A New Framework for Solving the Spatial Network Problems Based on Line Graphs     

Javad Saberian  Mohammad Reza Malek  Stephan Winter  Majid Hamrah 《Transactions in GIS》2014,18(5):767-782

In this article we define inverse line graphs of directed graphs as a new framework for solving some classical network analysis problems. The extraction method and theories of inverse line graphs are explained in this article. It is shown that by changing the analysis space from the original directed graph to the inverse line graph, complex problems can be changed into simpler problems. We show the usefulness of the proposed framework in two particular applications: shortest path computations and the more general route planning. Considering the implementation result, we expect that this framework could be used in many more network analysis problems.  相似文献   

Iron speciation and isotope fractionation during silicate weathering and soil formation in an alpine glacier forefield chronosequence     

Mirjam Kiczka  Jan G. Wiederhold  Jakob Frommer  Stephan M. Kraemer  Ruben Kretzschmar 《Geochimica et cosmochimica acta》2011,75(19):5559-5573

The chemical weathering of primary Fe-bearing minerals, such as biotite and chlorite, is a key step of soil formation and an important nutrient source for the establishment of plant and microbial life. The understanding of the relevant processes and the associated Fe isotope fractionation is therefore of major importance for the further development of stable Fe isotopes as a tracer of the biogeochemical Fe cycle in terrestrial environments. We investigated the Fe mineral transformations and associated Fe isotope fractionation in a soil chronosequence of the Swiss Alps covering 150 years of soil formation on granite. For this purpose, we combined for the first time stable Fe isotope analyses with synchrotron-based Fe-EXAFS spectroscopy, which allowed us to interpret changes in Fe isotopic composition of bulk soils, size fractions, and chemically separated Fe pools over time in terms of weathering processes. Bulk soils and rocks exhibited constant isotopic compositions along the chronosequence, whereas soil Fe pools in grain size fractions spanned a range of 0.4‰ in δ⁵⁶Fe. The clay fractions (<2 μm), in which newly formed Fe(III)-(hydr)oxides contributed up to 50% of the total Fe, were significantly enriched in light Fe isotopes, whereas the isotopic composition of silt and sand fractions, containing most of the soil Fe, remained in the range described by biotite/chlorite samples and bulk soils. Iron pools separated by a sequential extraction procedure covered a range of 0.8‰ in δ⁵⁶Fe. For all soils the lightest isotopic composition was observed in a 1 M NH₂OH-HCl-25% acetic acid extract, targeting poorly-crystalline Fe(III)-(hydr)oxides, compared with easily leachable Fe in primary phyllosilicates (0.5 M HCl extract) and Fe in residual silicates. The combination of the Fe isotope measurements with the speciation data obtained by Fe-EXAFS spectroscopy permitted to quantitatively relate the different isotope pools forming in the soils to the mineral weathering reactions which have taken place at the field site. A kinetic isotope effect during the Fe detachment from the phyllosilicates was identified as the dominant fractionation mechanism in young weathering environments, controlling not only the light isotope signature of secondary Fe(III)-(hydr)oxides but also significantly contributing to the isotope signature of plants. The present study further revealed that this kinetic fractionation effect can persist over considerable reaction advance during chemical weathering in field systems and is not only an initial transient phenomenon.  相似文献   

Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea   总被引：1，自引：0，他引：1  

Anja Reitz  Thomas Pape  Mark Schmidt  Florian Scholz  Giovanni Aloisi  Stephan M. Weise 《Geochimica et cosmochimica acta》2011,75(11):3250-46

Four seep sites located within an ∼20 km² area offshore Georgia (Batumi seep area, Pechori Mound, Iberia Mound, and Colkheti Seep) show characteristic differences with respect to element concentrations, and oxygen, hydrogen, strontium, and chlorine isotope signatures in pore waters, as well as impregnation of sediments with petroleum and hydrocarbon potential. All seep sites have active gas seepage, near surface authigenic carbonates and gas hydrates. Cokheti Seep, Iberia Mound, and Pechori Mound are characterized by oil-stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release. Pechori Mound is further characterized by deep fluid advection of lower salinity pore fluids. The Pechori Mound pore fluids are altered by mineral/water reactions at elevated temperatures (between 60 and 110 °C) indicated by heavier oxygen and lighter chlorine isotope values, distinct Li and B enrichment, and K depletion. Strontium isotope ratios indicate that fluids originate from late Oligocene strata. This finding is supported by the occurrence of hydrocarbon impregnations within the sediments. Furthermore, light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at Pechori Mound, Iberia Mound, and Colkheti Seep. C₁₅₊ hydrocarbons at the oil seeps are allochtonous, whereas those at the Batumi seep area are autochthonous. The presence of oleanane, an angiosperm biomarker, suggests that the hydrocarbon source rocks belong to the Maikopian Formation. In summary, all investigated seep sites show a high hydrocarbon potential and hydrocarbons of Iberia Mound, Colkheti Seep, and Pechori Mound are predominantly of thermogenic origin. However, only at the latter seep site advection of deep pore fluids is indicated.  相似文献   

Avoiding high concentrations of arsenic, manganese and salinity in deep tubewells in Munshiganj District, Bangladesh   总被引：1，自引：0，他引：1  

Stephan J. Hug  Dominique GaertnerLinda C. Roberts  Mario SchirmerThomas Ruettimann  Thomas M. RosenbergA.B.M. Badruzzaman  M. Ashraf Ali 《Applied Geochemistry》2011,26(7):1077-1085

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Atom‐probe analyses of nanodiamonds from Allende     

Philipp R. Heck  Frank J. Stadermann  Dieter Isheim  Orlando Auciello  Tyrone L. Daulton  Andrew M. Davis  Jeffrey W. Elam  Christine Floss  Jon Hiller  David J. Larson  Josiah B. Lewis  Anil Mane  Michael J. Pellin  Michael R. Savina  David N. Seidman  Thomas Stephan 《Meteoritics & planetary science》2014,49(3):453-467

Atom‐probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub‐nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of ¹²C/¹³C ratios in individual diamond grains, solving the decades‐old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.  相似文献   

High-resolution calculations of merging neutron stars – III. Gamma-ray bursts     

Stephan Rosswog  Enrico Ramirez-Ruiz  Melvyn B. Davies 《Monthly notices of the Royal Astronomical Society》2003,345(4):1077-1090

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TOF‐SIMS analysis of polycyclic aromatic hydrocarbons in Allan Hills 84001     

THomas Stephan  Elmar K. Jessberger  Christian H. Heiss  Detlef Rost 《Meteoritics & planetary science》2003,38(1):109-116

Abstract— The presence of polycyclic aromatic hydrocarbons (PAHs) in the Martian meteorite Allan Hills 84001 (ALH 84001) was considered to be a major sign of ancient biogenic activity on planet Mars (McKay et al. 1996). An asserted spatial association of PAHs with carbonates, carriers of so‐called nanofossils, was crucial for their suggested connection to early life forms. Although both observations can be explained individually without employing living organisms, a lateral correlation of PAHs and carbonates would suggest a genetic link between PAHs and the microstructures, favoring a biogenic explanation. On the other hand, without such a correlation, a biogenic or even a Martian origin of the PAHs cannot be inferred. Here we show that there is no correlation of PAHs and carbonates in ALH 84001. Furthermore, a general trend of high PAH concentrations at locations where terrestrial lead is present obviously suggests a terrestrial origin for PAHs in ALH 84001.  相似文献   

On the diversity of short gamma-ray bursts     

Stephan Rosswog  Enrico Ramirez-Ruiz 《Monthly notices of the Royal Astronomical Society》2003,343(2):L36-L40

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Pseudo-infinite guide stars for multi-conjugated adaptive optics on extremely large telescopes     

Roberto Ragazzoni  Stephan Kellner  Wolfgang Gaessler  Emiliano Diolaiti  Jacopo Farinato 《Monthly notices of the Royal Astronomical Society》2006,368(4):1796-1802

We introduce a novel concept to sense the wavefront for adaptive optics purposes in astronomy using a conventional laser beacon. The concept we describe involves treating the light scattered in the mesospheric sodium layer as if it comes from multiple rings located at infinity. Such a concept resembles an inverse Bessel beam and is particularly suitable for multi-conjugated adaptive optics on extremely large telescopes. In fact, as the sensing process uses light apparently coming from infinity, some problems linked to the finite distance and vertical extent of the guide source are solved. Since such a technique is able to sense a wavefront solely in the radial direction, we propose furthermore a novel wavefront sensor by combining the inverse Bessel beam approach with the recently introduced z -invariant technique for a pseudo-infinite guide star sensor.  相似文献   

TOF‐SIMS analysis of Allende projectiles shot into silica aerogel     

Thomas Stephan  Anna L. Butterworth  Friedrich Hrz  Christopher J. Snead  Andrew J. Westphal 《Meteoritics & planetary science》2006,41(2):211-216

Abstract— Powdered Allende projectiles were fired into silica aerogel at 6.1 km/sec in order to evaluate particle retrieval and analysis techniques for samples from the Stardust mission. Since particles may disintegrate and ablate along the penetration paths in a high‐porosity aerogel, TOF‐SIMS analysis may be a suitable method to determine the distribution of such materials along the tracks as well as potential compositional modifications. Therefore, two ?350 μm‐sized tracks, residing at the surface of a keystone specimen that was flattened between two silicon chips, were analyzed. TOF‐SIMS allows for a detailed study of the chemical composition of particles that survived the impact mostly intact and of fine‐grained material from disintegrated projectiles. In the investigated keystone, material from light gas gun debris dominated. Besides the two tracks, a continuous, 40‐μm‐thick surface layer of implanted material—probably gun residue—was found. One of the two analyzed tracks is compositionally distinct from this surface layer and is likely to contain residual material of an Allende projectile. The analyses clearly demonstrate that tracks, resulting from impactors in the 5–10 μm size range, can be successfully analyzed with TOF‐SIMS.  相似文献