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511.
David A. Allen 《Earth, Moon, and Planets》1971,2(4):435-462
This paper presents an infrared study of thermal anomalies during the lunar night. From observations of the most intense anomalies at several wavelengths it is deduced that fields of boulders are responsible for the thermal enhancement; the cooling curves of the remainder are consistent with such a model. High resolution Lunar Orbiter photographs of some of the thermal anomalies reveal boulders to be present within them in just the right numbers. The ages and distribution of thermal anomalies are discussed in the light of this model. 相似文献
512.
Antony J. Long Sarah A. Woodroffe Sue Dawson David H. Roberts Charlotte L. Bryant 《第四纪科学杂志》2009,24(4):345-359
In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
513.
David G. Ashworth 《Astrophysics and Space Science》1969,5(1):71-75
Boundary conditions are imposed upon the solutions of the conservation equations for non-thermal convective motion in a self-gravitating, homogeneous, non-rotating sphere of radiusR, consisting of a core extending to a fraction of the radius of the sphere and with a viscous mantle overlying the core. It is shown that convective modes are permissible in the mantle only for certain values ofn and . 相似文献
514.
A flare observed with the Hard X-Ray Imaging Spectrometer (HXIS) was studied during its rise to maximum temperature and X-ray emission rate. Two proximate flare loops, of lengths 2.8 × 109 cm and 1.1 × 1010 cm, rose to temperatures of 21.5 × 106 K and 30 × 106 K, respectively, in 30 s. Assuming equal heat flux F into each loop from a thermal source at the point where they met, we derive a simple relationship between temperature T and loop length
, which gives a loop temperture ratio of 0.68, in close agreement with the observed ratio of 0.72. The observations imply that heating in each loop was maintained by a thermal flux of 5 × 109 ergs cm-2 s-1. It is suggested that conductive heating adequately describes the rise and maximum phase emissions in the loops and that long flare loops reach higher temperatures than short loops during the impulsive phase because of an equipartition of energy between them at their point of interaction. 相似文献
515.
The discovery of large, solid particles in the clouds of Venus is one of the most significant findings of Pioneer Venus because it means that a substantial mass of the clouds is composed of a material other than sulfuric acid. The evidence which suggests that solid particles form a distinctive size mode is reexamined. The mode is defined by a discontinuity between two size ranges of the Pioneer Venus particle size spectrometer. This discontinuity could represent a real size mode. However, it could also be an artifact of the measurement technique. R. G. Knollenberg (1984) discusses several possible instrumental effects which might have caused this discontinuity. It is hypothesized herein that such effects did occur and that the large particles are really the tail of the mode 2 sulfuric acid particle size distribution and are not a separate mode of solid particles. Using such a revised size distribution, it is shown that all of the Pioneer Venus and Venera optical data from the lower clouds can be explained with sulfuric acid droplets without introducing any solid particles. As a by-product of this analysis, it is also found that the upper clouds of Venus must contain a material with a higher refractive index than sulfuric acid. A small quantity of sulfur could account for this observation. 相似文献
516.
Faith Vilas David J. Tholen Larry A. Lebofsky Humberto Campins Glenn J. Veeder Richard P. Binzel Alan T. Tokunaga 《Icarus》1985,63(2):201-205
Visual and infrared observations were made of Amor asteroid 1982 DV during its discovery apparition. Broadband visual and near-infrared photometry shows that it is an S-class asteroid. Narrowband spectrophotometry shows an absorption feature due to olivine or pyroxene or both centered at 0.93 μm. Applying a nonrotating thermal model to 10-μm photometry, the geometric albedo is calculated to be approximately 0.27. The geometric albedo for a slowly rotating, rocky surface was calculated for 1 night to be 0.15, consistent with S-class asteroid albedos. Thus, 1982 DV is either one of the most reflective S-class asteroids known, or a significant amount of bare rock is exposed on the asteroid's surface. For the nonrotating model, ellipsoidal dimensions for 1982 DV are 3.5 × 1.4 × 1.4 km. 相似文献
517.
David R. Soderblom 《Icarus》1985,61(2):343-345
Knowledge of a star's rotation period and ν sin i can be used to select stars that are seen pole-on, and thus are well suited to planetary searches by astrometric or direct-imaging means. A table of such stars is presented. This method is not suitable for discriminating equator-on systems and so cannot be used to select candidates for the photometric method of W. J. Borucki and A. L. Summers (1984, Icarus58, 121–134). 相似文献
518.
David E. Fisher 《Meteoritics & planetary science》1985,20(1):37-41
Uranium was measured by fission track analysis in meteoritic troilite and graphite. The distribution is extremely heterogeneous, with a few high-U grains dominating the total abundances. U/He ages cannot be estimated from such a distribution pattern, and therefore previously reported excessive ages are not valid. 相似文献
519.
We report photometry for nine asteroids at wavelengths of 1.25, 1.65, and 2.22 μm. Three C-type objects (88, 129, and 511) seem slightly redder in H?K and J?H color indices than four S-type objects (5, 6, 7, and 116) and an E-type object (64). Eros has an unusually red J?H color index; its infrared spectral reflectance is consistent with an appreciable quantity of metallic iron plus some pyroxene and olivine on its surface. JHK photometry is less diagnostic of composition than either higher resolution spectrophotometry in the infrared or spectrophotometry at shorter wavelengths. 相似文献
520.
David Herald 《Earth, Moon, and Planets》1976,15(1-2):91-107
Baily beads were observed from near the northern limit of totality during the eclipse of June 20, 1974; no attempt of identification was made at the time of observation. The observations were analysed to identify the features of the lunar profile which gave rise to the beads observed. They were then analysed to derive corrections to the relative positions of the Sun and Moon, and to investigate certain features of the lunar profile. 相似文献