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This review begins with a discussion of the techniques needed for observations of scattered light from cometary dust. After
an introduction into the basic concepts of the scattering process, observations of the phase curves of brightness, colour
and polarization are covered. Images of colour and polarization are presented and the observed relation of colour and polarization
in jets and shells is discussed. The interpretation of the measurements is based on the power law size distributions of dust
grains observed from space. The power index must lie between 2 and 4 to provide the mass budget and visibility of the dust
coma in accordance with the basic facts of cometary physics. Application of mechanical (radiation pressure) theory to cometary
images allows us to derive related power law distributions for comets not explored by spacecraft. Grain scattering models
are presented and compared with observations. A prediction is made of the spatial distribution of Stokes parameters U and
V in the presence of aligned particles. Up to now such patterns have not been observed. Future work should include the exploration
of comets at small and possibly very small phase angles and a detailed comparison of polarization and colour images of comets
with thermal images and with models based on mechanical theory.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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KLAUS DODDS 《Geographical review》2011,101(1):88-105
Generic action‐thriller films, especially The Bourne Ultimatum, the last in a series of three films, provide a useful resource for examining the gendered nature of geopolitics, the specification of place, and the role of geosurveillance in post‐9/11 national security. Using the dialogue of the film as key source material, I show how the private world of Jason Bourne, an assassin, is interwoven with the public sphere of international security, including covert operations: The personal is geopolitical. I conclude with some reflections on how we might use film as a critical pedagogical resource. 相似文献
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Ocean circulation and climate change 总被引:1,自引:0,他引:1
KLAUS HASSELMANN 《Tellus. Series B, Chemical and physical meteorology》1991,43(4):82-103
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KLAUS H. MICHELS 《Sedimentology》1995,42(1):31-38
The composition of sediment samples and/or the influence of current activity on the sediment can be easily determined using the dissection of settling velocity distributions. A new dissection method for the analysis of settling velocity distributions has been developed. The initial settling velocity distribution is decomposed by means of settling velocity distributions of the main biogenic constituents, three planktic and three benthic foraminifera species. A divergence from the natural size distribution of a foraminifera species can be attributed to current influence. Thus, negative or positive skewness of current-affected foraminifera populations indicate erosional or depositional sediment influence. The dissection of Holocene samples from the northern North Atlantic demonstrates the advantages of this method in the interpretation of sand-size material. 相似文献
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KROON NORRIS KLAUS IAN T. ALEXANDER LEON PAUL BARDOT CHARLES E. BARKER JEAN-PIERRE BELLIER CHARLES D. BLOME LEON J. CLARKE JOCHEN ERBACHER KRISTINA L. FAUL MARY ANNE HOLMES BRIAN T. HUBER MIRIAM E. KATZ KENNETH G. MACLEOD SANDRA MARCA FRANCISA C. MARTINEZ-RUIZ ISAO MITA MUTSUMI NAKAI JAMES G. OGG DOROTHY K. PAK THOMAS K. PLETSCH JEAN M. SELF-TRIAL NICHOLAS J. SHACKLETON JAN SMIT WILLIAM USSLERIII DAVID K. WATKINS JOEN WIDMARK & PAUL A. WILSON 《Geology Today》1998,14(6):222-226
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Abstract— We evaluate the consequences of explosive activity having taken place during volcanic eruptions on the differentiated asteroid 4 Vesta, which is the likely parent body of the howardite-eucrite-diogenite (HED) meteorites. For a wide range of magma volatile contents, we calculate the eruption speeds and subsequent trajectories of the pyroclastic magma droplets produced. By considering the size distribution and eruption speeds of the droplets, and the mass fluxes at which they are ejected, we show that, under all realistic circumstances, the droplets will have formed lava fountains that were extremely optically dense. As a result, virtually all of the droplets will have reached the surface having suffered a negligible amount of radiative cooling and will have coalesced into lava ponds feeding lava flows. Typically, <1% of the pyroclasts will have undergone enough cooling to allow them to accumulate into a recognizable fall deposit consisting of unwelded or partly welded volcanic glass beads. This result is consistent with the apparent absence of identifiable pyroclastic material in the HED (and other types of) differentiated meteorites. 相似文献
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It is well known that seismic inversion based on local model optimization methods, such as iterative use of linear optimization, may fail when prior information is sparse. Where the seismic events corresponding to reflectors of interest remain to be identified, a global optimization technique is required. We investigate the use of a global, stochastic optimization method, that of simulated annealing, to solve the seismic trace inversion problem, in which the two-way traveltimes and reflection coefficients are to be determined. The simulated annealing method is based on an analogy between the model-algorithm system and a statistical mechanical system. We exploit this analogy to produce improved annealing schedules. It is shown that even in cases of virtually no prior information about two-way traveltimes and reflection coefficients, the method is capable of producing reliable results. 相似文献
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