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21.
When three point masses form a hierarchical triple system, the short-period orbit can be severely modified by the long-period orbit if the two orbits are inclined to each other by more than about 39^deg (). Such an inclination can induce ‘Kozai cycles’ (Kozai, 1962), in which the eccentricity of the inner orbit cycles by a large amount while its period and therefore semimajor axis remains roughly constant. During those periastra when the eccentricity is largest, tidal friction may become important, and this can result in a secular shrinkage of the orbit, until it becomes circularised at a period of a few days.However, apsidal motion due to either GR or to the quadrupolar distortion of the components (if they are no longer treated as point masses) can reduce the range of eccentricity. We explore the limits on outer and inner orbital period that these perturbations imply.If the components are F/G/K/M dwarfs, then rotationally-driven dynamo activity can become important at the short periods that can occur in the right circumstances. It can cause the period to shorten further. The result may be a contact binary, and/or a merger in which the two stars of the inner pair coalesce to form a single rapidly rotating star. We suggest that this may be the origin of AB Dor, a very rapidly rotating K dwarf that is probably about 50 Myr old. 相似文献
22.
Jan Paav Ilja Knésl Anna Vymazalová Ivan Vavín Ludmila Ivanovna Gurskay Leonid Ruslanovich Kolbantsev 《地学前缘(英文版)》2011,2(1):81-85
The Polar Urals region of northern Russia is well known for large chromium (Cr)-bearing massifs with major chromite orebodies, including the Centralnoye I deposit in the Ray-Iz ultramafic massif of the Ural ophiolite belt. New data on platinum (Pt)-group elements (PGE), geochemistry and mineralogy of the host dunite shows that the deposit has anomalous iridium (Ir) values. These values indicate the predominance of ruthenium–osmium–iridium (Ru–Os–Ir)-bearing phases among the platinum-group mineral (PGM) assemblage that is typical of mantle-hosted chromite ores. Low Pt values in chromites and increased Pt values in host dunites might reflect the presence of cumulus PGM grains. The most abundant PGM found in the chromite is erlichmanite (up to 15 μm). Less common are cuproiridsite (up to 5 μm), irarsite (up to 4–5 μm), and laurite (up to 4 μm). The predominant sulfide is heazlewoodite, in intergrowth with Ni–Fe alloys, sporadically with pentlandite, and rarely with pure nickel. Based on the average PGE values and estimated Cr-ore resources, the Centralnoye I deposit can be considered as an important resource of PGE. 相似文献
23.
Larisa Frolova Larisa Nazarova Ludmila Pestryakova Ulrike Herzschuh 《Journal of Paleolimnology》2014,52(1-2):107-119
Subfossil Cladocera were sampled and examined from the surface sediments of 35 thermokarst lakes along a temperature gradient crossing the tree line in the Anabar-river basin in northwestern Yakutia, northeastern Siberia. The lakes were distributed through three environmental zones: typical tundra, southern tundra and forest tundra. All lakes were situated within the continuous permafrost zone. Our investigation showed that the cladoceran communities in the lakes of the Anabar region are diverse and abundant, as reflected by taxonomic richness, and high diversity and evenness indices (H = 1.89 ± 0.51; I = 0.8 ± 0.18). CONISS cluster analysis indicated that the cladoceran communities in the three ecological zones (typical tundra, southern tundra and forest-tundra) differed in their taxonomic composition and structure. Differences in the cladoceran assemblages were related to limnological features and geographical position, vegetation type, climate and water chemistry. The constrained redundancy analysis indicated that TJuly, water depth and both sulphate (SO4 2?) and silica (Si4+) concentrations significantly (p ≤ 0.05) explained variance in the cladoceran assemblage. TJuly featured the highest percentage (17.4 %) of explained variance in the distribution of subfossil Cladocera. One of the most significant changes in the structure of the cladoceran communities in the investigated transect was the replacement of closely related species along the latitudinal and vegetation gradient. The results demonstrate the potential for a regional cladoceran-based temperature model for the Arctic regions of Russia, and for and Yakutia in particular. 相似文献
24.
25.
Summary Time varying coordinates of points of a geodetic network are indirectly measured by a group of measurement devices with different characteristics of accuracy in several epochs. The design of the measurement is the same in all epochs. The ratio of the characteristics of accuracy is a priori unknown. The aim is to determine an estimator of the parameters of functions modelling changes of the coordinates, confidence regions of these functions and to construct a procedure for testing linear hypotheses on time varying coordinates of a geodetic network. As the characteristics of accuracy are a priori unknown, the problem of their estimation has to be solved simultaneously. The research of rules of recent crustal movements leads to studying the mentioned model. 相似文献
26.
Lubomír Kubáček Ludmila Kubáčková Reviewer M. Burda 《Studia Geophysica et Geodaetica》1978,22(4):330-335
Summary A mathematical model for optimum prediction, filtration and simultaneous prediction and filtration of the fields considered has been constructed using Hilbert spaces with a reproduction kernel, formed by the covariance function of the observed anomalous geophysical potential field under the assumption that the field is an inhomogeneous random function. 相似文献
27.
Zusammenfassung Es wurde eine Bestimmung der Kristallstruktur des Bismuthinits Bi2S3, die bisher nur als Analogie der Antimonitstruktur bekannt war, durchgeführt. Es zeigte sich, daß die Kristallstruktur des Bismuthinits weitgehend mit der von Antimonit übereinstimmt. Die Koordinationspolyeder sind allerdings regelmäßiger als beim Sb2S3 und bei einem der beiden kristallographisch unabhängigen Bi-Atome zeigt sich bei genauer Betrachtung ein deutlicher Unterschied, so daß die Koordination von diesem als 3+3+1 gegenüber 3+2+1 beim Antimonit bezeichnet werden kann.
Mit 1 Abbildung 相似文献
The crystal structure of bismuthinite
Summary The crystal structure of bismuthinite Bi2S3 was determined. It showed that the analogy to the structure of stibnite is correct in general. The coordination polyhedra are more regular compared to those in Sb2S3. One of the crystallographic independent Bi-atoms shows a distinct difference in coordination, 3+3+1, compared to the equivalent atom in antimonite, 3+2+1.
Mit 1 Abbildung 相似文献
28.
Ludmila Kubáčková Ivana Jakubcová Miloš Pick Stanislav Hrách Reviewer J. Anděl Reviewer Z. Šimon 《Studia Geophysica et Geodaetica》1979,23(1):10-16
Summary The theory of the restricted D-optimal design was used for the project of gravity measurements in a pressure chamber. An example of the measurements is presented. 相似文献
29.
Summary Using a general model, constructed for random fields defined on a Lyapunov surface, the stochastic properties of fields defined at points of the surface of a tri-axial rotational ellipsoid are investigated within the correlation theory of these fields. 相似文献
30.