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  • 1
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    Application of recursive manipulator dynamics to hybrid software/hardware simulation (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Computer simulations of robotic mechanisms have traditionally solved the dynamic equations of motion for an N degree of freedom manipulator by formulating an N dimensional matrix equation combining the accelerations and torques (forces) for all joints. The use of an alternative formulation that is strictly recursive is described. The dynamic solution proceeds on a joint by joint basis, so it is possible to perform inverse dynamics at arbitrary joints. The dynamic formulation is generalized with respect to both rotational and translational joints, and it is also directly extendable to branched manipulator chains. A hardware substitution test is described in which a servo drive motor was integrated with a simulated manipulator arm. The form of the dynamic equation permits calculation of acceleration given torque or vice versa. Computing torque as a function of acceleration is required for the hybrid software/hardware simulation test described. For this test, a joint servo motor is controlled in conjunction with the simulation, and the dynamic torque on the servo motor is provided by a load motor on a common driveshaft.
    Keywords: MAN/SYSTEM TECHNOLOGY AND LIFE SUPPORT
    Type: JPL, California Inst. of Tech., Proceedings of the NASA Conference on Space Telerobotics, Volume 5; p 11-20
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  • 2
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    Grand unified theories, topological defects and ultrahigh-energy cosmic rays (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The ultrahigh-energy (UHE) proton and neutrino spectra resulting from collapse or annihilations of topological defects surviving from the GUT era are calculated. Irrespective of the specific process under consideration (which determines the overall normalization of the spectrum), the UHE proton spectrum always 'recovers' at approximately 1.8 x 10 exp 11 GeV after a partial Greisen-Zatsepin-Kuz'min 'cutoff' at approximately 5 x 10 exp 10 GeV and continues to a GUT-scale energy with a universal shape determined by the physics of hadronic jet fragmentation. Implications of our results are discussed.
    Keywords: SPACE RADIATION
    Type: NASA-CR-189841 , NAS 1.26:189841 , FERMILAB-PUB-91/304-A
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  • 3
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    Late time cosmological phase transitions 1: Particle physics models and cosmic evolution (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We described a natural particle physics basis for late-time phase transitions in the universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultra-light pseudo-Nambu-Goldstone boson with an astronomically large (O(kpc-Mpc)) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultra-light bosons may also provide unclustered dark matter in a spatially flat universe, omega sub phi approx. = 1.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-189857 , NAS 1.26:189857 , FERMILAB-PUB-91/324-A
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  • 4
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    Statistical mechanics of soft-boson phase transitions (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The existence of structure on large (100 Mpc) scales, and limits to anisotropies in the cosmic microwave background radiation (CMBR), have imperiled models of structure formation based solely upon the standard cold dark matter scenario. Novel scenarios, which may be compatible with large scale structure and small CMBR anisotropies, invoke nonlinear fluctuations in the density appearing after recombination, accomplished via the use of late time phase transitions involving ultralow mass scalar bosons. Herein, the statistical mechanics are studied of such phase transitions in several models involving naturally ultralow mass pseudo-Nambu-Goldstone bosons (pNGB's). These models can exhibit several interesting effects at high temperature, which is believed to be the most general possibilities for pNGB's.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA-CR-188697 , NAS 1.26:188697 , FNAL-PUB-91/167-T/A , CMU-HEP91-08
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  • 5
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    Cosmological structure formation from soft topological defects (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Some models have extremely low-mass pseudo-Goldstone bosons that can lead to vacuum phase transitions at late times, after the decoupling of the microwave background.. This can generate structure formation at redshifts z greater than or approx 10 on mass scales as large as M approx 10 to the 18th solar masses. Such low energy transitions can lead to large but phenomenologically acceptable density inhomogeneities in soft topological defects (e.g., domain walls) with minimal variations in the microwave anisotropy, as small as delta Y/T less than or approx 10 to the minus 6 power. This mechanism is independent of the existence of hot, cold, or baryonic dark matter. It is a novel alternative to both cosmic string and to inflationary quantum fluctuations as the origin of structure in the Universe.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: NASA-CR-183371 , NAS 1.26:183371 , FERMILAB-PUB-88/120-A
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  • 6
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    An Ocean-Atmosphere Simulation for Studying Air-Sea Interactions (2019)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: During the past few years the Goddard Earth Observing System (GEOS) and Massachusetts Institute of Technology (MIT) modeling groups have produced, respectively, global atmosphere-only and ocean-only simulations with km-scale grid spacing. These simulations have proved invaluable for process studies and for the development of satellite and in-situ sampling strategies. Nevertheless, a key limitation of these "nature" simulations is the lack of interaction between the ocean and the atmosphere, which limits their usefulness for studying air-sea interactions and for designing observing missions to study these interactions. To remove this limitation, we aim to perform a coupled simulation using the km-scale GEOS atmosphere and the km-scale MIT ocean models. The initial attempt at the km-scale coupled simulation resulted in computational issues which will be presented here. As a preliminary step towards the km-scale objective, we present results from a high resolution but not yet km-scale simulation, wherein we have coupled a cubed-sphere-720 (~ 1/8) configuration of the GEOS atmosphere to a lat-lon-cap-1080 (~ 1/12) configuration of the MIT ocean. We compare near-surface diagnostics of this fully coupled ocean-atmosphere set-up to equivalent atmosphere-only and ocean-only simulations. A particular focus of the comparisons is the differences in interactions between Sea Surface Temperature (SST) and ocean surface wind for the coupled and uncoupled simulations. We discuss observed and modeled high temporal variability (~days) SST-wind cycle and how it is represented in the different systems. A mechanism for the cycle, which is driven by SST-wind feedback, is proposed.
    Keywords: Earth Resources and Remote Sensing; Meteorology and Climatology
    Type: GSFC-E-DAA-TN64698 , American Meteorological Society (AMS) Annual Meeting 2019; Jan 06, 2019 - Jan 10, 2019; Phoenix, AZ; United States
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  • 7
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    The Development of the New GEOS-MITgcm Atmosphere-Ocean Model for Coupled Data Assimilation System (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During the last two plus decades, The Goddard Earth Observing System (GEOS) and Massachusetts Institute of Technology (MIT) modeling groups have developed, respectively, atmosphere-only and ocean-only global general circulation models. These two models (GEOS and MITgcm) have demonstrated their data assimilation capabilities with the recent releases of the Modern Era Reanalysis for Research Applications, Version 2 (MERRA-2) atmospheric reanalysis and the Estimating the Circulation and Climate of the Ocean, Version 4 (ECCO-v4) ocean (and sea ice) state estimate. Independently, the two modeling groups have also produced global atmosphere-only and ocean-only simulations with km-scale grid spacing which proved invaluable for process studies and for the development of satellite and in-situ sampling strategies.Recently, a new effort has been made to couple these two models and to leverage their data-assimilation and high resolution capabilities (i.e., eddy-permitting ocean, cloud-permitting atmosphere). The focus in the model development is put on sub-seasonal to decadal time scales. In this talk, I discuss the new coupled model and present some first coupled simulation results. This will include a high-resolution coupled GEOS-MIT simulation, whereby we have coupled a cubed-sphere-720 (~ 1/8 deg) configuration of the GEOS atmosphere to a lat-lon-cap-1080 (~ 1/12 deg) configuration of the MIT ocean. We compare near-surface diagnostics of this fully coupled ocean-atmosphere set-up to equivalent atmosphere-only and ocean-only simulations. In the comparisons we focus in particular on the differences in air-sea interactions between sea surface temperature (SST) and wind for the coupled and uncoupled simulations.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN62546 , GSFC-E-DAA-TN62544 , IMS Seminar; Oct 16, 2018; Bet Dagan; Israel
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  • 8
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    Air-Sea Interactions in a High-Resolution Ocean-Atmosphere Simulation (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During the past few years the Goddard Earth Observing System (GEOS) and Massachusetts Institute of Technology (MIT) modeling groups have produced, respectively, global atmosphere-only and ocean-only simulations with km-scale grid spacing. These simulations have proved invaluable for process studies and for the development of satellite and in-situ sampling strategies. Nevertheless, a key limitation of these "nature" simulations is the lack of interaction between the ocean and the atmosphere, which limits their usefulness for studying air-sea interactions and for designing observing missions to study these interactions. We present here results from a coupled GEOS-MIT "nature run" simulation, wherein we have coupled a cubed-sphere-720 (~ 1/8) configuration of the GEOS atmosphere to a lat-lon-cap-1080 (~ 1/12) configuration of the MIT ocean. We compare near-surface diagnostics of this fully coupled ocean-atmosphere simulation to equivalent atmosphere-only and ocean-only simulations. A particular focus of the comparisons is the coupled versus uncoupled differences in interactions between Sea Surface Temperature (SST) and ocean surface wind. We discuss, in particular, a several-day mode of temporal variability in the SST-wind cycle and how it is represented in the different model simulations and in observationally-based products. A mechanism for the cycle, which is driven by SST-wind feedback, is proposed.
    Keywords: Oceanography
    Type: GSFC-E-DAA-TN64108 , American Geophysical Union (AGU) 2018 Fall Meeting; Dec 10, 2018 - Dec 14, 2018; Washington, D.C.; United States
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  • 9
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    A New Atmosphere-Ocean Model for Studying Air-Sea Interactions and Coupled Data Assimilation (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During the last two plus decades, The Goddard Earth Observing System (GEOS) and Massachusetts Institute of Technology (MIT) modeling groups have developed, respectively, atmosphere-only and ocean-only global general circulation models. These two models (GEOS and MITgcm) have demonstrated their data assimilation capabilities with the recent releases of the Modern Era Reanalysis for Research Applications, Version 2 (MERRA-2) atmospheric reanalysis and the Estimating the Circulation and Climate of the Ocean, Version 4 (ECCO-v4) ocean (and sea ice) state estimate. Independently, the two modeling groups have also produced global atmosphere-only and ocean-only simulations with km-scale grid spacing which proved invaluable for process studies and for the development of satellite and in-situ sampling strategies.Recently, a new effort has been made to couple these two models and to leverage their data-assimilation and high resolution capabilities (i.e., eddy-permitting ocean, cloud-permitting atmosphere). The focus in the model development is put on sub-seasonal to decadal time scales. In this talk, I discuss the new coupled model and present some first coupled simulation results. This will include a high-resolution coupled GEOS-MIT simulation, whereby we have coupled a cubed-sphere-720 (~ 1/8) configuration of the GEOS atmosphere to a lat-lon-cap-1080 (~ 1/12) configuration of the MIT ocean. We compare near-surface diagnostics of this fully coupled ocean-atmosphere set-up to equivalent atmosphere-only and ocean-only simulations. In the comparisons we focus in particular on the differences in air-sea interactions between sea surface temperature (SST) and wind for the coupled and uncoupled simulations.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN62549 , GSFC-E-DAA-TN62548 , Weizmann Institute of Science Department of Earth and Planetary Sciences Seminar; Oct 14, 2018; Rehovot; Israel|Tel Aviv University Department of Geophysics Seminar; Oct 15, 2018; Tel Aviv; Israel
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  • 10
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    Grand unified theories, topological defects, and ultrahigh-energy cosmic rays (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The ultrahigh-energy (UHE) proton and neutrino spectra resulting from collapse or annihilations of topological defects surviving from the GUT era are calculated. Irrespective of the specific process under consideration (which determines the overall normalization of the spectrum), the UHE proton spectrum always 'recovers' at approximately 1.8 x 10 exp 11 GeV after a partial Greisen-Zatsepin-Kuz'min 'cutoff' at approximately 5 x 10 exp 10 GeV and continues to a GUT-scale energy with a universal shape determined by the physics of hadronic jet fragmentation. Implications of the results are discussed.
    Keywords: SPACE RADIATION
    Type: Physical Review Letters (ISSN 0031-9007); 69; 4 Ju; 567-570
    Format: text
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