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181.
Izvestiya, Atmospheric and Oceanic Physics - The 100 000-year periodicity of climate changes during the Late Pleistocene (in the last 800 ka) may be related to the respective oscillations in... 相似文献
182.
183.
A catalog of maser spectra in the 1.35-cm water-vapor line towards the maser source NGC 2071 in a region of massive star formation
is presented for 1994–2010. The observations were carried out using the 22-m antenna of the Pushchino Radio Astronomy Observatory
with a spectral resolution of 0.101 km/s (0.0822 km/s after the end of 2005). Based on the data throughout the monitoring
since 1980, two very different cycles of maser activity were found. The first (1980–1992) is characterized by high activity
within a broad range of radial velocities. Emission at velocities near 7 km/s predominated in 1980–1986, and emission near
14–16 km/s, in 1987–1992. In 1997–2008, the maser intensity was appreciably lower than in the first activity cycle. Numerous
flares of individual emission features were observed. Identifications based on VLA data show that strong flares took place
in both maser sources, IRS1 and IRS3. Both sources demonstrated a low level of maser activity during essentially the same
epochs (1977, 1995–1997, and the close of 2009 through the beginning of 2010), although the sources are separated by at least
2000 AU. 相似文献
184.
185.
186.
Fumarolic encrustations and natrocarbonatite lava from the active crater of Oldoinyo Lengai volcano, Tanzania, were sampled and analysed. Two types of encrustation were distinguished on the basis of their REE content, enriched (~ 2800–5600 × [REEchondrite]) and depleted (~ 100–200 × [REEchondrite]) relative to natrocarbonatite (1700–1900 × [REEchondrite]. REE-enriched encrustations line the walls of actively degassing fumaroles, whereas REE-depleted encrustations occur mainly along cracks in and as crusts on cooling natrocarbonatite lava flows; one of the low REE encrustation samples was a stalactite from the wall of a possible fumarole. The encrustations are interpreted to have different origins, the former precipitating from volcanic gas and the latter from meteoric/ground water converted to steam by the heat of the overlying lava flow(s). REE-profiles of encrustations and natrocarbonatite are parallel, suggesting that there was no preferential mobilization of specific REE by either volcanic vapour or meteoric water vapour. The elevated REE-content of the first group of encrustations suggests that direct REE-transport from natrocarbonatite to volcanic vapour is possible. The REE trends observed in samples precipitating directly from the volcanic vapour cannot be explained by dry volatility based on the available data as there is no evidence in the encrustation compositions of the greatly enhanced volatility predicted for Yb and Eu. The observed extreme REE-fractionation with steep La/Sm slopes parallel to those of the natrocarbonatite reflects solvation and complexation reactions in the vapour phase that did not discriminate amongst the different REE or similar transport of REE in both the natrocarbonatite magma and its exsolving vapour. The low concentrations of REE in the encrustations produced by meteoric vapour suggest that the temperature was too low or that this vapour did not contain the ligands necessary to permit significant mobilization of the REE. 相似文献
187.
In high-Mg, Al metapelites, monophase sapphirine corona occur around spinel–corundum aggregates in monomineralic cordierite
layers, and bi-phase orthopyroxene–sillimanite aggregates replace locally warped sapphirine in polygonized cordierite aggregates.
P–T phase topologies computed (Perple_X software) using compositions of cordierite-rich layers that host the reaction textures
did not match the assemblages for the discontinuous reactions spinel + corundum + cordierite → sapphirine and sapphirine + cordierite → orthopyroxene + sillimanite.
Instead, the reaction assemblages were reproduced using P–T pseudosection analysis for micro-domain reaction volumes estimated from compositions of product phases in the volume proportion
they occur. The results are consistent with known phase relations deduced using Schreinmakers P–T grids. Apparently, the compositions of cordierite-rich layers that hosted the reaction textures were inadequate chemical
proxies for determining P–T–X relations of phase-boundary controlled reactions influenced by compositions of the nearest-neighbor minerals in the proportion
they react (effective composition), and not in the proportion they existed in the layer/bulk rock. In other words, P–T–X phase topologies and reconstructed P–T paths in dry and aluminous rocks may be best understood by thermodynamic modeling of reactions using effective reaction volume
compositions rather than the bulk composition of the rock or the mineralogical layer that host the reaction textures. 相似文献
188.
We studied the surface perturbations of a two-layer ideal fluid induced by a flow past a submerged obstacle (simulated by
a point dipole) in the vicinity of the density-jump layer. It is shown that the formation of two different types of surface
waves is possible behind the flowed past obstacle in the real conditions of the open sea. The comparison of the amplitudes
of the surface perturbations induced by the obstacle located above and below the density jump revealed their significant differences,
which seems to be important for the use of this effect in practical problems. 相似文献
189.
190.
G. L. Gdalevich A. Kh. Depueva N. I. Izhovkina V. D. Ozerov 《Geomagnetism and Aeronomy》2010,50(1):69-78
The results of the Cosmos-900 satellite observ ations of plasma density inhomogeneities in the geomagnetic equator region
and the longitudinal distributions of the equatorial spread-F, according to the Intercosmos-19 satellite data are presented. It is show n that the dependence of radiosignal propagation
in the ionosphere on geophysical parameters is related to development of the electrostatic instability of the inhomo-geneous
ionospheric plasma. The longitudinal dependence of the spread-F, can reflect the influence of the energetic sources, located outside the ionospheric layer that scatters a radio pulse, on
the ionosphere. The manifestation of the longitudinal effect in the equatorial spread-F, in the Atlantic region can be explained by the influence of the cone instability on the plasma electrodynamics in the South
Atlantic geomagnetic anomaly. 相似文献