Review of Acquisition and Signal Processing Methods for Electromagnetic Noise Reduction and Retrieval of Surface Nuclear Magnetic Resonance Parameters

Surveys in Geophysics - Surface nuclear magnetic resonance (sNMR) is an electromagnetic hydrogeophysical method directly sensitive to liquid phase water in the upper $$\approx $$ 100 m of the...     

NGI‐ADP: Anisotropic shear strength model for clay

Many geotechnical problems involve undrained behavior of clay and the capacity in undrained loading. Most constitutive models used today are effective stress based and only indirectly obtain values for the undrained shear strength. To match the design profiles of undrained shear strengths, in active (A), direct simple shear (D) and passive (P) modes of loading are complicated. This paper presents the elastoplastic constitutive model NGI‐ADP which is based on the undrained shear strength approach with direct input of shear strengths. Consequently, exact match with design undrained shear strengths profiles is obtained and the well‐known anisotropy of undrained shear strength and stiffness is accounted for in the constitutive model. A non‐linear stress path‐dependent hardening relationship is used, defined from direct input of failure strains in the three directions of shearing represented by triaxial compression, direct simple shear and triaxial extension. With its clear input parameters the model has significant advantages for design analysis of undrained problems. The constitutive model is implemented, into finite element codes, with an implicit integration scheme. Its performance is demonstrated by a finite element analysis of a bearing capacity problem. Copyright © 2011 John Wiley & Sons, Ltd.     

What do Δ14C changes across the Gerzensee oscillation/GI‐1b event imply for deglacial oscillations?

High‐resolution studies were performed on late‐glacial sediments from a small lake in western Denmark with respect to lithology, geochemistry, stable isotopes, pollen stratigraphy and radiocarbon dating on terrestrial macrofossils. One purpose was to detect the so‐called Gerzensee oscillation, or the GI‐1b event, in the later part of the Allerød warm period, and to describe the environmental impact of this short cooling. The other aim was to test the hypothesis that considerable Δ¹⁴C changes occur over this time, which can be related to ocean ventilation/thermohaline circulation changes. We find that the GI‐1b event had a major impact on both terrestrial and limnic ecosystems: large vegetation changes, increased soil erosion and lowered aquatic production. By correlations to events in the GRIP ice‐core and ¹⁴C patterns in the Cariaco basin we also transformed our ¹⁴C dated record into calendar years to calculate Δ¹⁴C values. The ¹⁴C dates show that the GI‐1b event both preceded, and was part of, the 11 400–11 300 ¹⁴C yr BP radiocarbon plateau, and was followed by the 11 000–10 900 ¹⁴C yr BP plateau; thus the later part of the event coincides with a distinct age decline. This delayed age drop (Δ¹⁴C rise) in relation to the hypothetical triggering mechanism behind the event, decreased ocean ventilation, could be explained by redeposited macrofossils at the onset of GI‐1b. This phenomenon, also seen at the onset of Younger Dryas, may also reflect increased soil erosion and redeposition at the start of cold periods. The independent Cariaco Basin record, however, implies that the very end of the cool GI‐1b event is related to a distinct rise in Δ¹⁴C. Likewise, the ¹⁰Be record from GISP2 shows a distinct rise in the middle of the event, precluding decreased solar forcing as the trigger of the climate event, but making it likely that high cosmic ray flux (low solar activity) may be the cause of the rising atmospheric ¹⁴C content. We thus conclude that the Δ¹⁴C changes over the Gerzensee oscillation (GI‐1b), being one of several coolings during the Last Termination, does not seem to be related to ocean ventilation changes. The reason behind this lack of coincidence between rising Δ¹⁴C and a fairly distinct Northern Hemisphere cooling may be due to the fact that the oceanic changes during some of these coolings are too subtle to give an atmospheric ¹⁴C imprint, or that an anti‐phase relationship between the two hemispheres blurs the Δ¹⁴C signal, or, finally, that a partly unknown mechanism may lie behind such coolings. Copyright © 2000 John Wiley & Sons, Ltd.     

The isolation and identification of gamma-lactones in the acidic fraction in Aleksinac (Yugoslavia) shale bitumen

Gas chromatography-mass spectrometry-computer assisted analysis of the acidic fraction of Miocene Aleksinac shale bitumen (26 million years old) has shown a great variety of organic compounds. Samples obtained from both benzene and benzene-methanol extracts were investigated and found to contain a homologous series of γ-lactones (C₇-C₁₅). These lactones possibly represent the only indication of unsaturated acids present during the shales deposition. In addition to the γ-lactones, straight chain aliphatic monocarboxylic acids (C₆-C₁₂), dicarboxylie acids (C₆-C₁₉), as well as many aromatic acids have been detected.     

The X-ray gas scintillation spectrometer experiment on the first spacelab flight

The First Spacelab mission, launched on Space ShuttleFlight STS-9 in November 1983 carried a multidisciplinary payload which was intended to demonstrate that valuable scientific results can be achieved from such short duration missions. The payload complement included a spectrometer to undertake observations of the brighter cosmic X-ray sources. The primary scientific objectives of this experiment were the study of detailed spectral features in cosmic X-ray sources and their associated temporal variations over a wide energy range from about 2 up to 30 keV. The instrument based on the gas scintillation proportional counter had an effective area of some 180 cm² with an energy resolution of 9% at 7 keV.The instrument parameters and the performance, using data from the flight and ground calibration, are discussed.     

Evaluation of scale effects in hydraulic models by analysis of laminar and turbulent flows

The paper presents an analysis of laminar and turbulent flow in porous stone material in order to evaluate the order of magnitude of scale effects in hydraulic models. Hydraulic model tests, such as for example breakwater model tests, are normally carried out at such small scales that the flow through the various layers of the breakwater is not completely turbulent. For this reason scale effects occur. A well-known method to compensate for the scale effects is to use larger stones than calculated by Froude's model law in certain regions of the model. The paper presents formulae for the calculation of the compensated stone sizes based on earlier work by Engelund. Further an evaluation of the energy dissipation in hydraulic models is made in order to determine the scale effect due to “laminar” flow.     

Geologic constraints on middle-crustal behavior during broadly synorogenic extension in the central East Greenland Caledonides

Structural and U-Pb geochronologic data from the Forsblad Fjord area of East Greenland (72°30'N) indicate close spatial and temporal ties between orogen-parallel shear and extensional deformation during Caledonian orogenesis. This territory is composed of three tectonostratigraphic units separated by two splays of the Fjord Region Detachment System (FRDS), a principal extensional fault system of the East Greenland Caledonides that was active in Silurian time. The oldest Caledonian fabrics in Forsblad Fjord, which developed at upper amphibolite facies metamorphic conditions, indicate that there was north-south, lateral extrusion of ductile middle-crustal material synchronous with approximately east-west shortening. U-Pb dating of synkinematic granitic leucosomes in migmatitic schists and gneisses demonstrates that this process was underway at ca. 425 Ma. Subsequently, east-west extension along the two splays of the FRDS truncated the older fabrics; the structurally highest of these shear zones - the Tindern detachment - was active as early as ca. 424 Ma. This implies either that there was a rapid transition from Caledonian shortening and possible transpressional deformation to post-orogenic collapse, or our preferred interpretation that extension was synorogenic. The FRDS shares many structural characteristics with the South Tibetan Detachment System of the Cenozoic Himalayan orogen but exhibits two important differences. First, while the South Tibetan system developed in the down-going Indian plate during the India-Eurasia collision, the Fjord Region system developed in the overriding Laurentian plate during the collision of Laurentia with Baltica. Second, whereas the exposed extensional structures in the Himalayas developed in the upper crust and are only inferred to have extended to deeper levels, those in the Forsblad Fjord area were demonstrably active at middle-crustal levels. Evidence for broadly coeval extension and contraction at differen t structural levels in both mountain belts emphasizes the general importance of crustal decoupling in the collisional orogenic process, and implies that synorogenic extensional deformation is not strictly an upper crustal phenomenon.     

Neoproterozoic basin evolution in Fennoscandia, East Greenland and Svalbard

Neoproterozoic successions of Fennoscandia, East Greenland and Svalbard are related to crustal extension and formation of sedimentary basins along the margins of northern Baltica （ Fennoscandia ） and eastern Laurentia （East Greenland and Svalbard）, preceding final break-up of Rodinia. The early rift stage （late Tonian-Cryogenian） is characterized by up to 16 km thick sedimentary successions of deep-marine sandstones and conglomerates linked to rift and strike-slip basins. Pericratonic basins expanded during Cryogenian-Cambrian coastal onlap. Cryogenian tropical climate is reflected by carbonate and evaporitic formations, most of which predate Cryogenian-Ediacaran glaciations. Glacial units, collectively referred to the Varanger Ice Age, may be equivalent to the Marinoan （c. 630 Ma） and the Gaskiers （c. 580 Ma） glacial periods. The final stage in break-up of Rodinia commenced with the emplacement of dolerite dyke swarms along the Baltoscandian margin at c. 600 Ma and the opening of the lapetus Ocean and other sea ways. No such dyke swarms have been recorded along the East Greenland segment of the Laurentian margin. Several Tonian-Cambrian tectonic and magmatic events recorded within the Kalak Nappe Complex in northern Finnmark make this unit an exotic terrane relative to the autochthonous Baltoscandian platform.     

Chronic exposure of adults and embryos of Pandalus borealis to oil causes PAH accumulation, initiation of biomarker responses and an increase in larval mortality

Adult shrimps (Pandalus borealis) and their embryos were exposed to an oil-water dispersion (OWD) at concentrations of 0.015, 0.06 and 0.25 mg/L using a continuous flow system. Lysosomal membrane stability was analysed in haemocytes using the neutral red retention assay and an alkaline unwinding assay was used to measure DNA damage in hepatopancreas tissue. Exposure to oil induced concentration and time dependent biomarker responses in adult shrimps together with the accumulation of PAH in their tissues. Oil exposure of shrimp embryos caused increased mortality in the resultant larvae, even if the larvae were kept in clean water after hatching. There were minor differences observed in larval stage development times in the first part of the experiments. The fatty acid composition of embryos exposed to oil was different to that of non-exposed larvae. PAH tissue concentration and biomarker responses correlated to the reduced survival of the shrimp larvae.