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  • 1
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    The formation of Charon’s red poles from seasonally cold-trapped volatiles (2016)
    Springer Nature
    In: Nature
    Details
    Publication Date: 2016-11-03
    Description: The formation of Charon’s red poles from seasonally cold-trapped volatiles Nature 539, 7627 (2016). doi:10.1038/nature19340 Authors: W. M. Grundy, D. P. Cruikshank, G. R. Gladstone, C. J. A. Howett, T. R. Lauer, J. R. Spencer, M. E. Summers, M. W. Buie, A. M. Earle, K. Ennico, J. Wm. Parker, S. B. Porter, K. N. Singer, S. A. Stern, A. J. Verbiscer, R. A. Beyer, R. P. Binzel, B. J. Buratti, J. C. Cook, C. M. Dalle Ore, C. B. Olkin, A. H. Parker, S. Protopapa, E. Quirico, K. D. Retherford, S. J. Robbins, B. Schmitt, J. A. Stansberry, O. M. Umurhan, H. A. Weaver, L. A. Young, A. M. Zangari, V. J. Bray, A. F. Cheng, W. B. McKinnon, R. L. McNutt, J. M. Moore, F. Nimmo, D. C. Reuter & P. M. Schenk A unique feature of Pluto’s large satellite Charon is its dark red northern polar cap. Similar colours on Pluto’s surface have been attributed to tholin-like organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location on Charon implicates the temperature extremes that result from Charon’s high obliquity and long seasons in the production of this material. The escape of Pluto’s atmosphere provides a potential feedstock for a complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon’s winter pole was proposed as an explanation for the dark coloration on the basis of an image of Charon’s northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon and the supply and temporary cold-trapping of material escaping from Pluto, as well as the photolytic processing of this material into more complex and less volatile molecules while cold-trapped. The model results are consistent with the proposed mechanism for producing the observed colour pattern on Charon.
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 2
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    McGraw‐Hill Encyclopedia of Physics and McGraw‐Hill Encyclopedia of Astronomy (1983)
    American Institute of Physics
    Details
    Publication Date: 1983-09-01
    Print ISSN: 0031-9228
    Electronic ISSN: 1945-0699
    Topics: Physics
    Published by American Institute of Physics
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  • 3
    Electronic Resource
    Electronic Resource
    Simulation of cylindrical ion temperature gradient modes in the Columbia Linear Machine experiment (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 3440-3448 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparison of the Columbia Linear Machine experiment [A. K. Sen, J. Chen, and M. Mauel, Phys. Rev. Lett. 66, 429 (1991)] with three-dimensional nonlinear electrostatic gyrokinetic simulation results is given, as well as comparisons with linear theory and simple theoretical predictions of nonlinear saturation. Linear theory is in reasonable agreement with the both experimental and simulation results. An analysis of the radial mode width which is localized by variation in the ion temperature gradient is given and compares well with both experiment and simulation. The theoretical estimate of the nonlinear saturation level is within a factor of 2 of what is observed in experiment and in simulation. In addition, both experiment and simulation show excitation of longer wavelength modes with poloidal mode numbers smaller than the linearly most unstable mode. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1488950
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  • 4
    Electronic Resource
    Electronic Resource
    Comparisons and physics basis of tokamak transport models and turbulence simulations (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 969-983 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The predictions of gyrokinetic and gyrofluid simulations of ion-temperature-gradient (ITG) instability and turbulence in tokamak plasmas as well as some tokamak plasma thermal transport models, which have been widely used for predicting the performance of the proposed International Thermonuclear Experimental Reactor (ITER) tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 1, p. 3], are compared. These comparisons provide information on effects of differences in the physics content of the various models and on the fusion-relevant figures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simplified plasma model and geometry which is an idealization of the plasma conditions and geometry in a Doublet III-D [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high confinement (H-mode) experiment. Most of the models show good agreements in their predictions and assumptions for the linear growth rates and frequencies. There are some differences associated with different equilibria. However, there are significant differences in the transport levels between the models. The causes of some of the differences are examined in some detail, with particular attention to numerical convergence in the turbulence simulations (with respect to simulation mesh size, system size and, for particle-based simulations, the particle number). The implications for predictions of fusion plasma performance are also discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873896
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  • 5
    Electronic Resource
    Electronic Resource
    Radially global gyrokinetic simulation studies of transport barriers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1959-1966 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Improvements in tokamak transport have recently been obtained in a variety of operational modes through the formation of transport barriers, or good confinement radial zones. Here global nonlinear three-dimensional toroidal gyrokinetic simulation is used to study three effects that are linearly stabilizing and may cause the formation of transport barriers, namely, sheared toroidal rotation, reversed magnetic shear, and peaked density profiles. The effect of toroidal shear flow on ion heat diffusivity is found to be relatively weak compared to mixing-length expectations based on linear calculations. In contrast, it is found that weak or negative magnetic shear (s〈1/2) in combination with a peaked density profile relative to the temperature profile greatly suppresses ion-temperature-gradient-driven turbulence in the central region of global nonlinear simulations. Similar features are seen experimentally in reversed magnetic shear tokamak plasmas. There is some nonlocal penetration (∼20–30ρi) of the turbulence into the subcritical core region. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871992
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of transport in gyrokinetic tokamaks (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2231-2235 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Progress toward a detailed understanding of the transport in full-volume gyrokinetic simulations of tokamaks is described. The transition between the two asymptotic regimes (large and small) of scaling of the heat flux with system size a/ρg reported earlier is explained, along with the approximate size at which the transition occurs. The larger systems have transport close to that predicted by the simple standard estimates for transport by drift-wave turbulence (viz., Bohm or gyro-Bohm) in scaling with a/ρg, temperature, magnetic field, ion mass, safety factor, and minor radius, but lying much closer to Bohm, which seems the result better supported theoretically. The characteristic downshift in the 〈kθ〉 spectrum observed previously in going from the linear to the turbulent phase is consistent with the numerically inferred coupling coefficients Mkpq of a reduced description of the system. An explanation of the downshift is given from the resemblance of the reduced system to the Hasegawa–Mima or Terry–Horton systems. These manifest an analogous downshift in slab geometry, and have Mkpq resembling those inferred from the gyrokinetic (GK) data. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871246
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  • 7
    Electronic Resource
    Electronic Resource
    Comparisons of gyrofluid and gyrokinetic simulationsf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1461-1468 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The gyrokinetic and gyrofluid models show the most promise for large scale simulations of tokamak microturbulence. This paper discusses detailed comparisons of these two complementary approaches. Past comparisons with linear theory have been fairly good, therefore the emphasis here is on nonlinear comparisons. Simulations include simple two-dimensional slab test cases, turbulent three-dimensional slab cases, and toroidal cases, each modeling the nonlinear evolution of the ion temperature gradient instability. There is good agreement in both turbulent and coherent nonlinear slab comparisons in terms of the ion heat flux, both in magnitude and scaling with magnetic shear. However, the nonlinear saturation level for ||Φ|| in the slab comparisons shows differences of approximately 40%. Preliminary toroidal comparisons show agreement within 50%, in terms of ion heat flux and saturation level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870696
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  • 8
    Electronic Resource
    Electronic Resource
    Transport in gyrokinetic tokamaks (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1217-1228 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive study of transport in full-volume gyrokinetic (GK) simulations of ion temperature gradient driven turbulence in core tokamak plasmas is presented. Though this "gyrokinetic tokamak'' is much simpler than experimental tokamaks, such simplicity is an asset, because a dependable nonlinear transport theory for such systems should be more attainable. Toward this end, two related lines of inquiry are pursued. (1) The scalings of GK tokamaks with respect to important system parameters are studied. In contrast to real machines, the scalings of larger GK systems (a/ρs(approximately-greater-than)64) with minor radius, with current, and with a/ρs are roughly consistent with the approximate theoretical expectations for electrostatic turbulent transport which exist as yet. Smaller systems manifest quite different scalings. (2) With the goal of developing a first-principles theory of GK transport, the GK data are used to infer the underlying transport physics. The data indicate that, of the many modes k present in the simulation, only a modest number (Nk∼10) of k dominate the transport, and for each, only a handful (Np∼5) of couplings to other modes p appear to be significant, implying that the essential transport physics may be described by a far simpler system than would have been expected on the basis of earlier nonlinear theory alone. Part of this analysis is the inference of the coupling coefficients Mkpq governing the nonlinear mode interactions, whose measurement from tokamak simulation data are presented here for the first time. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871482
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  • 9
    Electronic Resource
    Electronic Resource
    The Catalytic Activity of Metals Produced by the Reduction of Salts in Liquid Ammonia. III. Ruthenium, Rhodium and Palladium1 (1954)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 76 (1954), S. 5989-5993 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja01652a027
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  • 10
    Electronic Resource
    Electronic Resource
    Comment on "Constant-current-density model for the anomalous Hall effects in Hg0.8Cd0.2Te'' [Appl. Phys. Lett. 53, 307 (1988)] (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1480-1480 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101329
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