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  • Other Sources  (136)
  • American Chemical Society
  • American Meteorological Society
  • Copernicus
  • Institute of Physics
  • Springer Nature
  • 1
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    The boundary element method for stress concentrations and fracture problems (1986)
    Institute of Physics
    In:  Professional Paper, Boundary Element Methods. Theory and Application, Bristol, Institute of Physics, vol. 9, no. 16, pp. 1-23, (ISBN 1-4020-1729-4)
    Details
    Publication Date: 1986
    Keywords: Stress ; Rock mechanics ; Stress intensity factor ; Boundary Element Method ; Fracture ; ENDNOTE?
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Boundary Element Methods. Theory and Application (1986)
    Institute of Physics
    In:  Bristol, Institute of Physics, vol. 8, no. Publ. No. 12, pp. 95-104, (ISBN 0-865-42078-5)
    Details
    Publication Date: 1986
    Keywords: Rock mechanics ; Fracture ; Boundary Element Method ; Elasticity ; Dynamic
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Unusual marine unicellular symbiosis with the nitrogen-fixing cyanobacterium UCYN-A (2016)
    Springer Nature
    In:  Nature Microbiology, 2 (16214).
    Details
    Publication Date: 2020-06-24
    Description: Nitrogen fixation — the reduction of dinitrogen (N2) gas to biologically available nitrogen (N) — is an important source of N for terrestrial and aquatic ecosystems. In terrestrial environments, N2-fixing symbioses involve multicellular plants, but in the marine environment these symbioses occur with unicellular planktonic algae. An unusual symbiosis between an uncultivated unicellular cyanobacterium (UCYN-A) and a haptophyte picoplankton alga was recently discovered in oligotrophic oceans. UCYN-A has a highly reduced genome, and exchanges fixed N for fixed carbon with its host. This symbiosis bears some resemblance to symbioses found in freshwater ecosystems. UCYN-A shares many core genes with the 'spheroid bodies' of Epithemia turgida and the endosymbionts of the amoeba Paulinella chromatophora. UCYN-A is widely distributed, and has diversified into a number of sublineages that could be ecotypes. Many questions remain regarding the physical and genetic mechanisms of the association, but UCYN-A is an intriguing model for contemplating the evolution of N2-fixing organelles.
    Type: Article , PeerReviewed
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  • 4
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    Structure of an F430 Variant from Archaea Associated with Anaerobic Oxidation of Methane (2008)
    American Chemical Society
    In:  Journal of the American Chemical Society, 130 (32). pp. 10758-10767.
    Details
    Publication Date: 2020-07-16
    Description: Microbial mats collected at cold methane seeps in the Black Sea carry out anaerobic oxidation of methane (AOM) to carbon dioxide using sulfate as the electron acceptor. These mats, which predominantly consist of sulfate-reducing bacteria and archaea of the ANME-1 and ANME-2 type, contain large amounts of proteins very similar to methyl-coenzyme M reductase from methanogenic archaea. Mass spectrometry of mat samples revealed the presence of two nickel-containing cofactors in comparable amounts, one with the same mass as coenzyme F430 from methanogens (m/z = 905) and one with a mass that is 46 Da higher (m/z = 951). The two cofactors were isolated and purified, and their constitution and absolute configuration were determined. The cofactor with m/z = 905 was proven to be identical to coenzyme F430 from methanogens. For the m/z = 951 species, high resolution ICP-MS pointed to F430 + CH2S as the molecular formula, and LA-ICP-SF MS finally confirmed the presence of one sulfur atom per nickel. Esterification gave two stereoisomeric pentamethyl esters with m/z = 1021, which could be purified by reverse phase HPLC and were subjected to comprehensive NMR analysis, allowing determination of their constitution and configuration as (172S)−172-methylthio-F430 pentamethyl ester and (172R)−172-methylthio-F430 pentamethyl ester. The corresponding diastereoisomeric pentaacids could also be separated by HPLC and were correlated to the esters via mild hydrolysis of the latter. Equilibration of the pentaacids under acid catalysis showed that the (172S) isomer is the naturally occurring albeit thermodynamically less stable one. The more stable (172R) isomer (80% at equilibrium) is an isolation artifact generated under the acidic conditions necessary for the isolation of the cofactors from the calcium carbonate-encrusted mats.
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  • 5
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    Key Findings of the World’s First Offshore Methane Hydrate Production Test off the Coast of Japan: Toward Future Commercial Production (2017)
    American Chemical Society
    In:  Energy & Fuels, 31 (3). pp. 2607-2616.
    Details
    Publication Date: 2017-11-20
    Description: Marine methane hydrate in sands has huge potential as an unconventional gas resource; however, no field test of their production potential had been conducted. Here, we report the world’s first offshore methane hydrate production test conducted at the eastern Nankai Trough and show key findings toward future commercial production. Geological analysis indicates that hydrate saturation reaches 80% and permeability in the presence of hydrate ranges from 0.01 to 10 mdarcies. Permeable (1–10 mdarcies) highly hydrate-saturated layers enable depressurization-induced gas production of approximately 20,000 Sm3/D with water of 200 m3/D. Numerical analysis reveals that the dissociation zone expands laterally 25 m at the front after 6 days. Gas rate is expected to increase with time, owing to the expansion of the dissociation zone. It is found that permeable highly hydrate-saturated layers increase the gas–water ratio of the production fluid. The identification of such layers is critically important to increase the energy efficiency and the technical feasibility of depressurization-induced gas production from hydrate reservoirs.
    Type: Article , PeerReviewed
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  • 6
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    Enantiomeric Discorhabdin Alkaloids and Establishment of Their Absolute Configurations Using Theoretical Calculations of Electronic Circular Dichroism Spectra (2008)
    American Chemical Society
    In:  The Journal of Organic Chemistry, 73 (22). pp. 9133-9136.
    Details
    Publication Date: 2020-05-11
    Type: Article , PeerReviewed
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  • 7
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    Optical Interpretation of the Chemical Process of CH4–CO2 Exchange and Its Application to Gas Hydrate Production (2015)
    American Chemical Society
    In:  Journal of Physical Chemistry C, 119 (37). pp. 21353-21357.
    Details
    Publication Date: 2020-07-20
    Description: The guest-exchange method (or replacement) for methane production from gas hydrates has recently received attention because it can be used for both carbon dioxide sequestration and methane production. The structure of gas hydrates is maintained as a structure I (sI) hydrate while methane molecules are exchanged with carbon dioxide. In this study, CH4 + CO2 mixed gas hydrates were examined under terahertz light at various temperatures to simulate CH4–CO2 exchange reactions. Each gas hydrate composition examined was a representative composition at each step of the exchange reaction. The molecular composition was also accurately analyzed by gas chromatography. Refractive indices calculated by the terahertz time-domain spectroscopy (THz-TDS) of gas hydrate samples were correlated to the guest composition, and this novel method was proven to be used to quantify the extent of replacement via optical constant. Furthermore, changes in the water framework from the sI hydrate to ice using THz-TDS were investigated with an increasing temperature. Overall, this study reveals the process of guest exchange and phase transition from a gas hydrate to ice via the optical properties in the terahertz region, and it offers a powerful tool in gas hydrate production.
    Type: Article , PeerReviewed
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  • 8
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    IODP workshop: developing scientific drilling proposals for the Argentina Passive Volcanic Continental Margin (APVCM) – basin evolution, deep biosphere, hydrates, sediment dynamics and ocean evolution (2017)
    Copernicus
    In:  Scientific Drilling, 22 . pp. 49-61.
    Details
    Publication Date: 2017-11-01
    Description: The Argentine margin contains important sedimentological, paleontological and chemical records of regional and local tectonic evolution, sea level, climate evolution and ocean circulation since the opening of the South Atlantic in the Late Jurassic–Early Cretaceous as well as the present-day results of post-depositional chemical and biological alteration. Despite its important location, which underlies the exchange of southern- and northern-sourced water masses, the Argentine margin has not been investigated in detail using scientific drilling techniques, perhaps because the margin has the reputation of being erosional. However, a number of papers published since 2009 have reported new high-resolution and/or multichannel seismic surveys, often combined with multi-beam bathymetric data, which show the common occurrence of layered sediments and prominent sediment drifts on the Argentine and adjacent Uruguayan margins. There has also been significant progress in studying the climatic records in surficial and near-surface sediments recovered in sediment cores from the Argentine margin. Encouraged by these recent results, our 3.5-day IODP (International Ocean Discovery Program) workshop in Buenos Aires (8–11 September 2015) focused on opportunities for scientific drilling on the Atlantic margin of Argentina, which lies beneath a key portion of the global ocean conveyor belt of thermohaline circulation. Significant opportunities exist to study the tectonic evolution, paleoceanography and stratigraphy, sedimentology, and biosphere and geochemistry of this margin.
    Type: Article , PeerReviewed
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  • 9
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    The Conversion Process of Hydrocarbon Hydrates into CO2 Hydrates and Vice Versa: Thermodynamic Considerations (2011)
    American Chemical Society
    In:  The Journal of Physical Chemistry A, 115 (46). pp. 13324-13331.
    Details
    Publication Date: 2020-05-11
    Description: Microscopy, confocal Raman spectroscopy and powder X-ray diffraction (PXRD) were used for in situ investigations of the CO2-hydrocarbon exchange process in gas hydrates and its driving forces. The study comprises the exposure of simple structure I CH4 hydrate and mixed structure II CH4–C2H6 and CH4–C3H8 hydrates to gaseous CO2 as well as the reverse reaction, i.e., the conversion of CO2-rich structure I hydrate into structure II mixed hydrate. In the case of CH4–C3H8 hydrates, a conversion in the presence of gaseous CO2 from a supposedly more stable structure II hydrate to a less stable structure I CO2-rich hydrate was observed. PXRD data show that the reverse process requires longer initiation times, and structural changes seem to be less complete. Generally, the exchange process can be described as a decomposition and reformation process, in terms of a rearrangement of molecules, and is primarily induced by the chemical potential gradient between hydrate phase and the provided gas phase. The results show furthermore the dependency of the conversion rate on the surface area of the hydrate phase, the thermodynamic stability of the original and resulting hydrate phase, as well as the mobility of guest molecules and formation kinetics of the resulting hydrate phase.
    Type: Article , PeerReviewed
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  • 10
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    Phase-Controlled Colloidal Syntheses of Iron Sulfide Nanocrystals via Sulfur Precursor Reactivity and Direct Pyrite Precipitation (2017)
    American Chemical Society
    In:  Chemistry of Materials, 29 (19). pp. 8521-8530.
    Details
    Publication Date: 2020-07-27
    Description: In the colloidal synthesis of iron sulfides, a series of dialkyl disulfides, alkyl thiols, and dialkyl disulfides (allyl, benzyl, tert-butyl, and phenyl) were employed as sulfur sources. Their reactivity was found to tune the phase between pyrite (FeS2), greigite (Fe3S4), and pyrrhotite (Fe7S8). DFT was used to show that sulfur-rich phases were favored when the C–S bond strength was low in the organosulfurs, yet temperature dependent studies and other observations indicated the reasons for phase selectivity were more nuanced; the different precursors decomposed through different reaction mechanisms, some involving the oleylamine solvent. The formation of pyrite from diallyl disulfide was carefully studied as it was the only precursor to yield FeS2. Raman spectroscopy indicated that FeS2 forms directly without an FeS intermediate, unlike most synthetic procedures to pyrite. Diallyl disulfide releases persulfide (S–S)2– due to the lower C–S bond strength relative to the S–S bond strength, as well as facile decomposition in the presence of amines through SN2′ mechanisms at elevated temperatures.
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