Detection, identification and mapping of iron anomalies in brain tissue using X-ray absorption spectroscopy

International audienceThis work describes a novel method for the detection, identification and mapping of anomalous iron compounds in mammalian brain tissue using X-ray absorption spectroscopy. We have located and identified individual iron anomalies in an avian tissue model associated with ferritin, biogenic magnetite and haemoglobin with a pixel resolution of less than 5 μm. This technique represents a breakthrough in the study of both intra- and extra-cellular iron compounds in brain tissue. The potential for high-resolution iron mapping using microfocused X-ray beams has direct application to investigations of the location and structural form of iron compounds associated with human neurodegenerative disorders—a problem which has vexed researchers for 50 years

L'île aux Moutons (Fouesnant, Finistère)<br />Fouille 2005 - Rapport intermédiaire d'opération pluriannuelle

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An ice core perspective on the age of the Matuyama-Brunhes boundary

Two intervals of enhanced 10Be flux thought to be associated with periods of low dipole intensity and identified as the Matuyama-Brunhes transition and a precursor event have been observed in the bottom section of the EPICA Dome C ice core. The peaks span 764-776 ka and 788-798 ka on the new EDC3 chronology with a stated absolute age uncertainty of 6 ka (2σ). This chronology uses orbital tuning of atmospheric oxygen-18 (δ18Oatm) to correct for anomalies in ice flow in the bottom 500 m of the core. An additional 28 δ18Oatm data points have been measured to improve resolution and verify the accuracy of the tuning and the stated timescale uncertainty. Both the dating of the increased 10Be, and that relative to climatic records, are compared to paleointensity records found in orbitally tuned marine sediments. The mid-point of the 10Be peak associated with the M-B is approximately 10 ka younger than the age determined radioisotopically from lavas with transitional orientations, taking into account recent revisions to the 40Ar/39Ar dating standard and improved precision. Climatic constraints on the EDC3 agescale make an error of this magnitude in the ice chronology implausible. This age difference, however, is consistent with recent modeling suggesting that directional changes are spatially asynchronous, and may precede the dipole intensity minimum in some locations. Although formally less precise than the published age from astrochronologically dated marine sediments, ice core ages are potentially more accurate because they are not subject to lock-in depth uncertainties

Self‐reversal of magnetization in oceanic submarine basalts studied with XMCD

International audienceIn oceanic basalts, self‐reversal of magnetization can be produced during extreme low‐temperature oxidation of titanomagnetite by ionic reordering, which leads to Néel N‐type magnetism. Titanomaghemites showing N‐type reversal below room temperature were found in submarine basalts recovered during Ocean Drilling Program (ODP) Leg 197. In order to better understand the mechanism of self‐reversal, we carried out X‐ray magnetic circular dichroism (XMCD) at Fe K‐edge at room temperature and low‐temperature on such a titanomaghemite sample as well as on pure magnetite and maghemite samples. We found that the XMCD spectrum of the N‐type titanomaghemite at 20 K is a mirror image of the XMCD spectrum at 300 K, which shows that the octahedral and tetrahedral subnetworks reverse in this process. Ligand‐field multiplet calculations of XMCD at Fe K‐edge help identify the contributions of the different elements in the measured XMCD spectra. This mechanism could also cause self‐reversal above room temperature, which has important consequences for the reliability of paleomagnetic measurement