Organic tracers from biomass burning in atmospheric particulate matter over the ocean     

Bernd R. T. Simoneit  Vladimir O. Elias   《Marine Chemistry》2000,69(3-4)

Particulate matter from the atmosphere over the Atlantic Ocean along the South American and African Continents has been analyzed for organic tracers from natural and biomass burning emissions. The major biomarker compounds characterized are natural products from continental vegetation consisting primarily of epicuticular wax components. For example, n-alkanes ranged from C₂₅ to C₃₅, with an odd carbon number predominance and carbon maxima (C_max) at 29 or 31. Concentrations of n-alkanes varied from 0.3 to 680 ng/m³. Nevertheless, n-alkanols are the dominant terrestrial tracers in almost all samples (concentrations from 0.1 to 780 ng/m³) and ranged from C₂₂ to C₃₄ with an even carbon number predominance. Despite the major presence of the natural tracers, organic components from biomass burning emissions are also present in the particulate matter. The major tracers from this source are thermal degradation products from the biopolymer cellulose, namely the dianhydromonosaccharide derivatives levoglucosan, galactosan, and mannosan. In general, the concentrations of levoglucosan, the major derivative from this source in all samples, varied from 0.0008 to 0.15 ng/m³ in atmospheric samples collected over the ocean and from 0.04 to 4860 ng/m³ in terrestrial particulate matter, used as reference in this study. Dehydroabietic acid, another marker compound emitted from burning of Gymnosperm fuel, is also detectable in most oceanic samples at concentrations ranging from 0.0001 to 0.4 ng/m³, whereas in terrestrial aerosol particulate matter, this component is present at much higher concentrations (0.23–440 ng/m³). The presence of these tracers in atmospheric particulate matter over the ocean confirms the long-range transport of smoke from biomass burning off the continents.  相似文献   

Discrete simulations of a triaxial compression test for sand by DEM     

Jan Kozicki  Jacek Tejchman  Hans‐Bernd Mühlhaus 《国际地质力学数值与分析法杂志》2014,38(18):1923-1952

A quasi‐static homogeneous drained triaxial compression test on cohesionless sand under constant lateral pressure was simulated using a three‐dimensional discrete element method. Grains were modelled by means of particle clusters composed of rigid spheres or spheres with contact moments imitating irregular particle shapes. Attention was paid to the effect of initial void ratio and grain shape mixture on the shear strength, volume changes, force chains, kinetic, elastic and dissipated energies. In addition, the effect of the mean grain size, grain size distribution, grain size range, specimen size and roughness and stiffness of boundaries was numerically analysed in initially dense sand. Some numerical results were compared with available experimental results. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Engelhauptite,KCu3(V2O7)(OH)2Cl,a new mineral species from Eifel,Germany     

Igor V. Pekov  Oleg I. Siidra  Nikita V. Chukanov  Vasiliy O. Yapaskurt  Sergey N. Britvin  Sergey V. Krivovichev  Willi Schüller  Bernd Ternes 《Mineralogy and Petrology》2015,109(6):705-711

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Hydraulic properties of peat soils along a bulk density gradient—A meta study     

Haojie Liu  Bernd Lennartz 《水文研究》2019,33(1):101-114

Our understanding of hydraulic properties of peat soils is limited compared with that of mineral substrates. In this study, we aimed to deduce possible alterations of hydraulic properties of peat soils following degradation resulting from peat drainage and aeration. A data set of peat hydraulic properties (188 soil water retention curves [SWRCs], 71 unsaturated hydraulic conductivity curves [UHCs], and 256 saturated hydraulic conductivity [K_s] values) was assembled from the literature; the obtained data originated from peat samples with an organic matter (OM) content ranging from 23 to 97 wt% (weight percent; and according variation in bulk density) representing various degrees of peat degradation. The Mualem‐van Genuchten model was employed to describe the SWRCs and UHCs. The results show that the hydraulic parameters of peat soils vary over a wide range confirming the pronounced diversity of peat. Peat decomposition significantly modifies all hydraulic parameters. A bulk density of approximately 0.2 g cm^?3 was identified as a critical threshold point; above and below this value, macroporosity and hydraulic parameters follow different functions with bulk density. Pedotransfer functions based on physical peat properties (e.g., bulk density and soil depth) separately computed for bog and fen peat have significantly lower mean square errors than functions obtained from the complete data set, which indicates that not only the status of peat decomposition but also the peat‐forming plants have a large effect on hydraulic properties. The SWRCs of samples with a bulk density of less than 0.2 g cm^?3 could be grouped into two to five classes for each peat type (botanical composition). The remaining SWRCs originating from samples with a bulk density of larger than 0.2 g cm^?3 could be classified into one group. The Mualem‐van Genuchten parameter values of α can be used to estimate K_s if no K_s data are available. In conclusion, the derived pedotransfer functions provide a solid instrument to derive hydraulic parameter values from easily measurable quantities; however, additional research is required to reduce uncertainty.  相似文献   

Dimensionally reduced flow models in fractured porous media: crossings and boundaries     

Nicolas Schwenck  Bernd Flemisch  Rainer Helmig  Barbara I. Wohlmuth 《Computational Geosciences》2015,19(6):1219-1230

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Fluid-inclusion microthermometry and the Zr-in-rutile thermometer for hydrothermal rutile     

Alexandre Raphael Cabral  Francisco Javier Rios  Lucilia Aparecida Ramos de Oliveira  Francisco Robério de Abreu  Bernd Lehmann  Thomas Zack  František Laufek 《International Journal of Earth Sciences》2015,104(2):513-519

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Shells of Paphia undulata (Bivalvia) from the South China Sea as potential proxy archives of the East Asian summer monsoon: a sclerochronological calibration study     

Lina Yan  Bernd R. Schöne  Shengrong Li  Yan Yan 《Journal of Oceanography》2014,70(1):35-44

The climate of the South China Sea is dominated by the East Asian monsoon (EAM) system. Existing paleoclimate reconstructions offered an excellent insight into longer-term EAM variations. However, due to a lack of appropriate high-resolution paleoclimate data, relatively little is known about the frequency and strength of EAM extremes during the Holocene. To evaluate and establish a potential proxy archive for past variations of the EAM on shorter time-scales, we have carried out a calibration study on shells of the bivalve mollusk, Paphia undulata (Born 1778) from Daya Bay, China. This species has a short lifespan (3 years). Shells grow uninterruptedly between February/March and mid-November and are formed near oxygen isotopic (δ¹⁸O) equilibrium with the ambient environment. Shell growth patterns, δ¹⁸O_shell and δ¹³C_shell values, can be used to estimate the relative amount of precipitation and terrestrial runoff. Therefore, shells of this species can provide reliable, sub-seasonally resolved data on past East Asian summer monsoon strengths. The feasibility of this method has been tested with two Holocene shells from sediment cores taken from the nearby Beibu Gulf. A rather peculiar finding is that shell growth of P. undulata seems to be largely uncoupled to measured local environmental variables. Growth rates are negatively correlated to seawater temperature and chlorophyll a levels and positively to salinity. It is hypothesized here that extraordinary fast shell growth in early spring (February/March; low temperature and primary productivity) are facilitated by preserved energy resources, ensuring that the bivalve quickly reaches the predation window and the required size for reproduction.  相似文献   

The oxidation state of sulfur in magmatic fluids     

Bernd Binder  Hans Keppler 《Earth and Planetary Science Letters》2011,301(1-2):190-198

Sulfur compounds in volcanic gases are responsible for the global cooling after explosive eruptions and they probably controlled the early evolution of the Earth's atmosphere. We have therefore studied the oxidation state of sulfur in aqueous fluids under the pressure and temperature conditions and oxygen fugacities typical for magma chambers (0.5–3 kbar, 650–950 °C, Ni–NiO to Re–ReO₂ buffer conditions). Sulfur speciation was determined by Raman spectroscopy of quenched fluids trapped as inclusions in quartz. Our results show that sulfur in hydrothermal fluids and volcanic gases is much more oxidized than previously thought and in particular, some explosive eruptions may release a significant fraction of sulfur as SO₃ or its hydrated forms. In the pressure range from 500 to 2000 bar, the equilibrium constant K₁ of the reaction 2H₂S + 3O₂ = 2SO₂ + 2H₂O in aqueous fluids can be described by lnK₁ = ?(57.1 ± 7.1) + (173,480 ± 7592)T^? 1, where T is temperature in Kelvin. The equilibrium constant K₂ for the reaction SO₂ + ½O₂ = SO₃ in aqueous fluids, where SO₃ may include hydrated forms, such as H₂SO₄, was found to be strongly pressure dependent, with lnK₂ = ?(5.2 ± 5.7) + (19,243 ± 5993)T^? 1 at 1500 bar; lnK₂ = ?(11.1 ± 1.3) + (25,383 ± 1371)T^? 1 at 2000 bar and lnK₂ = ?(22.1 ± 2.2) + (37,082 ± 2248)T^? 1 at 2500 bar. Our data imply that volcanoes may directly inject hexavalent sulfur in the form of H₂SO₄ into the atmosphere, not only on Earth, but possibly also on Venus and on Mars, when it was still tectonically active. Remote measurements from satellites may have underestimated the sulfur yield of some recent eruptions. Moreover, the mechanisms of the interaction of volcanic gases with the stratosphere need to be reconsidered.  相似文献   

The geochemistry of aliphatic and polar organic tracers in sediments from Lake Bera, Malaysia     

Noorhazlina Abu BakarKheng Soo Tay  Nasr Yousef M.J. OmarM. Radzi Bin Abas  Bernd R.T. Simoneit 《Applied Geochemistry》2011,26(8):1433-1445

The molecular distributions of homologous aliphatic lipid compounds (n-alkanes, n-alkanoic acids, n-alkanols, n-alkanals and n-alkan-2-ones) were investigated in sediments of Lake Bera, Malaysia as well as in plant waxes from the vicinity using gas chromatography-mass spectrometry. In addition, triterpenoids of the oleanane, ursane, lupane and friedelane series, and their diagenetic products were also identified. Using the aquatic proxy P_aq, it was found that the n-alkanes present in surface sediments S1, S5 and S6 correspond to an input from emergent macrophytes, whereas in sediments collected from open water (S2, S3 and S4) they correspond to input from submerged/floating macrophytes. The presence of n-alkan-2-ols, a commonly found homologous series in the sediments as well as in the plant wax, is novel here. In addition, the presence of 24-methylcycloart-22-enol and 24-ethylcycloart-22-enol in sediments as well as the plant wax of Pandanus helicopus, a dominant reed around the lake, also supports the input of plant biomarkers to the sediments. The occurrence of 5-membered ring triterpenoid derivatives as major diagenetic products of the triterpenoids identified (e.g. friedelan-2,3-dione) shows that the degradation of the organic matter in the sediments occurs mainly under oxic conditions. Also, the presence of ring-A degraded triterpenoids (dihydroputranjivic acid, 3-nor-2,4-seco-friedelane, 4α- and 4β-3-norfriedelanes, A-norfriedel-10-one, and A-norfriedel-8-en-10-one) and the aromatized triterpenoid hydrocarbons (mono- and triaromatic derivatives) as minor diagenetic products indicates photochemical and microorganism-mediated alteration reactions of natural products in the sediments. Additional novel polyfunctional friedelane derivatives, namely friedelane-2,3-dione, friedelane-1,3-diol-2-one and friedel-1(10)-ene-1,3-diol-2-one were identified for the first time in this study. These novel polyfunctional triterpenoids were inferred to derive from the oxidation of the triterpenoids from higher plants in this oxic tropical environment. For future reference purposes, the mass spectra of the identified polar triterpenoids are also presented here. This study provides important data on the biogeochemistry of organic matter in a tropical lake of SE Asia.  相似文献   

Nonlinear Force-Free Magnetic Field Extrapolations: Comparison of the Grad Rubin and Wheatland Sturrock Roumeliotis Algorithm     

Bernd Inhester  Thomas Wiegelmann 《Solar physics》2006,235(1-2):201-221

We compare the performance of two alternative algorithms which aim to construct a force-free magnetic field given suitable boundary conditions. For this comparison, we have implemented both algorithms on the same finite element grid which uses Whitney forms to describe the fields within the grid cells. The additional use of conjugate gradient and multigrid iterations result in quite effective codes. The Grad Rubin and Wheatland Sturrock Roumeliotis algorithms both perform well for the reconstruction of a known analytic force-free field. For more arbitrary boundary conditions the Wheatland Sturrock Roumeliotis approach has some difficulties because it requires overdetermined boundary information which may include inconsistencies. The Grad Rubin code on the other hand loses convergence for strong current densities. For the example we have investigated, however, the maximum possible current density seems to be not far from the limit beyond which a force-free field cannot exist anymore for a given normal magnetic field intensity on the boundary.  相似文献