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21.
The stoichiometry and stability of arsenic gaseous complexes were determined in the system As-H2O ± NaCl ± HCl ± H2S at temperatures up to 500°C and pressures up to 600 bar, from both measurements of As(III) and As(V) vapor-liquid and vapor-solid partitioning, and X-ray absorption fine structure (XAFS) spectroscopic study of As(III)-bearing aqueous fluids. Vapor-aqueous solution partitioning for As(III) was measured from 250 to 450°C at the saturated vapor pressure of the system (Psat) with a special titanium reactor that allows in situ sampling of the vapor phase. The values of partition coefficients for arsenious acid (H3AsO3) between an aqueous solution (pure H2O) and its saturated vapor (K = mAsvapor /mAsliquid) were found to be independent of As(III) solution concentrations (up to ∼1 to 2 mol As/kg) and equal to 0.012 ± 0.003, 0.063 ± 0.023, and 0.145 ± 0.020 at 250, 300, and 350°C, respectively. These results are interpreted by the formation, in the vapor phase, of As(OH)3(gas), similar to the aqueous As hydroxide complex dominant in the liquid phase. Arsenic chloride or sulfide gaseous complexes were found to be negligible in the presence of HCl or H2S (up to ∼0.5 mol/kg of vapor). XAFS spectroscopic measurements carried out on As(III)-H2O (±NaCl) solutions up to 500°C demonstrate that the As(OH)3 complex dominates As speciation both in dense H2O-NaCl fluids and low-density supercritical vapor. Vapor-liquid partition coefficients for As(III) measured in the H2O-NaCl system up to 450°C are consistent with the As speciation derived from these spectroscopic measurements and can be described by a simple relationship as a function of the vapor-to-liquid density ratio and temperature. Arsenic(III) partitioning between vapor and As-concentrated solutions (>2 mol As/kg) or As2O3 solid is consistent with the formation, in the vapor phase, of both As4O6 and As(OH)3. Arsenic(V) (arsenic acid, H3AsO4) vapor-liquid partitioning at 350°C for dilute aqueous solution was interpreted by the formation of AsO(OH)3 in the vapor phase.The results obtained were combined with the corresponding properties for the aqueous As(III) hydroxide species to generate As(OH)3(gas) thermodynamic parameters. Equilibrium calculations carried out by using these data indicate that As(OH)3(gas) is by far the most dominant As complex in both volcanic gases and boiling hydrothermal systems. This species is likely to be responsible for the preferential partition of arsenic into the vapor phase as observed in fluid inclusions from high-temperature (400 to 700°C) Au-Cu (-Sn, -W) magmatic-hydrothermal ore deposits. The results of this study imply that hydrolysis and hydration could be also important for other metals and metalloids in the H2O-vapor phase. These processes should be taken into account to accurately model element fractionation and chemical equilibria during magma degassing and fluid boiling.  相似文献   
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23.
Abstract– To better explain the unusual distribution and relative abundances of several 6‐ and 7‐carbon amino acids found in meteorites, their thermodynamic properties were studied using accurate ab initio techniques. In addition to optimized structures and relative energies, vibrational frequency and thermochemical analysis of different diastereomers were performed at temperatures relevant to conditions of synthesis of these amino acids in meteorites. The results of calculations were compared with the measured content of the amino acids in the Murchison meteorite. The distribution of several longer chain amino acids in meteorites seems to point to at least some thermodynamic control in their formation. For diastereomeric compounds, on the other hand, the comparison suggests that their synthetic conditions, or those of their precursors, were far from thermodynamic equilibrium.  相似文献   
24.
Lithostratigraphic correlation of a 6–10‐km‐thick Aptian–Maastrichtian terrigenous sequence of the East Asian continental margin and Sakhalin and Hokkaido Islands has revealed the existence of a single marine basin. This basin was populated by mixed Tethyan–Boreal fauna and sloped eastward until the Middle Cenomanian. Intense volcanic and tectonic processes caused the uplift of the continental margin in the mid‐Albian to Cenomanian and eastward migration of the shoreline. Paleobotanical studies have discovered a number of climatic changes. Relatively warm conditions existed in the Aptian, changing to cooler conditions in the Early Albian. The maximum warming occurred from the Late Albian to Cenomanian when large‐leaved flowering plants dominated the population. In the Late Cretaceous, the East Asian volcanic belt created a mountain edifice up to 3000 m high, which controlled longitudinal climatic and floral zonation. This control was more efficient than the latitudinal control. A wide development of flowering Platanaceae flora in the Turonian points to a relative cooling. The floral assemblage shows a temperate climate from the Early Coniacian onwards, with an optimum in the Campanian that is consistent with global transgression. As a result of the warm climate, the early Maastrichtian is characterized by highly diverse biota. Furthermore, in the middle Maastrichtian floral and faunal diversity decreased and the seasonal prevalence increased. Cooling occurred in the latest Maastrichtian. Five periods of coal accumulation are recognized throughout the Late Cenomanian to Late Maastrichtian. Shelf, deltaic, and slope turbidite facies of the continental margin contain organic carbon ranging from 0.3% to 2.2%, which together with direct evidence for oil and gas, are believed to be prolific for hydrocarbon exploration.  相似文献   
25.
The possible low-frequency radio emission from the progenitors of gamma ray bursts can experience a delay from tens of seconds to hours on the way to the observer due to the dispersion in galactic and extragalactic plasma, and thus reach the observer as a radio afterglow of the burst. This opens a unique possibility (peculiar “time machine”) of seeing what happened at that place before the catastrophe.  相似文献   
26.
tWe analyse continuous measurements of groundwater level in two deep wells VS-3 and V-28 at the experimental hydro-meteorological station situated on the NE margin of the Bohemian Massif, central Europe, characterized by the weak intraplate seismic activity. The aim of our study is to examine the relationships between changes in the groundwater level and earthquake occurrence. Based on the tidal and barometric response of the water level, we estimated selected elastic parameters of the observed aquifers: the shear modulus G, the Skempton ratio B, the drained matrix compressibility β and the undrained compressibility βu. Using these parameters and assuming the homogeneous poroelastic material, we derived the sensitivity of the wells to the crustal volume strain. During the observation period from November 1998 to December 2005 we detected in the VS-3 well two pre-seismic steps, related to August 10, 2005 (M = 2.4) and October 25, 2005 (M = 3.3) earthquakes. Amplitudes of the recorded precursory changes (+6 cm and +15 cm) are several times higher than the values predicted from the theoretical precursory crustal strain and the strain sensitivity of the well. Therefore, we presume that the observed pre-seismic water level steps can be attributed to heterogeneity of poroelastic material. We consequently propose the hypothesis of the origin of precursory events based on the presumption of a sensitive site, at which the well is situated.  相似文献   
27.
During two sampling seasons we analyzed on weekly basis fatty acid (FA) composition of seston fraction <130 μm and zooplankton fraction >130 μm, and compared them using a multivariate canonical correlation analysis (CCA). Besides, we evaluated a possible impact of water temperature and inorganic nutrients on FA composition of the seston and the zooplankton.In spite of significant differences in percentages of several individual FAs, we found very strong canonical correlation (cross-correlation, 1-week lag) between FA composition of the seston and the zooplankton. The most important factor, providing the overall canonical cross-correlation between FA profiles of the seston and the zooplankton fractions was eicosapentaenoic acid (20:5ω3, EPA). FA composition of the zooplankton fraction had comparatively poor correlations with taxonomic composition of the zooplankton. Thus, seasonal variations of FA composition of the zooplankton were determined primarily by seasonal changes in FA composition of the seston, rather than by taxonomic differences of FA profiles between rotifers, cyclopoids and cladocerans. FA composition of the seston was strongly affected by its taxonomic composition, namely by that of phytoplankton. According to CCA, the highest factor loadings pertained to diatoms interacting with their marker acids, including EPA, and cyanobacteria and greens, interacting with their marker acids. Ciliates and small rotifers composed considerable and sometimes major part of the seston biomass, but according to CCA their contributions to seasonal variations of the total FA profile of the seston were insignificant. This finding indirectly support the conclusion of the other authors, that the main source of FAs presented in ciliates and rotifers must be sought in algae and that they do not modify FA composition of food consumed, apart from repackaging it.Water temperature was the principal environmental parameter which drove the overall variations of FA composition. Factor loadings for the inorganic nutrients were comparatively negligible. The main contribution in the seasonal variation of FA composition of the seston was given by negative interaction between water temperature and percentage of EPA in the seston.  相似文献   
28.
Quantitative diatom abundance and species composition was studied in the longest 81-m Lake Hovsgol drill core, HDP-04. Lake Hovsgol diatom biostratigraphy of the past 1 Ma includes 14 local diatom assemblage zones (LDAZ). Planktonic diatom flora of Lake Hovsgol is dominated by members of Stephanodiscus and Cyclotella. A large-scale shift from Stephanodiscus-dominated to Cyclotella-dominated flora occurred in the mid-Brunhes chron. Significant morphological variability of Cyclotella ocellata complex and Cyclotella cf. minuta, as well as the presence of new extinct endemic taxa of genus Stephanodiscus, suggest long speciation and/or adaptation history of diatom flora. The recognition of taxa morphologically similar to the extinct endemic species of Lake Baikal suggests potential correlation ties between Lake Hovsgol and Lake Baikal diatom biostratigraphies around the MIS 17, MIS 25, and, possibly, MIS 15 interglacial intervals. Narrow peaks of diatom abundance in the Lake Hovsgol sedimentary record are episodic and short-lived. These peaks may represent humid optima of past interglacials and/or interstadials, characterized by elevated surface runoff in the Hovsgol basin and relative highstands of the lake.  相似文献   
29.
Tectonic reconstructions based on the geodynamic analysis of geologic, paleomagnetic, structural and kinematic data of Cenozoic age from the western Bering Sea region are proposed in the present paper. The most active tectonic and magmatic processes took place in the Komandorsky segment of the Bering Sea, exemplified by the Late Cretaceous–Early Eocene Olutorsky Arc and Eocene–Oligocene Govena–Karaginsky Arc, which was built on the structures of the Olutorsky Arc. A model of the complex collision of these two arcs with the paleocontinental margin, which considers rotations of the geological blocks from the various structural zones of the western margin of the Bering Sea in the horizontal plane (paleomagnetic data), was proposed by the authors. According to this model the collision of the flanks of the Olutorsky and Govena–Karaginsky arcs took place in the Eocene, before the collision of the central parts in the Miocene.  相似文献   
30.
This is a memorial report on the biography and scientific heritage of M.A. Svechnikov — an outstanding scientist and teacher, the founder of the Ural school of close binary stars and the author of the classification scheme for eclipsing variable stars.  相似文献   
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