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1.
Two genetically different types of authigenic carbonate mounds are studied: those within an active hydrothermal field related to serpentinite protrusions in the zone of intersection of a transform fracture zone and the Mid-Atlantic Ridge, and those in an active field of methane seepings in the Dnieper canyon of the Black sea. The general geochemical conditions under which authigenic carbonate formation occurs in the two fields considered were found. They include the presence of reduced H2S, H2, and CH4 gases at the absence of free oxygen; the high alkalinity of the waters participating in the carbonate formation; the similarity of the textural and structural features of authigenic aragonite, which represents the initial mineral of the carbonate matter of the mounds; the paragenesis of aragonite with sulfide minerals; and the close relation of carbonate mounds with communities of sulfate-reducing and methane-oxidizing microorganisms. A new mechanism of formation of hydrothermal authigenic carbonates is suggested; it implies their microbial sulfate reduction over the hydrogen of the fluid in the subsurface zone (biosphere) of mixing between the hydrothermal solution and the adjacent seawater. 相似文献
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3.
Yu. A. Bogdanov A. Yu. Lein A. M. Sagalevich A. A. Ul’yanov S. A. Dorofeev N. V. Ul’yanova 《Geochemistry International》2006,44(4):403-418
Several hydrothermal sulfide structures were sampled using Mir manned submersibles in the relatively shallow Lucky Strike vent field, Mid-Atlantic Ridge; the bathymetric position of these structures varies by approximately 100 m. The investigation of the chemical and mineral compositions of hydrothermal ore occurrences led to the conclusion that the initial high-temperature ore-bearing solution ascending toward the surface became unstable and experienced phase separation beneath the ocean floor. The phase separation was responsible for the bathymetric control of hydrothermal ore formation in the ocean. 相似文献
4.
We present an analysis of a high-amplitude event in the flux curve of component A of the gravitational lens QSO 2237+0305 observed by the OGLE and GLITP groups in autumn 1999. Hypothesizing this event to be associated with microlensing of a fold caustic, we analyzed the observational data using a method for the successive reconstruction of branches of the one-dimensional strip brightness distribution across the source corresponding to positive and negative arguments. The search for the branches was carried out on compact sets of nonnegative, monotonically nonincreasing, convex downward functions. The resulting shape of the strip brightness distribution for the accretion disk of the quasar is in agreement with results obtained earlier via model fitting. Features in the lensing curve that could be associated with curvature of the caustic, nearness of a cusp, or the influence of nearby caustics are noted. 相似文献
5.
The results of JHKLM photometry of two carbon stars are presented: the irregular variable NQ Cas and the Mira star BD Vul. Data on the mean fluxes supplemented with mid-IR observations with the IRAS, AKARI, andWISE satellites are used to compute spherically symmetrical model dust envelopes for the stars, consisting of particles of amorphous carbon and silicon carbide. The optical depth in the visible for the comparatively cool dust envelope of BD Vul, with a dust temperature at its inner boundary T1 = 610 K, is fairly low: τV = 0.13. The dust envelope of NQ Cas is appreciably hotter (T1 = 1550 K), and has τV = 0.32. The estimated mass-loss rates are 1.5 × 10?7M⊙/yr for NQ Cas and 5.9 × 10?7M⊙/yr for BD Vul. 相似文献
6.
Brightness and color variations of V1016 Cyg are studied using many years of UBVRJHKLM photometric observations and information about its spectral energy distribution in the intermediate IR (7.7 to 22.7 µm) obtained with the IRAS and ISO low-resolution spectrometers. Models for its stationary, spherically symmetrical, extended dust envelope are computed for two cases of heating: by the radiation of the cool component only and by the combined radiation from both components. Model fitting of the IRAS and ISO observations shows that the model with a single central source—the Mira star—provides a better fit to the data, indicating that the hot component’s radiation is appreciably reprocessed by the ambient gas medium and has almost no direct influence on the IR spectrum of the symbiotic nova. The mean spectral energy distributions measured by IRAS in 1983 and ISO on October 1, 1996, differ considerably. The observed evolution of the envelope’s spectrum probably reflects an increasing grain concentration and decreasing grain temperature at the inner edge of the envelope, associated with decreased luminosity and increased temperature of the hot component. The total mass-loss rate, gas-expansion velocity at the outer edge of the envelope, and upper limit to the mass of the central radiation source are estimated. 相似文献
7.
The brightness and color variations of the symbiotic star CH Cygni are studied, and its stationary, spherically symmetric, extended dust envelope is modeled based on long-term UBVRJHKLM photometry, the mid-IR spectral energy distribution (7–23 µm), and far-IR fluxes measured by IRAS and ISO. The existence of a hot dust envelope, detected earlier in the near IR, is confirmed; the optical depth of the envelope has probably increased with time. Model fits to the IRAS and ISO data indicate that the V-band optical depth increased from 0.22 to 0.41 due to dust density enhancement during the 14 years between the observations by the two spacecraft. The mass-loss rate, gas-expansion velocity at the outer boundary of the envelope, and upper limit of the mass of the central source of emission are estimated assuming that the stellar wind of the system is driven by the pressure of the red giant's radiation on the dust, with subsequent momentum transfer to the gaseous medium. 相似文献
8.
We use JHKLM photometric data obtained in 1998–2001 to model the dust envelope of the unique object FG Sge, which formed around the star after several consecutive cycles of dust condensation beginning in Autumn 1992. Models with a spherically symmetric, extended envelope consisting of a mixture of spherical particles of amorphous carbon and silicon carbide with an MRN size distribution were fitted to match the mean observed spectral energy distributions of FG Sge during brightness maximum and minimum after 1998 for two values of the luminosity and effective temperature of the central star. The stellar-wind parameters and mass-loss rate have been estimated in each case. The observational data for the brightness maximum and minimum cannot be described by models with a fixed luminosity or fixed distance to the star. This is a consequence of the object’s unusual behavior, with synchronous flux decreases in all the observed bands. The inability of the model to adequately describe the minimum-brightness state is probably associated with the abrupt disruption of the spherical symmetry of the envelope due to the formation of a small, dense dust cloud in the line of sight. 相似文献
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Vernikovskaya A. E. Vernikovsky V. A. Matushkin N. Yu. Kadilnikov P. I. Metelkin D. V. Li Z.-X. Wilde S. A. Romanova I. V. Bogdanov E. A. 《Doklady Earth Sciences》2019,489(1):1285-1288
Doklady Earth Sciences - An Ediacaran complex of dike rocks has been identified for the first time in the Yenisei Ridge orogen. These igneous rocks are represented by basic, intermediate and acidic... 相似文献
10.
V. V. Bogdanov A. V. Pavlov A. L. Polyukhova 《Journal of Volcanology and Seismology》2010,4(6):412-422
The catalog of Kamchatka earthquakes is represented as a probability space of three objects {Ω, $
\tilde F
$
\tilde F
P}. Each earthquake is treated as an outcome ω
i
in the space of elementary events Ω whose cardinality for the period under consideration is given by the number of events.
In turn, ω
i
is characterized by a system of random variables, viz., energy class ki, latitude φ
i
, longitude λ
i
, and depth h
i
. The time of an outcome has been eliminated from this system in this study. The random variables make up subsets in the set
$
\tilde F
$
\tilde F
and are defined by multivariate distributions, either by the distribution function $
\tilde F
$
\tilde F
(φ, λ, h, k) or by the probability density f(φ, λ, h, k) based on the earthquake catalog in hand. The probabilities P are treated in the frequency interpretation. Taking the example of a recurrence relation (RR) written down in the form of
a power law for probability density f(k), where the initial value of the distribution function f(k
0) is the basic data [Bogdanov, 2006] rather than the seismic activity A
0, we proceed to show that for different intervals of coordinates and time the distribution f
elim(k) of an earthquake catalog with the aftershocks eliminated is identical to the distribution f
full(k), which corresponds to the full catalog. It follows from our calculations that f
0(k) takes on nearly identical numeral values for different initial values of energy class k
0 (8 ≤ k
0 ≤ 12) f(k
0). The difference decreases with an increasing number of events. We put forward the hypothesis that the values of f(k
0) tend to cluster around the value 2/3 as the number of events increases. The Kolmogorov test is used to test the hypothesis
that statistical recurrence laws are consistent with the analytical form of the probabilistic RR based on a distribution function
with the initial value f(k
0) = 2/3. We discuss statistical distributions of earthquake hypocenters over depth and the epicenters over various areas for
several periods 相似文献