ALBERT

Description: Regeneration of the Earth's magnetic field by convection in the liquid core produces a broad spectrum of time variation. Relative palaeointensity measurements in marine sediments provide a detailed record over the past 2 Myr, but an explicit reconstruction of the underlying dynamics is not feasible. A more practical alternative is to construct a stochastic model from estimates of the virtual axial dipole moment. The deterministic part of the model (drift term) describes time-averaged behaviour, whereas the random part (diffusion term) characterizes complex interactions over convective timescales. We recover estimates of the drift and diffusion terms from the SINT2000 model of Valet et al. and the PADM2M model of Ziegler et al. The results are used in numerical solutions of the Fokker–Planck equation to predict statistical properties of the palaeomagnetic field, including the average rates of magnetic reversals and excursions. A physical interpretation of the stochastic model suggests that the timescale for adjustments in the axial dipole moment is set by the dipole decay time d . We obtain d = 29 kyr from the stochastic models, which falls within the expected range for the Earth's core. We also predict the amplitude of convective fluctuations in the core, and establish a physical connection to the rates of magnetic reversals and excursions. Chrons lasting longer than 10 Myr are unlikely under present-day conditions. However, long chrons become more likely if the diffusion term is reduced by a factor of 2. Such a change is accomplished by reducing the velocity fluctuations in the core by a factor of 2, which could be attributed to a shift in the spatial pattern of heat flux from the core or a reduction in the total core heat flow.

Description: Characterization of geomagnetic field behaviour on timescales of centuries to millennia is necessary to understand the mechanisms that sustain the geodynamo and drive its evolution. As Holocene paleomagnetic and archeomagnetic data have become more abundant, strategies for regularized inversion of modern field data have been adapted to produce numerous time-varying global field models. We evaluate the effectiveness of several approaches to inversion and data handling, by assessing both global and regional properties of the resulting models. Global Holocene field models cannot resolve Southern hemisphere regional field variations without the use of sediments. A standard data set is used to construct multiple models using two different strategies for relative paleointensity calibration and declination orientation and a selection of starting models in the inversion procedure. When data uncertainties are considered, the results are similar overall regardless of whether we use iterative calibration and reorientation, or co-estimation of the calibration and orientation parameters as part of the inversion procedure. In each case the quality of the starting model used for initial relative paleointensity calibration and declination orientation is crucial and must be based on the best absolute information available. Without adequate initial calibration the morphology of dipole moment variations can be recovered but its absolute value will be correlated with the initial intensity calibrations, an effect that might be mitigated by ensuring an appropriate fit to enough high quality absolute intensity data with low uncertainties. The declination reorientation mainly impacts regional field structure and in the presence of non-zonal fields will result in a non-zero local average. The importance of declination orientation is highlighted by inconsistencies in the West Pacific and Australian sediment records in CALS10k.1b model. Great care must also be taken to assess uncertainties associated with both paleomagnetic and age data and to evaluate the effects of poor data distribution. New consistently allocated uncertainty estimates for sediment paleomagnetic records highlight the importance of adequate uncertainties in the inversion process, as they determine the relative weighting among the data and overall normalized misfit levels which in turn influence the complexity of the inferred field models. Residual distributions suggest that the most appropriate misfit measure is the L 1 norm (minimum absolute deviation) rather than L 2 (least squares), but this seems to have relatively minor impact on the overall results. For future Holocene field modelling we see a need for comprehensive methods to assess uncertainty in individual archeomagnetic data so that these data or models derived from them can be used for reliable initial relative paleointensity calibration and declination orientation in sediments. More work will be needed to assess whether co-estimation or an iterative approach to inversion is more efficient overall. This would be facilitated by realistic and globally consistent data and age uncertainties from the paleomagnetic community.

Description: Author(s): L. Chaix, R. Ballou, A. Cano, S. Petit, S. de Brion, J. Ollivier, L.-P. Regnault, E. Ressouche, E. Constable, C. V. Colin, A. Zorko, V. Scagnoli, J. Balay, P. Lejay, and V. Simonet The chiral Fe-based langasites represent model systems of triangle-based frustrated magnets with a strong potential for multiferroicity. We report neutron-scattering measurements for the multichiral Ba 3 M Fe 3 Si 2 O 14   ( M = Nb , Ta ) langasites revealing new important features of the magnetic order of these sy… [Phys. Rev. B 93, 214419] Published Thu Jun 16, 2016

Description: SUMMARY We present a new time-varying model for palaeomagnetic axial dipole moment (PADM) for the past 2 Myr and compare it with earlier virtual axial dipole moment (VADM) reconstructions which have been based on stacking and averaging scaled relative palaeointensity records. The PADM is derived from both absolute and relative palaeointensity data and constructed using a new penalized maximum likelihood (PML) approach to recover a cubic B-spline representation of axial-dipole field variations on million year timescales. The PML method is explicitly intended to reduce bias in estimating the true axial dipole moment that arises in average VADM reconstructions. We apply the PML method to a set of 96 032 published data (1800 palaeointensities from igneous rocks, 3300 archaeointensities and 86 relative palaeointensity time-series of variable lengths and resolutions). Two models are discussed: PADM2Mp is a trial model based on a subset of the nine longest available sedimentary records; PADM2M uses a comprehensive data set (76 records, 81 446 data; 10 records were eliminated) and is our preferred model. PADM2M has a lower mean than existing VADM reconstructions but shows similarities in long-period variability. Some differences in timing, amplitude and resolution of certain features can be attributed to variations in age assignments. Others result from our more comprehensive data set and a reduction in bias attributable to PML modelling. PADM2M has an average axial dipole moment over 0–2 Ma of 5.3 × 10 22  Am 2 with a standard deviation of 1.5 × 10 22  Am 2 . The Brunhes chron average ( 6.2 × 10 22  Am 2 ) is higher than for earlier epochs of Matuyama ( 4.8 × 10 22  Am 2 ), as seen in some previous studies. The power spectrum for our model agrees with previous estimates of the global palaeomagnetic power spectrum for frequencies up to about 10 2  Myr −1 . We see no distinctive evidence in the power spectrum for orbital forcing of geodynamo behaviour.

Description: LPS-induced TNF-α factor (LITAF) mediates cytokine expression in response to endotoxin challenge. Previously, we reported that macrophage-specific LITAF-deficient (macLITAF−/−) mice exposed to LPS have a delayed onset in the serum levels of proinflammatory cytokines and prolonged persistence of anti-inflammatory cytokines, but only partial protection from endotoxic shock. We postulated that greater protection might be achieved if LITAF were deleted from all LITAF-producing cells, including macrophages. Using a Cre-loxP system, we engineered a tamoxifen-induced recombination mouse [tamLITAF(i)−/−] that resulted in whole-body LITAF deficiency. Our findings demonstrate that (i) tamLITAF(i)−/− mice are more resistant to systemic Escherichia coli LPS-induced lethality than our previous macLITAF−/− mice, providing evidence that LITAF-producing cells other than LysMCre-positive cells play an important role in mediating endotoxic shock; (ii) tamLITAF(i)−/− mice show a similar pattern of cytokine expression with decreased proinflammatory and prolonged anti-inflammatory mediators compared with WT mice; and (iii) tamLITAF(i)−/− mice, compared with WT mice, display a significant reduction in bone resorption and inflammation associated with a local chronic inflammatory disease—namely, collagen antibody-induced arthritis. Our findings offer a unique model to study the role of LITAF in systemic and chronic local inflammatory processes, and pave the way for anti-LITAF therapeutic approaches for the treatment of TNF-mediated inflammatory diseases.

Description: Globally distributed paleomagnetic data from discrete volcanic sites have previously been used for statistical studies of paleosecular variation and the structure of the time-averaged field. We present a new data compilation, PSV10, selected from high-quality paleodirections recorded over the past 10 Ma and comprising 2,401 sites from 81 studies. We require the use of modern laboratory and processing methods, a minimum of four samples per site, and within-site Fisher precision parameter, kw, ≥50. Studies that identify significant tectonic effects or explicitly target transitional field states are excluded, thereby reducing oversampling of transitional time intervals. Additionally, we apply two approaches using geological evidence to minimize effects of short-term serial correlation. PSV10 is suitable for use in new global geomagnetic and paleomagnetic studies as it has greatly improved spatial coverage of sites, especially at equatorial and high latitudes. VGP dispersion is latitudinally dependent, with substantially higher values in the Southern Hemisphere than at corresponding northern latitudes when no VGP cutoff is imposed. Average inclination anomalies for 10° latitude bins range from about +3 ± 2° to −7.5 ± 2° for the entire data set, with the largest negative values occurring at equatorial and mid-northern latitudes. New 0–5 Ma TAF models (LN3 and LN3-SC) based on selections of normal polarity data from PSV10 indicate a (Formula presented.) term that is 3.0% of (Formula presented.). Non-zonal variations in field structure are observed near the magnetic equator and in regions of increased radial flux at high latitudes over the Americas, the Indian Ocean, and Asia. © 2018. American Geophysical Union. All Rights Reserved.