A review of volatile compounds in tektites,and carbon content and isotopic composition of moldavite glass     

Karel ŽÁK  Roman SKÁLA  Zdeněk ŘANDA  Jiří MIZERA 《Meteoritics & planetary science》2012,47(6):1010-1028

Abstract– Tektites, natural silica‐rich glasses produced during impact events, commonly contain bubbles. The paper reviews published data on pressure and composition of a gas phase contained in the tektite bubbles and data on other volatile compounds which can be released from tektites by either high‐temperature melting or by crushing or milling under vacuum. Gas extraction from tektites using high‐temperature melting generally produced higher gas yield and different gas composition than the low‐temperature extraction using crushing or milling under vacuum. The high‐temperature extraction obviously releases volatiles not only from the bubbles, but also volatile compounds contained directly in the glass. Moreover, the gas composition can be modified by reactions between the released gases and the glass melt. Published data indicate that besides CO₂ and/or CO in the bubbles, another carbon reservoir is present directly in the tektite glass. To clarify the problem of carbon content and carbon isotopic composition of the tektite glass, three samples from the Central European tektite strewn field—moldavites—were analyzed. The samples contained only 35–41 ppm C with δ¹³C values in the range from ?28.5 to ?29.9‰ VPDB. This indicates that terrestrial organic matter was a dominant carbon source during moldavite formation.  相似文献   

Benthic Phosphorus Dynamics in the Gulf of Finland, Baltic Sea     

Lena Viktorsson  Elin Almroth-Rosell  Anders Tengberg  Roman Vankevich  Ivan Neelov  Alexey Isaev  Victor Kravtsov  Per O. J. Hall 《Aquatic Geochemistry》2012,18(6):543-564

Benthic fluxes of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) were measured in situ using autonomous landers in the Gulf of Finland in the Baltic Sea, on four expeditions between 2002 and 2005. These measurements together with model estimates of bottom water oxygen conditions were used to compute the magnitude of the yearly integrated benthic SRP flux (also called internal phosphorus load). The yearly integrated benthic SRP flux was found to be almost 10 times larger than the external (river and land sources) phosphorus load. The average SRP flux was 1.25?±?0.56?mmol?m^?2?d^?1 on anoxic bottoms, and ?0.01?±?0.08?mmol?m^?2?d^?1 on oxic bottoms. The bottom water oxygen conditions determined whether the SRP flux was in a high or low regime, and degradation of organic matter (as estimated from benthic DIC fluxes) correlated positively with SRP fluxes on anoxic bottoms. From this correlation, we estimated a potential increase in phosphorus flux of 0.69?±?0.26?mmol?m^?2?d^?1 from presently oxic bottoms, if they would turn anoxic. An almost full annual data set of in situ bottom water oxygen measurements showed high variability of oxygen concentration. Because of this, an estimate of the time which the sediments were exposed to oxygenated overlying bottom water was computed using a coupled thermohydrodynamic ocean?Csea and ecosystem model. Total phosphorus burial rates were calculated from vertical profiles of total phosphorus in sediment and sediment accumulation rates. Recycling and burial efficiencies for phosphorus of 97 and 3%, respectively, were estimated for anoxic accumulation bottoms from a benthic mass balance, which was based on the measured effluxes and burial rates.  相似文献   

Impacts of Hypoxia on Zooplankton Spatial Distributions in the Northern Gulf of Mexico     

M. R. Roman  J. J. Pierson  D. G. Kimmel  W. C. Boicourt  X. Zhang 《Estuaries and Coasts》2012,35(5):1261-1269

The northern Gulf of Mexico (NGOMEX) was surveyed to examine the broad-scale spatial patterns and inter-relationships between hypoxia (<2?mg?L^?1 dissolved oxygen) and zooplankton biovolume. We used an undulating towed body equipped with sensors for conductivity, temperature, depth, oxygen, fluorescence, and an optical plankton counter to sample water column structure, oxygen, and zooplankton at high spatial resolution (1?m??vertical; 0.25?C1?km??horizontal). We contrast the distribution of zooplankton during summer surveys with different freshwater input, stratification, and horizontal and vertical extent of bottom-water hypoxia. Bottom-water hypoxia did not appear to influence the total amount of zooplankton biomass present in the water column or the areal integration of zooplankton standing stock in the NGOMEX region surveyed. However, where there were hypoxic bottom waters, zooplankton shifted their vertical distribution to the upper water column during the day where they normally would reside in deeper and darker waters. When bottom waters were normoxic (>2?mg?L^?1 dissolved oxygen), the daytime median depth of the water column zooplankton was on average 7?m deeper than the median depth of zooplankton in water columns with hypoxic bottom waters. A reduction in larger zooplankton when there were hypoxic bottom waters suggests that if zooplankton cannot migrate to deeper, darker water under hypoxic conditions, they may be more susceptible to size-selective predation by visual predators. Thus, habitat compression in the northern Gulf of Mexico due to hypoxic bottom water may have implications for trophic transfer by increasing the contact between predators and prey.  相似文献   

Erratum to: Orbital structure of the GJ876 extrasolar planetary system based on the latest Keck and HARPS radial velocity data     

Roman V. Baluev 《Celestial Mechanics and Dynamical Astronomy》2013,117(2):215-215

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Crystal structure of meteoritic schreibersites: determination of absolute structure     

Roman Skála  Ivana Císařová 《Physics and Chemistry of Minerals》2005,31(10):721-732

Minerals of the schreibersite–nickelphosphide series (Fe,Ni)₃P crystallize in the non-centrosymmetric space group . As a consequence, they can possess two different spatial arrangements of the constituting atoms within the unit cell, related by the inversion symmetry operation. Here, we present the crystal structure refinements from single crystal X-ray diffraction data for schreibersite grains from iron meteorites Acuña, Carlton, Hex River Mts. (three different crystals), Odessa (two different crystals), Sikhote Alin, and Toluca aiming for the determination of the absolute structure of the examined crystals. The crystals studied cover the composition range from ~58 mol% to ~80 mol% Fe₃P end-member. Unit-cell parameter a and volume of the unit cell V, as well as certain topological structural parameters tightly correlate with Fe₃P content. Unit-cell parameter c, on the other hand, does not show such strong correlation. Eight of the nine crystal structure refinements allowed unambiguous absolute structure assignment. The single crystal extracted from Toluca is, however, of poor quality and consequently the structure refinement did not provide as good results as the rest of the materials. Also, this crystal has only weak inversion distinguishing power to provide unequivocal absolute structure determination. Six of the eight unambiguous absolute structure determinations indicated inverted atomic arrangement compared to that reported in earlier structure refinements (here called standard). Only two grains, one taken from Odessa iron and the other from the Hex River Mts. meteorite, reveal the dominance of standard crystal structure setting.  相似文献   

An iterative algorithm for interactive multiobjective programming     

Shlomo P. Neuman  Roman Krzysztofowicz 《Advances in water resources》1977,1(1):1-14

A new iterative algorithm for interactive multiobjective programming is proposed. The algorithm is based on the Lagrange multiplier technique of generating noninferior solutions, and it is shown to converge under certain conditions. It reduces a complex multiobjective problem into a sequence of two-objective problems which the decision maker can handle more easily. The number of two-objective problems with which the decision maker is confronted, as well as the total number of noninferior solutions that must be generated, increase more or less linearly with the number of objectives. Computational efficiency is further enhanced by avoiding the need for regression. The decision maker interacts with the model directly in the functional space, and he is not required to translate his judgment of relative worth into numbers. Due to the iterative nature of the algorithm, the decision maker can articulate his preferences in a progressive manner. Furthermore, he may modify his attitude at any stage of the computation, based on partial results, without adversely affecting the quality of the solution. An example problem previously solved by other methods, including the surrogate worth trade-off approach, is used to illustrate the new algorithm.  相似文献   

Asymmetric continuum and anisotropy     

Roman Teisseyre 《Acta Geophysica》2006,54(3):225-238

We present a relation between stress moments and antisymmetric part of stresses and the related constitutive law joining those stresses with the particle/point rotations. Correspondence of the asymmetric continuum theory to the micromorphic theory is considered. An extension of the asymmetric continuum theory for the case of 2D anisotropy for antisymmetric stresses leads us to the problems of friction anisotropy and fracture pattern.  相似文献   

Monitoring food web changes in tide-restored salt marshes: A carbon stable isotope approach     

Andrew S. Wozniak  Charles T. Roman  Sam C. Wainright  Richard A. McKinney  Mary-Jane James-Pirri 《Estuaries and Coasts》2006,29(4):568-578

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, andFundulus heteroclitus isotope values (δ¹³C, δ¹⁵N, δ³⁴S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes. Study sites, located throughout the southern New England region (USA), ranged fromSpartina alterniflora-dominated reference marshes, marshes under various regimes and histories of tide restoration, and a severely tide-restrictedPhragmites australis marsh.Fundulus δ¹³C values were greater for fish from referenceSpartina marshes than for fish from adjacent tide-restricted or tide-restored marshes where higher percent cover of C₃ plants, lower water column salinities, and more negative dissolved inorganic δ¹³C values were observed. The difference inFundulus δ¹³C values between a tide-restrictedPhragmites marsh and an adjacent referenceSpartina marsh was great compared to the difference between marshes at various stages of tide restoration and their respective reference marshes, suggesting that food web support functions are restored as the degree of tidal restriction is lessened. While a multiple isotopic approach can provide valuable information for determining specific food sources to consumers, this study demonstrates that monitoringFundulus δ¹³C values alone may be useful to evaluate the trajectory of ecological change for marshes undergoing tidal restoration.  相似文献   

Aridic crusts and vein mineralisations in the playa Areg el Makrzene, South Tunisia     

Roman Fromm  Tarek Hachicha  Werner Smykatz-Kloss   《Chemie der Erde / Geochemistry》2005,65(4):357-373

The playa Areg el Makrzene is situated in the north of the escarpment of the Djebel Rehach in southern Tunisia. It is characterised by more than 70 spring mounds which are bound to faults in the Triassic sandstone, and by (sub-) recent calcareous and iron hydroxide precipitations. The artesian spring water contains high amounts of Na⁺, Ca²⁺, Mg²⁺ and Cl⁻, SO₄²⁻, and HCO₃, shows slightly alkaline character and a temperature of 25 °C. The spring mounds consist of porous travertine (calcite), goethite, gypsum and of Na–Mg evaporites and are up to 10 m high. Few metres away from the springs the amorphous iron hydroxides have altered to badly ordered goethite and ferrihydrite and finally to well ordered goethite. The muddy precipitate has altered to hard crusts (calcrete, ferricrete). The source of the precipitated material is discussed.

The faults in the sandstone are filled with (hydr-)oxides of iron and manganese, e.g. with goethite, hollandite and pyrolusite. The amount of Mn-oxides may reach 60 mass%.  相似文献