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  • 1
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    A small podocnemidoid (Pleurodira, Pelomedusoides) from the Late Cretaceous of Brazil, and the innervation and carotid circulation of side‐necked turtles (2021)
    Details
    Publication Date: 2021-07-01
    Description: Pleurodires are less diverse than cryptodires, together forming the two major lineages of crown turtles. Their fossil record, however, is rich. A particularly large number of fossil pleurodires, many belonging to the Podocnemidoidae, has been recovered from the Upper Cretaceous Bauru Group outcrops of south‐central Brazil. Herein we describe an additional pleurodire from this region, Amabilis uchoensis gen. et sp. nov., based on a partially preserved skull. A. uchoensis is recognized as belonging to the Podocnemidoidae by the small entrance to the antrum postoticum and completely developed cavum pterygoidei, being unique among other non‐podocnemidid podocnemidoids for its medially open fenestra postotica and absent basioccipital–opisthotic contact. Our cladistic analysis places A. uchoensis as a sister taxon to Hamadachelys + other podocnemidoids. We further explore the neuroanatomy of side‐necked turtles with the aid of micro‐computed tomography of specimens of the main pleurodiran lineages. Our data shed light on the different carotid circulation patterns in pleurodires, and we propose new phylogenetic characters to describe the neuroanatomical variation of the group. Optimization of these characters shows two independent acquisitions of a foramen for the palatal branch of the carotid in chelids and podocnemidoids, and a unique loss of the vidian nerve canal in chelids, in turtles in general.
    Description: Fundação de Amparo à Pesquisa do Estado de São Paulo
    Description: Natural Environment Research Council http://dx.doi.org/10.13039/501100000270
    Keywords: 567 ; Pleurodira ; micro‐computed tomography ; Podocnemidoidae ; Bauru Group ; neuroanatomy ; carotid circulation
    Type: article
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    CITATION GEO-LEO
  • 2
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    Interplanetary proton fluence model - JPL 1991 (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We describe an updated predictive engineering model for the interplanetary fluence of protons with energies respectively greater than 1, 4, 10, 30, and 60 MeV. This has been the first opportunity to derive a model from a data set that has been collected in space over a long enough period of time to produce a valid sample of solar proton events. The model provides a quantitative basis for estimating the exposures to solar protons of spacecraft during missions of varying length and of surfaces and atmospheres of solar system objects. The data sets contain several major proton events comparable to the 1972 event. For the cases of the over 10 and over 30 MeV particles, the fluences are somewhat lower than in our earlier model No over 1, over 4, and over 60 MeV proton fluence models have been published in the literature previously. We present our results in a convenient graphical form which may be used to calculate the 1 AU fluence expected at a given confidence level as a function of the length of the exposure. A method of extending this estimate to other heliocentric distances is described.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A8; p. 13,281-13,294.
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Solar energetic particle events: Statistical modelling and prediction (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Solar energetic particle events (SEPEs) can have a significant effect on the design and operation of earth orbiting and interplanetary spacecraft. In relation to this, the calculation of proton fluences and fluxes are considered, describing the current state of the art in statistical modeling. A statistical model that can be used for the estimation of integrated proton fluences for different mission durations of greater than one year is reviewed. The gaps in the modeling capabilities of the SEPE environment, such as a proton flux model, alpha particle and heavy ion models and solar cycle variations are described together with the prospects for the prediction of events using neural networks.
    Keywords: Solar Physics
    Type: ; 59-64
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Periodicities in the occurrence rate of solar proton events (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Power spectral analyses of the time series of solar proton events during the past three solar cycles reveal a periodicity around 154 days. This feature is prominent in all of the cycles combined, cycles 19 and 21 individually, but is only weak in cycle 20. These results are consistent with the presence of similar periodicities between 152 and 155 days in the occurrence rate of major solar flares, the sunspot blocking function (Ps), the 10.7 cm radio flux (F10.7), and the sunspot number (Rz). This suggests that the circa 154-days periodicity may be a fundamental characteristic of the sun. Periods around 50-52 days are also found in the combined data set and in the three individual cycles, in general agreement with the detection of this periodicity in major flares in cycle 19, and in Ps, F10.7, and Rz in cycle 21. The cause of the 155 day period remains unknown. The spectra contain lines (or show power at frequencies) consistent with a model in which the periodicity is caused by differential rotation of active zones and a model in which it is related to beat frequencies between solar oscillations, as proposed by Wolff (1974, 1983).
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 128; 415-422
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    NASA TECHNICAL REPORTS
  • 5
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    Space vehicle glow and its impact on spacecraft systems (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Spacecraft glow poses a contamination threat to low orbital altitude optical sensor systems. The complexity of the phenomena entails a multifaceted approach to system design for vehicle glow minimization. In the case of Space Shuttle cloud glow, which involves line and band emission, filtering and careful optical sensor wavelength selection may also prove useful; Space Shuttle thruster glow mitigation entails the limitation of thruster firings during sensor operations. Careful selection of instrument baffle materials and coatings, as well as control of surface temperatures, are recommended as ways of limiting glow impact for instruments directed in the direction of vehicle movement.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 25; 321-340
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    NASA TECHNICAL REPORTS
  • 6
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    An overview of charging environments (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A brief synopsis of the natural environments that play a role in spacecraft charging is presented. Environments that cause both surface and internal charging are discussed along with the mechanisms involved. The geosynchronous and low altitude regions of the Earth's magnetosphere/ionosphere are considered and simple descriptions of each environment presented. As material properties are critical to the charging process, definition of material properties important to charging, which can be affected by the environment, are also described. Several space experiments are proposed that would help fill the gaps in the knowledge of the performance of materials in a charging environment.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA, Langley Research Center, NASA(SDIO Space Environmental Effects on Materials Workshop, Part 2; p 495-509
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Working group report on beam plasmas, electronic propulsion, and active experiments using beams (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The JPL Workshop addressed a number of plasma issues that bear on advanced spaceborne technology for the years 2000 and beyond. Primary interest was on the permanently manned space station with a focus on identifying environmentally related issues requiring early clarification by spaceborne plasma experimentation. The Beams Working Group focused on environmentally related threats that platform operations could have on the conduct and integrity of spaceborne beam experiments and vice versa. Considerations were to include particle beams and plumes. For purposes of definition it was agreed that the term particle beams described a directed flow of charged or neutral particles allowing single-particle trajectories to represent the characteristics of the beam and its propagation. On the other hand, the word plume was adopted to describe a multidimensional flow (or expansion) of a plasma or neutral gas cloud. Within the framework of these definitions, experiment categories included: (1) Neutral- and charged-particle beam propagation, with considerations extending to high powers and currents. (2) Evolution and dynamics of naturally occurring and man-made plasma and neutral gas clouds. In both categories, scientific interest focused on interactions with the ambient geoplasma and the evolution of particle densities, energy distribution functions, waves, and fields.
    Keywords: PLASMA PHYSICS
    Type: Space Technology Plasma Issues in 2001; p 16-22
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Thrust for interorbital propulsion - A question of lifetime (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The most promising operational window for the use of magnetoplasmadynamic (MPD) thrusters is identified to be at megawatt power levels for orbital maneuvering. For such applications, the operation of a steady-state MPD thruster system imposes stringent requirements on the lifetime of thruster surfaces which will erode due to interactions with the plasma working fluid. Basic erosion mechanisms are presented and the problems associated with measuring the erosion rates are discussed. An experimental approach that would allow the development of a phenomenological model for erosion is proposed.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    High Energy Charged Particles in Space at One Astronomical Unit (1995)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: Single event effects and many other spacecraft anomalies are caused by positively charged high energy particles impinging on the vehicle and its component parts. Reviewed here are the current knowledge of the interplanetary particle environment in the energy ranges that are most important for these effects. State-of-the-art engineering models are briefly described along with comments on the future work required.
    Keywords: Solar Physics
    Type: IEEE Transactions on Nuclear Science
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Anomalies due to single event upsets (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The description of single event upsets (SEUs) in the spacecraft Anomalies Handbook is reviewed. The basic mechanism involved in SEUs is summarized and discussed in terms of circuit analysis. Calculation of SEU rate is analytically described and discussed. Departures from single step function dependence in the SEU rate is addressed.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 90-0174
    Format: text
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    NASA TECHNICAL REPORTS
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