Asteroid rotation: I. Tabulation and analysis of rates,pole positions and shapes     

Alan W. Harris  Joseph A. Burns 《Icarus》1979,40(1):115-144

Data are presented for the 182 asteroids whose rotational properties are available in the literature. Plots are provided for the asteroid rotational frequency f and lightcurve amplitude Δm versus asteroid size; the latter is determined using standard methods if data are available but otherwise is estimated from asteroid albedos, selected depending on taxonomic type or orbital position. A linear least-squares fit to all the data shows that f increases with decreasing size, confirming McAdoo and Burns' (1973) result; this is demonstrated to be primarily caused by relatively more small non-C than C asteroids in our sample, coupled with a slower mean rotation rate for C asteroids (P ≈ 11 hr) than non-C asteroids (P ≈ 9 hr). In terms of the collisional theory of Harris (1979a), this means that the C's are less dense than the other minor planets. Any slight tendency for smaller asteroids to spin faster, even within a taxonomic type, could be due to selection effects; our data are not extensive enough to determine whether the very smallest (? 10-km diameter) spin especially fast. The minor planets of our survey become more irregular at smaller sizes, disputing the conclusions of Bowell (1977b), Degewij (1977), and Degewij et al. (1978), based on other, perhaps more complete, data; selection effects may account for this disagreement. Shapes do not appear to depend on taxonomic type. The dispersion of asteroid rotation rates from the mean is found to be in excellent agreement with a three-dimensional Maxwellian distribution, such as would be developed in a collisionally evolved system. The rotation axes, therefore, appear to be randomly oriented in space. Rotation pole positions are also tabulated and calculated to likely be constant in space over the extent of past observation. Observers are encouraged to measure the rotational properties of faint objects and asteroids of unusual taxonomic types, and to carry out long-time studies of asteroids which over short periods do not seem to vary.  相似文献   

Porphyrin and chlorin distributions in a Late Pliocene lacustrine sediment     

Keely BJ  Harris PG  Popp BN  Hayes JM  Meischner D  Maxwell JR 《Geochimica et cosmochimica acta》1994,58(17):3691-3701

The tetrapyrroles in a highly immature Late Pliocene lacustrine sediment (Willershausen, Germany) show a simple distribution of both chlorin and porphyrin components as the free bases. The major components are C32 desoxophylloerythroaetioporphyrin (DPEP), a C33 bicycloalkano porphyrin, the chlorin analogue of the latter, and desoxophylloerythrin and its chlorin counterpart. The structure of the novel bicycloalkano chlorin was determined using a combination of two-dimensional phase-sensitive COSY NMR and nOe studies. Measurements of delta 13C and other data indicate that DPEP and the bicycloalkano porphyrin were derived from the chlorophyll(s) of photosynthetic organisms utilising a common source of CO2, probably diatoms. The occurrence of DPEP and other minor alkyl porphyrins indicates that the chlorophyll defunctionalisation pathway leading to these components can occur at low temperature and was probably biologically mediated, as was the condensation leading to the fused ring components.  相似文献   

ANNUAL MEETING OF THE NATIONAL RESEARCH COUNCIL     

Chauncy D. Harris  Edwin H. Hammond 《The Professional geographer》1966,18(4):256-256

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Three-dimensional sinkhole stability of spherical cavity     

Shiau  Jim  Chudal  Bishal  Keawsawasvong  Suraparb 《Acta Geotechnica》2022,17(9):3947-3958

Acta Geotechnica - Sinkhole occurrences due to underground water mains operations have piqued people’s curiosity. Most research works were in relation to geophysical practices to discover the...  相似文献   

Petrogenesis of the Swaziland and Northern Natal Rhyolites of the Lebombo Rifted Volcanic Margin, South East Africa   总被引：2，自引：0，他引：2  

Miller  Jodie A.; Harris  Chris 《Journal of Petrology》2007,48(1):185-218

The Jozini and Mbuluzi rhyolites and Oribi Beds of the southernLebombo Monocline, southeastern Africa, have geochemical characteristicsthat indicate they were derived by partial melting of a mixtureof high-Ti/Zr and low-Ti/Zr Sabie River Basalt Formation types.Compositional variations within the different rhyolite typescan largely be explained by subsequent fractional crystallization.The Sr- and Nd-isotope composition of the rhyolites is uniqueamongst Gondwana silicic large igneous provinces, having _Ndvalues close to Bulk Earth (–0·94 to 0·35)and low, but more variable, initial ⁸⁷Sr/⁸⁶Sr ratios (0·7034–0·7080).Quartz phenocryst ¹⁸O values indicate that the rhyolite magmashad ¹⁸O values between 5·3 and 6·7, consistentwith derivation from a basaltic protolith with ¹⁸O values between4·8 and 6·2. The low-¹⁸O rhyolites (< 6·0)come from the same stratigraphic horizon and are overlain andunderlain by rhyolites with more ‘normal’ ¹⁸O magmavalues. These low-¹⁸O rhyolites cannot have been produced byfractional crystallization or partial melting of mantle-derivedbasaltic material. The rhyolites have low water contents, makingit unlikely that the low ¹⁸O values are the result of post-emplacementalteration. Modification of the source by fluid–rock interactionat elevated temperatures is the most plausible mechanism forlowering the ¹⁸O magma value. It is proposed that the low-¹⁸Orhyolites were derived by melting of earlier altered rhyolitein calderas situated to the east, which were not preserved afterGondwana break-up. KEY WORDS: rhyolite; Lebombo; stable and radiogenic isotopes; low-¹⁸O magmas; partial melting  相似文献   

Tectonics may affect closed watersheds used to monitor climate change and human activity effects     

Alejandro Jiménez-Bonilla  Manuel Díaz-Azpiroz  Miguel Rodríguez Rodríguez 《地学学报》2023,35(1):58-65

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Relative current effect on short wave growth     

Guimarães  Pedro Veras  Ardhuin  Fabrice  Perignon  Yves  Benetazzo  Alvise  Bouin  Marie-Noëlle  Garnier  Valerie  Redelsperger  Jean-Luc  Accensi  Mickael  Thomson  Jim 《Ocean Dynamics》2022,72(8):621-639

Ocean Dynamics - Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and...  相似文献   

Numerical modeling and hazard implications of landslides at the Ardillas Volcanic Dome (Tacaná Volcanic Complex,Mexico-Guatemala)     

Vázquez  R.  Macías  J. L.  Alcalá-Reygosa  J.  Arce  J. L.  Jiménez-Haro  A.  Fernández  S.  Carlón  T.  Saucedo  R.  Sánchez-Núñez  J. M. 《Natural Hazards》2022,110(2):1305-1337

Natural Hazards - Both climate and land-use changes can influence drought in different ways. Thus, to predict future drought conditions, hydrological simulations, as an ideal means, can be used to...  相似文献   

Guest Editorial: What’s so big about Big Data? Finding the spaces and perils of Big Data   总被引：1，自引：0，他引：1  

Ryan Burns  Jim Thatcher 《GeoJournal》2015,80(4):445-448

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Consistent estimates of the dynamic figure parameters of the earth     

Wei Chen  Jian Cheng Li  Jim Ray  Wen Bin Shen  Cheng Li Huang 《Journal of Geodesy》2015,89(2):179-188

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