Combining advanced NMR techniques with ultrahigh resolution mass spectrometry: A new strategy for molecular scale characterization of macromolecular components of soil and sedimentary organic matter     

Junyan Zhong  Rachel L. SleighterElodie Salmon  Georgina A. McKeePatrick G. Hatcher 《Organic Geochemistry》2011,42(8):903-916

Molecular level characterization of complex biopolymers in nature is a key element to understanding the composition of natural organic matter (NOM) and fossil organic matter formation, such as kerogen and coal. Characterization of such geopolymers is difficult due to their heterogeneity and insolubility in common aqueous or organic solvents. Here, a strategy for extracting a representative sample is presented using the combined techniques of nuclear magnetic resonance (NMR) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) for chemical analysis and characterization of NOM. A variety of NOM samples (wood, kerogen, bitumen, whole sediments) are shown as examples for implementing the strategy, which include solvent extractions using pyridine. For most samples, the extracts are confirmed to be chemically representative of the insoluble solid, by comparing the liquids NMR spectrum of the extract to that of the whole, unfractionated NOM utilizing high resolution magic angle spinning (HRMAS) NMR. To assist in unambiguous peak assignment, a technique for post acquisition spectral denoising, using wavelet transformation (WT), is also employed on the 1D and 2D NMR spectra. The findings from the NMR data lay a foundation for the subsequent electrospray ionization FTICR-MS analysis of the pyridine extracts, since this instrument has the limitation of only analyzing liquid samples. The FTICR-MS analyses can, therefore, be used to molecularly represent the structural components of the NOM. Various compositional insights have been obtained on these samples, indicating the efficacy of the analytical techniques used.  相似文献   

Modelling tidal current turbine wakes using a coupled RANS-BEMT approach as a tool for analysing power capture of arrays of turbines     

Stephen R. Turnock  Alexander B. Phillips  Joe Banks  Rachel Nicholls-Lee 《Ocean Engineering》2011,38(11-12):1300-1307

An improved method is developed to couple an inner domain solution of the blade element momentum theory with an outer domain solution of the Reynolds averaged Navier Stokes equations for evaluating performance of tidal current turbines. A mesh sensitivity study shows that a mesh of at least 6 M cells with at least 40% of these within the turbine wake is required to ensure satisfactory convergence of the velocity deficit. In addition to the usually applied axial momentum source terms, angular momentum and turbulence intensity source terms are shown to be required to model the near wake evolution. Three different lateral turbine spacing of 2, 4 and 6 turbine diameters are used to demonstrate the influence of the effective channel blockage on the velocity distribution in the turbine bypass region, the rate of spread of the wake and the recovery of velocity distribution. A final study shows that for a fixed number of turbines minimising the lateral spacing within each row, with a small number of staggered rows spaced as longitudinally as far apart as practical, is the most effective strategy for energy capture.  相似文献   

Late Devonian OIB alkaline gabbro in the Yarlung Zangbo Suture Zone: Remnants of the Paleo-Tethys?     

Jingen Dai  Chengshan Wang  Réjean Hébert  Yalin Li  Hanting Zhong  Raoult Guillaume  Rachel Bezard  Yushuai Wei 《Gondwana Research》2011,19(1):232-243

The Yarlung Zangbo Suture Zone (YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys that occurred from early Mesozoic to early Cenozoic. We report here geochronological and petrological data obtained for newly discovered alkaline gabbro blocks embedded in a mélange zone of the western YZSZ. Single zircon U–Pb analyses from one representative gabbro sample by SIMS (Secondary Ion Mass Spectrometry) yielded a combined crystallization age of about 363.7 ± 1.7 Ma (1σ). In situ Hf isotopic analyses yielded ε_Hf(t) values of + 2.6 to + 5.5, suggesting an enriched mantle source. All of the gabbro samples show typical Ocean Island Basalt (OIB) affinity with little or no continental crust contamination. They also display strong geochemical similarities with the Hawaii basalts and the Xigaze seamount basalts suggestive of their intra-oceanic setting. These observations, in combination with the Early Carboniferous layered gabbros reported at Luobusa, indicate that these rocks could represent remnants of the Paleo-Tethys. We propose that a branch ocean separating the Western Qiangtang terrane and the Lhasa terrane from the Gondwana continent might have been present during the Late Devonian and the Early Carboniferous, providing new constrains on the configuration of Paleo-Tethys in Tibetan Plateau during early Late Paleozoic.  相似文献   

The chemical changes of DOM from black waters to coastal marine waters by HPLC combined with ultrahigh resolution mass spectrometry     

Zhanfei Liu  Rachel L. Sleighter  Junyan Zhong  Patrick G. Hatcher 《Estuarine, Coastal and Shelf Science》2011

How dissolved organic matter (DOM) undergoes chemical changes during its transit from river to ocean remains a challenge due to its complex structure. In this study, DOM along a river transect from black waters to marine waters is characterized using an offline combination of reversed-phase high performance liquid chromatography (RP-HPLC) coupled to electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS), as well as tandem ESI-FTICR-MS. In addition, a water extract from degraded wood that mainly consists of lignins is used for comparison to the DOM from this transect. The HPLC chromatograms of all DOM samples and the wood extract show two major well-separated components; one is hydrophilic and the other is hydrophobic, based on their elution order from the C₁₈ column. From the FTICR-MS analysis of the HPLC fractions, the hydrophilic components mainly contain low molecular weight compounds (less than 400 Da), while the hydrophobic fractions contain the vast majority of compounds of the bulk C₁₈ extracted DOM. The wood extract and the DOM samples from the transect of black waters to coastal marine waters show strikingly similar HPLC chromatograms, and the FTICR-MS analysis further indicates that a large fraction of molecular formulas from these samples are the same, existing as lignin-like compounds. Tandem mass spectrometry experiments show that several representative molecules from the lignin-like compounds have similar functional group losses and fragmentation patterns, consistent with modified lignin structural entities in the wood extract and these DOM samples. Taken together, these data suggest that lignin-derived compounds may survive the transit from the river to the coastal ocean and can accumulate there because of their refractory nature.  相似文献   

Actively rising surficial gneiss domes in Papua New Guinea     

C. D. Ollier  C. F. Pain 《Australian Journal of Earth Sciences》2013,60(1-2):33-44

Surficial gneiss domes are previously undescribed landforms two to three thousand metres high and tens of kilometres across, consisting of gneiss; they have the form of a dissected dome. On geomorphic grounds it is unlikely that the domes could be formed by differential erosion, so it is proposed that they emerged at the ground surface by shouldering the bounding rocks aside. Foliation in the gneiss is parallel to the dome surface, and therefore concentric in plan. Any small part of the dome surface looks like a fault scarp, but the ‘fault’ can be traced around the entire dome on Goodenough Island and around considerable arcs on other domes in southeast Papua New Guinea. We postulate that each dome originated by the pushing of a granite pluton and the foliation was created during the rise, whereas Davies (1978) has proposed that the domes are re‐folded thrust faults (which had earlier created the foliation) and that the granodiorite intrusions are later events only accidentally associated with the domes. In Davies’ hypothesis the topographic domes are created by differential erosion exposing orginally sub‐surface features, and some of the dome boundaries are fault‐line scarps. We consider that the topographic domes actually emerged at the ground surface, like a horst, and they are bounded by fault scarps. A review of the structural setting suggests that the domes may have been originally aligned as culminations on top of an elongated batholith rising beneath an axis of uplift along the Owen Stanley‐D'Entrecasteaux line. The domes are formed in an area of thick crust in a tensional environment.  相似文献   

Inversion of time-dependent nuclear well-logging data using neural networks     

Laura Carmine  Elsa Aristodemou  Christopher Pain  Ann Muggeridge  Cassiano de Oliveira 《Geophysical Prospecting》2008,56(1):115-140

The purpose of this work was to investigate a new and fast inversion methodology for the prediction of subsurface formation properties such as porosity, salinity and oil saturation, using time‐dependent nuclear well logging data. Although the ultimate aim is to apply the technique to real‐field data, an initial investigation as described in this paper, was first required; this has been carried out using simulation results from the time‐dependent radiation transport problem within a borehole. Simulated neutron and γ‐ray fluxes at two sodium iodide (NaI) detectors, one near and one far from a pulsed neutron source emitting at ～14 MeV, were used for the investigation. A total of 67 energy groups from the BUGLE96 cross section library together with 567 property combinations were employed for the original flux response generation, achieved by solving numerically the time‐dependent Boltzmann radiation transport equation in its even parity form. Material property combinations (scenarios) and their correspondent teaching outputs (flux response at detectors) are used to train the Artificial Neural Networks (ANNs) and test data is used to assess the accuracy of the ANNs. The trained networks are then used to produce a surrogate model of the expensive, in terms of computational time and resources, forward model with which a simple inversion method is applied to calculate material properties from the time evolution of flux responses at the two detectors. The inversion technique uses a fast surrogate model comprising 8026 artificial neural networks, which consist of an input layer with three input units (neurons) for porosity, salinity and oil saturation; and two hidden layers and one output neuron representing the scalar photon or neutron flux prediction at the detector. This is the first time this technique has been applied to invert pulsed neutron logging tool information and the results produced are very promising. The next step in the procedure is to apply the methodology to real data.  相似文献   

Influence of seepage undercutting on the stability of root‐reinforced streambanks     

Rachel M. Cancienne  Garey A. Fox  Andrew Simon 《地球表面变化过程与地形》2008,33(11):1769-1786

Several mechanisms contribute to streambank failure including fluvial toe undercutting, reduced soil shear strength by increased soil pore‐water pressure, and seepage erosion. Recent research has suggested that seepage erosion of noncohesive soil layers undercutting the banks may play an equivalent role in streambank failure to increased soil pore‐water pressure. However, this past research has primarily been limited to laboratory studies of non‐vegetated banks. The objective of this research was to utilize the Bank Stability and Toe Erosion Model (BSTEM) in order to determine the importance of seepage undercutting relative to bank shear strength, bank angle, soil pore‐water pressure, and root reinforcement. The BSTEM simulated two streambanks: Little Topashaw Creek and Goodwin Creek in northern Mississippi. Simulations included three bank angles (70° to 90°), four pore‐water pressure distributions (unsaturated, two partially saturated cases, and fully saturated), six distances of undercutting (0 to 40 cm), and 13 different vegetation conditions (root cohesions from 0·0 to 15·0 kPa). A relative sensitivity analysis suggested that BSTEM was approximately three to four times more sensitive to water table position than root cohesion or depth of seepage undercutting. Seepage undercutting becomes a prominent bank failure mechanism on unsaturated to partially saturated streambanks with root reinforcement, even with undercutting distances as small as 20 cm. Consideration of seepage undercutting is less important under conditions of partially to fully saturated soil pore‐water conditions. The distance at which instability by undercutting became equivalent to instability by increased soil pore‐water pressure decreased as root reinforcement increased, with values typically ranging between 20 and 40 cm at Little Topashaw Creek and between 20 and 55 cm at Goodwin Creek. This research depicts the baseline conditions at which seepage undercutting of vegetated streambanks needs to be considered for bank stability analyses. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Phosphorus sources and demand during summer in a eutrophic lake     

Amy M. Kamarainen  Rachel M. Penczykowski  Matthew C. Van de Bogert  Paul C. Hanson  Stephen R. Carpenter 《Aquatic Sciences - Research Across Boundaries》2009,71(2):214-227

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Geophysical and geochemical constraints on the age and paleoclimate implications of Holocene lacustrine cores from the Andes of central Chile          下载免费PDF全文

Rachel J. Tiner  Robert M. Negrini  Jose L. Antinao  Eric McDonald  Antonio Maldonado 《第四纪科学杂志》2018,33(2):150-165

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BiSON performance     

William J. Chaplin  Yvonne Elsworh  Rachel Howe  George R. Isaak  Clive P. McLeod  Brek A. Miller  H. B. Van Der Raay  Sarah J. Wheeler  Roger New 《Solar physics》1996,168(1):1-18

Since 1981 we have been operating the Birmingham Solar-Oscillations Network (BiSON), a global network of resonant-scattering spectrometers, observing the low-l solar p modes. Here we discuss historical developments, culminating in the establishment of a 6-station network in 1992 September, and the subsequent performance of that network. The data record of each station from 1992 to 1994 has been analysed in terms of weather and equipment breakdowns. Our early experience suggests that the best long-term coverage possible with a 6-station network is limited in practice to about 80%, which falls short of previous predictions.  相似文献