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571.
A regular perturbation analysis is presented for natural convection flow over an uniform flux vertical surface with temperature dependent viscosity. Numerical calculations are presented forP
r=6.7 which show that the first-order correction to the local temperature difference and to the local skin-fraction are negative whereas it is positive for the local Nusselt number. The effects of variable viscosity on the temperature, velocity profiles, the local temperature difference, the local Nusselt number and the local skin fraction are discussed. 相似文献
572.
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575.
The Mangala Valles system is an ∼
∼900 km fluvially carved channel system located southwest of the Tharsis rise and is unique among the martian outflow channels
in that it heads at a linear fracture within the crust as opposed to a collapsed region of chaos as is the case with the circum-Chryse
channels. Mangala Valles is confined within a broad, north–south trending depression, and begins as a single valley measuring
up to 350 km wide that extends northward from a Memnonia Fossae graben, across the southern highlands toward the northern
lowlands. Approximately 600 km downstream, this single valley branches into multiple channels, which ultimately lose their
expression at the dichotomy boundary. Previous investigations of Mangala Vallis suggested that many of the units mapped interior
to the valley were depositional, related to flooding, and that a minimum of two distinct periods of flooding separated by
tens to hundreds of millions of years were required to explain the observed geology. We use infrared and visible images from
the THermal EMission Imaging System (THEMIS), and topographic data from the Mars Orbiting Laser Altimeter (MOLA), to investigate
the nature of the units mapped within Mangala Vallis. We find that the geomorphology of the units, as well as their topographic
and geographic distribution, are consistent with most of them originating from a single assemblage of volcanic flow deposits,
once continuous with volcanic flows to the south of the Memnonia Fossae source graben. These flows resurfaced the broad, north–south
trending depression into which Mangala Vallis formed prior to any fluvial activity. Later flooding scoured and eroded this
volcanic assemblage north of the Mangala source graben, resulting in the present distribution of the units within Mangala
Vallis. Additionally, our observations suggest that a single period of catastrophic flooding, rather than multiple periods
separated by tens to hundreds of millions of years, is consistent with and can plausibly explain the interior geology of Mangala
Vallis. Further, we present a new scenario for the source and delivery of water to the Mangala source graben that models flow
of groundwater through a sub-cryosphere aquifer and up a fracture that cracks the cryosphere and taps this aquifer. The results
of our model indicate that the source graben, locally enlarged to a trough near the head region of Mangala, would have required
less than several days to fill up prior to any spill-over of water to the north. Through estimates of the volume of material
missing from Mangala (13,000–20,000 km3), and calculation of mean discharge rates through the channel system (∼
∼5 × 106 m3 s−1), we estimate that the total duration of fluvial activity through the Mangala Valles was 1–3 months. 相似文献
576.
577.
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579.
F.Z. Feygin YU.P. Kurchashov V.A. Troitskaya K. Dobeš 《Planetary and Space Science》1985,33(3):271-273
A high resolution numerical sonagram of Pc-1 magnetic record has shown that single narrow lines of Pc-1 spectra produce lower frequency (“red-shifted”) satellite lines more than twice as often as their higher frequency (“violet”) counterparts. The violet satellites usually emerge only when at least two ancestor lines are present simultaneously. 相似文献
580.
During a campaign of optical observations at high latitude, a bi-dimensional study of the wave structure of the OH layer has been performed in December 1981 from Sodankyla (Finland). This site is one of the three stations of the EISCAT ionosphere sounding system. It has been found that a wave field covering an area of 1 million km2 may extend to latitudes as high as 70°N. The OH wave structure shows many similarities with noctilucent clouds. The fairly large horizontal wavelength, of the order of 40 km cannot easily be explained by a wave motion at an interface. The observed wave structure seems to be a result of the propagation of an internal gravity wave in the 80–100 km region. This wave structure was often recorded during the same time as an active aurora was present. As a result, it appears that the perturbation might be correlated with particle precipitations at auroral latitudes. 相似文献