic, neural, and behavioral dimensions of these diseases, as well as articles on vulnerability factors, comparisons of findings from various countries, and works promoting multicenter and collaborative networking. More generally, our book covers a broad scope of human-research approaches (behavioral assessment, neuroimaging, electromagnetic techniques, brain connectivity, peripheral measures), animal methodologies (genetics, epigenetics, proteomics, metabolomics, other molecular biology tools), species (all human and non-human animals, sporadic, and genetic versions), and article types (original research, review, and opinion papers). Through this wide-ranging proposal, we hope to introduce a fresh approach to the challenges and opportunities of research on neurodegeneration in South America.
    Keywords: RC321-571 ; Q1-390 ; South America ; Multicenter research ; Neurodegenerative Diseases ; Neurosciences ; Public Health ; Animals ; Clinical Protocols ; Research ; Human Experimentation ; Dementia ; thema EDItEUR::P Mathematics and Science::PS Biology, life sciences::PSA Life sciences: general issues::PSAN Neurosciences
    Language: English
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  • 8
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    Neuropharmacological, Neurobiological and Behavioral Mechanisms of Learning and Memory (2021)
    Frontiers Media SA
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    Publication Date: 2024-04-04
    Description: This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact
    Keywords: drugs ; Behavior ; Memory tasks ; pre-clinical ; clinical ; Humans ; Animals ; thema EDItEUR::P Mathematics and Science::PD Science: general issues ; thema EDItEUR::M Medicine and Nursing::MK Medical specialties, branches of medicine::MKG Pharmacology
    Language: English
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  • 9
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    Niphargus-Thiothrix associations may be widespread in sulphidic groundwater ecosystems: evidence from southeastern Romania. (2018)
    Details
    Publication Date: 2021-04-25
    Description: Niphargus is a speciose amphipod genus found in groundwater habitats across Europe. Three Niphargus species living in the sulphidic Frasassi caves in Italy harbour sulphur-oxidizing Thiothrix bacterial ectosymbionts. These three species are distantly related, implying that the ability to form ectosymbioses with Thiothrix may be common among Niphargus. Therefore, Niphargus-Thiothrix associations may also be found in sulphidic aquifers other than Frasassi. In this study, we examined this possibility by analysing niphargids of the genera Niphargus and Pontoniphargus collected from the partly sulphidic aquifers of the Southern Dobrogea region of Romania, which are accessible through springs, wells and Movile Cave. Molecular and morphological analyses revealed seven niphargid species in this region. Five of these species occurred occasionally or exclusively in sulphidic locations, whereas the remaining two were restricted to nonsulphidic areas. Thiothrix were detected by PCR on all seven Dobrogean niphargid species and observed using microscopy to be predominantly attached to their hosts' appendages. 16S rRNA gene sequences of the Thiothrix epibionts fell into two main clades, one of which (herein named T4) occurred solely on niphargids collected in sulphidic locations. The other Thiothrix clade was present on niphargids from both sulphidic and nonsulphidic areas and indistinguishable from the T3 ectosymbiont clade previously identified on Frasassi-dwelling Niphargus. Although niphargids from Frasassi and Southern Dobrogea are not closely related, the patterns of their association with Thiothrix are remarkably alike. The finding of similar Niphargus-Thiothrix associations in aquifers located 1200 km apart suggests that they may be widespread in European groundwater ecosystems.
    Keywords: amphipods; ecology; sulphide; symbiosis; systematics; taxonomy ; 551 ; Amphipoda ; Animals ; DNA, Bacterial ; Ecosystem ; Groundwater ; Molecular Sequence Data ; Phylogeny ; RNA, Ribosomal, 16S ; Romania ; Sequence Analysis, DNA ; Sulfur ; Symbiosis ; Thiothrix
    Language: English , English
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  • 10
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    Coronal structure and heating: Comparison between SXT/Yohkoh observations of an active region and magnetogram (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have studied the magnetic structure in AR 7150 (S09E06) observed on 29 April 1992 by the Soft X-Ray Telescope (SXT) on Yohkoh. The observed X-ray images are compared with force-free magnetic fields with different values of alpha, extrapolated from the Marshall Space Flight Center (MSFC) photospheric magnetogram observed at the same time. The results show that the magnetic field of the active region is not potential. Different groups of loops are characterized by different values of alpha. Bright loops correlation between the brightness of individual loops with the amount of twist. Further investigation of the magnetic state of the loop structure requires accurate nonlinear force-free calculations.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 4-5; p. (4/5)205-(4/5)208
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  • 11
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    Ulysses at high latitudes: An overview of recent results (1996)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: After its fly-by of the planet Jupiter in February 1992, the Ulysses spacecraft is now in a highly inclined heliocentric orbit that will bring it above the south polar regions of the Sun in September 1994. The high-latitude phenomena observed to date have been strongly influenced by the near-minimum solar activity conditions encountered during this phase of the mission. In late April 1993, when Ulysses was at approximately 29 deg S heliographic latitude, the recurrent high speed solar wind stream that had been observed at the location of the spacecraft for 11 consecutive solar rotation underwent a dramatic change. The wind speed in the valleys between successive peaks increased in a single step from approximately 420 km/s to aopproximately 560 km/s. This change in solar wind flow was accompanied by the disappearance at the spacecraft of the magnetic sector structure that had been observed until then. Both these finding are consistent with Ulysses having climbed beyond the latitude of the coronal streamer belt in which is embedded the heliospheric current sheet (HCS). In its subsequent poleward journey, no further evidence for an encounter with the HCS has been seen at Ulysses. Other phenomena observed include the evolution with latitude of corotating interaction region (CIRs) and their influence on the acceleration of energetic particles, and the characteristics of the solar wind flows emanating from the south polar coronal hole. In this paper, we present details of the above observations. Finally, while the polar passes of the prime mission will take place near solar minimum, an extended mission will bring Ulysses back over the poles near the maximum of the next cycle. A summary of scientific goals for Ulysses at solar maximum is given.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 4-5; p. (4/5)293-(4/5)302
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  • 12
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    Studies of plasma flow past Jupiter's satellite Io (1996)
    In:  CASI
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    Publication Date: 2019-07-20
    Description: We have investigated the interaction of Io, Jupiter's innermost Galilean satellite, with the Io plasma torus. The interaction of Io with the plasma surrounding it has been a subject of interest for almost 30 years, dating from the discovery by Bigg (1964) that radio emissions from the Jovian magnetosphere are controlled by Io's position. Since that time, both ground-based and spacecraft observations have shown that Io is a unique satellite that influences the Jovian magnetosphere in important ways. In particular, material from Io is a major source of plasma for the magnetosphere, and the energy that this plasma harnesses from Jupiter's co-rotating magnetic field is an important power source for the magnetosphere. It is apparent that the local interaction of the torus plasma with Io plays a key role in the formation, composition, and energetics of the Io torus; the interaction is also highly nonlinear. We have modeled this interaction using time-dependent three-dimensional magnetohydrodynamic (MHD) simulations. During this past year, we have used NASA support to develop a new MHD code to study the interaction. As part of the Galileo spacecraft's recent successful insertion into orbit around Jupiter, the spacecraft passed within 900 km of Io's surface. Our calculations have focused on using Galileo particles and fields data to examine a question that was not resolved by the Voyager observations: Does Io have an intrinsic magnetic field? In this progress summary, we describe our efforts on this problem to date.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-200134 , NAS 1.26:200134 , SAIC-95/1381:APPAT-174 , NIPS-96-07877
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  • 13
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    New observational facts about particle acceleration and transport during solar flares (1996)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Extensive hard X-ray (HXR)/gamma-ray (GR) observations of solar flares, performed during solar cycles 21 and 22 have led to important new discoveries. These data, combined with observations obtained in other parts of the electromagnetic spectrum (soft X-ray, Hard X-ray, optical, and radio) largley contributed to get a better understanding and to develop new ideas on particle acceleration and transport during solar flares. This review presents new observational facts relevant to hard X-ray/gamma-ray producing flares. Among these are the frequent presence of sub-second time structure in the hard X-ray emission, the variability in hard X-ray and radio spatial distributions during a flare and from flare to flare, the evidence for strong gamma-ray line emission from the Corona and the existence of extended phases of the gamma-ray emission lasting for several hours after the flare onset. This ensemble of observations indicates that particle acceleration takes place at different sites in a complex and dynamic magnetic field environment.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 5-Apr; p. (4/5)71-(4/5)80
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  • 14
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    A new perspective on solar active regions (1996)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A flood of new observations of the solar corona have been made with high spatial resolution, good temporal coverage and resolution, and large linear dynamic range by the Soft X-ray Telescope (SXT) on Yohkoh. These data are changing our fundamental understanding of how solar magnetic fields emerge, interact, and dissipate. This paper reviews some of the results from Yohkoh in the context of earlier results from the Solar Maximum Mission (SMM) and in comjunction with ground-based optical and radio observations.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 5-Apr; p. (4/5)179-(4/5)188
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  • 15
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    Emerging flux and flares in NOAA 7260 (1996)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We have studied the relation between flux emergence and flare activity in the active region NOAA 7260, using images from the Soft X-ray Telescope (SXT) aboard the Yohkoh spacecraft and other supporting ground-based data. It is found that microflares start around the time of flux emergence as recorded in white-light data, which generally precedes a major flare by several hours. We interpret the microflares as due to fast reconnection that takes place intermittently in the slow reconnection stage while more energy is accumulated in preparation for a larger flare.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 5-Apr; p. (4/5)201-(4/5)204
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  • 16
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    Continuum Fatigue Damage Modeling for Critical Design, Control, and Fault Prognosis (1996)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: This paper develops a simplified continuum (continuous with respect to time, stress, etc.) fatigue damage model for use in critical design, Life Extending Control and fault prognosis. The work is based on the local strain cyclic damage modeling method. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modelling. Stress based continuum models are derived. Extension to plastic strain-strain rate models is also presented. Progress toward a non-zero mean stress based is presented. Also new nonlinear explicit equation forms in terms of stress amplitude are derived for this case. Application of the various models to design, control, and fault prognosis is considered.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-107065 , NAS 1.15:107065 , E-9926 , NIPS-96-08117 , International Symposium on Transport Phenomena and Dynamics of Rotating Machinery; Feb 25, 1996 - Feb 29, 1996; Honolulu, HI; United States
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  • 17
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    NASA solar missions (1996)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The paper lists US solar missions, both those planned and funded by NASA alone as well as those carried out in collaboration with other space agencies. Soe of the missions are now in operation, the others are either planned and approved or under active discussion. The paper also describes the principal scientific objects of the missions and gives some orbital characteristics.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 4-5; p. (4/5)363-(4/5)368
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  • 18
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    IPS observations of heliospheric density structures associated with active regions (1996)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Interplanetary scintillation (IPS) measurements of the 'disturbance factor' g, obtained with the Cambridge (UK) array can be used to explore the heliospheric density structure. We have used these data to construct synoptic (Carrington) maps, representing the large-scale enhancements of the g-factor in the inner heliosphere. These maps emphasize the stable corotating, rather than the transient heliospheric density enhancements. We have compared these maps with Carrington maps of Fe XIV observations National Solar Observatory ((NSO), Sacramento Peak) and maps based on Yohkoh Soft X-Ray Telescope (SXT) X-ray observations. Our results indicate that the regions of enhanced g tend to map to active regions rather than the current sheet. The implication is that act ve regions are the dominant source of the small-scale (approximately equal 200 km) density variations present in the quiet solar wind.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 5-Apr; p. (4/5)311-(4/5)314
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  • 19
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    Solar coronal structure: A comparison of NSO/SP ground-based coronal emission line intensities and temperatures with Yohkoh SXT and WSO magnetic data (1996)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The large-scale structure of the solar corona is investigated using synoptic maps produced from Fe XIV (530.3 nm), Fe X (637.4 nm) and Ca XV (569.4 nm) data obtained at National Solar Observatory (NSO/SP), Yohkoh/Soft X-ray Telescope (SXT) X-ray data and Wilcox Solar Observatory (WSO) 'source surface' maps. We find that the Fe XIV data are an excellent proxy for spatially-average Yohkoh/SXT data. Isolated emission features and large-scale structures are nearly identical in SXT and Fe XIV maps. In addition, coronal holes and other low-emission regions are very similar. Synoptic temperature maps, calculated from the Fe X/Fe XIV ratio, show a tendency for the highest temperatures to occur where the large-scale magnetic fields change polarity at high latitudes, while lower-latitude features, including active regions, have lower apparent tempertures. Regions of enhanced temperature generally follow the helisopheric current sheet (HCS) as defined by the WSO maps. Further, emission in Ca XV (formed at T is approximately equal to 3 MK), generally occurs only over low-latitude regions that are bright in both FE X (T approximately equal to 1 MK) and Fe XIV (T approximately equal to 2 MK). Thus, there is evidence for low (approximately equal to 1 MK), moderate (approximately equal to 2 MK) and high (approximately 3 MK) temperatures in close proximity in the low corona.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 5-Apr; p. (4/5)235-(4/5)238
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  • 20
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    Ulysses observations of double ion beams associated with coronal mass ejections (1996)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Coronal mass ejections (CME's) are thought to result from the loss of stability within a magnetically confined coronal structure leading to its radial expansion into interplanetary space. As the CME expands into the corona current sheets will form between the expanding CME and surrounding field lines in the ambient wind. This configuration may lead to reconnection between the CME and adjacemt field lines. Such reconnection may produce double ion beams as has been observed in the terrrestrial magnetosphere. We examine all 24 distinct signatures of CME's observed by Ulysses during the in-ecliptic portion of the mission. In 5 of these 24 cases the ion spectra were not clear and thus the presence of double ion beams could not be determined. In 13 of the remaining 19 CME's double ion beams were found on the leading and/or trailing edge of the CME but not in the interior of the CME. In 3 of the CME's double ion beams were found throughout the CME while in the remaining 3 CME's double ion beams were not present near or just inside of the CME. In contrast in a control sample of 19 randomly chosen intervals, double ion beams were present at the leading and/or trailing edges of the random intervals in only 3 of the 19 cases. There appears to be no correlation between probability of occurrence of double ion beams and a magnetic cloud or non-cloud configuration of the CME and no correlation between the presence of the double ion beams at the edges of the CME and the CME being a fast or slow CME.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 4-5; p. (4/5)303-(4/5)306
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    Characteristics of hard X-ray double sources in impulsive solar flares (1996)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: Imaging observations of solar flare hard X-ray sources with the Hard X-ray Telescope (HXT) aboard the Yohkoh satellite have revealed that hard X-ray emissions (greater than 30 ke V) originate most frequently from double sources. The double sources are located on both sides of the magnetic neutral line, suggesting that the bulk of hard X-rays is emitted from footpoints of flaring magnetic loops. We also found that hard X-rays from the double sources are emitted simultaneously within a fraction of second and that the weaker source tends to be located in the stronger magnetic field region, showing a softer spectrum. Physcial implications on the observed characteristics of the hard X-ray double sources are discussed.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 17; 4-5; p. (4/5)67-(4/5)70
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  • 22
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    Features of the solar background velocity field (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The scaling properties of a time series of Doppler images obtained in good visibility conditions are studied. A 28 cm vacuum telescope and a vacuum spectroheliograph in video spectra-spectroheliograph mode, are used. Sixty line-of-sight Doppler images of an area of the quiet sun are investigated. They were taken at 60 sec intervals over a one hour span and have a 2 arcsec resolution. After the removal of the five-minute oscillations, the time-spatial spectrum is calculated. To study the turbulence of photospheric flows, two scaling parameters in the spectra, are estimated: the exponent of the spatial part of the power spectrum, and the exponent governing the scaling of time correlations. The implied diffusive behavior is discussed. This includes the estimation of a diffusion coefficient and the type of diffusion involved.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 249-252
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  • 23
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    Non-local transport in turbulent MHD convection (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The nonlocal non-diffusive transport of passive scalars in turbulent magnetohydrodynamic (MHD) convection is investigated using transilient matrices. These matrices describe the probability that a tracer particle beginning at one position in a flow will be advected to another position after some time. A method for the calculation of these matrices from simulation data which involves following the trajectories of passive tracer particles and calculating their transport statistics, is presented. The method is applied to study the transport in several simulations of turbulent, rotating, three dimensional compressible, penetrative MDH convection. Transport coefficients and other diagnostics are used to quantify the transport, which is found to resemble advection more closely than diffusion. Some of the results are found to have direct relevance to other physical problems, such as the light element depletion in sun-type stars. The large kurtosis found for downward moving particles at the base of the convection zone implies several extreme events.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 253-258
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  • 24
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    Tracking magnetogram proper motions by multiscale regularization (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Long uninterrupted sequences of solar magnetograms from the global oscillations network group (GONG) network and from the solar and heliospheric observatory (SOHO) satellite will provide the opportunity to study the proper motions of magnetic features. The possible use of multiscale regularization, a scale-recursive estimation technique which begins with a prior model of how state variables and their statistical properties propagate over scale. Short magnetogram sequences are analyzed with the multiscale regularization algorithm as applied to optical flow. This algorithm is found to be efficient, provides results for all the spatial scales spanned by the data and provides error estimates for the solutions. It is found that the algorithm is less sensitive to evolutionary changes than correlation tracking.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 227-232
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  • 25
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    Solar wind eddies and the heliospheric current sheet (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Ulysses has collected data between 1 and 5 AU during, and just following solar maximum, when the heliospheric current sheet (HCS) can be thought of as reaching its maximum tilt and being subject to the maximum amount of turbulence in the solar wind. The Ulysses solar wind plasma instrument measures the vector velocity and can be used to estimate the flow speed and direction in turbulent 'eddies' in the solar wind that are a fraction of an astronomical unit in size and last (have either a turnover or dynamical interaction time of) several hours to more than a day. Here, in a simple exercise, these solar wind eddies at the HCS are characterized using Ulysses data. This character is then used to define a model flow field with eddies that is imposed on an ideal HCS to estimate how the HCS will be deformed by the flow. This model inherently results in the complexity of the HCS increasing with heliocentric distance, but the result is a measure of the degree to which the observed change in complexity is a measure of the importance of solar wind flows in deforming the HCS. By comparison with randomly selected intervals not located on the HCS, it appears that eddies on the HCS are similar to those elsewhere at this time during the solar cycle, as is the resultant deformation of the interplanetary magnetic field (IMF). The IMF deformation is analogous to what is often termed the 'random walk' of interplanetary magnetic field lines.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A7; p. 12,261-12,273
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    Mass of dust in the Martian atmosphere (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Estimates of the mass of dust suspended in the Martian atmosphere are derived from global and regional 9-micrometer opacity maps produced from Viking Infrared Thermal Mapper data. During the peak of the 1977b storm, a total dust mass of approximately 4.3 x 10(exp 14) g was suspended, equivalent to 4.3 x 10(exp -4) g/sq cm, or a layer 1.4 micrometers thick. During a local dust storm near Solis Planum at L(sub s) 227 deg, approximately 1.3 x 10(exp 13) g of dust were lofted, equal to about a 6-micrometer layer in that vicinity.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; E4; p. 7509-7512
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  • 27
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    Line-of-sight magnetic flux imbalances caused by electric currents (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Several physical and observational effects contribute to the significant imbalances of magnetic flux that are often observed in active regions. We consider an effect not previously treated: the influence of electric currents in the photosphere. Electric currents can cause a line-of-sight flux imbalance because of the directionality of the magnetic field they produce. Currents associated with magnetic flux tubes produce larger imbalances than do smoothly-varying distributions of flux and current. We estimate the magnitude of this effect for current densities, total currents, and magnetic geometry consistent with observations. The expected imbalances lie approximately in the range 0-15%, depending on the character of the current-carying fields and the angle from which they are viewed. Observationally, current-induced flux imbalances could be indicated by a statistical dependence of the imbalance on angular distance from disk center. A general study of magnetic flux balance in active regions is needed to determine the relative importance of other- probably larger- effects such as dilute flux (too weak to measure or rendered invisible by radiative transfer effects), merging with weak background fields, and long-range connections between active regions.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 157; 1-2; p. 185-197
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    Volcanic eruptions on Io: Heat flow, resurfacing, and lava composition (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We model an infrared outburst on Io as being due to a large, erupting lava flow which increased its area at a rate of 1.5 x 10(exp 5)/sq m and cooled from 1225 to 555 K over the 2.583-hr period of observation. The inferred effusion rate of 3 x 10(exp 5) cu m/sec for this eruption is very high, but is not unprece- dented on the Earth and is similar to the high eruption rates suggested for early lunar volcanism. Eruptions occur approxi- mately 6% of the time on Io. These eruptions provide ample resurfacing to explain Io's lack of impact craters. We suggest that the large total radiometric heat flow, 10(exp 14) W, and the size and temperature distribution of the thermal anomalies (McEwen et al. 1992; Veeder et al. 1994) can be accounted for by a series of silicate lava flows in various stages of cooling. We propose that the whole suite of Io's currently observed thermal anomalies was produced by multiple, high-eruptive-rate silicate flows within the past century.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 220-225
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    Oscillation-convection coupling: Cause of supergranulation (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A semianalytic method is derived for dealing simultaneously with large numbers of linear stellar oscillation modes trapped in a cavity (a shell) of fluid which is rotating and convecting. A simple generalization of mixing-length theory shows how convection is modulated by weak rotational effects and by the horizontal wind fields of linear r-mode oscillations. The modulated convection is then used to compute the energy lost to turbulent viscosity by a family of nondegenerate oscillations. Viscosity terms of fourth degree in the wind shear can be included if they are a perturbation affecting only a small portion of the r-mode. Viscous energy loss strenghthens convection in a narrow layer near the base of the H and He ionization zone. In the Sun, this layer is about 7 Mm thick and centered at 0.932 of a solar radius where convection cells have a typical size of about 20 Mm and a lifetime of 0.3 Ms, both similar to what is observed in supergranules. If the rms velocity of r-modes at the surface exceeds 5 m/s, then energy is deposited inside the Sun at a sufficient rate to power the supergranulation and impose on it a weak latitude dependence.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 443; 1; p. 423-433
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  • 30
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    Dust torus around Mars (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We investigate the orbital dynamics of small dust particles generated via the continuous micrometeoroid bombardment of the Martian moons. In addition to Mar's oblateness, we also consider the radiation pressure perturbation that is complicated by the planet's eccentric orbit and tilted rotational axis. Considering the production rates and the lifetimes of dust grains, we show that particles from Deimos with radii of about 15 micrometers are expected to dominate the population of a permanently present and tilted dust torus. This torus has an estimated peak number density of approximately equals 5 x 10(exp -12)/cu cm and an optical depth of approximately equals 4 x 10(exp -8).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; E2; p. 3277-3284
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    A slightly more massive young Sun as an explanation for warm temperatures on early Mars (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The valley network channels on the heavily cratered ancient surface of Mars suggest the presence of liquid water approximately 3.8 Gyr ago. However, the implied warm climate is difficult to explain in the context of the standard solar model, even allowing for the maximum CO2 greenhouse heating. In this paper we investigate the astronomical and planetary implications of a nonstandard solar model in which the zero-age, main-sequence Sun had a mass of 1.05 +/- 0.02 Solar Mass. The excess mass was subsequently lost in a solar wind during the first 1.2(-0.2, +0.4) Gyr of the Sun's main sequence phase. The implied mass-loss rate of 4(+3, -2) x 10(exp -11) M/yr, or about 10(exp 3) x that of the current Sun, may be detectable in several nearby young solar type stars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); p. 5457-5464
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    Geology and landscape evolution of the Hellas region of Mars (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Hellas basin on Mars has been the site of volcanism, tectonism, and modification by fluvial, mass-wasting, and eolian processes over its more than 4-b.y. existence. Our detailed geologic mapping and related studies have resulted in the following new interpretations. The asymmetric distribution of highland massifs and other structures that define the uplifted basin rim suggest a formation of the basin by the impact of a low-angle bolide having a trajectory heading S60E. During the Late Noachian, the basin was infilled, perhaps by lava flows, that were sufficiently thick (greater than 1 km) to produce wrinkle ridges on the fill material and extensional faulting along the west rim of the basin. At about the same time, deposits buried northern Malea Planum, which are interpreted to be pyroclastic flows from Amphitrites and Peneus Paterae on the basis of their degraded morphology, topology, and the application of a previous model for pyroclastic volcanism on Mars. Peneus forms a distinctive caldera structure that indicates eruption of massive volumes of magma, whereas Amphitrites is a less distinct circular feature surrounded by a broad, low, dissected shield that suggests generally smaller volume eruptions. During the Early Hesperian, an approximately 1-to 2km-thick sequence of primarily fined-grained, eolian material was deposited on the floor of Hellas basin. Subsequently, the deposit was deeply eroded, except where armored by crater ejecta, and it retreated as much as 200-300 km along its western margin, leaving behind pedestal craters and knobby outliers of the deposit. Local debris flows within the deposit attest to concentrations of groundwater, perhaps in part brought in by outflow floods along the east rim of the basin. These floods may have deposited approximately 100-200m of sediment, subduing wrinkle ridges in the eastern part of the basin floor. During the Late Hesperian and Amazonian, eolian mantles were emplaced on the basin rim and floor and surrounding highlands. Their subsequent erosion resulted in pitted and etched plains and crater fill, irregular mesas, and pedestal craters. Local evidence occurs for the possible former presence of ground ice or ice sheets approximately 100 km across; however, we disagree with a hypothesis that suggest that the entire south rim and much of the floor of Hellas have been glaciated. Orientations of dune fields and yardangs in lower parts of Hellas basin follow directions of the strongest winds predicted by a recently published general circulation model (GCM). Transient frost and dust splotches in the region are, by contrast, related to the GCM prediction for the season in which the images they appear in were taken.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); p. 5407-5432
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    Hematite, pyroxene, and phyllosilicates on Mars: Implications from oxidized impact melt rocks from Manicouagan Crater, Quebec, Canada (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Visible and near-IR refectivity, Moessbauer, and X ray diffraction data were obtained on powders of impact melt rock from the Manicouagan Impact Crater located in Quebec, Canada. The iron mineralogy is dominated by pyroxene for the least oxidized samples and by hematite for the most oxidized samples. Phyllosilicate (smectite) contents up to approximately 15 wt % were found in some heavily oxidized samples. Nanophase hematite and/or paramagnetic ferric iron is observed in all samples. No hydrous ferric oxides (e.g., goethite, lepidocrocite, and ferrihydrite) were detected, which implies the alteration occurred above 250 C. Oxidative alteration is thought to have occurred predominantly during late-stage crystallization and subsolidus cooling of the impact melt by invasion of oxidizing vapors and/or solutions while the impact melt rocks were still hot. The near-IR band minimum correlated with the extent of aleration Fe(3+)/Fe(sub tot) and ranged from approximately 1000 nm (high-Ca pyroxene) to approximately 850 nm (bulk, well-crystalline hematite) for least and most oxidized samples, respectively. Intermediate band positions (900-920 nm) are attributed to low-Ca pyroxene and/or a composite band from hematite-pyroxene assemblages. Manicouagan data are consistent with previous assignments of hematite and pyroxene to the approximately 850 and approximately 1000nm bands observed in Martian reflectivity spectra. Manicouagan data also show that possible assignments for intermediate band positions (900-920 nm) in Martian spectra are pyroxene and/or hematite-pyroxene assemblages. By analogy with impact melt sheets and in agreement with observables for Mars, oxidative alteration of Martian impact melt sheets above 250 C and subsequent erosion could produce rocks and soils with variable proportions of hematite (both bulk and nanophase), pyroxene, and phyllosilicates as iron-bearing mineralogies. If this process is dominant, these phases on Mars were formed rapidly at relativly high temperatures on a sporadic basis throughout the history of the planet. The Manicouagan samples also show that this mineralogical diversity can be accomplished at constant chemical composition, which is also indicated for Mars from the analyses of soil at the two Viking landing sites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); pp. 5319-5328
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    The initiation of coronal mass ejections by newly emerging magnetic flux (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present observational evidence that eruptions of quiescent filaments and associated coronal mass ejections (CMEs) occur as a consequence of the destabilization of large-scale coronal arcades due to interactions between these structures and new and growing active regions. Both statistical and case studies have been carried out. In a case study of a 'bulge' observed by the High-Altitude Observatory Solar Maximum Mission coronagraph, the high-resolution magnetograms from the Big Bear Solar Observatory show newly emerging and rapidly changing flux in the magnetic fields that apparently underlie the bugle. For other case studies and in the statistical work the eruption of major quiescent filaments was taken as a proxy for CME eruption. We have found that two thirds of the quiescent-filament-associated CMEs occurred after substantial amounts of new magnetic flux emerged in the vicinity of the filament. In addition, in a study of all major quiescent filaments and active regions appearing in a 2-month period we found that 17 of the 22 filaments that were associated with new active regions erupted and 26 of the 31 filaments that were not associated with new flux did not erupt. In all cases in which the new flux was oriented favorably for reconnection with the preexisting large-scale coronal arcades; the filament was observed to erupt. The appearance of the new flux in the form of new active regions begins a few days before the eruption and typically is still occurring at the time of the eruption. A CME initiation scenario taking account of these observational results is proposed.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3355-3367
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    Long-term total solar irradiance variability during sunspot cycle 22 (1995)
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    Publication Date: 2011-08-24
    Description: Total solar irradiance measurements from the 1984-1993 Earth Radiation Budget Satellite (ERBS) active cavity radiometer and 1978-1993 Nimbus 7 transfer cavity radiometer spacecraft experiments are analyzed to detect the presence of 11-, 22-, and 80-year irradiance variability components. The analyses confirmed the existence of a significant 11-year irradiance variability component, associated with solar magnetic activity and the sunspot cycle. The analyses also suggest the presence of a 22- or 80-year variability component. The earlier Nimbus 7 and Solar Maximum Mission (SMM) spacecraft irradiance measurements decreased approximately 1.2 and 1.3 W/sq m, respectively, between 1980 and 1986. The Nimbus 7 values increased 1.2 W/sq m between 1986 and 1989. The ERBS irradiance measurements increased 1.3 W/sq m during 1986-1989, and then decreased 0.4 W/sq m (at an annual rate of 0.14 W/sq. m/yr) during 1990-1993. Considering the correlations between ERBS, Nimbus 7, and SMM irradiance trends and solar magnetic activity, the total solar irradiance should decrease to minimum levels by 1997 as solar activity decreases to minimum levels, and then increase to maximum levels by the year 2000 as solar activity rises. The ERBS measurements yielded 165.4 +/- 0.7 W/sq m as the mean irradiance value with measurement accuracies and precisions of 0.2% and 0.02%, respectively. The ERBS mean irradiance value is within 0.2% of the 1367.4, 1365.9, and 1366.9 W/sq m mean values for the SMM, Upper Atmosphere Research Satellite (UARS), and Space Shuttle Atmospheric Laboratory for Applications and Science (ATLAS 1) Solar Constant (SOLCON) active cavity radiometer spacecraft experiments, respectively. The Nimbus 7 measurements yielded 1372.1 W/sq m as the mean value with a measurement accuracy of 0.5%. Empirical irradiance model fits, based upon 10.7 -cm solar radio flux (F10) and photometric sunspot index (PSI), were used to assess the quality of the ERBS, Numbus 7, SMM, and the UARS irradiance data sets and to identify irradiance variability trends which may be caused by drifts or shifts in the spacecraft sensor responses. Comparisons among the fits and measured irradiances indicate that the Nimbus 7 radiometer response shifted by a total of 0.8 W/sq m between September 1989 and April 1990 and that the ERBS and UARS radiometers each drifted approximately 0.5 W/sq m during the first 5 months in orbit.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A2; p. 1667-1675
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    Nonequilibrium, large-amplitude MHD fluctuations in the solar wind (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Compressible MHD simulations in one dimension with three-dimensional vectors are used to investigate a number of processes relevant to problems in interplanetary physics. The simulations indicate that a large-amplitude nonequilibrium (e.g., linearly polarized) Alfvenic wave, which always starts with small relative fluctuations in the magnitude B of the magnetic field, typically evolves to flatten the magnetic profile in most regions. Under a wide variety of conditions B and the density rho become anticorrelated on average. If the mean magnetic field is allowed to decrease in time, the point where the transverse magnetic fluctuation amplitude delta B(sub T) is greater than the mean field B(sub 0) is not special, and large values of delta B(sub T)/B(sub 0) do not cause the compressive thermal energy to increase remarkably or the wave energy to dissipate at an unusually high rate. Nor does the 'backscatter' of the waves that occurs when the sound speed is less than the Alfven speed result, in itself, in substantial energy dissipation, but rather primarily in a phase change between the magnetic and velocity fields. For isolated wave packets the backscatter does not occur for any of the parameters examined; an initial radiation of acoustic waves away from the packet establishes a stable traveling structure. Thus these simulations, although greatly idealized compared to reality, suggest a picture in which the interplanetary fluctuations should have small deltaB and increasingly quasi-pressure balanced compressive fluctuations, as observed, and in which the dissipation and 'saturation' at delta B(sub T)/B(sub 0) approximately = 1 required by some theories of wave acceleration of the solar wind do not occur. The simulations also provide simple ways to understand the processes of nonlinear steepening and backscattering of Alfven waves and demonstrate the existence of previously unreported types of quasi-steady MHD states.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3405-3415
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    Frequency shifts of high frequency p-modes (1995)
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    Publication Date: 2011-08-24
    Description: Frequency shifts of high frequency p-modes during the solar cycle are calculated for a non-magnetic polytrope convection zone model. An isothermal chromospheric atmosphere threaded by a uniform horizontal magnetic field is correlated to this model. The relevant observations of such frequency changes are discussed. The calculated simultaneous changes in the field strength and chromospheric temperature result in the frequency shifts that are similar to those of the observations.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 69-72
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    Reduction, analysis, and properties of electric current systems in solar active regions (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The specific attraction and, in large part, the significance of solar magnetograms lie in the fact that they give the most important data on the electric currents and the nonpotentiality of active regions. Using the vector magnetograms from the Marshall Space Flight Center (MSFC), we employ a unique technique in the area of data analysis for resolving the 180 deg ambiguity in order to calculate the spatial structure of the vertical electric current density. The 180 deg ambiguity is resolved by applying concepts from the nonlinear multivariable optimization theory. The technique is shown to be of particular importance in very nonpotential active regions. The characterization of the vertical electric current density for a set of vector magnetograms using this method then gives the spatial scale, locations, and magnitude of these current systems. The method, which employs an intermediate parametric function which covers the magnetogram and which defines the local `preferred' direction, minimizes a specific functional of the observed transverse magnetic field. The specific functional that is successful is the integral of the square of the vertical current density. We find that the vertical electric current densities have common characteristics for the extended bipolar (beta) (gamma) (delta)-regions studied. The largest current systems have j(sub z)'s which maximizes around 30 mA/sq m and have a linear decreasing distribution to a diameter of 30 Mn.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 982-998
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    Abundance ratios of oxygen, neon, and magnesium in solar active regions and flares: The FIP effect (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Relative abundances of oxygen, neon, and magnesium have been derived for a sample of nine solar active regions, flares, and an erupting prominance by combining plots of the ion differential emission measures. The observations were photographed in the 300-600 A range by the Naval Research Laboratory (NRL) spectroheliograph on Skylab. Methods for deriving the Mg/Ne abundance ratio-which measures the separation between the low- first ionization potential (FIP) and high-FIP abundnace plateaus-have been described in previous papers. In this paper we describe the spectroscopic methods for deriving the O/Ne abundance ratio, which gives the ratio between two high-FIP elements. The plot of the O/Ne ratio versus the Mg/Ne ratio in the sample of nine Skylab events is shown. The variation in the Mg/Ne ratio by a factor of 6 is associated with a much smaller range in the O/Ne ratio. This is broadly consistent with the presence of the standard FIP pattern of abundances in the outer atmosphere of the Sun. However, a real change in the relative abundances of oxygen and neon by a factor of 1.5 cannot be excluded.
    Keywords: SOLAR PHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 442; 1; p. 446-450
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    Time-distance helioseismology in the vicinity of sunspots (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We use the ray description of acoustic-gravity modes to calculate time-distance diagrams for the quiet Sun and for regions in the vicinity of a sunspot with a monolithic flux-tube structure. Time-distance curves for the quiet Sun match the observations of Duvall et al. In the vicinity of a sunspot these quiet Sun curves split into a family of closely spaced curves. The structure of this bandlike feature is found to be sensitive to the sunspot model and can be a diagnostic of the subsurface geometry of the sunspot flux tube.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 454-462
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    Solar variability in irradiance and oscillations (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The signature of the solar cycle appears in helioseismic frequencies and splittings. It is known that the changing outer superadiabatic region of the sun is responsible for this. The deeper solar-cycle mechanism from the surface changes, and, in particular, how magnetic fields perturb the global modes, the solar irradiance and the luminosity, is discussed. The irradiance and helioseismic changes are described. The interpretation of seismic and photometric data is discussed, considering current one-dimensional models and phenomenology. It is discussed how the long term solar-cycle luminosity effect could be caused by changes occurring near the base of the convection zone (CZ). It is shown that a thin toroidal flux sheath at the top of the radiative zone changed the thermal stratification immediately below the CZ over a solar-cycle timescale in two ways: the temperature of the magnetized fluid becomes hotter than the surrounding fluid, and the temperature gradient steepens above the magnetized region. The testing of CZ dynamics and extension of numerical experiments to global scales are considered.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 1: Invited Reviews and Working Group Reports; p 145-149
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    The relation between the period of oscillations and brightness in chromospheric bright points (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The chromospheric bright points are the sites where intense heating occurs in three minute period waves. The bright points are grouped into three classes depending on the amount of intensity enhancement and the pattern of their dynamical evolution. A 35-minute time series of photographic spectra in the Ca(II) H line on a quiet region ofthe center of the solar disk was used to show that the period of intensity oscillations seen at sites of the bright points is independent of their intensity enhancements. The series was also used to show that the period may not depend on the strength of the magnetic fields with which they are associated. A linear regression equation was fitted to a curve representing the variation of the period of intensity oscillations with the peak value of I(sub H2V). The correlation coefficient was found to be 0.19.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 525-527
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    Preliminary results of the analysis of CaII K spectroheliograms (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The preliminary results of the photometry of CaII K spectroheliograms are presented. From the spectrograms for 1992, plages, the magnetic network, intranetwork elements and the chromospheric background were separated using the histogram method. The intensity and area of these separated features, as well as the full disk intensity, were derived. The spatial K index was compared to the spectral CaII K index derived from line profiles. It was found that the spatial K index and intensity of plages, the network elements and the intranetwork and background regions were highly correlated with the MgII h and k c/w ratio.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 429-435
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  • 44
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    Test of the magneto optical filter during the comet P/Shoemaker-Levy 9 impacts on Jupiter. A Doppler signal detected? (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The observations made in July 1994 on the impact of fragment A of the comet P/Shoemaker-Levy 9 with Jupiter are described. The instrumentation used was a magneto-optical filter, acting as a two-channel filter. The data showed a double-peak transient which occurred after the impact, and whose general properties indicated a true jovian origin. The peaks appear in absorption. A numerical simulation can explain the main characteristics of the observed signal where the two peaks have the same polarity and appear only in the channel at shorter wavelengths. The simulation carried out appeared to indicate that the observed signal could be produced by the combination of shock waves and the expanding material with a velocity of 13 +/- 8 km/s. This implies that two separate impacts may have been observed. The developed simulation can be extended to predict long term effects.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 345-350
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  • 45
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    Is there a seismic signature of the sun's magnetic field? (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Both weak magnetic fields and latitudinally dependent acoustic perturbations remove the degeneracy of the azimuthal quantum number, m, of acoustic modes of otherwise spherically symmetrical solar model. In the case of acoustic perturbations, the degeneracy is removed because the range of latitude in which a mode propagates depends on m, and therefore modes of like principle order n and degree l sample the aspherical scalar sound speed distribution differently. In the magnetic case, the removal of the degeneracy is caused by the same geometrical effect, and is influenced by the anisotropy of the Lorentz forces. Asymptotic analysis is used to show that the frequency splittings cannot be unambiguously attributed to the direct effect of a magnetic field, and that the effect of such a field on frequency splittings can be reproduced by a perturbation to the sound speed.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 73-76
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  • 46
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    Intensity oscillations in Na(I) D1 and D2 lines (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The central intensities of Na(I) D1 and D2 linear profiles at the sites of the chromospheric bright points in the interior of the supergranulation cells were derived from photographic spectra. The observation scheme sampled spectra simultaneously in seven lines at a repetition rate of 12 sec. It is shown that the Na(I) D1 and D2 lines exhibit a four minute periodicity in their intensity oscillations. It is seen that the period of intensity oscillations decreases outwardly from the photosphere to the corona. It is surmised that the spatial and temporal relationships between intensity and/or velocity in the photosphere and chromosphere may explain the physical mechanisms of the underlying oscillations.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 521-524
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  • 47
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    Pole-equator difference and the variability of the brightness of the chromospheric CaII-K-network elements in quiet regions over the solar cycle (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The dependence of the brightness of chromospheric network elements on latitude was investigated for quiet solar regions. Calibrated photographic CaII K-spectroheliograms were used to compare the variation in brightness at the center of the disk with higher latitude of chromospheric network elements in a quiet region as a function of solar activity. It was found that there was no significant difference in brightness between the center of the solar disk and higher latitude. It is concluded that the brightness of the chromospheric network elements in a quiet region does not depend on the latitude, but that the variation in the intensity enhancement is related to the level of solar activity.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 437-438
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  • 48
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    L = 1 rotational splitting detected from a 69 day run using the magneto-optical filter installed at JPL (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The preliminary analysis of a 69 day observation run taken at the JPL using the magneto-optical filter is presented. The aim is to estimate the rotational splitting of l = 1 modes. A value of Delta nu = 0.44 +/- 0.09 micro-Hz is found. In a second, more accurate analysis, it is planned to investigate the low frequency part of the power spectrum. The observational statistics are presented.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 311-313
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  • 49
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    Plane-wave analysis of solar acoustic-gravity waves: A (slightly) new approach (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The plane-wave decomposition of the acoustic-gravity wave effects observed in the photosphere provides a computationally efficient technique that probes the structure of the upper convective zone and boundary. In this region, the flat sun approximation is considered as being reasonably accurate. A technique to be used for the systematic plane-wave analysis of Michelson Doppler imager data, as part of the solar oscillations investigation, is described. Estimates of sensitivity are presented, and the effects of using different planar mappings are discussed. The technique is compared with previous approaches to the three dimensional plane-wave problem.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 147-150
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  • 50
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    Changes in the upper turning point due to magnetism (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It was observed that the p-mode power is substantially suppressed in magnetic regions. One possible explanation is that the upper turning point, the acoustic cut-off point of the solar p-modes is lowered in the presence of a magnetic field. A related possibility is that the attenuation length scale in the evanescent region is reduced in the presence of a magnetic field. It is likely that the observations sample a different position in the evanescent tails of the eigenfunctions in magnetic regions because of different temperature structures in these regions. A model is used to quantify the first of these effects.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 63-67
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    Magnetohydrodynamic turbulence in the solar wind (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The fluctuations in magnetic field and plasma velocity in solar wind, which possess many features of fully developed magnetohydrodynamic (MHD) turbulence, are discussed. Direct spacecraft observations from 0.3 to over 20 AU, remote sensing radio scintillation observations, numerical simulations, and various models provide complementary methods that show that the fluctuations in the wind parameters undergo significant dynamical evolution independent of whatever turbulence might exist in the solar photosphere and corona. The Cluster mission, with high time resolution particle and field measurements and its variable separation strategies, should be able to provide data for answering many questions on MHD turbulence.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of the Cluster Workshops on Data Analysis Tools, and Physical Measurements and Mission-Oriented Theory; p 137-147
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    Solar wind double ions beams and the heliospheric current sheet (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Double ion beams are often observed in the solar wind, but little work has been done in relating these beams to structures within the solar wind. Double ion beams are observed as beams of a given ion species and charge state occurring at two different energies. We use the three-dimensional ion plasma instrument on board the Ulysses spacecraft to look for evidence of such beams associated with the heliospheric current sheet. In a subset chosen independently of plasma parameters consisting of 8 of cover 47 crossings of the current sheet made during the inecliptic phase of the Ulysses mission we find that these double ion beams are always present on either side of the current sheet. The double beams are present in both the proton and helium species. The secondary beam typically has a higher helium abundance, which suggests that these beams are formed in the helium-rich corona rather than in interplanetary space. The double beams are not present in the interior of the current sheet. Neither collisions nor effects of plasma beta can account for the disappearance of the double beams inside the current sheet in all eight cases. We postulate that these beams are formed by reconnection occurring near the Sun in the boundary region between the open field lines of the coronal holes and the closed field line region of the heliospheric current sheet. Such a scenario would be consistent with previous X ray measurements which suggect that reconnection is occurring in this region.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A5; p. 7881-7889
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    Heating of the solar middle chromosphere by large-scale electric currents (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A global resistive, two-dimensional, time-dependent magnetohydrodynamic (MHD) model is used to introduce and support the hypothesis that the quiet solar middle chromosphere is heated by resistive dissipation of large-scale electric currents which fill most of its volume. The scale height and maximum magnitude of the current density are 400 km and 31.3 m/sq m, respectively. The associated magnetic field is almost horizontal, has the same scale height as the current density, and has a maximum magnitude of 153 G. The current is carried by electrons flowing across magnetic field lines at 1 m/s. The resistivity is the electron contribution to the Pedersen resitivity for a weakly ionized, strongly magnetized, hydrogen gas. The model does not include a driving mechanism. Most of the physical quantities in the model decrease exponentially with time on a resistive timescale of 41.3 minutes. However, the initial values and spatial; dependence of these quantities are expected to be essentially the same as they would be if the correct driving mechanism were included in a more general model. The heating rate per unit mass is found to be 4.5 x 10(exp 9) ergs/g/s, independent of height and latitude. The electron density scale height is found to be 800 km. The model predicts that 90% of the thermal energy required to heat the middle chromosphere is deposited in the height range 300-760 km above the temperature minimum. It is shown to be consistent to assume that the radiation rate per unit volume is proportional to the magnetic energy density, and then it follows that the heating rate per unit volume is also proportional to the energy from the photosphere into the overlying chromosphere are briefly discussed as possible driving mechanisms for establishing and maintaining the current system. The case in which part of or all of the current is carried by protons and metal ions, and the contribution of electron-proton scattering to the current are also considered, with the conclusion that these effects do not change the qualitative prediction of the model, but probably change the quantitative predictions slightly, mainly by increasing the maximum magntiude of the current density and magnetic field to at most approximately 100 mA/m and approximately 484 G, respectively. The heating rate per unit mass, current density scale height, magnetic field scale height, temperatures, and pressures are unchanged or are only slightly changed by including these additional effects due to protons and ions.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 443; 1; p. 450-459
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    Uniqueness of a solution of a steady state photochemical problem: Applications to Mars (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Based on the conservation of chemical elements in chemical reactions, a rule is proved that the number of boundary conditions given by densities and/or nonzero velocities should not be less than the number of chemical elements in the system, and the boundary conditions for species given by densities and velocities should include all elements in the system. Applications of this rule to Mars are considered. It is shown that the problem of the CO2-H2O chemistry in the lower and middle atmosphere of Mars, say, in the range of 0-80 km does not have a unique solution, if only CO2 and H2O densities are given at the lower boundary, and the remaining boundary conditions are fluxes. Two examples of models of this type are discussed. Two models of the photochemistry of the Martian atmosphere, with and without nitrogen chemistry, are considered. The oxygen nonthermal escape ratio of 1.2 x 10(exp 8)/cu cm/s is given at 240 km and is balanced with the total hydrogen escape rate within an uncertainty of 1% for both models. Both models fit the measured O2 and CO mixing ratios, the O3 abundance, and the O2 1.27-micrometer dayglow almost within the uncertainties of the measured values, though the model without nitrogen chemistry fits better. The importance of nitrogen chemistry in the lower and middle atmosphere of Mars depends on a fine balance between production of NO and N in the upper atmosphere which is not known within the required accuracy.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; E2; p. 3263-3276
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    Reflectivity and other physicochemical properties of Mn-substituted goethites and hematites (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Goethite-bearing samples with values of Mn(s) (Mn/(Mn+Fe) mole fraction) up to 0.206 were synthesized by precipitation from alkaline solution. Samples with Mn(s) less than or equal 0.061 were single-phase Mn-goethites: samples with higher Mn(s) values contained another Mn-bearing phase (probably jacobsite). Mn-hematites were prepared by dehydroxylation of corresponding Mn-goethites at 500 C. Orthorhombic a and b unit cell dimensions of Mn-goethites changed in a linear manner with Mn(s), but not at rates predicted by the Vegrad law. Hexagonal unit cell dimensions of Mn-hematites did not vary with Mn(s). Moessbauer parameters isomer shift (IS), quadrupole splitting (QS), and hyperfine field (B(sub hf)) were measured at 293 and 15 K. For all single-phase Mn-goethites and Mn-hematites (Mn(s) less than or equal 0.061), magnetic splitting was observed at both temperatures. At 293 K, small but systematic decreases in B(sub hf) were observed with increasing Mn substitution; IS and QS were not dependent on Mn(s). Mn substitution strongly lowered the Morin transition temperature of hematite. At 15 K, the Morin transition was not present for Mn(s) greater than 0.020(4). The saturation magnetization of Mn-goethites and Mn-hematites (Mn(s) less than or equal 0.061) was the expected zero (within error) for antiferromagnetic goethite and for hematites obtained from dehydroxylation of goethites. Mn-geothites with Mn(s) greater than 0.061 were magnetic because of the presence of strongly magnetic jacobsite. For reflectivity spectra, bands resulting from MN(3+) were centered near 454 and 596 nm for Mn-goethites and near 545 and 700 nm for Mn-hematites. There is evidence for a approximately 700 nm band in spectral data for Martian bright regions, but association of it with Mn(3+) is not a unique interpretation. Comparison of laboratory and Martian spectral data implies that Mn(s) less than 0.032 for the Mn(3+) content of Martian hematites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; E2; p. 3285-3295
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    First realisation of the Space Absolute Radiometric Reference (SARR) during the ATLAS 2 flight period (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A number of different solar constant observations all made from space during the ATLAS 2 mission have been gathered and compared to each other. The Sun did not have a single sunspot during several days. As eight of the radiometric channels were all within 0.1%, the mean of the observations has been used to determine a set of adjustment factors providing de facto the definition of the Space Absolute Radiometric Reference (SARR). The differential absolute radiometers of Solar Constant (SOLCON) experiment and the Solar Variability-1 (SOVA 1) experiment, as well as the SOVA 2 and Active Cavity Radiometer (ACR) radiometers that have been brought back to the Earth may, if used in the same conditions, reproduce and maintain the SARR for the future.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 8; p. (8)17-(8)23
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    Mid-infrared transmission spectra of crystalline and nanophase iron oxides/oxyhydroxides and implications for remote sensing of Mars (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Ferric-iron-bearing materials play an important role in the interpretation of visible to near-IR Mars spectra, and they may play a similarly important role in the analysis of new mid-IR spacecraft spectral observations to be obtained over the next decade. We review exisiting data on mid-IR transmission spectra of ferric oxides/oxyhydroxides and present new transmission spectra for ferric-bearing materials spanning a wide range of mineralogy and crystallinity. These materials include 11 samples of well-crystallized ferric oxides (hematite, maghemite, and magnetite) and ferric oxyhydroxides (goethite, lepidocrocite). We also report the first transmission spectra for purely nanophase ferric oxide samples that have been shown to exhibit spectral similarities to Mars in the visible to near-IR and we compare these data to previous and new transmission spectra of terrestial palagonites. Most of these samples show numerous, diagnostic absorption features in the mid-IR due to Fe(3+) - 0(2-) vibrational transitions, structural and/or bound OH, and/or silicates. These data indicate that high spatial resolution, moderate spectral resolution mid-IR ground-based and spacecraft observations of Mars may be able to detect and uniquely discriminate among different ferric-iron-bearing phases on the Martian surface or in the airborne dust.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); p. 5297-5307
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    The Photogrammetric Appendage Structural Dynamics Experiment (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Photogrammetric Appendage Structural Dynamics Experiment (PASDE) is a Hitchhiker payload scheduled to fly as part of the International Space Station (ISS) Phase-1 flight program to the Russian Space Station Mir. The objective of the first flight of PASDE on STS-74 is to obtain video images of the Mir Kvant-2 solar array response to various structural dynamic excitation events. This experiment will demonstrate the use of photogrammetric techniques for on-orbit structural dynamics measurements. Photogrammetric measurements will provide a low cost alternative to appendage mounted accelerometers to the ISS program. The PASDE experiment hardware consists of three instruments each containing two video cameras, two video tape recorders, a modified video signal time inserter, and associated avionics boxes. The instruments were designed and built at the NASA Langley Research Center, and are integrated into standard Hitchhiker canisters at the NASA Goddard Space Flight Center. The Hitchhiker canisters are then installed into the Space Shuttle cargo bay in locations selected to achieve good video coverage and photogrammetric geometry. The measurement resolution of the instruments is expected to be on the order of 0.25 cm (0.1 in.).
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Goddard Space Flight Center, The 1995 Shuttle Small Payloads Symposium; p 73-82
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    Determination of the position of Jupiter from radio metric tracking of Voyager 1 (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Voyager 1 spacecraft flew by Jupiter on March 5, 1979. Spacecraft navigation was performed with radio tracking data from NASA's Deep Space Network. In the years since then, there has been a great deal of progress in the definition of celestial reference frames and in determining the orbit and orientation of the Earth. Using these improvements, the radio metric range and Doppler data acquired from the Voyager 1 spacecraft near its encounter with Jupiter have been reanalyzed to determine the plane-of-sky position of Jupiter with much greater accuracy than was possible at the time of the encounter. The position of Jupiter at the time of encounter has been determined with an accuracy of 40 nrad in right ascension and 140 nrad in declination with respect to the celestial reference frame defined by the International Earth Rotation Service. This position estimate has been done to improve the ephemeris of Jupiter prior to the upcoming encounter of the Galileo spacecraft with Jupiter.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: The Telecommunications and Data Acquisition Report; p 1-8
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  • 60
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    Comparison of measured and calculated dynamic loads for the Mod-2 2.5 mW wind turbine system (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Boeing Company, under contract to the Electric Power Research Institute (EPRI), has completed a test program on the Mod-2 wind turbines at Goodnoe Hills, Washington. The objectives were to update fatigue load spectra, discern site and machine differences, measure vortex generator effects, and to evaluate rotational sampling techniques. This paper shows the test setup and loads instrumentation, loads data comparisons and test/analysis correlations. Test data are correlated with DYLOSAT predictions using both the NASA interim turbulence model and rotationally sampled winds as inputs. The latter is demonstrated to have the potential to improve the test/analysis correlations. The paper concludes with an assessment of the importance of vortex generators, site dependence, and machine differences on fatigue loads. The adequacy of prediction techniques used are evaluated and recommendations are made for improvements to the methodology.
    Keywords: STRUCTURAL MECHANICS
    Type: DASCON Engineering, Collected Papers on Wind Turbine Technology; p 139-152
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    A model of rotationally-sampled wind turbulence for predicting fatigue loads in wind turbines (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Empirical equations are presented with which to model rotationally-sampled (R-S) turbulence for input to structural-dynamic computer codes and the calculation of wind turbine fatigue loads. These equations are derived from R-S turbulence data which were measured at the vertical-plane array in Clayton, New Mexico. For validation, the equations are applied to the calculation of cyclic flapwise blade loads for the NASA/DOE Mod-2 2.5-MW experimental HAWT's (horizontal-axis wind turbines), and the results compared to measured cyclic loads. Good correlation is achieved, indicating that the R-S turbulence model developed in this study contains the characteristics of the wind which produce many of the fatigue loads sustained by wind turbines. Empirical factors are included which permit the prediction of load levels at specified percentiles of occurrence, which is required for the generation of fatigue load spectra and the prediction of the fatigue lifetime of structures.
    Keywords: STRUCTURAL MECHANICS
    Type: Collected Papers on Wind Turbine Technology; p 17-26
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    Sensitivity analysis for the dynamic response of viscoplastic shells of revolution (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A computational procedure is presented for evaluating the sensitivity coefficients of the dynamic axisymmetric response of viscoplastic shells of revolution. The analytical formulation is based on Reissner's large deformation shell theory with the effects of transverse shear deformation, rotatory inertia and moments turning around the normal to the middle surface included. The material model is chosen to be isothermal viscoplasticity, and an associated flow rule is used with a von Mises effective stress. A mixed formulation is used with the fundamental unknowns consisting of six stress resultants, three generalized displacements and three velocity components. Spatial discretization is performed using finite elements, with discontinuous stress resultants across element interfaces. The temporal integration is performed by using an explicit central difference scheme (leap-frog method) with an implicit constitutive update. The sensitivity coefficients are evaluated using a direct differentiation approach. Numerical results are presented for a spherical cap subjected to step loading, and a circular plate subjected to impulsive loading. The sensitivity coefficients are generated by evaluating the derivatives of the response quantities with respect to thickness, mass density, Young's modulus, and two of the material parameters characterizing the viscoplastic response. Time histories of the response and sensitivity coefficients are presented, along with spatial distributions of these quantities at selected times.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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    Hypervelocity impact survivability experiments for carbonaceous impactors, part 2 (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Hypervelocity impact experiments were performed to further test the survivability of carbonaceous impactors and to determine potential products that may have been synthesized during impact. Diamonds were launched by the Ames two-stage light gas gun into Al plate at velocities of 2.75 and 3.1 km sec(exp -1). FESEM imagery confirms that diamond fragments survived in both experiments. Earlier experiments found that diamonds were destroyed on impact above 4.3 km sec(exp -1). Thus, the upper stability limit for diamond on impact into Al, as determined from our experimental conditions, is between 3.1 and 4.3 km sec(exp -1). Particles of the carbonaceous chondrite Nogoya were also launched into Al at a velocity of 6.2 km sec (exp -1). Laser desorption (L (exp 2) MS) analyses of the impactor residues indicate that the lowest and highest mass polycyclic aromatic hydrocarbons (PAH's) were largely destroyed on impact; those of intermediate mass (202-220 amu) remained at the same level or increased in abundance. In addition, alkyl-substituted homologs of the most abundant pre-impacted PAH's were synthesized during impact. These results suggest that an unknown fraction of some organic compounds can survive low to moderate impact velocities and that synthesized products can be expected to form up to velocities of, at least, 6.5 km sec(exp -1). We also present examples of craters formed by a unique microparticle accelerator that could launch micron-sized particles of almost any coherent material at velocities up to approximately 15 km sec(exp -1). Many of the experiments have a direct bearing on the interpretation of LDEF craters.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 385-399
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    Experimental investigation of the relationship between impact crater morphology and impacting particle velocity and direction (1995)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Interpretation of the wealth of impact data available from the Long Duration Exposure Facility, in terms of the absolute and relative populations of space debris and natural micrometeoroids, requires three dimensional models of the distribution of impact directions, velocities and masses of such particles, as well as understanding of the impact processes. Although the stabilized orbit of LDEF provides limited directional information, it is possible to determine more accurate impact directions from detailed crater morphology. The applicability of this technique has already been demonstrated but the relationship between crater shape and impactor direction and velocity has not been derived in detail. We present the results of impact experiments and simulations: (1) impacts at micron dimensions using the Unit's 2MV Van de Graaff accelerator; (2) impacts at mm dimensions using a Light Gas Gun; and (3) computer simulations using AUTODYN-3D from which an empirical relationship between crater shape and impactor velocity, direction and particle properties we aim to derive. Such a relationship can be applied to any surface exposed to space debris or micrometeoroid particles for which a detailed pointing history is available.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 499-508
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    Image and compositional characteristics of the LDEF Big Guy impact crater (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A 5.2 mm crater in Al-metal represents the largest found on LDEF. We have examined this crater by field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and time-of-flight/secondary ion mass spectroscopy (TOF-SIMS) in order to determine if there is any evidence of impactor residue. Droplet and dome-shaped columns, along with flow features, are evidence of melting. EDS from the crater cavity and rim show Mg, C, O and variable amounts of Si, in addition to Al. No evidence for a chondritic impactor was found, and it hypothesized that the crater may be the result of impact with space debris.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 475-481
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    The Alpha-Proton-X-ray Spectrometer deployment mechanism: An anthropomorphic approach to sensor placement on Martian rocks and soil (1995)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: On July 4,1997, the Mars Pathfinder spacecraft lands on Mars and starts conducting technological and scientific experiments. One experiment, the Alpha-Proton-X-ray Spectrometer, uses a sensor head placed against rocks and soil to determine their composition. To guarantee proper placement, a deployment mechanism mounted on the Mars Rover aligns the sensor head to within 20 deg of the rock and soil surfaces. In carrying out its task, the mechanism mimics the action of a human hand and arm. Consisting of a flexible wrist, a parallel link arm, a brush dc motor actuator, and a revolutionary non-pyrotechnic fail-safe release device, the mechanism correctly positions the sensor head on rocks as high as 0.29 m and on targets whose surfaces are tilted as much as 45 deg from the nominal orientation of the sensor head face. The mechanism weighs less than 0.5 kg, can withstand 100 g's, and requires less than 2.8 N x m of actuation torque. The fail-safe coupler utilizes Cerrobend, a metal alloy that melts at 60 C, to fuse the actuator and the rest of the mechanism together. A film heater wrapped around the coupler melts the metal, and Negator springs drive the mechanism into its stowed position. The fail-safe actuates using 6.75 Watts for 5 minutes in the event of an actuator failure.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Johnson Space Center, The 29th Aerospace Mechanisms Symposium; p 61-78
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    The Mode 1 mechanical crack tip stress field in hyperelastic and incompressible materials (1995)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: The finite deformation field of a plane strain Mode 1 crack in a hyperelastic and incompressible material was examined under the assumptions of small scale nonlinearity. Finite element analyses were performed for two different material laws, a Neo-Hookean material and a third order invariant of a Rivlin material. The numerical results for both materials were compared to the appropriate theoretical asymptotic solution. A local cavitation locus surrounding the crack tip was identified for the Neo-Hookean material. For the third order invariant Rivlin material, maximum values of the dominant stress component were found close to the surface of the crack, above and below the deformed crack tip.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, Computational Modeling of Tires; p 53-68
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    Submillimeter solar research with the KAO (1995)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: From 1981 to 1988 the KAO was used to measure the 30 to 670 micron continuum radiation from the Sun. The most significant result was te measurement of the limb brightness and extent during two total solar eclipses. The results clearly indicate a solar limb at 50 to 670 microns which is extended beyond that expected for an atmosphere in hydrostatic equilibrium. Unique measurements of far infrared solar oscillations and brightness of active regions were also carried out. A complete set of references is included.
    Keywords: SOLAR PHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 329-332
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    Recurrent structures of the interplanetary magnetic field observed by Ulysses (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Since its launch in October 1990, Ulysses has provided good quality magnetic field data, practically covering the whole time interval until now. We have studied the very long time scale evolution of the interplanetary magnetic field, in particlular, we have search for recurrent disturbances in the magnetic field. The magnetic field vectors have been mapped back to the Sun along Parker spirals, in order to determine the Heliographic longitude of the source regions in the corona. It was found that the position of many high field sources drifts systematically relative to the corona assumed to rotate with the equatorial rotation period of the Sun. The results are compared to similar observations on the eastward drift of magnetic sectors observed after about June 1992. Changes associated with both the declining phase of the solar cycle and the latitudinal excursion of Ulysses are also discussed.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)339
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    The Heliosphere During the Declining Solar Cycle; Symposium D1.1 of COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994 (1995)
    In:  Other Sources
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    Publication Date: 2019-03-30
    Description: The conference discussed the heliosphere during the declining solar cycle. Topics covered included: manifestations of solar activity, the solar wind, ion pick-up and anomalous cosmic rays, the interplanetary magnetic field, cosmic ray modulation, co-rotating interaction regions, and the heliosphere boundary, as well as several related topics.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1777); 16; 9
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    Cratering and penetration experiments in Teflon targets at velocities from 1 to 7 km/s (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Approximately 20 sq m of protective thermal blankets, largely composed of Teflon, were retrieved from the Long Duration Exposure Facility (LDEF) after the spacecraft had spent approximately 5.7 years in space. Examination of these blankets revealed that they contained thousands of hypervelocity impact features ranging from micron-sized craters to penetration holes several millimeters in diameter. We conducted impact experiments in an effort to reproduce such features and to -- hopefully -- understand the relationships between projectile size and the resulting crater or penetration-hole diameter over a wide range of impact velocity. Such relationships are needed to derive the size- and mass-frequency distribution and flux of natural and man-made particles in low-Earth orbit. Powder propellant and light-gas guns were used to launch soda-lime glass spheres of 3.175 mm (1/8 inch) nominal diameter (Dp) into pure Teflon FEP targets at velocities ranging from 1 to 7 km/s. Target thickness (T) was varied over more than three orders of magnitude from infinite halfspace targets (Dp/T less than 0.1) to very thin films (Dp/T greater than 100). Cratering and penetration of massive Teflon targets is dominated by brittle failure and the development of extensive spall zones at the target's front and, if penetrated, the target's rear side. Mass removal by spallation at the back side of Teflon targets may be so severe that the absolute penetration-hole diameter (Dh) can become larger than that of a standard crater (Dc) at relative target thicknesses of Dp/T = 0.6-0.9. The crater diameter is infinite halfspace Teflon targets increases -- at otherwise constant impact conditions -- with encounter velocity by a factor of V0.44. In contrast, the penetration-hole size is very thin foils (Dp/T greater than 50) is essentially unaffected by impact velocity. Penetrations at target thicknesses intermediate to these extremes will scale with variable exponents of V. Our experimental matrix is sufficiently systematic and complete, up to 7 km/s, to make reasonable recommendations for the velocity-scaling of Teflon craters and penetrations. We specifically suggest that cratering behavior and associated equations dominate all impacts in which the shock-pulse duration of the projectile (tp) is shorter than that of the target (tt). We also demonstrate that each penetration hole from space-retrieved surfaces may be assigned a unique projectile size, provided an impact velocity is known or assumed. This calibration seems superior to the traditional ballistic-limit approach.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 521
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    Dynamic sensitivity analysis of frictional contact/impact response of axisymmetric composite structures (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A computational procedure is presented for evaluating the sensitivity coefficients of the dynamic frictional contact/impact response of axisymmetric composite structures. The structures are assumed to consist of an arbitrary number of perfectly bonded homogeneous anisotropic layers. The material of each layer is assumed to be hyperelastic, and the effect of geometric nonlinearity is included. The sensitivity coefficients measure the sensitivity of the response to variations in different material, lamination and geometric parameters of the structure. A displacement finite element model is used for the discretization. The normal contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the nodal displacements, and the Lagrange multipliers associated with the contact conditions. The Lagrange multipliers are allowed to be discontinuous at interelement boundaries. Tangential contact conditions are incorporated by using a penalty method in conjunction with the classical Coulomb's friction model. Temporal integration is performed by using Newmark method. The Newton-Raphson iterative scheme is used for the solution of the resulting nonlinear algebraic equations, and for the determination of the contact region, contact conditions (sliding or sticking), and the contact pressures. The sensitivity coefficients are evaluated by using a direct differentiation approach. Numerical results are presented from the frictional contact/impact response of a composite spherical cap impacting on a rigid plate.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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    Postbuckling and large-deflection nonlinear analyses on distributed-memory computers (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A computational strategy is presented for postbuckling and nonlinear static analyses of large complex structures on distributed-memory parallel computers. The strategy is designed for message-passing parallel computer systems. The key elements of the proposed strategy are: (1) a multiple-parameter reduced basis technique; (2) a nested dissection (or multilevel substructuring) ordering scheme; (3) parallel assembly of global matrices; and (4) a parallel sparse equation solver. The effectiveness of the strategy is assessed by performing thermomechanical postbuckling analyses of stiffened composite panels with cutouts, and nonlinear large-deflection analyses of High Speed Civil Transport models on three distributed-memory computers. The numerical studies presented demonstrate the advantages of nested dissection-based solvers over traditional skyline-based solvers on distributed-memory machines.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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    Nonlinear structural analysis on distributed-memory computers (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A computational strategy is presented for the nonlinear static and postbuckling analyses of large complex structures on massively parallel computers. The strategy is designed for distributed-memory, message-passing parallel computer systems. The key elements of the proposed strategy are: (1) a multiple-parameter reduced basis technique; (2) a nested dissection (or multilevel substructuring) ordering scheme; (3) parallel assembly of global matrices; and (4) a parallel sparse equation solver. The effectiveness of the strategy is assessed by applying it to thermo-mechanical postbuckling analyses of stiffened composite panels with cutouts, and nonlinear large-deflection analyses of HSCT models on Intel Paragon XP/S computers. The numerical studies presented demonstrate the advantages of nested dissection-based solvers over traditional skyline-based solvers on distributed memory machines.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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    Nonlinear vibrations of thin-walled composite frames (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A reduced basis technique and a computational procedure are presented for generating the nonlinear vibrational response, and evaluating the first-order sensitivity coefficients of thin-walled composite frames. The sensitivity coefficients are the derivatives of the nonlinear frequency with respect to the material and lamination parameters of the frame. A mixed formulation is used with the fundamental unknowns consisting of both the generalized displacements and stress resultants in the frame. The flanges and webs of the frames are modeled by using geometrically nonlinear two-dimensional shell and plate finite elements. The computational procedure can be conveniently divided into three distinct steps. The first step involves the generation of various-order perturbation vectors, and their derivatives with respect to the material and lamination parameters of the frame, using the Linstedt-Poincare perturbation technique. The second step consists of using the perturbation vectors as basis vectors, computing the amplitudes of these vectors and the nonlinear frequency of vibration, via a direct variational procedure. The third step consists of using the perturbation vectors, and their derivatives, as basis vectors and computing the sensitivity coefficients of the nonlinear frequency via a second application of the direct variational procedure. Numerical results are presented for semicircular thin-walled frames with I and J section, showing the convergence of the nonlinear frequency and the sensitivity coefficients obtained by both the reduced-basis and perturbation techniques.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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    Heliospheric 2-3 kHz radio emissions and their relationship to large Forbush decreases (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Two intense heliospheric 2-3 kHz radio emission events have been observed by Voyagers 1 and 2, the first in 1983-84 and the second in 1992-93. These radio emission events occurred about 400 days after large Forbush decreases in mid-1982 and mid-1991. Since Forbush decreases are indicative of a strong interplanetary shock propagating outward through the heliosphere, this temporal relationship provides strong evidence that the radio emissions are triggered by the interaction of a shock with one of the outer boundaries of the heliosphere. From the travel time and the known speed of the shock, the distance to the interaction region can be estimated and is well beyond 100 AU. At this great distance the plasma frequency at the terminal shock (100 to 200 Hz) is believed to be too small to explain the observed emission frequencies, which extend up to 3.6 kHz. For this reason, we have proposed that the interaction takes place at or near the heliopause, where remote sensing measurements show that the plasma frequency is in a suitable range (approximately 3 kHz) for explaining the radio emission. From the travel time and shock propagation speed, the radial distance to the heliopause has been calculated for various candidate solar events. After taking into account the likely deceleration of the shock, the heliopause is estimated to be in the range from about 110 to 160 AU.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)279-(9)290
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    Expanding our knowledge of the heliosphere (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Milestones on our road to understanding the heliosphere between 1950 and 1988 are recalled. Among these are early studies of solar energetic particles suggesting a heliospheric boundary at 5 AU, the discovery of the solar wind and the sectored nature of the interplanetary magnetic field. Recent results, particularly from the Ulysses spacecraft, confirm the arrival of neutrals from interstellar space, the pick-up of singly charged ions by the solar wind and the acceleration of these ions to become anomalous cosmic rays. Two distinct solar wind regimes have been discovered. At low heliolatitudes a highly variable solar wind blows at an average speed around 450 km/s, while at high latitudes a relatively smooth 750 km/s flow is observed. No indicators of a dipole-like magnetic field have been seen by Ulysses in solar polar latitudes. The cosmic radiation increase with latitude is much smaller than predicted. The status of and plans for the Voyager 1 and 2, Pioneer 10 and 11, and Ulysses spacecraft are outlined.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)5-(9)23
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    Ulysses radio observations of the heliospheric activity in early June 1991 (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: The radio receiver of the URAP (Unified Radio and Plasma Wave) experiment on Ulysses has recorded a heliospheric activity particularly intense between late May and early June 1991. Many solar radio emissions of types III and II were observed together with interplanetary (IP) shocks. In the same time, the radio spectrograph ARTEMIS at Nancay (France) observed several intense type II bursts. We investigate the association and/or interaction of these radio emissions, which are remotely observed, with some IP shocks detected in situ, in the context of a Coronal Mass Ejection (CME) induced scenario.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)345
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    Microstructure of the IMF turbulences at 2.5 AU (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: A detailed analysis of small period (15-900 sec) magnetohydrodynamic (MHD) turbulences of the interplanetary magnetic field (IMF) has been made using Pioneer-11 high time resolution data (0.75 sec) inside a Corotating Interaction Region (CIR) at a heliocentric distance of 2.5 AU in 1973. The methods used are the hodogram analysis, the minimum variance matrix analysis and the cohenrence analysis. The minimum variance analysis gives evidence of linear polarized wave modes. Coherence analysis has shown that the field fluctuations are dominated by the magnetosonic fast modes with periods 15 sec to 15 min. However, it is also shown that some small amplitude Alfven waves are present in the trailing edge of this region with characteristic periods (15-200 sec). The observed wave modes are locally generated and possibly attributed to the scattering of Alfven waves energy into random magnetosonic waves.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)171-(9)174
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    Dynamic behavior of solar wind as revealed by a correlation study of magnetic fields observed at the Venus and Earth orbits (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Correlations between interplanetary magnetic fields (IMFs) at 0.72 AU and 1.0 AU have been examined using data sets obtained from the Pioneer Venus orbiter and Earth-orbiting spacecraft. While the two-sector structures are evident in long-term variations at these two heliocentric distances, the corresponding auto-correlation coefficients are consistently smaller at 1.0 AU than at 0.72 AU. This suggests that the IMF structures become less persistent at 1.0 AU due to the effects of changing solar wind dynamics between the Venus and Earth orbits. Short-term variations exhibit generally poor correlations between IMFs near Venus and those near Earth, though good correlations are sometimes obtained for well-defined structures when the Sun, Venus, and Earth are closely aligned. The rather poor correlations in the background streams indicate that the IMFs are still changing between the Venus and Earth orbits under the strong influence of solar wind dynamics.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)111-(9)114
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    Evidence for the equality of the solar photospheric and coronal abundance of iron (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: The Fe K-alpha and K-beta X-ray lines (wavelengths 1.94 and 1.76 A) in the solar X-ray spectrum are formed by fluoroescence of photospheric iron atoms, and the ratio of the intensity of either to the He-like iron (Fe XXV) resonance line at 1.85 A is a function of the photospheric-to-coronal abundance of iron. The temperature dependence of this ratio is weak as long as the flare temperature T(sub e) greater than or approximately equal to 15 x 10(exp 6)K. Comparison of the theoretical value of this intensity ratio with observations from crystal spectrometers on Yohkoh, Solar Maximum Mission (SMM) and P78-1 are consistent with the photospheric abundance of Fe being equal to the coronal.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 15; 7; p. (7)33-(7)36
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    Coronal abundances determined from energetic particles (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Solar energetic particles (SEPs) provide a measurement of coronal element abundances that is highly independent of the ionization states and temperature of the ions in the source plasma. The most complete measurements come from large 'gradual' events where ambient coronal plasma is swept up by the expanding shock wave from a coronal mass ejection. Particles from 'impulsive' flares have a pattern of acceleration-induced enhancements superimposed on the coronal abundances. Particles accelerated from high-speed solar wind streams at corotating shocks show a different abundance pattern corresponding to material from coronal holes. Large variations in He/O in coronal material are seen for both gradual and impulsive-flare events but other abundance ratios, such as Mg/Ne, are remarkably constant. SEP measurements now include hundreds of events spanning 15 years of high-quality measurement.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 15; 7; p. (7)41-(7)51
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    Exploration of Venus and Mars Atmospheres; Symposium C2 and Symposium C5 of the COSPAR Plenary Meeting, 29th, Washington DC, 28 August - 5 September, 1992 (1995)
    In:  Other Sources
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    Publication Date: 2019-03-30
    Description: Two symposia related to the exploration of the Venus and Mars atmospheres produced papers which described the results of spacecraft-based and ground-based observations of these two planets. The topics addressed included solar wind interactions, molecular ions, planetary magnetospheres, planetary ionospheres, planetary thermospheres, gravity waves, the homopause, radiative transfer, radiative balance, atmospheric water, planetary lightning, very low frequency bursts, cosmic-ray ionization, planetary loss, and future missions to study Mars aeronomy, energetic particles near Mars, radar exploration of Mars, and the Mars Environmental Survey (MESUR) mission.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 15; 4
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    Sensitivity analysis for large-deflection and postbuckling responses on distributed-memory computers (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A computational strategy is presented for calculating sensitivity coefficients for the nonlinear large-deflection and postbuckling responses of laminated composite structures on distributed-memory parallel computers. The strategy is applicable to any message-passing distributed computational environment. The key elements of the proposed strategy are: (1) a multiple-parameter reduced basis technique; (2) a parallel sparse equation solver based on a nested dissection (or multilevel substructuring) node ordering scheme; and (3) a multilevel parallel procedure for evaluating hierarchical sensitivity coefficients. The hierarchical sensitivity coefficients measure the sensitivity of the composite structure response to variations in three sets of interrelated parameters; namely, laminate, layer and micromechanical (fiber, matrix, and interface/interphase) parameters. The effectiveness of the strategy is assessed by performing hierarchical sensitivity analysis for the large-deflection and postbuckling responses of stiffened composite panels with cutouts on three distributed-memory computers. The panels are subjected to combined mechanical and thermal loads. The numerical studies presented demonstrate the advantages of the reduced basis technique for hierarchical sensitivity analysis on distributed-memory machines.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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    Reduction technique for tire contact problems (1995)
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    Publication Date: 2019-01-25
    Description: A reduction technique and a computational procedure are presented for predicting the tire contact response and evaluating the sensitivity coefficients of the different response quantities. The sensitivity coefficients measure the sensitivity of the contact response to variations in the geometric and material parameters of the tire. The tire is modeled using a two-dimensional laminated anisotropic shell theory with the effects of variation in geometric and material parameters, transverse shear deformation, and geometric nonlinearities included. The contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the stress resultants, the generalized displacements, and the Lagrange multipliers associated with the contact conditions. The elemental arrays are obtained by using a modified two-field, mixed variational principle. For the application of the reduction technique, the tire finite element model is partitioned into two regions. The first region consists of the nodes that are likely to come in contact with the pavement, and the second region includes all the remaining nodes. The reduction technique is used to significantly reduce the degrees of freedom in the second region. The effectiveness of the computational procedure is demonstrated by a numerical example of the frictionless contact response of the space shuttle nose-gear tire, inflated and pressed against a rigid flat surface.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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    Three-dimensional solutions for coupled thermoelectroelastic response of multilayered plates (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Analytic three-dimensional solutions are presented for the coupled thermoelectroelastic response of multilayered hybrid composite plates. The plates consist of a combination of fiber-reinforced cross-ply and piezothermoelastic layers. Both the thermoelectroelastic static response and its sensitivity coefficients are computed. The sensitivity coefficients measure the sensitivity of the response to variations in different mechanical, thermal and piezoelectric material properties of the plate. A linear constitutive model is used, and the material properties are assumed to be independent of the temperature and the electric field. The plates are assumed to have rectangular geometry and special material symmetries. A mixed formulation is used with the fundamental unknowns consisting of the three transverse stress components; three displacement components; transverse component of the electric displacement field; electric potential; transverse heat flux component, and temperature change. Each of the fundamental unknowns is expressed in terms of a double Fourier series in the Cartesian surface coordinates. A state space approach is used to generate the static response and to evaluate the sensitivity coefficients. Extensive numerical results are presented showing the effects of variation in the geometric parameters of the plate on the different response quantities and their sensitivity coefficients.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 87
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    Sensitivity analysis of frictional contact response of axisymmetric composite structures (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A computational procedure is presented for evaluating the sensitivity coefficients of the static frictional contact response of axisymmetric composite structures. The structures are assumed to consist of an arbitrary number of perfectly bonded homogeneous anisotropic layers. The material of each layer is assumed to be hyperelastic, and the effect of geometric nonlinearity is included. The sensitivity coefficients measure the sensitivity of the response variations in different material, lamination and geometric parameters of the structure. A displacement finite element model is used for the discretization. The normal contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of nodal displacements, and Lagrange multipliers associated with the contact conditions. The Lagrange multipliers are allowed to be discontinuous at interelement boundaries. Tangential contact conditions are incorporated by using a penalty method in conjunction with the classical Coulomb's friction model. The Newton-Raphson iterative scheme is used for the solution of the resulting nonlinear algebraic equations, and for the determination of the contact region, contact conditions (sliding or sticking), and the contact pressures. The sensitivity coefficients are evaluated by using a direct differentiation approach. Numerical results are presented for the frictional contact of a composite spherical cap pressed against a rigid plate.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 88
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    Thermomechanical postbuckling of multilayered composite panels with cutouts (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: The results of a study of the detailed thermomechanical postbuckling response characteristics of flat unstiffened composite panels with central circular cutouts are presented. The panels are subjected to combined temperature changes and applied edge loading (or edge displacements). The analysis is based on a first-order shear deformation plate theory. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the plate. The postbuckling displacements, transverse shear stresses, transverse shear strain energy density, and their sensitivity coefficients are evaluated. The sensitivity coefficients measure the sensitivity of the post-buckling response to variations in the different lamination and material parameters of the panel. Numerical results are presented showing the effects of the variations in the hole diameter, laminate stacking sequence, fiber orientation, and aspect ratio of the panel on the thermomechanical postbuckling response and its sensitivity to changes in panel parameters.
    Keywords: STRUCTURAL MECHANICS
    Type: Virginia Univ., Center for Computational Structures Technology; 1 p
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  • 89
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    Effect of mesh distortion on the accuracy of transverse shear stresses and their sensitivity coefficients in multilayered composites (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A study is made of the effect of mesh distortion on the accuracy of transverse shear stresses and their first-order and second-order sensitivity coefficients in multilayered composite panels subjected to mechanical and thermal loads. The panels are discretized by using a two-field degenerate solid element, with the fundamental unknowns consisting of both displacement and strain components, and the displacement components having a linear variation throughout the thickness of the laminate. A two-step computational procedure is used for evaluating the transverse shear stresses. In the first step, the in-plane stresses in the different layers are calculated at the numerical quadrature points for each element. In the second step, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of transverse shear stresses. Numerical results are presented showing no noticeable degradation in the accuracy of the in-plane stresses and their sensitivity coefficients with mesh distortion. However, such degradation is observed for the transverse shear stresses and their sensitivity coefficients. The standard of comparison is taken to be the exact solution of the three-dimensional thermoelasticity equations of the panel.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 90
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    Finite element buckling and postbuckling solutions for multilayered composite panels (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A study is made of the buckling and postbuckling responses of flat, unstiffened composite panels subjected to various combinations of mechanical and thermal loads. The analysis is based on a first-order shear deformation von Karman-type plate theory. A mixed formulation is used with the fundamental unknowns consisting of the strain components, stress resultants and the generalized displacements of the plate. The stability boundary, postbuckling response and the sensitivity coefficients are evaluated. The sensitivity coefficients measure the sensitivity of the buckling and postbuckling responses to variations in the different lamination and material parameters of the panel. Numerical results are presented for both solid panels and panels with central circular cutouts. The results show the effects of the variations in the fiber orientation angels, aspect ratio of the panel, and the hole diameter (for panels with cutouts) on the stability boundary, postbuckling response and sensitivity coefficients.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 91
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    Solar cycle variation of interplanetary shocks, coronal mass ejections, and stream interactions observed at 0.7 AU (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: A survey of the Pioneer Venus Orbiter (PVO) magnetometer and plasma data from 1979-1980, shows that the occurrence frequency of interplanetary shocks, coronal mass ejections (CMEs) and stream interactions observed at 0.7 AU exhibits a solar cycle variation. As previously found at 1 AU, the observed number of both interplanetary shocks and CMEs peaks during solar maximum (approximately 16 and approximately 27 per year, respectively) and reaches a low during solar minimum (approximately 0 and approximately 7 per year, respectively), in phase with the variation in smoothed sunspot number. The number of stream interactions observed varies in the opposite manner, having a minimum during solar maximum (approximately 15 per year) and a maximum during solar minimum (approximately 34 per year). The percentage of CMEs and stream interactions producing interplanetary shocks also varies during the solar-cycle and exhibits interesting behavior during the declining phase. While the number of CMEs observed during this phase is decreasing, the percentage of CMEs producing interplanetary shocks reaches a maximum. Also, while the number of stream interactions observed is increasing, but has not reached maximum during the declining phase, the percentage of stream interactions producing interplanety shocks is at a maximum.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)353
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  • 92
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    Generation of Venus' nightside ionospheric structure by particle streams from cosmoids (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: A newly discovered source of energetic particle streams directed at Venus' nightside may cause several exosphere phenomena. The streams evolve from dispersed cosmoids, a surreptitious population of meteoroids in nearly hyperbolic orbits, measured with three dust experiments on Pioneer 10/11. Loose fragile comet-like ensembles of frozen volatile material, they are orders of magnitude more populous than short-period meteoroids. Dispersion is forced near a planet masking the meteor signature at Earth, but recently terrestrial exosphere interactions have been detected principally from VLF radar returns and as suddenly formed layers of neutral sodium and iron probed by lidar. Venus influx is estimated greater than 10(exp -14)(g)/((sq cm)(s)) with nightside directed kinetic power of greater than 0.3 (erg)/((sq cm)s)). Compared to Earth, Venus, lacking a dipole field with almost no rotation, has a readily recognized set of nightside interaction signatures of these downward energetic particle streams: i.e., density depressions of the neutral thermosphere, hydrogen and helium bulges, a non-disappearing ionosphere, electron holes, nightglows, VLF bursty signals, and local magnetic fields. From Pioneer Venus Orbiter (PVO) measurements, the cosmoid population, its temporal and solar azimuthal variation may be determined.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 15; 4; p. (4)123-(4)129
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  • 93
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    Water in the deep atmosphere of Venus from high-resolution spectra of the night side (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: High-resolution, near-infrared (1.09 to 2.5 micrometers) spectra of the night side of Venus have been obtained in 1990 and 1991 using the Fourier Transform Spectrometer at the 3.6-m Canada-France-Hawaii telescope. Absorptions due to H2O were detected in spectral windows near 2.3, 1.74, and 1.18 micrometers. Our analysis of these absorptions constrains the abundance of water vapor in three different altitude ranges located between the clouds and the surface: 30-40 km, 15-25 km and 0-15 km. A constant water vapor mixing ratio of 30 +/- 15 ppm below the clouds can fit the observations. These values are consistent with recent near-infrared studies of the night side of Venus at lower spectral resolution. The atmosphere of Venus appears to be dryer than originally suggested by the in-situ measurements made by the Pioneer Venus and Venera mass-spectrometers and gas-chromatographs.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 15; 4; p. (4)79-(4)88
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  • 94
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    Planetary loss from light ion escape on Venus (1995)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Using Pioneer Venus data, hydrogen and deuterium ions are shown to escape from the hydrogen bulge region in the nightside ionosphere. The polarization electric field propels these light ions upward through the ionosphere and into the ion-exosphere, where H(+) and D(+) continue to be accelerated away from Venus and move into the ionotail and beyond. The vertical flow speeds of H(+) and D(+) are found to be about the same; therefore, selective escape between H(+) and D(+) is negligible for this mechanism. Present day planetary loss rates of about 8.6 x 10(exp 25)/s and 3.2 X 10(exp 23)/s were obtained for H(+) and D(+), respectively. Such rates, persisting over a few billion years, should have significantly affected the planetary water budget.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 15; 4; p. (4)117-(4)122
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  • 95
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    Assessment of computational models for thermoelectroelastic multilayered plates (1995)
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    Publication Date: 2019-01-25
    Description: A study is made of the accuracy of the steady-state (static) thermoelectroelastic response of multilayered hybrid composite plates predicted by five modeling approaches, based on two-dimensional plate theories. The plates consist of a combination of fiber-reinforced and piezothermoelastic layers. The standard of comparison is taken to be the exact three-dimensional thermoelectroelastic solutions, and the quantities compared include gross response characteristics (e.g., strain energy components, and average through-the-thickness displacements); detailed, through-the-thickness distributions of displacements and stresses; and sensitivity coefficients of the response quantities (derivatives of the response quantities with respect to material parameters of the plate). The modeling approaches considered include first-order theory; third-order theory; discrete-layer theory (with piecewise linear variation of the in-plane displacements, temperature and electric potential, in the thickness direction); and two predictor-corrector procedures.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 96
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    Sensitivity analysis for the dynamic response of thermoviscoplastic shells of revolution (1995)
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    Publication Date: 2019-01-25
    Description: A computational procedure is presented for evaluating the sensitivity coefficients of the dynamic axisymmetric, fully-coupled, thermoviscoplastic response of shells of revolution. The analytical formulation is based on Reissner's large deformation shell theory with the effects of large-strain, transverse shear deformation, rotatory inertia and moments turning around the normal to the middle surface included. The material model is chosen to be viscoplasticity with strain hardening and thermal hardening, and an associated flow rule is used with a von Mises effective stress. A mixed formulation is used for the shell equations with the fundamental unknowns consisting of six stress resultants, three generalized displacements and three velocity components. The energy-balance equation is solved using a Galerkin procedure, with the temperature as the fundamental unknown. Spatial discretization is performed in one dimension (meridional direction) for the momentum and constitutive equations of the shell, and in two dimensions (meridional and thickness directions) for the energy-balance equation. The temporal integration is performed by using an explicit central difference scheme (leap-frog method) for the momentum equation; a predictor-corrector version of the trapezoidal rule is used for the energy-balance equation; and an explicit scheme consistent with the central difference method is used to integrate the constitutive equations. The sensitivity coefficients are evaluated by using a direct differentiation approach. Numerical results are presented for a spherical cap subjected to step loading.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 97
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    Buckling and postbuckling of composite panels with cutouts subjected to combined edge shear and temperature change (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: The results of a detailed study of the buckling and postbuckling responses of composite panels with central circular cutouts are presented. The panels are subjected to combined edge shear and temperature change. The panels are discretized by using a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the panel. The fundamental unknowns consist of the average mechanical strains through the thickness and the displacement components. The effects of geometric nonlinearities and laminated anisotropic material behavior are included. The stability boundary, postbuckling response and the hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the buckling and postbuckling responses to variations in the panel stiffnesses, and the material properties of both the individual layers and the constituents (fibers and matrix). Numerical results are presented for composite panels with central circular cutouts subjected to combined edge shear and temperature change, showing the effects of variations in the hole diameter, laminate stacking sequence and fiber orientation, on the stability boundary and postbuckling response and their sensitivity to changes in the various panel parameters.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 98
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    A hybrid neurocomputing/numerical strategy for nonlinear structural analysis (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A hybrid neurocomputing/numerical strategy is presented for geometrically nonlinear analysis of structures. The strategy combines model-free data processing capabilities of computational neural networks with a Pade approximants-based perturbation technique to predict partial information about the nonlinear response of structures. In the hybrid strategy, multilayer feedforward neural networks are used to extend the validity of solutions by using training samples produced by Pade approximations to the Taylor series expansion of the response function. The range of validity of the training samples is taken to be the radius of convergence of Pade approximants and is estimated by setting a tolerance on the diverging approximants. The norm of residual vector of unbalanced forces in a given element is used as a measure to assess the quality of network predictions. To further increase the accuracy and the range of network predictions, additional training data are generated by either applying linear regression to weight matrices or expanding the training data by using predicted coefficients in a Taylor series. The effectiveness of the hybrid strategy is assessed by performing large-deflection analysis of a doubly-curved composite panel with a circular cutout, and postbuckling analyses of stiffened composite panels subjected to an in-plane edge shear load. In all the problems considered, the hybrid strategy is used to predict selective information about the structural response, namely the total strain energy and the maximum displacement components only.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 99
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    Recent advances in the sensitivity analysis for the thermomechanical postbuckling of composite panels (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Three recent developments in the sensitivity analysis for thermomechanical postbuckling response of composite panels are reviewed. The three developments are: (1) effective computational procedure for evaluating hierarchical sensitivity coefficients of the various response quantities with respect to the different laminate, layer, and micromechanical characteristics; (2) application of reduction methods to the sensitivity analysis of the postbuckling response; and (3) accurate evaluation of the sensitivity coefficients to transverse shear stresses. Sample numerical results are presented to demonstrate the effectiveness of the computational procedures presented. Some of the future directions for research on sensitivity analysis for the thermomechanical postbuckling response of composite and smart structures are outlined.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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  • 100
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    Sensitivity analysis of the non-linear dynamic viscoplastic response of 2-d structures with respect to material parameters (1995)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: A computational procedure is presented for evaluating the sensitivity coefficients of the viscoplastic response of structures subjected to dynamic loading. A state of plane stress is assumed to exist in the structure, a velocity strain-Cauchy stress formulation is used, and the geometric non-linearities arising from large strains are incorporated. The Jaumann rate is used as a frame indifferent stress rate. The material model is chosen to be isothermal viscoplasticity, and an associated flow rule is used with a von Mises effective stress. The equations of motion emanating from a finite element semi-discretization are integrated using an explicit central difference scheme with an implicit stress update. The sensitivity coefficients are evaluated using a direct differentiation approach. Since the domain of integration is the current configuration, the sensitivity coefficients of the spatial derivatives of the shape functions must be included. Numerical results are presented for a thin plate with a central cutout subjected to an in-plane compressive loading. The sensitivity coefficients are generated by evaluating the derivatives of the response quantities with respect to Young's modulus, and two of the material parameters characterizing the viscoplastic response. Time histories of the response and sensitivity coefficients, and spatial distributions at selected times are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Center for Computational Structures Technology; 1 p
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