A new greenland deep ice core.

The polar ice sheets are rich sources of information on past atmospheric conditions, including paleoclimates. A new deep ice core has been drilled in south Greenland. Comparison of the oxygen isotopic profile with that from camp Century and with a deep-sea foraminifera record indicates that the new core reaches back to about 90,000 years before present in a continuous sequence. The details in the Wisconsin part of the ice core records seem to be climatically, significant, and the general trends reveal all of the relevant Emiliani stages recorded in deep-sea cores. The redated Camp Century record suggests a dramatic termination of the Eem/Sangamon interglacial.

Detection and modelling of contacts in explicit finite-element simulation of soft tissue biomechanics.

PURPOSE: Realistic modelling of soft tissue biomechanics and mechanical interactions between tissues is an important part of biomechanically-informed surgical image-guidance and surgical simulation. This submission details a contact-modelling pipeline suitable for implementation in explicit matrix-free FEM solvers. While these FEM algorithms have been shown to be very suitable for simulation of soft tissue biomechanics and successfully used in a number of image-guidance systems, contact modelling specifically for these solvers is rarely addressed, partly because the typically large number of time steps required with this class of FEM solvers has led to a perception of them being a poor choice for simulations requiring complex contact modelling. METHODS: The presented algorithm is capable of handling most scenarios typically encountered in image-guidance. The contact forces are computed with an evolution of the Lagrange-multiplier method first used by Taylor and Flanagan in PRONTO 3D extended with spatio-temporal smoothing heuristics for improved stability and edge-edge collision handling, and a new friction model. For contact search, a bounding-volume hierarchy (BVH) is employed, which is capable of identifying self-collisions by means of the surface-normal bounding cone of Volino and Magnenat-Thalmann, in turn computed with a novel formula. The BVH is further optimised for the small time steps by reducing the number of bounding-volume refittings between iterations through identification of regions with mostly rigid motion and negligible deformation. Further optimisation is achieved by integrating the self-collision criterion in the BVH creation and updating algorithms. RESULTS: The effectiveness of the algorithm is demonstrated on a number of artificial test cases and meshes derived from medical image data. It is shown that the proposed algorithm reduces the cost of BVH refitting to the point where it becomes a negligible part of the overall computation time of the simulation. It is also shown that the proposed surface-normal cone computation formula leads to about 40 % fewer BVH subtrees that must be checked for self-collisions compared with the widely used method of Provot. The proposed contact-force formulation and friction model are evaluated on artificial test cases that allow for a comparison with a ground truth. The quality of the proposed contact forces is assessed in terms of trajectories and energy conservation; a [Formula: see text]0.4 % drop off in total energy and highly plausible trajectories are found in the experiments. The friction model is evaluated through a benchmark problem with an analytical solution and a maximum displacement error of 8.2 %, and excellent agreement in terms of the stick/slip boundary is found. Finally, we show with realistic image-guidance examples that the entire contact-modelling pipeline can be executed within a timeframe that is of the same order of magnitude as that required for standard FEM computations.

NMR spectroscopy study of the effect of 3-nitropropionic acid on glutamate metabolism in cultured astrocytes.

3-Nitropropionic acid (3-NPA) is a selective and irreversible inhibitor of succinate dehydrogenase. The effect of this compound on the metabolism of [U-13C]glutamate was studied in astrocytes using 13C nuclear magnetic resonance spectroscopy. The appearance of [1,2,3-13C]glutamate in cell extracts and [1,2,3-13C]glutamine and [U-13C]lactate in cell media demonstrated the metabolism of labeled glutamate via the tricarboxylic acid cycle. Such labeling was observed in the control situation and also in cells treated with 3 mM 3-NPA. In the cells treated with 3 mM 3-NPA, however, the labeling was significantly reduced, and with 10 mM 3-NPA no such labeling was observed. Labeled aspartate was observed in untreated cells only. Labeled succinate was not detectable under control conditions, but increased dose dependently in the presence of 3-NPA. Glutamate uptake and conversion of [U-13C]glutamate to [U-13C]glutamine was largely unaffected by 3-NPA, and ATP content was unchanged. In a previous study using cerebellar neurons, tricarboxylic acid cycle metabolism was blocked with 3 mM 3-NPA. The present results show that astrocyte metabolism is more adaptable to blockade of the tricarboxylic acid cycle by 3-NPA than neuronal metabolism.

Alpha-ketoisocaproate alters the production of both lactate and aspartate from [U-13C]glutamate in astrocytes: a 13C NMR study.

The present study determined the metabolic fate of [U-13C]glutamate in primary cultures of cerebral cortical astrocytes from rat brain and also in cultures incubated in the presence of 1 or 5 mM alpha-ketoisocaproate (alpha-KIC). When astrocytes were incubated with 0.2 mM [U-13C]glutamate, 64.1% of the 13C metabolized was converted to glutamine, and the remainder was metabolized via the tricarboxylic acid (TCA) cycle. The formation of [1,2,3-(13)C3]glutamate demonstrated metabolism of the labeled glutamate via the TCA cycle. In control astrocytes, 8.0% of the [13C]glutamate metabolized was incorporated into intracellular aspartate, and 17.2% was incorporated into lactate that was released into the medium. In contrast, there was no detectable incorporation of [13C]glutamate into aspartate in astrocytes incubated in the presence of alpha-KIC. In addition, the intracellular aspartate concentration was decreased 50% in these cells. However, there was increased incorporation of [13C]glutamate into the 1,2,3-(13)C3-isotopomer of lactate in cells incubated in the presence of alpha-KIC versus controls, with formation of lactate accounting for 34.8% of the glutamate metabolized in astrocytes incubated in the presence of alpha-KIC. Altogether more of the [13C]glutamate was metabolized via the TCA cycle, and less was converted to glutamine in astrocytes incubated in the presence of alpha-KIC than in control cells. Overall, the results demonstrate that the presence of alpha-KIC profoundly influences the metabolic disposition of glutamate by astrocytes and leads to altered concentrations of other metabolites, including aspartate, lactate, and leucine. The decrease in formation of aspartate from glutamate and in total concentration of aspartate may impair the activity of the malate-aspartate shuttle and the ability of astrocytes to transfer reducing equivalents into the mitochondria and thus compromise overall energy metabolism in astrocytes.