排序方式: 共有46条查询结果,搜索用时 10 毫秒
21.
GPS Solutions - Helical antennas have been developed that feature a cutoff pattern and are suitable for practical positioning at millimeter level. The antennas are in the form of a tube with... 相似文献
22.
Capture and escape in the elliptic restricted three-body problem 总被引:1,自引:0,他引:1
Sergey A. Astakhov David Farrelly 《Monthly notices of the Royal Astronomical Society》2004,354(4):971-979
23.
Valery Astakhov 《Polar research》2008,27(2):280-288
This paper summarizes the principal results produced by the European Science Foundation's programme, Quaternary Environment of the Eurasian North (QUEEN). These results concern the distribution of late Quaternary glaciers of different ages across northern Eurasia. The pattern of glaciation is compared with the west–east climatic gradient of the continent. Of particular significance is the coincidence of the Late Weichselian ice margin with the modern 30°C difference between the July and January mean air temperatures. The difference between west and east in the annual amplitude of air temperature did not decrease during the Pleniglacial. The asymmetry of the glacial history suggests a progressive aridification of the Eurasian North, with the result that by marine isotope stage 2 significant ice volumes could only accumulate along the Atlantic seaboard. The different climatic signals of thermochrons and cryochrons of the extreme west and east of the continent are discussed. The growth of continentality eastwards restrains the applicability of pollen proxies for climatic reconstructions. 相似文献
24.
Kolesnik O. N. Kolesnik A. N. Ren Xiangwen Karabtsov A. A. Astakhov A. S. Shi Xuefa 《Doklady Earth Sciences》2021,497(1):217-222
Doklady Earth Sciences - The distribution of rare-earth elements (REEs) in ferromanganese deposits (FMDs) from the southeastern Laptev Sea is considered. The ore part of FMDs consisting mainly of... 相似文献
25.
Mikhail Zhelezniak QingBai Wu Anatolii Kirillin Zhi Wen Aleksandr Zhirkov Vladimir Zhizhin 《寒旱区科学》2021,13(2):107-122
The Elkon Horst is a geological structure that consists of heterogeneous strata with highly variable geocryological and temperature conditions. Gaining accurate knowledge of permafrost distribution patterns within this structure is of both scientific and practical importance. In mountainous terrain, the ground thermal regime is controlled by both surface and subsurface conditions. Surface conditions include snow cover characteristics, the presence or absence of vegetation, vegetation density, etc.. In contrast, subsurface conditions involve rock lithology or petrography, density, quantity and depth of fissures, groundwater, etc.. This article examines ground thermal regimes in various geomorphological settings based on temperature measurement data from geotechnical boreholes. The occurrence and extent of permafrost were evaluated for the entire horst area using direct and indirect methods. The maximum permafrost thickness measured in the Elkon Horst is 330 m, and the estimated maximum is 450 m at higher elevations. Thermophysical properties were determined for the major rock types, and the geothermal heat flux was estimated for the study area. The thermal conductivities were found to vary from 1.47 to 4.20 W/(m·K), and the dry bulk densities to range between 2,236 kg/m~3 and 3,235 kg/m~3. The average geothermal heat flux was estimated to be 44 mW/m~2. 相似文献
26.
27.
Common choke ring ground planes are known to contribute to undesirable antenna pattern narrowing in the elevation plane which
is associated with difficulties of tracking low elevation satellites. Also known is the comparatively narrow frequency bandwidth
of the choke grooves structure. As an alternative, using a convex impedance ground plane has been suggested for full-spectrum
GNSS applications. With such ground planes a pin structure is utilized instead of choke grooves to allow a frequency bandwidth
increase. A semi-spherical shape of the ground plane is shown to provide increased antenna gain for low elevation angles.
Theoretical performance estimates along with experimental test data have been provided. 相似文献
28.
Signs of mercury input and dispersion in the water mass and the atmosphere over the submarine Piip Volcano have been revealed.
The mercury from hydrothermal vents has been found to release mostly as a component of hydrothermal-gas bubbles rising through
the water mass to the sea’s surface. The mercury’s dispersion and the seawater’s enrichment with it is a consequence of the
partial dissolution of the gas bubbles. The atmochemical dispersion zone is represented by an area of higher mercury concentration
with two maximums shifted in the direction of the wind (northeastward) from the northern and southern peak of the volcano. 相似文献
29.
New luminescence dates and lithostratigraphic information from key section Bolshoi Shar on the Lower Yenissei shed light on the history of terrestrial sedimentation between 100 and 40 ka BP and change the chronostratigraphic position of two major ice advances of the Late Pleistocene. 相似文献
30.
During an early phase of the Last Ice Age (Weichselian, Valdaian), about 90 000 yr ago, an ice sheet formed over the shallow Barents and Kara seas. The ice front advanced on to mainland Russia and blocked the north‐flowing rivers (Yenissei, Ob, Pechora, Dvina and others) that supply most of the freshwater to the Arctic Ocean. The result was that large ice‐dammed lakes were formed between the ice sheet in the north and the continental water divides to the south. Here we present reconstructions and calculations of the areas and volumes of these lakes. The lake on the West Siberian Plain was nearly twice as large as the largest lake on Earth today. The well‐mapped Lake Komi in northeast Europe and a postulated lake in the White Sea Basin would also rank before the present‐day third largest lake. The lakes overflowed towards the south and thus the drainage of much of the Eurasian continent was reversed. The result was a major change in the water balance on the continent, decreased freshwater supply to the Arctic Ocean, and increased freshwater flow to the Aral, Caspian, Black and Baltic seas. A sudden outburst of the lakes' water to the Arctic Ocean when the ice sheet thinned is postulated. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献